Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR PRODUCING GAS
OCCLUSION-FREE AND VOID-FREE COMPOUNDS
AND COMPOSITES
Baclceround of the Invention
Field of the Invention
The present invention relates to gas occlusion-free and void-free, two-primary
phase, solidifiable compounds. and derived void-free solidified composite
materials, and
more particularly to gas occlusion-free and void-free polymeric solidifiable
compounds
o and derived void-free solidified composites. including methods and apparatus
for
producing same.
Description of Related Art
a. Terminoloey
~5 Because certain terms in the field of the invention may be used in
different ways
to signify the same or slightly differing concepts, the following definitions
are provided to
promote clarity for the following description of the invention.
The term "primary solid phase'' is defined herein as one or more distinct
solid
substances each physicall~~ homogeneous, in solid state, which serves
primarily as
2o material reinforcement upon solidification of the primary liquid phase.
The term ''primary solidifiable liquid phase" is defined herein as one or more
distinct liquid substances. each physically homogeneous, in liquid state,
capable of
solidifying to constitute a solid continuous material matrix that binds the
primary solid
phase at ambient temperatures.
25 The term "compound" is defined as the unsolidified state of a composite.
The term "composite" is defined here as any solid primary phase mixed with any
primary solidifiable liquid phase, forming a monolithic two-phase solid state
material
upon solidification of the liquid primary phase.
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When the two primary phases are mixed to yield a compound, these primary
phases are no longer in their primary state but in an unsolidified,
multiphase, "mixed
state" as defined herein.
The term "voids" are defined herein as filled or unfilled spaces, within
interstices
of a packed primary solid phase or surface pores in solid constituents. Voids
are further
defined as gas phase occlusions within a primary liquid phase originating from
entrainment and/or adsorption of air, water vapor and other gases within the
interstices of
the solids in the primary solid phase, within the primary solidifiable liquid
phase or
within the multiphase, mixed unsolidified state of the t«~o phases. The term
"voids", as
1o defined above, specifcally excludes intermolecular and atomic spaces, which
are natural
unf fled spaces in matter. Furthermore, the scale of physical measurement of
voids herein
is about one micron ( 10'°m) or more.
b. Polvmeric Compounds and Composites
~ 5 An extremely wide range of products are being manufactured today from a
specific class of two primary phase compounds in which the primary
solidifiable liquid
phase is a polymeric resin. The process leading to the production of a
polymeric
composite involves mixing a generic primary solid phase with a polymeric resin
system,
thereby constituting a two-phase unsolidified compound. Upon further
processing, the
2o polymeric resin in the mixed unsolidified state is made to solidify, or
harden, in an
appropriate forming device, such as a mold or a die, yielding a formed, solid
composite
with the shape, or configuration, of the forming device.
The role of the polymeric liquid resin system in polymeric composites is to
provide an essential binding matrix to the primary solid phase upon
solidification.
35 Initially, its low viscosity provides an adequate liquid medium for mixing
with the solids
of the primary solid phase. Upon solidification, the resin matrix provides a
continuous
solid phase that enables the composite to behave monolithically as a single
solid material
body.
Resin systems in polymeric composites are further classified as either
3o thermoplastic, which soften when heated and may be shaped or reshaped while
.in a
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semifluid state or thermosetting, which are generally low viscosity liquids
that solidify
through chemical cross-linking. The most common resin systems in polymeric
composites are thermosetting, and the most predominant thermosetting resin is
unsaturated polyester. Other thermosetting resins include epoxies,
vinylesters, phenolics
and urethanes.
Certain thermosetting polymer resin systems consist of solid polymer particles
dissolved in a low viscosity liquid and solvent monomer, for example, an
unsaturated
polyester dissolved in monostyrene. The monomer plays the dual role of
providing a
solvent medium for the distribution of the polymer resin, and also has the
ability to react
1 o with the polymer into a final solid state. Such thermosetting resin
systems are made to
harden or solidify into a permanent shape by an irreversible chemical reaction
known as
curing or cross-linking, in which linear polymer chains and monomer chains in
the liquid
resin system are joined, or reacted, together to form complex, highly rigid,
three-
dimensional solid structures. This reaction requires anaerobic conditions;
i.e., the liquid
resin system will not harden in the presence of air. Thus the presence of O,
is known to
have an inhibitory effect on the polymerizationlsolidification process.
Additionally,
water, which is known to diffuse into liquid thermosetting resin systems,
significantly
impairs the cross linking solidification reaction.
An additional property of thermosets is that they are generally brittle. Thus,
2o thermosets are rarely used without some form of solid reinforcement.
However, high
resistance to weight ratio, ability to solidify at ambient temperatures and
retain their shape
and properties at somewhat elevated temperature as, well as good creep
resistance and
corrosion resistance properties, give thermoset resin systems significant
advantages over
thermoplastics. These advantages essentially are the reasons for their
preference in the
developmental history of polymeric composites.
The role played by the solids in the primary solid phase matrix of polymeric
composites is one of structural reinforcement. Moreover, the choice of
geometrical shape
of the solid phase constituents is a function of the intended reinforcement
requirement of
the particular polymeric composite in terms of the type of predominant
stresses from
3o externally applied forces that .are to be resisted. The geometrical shape
of the solid
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reinforcement generally can be of two generic classes: 1 ) filament shaped, or
fiber and 2)
granular/spherical shaped, or aggregate-type solid material. The fiber
reinforced
polymeric composites are intended for predominantly tensional,- mechanical
resistance
applications, whereas the aggregate reinforced polymeric composites are
intended for
a predominantly compressional, mechanical resistance applications. These
generic classes
of solids can be viewed as fonning two ends of the structural resistance
spectrum of
polymeric composites.
Polymer composites composed of fibrous solid materials mixed with
thermosetting polymeric resin are known as ''Fiber Reinforced Polymers" or
FRPs. The
t0 most common fcbers used in the present art are glass, graphite, ceramic and
polymeric
fibers. Depending on the particular production process used, this generic
class includes
polymeric composite materials such as "Glass Reinforced Plastics" (GRP),
produced by
open, manual or spray, lay up methods, pultrusion. filament winding, etc. or
by enclosed
methods such as "Resin Transfer Molding''' (RTM). Seeman Composites Resin
Infusion
~ 5 Manufacturing Process (SCRIMP), etc. Other FRP composites produced by
enclosed
methods are based on polymeric compound materials, such as "Bulk Molding
Compound" (BMC), "Sheet Molding Compound" (SMC), "Thick Molding Compound"
{TMC), etc. In the mixed solidifiable compound state, the latter fiber
reinforced
polymeric materials, appropriately handled, can be stored for extended periods
of time for
20 future forming and curing at appropriate combinations of pressure and
temperature into
final solid composite products.
Solid aggregate materials mixed with thermosetting polymeric resin (resins)
matrices comprise the generic class of polymeric composites known as cast
polymer
products, polymer concretes, polymer mortars or potmer grouts. To date, the
inorganic
25 aggregates for polymeric composites have not been systematically
characterized, but most
common aggregates used in the present art are siliceous. Silica aggregates are
widely
used in the production of polymer concretes due to their mechanical,
dielectric and
chemical resistance properties, as well as for their abundance and low cost.
Thermosetting polymeric composites offer inherent advantages over traditional
3o materials (metals, cement concrete, wood, ceramics and natural inorganic
materials),
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including energy efficiency, high strength-to-weight ratio, design
flexibility, parts
consolidation, corrosion resistance, high dielectric and thermal properties,
excellent
appearance, low maintenance and extended service life. A vast array of
thermosetting
polymeric composite products are currently available worldwide in over 50,000
successful applications developed over the past 45 years. Well over 95% of the
U.S.
production is dedicated to fiber reinforced polymeric composites, and the
industry's
shipments and growh are tracked under nine major market segments totaling over
3.2
billion pounds per year. Aggregate polymeric composites are widely used as
cast
materials for bath tubs, shower stalls, kitchen sinks and counters. flooring
and decorative
l0 panels in constmction. Cast polymer concrete products find use in
specialized niche
industrial applications, where the combination of high structural strength,
corrosion and
dielectric resistance is required.
Despite some differences, these two generic classes of polymeric composites
have
much in common in terms of certain characteristics and general behavior.
Generally, the
~ 5 functional concepts and behavioral aspects of the polymeric resin systems
are the same
for both classes of generic composites, despite specific differences in the
properties and
geometries of the solids within each class. Key common and inherent
characteristics of
polymeric composites include: 1) the composites are all heterogeneous and most
are
anisotropic; 2) the composites generally exhibit considerable variability in
their properties
2o compared to metals; this variability is directly related to the volume of
the respective
fractions of the nvo phases, i.e., the primary liquid phase versus the primary
solid phase;
and 3) the composites follow a general "rule of mixtures," in which a property
of the
composite is equal to the sum of solid and resin matrix properties weighted by
their
respective volume fractions. The rule of mixtures, however, is not valid for
most
25 properties in fiber reinforced polymeric composites, except for
longitudinal extensional
modulus. In aggregate reinforced polymeric composites, the correlation of
properties
determined by the "rule of mixtures" is reasonably valid for many properties
and supports
the art of solid filler additives, commonly used to enhance desired properties
in the
composite, and/or mitigate the. effects of undesired properties.
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Heterogeneity in a two-phase polymeric composite material refers to certain
properties that vary from point-to-point throughout the mass of the material.
In a random
selection of a point inside the material, properties can be very different,
depending on
whether the chosen point falls in the polymeric matrix or in the solid
component . While
it is true that generally all composite materials are heterogeneous at the
micron level, the
degree of heterogeneity is generally more pronounced in fiber polymeric
composites.
Additionally, the heterogeneity of these materials contributes to the
significant
variability of properties of thermosetting polymeric composites. In the case
of FRPs,
properties depend on the combination of several factors, such as the
properties of the
t o constituents, the form of the fiber reinforcement used (continuous fibers,
woven fibers.
chopped fibers, etc.), fiber volume fraction, length, distribution and
orientation, bond
strength between the phases, and void content. For example, strength and
hardness
characteristics of FRPs with continuous length fibers depend strongly on fiber
orientation,
spatial distribution and the variability of the properties of the specific
fiber chosen. As it
t5 is impossible to position each fiber individually in the mix, the
variability of the
properties of the material is inevitable. The variability of composites
reinforced with
discontinuous fibers, such as bulk molding compounds (BMC) and sheet molding
compounds (SMC) which are ultimately shape-molded and cured in closed dies, is
even
more enhanced due to the difficulty in controlling local uniforn~ity of fiber
content and
20 orientation in the face of material flow. Accordingly, material hardness
and strength in
the finished fiber reinforced composites made of BMC or SMC may var5~
considerably
from point-to-point throughout the material.
Anisotropy is another characteristic common to thermosetting polymeric
composites, and is generally more pronounced in fiber polymeric composites
than in
25 aggregate polymeric composites. An anisotropic material is one whose
properties vary
with direction. In the case of FRPs with straight, parallel and continuous
fibers, the
strength of the material is significantly stronger and stiffer in the
direction parallel to the
fibers than in the transverse direction.
Reinforcing fibers used in fiber polymeric composites are man-made in
continuous
3o processes yielding fine filaments that are quite brittle, and generally
consisting of
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diameters ranging from 2 to 13 microns. Filaments are normally in bundles of
several
strands as rovings or woven into fabrics. Glass fibers are the oldest,
cheapest and most
widely used. They have generally good chemical resistance, are noncombustible
and do
not adsorb water, although generally they adsorb humidity from air in
atmospheric
conditions. Their tensile strength-to-weight ratios are relatively high, with
elastic moduli
in the range of those of aluminum alloys. The internal structure of glass
fibers is
amorphous, i.e., noncrystaline, and are generally considered isotropic.
Reinforcing aggregates used in aggregate polymeric composites are natural
occurring inorganic materiais that require processing to remove undesirable
contaminants,
1 o such as clays, iron oxides, etc. This processing involves mechanically
sieving the
granules, separating them by sizes, and drying them within 0.1 % humidity by
weight to
assure compatibility with the resin systems. Humidity strongly affects
interfacial bonding
of the resin with a dramatic drop in compression and flexure strengths.
Geological origin,
impurity levels, particle size distribution, and particle shape all affect
uniformity and
t 5 homogeneity of dispersion of the aggregates in the liquid resin system.
These factors
influence, in turn. interfacial bond strength and void content. For high
corrosion
resistance, thoroughly washed and dried, high silica content aggregates are
generally
used. Rounded. spherical-shape aggregates generally provide better mechanical
and
physical properties than crushed, angular-edged aggregates, and also yield
higher packing
?o aggregate fractions with reduced void content and reduced resin fraction
volume.
C. Voids in Polymeric Compounds and Composites
Voids are a major factor significantly contributing to property variation
within a
polymeric composite. Voids tend to reduce the integrity of the material and
its
mechanical and dielectric strengths, cause optical defects and lower the
chemical
25 resistance.
Any open space or volume in the surface of solid matter, or the interstices of
fractured packed solids, exposed to atmosphere are subject to atmospheric air
pressure,
which will instantaneously fill these spaces with air. For example, when solid
silica is
fragmented and packed, as in the case of silica aggregates for polymeric
concretes, or
3o when filaments of molten silica glass are packed together to form glass
fiber, as in the
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case of fiberglass, the mass of the fragmented packed aggregates or packed
filaments
exhibit an "apparent or bulk density" which is significantly lower than the
respective
unfragmented or unfilamented specific density of the respective original solid
materials.
For example, silica has a specific density of 2.65 elcm' whereas the same
silica
fragmented into small diameter particles, approximately from say 100 microns
up to say 6
mm, has a "bulk" density of only 1.6 g/cm'. This "bulk density" indicates that
the silica
particles of irregular geometries in contact with each other, as when packed
in a heap,
leave random dimensional interstices or spaces - voids that are filled with
air. l~Teglecting
the weight of air, the sum of voids in one cubic centimeter of particulated
silica is
equivalent to the volume occupied by 1.05 grams of solid silica; that is,
39.6% of the
fragmented silica volume corresponds to "air in the voids within the silica
heap."
Since the formulations of polymeric composites are normally gravimetric, or by
weight of bulk solids and liquid fractions, and furthermore, since the
entrapped air is of
negligible weight, its presence is not recognized gravimetrically. However, as
detailed
~5 above, the properties of polymeric composites are related primarily to
volumes of the
constituent solid and liquid phase fractions, which, of course, include
whatever volumes
are actually occupied by air and water vapor entrapped in void spaces of
fragmented or
filamented solids. Moreover, the air, water vapor and other gases entrained in
the voids
of the solids add an important contribution to the total volume of the mixed
compound
2o material when the original solids are mixed with the liquid polymeric resin
system. In
fact, it is important to recognize that at the start of mixing of the two
primary phase
polymeric compound, actually three phases are present: (1) the original
primary solid
phase, (2) the original primary solidifiable liquid phase (e.g., a polymeric
resin system),
plus (3) a gaseous phase made up of the entrained air, water vapor and other
gases in the
z5 primary solid phase, plus entrained air, water vapor and other gases that
may be dispersed
in the resin system. Moreover, interfacially active substances generally added
in the
resin manufacture stabilize air inclusions.
The presence of voids in a solid composite material interferes with its
integrity
because voids randomly interrupt the continuity, not only of the primary
solidified liquid
3o phase, but more importantly, .also the continuity of the interfacial bond
between. the
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WO 99!26999 PCTIUS98I24818
priman~ phases. Void sizes, number, distribution, and especially , locations
are all critical
because voids determine singular points of discontinuity within the phases of
the material.
These discontinuities compromise the composite's integrity, strength, and
further, lead to
the initiation of failures due to the localized stress concentration points
they create.
Moreover, if these voids in the mixed unsolidified state are filled with air
and water
vapor. O, in air will cause an inhibitory effect on the polymerization
reaction of the resin.
Water, particularly in liquid state, can be even more detrimental than OZ to
the
polymerization reaction and to solidification. Thus, the removal of air, water
vapor and
other gases from the primary liquid resin system can result in more complete
polymerizatiom'solidification of the resin, thereby producing a material with
greater
strength and integrity.
For example, in fiber reinforced polymer composites, voids upset the rule of
mixtures. Interlaminar shear strength should increase with increasing fiber
volume
fraction content. Instead, shear strength actually decreases, even at
relatively low void
~s contents. Experiments show that a 5% void content causes a 35 to 40% drop
in
interlaminar shear strength in a fiber/epoxy composite. (Delaware Composites
Encyclopedia, Vol. l, page 29, Technomics Publishing Co. 1989). In many fiber
reinforced composite fabrication processes, void content tends to increase
with decreasing
resin content, i.e., with increased solid content. Again, it is notable that
all strength
zo properties of fiber reinforced polymer composites drop off at higher fiber
volume
fractions contents- generally above 50% fiber volume content, contrary to the
expectations of the rule of mixtures. A particular study for E-glass/epoxy
unidirectional
composite made by filament winding shows a reduction of 30% of linear fiber
stress
strength at failure with an increase of fiber volume fraction from 60% to 70%.
