JP3121772B2 - Method for producing thermosetting silicone rubber 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 thermosetting silicone rubber composition and a method for producing the same, and a cured product thereof. The present invention relates to a thermosetting silicone rubber composition capable of obtaining a silicone rubber excellent in storage stability due to little reversion and excellent in compression set and heat resistance, a method for producing the same, and a cured product thereof.

[0002]

Technical background of the invention and its problems Silicone rubber is
Due to its excellent weather resistance, heat resistance, cold resistance, electrical properties, etc., it is used in a large number of applications such as building gaskets, keypads, various rolls such as developing rolls and transfer rolls, electric wires, hoses and packings for automobiles, etc. Although used, in recent years there has been a demand for the development of silicone rubbers that are more excellent than ever. The silicone rubber compositions used in these compositions are generally obtained by blending a high-polymerization degree polyorganosiloxane with reinforcing fine powder silica and, if necessary, adding various property improvers. These silicone rubber compositions in which reinforcing silica powder is blended have properties that change with time due to poor compatibility between the high polymerization degree polyorganosiloxane and the reinforcing silica powder, and further, replasticization occurs. It is known. As a method of preventing these, organosilane, organochlorosilane, organosiloxane, or reinforcing fine powder silica which has been surface-treated in advance with an organosilicon compound such as organosilazane is compounded, or as described above during compounding and kneading. A method of performing a surface treatment with an organosilicon compound has been used.
According to this method, it is usually possible to increase the amount of the processing agent to be added, and to suppress the property change and plasticization return with time as the treatment degree is increased, but as the treatment degree is increased, the silicone rubber composition becomes Since the plasticity is reduced and stickiness is caused, the roll workability and moldability are extremely deteriorated, and there is a disadvantage that productivity of the silicone rubber is remarkably reduced. Particularly, in extrusion molding, it is difficult to mold due to reduced shape retention. As another method, JP-A-59-176325 and JP-A-59-176326 disclose mixing a low-viscosity hydroxyl-terminated polydiorganosiloxane with a filler and adding an alkaline catalyst such as sulfuric acid. A method has been proposed in which a low-viscosity hydroxyl-terminated polydiorganosiloxane is subjected to polycondensation to increase the molecular weight by a polycondensation method. And a polymerization step, and furthermore, it takes a very long time to sufficiently disperse the filler in order to mix the filler with the low-viscosity hydroxyl-terminated polydiorganosiloxane. Production energy is required. In addition, it is difficult to control the polymerization due to the influence of moisture and fillers, it is difficult to stably produce the silicone rubber composition produced therefor, and furthermore, the amount of generated low molecular siloxane is large. Low molecular siloxane is considered to cause wall contamination in building gasket materials, offset phenomenon in rolls for copiers, poor contact in keypads, etc., and a reduction in the amount of low molecular siloxane in silicone rubber compositions in each application. Is strongly required. Further, when a catalyst such as sulfuric acid which is decomposed by heat and cannot be eliminated from the system is used, there is a disadvantage that the heat resistance of the silicone rubber is deteriorated. In addition, acidic fillers such as fumed silica and precipitated silica, which are the most important fillers that have a reinforcing effect on silicone rubber, exhibit a polymerization inhibitory effect, and therefore, the amount thereof is 100 parts by weight of a low-viscosity hydroxyl-terminated polydiorganosiloxane. Parts are limited within the range of 1 to 40 parts by weight. For this reason, the characteristics of the obtained silicone rubber composition must be restricted. On the other hand, there is a need for the development of silicone rubber with better characteristics than ever before in various applications such as building gaskets, developing rolls and transfer rolls, as well as sealing materials and packing materials. As is well known.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve such problems. That is, the present invention relates to a thermosetting silicone rubber composition and a method for producing the same, and a cured product thereof, and more specifically, has good workability and moldability,
A thermosetting silicone rubber composition capable of easily obtaining a silicone rubber excellent in storage stability due to little change in properties over time and plasticization return over time, and a silicone rubber excellent in compression set, a method for producing the same, and a thermosetting silicone rubber composition. Related to cured product.

