JP5358934B2 - Method for producing silicone rubber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method for producing silicone rubber allowing crosslinking of a silicone rubber composition at high temperature in a short time, causing no surface crosslinking inhibition due to oxygen inhibition of an organic peroxide during crosslinking when the organic peroxide is used as a curing agent, and requiring no consideration on surface oxidation deterioration of silicone due to high temperature. <P>SOLUTION: In this method for producing silicone rubber, the silicone rubber composition comprising (A) an organopolysiloxane containing an alkenyl group combined with at least two silicon atoms in the molecule and (B) a curing agent sufficient in amount to cure the component (A) is hot-air crosslinked by using superheated steam of 120-600&deg;C in a normal pressure atmosphere. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a silicone rubber, and more specifically, a method for producing a silicone rubber in which a silicone rubber composition is crosslinked and molded using superheated steam at 120 to 600 ° C. as a heat source for atmospheric pressure hot-air crosslinking. It is about.

  Silicone rubber has excellent weather resistance, electrical properties, low compression set, heat resistance, cold resistance, and other properties, so it can be used in various fields including electrical equipment, automobiles, architecture, medical care, and foods. Widely used. For example, rubber contacts used as rubber contacts for remote controllers, typewriters, word processors, computer terminals, musical instruments, etc .; architectural gaskets; various rolls such as copier rolls, development rolls, transfer rolls, charging rolls, paper feed rolls, etc. Anti-vibration rubber for audio devices, etc .; use for compact disc packing used in computers, etc.

  Currently, the demand for silicone rubber is increasing, and the development of silicone rubber having excellent characteristics is desired. These silicone rubbers are generally used in the form of a composition containing a polyorganosiloxane having a high degree of polymerization and a reinforcing filler. This composition is prepared by, for example, mixing a reinforcing filler and various dispersion materials with a raw material polymer using a mixing apparatus such as a dough mixer or a two-roller.

As a method for molding the silicone rubber composition, a rubber composition to which a crosslinking agent has been added and mixed is compressed (pressed) for about several seconds to 60 minutes between iron plates heated to 100 to 250 ° C. to obtain a molded product. “Press molding”, “HAV molding (HotAir Vulcanization)”, which is held in a hot air drier or heating furnace set to an atmosphere of 100 to 500 ° C. for about several seconds to 30 minutes and is subjected to atmospheric pressure hot air crosslinking, steam pressure of 4 to 10 kg / Examples include “steam cross-linking” in which cross-linking is performed by holding in a pressure kettle set to about cm ^{2 for} about several minutes to 60 minutes.

As a method for molding the silicone rubber, a method in which heat energy can be efficiently applied in a short time and a method with simple molding workability are desirable, and a method in which the silicone rubber is more difficult to deteriorate (oxidize) during heating is desirable. Press crosslinking is difficult to oxidize due to heat during molding, but it is a batch molding method that uses a press die, and it is difficult to obtain a large amount of product. HAV molding requires a high heating temperature to shorten the molding time. There is a tendency to induce oxidation (silicaization) of the silicone surface. In addition, steam crosslinking requires high-pressure steam in order to obtain a high temperature. For example, a pressure of 16 kg / cm ² is necessary to obtain a temperature in the kettle of 200 ° C., which is not a simple molding method.

In addition, as a well-known document relevant to this invention, there exist the following.
Silicone Handbook (Kunio Ito, Nikkan Kogyo Shimbun) p296 9.2.5 Molding of silicone rubber

  The present invention has been made in view of the above circumstances, and is capable of crosslinking a silicone rubber composition at a high temperature and in a short time, and when an organic peroxide is used as a curing agent, An object of the present invention is to provide a simple method for producing a silicone rubber, which is free from the concern of inhibition of surface crosslinking due to inhibition and does not require consideration of surface oxidation degradation of silicone due to high temperature.

As a result of various studies on the heating method in order to achieve the above object, the present inventor is capable of crosslinking in a short time by using superheated steam when the silicone rubber composition is crosslinked. The silicone rubber crosslinked by this method has been found to have a low compression set and excellent heat resistance, and has led to the present invention.
Normal pressure hot air cross-linking with superheated steam can cross-link silicone rubber compositions by heating in a short time. Silicone rubber cross-linked with superheated steam in a low-oxygen atmosphere can cause oxidative degradation of the molding surface. It has few good surface conditions.

