Note: Descriptions are shown in the official language in which they were submitted.
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LINEAR LOW DENSITY POL~?ETEI~!LENE
IMPACT ~qODIFIER FOR THERMOPLP.STIC POLYE:STERS
_ _ _
This invention relates to thermoplastic molding
compositions, particularly thermoplastic polyester,
copolyester and poly-blend molding compositions,
having unexpected, improved impact strength by
incorporating therein, linear low density polyethylene
and glass fibers. More particularly, the invention
pertains to compositions of (a~ 5-92% by ~eight of a
polyester selected from the group consisting essentially
of poly(ethylene terephthalate), poly(l,4-butylene
terephthalate~, a copolyester, an aromatic polycarbonate,
or any combination thereof, each polyester comprising
0-100% of the polyester component; ~b~ 3-20% by weight
linear low density polye-thylene; and Cc~ 5-50~ by weight
glass fibers. Optionally, these compositions may
further comprise an effective amount of mica filler
for reinforcement and/or warp reduction.
Backg_ound of the Invention
High molecular weight linear polyesters and
copolyester of glycols and terephthalic or
isophthalic acid have been available for a number of
years. These are described inter alia in U.S. Patent
2,464,319, to Whinfield et al., and in U.S. Patent
3,047,539, issued July 31, 1982 to Pengilly. These
patents disclose that the polyesters are particularly
advantageous as film and fiber formers.
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With the development of molecular weight control,
the use of nucleating agents and two-step molding
cycles, poly(ethylene terephthalate~ has become an
important constituent of injection moldable compositions.
Further, poly(l,4-butylene terephthalate~, because of its
very rapid crystallization Erom the melt, is uniquely
useful as a component in such compositions. Work
pieces molded from such polyester resins, in comparison
with other thermoplastics, offer a high degree of
surface hardness and abrasion resistance, high gloss,
and lower surface friction.
Furthermore, in particular, poly(l,4-butylene
terephthalate) is much simpler to use in injection
molding techniques than poly(ethylene terephthalate~.
For example, it is possible to injection mold
poly(l,4-butylene terephthalate~ at low mold temperatures
of from about 30C to 60C to produce highly crystalline,
dimensionally stable moldings in short cycle times.
On account of the high rate of crystallization, even
at low mold temperatures, no difficulty is encountered
in removing the moldings from the molds. Additionally,
the dimensional stability of poly(l,4 butylene tereph-
thalate~ injection moldings is very good even at
temperatures near or well above the glass temperature
of poly(l,4-butylene terephthalate).
Simultaneously with the development of injection
molding grades of polyester resins, fiber glass
reinforced compositions were also provided. See for
example, U.S. Patent 3,368,995, issued February 20, 1968
to Furukawa et alu, and U.S. Patent 3,814,725, issued
June 4, 1974 to Zimmerman. These injection moldable
compositions provided all of the advantages of the
unfilled polyesters and, also because of the glass
reinforcement, the molded articles had higher rigidity,
yield strength, modulus and impact strength.
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Furthermore, stable polyblends of poly-
(1,4-butylene terephthalate~ and poly(ethylene tere~
phthalate~ can be molded into useEul unreinforced and
reinforced articles. See U~S. Patent 3,953,394,
Fox and Wambach. Additionally, copolyesters and block
copolyesters containing units derived primarily from
poly(l,4-butylene terephthalate~ and from aromatic/
aliphatic or aliphatic polyesters are also known.
Such copolyesters and block copolyesters are useful
per se as molding resins and also in intimate combination
with poly(l,4-butylene terephthalate~ and/or
poly(ethylene terephthalate). These compositions are
said to show enhanced impact strength.
It is also known to add polyolefins, especially
high pressure low density polyethylene and high
pressure high density polyethylene, to thermoplastic
polyesters to enhance or provide certain properties.
