JPH0548289A - Shield material for electromagnetic waves - Google Patents

Abstract

PURPOSE:To achieve that the shield effect of the shield material for electromagnetic waves is hardly changed by the incident direction of the electromagnetic waves by a method wherein a material-making liquid is foamed, short metal fibers or short metal-plated fibers in prescribed quantities are dispersed to its surface to form the shield material. CONSTITUTION:Short fibers of about 20mm or smaller so as to be nonoriented are used as short fibers; copper, iron, aluminum or the like is used as metal fibers. The title material is composed of a nonoriented nonwoven cloth which contains at least 10wt.% of the short metal fibers or the short metal-plated fibers. In order to manufacture the nonwoven cloth, a material-making solution which contains the short metal fibers or the short metal-plated fibers is foamed; the fibers are dispersed to the surface of air bubbles, and the nonoriented nonwoven cloth is formed. Thereby, a change in the shield effect of the title material does not change by the incident direction of electromagnetic waves; the short fibers plated in an electroless manner after a ferrite precipitated on the surface can form the shield material which shield the electromagnetic waves and whose electromagnetic-wave absorption is property also high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electromagnetic waves generated from various automation devices such as offices, factories, home electronics, etc., televisions, ICs such as video, or devices containing LSI, or automobiles, aircrafts, etc. The present invention relates to an electromagnetic wave shield material improved to shield an electromagnetic wave generated from a moving body or an influence of an electromagnetic wave coming from another.

[0002]

2. Description of the Related Art With the rapid increase in types of devices that generate electromagnetic waves, downsizing and high density of devices, the generated electromagnetic waves cause police radios, ME devices in hospitals, pacemakers for hearts embedded in the human body, and control of airports. It is reported that it will seriously affect the system.

Even if an electromagnetic wave is radiated, the electromagnetic wave can be shielded without any problem if the housing of the device or apparatus is made of metal. However, the operating current of the device used is weakened, and the housing is required to be compact, lightweight, and cost-reduced. With the progress of plasticization, the spread of digitalized electronic devices has caused leakage of high frequency electromagnetic waves, which has a strong influence on the surroundings, and countermeasures against electromagnetic interference have become more and more necessary.

Conducting plastics containing graphite, carbon black, metal powders, metal fibers, etc. have been studied in order to use plastics that are inexpensive and have high productivity. There are products that can be used. However, in these plastics, a large amount of the above-mentioned conductive material must be mixed in order to maintain a good electromagnetic wave shielding property, so that the appearance becomes poor, the moldability decreases, or the strength decreases. However, there are some inevitable drawbacks such as inviting a problem, which leaves a problem.

In this case, although the metal fiber or the metal-plated fiber as the conductive material has a performance superior to that of the powdery conductive material, it has an orientation during molding and a directionality in the shielding effect. It was inevitable to come out.
Therefore, when using this as an electromagnetic wave shielding material, it is necessary to design the housing using the numerical value in the direction with the least shielding effect, and inevitably measures such as increasing the mixing amount or increasing the housing thickness. Was taken.

[0006]

The present invention can be applied not only to the housing of equipment that generates electromagnetic waves, but also to larger measuring equipment laboratories, buildings, factory buildings, etc. The present invention has been completed by studying the development of a material that is excellent in moldability, has no deterioration in strength, is inexpensive, has no directionality, and has a high electromagnetic wave shielding effect.

[0007]

In order to achieve the above object, the present invention has developed an electromagnetic wave shielding material comprising a non-oriented nonwoven fabric containing at least 10% by weight of metal short fibers or metal-plated short fibers. Further, in order to produce this, a papermaking liquid containing metal short fibers or metal-plated short fibers is bubbled, the fibers are dispersed on the surface of the air bubbles, and the paper is made into a non-oriented non-woven fabric electromagnetic wave shield. The material was developed. In this case, a method of blending a filler having a thickness sufficiently larger than the diameter of the short fibers in order to promote randomization of the short fibers as necessary, or a constitution in which the filler is a thermosoftening resin having a binder effect. Has developed an electromagnetic wave shield material. Furthermore, we have developed an electromagnetic wave shield molded product in which a thermosetting resin, a thermoplastic resin, a hydraulic material or a pneumatic material is used as a shaping material for the electromagnetic wave shielding material.

The short fibers used in the present invention are short fibers having a length of about 20 mm or less, preferably about 5 mm or less in order to be non-oriented, and the metal fibers include copper, iron, aluminum, stainless steel and the like.

The metal-plated short fibers can be plated with metals such as nickel, iron, cobalt, silver and palladium. The base material of the fiber is synthetic fiber such as polyamide, polyester and acrylic, fiberized synthetic resin such as polypropylene, polyethylene and vinyl chloride, natural fiber such as cotton and wool, recycled fiber such as acetate and viscose, and organic material such as regenerated fiber. Examples thereof include materials and inorganic fibers such as glass fibers and carbon fibers.

The metal plating method is not particularly limited,
Ordinary degreasing, solvent treatment, etching, sensitization process with stannous chloride, method of electroless plating after activation process with palladium chloride, high temperature pretreatment (degreasing) to simplify solvent treatment, etching treatment process, A method of electroless plating after a sensitizing process or an activating process, or a method of performing a pre-treatment process (including a sensitizing process and an activating process) for these ferrites by a completely different concept and then immediately performing electroless plating. The metal-plated fiber can be used by the method of.

The papermaking liquid is the above-mentioned metal fibers or metal-plated short fibers, a surfactant as a foaming agent, and a thickener (for enhancing the stability of the foam and an auxiliary agent for dispersing the fibers on the foam surface ( In some cases, it may also serve as a binder.) In some cases, a filler, a heat-softenable short fiber as a binder, etc. are dispersed and dissolved in water.

It is not necessary to limit the type of the surface active agent as a foaming agent since it defoams after scooping out the foam, and therefore it is not necessary to limit the type. Anionic surface active agents, cationic surface active agents, nonionic surface active agents Although an agent, an amphoteric surfactant, etc. can be used, an anionic surfactant seems to be preferable in terms of foaming stability and cost.

As the thickening agent, polyvinyl alcohol, carboxymethyl cellulose, troloy mallow, water-soluble thermosetting resin prepolymer and the like are used. When polyvinyl alcohol, thermosetting resin prepolymer, etc. are used, they can be used as binders when heat setting of non-oriented nonwoven fabrics, and other thickeners have a role of binder during paper making. You can also

The material, shape and size of the filler can be changed according to the purpose of use. When you want to use a filler as a binder, you can use low melting point polyethylene, ethylene-vinyl acetate copolymer, vinyl chloride, etc., and if you need a bulky product, you can use a thermoplastic or thermosetting resin foam crushed or cut product. Alternatively, a crushed resin may be used. When used at high temperatures or when giving non-combustibility to shield materials, short fibers should be inorganic glass fibers, carbon fibers, etc., and lightweight aggregates such as pearlite perlite and vermiculite, and crushed products such as anti-fire stones or sand. be able to. In any case, these fillers need to be dispersed on the surface of the bubbles together with the metal short fibers or the metal-plated short fibers when the papermaking liquid is foamed, and when made into a nonwoven fabric, they are uniformly dispersed in the short fibers. Has the function of helping the non-orientation of the three-dimensional structure of the fiber.

When short fibers are blended as a binder, it is preferable to use short fibers of a thermoplastic resin having a low melting point such as polyethylene or ethylene-acetic acid copolymer, which melts at the temperature of hot pressing after papermaking. it can. When such a binder is blended, it can be molded as it is as a shield material by hot pressing, etc. Also, regardless of the presence or absence of the binder, the non-woven fabric can be molded by blending it with other resins, hydraulic substances, etc. It can also be used as a housing.

In addition to the above, fibers which are not metal-plated for increasing the mechanical strength of the nonwoven fabric, but not limited thereto, short fibers of synthetic fibers may be added for imparting strength. Regarding the amount of fibers other than metal short fibers or metal-plated short fibers, such as synthetic fibers and natural fibers, the shielding effect decreases as the amount used per unit weight increases. It is possible to regain the shielding effect by increasing the thickness of such a shield material, and such a non-woven fabric becomes soft, has a good tactile sensation, and has a high sound absorption property, so it is suitable for special applications. It is a material with excellent characteristics. Generally, for use as a shield material, at least 10% by weight of metal short fibers or metal-plated short fibers is desired in the shield material (when embedded as concrete in a molded body, the content in the molded body is It may be lower than this.).