[0004]

The inventors of the present invention have conducted intensive studies to achieve the above object. As a result, the polyorganosiloxane serving as a base polymer was replaced with a polyorganosiloxane having a terminal blocked with a hydroxyl group or an alkoxy group and a specific thermal decomposition. It is possible to produce a thermosetting silicone rubber composition obtained by a specific method by combining with a hydrophilic catalyst in a short time.
It has good workability and moldability, and has excellent storage stability due to little change in properties and reversion to plasticity over time, and it is easy to obtain silicone rubber with excellent compression set and heat resistance. And completed the present invention. That is, the present invention provides: (A) an average unit formula: R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group,
a represents a number in the range of 1.98 to 2.02) 100 parts by weight of polyorganosiloxane having an average degree of polymerization of 4000 to 20000 (B) Average unit formula: R ¹ _b SiO _{(4-b) / 2} (wherein R ¹ is a substituted or unsubstituted monovalent hydrocarbon group,
b represents a number in the range of 1.98 to 2.02), the terminal is blocked with a hydroxyl group or an alkoxy group, and the degree of polymerization is 6 to 70.
0 to 20 parts by weight of polyorganosiloxane (C) 5 to 200 parts by weight of finely powdered fumed silica (D) Average unit formula: M ¹ O (R ² _c SiO) _z M ² (where M ¹ is A tetraalkylammonium group , M ²
Is the same or hydrogen as M ¹ , R ² is a substituted or unsubstituted monovalent hydrocarbon group, c is a number in the range of 1.98 to 2.02, and z is a number of 1 to 1000) Thermal decomposition catalyst
0.01-5 parts by weight at a temperature lower than the decomposition temperature of component (D)
The components (A) to (D) are mixed together or the components (D)
After mixing the components (A) to (C) at a temperature lower than the decomposition temperature,
After adding component (D), heat to above the decomposition temperature of component (D)
Of a thermosetting silicone rubber composition characterized by
It is a manufacturing method .

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The average unit formula of the component (A) used in the present invention: R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group,
a represents a number in the range of 1.98 to 2.02), which is a base polymer of the curable silicone composition and is mainly used as a linear polymer. A branched or three-dimensional structure may be formed, and a homopolymer, a copolymer, or a mixture thereof may be used. The substituted or unsubstituted monovalent hydrocarbon group bonded to the silicon atom of the polyorganosiloxane includes, for example, an alkyl group such as a methyl group, an ethyl group and a propyl group; a vinyl group, an allyl group and a butadienyl group. An alkenyl group; an aryl group such as a phenyl group, a xenyl group, and a naphthyl group; a cycloalkyl group such as a cyclohexyl group; a cycloarenyl group such as a cyclohexenyl group; an aralkyl group such as a benzyl group; Alkylaryl group and the like. As the monovalent hydrocarbon group bonded to these silicon atoms, a methyl group is mainly used. For example, in the case of a vinyl group, 0 to 5 relative to the total number of organic groups from the viewpoint of mechanical strength and crosslinkability. %, And particularly preferably in the range of 0.05 to 3%. In addition, as a molecular chain terminal of the polyorganosiloxane, a hydroxyl group, an alkoxy group or a triorganosilyl group is exemplified, and a triorganosilyl group is more preferable. Examples of the triorganosilyl group include a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group, and a methyldiphenylsilyl group. The average polymerization degree of the component (A) is in the range of 4000 to 20000, preferably 6000 to 1000.
0. If the degree of polymerization is too small, it is difficult to obtain a sufficient mechanical strength, while if it is too large, it is difficult to mix the compound into the system.

The component (B) used in the present invention has an average unit formula: R ¹ _b SiO _{(4-b) / 2} (where R ¹ is a substituted or unsubstituted monovalent hydrocarbon group,
b represents a number in the range of 1.98 to 2.02), the terminal is blocked with a hydroxyl group or an alkoxy group, and the degree of polymerization is 6 to 70.
0, preferably 10 to 300, more preferably 15 to 200, a polyorganosiloxane which is mainly used in the form of a straight chain, but may have a partially branched or three-dimensional structure. Good. The substituted or unsubstituted monovalent hydrocarbon group used in the polyorganosiloxane includes
For example, alkyl groups such as methyl group, ethyl group and propyl group; alkenyl groups such as vinyl group, allyl group and butadienyl group; aryl groups such as phenyl group, xenyl group and naphthyl group; cycloalkyl groups such as cyclohexyl group A cycloarenyl group such as a cyclohexenyl group; an aralkyl group such as a benzyl group; an alkylaryl group such as a tolyl group or a xylyl group.
In consideration of the compatibility with the polyorganosiloxane of the component (A) serving as the base polymer, a group similar to the monovalent hydrocarbon group used in the component (A) is preferable. Further, the terminal of the molecular chain of the polyorganosiloxane is either a hydroxyl group or an alkoxy group. When the molecular weight of the component (B) is too high, the effect as a treating agent is reduced, and when the molecular weight is too low, the roll workability of the obtained compound is deteriorated, so that the degree of polymerization is 6 to 700, preferably 10 to 700. 300, more preferably in the range of 15 to 200. If the compounding amount of the component (B) is too large, the obtained compound becomes sticky,
If the amount is too small, the essential effects of shortening the kneading time and suppressing the change with time cannot be obtained. Therefore, it is used in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the component (A).

