Addition-curable silicone rubber composition and silicone rubber cured product

Abstract

The invention relates to an addition curing type silicone rubber composition. (A) 100 parts by mass of an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule; (B) 0.2-20 parts by mass of an organohydrogenpolysiloxane having two or more hydrogen atoms bonded to a silicon atom in one molecule; (C) a platinum-based catalyst in a catalytic amount; (D) 0.01-5.0 parts by mass of a thermally dissociable blocked polyisocyanate; and (F) 0.01 to 10 parts by mass of water, in an amount of 0.01 to 10.0 parts by mass. As a result, it is possible to provide an addition-curable silicone rubber composition and a silicone rubber cured product which are capable of obtaining a cured product having low compression set even under high-temperature conditions of 200 DEG C or higher.

Description

Technical Field

[0001] The present invention relates to an addition-curing silicone rubber composition and a silicone rubber cured product obtained by curing the composition. Background Art

[0002] Silicone rubber is widely used in the fields of automotive hoses and gaskets, copier rollers, microwave oven gaskets, electrical / electronic components, building components, fiber coatings, etc. due to its excellent heat resistance, cold resistance, safety, electrical insulation, weather resistance, and durability.

[0003] In addition, in recent years, with the miniaturization and high output of automobile engines, higher heat resistance is required for components around the engine. As a method for further improving the heat resistance of the silicone rubber composition, there is a method of adding metal oxides such as iron oxide, titanium oxide, and cerium oxide as a heat resistance improver. In this way, a silicone rubber cured product with little change in physical properties can be obtained even under higher temperature conditions.

[0004] In addition, when silicone rubber is used as a seal such as an O-ring or gasket, a lower compression permanent strain is sought to prevent seal leakage. In general, in order to reduce the compression permanent strain, the heat-cured rubber needs to be further subjected to a long-term secondary vulcanization at high temperature.

[0005] Patent Documents 1 and 2 describe silicone rubber compositions containing metal oxides (titanium oxide and iron oxide in Patent Document 1, and hydrous cerium oxide and hydrous zirconium oxide in Patent Document 2). Although it is reported that the heat resistance of the silicone rubber composition can be improved by adding the metal oxides, no research has been conducted on the compression set.

[0006] Patent Document 3 states that an addition-curable silicone rubber composition containing a triazole compound can reduce the compression set without secondary vulcanization. However, it is known that an addition-curable silicone rubber composition containing a triazole compound has difficulty in improving the compression set under high temperature conditions of 200° C. or higher.

[0007] Patent Documents 4 and 5 describe silicone rubber compositions containing blocked polyisocyanate compositions, and describe that: Patent Document 4 is characterized by good adhesion to woven fabrics and the ability to maintain adhesion even when stored for a long time at high temperature and high humidity, and Patent Document 5 is characterized by limiting the composition and content of the thermally dissociable blocked polyisocyanate composition and being able to impart flame retardancy. However, these silicone rubber compositions containing blocked polyisocyanate compositions do not improve their compression set at 200° C. or above when only a trace amount of the blocked polyisocyanate composition is added.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application No. 2016-518461

[0011] Patent Document 2: Japanese Patent Application Publication No. 2014-031408

[0012] Patent Document 3: Japanese Patent Application Publication No. 2017-165931

[0013] Patent Document 4: Japanese Patent Application Publication No. 2019-006956

[0014] Patent Document 5: Japanese Patent Application Publication No. 2020-070357 Summary of the invention

[0015] 1. Technical issues to be resolved

[0016] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an addition-curable silicone rubber composition and a silicone rubber cured product, wherein the addition-curable silicone rubber composition can obtain a cured product having a low compression permanent strain even under high temperature conditions of 200° C. or higher.

[0017] (II) Technical solution

[0018] In order to solve the above technical problems, the present invention provides an addition-curing silicone rubber composition, which contains:

[0019] (A) 100 parts by mass of an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule;

[0020] (B) 0.2 to 20 parts by mass of an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms in one molecule;

[0021] (C) platinum catalyst: catalytic amount;

[0022] (D) thermally dissociable blocked polyisocyanate: 0.01 to 5.0 parts by mass;

[0023] (E) heat resistance imparting agent: 0.01 to 10.0 parts by mass; and

[0024] (F) Water: 0.01 to 10 parts by mass.

[0025] According to such an addition-curing silicone rubber composition, a cured product having a low compression set even under high temperature conditions of 200° C. or higher can be obtained.

[0026] In the present invention, the (D) thermally dissociable blocked polyisocyanate is preferably a reaction product of a polyisocyanate and a thermally dissociable blocking agent, wherein the polyisocyanate is derived from at least one diisocyanate selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

[0027] Such a component (D) is preferred because it has a large effect of improving the compression set.

[0028] Furthermore, in the present invention, it is preferred that the (E) heat resistance imparting agent is one or more substances selected from the group consisting of iron oxide, titanium oxide doped with a metal oxide, and carbon.

[0029] Such a component (E) is preferred because it has a large effect of improving the compression set.

[0030] In the present invention, it is preferred to further contain an acetylene alcohol compound or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane as the component (G) in which 1 to 500 mol of acetylene bonds are contained per 1 mol of platinum atoms of the component (C).

