JPH0611808B2 - Silicone rubber composition for sponge - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a silicone rubber composition for sponges,
In particular, the present invention relates to a silicone rubber composition for sponges, which contains ferrite powder and is capable of foam hardening by high frequency dielectric heating.

[Technical Background of the Invention and Problems Thereof] It is generally accepted that a silicone rubber sponge is a material excellent in heat resistance, cold resistance, weather resistance and the like. As a method for obtaining such a silicone rubber sponge, an inorganic filler, an organic foaming agent such as azobisisobutyronitrile, and an organic peroxide are blended with silicone raw rubber,
A method is known in which a silicone rubber sponge is obtained by molding this into a predetermined shape and then heating and foaming and curing it. However, the following disadvantages are recognized in this method, and it is not possible to obtain a large-sized or thick homogeneous silicone rubber sponge. That is, when the foaming is performed by heating, the heating is performed from the outer peripheral surface, and the foaming and the curing first occur at the outer peripheral surface portion. Thus, before the inside of the foam body is foamed by heat transfer, the foaming phenomenon is completed in the outer peripheral surface portion, so that foaming is extremely suppressed even if the foaming agent inside is decomposed. For this reason, it is considered difficult to obtain a uniform-cell silicone rubber sponge.

However, as a method for solving such a nonuniform cell structure between the outer peripheral portion and the inner portion, a processing method by high-frequency dielectric heating is used for organic rubber, and this method is also used for silicone rubber sponge. Kosho 46-1
No. 8634) has been proposed. However, this method is limited to silicone rubber sponges using precipitated silica as a filler.

In addition, it is known that high frequency dielectric heating can be performed by blending a filler such as carbon black. In a silicone rubber sponge, an organic peroxide is generally used as a vulcanizing agent, but when carbon black is blended, a good silicone rubber sponge cannot be obtained because vulcanization by the organic peroxide is hindered.

As a method for obtaining a silicone rubber sponge having a uniform cell structure without using high-frequency dielectric heating, for example, in Japanese Patent Application Laid-Open No. 52-81378, an organic blowing agent in the presence of an organohydrogenpolysiloxane and a platinum catalyst is used. A method has been proposed in which, after aging at a temperature lower than the decomposition temperature, it is heated to a temperature not lower than the decomposition temperature of the organic foaming agent and foam-cured. Such a method is effective for the purpose of obtaining a silicone rubber sponge having a uniform cell structure, but has the disadvantage of requiring a period of aging and is not necessarily an industrially advantageous method. .

[Object of the Invention] The present invention is intended to solve such a conventional problem, and a silicone rubber sponge having uniform cells can be obtained by using high frequency dielectric heating without being particularly limited by thickness and the like. It is intended to provide a sponge composition.

[Structure of the Invention] As a result of various investigations by the present inventors to achieve such an object, ferrite powder is effective for high frequency dielectric heating,
It has been found that compounding ferrite powder with silicone rubber enables high-frequency dielectric heating, and by using a polysiloxane whose terminals are blocked with silanol groups, a silicone rubber sponge with a fine cell structure can be obtained. Invented.

That is, the silicone rubber composition for sponges of the present invention comprises (A) 100 parts by weight of polyorganosiloxane (B) 5 to 100 parts by weight of reinforcing filler silica (C) 10 to 200 parts by weight of ferrite powder (D) organic foaming Agent 0.5 to 10 parts by weight (E) Organic peroxide 0.1 to 10 parts by weight and (F) Polydiorganosiloxane having a terminal blocked with a silanol group and a viscosity at 25 ° C. of 500 to 10,000 cSt 1. It is characterized by comprising 10 to 10 parts by weight.

Polyorganosiloxane of the component (A) used in the present invention is to be a base polymer of the composition of the present invention, the general ^{_{formula: R 2 (R 1 2 SiO}} ) n SiR 1 2 R 2 ( wherein, R ¹ a monovalent substituted or unsubstituted hydrocarbon group, ^{R 2} represents a monovalent substituted or unsubstituted hydrocarbon group or a hydroxyl group, and 0.01 in ^{R 1} and ^{R 2.}
0 mol% is an alkenyl group, and n is 3,000 to on average.
(Representing a number of 10,000). Examples of the alkenyl group include vinyl group and allyl group. As R ¹ other than the alkenyl group in this polymer, an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, a decyl group and a dodecyl group; a phenyl group, a β-phenylethyl group , 3,3,3-trifluoropropyl group and the like are exemplified. If the alkenyl group is less than 0.01 mol% on average, the curing is not sufficiently performed, and if it exceeds 1.0 mol% on average, the heat resistance is lowered.

