JPS62102183A - Electromagnetic wave shielding 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 [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 when manufacturing a plastic molded article.

[Conventional technology]

In order to prevent the electromagnetic waves generated by various electrical or electronic devices from having a negative effect on other devices, and to prevent them from being interfered with by external electromagnetic waves, it is necessary to shield the cabinets of these devices from electromagnetic waves.

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 a conductive substance, such as metal fibers or aluminum flakes, into a plastic material and molding it. Addition of conductive substances impairs the formability of the material,
It is not easy to reduce the strength of the product and obtain a sufficient electromagnetic wave shielding effect, and the appearance of the resulting product cannot be said to be 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 in the "kneading method" described above, it requires a painting process and There are problems in terms of shedding of the film, reliability of the long-term performance of the coating film, and furthermore, in terms of cost.

As an electromagnetic wave velocity W&layer forming method that improves these points, the applicant proposed the use of an electromagnetic wave shielding sheet. This method uses a sheet in which a plastic conductive layer containing a conductive substance and a heat-sensitive adhesive layer are sequentially laminated on a plastic base sheet, and the sheet with the conductive layer is placed on the surface at the same time as the cabinet is formed. It is integrated and provides electromagnetic wave shielding ability.

Although this technology is useful, there is still room for improvement in terms of physical properties. This is because when forming a cabinet using the sheet, the adhesion between the base sheet and the conductive layer tends to decrease due to elongation, thermal strain, pressure, etc. that the sheet receives.

[Problems to be solved by the invention]

Therefore, the present invention aims to solve the problem that the adhesion between the base sheet and the conductive layer decreases due to elongation, thermal distortion, pressure, etc. that the sheet receives when molding a cabinet. .

Means for Solving Problem C] The present invention is directed to an electromagnetic wave device characterized in that a heat-resistant primer layer and a plastic conductive layer containing a conductive substance are sequentially laminated on a plastic base sheet. "Shielding sheet"
” is the gist.

As shown in FIG. 1, the electromagnetic wave shielding sheet 1 of the present invention has a heat-resistant primer N
3, and conductive J! 14 are sequentially stacked.

In addition to the structure shown in FIG. 1, the electromagnetic wave shielding sheet shown in FIG. 2 has an adhesive layer laminated on the conductive layer side.

(Plastic base material sheet) As the plastic base material sheet 2, one is selected that can undergo necessary deformation during molding of cabinets and the like, typically vacuum or pressure molding.

Specific examples include polyvinyl chloride, polyamide, polyvinylidene chloride, polyethylene terephthalate, polyethylene, polypropylene, polyurethane, polyvinyl alcohol, polycarbonate, cellulose, acetate, polystyrene, polyphenylene oxide, modified polyphenylene oxide, acrylic, ABS resin, and AS.
It is made of one kind or a mixture of two or more kinds of plastics such as resin and polyimide.

Usually, among the above, polyvinyl chloride, ABS resin, polystyrene, and polycarbonate are often used in consideration of the resin used for molding such as injection molding, but when a high degree of heat resistance is required. It is best to use polyphenylene oxide resins such as polyphenylene oxide, modified polyphenylene oxide, etc. If polyphenylene oxide resins are used, they will have flame retardancy, heat resistance, self-extinguishing properties, dimensional stability,
It has excellent moldability, can be made lightweight, and is also advantageous in terms of economy.

The thickness of the plastic base sheet 2 is 0.1 to 1.5 mm, depending on the conditions of use. Om m is appropriate.

It is preferable to subject the plastic base sheet 2 to a corona discharge treatment, an ozone treatment, or a flame treatment in order to improve the adhesion with the heat-resistant primer layer 3 described below.

If desired, the plastic base sheet 2 may be colored or printed on the side opposite to the heat-resistant primer layer 3, or may be embossed in a pattern, or may be processed by a combination of ■ and ■ to improve its appearance. It may be improved.

(Heat-resistant primer layer) The heat-resistant primer layer 3 is provided to improve the adhesion between the plastic base sheet 2 and the conductive layer 4.

As the material for the heat-resistant primer layer 3, thermoplastics with high heat resistance, thermosetting plastics, rubber, or the like can be used. Also, these materials! [Since the sheet to be shielded usually undergoes a forming process such as vacuum forming or pressure forming, it is preferable that the sheet is easily stretchable at the forming temperature.

Specific examples of thermoplastics with high heat resistance include acrylic, vinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl formal, polyvinyl chloride, polyamide, polyimide, polyvinylidene chloride, polyvinyl methyl ether, polybutene, and ethylene. /vinyl acetate copolymer, polyester acrylate, etc.

Here, the degree of heat resistance of the thermoplastic plastic is good as long as it does not melt at the temperature of the resin injected during injection molding.

When forming a heat-resistant primer layer using a thermoplastic, if the thermoplastic can be dissolved in the ink or paint used to form the conductive layer described below, the heat-resistant primer layer and the conductive layer must be combined. However, they may become compatible with each other near the interface, resulting in a decrease in the conductivity of the conductive layer. However, on the other hand, compatibilization also contributes to improving the adhesion between both layers, so it is not something that should be avoided. It is a good idea to consider this point.

Examples of thermosetting plastics forming the heat-resistant primer layer include urea, melamine, phenol, resorcinol, xylene, furan, epoxy, polyurethane, polyisocyanate, and unsaturated polyester.

These thermosetting plastics are superior to thermoplastic plastics in terms of adhesion, and are also superior in that heat resistance and elongation during molding can be selected at appropriate levels.

Among them, when using polyurethane, it has particularly excellent adhesion and heat resistance, and when forming a heat-resistant primer layer, the reaction rate can be freely controlled by selecting the main agent and curing agent, so it is easy to use when forming the layer. Usable life of paint (
There is an advantage in that the balance between the curing time (generally proportional to the time required for curing) and the curing time can be appropriately selected.

Another material used to form the heat resistant primer layer is rubber.

Specific examples include chlorinated rubber, SBR, NBR, MBR, nitrile rubber, chloroprene rubber, neoprene rubber, polysulfide rubber, and the like.

The above-mentioned thermoplastic plastics, thermosetting plastics, and rubbers may be used in combination with each other. Examples of mixtures include a combination of polyurethane resin and acrylic resin, and a combination of polyurethane resin and chloroprene rubber.

The heat-resistant primer layer 3 may be formed to have a thickness of about 1 μm to 0.3 mm, and usually has a thickness of 2 μm to 20 μm. When it is necessary to give the heat-resistant primer layer some rubber-like properties to make it durable against shearing forces,
20I is preferably 1 m to 0.2 mm.

(Conductive layer) Conductive N4 includes copper, nickel, 1 layer,
Powders such as carbon fiber, graphite, and aluminum are used alone or in combination.

The plastic that serves as the binder for the conductive material powder is selected in consideration of the suitability for coating with ink or paint made by mixing the powder. In general, acrylic resins and urethane resins have good heat resistance and elongation, so
It can be said to be optimal. The mixing ratio of the conductive substance and the plastic binder is selected depending on the conductivity (or resistivity) and other desired properties. From the viewpoint of coating suitability and storage suitability of the ink, the conductive substance in the composition should be 30 to 80%.
% (by weight), the conductive ink coating obtained by mixing the powder of the conductive substance with the plastic binder can be used for printing or printing such as gravure, gravure reverse, roll coating, flow coating, silk screen coating, etc. This can be done using coating technology. Apply two or more coatings if necessary to obtain the desired electromagnetic shielding ability.

(Adhesive layer) The adhesive layer 4 shown in FIG. 2 is a layer for adhering the conductive layer 4 to the surface of the plastic molded product, and an adhesive layer suitable for each material is selected. Commonly useful materials include polyvinyl chloride, polyamide, acrylic, polyvinyl acetate, polyurethane, polyvinyl alcohol, polyimide,
Cellulose acetate, etc. Formation of this layer can be performed by 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 having 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 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 such as performing preforming in an injection mold, for example.

[Action/effect of the invention]

Since the electromagnetic wave shielding sheet of the present invention has the above-mentioned structure, the adhesion between the plastic base sheet and the conductive layer, which was difficult to get acquainted with in the past, is improved, and the adhesion is reduced due to the heat during molding. It also avoids the disadvantage of insufficient adhesion in the combination of plastic base sheet and conductive material, which was not a problem with conventional painting methods, due to thermal distortion caused by the difference between mold temperature and resin temperature during molding. In the molded product obtained using the electromagnetic wave shielding sheet of the present invention,
The electromagnetic wave shielding sheet does not lift or peel off from the molded product.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views showing typical examples of the electromagnetic wave shielding sheet of the present invention. l...Plastic base sheet 2...
...Heat-resistant primer layer 3...Conductive layer 4...Adhesive layer

Claims (3)

[Claims] (1) An electromagnetic wave shielding sheet characterized in that a heat-resistant primer layer and a plastic conductive layer containing a conductive substance are sequentially laminated on a plastic base sheet. (2) The electromagnetic wave shielding sheet according to claim 1, wherein the heat-resistant primer layer is made of polyurethane resin or rubber. (3) Claim 1, characterized in that the plastic base sheet is a polyphenylene oxide resin.
The electromagnetic wave shielding sheet according to item 1 or 2.