The dispersion medium of the papermaking liquid is water, and metal fibers or metal-plated fibers, surfactants, thickeners, necessary fillers, short fibers for binder, and non-metallized short fibers are used according to the purpose. And mix them in appropriate amounts and mix well to obtain the raw papermaking liquid.

In the papermaking, the papermaking solution is vigorously agitated, air is blown as fine air bubbles, or a combination of both is used to sufficiently foam, and short metal fibers or metallized fibers, fillers, and short binders are used on the surface of the air bubbles. Fibers and non-metallized short fibers are dispersed, and this bubble portion is made into paper. The bubbles may be naturally defoamed, but from the viewpoint of productivity, they may be forcibly defoamed by means such as pressurization and suction. By adjusting the amount of scooping bubbles, the thickness of the nonwoven fabric after paper making can be changed. As a result, unlike conventional non-woven fabrics, short fibers have a three-dimensionally random orientation in the non-woven fabric, so that a product having almost no orientation can be obtained. This is pressed (dehydrated), dried, and hot pressed if necessary.

When an adhesive such as carboxymethyl cellulose is used as a binder, it may be simply dried. However, when a thermosetting resin prepolymer, a filler for a binder, or a short fiber for a binder is mixed, or a pressed nonwoven fabric is used. When heat setting is required by hot pressing such as spraying a thermosetting resin prepolymer or thermoplastic resin emulsion or solution as a binder, immersing in such a solution, or laminating with a low melting point resin film. Fix the non-orientation of the non-woven fabric at an appropriate temperature and use it as an electromagnetic wave shielding material. Further, as the binder of the inorganic material, cement-based, gypsum-based, silicic acid-based,
A hydraulic or air-hardening material such as a metal alkoxide type or an alkali metal salt type such as water glass can be used.

The electromagnetic wave shielding material can be used as it is or as a housing for electronic equipment. The electromagnetic wave shielding material is further shaped by a thermosetting resin prepolymer, a thermoplastic resin hydraulic material, or a gas hardening material to generate electromagnetic waves. The use of the shield molded body can be further expanded.

As the thermosetting resin and the thermoplastic resin, a general purpose resin used as a housing is sufficient.

The hydraulic substance includes cement, gypsum, etc., which can be formed into a molded product by a method such as press-fitting, coating, or covering the metal fiber (metal-plated fiber) non-woven fabric manufactured in advance. When pressure is insufficient with metallized fiber and filler, it becomes a porous non-woven fabric, and cement milk is injected into this, and the electromagnetic wave shield molding that uses the non-woven fabric as a kind of reinforcing material is non-combustible and lightweight as an outer wall material such as an anechoic chamber. In addition, it is a material that has high strength and is useful as a construction material that is easy to construct.

Further, instead of the hydraulic substance, a gas-hardening substance which is hardened by carbon dioxide gas in the air such as water glass can be used, but a clearer application than the hydraulic substance has not been found yet.

[0024]

The function of the electromagnetic wave shielding material of the present invention is to foam the papermaking liquid,
Since the metal short fibers or metal-plated short fibers are dispersed on the surface of the paper before it is made into paper, the orientation of the short fibers is a three-dimensionally random non-woven fabric. There is a characteristic that the shield effect hardly changes depending on the direction.

In this case, a bulky non-woven fabric can be obtained by selecting the kind of the filler and reducing the primary molding pressure, and also a non-woven fabric in which hydraulic substances such as cement milk can easily penetrate. In addition, it is also possible to make a hard electromagnetic wave shield plate material by hot pressing by using a thermosetting prepolymer as a filler and a thermoplastic resin as a binder.

When the electromagnetic wave absorbing material is used, short fibers plated with ferrite and then metal-plated may be used.