[0007] The finely powdered fumed silica as the component (C) may be a known one generally blended in silicone rubber or the like. The preferred particle size of these fumed silicas is 20μ.
m or less. These fumed silicas may not be surface-treated, or may be surface-treated with organosilane, organochlorosilane, organosiloxane, organosilazane, or the like. Wet silica is not preferred because it has a high water content and lowers the catalytic action of component (D). If the compounding amount of the component (C) is too large, the mechanical properties of the silicone rubber obtained by vulcanization decrease, and if too small, the mechanical properties decrease.
It is used in the range of 5 to 200 parts by weight per 100 parts by weight.

The component (D) used in the present invention is represented by an average unit formula: M ¹ O (R ² _c SiO) _z M ² (where M ¹ is a tetraalkylammonium group and M ²
Is the same or hydrogen as M ¹ , R ² is a substituted or unsubstituted monovalent hydrocarbon group, c is a number in the range of 1.98 to 2.02, and z is a number of 1 to 1000) Thermal decomposition catalyst. As the component (D), those having a degree of polymerization z in the range of 1 to 1000 are used, and preferably 5 to 100. If the degree of polymerization z exceeds 1000, the viscosity becomes high, handling becomes difficult, and workability decreases. The component (D) is obtained by reacting a tetraalkyl ammonium hydroxide wherein de polyorganosiloxane in a known manner. Here, it is conceivable that these hydroxides are used for the present purpose, but they are usually present as an aqueous solution of 50% by weight or less, so that the dispersibility in the silicone rubber compound becomes very poor, The desired shortening of the kneading time is not achieved, and even if dispersed, the water containing the catalyst which reduces the catalytic action is contained in the composition, so that control of the reaction is difficult, and the cohesion of the silicone rubber compound is lost. In some cases, it is difficult to obtain stable characteristics due to the fact that the device may fall apart and become unmanufacturable. In addition, an aqueous solution exceeding 50% by weight cannot be prepared, and in this case, it becomes solid, and it is very difficult to disperse this too. On the other hand, the component (D) of the present invention has a very good dispersibility in a silicone rubber compound, and since it does not contain water, the control of the reaction is easy and the silicone rubber composition of the present invention can be easily obtained in a short time. It becomes possible. In the present invention,
Stability of the surface or these catalysts, tetraalkylammonium silanolate is used. The component (D) is obtained by condensation polymerization of a hydroxyl group or an alkoxy group of the component (B) and a hydroxyl group on the component (C), and at the same time as performing a filler treatment, also condensation polymerization of the components (B). It is considered that a slight amount of water contained in the component (C) also promotes some equilibration of the silicone rubber composition at the same time. As a result, the residual hydroxyl groups and alkoxy groups in the silicone rubber composition are extremely small, and the components (A) and (C) are very well compatible with each other. It is possible to obtain a silicone rubber which is excellent in storage stability with little property change and plasticization return, and further excellent in compression set and heat resistance. The amount of the component (D) is preferably 0.01 to 5 parts by weight based on 100 parts by weight of the component (A). If the amount is less than 0.01 part by weight, the reaction does not proceed sufficiently. Odor is a problem. The decomposition temperature of the component (D) is not particularly limited, but is preferably 70 ° C. or higher from the viewpoint of stability, and is preferably 130 ° C. or lower from the viewpoint of reaction temperature.

The thermosetting silicone rubber composition of the present invention comprises (A) a high molecular weight polyorganosiloxane, (B) a low-viscosity polyorganosiloxane having a terminal blocked with a hydroxyl group or an alkoxy group, and (C) fumed silica. Can be obtained by simply adding (D) the thermally decomposable catalyst described above to the silicone rubber composition containing Therefore, JP-A-59-17
No need for dehydration step, polymerization step or long-time filler dispersion step at the time of production as shown in No. 6326, it is possible to produce by the well-known silicone rubber production method and obtain The silicone rubber composition is low in the amount of low molecular siloxane produced, and can incorporate a large amount of fumed silica, so that various silicone rubber compositions can be designed. Further, a reinforcing fine powder silica which has been surface-treated in advance with an organosilicon compound such as an organosilane, an organochlorosilane, an organosiloxane, or an organosilazane is blended, or the surface is treated with the above-described organosilicon compound during blending and kneading. Compared with the method, the aging time is greatly shortened, the plasticity of the silicone rubber composition is not reduced, and there is no stickiness, and the roll workability and moldability are good.

