Method for producing millable silicone rubber composition

Abstract

To provide a millable silicone rubber compound that exhibits performance on par with traditional ones without the need for heat treatment.SOLUTION: A millable silicone rubber compound includes the following components (A)-(D). (A) 100 pts.mass of organopolysiloxane raw rubber having two or more alkenyl groups binding to silicon atoms in one molecule, with an average degree of polymerization of 1,000-100,000, (B) 5-100 pts.mass of reinforcing silica with a specific surface area of 50-450 m2 / g, determined by the BET adsorption method, (C) 1.0-50.0 pt.mass of an organosiloxane having hydroxy silyl groups at both terminals, represented by the general formula (1) (R1's independently represent a C1-8 monovalent hydrocarbon group and m represents an integer of 1-50), and (D) 0.0001-0.1 pt.mass of an amine compound that is liquid at 25°C, with a boiling point of 30-60°C at 1013 hPa.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a millable type silicone rubber compound, a millable type silicone rubber composition, and a method for producing the millable type silicone rubber composition. [Background technology]

[0002] To manufacture silicone rubber, it is necessary to knead a reinforcing filler into an organopolysiloxane. A surface treatment agent called a dispersant is used for this purpose. To disperse reinforcing silica as a filler, an organosilane or siloxane containing silanol groups is used. However, the process of dispersing silica using this method is time-consuming, and shortening this time is desirable.

[0003] In addition to this dispersion process, a heat treatment process at high temperatures is also required, which requires a large amount of electricity. The process takes a long time and consumes a large amount of electricity, which also poses a problem of environmental impact. To solve this problem, attempts have been made to use a small amount of a silazane compound in combination with the dispersant as a condensation catalyst for the dispersant. However, this method has not yet provided a fundamental solution.

[0004] To solve the above problems, Patent Document 1 claims that increasing the amount of silazane compound used in combination with the dispersant eliminates the need for a heat treatment step and shortens the compounding time. While this method is said to produce a millable silicone rubber compound with performance equivalent to conventional compounds, on an industrial scale, the excess silazane compound cannot be completely removed. Therefore, when this silicone rubber compound is used in an addition-cure silicone rubber composition, the physical properties of the cured rubber may become unstable or the surface may become sticky. Therefore, there is a need for an easily removable catalyst to promote the condensation reaction between the dispersant and the silanol groups on the surface of the reinforcing silica. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-025846 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and aims to provide a millable type silicone rubber compound that does not require heat treatment and has performance equivalent to that of conventional compounds, and a silicone rubber composition containing a kneaded product of said silicone rubber compound. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides: The following components (A) to (D) (A) 100 parts by mass of organopolysiloxane gum having two or more silicon-bonded alkenyl groups per molecule and an average degree of polymerization of 1,000 to 100,000, (B) Specific surface area measured by BET adsorption is 50 to 450 m 2 / g reinforcing silica: 5 to 100 parts by mass, (C) an organosiloxane having hydroxysilyl groups at both ends, represented by the following general formula (1): 1.0 to 50.0 parts by mass, and [ka] (In the formula, R 1 are independently a monovalent hydrocarbon group having 1 to 8 carbon atoms, and m is an integer of 1 to 50. (D) Amine compound having a boiling point of 30 to 60°C at 1013 hPa and being liquid at 25°C: 0.0001 to 0.1 parts by mass The present invention provides a millable type silicone rubber compound comprising:

[0008] This will result in a millable type silicone rubber compound that has the same performance as conventional heat-treated silicone rubber compounds, even though heat treatment is not required for the surface treatment of the reinforcing silica.

[0009] The present invention also provides a millable type silicone rubber composition comprising a kneaded mixture obtained by kneading the above millable type silicone rubber compound and (E) a curing agent.

[0010] In this case, the component (A) and the component (E) can be reacted to give a cured product.

[0011] The component (E) is preferably a curing agent for the hydrosilylation reaction, which comprises a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst.

[0012] Such a material is suitable for the millable silicone rubber compound of the present invention, since it contains few impurities that inhibit addition curing.

[0013] The component (E) is preferably an organic peroxide.

[0014] Organic peroxides are also suitable as curing agents.

[0015] The present invention also provides a method for producing a millable type silicone rubber composition, which comprises kneading the above-mentioned millable type silicone rubber compound, and in the presence of the catalyst component (D), surface treating the component (B) with the component (C), removing the component (D) by stirring with heat, and then adding the curing agent (E).

[0016] With this production method, it is possible to release the unnecessary component (D) while proceeding with the surface treatment of the component (B) with the component (C). [Effects of the Invention]

[0017] According to the present invention, it is possible to obtain a millable type silicone rubber compound having performance equivalent to that of conventional compounds without the need for forced heat treatment during the surface treatment of the filler, and a silicone rubber composition obtained by compounding a curing agent into a kneaded product of the compound. DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0003] The present inventors conducted extensive research to achieve the above object and discovered that when preparing a silicone rubber compound using an organopolysiloxane and reinforcing silica, using an organosiloxane having silanol groups at both ends, adding a small amount of a specific amine compound allows the silica to be surface-treated quickly without heat treatment. This is because the heat of stirring generated when mixing the organopolysiloxane and silica allows the silica to be surface-treated quickly. Furthermore, as the surface treatment reaction progresses, the amine compound that is not used in the reaction is discharged from the system by the heat of stirring, so that a millable-type silicone rubber compound with performance equivalent to that of conventional compounds can be easily obtained without heat treatment, leading to the completion of the present invention.

