JPH10292252A - Electromagnetic wave-shielding net - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject net that can intercept electromagnetic waves as electric waves or microwaves occurring from portable telephones, personal computers, electric washing machines or electric dryers by using electrically conductive twisted yarns and knitting them in a net with a specific mesh. SOLUTION: A plurality of continuous filaments containing at least one of electroconductive filament are twisted to form an electroconductive twisted yarn. This conductive twisted yarn is knitted to a plain warp-knitted fabric having the mesh size of <=1.5 mm. The knitted fabric is retrained in their displacement at their yarn-crossing points whereby the mesh roughness is kept constant and the objective net is obtained that has effective electromagnetic wave shield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to radio waves and microwaves generated from home appliances such as communication devices such as mobile phones, electronic devices such as personal computers, televisions, washing machines, and dryers. The present invention relates to an electromagnetic wave blocking net that blocks electromagnetic waves such as ultrahigh frequency waves, and an electromagnetic wave blocking material using the electromagnetic wave blocking net.

[0002]

2. Description of the Related Art For example, a portable telephone has a frequency of 800 MHz or more.
It emits high frequency electromagnetic waves of 1.5 GHz. Recently, accidents in which medical equipment malfunctions or a heart pacemaker breaks down due to this electromagnetic wave have become social problems. In addition, there is no effective method for blocking radio waves in places where calling of a mobile phone is not preferable, such as a lecture hall or a conference room.

In addition, there is a danger that a computer malfunctions and leads to a serious accident due to the use of the mobile phone in a car, an airplane, or the like controlled by the computer. Furthermore, electromagnetic waves generated by the engine of the automobile may cause malfunction of the computer. Conversely, there is a danger that the computer control system of the vehicle may malfunction due to the noise generated by the electronic device brought into the vehicle.

There are various needs for an electromagnetic wave shield case of an electronic device in which the inside can be visually recognized from the outside. However, there has been no board of a shield case in which the inside can be easily recognized and which can be easily manufactured and which is inexpensive. .

[0005] Further, most home electric appliances around us are sources of electromagnetic waves, and the danger of high-frequency electromagnetic waves harming cells or the immune system of the human body has been regarded as a problem, and research has begun.

[0006] As products for preventing such harmful electromagnetic waves, OA aprons using a conventional polyester-coated fabric, metal fiber fabric, and the like, a transparent hard plastic VDT (Video Displa) have been proposed.
y Terminal) filters and the like are sold.

[0007]

For example, to block an electromagnetic wave emitted from a portable electronic device such as a mobile phone, the electronic device may be housed in a case having an electromagnetic wave blocking effect. However, when the material for the OA apron as described above is used as the material of this case, the portable electronic device has many chances to hold it in the hand, so that it is easy to get dirty and the dirt is conspicuous, and the material is thin. Therefore, the usability is poor such as the shape is easily collapsed.

[0008] In addition, since it is a necessary condition that operation parts such as switches and keys of an electronic device and display parts such as a display can be visually recognized from outside the case, their positions, functions, display contents, and the like are required. It is necessary to use a transparent material for the case part to cover. However, when a transparent hard plastic such as that used in the above-described VDT filter is used for the operation parts such as switches and keys, the switches and keys cannot be operated from the outside of the case. Impair the nature.

[0009] In order to weave the fabric with a metal fiber material of micro order, a special loom is required, so that the fabric becomes expensive. Therefore, if the area to be shielded from electromagnetic waves is large, such as a large home appliance such as a washing machine or a dryer, the cost required to block electromagnetic waves increases.

In order to solve this cost problem, it is conceivable to reduce the amount of metal fiber material by coarsely weaving the fabric in a mesh shape. Cause collapse. Therefore, it is not possible to maintain the 1.5 mm coarseness which has been experimentally found to provide a sufficient electromagnetic wave blocking effect.