[0031] Such an addition-curable silicone rubber composition is preferred because the curing start time can be controlled.

[0032] In the present invention, it is preferred that 5 to 100 parts by mass of reinforcing silica fine powder as the component (H) be further contained relative to 100 parts by mass of the component (A).

[0033] Such an addition-curing silicone rubber composition is preferred because the rubber strength is increased.

[0034] In this case, it is preferred that the component (H) has a specific surface area of ​​50 m 2 / g or more of fumed silica.

[0035] Such a component (H) is preferred because the rubber strength can be more reliably improved.

[0036] The present invention also provides a silicone rubber cured product obtained by curing the above-described addition-curable silicone rubber composition.

[0037] Such a cured product has low compression set even under high temperature conditions of 200° C. or higher.

[0038] (III) Beneficial effects

[0039] According to the present invention, an addition-curable silicone rubber composition and a silicone rubber cured product obtained by curing the composition can be provided. The addition-curable silicone rubber composition can provide a silicone rubber cured product having a low compression permanent strain for a long period of time even under a high temperature condition of 200°C. DETAILED DESCRIPTION

[0040] As described above, it is desired to develop an addition-curable silicone rubber composition and a silicone rubber cured product that can provide a cured product having a low compression set even under high temperature conditions of 200° C. or higher.

[0041] The inventors of the present invention have conducted intensive studies on the above technical problems and, as a result, have found that, by combining the components (D), (E) and (F) in a specific ratio in an addition-curing silicone rubber composition containing the following components, an addition-curing silicone rubber composition capable of obtaining a cured product having a low compression set even under high temperature conditions of 200° C. or higher can be obtained, thereby completing the present invention.

[0042] (A) an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule;

[0043] (B) an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms in one molecule;

[0044] (C) platinum-based catalysts;

[0045] (D) thermally dissociable blocked polyisocyanates;

[0046] (E) a heat resistance imparting agent; and

[0047] (F) Water.

[0048] That is, the present invention is an addition-curable silicone rubber composition comprising:

[0049] (A) 100 parts by mass of an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule;

[0050] (B) 0.2 to 20 parts by mass of an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms in one molecule;

[0051] (C) Platinum catalyst: catalytic amount;

[0052] (D) thermally dissociable blocked polyisocyanate: 0.01 to 5.0 parts by mass;

[0053] (E) heat resistance imparting agent: 0.01 to 10.0 parts by mass; and

[0054] (F) Water: 0.01 to 10 parts by mass.

[0055] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0056] [Addition-curing silicone rubber composition]

[0057] The addition-curable silicone rubber composition of the present invention contains the following components (A), (B), (C), (D), (E) and (F). In addition, it may also contain components (G) and (H). Each component is described below.

[0058] (A) Alkenyl-containing organopolysiloxane

[0059] The alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule of the component (A) is the main agent (base polymer) of the present composition.

[0060] The alkenyl group is preferably an alkenyl group having 2 to 10 carbon atoms, more preferably an alkenyl group having 2 to 8 carbon atoms, and still more preferably an alkenyl group having 2 to 6 carbon atoms. Among them, vinyl group is most preferred.

[0061] In addition, the content of alkenyl groups in the alkenyl group-containing organopolysiloxane is preferably 1.0×10 -6 ~5.0×10 -3 mol / g, particularly preferably 1.0×10 -5 ~2.0×10 -3 mol / g. If the content is 1.0×10 -6 ~5.0×10 -3 The alkenyl group may be bonded to the silicon atom at the end of the molecular chain, to the silicon atom in the middle of the molecular chain, or to both.

[0062] In addition, as a group other than the alkenyl group, a monovalent hydrocarbon group having 1 to 10 carbon atoms is preferred. Examples of the monovalent hydrocarbon group having 1 to 10 carbon atoms include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; and aralkyl groups such as benzyl, phenylethyl, and phenylpropyl. It is preferred that 90 mol% or more of all substituents are methyl groups, and it is particularly preferred that all substituents other than the alkenyl group are methyl groups.

[0063] The alkenyl-containing organopolysiloxane has a structure in which both ends of the molecular chain are capped with triorganosiloxy groups, and the main chain has a linear structure composed of repeated diorganosiloxane units, but may partially have a branched structure or a cyclic structure.

[0064] The molecular weight of the component (A) has an average degree of polymerization of 1,500 or less, usually 100 to 1,500, and preferably 150 to 1,000. When the average degree of polymerization is 100 to 1,500, a rubber-like material can be obtained and moldability is good.

[0065] The average degree of polymerization in the present invention refers to a number average degree of polymerization measured by gel permeation chromatography (GPC) under the following conditions using polystyrene as a standard substance.

[0066] [Measurement conditions]

[0067] Developing solvent: Toluene

[0068] Flow rate: 0.6mL / min

[0069] Detector: Differential refractive index detector (RI)

[0070] Column: TSK Guardcolumn SuperH-H

[0071] TSKgel SuperH5000(6.0mmI.D.×15cm×1)

[0072] TSKgel SuperH4000(6.0mmI.D.×15cm×1)

[0073] TSKgel SuperH3000(6.0mmI.D.×15cm×1)

[0074] (Both manufactured by TOSOH CORPORATION)

[0075] Column temperature: 40°C

[0076] Sample injection volume: 50 μL (toluene solution with a concentration of 0.5 mass %)

[0077] In addition, as the component (A), one or more alkenyl group-containing organopolysiloxanes having different molecular structures or polymerization degrees may be used simultaneously, as long as they are alkenyl group-containing organopolysiloxanes having two or more alkenyl groups bonded to silicon atoms in one molecule, such as alkenyl groups bonded to silicon atoms at both ends of the molecular chain.

