JPS6241011A - Process of electromagnetic wave shield molding - Google Patents

Abstract

PURPOSE:To manufacture a plastic molding having conductive bed integrally by preliminary preforming the base sheet by means of vacuum or compressed air according to the shape of product, painting the conducting paint inside of the product to be molded, and injection molding the molten plastic in the injection mold. CONSTITUTION:The ABC resin sheet of 0.6mm thickness is preformed in vacua, inside of which the paint mixture of copper dust and acrylic resin binder is sprayed to form a conductive bed of 50mu thickness. After being dried up, the molded conductive base sheet is placed in the injection mold, and ABC resin is injection molded in the cavity to produce an electromagnetic wave shield molding product. This molding product has the conductive bed not likely to peel or fall off, and is of a good capability of electromagnetic wave shielding. The said process can provide the conductive bed 2 having a uniform thickness and maintain a good contact of conducting particle in the bed. The conductive bed 2 is placed between the plastic bed 3 and the conductive bed 2 or the base sheet 1, which eliminates the peeling or falling off of conductive bed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a method for efficiently manufacturing a molded product with excellent electromagnetic shielding properties.

[Prior art 1] In order to prevent the electromagnetic waves generated from various electrical or electronic devices from having a negative effect on other devices, and to prevent interference from external electromagnetic waves, the cabinets of these devices must be shielded from electromagnetic waves. There is a need to.

When manufacturing cabinets from plastic, conductive paint is applied to the surface of the plastic molded product for the purpose of shielding electromagnetic waves. However, painting is problematic because of the influence of the solvent on the molded product, and it is also necessary to apply a top coat to prevent the applied conductive paint from peeling off and to improve the aesthetic appearance.

As a technology that solved the problem of solvents, a method was proposed in which a conductive coating was applied to the surface of the molding die and then plastic injection molding was performed to manufacture a housing with the conductive coating fused to the surface. (Japanese Patent Application Laid-Open No. 59-90994).

However, this method has drawbacks such as low working efficiency, the risk of peeling off and falling off because the conductive layer is exposed on the surface, and poor appearance.

The applicant uses a base sheet as a protective layer for the conductive coating, coats it with conductive paint, and places it in a mold.
We developed a technique to obtain a plastic molded product by deforming the base sheet and the conductive paint layer by vacuum/pressure forming and then injection molding them into one piece.

However, in areas where the molded product has a large elongation, the specific resistance of the conductive layer tends to be higher than when it is painted, and it has been experienced that advanced technology is required to obtain the expected shielding performance.

[Problems to be Solved by the Invention] An object of the present invention is to eliminate the drawbacks of the prior art and provide a method for efficiently manufacturing a plastic molded product with reliable electromagnetic shielding performance.

Structure of the Invention [Means for Solving the Problems] As shown in FIG. 1, the method for manufacturing an electromagnetic shielding molded product of the present invention is to form a base sheet 1 into a molded product by vacuum and/or pressure forming. The base sheet preform is preformed into a shape according to its shape or external shape, and as shown in FIG. 2, a conductive paint is applied to the inner surface of the base sheet preform, and as shown in FIG. By injection molding molten plastic within the mold, a plastic molded product having an integral conductive layer 2 is obtained, as shown in FIG.

The base sheet is selected to be sufficiently deformed during preforming and to have the necessary heat resistance for injection molding.
Specific examples include polyvinyl chloride, nylon, polyvinylidene chloride, polyethylene terephthalate, polyethylene, polypropylene, polyurethane, polyvinyl alcohol, polycarbonate, acetate, polystyrene, polyphenylene oxide resin, acrylic resin, and AS.
It is a plastic film or sheet made of resin, ABS resin, PPO resin, modified PPO resin, polyimide, etc. Preferred among these are nylon, polyvinylidene chloride, polypropylene and ABS resin. The appropriate thickness of the film is 0.02 to 0.8 #, and is selected from this range depending on the conditions of use.

As the conductive paint, a mixture of metal powder such as carbon black, graphite, silver, copper, or nickel, an acrylic or urethane binder resin, an auxiliary agent, and a solvent is used. A conductive layer is formed by applying this paint by spraying or other means.

The injection molded plastic layer is made of ABS, acrylic,
It is formed using thermoplastic resins such as polycarbonate, polyimide, polyvinyl chloride, polyethylene, polystyrene, polypropylene, and polyacetal.

Since the conductive layer is generally black or a dark color close to black, if this is not desirable due to the design requirements of the molded product, it is desirable to provide an appropriate decorative layer on the surface. For this purpose, a decorative layer may be provided on the surface of the base sheet.
Makeup can be optional, such as printing a pattern.

In another modification, after injection molding is performed with a release layer 4 provided between the base sheet 1 and the conductive layer 2,
It is possible to use a transfer method in which the base sheet 1 is peeled off. The obtained product has a cross-sectional structure as shown in FIG. In this case, a decorative layer or an insulating layer may be provided between the release layer and the conductive layer, if necessary. Of course, the base sheet may be used without being peeled off and left as it is.