[0019] That is, the present invention provides: The following components (A) to (D) (A) 100 parts by mass of organopolysiloxane gum having two or more silicon-bonded alkenyl groups per molecule and an average degree of polymerization of 1,000 to 100,000, (B) Specific surface area measured by BET adsorption is 50 to 450 m 2 / g reinforcing silica: 5 to 100 parts by mass, (C) an organosiloxane having hydroxysilyl groups at both ends, represented by the following general formula (1): 1.0 to 50.0 parts by mass, and [ka] (In the formula, R 1 are independently a monovalent hydrocarbon group having 1 to 8 carbon atoms, and m is an integer of 1 to 50. (D) Amine compound having a boiling point of 30 to 60°C at 1013 hPa and being liquid at 25°C: 0.0001 to 0.1 parts by mass The present invention relates to a millable type silicone rubber compound containing the above.

[0020] In the present invention, the mixture of the above components (A) to (D) before the curing agent is added is referred to as the silicone rubber compound, and the product of adding a curing agent to the kneaded product of this compound is referred to as the silicone rubber composition.

[0021] The present invention will be described in more detail below.

[0022] [Millable type silicone rubber compound] The millable type silicone rubber compound of the present invention is The following components (A) to (D) (A) 100 parts by mass of organopolysiloxane gum having two or more silicon-bonded alkenyl groups per molecule and an average degree of polymerization of 1,000 to 100,000, (B) Specific surface area measured by BET adsorption is 50 to 450 m 2 / g reinforcing silica: 5 to 100 parts by mass, (C) an organosiloxane having hydroxysilyl groups at both ends, represented by the following general formula (1): 1.0 to 50.0 parts by mass, and [ka] (In the formula, R 1 are independently a monovalent hydrocarbon group having 1 to 8 carbon atoms, and m is an integer of 1 to 50. (D) Amine compound having a boiling point of 30 to 60°C at 1013 hPa and being liquid at 25°C: 0.0001 to 0.1 parts by mass It includes:

[0023] The millable silicone rubber composition of the present invention further comprises the above millable silicone rubber compound kneaded together with (E) a curing agent.

[0024] Among these, it is preferable that the curing agent component is a curing agent for a hydrosilylation reaction, which is a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst.

[0025] -Component (A)- In the present invention, component (A) is an organopolysiloxane gum having two or more silicon-bonded alkenyl groups per molecule and an average degree of polymerization of 1,000 to 100,000.

[0026] The alkenyl group is preferably an alkenyl group having 2 to 8 carbon atoms, and more preferably an alkenyl group having 2 to 6 carbon atoms. Specific examples include a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group, and a cyclohexenyl group. Of these, a vinyl group is preferred.

[0027] Examples of the substituent other than the alkenyl group include monovalent hydrocarbon groups having 1 to 12 carbon atoms, particularly 1 to 8 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; aryl groups such as phenyl and tolyl; and aralkyl groups such as benzyl and 2-phenylethyl. Fluoroalkyl groups in which a portion of the alkyl group is substituted with a fluorine atom may also be used. Among these, methyl and phenyl groups are preferred, with methyl being particularly preferred.

[0028] Furthermore, the component (A) has two or more alkenyl groups per molecule, preferably 2 to 50, and more preferably 2 to 20 alkenyl groups. Of these, those containing vinyl groups are particularly preferred. In this case, it is preferred that 0.01 to 20 mol %, and particularly 0.02 to 10 mol %, of all siloxane units in the organopolysiloxane be siloxane units containing alkenyl groups. The alkenyl groups may be bonded to silicon atoms at the molecular chain terminals, or to silicon atoms in the middle of the molecular chain (non-terminal), or both, but it is preferred that they be bonded to silicon atoms at least at the molecular chain terminals.

[0029] Furthermore, it is desirable that of all siloxane units in the organopolysiloxane, preferably 80 mol % or more, more preferably 90 mol % or more, even more preferably 95 mol % or more, and particularly preferably all siloxane units excluding siloxane units having alkenyl groups, are dialkylsiloxy groups, and particularly dimethylsiloxy groups.

[0030] The molecular structure of the organopolysiloxane of component (A) is preferably linear or partially branched. Specifically, the repeating structure of the diorganosiloxane units constituting the main chain of the organopolysiloxane is preferably one consisting solely of repeating dimethylsiloxane units, or one in which diorganosiloxane units such as diphenylsiloxane units, methylphenylsiloxane units, methylvinylsiloxane units, or methyl-3,3,3-trifluoropropylsiloxane units have been introduced as part of the repeating structure.

