U.S. patent application number 11/170611 was filed with the patent office on 2007-01-04 for dynamic vulcanization of fluorocarbon elastomers containing peroxide cure sites.
This patent application is currently assigned to Freudenberg-NOK General Partnership. Invention is credited to Edward Hosung Park.
Application Number | 20070004865 11/170611 |
Document ID | / |
Family ID | 37590520 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070004865 |
Kind Code |
A1 |
Park; Edward Hosung |
January 4, 2007 |
Dynamic vulcanization of fluorocarbon elastomers containing
peroxide cure sites
Abstract
Processable rubber compositions contain a vulcanized elastomeric
material dispersed in a matrix of a thermoplastic polymeric
material. The vulcanized elastomeric material is a peroxide cure
polymeric material containing repeating units derived from
fluorine-containing monomers and at least one peroxide cure site
monomer. In one embodiment the matrix forms a continuous phase and
the vulcanized elastomeric material is in the form of particles
forming a non-continuous phase. The compositions are made by
combining a radical curing system, a fluorocarbon elastomer
material, and a fluoroplastic material, and heating the mixture at
a temperature and for a time sufficient to effect vulcanization of
the elastomeric material, while mechanical energy is applied to mix
the mixture during the heating step. Shaped articles may be readily
formed from the rubber compositions according to conventional
thermoplastic processes such as blow molding, injection molding,
and extrusion. Examples of useful articles include seals, gaskets,
O-rings, and hoses.
Inventors: |
Park; Edward Hosung;
(Saline, MI) |
Correspondence
Address: |
FREUDENBERG-NOK GENERAL PARTNERSHIP;LEGAL DEPARTMENT
47690 EAST ANCHOR COURT
PLYMOUTH
MI
48170-2455
US
|
Assignee: |
Freudenberg-NOK General
Partnership
|
Family ID: |
37590520 |
Appl. No.: |
11/170611 |
Filed: |
June 29, 2005 |
Current U.S.
Class: |
525/326.2 |
Current CPC
Class: |
C08F 214/18 20130101;
Y10T 428/139 20150115 |
Class at
Publication: |
525/326.2 |
International
Class: |
C08F 214/18 20060101
C08F214/18 |
Claims
1. A processable rubber composition comprising a vulcanized
elastomeric material dispersed in a matrix, wherein the vulcanized
elastomeric material comprises a peroxide cured fluorocarbon
elastomer comprising repeating units derived from at least one
fluorine containing olefinic monomer and at least one cure site
monomer, the cure site monomer comprising at least one of a C--Cl
bond, a C--Br bond, a C--I bond, and an olefin; and wherein the
matrix comprises a fluorine containing thermoplastic polymeric
material.
2. A composition according to claim 1, wherein the matrix forms a
continuous phase.
3. A composition according to claim 1, wherein the vulcanized
elastomeric material is in the form of particles forming a
non-continuous phase.
4. A composition according to claim 1, wherein the vulcanized
elastomeric material comprises repeating units derived from from
about 10 to about 90 mole % tetrafluoroethylene; from about 10 to
about 90 mole % C.sub.2-4 olefin; and up to about 30 mole % of one
or more additional fluorine containing monomers.
5. A composition according to claim 4, wherein the repeating units
are derived from from about 25 to about 90 mole %
tetrafluoroethylene and from about 10 to about 75 mole % propylene
or ethylene.
6. A composition according to claim 4, wherein the vulcanized
elastomeric material comprises repeating units derived from
vinylidene difluoride.
7. A composition according to claim 1, wherein the composition
comprises at least about 25 parts by weight vulcanized elastomeric
material per 100 parts of the vulcanized elastomeric material and
thermoplastic material combined.
8. A composition according to claim 7, wherein the composition
comprises at least about 50 parts by weight vulcanized elastomeric
material per 100 parts of the vulcanized elastomeric material and
thermoplastic material combined.
9. A method for making a rubber composition comprising, forming a
mixture by combining a radical curing system, an elastomeric
material, and a thermoplastic material; and heating the mixture at
a temperature and for a time sufficient to effect vulcanization of
the elastomeric material, wherein mechanical energy is applied to
mix the mixture during the heating step; wherein the elastomeric
material comprises a polymeric material comprising repeating units
derived from at least one fluorine containing olefinic monomer and
from at least one cure site monomer wherein the repeating unit
derived from the at least one cure site monomer comprises at least
one functional group selected from the group consisting of a C--Cl
bond, a C--Br bond, a C--I bond, and an olefin; and wherein the
thermoplastic material comprises a fluorine containing polymeric
material that softens and flows upon heating.
10. A method according to claim 9, wherein the elastomeric material
comprises repeating units derived from from about 10 to about 90
mole % tetrafluoroethylene; from about 10 to about 90 mole %
C.sub.2-4 olefin; and up to about 30 mole % of an additional
fluorine containing monomer.
11. A method according to claim 10, wherein the additional monomer
comprises vinylidene difluoride.
12. A method according to claim 9, wherein the radical curing
system comprises an organic peroxide and a crosslinking co-agent,
the co-agent comprising at least two sites of olefinic
unsaturation.
13. A method according to claim 9, comprising a continuous
process.
14. A method according to claim 13, carried out in a twin screw
extruder.
15. A method according to claim 9, comprising a batch process.
16. A method according to claim 9, wherein the combination
comprises at least about 25 parts by weight vulcanized elastomeric
material per 100 parts of the vulcanized elastomeric material and
thermoplastic material combined.
17. A method according to claim 16, wherein the combination
comprises at least about 50 parts by weight vulcanized elastomeric
material per 100 parts of the vulcanized elastomeric material and
thermoplastic material combined.
18. A shaped article comprising peroxide cured fluorocarbon
elastomer fluoroplastic particles dispersed in a fluoroplastic
matrix, wherein the particles comprise a peroxide cured copolymer
of at least one fluorine containing olefinic monomer and at least
one cure site monomer, wherein the at least one cure site monomer
comprises at least one functional group selected from the group
consisting of a C--Cl bond, a C--Br bond, a C--I bond, and an
olefin.
19. An article according to claim 18, wherein the vulcanized
copolymer comprises repeating units derived from from about 45 to
about 65 mole % tetrafluoroethylene, from about 20 to about 55 mole
% propylene or ethylene, and up to about 30% of additional fluorine
containing monomer or monomers.
20. An article according to claim 19, wherein the additional
monomer comprises vinylidene difluoride.
21. An article according to claim 18, wherein the fluoroplastic
comprises polyvinylidene fluoride.
22. An article according to claim 18, wherein the article comprises
at least about 25 parts by weight vulcanized elastomeric material
(per 100 parts of the vulcanized elastomeric material and
thermoplastic material combined).
23. A seal according to claim 18.
24. An O-ring according to claim 18.
25. A gasket according to claim 18.
26. A hose according to claim 18.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to thermoprocessable
compositions containing cured fluorocarbon elastomers. It also
relates to seal and gasket type material made from the compositions
and methods for their production by dynamic vulcanization
techniques.
BACKGROUND OF THE INVENTION
[0002] Cured elastomeric materials have a desirable set of physical
properties typical of the elastomeric state. They show a high
tendency to return to their original size and shape following
removal of a deforming force, and they retain physical properties
after repeated cycles of stretching, including strain levels up to
1000%. Based on these properties, the materials are generally
useful for making shaped articles such as seals and gaskets.
[0003] Because they are thermoset materials, cured elastomeric
materials can not generally be processed by conventional
thermoplastic techniques such as injection molding, extrusion, or
blow molding. Rather, articles must be fashioned from elastomeric
materials by high temperature curing and compression molding.
Although these and other rubber compounding operations are
conventional and known, they nevertheless tend to be more expensive
and require higher capital investment than the relatively simpler
thermoplastic processing techniques. Another drawback is that scrap
generated in the manufacturing process is difficult to recycle and
reuse, which further adds to the cost of manufacturing such
articles.
[0004] In today's automobile engines, the high temperatures of use
have led to the development of a new generation of lubricants
containing a high level of basic materials such as amines. Articles
made from elastomeric materials, such as seals and gaskets, are in
contact with such fluids during use, and are subject to a wide
variety of challenging environmental conditions, including exposure
to high temperature, contact with corrosive chemicals, and high
wear conditions during normal use. Accordingly, it is desirable to
make such articles from materials that combine elastomeric
properties and stability or resistance to the environmental
conditions.
[0005] To meet the demands of the new lubricant technology, a line
of fluorocarbon elastomers has been developed highly resistant to
the basic compounds found in the lubricating oils and greases.
