Note: Descriptions are shown in the official language in which they were submitted.
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BACK~ROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to reinforced thermoplastic mate-
rial and more specifically to apparatus and method for extruding
a stampable, reinforced thermoplastic composite sheet containing,
as reinforcement, a glass fiber mat.
DESCRIPTION OF THE PRIOR ART
In the apparatus and method used to form stampable rein-
forced thermoplastic composite sheets, a long glass fiber mat is
sandwiched between a glass fiber filled layer of thermoplastic
resin and a fiber-free layer of the resin, and laminated into a
multi-ply product while the fiber-free resin layer is in a molten
condition.
One of the major problems with such systems is the
difficulty of coating substantially all of the fibers of the mat
during lamination. The problem is particularly troublesome when
mats having a high concentration of glass fiber or utilizing
chopped glass fiber strands are employed. In order to alleviate
the problem of incomplete coating, it has often been necessary to
reduce mat weight and filler concentration, increase resin
quantity, utilize resin modifiers and decrease processing speeds.
These constraints increase the cost and reduce performance
characteristics of the laminated product.
SUMMARY OF THE INVENTION
The present invention provides a strong, light stamp-
able thermoplastic sheet and a method and means for producing such
sheet in an economical, reliable manner. The sheet is essentially
free of surface waviness and long glass show-through, comprising
in terms of percent by weight of each layer (a) at least one layer
comprising from about 40 percent to 100 percent of a synthetic
thermoplastic polymer, about 0 percent to 50 percent of a par-
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ticulate filler, and 0 percent to 45 percent short glass
fibers having a length ranging from 0.01 to 3/4 of an inch and
arranged generally parallel to the plane of the sheet surface,
(b) a reinforcing layer adjoining said one layer comprising 50
percent to 100 percent of synthetic thermoplastic polymer on an
extruded basis, a long glass fiber mat comprised of fibers having
a length of at least 1 inch and having a weight ranging from .1
to 16 ounces per square foot of mat surface area and particulate
fillers ranging from 0 percent to 50 percent, and (c) mat
positioning means disposed between said at least one layer and
said mat, for holding said mat within said reinforcing layer
during formation of said composite, said mat being substantially
encased in a matrix of the thermoplastic polymer and said
reinforcing layer being essentially free of short glass fibers.
In addition, the present invention provides composite
laminated sheet comprising the steps of (a) blending and extruding
a first sheet layer comprising from about 40 percent to 100 percent
of thermoplastic polymer, about 0 percent to 50 percent of a parti-
culate filler and 0 percent to 45 percent short glass fibers
having a length ranging from 0.01 to 3/4 of an inch and arranged
in a plane generally parallel to the sheet surface, (b) embossing
said first sheet layer in a roll stack to form an embossed surface
thereon containing a plurality of projections, (c) blending and
extruding a second sheet layer comprising from about 50 percent to
100 percent of synthetic thermoplastic polymer and from 0 percent
to 50 percent particulate filler, but being essentially free of
glass fibers, (d) feeding said first sheet, said second sheet and
a long fiber glass mat, the fibers of which have a length of at
least 1 inch, into the nip of a set of laminating rolls while the
resin of the second sheet is still in a molten condition, the
clearance between the rolls being less than the thickness of the
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sheets and glass mat being fed to the nip of said rolls, whereby
the long fiber glass mat is positioned within said second sheet
during impregnation of said mat thereby and said first and second
sheets are laminated into a smooth multi-ply product.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood and further
advantages will become apparent when reference is made to the
following detailed description and the accompanying drawings in
which:
Figure 1 illustrates schematically a system for pro-
ducing composite sheets of this invention;
Figure 2 illustrates a stamping press for the sheets of
of this invention;
Figure 3 illustrates a schematic cross section of a
composite sheet of this invention;
Figure 4 illustrates an alternate construction of the
sheet shown in Figure 3;
Figure 5 illustrates an alternate embodiment of the
i nventlon .
