JP2016056226A - Silicone rubber composition, and method for improving tear strength of silicone rubber-cured material - Google Patents

Abstract

SOLUTION: To provide a liquid-type addition curable silicone rubber composition including 100 pts.mass of organopolysiloxane (A) having at least average 2 alkenyl groups bonding to silicon atoms in one molecule, 0.5-20 pts.mass of organohydrogenpolysiloxane (B) having at least 2 hydrogen atoms bonding to silicon atoms in one molecule, 10-40 pts. mass of fumed silica (dry silica) (C) having a specific surface area by a BET method of 50-400 m/g, 2.5-3.5 pts.mass of wet silica (D) having an average particle size of not greater than 2 μm to a total mass of component (A), component (B), and component (C), and a catalytic amount of an addition reaction catalyst (E).EFFECT: The present invention enables a tear strength of a silicone rubber obtained by curing a liquid-type addition curable silicone rubber composition with heat to be improved stably.SELECTED DRAWING: None

Description

  The present invention relates to a liquid addition-curable silicone rubber composition that provides a cured silicone rubber with improved tear strength, and a method for stably improving the tear strength of silicone rubber obtained by heat curing the composition.

Silicone rubber is used in electrical / electronic parts, automobile parts, building material parts, and the like. Silicone containing a dry silica filler surface-treated with a silane coupling agent having a trimethyl group, an untreated dry silica filler, and a silane coupling agent having methacryloxy as a composition aimed at improving the tear strength of silicone rubber There is a rubber-based curable composition (Patent Document 1: Japanese Patent Application Laid-Open No. 2012-211231), and the acid strength in a state where fine particulate hydrophilic silica is dispersed in a nonpolar solvent is 2.0 to 9. Examples include organopolysiloxane compositions for wet silicone-blended liquid silicone rubbers within the range of 0 (Patent Document 2: Japanese Patent Publication No. 7-107137).
However, when the dry silica blend composition is used, there is a problem that the tear strength becomes unstable. When the wet silica blend composition is used, the tear strength is not improved.

JP 2012-211121 A Japanese Patent Publication No. 7-107137

  The present invention has been made in view of the above problems, and in a liquid addition-curable silicone rubber composition that gives a cured product having improved tear strength, and a silicone rubber obtained by heat curing this composition, the tear strength can be stabilized. It aims at providing the method of expressing.

  As a result of intensive studies to achieve the above object, the present inventor has obtained a liquid addition-curable silicone rubber composition containing a predetermined amount of fumed silica (dry silica) that is commonly used as a reinforcing silica-based filler. In combination, wet silica having a specific average particle size is used in a specific local compounding amount range, whereby the tear strength of a cured silicone rubber obtained by curing the composition is stably improved. As a result, the present invention has been completed.

Accordingly, the present invention provides the following liquid addition-curable silicone rubber composition and a method for stably improving the tear strength of silicone rubber obtained by heat-curing the composition.
[1]
(A) Organopolysiloxane containing an average of at least two alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass
(B) Organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule: 0.5 to 20 parts by mass
(C) Fumed silica (dry silica) having a specific surface area of 50 to 400 m ² / g by BET method: 10 to 40 parts by mass,
(D) Wet silica having an average particle size of 2 μm or less: 2.5 to 3.5% by mass with respect to the total mass of component (A), component (B) and component (C),
(E) Addition reaction catalyst: Liquid addition-curable silicone rubber composition containing a catalytic amount.
[2]
(A) Organopolysiloxane containing an average of at least two alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass
(B) Organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule: 0.5 to 20 parts by mass
(C) Fumed silica (dry silica) having a specific surface area of 50 to 400 m ² / g by BET method: 10 to 40 parts by mass,
(D) Wet silica having an average particle size of 2 μm or less: 2.5 to 3.5% by mass with respect to the total mass of component (A), component (B) and component (C),
(E) Addition reaction catalyst: A method for improving the tear strength of a cured silicone rubber, wherein a liquid addition-curable silicone rubber composition containing a catalytic amount is cured by heating to obtain a cured silicone rubber.
[3]
[2] The method for improving the tear strength of a cured silicone rubber according to [2], which provides a cured silicone rubber having a tear strength (crescent) of 30 kN / m or more based on JIS-K6249.

