Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a polyester composition,
and in particular to an elastomer modified polyester composition.
In general, injection molding grades of polyesters
are not blow moldable. slow moldable or extrusion grade polyester
is expensive. Obviously, if blow moldable polyesters can be
rendered extrudable or blow moldable, a substantial cost saving
can be realized.
The object of the present invention is to meet the
above described need by providing a polyester composition including
a low or injecti.on molding grade of polyester which is modified
to be blow moldable.
Accordingly, the present invention relates to a blow
moldable composition comprising a homogeneous mixture of an
injection molding gxade polyester and sufficient elastomer to
reduce the viscosity of the injection molding grade polyester
to level at which the latter can be blow molded.
The following is a list of trade marks used in the
detailed description of the invention.
Hytrel is an E.I. duPont de Nemours (hereinafter referred
to simply as duPont) trade mark for a copolyester prepared
by transesterification using readily available starting materials
such as dimethyl terephthalate polytetramethylene ether glycol
and 1,4-butanediol. The polymers are normally synthesized
by conventional equilibrium melt condensation polymerization
in the presence of an ester interchange catalyst. The resulting
products are random block copolymers consisting of crystalline
1,4-butanediol hard segments and amorphous elastomeric poly-
alkylene ether terephthalate soft segments. Hytrel provides
excelIent resistance to non-polar materials such as oils and
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hydraulic fluids even at elevated temperatures, and is resistant
to most polar fluids such as acids, bases, amines and glycols
at room temperature. The resistance of Hytrel to hot moist
enviroments is also good. In general, Hytrel is resistant
to the same classes of chemicals and fluids as polyurethanes,
both ester and ether based. However, Hytrel has better high
temperature properties than polyurethanes. Hytrel polyester
elastomers do not contain an extractable plasticizer as do
flexible vinyls, certain grades of nylon and many rubber compounds.
Many fluids and chemi.cals will extract the plasticizer from
these materials, causing a significant increase in stiffness
and volume shrinkage. Hytrel has excellent flexibility at
room temperature and low temperatures, excellent flex crack
resistance, resistance to tear, abrasion and impact, and has
a service temperature of -50 C to 110C.
Lomod B0100 and B0200 are General Electric trade marks
for a polyester.
Admer L2100 is a Mitsui Petrochemical Industries ltd.
trade mark for a maleic anhydride modified polyolefin adhesive.
Surlyn 1705 is a duPont trade mark for an ionomer
based on zinc salts of ethylene/(meth) acrylic acid copolymers.
The zinc ions neutralize from 10 to 90% of the acid groups,
and the remaining unsaturated carboxylic acids can be either
mono or dicarboxylic acids such as acrylic, methacrylic (preferred),
ethacrylic, itaconic, maleic-fumaric acids, hydrogen maleate
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and methyl hydrogen fumarate. Surlyn provides thermal stability,
excellent abrasion and impact resistance. Most ionomers are
insoluble in common organic solvents at room temperature, and
resist a~tack from most mild acids and bases. Outstanding
low temperature flex and impact toughness are characteristic.
The brittleness temperature for the polymers is as low as -110C.
Finally, the change in modulus versus temeprature is relatively
small.
Elvax 265 is an E.I. duPont de Nemours trade mark
for an ethylene-vinyl acetate (EVA) thermoplastic copolymer
including from 5 - 50~ by weight vinyl acetate in an ethylene
chain. EVA copolymers are polymerized under high pressure
using reactors of the type used to make conventional low density
polyethylene to yield a highly branched, copolymer with acetoxy
groups positioned randomly along the carbon chain. The vinyl
acetate reduces the polymers crystallinity which increases
flexibility, and improves low temperature flexibility, impact
strength, weatherability, and oil and grease resistance.
Nordel 5892 is a du Pont trade mark for ethylenepropylene
diene( EPDM), which is a terpolymer elastomer produced in several
variations, the principle variant being the diene mentioned
above. Dicyclopentadiene, ethylidene norbornene and 1,4-hexadiene
are the types usually selected as the nonconjugated diene component.
