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
2002-03-01
2004-09-14
Lipman, Bernard (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...
C525S326400
Reexamination Certificate
active
06790915
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparing a fluorine-containing elastomeric copolymer composition comprising a fluorine-containing elastomeric copolymer (hereinafter referred merely to as a “fluororubber”) and, more particularly, to a process for preparing a fluorine-containing elastomeric copolymer composition containing a polyhydroxy compound or a salt thereof as a vulcanization component.
RELATED ART
Fluororubbers obtained from vinylidene fluoride and at least one other fluorine-containing monomer have been used in various industries because of excellent heat resistance, chemical resistance and oil resistance. It is necessary to cure a polymer by vulcanization so as to satisfy the properties described above under severe conditions.
The fluororubber is prepared by copolymerizing a monomer using a water-soluble initiator and/or an oil-soluble initiator. For example, Japanese Kokoku (Examined) Patent Publication No. 56-29895 and Japanese Kokoku (Examined) Patent Publication No. 56-34009 (corresponding to U.S. Pat. No. 4,141,874) disclose a process for preparing a fluororubber by a two-stage polymerization, wherein a water-soluble initiator is used in a first stage of the polymerization and an oil-soluble initiator is used in a second stage of the polymerization. In the second stage of the polymerization using the oil-soluble initiator, the oil-soluble initiator is homogeneously dispersed by adding an emulsifier to a medium.
The resulting fluororubber is mixed with a vulcanizing agent (for example, a polyhydroxy compound) and a vulcanization accelerator (for example, a quaternary ammonium salt) to give a composition for vulcanization.
The process for mixing the fluororubber with the vulcanizing agent and the vulcanization accelerator is roughly classified into a process for coagulating an aqueous dispersion (of a fluororubber by adding a vulcanizing agent and a vulcanization accelerator to the aqueous dispersion, and a process of isolating a fluororubber from an aqueous dispersion of fluororubber by coagulation, drying the fluororubber and kneading the fluororubber with a vulcanizing agent and a vulcanization accelerator.
Japanese Kokoku (Examined) Patent Publication No. 56-34009 (corresponding to U.S. Pat. No. 4,141,874) discloses a fluororubber composition obtained by mixing a fluororubber with an acid acceptor, an aromatic polyhydroxy compound and a specific quaternary ammonium compound and kneading the mixture.
However, the kneading operability is poor and it is difficult to homogeneously mix the fluororubber with the vulcanizing agent and the vulcanization accelerator. Furthermore, the kneading of the fluororubber having high viscosity requires large energy. The quaternary ammonium compound adsorbs moisture in an atmospheric air because of its hygroscopicity and, therefore, it is inferior in handling properties.
Japanese Kokai (Unexamined) Patent Publication No. 56-147840 discloses a process for preparing a composition for vulcanization of a fluororubber, which comprises adding a quaternary ammonium compound and/or a quaternary phosphonium compound, as a vulcanization accelerator, to an aqueous emulsion or an aqueous dispersion of a fluororubber, thereby to cause coagulation. According to this process, the fluororubber, the vulcanizing agent and the vulcanization accelerator can be homogeneously mixed and the efficiency is better than that in case of kneading.
However, because of its hygroscopicity, the quaternary ammonium compound tends to be incorporated into the aqueous medium during the coagulation from the aqueous dispersion, together with the fluororubber. Therefore, when a predetermined amount of the quaternary ammonium compound is intended to be incorporated into the fluororubber, at least a predetermined amount of the quaternary ammonium compound must be added to the aqueous medium and the amount of it to be incorporated into the fluororubber is changeable.
Both of the aqueous fluororubber dispersion and the aqueous fluororubber emulsion obtained using an oil-soluble initiator contain an emulsifier. However, it is known that the action of the quaternary ammonium compound is inhibited by the emulsifier.
WO96/17876(PCT/JP95/2485) describes that a polyhydroxy aromatic compound and a quaternary phosphonium salt are incorporated into the fluororubber prepared by a two-stage polymerization described above by kneading. However, it is known that the action of the quaternary phosphonium salt is also inhibited by the emulsifier.
Japanese Kokoku (Examined) Patent Publication No. 57-14775 discloses that a fluororubber is kneaded with a solid solution of a quaternary ammonium compound and a polyhydroxy aromatic compound in order to avoid an influence of the hygroscopicity of the quaternary ammonium compound. However, according to this process, poor dispersion of the solid solution occurs and thus vulcanization physical properties of the molded article are not stable.
Japanese Kokai (Unexamined) Patent Publication No. 50-22048 discloses a process for preparing a fluorine-containing elastomeric copolymer composition, which comprises continuously feeding a wetted fluorine-containing elastomeric copolymer bulk having a water content of about 15 to 35% by weight, which is a coagulate of a fluorine-containing elastomeric copolymer latex, to a mixing region, feeding a vulcanizing agent and a vulcanization accelerator in the form of fine powders, and mixing them while maintaining the particle size of the fluorine-containing elastomeric copolymer bulk. The publication describes with respect to this mixing operation that the vulcanizing agent and the vulcanization accelerator should be fed to the mixing region in the form of fine powders in an aqueous dispersion and that the temperature should be maintained at low temperature enough to prevent the adverse reaction between the fluorine-containing elastomeric copolymer and the curing components or other additives, which are present in the mixture. However, the quaternary phosphonium salt as the curing component is easily dissolved because of its water solubility, so that the quaternary phosphonium salt is consumed together with separated water when treated in an apparatus such as extruder. Since the mixing operation is conducted while maintaining the particle size of the fluorine-containing elastomeric copolymer bulk, there is a limit in homogeneity of the composition. Furthermore, it is difficult to continuously feed a constant amount of a fine-powdery solid material and, therefore, a predetermined amount of it cannot be incorporated and vulcanization physical properties of the molded article are not stable.
The fluorine-containing elastomeric copolymer composition is generally prepared by kneading a fluororubber with a vulcanizing agent and a vulcanization accelerator using an apparatus such as kneader. However, the kneading operation in a kneader requires large energy and charge of raw materials into the kneader is hard for an operator. The vulcanizing agent and the vulcanization accelerator are usually in the form of powders and, therefore, risk to the operator in case of charging them into the kneader is considered to be a serious problem.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for preparing a composition for vulcanization of a fluororubber in a good efficiency.
Another object of the present invention is to provide a process which makes it possible to obtain a fluororubber composition having stable vulcanization physical properties, wherein a vulcanizing agent and a vulcanization accelerator are homogeneously dispersed in a fluororubber.
The present invention provides a process for preparing a fluorine-containing elastomeric copolymer composition comprising a fluorine-containing elastomeric copolymer, a vulcanizing agent and a vulcanization accelerator,
said process comprising the step of coagulating the copolymer from an aqueous dispersion of the fluorine-containing elastomeric copolymer and drying the resulting coagulate of the copolymer while knead
Higuchi Tetsuya
Komatsu Satoshi
Nakashima Akihiro
Ueta Yutaka
Birch & Stewart Kolasch & Birch, LLP
Daikin Industries Ltd.
Lipman Bernard
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