JPH0668053B2 - Acrylic rubber compound for gasket - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an acrylic rubber (AR) compound for a gasket, and is particularly suitable as a molding material for a cylinder head cover, an oil van gasket, etc. of an automobile. is there.

<Prior art> With the recent tendency of high temperature in the automobile engine room,
Cylinder head covers and oil bang gaskets are more demanding than ever before, in terms of sag resistance (compression set resistance) under high temperature atmosphere and deterioration oil resistance (crack resistance). ing. For this reason, AR, which can substantially satisfy these requirements, has begun to be used as a molding material instead of the conventional NBR. At the same time, the use of resin for the cylinder head cover is being considered from the viewpoint of weight reduction.

<Problems to be Solved by the Invention> The gasket molded from the AR compound has good sag resistance and deterioration oil resistance as described above, but has high rigidity and lacks flexibility (large module). Therefore, the first
As shown in the figure, when the gasket 1 is arranged between the cylinder head 2 and the cylinder head cover 3 and fastened with the stud bolts 5, a large compressive force must be applied to the gasket 1, and the resin cylinder The head cover has insufficient strength and may be deformed.

<Means for Solving Problems> As a result of intensive efforts for development to solve the above problems, the inventors of the present invention have come up with an AR composition for a gasket having the following constitution.

In an AR composition for a gasket in which a reinforcing filler is mixed with other auxiliary materials in AR, the reinforcing filler is a two-component mixed system consisting of a thermal particle having a specific particle size, and silane-treated silica, In addition, the distribution ratio of each component is within a specific range.

<Detailed Description of Means> (A) AR is an ACM system which is a copolymer of an alkyl ester and 2-chloroethyl vinyl ester, and an AN which is a copolymer of an alkyl ester and acrylonitrile.
Mention may be made of binary and terpolymers of M type and alkyl ester and modified alkyl ester.

As the acrylic ester, methyl acrylate
Examples thereof include ethyl / n-butyl / 2-ethylhexyl.

(B) For thermal black, the average particle size is 90 to 560 mμ
Use one. Specifically, the MT / FT type can be exemplified. If the average particle size is outside the above numerical range, the effect of the present invention is difficult to achieve.

(C) Silane-treated silica has an average particle size of 1 to 10 μm
Use one. If the average particle size is outside the above numerical range, the effect of the present invention is difficult to achieve.

(E) The blending ratio of the above two components constituting the reinforcing filler is + = 50 to 80 parts by weight (based on 100 parts by weight of acrylic rubber) / = 20/80 to 5 when thermal black and silane-treated silica are used. It becomes / 95.

If + is less than the above value, tensile strength will be caused, and if it exceeds the above value, module will be caused. If the thermal black ratio is too high, the modulus will be too high, and if the silica ratio is too high, problems will occur in tensile strength and sag resistance.

(F) Other auxiliary materials include those usually added to AR blends, vulcanization accelerators, waxes, stearic acid, antioxidants, and softeners.

(G) The AR composition of the present invention is prepared by mixing the above-mentioned AR with the above-mentioned two-component mixed reinforcing filler and other auxiliary materials and kneading the mixture with a kneading roll machine, Banbury mixer or the like to obtain a rubber material for a gasket. To do.

A gasket is formed from the rubber material thus obtained by compression, injection, transfer molding or the like.

<Operations and effects of the invention> The AR composition for a gasket of the present invention is a AR composition for a gasket in which a reinforcing filler is mixed with AR together with other auxiliary materials, and the reinforcing filler has a characteristic particle size. The two-component mixed system of thermal black and silane-treated silica, and the mixing ratio of each component being within a specific range, the strength and resistance of the gasket in a high temperature atmosphere as shown in Examples below. Tariability (compression set resistance)
The flexibility can be imparted to the gasket (the module can be made smaller) without decreasing the value. Therefore, as in the conventional case, when the gasket 1 is arranged between the cylinder head 2 and the cylinder head cover 3 and fastened with the stud bolts 5, it is not necessary to apply a large compressive force to the gasket 1, and the resin cylinder Since the head cover does not receive a large force, there is no risk of deformation.

<Examples> Hereinafter, examples performed to confirm the effects of the present invention will be described together with comparative examples.

In the following basic compounding formulation, the respective compounding ratios of the reinforcing filler are shown in Table 1, and a 2 mmt rubber sheet was obtained by compression molding (conditions; indicated below the table).

Combination recipe (parts by weight) AR (Ethyl acrylate / Butyl acrylate / Methoxyethyl acrylate ternary system) 100 MT Black (Average particle size; 270 mμ) Variable MAF Black (Average particle size; 30 mμ) Variable SRF Black (Average particle) Diameter; 60mμ) Variable silane-treated silica (average particle size; 3μm) Variable untreated silica (average particle size; 16μm) Variable Anti-aging agent 2 Stearic acid 2 Wax (paraffin type) 2 Vulcanizing agent 0.7 Lower particle accelerator 2 Above A test piece was obtained from each rubber sheet molded as described above, and the following tests were conducted.

(1) Normal physical properties: Based on JIS K6301.

(2) Compression set; JISK630 under heat treatment condition of 150 ℃ × 70h
Performed according to 1.

From the results shown in Table 1, the vulcanizates of the AR blends of the respective examples show that the rigidity (200% module) is significantly reduced with almost no deterioration in sag resistance and strength. I understand. Further, as in Comparative Example 3, when silica which is not treated with silane is used, the sag resistance is not good.

[Brief description of drawings]

FIG. 1 is a perspective view showing a mounting state of a cylinder head cover gasket which can be molded with the AR composition of the present invention. 1 ... Cylinder head cover gasket, 2 ... Cylinder head, 3 ... Cylinder head cover.

Claims (1)

[Claims] 1. An acrylic rubber composition comprising an acrylic rubber and a reinforcing filler mixed with other auxiliary materials, wherein the reinforcing filler is; a thermal black having an average particle size of 90 to 560 mμ, and an average particle size of 1. It is a two-component mixed system consisting of silane-treated silica of ˜10 μm, and the mixing ratio of each component is + = 50-80 parts by weight (based on 100 parts by weight of acrylic rubber) / = 20 / 80-5 / 95 An acrylic rubber compound for gaskets, which is characterized by: