JP3476543B2 - Silicone rubber sponge composition - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber sponge composition, and more particularly to a silicone rubber sponge capable of lowering its specific gravity and further reducing its specific gravity. The hardness of the rubber sponge is moderately high, the compression load is high,
The present invention relates to a silicone rubber sponge composition that is rich in elasticity, has excellent surface smoothness of a skin layer, and can obtain a silicone rubber sponge having a uniform and fine cell structure. BACKGROUND OF THE INVENTION [0002] Silicone rubber sponges have been well known as materials excellent in weather resistance, electrical properties, compression set and the like. In recent years, OA
There has been a demand for weight reduction of products in which silicone rubber sponges have conventionally been used, such as equipment and building materials, and further reduction in specific gravity of silicone rubber sponges is desired. Silicone rubber sponges are basically blended with an organic foaming agent such as azobisisobutyronitrile (AIBN), azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT) and a curing agent, and foamed by heating. Obtained by curing. Generally, increase the foaming ratio of this silicone rubber sponge,
In order to obtain a silicone rubber sponge having a low specific gravity, a method of increasing the amount of an organic foaming agent and increasing the amount of decomposition generated gas for foaming is used. However, in such a method, since the gas generated by decomposition of the organic foaming agent is captured by curing the silicone rubber sponge, the generated gas leaks from the sponge surface as the generated gas amount increases, and the generated gas is captured. The rate gradually decreases, and the expansion ratio becomes limited. Furthermore, the silicone rubber sponge obtained by such a method has a very low hardness, a low compressive load, lacks elasticity, and a large amount of decomposition generated gas of the organic foaming agent leaks from the sponge surface, There is a problem that the surface of the skin layer is inferior in surface smoothness, and at the same time, cells of the silicone rubber sponge are destroyed by a large amount of decomposition generated gas, so that a silicone rubber sponge having a uniform and fine cell structure cannot be obtained. on the other hand,
By blending a large amount of thermal expansion microcapsules,
Although it is possible to reduce the specific gravity of silicone rubber sponge,
Since the obtained silicone rubber sponge has a very high sponge hardness and lacks rubber elasticity, there is a problem that the molded product is easily damaged by deformation such as compression and the mechanical strength is greatly reduced. To solve such problems, no fundamental solution has been proposed so far. [0003] The present invention has been made to solve such problems. That is, the specific gravity of the silicone rubber sponge can be reduced, and the hardness of the silicone rubber sponge having a reduced specific gravity is appropriately high, the compression load is high, the elasticity is high, and the surface smoothness of the skin layer is excellent, It is another object of the present invention to provide a silicone rubber sponge composition capable of obtaining a silicone rubber sponge having a uniform fine cell structure. The present inventors have conducted intensive studies to achieve the above object, and as a result, an organic foaming agent and a specific heat-expandable microcapsule were added to a thermosetting millable silicone rubber composition. By mixing a specific amount of each, the specific gravity of the silicone rubber sponge can be reduced, and the hardness of the silicone rubber sponge with a reduced specific gravity is moderately high, the compression load is high, the elasticity is high, and the surface of the skin layer is excellent. It has been found that a silicone rubber sponge having excellent smoothness and a uniform and fine cell structure can be easily obtained, and the present invention has been completed. That is, the present invention relates to (A) a thermosetting millable silicone rubber composition containing (a) a polyorganosiloxane base polymer, (a ′) a reinforcing silica filler and (b) a curing agent as main components, and (B) ) 0.1-20 parts by weight of thermally expandable microcapsules that expand at a temperature of 80-200 ° C (vs. (a)
100 parts by weight) and (C) 0.5 to 10 parts by weight of organic blowing agent (vs. (a)
100 parts by weight of a silicone rubber sponge composition. First, components constituting the silicone rubber sponge composition of the present invention will be described. The present invention is characterized in that the specific heat-expandable microcapsules (B) and the organic foaming agent (C) are mixed with the thermosetting millable silicone rubber composition (A), The functional millable silicone rubber composition (A) comprises (a) a polyorganosiloxane base polymer, (a ′) a reinforcing silica filler,
(b) blending a curing agent and, if necessary, various additives,
It is uniformly dispersed. (a ') Reinforcing silica filler is a substance necessary for improving the processability, mechanical strength, etc. of silicone rubber, such as precipitated silica and fumed silica which have been generally used in the past. It is. (a ') The compounding amount of the reinforcing silica filler is generally in the range of 1 to 100 parts by weight with respect to 100 parts by weight of the (a) polyorganosiloxane base polymer, but is not particularly limited thereto. Absent. Among the various components used in such a silicone rubber composition, (a) a polyorganosiloxane base polymer and (b) a curing agent are appropriately selected according to a reaction mechanism for obtaining a rubber-like elastic body. It is. The reaction mechanism includes (1) a crosslinking method using an organic peroxide vulcanizing agent,
(2) A method by an addition reaction and the like are known, and it is well known that a preferable combination of the component (a) and the component (b), that is, a curing catalyst or a crosslinking agent is determined by the reaction mechanism. That is, when the crosslinking method of the above (1) is applied, the base polymer of the component (a) is usually a polymer having at least two vinyl groups among the organic groups bonded to silicon atoms in one molecule. Organosiloxane is used. Organic peroxide vulcanizing agents such as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide and cumyl-t-butyl peroxide are used as the curing agent of component (b). When it is performed, diacyl organic peroxides such as benzoyl peroxide and 2,4-dichlorobenzoyl peroxide are generally used. In addition, these organic peroxide vulcanizing agents are used as one kind or as a mixture of two or more kinds.
