Note: Descriptions are shown in the official language in which they were submitted.
2056248
PROC~SS FOR MAKING MOLDED POLYMERIC PRODUCT WITH MULTIPASS
EXPANSION OF POLYMER BEAD WITH LOW BLOWING AGENT CONTENT
BACKGROUND OF THE INVENTION
The present invention relates to a process for the
manufacture of expanded polymeric products. The process is
directed at the reduction of the amount of blowing agent
required in order to manufacture a low density foam product.
This is achieved by using: (1) a low level of blowing agent,
in combination with both (2) multiple premolding expansion
steps, as well as (3) a polymer having a certain molecular
weight distribution, which polymer is highly expandable. The
final result is a process which utilizes less blowing agent,
resulting in not only a cost savings, but more importantly,
reduced release of environmentally-damaging volatile organic
compounds (VOCs) into the atmosphere. Preferably the polymer
is polystyrene.
The production of molded polystyrene products has
required making an intimate mixture of a polystyrene polymer
and a blowing agent. In commercial operations, this intimate
mixture was generally made into solid (relatively "high-
density") beads of relatively small size (e.g. beads having
a diameter of from about 0.2 to 4 millimeters). The beads
were then expanded (via heating the mixture) in order to make
an expanded polystyrene product. The expansion was usually
carried out by heating the beads above their softening
temperature and above the boiling point of the blowing agent
(usually pentane), resulting in the vaporization of the
blowing agent. [The blowing agent must have a boiling
temperature below the softening temperature of the polymer
blowing agent mixture.] The vaporization of the blowing agent
caused an expansion of the beads to form individual particles
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of foam. The expansion was generally carried out by using a
first expansion step, whereafter expanded particles (referred
to as prepuff) were then aged, and thereafter placed into a
mold and again heated, whereby the prepuff further expanded
and, because of the confined volume, fused to form a unitary
object. Under optimal conditions, the bonds formed between
the individual prepuff particles were stronger than the
individual particles themselves. That is, upon stressing the
finished, molded object enough to cause it to break, the break
would occur mostly across the individual prepuff particles,
rather than at the junctions and interstices of the prepuff
particles.
Fundamental to the foaming operation is the
requirement that the polymer contain a blowing agent. In
prior commercial production, steam has been used to heat the
beads, the steam causing the blowing agent to vaporize, which
vaporization results in the formation of gaseous bubbles
within the polymer. These bubbles expand as the internal
pressure increases. A foam is produced because the bubbles,
for the most part, are trapped, resulting in the production
of a foam. Since the vast majority of the volume within the
foam is occupied by these bubbles, the resulting foam has a
density much lower than that of the unexpandable
polymer/blowing agent mixture. The blowing agent also
diffuses out over time.
A large fraction of the foamed polystyrene currently
being produced has a density of from 0.8 lb./cu.ft. to 1.1
lb./cu.ft. This density of material is generally used for
building insulation and/or for protective packaging. In order
to achieve this density, it has been the practice of the
commercial manufacturers of such "low-density" expandable
polystyrene to incorporate from about 6 to about 8 weight
percent of pentane into the polystyrene polymer. Beads are
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formed via a suspension polymerization during or after which
pentane is introduced into the beads. These beads are then
heated in a single premolding expansion step in which the
beads are expanded in volume by a factor of about 40 (i.e. to
a density of about 1.0 lb/cu.ft.). The now preexpanded beads
(prepuff) are allowed to cool and equilibrate (i.e. aged) by
permitting air to diffuse thereinto, and are then put into a
mold where they are again heated, resulting in the further
expansion and fusion of the preexpanded prepuff, so that the
prepuff particles are bonded together.
U.S. 2,884,386 describes a process for making
cellular bodies of organic thermoplastic materials. The
process described therein involves making an intimate mixture
of a blowing agent with a thermoplastic resin and thereafter
expanding the mixture to form a cellular thermoplastic body.
The specification refers to the use of cycles of expanding
operations that, if used repeatedly, cause further expansion
of the prepuff particles made in accordance therewith.
However, the '386 patent nowhere provides any general
statement as to how many premolding expansion steps should be
utilized.
The '386 patent nowhere provides any general
description of the amount of blowing agent to be used in the
process. However, the '386 patent does state that the
preferred primary blowing agent is dichlorodifluoromethane,
and the Examples in the '386 patent all utilize only
halogenated methanes as the blowing agent. Example 1 of the
'386 patent utilizes 2 weight percent dichlorodifluoromethane
with eight expansion steps to achieve an undisclosed final
product density. Example 2 utilizes 8.11 weight percent
dichlorodifluoromethane with nine expansion steps to effect
a 150x volumetric increase (the density of the final product
was undisclosed). Example 4 utilized 20 volume percent of
205624~
dichlorodifluoromethane in a three step expansion process, to
effect a final product density of 0.938 lb./cu. ft. In
comparison with the process of the present invention, these
examples (as well as the remaining examples of the '386
patent) utilize such a high level of blowing agent (and/or
such a high number of expansion steps) that the process of the
present invention is not only not suggested, the process of
the present invention is also taught away from.
The '386 patent also fails to provide one with the
unexpected result of the present invention: i.e. that if one
were to use merely from 2 to 4.4 weight percent of a blowing
agent, a product of relatively low density (i.e. from 0.8 to
about 1.1 lb/cu.ft.) could be produced with only from 2 to 5
expansion steps. The gist of the '386 patent is the
generalized notion that multiple expansion steps can be used
to effectuate a volumetric increase greater than the
theoretical volumetric increase possible from the expansion
of the blowing agent alone. As the '386 patent states
repeatedly, this increase is brought about allowing a more
permeable secondary blowing agent, such as air, to diffuse
into the foam whereupon after cooling an additional heating
will produce further expansion due to the presence of this
secondary blowing agent in further heating/expansion steps.
Although the process of the present invention certainly
utilizes this mechanism of increasing the degree of expansion,
the process of the present invention is directed towards a
specific area wherein this mechanism is used in addition to
other critical process steps, i.e. the use of a low (2-4.4
weight percent) level of blowing agent, in combination with
the use of only 2 to 5 expansion steps, as well as the use of
a specific polymer type (i.e. a polymer exhibiting three
characteristics: (1) a polydispersity of from about 1 to less
than 2.5; (2) a weight average molecular weight of from
1~
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greater than 180,000 to about 300,000; (3) a Mz:Mn of from
about 2 to about 4.5; and (4) is branched to from 0 to 5
weight percent). It should be noted that the '386 patent
nowhere discloses a polymer having such characteristics.
Furthermore, the process of the present invention
isolates a specific area of improvement over the subject
matter disclosed in the '386 patent. The process of the
present invention relates to the use of beads of thermoplastic
polymer which contain only from about 2 weight percent to
about 4.4 weight percent of a hydrocarbon blowing agent. It
has surprisingly been found that even with such a small amount
of the blowing agent, the bead can be expanded to a final
density of from about 0.8 to about 1.1 lb./cu. ft., while
using only 2 to 5 expansion steps (or 2 to 4 preexpansion
steps before the molding step). The '386 patent nowhere
achieves such final product densities while utilizing so
little blowing agent.
Applicants have discovered that the use of a low
amount of blowing agent provides many important advantages,
among which are:
(1) a reduction in the amount of blowing agent
required, resulting in cost savings;
(2) reduced environmental pollution since less
blowing agent (generally a volatile organic
compound, i.e. a VOC) is released into the
environment both during manufacture and during
consumer use;
- 30
(3) processing advantages such as:
(a) a lower shrinkage in the molding step;
(b) quicker cooling in the molding step,
~/~
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resulting in shorter processing times;
(c) shorter aging time between the pre-
expansion steps and between the last
preexpansion step and the molding step,
resulting in shorter processing times;
and
(d) ability to be easily molded with
acceptable fusion and dimensional
stability on molding while using a low
level of blowing agent.
U.S. 4,839,396 describes a process for making
expandable alkenyl aromatic polymer particles. These
particles have the ability to use a decreased amount of
blowing agent while maintaining the potential to produce a
bulk density equivalent to that achieved by particles
comprising a greater amount of blowing agent. This is
achieved through the use of from 0.005 to 0.5 weight percent
of a "density modifier". The '396 patent describes the
density modifier as a compound providing thermal stability for
the alkenyl aromatic polymer at extrusion and expansion
conditions and which is also a liquid plasticizer at expansion
conditions. These density modifiers are stated to include
octadecyl 3 ,5-di-tert-butyl-4-hydroxyhydrocinnamate, as well
as ethylene bis(oxyethylene)bis(3-tert-butyl-4-hydroxy-5-
methylhydrocinnamate).
The specification of the '396 patent states that the
"volatile fluid foaming agents" (i.e. the blowing agents)
usually are employed in amounts corresponding to from about
5 to about 15 percent of the weight of the total formulation.
