JPH0454400B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention relates to a method for manufacturing an electromagnetic shielding case, and its purpose is to shield electromagnetic noise emitted from digital equipment, and to manufacture an electromagnetic shielding case that is thin and has strong mechanical strength in a few steps. It is an object of the present invention to provide a method for manufacturing an electromagnetic shielding casing, which also allows an electromagnetic shielding object to be uniformly placed inside the casing. (Prior art and its problems) In recent years, with the spread of digital devices (computers, minicomputers, microcomputers, etc.), the electromagnetic noise oscillated by the clock frequency oscillators built into these digital devices has become a major issue in the electricity supply in ordinary homes. This has become a problem as it often causes interference with equipment. In order to prevent this electromagnetic noise, there are disclosures of electromagnetic shielding technology that involves spraying a shield coating or zinc coating on the surface of the housing, but the shielding paint is a combination of the synthetic resin that makes up the housing and the synthetic resin that forms the paint vehicle. The problem was that there was no shielding paint that could be used on any type of housing. Furthermore, the uniformity of the coating film became a problem, and when the environment in which the digital equipment was used deteriorated, the coating film was damaged and the shielding ability was sometimes reduced. Moreover, there was also the drawback that there were many manufacturing steps. Therefore, in many cases, the surface of the digital device's case is treated with or without shielding, and the current situation is to cover the entire case of the digital device with a large metal case to provide electromagnetic shielding. in,
I hated having digital devices take up so much space. On the other hand, as shown in FIGS. 3A and 3B, electromagnetic shielding material 3 such as mesh metal or wire mesh is formed by compression molding method in which synthetic resin is molded using upper and lower separated molds 1 and 2.
The present inventors have attempted to simultaneously mold the molten synthetic resin 4. According to this method, a large-sized object can be molded with a uniform thickness using less pressure than the injection method. In addition, the housing 5 manufactured by this method has a superior shielding effect compared to a shield-coated housing, and
It has excellent manufacturing workability. However, the housing 5 manufactured by this method is shown in Fig. 3B.
As shown in the figure, the electromagnetic shield 3 has poor filling properties,
As shown in locations A and B, the electromagnetic shield 3 is exposed on the surface of the casing 5, giving a poor appearance, and as a casing actually used for electrical equipment, there is concern that it may have an adverse effect on the digital equipment itself. Moreover, this method requires the electromagnetic shield 3 to maintain its own shape, and has the disadvantage that the electromagnetic shield 3 made of considerably thick metal fibers must be used. Moreover, compression-molded electromagnetic shielding casings are disclosed in Japanese Patent Laid-Open No. 58-73198 and Japanese Patent Laid-Open No. 58-73199. This electromagnetic shielding casing is made by laminating a reinforcing glass fiber or polyester fiber with a metallized carbon fiber, metal fiber, or non-metal fiber material, and the net is coated with a conductive composite polymer matrix. It is disclosed as an electromagnetic shielding casing that is laminated and has improved shielding ability and tensile strength. However, since this electromagnetic shielding casing is made by laminating a conductive composite polymer matrix on a net or the like and compression molding it, the net or the like may come out from the surface of the matrix, as described above. Furthermore, there is a technique disclosed in Japanese Patent Publication No. 43-7450 as a method for producing a molded article having different colors inside and outside by heat-pressing molding. In the first step, the method for manufacturing a molded product with different internal and external colors involves filling a female mold with a known molding material that will give the external color (or internal color) and molding under heat and pressure to form an incompletely cured molded product. Next, the mold is opened, and in the second step, a heat-flowable and fast-curing colored molding material is added onto the molded product (or between the molded product and the female mold), and the mold is refilled. It is disclosed as a method for manufacturing a molded product which is formed by heating and pressure molding and has a different color inside and outside. In particular, in the first step, the molded product with the internal color is molded,
There was a problem when molding a molded product with an external color in the second step. That is, in the second step, since the thermofluid and fast-curing molding material comes into direct contact with the female mold, the curing time is shortened and it hardens quickly, and the hardening reduces the spreadability. It was difficult to mold the molding material into the desired shape on the female mold. Further, there is a technique disclosed in Japanese Patent Publication No. 37-13779 as a method for producing a molded article having different colors inside and outside by heat-pressing molding. This method of manufacturing a molded product with different colors inside and outside is as follows: In the first step, synthetic resin powder is heated and pressed using a female mold and a male mold to mold the outer layer, and in the second step, the innermost layer of the female mold is molded in the first step. This patent discloses a method for manufacturing a molded article with different inner and outer colors, in which the outer layer and the inner layer are molded by heating and pressing synthetic resin powders of different colors from the outer layer using a male mold. However, in this disclosed technique, since the inner layer is molded after the outer layer is molded, it cannot be applied to a molded body in which the inner layer is molded first and then the outer layer is covered. Furthermore, ``radio wave shielding material'' was also disclosed in Japanese Patent Application Laid-Open No. 54-60504. This disclosed technology consists of a plate-shaped resin serving as a base material, and a conductive fiber fabric that is integrally bonded to the resin and held substantially parallel to the plate-shaped surface, and is made of a sandwich fabric. It is disclosed as a radio wave shielding material that can also have a structure. However, when the sandwich structure is adopted, the radio wave shielding material becomes thick, making it unsuitable for use in a radio wave shielding case. That is, in order to form an electromagnetic shielding case with a small outer diameter and a large internal volume, it is necessary to have a structure that is as thin as possible and has excellent mechanical strength. (Means for Solving the Problems) This invention uses a mold with upper and lower parts separated, and an electromagnetic shield is placed in the lower mold of the mold, and the lower mold has a weak mechanical strength. After supplying the molten synthetic resin, a first step of interlocking the upper and lower molds;
The molded body formed in the process is inserted into the lower mold of a separately prepared top-bottom mold, and then placed between the molded body and the upper surface of the lower mold at the approximate center of the lower mold. All of the above problems are solved by a method for manufacturing an electromagnetic shielding casing, which comprises a second step of supplying molten synthetic resin through the provided resin supply hole and then engaging the upper and lower molds. (Example) Hereinafter, an example of the present invention will be described based on the drawings. The method of this invention is shown in FIGS. 2A to 2G. First, as shown in FIGS.
13 is used to carry out the first step. First, the electromagnetic shield 7 is placed on the lower mold 13. The mesh unit of the electromagnetic shielding case 7 is 2 mm.
A highly conductive metal member such as copper, iron, or stainless steel, such as a mesh metal or punched metal with a diameter of 5 mm to 5 mm, is preferably used. The molten synthetic resin 10 is supplied into the lower mold 13. As the molten synthetic resin 10 used here, general-purpose synthetic resins with low mechanical strength, such as polyethylene and polypropylene, can be suitably used. As shown in FIG. 2B, the upper mold 12 is driven to engage the upper and lower molds 12 and 13. Then, as shown in FIG. 2C, the electromagnetic shield 7 is filled in the molten synthetic resin and shaped. In this way, a molded body 14 as shown in FIG. 2D is obtained. Even if the molded body 14 has a large shape, it can be molded into a casing with a uniform thickness due to the above-mentioned characteristics of the compression molding method (lower pressure is required than in the injection molding method). However, as described in the related art section, this molded body 14 often has a portion where the electromagnetic shield 7 is exposed on the surface. Next, upper and lower molds 15 and 16 are separately prepared and a second step is performed (see FIG. 2 E and F). The molded body 14 produced in the first step is inserted into the lower mold 16 (FIG. 2E). Next, a molten synthetic resin 11 having strong mechanical strength is passed through a resin supply hole 1 provided approximately in the center of the lower mold 16 between the surface of the molded body 14 and the upper surface of the lower mold 16.
8. In this way, melt-fused synthetic resin 1 with strong mechanical strength
By supplying molten synthetic resin 11 from below through the resin supply hole 18, the molten synthetic resin 11 can be dispersed on the lower mold 16 and uniformly filled therein. The melt-fused synthetic resin 11 used in this second step may be the same as the melt-fused synthetic resin 10, but is preferably Noryl (manufactured by EPL (trade name)).
Engineering plastics, such as, are suitable. After this, as shown in FIG. 2F, the upper and lower molds 15,
16 are engaged with each other to form the covering layer 9. In this way, the electromagnetic shielding casing 6 shown in FIG. 2G or FIGS. 1A and 1B is obtained. In this way, this electromagnetic shield 6 is shown in FIGS.
Since the surface of the synthetic resin 8 with weak mechanical strength is covered with the coating layer 9 with strong mechanical strength, the electromagnetic shield 7 is exposed from the surface of the synthetic resin 8. will also be covered with the covering layer 9. Test examples and comparative examples are shown below. Test example: Molded objects were made from polypropylene resin by compression molding, and the length, width, and height were 40 cm, 45 cm, and 13 cm, and the thickness was 2.
The molded body was constructed as an open body with a diameter of 5 mm, and a 5 mm mesh stainless wire gauze was placed inside the molded body. This wire mesh is made of 0.2mm stainless steel fiber. Wire mesh was exposed at three locations on the surface of this molded product. In the second method of this invention, a coating layer made of Noryl (manufactured by EPL (trade name)) is applied to the surface of this molded body.
It was molded to a thickness of 2 mm using the compression molding method in the process. Comparative Example 1 Apertures with length, width, and height of 45 cm, 45 cm, and 13 cm and a thickness of 4 mm were formed from Noryl (manufactured by EPL (trade name)) using the usual method, and a lead coating with a thickness of 0.02 mm was applied to the surface. Sprayed. Comparative Example 2 Opening bodies with length, width, and height of 45 cm, 45 cm, and 13 cm and a thickness of 4 mm were formed from the Noryl in a conventional manner, and coated with electromagnetic shielding paint 0.04 mm thick. As this electromagnetic shielding paint, we used a paint in which nickel powder was dispersed and a synthetic resin was used as a vehicle. Damage test These casings were tested in an atmosphere of 60℃ and 40% humidity.
It was left for one day to damage the surface in an apparatus that rotates 4 revolutions per minute (rotation). This damage test corresponds to two years of use. These casings are manufactured by Nippon Data General Co., Ltd.
-4000 and 32-bit super minicomputers, respectively, and the field strength of the radiated interference radio waves (30 m, 40 MHz) was measured before and after the above damage test. The results are shown in the table below.

