Multi-liquid sponge-forming silicone rubber composition

Abstract

Provided is a multi-pack type sponge-forming silicone rubber composition which has excellent storage stability and which forms a sponge having fine and uniform continuous bubbles after mixing. The invention relates to a multi-liquid type composition, which consists of a liquid I, a liquid II and a liquid III which are mixed to form a composition containing the following components: (A) organopolysiloxane with at least two alkenyl groups in one molecule; (B) an organopolysiloxane having at least two silicon atoms bonded to hydrogen atoms in one molecule; (C) water; (D) a thickening agent; (E) a surfactant; (F) silica micropowder; (G) an organosiloxane oligomer having a silicon atom-bonded hydroxyl group; and (H) a hydrosilylation reaction catalyst, in which the liquid I contains component (A) and component (H) and does not contain component (B), the liquid II contains component (B) and does not contain component (H), the liquid III contains component (C) and component (D), and any one of the liquid I and the liquid II, which does not contain component (B) and component (H) at the same time and contains component (E) and component (F), further contains component (G).

Description

Technical Field

[0001] The present invention relates to a multi-liquid sponge-forming silicone rubber composition. Background Art

[0002] Silicone rubber sponge has excellent heat resistance and weather resistance and is lightweight, so it is used in automotive parts; rollers and belts of image forming devices such as copiers and printers; in addition, various sealing parts such as packaging, gaskets, and O-rings.

[0003] As a method for forming such a silicone rubber sponge, there is known a method of uniformly dispersing water in a liquid silicone rubber composition and then removing the water after curing the composition or while curing the composition. Examples of the sponge-forming silicone rubber composition used in this method include: a sponge-forming silicone rubber composition (see Patent Document 1) comprising: a diorganopolysiloxane having at least two silicon-bonded alkenyl groups in one molecule, an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, water containing smectite clay, a silica filler, a nonionic surfactant, and a catalyst for a hydrosilylation reaction; and a sponge-forming silicone rubber composition (see Patent Document 2) comprising: a diorganopolysiloxane having alkenyl groups at both ends of the molecular chain and having no alkenyl groups in the side chains of the molecular chain, a diorganopolysiloxane having at least two alkenyl groups in the side chains of the molecular chain, an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, a mixture of water and smectite clay, a silica filler, a nonionic surfactant, a catalyst for a hydrosilylation reaction, and a curing retarder.

[0004] When such a sponge-forming silicone rubber composition is stored, it is generally divided into at least three liquids: a component comprising an alkenyl-containing organopolysiloxane and a catalyst for a hydrosilylation reaction, and not comprising an organopolysiloxane containing hydrogen atoms bonded to silicon atoms; a component comprising an organopolysiloxane containing hydrogen atoms bonded to silicon atoms and not comprising a catalyst for a hydrosilylation reaction; and a component comprising water and smectite clay, and not comprising both an organopolysiloxane containing hydrogen atoms bonded to silicon atoms and a catalyst for a hydrosilylation reaction. During curing, these three liquids are mixed (see Patent Document 3).

[0005] However, among these liquids, the liquid containing both a surfactant and a silica filler has a problem of increasing in thickness over time. Furthermore, due to the increase in thickness, the dispensing properties thereof change, and the properties of the obtained silicone rubber sponge change.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2004-346248

[0009] Patent Document 2: Japanese Patent Application Publication No. 2008-214625

[0010] Patent Document 3: International Publication No. WO2010 / 013847 Pamphlet Summary of the invention

[0011] Problems to be solved by the invention

[0012] An object of the present invention is to provide a multi-component sponge-forming silicone rubber composition having excellent storage stability of each liquid before mixing and forming a silicone rubber sponge having fine and uniform interconnected cells by mixing the liquids.

[0013] Solutions for solving problems

[0014] The multi-liquid sponge-forming silicone rubber composition of the present invention is composed of liquid I, liquid II and liquid III, and each liquid is mixed to form a composition comprising the following:

[0015] (A) 100 parts by mass of an organopolysiloxane having at least two alkenyl groups in one molecule;

[0016] (B) an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule {the silicon-bonded hydrogen atoms in this component are in an amount of 0.4 to 20 mol per 1 mol of alkenyl groups in the component (A)};

[0017] (C) 20 to 1,000 parts by weight of water;

[0018] (D) a thickener {0.01 to 15 parts by mass based on 100 parts by mass of the component (C)};

[0019] (E) 0.1 to 15 parts by weight of a surfactant;

[0020] (F) 1 to 20 parts by weight of silicon dioxide fine powder;

[0021] (G) 0.1 to 10 parts by mass of an organosiloxane oligomer having a silicon atom-bonded hydroxyl group; and

[0022] (H) a catalyst for a hydrosilylation reaction in an amount sufficient to crosslink the composition,

[0023] The multi-liquid sponge-forming silicone rubber composition is characterized in that:

[0024] The liquid I contains the component (A) and the component (H), but does not contain the component (B).

[0025] The liquid II contains the component (B) and does not contain the component (H).

[0026] The liquid III contains the component (C) and the component (D), but does not contain the component (B) and the component (H) at the same time.

[0027] At least one of the liquid I and the liquid II containing both the component (E) and the component (F) further contains the component (G).

