Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-11-16
2004-05-18
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S194000, C525S199000
Reexamination Certificate
active
06737479
ABSTRACT:
BACKGROUND OF THE INVENTION
Dynamic vulcanizates are known in the prior art, both in rubber/plastic blends, and in rubber/rubber dynamic vulcanizates. For example, U.S. Pat. No. 5,053,450 teaches dynamic vulcanization of acrylate copolymer elastomers in a matrix of fluoroelastomer, but no prior art patent suggests that one grade of fluoroelastomer might usefully be dynamically vulcanized while being blended with a second type of fluoroelastomer.
A key raw material used in some of the dynamic vulcanizates of this invention are the iodine-terminated peroxide-curable FKMs of U.S. Pat. No. 4,158,678. These polymers have iodine groups only on the chain termini (i.e., they are “telechelic” polymers). The reactivity of the iodine terminal groups is very high, so that substantially all of them can be incorporated into crosslinks. These polymers have the property that, provided there is enough peroxide and coagent to cause the reaction of all the iodine-functional endgroups into the elastomer network, adding more peroxide and coagent has little additional effect.
SUMMARY OF THE INVENTION
It has been found that elastomeric polymer blends that include:
1. a first portion of one or more fluoroelastomers, known collectively as fluoroelastomer phase 1, which is readily crosslinkable by a cure system 1 that does not crosslink fluoroelastomer phase 2 (or which crosslinks as fluoroelastomer phase 2 at a much slower rate than fluoroelastomer phase 1), and
2. a second portion of one or more fluoroelastomers, known collectively as fluoroelastomer phase 2, which is capable of being crosslinked by a different cure system 2 than is used to crosslink fluoroelastomer phase 1,
can be dynamically cured during intensive mixing using cure system 1 under conditions where fluoroelastomer phase 1 is crosslinked but not fluoroelastomer phase 2. These dynamic vulcanizates can subsequently be mixed (at low temperature) with cure system 2 to produce a fluoroelastomer compound with one or more of these special properties:
high green strength due to the high gel content, which leads to good shape retention of extrusions and low extrusion die swell;
low tendency to blister, to the extent that some versions can be cured at atmospheric pressure without blistering;
low cost compared to similar compounds based on only one type of fluoroelastomer (in some commercially significant cases);
relatively high tear strength compared to a standard (non-dynamically cured) fluoroelastomers using the same filler system.
The invention includes polymer blends containing at least two and possibly three or more non-miscible fluoroelastomers, at least one of which is dynamically vulcanized. All the fluoroelastomers that cure during dynamic vulcanization of a blend of the present invention are said to constitute “fluoroelastomer phase 1”. Fluoroelastomer phase 1 can contain several different types of crosslinked fluoroelastomers. All the fluoroelastomers that do not cure during dynamic vulcanization of a blend of the present invention are said to constitute “fluoroelastomer phase 2”. Fluoroelastomer phase 2 can also contain several different types of flowable, non-crosslinked fluoroelastomers. These fluoroelastomer phases can in general consist of any workable blend of elastomers that have more than 17% by weight elemental fluorine, including all the known commercial classes of fluoroelastomer. This includes specifically blends of:
elastomeric copolymers of vinylidene fluoride and hexafluoropropene (“FKM dipolymers” herein);
elastomeric copolymers that are derived from at least three monomers, including vinylidene fluoride and hexafluoropropene which also contain polymerized residues from other monomers, such special cure site monomers, tetrafluoroethylene, ethylene and/or perfluorovinylethers. (“FKM copolymers” herein);
elastomeric “peroxide-curable FKM” refers to FKM copolymers that are derived from at least three monomers: vinylidene fluoride, hexafluoropropene, and one or more special reactive cure site monomers that confer peroxide-reactivity to the polymer. Peroxide-curable FKMs can also contain tetrafluoroethylene, ethylene, and/or perfluorovinylethers.