Accordingly, the present invention provides the following method for producing a silicone rubber.
[1] (A) an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule;
(B) Curing agent: an amount capable of curing the component (A) ,
(C) Dry silica as reinforcing silica: A silicone rubber composition containing 1 to 60 parts by mass with respect to 100 parts by mass of component (A) is 150 ° C. or higher and 600 ° C. or lower in a normal pressure atmosphere. method for producing a free silicone rubber of foamed, characterized in that the hot air crosslinking with atmospheric pressure superheated steam.

The method for producing a silicone rubber of the present invention is excellent in thermal efficiency, can be crosslinked in a short time, and the surface of the silicone molded product is not oxidized and deteriorated. Moreover, it is a manufacturing method in which atmospheric pressure hot-air crosslinking using an organic peroxide that cannot be used for inhibiting oxygen in the air is possible.
The method of the present invention, particularly addition cure or organic peroxide curing type hose, is effective for electric wire or the like.

In the production method of the present invention,
(A) an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule;
(B) A silicone rubber composition containing a curing agent is used, and the composition is hot-air crosslinked using superheated steam at 120 ° C. or higher and 600 ° C. or lower under an atmospheric pressure atmosphere.

  The component (A) of the silicone rubber composition used in the present invention is an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule, and is preferably a liquid or raw rubber-like disiloxane at room temperature. An organopolysiloxane that is 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 A positive number in the range of .8 to 2.5.)

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, Preferably, at least 90 mol% of all R ¹ is a methyl group.

Further, at least two of R ¹ must be alkenyl groups (preferably having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and particularly preferably a vinyl group). The alkenyl group content in the organopolysiloxane is 1.0 × 10 ^{−6 to} 5.0 × 10 ⁻³ mol / g, particularly 5.0 × 10 ^{−6 to} 1.0 × 10 ⁻³ mol / g. g is preferable. When the amount of the alkenyl group is less than 1.0 × 10 ⁻⁶ mol / g, crosslinking may be insufficient and the gel may be formed. When the amount is more than 5.0 × 10 ⁻³ mol / g, There is a possibility that the crosslink density becomes too high and the rubber becomes brittle.

  The alkenyl group may be bonded to the silicon atom at the end of the molecular chain, may be bonded to the silicon atom in the middle of the molecular chain (that is, non-terminal of the molecular chain), or may be bonded to both. The molecular weight is liquid or raw rubber at room temperature, and the degree of polymerization is preferably 50 to 50,000, more preferably 80 to 20,000.

The structure of this organopolysiloxane basically has a main chain, for example, a diorganosiloxane unit such as a dimethylsiloxane unit, a diphenylsiloxane unit, a methylphenylsiloxane unit, a methyltrifluoropropylsiloxane unit, or a vinylmethylsiloxane unit. (R ¹ ₂ SiO _2/2 ), and both ends of the molecular chain are, for example, trimethylsiloxy group, vinyldimethylsiloxy group, divinylmethylsiloxy group, trivinylsiloxy group, vinyldiphenylsiloxy group, vinylmethylphenylsiloxy Has a linear structure blocked with a triorganosiloxy group (R ¹ ₃ SiO _1/2 ) such as a phenyl group, phenyldimethylsiloxy group, diphenylmethylsiloxy group, etc., but partially branched structure, cyclic structure, etc. It may be.

The curing agent of component (B) is a known curing agent by addition reaction or organic peroxide curing agent.
In this case, the addition reaction curing agent is a combination of (B-1) an organohydrogenpolysiloxane and (B-2) an addition reaction catalyst.

The organohydrogenpolysiloxane (B-1) acts as a crosslinking agent for curing the composition by a hydrosilylation addition reaction with the alkenyl group-containing organopolysiloxane of the component (A). 2)
R ² _b H _c SiO _{(4-bc) / 2} (2)
(Wherein R ² is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, b is 0.7 to 2.1, particularly 0.8 to 2.0, and c is 0.8. 001 to 1.0 and b + c is a positive number satisfying 0.8 to 3.0, particularly 1.0 to 2.5.)
At least 2, preferably 3 or more (usually about 3 to 200), more preferably 3 to 100, especially 3 to 50 silicon atom-bonded hydrogen atoms (SiH group) in one molecule. Those having the following are preferably used.

