WO2017110565A1

WO2017110565A1 - Sponge-forming liquid silicone rubber composition and silicone rubber sponge

Info

Publication number: WO2017110565A1
Application number: PCT/JP2016/086943
Authority: WO
Inventors: 昭宏中村; 正和入江; 次雄野副; 遠藤　修司
Original assignee: 東レ・ダウコーニング株式会社
Priority date: 2015-12-25
Filing date: 2016-12-12
Publication date: 2017-06-29
Also published as: TW201736517A; TWI726025B; JP6958984B2; JPWO2017110565A1

Abstract

A sponge-forming liquid silicone rubber composition which forms a low-density sponge having a uniform and fine open cell structure, and which is composed at least of (A) an organopolysiloxane having at least two alkenyl groups in each molecule, (B) an organopolysiloxane having at least two silicon atom-bonded hydrogen atoms in each molecule, (C) a mixture of water and an inorganic thickening agent, (D) a surfactant that is composed of a nonionic surfactant having an HLB value of 3 or more and a nonionic surfactant having an HLB value of less than 3, (E) a hydrosilylation catalyst and (F) a curing retardant .

Description

Sponge-forming liquid silicone rubber composition and silicone rubber sponge

The present invention relates to a sponge-forming liquid silicone rubber composition and a silicone rubber sponge obtained by crosslinking the composition and then removing water.

Silicone rubber sponge is excellent in heat resistance and weather resistance, and is lightweight, so it is used for automobile parts; rolls and belts for image forming apparatuses such as copying machines and printers; and other various sealing parts.

Examples of the silicone rubber composition for forming such a silicone rubber sponge include diorganopolysiloxane having at least two silicon atom-bonded alkenyl groups in one molecule, and at least two silicon atoms in one molecule. Sponge-forming liquid silicone rubber composition comprising organopolysiloxane having bonded hydrogen atoms, water containing smectite clay, nonionic surfactant, and hydrosilylation reaction catalyst (see Patent Document 1). Diorganopolysiloxane blocked with an alkenyl group and having no alkenyl group in the side chain of the molecular chain, diorganopolysiloxane having at least two alkenyl groups in the side chain of the molecular chain, and at least two silicon atom bonds in one molecule Organopolysiloxane with hydrogen atoms, water and smecta Mixture consisting Tokure, nonionic surfactants, a catalyst for hydrosilylation reaction, and sponge-forming liquid silicone rubber composition comprising a retarder (see Patent Document 2) are known.

However, since such a sponge-forming liquid silicone rubber composition is used to form a low-density sponge, it is difficult to uniformly disperse the silicone rubber composition in water if the amount of water added is increased. In addition, it is difficult to form a uniform and fine open-cell structure in the obtained silicone rubber sponge.

JP 2004-346248 A JP 2008-214625 A

An object of the present invention is to provide a sponge-forming liquid silicone rubber composition that forms a low-density silicone rubber sponge having a uniform and fine open-cell structure. Another object of the present invention is to provide a silicone rubber sponge having a uniform and fine open-cell structure and a low density.

The sponge-forming liquid silicone rubber composition of the present invention comprises:
(A) 100 parts by mass of an organopolysiloxane having at least two alkenyl groups in one molecule;
(B) Organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule {The amount of silicon-bonded hydrogen atoms in this component is 0.4 with respect to 1 mol of the alkenyl group in component (A). Amount to be ~ 20 mol},
(C) 100 to 1000 parts by mass of a mixture of water and an inorganic thickener,
(D) (D-1) a nonionic surfactant having an HLB value of 3 or more, and (D-2) a surfactant comprising a nonionic surfactant having an HLB value of less than 3 {provided ( The mass ratio of the component (D-1) to the component D-2) is at least 1. } 0.1 to 15 parts by mass,
(E) a catalyst for hydrosilylation reaction (an amount sufficient to crosslink the composition) and (F) a curing retarder of 0.001 to 5 parts by mass.

Component (A) comprises (A-1) 10 to 90% by mass of diorganopolysiloxane having an average of two alkenyl groups at the molecular chain terminals and no alkenyl groups in the molecular chain side chains, and (A-2 ) A diorganopolysiloxane having at least two alkenyl groups in the side chain of the molecular chain is preferably an organopolysiloxane composed of 10 to 90% by mass.

The inorganic thickener in component (C) is preferably smectite clay.

Further, the composition preferably contains (G) fine silica powder at most 20 parts by mass with respect to 100 parts by mass of component (A).

The silicone rubber sponge of the present invention is obtained by removing water from the silicone rubber after crosslinking the sponge-forming liquid silicone rubber composition.

This silicone rubber sponge preferably has an average cell diameter of 1 μm or more and less than 50 μm and an open cell ratio of 90% or more.

The sponge-forming liquid silicone rubber composition of the present invention can form a low-density sponge having a uniform and fine open-cell structure with good moldability. The silicone rubber sponge of the present invention has a uniform and fine open-cell structure and a low density.

Component (A) is the main component of the composition and is an organopolysiloxane having at least two alkenyl groups in one molecule. Examples of the alkenyl group in component (A) include alkenyl groups having 2 to 12 carbon atoms such as vinyl group, allyl group, hexenyl group and the like, and vinyl group is preferable. Examples of the silicon atom-bonded organic group other than the alkenyl group in the component (A) include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, An alkyl group having 1 to 12 carbon atoms such as undecyl group and dodecyl group; an aryl group having 6 to 12 carbon atoms such as phenyl group, tolyl group, xyl group and naphthyl group; 7 to 12 carbon atoms such as benzyl group and phenethyl group An aralkyl group of the above; halogen-substituted alkyl groups such as 3-chloropropyl group and 3,3,3-trifluoropropyl group are exemplified, and a methyl group is preferable.

The molecular structure of the component (A) is not limited, and examples thereof include straight-chain, partially-branched straight-chain, branched-chain, cyclic and dendritic, preferably straight-chain and partially-branched straight-chain It is. The component (A) may be a mixture of two or more having these molecular structures.

Such a component (A) includes (A-1) diorganopolysiloxane having two alkenyl groups on the molecular chain terminal and no alkenyl group on the molecular chain side chain and (A-2) molecular chain. A mixture of diorganopolysiloxanes having at least two alkenyl groups in the side chain is preferred.

The component (A-1) is a diorganopolysiloxane having an average of two alkenyl groups at the molecular chain terminals and no alkenyl groups in the molecular chain side chain. Specifically, dimethylvinylsiloxy group-blocked dimethyl Polysiloxane, dimethylvinylsiloxy group-blocked dimethylsiloxane / methylphenylsiloxane copolymer, the main chain consists of repeating dimethylsiloxane units, part of the main chain is branched, and the molecular chain ends are blocked with dimethylvinylsiloxy groups A branched dimethylpolysiloxane is exemplified, and a diorganopolysiloxane having a substantially linear main chain is preferable. The viscosity of the component (A-1) at 25 ° C. is not limited, but is preferably in the range of 0.05 to 1000 Pa · s.

The component (A-2) is a diorganopolysiloxane having at least two alkenyl groups in the side chain of the molecular chain, and specifically, a trimethylsiloxy group-capped methylvinylpolysiloxane, a trimethylsiloxy group-capped dimethylsiloxane / methylvinyl. Siloxane copolymer, trimethylsiloxy group-blocked dimethylsiloxane / methylvinylsiloxane / methylphenylsiloxane copolymer, the main chain consists of repeating dimethylsiloxane units and methylvinylsiloxane units, and part of the main chain is branched and molecular chain A branched dimethylsiloxane / methylvinylsiloxane copolymer whose end is blocked with a trimethylsiloxy group is exemplified, and diorganopolysiloxane having a substantially linear main chain is preferable. The viscosity of the component (A-2) at 25 ° C. is not limited, but is preferably in the range of 0.05 to 1000 Pa · s.

The blending ratio of the component (A-1) and the component (A-2) is not limited. However, since the shrinkage rate of the resulting silicone rubber sponge is improved, the component (A) is composed of the components (A-1) 10 to 90% by mass and the component (A-2) are preferably 10 to 90% by mass.

