JPH06155479A - Rubber molding die - Google Patents

Abstract

PURPOSE:To improve corrosion resistance and mold release property of a die with respect to rubber by layering in sequence Ni film, NiP film, and NiSn film at a part with which rubber in a rubber molding die comes in contact. CONSTITUTION:On a metal surface from which oxide film is removed, an Ni film having a thickness of 1-10mum is formed by ordinary electric plating. For a second layer, an NiP film of 1mum or above is formed by electroless plating. For a third layer, an NiSn film having excellent corrosion resistance and mold release property with a thickness of 1-50mum is formed by the electric plating. Thereafter, it is treated with heat for raising the hardness. In this die, the whole film holds a high adhesion to a parent material by the Ni film, the NiP film heightens the adhesion to the Ni film and holds the hardness of the NiSn film of the third layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to ethylene / propylene / diene / methylene rubber (hereinafter referred to as EPDM), isobutylene / isoprene rubber (hereinafter referred to as IIR), polyisobutylene rubber, natural rubber, styrene / butadiene rubber (SBR), The present invention relates to a rubber molding die that is used for molding rubber such as chloroprene rubber (CR) and nitrile rubber (NBR) and that has excellent corrosion resistance and releasability.

[0002]

Rubbers are widely used mainly in the fields of automobiles such as hoses, weather strips, sealing materials, vehicle parts such as bellows, general belts, tires and tubes.

Molds for molding parts for these various uses are made of iron, stainless steel or the like, and the surface treatment is usually performed by industrial chrome plating. This industrial chrome plating is applied to improve the wear resistance, corrosion resistance, heat resistance, releasability, etc. of the surface of iron, stainless steel or the like.

[0004]

However, when molding rubber, the durability is insufficient only by applying the industrial chrome plating to the inner surface of the mold. In particular, when molding EPDM, sufficient performance cannot be obtained in terms of corrosion resistance and releasability. If the corrosion resistance is low, rust and dross will be generated due to corrosion, and contamination due to the deposition of compounded chemicals, non-rubber components in the polymer, etc. will cause unsatisfactory release properties.
Since these are factors that directly affect the quality of rubber products and productivity, their solution is strongly desired.

As a conventional solution to mold contamination, a fixed amount of molding is performed by solvent cleaning or mechanical removal of chemicals adhering to the inner surface of the mold and non-rubber components in the polymer. You are dealing with it in a complicated way. Further, the mold releasability is dealt with by using a mold release agent, but there have been problems that it takes time and labor, productivity is lowered, mold cooling and defective products occur.

The inventors of the present invention have found that the mold for molding rubber has a corrosion resistance of the mold in view of a decrease in productivity and an increase in defective products.
Considering that there is a point that must be improved in terms of releasability, as a result of intensive studies, it was found that the formation of the NiSn alloy film is extremely excellent in terms of corrosion resistance to rubber and releasability. The present invention has been made based on the above findings, and an object of the present invention is to provide a rubber molding die having excellent corrosion resistance, releasability and the like.

[0007]

A rubber molding die of the present invention has a Ni film as a first layer, a NiP film as a second layer, and a NiSn layer as a third layer, in a portion of the rubber molding die that comes into contact with rubber. It is characterized in that the films are formed in layers.

[0008]

In the rubber molding die of the present invention, the Ni film keeps high adhesion to the base material as a whole by the Ni film, and the NiP film covering the Ni film strengthens the adhesion to the Ni film.
It is used as the third layer and has the function of assisting the hardness of the NiSn film that exhibits corrosion resistance and release properties against rubber.

[0009]

EXAMPLE An example of the rubber molding die of the present invention will be described below. Metals such as iron and stainless steel are used as the base material of the rubber mold, and an oxide film is formed on the surface of these metals. The oxide film is removed by washing with hydrochloric acid or the like. On the surface of the metal from which the oxide film has been removed, a Ni film is formed by ordinary electric Ni plating.

The Ni coating is used for the coating formed by the subsequent surface treatment to maintain the adhesion to the base material. The thickness of this Ni film is 1 to 10 μm,
Particularly, 1 to 5 μm is preferable. Ni film thickness is 10 μm
If it exceeds the range, a film having a non-uniform thickness is formed and unevenness is formed on the surface of this film, which is not preferable.

A NiP film is formed on the second layer by electroless plating. This NiP layer is coated with a uniform film thickness on the surface of the mold having a complicated shape because of the electroless plating method. The NiP film is excellent in corrosion resistance and has a Vickers hardness (hereinafter referred to as HV) of 600 to 700, so that it is also excellent in abrasion resistance. The NiP layer preferably has a thickness of 1 μm or more, particularly 5 μm or more. If the thickness is less than 1 μm, it does not help to maintain the hardness at 500 or more at HV.

Then, as a third layer, a NiSn film having excellent corrosion resistance and releasability is formed by electroplating. This N
The thickness of the iSn coating is preferably 1 to 50 μm, and particularly 10 to
30 μm is preferable. The NiSn coating is subjected to a heat treatment at 100 to 500 ° C. for 1 to 2 hours after the electroplating treatment to increase the hardness. The temperature for increasing the hardness of NiSn is preferably 400 to 500 ° C., but if the heat treatment temperature is not set below the tempering temperature of the material of the die base material, the die base material may be deformed. Therefore, it is suitable to set the heat treatment temperature to around 200 ° C. in order to maintain the precision of the mold itself.

Examples 1 and 2 and Comparative Examples 1 to 6 For evaluation of releasability, EPDM (two kinds of sponge type and solid type) was used, and NiSn film, chrome plating film (20 μm), and electroless NiP were used. Plating (20μ
m) and a Ti film (2μ by the ion plating method)
The result of the rubber adhesion test with m) is the sponge type E
The results of PDM are shown in Table 1 as Example 1 and the results of solid type EPDM are shown in Table 2 as Example 2.

[0014]

[Table 1]

[0015]

[Table 2]

Here, as a rubber adhesion test method, FIG.
As shown in, a pair of test pieces T1, T
2 is prepared for each film. These test pieces T
1 and T2 are composed of an iron plate as a base material and the respective coatings formed on the surface of the iron plate. Then, with the coating of the test piece T1 facing upward, the test piece T1
Place on a workbench. An unvulcanized rubber S mixed with a predetermined amount is placed on the upper surface of the film of the test piece T1.
The test piece T2 is placed on the upper surface of the unvulcanized rubber S with the coating of the test piece T2 facing downward. For this reason,
The unvulcanized rubber S is sandwiched between the films of the test pieces T1 and T2.

Then, with the unvulcanized rubber S sandwiched between the test pieces T1 and T2, the unvulcanized rubber S is put into a drying oven, and the unvulcanized rubber S is held at 200 ° C. for 30 minutes. And vulcanized. After vulcanization, the rubber S is air-cooled for 2 minutes, one test piece T1 is fixed to a workbench, and the other test piece T2 is pulled up by the spring 1 only. The tensile force (kgf) when the rubber S is peeled off from the other test piece T2 is measured, and the value obtained by dividing the measurement result of this tensile force by the adhesion area (cm ³ ) of the rubber S is shown in Tables 1 and 2. Adhesiveness of This operation is repeated 10 times for each film, and the adhesive force of rubber is calculated. Here, "impossible" means that the adhesive force of the rubber is strong (the adhesive force is 0.7 or more) and the film on the test piece T1 is peeled off from the iron plate.

On the other hand, the color of the test piece T2 before vulcanization and after 10 vulcanization operations is measured by a color meter, and the degree of discoloration before and after vulcanization is calculated by the following color difference formula. here,
ΔE ^* is a color difference, L ^* is a lightness index, a ^* and b ^* are chromatic indices, X, Y, and Z are tristimulus values, and Xn, Yn, and Zn are standard light values. And the tristimulus values in the double visual field. ΔE ^* = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ] ^1/2 L ^* = 116 (Y / Yn) ¹ / 3-16 a ^* = 500 {(X / Xn) ¹ / 3- (Y / Yn) ^1/3 } b ^* = 200 {(Y / Yn) ¹ / 3- (X / Xn) ^1/3 }

As shown in Tables 1 and 2, in Comparative Example 1 showing the results of the test piece having the surface plated with chromium,
Although the amount of rubber adhered is small and the mold releasability is excellent, the adhesive force of the rubber increases and the releasability of the rubber deteriorates as the number of molding times of the rubber increases. Therefore, the frequency of cleaning the surface of the mold increases.

In Comparative Example 2 showing the result of the test piece having the surface coated with the NiP film by electroless plating, the rubber adheres firmly to the surface of the test piece even if the rubber is molded several times. Then, sulfuration by the sulfur compound contained in the rubber vulcanizing agent and nickel ammonia attacked by urea ammonia gas resulting from the foaming agent and the foaming auxiliary agent cause the test pieces T1 and T2 to change color to black, and the test pieces T1 and T2 are vulcanized 10 times. After the sulfurization operation, the color changes to black.

In Comparative Example 3 showing the results of a test piece having TiN ion-plated on its surface, the mold releasability is preferable when the rubber is vulcanized several times, but the test piece T1 is tested when it is exceeded several times. The rubber adheres to the test piece T1 and cannot be removed from the test piece T1. Then, the surface of the test piece T1 is discolored from gold to true black due to the sulfurization or thermal oxidation of the rubber, and the surface of the test piece T1 is corroded. Further, with ion plating, a thick film cannot be formed, and pitting corrosion easily occurs on the test piece T1.

Example 3 and Comparative Examples 7 to 9 For the evaluation of releasability, chloroprene (neoprene) rubber was used to form each film as in Examples 1 and 2, and a rubber adhesion test for each film was performed. The results are shown in Table 3 as Example 3. Here, when using chloroprene rubber, since this chloroprene rubber has a structure containing chlorine, the mold is easily corroded during vulcanization.

[0023]

[Table 3]

As shown in Table 3, the nickel type has excellent corrosion resistance to chlorine ions, but the chromium type as shown in Comparative Example 7 has low acid resistance and the die life is shortened. For this reason, the NiSn film has excellent mold releasability and corrosion resistance even with respect to chloroprene rubber, so that the life of the mold can be extended.

Examples 4 to 6 and Comparative Examples 10 to 12 For the evaluation of releasability, EPDM without addition of a release agent, IIR,
A weather strip was molded using natural rubber, and the number of continuous moldings until the adhesion of dust was observed was measured. The measurement was performed on 5 samples, and the average value of the 5 samples is shown in Table 4.

[0026]

[Table 4]

As shown in Table 4, the die having the NiSn film coated on the surface has a larger number of continuous forming times for any rubber than the die having the surface plated with chromium. For this reason,
The work of cleaning the mold is reduced.

Example 7 Using a weatherstrip molding die, a die in which a Ni film as a first layer, a NiP film as a second layer, and a NiSn film as a third layer were respectively laminated at a portion in contact with rubber was used. , EPD
Using M, continuous molding was carried out at a mold temperature setting of 175 ° C. and a vulcanization time of 3 minutes (about 120 shots per day). It was 35 days until the release agent was first applied but not replenished, good release property was maintained, and rubber adhesion and stain (discoloration) occurred. Comparative Example 13 Example 4 except that a metal mold plated with industrial chrome was used.
However, it was necessary to frequently apply a mold release agent to the mold to restore the mold releasability. Rubber adhesion and contamination started to occur from around 10 shots, and the mold had to be cleaned every day.

[0029]

As described above, according to the mold for rubber molding of the present invention, the corrosion resistance and the releasability are greatly improved as compared with the conventional mold, and the productivity of the rubber molded product is improved. It is possible to improve, the defective rate of the rubber molded product can be reduced, and the workability of rubber molding can be improved. In addition, the amount of release agent used can be greatly reduced. Therefore, it is possible to exert an effect of greatly contributing to the field of rubber molding.

[Brief description of drawings]

FIG. 1 is a front view showing a rubber adhesion test method.

Claims (1)

[Claims] 1. A Ni film is formed on the first layer, a NiP film is formed on the second layer, and a Ni layer is formed on the third layer, at a portion of the rubber molding die which comes into contact with the rubber.
A rubber molding die, characterized in that Sn films are laminated.