In consideration of the adhesion between the base sheet 1 and the conductive layer 2, the materials for the release layer 4 provided when the transfer method is adopted include polymethacrylic acid ester, polyvinyl chloride, polyvinylidene chloride, chlorinated rubber, polystyrene, Choose from As resin, ABS resin, etc.

If sufficient adhesion between the conductive layer and the plastic layer is desired, it is preferable to provide a layer of adhesive on the surface of the former and perform injection molding.

This adhesive is selected from resins such as polyvinyl chloride, nylon, acrylic resin, polypropylene, polyurethane, polyvinyl alcohol, polyimide, and acetate.

The above explanation is for the case where there is a conductive layer on the front side of the plastic layer of the injection molded product, but there may be a conductive layer on the back side, and such cases are of course included in the present invention. be.

[Function] When we investigated cases where the shielding performance was low in the electromagnetic shielding molded products manufactured using the technology developed earlier, we found that one of the findings was that the conductive paint decoy was strongly stretched during molding and became thin. It turned out to be the cause. In addition, conductive paints do not have good moldability, and when the paint film is stretched during molding, the conductive particles lose contact with each other, increasing the specific resistance, which is another cause of deterioration in shielding performance. It turned out to be.

According to the method for manufacturing an electromagnetic shielding molded product of the present invention, it is possible to make the thickness of the conductive layer 2 uniform and to maintain good contact between the conductive particles in the layer. Since the conductive layer 2 is located between the base sheet 1 or the release layer 4 and the plastic layer 3, the conductive layer 2 is not peeled off or worn out.

In a preferred embodiment, by providing a decorative layer on the surface of the base sheet, it is possible to obtain a molded article with an excellent design. It is also possible to use the transcription method,
In that case, by providing a decorative layer or an insulating layer between the release layer and the conductive layer, a molded article with excellent design and excellent insulation properties can be obtained.

[Example] A sheet of ABS resin with a thickness of 0.68 mm was preformed by vacuum forming, and a paint made by mixing copper powder with an acrylic resin binder was sprayed on the inner surface of the sheet to form a sheet with a thickness of 50 μm.
A conductive layer was formed. After drying, this molded conductive base sheet is placed in an injection mold and A is placed in the cavity.
BS resin was injection molded to obtain an electromagnetic shield molded product.

The obtained molded product exhibited good electromagnetic shielding performance with no peeling or falling of the conductive layer.

Effects of the Invention In the method for producing an electromagnetic shielding molded product of the present invention, the preforming of the sheet and the application of the conductive paint are performed separately from the injection molding, and the injection mold can be used only for injection molding. , which is more productive than known techniques of applying conductive paint to molds. The product has a uniform conductive layer thickness and low specific resistance, ensuring reliable electromagnetic shielding performance. Since the conductive layer is protected by a base sheet or a peeling cylinder, there is no peeling or falling off, good i'l abrasion resistance, and shielding performance is maintained for a long time.

In a preferred embodiment, by providing a decorative layer on the surface of the base sheet, it is possible to obtain a molded article with excellent design. In a modified embodiment, a transfer method can be used. In this embodiment, by providing a decorative layer or an insulating layer between the release layer and the conductive layer, a molded article with excellent design and excellent insulation properties can be obtained.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views for explaining the manufacturing process of the electromagnetic shielding molded product of the present invention, in which FIG. 1 shows a preformed base sheet, and FIG. A conductive layer is provided on the inner surface of the base sheet, and FIG. 3 shows a base sheet having a conductive layer placed in a mold. FIG. 4 is a sectional view of an electromagnetic shield molded product manufactured by the method shown in FIGS. 1 to 3. FIG. 5 is a sectional view similar to FIG. 4, showing another example of the electromagnetic shielding molded product of the present invention. 1...Base material sheet 2...Conductive layer 3...Plastic layer 4...Peeling layer 5...Injection mold patent applicant Dainippon Printing Co., Ltd. agent Patent attorney Sou Suga Canister 1 Figure 2 Figure 311 Figure 4

Claims (5)

[Claims] (1) Preforming the base sheet into a shape according to the internal or external shape of the molded product by vacuum and/or pressure forming,
Apply conductive paint to the inner surface of the base sheet preform,
1. A method for producing an electromagnetic shielding molded product, which comprises obtaining a plastic molded product integrally having a conductive layer by placing the molten plastic in an injection mold and injection molding the molded product. (2) The method according to claim 1, which is carried out using a base sheet provided with a decorative layer on the surface. (3) The method according to claim 1, wherein a release layer is provided between the base sheet and the conductive layer, and the base sheet is peeled off after injection molding. (4) The method according to claim 3, which is carried out by providing a decorative layer or an insulating layer between the release layer and the conductive layer. (5) The method according to any one of claims 1 to 4, which is carried out by providing an adhesive layer on the surface of the conductive layer that contacts the plastic body.