JP3464584B2 - Silicone rubber composition and silicone rubber molding method - Google Patents

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 an electric wire coating material, and a method for molding the silicone rubber.

[0002]

2. Description of the Related Art Silicone rubber is widely used as an extrusion molding material for tubes, tapes, sheets, wire coating materials and the like because it is excellent in heat resistance, cold resistance, weather resistance and electric characteristics. In order to cure the silicone rubber composition (silicone rubber composition for extrusion molding) that has been conventionally used as such an extrusion molding material, 2,4
-Dichlorobenzoyl peroxide was used. However, the silicone rubber composition containing this organoperoxide gives off an offensive odor during curing, and after curing,
It has a defect that tackiness is generated on the surface of the molded product, and has a defect that blooming occurs on the surface of the silicone rubber molded product. Blooming is a phenomenon in which the decomposition product of the curing agent gradually stains and the surface of the molded product becomes white. To solve these problems, many studies have been made to date. For example, JP-A-54
JP-A-48870 proposes a method for obtaining a silicone rubber having less stickiness on the surface of a molded article by using bis (2,4-dichlorobenzoyl) peroxide and ditert-butyl peroxide as curing agents. But,
Even when this method is used, an unpleasant odor is generated during curing and stickiness on the surface of the molded article cannot be completely prevented, which is not always satisfactory. On the other hand, JP-A-59-18758 proposes a method of using bis (orthomethylbenzoyl) peroxide as a curing agent for a silicone rubber composition. According to this method, it is said that the above-mentioned offensive odor does not occur and blooming does not occur. Further, Japanese Patent Laid-Open No. 62-185750 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 occur. The points are said to be resolved. However, the silicone rubber composition obtained by the former method has a drawback that the silicone rubber molded product becomes yellowish (yellowing) after heat curing. Further, the silicone rubber composition obtained by the latter method has a problem that the curing speed is slow and foaming during curing tends to generate fine bubbles (voids).

[0003]

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have solved the above problems by using a specific organic peroxide in combination as a curing agent for a silicone rubber composition. Therefore, the present invention has been completed. That is, the object of the present invention is to form a silicone rubber composition which does not give off a strange odor upon curing, does not cause foaming, has less stickiness on the surface after curing, and can be a yellowed silicone rubber molded product, and molding of a silicone rubber. To provide a method.

[0004]

Means for Solving the Problems The above-mentioned object is (A) average composition formula R _a SiO _{(4-a) / 2} (wherein R is a substituted or unsubstituted monovalent hydrocarbon group, and a is 1.9). To 100 parts by weight, (B) fine powder silica 10 to 100 parts by weight, (C) bis (orthomethylbenzoyl) peroxide 0.1 to 5 Parts by weight, (D) bis (para-methylbenzoyl) peroxide 0.1 to 5 parts by weight, and the ratio of the component (C) to the component (D) is (1:
9) to (8: 2), the silicone rubber composition, and the above silicone rubber composition are introduced into an extrusion molding machine to form an uncured molded article, and then the molded article is cured in hot air under normal pressure. Accordingly, the present invention relates to a method for molding a silicone rubber, which is a silicone rubber molded article.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The organopolysiloxane raw rubber of the component (A) used in the composition of the present invention is the main component of the composition of the present invention and is represented by the average composition formula R _a SiO _{(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 or an allyl group. Group, alkenyl group such as butynyl group and hexenyl group, aryl group such as phenyl group and tolyl group, 3,3,3
-Trifluoropropyl group, 2-phenylethyl group, 2
1 exemplified by a substituted hydrocarbon group such as -cyanoethyl group
Examples include valent hydrocarbons. Also, a is a number of 1.9 to 2.1. The molecular structure of this component is preferably substantially linear, but may be partially branched. The degree of polymerization of this component may be within the range called organopolysiloxane raw rubber in the art, and is usually 25 ° C.
The viscosity is 10 ⁷ centistokes or more and the average molecular weight of 25 × 10 ⁴ or more is used.

The fine powdery silica as the component (B) used in the composition of the present invention is essential for imparting excellent mechanical strength to the silicone rubber molded product obtained by vulcanizing the composition of the present invention. It is a component. Examples of such finely divided silica include dry process silica such as fumed silica and wet process silica such as precipitated silica.
It is also possible to use fine powdery silica that has been hydrophobized with an organosilicon compound such as organochlorosilane, hexaorganodisilazane, and diorganocyclopolysiloxane. This component has a particle size of 50 μm or less and a specific surface area of 5
It is preferably 0 m ² / g or more, and further 100 m ²
/ G or more is more preferable. The amount of this ingredient is
The amount is in the range of 10 to 100 parts by weight with respect to 100 parts by weight of the component (A). This is because if it is less than 10 parts by weight, the mechanical strength of the composition of the present invention after curing will be insufficient, and if it exceeds 100 parts by weight, it will be difficult to mix it with the component (A).

