JPH05148422A - Silicone rubber composition and plug boots - Google Patents

Abstract

PURPOSE:To obtain a silicone rubber composition excellent in vulcanization moldability without any fixing on metal, glass, etc., even at high temperatures and plug boots, made of the silicone rubber, composed of the composition and hardly bonding to spark plugs. CONSTITUTION:A silicone rubber composition is obtained by blending (A) 100 pts.wt. polyorganosiloxane, expressed by formula I [R<1> is monovalent (substituted)hydrocarbon; (a) is 1.98-2.02] and containing vinyl group in an amount of 0.01-1mol% based on organic groups bound to silicon atom and methyl group in an amount of >=95mol% based on the organic groups and having 2000-10000 average polymerization degree with (B) 0.1-3 pts.wt. polyorganosiloxane, expressed by formula II [R<2> is methyl, phenyl, etc.; (b) is 1.98-2.02] and containing a perfluoroalkyl group in an mount of 10-50mol% based on organic groups bound to silicon atom, (C) 1-20 pts.wt. polyorganosiloxane, expressed by formula III [R<3> is methyl, etc.; (c) is 1.98-2.02] and containing phenyl group in an amount of 5-50mol% based on organic groups bound to silicon atom and having 5-10000cP viscosity, (D) 5-150 pts.wt. silica powder having the treated surface and >=50m<2>/g specific surface area and (E) a curing material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION The present invention relates to an oil bleeding silicone rubber composition, and more particularly to a silicone rubber composition which does not stick to metal, glass or the like at high temperature.
Further, the present invention relates to a silicone rubber plug boot that is difficult to adhere to a spark plug insulator obtained by molding this silicone rubber composition.

[0002]

TECHNICAL BACKGROUND AND PROBLEMS OF THE INVENTION Silicone rubber is excellent in heat resistance, oil resistance, cold resistance and chemical resistance.
It is used for rubber packing, gaskets, anti-vibration rubber, etc. around automobile engines. Particularly, as a plug boot material for fixing the spark plug and the ignition cable, heat resistance, compression set resistance, and the like are required, and thus silicone rubber has been widely used. However, gaskets and plug boots are in close contact with each other at high temperature for a long time because of their applications.For example, in the case of plug boots, the silicone rubber adheres strongly to the spark plug insulator and cannot be removed when maintenance or inspection is required. There is a problem that it becomes difficult or damage occurs, and there has been a strong demand for a solution to the problem. As a countermeasure against this problem, there is a method of using powder such as talc as an anti-sticking agent between the spark plug and the plug boot. However, the process is complicated, and the work environment for handling the powder is low. There was a problem. Further, when this powder sticking preventive agent is used, there is another problem that the sealing property between the spark plug and the plug boot is poor. On the other hand, conventionally, in connector seal parts, etc., silicone rubber blended with phenyl group-containing silicone oil, which has poor compatibility with silicone rubber, has been used for the purpose of improving the insertability of the wire and the sealability with the wire. There is. This is because the phenyl group-containing silicone oil bleeds out from the silicone rubber over time and forms a preferable oil film. Therefore, in order to prevent the adhesion between the silicone rubber plug boot and the spark plug insulator, it is conceivable to add such a phenyl group-containing silicone oil to the silicone rubber plug boot, but in this method when using at high temperature However, the compatibility between the silicone rubber and the phenyl group-containing silicone oil increases, and the phenyl group-containing silicone oil penetrates into the silicone rubber, resulting in a very small effect of preventing sticking. A method of incorporating a fluorosilicone oil having a perfluoroalkyl group into a silicone rubber is also disclosed in Japanese Patent Publication No. 63-24623, and the fluorosilicone oil having a perfluoroalkyl group is compatible with the silicone rubber. Due to its low solubility, if a large amount is blended, the silicone rubber will bleed out even in an unvulcanized state, resulting in poor joints during vulcanization, and a good molded product cannot be obtained. When molded into a plug boot and used, the waterproof seal between the plug and the plug boot cannot be expected.

