JPH0313000A - Electromagnetic shielding structure - Google Patents

Abstract

PURPOSE:To improve electromagnetic shielding property, the outside view, and secondary processing property by bonding a singly layer or plural layers of unweaved cloth comprising complex metal fiber and heat fusion fiber under pressure so as to produce a thin film or making heat fusion of said fiber on the surface of a base material or between the base materials. CONSTITUTION:A single layer or plural layers of unweaved cloth comprising complex metal fiber and heat fusion fiber are heat-bonded so that they may be turned into a thin film or they are hot-adhered with the surface of a base material or between base materials. As for the complex metal fiber, a metal fiber base material whose surface is metal-plated, is used while fiber having heat fusion performance, such as polyolefin-group fiber is used for the heat fusion fiber. The complex metal fiber hot-bonded on the surface of the base material or between the base materials are capable of following the bending or elongation of a structure bonded with the fiber when it is served as secondary processing. This flexibility prevents the outside view of the structure from being damaged. It is, therefore, possible to improve electromagnetic property, outside view and secondary processing characteristics as well.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electromagnetic shielding structure that has excellent electromagnetic shielding properties, appearance and secondary workability, and is also advantageous in terms of manufacturing process. .

BACKGROUND OF THE INVENTION It is essential to provide electromagnetic shielding properties to the housings, flat cables, etc. of electronic devices.

Methods for imparting electromagnetic shielding properties include: ■ A method in which conductive fibers are blended into a molding resin and molded, ■ A method in which a conductive filler is blended into a molding resin and molded, and ■ A conductive paint is applied to the surface of the molded product. ■Method of spraying metal such as zinc onto the surface of the molded product;■Method of applying metal plating to the surface of the molded product;■Method of attaching metal foil to the surface of the molded product;■Method of applying vacuum evaporation or sputtering to the surface of the molded product. A method of forming a metal layer using a method of forming a metal layer is appropriately selected and adopted.

Although the purpose is to prevent static electricity, Japanese Patent Application Laid-Open No. 581559
17, JP 58-166035, JP 58-169706, JP 59-146104
The publication discloses a structure in which a cloth-like material made of entangled conductive fibers and heat-fusible fibers is heat-sealed to the surface of a base material such as plastics.

It is necessary to provide electromagnetic shielding properties not only to the housing of electronics/ronics equipment, but also to transparent surfaces such as viewing windows. A technology has been developed to create laminated glass by sandwiching it between two sheets of interlayer film. (for example,
"Industrial Materials", Vol. 36, No. 4, pp. 51-54 (19
(Refer to 88) Problems to be Solved by the Invention However, the methods described in -1- (1) and (2) require a large amount of conductive fibers or conductive fillers to be blended into the molding in order to obtain the desired electromagnetic shielding properties. 2. It is difficult to obtain thin sheets or films due to the mechanical properties of the plastic molded product.
Disadvantages include poor appearance of molded products in terms of smoothness and coloring.

-1: The methods described in ■ to ■ are limited to shapes of molded products that are flat I, and that the surface conductive layer may be destroyed if the resulting molded product is subjected to secondary processing such as vacuum forming. Disadvantages include not only the appearance, but also problems in terms of electromagnetic shielding, the complexity of the work process, the low energy consumption of the work environment, the difficulty in automating the manufacturing process, and the cost. There is.

Although the method disclosed in JP-A-58-155917 is interesting, even if ordinary metal fibers such as stainless steel fibers are used as the conductive layer Mt, satisfactory electromagnetic shielding properties cannot necessarily be obtained. I can't do it"-1
There were problems such as poor homogeneity and operability when manufacturing nonwoven fabrics from metal fibers and heat-fusible fibers, and the surface of the resulting product had the same luster as metallic luster and lacked a sense of depth. .

The method of making a laminated glass by sandwiching a metal mesh or a metal-plated synthetic fiber mesh between two interlayer films also leaves room for improvement in terms of electromagnetic shielding properties and appearance.

An object of the present invention is to provide an electromagnetic shielding structure that does not have the disadvantages mentioned above.

