Patent Description:
Silicone rubber is known as a rubber component having high oxygen plasma resistance but slightly low fluorine plasma resistance. A vinylidene fluoride fluororubber (hereinafter referred to as "FKM") is known as a rubber component having high fluorine plasma resistance but slightly low oxygen plasma resistance. A tetrafluoroethyleneperfluorovinylether fluororubber (hereinafter referred to as "FFKM") is known as a rubber component that has high oxygen plasma resistance and high fluorine plasma resistance but is more expensive as compared to silicone rubber and FKM. It is therefore proposed to use a mixture of these rubber components. For example, Patent Document <NUM> discloses the use of a mixture of silicone rubber and FFKM and the use of a mixture of FKM and FFKM. Patent Document <NUM> discloses the use of a mixture of FKM and FFKM. Patent Document <NUM> discloses the use of a mixture of silicone rubber and FKM.

As a technique that increases plasma resistance, Patent Documents <NUM> and <NUM> disclose adding a reactive fluorine compound to FKM. Patent Document <NUM> discloses adding an excess of crosslinking aid to FKM, heating the FKM to crosslink the FKM by the crosslinking aid, and irradiating the FKM to further crosslink the FKM by the excess crosslinking aid, thereby increasing the crosslinking density and thus improving rubber's physical properties.

Document <CIT> discloses a rubber composition obtained from a fluororubber. Document <CIT> discloses a vulcanizable rubber composition.

The present invention relates to a method for manufacturing a rubber product in accordance with the appended set of claims.

An embodiment will be described in detail below.

In the method of the invention, an uncrosslinked rubber composition is suitably used for manufacturing of rubber products, especially highly plasma resistant sealing materials such as an O-ring which are used for, e.g., systems using plasma such as a semiconductor etching system and a semiconductor plasma CVD system. The uncrosslinked rubber composition contains a hydrogen-containing fluororubber that is a rubber component, a thermal crosslinking agent, and a hydrogen site protective agent.

The "hydrogen-containing fluororubber" herein refers to a fluororubber that contains carbons bonded to hydrogens in its polymer main chain. It is preferable that the hydrogen-containing fluororubber contain, e.g., vinylidene fluoride (VDF), propylene (Pr), or ethylene (E), as a monomer.

Examples of the hydrogen-containing fluororubber include polymers (PVDF) of vinylidene fluoride (VDF), copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), copolymers of vinylidene fluoride (VDF), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE), copolymers (FEP) of tetrafluoroethylene (TFE) and propylene (Pr), copolymers of vinylidene fluoride (VDF), propylene (Pr), and tetrafluoroethylene (TFE), copolymers (ETFE) of ethylene (E) and tetrafluoroethylene (TFE), copolymers of ethylene (E), tetrafluoroethylene (TFE), and perfluoromethylvinylether (PMVE), copolymers of vinylidene fluoride (VDF), tetrafluoroethylene (TFE), and perfluoromethylvinylether (PMVE), and copolymers of vinylidene fluoride (VDF) and perfluoromethylvinylether (PMVE). It is preferable that the hydrogen-containing fluororubber contain one or more of these.

The thermal crosslinking agent is a compound that crosslinks the hydrogen-containing fluororubber when heated to a predetermined temperature. The thermal crosslinking agent is a peroxide. Examples of peroxides include <NUM>,<NUM>-bis(t-butylperoxy)-<NUM>,<NUM>,<NUM>-trimethylcyclohexane, <NUM>,<NUM>-dimethylhexane-<NUM>,<NUM>-dihydroperoxide, di-t-butylperoxide, t-butylcumylperoxide, dicumylperoxide, α,α-bis(t-butylperoxy)-p-diisopropylbenzene, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-di(t-butylperoxy)hexane, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-di(t-butylperoxy)-hexyne-<NUM>, benzoylperoxide, t-butylperoxybenzene, t-butylperoxymaleic acid, t-butylperoxy isopropyl carbonate, and t-butylperoxybenzoate. The thermal crosslinking agent preferably contains one or more of these and more preferably contains <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-di(t-butylperoxy)hexane. The content (A) of the thermal crosslinking agent is preferably <NUM> parts by mass or more and <NUM> parts by mass or less, and more preferably <NUM> parts by mass or more and <NUM> parts by mass or less, per <NUM> parts by mass of the hydrogen-containing fluororubber in order to cause crosslinking to proceed sufficiently and obtain satisfactory physical properties as a sealing material.

