JPS62139400A - Molded unit with electromagnetic shielding properties - 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 [Field of Industrial Application] The present invention relates to a molded product having electromagnetic shielding properties suitable for use in structures such as housings and electronic parts of various electronic devices.

[Conventional technology]

In recent years, with the development of electronic devices such as office automation equipment, computer equipment, and communication equipment that incorporate ICs and LSIs, electromagnetic waves generated by various electronic devices can interfere with the functions of other devices and interfere with their normal operation. It has become a fat woman problem. Synthetic resins or rubber-like materials are widely used as housing materials for various electronic devices and structural materials for electronic components, but because they themselves are electrically insulating, they do not have the ability to shield electromagnetic waves. Therefore, various electrically conductive processing methods have been attempted on synthetic resin or rubber-like material (hereinafter collectively referred to as molding raw material) K for the purpose of imparting electromagnetic wave shielding ability. That is, methods have conventionally been used in which a conductive coating is formed on the inner surface of a molded product made using these molding raw materials by applying a conductive paint or by thermally spraying a metal.

However, with this method, it is difficult to uniformly form a conductive film on the inner surface of a molded product that has uneven or curved parts, and the adhesion strength between the molding raw material and the conductive film is not sufficient, resulting in partial peeling. There is a risk that electromagnetic shielding properties may be lost or harm may be caused to internal electrical circuits. There is also a method of mixing conductive fillers such as metal fibers or metal flakes into the molding raw material to make the molding raw material itself conductive. This method has the advantage of being highly suitable for mass production and producing conductive molded products in one step.

Incidentally, in order to attach electronic components or the like inside the molded product, it is generally necessary to provide an electrically insulating protrusion on the inner surface of the molded product. In both of the above two electrically conductive processing methods, the inner surface of the molded product is made entirely conductive, so it is necessary to mask only the portion that is desired to be insulating. In this case, especially in the former conductive processing method, since the conductive film is lost only in the masked part, there is a risk that electromagnetic waves will leak from that part and the electromagnetic wave shielding performance will be greatly reduced.

Furthermore, in the latter conductive processing method, it is necessary to apply an insulating paint to only the protrusion or the entire inner surface. Therefore, as with the former method, there is a risk that the insulating paint may partially peel off, exposing the conductive portion, resulting in poor insulation. Also,
In either method, masking and demasking operations are labor-intensive and complicated.

[Problem that the invention seeks to solve]

The purpose of the present invention is to solve the above-mentioned problems of conventionally known molded products with electromagnetic shielding properties, to maintain durable and durable electromagnetic shielding properties, and to have a protrusion inside the molded product. It is an object of the present invention to provide a molded product having electromagnetic shielding properties that is easy to manufacture and whose entire inner surface is electrically insulating.

[Means for solving problems]

The present invention provides a molded product comprising a molding raw material made of a synthetic resin or rubber-like material containing conductive filaments and an insulating fabric material, wherein when molding the molded product, the molding raw material is an insulating fabric having a large number of permeable gaps is disposed along any surface of the molded article and integrally with the molding raw material, and at least one surface of the molded article - A molded product having electromagnetic shielding properties, characterized in that it is provided with at least one electrically insulating protrusion formed from the molding raw material.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings showing an embodiment of a molded product having electromagnetic shielding properties according to the present invention.

FIG. 1 shows a perspective view of an embodiment of a molded product having electromagnetic shielding properties according to the present invention.

The molded product 1 shown in FIG. It is composed of an insulating fabric 3 that is disposed integrally with the molding raw material, and a protrusion 4 is provided on the inside of the base body 2 . FIG. 2 shows a part of the cross-sectional structure of a molded product according to the present invention.

As shown in the figure, the protruding portion 4 is formed by molding a molding raw material across the gap between the insulating fabrics 3 and integrally with the base portion 2.

When the molding raw material passes through the gap between the insulating fabrics, the conductive filler in the molding raw materials is filtered out by the insulating fabrics, so the protrusions contain almost no conductive filler and are electrically insulating. becomes.

Therefore, the entire inner surface of the molded product 1, including the protrusion 4, becomes electrically insulating. In other words, this molded product 1 has a structure in which the outside is conductive and the inside is insulating.

The shape, shape, and number of the protrusions may be arbitrarily determined depending on the shape and number of electronic components when attaching them to the inside of the molded product, and the shape of the protrusion 4 shown in FIG. And the number is not limited.

In the present invention, electrically insulating means that the surface resistance is 106
Conductivity means when the surface resistance is Ω/a1 or more, and conductivity means when the surface resistance is less than 10 6 Ω/cd.

Molding raw materials used for the molded product having electromagnetic shielding properties according to the present invention include thermoplastic synthetic resins such as ABS resin, polystyrene resin, modified PPE resin, and polyolefin resin, thermosetting resins such as phenol resin and polyester resin, and butadiene resins. A rubber-like material made of synthetic rubber such as rubber or polyolefin rubber can be used.

Conductive fillers used in the molded product with electromagnetic shielding properties according to the present invention include metal fibers such as brass, aluminum, and stainless steel, carbon fibers, organic fibers or inorganic fibers whose surfaces are plated with metal, aluminum, nickel, etc. metal flakes, etc.

