JPH10212412A - Silicone rubber composition and molding of silicone rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicone rubber composition free from emission of ill odor and foaming in curing and giving a molded silicone rubber article having little surface stickiness (surface tackiness) and small compression set by curing. SOLUTION: This composition is composed of (A) 100 pts.wt. of an organopolysiloxane raw rubber expressed by the average compositional formula Ra SiO(4-a)/2 (R is a substituted or unsubstituted univalent hydrocarbon group; (a) is 1.8-2.3) and having at least two alkenyl groups bonded to Si atom in one molecule, (B) 10-100 pts.wt. of fine silica power, (C) 0.05-10 pts.wt. of methyl- substituted benzoyl peroxide and (D) 0.05-10 pts.wt. of a dialkyl peroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a silicone rubber composition and a method for molding a silicone rubber.
The present invention relates to a silicone rubber composition used as an extrusion molding material such as a tube, a sheet, and a wire covering material, and a method of molding a silicone rubber.

[0002]

2. Description of the Related Art Silicone rubber is widely used as an extruded material for tubes, tapes, sheets, electric wire covering materials, etc. because of its excellent heat resistance, cold resistance, weather resistance, electrical properties and the like. In order to cure a silicone rubber composition (silicone rubber composition for extrusion molding) conventionally used as such an extrusion molding material, 2,4
-Dichlorobenzoyl peroxide was used. However, the silicone rubber composition containing this organoperoxide emits an unpleasant odor during curing, and after curing,
There is a disadvantage that stickiness (surface tackiness) occurs on the surface of the silicone rubber molded product, and there is a disadvantage that blooming occurs on the surface of the silicone rubber molded product. Blooming is a phenomenon in which a decomposition product of a curing agent is gradually stained and the surface of a molded product becomes white. Many studies have been made to date to solve such problems.
For example, JP-A-54-48870 proposes a method of using bis (2,4-dichlorobenzoyl) peroxide and ditertiary-butyl peroxide as a curing agent to obtain a silicone rubber having low tackiness on the surface of a molded product. Have been. However, according to this method, an unpleasant odor is generated at the time of curing, so that the tackiness of the surface of the molded product cannot be completely prevented, and the permanent compression set of the molded product is lowered, which is not always satisfactory. On the other hand,
No. 9-18758 proposes a method using bis (ortho-methylbenzoyl) peroxide as a curing agent for a silicone rubber composition. According to this method, it is said that the above-mentioned odor does not occur and blooming does not occur. Also, JP-A-62-18
No. 5750 proposes a method of using bis (para-methylbenzoyl) peroxide as a curing agent for a silicone rubber composition. According to this method, the above-mentioned problems are solved. It has been. However, the silicone rubber composition obtained by the former method has a disadvantage that the silicone rubber molded product becomes yellowish (yellowing) after heat curing. In addition, the silicone rubber composition obtained by the latter method has a problem that the curing speed is low, and foaming occurs during curing, and fine bubbles (voids) are easily generated. In particular, there is a problem that the silicone rubber molded product obtained by these methods has a large compression set and cannot be used depending on the application.

[0003]

The present inventors have conducted intensive studies to solve the above problems, and as a result, the above problems can be solved by using a specific organic peroxide in combination as a curing agent for a silicone rubber composition. And completed the present invention. That is, an object of the present invention is to provide a silicone rubber composition which does not emit an off-flavor at the time of curing, does not cause foaming, has low surface tackiness after curing, and can be a silicone rubber molded product having a small compression set. Is to do.

[0004]

The object of the present invention is to provide (A) an average compositional formula R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group, and a is 1 Of 0.8 to 2.3), 100 parts by weight of an organopolysiloxane raw rubber having at least two silicon-bonded alkenyl groups in one molecule, (B) finely divided silica This is achieved by a silicone rubber composition comprising 100 parts by weight, (C) 0.05 to 10 parts by weight of a methyl-substituted benzoyl peroxide, and (D) 0.05 to 10 parts by weight of a dialkyl peroxide.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The organopolysiloxane raw rubber (A) used in the present invention is a main component of the composition of the present invention, and has an average composition formula R
_a It is represented by SiO 2 _{(4-a) / 2} . Here, in the formula, R is a substituted or unsubstituted monovalent hydrocarbon group, specifically, an alkyl group such as a methyl group, an ethyl group or a propyl group, a cycloalkyl group such as a cyclohexyl group, a vinyl group, an allyl group. Alkenyl groups such as phenyl, butynyl, and hexenyl groups; aryl groups such as phenyl and tolyl; substituted hydrocarbon groups such as 3,3,3-trifluoropropyl, 2-phenylethyl, and 2-cyanoethyl; The monovalent hydrocarbon group illustrated is mentioned. A is a number from 1.9 to 2.1. The molecular structure of this component is preferably substantially linear,
A structure having a branch in part may be used. The polymerization degree of this component is
Those within the range called organopolysiloxane raw rubber in the art can be used, and those having a viscosity at 25 ° C. of at least 10 ⁶ centistokes and an average molecular weight of at least 25 × 10 ⁴ are used. You.

