Addition-curable liquid silicone rubber composition and silicone rubber molded body

Abstract

To provide an addition-curable liquid silicone rubber composition which provides silicone rubber which is rapid in curing, and has proper hardness after curing, and is difficult to deform.SOLUTION: An additive-curable liquid silicone rubber composition comprises:(A) liquid organopolysiloxane with an average degree of polymerization of 1,500 or less and having two or more silicon-bonded alkenyl groups in one molecule;(B)(B-1) terminal trialkylsiloxy group-sealed organohydrogen polysiloxane having 4 or more hydrogen atoms by average in one molecule bonded to a silicon atom on a side chain; (B-2) a terminal trialkyl siloxane group-sealed organohydrogen polysiloxane having 1,5 to 2.5 hydrogen atoms by average in one molecule bonded to a silicon atom on a side chain;(B-3) dialkyl hydrogen siloxane group at both ends-sealed linear organohydrogen polysiloxane in which a main chain is made of only a dialkyl siloxane unit; (C) fumed silica, and (D) an addition reaction catalyst.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an addition-curable liquid silicone rubber composition and a silicone rubber molded article. [Background technology]

[0002] Silicone rubber is widely used as a material for molding toys for infants, tableware, toothbrushes, etc., due to its heat resistance, cold resistance, safety, good appearance (transparency), pleasant texture, and durability. In particular, it is preferably used as a material for molding nipples for baby bottles and pacifiers for babies. In particular, addition reaction curing type silicone rubber compositions are preferably used for the above applications from the viewpoint of safety, since they do not produce by-products.

[0003] Currently, the hardness of silicone rubber baby bottle nipples in widespread use is approximately 30 to 50 in durometer type A hardness. However, in order to diversify designs or for babies with weak suction, there has been a demand for nipples with even lower hardness. On the other hand, low-hardness silicone rubber may be used in the part of the mask that comes into contact with the face. When low-hardness rubber is used as a mask material, it is possible to reduce discomfort when wearing the mask. However, if the amount of reinforcing silica contained in the raw material is reduced in an attempt to produce low-hardness silicone rubber, the strength of the molded rubber decreases. As a result, the rubber cracks when the molded product is removed from the mold after molding, and the rubber is easily cut during use. In addition, if the crosslinking density is reduced to reduce the hardness, the rubber becomes sagging or has a sticky surface, which makes it difficult to feel when used as a nipple for a baby bottle or as a mask material.

[0004] To solve the above problems, a method has been proposed in which silicone raw rubber is added to a liquid silicone rubber composition to reduce the hardness of the rubber and eliminate the sticky feeling (Patent Document 1). However, when the hardness is reduced to 15 or less using this method, problems occur such as the rubber having a sticky surface, low curing properties, and excessively long vulcanization times during molding. For this reason, a silicone rubber composition has been proposed that cures quickly and has high strength even if its hardness is 15 or less by using appropriate amounts of three types of crosslinking agents with different numbers of crosslinking points (Patent Document 2). However, when the silicone rubber composition produced by this method is molded in a metal mold, the molded product may stretch and deform when demolded. Even if the composition can be molded successfully, the molded product may not have sufficient shape recovery if it is used without secondary vulcanization. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-321609 A [Patent Document 2] JP 2017-222814 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in order to improve the above-mentioned circumstances, and has an object to provide an addition-curable liquid silicone rubber composition which is capable of giving a silicone rubber which cures quickly and has appropriate hardness after curing, has high tear strength, and is resistant to deformation. [Means for solving the problem]

[0007] As a result of intensive research conducted by the present inventors in order to achieve the above-mentioned object, it was discovered that by combining an organopolysiloxane which has two or more silicon-bonded alkenyl groups per molecule, has a specific average degree of polymerization, and is liquid at 25°C, and multiple types of organohydrogenpolysiloxanes which have a specific number of silicon-bonded hydrogen atoms, with reinforcing silica, it is possible to provide a low-hardness silicone rubber which is excellent in curability and which has the desired hardness and tear strength and is resistant to deformation by only primary vulcanization, thereby completing the present invention.

[0008] Accordingly, the present invention provides the following addition-curable liquid silicone rubber composition, cured product, and silicone rubber molded article. [1] The following components (A) to (D): (A) 100 parts by mass of an organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in each molecule, an average degree of polymerization of 1,500 or less, and being liquid at 25°C; (B) The following components (B-1) to (B-3): (B-1) an organohydrogenpolysiloxane containing an average of four or more hydrogen atoms bonded to silicon atoms in each molecule in its side chains and terminated at the ends with trialkylsiloxy groups; (B-2) an organohydrogenpolysiloxane containing an average of 1.5 to 2.5 hydrogen atoms bonded to silicon atoms in each molecule in the side chain and terminated at the terminals with trialkylsiloxy groups; (B-3) Linear organohydrogenpolysiloxanes whose main chain consists solely of dialkylsiloxane units and whose both ends are blocked with dialkylhydrogensiloxy groups: the number of moles of Si-H groups in each of the components (B-1), (B-2), and (B-3) relative to the total number of moles of silicon-bonded hydrogen atoms (Si-H groups) in the components (B-1), (B-2), and (B-3) (total Si-H groups) is [Si-H groups (B-1)] / [total Si-H groups]=50 to 80 mol %, [Si-H group (B-2)] / [total Si-H group]=5 to 40 mol %, [Si-H group (B-3)] / [total Si-H group]=5 to 15 mol %, and the molar ratio of the total Si-H groups to the total alkenyl groups in the composition (total alkenyl groups) is [total Si-H groups] / [total alkenyl groups]=1 to 1.8; (C) Specific surface area by BET method is 130m 2 / g or more: 5 to 40 parts by mass of fumed silica, (D) Addition reaction catalyst: 0.5 to 100 ppm as platinum group metal (by mass) relative to the mass of component (A). An addition-curable liquid silicone rubber composition comprising: [2] The addition-curable liquid silicone rubber composition according to [1] further contains (E) 1 to 200 parts by mass of an organopolysiloxane having an average degree of polymerization of 2,000 or more and in a raw rubber state at 25°C, per 100 parts by mass of component (A). [3] The addition-curable liquid silicone rubber composition according to [1] or [2] further contains 1 to 200 parts by mass of (F) an organopolysiloxane that has an average degree of polymerization of 500 or less, is liquid at 25°C, and does not contain addition-reactive substituents, per 100 parts by mass of component (A). [4] The addition-curable liquid silicone rubber composition according to any one of [1] to [3], wherein the component (B-2) is a linear organohydrogenpolysiloxane. [5] A cured product of the addition-curable liquid silicone rubber composition according to any one of [1] to [4]. [6] [5] A silicone rubber molded article comprising the cured product according to the present invention. Effect of the Invention

[0009] The addition-curable liquid silicone rubber composition of the present invention has excellent curing properties, and is capable of providing a silicone rubber that has suitable hardness and tear strength and is resistant to deformation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will now be described in further detail. [(A) Alkenyl-containing organopolysiloxane] First, component (A) is the main component (base polymer) of the composition of the present invention. It is an organopolysiloxane that has two or more alkenyl groups bonded to silicon atoms in each molecule, has an average degree of polymerization of 1,500 or less, and is liquid at 25°C. In the composition of the present invention, the alkenyl-containing organopolysiloxane that is liquid at 25° C. (that is, has self-flowing properties) consists solely of this organopolysiloxane (component (A)).