[0031] Furthermore, both molecular chain terminals are preferably capped with a group selected from, for example, trimethylsiloxy groups, dimethylphenylsiloxy groups, vinyldimethylsiloxy groups, divinylmethylsiloxy groups, trivinylsiloxy groups, etc., and are particularly preferably capped with vinyldimethylsiloxy groups.

[0032] Examples of organopolysiloxanes of component (A) include methylvinylpolysiloxane, methylphenylvinylpolysiloxane, and methyltrifluoropropylvinylpolysiloxane.

[0033] Such organopolysiloxanes can be obtained, for example, by (co)hydrolytic condensation of one or more organohalogenosilanes, or by ring-opening polymerization of cyclic polysiloxanes (such as siloxane trimers and tetramers) using an alkaline or acidic catalyst.

[0034] The organopolysiloxane has an average degree of polymerization of 1,000 to 100,000, preferably 2,000 to 50,000, more preferably 2,500 to 30,000, and particularly preferably 3,000 to 20,000. The organopolysiloxane has no self-flowing properties at room temperature (25°C), being a so-called raw rubber (non-liquid). If the average degree of polymerization is too low, problems such as roll adhesion can occur when the compound is formed, resulting in poor roll workability. The degree of polymerization can be measured as a weight-average degree of polymerization in terms of polystyrene by gel permeation chromatography (GPC) analysis.

[0035] The component (A) may be a single type, or a mixture of two or more types differing in molecular weight (degree of polymerization) or molecular structure.

[0036] -(B) Component- The reinforcing silica of component (B) is a filler added to obtain a silicone rubber composition with excellent mechanical strength. For this purpose, it is necessary to use a filler having a specific surface area (BET adsorption method) of 50 to 450 m 2 / g, and preferably 100 to 450 m 2 / g, more preferably 100 to 300m 2 / g. The specific surface area is 50m 2 If it is less than 1 / g, the mechanical strength of the cured product will be low.

[0037] Examples of such reinforcing silica include fumed silica and precipitated silica, and those whose surfaces have been hydrophobized with chlorosilane, hexamethyldisilazane, etc. are also preferably used. Of these, fumed silica is preferred because of its excellent dynamic fatigue properties.

[0038] The component (B) may be used alone or in combination of two or more.

[0039] The amount of reinforcing silica (B) blended is 5 to 100 parts by mass, preferably 10 to 50 parts by mass, per 100 parts by mass of the organopolysiloxane (A) blended. If the amount of component (B) blended is too small, the reinforcing effect cannot be obtained, whereas if the amount is too large, processability deteriorates, mechanical strength decreases, and dynamic fatigue durability also deteriorates.

[0040] -(C) component- In the present invention, the component (C) is an organosiloxane having hydroxysilyl groups (silanol groups) at both ends, as represented by the following general formula (1). [ka] (In the formula, R 1 are independently a monovalent hydrocarbon group having 1 to 8 carbon atoms, and m is an integer of 1 to 50.

[0041] where R 1 are independently a monovalent hydrocarbon group having 1 to 8 carbon atoms, and specifically, are preferably alkyl groups having 1 to 8 carbon atoms such as methyl, ethyl, propyl, isopropyl, and butyl, alkenyl groups having 2 to 8 carbon atoms such as vinyl and allyl, and aryl groups having 6 to 8 carbon atoms such as phenyl and tolyl, and more preferably methyl and vinyl groups.

[0042] Furthermore, m is an integer of 1 to 50, preferably 2 to 20.

[0043] The amount of component (C) used is 1.0 to 50.0 parts by mass, and preferably 2.0 to 20.0 parts by mass, per 100 parts by mass of component (A). If the amount of organopolysiloxane end-blocked with silanol groups used is too small, plastic reversion (creep hardening) becomes significant, while if it is too large, the plasticity of the compound becomes too low, causing roll stickiness in kneading means such as a roll mill, and reducing roll workability.

[0044] -(D) Component- Component (D) is a condensation reaction catalyst that causes the hydroxysilyl groups (silanol groups) present on the silica surface of component (B) and the hydroxysilyl groups (silanol groups) of component (C) to undergo a mutual condensation reaction.

[0045] The condensation reaction catalyst of component (D) is an amine compound that is liquid at 25°C and has a boiling point of 30 to 60°C at 1013 hPa. Specific examples of component (D) include lower alkylamines such as propylamine (melting point: -83°C, boiling point: 49°C), isopropylamine (melting point: -101°C, boiling point: 33°C), and tert-butylamine (melting point: -72.65°C, boiling point: 46°C), and lower dialkylamines such as diethylamine (melting point: -50°C, boiling point: 56°C). The melting and boiling points described above are the temperatures listed in the SDS published by Fujifilm Wako Pure Chemical Industries, Ltd.

[0046] The method of adding component (D) is not particularly limited, but it is preferable to add component (D) to component (C) and then quickly add it to the vessel containing component (B). This allows the condensation reaction between the hydroxysilyl groups (silanol groups) of component (B) and the hydroxysilyl groups (silanol groups) of component (C) to proceed efficiently. To facilitate kneading component (D) using a twin-roll mill or kneader, component (D) may be pre-pasted with an organopolysiloxane or the like.

