Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THF INVENTION
Polybutylene terephthalate (PBT) reinforced with thermally stable
reinforcing fibers such as glass fibers is well known as a molding resin and
is described in numerous patents and publications including for instance
United States 2,814,725, United States 4,124,561, United States 3,814,786
and United States 3,625,024. Fiber reinforcement generally improves the
tensile strength, flexural strength, flexural modulus and heat distortion
temperature of the molding composition. However, moldings, cspecially injec-
tion moldings of large fiber glass reinforced articles of PBT, nylon and
other semicrystalline thermoplastics tend to display distortion or warping
while glass fiber reinforced armorphous thermoplastic compo~mds do not pre-
sent such problems. It is believed that strains resulting from the different
degrees of volumetric contraction parallel to and transverse to the direction
of plastic melt flow into the mold during the cooling of molded articles are
responsible for such warping. Orientation of the glass fibers parallel to
the direction of melt flow during molding produces this directional difference
in volumetric contraction. The warping is thus believed due to the presence
of the very reinforcing fibers which contribute to the enhanced physical
characteristics of the finished product. It is known that addition of mica
to fiberglass reinforced PBT reduces warping. Unfortunately, the mica also
greatly reduces impact strength.
Various impact modifiers are also known which improve the impact
strength of molded PBT compositions. Some of these are described for
instance in United States patents 4,096,202 and 4,034,013. It is generally
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believed and unEortunately true, that some modifiers which improve
impact characteristics of PB~ or other poly (C2-C4 alkylene tere
phthalate) molding compositions, including fiber reinforced compo-
sitions, also tend to increase the warping characteristics of the
compositions.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide
an improved poly (C2-C4 alkylene terephthalate) molding composition
and method for producing same as well as molded articles of such
composition. As compared with known prior art compositions, the
molded compositions of the invention have an especially desirable
combination of properties including less than anticipated warpage
and improved impact strength.
Improved polyester molding compositions of the invention
consist essentially of at least about 40 wt% poly (C2-C4 alkylene
terephthalate) with at least about 50 wt% of such poly (C2-C4
alkylene terephthalate) being polybutylene terephthalate having an
intrinsic viscosity between about 0.5 and about 2.0 dl/g, such
composition containing:
(a) between about 1 and about 40 wt% based on total molding
composition of phlogophite mica flakes having an average particle
size between about 40 and 325 mesh with at least 90% of all mica
flakes present in the composition having particle sizes between
about 40 and about 200 mesh; and
(b) between about 5 and about 30 wt% based on total mslding
composition of a multiphase composite polymer comprising:
(1) about 25 to about 95 wt% of a first elastomeric phase poly-
merized from a monomer system comprising about 75 to 99.8% by
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weight Cl to C6 alkyl acrylate, 0.1 to 5% by weight crosslinking
monomer, and 0.1 to 5% by weight graftlinking monomer, said cross-
linking monomer being a polyethylenically unsaturated monomer hav-
ing a plurality of addition polymerizable reactive groups all of
which polymerize at substantially the same rate of reaction, and
said graftlinking monomer beiny a polyethylenically unsaturated
monomer having a plurality o~ addition polymerizable reactive
groups, at least one of which polymerizes at a substantially diff-
erent rate of polymerization from at least one other of said reac-
tive groups; andt2) about 75 to 5 wt% of a final, rigid thermoplastic phase
polymerized in the presence of said elastomeric phase.
Preferred compositions of the invention include use of
glass or other thermally stable reinforcing fibers and the use of
the preerred multiphase polymers described below. Preferred
thermally stable reinforcing fibers are glass fibers. Where used,
thermally stable reinforcing fibers are preferably present in
amounts between about 3 and about 50 wt% based on total molding
composition and preferably have diameters between about 5 and about
20 microns and aspect ratios of at least about 5.
DETAILED DESCRIPTION_OF T~IE IN~ENTION
As mentioned above; the invention includes a novel mold-
ing composition, molded articles of such composition and method for
producing such composition. The molding composition broadly com-
prises poly (C2-C~ alkylene terephthalate) containing, mica, multi-
phase composite polymer and preferably thermally stable reinforcing
fibers, as described herein.
Polybutylene terephthalate (PBT) used in the invention may
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be produced in any suitable manner such as by reacting terephthalic
acid or a dialkyl ester of terephthalic acid, e.g., dimethyl, tere-
phthalate, with diols having four carbon atoms, e.g., tetramethylene
glycol. PBT for use in the invention has an intrinsic viscosity
(I.V.) between about 0.5 and about 2.0 dl/g measured in ortho-
chlorophenol at 25C., with material having an I.V. between about
0.5 and about 1.1 dl/g being preferred. Manufacture of PBT is
well known to those skilled in the art as are the techniques for
obtaining PBT of desired instrinsic viscosi-ty. Such conventional
production techniques
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for PBT are discussed in greatar detail, for instance, in United States
Patent 3,465,319.
In addition to PBT, compositions of the in~ention may also in-
clude polyethylene terephthalate (PET) or polypropylene terephthalate
although PBT must, as indicated above, account for at least 50 wt% of the
poly (C2-C~ alkylene terephthalate) used. PET and polypropylene terephtha-
late may, like PBT, be produced by any suitable conventional methods. PET
where used is preferably present in amounts between about 1 and about 35
wt% based on total composition:
Where PET is used in compositions of the invention a nucleating
agent such as talc etc, is also preferably employed in amounts between about
.01 and about 10 wt% based on total composition. The PET function is to
reduce warpage probleMs and reduce cost. PET having an intrinsic viscosity
between about 0.4 and about 1.2 dl/g as measured in orthochlorophenol at
25C is preferred.
Thermally stable reinforcing fibers used in the invention may be
any such fibers which are thermally stable at the conditions normally used
in the production of products from PBT molding compositions and include, for
instance, fibers of materials such as glass, aramid, calcium sulfate,
aluminum metal, boron, asbestos, carbon, fibrous potassium titanate, iron
whiskers, etc. Such fibers should normally have diameters between about
5 and about 20 microns and aspect ratios (ratio of length of fiber to
diameter of fiber) of at least about 5. Glass fibers are preferred for
use in the invention. Glass fibers, where used, preferably have diameters
between about 10 and about 15 microns and aspect ratios of at least about
20.
Reinforcing fibers used in the invention are normally used in
amounts between about 3 and about 50 wt% based on total weight of molding
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composltion, more preferably in amounts between about 3 and about 20 wt% on
the same basis. As is commonly recognized, the use of such fibers improves
substantially such physical properties as tensile strength, flexural
strength, flexural modulus and heat distortion temperature of the molding
composition. Glass or other fibers for use in the invention may be manu-
factured and incorporated into the molding composition in any suitable
manner, such as by separate extrusion blending with the PBT, extrusion blend-
ing with other ingredients of the compositions of the invention or incorporat-
ing into the PBT or PBT containing composition during injection molding of
products from the molding composition of the invention.
Molding composition of the invention contains between about 1 and
about 40 wt% phlogophite mica flake having an average particle size between
about 40 and about 325 mesh (i.e. passing through a 40 mesh screen but
retained on a 325 mesh screen~ with amounts between about 10 and about 30 wt%
being preferred. Such mica is readily obtainable from a number of suppliers
and is sold for instance by ~arietta Resources International under the trade
name Suzorite ~R in various size grades. One commonly used grade of such
mica, is for instance identified as ~IAR 60-S and has at least about 90%
particles in the size range between about 40 and about 200 mesh.
As mentioned, the invention also required the presence of between
about 5 and about 30 wt% based on total molding composition of a multiphase
composite polymer comprising:
(1) about 25 to about 95 wt% of a first elastomeric phase polymeriz-
ed from a monomer system comprising about 75 to 99.8% by weight Cl to C6
alkyl acrylate, 0.1 to 5% by weight crosslinking monomer, and 0.1 to 5% by
weight graftlinking monomer, said crosslinking monomer being a polyethylenical-
ly unsaturated monomer having a plurality of addition polymerizable reactive
groups all of which polymerize at substantially the same rate of reaction,
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and said graftlinking monomer being a polyethylenically unsaturated monomer
having a plurality oE addition polymerizable reaction groups, at least one
of which polymerizes at a substantially different rate o:E polymerization
from at least one other of said reactive groups; and
(2) about 75 to 5 wt% of a final, rigid thermoplastic phase
polymerized in the presence of said elastomeric phase.
The multiphase composite polymer used in compositions of the
invention comprises from about 25 to about 95 wt% of a first elastomeric
phase and about 75 to 5 wt% of a final rigid thermoplastic phase. One or
more intermediate phases are optional, for example, a middle stage poly-
merized from about 75 to 100 percent by weight styrene. The first stage is
polymerized from about 75 to 99.8 wt% Cl to C6 acrylate resulting in an
acrylic rubber core having a glass transition temperature below about 10C
and crosslinked with 0.1 to 5 percent crosslinking monomer and further
containing 0.1 to 5 percent by weight graftlinking monomer. The preferred
alkyl acrylate is butyl acrylate. The crosslinking monomer is a poly-
ethylenically unsaturated monomer having a plurality of addition polymerizable
reactive groups all of which polymerize at substantially the same rate of
reaction. Suitable crosslinking monomers include poly acrylic and poly
methacrylic esters of polyols such as butylene diacrylate and dimethacrylate,
trimethylol propane trimethacrylate, and the like; di- and trivinyl benzene,
vinyl acrylate and methacrylate, and the like. The preferred crosslinking
monomer is butylene diacrylate. The graftlinking monomer is a poly-
ethylenically unsaturated monomer having a plurality of addition poly-
merizable reactive groups, at least one of which polymerizing at a sub-
stantially diferent rate of polymerization from at least one other of said
reactive groups. The function of the graftlinking monomer is to provide a
residual level of unsaturation in the elastomeric phase, particularly in
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the latter stages oE polymerization and, consequently, at or near the surface
of the elastomer particles.
When the rigid thermoplastic phase is subsequently polymerized at
the surface of the elastomer, the residual ~msaturated addition poly~
merizable reactive group contributed by the graftlinking monomer participates
in the subsequent reaction so that at least a portion of the rigid phase
is chemically attached to surface of the elastomer. Among the effective
graftlinking monomers are allyl group-containing monomers of allyl esters
of ethylenically unsaturated acids such as allyl acrylate, allyl methacrylate,
diallyl maleate, diallyl fumarate, diallyl itaconate, allyl acid maleate,
allyl acid fumarate, and allyl acid itaconate. Somewhat less preferred are
the diallyl esters of polycarboxylic acids which do not generally have
a favorable polymerization rate. The preferred graftlinking monomers are
allyl methacrylate and diallyl maleate. A most preferred interpolymer has
only two stages, the first stage comprising about 60 to 95 percent by weight
of the interpolymer and being polymerized from a monomer system comprising
95 to 99.8 percent by weight butyl acrylate, 0.1 to 2.5 percent by weight
; butylene diacrylate as crosslinking agent, 0.1 to 2.5 percent by weight
allyl methacrylate or diallyl maleate as a graftlinking agent, with a
final stage polymerized from about 60 to 100 percent by weight methyl
methacrylate.
The final stage monomer system can be comprised of Cl to C16
methacrylate, styrene, acrylonitrile, alkyl acrylates, allyl acrylates,
allyl methacrylate, diallyl methacrylate, and the like, as long as the over-
all glass transition temperature is at least about 20C. Preferably the
final stage monomer system is at least about 50 wt% Cl to C4 alkyl meth-
acrylate. In a preferred embodiment the final stage monomer system may
also contain epoxy functionality. By "epoxy functionality" is meant epoxy
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lmits which are pendant from the final stage polymer. The preferred way
of incorporating epoxy functionali~y into the final stage polymer is by
use of epoxy containing monomer such as glycidyl acrylate of glycidyl
methacrylate in the final stage monomer mixture. Alternate epoxy cont~ining
monomers are butadiene monoepoxide, allyl glycidyl ether, 4, S-epoxy
pentyl methacrylate or acrylate, 10, ll-epoxy undecyl methacrylate, or
other opoxy-containing ethylenically unsaturated monomers. Other ways of
introducing epoxy unctionality into the final stage of the mul~iple stage
pulymer are possible, such as post epoxidation. It is further preferred
that the final stage polymer be free of units which tend to degrade poly
~alkylene terephthalates), for example, acid, hydroxyl, amino, and amide
groups.
For futher descriptions and e~amples of various multiphase
polymers suitable for use in the present invention, reference may be had
to the aforementioned llnited States Patent 4,096~202 the disclosure of
hich is incorporated herein by reference. Additional examples of multi-
phase polymers suitable for use in the invention may be found in United
States Patent 4,034,013.
