Liquid silicone rubber composition

Abstract

Provided is a liquid silicone rubber composition containing (A) a liquid organopolysiloxane having two or more alkenyl groups that bond with silicon atoms per molecule, (B) a filler having an average particle size of 0.1-300 μm, (C) a 3-glycidyloxypropylsilanol oligomer represented by formula (1) (in the formula, R1 is a monovalent hydrocarbon group, R2 is a monovalent hydrocarbon group optionally substituted by a glycidyloxy group, R3 is a monovalent aliphatic hydrocarbon group, a, b, c, and d are numbers that satisfy a≥0.5, b≥0, c≥0, d≥0, a+b+c+d=1, x and y are numbers that satisfy x≥1.0, y≤0.5.), and (D) a curing agent.

Description

Liquid silicone rubber composition

[0001] The present invention relates to a liquid silicone rubber composition.

[0002] Various methods can be used to impart thixotropy to a liquid silicone rubber composition, and Patent Document 1 proposes a method of adding surface-treated silica fine powder. However, with this method, the surface-treated silica fine powder acts as reinforcing silica for the silicone rubber, which generally results in an increase in the hardness of the silicone rubber and a deterioration in rebound resilience and compression set.

[0003] Furthermore, Patent Document 2 proposes a method of adding a silane coupling agent containing an alkoxysilyl group, an epoxy group, an acid anhydride group, a peroxysilyl group, or the like. However, with this method, there is a risk that the silane coupling agent will volatilize during storage, resulting in a decrease in the active ingredient, or that it will be hydrolyzed by moisture to generate alcohol, etc. Therefore, there is a concern that foaming or pinholes will occur when the silicone composition is heat-cured, and a drying process or the like before use may be required.

[0004] Furthermore, Patent Document 3 proposes a method of adding an organosilane or organopolysiloxane having one or two silanol groups per molecule for the purpose of controlling the thixotropy (storage stability) of a liquid silicone rubber composition. However, organosilanes and organopolysiloxanes containing silanol groups may also generate volatile organic compounds (VOCs), similar to silane coupling agents, depending on the molecular weight. Furthermore, the silanol groups may cause a deterioration in the elasticity and hardness of the silicone rubber molded product after crosslinking, making it difficult to achieve both thixotropy and rubber physical properties.

[0005] As mentioned above, there have been no examples of proactive proposals for low-VOC thixotropy-imparting technology that allows for free control of thixotropy without adversely affecting the physical properties of silicone rubber after curing. Furthermore, in recent years, the trend toward reducing environmental impact has led to demand for low-VOC materials, and materials that generate less volatile additives and solvents are also in demand.

[0006] JP 9-316339, JP 6-306290, JP 2016-145301

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide a liquid silicone rubber composition that has excellent storage stability, is imparted with thixotropy without increasing the VOC content, and does not deteriorate the hardness or compression set of the cured product.

[0008] As a result of extensive research conducted by the present inventors to solve the above problems, they discovered that by adding a specific 3-glycidyloxypropylsilanol oligomer to a liquid silicone rubber composition, it is possible to obtain a liquid silicone rubber composition that exhibits excellent storage stability and does not change over time, and that does not increase the VOC content; and it is also possible to impart thixotropy to the cured product without deteriorating its hardness or compression set, which led to the present invention.

[0009] That is, the present invention provides the following liquid silicone rubber composition: 1. (A) a liquid organopolysiloxane containing two or more silicon-bonded alkenyl groups per molecule, (B) a filler having an average particle size of 0.1 to 300 μm, and (C) a 3-glycidyloxypropylsilanol oligomer represented by the following formula (1): (In the formula, R 1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, and R 2 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms which may be substituted with a glycidyloxy group, and R 3 is a monovalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, a, b, c, and d are numbers that satisfy a≧0.5, b≧0, c≧0, d≧0, a+b+c+d=1, and x and y are numbers that satisfy x≧1.0, y≦0.5.) (D) a curing agent: a curing effective amount. 2. The liquid silicone rubber composition according to 1, wherein the filler of component (B) is an inorganic filler. 3. The liquid silicone rubber composition according to 1 or 2, wherein component (C) has a weight average molecular weight of 500 to 10,000. 4. The liquid silicone rubber composition according to any one of 1 to 3, wherein in formula (1), b, c, and d are numbers that satisfy b=0, 0≦c≦0.5, and 0≦d≦0.2.

[0010] Liquid silicone rubber compositions containing the 3-glycidyloxypropylsilanol oligomer of the present invention can exhibit thixotropy after curing without deterioration in hardness or compression set. Furthermore, the liquid silicone rubber composition of the present invention can provide a cured liquid silicone rubber that is easy to handle and in which the filler and silicone oil are less likely to separate, without increasing the VOC content.

[0011] The 3-glycidyloxypropylsilanol oligomer (C) used in the present invention synthesized in Synthesis Example 1 1 1 is a H-NMR spectrum chart.

[0012] The present invention is described in detail below, but is not limited thereto. (1) Liquid Silicone Rubber Composition The liquid silicone rubber composition of the present invention contains the following components (A) to (D): (A) a liquid organopolysiloxane containing two or more silicon-bonded alkenyl groups per molecule; (B) a filler having an average particle size of 0.1 to 300 μm; and (C) a 3-glycidyloxypropylsilanol oligomer represented by the following formula (1): (D) Curing agent

[0013] [Component (A)] Component (A) is a liquid organopolysiloxane (particularly liquid at 25°C) that contains two or more silicon-bonded alkenyl groups per molecule.

[0014] The molecular structure of component (A) can be, for example, linear, cyclic, branched, or three-dimensional network (resinous), but is preferably a linear diorganopolysiloxane whose main chain is basically composed of repeating diorganosiloxane units and whose molecular chain ends are blocked with triorganosiloxy groups.When the molecular structure of the organopolysiloxane of component (A) is linear or branched, the position of the silicon atom to which the alkenyl group is bonded in the organopolysiloxane molecule may be either or both of the molecular chain end (i.e., triorganosiloxy group) and the molecular chain middle (i.e., bifunctional diorganosiloxane unit or trifunctional monoorganosilsesquioxane unit located at non-terminal positions of the molecular chain).Particularly preferred as component (A) is a linear diorganopolysiloxane containing alkenyl groups bonded to silicon atoms at both molecular chain ends.

[0015] The alkenyl group bonded to a silicon atom in component (A) typically contains 2 to 8 carbon atoms, and preferably 2 to 6 carbon atoms. Specific examples include vinyl, allyl, butenyl, pentenyl, hexenyl, cyclohexenyl, and heptenyl groups, with vinyl being preferred.

[0016] The content of silicon-bonded alkenyl groups in component (A) is preferably 0.001 to 2 mol / 100 g, more preferably 0.001 to 0.5 mol / 100 g, and even more preferably 0.001 to 0.1 mol / 100 g, based on the total number of silicon-bonded substituents.

[0017] As a substituent bonded to a silicon atom in component (A) other than an alkenyl group, a monovalent hydrocarbon group is preferred. There are no particular limitations on the monovalent hydrocarbon group, but examples include monovalent hydrocarbon groups having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms. The monovalent hydrocarbon group may be linear, branched, or cyclic, and specific examples include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, and heptyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; and aralkyl groups such as benzyl and phenethyl. Of these, a methyl group is particularly preferred.

[0018] The viscosity of component (A) at 25°C is 50 to 500,000 mPa·s, preferably 100 to 200,000 mPa·s, and more preferably 100 to 100,000 mPa·s. When the viscosity is within this range, the resulting silicone rubber composition is easy to handle and work with, and the resulting cured product of the silicone rubber composition exhibits good mechanical properties. In this specification, viscosity refers to the value measured at 25°C using a rotational viscometer according to the method described in JIS K 7117-1:1999.

[0019] Specific examples of organopolysiloxanes of component (A) include dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, methylvinylpolysiloxanes capped at both molecular chain terminals with trimethylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, dimethylpolysiloxanes capped at both molecular chain terminals with dimethylvinylsiloxy groups, methylvinylpolysiloxanes capped at both molecular chain terminals with dimethylvinylsiloxy groups, and dimethylsiloxane-methylvinylpolysiloxanes capped at both molecular chain terminals with dimethylvinylsiloxy groups. and mixtures of two or more of these organopolysiloxanes.

[0020] The organopolysiloxane of component (A) may be used alone or in combination of two or more. Of these, a dimethylsiloxane-methylvinylsiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups is preferred as component (A). Furthermore, two or more types may be used in combination, as this makes it easier to adjust the viscosity of the composition of the present invention to a preferred range.

[0021] [Component (B)] Component (B) is a filler used to impart functions such as improved thermal conductivity and strength, and color appearance adjustment to the silicone rubber composition of the present invention. Its average primary particle size is 0.1 to 300 μm, preferably 0.5 to 300 μm, more preferably 0.5 to 200 μm, even more preferably 0.5 to 100 μm, and particularly preferably 1 to 10 μm. Particles with an average primary particle size of 0.1 μm or greater are easy to manufacture, have good dispersibility in silicone polymers (e.g., the alkenyl-group-containing organopolysiloxane of component (A), the base polymer), facilitate primary particle dispersion, and are easily compounded in large quantities. Particles exceeding 300 μm will impair the mechanical strength of the cured rubber. In the present invention, the average primary particle size can be determined as the cumulative weight average value D50 (or median size) using a particle size distribution analyzer using laser diffraction or other methods.

[0022] The filler used in the present invention is not particularly limited as long as it has the above-mentioned average particle diameter, and examples thereof include inorganic fillers and organic resin fillers. Specific examples of inorganic fillers include powders of calcium silicate, titanium dioxide, ferric oxide, diatomaceous earth, calcium carbonate, crystalline silica (quartz), aluminum hydroxide, metallic silicon, alumina, aluminum, silicon carbide, silicon nitride, magnesium oxide, magnesium carbonate, zinc oxide, and aluminum nitride. Specific examples of organic resin fillers include silicone powders such as silicone resin powder, silicone rubber powder, and silicone composite powder; hollow fillers formed by polymerizing a monomer selected from vinylidene chloride, acrylonitrile, methacrylonitrile, acrylic acid esters, and methacrylic acid esters, or copolymerizing two or more of these monomers, and encapsulating a volatile substance or a low-boiling substance in an organic resin shell, and organic resin balloons such as hollow fillers with inorganic fillers or the like attached to their surfaces; organic resin particles formed by polymerizing a monomer selected from vinylidene chloride, acrylonitrile, methacrylonitrile, acrylic acid esters, and methacrylic acid esters, or copolymerizing two or more of these monomers.Among these, inorganic fillers are preferred, more preferably diatomaceous earth, crystalline silica (quartz) powder, metallic silicon, silicon carbide, alumina, and zinc oxide powder, and even more preferably crystalline silica (quartz) powder.

[0023] Furthermore, the filler of component (B) may be surface-treated with a surface treatment agent such as a silane coupling agent or a partial hydrolyzate thereof, an alkylalkoxysilane or a partial hydrolyzate thereof, an organic silazanes, a titanate coupling agent, an organopolysiloxane oil, or an organopolysiloxane containing a hydrolyzable functional group, for the purpose of improving the thermal stability of the silicone rubber composition or the compoundability of the filler, as long as the effects of the present invention are not impaired. Such treatment may be carried out by pretreating the filler itself, or by carrying out the surface treatment under heating when components (A) and (B) are mixed.

[0024] The amount of filler (B) blended is preferably 1 to 500 parts by mass, more preferably 5 to 400 parts by mass, even more preferably 10 to 300 parts by mass, and particularly preferably 10 to 100 parts by mass, per 100 parts by mass of component (A). If it is less than 1 part by mass, the physical strength of the silicone rubber may decrease, and if it exceeds 500 parts by mass, the fluidity of the material may be impaired. Note that component (B) may be used alone or in combination of two or more types.

[0025] [Component (C)] In the present invention, 3-glycidyloxypropylsilanol oligomer represented by the following formula (1) is used as component (C). This component (C) can impart thixotropy to the composition without deteriorating the hardness and compression set of the cured product, and can provide a liquid silicone rubber composition in which the filler and silicone oil are resistant to separation without increasing the VOC content.

[0026]

[0027] In the above formula, R 1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms. 1 The monovalent hydrocarbon group may be linear, branched, or cyclic, and specific examples thereof include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, and decyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; alkenyl groups such as vinyl and allyl groups; and aryl groups such as phenyl and naphthyl groups. Among these, methyl, ethyl, propyl, and phenyl groups are preferred, methyl and ethyl groups are more preferred, and methyl groups are even more preferred.

[0028] R 2 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms, which may be substituted with a glycidyloxy group. 2 The monovalent hydrocarbon group may be linear, branched, or cyclic, and specific examples thereof include the above-mentioned R 1and glycidyloxy-substituted alkyl groups such as glycidyloxypropyl and glycidyloxyoctyl groups. 2 is a monovalent hydrocarbon group substituted with a glycidyloxy group, the number of carbon atoms does not include the number of carbon atoms of the glycidyloxy group. Among these, methyl, ethyl, propyl, glycidyloxypropyl, and phenyl groups are preferred, methyl and ethyl groups are more preferred, and methyl group is even more preferred.

[0029] R 3 R is a monovalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and more preferably a monovalent saturated or unsaturated aliphatic hydrocarbon group having 1 to 4 carbon atoms. 3 The monovalent aliphatic hydrocarbon group may be linear, branched, or cyclic, and specific examples thereof include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, and decyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; and alkenyl groups such as vinyl and allyl groups. Of these, methyl, ethyl, propyl, and butyl groups are preferred, with methyl and ethyl groups being more preferred, and methyl groups being even more preferred.

[0030] a, b, c, and d represent the molar ratios of the respective siloxane units present, and are numbers that satisfy a≧0.5, b≧0, c≧0, d≧0, and a+b+c+d=1. a is preferably a number that satisfies 0.5≦a≦1. If a is less than 0.5, the amount of available epoxy groups will be reduced, and the intended effects will not be achieved. In addition, the resulting silanol oligomer will become highly viscous, gummy, or solid, making handling difficult. b is preferably a number that satisfies 0≦b<0.5, and more preferably 0. c is preferably a number that satisfies 0≦c≦0.5. d is preferably a number that satisfies 0≦d≦0.2, and more preferably 0.

[0031] x and y are the numbers of hydroxyl groups or alkoxyl groups bonded to 1 mole of silicon atoms in the siloxane units a to d, and are numbers that satisfy x≧1.0 and y≦0.5. x is preferably a number that satisfies 1≦x≦2. y is preferably a number that satisfies y≦0.4, and more preferably a number that satisfies y≦0.3.

[0032] The component (C) is preferably one represented by the following formula (1a).

[0033] In the above formula, R 2 and R 3 are the same as above, a1, c1, and d1 are numbers that satisfy a1≧0.5, 0≦c1≦0.5, 0≦d1≦0.2, and a1+c1+d1=1, and x1 and y1 are numbers that satisfy x1≧1.0 and y1≦0.5. The component (C) may be used singly or in combination of two or more types.

[0034] The weight-average molecular weight of the oligomer of component (C) is preferably 500 to 10,000, and more preferably 500 to 1,000, from the viewpoint of the handling viscosity of the composition of the present invention. The weight-average molecular weight in the present invention is a value determined by gel permeation chromatography (GPC) measured under the conditions shown below, converted using polystyrene of known molecular weight as the standard substance. If the weight-average molecular weight is 500 or more, the high boiling point eliminates concerns about loss of active ingredient due to volatilization during storage, or foaming or pinhole formation when the silicone composition is heat-cured, and therefore eliminates the need for a drying step before use.

[0035] [Measurement conditions] Apparatus: HLC-8320GPC manufactured by Tosoh Corporation Developing solvent: tetrahydrofuran (THF) Flow rate: 0.6 mL / min Detector: differential refractive index detector (RI) Column: TSK Guard column Super H-H TSKgel Super HM-N (6.0 mm I.D. × 15 cm × 1) TSKgel Super H2500 (6.0 mm I.D. × 15 cm × 1) (all manufactured by Tosoh Corporation) Column temperature: 40°C Sample injection volume: 50 μL (THF solution with a concentration of 2.0% by mass) Standard: monodisperse polystyrene

[0036] The method for producing the component (C) used in the present invention is not particularly limited, but it can be produced, for example, by using a 3-glycidyloxypropyl group-containing silane compound such as 3-glycidyloxypropyltrimethoxysilane or 3-glycidyloxypropyltriethoxysilane represented by the following formula (i) or a mixture thereof as the essential silane monomer raw material, and, if necessary, (co)hydrolyzing under acidic conditions a silane monomer containing one or more of a silane compound represented by the following formula (ii), a silane compound represented by the following formula (iii), and a silane compound represented by the following formula (iv):

[0037] (In the formula, R 1 ~R 3 is the same as above.)

[0038] Specific examples of the 3-glycidyloxypropyl group-containing silane compound represented by the above formula (i) include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyltripropoxysilane, 3-glycidyloxypropyltributoxysilane, etc. Specific examples of the silane compound represented by the above formula (ii) include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, and decyltriethoxysilane. Specific examples of silane compounds represented by formula (iii) include dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, methylethyldimethoxysilane, methylethyldiethoxysilane, methylpropyldimethoxysilane, methylpropyldiethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane, cyclopentylmethyldimethoxysilane, cyclohexylmethyldimethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, and methyloctyldimethoxysilane. Specific examples of silane compounds represented by formula (iv) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. Hydrolysis and condensation products of these compounds can also be used. These compounds may be used alone or in combination of two or more.

[0039] The amount of these silane monomers used is preferably adjusted according to the molar ratio of each siloxane unit constituting the desired organopolysiloxane (the values ​​of a to d in formula (1)).

[0040] The amount of water used in the hydrolysis condensation reaction is determined by the amount of Si(OR) of the alkoxysilyl group of the silane monomer used as the raw material. 3 ) group (R 3 is the same as above.) is preferably used in an amount of 0.8 to 1.1 times by mole per 1 mole of the compound.

