JPH0718110A - Silicone rubber composition for sponge - Google Patents

Abstract

PURPOSE:To obtain a silicone rubber composition for sponge having uniform and fine cell structure, excellent heat resistance, not causing blocking of mutual molded articles. CONSTITUTION:This silicone rubber composition for sponge comprises (A) 100 pts.wt. of a polyorganosiloxane not containing a fluorine atom in an organic group bonded to a silicon atom, (B) 5-200 pts.wt. of silica for reinforcing packing, (C) 0.1-5 pts.wt. of a specific perfluoroalkyl group-containing polyorganosiloxane, (D) 0.01-10 pts.wt. of an organic peroxide and (E) 0.5-10 pts.wt. of an organic blowing agent.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a silicone rubber composition for sponges, and more particularly, to a sponge which has a uniform and fine cell structure, is excellent in heat resistance and does not cause blocking between molded articles. The present invention relates to a moldable silicone rubber composition for sponges and a silicone rubber sponge using the same.

[0002]

TECHNICAL BACKGROUND AND PROBLEMS OF THE INVENTION Silicone rubber sponges are excellent in heat resistance, cold resistance, weather resistance, electrical characteristics, flame retardancy, etc., and are widely used in various applications by taking advantage of these characteristics. . This silicone rubber sponge is basically obtained by foaming and curing a composition obtained by mixing a silicone rubber base polymer with a curing agent and a foaming agent.
It is important that the cell structure is uniform and fine, and that the original characteristics of the silicone rubber are not impaired. As a method of making the cells of a silicone rubber sponge uniform and fine, Japanese Patent Publication No. 47-43294 discloses a method of foaming and curing by an addition reaction using an organohydrogenpolysiloxane as a curing agent and a platinum catalyst. However, it is difficult to obtain a stable sponge because the addition reaction partially proceeds. As a method of improving this, Japanese Patent Publication No. Sho 53-1459
No. 2 proposes a method of obtaining a silicone rubber sponge having a uniform and fine cell structure by blending a silicone rubber compound with an organohydrogenpolysiloxane, a platinum catalyst, and an organic foaming agent, aging at low temperature, and then foaming. However, since aging requires time, productivity is poor, and the addition reaction is forced to partially proceed, it cannot be said to be suitable as a method for obtaining a stable sponge. Further, Japanese Patent Publication No. 53-41710 discloses a method of blending a diorganopolysiloxane-polyoxyalkylene copolymer, but it has a drawback of lowering heat resistance. Further, JP-A-2-251542
In No. 6, a method of performing high frequency dielectric heating using a silicone rubber composition containing ferrite powder is proposed, but in order to obtain a sufficient heating effect, it is necessary to add a large amount of ferrite powder. The mechanical strength of the rubber sponge is remarkably lowered, and coloring is difficult. Further, since the specific gravity becomes high, the heat insulating property also deteriorates, and further, in order to perform high frequency dielectric heating, there is a restriction on the molding apparatus, and hot air vulcanization (H
The AV) molding has a drawback that fine cells cannot be obtained. On the other hand, the silicone rubber sponge has a problem that blocking occurs when the molded products are kept in contact with each other. That is, in general, a silicone rubber sponge is subjected to secondary vulcanization at a temperature of about 150 to 250 ° C for several hours after foaming and curing, in order to remove decomposition residues of a foaming agent and a vulcanizing agent. It often causes blocking. For this reason, at present, powder such as talc is applied to the surface of the molded product to prevent blocking, but this deteriorates productivity and is not preferable in terms of working environment.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a uniform and fine cell structure, excellent heat resistance, and silicone rubber for sponges which does not cause blocking between molded products. It is intended to provide a composition.

[0004]

The present inventors have conducted extensive studies to achieve such an object, and as a result, a silicone rubber containing a polyorganosiloxane containing no fluorine atom in an organic group bonded to a silicon atom as a base polymer. A polyorganosiloxane containing a perfluoroalkyl group, an organic peroxide and an organic foaming agent are blended in the composition, and the mixture is foamed and cured to have a uniform and fine cell structure, excellent heat resistance, and molding. The inventors have found that a silicone rubber sponge that does not cause blocking between products can be obtained, and completed the present invention. That is, the present invention relates to (A) 100 parts by weight of polyorganosiloxane containing no fluorine atom in the organic group bonded to a silicon atom (B) 5 to 200 parts by weight of reinforcing filler silica (C) Average composition formula R ¹ _a SiO _{(4-a) / 2} (wherein R ¹ represents a group selected from a methyl group, a phenyl group and a perfluoroalkyl group, and a is 1.98 to 2.02), and a silicon atom 10 of the organic groups that can be bound to
Polyorganosiloxane, 50 mol% of which is perfluoroalkyl group 0.1 to 5 parts by weight (D) Organic peroxide 0.01 to 10 parts by weight (E) Organic blowing agent 0.5 to 10 parts by weight, for sponge It is a silicone rubber composition.