For example, U.S. Patent 3,405,198, issued
October 8, 1968 to Rein et al., disclose the use of
polyethylene in poly(ethylene terephthalate) as
an impact modifier. U.S. Patent 4,122,061~ i~sued
October 24, 1978 to Holub et al., disclose polyester
compositions which comprise a poly(l,4-butylene
terephthalate~ resin, a poly(ethylene terephthalate)
resin, a fibrous glass reinforcement, alone or in
combination with a mineral filler and, as an impact
modifier there~or, a polyolefin or olefin based copolymer
resin including polyethylene and propylene-ethylene
copolymer. U.S. Patent 4,185,047, issued January 22,
1980 to Cohen et al., disclose the use of high
pressure low density polyethylene in thermoplastic
polyester compositions, particularly poly(ethylene
terephthalate) and poly(l,4-butylene terephthalate~
for improved mold releasability
More recently, it has been discovered that linear
low density polyethylene when added to an aromatic
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polycarbonate resin results in molding composi.t.ions
having improved weld line strength and heat stability
while retaining their good impact strength at
increased part thickness as compared to control samples
of either standard polycarbonate or a commercial
polycarbonate blend with polyethylene. See for
example Research Disclosure #20819 p. 309 ~ugust 1981.
It has now been discovered that thermoplastic
polyester compositions show unexpected improvement in
impact strength when low amounts, from about 3 to
about 20% by weight, preferably 5 to 15~ by weight, of
linear low density polyethylene and from about 5 to
50% by weight fibrous glass are incorporated therein.
The impact strength of the compositions of this
invention are much improved over thermoplastic poly-
ester compositions having incorporated therein high
pressure low density polyethylene or glass or ~oth.
Although the exact mechanism by which this unexpected
improvement in impact strength arises is unknown,
those skilled in th.e art will recognize synergism
between the linear low density polyethylene, at the
levels used, and the glass fibers accounting for the
resultant improvement.
Summary
According to this invention, there are provided
thermoplastic compositions which are useful for
molding or extrusion, e.g., injection molding,
injection blow molding, compression molding, transfer
molding, profile extrusion, sheet extrusion, wire
coating, extrusion blow molding and the like, the
compositions having improved impact strength, comprising:
(a~ 30-92% by weight of a high molecular weight
polyester selected from the group consisting
essentially of poly~ethylene terephthalatel,
poly(l,4-butylene terephthalate~, copoly-
esters, and an aromatic polycarbonate or any
combination thereof;
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(b) 5-50% by weight glass fibers, alone or
combined with an effective amount of rein-
forc.ing filler; and
(c~ 3-20~ by weight of linear low densit~
polyethylene
More specifically, the composition of the present
invention comprises:
(a) 30-92% by weight
i~ poly(l,4-butylene terephthalate~;
ii~ an aliphatic/aromatic copolyester
derived from one or more dicarboxylic
acids ~elected from the group consist-
ing essentially of terephthalic acid;
isophthalic acid; naphthalene dicarb-
oxylic acids; phenyl indane dicarb-
oxylic acid; compounds of the formula:
O O
HO-~- ~ -X- ~ -C-OH
in which X may be alkylene or alkylidene
of from 1 to 4 carbon atoms, carbonyl,
sulfonyl, oxygen or a bond between
benzene rings, and an aliphatic dicarb~
oxylic acid having from 6 to 12 carbon
atoms in the chain and one or more
straight or branched chain dihydric
aliphatic or cycloaliphatic glycols
having from 2 to 10 carbon atoms in the
chain;
iii~ a block copolyester derived from
terminally-reactive blocks of (i~ and
terminally-reactive blocks of copoly-
ester (ii~, wherein sai.d copolyester
(ii) has at least 10~ of a aliphatic
units being derived from a dicarbo~ylic
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acid, or a terminally reacti~e aliphatic
polyester of a straight chain a]iphatic
or cyclo-aliphatic glycol, said blocks
being connected by interterminal linkayes;
iv~ polyCethylene terepthalate)-;
v~ an aromatic polycarbonate of preferably
bisphenol-A, or
(b) 5-50~ by weight of ylass fibers, and
~c~ from about 3 to about 20% by weiyht, preferably
5 to 10% by weight, of linear low density
polyethylene.
The compositions of the invention may also contain
an effective amount of mica or clay to reduce warpage
and/or talc to enhance electrical properties. Further,
these compositions may contain an additional impact
modifier including, but not limited to, coreshell
type acrylic elastomers, ethylene-vinyl acetate
copolymers and ethylene-ethylacryla-te copolymers.
Furthermore, these compositions may contain one or
more of the following additives: mold release agent,
flame retardant, coloring agent, nucleating agents,
stabilizers, fillers and flow promoters, and the like.