The average degree of polymerization n of the polyorganosiloxane (A) is 3,
If it is less than 000, sufficient mechanical strength cannot be obtained, and
This is because if it exceeds 00, it becomes difficult to add the reinforcing filler silica of (B). The molecular structure of the component (A) is preferably substantially linear, but may be branched within an allowable range. The polyorganosiloxane (A) may be used alone or as a blend of two or more having different degrees of polymerization and organic groups.

Examples of the reinforcing filler silica as the component (B) used in the present invention include fumed silica, precipitated silica, calcined silica, and silica aerosol. These reinforcing silica for filling may be those whose surface is not treated, or those which have been previously surface-treated with an organosilicon compound such as organochlorosilane, polydioganosiloxane, hexaorganodisilazane, or the above at the time of compounding and kneading. The surface treatment with an organosilicon compound such as the above can be used. The blending amount of such a component (B) is
It is 5 to 100 parts by weight, preferably 20 to 70 parts by weight, relative to 100 parts by weight of the component (A). If the blending amount is less than 5 parts by weight, the reinforcing effect is insufficient and sufficient mechanical strength cannot be obtained, and if the blending amount is more than 100 parts by weight, the silicone composition becomes hard and it is difficult to obtain a sponge.

The (C) component ferrite powder used in the present invention is the most important component in the present invention, and by blending the (C) component, high frequency dielectric heating becomes possible. The component (C) that imparts the desired effect of the present invention is represented by the general formula: M ²⁺ Fe ³⁺ ₂ O ₄ or MO.Fe ₂ O ₃ (wherein M: Mn, Zn, Ni, Cu, etc. It is used in transformers and coil cores (magnetic cores), and is relatively easily available. The average particle diameter is preferably 1 to 50 μm. 1
If it is less than μm, it is difficult to obtain it, and if it exceeds 50 μm, mechanical strength cannot be obtained. The blending amount of the component (C) is selected from the range of 10 to 200 parts by weight with respect to 100 parts by weight of the component (A). If the blending amount of this component (C) is less than 10 parts by weight, heat generation is not sufficient due to high frequency, and 2
If it exceeds 100 parts by weight, the mechanical strength of the silicone rubber is impaired.

The organic foaming agent of the component (D) used in the present invention is for foaming the composition of the present invention into a sponge form.
This may be any of those used in the production of conventional silicone sponges, including azo compounds such as azobisisobutyronitrile, azodicarbonamide, diazoaminobenzene, dinitropentamethylenetetramine and N. , N-dimethyl-N, N-dinitrosoterephthalamide and the like are exemplified, and these compounds decompose to generate N ₂ or CO ₂ gas when heated to a temperature equal to or higher than the decomposition temperature.
The blending amount of the component (D) is selected from the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the component (A). If the blending amount of the component (D) is less than 0.5 parts by weight, a sponge cannot be obtained, and if it exceeds 10 parts by weight, the sponge obtained is apt to be deformed and the quality of the sponge deteriorates.

The component (E) used in the present invention may be an organic peroxide which is usually used in this type of silicone rubber composition, and typical examples thereof include benzoyl peroxide and 2,4.
-Dichlorobenzoyl peroxide, p-chlorobenzoyl peroxide, dicumyl peroxide, 2,
5-bis (t-butylperoxy) -2,5-dimethylhexane, 2,5-bis (t-butylperoxy)-
2,5-dimethylhexyne, di-t-butyl peroxide, t-butyl peroxide dibenzoate, bis (4
Examples include -t-butylcyclohexyl) peroxycarbonate. Regarding the composition of (E) like this,
One kind or a mixture of two or more kinds may be used.
In general, in order to manufacture a sponge, it is scattered among those skilled in the art that a plurality of peroxides may be used in combination in consideration of the foam size of the sponge, the surface condition or the expansion ratio. The compounding amount of the component (E) is 10 parts of the component (A).
It is selected from the range of 0.1 to 10 parts by weight with respect to 0 parts by weight. If the content of the component (E) is less than 0.1 parts by weight, vulcanization becomes difficult, and if it exceeds 10 parts by weight, properties such as heat resistance are deteriorated.

