U.S. patent application number 14/715874 was filed with the patent office on 2017-03-09 for heat aging resistant ethylene vinyl acetate copolymer composition and process for its production.
The applicant listed for this patent is E. I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to Steven R. Oriani.
Application Number | 20170066916 14/715874 |
Document ID | / |
Family ID | 49881003 |
Filed Date | 2017-03-09 |
United States Patent
Application |
20170066916 |
Kind Code |
A9 |
Oriani; Steven R. |
March 9, 2017 |
HEAT AGING RESISTANT ETHYLENE VINYL ACETATE COPOLYMER COMPOSITION
AND PROCESS FOR ITS PRODUCTION
Abstract
Heat resistant ethylene vinyl acetate copolymer compositions
comprising a blend of ethylene vinyl acetate copolymer, peroxide
curable polyacrylate elastomer, and polyamide are described. When
crosslinked with a peroxide curative, the ethylene vinyl acetate
copolymer compositions exhibit enhanced resistance to heat aging
compared to conventional ethylene vinyl acetate elastomer
compositions.
Inventors: |
Oriani; Steven R.;
(Landenberg, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
E. I. DU PONT DE NEMOURS AND COMPANY |
Wilmington |
DE |
US |
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|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20150247030 A1 |
September 3, 2015 |
|
|
Family ID: |
49881003 |
Appl. No.: |
14/715874 |
Filed: |
May 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14085019 |
Nov 20, 2013 |
9062193 |
|
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14715874 |
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61733081 |
Dec 4, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08L 31/04 20130101;
C08L 23/0853 20130101; Y10T 428/139 20150115; C08L 2205/02
20130101; C08L 31/04 20130101; C08L 23/0853 20130101; C08L 23/0853
20130101; C08L 77/00 20130101; C08L 77/00 20130101; C08L 31/04
20130101; C08L 23/0869 20130101; C08L 77/00 20130101; C08L 33/08
20130101; C08L 23/0869 20130101; C08L 33/08 20130101; C08L 2312/00
20130101; C08L 77/00 20130101 |
International
Class: |
C08L 31/04 20060101
C08L031/04 |
Claims
1. A blend composition of ethylene vinyl acetate copolymer,
peroxide curable polyacrylate elastomer, and polyamide, said blend
composition consisting essentially of (A) from about 10 wt % to
about 98 wt % of an ethylene vinyl acetate copolymer component said
ethylene copolymer component comprising one or more ethylene vinyl
acetate copolymers of at least 40% by weight copolymerized vinyl
acetate monomer units; and (B) from about 1 wt % to about 50 wt %
of a one or more of peroxide curable polyacrylate elastomer
component comprising copolymerized units of alkyl acrylate, and at
least 0.03 mol % of an amine or acid reactive monomer selected from
the group consisting of unsaturated carboxylic acids, anhydrides of
unsaturated carboxylic acids, and unsaturated epoxides; and (C)
from about 1 wt % to about 60 wt % of a polyamide component
comprising one or more polyamides having a melting peak temperature
of at least 160.degree. C., wherein said blend composition has a
Mooney viscosity (ML 1+4, 100.degree. C.) determined according to
ASTM D1646 of 5 to 200; and wherein each of the weight percentages
of the ethylene vinyl acetate copolymer, polyacrylate elastomer,
and polyamide components are based on the combined weight of the
ethylene vinyl acetate copolymers, polyacrylate elastomers, and
polyamides in the blend composition.
2. (canceled)
3. The composition of claim 1 wherein the polyamide is nylon 6 or
nylon 6/6.
4. The composition of claim 1 wherein the polyamide has an inherent
viscosity greater than 0.9 dL/g.
5. The composition of claim 1 wherein the polyamide is present in
the form of particles having an aspect ratio of less than 10 to
1.
6. (canceled)
7. The composition of claim 1 wherein the polyacrylate elastomer
comprises at least 50 mol % ethylene.
8. The composition of claim 1, said composition comprising from
about 50 wt % to about 90 wt % of the ethyl vinyl acetate copolymer
component, 5 wt % to 20 wt % of the polyacrylate elastomer
component, and 5 wt % to 30 wt % of the polyamide component.
9. The composition of claim 1, wherein upon addition of a curative
said composition exhibits an increase in torque MH-ML of at least
2.5 dN-m as measured per ASTM D5289-07a operating at 0.5.degree.
arc, and test conditions of 177.degree. C. for 24 minutes.
10. A process for production of the composition of claim 1, said
process comprising the steps (A) providing (i); (ii); and (iii);
(B) mixing (i), (ii), and (iii) together at a temperature above the
melting peak temperatures of the one or more polyamides to disperse
the one or more polyamides within the blend of one or more ethylene
vinyl acetate copolymers and polyacrylate elastomers, such that one
or more ethylene vinyl acetate copolymer comprise 10 wt % to 98 wt
%, the one or more peroxide curable polyacylate elastomers comprise
1 wt % to 50 wt %, and the one or more polyamides comprise 1 wt %
to 60 wt % of the blend based on the total weight of ethylene vinyl
acetate copolymers, polyacrylate elastomers, and polyamides
present, to produce a mixture; and (C) cooling the mixture to a
temperature below the crystallization peak temperatures of the one
or more polyamides, thereby forming a blend composition having a
Mooney viscosity (ML 1+4, 100.degree. C.) of 5 to 200, as
determined according to ASTM D1646.
11. A process for preparing the composition of claim 1, said
process comprising the steps: (A) providing: (i) one or more
curable polyacrylate elastomers comprising copolymerized units of
alkyl acrylate, and at least 0.03 mol % of an amine or acid
reactive monomer selected from the group consisting of unsaturated
carboxylic acids, anhydrides of unsaturated carboxylic acids, and
unsaturated epoxides; and (ii) one or more polyamides having a
melting peak temperature of at least 160.degree. C.; and (B) mixing
the one or more curable polyacrylate elastomers and one or more
polyamides at temperature above the melting peak temperatures of
the one or more polyamides to disperse the one or more polyamides
within the one or more polyacrylate elastomers; to provide a
mixture and (C) cooling the mixture of part B to a temperature
below the peak crystallization temperatures of the one or more
polyamides to produce an intermediate blend composition having a
Mooney viscosity (ML 1+4, 100.degree. C.) less than 200 as
determined according to ASTM D1646; and (D) providing one or more
ethylene vinyl acetate copolymers comprising at least 40% by weight
vinyl acetate monomer; and (E) mixing the intermediate blend
composition of step (C) with the one or more ethylene vinyl acetate
copolymers of step (D) to provide a blend composition comprising 10
wt % to 98 wt % ethylene vinyl acetate copolymer, 1 wt % to 50 wt %
curable polyacylate elastomer, and 1 wt % to 60 wt % polyamide,
each being based on the combined weight of the ethylene vinyl
acetate copolymers, polyacrylate elastomers, and polyamides in the
blend composition.
12. The process of claim 10, wherein said blend composition
comprises 50 wt % to 90 wt % of the ethyl vinyl acetate copolymer
component; 5 wt % to 20 wt % of the polyacrylate elastomer
component; and 5 wt % to 30 wt % of the polyamide component
13. The process of claim 10 wherein the polyamide is nylon 6 or
nylon 6/6.
14. The process of claim 10 wherein the polyamide has a melting
peak temperature greater than 200.degree. C. and less than
270.degree. C.
15. The process of claim 10, said process further comprising,
adding one or more antioxidant in an amount of from 0.5 to 5
phr.
16. The process of claim 10, wherein upon addition of a curative
the composition has a cure response MH-ML of at least 2.5 dN-m as
determined according to ASTM D5289-07a, operating at 0.5.degree.
arc and test conditions of 177.degree. C. for 24 minutes.
17. (canceled)
18. (canceled)
19. The process of claim 10 for forming an article selected from
the group consisting of wire jacketing, cable jacketing, molded or
extruded tubing or hose, or molded boots, belts, grommets, seals
and gaskets, said process further comprising the step of forming
the article.
20. An article formed by the process of claim 19.
21. The blend composition of claim 1, wherein the polyamide has a
melting peak temperature greater than 200.degree. C. and less than
270.degree. C.
22. The blend composition of claim 1, further comprising one or
more antioxidants in an amount of from 0.5 to 5 phr.
23. An article comprising the blend composition of claim 1.
24. The process of claim 11 for forming an article selected from
the group consisting of wire jacketing, cable jacketing, molded or
extruded tubing or hose, or molded boots, belts, grommets, seals
and gaskets, said process further comprising the step of forming
the article.
25. An article formed by the process of claim 24.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Patent
Application No. 61/733,081, filed on Dec. 4, 2012, which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention is directed to a peroxide curable
ethylene vinyl acetate copolymer composition, a process for
producing a thermoset ethylene vinyl acetate elastomer composition
having enhanced heat aging performance, and to articles formed from
the thermoset elastomer composition.
BACKGROUND OF THE INVENTION
[0003] Oil resistant ethylene vinyl acetate copolymers are
well-known synthetic materials formed by copolymerizing ethylene
and at least 40 wt % vinyl acetate. The ethylene vinyl acetate
copolymers may contain only copolymerized ethylene units and vinyl
acetate units or the copolymers may comprise additional
copolymerized monomers, for example esters of unsaturated
carboxylic acids, such as methyl acrylate or butyl acrylate. The
raw polymers, also known as gums or gum rubbers, may be cured by
free radical generators such as peroxides, azides, or by use of
high energy radiation. Examples of commercially available ethylene
vinyl acetate copolymers include Elvax.RTM. resin products from E.
I. du Pont de Nemours and Company and Levapren.RTM. products from
Lanxess Corp.
[0004] In view of their low cost compared to other oil resistant
elastomers, ethylene vinyl acetate copolymers are widely used in
the manufacture of wire and cable jacketing as well as in the
production of automotive parts such as hoses and seals.
[0005] Resistance to heat aging is a particularly desirable
property in rubber parts that are used in under the hood automotive
applications, e.g. hoses, gaskets, and seals. Because such parts
may be exposed to temperatures in excess of 160.degree. C. for
periods of time, including up to several hours on a regular basis,
degradation of physical properties through oxidative embrittlement
can occur. In ethylene vinyl acetate rubbers, this often results in
a reduction in extensibility and an increase in hardness and
modulus of the rubber article. Such effects are disclosed for
example in published disclosure EP1081188. Methods to enhance hot
air or heat aging resistance of ethylene vinyl acetate rubbers have
involved attempts to identify more effective antioxidant systems.
However, there is still a need to improve the high temperature
resistance of these copolymers.
[0006] It has now been found that it is possible to produce cured
ethylene vinyl acetate copolymer compositions of high hardness,
strength, and elasticity that exhibit excellent heat aging
resistance by dispersing particles of polyamide in a blend of
ethylene vinyl acetate copolymer and a peroxide curable
polyacrylate elastomer. The peroxide curable polyacrylate elastomer
comprises copolymerized units of alkyl acrylate, and an amine or
acid reactive monomer selected from the group consisting of
unsaturated carboxylic acids, anhydrides of unsaturated carboxylic
acids, and unsaturated epoxides. The amine or acid reactive monomer
allows the polyacrylate elastomer to compatibilize the polyamide
and the ethylene vinyl acetate copolymer, thereby improving
physical properties such as strength and elongation to break.
Polyacrylate elastomers comprising only polymerized units of
acrylate monomers generally exhibit a poor cure response to
peroxide. This is because contiguous polymerized units of acrylate
monomers may lead to significant chain scission in the presence of
free radicals, so the net increase in crosslink density is low. As
defined herein, a peroxide curable acrylate elastomer must either
comprise at least 0.5 mol % of an unsaturated pendant group which
functions as a peroxide cure site monomer, or at least 50 mol %
copolymerized units of ethylene. Copolymerized ethylene monomer
units act as spacers between polymerized acrylate monomer units to
limit .beta.-scission.
[0007] A number of ethylene vinyl acetate copolymer-polyamide blend
compositions have been disclosed in the prior art. For example, it
is known to add uncured ethylene vinyl acetate copolymers (i.e.
gums) to polyamides to form toughened thermoplastic compositions.
U.S. Pat. No. 4,174,358 exemplifies the use of uncured ethylene
vinyl acetate copolymers at levels up to 20 wt % as toughening
additives for polyamides. A compatibilizer such as a maleic
anhydride grafted ethylene vinyl acetate copolymer may also be
included in the ethylene vinyl acetate copolymer-polyamide blend,
as disclosed in J. Polymer Science: Part B: Polymer Physics, Vol.
47, 877-887 (2009). The polyamide component in these compositions
comprises the continuous polymer matrix and the uncured ethylene
vinyl acetate copolymer is a minor additive. When polyamide
comprises the continuous phase in the blend the composition
generally cannot be processed at temperatures below the melting
temperature of the polyamide, or can be processed only with great
difficulty at such temperatures.
[0008] It is also known to form thermoplastic elastomer
compositions comprising ethylene vinyl acetate copolymer and
polyamide. For example, U.S. Pat. No. 5,948,503 discloses
compositions comprising an uncured elastic polymer, a polyamide in
the form of fine fibers, and a polyolefin having a melting
temperature from 80.degree. C. to 250.degree. C. In addition,
certain vulcanized compositions are disclosed therein.
[0009] Thermoplastic vulcanizates comprising ethylene vinyl acetate
copolymer and polyamide, in which the ethylene vinyl acetate
copolymer is dynamically crosslinked (i.e., crosslinked under shear
mixing to create a dispersion of elastomer particles in a
continuous phase of another polymer) are also known. Such
compositions are disclosed in EP2098566, and may be improved by the
use of a coupling agent such as maleic anhydride grafted ethylene
vinyl acetate copolymer as disclosed in U.S. Pat. No.
7,691,943.
[0010] U.S. Pat. No. 7,608,216 and U.S. Patent Application
Publication 2006/0100368 disclose compositions prepared by admixing
an uncured elastomer, for example an ethylene vinyl acetate
copolymer, with a thermoplastic polymer or another uncured (gum)
elastomer. Techniques such as fractional curing, partial dynamic
vulcanization, or the use of high performance reinforcing fillers
are disclosed to increase the green strength of the uncured or
partially cured compound. The admixed compositions may be
subsequently crosslinked with a curing agent for the elastomer
component.
[0011] A number of acrylate rubber-polyamide blend compositions
have been disclosed in the prior art. For example, it is known to
add uncured acrylate elastomers (i.e. gums) to polyamides to form
toughened thermoplastic compositions. U.S. Pat. No. 4,174,358
discloses the use of various uncured acrylate elastomers or
ethylene based thermoplastic resins comprising up to 95 mole
percent ethylene, such as ethylene/methyl acrylate/monoethyl
maleate/ethylene dimethacrylate tetrapolymers or ionomers of
ethylene/methyl acrylate/monoethyl maleate terpolymers, as
toughening additives for polyamides. The polyamide component in
such compositions comprises the continuous polymer matrix and the
uncured acrylate elastomer is a minor additive.
[0012] U.S. Pat. No. 5,070,145 discloses thermoplastic blends of
polyamides with ethylene copolymers comprising copolymerized units
of dicarboxylic acid anhydrides and optionally alkyl
(meth)acrylates. U.S. Pat. No. 7,544,757 discloses that blends of
ethylene-alkyl acrylate polymers may be blended at levels up to 30%
by weight in polyamide to produce toughened polyamide
compositions.
[0013] Blends of uncured ethylene acrylic elastomers, polyamides
and powdered metals are disclosed in Japanese Patent
2001-1191387.
[0014] U.S. Pat. No. 3,965,055 discloses vulcanizates prepared from
a blend of rubber and 2 wt % to 10 wt % of a crystalline
fiber-forming thermoplastic, wherein the thermoplastic is dispersed
in the rubber component in particles not greater than 0.5 micron in
cross section with a length to diameter ratio greater than 2. The
high aspect ratio of the thermoplastic particles enables
pressureless curing without void formation.
[0015] Japanese Patent Application Publication H10-251452 discloses
a dispersion of polyamide particles in a hydrogenated nitrile
rubber (HNBR) matrix wherein a compatibilizing polymer that may be
an ethylene copolymer or an acrylate elastomer is also present. The
compatibilizing polymer is ionically crosslinked by metal oxide
during mixing with the HNBR and polyamide which prevents the
acrylate elastomer from forming a continuous phase. The HNBR
component is then cured with a peroxide or with sulfur.
[0016] U.S. Pat. No. 6,133,375 discloses blends of functionalized
rubbers with thermoplastics in which the thermoplastic component is
dispersed in the rubber phase. Following addition of a curative for
the rubber, the composition is crosslinked to produce a vulcanized
article. Examples of functionalized rubbers which are disclosed
include acrylic rubbers such as nitrile-butadiene rubber,
hydrogenated nitrile-butadiene rubber, epichlorohydrin rubber, and
rubbers on which reactive groups have been grafted, such as
carboxylated nitrile-butadiene rubber. Thermoplastics that are
disclosed include polyetherester block copolymers, polyurethanes,
polyamides, polyamide ether or ester block copolymers, and mixtures
of polyamides and polyolefins. In the latter case, ethylene-alkyl
acrylate copolymers comprising grafted or co-polymerized maleic
anhydride, glycidyl methacrylate, or (meth)acrylic acid units may
be used to compatibilize the polyamide-polyolefin blend.
[0017] U.S. Pat. No. 4,694,042 discloses an elastomeric
thermoplastic molding material containing a coherent phase of
polyamide and crosslinked elastomeric polyacrylate core shell
polymers.
[0018] U.S. Pat. No. 4,275,180 discloses blends of thermoplastic
polymers with acrylate rubbers, the blends being crosslinked or
crosslinkable by radiation or peroxide. Fillers may be used in
amounts of up to 40% by weight of the composition.
[0019] U.S. Patent Application 2006/0004147 discloses blends of
elastomers, for example acrylate elastomers, with thermoplastic
polymers such as polyamides, in which both polymers are coupled and
crosslinked by free radicals, e.g., by electron beam radiation. The
compositions may comprise a continuous phase of thermoplastic with
dispersed crosslinked elastomer particles, or a continuous
crosslinked elastomer phase with dispersed crosslinked particles of
what was initially thermoplastic.
[0020] U.S. Pat. No. 8,142,316 discloses cured blends of elastomers
and thermoplastics for use in power transmission belts. The
elastomer may be an ethylene acrylic elastomer, and the
thermoplastic may be a polyamide. Free radical curatives are
disclosed as curing agents.
[0021] It is also known to form dynamically cured thermoplastic
compositions having a polyamide matrix continuous phase and a cured
acrylate rubber phase that is present in the form of discrete
particles. Thermoplastic elastomeric compositions comprising blends
of polyamide and ionically crosslinked ethylene acrylic rubber are
disclosed in U.S. Pat. No. 4,310,638. U.S. Pat. Nos. 5,591,798 and
5,777,033 disclose thermoplastic elastomer compositions comprising
a blend of polyamide resins and covalently-crosslinked acrylate
rubber.
[0022] Polyacrylate rubber-polyamide blend compositions disclosed
in Zeon Chemicals L. P., HyTemp.RTM. Technical Manual, Rev. 2009-1,
p. 46 (2009) are said to improve impact strength of plastics. They
may also be used to produce thermoplastic elastomers.
[0023] It has now been found that when a dispersion of polyamide
particles is present in a blend comprising ethylene vinyl acetate
copolymer and peroxide curable polyacrylate elastomer, the
resultant compositions, when cured by a free radical generator,
exhibit enhanced resistance to physical property loss during heat
aging. In addition, such compositions maintain excellent tensile
strength, modulus, hardness, and elastic properties such as
compression set and elongation at break that characterize
conventional ethylene vinyl acetate compositions lacking
polyacrylate elastomer and polyamide.
SUMMARY OF THE INVENTION
[0024] Disclosed herein is a blend composition of ethylene vinyl
acetate copolymer, peroxide curable polyacrylate elastomer, and
polyamide, said blend composition consisting essentially of (A) 10
wt % to 98 wt % of an ethylene vinyl acetate copolymer component
said ethylene copolymer component comprising one or more ethylene
vinyl acetate copolymers of at least 40% by weight copolymerized
vinyl acetate monomer units; and (B) 1 wt % to 50 wt % of a one or
more of peroxide curable polyacrylate elastomer component
comprising copolymerized units of alkyl acrylate, and at least 0.03
mol % of an amine or acid reactive monomer selected from the group
consisting of unsaturated carboxylic acids, anhydrides of
unsaturated carboxylic acids, and unsaturated epoxides; and (C) 1
wt % to 60 wt % of a polyamide component comprising one or more
polyamides having a melting peak temperature of at least
160.degree. C., wherein said blend composition has a Mooney
viscosity (ML 1+4, 100.degree. C.) determined according to ASTM
D1646 of 5 to 200; and wherein each of the weight percentages of
the ethylene vinyl acetate copolymer, polyacrylate elastomer, and
polyamide components are based on the combined weight of the
ethylene vinyl acetate copolymers, polyacrylate elastomers, and
polyamides in the blend composition.
[0025] Also disclosed herein is a curable blend composition
comprising (A) a blend composition of ethylene vinyl acetate
copolymer, peroxide curable polyacrylate elastomer, and polyamide
comprising: (i) 10 wt % to 98 wt % of an ethylene vinyl acetate
copolymer component comprising one or more ethylene vinyl acetate
copolymers wherein the ethylene vinyl acetate copolymer comprises
at least 40% by weight copolymerized vinyl acetate units; and (ii)
1 wt % to 50 wt % of one or more of a peroxide curable polyacrylate
elastomer comprising copolymerized units of alkyl acrylate, and at
least 0.03 mol % of an amine or acid reactive monomer selected from
the group consisting of unsaturated carboxylic acids, anhydrides of
unsaturated carboxylic acids, and unsaturated epoxides; and (iii) 1
wt % to 60 wt % of a polyamide component comprising one or more
polyamides having a melting peak temperature of at least
160.degree. C., wherein the blend composition (A) has a Mooney
viscosity (ML 1+4, 100.degree. C.) determined according to ASTM
D1646 of 5 to 200; and wherein the weight percentages of each of
the ethylene vinyl acetate copolymer, polyacrylate elastomer, and
polyamide components are based on the combined weight of the
components of the blend; and
[0026] B a curative.
[0027] Also disclosed herein is a process for production of a
curable blend composition comprising ethylene vinyl acetate
copolymer, peroxide curable polyacrylate elastomer, polyamide, and
peroxide curative comprising the steps (A) providing: (i) one or
more ethylene vinyl acetate copolymers comprising at least 40% by
weight vinyl acetate monomer; (ii) one or more peroxide curable
polyacrylate elastomers comprising copolymerized units of alkyl
acrylate, and at least 0.03 mol % of an amine or acid reactive
monomer selected from the group consisting of unsaturated
carboxylic acids, anhydrides of unsaturated carboxylic acids, and
unsaturated epoxides; and (iii) one or more polyamides having a
melting peak temperature of at least 160.degree. C.; (B) mixing
A(i), A(ii), and A(iii) at a temperature above the melting peak
temperatures of the one or more polyamides to disperse the one or
more polyamides within the blend of one or more ethylene vinyl
acetate copolymers and polyacrylate elastomers, such that one or
more ethylene vinyl acetate copolymer comprise 10 wt % to 98 wt %,
the one or more peroxide curable polyacylate elastomers comprise 1
wt % to 50 wt %, and the one or more polyamides comprise 1 wt % to
60 wt % of the blend based on the total weight of ethylene vinyl
acetate copolymers, polyacrylate elastomers, and polyamides present
and; (C) cooling the blend composition to a temperature below the
crystallization peak temperatures of the one or more polyamides,
thereby forming a blend composition having a Mooney viscosity (ML
1+4, 100.degree. C.) of 5 to 200, as determined according to ASTM
D1646; and (D) adding a peroxide curative to the blend of part C at
a temperature less than 160.degree. C.
[0028] A further disclosure herein is a process for preparing a
curable blend composition comprising polyacrylate elastomer,
polyamide, ethylene vinyl acetate copolymer, and peroxide curative,
said process comprising the steps: (A) providing (i) one or more
peroxide curable polyacrylate elastomers comprising copolymerized
units of alkyl acrylate, and at least 0.03 mol % of an amine or
acid reactive monomer selected from the group consisting of
unsaturated carboxylic acids, anhydrides of unsaturated carboxylic
acids, and unsaturated epoxides; and (ii) one or more polyamides
having a melting peak temperature of at least 160.degree. C.; and
(B) mixing the one or more peroxide curable polyacrylate elastomers
and one or more polyamides at temperature above the melting peak
temperatures of the one or more polyamides to disperse the one or
more polyamides within the one or more polyacrylate elastomers; (C)
cooling the mixture of part B to a temperature below the peak
crystallization temperatures of the one or more polyamides to
produce an intermediate blend composition having a Mooney viscosity
(ML 1+4, 100.degree. C.) less than 200 as determined according to
ASTM D1646; (D) providing one or more ethylene vinyl acetate
copolymers comprising at least 40% by weight vinyl acetate monomer;
and (E) mixing the intermediate blend composition of step (C) with
the one or more ethylene vinyl acetate copolymers of step (D) to
provide the blend composition, wherein said blend composition
comprises 10 wt % to 98 wt % ethylene vinyl acetate copolymer, 1 wt
% to 50 wt % peroxide curable polyacylate elastomer, and 1 wt % to
60 wt % polyamide, each being based on the combined weight of the
ethylene vinyl acetate copolymers, polyacrylate elastomers, and
polyamides in the blend composition, and wherein said blend
composition having a Mooney viscosity (ML 1+4, 100.degree. C.) of
5-200, as determined according to ASTM D1646; and (E) and adding a
peroxide curative to the blend of part D at a temperature less than
160.degree. C.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention is directed to compositions comprising
a blend of ethylene vinyl acetate copolymer, peroxide curable
polyacrylate elastomer, and polyamide that, when cured with a free
radical source such as a peroxide curative system, exhibit enhanced
resistance to physical property loss during heat aging. The
invention is also directed to compositions consisting essentially
of blends of ethylene vinyl acetate copolymer, peroxide curable
polyacrylate elastomer, and polyamide, and to curable compositions
comprising ethylene vinyl acetate copolymer, peroxide curable
polyacrylate elastomer, polyamide, and peroxide curative. The
invention is also directed to curable blend compositions
additionally comprising peroxide curative, and to a process to a
process for preparation of cured articles from the heat resistant
ethylene vinyl acetate copolymer compositions.
[0030] Disclosed herein are compositions wherein polyamide
particles are dispersed in blends of ethylene vinyl acetate
copolymers, (also known as EVM rubbers) and peroxide curable
polyacrylate elastomers. The resultant compositions, when cured,
exhibit surprising improvements in physical properties. That is,
the curing process, which is also commonly referred to as
crosslinking or vulcanization, converts the blend of ethylene vinyl
acetate copolymer, polyacrylate elastomer, and polyamide to an
elastomer composition that exhibits enhanced heat aging resistance
compared to ethylene vinyl acetate elastomer compositions lacking
both the polyacrylate elastomer and polyamide.
[0031] Another disclosure herein is a blend composition of ethylene
vinyl acetate copolymer, peroxide curable polyacrylate elastomer,
and polyamide, said blend composition consisting essentially of:
(A) 10 wt % to 98 wt % of an ethylene vinyl acetate copolymer
component, said ethylene copolymer component comprising one or more
ethylene vinyl acetate copolymers of at least 40% by weight
copolymerized vinyl acetate monomer units; and (B) 1 wt % to 50 wt
% of a one or more of a peroxide curable polyacrylate elastomer
component comprising copolymerized units of alkyl acrylate and at
least 0.03 mol % of an amine or acid reactive monomer selected from
the group consisting of unsaturated carboxylic acids, anhydrides of
unsaturated carboxylic acids, and unsaturated epoxides; and (C) 1
wt % to 60 wt % of a polyamide component comprising one or more
polyamides having a melting peak temperature of at least
160.degree. C., wherein said blend composition has a Mooney
viscosity (ML 1+4, 100.degree. C.) determined according to ASTM
D1646 of 5 to 200; and wherein each of the weight percentages of
the ethylene vinyl acetate copolymer, polyacrylate elastomer, and
polyamide components are based on the combined weight of the
ethylene vinyl acetate copolymers, polyacrylate elastomers, and
polyamides in the blend composition.
[0032] One embodiment of the invention is a curable ethylene vinyl
acetate copolymer blend composition that comprises and a curative,
preferably a peroxide curative. The blend composition is
characterized by having a Mooney viscosity of 5 to 200 as
determined in accordance with ASTM D1646, ML 1+4, 100.degree.
C.
[0033] The blend composition comprises, or in some embodiments
consists essentially of, three polymer components: an ethylene
vinyl acetate copolymer component, a polyacrylate elastomer
component, and a polyamide component, and when combined with
peroxide curative to form a curable composition is referred to
herein as a heat resistant ethylene vinyl acetate copolymer
composition. The ethylene vinyl acetate copolymer component of the
blend comprises one or more ethylene vinyl acetate copolymers, each
comprising at least 40 wt % vinyl acetate copolymerized units.
[0034] As used herein, the term "consisting essentially" means with
respect to the blend composition that no more than 30 parts of a
polyolefin having a melting peak temperature greater than
80.degree. C. is present per hundred parts by weight based on the
weight of the sum of the ethylene vinyl acetate copolymer component
and the polyacrylate elastomer component. When more than 30 parts
by weight of such high melting point polyolefin is present in the
blend composition, the blend composition can be difficult to
process into a curable composition, and if successfully processed,
it may have poor elasticity.
[0035] The ethylene vinyl acetate copolymers useful in the practice
of the invention described herein comprise copolymerized units of
ethylene and vinyl acetate comonomers. Other comonomers may
optionally be present, including alkyl esters or alkoxyalkyl esters
of propenoic acid, carbon monoxide, alpha-olefins such as propene,
1-butene, 1-hexene, and the like, or comonomers that provide
epoxide or acid functionality in the ethylene vinyl acetate
polymer, for example. glycidyl methacrylate, maleic anhydride and
its half esters, or (meth)acrylic acid.
[0036] The concentration of vinyl acetate comonomer present in
these ethylene vinyl acetate copolymers will be at least 40 weight
percent, based on the weight of the ethylene and vinyl acetate
comonomer units in the copolymer. Preferably, the concentration
will be at least 45 weight percent, and more preferably at least 50
weight percent. If the concentration of vinyl acetate is less than
40 wt %, the ethylene vinyl acetate copolymer will lack elastic
properties.
[0037] Examples of ethylene vinyl acetate copolymers include
Elvax.RTM. 40L03 resin, available from E. I. du Pont de Nemours and
Company, Wilmington, Del., USA and Levapren.RTM. grades 400 through
900, available from Lanxess Corp., Germany.
[0038] The ethylene vinyl acetate copolymers that are used to
prepare the heat resistant ethylene vinyl acetate copolymer
compositions of the invention are curable gums, i.e. they are
substantially uncured rubbers. By substantially uncured is meant
that the unblended ethylene vinyl acetate copolymer has a
sufficiently low viscosity to be blended with polyacrylate
elastomer and polyamide. Preferably, the Mooney viscosity (ASTM
D1646, ML 1+4 at 100.degree. C.) of the ethylene vinyl acetate
copolymer is less than 120, more preferably less than 80 and most
preferably less than 40.
[0039] The polyacrylate elastomers useful in the practice of the
invention described herein are amorphous. That is, the heat of
fusion of the polyacrylate elastomer will generally be less than 4
J/g as measured by ASTM D3418-08, preferably less than 2 J/g, and
most preferably about 0 J/g. The polyacrylate elastomers comprise
polymerized units of alkyl esters and/or alkoxyalkyl esters of
propenoic acid. Examples of such esters include alkyl acrylates,
and alkoxyalkyl acrylates as well as species wherein the propenoic
acid is substituted with a C1-C10 alkyl group. Examples of such
species include alkyl methacrylates, alkyl ethacrylates, alkyl
propacrylates, and alkyl hexacrylates, alkoxyalkyl methacrylates,
alkoxyalkyl ethacryates, alkoxyalkyl propacrylates and alkoxyalkyl
hexacrylates. In addition, the alkyl ester groups of the propenoic
acid esters may be substituted with cyano groups or one or more
fluorine atoms. That is, the ester group will be a C1-C12
cyanoalkyl group or a C1-C12 fluoroalkyl group. The acrylate
polymers may also comprise copolymerized units of more than one
species of the alkyl esters and/or alkoxyalkyl esters, for example
two alkyl acrylates.
[0040] The alkyl and alkoxyalkyl esters of propenoic acid and
substituted propenoic acids are preferably C1-C12 alkyl esters of
acrylic or methacrylic acid or C1-C20 alkoxyalkyl esters of acrylic
or methacrylic acid. Examples of such esters include methyl
acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate,
butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate,
2-methoxyethylacrylate, 2-ethoxyethylacrylate,
2-(n-propoxy)ethylacrylate, 2-(n-butoxy)ethylacylate,
3-methoxypropylacrylate and 3-ethoxypropylacrylate. Examples of
esters that contain C1-C12 cyanoalkyl and fluoroalkyl groups
include cyanomethylacrylate, 1-cyanoethylacrylate,
2-cyanopropylacrylate, 3-cyanopropylacrylate, 4-cyanobutylacrylate,
1,1-dihydroperfluoroethyl methacrylate, 1,1-dihydroperfluoroethyl
acrylate, 1,1-dihydroperfluoropropyl methacrylate,
1,1-dihydroperfluoropropyl acrylate, and
1,1,5-trihydroperfluorohexyl (meth)acrylate, and
1,1,5-trihydroperfluorohexyl methacrylate. Preferably, the ester
group will comprise C1-C8 alkyl groups. More preferably, the ester
group will comprise C1-C4 alkyl groups. Particularly useful alkyl
acrylate esters are methyl acrylate, ethyl acrylate and butyl
acrylate. A particularly useful alkyl methacrylate ester is methyl
methacrylate. Minor amounts of unsaturated acetates such as ethenyl
acetate or 3-butenyl acetate may be incorporated into the
polyacrylate elastomer without deviating from the scope of this
invention. By minor amounts is meant less than 1 wt %, based on the
weight of the polyacrylate elastomer.
[0041] Esters that comprise comonomer units in the polyacrylate
elastomers may be generally represented by the formula
##STR00001##
[0042] where R1 is H or C1-C10 alkyl and R2 is C1-C12 alkyl, C1-C20
alkoxyalkyl, C1-012 cyanoalkyl, or C1-C12 fluoroalkyl.
[0043] In certain embodiments, the polyacrylate elastomers may be
polymers derived from copolymerization of more than one acrylate
comonomer. Examples of such acrylate polymers include copolymers of
methyl acrylate and butyl acrylate; copolymers of methyl acrylate,
butyl acrylate and the monoethyl ester of 1,4-butenedioic acid.
[0044] The concentration of propenoic acid ester comonomers that
are present in the polyacrylate elastomer will be at least 50
weight percent, based on the weight of the polymer. Preferably, the
concentration will be at least 55 weight percent, and more
preferably at least 60 weight percent. If the concentration of
propenoic acid ester is below 50 wt %, the likelihood that some
crystallinity will be present is high, for example in acrylate
polymers that are ethylene acrylate ester copolymers. In addition,
a high content of non-polar monomer such as ethylene diminishes
compatibility of the polyacrylate polymer with polyamide, and
therefore physical properties of the blend will be decreased.
[0045] The polyacrylate elastomers useful in the practice of this
invention are peroxide curable, meaning that they comprise either a
diene cure site monomer at a level of at least 0.5 mol %, or at
least 50 mol % ethylene. For example, the polyacrylate may comprise
diene cure site monomers to form pendant unsaturation that can form
crosslinks in the presence of free radicals, such 1,4-butadiene,
1,6-hexadiene, ethylidene norbornene, and the like. If
copolymerized diene cure site monomers are not present at a level
of at least 0.5 mol %, the acrylate polymers must comprise at least
50 mol % ethylene to confer peroxide curability on the polyacrylate
elastomer.
[0046] The polyacrylate elastomers useful in the practice of the
invention further comprise copolymerized monomer units selected
from the group consisting of unsaturated carboxylic acids,
anhydrides of unsaturated carboxylic acids, unsaturated epoxides,
and mixtures of two or more thereof. These monomer units contain
chemical groups (e.g., carboxyl and epoxy groups) that react with
end groups common in polyamides, e.g. amines and carboxylic acids,
and improve the physical properties of the blend.
[0047] Unsaturated carboxylic acids include for example, acrylic
acid and methacrylic acid, 1,4-butenedioic acids, citraconic acid,
and monoalkyl esters of 1,4-butenedioic acids. The 1,4-butenedioic
acids may exist in cis- or trans-form or both, i.e. maleic acid or
fumaric acid, prior to polymerization. Useful copolymerizable cure
site monomers also include anhydrides of unsaturated carboxylic
acids, for example, maleic anhydride, citraconic anhydride, and
itaconic anhydride. Preferred cure site monomers include maleic
acid and any of its half acid esters (monoesters) or diesters,
particularly the methyl or ethyl half acid esters (e.g., monoethyl
maleate); fumaric acid and any of its half acid esters or diesters,
particularly the methyl, ethyl or butyl half acid esters; and
monoalkyl and monoarylalkyl esters of itaconic acid. The presence
of these copolymerized monomers produces polyacrylate elastomer
compositions that exhibit good blend compatibility with
polyamides.
[0048] Examples of useful unsaturated epoxides include for example,
glycidyl (meth)acrylate, allyl glycidyl ether, glycidyl vinyl
ether, and alicyclic epoxy-containing (meth)acrylates.
[0049] Preferably, the acrylate copolymer gum rubber comprises at
least 0.03 mol % of cure site monomer units bearing the amine or
acid reactive group, based on the total number of moles of monomer
in the copolymer, more preferably at least 0.1 mol %, and most
preferably more than 0.2 mol %.
[0050] In some embodiments, the polyacrylate elastomers useful in
the practice of the invention will also comprise copolymerized
units of additional comonomers, for example ethylene and other
olefins such as propylene, 1-butene, 1-hexene, 1-octene, and the
like. The olefin will be present at a concentration of less than 50
wt %, more preferably less than 45 wt %, and most preferably about
40 wt % or less, based on the weight of the polyacrylate
polymer.
[0051] The heat resistant ethylene vinyl acetate copolymer
compositions described herein comprise from about 1 wt % to about
60 wt % of one or more polyamides based on the combined weights of
ethylene vinyl acetate copolymer, polyacrylate elastomer, and
polyamide components, wherein the polyamide component has a melting
peak temperature of at least about 160.degree. C., more preferably
at least 180.degree. C., and most preferably at least 200.degree.
C., and preferably less than 270.degree. C. as determined in
accordance with ASTM D3418-08. Preferably the polyamide is solid at
the curing temperature of the heat resistant ethylene vinyl acetate
copolymer composition, meaning that the curing temperature is less
than the melting peak temperature of the polyamide. While not
wishing to be bound by theory, when the polyamide is not solid at
the curing temperature, curative readily diffuses into the
polyamide, rendering the blend difficult to cure. Polyamide resins
are well known in the art and embrace those semi-crystalline resins
having a weight average molecular weight of at least 5,000 and
include those compositions commonly referred to as nylons. Thus,
the polyamide component useful in the practice of the invention
includes polyamides and polyamide resins such as nylon 6, nylon 7,
nylon 6/6, nylon 6/10, nylon 6/12, nylon 11, nylon 12, polyamides
comprising aromatic monomers, and polyamide block elastomers such
as copoly(amide-ether) or copoly(amide-ester). The resins may be in
any physical form, such as pellets and particles of any shape or
size, including nanoparticles.
[0052] The viscosity of the polyamide resins can vary widely while
meeting the aims of the present invention. To ensure that the
polyamide becomes dispersed within a continuous phase of ethylene
vinyl acetate copolymer, it is desirable that the polyamide have an
inherent viscosity greater than 0.9 dL/g, more preferably greater
than 1.1 dL/g, and most preferably greater than 1.3 dL/g, as
measured in accordance with ASTM D2857-95, using 96% by weight
sulfuric acid as a solvent at a test temperature of 25.degree.
C.
[0053] In general, as the concentration of the polyamide in the
heat resistant ethylene vinyl acetate elastomer composition
increases, the use of a polyamide of higher inherent viscosity
becomes more desirable.
[0054] The polyamide resin can be produced by condensation
polymerization of equimolar amounts of a saturated dicarboxylic
acid containing from 4 to 12 carbon atoms with a diamine, which
diamine contains from 4 to 14 carbon atoms. The polyamide may also
be prepared by a ring opening polymerization reaction such as nylon
6, or by condensation of aminocarboxylic acids such as nylon 7 or
11.
[0055] Examples of polyamides include polyhexamethylene adipamide
(66 nylon), polyhexamethylene azelaamide (69 nylon),
polyhexamethylene sebacamide (610 nylon) and polyhexamethylene
dodecanoamide (612 nylon), the polyamide produced by ring opening
of lactams, i.e. polycaprolactam, polylauriclactam,
poly-11-aminoundecanoic acid, and
bis(p-aminocyclohexyl)methanedodecanoamide. It is also possible to
use polyamides prepared by the polymerization of two of the above
polymers or terpolymerization of the above polymers or their
components, e.g. an adipic acid isophthalic acid hexamethylene
diamine elastomer.
[0056] Typically, polyamides are condensation products of one or
more dicarboxylic acids and one or more diamines, and/or one or
more aminocarboxylic acids, and/or ring-opening polymerization
products of one or more cyclic lactams. Polyamides may be fully
aliphatic or semi-aromatic.
[0057] Fully aliphatic polyamides useful in practice of the present
invention are formed from aliphatic and alicyclic monomers such as
diamines, dicarboxylic acids, lactams, aminocarboxylic acids, and
their reactive equivalents. A suitable aminocarboxylic acid is
11-aminododecanoic acid. Suitable lactams are caprolactam and
laurolactam. In the context of this invention, the term "fully
aliphatic polyamide" also refers to elastomers derived from two or
more such monomers and blends of two or more fully aliphatic
polyamides. Linear, branched, and cyclic monomers may be used.
[0058] Carboxylic acid monomers comprised in the fully aliphatic
polyamides include, but are not limited to aliphatic carboxylic
acids, such as for example adipic acid, pimelic acid, suberic acid,
azelaic acid, decanedioic acid, dodecanedioic acid, tridecanedioic
acid, tetradecanedioic acid, and pentadecanedioic acid. Diamines
can be chosen from diamines having four or more carbon atoms,
including, but not limited to tetramethylene diamine, hexamethylene
diamine, octamethylene diamine, decamethylene diamine,
dodecamethylene diamine, 2-methylpentamethylene diamine,
2-ethyltetramethylene diamine, 2-methyloctamethylenediamine;
trimethylhexamethylenediamine, meta-xylylene diamine, and/or
mixtures thereof.