Specifically, cured elastomers based on copolymers of
tetrafluoroethylene and propylene have met commercial success. As a
thermoset material, the cured fluorocarbon rubber is subject to the
processing disadvantages noted above.
[0006] It would be desirable to provide an elastomeric or rubber
composition that would combine a high level of chemical resistance
with the advantages of thermoplastic processability. It would
further be desirable to provide methods for formulating chemically
resistant rubbers having such advantageous properties.
SUMMARY OF THE INVENTION
[0007] These and other advantages are achieved with a processable
rubber composition containing a vulcanized elastomeric material
dispersed in a matrix of a thermoplastic polymeric material. The
vulcanized elastomeric material comprises a peroxide cured
polymeric material comprising repeating units derived in one
embodiment from tetrafluoroethylene, at least one C.sub.2-4 olefin,
optionally one or more additional fluorine-containing monomers, and
low levels of a peroxide cure site monomer that contains at least
one of a C--Cl bond, a C--Br bond, a C--I bond, and an olefin. In
one embodiment the matrix forms a continuous phase and the
vulcanized elastomeric material is in the form of particles forming
a non-continuous phase. In various embodiments, the processable
compositions are thermally processed into molded articles that
exhibit a high degree of base resistance, especially a high degree
of resistance to degradation of physical properties upon exposure
to fluids containing strong nucleophiles such as amines.
[0008] A method for making a rubber composition comprises combining
a radical curing system, a curable elastomeric material having cure
sites highly reactive to radical initiators, and a thermoplastic
material, and heating the mixture at a temperature and for a time
sufficient to effect vulcanization of the elastomeric material,
while mechanical energy is applied to mix the mixture during the
heating step. The elastomeric material is a fluorocarbon polymer
and the thermoplastic material comprises a fluorine containing
polymeric material that softens and flows upon heating.
[0009] Shaped articles may be readily formed from the rubber
compositions according to conventional thermoplastic processes such
as blow molding, injection molding, and extrusion. Examples of
useful articles include seals, gaskets, O-rings, and hoses.
[0010] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] The following description of the preferred embodiment(s) is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0012] The headings (such as "Introduction" and "Summary,") used
herein are intended only for general organization of topics within
the disclosure of the invention, and are not intended to limit the
disclosure of the invention or any aspect thereof. In particular,
subject matter disclosed in the "Introduction" may include aspects
of technology within the scope of the invention, and may not
constitute a recitation of prior art. Subject matter disclosed in
the "Summary" is not an exhaustive or complete disclosure of the
entire scope of the invention or any embodiments thereof.
[0013] The citation of references herein does not constitute an
admission that those references are prior art or have any relevance
to the patentability of the invention disclosed herein. All
references cited in the Description section of this specification
are hereby incorporated by reference in their entirety.
[0014] The description and specific examples, while indicating
embodiments of the invention, are intended for purposes of
illustration only and are not intended to limit the scope of the
invention. Moreover, recitation of multiple embodiments having
stated features is not intended to exclude other embodiments having
additional features, or other embodiments incorporating different
combinations of the stated features. Specific Examples are provided
for illustrative purposes of how to make, use and practice the
compositions and methods of this invention and, unless explicitly
stated otherwise, are not intended to be a representation that
given embodiments of this invention have, or have not, been made or
tested.
[0015] As used herein, the words "preferred" and "preferably" refer
to embodiments of the invention that afford certain benefits, under
certain circumstances. However, other embodiments may also be
preferred, under the same or other circumstances. Furthermore, the
recitation of one or more preferred embodiments does not imply that
other embodiments are not useful, and is not intended to exclude
other embodiments from the scope of the invention.
[0016] As used herein, the word "include," and its variants, is
intended to be non-limiting, such that recitation of items in a
list is not to the exclusion of other like items that may also be
useful in the materials, compositions, devices, and methods of this
invention. All percentages herein are by weight, unless stated
otherwise.
[0017] When exposed to environments containing strong nucleophiles
such as the amines in modern day engine oils in automotive
applications, rubbers tend to change their elastomeric properties
with time of exposure. Normally the rubbers degrade over time when
exposed to such fluids. The degradation is expressed as a change in
physical parameters such as tensile strength, modulus, hardness,
elongation at break, and others. According to various embodiments
of the invention, it has been found that base resistance is
enhanced when fluorocarbon rubbers are cured by radical curing
systems in the presence of thermoplastic materials as discussed
herein. The processable compositions are made into various molded
articles such as seals, gaskets, o-rings, hoses, and the like. The
molded articles exhibit an advantageous combination of elastomeric
properties. Furthermore, in various embodiments, the base
resistance of articles made from the processable compositions of
the invention is higher than that of articles made of the cured
fluorocarbon rubbers themselves.
[0018] In one embodiment, the invention provides processable rubber
compositions that contain a vulcanized elastomeric material
dispersed in a matrix. The vulcanized elastomeric material is a
peroxide cured fluorocarbon elastomer comprising repeating units
derived from at least one fluorine containing olefinic monomer and
at least one cure site monomer, with the cure site monomer
comprising at least one of a C--Cl bond, a C--Br bond, a C--I bond,
and an olefin. The matrix comprises a thermoplastic polymeric
material, preferably a fluorine containing material, also called a
fluoroplastic. In a preferred embodiment, the vulcanized
elastomeric material is a polymeric material containing repeating
units derived from tetrafluoroethylene and from at least one
C.sub.2-4 olefin, and containing crosslinks resulting from the
reaction of peroxide curing agents and co-agents with radical cure
site monomers in the polymeric material.
[0019] In one aspect, the matrix forms a continuous phase and the
vulcanized elastomeric material is in the form of particles forming
a non-continuous phase. In another aspect, the elastomeric material
and the matrix form co-continuous phases.
[0020] In another embodiment, the invention provides methods for
making the processable rubber compositions by dynamic vulcanization
of the elastomeric component in the presence of the thermoplastic
component. In one embodiment, the method comprises forming a
mixture by combining a radical curing system, an elastomeric
material, and a thermoplastic material, and heating the mixture at
a temperature and for a time sufficient to effect vulcanization of
the elastomeric material. Mechanical energy is applied to mix the
mixture during the heating step. The elastomeric material comprises
a polymeric material comprising repeating units derived from at
least one fluorine containing olefinic monomer and from at least
one cure site monomer; the repeating unit derived from the at least
one cure site monomer comprises at least one functional group
selected from the group consisting of a C--Br bond, a C--I bond,
and an olefin. The thermoplastic material comprises a fluorine
containing polymeric material that softens and flows upon
heating.
[0021] In various embodiments, the method of the invention provides
for mixing the elastomer and thermoplastic components in the
presence of a curing system and heating during the mixing to effect
cure of the elastomeric component. In one embodiment, the
elastomeric material and thermoplastic material are mixed for a
time and at a shear rate sufficient to form a dispersion of the
elastomeric material in a continuous thermoplastic phase.
Thereafter, a radical curing system such as a peroxide and
crosslinking co-agent is added to the dispersion of elastomeric
material and thermoplastic material while continuing the mixing.
Finally, the dispersion is heated while continuing to mix to
produce a processable rubber composition of the invention.
[0022] In various embodiments, the processable rubber compositions
of the invention are readily processable by conventional plastic
processing techniques. In one embodiment, shaped articles are
provided comprising the vulcanized elastomeric materials dispersed
in a thermoplastic matrix. Shaped articles of the invention
include, without limitation, seals, O-rings, gaskets, and
hoses.
[0023] Various types of fluoroelastomers may be used. One
classification of fluoroelastomers is given in ASTM-D 1418,
"Standard practice for rubber and rubber latices-nomenclature." The
designation FKM is given for fluoro-rubbers that utilize vinylidene
fluoride as a co-monomer. Several varieties of FKM fluoroelastomers
are commercially available. A first variety may be chemically
described as a copolymer of hexafluoropropylene and vinylidene
fluoride. These FKM elastomers tend to have an advantageous
combination of overall properties. Some commercial embodiments are
available with about 66% by weight fluorine. Another type of FKM
elastomer may be chemically described as a terpolymer of
tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride.
Such elastomers tend to have high heat resistance and good
resistance to aromatic solvents. They are commercially available
with, for example 68-69.5% by weight fluorine. Another FKM
elastomer is chemically described as a terpolymer of
tetrafluoroethylene, a fluorinated vinyl ether, and vinylidene
fluoride. Such elastomers tend to have improved low temperature
performance. In various embodiments, they are available with 62-68%
by weight fluorine. A fourth type of FKM elastomer is described as
a terpolymer of tetrafluoroethylene, propylene, and vinylidene
fluoride. Such FKM elastomers tend to have improved base
resistance. Some commercial embodiments contain about 67% weight
fluorine. A fifth type of FKM elastomer may be described as a
pentapolymer of tetrafluoroethylene, hexafluoropropylene, ethylene,
and a fluorinated vinyl ether and vinylidene fluoride. Such
elastomers typically have improved base resistance and have
improved low temperature performance.
