JP3277748B2 - Foamable silicone rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamable silicone rubber composition which gives a silicone rubber sponge having fine cells (cells) while having low toxicity and high safety of a decomposition product of a foaming agent.

[0002]

2. Description of the Related Art In general, it is known that silicone rubber sponges can be obtained roughly by the following two methods. That is, one is a method using a low-boiling substance by-produced in a condensation reaction between siloxanes represented by the following formula, and the other is to add a curing agent and a foaming agent to the silicone rubber composition. Is the way. {SiOH + HSi} → {SiOSi} + H ₂ } In the case of the former method, if the number of functional groups involved in the condensation reaction between siloxanes in the silicone rubber composition is small, the expansion ratio is significantly reduced, and the sponge-like silicone May not give rubber. This is often seen when a high degree of polymerization siloxane (silicone raw rubber) is used. In addition, since the gas generated by the chemical reaction is used for foaming, it is difficult to control the reaction speed, cell size, and the like. The silicone rubber sponge obtained by this method has extremely low strength, and its usable applications are limited.
In the latter method, azobisisobutyronitrile (AIBN) is generally used as a blowing agent (Japanese Patent Publication No. 44-461). The silicone rubber sponge obtained by this method has a relatively dense and uniform cell, but when AIBN is used, the decomposition product of tetramethylsuccinonitrile has a high toxicity of LD ₅₀ = 39, and this treatment method is complicated. And the working conditions are also limited. For this reason, studies on the production of silicone rubber sponges without using AIBN have been conducted for a long time (JP-B-47-14592, JP-B-53-16025).
No. JP-A-5-59207).

[0003] However, all of these proposals use a step cure or cure by a hydrosilylation reaction, which limits the working time and curing conditions.
A sponge having dense and uniform cells was not obtained, and there were many problems in practical use.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages. A silicone rubber sponge which has high safety when cured and foamed without using AIBN, and which easily has dense and uniform cells. It is an object of the present invention to provide a silicone rubber composition.

[0005]

The present inventors have made intensive studies to achieve the above object, and as a result, (A) the following average composition formula (1) R _n SiO _{(4-n) / 2} ( 1) 100 parts by weight of an organopolysiloxane represented by the following formula: wherein R is the same or different, unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number from 1.98 to 2.02. ) Reinforcing silica having a specific surface area of 50 m ² / g or more
In the foamable silicone rubber composition containing 100 parts by weight, (C) a foaming agent and (D) a curing agent, the foaming agent is represented by the following general formula (2), provided that azobisisobutyronitrile (AIBN) is used. It was found that when azo foaming agents were used, no harmful by-products as in the case of using AIBN were produced, and a good-touch silicone rubber sponge having uniform and dense cells was obtained. The invention has been completed.

[0006]

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Now, the present invention will be described in further detail. The foamable silicone rubber composition of the present invention comprises (A) an organopolysiloxane, (B) a reinforcing silica, and (C) an azo foam of the above formula (2). Agents (excluding AIBN),
(D) A curing agent is an essential component.

Here, the organopolysiloxane of the component (A) has the following average composition formula (1) R _n SiO _{(4-n) / 2} (1) (where R is the same or different, unsubstituted or substituted) A monovalent hydrocarbon group, n is a positive number from 1.98 to 2.02).

In this case, R represents an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group; a cycloalkyl group such as a cyclohexyl group; an alkenyl group such as a vinyl group, an allyl group, a butenyl group or a hexenyl group; A phenyl group, an aryl group such as a tolyl group, or a chloromethyl group in which some or all of the hydrogen atoms bonded to carbon atoms of these groups are substituted with a halogen atom, a cyano group, or the like;
The same or different preferably 1 to 10 carbon atoms selected from trifluoropropyl group, cyanoethyl group and the like;
More preferred are unsubstituted or substituted monovalent hydrocarbons having 1 to 8 carbon atoms, and n is a positive number from 1.98 to 2.02, and the organopolysiloxane has a trimethylsilyl group at the molecular chain terminal, It may be blocked with a dimethylvinyl group, a dimethylhydroxysilyl group, a trivinylsilyl group, or the like.