The only examples in the '396 patent utilize from 8.8 to 10.3
weight percent of the blowing agent. These examples show that
the amount of the blowing agent was reduced from a level of
10.0-10.3 weight percent down to about 8.8 weight percent
A
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(i.e. a reduction of about 12 to 15 percent in the amount of
blowing agent used), while achieving the same final density
as in the comparative run having the greater amount (i.e.
10.0- 10.3 weight percent) of blowing agent present.
The process of the present invention also has as a
goal the reduction in the amount of blowing agent used in the
manufacture of an expanded polymer. However, relative to the
' 396 patent, the process of the present invention permits at
least as much as twice the percentage reduction in the amount
of blowing agent (e.g. most preferably a reduction of from
about 6 weight percent to about 3.5 weight percent, which is
approximately a 40 percent reduction). The process of the
present invention produces this comparatively large reduction
in blowing agent via an approach which is different from the
approach taken in the ' 396 patent. This approach is the use
of an initially low level of the blowing agent (i.e. a blowing
agent level of from 2 to 4.4 weight percent) while
simultaneously using multiple preexpansion steps. It should
be noted that although the ' 396 patent suggests the use of
multiple preexpansion steps before the molding step, the ' 396
patent fails to make any connection between the use of low
amounts of blowing agent and the use of multiple preexpansion
steps, and the ' 396 patent has a very broad, undirected
disclosure of the amount of blowing agent which can be used.
Furthermore, the ' 396 patent suggests the use of only
relatively high amounts of blowing agent (i.e. 5 to 15%
broadly, with examples limited to from 8.8% to 10. 3% by
weight).
U.S. 4, 520,135 and 4, 525, 484 (a divisional of the
30 application filed for the ' 135 patent) are both directed at
a polystyrene particles containing a blowing agent, wherein
the polystyrene has an improved expandability. More
particularly, the polystyrene particles are comprised of a
2056248
polymer which has a molecular weight of from about 130,000 to
about 180,000. The ' 484 patent describes several methods for
making this polymer, i.e. via the use of chain transfer
agents, the use of oligomers, or polymerizing in the presence
of the blowing agent. The ' 484 patent states that the
resulting polystyrene particles can be expanded by
conventional methods (e.g. steam expansion). The ' 484 patent
states that the blowing agent can be present in an amount
generally from 3 to 12 weight percent tpreferably from 5 to
10 8 weight percent, and the only example in the ' 484 patent
utilizes approximately 7 weight percent pentane). However,
the ' 484 patent nowhere makes any statement regarding the use
of multiple premolding expansion steps. In contrast, the
process of the present invention utilizes a polymer which is
different from the polymer described in the ' 484 patent in
that it exhibits three characteristics which are different
from the polymer described in the ' 484 patent. Foremost among
these differences is the fact that the weight average
molecular weight of the polymer used in the process of the
present invention is higher than that of the polymer described
in the ' 484 patent. Surprisingly, this higher molecular
weight polymer has a degree of expandability at least as high
as the polymer described in the ' 484 patent. In further
contrast, the process of the present invention requires the
use of from 2 to 4 premolding expansion steps, whereas the
' 484 patent makes no mention of multiple expansion steps
either with or without molding.
U. S . 4,485,193 describes a process for making
resilient foam particles and moldings with a "lightly
crosslinked" polymer, which could be a styrene polymer. The
process entails the use of a volatile fluid foaming agent that
has low permeability through the polymer, and the process also
uses multiple expansion steps for the production of foams of
20562~8
low density, i.e. suitable for molding. The process described
and claimed in the ' 193 patent requires that the once-expanded
particles are subjected to a superatmospheric pressure of at
least 3 atmospheres in air, whereafter the now "pressurized"
particles are further expanded by heating the particles above
the glass transition temperature of the polymer after the
particles are returned to a normal atmospheric pressure.
The '193 patent nowhere provides any generalized
description of the amount of blowing agent which may be
employed in the process described therein. However, of the
43 Samples discussed in the ' 193 patent: Samples 1-17
contained blowing agent in an amount of from about 20 to about
30 weight percent; Samples 18-21 were foams made "in accord"
with the specification of the ' 193 patent but no data was
provided re the amount of blowing agent employed in the making
of the foam; Sample 22 was a foam made in accord with the
conditions of Sample 2 (and Sample 2 utilized 28.9 weight
percent blowing agent); Samples 23-38 contained blowing agent
in an amount of from 6.12 to about 7.0 weight percent;
Samples 39-41 do not contain any description of the amount of
blowing agent, but merely state that blowing agent was
permitted to diffuse into the already-formed beads; and
Samples 42 and 43 appear to utilize blowing agent in an amount
of at least 11 weight percent. In summary, the ' 193 patent
teaches the use of blowing agent in an amount which is
considerably higher than the amounts involved in the present
invention.
U. S . 3,639,551 describes a cyclic method for
producing low-density polystyrene foam beads, wherein the
30 beads are expanded in a plurality of expansion steps.
However, the gist of the ' 551 patent is that in between the
expansion steps the now partially-expanded beads are reheated
to restore the majority of the "lost volume" (i.e. the volume
20562~8
lost upon the cooling of the beads immediately after they were
expanded). This reheating step precedes the next expansion
step. By this method, the shrinkage of the beads will be
prevented from substantially affecting the ultimate degree of
expansion obtained.
The '551 patent nowhere provides any discussion of
the quantity of blowing agent to be employed in expanding the
beads. The '551 patent has a single example which states
that:
1000 pounds of a commercial grade acrylonitrile
styrene copolymer beads having low boiling
hydrocarbon propellant (pentane) included therein
and a diameter between about 1/64 to about 1/32
inch were stored in a hopper and fed into a
"Buccaneer" preexpander (available from TRI
Manufacturing & Sales Co., Lebanon, Ohio) having an
expansion chamber substantially as described above.
The '551 patent nowhere states how much of the low
boiling propellant (pentane) was present in the beads.
In stark contrast to the '551 patent, the process
of the present invention utilizes a low level of blowing agent
(from about 2 to about 4.4 weight percent) in combination with
multipass expansion in order to achieve a product having a
density of from about 0.8 to 1.1 pounds per cubic foot. The
'551 patent nowhere mentions the use of such an
unconventionally low amount of blowing agent. The process of
the present invention further requires the use of a specific
polymer, which polymer the '551 patent nowhere discloses.
U.S. 3,631,133 describes a process for expanding
polystyrene beads in order to produce a bead having an
exceptionally low density (i.e. 5 kg./cu. meter, or less,
which equals approximately 0.3 lb./cu. ft., or less). The
method described in the '133 patent is generally described
205624~
as:
(1) insufflating (i.e. pre-expanding to produce a
partly expanded product) polystyrene granules
containing blowing agent, the insufflating
being carried out with steam at about
atmospheric pressure, whereby the granules are
partially expanded;
(2) conditioning the partially expanded granules
at atmospheric pressure;
(3) subjecting the partially expanded granules (in
a confined space) to steam at about 150 g./sq.
cm. pressure; and
(4) restoring the expanded granules to atmospheric
temperature and pressure.
The gist of the '133 patent is that of using
multiple expansion steps in combination with a conditioning
step, in order to ultimately produce a low density product.
The '133 patent nowhere refers to the quantity of blowing
agent to be utilized in the process. Rather, all the
specification (including Examples) has to say about the
blowing agent is:
The starting material consisting of granules of
polystyrene containing (sic) a pentane petroleum fraction as
a blowing agent. [Col. 2, lines 61-63]
In stark contrast to the '133 patent, the process
of the present invention utilizes a low level of blowing agent
in combination with multipass expansion in order to achieve
a product having a density of from 0.8 to 1.1 pounds per cubic
20562~
foot. The '133 patent nowhere mentions the use of such an
unconventionally low amount of blowing agent. Furthermore,
the '133 patent nowhere refers to the characteristics of the
polystyrene polymer used therein as providing anything other
than a conventional level of expandability.
U.S. 3,598,769 describes a process for expanding
polystyrene, this process involving:
(1) subjecting (for a few minutes) polystyrene
granules to steam at low pressure;
(2) conditioning the granules for a few hours at
about 20C to 40C;
(3) reheating the expanded granules to about 100C
with hot air;
(4) then treating the granules with steam for 30
to 40 seconds; followed by
(5) conditioning the granules for 1 to 24 hours.
The objective of the '769 patent is to provide a
process for producing beads of polystyrene having an apparent
specific mass less than about 7 kg./cu. meter (i.e. a density
of about 0.44 lb/cu.ft., or less). The gist of the '769
patent is to provide a very specific process for using two of
expansion steps and a conditioning step after each expansion
step. Furthermore, the '769 patent is directed at carrying
out this process on a continuous conveyor belt.
As with the '133 patent, the '769 patent nowhere
describes the amount of blowing agent to be used in the
process.
-
.~, .
2056248
In stark contrast to the ' 769 patent, the process
of the present invention utilizes a low level of blowing agent
in combination with multipass expansion in order to achieve
a product having a density of from 0.8 to 1.1 pounds per cubic
foot. The ' 769 patent nowhere mentions the use of such an
unconventionally low amount of blowing agent. Furthermore,
the ' 769 patent nowhere mentions the use of a polymer having
an extraordinary degree of expandability.