The unsaturation remaining after the initial syntheses is utilized
in classical sulfur type vulcanization. Nordel hydrocarbon
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elastomers are extremely resistant to attack by ozone, oxygen
and weather. Moreover, properly prepared vulcanizates of Nordel
are outstanding in resistance to deterioration by heat, steam
and many chemicals.
Kraton G1650 is a Shell trade mark for styrene-ethylene-
butylene-styrene block copolymer of the A-s-A type, where A
represents polystyrene end blocks and s represents a polyolefin
rubber midblock. Since Kraton G rubbers have a unique olefin
rubber midblock, they are heat and shear stable at processing
temperatures as high as 500F. Finished articles formed of
Kraton G rubbers are highly resistant to ozone attack, oxidation
and degradation from exposure to sunlight. The elastomers provide
excellent resistance to water, acids and bases, and are flexible
at low temperatures.
Kraton G7610X is a Shell trade mark for an experimental
copolymer of the above-described type.
NDG 4167 is a duPont trade mark for a preblended com-
bination of Nordel (EPDM) and high density polyethylene having
outstanding low temperature toughness and high stiffness.
GEOLAST 703-40 is a Monsanto trade mark for a thermo-
plastic elastomer with superior oil resistance and excellent
heat aging.
Several compositions were produced in an effort to
convert high viscosity injection molding grade material to
a lower viscosity material for use in a wide range oE applications
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such as blow molding, extrusion and perhaps injection blow molding.
It has been found that the introduction of an elastomer into
the polyester lowers the melt flow of the material and subsequently
the viscosity. Several of the compositions were tested for
blow moldability by producing parts using conventional blow
molding techniques.
In general terms, the blow molding technique involves
the extrusion of a tubular parison into a mold, closing of the
mold, and blowing of air into the parison to conform the shape
thereof to that of the mold. The temperatures used are dependent
upon the combinations of materials in the parison, and a consideration
of the melt temperatures at lowest possible processing temperature
of the combinations. Some of the compositions were coextruded
into three layer articles by coextruding three thermoplastic
masses through a common extrusion nozzle, each mass being in
the form of a layer, whereby a three layer body is formed. The
three thermoplastic resins are fed from three separate hoppers,
the thickness of each layer varying in accordance with the rate
of revolution and dimensions of the three individual screws
leading from the hoppers. The thickness of each layer can range
from 2 - 98% of the total thickness of the coextrusion. All
of the compositions tested for extrusion and blow molding proved
to be quite successful.
Table 1 below provides three examples of compositions,
which were blow molded using the above described technique at
a melt temperature of 220C.
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TABLE 1
INGREDIENTS COMPOSITION
EX.l EX.2 EX.3
HYTREL 5556 40~ 40% 40%
NORDEL 5892 (EPDM) 40% 46%
NDG 4167 (EPDM) 40%
ELVAX 265 (EVA~ 20% 14% 20%
TEST RESULTS
Melt flow (g/lOmin) 1.64 1.03 3.98
Hardness (Shore D) 40 38 49
Specific gravity 1.010 1.003 1.100
Tensile Properties
Type: Inj. Moulded
Tensile strength (MPs) 15.7 13.5 11.0
Elongation, break (%) 480 400 475
Flexural Modulus (MPa) 46.3 43.7 67.9
In general, for a polymer to be blow moldable, the
polymer must have a melt flow in the range of 0.8 - 6g/lOmin
at the lower end of the polymers processing temperature range
(without unmelted material being extruded). Although the above
table provides a small sampling of compositions, which prove
to be blow moldable, it is readily apparent that it should
be possible to blow mold virtually any elastomer modified polyester,
2~ i.e. to convert a injection molding grade polyester to a b].ow
molding grade polyester by elastomeric modification thereof.
All of the compounds listed in Table 1 have similar
basic physical properties. With the use of elastomers, hardness
decreases so that any element produced with the compositions
has increased flexibility. Because of the low tensile flexural
modulus elongation and hardness values, the compositions could
be used for articles such as strut covers, dust shields and
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air ducts where flexibility is important. The use of EVA helps
maintain the excellent physical properties exhibited by the
base resin (polyester). The use of EPDM (Nordel 5892) results
in a low blow molding melt flow range, and the use of EPDM
(NDG 4167) results in a high blow molding melt flow range.