  This silicon-bonded hydrogen atom is bonded to both silicon atoms bonded to both silicon atoms at the molecular chain end and those bonded to the silicon atom in the middle of the molecular chain (non-terminal molecular chain). It may be a thing.

Here, as R ^2, there may be mentioned the same groups as R ^l in formula (1), preferably those free of aliphatic unsaturated bonds such as alkenyl radicals.

Examples of the organohydrogenpolysiloxane include tris (dimethylhydrogensiloxy) methylsilane, tris (dimethylhydrogensiloxy) phenylsilane, 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetra. Methylcyclotetrasiloxane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, both ends trimethylsiloxy group-blocked methylhydrogenpolysiloxane, both ends trimethylsiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane Polymer, both ends dimethylhydrogensiloxy-blocked dimethylpolysiloxane, both ends dimethylhydrogensiloxy-blocked dimethylsiloxane methylhydrogen Hexane copolymers, both end trimethylsiloxy-blocked methylhydrogensiloxane-diphenylsiloxane copolymers, both end trimethylsiloxy-blocked methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane _{copolymer, (CH 3) 2 HSiO 1} / _A copolymer comprising ₂ units and SiO _4/2 units, a copolymer comprising (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) SiO _3/2 units, etc. In addition, in these exemplified compounds, a part or all of the methyl group may be another alkyl group such as ethyl group or propyl group, an aryl group such as phenyl group, or a halogen-substituted alkyl group such as 3,3,3-trifluoropropyl group. And the like substituted with.

  The molecular structure of this organohydrogenpolysiloxane may be any of linear, cyclic, branched, and three-dimensional network structures, but the number (or degree of polymerization) of silicon atoms in one molecule is 2 to 1. 1,000, preferably 3 to 500, more preferably 3 to 300, and particularly preferably about 4 to 150 can be used.

The amount of the organohydrogenpolysiloxane is preferably 0.1 to 50 parts by weight, more preferably 0.1 to 30 parts by weight, more preferably 100 parts by weight of the organopolysiloxane (A). Preferably it is 0.3-30 mass parts, Most preferably, it is 0.3-20 mass parts.
In addition, this organohydrogenpolysiloxane has a molar ratio of hydrogen atoms bonded to silicon atoms in the component (B-1) to alkenyl groups bonded to silicon atoms in the component (A) (that is, SiH groups) [( B-1) SiH group in component / alkenyl group in component (A)] is 0.5-5 mol / mol, preferably 0.8-4 mol / mol, more preferably 1-3 mol / mol. It can also be blended in such an amount.

The addition reaction catalyst (B-2) is a catalyst for promoting the hydrosilylation addition reaction between the alkenyl group bonded to the silicon atom in the component (A) and the SiH group of the organohydrogenpolysiloxane (B-1). Examples of the addition reaction catalyst include platinum black, platinous chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and an olefin, platinum bisacetoacetate, etc. Examples thereof include platinum group metal catalysts such as platinum-based catalysts, palladium-based catalysts, and rhodium-based catalysts.
In addition, although the compounding quantity of this addition reaction catalyst can be made into a catalytic amount, 0.5-1,000 ppm normally with respect to the total mass of (A) and (B-1) component as a platinum group metal normally. About 1 to 500 ppm is preferably blended.

On the other hand, a conventionally well-known thing can be used as an organic peroxide hardening | curing agent (B-3). For example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-bis (2,5- t-butylperoxy) hexane, di-t-butylperoxide, t-butylperbenzoate, 1,1-bis (t-butylperoxycarboxy) hexane, and the like, but are not particularly limited thereto. Absent.
The addition amount of the organic peroxide is a catalyst amount and may be appropriately selected according to the curing rate. Usually, it is 0.1 to 10 parts by mass, preferably 0 to 100 parts by mass of the component (A). .2 to 2 parts by mass.