The component (C) bis (orthomethylbenzoyl) peroxide and the component (D) bis (para-methylbenzoyl) peroxide used in the composition of the present invention are curing agents for curing the composition of the present invention. Is. Then, the mixing ratio of the component (C) and the component (D) is (1 :) by weight.
9) to (8: 2) are required. When the compounding ratio of the bis (ortho-methylbenzoyl) peroxide as the component (C) becomes smaller and becomes smaller than (1: 9), the curing speed becomes slow and a foaming phenomenon occurs, causing bubbles inside the silicone rubber molded product. Like Further, when the compounding ratio of bis (orthomethylbenzoyl) peroxide becomes large and becomes larger than (2: 8), that is, when the compounding ratio of bis (para-methylbenzoyl) peroxide becomes smaller, it is introduced into the silicone rubber compound. After kneading, it tends to cause yellowing due to aging,
In addition, tackiness will occur on the surface of the cured silicone rubber molded product. The blending amounts of these two types of organoperoxides are each within the range of 0.1 to 5 parts by weight. This is because if the amount is less than 0.1 part by weight, the strength of the silicone rubber molded product will decrease, and if it exceeds 5 parts by weight, the silicone rubber molded product will become too hard.

The composition of the present invention comprises the above-mentioned components (A) to (D).
Although it is a silicone rubber composition consisting of components, it is an object of the present invention to add various additives which are conventionally known to be blended to a silicone rubber composition in addition to these components. It doesn't matter as long as it doesn't hurt.
Examples of such additives include diorganosiloxane oligomers capped with silanol groups at both ends, crepe hardening inhibitors such as organohydroxysilane and hexaorganodisilazane, diatomaceous earth, quartz powder, calcium carbonate, inorganic fillers such as carbon black, Examples include heat-resistant agents such as cerium hydroxide, cerium silanolate, and cerium fatty acid salts, and mold release agents such as stearic acid, zinc stearate, calcium stearate, and other fatty acids, and metal salts thereof.

The composition of the present invention can be easily prepared by uniformly mixing the above-mentioned components (A) to (D).
After the components (A) and (B) are uniformly heated and kneaded by a kneader such as a kneader mixer, the components (C) and (D) may be added and blended using a kneading means such as a two-roll mill. preferable.

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 atmospheric pressure to obtain a silicone rubber molded product. Here, as the extrusion molding machine, a conventionally known extrusion molding machine used for extrusion molding of a silicone rubber composition can be used. The temperature for curing the silicone rubber composition in hot air is generally within the range of 200 ° C to 500 ° C.

The above-mentioned composition of the present invention does not give off a bad odor upon curing, does not cause foaming, and has little stickiness on the surface after curing, resulting in a silicone rubber molded product which does not yellow, so that such characteristics are obtained. Is extremely useful as a material for extrusion molding such as tubes, sheets, and electric wire coating materials.

[0012]

EXAMPLES Next, the present invention will be described with reference to Examples and Comparative Examples. In the examples, "parts" means "parts by weight", and o-M
eBPO means bis (orthomethylbenzoyl)
The term "p-MeBPO" means bis (para-methylbenzoyl) peroxide.

[0013]

Example 1 100 parts of a diorganopolysiloxane raw rubber having a dimethylvinylsiloxy group blocked at both ends and composed of 99.6 mol% of dimethylsiloxane units and 0.4 mol% of methylvinylsiloxane units (polymerization degree of 5,000) at 25 ° C. 9.0 parts of a dimethylsiloxane oligomer capped with silanol groups at both ends and having a viscosity of 60 centistokes, and 40 parts of dry process silica having a specific surface area of 200 m ² / g are charged into a kneader mixer and homogenized at 175 ° C. for 60 minutes under reduced pressure. The mixture was kneaded until a silicone rubber base compound was obtained. Then, to 100 parts of this base compound, bis (orthomethylbenzoyl) peroxide and bis (para-methylbenzoyl) peroxide were added in amounts shown in Table 1 on a two-roll mill and kneaded to produce a silicone rubber composition. did. The obtained silicone rubber composition immediately after kneading was introduced into a 65 mmφ uniaxial extruder for tube molding, and extruded into a tube shape from a die having an inner diameter of 10 mm and an outer diameter of 16 mm. Then, the obtained tubular product was introduced into a hot air vulcanizing furnace set at a temperature of 350 ° C., and passed through for 1 minute to mold a silicone rubber tube. The silicone rubber composition immediately after kneading obtained above was allowed to stand for 3 days at room temperature (20 ° C.),
A silicone rubber tube was molded from the silicone rubber composition 3 days after the kneading in the same manner as above. The degree of stickiness, the degree of yellowing, and the occurrence of bubbles on the surface of the obtained silicone rubber tube were measured. The degree of stickiness on the surface was touched with a finger, and the degree of yellowing was visually observed. The degree of bubble generation was measured by cutting the silicone rubber tube and observing the cut surface with a microscope. The results of these measurements are shown in Table 1.