[0024] Another category of fluorocarbon elastomers is designated as
FFKM. These elastomers may be designated as perfluoroelastomers
because the polymers are completely fluorinated and contain no
carbon hydrogen bond. As a group, the FFKM fluoroelastomers tend to
have superior fluid resistance. They were originally introduced by
DuPont under the Kalrez.RTM. trade name. Additional suppliers
include Daikin and Ausimont.
[0025] A third category of fluorocarbon elastomer is designated as
FTPM. Typical of this category are the copolymers of propylene and
tetrafluoroethylene. The category is characterized by a high
resistance to basic materials such as amines.
[0026] Fluorocarbon elastomers include commercially available
copolymers of one or more fluorine containing monomers, chiefly
vinylidene fluoride (VDF), hexafluoropropylene (HFP),
tetrafluoroethylene (TFE), and perfluorovinyl ethers (PFVE).
Preferred PFVE include those with a C.sub.1-8 perfluoroalkyl group,
preferably perfluoroalkyl groups with 1 to 6 carbons, and
particularly perfluoromethyl vinyl ether and perfluoropropyl vinyl
ether. In addition, the copolymers may also contain repeating units
derived from olefins such as ethylene (Et) and propylene (Pr).
[0027] The fluorocarbon elastomers and cured fluorocarbon
elastomers used in the compositions and methods of the invention
contain repeating units derived from one or more fluorine
containing olefinic monomers as described above, and further
contain repeating units derived from so-called peroxide cure site
monomers, which are described in further detail below. The
repeating units are derived from the corresponding monomers in the
sense that the structure of the polymer results from a
copolymerization of the olefinic monomers and the resulting
structure is recognized as the addition polymerization product of
the monomers. In the cured elastomers, at least some of the
repeating units derived from the cure site monomers contain
so-called peroxide crosslinks. In one embodiment, the peroxide
crosslinks are formed by the reaction of polyolefinic co-agents
with radicals on the cure site monomers induced by the action of
the peroxide component of the radical curing system.
[0028] Preferred copolymer fluorocarbon elastomers include
VDF/HFP/CSM, VDF/HFP/TFE/CSM, VDF/PFVE/TFE/CSM, TFE/Pr/CSM,
TFE/Pr/NVDF/CSM, TFE/Et/PFVE/VDF/CSM, TFE/Et/PFVE/CSM and
TFE/PFVE/CSM, where CSM represents the peroxide cure site monomers.
The elastomer designation gives the monomers from which the
elastomer gums are synthesized. In some embodiments, the elastomer
gums have viscosities that give a Mooney viscosity in the range
generally of 15-160 (ML1+10, large rotor at 121.degree. C.), which
can be selected for a combination of flow and physical properties.
Elastomer suppliers include Dyneon (3M), Asahi Glass
Fluoropolymers, Solvay/Ausimont, DuPont, and Daikin.
[0029] As used herein, elastomer refers, according to context, to
either a non-cured or a cured fluorocarbon elastomer. The terms
"cured elastomer", "peroxide cured fluorocarbon elastomer", and the
like describe the product of curing or crosslinking the un-cured
elastomer with a radical curing system.
[0030] In various preferred embodiments, the elastomeric material
is described chemically as a copolymer of tetrafluoroethylene and
at least one C.sub.2-4 olefin and further containing cure site
monomer. Optionally, the elastomeric material contains repeating
units derived from one or more additional fluorine-containing
monomers. As such, the cured elastomeric material comprises
repeating units derived from tetrafluoroethylene and at least one
C.sub.2-4 olefin, and further comprises peroxide crosslinks.
[0031] In a preferred embodiment, the elastomeric material
comprises repeating units derived from 10-90 mole %
tetrafluoroethylene, 10-90 mole % C.sub.2-4 olefin, and up to 30
mole % of one or more additional fluorine-containing monomers.
Preferably, the repeating units are derived from 25-90 mole %
tetrafluoroethylene and 10-75 mole % C.sub.2-4 olefin. In another
preferred embodiment, the repeating units are derived from 45-65
mole % tetrafluoroethylene and 20-55 mole % C.sub.2-4 olefin.
[0032] In particularly preferred embodiments, the molar ratio of
tetrafluoroethylene units to C.sub.2-4 olefin repeating units is
from 60:40 to 40:60. In another embodiment, the elastomeric
material comprises alternating units of C.sub.2-4 olefins and
tetrafluoroethylene. In such polymers the molar ratio of
tetrafluoroethylene to C.sub.2-4 olefin is approximately 50:50.
[0033] In another embodiment, the elastomeric materials are
provided as block copolymers having an A-B-A structure, wherein A
represents a block of poly-tetrafluoroethylene and B represents a
block of polyolefin.
[0034] A preferred C.sub.2-4 olefin is propylene. Elastomeric
materials based on copolymers of tetrafluoroethylene and propylene
are commercially available, for example from Asahi under the
Aflas.RTM. trade name.
[0035] A preferred additional monomer in the vulcanized elastomeric
material is vinylidene difluoride. Other fluorine-containing
monomers that may be used in the elastomeric materials of the
invention include without limitation, perfluoroalkyl vinyl
compounds, perfluoroalkyl vinylidene compounds, and perfluoroalkoxy
vinyl compounds. Hexafluoropropylene (HFP) is an example of
perfluoroalkyl vinyl monomer. Perfluoromethyl vinyl ether is an
example of a preferred perfluoroalkoxy vinyl monomer. For example,
rubbers based on copolymers of tetrafluoroethylene, ethylene, and
perfluoromethyl vinyl ether are commercially available from DuPont
under the Viton.RTM. ETP trade name.
[0036] Fluorocarbon elastomeric materials used to make the
processable rubber compositions of the invention may typically be
prepared by free radical emulsion polymerization of a monomer
mixture containing the desired molar ratios of starting monomers.
Initiators are typically organic or inorganic peroxide compounds,
and the emulsifying agent is typically a fluorinated acid soap. The
molecular weight of the polymer formed may be controlled by the
relative amounts of initiators used compared to the monomer level
and the choice of transfer agent if any. Typical transfer agents
include carbon tetrachloride, methanol, and acetone. The emulsion
polymerization may be conducted under batch or continuous
conditions. Such fluoroelastomers are commercially available as
noted above.
[0037] In various embodiments, the fluoroelastomers of the
compositions of the invention contain repeating units derived from
peroxide cure site monomers. In various embodiments, the
fluorocarbon elastomers contain up to 5 mole % and preferably up to
3 mole % of repeating units derived from the so-called cure site
monomers. In one embodiment, the cure site repeating units are
derived from halogen-containing olefin monomers, wherein the
halogen is chlorine, bromine, iodine, or combinations of any of
them. If used, preferably the repeating units of a
halogen-containing olefin are present in a level to provide at
least about 0.05% halogen in the polymer, preferably 0.3% halogen
or more. In a preferred embodiment, the total weight of halogen in
the polymer is 1.5 wt. % or less.
[0038] The cure site monomers provide sites on the elastomeric
material that react at a high rate with radical initiators such as
peroxides. The cure site monomer sites react faster with the curing
system than other parts of the elastomer. Crosslinking thus occurs
preferentially at the cure site monomers. It is believed that this
crosslinking action is responsible at least in part for development
of elastomeric properties in the elastomer. The cure site monomers
are preferably selected from the group consisting of brominated,
chlorinated, and iodinated olefins; brominated, chlorinated, and
iodinated unsaturated ethers; and non-conjugated dienes.
[0039] In preferred embodiments, the fluoroelastomers comprise at
least one halogenated cure site or a reactive double bond resulting
from the presence of a copolymerized unit of a non-conjugated
diene. The double bond of the cure site monomer is referred to
herein as an olefin. Functional groups associated with the cure
sites thus include a carbon bromine (C--Br) bond, a carbon iodine
(C--I) bond, a carbon chlorine (C--Cl) bond, and an olefin. In
various embodiments, halogenated cure sites are provided by
copolymerized cure site monomers and/or by halogen atoms that are
present at terminal positions of the fluoroelastomer polymer chain.
