JP2002226978A - Stainless steel sheet for gasket, and gasket made of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stainless steel sheet for a gasket suppressing the reduction of adhesion between the stainless steel and a rubber layer over a long period, and a gasket made of the rubber-covered stainless steel sheet which has excellent sealability and durability. SOLUTION: In the gasket made of a stainless steel for a gasket, a chromate film in which the weight ratio of (Cr6+)/(the total Cr) is 0 to 0.2, and the total coating weight of Cr is 20 to 100 mg/m2 is formed at least on a part of the surface of a stainless steel base material. The chromate film can contain one or more kinds selected from phosphate, silica and acrylic resin. A rubber-covered layer is formed on the chromate film, so that the steel sheet is used as a gasket.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel plate for a gasket and a gasket made of the stainless steel plate, which are incorporated in a cylinder head of an automobile engine and exhibit excellent adhesion to a rubber coating layer.

[0002]

2. Description of the Related Art As a gasket material for an automobile engine,
The use of rubber-coated metal sheets has become common. Since rubber-coated metal plates for cylinder heads are exposed to high temperature, high pressure and severe corrosive atmosphere, stainless steel excellent in heat resistance and corrosion resistance is used as a base material. For use as a gasket for a cylinder head, sealing properties and durability are also important characteristics required for a gasket material. Although a rubber coating layer is provided on the gasket base material in order to improve the sealing property, simply providing the rubber coating layer causes interfacial peeling between the gasket base material and the sealing property, thereby deteriorating. Therefore, prior to the formation of the rubber coating layer, the gasket substrate is subjected to surface treatment such as roughening, galvanizing, and chromate coating. Among the surface treatments, the coating type chromate treatment is more excellent in operability than the reaction type chromate treatment and the electrolytic treatment, and is disclosed in JP-A-3-227622, JP-B-7-92149, etc. via the chromate coating. A gasket material provided with a rubber coating layer is introduced.

[0003]

However, depending on the conditions of the chromate treatment, the adhesion at the rubber / stainless steel interface becomes insufficient due to environmental degradation, and the rubber coating layer is peeled off, which is required for gaskets. In some cases, performance such as sealing performance is not stable. The decrease in the sealing performance is presumed as follows. The gasket is used in an atmosphere that is constantly in contact with an engine coolant mainly containing a mixture of ethylene glycol and water at a temperature of about 120 to 150 ° C., and water permeates into the inside from a rubber surface layer swollen by ethylene glycol. . The permeated water undergoes a hydration reaction or is adsorbed with Cr ⁶⁺ ions in the chromate film present at the rubber / stainless steel interface, and blisters serving as a starting point of peeling are generated.

[0004]

SUMMARY OF THE INVENTION The present invention is based on the premise that the adsorption of permeated water or the hydration reaction with Cr ⁶⁺ ions is the cause of the deterioration of the sealing performance. Provide a stainless steel / rubber coated stainless steel plate gasket and a gasket made of rubber-coated stainless steel plate, which maintain the adhesion of the stainless steel / rubber coating layer at a high level for a long period of time by modifying the chromate film to be used. The purpose is to:

[0005] The stainless steel sheet for a gasket of the present invention comprises:
In order to achieve the object, the weight ratio of (Cr ⁶⁺ ) / (total Cr) is 0 to 0.2 and the total amount of deposited Cr is 20 to 100 mg / m 2.
^{The second} chromate film is formed on at least a part of the surface of the stainless steel substrate. When used as a gasket, a rubber coating layer is formed on a chromate film. The chromate film may include one or more of phosphate, silica, and acrylic resin.

[0006]

In consideration of the use environment of the gasket, the decrease in the adhesion of the rubber coating layer is largely affected by ethylene glycol contained in the engine cooling water. The effect of ethylene glycol can be explained using solubility parameters. For example, the solubility parameter of NBR used for gasket rubber is 8.7 to 10.3, and the solubility parameter of fluororubber is 8 to 10. On the other hand, the solubility parameter of ethylene glycol is 14.2 and the solubility parameter of water is 23.4. As the solubility parameter of the rubber component approaches the solubility parameter of the solution, the compatibility increases. In an environment where an engine coolant containing ethylene glycol is used, the solubility parameter approaches the solubility parameter of the rubber component as compared with the environment of water alone, so that ethylene glycol permeates the rubber coating layer and the rubber coating layer. Swelling and moisture penetration easily occur.