Detailed Description of the Invention
The high molecular weight polyes-ters used in the
practice of the present invention are polymeric glycol
esters of terephthalic acid and isophthalic acid. They
are widely available commerically, e.g.~ General Electric
Company, Pittsfield, Massachusetts - poly(l,4-butylene
terephthalate~ resins under the Trademark VALOXR and
3a Goodyear Tire and Rubber Company, Poly(ethylene
terephthalate) under the Tradename VITUF. Otherwise,
they can be readily prepared by known techniques,
such as by the alcoholysis of esters of terephthalic
and/or isophthalic acid with a glycol and subsequent
polymerization, by heating glycols with free acids or with
halide derivatives thereof, and similar processes.
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These are described in U.S. ~atent Nos. 2,465,319 and
3,047,539, and elsewhere.
~ lthough the glycol portion of the polyester can
contain from 2 to 10 atoms, it is preferred that it
contain from 2 to 4 carbon atoms in the form of linear
methylene chains.
Preferred polyesters will be of the family
consisting of high molecular weight polymeric glycol
terephthalates or isophthalates having repeating units
of the general formula: O
O / ~_
-O -(CH2~n~-O~C ~
wherein n is a whole number of from 2 to 4, and
mixtures o~ such esters, including copolyesters of
terephthalic and isophthalic acids of up to 30 mole
percent isophthalic units.
Especially preferred polyesters are poly(ethylene
terephthalate~ and poly(l,4-butylene terephthalate~.
Special mention is made of the latter because it
crystallizes at such a good rate that it may be used
for injection molding without the need for nucleating
agents or long cycles, as is sometimes necessary with
poly~ethylene terephthalate).
Illustratively, high molecular weight polyesters,
such as poly(l,4-butylene terephthalate~, will
; 25 have an intrinsic viscosity of at least about 0.7
deciliters/gram and, preferably, at least 0.8 decil-
iters/gram as measured in a 60:40 phenol tetrachloro-
ethane mixture at 30 C. At intrinsic viscosities of
at least about 1.0 deciliters/gram, there is further
enhancement of toughness of the present compositions.
The copolyesters useful for the present
compositions are preferably prepared from terephthalic
acid, isophthalic acid, or reactive derivatiyes thereof,
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or any combination of the foregoing, and a glycol, which
may be a straight or branchedchain aliphatic and/or
cycloaliphatic glycol. Illustratively, the glycol
will be ethylene glycol; 1,4-butanediol;
1,5-pentanediol; 1,6-hexanediol; l,9-nonanediol;
l,10-decanediol; neopentyl glycols; i,4-cyclohex-
anediol; 1,4-cyclohexane dimethanol; a mixture of any
o~ the foregoing, or the like. Additionally, other
dicarboxylic acids useful for the acid component of
the copolyesters include, without limi-tation, aromatic
dicarboxylic acids such as naphthalene dicarboxylic
acid, and compounds of the formula:
O O
HO-C- ~ -X- ~ -C-OH
in which X may be alkylene or alkylidene of from 1 to
4 carbon atoms, carbonyl, sulfonyl, oxygen or a bond
between the benzene rings, and the like, and aliphatic
dicarboxylic acids having from 6 to 12 carbon atoms in
the chain including suberic acid, sebacic acid,
azelaic acid, adipic acid and the like.
The foregoing copolyesters may be prepared by
ester interchange in accordance with standard procedures.
These copolyesters may preferably be derived from at
least 50% poly(l,4-butylene terephthalate~ units.
Also useful for the compositions of the present
invention are block copolyesters derived from blocks
of i~ terminally-reactive poly(l,4-butylene tereph-
thalate~, preferably of low molecular weight, and ii~
terminally-reactive copolyesters, as described above~
or iii~ a terminally-reactive aliphatic polyester, or
any combination thereof. The terminal groups can
comprise hydroxyl, carboxyl, carboalkoxy, and the
like, including reactive derivatives thereof.
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Generally, these block copolyesters may be
prepared by reacting the aforementioned terminally-
reactive units in the presence of a catalys-t for
transesterification, such as zinc acetate, manganese
acetate, titanium esters and the like. After initial
mixing polymerization is carried out under standard
conditions, e.g., 220 to 280C, in a high vacuum e.g.,
0.1 to 2mm Hg, to form the block copolymer of minimum
randomization in terms of distribu-tion of chain
segments.
Preferably, the copolyester units (ii~ are
derived from an aliphatic glycol and a mixture of
aromatic and aliphatic dibaslc acids in which the mole
ratio concentration of aromatic to aliphatic acids is
from 1 to 9 to about 9 to 1, with an especially
preferred range being from 3 to 7 to about 7 to
3.
Further, the terminally-reactive aliphatic
polyester units (iii~ will contain substantially
stoichiometric amounts of the aliphatic diol and the
aliphatic dicarboxylic acid, although hydroxy-contain-
ing terminal groups are preferred.
In addition, to their ease of formation by well
known procedures, both the aromatic/aliphatic copoly-
esters (ii~ and the aliphatic polyesters (iii~ are
commercially available. One source for such materials
is the Ruco Division/Hooker Chemical Company,
Hicksville, New York, which designates its compounds
as "Rucoflex".
In general, the block copolyesters useful for the
invention preferably comprise from 95 to 50 parts by
weight of segments of poly~l,4-butylene tereph-
thalate). Those poly(l,4-butylene terephthalate~
blocks, before incorporation into the block copoly-
ester, will preferably have an intrinsic viscosity of
above 0.1 dl/g. and more preferably, between 0.1 to
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0.5 dl/g., as measured in a 60:40 mixture of phenol
tetrachloroethane at 30C. The balance, 50 to 5 parts
by weight of the block copolyester will comprise
blocks of copolyester (ii~ and aliphatic polyester
(iii) above.
As will be understood by those skilled in the
art, the poly(l,4-butylene terephthalate) block can be
straight chain or branched, e.g., by use of a branch
ing component which contains at least 3 ester-forming
groups. This can be a polyol, e.g., pentaerythritol,
trimethylolpropane, and the 'ike, or a polybasic acid
compound, e.g., trimethyl trimesitate, and the like.
Branched poly(l,4-butylene terephthalate) resins and
their preparation are described in U.S. Patent
3,953,404, issued April 27, 1976 to Borman.
The invention is also useful for high molecular
weight aromatic polycarbonates and blends of poly-
carbonate with poly(ethylene terephthalate~ and/or any
of the foregoing poly(l,4-butylene terephthalate)
resins. The aromatic polycarbonate resins useful for
the invention include any of those known in the art.
Generally speaking, said polycarbonates may be
prepared by reacting a dihydric phenol with a carbonate
precursor such as phosgene, a haloformate or a
carbonate ester. Such carbonate polymers may be typified
as possessing recurring structural units of the formula:
_ _
11
- O-A-O-C - -
Where A is a divalent aromatic radical of the
dihydric phenol employed in the polymer producing
reaction. By "high molecular weight" aromatic
carbonate polymers, carbonate polymers having intrin-
sic viscosities (as measured in methylene chloride in
deciliters/gram at 25C) of greater than about 0.30.
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The dihydric phenols which may be used to produce
such aromatic carbonate polymers are mononuclear or
polynuclear aromatic compounds, containing as
functional groups, two hydroxyl radicals, each of which
is attached directly to a carbon atom of an aromatic
nucleus. Typical dihydric phenols are
2,2-bis-(A-hydroxylphenyl~propane; 2,2-bis-~4-hydroxy
phenyl~pentane; 2,2-bis-(4-hydroxy 3-methyl phenyl~-
propane; 2,2-bis-(4-hydroxy 3,5-dichlorophenyl~-
propane; 2,2-bis-(4-hydroxy 3,5-dibromophenyllpropane;
1,1-bis-(4-hydroxy phenyl~ethane, and 4,4-dihyd-
roxy-3,3-dichlorodiphenyl ether. A variety of addi-
tional dihydric phenols which may be employed to
provide such carbonate polymers are disclosed in
Goldberg - U.S. Patent 2,993,835 - assigned to the
assignee of the present invention. Most preferably,
the dihydric phenol used is 2,2-bis-(4-hydroxy
phenyl)propane.
It is of course possible to employ two or more
different dihydric phenols or a dihydric phenol in
combination with a glycol, a hydroxy or acid term-
inated polyester, or a dibasic acid in the event a
carbonate copolymer rather than a homopolymer is
desired. Thus it should be understood that the term
polycarbonate resin embraces within its scope carb-
onate copolymers.