Next, in producing the present composition, (A)
~ (D) components may be mixed together, or (A) ~ (C)
After mixing the components, the component (D) may be added. However, the component (D) needs to be added at a temperature lower than its decomposition temperature, and after the addition, it needs to be higher than the decomposition temperature. However, the production process shown here is only a process for producing a normal silicone rubber composition with the addition of the component (D),
Those skilled in the art can easily manufacture without introducing a manufacturing apparatus or performing a process such as decompression and dehydration.

Further, the silicone rubber composition of the present invention becomes a rubbery elastic body by blending and curing a curing agent. The curing agent cures the composition consisting essentially of the components (A) to (D) to form a rubber-like elastic body. Examples of the curing method include a curing method using an organic peroxide and a curing method using an addition type crosslinking agent and a catalyst. As a curing agent using an organic peroxide, conventionally known benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-tert-butyl peroxide,
Examples thereof include dicumyl peroxide and 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane. These are 0.1 to 5 parts by weight per 100 parts by weight of the component (A).
Used in parts by weight. Further, as a curing agent by the addition-type reaction, a polyorganosiloxane having a hydrogen atom bonded to an average of two or more silicon atoms in one molecule is used as a crosslinking agent, and a platinum-based catalyst is used as a curable catalyst. . The compounding amount of the above polyorganosiloxane having a hydrogen atom is such that one alkenyl group bonded to a silicon atom in the polyorganosiloxane in the component (A) and the component (C) is 0.5 hydrogen atom bonded to a silicon molecule. The amount of the platinum-based catalyst is generally about 1 to 1000 ppm based on the total amount of the component (A) and the component (C). The silicone rubber thus obtained has very few residual hydroxyl groups and alkoxy groups, and has very good compatibility with each component, so that it is very excellent in compression set and heat resistance.

The silicone rubber composition used in 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. Furthermore, it is also possible to mix carbon ferrite powder and the like and to mold by high frequency dielectric heating.

[0013]

Industrial Applicability The silicone rubber composition obtained by the present invention has good workability and moldability, and has excellent storage stability due to little change in properties over time and reversion to plasticization. Silicone rubber with excellent heat resistance and heat resistance can be easily obtained.
The present composition can be produced in a short time without going through steps such as decompression and dehydration.

[0014]

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to the following examples. Also,
Parts in the examples represent parts by weight. Example 1 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ = CH) SiO units
100 parts of a polyorganosiloxane having a polymerization degree of 6000 and comprising 12 mol% and capped with a dimethylvinylsilyl group and 5 parts of a polydiorganosiloxane capped with a silanol group and having a degree of polymerization of 60; Silica (AE
ROSIL 130) 45 parts are kneaded with a kneader mixer until uniform, and tetramethylammonium silanolate (z = 2
0) 0.3 part was added and kneaded. The temperature at this time is 60 ° C
Met. Thereafter, heat treatment was performed at 130 ° C. for 1 hour to obtain a silicone rubber composition. The resulting silicone rubber composition had a plasticity of 270 and was not sticky. When low molecular siloxanes (D3 to D20) of this composition were measured, 832
It was 0 ppm. To this composition, 0.2 part of 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition.
At this time, the roll workability was evaluated and was very good. Next, this composition was heated at a temperature of 170 ° C. and a pressure of 100 kgf / c.
m ² , primary vulcanization by press for 10 minutes, air circulation dryer
Perform secondary vulcanization at 200 ° C x 4 hours, 200mm x 200mm x 2m
An m-size sheet and a test piece for compression set were prepared. Using this, hardness and compression set according to JIS C 2123 were measured. The hardness was 50 and the compression set (25% compression) at 180 ° C. for 22 hours was 5%. Also, 23
When an air heat aging test was performed at 0 ° C. for 14 days, the hardness was 52, and there was no significant change. In addition, the composition may be
After leaving it for two weeks at the condition of 90% and a temperature of 60 ° C., it was put into a 6-inch double roll, and the state of plasticization return was observed. . No plasticization return, immediately wrapped around two rolls,
The roll workability was also good. The plasticity was 268, the hardness was 50, the compression set was 5%, and no property change was observed.

