Note: Descriptions are shown in the official language in which they were submitted.
8CH-2670
3~
This invention relates to improved, unfilled
thermoplastic molding compositions and, more particularly,
to improved unfilled thermoplastic molding compositions.
High molecular weight linear polyesters and
copolyesters of glycols and terephthalic or isophthalic
acid have been available for a number of years. These
are described inter alia in Whinfield et al, U.S. Patent
No. 2,465,319 - dated March 22, 1949, and in U.S. Patent
3,047,539 - dated July 31, 1962. These patents disclose
that the polyesters are particularly advantageous as film
and fiber formers.
With the developement 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. Poly
(1,4-butylene terephthalate), because of its very rapid
crystallization from the melt, is uniquely usef~l as a
component in such compositions. Workpieces 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.
Recently, block copolyesters, wherein the major
portion of the repeating units are poly(l,4-butylene
terephthalate) blocks, have been found to have enhanced
impact resistance.
U.S. Patent No. 3,937,757 - dated February 10,
1976 - Seydl et al teaches that the tracking resistance
of poly(l,4~butylene terephthalate) compositions can be
improved by the addition of from 5 to 5Q% by weight of a
polyolefin or ethylene copolymers, containing at least 50%
by weight ethylene units, thereto.
It has now been surprisingly discovered that if
a small amount, i.e., less than 5% by weight, of a
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copolymer of ethylene and viny' acetate is incorporated
in unfilled thermoplastic molding compositions comprised
of high molecular weight linear polyester such as those
described hereinbefore, the compositions exhIbit vastly~
improved impact resistance. By the term "unfilled" herein,
is meant that the compos~tions of this inYention do not
contain fillers like talc and mica or xe-in~orcements,
such as glass or conventional flame-~retardants.
According to this invention then, there are pro-
vided unfilled thermoplastic compositions w~ich are use~ul
for molding or extrusion, e.g~, injection moldingr
injection blow molding, compression molding, transfex !
molding, profile extrusion, sheet extrusion, wire coating,
extrusion blow molding and the like, the compositions have
impro~ed impact resistance, said compositions comprising:
(a~ a high molecular weight linear polyester;
and (b) from about 0.1 to 4~5~, by weight, based on
the weight of the total composition, of a copolymer of
ethylene and yinyl acetate,
; 20 The high molecular weight linear polyesters used
in the praçtice of the pxesent invention are polymeric
glycol esters of terephthalic acid and isophthalic acids~
They are available commercially or can be prepared hy
kno~n techniques, such as by the alcoholysis of esters of
the phthalic acid with a ~lycol and subsequent
polymerization, by~ heating ghycols with the free acids or
~ith halide deriyatives thereof, and similar processes.
These are descxibed in ~S. Patent No. 2,465,319 - dated
March 22, 1949 - Whi~nfield et al and U,S. Patent No.
3~ 3,047,539 - dated July 31~ 1962 - Pengilly, and elsewhere.
Although the glycol portion of the polyester can
contain from two to ten carbon atoms, it is preferred that
it contain from two to four carbon at~ms in the form of
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1~ 4 73'~ 8CH-2670
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:
2)n - C - ~ ~
wherein n is a whole number of from two to four, and
mixtures of such esters, including copolyesters of
terephthalic and isophthalic acids of up to about 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
will have an intrinsic viscosity of at least about 0.4
deciliters/gram and, preferably, at least 0.7 deciliters/
gram as measured in a 60:40 phenol tetrachloroethane
mixture at 30 C. At intrinsic viscosities of at least
about 1.1 deciliters/gram, there is a further enhancement
in toughness of the present compositions.
The copolymers of ethylene and vinyl acetate
which are used in accordance with the present invention are
well known to those of ordinary skill in the art and for
the most part are commercially available. For the purposes
of the invention, i.e., providing improvement in impact
1~4734 8C~ 2670
resistance, it has been found that high or low vinyl
- content copolymers can be employed. That is, ethylene-
vinyl acetate copolymers containing less than, equal to,
or greater than 50% vinyl content can be used herein.
Thus, illustrative copolymers of ethylene and vinyl acetate
which are encompassed within the scope of this invention
include ethylene-vinyl acetate copolymer having a vinyl
TM
content of about 15~ by weight (Alathon 3152, sold by DuPont),
ethylene-vinyl acetate copolymer containing 25~ by weight
vinyl acetate (Alathon 3892, sold by DuPont), ethylene-
vinyl acetate copolymer containing 28~ by weight vinyl
acetate (Alathon 3180, DuPont), ethylene-vinyl acetate
copolymer containing 45% by weight vinyl acetate
TM
(Vynathene EY 903, sold by U.S.I. Chemicals, N.Y., N.Y.),
and ethylene-vinyl acetate copolymer containing 52% by
weight vinyl acetate (Vynathene EY 904, sold by U.S.I.
