JPS5968236A - Composite sheet for electromagnetic shielding - 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 The present invention relates to a novel composite sheet for electromagnetic shielding. In particular, the present invention relates to a novel composite sheet that has excellent electromagnetic shielding effects, high electrical resistance, and good antistatic properties.

In recent years, with the remarkable development of electronic equipment that fully applies digital technology, which is dominated by high-density, high-output computer equipment, radio,
Televisions and peripheral devices are becoming subject to radio wave interference due to severe electromagnetic interference, and various methods have been proposed and implemented to completely shield this interference.

One method for electromagnetic shielding is the thermal spraying of metal, particularly zinc, but although this method has a great shielding effect, it has drawbacks such as high cost, the need for surface treatment, and poor mass productivity. Also, the method of applying conductive paint is generally not sufficiently effective;
It has drawbacks such as poor durability. Vacuum deposition and sputtering methods are expensive and have many practical problems. In addition, the method of mixing conductive fillers such as aluminum, nickel, graphite, carbon blank, carbon fiber, etc. into plastics has been particularly developed in recent years, but in order to achieve a sufficient effect, it is necessary to mix in the great material. This often results in poor moldability and a significant reduction in the mechanical properties of the product.

Based on the above circumstances, the present inventors have conducted various studies to develop a simple, highly effective, and highly durable electromagnetic shielding material, and as a result, they have arrived at the present invention.

In other words, does the present invention apply to both sides of the conductive metal layer? [This is a composite sheet for electromagnetic shielding made by laminating insulating plastic layers. 1 to 3 show structural examples of composite sheets according to embodiments of the present invention.

Figure 1 shows one embodiment of the present invention, in which a conductive metal foil (1) and an electrically insulating plastic film (2) and (3) are combined with an adhesive layer (4) and a full plate. A composite sheet for electromagnetic shielding is shown by laminating a composite sheet for electromagnetic shielding. Fig. 2 also shows an embodiment of the present invention, in which a plastic film (6) on which a conductive metal thin layer (IA) is deposited and an electrically insulating plastic film. or a composite sheet for electromagnetic shielding by laminating sheets (2) and (3) through all adhesive layers (4) and (5). FIG. 3 also fully shows one embodiment of the present invention, and shows a plastic film (electrically insulating plastic film or sheet) (2B) in which conductive metal foil (IB) is laminated with an adhesive layer (7) interposed therebetween. 3B)'
An electromagnetic effect created by laminating the fc adhesive layers (4) and (5) all through! A composite sheet for I-covering is shown.

As the conductive metal layer, a metal foil, a multilayer of metal foil and a plastic film, or a plastic film on which a thin metal layer is completely deposited can be used.

As the metal foil used in the present invention, conductive metals such as aluminum, aluminum, copper, tin, zinc, titanium, etc., or alloys thereof are suitable, and the thickness thereof varies depending on the required electromagnetic shielding performance. 200 microns, especially 20 to 1
00 microns is suitable. If the thickness is less than 15 microns, the effect will not be sufficient, and if the thickness is more than 20 microns, it is unnecessary in terms of performance, and the laminated sheet will become heavy and expensive, so it is not a good idea.

Various electrically insulating plastics are used as the material for the plastic film or sheet used in the present invention, examples of which include hard and soft polyvinyl chloride, polyethylene, polypropylene, general and impact-resistant polystyrene, and As resin. , ABS fi resin, acrylic resin, nylon resin, polyacetal, saturated polyester μ,
Thermoplastic resins such as polycarbonate, polyphenylene oxide, aromatic polyester μ, polyphenylene sulfide, polysulfone, copolymers thereof, various polyblends, inorganic substance blends, and phenol
There are thermosetting resins such as /I/ resins, urea resins, melamine resins, unsaturated polyesters, diaryl resins, epoxy resins, polyimide resins, copolymers thereof, and various blends and inorganic compounds. The plastics of the present invention include natural rubber, polybutadiene,
Elastomers such as SBR, Nitri) v rubber, chloroprene rubber, FJP rubber, styrene-butadiene block polymers, styrene-isoprene block polymers,
Thermoplastic elastomers such as ethylene propylene thermoplastic elastomers, polyurethane thermoplastic elastomers, polyester nylon elastomers, and nylon-12 engineered elastomers are also included. Particularly preferred is polyvinyl chloride,
They are polypropylene, Ans41 resin, 9-component polyphenylene oxide, phenol resin, and 1% ethylene propylene plastic distomer.

The thickness of the glass film and sheet varies depending on the application, but is preferably 0.05 to 3 mm, particularly preferably 0.3 to 1 mm.
．． This is the 5th term.

The plastics used in the glass film on which the metal thin layer is completely deposited include polyethylene tere-7-talate, polyethylene, polypropylene, hard and soft polyvinyl chloride, cellulose acetate plastic, polymethymu methacrylate, and those containing these as main ingredients. Among these copolymers, polyethylene terephthalate is particularly preferred. The thickness of the film is 10 to 100 microns, particularly preferably 2.
0 micron to 60 micron.

Metals to be deposited include aluminum, nickel, chromium, iron, copper, zinc, etc., and various alloys of these.
Particularly preferred is aluminum. Deposition methods include vacuum evaporation, chemical plating, sputtering, ion blating, etc., and the thickness of the deposited metal thin layer is 50 to 800 angstroms, particularly preferably 100 to 600 angstroms. When the thickness is about 100 microns, there is considerable transparency, but when the thickness is thinner than this, the electromagnetic shielding effect is often insufficient.

Metal foil, multilayer film of metal foil and plastic, metal #
In some cases, simple heating and pressure may be sufficient to form a multilayer plastic film and plastic layer, but in many cases lamination via a suitable adhesive layer is preferred. As the adhesive, a wide variety of adhesives can be used as required, such as rubber adhesives, polyolefin-based or polyamide-based hot-melt adhesives, epoxy thread adhesives, urethane-based adhesives, and the like. As a lamination method, a batch press molding method, a dry lamination method using a heating roll method, and an extrusion lamination method using a sheet extrusion method of molten resin are all possible.

Next, 4? of the composite (multilayer) sheet according to the present invention? The first characteristic is that it has excellent electromagnetic shielding performance.

The electromagnetic shielding properties can be varied over a wide range by adjusting the type and thickness of the metal foil used or the type and thickness of the metal deposited on the plastic film, but the usual electromagnetic shielding targets In the electromagnetic wave region of 10 kilohertz to 1000 megahertz, the shielding effect is 20
It is possible to easily produce decibels or more.

Generally, in the case of a structure in which the intermediate layer is a plastic film on which a thin metal layer is deposited, the shielding effect is 20 to 50 decibels,
In the case of a structure with all metal foil intermediate layers, the shielding effect is 40 to 10
One with 0 decibel is practical.

Since the configuration of the present invention has a continuous electrically conductive layer perpendicular to the sheet, there is no risk of non-uniformity of the local shielding effect.

Next, since the composite sheet of the present invention is composed of electrically insulating plastic layers on both sides, it is possible to easily obtain a volume resistivity of 10'6 ohm centimeter or more, depending on the type of plastic used. Due to its high degree of electrical insulation, there is no risk of electric shock associated with other electromagnetic shielding methods.

What should also be noted is the antistatic property (antistatic performance) of the multilayer sheet of the present invention. Perhaps because the sheet of the present invention has a conductive layer in the middle layer, it exhibits good electrostatic properties even when both surfaces are made of plastic that is easily charged with static electricity.

A further advantage of the composite sheet of the present invention is that since both sides are chemically stable plastic layers, metal oxidation and corrosion are difficult to occur and the electromagnetic shielding performance is stable over a long period of time.

As mentioned above, the composite sheet of the present invention has excellent electromagnetic shielding performance, good 7z electrical insulation properties, and good antistatic properties, and has remarkable characteristics compared to other conventional electromagnetic shielding methods and materials. ing. Furthermore, to add to this desire, there is a continuous conductive layer in the middle layer, so it is easy to ground, and since it is in a sheet shape, it can be easily cut, and it can be easily and arbitrarily set in places where electromagnetic shielding is required. It is possible to perform vacuum forming, pressure forming, press forming, etc., not only for the glass layer on both sides, but also for the middle metal layer.Since both sides are made of plastic, it is possible to use thermal bonding, solvent bonding, and bonding. It has many advantages in practical use, such as ease of adhesion with an agent.