[0041] The acid component used to adjust the acidic conditions during the hydrolysis reaction is not particularly limited as long as it is a commercially available Brønsted acid, but from the viewpoint of ease of availability, formic acid, acetic acid, citric acid, hydrochloric acid, and nitric acid are preferred. The amount of acid used is preferably 0.0001 to 0.01 moles per mole of silane monomer, from the viewpoint of suppressing an increase in the molecular weight of the organopolysiloxane obtained by an excessive dehydration condensation reaction between silanols and a decrease in water solubility due to a decrease in the amount of silanol groups.

[0042] In the hydrolysis reaction, an organic solvent may be used, if necessary, to the extent that it does not inhibit the reaction. The organic solvent used is preferably one that is compatible with water, which is the reaction raw material, and alcohols, esters, ketones, ethers, etc. are preferred. Furthermore, taking into consideration the distillation conditions for removing the generated alcohol, the organic solvent preferably has a low boiling point, and a solvent having a boiling point of 150°C or less under atmospheric pressure is desirable. Specific examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentyl alcohol, neopentyl alcohol, hexyl alcohol, cyclohexyl alcohol, etc. Specific examples of esters include ethyl acetate and butyl acetate. Specific examples of ketones include acetone, methyl ethyl ketone, cyclohexanone, etc. Specific examples of ethers include tetrahydrofuran, tetrahydropyran, dioxane, etc.

[0043] As reaction conditions, it is preferred to mix the silane monomer with water and stir the mixture at 55 to 70°C for 1 to 5 hours to allow the hydrolysis and condensation reaction of the silane monomer to proceed, and then distill off the water / alcohol mixture under reduced pressure at a temperature in the range of 30 to 80°C.

[0044] The 3-glycidyloxypropylsilanol oligomer used in the present invention preferably has a water and free alcohol content of 1% by mass or less. Such a composition allows the substance to be free of volatile organic compounds (VOCs), which is advantageous for reducing the VOCs of the entire silicone composition to which it is added. In the present invention, "VOC-free" means that the free alcohol content in the oligomer or the composition of the present invention is preferably 1% by mass or less. Here, alcohol refers specifically to methanol or ethanol. Furthermore, while water does not fall under the category of VOCs, if present in excess, it can react with epoxy groups, so it is desirable to minimize its inclusion. A content of 1% by mass or less is unlikely to result in a decrease in the active ingredient due to volatilization during storage, or in the generation of alcohols due to hydrolysis by moisture in the silicone composition or moisture in the air. This eliminates concerns about foaming or pinhole formation during heat curing of the silicone composition, and obviates the need for a drying process before use.

[0045] The amount of component (C) added is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 2.0 parts by mass, and even more preferably 0.5 to 1.7 parts by mass, per 100 parts by mass of component (A). If the amount of component (C) added is less than 0.01 part by mass, it may not contribute to imparting the desired thixotropy, while if it exceeds 10 parts by mass, the mechanical properties such as tensile strength of the cured silicone rubber may be reduced.

[0046] [Component (D)] Component (D) is a curing agent. There are no particular limitations on the curing agent as long as it can cure component (A). Generally, a curing agent known as a rubber curing agent can be used, and examples thereof include the following components (D1) and (D2). (D1) An addition reaction (hydrosilylation reaction) type curing agent, i.e., a hydrosilylation reaction curing agent consisting of a combination of an organohydrogenpolysiloxane (crosslinking agent) and a hydrosilylation catalyst. (D2) An organic peroxide. Each of these is described in detail below.

[0047] [(D1) Addition Reaction Curing Agent] (D11) Organohydrogenpolysiloxane The organohydrogenpolysiloxane used as the crosslinking agent for the addition reaction curing agent (D1) is preferably one having two or more hydrosilyl groups per molecule, and is particularly preferably an organohydrogenpolysiloxane represented by the following formula (2):

[0048]

[0049] Here, R 4 are each independently a hydrogen atom, and a group selected from an alkyl group having 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms; a cycloalkyl group having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms; an aryl group having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms; and an aralkyl group having 7 to 10 carbon atoms, preferably 7 to 9 carbon atoms. However, there may be two or more, preferably 2 to 200, more preferably 2 to 130 R groups in one molecule. 4 is a hydrogen atom.

[0050] R 4 The alkyl group may be linear or branched, and specific examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl groups. Specific examples of cycloalkyl groups include cyclopentyl and cyclohexyl groups. Specific examples of aryl groups include phenyl and tolyl groups. Specific examples of aralkyl groups include benzyl and 2-phenylpropyl groups. Fluoroalkyl groups in which some or all of the hydrogen atoms in these groups have been substituted with halogen atoms such as fluorine atoms may also be used.

[0051] e is an integer that satisfies 2≦e≦30, preferably 2≦e≦20. f is an integer that satisfies 0≦f≦300, preferably 3≦f≦200. g is an integer that satisfies 0≦g≦10, preferably 0≦g≦5. h is an integer that satisfies 0≦h≦30, preferably 0≦h≦20.

[0052] The molecular structure of the organohydrogenpolysiloxane may be linear, cyclic, branched, or three-dimensional network. In this case, the number of silicon atoms (or degree of polymerization) per molecule is preferably 2 to 300, more preferably 4 to 200, and a liquid at 25°C is preferably used. The hydrosilyl groups may be located at either the molecular chain terminals or side chains (in the middle of the molecular chain), or may be located at both. The method for measuring the degree of polymerization is as explained for component (C).

[0053] The organohydrogenpolysiloxanes may be used alone or in combination of two or more.

[0054] Specific examples of such organohydrogenpolysiloxanes include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, methylhydrogenpolysiloxanes blocked at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers blocked at both ends with trimethylsiloxy groups, dimethylpolysiloxanes blocked at both ends with dimethylhydrogensiloxy groups, and copolymers of dimethylsiloxanes blocked at both ends with dimethylhydrogensiloxy groups. Methylhydrogensiloxy group-blocked dimethylsiloxane-methylhydrogensiloxane copolymer, both-end trimethylsiloxy group-blocked methylhydrogensiloxane-diphenylsiloxane copolymer, both-end trimethylsiloxy group-blocked methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane-dimethylsiloxane copolymer, cyclic methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer, (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 a copolymer consisting of (CH3)2HSiO units, 1 / 2 Units and SiO 4 / 2 Units and (C6H5)SiO 3 / 2 and copolymers consisting of units, and the above-mentioned exemplary compounds in which some or all of the methyl groups have been substituted with other alkyl groups such as ethyl groups or propyl groups, or aryl groups such as phenyl groups. Specific examples of such organohydrogenpolysiloxanes include compounds of the following structural formula:

[0055] (In the formula, k is an integer of 2 to 10, and s and t are each independently an integer of 0 to 60, preferably 0 to 20, and more preferably 0 to 10.)

[0056] The organohydrogenpolysiloxane preferably has a viscosity at 25°C of 0.5 to 10,000 mPa·s, and more preferably 1 to 300 mPa·s.

[0057] The organohydrogenpolysiloxane is desirably blended in an amount such that the molar ratio of hydrogen atoms bonded to silicon atoms in the organohydrogenpolysiloxane (i.e., hydrosilyl groups) to alkenyl groups bonded to silicon atoms in component (A) (hydrosilyl groups / alkenyl groups) is preferably 0.5 to 10, more preferably 0.6 to 6, and even more preferably 0.7 to 5. If the ratio is less than 0.5, crosslinking may be insufficient and sufficient mechanical strength may not be obtained, while if the ratio exceeds 10, the physical properties after curing may be reduced, and in particular, heat resistance and compression set resistance may be significantly deteriorated.

[0058] (D12) Hydrosilylation catalyst The hydrosilylation catalyst used in the (D1) addition reaction curing agent is a catalyst that promotes the addition reaction between the alkenyl groups in the (A) component and the hydrosilyl groups in the organohydrogenpolysiloxane used as a crosslinking agent. Examples of hydrosilylation catalysts include platinum group metal catalysts such as ruthenium and platinum. Platinum group metal catalysts include these platinum group metals and their compounds. Any catalyst that has been known as a catalyst for addition reaction curing silicone rubber compositions can be used. Specific examples thereof include fine particle platinum metal platinic chloride adsorbed on a carrier such as platinum black, silica, alumina or silica gel, chloroplatinic acid, reaction products of chloroplatinic acid with monohydric alcohols, complexes of chloroplatinic acid with olefins, complexes of chloroplatinic acid with vinyl group-containing (poly)siloxanes, complexes of chloroplatinic acid with phosphite esters, and complexes of these with vinyl group-containing (poly)siloxanes; palladium catalysts; rhodium catalysts; ruthenium catalysts, etc. Among these, platinum or platinum compounds are particularly preferred.

[0059] The amount of hydrosilylation catalyst added may be any amount that is sufficient to promote the addition reaction, i.e., a catalytic amount, and is usually preferably 1 ppm to 1 mass %, and more preferably 10 to 500 ppm, calculated as the mass of platinum group metal relative to the mass of component (A). If the amount added is less than 1 ppm, the addition reaction may not be sufficiently promoted, resulting in insufficient curing. On the other hand, if the amount added exceeds 1 mass %, the effect on reactivity is minimal, and adding more than this amount may be uneconomical.

[0060] In addition to the above catalysts, an addition crosslinking inhibitor may be used to adjust the curing rate, specific examples of which include ethynylcyclohexanol and tetramethyltetravinylcyclotetrasiloxane.

[0061] [(D2) Organic Peroxide] On the other hand, examples of the (D2) organic peroxide include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, di-t-butyl peroxide, t-butyl perbenzoate, and 1,6-hexanediol-bis-t-butylperoxycarbonate.

[0062] The amount of organic peroxide added is an effective curing amount, preferably 0.1 to 15 parts by mass, more preferably 0.2 to 10 parts by mass, per 100 parts by mass of component (A). If the amount added is sufficient, the crosslinking reaction proceeds sufficiently, and deterioration of physical properties such as reduced hardness, insufficient rubber strength, and increased compression set does not occur. Furthermore, if the amount added does not exceed the above amount, it is economically preferable, and the amount of decomposition products of the curing agent is sufficiently small, preventing deterioration of physical properties such as increased compression set and increased discoloration of the resulting sheet.

[0063] The curing agent can be either component (D1) or (D2), but in the present invention, it is preferable to use an addition reaction type curing agent of component (D1).

[0064] [Other Components] Other components can be added to the silicone rubber composition of the present invention as long as the effects of the present invention are not impaired. For example, the addition of an inorganic filler other than the above-mentioned component (B) to the silicone rubber composition of the present invention is optional, and a reinforcing silica fine powder can be added.

[0065] The reinforcing silica fine powder should have a specific surface area of ​​10 m2 as measured by the BET adsorption method in order to obtain a silicone rubber composition with excellent mechanical strength. 2 / g or more is preferable, and 50 to 400m 2 / g is more preferable, and 50 to 200m 2 / g is more preferable. Examples of reinforcing silica fine powder include fumed silica (dry silica) and precipitated silica (wet silica), and among these, fumed silica (dry silica) is preferred.

[0066] Commercially available examples of usable reinforcing silica fine powders include Aerosil (registered trademark) 130, 150, 200, and 300 manufactured by Nippon Aerosil Co., Ltd.; Reolosil (registered trademark) QS-102 and QS-30 manufactured by Tokuyama Corporation; CAB-O-SIL (registered trademark) H-300 manufactured by CABOT Corporation; and Nipsil (registered trademark) LP manufactured by Tosoh Silica Corporation. Furthermore, the surfaces of these powders may be hydrophobized with a treating agent such as organopolysiloxane, organopolysilazane, chlorosilane, or alkoxysilane. These silica fine powders may be used alone or in combination of two or more. Regarding the hydrophobization treatment, the reinforcing silica fine powder may be treated with the hydrophobizing agent while being blended, or commercially available hydrophobized reinforcing silica fine powder may be used.