[0014]

[Table 1]

[0015]

Example 2 Dimethylsiloxane unit 99.84 mol%
And 0.16 mol% of methyl vinyl siloxane unit at both ends dimethyl vinyl siloxy group-blocked diorganopolysiloxane raw rubber (polymerization degree 5,000) 100 parts, diphenylsilane diol 3.0 parts, viscosity at 25 ° C is 6
3.0 parts of 0 centistokes silanol group-blocked methylphenylsiloxane oligomer, 3.0 parts, specific surface area: 200
40 parts of m ² / g dry process silica was put into a kneader mixer and kneaded under reduced pressure at 160 ° C. for 90 minutes until uniform, and then 5 parts of diatomaceous earth and 10 parts of quartz powder were added and mixed. A silicone rubber base compound was prepared by kneading. To 100 parts of this base compound, the amounts of bis (orthomethylbenzoyl) peroxide and bis (para-methylbenzoyl) peroxide shown in Table 2 were added on a two-roll mill and kneaded to produce a silicone rubber composition. This silicone rubber composition immediately after kneading was introduced into a 65 mmφ single-screw extruder for coating electric wires, and a tin-plated annealed copper wire with an outer diameter of 1.0 φmm (0.18 mm / 20 twisted wire) had a thickness of 0.5 mm. The silicone rubber composition was coated so that This silicone rubber composition-coated electric wire
It was introduced into a hot-air heating furnace at 0 ° C. and heat-treated for 12 seconds to be cured to obtain a silicone rubber-coated electric wire. The silicone rubber composition immediately after kneading obtained as described above was allowed to stand for 3 days at room temperature (20 ° C.), and 3 days later, a silicone rubber-coated electric wire was prepared in the same manner as above from the silicone rubber composition. Molded. The degree of stickiness, the degree of yellowing, and the presence / absence of bubbles on the surface of the obtained silicone rubber-coated electric wire were measured. The degree of stickiness on the surface was touched with a finger, and the degree of yellowing was visually observed. The degree of bubble generation was measured by cutting the silicone rubber-coated electric wire and observing the cut surface with a microscope. The results of these measurements are shown in Table 1. Further, in order to determine how much the curing speed of these silicone rubber compositions is, the maximum linear velocity [m / min] capable of coating the silicone rubber was measured. Here, the maximum linear velocity that can be coated with silicone rubber means that an electric wire coated with an uncured silicone rubber composition is passed through a heating furnace at different speeds, and the uncured silicone rubber composition is cured to become a cured silicone rubber. Is the linear velocity at that time. The results are shown in Table 2.

[0016]

[Table 2]

[0017]

The silicone rubber composition of the present invention comprises the above-mentioned components (A) to (D), and in particular, component (C) bis (orthomethylbenzoyl) peroxide and (D).
Since the component bis (para-methylbenzoyl) peroxide is contained in an amount such that the weight ratio thereof is (1: 9) to (8: 2), it does not give off a strange odor upon curing and causes foaming. It has the characteristics that it does not occur and has little stickiness on the surface after curing and can be a silicone rubber molded product that does not cause yellowing. The method for molding silicone rubber is characterized in that a silicone rubber molded product can be efficiently produced from the silicone rubber composition comprising the above components (A) to (D).

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takao Matsushita 2-2 Chikusaigan, Ichihara-shi, Chiba Toray Dow Corning Silicone Co., Ltd. Research and Development Division (56) Reference JP-A-4-304235 (JP , A) European Patent Application Publication 839860 (EP, A 1) (58) Fields searched (Int.Cl. ⁷ , DB name) C08L 83/00-83/16 C08K 3/00-13/08 CAPLUS (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] 1. (A) Average composition formula _Ra SiO _{(4-a) / 2} (wherein R is a substituted or unsubstituted monovalent hydrocarbon group, and a is 1.9 to 2.1). 100 parts by weight of organopolysiloxane raw rubber represented by the formula (B), 10 to 100 parts by weight of finely divided silica (B), 0.1 to 5 parts by weight of (C) bis (orthomethylbenzoyl) peroxide, (D) ) Bis (para-methylbenzoyl) peroxide 0.1 to 5 parts by weight, wherein the ratio of the component (C) and the component (D) is (1:
9) to (8: 2), which is a silicone rubber composition. 2. The silicone rubber composition according to claim 1, which is a silicone rubber composition for extrusion molding. 3. A silicone rubber molded product is obtained by introducing the silicone rubber composition according to claim 1 into an extruder to form an uncured molded product, and then curing the molded product in hot air under normal pressure. A method for molding silicone rubber, comprising: