JPH0791469B2 - Non-fluidic heat-curable silicone rubber composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-fluidic heat-curable silicone rubber composition, and more specifically, it is non-fluidic before heat-curing, roll workability, extrudability, etc. The present invention relates to a non-flowable heat-curable silicone rubber composition which has a feature of being excellent in processability and can be a silicone rubber molded product having a low hardness and a small compression set after being heat-cured.

[Prior Art] Silicone rubber has a property as a rubber elastic body having excellent properties in a wide temperature range, and is therefore widely used in electric wire coating materials, keyboards, gaskets, packings, medical tubes and the like.

Such a silicone rubber is an organopolysiloxane composition composed of an organopolysiloxane raw rubber as a base polymer, finely divided silica as a reinforcing filler, and an organic peroxide as a curing catalyst (hereinafter referred to as a silicone rubber composition). Is obtained by heating and curing.

On the other hand, recently, among silicone rubbers, a silicone rubber having a JIS-A hardness of 40 degrees or less obtained by greatly reducing the compounding amount of fine powder silica (hereinafter, a silicone rubber having a JIS-A hardness of 40 degrees or less is a low hardness silicone rubber). However, it has been found that it has excellent properties that conventional high hardness silicone rubbers do not have, and it has begun to be used in large quantities as a material for keyboards, rolls and the like.

However, since the silicone rubber composition obtained by significantly reducing the amount of finely divided silica exhibits fluidity, it has drawbacks in that it is inferior in roll workability and that it is difficult to uniformly extrude it. As one of the methods for improving such drawbacks, a method has been proposed in which polytetrafluoroethylene powder is added and blended to a silicone rubber composition to improve its processability (see JP-B-53-21892). .

[Problems to be Solved by the Invention] However, the silicone rubber molded product obtained by the method of Japanese Patent Publication No. 53-21892 has a drawback that polytetrafluoroethylene powder is scattered on the surface of the molded product to cause a poor appearance. It was

Therefore, as a result of research to improve such drawbacks of the conventional techniques, the present inventors have found that a silicone rubber composition containing a specific organopolysiloxane is non-flowable,
The present invention has been completed, and has reached the present invention by finding that it can be a silicone rubber molded product having excellent workability, low hardness after heat curing, and low compression set.

That is, the object of the present invention is a silicone rubber composition that is non-fluid before heat curing, and has excellent workability such as roll workability and extrudability, and has a low hardness and a small compression set after heat curing. Another object of the present invention is to provide a non-flowing heat-curable silicone rubber composition that can be used as a molded product.

[Means for Solving Problems and Their Actions] The present invention as described above includes (A) general formula (HO) R ¹ ₂ SiO [R ² ₂ SiO] _n SiR ³ ₂ R ⁴ (wherein R ¹ monovalent carbonization A hydrogen group, R ² and R ³ are substituted or unsubstituted monovalent hydrocarbon groups, R ⁴ is a monovalent hydrocarbon group or a hydroxyl group, and n is the organopolysiloxane having a weight average molecular weight of 250,000. However, in the formula, the total number of moles of the hydroxyl group, R ¹ , R ² , R ³ and R ⁴ is 0.05.
Mol% to 2.0 mol% are vinyl groups. Organopolysiloxane gum 100 parts by weight expressed as), (B) In the general formula _{^{HO (R ▲ 5 2 ▼ SiO}} ) n H ( wherein, R ⁵ is a substituted or unsubstituted monovalent hydrocarbon group, the At least one of them is a phenyl group, and n is 2
It is a number of ~ 50. A non-flowable heat-curable silicone rubber comprising 0.5 to 10 parts by weight of an organopolysiloxane represented by the formula ( ² ), (C) 2 to 20 parts by weight of finely divided silica having a specific surface area of 50 m ² / g or more, and (D) a curing catalyst. It is a composition.

