Note: Descriptions are shown in the official language in which they were submitted.
1~3~9~`~S
BACKGROUND OF THE 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
3,814,725, United States 3,814,786 and United States 3,624,024.
Fiber reinforcement generally improves ~he tensile strength,
flexural strength, flexural modulus and heat distortion
temperature of the molding composition. However, moldings,
especially injection moldings of large fiber glass reinforced
articles of PBT, nylon and other semicrystalline thermo-
plastics tend to display distortion or warping whi]e glass
fiber reinforced amorphous thermoplastic compounds do
not present 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.
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, .,
e~
Various impact modifiers are also known which improve ~he 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
believed and unfortunately true, that some modifiers which improve impact
characteristics of PBT molding compositions, especially fiber reinforced
compositions, also tend to increase the warping characteTistics of the compo-
sitions.
Therefore, this invention seeks to provide an improved fiber glass
reinforced PBT 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 reduced warpage and improvecl
impact strength.
Improved polyester tnolding compositions of the invention consist
essentially of at least about 40 wt% PBT having an intrinsic viscosity
between about 0.5 and about 2.0 deciliters per gram ~dl/g). Such molding
compositions also include:
(a) between about 3 and about 50 wt% based on total molding
composition of thermally stable reinforcing fibers having diameters between
about 5 and about 20 microns and aspect ratios of at least about 5;
~, ~
(b) between about 1 and about 40 wt% based on total
molding composition of phlogophite mica flake having an
average particle size between about 40 and about 325 mesh ~nd
with at least about 90% of such mica having particle si es
between about 40 and about 200 mesh; and
(c) between abou~ 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 polymerized 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 ko 5% by weight
graftlinking monomer, said crosslinking monomer heing a
polyethylenically unsaturated monomer having a plurality of
addition polymerizable reactive groups all of which polymerize
at substantially the same rate of reaction, and said
graftli~king monomer being a polyethylenically unsaturated
monomer having a plurality of addition polymerizable reactive
groups, at least one of which polymerizes at a substantially
2d different rate of polymerization from at least one other of
said reactive groups; and
(2) about 75 to S wt~ of a final, rigid
thermoplastic phase polymerized in the presence of said
elastomeric phase.
Preferred compositions of the invention i~clude use
of glass fibers as the thermally stable reinforcing fibers and
the use of the preferred multiphase polymers described below.
1~3~
As mentioned above, the invention includes a novel
molding composition, molded articles o such composition and
method for producing such composition. The molding
composition broadly comprises at least a~out 40 wt% of PBT
having an intrinsic viscosity between about 0.5 and about 2.g
dl/g and containing thermally stable reinforcing fibers, mica
and multiphase composite polymer as described herein.
Polybutylene terephthalate (PBT) used in the
invention may be produced in any suitable manner such as by
reacting terephthalic acid or a dialkyl ester of terephthalic
acid, e.g., dimethyl terephthalate, with diols having our
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 orthochlorophenol 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 ar~ as are the techniques for obtaining
PBT of desired intrinsic viscosity. Such conventional
production techniques for P~T are disc~ssed in greater detail,
for instance, in U.S. Patent 3,465,319.
Thermally stable reinforcin~ 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,
~ 3~
aluminum metal, boron, asbestos, carbon, ibrous potassium
titanate, iron whiskers, etc9 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 pref~rred 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 PBT molding composition, more
preferably in amounts between about 3 and about 20 wt% on the
same basis. As is commonly recognized, the use of such ibers
improves substantially such ph~sicaL properties as tensile
strength, Elexural strength, flexural modulus and heat
distortion temperature of the PBT. GIass or other fibers for
use in the invention may be manufactured and incorporated into
the P~T in any suitable manner, such as by separate extrusion
blending with the PBT, extrusion blending with other
ingredients of the compositions of the invention or
incorporating into the PBT or PBT containing composition
during injection molding of products from the PBT.
As mentioned above, products molded from fiber
reinforced PBT, while having substantially improved physical
properties in certain respects, suffer from excessive warpage
believed to be due to the preferential orientation of the
fibers parallel to the direction of melt flow within the mold.