Chemicals).
In general, the ethylene-vinyl acetate copolymer
additives are employed herein in amounts ranging from about
0.1% to 4.5~, by weight, of the total weight of the
composition.
The compositions of the present invention are pre-
pared in conventional ways. For example, in one way, the
ethylene-vinyl acetate copolymer is put into an extrusion
compounder with the polyester resin to produce molding
pellets. The copolymer is dispersed in a matrix of the
polyester resin in the process. In another procedure, the
copolymer is mixed with the polyester resin by dry
blending, then either fluxed on a mill and comminuted, or
they are extruded and chopped. The ethylene-vinyl acetate
copolymer can also be mixed with powdered or granular
polyester resin and directly molded, e.g., by injection or
~'
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transfer molding techniques. It is always important to
thoroughly free the polyester resin from as much water
as possible.
In addition, compounding should be carried out to
ensure that the residence time in the machine is short;
the temperature is carefully controlled, the friction heat
is utilized, and an intimate blend between the copolymer
and the polyester resin is obtained.
Although it is not essential, best results are ob-
tained if the ingredients are pre-compounded, pelletized,
and then molded. Pre-compounding can be carried out in
conventional equipment. For example, after carefully pre-
drying the polyester resin, e.g., at 125C for 4 hours, a
single screw extruder is fed with a dry blend of the
polyester and the thylene-vinyl acetate copolymer, the
screw employed having a long transition and metering section
to ensure melting. On the other hand, a twin screw
extrusion machine, e.g., a 28 mm Werner Pfleiderer machine
can be fed with resin and additive at the feed port. In
2Q either case, a generally suitable machine temperature
will be about 450 to 570F.
The pre-compounded composition can be extruded
and cut up into molding compounds such as conventional
granules, 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), 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., 1500F. On the other
hand, with poly(ethylene terephthalate), because of the
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8CH-2670
lack of uniformity of crystallinization from interior
to exterior of thick pieces, somewhat less conve;~tional
but still well-known techniques can be used. For example,
a nucleating agent such as graphite or a metal oxide, e.g.,
ZnO or MgO can be included and standard mold temperature
of at least 230 F. will be used.
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.
Examples 1-6
The following formulations are mechanically
blended, then extruded and molded into test pieces in
a Van Dorn injection molding machine. The properties
are also summarized in the table below.
Table 1
Example 1 2 -3 4 5 6 7
Inqreditents
(parts by weight)
TM a 99.8 95.3 95.398.897.395.3 97.3
Alathon 3180b 4.5 1.0 2.5 4.5
Vynathene EY903 4.5
Vynathene EY904d 2.5
Irganox 10930.150.15 0.15 0.15 0.15 0.15 0.05
Ferro 904f0.05 0.05 0.05 0.05 0.05 0.05 .S
Properties
Notched Izod
Impact ft.lb./in1.08 1.62 1.681.221.331.59 1.34
Unnotched Iæod48.039.5 41.645.145.349.3 43.2
Impact ft.lb./in
Tensile strength
psi 7991 6804 6920773673487236 7516
Elongation %303 396 289304351 316 329
Gardner Impact 9/10 10/10 10/10 10/10 10/10 10/10 5/10
@ 350 in.lbs.
Non Shatter~total tested
-- 6 --
A
.
1~47;~ 8CH- 2 6 7 0
Table 1 continued.......
* Control
(a) poly(l,4-butylene ~erephthalate)about 0.9 intrinsic
viscosity measured in a solution of phenol and
tetrachloroethane (60:40) at 30c, available from G.E.
(b) ethylene vinyl acetate copolymer, 28% vinyl acetate
(DuPont)
(c) ethylene-vinyl acetate copolymer, 45O vinyl acetate
(U.S.I. Chemicals)
(d) ethylene-vinyl acetate copolymer, 52% vinyl acetate
(U.S.I. Chemicals)
(e) tetrakis (3,5-di-t-butyl-4 hydroxy phenylpropionyloxy
methyl)methane
~f) diphenyl decylphosphite
The above data show the improved notched IZOd
impact resistance of the compositions within the scope of
the invention herein in comparison to the control sample
which does not employ the copolymer additive.
Obviously, other modifications and variations of
the present invention are possible in light of the above
teachings. For example, small amounts of materials such
as dyes, pigments, stabilizers and plasticizers and the
like can be added to the present compositions. It is to
be understood, therefore, that changes may be in the
particular embodiments of the invention described which
are within the full intended scope of the invention as
defined by the appended claims.
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