JP3403495B2 - Silicone rubber composition for sponge - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber composition for a sponge, and more particularly, to a uniform and fine cell structure, excellent heat resistance, and high strength. The present invention relates to a silicone rubber composition for a sponge, which can easily form a sponge which has high tearing property and does not cause blocking between molded articles, and a silicone rubber sponge using the same. TECHNICAL BACKGROUND AND PROBLEMS OF THE INVENTION Silicone rubber sponges are excellent in heat resistance, cold resistance, weather resistance, electric characteristics, flame retardancy, etc., and are widely used in various applications by utilizing these characteristics. Have been. This silicone rubber sponge is basically obtained by foaming and curing a composition obtained by blending a curing agent and a foaming agent with a silicone rubber base polymer. in this case,
It is important that the cell structure is uniform and fine, and that the original properties of silicone rubber are not impaired. However, in OA equipment and building materials, the long-term durability of the conventionally used parts of silicone rubber sponge is required. As a result, there has been a greater demand for uniform and finer sponge cell structures, which have a significant effect on durability. As a method for 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 and a platinum-based catalyst as a curing agent. However, the addition reaction partially proceeds and it is difficult to obtain a stable sponge. As a method of improving this, Japanese Patent Publication No. 53-1459
No. 2 proposes a method of obtaining a silicone rubber sponge with a uniform and fine cell structure by blending an organohydrogenpolysiloxane, a platinum-based catalyst, and an organic blowing agent into a silicone rubber compound, aging at a low temperature, and then foaming. However, it takes a long time for aging, the productivity is poor, and the addition reaction is partially forcibly advanced, so that it is not 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 has a drawback of lowering heat resistance. Further, JP-A-2-251542
In the publication, 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 mix a large amount of ferrite powder, The mechanical strength of the silicone rubber sponge is remarkably reduced, and coloring is difficult. In addition, since the specific gravity is high, the heat insulating property is also reduced. Further, in order to perform high-frequency dielectric heating, there are limitations on the molding apparatus, and fine cells can be obtained by the usual hot air vulcanization (HAV) molding. There was a disadvantage that it could not be done. In addition, the silicone rubber sponge has a low strength and tends to have a lower strength when it is made of a highly foamed material. Here, among silicone rubber sponges, there is a trade-off between the fact that if the strength is given priority, the expected expansion ratio cannot be obtained. In order to obtain a sponge with high foaming and high strength characteristics, coating is applied to the outside of the sponge or a solid layer is provided to secure the strength, but it is extremely disadvantageous due to technical restrictions and costs. At present, the strength of the sponge itself has not increased. 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, generally, a silicone rubber sponge is subjected to foaming and curing, and then, about 150 to 25 to remove decomposition residues of a foaming agent and a vulcanizing agent.
Secondary vulcanization is carried out for several hours at a temperature of 0 ° C., which often causes blocking. For this reason, at present, talc powder is applied to the surface of the molded article to prevent blocking, but this degrades productivity and is not preferable in terms of work environment. [0003] The present invention has been made in view of the above-mentioned problems of the prior art, and has a uniform and fine cell structure, excellent heat resistance, high strength and high tearability. It is an object of the present invention to provide a silicone rubber composition for a sponge which does not cause blocking between molded articles. The present inventors have conducted intensive studies to obtain such a silicone rubber composition for sponge and foam, and as a result, polytetrafluoroethylene was blended with a polyorganosiloxane base polymer. It has been found that the above-mentioned object can be achieved, and the present invention has been completed. That is, the present invention relates to (A) 100 parts by weight of a polyorganosiloxane having an average degree of polymerization of 1,000 to 30,000 (B) 5-200 parts by weight of silica for reinforcing filler (C) 0.01 to 5 parts by weight of polytetrafluoroethylene (D A sponge silicone rubber composition comprising 0.1 to 10 parts by weight of an organic peroxide (E) and 0.5 to 10 parts by weight of an organic foaming agent. Hereinafter, the configuration of the present invention will be described in detail. The polyorganosiloxane as the component (A) of the present invention, the general _{^{formula; R 2 (R 1 2 SiO}} ) n SiR 1 2 R 2 ( wherein, R ¹ represents a monovalent substituted or unsubstituted hydrocarbon group And 0.01 to 1.0 mol% of these hydrocarbon groups are vinyl groups, and R ² represents a methyl group, a vinyl group or a hydroxyl group,
n represents a number of 1,000 to 30,000). Examples of the group other than the vinyl group of R ^{1 in} the polymer include an alkyl group such as a methyl group and a propyl group, a phenyl group, an alkenyl group and the like. Also,
The vinyl group content of R ¹ is 0.01 to 1.0 mol%, and 0.01 mol%
If it is less than 10%, the vulcanization will not proceed sufficiently, and if it exceeds 1.0 mol%, the characteristics of silicone rubber, which is inherently wide in the operating temperature range, will be impaired, such as poor heat resistance. On the other hand, if the degree of polymerization n is less than 1000, the mechanical strength after vulcanization decreases, and a high-strength sponge, which is originally intended, cannot be obtained. When the degree of polymerization n exceeds 30,000, it becomes difficult to compound the filler, and the workability is reduced. This polymer is preferably substantially linear, but may be partially branched as long as it can be used. Examples of the silica filler for reinforcing component (B) include those having a specific surface area of 50 m ² / g or more such as wet silica, fumed silica and silica aerogel. Non-reinforcing silica such as soil may be used in combination. These fillers may be used as they are, or may be surface-treated with an organosiloxane, a polyorganosiloxane, hexaorganodisilazane, or the like. The compounding amount is from 5 to 200 parts by weight, more preferably from 20 to 100 parts by weight, per 100 parts by weight of the polyorganosiloxane (A).