[0028] Preferably, the component (A) is an organopolysiloxane composed of 10 to 90% by mass of (A-1) a diorganopolysiloxane having an average of two alkenyl groups at the ends of the molecular chain and no alkenyl groups in the side chains of the molecular chain, and 10 to 90% by mass of (A-2) a diorganopolysiloxane having at least two alkenyl groups in the side chains of the molecular chain.

[0029] Preferably, component (D) is at least one thickener selected from the group consisting of an inorganic thickener, cellulose fiber, a water-soluble polymer, a water-absorbent polymer, a hydrophilic complex consisting of the inorganic thickener and the water-soluble polymer, and a hydrophilic complex consisting of the inorganic thickener and the water-absorbent polymer.

[0030] Preferably, the component (E) is a surfactant consisting of a nonionic surfactant (E-1) having an HLB value of 3 or more and a nonionic surfactant (E-2) having an HLB value of less than 3 {wherein the mass ratio of the component (E-1) to the component (E-2) is at least 1.}.

[0031] The component (G) is preferably an organosiloxane oligomer having a silicon atom-bonded hydroxyl group content of 1 to 10% by mass.

[0032] Effects of the Invention

[0033] The multi-liquid sponge-forming silicone rubber composition of the present invention is characterized in that each liquid before mixing has excellent storage stability and a silicone rubber sponge having fine and uniform interconnected cells is formed by mixing the liquids. DETAILED DESCRIPTION

[0034] <Definition of terms>

[0035] The term "viscosity" used in this specification refers to the value at 25°C measured by a B-type rotational viscometer specified in JIS K 7117-1:1999 "Plastics - Liquid, emulsified or dispersed resins - Determination of apparent viscosity using a Brookfield type rotational viscometer" (unit: mPa·s or Pa·s). In addition, the "kinematic viscosity" refers to the value at 25°C measured by an Ubbelohde viscometer in accordance with JIS Z8803 (unit: mm 2 / s).

[0036] The multi-liquid sponge-forming silicone rubber composition of the present invention will be described in detail.

[0037] The present composition is composed of liquid I, liquid II, and liquid III, and each liquid is mixed to form a composition containing the above-mentioned components (A) to (H).

[0038] (A) component is the main agent of the present composition, and is an organopolysiloxane having at least two alkenyl groups in one molecule. As the alkenyl group in the (A) component, examples thereof include vinyl, allyl, isopropenyl, butenyl, isobutenyl, pentenyl, hexenyl, heptenyl, octenyl, pentenyl, nonenyl, decenyl, dodecenyl and the like alkenyl groups having 2 to 12 carbon atoms, preferably vinyl. The bonding position of the alkenyl group is not limited, and the alkenyl group may be bonded to the silicon atom at the end of the molecular chain and / or the silicon atom in the molecular chain. In addition, examples of silicon-bonded organic groups other than alkenyl groups in component (A) include: alkyl groups having 1 to 12 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl; cycloalkyl groups having 5 to 12 carbon atoms, such as cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl; aryl groups having 6 to 12 carbon atoms, such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups having 7 to 12 carbon atoms, such as benzyl and phenethyl; and groups in which a part or all of the hydrogen atoms in these groups are substituted with halogen atoms such as fluorine and chlorine, preferably methyl and phenyl.

[0039] The molecular structure of the component (A) is not limited, and examples thereof include linear, partially branched linear, branched, cyclic, and resinous, preferably linear or partially branched linear. The component (A) may be a mixture of two or more organopolysiloxanes having these molecular structures.

[0040] Examples of such component (A) include dimethyl polysiloxanes terminated at both ends of the molecular chain by dimethylvinylsiloxy groups, dimethyl polysiloxanes terminated at both ends of the molecular chain by diphenylvinylsiloxy groups, dimethyl siloxane / methyl phenyl siloxane copolymers terminated at both ends of the molecular chain by dimethylvinylsiloxy groups, dimethyl siloxane / diphenyl siloxane copolymers terminated at both ends of the molecular chain by dimethylvinylsiloxy groups, dimethyl siloxane / methyl phenyl siloxane copolymers terminated at both ends of the molecular chain by diphenylvinylsiloxy groups, dimethyl siloxane / methyl phenyl siloxane copolymers terminated at both ends of the molecular chain by dimethylvinylsiloxy groups, and dimethyl polysiloxanes terminated at both ends of the molecular chain by dimethylvinylsiloxy groups. The present invention relates to a copolymer of dimethylsiloxane / methylphenylsiloxane / methylvinylsiloxane terminated with dimethylvinylsiloxane / diphenylsiloxane / methylvinylsiloxane, a copolymer of dimethylvinylsiloxane / diphenylsiloxane / methylvinylsiloxane terminated with dimethylvinylsiloxane at both ends of the molecular chain, a copolymer of methylvinylsiloxane / methylphenylsiloxane terminated with trimethylsiloxy at both ends of the molecular chain, a copolymer of methylvinylsiloxane / diphenylsiloxane terminated with trimethylsiloxy at both ends of the molecular chain, a copolymer of dimethylsiloxane / methylvinylsiloxane terminated with trimethylsiloxy at both ends of the molecular chain, and a mixture of two or more of these organopolysiloxanes.

[0041] The viscosity of the component (A) is not limited, but is preferably 50 mPa·s or more or 100 mPa·s or more at 25° C., and on the other hand, 100,000 mPa·s or less. This is because, when the viscosity of the component (A) is above the lower limit and below the upper limit, it is easy to obtain a silicone rubber sponge having stable emulsions of the silicone rubber composition and uniform cells.