The invention is also applicable to blends of
poly(ethylene terephthalate~, poly(l,4-butylene
terephthalate~, the foregoing copolyesters and/or
block copolyesters and/or derivatives thereof,
aromatic polycarbonates, or any combination of these.
The true invention as manifested by the
unexpected improvement in impact strength of any one or
combination of the foregoing polymers is the incorpor-
ation therein of glass fibers and 3 to 20% preferably5 to 15% by weight of linear low density polyethylene.
.
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The linear low density polyethylene useful for
the present invention are well known materials, they
are available commercially, e.g., from Exxon under the
tradename Escorene, from Dow Chemicals under the
tradename DOWLEX or from Union Carbide under the
tradename G ~esins. Alternatively, they may readily
be prepared by state of the art polymerization
processes such as those described in U.S. Patent
4,354,009, issued October 12, 1982, U.S. Patent
4,076,698, issued February 28, 1978, European Patent
Application 4645 (published 10-17-79~ and U.S. Patent
4,128,607, issued December 5, 1978. These polymers
have a density between about 0.8~ and 0.96 gram/cc,
preferably between about 0.915 and 0.945 grams/cc.
These linear low density polyethylene polymers are
actually copolymers of ethylene and a minor amoun-t,
less than 20 mole percent, preferably less than 15
mole ~, of an alpha olefin of 3 to 15 carbon atoms,
preferably 3 to 10 carbon atoms, most preferably 4
to 8 carbon atoms. These linear low density polyethylenes
are distinguishable from polymers such as high pressure
low density polyethylene and high density polyethylene
made from coordination catalyst systems in that they are
substantially free of side chain branching, having a
controlled concentration of simple side chain branching
as opposed to random branching.
The preferred linear low density polyethylene
copolymers are prepared from ethylene and one or more
alpha olefins selected from the gxoup consisting of
propylene, butene-l, pentene-l, 4 methyl pentene-l,
hexene-1 and octene-l, most preferably butene-l and
octene-l. Polymers of desired density may be obtained
hy controlling the copolymerization ratio of alpha
olefin and the formation proportion of the polymer
during copolymerization. The addition of increasing
amounts of the comonomers to the copolymers results in
lowering the density of the copolymer.
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In general, the copolymerization of linear low
density polyethylene can take place in either a gas
phase fluidized bed reactor or liquid phase solution
process reactor, preferably the former, at pressures
ranging from normal to 5000 psi, preferably less than
1000 psi and at temperatures of from 20C to 310C,
preferably 30 C to 115C in the presence of suitable
high activity catalysts. Typical catalyst systems
comprise transition metal complex catalyst preferably
composed of at least one compound of a transition
element of groups IVa, ~a, and VIa having a halide
and/or hydrocarbon group attached to said transition
metal and a reducing component such as a metal halide
or a compound having me-tal attached directly to
carbon, e.g., metal alkyl. High satisfactory catalyst
systems have a halide of titanium and wherein the
effective organo metallic components are metal alkyl
compounds having aluminum as the metal, especially
LiAl(hydrocarbon~4. Such systems include for
example TiC14 & LiAl(alkyl)4, VOC13 & Li(alkyl),
MoC13 & Al(Alkyl~3, TiC14 & alkylMgBr, etc.
Catalyst systems such as these as well as other useful
catalysts systems are disclosed in UOS. Patent
4,354,009, U.S. 4,076,698, Eur. Application 4645 and
U.S. 4,128,607 above. Such catalyst systems are used
in a molar ratio of ethylene to catalyst in a range of
35,000 to 400,000 to one.
The preferred linear low density polyethylene
copolymers so produced having an unsaturated group
content of < 1 and preferably from about 0.1 to about
0.3 C=C/1000 carbon atoms and a n-hexane extractables
content ~at 50C) of less than about 3 preferably less
than 2 weight percent. The preferred materials are
made by the Unipol process which is described in Chem.
Eng., Dec. 3, 1979, pp. 80-85.
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The compositions of the present invention must
also contain glass fibers. The fibrous (filamentous~
glass may be untreated, or preferably, treated with
silane or titanate coupling agents, etc. The fila-
mentous glass to be employed are well known in the art
and are widely available from a number of manufacturers.
