Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
PRODUCT AND PROCESS
FIELD OF THE INVENTION
This invention relates to polyethylene
terephthalate resins useful in molding applications.
More particularly, this invention relates to
polyethylene terephthalate resins containing an
inorganic reinforcing or filler material.
BACKGROUND
It is desirable to enhance the strength
of articles molded from polyethylene terephthalate
resin by employing a reinforcing material, such as
glass fibers, asbestos fibers or other fibrous
mineral materials with a coupling agent, in
the resin. ~urthermore, it is sometimes sufficient
to merely increase the modulus by use o~ a filler,
such as beads or a mineral of low aspect ratio, in
the resin. However, heretofore, it was necessary
to use very high~mold temperatures, on the order
of 130C, to obtain molded articles from such
reinforced or filled resins which had a glossy surface
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and which were rot rough in texture. If these high
mold temperatures were not employed, the molded
articles had a rough surface with poor gloss. It
is believed that the crystallization rate of poly-
ethylene terephthalate is too slow below about 130Cto result in a molded article having good surface
characteristics.
While good surface characteristics can
be obtained at molding temperatures of 130C or
more, the use of such temperatures is not practical
in the molding field, for most molds are heated
with water and attain temperatures of only about
85-110C.
A few molding devices employ heating means
such as oil to reach temperatures higher than 85-
110C but these generally are inconvenient to
use and still either do not generally reach such
temperatures or reach them unevenly because of
inadequate coring. Because of these heating problems,
it has proven commercially unattractive to employ
these high temperature molding devices with reinforced
or filled polyethylene terephthalate resins.
SUMMARY OF THE INVENTION
It is desirable to provide a
reinforced or filled polyethylene terephthalate
resin ~hat can be molded at mold temperatures
below about 110C to produce a molded article
having a smooth and glossy surface. The reinforced
or filled polyethylene terephthalate resins of this
invention achieve the foregoing by having incorpor-
ated therein 1) a sodium or potassium salt of a
selected organic polymer containing pendant carboxyl
g~oups and 2) a selected low molecular weight
~ organic ester.
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Speci~ically, the resins of this invention
are compositions consisting essentially of:
A. polyethylene terephthalate having an
inherent viscosity of at least about 0.4;
5B. between about 10 and about 60 percent
by weight reinforcing or filling material;
C. a sodium or potassium salt of an organic
polymer which contains pendant carboxyl groups, said
material present in an amount sufficient to provide
a ~H~/aHC ratio of less than 0.25 to a mixture of
components A, B and C;
D. a compound present in an amount ~u~
cient to provide a Tpk at least 4C lower than the Tpk
of a mixture of components A, B and C, said compound
being an organic ester selected from the
product of an aliphatic carboxylic acid of 1 to 20
carbon atoms containing 1-3 carboxyl groups, and an
alcohol of the formula HO~R"O~ "t wherein R" is a
hydrocarbon radical of 2-15 carbon atoms (preferably
2-8 carbon atoms), Rtlt is -H or a hydrocarbon radlcal
of 2-20 carbon atoms (pre~erably ~-12 carbon atoms),
and when R"l is H, y is a cardinal number between
2 ~nd 15 (preferably between 2 and 8) and when R"
i.s a hydrocarbon radical, y is a cardinal number
between 1 and 15 (preferably between 2 and 8).
DESCRIPTION OF THE INVENTION
The polyethylene terephthalate employed
herein is one which has an inherent viscosity of
at least 0.4. The polyethylene terephthalate
preferably has an upper limit on inherent viscosity
of about 1.2. Inherent viscosity is measured at 30C
using 0.5 g of polyethylene terephthalate per 100 ml of
a liquid that is a mixture, at a 3:1 ratio by volume, of
methylene chloride and trifluoroacetic acid i.e. using the
procedure o~ ASTM D-2857. The polyethylene terephthalate
can contain minor amounts of other comonomers such as
diethylene glycol or glutaric acid.
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The reinforcing or filler material employed
herein include glass fibers, glass beads, aluminum
silicate, asbestos, mica and the like, or combinations
thereof, as for example a mixture of mica and glass
fibers.
Materials present in an amount sufficient
to cause the compositions of the invention to have a
iHH/~HC ratio of less than 0.25 (component C defined
above) include the sodium or potassium salts of car-
boxyl containing organic polymers, such as copolymersof olefins and acrylic or methacrylic acids, or co-
polymers of aromatic olefins and maleic anhydride.
Preferably these materials include the sodium or
potassium salt of ethylene/methacrylic acid
copolymers (including both wholly or partially
neutralized salts e.g., at least about 30%
neutralized), and the sodium salt of styrene/
maleic anhydride copolymers (including both
wholly or partially neutralized salts e.g., at
least about 30% neutralized). In the co-
polymers listed above the olefin or aromatic olefin
moiety ordinarily comprises 50-98 percent by weight
of the copolymer, and preferably 80-98 percent. An
especially preferred material is the sodium salt
of ethylene/methacrylic acid copolymer. The
copolymers may be prepared by conventional high
pressure polymerization technology.
Preferred organic esters of component D
recited above are those in which the aliphatic car-
boxylic acids are hydrocarbon acids containing 1-3
carboxyl groups, preferably 1 or 2, and are of 4-10
carbon atoms and the alcohols are aliphatic.
In other words, the R groups in the alcohols are alkyl
or alkylene depending upon the particular R group.
Preferably also when the carboxylic acids contain two
or more carboxyl groups, the carboxyl groups are all
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reacted to ~orm ester (CO0) linkages, that is,
there will be no free carboxyl groups present in
the ester. Preferably, all the hydroxyl groups of
the alcohols will also be reacted to form ester (COO)
5 linkages, that is, there will be no free hydroxyl
groups present in the ester.