First, the constituent components of the silicone rubber composition for sponges of the present invention will be described. The polyorganosiloxane of the component (A) used in the present invention serves as a base polymer of the composition of the present invention, and 0.01 to 1.0 mol of the groups bonded to the silicon atom in one molecule are alkenyl groups. It is a polyorganosiloxane. Examples of the alkenyl group include vinyl group and allyl group. The group bonded to a silicon atom other than the alkenyl group in this polymer is a hydroxyl group, a monovalent substituted or unsubstituted hydrocarbon group, and the monovalent substituted or unsubstituted hydrocarbon group is methyl group. Group, ethyl group, propyl group, butyl group, hexyl group, octyl group, decyl group, alkyl groups such as dodecyl group, phenyl group, β-phenylethyl group, and the like, but are 3,3,3- Those containing a fluorine atom such as a trifluoropropyl group are not suitable for obtaining the effects of the present invention. That is, in the present invention, (A) a polyorganosiloxane containing no fluorine atom in an organic group bonded to a silicon atom is used as a base polymer, and a specific amount of (C) a perfluoroalkyl group-containing polyorganosiloxane described below is used. It is characterized in that it is used together with.

The composition of the present invention contains a reinforcing filler silica as the component (B). This reinforcing filling silica is
It is added for the purpose of reinforcing, thickening, improving processability, and increasing the amount of the silicone rubber foam. For example, fumed silica, wet silica, fumed silica or wet silica whose surface is hydrophobized, quartz fine powder, One or more kinds of diatomaceous earth can be used, and the specific surface area is 1
Those having m ² / g or more can be preferably used. Here, the compounding amount of the reinforcing filler silica is 5 to 200 parts by weight, particularly 10 to 10 parts by weight based on 100 parts by weight of the polyorganosiloxane as the component (A).
0 parts by weight is preferred. Reinforcing silica for filling is 5
If it is less than 100 parts by weight, the reinforcing property may be poor, and if it exceeds 200 parts by weight, foaming may be insufficient.

In the present composition, the polyorganosiloxane containing a perfluoroalkyl group as the component (C) makes the cell structure of the sponge uniform and fine, and further,
It is intended to provide an effect of preventing blocking between molded products. This polyorganosiloxane is represented by the above average composition formula, and the organic group R ¹ bonded to the silicon atom is a methyl group, a phenyl group and -CH ₂ CH ₂ R _f (R _f is a carbon number of 1
To a perfluoroalkyl group of 3), and a is a substantially linear one having a number of 1.98 to 2.02. Among the organic groups causing bonded to a silicon atom for achieving the above effects, -CH ₂ CH ₂ R _f is required to be 10 to 50 mol%. If it is less than 10 mol%, the cell structure will be uniform and fine, and there will be no effect of preventing blocking between molded products, and if it exceeds 50 mol%, synthesis will be difficult. Although the viscosity of the component (C) is not particularly limited, it is preferable that the degree of polymerization is lower than that of the polyorganosiloxane of the component (A), at 25 ° C., from the viewpoints of uniform and finer sponge cell structure and antiblocking effect. The viscosity is preferably 1,000,000 cP or less. Also, the blending amount is
It is 0.1 to 5 parts by weight with respect to 100 parts by weight of the component (A). If the amount is too small, the above-mentioned effect does not occur.
Furthermore, a sponge having a good cell structure cannot be obtained.

The peroxide with component (D) is a vulcanizing agent. The organic peroxide as the component (D) may be any of those commonly used in silicone rubber compositions of this type, such as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide and 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 peroxybenzoate, bis (4-t-butylcyclohexyl) peroxydicarbonate and the like are exemplified. These organic peroxides may be used alone or in combination of two or more. In general, it is well known that in order to produce a sponge, a plurality of kinds of organic peroxides may be used in combination in consideration of the foam size, surface condition or foaming ratio of the sponge. The blending amount of the organic peroxide as the component (D) is 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the polyorganosiloxane as the component (A). If the compounding amount is less than 0.01 parts by weight, vulcanization becomes difficult, and if it exceeds 10 parts by weight, properties such as heat resistance deteriorate.

The organic foaming agent as the component (E) is for foaming the silicone rubber composition of the present invention into a sponge form. The organic foaming agent may be any one that has been conventionally used in the production of silicone rubber sponges,
Azobisisobutyronitrile, azodicarbonamide,
Examples thereof include azo compounds such as diazoaminobenzene and nitroso compounds such as dinitrosopentamethylenetetramine and N, N-dimethyl-N, N-dinitrosoterephthalamide. These compounds decompose to generate N ₂ or CO ₂ gas when heated to a temperature above the decomposition temperature.
The amount of the organic blowing agent as the component (E) is 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of the polyorganosiloxane as the component (A). If the blending amount is less than 0.5 parts by weight, a sponge cannot be obtained, and if the blending amount exceeds 10 parts by weight, the resulting sponge is likely to be deformed, and the quality of the sponge may be deteriorated.

In addition to the above components, the silicone rubber composition for sponges of the present invention may contain a semi-reinforcing or non-reinforcing filler within a range that does not impair the effects of the present invention. As the semi-reinforcing or non-reinforcing filler, ground silica, diatomaceous earth, metal carbonate, clay,
Talc, titanium oxide, etc. can be mentioned. Also,
Heat resistant additives, flame retardants, antioxidants, processing aids, etc., which have been conventionally used, can be added to the silicone rubber composition.

[0011]

EFFECT OF THE INVENTION The silicone rubber composition for sponges of the present invention is prepared by blending a polysiloxane containing a perfluoroalkyl group with an organic peroxide and an organic foaming agent, followed by foaming and curing to obtain uniform and fine cells. It is possible to obtain a silicone rubber sponge which has a structure, is excellent in heat resistance, and does not cause blocking between molded products. The obtained silicone rubber sponge is very useful as a gasket, a heat insulating material, a cushioning material, a sealing material, etc. having a wide operating temperature range due to these excellent properties.

[0012]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
All parts in Examples and Comparative Examples represent parts by weight. Examples 1 to 3 and Comparative Examples 1 to 2 Polydimethylsiloxane (average degree of polymerization 6000) having 0.2 mol% of methylvinylsiloxane units at the end was blocked with a dimethylvinylsilyl group was used as a base polymer, and 100 parts of this base polymer were used. Was placed in a kneader and then surface treated with dimethyldichlorosilane to give a specific surface area of 200 m ² /
25g of fumed silica was added and kneaded, and then 150 ℃
The temperature was raised to kneading and kneading for 2 hours, followed by cooling to obtain a base compound. To this base compound, 2 parts by weight of polytrifluoropropyl (methyl) siloxane having a viscosity of 1000 cP and consisting of 100% of 3,3,3-trifluoropropyl (methyl) siloxane units at the both ends blocked with trimethylsilyl groups were kneadered. The resulting mixture was mixed uniformly with 1.5 parts of azobisisobutyronitrile as a foaming agent and 0.6 parts of 2,4-dichlorobenzoyl peroxide as a curing agent and 0.7 parts of dicumyl peroxide as a curing agent. A silicone rubber compound was prepared (Example 1). In addition, both ends are capped with trimethylsilyl groups, the balance consists of 100% 3,3,3-trifluoropropyl (methyl) siloxane units, with a viscosity of 100 cP and 1000
Silicone rubber compounds were similarly prepared using 0 cP of polytrifluoropropyl (methyl) siloxane (Examples 2 and 3). Further, a silicone rubber compound was prepared by adding a foaming agent / vulcanizing agent to the base compound in the same manner as in Examples 1 to 3 without adding polytrifluoropropyl (methyl) siloxane (Comparative Example 1). or,
A silicone rubber compound was obtained in the same manner as in Example 1 except that the compounding amount of polytrifluoropropyl (methyl) siloxane was 15 parts (Comparative Example 2). Next, the silicone rubber compound was fed to an extruder equipped with a die having an outer diameter of 7 mmφ, and continuously extruded at 5 m / min.
A round bar-shaped silicone rubber molding was obtained. This is 30 cm in length
It was cut into pieces and left in a dryer at 250 ° C. for 5 minutes to obtain a silicone rubber sponge. This round-bar silicone rubber sponge was placed in a dryer at 200 ° C and piled up, and after post-vulcanization was performed for 4 hours, it was taken out and checked for blocking. C) was measured. Thereafter, the sponge was left in a dryer at 250 ° C. for 72 hours to measure the hardness of the sponge, and the surface state of the sponge was visually observed. The results are shown in Table 1.

[0013]

[Table 1]

Claims (1)

[Claims] 1. (A) 100 parts by weight of a polyorganosiloxane containing no fluorine atom in an organic group bonded to a silicon atom (B) 5 to 200 parts by weight of reinforcing filler silica (C) Average composition formula R ¹ _a SiO _{(4-a) / 2} (in the formula, R ¹ represents a group selected from a methyl group, a phenyl group and a perfluoroalkyl group, and a is 1.98 to 2.02), 10 to 10 organic groups
Polyorganosiloxane 50 mol% is perfluoroalkyl group 0.1 to 5 parts by weight (D) Organic peroxide 0.01 to 10 parts by weight (E) Organic blowing agent 0.5 to 10 parts by weight for sponge Silicone rubber composition.