[0078] (B) Organohydrogenpolysiloxane

[0079] The component (B) is an organohydrogenpolysiloxane containing two or more hydrogen atoms (hydrogen silyl groups) bonded to silicon atoms in one molecule, preferably an organohydrogenpolysiloxane containing three or more hydrogen atoms (hydrogen silyl groups) bonded to silicon atoms in one molecule, and the hydrosilyl groups in the molecule are cross-linked with the alkenyl groups bonded to silicon atoms in the component (A) by a hydrosilylation addition reaction, thereby playing the role of a curing agent (cross-linking agent) for curing the addition-curing silicone rubber composition.

[0080] As the organohydrogenpolysiloxane of the component (B), it is preferable to use an organohydrogenpolysiloxane having 2 or more, preferably 3 or more, more preferably 3 to 100, particularly preferably 4 to 50 hydrogen atoms (hydrosilyl groups) bonded to silicon atoms in one molecule.

[0081] Here, as the substituent other than the hydrogen atom bonded to the silicon atom, a monovalent hydrocarbon group can be cited. Among them, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, etc. can be cited. As specific examples and preferred examples of each, the same substituents as those exemplified for the component (A) except for the alkenyl group can be cited.

[0082] The molecular structure of the organohydrogenpolysiloxane may be any one of a linear structure, a cyclic structure, a branched structure, and a three-dimensional network structure.

[0083] The content of the hydrosilyl group in the organohydrogenpolysiloxane is preferably 0.0005 to 0.020 mol / g, and particularly preferably 0.001 to 0.017 mol / g. When the amount of the hydrosilyl group is 0.0005 mol / g or more, crosslinking is sufficient, and when it is 0.020 mol / g or less, the organohydrogenpolysiloxane is a stable substance.

[0084] In this case, it is preferred to use an organohydrogenpolysiloxane that is liquid at room temperature (25° C.) and has a silicon atom number (or polymerization degree) of 2 to 300, particularly 3 to 150, and especially 4 to 100 in one molecule. The hydrogen atom bonded to the silicon atom may be located at any position of the molecular chain terminal, the middle of the molecular chain (non-terminal), or both.

[0085] Examples of the organohydrogenpolysiloxane of the component (B) include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris(hydrogendimethylsiloxy)methylsilane, tris(hydrogendimethylsiloxy)phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, methylhydrogenpolysiloxane terminated at both ends with trimethylsiloxy groups, dimethylhydrogenpolysiloxane-methylhydrogencopolymer terminated at both ends with trimethylsiloxy groups, dimethylhydrogenpolysiloxane-dimethylhydrogencopolymer terminated at both ends with dimethylhydrogensiloxy groups, and dimethylhydrogenpolysiloxane terminated at both ends with dimethylhydrogensiloxy groups. Siloxane-methyl hydrogen siloxane copolymer, methyl hydrogen siloxane-diphenyl siloxane copolymer terminated by trimethylsiloxy groups at both ends, methyl hydrogen siloxane-diphenyl siloxane-dimethyl siloxane copolymer terminated by trimethylsiloxy groups at both ends, methyl hydrogen siloxane-methyl phenyl siloxane-dimethyl siloxane copolymer terminated by trimethylsiloxy groups at both ends, methyl hydrogen siloxane-dimethyl siloxane-diphenyl siloxane copolymer terminated by dimethyl hydrogen siloxane groups at both ends, methyl hydrogen siloxane-dimethyl siloxane-methyl phenyl siloxane copolymer terminated by dimethyl hydrogen siloxane groups at both ends, (CH3)2HSiO 1 / 2 Unit and (CH3)3SiO 1 / 2 Unit and SiO 4 / 2 The copolymer is composed of (CH3)2HSiO 1 / 2 Unit and SiO 4 / 2 The copolymer is composed of (CH3)2HSiO 1 / 2 Unit and SiO 4 / 2 Unit and (C6H5)SiO 3 / 2 Copolymers consisting of units or organohydrogenpolysiloxanes in which part or all of the methyl groups in these exemplified compounds are substituted with other alkyl groups, phenyl groups, or the like.

[0086] In addition, the organohydrogenpolysiloxane as the component (B) may be an organohydrogenpolysiloxane containing a polyvalent aromatic ring, which is an organohydrogenpolysiloxane containing a hydrocarbon skeleton containing a generally divalent to tetravalent aromatic ring (for example, a phenylene skeleton, a bisphenylene skeleton, a bis(phenylene) ether skeleton, a bis(phenylene) methane skeleton, a 2,2-bis(phenylene) propane skeleton, a 2,2-bis(phenylene) hexafluoropropane skeleton, etc.) in a part of the siloxane skeleton (-Si-O-Si-) constituting the molecule in the above-mentioned exemplified compounds, etc. (generally a part of the position of the oxygen atom forming the siloxane bond).