[0047] The amount of component (D) added is 0.0001 to 0.1 parts by mass, preferably 0.001 to 0.1 parts by mass, and more preferably 0.01 to 0.05 parts by mass per 100 parts by mass of component (A). If the amount of component (D) used is too small, the time required for surface treatment of the reinforcing silica may be extended, or the degree of surface treatment may be reduced, making it impossible to obtain a silicone rubber compound. Conversely, if the amount of component (D) used is too large, component (D) may not be removed from the resulting silicone rubber compound, resulting in an increase in the plasticity of the silicone rubber compound over time. When silicone rubber is obtained using addition curing with a platinum catalyst, the resulting rubber may have unstable physical properties or may develop tackiness on the rubber surface due to insufficient curing.

[0048] The millable silicone rubber compound of the present invention is preferably produced using an apparatus capable of uniformly kneading the predetermined amounts of the above-mentioned components (A) to (D). There are no particular restrictions on the apparatus capable of uniformly kneading, but considering the reactivity of the above-mentioned component (D) and its removal after the reaction is complete, it is preferable to use an apparatus that is likely to generate heat during stirring. Specifically, the millable silicone rubber compound can be obtained by kneading using a kneader, Banbury mixer, roll mill, etc., but it is particularly preferable to produce it using a kneader.

[0049] When components (A) to (D) are mixed, component (C), an organosiloxane capped at both ends with hydroxysilyl groups (silanol groups), acts as a wetter for component (B), the reinforcing silica. To enhance this wetter effect, it is effective to add component (D), a condensation reaction catalyst. Adding this component accelerates the wetter action of component (B), the reinforcing silica. To effectively treat the surface of component (B), it is essential that component (C) has hydroxysilyl groups (silanol groups) at both ends.

[0050] The mixing temperature of the components (A) to (D) is preferably in the range of 0 to 120° C., more preferably 30 to 100° C., and even more preferably 30 to 90° C. The time for mixing the components (A) to (D) is not particularly limited, but considering production efficiency, it is desirable to set the mixing time to 1 to 300 minutes, more preferably 10 to 120 minutes.

[0051] When the above-mentioned components (A) to (D) are mixed using the above method, heat of agitation is generated. The heat of agitation varies depending on the degree of polymerization of the component (A), the amount of reinforcing silica in the component (B), and the ratio of the components (A) to (B). However, when a composition suitable for a millable silicone rubber compound, i.e., a composition similar to that of a conventional millable silicone rubber compound, is used, heat of agitation of approximately 30 to 120°C is generated. The component (D) used in the present invention is liquid during blending, making it easy to handle and providing excellent reactivity between the components (B) and (C). In addition, because its boiling point at normal pressure (1013 hPa) is 30 to 60°C, the heat of agitation generated during blending alone can remove the component (D) from the millable silicone rubber compound. This allows for the supply of conventional millable silicone rubber compounds to the market while contributing to environmental issues such as a decarbonized society and reduced CO2 emissions.

[0052] The millable type silicone rubber compound obtained as described above can be kneaded and then blended with the curing agent (E) described below to obtain a millable type silicone rubber composition.

[0053] [Millable-type silicone rubber composition and manufacturing method] The millable silicone rubber composition of the present invention is obtained by removing the component (D) from the millable silicone rubber compound by kneading and adding the component (E) described below.

[0054] Specifically, a method for producing a millable type silicone rubber composition is provided, which comprises kneading the millable type silicone rubber compound, and in the presence of the catalyst component (D), surface treating the component (B) with the component (C), removing the component (D) by stirring under heat, and then adding the curing agent (E).

[0055] -(E) Component- The millable silicone rubber composition of the present invention contains a kneaded mixture obtained by kneading the millable silicone rubber compound and (E) a curing agent.

[0056] The (E) curing agent is not particularly limited as long as it is capable of curing the above-mentioned component (A). However, (E1) addition reaction (hydrosilylation reaction) curing agents generally known as rubber curing agents, i.e., hydrosilylation reaction curing agents comprising a combination of an organohydrogenpolysiloxane (crosslinking agent) and a hydrosilylation catalyst, or (E2) organic peroxides are preferred.

[0057] In particular, the millable silicone rubber compound of the present invention is suitable for use with addition reaction type curing agents because it contains almost no impurities that inhibit addition curing.

[0058] The organohydrogenpolysiloxane used as the crosslinking agent for the addition reaction curing agent (E1) preferably has two or more hydrosilyl groups in one molecule, and is particularly preferably an organohydrogenpolysiloxane represented by the following general formula (2): [ka] (In the formula, R 2 are independently a hydrogen atom or a group selected from an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms, and two or more R 2is a hydrogen atom. Note that two or more hydrogen atoms cannot exist on the same silicon atom. a is an integer of 2≦a≦30, b is an integer of 0≦b≦300, c is an integer of 0≦c≦10, and d is an integer of 0≦d≦30. Note that the bonding of each siloxane unit may be block or random.