[0059] Semi-aromatic polyamides are also suitable for use in the
present invention. Such polyamides are homopolymers, dipolymers,
terpolymers or higher order polymers formed from monomers
containing aromatic groups. One or more aromatic carboxylic acids
may be terephthalic acid or a mixture of terephthalic acid with one
or more other carboxylic acids, such as isophthalic acid, phthalic
acid, 2-methyl terephthalic acid and naphthalic acid. In addition,
the one or more aromatic carboxylic acids may be mixed with one or
more aliphatic dicarboxylic acids. Alternatively, an aromatic
diamine such as meta-xylylene diamine can be used to provide a
semi-aromatic polyamide, an example of which is a homopolymer
comprising meta-xylylene diamine and adipic acid.
[0060] Block copoly(amide) elastomers are also suitable for use as
the polyamide component provided the melting peak temperature of
the polyamide block is at least 160.degree. C. If a low softening
point material comprises the block copoly(amide) elastomer, e.g., a
polyether oligomer or a polyalkylene ether, for example,
poly(ethylene oxide), then the block polymer will be a
copoly(amide-ether). If a low softening point material of the block
copoly(amide) elastomer comprises an ester, for example, a
polylactone such as polycaprolactone, then the block elastomer will
be a copoly(amide-ester). Any such low softening point materials
may be used to form a block copoly(amide) elastomer. Optionally,
the lower softening point material of the block copoly(amide)
elastomer may comprise a mixture, for example, a mixture of any of
the above-mentioned lower softening point materials. Furthermore,
said mixtures of lower softening point materials may be present in
a random or block arrangement, or as mixtures thereof. Preferably,
the block copoly(amide) elastomer is a block copoly(amide-ester), a
block copoly(amide-ether), or mixtures thereof. More preferably,
the block copoly(amide) elastomer is at least one block
copoly(amide-ether) or mixtures thereof. Suitable commercially
available thermoplastic copoly(amide-ethers) include PEBAX.RTM.
polyether block amides from Elf-Atochem, which includes PEBAX.RTM.
4033 and 6333. Most preferably, the polyamide is other than a block
copoly(amide-ether) or copoly(amide-ester). Other polyamides have
generally higher melting peak temperatures and exhibit better hot
air aging as compared to polyamide block copoly(amide-ether) or
copoly(amide-ester).
[0061] Preferred polyamides are homopolymers or copolymers wherein
the term copolymer refers to polyamides that have two or more amide
and/or diamide molecular repeat units.
[0062] The polyamide component may comprise one or more polyamides
selected from Group I polyamides having a melting peak temperature
of at least about 160.degree. C., but less than about 210.degree.
C., and comprising an aliphatic or semiaromatic polyamide, for
example poly(pentamethylene decanediamide), poly(pentamethylene
dodecanediamide), poly(.epsilon.-caprolactam/hexamethylene
hexanediamide), poly(.epsilon.-caprolactam/hexamethylene
decanediamide), poly(12-aminododecanamide),
poly(12-aminododecanamide/tetramethylene terephthalamide), and
poly(dodecamethylene dodecanediamide); Group (II) polyamides having
a melting peak temperature of at least about 210.degree. C., and
comprising an aliphatic polyamide selected from the group
consisting of poly(tetramethylene hexanediamide),
poly(.epsilon.-caprolactam), poly(hexamethylene hexanediamide),
poly(hexamethylene dodecanediamide), and poly(hexamethylene
tetradecanediamide); Group (III) polyamides having a melting peak
temperature of at least about 210.degree. C., and comprising about
20 to about 35 mole percent semiaromatic repeat units derived from
monomers selected from one or more of the group consisting of (i)
aromatic dicarboxylic acids having 8 to 20 carbon atoms and
aliphatic diamines having 4 to 20 carbon atoms; and about 65 to
about 80 mole percent aliphatic repeat units derived from monomers
selected from one or more of the group consisting of an aliphatic
dicarboxylic acid having 6 to 20 carbon atoms and said aliphatic
diamine having 4 to 20 carbon atoms; and a lactam and/or
aminocarboxylic acid having 4 to 20 carbon atoms; Group (IV)
polyamides comprising about 50 to about 95 mole percent
semi-aromatic repeat units derived from monomers selected from one
or more of the group consisting of aromatic dicarboxylic acids
having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20
carbon atoms; and about 5 to about 50 mole percent aliphatic repeat
units derived from monomers selected from one or more of the group
consisting of an aliphatic dicarboxylic acid having 6 to 20 carbon
atoms and said aliphatic diamine having 4 to 20 carbon atoms; and a
lactam and/or aminocarboxylic acid having 4 to 20 carbon atoms;
Group (V) polyamides having a melting peak temperature of at least
about 260.degree. C., comprising greater than 95 mole percent
semi-aromatic repeat units derived from monomers selected from one
or more of the group consisting of aromatic dicarboxylic acids
having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20
carbon atoms; and less than 5 mole percent aliphatic repeat units
derived from monomers selected from one or more of the group
consisting of an aliphatic dicarboxylic acid having 6 to 20 carbon
atoms and said aliphatic diamine having 4 to 20 carbon atoms; and a
lactam and/or aminocarboxylic acid having 4 to 20 carbon atoms. The
polyamide may also be a blend of two or more polyamides.
[0063] Preferred polyamides include nylon 6, 6/10, 10/10, 11, 6/12,
12, 6/6, and Group IV polyamides having a melting peak temperature
less than about 270.degree. C. These polyamides have a melting peak
temperature sufficiently high so as not to limit the scope of
applications for the heat resistant ethylene vinyl acetate
copolymer compositions, but not so high that production of the
blends causes significant degradation of the ethylene vinyl acetate
copolymer or polyacrylate elastomer. Also preferred are polyamides
formed by ring opening or condensation of aminocarboxylic
acids.
[0064] Polyamides suitable for use in the invention are widely
commercially available, for example Zytel.RTM. resins, available
from E. I. du Pont de Nemours and Company, Wilmington, Del., USA,
Durethan.RTM. resins, available from Lanxess Corp., Germany, and
Ultramid.RTM. resins available from BASF Corp., USA.
[0065] Preferably, the polyamide component of the heat resistant
ethylene vinyl acetate copolymer compositions is present in the
blend composition in the form of approximately spherical particles,
i.e., the aspect ratio of the particles is less than 10 to 1. When
the aspect ratio exceeds about 10 to 1, the viscosity of the blend
composition is increased and molding or extruding the blend
composition at a temperature less than the melting peak temperature
of the polyamide component becomes difficult. Generally, the size
of the polyamide particles is relatively unimportant, though
tensile strength of the cured composition becomes optimal when most
of the particles are about 2 micrometers in diameter or smaller.
Such blend compositions can be mixed, molded and/or extruded using
conventional techniques to produce curable compositions that may be
crosslinked with conventional curative systems to form a wide
variety of elastomer articles.
[0066] The blend compositions of the invention comprise, or in some
cases consist essentially of, from about 10 to about 98 weight
percent of the ethylene vinyl acetate copolymer component described
herein, from about 1 to about 50 weight percent of the polyacrylate
elastomer component described herein, and from about 1 to about 60
weight percent of the polyamide component described herein, based
on the total weight of the ethylene vinyl acetate copolymer,
polyacrylate elastomer, and polyamide components. The ethylene
vinyl acetate copolymer component may be made up of one or more
than one ethylene vinyl acetate copolymers of the type described
herein as being suitable for use in the practice of the invention.
Similarly, the polyacrylate elastomer or polyamide component may be
made up of one or more than one polyacrylate elastomers or
polyamides of the type described herein as being suitable for use
in the practice of the invention. Preferably, the curable
compositions will comprise from about 30 to about 90 weight percent
ethylene vinyl acetate copolymer component, from about 5 to about
30 weight percent polyacrylate elastomer, and from about 5 to about
40 weight percent polyamide component, based on the total weight of
the ethylene vinyl acetate copolymer and polyamide components. More
preferably, the curable compositions will comprise from about 50 to
about 90 weight percent ethylene vinyl acetate copolymer component,
from about 5 to about 20 weight percent of the polyacrylate
elastomer component, and form about 5 to about 30 weight percent
polyamide component based on the total weight of the ethylene vinyl
acetate copolymer and polyamide components. These percentages
provide a heat resistant ethylene vinyl acetate copolymer
composition such that a cured article made therefrom can, undergo
heat aging for one week at 190.degree. C. or two weeks at
175.degree. C. and maintain an elongation to break of at least
100%. In addition, the polymer blends exhibit Mooney viscosities
(ML 1+4, 100.degree. C.), as determined according to ASTM D1646, of
5-200, preferably 10-150, and most preferably 10-100.
[0067] Various blending options can be used, including: (i) mixing
polyacrylate elastomers and ethylene vinyl acetate copolymers with
molten polyamides, or (ii) mixing polyacrylate elastomers with
molten polyamides that are subsequently cooled to solidify the
polyamide and then mixed with ethylene vinyl acetate copolymers.
These blending options may result in a wide range of blend
morphologies, ranging from (i) those wherein discrete,
discontinuous polyamide particles exist within a continuous matrix
of polyacrylate elastomer and ethylene vinyl acetate copolymer, to
(ii)) compositions wherein high aspect ratio polyamide "fibers" are
present, to (iii) compositions that comprise co-continuous
structures, to (iv) compositions comprising discrete domains of
polyacrylate elastomer and ethylene vinyl acetate copolymer within
a continuous phase of polyamide. Most of these compositions have
morphologies that are unsuitable for use in the present invention,
because the blends have very high Mooney viscosities, i.e. Mooney
viscosity ML 1+4, 100.degree. C. of greater than about 200, or
exhibit such poor processability at temperatures less than the
melting peak temperature of the polyamide that the Mooney viscosity
cannot be measured. A Mooney viscosity greater than 200, or the
inability to measure Mooney viscosity, indicates that the polyamide
comprises a continuous or a high aspect ratio fibrous phase in the
blend. Such blends exhibit poor processability for extrusion or
molding, and poor elastic properties after curing if a cured
article can successfully be formed. A Mooney viscosity less than
200, preferably less than 150, and most preferably less than 100,
is confirmatory of a blend morphology wherein the polyamide
comprises a discontinuous phase that does not have a high aspect
ratio.
[0068] With respect to the polyamide of the present invention, by
"discontinuous" is meant that the polyamide is present in the blend
compositions of the invention as dispersed particles or domains
surrounded by ethylene vinyl acetate copolymer and polyacrylate
elastomer. By "high aspect ratio" is meant that the ratio of the
largest to smallest dimensions of a typical polyamide domain in the
blend is greater than about 10. In general, the polyamide domains
in the heat resistant ethylene vinyl acetate copolymer compositions
of the invention will preferably be completely isolated from each
other within the continuous ethylene vinyl acetate copolymer and
polyacrylate elastomer matrix, and be approximately spherical.