[0087] The amount of the organohydrogenpolysiloxane as the component (B) is 0.2 to 20 parts by mass, preferably 0.3 to 10 parts by mass, relative to a total of 100 parts by mass of the component (A). In addition, the molar ratio of the hydrogen atoms (hydrosilyl groups) bonded to silicon atoms in the organohydrogenpolysiloxane of the component (B) to the total amount of alkenyl groups bonded to silicon atoms in the components (A) and (B) (particularly in the component (A)) (hydrosilyl groups / alkenyl groups) is preferably 0.8 to 10, more preferably 1.0 to 5. As long as the ratio is 0.8 or more, the curing (crosslinking density) is sufficient and the rubber will not become sticky. As long as the ratio is 10 or less, no foaming will be found in the silicone rubber molded product, and it will not be difficult to release from the mold.

[0088] (C) Platinum catalyst

[0089] (C) Components include platinum-based catalysts such as platinum black, platinum chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monovalent alcohol, a complex of chloroplatinic acid and olefins, and bisacetoacetate platinum.

[0090] The amount of the platinum catalyst added is a catalytic amount, and is usually preferably 0.5 to 500 ppm, and particularly about 1 to 200 ppm, relative to the mass of the component (A), in terms of platinum metal (mass conversion). The platinum catalyst of the component (C) may be used alone or in combination of two or more.

[0091] (D) Thermally dissociable blocked polyisocyanate

[0092] The thermally dissociable blocked polyisocyanate of the component (D) is a component for improving the compression set of the cured product of the addition-curing silicone rubber composition of the present invention by adding it together with the heat resistance imparting agent of the component (E). The blocked product of the thermally dissociable blocked polyisocyanate can maintain the effect of reducing the compression set stably for a long time after thermal dissociation.

[0093] (D) component thermally dissociated blocked polyisocyanate is preferably a blocked polyisocyanate obtained from a reaction product of a polyisocyanate and a thermally dissociated blocking agent, and the polyisocyanate is derived from one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates. In addition, the blocked polyisocyanate is more preferably a blocked polyisocyanate obtained from a reaction product of a polyisocyanate derived from a diisocyanate and a thermally dissociated blocking agent, and the thermally dissociated blocking agent is more than 1 mole of free NCO groups relative to 1 mole of the polyisocyanate derived from the diisocyanate. As aliphatic diisocyanates, butane diisocyanate, pentane diisocyanate, and hexamethylene diisocyanate can be exemplified. As alicyclic diisocyanates, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, etc. can be exemplified. Among them, hexamethylene diisocyanate and toluene diisocyanate are easily available in industry, so they are preferred. These aliphatic diisocyanates or alicyclic diisocyanates may be used alone or in combination of two or more.

[0094] Examples of the polyisocyanate include oligomers obtained by urethanizing, ureaizing, allophanating, biuretizing, and isocyanurating aliphatic diisocyanates or alicyclic diisocyanates, for example, polyisocyanates whose chain length is extended by reaction with a diol, or polyisocyanates that are three-dimensionally grown by reaction with a triol.

[0095] The thermally dissociable end-capping agent is preferably selected from, for example, oxime-based, alcohol-based, acid amide-based, acid imide-based, phenol-based, amine-based, active methylene-based, imidazole-based, pyrazole-based, and triazole-based compounds, alone or in combination.

[0096] The thermal decomposition temperature of the thermally dissociable blocked polyisocyanate varies depending on the thermally dissociable blocking agent, and is, for example, 100 to 300° C. The heat curing temperature of the addition-curing silicone rubber composition is 40 to 230° C. and the heating treatment (primary vulcanization) condition is about 3 seconds to 160 minutes. It is not easy to thermally decompose when stored at room temperature or when vulcanized once, and it is preferred that the blocker thermally dissociates when it is secondary vulcanized or used as a molded product.

[0097] Relative to 100 parts by mass of component (A), the amount of thermally dissociable blocked polyisocyanate is 0.01 to 5.0 parts by mass, preferably 0.01 to 1.0 parts by mass. If it is less than 0.01 parts, it is difficult to obtain the improvement effect of compression permanent strain, and if it is greater than 5.0 parts by mass, it is possible to cause curing delay. In addition, the thermally dissociable blocked polyisocyanate can be used alone or in combination of two or more. When two or more are used simultaneously, the amount of the blending as a whole is within the above range.

[0098] (E) Heat resistance imparting agent

[0099] The heat resistance imparting agent of component (E) is a component that significantly improves the compression permanent strain of the silicone rubber cured product at high temperature by being added together with the component (D). As the component (E), cerium oxide, cerium hydroxide, iron oxide (e.g., yellow iron oxide), titanium oxide (e.g., titanium oxide doped with metal oxide), carbon black (carbon), etc. can be exemplified. Among them, iron oxide, titanium oxide doped with metal oxide, and carbon are preferred because of their large effect of improving the compression permanent strain. These heat resistance imparting agents can be used alone or in combination of two or more.

[0100] The amount of component (E) is 0.01 to 10.0 parts by mass, preferably 0.01 to 5.0 parts by mass, and more preferably 0.01 to 1.0 parts by mass relative to 100 parts by mass of component (A). If it is less than 0.01 parts, it is difficult to obtain the effect of improving the compression permanent set, and if it is more than 10.0 parts by mass, it may lead to a decrease in physical properties.