The low blow molding melt flow range usually provides a more
stable parison for use in the production of thick parts, while
the higher melt flow materials are often used for the production
of thin walled parts.
Table 2 lists a second set of compositions (Examples
4 to 7) of compositions produced in accordance with the present
invention.
TABLE 2
INGREDIENTS COMPOSITION
EX.4 EX.5EX.6 EX.7
15 HYTREL 4774 60% 60~ 60% 60~
NORDEL 58g2 (EPDM) 15~ 10% 14% 20%
ELVAX 265 (EVA) 25% 30% 20% 20
CaCO 6%
TEST RESULTS
Melt flow (g/lOmin) 6.77 8.54 6.10 5.27
Hardness (Shore D) 40 41 42-43 41
Specific gravity 1.070 1.0721.110 1.063
Tensile Properties
Type: Inj. Moulded
Tensile strength (MPa) 16.0 13.6 13.4 13.5
Elongation,break(%) 430 388 310 363
Flexural Modulus (MPa) 50.5 51.0 57.3 50.0
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All of the compositions listed in Table 2 have similar
basic physical properties. The hardness of the basic polyester
is reduced providing increased flexibility. The high values
for melt flow means that the compositions can be used for the
production of thin-walled elements. The use of ethylene-vinyl
acetate helps to maintain the excellent physical properties
of the base resin (polyester).
A third set of three compositions having the same
constituents as each other is listed in Table 3.
TABLE 3
INGREDIENTS COMPOSITION
EX.8 EX.9 EX.10
HYTREL 5556 48% 46% 40~
NORDEL 5892 (EPDM)47% 44% 40%
SURLYN 1705 5% 10% 20%
TEST RESULTS
Melt flow (g/lOmin)1.04 1.13 1.18
Hardness (Shore D)42-43 45 44-46
Specific gravity1.018 1.020 0.996
Tensile Properties
Type: Inj. Moulded
Tensile strength (MPa) 13.6 15.1 17.5
Elongation, break (%) 405 430 445
Flexural Modulus (MPa) 56.3 60.7 79.8
Except for the one relating to the melt flow values,
the comments with respect to Examples 4 to 7 are also applicable
to Examples 8 to 10. The low melt flow values of the composition
of Examples 8 to 10 provide a more stable parison for use in
the production of thicker parts.
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Table 4 provides details of two examples oE modified
polyesters which have similar physical properties, including
low melt flows, reduced hardness, and good tensile, elongation
and flexural modulus values. The dramatically reduced melt
flow results in slow extrusion of material and minimum parison
stretching, enabling the production of thick walled components.
The combination of low melt flow and low hardness means that
the compositions can be used in the production of components
which are expected to have a long life span (increased flexibility
due to decreased hardness) and durability (thicker parts because
of low melt flow). The good tensile, elongation and flexural
modulus properties make the compositions useful for the production
of constant velocity, stearing gear, suspension struts and
shock absorber boots or covers.
TABLE 4
INGREDIENTS COMPOSITION
EX.ll EX.12
HYTREL 5556 40% 40~
KRATON 1650 40% 46%
SURLYN 1705 20% 14%
TEST RES LTS
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Melt flow (g/lOmin) 0.94 0.98
Hardness (Shore D) 49-50 43
Specific gravity 1.030 1.012
Tensile Properties
Type: Inj. Moulded
Tensile strength (MPa)22.5 21.0
Elongation, break (%) 530 550
Flexural Modulus (MPa)92.3 73.0
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The compositions listed in Table 5 also have similar
physical properties.
TABLE 5
INGREDIENTS COMPOSITION
EX.13 EX.14 EX.15
HYTREL 5556 50~ 50%
HYTREL 4774 60~
ELVAX 265 (EVA) 22% 30% 30%
KRATON G7610X 28~ 20~ 10%
TEST RESULTS
Melt flow (g/lOmin)17.5 7.16 16.33
Hardness (Shore D) 35 40 40
Specific gravity 1.075 1.070 1.085
Tensile Properties
Type: Inj. Moulded
Tensile strength (MPa) 11.0 11.2 14.9
Elongation,break (%) 310 380 410
Flexural Modulus (MPa) 60.9 63.7 49.4
The high melt flow, which is out of blow molding range
means that the compositions can be used for injection blow
molding. Reduced hardness leads to increased flexibility.