The present invention has been made to solve such problems, and a conductive fiber material is
Since the stitches are knitted in a mesh shape of 1.5 mm or less, it can be knitted by a general knitting machine such as a tricot knitting machine, and the amount of fiber material to be used is small. Even if the area that blocks electromagnetic waves is large like a product, the cost is low, and the vertical and horizontal stitches of the stitches constrain each other's movement, keeping the eye roughness constant and entangled at the intersection of the stitches It is an object of the present invention to provide an electromagnetic wave shielding net in which the amount of reflection and absorption of electromagnetic waves is increased due to conduction between the fiber materials, and the electromagnetic wave shielding effect is high.

Another object of the present invention is to provide a low-cost shield box board for an electronic device or the like that blocks electromagnetic waves by heat-sealing the above-described electromagnetic wave blocking net to a plastic or the like. . In addition, the board is used as a simple electromagnetic wave shielding material around a driver's seat of an automobile, around a cockpit or a passenger seat of an airplane, an outer wall surface of a home appliance, a wall surface in a room, and the like. The net material can be used as it is or by backing it as an electromagnetic wave shielding curtain.

[0013] Further, the present invention provides an electromagnetic wave shielding net formed by twisting a conductive fiber material and knitting it into a mesh, and laminating the transparent and flexible sheet material such as soft polyvinyl chloride. By being bonded by processing or the like, it is possible to provide a transparent, flexible and resilient electromagnetic wave shielding material.

Further, in the present invention, since the conductive fiber material is twisted, the conductive fiber material is coiled to increase the surface area, thereby increasing the amount of electromagnetic wave reflection and absorption. It is another object of the present invention to provide an electromagnetic wave shielding net and an electromagnetic wave shielding material having a high electromagnetic wave shielding effect.

[0015]

An electromagnetic wave shielding net according to the present invention is obtained by twisting a plurality of conductive yarns into a twisted yarn, and weaving the twisted yarn into a net shape. Further, the electromagnetic wave shielding net according to the present invention is obtained by forming a conductive yarn into a twisted yarn and weaving the net-like fiber by tricot knitting using the twisted yarn.

In the electromagnetic wave shielding board according to the present invention, a plurality of the conductive yarns are twisted to form a twisted yarn, and the electromagnetic wave shielding net woven in a net shape using the twisted yarn is thermally fused to the board. Thus, an electromagnetic wave shielding board is formed.

Further, the electromagnetic wave shielding board according to the present invention is characterized in that a conductive yarn is a twisted yarn, and a net-like fiber woven by tricot knitting is heat-fused to the board using the twisted yarn. It is what formed the board for use. The conductive yarn is preferably a nylon yarn plated with silver.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is an enlarged view of the electromagnetic wave shielding net of the present invention. The electromagnetic wave shielding net 2 is formed by twisting together two conductive fiber materials such as metal fibers (nylon or other fibers plated with a highly conductive metal such as silver, copper or nickel) or carbon fibers. As a result, a twisted yarn 1 is made as shown in FIG. 1 (b), and three twisted yarns 1 are used to form a tricot. The roughness of the net is 1.5 mm or less, which has been experimentally found to provide a sufficient electromagnetic wave blocking effect, and effectively blocks microwave band electromagnetic waves.

The strength of the fiber material is increased by forming it into a twisted yarn, and the fiber material can be processed by an ordinary tricot knitting machine. Since the above-mentioned processing can be performed with a normal tricot knitting machine, no new equipment is required, and the net can be woven at a much lower cost than those using a special loom or knitting machine. In addition, since the net is a coarse net, the amount of the conductive fiber material (yarn) that is more expensive than the cloth-like conductive fiber can be used, and can be manufactured at a lower cost.

[0020] Tricot knitting is basically different from twill weaving or knitting with one thread in that it is knitted with three threads, and is knitted with three strands to form a hexagonal mesh and fix the fabric. There is an effect to make it. That is, by knitting in a tricot shape, the fibers in the vertical and horizontal directions of the stitch restrain each other, so that the roughness of the stitch is maintained constant and the stitch does not collapse. Therefore, it is possible to prevent a reduction in conductivity (shielding effect) due to expansion of the stitch due to expansion and contraction.

Furthermore, as shown in the figure, the net of the tricot knit has individual squares having a substantially hexagonal shape, and the swelling of the fibers entangled at the intersection of the stitches increases the effect of reflecting and absorbing electromagnetic waves. The effect of blocking electromagnetic waves is greater than that of vertical and horizontal nets. That is, the conductive fiber material (yarn) is spirally entangled by twisting, the mass per area is increased, and the electromagnetic wave shielding effect is enhanced, and the spiral structure of the conductive fiber material (yarn) is Research reports have shown that there is even an absorption effect.

This material has both the electromagnetic wave blocking effect of the conductive metal, the flexibility of the fiber, and the ease of processing. The coarse eyes also have transparency. Due to these advantages, the versatility of this material is very high, and it can be applied to various secondary materials and products as described later.

It is preferable to use the conductive fiber material (yarn) for both of the two twisted yarns. However, in the case of tricot knitting without collapse, since each square is within 1.5 mm, cost is reduced. From the point of view, even if only one is made of a conductive material and the other is made of a normal non-conductive material (for example, nylon thread), the performance is not so inferior in performance, so that the structure can be used. Conversely, in the case where both are made of a conductive yarn (yarn) and made of a twisted yarn, the net may be knitted in another knitting method that is somewhat collapsed since the effect of blocking electromagnetic waves is large.

The conductive material (yarn) is preferably a nylon yarn plated with silver. This material has a specific resistance of 0.05 Ω / sq. Or less, and has higher conductivity than conductive rubber. Therefore, the material can be used also for the contact portion of the switch element.

FIGS. 10 and 11 show experimental results of the electromagnetic wave blocking ratio of the electromagnetic wave blocking net of the present invention. The measurement is shown in FIG.
The experiment was carried out at the University of Pennsylvania using the apparatus described in Table 1 below. In Table 1,
MG net is a product name of the electromagnetic wave shielding net of the present invention.

[0026]

[Table 1]

FIGS. 10 and 11 show the measurement results of the electromagnetic wave absorption rate and transmission attenuation rate in the apparatus shown in FIG.
The amount of transmission attenuation when the electromagnetic wave shielding net of the present invention is placed on a free space is measured,
The shielding effect of the electromagnetic wave shielding net is evaluated. Further, by calculating the remaining part of the sum of the transmission attenuation rate and the reflection coefficient of the net, the electromagnetic wave absorption rate of the net is calculated. From the figure, it is clear that the electromagnetic wave shielding net of the present invention has a sufficient electromagnetic wave shielding effect from low frequencies to high frequencies. The absorption amount is 97 at 1.4 GHz or less.
% In the vicinity of 10 GHz. In this experiment, although the net has a single layer, it is clear that the more nets are added, the higher the blocking effect is.

The electromagnetic wave blocking net 2 of the present invention as described above
Can be used as a material for various processed products. In addition, clothing interlining, electric carpet lining,
It can be used for lining of building materials (inner wall materials, ceiling materials, floor materials, etc.).

FIG. 2 is a perspective view of an application example of the electromagnetic wave shielding net of the present invention. The electromagnetic wave shielding material of this example is obtained by bonding the above-described electromagnetic wave shielding net 2 to the back surface of a sheet material 4 provided with decorative elements such as a wallpaper and a curtain. An electromagnetic wave blocking effect can be obtained without impairing the decorativeness of the sheet material 4 including the elements.

FIG. 3 is a perspective view of another application example of the electromagnetic wave shielding net of the present invention. The electromagnetic wave shielding material of this example forms an electromagnetic wave shielding sheet by laminating an adhesive or adhesive sheet 3 on one side of the net 2. This sheet can be easily adhered to a synthetic resin or the like. In this case, since it is simply pasted on another material, handling is easy and cost performance is high. This seat is used for home appliances (TV, washing machine, dryer, microwave oven, etc.), telephone base, communication equipment such as mobile phones, electronic equipment such as personal computers and monitors, around the engine of a car, around the driver's seat, and the cockpit of an aircraft. It can be used for lining around equipment, such as around the customer seat or inside and outside.

