JPH0214599A - Electromagnetic shielding sheet - Google Patents

Abstract

PURPOSE:To provide a conductive sheet with a dust-free property and an excellent lamination characteristic by establishing a hot-melt resin layer on at least one side of the conductive sheet which is obtained by making paper from material fiber blended with a specific amount of conductive fiber. CONSTITUTION:For conductive fiber, metal such as stainless steel, brass, copper or aluminum or metal fiber made of alloy of these metals, or metallized fiber, which is natural fiber, synthetic fiber or inorganic fiber plated or coated with metal and is surface treated, is desirable. For thermal molten resin, polyethylene, polypropylene, polystyrene, etc., would be nice. First, pulp, a paper reinforcing agent, an adhesive and other material are added to the conductive fiber and a conductive sheet 2 is manufactured by a wet paper manufacturing method. At this time, the ratio of the conductive fiber to be blended is 30 to 95wt.% to the obtained fiber. Then, a hot-melt resin layer 1 is established on both sides or one side of the conductive sheet. By this method, the sheet is free of exfoliation or cracking after a long time use and has an excellent lamination characteristic and a dust-free property.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electromagnetic shielding sheet that has excellent electromagnetic shielding properties and is highly flexible.

[Conventional technology]

In recent years, with the rapid development of electronic devices, electromagnetic interference has become a major problem. Various electromagnetic wave shielding methods have been developed as measures to prevent electromagnetic interference, and among these, the following methods are known as shielding methods for containing unnecessary radio waves at the electromagnetic wave generation source. (1) A method of applying conductive paint to the inner surface of the housing of an electronic device, such as a personal computer.

(2) A method of pasting a shielding material, such as metal foil, on the inner surface of the housing. (3) A method of dispersing and kneading a conductive filler in a synthetic resin to form a housing having a shielding function.

[Problems to be solved by the present invention]

However, in method 1), the shielding effect varies depending on the thickness of the coating film, and the coating film may peel off. When applying method (2) to the inner surface of the housing, it is difficult to adhere to the corners, the metal foil may peel or crack, and depending on the material, the surface may be significantly oxidized. In addition, the method (3) has the disadvantage that when injection molding the housing, the conductive filler remains in the nozzle or bent portion, making it impossible to obtain uniform shielding properties after molding.

The present inventors have conducted research in order to develop an electromagnetic shielding sheet that is dust-free, has excellent lamination processability, adhesion to the housing, and durability, and can be manufactured economically. As a result, the present invention was completed.

[Means to solve the problem]

The present invention provides electromagnetic waves in which a thermofusible resin layer is provided on both or one side of a conductive sheet obtained by paper-making using a wet papermaking method from raw material fibers containing 30 to 95% by weight of conductive fibers. This is a shield sheet.

The conductive fibers used in the present invention include metal fibers made of metals such as stainless steel, brass, copper, and aluminum, or alloys thereof, or natural fibers, synthetic fibers, inorganic fibers, etc., whose surfaces are plated or coated with metal. Fibers surface-treated with metal such as metallized fibers are preferred, and these may be used alone or as a mixture of two or more types.

Fiber diameter 2-20 μm, especially 2-12 μm, fiber length 2-20
In particular, 3 to 10 fibers are preferred.

As the heat-melting resin, for example, polyethylene, polypropylene, polystyrene, a copolymer of styrene and acrylonitrile or acrylic ester, etc. are used. Polycarbonate and ABS used in No-Using
It is preferable to use a material that has good adhesion to plastics such as resins and conductive sheets.

When producing the electromagnetic shielding sheet of the present invention, first, pulp, a paper strength enhancer, a sticky agent, etc. are added to conductive fibers, and paper is made by a wet papermaking method to produce a conductive sheet.

The amount of conductive fibers is 30 to 95% by weight based on the total fibers.
Preferably it is 40 to 70% by weight. If the compounding amount is 30% by weight without grooves, sufficient electromagnetic shielding properties cannot be obtained.
Moreover, if it exceeds 95% by weight, the bonding of the conductive fibers will deteriorate, making it impossible to obtain a conductive sheet with sufficient strength.

By providing a hot-melt resin layer on both or one side of the conductive sheet thus obtained, the desired electromagnetic shielding sheet can be obtained.

To provide the heat-melt resin layer, an extruded film of the heat-melt resin is laminated on the conductive sheet, for example, by an extrusion lamination process. By increasing the extrusion temperature of the resin, it is also possible to increase the adhesive strength between the conductive note and the hot-melt resin. The thickness of the hot-melt resin layer is not particularly limited, but is preferably about 5 to 50 μm in view of the tensile strength, adhesive strength, etc. required during processing into an adherend.

Normally, the width of the resin layer is the same as the conductive sheet, but if grounding is required depending on the location where it is pasted, narrow the width of the resin layer to expose the conductive part and make it easier to connect to the ground. You can stay there.

When a thermofusible resin layer is provided on one side of the conductive sheet,
It is preferable to provide an adhesive layer on the other surface. As the resin for the adhesive layer, for example, acrylic resin, polyimbutylene, etc. are used. The surface of the adhesive layer is preferably covered with a release paper such as polar silicone or fluororesin paper or film.

The structure of the electromagnetic shielding sheet of the present invention will be explained with reference to the drawings. Figure 1 is a longitudinal cross-sectional view of an electromagnetic shielding sheet in which a heat-melting resin layer is provided on both sides of a conductive sheet, and Figure 2 is a longitudinal cross-sectional view of an electromagnetic shielding sheet in which a heat-melting resin layer is provided on one side of a conductive sheet. It is a vertical cross-sectional view, and the symbol 1 in the figure indicates a hot-melt resin layer, 2 a conductive sheet, 3 an adhesive layer, and 4 a release paper.

〔Effect of the invention〕

The electromagnetic shielding sheet of the present invention exhibits stable and excellent electromagnetic shielding properties. Furthermore, the adhesive layer properties with the housing of an electronic device using a heat-pressing method are also good. Furthermore, since the surface is coated with heat-melting resin, the sheet does not peel or crack even after long-term use, and it remains dust-free, so it can be used in clean rooms. The electromagnetic wave shielding sheet of the present invention can be manufactured by a relatively simple method, and can be manufactured using a shielding tape,
It can also be used as bags, etc.

Example 1 Stainless steel fibers (Susmic manufactured by Tokyo Seami Co., Ltd.) with a fiber diameter of 8 μm and a fiber length of 4 were used as conductive fibers, and 50 parts by weight of the conductive fibers and natural wood pulp (NBKP) beaten to 40° 8R were used. /LBKP=i/1) 50 weight and 1 part, and then a wet paper strength enhancer (Polyfix 301 manufactured by Showa Kobunshi Co., Ltd.) was added to the pulp 1 weight. 6 and a synthetic adhesive (Acrivers, manufactured by Diafloc Co., Ltd.) were added, and wet papermaking was carried out at a basis weight of 65 and j9/m2 to produce a stainless fiber mixed paper. Next, by melt extrusion, a modified polyester copolymer (Bondfirth 1-VC-40 manufactured by Sumitomo Chemical Co., Ltd.) is fused to both sides of the stainless fiber mixed paper to a thickness of 30 μm on each side, resulting in the desired electromagnetic shielding sheet. is obtained.

The electromagnetic shielding effect of the obtained sheet was measured using TR17301 manufactured by Atopan Test Co., Ltd. A sample (145 x 145 mm) was sandwiched between a copper sample frame (2 mm thick, external dimensions 150 x 150 mm, internal dimensions 110 l, 10 x 110 mm), and the electric field and magnetic field shielding effects were measured using the attached Rondo antenna and loop antenna.Measurement of electric field shielding effect. The results are shown in Fig. 6, and the measurement results of the magnetic field shielding effect are shown in Fig. 4. The vertical axes in Figs. 3 and 4 indicate the shielding effect calculated from the following equation.

Further, the amount of wear indicating dust-free property was measured using a taper abrasion tester under the conditions of a load of 1 kg and a rotation speed of 100 times.

As a result, there was no wear at all.

Example 2 A modified polyester copolymer was fused to a thickness of 30 μm on one side of the same stainless fiber mixed paper as in Example 1, and then
A double-sided adhesive tape (manufactured by Nitto Denko Corporation, A597) was attached as an adhesive sheet to the opposite side to prepare an electromagnetic shielding sheet. The electromagnetic shielding effect and amount of wear of the obtained sheet were similar to those of the sheet of Example 1.

Comparative Example 50 parts by weight of stainless steel fiber 5R with a fiber diameter of 8 μm and a fiber length of 4 mm and natural wood pulp beaten to 40 μm (
NBKP/LBKP = V, ) using 50 parts by weight,
In the same manner as in Example 1, a stainless steel fiber mixed paper with a basis weight of 65 g/m2 was produced. The shielding effect of this stainless fiber mixed paper was comparable to that of the sheet of Example 1.

When a taper abrasion test was conducted under the same conditions as in Example 1, the amount of abrasion was 75 m 97,100 times, which was unsatisfactory.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of an electromagnetic shielding sheet with a heat-melting resin layer on both sides of a conductive sheet, and Figure 2 is a longitudinal cross-sectional view of an electromagnetic shielding sheet with a heat-melting resin layer on one side of a conductive sheet. 3 is a graph showing the electric field shielding effect of the electromagnetic shielding sheet, and FIG. 4 is a graph showing the magnetic field shielding effect. In the figure, symbol 1 is 1 layer of thermal melting, 1 layer of snow, and 2 is a graph showing the effect of shielding magnetic field. A conductive sheet, 3 an adhesive layer, and 4 an 'S pattern paper.

Claims (1)

[Claims] An electromagnetic wave shielding sheet comprising a heat-melting resin layer provided on both or one side of a conductive sheet obtained by making paper by a wet papermaking method from raw material fibers containing 30 to 95% by weight of conductive fibers.