In a product such as an oil seal, a gasket or the like in which a rubber is formed on a metal, a sufficient adhesive force can not be obtained between the metal and the rubber by forming the rubber directly on the metal. Accordingly, as shown in FIG. 8, a rubber c is formed on a metal a via an adhesive agent b such as a phenol resin or the like. Further, in the case of directly applying the adhesive agent onto the metal surface, a contact force between the metal and the adhesive agent is weak, and it is impossible to form a good adhesive layer. Then, there is executed a surface treatment for roughening the surface of the metal part before the adhesive agent is applied, in accordance with a zinc phosphate treatment to precipitate a zinc phosphate on the metal surface, a shot blast treatment to form irregularity by hitting the metal surface with hard balls, or the like. That is, in order to form the good adhesive layer, there is executed each of “the zinc phosphate treatment or the shot blast treatment (called as a preliminary treatment)”, “an adhesive agent tank dipping”, “a swishing-off and drying” and “a baking”. As a method of forming the adhesive layer, there is employed a dipping method of directly dipping a plurality of metal parts into the adhesive agent tank in the state of receiving the metal parts in a cage or the like for the reason of nature of the adhesive layer, and the metal parts is swished off together with the cage to prevent a liquid pool from being generated after drawing up the metal parts from the adhesive agent tank, and dried.
However, in the conventional metal part, the metal part and the rubber are not sufficiently adhered and an adhesive failure occurs because of the following reasons.
{circle around (1)} An adhesive area (relating to a kind of the adhesive agent (the adhesive force) though) between the metal part and the rubber is insufficient.
{circle around (2)} A physical contacting force (an anchor effect) between the adhesive layer and the metal surface (after the preliminary treatment) is insufficient.
{circle around (3)} The adhesive agent flows out from the rubber adhered portion to be insufficient, at a time of swishing off or a forming the rubber.
Further, in the conventional metal part, a certain level (magnitude) of irregularity is applied to the surface of the metal part in accordance with the preliminary treatment (the zinc phosphate treatment or the shot blast treatment) or the like for the purpose of forming the good adhesive film as mentioned above, however, it is impossible to sufficiently obtain an effect of preventing the items {circle around (1)} to {circle around (3)} mentioned above in this level of irregularity. Further, on the contrary, when the whole of the metal part is largely roughened for the purpose of obtaining an enough effect of preventing the items {circle around (1)} to {circle around (3)} mentioned above, there occurs a trouble such as a rubber leakage at a time of molding, a size failure in the metal part, a deformation of the metal part or the like, so that this method can not be employed.
Further, the zinc phosphate treatment or the shot blast treatment has been conventionally carried out as mentioned above for the method of roughening the surface of the metal part, however, it is hard to work only a specific part of the metal, and a lot of man hour is required for keeping a working accuracy (roughness) and maintaining the apparatus. Further, since an independent working step is provided, as a matter of course, a working cost and a working time are increased.
Further, in a product such as an oil seal, a gasket or the like in which the rubber is formed on the metal, the adhesive agent is coated on a surface of a metal ring corresponding to the metal part, for the purpose of adhering the metal to the rubber. As the coating method, a dipping method (in which the metal ring is dipped into the adhesive agent solution tank, thereafter dried and baked) is frequently employed due to the film nature of the adhesive agent and a working efficiency, however, when a plurality of metal rings d are simultaneously dipped into an adhesive agent solution e as shown in FIG. 9A, the metal rings d are agglutinated with each other via the adhesive agent solution e as shown in FIG. 9B. Accordingly, when executing the drying and sintering operation in this state, the metal rings d are firmly bonded to each other via an adhesive agent e′ as shown in FIG. 9C, and there occurs an bonding failure which is a so-called “two-sheet ring (two sheets of metal rings d are bonded to form one piece)”. This bonding failure frequently occurs particularly in the case that the metal ring d is in a thin and flat shape and is small.
A mechanism by which the bonding failure occurs is as follows.
{circle around (1)} The metal rings d are gathered in the adhesive agent solution e (refer to FIG. 9A).
{circle around (2)} The metal rings d are bonded to each other due to a surface tension of the adhesive agent solution e between the metal rings d overlapping with each other, at a time of drawing up the metal rings d from the adhesive agent solution e (refer to FIG. 9B).
{circle around (3)} The metal rings d are bonded to each other via the adhesive agent e′ which is solidified in the following drying and sintering step.
Against the bonding failure, there has been developed an adhesive agent by which the bonding is hard to occur, for the conventional bonding prevention measure, however, a complete countermeasure for all of the products has not been yet carried out due to the product functions.
Accordingly, a “disassembling step” of applying an impact to the metal rings d overlapping with each other so as to separate the metal rings d is added after drawing up the metal rings d from the adhesive agent solution e, and therefore, an extra man hour is required. Further, in this “disassembling step”, since a magnitude of the impact which can be applied thereto is limited (it is necessary that a magnitude of the applied impact should not be so large as the metal ring d is deformed), it is a reality that a sufficient effect can not be obtained for the metal ring d which has a thin and flat shape and is small.
The present invention is made by taking the points mentioned above into consideration, and an object of the present invention is to improve an adhesive property between a metal and a rubber, and more particularly to prevent an adhesive failure by adding a roughness (a surface roughness) within a certain level to a metal surface portion on which a rubber is formed, thereby improving an adhesive strength of the portion. Further, another object of the present invention is to make it easy to form a surface roughness on a specific part of the metal part, and to achieve an improvement of working accuracy in the surface roughness, an improvement of mold maintenance property, a reduction of working cost, a reduction of man hour and the like.
Further, another object of the present invention is to prevent an bonding failure (a so-called “two-sheet ring” phenomenon) from occurring in the work that a plurality of metal parts are simultaneously dipped into the adhesive agent solution and the adhesive agent solution is applied to the respective metal parts in the manner mentioned above.