[0011] The organopolysiloxane of component (A) is represented by the following average composition formula (1) and is liquid at 25°C. R 1 a SiO (4-a) / 2 (1)

[0012] In the formula, R 1 are the same or different, unsubstituted or substituted monovalent hydrocarbon groups having 1 to 20 carbon atoms, and a is a positive number of 1.5 to 2.8.

[0013] R 1 The monovalent hydrocarbon group may be linear, branched, or cyclic, and examples thereof include an alkyl group having 1 to 20, preferably 1 to 10, more preferably 1 to 8, and even more preferably 1 to 6 carbon atoms; an aryl group having 6 to 20, preferably 6 to 10, and more preferably 6 to 8 carbon atoms; an aralkyl group having 7 to 20, preferably 7 to 10 carbon atoms; and an alkenyl group having 2 to 20, preferably 2 to 10, and more preferably 2 to 8 carbon atoms. R 1 Specific examples of the monovalent hydrocarbon group 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; aralkyl groups such as benzyl, phenylethyl, and phenylpropyl; and alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexenyl, and octenyl. Also included are groups in which some or all of the hydrogen atoms of these groups have been substituted with halogen atoms such as fluorine, chlorine, and bromine, or with cyano groups, such as chloromethyl, chloropropyl, bromoethyl, trifluoropropyl, and cyanoethyl. Among these, R 1 is preferably a methyl group, an ethyl group, or a propyl group, more preferably a methyl group, and all R 1 Of these, it is preferred that 90 mol % or more, excluding alkenyl groups, are methyl groups.

[0014] Also, all R 1 Among these, two or more are alkenyl groups, and the alkenyl groups preferably have 2 to 6 carbon atoms, and more preferably are vinyl groups. The alkenyl group content in the organopolysiloxane is 1.0×10 -6 ~3.0×10 -3 mol / g is preferred, 1.0×10 -5 ~2.0×10 -3 The amount of alkenyl groups is preferably 1.0×10 -6 ~3.0×10 -3 Within this range of moles / g, a rubber with high strength and low hardness can be obtained. a is a positive number from 1.5 to 2.8, preferably from 1.8 to 2.5, and more preferably from 1.95 to 2.05.

[0015] The structure of the organopolysiloxane of component (A) is basically a straight-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 partially have a branched structure or a cyclic structure containing monoorganosilsesquioxane units.

[0016] The alkenyl group may be bonded to a silicon atom at the molecular chain terminal (both terminals or one terminal) or to a silicon atom in the molecular chain (non-terminal), but in the (A) component of the present invention, it is preferable that the molecule contains at least one, preferably at least two, alkenyl groups bonded to a silicon atom at the molecular chain terminal (i.e., a silicon atom in a triorganosiloxy group), and it may or may not contain an alkenyl group bonded to a silicon atom in the molecular chain (i.e., a silicon atom in a diorganosiloxane unit or a monoorganosilsesquioxane unit). If the molecule does not contain at least one, preferably at least two, alkenyl groups bonded to a silicon atom at the molecular chain terminal, a cured rubber product with low hardness and high tear strength may not be obtained.

[0017] The average degree of polymerization of the organopolysiloxane of component (A) is no greater than 1,500, preferably from 100 to 1,500, and more preferably from 150 to 1,100. When it is no greater than 1,500, the composition has a viscosity that makes it easy to mold. In the present invention, the average degree of polymerization refers to a number-average degree of polymerization, and refers to an 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: 1mL / min Detector: Refractive index detector (RI) Column: KF-805L x 2 (Shodex) Column temperature: 25℃ Sample injection volume: 30 μL (toluene solution with a concentration of 0.2% by mass)

[0018] The viscosity of the organopolysiloxane of component (A) is preferably 0.1 to 1,000 Pa s, more preferably 1 to 500 Pa s, and even more preferably 1 to 200 Pa s at 25° C., as measured by Brookfield viscosity measurement based on JIS K 7117-1; 1999. When the viscosity is within this range, the composition is easily molded.

[0019] Specific examples of such organopolysiloxanes of component (A) include diorganopolysiloxanes capped at both molecular chain terminals with diorganoalkenylsiloxy groups, diorganopolysiloxanes capped at both molecular chain terminals with organodialkenylsiloxy groups, diorganopolysiloxanes capped at both molecular chain terminals with trialkenylsiloxy groups, diorganosiloxane-organoalkenylsiloxane copolymers capped at both molecular chain terminals with diorganoalkenylsiloxy groups, and diorganosiloxane-organoalkenylsiloxane copolymers in which one molecular chain terminal is capped with diorganoalkenylsiloxy groups and the other terminal is capped with triorganosiloxy groups. Among these, preferred are diorganopolysiloxanes capped at both molecular chain terminals with diorganoalkenylsiloxy groups, diorganosiloxane-organoalkenylsiloxane copolymers capped at both molecular chain terminals with triorganosiloxy groups, and diorganosiloxane-organoalkenylsiloxane copolymers capped at both molecular chain terminals with diorganoalkenylsiloxy groups. The "organo group" in each of the above siloxanes is R 1 Among these, it means the same as an unsubstituted or substituted monovalent hydrocarbon group excluding an alkenyl group. The component (A) may use one type alone, or two or more types in combination.

[0020] [(B) Organohydrogenpolysiloxane] Component (B) is an organohydrogenpolysiloxane having hydrogen atoms bonded to silicon atoms (Si-H groups), and is characterized by the use of three types of organohydrogenpolysiloxanes in combination: components (B-1), (B-2), and (B-3) below. Component (B) acts as a curing agent for curing the composition by crosslinking the Si-H groups in the molecule with the alkenyl groups bonded to silicon atoms in component (A) through a hydrosilylation addition reaction. (B-1) Organohydrogenpolysiloxane containing an average of four or more hydrogen atoms bonded to silicon atoms in each molecule in the side chain and terminated at the terminals with trialkylsiloxy groups. (B-2) Organohydrogenpolysiloxane containing an average of 1.5 to 2.5 hydrogen atoms bonded to silicon atoms in each molecule in the side chain and terminated at the ends with trialkylsiloxy groups. (B-3) A linear organohydrogenpolysiloxane whose main chain is composed only of dialkylsiloxane units and whose both ends are blocked with dialkylhydrogensiloxy groups. Incidentally, the term "containing a hydrogen atom bonded to a silicon atom in a side chain" means containing a hydrogen atom bonded to a silicon atom in the middle of the molecular chain (non-terminal of the molecular chain).

[0021] [(B-1) component] The organohydrogenpolysiloxane of component (B-1) may have any of a linear, branched, or three-dimensional network structure, but linear structures are preferred and are preferably used, as represented by the following average structural formula (2), which has an average of 4 or more, preferably an average of 6 or more, more preferably an average of 6 to 100, and even more preferably an average of 6 to 50 silicon-bonded hydrogen atoms (Si-H groups) per molecule.

[0022] [ka]

[0023] In formula (2), R 2 are the same or different, unsubstituted or substituted alkyl groups having 1 to 10 carbon atoms, b is a number of 4 or more, and c is a number of 0 to 300. The bonding order of the siloxane units shown in the parentheses is arbitrary.

[0024] Here, the above R 2 The alkyl group having 1 to 10 carbon atoms in R preferably has 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 3 carbon atoms. 2 The alkyl group may be linear, branched or cyclic, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a neopentyl group, a hexyl group, a cyclohexyl group, an octyl group, a nonyl group, a decyl group, etc. Also included are groups in which some or all of the hydrogen atoms of these groups have been substituted with halogen atoms such as fluorine, chlorine or bromine, or with a cyano group, etc., such as a chloromethyl group, a chloropropyl group, a bromoethyl group, a trifluoropropyl group, a cyanoethyl group, etc., but those not having an aliphatic unsaturated group are preferred. Among these, R 2 As the alkyl group, a methyl group, an ethyl group, or a propyl group is preferable, and a methyl group is more preferable. b is preferably a number of 6 or more, more preferably a number from 6 to 100, and even more preferably a number from 6 to 50;

[0025] The content of Si-H groups in the component (B-1) is preferably 0.001 to 0.017 mol / g, and more preferably 0.002 to 0.017 mol / g, in the organohydrogenpolysiloxane.

[0026] The number of silicon atoms (or average degree of polymerization) in one molecule of component (B-1) is preferably from 6 to 500, more preferably from about 8 to 300, even more preferably from about 8 to 100, and particularly preferably from about 8 to 50. As component (B-1), a compound that is liquid at 25°C is preferably used.

[0027] Specific examples of the organohydrogenpolysiloxane of component (B-1) above include methylhydrogenpolysiloxane capped at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with trimethylsiloxy groups, and compounds in which some or all of the methyl groups in these exemplary compounds have been substituted with other alkyl groups, etc. The component (B-1) may use one type alone, or two or more types in combination.

[0028] [(B-2) component] The organohydrogenpolysiloxane of component (B-2) may have a linear, branched, or three-dimensional network structure, but linear structures are preferred and are represented by the following average structural formula (3) and have an average of 1.5 to 2.5, and preferably 1.6 to 2.4, silicon-bonded hydrogen atoms (Si-H groups) per molecule.

[0029] [ka]

[0030] In formula (3), R 2 is the same as above, d is a number from 1.5 to 2.5, preferably 1.6 to 2.4, and e is a number from 0 to 100, preferably 1 to 100. The bonding order of the siloxane units shown in the parentheses is arbitrary.

[0031] The content of Si-H groups in the component (B-2) is preferably 0.0002 to 0.010 mol / g, and more preferably 0.0004 to 0.008 mol / g, in the organohydrogenpolysiloxane.

[0032] The number of silicon atoms (or average degree of polymerization) in one molecule of the component (B-2) is preferably from 4 to 100, and more preferably from about 8 to 50. As the component (B-2), one that is liquid at 25°C is preferably used.

[0033] Specific examples of the organohydrogenpolysiloxane of component (B-2) above include methylhydrogenpolysiloxane capped at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with trimethylsiloxy groups, and compounds in which some or all of the methyl groups in these exemplary compounds have been replaced with other alkyl groups, etc. The component (B-2) may use either a single type alone, or two or more types in combination.

[0034] [(B-3) component] The organohydrogenpolysiloxane of the component (B-3) is preferably one represented by the following average structural formula (4) which has silicon-bonded hydrogen atoms (Si-H groups) only at both ends.

[0035] [ka]

[0036] In formula (4), R 2 is the same as above, and f is a number from 0 to 300, preferably 1 to 300.

[0037] The content of Si-H groups in the component (B-3) is preferably 0.00009 to 0.015 mol / g, and more preferably 0.0001 to 0.005 mol / g, in the organohydrogenpolysiloxane.

[0038] The number of silicon atoms (or average degree of polymerization) in one molecule of the component (B-3) is preferably from 2 to 300, more preferably from about 4 to 150, and even more preferably from about 4 to 50. As the component (B-3), one that is liquid at 25°C is preferably used.

[0039] Specific examples of the organohydrogenpolysiloxane of the above component (B-3) include 1,3-dihydro-1,1,3,3-tetramethyldisiloxane, dimethylpolysiloxane blocked at both ends with dimethylhydrogensiloxy groups, and compounds in which some or all of the methyl groups in these exemplary compounds have been substituted with other alkyl groups, etc. Among these, dimethylpolysiloxane blocked at both ends with dimethylhydrogensiloxy groups is particularly preferred. The component (B-3) may use either a single type alone, or two or more types in combination.

[0040] The compounding ratios of components (B-1) to (B-3) are such that the number of moles of Si-H groups in each component relative to the total number of moles of silicon-bonded hydrogen atoms (Si-H groups) contained in these three components (total Si-H groups) is within the following range: [Si-H group (B-1)] / [total Si-H group] is 50 to 80 mol %, preferably 60 to 75 mol %. When the compounding ratio is 50 to 80 mol %, curing is rapid and rubber strength is high. [Si-H group (B-2)] / [total Si-H group] is 5 to 40 mol%, preferably 5 to 35 mol%, more preferably 5 to 30 mol%. When the compounding ratio is 5 to 40 mol%, curing is rapid, and the hardness of the cured product is low while deformation is suppressed. [Si-H group (B-3)] / [total Si-H group] is 5 to 15 mol %, preferably 8 to 15 mol %. When the above blending ratio is in the range of 5 to 15 mol %, the hardness of the cured product can be reduced while deformation can be suppressed.

[0041] The total amount of the (B-1) to (B-3) components is such that the molar ratio (total Si-H groups / total alkenyl groups) of the total Si-H groups in the organohydrogenpolysiloxanes of the (B-1) to (B-3) components to the total amount of alkenyl groups in the composition (particularly the alkenyl groups of the (A) component described above, or the total of the alkenyl groups of the (A) component and the (E) component described below when an alkenyl group-containing component is used) is 1 to 1.8, preferably 1.1 to 1.7. Within this range, curing is rapid and deformation of the cured product can be suppressed.