  According to the method of the present invention, the tear strength of silicone rubber obtained by heat curing a liquid addition-curable silicone rubber composition can be stably improved.

The present invention will be described in detail below.
In the method for improving the tear strength of silicone rubber obtained by curing the liquid addition-curable silicone rubber composition of the present invention, the liquid addition-curable silicone rubber composition is:
(A) Organopolysiloxane containing an average of at least two alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass
(B) Organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule: 0.5 to 20 parts by mass
(C) Fumed silica (dry silica) having a specific surface area of 50 to 400 m ² / g by BET method: 10 to 40 parts by mass,
(D) Wet silica having an average particle size of 2 μm or less: 2.5 to 3.5% by mass with respect to the total mass of component (A), component (B) and component (C),
(E) Addition reaction catalyst: A catalyst containing a catalyst amount.

The organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms in one molecule of the component (A) acts as a main agent (base polymer) of the composition of the present invention. In general, those represented by the following average composition formula (1) can be used.
R ¹ _a SiO _{(4-a) / 2} (1)
Wherein R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having the same or different carbon number of 1 to 10, preferably 1 to 8, and a is 1.5 to 2.8, preferably 1 .8 to 2.5, more preferably a positive number in the range of 1.95 to 2.05.)

Here, as the unsubstituted or substituted monovalent hydrocarbon group bonded to the silicon atom represented by R ¹ , a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, Pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, alkyl group such as decyl group, aryl group such as phenyl group, tolyl group, xylyl group, naphthyl group, benzyl group, phenylethyl group, phenylpropyl Aralkyl groups such as groups, vinyl groups, allyl groups, propenyl groups, isopropenyl groups, butenyl groups, hexenyl groups, cyclohexenyl groups, octenyl groups and other alkenyl groups, and some or all of the hydrogen atoms of these groups are fluorine. Substituted with halogen atoms such as bromine, chlorine, cyano groups, etc., such as chloromethyl group, chloropro Group, bromoethyl group, trifluoropropyl group, but cyanoethyl group and the like, that more than 90 mole% of the total R1 is a methyl group, in particular, that all of R ¹ other than the alkenyl group is a methyl group Is preferred.

Of R ¹ , at least 2 (usually 2 to 50), particularly about 2 to 20 are alkenyl groups (preferably those having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, It is preferably a vinyl group. In addition, this alkenyl group can be 0.05-20 mol% with respect to all R < ¹ > groups, Preferably it is 0.1-10 mol%, More preferably, it can be about 0.1-5 mol%.

The alkenyl group content is preferably 5 × 10 ^{−6 to} 5 × 10 ⁻³ mol / g, particularly 1 × 10 ⁻⁵ to 1 × 10 ⁻³ mol / g in the organopolysiloxane. If the amount of the alkenyl group is less than 5 × 10 ⁻⁶ mol / g, the resulting cured product has low rubber hardness, and there is a risk that sufficient sealing performance may not be obtained, and more than 5 × 10 ⁻³ mol / g. If the amount is too large, the resulting cured product has too high a crosslinking density, which may result in brittle rubber.
This alkenyl group may be bonded to a silicon atom at the end of the molecular chain, may be bonded to a silicon atom in the middle of the molecular chain (non-terminal), or may be bonded to both.

The structure of this organopolysiloxane is usually composed of repeating main chain of diorganosiloxane units (R ¹ ₂ SiO _2/2 ) (R ¹ is the same as above), and both ends of the molecular chain are blocked with triorganosiloxy groups. Is basically a linear diorganopolysiloxane, but partially contains a small amount of branching units (R ¹ SiO _3/2 ) (R ¹ is the same as above) A branched chain structure or a cyclic structure may also be used.

