JPS61209153A - Electromagnetic-wave shield sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

R-plate Gogatsuto

[Industrial application field]

The present invention relates to an electromagnetic wave shielding sheet for forming a layer having electromagnetic wave shielding ability on the front or back surface of a molded product when manufacturing a plastic molded product.

[Conventional technology]

In order to prevent the electromagnetic waves generated by various electric or electronic devices from having a negative effect on other devices, and to prevent interference from external electromagnetic waves, it is necessary to electromagnetically shield the cabinets of these devices. When manufacturing cabinets from plastic, the methods that have been tried in the past to shield electromagnetic waves are mainly the "kneading method" and the "painting method." The "kneading method" involves kneading and molding a conductive substance, such as carbon powder or aluminum flakes, into a plastic material. Addition of a conductive substance impairs the moldability of the material and reduces the strength of the product, and it is difficult to obtain a sufficient electromagnetic wave shielding effect. The appearance of the molded product is also not good. The "painting method" applies a paint containing powdered conductive material to the surface of the molded product, and although it solves the problems inherent to the above-mentioned kneading method, it requires a painting process, and the molded product In order to improve the appearance of the product, it is necessary to apply a finishing coat and apply a decorative sheet. As a method for forming an electromagnetic shielding layer that improves these points, the applicant proposed the use of a transfer sheet (Japanese Unexamined Patent Publication No. 59-136).
No. 998). This method uses a transfer sheet in which a plastic electrically insulating layer, a plastic conductive layer containing a conductive material, and a heat-sensitive adhesive layer are sequentially laminated on a plastic base film, and conducts electricity at the same time as the cabinet is formed. A layer is integrated into its surface to provide electromagnetic shielding capability. Although this technology is useful, there is still room for improvement in terms of cost. This is because, in manufacturing the above-mentioned sheet, the material cost of the conductive layer laminated on the entire surface of the base film accounts for a large proportion of the cost, and on the other hand, even if the conductive layer is formed on the entire surface of the base film, This is because the conductive layer is rarely used in its entirety, and the conductive layer does not necessarily have to be in the form of a plane, and even if it is in the form of a mesh, it can exhibit its shielding ability. Roughly speaking, if the conductive layer is greatly stretched due to deformation during molding, there is a risk that the shielding ability of that part will be insufficient.
This measure was also required.

[Problems to be solved by the invention]

In view of the above, an object of the present invention is to provide an electromagnetic wave shielding sheet that reduces costs by minimizing the use of expensive conductive materials. Furthermore, it is another object of the present invention to provide an electromagnetic wave shielding sheet that can ensure the shielding ability of that portion even if the conductive layer is stretched significantly during molding. Oiri Goshomi

[Means to solve the problem]

As shown in FIG. 1, the electromagnetic wave shielding sheet of the present invention is a sheet formed by laminating a plastic conductive layer 3 containing a conductive substance and a heat-sensitive adhesive layer 4 on a plastic base film 1. , the conductive layer 3 is formed on a portion of the base film by a screen printing method, as shown in FIG. The above sheet can also be formed into a transferable material,
This can be said to be a typical aspect of the present invention. FIG. 1 shows an example of this, and 2 is a peeling layer provided between the base film 1 and the conductive layer 3 for transfer. In order to prevent the electromagnetic wave shielding ability from decreasing due to the elongation caused by molding, the conductive layer may be partially formed thicker to allow for the elongation. Screen printing is the printing technique that can provide the thickest printed layer, but where necessary, multilayer screen printing of two or more layers is applied. As described above, in order to obtain electromagnetic wave shielding ability, the conductive layer does not need to be present on the entire surface, and can be formed into a mesh shape with openings corresponding to the frequency of the electromagnetic waves intended to be shielded.
An example is shown in FIG. The conductive layer is generally black or a dark color close to black, so if this is not desirable due to the design requirements of the molded product, an appropriate decorative layer 5 may be provided on the surface as shown in Figure 2. good. Makeup can be optional, such as printing a pattern. If necessary, a decorative layer 5 is placed on top of the concealing layer 6.

[For use]