[0042] Such component (A) is preferably a mixture of (A-1) a 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 molecular chain side chains.

[0043] The component (A-1) is a diorganopolysiloxane having an average of two alkenyl groups at the molecular chain terminals and no alkenyl groups at the molecular chain side chains. Specifically, examples thereof include: dimethylvinylsiloxy-terminated dimethylpolysiloxane; dimethylvinylsiloxy-terminated dimethylsiloxane / methylphenylsiloxane copolymer; and branched dimethylpolysiloxane having a main chain composed of repeating dimethylsiloxane units, a portion of the main chain being branched, and the molecular chain terminals being terminated with dimethylvinylsiloxy groups. Preferably, the diorganopolysiloxane has a substantially linear main chain.

[0044] Component (A-2) is a diorganopolysiloxane having at least two alkenyl groups in a side chain of the molecular chain, and specifically, examples thereof include: trimethylsiloxy-terminated methylvinylpolysiloxane; trimethylsiloxy-terminated dimethylsiloxane / methylvinylsiloxane copolymer; dimethylvinylsiloxy-terminated methylvinylpolysiloxane; dimethylvinylsiloxy-terminated dimethylsiloxane / methylvinylsiloxane copolymer; trimethylsiloxy-terminated dimethylsiloxane / methylvinylsiloxane / methylphenylsiloxane copolymer; a branched dimethylsiloxane / methylvinylsiloxane copolymer having a main chain composed of a repeating dimethylsiloxane unit and a methylvinylsiloxane unit, a portion of the main chain being branched, and a molecular chain terminal being terminated with a trimethylsiloxy group, preferably a diorganopolysiloxane having a substantially linear main chain.

[0045] The mixing ratio of component (A-1) to component (A-2) is not limited, but from the viewpoint of improving the shrinkage rate of the obtained silicone rubber sponge, component (A) is preferably composed of 10 to 90% by mass of component (A-1) and 10 to 90% by mass of component (A-2).

[0046] The component (B) is a crosslinking agent of the present composition and is an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule. The silicon-bonded hydrogen atoms in the component (B) can be bonded to the silicon atoms at the ends of the molecular chain and / or the silicon atoms in the molecular chain. The molecular structure of the component (B) is not limited and examples thereof include: linear, linear with a portion of branches, branched, cyclic, and dendritic, preferably linear, and linear with a portion of branches. The component (B) is preferably a linear organopolysiloxane.

[0047] As such component (B), there can be exemplified: dimethyl polysiloxane terminated with dimethyl hydrogen siloxy groups at both ends of the molecular chain; dimethyl siloxane / methyl phenyl siloxane copolymer terminated with dimethyl hydrogen siloxy groups at both ends of the molecular chain; dimethyl siloxane / methyl hydrogen siloxane copolymer terminated with dimethyl hydrogen siloxy groups at both ends of the molecular chain; dimethyl siloxane / methyl hydrogen siloxane copolymer terminated with trimethyl siloxy groups at both ends of the molecular chain; 1 / 2 Unit and SiO 4 / 2 Organic polysiloxane composed of units; and H(CH3)2SiO 1 / 2 Unit, (CH3)3SiO 1 / 2 Unit and SiO 4 / 2 Unit composition of organic polysiloxane.

[0048] The viscosity of the component (B) is not limited, but the kinematic viscosity at 25° C. is preferably 1 mm 2 / s or more and 1,000mm 2 / s or less. Alternatively, the viscosity at 25°C is preferably 5 mPa·s or more, and on the other hand, 1,000 mPa·s or less. This is because if the viscosity of the component (B) is above the above lower limit and below the above upper limit, it is easy to obtain a silicone rubber sponge having a stable emulsion of the silicone rubber composition and uniform bubbles.

[0049] The content of component (B) is in the range of 0.4 to 20 moles of silicon-bonded hydrogen atoms per 1 mole of alkenyl groups in component (A), preferably, the lower limit is 1.0 mole, 1.5 mole or 1.8 mole, and the upper limit is 10 mole or 5 mole. This is because if the content of component (B) is within the above range, the compression set of the obtained silicone rubber sponge is improved.

[0050] The water of the component (C) is a component used to make the silicone rubber porous by removing it from the silicone rubber after crosslinking the present composition. The content of the component (C) is in the range of 20 to 1,000 parts by mass relative to 100 parts by mass of the component (A), and preferably the lower limit is 20 parts by mass, 30 parts by mass, 40 parts by mass or 50 parts by mass, and on the other hand, the upper limit is 800 parts by mass, 650 parts by mass or 500 parts by mass. This is because if the content of the component (C) is above the lower limit of the above range, the obtained silicone rubber sponge is easy to have uniform bubbles in a porous state, and on the other hand, if the content of the component (C) is below the upper limit of the above range, it is easy to obtain a silicone rubber sponge.

[0051] The water of the component (C) is not limited, and tap water, well water, ion-exchanged water, distilled water, etc. can be used. In particular, the component (C) is preferably ion-exchanged water from the viewpoint of stable dispersion in the component (A).

[0052] The thickener of the component (D) is a component for thickening the water of the component (C), facilitating the dispersion of the component (C) in the component (A), stabilizing the dispersion state of the component (C) in the component (A), and making the obtained silicone rubber uniformly porous. Such a component (D) is preferably at least one selected from the group consisting of an inorganic thickener, cellulose fiber, a water-soluble polymer, a water-absorbent polymer, a hydrophilic composite composed of the above inorganic thickener and the above water-soluble polymer, and a hydrophilic composite composed of the above inorganic thickener and the above water-absorbent polymer.