[0042] Furthermore, the combined amount of components (B-1) to (B-3) is preferably 0.2 to 20 parts by mass, and more preferably 0.3 to 10 parts by mass, per 100 parts by mass of component (A).

[0043] [(C) Fumed Silica] Component (C) has a specific surface area of ​​130 m2 by the BET method. 2 The fumed silica in component (C) is essential for imparting sufficient strength to the resulting silicone rubber. The specific surface area of ​​the fumed silica measured by the BET method is 130 m 2 / g or more, preferably 130 to 400m 2 / g, more preferably 130 to 380 m 2 / g. 130m 2 When it is greater than 1 / g, the molded product has high transparency and high strength.

[0044] The amount of fumed silica in the component (C) is 5 to 40 parts by mass, and preferably 5 to 30 parts by mass, per 100 parts by mass of the component (A). Within this range, the hardness can be reduced while the strength can be increased.

[0045] The fumed silica of component (C) is preferably surface-treated to be hydrophobic. If the surface is not treated, the silica will not disperse well in the composition, and may form aggregates of the fumed silica or may be difficult to blend. The surface treatment of the fumed silica may be performed directly in a powder state before mixing with component (A), or the surface may be treated by heating and mixing with a silica surface treatment agent when mixing with component (A). As the treatment method, a conventionally known method can be adopted, for example, untreated fumed silica and a silica surface treatment agent can be placed in a mechanical kneading device or fluidized bed sealed at normal pressure, and mixed at room temperature or by heating in the presence of an inert gas as necessary. In some cases, a catalyst may be used to promote the treatment. After kneading, the mixture is dried to produce a surface-treated silica fine powder.

[0046] As mentioned above, the silica surface treatment agent can be used to hydrophobize the surface of the fumed silica, which is the component (C).Specific examples of the silica surface treatment agent include silazanes such as hexamethyldisilazane and divinyltetramethyldisilazane; silane-based coupling agents such as methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylmethoxysilane, triethylmethoxysilane, vinyltris(methoxyethoxy)silane, trimethylchlorosilane, dimethyldichlorosilane, divinyldimethoxysilane and chloropropyltrimethoxysilane; and organosilicon compounds such as polymethylsiloxane and organohydrogenpolysiloxane.Among these, silane-based coupling agents or silazanes are particularly preferred as the treatment agent.

[0047] When a surface treatment agent containing an alkenyl group such as a vinyl group is used as the silica surface treatment agent, the amount of the alkenyl group treated on the surface is to be included in the amount of alkenyl groups in the composition when calculating the amount of component (B) to be blended. The amount of the silica surface treatment agent used is not particularly limited, but is preferably 5 to 75 parts by mass, and more preferably 5 to 60 parts by mass, per 100 parts by mass of the component (C).

[0048] As the fumed silica of component (C), a commercially available product can be used, and examples thereof include the Aerosil series, such as Aerosil 130, Aerosil 200, Aerosil 300, Aerosil R-812, and Aerosil R-974 (manufactured by Nippon Aerosil Co., Ltd.), and Reolosil QS-102 and 103 (manufactured by Tokuyama Corporation), which are surface-untreated or surface-hydrophobized fumed silica.

[0049] [(D) Addition reaction catalyst] Component (D) is an addition reaction catalyst. Any known catalyst can be used as the addition reaction catalyst for component (D), and specific examples thereof include platinum-based catalysts such as platinum black, platinic chloride, chloroplatinic acid, a reaction product of chloroplatinic acid with a monohydric alcohol, a complex of platinum with an olefin, and platinum bisacetoacetate; and platinum group metal catalysts such as palladium-based catalysts and rhodium-based catalysts. The amount of this addition reaction catalyst added can be a catalytic amount, which is usually 0.5 to 100 ppm, and preferably about 1 to 20 ppm, of platinum group metal (by mass) relative to the mass of component (A).

[0050] [(E) Raw rubber-like organopolysiloxane] Next, component (E) can be blended into the composition of the present invention. Component (E) is an organopolysiloxane that has an average degree of polymerization (number average degree of polymerization) of 2,000 or more and is in the form of raw rubber at 25°C (i.e., non-liquid and has no self-flowing properties).

[0051] The organopolysiloxane of component (E) can be one represented by the following average composition formula (5). R 3 g SiO (4-g) / 2 (5)

[0052] In the formula, R 3 are the same or different, unsubstituted or substituted monovalent hydrocarbon groups having 1 to 20 carbon atoms, and g is a positive number of 1.8 to 2.5.

[0053] Here, R 3Specific examples of monovalent hydrocarbon groups include R 1 Among them, a methyl group, an ethyl group, and a propyl group are preferable, a methyl group is more preferable, and all R 3 It is preferred that 90 mol % or more of the above be methyl groups, with the remainder being vinyl groups.

[0054] Also, R 3 may or may not contain an alkenyl group, but when it does contain an alkenyl group, the content is preferably 0.0026 mol / g or less, more preferably 0.0014 mol / g or less. When the amount of alkenyl groups is 0.0026 mol / g or less, curing is rapid and the cured product becomes a rubber with low hardness. This alkenyl group may be bonded to a silicon atom at the end of the molecular chain, or to a silicon atom in the middle of the molecular chain, or to both. In addition, this alkenyl group is more preferably one having 2 to 6 carbon atoms, and even more preferably a vinyl group. g is a positive number of 1.8 to 2.5, preferably 1.9 to 2.1, and more preferably 1.98 to 2.01.

[0055] The structure of this organopolysiloxane is basically the same as that of component (A) above, with both molecular chain terminals blocked with triorganosiloxy groups and the main chain having a linear structure consisting of repeating diorganosiloxane units, but it may also have a partially branched structure or cyclic structure.

[0056] Regarding the molecular weight, it is preferable that the average degree of polymerization is 2,000 or more (usually about 2,000 to 100,000) and is in a raw rubber state (i.e., non-liquid state without self-flowing) at 25° C., and preferably the average degree of polymerization is 3,000 or more (about 3,000 to 80,000). When the average degree of polymerization is 2,000 or more, the viscosity of the composition can be increased and adjusted to a viscosity that is easy to mold, and stickiness of the rubber surface can be suppressed.