In the present invention, in addition to the organopolysiloxane having an average of 2 or more alkenyl groups in one molecule of the component (A), as an optional component as required, (F) an average of 1 alkenyl groups in one molecule One organopolysiloxane can be used in combination. Examples of the organopolysiloxane of component (F) include those represented by the following average composition formula (2).
R ² _b SiO _{(4-b) / 2} (2)
Wherein R ² is an unsubstituted or substituted monovalent hydrocarbon group having the same or different carbon number of 1 to 10, preferably 1 to 8, and b is 1.5 to 2.8, preferably 1 .8 to 2.5, more preferably a positive number in the range of 1.95 to 2.05.)

In this case, R ² may be the same as R ¹ , but an average of one alkenyl group such as a vinyl group contained in one molecule. Although b is as above-mentioned, since a linear thing is preferable, 1.95-2.05 are especially preferable for b.

As such an organopolysiloxane having an average of one alkenyl group in one molecule of component (F), for example, one end of the molecular chain is blocked with a diorganoalkenylsiloxy group and the other end is a triorganosiloxy group. Linear organopolysiloxane having a blocked main chain composed of a diorganosiloxane unit (in this case, the organo group means an unsubstituted or substituted monovalent hydrocarbon group other than an alkenyl group in the above R ² ), etc. Is mentioned. Such an organopolysiloxane containing only one alkenyl group in one molecule is used in combination with the component (A) from the viewpoints of room temperature shrinkage and carbon drop resistance of the cured silicone rubber. desirable. The blending ratio (mass ratio) when the components (A) and (F) are used in combination is such that the component (A): component (F) is 80:20 to 20:80, particularly about 75:25 to 50:50. Preferably there is.

  In any of (A) component organopolysiloxane and (F) component organopolysiloxane, the molecular weight is preferably 1,500 or less, usually 100 to 1,500, more preferably, Preferably it is 150-1,000. If it is less than 100, sufficient rubber feeling may not be obtained, and if it is higher than 1,500, the viscosity becomes high and molding may be difficult. In the present invention, the degree of polymerization (or molecular weight) can be usually determined as the weight average degree of polymerization (or weight average molecular weight) in terms of polystyrene in gel permeation chromatography (GPC) analysis using toluene or the like as a developing solvent. .

Component (B) is an organohydrogenpolysiloxane having at least 2, preferably 3 or more hydrogen atoms (SiH groups) bonded to silicon atoms in one molecule. The SiH group in the molecule crosslinks with the alkenyl group bonded to the silicon atom in the component (A) by a hydrosilylation addition reaction, and acts as a curing agent (crosslinking agent) for curing the composition. This (B) component organohydrogenpolysiloxane has the following average composition formula (3)
R ³ _c H _d SiO _{(4-cd) / 2} (3)
Wherein R ³ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, which are the same or different from each other. C is 0.7 to 2.1, d Is a positive number satisfying 0.001 to 1.0 and c + d = 0.8 to 3.0.)
And at least 2 (usually 2 to 300), preferably 3 or more (for example, 3 to 100), more preferably about 3 to 50 hydrogen atoms bonded to a silicon atom in one molecule ( Those having SiH groups) are preferably used. Here, in the above formula (3), examples of the unsubstituted or substituted monovalent hydrocarbon group represented by R ³ include the same groups as those exemplified for R ¹ described above. Those having no group unsaturated bond are preferred. C is preferably 0.8 to 2.0, d is preferably 0.01 to 1.0, and c + d is preferably 1.0 to 2.5.

  The molecular structure of the organohydrogenpolysiloxane may be any of linear, cyclic, branched, or three-dimensional network structures, and the number of silicon atoms in one molecule or the degree of polymerization is 2 to 2. 300 (pieces), particularly 4 to 150 (pieces) room temperature (25 ° C.) and liquid (usually 1,000 mPa · s or less, preferably about 0.1 to 500 mPa · s at 25 ° C.) are suitable. Used. Here, this viscosity value is a value measured by a rotational viscometer (for example, BL type, BH type, BS type, cone plate type, rheometer, etc.).

  In addition, the hydrogen atom couple | bonded with a silicon atom may be located in any of the molecular chain terminal and the middle of a molecular chain, and may be located in both.

Examples of the organohydrogenpolysiloxane of the component (B) include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris (hydrogendimethylsiloxy) methylsilane, Tris (hydrogendimethylsiloxy) phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, trimethylsiloxy group-blocked methylhydrogenpolysiloxane at both ends, trimethylsiloxy group-blocked dimethylsiloxane at both ends Methyl hydrogen siloxane copolymer, both ends dimethyl hydrogen siloxy group-capped dimethyl polysiloxane, both ends dimethyl hydrogen siloxy group capped dimethyl siloxane methyl high Rogen siloxane copolymer, trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane copolymer, trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, both-end trimethylsiloxy group-blocked Methylhydrogensiloxane / methylphenylsiloxane / dimethylsiloxane copolymer, both ends dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane / diphenylsiloxane copolymer, both ends dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane-methylphenylsiloxane copolymer, (CH _{3) 2} HSiO _1/2 units and (CH _{3) 3} SiO _1/2 units and SiO _4/2 Position and a copolymer, (CH ₃₎ a copolymer consisting of ₂ HSiO _1/2 units and SiO _4/2 units, and (CH _{3) 2} HSiO _1/2 units and SiO _4/2 units (C Examples thereof include copolymers composed of ₆ H ₅ ) ₃ SiO _1/2 units, and compounds obtained by substituting part or all of the methyl groups with other alkyl groups or phenyl groups in the above exemplified compounds.

  (B) The compounding quantity of organohydrogenpolysiloxane of a component is 0.5-20 mass parts with respect to 100 mass parts of (A) component, Preferably it is 0.6-15 mass parts. Further, the molar ratio of silicon atom-bonded hydrogen atoms (SiH groups) in component (B) to the sum of silicon-bonded alkenyl groups contained in the entire composition, particularly alkenyl in components (A) and (F) The molar ratio of the hydrogen atom (SiH group) bonded to the silicon atom in the component (B) to the group is hydrogen atom (SiH group) / alkenyl group bonded to the silicon atom = 0.8 to 5.0, particularly 1. It is preferable to blend the organohydrogenpolysiloxane of component (B) so as to be 0 to 3.0. When the blending amount (mass) of the component (B) is too small, or when this ratio is less than 0.8, sufficient rubber hardness cannot be obtained in the resulting cured product, and the blending amount (mass) of the component B). ) Is too large, or if this ratio is greater than 5.0, foaming of the resulting rubber may be observed, or release from the mold may be difficult.

Component (C), fumed silica (dry silica), is essential to give sufficient strength to the resulting silicone rubber. The specific surface area of fumed silica by the BET method is usually 50 m ² / g or more (for example, 50 to 400 m ² / g), preferably 150 to 350 m ² / g, and a cured product obtained when the BET specific surface area is too small. The rubber strength of the rubber becomes poor, and if the BET specific surface area is too large, it may become difficult to mix the rubber or change its color.

  Component (C), fumed silica (dry silica) is Aerosil 130, 200, 300 (manufactured by Aerosil Japan, manufactured by Degussa), Cabosil MS-5 as hydrophilic silica (ie, untreated silica). MS-7 (manufactured by Cabot Corp.), Rheorosil QS-102, 103 (manufactured by Tokuyama Corp.), etc. as the hydrophobic silica, Aerosil R-812, R-812S, R-972, R-974 (manufactured by Degussa) ), Rheorosil MT-10 (manufactured by Tokuyama Corporation) and the like. By using a material that has been previously treated with a surface hydrophobizing agent or by adding a surface treating agent during kneading with a silicone oil (for example, an alkenyl group-containing organopolysiloxane of component (A)) It is preferable to use it. As these surface treatment agents, known surface treatment agents such as alkylalkoxysilanes, alkylchlorosilanes, alkylsilazanes, silane coupling agents, titanate treatment agents and fatty acid esters may be used alone, or two or more of them may be used simultaneously. Or you may use at a different timing. Further, when kneading with a silicone oil (for example, the alkenyl group-containing organopolysiloxane of the component (A)), silica that has been surface-treated in advance by adding a surface-treating agent may be surface-treated again with the surface-treating agent. Good.