[0053] The inorganic thickener of the component (D) is a natural or synthetic inorganic thickener, and examples thereof include natural or synthetic smectite clays such as bentonite, hectorite, saponite, sauconite, beidellite, and nontronite, which are clay minerals as the main components. Such smectite clays can be obtained, for example, by using Sumecton (registered trademark of Kunimine Industries, Ltd.), Rucentite (registered trademark of Co-op Chemical Co., Ltd.), which are hydrothermally synthesized products, Kunipia (registered trademark of Kunimine Industries, Ltd.), BEN-GEL (registered trademark of Hojun Co., Ltd.), Benton (registered trademark of Elementis Co., Ltd.), and VEEGUM (registered trademark of Vanderbilt Co., Ltd.), which are natural refined products. The inorganic thickener is preferably bentonite, hectorite, or saponite, from the viewpoint of being able to increase the viscosity when dispersed in water and reduce the content of the component (E). From the viewpoint of maintaining the heat resistance of the silicone rubber sponge, the pH of these smectite clays is preferably in the range of pH 5.0 to 9.0. In addition, a hydrophilic composite composed of such smectite clays and a water-soluble polymer or a water-absorbing polymer such as polyacrylic acid may also be used.

[0054] The cellulose fiber of component (D) is a material obtained by nanofibrillating natural or synthetic cellulose fibers by chemical treatment or physical treatment. From the viewpoints of dispersibility and thickening, the number average fiber diameter of such cellulose fibers is preferably within the range of 2 to 150 nm, within the range of 2 to 100 nm, or within the range of 2 to 10 nm. This is because, if the number average fiber diameter is within the above range, it is not easy to settle when dispersed in water, and can maintain fluidity and thicken.

[0055] The cellulose fibers of the component (D) can be obtained using an aqueous dispersion of cellulose nanofibers manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. (trade name: Rheocrysta C-2SP).

[0056] Examples of the water-soluble polymer of the component (D) include alginic acid, sodium alginate, sodium salts of carboxylic acid esters, sodium salts of carboxycellulose, methyl cellulose, cellulose ether, hydroxyethyl cellulose, modified starch, polyvinyl alcohol, polyacrylates, or sodium salts of polyacrylates.

[0057] Moreover, as a water-absorbent polymer of (D)component, a polyacrylic acid salt crosslinked body and a polyoxyalkylene type water-absorbent resin can be illustrated.

[0058] The content of component (D) is within the range of 0.01 to 15 parts by mass relative to 100 parts by mass of component (C), preferably, the lower limit is 0.05 parts by mass or 0.1 parts by mass, and the upper limit is 10 parts by mass or 5 parts by mass. This is because, if the content of component (D) is greater than the lower limit of the above range, component (C) can be sufficiently thickened, and, on the other hand, if the content of component (D) is less than the upper limit of the above range, the emulsification of the silicone rubber composition can be stabilized.

[0059] The component (E) is a surfactant used to uniformly emulsify water in the silicone rubber composition and make the obtained silicone rubber uniformly porous. As such component (E), anionic, cationic, zwitterionic and nonionic surfactants can be exemplified, and specifically, nonionic surfactants such as glycerol fatty acid esters, polyglycerol fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, polyethylene glycol fatty acid esters, polypropylene glycol fatty acid esters, polyoxyethylene glycerol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene / polyoxypropylene block copolymers, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene fatty acid amides can be exemplified; nonionic surfactants composed of polyorganosiloxanes such as polysiloxane / polyoxyethylene graft copolymers; cationic surfactants such as aliphatic amine salts, quaternary ammonium salts, and alkyl pyridinium salts; anionic surfactants such as higher fatty acid salts, higher alcohol sulfate ester salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, and polyethylene glycol sulfate ester salts; and zwitterionic surfactants of carboxybetaine type or glycine type. In particular, nonionic surfactants are preferred from the viewpoint of having little influence on crosslinking caused by the hydrosilylation reaction of the present composition.

[0060] These surfactants can be used alone or in combination of two or more. The HLB value of the emulsifier (it should be noted that when two or more surfactants are used in combination, the weight average HLB value) is preferably 1 to 10, 1.5 to less than 6, or 3.5 to less than 6.

[0061] As the component (E), it is preferred to use a surfactant composed of a nonionic surfactant having an HLB value of 3 or more (E-1) and a nonionic surfactant having an HLB value of less than 3 (E-2). The mass ratio of the component (E-1) to the component (E-2) is at least 1, preferably at least 5, at least 8, at least 10, or at least 15. In addition, the mass ratio of the component (E-1) to the component (E-2) is preferably at most 100 or less, more preferably at most 80, at most 70, at most 60, or at most 50. This is because if the mass ratio is at least the lower limit, a low-density sponge having a uniform and fine interconnected cell structure can be formed, and on the other hand, if the mass ratio is at most the upper limit, the component (C) and the component (D) can be dispersed in the component (A) with good stability, and as a result, a silicone rubber sponge having a uniform and fine interconnected cell structure can be formed.