The hydrogen site protective agent is a compound that bonds to carbon radicals resulting from breakage of carbon-hydrogen bonds of the hydrogen-containing fluororubber which occurs under irradiation. The "hydrogen site" herein refers to the site of carbon bonded to hydrogen in the polymer main chain of the hydrogen-containing fluororubber. Specifically, the "hydrogen site" refers to, e.g., a C-H bond site in a VDF component. The hydrogen site protective agent contains a compound with a perfluoro skeleton having an alkenyl group that bonds to a carbon radical of the hydrogen-containing fluororubber in its molecule and a compound with a siloxane skeleton having an alkenyl group that bonds to a carbon radical of the hydrogen-containing fluororubber in its molecule.

Examples of the alkenyl group include a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group, and a heptenyl group. The alkenyl group is preferably a vinyl group.

Examples of the compound with a perfluoro skeleton having an alkenyl group in its molecule include compounds with a perfluoropolyether structure and compounds with a perfluoroalkylene structure.

Examples of the compound with a siloxane skeleton having an alkenyl group in its molecule include polymers of methylvinylsiloxane, polymers of dimethylsiloxane, copolymers of dimethylsiloxane and methylvinylsiloxane, and copolymers of dimethylsiloxane, methylvinylsiloxane, and methylphenylsiloxane. Other example includes organopolysiloxanes having an alkenyl group in its molecule which are addition-polymerized liquid silicone rubber.

It is preferable that the compound with a perfluoro skeleton and the compound with a siloxane skeleton have two or more alkenyl groups in its molecule. The two or more alkenyl groups may be the same or different from each other. The hydrogen site protective agent having two or more alkenyl groups not only protects hydrogen sites but also functions as a crosslinking aid that crosslink molecules of the hydrogen-containing fluororubber.

The hydrogen site protective agent preferably contains one or more of the above examples, more preferably contains a compound with a perfluoropolyether structure having an alkenyl group in its molecule, and even more preferably contains a compound with a perfluoropolyether structure having two or more alkenyl groups in its molecule.

It is preferable that the hydrogen site protective agent be a one-component liquid material. In that case, the viscosity of the hydrogen site protective agent at <NUM> is preferably <NUM> Pa·s or more and <NUM> Pa·s or less and more preferably <NUM> Pa·s or more and <NUM> Pa·s or less in the case of the compound with a perfluoro skeleton, and is preferably <NUM> Pa·s or more and <NUM> Pa·s or less and more preferably <NUM> Pa·s or more and <NUM> Pa·s or less in the case of the compound with a siloxane skeleton.

The content (B) of the hydrogen site protective agent is preferably <NUM> part by mass or more and <NUM> parts by mass or less, and more preferably <NUM> parts by mass or more and <NUM> parts by mass or less, per <NUM> parts by mass of the hydrogen-containing fluororubber in order to increase plasma resistance. The content (B) of the hydrogen site protective agent is preferably higher than the content (A) of the thermal crosslinking agent in order to increase plasma resistance. The ratio (B/A) of the content (B) of the hydrogen site protective agent to the content (A) of the thermal crosslinking agent is preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less, in order to increase plasma resistance.

The uncrosslinked rubber composition may further contain a crosslinking aid. The crosslinking aid is a compound that bonds to the hydrogen-containing fluororubber so as to be located between molecules of the hydrogen-containing fluororubber when the hydrogen-containing fluororubber is crosslinked by the thermal crosslinking agent.

Examples of the crosslinking aid include triallyl cyanurate, trimethallyl isocyanurate, triallyl isocyanurate, triacrylformal, triallyl trimellitate, N,N'-m-phenylene bismaleimide, dipropargyl terephthalate, diallyl phthalate, tetraallyl terephthalate amide, triallyl phosphate, bismaleimide, fluorinated triallyl isocyanurate(<NUM>,<NUM>,<NUM>-tris(<NUM>,<NUM>,<NUM>-trifluoro-<NUM>-propenyl)-<NUM>,<NUM>,<NUM>-triazine-<NUM>,<NUM>,<NUM>-trione), tris(diallylamine)-S-triazine, triallyl phosphite, N,N-diallyl acrylamide, <NUM>,<NUM>-divinyldodecafluorohexane, hexaallyl phosphoramide, N,N,N',N'-tetraallylphthalamide, N,N,N',N'-tetraallylmalonamide, trivinyl isocyanurate, <NUM>,<NUM>,<NUM>-trivinylmethyltrisiloxane, tri(<NUM>-norbornene-<NUM>-methylene)cyanurate, and triallyl phosphite. The crosslinking aid preferably contains one or more of these and more preferably contains triallyl isocyanurate.

The content (C) of the crosslinking aid is preferably <NUM> part by mass or more and <NUM> parts by mass or less, and more preferably <NUM> parts by mass or more and <NUM> parts by mass or less, per <NUM> parts by mass of the hydrogen-containing fluororubber in order to obtain satisfactory physical properties as a sealing material. The content (C) of the crosslinking aid is preferably higher than the content (A) of the thermal crosslinking agent in order to increase plasma resistance. The ratio (C/A) of the content (C) of the crosslinking aid to the content (A) of the thermal crosslinking agent is preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less, in order to cause the crosslinking aid to react without excess or deficiency and obtain satisfactory physical properties as a sealing material.

The uncrosslinked rubber composition may contain a fluororubber that does not contain carbons bonded to hydrogens in its polymer main chain such as silicone rubber and a copolymer of tetrafluoroethylene and perfluorovinylether, which are rubber components other than the hydrogen-containing fluororubber, as long as the content of such a fluororubber is lower than that of the hydrogen-containing fluororubber. Depending on the rubber product to be manufactured, the uncrosslinked rubber composition may contain a reinforcing material such as carbon black and silica, a plasticizer, a processing aid, a vulcanization accelerator, or an anti-aging agent. However, when used to manufacture such a rubber product that generation of particles in a plasma atmosphere is a problem, the content of a powdered inorganic filler such as carbon black, silica, and a metal oxide is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, and most preferably <NUM> parts by mass per <NUM> parts by mass of the hydrogen-containing fluororubber. A powdered organic filler such as hydrogen-containing fluororesin powder like PVDF or ETFE is expected to improve physical properties due to crosslinking with the hydrogen-containing fluororubber when irradiated as described below.

The uncrosslinked rubber composition can be manufactured using an open rubber kneading machine such as an open roll or a sealed rubber kneading machine such as a kneader.

Next, an embodiment of the method of the invention for manufacturing a rubber product using an uncrosslinked rubber composition will be described.

In the method for manufacturing a rubber product, a cavity of a preheated mold is first filled with a predetermined amount of uncrosslinked rubber composition, and the mold is then closed. Thereafter, the mold is kept in this state at a predetermined molding temperature and a predetermined molding pressure for a predetermined molding time. At this time, the uncrosslinked rubber composition is molded into the shape of the cavity and loses its plasticity due to crosslinking of the hydrogen-containing fluoroelastomer by the thermal crosslinking agent. This molding may be either press molding or injection molding. The molding temperature is, e.g., <NUM> or higher and <NUM> or less. The molding pressure is, e.g., <NUM> MPa or higher and <NUM> MPa or less. The molding time is, e.g., <NUM> minutes or more and <NUM> minutes or less.

The mold is then opened, and the molding is taken out of the mold and cooled. The molding is then irradiated. When irradiated, the carbon-hydrogen bonds at the hydrogen sites of the hydrogen-containing fluororubber are broken and carbon radicals are formed. The hydrogen site protective agent bonds to the carbon radicals. Examples of the radiation include α-rays, β-rays, γ-rays, electron beams, and ions. Among these, the radiation is preferably electron beams or γ-rays. In order to increase plasma resistance, the radiation dose is preferably <NUM> kGy or more and <NUM> kGy or less, and more preferably <NUM> kGy or more and <NUM> kGy or less.

A rubber product that is made of a rubber composition in which a hydrogen-containing fluororubber has been crosslinked by a thermal crosslinking agent and a hydrogen site protective agent has bonded to carbons resulting from breakage of carbon-hydrogen bonds of the hydrogen-containing fluororubber is thus produced using the uncrosslinked rubber composition.

According to the uncrosslinked rubber composition having the above configuration, the hydrogen sites of the hydrogen-containing fluororubber, which are sites with low plasma resistance, are protected as the hydrogen site protective agent bonds to carbon radicals resulting from breakage of the carbon-hydrogen bonds which occurs under irradiation. A rubber product with high plasma resistance can thus be manufactured using this uncrosslinked rubber composition. Since the hydrogen site protective agent reacts with hydrogen-containing fluororubber, bleedout will not occur.

Rubber compositions of Examples <NUM> and <NUM> and Comparative Examples <NUM> to <NUM> were prepared. The configurations of these rubber compositions are also shown in Table <NUM>.

An uncrosslinked rubber composition was prepared by adding <NUM> parts by mass of <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-di(t-butylperoxy)hexane (PERHEXA 25B, made by NOF CORPORATION), which is a peroxide as a thermal crosslinking agent, <NUM> parts by mass of a compound with a perfluoro skeleton having a vinyl group in its molecule (SIFEL3590-N, made by Shin-Etsu Chemical Co. , viscosity (<NUM>): <NUM> Pa·s), which is a one-component liquid material as a hydrogen site protective agent, and <NUM> parts by mass of triallyl isocyanurate (TAIC, made by Nihon Kasei CO. ) as a crosslinking aid to <NUM> parts by mass of a hydrogen-containing fluororubber made of a copolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene (DAI-EL G912, made by DAIKIN INDUSTRIES, LTD. ) and kneading the mixture. Subsequently, the uncrosslinked rubber composition was press-molded at <NUM> and <NUM> MPa for <NUM> minutes and then heat-treated at <NUM> for <NUM> hours to produce a sheet-like rubber composition. The sheet-like rubber composition was irradiated with γ-rays at a dose of <NUM> kGy. Example <NUM> is the sheet-like rubber composition thus irradiated with γ-rays.

Example <NUM> is a sheet-like rubber composition produced in a manner similar to that of Example <NUM> except that a compound with a siloxane skeleton having a vinyl group in its molecule (KE-<NUM>, made by Shin-Etsu Chemical Co. Viscosity (<NUM>): <NUM> Pa·s), which is a one-component liquid material, was added as a hydrogen site protective agent.

Comparative Example <NUM> is a sheet-like rubber composition produced in a manner similar to that of Example <NUM> except that no hydrogen site protective agent was added.

Comparative Example <NUM> is a sheet-like rubber composition produced in a manner similar to that of Example <NUM> except that no hydrogen site protective agent was added and <NUM> parts by mass of silicone rubber (KE-<NUM>-U, made by Shin-Etsu Chemical Co. ) was added to <NUM> parts by mass of the hydrogen-containing fluororubber.

Comparative Example <NUM> is a sheet-like rubber composition produced in a manner similar to that of Example <NUM> except that no hydrogen site protective agent was added and <NUM> parts by mass of a copolymer of tetrafluoroethylene and perfluorovinylether (FFKM: AFLAS Premium PM1100, made by AGC Inc. ) was added to <NUM> parts by mass of the hydrogen-containing fluororubber.

For each of Examples <NUM> and <NUM> and Comparative Examples <NUM> to <NUM>, an O<NUM> plasma irradiation test and a CF<NUM> plasma irradiation test were performed using a microwave plasma generator at <NUM>% elongation to check for mass loss, any cracks, and any particles. In the tests, O<NUM> and CF<NUM> were used as reactant gases. The flow rate of O<NUM> to CF<NUM> was <NUM> to <NUM> in the O<NUM> plasma irradiation test and was <NUM> to <NUM> in the CF<NUM> plasma irradiation test. The reaction pressure was <NUM> Pa and the plasma irradiation time was <NUM> minutes.

For each of Examples <NUM> and <NUM> and Comparative Examples <NUM> to <NUM>, a tensile test was performed based on JIS K <NUM> to measure <NUM>% modulus (M<NUM>: tensile stress at <NUM>% elongation), tensile strength (TB), and elongation at break (EB).

For each of Examples <NUM> and <NUM> and Comparative Examples <NUM> to <NUM>, compression set was measured based on JIS K <NUM>: <NUM>. The test time was <NUM> hours and the test temperature was <NUM>.

According to Table <NUM>, Examples <NUM> and <NUM> using a hydrogen site protective agent have high resistance to both O<NUM> plasma and CF<NUM> plasma. With O<NUM> plasma irradiation, Comparative Examples <NUM> to <NUM> using no hydrogen site protective agent produced no particles but had great mass loss (especially Comparative Example <NUM>) and developed cracks. Comparative Examples <NUM> to <NUM> have high resistance to CF<NUM> plasma. With CF<NUM> plasma irradiation, however, Comparative Example <NUM> produced no particles but had great mass loss and developed cracks. No significant difference in tensile properties and compression set was observed between Examples <NUM> and <NUM> and Comparative Examples <NUM> to <NUM>.

Claim 1:
A method for manufacturing a rubber product comprising:
- A) heating an uncrosslinked rubber composition containing:
a hydrogen-containing fluororubber;
a thermal crosslinking agent that crosslinks the hydrogen-containing fluororubber when heated to a predetermined temperature; wherein said thermal crosslinking agent is a peroxide; and
a hydrogen site protective agent that bonds to carbon radicals resulting from breakage of carbon-hydrogen bonds of the hydrogen-containing fluororubber which occurs under irradiation, wherein said hydrogen site protective agent contains a compound with a perfluoro skeleton having an alkenyl group that bonds to the carbon radical of the hydrogen-containing fluororubber in its molecule and a compound with a siloxane skeleton having an alkenyl group that bonds to a carbon radical of the hydrogen-containing fluororubber in its molecule, to said predetermined temperature to crosslink the hydrogen-containing fluororubber by the thermal crosslinking agent,
- B) irradiating the rubber composition obtained at step A) so that the hydrogen site protective agent bonds to the carbon radicals resulting from breakage of the carbon hydrogen bonds of the hydrogen containing fluororubber to obtain the rubber product.