  In the present invention, the above addition crosslinking and organic peroxide crosslinking may be used in combination. Note that addition crosslinking is recommended for curing the liquid organopolysiloxane composition.

The silicone rubber composition of the present invention, that is added further (C) reinforcing silica fine powder. The reinforcing silica fine powder is necessary for obtaining a silicone rubber sponge having excellent mechanical strength. For this purpose, the specific surface area by the BET method is 50 m ² / g or more. Is more preferable, and 100 to 400 m ² / g is more preferable. If the specific surface area is less than 50 m ² / g, the reinforcing property may not be sufficient, and the rubber strength may decrease.

Examples of the silica fine powder include fumed silica (dry silica) and precipitated silica (wet silica), and particularly fumed silica (dry silica) is used . Further, these surfaces may be hydrophobized with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, or the like. These silicas may be used alone or in combination of two or more.

The amount of the silica fine powder, 1 to 60 parts by weight of the organopolysiloxane 100 parts by weight of component (A), preferably 5 to 50 parts by weight, particularly preferably Ru 10-40 parts by der. No sufficient reinforcing effect can be obtained too small is less than 1 part by mass, to more than 60 parts by weight the workability is poor, also the physical properties of the resulting silicone rubber you decrease.

In the present invention, the silicone rubber composition can be further blended with (D) a foaming agent to obtain a silicone rubber foam.
Specific examples of the foaming agent for component (D) include inorganic foaming agents such as sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate, and ammonium nitrite; N, N′-dimethyl-N, N′-dinitroso Nitroso compounds such as terephthalamide, N, N′-dinitrosopentamethylenetetramine; azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, azodiaminobenzene, 2,2′-azobis-2-methylbutyronitrile , 2,2′-azobis-2,4-dimethylvaleronitrile, 1,1′-azobis (1-acetoxy-1-phenylethane), barium azodicarboxylate, and other organic azo compounds; benzenesulfonyl hydrazide, toluenesulfonyl Hydrazide, p, p'-oxybis (benzenesulfonylhydride) Razide), sulfonylhydrazide compounds such as diphenylsulfone-3,3′-disulfonylhydrazide, 4,4′-oxybis (benzenesulfonylhydrazide), paratoluenesulfonylhydrazine; calcium azide, 4,4-diphenyldisulfonylazide, p -Organic foaming agents such as azide compounds such as toluenesulfuronyl azide. In these, an organic foaming agent is preferable and especially an organic azo compound is preferable.

  (D) The compounding quantity of a component is an quantity which can foam a composition, Preferably it is 0.1-20 mass parts with respect to 100 mass parts of (A) component, Most preferably, it is 0.2-10 mass parts. is there. (D) When mix | blending component, when there are too few compounding quantities, rubber | gum may not become sponge-like, and when too large, there may be a case where gas escapes or bursts.

  In the present invention, it is optional to add a conductive material to obtain a conductive silicone rubber composition. The type and blending amount of the conductive material are not limited, but conductive carbon black, conductive zinc white, metal powder and the like can be used, and the conductive material may be used alone or in combination of two or more. As the carbon black, those usually used in conductive rubber compositions can be used, and examples thereof include acetylene black, conductive furnace black (CF), super conductive furnace black (SCF), extra conductive furnace black (XCF), Examples thereof include conductive channel black (CC), furnace black and channel black heat-treated at a high temperature of about 1,500 to 3,000 ° C. Specifically, Denka Black (manufactured by Electrochemical Co., Ltd.), Shaunigan acetylene black (manufactured by Shaunigan Chemical Co., Ltd.), etc. are used as acetylene black, Continex CF (manufactured by Continental Carbon Co.), Vulcan, etc. as conductive furnace black. C (manufactured by Cabot), etc., Superconductive furnace black, Continex SCF (manufactured by Continental Carbon), Vulcan SC (manufactured by Cabot), etc. As extra-conductive furnace black, Asahi HS-500 (Asahi Carbon) Co., Ltd.), Vulcan XC-72 (manufactured by Cabot Corp.), etc., examples of the conductive channel black include Kourax L (manufactured by Degussa), etc. It is also possible to use a fine-Ketchen black EC-600JD (manufactured by Ketchen Black International Co., Ltd.). In furnace black, the amount of impurities, particularly sulfur and sulfur compounds, is 6,000 ppm or less, more preferably 3,000 ppm or less in terms of the concentration of elemental sulfur. Among these, acetylene black has a low impurity content and has a developed secondary structure structure, so that it has excellent conductivity and is particularly preferably used in the present invention.

The conductive material may be added in any amount as long as the resistance of the conductive silicone rubber composition becomes conductive, that is, the volume resistivity is 10 ¹⁴ Ω · m or less. It is preferable to set it as 1-50 mass parts with respect to 100 mass parts, especially 5-20 mass parts. If the addition amount is less than 1 part by mass, the desired conductivity may not be obtained. If the addition amount exceeds 50 parts by mass, physical mixing may be difficult or the mechanical strength may be reduced. The rubber elasticity may not be obtained.

  In addition to the above components, the silicone rubber composition of the present invention comprises, if necessary, a filler, non-reinforcing silica as a filler, fused silica, calcined silica, sol-gel spherical silica, crystalline silica (quartz powder) ), Silica fine particles such as diatomaceous earth, calcium carbonate, clay, diatomaceous earth, titanium dioxide reinforcing, semi-reinforcing fillers, silicone resins that serve as reinforcing agents, nitrogen-containing compounds, acetylene compounds, phosphorus compounds, Hydrosilylation reaction control agents such as nitrile compounds, carboxylates, tin compounds, mercury compounds and sulfur compounds, heat-resistant agents such as iron oxide and cerium oxide, internal mold release agents such as dimethyl silicone oil, adhesion promoters, thixotropic properties An imparting agent and the like can be arbitrarily blended within a range not impairing the effects of the present invention. In addition, heat resistance improvers such as iron oxide, cerium oxide, and iron octylate, various carbon functional silanes for improving adhesion and moldability, nitrogen compounds that impart flame retardancy, and halogen compounds are added and mixed. May be. A low molecular weight siloxane having a degree of polymerization of 100 or less, a silanol group-containing silane, an alkoxy group-containing silane, or the like may be added as a dispersion aid.

These heat conductive inorganic powders may be mixed with the components (A) and (B) at room temperature using a planetary mixer or a kneader, or at a high temperature of 100 to 200 ° C. May be.
When heat treatment is performed, for example, components (A) and (B) and a finely divided silica filler are mixed in advance to prepare a base compound, and various additives, carbon black powder and the like are similarly mixed into the kneader. It may be prepared by mixing with, and a curing agent may be added and mixed.

In the present invention, the method for heating the silicone rubber composition is characterized by curing and foaming by heating with atmospheric superheated steam.
Normal pressure superheated steam (hereinafter referred to as superheated steam) is colorless and transparent H ₂ O gas obtained by heating saturated steam evaporated at 100 ° C. to a higher temperature while maintaining normal pressure. Conventionally, water vapor of 100 ° C. or higher refers to high-pressure water vapor in a sealed container, but it is necessary to increase the pressure in order to increase the atmospheric temperature. A pressure of ² was required, and a large device was required. In contrast, this superheated steam can apply heat to the object to be heated at atmospheric pressure (normal pressure), the heating temperature can be arbitrarily heated to 100 to 800 ° C., and the apparatus is also simple. It is possible to create continuous heating lines by continuous heating by conveyors and extrusion of tubes.

  The heat transfer capability of superheated steam is high, and HAV molding, which is widely used as a continuous heating method for silicone rubber, is mainly used for convective heat transfer by hot air, whereas superheated steam has a convection heat transfer It is excellent in thermal efficiency because it can be heated by coagulated water and radiant heat transfer capability (thermal radiation gas) and three heating principles.

  Although the mechanism for generating superheated steam is not particularly limited, usually superheated steam is generated by a combination of a mechanism for generating saturated steam at 100 ° C. and a super heater for heating to a temperature of 100 ° C. or higher. . A super heater is a heater that raises the temperature of saturated steam at 100 ° C. Indirect heating with an oil burner or gas burner, and heating by directly feeding steam to an electric heater or resistance heating element by induction heating. A typical example is a heater structure such as an electric heating method.

  Such hot air cross-linking with superheated steam does not cause deterioration of the material due to oxidation because there is no gaseous oxygen in the heating atmosphere. In addition, when an organic peroxide is used as the crosslinking agent, the radicals generated by the decomposition of the organic peroxide are lost by oxygen, so-called crosslinking inhibition factors due to oxygen inhibition are eliminated, so that conventional crosslinking is impossible. Atmospheric pressure hot air cross-linking with organic peroxides that cannot be used in is also possible. Also, because of the high heating efficiency, curing can be performed for a short time at the same temperature as compared with HAV heating. Furthermore, even when flammable gas such as decomposition product of organic peroxide is generated, there is no risk of explosion in the heating furnace because gaseous oxygen does not exist.

The conditions for hot air crosslinking with superheated steam are not particularly limited, but are preferably 120 to 600 ° C., more preferably 150 to 450 ° C. for several seconds to one hour. If the temperature is lower than 120 ° C., there is a possibility that the silicone rubber is not sufficiently cured, and if the temperature is higher than 600 ° C., the water vapor may be decomposed into oxygen and hydrogen. Furthermore, when secondary vulcanization is performed after molding, secondary vulcanization is preferably performed at 150 to 250 ° C. for 1 to 30 hours.
Furthermore, in addition to a heating mechanism using superheated steam as a heating furnace structure, a heating furnace using a heater such as a ceramic heater in combination with a heating furnace may be used as used in normal HAV molding. The heating furnace combined with the heater can also be cross-linked under the same conditions as hot air cross-linking with superheated steam.

  The silicone rubber obtained by the method of the present invention is effective for hoses, electric wires, sponge rolls, sponge gaskets and the like.

  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 addition, the part in the following example shows a mass part.

[Example 1]
75 parts of organopolysiloxane comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000, reinforcing silica 40 parts of dry silica Arosil 200 (manufactured by Nippon Aerosil Co., Ltd.) with a BET surface area of 200 m ² / g, 5 parts of dimethylpolysiloxane having silanol groups at both ends and a viscosity of 29 cs (23 ° C.) in a kneader, Heat treatment was carried out at 180 ° C. for 2 hours to produce rubber compound A.
0.5 parts / 2.0 parts of C-25A (platinum catalyst) / C-25B (organohydrogenpolysiloxane) (both manufactured by Shin-Etsu Chemical Co., Ltd.) as addition crosslinking curing agents with respect to 100 parts of the obtained rubber compound A After kneading with two rolls, a sheet with a thickness of 2 mm was produced with two rolls. This was put into a superheated steam furnace heated to 240 ° C. and cured by heating. The physical properties and surface cross-linking state of the molded sheet were measured. Further, the foaming contained in the rubber was visually observed.

A method for measuring physical properties and a method for testing foaming properties during normal pressure hot air vulcanization are shown below.
Physical property measurement method;
A hot-air crosslinked 2 mm thick rubber sheet was measured for physical properties such as hardness (durometer A), tensile strength, and elongation according to JIS K6249.

Sheet surface condition;
○: The sheet surface is completely cured and does not have a tactile sensation. △: The sheet surface has a tactile sensation.

Pinhole test for crosslinked rubber;
Foaming is less = 1 1 cm moderate foaming those bubbles are not observed in the range of ² = range of 2 1 cm ² to those bubbles is 1-50 observed foaming often = 3 bubbles in the range of 1 cm ² is 51 pieces What is observed above

[ Reference Example 1 ]
A rubber compound B is produced in the same manner as in Example 1 except that 40 parts of wet silica NipsilLP (manufactured by Nippon Silica Kogyo Co., Ltd.), which is a wet silica BET surface area of 200 m ² / g, is used instead of the reinforcing silica Arosil200. did. Thereafter, the rubber compound B was produced under the same conditions as in Example 1 to produce a 2 mm thick sheet with two rolls, hot-air cross-linked, and the molded sheet was evaluated.

[Example 2 ]
Sheet preparation and hot-air crosslinking in the same manner as in Example 1 except that 0.9 part of 2,4-dicumyl peroxide was used as the organic peroxide-based curing agent instead of the platinum-based curing agent of Example 1. And evaluated.

[Example 3 ]
Instead of the 240 ° C. superheated steam furnace, which is the heating method of Example 1, a ceramic heater was added to the superheated steam furnace, and the temperature in the furnace was changed to 350 ° C. And evaluated.

[Example 4 ]
Instead of 240 ° C. superheated steam oven is the method of heating in Example 2, additional ceramic heater superheated steam furnace, except that the furnace temperature was 350 ° C., the sheet prepared in the same manner as in Example 2, hot air crosslinking And evaluated.

[Comparative Example 1]
A sheet was prepared and evaluated in the same manner as in Example 1 except that instead of the 240 ° C. superheated steam furnace, which is the heating method of Example 1, HAV molding was performed at a temperature of 240 ° C. in a normal hot air dryer. It was.

[Comparative Example 2]
A sheet was prepared and evaluated in the same manner as in Reference Example 1 except that instead of the 240 ° C. superheated steam furnace that is the heating method of Reference Example 1 , HAV molding was performed at a temperature of 240 ° C. in a normal hot air dryer. It was.

[Comparative Example 3]
A sheet was prepared and evaluated in the same manner as in Example 2 except that instead of the 240 ° C. superheated steam furnace which is the heating method of Example 2 , HAV molding was performed at a temperature of 240 ° C. in a normal hot air dryer. It was.

[Comparative Example 4]
Instead of a heating process is 350 ° C. superheated steam oven + a ceramic heater combined heating Example 3, at the exception of performing the HAV molded at a temperature of 350 ° C. ordinary hot air dryer, in the same manner as in Example 3 Sheet Fabrication and evaluation were performed.

[Comparative Example 5]
Instead of a heating process is 350 ° C. superheated steam oven + ceramic heater combined heating Example 4, at the exception of performing the HAV molded at a temperature of 350 ° C. ordinary hot air dryer, in the same manner as in Example 4 Sheet Fabrication and evaluation were performed.

  These results are shown in Tables 1 and 2.

  It can be seen that cross-linking with superheated steam (Example) has a good surface property with less air (foaming) and no tackiness.

Silicone sponge molding [ Reference Example 2 ]
With respect to 100 parts of rubber compound A used in Example 1, 0.9 part of 2,4-dicumyl peroxide as an organic peroxide curing agent and organic azo foaming agent 1,1′-azobis (cyclohexane) as a foaming agent After pulverizing 1.5 parts of (-1-methylcarboxylate) with two rolls, a sheet with a thickness of 5 mm was prepared with two rolls. This was put into a superheated steam furnace heated to 240 ° C. and heated and foamed for 15 minutes to obtain a sponge sheet. The prepared sponge sheet was measured for hardness, density, cell state of cross section cut by a cutter, and average cell diameter by the following methods.
Sponge hardness: Asker C hardness according to JIS S 6050.
Sponge density: JIS K 6249
Cell state: Observed visually.
Average cell diameter: Average cell diameter on the sponge cut surface.
Presence or absence of surface tack: Is there a sticky surface on the sponge surface (skin layer)?

[Comparative Example 6]
A sheet was prepared and evaluated in the same manner as in Reference Example 2 except that instead of the 240 ° C. superheated steam furnace, which is the heating method of Reference Example 2 , HAV molding was performed at a temperature of 240 ° C. in a normal hot air dryer. .
These results are shown in Table 3.

発泡剤：１，１’−アゾビス（シクロヘキサン−１−メチルカルボキシレート）
過熱水蒸気によるスポンジ発泡（参考例２）は、良好なスポンジが得られていることがわかる。

Foaming agent: 1,1′-azobis (cyclohexane-1-methylcarboxylate)
It can be seen that the sponge foamed by superheated steam ( Reference Example 2 ) has a good sponge.

Claims (1)

(A) an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule;
(B) Curing agent: an amount capable of curing the component (A) ,
(C) Dry silica as reinforcing silica: A silicone rubber composition containing 1 to 60 parts by mass with respect to 100 parts by mass of component (A) is 150 ° C. or higher and 600 ° C. or lower in a normal pressure atmosphere. method for producing a free silicone rubber of foamed, characterized in that the hot air crosslinking with atmospheric pressure superheated steam.