U . S . 3,126,432 describes a process for producing
super-low density thermoplastic foam, namely polystyrene foam.
The process described in the ' 432 patent involves expanding
particles of polystyrene having a vaporizable liquid (butane
or pentane) inflating agent therein, and thereafter aging the
expanded particles first at atmospheric pressure and
thereafter at superatmospheric air pressure ( 2 to 8
atmospheres) for several hours. This exposure to
superatmospheric air pressure has the effect of causing a
secondary blowing agent to migrate into the expanded
particles. Thereafter, the pressure is released and within
20 five hours the particles are heated in a closed mold. Thus
the gist of the ' 432 patent is to "pump up" the expanded
particles by exposing the particles to superatmospheric air,
and thereafter carrying out a second expansion step by taking
advantage of the relatively high internal pressure within the
particles, once they are released from the pressure chamber.
The ' 432 patent nowhere has any general discussion
of the amount of blowing agent to be utilized in making
polystyrene foams. Of the five examples given in the ' 432
patent, only Examples I, III, and V provide any information
30 as to the amount of blowing agent used in the process. In
each of these Examples, the blowing agent used is pentane, and
the pentane is present in an amount of 6% by weight of the
polystyrene globules. Thus it is clear that the ' 432 patent
205624~
does not teach towards any process which utilizes a blowing
agent in an amount less than 6% by weight.
In stark contrast to the ' 432 patent, the process
of the present invention utilizes a low level of blowing agent
in combination with multipass expansion in order to achieve
a product having a density of from 0.8 to 1.1 pounds per cubic
foot. The ' 432 patent nowhere mentions the use of such an
unconventionally low amount of blowing agent. Furthermore,
the ' 462 patent nowhere mentions a polymer exhibiting the
properties of the present invention.
U. S . 3,056,753 describes the production of
expandable polymeric particles having a foamed polymeric
structure. The process described therein involves:
(1) partially expanding the polymeric particles;
followed by
(2) crushing the particles; followed by
(3) again partially expanding the particles.
The gist of the ' 753 patent is to decrease the
molding cycle time, whereby molded articles can be removed
from the mold after permitting a cooling period of lower
duration. Nowhere in the ' 753 patent is there any mention of
the amount of blowing agent to be utilized in the process.
In fact, even the seven examples within the ' 753 patent fail
to provide any information as to the amount of blowing agent
utilized.
In stark contrast to the ' 753 patent, the process
of the present invention utilizes a low level of blowing agent
in combination with multipass expansion in order to achieve
a product having a density of from 0.8 to 1.1 pounds per cubic
14
~056248
foot. The '753 patent nowhere mentions the use of such an
unconventionally low amount of blowing agent. Furthermore,
the '753 patent nowhere mentions a polymer having the
characteristics of the polymer of the present invention.
U.S. 4,721,588 describes a closed circuit process
for the production of expanded polystyrene foam. This process
comprises the steps of:
(a) pre-expanding raw polystyrene beads containing
a blowing agent in a pre-expansion vessel;
(b) storing the beads in one or more closed
storage containers to allow the internal
pressure within the expanded beads to return
to substantially atmospheric pressure;
(c) molding the expanded beads to a desired
configuration in a closed mold with steam; and
(d) removing the thus-formed article from the mold
and placing such in an aging room, wherein at
each stage the blowing agent released from the
beads is recovered, separated from any
residual steam by means of a condensing
system, and introduced into the burner of a
steam generator, thereby serving as fuel for
the process.
As can be seen from the above description of steps,
the gist of the process described in the '588 patent is the
recovery of the blowing agent and its re-use as a fuel for the
heating step. This produces the dual effects of (1) reducing
the amount of volatile organic compounds released into the
atmosphere, as well as (2) obtaining a double use for the
blowing àgent which escapes from the polystyrene during the
pre-expansion and molding steps.
The '588 patent also mentions that the blowing agent
can be n-pentane, or mixtures of n- and iso-pentane (up to
1~
205624~
about 25% iso-pentane by weight). The '588 patent also states
that the initial blowing agent content of the expandable
polystyrene beads can be 4-8 weight percent. However, the
' 588 patent nowhere states that a low density foamed
polystyrene product can be obtained if one utilizes less than
5 weight percent of the blowing agent. In fact, aside from
the statement that a blowing agent content of 4-8 weight
percent can be used, the ' 588 patent makes absolutely no
mention of actual product densities or any further mention of
the amount of blowing agent in any actual composition.
Finally, the ' 588 patent makes no mention of the use of
multiple pre-molding expansion steps. Rather, the ' 588 patent
teaches one to simply perform one pre-molding expansion step
and to thereafter follow this step with the molding step.
In contrast to the ' 588 patent, the process of the
present invention utilizes a low level of blowing agent in
combination with multipass expansion in order to achieve a
product having a density of from 0. 8 to 1.1 pounds per cubic
foot. The ' 588 patent nowhere mentions the use of the
combination of a level of blowing agent less than 5 weight
percent with multipass expansion in order to achieve a product
density of from 0. 8 to 1.1 pounds per cubic foot.
Furthermore, the ' 588 patent nowhere mentions a polymer having
the characteristics of the polymer used in the process of the
present invention.
In recent years the emissions of volatile organic
compounds (i.e. VOC's) have come under increasing scrutiny by
the EPA, state and local air quality boards as mandated by the
Clean Air Act of 1977. Because hydrocarbon emissions have
been shown to contribute to photochemical smog, the expanded
polystyrene industry which uses pentane as a blowing agent has
come under pressure to limit its use and/or emissions of
pentane.
~; ~;..
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Since the early months of 1990, the inventors'
process has enjoyed a high level of commercial success, with
sales of at least 3 million pounds of a formulation which has
been expanded to 0.8-1.1 lb./cu. ft. only with the inventor's
process, which formulation has a highly-expandable polymer
present in an amount of about 96 weight percent, based on the
total weight the formulation. Thus there has been a high
level of commercial success of both the process as well as the
formulation utilized in practicing the process.
For several years BASF Corporation has been involved
in the manufacture and sale of a number of expandable
polystyrene formulations having approximately 6 weight percent
pentane therein. Typically these formulations contained a
polymer having a polydispersity of 2.2, a weight average
molecular weight of about 190,000, and an Mz:Mn of about 3.5.
In stark contrast, the product of the present invention has
a polydispersity of from 1 to less than 2, a weight average
molecular weight of from about 200,000 to about 300,000, and
an Mz:Mn of from about 2 to less than 3.
One polymer which has been commercialized for
several years has a polydispersity of about 1.9, a weight
average molecular weight of about 190,000, and furthermore,
upon analysis, yielded a ratio of Mz to Mn of 3 04
Furthermore, this polymer was produced only in formulations
bearing blowing agent in an amount of about 6 weight percent.
In contrast, the polymer of the present invention has a
combination of characteristics (polydispersity, weight average
molecular weight, and Mz:Mn) which differs from the
aforementioned commercially available polymer. Furthermore,
the formulation of the present invention utilizes blowing
agent in an amount of only from about 2 weight percent to
about 4.4 weight percent.
2056248
BRI~F SllMMZ~RY OF THE INVENTION
The process of the present invention pertains to
making a closed-cell foamed thermoplastic resinous object.
The process is carried out by expanding beads in from 2 to 5
expansion steps. The beads are comprised of a blowing agent
and a polymer. The blowing agent is homogeneously dispersed
in the polymer and the blowing agent may be, in general,
hydrocarbons which are gaseous or liquid at standard
temperature and pressure, do not dissolve the styrene polymer,
and boil below the softening point of the polymer. The
blowing agent is preferably at least one member selected from
the group consisting of:
pentane, cyclopentane, neopentane, isopentane,
pentane petroleum distillate fractions, propane,
butane, isobutane, hexane, isomers of hexane, 2-
methyl pentane, 3-methyl pentane,
methylcyclopentane, cyclohexane, methylcyclohexane,
heptane, propylene, 1-butylene, 2-butylene,
isobutylene, mixtures of one or more aliphatic
hydrocarbons having a molecular weight of at least
42 and a boiling point not higher than 95C at 760
millimeters absolute pressure, water, carbon
dioxide, ammonium carbonate, and azo compounds that
are decomposable to form a gas at a heat-
plastifying temperature to which the polymer is
brought.
The blowing agent is present in the beads in an
amount of from about 2 weight percent to about 4.4 weight
percent based on the weight of the beads.
The polymer making up the beads may be one or more
polymers produced from at least one of a variety of monomers.
The monomer is at least one member selected from the group
18
2056248onsisting of:
styrene, derivatives of styrene, vinyltoluene,
mono- and polyhalogenated vinyltoluenes which form
linear polymers, acrylonitrile, and methyl
methacrylate.
