JPH0482023B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a silicone rubber composition, and more specifically, a method for producing a silicone rubber composition that has high electrical insulation properties after curing even when wet silica is used as a filler. Regarding the method. [Prior Art and Problems to be Solved] Silicone rubber inherently has high electrical insulation properties, so it is particularly suitable for use in the electrical and electronic industries ^; Ω・cm
In many cases, extremely high electrical insulation properties such as above are required. Powdered silica is used as a reinforcing filler for this silicone rubber, and there are two types of silica, typified by dry silica and wet silica. Among these, when wet silica is used, it is cheaper than when dry silica (fumed silica) is used, but its volume resistivity is inferior, and it is difficult to obtain silicone rubber with high electrical insulation properties of 10 ¹⁵ Ω・cm or more. It was difficult. In particular, the volume resistivity after immersion in water is 10 ¹² ~
The resistance was 10 ¹³ Ω·cm, which was insufficient. Incidentally, attempts have been made in the past to improve the physical properties of silicone rubber by surface-treating the surface of finely divided silica to be blended with silicone rubber with an organosilicon compound such as organosilane, organosilazane, or organopolysiloxane to make it hydrophobic. for example,
Special Publication No. 33-9296, Publication No. 5991-1970,
JP 49-20739, JP 54-101795, JP 56-41263, JP 56-164008
Publications, etc. However, in both cases, the silica is treated and then blended into the silicone rubber composition, so equipment and processes for treating the silica are required, resulting in high costs. In view of the drawbacks of the prior art, the present invention uses wet silica, which is low in cost and has a low volume resistivity.
The object of the present invention is to provide a method for producing a silicone rubber composition having high electrical insulation properties of 10 ¹⁵ Ω·cm or more. [Means for solving the problem and their effects] The purpose is to (A) produce an organopolysiloxane having a viscosity of at least 100 centistokes at 25°C;
100 parts by weight (B) 5 to 200 parts by weight of wet silica and (C) 1 to 100 parts by weight of organosilane or organopolysiloxane having at least one hydrogen atom bonded to a silicon atom are mixed, and the mixture is heated under normal pressure or reduced pressure. This can be achieved by a method for producing a silicone rubber composition, which is characterized by heat treatment at a temperature of 80° C. or higher, followed by mixing a crosslinking agent. The organopolysiloxane (A) component used in the present invention serves as a base material for silicone rubber, and has an average unit formula of (In the formula, R is a monovalent hydrocarbon group, a is 1.95
~2.05) is a linear or slightly branched linear polymer. R includes unsubstituted monovalent hydrocarbon groups such as methyl group, ethyl group, propyl group, octyl group, vinyl group, allyl group, phenyl group, 2-cyanoethyl group, 3,3,3-trifluoropropyl group, etc. The substituted monovalent hydrocarbon group is exemplified. The reason why the viscosity is set to at least 100 centistokes at 25°C is because if it is less than 100 centistokes, the physical properties after curing become hard and brittle, and the upper limit is within the range of a gum-like state that can be produced. In view of workability and physical properties, the viscosity at 25° C. is preferably in the range of 1,000 to 1,000,000 centistokes. Organic peroxides are often used as the crosslinking agent for the silicone rubber composition of the present invention, but organohydrodiene polysiloxane is used as the crosslinking agent, and in the presence of a platinum-based compound as a catalyst,
In the case of crosslinking by addition reaction, it is necessary that at least two alkenyl groups exist in one molecule of component (A). The molecular chain terminal of component (A) is not particularly limited, and includes trimethylsilyl group, dimethylphenylsilyl group, dimethylvinylsilyl group,