However, in certain instances a small percentage, less than about
5%, of localized sites in the blend composition may exist wherein
the polyamide domains are aggregated or connected to each other, or
have an aspect ratio greater than about 10. After cooling, the
polyamide domains no longer flow and the morphology of the
polyamide component remains unchanged during further mixing
processes at temperatures less than the melting peak temperature of
the polyamide.
[0069] A preferred method of producing the blend compositions
involves a sequential blending process. A peroxide curable
polyacrylate elastomer component comprising copolymerized units of
alkyl acrylate and at least 0.03 mol % of an amine or acid reactive
monomer selected from the group consisting of unsaturated
carboxylic acids, anhydrides of unsaturated carboxylic acids, and
unsaturated epoxides and a polyamide component are first mixed at a
temperature above the melting peak temperature of the polyamide, to
disperse the polyamide in a continuous phase of polyacrylate
elastomer. The polyacrylate elastomer-polyamide blend is then
cooled and blended with ethylene vinyl acetate copolymer at a
temperature less than the melting peak temperature of the polyamide
to form a blend composition comprising 10-98 wt % ethylene vinyl
acetate, 1-50 wt % polyacrylate, and 1-60 wt % polyamide. Because
the polyamide morphology is determined by the initial melt mixing
step with polyacrylate elastomer, to ensure the polyamide does not
comprise the continuous phase of the polyacrylate
elastomer-polyamide blend, the Mooney viscosity (ML 1+4,
100.degree. C.) of this blend must be measurable and less than 200,
preferably less than 150, most preferably less than 100. Sequential
blending as described eliminates the need to expose the relatively
thermally unstable ethylene vinyl acetate copolymer to the high
temperatures needed for melt mixing with polyamide. In addition,
the compatibilization reaction between polyamide and acid or amine
reactive sites on the polyacrylate elastomer is favored when
ethylene vinyl acetate copolymer is substantially absent during the
melt mixing process.
[0070] Alternatively, one is able to prepare a blend composition,
as disclosed herein by the following process. The process starts
with providing one or more ethylene vinyl acetate copolymers
comprising at least 40% by weight vinyl acetate monomer; one or
more peroxide curable polyacrylate elastomers comprising
copolymerized units of alkyl acrylate, and at least 0.03 mol % of
an amine or acid reactive monomer selected from the group
consisting of unsaturated carboxylic acids, anhydrides of
unsaturated carboxylic acids, and unsaturated epoxides; and one or
more polyamides having a melting peak temperature of at least
160.degree. C. The process then requires mixing the components at a
temperature above the melting peak temperature(s) of the one or
more polyamides to disperse the one or more polyamides within the
one or more ethylene vinyl acetate copolymers and polyacrylate
elastomers, such that one or more ethylene vinyl acetate copolymer
comprise from about 10 wt % to about 98 wt %, the one or more
peroxide curable polyacylate elastomers comprise from about 1 wt %
to about 50 wt %, and the one or more polyamides comprise from
about 1 wt % to about 60 wt % of the blend based on the total
weight of ethylene vinyl acetate copolymers, polyacrylate
elastomers, and polyamides present. After mixing these, the mixture
is cooled to a temperature below the crystallization peak
temperatures of the one or more polyamides, thereby forming a blend
composition having a Mooney viscosity (ML 1+4, 100.degree. C.) of 5
to 200, as determined according to ASTM D1646.
[0071] A heat resistant ethylene vinyl acetate copolymer
composition may be formed by a process that includes mixing a
peroxide curative into a blend composition comprising 10-98 wt %
ethylene vinyl acetate, 1-50 wt % polyacrylate, and 1-60 wt %
polyamide having a Mooney viscosity (ML 1+4, 100.degree. C.) of 5
to 200, as determined according to ASTM D1646, at a temperature
below the melting peak temperature of the one or more
polyamides.
[0072] The heat resistant ethylene vinyl acetate copolymer
compositions may only be formed by mixing the polyamide component
into the polyacrylate elastomer component and optionally the
ethylene vinyl acetate component at temperatures above the melting
peak temperature of the polyamide, under conditions that do not
produce a dynamic cure of the polyacrylate elastomer or the
ethylene vinyl acetate copolymer, followed by cooling the
thus-produced polymer blend. That is, the curative, generally a
peroxide curative, will not be present when the polyamide
component, polyacrylate elastomer component, and optionally the
ethylene vinyl acetate copolymer component are being mixed. This is
because the mixing temperature specified (above the melting peak
temperature of the one or more polyamides) is above that at which
crosslinking and/or gelling of the polyacrylate elastomer or
ethylene vinyl acetate copolymer will occur in the presence of
peroxide. Gelling or crosslinking of the polyacrylate elastomer or
ethylene vinyl acetate copolymer during mixing with molten
polyamide forces the polyamide to become the continuous phase in
the blend, so that after the blend composition has cooled and the
polyamide has solidified, the blend composition becomes difficult
or impossible to further process at a temperature less than the
melting peak temperature of the polyamide component. In particular,
a blend composition with a continuous polyamide phase may exhibit a
Mooney viscosity (ML 1+4, 100.degree. C.) greater than 200, or it
may exhibit flow behavior such that the Mooney viscosity cannot be
measured. Inability to measure a Mooney viscosity of the blend
composition occurs either because the blend cannot be formed into
the Mooney test specimen by conventional rubber processing
techniques at a temperature less than the melting peak temperature
of the polyamide, or because the test specimen crumbles during the
Mooney test.
[0073] Cooling of the blend composition formed by mixing the
polyacrylate elastomer component, polyamide component, and
optionally the ethylene vinyl acetate component serves to
crystallize the polyamide domains so that the polyamide becomes
solid and therefore cannot coalesce to form a continuous phase upon
subsequent mixing, e.g., when mixed with an peroxide curative to
form a curable composition. The resulting mixture can be an
intermediate blend composition in the case where one or more
ethylene vinyl acetate copolymers are added, for example if
ethylene vinyl acetate copolymer was not present during the mixing
of the polyacrylate elastomer and polyamide, or if additional
ethylene vinyl acetate copolymers are added to a blend of
polyacrylate elastomer, ethylene vinyl acetate copolymer, and
polyamide. Preferably, the ethylene vinyl acetate copolymer is
mixed with the intermediate blend at a temperature less than the
melting peak temperature of the polyamide. The temperature below
which the blend must be cooled can be determined by measuring the
crystallization peak temperature according to ASTM D3418-08. The
blends of ethylene vinyl acetate copolymer, polyacrylate elastomer,
and polyamide may exhibit multiple crystallization peak
temperatures. In such cases, the lowest crystallization peak
temperature is taken as the temperature below which the blend must
be cooled to fully solidify the polyamide component. Generally, the
blend is cooled to 40.degree. C. or less, which is sufficient to
solidify the polyamides useful in the practice of the present
invention.
[0074] The curable compositions that are heat resistant ethylene
vinyl acetate copolymer compositions described herein also comprise
a peroxide curative. By "curable" is meant that the increase in
torque measured in accordance with ASTM D5289-07a using an MDR 2000
from Alpha Technologies operating at 0.5.degree. arc and at test
conditions of 177.degree. C. for 24 minutes is at least 2.5 dN-m.
More preferably the torque increase is at least 4 dN-m, and most
preferably at least 5.5 dN-m. The increase in torque is the
difference MH-ML, where ML refers to the minimum torque value
measured and MH refers to the maximum torque value attained after
the measurement of ML. Suitable peroxide curatives, also known as
peroxide curing systems, comprise a peroxide and optionally a
coagent. Examples of peroxides and coagents include curative
systems as generally known in the art, including those described
herein, operative at the temperature employed during vulcanization.
For example, useful organic peroxides are those that decompose
rapidly within the temperature range of 150.degree. C. to
250.degree. C. These include, for example, dicumyl peroxide,
2,5-bis(t-butylperoxy)-2,5-dimethylhexane, and
.alpha.',.alpha.'-bis(t-butylperoxy)-diisopropylbenzene (available
from Arkema Inc. under the tradename Vul-Cup.RTM. peroxide). In a
typical curable composition the peroxide is present in amounts of
from about 0.5 to 5 parts phr (parts per hundred parts rubber, i.e.
parts per hundred parts of the sum of the ethylene vinyl acetate
copolymers and polyacrylate elastomers present). The peroxide may
be adsorbed on an inert carrier such as calcium carbonate, carbon
black or kieselguhr; however, the weight of the carrier is not
included in the above range. Generally, an optional coagent will be
present to increase the state of cure of the finished part. The
coagent can be for example, N,N'-(m-phenylene)dimaleimide,
trimethylolpropane trimethylacrylate, tetraallyloxyethane, triallyl
cyanurate, tetramethylene diacrylate, or polyethylene oxide glycol
dimethacrylate. A preferred coagent is
N,N'-(m-phenylene)dimaleimide, available from E. I. du Pont de
Nemours and Company as HVA-2. The amount of the coagent used is
generally about 0 to 5 parts by weight per 100 parts (phr) of the
sum of the ethylene vinyl acetate copolymer and polyacrylate
elastomer, preferably about 1 to 5 parts phr. The coagents usually
contain multiple unsaturated groups such as allyl groups or acrylic
ester groups.
[0075] The addition of curative to the blend composition will
desirably take place at a temperature below the decomposition
temperature of the peroxide and below the temperature at which the
crosslinking reaction occurs. Generally, the addition will take
place at a temperature below 160.degree. C., preferably below
140.degree. C., and most preferably at a temperature no greater
than 120.degree. C. The addition of the curative may take place
simultaneously with the addition of optional processing
ingredients, such as colorants, conventional carbon black or
mineral reinforcing agents, antioxidants, processing aids, fillers
and plasticizers, or it may be an operation separate from addition
of the other ingredients. The addition may be conducted on a
two-roll rubber mill or by using internal mixers suitable for
compounding gum rubber compositions, including Banbury.RTM.
internal mixers, Haake Rheocord.RTM. mixers, Brabender
Plastograph.RTM. mixers, Farrel Continuous Mixers, or single and
twin screw extruders.
[0076] After addition of the curatives and other optional
ingredients such as fillers, plasticizers, pigments, antioxidants,
process aids, etc., to the blend composition, the resulting heat
resistant ethylene vinyl acetate copolymer composition desirably
exhibits a strong (meaning favorable) cure response as determined
in accordance with ASTM D5289-07a using an MDR 2000 from Alpha
Technologies, Ohio, USA operating at 0.5.degree. arc and at test
conditions of 177.degree. C. for 24 minutes.
[0077] In another embodiment, the invention is directed to a
curable composition that is a heat resistant ethylene vinyl acetate
copolymer composition comprising ethylene vinyl acetate copolymer,
polyacrylate, polyamide, and a peroxide curative. Said curable
composition exhibits an increase in torque of at least 2.5 dN-m,
preferably at least 4.0 dN-m, and most preferably at least 5.5
dN-m, as determined in accordance with ASTM D5289-07a using an MDR
2000 from Alpha Technologies operating at 0.5.degree. arc and at
test conditions of 177.degree. C. for 24 minutes.