Means for Solving the Problems The electromagnetic shielding structure of the present invention has a metal fiber substrate (1
A nonwoven fabric (a) consisting of a composite metal fiber (1) on which a metal plating layer (1b) is formed and a thermofusible fiber (2)
The single layer or multiple layers of 3) are either thermocompressed to form a thin film, or are thermally fused on the surface of the base material (4) or between the base materials (4) and (4).

The present invention will be explained in detail below.

The composite metal fiber (1) used is one in which a metal plating layer (1b) is formed on the surface of a metal fiber base (la). The electromagnetic wave shielding property of the metal fiber base (1a) alone is not sufficient, and the intended purpose can only be achieved by forming a metal plating layer (1b) on the surface of the metal fiber base (1a).

Various metal fibers can be used as the metal fiber substrate (1a), but stainless steel fibers are particularly preferred, and aluminum fibers and copper fibers are also preferred fibers. It is also possible to use metal fibers other than these.

The metal plating layer (1b) may be an electroless plating layer, an electrolytic plating layer, or an electrolytic plating layer on an electroless plating layer, but an electroless plating layer is better in terms of electromagnetic shielding properties. results.

Particularly useful are electroless plated layers of nickel, copper, silver or titanium.

Electroless plating is performed according to a conventional method, but at this time, it is also preferable to perform plating with a fluororesin such as polytetrafluoroethylene added to the plating bath.

The thickness of the fibers in the composite metal fiber (1) in which a metal plating layer (1b) is formed on the surface of the metal fiber base (1a) is:
Although it is desirable that the thickness be as thin as possible, it is usually set in the range of about 10-100 ui+, taking into consideration manufacturing constraints. However, there is no problem even if the thickness is outside this range. The length of the fibers can be set arbitrarily, but from the viewpoint of process constraints during nonwoven fabric production and nonwoven fabric strength, the length of the fibers is 2 to 200 m.
It is often set to about m, especially about 5 to 100 mm.

As the heat-melting fiber (2), polyolefin fiber,
Heat-meltable fibers such as polyamide fibers, polyester #11 fibers, acrylic fibers, and polyvinyl chloride fibers
ag is used. In particular, those having a melting point or softening point of 70 to 2
Fibers having a temperature of about 00°C, especially 80 to 180°C, are useful. The thickness and length of the fiber can be set in the same manner as in the case of the composite metal fiber (1), but the thickness can be made thinner.

The nonwoven fabric (3) is produced by mixing the above-mentioned composite metal fiber (1) and heat-fusible fiber (2) by a conventional method (particularly by a dry method). In this case, an appropriate amount of other fibers, such as fibers that do not exhibit thermal meltability at least at the temperature during the heat-sealing process described below, may be mixed.

The ratio of composite metal fiber (1) in nonwoven fabric (3) is 1 to 98
Weight%, especially 5 to 90% by weight, is appropriate; if the ratio is too low, the electromagnetic shielding properties will be insufficient, and if the ratio is too high, the film will become thinner during thermocompression bonding or heat fusion to the base material (4). Sexuality becomes insufficient. A particularly preferable range is 10 to
It is 50% by weight.

Then, the single layer or multiple layers of the nonwoven fabric (3) described above may be thermocompressed to form a thin film, or the nonwoven fabric (3) may be thermally bonded to the surface of the base material (4) or between the base materials (4), (4). In this way, the desired electromagnetic shielding structure is manufactured.

As the base material (4), polyolefin resin, polyamide resin, acrylic resin, polystyrene resin, AB
S resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyacetal resin, polycarbonate resin, polyester resin, polyurethane resin, polyvinyl butyral resin, polyvinyl ester resin, vinyl alcohol copolymer, polyimide resin Resin, polysulfone resin, polyether sulfone resin, polyphenylene oxide resin, polyarylene ester resin, polyether ether ketone resin, phenol resin, urea resin, melamine resin, guanamine resin,
Molded products of thermoplastic resins, thermosetting resins, or rubber resins including epoxy-based polar resins, diallyl phthalate-based resins, and unsaturated polyester-based resins are preferably used.
Other materials used include glass, metal, and naturally occurring materials. Among these, molded articles made of thermoplastic resins, particularly resins having high fusion properties with the thermofusible fibers (2) used, are particularly preferred.