It is thus nPcessary in accordance with the present invention
to incorporate in the compositions and the produc~s of the
~ 3~
invention additional filler material for the purpose of
reducing the adverse effec~ of the reinforcing fibers on
warpage. More specifically, ~he present invention re~uires
the use o between about 1 and about: 40 wt% based on total
molding compositlon of phlogophite mica having an average
particle size be~ween about 40 and about 325 mesh with at
least about 90% of such mica having particle sizes between
about 40 and about 200 mesh (i.e. passing through a 40 mesh
screen but retained on a 200 mesh screen). ~o alleviate the
la adverse effect of mica on impact strength, the invention also
requires 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 polymerized 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 polyethylenically
unsaturated monomer having a plurality of addition
2Q polymerizable reactive groups all of which polymerize at
substantially the same rate of reaction, and said graftlinking
monomer being a polyethylenically unsaturated monomer having a
plurality of addition polymerizable reaction groups, at least
one of which polymerizes at a substantially different rate of
polymerization from at leas~ one other of said reactive
groups; and
(2~ about 75 ts 5 wt~ of a ~inal, rigid
thermoplastic phase polymerized in the presence of said
elastomeric phase.
9~5
The multiphase composite poly~er 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
s phases are optional, for example, a rniddle s~age polymerized
from about 75 to 100 percent by weight s~yreneO 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 bel~w 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 polyethylenically unsaturated monomer having a
plurality of addition polymerizable reactve groups all o
which polymerize at ~ubstantially 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 i-s butylene diacrylate. The graftlinking monomer is a
polyethylenically unsaturated monomer having a plurality of
adition polymerizable reactive groups, at least one of which
polymerizing at a substantially different rate of
pol~merization 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 the latter stages of polymerization
and, consequently, at or near the surface of the elastomer
particles.
~ 3~ 5
When the rigid thermoplastic phase is subsequently
polymerized at ~he surface of the elastomer, the residual
unsa~urated addition polymerizable r~active group contributed
by the graftlinking monomer participates in the subse~uent
reaction sa 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 o~ allyl esters of ethylenically unsaturated acids
such as allyl acrylate, allyl methacrylate, diallyl maleate,
diallyl fumaratet 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 gra~tlinking monomers are allyl methacrylate and
diallyl maleate. A most pref~rred interpolymer has only two
stages, the first s~age 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 methacrylate, diallyl methacrylate, and the
like, as long as the overall glass transition temperature is
at least about 20C. Preferably the final stage monomer
system is at least about 50 wt~ Cl to C4 alkyl methacrylate.
In a pre~erred embodiment the final stage monomer system may
also contain epoxy functionality. By "epaxy functionality" is
9'~5
meant epoxy units which are pendant from the final stage
polymer. The preferred way of incorporating epoxy
functionality-into the final stage polymer is by use of epoxy
containing ~onomer such as glycidyl acrylate or glycidyl
methacrylate in the final stage monomer mixture. Alternate
epoxy containing monomers are butadiene monoepoxide, allyl
glycidyl ether, 4,5-epoxy pentyl methacrylate or acrylate, l0,
ll-epoxy undecyl methacrylate, or other expoxy-containing
ethyleneically unsaturated monomers. Other ways of
introducing epoxy functionality into the final stage of the
multiple stage polymer are possible, such as post
expoxidation. It is further preferred that the final stage
polymer be free oE units which tend to degrade poly (alkylene
terephthalates), for example, acid, hydroxyl, amino, and amide
groups.
For further descriptions and examples of various
multiphase polymers suitable for use in the present invention~
reference may be had to the aforementioned U.S. Patent
4,096,202 the disclosure of which is incorporated herein by
reference. Additional examples of multiphase ~olymers
suitable for use in the invention may be found in U.S. Patent
4,034,013 the disclosure of which is also incorporated herein
by reference.
In addition to the ingredients mentioned above,
compositions and products of the invention may contain
suitable flame retardant additives in amounts up to about 2Q
wt% based on total molding composition and may contain
relatively minor amounts of other materials which do not
unduly affect the desired characteristics oE the finished
~3~3`9'~
product. Such additional materials, may, depending upon the
par~icular compositions employed and products desired, include
for instance, colorants and lubricants. Where present, such
additional materials normally comprise no more than about 5
wt% of the total composition or finished product.
In preparing molded compositions of the invention,
the reinforcing fibers may be intimately blended into the PBT
by any suitable means suc~ as by dry blending followed by melt
blending, blending in extruders, heated rolls or other types
I~ of mixers, etc. Conventional master batching techniques may
also be used. The same considerations apply to addition of
the other essential or op~ional ingredients of the composition
o ~he invention. Suitable blending and molding techniques
are well known in the art and need not be described in detail
15, herein~ In a preferred embodiment o~ the invention, the
composition o the invention is compounded by dry blending
ollowed by melt mixing in an extruder with barrel
temperatures between about 240 and about 270C. Likewise, in
molding products of the invention from molding compositions of
~a the invention, injection molding is preferred. When injection
molding is used, barrel temperatures between 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 pelletized extrudate.