Generically, the halogenated cure sites are said to be repeating
units derived from a cure site monomer. Co-polymerized cure site
monomers, reactive double bonds, and halogenated end groups are
capable of reacting to form crosslinks, especially under conditions
of catalysis or initiation by the action of peroxides.
[0040] As is clear from this discussion, the repeating units of an
uncured elastomer derived from the cure site monomers contain one
or more of those functional groups. On the other hand, in cured
elastomers, some of the functional groups will be reacted with the
curing system. In both cases, it is said that the elastomer
contains repeating units derived from peroxide cure site
monomers.
[0041] Brominated cure site monomers may contain other halogens,
preferably fluorine. Examples are bromotrifluoroethylene,
4-bromo-3,3,4,4-tetrafluorobutene-1 and others such as vinyl
bromide, 1-bromo-2,2-difluoroethylene, perfluoroallyl bromide,
4-bromo-1,1,2-trifluorobutene,
4-bromo-1,1,3,3,4,4,-hexafluorobutene, 4-bromo-3-chloro-
1,1,3,4,4-pentafluorobutene, 6-bromo-5,5,6,6-tetrafluorohexene,
4-bromoperfluorobutene-1 and 3,3-difluoroallyl bromide. Brominated
unsaturated ether cure site monomers useful in the invention
include ethers such as 2-bromo-perfluoroethyl perfluorovinyl ether
and fluorinated compounds of the class CF.sub.2
Br--R.sub.f--O--CF.dbd.CF.sub.2 (R.sub.f is perfluoroalkylene),
such as CF.sub.2 BrCF.sub.2 O--CF.dbd.CF.sub.2, and fluorovinyl
ethers of the class ROCF.dbd.CFBr or ROCBr.dbd.CF.sub.2, where R is
a lower alkyl group or fluoroalkyl group, such as
CH.sub.3OCF.dbd.CFBr or CF.sub.3 CH.sub.2 OCF.dbd.CFBr.
[0042] Iodinated olefins may also be used as cure site monomers.
Suitable iodinated monomers include iodinated olefins of the
formula: CHR.dbd.CH-Z-CH.sub.2CHR--I, wherein R is --H or
--CH.sub.3; Z is a C.sub.1-C.sub.18 (per)fluoroalkylene radical,
linear or branched, optionally containing one or more ether oxygen
atoms, or a (per)fluoropolyoxyalkylene radical as disclosed in U.S.
Pat. No. 5,674,959. Other examples of useful iodinated cure site
monomers are unsaturated ethers of the formula: I(CH.sub.2 CF.sub.2
CF.sub.2).sub.nOCF.dbd.CF.sub.2 and
ICH.sub.2CF.sub.2O[CF(CF.sub.3)CF.sub.2O].sub.nCF.dbd.CF.sub.2, and
the like, wherein n=1-3, such as disclosed in U.S. Pat. No.
5,717,036. In addition, suitable iodinated cure site monomers
including iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1;
3-chloro-4-iodo-3,4,4-trifluorobutene;
2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane;
2-iodo-1-(perfluorovinyloxy)-1,1,2,2-tetrafluoroethylene; 1,1,2,3,3
3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane; 2-iodoethyl vinyl
ether; 3,3,4,5,5,5-hexafluoro-4-iodopentene; and
iodotrifluoroethylene are disclosed in U.S. Pat. No. 4,694,045.
[0043] Examples of non-conjugated diene cure site monomers include
1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene and others, such as
those disclosed in Canadian Patent 2,067,891. A suitable triene is
8-methyl-4-ethylidene-1,7-octadiene.
[0044] Of the cure site monomers listed above, preferred compounds
include 4-bromo-3,3,4,4-tetrafluorobutene-1;
4-iodo-3,3,4,4-tetrafluorobutene-1; and bromotrifluoroethylene.
[0045] Additionally, or alternatively, cure site monomers and
repeating units derived from them containing iodine, bromine or
mixtures thereof are present at the fluoroelastomer chain ends as a
result of the use of chain transfer or molecular weight regulating
agents during preparation of the fluoroelastomers. Such agents
include iodine-containing compounds that result in bound iodine at
one or both ends of the polymer molecules. Methylene iodide;
1,4-diiodoperfluoro-n-butane; and
1,6-diiodo-3,3,4,4,tetrafluorohexane are representative of such
agents. Other iodinated chain transfer agents include
1,3-diiodoperfluoropropane; 1,4-diiodoperfluorobutane;
1,6-diiodoperfluorohexane; 1,3-diiodo-2-chloroperfluoropropane;
1,2-di(iododifluoromethyl)perfluorocyclobutane;
monoiodoperfluoroethane; monoiodoperfluorobutane; and
2-iodo-1-hydroperfluoroethane. Particularly preferred are
diiodinated chain transfer agents. Examples of brominated chain
transfer agents include 1-bromo-2-iodoperfluoroethane; 1
-bromo-3-iodoperfluoropropane; 1-iodo-2-bromo- 1,1-difluoroethane
and others such as disclosed in U.S. Pat. No. 5,151,492.
[0046] A wide variety of thermoplastic polymeric materials can be
used in the invention. In one embodiment, the thermoplastic
polymeric material used is a thermoplastic elastomer. Preferred
thermoplastic elastomers include those having a crystalline melting
point of 120.degree. C. or higher, preferably 150.degree. C. or
higher, and more preferably 200.degree. C. or higher.
[0047] Thermoplastic elastomers have some physical properties of
rubber, such as softness, flexibility and resilience, but can be
processed like thermoplastics. A transition from a melt to a solid
rubber-like composition occurs fairly rapidly upon cooling. This is
in contrast to convention elastomers, which hardens slowly upon
heating. Thermoplastic elastomers may be processed on conventional
plastic equipment such as injection molders and extruders. Scrap
may generally be readily recycled.
[0048] Thermoplastic elastomers have a multi-phase structure,
wherein the phases are generally intimately mixed. In many cases,
the phases are held together by graft or block copolymerization. At
least one phase is made of a material that is hard at room
temperature but fluid upon heating. Another phase is a softer
material that is rubber like at room temperature.
[0049] Some thermoplastic elastomers have an A-B-A block copolymer
structure, where A represents hard segments and B is a soft
segment. Because most polymeric material tend to be incompatible
with one another, the hard and soft segments of thermoplastic
elastomers tend to associate with one another to form hard and soft
phases. For example, the hard segments tend to form spherical
regions or domains dispersed in a continuous elastomer phase. At
room temperature, the domains are hard and act as physical
crosslinks tying together elastomeric chains in a 3-D network. The
domains tend to lose strength when the material is heated or
dissolved in a solvent.
[0050] Other thermoplastic elastomers have a repeating structure
represented by (A-B)n, where A represents the hard segments and B
the soft segments as described above.
[0051] Many thermoplastic elastomers are known. They in general
adapt either the A-B-A triblock structure or the (A-B).sub.n
repeating structure. Non-limiting examples of A-B-A type
thermoplastic elastomers include
polystyrene/polysiloxane/polystyrene,
polystyrene/polyethylene-co-butylene/polystyrene,
polystyrene/polybutadiene polystyrene,
polystyrene/polyisoprene/polystyrene, poly-.alpha.-methyl
styrene/polybutadiene/poly-.alpha.-methyl styrene,
poly-.alpha.-methyl styrene/polyisoprene/poly-.alpha.-methyl
styrene, and
polyethylene/polyethylene-co-butylene/polyethylene.
[0052] Non-limiting examples of thermoplastic elastomers having a
(A-B).sub.n repeating structure include polyamide/polyether,
polysulfone/polydimethylsiloxane, polyurethane/polyester,
polyurethane/polyether, polyester/polyether,
polycarbonate/polydimethylsiloxane, and polycarbonate/polyether.
Among the most common commercially available thermoplastic
elastomers are those that contain polystyrene as the hard segment.
Triblock elastomers are available with polystyrene as the hard
segment and either polybutadiene, polyisoprene, or
polyethylene-co-butylene as the soft segment. Similarly, styrene
butadiene repeating co-polymers are commercially available, as well
as polystyrene/polyisoprene repeating polymers.
[0053] In a preferred embodiment, a thermoplastic elastomer is used
that has alternating blocks of polyamide and polyether. Such
materials are commercially available, for example from Atofina
under the Pebax.RTM. trade name. The polyamide blocks may be
derived from a copolymer of a diacid component and a diamine
component, or may be prepared by homopolymerization of a cyclic
lactam. The polyether block is generally derived from homo- or
copolymers of cyclic ethers such as ethylene oxide, propylene
oxide, and tetrahydrofuran.