The shapes of these base materials (4) include films, sheets, plates,
It can be anything including pipes, casings, and containers.

When the base material (4) has transparency such as glass, polymethyl methacrylate plate, polycarbonate plate, polystyrene plate, etc., the nonwoven fabric (3) is attached to the base material (4), (4)
) It is also a preferable embodiment to heat-seal the material while being interposed between the two. An example of such an embodiment is a laminated glass having a layer structure of glass/polyvinyl butyral interlayer/nonwoven fabric (3)/polyvinyl butyral interlayer V/glass. The glass/polyvinyl butyral interlayer corresponds to the base material (4).

Examples of heat-sealing means for bonding the nonwoven fabric (3) and the base material (4) include: (1) a method of superimposing the nonwoven fabric (3) on the base material (4) and thermocompression bonding; (2) bonding the nonwoven fabric (3) to the base material (4); (4) Method of heating and melting after laminating on the top; ■ Method of extrusion coating the nonwoven fabric (3) with a resin melt for the plastic molded product base material (4) (applying a cover film from behind the melt) ■ A method in which the nonwoven fabric (3) is inserted into the mold in advance and a molten resin for the base material (4) of the plastic molded product is injected into it (injection molding method); non-woven fabric (
3) is inserted and the heat-softened plastic molded product base material (4) is pressed into it (vacuum forming method, deep drawing method), (D Compression molding of the plastic molded product base material (4) A method of inserting the nonwoven fabric (3) into the mold during press molding, transfer molding, etc. is adopted.

If the base material (4) has bendability or extensibility at room temperature or when heated, it may be subjected to secondary processing such as vacuum forming, bending, and stretching after heat-sealing the nonwoven fabric (3). can.

The electromagnetic shielding structure of the present invention can be used in various applications that require prevention of leakage of electromagnetic waves to the outside or prevention of intrusion of electromagnetic waves from the outside, such as housings of electronic equipment, viewing windows, and materials for flat cables. Useful for applications.

Effects of the invention The composite metal fiber (1) in which the metal plating layer (1b) is formed on the surface of the metal fiber base (1a) is
) The metallic luster of itself is improved, resulting in a deep and pleasant texture.6 Also, this composite metal fiber (1) has improved slipperiness compared to the metal fiber base (la), so it has a significantly different specific gravity. Although the composite metal fiber (1) and the thermofusible fiber (2) are mixed to form the nonwoven fabric (3), each process of compounding, opening, carding, and web formation during parallel web production is difficult. In addition to improving the homogeneity and operability, the uniformity of the obtained nonwoven fabric is also improved. In the case of random web formation, a homogeneous web with little directionality is also obtained.

When the metal plating R (1b) is formed on the surface of the metal fiber substrate (1a) by performing plating with a fluororesin such as polytetrafluoroethylene added to the plating bath, the results are even better. is obtained.

Then, a single layer or multiple layers of the nonwoven fabric (3) consisting of the composite metal fiber (1) and the heat-fusible fiber (2) are thermocompressed to form a thin film, or the surface or base of the base material (4) is Material (4)
, (4), the heat-fusible fiber (2) melts and disappears, forming a film in the former case, and forming a film on the surface of the base material (4) in the latter case. or base material (4
) and (4), the composite metal fiber (1) is fused in a thin layer between them. The resulting structure exhibits excellent electromagnetic shielding properties due to the presence of the thinned or fused composite metal edge M (1) layer. Such excellent electromagnetic shielding properties cannot be obtained simply by thinning or fusing the metal fiber base (1a).

In the latter case, the surface of the substrate (4) or the substrate (4).

(4) Since the composite metal fiber (1) is fused only between the base material (4), the inherent characteristics of the base material (4) are not impaired in any way. Even if the base material (0) is thin like a plastic film, there is no risk of forming pinholes, and the mechanical strength is maintained.The surface of the base material (4) or the base material (4),
(4) The composite metal fiber (1) fused between will follow the deformation even if the resulting structure is subjected to secondary processing that involves elongation or bending, so the appearance of the structure will be impaired. That's not true. Even if the base material (4) is colored or has transparency, the coloring or transparency can be substantially maintained.