Further, in the present invention, the polydiorganosiloxane in which less than the component (F) is blocked with silanol groups is to obtain a closed-cell silicone rubber sponge with a high expansion ratio. This siloxane has a viscosity at 25 ° C. of 500-
If it is 10,000 cSt and the viscosity is less than 500 cSt, the plasticity of the silicone composition is lowered and the cell becomes large, and if it exceeds 10,000 cSt, it becomes difficult to obtain a closed-cell silicone rubber sponge. The compounding amount of the component (F) is 1 to 10 parts by weight with respect to 100 parts by weight of the component (A). If the amount is less than 1 part by weight, the effect is insufficient, and if the amount is more than 10 parts by weight, the silicone composition becomes soft and roll workability is impaired.

In the present invention, as the semi-reinforcing filler or non-reinforcing filler, pulverized silica, diatomaceous earth, metal carbonate, clay, talc, titanium oxide and the like can be used together.
It is needless to say that the heat-resistant additive, antioxidant, and processing aid conventionally used in the silicone rubber can be present in the silicone rubber composition for sponges of the present invention. In particular, as in Example 1,
Blending of the alkoxy group-containing polyorganosiloxane is advantageous for obtaining a uniform and fine silicone rubber sponge with closed cells.

[Advantages of the Invention] The silicone rubber composition for sponges of the present invention enables high-frequency dielectric heating with ferrite powder, and provides a fine and uniform silicone rubber sponge.
The sponge thus obtained is useful as, for example, a gasket, a heat insulating material, a cushioning material, a sealing material in a wide temperature range.

[Examples of the Invention] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. All parts in Examples and Comparative Examples represent parts by weight.

Example 1 A kneader was charged with 100 parts of polydimethylsiloxane (average polymerization degree: 6,000), the terminal of which was closed with a dimethylvinylsilyl group and containing 0.2 mol% of methylvinylsiloxane units, and then a specific surface area of 200 m ² / 40 parts of fumed silica, 5 parts of which is blocked with a dimethylmethoxysilyl group at the end and 5 parts of linear polydimethylsiloxane having a viscosity of 20 cSt at 25 ° C., and the end of which is blocked with a silanol group, having the viscosity shown in Table 1. 3 parts of polydimethylsiloxane was added and kneaded until uniform. Each of the compounds obtained here was further kneaded by heating at 150 ° C. for 2 hours, and then cooled to obtain a base compound.

148 parts of each of the base compounds were mixed with 80 parts of ferrite powder and uniformly kneaded to obtain compositions of Examples 31 to 33 and compositions of Comparative Examples 33 to 35.

30 from a silicone rubber compound prepared by compounding 100 parts of each composition described above with 3 parts of azobisisobutyronitrile (foaming agent) and 0.75 part of organic peroxide in a two-roll system.
First, a sheet of mm × 30 mm × 10 mm was prepared.
The silicone rubber compound sheet thus obtained is stored in a microwave oven, and the frequency is 2450 MHz and the output is 600.
When heated at W for 2 minutes, a silicone rubber sponge was obtained. The results of observing the foaming state of this silicone rubber sponge cut at approximately the center are shown in Table 1.

As can be seen from the results in the table, the compositions 31 to 3 of the examples
In Comparative Example 3, as compared with the compositions 34 to 35 of Comparative Examples, uniform and fine closed-cell cells are formed, and a sponge having a high expansion ratio is obtained.

Claims (1)

[Claims] (A) 100 parts by weight of polyorganosiloxane (B) 5 to 100 parts by weight of reinforcing filler silica (C) 10 to 200 parts by weight of ferrite powder (D) 0.5 to 10 parts by weight of organic foaming agent (E) 0.1 to 10 parts by weight of an organic peroxide and (F) 1 to 10 parts by weight of a polydiorganosiloxane having a silanol group-blocked end and a viscosity of 500 to 10,000 cSt at 25 ° C. A characteristic silicone rubber composition for sponges.