[0054] The thermoplastic polymeric material may also be selected
from among solid, generally high molecular weight, plastic
materials. In one embodiment, the materials are crystalline or
semi-crystalline polymers, preferably having a crystallinity of at
least 25% as measured by differential scanning calorimetry.
Amorphous polymers with a suitably high glass transition
temperature are also acceptable as the thermoplastic polymeric
material. In a preferred embodiment, the thermoplastic has a melt
temperature or a glass transition temperature in the range from
about 80.degree. C. to about 350.degree. C., but the melt
temperature should generally be lower than the decomposition
temperature of the thermoplastic vulcanizate. In various
embodiments, the melting point of crystalline or semi-crystalline
polymers is 120.degree. C. or higher, preferably 150.degree. C. or
higher, and more preferably 200.degree. C. or higher. Suitable
thermoplastic materials include both fluoroplastics and
non-fluoroplastics.
[0055] Non-limiting examples of thermoplastic polymers include
polyolefins, polyesters, nylons, polycarbonates,
styrene-acrylonitrile copolymers, polyethylene terephthalate,
polybutylene terephthalate, polyamides including aromatic
polyamides, polystyrene, polystyrene derivatives, polyphenylene
oxide, polyoxymethylene, and fluorine-containing thermoplastics.
Polyolefins are formed by polymerizing a-olefins such as, but not
limited to, ethylene, propylene, 1-butene, 1-hexene, 1-octene,
2-methyl-1-propene, 3-methyl-1-pentene, 4-methyl-1-pentene,
5-methyl-1-hexene, and mixtures thereof. Copolymers of ethylene and
propylene or ethylene or propylene with another .alpha.-olefin such
as 1-butene, 1-hexene, 1-octene, 2-methyl-1-propene,
3-methyl-1-pentene, 4-methyl-1-pentene, 5-methyl-1-hexene or
mixtures thereof are also contemplated. These homopolymers and
copolymers, and blends of them, may be incorporated as the
thermoplastic polymeric material of the invention.
[0056] Polyester thermoplastics contain repeating ester linking
units in the polymer backbone. In one embodiment, they contain
repeating units derived from low molecular weight diols and low
molecular weight aromatic diacids. Non-limiting examples include
the commercially available grades of polyethylene terephthalate and
polybutylene terephthalate. Alternatively, the polyesters may be
based on aliphatic diols and aliphatic diacids. Exemplary are the
copolymers of ethylene glycol or butanediol with adipic acid. In
another embodiment, the thermoplastic polyesters are polylactones,
prepared by polymerizing a monomer containing both hydroxyl and
carboxyl functionality. Polycaprolactone is a non-limiting example
of this class of thermoplastic polyester.
[0057] Polyamide thermoplastics contain repeating amide linkages in
the polymer backbone. In one embodiment, the polyamides contain
repeating units derived from diamine and diacid monomers such as
the well known nylon 66, a polymer of hexamethylene diamine and
adipic acid. Other nylons have structures resulting from varying
the size of the diamine and diacid components. Non-limiting
examples include nylon 610, nylon 612, nylon 46, and nylon 6/66
copolymer. In another embodiment, the polyamides have a structure
resulting from polymerizing a monomer with both amine and carboxyl
functionality. Non-limiting examples include nylon 6
(polycaprolactam), nylon 11, and nylon 12.
[0058] Other polyamides made from diamine and diacid components
include the high temperature aromatic polyamides containing
repeating units derived from diamines and aromatic diacids such as
terephthalic acid. Commercially available examples of these include
PA6T (a copolymer of hexanediamine and terephthalic acid), and PA9T
(a copolymer of nonanediamine and terephthalic acid), sold by
Kuraray under the Genestar tradename. For some applications, the
melting point of some aromatic polyamides may be higher than
optimum for thermoplastic processing. In such cases, the melting
point may be lowered by preparing appropriate copolymers. In a
non-limiting example, in the case of PA6T, which has a melting
temperature of about 370.degree. C., it is possible to in effect
lower the melting point to below a moldable temperature of
320.degree. C. by including an effective amount of a non-aromatic
diacid such as adipic acid when making the polymer.
[0059] In another preferred embodiment, an aromatic polyamide is
used based on a copolymer of an aromatic diacid such as
terephthalic acid and a diamine containing greater than 6 carbon
atoms, preferably containing 9 carbon atoms or more. The upper
limit of the length of the carbon chain of the diamine is limited
from a practical standpoint by the availability of suitable
monomers for the polymer synthesis. As a rule, suitable diamines
include those having from 7 to 20 carbon atoms, preferably in the
range of 9 to 15 carbons, and more preferably in the range from 9
to 12 carbons. Preferred embodiments include C9, C10, and C11
diamine based aromatic polyamides. It is believed that such
aromatic polyamides exhibit an increase level of solvent resistance
based on the oleophilic nature of the carbon chain having greater
than 6 carbons. If desired to reduce the melting point below a
preferred molding temperature (typically 320.degree. C. or lower),
the aromatic polyamide based on diamines of greater than 6 carbons
may contain an effective amount of a non-aromatic diacid, as
discussed above with the aromatic polyamide based on a 6 carbon
diamine. Such effective amount of diacid should be enough to lower
the melting point into a desired molding temperature range, without
unacceptably affecting the desired solvent resistance
properties.
[0060] Other non-limiting examples of high temperature
thermoplastics include polyphenylene sulfide, liquid crystal
polymers, and high temperature polyimides. Liquid crystal polymers
are based chemically on linear polymers containing repeating linear
aromatic rings. Because of the aromatic structure, the materials
form domains in the nematic melt state with a characteristic
spacing detectable by x-ray diffraction methods. Examples of
materials include copolymers of hydroxybenzoic acid, or copolymers
of ethylene glycol and linear aromatic diesters such as
terephthalic acid or naphthalene dicarboxylic acid.
[0061] High temperature thermoplastic polyimides include the
polymeric reaction products of aromatic dianhydrides and aromatic
diamines. They are commercially available from a number of sources.
Exemplary is a copolymer of 1,4-benzenediamine and
1,2,4,5-benzenetetracarboxylic acid dianhydride.
[0062] In a preferred embodiment, the thermoplastic polymeric
material comprises a fluorocarbon thermoplastic polymer, also
referred to as a "fluoroplastic". Commercial embodiments are
available that contain 59 to 76% by weight fluorine. They may
either be fully fluorinated or partially fluorinated. In various
other preferred embodiments, the thermoplastic is selected from
thermoplastic elastomers, high molecular weight plastic materials,
and other thermoplastic polymeric materials that do not contain
fluorine. Mixtures of fluoroplastics and non-fluoroplastics may
also be used.
[0063] Fully fluorinated thermoplastic polymers include copolymers
of tetrafluoroethylene and perfluoroalkyl vinyl ethers. The
perfluoroalkyl group is preferably of 1 to 6 carbon atoms. Examples
of copolymers are PFA (copolymer of TFE and perfluoropropyl vinyl
ether) and MFA (copolymer of TFE and perfluoromethyl vinyl ether).
Other examples of fully fluorinated thermoplastic polymers include
copolymers of TFE with perfluoro olefins of 3 to 8 carbon atoms.
Non-limiting examples include FEP (copolymer of TFE and
hexafluoropropylene).
[0064] Partially fluorinated thermoplastic polymers include E-TFE
(copolymer of ethylene and TFE), E-CTFE (copolymer of ethylene and
chlorotrifluoroethylene), and PVDF (polyvinylidene fluoride). A
number of thermoplastic copolymers of vinylidene fluoride are also
suitable thermoplastic polymers for use in the invention. These
include, without limitation, copolymers with perfluoroolefins such
as hexafluoropropylene, and copolymers with
chlorotrifluoroethylene. Thermoplastic terpolymers may also be
used. These include thermoplastic terpolymers of TFE, HFP, and
vinylidene fluoride. Fully fluorinated fluoroplastics are
characterized by relatively high melting points, when compared to
the vinylidene fluoride based thermoplastics that are also included
in the fluoroplastic blend of the invention. As examples, PFA has a
melting point of about 305.degree. C., MFA has a melting point of
280-290.degree. C., and FEP has a melting point of about
260-290.degree. C. The melting point of individual grades depends
on the exact structure, processing conditions, and other factors,
but the values given here are representative.
[0065] Partially fluorinated fluoroplastics such as the vinylidene
fluoride homo- and copolymers described above have relatively lower
melting points than the fully fluorinated fluoroplastics. For
example, polyvinylidene fluoride has a melting point of about
160-170.degree. C. Some copolymer thermoplastics have an even lower
melting point, due to the presence of a small amount of co-monomer.