[0078] To achieve optimal heat aging resistance, an antioxidant may
be added to the curable ethylene vinyl acetate copolymer
composition prior to curing. Useful antioxidants include, but are
not limited to, aryl amines, phenolics, imidazoles, and phosphites.
Thus, in some embodiments, the antioxidant will be a phosphorus
ester antioxidant, a hindered phenolic antioxidant, an amine
antioxidant, or a mixture of two or more of these compounds. The
proportion of the antioxidant compound in the composition is
typically 0.1 to 5 phr, preferably about 0.5 to 2.5 phr. The weight
ratio of the phenolic or amine antioxidant to the phosphorus
compound in the mixtures is about 0.5 to 3, and preferably the
ratio is about 1.
[0079] Examples of aryl amines that may be useful antioxidants
include 4,4'-bis(.alpha.,.alpha.-dimethylbenzyl)diphenylamine,
diphenylamine and alkylated diphenylamines, 4-aminodiphenyl amine,
and N-phenyl-N'-(p-toluenesulfonyl)-p-phenylenediamine. Examples of
phenolic antioxidants include 4,4'-butylenebis(6-t-butyl-m-cresol),
1,3,5-trimethyl-2,4,6-tris-(3,5-di-t-butyl-4-hydroxybenzyl)benzene,
and 4,4'-thiobis-(3-methyl-6-t-butylphenol). Examples of phosphite
antioxidants include triphenylphosphite,
bis(2,4-di-t-butylphenyl)pentraerythritol diphosphite, and
tris(2,4-ditert-butylphenyl)phosphite. Examples of imidazole
antioxidants include 2-mercaptomethylbenzimidazole,
2-mercaptobenzimidazole, and zinc 4- and
-5-methyl-2-mercapto-benzimidazole. Combinations of antioxidants
may be used, generally at levels between 0.1 and 5 phr based on 100
parts of the ethylene vinyl acetate copolymer in the compound.
[0080] Suitable hindered phenolic antioxidants can be, for example
4,4'-butylidenebis(6-t-butyl-m-cresol),
1,3,5-trimethyl-2,4,6-tris-(3,5-di-t butyl-4-hydroxybenzyl)benzene,
2,6-di-t-butyl-.alpha.-dimethylamino-p-cresol and
4,4'-thiobis-(3-methyl-6-t-butylphenol).
[0081] Antioxidants comprising the salt of a strong base and a weak
acid, optionally combined with a carbodiimide, as disclosed in
EP1081188, may also be used in the heat resistant ethylene vinyl
acetate copolymer compositions.
[0082] Preferred antioxidant compositions contain tri(mixed mono-
and dinonylphenyl) phosphate mixed with either
4,4'-butylidenebis(6-t-butyl-m cresol) or
4,4'-bis(.alpha.,.alpha.-dimethylbenzyl)diphenylamine. Preferred
antioxidant compositions contain
4,4'-bis(.alpha.,.alpha.-dimethylbenzyl)diphenylamine (available
commercially as Naugard.RTM. 445 from Chemtura Corp.) or
4-aminodiphenyl amine. Antioxidants may be added while the ethylene
vinyl acetate copolymer is melt mixed with the polyamide, or after
the blend has cooled.
[0083] In other embodiments, the heat resistant ethylene vinyl
acetate copolymer compositions of the invention may be blended with
another polymer, e.g. an elastomer, to dilute the polyamide content
of the inventive composition by any mixing process, either above or
below the melting peak temperature peak of the polyamide, providing
the presence of the additional polymer does not increase the Mooney
viscosity (ML 1+4, 100.degree. C.) of the resulting composition to
above 200. The polymer used for the blending process may be an
ethylene vinyl acetate copolymer or polyacrylate elastomer, and may
further comprise fillers, curatives, or other ingredients.
Preferably, such dilution occurs at a temperature below that of the
melting peak temperature of the polyamide, and if a curative is
present, below the temperature needed to initiate curing.
[0084] In addition, the heat resistant ethylene vinyl acetate
copolymer compositions may optionally comprise additional
components including fillers, including but limited to carbon
black, mineral fillers, scorch retarders, ignition resistant
fillers and additives, plasticizers, process aids, waxes, pigments,
and colorants. Such optional components will generally be present
in amounts of from about 0.1 phr to about 200 phr, based on the
weight of the sum of the ethylene vinyl acetate copolymer and
polyacrylate elastomer. The addition of such optional components
may take place during preparation of the polymer blend or at the
time of mixing of curative into the composition.
[0085] Curing or crosslinking (also referred to as vulcanization)
of the curable compositions of the invention typically involves
exposing the heat resistant ethylene vinyl acetate copolymer
composition to elevated temperature and elevated pressure for a
time sufficient to crosslink the ethylene vinyl acetate copolymer
and polyacrylate elastomer. Such operations generally are conducted
by placing the curable heat resistant ethylene vinyl acetate
composition into a mold that is heated in a press (often referred
to as press-curing). Alternatively, the curable compositions may be
extruded into various shapes. Such extruded shapes or parts are
often cured in a pressurized autoclave. After the press cure or
autoclave cycle is completed, this initial cure may be followed by
an optional post-cure heating cycle at ambient pressure to further
cure the heat resistant ethylene vinyl acetate copolymer
composition. For example, the vulcanizate may be formed and cured
using conventional press cure procedures at about 160.degree. C. to
about 220.degree. C. for about 1 to 60 minutes. Post-cure heating
may be conducted at about 160.degree. C. to about 200.degree. C.
for one to several hours. Once crosslinked, the compositions
described herein are not thermoplastic, but thermoset. Suitable
cure conditions will depend on the particular curable compound
formulation and are known to those of skill in the art.
[0086] The vulcanizates prepared from the heat resistant ethylene
vinyl acetate copolymer compositions described herein exhibit
unusually good resistance to embrittlement during heat aging, as
evidenced by retention of tensile elongation at break following
heat aging at 190.degree. C. for one week or two weeks at
175.degree. C. and a reduction in the increase in Shore A hardness
as a result of heat aging. For example, replacement of one quarter
of the ethylene vinyl acetate copolymer in a curable compound by a
blend of polyacylate elastomer and polyamide can provide over five
times greater elongation at break after one week heat aging at
190.degree. C., and over five times less change in Shore A
hardness. This degree of improvement is unusual. Furthermore, these
advantages in heat aging are gained with no sacrifice in
compression set resistance.
[0087] Heat resistant ethylene vinyl acetate copolymer compositions
prepared by the processes described herein can be used in a wide
variety of industrial applications, for production of articles
including wire and cable jacketing, spark plug boots, hoses, belts,
miscellaneous molded boots, molded or extruded tubing or hose,
molded boots, belts, grommets, seals and gaskets, vibration
dampeners, weather stripping, seals and gaskets. Hose applications
include turbocharger hoses, transmission oil cooler hoses, power
steering hoses, air conditioning hoses, air ducts, fuel line
covers, and vent hoses.
[0088] Examples of seals include engine head cover gaskets, oil pan
gaskets, oil seals, lip seal packings, O-rings, transmission seal
gaskets, seal gaskets for a crankshaft or a camshaft, valve stem
seals, power steering seals, and belt cover seals.
[0089] Automotive tubing applications include axle vent tubing, PCV
tubing and other emission control parts. The vulcanizates are also
useful for manufacture of crankshaft torsional dampers where high
damping over a broad temperature range is needed under high
compressive and shear strains. The vulcanizates also can be used to
prepare noise management parts such as grommets.
[0090] The invention is further illustrated by the following
examples wherein all parts are by weight unless otherwise
indicated.
EXAMPLES
Materials
Ethylene Vinyl Acetate Copolymer (EVA)
[0091] EVA1 Copolymer of ethylene and 50 wt % vinyl acetate, Mooney
viscosity (ML 1+4 at 100.degree. C.) of 25, available from Lanxess
Corp. as Levapren.RTM. 500 resin.
[0092] EVA2 Copolymer of ethylene and 45 wt % vinyl acetate, Mooney
Viscosity (ML1+4 at 100.degree. C.) of 19, available from Lanxess
Corp. as Levapren.RTM. 450 resin.
Polyacrylate Elastomer
[0093] AE1 Amorphous copolymer of methyl acrylate, ethylene and
monoethyl maleate comprising 55 wt % (about 29 mole %)
copolymerized methyl acrylate units, 43 wt % coplymerized ethylene
units (about 70 mol %), and approximately 2 wt %(about 0.6 mol %)
copolymerized units of monoethyl maleate; Mooney viscosity (ML 1+4)
at 100.degree. C. of 33.
Polyamide
[0094] P1 Polyamide 6, inherent viscosity 1.450 dL/g, melting peak
temperature 220.degree. C., available from BASF as Ultramid.RTM.
B40.
[0095] P2 Polyamide 6/6, melting peak temperature 262.degree. C.,
available from E.I. duPont de Nemours as Zytel.RTM. 42A.
Other Ingredients
[0096] Peroxide: mixture of the para and meta isomers of an
.alpha.,.alpha.'-bis(tert-butylperoxy)-diisopropylbenzene, 40%
peroxide active ingredient on kaolin clay carrier, Vul-Cup.RTM.
40KE, available from Arkema Inc. Coagent:
N,N'-(m-phenylene)dimaleimide, HVA-2, available from DuPont. Carbon
black: N550 grade, Sterling.RTM. SO carbon black, available from
Cabot Corp. Antioxidant (AO): Naugard.RTM. 445 antioxidant,
available from Chemtura Corp.
Test Methods
[0097] Mooney viscosity: ASTM D1646, ML 1+4, 100.degree. C. Cure
response: Measured per ASTM D5289-07a using an MDR 2000 from Alpha
Technologies operating at 0.5.degree. arc. Test conditions of
177.degree. C. for 24 minutes. ML refers to the minimum torque
value measured during the test, while MH refers to the maximum
torque value attained after ML. Compression set: ISO 815-1:2008,
25% compression, using type B molded buttons prepared using press
cure conditions of 175.degree. C. for 10 minutes. Time and
temperature of the test conditions as specified. Data reported are
the median values of 3 specimens. Tensile properties: ASTM D412-06,
die C. Samples cut from 1.5 to 2.5 mm thick molded plaques press
cured at 175.degree. C. for 10 minutes and optional post cure of 30
minutes at 175.degree. C. as noted followed by aging for 24 hours
at ambient conditions of 23.degree. C. and 50% relative humidity.
Data reported are the median value of 3 specimens. The rupture
properties of tensile strength and elongation are indicated as Tb
and Eb, (tensile at break and elongation at break, respectively).