(Delaware
25 Composites Encyclopedia, Vol. 1, page 66), Technomics Publishing Co.,
1989). On a
weight basis, typically a 60% glass fiber volume fraction is generally
attained with
machine processes and represents 78% of total weight of the composite. The
highest
reported glass fiber volume fraction content in non-machine processed
composites in the
industry, such as in RTM or SCRIMP, is generally about 70% by weight, which is
equivalent to just SO% of fiber content by volume.
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In the case of aggregate polymeric composites, however, strengths follow the
rule
of mixtures, and properties, particularly compression strength, actually
increase with
increasing aggregate volume fraction content (provided that the aggregate
fraction's
particle size distribution is suitably graded for highest aggregate volume
packing).
Moreover, this increase in mechanical properties is observed in spite of the
increased void
content accompanying the increased aggregate volume fraction. In this case,
the
increased number of gas occlusions producing voids can be offset by mechanical
vibration and vacuum of the mix, resulting in a somewhat degassed mix.
Notwithstanding this fact, random voids remaining in aggregate polymeric
composites
also constitute points of stress concentration which are detrimental to
mechanical strength
properties of the material and contribute significantly to the variabilim of
properties
exhibited by the final composite materials.
E. Degassing devices
The present state of the art attempts to deal with the removal of the
entrained
gaseous phase after the mixing the two primary phases. To deal with gas
occlusions,
conventional fabrication processes of polymeric composites generally require
that the
viscous compound mix, with or without special air release additives, be
degassed under
vacuum and/or pressurized and, in some cases, also mechanically agitated,
vibrated,
2o compacted, or combinations thereof. The application of these process steps
enables
movement of the gaseous phase within the viscous liquid mix assisting it to
migrate
towards the external surfaces of the liquid mass, escaping outside into the
sunounding
space. The freed gases then can be extracted by vacuum. Essentially, in the
prior art, the
gaseous phase is brought into the mixture entrained by the solids andlor by
the liquid
resin system and gets dispersed into the mixed unsoiidified state. Therefore ,
in order to
allow complete wet-out of the solids by the liquid resin system, some
mechanism for
removal of the gaseous phase is required. This is generally accomplished by
degassing
thin films of the mix under vacuum, which allows the occluded gas bubbles
within the
thin section to move towards its external surface. Moreover, these external
surfaces are
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WO 99126999 PCTNS98I24818
maintained at a lower pressure than the thin mass itself, thus facilitating
evacuation by
vacuum.
Present state of the art phase-mixing processes used to process polymeric
composites, hov~ever, are not designed, nor intended, to eliminate entrained
air, water
vapor and other gases in the solids and liquid phases prior to the mixing
process.
Generally, the prior art methods of degassing are designed to work with the
untreated
primary phases already in the mixed state. Evacuation of gases from the mix is
not only
more inefficient and difficult but also less effective. Moreover, the mix can
only be
partially evacuated through mechanical and vacuum methods. Thus, the presence
of
1o voids in the final composite is inevitable using prior art methods.
For example, application of vacuum in a fiber polymeric composite made in a
typical RTM or SCRIMP process does diminish entrapped air within the closed
mold, or
system, and from the glass fiber materials. Also gas vapors from the
constituents of the
resin system or from entrained air can be diminished by the application of
vacuum, as
~ 5 evidenced by the reduction of visible occlusions in the solidified two-
phase material.
Likewise, vacuum applied to the thin sections of aggregate polymeric compounds
in
mixed state, especially in conjunction with mechanical vibration, which allows
entrained
air to be dislodged, and with air release additives that reduce interfacial
tension,
diminishes the total entrapped air and gases, and consequently, substantially
diminishes
20 occlusions/voids in the solidified two-phase material.
In particular cases, such as aggregate polymeric compounds involving
resin/small
diameter particulate microfiller mixtures, degassing a thin film of this mix
with high
vacuum. as described in Patent No. 5,534,047, results in substantial
elimination of gases
from the mix and accordingly, a substantially "void free" composite is
obtained. The
25 success of this method is largely due to the miciosize range of the filler
in the primary
solid phase and to relatively high resin matrix fraction volume of low
viscosity, which
allow good homogeneous dispersion of the solids in the liquid resin matrix. In
this case,
the primary solidifiable liquid phase resembles a low viscosity liquid, and
therefore,
behaves more like a pure liquid system. However, degassing by thin film vacuum
as
30 suggested in Patent No. 5,534,047, is limited to a narrow range of
applications. These
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applications involve either low viscosity liquids or low or moderate viscosity
solid/liquid
mixes that are capable of uniform gravity flow as thin films over flat
surfaces, and that
allow for relatively unimpeded movement of entrained gas occlusions by
pressure
differential through the viscous liquid film. Generally, however, in the prior
art, two
primary phase polymeric compounds are known to be incapable of being
completely
degassed by conventional methods including high vacuum.
F. Conclusion
Overall then, it appears that conventional processes as practiced in the
present art
of producing polymeric compounds cannot completely eliminate gas occlusions
and voids
from the compounds, and accordingly, from the corresponding solidified
composites thus
obtained from them. Polymeric composites produced in the prior art, therefore
exhibit,
high variability as well as decreased mechanical and physical properties as
compared with
the expected capabilities and performance of final composites produced ideally
void free
Moreover, the apparent acceptance in the composites industry of the presence
of voids as
unavoidable in the production of polymeric composite materials has precluded
their
potential cost effective penetration into new more technically demanding
applications.
Polymeric resin system materials cost is one of the major factors affecting
overall
zo composite costs. Efforts to decrease resin system cost far increased
composites
competitiveness in market penetration have been generally frustrated because
associated
increases in solid content generally worsen rather than improve mechanical,
physical and
chemical properties, while significantly increasing production difficulty.
~5 Thus, these exists a need to produce polymeric composites-both in fiber and
aggregate classes-meeting a stricter and more rigorous criterion regarding
freedom from
gas occlusions and voids. If void-free, two-phase solid polymeric composite
materials
can be readily produced , they will at least exhibit increased mechanical,
chemical
resistance and physical strength, decreased variability of properties and
enhanced
30 reliability and performance. ' Polymeric composites in such a void-free
solid state
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WO 99126999 PGTNS98/24818
condition would both lower costs and improve quality in existing applications
and thus,
enable cost effective access to new, more demanding applications.
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Summary of the Invention
The present invention comprises a method for producing at least a two primary
phase compound that is substantially free of air and other gases by separately
treating the
a solid primary phase and the liquid primary phase prior to bringing the two
phases into
contact. Treatment of the two phases entails washing the primary solid phase
with a
condensable gas, so as to substantially remove and replace the solid phase's ~-
oid contents;
and separately degassing the primary solidifiable liquid phase by conventional
means.
Once treated, the primary solid phase (whose voids are substantially filled
with the
t o condensable gas) and the primary solidifiable liquid phase, are combined
in a mixing step,
and the condensable gas is condensed or liquefied in the mixed state. The
resulting void-
free, solidifiable compound thus comprises at least a solid phase and a
solidifiable liquid
phase. The solid primary phase may consist of either particulate or fibrous
materials or
combinations of both. The primary solidifiabie liquid phase may consist of a
t S thermoplastic polymeric resin system, a thermosetting polymeric resin
system, a
combination of both systems, or an inorganic binding system. Further, both the
washing
and mixing steps may be carried out in a batch or continuous mode, or in a
combination
batch-continuous mode. Additionally, the two primary phase solidifiabie
compound
having a gas phase composed substantially of the condensable gas may be stored
for later
2o use.
The present invention also includes two primary phase solidifiable compounds
made in accordance with the inventive method, as well as substantially void
free
polymeric composites formed from the solidifiable compounds. Note, the
condensable
gas that is used to wash the primary solid phase in the inventive method, may
be
2s condensed prior to or at solidification of the two phase compound, and may
be partially or
completely condensed in the mixed state. Void-free composites made from the
inventive
method are especially useful as electrical insulators.
The present invention also includes an apparatus for continuous production of
the
substantially void-free, two primary phase solidifiable compound. The
apparatus is
comprised of an enclosed container for the primary solid phase, and a means
for
producing vacuum within the enclosed container; a mixing device that is in
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communication «rith the enclosed container, and that is used both to combine
the
separately treated primary solid phase and the primary solidifiable liquid
phase, and at
least partially, to condense the condensable gas. The apparatus also comprises
a
condensable gas inlet in the initial region of the mixing device, so that the
condensable
gas flows continuously within the enclosed container in a direction counter to
the flow of
the primary solid phase; and a primary solidifiable liquid phase inlet located
downstream
of the condensable gas inlet within the mixing device. Finally, the apparatus
contains a
port for discharging the mixed, and substantially air-free, solidifiable
compound.
Optionally, the discharge port may consist of an airtight, expandable spout
that allows for
1o intermittent discharge of discrete amounts of the air-free compound while
the mixing
device continues to run.
Additionally, the invention includes an apparatus for batch production of a
two
primary phase solidifiable compound that is substantially free of air and
other gases and
voids. The apparatus is comprised of a closed revolving chamber for containing
and
t 5 mixing the primary solid phase, the primary solidifiable liquid phase, and
the condensable
gas phase; a means for applying vacuum and pressure within the chamber; one or
more
ports for discharging the chamber contents; and fixed or detachable molds that
are
attached to the discharge ports and are used to form the solidified composite.
In addition
to rotation about its longitudinal axis, the apparatus may also rotate about a
transverse
2o axis to aid in material handling.
Finally, the invention encompasses an apparatus for batch production of a
substantially void-free soiidifiable polymer concrete material. The apparatus
is
comprised of an enclosed mixing chamber, an enclosed molding chamber, and an
enclosed conduit that provides for communication of the mixing chamber with
the
25 molding chamber. Moreover, the apparatus can be rotated in a vertical plane
about an
axis perpendicular to the longitudinal axis of the apparatus. This allows the
contents of
the mixing chamber to flow by gravity into the molding chamber. The apparatus
may
also provide a means for rotation about its longitudinal axis to mix the
polymer concrete
components. The apparatus may also contain a material holding hopper that can
be
3o interchanged with the molding chamber. This hopper is equipped with an
intermittent
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dispensing device that provides for discharge of discrete and metered amounts
of the
solidifiable polymer concrete material.
Brief Description of the Drawings
FIGURE 1 is a schematic diagram illustrating the generic method of the present
invention for processing a generic void-free, gas occlusion-free two primary
phase
solidifiable compound material.
FIGURE 2 is an illustration of some of the forms of voids.
t0 FIGURE 3 is a schematic representation of another application of the
present
method in which a void-free polymer concrete composite material is produced by
a batch
mix and molding method.
FIGURE 4 is a schematic representation of }~et another application of the
present
method in which a void-free polymer concrete compound is produced by a
conventional
continuous mixing method, and where a polymer concrete composite is produced
by a
mixer to storage to mold method.
FIGURE 5 is a schematic representation of still another application of the
present
method in which a void-free fiber reinforced polymer composite is produced by
a Resin
Transfer Molding (RTM) method.
2o FIGURE 6 is a schematic diagram of an apparatus of the present invention,
used in
this case to produce a batch mixed polymer concrete material, as illustrated
in FIGURE 3.
FIGURE 7 is a schematic diagram of another apparatus of the present invention
used, in this case, to continuously produce a void-free polymer concrete
material, as
illustrated in FIGURE 4.
FIGURE 8 is a schematic representation of an electric insulator machined from
a
void-free polymer concrete composite material produced according to FIGURE 3.
Detailed Description of the Preferred Embodiments
The present invention relates to methods, materials and apparatus used to
produce
3o a variety of void-free materials. These void-free materials, and the
methods and apparatus
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for producing same are also detailed herein. The generic void-free method can
be used to
produce any two primary phase soIidifiable compound and composite.
A key step in this inventive method is to replace the pre-existing entrained
or
entrapped gases with a selected "condensable gas" as defined herein. The
"condensable
gas" utilized in the present invention is defined herein as one or more
substances that at
normal ambient temperature and up to 50 atmosphere of absolute pressure,
exists as a
liquid. The purpose of the condensable gas in the invention is to displace and
replace air,
water vapor and other gases present within the voids and interstices of the
primary solid
phase. "Non-condensable gases" are defined herein as air, water vapor and
other gases,
t0 which originally exist as gases filling the voids, and subsequently, are
replaced by a
selected condensable gas. Thus, a "non-condensable gas" is any gas other than
the
selected condensable gas used to replace the pre-existing gases, or displaced
gases, in the
system.
The present invention is an environmentally safe generic process of universal
t 5 application to fabricate all types of two primary phase solidif able
compounds and
composites, comprising a primary phase of reinforcing solid mixed with a
primary of
solidifiable liquid binder phase. It is applicable to the production of void-
free polymeric
composites in general. In particular, the method is applicable where the
solidification
mechanism of the primary solidifiable liquid phase involves solidification of
its entire
20 liquid phase. Additionally, the method is particularly applicable where
thermosetting
polymeric resin matrices are used as the primary solidifiable liquid phase.
Generic Method of Production
The generic method leading to void-free and gas occlusion compounds involves
25 three essential stages in the production process. These stages are
applicable to any
method of production to yield a wide variety of compounds and composites.
The state of the two primary phases in the generic process are characterized
in the
invention at each of three successive generic processing stages:
Stage 1- Washing the primary solid phase with a condensable gas, in the gas or
30 liquid state, and in parallel de-airingldegassing the primary solidifable
liquid phase.
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Stage 2- Mixin the above two primary phases, air-free, and in presence of a
condensable gas phase.
Stage 3- Condensine of the above condensable gas phase within the mixed state
compound.
Application of the above method yields a two-primary phase, non-condensable
gas
occlusion free and void-free solidifiable mixed state compound, which can be
cured
immediately or stored uncured for future curing.
FIGURE 1 shows a schematic of the generic process used to produce a generic
non-condensable gas occlusion free and void-free two-primary phase
solidifiable
t o compound as disclosed in the present invention. The initial steps 1 and 2.
consist of
separating the primary solid and liquid phase for the purpose of independently
removing
air, water vapor and other gases entrained in each phase prior to mixing. As
indicated,
each primary phase contains entrained non-condensable gases, which in the case
of the
primary solid phase, are removed by the inventive method.
~5
A. Stage I
An important step in the process is 5, shown in FIGURE l, where the primary
phase solids are de-aired/degassed by total replacement with a condensable gas
4. This
step 5 is significant to produce a non-condensable gas occlusion free and void-
free
20 compound because it permits the complete replacement of air/gases by
washing the solids
with a condensable gas chosen to adequately work within the parameters of
conventional
fabrication processes. The addition of this step to the overall void-free
method recognizes
the fact that it is essentially impossible to completely degas solids, or
mixtures of solids
and liquids, using conventional techniques with or without the application of
vacuum.
25 Thus, the present invention replaces air, water vapor and other non-
condensable gases
entrained in the solid with a condensable gas that can be liquefied within the
mixed
unsolidified state compound in the range of temperatures and pressures in
which the
production processes are carried out. Ideally, the condensable gas utilized,
when
liquefied, would be reacted within the primary soIidifiable liquid phase prior
to, or at,
3o solidification to form a solid void-free composite in a subsequent step.
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As illustrated in 3, after washing the solids in a stream of condensable gas,
the
displaced air with associated water vapor and other gases can be removed by
vacuum
together with the stream of condensable gas. With the application of vacuum,
at this
point in step 5, the condensable gas in filling the voids in the solids as the
air associated
with water vapor and other gases are being removed, and the condensable gas is
also
simultaneously being fed into the primary solid phase, as seen in 4.
The condensable gas as a liquid state substance is vaporized to its gas state
by
some appropriate combination of pressure and temperature. The preferred
vaporization
conditions are at ambient temperature together with sufficient vacuum for
vaporization.
to The preferred choice of a condensable gas is one that in its condensed
liquid state would
be capable of further reaction with the primary solidifiable liquid phase upon
its
solidification. There are essentially three classes of condensable gases
disclosed in the
present invention. Class I uses one or more liquid substances contained in. or
forming
part of, the solidifiable liquid system as sources of condensable gas to wash
the primary
solid phase. Class II uses one or more liquid substances, other than those
forming part of
the solidifiable liquid system, as a source of condensable gas to wash the
primary solid
phase. In the case of Class II, the liquid substances are functionally
equivalent to those
contained in Class I, in that Class II liquids are also capable of reacting in
the
solidification, or curing, process. Class III substances do not utilize a
reactive or
2o functionally equivalent fluid substance as a source of the condensable gas,
but instead
uses one or more fluids that are either soluble or insoluble in the
solidifiable liquid system
process conditions. Thus, for e~:ample, where the primary solidifiable liquid
phase is an
unsaturated polyester, styrene monomer would serve as a Class I condensable
gas.