Tables 6 and 7 list additional compositions which
have similar basic physical properties, including melt flows
at the high end of the blow molding melt flow range enabling
the production of thin-walled elements. Because of the low
tensile and elongation (especially tensile) properties, the
compositions are best suited for the production of flexible
elements, e.g. dust covers and air ducts. For such elements,
the tensile and elongation values need not be high, and the
material must be sufficiently soft to flex under extreme temperature
conditions.
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TABLE 6
INGREDIENTS COMPOSITION
EX.16 EX.17
LOMOD B0100 40%
LOMOD B0200 40%
NORDEL 5892 (EPDM) 40% 40%
ELVAX 265 (EVA) 20~ 20%
TEST RESULTS
Melt flow (g/lOmin) 4.28 4.05
Hardness (Shore D) 29 35
Specific gravity 0.093 1.000
Tensile Properties
Type: Inj. Moulded
Tensile strength (MPa) 6.7 10.4
Elonyation, break (%) 370 400
Flexural Modulus (MPa) 26.3 41.8
TABLE 7
INGREDI_NTS COMPOSITION
EX.18
HYTREL 5556 40~
GEOLAST 703-40 40%
ELVAX 265 (EVA) 20%
TEST RESULTS
Melt flow (g/lOmin) 0.32
20 Hardness 31
Specific gravity 0.956
Tensile Properties
Type: Inj. Moulded
Tensile strength (MPa) 9.1
Elongation, break (~) 200
Flexural Modulus (MPa) 28.7
For comparison purposes, the characteristics of the
basic polyesters and elastomers used in the above described
compositions are listed in Table 8.
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From the foregoing, it will be appreciated that
preferred polyester compositions of the present invention
include the following:
(i) a homogeneous mixture of from 40 to 60% by
weight of an injection molding grade copolyester dimethyl
terephthalate polytetramethylene ether glycol and 1,4-
butanediol, from 10 to 50~ by weight of ethylene propylene
diene terpolymer; and from 10 to 30% by weight of ethylene-
vinyl acetate thermoplastic copolymer;
(ii) the composition of (i) above including 0 to 6%
by weight of calcium carbonate;
(iii) a homogeneous mixture of from 40 to ~0% by
weight of an injection molding grade copolyester of dimethyl
terephthalate polytetramethylene ether glycol and 1,4-
butanediol, from 40 to 50% by weight of ethylenepropylene
diene terpolymer and from 5 to 20% by weight of an ionomer
based on zinc salts of ethylene/(meth) acrylic acid
copolymers;
(iv) the composition of (iii) above containing
approximately 40% by weight of the copolyester, from 40 to 50%
by weight of the terpolymer and from 10 to 20% by weight of
the ionomer;
(v) a homogeneous mixture of from 50 to 60~ by
weight of an in~ection molding grade copolyester of dimethyl
terephthalate polytetramethylene ether glycol and 1,4-
butanediol, from 20 to 30% by weight ethylene-vinyl acetate ~.
copolymer, and from 10 to 30% by weight styrene-ethylene-
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butylene-styrene block copolymer of the A-B-A type, where A
represents polystyrene end blocks and B represents a
polyolefin rubber midblock;
(vi) a homogeneous mixture of approximately 40% by
weight of an injection molding grade polyester, approximately
40% by weight of ethylene-propylene diene terpolymer and
approximately 20% by weight of ethylene-vinyl acetate
thermoplastic copolymer; and
(vii) a homogeneous mixture of approximately 40% by
weight of an injection molding grade copolyester of dimethyl
terephthalate polytetramethylene ether glycol and 1,4-
butanediol; approximately 40% by weight of a thermoplastic
elastomer and approximately 20% by weight of ethylene-vinyl
acetate thermoplastic copolymer.
Obviously, the ingredients of the various compositions must be
compatible.
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