This type of organopolysiloxane is usually obtained by cohydrolyzing and condensing one or more selected organohalogenosilanes, or a cyclic polysiloxane (such as a siloxane trimer or tetramer). Can be obtained by ring-opening polymerization using an alkaline or acidic catalyst, which is basically a linear diorganopolysiloxane,
It may be a mixture of two or more kinds having different molecular structures. The viscosity of this organopolysiloxane is
Those having a viscosity at 25 ° C. of 1,000 cs or more are preferred. More preferably, 100,000 to 10,000,
000 cs. The degree of polymerization is preferably 300 or more,
It is more preferably from 2,000 to 100,000, and still more preferably from 5,000 to 10,000.

Next, the reinforcing silica as the component (B) is essential for obtaining a silicone rubber having excellent mechanical strength. For this purpose, a specific surface area of 50% is required.
m ² / g or more, preferably should be those of the 100 to 400 m ² / g. Typical examples of the reinforcing silica include fumed silica, precipitated silica, and silica whose surface has been subjected to a hydrophobic treatment. If the amount of the silica powder is less than 10 parts by weight with respect to 100 parts by weight of the organopolysiloxane (A), a sufficient reinforcing effect cannot be obtained. The amount is from 10 to 100 parts by weight, preferably from 30 to 80 parts by weight, as the resulting silicone rubber deteriorates and the physical strength of the obtained silicone rubber decreases.

In the present invention, an azo foaming agent represented by the following general formula (2) is used as the foaming agent of the component (C) (wherein, in the formula (2), R ¹ and R ⁴ are each a nitrile) Azobisisobutyronitrile, wherein R ² , R ³ , R ⁵ and R ⁶ are each a methyl group).

[0013]

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Here, the unsubstituted alkyl group of R ^{1 to} R ⁶ preferably has 1 to 6 carbon atoms.

Examples of such azo foaming agents include 2,
2'-azobis (2-methylbutyronitrile), 2,
2'-azobis (2,4-dimethylvaleronitrile),
Dimethyl-2,2-azobisisobutyrate, 2,2 '
Azobis (2,4,4-trimethylpentane), 2,
2'-azobis (2-methylpropionamide) dihydrate, 4,4'-azobis (4-cyanovaleric acid), 1,1'-azobis (cyclohexane-1-carbonitrile), dimethyl-2,2'- Azobis (2-methylpropionate) and the like.

Of these, preferred are 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile),
2,2-azobisisobutyrate, 2,2′-azobis (2,4,4-trimethylpentane), 2,2′-azobis (2-methylpropionamide) dihydrate,
4,4'-azobis (4-cyanovaleric acid). Most preferred is 2,2'-azobis (2-methylbutyronitrile). Component (C) is added in an amount of 0.5 to 30 parts by weight per 100 parts by weight of component (A). If the amount is less than 0.5 part by weight, sufficient foaming is not performed, and it is difficult to form a sponge. If the amount exceeds 30 parts by weight, the foaming is sufficient, but the foaming ratio is too high and the silicone sponge obtained may have cracks or deformation. Is likely to occur and the sponge quality is reduced.
It must be in the range of 30 parts by weight. More preferably, it is 1 to 20 parts by weight.

The foamable silicone rubber composition of the present invention can be cured into a sponge by either a method utilizing a conventionally known hydrosilylation reaction or a method involving vulcanization using an organic peroxide as a catalyst. Can be cured. Therefore, when the curing agent of the component (D) is cured by utilizing a hydrosilylation reaction, a combination of an organohydrogen polysiloxane and a platinum group metal-based catalyst,
Or it becomes an organic peroxide.

In the case of sponging using a hydrosilylation reaction, the organopolysiloxane of the component (A) must have at least two alkenyl groups bonded to silicon atoms. Represents two or more Si atoms in one molecule.
Any organopolysiloxane having an H group may be used, and it may be linear, cyclic, or branched. Also,
Such a SiH group may be at the terminal of the polysiloxane chain or may be in the middle. Such an organohydrogenpolysiloxane contains 0.5 to 3 SiH groups per mole of the alkenyl groups of the organopolysiloxane (A).
It is used in a molar proportion, in particular 1 to 2 mol. The platinum group metal-based catalyst used simultaneously serves as a catalyst for the hydrosilylation reaction between the alkenyl group in the organopolysiloxane of (A) and the SiH group in the organohydrogenpolysiloxane. Is used in the range of 0.1 to 1,000 ppm, preferably 1 to 100 ppm (as platinum metal), based on the total amount of the organopolysiloxane and the organohydrogenpolysiloxane. As such a platinum group metal-based catalyst, for example, chloroplatinic acid catalyst, platinum-hydrocarbon complex compound, chloroplatinic acid-olefin complex compound, platinum-vinylsiloxane complex and the like can be used. Further, when curing by a hydrosilylation reaction, in order to maintain good storage stability at room temperature and maintain an appropriate pot life,
Reaction control agents such as methylvinylcyclotetrasiloxane and acetylene alcohols can also be added.

[0019]

[0020]

The organic peroxide-curable type is more preferable than the hydrosilylation type because the sponge cells can be made uniform and dense. In particular, in order to miniaturize the cells of the silicone sponge and stabilize the expansion ratio, it is preferable to use a combination of a low-temperature decomposition type organic peroxide catalyst and a high-temperature decomposition type organic peroxide catalyst. The low-temperature decomposition type organic peroxide catalyst thickens the silicone rubber before the decomposition of the blowing agent in the initial stage of heating and curing of the silicone rubber, and the gas generated during the decomposition of the blowing agent can be efficiently taken into the silicone sponge, resulting in a dense cell. become. Further, the surface adhesion of the molded sponge is reduced in order to improve the vulcanization of the surface of the silicone sponge. On the other hand, the high-temperature decomposition type organic peroxide catalyst works to complete the vulcanization and curing of the sponge after decomposition of the blowing agent, improves the dimensional stability of the sponge at the time of molding,
Improves mechanical properties such as compression set and tensile strength of the sponge after molding.

The organic peroxide can be used without any particular limitation as long as it is generally used for curing an organic peroxide-curable silicone rubber composition. For example, benzoyl peroxide, bis ( 2,4-dichlorobenzoyl) peroxide, bis (o-chlorobenzoyl) peroxide, di-t-butyl peroxide, 2,5-dimethyl-di-t-butylperoxyhexane, t-butyl perbenzoate, t -Butyl peroxyisopropyl carbonate, dicumyl peroxide and the like. Among the specific examples of the organic peroxides mentioned above, the low-temperature decomposition type organic peroxide catalysts include bis (2,4-dichlorobenzoyl) peroxide, bis (o-chlorobenzoyl) peroxide, and bis (p-methyl). Benzoyl) peroxide, bis (o-methylbenzoyl)
High temperature decomposition type organic peroxide catalyst is a peroxide.
t-butyl peroxide, 2,5-dimethyl-di-t
-Butyl peroxyhexane, t-butyl perbenzoate, t-butyl peroxyisopropyl carbonate, and dicumyl peroxide.

That is, a low-temperature decomposition type organic peroxide catalyst is an organic peroxide having a half-life of 1 hour or less at a temperature of 100 ° C.
It is an organic peroxide having a half-life of 0 hour or more, and it is desirable to mold with a combination of these two types of organic peroxides.

In particular, when bis (o-chlorobenzoyl) peroxide is used as the low-temperature decomposition type organic peroxide catalyst, a molded sponge having a uniform cell size is preferably obtained.

The ratio between the low-temperature decomposition type organic peroxide catalyst and the high-temperature decomposition type organic peroxide catalyst is 1:10 to 5: 1 by weight, more preferably 1: 5 to 2: 1. Range. In this case, the low-temperature decomposition type organic peroxide catalyst is used in an amount of 0.01 to 2 parts by weight based on 100 parts by weight of component (A), and the high-temperature decomposition type organic peroxide catalyst is used in 100 parts by weight of component (A). It is in the range of 0.1 to 8 parts by weight.

The silicone rubber composition of the present invention is obtained by uniformly mixing the above-mentioned components (A) to (D) using a rubber kneader such as a two-roll mill, a Banbury mixer or a dough mixer (kneader). It can be obtained by subjecting it to a heat treatment as needed, but a filler such as crushed quartz or calcium carbonate as an extender may be added as needed. Further, if necessary, various additives such as a coloring agent, a heat resistance improver, a flame retardant improver, and a release agent or a dispersant for a filler such as diphenylsilanediol, various alkoxysilanes, and carbon functional silane. It is optional to add a silanol group-containing low molecular siloxane.

The foamable silicone rubber composition thus prepared can be easily foamed and cured by heating to obtain a silicone rubber sponge. The curing and foaming method may be any method that can apply sufficient heat to the decomposition of the foaming agent and the vulcanization of the silicone rubber. The molding method is also particularly limited, such as continuous vulcanization by extrusion molding, press molding, and molding by injection. It is not something to be done.