[0101] (F) Water

[0102] The water in the component (F) is a component that significantly improves the compression set of the silicone rubber cured product at high temperatures by being added together with the component (D). It is speculated that the use of water together with the blocked polyisocyanate has the effect of promoting the decomposition of the blocking agent of the blocked polyisocyanate under high temperature conditions.

[0103] The amount of component (F) is 0.01 to 10 parts by mass, preferably 0.01 to 2 parts by mass, and more preferably 0.01 to 1 part by mass relative to 100 parts by mass of component (A). If the amount is less than 0.01 parts, it is difficult to obtain the effect of improving the compression permanent strain, and if the amount is greater than 10 parts by mass, water may seep out onto the surface of the cured product.

[0104] (G) Reaction control agent

[0105] The addition-curing silicone rubber composition of the present invention may also contain, in addition to the above-mentioned components (A) to (F), an acetylene alcohol compound or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane as a component (G). The component (G) functions as a reaction controller for the platinum catalyst of the component (C), and can control the curing start time according to the amount added.

[0106] The acetylene alcohol compound of the component (G) may be a compound having an acetylene group and a hydroxyl group in the same molecule, but preferably the acetylene group and the hydroxyl group are bonded to the same carbon atom. Specific examples include the following compounds.

[0107] [Chemical formula 1]

[0108]

[0109] The compound in which the alcoholic hydroxyl group of the acetylene alcohol compound is modified with silane or siloxane is a compound in which the hydroxyl group of the acetylene alcohol compound is bonded to silane or siloxane in the form of a Si-OC bond.

[0110] [Chemical formula 2]

[0111]

[0112] Here, s is an integer of 0 to 50, preferably an integer of 3 to 20, and t is an integer of 1 to 50, preferably an integer of 3 to 20.

[0113] As the blending amount of the (G) component, the acetylene bond is preferably 1 to 500 moles, more preferably 1 to 300 moles, and further preferably 2 to 200 moles relative to 1 mole of platinum atoms of the (C) component. As long as the blending amount is 1 to 500 moles, the curing property is good and a sufficient pot life can be obtained for operation. The (G) component can be used alone or in combination of two or more. When two or more are used in combination, the blending amount as a whole is within the above range.

[0114] (H) Reinforcing silica powder

[0115] The addition-cured silicone rubber composition of the present invention preferably contains reinforcing silica fine powder as component (H). The reinforcing silica fine powder as component (H) is not particularly limited to the type of silica, and can be a substance commonly used as a reinforcing agent for rubber. As the reinforcing silica fine powder, the reinforcing silica fine powder previously used for silicone rubber compositions can be used, but preferably a silica fine powder having a specific surface area of ​​50 m2 based on the BET method is used. 2 / g or more reinforcing silica fine powder. It is particularly preferred to use a specific surface area of ​​50 to 400 m based on the BET method. 2 / g, especially 100~350m 2 / g of precipitated silica (wet silica), fumed silica (dry silica), calcined silica, etc., and fumed silica is preferred for the purpose of increasing rubber strength. In addition, the reinforcing silica fine powder may also be a silica fine powder whose surface is hydrophobic, for example, using a surface treatment agent such as (usually hydrolyzable) organosilicon compounds such as chlorosilane, alkoxysilane, and organosilazane. At this time, these silica fine powders can be directly hydrophobic in the state of powder by a surface treatment agent, or they can be hydrophobic by adding a surface treatment agent when kneading with silicone oil (for example, the alkenyl-containing organopolysiloxane of the above-mentioned (A) component).

[0116] As a surface treatment method, the surface treatment can be performed by a known technique, for example, the above-mentioned untreated silica powder and the surface treatment agent are added to a closed mechanical kneading device or a fluidized bed at normal pressure, and mixed at room temperature or by heat treatment (heating) in the presence of an inert gas as required. A catalyst (hydrolysis promoter, etc.) can also be used to promote the surface treatment according to the circumstances. After kneading, the surface treated silica powder can be obtained by drying. The amount of the surface treatment agent added is an amount calculated based on the coverage area of ​​the treatment agent.

[0117] As the surface treatment agent, specifically, silazanes such as hexamethyldisilazane can be listed; silane coupling agents such as methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylmethoxysilane, triethylmethoxysilane, vinyltri(methoxyethoxy)silane, trimethylchlorosilane, dimethyldichlorosilane, divinyldimethoxysilane and chloropropyltrimethoxysilane; organosilicon compounds such as polymethylsiloxane and organohydrogenpolysiloxane are used for surface treatment as hydrophobic silica powder. As the surface treatment agent, silane coupling agents or silazanes are particularly preferred. The reinforcing silica powder of component (H) can be used alone or in combination of two or more.

[0118] The blending amount of the component (H) is preferably 5 to 100 parts by mass relative to 100 parts by mass of the component (A).

[0119] [Method for preparing addition-curing silicone rubber composition]

[0120] The addition-curing silicone rubber composition of the present invention can be obtained simply by uniformly mixing the above-mentioned (A) to (F) components and any components at room temperature, but when the (H) component is included, it is preferably obtained by the following method: using a planetary mixer or a kneader, the (H) component is heat-treated together with the total amount of the (A) component or a part thereof at a temperature of 100 to 200° C. for 1 to 4 hours, and after cooling to room temperature, the remaining components and any components are added and mixed. In addition, the water added at this time is added to promote the treatment of the (H) component with the surface treatment agent. Since the excess portion evaporates due to the heat treatment, it does not play a role as the (F) component.

[0121] [Molding method of addition-curing silicone rubber composition / cured silicone rubber]

[0122] As a molding and curing method of the addition-curing silicone rubber composition, conventional methods can be used. As a molding method, the best method that meets the purpose can be selected from injection molding, transfer molding, injection molding, compression molding, etc. As a curing condition, a heating treatment at 40 to 230°C for about 3 seconds to 160 minutes (primary vulcanization) can be used. In addition, a secondary vulcanization (post-curing) at 40 to 230°C for about 10 minutes to 24 hours can also be optionally performed as needed.

[0123] The cured product obtained by curing the addition-curing silicone rubber composition of the present invention preferably has a compression permanent strain of 80% or less at 230°C x 125 hours at a compression rate of 25%. If the value is below this value, the product can be suitably used as a material for an O-ring or a gasket.

[0124] In addition, the said compression permanent strain in this invention is the value measured by the method described in JIS K 6262: 2013. In addition, in this standard, as a test piece used for measurement, the following two types can be mentioned.

[0125] [Table 1]

[0126]

[0127] The compression permanent strain of the cured product of the addition-curing silicone rubber composition of the present invention is measured using these two test pieces. Preferably, the above-mentioned compression permanent strain of the two test pieces is 80% or less. In addition, the compression permanent strain is calculated by the following calculation formula.

[0128] Compression permanent strain = [{(initial test piece thickness) - (test piece thickness after heating)} / (initial test piece thickness)] × 100 (%)

[0129] The above-mentioned compression set can be achieved by using an addition-curable silicone rubber composition obtained by uniformly blending components (D), (E) and (F) at the above-mentioned blending ratio into an addition-curable silicone rubber composition containing components (A) to (C).

[0130] Example

[0131] Hereinafter, the present invention will be specifically described using Examples and Comparative Examples, but the present invention is not limited thereto. In addition, in the following examples, parts represent parts by mass. In addition, the average degree of polymerization represents the number average degree of polymerization obtained by the above-mentioned determination method.

[0132] Hereinafter, specific examples of the components used in the examples and comparative examples of the present invention will be described.

[0133] (A) Alkenyl-containing organopolysiloxane

[0134] (A1) dimethylpolysiloxane having an average polymerization degree of 750 and end-capped with dimethylvinylsiloxy groups at both ends of the molecular chain (amount of vinyl groups: 0.034×10 -3 mol / g, number of olefin groups: 2)

[0135] (A2) dimethyl polysiloxane having an average polymerization degree of 220 and end-capped with dimethyl vinyl siloxy groups at both ends of the molecular chain (olefin content: 0.12×10 -3 mol / g, number of olefin groups: 2)

[0136] (A3) a diorganopolysiloxane having an average polymerization degree of 200 (alkenyl group content: 0.065×10 -3 mol / g, number of olefin groups: 20)

[0137] (B) Organohydrogenpolysiloxane

[0138] (B1) a dimethylsiloxane-methylhydrogensiloxane copolymer having trimethylsilyl groups capped at both ends of the molecular chain and having hydrosilyl groups at the side chains (polymerization degree: 99, hydrosilyl group amount: 0.00517 mol / g, number of hydrosilyl groups: 35)

[0139] (C) Platinum catalyst

[0140] (C1) Toluene solution of a complex of platinum and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (containing 1% by mass in terms of platinum atoms)

[0141] (D) Thermally dissociable blocked polyisocyanate

[0142] (D1) A mixture of a blocked polyisocyanate derived from toluene diisocyanate (TDI) and (F) water (blocked polyisocyanate: water = 44:56 [mass ratio], manufactured by Meisei Chemical Works, Ltd., trade name: MEIKANATE TP-10)

[0143] (D2) A mixture of a blocked polyisocyanate derived from hexamethylene diisocyanate (HDI) and (F) water (blocked polyisocyanate: water = 40:60 [mass ratio], manufactured by Meisei Chemical Works, Ltd., trade name: NBP-211)

[0144] (D3) A mixture of a blocked polyisocyanate derived from toluene diisocyanate (TDI) and (F) water (blocked polyisocyanate: water = 40:60 [mass ratio], manufactured by Meisei Chemical Works, Ltd., trade name: MEIKANATEWEB)

[0145] (D4) Toluene diisocyanate (TDI, for comparative example)

[0146] (D5) Hexamethylene diisocyanate (HDI, for comparative example)

[0147] (D6) Benzotriazole (BTZ, for comparative example)

[0148] (D7) A substance obtained by distilling water off from (D1) in advance (for comparative example)

[0149] (D8) Blocked isocyanate derived from toluene diisocyanate obtained by blocking with BTZ (for comparative example)

[0150] (E) Heat resistance imparting agent

[0151] (E1) Titanium oxide (manufactured by EVONIK, trade name: AEROXIDE TiO2PF2)

[0152] (E2) Iron oxide (manufactured by TODA KOGYO CORP., trade name: BenGara 130ED)