Furthermore, other ethenic polymerization monomers could serve as Class II
condensable
gases, including, acrylamide, methyl acrylate, methyl methacrylate, vinyl
acetate and the
like. Finally, suitable Class III condensable gases would be organic solvents
having
normal boiling points between about SO°C and 100°C, including
acetone, methanol,
ethanol, isopropanol, acetonitrile, and the like.
Preparation of the substance to be used as condensable gas in the invention
can be
3o done by methods generally known in the art, which include evaporation of
the gasifiable
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liquid into a condensable gas with subsequent feeding of the gas thus produced
into a gas
replacement chamber S. Preferably for continuous washing, evaporation of the
gasifiable
liquid may take place outside of the gas-replacement chamber, and then fed
into the gas
replacement chamber 5. Alternatively, preferably in the case of batch
processes,
evaporation of the condensable gas can take place within the gas replacement
process
chamber 5. In the case of Class I Liquid/gases, one or more of the liquid
substances from
within the solidifiable liquid system can be selectively evaporated from it
and fed into the
gas replacement process chamber 5. In still another alternative, evaporation
into a
condensable gas, using an appropriate temperature and pressure, can take place
outside
t o the gas replacement process and fed into it at elevated temperature, so
that it is made to
condense inside the gas replacement process chamber at process temperature and
then
subsequently re-evaporated within chamber 5 by a combination of pressure and
temperature.
In parallel, the present invention requires that the primary liquid phase 2 be
t 5 degassed by conventional vacuum methods, preferably thin film vacuum
methods. This
step allows removal of the entrapped air, water vapor or other gases within
this primary
phase. The de-airing/degassing of the primary liquid phase takes place in a
degasifying
process chamber b. Reference numeral 7 illustrates that the air, water vapor
or other
gases entrained in the primary liquid phase are removed by the application of
thin film
2o vacuum methods which are generally more effective.
B. Stage II
Reference numeral 8 and 9, shown in FIGURE 1, represents that the two primary
phases having been separately treated to remove entrained air, water vapor and
other non
z5 condensable gases, and now, being de-aired/degassed by conventional methods
in the case
of the liquid phase, and condensable gas-replaced by washing with condensable
gas in the
case of the primary solid phase, can proceed to be mixed to form a non-
condensable gas
free, void-free solidifiable compound. Reference numeral 10 represents the air-
free
mixing processes into which each pretreated primary phase is contacted to
begin the
30 mixing process of what is now a primary solid phase, a primary solidifiable
liquid phase
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and a condensable gas system, to yield a mixed state non-condensable gas
occlusion free
and void-free solidifiable compound. The mixing step 10 must be conducted only
in air-
free conditions and with the presence of the condensable gas in the gaseous
phase.
The condensable gas in the mixing chamber may or may not be uniformly
a dispersed in the solidifiable liquid phase. An optional step can be
performed at this point
to disperse the condensable gas more homogeneously within the solidifiable
liquid phase.
This optional step can be accomplished by applying vibration or mechanical
work to the
mixed state compound. Additionally, if elimination of excess condensable gas
is desired,
as it might in batch mixing process, vacuum and mechanical work can be applied
at this
t o point to achieve this end.
C. St, age III
The next step is significant to the overall void-free process and production
of the
non-condensable gas occlusion free and void-free compound to yield a final
void-free
15 composite material. This step involves condensation of the condensable gas
preferably
within a condensation chamber 12, as shown in FIGURE 1. Later, at the time of
forming
and hardening of the compound, pressure and/or heat can be applied to form a
final solid
composite. This essential step 12 takes the condensable gas to its
corresponding liquid
state at process temperature by application of pressure 13, or by some
appropriate
2o combination of temperature and pressure. Upon condensation of the
condensable gas
throughout the mixed state solidifiable liquid system, all spaces in the mix
previously
occupied by the condensable gas, as a gaseous state substance, are available
to be
occupied by the soiidifiable liquid system which does so assisted by its own
pressure, so
the mixture becomes a non-condensable gas occlusion free compound. Concurrent
with
2s this essential condensation step, the solidifiable compound may be vibrated
or
mechanically worked upon, as illustrated in 14, so that the condensed gas, now
in liquid
state, may be dispersed within the liquid phase of the mixture, thus allowing
penetration
of the liquid phase into interstices and voids on the surfaces of the solids.
Alternatively,
vibration need not be applied because the element of time can be used to allow
for
3o diffusion of the condensed gas liquid droplets within the liquid system as
seem in .15.
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Reference numeral 16 represents the end product of the generic process,
yielding a non-
condensable gas occlusion free, and void-free, two primary phase solidifiable
compound
that can now be immediately hardened or stored for future solidification.
The effectiveness of the method and mixing conditions disclosed in the present
invention, specifically, in terms of prior displacement of air, water vapor
and other gases
from voids in the dry solids by washing with a condensable gas and subsequent
total
replacement with a condensable gas, cannot be attained by present art vacuum
only
processes. The reason stems not only from the fact that perfect vacuum
conditions cannot
be achieved, so the entrained gases in the solids can only be rarefied at
best, and
to moreover, because total dependence on high vacuum to maintain an air-free
condition of
the primary solid phase is unfeasible and impractical. It is perhaps for this
latter reason
that vacuum degassing pretreatment of the solids has not been considered in
present art
nor included in conventional processes.
As stated above, in contrast to the present invention, the typical prior art
degassing
t5 processes shifr all attempts of gas removal to the wet mixing stage of the
two primary
phases. In that case, the non-condensable gases naturally present in the
mixing process
become dispersed throughout the mixed state compound mass, making vacuum
degassing
at this stage ineffective and inefficient. Again in contrast to the present
invention, the
prior art procedure is considerably more difficult and less effective in high
viscosity
2o systems. In fact, in the prior art methods, gas phase removal becomes
virtually
impossible in cases where the resulting mixture viscosity of the mixed state
of the solid
and liquid phases is significantly increased by their addition.
Void-Free Considerations in Polymeric Compounds and Comp-osites
25 It is somewhat surprising that current technical literature on voids does
not delve
into the causes or origins of voids in solid state polymeric composites, and
no link has
been established, or suggested, to identify their origin as gas occlusions
already pre-
existing in the original solidifiable- two phase mixed state compound. Voids
in the
compound are then transported into the solidified resin matrix of the
composite. In
3o developing the present invention, it has been discovered that the success
of any air-gas
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phase removal strategy from the mass of a two primary phase mix containing a
gaseous
phase depends on the following:
* ratios or surface tensions existing between the gaseous, liquid and solid
phase present in the mix;
* average size of the air and gas occlusions;
* pressure differentials that can be established between those within the
different gas occlusions, and that of the external surface of the mass
maintained at a lower pressure;
* viscosity and rheology of the liquid state mixture;
to * geometry of the specific masses;
* length of the paths the occlusion gas bubbles need to move to access the
lower pressure external surfaces;
* obstacles intercepting the paths of the occluded gas bubbles;
* ability of mechanical vibration applied to the mass to pack the solids
within the liquid for displacing gas occlusions;
* time that the vacuum originating the pressure differential is maintained;
Given that we are surrounded by air and atmospheric pressure, the natural
state of
voids in open atmosphere is to be filled with air, water vapor and other gases
as defined
herein. Ideally. upon mixing the two primary phases into the unsolidified,
multiphase,
mixed state, voids in the primary solid phase and in the mixed unsolidif ed
state should be
completely occupied by the solidifiable liquid phase. The occupation, however,
is
generally precluded by the counter pressures exerted by the gases in gaseous
state filling
the voids. Therefore, this gaseous phase f lling voids will be retained in the
mixed,
unsolidified state. Moreover, if no effort is made for their elimination, the
gas occlusions
will remain in the mixed state solidifiable compound, and thus, will
irremediably appear
as voids in the final solid composite.
In the final solid composite, voids or unfilled spaces within the solidified
liquid
phase may be generated by one or more constituents materials of the mixed
state gas
occlusion free solidifiable compound, or during subsequent storage, handling
and
3o processing. Such voids in the solidified composite are not caused by non-
condensable gas
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filled voids or unfilled resin voids pre-existing in the mixed state gas
occlusion free
solidifiable compound, and thus the invention remains valid.
In the invention, the primary solidifiable liquid phase is a polymeric resin
system
generally exhibiting typical viscosities at normal process temperatures. These
viscosities
determine a behavior of the gaseous phase that require further description.
Gaseous phase
occlusions are suspended in the polymeric resin system occurring naturally as
discrete
spherical volumes maintained by a pressure and surface tension equilibrium
that is
established between the liquid and gas phases. Also, gaseous phase occlusions
may
occur as amorphous thin layer gas filled voids of large surface to volume
ratio, lodged in
the interstices within fibers or formed around closely packed aggregates in
the primary
solid phase upon mixing with the polymer resin system, particularly in
compounds having
high volume fraction of solids.
In the mixed unsolidified state, the voids in the primary solid phase may
release
some of the entrained gaseous phase into the primary liquid phase, where it
may join
~ 5 other entrained gases found in the primary liquid phase. Mechanical v~ork
applied to the
mixed state of the two primar}~ phases containing entrained third gaseous
phase will
generally help the release of the gaseous phase lodged in voids of the primary
solid phase
into the primary liquid phase and also help disperse the easeous~ phase within
the liquid
phase. Mechanical dispersion of the gaseous phase can also increase the
surface to
?o volume ratio of the gas occlusions. Some gas occlusions get broken down
into smaller
spherical sizes, while others may adopt other than spherical shapes, generally
of high
surface relative to their initial volume, such as the amorphous thin layers
voids described
above. Gases filling these amorphous, thin layer voids are completely
entrapped in the
interstices within fibers or within packed f bers or aggregates by the
surrounding primary
?5 liquid phase, forming localized and enclosed micro-gaseous phase systems
separating
the two primary phases in mixed state at discrete locations. Moreover, the
volumes of
localized, enclosed micro-gaseous phase systems will be determined by a
pressure
equilibrium existing between the gaseous phase systems internal pressure and
the
surrounding liquid phase at a given process temperature. This pressure barrier
prevents
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the surrounding liquid phase from wetting out the interstices of the solids
where the
micro-gaseous systems are lodged.
As indicated above, voids can take several typical forms within the primary
phase
materials. FIGURE 2 provides an illustration of some typical void forms in
solid primary
phases, prior to mixing. Voids can be viewed as spaces between the interstices
of packed
solids of a primary phase, prior to mixing, as shown in 21 in aggregates, and
as shaven in
22 in fibers. The amorphous, high surface to volume voids, in the form of thin
layers of
gas adsorbed on the surface of solid in the mixed state are shown in 23 in an
aggregate/resin system, and in 24 in a unidirectional and random oriented
fiber/resin
systems. Reference numeral 25 illustrates the typical natural spherical gas
bubble shape
upon mixing of the primary phases. The above characterized voids shown in 23,
24 and
2~ are formed typically in the mixed state and will be retained in the final
composite
material upon solidification, if no effort is made for their removal.
The significant deleterious effect of even low void content, with their
associated air,
i 5 water vapor and other non-condensable gases, in fiber reinforced polymeric
compounds in
the mixed state and carried over to the solid composite state are not
generally fully
recognized. Voids remain one of the major unrecognized source of problems
fiber
reinforced organic polymeric composites face today. Specifically, amorphous
thin gas
layers randomly located constitute a barrier intercepting contact of the fiber
and liquid
2o phases, and thus significantly affect proper resin wet out . More
particularly, this burner
discretely interrupts the continuity of interfacial bonding. For an
illustration, consider a
typical 9 micron fiber diameter fiber reinforced polymeric composite with a 1
% void
content by volume - a void level which is generally considered acceptable by
industrial
quality standards. The effect of that 1 % void content, if present as random
thin gaseous
25 layers of sub micron thickness on the fiber surfaces, as would be ypical in
fiber
reinforced composites manufactured through mechanical work, could be
interpreted as
being equivalent to compromising, or nullifying, the overall contribution to
tensile
strength at failure of approximately 5 to 7% of the fiber volume fraction
present in the
composite.
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If no mechanical work is involved in the production of the fiber reinforced
compound, such as in RTM or SCRIMP, it is reasonable to expect that more voids
will be
as gas occlusions randomly suspended in the resin of the liquid phase, which
generally do
not affect fiber wet out and interfacial bonding as much as gas layers lodged
within or
around the fibers. Moreover, also in this case resin volume fractions are
generally
higher, and the overall fiber contribution nullified by voids would tend to be
less
dramatic. However, there is a practical fiber volume fraction limit in non-
machine
processed products in industry today, at around 50% by volume. This is imposed
not only
by the generally practical difficulty of achieving higher fiber volume
fraction packings,
but also by the effects of voids at high fiber volume fractions, forniing
amorphous thin
layer gaseous random entrapments of very high surface to volume ratios in the
interstices
of the highly packed fiber arrangements. . The counter pressures of such
~~oids prevent
resin wet out of longitudinal contact surfaces of the fibers and within fiber
interstices.
These gas occlusions cannot be removed by the normal vacuum levels of RTM or
~ 5 SCRIMP processes, so attempts to increase fiber volume fraction in these
types of fiber
reinforced polymeric composites, unless voids are first eliminated as per the
invention,
would not be productive.
The application of the general rule of mixtures to fiber reinforced composites
for
longitudinal and transverse extensional moduli suggests a linear increase of
moduli with
2o increasing fiber volume fraction. However, as pointed out above, this is
not evidenced at
high fiber volume fractions beyond SO%, where material properties in fact
actually
decrease. Presumably, such anomalies could be attributed to the deleterious
effects of
voids in the fibers preventing proper fiber wet out and overall interfacial
bonding which is
additionally severely affected by reduced levels of available resin matrix
content in high
25 fiber volume fraction compounds.
Therefore, unless void are first completely eliminated from the mixed state
compound, making accessible to the liquid resin all available fiber contact
surfaces, which
will be otherwise partially blocked by the voids, any increments of fiber
volume fraction
will generally have the equivalent effect of nullifying several times more
fibers than are
3o added.
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It is impossible to control or predict with any accuracy the forms or
locations of
entrained air, water vapor and other gases from the primary phases forming
voids in the
mixed state of a two phase polymeric compound. A wise strategy to improve
maximum
wet out of the phases and obtain optimal interfacial bonding of the surfaces
of the total
fiber available with resin is. prior to mixing, to eliminate air/water vapor
gases
completely from the fibers, and likewise, to completely degas the liquid resin
phase and
eliminate its entrained air and other gases. Moreover, the adoption of a
rigorous
elimination of voids in the production of fiber reinforced polymer composites,
particularly
at higher fiber volume contents, will facilitate increasing composite strength
with
t o increasing fiber volume content, and thus approximate the composite
behavior to that
expected by the rule of mixtures. An important corollary of this is that at
high fiber
volume contents and diminished resin volume contents, the ratio of fiber
contact surface
to available resin volume increases and interfacial boding becomes critical.
In this case,
overall strength appears foremost related to actually achieving maximum
successfully
t 5 bonded surface adhesions between the two primary phases rather than to the
particular
resin strength properties themselves.
The present invention allows reaching a substantially void-free condition. A
non-
condensable gas occlusion-free and void-free material is defined as a two
primary phase
solidif able polymer compound when in substantially the liquid state, and as a
void-free
2o composite when in the solid state. Polymer composites made in accordance
with present
invention exhibit no gas occlusion voids, in the size range of one micron
visually
detected under 1250x magnification in any random cross-section sample of at
least 400
mm2. It is significant to point out that just one void of one micron diameter
in a I mm2
area represents less than 1 part per million .
25 In the case of fiber polymeric composites, if voids were to occur in
diameter sizes
below the above visual count level, given their relative size and dispersion
with respect to
known fiber diameter of 2 to 13 microns, in the prior art, voids could still
affect fber
wet out by the resin, if they are very numerous and in the form of very thin
gas layers.
Such voids would still significantly interrupt interfacial boding, and thus,
affect
30 mechanical properties. Iv'otwithstanding, a method capable of achieving
void freeness
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could still be expected to generally increase significantly the longitudinal
and transverse
elongation moduli and associated strengths, and particularly transverse
strength
properties.
Likewise, in the case of aggregate polymeric composites. void-free polymer
concrete composites made with the formulation of one of the examples in the
invention,
do not exhibit oscilloscopically discernible partial discharges in prototype
insulators when
subjected to high voltages, at least below 90-100KV, while only very modest
partial
discharges would be seen starting above this range. Optimized aggregate and
resin
formulations of dielectric polymer concrete composites, on the other hand, can
to significantly increase the above-threshold of partial discharge initiation
and the ov°erall
dielectric strength of void-free aggregate polymeric composites.
In conclusion, using this new understanding of voids and their sources, a
generic
inventive method yielding a void-free and occlusion free composite material
was derived.
~s Application of the Generic Method to Fabrication Processes
The generic method of the invention for producing two primary phase void-
free/gas
occlusion free unsolidified compounds can be applied to specific present art
fabrication
processes. In particular, the generic method can be most effective in the
manufacture of
thermosetting polymeric compounds and composites where the primary solid phase
.o materials, (are either packed fibers in fiber reinforced polymer composites
or granular
aggregates in aggregate reinforced polymer composites). Such composites and
compounds generally exhibit low bulk densities indicating large amounts of
entrained air
and other gases in the solids.
Tables 1 and 2, and the accompanying legend, further illustrate how the
generic
35 method can be applied to produce two primary phase, thermosetting polymeric
compounds and composites, combining the void free method with conventional
mixing
and forming processes (batch mixing, continuous mixing or combinations of
both). As
further shown in Tables 1 and 2, the void free method can be used to fabricate
a vast array
of thermosetting polymeric composites where the reinforcing solids in the
primary solid
3o phase can be either fiber or aggregates, or a combination of both, and
where the primary
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liquid phase can be any thermosetting polymer resin system and monomer, either
extended or not with filler solid materials intended to modify the properties
of the binding
resin matrices.
s A. Batch Mixin,~and Batch Forming Processes
As illustrated in table 1, the generic method can be used in batch mixing and
forming processes. Moreover, using the inventive method, these batch
fabrication
processes can be used to produce an array of void-free and gas occlusion free
compounds
and composites. The choice of matrix reinforcement for the batch processes can
be
to selected from either the fiber or aggregate class of solids. The legend,
seen below, gives
an explanation for each of the numbers contained in Table 1.
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TABLE 1
BATCH MIXING AND BATCH FORMING PROCESSES
PROCESS STAGES & CHARACTERIZATIONS OF TI'PICAL
THERMOSETTING
POLYMERIC COMPOUNDS AND COMPOSITES WITHIN RANGE OF
PATENT
PROCESSES TWO PHASE
BATCH
MfXING
BATCH
FORMING
IN MOLD MIXER MIXER
MIX TO
MIXING TYPE AND FORM STORAGE TO MOLD
TO
STAGES MOLD
MATRIX FIBER FIBER AGGRE AGGRE
REINFORCEMENT GATE GATE
GENERIC PRODUCTSFRP/RTM BMC PC PC
STAGE
Washing
primary
I Solid
Phase
with
Condensable 1.1. and 1:1. 1.1. 1.1.
Gas. and and and
(Primary 1.2 1.2 1.2 1.2
Liquid
Phase
degassed
by
conventional
methods.)
Air free
Mixing
of lwo
STAGE
Primary
Phases
in
II presence 2.2 2.5 2.1 2.1
of
condensable
gas
only
STAGE 3.1
Condensation and
of
III Condensable 3.3 3.2 3.4 3.1
Gas.
STAGE
Uncured
compound
IV storage NIA 4.1 4.1 NIA
STAGE 5.1 5.1
Composite and and
final
V forming 5.1 5.2 5.2 5.1
and
curing
LEGEND TO TABLES 1 AND 2
PROCESS STAGES AND CHARACTERIZATION OF TYPICAL
THERMOSETTING POLYMERIC COMPOUNDS AND COMPOSITES
WITHIN RANGE OF PATENT
Stage 1 De-airing of the hYO primary phases prior to their mixing
Process 1.1. Replace air in solids by washing with a condensable gas
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Process 1.2 Conventional thin film vacuum de-airing of liquid resin system
Characterization at Stage 1-Voids inside solids are occupied only by
condensable gas
and solid mass is soaked in a condensable gas medium. Liquid resin system is
air free.
Stage 2 Air-free mixing of the primary phases in presence of condensable gas
phase
only
Process 2.1 Mechanical agitation in mixing device
Process 2.2 Pressurized injection of liquid resin system into solids
Process 2.3 Combination of Process 2.1 and 2.2
Process 2.4 Continuous immersion of solids in liquid resin system tank
Process 2.5 Mechanical kneading in mixing device
Process 2.6 Mechanical pressure kneading in SMC machine
Characterization at Stage 2-Unsolidified, two-primary phase mixed state
compound
having dispersed occlusion bubbles of condensable gas only.
Stage 3 Condensation of condensable gas, dispersion and diffusion of condensed
gas
Process 3.1 Mechanical vibration under vacuum and condensable gas
Process 3.2 Mechanical pressure
Process 3.3 Hydraulic pressure on resin system
Process 3.4 Gas pressure
Characterization at Stage 3-Unsolidified two primary phase mixed state
compound
lacking voids and gas occlusions.
Stage 4 Unsoiidified void-free compound storage (if applicable)
Process 4.1 Storage at below ambient temperature
Note: Storage conditions must maintain Stage 3 characterization.
Stage 5 Solid composite final forming and curing under absolute pressure at
least
35 equal to vapor pressure of condensable gas at specified maximum process
temperatures
Process 5.1 External pressure applied to composite in mold
Process 5.2 Mechanical pressure and heat of forming dies
Process 5.3 Process' own pressure
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Final Characterization-Formed solid composite product free from air and gas
occlusions, voids.
B. Continuous Processes
As illustrated in Table 2, the generic method can be used in continuous mixing
processes. In this case, the forming protocol can be either batch or
continuous.
Moreover, using the inventive method, these continuous fabrication processes
can be used
to produce an array of void-free and occlusion free compounds and composites.
'The
choice of matrix reinforcement for the batch processes can be selected from
either the
fiber or aggregate class of solids. The legend above gives an explanation for
each of the
numbers contained in Table 2.
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TABLE 2
CONTINUOUS MIXING WITH BATCH AND CONTINUOUS FORMING
PROCESS STAGES & CHARACTERIZATIONS OF TYPICAL
THERMOSETTING
POLYMERIC COMPOUNDS AND COMPOSITES WITHIN THE RANGE
OF PATENT
PROCESSES _ TWO E UOUS
PHAS CONTINMIXING
BATCH NG CONTINUOUS
FORMI FORMING
MIXER MIXER
TO
MIXING TYPE STORAGE TO IN LINE
TO MIXING
FORMING
MOLD
MOLD
STAGESMATRIX FIBER AGGRE AGGRECONTINUOUS AGGRE
REINFORCEMENT GATE GATE FIBER GATE
PULTRU FILAMENTCENTRU
GENERIC SMC/TMCPC PC SION WIND FUGAL
PRODUCTS FRP FRP PC
STAGE
Washing
primary
1 Solid
Phase
with
Condensable 1.1. 1.1. 1.1. 1.1. 1.1. 1.1,
Gas. and and and and and and
(Primary 1.2 1.2 1.2 1.2 1.2 1.2
Liquid
Phase
degassed
by
conventional
methods.)
Air
free
Mixing
of
two
STAGE
Primary
Phases
in
II 2.6 2.3 2.3 2.4 2.4 2.3
presence
of
condensable
gas
only
STAGE
Condensation
of
III 2.6 3.2 3.2 5.3 5.1 5.3
Condensable
Gas.
STAGE
Uncured
compound
IV 4.1 4.1 NIA NIA NIA NIA
storage
STAGE 5.1
Composite and
final
V forming 5.2 5.2 5.1 5.3 5.3 5.3
and
curing
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In fabricating polymeric thermosetting composites by the void free method,
conventional pressure vessels adapted as needed, are used to maintain a
pressure- ,
controlled, air-free environment. Most preferably, a vacuum source should be
used. In
particular, in the three stages of the generic method, the pressure vessel
must be
connected to external pressure sources designed to operate at process
temperatures in a
pressure range from about 1.2 to 3 times the vapor pressure of the condensable
gas
selected. These pressures will generally be sufficient to force the liquid
phase to fill the
voids during stage III.
Application of the Generic Method to the Production of Compounds and
Composites
The generic process of the invention for two primary phase, non-condensable
gas
occlusion free and void-free solidifiable compounds can be applied
specifically to various
technologies common in the field of polymeric composites. FIGURES 3-5
illustrate how
both thermosetting polymer concrete composites and fiber reinforced
thermosetting
polymer composites can be produced from the generic method of the present
invention
with two additional successive processing stages that take the characterized
non-
condensable gas occlusion free and void-free compound to final void-free
polymeric
composite.
Detailed descriptions of preferred embodiments illustrating the application of
the
2o generic inventive method to the production of two-primary phase, void-free
compounds
and composites are shown in FIGURES 3-S. These figures are illustrations of
the
inventive generic method used to produce void-free polymeric composites by a
variety of
methods known in the art. FIGURES 3 and 4 are examples of void-free polymer
concrete
composites, and FIGURE 5 is an example of a void-free fiber reinforced polymer
composite produced by Resin Transfer Molding (RTM). Additionally, these
figures show
flow charts of specific fabrication methods applied in each of the successive
three stages
described in the inventive generic production method, followed by up to two
additional
successive stages required to yield the respective final void-free polymeric
composites.
The generic method is likewise applicable to paints and gel coats, which are
used as
3o barriers to protect the external surfaces of reinforced polymer composites
and polymer
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concrete. Gel coats are polymeric compounds (solidifiable liquids) filled with
thixotropic
solids (pyrogenic or fumed silicas, for example) and are known in the industry
to contain
a significant amount of voids due to entrained air. Because these large and
numerous
voids are unsightly, gel coats are heavily pigmented to mask their presence.
A. Polvmer Concrete Composites, Methods and Materials
1. Batch Polymer Concrete
Polymer concrete (PC) composite sample in FIGURE 3 is made by batch processes
in four successive stages to yield a non-condensable gas occlusion free and
void-free solid
polymer concrete material. The description of these stages is as follows per
FIGURE 3
and as specified in Table 3.
i. Sta;~e I - Elimination of air water vapor and other gases from the ~riman~
solid phase in parallel with degassing of the primary solidifiable polymer
liquid phase
Using the present invention, the two primary phases are generally processed
prior to
their mixing, with each phase being degassed separately by a different method.
These
two degassed phases are then brought together and mixed under air free
conditions. The
key objectives in the method are: I ) to completely eliminate air with
associated water
2o vapor and traces of any other gases by displacing them, and, thereby,
filling the voids of
the primary solid phase materials with a condensable gas prior to mixing, and
2) in a
separate process, to eliminate air and traces of other gases from the liquid
resin system by
degassing the liquid under high vacuum using conventional thin film methods
prior to
mixing. The two air free phases can then be mixed under air free conditions
where the
only gas present is the condensable gas used to wash the solid materials.
Air and associated water vapor and other gases which fill or are entrained in
dry
reinforcing materials, used in this batch mixing example, are eliminated by
placing the
solids inside a vessel connected to a vacuum source while using the apparatus
illustrated
in FIGURE 6. Condensable gas in the liquid state at ambient temperature and
3o atmospheric pressure is fed into the inclined vessel. The amount of
condensable gas in
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the liquid state is dosed so that at least twice the void volume of the vessel
and void
volume in the packed aggregates will be occupied by the condensable gas upon
its
evaporation. Evaporation of the condensable gas in the liquid state is
initiated by
applying a vacuum to the closed vessel, preferably with the vessel and
contents at rest,
and with a stream of condensable gas rising from the bottom surface of the
vessel upward
through the packed solids to the upper vacuum port. This vacuum is pulled
until the
entire liquid content has evaporated and then the vacuum port is closed. The
chosen
condensable gas will thus have completely displaced and replaced the entrained
air, water
vapor, and other gases in the voids of the solids and in the free volume of
the vessel.
t o Optionally, the vessel can be heated externally in order to maintain the
initial system
temperature to compensate for the heat intake of the endothermic evaporation
process of
the condensable gas and also to ensure the condensable gas remains in gaseous
state. The
gas process conditions at the end of evaporation of the condensable gas must
be
maintained so that external air is prevented from contaminating the contents
of solids
t 5 soaked with condensable gas in gaseous state, and more importantly, to
prevent reversion
of the condensable gas replacement in the solids by external air. The
degassified
solidified liquid resin phase is then fed into the closed vessel to begin
batch mixing with
the solids soaked with condensable gas.
Air, water vapor, and other gases dispersed in the liquid thermosetting resin
system
2o are likewise also eliminated prior to mixing in a separate process by using
any
conventional, effective, thin film vacuum degassing process. As previously
stated, the
resin system is a second source of potentially large volumes of air and other
gases that
would be incorporated into the two primary phase mixed compound if, as in
prior art, no
step is performed to ensure their complete removal.
ii. Staae II - Air free mixing of the two air free primar~phases
The two air-free phases are then mixed under air free conditions in the closed
mixer
at process temperature and a suitable condensable gas vaporization pressure.
Here the
only gas present is the condensable gas used previously to wash the solid
materials.
3o Moreover, mixing occurs in an atmosphere of the condensable gas. Thus, in
the inventive
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process the mixing process of the two primary phases takes place in a medium
where the
third phase, i.e., the gas phase has been rendered free of air by condensable
gas
replacement per the invention.
When mixing is complete, the condition of the mixed state compound will be
otherwise identical to that in prior art processes, except that in the
invention the third
phase consists of a condensable gas phase, instead of air, water vapor and
other gases.
Furthermore, the condensable gas is randomly dispersed throughout the viscous
liquid
phase by the mixing of the phases. At this point, the gas phase is in the fonn
of discrete
spheres or bubbles suspended in the liquid phase or entrapped in the
interstices within the
primary solid phase.
In this example of batch mixing and forming, the two primary phase polymeric
compound, as shown in FIGURE 6, is poured into the mold section of the vessel
maintaining the mixing process conditions. To accomplish this, as illustrated
in FIGURE
6, the mold is attached to , and forming part of, the mixing chamber in the
vessel, and by
pivoting the assembly, the contents in the mixing chamber are gravity fed into
the mold
cavity. The accommodation of the two phase mixed compound in the mold is
completed
by mechanical vibration to pack the two phase mixed compound tightly to the
shape of
the mold, thus ensuring all corners are filled, and at the same time,
dispersing the
condensed gas droplets into the soiidifiable liquid system.
iii. Stage III - Condensation of the condensable has
With the two phase compound in the mixed state sufficiently packed into the
mold,
as shown above, the process pressure is made at least equal to, or preferably
higher than
the condensable gas vapor pressure at the process temperature. This enables
the absolute
2s pressure at any point within the mixed state compound mass to be at, or
above, the
condensable gas vapor pressure, thus ensuring all dispersed condensable gas
bubbles will
condense, and all voids thereby, will be filled with liquid resin. Under these
conditions,
the condensable gas phase is totally condensed. Sufficient time is allowed for
the
condensed gas in the liquid state to fill voids throughout the mixed state
compound,
3o yielding a void-free polymer concrete compound.
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iv. Stale IV-Void-free compound solidification to form a final solid void free
nolymer concrete composite shaped by the mold
The void-free polymeric concrete compound is allowed to solidify in the mold.
Upon complete cure, the void-free solid polymer concrete composite part is
removed from
the mold.
As detailed in Table 3 below, this polymer concrete example has been produced
according to the four stage method described herein The particular formulation
of the
phases, choice of the condensable gas, and process parameters were adjusted to
produce a
void-free dielectric class polymer concrete composite meeting the visual count
void-free
criteria and the electrical partial discharge criteria indicated in the
invention herein, and
illustrated in Figure 8. Moreover, under these conditions, the final composite
is also a
readily machineable material suitable for mass production of a high voltage
electric
current insulator, as illustrated in Figure 8.
~ 5 EXAMPLE 1
Table 3 reveals the material specification and process parameters used to
yield a
void-free and occlusion free polymer concrete material. The specific
application of the
generic method used to produce the example material given in Table 3 is
illustrated in
FIGURE 3.
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TABLE 3
TYIO PRIP.1ARY PHASE BATCH taIXItiG, BATCH MOLDitiG, MIXER TO tlOLD ttETHOD
oni vr_~.=a enntca~rF cnw.IP~SiTE
Cast Dielectric
A Polymer Concrete
t.IATERIAL
SPECIFtCATIOt:S
B23
SOLID
REINFORCEt.IENT
A
gregates,
Silica, (gr) 3474.0
a~
Buik
density
7.6
grlcc.
m
Specific
density
2.6
gricc,
hlax. Diam.(mm)Min. Diam.(mm
0.595 0.420 22.40:: [grJ 778.2
0.420 0.297 20.20ie ( 701'7
r)
0.297 0.149 35.501: r) 7233.3
0.149 0.000 21.90:: (gr) 760.8
ATH ( 1362.0
BACO r)
SS
Total 4838.0
Solids
CONDENSABLE
GAS
- ( 48.4
Methylttethacrilate. r
tdhlA
LIQUID
RESIN
bIATRIX
- (gr) 987
Thermoses
Resin
palatal
A
430,
bisphenol
A
pot
ester
resin
- [gr 177
tAono
Styreno
- (sec) 34
Resin
Matrix
Viscosity
,
Ford
x
4
ASTt.1
cup
~
25C
Cstalyzation
System
(Inmediate
use)
-
Cobalt (% 0.10%
Ocloale resin
6%. bdSe)
- (% 0.15'/.