[0057] Specific examples of organopolysiloxanes of component (E) that do not contain alkenyl groups in the molecule include diorganopolysiloxane raw rubber capped with triorganosiloxy groups at both molecular chain terminals, and examples that contain alkenyl groups in the molecule include diorganopolysiloxane raw rubber capped with diorganoalkenylsiloxy groups at both molecular chain terminals, diorganopolysiloxane raw rubber capped with organodialkenylsiloxy groups at both molecular chain terminals, and diorganopolysiloxane raw rubber capped with trialkenylsiloxy groups at both molecular chain terminals. Examples of such rubbers include diorganopolysiloxane raw rubber, diorganosiloxane-organoalkenylsiloxane copolymer raw rubber with both molecular chain ends blocked with triorganosiloxy groups, diorganosiloxane-organoalkenylsiloxane copolymer raw rubber with both molecular chain ends blocked with diorganoalkenylsiloxy groups, and diorganosiloxane-organoalkenylsiloxane copolymer raw rubber in which one molecular chain end is blocked with diorganoalkenylsiloxy groups and the other end is blocked with triorganosiloxy groups. Of these, preferred are diorganopolysiloxane raw rubber capped at both molecular chain terminals with triorganosiloxy groups, diorganopolysiloxane raw rubber capped at both molecular chain terminals with diorganoalkenylsiloxy groups, diorganosiloxane-organoalkenylsiloxane copolymer raw rubber capped at both molecular chain terminals with triorganosiloxy groups, and diorganosiloxane-organoalkenylsiloxane copolymer raw rubber capped at both molecular chain terminals with diorganoalkenylsiloxy groups. The "organo group" in each of the above siloxanes is R 3 Among these, it means the same as an unsubstituted or substituted monovalent hydrocarbon group excluding an alkenyl group.

[0058] Component (E) is an optional component, but when it is added, it is preferably 1 to 200 parts by mass, more preferably 3 to 150 parts by mass, and even more preferably 5 to 120 parts by mass, per 100 parts by mass of component (A). Within the above range, the viscosity of the composition can be controlled to an easily moldable level, and the sticky feeling on the surface of the cured product can be reduced.

[0059] [(F) Organopolysiloxane containing no addition-reactive substituents] The composition of the present invention may also contain component (F), which is an organopolysiloxane that has an average degree of polymerization (number average degree of polymerization) of 500 or less, is liquid at 25° C., and contains no addition-reactive substituents. Here, the above-mentioned "substituent having addition reactivity" refers to a group that can be subjected to a hydrosilylation reaction (addition reaction), such as an alkenyl group.

[0060] The organopolysiloxane of component (F) can be one represented by the following average composition formula (6). R 4 h SiO (4-h) / 2 (6)

[0061] In the formula, R 4 are the same or different, unsubstituted or substituted monovalent hydrocarbon groups having 1 to 20 carbon atoms and containing no aliphatic unsaturated bonds, and h is a positive number of 1.8 to 2.5.

[0062] R 4 Specific examples of monovalent hydrocarbon groups include R 1 Among the groups exemplified in 1, the same groups as those other than the alkenyl group can be mentioned. Among these, a methyl group, an ethyl group, a propyl group, and a phenyl group are preferable, a methyl group is more preferable, and it is preferable that 90 mol % or more of all the substituents are methyl groups. h is a positive number from 1.8 to 2.5, preferably from 1.9 to 2.1, and more preferably from 1.98 to 2.01.

[0063] The structure of this organopolysiloxane is basically the same as that of component (A) above, with both molecular chain terminals blocked with triorganosiloxy groups and the main chain having a linear structure consisting of repeating diorganosiloxane units, but it may also have a partially branched structure or cyclic structure.

[0064] Regarding the molecular weight, the average degree of polymerization is 500 or less and is liquid at 25° C., preferably the average degree of polymerization is 20 to 500, and more preferably 30 to 300. If the average degree of polymerization is 500 or less, it is possible to provide a rubber with low hardness while suppressing stickiness of the rubber surface.

[0065] Specific examples of such organopolysiloxanes of component (F) include dimethylpolysiloxanes capped at both molecular chain terminals with trimethylsiloxy groups, methylphenylpolysiloxanes capped at both molecular chain terminals with trimethylsiloxy groups, diphenylpolysiloxanes capped at both molecular chain terminals with trimethylsiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, dimethylsiloxane-diphenylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, etc. Among these, dimethylpolysiloxanes capped at both molecular chain terminals with trimethylsiloxy groups are preferred.

[0066] Component (F) is an optional component, but when it is added, it is preferably 1 to 200 parts by mass, more preferably 3 to 150 parts by mass, and even more preferably 5 to 120 parts by mass, per 100 parts by mass of component (A). Within this range, the hardness can be reduced while maintaining high strength of the cured product.

[0067] [Other ingredients]

[0043] The addition-curable liquid silicone rubber composition of the present invention may optionally contain other components, as necessary, within the limits that do not impair the effects of the present invention, such as fillers such as precipitated silica, quartz powder, diatomaceous earth, calcium carbonate, etc.; conductive agents such as carbon black, conductive zinc oxide, metal powder, etc.; hydrosilylation reaction inhibitors such as nitrogen-containing compounds, acetylene compounds, phosphorus compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds, sulfur compounds, etc.; heat resistance agents such as iron oxide, cerium oxide, etc.; internal release agents such as dimethyl silicone oil, etc.; adhesion imparting agents (particularly organosilicon compounds such as alkoxysilanes which contain at least one functional group in the molecule selected from alkenyl groups, epoxy groups, amino groups, (meth)acryloxy groups, mercapto groups, etc., and which do not contain Si-H groups in the molecule);

[0068] Regarding the curing speed of the addition curable liquid silicone rubber composition of the present invention, when the efficiency is emphasized, the 10% curing time (i.e., the time from the start of measurement when 10% of the maximum torque value in 2 minutes from the start of measurement at 150°C is given) when measured for 2 minutes at 150°C using a curing tester [moving die rheometer (MDR)] is T10 (seconds), and the 90% curing time (i.e., the time from the start of measurement when 90% of the maximum torque value in 2 minutes from the start of measurement at 150°C is given) is T90 (seconds). T10 is preferably 5 seconds or more, more preferably 8 seconds or more, while T90 is preferably 50 seconds or less, more preferably 40 seconds or less. With this curing speed, it is possible to shorten the molding cycle and perform continuous molding while suppressing short circuits and air bubbles during molding.

[0069] The addition-curable liquid silicone rubber composition of the present invention can be molded and cured by any conventional method, but the preferred molding method is liquid injection molding. The curing conditions are as follows: At 100 to 230°C for 3 seconds to 30 minutes, preferably 110-210℃ for 5 seconds to 20 minutes, especially Heat treatment conditions may be 120 to 200° C. for 5 seconds to 10 minutes. If necessary, post-cure (secondary vulcanization) may be performed at 80 to 230° C., particularly 100 to 210° C., for 10 minutes to 24 hours, particularly 30 minutes to 10 hours.