100 parts by weight are preferred. When the component (B) is less than 5 parts by weight,
The rubber sponge after curing is not given sufficient strength,
If the amount exceeds the weight part, it becomes difficult to mix the filler. The polytetrafluoroethylene as the component (C) has a uniform and fine cell structure, is excellent in heat resistance, has high strength and high tearability, which is the object of the present invention.
It is a characteristic component for obtaining a silicone rubber sponge that does not cause blocking between molded articles. Polytetrafluoroethylene is a resin powder, and the shape of the primary particles is arbitrary, such as an oval shape, a flake shape, a spherical shape, a cylindrical shape, and the size is generally 100 μm or less. Such a component is difficult to disperse in silicone rubber, and in order to form a sponge having a uniform and fine cell structure, usually a 30% to 70% by weight wet silica-water suspension is contained. It is effective to use. The compounding amount of the component (C) is 0.01 to 100 parts by weight of the polyorganosiloxane of the component (A).
5 parts by weight are preferred. If the amount is less than 0.01 part by weight, a sufficient effect cannot be obtained. If the amount exceeds 5 parts by weight, the compound is not suitable for foaming, and a good sponge cannot be obtained. Here, reports using polytetrafluoroethylene for the silicone rubber composition have been reported in JP-A-58-27749 and JP-B-43-3980, but these are addition type or roll workability. It is only described as effective for improvement. The present inventors have found that a silicone rubber sponge containing polytetrafluoroethylene has a uniform and fine cell structure, is excellent in heat resistance, has high strength and high tearability,
In addition, they have found for the first time that blocking between molded articles does not occur, and have reached the present invention. The organic peroxide as the component (D) may be any of those used as vulcanizing agents for ordinary silicone rubbers. Typical examples thereof include benzoyl peroxide, 2,4
-Dichlorobenzoyl peroxide, p-chlorobenzoyl peroxide, dicumyl peroxide, 2,5
-Bis (t-butylperoxy) -2,5-dimethylhexane, di-t-butyl peroxide and the like. With regard to the blending of the component (D), one or more of the components may be used in combination. In particular, in order to obtain a good foam, two or more types of the component (D) are used in combination. To do is generally known. (A)
With respect to 100 parts by weight of the component polyorganosiloxane, 0.
1 to 10 parts by weight is preferred. If the amount is less than 0.1 part by weight, vulcanization becomes difficult. If the amount exceeds 10 parts by weight, a good foam cannot be obtained, and the heat resistance is adversely affected. The organic foaming agent as the component (E) is used for foaming in the form of a sponge, and any foaming agent may be used as long as it is used as a usual foaming agent for silicone rubber sponges. These include azo compounds such as azobisisobutyronitrile and azodicarbonamide, dinitrilopentamethylenetetramine, N, N-dimethyl-N,
Examples thereof include nitroso compounds such as N-dinitrosoterephthalamide. The compounding amount of the component (E) is selected in the range of 0.5 to 10 parts by weight based on 100 parts by weight of the polyorganosiloxane of the component (A). If the component (E) is less than 0.5 parts by weight,
Gas sufficient for sponge formation is not generated, and a foam cannot be obtained. Further, when the amount is more than 10 parts by weight, the sponge is liable to be deformed and the quality is not stable. In the present invention, in addition to these, a heat-resistant additive, an antioxidant, a processing aid and the like conventionally used in silicone rubber are blended into the sponge composition of the present invention to obtain a foam. It does not matter. The silicone rubber composition for a sponge of the present invention is obtained by blending an organic peroxide and an organic foaming agent with a polyorganosiloxane containing polytetrafluoroethylene and silica for reinforcing filler. -By curing, a sponge having a uniform and fine cell structure, excellent heat resistance, high strength and high tearability, and free from blocking between molded products can be easily molded. And the obtained silicone rubber sponge has a gasket with a wide operating temperature range due to these excellent properties.