DA1A resin
N,N~dimethylaniline. base)
- {/. 1.00/
hIEKP. resin
hlethyi base)
thyi
Ketone,
Peroxide.
B
PROCESS
PARAt.IETERS
STAGE
t,
SMASHING
PRlt.IARY
SOLID
PHASE
YIetNng
Solid
phase
with
liquid
GlhlA
Closed [rpm 40
mixer
can
, (Hg 760
- mm)
Absotule
pressure,
S [C( 30
stem
temperature,
- (minutes) 10
Time.
Gas
vapotisatfon,
mashing
and
air
replacement
with
gas
AlhlA
- rpm) 0
Closed
mixer
can,
- (Hg 50
Absolute mm)
pressure.
- 'C) 30
Initiai
Temperature,
- minutes) 15
Time,
STAGE
II,
AIR
FREE
MIXING
OF
T1'10
PRIhIARY
PHASES
Mixing
Process
Resin
In
eclion
This
rocess 780
re
wires
revious
dealred
ii
uid
hase
- (Hg
Absolute mm)
pressure,
Closed Vim) ,
mixer 0
can.
- ('C) 25
Temperature,
- [minutes) 5
Time,
Mixing
in
presence
of
condensable
gas
- (rpm) 40
Closed
mixer
can.
- (H 250
Absolute mm)
pressure.
- . 30
Temperature. 'C
- (minutes) 5
Time,
Alotd
Failing
Process
htald
attached
to
mixer
(Hg 250
mm)
- ('C) 30
Absolute
pressure,
Temperature, [minutes) 1
-
Time,
STAGE
ill,
CONDENSATION
OF
CONDENSABLE
GAS
(bar) 70
Absolute (minutes Included in
pressure, Stage IV
-
Time,
STAGE
IV,
COt,IPOSITE
FINAL
FORt.IING
L
CURING
Curing
{bar) 10
- ('C) Room temperature
Absolute
pressure,
- (minutes) 60
Temperature,
_
r.,.,w-..em:...,
e,.....f...,
rmrtnn
and
Demoldind
Time.
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2. Continuous Miring Polymer Concrete
FIGURE 4 illustrates a continuous mixing process in five successive stage to
yield a
void-free polymer concrete composite material, including an optional storage
stage
between the characterized two phase non-condensable gas occlusion free and
void-free
polymer concrete compound and the final solid void-free polymer concrete
composite.
The description of these stages is as follows, as shown in FIGURE 4.
i. Stage I-Elimination of air and other eases from the primary solid phase in
parallel with degassing of the primary solidifiable polymer liguid phase
The two primary phases are generally processed as in Stage I above. However,
as
this embodiment is produced in a continuous process, there are differences in
the
condensable gas washing method.
In continuous mixing apparatus embodiments for polymer concrete, illustrated
in
~ s FIGURE 7, the solids with entrained air, water vapor, or other gases are
first gravity fed
continuously under ambient conditions into a closed vertical solid loading
hopper, and
through a rotary seal valve located on the top of the hopper that prevents
external air from
entering and breaking vacuum. Vacuum in the loading hopper reduces the volume
of
entrained air and other gases in the solids and prepares the primary solid
phase for gravity
2o discharge through a lower seal valve into a vertical condensable gas
replacement column,
which is also under vacuum. The gas replacement column has a lower discharge
through
the shroud into the internal screw chamber of a conventional, continuous screw
type, two
primary phase soIid/liquid mixing machine. Condensable gas, which is
evaporated
externally and fed through valves in the shroud of the continuous mixing
machine first
25 soaks the solids inside the screw chamber, and then streams upward towards
the upper
zone of the gas replacer column, soaking, in counter-current, the downward
traveling
solids of the primary solid phase. Continuous feed of de-aired solids for
mixing is
produced by the rotation of the mixing screw which advances the de-aired
solids forward,
where they are soaked in condensable gas, and allowing continuous gravity feed
of
3o processed solids from the filled gas replacement column.
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The primary liquid polymeric resin phase is degassed free from air and other
gases
in a separate process using any conventional, effective, thin film degassing
process.
ii. Stave II and Staye III-Air free mixing of the twoprimar~phases and
subsequent condensation
Air free continuous mixing process in the screw type machine is accomplished
by
screw rotation which advances forward the primary phase solids soaked in
condensable
gas and by feeding the degassed solidifiable liquid phase into the screw
shroud. 'Mixing
is followed by pressurized condensation of the condensable gas and
densification of the
1 o mixed state compound in the screw type mixing machine. These steps are
represented b~~
successive adjacent zones, as illustrated in FIGURE 7. The two phase void-free
unsolidified compound characterized in the generic method of invention is
discharged
from the continuous mixing machine through a collapsible rubber spout choked
by
adjustable springs set to close down when the machine looses process speed, or
to shut
when stopped. The spout allows essential air-free continuous discharge as it
prevents
atmosphere air from penetrating inside the screw and shroud of the machine
discharge
port. The rubber spout is sized to suit the machine speed or capacity,
compound
characteristics, and other process parameters.
2o iii. Staye IV-Void-free com,.pound packaging for storaee
Void-free compound packaging for storage is done using collapsed, air free,
flexible
material packaging containers of desired shape and dimension, which are
attached onto
the discharge spout of the continuous mixing machine to successively receive
the void-
free solidifiable polymer concrete compound. Pressure exerted by the rotation
of the
mixing screw will force the compound out of the discharge port of the machine
into the
collapsible rubber spring loaded spout, which is forced to remain open by the
moving
void-free material pressing against the set pressure of the closing springs.
In this way, the
compound is loaded into the collapsed flexible container attached to the
spout. As an
individual container is filled, a proximity signal mechanism increases the
closing spring
3o tension, collapsing the rubber spout shut while the mixing machine
continues to run. . At
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this point, the volume of compound discharged expands the rubber body of the
shut spout,
which now acts as a compound accumulator, increasing its original volume.
Meanwhile,
the compound filled container is externally detached from the rubber spout and
a new
empty collapsed, air free, flexible container is re-attached on the spout to
begin a new
cycle. The high tension level of the springs is then signaled to start
releasing back to the
normal setting. The accumulated volume of void-free compound in the rubber
spout thus
begins to force itself out of the spout and into the new empty collapsed
flexible container,
as the spout spring tension becomes released to allow material discharge.
If used as forming molds, the containers filled with void-free unsolidif ed
to compound are sealed and the placed into a conventional autoclave, to harden
in the shape
of the containers at adequate combinations of pressure, temperature and time.
Alternatively, the flexible container with unsolidified compound can be
subsequently
shaped by placing the sealed container and contents into a two or more part
sectional
mold, in which, by a combination of pressure and temperature the void-free
unsolidified
compound will harden into a solid, void-free, shaped polymer concrete
composite.
Alternatively, if desired the filled flexible containers are sealed and placed
in
storage at reduced temperature, preferably in the range of +20°C to-
20°C, for up to 6
months depending on the characteristics of the solidification substances
incorporated in
the liquid resin system.
B. Fiber Reinforced Polymeric Composites. Methods and Materials
FIGURE 5 illustrates a batch mix and forming processing by the inventive
method
in four successive stages to yield a void-free, solid, fiber reinforced
polymer composite
material in laminar shape, formed by Resin Transfer Method (RTM). The
description of
the RTM process stages are as follows, as per FIGURE 5 and Table 4:
i. Stage I-Elimination of air and other eases from the priman~ solid phase in
parallel with deeassin~ of the~rimat-~solidifiable polymer liquid phase.
For RTM, and similarly for the newer SCRIMP process, vacuum is applied in the
fiberglass solids in the mold before mixing with the resin. In the generic
method, the
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fiber is first washed with a stream of condensable gas through the same resin
injection
ports (particularly in SCRIMP), and the condensable gas is injected or infused
while the
system is still under vacuum. The process is continued until condensable gas
is detected
at the vacuum exhaust ports. Under these conditions the condensable gas stream
will
s have adequately replaced all entrained air, traces of water vapor in the
fibers, and other
gases that may have been entrained by the solids. However, in the case of
complex shape
parts, or where mold corners are remote or difficult to access by the
condensable gas
stream, the gas replacement may not be totally effective. For this case, the
generic
process offers an additional alternative which consists of cutting the vacuum
flow, but
retaining vacuum presence in the system. This step is followed by pressure
injected,
outside evaporated, condensable gas at an elevated temperature, above the
system's
temperature, generally in a range of up to + 40°C above ambient
temperature. This gas
injection is continued until the gas pressure in the outside evaporator, at
the constant
above ambient temperature selected, is in equilibrium with the internal
pressure of the
15 system. This step is maintained until the amount of liquid in the external
gas evaporation
chamber has been evaporated. The additional external condensable gas at higher
temperature that has been introduced will thereby elevate the temperature of
the fiber
solids and, thus, is able to reach the mold corners and other difficult spots
because of its
higher pressure. In this manner, the condensable gas is able to disperse some
of the
20 original entrained air. water vapor and other non-condensable gases that
may not have
been totally remo~~ed. As the temperature of the condensable gas drops by
giving off its
heat to the colder solids, it will partially condense until pressures are in
equilibrium. At
this stage vacuum is reestablished in the system and the condensable gas that
has
condensed will re-evaporate at each condensation spot and stream out under the
vacuum,
z5 entraining the remaining air, water vapor and other gases. The solids are
now air-free,
water vapor-free and soaked with condensable gas.
The reinforcing solid, in Example 2, is a laminar fiberglass mat which is
placed
inside a close mold. The same mold will serve, in this case, as a degassing
device, mixing
device, condensation device and solidificationlmolding device. Upon placement
of the
3o fiberglass mat. the mold is closed and evacuated while a condensable gas,
preferably
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WO 99/26999 PCT/US98/24818
evaporated externally from a gasifiable liquid, is fed into the closed mold
under vacuum
for a sufficient time to completely soak the f ber glass mat and to displace
all entrained air
and other gases in the fiber glass solid. O, presence in the exhaust ports of
the mold can
be monitored with an OZ, sensor. The processed primary fiber glass phase is
now air-free,
s soaked with condensable gas, and ready for mixing with a separately degassed
primary~
liquid polymer resin phase. Liquid phase degassing is done by conventional
thin film
technology as disclosed in prior art.
ii. Stage II-Air free mixine of the two air free primary phases
Stage iI, air-free, tmo-primary phase mixing begins by infusing (SCRIMP) or
injecting (RTM) the degassed primary liquid resin system under vacuum in the
system. It
is particularly important that the resin system is degassed and air-free. Once
the liquid
resin has been introduced filling the mold and soaking the solid phase,
condensable gas in
the system will be occluded in the mix.
1s Liquid polymer resin is injected under positive pressure per conventional
RTM
technology through conveniently located ports and distribution channels into
the mold,
until the liquid resin emerges from the separate vacuum exhaust ports. At this
point both
the vacuum and resin ports are closed and left closed until the beginning of
the
condensable gas condensation.
iii. Staee III-Condensation of the condensable ,gas
Depending on the choice of condensable gas, condensation of the condensable
gas,
typically Stage III may have already occurred in Stage II, under the pressure
of the resin
injection. This is more likely in cases such as the straight forward laminar
shape of the
2s mold used in Example 2, and detailed in Table 4. However, in more complex
shapes,
and/or pieces with variable sections, it is preferred to place the closed mold
with contents
in a pressure chamber and pressurize she system to an adequate pressure for a
sufficient
time to achieve a void-free fiber reinforced polymer compound of the quality
level
required per conventional RTM technology. The characterized compound invention
3o condition will have been reached when:
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1 ) Washing of air, water vapor and other gases by the condensable gas has
been accomplished; here entrained water vapor is deleterious and
eliminating it improves the polymerization reaction. _
2) Soaking of the fiber surfaces with condensable gas modifies and lowers the
glass fiber surface tension level; the liquid when coming in contact with
the fiber to forni the interfacial bond now comes in contact first with the
condensable gas soaked fiber surfaces; and, moreover, without back
pressures from non-condensable gas occlusions; wet out of the fiber by the
resin and interfacial bonding will be improved.
iv. Stave IV- Solidification of the void-free fiber reinforced polymeric
compound into a void-free composite shaped by the mold
~ s Solidification of the compound v~ill occur, according to the
polymerization art
described in RTM technology, to produce a f pal solid, laminar shaped, void-
free fiber
reinforced polymer composite that complies with the visual count void-free
criteria
established in the invention. A detailed data sheet is given in Example 2
below.
2o EXAMPLE 2
Table 4 reveals the material specifications and process parameters to yield a
void-
free and occlusion free fiber reinforced polymer (FRP) material. The specific
application
of the generic method used to produce the example material given in Table 4 is
shown in
FIGURE 5.
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' TABLE 4
T~'JO PRIl.IARY PHASE BATCH lAOLDING,
IN N10LD lJIIX AND FORh1 BY RTl.1 PlETHOD
LAl:IINAR FRP COMPOSITE
La"Zinar F.R.P.
A l.IATERIAL SPECIFICATIONS R.T.hI.
(FV-9)
SOLID REINFORCE~~AEI
Filament Fiber ,
Glass fiber (MAT 450 r/m2) [ r i21
CONDENSABLE GAS
- Meth I-Me;hacrilate, MMA [ml 6
LIQUID RESIN MATRIX
Thermoset Resin
- Palatal P t30, tJnsalurated [ r] 314.5
pot ester,
- Viscosity , Ford t; 4 ASTM [sac] 34
cup ~ 25'
Catalyzation System (Inmediate
use)
- Cobalt Octoate 6%, [% resin base]O.tO:o
- DMA N,N-dimeth !aniline. [% resin base]0.15%
D.leth I Ethyi Ketone, Peroxide,[% resin base]1.00%
8 PROCESS PARAlAETERS
STAGE i,1YASHING PRIMARY SOLID NIA
PHASE
Gas replacement '
RTM mold
- Absolute pressure, [Hg mm) 40
- Temperature, eC~ __ 30
- Time, [minutes] 12
STAGE tl, AIR FREE MIXING OF
TV'!O PRIMARY PHASES
l~Aixlng Process
Resin Injection
This process requires pevious
desired liquid phase I
- Absolute pressure, [Hg mm] 760
- Temperature, . [C] 25
- Time, [minutes 3
Fiber Glass In RTM mold
RTM mold tilled with fiber glass
and inunded with condensable
as
- Absolute pressure, [H mm) 250
- Temperature, [C 2~
STAGE III, CONDENSATION OF CONDENSABLE
GAS
- Absolute pressure, bar] 6
- Time, [minutes Included in
Stage iV
STAGE IV, COMPOSITE FINAL FORMING
Ix CURING
Curing
- Absolute pressure, [bar) 6
- Initial temperature, C] Room temperature
- Time, [minutes 35
- Condensation, Forming, Curin 90
and Demolding Time,
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C. Conclusion
The descriptions detailed above illustrate the many facets and applications of
the
generic void-free method in composite technology and production. The inventive
method
can be utilized to produce a vast array of void-free polymeric compounds and
composites.
s Moreover, a polymer concrete sample and a fiber reinforced polymer composite
sample
free of gas occlusions and voids has been produced and detailed herein.
Apparatus
to a. Aooaratus for Batch Production of Void-Free Polymer Concrete
Compound and Composites
F1GURE 6 illustrates a preferred embodiment of the apparatus for batch
replacement of air, water vapor, or other gases normally contained within the
interstices,
spaces or voids of the primary solid phase at ambient temperature and
pressure, by a
t s condensable gas prior to batch mixing with a solidifiable liquid phase to
yield, a two-
primary phase solidifiable polymer concrete compound free from non-condensable
gas
occlusions. The compound is poured from the mixer into a mold in air-free and
non-
condensable gas free environment. When the solidifiable compound is in the
mold, the
apparatus is pressurized to condense the condensable gas in the compound
already in the
mold, and optionally, can be solidified in the mold to produce a gas occlusion
free and
void-free composite formed in the shape or configuration of the mold. The
apparatus 30
shown in FIGURES 6A and 6B include mixing chamber 31 with a mold 32 attached
to it.
The apparatus 30 has 2 operating positions : for mixing (FIGURE 6a) and for
pouring the
solidifiable mi~;ed compound into the mold (FIGURE 6b). The primary solid
phase is
~5 placed in the mixing chamber 31, preferably with~a Class I gasifiable
liquid. Vacuum is
applied through the vacuum inlet port 33 and the entire assembly is rotated
mechanically
about its longitudinal axis as indicated at 34 for 1 to 2 minutes with vacuum
shut off. The
contents of solids and gasifiable liquid are washed thoroughly together. This
allows the
gasifiable liquid to completely wet out the solids and to begin an evaporation
process.
3o The resulting condensable gases evaporated from the liquid to replace the
air, water vapor
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associated with air, or other gases in the solids. The system is stopped for I
or 2 minutes
and vacuum reestablished to evacuate the air, water vapor associated with air
or other
gases entrained in the condensable gas. The wash cycle is repeated, preferably
at least
four times, without addition of condensable gas. Upon completion of the
washing stage,
the primary solid phase will have all its voids filled with condensable gas.
At this point the primary solidifiable liquid resin system previously degassed
is
infused by vacuum into the apparatus through the inlet port shown in FIGURE
6a. A
mixing cycle of the two primary phases in the presence of condensable gas only
is started
by mechanical rotation of the apparatus, with vacuum shut off, and continued
for 4 to S
to minutes. At the end of the mixing cycle the two primary phase solidifiable
mixed
compound is free from non-condensable gas occlusions and ready to be poured
and
gravity fed into the attached mold 32.
As illustrated in FIGURE 6b, this step is accomplished by rotation of the
apparatus
30 until the attached mold 32 is in the bottom position. Once the solidifiable
mixed state
t 5 compound is lodged in the mold, at rest, a thin film of liquid resin is
formed over the top
exposed surface after a short period of vibration (depending on the size and
shape of the
mold of) I or more minutes with the vibration device 39. Pressure in the
apparatus 30 is
increased by allowing pure CO, gas to enter into the apparatus through inlet
port 3~. This
pressurizing gas is at atmospheric pressure or preferably at an absolute
pressure at least
2o equal to 2 times the condensable gas vapor pressure at the process
temperature. The CO,
gas environment maintains the system air free and eliminates presence of OZ
from outside
air to ensure optimal solidification of the primary solidifiable liquid phase
in the
compound. Upon pressurization, the pressure of the C02 is exerted on the mold
contents
through the thin barrier layer of resin on its upper exposed surface, which is
sufficient to
25 prevent CO, gas dispersion into the material in the mold, yet its pressure
will condense
the condensable gas within the solidifiable mixed state compound in the mold ,
and
further maintenance of COZ gas pressurized condition for at least I minute
will ensure the
solidifiable liquid phase will enter all voids in the compound. At this stage,
the two
primary phase solidifiable compound in mixed state in the mold 32 will have
reached the
3o characterized condition of freedom from non-condensable gas occlusions and
voids. . To
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obtain a void-free molded composite, the mixed state compound is left to
solidify in the
mold 32 under positive CO, absolute pressure conditions. If desired,
consolidation of the
solidifiable compound in the mold can be facilitated by the use of a vibration
device 39
mounted on the mold 32, prior to curing. .
It will also be noted that, in the apparatus 30, the mold 32 is removable as
indicated
by the bolted joint 36 and bolt fasteners 37. This allows the compound to be
cured in the
mold 32 off line while a new, empty mold is reattached to the apparatus 30 so
that
compound production can be expedited. Likewise, the mixer 31 is demountable at
a
similar bolted joint 38 to allow maintenance and repair, and also to allow
attachment of
other mixing chambers 31 of differing capacities and geometrical shapes, or
allow
attachment of a hopper equipped with a conventional air tight auger screw type
discharge
device in place of mold 32. to intermittently discharge discrete metered
amounts of gas
occlusion free solidifiable compound from the apparatus into external molds.
~ 5 b. Apparatus for Continuous Void-Free Polymer Concrete Compound
Production
FIGURE 7 illustrates a preferred embodiment of an apparatus 40 for continuous
void-free production of polymer concrete. As explained above in detail, the
apparatus 40
can be used in a method of production involving the replacement of air, water
vapor or
20 other gases normally contained within the interstices, spaces or voids of
the primary solid
phase at ambient temperature and pressure, by a condensable gas prior to
continuously
mixing with a solidifiable polymer concrete compound free from non-condensable
gas
occlusion and voids.
The apparatus 40 includes a condensable gas displacementlreplacement counter
25 current column 46 with an upper zone vacuum chamber 26. Within the chamber
26, a
controlled vacuum condition is maintained to exhaust air, vapors and gases,
normally
entrained in the priman~ solid phase which are continuously displaced/replaced
by a
stream of condensable gas. A lower discharge zone 27 is connected at one end
to the
column 46 and to the shroud 49 of a continuous screw type mixing apparatus 28.
Inlets
48 for the condensable gas are provided in the shroud 49 to flood with the
condensable
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gas the discharge zone 27 of the column 46 and the adjacent volume inside the
shroud
where processed solids are discharged. Condensable gas horizontal deflector
baffles 47
are provided inside the column wail to effectively distribute the upward
stream of
condensable gas, traveling towards the upper zone vacuum chamber 26, with the
primary
s solid phase falling by gravity in the column. This counter flow of
condensable gas
produces a washing effect which displaces and replaces entrained air and other
gaseous
substances in the primary solid phase by the condensable gas.
Since the counter flow of condensable gas is at positive pressure flow to
facilitate
the washing process, it will be recognized that this streaming condition
reduces
consumption of the condensable gas and increases the efficiency of the
apparatus 40.
Oxygen sensing devices 62 are provided in the column 46 at different levels to
monitor
the presence of air and to ensure no oygen is detectable in the lower
discharge zone 27 or
in the flooded shroud zone 49 of the continuous mixing apparatus 40. This
monitoring is
achieved by means of a gas control and feedback system 30. If oxygen is
detected by the
~ 5 monitors 62. the control system 30 appropriately adjusts the Level of
condensable gas
entering the inlets 48. Optionally, in a preferred embodiment. a vibrating
device 60 with
vibration control mechanism is attached externally to the column wall to avoid
agglomeration and promote free flow of the primary solid phase, and also to
ensure its
continuous gravity downward travel.
2o Flexible connections 63 are provided at the upper and lower extremes of the
column
46, to connect the column with the upper zone vacuum chamber 26, and to
connect the
lower discharge zone 27 with the shroud 49. Structure is provided above the
upper zone
46 of the column for a vacuum chamber 44 with an exhaust and a receiving
hopper 43,
also under vacuum. for controlled feeding of the primary solid phase into the
column 46.
25 The receiving hopper 43 is provided with rotating seal valves 42 and 45
located at its
upper inlet port 41 and at its Lower discharge port to provide passage, under
vacuum, of
the primary solid phase from atmospheric conditions into the controlled vacuum
gas
displacer column 46. The upper inlet port seal valve 42 of the hopper 43 is
connected to
the external supply of primary solid phase at open atmospheric conditions and
prevents
3o breaking vacuum inside the receiving hopper 43. The vacuum chamber 44 in
the hopper
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43 is provided with vacuum to also assist in the reduction of the amounts of
entrained
gases and vapors in the incoming primary solid phase as it continuously passes
through
the hopper 43, so upon its discharge into the upper zone 26 of the gas
displacer/replacer
column apparatus, the entrained air, gas and vapor substances in the solids
have. been
significantly reduced by vacuum. The lower discharge seal valve 45 of the
receiving
hopper 43 allows the maintenance of differential vacuum levels between the
hopper 43
and the column 46 for more effective control of the displacement/replacement
function in
the gas replacer column apparatus. At the lower discharge 27 of the column 46
into the
continuous mixing device 49, the processed primary solid phase is air and
water vapor
to free and flooded with condensable gas, essentially ready to begin the
continuous mixing
process with a primary solidifiable liquid phase (which has been previously
degassed
externally), to form a two primary phase unsolidified polymer concrete
compound exempt
of gas occlusions, and voids, as per the present invention.
The mixing apparatus 40 of the present invention is also provided with a motor
control 68 for controlling the operation of the rotating seal valves 42,45.
Sensors 69,70
located in the hopper 43 sense the level of the solids therein and provide a
signal to the
controller 68. A control signal is then provided from the controller 68 to the
DC motor 72
controlling the operation of the upper rotating valve 42. Likewise, sensors 64
and 65
located in column 16 sense the level of the solids therein and provide a
signal to the
controller 68. A control signal is then provided to DC motor 67 for
controlling the
operation of the lower rotating seal valve 45. Meters 66, 71 are provided in
column 46
and the hopper 43, respectively, in order to sense the vacuum level within
these enclosed
containers.
The continuous mixing apparatus 40 comprises preferably a continuous mixing
2s device 27 of the shrouded rotating screw type, appropriately modified to
comply with the
following requirements:
1. Condensable gas inlet ports 48 into the screw shroud 49 must be provided
with a mechanism 30 for adjusting the pressure and flow of the condensable
gas. Inlet
ports 48 should be suitably located adjacent to the column discharge zone 27
where the
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air-free primary solid phase, soaked with condensable gas, enters the screw
shroud 49, so
as to provide a continuous counter-current stream of condensable gas through
the
connection between the shroud and the discharge zone moving upwards into the
gas
replacer column 4b.
2. The internal zone within the screw sluoud 49 must be maintained
continuously flooded «rith condensable gas at all times when the mixer 28 is
running.
Furthermore, that zone must be provided with a shielding, such as a double
seas device ~5
to maintain the drive extension 31 of the mixing screw 28 flooded with
condensable gas
in liquid state to prevent contamination from leaks of external atmospheric
air.
Furthermore, the drive extension 31 connects a reducer 59 mounted on the drive
output of
DC motor 58 which rotates the mixing screw 28. The level of liquid state
condensable
gas in the double seal chamber ~5 can be determined by the gas level device
57.
~5 3. The entry port 50 for feeding degassed, air-free primary solidifiable
liquid
phase into the continuous mixing device 40 must be suitably located
downstream, and
sufficiently away from the processed primary solid phase entry zone 32 of the
shroud 49.
4. The downstream configuration of the mixing screw 28 and shroud 49 in the
?o continuous mixing device between the solidifiable liquid phase enter zone
33 and the final
discharge port 53 of the continuous mixing device is subject to the following
design
requirements:
i) The rotating screw 28 must impart sufficient absolute pressure
within any paint of the two primary phase mixed state compound being formed as
it
2s advances towards the discharge port 53 and to completely condense the
condensable gas
within the primary liquid phase of the mix and to force liquid resin into any
voids. Such
pressure must be maintained over the range of screw operational speeds,
including its
minimum speed. This may be accomplished by means of an enlarged diameter
section 54
of the multisection mixing screw 28. This section 54 serves to increase the
pressure of
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the mixture within this condensation zone 34 by reducing the annular space
bet<veen the
screw 2$ and the shroud 49.
ii) The liquid state condensed gas must be sufficiently dispersed and
diffused within the solidifiable liquid phase of the mix in the condensation
zone 34,
before the compound mix reaches the discharge port 53 of the mixing device 40.
iii) Atmospheric air must be prevented from entering the compound
mix through the discharge port 53 and contaminating the gas occlusion and void
free two
priman~ phase mixed unsolidified compound.
to 5. Machine void-free compound discharge must provide means for discharge
of a non-condensable gas occlusion free and void-free compound so that its
characteuzation is assured when the machine stops, such as an air tight,
sealable, flexible
spout 73 to seal off the external air entrance. Also provided is a means for
discharging
the compound so that its void-free characterization is assured, such as air
tight, sealable,
t5 flexible spout stops 35 as having spring or other biasing means to maintain
tight closure.
The apparatus is further capable of accumulating discrete and sufficient
amounts of void-
free polymer concrete compound in it to enable intermittent discharge of the
void-free
material into discrete receiving containers of discrete unit volume, under air
free
conditions.
2o Thus, it will be appreciated that the principles of the apparatus of the
present
invention can be applied to numerous other continuous mixing devices having
similar
features.
Product and Annlications
25 Electric insulators intended for high voltage applications previously have
been
preferably made of porcelain materials. However, more recently it bas been
found that
polymer concrete could be used as the material for such insulator
applications.
Additionally, these insulators provide advantages in both cost and
performance. U.S,
Patent No. 4,210,774, for example, discloses a polymer concrete insulator
having
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dielectric and mechanical properties far superior to those of conventional
porcelain
insulators.
However, an inherent disadvantage of polymer concrete electric insulators has
been
the presence of voids or gas occlusions, as the result of insufficient or
inadequate
degassing and mixing of the solidified material. It is well known that
increased number
of voids, or gas occlusion porosity, resulting from air and associated water
vapor
entrainment in solids, adversely affects the dielectric and mechanical
strength of
insulators, and encourages partial discharges leading to early failure within
the material
body. To overcome this problem, ideally, a void-free material would be
desirable for use
t0 in high voltage electrical insulators.
The insulators prepared from special formulations for void-free dielectric
polymer
concrete, as detailed in Example 1, produced by the generic void-free method
of the
present invention. are designed to be formed or shaped by machining the
insulator shape
directly from cast void-free polymer concrete cylindrical stock, or by
conventional shape
IS molding methods. The resulting insulators formed by machining have
controllable
surface finish and very tight dimensional tolerances, as well as excellent and
improved
dielectric characteristics and mechanical strength. The finish of the machined
surfaces
can be controlled for enhanced adhesion of specialized material coatings in
thin films on
to the machined surfaces, rendering the insulator non-hygroscopic and
hydrophobic for
20 outdoor service.
Moreover, insulators fabricated from void-free dielectric polymer concrete
made in
accordance with the present invention exhibit dramatically increased voltage
threshold for
initiation of partial discharges within the body of the insulator, thus
extending their useful
life.
25 FIGURE 8A-8C illustrate an insulator produced from methods and materials of
the
present invention. FIGURE 8A and 8C are top and bottom views, respectively,
and
FIGURE 8B is a longitudinal cross-sectional view. The insulator 80 in FIGURE 8
is a
resistive voltage grading device whose body 81, shields 84, all bores 83 and
holes 85 to
install threaded metallic contacts 82, have been machined from a cylindrical
stock of
3o void-free polymer concrete composite material complying with both the
visual count
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void-free criteria of no visible voids of 0.5 micron diameter at 1250x
magnification and
dielectric criteria of no visible partial discharges seen in an oscilloscope
screen when
subjected to voltages of 90-100KV.
The good machinability of the void-free dielectric polymer concrete material
of the
present invention enables production of all classes and types of electric
transmission and
distribution insulators, as well as other devices such as bushings and
insulator plates or
rings. Insulators include suspension pin type, strain, line post, etc.,
preferably in higher
voltages ranges up to 100KV or even beyond. One important discovery from the
work
done in this invention is that material formulations appropriate for void-
free, dielectric
t o polymer concretes have also excellent machinability. Another discovery is
that finished
electric insulators of high quality can be efficiently shaped by conventional
machining
with special cutting tools from cast polymer concrete stock material produced
using the
inventive void-free method. Yet another discover is that machining is a high
efficiency
and high productivity forming method far superior to the conventional method
of forming
insulators by shape molding materials in conventional shape molds, in that
better quality
insulators can be produced faster, with shorter lead times and at much reduced
mold and
labor costs. Likewise, very accurately dimensioned dielectric polymer concrete
flat plates
parts can be produced, cut from cast polymer concrete stock into slabs and
then surface
finished by milling, drilling, boring, etc. as required.
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Production of High Solids-Low Resin Void-Free Compounds c~ Composites
As discussed below, void-free technology (VFT) coupled with rigorous control
of
particle size distribution of aggregates allows formulators of aggregate-
reinforced
polymer composites to substantially reduce resin content while increasing
material
strength. Since resin typically accounts for seventy percent or more of the
material cost of
aggregate reinforced polymer composites, minimizing resin content should
render some
polymer composites, such as polymer concrete (PC), cost-competitive with other
aggregate-reinforced materials, including even Portland Cement Concrete (PCC)
in
certain applications.
to The improvement in material strength associated with decreasing resin
content
should also provide additional cost savings since molded, high solids-low
resin polymer
composites can be made with thinner cross-sections than conventional resin-
rich
composites, further reducing material costs by reducing volume of material
applied to
molded products.
Conventional aggregate-reinforced polymer molding compounds are typically
made resin-rich to lower viscosity, and thereby improve processing. Two
factors generally
limit the allowable viscosity of conventional polymer compounds. First, the
viscosity
must be low enough so that the compound can be de-aerated in the mold prior to
solidification. In a typical pour cast de-aeration process, the mold is
vibrated while the
2o polymer compound is exposed to vacuum. Under vacuum, gas bubbles increase
their
diameter, coalesce, and move toward a free surface where they escape from the
compound. Since gas bubble displacement speed depends strongly on the
viscosity of the
molding compound, low viscosity improves effectiveness of the de-aeration
process.
Normally, the de-aeration process requires a lower compound viscosity than the
forming
process. Second, the viscosity must be low enough so that the polymer compound
can be
formed properly. In most cases, the compound is pour cast into molds, which
requires
fluidity (other forming processes, such as injection molding and press molding
can
tolerate higher compound viscosity, but still must be de-aerate).
