JP7540975B2 - Addition-curing silicone rubber composition and cured silicone rubber - Google Patents

Description

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

Due to its excellent heat resistance, cold resistance, safety, electrical insulation, weather resistance, and durability, silicone rubber is used in a wide range of applications, including automotive hoses and gasket materials, electrical and electronic parts such as rolls for copying machines and packing for microwave ovens, building materials, and textile coating materials.

In recent years, as automobile engines have become smaller and more powerful, there is a demand for high heat resistance in engine components. One method for further improving the heat resistance of silicone compositions is to add metal oxides such as iron oxide, titanium oxide, and cerium oxide as heat resistance enhancers. This makes it possible to obtain a cured silicone rubber product whose physical properties change little even under higher temperature conditions.

Furthermore, when silicone rubber is used as a gasket such as an O-ring or packing, low compression set is required to prevent seal leakage. Normally, to reduce compression set, the rubber that has been molded by heat curing must be further vulcanized at high temperatures for a long period of time.

Patent Document 1 and Patent Document 2 describe silicone compositions containing metal oxides (titanium oxide and iron oxide in Patent Document 1, and cerium oxide hydrate and zirconium oxide hydrate in Patent Document 2). It is reported that the addition of the metal oxides can improve the heat resistance of silicone rubber compositions, but compression set is not discussed.

Patent Document 3 describes that an addition-curing silicone rubber composition containing a triazole-based compound can reduce compression set without secondary vulcanization. However, it is known that silicone rubber compositions containing triazoles are difficult to improve compression set under high temperature conditions such as 200°C or higher.

Patent Document 4 and Patent Document 5 describe silicone rubber compositions containing a blocked polyisocyanate composition. Patent Document 4 describes that the composition has good adhesion to textiles and can maintain adhesion even during long-term storage under high temperature and high humidity, while Patent Document 5 describes that the composition and content of the thermally dissociable blocked isocyanate composition are specified and that the composition is flame retardant. However, silicone rubber compositions containing these blocked polyisocyanate compositions do not improve compression set at temperatures of 200°C or higher by simply adding a small amount of the blocked polyisocyanate composition. In addition, when a blocked (poly)isocyanate, especially an isocyanate, is used as an additive in an addition-curing silicone rubber composition, the curing speed is likely to be delayed. Therefore, the amount added must be small enough to avoid impairing the physical properties after curing.

Special Publication No. 2016-518461 JP 2014-031408 A JP 2017-165931 A JP 2019-006956 A JP 2020-070357 A

The present invention has been made in consideration of the above circumstances, and aims to provide an addition-curing silicone rubber composition and a silicone rubber cured product that have low compression set and are less prone to delayed curing.

In order to solve the above problems, the present invention provides an addition-curable silicone rubber composition, comprising:
(A) an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in each molecule: 100 parts by mass,
(B) an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms per molecule: 0.2 to 20 parts by mass,
(C) Platinum-based catalyst: catalyst amount,
(D) Compound containing an isocyanate group: 0.01 to 5.0 parts by mass,
(E) heat resistance imparting agent: 0.01 to 10.0 parts by mass,
The present invention provides an addition-curable silicone rubber composition comprising:

Such an addition-curing silicone rubber composition will give a cured product with low compression set and less delay in curing.

In addition, in the present invention, it is preferable that the (D) compound containing an isocyanate group is one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

This type of component (D) is preferred because it has a large effect of improving compression set and is easy to harden.

In addition, in the present invention, it is preferable that the heat resistance imparting agent (E) is titanium oxide doped with a metal oxide.

This type of component (E) is preferred because it has a large effect of improving compression set and is easy to harden.

In addition, the present invention further includes (F) an acetylene alcohol compound, or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane: it is preferable that the compound contains 1 to 500 moles of acetylene bonds per mole of platinum atoms in component (C).

This type of addition-curing silicone rubber composition is preferable because it allows you to control the time when curing begins.

In addition, the present invention preferably further contains (G) reinforcing silica fine powder: 5 to 100 parts by mass per 100 parts by mass of component (A).

Such an addition-curing silicone rubber composition is preferable because it can improve the rubber strength.

In this case, the component (G) is preferably fumed silica having a specific surface area of 50 m ² /g or more as measured by the BET method.