Example 2 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ = CH) SiO units
100 parts of a polyorganosiloxane having a polymerization degree of 6000 and comprising 12 mol% and capped with a dimethylvinylsilyl group and 5 parts of a polydiorganosiloxane capped with a silanol group and having a degree of polymerization of 60; Silica (AE
ROSIL 130) 45 parts are kneaded with a kneader mixer until uniform, and tetrabutylphosphonium silanolate (z =
10) 0.5 part was added and kneaded. The temperature at this time is 70 ° C
Met. Thereafter, heat treatment was performed at 150 ° C. for 1 hour to obtain a silicone rubber composition. The resulting silicone rubber composition had a plasticity of 274 and was not sticky. When the low molecular siloxane (D3-D20) of this composition was measured, it was 8560p
pm. To this composition, 0.2 part of 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. At this time, the roll workability was evaluated and was very good. Next, a test piece was prepared from this composition in the same manner as in Example 1,
Hardness and compression set were measured. The hardness was 50 and the compression set (25% compression) at 180 ° C. for 22 hours was 6%. Furthermore, the composition does not return to plasticity even after being left for two weeks at a humidity of 90% and a temperature of 60 ° C.
Immediately wound around the two rolls, the roll workability was also good. Plasticity is 274, hardness 50, compression set 5
% And no characteristic change was observed.

EXAMPLE 3 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ CHCH) SiO units
100 parts of a polyorganosiloxane having a polymerization degree of 6000, comprising 12 mol% and capped with a dimethylvinylsilyl group, and 2 parts of a polydiorganosiloxane capped with a silanol group and having a degree of polymerization of 60; 2 parts of polydiorganosiloxane closed with trimethylsilyl group and having a degree of polymerization of 20, surface treated fumed silica (AEROSIL R-97
4) 50 parts were kneaded with a kneader mixer until uniform, 0.1 part of tetramethylammonium silanolate (z = 25) was added and kneaded. The temperature at this time was 70 ° C.
Thereafter, heat treatment was performed at 150 ° C. for 30 minutes to obtain a silicone rubber composition. The plasticity of the obtained silicone rubber composition is
It was 284 and there was no stickiness. The low molecular siloxane (D3 to D20) of this composition was measured and found to be 7560 ppm. To this composition, 0.2 part of 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. At this time, the roll workability was evaluated and was very good. Next, a test piece was prepared from this composition in the same manner as in Example 1, and the hardness and compression set were measured. Hardness is 54, 180 ℃
The compression set (25% compression) at 22 hours was 5%. Furthermore, the composition did not return to plasticity even after being left for 2 weeks at a condition of 90% humidity and a temperature of 60 ° C., immediately wound around a two-roll mill, and had good roll workability. The degree of plasticity was 285, the hardness was 54, and the compression set was 5%. No characteristic change was observed.

Example 4 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ = CH) SiO units
100 parts of a polyorganosiloxane having a polymerization degree of 6000, comprising 12 mol% and having a terminal blocked with a dimethylvinylsilyl group, and a terminal having a polymerization degree of 20 having a terminal closed with a trimethylsilyl group.
5 parts of polydiorganosiloxane and 45 parts of fumed silica (AEROSIL 130) were kneaded with a kneader mixer until uniform, and 0.5 part of tetramethylammonium silanolate (z = 25) was added and kneaded. The temperature at this time was 70 ° C. Thereafter, heat treatment was performed at 150 ° C. for 30 minutes to obtain a silicone rubber composition. The resulting silicone rubber composition had a plasticity of 255 and was not sticky. The low molecular weight siloxane (D3 to D20) of this composition was measured and found to be 9560 ppm. 2,5-dimethyl 2,5
0.2 parts of di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. At this time, the roll workability was evaluated and was very good. Next, a test piece was prepared from this composition in the same manner as in Example 1, and the hardness and compression set were measured. Hardness is
The compression set at 180 ° C for 22 hours (25
% Compression) was 3%. In addition, the composition has a humidity of 90
%, The plasticization did not return even after being left for 2 weeks at a temperature of 60 ° C., the film was immediately wound around the two rolls, and the roll workability was good. The plasticity was 254, the hardness was 47, the compression set was 3%, and no property change was observed.

COMPARATIVE EXAMPLE 1 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ = CH) SiO units
100 parts of a polyorganosiloxane having a polymerization degree of 6000, comprising 12 mol% and having a terminal blocked with a dimethylvinylsilyl group, and a terminal having a polymerization degree of 20 having a terminal closed with a trimethylsilyl group.
5 parts of polydiorganosiloxane and 45 parts of fumed silica (AEROSIL 130) were kneaded with a kneader mixer until uniform, and then heat-treated at 150 ° C. for 30 minutes to obtain a silicone rubber composition. The obtained silicone rubber composition had a plasticity of 277 and was slightly sticky. The low molecular siloxane (D3 to D20) of this composition was measured to be 14970 ppm. 2,5-dimethyl 2,5
0.2 parts of di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. At this time, the roll workability was evaluated, but there was slight stickiness. Next, a test piece was prepared from this composition in the same manner as in Example 1, and the hardness, compression set, and hardness after the heat test were measured. The hardness was 55 and the compression set (25% compression) at 180 ° C for 22 hours was 29%. Further, the hardness after the heat resistance test was 62, and a change was recognized. Furthermore, after leaving this composition for 2 weeks under the conditions of 90% humidity and 60 ° C., it replasticized, and it took time for it to be wound around the two rolls neatly. The plasticity was 258, the hardness was 50, the compression set was 20%, and the property was changed.

COMPARATIVE EXAMPLE 2 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ = CH) SiO units
Consists 12 mol%, terminals blocked with dimethyl vinyl silyl group, a polyorganosiloxane 100 parts of polymerization degree 6000, end is closed by trimethylsilyl groups, the degree of polymerization is 20
5 parts of polydiorganosiloxane and 45 parts of fumed silica (AEROSIL 130) were kneaded with a kneader mixer until uniform, and 2 parts of hexamethyldisilazane was added and kneaded. The temperature at this time was 50 ° C. After this, 150 ℃
Heat treatment was performed for 3 hours to obtain a silicone rubber composition. The obtained silicone rubber composition had a plasticity of 240 and was quite sticky. The low molecular weight siloxane (D3 to D20) of this composition was measured and found to be 13440 ppm. To this composition, 0.2 part of 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. At this time, the workability of the roll was evaluated. Next, a test piece was prepared from this composition in the same manner as in Example 1, and the hardness and compression set were measured. Hardness is 47, 180
13% compression set (25% compression) at 22 ° C for 22 hours
Met. Furthermore, the composition did not return to plasticity even after being left for 2 weeks at a condition of 90% humidity and a temperature of 60 ° C., immediately wound around a two-roll mill, and had good roll workability. The plasticity was 231 and the hardness was 45, the compression set was 9%, and the properties were changed.

Comparative Example 3 In place of tetramethylammonium silanolate in Example 1, tetramethylammonium hydroxide (30
% Aqueous solution), but when the temperature reached about 110 ° C., the silicone rubber composition became loose and separated.

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08L 83/04 C08K 3/36 C08K 5/5415 C08L 83/06 C08L 83/08 C08L 83/07

Claims (1)

(57) [Claims] (A) Average unit formula: R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group,
a represents a number in the range of 1.98 to 2.02) 100 parts by weight of polyorganosiloxane having an average degree of polymerization of 4000 to 20000 (B) Average unit formula: R ¹ _b SiO _{(4-b) / 2} (wherein R ¹ is a substituted or unsubstituted monovalent hydrocarbon group,
b represents a number in the range of 1.98 to 2.02), the terminal is blocked with a hydroxyl group or an alkoxy group, and the degree of polymerization is 6 to 70.
0 to 20 parts by weight of polyorganosiloxane (C) 5 to 200 parts by weight of finely powdered fumed silica (D) Average unit formula: M ¹ O (R ² _c SiO) _z M ² (where M ¹ is A tetraalkylammonium group , M ²
Is the same or hydrogen as M ¹ , R ² is a substituted or unsubstituted monovalent hydrocarbon group, c is a number in the range of 1.98 to 2.02, and z is a number of 1 to 1000) Thermal decomposition catalyst
0.01-5 parts by weight at a temperature lower than the decomposition temperature of component (D)
The components (A) to (D) are mixed together or the components (D)
After mixing the components (A) to (C) at a temperature lower than the decomposition temperature,
After adding component (D), heat to above the decomposition temperature of component (D)
Of a thermosetting silicone rubber composition characterized by
Production method.