JPH0627404Y2 - Rubber-coated stainless steel plate for gasket - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a rubber-coated stainless steel sheet for gaskets having a rubber coating layer formed on the surface of a steel sheet, with improved adhesion of the rubber coating layer.

(Prior Art) Conventionally, asbestos sheets and graphite sheets have been used as gasket materials for automobile engines, but since these materials have a problem of carcinogenicity, rubber-coated metal plates have come to be used in recent years. Is coming. Of the gasket materials of this rubber-coated metal plate, the one used for the cylinder head is a stainless steel plate with excellent heat resistance and corrosion resistance as the base metal plate is exposed to high temperature, high pressure, and severe corrosive environment. Are using. The gasket material of this stainless steel sheet base material has a poor adhesion of the rubber coating layer when the rubber coating layer is directly formed on the stainless steel sheet, so when forming the rubber coating layer, the surface of the stainless steel sheet is roughened, or the surface of the stainless steel sheet is roughened. Surface treatment such as galvanization is applied to improve adhesion.

(Problems to be solved by the invention) However, if the surface of a stainless steel plate is roughened, the fatigue strength of the steel plate will decrease, so cracks are likely to occur when molded into a gasket and incorporated into an automobile engine. there were. Further, when the surface treatment is galvanized, zinc in the plating layer is eluted by the circulating cooling water of the engine, which may cause peeling of the rubber coating layer.

In view of this point, the present invention provides a rubber-coated stainless steel plate for a gasket that does not reduce the strength of the stainless steel plate or the adhesion of the rubber coating layer.

(Means for Solving Problems) The rubber-coated stainless steel plate for gaskets of the present invention forms an undercoating film of an epoxy resin containing a chromate-based rust preventive pigment on the surface of the stainless steel plate, and the undercoating film is formed. An intermediate coating film obtained by mixing a rubber having an unsaturated double bond and a carboxyl group with an epoxy resin was formed thereon, and an upper coating film of a rubber having an unsaturated double bond was sequentially formed.

(Operation) FIG. 1 schematically shows a cross section of the rubber-coated stainless steel plate for gasket of the present invention. In FIG. 1, 1 is a base material stainless steel plate, 2 is an undercoating film formed on both sides of the stainless steel plate 1, and is made of an epoxy resin containing a chromate-based rust preventive pigment. Reference numeral 3 is an intermediate coating film formed on these undercoating films 2, which is composed of a mixture of a rubber having an unsaturated double bond and a carboxyl group and an epoxy resin. Reference numeral 4 denotes a rubber top coat film having an unsaturated double bond formed on the intermediate coat film 3.

In the present invention, an epoxy resin is used as the main component of the undercoat coating film to improve the adhesion with the stainless steel plate. The epoxy resin is preferably a bisphenol type epoxy resin generally used in thermosetting paints, and the curing agent thereof may be urethane resin, urea resin, melamine resin, phenol resin or the like.

Although the undercoat contains a chromate-based rust preventive pigment,
In addition to improving the corrosion resistance of the undercoating film, the surface passivation film of the stainless steel plate is a chromium oxide film, so it is well compatible with chromate and improves the adhesion between the undercoating film and the stainless steel plate. It can be done. Examples of this chromate-based rust preventive pigment include strontium chromate, lead chromate, calcium chromate, zinc chromate and barium chromate. The content is preferably 20 to 80 parts with respect to 100 parts (weight) of the resin. If it is less than 20 parts, the effect of improving the adhesiveness is small, and if it exceeds 80 parts, the workability of the undercoat coating film is deteriorated.

The thickness of the undercoat coating film is preferably 2 to 8 μm as a dry coating film. If it is less than 2 μm, the effect of improving corrosion resistance and coating adhesion is small, and even if it is more than 8 μm, the effect of improving them is saturated.

In the present invention, an upper coating film is not directly formed on the undercoating film, but both coating films are adhered via an intermediate coating film. For gaskets,
The top coat must be a rubber with excellent heat resistance and oil resistance, but since such a rubber does not have a functional group that reacts with the epoxy resin, adhesion with the epoxy resin Is inferior. Therefore, in the present invention, an intermediate coating film is provided and the undercoating film and the topcoating film are bonded together.

However, when this intermediate coating film is made into a mixture of a rubber having an unsaturated double bond and a carboxyl group and an epoxy resin, the carboxyl group of the rubber component becomes an undercoat coating film during heating and drying for forming the intermediate coating film. Since it undergoes a crosslinking reaction with the epoxy resin and the epoxy resin component in the intermediate coating film, the intermediate coating film firmly adheres to the undercoating film and the strength of the intermediate coating film becomes strong.