The polymer is present in the beads in an amount of
f~o~ ~bout D3
19
2Q56248
weight percent to about 98 weight percent based on the
weight of the beads. The polymer exhibits the following
three characteristics: (1) a polydispersity of from about 1
to less than 2.5; (2) a weight average molecular weight of
from greater than about 180,000 to about 300,000: and (3) an
Mz:Mn of from about 2 to about 4.5. Furthermore, the
polymer is branched to from 0 to less than 5 weight percent.
The blowing agent is added to the polymer during
polymerization.
The expansion steps are carried out in an expander
at substantially atmospheric pressure. The expansion steps
result in "finally-expanded" beads. The expansion of the
polystyrene beads is carried out in a manner so that the
finally-expanded beads have a density of from about 0.8
pounds per cubic foot to about 1.1 pounds per cubic foot.
After each of the expansion steps, the expanded beads are
aged from 1 hour to 80 hours.
Furthermore, the process is carried out so that
the blowing agent emitted in the expansion steps in only
from about 0.3 to about 1.5 weight percent based on the
weight of the beads. The expansion steps result in
~finally-expanded" beads. The expansion of the beads is
carried out in a manner so that the finally-expanded beads
have a density of from about 0.8 pounds per cubic foot to
about 2 pounds per cubic foot.
The process of the present invention also pertains
to a process for making a closed-cell foamed thermoplastic
resinous molded object. The process is carried out by
expanding beads in from 2 to 4 preexpansion steps, and
thereafter carrying out a molding step in which the beads
are further expanded and fused into a unitary object. In
the process in which there is a molding step, the expansion
steps which precede the molding step are termed
"preexpansion" steps because they precede the molding step.
- 20 -
2Q56248
It should be noted that the molding step generally causes at
least some further expansion, along with bonding the
preexpanded beads to one another (i.e. fusion).
. The beads are comprised of a blowing agent and a
polymer. Although the blowing agent may generally be as
described above, preferably the blowing agent is at least
one member selected from the group consisting of:
~ A-
205~24~
pentane, cyclopentane, neopentane, isopentane,
pentane petroleum distillate fractions, propane,
butane, isobutane, hexane, isomers of hexane, 2-
methyl pentane, 3-methyl pentane, methylcyclo-
pentane, cyclohexane, methylcyclohexane, heptane,
propylene, l-butylene, 2-butylene, isobutylene,
mixtures of one or more aliphatic hydrocarbons
having a molecular weight of at least 42 and a
boiling point not higher than 95C at 760
millimeters absolute pressure, water, carbon
dioxide, ammonium carbonate, and azo compounds that
are decomposable to form a gas at a heat-
plastifying temperature to which the polymer is
brought.
The blowing agent is present in the beads in an
amount of from about 2 weight percent to about 4.4 weight
percent based on the weight of the beads.
The polymer making up the beads may be one or more
polymers produced from at least one of a variety of monomers.
The monomer is at least one member selected from the group
consisting of:
styrene, derivatives of styrene, vinyltoluene,
mono- and polyhalogenated vinyltoluenes which form
linear polymers, acrylonitrile, and methyl
methacrylate.
The polymer is present in the beads in an amount of
from about 93 weight percent to about 98 weight percent based
on the weight of the beads. The polymer exhibits the following
three characteristics: (1) a polydispersity of from about 1
to less than 2.5; (2) a weight average molecular weight of
from greater than about 180,000 to about 300,000; and (3) an
Mz:Mn of from about 2 to about 4.5. Furthermore, the polymer
is branched to from 0 to less than 5 weight percent.
~'
2056248
The blowing agent is added to the polymer during
polymerization.
The preexpansion steps are carried out in an
expander at substantially atmospheric pressure. The comple-
tion of the preexpansion steps results in the production of
"finally-preexpanded" beads. The finally-preexpanded beads
are then molded in order to further expand and fuse the
finally-preexpanded beads. Both the preexpansion steps and
the molding step are carried out so that a molded foamed
object having a density of from about 0.8 to about 1.1 pounds
per cubic foot is formed.
It is an object of the present invention to reduce
the amount of blowing agent used in the production of low
density, closed cell, foamed thermoplastic resinous objects.
It is an object of the present invention to reduce
the level of environmental impact (i.e. reduced VOC emissions)
in the production of low density, closed cell, foamed
thermoplastic resinous objects.
It is an object of the present invention to provide
a process which will lower the shrinkage upon molding in the
production of closed cell, foamed thermoplastic resinous
objects.
It is an object of the present invention to provide
a process which results in a lowering of the required cooling
times both between expansion (and preexpansion) steps as well
as in any molding step which is utilized.
It is an object of the present invention to provide
a process for efficiently using a polystyrene polymer having
a high degree of expandability.
It is a further object of the present invention to
provide a process for utilizing an expandable polystyrene
formulation in the production of expanded polystyrene
products.
2056?48 ,
-
It is a further object of the present invention to
provide a process wherein a polystyrene polymer as well as a
formulation for making expanded polystyrene products can be
utilized with a lesser amount of blowing agent emitted, so
that there is less blowing agent emitted into the atmosphere
and/or pollution abatement equipment.
It is a further object of the present invention to
provide a process for producing expanded polystyrene products
while using a formulation having a greater ratio of resin to
blowing agent, so that more resin is present per pound of
formulation.
It is a further object of the present invention to
enable the production of expanded polystyrene products using
decreased molding cycle times, as well as decreased shrinkage
upon molding, as well as decreased aging times between
expansion steps.
It is a further object of the present invention to
enable the production of an expanded polystyrene product
having decreased susceptibility to damage during processing.
It is a further object of the present invention to
enable the production of an expanded polystyrene beads having
increased shelf life before the molding step due to a lower
rate of loss of blowing agent therefrom.
It is a further object of the present invention to
enable a process for making expanded polystyrene products in
which there is decreased sensitivity to steam during the
expansion and molding steps, thereby permitting a "broader
molding range process" with respect to the use of steam in the
pre~x~n~ion and molding steps and its effect on fusion, cycle
time, and dimensional stability upon molding.
Each of the above objects can further be understood
as providing a respective advantage to the process of the
present invention. Although the term "polystyrene" is found
2056248
in the above object statements, these objects should be
understood as being applicable to all polymers which may be
utilized in the process of the present invention, as well as
a preferred applicability to polystyrene.
DETAILED DESCRIPTION OF TH~ PREFERRED EMBODIMENTS
The process of the present invention involves
expanding a substantially solid thermoplastic polymer to form
a foam. The expansion of the polymer is effectuated by
intimately mixing a blowing agent with the polymer, and
thereafter heating the mixture so that the blowing agent
vaporizes within the polymer particles, causing the polymer
particles to expand during a period in which the polymer is
in a softened state. The vaporization of the blowing agent
is produced by the application of heat. Likewise, the heat
also softens the polymer. Enough heat must be applied to
cause the temperature of the polymer to exceed its softening
point. The vaporization of the blowing agent within the
softened polymer causes the mixture to expand and form a foam.
The foam is then allowed to cool, while remaining
substantially expanded.
During cooling, the pressure within the foam cells
decreases due to cooling and condensing of the blowing agent.
This causes gases which can permeate the polymer (e.g. air,
steam, etc.) to migrate into the cells, thereby somewhat
restoring (i.e. to atmospheric pressure) the relatively low
internal pressure within the cells. Although components
within the atmosphere (i.e. oxygen, carbon dioxide, nitrogen,
etc) are to some degree able to diffuse into the cells, if
steam is used as the source of heat for the expansion steps
(or the molding step), it generally is the most permeable of
the gases diffusing into the cells of the foam. Upon
24
A
2056248
substantial equilibration (i.e. when the pressure within the
cells is substantially that of ambient atmospheric pressure)
of the foam, the now cooled foam can again be heated,
resulting in further expansion of the foam. Thus by utilizing
multiple "cycles", or "passes" of such expansion, cooling, and
"aging" (i.e. substantial equilibration of pressure),
sequential volumetric increases can be achieved.
Optionally, the foam can be further expanded and
fused in order to form a molded object. Molding is
effectuated by placing preexpanded beads into a mold, closing
the mold so that a substantially confined volume is produced,
and thereafter further heating the preexpanded beads so that
they further expand and substantially fill the volume within
the mold and fuse (i.e. bond) to one another.
24a
A
2Q56248
-
In general in the process of the present invention
in which there is no molding step, blowing agent is emitted
in an amount of from about 0.3 weight percent to about 1.5
weight percent, based on the total weight of the beads.
Preferably the emission of blowing agent is from about 0.5
to about 1.2 weight percent, and most preferably the
emission of blowing agent is from about 0.6 to about 0.7
weight percent. These emission figures represent the sum
total of blowing agent which is released to the environment
during the expansion steps themselves as well as each of the
aging periods between each of the expansion steps.
In general in the process of the present invention
in which there is a molding step, blowing agent is emitted
in an amount of from about 1 weight percent to about 2.5
weight percent, based on the total weight of the beads.
Preferably this emission of blowing agent is from about 1.5
to about 1.9 weight percent, and most preferably this
emission of blowing agent is from about 1.6 to about 1.8
weight percent. These emission figures represent the sum
total of blowing agent which is emitted during the
preexpansion steps themselves plus each of the aging periods
after each preexpansion step, plus the emissions produced by
the molding step.