For compositions ultimately to be employed for
electrical use, it is preferred to use fibrous glass
filaments comprised of lime-aluminum borosilicate
glass that is soda free. This is commonly known as
"E" glass. However, other glasses are useful where
electrical properties are not so important, e.g., the
low soda glass known as "C" glass. Most preferred,
however, is "G" filament of "E" glass because of its
smaller diameter than "K" filament. The filaments are
made by standard process e.g., by steam or air blowing,
flame blowing and mechanical pulling. The preferred
filaments for plastic reinforcement are made by
mechanical pulling.
The length of the glass filaments and whether or
not they are bundled into fibers and the fibers bundled
in turn to yarns, ropes or rovings, or woven into
mats, and the like are not cricital to the invention.
However, in preparing the molding compositions, it is
convenient to use the filamentous glass in the form of
chopped strands of from about one eighth to about 2
inches long. In articles molded from the compositions,
on the other hand, even shorter lengths will be
encountered because, during compounding, considerable
fragmentation will occur. This is desirable, however,
because the best properties are exhibited by thermo-
plastic injection molded articles in which the
filament lengths lie between about 0.0005 to 0.125
inch.
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Optionally, the composition of the present
invention may further comprise an e~ective amount of
any of the known impact modifiers useful for polyesters
including polycarbonates, and polyester blends.
The preferred impact modifiers generally comprise
an acrylic or methacrylic grafted polymer of conjugated
diene or an acrylate elastomer, alone or copolymerized
with a vinyl aromatic compound. Especially preferred
grafted polymers are the core-shell polymers of the
10 ~ type available from Rohm & Haas, for example Acryloid
KM653, Acryloid KM330 and Acryloid KM611. In general
these impact modifiers contain units derived from
butadiene or isoprene, alone or in combination with
a vinyl aromatic compound, or n-butyl acrylate, alone
or in combination with a vinyl aromatic compound. The
aforementioned impact modifiers are believed to be
disclosed in U.S. Patent 4,180,494, issued
December 25, 1979 to Eromuth et al; U.S. 3,808,180,
issued April 30, 1974 to Owens; U.S. 4,096,202, issued
June 20, 1978 to Farnham et al; and U.S. 4,260,693,
issued April 7, 1981 to Cohen et al. Most preferably,
the impact modifier will comprise a two stage polymer
having either a butadiene or n-butyl acrylate based
rubbery core and a second stage polymerized from
methymethacrylate alone or in combination with styrene.
Also present in the first stage are cross linking
monomers and graft linking monomers. Examples
of the cross linking monomers include 1,3-butylene
diacrylate, divinyl benzene and butylene
dimethacrylate. Examples of graft linking monomers
are allyl acrylate, allyl methacrylate and diallyl
maleate.
Additional preferred impact modifiers are of the
type disclosed in U.S. 4,292,233, issued October 6, 1981.
These impact modifiers comprise, generally~ a relatively
high content of a crosslinked butadiene polvmer grafted
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base having grafted thereon acrylonitrite an~ styrene.
other suitable impact modifiers include, but are
not limited to ethylene vinyl acetate, ethylene
ethylacrylate copolymers/ etc.
The compositions of the present invention can be
rendered flame retardant with an effective amount of
conventional flame retardant agents. As is well known,
flame retardants can be based on elementary red
phosphorus, phosphorus compounds, halogen and nitrogen
compounds, alone or preferably in further combination
with synergists, such as antimony compounds.
Especially useful are polymeric and oligomeric flame
retardant agents comprising tetrabromo bisphenol-A
carbonate units, e.g., U.S. Patent ~o. 3,833,685,
issued September 3, 1974 to Wambach.
The compositions of the present invention may
further comprise fillers such as, but not limited to,
mica or clay for reinforcement and warp reduction or
talc for electrical properties, in effective amounts.
Finally, the compositions of this invention may
also contain effective amounts of any one or more of the
followins additives: flow promoters, nucleating
agents, coloring agents, stabilizers, coupling agents,
and the like.
The proportionment of the ingredients of the
compositions of the invention vary depending upon the
number of ingredients, the specific ingredients used
and the desired properties and end uses for the
plastics so produced. In general, the compositions
comprise in percent by weight based on the final
composition, 30 to 92% of a thermoplastic polyester
resin, including blends, 3 to 20% linear low density
polyethylene and 5 to 50% of glass fibers. Preferably,
the composition comprises 30 to 80% polyester, 5 to
15% linear low density polyethylene and 15-35% glass.