[0067] From the viewpoint of improving compression set and further suppressing filler separation and sedimentation, it is desirable to add a small amount of the reinforcing silica fine powder to the silicone rubber composition. To achieve better suppression of filler separation and sedimentation and compression set while incorporating the reinforcing silica fine powder, the amount is preferably 0 to 10 parts by mass per 100 parts by mass of the organopolysiloxane (A) of the silicone rubber composition. When incorporating the reinforcing silica fine powder, the lower limit of the amount can be set to 0.1 parts by mass or more, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass. Furthermore, incorporating the reinforcing silica fine powder is preferable because it improves thixotropy through a synergistic effect compared to using component (C) alone. In addition, while the use of the reinforcing silica fine powder in combination with component (C) may be less effective in improving compression set due to an increase in the amount of the reinforcing silica fine powder, it is preferable because it further improves the phenomenon of a decrease in viscosity from the initial viscosity upon re-stirring, preventing the viscosity from further decreasing from the initial viscosity upon re-stirring.

[0068] Furthermore, if necessary, the liquid silicone rubber composition of the present invention may optionally further contain hydrosilylation reaction inhibitors such as nitrogen-containing compounds, acetylene compounds, phosphorus compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds, and sulfur compounds, various additives, flame retardants such as iron oxides and halogen compounds, and heat resistance agents.

[0069] (2) Preparation of Liquid Silicone Rubber Composition and Molding Thereof The method for producing the liquid silicone rubber composition of the present invention is not particularly limited, and it can be prepared by uniformly mixing the above components (A) to (D) and, if necessary, other components (reinforcing silica fine powder and various other additives) using a conventional mixer / stirrer, kneader, etc. The form of the composition is also not particularly limited, and it may be a one-component type or a two-component type.

[0070] A one-component composition can be obtained, for example, by placing components (A) to (D) and, if necessary, other components (reinforcing silica fine powder and various other additives) in a Gate Mixer (trade name: Planetary Mixer, manufactured by Inoue Seisakusho Co., Ltd.) and mixing them at 20 to 50°C for 10 minutes to 1 hour.

[0071] On the other hand, two-component compositions can be composed of any combination as long as components (A) and (D) do not coexist. For example, when an addition reaction curing agent (D1) is used as the curing agent, components (A), (B), and (C) are placed in a gate mixer and mixed at a predetermined temperature for a predetermined time. Then, a hydrosilylation catalyst (D12) is added and mixed, resulting in a composition designated as component A. Next, components (A), (B), and (C) are placed in a gate mixer and mixed at a predetermined temperature for a predetermined time. Then, a reaction inhibitor is added and mixed, and then an organohydrogenpolysiloxane (D11) is added and mixed, resulting in a composition designated as component B. This allows for a two-component composition consisting of components A and B to be obtained.

[0072] Methods for molding the silicone rubber composition of the present invention include, for example, cast molding, injection molding, and coating, and suitable curing conditions include, for example, press curing for 10 seconds to 1 hour at a temperature of 100 to 300° C. Furthermore, for purposes such as reducing the amount of low-molecular-weight siloxane components, a post-cure (secondary cure) of approximately 30 minutes to 70 hours may be carried out after molding in an oven at 120 to 250° C.

[0073] The present invention will be specifically explained below using synthesis examples, examples, and comparative examples, but the present invention is not limited thereto. In the following examples, "parts" means "parts by mass" unless otherwise specified. The devices and measurement methods used in the examples are as follows.

[0074] (1) GPC Measurement Conditions (Measurement of Weight-Average Molecular Weight) Apparatus: HLC-8320GPC manufactured by Tosoh Corporation Developing solvent: tetrahydrofuran (THF) Flow rate: 0.6 mL / min Detector: Differential refractive index detector (RI) Column: TSK Guard column Super H-H TSKgel Super HM-N (6.0 mm I.D. × 15 cm × 1) TSKgel Super H2500 (6.0 mm I.D. × 15 cm × 1) (all manufactured by Tosoh Corporation) Column temperature: 40°C Sample injection volume: 50 μL (THF solution with a concentration of 2.0% by mass) Standard: Monodisperse polystyrene (2) Proton nuclear magnetic resonance spectrum ( 1 H-NMR spectrum) Measurement conditions: Apparatus: BURKER AVANCE III 400 Solvent: CDCl3 (deuterated chloroform) Internal standard: tetramethylsilane (TMS) (3) Viscosity: Measured at 25°C using a rotational viscometer according to the method described in JIS K7117-1: 1999. (4) Kinematic viscosity: Measured using a Canon-Fenske viscometer according to the method described in JIS Z8803: 2011.

[0075] (5) Measurement of physical properties of silicone rubber composition: The liquid silicone rubber compositions obtained in Examples 1 to 7 and Comparative Examples 1 to 7 described below were stored at 23°C for 7 days after preparation, and then measured for shear viscosity at 25°C and a shear rate of 0.9 s using a HAAKE MARS40 Rheometer (manufactured by Thermo Fisher Scientific). -1 , and 10s -1 The viscosity was measured at 100°C, and the results are shown in Table 1.

[0076] (6) Measurement of physical properties of cured silicone rubber: The liquid silicone rubber compositions obtained in Examples 1 to 7 and Comparative Examples 1 to 7 described below were press-cured at 120°C for 10 minutes immediately after preparation to form silicone rubber sheets, which were then post-cured at 200°C for 4 hours to prepare 2 mm thick and 6 mm thick test sheets, as well as cylindrical rubber molded articles measuring 12.5 mm thick and 29 mm in diameter. The density and compression set (180°C / 22 hours, 25% compression) of the test sheets and molded articles were measured according to JIS K6249:2003. Additionally, the Asker C hardness was measured according to JIS S 6050:2008. The results are shown in Table 1.

[0077] [1] Synthesis of Water-Soluble 3-Glycidyloxypropylsilanol Oligomer [Synthesis Example 1] Synthesis of Component (C-1) 472 g (2.0 mol) of 3-glycidyloxypropyltrimethoxysilane was placed in a 1 L three-neck flask equipped with a stirrer, a condenser, a dropping funnel, and a thermometer. 108 g of 0.2 mass % hydrochloric acid (6.0 mol as water) was added dropwise to the flask. During the dropwise addition, the temperature was controlled by appropriate cooling so that the internal temperature was in the range of 20 to 40°C. After the dropwise addition, the hydrolysis reaction proceeded and the temperature of the reaction solution rose, but the temperature was controlled by air or water cooling so that the reaction proceeded within the internal temperature range of 20 to 40°C. After the dropwise addition was completed, the mixture was heated and stirred at 70°C for 1 hour to allow the hydrolysis and condensation reaction of the methoxysilyl groups to proceed, and then the alcohol generated by the hydrolysis reaction and excess water were removed by distillation under reduced pressure at 70°C to obtain a colorless, transparent liquid (3-glycidyloxypropylsilanol oligomer). This liquid was compatible and soluble in water as desired, and had a kinematic viscosity of 726 mmHg at 25°C. 2The oligomer had a functional group content of 189 g / mol and a weight average molecular weight of 830. 1 Analysis by H-NMR, GPC, etc. revealed that this product had the average composition structure shown in formula (3) below. 1 The H-NMR spectrum chart is shown in FIG.