[0062] The content of component (E) is in the range of 0.1 to 15 parts by mass relative to 100 parts by mass of component (A), preferably, the lower limit is 0.2 parts by mass, and the upper limit is 10 parts by mass. This is because, if the content of component (E) is greater than the lower limit of the above range, component (C) can be uniformly dispersed in component (A), and, if the content of component (E) is less than the lower limit of the above range, the mechanical properties and electrical properties of the obtained silicone rubber sponge will not be affected.

[0063] Component (F) is a silica powder formulated to improve the mechanical strength of the obtained silicone rubber sponge. Examples of component (F) include fumed silica and precipitated silica. In addition, these silica powders can be surface treated with chain polyorganosiloxane, cyclic polyorganosiloxane, hexamethyldisilazane, various organosilanes, etc. In addition, the specific surface area of ​​component (F) measured by the BET adsorption method is preferably 50 to 500 m 2 / g or 80~450m 2 / g.

[0064] The content of the component (F) is in the range of 1 to 20 parts by mass relative to 100 parts by mass of the component (A). This is because, if the content of the component (F) is at least the lower limit of the above range, the mechanical strength of the obtained silicone rubber sponge can be improved, while on the other hand, if the content of the component (F) is at most the upper limit of the above range, the uniformity and fineness of the bubbles of the obtained silicone rubber sponge will not be impaired.

[0065] The component (G) is an organosiloxane oligomer having a silicon atom-bonded hydroxyl group, which is formulated in order to improve the storage stability of each liquid when the multi-liquid sponge-forming silicone rubber composition is prepared. Examples of the silicon atom-bonded organic group in the component (G) include: alkyl groups having 1 to 12 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl; cycloalkyl groups having 5 to 12 carbon atoms, such as cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl; alkenyl groups having 2 to 12 carbon atoms, such as vinyl, allyl, isopropenyl, butenyl, isobutenyl, pentenyl, hexenyl, heptenyl, octenyl, pentenyl, nonenyl, decenyl and dodecenyl; aryl groups having 6 to 12 carbon atoms, such as phenyl, tolyl, xylyl and naphthyl; aralkyl groups having 7 to 12 carbon atoms, such as benzyl and phenethyl; and groups in which some or all of the hydrogen atoms in these groups are substituted with halogen atoms such as fluorine and chlorine, preferably methyl, vinyl and phenyl. The content of silicon-bonded hydroxyl groups (i.e., silanol groups) in the component (G) is not particularly limited, but is preferably 1 to 10% by mass. Examples of such component (G) include: dimethylsiloxane / methylvinylsiloxane copolymer oligomers terminated with dimethylhydroxysiloxy groups at both ends of the molecular chain; methylvinylsiloxane oligomers terminated with dimethylhydroxysiloxy groups at both ends of the molecular chain; dimethylsiloxane oligomers terminated with dimethylhydroxysiloxy groups at both ends of the molecular chain; and methylphenylsiloxane oligomers terminated with methylphenylhydroxysiloxy groups at both ends of the molecular chain.

[0066] The content of the component (G) is in the range of 0.1 to 10 parts by mass, preferably in the range of 0.1 to 5 parts by mass or in the range of 0.1 to 3 parts by mass, relative to 100 parts by mass of the component (A). This is because, if the content of the component (G) is at least the lower limit of the above range, the storage stability of each liquid when the multi-liquid sponge-forming silicone rubber composition is prepared can be improved, while on the other hand, if the content of the component (G) is at most the upper limit of the above range, the mechanical properties of the obtained silicone rubber sponge will not be affected.

[0067] The component (H) is a catalyst for the hydrosilylation reaction for promoting the hydrosilylation reaction of the present composition, and examples thereof include: a platinum-based catalyst, a palladium-based catalyst, and a rhodium-based catalyst, preferably a platinum-based catalyst. Examples of such component (H) include: chloroplatinic acid; alcohol-modified chloroplatinic acid; a coordination compound of chloroplatinic acid and an olefin, vinyl siloxane, or acetylene compound; a coordination compound of platinum and an olefin, vinyl siloxane, or acetylene compound, and a platinum-based catalyst such as a powdered platinum-based catalyst dispersed in a thermoplastic resin; in addition, palladium-based catalysts such as tetrakis(triphenylphosphine)palladium, and rhodium-based catalysts such as chlorotris(triphenylphosphine)rhodium.

[0068] The content of the component (H) is an amount sufficient to crosslink the present composition. Specifically, the catalyst metal in the component (H) is preferably in an amount within a range of 0.01 to 500 ppm, or in an amount within a range of 0.1 to 100 ppm, in terms of mass unit, relative to the total amount of the components (A) and (B).

[0069] In order to adjust the crosslinking speed and the usable time of the present composition, a hydrosilylation reaction inhibitor may be further contained in the present composition. Examples of the hydrosilylation reaction inhibitor include: alkyl groups such as 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyl-3-ol, 3-phenyl-1-butyn-3-ol, and 1-ethynyl-1-cyclohexanol; enyne compounds such as 3-methyl-3-pentene-1-yne and 3,5-dimethyl-3-hexene-1-yne; tetramethyltetravinylcyclotetrasiloxane and tetramethyltetrahexenylcyclotetrasiloxane; and alkyne-containing silanes such as methyltris(1,1-dimethyl-2-butoxy)silane and vinyltris(1,1-dimethyl-2-butoxy)silane.

[0070] The content of the hydrosilylation reaction inhibitor is not limited, but is appropriately selected according to the method of use of the present composition and the molding method. From the viewpoint of being able to sufficiently adjust the crosslinking speed of the present composition and the usable time of the operation, it is preferably in the range of 0.001 to 5 parts by mass relative to 100 parts by mass of the component (A).

