JPH0112648B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of manufacturing an electromagnetic shielding case by injection molding.

[Technical Background of the Invention] In recent years, with the development of digital electronic devices, electromagnetic waves generated by these electronic devices may interfere with other devices such as nearby televisions, or may be caused by electromagnetic waves from other devices. The problem of erroneous operation caused by overloading has become a major focus of attention.

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

However, from the viewpoints of mass production, economy, lightness, etc., cases made of synthetic resin are often used.

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 in the background art] However, in method (a) of these methods, there is a risk that the electromagnetic shielding layer may peel or fall off due to impact from falling or thermal cycles, and the peeled pieces may There is a problem in that if it falls onto an electronic circuit, it can easily lead to serious accidents such as short circuits and fires.

In addition, in method (b), the cavity of the mold is Molding is carried out by keeping the surface temperature of the side as high as possible (usually 60°C or higher, depending on the type of thermoplastic resin) so that the conductive filler is not exposed from the surface. Electromagnetic shielding occurs due to loss of contact between the conductive fillers or between the conductive filler and the metal chassis at the fitting part of the case or the contact part when the case is brought into contact with the metal chassis to establish grounding. There was a problem that the electromagnetic shielding effect was reduced. Therefore, when a shield case is manufactured using this method, the surface of the fitting part or contact part must be removed until the conductive filler is uniformly exposed, which has the disadvantage that secondary processing is time-consuming. It was hot.

[Objective of the Invention] The present invention has been made to address the above-mentioned problems, and provides a method for manufacturing an electromagnetic shielding case that has an excellent electromagnetic shielding effect without requiring secondary processing as described above. The purpose is to

[Summary of the Invention] That is, the method for manufacturing an electromagnetic shielding case of the present invention includes forming a non-conductive layer made of a non-conductive thermoplastic composition on the outer surface of an electromagnetic shielding layer made of a conductive thermoplastic composition containing a conductive filler. manufacturing an electromagnetic shielding case in which the conductive filler is exposed only in a part of the electromagnetic shielding layer to form a conductive surface, and the conductive surface is brought into contact with another conductor for electrical continuity. In doing so, the conductive thermoplastic is heated and plasticized while being cooled so that the part where the conductive surface of the mold cavity corresponding to the electromagnetic shielding layer is to be formed is at a lower temperature than the part where the other parts are to be formed. An electromagnetic shielding layer having a conductive surface is filled with the composition, and then this electromagnetic shielding layer is loaded into a mold corresponding to the nonconductive layer, and the nonconductive layer is heated and plasticized into the mold. It is characterized in that it is filled with a thermoplastic composition and molded into a non-conductive layer.

In the present invention, the thermoplastic composition used for forming the non-conductive layer includes thermoplastic elastomer, polystyrene, ABS resin, polypropylene,
Examples include thermoplastic resins such as modified polyphenylene oxide.

In addition, the conductive thermoplastic composition forming the electromagnetic shielding layer may be a base polymer made of the above-mentioned composition and a conductive material such as powdered, fibrous or flaky carbon, iron, copper, copper alloy, aluminum, nickel, etc. Examples include those mixed with sex fillers. In particular, a thermoplastic elastomer is suitable as the base polymer for this conductive thermoplastic composition.

When thermoplastic elastomer is used, for example, when two or more molded products are fitted together to construct an electromagnetic shielding case, the surfaces of the electromagnetic shielding layers that come into contact with each other are completely pressed together by rubber elasticity, and the Excellent conductivity can be obtained.

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

FIG. 1 shows a vertical sectional view of a mold and an injection cylinder of an injection molding machine used in an embodiment of the method of the present invention.

In the figure, reference numeral 1 denotes a movable side template 2, and an electromagnetic shielding layer molding which forms a cavity 3a corresponding to the shape of the electromagnetic shielding layer of the inner layer of the electromagnetic shielding case to be molded in combination with the movable side template 2. Fixed side template 4a and moving side template 2
It consists of a fixed side mold plate 4b for molding a non-conductive layer, which is combined with the electromagnetic shielding layer 5 molded and fitted thereon to mold a cavity 3b corresponding to the non-conductive layer of the electromagnetic shielding case to be molded thereon. It shows a split mold for two-color molding.