It may be a triorganosilyl group such as a methylphenylvinylsilyl group, a silanol group, or an alkoxy group. Specific examples of component (A) include dimethylpolysiloxane, dimethylsiloxane/methylvinylsiloxane copolymer, dimethylsiloxane/methylphenylsiloxane copolymer, dimethylsiloxane/methylvinylsiloxane/methylphenylsiloxane copolymer, dimethyl Siloxane/diphenylsiloxane copolymer, dimethylsiloxane/methylvinylsiloxane/diphenylsiloxane copolymer, methyl(3,3,3-trifluoropropyl)siloxane/methylvinylsiloxane copolymer, dimethylsiloxane/methylphenyl A siloxane/methyl(3,3,3-trifluoropropyl)siloxane copolymer is shown, and these copolymers may be used singly or as a mixture of two or more types. The wet silica as component (B) used in the present invention provides reinforcing properties to silicone rubber when cured. In addition, although the volume resistivity of silicone rubber is poor when using component (B) alone, excellent volume resistivity can be given by heat treatment with component (C). As component (B), all conventionally known wet silicas can be used. One example of its production method is by reacting an alkali metal silicate such as sodium silicate with a mineral acid. If the amount of component (B) is too large or too small, the mechanical properties of the silicone rubber obtained by vulcanization will deteriorate. do. Preferably it is in the range of 10 to 100 parts by weight. Component (C) is a treatment agent for hydrophobizing component (B), and increases the volume resistivity after vulcanization of the silicone rubber composition of the present invention by heating both components. It is an important ingredient that can (C) component is the average unit formula (In the formula, R is a monovalent hydrocarbon group, and examples include a methyl group, an ethyl group, an octyl group, a vinyl group, a phenyl group, and a 3,3,3-trifluoropropyl group. b is 1≦b ≦4, c is 0≦c≦3,
However, b+c is 1≦b+c≦4. ) and is an organosilane or organopolysiloxane having at least one hydrogen atom bonded to a silicon atom in one molecule. The organopolysiloxane may be linear, cyclic, or partially branched linear, but is preferably linear or cyclic, and contains 5 mol% or more of hydrogen atoms bonded to silicon atoms. It is something to do. Examples of the molecular chain terminal include a trimethylsilyl group, a dimethylphenylsilyl group, a dimethylhydrodienesilyl group, and a methylphenylhydrodienesilyl group. Specific examples of component (C) include methylsilane, phenylsilane, dimethylsilane, methylphenylsilane, dimethylphenylsilane, trimethylsilane, methylhydrodiene polysiloxane, dimethylsiloxane/methylhydrodiene siloxane copolymer, methylphenyl Siloxane/methylhydrogensiloxane copolymer, tetramethyltetrahydrogencyclotetrasiloxane,
Examples include pentamethyltrihydrodienecyclotetrasiloxane and tri(dimethylhydrodienesiloxane)methylsilane. The blending amount of component (C) is 1 part by weight for 100 parts by weight of component (A).
It is used in the range of ~100 parts by weight, but from the processing efficiency of component (B), preferably the weight ratio with component (B) is in the range of component (C)/component (B) = 1/50 to 1.5. be. Component (C) is added when mixing components (A) and (B),
The surface of component (B) is treated by heating, and the temperature is 80℃ or higher under normal pressure or reduced pressure, but in order to shorten the heating time, the temperature is 100℃ or higher.
Above, it is desirable to heat preferably at 150°C or higher. Usually, the temperature is 150 to 250°C for 1 to 4 hours.
This heat treatment significantly improves the volume resistivity. In addition to the above-mentioned components (A) to (C), the present invention may optionally include dry silica, fine quartz powder, diatomaceous earth, zinc white, aluminum silicate, iron oxide, cerium oxide, cerium hydroxide, titanium, asbestos,
Glass fibers, pigments, antioxidants, etc. can be added. These additives may be added when mixing components (A) to (C), during heating, or after completion of heating components (A) to (C). However, the crosslinking agent and catalyst should preferably be removed after heating.
Add after the temperature is below 50℃. Particularly in the case of an addition reaction type in which an organohydrodiene polysiloxane is used as a crosslinking agent and a platinum compound is used as a catalyst, it is necessary to add the mixture after the temperature reaches around room temperature. Organic peroxides as crosslinking agents include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 2,5-bis(t-butylperoxy)-2,5-dimethylhexane, dicumyl peroxide, and monochlorobenzoyl peroxide. Examples include benzoyl peroxide and t-butyl perbenzoate, and the amount is usually 0.1 to 100 parts by weight of component (A).
It is used in a range of 5 parts by weight. The organohydrodiene polysiloxane used as a crosslinking agent may have a linear, cyclic, or branched structure, has at least two silicon-bonded hydrogen atoms in one molecule, and has a degree of polymerization of at least It is necessary to be 2. In order to achieve sufficient curing, the total number of alkenyl groups in one molecule of component (A) and the number of SiH groups in one molecule of organohydrodiene polysiloxane must be at least 5. Conditions are required. Usually, the molar ratio of SiH group to alkenyl group of component (A) is
It is in the range of 0.5:1 to 5:1. Note that the same organohydrodiene polysiloxane as the component (C) exemplified above can be used as the crosslinking agent.
The amount of organohydrodiene polysiloxane used is usually 0.5 to 10 parts by weight per 100 parts by weight of component (A). Addition reaction catalysts used with organohydrodiene polysiloxane include platinum black or platinum supported on a carrier, chloroplatinic acid, chloroplatinic acid dissolved in alcohols or ketones, tetrachloroplatinic acid, Examples include a complex of chloroplatinic acid and olefin, a complex of chloroplatinic acid and methylvinylsiloxane, a rhodium compound, a palladium compound, and cobalt carbonyl. The amount of addition reaction catalyst added is (A)
It is usually used in a range of 0.5 to 200 ppm in terms of platinum, and 1 to 2000 ppm in terms of metals other than platinum. Furthermore, small amounts of acetylene compounds, hydrazines, triazoles, phosphines, and mercaptans may be added as additives for suppressing addition reactions at room temperature. [Example] Next, the present invention will be explained by referring to an example. In Examples and Comparative Examples, parts are parts by weight, and viscosity is the value at 25°C. Examples 1 to 2 100 parts of organopolysiloxane raw rubber (degree of polymerization 3000) consisting of 99.8 mol% dimethylsiloxane units and 0.2 mol% methylvinylsiloxane units, and Nipseal LP manufactured by Nippon Silica Co. as wet silica.
After uniformly mixing 45 parts and 5 parts of methylhydrodiene polysiloxane with a viscosity of 10 centistokes,
The mixture was heated at 170° C. for 2 hours under a reduced pressure of 200 mmHg. After cooling this silicone rubber composition to near room temperature, 2.
0.3 part of 5-dimethyl-2,5-di(tert-butylperoxy)hexane was mixed and the mixture was pressure-molded at 170°C for 10 minutes. Molded silicone rubber sheet
In accordance with JIS-C2123, physical properties and volume resistivity in normal state and after immersion in water were measured. Also, in the above,
0.8 parts of 2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexane in place of
Regarding a sheet mixed with 4-dichlorobenzoyl peroxide and pressure-formed at 120°C for 10 minutes,
Physical properties and volume resistivity were measured in the same manner as above. As a comparative example, rubber sheets were prepared with the same composition and conditions as above, except that methylhydrodiene polysiloxane was removed from each of the above two compositions and no heat treatment was performed, and the physical properties and volume resistivity were measured. Further, although the composition itself was the same as in Example 1, a rubber sheet was prepared under the same conditions without heat treatment, and the physical properties were measured.
These results are shown in Table 1. The volume resistivity of all the samples added with methyl hydrodiene polysiloxane and heat treated was a good value of 10 ¹⁵ Ω·cm or more.

[Table] Examples 3 to 4 100 parts of the organopolysiloxane raw rubber used in Examples 1 to 2, 60 parts of Nipseal G300 manufactured by Nippon Silica Co. as wet silica, and 8 parts of methylhydrodiene polysiloxane with a viscosity of 10 centistokes.
After uniformly mixing them, they were heated at 170° C. for 2 hours under a reduced pressure of 200 mmHg. After cooling, a rubber sheet was produced using the organic peroxide used in Examples 1 and 2 under the same conditions, and its physical properties were measured. As comparative examples, rubber sheets were prepared according to Comparative Examples 1 and 2, and their physical properties were measured.
However, in Comparative Example 6, wet silica treated in advance under the same conditions was mixed into a silicone rubber composition. These results are shown in Table 2.

[Table] Example 5 100 parts of the organopolysiloxane raw rubber used in Examples 1 and 2 and Nipseal LP manufactured by Nippon Silica Co., Ltd.
After uniformly mixing 50 parts of pentamethyltripropyldihydrodienecyclopentasiloxane and 5 parts of pentamethyltripropyldihydrodienecyclopentasiloxane, the mixture was heated at 180°C for 3 hours. then more
The mixture was heated at 180° C. for 1 hour under a reduced pressure of 200 mmHg. After cooling this composition, 2,5-dimethyl-2,5-
Di(tertiarybutylperoxy)hexane 0.3
A rubber sheet was prepared by mixing the two parts and heating and molding the mixture at 170°C for 10 minutes, and the physical properties of the rubber sheet were measured. As a comparative example, a rubber sheet was prepared from the above composition without pentamethyltripropyldihydrodienecyclopentasiloxane and without heat treatment, and its physical properties were measured. These results are shown in Table 3.

[Table] Example 6 100 parts of dimethylpolysiloxane with a viscosity of 12,000 centistokes having dimethylvinylsilyl groups at both ends of the molecular chain, Nipseal manufactured by Nippon Silica Co., Ltd.
30 parts of G300, and formula 5 parts of the organohydrodiene polysiloxane shown below were heat treated at 170° C. for 2 hours, and then heated at 200 mmHg for 1 hour to remove excess organohydrodiene polysiloxane. After cooling this composition to room temperature, 3 parts of the above organohydrodiene polysiloxane and 2-chloroplatinic acid were added.
Add and mix ethylhexanol solution to the dimethylpolysiloxane base material at a concentration of 5 ppm.
The volume resistivity of a rubber sheet prepared by pressure molding at 120° C. for 10 minutes was measured and found to be 5×10 ¹⁵ Ω·cm under normal conditions and 4×10 ¹⁵ Ω·cm when immersed in water. As a comparative example, the organohydrodiene polysiloxane that was not heat-treated had a normal temperature of 3.
×10 ¹⁴ Ω・cm, and 8 × 10 ¹² Ω・cm due to flooding. Example 7 A rubber sheet was produced in the same manner as in Example 1, except that 4 parts of dimethylphenylsilane was added instead of the methylhydrodiene polysiloxane treatment agent, and its volume resistivity was measured. As a result, the resistance was 4×10 ¹⁵ Ω・cm under normal conditions, and 3× when submerged in water.
It was 10 ¹⁵ Ω・cm. [Effect of the invention] The method for producing a silicone rubber composition of the present invention includes:
Cheap wet silica is heat-treated with an organosilane or organopolysiloxane having a hydrogen atom bonded to a silicon atom to form hydrophobic silica, which is carried out during kneading of a silicone rubber composition. Therefore, compared to the case of mixing with a conventional silicone rubber composition that has been previously hydrophobized, there is no need for equipment or equipment for hydrophobization, and the process can be simplified, resulting in a significant reduction in manufacturing costs. Furthermore, since the wet silica is substantially hydrophobic, the electrical properties (volume resistivity) of the silicone rubber can be significantly improved. In this way, it is possible to supply inexpensive and high-performance silicone rubber to the electrical, electronic, communication fields, etc., which is extremely beneficial from an industrial and economical point of view.

Claims (1)

[Claims] 1(A) An organopolysiloxane having a viscosity of at least 100 centistokes at 25°C.
100 parts by weight (B) 5 to 200 parts by weight of wet silica and (C) 1 to 100 parts by weight of organosilane or organopolysiloxane having at least one hydrogen atom bonded to a silicon atom are mixed, and the mixture is heated under normal pressure or reduced pressure. 1. A method for producing a silicone rubber composition, which comprises heating at a temperature of 80° C. or higher, followed by mixing a crosslinking agent.