In the process of the present invention it is an
objective to provide a commercially viable process which
reduces the emission of volatile organic compounds (VOCs) in
comparison with currently viable commercial processes. In
part, this objective is achieved by utilizing a lower amount
of blowing agent than has been used in prior art
commercially viable processes. This is effectuated by using
from 2 to 4.4 weight percent of the blowing agent, based on
the weight of the polymer.
- 25 -
2056248
Any one or more of a wide variety of blowing agents
can be utilized in the process of the present invention.
These blowing agents include: hydrocarbons which are gaseous
or liquid under normal conditions, do not dissolve the styrene
polymer, and boil below the softening point of the polymer.
Among the blowing agents preferred for use in the process are,
for example: pentane (including isomers of pentane such as
cyclopentane, methylcyclopentane, neopentane, isopentane, as
well as pentane petroleum distillate fractions), propane,
butane, isobutane, hexane, isomers of hexane, 2-methyl
pentane, 3-methyl pentane, 2,2-dimethylbutane, 2,3-
dimethylbutane, methylcyclopentane, cyclohexane, heptane,
propylene, 1-butylene, 2-butylene, isobutylene, mixtures of
one or more aliphatic hydrocarbons having a molecular weight
of at least 42 and a boiling point not higher than 95 C at
760 millimeters absolute pressure, water, carbon dioxide,
ammonium carbonate, and azo compounds that are decomposable
to form a gas at a heat-plastifying temperature to which the
polymer is brought. A more preferred group of blowing agents
comprises pentane, cyclopentane, methylcyclopentane,
neopentane, isopentane, pentane petroleum distillate
fractions, 2-methyl pentane, 3-methyl pentane, propane,
butane, isobutane, isobutylene, hexane, isomers of hexane,
cyclohexane, and heptane.
The blowing agent is incorporated into the polymer
during polymerization. In the process of the present
invention, the blowing agent is incorporated into the polymer
in an amount of from 2 to 4.4 weight percent, based on the
total bead weight. Preferably the blowing agent is
incorporated in an amount of from about 2.5 to about 4.4
weight percent, still more preferably from about 3 to about
4, and most preferably the blowing agent is incorporated in
an amount of about 3.5 weight percent. Most preferably the
26
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2056248
blowing agent is pentane (either n-pentane or a mixture of n-
pentane together with isomers of pentane). As aforesaid
pentane is added to the polymer during the polymerization
process, most preferably at a styrene conversion of from 20-
60%.
The process of the present invention is carried out
on an unexpanded bead. The term "unexpanded bead" is herein
defined as a discrete particle which is comprised of a polymer
and a blowing agent. According to the process of the present
invention, unexpanded beads are expanded in from 2 to 5
expansion steps. The preferred process of the present
invention involves carrying out 2 or 3 preexpansion steps,
followed by a molding step. That is, from 2 to 3 premolding
expansion steps are utilized to produce finally-preexpanded
beads. Most preferably this process utilizes only 2
preexpansion steps.
If the process is being utilized to make a non-
molded product, the preferred process is to use from 2 to 3
expansion steps to produce finally-expanded beads. Most
preferably this process utilizes only 2 expansion steps.
If the beads are expanded and not fused into a
molded object, the beads are herein termed as "finally
expanded beads". If, however, the beads are ultimately to be
fused into a molded object, the expansion steps are termed
"preexpansion steps". Once these beads are "finally
preexpanded", they are thereafter further expanded and fused
into a molded object in a molding step which also serves as
a final "~p~n~ion" step. Regardless of whether the beads are
expanded or preexpanded, according to the process of the
present invention the total number of expansion (including
pree~r~n~ion) steps is no greater than 5 and no less than 2.
It has surprisingly been found that with as little as from 2
to 4.4 weight percent of blowing agent, a final product
2056248
density as low as from 0.8 to 1.1 lb/cu.ft. can be obtained.
Foams having this density are useful as insulation and/or for
protective packaging.
The expansion of the beads is typically carried out
in a batch expander closed vessel having steam injected
thereinto. Examples of such expanders include: Tri* 502,
Tri* 905, Weiser* VN400, Kurtz* KV1000, Dingledein* VA2000.
The exr~nsion of the beads is carried out by passing the beads
through an expander so that the beads are heated and become
soft enough that they expand due to the rising pressure
produced by the vaporization of the blowing agent and other
internal gases. As a general rule, the rate of passage of the
beads through the expander determines the amount of expansion
which will result during that e~p~nsion step. Of course, the
lower the rate of passage of beads through the expander, the
greater the amount of heat transferred to the beads, and the
higher the resulting degree of expansion produced. However,
there is a m~i m~lm amount of expansion which any one expansion
step can produce for any given bead composition. Thus, it has
been found that in general the flow rate of the beads through
the expander should be pounds per hour per cubic foot of
expander volume (i.e. lb/hr./cu.ft.) from about 5 to about 120
lb/hr/cu.ft. At flow rates below about 5 lb/hr/cu.ft., the
beads remain in the expander so long that lumping accurrs, and
processing time is uneconomical. At flow rates above 120
lb/hr/cu.ft., the beads do not remain in the expander long
enough to cause sufficient expansion to result in a process
of expanding with a reasonable degree of efficiency.
Preferably, the expansion rate is from about 7 to about 100
lb/hr/cu.ft., and most preferably the expansion rate is from
about 12 to about 80 lb/hr/cu.ft.
* trade marks
28
2056248
The process of the present invention can be carried
out either with or without a molding step. The following is
a description of the molding step which can be utilized in the
process:
The prepuff (i.e. the preexpanded beads) were
placed into a Kurtz vacuum block mold of internal
dimensions of approximately 48" x 96" x 33". The
molding steps were as follows: presteaming vacuum
to
28a
2(~56248 -
approximately 0.5 bar absolute pressure, followed
by steaming into vacuum for approximately 3
seconds, then cross-steaming through the block for
about 3-6 seconds, then autoclaving for another 3-
8 seconds to a miximum foam pressure of
approximately 0.5 - 1.0 bar. Vacuum was then
applied to the block in the mnold to assist in
cooling the block to a foam pressure of
approximately 0-0.1 bar, allowing the block to be
removed from the mold without significant post-
expansion or shrinkage occurring.
The use of low aging times, as is described
herein, enables a greater process effeciency by completing
the process within a shorter time period. Furthermore, by
using a low level of blowing agent in combination with
completing the process within a shorter time period, there
is a lower level of emissions of blowing agent into the
environment.
In general, the aging time after each first
expansion (or first preexpansion) pass is from about 1 hour
to about 80 hours. Preferably this aging period is from
about 2 hours to about 6 from 1.2 hours to about 8 hours,
and most preferably this aging period is from 1.5 hours to
about 2.5 hours.
The polystyrene beads can also contain other
additives which impart particular properties to the
expandable products, such as antistatic agents, stabilizers,
colorants, lubricants, fillers, substances which prevent
agglomeration during prefoaming, e.g. zinc stearate,
melamine-formaldehyde condensates or silica, and agents for
reducing the demolding time during final foaming, e.g.
glycerol ester or
- 29 -
205624~3
hydroxycarboxylic acid esters. Depending on their intended
effect, the additives may be homogeneously dispersed in the
particles or be present as a surface coating.
A total of about 0.7 parts (based on 100 parts
styrene) of free radical initiators are added to the organic
phase at the beginning of the polymerization reaction.
Preferably the initiator is a mixture of benzoyl peroxide,
dicumyl peroxide, t-butyl perbenzoate. While the benzoyl
peroxide acts as a "low temperature" initiator, the t-butyl
benzoate acts as a "high temperature" initiator. Furthermore,
any excess dicumyl peroxide (which is left after the
polymerization reaction is complete) serves as a synergist for
flame retardant properties.
The process of the present invention also may
optionally utilize poly-n-vinylpyrollidone as a protective
colloid which coats the beads. The poly-n-vinylpyrollidone
is added at a time during the polymerization reaction when the
beads are at the size desired. The poly-n-vinylpyrollidone
has the effect of coating the beads so that they cannot adhere
to one another, resulting in arresting the growth of the
beads, thereby "freezing" their size. The poly-n-
vinylpyrollidone is preferably added to the reaction mixture
at a level of about 0.3 weight percent, based on the weight
of the polymer present.
Generally, the polymers to be used in the process
of the present invention may be produced from one or more of
any of a wide variety of monomers. Such monomers include
monovinyl compounds which undergo addition polymerization to
provide generally linear polymers. It is preferred that such
polymers are also capable of forming structures crosslinked
to a desired degree when polymerized in the presence of a
crosslinking quantity of a polyvinyl compound (e.g. ethylene
glycol, dimethacrylate, divinylbenzene, etc.). The monovinyl
2056248
.
compounds useful in the process are, for example, styrene (and
derivatives thereof), vinyltoluene, mono- and polyhalogenated
vinyltoluenes which form linear polymers, acrylonitrile,
methyl methacrylate, and vinyl toluene.