Though higher resin content than that required to just fill the gaps between
the dry
3o compacted aggregate particles improves compound workability, the mechanical
strength
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of resin-rich polymer composite decreases. The excess resin tends to pool at
exposed free
surfaces or in pockets and layers that appear randomly throughout the
structure of the
solidified composite. Loss of mechanical strength can be traced to these
pockets or layers
of neat resin, which often lead to uneven resin curing, poor adhesion between
resin and
solids, and low-modulus, weak resin-rich spots in the composite structure. In
addition, the
resin rich pockets create regions of high local stress due to resin shrinkage
at
solidification, which generate micro-cracks in the polymer composite matrix.
Moreover,
during extended vibration of resin-rich polymer molding compounds in de-
aeration or
mold filling steps, the larger diameter solid particles often settle to the
bottom of the
mold. This segregation of solids disnipts the homogeneity of the molding
compound,
creating weaker regions at the top and bottom of the molded polymer composite
where,
respectively, the composite material is relatively resin-rich and resin-poor.
Void-free technology, along with careful management of the solid particle
distribution, helps minimize resin use in aggregate-reinforced polymer
compounds while
~ 5 improving material strength. Because the solid phase and solidifiable
liquid phase are
independently degassed prior to mixing, polymer molding compounds of the
present
invention do not require a separate de-aeration step after mold filling. Since
the de-
aeration step generally sets the upper limit of compound viscosity in non-VFT
processes,
polymer compounds of the present invention can be processed with higher
viscosity than
2o conventional resin-rich compounds, and therefore can be formulated with
little or no
excess resin. As mentioned, this results in substantial material cost savings
and
improvement in material strength over conventional resin-rich composites.
Because there
is just enough resin to fill the gaps between aggregate particles, there is
also less particle
segregation. Highly filled polymer molding compounds in the present invention
25 substantially prevent aggregate/resin segregation because there are neither
empty spaces
where particles can move, nor sufficient resin for particles to move through.
Overall, the
formulations with reduced resin contents of the present invention provide more
homogeneous, better-formed composite material structures, which in turn,
account for
improved mechanical properties with consistent, repeatable strength values.
3o A. Minimizing Resin Content in Void-Free Polymer Compounds & Comvosites
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1. Continuous Grading of Ag_ere~ate Solids Particle Size
One can minimize resin content in a void-free polymer compound by continuous
grading of the aggregate particles. Continuous grading refers to aggregate
systems in
which particles are bounded in a diametral range and in which the volume
contributed by
s the particles of each size is determined by a continuous diametral
distribution. In practice,
continuously graded aggregate systems must be built, because neither nature
nor standard
industrial processes provide particles in the desired size, shape, and
required diametral
distribution. To build a continuously graded aggregate system one must f rst
subdivide the
desired particle diametral range into N convenient, non-overlapping segments
or fractions
spanning the entire range. This transforms the procurement of continuously
graded
particles from one large, unmanageable problem into N smaller problems.
Second, one
must procure continuously graded particles within each of the N fractions.
This can be
done by passing the bulk aggregates through a series of N+1 sieves whose
opening sizes
correspond to the diametral boundaries of each fraction. 11~' is established
by how closely
~ 5 the gradation of the actual aggregates needs to conform or fit the desired
continuous
gradation distribution. For coarse fractions, the ratio between the maximum
particle
diameters of successive fractions should typically be two. For fractions below
ASTM
mesh #325, in the present patent, this ratio should typically be between two
and three.
Third, fractions must be combined in proper amounts to fit the desired
continuous
2o diametral distribution. The resulting spatial arrangement of particles will
produce a global
aggregate system with minimum unfilled volume or maximum theoretical solids
packing
density.
One useful empirical formula for calculating the volume of a continuously
graded
system below a certain particle diameter, deduced.from the work published by
A. H. M.
25 Andreason & J. Anderson, 50 Koll. Z. 217 (I930), B Fuller and others, can
be written as:
y=y« D~~ G_~ I
DAUr
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where Dn is the diameter of the largest particles in the fraction "n"; D~ is
the diameter
of the largest particles in the system; V is the cumulative volume of all
particles in
fractions 1, 2, up through n; Vp is the measured total volume of the compacted
aggregate
system, which includes spaces between particles; a is a constant obtained
through
s experimentation, typically, 0.45 to 0.6, depending on the shape of the
particles in the
system (if all particles were perfect spheres, constant a would be 0.5); and
is a positive
term to account for the fact that the continuous gradation does not go down to
particles of
infinitesimal diameters, but rather the smallest particle diameter in the
system is limited
by practical industrial availability and management of fine aggregates. Thus,
the volume
of solid aggregate in fraction n is Vn-Vn_l, or expressed in volume percent yV
, can he
U
calculated from the expression:
a a
_l~V _ D" D"'' x 100 II
Vn Dna.r DAU.c
Formula II has greater practical use than formula I because the error term is
cancelled out
and therefore the calculated volume is accurate enough for constructing
practical
I S continuously graded aggregate systems.
The unfilled volume of the aggregate system can be determined from experiment
in at least two ways. In a first method, prior to processing, one measures the
bulk density,
pg, of the solid particles that were continuously graded in accordance with
equation II.
One simple way to experimentally determine pB is to measure the compacted
volume and
2o the mass of a representative sample of the continuously graded aggregate.
The unfilled
volume represents the theoretical minimum resin content required to fill gaps
between the
particles, and can be estimated from the expression:
y~ =I 1-pg~ x 100 III
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where y is the specific gravity of the aggregate solids, VR is the resin
volume and Vp is
the compacted volume of the dry aggregate system (including unfilled spaces
between
particles).
Instead of measuring pp for each lot of continuously graded particles, one may
also
correlate pB, and hence vR , with Dll~,y and Dp. Assuming a power iaw
relationship
Vu
between pg and the minimum and maximum particle diameters, equation IV
becomes:
Vn _ CI _ bD',c~.,.D~; ~ X 100 IV
t ~,
In equation IV, b, c and d are constants obtained experimentally for a
particular aggregate
system. For example, 104 continuously graded silica aggregate samples
comprised of
to particles without sharp edges and reasonably spherical in shape were
correlated using
equation II with a = 0.45. All of the samples were obtained from the same
mineral deposit
and had particle diameters between about 0.044 mm and 9.525 mm (3/8 inches).
The
correlation resulted in b = 1.382, c = 0.07 1, and d = -0.0442, for y= 2.6
g/cm', and for
D~ and Dp expressed in mm. The calculated unfilled volume was 27.65%. If the
t 5 same continuous gradation is extended with continuously graded particles
from 0.044 mm
down to 0.001 mm, the calculated unfilled volume is 14.48%, but if extended
further in
the same manner from 0.001 mm down to 0.0001 mm (100nm), the calculated
unfilled
volume is 5.33%.
2. Formulatine Low-Resin. Hieh-Solids Polymer Compounds
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Figure 9 schematically illustrates a general method 100 of formulating low-
resin,
high-solids, void free polymer compounds. The method 100 generally comprises
the steps
of selecting 102 values of parameters for continuous grading of the solid
phase,
calculating 104 the amount of particles required in each fraction to yield a
continuous
grading, and estimating 106 the minimum resin volume needed to form the
polymer
compound.
In the selecting 102 step, the relevant parameters include the number of
particle
fractions for laboratory analysis, N, the diameter of the largest particles,
DM,qX, and the
diameter of the smallest particles, Dp. Typically, N is chosen based on the
end use of the
0 polymer composite material. For example, in structural polymer composites
materials
such as in PC pipes. analysis and adjustment of the continuously graded
aggregate system
generally requires from about four to about eighteen fractions. Dielectric
polymer
composite materials such as in electrical insulators, similar to those shown
in Fig. 8,
generally require from about four to about six fractions. Similarly, materials
used in cast
~ 5 polymer such as in bathtubs, sinks, kitchen countertops, and the like,
ordinarily require
about three or four fractions.
Although D,t.~ and Dp will often be chosen based on cost, visual appearance,
availability, and other non-performance criteria, at least in structural
composite material
applications, D~~ should be no greater than about one-third the thickness of a
20 characteristic cross-section of the molded polymer composite.
Once N, DN~,y, and Dp are known, equation II can be used to compute the
amount of aggregate in a particular fraction, °v , and equation III
orIV can be used to
Vo
estimate the unfilled volume of the system, which is the theoretically minimum
amount of
resin, j~ , needed to fill the spaces in the continuously graded aggregate
solids.
0
25 The minimum and maximum particle sizes defining each fraction correspond to
the sizes of the openings of standard sieving screens. For example, Table 5
shows four
fractions of quartz aggregate obtained from Oso Regalon deposit near
Constitution, Chile
(fractions 1 and 2), and from Zotti S.A., a Chilean industrial quartz
supplier(fractions 3
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and 4). According to the supplier's specs, the first fraction corresponds to
particles that
pass through a #16 mesh (ASTM) screen, but are retained on a # 70 mesh screen;
the
second fraction corresponds to particles that pass through a n 70 mesh screen,
but are
retained on a # 140 mesh, and so on.
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Tabie 5.
Maximum Minimum CumulativeFraction
Diameter Diameter
ASTM mm ASTM Meshmm Volume Volume
Mesh % %P
racoon 1. 0 + #7 0. 0 100/0- . D
fraction -#70 0.210 + 1 0 .105 42.0D 1 . o
2 .
racoon 0. 5 + . 44 9.7 0 1
-- - .5 D
racoon -#~2~ 0. 44 unspeci 0.000 1 .2D 19. o
4 red
Table 6.
Ma><.Mirl.FracuonracroonracdonFrse ActuH Theontieal
Oiam.Diem 1 2 7 on Content Content
4 wl
Theo.
mill
mm mm 116 a78 IIbD belowFractionCumulativeFraU~c~Cucnula:ne
to to l0 IJ25
x70 0150 9326
racoont. a . ~ 1
0
raetion1 . . . io . /0 1 ve
o .
:o
Ffetii0n0.8410.59513.7% 7.8% 90.4% 13.4%84.1%
C
FraCliOn0.5950.42011,8% 8.8% 82.5% 11.3%70.7%
p
FfeCliOn0.4200.29717.2h3.5% 10.4/075.6% 9.5% 59.4'/0
E
FlaCltOn0.2970.21018.5.012.7% 11.1.065.2% 7,9% 50.0%
F
fathOn. . .o . io . 0 8.8% 42.D'.e
o
FfaCLiOn0.149(1.10510.5%24.1k0.8% 9.1e 43.8% 5.7l035.4:0
H ~
hfaCtlOn0.105D.D741.9% 15.9%6.2'YS 3.7 34.5% 4.87029.7%
1 ii
FteC2i0n0.0740.0441.0% 8.7h ) 6.8% 11.6'/030.8% 5.7.024.9%
J 85.2%
FtathOnO.D44D.D31 2.9% 7.2% 22.5I65.4% 18.1% 3.1 18.2%
K io
FfeClIOn0.0310.022 0.9% 40.4%7.9% 13.7% 2.6% 18.2%
!.
FreCliOn0.0220.018 2B.8%5.2/a 5.8% 2.2% 13.8/a
M
FfaGliOn0.0180.011 3.5% 0.7% 0.7% 1.8% 11.4h
N
FfeCliOn0.0110.000 0.0% 0.0% 9.6% 9.6%
O
NOte:
Real Iredions i and 2 from Oso Mine, Chite
Real fractions 3 and 4 from Zotli
Table 7.
ax. in. Fneuon neuenFactionactionFneeienFnerfonactionActuall
'am Diem1 3 4 b a T 1 Conanwl
neuon Ad/.
Mx
mm mm 11110170 1155 1176TT4 11 W /for FnC110ntumulaev0
~ i to to l0 l0 l0 sot.
ITa I~IS TI..11v 6f 4u only)
l0 ~
1130
racliOtloov . -~ ~ .;,r
ni
ncl,an: .a i h
t
Fraa~on0 0 13.7% 0 t
C 641 595 4 00
% %
Fract:0~~ 0.420~ O fr9
D 0 t 3 %
595 1.8% %
Faction0 0 17.2%3.5% 2.1':099%
E 420 297
Fnchon0.2970.21016.5!112.7% 6 96
f 5% 7
%
radon0 9 0 . x
c
FracUCn0 0.1510.5%24.1'60.6% 11.9%73.6%
H 149
racoono. .tr .9 .c
~
Fraction0.0740 1.0 6.7%85.2%6 11 53
J 044 % 8% 8% 5
%
racoonv u. 9
Ftaetien0 0.22 0 40.4!S11.2% 5 37.0%
L 031 9% 6%
ra ~. a
.on c
Fraction0.0160.011 3.5%23.8%7 2 2
N 9% 6 S
% B6
racban, . c
FranionO.D080 0 49.891 3A 19
P 006 B% % 8%
ractwn:o
roc
an
us1 onm . .e n rn
Note:
RuI frsetions 1 and 2 from Oso Mine, Chite
Real Iradions 3 Ihrouyh 7 from 2:otli
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It is often necessary to increase ~\' for laboratory analysis because the
particle size
distribution of commercially available fractions frequently deviates sharply
from the
continuous grading distribution required by equation II. For example, Table 6
lists the
amount, in voltune percent, of fractions 1-4 of Table 5, further divided into
fractions A-O.
As is the case with Tyler Standard Screen Sieves, fractions A-I and K-N
correspond to
D"/D"_, _ ~. Note in Table 6 that each of the convnercially available
fractions (1-4)
contain meaningful amounts of particles that lie outside the diameter range
reported by
the suppliers. Therefore, simply combinine fractions 1-4 in accordance with
equation II,
results in significant deviations from the desired continuous grading curve:
in Table 6,
to compare values of V and ~v obtained from experiment with values of V and ~V
1 n Vo
calculated using equation 1I. The significant deviation is perhaps best seen
in Fig. 10,
which compares the computed 130 continuous grading curve with the measured 132
continuous grading curve.
Table 7 shows how one may add particles having diameters less than about 44
micron to adjust the measured 132 continuous grading curve of Fig. 10 to more
closely
conform to the computed 130 continuous grading cun~e. The adjustment method
described above allows the manufacturer of polymer compounds to understand and
use
more effectively commercially available a~~regates, which are supplied in
relatively
broad particle size ranges, such as fractions 1-4 in Table 5 and 6. This is
important since
bulk aggregate suppliers are reluctant to incur the processing costs required
to provide
aggregates in narrow particle size ranges such as fractions A-O in Table 6
(and dealing
with the material surplus that remain from bulk processing).
The result of one successful adjustment is shown in Table 7. Note, the
adjusted
formulation disclosed in Table 7 contains a substantial fraction of particles,
45.2 vol. %,
that are less than 0.044 mm.
There has been little, if any, appreciation of the importance of managing the
smallest particles in polymer compounds. When compared to the formulation
shown in
Table 7, non-VFT polymer compounds, including conventional structural polymer
concrete, not only usually contain a much smaller fraction of particles that
are less than
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0.044 nun, but the particle sizes in this fraction are typically not
controlled. Further, for
viscosity reasons, manufacturers of conventional polymer compounds typically
minimize
the amount of particles less than 0.044 mm to ensure the compound can be de-
gassed
under vacuum. Although continuous grading of the smallest particles would
perhaps
allow manufacturers to adequately mix, transfer, and form polymer compounds
having a
larger proportion of managed sub-44 micron particles, the resulting viscosity
of such
compounds would be excessive for adequate de-aerating, including vacuum
degassing.
Thus. adding a substantial, but properly managed fraction of small particles
makes
practical sense only when, prior to mixing. the resin is degassed separately
under vacuum,
1 o and non-condensable gases trapped within the solid phase are replaced with
a condensable
fluid.
B. Alixinc Low-Resin PC Compounds
Generally, the use of continuously graded aggregate systems including graded
fine
diameter particles affects the mixing of void-free polymer compounds. Upon
adding finer
~ 5 fractions. the fines displace the free resin between interstices of Iarge-
diameter particles,
displacing it and increasing the resin film surrounding the particles. The
first positive
effect is a lowering of the viscosity of the system while increasing its
average density. As
the density of the compound is increased, the second positive effect is that
the
sedimentation speed of particles in the system is reduced and the homogeneity
of the
2o compound is maintained. Offsetting these two positive affects, continued
incorporation of
fines increases the total surface of solids in the system, exponentially
increasing viscosity
to unmanageable levels. To handle these higher-viscosity compounds particular
attention
has to be placed on the type of mixing required to completely wet all the
particles and
provide desired homogeneity. In accordance with Fig. 3 or 4, continuously
graded
25 particles can be treated with a replacement fluid in Stage I of the void-
free method, and
then mixed with degassed resin in Stage II. However, in certain cases-when
using clays,
for instance-the smallest particles, when dispersed in the resin, will
agglomerate into
larger diameter, "lumped" particles. When this occurs, the fines should be
mixed
separately from the larger particles since high shear mixing is needed to
breakup the
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lumped particles while it is not necessary for the coarser fractions. In the
disclosure
below, a void-free polymer compound comprised of degassed resin and Stage I
treated
fines is called a primary void-free compound.