[0003]

It is an object of the present invention to provide a silicone rubber composition which is free from sticking of rubber to rubber, rubber to glass, rubber to metal, etc. even at high temperatures, and which is also excellent in vulcanization moldability, and this silicone rubber composition. An object of the present invention is to provide a silicone rubber plug boot that is obtained by molding and does not require a complicated process such as the use of a powder sticking preventive agent and that is difficult to adhere to a spark plug.

[0004]

The present inventors have conducted extensive studies to achieve the above object, and as a result, by using a polysiloxane containing a perfluoroalkyl group and a polysiloxane containing a phenyl group in a silicone rubber composition, The inventors have found that a silicone rubber composition useful for plug boots in which the above problems are solved can be obtained, and have completed the present invention. The present invention provides, namely, (A) average composition formula R ¹ _a SiO _{(4-a) / 2} (wherein R ¹ represents a monovalent substituted or unsubstituted hydrocarbon group, and a is 1.98 to 2.02) , 0.01 to 1.00 mol% of the organic groups bonded to silicon atoms are vinyl groups and 95 mol% or more are methyl groups, and 100 parts by weight of polyorganosiloxane having an average degree of polymerization of 2000 to 10000 (B). Average composition formula R ² _b SiO _{(4-b) / 2} (wherein R ² represents a group selected from a methyl group, a phenyl group and a perfluoroalkyl group, and b is 1.98 to 2.02) , Polyorganosiloxane in which 10 to 50 mol% of organic groups bonded to silicon atoms are perfluoroalkyl groups 0.1 to 3 parts by weight (C) Average composition formula R ³ _c SiO _{(4-c) / 2} (wherein R is ³ represents a group selected from a methyl group and a phenyl group, and c represents 1.98 to 2.02), and is 5 to 50 mol% of the organic group bonded to the silicon atom. Is a phenyl group, polyorganosiloxane having a viscosity at 25 ° C of 5 to 10000 cP 1 to 20 parts by weight (D) Surface-treated silica powder having a specific surface area of 50 m ² / g or more 5 to 150 parts by weight and (E) A silicone rubber composition, which is basically composed of a catalytic amount of a curing agent, and a plug boot obtained by molding the silicone rubber composition.

The component (A) of the present invention is a polyorganosiloxane raw rubber having an average degree of polymerization of 2000 to 10000 which serves as a base polymer of the composition, and R ¹ is a monovalent substituted or unsubstituted hydrocarbon group. , A is a substantially straight chain having a number of 1.98 to 2.02. Further, the polyorganosiloxane needs to have 0.01 to 1.00 mol% of vinyl groups bonded to silicon atoms, preferably 0.05 to 0.3 mol%. If it is less than 0.01 mol%, the compression set is deteriorated and the sealing performance of the molding pair is deteriorated. If it is 1.00 mol% or more, the vulcanized rubber becomes brittle and cannot be used. Further, the polyorganosiloxane must have at least 95 mol% of methyl groups bonded to silicon atoms. When it has 5 mol% or more of organic groups other than methyl group,
B component and (C) component may not bleed out. As the organic group other than methyl group and vinyl group, ethyl group, propyl group, butyl group, hexyl group, dodecyl group, phenyl group, β-phenylethyl group, β-phenylpropyl group, chloromethyl group, 3,3, Examples thereof include a 3-trifluoropropyl group, an allyl group, a 1-butenyl group and a 2-hexenyl group.

The component (B), a polyorganosiloxane containing a perfluoroalkyl group, is a feature of the present invention that imparts an anti-sticking effect in the present composition. Moreover, the sealing performance can be improved by imparting excellent water repellency. The organic group R ² bonded to the silicon atom of this polyorganosiloxane is a methyl group, a phenyl group or a perfluoroalkyl group represented by -CH ₂ CH ₂ R _f (R _f is a perfluoroalkyl group having 1 to 3 carbon atoms). And b is substantially linear with a number between 1.98 and 2.02. Among the organic groups causing bonded to a silicon atom for achieving the above effects, -CH ₂ CH ₂ R _f is required to be 10 to 50 mol%. If it is less than 10 mol%, there is no effect of preventing adhesion, and if it exceeds 50 mol%, it is difficult to synthesize. The viscosity is not particularly limited, but in terms of adhesion prevention effect
The degree of polymerization is preferably lower than that of the polyorganosiloxane as the component (A), and the viscosity at 25 ° C. is preferably 1,000,000 cP or less. Further, the compounding amount is 0.1 to 100 parts by weight of (A)
It is 3 parts by weight, and if it is too small, there is no adhesion preventing effect, and if it is too large, it is separated from the system in an unvulcanized state, which causes defective molding during vulcanization.

The phenyl group-containing polyorganosiloxane of component (C), when used in combination with component (B), promotes bleed-out of the component (B) onto the surface of the molded article after vulcanization and has an effect of preventing sticking. This is to increase the oil bleeding property and increase the sealing property and the slip property by bleeding out to the rubber surface, which is the original characteristic of the oil bleeding silicone rubber.

By using the component (C) and the component (B) together
The amount of component (B) can be reduced and molding defects can be eliminated. Furthermore, since the component (C) penetrates into the system at high temperature, it does not cause molding failure even if it is mixed in a large amount. In order to obtain the above effects, it is necessary that the phenyl group is 5 to 50 mol% among the organic groups bonded to the silicon atom. If it is less than 5 mol%, the oil does not bleed out, and if it exceeds 50 mol%, it is difficult to synthesize. The viscosity of the oil must be 5 to 10000cP. At 5cP or less, the oil volatilizes at high temperature, and at 10000cP or more, the oil does not bleed out and the effect of preventing the (B) component sticking can be increased. Disappear. Also, the compounding amount is (A) 1
The amount is 1 to 20 parts by weight with respect to 00 parts by weight. If the amount is too small, the anti-adhesion effect and the waterproof sealing effect are not obtained, and if the amount is too large, the mechanical strength is lowered.

The surface-treated silica powder of the component (D) is
With the basic function of imparting mechanical strength, the (B) component,
The combined use with the component (C) imparts an excellent anti-adhesion effect. Treatment of such silica powder is known, and fumed silica, precipitated silica, etc. are mixed with silazanes such as hexamethyldisilazane, chlorosilanes, cyclic polysiloxanes, linear low-molecular polysiloxanes, etc., and heated and stirred. It is obtained by doing. It is also possible to add the above treatment agent together with the component (A) and the component (B) and the silica powder with a mixer such as a kneader for treatment. When treating with a mixer such as a kneader, silazanes such as hexamethyldisilazane, silanes such as diphenylsilanediol, and linear low-molecular-weight polysiloxanes with silanol groups or methoxy groups at the ends Processing aids and the like that it has are used. The compounding amount of the component (D) is 5 to 150 parts by weight, preferably 10 to 100 parts by weight, based on 100 parts by weight of the component (A). If the amount is too small, the mechanical strength and the adhesion preventing effect cannot be exhibited, and if the amount is too large, it is difficult to mix and homogenize, and the mechanical strength is also lowered.

As the curing agent for the component (E), a curing catalyst such as an organic peroxide or a curing agent for addition reaction is used. For example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl-t-
Butyl peroxide, 2,5-dimethyl-2,5-di-t-
Butyl peroxin hexane, various organic peroxides such as di-t-butyl peroxide, chloroplatinic acid, alcohol-modified chloroplatinic acid, platinum-olefin complexes, platinum-ketone complexes, platinum-vinylsiloxane A complex of
Platinum-based compound exemplified by platinum black supported on a carrier such as alumina or silica, tetrakis (triphenylphosphine) palladium, palladium-based compound exemplified by a mixture of palladium black and triphenylphosphine, etc. Alternatively, rhodium compounds are exemplified as the general ones.