Further, the insulating fabric refers to a knitted fabric or non-woven fabric made of electrically insulating fibers.

Materials for insulating fabrics include natural fibers, recycled fibers,
Any organic fibers such as synthetic fibers and inorganic fibers such as glass fibers can be used.

The method of manufacturing a molded product having electromagnetic shielding properties according to the present invention will be explained below. The molded product having electromagnetic shielding properties according to the present invention is produced by placing an insulating fabric in a mold in advance, and then using an injection molding machine or the like to melt the molding material in a flowable state into the mold under high pressure. It can be obtained by introducing it by injection or the like and then cooling or heating to harden it. In other words, if an insulating fabric is placed inside a mold and, for example, molten molding material is injected,
The fabric is pressed against the inner surface of the mold on the side opposite to the gate by the pressure of the molding raw material, and is deformed along the shape of the mold. By curing the molding raw material as it is, an integrally molded product with an insulating fabric bonded to the surface portion is formed. However, if there is a concave part with a large curvature that prevents the fabric from entering the mold on the opposite side of the gate,
The molding material that has passed through the gaps in the structure of the fabric enters this portion and is formed as a protrusion. During the formation of the protrusions, the conductive filler contained in the molding raw material is treated by the structure of the insulating fabric, so the protrusions become electrically insulating. The maximum diameter of the gap in the fabric that can be penetrated by the molding raw material and cannot be penetrated by the conductive filler depends on the size and shape of the conductive filler, the molding raw material, molding conditions, and the like. For example, using short stainless steel fibers (length 5 cm, fiber diameter 12 μm) as a conductive fiber, adding 2 volumes of stainless steel short fibers to ABS resin (general type), injection pressure 400 Kf/cd,
When injecting from an injection molding machine at a resin temperature of 240°C, the maximum diameter of the gap is 0.4 as an insulating fabric.
~1.0 m of fabric is preferred. The maximum diameter of the gap is 0.4
If it is less than tm, the resin cannot penetrate into the gap between the fabrics, and the adhesion between the resin and the fabrics is poor. On the other hand, if the maximum diameter of the gap is larger than 1.0 dew, it becomes difficult to filter the conductive filler and it becomes impossible to make the surface of the protrusion insulating.

Generally, a molded product such as a housing for an electronic device is a three-dimensional structure having a curved surface portion having various curvatures and a flat portion, and having various protrusions inside. In order to uniformly integrate an insulating fabric onto the surface of such a complex molded product, it is necessary to use various types of insulating fabric depending on the shape. In the flat part, the insulating fabric does not need to be elastic, but in the curved part, the insulating fabric needs to have elasticity in order to flexibly follow the mold. Therefore, various knitted fabrics with high elasticity are suitable as the insulating fabric material for the curved surface portion. In other than knitted fabrics, such as dry felt where the fibers are not bonded, the short fibers are loosened and can follow the elongation of the curved surface. In addition, woven and non-woven fabrics made of drawn yarns and semi-drawn yarns,
Fabrics made from processed yarns also have stretchability, so they can conform to curved surfaces.

On the other hand, the insulating fabric used for the purpose of filtering the conductive filler in the protrusion needs to have a strong structure because the pressure of the molding raw material is applied locally during molding. It must be ensured that the conductive fin 2- will not be deformed by locally applied pressure and the gaps between the fiber structures will widen, allowing the conductive fin 2- to pass through. Therefore, a woven fabric with a tight texture is generally suitable as the insulating fabric.

From the above, in the case of a molded product having both a curved surface portion and various protrusions on the inner surface, a combination of a plurality of insulating fabrics is used as necessary. For example, a stretchable knitted fabric is fixed to the entire inner surface of the mold, and a protrusion is placed on the opposite side of the gate of the knitted fabric to prevent the penetration of conductive filler that has penetrated through the gap in the knitted fabric. By locally laminating a high-density fabric and integrally injection molding it, the entire inner surface where the protrusions are located can be made insulative.

The insulating fabric does not necessarily need to be integrated over the entire surface of the molded product. Localized integration may be performed only on the surface of the part of the molded product to which the electronic circuit is attached.

In the molded product having electromagnetic shielding properties according to the present invention, a part of the molding raw material enters or penetrates the gap between the insulating fabrics, so the anchor effect causes the insulating fabrics to firmly adhere to the molded product. .

In particular, when a knitted fabric made of spun yarn is used, the fluff of the spun yarn and the molding material become entangled with each other, resulting in a very high adhesion strength.

〔Example〕

Hereinafter, specific examples of molded products having electromagnetic shielding properties according to the present invention will be shown in comparison with comparative examples.

Example 1 A mold in the shape of a bottom lid of a keyboard was used, which had a protrusion on the flat bottom part at the center of the inner surface and a curved side wall around the bottom part. The degree of elongation of this mold in the vertical and horizontal directions (the increase ratio of the length along the inner surface of the mold to the length of a straight line connecting both ends of the inner surface of the mold) is 11.
%, 7%. In addition, the bottom of the mold has a diameter of 10 cm.
There are four cylindrical protrusions with a height of 4 cm and two prismatic protrusions with a length of 18 m, a width of 6 cm, and a height of 7 m.

As an insulating fabric, a high-density rubber knitted fabric made of acrylic spun yarn (manufactured by Asahi Kasei Industries, Ltd., Cashmilon 1152) was used.
Using Nm, elongation vertically 3 at 1oof/1crr 1 width load
The bottom part is made of polyester monofilament plain weave (using 54d, weaving density (pieces/1nch): length 90/width 85, maximum mesh diameter 0).
．． 4) were used in a stacked manner.

As the conductive filler, short stainless steel fibers (manufactured by Nippon Seiren ■, Naslon ■), length 5 m, fiber diameter 12 μm were used, and molding was carried out under the following conditions.

Rubber knitted fabric is placed entirely between a pair of molds, and a plain woven fabric is further laminated on the opposite side of the gate of the rubber knitted fabric in the bottom part of the center, and the fabric is sandwiched between the molds on both sides. The area around the object was tightly fixed. Modified PPE resin containing 2 volumes of conductive filler (manufactured by Asahi Kasei Corporation) was produced using an injection molding machine.
Zylon (■) 1-Injection pressure-s o o Ky/a11 Injected from the front side of the bottom lid of the keyboard at a resin temperature of 250C, and after cooling, the integrally molded product was taken out. The insulating fabric adheres closely along the curved surface of the inner surface of the molded product, and the resin penetrates into the gaps between the fabrics, so the adhesion is good. The protrusions present on the inner surface of the molded product were molded with resin that had penetrated through the gaps in the fabric.

The surface resistance of the protrusion shall be 106Ω/d or more, and the surface resistance of the inner surface of the molded product other than the protrusion shall be 10'Ω/cd or more. The surface resistance of the outer surface of the molded product is 0.9Q/ad, and the electromagnetic shielding property (IQ OMB2-IGO
OMB2.

electric field) was 39 dB or more.

Example 2 An insulating fabric was used as a plain weave fabric made of polyester spun yarn (30/-, weaving density (strands/1 nch) length 68/width 6G, elongation at break (length 45/width 55, maximum gap) 0.5M in diameter), and the conductive filament 2 was made of short brass fibers (length 411 mm, made by the vibration cutting method).
J, thickness 60 μm), and the same Venus as in Example 1 was used for molding. An insulating fabric material was fixed only on the flat bottom part of the mold, and ABS resin containing 50% by weight of conductive filler (Asahi Kasei Kogyo Trap) was molded using an injection molding machine.
An integrally molded product was obtained by injecting STYRAC-ABS■) at an injection pressure of 400/-1 and a resin temperature of 240°C.

The insulating fabric adhered well to the inner surface of the bottom part of the molded product. The protrusions were molded with resin that penetrated the gaps in the fabric. The surface resistance of the inner surface of the bottom of the molded product should be 10'Ω or more, and the surface resistance of the outer surface of the molded product should be 8.
It was Ω/d. Electromagnetic shielding performance is 31dB or higher.

Comparative Example A molded product made only of ABS resin was obtained using the bottom mold of the next keyboard used in Example 1.

The inner surface of this molded product was coated with a conductive paint (acrylic resin paint containing Keckel powder) to a thickness of SO/jm. Surface resistance 1.
00/-, and the electromagnetic shielding property was 32 dB. On the other hand, the protrusions present on the inner surface of the molded product were masked, and then a conductive paint was applied to a thickness of 50 μm, and after drying, it was demasked. The surface resistance of the conductive film of this molded product is 1
．． Although it was 0Ω/-, the electromagnetic shielding property was 11dBK.
It decreased significantly at t.

〔Effect of the invention〕

Since the molded product having electromagnetic shielding properties according to the present invention is configured as described above, even if it is a complex molded product having curved surface portions with various curvatures, it can also be used at any location on the inner surface of the molded product. Furthermore, even when protrusions of arbitrary shapes are arranged, the entire inner surface of the molded product can be electrically insulated. Furthermore, since the insulating fabric in the molded product according to the present invention is molded integrally with the molding raw material, there is no risk of it peeling off. Furthermore, the molded product according to the present invention can be manufactured by a simple process.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of a molded product having electromagnetic shielding properties according to the present invention. FIG. 2 is a cross-sectional view showing a partial cross-sectional structure of a molded product having electromagnetic shielding properties according to the present invention. DESCRIPTION OF SYMBOLS 1... Molded product having electromagnetic wave shielding properties, 2... Base part, 3... Insulating fabric-like material, 4... Protrusion part.

Claims (1)

[Claims] A molded product made of a molding raw material made of a synthetic resin or a rubber-like material containing a conductive filler and an insulating fabric, the molded product having a plurality of layers through which the molding raw material can pass through when molding the molded product. An insulating fabric having a gap is disposed along any surface of the molded product and integrally with the molding raw material, and is formed from the molding raw material on at least one surface of the molded product. A molded product having electromagnetic shielding properties, characterized in that it is provided with at least one electrically insulating protrusion.