JP3419279B2 - Silicone rubber sponge 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 silicone rubber sponge composition which gives a silicone rubber sponge used for building gaskets, sponge rolls, heat insulating sheets and the like.

[0002]

2. Description of the Related Art Silicone rubber sponges have physical properties peculiar to silicone rubber and are excellent in heat resistance, cold resistance, electrical insulation, flame retardancy, compression set and the like. Have This silicone rubber sponge is basically a combination of a thermosetting silicone rubber composition, a curing agent and a foaming agent, and is foamed by heating,
It cures to form a sponge, but in that case it has excellent foamability, has a uniform and fine cell structure, the surface of the skin layer is smooth, there is no adhesiveness, and the physical properties unique to silicone rubber It is important not to impair the properties.

As a processing and molding method, curing and foaming are carried out in hot air at atmospheric pressure which enables continuous molding. Organic peroxides capable of atmospheric pressure hot air vulcanization are generally those having a halogen group such as 2,4-dichlorobenzoyl peroxide. When a peroxide having a halogen group is used, after curing, However, the decomposed product remains in the molded product and bleeds on the surface over time, and long-term post cure is required due to its own toxicity.

Although benzoyl peroxide having no halogen can be vulcanized under atmospheric pressure, it has a problem that excellent sponge properties cannot be obtained in terms of foamability, cell structure and the like.

Therefore, in JP-A-5-43802, it has been proposed to use a halogen-free percarbonate as a curing agent, but this has the drawback that the vulcanization rate is slow because of the high decomposition temperature and the productivity is poor. is there.

The present invention has been made in order to overcome the above problems. Even if an organic peroxide having no halogen is used, the workability is not lowered as compared with the case of using an organic peroxide having halogen. An object of the present invention is to provide a silicone sponge composition capable of shortening post-curing time, excellent in foamability, having a uniform and fine cell structure, and having a smooth skin layer surface and no tackiness. .

[0007]

Means for Solving the Problems and Modes for Carrying Out the Invention The present inventors have conducted extensive studies in order to achieve the above object, and as a result, (A) the following average composition formula (I):

[Chemical 3] (R ¹ is the same or different, unsubstituted or substituted monovalent hydrocarbon group, a is a positive number from 1.95 to 2.04), (B) specific surface area 50 m ² /
A silicone rubber sponge composition containing at least g of fine silica powder, (C) paramethylbenzoyl peroxide, (D) organic foaming agent, (E) dialkyl-based organic peroxide or peroxyester-based organic peroxide is obtained. A silicone rubber sponge that can be hot-air vulcanized at atmospheric pressure, does not require post-curing for a long time, has excellent foamability, has a uniform and fine cell structure, and has a smooth skin layer surface and no tackiness. It was found to give.

Therefore, the present invention provides (A) an organopolysiloxane represented by the following average composition formula:

[Chemical 4] (R ¹ is the same or different, unsubstituted or substituted monovalent hydrocarbon group, a is a positive number of 1.95 to 2.04) 100 parts by weight, (B) silica having a specific surface area of 50 m ² / g or more Fine powder 5
˜100 parts by weight, (C) 0.1 to 10 parts by weight of paramethylbenzoyl peroxide, (D) 0.01 organic blowing agent
A silicone rubber sponge composition is characterized by containing ˜50 parts by weight and (E) 0.1-10 parts by weight of a dialkyl-based organic peroxide or a peroxyester-based organic peroxide as essential components.

The present invention will be described in detail below. The organopolysiloxane as the component (A) has the following average composition formula [I].

[Chemical 6] (In the formula, R ¹ is the same or different substituted or unsubstituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.04.)
It is an organopolysiloxane represented by.