Test temperature is 23.degree. C.+2.degree. C. Shore A hardness:
measured using 6 mm thick samples composed of 2 mm thick plies,
cured as described for tensile properties, aged for 24 hours at
ambient conditions of 23.degree. C. and 50% relative humidity, per
ASTM D2240-05 test method, using a type 2 operating stand. The
median value of 5 readings is reported. Heat aging: Tensile
specimens, prepared as described above are hung in a hot air oven
for the specified time and temperature. The specimens are
conditioned at ambient conditions of 23.degree. C. and 50% RH for
at least 24 hours before tensile properties are measured. Inherent
viscosity of polyamides: Measured in accordance with ASTM D2857-95,
using 96% by weight sulfuric acid as a solvent at a test
temperature of 25.degree. C. Samples were dried for 12 hours in a
vacuum oven at 80.degree. C. prior to testing. Melting peak
temperature: Measured in accordance with ASTM D3418-08.
Example 1
[0098] Blend B1, comprising polyacrylate elastomer and polyamide,
was produced as follows. Polyamide P1 was metered by weight loss
feeder into the first barrel section of a 43 mm Berstorff.RTM.
co-rotating twin screw extruder with twelve barrel sections,
operating at a screw speed of 250 rpm. At the same time,
polyacrylate elastomer AE1 was metered into the fourth section of
the extruder via a specially configured extruder and a melt pump
for accurate feed rates. Melt temperature of the blend reached
about 280.degree. C. After exiting the twelfth barrel section, the
resultant blend was pelletized and cooled to 25.degree. C. before
further processing. Composition and properties of blend B1 are
shown in Table 1. Transmission electron micrographs of blend B1
indicate that the polyacrylate elastomer is the continuous phase in
the blend, and the polyamide is dispersed in roughly spherical
domains of approximately 0.5 to 2 um diameter.
TABLE-US-00001 TABLE 1 B1 % AE1 60 P1 40 Mooney Viscosity ML1 + 4,
100 C. 62
B1 was then further blended with EVA1 at approximately 40.degree.
C. on a roll mill to produce blends B2-B4, as shown in Table 2.
TABLE-US-00002 TABLE 2 Blend B2 B3 B4 phr phr phr B1 107.1 62.5
27.8 EVA1 35.7 62.5 83.3 Mooney Viscosity ML1 + 4, 100 C. 45 34 27
Composition in weight % EVA1 25 50 75 AE1 45 30 15 P1 30 20 10
[0099] The formulations and properties of curable heat resistant
ethylene vinyl acetate compositions E1-E6 and comparative curable
ethylene vinyl acetate compositions CE1-CE5 are shown in Table 3.
The curable compositions were prepared by charging the ingredients
as shown to a Brabender.RTM. mixing bowl fitted with cam rotors,
operating at 50 rpm. The bowl set temperature was 50.degree. C.,
and the mixing time was three minutes. The batch temperatures did
not exceed 100.degree. C. After removing the compounds from the
mixing bowl, they were sheeted on a cold roll mill, and preforms
were stamped out for molding plaques, compression set buttons, and
for measuring cure response.
[0100] Results in Table 3 show that all the curable compounds
exhibit a good cure response. Compounds E1, E2, and E3 do not
contain carbon black, yet exhibit much greater tensile strength and
Shore A hardness after press cure than the comparative composition
CE1, which also does not contain carbon black. After heat aging for
one week at 190.degree. C., all the inventive compositions have
tensile elongation to break greater than 100% and very slight
changes in Shore A hardness (less than 5 points) wherein
comparative compositions exhibit less than 20% elongation to break
and Shore A hardness increases of at least 18 points.
TABLE-US-00003 TABLE 3 E1 E2 E3 E4 E5 E6 CE1 CE2 CE3 CE4 CE5 phr
phr phr phr phr phr phr phr phr phr phr B2 142.9 142.9 B3 125.0
125.0 B4 111.1 111.1 EVA1 100 100 100 100 100 Peroxide 5 5 5 5 5 5
5 5 5 5 5 Coagent 2 2 2 2 2 2 2 2 2 2 2 Antioxidant 1 1 1 1 1 1 1 1
1 1 1 Carbon 9 18 27 9 18 27 36 black Weight percent of EVA1, AE1,
and P1 based on the total polymer content EVA1 (%) 25 50 75 25 50
75 100 100 100 100 100 AE1 (%) 45 30 15 45 30 15 0 0 0 0 0 P1 (%)
30 20 10 30 20 10 0 0 0 0 0 Cure Response ML (dN-m) 0.4 0.3 0.3 0.5
0.3 0.3 0.2 0.2 0.2 0.3 0.5 MH (dN-m) 12.4 10.1 8.2 13.9 12.4 12
7.4 7.9 9 11.5 14.3 MH - ML 12.0 9.8 8.0 13.4 12.1 11.7 7.2 7.7 8.8
11.2 13.9 (dN-m) Tensile properties and Shore A hardness after
press cure Shore A 57 50 44 61 61 61 40 46 50 58 62 Tb (MPa) 12.6
10 6.8 17.9 16.1 17.6 1.7 5.2 12.5 15.2 16 Eb (%) 225 240 270 235
230 245 200 240 260 245 205 Tensile properties and Shore A hardness
after press cure followed by one week hot air aging at 190 C. Shore
A 54 45 42 57 60 63 79 65 75 78 80 Tb (MPa) 10.7 7.8 4.8 11.6 11.7
8.8 * 5.2 5.3 7 4.5 Eb (%) 230 240 235 190 180 135 * 5 15 20 15
change in * too brittle to test Sh A (pts) -3 -5 -2 -4 -1 2 39 19
25 20 18 Tb (%) -15 -22 -29 -35 -27 -50 -100 0 -58 -54 -72 Eb (%) 2
0 -13 -19 -22 -45 -100 -98 -94 -92 -93 Compression set, 70 hrs at
150 C. (%) 28 21 16 36 31 33 16 17 19 24 16
Example 2
[0101] Blend B5 comprises polyacrylate AE1 and polyamide P2 as
shown in Table 4, and is produced according to the method of blend
B1 in Example 1. Transmission electron micrographs of blend B5
indicate that the polyacrylate elastomer is the continuous phase in
the blend, and the polyamide is dispersed in roughly spherical
domains of approximately 2 to 5 um diameter.
TABLE-US-00004 TABLE 4 B5 % AE1 55 P2 45 Mooney Viscosity ML1 + 4,
100 C. 69
[0102] B5 was further blended with EVA2 on a roll mill at
approximately 40.degree. C. to produce blends B6-B10 as shown in
Table 5, ranging in polyamide content from 10 wt % to 0.2 wt %.
TABLE-US-00005 TABLE 5 Blend B6 B7 B8 B9 B10 phr phr phr phr phr
EVA2 88.61 94.67 97.95 99.5 99.8 B5 25.32 11.83 4.56 1.12 0.45
Mooney Viscosity ML1 + 4, 100 C. 20 18 17 16 16 Composition in
weight % EVA2 77.78 88.89 95.55 98.89 99.55 AE1 12.22 6.11 2.45
0.61 0.25 P2 10 5 2 0.5 0.2
[0103] Blends B6-B10 were further compounded to produce curable
compounds E7-E9, CE6, and CE7 as shown in Table 6, using a
Brabender.RTM. mixing bowl as described in Example 1.
[0104] A control compound (CE8) using EVA2 as the sole polymer
component was also produced via the Brabender mixing bowl procedure
as described in Example 1. Results in Table 6 show that all the
compounds exhibit a strong cure response, and similar Shore A
hardness and tensile properties after press cure. After hot air
aging for two weeks at 175.degree. C., however, the inventive
compounds comprising at least 1% polyamide and 1% polyacrylate
elastomer exhibit only a 3 point increase in Shore A hardness,
compared with 10 points or more for the comparative examples. In
addition, after heat aging the inventive compositions have more
than three times greater tensile elongation to break than the
comparative examples.
TABLE-US-00006 TABLE 6 E7 E8 E9 CE6 CE7 CE8 Compound phr phr phr
phr phr phr B6 113.93 B7 106.5 B8 102.51 B9 100.62 B10 100.25 EVA2
100 Coagent 2 2 2 2 2 2 Peroxide 5 5 5 5 5 5 Antioxidant 1 1 1 1 1
1 Carbon black 30 30 30 30 30 30 Cure Response ML (dN-m) 0.3 0.3
0.3 0.3 0.3 0.3 MH (dN-m) 10.5 9.5 9.3 9 9.1 9 MH - ML (dN- 10.2
9.2 9 8.7 8.8 8.7 m) Tensile properties and Shore A hardness after
press cure Shore A 60 61 61 59 60 59 Tb (MPa) 13.6 13.9 12.8 12.3
12.2 12.2 Eb (%) 210 240 235 205 230 210 Tensile properties and
Shore A hardness after press cure and two weeks hot air aging at
175.degree. C. Shore A 63 58 64 69 76 79 Tb (MPa) 10.1 7.2 4.5 3.3
4.4 5.3 Eb (%) 170 125 75 20 20 20 change in Sh A (pts) 3 -3 3 10
16 20 Tb (%) -26 -48 -65 -73 -64 -57 Eb (%) -19 -48 -68 -90 -91
-90
Example 3
[0105] Blends B11 and B12 were produced by charging EVA2, AE1, and
P1 in the proportions shown in Table 7 to a Brabender.RTM. mixing
bowl. The bowl was fitted with roller blades, and preheated to
240.degree. C. The three polymers were mixed at a rotor speed of
100 rpm. As the temperature of the batch achieved 220.degree. C.
(the melting peak temperature of P1), a timer was started and air
cooling initiated to maintain a batch temperature of about
240.degree. C. After 3 minutes of mixing, the blends were
discharged from the bowl, and cooled to room temperature before
further processing.
TABLE-US-00007 TABLE 7 Blend B11 B12 % % EVA2 67 60 AE1 3 10 P1 30
30 Mooney Viscosity ML1 + 4, 100 C. 36 36
[0106] Curable compositions E10 and E11 were produced according to
the formulations in Table 8 by roll mill mixing at a temperature of
about 40.degree. C. These compositions exhibit strong cure
response, and excellent physical properties after press cure
followed by a post cure of 30 minutes at 175.degree. C., as well as
after hot air aging of one week at 190.degree. C.
TABLE-US-00008 TABLE 8 Compound E10 E11 phr phr B11 142.9 B12 142.9
Coagent 2 2 Peroxide 5 5 Antioxidant 1 1 Cure Response ML (dN-m)
0.4 0.4 MH (dN-m) 11.8 11.4 MH-ML (dN-m) 11.4 11 Tensile properties
and Shore A hardness after press cure 10 min/ 175.degree. C. and
post cure 30 minutes/175.degree. C. Shore A 60 60 Tb (MPa) 13.5
13.4 Eb (%) 200 215 Tensile properties and Shore A hardness after
press cure, post cure and 1 week hot air aging at 190.degree. C.
Shore A 56 57 Tb (MPa) 9.1 9.4 Eb (%) 180 185
* * * * *