Explaining this, the component (A) is the main component of the composition of the present invention, and in the above formula, R ¹ is an alkyl group such as a methyl group, an ethyl group or a propyl group; an alkenyl group such as a vinyl group or an allyl group; Cycloalkyl group such as cyclohexyl group; β-
Aralkyl groups such as phenylethyl group; monovalent hydrocarbon groups exemplified by aryl groups such as phenyl group, R ² and R ³ are alkyl groups such as methyl group, ethyl group, propyl group; vinyl group, allyl group An alkenyl group such as; a cycloalkyl group such as a cyclohexyl group; an aralkyl group such as a β-phenylethyl group; an aryl group such as a phenyl group and a substitution exemplified by a hydrogen atom of these groups substituted with a cyano group or the like; It is an unsubstituted monovalent hydrocarbon group, and R ⁴ is a monovalent hydrocarbon group or a hydroxyl group similar to R ¹ . In the present invention, it is necessary that the end of the molecular chain of the component (A) has at least one hydroxyl group, and it is preferable that the end of the molecular chain of the component (A) has a hydroxyl group. This is because the silicone rubber composition becomes fluid when no hydroxyl group is present. Further, 0.05 mol% to 2.0 mol% of the total number of moles of R, R ¹ , R ² , R ³ and R ⁴ is a vinyl group,
The range of mol% to 1.0 mol% is more preferable. This is 0.05
This is because if it is less than mol%, the crosslinking density tends to be too low and the compression set tends to be large, and if it exceeds 2.0 mol%, the hardness becomes too high and a low hardness silicone rubber cannot be obtained.

The molecular weight of the component (A) may be within the range of the molecular weight of the organopolysiloxane raw rubber used in ordinary silicone rubber, and is not particularly limited, but in order to obtain a silicone rubber having high mechanical strength, the weight average molecular weight is 25 It is preferably 10,000 or more, more preferably 300,000 or more. The position of the vinyl group may be present at the molecular chain terminal of the component (A), at the main chain, or at both, and is not particularly limited, but in order to obtain a silicone rubber having high mechanical strength, at least one vinyl group is present. It is preferable that the vinyl group (1) exists at the terminal of the molecular chain of the component (A).

The component (B) functions to render the composition of the present invention non-fluid and to improve processability such as roll workability and extrusion characteristics. Such a function is exhibited by using the component (B) and the component (A) together. In the component (B), R ⁵ in the above formula is a substituted or unsubstituted monovalent hydrocarbon group similar to the above R ² , at least one of which is a phenyl group, and n is a number from 2 to 50. It is an organopolysiloxane.
Although the mechanism for preventing the fluidity of the component (B) has not been sufficiently clarified, in addition to the entanglement between the hydroxyl group of the component (A) and the component (B), the bulkiness of the phenyl group of the component (B) is the present invention. It is believed to have rendered the composition non-flowing.
Specific examples of the component (B) include, for example, the following α and ω
-Dihydroxydiorganopolysiloxanes.

Such α, ω-dihydroxydiorganopolysiloxane can be obtained, for example, by hydrolyzing methylphenyldichlorosilane and subjecting this to polycondensation.
The blending amount of the component (B) is 0.5 with respect to 100 parts by weight of the component (A).
To 10 parts by weight, preferably 1 to 5 parts by weight. This is because if it is less than 0.5 part by weight, the effect of preventing the fluidity of the silicone rubber composition is poor, and if it exceeds 10 parts by weight, this effect does not increase any more and it is economically disadvantageous.

The component (C) is fine powder silica having a specific surface area of 50 m ² / g or more, and may be one that has been conventionally used for silicone rubber, and is not particularly limited. Examples of such fine powder silica include fumed silica and precipitated silica.

The compounding amount of the component (C) is in the range of 2 to 20 parts by weight, preferably 2 to 15 parts by weight. This is because if it is less than 2 parts by weight, sufficient non-fluidity cannot be obtained, and if it exceeds 20 parts by weight, a silicone rubber having a low hardness and a small compression set cannot be obtained.