Specific compounds within these definitions
are listed following (The number in parenthesis after
each compound is the number of degrees centigrade
that 1 percent by weight of the compound present
(based on polyethylene terephthalate) in the
reinforced or filled polyethylene terephthalate
lowers the Tpk): butyl carbitol* adipate (2.9), tri~
ethylene glycol caprate-caprylate (2.7).
Components (C) and (D) in the compositions
of this invention aid in obtaininy molded articles
of high surface gloss at molding temperatures below
110C by increasing the rate of crystallization of
polyethylene terephthalate. Component (C) is
believed to primarily aid in increasing the rate
of crystallization while component (D) is believed
to primarily improve the mobility of the polyethylene
terephthalate in its supercooled state by reducing the
viscosity of the supercooled mixture. Both are necessary
to obtain the high gloss found in the articles molded
from the composition.
The amount of component (C) present in
the compositions of this invention is an amount which
will result in a~HH/~Hc ratio of the composition
less than 0.25. To find theaHH/aHc ratio, poly-
ethylene terephthalate is molded at 70C into 1/16"
thick bars. The bars are heated and at between
95C and 120C an exotherm (termed ~HH) is recorded
on a differential scanning calorimeter (DSC) cell
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attached to a Du Pont 900 Differential Thermal
Analysis (DTA) device. Th~ bar is heated to 290
(which is above its melting point) and the melted
sample cooled at 10C/minute. Another exotherm
at between about 200-220C (termed ~Hc) is the
exotherm recorded on freezing of the sample. It
has been found that the QHH/~HC ratio is a convenient
method of measuring the degree of crystallization.
The Tpk of the composition of this invention
is the temperature at which heat evolves most
rapidly during the heating cycle recited in the
previous paragraph. As stated earlier the amount
of component (D) present in the composition of this
invention is an amount which lowers the Tpk of the
15 composition by at least 4C over that of an identical
composition that does not contain component (D).
The upper limits on the amounts of
components C and D are not critical. However,
physical properties may become adversely a~fected
as amounts increase. In general, the upper amount
employed for any one component will usually be about
12 percent by weight based on weight polyethylene
terephthalate, while the lower limit will be about
1 percent. For the preferred component (C) salts
of ethylene/methacrylic acid copolymer the upper
limit on the amount present will be about 12 percent
by weight based on weight of polyethylene
terephthalate while the lower limit will be about
0.5 percent, but preferably an amount within
the range of 2-7 percent will be used.
In addition to the components discussed
hereinabove, the compositions of this invention
may contain additives commonly employed with poly-
35 ester resins, such as colorants, mold release
agents, antioxidants, ultraviolet light stabilizers,flame retardants and the like. Additi~es which improve
physical properties, such as tensile strength and
elongation can also be employed; such additives include
epoxy compounds (e.g., an epoxy compound formed from
bisphenol-A and epichlorohydrin) present in amounts of
from 0.1-1.5 percent by weight based on weight of
composition.
The compositions of this invention are
prepared by blending the components together by
any convenient means. Neither temperature nor
pressure are critical. For example, the poly-
ethylene terephthalate can be mixed dry in any
suitable blender or tumbler with components B, C
and D and the mixture melt-extruded. The extrudate
can be chopped and mixed with reinforcing agent
and then this mixture melt extruded. More con-
veniently, all the components can be mixed dry in
any suitable blender or tumbler and the mixture then
melt extruded.
Described in the following Example is
the best mode of carrying out the invention. The
~HH/aHC ratio and the Tpk were determined as described
above. The gloss of molded sample was measured with
a Gardner Multi Angle Gloss* (Model GG-9095) set at
a selected degree angle set forth in the Examples.
EXAMPLE
Dry polyethylene terephthalate (PET)
having an inherent viscosity of about 0.6 was
mixed manually with 25~ (based on total weight of OCF
277B glass fiber, 5.7~ (based on weight of PET)
ethylene/methacrylic acid copolymer (85/15 by weight)
which had been 60 percent neutralized with sodium
(which is component C herein) and with 5.7~ (based
on weight of PET) triethylene glycol caprate-caprylate
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(which is component D herein), 0.6% (based on total
weight) of the product of bisphenol A and epichlor~-
hydrin, and 0.3~ (based on total weight) of a phenolic
antioxidant. Component C provided a ~ c of 0.16
and Component D provided a Tpk of 15.4~ lower than
the Tpk f a mixture the other ingredients.
The resulting mixture was then extruded
through a two-stage two inch single screw extruder
at a melt temperature of 285C and at a vacuum of 28
inches. The extruded strand was cut and the resulting
resin pellets dried at 110C in a vacuum oven for
about 16 hours. The resin pellets were then molded
into tumblers that were 9.2 cm high, 7.5 cm in
diameter at the top, 5.5 cm in diameter at the bottom
and which had a wall thickness of 0.19 cm. Melt
temperature in the molding machine was 295C; while
the surface temperature of the mold was 85C. at a
cycle time of 10/20.
Gloss was measured at an angle of 60 by
the Gardner Multi Angle Gloss Meter (Model GG-9095)
several times for each sample. Gloss was measured
around the circumference of the tumbler, at one-
third the way down from the top. The highest
rea~ing was 64 and the lowest reading was 50.
~5 In a comparison experiment, the identical
ingredients were employed except that no triethylene
glycol caprate-caprylate was used. The highest gloss
reading obtained was 20 and the lowest was 15. Also
the molding cycle had to be increased to 10/30
seconds injection over hold to get parts off the
mold. Thus, it is seen that component D is
necessary to obtain substantially higher gloss values.