  Moreover, the compounding quantity of a fumed silica is 10-40 mass parts with respect to 100 mass parts of (A) component, and it is preferable that it is 15-35 mass parts. If the blending amount is less than 10 parts by mass, sufficient rubber strength cannot be obtained in the resulting cured product, and if it exceeds 40 parts by mass, the resulting rubber hardness is increased.

  The wet silica having an average particle size of 2 μm or less of the component (D) is a component that is a feature of the present invention, but those conventionally used in conventional silicone rubber compositions can be used, and the average particle size of 2 μm or less (usually, 0.01 to 2 μm, preferably 0.1 to 2 μm) wet silica is essential. In the case of wet silica larger than 2 μm, the tear strength is not improved regardless of the blending amount. In addition, this average particle diameter can be calculated | required as cumulative mass average diameter D50 (or median diameter) etc. in the particle size distribution measurement by a laser beam diffraction method, for example.

  The amount of wet silica having an average particle diameter of 2 μm or less of the component (D) is essential to be 2.5 to 3.5 mass% with respect to the total mass of the components (A), (B) and (C). is there. If it is less than 2.5% by mass, the tear strength is not improved. Moreover, when it exceeds 3.5 mass%, tear strength will not improve similarly. In addition, the blending ratio 2.5 to 3.5% by mass of the component (D) with respect to the total mass of the components (A) to (C) is usually (D) component to 100 parts by mass of the component (A). A very local range corresponding to about 2.75 to 5.60 parts by mass, preferably about 3.0 to 5.0 parts by mass, more preferably about 3.2 to 4.8 parts by mass. .

  The wet silica may be either a hydrophilic wet silica or a hydrophobic wet silica. As the hydrophilic wet silica, Fine Seal US-F (manufactured by Tokuyama), Nipsil LP (manufactured by Nippon Silica), etc. Examples of silica include Nipsil SS series (manufactured by Nippon Silica). These silica-based fillers may be used as they are, but those previously surface-treated with a silylating agent (surface treatment agent) may be used, or silicone oil (for example, (A) component alkenyl group-containing organopolysiloxane may be used. ) And a surface treated by adding a silylating agent during kneading. These silylating agents may be any known ones such as alkylalkoxysilanes, alkylchlorosilanes, alkylsilazanes, silane coupling agents, titanate treatment agents, fatty acid esters, etc. You may use simultaneously or at a different timing. In addition, silica that has been surface-treated in advance by adding a silylating agent during kneading with silicone oil (for example, the alkenyl group-containing organopolysiloxane of component (A)) may be surface-treated again with the silylating agent. .

The (E) component addition reaction catalyst comprises a silicon atom-bonded alkenyl group in component (A) or (A), (F) and a hydrogen atom (SiH group) bonded to a silicon atom in component (B). This is a catalyst for hydrosilylation addition reaction. Examples of the addition reaction catalyst include platinum black, platinum chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and olefins, and a platinum-based catalyst such as platinum bisacetoacetate. Platinum group metal catalysts such as palladium-based catalysts and rhodium-based catalysts, and the like, and platinum-based catalysts are particularly preferable.
The addition amount of the addition reaction catalyst can be a catalytic amount, and is usually 0.5 to 500 ppm in terms of the mass of the platinum group metal with respect to the total of the component (A) or the components (A) and (F). In particular, it can be about 1 to 100 ppm.

  In the liquid silicone rubber composition of the present invention comprising these (A) to (E) components or (A) to (F) components, adjustment of the curing time (pot life) for practical use of the composition. When it is necessary to carry out the reaction, as a reaction control agent (reaction inhibitor) for the hydrosilylation addition reaction, a low molecular (cyclic) siloxane oligomer containing a high vinyl group such as tetramethyltetravinylcyclotetrasiloxane, triallyl Using nitrogen-containing compounds such as isocyanurate, tetramethylethylenediamine, and benzotriazole, alkyl maleates, acetylene alcohols and their silane or siloxane modifications, hydroperoxides, and compounds selected from the group, etc. There is no problem.