[0070] The addition-curable liquid silicone rubber composition of the present invention can be cured under the conditions of 120°C / 10 minutes press cure to give a silicone rubber elastomer with low hardness but high strength. Specifically, the hardness (durometer type A) based on JIS K 6253-3:2012 is preferably 5 to 15, more preferably 7 to 13, and the tear strength (crescent type) based on JIS K 6252:2007 is preferably 10 kN / m or more, more preferably 12 kN / m or more. Furthermore, the addition-curable liquid silicone rubber composition of the present invention preferably has a tensile permanent set of 15% or less in a constant elongation tensile permanent set test measured under conditions of 100% elongation and 120°C / 24 hours based on JIS K 6273: 2018 on the cured product molded under the above-mentioned conditions. If the tensile permanent set is 15% or less, deformation during demolding or when the molded product is stored in a bent state can be suppressed. In order for the obtained silicone rubber to have the above values ​​of hardness, etc., this can be achieved by blending the above-mentioned components (A) to (D), and optionally components (E) and (F), in the composition in an appropriate ratio (mass ratio).

[0071] The addition-curable liquid silicone rubber composition of the present invention has excellent curing properties and, after curing, gives cured products and silicone rubber molded articles that have low hardness and high tear strength and are resistant to deformation. These compositions are suitable for use as materials for baby bottle nipples, pacifiers, masks, etc. EXAMPLES

[0072] 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" refers to parts by mass. Viscosity refers to the value at 25°C in Brookfield viscosity measurement based on JIS K 7117-1;1999.

[0073] [Example 1] 65 parts of dimethylpolysiloxane (A1, which corresponds to a = 2.0027 in the above formula (1)) whose both ends are blocked with dimethylvinylsiloxy groups, has an average degree of polymerization of 750, and has a viscosity of 31 Pa s at 25 °C; 2 40 parts of fumed silica (C1) (Aerosil 300, Nippon Aerosil Co., Ltd.) having a molecular weight of 1.0 to 1.0 g, 8 parts of hexamethyldisilazane, 0.1 parts of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and 2.0 parts of water were mixed at 25°C for 30 minutes, and then heated to 150°C, stirred for 3 hours, and cooled to obtain a silicone rubber base. 29Measurement of Si solid-state NMR revealed that half of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane was immobilized on the silica (corresponding to 0.00054 mol of vinyl groups).

[0074] To 105 parts of this silicone rubber base, 25 parts of the above dimethylpolysiloxane (A1), 30 parts of dimethylpolysiloxane raw rubber (E1, corresponding to g=2.00025 in the above formula (5)) whose both ends are blocked with dimethylvinylsiloxy groups and whose average degree of polymerization is 8,000, and 50 parts of dimethylpolysiloxane (F1, corresponding to h=2.013 in the above formula (6)) whose both ends are blocked with trimethylsiloxy groups, whose average degree of polymerization is 60 and which does not contain vinyl groups in the molecule, were added, and stirring was continued for 30 minutes. After that, a crosslinking agent represented by the following formula (7) was further added. [ka] The copolymer (B-1-1) (average degree of polymerization: 32, amount of Si-H groups: 0.0069 mol / g) represented by the following formula (8) was used. [ka] The copolymer (B-2-1) (average degree of polymerization: 30, amount of Si-H groups: 0.00091 mol / g) represented by the following formula (9) was used. [ka] 0.56 parts of dimethylpolysiloxane (B-3-1) (average degree of polymerization 20, Si-H group amount 0.0014 mol / g) having both ends blocked with dimethylhydrogensiloxy groups and no Si-H groups on the side chains, and 0.02 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture.

[0075] In this mixture, the compounding ratios of Si-H groups in components (B-1-1), (B-2-1), and (B-3-1) relative to the total Si-H groups in the entire mixture were 65 mol % for component (B-1-1), 23 mol % for component (B-2-1), and 12 mol % for component (B-3-1), and the molar ratio of the total Si-H groups to the total vinyl groups in the entire mixture (Si-H groups / vinyl groups) was 1.55.

[0076] 0.04 parts of a platinum catalyst (platinum / 1,3-divinyltetramethyldisiloxane complex, Pt concentration 1% by mass) (D1) was mixed into this silicone rubber mixture to obtain a silicone rubber composition. The resulting composition was subjected to the following evaluations, and the results are shown in Table 1.

[0077] [Curability of the composition] Using a rheometer MDR2000 (manufactured by Alpha Technologies), the curability T10 and T90 were measured at 150°C for 2 minutes. Note that T10 and T90 refer to the time from the start of measurement when 10% and 90% torque values ​​of the maximum torque value in 2 minutes from the start of measurement at 150°C are obtained. [Physical properties of the cured product] The composition was press-cured at 120° C. for 10 minutes to produce a 2 mm thick sheet of the cured product, which was then measured for the following physical properties. Hardness: Durometer type A hardness measured according to the method described in JIS K 6253-3:2012 Tear strength: Tear strength measured using a crescent-shaped test piece according to the method described in JIS K 6252:2007 · Permanent tensile set at constant elongation: Permanent tensile set at constant elongation measured at 100% elongation and 120℃ / 24 hours according to the method described in JIS K 6273:2018

[0078] [Example 2] 65 parts of dimethylpolysiloxane (A2, corresponding to a=2.0020 in formula (1) above) having an average degree of polymerization of 1,000, both ends of which are blocked with dimethylvinylsiloxy groups, and a viscosity of 98 Pa·s at 25°C, 40 parts of the above fumed silica (C1), 8 parts of hexamethyldisilazane, 0.1 parts of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and 2.0 parts of water were mixed at 25°C for 30 minutes, then the mixture was heated to 150°C, stirred for 3 hours, and cooled to obtain a silicone rubber base. Note that this silicone rubber base 29 Si solid-state NMR measurements revealed that half of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane was immobilized on the silica.

[0079] To 105 parts of this silicone rubber base, 25 parts of a dimethylpolysiloxane (A3, corresponding to a=2.0040 in the above formula (1)) which is endblocked at both ends with dimethylvinylsiloxy groups, has an average degree of polymerization of 500, and has a viscosity at 25°C of 10 Pa s, 30 parts of the above dimethylpolysiloxane raw rubber (E1), and 50 parts of the above dimethylpolysiloxane (F1) were added, and stirring was continued for 30 minutes. After that, a crosslinking agent represented by the following formula (10) was further added. [ka] The copolymer (B-1-2) (average degree of polymerization: 42, amount of Si-H groups: 0.0070 mol / g) represented by the following formula (11) was used. [ka] The copolymer (B-2-2) (average degree of polymerization: 20, amount of Si-H groups: 0.0012 mol / g) represented by the following formula (12) was used. [ka] 0.88 parts of dimethylpolysiloxane (B-3-2) (average degree of polymerization 40, Si-H group amount 0.00068 mol / g) having both ends blocked with dimethylhydrogensiloxy groups and no Si-H groups on the side chains, and 0.02 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture.

