Fluorine-containing elastomer composition

Details Fluorine-containing elastomer composition Fluorine-containing elastomer composition

1999-11-24

2001-05-08

Seidleck, James J. (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...

C525S276000, C525S106000, C524S463000, C524S545000, C524S504000, C524S505000, C524S520000

Reexamination Certificate

active

06228943

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a fluorine-containing elastomer composition. In particular, the present invention relates to a peroxide-curable fluorine-containing elastomer composition, which has improved molding and processing properties, while it has good tensile properties, heat resistance, oil resistance and high temperature sealing properties comparable to those of known peroxide-curable fluorine-containing elastomer compositions.
BACKGROUND ART
Fluorine-containing elastomer compositions are used as materials of O-rings, gaskets, oil seals, diaphragms, hoses, rolls, seat members, etc. in various industrial fields such as automobile, ships, aircraft, hydraulic machines and general machine industries as well as environmental pollution-related fields. In particular, peroxide-curable fluorine-containing elastomers can be cured when fluororubbers have high fluorine concentrations, unlike the polyol curing or polyamine curing system. Furthermore, fluororubbers having iodine atoms at polymer chain ends have an advantage that they can be cured with peroxides without compounding metal oxides.
However, although peroxide-curable fluorine-containing elastomers have such good properties, they have low mold releasing properties and anticontamination of molds in the curing and molding steps. Thus, it is difficult to improve the working efficiency, and also the productivity tends to deteriorate due to the decrease of yields by cracking or breakage, when articles having complicated shapes are molded. Thus, external mold release. agents or internal mold release agents are used to improve the mold releasing properties of fluorine-containing elastomers. However, when internal mold release agents are used, a problem arises, that the physical properties of cured products deteriorate. When external mold release agents are used, the effect to improve the mold releasing properties decreases as the number of molding cycles increases. Therefore, it is necessary to repeatedly apply the external mold release agents to a mold, and further the commercial value of products may decrease since marks of the external release-agents remain on the surfaces of molded articles.
In the case of peroxide curing, burrs formed in the course of compression molding, in particular, parts of burrs which are in contact with an air, are not sufficiently cured, and thus stain the surfaces of molds or molded articles.
Various improvements have been proposed to solve the above problems of peroxide-curable fluorine-containing elastomer compositions, but they have their own drawbacks.
For example, fluorine-containing block polymers, which are disclosed in JP-A-59-40066 relating to a sealing material resistant to lubricant oils and JP-B-61-49327 relating to a fluorine-containing segmented polymer, contain 5 wt. % or more of non-elastomeric polymer chain segments, and thus they have drawbacks that properties greatly deteriorate when they are formulated in the form of fluororubber compositions and cured.
A non-tacky fluororubber composition, which is prepared by a method disclosed in JP-A-8-176388 comprising mixing a fluororubber and a fluorine-containing block polymer, can achieve effects to some extent. However, it has-a drawback that the content of a non-elastomeric component in the used fluororubbery thermoplastic elastomer is high, and thus it is not easy to mix the fluororubber and the fluorine-containing block polymer.
SUMMARY OF THE INVENTION
One object of the present invention is to solve the problems or drawbacks of the peroxide-curable fluorine-containing elastomer compositions disclosed in the above prior arts without deteriorating other good properties of the compositions.
According to the present invention, this object can be accomplished by a peroxide-curable fluorine-containing elastomer composition comprising
(a) 100 parts by weight of a fluorine-containing block polymer comprising at least one elastomeric polymer chain segment and at least one non-elastomeric polymer chain segment in which the content of said non-elastomeric polymer chain segment is less than 5% by weight,
(b) 0.05 to 10 parts by weight, preferably 0.3 to 5 parts by weight, more preferably 1 to 5 parts by weight, of an organic peroxide, and
(c) 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, more preferably 0.5 to 5 parts by weight, of a polyfunctional co-crosslinking agent.
DETAILED DESCRIPTION OF THE INVENTION
The components contained in the composition of the present invention will be explained.
(a) Particularly preferred examples of the fluorine-containing block polymer used according to the-present invention are fluorine-containing block polymers each comprising a chain consisting of two or three-polymer chain segments, an iodine atom present at one end of the chain, and a residue that is present at the other end of the chain and derived from an iodide compound by removing at least one iodine atom therefrom, in which one of the polymer chain segments (when the chain consists of two polymer chain segments), or two of the polymer chain segments (when the chain consists three polymer chain segments) is or are one or two elastomeric polymer chain segment(s) having a molecular weight of 30,000 to 1,200,000 selected from the group consisting of:
(1) a vinylidene fluoride-(hexafluoropropylene or. pentafluoropropylene)-tetrafluoroethylene polymer (molar ratio=45-90:5-50:0-35), in particular, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene polymer (molar ratio=40-90:10-50:0-30),
(2) a perfluoro(C
1
-C
3
alkyl vinyl ether) (including one having a plurality of ether bonds)-tetrafluoroethylene-vinylidene fluoride polymer (molar ratio=15-75:0-85:0-85), in particular, a perfluoro(C
1
-C
3
alkyl vinyl ether)-tetrafluoroethylene (molar ratio=15-60:40-85), and
(3) a tetrafluoroethylene-propylene-comonomer (e.g. ethylene, isobutyrene, acrylic acid and its esters, methacrylic acid and its esters, vinyl fluoride, hexafluoropropylene, vinylidene fluoride, chloroethyl vinyl ether, chlorotrifluoroethylene, or perfluoro (C
1
-C
3
alkyl vinyl ether)) polymer (molar ratio=40-70:30-60:0-20), and the remaining polymer chain segment is a non-elastomeric polymer chain segment selected from the group consisting of:
(4) a vinylidene fluorine-tetrafluoroethylene polymer (molar ratio=0-100:0-100), in particular, a vinylidene fluoride-tetrafluoroethylene polymer (molar ratio=70-99:1-30), a tetrafluoroethylene homopolymer, or a vinylidene fluoride homopolymer,
(5) an ethylene-tetrafluoroethylene- (hexafluoropropylene, 3,3,3-trifluoropropylene-1, 2-trifluoromethyl-3,3,3-trifluoropropylene-1 or perfluoro (C
1
-C
3
alkyl vinyl ether)) polymer (molar ratio=40-60:60-40:0-30),
(6) a polymer of tetrafluoroethylene and a fluorine-containing vinyl compound of the formula:
CF
2
═CF—Rf
wherein Rf is a trifluoroalkyl group or a group of the formula: —ORf
1
in which Rf
1
is a C
1
-C
5
perfluoroalkyl group (molar ratio=85-99.7:0.3-15),
(7) a vinylidene fluoride-tetrafluoroethylene-chlorotrifluoroethylene polymer (molar ratio=50-99:0-30:1-20), and
(8) a vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene polymer (molar ratio=60-99:0-30:1-10), wherein a weight ratio of the elastomeric polymer chain segment(s) to the non-elastomeric polymer chain segment is 95-100:0-5 (both ends exclusive).
As the content of the non-elastomeric polymer chain segment may increase, the effects to solve the problems in curing and molding improves, while the properties of cured products worsen. Thus, the content of the non-elastomeric polymer chain segment is less than 5% by weight, preferably from 0.5 to less than 5% by weight, more preferably from 0.5 to 3% by weight.
A typical chemical structure of a fluorine-containing block polymer is represented by, for example, the following formula:
Q[(A—B— . . . )I]
n
wherein Q is a residue of an iodide compound from which an iodine atom is removed, and A, B, . . . represent polymer chain segments, at least one

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