In the average composition formula [I], R ¹ is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group or a dodecyl group, a cycloalkyl group such as a cyclohexyl group, a vinyl group or allyl. Group, butenyl group, alkenyl group such as hexenyl group, phenyl group, aryl group such as tolyl group, aralkyl group such as β-phenylpropyl group, or part or all of hydrogen atoms bonded to carbon atoms of these groups. The same or different, preferably selected from a chloromethyl group substituted with a halogen atom, a cyano group, etc., a trifluoropropyl group, a cyanoethyl group, etc., preferably having 1 to 12 carbon atoms, more preferably 1 carbon atom.
~ 8 unsubstituted or substituted monovalent hydrocarbon groups.
Further, n is a positive number of 1.95 to 2.04, and this organopolysiloxane has a molecular chain terminal blocked with a trimethylsilyl group, a dimethylvinylsilyl group, a dimethylhydroxysilyl group, a trivinylsilyl group, or the like. However, in the present invention, the organopolysiloxane is required to have at least two alkenyl groups in the molecule, and 0.001 to 5 mol% of R ¹ , particularly 0.01 to 0, It is preferable that 0.5 mol% is an alkenyl group, particularly a vinyl group.

This type of organopolysiloxane is obtained by cohydrolytically condensing one or more selected organohalogenosilanes, or a cyclic polysiloxane (such as a trimer or tetramer of siloxane).
Can be obtained by ring-opening polymerization using an alkaline or acidic catalyst, which is basically a linear diorganopolysiloxane, but may be partially branched. It may also be a mixture of two or more different molecular structures. The organopolysiloxane has a viscosity of 100 cs at 25 ° C.
The above is preferable. More preferably 100,000
It is 10,000,000 cs. 100 degree of polymerization
Above, in particular, 3,000 or more are preferable, and the upper limit thereof is preferably 100,000, more preferably 10.0.
00.

The fine silica powder as the component (B) is essential for obtaining a silicone rubber sponge having excellent mechanical strength, but for this purpose, a specific surface area is 50.
m ² / g or more, preferably 100 to 400 m ² / g. Examples of the silica fine powder include fumed silica (dry silica) and precipitated silica (wet silica), and fumed silica (dry silica) is preferable. Further, these surfaces may be hydrophobized with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane or the like. These silicas may be used alone or in combination of two or more. If the amount of the fine silica powder added is less than 5 parts by weight relative to 100 parts by weight of the organopolysiloxane (A), a sufficient reinforcing effect cannot be obtained.
If the amount is more than 10 parts by weight, the processability is deteriorated and the physical strength of the obtained silicone rubber is lowered, so that it is 5 to 10
It is 0 part by weight, preferably 10 to 90 parts by weight, particularly preferably 30 to 80 parts by weight.

Paramethylbenzoyl peroxide is used as the organic peroxide as the component (C).

[0014]

The component (C) is added in an amount of 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight, based on 100 parts by weight of the organopolysiloxane of the component (A). If the amount is less than 0.1 part by weight, the crosslinking will be insufficient, and even if it exceeds 10 parts by weight, the curing rate will not be improved, and it will take a long time to remove unreacted substances and decomposition residues.

Further, it is preferably used in combination with a dialkyl peroxide or a peroxy ester for the purpose of increasing the expansion ratio and obtaining a more uniform cell. Specifically, dicumyl peroxide, 2,5-dimethyl-2,5-bis (t-butylperoxyhexane), 2,5-dimethyl-2,5-bis (t-butylperoxy) hexyne, t
-Butyl peroxybenzoate, 1,6-bis (t-
Butyl peroxy carboxy) hexane etc. are illustrated.

The dialkyl peroxide and the peroxy ester are preferably added in an amount of 0.1 to 10 parts by weight, particularly 0.2 to 5 parts by weight, based on the organopolysiloxane as the component (A).

Further, the silicone sponge composition of the present application may contain an addition type crosslinking agent in order to improve the compression set of the sponge and obtain more uniform cells. As the addition-type crosslinking agent, known ones may be used, and in general, a platinum catalyst and an organohydrogenpolysiloxane having two or more SiH groups in one molecule can be used.

The platinum-based catalyst may be any of those conventionally known as an addition reaction catalyst, and specifically, a platinum group metal simple substance and its compound can be used.
For example, fine particle platinum metal adsorbed on a carrier such as silica, alumina or silica gel, platinum chloride, chloroplatinic acid, a complex of chloroplatinic acid hexahydrate with olefin or divinyldimethylpolysiloxane, chloroplatinic acid. Examples include hexahydrate alcohol solutions, palladium catalysts, rhodium catalysts, and the like. The addition amount of these catalysts is a catalytic amount,
It is used in the range of 1 to 1,000 ppm in terms of platinum-based metal amount, preferably 10 to 100 ppm. If it is less than 1 ppm, the crosslinking reaction will not be sufficiently promoted and curing will be insufficient.
Addition of a large amount has little effect on reactivity and is uneconomical.

The organohydrogenpolysiloxane having two or more SiH groups in one molecule may be linear, cyclic or branched, and cures an addition reaction curable silicone rubber composition. Known organohydrogenpolysiloxanes can be used as the agent, but in general, the following average composition formula (2) R ² _a H _b SiO ² _{(4-ab) / 2} (2) (wherein R ² is the above The same as R ¹ preferably has 1 to 1 carbon atoms.
12, particularly 1 to 8 are an alkyl group, an alkenyl group, an aryl group, an aralkyl group, or an unsubstituted or substituted monovalent hydrocarbon group such as a halogen substitution product or a cyano group substitution product thereof, and a and b are 1 ≦. a ≦ 2.2, 0.002 ≦ b ≦ 1,
It is a positive number that satisfies 1.002 ≦ a + b ≦ 3. ) Can be used. The SiH group has two or more, preferably three or more, in one molecule, but this may be at the end of the molecular chain or in the middle. Also, this organohydrogenpolysiloxane has a temperature of 25 ° C.
It is preferable that the viscosity at is 300 cs or less.

The amount of the organohydrogenpolysiloxane blended is 100 parts of the organopolysiloxane (A).
0.01 to 10 parts by weight is blended with respect to parts by weight. Preferably, the ratio of hydrogen atoms bonded to a silicon atom (≡SiH group) is 0.1 per 1 alkenyl group in the component (A).
The range of 5 to 10 is suitable, and the range of 1 to 4 is suitable. If it is less than 0.5, the crosslinking may not be sufficient, and sufficient mechanical strength may not be obtained.
On the other hand, if it is more than 10, the physical properties after curing may be deteriorated, and particularly heat resistance and compression set may be significantly deteriorated.

The organic foaming agent of the component (D) is azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 1 , 1'-azobis (1-acetoxy-
1-phenylethane), organic azo compounds such as azodicarbonamide, nitroso compounds such as dinitrosopentamethylenetetramine, 4,4′-oxybis (benzenesulfonylhydrazide), hydrazine derivatives such as paratoluenesulfonylhydrazine, and the like, Organic azo compounds are preferable, and azobisisobutyronitrile is particularly preferable.

The compounding amount of the component (D) is 0.01 with respect to 100 parts by weight of the silicone rubber compound of the component (A).
-50 parts by weight, preferably 0.5-10 parts by weight.
If it is less than 0.01 part by weight, foaming is insufficient, and
If the amount is more than the weight part, the cells become large and non-uniform, and the skin layer is not formed.

In the silicone rubber sponge composition of the present invention, if necessary, ground quartz, non-reinforcing silica such as diatomaceous earth, carbon black such as acetylene black, furnace black and channel black, filler such as calcium carbonate and coloring. Agent, heat resistance improver, flame retardant improver, acid acceptor, thermal conductivity improver and other additives and mold release agent, alkoxysilane, diphenylsilanediol, carbon functional silane, silanol-capped low molecular siloxane at both ends You may add dispersants etc.