[0071] In order to impart conductivity to the obtained silicone rubber sponge, the present composition may also contain a conductive filler. Examples of the conductive filler include carbon-based conductive agents such as carbon black, carbon fiber, carbon nanotubes, and graphite; metal powders such as gold, silver, and nickel; conductive zinc oxide, conductive titanium oxide, and conductive aluminum oxide; conductive fillers that have been subjected to a conductive coating treatment on the surface of various fillers, such as metal plating treatment; and mixtures of two or more of these. From the perspective of obtaining good conductivity by adding a small amount, the conductive filler is preferably carbon black, and specifically, examples include acetylene black, conductive furnace black (CF), superconducting furnace black (SCF), special conductive furnace black (XCF), conductive slot black (CC), and furnace black or slot black that has been heat-treated at a high temperature of about 1500°C. The content of the conductive filler is not limited, but from the perspective of being able to obtain a good sponge, it is preferably 100 parts by mass or less or 70 parts by mass or less relative to 100 parts by mass of component (A).

[0072] As for the present composition, as long as it does not impair the purpose of the present invention, it may also contain as other arbitrary components: reinforcing fillers other than silica such as fumed titanium oxide; non-reinforcing fillers such as quartz powder, diatomaceous earth, aluminosilicate, iron oxide, zinc oxide, calcium carbonate, aluminum oxide, cerium oxide, mica, clay, zinc carbonate, etc.; fillers whose surface is treated with organic silicon compounds such as organic silane and polyorganosiloxane; in addition, preservatives, rust inhibitors, pigments, heat resisters, flame retardants, internal mold release agents, plasticizers, acid absorbers, and non-functional silicone oils.

[0073] The present composition is characterized in that it is composed of liquid I, liquid II, and liquid III, and each liquid is mixed to form a composition containing the above-mentioned components (A) to (H).

[0074] The above-mentioned liquid I contains the above-mentioned component (A) and the above-mentioned component (H), but does not contain the above-mentioned component (B).

[0075] The liquid II contains the component (B) and does not contain the component (H).

[0076] The liquid III contains the component (C) and the component (D), but does not contain the component (B) and the component (H) at the same time.

[0077] At least one of the above liquids I and II containing both the above components (E) and (F) further contains the above component (G). It has been found that in the above liquid containing both the above components (E) and (F), the silanol groups on the surface of the above component (F) are promoted by the hydrophilic groups in the above component (E) to cause pseudo crosslinking and increase in viscosity over time. In contrast, the present invention further contains the above component (G) to suppress the increase in viscosity, thereby completing the present invention.

[0078] That is, when liquid I contains the above-mentioned component (A) and the above-mentioned component (H), and further contains the above-mentioned component (E) and the above-mentioned component (F), the above-mentioned liquid I needs to further contain the above-mentioned component (G). On the other hand, when liquid II contains the above-mentioned component (B), and further contains the above-mentioned component (E) and the above-mentioned component (F), the above-mentioned liquid II needs to further contain the above-mentioned component (G). It should be noted that liquid III contains the above-mentioned component (C) and the above-mentioned component (D), but there is almost no mode in which the above-mentioned component (E) and the above-mentioned component (F) are contained at the same time.

[0079] In order to improve heat resistance, when a metal oxide such as cerium oxide, iron oxide, or titanium oxide is blended, it is preferably not contained together with the component (E) in order not to impair the chemical stability of the component (E).

[0080] There is no limitation on the method of forming a silicone rubber sponge using the present composition. For example, after uniformly emulsifying the present composition, it is injected into the cavity of a molding die and maintained at a temperature of less than 100°C, preferably 50 - 90°C, under pressure to form a silicone rubber molded body in a water-containing state. After taking it out of the die, it is vulcanized twice at 120 - 250°C, more preferably 120 - 210°C, and water is removed from the water-containing silicone rubber molded body, whereby a silicone rubber sponge having fine and uniform air bubbles can be obtained. Alternatively, the present composition may be discharged in a rod shape from a nozzle, for example, introduced into hot water at 80 - 100°C to be cured, and the cured product is dried with hot air to produce a cord-shaped silicone rubber sponge. Alternatively, the present composition may be coated on a peelable substrate such as a resin film, for example, heated to 50 - 120°C to be cured, and dried with hot air to remove water, or while heating to remove water and curing it, the peelable substrate is removed to form a silicone rubber sponge sheet. Or, the present composition may be coated on a synthetic fiber fabric or a glass cloth, for example, heated to 50 - 120°C to be cured, and dried with hot air to remove water, or while heating to remove water and curing it, to form a silicone rubber sponge-coated cloth.

[0081] The silicone rubber sponge has excellent water absorption and water retention properties, and is not prone to volume expansion even when absorbing water, that is, it is not prone to swelling. Therefore, it is suitable as a cooling sheet material and a water absorption pad material. In addition, the silicone rubber sponge is also suitable as an absorption material and a retention material for aqueous solutions of inorganic salts, organic compounds, or hydrophilic organic compounds other than water. The thickness of the silicone rubber sponge layer is not limited, and from the viewpoint of effectively utilizing rubber elasticity, it is preferably in the range of 0.05 - 80 mm or 0.1 - 50 mm.