As mentioned above, one of the major advantages of
the compositions and products of the invention is that the
addition of mica and the above described multiphase polymers
to glass fiber reinforced PBT substantially reduces shrinkage
--10--
s
and warpage normally associated with the use of reinforcing
fibers without substantial harm to the desira~le improvements
in physical proper~ies associated with the use of such fibers.
While warpage is freqent:Ly determined by visual
S inspection, a quantitative de~inition can be expressed in
terms of percent warp equals (dm-t)tl 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 o~ the visual efect of the warp.
Part warp (PW) may therefore be defined as PW =
wherein PW e~uals 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, an
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.
In addition to required and optional ingredients
mentioned above, compositions of the invention may also
include between about l and about 35 wt% based on total
composition of polyethylene terephthalate (PET). 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 or~hochlorophenol at 25C is ~referred.
The following examples are intended to illustrate
the applicat~on and useulness oE the invention without
limiting the scope thereof~ In the example, all quantities
are given in terms of wt% based on ~otal composition unless
otherwise specified~ Physical properties, including warpage,
were measured by the following criteria and reported as an
average for samples of each composition tested:
PropertY Test Procedures
Tensile Yield Strength ASTM D-638
Flexural Yield Strength AS~M D-790
Flexural Modulus ASTM D-790
Notched Izod Impact Strength ASTM D-256
Cantilever Beam Reversed
Notch Izod Impact Strength ASTM D-256
Percent warp As defined above
Example I
PBT (O.8 I.Y.~ was compounded on a Midland Ross 1.5
inch extruder with various amounts of phlogophite mica and
other ingredients as specified below to form various molding
compositions as speci~ied in Table I below. The mica used was
. Marietta Resources International Su~orite HAR 60-S mica flake
having the ~ollowing size distribution.
trace -20 + 40 mesh (U.S. sieve)
76~ -40 + 100 mesh
19% -100 + 200 mesh
3% -200 + 325 mesh
2~ -325 mesh
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9~S
Marietta Resources ~nternational Suzorite ~AR 200~S
mica flake was also used. T~is ma~erial had the ollowing
size distribution:
trace -20 ~ 4a mesh (U.S. sieve)
1% -40 + 100 mesh
55% -100 + 200 mesh
20% -200 + 325 mesh
24~ -325 mesh
The following conditions were employed:
I~Extruder Zone Temperatures Back Pressure 0-200
1 270C Amperage 12 25
2 265C Screw rpm 90
3 260C.
4 255~C. Melt temperature 243-251C.
250C.
Each o~ the experimental molding compositions specified
in Table I and produced as described above was then molded on a
50 ton 3 ounce reciprocating .screw injection molding machine
to provide ASTM test specimens. Parts suitable for measuring
warpaye (camera slide storage box with four large flat sides)
were molded on a 250 ton 36 ounce Impco screw ram machine.
~olding conditions were:
~13V~S
Barrel temperature --- front 480F
rear 480F.
nozzle 480F~
Injection pressure 1100 psi
9crew rpm 75
Injection time 10 sec.
Mold time 20 sec.
Total cycle time 30 Oec.
Mold temperature 100 F.
36 oz., 350 ton moldlng machine
Barr~l temperature --- front 480F.
center 480 F.
rear 480F.
nozzle 490F.
Measured melt temperature 420F.
Screw rpm
Total cycle time 94 Oec.
Mold temperature 175 F.
Mold time 40 sec.
Ihjection pressure 1100 psi
Physical properties were as shown in Table 2 below.
TABLE I
EXPERIMENTAL MOLDING COMPOUNDS
Wt %
In~redient 1 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 (OC~ 419 AA
3/16 inch) 20 20 20
RM 330 Acrylic Impact
Modif er 14.3 14.3 14.3
Acrowax C Lubricant 0.2 0.2 0.2
Epon 815 Diepoxy Modifier0.5 0.5 0O5
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TABLE II
Wt %
2 3
Warp Annealed 100 120
% Warp Unannealed 81 97
Notched Izod Impact Strength
(Foot Pounds per Inch)1.8 1.7 1.4
Cantilever Beam Reversed Notch
I~ Izod Impact Strength
(Foot Pounds per Inch)7.8 8.2 7.5
Flexural Strength (psi)18,00019,10016t300
Flexural Modulus (psi)1.23 1.27 .gO
. Tensile Strength (psi)11,43012,308 10,000
While the invention has been descr:ibed 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 depar~ing from the spirit or
scope of the invention.