  Furthermore, if necessary, inorganic pigments such as cobalt blue and ultramarine blue, colorants such as organic dyes, heat resistance and flame retardancy improvers such as cerium oxide, zinc carbonate, manganese carbonate, titanium oxide, and iron oxide. For the purpose of adjusting the viscosity of the silicone rubber composition and adjusting the hardness of the cured silicone rubber, it is also possible to add an organopolysiloxane containing an average of less than one alkenyl group in the molecule.

In the present invention, a cured silicone rubber can be obtained by heat-curing (molding) the liquid addition-curable silicone rubber composition of the present invention by a molding method such as compression molding, injection molding, injection molding, or transfer molding. it can. The curing conditions (primary curing) of the liquid addition curable silicone rubber composition are preferably 100 to 200 ° C., more preferably 120 to 180 ° C. for 30 seconds to 30 minutes, and particularly preferably 1 to 15 minutes.
In addition, the obtained conductive silicone rubber is post-cured (secondarily cured), for example, at 150 to 220 ° C., particularly at 180 to 200 ° C. for 30 minutes to 6 hours, particularly for about 1 to 4 hours, as necessary. May be.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In the following examples,% is mass%. The degree of polymerization is a weight average degree of polymerization in terms of polystyrene in gel permeation chromatography (GPC) analysis using toluene as a developing solvent.

[Example 1]
84 parts by mass of dimethylpolysiloxane (vinyl group content = 0.000034 mol / g) having an average degree of polymerization of 750 blocked at both ends with dimethylvinylsiloxy groups, and average polymerization with both ends blocked with trimethylsiloxy groups Fumed silica 40 having a degree of about 230, 5 parts of dimethylpolysiloxane having 5 mol of vinyl groups in the side chain (vinyl group content = 0.00065 mol / g), and BET specific surface area of 300 m ² / g Mass parts, 8 parts by mass of hexamethyldisilazane, and 2.0 parts by mass of water were mixed at room temperature for 30 minutes, then heated to 150 ° C., stirred for 3 hours and cooled to obtain a silicone rubber base.
To 128 parts by mass of this silicone rubber base, 4.4 parts by mass of wet silica (manufactured by File Seal US-F Tokuyama) having an average particle diameter of 2 μm (2.5% by mass with respect to the total of components (A) to (C)) Corresponding, the same shall apply hereinafter.), 46 parts by mass of dimethylpolysiloxane having an average degree of polymerization of 750 blocked at both ends with dimethylvinylsiloxy groups, and a trimethylsiloxy group blocked at both ends of the molecular chain having 20 SiH groups in the side chain 1.75 parts by mass of methylhydrogensiloxane / dimethylsiloxane copolymer (degree of polymerization 38, SiH group amount 0.0074 mol / g), and methylhydrogensiloxane / dimethylsiloxane copolymer having SiH groups at both ends ( The degree of polymerization is 18 and the amount of SiH groups is 0.0014 mol / g) is 1.75 parts by mass relative to all alkenyl groups in the silicone rubber composition The molar ratio of all SiH functional groups is SiH group / alkenyl group = 2.0, and 0.06 part by mass of ethynylcyclohexanol and 0.1 part by mass of platinum catalyst (Pt concentration 1% by mass) are added as reaction control agents. The mixture was stirred and mixed for 15 minutes to obtain a silicone rubber composition. The viscosity of this silicone rubber composition was measured as a viscosity at a shear rate of 0.9 s ⁻¹ at 23 ° C. using a cone and plate measuring jig of a precision rotary viscometer HAAKE Rotovisco RV-1 (manufactured by Thermo scientific). did. The obtained results are shown in Table 1.
The silicone rubber composition was press-cured at 120 ° C. for 10 minutes, and further post-cured in an oven at 150 ° C. for 1 hour to prepare a cured silicone rubber sheet having a thickness of 2 mm. Table 1 shows the results of measurement of hardness, tensile strength, elongation at break, and tear strength (crescent) from the cured sheet based on JIS-K6249.