[0082] Examples

[0083] The multi-liquid type sponge-forming silicone rubber composition of the present invention will be described in more detail by way of examples. It should be noted that the viscosity in the examples is the value at 25°C.

[0084] <Viscosity change of Liquid I and Liquid II>

[0085] Liquid I and Liquid II were stored at 25°C, and their viscosities at the initial stage, one month later, two months later, and three months later were measured using a B-type rotational viscometer according to the method for measuring the apparent viscosity of plastics - liquid, emulsion, or dispersed resins - using a Brookfield type rotational viscometer specified in JIS K 7117-1:1999.

[0086] <Density>

[0087] The density of the silicone rubber sponge was measured in accordance with JIS K 6249:2003 "Test Methods for Uncured and Cured Silicone Rubbers".

[0088] <Asker C Hardness>

[0089] The Asker C hardness of the silicone rubber sponge was measured in accordance with the test method of the C-type hardness tester specified in JIS K 7312:1996 "Physical Test Methods for Thermosetting Polyurethane Elastomer Mouldings". It should be noted that in the measurement, two test pieces of the silicone rubber sponge with a thickness of 6 mm were overlapped and used.

[0090] <Tensile Strength, Elongation at Break>

[0091] The tensile strength and elongation at break of the silicone rubber sponge were measured in accordance with the method specified in JIS K 6249:2003 "Test Methods for Uncured and Cured Silicone Rubbers".

[0092] <Tear Strength>

[0093] The tear strength of the silicone rubber sponge was measured in accordance with the method specified in JIS K 6249:2003 "Test Methods for Uncured and Cured Silicone Rubbers". It should be noted that the measurement was carried out through a test piece of the silicone rubber sponge with a thickness of 6 mm.

[0094] <Rebound Elasticity>

[0095] The resilience of the silicone rubber sponge was measured in accordance with the method specified in JIS K 6255:1996 "Vulcanized Rubber and Thermoplastic Rubber - Method of Determining Rebound Elasticity".

[0096] <Compression Set>

[0097] The compression set of the silicone rubber sponge was measured in accordance with the method specified in JIS K 6249:2003 "Test Methods for Uncured and Cured Silicone Rubbers". It should be noted that the compression set is the value after being treated at 180 °C and 25% compression for 22 hours.

[0098] [Examples 1 to 3, Comparative Example 1]

[0099] The following components were respectively put into a homogenizing mixer (manufactured by Tokushu Kika Co., Ltd.) according to the blending amounts in Table 1, and mixed at 25 °C until uniform to prepare Liquid I and Liquid II. The viscosity change of Liquid I and Liquid II at 25 °C was measured. In addition, Liquid I and Liquid II were mixed with Liquid III prepared separately to prepare a sponge-forming silicone rubber composition. It should be noted that in the silicone rubber composition, the molar ratio of the total of the silicon-bonded hydrogen atoms in the component equivalent to component (B) to the vinyl group in the component equivalent to component (A) was set to 3.

[0100] The obtained sponge-forming silicone rubber composition was crosslinked / cured at 90°C / 10 minutes using a compression molding machine to produce a silicone rubber test piece in a water-containing state. Next, the test piece was placed in an open system at 200°C for 4 hours to remove the water in the test piece to obtain a silicone rubber sponge test piece. Using the silicone rubber sponge test piece, the density, Asker C hardness, tensile strength, elongation at break, tear strength, rebound elastic modulus, and compression set were measured, and the results are shown in Table 2.

[0101] As the component (A-1), the following components were used.

[0102] Component (a1): dimethylpolysiloxane having a viscosity of 10 Pa·s and having dimethylvinylsiloxy groups capped at both ends of the molecular chain (vinyl content = 0.14% by mass).

[0103] As the component (A-2), the following components were used.

[0104] Component (a2): dimethylmethylvinyl polysiloxane having a viscosity of 38 Pa·s and having trimethylsiloxy groups capped at both ends of the molecular chain (vinyl content = 0.50% by mass).

[0105] Component (a3): a dimethylsiloxane / methylvinylsiloxane copolymer having a viscosity of 350 mPa·s and end-capped with dimethylvinylsiloxy groups at both ends of the molecular chain (vinyl content = about 1.17% by mass).

[0106] As (B) component, the following components were used.

[0107] Component (b1): dimethylsiloxane / methylhydrogensiloxane copolymer having a molecular chain end-terminated with trimethylsiloxy groups and a viscosity of 52 mPa·s (silicon atom-bonded hydrogen atom content = about 0.70 mass %)

[0108] As the (C) component, (c1) ion exchange water was used, and as the (D) component, (d1) smectite clay (organic polymer composite purified bentonite manufactured by HOJUN Co., Ltd.; pH 6.5) was used. 0.85 parts by mass of smectite clay and 99.15 parts by mass of ion exchange water were added to a homogenizer in advance, and mixed at room temperature until uniform, to prepare liquid III. It should be noted that the same liquid III was used in Examples 1 to 3 and Comparative Example 1.

[0109] As the (E) component, the following components were used.

[0110] (e1) Component: nonionic surfactant having an HLB value of 4.3 (sorbitan fatty acid ester, Rheodol SP-010V manufactured by Kao Corporation).

[0111] (e-2) Component: nonionic surfactant having an HLB of 1.8 (sorbitan fatty acid ester, Rheodol SP-030V manufactured by Kao Corporation).

[0112] As the component (F), the following silica master particles were used.