Preferably the monomer is at least one member
selected from the group consisting of styrene and derivatives
of styrene. Polystyrene is the most preferred polymer for the
process of the present invention. Although pure polystyrene
is the most preferred styrene polymer for use in the present
invention, monomers herein termed "derivatives of styrene"
which can be polymerized and used in the process of the
present invention include:
alpha-methylstyrene, o-methylstyrene, m-methyl-
styrene, p-methylstyrene, ar-ethylstyrene, ar-
vinylxylene, ar-chlorostyrene, and ar-bromostyrene,
or solid copolymers of two or more of such alkenyl
aromatic compounds with minor amounts of other
readily polymerizable olefinic compounds such as
divinylbenzene, methylmethacrylate or acryloni-
trile, etc.
The process of the present invention requires the
use of a polymer which exhibits the following three
characteristics: (1) a polydispersity within a given range;
(2) a weight average molecular weight within a given range;
and (3) an Mz:Mn within a given range. Furthermore, the
polymer used in the process of the present invention is herein
defined in terms of weight average molecular weight (Mw),
number average molecular weight (Mn)~ z-average molecular
weight (Mz). The number average molecular weight is the
arithmetic mean value obtained by diving the sum of the
molecular weight by the number of molecules. The weight
average molecular weight is the second power average molecular
weight in the polydisperse polymer. The z-average molecular
2056248
weight molecular weight is the third power average molecular
weight in the polydisperse polymer. More extensive and
descriptive definitions of these various molecular weights
were described by Billmeyer, F.W., Jr., Textbook of Polymer
Science, 2nd Ed., 1971, Wiley-Interscience, N.Y., N.Y., pp 6,
66, 78, and 92.
The inventors of the process of the present
invention have unexpectedly discovered that such a polymer can
also be used to make a low density (i.e. 0.8-1.1 lb/cu.ft.)
foam while using an unexpectedly low amount of blowing agent,
if from just two to five expansion steps are utilized in the
process.
The process of the present invention utilizes a
polymer having a particular set of characteristics, which
characteristics are derived from the molecular weight
distribution curve of the polymer. The molecular weight
distribution curve is determined by gel permeation
chromatography. This method is described in detail in G.
Glockler, Polymercharakterisierung, Chromatographische
Methoden, volume 17, published by Huthig, Heidelberg 1982.
The first of these characteristics, i.e.
polydispersity, is determined by analyzing the molecular
weight distribution curve for the reaction product of the
polymerization. Polydispersity is calculated by dividing the
weight average molecular weight by the number average
molecular weight. Thus, the polydispersity is a measure ofthe
breadth of the molecular weight distribution. The polymer
generaly exhibits a polydispersity of from about 1 to less
than 2.5. Preferably, the polymer exhibits a polydispersity
of from about 1 to less than 2.0, still more preferably from
about 1.5 to less than 2.0, and most preferably the polymer
exhibits a polydispersity of from about 1.7 to about 1.98.
Example 7 (infra) discribes the method of analysis of the
2056248
polymeric reaction product, this method providing the means
for determintion of weight average molecular weight, number
average molecular weight, and "z-average molecular weight".
Thus this analytical procedure provides the data from which
one may then calculate polydispersity, weight average
molecular weight, and the Mz:Mn ratio.
The second characteristic which the polymer exhibits
(i.e. the weight average molecular weight) is, in general,
from greater than about 180,000 to about 300,000. Preferably,
the polymer used in the process of the present invention has
a weight average molecular weight of from greater than 190,000
to about 250,000. Most preferably, the polymer exhibits a
weight average molecular weight of from about 200,000 to about
220,000. As with polydispersity, the weight average molecular
is determined the analysis provided in Example 7, infra.
The third characteristic is Mz:Mn, i.e. the ratio
of the z-average molecular weight to the number average
molecular weight. This ratio is related to the steepness of
slope of the upper end of the molecular distribution curve.
In general, the polymer exhibits an Mz:Mn ratio of from about
to 2.5 to about 3.3. Most preferably the polymer exhibits an
Mz:Mn ratio of from about 2.7 to about 3Ø As with
polysidpersity and weight average molecular weight, the Mz:Mn
ratio can be calculated based upon the analytic results
obtained from the procedure of Example 7. This procedure, of
course, results in obtaining a molecular weight distribution
curve. The value for weight average molecular weight, number
average molecular weight, and "z-average molecular weight" can
be determined. These values permit the calculation of
polydispersity as well as Mz:Mn ratio.
The polymer used in the process of the present
invention is a substantially linear polymer, i.e. is a
substantially unbranched polymer. In general the polymer has
2056248
a degree of branching of from 0 to less than 5 weight percent.
The phrase "... branched to from 0 to less than 5 weight
percent ..." is herein defined as referring to a polymeric
chain in which at least 95 percent of the molecular weight of
the polymer resides in that portion of the molecule which
constitutes the linear chain. For purposes of calculating the
weight percent of the polymer which resides in branches (as
opposed to the linear portion of the polymer molecule), carbon
atoms which are not part of the main polymeric chain are
considered to be located on branches, and any atoms which are
attached to the branch carbon atoms are likewise considered
to be located on the branch portion of the polymer molecule.
Non-carbon atoms which are bonded to a carbon atom of the
linear polymer backbone (but which themselves do not make up
a portion of the backbone) are considered substituents, rather
than branches. However, if a substituent atom is bonded
directly or indirectly to a second carbon atom wherein the
second carbon atom is not part of the linear polymer backbone,
the substituent as well as any atoms attached thereto (which
are not part of the polymer backbone) are considered to be on
a branch. The polymer is preferably branched to from 0 to
less than 2 weight percent. Most preferably the polymer is
branched to from 0 to less than 1 weight percent.
The polymer is preferably a substantially homo-
polymeric polystyrene polymer. That is, the polymer is
preferably derived for a single monmer, that monomer being
styrene. The phrase "substantially homopolymeric polymer" is
herein deflned as a polymer in which at least 99 percent of
the monomeric units (which reacted to form the polystyrene)
were a single monomer. Preferably, at least 99.9 percent of
the monomeric units which are reacted to form the polymer are
a single monomer species.
Preferably the polymer is a substantially unsub-
34
2056248
stituted polymer. The phrase "substantially unsubstituted
polymer" is herein defined as a polymer having a carbon
backbone and branches in which less than 2 percent of the
available sites for substitution have atoms other than
hydrogen thereon. Still more preferably, the degree of
substitution is less than 0.5 percent, based on the total
number of positions for substitution available on the polymer.
A preferred polymer of the present invention
exhibits: (1) a polydispersity of from about 1.5 to less than
2.0; (2) a weight average molecular weight of from greater
than 190.000 to about 250,000; and (3) an Mz:Mn of from about
to 2.5 to about 3.3. Furthermore, this preferred polymer is
branched to from 0 to less than 2 weight percent. Finally,
this preferred polymer is a substantially homopolymeric,
unsubstituted polymer.
A still more preferred polymer of the present
invention exhibits: (1) a polydispersity of from about 1.7 to
about 1.98; (2) a weight average molecular weight of greater
than about 200,000 to about 220,000; and (3) an Mz:Mn of from
about 2.7 to less than about 3Ø Furthermore, this still
more preferred polymer is branched to from 0 to less than 1
weight percent. Finally, this still more preferred polymer
is a substantially homopolymeric, unsubstituted polymer.
Preferably the formulation of the present invention
further comprises a chain transfer agent. Chain transfer
agents having a transfer constant K (as defined in Vollmert,
Grundriss der Makromolekularen Chemie, published by Springer
1962, pages 52 and 71) of from 0.1 to 50, preferably from 1
to 30, are used. Examples of suitable chain transfer agents
are:
n-Dodecyl mercaptan (K=19)
tert.-Dodecyl mercaptan (K=3)
n-Butyl mercaptan (K=22)
.., , ~
2056248
-
tert.-Butyl mercaptan (K=3.6)
Carbon tetrabromide (K=2.2)
Pentaphenylethane (K=2.0)
Optionally (but preferably) the process of the
present invention utilizes a flame retardant in the mixture
of components which makes up the formulation of the expandable
beads. In general, the flame retardant is an organic bromine
- or chloring flame retardant compound present in an amount of
from about 0.2 to about 2 weight percent, based on the weight
of the total formulation. More preferably the formulation
comprises a brominated hydrocarbon flame retardant in an
amount of from about 0.5 to about 1.5 weight percent, based
on the weight of the total formulation. still more preferably
the formulation comprises a flame retardant which is at least
one member selected from the group consisting of trisdibromo-
propylphosphate, hexabromocyclododecane and bis allyl ether
of tetrabromo-bis-phenol A, wherein the flame retardant is
present in an amount of from about 0.6 to about 1.2 weight
percent, based on the total weight of the formulation.