[0153] (E3) Carbon black (manufactured by Denka Company Limited., trade name: Denka Black)

[0154] (F) Water

[0155] (G) Reaction control agent

[0156] (G1) Ethynyl cyclohexanol

[0157] (H) Reinforcing silica powder

[0158] (H1) The specific surface area based on the BET method is 300m 2 / g of fumed silica (manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil 300)

[0159] [Preparation Example 1]

[0160] At room temperature, 60 parts of dimethylpolysiloxane (A1) having an average polymerization degree of 750 and end-capped with dimethylvinylsiloxy groups at both ends of the molecular chain, and 40 parts of a polysiloxane having a specific surface area of ​​300 m based on the BET method were mixed. 2 / g of fumed silica (H1) (manufactured by Nippon Aerosil Co., Ltd., Aerosil 300), 8.0 parts of hexamethyldisilazane, and 2.0 parts of water were mixed for 60 minutes, heated to 150°C, and stirred for 4 hours. Then, 30 parts of dimethylpolysiloxane (A1) were further added, mixed evenly and cooled to obtain silicone rubber base A. In addition, the water added at this time is water added to promote the treatment of component (H) with a surface treatment agent. Since the excess part will evaporate due to the heat treatment, it will not play a role as component (F). In addition, since the excess hexamethyldisilazane will evaporate due to the heat treatment, in the calculation of the following blending amount, the silicone rubber base A can be regarded as a substance composed of 100 parts by mass of dimethylpolysiloxane (A1) and 44 parts by mass of fumed silica (H) surface-treated with hexamethyldisilazane.

[0161] [Examples 1 to 5, Comparative Examples 1 to 7]

[0162] Hereinafter, addition-curable silicone compositions A to L were prepared in the proportions shown in Table 2. As for the preparation method, the method of Example 1 is described as an example. The other examples and comparative examples were prepared in the same manner.

[0163] [Example 1]

[0164] To 144 parts of silicone rubber base A (wherein 100 parts of dimethylpolysiloxane A1) were added 23 parts of dimethylpolysiloxane (A2) having an average polymerization degree of 220 and having dimethylvinylsiloxy groups at both ends of the molecular chain blocked, and 1.7 parts of dimethylpolysiloxane (A2) having an average polymerization degree of 200 and having trimethylsiloxy groups at both ends of the molecular chain blocked and 10 mol % of the methyl groups in the side chains (i.e., monovalent groups or atoms bonded to silicon atoms in diorganosiloxane units constituting the main chain, the same shall apply hereinafter) being vinyl groups. Methyl polysiloxane (A3), 3.6 parts of a methyl hydrogen polysiloxane (B1) having trimethylsilyl groups capped at both ends of the molecular chain and having hydrosilyl groups in the side chains as a crosslinking agent (a copolymer of dimethylsiloxane-methyl hydrogen siloxane having trimethylsilyl groups capped at both ends of the molecular chain and having a degree of polymerization of 99 and a hydrosilyl group content of 0.00517 mol / g), 0.07 parts of a mixture of a blocked polyisocyanate (D1) derived from toluene diisocyanate (TDI) and water (F) (Meisei Chemical Works, Ltd. (MEIKANATE TP-10) (blocked polyisocyanate (D1): water (F) = 44:56 [mass ratio]), 0.53 parts of AEROXIDE TiO2PF2 (E1) manufactured by EVONIK as a heat resistance imparting agent of titanium oxide, and 0.04 parts of ethynyl cyclohexanol (G1) (acetylene / Pt atom = 38 mol / mol) as a reaction control agent, and stirred for 15 minutes. Then, 0.12 parts of a toluene solution (C1) of a complex of platinum and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (platinum atom 1 mass%) was added, and stirred for 30 minutes to obtain a uniform addition-curing silicone rubber composition A.

[0165] In addition, in this composition, the molar ratio of the total amount of hydrosilyl groups to the total amount of vinyl groups in the entire composition (hydrosilyl groups / vinyl groups) was 2.2.

[0166] (Preparation of Cured Material)

[0167] After the addition curing type silicone rubber composition A was mixed, it was pre-cured at 150° C. for 15 minutes to obtain cured product samples of two sizes shown in Table 1. The results of measuring the compression permanent strain are shown in Table 2. The compression permanent strain was measured at a compression rate of 25% according to the method described in JIS K 6262:2013.

[0168] [Table 2]

[0169]

[0170] *1: Content of blocked polyisocyanate in component (D) to be blended.

[0171] *2: Content of (F) water in (D) component to be blended. In Comparative Example 7, it is the amount of (F) component to be blended separately.

[0172] As can be seen from Table 2, for Examples 1 to 5 using the addition-curing silicone rubber composition of the present invention, both the large test pieces and the small test pieces gave cured products having small compression set even under high temperature conditions of 200° C. or higher.

[0173] On the other hand, in Comparative Examples 1 and 2 not containing both the component (D) and the component (E), Comparative Examples 3, 5, and 7 in which the component (D) was not a thermally dissociable blocked polyisocyanate, and Comparative Example 6 not containing the component (F), a cured product having a small compressive permanent strain under high temperature conditions of 200° C. or higher could not be obtained. In Comparative Example 4 in which the component (D) was not a thermally dissociable blocked polyisocyanate, a cured product having a small compressive permanent strain even under high temperature conditions of 200° C. or higher could be obtained for the small test piece, but a cured product having a small compressive permanent strain under high temperature conditions of 200° C. or higher could not be obtained for the large test piece.