For example, a vinylidene fluoride copolymer with a small amount of
hexafluoropropylene, exemplified in a commercial embodiment such as
the Kynar Flex series, exhibits a melting point in the range of
about 105-160.degree. C., and typically about 130.degree. C. These
low melting points lead to advantages in thermoplastic processing,
as lower temperatures of melting lead to lower energy costs and
avoidance of the problem of degradation of cured elastomers in the
compositions.
[0066] The fluorocarbon elastomers described above are dynamically
cured in the presence of the thermoplastic polymeric material and a
radical curing system. The radical curing system contains a radical
initiator and a crosslinking co-agent. The radical initiator is
believed to function by first extracting a hydrogen or halogen atom
from the fluorocarbon elastomer to create a free radical that can
be crosslinked. It is believed that the cure site monomers
described above provide sites that react with the radical initiator
at an accelerated rate, so that subsequent crosslinking described
below occurs mainly at the cure site monomers. Crosslinking
co-agents are normally included in the radical curing system. They
contain at least two sites of olefinic unsaturation, which react
with the free radical on the fluorocarbon elastomer molecule
generated by the reaction of the initiator.
[0067] In various embodiments, the initiators have peroxide
functionality. As examples of initiators, a wide range of organic
peroxides is known and commercially available. The initiators,
including the organic peroxides, are activated over a wide range of
temperatures. The activation temperature may be described in a
parameter known as half-life. Typically values for half-lives of,
for example, 0.1 hours, 1 hour, and 10 hours are given in degrees
centigrade. For example a T.sub.1/2 at 0.1 hours of 143.degree. C.
indicates that at that temperature, half of the initiator will
decompose within 0.1 hours. Organic peroxides with a T.sub.1/2 at
0.1 hours from 118.degree. C. to 228.degree. C. are commercially
available. Such peroxides have a half-life of at least 0.1 hours at
the indicated temperatures. The T.sub.1/2 values indicate the
kinetics of the initial reaction in crosslinking the fluorocarbon
elastomers, that is decomposition of the peroxide to form a radical
containing intermediate.
[0068] In some embodiments, it is preferred to match the T.sub.1/2
of the initiator such as an organic peroxide to the temperature of
the molten material into which the curing composition is to be
added. In various embodiments, the initiator has a thermal
stability such that the half-life is at least 0.1 hours at
temperatures of 180.degree. C. or higher. In other embodiments,
suitable initiators have a half-life of 0.1 hours at 190.degree. C.
or higher, or at temperatures of 200.degree. C. or higher.
Non-limiting examples of peroxides and their T.sub.1/2 for a
half-life of 0.1 hours include Trigonox 145-E85
(T.sub.1/2=182.degree. C.), Trigonox M55 (T.sub.1/2=183.degree.
C.), Trigonox K-90 (T.sub.1/2=195.degree. C.), Trigonox A-W70
(T.sub.1/2=207.degree. C.) and Trigonox TAHP-W85
(T.sub.1/2=228.degree. C.). A non-limiting example of a
non-peroxide initiator is Perkadox-30 (T.sub.1/2=284.degree. C.).
The Trigonox and Perkadox materials are commercial or developmental
products of AkzoNobel.
[0069] Non-limiting examples of commercially available organic
peroxides for initiating the cure of fluorocarbon elastomers
include butyl 4,4-di-(tert-butylperoxy)valerate; tert-butyl
peroxybenzoate; di-tert-amyl peroxide; dicumyl peroxide;
di-(tert-butylperoxyisopropyl)benzene;
2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; tert-butyl cumyl
peroxide; 2,5,-dimethyl-2,5-di(tert-butylperoxy)hexyne-3;
di-tert-butyl peroxide;
3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane;
1,1,3,3-tetramethylbutyl hydroperoxide; diisopropylbenzene
monohydroperoxide; cumyl hydroperoxide; tert-butyl hydroperoxide;
tert-amyl hydroperoxide; tert-butyl peroxyisobutyrate; tert-amyl
peroxyacetate; tert-butylperoxy stearyl carbonate;
di(1-hydroxycyclohexyl) peroxide; ethyl
3,3-di(tert-butylperoxy)butyrate; and tert-butyl 3-isopropenylcumyl
peroxide.
[0070] Non-limiting examples of crosslinking co-agents include
triallyl cyanurate; triallyl isocyanurate;
tri(methallyl)-isocyanurate; tris(diallylamine)-s-triazine,
triallyl phosphite; N,N-diallyl acrylamide; hexaallyl
phosphoramide; N,N,N',N'-tetraallyl terephthalamide;
N,N,N',N'-tetraallyl malonamide; trivinyl isocyanurate;
2,4,6-trivinyl methyltrisiloxane; and tri(5-norbornene-2-methylene)
cyanurate. The crosslinking co-agents preferably contain at least
two sites of olefinic unsaturation. The sites of unsaturation react
with the free radical generated on the fluorocarbon elastomer
molecule and crosslink the elastomer. A commonly used crosslinking
agent is triallylisocyanurate (TAIC).
[0071] In a preferred embodiment, plasticizers, extender oils,
synthetic processing oils, or a combination thereof may be used in
the compositions of the invention. The type of processing oil
selected will typically be consistent with that ordinarily used in
conjunction with the specific rubber or rubbers present in the
composition. The extender oils may include, but are not limited to,
aromatic, naphthenic, and paraffinic extender oils. Preferred
synthetic processing oils include polylinear .alpha.-olefins. The
extender oils may also include organic esters, alkyl ethers, or
combinations thereof. As disclosed in U.S. Pat. No. 5,397,832, it
has been found that the addition of certain low to medium molecular
weight organic esters and alkyl ether esters to the compositions of
the invention lowers the Tg of the polyolefin and rubber
components, and of the overall composition, and improves the low
temperatures properties, particularly flexibility and strength.
These organic esters and alkyl ether esters generally have a
molecular weight that is generally less than about 10,000.
Particularly suitable esters include monomeric and oligomeric
materials having an average molecular weight below about 2000, and
preferably below about 600. In one embodiment, the esters may be
either aliphatic mono- or diesters or alternatively oligomeric
aliphatic esters or alkyl ether esters.
[0072] In addition to the elastomeric material, the thermoplastic
polymeric material, and curative, the processable rubber
compositions of this invention may include other additives such as
stabilizers processing aids, curing accelerators, fillers,
pigments, adhesives, tackifiers, and waxes. The properties of the
compositions and articles of the invention may be modified, either
before or after vulcanization, by the addition of ingredients that
are conventional in the compounding of rubber, thermoplastics, and
blends thereof.
[0073] A wide variety of processing aids may be used, including
plasticizers and mold release agents. Non-limiting examples of
processing aids include Caranuba wax, phthalate ester plasticizers
such as dioctylphthalate (DOP) and dibutylphthalate silicate (DBS),
fatty acid salts such as zinc stearate and sodium stearate,
polyethylene wax, and keramide. In some embodiments, high
temperature processing aids are preferred. Such include, without
limitation, linear fatty alcohols such as blends of
C.sub.10-C.sub.28 alcohols, organosilicones, and functionalized
perfluoropolyethers. In some embodiments, the compositions contain
about 1 to about 15% by weight processing aids, preferably about 5
to about 10% by weight.
[0074] Acid acceptor compounds are commonly used as curing
accelerators or curing stabilizers. Preferred acid acceptor
compounds include oxides and hydroxides of divalent metals.
Non-limiting examples include Ca(OH).sub.2, MgO, CaO, and ZnO.
[0075] Non-limiting examples of fillers include both organic and
inorganic fillers such as, barium sulfate, zinc sulfide, carbon
black, silica, titanium dioxide, clay, talc, fiber glass, fumed
silica and discontinuous fibers such as mineral fibers, wood
cellulose fibers, carbon fiber, boron fiber, and aramid fiber
(Kevlar). Some non-limiting examples of processing additives
include stearic acid and lauric acid. The addition of carbon black,
extender oil, or both, preferably prior to dynamic vulcanization,
is particularly preferred. Non-limiting examples of carbon black
fillers include SAF black, HAF black, SRP black and Austin black.
Carbon black improves the tensile strength, and an extender oil can
improve processability, the resistance to oil swell, heat
stability, hysteresis, cost, and permanent set. In a preferred
embodiment, fillers such as carboxy block may make up to about 40%
by weight of the total weight of the compositions of the invention.
Preferably, the compositions comprise 1-40 weight % of filler. In
other embodiments, the filler makes up 10 to 25 weight % of the
compositions.
