JPS61224204A - Conducting 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 a conductive sheet having excellent conductivity, particularly high electromagnetic shielding properties.

<Prior art> With the rapid development of computer equipment in recent years, it has become a problem that high frequency pulses are generated by the large number of ICs and L8.1 used in computer equipment, and have a large impact on surrounding televisions, radios, and peripheral equipment. On the other hand, it is also conceivable that computers used in all sorts of fields, such as factories, offices, Shinkansen trains, online banks, etc., could malfunction due to unnecessary radio waves from outside, causing great social chaos.

In particular, in the past, sheet metal housings were used as housing cases for computer equipment due to its large size and small volume production, but with the recent spread of office computers and personal computers, the use of plastic housing has increased, and the problem of electromagnetic interference has once again been brought into focus. It's coming. In other words, plastic itself has high electrical insulation properties and transmits electromagnetic waves as it is, so it is not effective in shielding electromagnetic waves that are generated by digital devices and become noise that interferes with the reception function of radios, televisions, etc. A common method for shielding plastic is to form a conductive layer on the surface, but this method involves molding each case, applying a surface treatment, and then applying a conductive agent, which is costly. There was a problem with the durability of the surface coating layer. In addition, the method of kneading conductive filler into plastic to create a shield has poor dispersion of the conductive filler, and when the mixed material is injection molded, the conductive filler tends to stay in the nozzle or bent part. Furthermore, it is difficult to obtain a uniform seal, and furthermore, the contact between the conductive fillers is likely to be inhibited by the plastic, so that the shielding effect is often insufficient.

<Problems to be Solved by the Invention> The present invention provides a novel conductive sheet that can replace the above-mentioned plastic materials, and has excellent conductivity, especially high electromagnetic shielding properties, which could not be obtained with the conventional technology. The purpose is to obtain a conductive sheet that is inexpensive and durable.

Means for Solving Problems〉 The feature of the present invention is that by employing a wet papermaking method as a sheet forming means, the fiber diameter can be reduced to 12uu+.
This is due to the high blending ratio of the following ultra-fine stainless steel fibers. That is, the sheet is composed of 60 to 95% by weight of ultrafine stainless steel fibers with a fiber diameter of 12 um or less, and the remainder is binder fibers, and has a volume resistivity of 10-'-
A conductive sheet having a resistance of 10-'Ω·C11 is provided.

The stainless steel fiber used in the present invention has a fiber diameter of 12 u.
Ultra-fine, preferably 4 to 811+11! &Awl is applied. If this is larger than 12+on, a dense entangled structure will not be formed in the wet papermaking process,
Not only is it impossible to obtain the desired density and electromagnetic shielding properties, but also it is difficult to obtain the physical strength of the sheet due to the reduction in the contact area between the stainless steel fibers. The stainless steel fibers used are fibers having a predetermined fiber diameter that are bundled with a binding agent and cut into lengths of 10 nI or less, preferably 4 to 8 mm.

On the other hand, as the binder fiber to be mixed with the stainless steel fiber, for example, easily soluble PVA fiber is used, which has an adhesive ability that can strongly bond the stainless steel fibers even if mixed in a small amount. Easily soluble PVA fibers retain their fiber form during the wet paper forming process on a wet paper machine, and when heated and pressed onto a drying drum during the drying process, they easily dissolve between the stainless steel fibers and act as a binder. It is a device that performs the following functions.

Since the blending ratio of stainless steel fibers and binder fibers has a great effect on the electromagnetic shielding properties, the inventors of the present invention conducted extensive studies on the blending ratio, and found that the stainless steel fibers accounted for 60 to 95% by weight of the total sheet weight. It has been discovered that good properties can be obtained by blending so as to achieve the following. In this case, the wet strength required for continuous sheeting cannot be obtained in the wet papermaking process in which stainless steel fibers account for 95% by weight or more, and the physical properties such as tensile strength of the resulting conductive sheet are also weak, causing problems in practical use. . On the other hand, if the stainless steel fiber is less than 60% by weight, the volume resistivity becomes high due to the presence of binder fibers made of an insulating organic substance, and sufficient electromagnetic shielding properties cannot be obtained. The method for blending stainless steel fibers at a high blending ratio of 60 to 95% by weight of the total sheet weight is as described below.

Stainless steel fibers treated with a sizing agent and binder fibers are dispersed in cold or hot water, and slowly stirred with a low-speed stirrer such as an ashter to disintegrate the fibers and prepare a slurry. The obtained slurry is compressed and dried on a drying drum using a wet paper machine. In this case, the wet paper machine may be a Fourdrinier or a circular paper machine, but special attention must be paid to the setting conditions of press pressure and dryer temperature, as these are important points in obtaining a uniform paper sheet. The obtained sheet is subjected to pressure treatment using a press device such as a calendar at room temperature or under heating.

This results in good contact between the stainless steel fibers, resulting in a low and stable volume resistivity and improved electromagnetic shielding effect.

As mentioned above, the use of a high blending ratio of ultrafine stainless steel fibers with a fiber diameter of 12νo1 or less, the combined use of highly adhesive binder fibers, and the pressure treatment after wet papermaking have resulted in a volume resistivity of I
A conductive sheet having a resistance of O-' to 10-4Ω·C1n can be obtained.

Note that the measurement of volume resistivity in the present invention is based on the length 7011
Both lengthwise ends of a sample piece of 1111 and r1150 mm were held between clip-shaped electrodes so that the span was 50n+m, and current was applied to measure the voltage and current.The measured resistance was calculated using the following formula.

Volume resistivity (ρv)=RXS/Q The conductive sheet of the present invention can be used in a wide range of applications other than electromagnetic shielding, such as conductive material for avoiding electrostatic interference.

<Examples> The present invention will be described in detail below with reference to Examples and Comparative Examples.

Example 1 90 parts by weight of stainless steel fiber (Susmic manufactured by Tokyo Seizuna Co., Ltd.) with a fiber diameter of 8 and fiber length of 6 mm and 10 parts by weight of PVA fiber with a fiber length of 3 mm (Fibribond VPB105-2 manufactured by Kuraray Co., Ltd.)
Parts by weight were dispersed in water at room temperature and stirred in an agitator for 10 minutes. Separately, 3 parts by weight of acrylamide (Acriverse manufactured by Diafloc) was added as an anti-settling agent, and the solid content was 0.
．． A 0.05% slurry was prepared. This slurry was made into paper using a Fourdrinier paper machine with a target weight of 55 g/J, and a wet fiber sheet obtained by dehydration pressing was pressed and heated using a dryer heated to 100°C to obtain a dry sheet.

Add this sheet to 100 kg/cn on a calendar.
? Pressure treated at a pressure of 56 g/a? , thickness 31μ
ml of conductive sheet was obtained. The volume resistivity value of this sheet was 3.7XIO-3Ω·cin, and it had sufficient electrical conductivity.

In addition, the spectrum analyzer TR41 manufactured by Takeda Riken Co., Ltd.
When the attenuation against an electric field at 500 MHz was measured using Model 72, 40 dB was obtained, confirming an excellent shielding effect. Furthermore, the physical strength such as tensile strength was sufficient for practical use.

Example 2 Using the production conditions of Example 1, the rice weight was 105 g/J.

A conductive sheet with a thickness of 58 um was obtained. The volume resistivity of this sheet was 6.8XlO-3Ω·Om, and it had sufficient electrical conductivity.

Furthermore, when the attenuation amount with respect to the electric field at 500 MHz was measured, 45 dB was obtained, confirming an excellent shielding effect. Furthermore, the physical strength such as tensile strength was sufficient for practical use.

Example 3 75 parts by weight of stainless steel fiber (Susmic manufactured by Tokyo Seizuna Co., Ltd.) with a fiber diameter of 8 μII+ and a fiber length of 6 mm and P with a fiber length of 3 mm
VA fiber (Fibribond VPB105-2 manufactured by Kuraray Co., Ltd.
) was dispersed in water at room temperature and stirred for 10 minutes using an ashter. Separately, 3 parts by weight of acrylamide (Acriverse, manufactured by Diafloc Co., Ltd.) was added as an anti-settling agent to prepare a slurry with a solid content concentration of 0.05%.

This slurry was made into paper using a Fourdrinier paper machine with a target weight of 70 g/J, and a wet fiber sheet obtained by dehydrating and pressing was
A dry sheet was obtained by pressing and heating with a dryer heated to ℃. This sheet was further pressure-treated with a calender at 100 kg/c-pressure to give a rice weight of 71.6 g/I+? , thickness 40a
A conductive sheet of ta was obtained. The volume resistivity value of this sheet was 1.0XlO-3Ω·Cl11, and it had sufficient electrical conductivity.

Furthermore, when the attenuation amount with respect to the electric field at 500 MHz was measured, 37 dB was obtained, confirming an excellent shielding effect. Furthermore, the physical strength such as tensile strength was sufficient for practical use.

Comparative example Stainless steel fiber with fiber diameter 8 μm and 0% fiber length 6 nIn+ (
Susmic (manufactured by Tokyo Seizu Co., Ltd.) 50 parts by weight and fiber length 3mm+
PVA fiber (Fibribond VPB105 manufactured by Kuraray Co., Ltd.)
-2) 20 parts by weight and 30 parts by weight of NBKP wood pulp were dispersed in water and stirred for 10 minutes using an agitator.

- Separately, 2 parts by weight of acrylamide (Acriverse, manufactured by Diaflick) was added as an anti-settling agent, and the solid content was 0.
．． A 0.05% slurry was prepared. This slurry was made into paper using a fourdrinier paper machine with a rice basis weight of 55g/I&, and the wet fiber sheet obtained by dehydration pressing was heated and dried.
A stainless steel fiber blended sheet having a weight of 3 g/J and a thickness of 68 um was obtained. The physical strength such as tensile strength of this sheet was sufficient for practical use, but the volume resistivity value was 3X100.
Ω·cIll, which was unsatisfactory in terms of conductivity.

Furthermore, when the attenuation against an electric field at 500 MHz was measured, it was found to be 20 dB, which did not cause any problems in mounting, and a shielding characteristic was obtained.

<Effects of the Invention> Since the present invention has the above-described configuration, the conductivity of the stainless steel fiber itself can be fully utilized in the sheet-like material, and a stable and low electrical resistance value can provide uneven electromagnetic wave shielding properties. I was able to do that. In addition, it is cheaper and more durable than conventional shielding materials, so it can be used in a wider range of applications.

Claims (1)

[Claims] Ultra-fine stainless steel fibers with a fiber diameter of 12 μm or less are 60 to 95
% by weight, the rest is a sheet consisting of binder fibers, and has a volume resistivity of 10^-^1 to 10^-^4 Ω・c
An electrically conductive sheet characterized by being m.