(b) The compounding amount of the organic peroxide as a curing agent of the component is (a)
The range is preferably 0.05 to 15 parts by weight based on 100 parts by weight of the silicone base component. If the compounding amount of the organic peroxide is less than 0.05, the vulcanization is not sufficiently performed, and if the compounding amount exceeds 15 parts by weight, not only no further special effect is exerted, but also the physical properties of the obtained silicone rubber are adversely affected. This is because it may be given. When the addition reaction of the above (2) is applied, the same base polymer as the above (1) is used as the base polymer of the component (a). As the curing agent of the component (b), a platinum catalyst such as chloroplatinic acid, platinum olefin complex, platinum vinyl siloxane complex, platinum black, and platinum triphenylphosphine complex is used as a curing catalyst. As the agent, a polyorganosiloxane having an average of at least two hydrogen atoms bonded to silicon atoms per molecule is used. Of the curing agent (b), the amount of the curing catalyst is preferably in the range of 1 to 1000 ppm in terms of platinum element based on the base polymer (a). If the amount of the curing catalyst is less than 1 ppm as platinum element, curing will not proceed sufficiently, and if it exceeds 1000 ppm, no particular improvement in curing speed can be expected. The amount of the cross-linking agent is preferably such that the number of hydrogen atoms bonded to silicon atoms in the cross-linking agent is 0.5 to 4.0 per alkenyl group in the component (a), and more preferably, 1.0 to
The quantity is 3.0. When the amount of hydrogen atoms is less than 0.5, curing of the composition does not proceed sufficiently, and the hardness after curing becomes low, and when the amount of hydrogen atoms exceeds 4.0, the composition after curing becomes hard. Physical properties and heat resistance decrease. Used in various reaction mechanisms as described above (a)
The organic group other than the alkenyl group in the polyorganosiloxane as the base polymer of the component is a monovalent substituted or unsubstituted hydrocarbon group, and includes a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, and a dodecyl group. Such as an alkyl group, an aryl group such as a phenyl group, an unsubstituted hydrocarbon group such as an aralkyl group such as a β-phenylpropyl group, a chloromethyl group, and a 3,3,3-trifluoropropyl group. A substituted hydrocarbon group is exemplified. In general, a methyl group is frequently used because of ease of synthesis and the like. The average degree of polymerization of the polyorganosiloxane as the base polymer of the component (a) is from 3,000 to 30,000.If the degree of polymerization is less than 3,000, the mechanical strength of the silicone rubber sponge decreases, and the degree of polymerization exceeds 30,000. And it becomes difficult to mix the filler, and the workability is reduced. This polymer is desirably substantially linear, but may be partially branched as long as it can be used. [0006] The heat-expandable microcapsules which expand at a temperature of 80 to 200 ° C of the component (B) are a characteristic feature for imparting the effects of the present invention. Here, the heat-expandable microcapsules which expand at a temperature of 80 to 200 ° C. need to have an average particle size of 1 to 50 μm, and if it is smaller than 1 μm, the dispersion in rubber becomes insufficient, and if it exceeds 50 μm, the silicone particles become silicone. The strength of the rubber sponge is greatly reduced. Further, the expansion ratio is preferably 10 to 100 times. If the expansion ratio is less than 10 times, a sufficient expansion ratio cannot be obtained, and if it exceeds 100 times, it is difficult to obtain uniform fine cells. As such a heat-expandable microcapsule, an outer shell of vinylidene chloride / acrylonitrile copolymer and containing isobutane (for example, Expancel manufactured by Expancel, Matsumoto Microsquare manufactured by Matsumoto Yushi Pharmaceutical) is used. Are commercially available and can be easily obtained. Component (B) is used in an amount of 0.1 to 20 parts by weight, preferably 1 to 100 parts by weight of the polyorganosiloxane base polymer of component (a).