In the electromagnetic wave shielding sheet of the present invention, the conductive layer is provided only in the areas necessary for shielding electromagnetic waves, whether the sheet is integrated with the base film and the molded product or is transferred. Therefore, the cost can be reduced compared to the case of using a conventional transfer sheet. This effect is particularly great when plastic containing a conductive material is printed in a mesh-like pattern. If the necessary parts of the conductive layer are printed thickly, the electromagnetic wave shielding ability will not be insufficient even if those parts are expanded significantly during molding. [Embodiment 1] The base material 1 is selected to have the necessary heat resistance and to be sufficiently deformable when molding a cabinet or the like, typically injection molding. Specific examples include plastic films such as polyvinyl chloride, nylon, polyvinylidene chloride, polyethylene terephthalate, polyethylene, polypropylene, polyurethane, polyvinyl alcohol polystyrene, polyphenylene oxide resin, acrylic resin, As resin, ABS resin, and polyimide. It is. Preferred among these are nylon, polyvinylidene chloride and polypropylene, with nylon being the best. The thickness of the film is suitably 0.02 to 0.8 m, and is selected from this range depending on the conditions of use. The material of the release layer 2 provided when forming it on the transfer sheet is as follows:
Considering the adhesion between the base film 1 and the conductive layer 3,
Polymethacrylic acid ester, polyvinyl chloride, polyvinylidene chloride, chlorinated rubber, polystyrene, As resin, AB
Selected from SIIll etc. Conductive materials used for the conductive layer include carbon black, graphite, silver, copper, nickel, stainless steel, and copper.
Silver, nickel-silver, tin oxide, aluminum, etc. can be used, and those having a specific resistance of 5×10 −3 to 9×1 Q′Ωcm are preferable. The suitable size is 50 to 300 meshes, and short fibers have the highest electromagnetic wave shielding ability, followed by flakes and particles in that order. Plastic materials containing such conductive substances include polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyethylene terephthalate, polycarbonate, nylon, acrylic resin, polyurethane, polystyrene, ABS resin, ethylene-vinycetate copolymer, and ionomer. , acetate, polysulfone, polyimide, etc. can be used. Among these, acrylic resin and urethane are superior in terms of elongation, and when heat resistance is also considered, acrylic resin is optimal. It is appropriate that the conductive substance and the above-mentioned plastic are mixed so that the former accounts for 50 to 80% by volume.
The weight ratio will be in the range of 40-90%. Guidance! The layer is formed by forming the above formulation into an ink composition and applying it to a thickness of 20 to 200 microns by screen printing. This thickness is set to a required value depending on the type and content of the conductive substance and the amount of elongation expected in each part during molding. Needless to say, the heat-sensitive adhesive layer 4 is for adhesion between the conductive layer and the plastic molded into the cabinet, etc., so it is selected to be suitable for each material. Commonly useful ones will be found among polyvinyl chloride, nylon, acrylics, polypropylene, polyurethane, polyvinyl alcohol, polyimide, acetate, and the like. Formation of this layer can be carried out according to known techniques. The electromagnetic wave shielding sheet of the present invention is typically used by a so-called "painting" technique during injection molding. In other words, a sheet with a conductive layer of a shape, size, and thickness corresponding to the shape and size of the part where electromagnetic shielding ability is to be imparted to the molded product is prepared, and the necessary preforming is performed by means such as vacuum forming. Thereafter, this is placed in a mold and injection molded into a cabinet or the like, and in the case of transfer, the base film is peeled off and a conductive layer is provided at a desired position on the molded product. In order to shorten the molding cycle, it is possible to adopt a technique in which, for example, preforming is performed in an injection mold. The electromagnetic wave shielding sheet of the present invention differs from conventional electromagnetic wave shielding layer transfer sheets in that the layer containing an expensive conductive substance is provided only in the necessary areas, resulting in waste during use. Since there is no such thing, the cost is low. This effect is even greater if the conductive layer is printed in a mesh-like pattern. If there is a part where there is a large elongation due to molding, by printing the conductive layer thicker in that part, it is possible to prevent a partial lack of electromagnetic wave shielding ability. When using a conventional sheet with a conductive layer of uniform thickness, the overall thickness must be determined for the part that will be stretched the most, and this is due to the conductive material being drilled in other parts. It means waste. By providing a decorative layer, a decorative layer, and a decorative layer with a concealing layer if necessary, a molded product with excellent design can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a typical example of the electromagnetic wave shielding sheet of the present invention. FIG. 2 shows another example of the electromagnetic wave shielding sheet of the present invention.
2 is a sectional view similar to FIG. 1; FIG. 3 is a plan view of the sheet of FIG. 1; FIG. 1... Base film 2... Peeling @ layer 3... Conductive layer 4... Heat sensitive adhesive layer

Claims (5)

[Claims] (1) A sheet formed by laminating a plastic conductive layer containing a conductive substance and a heat-sensitive adhesive layer on a plastic base film, in which the conductive layer is printed on a portion of the base film by screen printing. An electromagnetic wave shielding sheet characterized by being formed. (2) The electromagnetic wave shielding sheet according to claim 1, which is formed to be transferable by providing a release layer between the base film and the conductive layer. (3) The electromagnetic wave shielding sheet according to claim 1 or 2, wherein the conductive layer is partially formed by multilayer screen printing. (4) The electromagnetic wave shielding sheet according to claim 1 or 2, wherein the conductive layer is printed in a mesh pattern. (5) Claim 1 in which a decorative layer is provided on the conductive layer.
Electromagnetic wave shielding sheet in item 2 or item 2.