Each fixed side template 4 of this split mold 1 for two-color molding
a, 4b have nozzle touch portions 8a, 8 which are in contact with the nozzles 7a, 7b of the injection cylinders 6a, 6b.
b is provided. In each cavity 3a, 3b of the two-color molding die 1, these nozzles 7a,
7b and nozzle touch parts 8a, 8b,
The injection cylinders 6a, 6b are filled with a plasticized conductive thermoplastic composition or non-conductive thermoplastic composition by the propulsion force of the screws 9a, 9b rotating, respectively.

In addition, the fixed side mold plate 4a for molding the electromagnetic shield layer
A refrigerant passage 10 is provided around the position corresponding to the end of the electromagnetic shield layer, and by passing a refrigerant such as water through the refrigerant passage 10, the refrigerant passage 10
The temperature of the mold surface on the cavity side adjacent to the mold can be cooled to around room temperature, for example, below 30°C.

FIG. 2 is a sectional view taken along the - line in FIG. 1, and shows the arrangement of the refrigerant passages 10 of the fixed side mold plate 4a for molding the electromagnetic shielding layer. In this embodiment, four independent refrigerant passages 10 are provided on the inner side of the joint of the fixed side mold plate 4a for electromagnetic shield molding, and by passing water through each of these refrigerant passages, a The mold surface on the side of the cavity 3a can be efficiently cooled.

Next, an example of manufacturing an electromagnetic shielding case with a fitting structure using this split mold will be described.

That is, first, as shown in FIG. 1, the nozzle 7 of the injection cylinder 6a is opened in a state in which the movable mold plate 2 and the fixed mold plate 4a for forming the electromagnetic shielding layer are combined.
a is brought into contact with the nozzle touch part 8a of the fixed side template 4a for forming the electromagnetic shielding layer, and water is passed through the coolant passage 10 of the fixed template 4a for forming the electromagnetic shielding layer to clean the conductive surface of the electromagnetic shielding layer at the left end in the figure. A plasticized conductive thermoplastic composition, such as ABS resin containing aluminum fibers, is press-fitted into the cavity 3a while cooling the area near the part to be formed to 30°C or lower (other parts to 60°C or higher). Then, an electromagnetic shielding layer is formed. At this time, the conductive thermoplastic composition press-fitted into the part of the mold near the refrigerant passage 10 where the temperature is below 30°C is rapidly cooled, the base polymer rapidly shrinks, and the conductive filler is solidified with the conductive filler exposed from the surface. , while the conductive thermoplastic composition press-fitted into the other mold part above 60℃, the conductive filler is embedded under the surface and the thermoplastic composition forms a smooth, non-conductive surface. .

Next, the movable side template 2 is extracted from the fixed side template 4a for molding the electromagnetic shielding layer, and is moved as shown by the arrow while keeping the molded electromagnetic shielding layer 5 fitted, and the cavity 3b is removed as shown by the dotted line.
is set to

Thereafter, the non-conductive thermoplastic composition, such as ABS resin, is plasticized in the injection cylinder 6b.
It is press-fitted into the cavity 3b via the nozzle 7b and the nozzle touch part 8b, and is solidified by being integrated with the electromagnetic shielding layer 5 formed previously.

FIG. 3 shows the electromagnetic shielding case 11 having a fitting structure formed in this way, and this electromagnetic shielding case 11 is composed of a main body part 12 and a lid part 13.

Thus, the main body part 12 and the lid part 13 each have inner electromagnetic shielding layers 12a, 13a and non-conductive layers 12b, 13 integrally formed thereon.
It consists of b. In addition, each electromagnetic shield layer 1
2a, 13a and the non-conductive layers 12b, 13b are different in level at the fitting portion, and the protrusion a of the electromagnetic shielding layers 12a, 13a is higher than the non-conductive layer 12.
It is slightly longer than the protrusion b of b, 13b.