It is very useful as a heat insulating material, a cushion material, a sealing material, and the like. The present invention will be described more specifically below with reference to examples and comparative examples. In addition, all the parts in an Example represent a weight part. Examples 1 to 3 and Comparative Examples 1 and 2 The base polymer was polydimethylsiloxane (average degree of polymerization: 6000) whose terminal was blocked by a dimethylvinyl group and contained 0.1 mol% of methylvinylsiloxy units, and 100 parts of the base polymer was used. The mixture was charged into a kneader, and then 40 parts of fumed silica having a specific surface area of 130 m ² / g, which had been surface treated with dimethyldichlorosilane, was added and kneaded. I got the compound. The base compound was mixed with 0.5 part of a 60% aqueous suspension of polytetrafluoroethylene and kneaded sufficiently to be uniform. The mixture was heated and kneaded at 150 ° C. for 1 hour, and further, with two rolls, 1.5 parts of azobisisobutyronitrile as a foaming agent, 0.6 parts of 2,4-dichlorobenzoyl peroxide as a curing agent, and dicumylperoxide. 0.7 parts of oxide was blended to obtain a silicone rubber compound (Example 1). In addition, polytetrafluoroethylene 60%
A silicone rubber compound was obtained in the same manner as in Example 1 except that the amount of the aqueous suspension was changed to 2.0 parts (Example 2). In addition, the amount of azobisisobutyronitrile is 2.5
A silicone rubber compound was obtained in the same manner as in Example 1 except that the above parts were used (Example 3). Further, a foaming agent and a curing agent were added to the base compound in the same manner as in Example 1 without adding a 60% aqueous suspension of polytetrafluoroethylene to obtain a silicone rubber compound (Comparative Example 1). In addition, the amount of azobisisobutyronitrile is 2.5
A silicone rubber compound was obtained in the same manner as in Comparative Example 1 except that the above components were used (Comparative Example 2). Next, the silicone rubber compound was supplied to an extruder equipped with a die having an outer diameter of 7 mmφ. Continuous extrusion was performed at a rate of 5 m / min to obtain a round bar-shaped silicone rubber molded product. This was cut into a length of 30 cm and left in a dryer at 250 ° C. for 5 minutes to obtain a silicone rubber sponge. This round bar shaped silicone rubber sponge
After stacking in a dryer at 200 ° C. and performing post-curing for 4 hours, it was taken out and checked for the presence of blocking. At the same time, the sponge cell state was observed, and the specific gravity and hardness (Asker C) were measured. Then, it was left in a dryer at 200 ° C. for 72 hours to measure the sponge hardness, and the sponge surface condition was visually observed. Further, the silicone rubber compound was dispensed into a thickness of about 2 mm using two rolls of 16 inches and left in a dryer at 250 ° C. for 5 minutes to obtain a flat silicone rubber sponge. After vulcanization was performed. The center portion of the obtained silicone rubber sponge was punched with a No. 2 dumbbell, and the tensile strength was measured. Similarly, a tear strength A type test piece was punched out, and the tear strength A type was measured. Table 1 shows the results. [Table 1] As Comparative Example 3, except that the amount of the 60% aqueous polytetrafluoroethylene suspension was changed to 15 parts,
A silicone rubber compound was obtained and supplied to an extruder in the same manner as in Example 1, but could not be extruded because the viscosity of the silicone rubber compound was high.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08J 9/04 C08L 83/04

Claims (1)

(57) [Claims] [Claim 1] (A) 100 parts by weight of a polyorganosiloxane having an average degree of polymerization of 1,000 to 30,000 (B) 5-200 parts by weight of silica for reinforcing filling (C) Polytetra A silicone rubber composition for a sponge, comprising 0.01 to 5 parts by weight of fluoroethylene (D) 0.1 to 10 parts by weight of an organic peroxide (E) and 0.5 to 10 parts by weight of an organic foaming agent.