[0078]

[0079] Synthesis Example 2 Synthesis of Component (C-2) The target 3-glycidyloxypropyl group-containing silanol oligomer was obtained in the same manner as in Synthesis Example 1, except that 425 g (1.8 mol) of 3-glycidyloxypropyltrimethoxysilane, 24 g (0.2 mol) of dimethyldimethoxysilane, and 104.4 g (5.8 mol as water) of 0.2 mass% hydrochloric acid were used. The kinematic viscosity of the resulting oligomer at 25°C was 429 mm 2 The epoxy functional group content was 202 g / mol and the weight average molecular weight was 610. 1 Analysis by H-NMR and GPC measurements revealed that this product had the structure shown in formula (4) below.

[0080]

[0081] Synthesis Example 3 Synthesis of Component (C-3) The target 3-glycidyloxypropyl group-containing silanol oligomer was obtained in the same manner as in Synthesis Example 1, except that 236 g (1.0 mol) of 3-glycidyloxypropyltrimethoxysilane, 120 g (1.0 mol) of dimethyldimethoxysilane, and 90 g (5.0 mol) of 0.2 mass% hydrochloric acid were used. The kinematic viscosity of the resulting oligomer at 25°C was 218 mm 2 The epoxy functional group content was 258 g / mol and the weight average molecular weight was 700. 1 Analysis by H-NMR and GPC measurements revealed that this product had the structure shown in formula (5) below.

[0082]

[0083] Synthesis Example 4 Synthesis of Component (C-4) The target 3-glycidyloxypropyl group-containing silanol oligomer was obtained in the same manner as in Synthesis Example 1, except that 425 g (1.8 mol) of 3-glycidyloxypropyltrimethoxysilane, 44 g (0.2 mol) of 3-glycidyloxypropylmethyldimethoxysilane, and 104.4 g (5.8 mol as water) of 0.2 mass% hydrochloric acid were used. The kinematic viscosity of the resulting oligomer at 25°C was 361 mm 2 The epoxy functional group content was 200 g / mol and the weight average molecular weight was 510. 1 Analysis by H-NMR and GPC measurements revealed that this product had the structure shown in formula (6) below.

[0084]

[0085] [2] Production of silicone rubber composition, production of cured product and evaluation 1 [Example 1] A silicone rubber composition in which both molecular chain ends are capped with trimethylsiloxy groups and the amount of alkenyl groups is 1.0 × 10 -2 100 parts of a dimethylsiloxane-methylvinylsiloxane copolymer (A) terminated at both molecular chain ends with trimethylsiloxy groups and having five vinyl groups in the side chains and a viscosity of 20,000 mPa s, 0.07 parts of 1-ethynylcyclohexanol, 0.13 parts of a dimethylpolysiloxane solution (D12) containing 1% by mass of chloroplatinic acid / 1,3-divinyltetramethyldisiloxane complex in terms of platinum atom content, and a BET specific surface area of ​​110 m 2 / g), 1.4 parts of hydrophobized fumed silica (R-972 manufactured by Nippon Aerosil Co., Ltd.), 50 parts of filler (B) (pulverized crystalline silica powder, average primary particle size 4 μm), 0.78 parts of 3-glycidyloxypropylsilanol oligomer (C-1), dimethylsiloxane-methylhydrogensiloxane copolymer (D11) capped at both ends with dimethylhydrogensiloxy groups and having a viscosity of 11 mPa s, represented by the following formula (7) (content of silicon atom-bonded hydrogen atoms = 3.2 × 10 -1A composition was prepared by blending 1.84 parts of a silicone rubber composition (1.84 parts by weight of dimethylpolysiloxane solution containing 50% by weight of iron oxide) in this order and mixing with a planetary mixer at room temperature (25°C) for 30 minutes. The prepared composition was then press-cured at 120°C for 10 minutes to form a silicone rubber sheet, which was then post-cured at 200°C for 4 hours to obtain a rubber sheet and a rubber molded product. The rubber properties shown in Table 1 were evaluated using the resulting rubber sheet and rubber molded product. The results are also shown in Table 1.

[0086] (wherein the siloxane units may be bonded in blocks or randomly)

[0087] [Examples 2 to 7, Comparative Examples 1 to 7] As shown in Table 1, silicone rubber compositions were prepared by compounding Examples 2 to 7 and Comparative Examples 1 to 7, and rubber sheets and molded rubber articles were produced in the same manner as in Example 1, and various rubber properties were evaluated. The results are also shown in Table 1.

[0088]

[0089] [3] Preparation of Silicone Rubber Composition, Preparation of Cured Product, and Evaluation 2 [Example 4a, Comparative Examples 3a and 4a] (7) Evaluation of Storage Stability of Silicone Rubber Composition 1: Using the same components as in Example 4 and Comparative Examples 3 and 4, each was divided into two liquids so that the platinum catalyst was separated from the reaction inhibitor and hydrogen polysiloxane. Each was sealed and stored at 70°C for 7 days. The two liquids were mixed at the initial stage of preparation (immediately after preparation, no storage) or after storage to prepare the composition of each example, and then press-cured at 120°C for 10 minutes to form a silicone rubber sheet. Subsequently, post-curing was performed for 4 hours at 200°C to prepare a 6 mm thick test sheet and a 12.5 mm thick, 29 mm diameter cylindrical rubber molded product. The compression set (180°C / 22 hours, 25% compression) of the prepared test sheet and molded product was measured according to the description of JIS K6249:2003. In addition, the Asker C hardness according to JIS S 6050:2008 was measured. The results are shown in Table 2.