Example Next, the present invention will be further explained with reference to Examples.

Hereinafter, "%" means % by weight.

Example 1 A stainless steel long fiber with a thickness of 30 gm as an example of the metal fiber substrate (1a) was subjected to electroless plating with nickel to form a metal plating layer (1b), and then cut into a length of 51 mm. A composite metal fiber (1) was produced.

This composite metal fiber (1) 30% and a thickness of 25 ml (approximately 6
denier), 51 mm in length, and 70% of heat-melt fiber (2) made of polyamide fiber with a melting point of 120°C,
A uniform non-woven fabric (3
) was manufactured. Manufacturing was extremely smooth.

Next, this nonwoven fabric (3) is made of polyamide and has a thickness of 801 mm.
Laminated on the surface of the base material (4) consisting of films j and m,
When heat-fused by passing it between rolls at a temperature of 150°C and then passing it between cooling rolls, the heat-fusible fiber (2) melted and its appearance disappeared, leaving only the composite metal fiber (1). A desired molded product was obtained which was fused to the surface of the base material (4). The surface of this molded product was smooth and had a deep, subdued luster.

The damping rate (m-field) of the obtained molded product is at a frequency of 10 MHz.
50 dB at a frequency of 500 MHz, and 35 dB at a frequency of 500 MHz.
It had good electromagnetic shielding properties over a wide range of frequencies.

Even when the above-mentioned molded product was subjected to vacuum forming, the fused composite metal fiber (1) closely followed the elongation during vacuum forming,
No problems such as twitching, surface roughness, or deterioration in appearance occurred.

Example 2 Example 1 was repeated except that electroless plating was performed with silver instead of nickel.

The attenuation rate (electric field) of the obtained molded product is at a frequency of 10 MH
z Terrorism was 5 dB and 45 dB at a frequency of 500 MHz.

Example 3 Example 1 was repeated except that electroless plating was performed with copper instead of nickel.

The attenuation rate (electric field) of the obtained molded product is at a frequency of 10 MHz.
It was 60 dB at a frequency of 500 MHz, and 40 dB at a frequency of 500 MHz.

Comparative Example 1 Example 1 was repeated except that stainless steel long fibers without nickel plating were used in place of the composite metal fiber (1). The production of the nonwoven fabric was not necessarily smooth, and the uniformity of the obtained nonwoven fabric was inferior to that of Example 1.

The attenuation rate (electric field) of the molded product after fusion is at a frequency of 10 MHz.
45 dB at a frequency of 500 MHz, and 10 dB at a frequency of 500 MHz.
Compared to Example 1, the electromagnetic shielding property was inferior.

The surface of this molded product retained the metallic luster of stainless steel.

Example 4 An aluminum short fiber having a thickness of 30 g and a length of 51 m+a as an example of the metal fiber substrate (1a) was electrolessly plated with nickel to form a metal plating layer (1b),
A composite metal fiber (1) was produced.

This composite metal fiber (1) 30% and thickness 18 ru shoulder (about 3
(denier), 51 m shoulder length, 56 polypropylene fibers with a melting point of 130°C (2) 70%
A uniform nonwoven fabric (3) with a basis weight of about 90 g/m' was produced by a dry method. Manufacturing was extremely smooth.

Next, this nonwoven fabric (3) was laminated on the surface of a base material (4) made of a polypropylene acid board and heat-pressed and heat-fused at a temperature of about 160°C. The desired molded product was obtained in which the metal fibers (1) appeared to disappear and only the composite metal fibers (1) were fused to the surface of the base material (4). The surface of this molded product was smooth and had a deep, subdued luster.

The attenuation rate (electric field) of the obtained molded product is at a frequency of 10 MHz.
45 dB at a frequency of 500 MHz, and 30 dB at a frequency of 500 MHz.
It had good electromagnetic shielding properties over a wide range of frequencies.

Comparative Example 2 Example 2 was repeated except that short aluminum fibers without nickel plating were used in place of the composite metal fiber (1). The production of the nonwoven fabric was not necessarily smooth, and the uniformity of the obtained nonwoven fabric was inferior to that of Example 1.

The attenuation rate (electric field) of the obtained molded product is at a frequency of 10 MHz.
It was 30 dB at a frequency of 500 M) and 1 O dB at a frequency of 500 M), and the electromagnetic shielding property was inferior to that of Example 4.

The surface of the molded product after fusion retained the metallic luster of aluminum.

Example 5 A stainless steel short fiber having a thickness of 30 m and a length of 51 mm as an example of the metal fiber substrate (1a) was electrolessly plated with copper to form a metal plating layer (1b), and a composite metal fiber was formed. (1) was produced. Note that during electroless plating, a small amount of polytetrafluoroethylene fine particles were allowed to coexist in the plating bath.

25% of this composite metal fiber (1) and 75% of heat-fusible fiber (2) made of polyester fiber having a thickness of 25 IL layer (approximately 6 denier), a length of 51 mm, and a melting point of 120°C are mixed and A uniform non-woven fabric (3) with a basis weight of about 120 g/m'' was produced using the above method. The production of the non-woven fabric (3) was even smoother than that of Example 1.

Next, this nonwoven fabric (3) was inserted into a mold of an injection molding machine, and injection molding was performed using ABS resin for the base material (4) to form a casing for a personal computer.

As a result, the heat-fusible fiber (2) was thermally melted and its appearance disappeared, and a casing in which only the composite metal fiber (1) was fused to the inner surface of the base material (4) was obtained. The inner surface of this case was smooth and had a deep, deep luster.

The attenuation rate of the obtained casing was almost the same as that of Example 3.

Comparative Example 3 Example 5 was repeated except that stainless steel fiber without copper plating was used in place of the composite metal fiber (1). The production of the nonwoven fabric was not necessarily smooth, and the uniformity of the obtained nonwoven fabric was considerably inferior to that of Example 5.

The inner surface of this case retains the full luster of stainless steel.

Example 6 A molten polypropylene extruded at a temperature of 180° C. was brought into contact with the nonwoven fabric (3) of Example 4, and at the same time a cover film of 80 colors thick was applied from behind the extruded polypropylene melt. A polypropylene film was applied and passed between rolls for pressure bonding and cooling.

As a result, the heat-fusible fibers (2) are thermally melted and their appearance disappears, and only the composite metal fibers (1) are fused to the surface of the base material (4) made of a two-layered polypropylene film. I got something.

The damping rate of the obtained molded product was as favorable as in Example 4.

Example 7 Heat-melt fiber (2
) A nonwoven fabric (3) was produced in the same manner as in Example 5, except that nonwoven fabric (3) was used.

The nonwoven fabric (3) obtained above was sandwiched between two polyvinyl butyral membranes, and this was further sandwiched between two glass plates, taking care not to trap air. Subsequently, heat and pressure bonding was performed from the outside of the glass to melt the heat-fusible fiber (2) and integrate it with the polyvinyl butyral film.

The laminated glass thus obtained had good electromagnetic shielding properties over a wide range of frequencies.

Comparative Example 4 Example 7 was repeated except that stainless steel fiber without copper plating was used instead of composite metal fiber (1).

The electromagnetic shielding property of the obtained laminated glass was clearly inferior to that of Example 7.

Example 8 Two sheets of the nonwoven fabric (3) obtained in Example 1 were stacked together and
A film was obtained by heat pressing at ℃.

The electromagnetic shielding property of the obtained film was one degree better than that of Example 1.

1

Claims (3)

[Claims] 1. A metal plating layer (1) is formed on the surface of the metal fiber base (1a).
Composite metal fiber (1) formed with b) and heat-fusible fiber (
A single layer or multiple layers of the nonwoven fabric (3) consisting of (2) and (2) are either thermocompressed to form a thin film, or heat fused on the surface of the base material (4) or between the base materials (4), (4). An electromagnetic shielding structure made of 2. 2. A structure according to claim 1, wherein the metal fiber substrate (1a) is a stainless steel fiber, an aluminum fiber or a copper fiber. 3. 2. A structure according to claim 1, wherein the metal plating layer (1b) is an electroless plating layer of nickel, copper, silver or titanium.