[0076] The vulcanized elastomeric material, also referred to herein
generically as a "rubber", is generally present as small particles
within a continuous thermoplastic polymer matrix. A co-continuous
morphology is also possible depending on the amount of elastomeric
material relative to thermoplastic material, the cure system, and
the mechanism and degree of cure of the elastomer and the amount
and degree of mixing. Preferably, the elastomeric material is fully
crosslinked/cured.
[0077] The full crosslinking can be achieved by adding an
appropriate curative or curative system to a blend of thermoplastic
material and elastomeric material, and vulcanizing the rubber to
the desired degree under conventional vulcanizing conditions. In a
preferred embodiment, the elastomer is crosslinked by the process
of dynamic vulcanization. The term dynamic vulcanization refers to
a vulcanization or curing process for a rubber contained in a
thermoplastic composition, wherein the curable rubber is vulcanized
under conditions of high shear at a temperature above the melting
point of the thermoplastic component. The rubber is thus
simultaneously crosslinked and dispersed as particles within the
thermoplastic matrix. Dynamic vulcanization is effected by mixing
the elastomeric and thermoplastic components at elevated
temperature in the presence of a curative in conventional mixing
equipment such as roll mills, Moriyama mixers, Banbury mixers,
Brabender mixers, continuous mixers, mixing extruders such as
single and twin-screw extruders, and the like. An advantageous
characteristic of dynamically cured compositions is that,
notwithstanding the fact that the elastomeric component is fully
cured, the compositions can be processed and reprocessed by
conventional plastic processing techniques such as extrusion,
injection molding and compression molding. Scrap or flashing can be
salvaged and reprocessed.
[0078] Heating and mixing or mastication at vulcanization
temperatures are generally adequate to complete the vulcanization
reaction in a few minutes or less, but if shorter vulcanization
times are desired, higher temperatures and/or higher shear may be
used. A suitable range of vulcanization temperature is from about
the melting temperature of the thermoplastic material (which is
preferably about 120.degree. C. or higher, more preferably
150.degree. C. or higher) to about 300.degree. C. or more. Without
limitation, the range is from about 150.degree. C. to about
250.degree. C. A preferred range of vulcanization temperatures is
from about 180.degree. C. to about 220.degree. C. It is preferred
that mixing continue without interruption until vulcanization
occurs or is complete.
[0079] If appreciable curing is allowed after mixing has stopped,
an unprocessable thermoplastic vulcanizate may be obtained. In this
case, a kind of post curing step may be carried out to complete the
curing process. In some embodiments, the post curing takes the form
of continuing to mix the elastomer and thermoplastic during a
cool-down period.
[0080] After dynamic vulcanization, a homogeneous mixture is
obtained, wherein the rubber is in the form of small dispersed
particles essentially of an average particle size smaller than
about 50 .mu.m, preferably of an average particle size smaller than
about 25 .mu.m, more preferably of an average size smaller than
about 10 .mu.m or less, and still more preferably of an average
particle size of 5 .mu.m or less.
[0081] The progress of the vulcanization may be followed by
monitoring mixing torque or mixing energy requirements during
mixing. The mixing torque or mixing energy curve generally goes
through a maximum after which mixing can be continued somewhat
longer to improve the fabricability of the blend. If desired, one
can add additional ingredients, such as the stabilizer package,
after the dynamic vulcanization is complete. The stabilizer package
is preferably added to the thermoplastic vulcanizate after
vulcanization has been essentially completed, i.e., the curative
has been essentially consumed.
[0082] The processable rubber compositions of the invention may be
manufactured in a batch process or a continuous process.
[0083] In a batch process, predetermined charges of elastomeric
material, thermoplastic material and curative agents are added to a
mixing apparatus. In a typical batch procedure, the elastomeric
material and thermoplastic material are first mixed, blended,
masticated or otherwise physically combined until a desired
particle size of elastomeric material is provided in a continuous
phase of thermoplastic material. When the structure of the
elastomeric material is as desired, a curing system containing the
radical initiator and crosslinking co-agent is then added while
continuing to apply mechanical energy to mix the elastomeric
material and thermoplastic material. Curing is effected by heating
or continuing to heat the mixing combination of thermoplastic and
elastomeric material in the presence of the curative agent.
Following cure, the processable rubber composition is removed from
the reaction vessel (mixing chamber) for further processing.
[0084] It is preferred to mix the elastomeric material and
thermoplastic material at a temperature where the thermoplastic
material softens and flows. If such a temperature is below that at
which the curative agent is activated, the curative agent may be a
part of the mixture during the initial particle dispersion step of
the batch process. In some embodiments, a curative is combined with
the elastomeric and polymeric material at a temperature below the
curing temperature. When the desired dispersion is achieved, the
temperature may be increased to effect cure. However, if the
curative agent is activated at the temperature of initial mixing,
it is preferred to leave out the curative until the desired
particle size distribution of the elastomeric material in the
thermoplastic matrix is achieved. In another embodiment, curative
is added after the elastomeric and thermoplastic materials are
mixed. Thereafter, in a preferred embodiment, the curative agent is
added to a mixture of elastomeric particles in thermoplastic
material while the entire mixture continues to be mechanically
stirred, agitated or otherwise mixed.
[0085] Continuous processes may also be used to prepare the
processable rubber compositions of the invention. In a preferred
embodiment, a twin screw extruder apparatus, either co-rotation or
counter-rotation screw type, is provided with ports for material
addition and reaction chambers made up of modular components of the
twin screw apparatus. In a typical continuous procedure,
thermoplastic material and elastomeric material are combined by
inserting them into the screw extruder together in a first hopper
using a feeder (loss-in-weight or volumetric feeder). Temperature
and screw parameters may be adjusted to provide a proper
temperature and shear to effect the desired mixing and particle
size distribution of an uncured elastomeric component in a
thermoplastic material matrix. The duration of mixing may be
controlled by providing a longer or shorter length of extrusion
apparatus or by controlling the speed of screw rotation for the
mixture of elastomeric material and thermoplastic material to go
through during the mixing phase. The degree of mixing may also be
controlled by the mixing screw element configuration in the screw
shaft, such as intensive, medium or mild screw designs. Then, at a
downstream port, by using side feeder (loss-in-weight or volumetric
feeder), the curative agent may be added continuously to the
mixture of thermoplastic material and elastomeric material as it
continues to travel down the twin screw extrusion pathway.
Downstream of the curative additive port, the mixing parameters and
transit time may be varied as described above. By adjusting the
shear rate, temperature, duration of mixing, mixing screw element
configuration, as well as the time of adding the curative agent,
processable rubber compositions of the invention may be made in a
continuous process.
[0086] The compositions and articles of the invention will contain
a sufficient amount of vulcanized elastomeric material ("rubber")
to form a rubbery composition of matter, that is, they will exhibit
a desirable combination of flexibility, softness, and compression
set. Preferably, the compositions should comprise at least about 25
parts by weight rubber, preferably at least about 35 parts by
weight rubber, even more preferably at least about 45 parts by
weight rubber, and still more preferably at least about 50 parts by
weight rubber per 100 parts by weight of the rubber and
thermoplastic polymer combined. More specifically, the amount of
cured rubber within the thermoplastic vulcanizate is generally from
about 5 to about 95% by weight, preferably from about 35 to about
85% by weight, and more preferably from about 50 to about 80% by
weight of the total weight of the rubber and the thermoplastic
polymer combined.
[0087] The amount of thermoplastic polymer within the processable
rubber compositions of the invention is generally from about 5 to
about 95% by weight, preferably from about 15 to about 65% by
weight and more preferably from about 20 to about 50% by weight of
the total weight of the rubber and the thermoplastic combined.
[0088] As noted above, the processable rubber compositions and
shaped articles of the invention include a cured rubber and a
thermoplastic polymer. Preferably, the thermoplastic vulcanizate is
a homogeneous mixture wherein the rubber is in the form of
finely-divided and well-dispersed rubber particles within a
non-vulcanized matrix. It should be understood, however, that the
thermoplastic vulcanizates of this invention are not limited to
those containing discrete phases inasmuch as the compositions of
this invention may also include other morphologies such as
co-continuous morphologies. In especially preferred embodiments,
the rubber particles have an average particle size smaller than
about 50 .mu.m, more preferably smaller than about 25 .mu.m, even
more preferably smaller than about 10 .mu.m or less, and still more
preferably smaller than about 5 .mu.m.