[0090] [4] Production of silicone rubber composition, production of cured product and evaluation 3 [Example 4b, Comparative Examples 5b and 7b] (8) Evaluation of storage stability 2 of silicone rubber composition: Using the same components as in Example 4 and Comparative Examples 5 and 7, each composition was divided into two parts so that the platinum catalyst was separated from the reaction inhibitor and hydrogen polysiloxane, and each part was sealed and stored for 14 days at 23° C. After that, without mixing the two parts, each part was measured at a shear rate of 0.9 s at 25° C. using a shear viscometer: HAAKE MARS40 Rheometer (manufactured by Thermo Fisher Scientific). -1 , and 10s -1 The viscosity at 25°C was measured. This measurement result is referred to as "initial". Thereafter, the two liquid compositions stored at 23°C for 14 days were mixed for 10 minutes using a planetary mixer, each sealed, and stored at 23°C for 14 days. Thereafter, without mixing the two liquids, each was measured at 25°C and a shear rate of 0.9 s using a shear viscometer: HAAKE MARS40 Rheometer (manufactured by Thermo Fisher Scientific). -1 , and 10s -1 The viscosity at this time was measured. This measurement result is referred to as "after re-stirring." The results are shown in Table 3.

[0091] The compositions used in Evaluation 2 were prepared according to standard methods as follows. In Example 4b, the same components as in Example 4 were used. Agent A was a composition obtained by mixing 100 parts of component (A), 50 parts of component (B), 0.77 parts of component (C), 1.4 parts of fumed silica, 0.25 parts of the hydrosilylation catalyst (D12), and 3 parts of the iron oxide solution. Agent B was a composition obtained by mixing 100 parts of component (A), 50 parts of component (B), 0.80 parts of component (C), 2.1 parts of fumed silica, 0.18 parts of 1-ethynylcyclohexanol, 3 parts of the iron oxide solution, and 2.42 parts of the organohydrogenpolysiloxane (D11). In Comparative Example 5b, the same components as in Comparative Example 5 were used, but the composition obtained by mixing 100 parts of component (A), 48 parts of component (B), 7 parts of fumed silica, 0.25 parts of the hydrosilylation catalyst (D12), and 3 parts of the iron oxide solution was designated as component A. Also, the composition obtained by mixing 97 parts of component (A), 48 parts of component (B), 7 parts of fumed silica, 0.14 parts of 1-ethynylcyclohexanol, 3 parts of the iron oxide solution, and 1.62 parts of the organohydrogenpolysiloxane (D11) was designated as component B. In Comparative Example 7b, the same components as in Comparative Example 7 were used, but the composition obtained by mixing 100 parts of component (A), 50 parts of component (B), 2.18 parts of fumed silica, 0.25 parts of the hydrosilylation catalyst (D12), and 3 parts of the iron oxide solution was designated as component A, and the composition obtained by mixing 100 parts of component (A), 50 parts of component (B), 2.9 parts of fumed silica, 0.18 parts of 1-ethynylcyclohexanol, 3 parts of the iron oxide solution, and 2.42 parts of the organohydrogenpolysiloxane (D11) was designated as component B.

[0092]

[0093]

[0094] [Evaluation Results] As shown in Table 1, the liquid silicone rubber compositions obtained in Examples 1 to 7 all fulfilled the requirements of the present invention, and the physical properties of the liquid silicone rubber compositions, molding test sheets, and molded products of Examples 1 to 7 to which the 3-glycidyloxypropylsilanol oligomer of component (C) had been added demonstrate that, compared to Comparative Examples 1 to 7, there was no adverse effect on hardness or compression set, and there was no risk of increasing the amount of VOCs emitted, and thixotropy could be freely controlled.

[0095] In contrast, Comparative Example 4 is a composition to which 3-glycidyloxypropyltrimethoxysilane, the starting material for the 3-glycidyloxypropylsilanol oligomer of component (C-1), was added. Although the viscosity was improved compared to Comparative Example 3, as shown in Table 2, the compression set deteriorated after the storage stability test (70°C / 7 days). In addition, there was a high possibility of methanol being generated over time, which could result in an increase in the amount of VOCs generated.

[0096] Furthermore, Comparative Example 5 is a composition in which the amount of reinforcing silica fine powder was increased compared to Comparative Example 1, and Comparative Example 7 is a composition in which the amount of reinforcing silica fine powder was increased compared to Comparative Example 3. However, as shown in Table 3, although the initial viscosity was high, the viscosity decreased from the initial level upon re-mixing, and there is a risk that the viscosity may decrease below the target level if stress is applied to the composition due to storage or transportation conditions. In addition, as shown in Table 1, the hardness of the cured product increased compared to Example 1 and Comparative Example 1, and the compression set in Comparative Example 5 worsened.

[0097] The above results show that the liquid silicone rubber compositions of Examples 1 to 7, to which 3-glycidyloxypropylsilanol oligomer was added, were able to freely control thixotropy without adversely affecting hardness or compression set, without posing a risk of increasing VOC emissions.

Claims

1. (A) A liquid organopolysiloxane containing two or more alkenyl groups bonded to silicon atoms in each molecule. (B) A filler having an average particle size of 0.1 to 300 μm. (C) A 3-glycidyloxypropylsilanol oligomer represented by the following formula (1): (In the formula, R 1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, R 2 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms which may be substituted with a glycidyloxy group, R 3 is a monovalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, a, b, c and d are numbers that satisfy a≧0.5, b≧0, c≧0, d≧0, a+b+c+d=1, and x and y are numbers that satisfy x≧1.0, y≦0.5.) (D) a curing agent: an effective curing amount.

2. The liquid silicone rubber composition according to claim 1, wherein the filler of component (B) is an inorganic filler.

3. The liquid silicone rubber composition according to claim 1 or 2, wherein the weight average molecular weight of component (C) is 500 to 10,000.

4. The liquid silicone rubber composition according to any one of claims 1 to 3, wherein in the above formula (1), b, c, and d are numbers that satisfy b=0, 0≦c≦0.5, and 0≦d≦0.2.

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