Preferably (but optionally) the formulation further
comprises a "flame retardant synergist", i.e. one or more
compounds which increase the effectiveness of the flame
retardant when used in combination therewith. The flame
retardant synergist may at least one member selected from the
group consisting of dicumyl peroxide and other organic
peroxides which have a half-life of one hour at temperatures
of from about 110C to about 150C.
The formulation may further comprise additional
additives which impart particular properties to the expandable
products. Examples include flameproofing agents based on
organic bromine or chlorine compounds, e.g. trisdibromopropyl
phosphate, hexabromocyclododecane and chloroparaffin as well
as synergists for flameproofing agents, such as dicumyl
36
2056248
peroxides and other organic peroxides which decompose at high
termperatures, antistatic agents, stabilizers, colorants,
lubricants, fillers, substances which prevent agglomeration
during prefoaming, e.g. zinc stearate, melamine-formaldehyde
condensates or silica, and agents for reducing the demolding
time during final foaming, e.g. glycerol esters or
hydroxycarboxylic acid esters. Depending on their intended
effect, the additives may be homogeneously dispersed in the
particles or be present as a surface coating.
The unexpanded beads are of course primarily
comprised of one or more polymers having the characteristics
described above. Preferably the polymer is polystyrene or
polymers produced by polymerizing monomers which are
derivatives of polystyrene. In general, the bead is comprised
of polymer in an amount of from about 93 to about 98 weight
percent, based on total bead weight. Preferably the bead is
comprised of polymer in an amount of from about 94 to about
97.5 weight percent. Still more preferably the bead is
comprised of polymer in an amount of from about 95 to 97
percent, and most preferably the bead is comprised of polymer
in an amount of about 96 weight percent.
If a crosslinking polyvinyl compound is present, it
should not be present in an amount which produces an
undesirably high amount of crosslinking. This is because the
polymer will not undergo expansion if the degree of
crosslinking is too high. The crosslinking agents which may
be employed in the process of the present invention comprise:
divinylbenzene, diethylene glycol dimethacrylate,
diisopropenylbenzene, diisopropenyldiphenyl, diallylmaleate,
diallylphthalate, allylacrylates, allylmethacrylates,
allylfumarates, allyllitaconates, alkyd resin types, butadiene
or isoprene polymers, cyclooctadiene, methylene norbornylenes,
divinyl phthalates, vinyl isopropenylbenzene, divinyl
2056248
biphenyl, as well as any other di- or poly-functional compound
known to be of use as a crosslinking agent in polymeric vinyl-
addition compositions.
38
2056248
Example 1 (Method of Making Polymer)
A mixture of 87 parts of water, 0.16 parts of sodium
pyrophosphate, and 0.27 parts of magnesiun sulfate
heptahydrate was reacted with stirring at ambient temperature
in a stainless steel pressure resistant vessel. To this
mixture was added a mixture of 100 parts of styrene, 014 parts
of benzoyl peroxide, 0.32 parts t-butylperbenzoate, 0.62 parts
of hexabromocyclododeane, and 0.21 parts of dicumyl peroxide,
with stirring. The vessel was heated for at least 2 hours at
a constant rate to 85C and then to 115C over 4.5 hours.
Sixty-five to seventy-five minutes after the vessel reached
80C, 2.9 parts of a 10% aqueous solution of poly-n-
vinylpyrrolidone was added to the reaction mixture. After an
additional 100-120 minutes, a solution of 0.10 parts of chain
transfer agent in 4.7 parts of n-pentane was added to the
reaction vessel. After reaching 115C, the vessel was held
at constant temperature for 3 hours, whereupon it was cooled
to ambient temperature over 3 hours.
~mple 2
A polystyrene polymer was prepared substantially as
described in Example 1. The polymer contained approximately
3.1 percent pentane (blowing agent). The resulting expandable
polystyrene beads were analyzed according to the procedure of
Example 7, and were found to have contained polymer having a
polydispersity of 1.82, a weight average molecular weight of
202,000, and an Mz:Mn of 2.70. The beads were screened to
0.6-1.3 mm diameter, dried to remove surface moisture, and
coated with 0.12 weight percent of a mixture of powdered
lubricants and antilumping agents commonly used in the
industry as screening aids and antilumping agents. The
pentane content of the beads out of the polymerization reactor
was 3.41 weight percent. However, as was typical, about 0.3
39
A~
2~56248
weight percent of pentane was lost during subsequent
processing, making 3.1 weight percent the actual pentane
content at the time of expansion.
The coated beads were expanded in a Tri
Manufacturing Model 502 expander. The inlet steam temperature
was about 211 F, and the inlet steam flow rate was
approximately 74 pounds per hour. The first-pass expansion
rate was about 208 pounds per hour and the outlet density of
the prepuff was about 1.9 pounds per cubic foot. A fluidized
bed drier (as commonly used in the industry) was utilized to
cool and partially stabilize the resulting prepuff. The
fluidized bed dryer was equipped with a blower which fluidized
a portion of the beads with ambient air. The prepuff was then
pneumatically conveyed to storage bags and aged at ambient
temperature and humidity for about 3 hours. Following aging,
the prepuff was expanded again in the same expander operated
at the same conditions, the result being a prepuff having a
density of about 1.10 lb/cu.ft., the expander operating at a
throughput of about 217 pounds per hour. The resulting
prepuff was again passed through the fluidized bed dryer.
After airveying again to storage bags and aging for about
three hours, the prepuff was transferred to a Kurtz vacuum
block mold (4' x 8' x 34") and molded. The molding cycle
consisted of presteaming vacuum to about 0.5 bar absolute
pressure, followed by cross-steaming and autoclaving with
steam. The resulting block was then cooled with vacuum until
the foam pressure was stabilized. The pressure release time
was about 30 seconds, and the resultant block had an average
of 10% fusion, 1% shrinkage (defined as actual block length
shrinkage 24 hours after molding compared to actual mold
length), 1.6% collapse (defined as actual thickness shrinkage
in middle of block compared to actual mold thickness), and a
bulk density of 1.10 lb/cu.ft. (defined as weight of block
205624~
divided by actual mold volume).
Example 3
This example illustrates the expansion and molding
of relatively large polystyrene beads containing 4.4 weight
percent pentane. The effect of insufficient aging time prior
to molding is herein demonstrated. In addition, a comparison
is given with respect to materials containing conventional
amounts of pentane. Also shown is the effect of too short an
aging time (after the second preexpansion pass but before
molding) with respect to pentane materials containing
conventional amounts of pentane (approximately 6 weight
percent).
An expandable polystyrene bead product containing
an average of 4.40 weight percent pentane and a bead diameter
of 1.3-1.9 mm was expanded in a Kurtz KV1000 expander equipped
with a Kurtz automatic density control system which adjusted
inlet steam flow to achieve desired prepuff outlet density.
A fluidized-bed dryer was utilized for both expansions. The
first-pass expansion was at a rate of 2000 lbs/hr and a
density of 1.22-1.25 lbtcu.ft. After about two hours age, the
prepuff was expanded again, at a rate of 3000 lbs/hr to a
density of 0.88-0.90 lb/cu.ft. The prepuff was then molded
on a Kurtz vacuum block mold (26" x 49.5" x 196"). No pre-
steam vacuum was used. Steam was added at a pressure of about
0.6 bar for about 6 seconds cross-steam followed by about 10
seconds autoclave. Vacuum was used to cool the block in the
mold. After only one hour prepuff aging, the blocks were of
poor quality, i.e. poorly fused and deformed (poor dimensional
stability). After 3-4 hours prepuff aging, the blocks were
molded to 0.7 bar m~ximllm foam pressure and were of excellent
quality with a total cycle time of 160-170 seconds. Typical
cycle times with normal pentane product after 24-36 hours
2056248
aging were 300-360 seconds.
~ple 4
This example illustrates how the use of a 4.4%
pentane formulation compares favorably with respect to the use
of a conventional formulation. Expansion and molding results,
cycle time, fusion, and dimensional stability were acheived
with the 4.4% pentane formulation over a conventional 6%
pentane formulation.
An expandable polystyrene bead product containing
an average of 4.40% pentane and a bead diameter of 0.6-1.3 mm
was expanded in a Weiser VN400 expander equipped with a
fluidized-bed dryer. The first-pass rate was about 2600 lbthr
at an outlet density of about 1.20 lb/cu.ft. After aging for
about four hours, the prepuff was expanded again, at a rate
of about 4000 lb/hr and at an outlet density of about 0.79-
0.88 lb/cu.ft. After about one hour of aging, the prepuff was
molded in a Weiser VacuCompact block mold (196" x 49" x 31").
Cycle times, fusion, and dimensional stability were equal to
or better than that of products of normal (6%) pentane content
which had been aged overnight (i.e. over eight hours of
aging).
~mple 5
This example illustrates, among other results, the
advantageous performance of a formulation comprising 3.6%
pentane. Note the highly desirable low aging time as well as
the desirable molding cycle time with accompanying high
dimensional stability after molding.
