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
2000-06-30
2002-10-15
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S200000, C525S326300, C525S340000, C525S377000, C525S378000, C525S387000, C526S247000, C526S249000, C526S250000, C526S310000
Reexamination Certificate
active
06465576
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to peroxide-curable fluoroelastomer compositions. In another aspect, the invention relates to articles, including molded articles such as o-rings, seals and gaskets, made from curable fluoroelastomer compositions.
BACKGROUND OF THE INVENTION
Fluoroelastomers (i.e., elastomeric fluoropolymers) are polymeric materials that exhibit significant tolerance to high temperatures and harsh chemical environments. Consequently, fluoroelastomers are particularly well adapted for use as seals and gaskets and other molded elastomeric parts in systems that are exposed to elevated temperatures and/or corrosive chemicals. Such parts are widely used in the chemical processing, semiconductor, aerospace and petroleum industries, among many others.
The unique properties of fluoropolymers are attributable largely to the stability and inertness of the copolymerized fluorinated monomer units that make up the major portion of a polymer backbone. Perfluorinated monomers, such as tetrafluoroethylene, hexafluoropropene, and perfluorovinyl ethers are among such fluorinated monomer units. In order to develop the elastomeric properties of the fluorinated polymers completely, the polymers typically are cross-linked, i.e., they are vulcanized. To accomplish this, a small percentage of a cure site monomer is copolymerized with perfluorinated monomer units. Many cure site monomers are known, including those with at least one bromo or iodo group. Such cure site monomers, when combined with a peroxide and a coagent, will provide a suitably cured composition.
One important property of cured fluoroelastomer compositions is measured as compression set. The compression set of a cured polymer, most often expressed as a percentage, provides an indication of its response to deformation forces. The higher the compression set for the cured elastomer composition, the more it permanently deforms when subjected to compressive forces. Conversely, the lower the compression set for a cured polymer, the more likely the polymer will resist permanent deformation under compressive forces. The lower the compression set of a given cured fluoroelastomer, the more generally useful that elastomer is for most applications.
The presence or absence of various adjuvants in the curable fluoroelastomer composition can affect the resulting compression set of the cured polymer. For example, semiconductor-grade fluoroelastomers typically are formulated without inorganic acid acceptors such as, for example, calcium carbonate, calcium hydroxide and zinc oxide, all of which can leave traces of extractable metallic compounds in the cured composition. Fluoroelastomer compositions formulated without an acid acceptor, however, typically suffer from increased compression set, making them less desirable, and in some cases unacceptable, for some demanding applications.
SUMMARY OF THE INVENTION
The fluoroelastomer compositions of the present invention employ at least one of an organo onium, phosphate, phosphine or amine oxide, alkyl amine, or heterocyclic amine as an additive that provides improved compression set. These additives can be incorporated into a wide range of fluoroelastomer formulations, including those formulated without an acid acceptor. The compositions of this invention find particular utility in molded parts used for semiconductor applications.
In one aspect, the invention provides a curable fluoroelastomer composition comprising:
(1) a fluoroelastomer comprising interpolymerized units derived from (a) at least one perfluoroolefin; (b) at least one perfluorovinyl ether selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and mixtures thereof; and (c) a cure site component capable of participation in a peroxide cure reaction;
(2) at least one additive selected from the group consisting of organo-oniums, phosphates, phosphine oxides, amine oxides, alkyl amines, and heterocyclic amines and salts of heterocyclic amines;
(3) a peroxide curative; and
(4) optionally a coagent.
In another aspect, the invention provides molded articles, including o-rings, gaskets and seals, made from the above curable fluoroelastomer compositions.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Fluoroelastomers are polymeric compositions generally formed of interpolymerized units of at least two principal monomers. Generally, one of the monomers is a perfluoroolefin and the other is a perfluorovinyl ether, typically either a perfluoro(vinyl alkyl) ether or a perfluoro(vinyl alkoxy) ether. Representative of the perfluoroolefin monomers are tetrafluoroethylene and hexafluoropropene.