[0059] where R 2 are independently a hydrogen atom, or a group selected from an alkyl group having 1 to 8 carbon atoms, preferably 1 to 6, an aryl group having 6 to 10 carbon atoms, preferably 6 to 8, and an aralkyl group having 7 to 10 carbon atoms, preferably 7 to 9. However, there are two or more, preferably 2 to 200, more preferably 2 to 130 R 2 is a hydrogen atom. Examples of alkyl groups include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl groups, and cycloalkyl groups such as cyclohexyl groups. Examples of aryl groups include phenyl and tolyl groups. Examples of aralkyl groups include benzyl and 2-phenylpropyl groups. Note that fluoroalkyl groups in which an alkyl group is partially substituted with a fluorine atom may also be used. Furthermore, a is an integer satisfying 2≦a≦30, preferably 2≦a≦20. b is an integer satisfying 0≦b≦300, preferably 3≦b≦200. c is an integer satisfying 0≦c≦10, preferably 0≦c≦5. and d are integers satisfying 0≦d≦30, preferably 0≦d≦20.

[0060] The molecular structure of the organohydrogenpolysiloxane may be linear, cyclic, branched, or three-dimensional network. In this case, the number of silicon atoms (or degree of polymerization) per molecule is preferably 2 to 300, particularly about 4 to 200, and is liquid at 25°C. The hydrosilyl group may be located at the molecular chain terminal, on a side chain (in the middle of the molecular chain), or both.

[0061] Examples of the organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, methylhydrogenpolysiloxane capped at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with trimethylsiloxy groups, and methylhydrogenpolysiloxane capped at both ends with dimethylsiloxy groups. Siloxy-group-blocked dimethylpolysiloxane, dimethylhydrogensiloxy-blocked dimethylsiloxane-methylhydrogensiloxane copolymer at both ends, trimethylsiloxy-blocked methylhydrogensiloxane-diphenylsiloxane copolymer at both ends, trimethylsiloxy-blocked methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer at both ends, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane-dimethylsiloxane copolymer, cyclic methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer, (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 A copolymer consisting of (CH3)2HSiO units 1 / 2 Units and SiO 4 / 2 Units and (C6H5)SiO 3 / 2 and copolymers consisting of units, and the above-mentioned exemplary compounds in which some or all of the methyl groups have been substituted with other alkyl groups such as ethyl groups or propyl groups, or aryl groups such as phenyl groups. Specific examples of such organohydrogenpolysiloxanes include compounds of the following structural formula:

[0062] [ka] (In the formula, k is an integer of 2 to 10, and s and t are each an integer of 0 to 10.)

[0063] The organohydrogenpolysiloxane preferably has a viscosity of 0.5 to 10,000 mPa·s, and particularly preferably 1 to 300 mPa·s, at 25° C. The viscosity is measured using a rotational viscometer according to the method described in JIS K7117-1:1999.

[0064] The organohydrogenpolysiloxane is preferably blended in an amount such that the molar ratio of silicon-bonded hydrogen atoms (i.e., hydrosilyl groups) in the organohydrogenpolysiloxane to silicon-bonded alkenyl groups in component (A) (hydrosilyl groups / alkenyl groups) is preferably 0.5 to 10, more preferably 0.8 to 6, and even more preferably 1 to 5. A ratio of 0.5 or greater ensures sufficient crosslinking and mechanical strength. A ratio of 10 or less prevents a decrease in physical properties after curing, particularly heat resistance and compression set resistance.

[0065] The hydrosilylation catalyst used in the (E1) addition reaction curing agent promotes the addition reaction between the alkenyl groups in component (A) and the hydrosilyl groups in the organohydrogenpolysiloxane crosslinker. Examples of hydrosilylation catalysts include platinum group metal catalysts such as ruthenium and platinum. Platinum group metal catalysts include these platinum group metals and their compounds. These catalysts are conventionally known as catalysts for addition reaction curing silicone rubber compositions. Examples include finely divided platinum metal adsorbed on a carrier such as silica, alumina, or silica gel; platinic chloride; chloroplatinic acid; reaction products of chloroplatinic acid and monohydric alcohols; complexes of chloroplatinic acid and olefins; complexes of chloroplatinic acid and vinyl group-containing (poly)siloxanes; palladium catalysts; rhodium catalysts; and ruthenium catalysts. Platinum or platinum compounds are particularly preferred.

[0066] The amount of hydrosilylation catalyst added may be a catalytic amount sufficient to promote the addition reaction, and is typically used in a range of 1 ppm to 1 mass % (calculated as the mass of platinum group metal) relative to the amount of component (A), with a range of 10 to 500 ppm being preferred. Addition of 1 ppm or more sufficiently promotes the addition reaction, resulting in sufficient curing. Addition of 1 mass % or less is economical, as the effect on reactivity is commensurate with the amount added.

[0067] In addition to the above catalysts, an addition crosslinking inhibitor may be used to adjust the curing rate, such as ethynylcyclohexanol or tetramethyltetravinylcyclotetrasiloxane.

[0068] On the other hand, examples of the (E2) organic peroxide include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, di-t-butyl peroxide, t-butyl perbenzoate, and 1,6-hexanediol-bis-t-butylperoxycarbonate.