Such a (G) component is preferable because it can more reliably improve the rubber strength.

The present invention also provides a silicone rubber cured product obtained by curing the addition-curing silicone rubber composition.

Such a cured product has low compression set, is less likely to have delayed curing, and has good heat resistance.

The present invention provides an addition-curing silicone rubber composition that has no cure delay, good curability, and can produce a silicone rubber with low compression set even at high temperatures such as 200°C, as well as a cured silicone rubber product obtained by curing the composition.

As mentioned above, there was a need to develop an addition-curing silicone rubber composition that has low compression set and is less susceptible to delayed curing.

As a result of extensive research into the above-mentioned problems, the present inventors have found that
(A) an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in each molecule;
(B) an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms in each molecule;
(C) a platinum-based catalyst,
(D) a compound having an isocyanate group,
(E) a heat resistance imparting agent,
The present inventors have discovered that by combining the (D) and (E) components in an addition-curable silicone rubber composition containing the above-mentioned compound, it is possible to obtain an addition-curable silicone rubber composition and a cured silicone rubber product which have a low compression set and are less susceptible to delayed curing, and have thus completed the present invention.

That is, the present invention provides an addition curing type silicone rubber composition,
(A) an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in each molecule: 100 parts by mass,
(B) an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms per molecule: 0.2 to 20 parts by mass,
(C) Platinum-based catalyst: catalyst amount,
(D) Compound containing an isocyanate group: 0.01 to 5.0 parts by mass,
(E) heat resistance imparting agent: 0.01 to 10.0 parts by mass,
The addition curing type silicone rubber composition contains

The present invention is described in detail below, but is not limited to these.

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

[0043] Component (A) is an organopolysiloxane that contains two or more alkenyl groups bonded to silicon atoms in each molecule, and is the main component (base polymer) of the composition. As component (A), any of the following average compositional formula (1) can be used.
R ¹ _a SiO _(4-t)/2 ...(1)
(In the formula, R ¹ is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, with the proviso that at least two of all R ¹ in one molecule are alkenyl groups having 2 to 10 carbon atoms, and a is a positive number ranging from 1.5 to 2.8, preferably 1.8 to 2.5, and more preferably 1.95 to 2.05.)

Here, examples of the monovalent hydrocarbon group having 1 to 10 carbon atoms represented by R ¹ include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl groups; aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups; aralkyl groups such as benzyl, phenylethyl, and phenylpropyl groups; and alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexenyl, and octenyl groups. It is preferable that 90 mol % or more of all R ^1s , and particularly all R ^1s except for the alkenyl groups, are methyl groups.

At least two of ^R1 must be alkenyl groups having 2 to 10 carbon atoms. Among them, those having 2 to 8 carbon atoms are preferred, those having 2 to 6 carbon atoms are more preferred, and a vinyl group is particularly preferred.
The content of alkenyl groups in the alkenyl group-containing organopolysiloxane is preferably 1.0×10 ^-6 to 5.0×10 ^-3 mol/g, particularly preferably 1.0×10 ^-5 to 2.0×10 ^-3 mol/g. If the content of alkenyl groups is 1.0×10 ^-6 to 5.0×10 ^-3 mol/g, a rubber-like substance can be obtained. The alkenyl groups may be bonded to silicon atoms at the ends of the molecular chain, to silicon atoms in the middle of the molecular chain, or to both.

The structure of this alkenyl-containing organopolysiloxane basically has a linear main chain structure in which both molecular chain terminals are blocked with triorganosiloxy groups and the main chain is made up of repeating diorganosiloxane units, but it may also have a partially branched structure, cyclic structure, etc.
Regarding the molecular weight of the component (A), the average degree of polymerization is 1,500 or less, usually 100 to 1,500, and preferably 150 to 1,000. If the average degree of polymerization is 100 to 1,500, a rubber-like substance is obtained, and the moldability is good.
In the present invention, the average degree of polymerization refers to the number-average degree of polymerization measured by gel permeation chromatography (GPC) under the following conditions using polystyrene as a standard substance.
[Measurement conditions]
Developing solvent: toluene Flow rate: 0.6 mL/min
Detector: Refractive index detector (RI)
Column: TSK Guard column Super H-H
TSKgel SuperH5000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH4000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH3000 (6.0mm I.D. x 15cm x 1)
(Both manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 50 μL (toluene solution with a concentration of 0.5% by mass)

In addition, as component (A), one or more alkenyl-containing organopolysiloxanes having two or more alkenyl groups bonded to silicon atoms in one molecule, such as those having alkenyl groups bonded to silicon atoms at both ends of the molecular chain, with different molecular structures and degrees of polymerization can be used in combination.

Component (B) is an organohydrogenpolysiloxane having two or more, and preferably three or more, hydrogen atoms bonded to silicon atoms (hydrosilyl groups) per molecule. The hydrosilyl groups in the molecule crosslink with alkenyl groups bonded to silicon atoms in component (A) via a hydrosilylation addition reaction, and act as a curing agent (crosslinking agent) for curing the addition-curing silicone rubber composition.

The organohydrogenpolysiloxane of component (B) is, for example, represented by the following average composition formula (2), and is suitably used which has at least 2, preferably at least 3, more preferably from 3 to 100, and particularly preferably from 4 to 50 hydrogen atoms bonded to silicon atoms (hydrosilyl groups) per molecule.
R ² _b H _c SiO _(4-b-c)/2 (2)
(In the formula, ^R2 is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms. In addition, b is a positive number of 0.7 to 2.1, c is a positive number of 0.001 to 1.0, and b+c is a positive number satisfying 0.8 to 3.0.)

Here, examples of the monovalent hydrocarbon group of ^R2 include an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms. Specific and preferred examples of each are the same as those of ^R1 .

In addition, b is a positive number between 0.7 and 2.1, preferably between 0.8 and 2.0, c is a positive number between 0.001 and 1.0, preferably between 0.01 and 1.0, and b+c is a positive number between 0.8 and 3.0, preferably between 1.0 and 2.5. The molecular structure of the organohydrogenpolysiloxane may be any of linear, cyclic, branched, and three-dimensional mesh structures.

The content of hydrosilyl groups in the organohydrogenpolysiloxane is preferably 0.0005 to 0.020 mol/g, and more preferably 0.001 to 0.017 mol/g. If the amount of hydrosilyl groups is 0.0005 mol/g or more, crosslinking is sufficient, and if it is 0.020 mol/g or less, the organohydrogenpolysiloxane becomes a stable substance.

In this case, it is preferable to use a compound that is liquid at room temperature (25°C) and has a number of silicon atoms (or degree of polymerization) in one molecule of 2 to 300, particularly 3 to 150, and especially 4 to 100. The hydrogen atoms bonded to the silicon atoms may be located at either the ends of the molecular chain, or in the middle of the molecular chain (non-terminal), or may be located at both.

Examples of the organohydrogenpolysiloxane of 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 blocked at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer blocked at both ends with trimethylsiloxy groups, dimethylpolysiloxane blocked at both ends with dimethylhydrogensiloxy groups, Dimethylsiloxane-methylhydrogensiloxane copolymer, methylhydrogensiloxane-diphenylsiloxane copolymer both ends blocked with trimethylsiloxy groups, methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer both ends blocked with trimethylsiloxy groups, methylhydrogensiloxane-methylphenylsiloxane-dimethylsiloxane copolymer both ends blocked with trimethylsiloxy groups, methylhydrogensiloxane-dimethylsiloxane-diphenylsiloxane copolymer both ends blocked with dimethylhydrogensiloxy groups, methylhydrogensiloxane-dimethylsiloxane-diphenylsiloxane copolymer both ends blocked with dimethylhydrogensiloxy groups, methylhydrogensiloxane-dimethylsiloxane-methylphenylsiloxane copolymer both ends blocked with dimethylhydrogensiloxy groups, (CH Examples of the copolymer include a copolymer consisting of ( _CH3 ) _{2HSiO1 /2} units, ( _CH3 ) _{3SiO1 /2} units, and SiO4 _/2 units, a copolymer consisting of ( _CH3 ) _2HSiO1 / ₂ units and SiO4 _/2 units, a copolymer consisting of ( _CH3 )2HSiO1 _{/2 units} , SiO4 _/2 units, and ( _C6H5 ) _{SiO3 /2} units, and copolymers in which part or all of the methyl groups in these exemplary compounds have been substituted with other alkyl groups, phenyl groups, or the like.