Component (B) is an organopolysiloxane that is a crosslinking agent of the present composition and has at least two silicon-bonded hydrogen atoms in one molecule. The bonding position of silicon atom-bonded hydrogen atoms in component (B) is not limited, and examples include molecular chain terminals and / or molecular chain side chains. Examples of the silicon-bonded organic group in the component (B) include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, etc. An alkyl group having 1 to 12 carbon atoms; an aryl group having 6 to 12 carbon atoms such as phenyl group, tolyl group, xyl group and naphthyl group; an aralkyl group having 7 to 12 carbon atoms such as benzyl group and phenethyl group; Examples of the halogen-substituted alkyl group such as chloropropyl group and 3,3,3-trifluoropropyl group are exemplified, and a methyl group is preferable.

Examples of such component (B) include dimethylhydrogensiloxy group-capped dimethylpolysiloxane, dimethylhydrogensiloxy group-capped dimethylsiloxane / methylhydrogensiloxane copolymer, trimethylsiloxy group-capped methylhydrogenpolysiloxane, and trimethylsiloxy group. Blocked dimethylsiloxane / methylhydrogensiloxane copolymer, represented by (CH ₃ ) ₃ SiO _1/2 siloxane unit, H (CH ₃ ) ₂ SiO _1/2 siloxane unit and SiO _4/2 Illustrative are organopolysiloxanes composed of siloxane units, preferably linear organopolysiloxanes.

The content of the component (B) is such that the silicon-bonded hydrogen atom in this component is in the range of 0.4 to 20 mol with respect to 1 mol of the alkenyl group in the component (A), preferably An amount that falls within the range of 1.5 to 20 moles, or an amount that falls within the range of 1.5 to 10 moles. This is because the compression set of the resulting silicone rubber sponge is improved when the number of moles of silicon-bonded hydrogen in the component (B) is within the above range.

Component (C) is a mixture composed of water and an inorganic thickener. By removing water in component (C) from a silicone rubber obtained by crosslinking the composition, a silicone rubber sponge is obtained. It is an ingredient. Since the component (C) is stably dispersed in the component (A), the water in the component (C) is preferably ion-exchanged water.

The inorganic thickener in component (C) is added to increase the viscosity of water, to easily disperse component (C) in component (A), and to stabilize the dispersion state of component (C). . These inorganic thickeners include natural or synthetic ones, natural or synthetic smectite clays such as bentonite, montmorillonite, hectorite, saponite, sauconite, beidellite and nontronite; aluminum magnesium silicate; and these And a water-soluble organic polymer such as carboxyvinyl polymer is exemplified, and a smectite clay such as bentonite and montmorillonite is preferable. As such a smectite clay, for example, smecton SA (manufactured by Kunimine Kogyo Co., Ltd.) which is a hydrothermal synthesis product and Bengel (manufactured by Hojun Co., Ltd.) which is a natural refined product are available. The pH of these smectite clays is preferably in the range of pH 5.0 to 9.0 from the viewpoint of maintaining the heat resistance of the silicone rubber sponge. In addition, the content of the inorganic thickener in the component (C) is in the range of 0.1 to 10 parts by mass, or in the range of 0.5 to 5 parts by mass with respect to 100 parts by mass of water. Is preferred.

The content of component (C) is in the range of 100 to 1000 parts by weight, preferably in the range of 100 to 800 parts by weight, in the range of 100 to 500 parts by weight, with respect to 100 parts by weight of component (A). It is in the range of 200 to 500 parts by mass, or in the range of 200 to 350 parts by mass. This is because when the content of the component (C) is at least the lower limit of the above range, a low-density silicone rubber sponge can be formed. On the other hand, when it is below the upper limit of the above range, uniform and fine open cells This is because a sponge having a structure can be formed.

The component (D) surfactant comprises (D-1) a nonionic surfactant having an HLB value of 3 or more, and (D-2) a nonionic surfactant having an HLB value of less than 3. . (D) Component surfactant includes glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, sucrose fatty acid ester, polyethylene glycol fatty acid ester, polypropylene glycol fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyoxyethylene sorbitan fatty acid Examples include esters, polyoxyethylene / polyoxypropylene block copolymers, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and polyoxyethylene fatty acid amides.