The finely divided silica (B) used in the present invention is a component essential for imparting excellent mechanical strength to the silicone rubber obtained by curing the composition of the present invention. is there. Examples of such finely powdered silica include dry-process silica such as fumed silica and wet-process silica such as precipitated silica, and the surface thereof is coated with an organic such as organochlorosilane, hexaorganodidisilazane, diorganocyclopolysiloxane. Finely divided silica that has been hydrophobized with a silicon compound can also be used. This component has a specific surface area of preferably 50 m ² / g or more, more preferably 100 m ² / g or more. The amount of this component is 10 to 100 parts by weight per 100 parts by weight of component (A).
It is in the range of parts by weight. This is because if it is less than 10 parts by weight, the mechanical strength decreases, and if it exceeds 100 parts by weight, it becomes difficult to mix it with the component (A).

The methyl-substituted benzoyl peroxide of the component (C) used in the present invention is a curing agent for curing the composition of the present invention.
Monomethylbenzoyl peroxide such as bis (ortho-methylbenzoyl) peroxide, bis (meta-methylbenzoyl) peroxide, bis (para-methylbenzoyl) peroxide, and dimethyl such as bis (2,4-dimethylbenzoyl) peroxide Trimethylbenzoyl peroxide such as benzoyl peroxide and bis (2,4,6-trimethylbenzoyl) peroxide is exemplified. The addition amount of this component is 0.05 to 100 parts by weight of the organopolysiloxane of the component (A).
It is within the range of 10 parts by weight, preferably within the range of 0.1 to 5 parts by weight.

[0008] The dialkyl peroxide of the component (D) used in the present invention is a curing agent similarly to the component (C). When this is used in combination with the component (C), the silicone rubber, which is a cured product of the composition of the present invention, has improved compression set and surface tackiness. Such dialkyl peroxides include dicumyl peroxide, 2,
5-dimethyl-2,5-di (t-butylperoxy) hexane, di-t-butyl peroxide and t-butylcumyl peroxide are exemplified. The amount of this component added
It is in the range of 0.05 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the organopolysiloxane of the component (A). The amount of the component (D) is the same as that of the component (C) 1
It is preferably in the range of 10 to 90 parts by weight, more preferably in the range of 10 to 50 parts by weight with respect to 00 parts by weight.

The composition of the present invention comprises the above-mentioned component (A)
The silicone rubber composition comprising the component (D). In addition to these components, the addition and blending of various additives which are conventionally known to be blended in the silicone rubber composition is not limited to the present invention. It does not matter unless the purpose is impaired. Examples of such additives include crepe hardening inhibitors such as diorganosiloxane oligomers having silanol groups blocked at both ends, organohydroxysilane, hexaorganodisilazane, diatomaceous earth, quartz powder, calcium carbonate,
Inorganic fillers such as carbon black, cerium hydroxide,
Heat-resistant agents such as cerium silanolate and cerium fatty acid salts,
Mold release agents such as fatty acids such as stearic acid, zinc stearate, calcium stearate and metal salts thereof;
Examples include pigments, foaming agents, flame retardants, and conductivity agents.

The composition of the present invention is easily produced by uniformly mixing the above components (A) to (D), but the components (A) and (B) are previously mixed with a kneading machine such as a kneader mixer. It is preferred that the components (C) and (D) are added and blended using a kneading means such as a two-roll mill.

In order to produce a silicone rubber molded article using the composition of the present invention, for example, the composition of the present invention is continuously introduced into an extruder to form an uncured silicone rubber molded article. Next, the molded product is cured in hot air under normal pressure to obtain a silicone rubber molded product. Here, as the extruder, a conventionally well-known extruder used for extrusion of a silicone rubber composition can be used. The temperature at which the silicone rubber composition is cured in hot air is generally in the range of 200C to 500C.

The composition of the present invention as described above is a silicone rubber molded product that does not emit an off-flavor during curing, does not cause foaming, has low surface tackiness after curing, and does not yellow.
Since it becomes a silicone rubber molded product with a small compression set,
It is extremely useful as an application requiring such properties, for example, as a material for extrusion molding of tubes, tapes, sheets, wire covering materials and the like.

[0013]

Next, the present invention will be described with reference to examples and comparative examples. In Examples, “parts” means “parts by weight”. In the examples, the compression set was measured according to the method defined in JIS K6301 Method for measuring physical properties of vulcanized rubber.