FIG. 4 is a sectional view showing a state in which the main body part 12 and the lid part 13 are fitted together.

As shown in this figure, in the electromagnetic shielding case of this embodiment, the exposed surfaces of the conductive fillers of the electromagnetic shielding layers 12a and 13a are pressed against each other by rubber-like elasticity at the fitting part, so that complete conduction of the contact part is achieved. is obtained. In the figure, f indicates a conductive filler, and c indicates a bulge formed by elastically deforming the edge of the electromagnetic shielding layer.

Furthermore, non-conductive layers 12b and 13 made of a thermoplastic composition are provided on the electromagnetic shielding layers 12a and 13a.
b is provided, there is no risk of poor appearance or charging due to electric charge being supplied from the outside, and even if the electromagnetic shielding layer is made of a thermoplastic elastomer, the type and composition of the thermoplastic composition of the non-conductive layer, etc. By appropriately selecting the material, it is possible to improve the strength and obtain an electromagnetic shielding case having an arbitrary color.

[Effects of the Invention] As explained above, according to the method of the present invention, the electromagnetic shielding layer and the non-conductive layer are continuously molded using a two-color injection molding machine, so the electromagnetic shielding effect can be achieved extremely easily without the need for secondary processing. A case with excellent electromagnetic shielding can be obtained.

[Brief explanation of drawings]

Figure 1 is a longitudinal sectional view of an injection molding machine used in the method of the present invention, Figure 2 is a sectional view taken along the - line in Figure 1, and Figure 3 is a sectional view of an electromagnetic shielding case obtained by the method of the present invention. , FIG. 4 is a sectional view showing the assembled state. 1...Split mold for two-color molding, 2...Moving side mold plate, 3a, 3b...Cavity, 4a...Fixed side mold plate for electromagnetic shielding layer molding, 4b...Fixed side mold for electromagnetic shielding case molding Plate, 5... Electromagnetic shielding layer, 6a, 6b... Injection cylinder, 7a,
7b... Nozzle, 8a, 8b... Nozzle touch part, 10... Refrigerant passage, 11... Electromagnetic wave shielding case, 12a, 13a... Electromagnetic wave shielding layer,
12b, 13b...non-conductive layer, f...conductive filler.

Claims (1)

[Scope of Claims] 1. A non-conductive layer made of a non-conductive thermoplastic composition is provided on the outer surface of an electromagnetic shielding layer made of a conductive thermoplastic composition containing a conductive filler, and one of the electromagnetic shielding layers is provided with a non-conductive layer made of a non-conductive thermoplastic composition. In manufacturing an electromagnetic wave shielding case in which the conductive filler is exposed only in a portion to form a conductive surface, and this conductive surface is brought into contact with another conductor to provide electrical continuity, the electromagnetic wave shielding case corresponds to the electromagnetic wave shielding layer. While cooling the mold cavity so that the part where the conductive surface is to be formed is at a lower temperature than the part where the other parts are to be formed,
The conductive thermoplastic composition that has been heat-plasticized is filled to form an electromagnetic shielding layer having a conductive surface, and then this electromagnetic shielding layer is loaded into a mold corresponding to the non-conductive layer. 1. A method for manufacturing an electromagnetic shielding case, comprising filling the non-conductive thermoplastic composition heated and plasticized to form a non-conductive layer. 2. Claims that, in the molding process of the electromagnetic shielding layer, the heated and melted conductive thermoplastic composition is filled into the mold while maintaining the temperature of the part of the mold where the conductive surface is to be formed at 30°C or less. A method for manufacturing an electromagnetic shielding case according to item 1. 3. The method for manufacturing an electromagnetic shielding case according to claim 1 or 2, wherein the conductive thermoplastic composition is based on a thermoplastic elastomer.