The component (D) comprises a component (D-1) and a component (D-2), and the mass ratio of the component (D-1) to the component (D-2) is at least 1, preferably at least 5, At least 8, at least 10, or at least 15. The mass ratio of the component (D-1) to the component (D-2) is preferably at most 100, more preferably at most 80, at most 70, at most 60, or at most 50. It is. This is because if the mass ratio is equal to or higher than the above lower limit, a low-density sponge having a uniform and fine open-cell structure can be formed. On the other hand, if the mass ratio is equal to or lower than the upper limit, the component (A) This is because the component (C) can be dispersed with good stability, and as a result, a sponge having a uniform and fine open-cell structure can be formed.

The content of the component (D) is in the range of 0.1 to 15 parts by mass, preferably in the range of 0.2 to 3 parts by mass with respect to 100 parts by mass of the component (A). This is because when the content of the component (D) is not less than the lower limit of the above range, a sponge having a uniform and fine open-cell structure can be formed. This is because an excellent silicone rubber sponge can be formed.

Component (E) is a hydrosilylation reaction catalyst for promoting the hydrosilylation reaction of the present composition. Examples thereof include platinum-based catalysts, palladium-based catalysts, and rhodium-based catalysts, and platinum-based catalysts are preferred. . Such component (E) includes: chloroplatinic acid; alcohol-modified chloroplatinic acid; coordination compound of chloroplatinic acid and olefins, vinylsiloxane or acetylene compound; platinum and olefins, vinylsiloxane or acetylene compound Coordination compounds; other examples include tetrakis (triphenylphosphine) palladium and chlorotris (triphenylphosphine) rhodium.

The content of the component (E) is an amount sufficient to crosslink the composition, and specifically, the catalyst metal in the component (E) with respect to the total amount of the component (A) and the component (B). Is preferably in an amount in the range of 0.01 to 500 ppm, or in an amount in the range of 0.1 to 100 ppm.

(F) component is a curing retarder for adjusting the curing speed and working life of the composition. Examples of such component (F) include 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 3-phenyl-1-butyn-3-ol, 1- Alkyne alcohols such as ethynyl-1-cyclohexanol; Enyne compounds such as 3-methyl-3-penten-1-yne, 3,5-dimethyl-3-hexen-1-yne; Tetramethyltetravinylcyclotetrasiloxane, Tetra Alkenyl group-containing cyclic siloxane such as methyltetrahexenylcyclotetrasiloxane; methyl-tris (3-methyl-1-butyne-3-oxy) silane, vinyl-tris (3-methyl-1-butyne-3-oxy) silane, etc. The alkyne-containing silane is exemplified.

The content of the component (F) is appropriately selected according to the method of use of the present composition and the molding method, but in general, 0.001 to 5 parts by mass with respect to 100 parts by mass of the component (A). Within range.

In order to improve the strength of the resulting silicone rubber sponge, the composition may further contain (G) silica fine powder. Examples of such component (G) include fumed silica, precipitated silica; the surface of these silica fine powders, for example, chain organopolysiloxane, cyclic organopolysiloxane, hexamethyldisilazane, or various organosilanes. The thing surface-treated by etc. is illustrated. The BET specific surface area of such component (G) is not limited, but is preferably in the range of 50 to 350 m ² / g, or in the range of 80 to 250 m ² / g.

The content of the component (G) is at most 20 parts by mass, preferably at most 15 parts by mass, or at most 10 parts by mass with respect to 100 parts by mass of the component (A). Moreover, it is preferable that content of (G) component is at least 0.1 mass part with respect to 100 mass parts of (A) component.

In the present composition, reinforcing fillers such as fumed titanium oxide; such as pulverized quartz, crystalline silica, diatomaceous earth, asbestos, aluminosilicic acid, iron oxide, zinc oxide, calcium carbonate, and the like, as long as the object of the present invention is not impaired. Non-reinforcing fillers; these fillers surface-treated with organosilicon compounds such as organosilanes and organopolysiloxanes; pigments such as carbon black and bengara; other heat-resistant agents, flame retardants, internal release agents, plastics An agent or the like may be contained.

The present composition can be easily produced by uniformly mixing the above-described components or a composition in which various additives are added to these components as necessary, using a known kneading means. Examples of the mixer used here include a homomixer, a paddle mixer, a homodisper, a colloid mill, a vacuum mixing and stirring mixer, and a rotation and revolution mixer, but the (C) component and the (D) component are sufficient for the (A) component. There is no particular limitation as long as it can be dispersed in the solution.

