Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-04-24
2003-07-15
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S115000, C524S154000, C524S544000, C524S186000, C525S387000, C526S242000, C526S255000
Reexamination Certificate
active
06593416
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fluoropolymers, especially elastomeric fluoropolymers (i.e., fluoroelastomers), compositions incorporating such fluoropolymers, articles employing such fluoropolymers, and methods of making and using such fluoropolymers.
BACKGROUND
Cured compositions containing fluoropolymers are desirable for a number of applications. For example, they can be used as gaskets and O-rings. Such shaped articles having good compression set (i.e., little or no deformation of the cured article after a load is applied and removed) are particularly desirable.
Also, high purity fluoropolymers are used in a number of industries. They are especially preferred for use in the electronic, semiconductor, optical, medical, and pharmaceutical industries, to name a few. These polymers have a relatively low level of water extractable metals and metal compounds.
Inorganic acid acceptors are often added to fluoroelastomers utilizing peroxide cure systems. Optionally, at least one metal compound selected from divalent metal oxides or divalent metal hydroxides is frequently blended with the fluoroelastomer during preparation or before it is cured. While the presence of such compounds improves the heat aging resistance and thermal stability of the polymer (see, for example, U.S. Pat. No. 5,077,359), the addition of such acid acceptors has a very detrimental effect on the content of ions and extractables of the resulting elastomer composition. EP Pat. No. B-708 797 discloses the use of peroxide-curable fluoroelastomers with a fluoropolymer micropowder filler for semiconductor applications. There is no disclosure of how the materials were purified; however, due to the fact that this process requires acid acceptors the overall ion content seems to be unsatisfactorily high. Other fluoroelastomers that include such inorganic acid acceptors include EP 0 140 207 and U.S. Pat. Nos. 4,233,421 and 4,912,171, for example.
SUMMARY OF THE INVENTION
The present invention provides curable fluoroelastomer compositions, cured compositions, which can be secured to (e.g., coated on) a substrate, cured articles (e.g., shaped articles), and methods. Preferably, the compositions of the present invention are particularly useful as shaped articles such as gaskets and O-rings. In certain aspects of the invention, the fluoroelastomer compositions have improved compression set after being cured. In certain other aspects of the invention, the fluoroelastomer compositions are of a relatively high purity.
Preferably, the curable fluoroelastomer compositions of the present invention have improved compression set after they are cured. These curable compositions include a fluoroelastomer having units derived from a cure-site monomer and capable of peroxide cure, a peroxide curative for the fluoroelastomer, optionally a co-agent for the curative, and a non-fluorine-containing organo-onium. The improvement in compression set can be demonstrated by a comparison of cured fluoroelastomers with and without the organo-onium present. Those fluoroelastomers that contain the organo-onium have surprisingly better compression set properties than those of a similar or the same fluoropolymer composition but not employing the organo-onium. That is, there is little or no deformation of the cured article after a load is applied and removed using the test procedure described in the Examples Section when the fluoroelastomers are made using an organo-onium compared to when they are not. Preferably, the curative used in this embodiment is a peroxide.
This improvement is believed to be achieved whether or not the fluoroelastomer is of relatively high purity, although high purity can be desirable. Thus, in one aspect, the present invention provides a relatively high purity polymer that is essentially free of inorganic acid acceptors, which are typically bases such as oxides and hydroxides of calcium, magnesium, zinc, lead, etc. In an alternative embodiment, a relatively high purity polymer is essentially free of all ions other than NH
4
+
, H
+
, and OH
−
. In these embodiments, the fluoroelastomer includes one or more units derived from a hydrogen-containing monomer and one or more units derived from a cure-site monomer. When the hydrogen-containing monomer is a vinylidene fluoride, the curable fluoroelastomer composition is essentially free from one or more inorganic acid acceptors. The preferred high purity elastomeric fluoropolymer is a peroxide-curable elastomer, optionally having pendant nitrile groups.
In one embodiment, the present invention provides a curable fluoropolymer composition that includes: a hydrogen-containing fluoroelastomer having units derived from a cure-site monomer, wherein the fluoroelastomer is capable of peroxide cure; a peroxide curative; optionally, a co-agent for the curative; and a non-fluorine-containing organo-onium; with the proviso that when the hydrogen-containing fluoroelastomer includes one or more units derived from vinylidene fluoride, the composition is essentially free from one or more inorganic acid acceptors.
In another embodiment, the present invention provides a process for improving compression set of a cured fluoroelastomer. The method includes providing a curable fluoroelastomer composition and curing the curable composition. The curable fluoroelastomer composition includes: a fluoroelastomer having units derived from at least one monomer including a carbon-bonded hydrogen and units derived from a cure-site monomer, wherein the fluoroelastomer is capable of peroxide cure; a peroxide curative; optionally, a co-agent for the curative; and a non-fluorine-containing organo-onium; with the proviso that when the hydrogen-containing fluoroelastomer includes one or more units derived from vinylidene fluoride, the composition is essentially free from one or more inorganic acid acceptors.
In yet another embodiment, the present invention provides a cured fluoroelastomer that includes the reaction product of a curable composition including: a hydrogen-containing fluoroelastomer having units derived from a cure-site monomer, wherein the fluoroelastomer is capable of peroxide cure; a peroxide curative; optionally, a co-agent for the curative; and a non-fluorine-containing organo-onium; with the proviso that when the hydrogen-containing fluoroelastomer includes one or more units derived from vinylidene fluoride, the composition is essentially free from one or more inorganic acid acceptors.
As used herein, the terms “a,” “an,” “the,” “one or more,” and “at least one” are used interchangeably.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The present invention provides curable fluoropolymer compositions that include a hydrogen-containing fluoroelastomer having units derived from a cure-site monomer, a curative, and an organo-onium. Optionally, the compositions can include a co-agent for the curative and a partially crystalline fluoropolymer (e.g., fluorothermoplast or other fluoropolymer such as polytetrafluoroethylene) as a filler. Certain embodiments of the present invention are directed to polymers that have improved compression set and certain embodiments of the present invention are directed to polymers that have relatively high purity (i.e., polymers that are essentially free of ions other than NH
4
+
, H
+
, and OH
−
and/or essentially free of inorganic acid acceptors).
The cured fluoroelastomer preferably has improved compression set relative to the same cured fluoroelastomer made without the organo-onium. Herein, an “improvement” is a decrease in the residual deformation reported as a percentage compression set as determined by the test method described in the Examples Section. Preferably, the compression set is less than about 20%, more preferably, less than about 15%, even more preferably, less than about 10%, and most preferably, zero.
In cases where improved compression set is desired, the addition of organo-onium compounds are beneficial to improve properties in formulations that do not contain inorganic acid acceptors
Coggio William D.
Grootaert Werner M. A.
Hintzer Klaus
Kolb Robert E.
Löhr Gernot
3M Innovative Properties Company
Lilly James V.
Szymanski Brian E.
Zitomer Fred
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