JPH0315358B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing an electromagnetic shielding case constructed by fitting two or more electromagnetic shielding synthetic resin molded products.

[Technical background of the invention]

In recent years, with the development of digital electronic devices, it has been reported that the electromagnetic waves generated by these electronic devices can interfere with other nearby devices such as televisions, or cause malfunctions due to electromagnetic waves from other devices. The problem is getting a lot of attention.

These problems can be solved by providing an electromagnetic shielding effect to the case surrounding the electronic circuit.

However, in such cases, mass production,
Products made of synthetic resin are often used due to their economic efficiency and light weight, and due to technical constraints of injection molding and convenience in assembling internal equipment, two or more molded products are often fitted together. Manufactured.

Various methods as described below have been used to provide electromagnetic shielding properties to such cases.

(b) A metallic electromagnetic shielding layer is provided on the outer or inner surface of the synthetic resin case by plating, painting, thermal spraying, foil adhesion, etc.

(b) The case is molded from thermoplastic resin mixed with conductive filler such as metal powder, carbon powder, metal foil, metal fiber, carbon fiber, etc.

[Problems with background technology]

However, in method (a) of these methods, there is a risk that the electromagnetic shielding layer may peel off or fall off due to impact from dropping or thermal cycling, and in the unlikely event that a peeled piece falls onto the electronic circuit. However, there was a problem in that it could easily lead to serious accidents such as short circuits and fires.

In addition, in the method (b), the surface temperature of the mold cavity is usually kept as high as possible (usually 60°C or higher, depending on the type of thermoplastic resin) to ensure a smooth appearance and prevent static electricity. This prevents the conductive filler from being exposed to the surface of the molded product, but as a result, there is no contact of the conductive filler at the fitting part of the electromagnetic shielding case.
There was a problem with electromagnetic waves leaking in this part. Therefore, the contact surface of the mating part must be removed until the conductive filler is uniformly exposed.
The drawback was that secondary processing was time-consuming.

[Purpose of the invention]

The present invention has been made in view of these points, and an object of the present invention is to provide a method for manufacturing an electromagnetic shielding case that has conductivity at the fitting portion without requiring secondary processing as described above. do.

[Summary of the invention]

That is, the method for manufacturing an electromagnetic shielding case of the present invention is to manufacture an electromagnetic shielding case configured by fitting two or more molded products made of electromagnetic shielding synthetic resin, and to produce a part that becomes a fitting part of the molded product. - in the mold cavity in advance.
A metal plate cooled to 40 to 20℃ is inserted, the surface temperature of the mold is maintained at 60℃ or higher, and the cavity is filled with electromagnetic shielding synthetic resin and solidified, exposing the metal plate at the mating part. However, it is characterized by manufacturing a molded product in which the conductive filler is not exposed on the case surface.

The electromagnetic shielding synthetic resin used in the present invention is a conductive filler such as metal powder, carbon powder, metal foil, metal fiber, or carbon fiber, and a styrene resin such as polystyrene, ABS resin, or olefin resin such as polypropylene. , blended with thermoplastic resins such as polycarbonates, polyamides and polyesters.

In addition, the metal plate used in the present invention includes:
Examples include plate-shaped or L-shaped iron, copper, aluminum, alloys thereof, and those with plated surfaces.

Next, the method of the present invention will be explained using the drawings.

FIG. 1 is a cross section of a mold used in the method of the present invention. In the figure, reference numerals 1 and 2 are the stationary mold plate and the movable mold plate of the mold, respectively. The temperature is controlled at an appropriate temperature of 60°C or higher to prevent the conductive filler from being exposed on the surface of the molded product. Reference numeral 7 is a metal plate that is a feature of the present invention and is inserted into the mold cavity and serves as a molded product fitting part. This metal plate 7 is pre-cooled to -40 to 20°C so that the electromagnetic shielding synthetic resin filled therein is rapidly solidified and the conductive filler is exposed. Inserted into the mold cavity.

In the present invention, using such a mold, first, the electromagnetic shielding synthetic resin plasticized in the cylinder of the injection machine is applied to the nozzle touch part 8 of the mold.
After that, it is filled into the mold cavity. At this time, the conductive filler is not exposed on the fixed side cavity surface and the moving side cavity surface due to the influence of the heat medium in the heat medium flow paths 5 and 6, but is exposed on the surface of the metal plate 7 which is in a low temperature state. The electromagnetic shielding synthetic resin solidifies in a state where the metal plate 7 and the conductive filler are electrically connected.

In other words, when a mold is filled with molten electromagnetic shielding synthetic resin that is a mixture of a conductive filler and a thermoplastic resin, the surface of the mold is heated to a temperature of 60°C or higher. In this case, since the resin is sufficiently melted to be in a fluid state, the resin component is concentrated near the surface of the mold rather than the conductive filler, and solidifies in a resin-rich state. Therefore, the conductive filler is not exposed on the surface of the molded shield case when removed from the mold, and an insulating layer with excellent smoothness and rich resin is formed, as if a film was formed from the resin component. It turns out.

On the other hand, at the fitting part of the mold into which a metal plate at -40 to 20°C is inserted, the filled synthetic resin with electromagnetic shielding properties comes into contact with the cooled metal plate and is rapidly cooled, solidifying as it is. The flow state time is short, and the resin components do not come together to form a coating on the metal plate. That is, the resin component and the conductive filler are solidified in a dispersed state, and the conductive filler is brought into contact with the exposed metal plate.

Figure 2a shows a cross section of an electromagnetic shielding case formed by fitting the molded products 9 and 10 with exposed metal plates into the fitting portion formed in this way with the metal plates 7 and 7 in contact. An enlarged cross-section of the joint is shown in Figure 2b. As shown in FIG. 2b, the conductive filler f in the molded product 9 is electrically connected to the metal plate 7, and the metal plate comes into contact with the metal plate 7' of the other molded product 10. Since the metal plate 7' is electrically connected to the conductive filler in the molded product 10, the entire fitting portion of the electromagnetic shielding case is in a conductive state, and leakage of electromagnetic waves at the fitting portion can be prevented.

Further, since the conductive filler is not exposed on the surface of the shield case and the insulating layer t is present, the appearance is smooth and there is no fear of being charged by contact with the conductive filler f.

[Embodiments of the invention]

Next, examples of the present invention will be described.

Example A nickel-plated iron plate cooled to a temperature of 5° C. at the time of insertion was inserted into a mold cavity serving as a fitting portion. In this state, the injection pressure was 900Kg/cm ² from the nozzle touch part of the mold, and the resin temperature was 230℃.
Filled with electromagnetic shielding synthetic resin made of ABS resin containing 40% by weight of brass fibers. The mold temperature was adjusted so that the fixed side cavity surface temperature was 75°C and the moving side cavity surface temperature was 70°C. The molding time is 18 seconds for injection and 60 seconds for cooling in the upper case, and 16 seconds for injection and 55 seconds for cooling in the lower case.
Seconds.

In this way, the width is 300mm, the length is 400mm, and the height is 200mm.
mm, wall thickness 3mm upper case, width 300mm, length 400mm,
A lower case with a height of 150 mm and a wall thickness of 3 mm was manufactured, a DC motor was built into these molded products, and the upper and lower cases were fitted together. After that, the DC motor is rotated, and the noise radio waves generated from the brush are
It was caught using a dipole antenna at a position 3 mm outside the case, and the side was determined using a spectrum analyzer. The measurement results were as shown in the graph of FIG. 3a.
On the other hand, an electromagnetic shielding case was manufactured in the same manner as in the example except that no metal plate was used during molding of the electromagnetic shielding synthetic resin, and a DC motor was incorporated therein to measure noise radio waves. The measurement results are shown in Figure 3b.
The results were as shown in the graph below.

As is clear from this graph, the electromagnetic shielding case of the example produced small noise radio waves and was found to have a good electromagnetic shielding effect.

〔Effect of the invention〕

As explained above, according to the method of the present invention, it is possible to obtain an electromagnetic shielding case that has conductivity at the mating part and has an insulating surface, which eliminates the need for secondary processing of the molded product and provides an electromagnetic shielding with a large electromagnetic shielding effect. You get a case.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a mold used in the method of the present invention;
Figure 2a is an assembled sectional view of the electromagnetic shielding case obtained by the method of the present invention, Figure 2b is Figure 2a
3A and 3B are graphs showing the electromagnetic shielding performance of the electromagnetic shielding case obtained by the method of the present invention and the electromagnetic shielding case obtained by the conventional method, respectively. 1... Fixed side template, 2... Moving side template, 3...
Fixed side cavity, 4...Movable side cavity,
5, 6... Heat medium flow path, 7, 7'... Metal plate, 9,
10... Molded product.

Claims (1)

[Scope of Claims] 1. In manufacturing an electromagnetic shielding case constructed by fitting two or more molded products made of electromagnetic shielding synthetic resin, the inside of the mold cavity in the part that becomes the fitting part of the molded products. A metal plate pre-cooled to -40 to 20℃ is inserted into the mold, the surface temperature of the mold is maintained at 60℃ or higher, and electromagnetic shielding synthetic resin is filled into the cavity and solidified. A method for manufacturing an electromagnetic shielding case, characterized by manufacturing a molded product in which a plate is exposed and a conductive filler is not exposed on the case surface.