[0174] This specification includes the following protocols.

[0175] [1]: An addition-curing silicone rubber composition, characterized in that it contains:

[0176] (A) 100 parts by mass of an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule;

[0177] (B) 0.2 to 20 parts by mass of an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms in one molecule;

[0178] (C) platinum catalyst: catalytic amount;

[0179] (D) thermally dissociable blocked polyisocyanate: 0.01 to 5.0 parts by mass;

[0180] (E) heat resistance imparting agent: 0.01 to 10.0 parts by mass; and

[0181] (F) Water: 0.01 to 10 parts by mass.

[0182] [2]: The addition-curing silicone rubber composition according to [1] above, characterized in that the (D) thermally dissociable blocked polyisocyanate is a reaction product of a polyisocyanate and a thermally dissociable blocking agent, and the polyisocyanate is derived from one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

[0183] [3]: The addition-curable silicone rubber composition according to [1] or [2] above, characterized in that the (E) heat resistance imparting agent is one or more selected from the group consisting of iron oxide, titanium oxide doped with a metal oxide, and carbon.

[0184] [4]: The addition-curable silicone rubber composition according to [1], [2] or [3], further comprising as component (G) an acetylene alcohol compound having 1 to 500 moles of acetylene bonds per 1 mole of platinum atoms in component (C) or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane.

[0185] [5]: The addition-curable silicone rubber composition according to [1], [2], [3] or [4], further comprising 5 to 100 parts by mass of reinforcing silica fine powder as component (H) relative to 100 parts by mass of component (A).

[0186] [6]: The addition-curable silicone rubber composition according to [5] above, wherein the component (H) has a specific surface area of ​​50 m 2 / g or more of fumed silica.

[0187] [7]: A cured silicone rubber product, characterized in that it is a cured silicone rubber product obtained by curing the addition-curing silicone rubber composition of [1], [2], [3], [4], [5] or [6].

[0188] In addition, the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and technical solutions having substantially the same structure and exerting the same technical effects as the technical concept described in the claims of the present invention are all included in the technical scope of the present invention.

Claims

1. An addition-curing silicone rubber composition, characterized in that: contain: (A) 100 parts by mass of an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule; (B) 0.2 to 20 parts by mass of an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms in one molecule; (C) platinum catalyst: catalytic amount; (D) thermally dissociable blocked polyisocyanate: 0.01 to 5.0 parts by mass; (E) heat resistance imparting agent: 0.01 to 10.0 parts by mass; and (F) Water: 0.01 to 10 parts by mass.

2. The addition-curing silicone rubber composition according to claim 1, characterized in that: The (D) thermally dissociable blocked polyisocyanate is a reaction product of a polyisocyanate and a thermally dissociable blocking agent, wherein the polyisocyanate is derived from at least one diisocyanate selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

3. The addition-curing silicone rubber composition according to claim 1, characterized in that: The (E) heat resistance imparting agent is at least one selected from the group consisting of iron oxide, titanium oxide doped with a metal oxide, and carbon.

4. The addition-curing silicone rubber composition according to claim 2, characterized in that: The (E) heat resistance imparting agent is at least one selected from the group consisting of iron oxide, titanium oxide doped with a metal oxide, and carbon.

5. The addition-curable silicone rubber composition according to claim 1, characterized in that: The present invention further contains, as the component (G), an acetylene alcohol compound or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane, in which the acetylene bond is 1 to 500 mol per 1 mol of platinum atoms of the component (C).

6. The addition-curable silicone rubber composition according to claim 2, characterized in that: The present invention further contains, as the component (G), an acetylene alcohol compound or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane, in which the acetylene bond is 1 to 500 mol per 1 mol of platinum atoms of the component (C).

7. The addition-curing silicone rubber composition according to claim 3, characterized in that: The present invention further contains, as the component (G), an acetylene alcohol compound or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane, in which the acetylene bond is 1 to 500 mol per 1 mol of platinum atoms of the component (C).

8. The addition-curable silicone rubber composition according to claim 4, characterized in that: The present invention further contains, as the component (G), an acetylene alcohol compound or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane, in which the acetylene bond is 1 to 500 mol per 1 mol of platinum atoms of the component (C).

9. The addition-curing silicone rubber composition according to any one of claims 1 to 8, characterized in that: The invention further contains 5 to 100 parts by mass of reinforcing silica fine powder as the component (H) based on 100 parts by mass of the component (A).

10. The addition-curing silicone rubber composition according to claim 9, characterized in that: The component (H) has a specific surface area of ​​50 m 2 / g or more of fumed silica.

11. A cured silicone rubber product, characterized in that: This is a silicone rubber cured product obtained by curing the addition-curing silicone rubber composition according to any one of claims 1 to 8.

12. A cured silicone rubber product, characterized in that: This is a silicone rubber cured product obtained by curing the addition-curing silicone rubber composition according to claim 9.

13. A cured silicone rubber product, characterized in that: This is a silicone rubber cured product obtained by curing the addition-curing silicone rubber composition according to claim 10.

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