The multiphase polymer serves as an impact modifier to improve
impact characteristics of molded articles made from molding composition of
the invention. The mica flakes serve a completely unexpected function in
eliminating or very substantially reducing the warpage of molded parts
~hich would normally be expected because of the presence of the multiphase
polymer of the combination of multiphase polymer and thermally stable
reinforcing fibers in molding composition and products of the invention.
In addition to the ingredients mentioned above, compositions ~Id
products of the invention may contain suitable flame retardant additives in
amounts up to about 25 wt% based on total molding composition and may
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contain relatively minor amounts of other materials which do not unduly
affect the desired characteristics o the finished product. Such additional
materials, may, depending upon the particular compositionsemployed and
products desired, include for instance, colorants and lubricants. Where
present, such additional materials normally comprise no more than about 20
wt~ of the total composition or finished product.
In preparing molded compositions of the invention, the rein-
forcing fibers may be intimately blended into the PBT by any suitable means
such as by dr~ blending followed by melt blending, blending in extruders,
heated rolls or other types of mixers, etc. Conventional master batching
techniques may also be used. The same considerations apply to addition
of the other essential or optional ingredients of the composition of the
invention. Suitable blending and molding techniques are well known in the
art and need not be described in detail herein. In a preferred embodiment
of the invention, the composition of the invention is compounded by dry
blending followed b~ melt mixing in an extruder with barrel temperatures
between about 240 and about 270C. Likewise, in molding products o the
invention from molding compositions o the invention,linjection molding is
preferred. When injection molding is used~ barrel temperatures between
20 about 250C and 265C are preferred. In a preferred embodiment, the
molding composition of the invention is formed by extrusion and pelletized.
Products of the invention are then produced by injection molding the pel-
letized extrudate.
As mentioned above, one of the major advantages of th~ compositions
and products of the invention is that the use of mica in molding compositions
of the invention substantially reduces shrinkage and warpage otherwise
associated with the use of the multiphase polymer or combination of multi-
phase polymer and reinforcing fibers without substantial harm to the
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desirable improvements in physical propert:ies associated with the use of
such fibers.
While warpage is frequently determined by visual inspection, a
quantitative definition can be expressed in terms of percent warp equals
~dm TtXloo where "dm" equals maximum distance from a flat surface to a
point on a warped side of the article being evaluated, and "t" equals the
thickness of the warped side of the article. This equation defines warp
in terms of wall thickness without regard to length of the part. Since
some absolute deviation from a straight line gives the same percent warp,
a correction for part length must also be included to more accurately
define warpage of a part in terms of the visual effect of the warp. Part
warp (PW) may therefore be defined as PW = ~ = (dmtT~XlLoo wherein
PW equals part warp, "L" equals total length of the warp member and the
other values are as stated immediately above. In evaluating warpage of
samples and products, and average warpage value for a five sided plain box
is frequently calculated based upon measurements of warpage of the right,
left, front and back sides of the box.
The follo~ing examples are intended to illustrate the application
and usefulness of the invention without limiting the scope ~hereof, In
the example, all quantities are given in terms of wt% based on total com-
position unless otherwise specified. Physical properties, including
~arpage, were measured by the following criteria and reported as an average
for samples of each composition tested:
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Property Test Procedures
Tensile Yield Strength ASTM D-638
Flexural Yield Strength ASTM D 790
Flexural Modulus ASTM D-790
Notched Izod Impact Strength
Cantilever Beam Reversed
Notch Izod Impact Strength AS'~ D 256
Percent warp As de~ined above
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PBT (0.8 I.V.) was compounded on a Midland Ross 1.5 inch extruder
with various amoun~s of phlogophite mica and other ingredients as specified
below to form various molding compositions as specified in Table I below.
The mica used was Marietta Resources International Suzorite HAR 60-S mica
flake having the following size distri'bution.
trace - 20 + 40 mesh ~U.S. sieve)
76% - 40 + 100 mesh
19% -100 ~ 200 mesh
3% -200 + 325 mesh
2% -325 mesh
Marietta Resources International Suzorite ~IAR 200-S mica flake was
also used. This material had the following size distribution:
trace - 20 + 40 mesh (U.S. sieve)
1% - 40 + 100 mesh
55% -100 + 200 mesh
20% -200 + 325 mesh
24% -325 mesh
The following conditions were employed:
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Extruder Zone Températures Back Pressure 0-200
1 270C Amperage 12-25
2 265C Screw rpm 90
3 260C.
4 255C. Melt temperature 243-251C.
250C.
Each of the experimental molding compositions specified in Table
I and produced as described above was then molded on a 50 tOII 3 ounce recipro-
cating screw injection molding machine to provide ASTM test specimens. Parts
suitable for measuring warpage ~camera slide storage box wi~h four large flat
sides) were molded on a 250 ton 36 ounce Impco screw ram machine. Molding
conditions were:
3 oz., 50 ton molding machine
Barrel temperature --- front 480F.
rear 480F.
nozzle 480F.
Injection pressure 1100 psi
Screw rpm 75
Injection time 10 sec.
Mold time 20 sec.
Total cycle time 30 sec.
Mold temperature 100F
36 oz., 350 ton molding machine
20 Barrel temperature --- front 480P
center 480F.
rear 480F.
nozzle 490F.
Measured melt temperature 420F.
Screw rpm 80
Total cycle time 94 sec.
Mold temperature 175F.
Mold time 40 sec.
Injection pressure 1100 psi
Physical properties were as shown in Table II below.
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TABLE I
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EXPERIMENTAL MOLDING COMPOUNDS
Wt %
Ingredient _ 2 3_
PBT (0.8 I.V) 25 25 30
PET ~0.8 I.V) 20 20 20
60-S Mica Flake 20
200-S Mica Flake 20 15
Glass Fibers ~OCF 419 AA
3/16 inch) 20 20 20
KM 330 Acrylic Impact
Modifier 14.3 14.3 14.3
Acrawax C Lubricant 0.2 0.2 0.2
Epon 815 Uiepoxy Modifier 0.5 0.5 0.5
TABLE II
PHYSICAL PROPERTIES OF EXPERIMENTAL MOLDING COMPOSITIONS
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Wt %
_ 2 3
% Warp Annealed 100 120
% ~arp Unannealed 81 97
Notched IZod Impact Strength
~Foot Pounds per Inch) 1.8 1.7 1.4
: 20
Cantilever Beam Reversed Notch
Izod Impact Strength
(Foot Pounds per Inch) 7.8 8.2 7.5
: Flexural Strength (psi)1&~000 19,100 16,300
Flexural Modulus (psi) x 106 1.23 1.27 .90
Tensile Strength (psi)11,430 12,308 10,000
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EXAMPLE 2
In order to evaluate the effect of various additives and combina-
tions of additives or warpage characteristics of injection molded PBT arti-
cles, a number of molding compositions were prepared from which parts were
molded and tested for warpage, all as described in Example 1. The composi-
tions tested and warpage data obtained are shown in table III. To simplify
comparisons, table III also shows warpage as a percent of the warpage obtained
using PBT molding compound with no additives.
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~ rom table III it can be seen that the presence of mica flakes,
especially the 60-S grade, resulted in much less warpage of molded parts than
would have been expected based on warpage of parts containing multiphase poly-
mer or a combination of multiphase polymer and glass fibers.
As mentioned above, flame retardant additives may be used in compo-
sitions and products of the invention. Pre:Eerred flame retardant additives
for this purpose include decabromodiphenyl ether, brominated phenylene oxide,
brominated polycarbonate, brominated polystyrene, tctrabromo phthalic anhy-
dride and antimony trioxide.
Between about 5 and about 40 wt% based on total molding composition
of Poly(C2-C4 alkylene terephthalate-co-alkylene-oxide) is also preferably
used in compositions of the invention. Preferred Poly(C2-C4 alkylene tere-
phthalate-co-alkylene-oxide) for use in the invention is poly(butylene tere-
phthalate-co-tetramethylene oxide). Suitable Poly(C2-C4 alkylene terephtha-
late-co-alkylene-oxide) elastomers and their pre~aration are well known as
described for instance in United States patent 3,766,146. Poly(butylene tere-
phthalate-co-tetramethylene-oxide) having a Shore D hardness between about 50
and about 60 and a melt index between about 7 and about 9 is particularly
preferred.
While the invention has been described above with respect to certain
preferred embodiments thereof, it will be apparent to those skilled in the art
that various changes and modifications can be made without departing from the
spirit or scope of the invention.
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