[0069] The amount of organic peroxide added is preferably 0.1 to 15 parts by mass, and particularly preferably 0.2 to 10 parts by mass, per 100 parts by mass of the component (A). If the amount added is sufficient, the crosslinking reaction proceeds sufficiently, and deterioration of physical properties such as reduced hardness, insufficient rubber strength, and increased compression set does not occur. Furthermore, adding an amount not exceeding the above amount is economically preferable, and the amount of decomposition products of the curing agent is sufficiently small, preventing deterioration of physical properties such as increased compression set and increased discoloration of the resulting sheet.

[0070] In addition to the above components, the millable silicone rubber composition of the present invention may contain additives such as conductivity imparting agents such as carbon black, flame retardant imparting agents such as iron oxides and halogen compounds, softeners, antioxidants, ultraviolet absorbers, colorants, etc.

[0071] The millable silicone rubber composition of the present invention obtained in this manner can be cured at 80 to 300°C, particularly 100 to 200°C, for 5 seconds to 1 hour, particularly 30 seconds to 30 minutes to obtain a cured silicone rubber. [Example]

[0072] The present invention will be described in detail below with reference to Examples, Reference Examples, and Comparative Examples, but is not limited to the following Examples. The melting point and boiling point are measured at 1013 hPa, the average degree of polymerization is measured as a weight average degree of polymerization in terms of polystyrene by gel permeation chromatography (GPC) analysis, and the viscosity is measured with a rotational viscometer according to the method described in JIS K7117-1:1999.

[0073] [Example 1] In a 3-liter kneader, 100 parts by mass of organopolysiloxane gum consisting of 99.825 mol% dimethylsiloxane units, 0.15 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxy units, with an average of 12 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 6,000, and a BET specific surface area of ​​200 m were added. 2 40 parts by mass of fumed silica (Aerosil 200, Nippon Aerosil Co., Ltd.) with a molecular weight of 1 / g, 6.0 parts by mass of dimethylpolysiloxane with silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C as a dispersant, and 0.01 parts by mass of isopropylamine (melting point: -101°C, boiling point: 33°C) were added and kneaded uniformly. The temperature was 27°C before kneading, but rose to 64°C one hour after the start of kneading (Sampling 1). Two hours after kneading, the temperature rose to 75°C (Sampling 2). For reference, this silicone rubber compound was then heat-treated at 160°C for two hours to confirm the differences in physical properties from the two samples above (Sampling 3).

[0074] [Example 2] In a 3-liter kneader, 100 parts by mass of organopolysiloxane gum consisting of 99.825 mol% dimethylsiloxane units, 0.15 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxy units, with an average of 12 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 6,000, and a BET specific surface area of ​​200 m were added. 2 40 parts by mass of fumed silica (Aerosil 200, Nippon Aerosil Co., Ltd.) with a molecular weight of 1 / g, 6.0 parts by mass of dimethylpolysiloxane with silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C as a dispersant, and 0.01 parts by mass of diethylamine (melting point: -50°C, boiling point: 56°C) were added and kneaded uniformly. The temperature was 24°C before kneading, but rose to 67°C one hour after the start of kneading (Sampling 4). Two hours after kneading, the temperature rose to 78°C (Sampling 5). For reference, this silicone rubber compound was then heat-treated at 160°C for two hours to confirm the differences in physical properties from the two samples above (Sampling 6).

[0075] [Example 3] In a 3-liter kneader, 100 parts by mass of organopolysiloxane gum consisting of 99.825 mol% dimethylsiloxane units, 0.15 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxy units, with an average of 12 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 6,000, and a BET specific surface area of ​​200 m were added. 2 40 parts by mass of fumed silica (Aerosil 200, Nippon Aerosil Co., Ltd.) with a molecular weight of 1 / g, 6.0 parts by mass of dimethylpolysiloxane with silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C as a dispersant, and 0.01 parts by mass of tert-butylamine (melting point: -72.65°C, boiling point: 46°C) were added and kneaded uniformly. The temperature was 20°C before kneading, but rose to 63°C one hour after the start of kneading (Sampling 7). Two hours after kneading, the temperature rose to 75°C (Sampling 8). For reference, this silicone rubber compound was then heat-treated at 160°C for two hours to confirm the differences in physical properties from the two samples above (Sampling 9).

[0076] [Example 4] In a 3-liter kneader, 100 parts by mass of organopolysiloxane gum consisting of 99.825 mol% dimethylsiloxane units, 0.15 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxy units, with an average of 12 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 6,000, and a BET specific surface area of ​​200 m were added. 2 40 parts by mass of fumed silica (Aerosil 200, Nippon Aerosil Co., Ltd.) with a molecular weight of 1 / g, 6.0 parts by mass of dimethylpolysiloxane with silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C as a dispersant, and 0.05 parts by mass of isopropylamine (melting point: -101°C, boiling point: 33°C) were added and kneaded uniformly. The temperature was 23°C before kneading, but rose to 62°C one hour after the start of kneading (Sampling 10). Two hours after kneading, the temperature rose to 72°C (Sampling 11). For reference, this silicone rubber compound was then heat-treated at 160°C for two hours to confirm the differences in physical properties from the two samples above (Sampling 12).