An expandable polystyrene bead product containing
an average of 3.58% pentane and a bead diameter of from 0.6-
1.3 mm was expanded in a Weiser VN400 expander equipped with
fluidized bed drying. The first-pass expansion rate was about
42
2056248
3100 lb/hr at an outlet density of about 1.59 lbtcu.ft.
After aging about four hours, the prepuff was expanded again,
at a rate of about 3400 lb/h and outlet density of about 0.84-
0.86 lb/cu.ft. After about one hour age, the prepuff was
molded on a Weiser VacuCompact block mold. Pressure-release
(i.e., cooling) time was only 29 seconds. All blocks were
well fused and dimensionally stable.
~x~m~le 6
This example illustrates, among other advantages,
how a formulation comprising 3.63 percent pentane permits a
highly advantageous molding cycle time, with accompanying 50%
increase in productivity in the molding step, due to the lower
molding cycle time. Good fusion and dimensional stability are
also shown.
An expandable polystyrene bead product containing
an average of 3.63% pentane and a bead diameter of from 0.6-
1.3 mm was expanded in a Dingledein & Herbert VA-K2000
expander. The first-pass expansion rate was 3000 lb/hr at an
outlet density of 1.66-1.75 lb/cu.ft. After aging for about
24 hours, the prepuff was expanded again, at a rate of about
4000 lb/hr and an outlet density of about 0.92-0.94 lb/cu.ft.
After aging for about two hours, the prepuff was molded in
a 16' Tri Manufacturing block mold. Well-fused, dimensionally
stable blocks were produced at a rate of about 15 blocks per
hour, as compared to 10 blocks per hour for normal pentane-
content beads.
~m~le 7
(Molecular Weight Distribution Curve Determination)
The following equipment and procedure was utilized
in order to generate the molecular weight distribution curve
43
~r
2056~48
for polystyrene polymers. This procedure was utilized to both
determine the molecular weight distribution of the polystyrene
polymer of the present invention, as ~ell as to analyze
products which are herein compared and contrasted with the
polymer and formulation of the present invention.
Chromatography Equipment and Con~itions
The apparatus consisted of a Waters 6000A pump with
a U6K injector, a Viscotek-supplied pulse dampener, two 30 cm
PLGel 5 um Mixed Bed polystyrene columns, a Viscotek Model 100
differential visometer (DV) and a Waters R401 differential
refractometer (RI). The data acquisition and analysis
hardware consisted of an IBM PC AT equipped wit 640 kb RAM,
a 30 Mb fixed disk and two 5.25" floppy disk drives; a dot
matrix printer and an HP 7475A plotter. The software used was
Unical Ver. 3.11 (an ASYST-based package) modified to display
Mz+l and obtained from Viscotek.
The chromatographic conditions were as follows:
Nominal flow rate: 1.0 ml/min
Solvent: THF, high purity, non-spectro grade
sample Injection Volume: 0.100 ml
RI Detector: Attenuation: 16x
Polarity: +
DV Detector: Temperature: 31.0 + 0.1C
Full Scale Output: 50 Pa
DPT Sensitivity: 0.2074
Data Acquisition: Start Time: 6 min.
Stop Time: 24 min.
~nalyt;cal Procedure
The THF to be used as the mobile phase for the GPC
system was filtered through a 0.45 um fritted filter and then
degassed under an aspirator vacuum for approximately 45
20562~
-
minutes. The THF and the flask were then transferred to the
GPC system and the THF maintained under a pad of helium.
Samples were made up to a concentration of 5 mg/ml and
filtered through a Gelman Acrodisc cR PTEE 0.45 um filter
prior to injection.
Only freshly prepared solutions were used as polymer
degradation was apparent with aged solutions. All solutions
were analyzed twice. The EPS (expanded polystyrene) samples
were not purified by precipitation prior to dissolution and
analysis, as comparison of purified and raw EPS polymer
results indicated no significant differences. To obtain
accurate solution concentrations for the unprecipitated EPS,
the initial solution concentrations were corrected for
volatiles determined by GC and coulombmetric analysis for
pentane and moisture, respectively, or gravimetrically by
baking a sample for total volatiles.
To correct for fluctuations in flow rate, each
chromatogram was normalized to the flow rate present during
calibration. This was accomplished by calculating the ratio
of the void volumes (total exclusion volume, earliest negative
peak in chromatogram) of the calibration chromatograms to the
sample chromatogram. The calibration void volume was
determined to be 19.72 ml. The ratio was then entered into
the data analysis package as the corrected flow rate.
20562~8
~x~m~les 8-lS
The procedure of Example 1 was substantially
followed in making a polystyrene formulation according to the
present invention. This polymer formulation is identified as
Example 8 in Table I (infra). The polymer formulation of
Example 9 contained a blowing agent (pentane) in an amount of
about 3.5 weight percent. The polymer of Example 9 was
analyzed according to the procedure set forth in Example 7,
and from this analysis the number average molecular weight
(Mn), the weight average molecular weight (Mw), and the z-
average molecular weight (Mz) were determined. From these
values the polydispersity (PD) and the Mz:Mn were calculated.
The analytical procedure of Example 7 was also
performed for several current commercial products (i.e.
Examples 9-14), each of which contained blowing agent in an
amount of 5.5 weight percent to at least 7 weight percent.
Example 10 had blowing agent therein at a level of
approximately 6 weight percent. From this analysis, the same
molecular weight determinations were made. Table I (below)
provides the results of the analyses for both the formulation
of the present invention (Example 9) as well as several
commercial formulations currently available.
As can be seen from Table I, only the formulation
of the present invention had all three identifying
characteristics within the scope of those which are identified
as pertaining to the polymer of the present invention. Even
though each of these polymers falls within the definition of
the polymer utilized in the formulation of the present
invention, none of these formulations had the amount of
blowing agent required in the formulation of the present
invention.
46
2056248
.
T~RLE I: POLYM~ CH~ACTERISTICS
EXAMPLE Mn x10E5 Mw x10E5 PD Mz x10E5 Mz:Mn
(g/mol)(g/mol) (g/mol)
8 1.12 2.02 1.823.00 2.70
9 1.12 2.17 1.953.35 2.99
0.87 1.93 2.203.11 3.56
11 1.37 2.89 2.105.28 3.84
10 12 1.20 2.51 2.094.58 3.81
13 1.01 1.89 1.883.07 3.04
14 1.13 2.20 1.943.83 3.37
1.27 2.73 2.155.03 3.96
[polydispersity was calculated as MW/Mn, and the ratio of Mz
to Mw was calculated by dividing the value obtained for Mz by
the value obtained for Mn]
~X~MPT.~S 16-17
These two examples illustrate the difference in both
(1) total emissions, as well as (2) emissions during aging,
for expanded polystyrene which was produced according to the
process described in Example 1. Example 16 illustrates the
emissions from a "conventional" process which employs a
blowing agent (pentane) in an amount of 6 weight percent.
Example 17 illustrates, in contrast, the emissions from a
process employing a formulation which comprises only 3.5
weight percent pentane. For Example 16 the amount of blowing
agent added during the polymerization was approximately 6
weight percent, whereas for Example 17 only about 3.5 weight
percent blowing agent was added during the polymerization.
Table II (infra) provides the results of emissions during each
of the expansion steps for each Example, for each aging period
for each Example, and during the molding step for each
47
2056248
-
Example. The bottom row of Table II provides figures for the
total emissions during the entire process of expansion, aging
and molding.
As can be seen from the figures in Table II, the
polystyrene having the low initial level of blowing agent
(i.e. Example 17) exhibited a total emissions of only from 42
to 79 percent as much as for Example 16. Furthermore, the
total emissions during aging was only from about 17 percent
to about 48 percent for Example 17 as compared with Example
16. Accordingly, the formulation (and polymer) of the present
invention exhibit a substantial reduction in both the total
emissions as well as the emissions during aging.
Table II
Example 16 Example 17
blowing agent content 6 wt. percent 3.5 wt. percent
1st Pass Expansion .76 .45
1st pass aging emissions 2.0 .12
1st pass aging time 24 hours 4 hours
2nd pass Expansion N/A .07
20 2nd pass aging emissions N/A .22
2nd pass aging time N/A (2 hours)
molding emissions 0.6-1.1 0.76%
Total Emissions 3.36-3.86% 1.62%
Example 18
(Method of Determining and Calculating the Degree of
Branching)
Branching can be determined using a Viscotek differential
viscometer and related software according to the theory of
Zimm and Stockmayer. More extensive and descriptive
discussions o~ this theory, as well as related subject matter,
can be found in Billmeyer, F.W., Jr., Textbook of Polymer
Science, 2nd Ed., 1971, Wiley-Interscience, N.Y., N.Y.,
48
2056248
-
especially pages 89-90. Using the Mark-Houwink constants for
known linear samples of polystyrene, one can calculate the
branching frequency of the number of branches per 100 monomer
units. More extensive and descriptive discussions of these
constants, as well as related subject matter, can be found in
Billmeyer, F.W., Jr., Textbook of Polymer Science, 2nd Ed.,
1971,Wiley-Interscience, N.Y., N.Y., especially pages 86-87.
4g