[Example 2]
In Example 1, the viscosity and hardness were the same as in Example 1 except that wet silica (manufactured by File Seal US-F Tokuyama) having an average particle diameter of 2 μm was changed to 6.2 parts by mass (3.5% by mass). Table 1 shows the results of measurement of the tensile strength, elongation at break, and tear strength (crescent).

[Comparative Example 1]
In Example 1, the viscosity, hardness, tensile strength, elongation at break were the same as in Example 1 except that wet silica (manufactured by File Seal US-F Tokuyama) having an average particle size of 2 μm was changed to 0 parts by mass. The results of measuring the tear strength (crescent) are shown in Table 1.

[Comparative Example 2]
In Example 1, the viscosity and hardness were the same as in Example 1 except that the wet silica (manufactured by File Seal US-F Tokuyama) having an average particle size of 2 μm was changed to 3.6 parts by mass (2.0% by mass). Table 1 shows the results of measurement of the tensile strength, elongation at break, and tear strength (crescent).

[Comparative Example 3]
In Example 1, the viscosity and hardness are the same as in Example 1 except that wet silica (manufactured by File Seal US-F Tokuyama) having an average particle size of 2 μm is changed to 7.1 parts by mass (4.0% by mass). Table 1 shows the results of measurement of the tensile strength, elongation at break, and tear strength (crescent).

[Comparative Example 4]
In Example 1, the viscosity and hardness were the same as in Example 1 except that the wet silica (manufactured by File Seal US-F Tokuyama) having an average particle diameter of 2 μm was changed to 8.9 parts by mass (5.0% by mass). Table 1 shows the results of measurement of the tensile strength, elongation at break, and tear strength (crescent).

[Comparative Example 5]
Example 1 is the same as Example 1 except that the wet silica having an average particle diameter of 2 μm is changed to 4.4 parts by mass (2.5% by mass) of wet silica having an average particle diameter of 8 μm (nipsil LP manufactured by Nippon Silica). Table 1 shows the results of measuring the viscosity, hardness, tensile strength, elongation at break, and tear strength (crescent).

[Comparative Example 6]
Example 1 is the same as Example 1 except that the wet silica having an average particle diameter of 2 μm is changed to 6.2 parts by mass (3.5% by mass) of wet silica having an average particle diameter of 8 μm (nipsil LP manufactured by Nippon Silica). Table 1 shows the results of measuring the viscosity, hardness, tensile strength, elongation at break, and tear strength (crescent).

Claims (3)

(A) Organopolysiloxane containing an average of at least two alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass
(B) Organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule: 0.5 to 20 parts by mass
(C) Fumed silica (dry silica) having a specific surface area of 50 to 400 m ² / g by BET method: 10 to 40 parts by mass,
(D) Wet silica having an average particle size of 2 μm or less: 2.5 to 3.5% by mass with respect to the total mass of component (A), component (B) and component (C),
(E) Addition reaction catalyst: Liquid addition-curable silicone rubber composition containing a catalytic amount. (A) Organopolysiloxane containing an average of at least two alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass
(B) Organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule: 0.5 to 20 parts by mass
(C) Fumed silica (dry silica) having a specific surface area of 50 to 400 m ² / g by BET method: 10 to 40 parts by mass,
(D) Wet silica having an average particle size of 2 μm or less: 2.5 to 3.5% by mass with respect to the total mass of component (A), component (B) and component (C),
(E) Addition reaction catalyst: A method for improving the tear strength of a cured silicone rubber, wherein a liquid addition-curable silicone rubber composition containing a catalytic amount is cured by heating to obtain a cured silicone rubber.   The method for improving the tear strength of a cured silicone rubber according to claim 2, which gives a cured silicone rubber having a tear strength (crescent) of 30 kN / m or more based on JIS-K6249.