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, a first extruder 11 receives
a mixture of thermoplastic resin such as nylon, short glass and
particulate filler and extrudes same through a die to produce a
filled sheet 13 which is embossed by roller 70 of stack 14 so as
to form an embossed surface 72 thereon containing a plurality of
projections 74. A similar thermoplastic sheet 15 is produced from
extruder 16 and embossed in similar fashion by roller 76 of stack
17. A third extruder 19 feeds a thermoplastic sheet 20 into
laminating rolls 21 simultaneously with sheets 13 and 15, and long
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glass mat or mats 23 which are fed from roll or rolls 24. It is
important that the sheet 20 be in a molten condition at the point
where the sheets converge on the rolls 21 and that the sheets 13
and 15 be below the melting point of the polymer so that projec-
tions 74 position the glass mat or mats 23 within the molten sheet
20 during impregnation of the mat(s) 23 by the sheet 20. In this
manner, the long glass reinforcing mat becomes substantially
encased in the sheet 20 and does not affect surface qualities of
sheets 13 and 15 when they are laminated together. The sheet is
subsequently cut with cutter mechanism 26 on conveyor 27 and fed
to stacking table 28.
An important feature of this embodiment of the method
is the processing conditions at the roll stack 21.
The clearance between rolls 21(a) and 21(b) is less than
the combined thickness of the four components 13, 15, 20 and 23.
(Thickness of mat 23 is measured under little or no compression.)
This is necessary to effect an impregnation of mat 23 by sheet 20,
and lamination of the resulting product to sheets 13 and 15.
The temperature of the sheet 20 should be above (at
least 10 C. above) the thermoplastic melting point to provide
adequate residual heat to allow for cooling of sheet 20 between
the e~truder die 30 and the roll stack 21 and allow the glass mat
to be uniformly impregnated thereby. Preferably, the sheet is
50C. to 100C. above the polymer melting point at the point of
convergence between rolls 21(a) and 21(b~. Heating the sheet to a
temperature higher than 350C. in the extruder may cause degrada-
tion of the polymer and results in excessive energy consumption.
Lower temperatures result in inadequate impregnation of the mat 23
by sheet 20, including inadequate flow of the polymer into the
interstices of the glass mat, inadequate bonding of sheets 13 and
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15 to sheet 20r and inadequate binding of the fibers to the poly-
mer resulting in poor physical properties in the final product.
For the same reasons, the pressure applied by rolls
21(a) and 21(b) should range from 100 to 1500 pounds per linear
inch, and preferably from 150 to 400 pounds per linear inch, to
ensure adequate bonding of the layers and impregnation of the
glass mat 23 by sheet 20. Rolls 21(a) and 21(b) must have ade-
quate diameter and wall thickness and bearings of sufficient load
bearing capacity to prevent excessive deflection of rolls 21(a)
and 21~b). Excessive deflection of rolls 21(a) and 21(b)r that is
deflection of the order of about 3 thousandths inch or morer can
result in non-uniform impregnation of glass mat 23 by sheet 20r
non-uniform bonding of sheets 13 and 15 to sheet 20r non-uniform
surface appearancer and non-uniform thickness of sheet 25.
Sheet 13 after leaving embossing stack 14 contacts roll
21(d) and then roll 21(a). Sheet 15, after leaving embossing stack 17
contacts roll 21(c) and then roll 21(b). Rolls 21(c) and 21(d)
are maintained at a temperature close to but below the polymer
melting point, preferably 5 to 40C. below the polymer melting
point. Rolls 21(a) and 21(b) are maintained at a temperature 10
to 70C. below the polymer melting point. The temperatures of
rolls 21(a), 21(b), 21(c) and 21(d) and infrared heaters 30(a),
30(b) are adjusted so that the temperature of sheets 13 and 15 is
high enough to achieve strong bonding of sheets 13 and 15 to sheet
20, but not so high as to result in sticking of sheet 13 to roll
21(d) or 21(c) or of sheet 15 to roll 21(a) or 21(b), softening of
projections 74 or degradation of the surface quality of sheet 25.
Cooling rolls, such as rolls 29(a) and 29(b), can be used
to quickly lower the temperature of laminate 25 sufficiently for
easy cutting on cutter mechanism 26.
An alternate embodiment, illustrated in Figure 5, would
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have the glass mat 123 impregnated by sheet 120 in a separate
operation. Under these circumstances the roll 121(a) is provided
with a plurality of projections 174 for positioning the mat 123
within sheet 120 during impregnation of the mat 123 by the sheet
120. The ends of the projections force the mat 123 into the sheet
120, causing molten portions of the sheet 120 from extruder 119
to flow within passageways formed by adjacent projections to encom-
pass the mat 123. The projections thus position the mat centrally
of the sheet 120 and hold it therewithin, facilitating coating of
the mat 123 by the sheet during impregnation. The impregnated mat
125 thus produced can be used in a stamping operation or laminated
to sheet(s) 13, 15 as described hereinafter in more detail. Fur-
ther, a plurality of embossing rolls 121(a) and 121(b) can be
employed, the roll 121(b) being provided with a plurality of
projections 174l similar to projections 174 of roll 121(a), for
positioning mat 123' in sheet 120.
Mat positioning may also be accomplished by means of a
screen 80, show in Figures 3 and 4, interposed between sheet 13
and mat 23 prior to lamination, the strands of the screen 80 form
ing porjections and the openings thereof forming passageways that
function in substantially the same way as the projections and
passageways of sheets 13, 15 or roll 21(a). The screen 80
facilitates impregnation of mat 23 melt 20 and provides a
further reinforcing means for the composite sheet. Typically, the
screen 80 has a mesh size ranging from about 1 in. to No. 8 U.S.
Sieve Size, and is composed of metal, plastic, fibrous material
such as glass, graphite, cotton, nylon, polyester, cellulose
acetate or the like. As used herein, the term is intended
to include such mat positioning means as a perforated plate,
expanded metal sheet, scrim and the like.
Whether the projections are located on the sheets 13,
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15 or on the roll 21(a), their number and configuration will vary
depending on such processing parameters as mat density, filler
concentration, laminating time and temperature and the like.
Typically, the projections are cone-shaped members having a height
of about .01 to .1 inch and a base perimeter of about .2 to .8
inch, and either randomly or regularly spaced about .06 to 1 inch
apart over substantially the entire area of the mat contacting
surface of the sheet or laminating roll employed. The projections
can, alternatively, be shaped in the form of a pyramid, cylinder,
cube, or the like of regular or irregular configuration arranged
to form a regular pattern or an irregular pattern such as a
doodle or the like.
Following impregnation of glass mat 123 by sheet 120 in
a separate operation, the combined sheet 125 can be laminated to
sheet 13, or to sheets 13 and 15 in a laminating process wherein
the layers are bonded under heat and pressure. Lamination of the
combined sheet 125 to sheet 13 or to sheets 13 and 15 may also be
effected during the heating and stamping operation wherein differ-
ent laminates are assembled depending on the part to be produced.
An example of the latter method is shown in Fig. 2. A sandwich 25
built from layers 13, 15 and combined sheet 125 is heated in oven
34. This heating step serves to condition the sheets for stamping
in press 36 and also to effect a slight bond between the layer
interfaces. The subsequent pressure in press 36 has the effect of
simultaneously laminating the mat containing sheet 125 to sheets
13, 15 and forming the resulting composite into a part.
A composite sheet typically produced is illustrated in
Fig. 3. It comprises: (a) one or more surface layers containing
40% to 100% polymer, 0% to 45% of well-dispersed, randomly ori-
ented, short glass fibers and 0% to 50% particulate filler, (b) areinforcing layer consisting essentially of long glass reinforcing
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- weighing .1 to 16 ounces per square foot, together with the
mat positioning means herein shown in the form of a screen 80,
encased in a thermoplastic polymer matrix containing, on an
extruded basis, from 50 to 100 percent thermoplastic resin and
from 0 to 50 percent particulate filler, such that there is
essentially no migration of the long glass fibers to the surface
layer 13 and no migration of the short glass fibers, if present,
to the reinforcing layer.
The stampable composite sheet may have one or two defect-
free surfaces. The short, well-dispersed fibers 38, if present,
are randomly but predominantly two-dimensionally oriented in the
plane of the sheets 13 and 15. That is, more than 50~ of the
fibers are aligned substantially parallel to the plane of the
sheet. Such orientation of the short fiber is easily achieved in
extrusion, rolling, drawing or similar orientation-inducing
processes, and is preferable for purposes of this invention in
achieving smooth surfaced sheets.
The thickness of the surface sheet should be at least
10 mils greater than the height of the projections 74, if present
thereon, to prevent tearing during lamination. Typically, the
surface sheet 13 has a thickness of at least 20 mils. A thinner
surface sheet may also permit the pattern of the reinforcing mat
23 to be visible on the surface of the composite sheet 25. The
minimum thickness of sheet 20 is determined by the need to impreg-
nate glass fiber mat 23 and is typically about 30-80 mils. If
thickness of sheet 20 is less than about 30 mils, then glass fiber
mat 23 is likely to be non-uniformly impregnated into sheet 20 and
composite sheet 25 is likely to have non-uniform properties. I
The thermoplastic polymers which can be used in forming
the sheet compositions which may be stamped into shaped objects in
ascordance with the methods of the present invention include the
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various thermoplastic materials normally used in injection molding,
extrusion, vacuum forming, blow molding, fiber spinning, or simi-
lar thermoplastic processing techniques.
Suitable thermoplastic resinous materials which may be
utilized in making the composite laminate of the invention include,
for example, the alkenyl aromatic resins typified by polystyrene,
styrene copolymers, blends and graft copolymers of styrene and
rubber and the like. The invention may be practiced utilizing
polyvinyl chloride or copolymers of vinyl chloride or vinylidene
chloride.
Particularly desirable thermoplastics in such composi-
tions are the polyamides, that is, polymers having regularly
recurring amide groups as an integral part of the main chain.
Polyamides such as nylon 6,6 (a condensation product of hexa-
methylene diamine and adipic acid) and nylon 6 (the polymerization
product of e-aminOcaprOiC acid or e-caprolactam) are examples of
two polyamides or nylons.
Polyolefins may also be employed, including polymers and
copolymers of ethylene, propylene, methylpentene and blends thereof.
Additional polymers which can be utilized include poly-
urethane, polysulfone, polycarbonate and linear polyesters such as
polyethylene terephthalate and polybutylene terephthalate; cellu-
lose esters such as cellulose acetate, and cellulose propionate;
halogenated polylefins and polyacetals.
Also included in the term "polymer" are blends or copoly-
mers of two or more polymeric materials. Illustrative of such
polymers are polyethylene/polypropylene, ethylene-acrylic acid-
vinylacetate terpolymers and the like.
The glass fiber used in making the fiber mat is prefer-
ably used in the form of strands or bundles which are at least
about 1 inch to continuous in length. The reinforcing mat may be
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woven or nonwoven. The strands or fiber comprising the reinforc-
ing mat, if nonwoven, are held together either by resinous adhe-
sive binders (thermosetting or thermoplastic resins) or by "need-
ling" or, if woven, by the mechanical interaction of the randomly
patterned weblike structure.
The individual glass strands in the mat are comprised of
about 2 to 400, preferably 5 to 120, filaments per strand. Each
filament is about 0.00030 to about .001 inch, preferably 0.00035
to 0.00085 inch in diameter. The glass mat comprising the rein-
forcing phase may have a weight of from 0.3 to 16 ounces persquare foot.
The short glass fiber reinforcement is at least about
0.01 inch in average length in the final product. These short
lengths of fibrous reinforcement are obtained because of the
characteristics of the processing apparatus used to compound
or blend this reinforcement with the thermoplastic resin. For
example, if fibers 1/8 inch or longer are placed in the feed hopper
of a single screw extruder along with the resin, the fibers will
ordinarily be broken down into lengths shorter than the original
1/8 inch starting length because of abrasion, shear, turbulence,
and mechanical work performed upon the fibers. Longer lengths
(e.g., mean lengths longer than 0.010 inch in a major portion of
the short fiber reinforcement) may be retained by minimizing the
amount of shear or mechanical breakdown of fiber length, with
some sacrifice in homogeneity or prolonged processing times
although lengths greater than 3/4 inch are not desirable for the
object of this invention since they must flow into ribs, etcO
during stamping. Another processing machine which may be used to
blend and/or manufacture the short fiber-filled resinous sheet is
a twin screw extruder. In this case, the filamentary reinforcing
material may be added to agitated heat plastified polymer between
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:he screws of the extruder through a feed port such as a volatile
(vent) port. In the latter case, the filamentary reinforcing
material may be fed to the twin screw extruder in the form of yarn
or roving, and the short fiber lengths would be obtained by the
mechanical breakup performed by the mixing action of the screws.
Glass fibers as normally used for reinforcement of
thermoplastics may be treated or coated with a sizing composition.
Standard sizing agents usually consist of several components, each
of which possesses a distinct function. For example, a binder or
film former gives the glass fiber strand integrity for workability
and prevents fuzzing and aids in distribution of the sizing agent;
a lubricant prevents destruction of the strand by abrasion of the
individual filaments against each other and against fiber handling
equipment; a coupling agent assists in obtaining greater adhesion
between the glass fibers and the polymeric resin yielding improved
strength characteristics; an emulsifying or dispersing agent
allows sufficient dissolution of the various ingredients in the
required carrying agent (frequently water) and improves compati-
bility between the various ingredients. In addition, pH adjusters,
antistatic agents, wetting agents and surfactants are also often
added to sizing formulations. Ordinarily, organosilicon compounds
may suitably be employed as coupling agents. For example, halo-
genated or nonhalogenated vinyl and alkyl containing, alkylalkoxy,
alkenyl, aminoalkyl, aminoalkoxy, acyloxy, alkenyl acyloxy and
similar silanes, their hydrolysis products and polymers of the
hydrolysis products are suitable for such use. Formulations of
this kind and methods of use are known to those skilled in the art.
Another constituent of the improved thermoplastic sheet
material herein described is particulate filler. Such fillers may
be selected from a wide variety of minerals, metals, metal oxides,
siliceous materials, metal salts, and mixtures thereof. These
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fillers may optionally be treated with various coupling agents or
adhesion promoters, as is known to those skilled in the art. Ad-
vantageous physical properties are achieved if the filler material
has a Young's modulus of 107 psi or greater and at least a Young's
modulus twice as great as that of the polymer. Examples of
fillers included in these categories are alumina, aluminum
hydrates, feldspar, asbestos, talc, calcium carbonates, clay,
carbon black, ~uartz, novaculite and other forms of silica, kaoli-
nite, bentonite, garnet, mica, saponite, beidellite, calcium
oxide, calcium hydroxide, etc. The foregoing recited fillers are
illustrative only and are not meant to limit the scope of fillers
that can be utilized in this invention.
The particulate filler may be added to the thermo-
plastic resin before, during, or after the addition of the short
glass fibers to the resin. Thus, for example, filler and resin
pellets may be fed to the feed hopper of a single screw extruder;
the mixture is blended and conveyed towards the die. Short glass
fibers can be added to the molten mixture at a vent hole or other
such opening downstream of the feed hopper, and the mixture then
extruded into pellets, or preferably, directly into sheet of the
appropriate thickness for lamination with the glass mat reinforce-
ment. In the extrusion process, the short fibers will emerge
oriented randomly in the plane of the extruded sheet.
Other minor additives which may be of value in sheet
formulations include antistatic agents, plasticizers, lubricants,
nucleating agents, impact modifiers, colorants, heat and light
stabilizers, or other similar processing aids and adjuvants.
Each of the foregoing constituents performs a specific
function within the composite material. The thermoplastic resin
is, of course, the matrix which binds the other constituents
together. As the matrix, the resin influences the mechanical and
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physical properties of the composite sheet. If a stamped producthaving an extremely high thermal resistance is required, for
example, a nylon or linear polyester would be utilized as the
matrix rather than polyethylene or polypropylene. If an extremely
high impact resistance was required, for example, an impact resis-
tant styrene copolymer or polycarbonate may be used rather than
polystyrene or a more brittle linear polyester.
With sheets formed of nylon 6 resin, it is preferred to
utilize talc as a nucleating agent for the nylon. For this pur-
pose about .5 to 1.5% or more talc by weight of the nylon is
incorporated into the sheet. Preferably, the sheet contains about
1% talc based on the weight of the nylon. Other nucleating agents
may alternatively be employed in similar amounts with nylon or
other crystalline polymers.
While composites without filler may be formed, the most
desirable sheets include filler.
The functions of the particulate filler are: (1) to
increase the modulus and stiffness of the composite sheet and (2)
to provide a more economical composition.
The functions of the short fiber reinforcement are: (1)
to increase the sheet stiffness and mechanical strength, (2) to
increase the resin-phase melt viscosity, (3) to provide reinforce-
ment in addition to that provided by the long glass fiber mat, (4)
to allow flow of a reinforced plastic mixture into small holes,
bosses, ribs, apertures, etc., during stamping and (5) to yield an
improved surface in which most short dispersed fibers are oriented
and lie in the plane of the sheet. In addition to the ability to
form relatively narrow reinforced ribs, bosses, or similar sec-
tions, because of flow of short fibers into such sections, the
high melt viscosity of the resin-filler-short fiber mixture aids
in promoting uniformity of properties. Furthermore, because of
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the generally enhanced moldability of the present compositions,longer, thinner and more complex configurations or parts can be
molded than heretofore known.
The short fibers oriented parallel to the plane of the
sheet (in distinction to perpendicular to the plane of the sheet)
result in a smooth surface free of glass mat and projecting fiber
ends.
The present invention is more particularly described in
the following examples which are intended as illustrative only since
numerous modifications and variations therein will be apparent to
those skilled in the art.
Shaping of the sheet can be accomplished in a deep
drawing press which has a polished steel die-set to produce 5-inch
diameter cylindrical cups. The temperature of the polished steel
die-set can be adjusted by means of electric heaters, and main-
tained at approximately 140 C. The steel molds used are highly
polished and chrome-plated (mirror finished).
The preheated sheet can be transferred to the stamping
press, and stamped at a pressure of 800 psi maintained for 10
seconds. The stamped part can be cooled to room temperature, main-
tained at room temperature for 24 hours, and the flat bottom of the
cup then cut out for surface roughness testing.
The following examples are presented to provide a more
complete understanding of the invention. The specific techniques,
conditions, materials, proportions and reported data set forth to
illustrate the principles and practice of the invention are exem-
plary and should not be construed as limiting the scope of the
invention.
EXAMPLE
Nylon 6 resin is blended with 25% short glass fibers
and 15~ kaolin in extruder 11 and extruded into sheet 13. A
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sheet 15 of similar composition is extruded by extruder 16. Sheet.s
13, 15 are embossed by rolls 70, 76 to provide each of the sheets
with a mat contacting surface having a plurality of projections 74.
Both sheets 13, 15 are brought together with glass mats 23 and
molten sheet 20 at the nip of laminating rolls 21(a), 21(b). The
mats 23 are positioned within sheet 20 by projections 74 to form
a middle reinforcing sheet comprising 75~ nylon and 25~ glass mat.
The resulting sandwich is laminated and finished in the nip of
rolls 21(a), 21(b) and on rolls 29(a), 29(b). The resulting sheet
is cut into discrete blanks and stored.
Having thus described the invention in rather full detail,
it will be apparent that these details need not be fully adhered to
but that various changes and modifications may suggest themselves
to one skilled in the art, all falling within the scope of the
invention as defined by the subjoined claims.