[0027]

EXAMPLES The present invention will be described more specifically below with reference to examples. (Example 1) 1: 1 by weight ratio of ferrous chloride and ferric chloride
50 g of acrylic short fiber having a thickness of 16 μm and a length of 5 mm per 1 liter of the pretreatment liquid at a treatment temperature of 9
Pretreatment was performed at 5 ° C for 10 minutes. Then, after being immersed in a 1% aqueous ammonia solution for 24 hours, it was dried at 120 ° C. to be ferritic and pretreated.

Nickel sulfate hexahydrate 30 g / l, ammonium chloride 50 g / l, sodium hypophosphite 10 g / l
The electroless plating bath having a pH of 8 to 10 was treated at a temperature of about 90 ° C., and the plating state was observed with a microscope. The plating was smooth.

A non-woven fabric was produced using this, hot pressed into a sheet, and the shielding property against electromagnetic waves was tested.

As a papermaking method, polyvinyl alcohol 1
g, foaming agent (cationic surfactant; ribolane PJ 4
00 0.5 g), 10 g of plated fiber and 3 g of anti-fire stone (0.1 to 0.6 mm) are mixed in a ratio of 1 liter of water to prepare a papermaking liquid, which has a thickness of 1 mm and a basis weight of 200 g /
It was a nonwoven fabric of m ² . Then low pressure press (10Kg / c
40 kg / cm ² , 80 ° C. and 10 after dehydration with m ² ).
It was formed into a sheet by a high pressure hot press at 0 Kg / cm ² and 80 ° C.

This sheet is manufactured by Advantest TR41
A 31 electromagnetic shielding test apparatus was used to test electromagnetic wave shielding.

The electromagnetic wave shielding property was measured by wrapping the connection part of the test device of the sample metallized fiber sheet with a metal copper foil and setting it in a conductive state of the measuring device and by wrapping the sample metal fiber sheet with a polypropylene film. The results are shown in Table 1.

For comparison, as Experiment No. 2, a foamed paper was made in the same manner as in the Example without adding anti-fire stone as a filler, Experiment No. 3 was made in the same manner as the ordinary papermaking method, and Experiment No. 4 was made. Metallized fibers by conventional electroless plating [degreasing, solvent treatment, etching, 3 times SnCl
Sensitive step by ₂ 5 g / l solution, 3 times of PdCl
₂ Electromagnetic waves obtained by foaming a fiber obtained by pre-treating the activation step with 0.1 g / l and plating with an electroless plating bath at room temperature (180 minutes) similar to that in Example 1] in the same manner as in Example 1. Shield tested.

[0034]

Example 2 Acrylic short fibers having a thickness of 16 μm and a length of 5 mm were degreased at 80 ° C. with a diluted hydrochloric acid aqueous solution and then with a diluted caustic soda aqueous solution at the same temperature, washed with water and dried. This was subjected to a sensitizing treatment by immersing it in a 5 g / l stannous chloride solution of hydrochloric acid at 95 ° C. for 10 minutes, and then immersing in a 0.1 g / l aqueous solution of palladium chloride at the same temperature for activating treatment. went. This pretreated acrylic short fiber is nickel sulfate 6
Electroless plating bath (pH: 30 g / l water salt, 10 g / l sodium acetate, 10 g / l sodium hypophosphite)
5, bath temperature 90 ℃), nickel plating thickness 1μm
A metal-plated short fiber of

10 g of this metal-plated short fiber, sodium alcohol sulfonate as a surfactant, and polyvinyl alcohol were mixed in the proportions shown in Table 2 to prepare a papermaking liquid, which was stirred and foamed to give a basis weight of 500 g / A bubble portion was transferred onto the cloth with the target of m ² and left to be defoamed. Then, it was sandwiched with a 60-mesh wire mesh, pressed at a pressure of 3 Kg / cm ² , and dehydrated to obtain a nonwoven fabric (1). Next, this non-woven fabric (1) was hot pressed at 120 ° C. and a pressure of 50 Kg / cm ² to obtain a non-woven fabric (2) (electromagnetic wave shielding material). This was subjected to an electromagnetic wave shielding test in the same manner as in Example 1. The results are shown in Table 2. The orientation of the nonwoven fabric was visually measured.

[0037]

From the above results, the electromagnetic wave shield materials of Experiment Nos. 2 to 4 are wrapped with a polypropylene sheet, and the shield material is electrically grounded to the tester even if it is electrically insulated from the tester. Even in the case, the measured data maintains a high dB attenuation amount. On the other hand, the shield materials of Experiment Nos. 1 and 5 having a planar orientation give better results than the shield material of the present invention when grounded.
When insulated with a P sheet, the amount of dB attenuation is greatly reduced, indicating that there is no randomness.

Example 3 The nickel-plated acrylic fiber used in Example 2, stainless steel fiber (thickness 5 μm, length 5 mm), acrylic fiber (2 denier, 5)
mm) and glass fiber (thickness 15 μm, 5 mm) were prepared. A papermaking liquid containing these in the proportions shown in Table 3 was prepared. 10 g of short fibers, 5 g of polyvinyl alcohol, and 0.5 g of sodium alkyl sulfonate were dissolved and dispersed in 1 liter of water, a nonwoven fabric (1) was produced in the same manner as in Example 1, and its surface resistance was measured. Furthermore, it was confirmed that epoxy resin [Epotite; Showa Highpolymer Co., Ltd.] was injected into the nonwoven fabric (1) to facilitate impregnation.

[0040]

In this case, even if there was a difference in specific gravity between the fibers used, the dispersion was carried out uniformly, and the surface resistance of the non-woven fabric of metal fibers produced by the usual production method is 10 ^-2 to 10 ^-3 Ω. It is recognized that it is abnormally large compared to This non-woven fabric also has an electromagnetic wave shielding effect.

Example 4 Using the stainless steel short fibers used in Example 3, polyethylene (size 0.2 to 2.0 mm) as filler and anti-firestone powder (size 0.
2 to 1.0 mm) and tested. Short fiber 10 g, filler, polyethylene powder and anti-firestone powder 0.5 g and 5
g, the thickener and the foaming agent are the same as in Example 3,
Papermaking was also performed in the same manner. From the obtained non-woven fabric (1), one side is subjected to a press-in test immediately after mixing with ordinary cement and an epoxy resin (epotite) injection test, and after curing, the fiber on the opposite side of the non-woven fabric is scratched to extract the fiber. The results of a shield test in the state of wrapping a non-woven fabric cured with polypropylene are shown. The results are shown in Table 4.

[0043]

Since a small amount of the epoxy resin reached the back surface, the fibers were slightly peeled off. The one containing the filler has a good impregnation property and is not scratched even in the scratch test. It is considered that this is because the gap created by the filler improved the impregnation property of the shaping material. This sample also naturally has excellent properties.

[0045]

EFFECT OF THE INVENTION An electromagnetic wave shielding material made of a short fiber non-woven fabric. Since the short fibers of the non-woven fabric are non-oriented, the shielding effect does not vary depending on the incident direction of the electromagnetic wave, and the surface is electroless plated after ferrite deposition. It has been found that short fibers can not only shield electromagnetic waves but also provide a shield material having high electromagnetic wave absorption. Therefore, the present invention can provide an electromagnetic wave shielding material that does not have anisotropy in electromagnetic wave shielding property and is easy to design a housing of an electronic device.

Further, by selectively using a filler, it is possible to provide an electromagnetic wave shield material for various purposes such as a shield material having high heat resistance and a lightweight shield material.

Claims (4)

[Claims] 1. An electromagnetic shielding material comprising a non-oriented nonwoven fabric containing at least 10% by weight of metal short fibers or metal-plated short fibers. 2. An electromagnetic wave shield characterized in that a papermaking liquid containing short metal fibers or metal-plated short fibers is foamed to disperse the short fibers on the surface of the air bubbles, and this is made into a non-oriented nonwoven fabric. Material. 3. A non-oriented nonwoven fabric obtained by mixing paper with a binder comprising at least two kinds of metal short fibers or metal-plated short fibers and a filler, a thermoplastic resin fiber, or a thermosetting resin prepolymer. The electromagnetic wave shielding material described in 2. 4. An electromagnetic wave shield molding obtained by molding the electromagnetic wave shield material according to claim 1 as a shaping material of a thermosetting resin, a thermoplastic resin, a hydraulic material or a gas-hardening material.