The silicone rubber composition containing the components (A) to (F) or the components (A) to (G) can be produced, for example, by the following method. In addition, when blending the (G) component, after preparing a silica masterbatch that blends a part of the (A) component and the (G) component in advance, the remaining (A) component and other components are mixed. It is preferable to do.

(A) component, (B) component, (C) component, (D) component, (F) component, and (G) component as needed are put into a mixer, stirred and mixed for a predetermined time, and immediately before use ( E) Method of blending component; (A) component, (C) component, (D) component, (E) component and, if necessary, (G) component are put into a mixer, and stirred and mixed for a predetermined time. Immediately before blending the (B) component and the (F) component; (A) component, (C) component, (D) component and, if necessary, (G) component are put into a mixer and stirred for a predetermined time. And the method of mix | blending (B) component, (E) component, and (F) component just before use is illustrated.

From the point of storage stability, it is composed of (A) component, (C) component, (D) component, (E) component, and (G) component as required, including (B) component and (F) component No composition (I); consisting of (A) component, (C) component, (D) component, (F) component, and (G) component as required, including (B) component and (E) component Composition (II) not comprising composition (B) and not comprising component (C), component (E), and component (F) (III); component (A), component (C), (D ) Component, (E) component, and optionally (G) component, and (B) component and (F) component free composition (I); consisting of (F) component, (B) component, Composition (II) which does not contain (C) component and (E) component; (B) component, and does not contain (C) component, (E) component, and (F) component Save as 3 sponge-forming liquid silicone rubber composition comprising an object (III), it is preferred to mix the composition (I) ~ (III) immediately before subjected to molding. In addition, a composition (I) comprising (A) component, (C) component, (D) component, (E) component, and (G) component as required, which does not contain (B) component and (F) component (I) '); Stored as a two-component sponge-forming liquid silicone rubber composition comprising a component (II' ') comprising the components (B) and (F) and not including the components (C) and (E). The compositions (I ′) and (II ″) are preferably mixed immediately before being subjected to molding.

A silicone rubber sponge can be formed from this composition by various methods. Specifically, the composition is poured into a cavity of a molding die, and a silicone rubber molded body in a water-containing state is molded by maintaining the pressure under 100 ° C., preferably 50 to 90 ° C., A silicone rubber sponge having fine and uniform open cells can be obtained by removing the water from the silicone rubber molded body in a water-containing state by taking out from the mold and heating at 120 to 250 ° C. Alternatively, the present composition may be ejected in a rod form from a nozzle, introduced into hot water at 80 to 100 ° C. and cured, and the cured product is dried with hot air to produce a string-like silicone rubber sponge. it can. Further, the present composition is coated on a peelable substrate such as a resin film, and is cured by heating to, for example, 50 to 120 ° C. and dried by hot air to remove water, or while removing water by heating. After curing, a silicone rubber sponge sheet can be formed by removing the peelable substrate. Alternatively, the composition may be coated on a synthetic fiber fabric or glass cloth and cured by, for example, heating to 50 to 120 ° C. and drying with hot air to remove water, or curing while removing water by heating. By doing so, a silicone rubber sponge coated fabric can be formed.

Although the thickness of the silicone rubber layer is appropriately selected, it is preferably 0.05 to 80 mm, and particularly preferably 0.1 to 50 mm from the viewpoint of effectively utilizing the rubber elasticity of the silicone rubber. The thickness of the fluororesin or fluororubber layer formed thereon is preferably 5 to 200 μm, particularly 10 to 100 μm.

In the silicone rubber sponge of the present invention, it is preferable that 90% or more of the bubbles are open cells from the viewpoint of small thermal deformation (thermal expansion) due to heating and excellent deformation recovery. Whether or not the bubbles are continuous bubbles can be examined by submerging the sponge in water and reducing the pressure for a predetermined time to replace the air in the sponge bubbles with water.

The sponge-forming liquid silicone rubber composition and the silicone rubber sponge of the present invention will be described in detail with reference to examples, and the viscosity in the examples is a value at 25 ° C.

<Density>
The density of the silicone rubber sponge was measured according to JIS K 6268.

<Hardness (Asker C)>
The hardness of the silicone rubber sponge was measured according to a test method using a type C hardness tester defined in JIS K 7312. In the measurement, two silicone rubber sponge test pieces each having a thickness of 6 mm were used.

<Tensile strength, elongation>
The tensile strength and elongation of the silicone rubber sponge were measured according to JIS K 6251.

<Bubble state>
Observe the cross section of the silicone rubber sponge test piece visually,
-Uniform air bubbles in the entire cross section
・ Those with some excessive bubbles were evaluated as non-uniform.

<Average bubble diameter>
The center part of the silicone rubber sponge test piece cut with a razor blade is observed with a scanning electron microscope, and the diameter of the bubbles per 0.04 mm ² area (the number of bubbles is about 200 to 300) is measured. The average value was defined as the average cell diameter.

<Shrinkage rate>
The length in the longitudinal direction of a test piece for hardness measurement made of a silicone rubber sponge molded using a mold having a cavity with a length of 70 mm, a width of 50 mm, and a thickness of 6 mm was measured. Asked.

<Open cell ratio>
The mass and density of the silicone rubber sponge test piece were measured and substituted into the following formula to determine the volume of the bubble part. In the formula, the density of the silicone rubber is a density of a silicone rubber test piece obtained by crosslinking and curing a silicone rubber composition prepared in the same manner except that it does not contain the components (C) and (D).

Furthermore, hold the silicone rubber sponge test piece in water, leave it under a reduced pressure of 760 mmHg for 3 minutes to absorb the water, measure the mass of the absorbed water, and set the density of the water to 1.0 g / cm ³ and substitute it into the following equation: The open cell ratio was determined.

[Examples 1 and 2, Comparative Examples 1 and 2]
The following silica masterbatch, (A) component, (C) component, (D) component and other components are introduced into a homomixer (made by Tokushu Kika Co., Ltd.) at the mixing ratio shown in Table 1 and uniformly at 25 ° C. Mix until. A part of the obtained mixture was preserved and examined for storage stability. Subsequently, (B) component, (E) component, and (F) component were mix | blended with the obtained mixture, and it deaerated, and prepared the sponge-forming liquid silicone rubber composition. In Table 1, [SiH / Vi] is the molar ratio of silicon atom-bonded hydrogen atoms in the component corresponding to component (B) to the total vinyl groups in the component corresponding to component (A) in the composition. Represents.

The obtained sponge-forming liquid silicone rubber composition was crosslinked and cured under a condition of 90 ° C./10 minutes using a compression molding machine to prepare a water-containing silicone rubber test piece. Next, this test piece was left in an open system at 200 ° C. for 4 hours to remove water in the test piece, thereby obtaining a silicone rubber sponge test piece. Using this silicone rubber sponge test piece, density, hardness, tensile strength, elongation, shrinkage rate, and open cell rate were measured, and the results are shown in Table 1.

As a silica master batch, 100 parts by mass of dimethylpolysiloxane blocked with dimethylvinylsiloxy group at both ends of a molecular chain having a viscosity of 40 Pa · s, 40 parts by mass of fumed silica having a BET specific surface area of 225 m ² / g, 7 parts by mass of hexamethyldisilazane, water 2 parts by weight, dimethylhydroxysiloxy group-blocked dimethylsiloxane / methylvinylsiloxane copolymer with a viscosity of 20 mPa · s (vinyl group content = about 10.9% by weight) 0.2 parts by weight are put into a loss mixer The mixture was mixed until uniform at room temperature, and then heat-treated at 200 ° C. for 2 hours under reduced pressure.

The following components were used as the component (A-1).
Component (a-1): dimethylpolysiloxane blocked with a dimethylvinylsiloxy group blocked at both ends of a molecular chain having a viscosity of 9 Pa · s (vinyl group content = 0.14% by mass).
Component (a-2): dimethylpolysiloxane blocked with dimethylvinylsiloxy group-blocked dimethylpolysiloxane having a viscosity of 2 Pa · s (vinyl group content = 0.23 mass%).

The following components were used as the component (A-2).
Component (a-3): a trimethylsiloxy group-capped dimethylmethylvinylpolysiloxane having a viscosity of 7.5 Pa · s (both vinyl group content = 0.31% by mass).
Component (a-4): a dimethylvinylsiloxy group-capped dimethylsiloxane / methylvinylsiloxane copolymer having a viscosity of 350 mPa · s (vinyl group content = about 1.17% by mass).
Component (a-5): a trimethylsiloxy group-capped dimethylsiloxane / methylvinylsiloxane copolymer having a viscosity of 350 mPa · s (vinyl group content = about 0.9% by mass).

As the component (B), a trimethylsiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer having a viscosity of 63 mPa · s (silicon atom-bonded hydrogen atom content = about 0.70% by mass) was used.

As component (C), 1 part by weight of smectite clay (organic polymer composite purified bentonite manufactured by Hojun Co., Ltd .; pH 6.5) and 99.0 parts by weight of ion-exchanged water are charged into a homomixer and mixed until uniform at room temperature. A mixture of water and smectite clay was used.

As the component (D), the following components were used.
Component (d-1): Nonionic surfactant of HLB 4.3 (Sorbitan fatty acid ester, Rheidol SP-O10V manufactured by Kao Corporation).
Component (d-2): Nonionic surfactant of HLB 1.8 (sorbitan fatty acid ester, Rheidol SP-O30V manufactured by Kao Corporation).

As the component (E), a 1,3-divinyltetramethyldisiloxane solution of platinum with a 1,3-divinyltetramethyldisiloxane complex (platinum metal content = about 4000 ppm) was used. .

As component (F), 2 parts by mass of 1-ethynyl-1-cyclohexanol and dimethylpolysiloxane blocked with a dimethylvinylsiloxy group at both ends of a molecular chain having a viscosity of 10 Pa · s (vinyl group content = 0.13% by mass), 98 parts by mass Was used.

As a pigment masterbatch, Bengala (trade name: Bayferrox, manufactured by Bayer) 40 parts by mass and a dimethylvinylsiloxy group-capped dimethylpolysiloxane having a viscosity of 10 Pa · s (vinyl group content = 0.13% by mass) 60 A part by weight of the mixture was used.

Since the sponge-forming liquid silicone rubber composition of the present invention can form a low-density sponge having a uniform and fine open-cell structure, an electrophotographic copying machine, a laser beam printer, an on-demand printing machine, a facsimile machine, etc. It is suitably used for forming silicone rubber sponges used at high temperatures such as elastic materials for rolls and belts used in the above image forming apparatuses; heat insulating materials, sound absorbing materials, cushions, packings, gaskets, pads and the like.

Claims

(A) 100 parts by mass of an organopolysiloxane having at least two alkenyl groups in one molecule;
(B) Organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule {The amount of silicon-bonded hydrogen atoms in this component is 0.4 with respect to 1 mol of the alkenyl group in component (A). Amount to be ~ 20 mol},
(C) 100 to 1000 parts by mass of a mixture of water and an inorganic thickener,
(D) (D-1) a nonionic surfactant having an HLB value of 3 or more, and (D-2) a surfactant comprising a nonionic surfactant having an HLB value of less than 3 {provided ( The mass ratio of the component (D-1) to the component D-2) is at least 1. } 0.1 to 15 parts by mass,
A sponge-forming liquid silicone rubber composition comprising (E) a catalyst for hydrosilylation reaction (a sufficient amount for crosslinking the present composition) and (F) a curing retarder of 0.001 to 5 parts by mass.
Component (A) is (A-1) diorganopolysiloxane having two alkenyl groups on the molecular chain terminal and no alkenyl group on the molecular chain side chain, 10 to 90% by mass, and (A-2) 2. The sponge-forming liquid silicone rubber composition according to claim 1, which is an organopolysiloxane composed of 10 to 90% by mass of a diorganopolysiloxane having at least two alkenyl groups in the side chain of the molecular chain.
The sponge-forming liquid silicone rubber composition according to claim 1 or 2, wherein the inorganic thickener in component (C) is smectite.
The sponge-forming liquid silicone rubber composition according to claim 1, further comprising (G) silica fine powder at most 20 parts by mass with respect to 100 parts by mass of component (A).
A silicone rubber sponge obtained by crosslinking the sponge-forming liquid silicone rubber composition according to any one of claims 1 to 4 and then removing water from the silicone rubber.
6. The silicone rubber sponge according to claim 5, wherein the average bubble diameter is 1 μm or more and less than 50 μm, and the open cell ratio is 90% or more.