elastomeric copolymers of propene and tetrafluoroethylene (“FEPM copolymers” herein);
perfluoroelastomers (“FFKM copolymers” herein) of the polymethylene type having all fluoro, perfluoroalkyl, or perfluoroalkoxy substituent groups on the polymer chain; a small fraction of these groups may contain functionality to facilitate vulcanization;
elastomeric perfluoropolyethers, such as poly(perfluoropropyleneoxide) and copolymers thereof containing cure sites;
fluorosilicones, which consist of polydialkylsiloxanes in which at least 28% of the siloxane residues have at least one 3,3,3-trifluoropropyl residue attached to the silicon atom.
As will become be clear in the detailed discussion below, only certain particular mixtures of fluoroelastomers actually work to form the blends of this invention by dynamic vulcanization.
The presence of microscopic crosslinked fluoroelastomer particles (“fluoroelastomer phase 1”) in the presence of one or more flowable fluoroelastomers (“fluoroelastomer phase 2”) confers several useful properties, including greater resistance to blistering in low temperature curing, improved green strength, reduced extrusion die swell, improved tear strength, and/or improved economics. Improved economics comes about primarily because the method makes it possible to blend relatively inexpensive fluoroelastomers, such as for example copolymers of vinylidene fluoride and hexafluoropropene (“FKM dipolymers”) with more expensive peroxide-curable copolymers, fluorosilicone polymers, or perfluoroelastomers. The requirement for the process to work is that independent (or nearly so) cure systems must exist for fluoroelastomer phase 1 and fluoroelastomer phase 2, and also fluoroelastomer phase 1 must not be miscible with fluoroelastomer phase 2.
Definitions of Terms
For purposes of this disclosure, “fluoroelastomer” means elastomeric copolymers containing 17% or more elemental fluorine. Fluoroelastomers include FKM, perfluoroelastomers, and fluorosilicone polymers.
For purposes of this disclosure, “FKM” without modifiers means elastomeric copolymers that are derived from at least two monomers, vinylidene fluoride and hexafluoropropene. FKM may also contain polymerized residues from other monomers, such as tetrafluoroethylene, ethylene, special cure site monomers, and/or perfluorovinylethers.
For purposes of this disclosure, “FKM dipolymer” means copolymers that are derived from only two monomers, vinylidene fluoride and hexafluoropropene, with vinylidene fluoride content from 40-70% by weight.
For purposes of this disclosure, “FKM copolymer” means elastomeric copolymers that are derived from at least three monomers, including vinylidene fluoride and hexafluoropropene which also contain polymerized residues from other monomers, such as tetrafluoroethylene, ethylene, and/or perfluorovinylethers. FKM dipolymers and copolymers are not readily crosslinkable by peroxides and/or peroxides+coagents.
For purposes of this disclosure, “peroxide-curable FKM” refers to FKM copolymers that are derived from at least three monomers: vinylidene fluoride, hexafluoropropene, and one or more special reactive cure site monomers that confer peroxide-reactivity to the polymer. Peroxide-curable FKMs can also contain tetrafluoroethylene, ethylene, and/or perfluorovinylethers. Peroxide-curable FKMs can be crosslinked by peroxide or another source of reactive free radicals, and preferably also a reactive coagent such as triallylisocyanurate (TAIC) or various other multifunctional vinyl group-containing coagents.
For purposes of this disclosure, perfluoroelastomers (also “FFKM” copolymers” herein) are polymers of the polymethylene type having all fluoro, perfluoroalkyl, or perfluoroalkoxy substituent groups on the polymer chain; a small fraction of these groups may contain functionality to facilitate vulcanization.
For purposes of this disclosure, “perfluoropolyethers” refer to elastomeric fluoropolye
Dingman, Esq. Brian M.
Immix Technologies, LLC
Mirick, O'Connell, DeMaillie & Lougee, LLP
Nutter Nathan M.
LandOfFree
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