Naturally, the plastic layers on both sides are colored with dyes and pigments.
Painting, printing, etc. are also possible, and products with various colors and designs can be made.

Although it is clear that the composite sheet of the present invention has many uses as an electromagnetic shielding material by utilizing the above-mentioned characteristics,
Especially computer equipment, radios, televisions, microwave ovens, information processing equipment, digital weight scales, electronic games,
Widely used for electromagnetic shielding of electronic cash registers, large digital clocks, etc., and rooms where these are handled.

Next, the present invention will be explained in detail based on examples, but these are for the purpose of fully explaining the present invention, and it goes without saying that the present invention is not limited thereto.

Example 1 This example relates to a composite sheet having a multilayer structure in which a plastic film on which a thin metal layer is deposited is sandwiched between plastic sheets. That is, this sheet has the structure shown in FIG. 2, and each layer is made of the following materials.

(LA)... Vapor-deposited aluminum thin layer (thickness approximately 220 angstroms) (6)... Biaxially stretched polyethylene terephthalate film (thickness 25 microns) (2)... Rigid vinyl chloride sheet (thickness o, 4 friends)
(3)... Hard vinyl chloride sheet (thickness 0.4m)
(4)... Water-resistant polyolefin true melt adhesive film (thickness: 30 microns) (5)... Same as (4), this composite sheet is made of aluminum vapor-deposited polyester film.
A special water-resistant polyolefin hot melt adhesive film is laminated on both sides of the film using a dry lamination method.
It was manufactured by laminating multiple layers of hard chloride and 2P on both sides by extrusion lamination.

The electromagnetic shielding effect of this composite sheet was measured using a shielding effect evaluator TR17301 and a spectrum analyzer 'I'R4174' (J manufactured by Takeda Riken Kogyo Co., Ltd.).

The sheet samples used were 200 x 200 arm squares. The results are shown in Figure 4. The horizontal axis of the figure is the measurement frequency, and the vertical axis is expressed in clB! This is a shielding effect.

Further, curve (8) shows electric field shielding, and curve (9) shows Fi magnetic field shielding. The actual curve shows many fine and sharp local maxima and local minima, but the diagram is drawn by smoothing out their average values.

As you can see from the figure, electric field shielding is 20 to 25 dB and magnetic field shielding is 10 to 25 dB in the 100 to 800 MHz band.
It shows a certain degree of electromagnetic shielding effect.

This sheet could be cut with scissors and vacuum formed into trays 20 cIn long x 12 cm rp x 5 am deep.

The water resistance of this sheet was measured by immersing it in hot water at 60°C for 8 hours, then leaving it at room temperature for 16 hours, and repeating the cycle/l/'i 60 times. There was no peeling of each layer, and the vapor deposition was 7 μm.
No deterioration of the minium was observed at all.

The total volume resistivity of this sheet was measured to be 6.5x.
xoj 6 ohm centimeter, highly insulating metal.

Further, the antistatic properties of this sheet were measured using an honest meter, and the results showed that the charging voltage was 5 mV and the half-life was 16 seconds. In addition, the charging voltage of the hard vinyl chloride IV sheet is 6…■, and the half-life is 35.
It was 0 seconds.

Example 2 This example is a composite sheet having a multilayer structure of metal foil and plastic sheet. That is, this sheet has the structure shown in FIG. 1, and each layer is made of the following materials.

(1)... Aluminum foil (thickness 25 microns) (
2)... Hard vinyl chloride/I/7-t (thickness 0.4 mm) (3)... Same as (2) (4)... Water-resistant polyolefin adhesive film ( Thickness: 30 microns) (Same as (4)) This composite sheet is made by extrusion coating a special water-resistant polyolefin hot-melt adhesive on both sides of aluminum foil, and then laminating hard PVC plates on both sides using a fully heated press method. It was manufactured by

The electromagnetic shielding effect of this composite sheet was measured in the same manner as in Example-1, and the results are shown in FIG.

