JPH05191077A - Vacuum formed electromagnetic shielding film - Google Patents

Abstract

PURPOSE:To provide a vacuum-formed laminated film which is excellent in electromagnetic shielding effect. CONSTITUTION:A laminated film of this invention is composed of three kinds of films formed of thermoplastic polymer 1, thermoplastic adhesive polymer 2, and low melting metal or alloy 3 respectively. Each of them is formed in film of about 2-100mum and the films are laminated together. The thermoplastic polymer 1 serves as reinforcing material which enhances the laminated film in strength, the thermoplastic adhesive polymer 2 serve as adhesive agent, and the metal or alloy 3 serves as electromagnetic shield. As metal or alloy is used in film, it is high in electromagnetic shielding effect. As metal or alloy is low in melting point, the laminated film can be vacuum-formed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a material for shielding electromagnetic waves. IC, the most important part of the computer
The device operates with a small current. Therefore, it may operate by picking up electromagnetic waves emitted by other things around. For that computer, this is a malfunction. Such malfunctions are easily caused not only by natural phenomena such as lightning strikes, but also by electromagnetic waves emitted from devices such as transceivers. In recent years, the performance of computers has improved,
As it is used in various industries, prevention of malfunction has become a major issue. The film of the present invention is used for the purpose of shielding electromagnetic waves from the outside so that the equipment does not malfunction, or shielding electromagnetic waves emitted by the equipment itself so as not to affect surrounding equipment.

[0002]

2. Description of the Related Art There are the following materials for electromagnetic wave shielding of devices such as computers. -Conductive paint-Molding material for electromagnetic wave shielding These are explained below.

Conductive paints Conductive paints include synthetic resin paints such as acrylic, acrylic urethane, and urethane resins, and silver, nickel, copper,
It is filled with a conductive material such as conductive carbon. Apply this paint to the inside of the housing of the device you want to shield electromagnetic waves. It is an important point that the conductive paint has a film having a certain thickness or more uniformly applied to the housing. However, the corners, ribs, and bosses are difficult to apply, and may be left uncoated or the film thickness may be reduced. External electromagnetic waves come in from this part, and the noise of the device leaks out. Then, the electromagnetic wave shielding effect is drastically reduced. Even if it can be applied uniformly, the paint may be oxidized and deteriorated over time, and the shielding effect may be reduced. Further, the conductive paint may peel off from the housing. Then, not only the shield effect of the peeled portion is deteriorated, but also the circuit may be short-circuited by the peeled paint. This can lead to fire.

Molding Material for Electromagnetic Wave Shield The molding material for electromagnetic wave shielding is a plastic filled with a conductive material. Unlike a paint that imparts conductivity by post-treating the molded housing, the molded product itself becomes electrically conductive, so there is a feature that no post-treatment is required.

Since the plastic has no conductivity at all, the conductive material is responsible for this. The conductive material is
Metal fibers such as aluminum and brass, metal flakes such as aluminum and brass nickel, and conductive carbon are used. Of these, the conductivity of conductive carbon is only about 1/100 that of metal fibers. Therefore, the molding material mixed with conductive carbon can only be used as a countermeasure against static electricity.

Although metal fibers and metal flakes have a high conductivity, the shielding effect cannot be obtained unless they are added to the plastic in an amount of 30 to 40% by weight. Since it is a material that contains a lot of metal like this, it has some problems. ○ The molding is heavy. Plastic has the characteristic of being light, but this characteristic is lost due to the addition of a lot of metal. ○ Moldability is poor. Since a material containing a lot of metal is molded, the flow is poor and it is difficult to mold. The appearance of the molded product also deteriorates. ○ Loss of mechanical properties. Since a large amount of metal is mixed with plastic, the mechanical properties (for example, strength) of the plastic itself are impaired. ○ Loss of insulation. Since this molded product becomes electrically conductive as a whole, it loses the insulating property, which is a characteristic of plastics.

The addition of such a large amount of metal causes many problems. However, even if a large amount of metal is added to the plastic, the shielding effect of the molded product may not be sufficiently improved. In order to improve the shielding effect, the uniform distribution of metal in the molded product is the most important. However, the dispersibility of metal in plastic is not very good. If the dispersion of the metal is not sufficient, the molded product may partially have an uneven amount of the metal. If a portion with a small amount of metal is formed, external electromagnetic waves easily enter from here, and the shielding effect is reduced.

[Problems to be Solved by the Invention]

The film of the present invention solves the problems of the electromagnetic wave shielding material as follows.

A case having a uniform electromagnetic wave shielding property can be manufactured. If the coating is uneven like a conductive paint, or if the metal is not uniformly dispersed like a conductive molding,
Due to the housing part, a part that does not shield electromagnetic waves is created. If there is such a portion, the electromagnetic wave shielding effect is greatly reduced. In the present invention, in order to avoid such a problem,
It is possible to form a housing having a uniform electromagnetic wave shielding property. ○
The electromagnetic wave shielding effect is stable over time. In the conductive paint, the conductive material is oxidized and deteriorated, but the present invention does not have such a problem. Therefore, the electromagnetic wave shielding effect does not change for a long period of time. ○ There is no risk of short circuit. Conductive paint is
Although it may peel off from the housing, the present invention does not have such a case. Therefore, the circuit is not short-circuited. ○ High electromagnetic wave shielding effect. ○ The molding is not heavy. ○ Good moldability. ○ The mechanical properties and insulation of the case are not lost.

[0010]

The film of the present invention has the following constitution. Three types of materials used, namely thermoplastic polymers,
Choose thermoplastic adhesive polymers, low melting point alloys and metals. Each of the three types of materials is used as a film, and the thermoplastic adhesive polymer is used as an intermediate layer, and the thermoplastic polymer and a film of a low melting point alloy or metal are laminated. This will be described in detail below.

The three types of materials used are selected: thermoplastic polymers, thermoplastic adhesive polymers, low melting alloys and metals. The present invention is composed of these three types of materials. Each will be described. The thermoplastic polymer is selected from thermoplastic polymers such as thermoplastics and thermoplastic elastomers. Specifically, acrylonitrile / butadiene / styrene copolymer, modified polyphenylene oxide, polyethylene, polypropylene, polystyrene, polyamide, polyester, ethylene / vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, polymethylpentene, It is possible to use thermoplastics such as polyimide, polycarbonate, polyacetal, polysulfone, polyphenylene sulfide, and fluoropolymers, and thermoplastic elastomers such as styrene, olefin, ester, urethane, isoprene, butadiene, and vinyl chloride. it can. Two or more may be selected from these and mixed and used. In that case, make sure to choose one with good compatibility.

As the thermoplastic adhesive polymer, any thermoplastic polymer having high adhesiveness to a metal can be used.
Many of these polymers have high polarity by introducing a polar group into a thermoplastic polymer. Among them, a polymer in which a polar group is introduced by modifying a thermoplastic polymer with an acid such as maleic anhydride or carboxylic acid is easily available. Modified with maleic anhydride using thermoplastics such as low density polyethylene, high density polyethylene, polypropylene, ethylene / vinyl acetate copolymer, and thermoplastic elastomers such as styrene / ethylene / butylene / styrene copolymer. Things are actually commercialized. Two or more may be selected from these and mixed and used.

Low melting point alloys and metals are about 80-280.
Any alloy or metal that melts at ℃, preferably about 100-230 ℃ can be used in the present invention. Considering environmental issues, those with low toxicity are preferable. Specifically, it can be selected from alloys such as zinc alloy, lead alloy, tin alloy, bismuth alloy, and aluminum alloy, and metals such as tin and indium. More specifically, the alloy may be a zinc aluminum alloy, a ZDC alloy, a lead antimony alloy, a lead calcium alloy, a lead tin alloy, a tin lead alloy, a tin antimony alloy, an aluminum magnesium alloy, an aluminum zirconium alloy, or the like.

The three kinds of materials are respectively formed into films, and the thermoplastic adhesive polymer is used as an intermediate layer, and the thermoplastic polymer and the film of alloy or metal having a low melting point are laminated. Laminate the 3 types of materials selected in step 1 into films. The simplest laminated film is shown in FIG. The thickness of each film is about 10 to 100 μm for the thermoplastic polymer, about 2 to 20 μm for the thermoplastic adhesive polymer, and about 2 to 70 μm for the low melting point alloy or metal.
Try to be around. If a low-melting alloy or metal with low electrical conductivity is selected, use a thicker film.
These may be formed into a film by any means. For example, thermoplastic polymers and thermoplastic adhesive polymers
Inflation molding, T-die molding, and calendar molding are recommended. The low melting point alloy or metal can be formed into a film by rolling the alloy or metal by calendar molding or the like.

[0015]

[Figure 1]

The three kinds of films are laminated so that the thermoplastic adhesive polymer film is inserted between the thermoplastic polymer film and the low melting point alloy or metal film. Each film may be first molded and then heated and laminated through a hot roll or the like. Alternatively, a thermoplastic polymer and a thermoplastic adhesive polymer may be laminated, and an alloy or metal may be rolled thereon. However, it is easy to mold three types of films and simultaneously laminate them with a heat roll.
The temperature of the heating roll is set to a temperature at which one of the thermoplastic adhesive polymer, the low melting point alloy and the metal melts, or higher. The thickness of the laminated film is about 15-50
It should be about 0 μm.

[0017]

The present invention is a laminate of three types of films of a thermoplastic polymer, a thermoplastic adhesive polymer, and a low melting point alloy or metal. The inventor has been
Invented an alloy that kneaded the person. (Patent application No. 2 of 1991)
No. 98607) The film of the present invention is based on this and has improved conductivity and moldability. The three types of materials are
It has the following roles. Each will be described.

The thermoplastic polymer imparts strength such as tensile strength and bending strength to the film. The thermoplastic adhesive polymer serves as an adhesive between the thermoplastic polymer and an alloy or metal having a low melting point. Since the thermoplastic polymer has a lower polarity than alloys and metals, it has low adhesion to alloys and metals having low melting points. However, when a polar group is introduced into the thermoplastic polymer, the polarity becomes high and the metal also adheres. Polypropylene modified with maleic anhydride is actually used for the laminated film. Even when trying to laminate nylon with good gas barrier property and polypropylene with good heat seal property, it does not adhere. However, this maleic anhydride-modified polypropylene was
When sandwiched between different types of sheets, they can be laminated. That is, the maleic anhydride-modified polypropylene serves as the adhesive layer. When a polar group is introduced into the thermoplastic polymer, it becomes possible to adhere to such a low-polarity polymer, a high-polarity polymer and a metal. Therefore, a thermoplastic adhesive polymer film is placed between the thermoplastic polymer film and the low melting point alloy or metal film.
All three types of film are heated, that is,
Since it is laminated with the surface of the film activated, it has high adhesiveness. Therefore, it does not peel off for a long time.

The alloy or metal having a low melting point is for producing an electromagnetic wave shielding effect. Since the two types of thermoplastic polymers described above are thermoplastic, they can be easily formed into a film. Some alloys and metals are difficult to make into films. However, in the present invention, the melting point is 80 to 280 ° C.
Since the alloy or metal of No. 2 is used, a film having a thickness of about 2 to 50 μm can be formed. Since the conductive material is used as a film in this way, the laminate film of the present invention has high conductivity and partial unevenness in conductivity is generated as compared with a molding material using metal flakes or the like. There is no.

Next, a method of using the film of the present invention will be described. The present invention is not intended to make an electromagnetic wave shielding molded product (for example, a computer housing) by itself. The housing is required to have impact strength. This is made using a shock-resistant resin such as an acrylonitrile / butadiene / styrene copolymer, modified polyphenylene oxide, polystyrene, or polycarbonate. Make a mold with the same shape as the inside of the housing. Using the film of the present invention,
Vacuum mold with this mold. Insert the molded film into the inside of the housing made earlier. In this way, the housing becomes electromagnetic wave shielding. By vacuum forming, the thickness of the alloy or metal film is partially reduced. However, since the alloy or metal film will not be broken, the electromagnetic wave shielding property of the molded product will not be uneven.

The laminate film of the present invention comprises a thermoplastic polymer, a thermoplastic adhesive polymer and a low melting point alloy or metal. The former two can be easily vacuum-formed. The present invention has one feature in using a conductive metal having a low melting point. We chose alloys and metals whose melting points are close to those of thermoplastic polymers. Moreover, thin films of alloys and metals are used. Therefore, during vacuum forming, the alloy or metal can be stretched together with the thermoplastic polymer or the like. As described above, the film of the present invention contains a metal, but is a vacuum formable film.

With respect to the conductive paint, it has been mentioned above that there is a risk of short-circuiting the circuit. In the film of the present invention, since the low melting point alloy or metal and the thermoplastic adhesive polymer are strongly bonded, the alloy or metal does not peel off. However, in order to avoid this danger, vacuum forming is performed with the low melting point alloy or metal on the outside. That is, it may be molded so that the alloy or metal film comes into contact with the molded product serving as the housing. For higher safety, a laminated film sandwiching an alloy or metal with a polymer is used. That is, a thermoplastic polymer, a thermoplastic adhesive polymer, a low melting point alloy or metal,
5 in order of thermoplastic adhesive polymer, thermoplastic polymer
A laminated film composed of layers. (Fig. 2) By doing this, there is no fear that the alloy or metal will peel off.

[0023]

[Fig. 2]

For the sake of clarity, the description has centered on a simple laminate. Any number of layers may be stacked as long as the thickness allows vacuum forming and the order is such that the film is not peeled off. For example, another thermoplastic polymer may be overlaid on the thermoplastic polymer. Further, for example, a thermoplastic adhesive polymer may be laminated on a low-polarity thermoplastic polymer, and a high-polarity thermoplastic polymer may be laminated thereon.

[0025]

【Example】

Example A) Example in which zinc-tin alloy is used as low melting point alloy or metal Zinc-tin alloy has a melting temperature of 200 ° C or higher, which is higher than the melting temperature of general thermoplastic polymers. Therefore, as the thermoplastic polymer, those which are resistant to high temperature were selected. 6,6-Nylon was used as the thermoplastic polymer, and maleic anhydride modified polypropylene (Admer OF 305, Mitsui Petrochemical Industry Co., Ltd.) was used as the thermoplastic adhesive polymer.
As the zinc-tin alloy, 70% zinc was used. Each film was molded and laminated at the same time so that nylon was about 20 μm, Admer was about 5 μm, and zinc-tin alloy was about 15 μm. The laminate is made of Admer alloy and sandwiched with nylon,
Laminated in 5 layers at ° C. This laminate film can be vacuum formed at 220 to 250 ° C. The molded product does not peel off in each layer.

Example B) Example in which lead-tin-zinc alloy is used as low melting point alloy or metal Styrene / butadiene thermoplastic elastomer modified with polystyrene as thermoplastic polymer and maleic anhydride modified as thermoplastic adhesive polymer (Asahi Kasei (Tuftec Co., Ltd. M1913), and a low-melting point alloy or metal, a lead-tin-zinc alloy (63% lead, 34% tin, 3% zinc) was selected. This example also uses a 5-layer laminated film. Center thickness is 20 μm
Of the lead-tin-zinc alloy film, the tough tech film having a thickness of about 5 μm on both sides, and the polystyrene film having a thickness of about 25 μm on the outermost side. Each film was molded and laminated at the same time. This laminate film can be vacuum formed at 170 to 220 ° C. The molded product is relatively shock resistant and easy to handle. Further, even if it is bent, it does not peel off for each film.

Example C) Example in which aluminum alloy is used as low melting point alloy or metal Acrylonitrile / butadiene / styrene copolymer (Kane Ace MUH, Kanegafuchi Chemical Co., Ltd.), thermoplastic adhesive polymer Maleic anhydride modified polypropylene (Mitsui Petrochemical Industry Co., Ltd.)
Admer OF 551), low melting point alloys and metals, aluminum alloys (aluminum, iron, magnesium alloys)
I chose. An Admer film having a thickness of about 8 μm was sandwiched between a Kane Ace film having a thickness of about 40 μm and an aluminum alloy film having a thickness of 25 μm, and laminated at about 200 ° C. This laminated film is 220 ~
Can be vacuum molded at 230 ° C. The molded product is thin, but strong against impact. Moreover, it is not peeled off to each film.

(Experiment) The films of Examples A to C were tested for electromagnetic wave shielding effect. The test method was in accordance with the Advantest method, and the shield effect of the electric field and the magnetic field at 200 MHz was tested. As a control, an acrylonitrile-butadiene-styrene copolymer containing 60% by weight of brass fiber (thickness 1 m
m) was selected. The results are shown in Table 1. The film of the present invention was thinner than the control sample, but had a high electromagnetic wave shielding effect.

[0029]

[Table 1]

[0030]

[Effect] The laminate film of the present invention uses a conductive material as a film. Therefore, the electromagnetic wave shielding effect is high. In addition, the conductive coating material having uneven coating and the conductive molding having uneven metal dispersion may not have uniform electromagnetic wave shielding properties. In this case, the electromagnetic wave shielding effect of the case is greatly reduced. However, in the present invention, since the conductive material is a film, this is not the case. Also, since the conductive material is a thin film, the molded product is light. It is not the present invention that the conductive molding becomes heavy like a conductive molding filled with a large amount of conductive material.

In the laminated film of the present invention, a conductive material can be sandwiched between plastics. Since the conductive material is not oxidized, the electromagnetic wave shielding effect is stable for a long period of time. Further, since the conductive material is not peeled off, there is no fear of short circuit.

The laminated film of the present invention uses an alloy or metal having a low melting point. Therefore, vacuum molding, which is a simple molding method, can be adopted. Items made by vacuum molding are fitted into a separately made case. Therefore, the mechanical characteristics and insulating properties of the housing are not lost.

[Brief description of drawings]

FIG. 1 is a sectional view of the simplest laminated film.

FIG. 2 is a cross-sectional view of a laminated film in which an alloy or metal is sandwiched between thermoplastic polymers.

[Explanation of symbols]

 1 thermoplastic polymer 2 thermoplastic adhesive polymer 3 low melting point alloys and metals

Claims (1)

[Claims] 1. A thermoplastic comprising a thermoplastic polymer, a thermoplastic adhesive polymer, an alloy having a melting point of 80 ° C. to 280 ° C. and / or a metal having a melting point of 80 ° C. to 280 ° C. A laminate film comprising a layer of a thermoplastic adhesive polymer between a layer of polymer and a layer of the metal or / and the alloy.