[0080] In this mixture, the compounding ratios of Si-H groups in components (B-1-2), (B-2-2), and (B-3-2) relative to the total Si-H groups in the entire mixture were 66.7 mol % for component (B-1-2), 23.8 mol % for component (B-2-2), and 9.5 mol % for component (B-3-2).The molar ratio of the total Si-H groups to the total vinyl groups in the entire mixture (Si-H groups / vinyl groups) was 1.60.

[0081] 0.04 parts of platinum catalyst (Pt concentration 1% by mass) (D1) was mixed into this silicone rubber mixture to obtain a silicone rubber composition. The curability and physical properties of the cured product were measured for the resulting composition in the same manner as in Example 1, and the results are shown in Table 1.

[0082] [Example 3] 60 parts of the dimethylpolysiloxane (A1), 40 parts of the fumed silica (C1), 8 parts of hexamethyldisilazane, 0.1 parts of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and 2.0 parts of water were mixed at 25°C for 30 minutes, and then heated to 150°C, stirred for 3 hours, and cooled to obtain a silicone rubber base. 29 Si solid-state NMR measurements revealed that half of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane was immobilized on the silica.

[0083] To 100 parts of this silicone rubber base, 30 parts of the above dimethylpolysiloxane (A1), 15 parts of dimethylpolysiloxane raw rubber (E2, corresponding to g = 2.00050 in the above formula (5)) whose both ends are blocked with dimethylvinylsiloxy groups and whose average polymerization degree is 4,000, 15 parts of dimethylpolysiloxane raw rubber (E3, corresponding to g = 2.00025 in the above formula (5)) whose both ends are blocked with trimethylsiloxy groups and whose average polymerization degree is 8,000, and 40 parts of dimethylpolysiloxane (F2, corresponding to h = 2.033 in the above formula (6)) whose both ends are blocked with trimethylsiloxy groups, has an average polymerization degree of 150 and does not contain vinyl groups in the molecule, and is further added as a crosslinking agent, [ka] The copolymer (B-1-3) (average degree of polymerization: 27, amount of Si-H groups: 0.0053 mol / g) represented by the following formula (14) was used. [ka] The copolymer (B-2-3) (average degree of polymerization: 34, amount of Si-H groups: 0.00088 mol / g) represented by the following formula (15) was used. [ka] 0.41 parts of dimethylpolysiloxane (B-3-3) (average degree of polymerization 17, Si-H group amount 0.0016 mol / g) having both ends blocked with dimethylhydrogensiloxy groups and no Si-H groups on the side chains, and 0.02 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture.

[0084] In this mixture, the compounding ratios of Si-H groups in components (B-1-3), (B-2-3), and (B-3-3) relative to the total Si-H groups in the entire mixture were 60 mol % for component (B-1-3), 30 mol % for component (B-2-3), and 10 mol % for component (B-3-3), and the molar ratio of the total Si-H groups to the total vinyl groups in the entire mixture (Si-H groups / vinyl groups) was 1.60.

[0085] 0.04 parts of platinum catalyst (Pt concentration 1% by mass) (D1) was mixed into this silicone rubber mixture to obtain a silicone rubber composition. The curability and physical properties of the cured product were measured for the resulting composition in the same manner as in Example 1, and the results are shown in Table 1.

[0086] [Comparative Example 1] 65 parts of the above dimethylpolysiloxane (A1), 40 parts of the above fumed silica (C1), 8 parts of hexamethyldisilazane, 0.1 parts of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and 2.0 parts of water were mixed at 25°C for 30 minutes, then heated to 150°C, stirred for 3 hours, and cooled to obtain a silicone rubber base. 29 Si solid-state NMR measurements revealed that half of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane was immobilized on the silica.

[0087] To 105 parts of this silicone rubber base, 25 parts of the dimethylpolysiloxane (A1), 35 parts of the dimethylpolysiloxane raw rubber (E1), and 55 parts of the dimethylpolysiloxane (F1) were added and stirring was continued for 30 minutes, after which 0.71 parts of the methylhydrogensiloxane-dimethylsiloxane copolymer (B-1-1) both ends of which were capped with trimethylsiloxy groups as a crosslinking agent, 0.90 parts of the dimethylpolysiloxane (B-3-1) both ends of which were capped with dimethylhydrogensiloxy groups, and 0.02 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture.

[0088] In this mixture, the compounding ratios of Si-H groups in the components (B-1-1) and (B-3-1) to the total amount of Si-H groups in the entire mixture were 80 mol % for component (B-1-1) and 20 mol % for component (B-3-1), and the molar ratio of the total amount of Si-H groups to the total amount of vinyl groups in the entire mixture (Si-H groups / vinyl groups) was 1.50.

[0089] 0.04 parts of platinum catalyst (Pt concentration 1% by mass) (D1) was mixed into this silicone rubber mixture to obtain a silicone rubber composition. The curability and physical properties of the cured product were measured for the resulting composition in the same manner as in Example 1, and the results are shown in Table 1.

[0090] [Comparative Example 2] 65 parts of the above dimethylpolysiloxane (A1), 40 parts of the above fumed silica (C1), 8 parts of hexamethyldisilazane, 0.1 parts of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and 2.0 parts of water were mixed at 25°C for 30 minutes, then heated to 150°C, stirred for 3 hours, and cooled to obtain a silicone rubber base. 29 Si solid-state NMR measurements revealed that half of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane was immobilized on the silica.

[0091] To 105 parts of this silicone rubber base, 25 parts of the dimethylpolysiloxane (A1), 35 parts of the dimethylpolysiloxane raw rubber (E1), and 70 parts of the dimethylpolysiloxane (F2) were added and stirring was continued for 30 minutes, after which 0.80 parts of the methylhydrogensiloxane-dimethylsiloxane copolymer (B-1-1) both ends of which were blocked with trimethylsiloxy groups as a crosslinking agent, 0.45 parts of the dimethylpolysiloxane (B-3-1) both ends of which were blocked with dimethylhydrogensiloxy groups, and 0.02 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture.

[0092] In this mixture, the compounding ratios of Si-H groups in components (B-1-1) and (B-3-1) to the total amount of Si-H groups in the entire mixture were 90 mol % for component (B-1-1) and 10 mol % for component (B-3-1), and the molar ratio of the total amount of Si-H groups to the total amount of vinyl groups in the entire mixture (Si-H groups / vinyl groups) was 1.50.