On the other hand, the surface of the rubber coating layer is heated to about 120 to 150 ° C. during operation of the engine. The heated rubber coating layer is more susceptible to the swelling action of ethylene glycol. In such a situation, moisture easily penetrates and permeates the rubber coating layer, and the hydration reaction between Cr ⁶⁺ ions in the chromate film present at the rubber / stainless steel interface and the permeate water and the permeate water adsorption Occurs. as a result,
The osmotic pressure at the rubber / stainless steel interface increases, and minute osmotic pressure blisters easily occur. The osmotic blister acts as a starting point of peeling, and promotes peeling of the rubber coating layer.

[0008] On the premise that ethylene glycol contained in the engine coolant and Cr ^{6+ of the} chromate film formed on the surface of the stainless steel base material affect the decrease in adhesion of the rubber coating layer. Various investigations and examinations were made on chromate films which are less affected by the decrease in adhesion. as a result,
Found chromate film having reduced hexavalent chromium component to be effective adhesion suppressing reduction, especially the weight ratio of hexavalent chromium component to all the chromium component (Cr ⁶⁺⁾ / (total Cr) 0
It has been clarified that a gasket made of a stainless steel sheet having excellent rubber adhesion and durability can be obtained when it is set to 0.2.

The weight ratio (Cr ⁶⁺ ) / (total Cr) is from 0 to 0.
The chromate film adjusted to the range of 2 is formed by drying the chromate film at a high temperature and / or reducing the Cr ⁶⁺ using methanol, formalin, phosphoric acid or the like. For example, when the chromate film is dried at 100 to 150 ° C., the weight ratio (Cr ⁶⁺ ) / (total Cr) becomes 0.2 to 0.3, but the drying temperature is set to 180 to 250 ° C. The weight ratio (Cr ⁶⁺ ) / (total Cr) is reduced to 0 by combination with the reduction treatment using chromium, formalin, phosphoric acid, etc.
It can be adjusted to the range of 0.2. High-temperature drying is effective in promoting all- or oxol-forming of the trivalent chromium hydroxide and forming a stable film having a higher molecular weight. The chromate film is formed such that the total amount of deposited Cr is 20 to 100 mg / m ² . If the total amount of Cr adhered is less than 20 mg / m ² , the effect of improving rubber adhesion is insufficient. Conversely 10
If the total amount of Cr exceeds 0 mg / m ² , cracking or powdering is likely to occur in the chromate film due to processing, and as a result, the adhesion of the rubber coating layer is reduced.

The chromate treatment solution used has a total Cr concentration of 10 to 60 g / l and a weight ratio of (Cr6 +) / (total C
r): a processing solution having a pH of 0.3 to 0.7 and a pH of 1 to 4 is preferable. The chromate treatment liquid is applied to a stainless steel plate by a commonly employed roll coat or the like. It is not necessary to particularly heat the chromate treatment liquid at the time of application, and a chromate treatment liquid at room temperature can be applied. The chromate treatment solution can contain an appropriate amount of phosphate, silica, acrylic resin, or the like. Phosphate, silica, acrylic resin and the like in the chromate treatment liquid migrate to the chromate film. Elution of Cr is suppressed by the addition of phosphate or silica,
Long-term corrosion resistance is provided. The acrylic resin has an effect of improving the adhesion of the rubber coating layer.

The stainless steel sheet used for the gasket base material is preferably cleaned in advance using an alkaline cleaning liquid and / or an acidic aqueous solution of phosphoric acid, hydrofluoric acid, nitric acid, hydrochloric acid or the like. This cleaning removes oil, surface oxides, and the like from the surface of the stainless steel, and refines the surface to have a high affinity for the chromate treatment solution. Therefore, when the washed stainless steel is subjected to chromate treatment, a gasket substrate coated with a uniform chromate film is obtained. Since the rubber coating layer is formed via the chromate film, the adhesion of the rubber coating layer to the gasket substrate is good. As the rubber coating layer, commonly used NBR, water-added N
BR, fluorine rubber, silicone rubber, acrylic rubber, epichlorohydrin rubber, EPDM, chlorinated rubber, chlorosulfonated polyethylene and the like are used. In addition, Cr ⁶⁺
Swelling due to the hydration reaction between water and permeated water or the adsorption of permeated water is suppressed, so that good adhesion is maintained over a long period of time. Moreover, since stainless steel is used for the gasket base material, the gasket satisfies the required level with respect to corrosion resistance.