Furthermore, the -thermoplastic polyester resin itself
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comprises 0-100% polyCethylene terephthalate), 0-100%
of a poly(l,4-butylene terephthalate~ resin, and
0-100% of an aromatic polycarbonate, or any combination
thereof wherein the total is 100%. Optionally, a
preferred composition may also contain 0-40% b~ weight
of mica or clay for reinforcement and warpage reduction
or 0-40% by weight of talc for electrical properties.
Further, the compositions may contain up to 25%,
preferably 5-25% of an impact modifier.
The compositions of the present invention are
prepared in conventional ways. For example, in one
method, the linear low density polyethylene and glass
are placed into an extrusion compounder with the
thermoplastic polyester resin to produce molding
pellets. The linear low density polyethylene and
glass is thus dispersed in a matrix of the thermoplastic
polyester. In another procedure, the linear low density
polyethylene and the glass are mixed with the thermoplastic
polyester resin by dry-blending~ then either fluxed on
a mill and comminuted, or extruded and chopped.
Alternatively, the ingredients can be mixed with the
powdered or granular thermoplastic polyester resin and
directly molded, e.g~, by injection or transfer molding
techniques.
Ordinarily, it is important to thoroughly free
the ingredients from as much water as possible.
However, it has recently been disclosed that polyester
molding compositions may be prepared having a small
moisture content. See U.S. Patent No. 4,351,758,
issued September 28, 1982 to Lu et al. Furthermore,
compounding should be carried out to insure that
the residence time in the machine is short; the
temperature carefully controlled, the friction heat is
utilized, and an intimate blend between the additives
and the thermoplastic resin is obtained.
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8CV-3976
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Although it is not essential, best results are
obtained i~ the ingredients are precompounded, pellet-
ized, and then molded. Precompoundiny can be carried
out in conventional equipment. For example, after
carefully predrying the thermoplastic polyester, e.g.,
at 125C for 4 hours, a single screw extruder is fed
with a dry blend of the polyester resin, the linear
low density polyethylene and the glass, and whatever
other additives may be used, if any; the screw employed
having a long transition and metering section to insure
melting. On the other hand, a twin screw extrusion
machine, e.g., a 28mm Werner Pfleiderer machine can
be fed with resin, linear low density polyethylene
and glass at the feed port. In either case, a
generally suitable machine temperature will be about
450 to 57QF.
The precompounded composition can be extruded and
cut up into molding compounds such as conventional
granules, pellets, etc., by standard techniques.
The compositions of this invention can be molded
in any equipment conventionally used for thermoplastic
compositions. For example, with poly(l,4-butylene
terephthalate) based compositions, good results will
be obtained in an injection molding machine, e.g., of
the Newbury type with conventional cylinder temperature,
e.g., 450F and conventional mold temperatures,
e.g., 150F. On the other hand, with poly(ethylene
terephthalate) based composition, because of the lack
of uniformity of crystallization from interior to
exterior of thick pieces, somewhat less conventional
but still well known techniques can be used. For
example, a nucleating agent such as LioH, sodium
stearate, graphite, or a metal oxide, e.g., ZnO or
MgO, can be included and standard mold temperatures of
at least 180F will be used.
~211Z~5
8CV-3976
--19--
Description of the Pref_rred Emhodiments
In order that those skilled in the art may better
understand how to practice the present invention, the
following examples are given by way of illustration and
not by way of limitation~
Example 1~7~and C mparative Examples 1-4
Dry blends of poly(.l,4-butylene terephthalate~
resin, glass and linear low density polyethylene were
compounded and extruded through a single screw extruder
at 500 to 550F. For comparative purposes dry blends
of poly~1,4-butylene terephthalate~ and linear low
density polyethylene and poly(l,4-butylene terephthalate)
and glass were similarly prepared. The extrudates were
pelletized and injection molded at 490F on a VanDorn
molding machine, mold temperature 150F. The
formulations and physical properties are shown in
Table 1.
,
12~L~2'~5
8CV-3976
--20--
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8CV-3976
-21-
As is apparent from the results shown in Table l,
adding linear low density polyethylene alone to
poly(l,4-butylene terephthalate~ has vexy little
effect on the properties thereof (Comparative Examples
1-3). Further, as is well known in the art, the
addition of glass fibers to poly(l,4-butylene tereph-
thalate) improves the Notched Izod impact s-trength
(Comparative Example 41. However, totally unpredicted
is the significant improvement in notched izod impact
strength when both glass fibers and linear low density
polyethylene is added to poly(l,4-butylene terephthalate),
Examples 1-7. Improvement is also apparent in the
unnotched izod impact strength in examples 2 - 4 of the
invention as compared to glass reinforced poly (l,4-
butylene terephthalatel of comparative Example 4.
Finally, it is also evident from Table l, examplesl through 7, that this effect is not specific to one
species of linear low density polyethylene nor for just low
levels as both 5% and 7% by weight linear low density
2Q polyethylene improved impact strength. Further, as
shown in these examples, the melt indices of the linear
low density polyethylene, even within the same species,
may vary widely with only a slight variation in the
resultant improved impact strength.
Examples 8 14 and Comparative Example 5-6
Dry blends of poly(l,4 butylene terephthalate~,
glass, linear low density polyethylene and polycarbonate
or poly~ethylene terephthalate~ or both were prepared
according to the method disclosed in examples 1-7.
The specific compositions and physical properties
thereof are shown in Table 2.
8CV-3976
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8C~-3976
-23-
Once again, from comparative example 5 and
example 8, it is evident that the incorporation of
linear low density polyethylene greatly increases the
impact strengthof reinforced poly(l,4-butylene
terephthalate),. Further, as shown i.n comparative
Example 6 and examples 9-14, the impact strength of
glass reinforced polyester blends of poly(l,4-butylene
terephthalate) and polycarbonate or poly(l,4-butylene
terephthalate) and both polycarbonate and poly-
ethylene terephthalatel are greatly increased by theaddition of linear low density polyethylene at both
high and low levels of incorporation, but not at 1%
levels.
Examples 15 - 22
; 15 Dry blends of filled and unfilled glass rein-
forced polyblends of poly(l,4-butylene terephthalate)
and poly(ethylene terephthalate~ or an aromatic
polycarbonate having incorporated therein linear low
density polyethylene alone or with a certain amount of
an additional impact modifier comprising either
ethylene-vinyl acetate copolymer, ethylene ethyl-
acrylate copolymer or core-shell type acrylic elastomers
were prepared according to the procedure in Examples
1-7 the compositions and physical properties thereof
are shown in Table 3.
s
8CV-3976
-2!1-
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8CV~3976
-25-
Once again, the impact properties of the poly-
blend compositions are improved by the incorporation
therein of linear low density polyethylene. This is
true for filled compositions as well: t~e addltion of
mica accounting for a reduction in warpage. Although
the addition of mica to these compositions reduces
impact strenth, compare examples 15 and 18, good
impact strength is still achieved, examples 15 - 17.
Furthermore, as shown in examples 16 and 19,
examples 17 and 20 and examples 21 and 22, certain
accounts of ethylene ethylacrylate, ethylene vinyl
acetate, and core-shell acrylate elastomers (KM330),
respectively, may be added to or substituted in part
for or by a certain amount of the linear low density
polyethylene with the compositions retaining the
improved impact strength realized from the linear low
density polyethylene.
Examples 23 - 28
Additional mica filled compositions further
containing talc for electrical properties, or flame
retardant were prepared according to the aforementioned
procedures. The compositions and physical properties
are shown in Table ~.
-
~2~ 45
8C~-3 97 6
--26--
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8CV-3976
-27-
Examples 23 - 28 demonstrate that good impact
strength was retained in mica filled, glass reinforced
poly blends of high poly(ethylene terephthalate).
content haviny incorporated therein moderate amounts
of linear low density polyethylene when varying
amounts of talc were added to enhance electrical
properties~
Furthermore, examples 27 and 28 demonstrate that
good impact strength is likewise retained in
compositions of the present invention which have been
rendered flame retardant.
Obviously~ other modifications and varia-tions of
the present invention are possible in light of the above
teachings. All such obvious modifications which may be
made in the particular embodiments described above are
within the full scope of the invention as defined in
the appended claims.