[0077] [Example 5] In a 3-liter kneader, 100 parts by mass of organopolysiloxane gum consisting of 99.825 mol% dimethylsiloxane units, 0.15 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxy units, with an average of 12 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 6,000, and a BET specific surface area of ​​200 m were added. 240 parts by mass of fumed silica (Aerosil 200, Nippon Aerosil Co., Ltd.) with a molecular weight of 1 / g, 6.0 parts by mass of dimethylpolysiloxane with silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C as a dispersant, and 0.10 parts by mass of isopropylamine (melting point: -101°C, boiling point: 33°C) were added and kneaded uniformly. The temperature was 22°C before kneading, but rose to 64°C one hour after the start of kneading (Sampling 13). Two hours after kneading, the temperature rose to 78°C (Sampling 14). For reference, this silicone rubber compound was then heat-treated at 160°C for two hours to confirm the differences in physical properties from the two samples above (Sampling 15).

[0078] [Comparative Example 1] In a 3-liter kneader, 100 parts by mass of organopolysiloxane gum consisting of 99.825 mol% dimethylsiloxane units, 0.15 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxy units, with an average of 12 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 6,000, and a BET specific surface area of ​​200 m were added. 2 40 parts by mass of fumed silica (Aerosil 200, Nippon Aerosil Co., Ltd.) with a molecular weight of 1 / g, 6.0 parts by mass of dimethylpolysiloxane (dispersant) with silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C, and 0.01 parts by mass of hexamethyldisilazane (melting point: -78°C, boiling point: 125°C) were added and kneaded uniformly. The temperature was 24°C before kneading, but rose to 66°C one hour after the start of kneading (Sample 16). Two hours after kneading, the temperature rose to 76°C (Sample 17). For reference, this silicone rubber compound was then heat-treated at 160°C for two hours to confirm the differences in physical properties from the two samples above (Sample 18).

[0079] Comparative Example 2 In a 3-liter kneader, 100 parts by mass of organopolysiloxane gum consisting of 99.825 mol% dimethylsiloxane units, 0.15 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxy units, with an average of 12 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 6,000, and a BET specific surface area of ​​200 m were added. 2 40 parts by mass of fumed silica (Aerosil 200, Nippon Aerosil Co., Ltd.) with a molecular weight of 1 / g, 6.0 parts by mass of dimethylpolysiloxane with silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C as a dispersant, and 0.30 parts by mass of isopropylamine (melting point: -101°C, boiling point: 33°C) were added and kneaded uniformly. The temperature was 18°C ​​before kneading and rose to 60°C one hour after the start of kneading (Sampling 19). Two hours after kneading, the temperature rose to 73°C (Sampling 20). For reference, this silicone rubber compound was then heat-treated at 160°C for two hours to confirm the differences in physical properties from the two samples above (Sampling 21).

[0080] Comparative Example 3 In a 3-liter kneader, 100 parts by mass of organopolysiloxane gum consisting of 99.825 mol% dimethylsiloxane units, 0.15 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxy units, with an average of 12 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 6,000, and a BET specific surface area of ​​200 m were added. 2 40 parts by mass of fumed silica (Aerosil 200, Nippon Aerosil Co., Ltd.) with a molecular weight of 1 / g and 6.0 parts by mass of dimethylpolysiloxane with silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C as a dispersant were added and kneaded uniformly. The temperature was 19°C before kneading, but rose to 73°C one hour after the start of kneading (Sampling 22). After that, the temperature rose to 88°C two hours after kneading (Sampling 23). For reference, this silicone rubber compound was then heat-treated at 160°C for two hours to confirm the differences in physical properties from the two samples above (Sampling 24).

[0081] [test] Millable silicone rubber compositions were prepared using the kneaded mixtures of the silicone rubber compounds obtained as the compositions of Examples 1 to 5 and Comparative Examples 1 to 3, and each silicone rubber compound, and then molded test sheets were used to test the results, which are shown in Table 1.

[0082] Plasticity measurement The silicone rubber compound samples taken under each condition were kneaded 15 times on a three-roll mill, and the Williams plasticity was measured 10 minutes later (initial), followed by the plasticity after one day at 40°C. The change over time after one day at 40°C relative to the initial value was calculated. Results (plasticity change) within ±50 of the heat-treated silicone rubber compound kneaded sample were judged to be acceptable (equivalent to conventional products), while results that deviated from this were judged to be unacceptable (different from conventional products). The comparative values ​​can be calculated using the following formula: (Comparative value) = (Plasticity change of the heat-treated kneaded material) - (Plasticity change of the kneaded material of the present invention)