The organohydrogenpolysiloxane of component (B) may be a polyvalent aromatic ring-containing organohydrogenpolysiloxane, which contains a hydrocarbon skeleton containing an aromatic ring, usually divalent to tetravalent (e.g., 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 part of the siloxane skeleton (-Si-O-Si-) that constitutes the molecule (usually part of the position of the oxygen atom that forms the siloxane bond) in the compound exemplified above.

The amount of organohydrogenpolysiloxane, component (B), is 0.2 to 20 parts by mass, preferably 0.3 to 10 parts by mass, per 100 parts by mass of component (A). The molar ratio (hydrosilyl group/alkenyl group) of hydrogen atoms bonded to silicon atoms in the organohydrogenpolysiloxane, component (B), to the total amount of alkenyl groups bonded to silicon atoms in components (A) and (B) (particularly in component (A)) is preferably 0.8 to 10, more preferably 1.0 to 5. If this ratio is 0.8 or more, curing (crosslink density) is sufficient and the rubber does not become sticky, and if it is 10 or less, foaming is not observed in the silicone rubber molding, and release from the mold is not difficult.

(C) Platinum-based catalyst Examples of the component (C) include platinum-based catalysts such as platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid with monohydric alcohols, complexes of chloroplatinic acid with olefins, and platinum bisacetoacetate.

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

(D) Compound containing an isocyanate group The compound containing an isocyanate group of component (D) is a component that improves the compression set of the cured product of the addition-curable silicone rubber composition of the present invention when used in combination with the heat resistance imparting agent of component (E).

The compound containing an isocyanate group of component (D) is preferably one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates. Examples of aliphatic diisocyanates include butane diisocyanate, pentane diisocyanate, and hexamethylene diisocyanate. Examples of alicyclic diisocyanates include isophorone diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate. Among these, hexamethylene diisocyanate and toluene diisocyanate are preferred because they are easily available industrially.

Aliphatic diisocyanates and alicyclic diisocyanates may be used as monomers, or as oligomers such as urethane, urea, allophanate, biuret, and isocyanurate. For example, they may be used as polyisocyanates whose chain length has been extended by reaction with a diol, or whose three-dimensional growth has been achieved by reaction with a triol. In order to stabilize the effect of reducing compression set after the isocyanate is thermally dissociated, it is preferable to use them as oligomers or polymers. These aliphatic diisocyanates and alicyclic diisocyanates may be used alone or in combination of two or more kinds.

The amount of the (D) component is 0.01 to 5.0 parts by mass, preferably 0.01 to 1.0 parts by mass, per 100 parts by mass of the (A) component. If it is less than 0.01 parts, it is difficult to obtain the effect of improving compression set, and if it is more than 5.0 parts by mass, curing may be delayed. The compound containing an isocyanate group may be used alone or in combination of two or more types. When two or more types are used in combination, the total amount may be within the above range.

(E) Heat resistance imparting agent The (E) component is a component that improves the curing property and significantly improves the compression set of the cured product at high temperatures when used in combination with the (D) component. Examples of the (E) component include titanium oxide (e.g., titanium oxide doped with a metal oxide). Among them, titanium oxide doped with a metal oxide is preferred. These may be used alone or in combination of two or more.

The amount of component (E) to be blended 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, per 100 parts by mass of component (A). If it is less than 0.01 part, it is difficult to obtain an improvement effect in compression set, and if it is more than 10.0 parts by mass, physical properties may deteriorate.

(F) Reaction Regulator In addition to the above-mentioned components (A) to (E), the addition-curable silicone rubber composition of the present invention may contain, as component (F), an acetylene alcohol compound or a compound in which the alcoholic hydroxyl group of the compound has been modified with a silane or siloxane. This component (F) functions as a reaction regulator for the platinum catalyst of component (C), and the curing start time can be controlled by the amount added.

The acetylene alcohol compound of component (F) may be one in which an ethynyl group and a hydroxyl group are present in the same molecule, but it is preferable that the ethynyl group and the hydroxyl group are bonded to the same carbon atom. Specific examples include the following compounds.