The component (D) is a curing catalyst for curing the composition of the present invention, and usually an organic peroxide is used. A combination of an organohydrogenpolysiloxane and a platinum compound is also used. As the organic peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5- Dimethyl-2,5-di (t
-Butylperoxy) hexyne, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, parachlorobenzoyl peroxide are exemplified. . As the platinum compound, finely divided platinum, finely divided platinum adsorbed on a carbon powder carrier, chloroplatinic acid, alcohol modified chloroplatinic acid, a chelate compound of platinum, coordination of chloroplatinic acid and olefins A compound is illustrated.
The blending amount of the component (D) is preferably within the range of 0.1 to 10 parts by weight.

The composition of the present invention can be obtained by kneading a predetermined amount of the components (A) to (D) described above with a two-roll mill, a kneader, a Banbury mixer or the like. , Titanium oxide as a heat resistant additive,
Red iron oxide, cerium oxide, barium zirconate, a halogen compound as a flame retardant, antimony oxide, carbon functional silane as a physical property modifier, organohydrogenpolysiloxane, etc. are added and blended unless the object of the present invention is impaired. It doesn't matter.

[Examples] Next, the present invention will be described with reference to Examples. The middle part of the examples means parts by weight. The fluidity of the silicone rubber composition was evaluated according to the following method.

<Method of evaluating fluidity of silicone rubber composition> The method was performed according to JIS-A5758. A groove type container for slump test specified in JIS-A5758 was used. The groove type container for slump test was filled with the silicone rubber composition, allowed to stand at room temperature for 24 hours, and the distance at which the silicone rubber composition flowed out under the groove was measured. The distance was expressed in mm. Usually, it is determined that less than 3 mm is non-fluid and 3 mm or more is fluid.

<Measurement of molecular weight of organopolysiloxane raw rubber> An organopolysiloxane raw rubber was dissolved in toluene to prepare a sample for gel permeation chromatography (hereinafter referred to as GPC) measurement, which was measured by a GPC measuring instrument [manufactured by Toyo Soda Co., Ltd.]. The molecular weight calculated by "HLC-802A"] was calculated based on a polystyrene standard sample. Therefore, the molecular weight of the obtained organopolysiloxane raw rubber is a polystyrene-equivalent weight average molecular weight.

Example 1 Both ends of the molecular chain were blocked with dimethylhydroxysiloxy groups, (CH ₃ ) ₂ SiO units 99.8 mol%, (CH ₃ ) (CH ₂ ═CH) S
100 parts of methyl vinyl polysiloxane raw rubber having a weight average molecular weight of 400,000 and consisting of 0.15 mol% of iO unit is wrapped around two rolls, and fumed silica having a specific surface area of 200 m ² / g [Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.] 10 parts and formula Was added and 3 parts of α, ω-dihydroxymethylphenylpolysiloxane represented by the following formula was added and kneaded uniformly to prepare a silicone rubber compound.

Then, this compound was kneaded at 150 ° C for 2
Heat treated for hours. To 100 parts of this compound, 0.5 part of 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. Then, the silicone rubber composition is press-vulcanized under the conditions of 100 kg / cm ² and 170 ° C. to make a right cylindrical silicone rubber molded product having a thickness of 12.7 mm and a diameter of 29.0 mm, and its hardness and compression The strain was measured based on JIS-K6301. The results are shown in Table 1.

For comparison, in the above, the same structure as above except that both ends of the molecular chain are blocked with dimethylvinylsiloxy groups instead of the methylvinylpolysiloxane raw rubber whose both ends are blocked with dimethylhydroxysiloxy groups. A silicone rubber composition was obtained in the same manner except that vinyl polysiloxane raw rubber was used. Further, in the above, α, ω-dihydroxymethylphenylpolysiloxane was replaced by α, ω-dihydroxydimethylpolysiloxane having a degree of polymerization of 4 to 6, and the same procedure was followed to obtain a silicone rubber composition.