[0012]

[Example 1] SUS3 having a thickness of 0.25 mm
After the rolled material of the 01H stainless steel plate was treated with the phosphating solution, the chromating solution was applied and dried at 200 ° C. for 1 minute to form a chromate film. As the chromate treatment liquid, Cr ⁶⁺ : 20 g / l, Cr ³⁺ : 20
g / l, H ₃ PO ₄ : 40 g / l, SiO ₂ : 80 g /
1, polymethyl methacrylate: a treatment solution having a composition of 40 g / l and adjusted to pH 2.5 was used. Liquid temperature 23
Chromate treatment solution at ℃ 20
By drying at 0 ° C. for 1 minute, the total amount of deposited Cr: 40 mg / m
A chromate film of No. ² was formed. A 35 mm × 35 mm test piece was cut out from the chromate-treated stainless steel plate, and the chromate film was analyzed by XRF. After immersing the same test piece in boiling pure water for 10 minutes,
The concentration was analyzed by ICP as r ⁶⁺ . The weight ratio (Cr ⁶⁺ ) / (total Cr) calculated from the analysis value was 0.1.

[Invention Example 2] The drying temperature was 230 ° C.
A chromate film was formed under the same conditions as in Inventive Example 1 except that the amount of r was changed to 25 mg / m ² . The weight ratio of this chromate film (Cr ⁶⁺ ) / (total Cr) is 0.05
Met. [Invention Example 3] The drying temperature was 180 ° C. and the total amount of Cr deposited was 1
A chromate film was formed under the same conditions as in Inventive Example 1 except that the amount was changed to 00 mg / m ² . The weight ratio (Cr ⁶⁺ ) / (total Cr) of this chromate film was 0.13. [Invention Example 4] A chromate treatment solution reduced with methanol was applied to a stainless steel plate and dried at 150 ° C for 1 minute to form a chromate film having a total Cr adhesion of 70 mg / m ² . The weight ratio of the resulting chromate film (Cr ⁶⁺⁾ / (total Cr) was 0.15.

[Conventional example] The drying temperature of the chromate film is set to 1
A chromate film was formed under the same conditions as in Inventive Example 1 except that the temperature was changed to 00 ° C. The weight ratio (Cr ⁶⁺ ) / (total Cr) of this chromate film was 0.3. Comparative Example 1 A chromate film was formed under the same conditions as in Example 1 of the present invention except that the chromate film was dried at 150 ° C. Weight ratio of this chromate film (Cr ⁶⁺ ) / (total C
r) was 0.3. Comparative Example 2 A chromate film was formed under the same conditions as in Example 1 of the present invention except that the total amount of deposited Cr was changed to 10 mg / m ² . The weight ratio (Cr ⁶⁺ ) / (total Cr) of this chromate film was 0.1. Comparative Example 3 A chromate film was formed under the same conditions as in Example 1 of the present invention, except that the total amount of deposited Cr was changed to 120 mg / m ² . Weight ratio of this chromate film (Cr ⁶⁺ ) /
(Total Cr) was 0.1.

An adhesive containing a silane coupling agent is applied to the stainless steel plate on which the chromate film has been formed, and 18
After heat treatment at 0 ° C. × 10 minutes, a rubber coating layer was provided. For the formation of the rubber coating layer, a polyol vulcanization type paint (Daiel DPA-351 manufactured by Daikin Industries, Ltd.) in which a vinylidene fluoride-fluoropropene copolymer is made into a solution is used, and the film thickness after vulcanization becomes 20 μm. And apply 20
A fluororubber film was formed by vulcanization at 0 ° C. × 1 hour. An aqueous solution containing 50% of antifreeze for automobile engines (Toyota genuine long life coolant) was heated to 120 ° C., and each rubber-coated stainless steel plate was immersed. When the immersion time reached 500 hours, the rubber-coated stainless steel plate was pulled up from the aqueous solution, and after 24 hours, the adhesion test of the rubber-coated layer was performed.