（但し、ｓは０～５０の整数、好ましくは３～２０の整数、ｔは１～５０の整数、好ましくは３～２０の整数である。） In addition, a compound in which an alcoholic hydroxyl group of an acetylene alcohol compound is modified with a silane or siloxane is a compound in which the hydroxyl group of the acetylene alcohol compound is converted into a Si—O—C bond and bonded to the silane or siloxane. Examples of the compound include the following compounds.

(wherein 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.)

The amount of component (F) is 1 to 500 moles of acetylene bonds per mole of platinum atoms in component (C), preferably 1 to 300 moles, and more preferably 2 to 200 moles. If the amount is 1 to 500 moles, the curing property is good and a pot life sufficient for working can be obtained. Component (F) may be used alone or in combination of two or more types. When two or more types are used in combination, the total amount may be within the above range.

(G) Reinforcing silica fine powder The addition curing silicone rubber composition of the present invention preferably contains a reinforcing silica fine powder as component (G). The reinforcing silica fine powder of component (G) is not particularly limited in type of silica, and may be any silica that is normally used as a reinforcing agent for rubber. The reinforcing silica fine powder may be one used in conventional silicone rubber compositions, but it is preferable to use a reinforcing silica fine powder having a specific surface area of 50 m ² /g or more as measured by the BET method, more preferably 50 to 400 m ² /g, and particularly preferably 100 to 350 m ² /g. Examples of reinforcing silica fine powder include precipitated silica (wet silica), fumed silica (dry silica), and calcined silica, and among these, fumed silica is preferred because it improves rubber strength.

The reinforcing silica fine powder may be a silica fine powder whose surface has been hydrophobized with a surface treatment agent such as a (usually hydrolyzable) organosilicon compound, for example, chlorosilane, alkoxysilane, or organosilazane. In this case, the silica fine powder may be one whose surface has been hydrophobized directly with a surface treatment agent in advance in a powder state, or one whose surface has been hydrophobized by adding a surface treatment agent when kneading with silicone oil (for example, the alkenyl-containing organopolysiloxane of component (A) above).

Surface treatment can be performed by known techniques. For example, the untreated silica fine powder and the surface treatment agent are placed in a mechanical mixer or fluidized bed sealed at normal pressure, and mixed at room temperature or by heat treatment (heating) in the presence of an inert gas as necessary. Optionally, a catalyst (such as a hydrolysis promoter) may be used to promote the surface treatment. After mixing, the mixture is dried to produce the surface-treated silica fine powder. The amount of the surface treatment agent may be equal to or greater than the amount calculated from the coverage area of the treatment agent.

Specific examples of surface treatment agents include silazanes such as hexamethyldisilazane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylmethoxysilane, triethylmethoxysilane, vinyltris(methoxyethoxy)silane, trimethylchlorosilane, dimethyldichlorosilane, divinyldimethoxysilane, and chloropropyltrimethoxysilane, and organic silicon compounds such as polymethylsiloxane and organohydrogenpolysiloxane. The surface is treated with these and used as hydrophobic silica fine powder. As the surface treatment agent, silane coupling agents or silazanes are particularly preferred. The fine silica powder of component (G) may be used alone or in combination of two or more types.

The amount of component (G) is preferably 5 to 100 parts by mass per 100 parts by mass of component (A).

[Method for preparing addition-curable silicone rubber composition]
The addition-curable silicone rubber composition of the present invention can be obtained simply by uniformly mixing the above-mentioned components (A) to (E) and any optional components at room temperature. However, when component (G) is included, it may also be obtained by heat-treating component (G) together with the surface treatment agent and water, all or a part of component (A) in a planetary mixer or kneader or the like at a temperature of 100 to 200°C for 1 to 4 hours, and then cooling to room temperature, followed by adding and mixing the remaining components and any optional components.

[Method of molding addition-curable silicone rubber composition/cured silicone rubber]
Conventional methods can be used for molding and curing this addition curing silicone rubber composition, but the molding method can be selected from injection molding, transfer molding, injection molding, compression molding, etc., and the most suitable means for the purpose can be selected. Curing conditions can be heat treatment (primary vulcanization) conditions at 40 to 230°C for about 3 seconds to 160 minutes. Furthermore, secondary vulcanization (post cure) can be optionally performed at 40 to 230°C for about 10 minutes to 24 hours, if necessary.

The cured product obtained by curing the addition-curing silicone rubber composition of the present invention preferably has a compression set of 60% or less at 200°C for 22 hours at a compression ratio of 25%. If it is below this value, it can be suitably used as a material for O-rings and packing.

The compression set in the present invention refers to a value measured by the method described in JIS K 6262: 2013. The standard lists the following two types of test pieces to be used for the measurement.

The compression set of the cured product of the addition-curable silicone rubber composition of the present invention was measured using these two types of test pieces. In either case, the compression set is preferably 60% or less. The compression set can be calculated using the following formula:
Compression set = {(initial thickness of test piece) - (thickness of test piece after heating)} / (initial thickness of test piece) x 100 (%)

In addition, such a compression set can be achieved by using an addition-curing silicone rubber composition containing components (A) to (C) in which components (D) and (E) are uniformly blended in the blending ratio described above.

The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, parts indicate parts by mass. Also, the average degree of polymerization indicates the number-average degree of polymerization.

[Preparation Example 1]
60 parts of dimethylpolysiloxane (A1) with both molecular chain terminals blocked with dimethylvinylsiloxy groups and an average degree of polymerization of 750, 40 parts of fumed silica (G1) (Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) with a specific surface area of 300 ^m2 /g as measured by the BET method, 8.0 parts of hexamethyldisilazane, and 2.0 parts of water were mixed at room temperature (25°C) for 60 minutes, then heated to 150°C and stirred for 4 hours. Next, an additional 30 parts of dimethylpolysiloxane (A1) was added, mixed until uniform, and cooled to obtain silicone rubber base A.

[Example 1]
A mixture of 100 parts of silicone rubber base A and 15.8 parts of dimethylpolysiloxane (A2) having an average degree of polymerization of 220 and both molecular chain terminals blocked with dimethylvinylsiloxy groups, 1.2 parts of dimethylpolysiloxane (A3) having an average degree of polymerization of 200 and having both molecular chain terminals blocked with trimethylsiloxy groups and in which 10 mol % of the methyl groups in the side chains (i.e., monovalent groups or atoms bonded to silicon atoms in the diorganosiloxane units constituting the main chain; the same applies hereinafter) are vinyl groups, was added to 100 parts of silicone rubber base A. 2.5 parts of methylhydrogenpolysiloxane (B1) (a dimethylsiloxane-methylhydrogensiloxane copolymer blocked at both molecular chain ends with trimethylsiloxy groups and having hydrosilyl groups on the side chains with a degree of polymerization of 99 and a hydrosilyl group content of 0.00517 mol/g) having both chain ends blocked with trimethylsiloxy groups, 0.05 parts of toluene diisocyanate (TDI) (D1), 0.37 parts of AEROXIDE _TiO2 PF2 (E1) manufactured by EVONIK as titanium oxide doped with a metal oxide serving as a heat resistance imparting agent, and 0.03 parts of ethynylcyclohexanol (F1) (acetylene/Pt atom=38 mol/mol) as a reaction inhibitor, were added and stirred for 15 minutes. Next, 0.08 parts of a toluene solution (C1) of a complex of platinum and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (platinum atom content: 1% by mass) was added and stirred for 30 minutes to obtain a homogeneous addition-curable silicone rubber composition A.
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.
The curability of this composition at 130°C was measured using a rheometer MDR2000 (manufactured by Alpha Technologies), and the results are shown in Table 2. Here, T10 and T90 are the times (unit: seconds) from the start of measurement when 10% and 90% torque values of the maximum torque value at 130°C for 3 minutes from the start of measurement are obtained, respectively.
After mixing addition-curable silicone rubber composition A, the mixture was press-cured at 150° C. for 15 minutes to obtain a cured product, and the compression set was measured. The results are shown in Table 2. The compression set was measured at a compression ratio of 25% according to the method described in JIS K 6262:2013.

[Example 2]
An addition-curable silicone rubber composition B was prepared in the same manner as in Example 1, except that D1 was replaced with 0.05 parts of hexamethylene diisocyanate (HDI) (D2). The results of evaluations performed in the same manner as in Example 1 are shown in Table 2.

[Example 3]
An addition-curable silicone rubber composition C was prepared using the same recipe as in Example 1, except that 0.05 parts of toluene diisocyanate (TDI) (D1) was used as the isocyanate and 0.1 parts of blocked isocyanate (D3) using benzotriazole as the blocking agent was used. The results of evaluations performed in the same manner as in Example 1 are shown in Table 2.

[Example 4]
An addition-curable silicone rubber composition D was prepared using the same recipe as in Example 1, except that 0.05 parts of diphenylmethane diisocyanate (MDI) (D4) was used as the isocyanate and 0.1 parts of blocked isocyanate (D3) using benzotriazole as the blocking agent was used. The results of evaluations performed in the same manner as in Example 1 are shown in Table 2.

[Comparative Example 1]
An addition-curing silicone rubber composition E was prepared using the same recipe as in Example 1, except that it did not contain 0.37 parts of AEROXIDE TiO ₂ PF2 (E1) manufactured by EVONIK Corporation as the metal oxide-doped titanium oxide heat resistance agent, and the results of evaluations performed in the same manner as in Example 1 are shown in Table 2.

[Comparative Example 2]
In Example 2, an addition-curing silicone rubber composition F was prepared with the same recipe except that it did not contain 0.37 parts of AEROXIDE TiO ₂ PF2 (E1) manufactured by EVONIK Corporation as the metal oxide-doped titanium oxide heat resistance agent, and the results of evaluation in the same manner as in Example 1 are shown in Table 2.

[Comparative Example 3]
An addition-curing silicone rubber composition G was prepared using the same recipe as in Example 3, except that it did not contain 0.37 parts of AEROXIDE TiO ₂ PF2 (E1) manufactured by EVONIK Corporation as the metal oxide-doped titanium oxide heat resistance agent, and the results of evaluations performed in the same manner as in Example 1 are shown in Table 2.

[Comparative Example 4]
In Example 4, an addition-curing silicone rubber composition H was prepared using the same recipe except that it did not contain 0.37 parts of AEROXIDE TiO ₂ PF2 (E1) manufactured by EVONIK Corporation as the metal oxide-doped titanium oxide heat resistance agent, and the results of evaluation in the same manner as in Example 1 are shown in Table 2.

As can be seen from Table 2, in Examples 1 to 4, which used the addition-curing silicone rubber composition of the present invention, both the large and small test pieces gave cured products with low compression set and whose curing properties were not easily delayed.

On the other hand, Comparative Examples 1 to 4, which did not contain both components (D) and (E), showed low compression set and delayed curing in both the large and small test pieces.

The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.

Claims (6)

An addition curing type silicone rubber composition,
(A) an alkenyl group-containing organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in each molecule: 100 parts by mass,
(B) an organohydrogenpolysiloxane containing two or more hydrogen atoms bonded to silicon atoms per molecule: 0.2 to 20 parts by mass,
(C) Platinum-based catalyst: catalyst amount,
(D) Compound containing an isocyanate group: 0.01 to 5.0 parts by mass,
(E) titanium oxide doped with metal oxide : 0.01 to 10.0 parts by mass,
An addition-curable silicone rubber composition comprising: The addition-curable silicone rubber composition according to claim 1, characterized in that the (D) compound containing an isocyanate group is one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates. Furthermore, (F) an acetylene alcohol compound or a compound in which the alcoholic hydroxyl group of the compound is modified with silane or siloxane: 1 to 500 moles of acetylene bonds per mole of platinum atom of the component (C);
The addition-curable silicone rubber composition according to claim 1 or 2, further comprising: Furthermore, (G) reinforcing silica fine powder: 5 to 100 parts by mass per 100 parts by mass of the component (A),
The addition-curable silicone rubber composition according to any one of claims 1 to 3 , further comprising: 5. The addition-curable silicone rubber composition according to claim 4 , wherein the component (G) is a fumed silica having a specific surface area of 50 m ² /g or more as measured by the BET method. A cured silicone rubber product obtained by curing the addition-curable silicone rubber composition according to any one of claims 1 to 5 .