[Table] From the above results, it can be seen that an excellent electromagnetic shielding casing can be manufactured by the method of the present invention. (Effects of the Invention) This invention uses a mold with upper and lower parts separated, an electromagnetic shield is laid in the lower mold of the mold, and a molten synthetic resin with low mechanical strength is supplied into the lower mold. After that, the first step is to engage the upper and lower molds, and this first step
The molded body formed in the process is inserted into a lower mold of a separately prepared upper and lower mold, and then a substantially central portion of the lower mold is inserted between the molded body and the upper surface of the lower mold. This method of manufacturing an electromagnetic shielding casing includes the second step of supplying a molten synthetic resin with strong mechanical strength through a resin supply hole provided in the resin supply hole, and then engaging the upper and lower molds, so that it has the following effects. . That is, in the first step, a resin with low mechanical strength that has embedding properties is used, and in the second step, a resin with strong mechanical strength that has shape retention is used for molding, and in the second step, the lower mold is Since the molten resin is fed through the resin distribution hole provided approximately at the center of the mold, the molten resin is evenly distributed over the lower mold. Therefore, the electromagnetic shielding material does not appear on the surface as in the past, and compared to electromagnetic shielding paint, the electromagnetic shielding effect can be maintained for a longer period of time, and the electromagnetic shielding material itself acts as a reinforcing material, increasing mechanical strength. The present invention has an excellent effect in that a thin electromagnetic shielding casing can be manufactured extremely efficiently.

[Brief explanation of the drawing]

FIG. 1A is a partially cutaway external view of an electromagnetic shielding casing manufactured by the method of this invention, FIG. 1B is a sectional view of the same electromagnetic shielding casing, and FIGS. 2A to G show each step of the method of this invention. 3A and 3B are cross-sectional explanatory views of a conventional example. 6 ... Electromagnetic shielding casing, 7... Electromagnetic shielding, 8...
... Synthetic resin, 9 ... Covering layer, 10, 11 ... Molten synthetic resin, 12, 13 ... Upper and lower molds used in the first step, 14 ... Molded object molded in the first step, 15 , 16... Upper and lower molds used in the second step, 18... Resin supply hole.

Claims (1)

[Scope of Claims] 1. After using a vertically separated mold, placing an electromagnetic shield in the lower mold of the mold, and supplying a molten synthetic resin with low mechanical strength into the lower mold. , a first step of interlocking the upper and lower molds, and inserting the molded object formed in this first step into a lower mold of a separately prepared upper and lower mold, and then inserting the molded object and the lower mold. A second step of interlocking the upper and lower molds after supplying a molten synthetic resin with strong mechanical strength through a resin supply hole provided approximately at the center of the lower mold between the upper surface of the mold and the upper mold. A method of manufacturing an electromagnetic shielding case. 2 Mesh unit is 2mm to 5mm as an electromagnetic shield
2. The method of manufacturing an electromagnetic shielding casing according to claim 1, wherein a highly conductive metal member of mm is laid.