[0093] 0.04 parts of platinum catalyst (Pt concentration 1% by mass) (D1) was mixed into this silicone rubber mixture to obtain a silicone rubber composition. The curability and physical properties of the cured product were measured for the resulting composition in the same manner as in Example 1, and the results are shown in Table 1.

[0094] [Comparative Example 3] 65 parts of the above dimethylpolysiloxane (A1), 40 parts of the above fumed silica (C1), 8 parts of hexamethyldisilazane, 0.1 parts of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and 2.0 parts of water were mixed at 25°C for 30 minutes, then heated to 150°C, stirred for 3 hours, and cooled to obtain a silicone rubber base. 29 Si solid-state NMR measurements revealed that half of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane was immobilized on the silica.

[0095] To 105 parts of this silicone rubber base, 25 parts of the dimethylpolysiloxane (A1), 30 parts of the dimethylpolysiloxane raw rubber (E1), and 50 parts of the dimethylpolysiloxane (F2) were added and stirring was continued for 30 minutes, after which 0.57 parts of the methylhydrogensiloxane-dimethylsiloxane copolymer (B-1-1) both ends of which are capped with trimethylsiloxy groups as a crosslinking agent, 2.17 parts of the methylhydrogensiloxane-dimethylsiloxane copolymer (B-2-2) both ends of which are capped with trimethylsiloxy groups, and 0.02 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture.

[0096] In this mixture, the compounding ratios of Si-H groups in components (B-1-1) and (B-2-2) to the total amount of Si-H groups in the entire mixture were 60 mol % for component (B-1-1) and 40 mol % for component (B-2-2), and the molar ratio of the total amount of Si-H groups to the total amount of vinyl groups in the entire mixture (Si-H groups / vinyl groups) was 1.60.

[0097] 0.04 parts of platinum catalyst (Pt concentration 1% by mass) (D1) was mixed into this silicone rubber mixture to obtain a silicone rubber composition. The curability and physical properties of the cured product were measured for the resulting composition in the same manner as in Example 1, and the results are shown in Table 1.

[0098] [Comparative Example 4] 65 parts of the above dimethylpolysiloxane (A1), 40 parts of the above fumed silica (C1), 8 parts of hexamethyldisilazane, 0.1 parts of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and 2.0 parts of water were mixed at 25°C for 30 minutes, then heated to 150°C, stirred for 3 hours, and cooled to obtain a silicone rubber base. 29 Si solid-state NMR measurements revealed that half of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane was immobilized on the silica.

[0099] To 105 parts of this silicone rubber base, 25 parts of the dimethylpolysiloxane (A1), 30 parts of the dimethylpolysiloxane raw rubber (E1), and 60 parts of the dimethylpolysiloxane (F2) were added, and stirring was continued for 30 minutes. Then, as a crosslinking agent, 0.58 parts of the methylhydrogensiloxane-dimethylsiloxane copolymer (B-1-1) both ends of which are capped with trimethylsiloxy groups, 0.67 parts of the dimethylpolysiloxane (B-3-1) both ends of which are capped with dimethylhydrogensiloxy groups, and a compound represented by the following formula (16): [ka] 0.89 parts of methylhydrogensiloxane-dimethylsiloxane copolymer (B-4-1), which has an average of 3.0 Si-H groups on the side chains and is capped with trimethylsiloxy groups at both ends (represented by the formula: B-4-1), and 0.02 parts of ethynylcyclohexanol as a reaction inhibitor were added, and the mixture was stirred for 15 minutes to obtain a silicone rubber mixture.

[0100] In this mixture, the compounding ratios of Si-H groups in components (B-1-1), (B-3-1), and (B-4-1) relative to the total Si-H groups in the entire mixture were 65 mol % for component (B-1-1), 15 mol % for component (B-3-1), and 20 mol % for component (B-4-1), and the molar ratio of the total Si-H groups to the total vinyl groups in the entire mixture (Si-H groups / vinyl groups) was 1.50.

[0101] 0.04 parts of platinum catalyst (Pt concentration 1% by mass) (D1) was mixed into this silicone rubber mixture to obtain a silicone rubber composition. The curability and physical properties of the cured product were measured for the resulting composition in the same manner as in Example 1, and the results are shown in Table 1.

[0102] [Table 1]

Claims

1. The following components (A) to (D): (A) an organopolysiloxane that has two or more alkenyl groups bonded to silicon atoms in each molecule, has an average degree of polymerization of 1,500 or less, and is liquid at 25° C.: 100 parts by mass, (B) The following components (B-1) to (B-3): (B-1) an organohydrogenpolysiloxane containing an average of four or more hydrogen atoms bonded to silicon atoms in each molecule in its side chains and terminated at the terminals with trialkylsiloxy groups; (B-2) an organohydrogenpolysiloxane containing an average of 1.5 to 2.5 hydrogen atoms bonded to silicon atoms in each molecule in the side chain and terminated at the terminals with trialkylsiloxy groups; (B-3) A linear organohydrogenpolysiloxane whose main chain is composed only of dialkylsiloxane units and whose both ends are blocked with dialkylhydrogensiloxy groups: the number of moles of Si—H groups in each component relative to the total number of moles of silicon-bonded hydrogen atoms (Si—H groups) in component (B-1), component (B-2), and component (B-3) (total Si—H groups) is [Si—H groups (B-1)] / [total Si—H groups]=50 to 80 mol %, [Si—H groups (B-2)] / [total Si—H groups]=5 to 40 mol %, [Si—H group (B-3)] / [total Si—H groups]=5 to 15 mol %, and an amount such that the molar ratio of the total Si—H groups to the total alkenyl groups in the composition (total alkenyl groups) is [total Si—H groups] / [total alkenyl groups]=1 to 1.8; (C) The specific surface area measured by the BET method is 130 m 2 / g or more: 5 to 40 parts by mass of fumed silica, (D) Addition reaction catalyst: 0.5 to 100 ppm of platinum group metal (by mass) relative to the mass of component (A). An addition-curable liquid silicone rubber composition comprising:

2. The addition-curable liquid silicone rubber composition according to claim 1, further comprising (E) 1 to 200 parts by mass of an organopolysiloxane having an average degree of polymerization of 2,000 or more and in a raw rubber state at 25° C., per 100 parts by mass of component (A).

3. The addition-curable liquid silicone rubber composition according to claim 1 or 2, further comprising 1 to 200 parts by mass, per 100 parts by mass of component (A), of (F) an organopolysiloxane which has an average degree of polymerization of 500 or less, is liquid at 25°C, and contains no addition-reactive substituents.

4. The addition-curable liquid silicone rubber composition according to any one of claims 1 to 3, wherein component (B-2) is a linear organohydrogenpolysiloxane.

5. A cured product of the addition-curable liquid silicone rubber composition according to any one of claims 1 to 4.

6. A silicone rubber molded article comprising the cured product according to claim 5.

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