The silicone rubber sponge composition of the present invention contains the above-mentioned components in two rolls, a Banbury mixer,
It can be obtained by uniformly mixing with a rubber kneader such as a do-mixer (kneader).

The silicone rubber sponge composition thus prepared can be easily obtained by heating, foaming and curing it. The curing and foaming method may be any method as long as sufficient heat can be applied to decompose the foam and vulcanize the silicone rubber, and the molding method is also not particularly limited, such as continuous vulcanization by extrusion molding, pressing, or molding by injection. It's not something
Particularly, atmospheric pressure hot air vulcanization is preferably adopted in the present invention. In this case, the heating temperature is 100 to 500 ° C., especially 200 to 400.
The temperature and the temperature are preferably several seconds to one hour, particularly 10 seconds to 30 minutes. In addition, if necessary, 1 at 180-250 ℃
Secondary vulcanization may be performed for about 10 hours.

[0027]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following examples, parts indicate parts by weight.

[0028]

Example 1 2 parts of azobisisobutyronitrile and 0.5 part of paramethylbenzoyl peroxide to 100 parts of a thermosetting silicone rubber compound (trade name: KE904FU manufactured by Shin-Etsu Chemical Co., Ltd.), Dicumyl peroxide 0.
Using 6 rolls and 2 rolls, a 2 mm thick sheet was prepared and heated at 250 ° C. for 10 minutes.
The foaming ratio of the obtained sponge was 600%, and there was no coloration and the cell size was uniform at 1 mm or less, and the surface was smooth without sticking. Furthermore, the compression set of the obtained sponge (50% compression 180 ° C x 22 hours) is 20%.
Met.

[0030]

[0031]

Comparative Example 1 100 parts of the same silicone rubber compound as in Example 1 was mixed with 2 parts of azobisisobutyronitrile and 0.7 part of dicumyl peroxide, and two rolls were used. Make a 2mm thick sheet,
This was heated at 250 ° C. for 10 minutes. The expansion ratio of the obtained sponge was 380% and the compression set of the sponge (50% compression 180 ° C. × 22 hours) was 55%.

Comparative Example 2 To 100 parts of the same silicone rubber compound as in Example 1, 2 parts of azobisisobutyronitrile and 0.5 part of a polyvinylsiloxane complex of a platinum compound, 1-ethynylcyclohexan-1-ol were used. 0.05 part, 1.0 part of dimethylsiloxane / methylhydrogensiloxane copolymer (Si-H 0.007 mol / g) blocked with trimethylsiloxy groups at both ends were blended,
A sheet having a thickness of 2 mm was prepared using two rolls and heated at 250 ° C. for 10 minutes. The expansion ratio of the obtained sponge was 300% and the compression set (50% compression 18
(0 ° C. × 22 hours) was 80%.

Example 2 An organopolysiloxane comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8000. 100 parts, 45 parts of fumed silica having a specific surface area of 200 m ² / g (manufactured by Nippon Aerosil Co., Ltd.), having silanol groups at both ends as a dispersant, an average degree of polymerization of 13, and a viscosity at 25 ° C. of 15 cs. 10 parts of dimethylpolysiloxane was kneaded with a kneader and heat-treated at 180 ° C. for 3 hours to prepare a base compound 1. 1.5 parts of azobisisobutyronitrile as a foaming agent and 0.5 parts of paramethylbenzoyl peroxide and 1.0 part of dicumyl peroxide as a cross-linking agent are mixed with the above base compound 1 by a two-roll mill. And make a 2mm thick sheet,
It was vulcanized at 50 ° C. for 10 minutes. The obtained silicone rubber sponge had a foaming ratio of 400%, a diameter of the sponge cell of about 200 μm, was uniform, had no surface sticking, and had a smooth surface. The compression set of the obtained silicone rubber sponge was 50% and 9% at 180 ° C. for 22 hours.

[0035]

Example 3 An organopolysiloxane comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 8000. 100 parts, specific surface area of 200 m ² / g and surface of fumed silica treated with chlorosilane (manufactured by Nippon Aerosil Co., Ltd.) 50
Parts, 5 parts of a dimethylpolysiloxane having a silanol group at both ends as a dispersant, an average degree of polymerization of 13, and a viscosity of 15 cs at 25 ° C. were kneaded with a kneader to obtain 180 ° C.
The base compound 2 was prepared by heating for 3 hours. 1.5 parts of azobisisobutyronitrile as a foaming agent and 0.5 part of paramethylbenzoyl peroxide and 1.0 part of dicumyl peroxide as a cross-linking agent are mixed with the above base compound 2 by a two-roll mill. 2m
An m-thick sheet was prepared and vulcanized at 250 ° C. for 10 minutes. The obtained silicone rubber sponge has an expansion ratio of 50.
0%, the diameter of the sponge cell was about 250 μm and was uniform, and there was no surface stickiness, and the surface was smooth. The compression set of the obtained silicone rubber sponge is 50%.
It was 15% when compressed at 180 ° C. for 22 hours.

Example 4 2.0 parts of 2,2'-azobis-2-methylbutyronitrile as a foaming agent, 0.5 parts of paramethylbenzoyl peroxide as a cross-linking agent and dicumyl were added to the above base compound 1. 1.0 part of peroxide was blended with a two-roll mill to prepare a sheet having a thickness of 2 mm, and heat-treated at 250 ° C. for 10 minutes. The obtained silicone rubber sponge had a foaming ratio of 380%, a diameter of the sponge cell of about 300 μm, was uniform, had no surface tack, and had a smooth surface. The compression set of the obtained silicone rubber sponge was 50% compression and 13% at 180 ° C./22 hours.

[0038]

Since the silicone rubber sponge composition of the present invention uses an organic peroxide containing no halogen, it is highly safe without the need for post-curing for a long time, has excellent foamability, and is uniform and fine. It is possible to obtain a silicone rubber sponge having various cells and having a smooth skin layer surface and no tackiness.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaharu Takahashi, 1-person, Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (72) Inventor Shin Sekiguchi Matsui, Usui-gun, Gunma Prefecture Tamachi Oji 1 Hitomi 10 Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (72) Inventor Tsutomu Nakamura Matsuida-cho, Gunma Prefecture Usida-gun 1 Hitomi 10 Shin-Etsu Chemical Industrial Silicone Electronic Materials Research Institute (56) References Japanese Unexamined Patent Publication No. 10-120817 (JP, A) Japanese Unexamined Patent Publication No. 10-67936 (JP, A) Japanese Patent Publication No. 6-4716 (JP, B2) Japanese Patent Publication No. 44-461 (JP, B1) (JP 58) Fields investigated (Int.Cl. ⁷ , DB name) C08L 83/00-83/16 C08K 3/00-13/08

Claims (4)

(57) [Claims] 1. (A) An organopolysiloxane represented by the following average composition formula (I): (R ¹ is the same or different, unsubstituted or substituted monovalent hydrocarbon group, a is a positive number of 1.95 to 2.04) 100 parts by weight, (B) silica having a specific surface area of 50 m ² / g or more Fine powder 5
˜100 parts by weight, (C) 0.1 to 10 parts by weight of paramethylbenzoyl peroxide, (D) 0.01 organic blowing agent
˜50 parts by weight, and (E) 0.1-10 parts by weight of a dialkyl-based organic peroxide or a peroxyester-based organic peroxide as essential components, a silicone rubber sponge composition. 2. The silicone rubber sponge composition according to claim 1, wherein the fine silica powder as the component (B) is fumed silica. 3. The silicone rubber sponge composition according to claim 1, wherein the organic foaming agent is an organic azo compound. 4. A platinum-based catalyst and two or more Si atoms in one molecule.
The silicone rubber sponge composition according to claim 1, wherein an addition-type crosslinking agent composed of an organohydrogenpolysiloxane having an H group is added.