It is selected in the range of ~ 10 parts by weight. If the component (B) is less than 0.1 part by weight, a sufficient foaming ratio cannot be obtained, and if it exceeds 20 parts by weight, the sponge hardness becomes very high,
Due to lack of rubber elasticity, the molded product is easily damaged by deformation such as compression, and the mechanical strength is greatly reduced. The thermally expandable microcapsules of the component (B) described above, which expand at a temperature of 80 to 200 ° C., expand by heat, and thus generate a large amount of decomposition generated gas as in the case of high foaming using an organic blowing agent. This does not occur, and therefore, the amount of gas captured by curing of the rubber is reduced, so that the decomposition generated gas is less likely to leak from the sponge surface, and a silicone rubber sponge excellent in surface smoothness of the skin layer is easily obtained. It becomes possible. In addition, 80-200 of component (B)
Since the heat-expandable microcapsules that expand at a temperature of ℃ have an outer shell made of vinylidene chloride / acrylonitrile copolymer or the like that shows high hardness at room temperature, they give silicone rubber sponge an appropriate hardness and compressive load force of silicone rubber sponge. And an elastic silicone rubber sponge can be obtained. In the case of a heat-expandable microcapsule having an expansion temperature of less than 80 ° C., the compression set becomes poor, and if it exceeds 200 ° C., the productivity becomes poor. The organic foaming agent of the component (C) may be any one as long as it is used as a usual silicone rubber sponge foaming agent. These include azo compounds such as azobisisobutyronitrile and azodicarbonamide, dinitrosopentamethylenetetramine, N, N
And nitroso compounds such as -dimethyl-N, N-dinitrosoterephthalamide. The amount of the component (C) is (a)
It is selected in the range of 0.5 to 10 parts by weight based on 100 parts by weight of the component polyorganosiloxane base polymer. (C)
If the component is less than 0.5 parts by weight, sufficient decomposition generation gas for sponge formation will not be generated, and if it exceeds 10 parts by weight, a large amount of decomposition generation gas will be generated, and the decomposition generation gas will leak from the sponge surface, The surface smoothness of the skin layer is significantly deteriorated. The silicone rubber sponge composition of the present invention may contain a semi-reinforcing or non-reinforcing filler in addition to the above components, as long as the effect of the present invention is not impaired. Examples of the semi-reinforcing or non-reinforcing filler include crushed silica, diatomaceous earth, metal carbonate, clay, talc, mica, and titanium oxide.
Further, a heat-resistant additive, a flame retardant, an antioxidant, a processing aid, and the like, which have been conventionally used, can be added to the silicone rubber composition. Further, it is possible to mix carbon, ferrite powder and the like, and to perform molding by high-frequency dielectric heating. The silicone rubber sponge composition of the present invention is obtained by blending a specific heat-expandable microcapsule and an organic foaming agent into the heat-effective millable silicone rubber composition. A low-density silicone rubber sponge with a low specific gravity that has a moderately high hardness, a high compression load, high elasticity, and excellent skin smoothness of the skin layer, and uniform fine cells A silicone rubber sponge having a structure can be obtained. And the obtained silicone rubber sponge is very useful as a gasket, a heat insulating material, a cushion material and the like. Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, the part in an Example represents a weight part. Example 1 For 100 parts of a thermosetting millable silicone rubber compound (YE3465U manufactured by Toshiba Silicone), 4 parts of azobisisobutyronitrile (ME800 manufactured by Toshiba Silicone) were used as an organic foaming agent, and the outer shell was made of vinylidene chloride.