Further, the present composition may appropriately contain a non-reinforcing filler, a heat-resistant additive, an internal release agent and the like which are generally used in silicone rubber.

The plug boot of the present invention can be obtained by molding such a composition by a known method. Generally, the molded product after press vulcanization is
Apply atto vulcanization for ~ 5 hours.

[0013]

EFFECTS OF THE INVENTION A molded article made of the composition obtained by the present invention maintains a difficult adhesion property even when it is in contact with rubber, glass, metal or the like at a high temperature for a long time. The silicone rubber plug boot obtained by molding this silicone rubber composition, for example, retains its difficulty in adhesion even when it is in contact with a spark plug insulator for a long time at high temperature, and also adheres to powder. There is no need for complicated steps such as the use of an inhibitor, and there is no problem such as poor sealability.

[0014]

EXAMPLES The present invention will now be described with reference to examples, but the present invention is not limited thereto.

Examples 1 and 2, Comparative Examples 1 to 3 Polydimethylsiloxane (A) having both ends blocked with trimethylsilyl groups and the balance consisting of 99.8 mol% of dimethylsiloxane units and methylvinylsiloxane units and having an average degree of polymerization of 6000. Both ends were blocked with trimethylsilyl groups, leaving the remainder at 3,
Poly (trifluoropropyl (methyl) siloxane) (B-1) consisting of 3,3-trifluoropropyl (methyl) siloxane unit of 100% and having a viscosity of 1000 cP Both ends are blocked with trimethylsilyl group, and the rest is 70% of dimethylsiloxane unit, diphenyl Siloxane unit 30%
Copolymerization of diphenylsiloxane and dimethylsiloxane with a viscosity of 100 cP Siloxane (C-1) 20 per 100 parts by weight of fumed silica with a specific surface area of 200 m ² / g
Using the filler (D-1) treated with 1 part by weight of hexamethyldisilazane to make the amount of silanol groups on the surface 2 / nm ² , these are uniformly mixed in the amount shown in Table 1 using a kneader mixer. Then, a silicone rubber compound was prepared. To 100 parts by weight of this silicone rubber compound, 0.5 part by weight of 2,5-dimethyl-2,5-bis (t-butylperoxy) -hexane was added and press-vulcanized at 170 ° C. for 10 minutes to obtain 13 cm × A 13 cm × 0.2 cm rubber sheet was molded. With these two rubber sheets stacked, put a weight on them so that a pressure of 5 g / cm ² is applied, and at 200 ℃ and 250 ℃, 4 hours each,
It was heat-aged for 168 hours. Next, after taking out the rubber sheet, peel off the two stacked sheets, the one with the same ease of peeling at that time as ○, the one that is hard to peel off the sheet △, the rubber is adhered and the rubber What was damaged was evaluated as x. Furthermore, in order to confirm the moldability, the rubber compound was placed in 2 pieces in a 13 cm x 13 cm x 0.2 cm mold, and this was press vulcanized and 2
The two rubber compounds were vulcanized and adhered, and the vulcanized and adhered portion was observed. Also, the amount of oil bleeding out to the rubber surface, which is the standard for the sealing property, was measured. Regarding the amount of oil bleed-out, the surface oil of a 13 cm × 13 cm × 0.2 cm sheet was wiped off 72 hours after molding and the weight was measured. The results are shown in Table 1.

[0016]

[Table 1]

Example 3 A sample was prepared in the same manner as in Example 1 except that the polytrifluoropropyl (methyl) siloxane (B-1) of Example 1 having a viscosity of 100 cP (B-2) was used. Created and tested.

Comparative Example 4 Copolymerization of diphenylsiloxane and dimethylsiloxane of Example 1 Siloxane (C-1) having a viscosity of 100000 cP
A sample was prepared and tested in the same manner as in Example 1 except that (C-2) was used.