When the intermediate coating film has the composition as described above and the top coating film is a rubber having an unsaturated double bond, the intermediate coating film is heated and dried during the formation of the top coating film or irradiated with radiation. Since the rubber component unsaturated double bond undergoes a crosslinking reaction with the unsaturated double bond of the top coating film rubber and the action of the vulcanizing agent and radiation,
Firmly adheres to the top coat.

Furthermore, when the intermediate coating film is a mixture of the epoxy resin of the undercoating film and the rubber of the topcoating film in this way, the compatibility with both coating films is good, and the physical adhesion is also good. .

Examples of the rubber of the intermediate coating film include NBR (nitrile rubber) or SBR (styrene butydiene rubber) having a carboxyl group at the terminal or side chain of the molecule, water-added NBR having a carboxyl group in the same manner, and the like. Examples of the rubber for top coating film include NBR, water-added NBR, BR (polybutadiene rubber), and SBR. Here, the water-added NBR is a rubber in which the double bond portion is hydrogenated and saturated for the purpose of improving the heat resistance of the NBR. This type of rubber is commercially available under the trade names Zetpol [Nippon Zeon Co., Ltd.] and TORNAC [POLYSAR].

The mixing ratio of the rubber and the epoxy resin in the intermediate coating film is set to rubber / epoxy resin = 40/60 to 10/90 from the viewpoint of the mechanical strength of the coating film and the adhesion between the upper and lower coating films. Is preferred.

Further, if the thickness of the intermediate coating film is less than 2 μm, it is difficult to form a coating film by a roll coating method or the like, and if it is 10 μm, sufficient adhesion to the upper and lower undercoating films and the top coating film can be secured, It is preferably 2 to 10 μm. If the thickness of the top coating film is less than 15 μm, the sealing property will be poor. Therefore, the thickness is preferably 15 μm or more, and the upper limit is preferably 50 μm or less from the viewpoint of economy.

Incidentally, the top coating film, additives commonly used as a compounding agent of rubber, for example, carbon black, talc,
It is also possible to contain calcium carbonate, silica, a vulcanizing agent, a vulcanizing aid, a processing aid, an antioxidant, an activator, a pigment, a plasticizer and the like.

(Example) Stainless steel plate (when the surface is SUS301, cold rolled, SUS3
In the case of 04, the surface of 2D finish) was washed with alkali and washed with hot water, and then a thermosetting epoxy resin paint was applied as an undercoat paint, and dried in a hot air oven at 240 ° C. for 1 minute to be hardened. Next, a thermosetting epoxy resin coating material, rubber and an intermediate coating material containing a carboxyl group are applied,
It was dried and cured as in the case of the undercoat paint. Then,
On this intermediate coating film, apply a topcoat paint in which rubber is diluted with an organic solvent and dry for 1 minute at 200 ° C in a hot air oven, and then use an electron beam accelerator at an accelerating voltage of 200 KV and an electron flow of 10 mA. It was irradiated with an electron beam of 10 Mrad and vulcanized. A rubber-coated stainless steel plate having a structure as shown in Table 1 was prepared by the above procedure.

Next, the rubber-coated stainless steel sheet thus prepared was immersed in an antifreeze solution for automobile engines (long life coolant) heated to 130 ° C. for 240 hours, taken out and subjected to a coating adhesion test.

The adhesion test is a method in which 100 cuts of a grid pattern that reach the steel substrate with a cutter knife are inserted 100 times, cellophane tape is attached to the cuts, and then peeled off, and the state of film peeling is evaluated by the following criteria. went.

Symbol Film peeling state ○ No peeling Δ Peeling 20% or less × Peeling 21% or more Table 1 shows the test results.

(Effects of the Invention) As described above, the rubber-coated stainless steel sheet for gaskets of the present invention is subjected to surface treatment such as shot blasting, which lowers fatigue strength or corrosion resistance, such as galvanizing, on the surface of the stainless steel sheet. No deterioration in fatigue strength and corrosion resistance is observed since it has not been rubbed.

[Brief description of drawings]

FIG. 1 schematically shows a cross section of a rubber-coated stainless steel plate for gasket of the method of the present invention. 1 ... stainless steel plate, 2 ... undercoating film, 3 ... intermediate coating film, 4 ... topcoating film,

Claims (1)

[Scope of utility model registration request] 1. An undercoating film of an epoxy resin containing a chromate rust preventive pigment is formed on the surface of a stainless steel plate, and a rubber and an epoxy having an unsaturated double bond and a carboxyl group are formed on the undercoating film. A rubber-coated stainless steel sheet for gaskets, characterized in that an intermediate coating film formed by mixing with a base resin and an upper coating film of rubber having an unsaturated double bond are sequentially formed.