Acrylonitrile copolymer, encapsulating isobutane, having an expansion temperature of 110-150 ° C, an average particle size of 5-30 μm, and a thermal expansion microcapsule having an expansion ratio of about 60 times (Expancel Corp. Cell 461D
U) 2 parts, 0.5 part of platinum complex of chloroplatinic acid and tetramethylvinyldisiloxane as a curing catalyst (15 ppm based on the total weight as platinum), and dimethylsiloxane / methylhydrogensiloxane having a trimethylsiloxy group at both terminals as a crosslinking agent. 1.0 part of a copolymer (silicon-bonded hydrogen atom content: 0.8%) and 1.0 part of triallyl isocyanate as a curing inhibitor were blended and mixed with a two-roll mill until uniform. Next, the silicone rubber compound was supplied to an extruder and continuously extruded at a rate of 5 m / min to obtain a silicone rubber compound having a circular cross section having an inner diameter of about 10 mm and an outer diameter of about 12 mm. This is length 50
C. and cut in a dryer at 200.degree. C. for 10 minutes to obtain a silicone rubber sponge. The obtained silicone rubber sponge had a uniform and fine cell structure. The specific gravity was 0.20 and the hardness was 8 (Asker C). Next, the surface roughness of the silicone rubber sponge was measured by an ISO method (ten-point average method) using a surface roughness measuring device Surfcon 570A manufactured by Tokyo Seimitsu Co., Ltd. and found to be 10.2 μm, which was a very preferable appearance. . Also, add 10 pieces of silicone rubber sponge.
It was cut to a length of 0 mm, and the compression load when it was compressed by 40% in the system direction at a speed of 20 mm / min was measured.
/ 100mm, which was very elastic. Example 2 For 100 parts of a thermosetting millable silicone rubber compound (YE3465U manufactured by Toshiba Silicone), 4 parts of azobisisobutyronitrile (ME800 manufactured by Toshiba Silicone) were used as an organic foaming agent, and the outer shell was made of chloride. Vinylidene
Acrylonitrile copolymer, encapsulating isobutane, having an expansion temperature of 110-150 ° C, an average particle size of 5-30 μm, and a thermal expansion microcapsule having an expansion ratio of about 60 times (Expancel Corp. Cell 461D
U) 2 parts, benzoyl peroxide 0.6 as curing agent
And 0.8 part of dicumyl peroxide were blended and mixed with a two-roll mill until uniform. Next, a silicone rubber sponge was obtained in the same manner as in Example 1. The obtained silicone rubber sponge had a uniform and fine cell structure. The specific gravity was 0.18 and the hardness was 7 (Asker C). Next, the surface roughness of the silicone rubber sponge was measured using a surface roughness measuring device Surfcon 570A manufactured by Tokyo Seimitsu Co., Ltd.
When measured by the ISO method (ten-point average method), it was 9.7 μm, which was a very preferable appearance. Also, when the silicone rubber sponge was cut into a length of 100 mm and the compression load was measured at a speed of 20 mm / min and compressed 40% in the system direction, the compression load was 1.1 kgf / 100 mm. Was out. Comparative Example 1 A silicone rubber sponge was prepared in the same manner as in Example 2 except that 7 parts of azobisisobutyronitrile (ME800, manufactured by Toshiba Silicone) was blended as an organic foaming agent without blending the thermally expandable microcapsules. I got The cell structure of the obtained silicone rubber sponge was not uniform and lacked in fineness. Specific gravity is 0.32 and hardness is 2 (Aske
r C). Next, the surface roughness of the silicone rubber sponge was measured using a surface roughness measuring device Surfcon 570A manufactured by Tokyo Seimitsu.
Measured by ISO method (ten-point average method) using
It was 25.9 μm, and the sponge surface was notably uneven. Also cut the silicone rubber sponge into 100mm length,
The compression load when compressed 40% in the system direction at a speed of 20 mm / min was 0.1 kgf / 100 mm, indicating little elasticity. Comparative Example 2 A silicone rubber sponge was prepared in the same manner as in Example 2, except that 10 parts of azobisisobutyronitrile (ME800, manufactured by Toshiba Silicone) was blended as an organic foaming agent without blending the heat-expandable microcapsules. I got The cell structure of the obtained silicone rubber sponge was not uniform and lacked in fineness. The specific gravity is 0.29, and the hardness is 1 (Aske
r C). Next, the surface roughness of the silicone rubber sponge was measured using a surface roughness measuring device Surfcon 570A manufactured by Tokyo Seimitsu.
Measured by ISO method (ten-point average method) using
It was 28.5 μm, and the sponge surface was notably uneven. Also cut the silicone rubber sponge into 100mm length,
When the compression load at the time of compressing 40% in the system direction at a speed of 20 mm / min was measured, it was 0.1 kgf / 100 mm, and there was almost no elasticity.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08J 9/04 C08L 83/04

Claims (1)

(57) [Claims] (1) A thermosetting millable having (a) a polyorganosiloxane base polymer, (a ') a reinforcing silica filler and (b) a curing agent as main components. (B) 0.1 to 20 parts by weight of heat-expandable microcapsules (based on (a) 100 parts by weight) and (C) 0.5 to 10 parts by weight of an organic foaming agent. (100 parts by weight of (a)) was blended with the silicone rubber sponge composition.