Comparative Example 5 The amount of silanol groups on the surface not treated with hexamethyldisilazane in place of the fumed silica (D-1) of Example 1 was 4
Samples were prepared and tested in the same manner as in Example 1 except that the filler (D-2) of particles / nm ² was used. The results are shown in Table 2.

[0020]

[Table 2]

Examples 4 and 5, Comparative Examples 6 to 8 Polydimethylsiloxane (A), polytrifluoropropyl (methyl) siloxane (B-1), copolymerized siloxane
Using (C-1) and the filler (D-1), the amounts shown in Table 3 were uniformly mixed using a kneader mixer to prepare a silicone rubber compound. To 100 parts by weight of this silicone rubber compound, 0.5 part by weight of 2,5-dimethyl-2,5-bis (t-butylperoxy) -hexane was added, and press vulcanization was performed at 170 ° C for 10 minutes, and at 200 ° C. Atto vulcanization was performed for 4 hours to form plug boots. Spark plug (N-20 Denso Co., Ltd.) W-20-ET
-S) was attached and heat aging was performed at 180 ° C., 200 ° C., and 250 ° C. for 72 hours. Next, after pulling out the plug, the spark plug insulator was observed to evaluate the adhesion state (adhesion ratio) of the silicone rubber to the surface in contact with the plug boot. Moreover, the force at the time of pulling out was measured.
The results are shown in Table 3. The ratio of adhesion was calculated by the following formula.

[0022]

[Equation 1]

[0023]

[Table 3]

Example 6 A sample was prepared in the same manner as in Example 4 except that the polytrifluoropropyl (methyl) siloxane (B-1) of Example 4 having a viscosity of 100 cP (B-2) was used. Created and tested.

Comparative Example 9 Copolymerization of diphenylsiloxane and dimethylsiloxane of Example 4 Siloxane (C-1) having a viscosity of 100000 cP
A sample was prepared and tested in the same manner as in Example 4 except that (C-2) was used.

Comparative Example 10 The amount of silanol groups on the surface not treated with hexamethyldisilazane in place of the fumed silica (D-1) of Example 4 was 4
Samples were prepared and tested in the same manner as in Example 4 except that the filler (D-2) of the number of particles / nm ² was used. The results are shown in Table 4.

[0027]

[Table 4]

Claims (2)

[Claims] 1. (A) Average composition formula R ¹ _a SiO _{(4-a) / 2} (wherein R ¹ represents a monovalent substituted or unsubstituted hydrocarbon group, and a is 1.98 to 2.02) , 0.01 to 1.00 mol% of the organic groups bonded to silicon atoms are vinyl groups and 95 mol% or more are methyl groups, and 100 parts by weight of polyorganosiloxane having an average degree of polymerization of 2000 to 10000 (B). Average composition formula R ² _b SiO _{(4-b) / 2} (wherein R ² represents a group selected from a methyl group, a phenyl group and a perfluoroalkyl group, and b is 1.98 to 2.02) , Polyorganosiloxane in which 10 to 50 mol% of organic groups bonded to silicon atoms are perfluoroalkyl groups 0.1 to 3 parts by weight (C) Average composition formula R ³ _c SiO _{(4-c) / 2} (wherein R is ³ represents a group selected from a methyl group and a phenyl group, and c represents 1.98 to 2.02), and 5 to 50 mol% of the organic group bonded to the silicon atom is a phenol group. Nyl group, polyorganosiloxane having a viscosity of 5 to 10,000 cP at 25 ° C. 1 to 20 parts by weight (D) Surface-treated silica powder having a specific surface area of 50 m ² / g or more 5 to 150 parts by weight and (E) catalyst A silicone rubber composition characterized in that it consists essentially of an amount of a curing agent. 2. A plug boot obtained by molding the silicone rubber composition according to claim 1.