Suitable perfluorinated vinyl ethers include those of the formula:
CF
2
═CFO(R′
f
O)
n
(R″
f
O)
m
R
f
(1)
where:
R′
f
and R″
f
are the same or are different linear or branched perfluoroalkylene groups of 2-6 carbon atoms;
m and n are, independently, 0 or an integer from 1 to 10; and
R
f
is a perfluoroalkyl group of 1-6 carbon atoms.
A preferred class of perfluoro(alkyl vinyl) ethers includes compositions of the formula:
CF
2
═CFO(CF
2
CFXO)
n
R
f
(2)
where: X is F or CF
3
; n is 0-5, and R
f
is a perfluoroalkyl group of 1-6 carbon atoms.
Most preferred perfluoro(alkyl vinyl) ethers are those where, in reference to either Formula 1 or 2 above, n is 0 or 1 and R
f
contains 1-3 carbon atoms. Examples of such perfluorinated ethers include perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, and perfluoro(propyl vinyl) ether.
Other useful perfluorinated monomers include those compounds of the formula:
CF
2
═CFO[(CF
2
)
m
CF
2
CFZO]
n
R
f
(3)
where R
f
is a perfluoroalkyl group having 1-6 carbon atoms, m is 0 or 1, n is 0-5, and Z is F or CF
3
. Preferred members of this class are those in which R
f
is C
3
F
7
, m is 0, and n is 1.
Additional perfluoro(alkyl vinyl) ether monomers useful in the invention include those of the formula:
CF
2
═CFO[(CF
2
CFCF
3
O)
n
(CF
2
CF
2
CF
2
O)
m
(CF
2
)
p
]C
x
F
2x+1
(4)
where m and n each are 0 or an integer from 1-10, p is 0-3, and x is 1-5. Preferred members of this class include compounds where n is 0 or 1, m is 0 or 1, and x is 1.
Perfluoro(alkoxy vinyl) ethers useful in the invention include those of the formula:
CF
2
═CFOCF
2
CF(CF
3
)O(CF
2
O)
m
C
n
F
2n+1
(5)
where n is 1-5, preferably 1, and m is 1-3. Specific, representative, examples of useful perfluoro(alkoxy vinyl) ethers include CF
2
═CFOCF
2
OCF
2
CF
2
CF
3
, CF
2
═CFOCF
2
OCF
3
, CF
2
═CFO(CF
2
)
3
OCF
3
, and CF
2
═CFOCF
2
CF
2
OCF
3
.
Mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl) ethers may also be employed.
Preferred fluorinated copolymers are composed of tetrafluoroethylene and at least one perfluoro(alkyl vinyl) ether as principal monomer units. In such copolymers, the copolymerized perfluorinated ether units constitute from about 15 to about 50 mole percent of total monomer units present in the polymer.
The fluorinated monomers of the invention may be polymerized by methods known in the art. For example, the polymerization process can be carried out by free-radical polymerization of the monomers alone or as solutions, emulsions, or dispersions in an organic solvent or water. Polymerization in an aqueous emulsion or suspension often is preferred because of the rapid and nearly complete conversion of monomers, easy removal of the heat of polymerization, and ready isolation of the polymer. Emulsion or suspension polymerization typically involves polymerizing monomers in an aqueous medium in the presence of an inorganic free-radical initiator system, such as ammonium persulfate or potassium permanganate, and surfactant or suspending agent.
Aqueous emulsion polymerization can be carried out continuously under steady-state conditions in which, for example, monomers, water, surfactants, buffers and catalysts are fed continuously to a stirred reactor under optimum pressure and temperature conditions while th
Grootaert Werner M. A.
Kolb Robert E.
Dyneon LLC
Harts Dean M.
Lilly James V.
Zitomer Fred
LandOfFree
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