[0014]

EXAMPLE 1 100 parts of an organopolysiloxane rubber having a dimethylvinylsiloxy group at both ends and having 99.6 mol% of dimethylsiloxane units and 0.4 mol% of methylvinylsiloxane units (polymerization degree: 5,000), viscosity at 25 ° C. Is 60 centistokes, 9.0 parts of a dimethylsiloxane oligomer having silanol groups at both ends and a specific surface area of 2
45 parts of 00 m ² / g fumed silica was charged into a kneader mixer and kneaded under heating until uniform to obtain a silicone rubber-based compound. Then, based on 100 parts of the silicone rubber-based compound, 1.2 parts of a 50% by weight silicone oil paste of bis (ortho-methylbenzoyl) peroxide and 0.2% of a 40% by weight silicone oil paste of dicumyl peroxide were used.
Five parts were added on a two-roll mill and kneaded to produce a silicone rubber composition. About this silicone rubber composition,
A test piece for measuring compression set was prepared in accordance with the method specified in JIS K6301. The curing conditions of the silicone rubber composition were compression heating at 120 ° C. for 10 minutes, and further heating in hot air at 200 ° C. for 4 hours.
The compression set of this test piece after compression heating at 100 ° C. for 22 hours was 16%. This silicone rubber composition was introduced into a 65 mmφ single-screw extruder for forming a tube, extruded into a tube, and then passed through a heating furnace at 400 ° C. for 45 seconds. Inner diameter 10
A 2 mm thick silicone rubber tube was extruded. At this time, no off-flavor was generated. In order to measure the surface tackiness of this tube, the tube was wound into a coiled shape, heated at 200 ° C. for 4 hours, and then the contact portion of the tube was peeled off to leave a trace of the contact portion. It was observed whether it remained. As a result, no trace of the contact portion of the tube was observed, and no surface tackiness was observed.

[0015]

Example 2 Dicumyl peroxide was prepared in the same manner as in Example 1, except that the 50% by weight silicone oil paste of bis (ortho-methylbenzoyl) peroxide was replaced with a 50% by weight silicone oil paste of bis (para-methylbenzoyl) peroxide. Silicone rubber composition was prepared in the same manner as in Example 1 except that the 40% by weight silicone oil paste of Example 1 was replaced with a 50% by weight silicone oil paste of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane. Was manufactured. At this time, no off-flavor was generated. When the characteristics of this silicone rubber composition were measured in the same manner as in Example 1, the compression set was 14%.
Met. In addition, no trace of the contact portion of the tube was observed.

[0016]

Comparative Example 1 A silicone rubber composition was produced in the same manner as in Example 1 except that the silicone oil paste of 40% by weight of dimil peroxide was not added and blended. When the characteristics of this silicone rubber composition were measured in the same manner as in Example 1, the compression set was 27%.
Met. In addition, traces of the contact portion of the tube were observed, and surface tackiness was observed.

[0017]

Comparative Example 2 In Example 2, 2,5-dimethyl-2,2
50% by weight of 5-di (t-butylperoxy) hexane
A silicone rubber composition was produced in the same manner as in Example 2 except that the silicone oil paste was not added and blended. When the characteristics of this silicone rubber composition were measured in the same manner as in Example 1, the compression set was 24%.
In addition, traces of the contact portion of the tube were observed.

[0018]

[Table 1]

[0019]

The silicone rubber composition of the present invention comprises (A)
Component-component (D), in particular, because it contains a predetermined amount of methyl-substituted benzoyl peroxide of component (C) and a predetermined amount of dialkyl peroxide of component (D), it does not emit off-flavor during curing, It does not cause foaming, and after curing, has a characteristic that it can be a silicone rubber molded product having a low surface tackiness (surface tackiness) and a small compression set.

Continued on the front page (72) Inventor Takao Matsushita 2-2 Chikusa Beach, Ichihara-shi, Chiba Dow Corning Silicone Co., Ltd.

Claims (3)

[Claims] (A) an average compositional formula: R _a SiO _{(4-a) / 2} (wherein R is a substituted or unsubstituted monovalent hydrocarbon group, and a is 1.8 to 2.3) 100 parts by weight of an organopolysiloxane raw rubber having at least two silicon-bonded alkenyl groups in one molecule, (B) 10 to 100 parts by weight of finely divided silica, (C) A silicone rubber composition comprising 0.05 to 10 parts by weight of a methyl group-substituted benzoyl peroxide and 0.05 to 10 parts by weight of (D) a dialkyl peroxide. 2. The silicone rubber composition according to claim 1, which is a silicone rubber composition for extrusion molding. 3. The silicone rubber composition according to claim 1, which is introduced into an extruder to form an uncured molded product.
A method for molding silicone rubber, comprising curing the molded product in hot air under normal pressure to obtain a silicone rubber molded product.