[0089] The term vulcanized or cured rubber refers to a natural or
synthetic rubber that has undergone at least a partial cure. The
degree of cure can be measured by determining the amount of rubber
that is extractable from the thermoplastic vulcanizate by using
boiling xylene or cyclohexane as an extractant. This method is
disclosed in U.S. Pat. No. 4,311,628. By using this method as a
basis, the cured rubber of this invention will have a degree of
cure where not more than 15% of the rubber is extractable,
preferably not more than 10% of the rubber is extractable, and more
preferably not more than 5% of the rubber is extractable. In an
especially preferred embodiment, the elastomer is technologically
fully vulcanized. The term fully vulcanized refers to a state of
cure such that the crosslinked density is at least
7.times.10.sup.-5 moles per ml of elastomer or that the elastomer
is less than about 3% extractable by cyclohexane at 23.degree.
C.
[0090] The degree of cure can be determined by the cross-link
density of the rubber. This, however, must be determined indirectly
because the presence of the thermoplastic polymer interferes with
the determination. Accordingly, the same rubber as present in the
blend is treated under conditions with respect to time,
temperature, and amount of curative that result in a fully cured
product as demonstrated by its cross-link density. This cross-link
density is then assigned to the blend similarly treated. In
general, a cross-link density of about 7.times.10.sup.-5 or more
moles per milliliter of rubber is representative of the values
reported for fully cured elastomeric copolymers. Accordingly, it is
preferred that the compositions of this invention are vulcanized to
an extent that corresponds to vulcanizing the same rubber as in the
blend statically cured under pressure in a mold with such amounts
of the same curative as in the blend and under such conditions of
time and temperature to give a cross-link density greater than
about 7.times.10.sup.-5 moles per milliliter of rubber and
preferably greater than about 1.times.10.sup.-4 moles per
milliliter of rubber.
[0091] Advantageously, the shaped articles of the invention, are
rubber-like materials that, unlike conventional rubbers, can be
processed and recycled like thermoplastic materials. These
materials are rubber-like to the extent that they will retract to
less than 1.5 times their original length within one minute after
being stretched at room temperature to twice their original length
and held for one minute before release, as defined in ASTM D1566.
Also, these materials satisfy the tensile set requirements set
forth in ASTM D412, and they also satisfy the elastic requirements
for compression set per ASTM D395.
[0092] The reprocessability of the rubber compositions of the
invention may be exploited to provide a method for reducing the
costs of a manufacturing process for making shaped rubber articles.
The method involves recycling scrap generated during the
manufacturing process to make other new shaped articles. Because
the compositions of the invention and the shaped articles made from
the compositions are thermally processable, scrap may readily be
recycled for re-use by collecting the scrap, optionally cutting,
shredding, grinding, milling, otherwise comminuting the scrap
material, and re-processing the material by conventional
thermoplastic techniques. Techniques for forming shaped articles
from the recovered scrap material are in general the same as those
used to form the shaped articles - the conventional thermoplastic
techniques include, without limitation, blow molding, injection
molding, compression molding, and extrusion.
[0093] The re-use of the scrap material reduces the costs of the
manufacturing process by reducing the material cost of the method.
Scrap may be generated in a variety of ways during a manufacturing
process for making shaped rubber articles. For example, off-spec
materials may be produced. Even when on-spec materials are
produced, manufacturing processes for shaped rubber articles tend
to produce waste, either through inadvertence or through process
design, such as the material in sprues of injection molded parts.
The re-use of such materials through recycling reduces the material
and thus the overall costs of the manufacturing process.
[0094] For thermoset rubbers, such off spec materials usually can
not be recycled into making more shaped articles, because the
material can not be readily re-processed by the same techniques as
were used to form the shaped articles in the first place. Recycling
efforts in the case of thermoset rubbers are usually limited to
grinding up the scrap and the using the grinds as raw material in a
number products other than those produced by thermoplastic
processing technique.
EXAMPLES
[0095] Viton.RTM. ETP 600S is a peroxide curable base resistant
elastomer from DuPont Dow Elastomers. It is based on a copolymer of
tetrafluoroethylene, ethylene, perfluoromethyl vinyl ether, and a
cure site monomer.
[0096] Tecnoflon.RTM. P 757 is a peroxide curable fluorocarbon
elastomer with cure site monomers, from Solvay. It is based on a
terpolymer of tetrafluoroethylene, hexafluoropropylene, and
vinylidene fluoride.
[0097] Hylar.RTM. MP 10 is a polyvinylidene fluoride thermoplastic
polymer from Solvay.
[0098] Kynar Flex 2500-20 is a polyvinylidene fluoride based
thermoplastic polymer from Atofina. It is based on a vinylidene
fluoride copolymer.
[0099] Luperox.RTM. 101XL45 is a peroxide initiator from
Arkema.
[0100] The comparative example is a molded base resistant
fluorocarbon rubber prepared by blending the following according
the manufacturer's instructions. TABLE-US-00001 Viton ETP 600S: 100
pph Luperox 101XL45: 3 pph TAIC: 3 pph ZnO: 3 pph Carbon black: 30
pph
The rubber is cured in a mold for 7 minutes at 177.degree. C., and
post-cured 16 hours at 232.degree. C.
[0101] Examples 1 and 2-4 are made by dynamic vulcanization of a
fluorocarbon elastomer (ETP 600S and P 757, respectively) with a
radical curing system (Luperox 101XL45, triallylisocyanurate, and
ZnO) in the presence of a thermoplastic (Hylar MP 10 and Kynar Flex
2500-20, respectively).
[0102] In a batch process, the peroxide curable elastomer
(Tecnoflon P757 or Viton ETP 600S)) and the thermoplastic (Hylar
MP-10 or Kynar Flex 2500-04) are mixed and melted in a Brabender or
Banbury type batch mixer at 160.degree. C. for 5 minutes. The zinc
oxide and carbon black are then stirred in. A curative package
consisting of Luperco 101 XL and TAIC is added to the mixer and
stirred for an additional 3-5 minutes at 160.degree. C. to form a
fully cured thermoplastic vulcanizate. The composition is then
discharged from the batch mixer and granulated to make small size
pellets for use in subsequent shaped article fabrication processes,
such as injection molding, compression molding, blow molding,
single layer extrusion, multi-layer extrusion, insert molding, and
the like.
[0103] A continuous process is carried out in a twin-screw
extruder. Pellets of fluoroelastomer (Tecnoflon P757 or Viton ESP
600S) and thermoplastic (Hylar MP-10 or Kynar Flex 2500-04) are
mixed and added to a hopper. The pellets are fed into the barrel,
which is heated to 160.degree. C. The screw speed is 100-200 rpm. A
curative package consisting of Luperco 101 XL, TAIC, ZnO and carbon
black is then fed into the barrel at a downstream port located
about one third of the total barrel length from the extruder exit.
The ingredients are melted and blended with the molten elastomer
and fluoroplastic mixture for a time determined by the screw speed
and the length of the barrel. For example, the residence time is
about 4-5 minutes at 100 rpm and about 2-2.5 minutes at 200 rpm.
The cured material is extruded through 1-3 mm diameter strand die
and is quenched by cooling in a water bath before passing through a
strand pelletizer. The pellets are to be processed by a wide
variety of thermoplastic techniques into molded articles. The
material is also being formed into plaques for the measurement of
physical properties.
[0104] Test pieces of the comparative Example and Examples 1-4 are
tested for base resistance by submerging them in a test fluid for
168 hours at 150.degree. C. The test fluid is a mixture of 94%
Stuarco 7061 gear oil with 6% Stuarco 7098 modifier.
[0105] Changes in physical properties are measured after the test
and expressed as a percentage change from the value measured before
the exposure. Values are reported in the Table. TABLE-US-00002
Compar- ative Exam- Exam- Exam- Exam- Example, ple 1, ple 2, ple 3,
ple 4, phr phr phr phr phr Viton ETP 600S 100 100 Tecnoflon P757
100 100 100 ZnO 3 3 5 5 5 triallylisocyanurate 3 3 3 3 3 Luperox
101XL45 3 3 3 3 3 Carbon black 30 10 10 10 10 Hylar MP-10 25 Kynar
Flex 2500-20 50 100 150 Filler 20 % % % % % Change in tensile
strength -27 -13 -26 10 10 Change in 50% modulus -30 -11 2 -10 -6
Change in 100% modulus -37 4 6 -- -- Change in elongation 19 -12
-32 -20 -12 Change in hardness (Shore A) -3 -9 -48 -2 -1 Change in
volume 3 11 18 3 2
[0106] While the invention has been disclosed herein with regard to
various enabling description, it is to be understood the invention
is not limited to the disclosed embodiments. Modifications and
variations that will occur to one of skill in the art upon reading
the description are also within the scope of the invention.
* * * * *