The fluidity of these silicone rubber compositions and the compression set of silicone rubber moldings were measured. The results are shown in Table 1 as Comparative Example 1 and Comparative Example 2, respectively.

Examples 2 to 4 Both ends of the molecular chain were capped with dimethylhydroxysiloxy groups, (CH ₃ ) ₂ SiO unit 89.85 mol%, (CH ₃ ) (CH ₂ ═CH)
100 parts of a methylphenylvinylpolysiloxane raw rubber having a weight average molecular weight of 500,000 consisting of 0.15 mol% of SiO unit and 10.0 mol% of C ₆ H ₅ ) ₂ SiO unit was wound around a two-roll, and 10 parts of quartz powder was used around this. 2 parts of the same α, ω-dihydroxymethylphenylpolysiloxane as above and 10 parts of fumed silica [Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.]
The amounts shown in the table were added, the mixture was kneaded, and further heat-treated at 150 ° C. for 2 hours to obtain a silicone rubber composition. After 0.5 part of dicumyl peroxide was added to these silicone rubber compositions and mixed uniformly, silicone rubber molded articles were prepared in the same manner as in Example 1 and their hardness and compression set were measured. The results are shown in Table 2 as Example 2, Example 3 and Example 4.

For comparison, a silicone rubber composition containing 25 parts of fumed silica was evaluated in the same manner as above, and the results are shown in Table 2 as Comparative Example 3. From Table 2, the silicone rubber composition containing 25 parts of fumed silica is non-fluid, but has a large value of compression set and is unsuitable as a material for keyboards and rolls.

Example 5 Same as Example 1 except that both ends of the molecular chain are capped with methylvinylhydroxysiloxy groups instead of the methylvinylpolysiloxane raw rubber whose both ends are capped with dimethylhydroxysiloxy groups. A silicone rubber composition was obtained in the same manner as in Example 1, except that a methyl vinyl polysiloxane raw rubber having a structure was used. For this silicone rubber composition, the fluidity and the compression set of the silicone rubber molded product were measured in the same manner as in Example 1. The measurement results were as follows.

Fluidity of silicone rubber composition (mm) 0 mm (non-fluidity) Hardness of silicone rubber molded product (JIS) 25 Compression set of silicone rubber molded product 12% [Effect of the invention] It is a non-fluidizing heat-curable silicone rubber composition comprising the component (D), and in particular, the silicone rubber composition containing the components (A) and (B) is non-fluidic before heating and curing. It has a feature that it is excellent in workability such as roll workability and extrudability, and has a feature that it has a low hardness after heat curing and can be a silicone rubber molded product having a small compression set.

Therefore, the composition of the present invention is suitably used as a material for keyboards, rolls and the like.

Claims (1)

[Claims] (A) General formula (HO) R ¹ ₂ SiO [R ² ₂ SiO] _n SiR ³ ₂ R ⁴ (wherein R ¹ is a monovalent hydrocarbon group, and R ² and R ³ are It is a substituted or unsubstituted monovalent hydrocarbon group, R ⁴ is a monovalent hydrocarbon group or a hydroxyl group, and n is an integer by which the weight average molecular weight of the organopolysiloxane is 250,000 or more. , Hydroxyl group, R ¹ , R ² , R ³ , R ⁴ total mole number of 0.
05 mol% to 2.0 mol% are vinyl groups. Organopolysiloxane gum 100 parts by weight represented by), (B) In the general formula _{^{HO (R 5 2 SiO) n}} H ( wherein, R ⁵ is a substituted or unsubstituted monovalent hydrocarbon group, of which at least one Is a phenyl group and n is 2
It is a number of ~ 50. A non-flowable heat-curable silicone rubber comprising 0.5 to 10 parts by weight of an organopolysiloxane represented by the formula ( ² ), (C) 2 to 20 parts by weight of finely divided silica having a specific surface area of 50 m ² / g or more, and (D) a curing catalyst. Composition.