In the band from 100 to 900 MHz, the electric field coefficient is 40 to 5
5 dB, magnetic field seed μ 40-45 dB, all with excellent effects. It is noteworthy that magnetic field shielding, which is said to be particularly difficult to shield, shows values close to electric field shielding.

This sheet could be cut with scissors and molded into a hemisphere with a diameter of 30 m and a depth of 15 cm by heat-pressure forming.

The water resistance was completely measured in the same manner as in Example 1, and there were no abnormalities at all, and the measured value of the volume resistivity was 6.2×10 16 ohms σ. In addition, the antistatic property measurement results were a charging voltage of 4 mV,
The half-life was 12 seconds.

Example 3 A composite sheet was produced in the same manner as in Example 2, except that modified polyphenylene oxide sheet T- was used instead of the hard vinyl chloride sheet. The softness temperature of the hard vinyl chloride sheet is 68°C, but the softness temperature of the modified polyphenylene oxide sheet is 115°C, which means that it has significantly superior reed and heat resistance.

The electromagnetic shielding effect of this composite sheet was measured in the same manner as in Example-1. The main results are shown in the table below, and it is clear that it has sufficient effects.

The volume resistivity value is 6.8 x YuoI6oam, 1i
The lJ conductivity measurement results are a charging voltage of 4.5 mV and a half-life of 1.
It was 0 seconds.

Example 4 A composite sheet la was produced in exactly the same manner as in Example 2 except that a steel foil with a thickness of 30 microns was used in place of the aluminum foil. The electromagnetic 3[1iiiE effect is shown in the table below, and shows a sufficient effect.

The volume resistivity value was 5.6 x 10'' ohms, and the antistatic property was measured to have a charging voltage of 4.2 mvs and a half-life of 15 seconds.

Example 5 Composite sheet 1 was produced in exactly the same manner as in Example 2 except that the total thickness of the aluminum foil was 50 microns. Its electromagnetic shielding effect is very good as shown in the table below.

Example-6 The sheet of this example had the structure shown in FIG. 3, and each layer was made of the following materials.

(lB)...Copper foil (thickness 25 microns) (7)a...
Nylon-12 hot melt adhesive film [thickness 20 microns] (6)... 2MM stretched polyethylene terephthalate film (thickness 25 microns) (2B) --- General ABS sheet (thickness o , 4 m
) (3B)... Same as (2B) (4)... Water-resistant polyolefin hot melt adhesive film (thickness 30 microns) (5)... Same as (4) One side of the copper foil is coated with a nylon-12 true melt adhesive by extrusion coating, and this is laminated with polyester μ film by dry lamination. In this way, the relatively flexible copper foil is backed and reinforced with a tough polyester, making it more resistant to wrinkling during the subsequent dry lamination process. Next, a water-resistant polyolefin adhesive is laminated on both sides of this laminated film by extrusion coating.
All of the composite sheets of this example were manufactured by laminating ABS sheets using a hot press method.

The electromagnetic shielding effect of this composite sheet was as shown in the table below.

The volume resistivity value was 6.2 x 10'' ohm a, and the antistatic properties were measured to have a charging voltage of 4.0 mV and a half-life of 8 seconds.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are cross-sectional views showing different embodiments of the electromagnetic shielding composite sheet according to the present invention, and Figures 4 and 5 are diagrams of the electromagnetic shielding effects of Examples 1 and 2, respectively. be. (1)...Aluminum foil, (LA)...Vapour-deposited aluminum layer, (IB)...Copper foil, (2)/(3)
...Hard vinyl chloride sheet, (2B)/(3B)-◆
ABS sheet, (4)...Water resistant polyolefin hot melt adhesive, (6)J...biaxially oriented polyethylene tele7 tallate film, (7)...nylon-12 hot melt adhesive adhesive film, (S)-・
#Electric field shield, (9)...Magnetic field shield. Figure 1 Figure 2 Figure 30 Figure 4! ＼ ”L- 5 blank figures...：[＼

Claims (1)

[Claims] 1. Composite sheet for electromagnetic shielding made by laminating all electrically insulating plastic layers on both sides of a conductive metal layer.