In the adhesion test, a 100 mm square cut was made with a cutter knife at an interval of 1 mm to reach the base steel, a pressure-sensitive adhesive tape was attached, and then the pressure-sensitive adhesive tape was forcibly peeled off. After peeling off the pressure-sensitive adhesive tape, the state of peeling of the rubber coating layer was observed, and the number of peeled was counted as the peeling degree (%).

In the workability test, a test piece was used in which a chromate film was formed in the same procedure as in Invention Example 1 and then a fluororubber film was formed so that the film thickness after vulcanization was 5 μm.
In addition, since the appearance of the chromate film coated with fluororubber cannot be directly observed, the phenomenon of adhesion to rubber due to cracking or powdering that occurs in the film during close contact bending was used as an index of workability. The test piece was tightly bent to 0 t so that the rubber coating layer was on the outside, and a pressure-sensitive adhesive tape was attached to the processed portion, and then the pressure-sensitive adhesive tape was forcibly peeled off. After peeling of the pressure-sensitive adhesive tape, the presence or absence of peeling of the rubber coating layer was confirmed. The workability was evaluated as ○ when no peeling was observed in the rubber coating layer, and as × when partial peeling occurred.

As can be seen from the test results in Table 1, in the example of the present invention in which a chromate film having a weight ratio (Cr ⁶⁺ ) / (total Cr) of 0.2 or less was formed, the degree of peeling was 5% or less. This indicates that the adhesion of the rubber coating layer is significantly improved as compared with the conventional example and Comparative Example 1. Weight ratio (Cr ⁶⁺ ) /
Even if (total Cr) is 0.2 or less, the total amount of deposited Cr is 10
In Comparative Example 2 as low as mg / m ² , the effect of the chromate film on the improvement in adhesion was not sufficient. On the other hand, in Comparative Example 3 in which a large amount of a chromate film having a weight ratio (Cr ⁶⁺ ) / (total Cr) of 0.2 or less was adhered, cracks occurred in the chromate film during close contact processing. Was bad.

[0019]

[0020]

As described above, in the present invention, a stainless steel plate is used as a base material, and the ratio of a trivalent chromium component is increased as compared with a chromate film provided on a conventional coated steel plate. By relatively suppressing the ratio of the valent chromium component, the adhesion of the rubber coating layer in contact with the engine coolant to the gasket substrate is maintained at a high level for a long time. Therefore, it is used as a gasket for a cylinder head of an automobile engine having excellent sealing properties and durability while utilizing the excellent corrosion resistance inherent in stainless steel.

Continued on the front page (72) Inventor Tetsuo Sakai 7-1 Takaya Shinmachi, Ichikawa-shi, Chiba F-term (reference) in Nisshin Steel Ichikawa Works 3J040 BA07 EA25 EA27 EA43 EA46 FA02 FA05 HA06 HA07 HA17 4K026 AA04 AA21 BA03 BA06 BA07 BA12 BB08 BB10 CA13 CA17 CA18 CA20 CA23 CA39 DA02 DA03 DA11 EA08

Claims (4)

[Claims] (1) The weight ratio of (Cr ⁶⁺ ) / (total Cr) is 0 to 1.
A gasket stainless steel sheet having a chromate film having a total Cr adhesion amount of 20 to 100 mg / m ² at 0.2 on at least a part of the surface of a stainless steel base material and having an excellent effect of preventing the rubber coating layer from lowering adhesion. 2. The stainless steel plate for a gasket according to claim 1, wherein the chromate film contains at least one of phosphate, silica, and acrylic resin. 3. The weight ratio of (Cr ⁶⁺ ) / (total Cr) is from 0 to 3.
A chromate film having a total Cr adhesion of 20 to 100 mg / m ² at 0.2 is formed on at least a part of the surface of the stainless steel base material, and a rubber coating layer is formed via the chromate film. Stainless steel gasket. 4. The gasket made of a stainless steel sheet according to claim 3, wherein the chromate film contains one or more of phosphate, silica and acrylic resin.