[0028]

EFFECTS OF THE INVENTION The foamable silicone rubber composition of the present invention has low toxicity, high safety,
A silicone rubber sponge having uniform cells can be obtained.

[0029]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 7, Comparative Examples 1 and 2] Consisting of 99.825 mol% of dimethylsiloxane unit, 0.15 mol% of methylvinylsiloxane unit and 0.025 mol% of dimethylvinylsiloxane unit. Is about 8.0
100 parts by weight of an organopolysiloxane of No. 00, 45 parts by weight of fumed silica having a specific surface area of 200 m ² / g [manufactured by Nippon Aerosil Co., Ltd.] 13, 10 parts by weight of dimethylpolysiloxane having a viscosity of 15 cs at 25 ° C. was kneaded with a kneader and heat-treated at 160 ° C. for 2 hours to prepare a base compound.

To the base compound, a foaming agent and a curing agent listed in Tables 1 to 3 were added and mixed with two rolls, and mixed.
The hardness and the foaming ratio of the product cured for 10 minutes in a dryer at a temperature of ° C. and the size of the cell were observed with a microscope. Table 1 shows the results
3 are shown.

In the table, as the platinum catalyst and the crosslinking agent,
The following are shown. Further, the amount added is part by weight based on 100 parts by weight of the base compound. Platinum catalyst: a platinum catalyst having a platinum content of 1% by weight with a solution of chloroplatinic acid in octyl alcohol. Crosslinking agent: 17 methylhydrodienesiloxane units having a viscosity of 12 cs and both ends of which are blocked with dimethylhydrogensiloxy groups. Methyl hydrogen polysiloxane containing mole%

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

Continuation of the front page (72) Inventor Masaharu Takahashi 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture Inside the Silicone Electronics Materials Research Laboratory, Shin-Etsu Chemical Co., Ltd. (56) References JP-A-8-176333 (JP, A (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08J 9/06-9/10 C08K 3/36 C08K 5/14 C08K 5/23 C08L 83/04

Claims (3)

(57) [Claims] (A) The following general formula (1): R _n SiO _{(4-n) / 2} (1) (wherein R is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is 1 100 parts by weight of an organopolysiloxane represented by the following formula: (B) a reinforcing silica having a specific surface area of 50 m ² / g or more.
100 parts by weight, (C) the following general formula (2) (Wherein, R ^{1 to} R ⁶ are an unsubstituted alkyl group, a nitrile group, or an NH ₂ —CO— group) (excluding azobisisobutyronitrile). 0.5 to 30 parts by weight, (D) an organohydrogenpolysiloxane having two or more SiH groups in one molecule as a curing agent (A)
The amount of the SiH group to be 0.5 to 3 moles per mole of the alkenyl group of the organopolysiloxane of the component, and the platinum group metal-based catalyst in the total amount of the organopolysiloxane of the component (A) and the organohydrogenpolysiloxane On the other hand, an expandable silicone rubber composition comprising 0.1 to 1,000 ppm of platinum metal as an essential component. (A) R _n SiO _{(4-n) / 2} (1) wherein R is the same or different, unsubstituted or substituted monovalent hydrocarbon group, and n is 1 100 parts by weight of an organopolysiloxane represented by the following formula: (B) a reinforcing silica having a specific surface area of 50 m ² / g or more.
100 parts by weight, (C) the following general formula (2) (Wherein, R ^{1 to} R ⁶ are an unsubstituted alkyl group, a nitrile group, or an NH ₂ —CO— group) (excluding azobisisobutyronitrile). 0.5 to 30 parts by weight, (D) 0.01 to 2 parts by weight of a low-temperature decomposable organic peroxide having a half life of 1 hour or less at a temperature of 100 ° C. as a curing agent and 10 hours or more at a temperature of 100 ° C. 0.1 to 8 parts by weight of a high-temperature decomposable organic peroxide having a half-life [however, the mixing ratio of the low-temperature decomposable organic peroxide and the high-temperature decomposable organic peroxide is 1:
10-5: 1 (weight ratio)] as an essential component. 3. The foaming agent of component (C) is 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), dimethyl-
2,2-azobisisobutyrate, 2,2'-azobis (2,4,4-trimethylpentane), 2,2'-azobis (2-methylpropionamide) dihydrate or 4,4'-azobis (4 The foamable silicone rubber composition according to claim 1, wherein the composition is (cyanovaleric acid).