In cases where the coarse and fine particles should be mixed separately, Fig.
12
illustrates a technique for determining the cut-off particle size 150 between
the two
particle ranges. Fig. 12 shows particle size distributions for aggregate
particles dispersed
in the polymer compound resin 152 and in an optimal dispersing solvent 154.
The cut-off
particle size 150 can be approximated by the intersection of the particle size
distribution
curves.
1. Primary Void-Free Polymer Compounds & Two Stet/ Mixin
Following determination of the cut-off particle size, fines and coarse
aggregate are
continuously graded and treated in separate operations as shown in Fig. 13.
Both sets of
particles undergo Stage I treatment with a replacement fluid. In Stage II, the
treated fines
and degassed resin are combined, forming a primary void-free polymer compound.
The
~ 5 treated fines in the primary void-free polymer compound are dispersed in
degassed resin
using high shear mixing. Because of the high solids content of the primary
compound, its
high viscosity, and the small size of the dispersed particles, the primary
compound
experiences little settling. As a result, the primary compounds can be
utilized after storage
for several weeks. In Stage III, the primary compound is mixed with treated
coarse
2o aggregate and, if necessary, additional degassed resin, yielding a low
resin, and final void-
free polymer compound apt for molding. Since fines are difficult to handle,
specialists can
produce the primary void-free polymer compounds and supply them to molders of
finished polymer composite parts. In Stage IV, the void-free final polymer
compound is
shaped by pour casting, injection molding, press molding, and the like, and
then cured to
25 form a void-free polymer composite. At every stage in Fig. 13, care should
be taken to
prevent air from entering the process.
1. Priman~ Void-Free Polymer Com~~ounds & Two Step Mixing of Solids
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Following determination of the cut-off particle size, fines and coarse
aggregate are
continuously graded and treated in separate operations as shown in Fig. 13.
Both sets of
particles undergo Stage I treatment with a replacement fluid. In Stage II, the
treated fines
and degassed resin are combined, forming a primary void-free polymer compound.
The
s treated fines in the primary void-free polymer compound are dispersed in
degassed resin
using high shear mixing. Because of the high solids content of the primary
compound, the
small size of the particles, and the relatively high viscosity of the neat
resin, the particles
in the primary compound experience little settling. As a result, the primary
compounds
can be stored for weeks, months, or even years with little change in
properties. In Stage
III. the primary~ compound is mixed with treated coarse aggregate and, if
necessary.
additional degassed resin, yielding a low resin, void-free polymer compound.
Since fines
are difficult to handle, the primary void-free polymer compound can be
produced by
specialists who supply the primary compound to polymer composite
manufacturers. In
Stage IV, the void-free polymer compound is shaped by pour casting, injection
molding,
is press molding, and the like, and then cured to form a void-free polymer
composite. At
every stage in Fig. 13, care should be taken to prevent air from inf ltrating
the void-free
polymer compound.
2. One SteQ Mixine of Solids
Fig. 14 schematically shows an apparatus 200 for making low-resin, void-free
20 polymer composites with one step mixing of solids. The apparatus 200
comprises a
mixing unit 202 for treating continuously graded aggregate solids with a
replacement
fluid and for mixing the treated solids with a degassed resin. A suitable
mixing unit 202
includes, but is not limited to, a ribbon mixer.
At the beginning of a production run, continuously graded aggregate is loaded
into
25 the mixing unit 202, along with a liquid replacement fluid, such as a
liquid monomer,
through a flanged portal 204. Following loading of the solids and replacement
fluid, a
transfer unit 206 with its open end closed with plug 260, is attached to the
mixing unit
202 at the flanged portal 204. An sirtight seal 208 at the interface between
the transfer
unit 206 and flanged portal 204 prevents ambient air intrusion into the mixing
unit 202
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and transfer unit 206. A heating blanket 210 regulates the temperature of the
contents of
the mixing unit 202.
The apparatus 200 further comprises a vacuum flask 2I2 for degassing the
resin.
The vacuum flask 212 is connected to a resin source 214 through a first
transfer line.216.
A vacuum flask inlet valve 218, located along the first transfer line 2I6, can
be used to
isolate the resin source 214 from the vacuum flask 212. A second transfer line
220
provides a fluid connection between the mixing unit 202 and the vacuum flask
212. A
vacuum flask outlet valve 222 and a resin inlet valve 224, which are located
along the
second transfer line 220, can be used to isolate the vacuum flask 212 from the
mixing unit
202.
As shown in Fig. 14, the apparatus 200 further comprises a vacuum source 226,
which communicates with the mixing unit 202 and vacuum flask 212 through a
first
vacuum line 228 and a second vacuum line 230, respectively. Two valves located
along
the first vacuum line 228-a mixing unit inlet valve 232 and a first isolation
valve 234-
~ 5 can be used to break the fluid connection between the vacuum source 226
and the mixing
unit 202. Similarly, a second isolation valve 236, which is located along the
second
vacuum line 230, can be used to interrupt fluid communication between the
vacuum
source 226 and the vacuum flask 212.
The vacuum source 226 is also in fluid communication with a condensable fluid
2o source 238 through a third vacuum line 240. As discussed below, the
condensable fluid,
which is maintained at a pressure at least tvwice ambient, is used to blanket
the polymer
compound following mixing. The condensable fluid can be the same or different
than the
liquid replacement fluid that is loaded into the mixing unit 202 at the
beginning of the
production run. Two valves located along the third vacuum line 240-a fluid
source outlet
~5 valve 242 and a third isolation valve 244-can be used to break the fluid
connection
between the vacuum source 226 and the condensable fluid source 238.
The first 228. second 230 and third 240 vacuum lines are connected to the
vacuum
source 226 via a main vacuum line 246. A main isolation valve 248 can be used
to
prevent fluid communication between the vacuum source 226 and the first 228,
second
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230 and third 240 vacuum lines. A vacuum gauge 250 is located downstream of
the main
isolation valve 248 along the main vacuum line.
After attaching the transfer unit 206 to the mixing unit 202, the solids and
liquid
replacement fluid are agitated as vacuum is applied. Vacuum is applied in the
mixing unit
202 and throughout the apparatus 200 by opening the mixing unit inlet valve
232, the
resin inlet valve 224, the vacuum flask outlet valve 222, the first isolation
valve 234, the
second isolation valve 236, the third isolation valve 244, and the main
isolation valve 248.
The liquid replacement fluid vaporizes in mixer 202 and drawn through the
system by
vacuum source 226, replacing air from the solids, and purging air from the
mixing unit
202. the transfer unit 206, the vacuum flask 212, the second transfer line
220, and the first
228. second 230, and third 240 vacuum lines. Vacuum is maintained until
substantially all
of the replacement fluid is purged from the apparatus 200. At this point, the
vacuum flask
outlet valve 222, the first isolation valve 234, and the third isolation valve
244 are closed.
Following treatment of the solids with the replacement fluid, the resin is
degassed
under vacuum. Resin is transferred from the resin source 214 to the vacuum
flask 212
through the first transfer line 216 by opening the vacuum flask inlet valve
218. After
sufficient resin has been transferred to the vacuum flask 212, the vacuum
flask inlet valve
218 is closed. Air and other non-condensable gases dissolved in the resin
escape from the
resin and exit the vacuum flask 212 through the second vacuum line 230. Once
the resin
?o in the vacuum flask 212 stops bubbling, indicating sufficient degassing has
been
accomplished, the second isolation valve 236 is closed. The vacuum flask inlet
valve 218
is then slowly opened to break the vacuum in the vacuum flask 212.
In preparation for transferring the degassed resin to the mixing unit 202, the
first
isolation valve 234 and the third isolation valve 244 are opened, which purges
residual
25 vapor from the first 228 and third 240 vacuum lines, as well as the mixing
unit 202. While
the mixing unit 202 is operating, degassed resin is injected into the treated
solids by
opening the vacuum flask outlet valve 222 and the mixing unit valve 224. The
resin inlet
valve 224 is closed after the requisite amount of degassed resin is
transferred into the
mixing unit 202. To prevent air from entering the mixing unit 202, the resin
inlet valve
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224 must be closed before all of the degassed resin in the vacuum flask 212 is
transferred
into the mixing unit 202.
The treated aggregate and degassed resin are agitated in the mixing unit 202
for a
time sufficient to ensure that all of the solids are evenly dispersed in the
resin. Following
agitation, the mixing unit 202 is stopped, and the main isolation valve 248 is
closed. The
fluid source outlet valve 242 is then opened. Condensable fluid flows from the
condensable fluid source 238 through the third 240 and first 228 vacuum lines,
blanketing
the polymer compound in the mixing unit 202 with condensable fluid. The fluid
source
outlet valve 242 is closed after the pressure in the mixing unit 202 and the
transfer unit
0 206 is about S00 mm Hg. Because the condensable fluid pressure is above
ambient, it
prevents air intrusion into the void-free polymer compound when it is poured
from the
mixing unit 202 into the transfer unit 206.
To pour the polymer compound into the transfer unit 206, the mixing unit is
rotated approximately 180 degrees about an axis 2~2 so that the transfer unit
206 is
1 s pointing downward. While the mixing unit 202 is operating, a vibrator 2S4
located along
a conical shaped portion 2S6 of the transfer unit 206. helps transport the
polymer
compound into a discharge portion 2S8 of the transfer unit 206. A removable
plug 260
prevents the polymer compound from exiting the discharge portion 258 of the
transfer
unit 206. When the polymer compound is ready to be cast, the transfer unit 206
is
2o detached from the mixing unit 202.
Fig. 1S shows a cross section of a casting apparatus 300. The casting
apparatus
includes the transfer unit 206 and mold 302. The mold 302 shown in Fig. 15 is
suitable
for manufacturing a section of PC pipe and comprises a cylindrical outer wall
304 and a
coaxial cylindrical mandrel 306. Polymer compound is cast into an annular
region 308
25 defined by the cylindrical outer wall 304 and mandrel 306.
Prior to casting, a motorized discharge device 310 is coupled to the transfer
unit
206. The motorized discharge device 310 comprises a motor connected to an
auger 312,
which extends through the polymer compound into the discharge portion 2S8 of
the
transfer unit 206. The plug 260 shown in Fig. 14 is removed, and a tube 314 is
secured to
3o the exit 316 of the discharge portion 2S8 of the transfer unit 206.
. '70 -
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When ready to cast, a small amount of resin is poured into the bottom of mold
304
resulting in a puddle at the bottom of the annular region 308 of the mold 304.
The auger
312 pushes the polymer compound through the tube 314, expelling the air inside
tube
314. When the compound reaches the end 318 of tube 314, the end 318 is
immersed in
s the puddle of resin, which acts as a seal against air intrusion into the
system. The auger
312 continues to pushthe polymer compound through the tube 314 into the
annular region
308 of the mold 304. Throughout casting, the end 318 of the tube 314 is kept
just belo~~sr
the free surface 320 of the polymer compound to prevent the compound from
trapping air.
A vibrator 322 located along the bottom 324 of the mold 304 helps consolidate
the
io polymer compound into the mold cavity.
Fig. 16 shows an aggregate consolidation and polymer compound curing
apparatus 400. Once the mold 304 is filled with void-free polymer compound, a
piston
ring 402 is placed on the surface 404 of the polymer compound. A resilient
sealing
membrane 406 is sandwiched between the piston ring 402 and a lid .408, which
is attached
t5 to the mold 304 using air-tight fasteners, clamps, and the like. Compressed
air is provided
at one surface 4I0 of the sealing membrane 406 through line 412. A control
valve 414
and a pressure gauge 416, which are located along gas line 412, are used to
regulate the
air pressure on the surface 410 of the sealing membrane 406. An exhaust port
(not shown)
is used to relie~~e pressure on the membrane 406.
20 To consolidate the aggregate system within the polymer compound, air
pressure is
applied on the surface 410 of the membrane 406, which results in a pressure
force on the
piston ring 402 and the surface 404 of the polymer compound. As the piston
ring moves
downward by the pressure, it exerts mechanical force on the aggregates in the
compound,
squeezing out resin from within the aggregate system towards the mold walls
and past the
25 piston ring itself towards membrane 406. Rapidly cycling the pressure about
three times
between ambient air pressure and about six bar jolts the piston ring 402 with
sufficient
force to properly compact the aggregates within the compound and the compound
itself
within the mold 304. Following piston ring ramming, the lid 408, membrane 406,
and
piston ring 402 are removed. The polymer compound temperature in the mold is
3o maintained using heating blanket 418, allowing the compound viscosity to be
reduced to
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enhance the effectiveness of piston ring ramming. Likewise, upon gelation of
the resin,
the heating blanket 418 can be used to initiate cure of the compound at
elevated
temperature.
C. Examples of Low Resin PC
1. Example 1-8. Comparison of polymer concrete made in accordance with
the presentation invention with prior art
Table 8 lists formulations-aggregate volume fractions and resin contents-for
eight PC material samples made using void-free technology and continuously
graded
aggregates. Each sample was compounded with silica obtained from Oso Regalon
deposit
0 near Constitucion, Chile, mixed with vinylester resin Palatal A430, obtained
from BASF
Chile. These compounds only differ in the maximum particle diameter of their
aggregate
systems. AlI of the samples were processed via one-step mixing, using the
equipment
shown in Fig. 14 and 1 S, but replacing the transfer unit 206 with a testing
mold. Cast
polymer composite material was tested for mechanical properties as indicated
below.
Fig. 17 shows resin content of the eight samples plotted against maximum
aggregate diameter. For comparison purposes, Fig. 17 also shows resin content
of
conventional poly~ester/silica polymer concrete samples reported by T.
Hornikel,
Kunststoffe im Bau vol 6 (1974) .
Fig. 18 shows flexural strength and compression strength of the eight samples
2o plotted against maximum aggregate diameter. Flexural strength and
compression strength
were measured in accordance with standard polymer concrete test methods, SPI
5.0 and
SPI 6.0, respectively, proposed by the Composites Institute of the Society of
the Plastics
Industry, Inc. SPI 5.0 is based on ASTM C 78, "Test Methods for Flexural
Strength of
Concrete (Using Simple Beam with Third-Point Loading)"; SPI 6.0 is based on
ASTM C
1I6, "Test Method for Compressive Strength of Concrete Using Portions of Beams
Broken in Flexure.''
Average flexural strengths of these reduced resin content, void-free PC
composites
are typically 30 to 40 percent higher than those of conventional polymer
concretes of the -
same aggregate compositions (average 1$ N/mm2), in the range between 5/8
inches and
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ASTM mesh #6 maximum diameter formulations, but average strength increases to
200
percent or more in the range between ASTM mesh #6 and ASTM mesh #30 maximum
diameter formulations. Similarly average compression strength of these same PC
composites is over 200 percent of typical average compression strength of
conventional
vinylester PCs in present art without using organofunctional coupling
substances typically
used to increase PC mechanical strengths. The continuously graded aggregate
systems in
the present invention together with void-free methods provide exceptional
property
increases with reduced resin contents and material economy.
2. PC Composites for Highway Overlays
Fig. 19 shov~s a cross section of a roadway portion 450 having a polymer
concrete
overlay 452. The PC overlay 452 comprises a void-free polymer concrete having
a
continuously graded solid phase. The overlay 452 is bonded to a steel-
reinforced, Portland
Cement Concrete (PCC) structural base slab 454 through a thin polymer
impregnated
concrete (PIC) intermediate layer 456. With the addition of the PC overlay
452, the
~ 5 thickness of the PCC structural base slab 454 can be significantly reduced
compared to
conventional steel-reinforced monolithic PCC slabs. Typically, the PC overlay
452 should
be about 0.5 inches to about 1 inch thick.
The PC overlay 452 material can be mixed offsite and then brought to the
roadway
construction site. Alternatively, the void-free polymer compound can be mixed
onsite.
2o Typically, a primary void-free compound and continuously graded coarse
aggregate will
be prepared offsite and then mixed at the roadway construction site in either
batch or
continuous mixers. A transfer unit, such as the one shown in Fig. 14, could be
mounted
on wheels and then used to apply the PC compound to the PIC intermediate layer
456.
The use of a PC overlay 452 offers many advantages over conventional,
25 monolithic steel-reinforced PCC roadways. First, reduction in thickness of
the PCC
structural slab reduces overall cost of materials and labor. Second, the PC
overlay 452 and
PIC intermediate layer 456 prevent migration of water, salt, fuel and other
corrosive
materials into the PCC structural layer thereby protecting the steel
reinforcement. Finally,
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the use of the PC overlay 452 allows for rapid and cost effective highway
rehabilitation
since the PC overlay 4S2 can be very quickly applied or repaired.
The present invention can be implemented in many apparatus, methods and
processes to produce a variety of void-free compounds and composites.
Accordingly, the
scope of the invention should be detenmined by the claims and not limited to
the preferred
embodiments described above.
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