[0083] ○Measurement of physical properties For 100 parts by mass of the kneaded silicone rubber compound sampled under each condition, 0.01 parts by mass of a platinum catalyst (manufactured by Shin-Etsu Chemical Co., Ltd.) containing 1% by mass of platinum atomic mass equivalent of chloroplatinic acid-divinyldisiloxane complex as an addition reaction type curing agent and the following formula [ka] 0.85 parts by mass of an organohydrogenpolysiloxane (Shin-Etsu Chemical Co., Ltd.) represented by the formula (I) was added and mixed uniformly to prepare a millable silicone rubber composition. This composition was then press-cured at 120°C for 10 minutes to produce a test sheet, and then post-cured under the same conditions as above for 4 hours at 200°C to produce a test sheet. The test sheets prepared under both conditions were measured for density, hardness (Durometer A), tensile strength, elongation at break, rebound resilience, and compression set (150°C / 22 hours, 25% compression). Values ​​within ±20% error compared with the results of test sheets prepared using a heat-treated silicone rubber compound mixture were evaluated as passing (equivalent to conventional products), while values ​​outside this range were evaluated as failing (different from conventional products). The comparison values ​​can be calculated using the following formula: (Error) = {(Physical property value of the cured product obtained using the kneaded product of the present invention) - (Physical property value of the cured product obtained using the kneaded product that has been heat-treated)} ÷ (Physical property value of the cured product obtained using the kneaded product that has been heat-treated). [Table 1]

[0084] [Evaluation results] Each of the silicone rubber compounds obtained in Examples 1 to 5 met the requirements of the present invention, and it was found that the physical properties of the kneaded products of each silicone rubber compound, as well as the physical properties of the molding test sheets of the cured products of the millable silicone rubber compositions prepared using them, were almost the same as when silicone rubber compounds produced using conventional heat treatment were used, i.e., they exhibited performance equivalent to that of conventional products.

[0085] In contrast, in Comparative Example 1, the boiling point of hexamethyldisilazane, which replaces the amine compound used in the present invention, is high, and therefore, when the same amount is blended, the change in plasticity of the silicone rubber compound is greater than that of the silicone rubber compound produced using heat treatment. As a result, the stability of the silicone rubber compound over time is reduced. Furthermore, when the mixing time was 1 hour, the compression set after post-cure was also large.

[0086] In Comparative Example 2, the amine compound described in the present invention was used, but the compounding amount was different. As a result, the amine compound could not be removed from the silicone rubber compound by stirring alone, and the change in plasticity of the silicone rubber compound was significantly greater than that of silicone rubber compounds produced using heat treatment. In this case, the millable silicone rubber composition produced using this silicone rubber compound cured into a molding test sheet. However, if a large amount of the amine compound remained, the platinum catalyst may be deactivated by the amine compound, making it impossible to obtain a molding test sheet. Therefore, deviation from the compounding amount can be considered a fatal flaw. Furthermore, when the silicone rubber compound was not heat-treated, the compression set after press curing was also large. Furthermore, when the stirring time was 1 hour, the elongation at break was large.

[0087] In Comparative Example 3, a silicone rubber compound was obtained without using a condensation reaction catalyst. As in Comparative Examples 1 and 2, the change in plasticity of the silicone rubber compound was greater than that of silicone rubber compounds produced using heat treatment. Therefore, the stability of the silicone rubber compound over time also decreased in this case. Furthermore, when the mixing time was 1 hour, the elongation at break after post-cure decreased.

[0088] The above results show that the silicone rubber compound kneaded product obtained by the manufacturing method of the present invention exhibits the same stability over time as conventional products, even without forced heat treatment, and that the physical properties of silicone rubber compositions made using it also exhibit performance equivalent to conventional products.This means that a silicone rubber compound kneaded product equivalent to conventional products can be obtained even without the heat treatment step, thereby contributing to energy savings and a carbon-free society. [Industrial Applicability]

[0089] The method for producing a millable silicone rubber compound of the present invention, and the method for producing a silicone rubber composition obtained by blending a curing agent with a kneaded product of the compound, can easily produce a millable silicone rubber compound having properties similar to those of conventional compounds without the need for forced heat treatment.As a result, it is possible to contribute to the recent trend toward energy conservation and a carbon-free society.Furthermore, silicone rubber compositions using this silicone rubber compound are expected to have a wide range of applications, including in the fields of electrical equipment, automobiles, construction, medicine, and food.

[0090] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

[Claim 1] The following components (A) to (D): (A) 100 parts by mass of organopolysiloxane gum having two or more silicon-bonded alkenyl groups per molecule and an average degree of polymerization of 1,000 to 100,000; (B) reinforcing silica having a specific surface area of ​​50 to 450 m 2 / g as measured by the BET adsorption method: 5 to 100 parts by mass; (C) 1.0 to 50.0 parts by mass of an organosiloxane having hydroxysilyl groups at both ends, represented by the following general formula (1): 【Chemical 1】 (In the formula, R 1 is independently a monovalent hydrocarbon group having 1 to 8 carbon atoms, and m is an integer from 1 to 50.) (D) an amine compound (excluding diethylamine) that is liquid at 25°C and has a boiling point at 1013 hPa of 30 to 60°C: 0.0001 to 0.1 parts by mass A method for producing a millable type silicone rubber composition, characterized by kneading a millable type silicone rubber compound containing the above components, and in the presence of the catalyst component (D), removing component (D) by stirring with heat while surface treating component (B) with component (C), and then adding a curing agent (E).

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