Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1996-10-07
1998-02-10
Clark, W. Robinson H.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
5253264, 526242, 526247, 526250, 526255, C08F 1416, C08F 1422, C08F25908
Patent
active
057170363
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention related to a fluororubber copolymer and a curable composition thereof. In particular, the present invention relates to a fluororubber copolymer which has an improved sealing property at low temperature while maintaining excellent properties of conventional fluororubbers, and a curable composition comprising said copolymer.
PRIOR ART
Since a fluororubber comprising vinylidene fluoride (VdF) units is excellent in heat resistance, chemical resistance, solvent resistance, oil resistance, and so on, it is molded in the form of an O-ring, a hose, a stem seal, a shaft seal, a diaphragm, and so on and widely used in the fields of automobile industry, semiconductor industry, chemical industry, and the like.
However, it is pointed out that the conventionally used fluororubbers have inferior cold resistance to other rubber materials. In general, with an uncured copolymer, its cold resistance is evaluated in terms of a glass transition temperature, while with a molded article, its cold resistance is evaluated by the Gehman torsion test, the TR test (ASTM D 1329), and the low temperature brittleness test. When the rubber is used as a sealing material such as the O-ring, a degree of liquid leakage at low temperature, that is, a low temperature compression set of the material is a straightforwardly important index.
To improve the cold resistance of the fluororubbers, various studies have been made for a long time. GB Patent Nos. 953,152 and 952,098 proposed the use of a perfluoroalkyl vinyl ether in place of or in addition to a conventional monomer of the fluororubber, and achieved a glass transition temperature of -30.degree. C. or lower. But, the low temperature compression set did not reach a sufficient level.
It is proposed to use a specific iodine compound as a chain transfer agent in the radical polymerization for the production of the fluororubber copolymer, whereby an iodine atom is bonded to a molecular terminal of the copolymer, and to perform a peroxide curing reaction by making use of a high radical activity of the iodine atom (JP-A-53-125491). It is reported that a cured material of a copolymer, which is obtained by using the above technique and polymerizing a monomer mixture having a specific composition, is excellent in the low temperature property (JP-A-6-508161). But, the low temperature property was evaluated only by the Gehman torsion test, and the compression set was measured only at a high temperature (200.degree. C. for 70 hours).
JP-A-62-12734 describes a simple method for producing an iodine-containing peroxide-curable fluororubber which is excellent in the compression set. But, this patent publication does not describe a low temperature compression set and a composition suitable for the low temperature compression set.
JP-B-53-4035 discloses a copolymer comprising vinylidene fluoride (VdF), perfluoro(methyl vinyl ether) (PMVE), hexafluoropropylene (HFP) and tetrafluoroethylene (TFE) and containing 17 to 30 wt. % of PMVE, and FR Patent No. 2347389 discloses a copolymer comprising the same monomers as above and containing 10 to 17 wt. % of PMVE, and both copolymers provide a molded article having good low temperature compression set when they are cured with a polyol. But, as described in JP-A-6-128334, these copolymers suffer from a problem that they tend to foam when they are subjected to the polyol curing. Further, JP-A-6-128334 describes that when a copolymer comprising vinylidene fluoride (VdF), perfluoro(methyl vinyl ether) (PMVE), hexafluoro-propylene (HFP) and tetrafluoroethylene (TFE) and containing 3 to 9 wt. % of PMVE is polyol cured, a molded article having a high compression set at a low temperature (0.degree. C.) is obtained. But, the molded article of this copolymer does not have sufficient tensile strength and elongation at break.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a fluororubber copolymer which has excellent compression set in a wide temperature range from low temperature to high temperature w
REFERENCES:
patent: 4361678 (1982-11-01), Tatemoto et al.
patent: 4886862 (1989-12-01), Kuwamura et al.
Kishine Mitsuru
Kitaichi Masanori
Saito Hideya
Ueta Yutaka
Clark W. Robinson H.
Daikin Industries Ltd.
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