[0113] Component (f1): 100 parts by mass of dimethyl polysiloxane (vinyl content = 0.09 mass %) with a molecular chain end-terminated by dimethylvinylsiloxy groups and a viscosity of 40 Pa·s and a BET specific surface area of ​​380 m2 was added to a Ross mixer. 2 50 parts by mass of fumed silica (10 parts by mass of hexamethyldisilazane) and 2 parts by mass of water were mixed at room temperature until uniform, and then heated at 200°C for 2 hours under reduced pressure to prepare a silica masterbatch.

[0114] As (G) component, the following components were used.

[0115] (g1) Component: dimethylsiloxane / methylvinylsiloxane copolymer having molecular chain ends blocked with dimethylhydroxysiloxy groups and a viscosity of 19 mPa·s (content of silicon-bonded hydroxyl groups = 8.2% by mass)

[0116] Component (g2): dimethylsiloxane oligomer terminated with dimethylhydroxysiloxy groups at both ends of the molecular chain with a viscosity of 21 mPa·s (content of hydroxyl groups bonded to silicon atoms = 8.5% by mass)

[0117] Component (g3): a methylphenylsiloxane oligomer having a viscosity of 440 mPa·s and end-capped with methylphenylhydroxysiloxy groups at both ends of the molecular chain (content of hydroxyl groups bonded to silicon atoms = 6.5% by mass)

[0118] As the (H) component, the following components were used.

[0119] Component (h1): A fine particle platinum-based catalyst having an average particle size of 1 μm and composed of a thermoplastic silicone resin having a softening point of 65° C. and containing a 1,3-divinyltetramethyldisiloxane complex of platinum in an amount of about 0.4% by mass as platinum metal.

[0120] As other components, the following pigment pastes were used.

[0121] (i1) Component: A mixture of 60 parts by mass of dimethyl polysiloxane (vinyl content = 0.14% by mass) having a viscosity of 10 Pa·s and having dimethylvinylsiloxy groups at both ends of the molecular chain blocked with dimethyl polysiloxane (vinyl content = 0.14% by mass) and 40 parts by mass of iron oxide (product name: Bayferox, manufactured by Bayer AG) having an average particle size of 0.17 μm

[0122] [Table 1]

[0123]

[0124] [Table 2]

[0125]

[0126] Industrial Applicability

[0127] The multi-liquid sponge-forming silicone rubber composition of the present invention has excellent storage stability of each liquid before mixing, and a silicone rubber sponge having fine and uniform continuous cells is formed by mixing the liquids. Therefore, it is suitable for forming silicone rubber sponges used in harsh environments such as heat insulating materials, sound absorbing materials, cushions, seals, gaskets, and liners.

Claims

1. A multi-liquid sponge-forming silicone rubber composition, comprising liquid I, liquid II and liquid III, wherein each liquid is mixed to form a composition comprising: (A) 100 parts by mass of an organopolysiloxane having at least two alkenyl groups in one molecule; (B) an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule {the silicon-bonded hydrogen atoms in this component are in an amount of 0.4 to 20 mol per 1 mol of alkenyl groups in the component (A)}; (C) 20 to 1,000 parts by weight of water; (D) a thickener {0.01 to 15 parts by mass based on 100 parts by mass of the component (C)}; (E) 0.1 to 15 parts by weight of a surfactant; (F) 1 to 20 parts by weight of silicon dioxide fine powder; (G) 0.1 to 10 parts by mass of an organosiloxane oligomer having a silicon atom-bonded hydroxyl group; and (H) a catalyst for a hydrosilylation reaction in an amount sufficient to crosslink the composition, The multi-liquid sponge-forming silicone rubber composition is characterized in that: The liquid I contains the component (A) and the component (H), but does not contain the component (B). The liquid II contains the component (B) but does not contain the component (H). The liquid III contains the component (C) and the component (D), but does not contain the component (B) and the component (H) at the same time. At least one of the liquid I and the liquid II containing both the component (E) and the component (F) further contains the component (G) and a multi-liquid sponge-forming silicone rubber composition.

2. The multi-liquid sponge-forming silicone rubber composition according to claim 1, wherein The component (A) is an organopolysiloxane composed of 10 to 90% by mass of (A-1) a diorganopolysiloxane having an average of two alkenyl groups at the molecular chain terminals and no alkenyl groups in the molecular chain side chains and 10 to 90% by mass of (A-2) a diorganopolysiloxane having at least two alkenyl groups in the molecular chain side chains.

3. The multi-liquid sponge-forming silicone rubber composition according to claim 1, wherein Component (D) is at least one thickener selected from the group consisting of an inorganic thickener, cellulose fiber, a water-soluble polymer, a water-absorbing polymer, a hydrophilic complex consisting of the inorganic thickener and the water-soluble polymer, and a hydrophilic complex consisting of the inorganic thickener and the water-absorbing polymer.

4. The multi-liquid sponge-forming silicone rubber composition according to claim 1, wherein The component (E) is a surfactant composed of a nonionic surfactant (E-1) having an HLB value of 3 or more and a nonionic surfactant (E-2) having an HLB value of less than 3 {wherein the mass ratio of the component (E-1) to the component (E-2) is at least 1}.

5. The multi-liquid sponge-forming silicone rubber composition according to claim 1, wherein The component (G) is an organosiloxane oligomer having a silicon atom-bonded hydroxyl group content of 1 to 10% by mass.

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