In FIG. 3, reference numeral 3 denotes a transparent plastic board, and the net 2 is 5 to 15 cm.
An application example of heat-sealing the board at intervals is also effective. The board is formed into a box shape with the side where the net is fused inward, and is used, for example, as a shield box for electronic equipment. A simple and inexpensive shield box that can prevent an electronic device from malfunctioning due to external noise can be provided.

FIG. 4 is an exploded structural view of still another application example of the electromagnetic wave shielding net of the present invention. In the figure, reference numeral 6 denotes a synthetic leather base cloth made of a tricot fabric having a small shrinkage, that is, hardly stretched. As shown in FIGS. 4A and 4B, the above-described electromagnetic wave shielding net 2 is bonded to the base cloth 6. Next, as shown in FIG. 4 (c), a surface layer 63 of the synthetic leather is formed by coating a polyurethane resin on a surface of the base cloth 6 on which the electromagnetic wave shielding nets 2 are bonded together. ing. The coating is performed by wet-coating the polyurethane resin and then dry-coating. The electromagnetic wave shielding material of this example does not lose its shape even when it is sewn three-dimensionally, such as a storage case of a mobile phone, and has a high-grade feeling.

FIG. 5 (a) is an exploded structural view of still another application example of the electromagnetic wave shielding net of the present invention. In the figure, 51
And 53 are transparent and flexible polyvinyl chloride (PV)
The soft sheet material C) 52 is the above-mentioned electromagnetic wave shielding net, and the stitch has a roughness of 1.5 mm or less and a roughness that maintains light transmission. This electromagnetic wave shielding material is shown in FIG.
As shown in (b), the above-mentioned soft sheet materials 51 and 53 are bonded to both surfaces of the electromagnetic wave shielding net 52 by laminating. The electromagnetic wave shielding material (transparent laminate sheet) of this example is transparent, flexible, and elastic. This example has a structure in which soft sheet materials 51 and 53 are bonded to both surfaces of an electromagnetic wave shielding net 52 by laminating, but the soft sheet material 51 or 53 becomes an electromagnetic wave shielding net 52 serving as a surface of the electromagnetic wave shielding material. May be bonded to only one side by lamination.

The electromagnetic wave shielding net and the electromagnetic wave shielding material of the present invention as described above have the function of the electromagnetic wave shielding net 2 having a coarseness of 1.5 mm or less reflecting or absorbing electromagnetic waves and converting them into thermal energy. It blocks microwaves of 200 MHz or more by 90% or more. However, with a roughness of 1.5 mm or more, the shielding effect decreases in proportion to the size of the eyes.

Next, an example of a product using the electromagnetic wave shielding net of the present invention will be described. FIGS. 6 and 7 show a CD player case using the electromagnetic wave shielding net of the present invention, and FIGS. 8 and 9 show a completely sealed type mobile phone case. These are electromagnetic wave shielding goods using general synthetic leather or cloth as a surface material, and using the electromagnetic wave shielding net of the present invention as a lining. This is to prevent the electromagnetic wave from leaking outside by completely sealing the electronic device that generates the electromagnetic wave. When these electronic devices are brought into a hospital or an airplane in flight, if the power is accidentally forgotten to be turned off, if they are placed in the shield case, malfunctions to other electronic devices and instruments can be prevented. Therefore, a use form in which the use of a mobile phone is prohibited in a case at the entrance of a hospital or a movie theater, which is prohibited, may be considered. In the case of a CD player, an earphone and a remote control are attached, so that they can be used in the above case by using them. Therefore, by using the above case, it is possible to use a device whose use is prohibited during a flight or the like.

The electromagnetic wave shielding net according to the present invention can be applied to various uses by being superimposed on another base material in addition to using the net itself. As a method of superposition, there is a method of sandwiching both sides of the net with another material or a method of laminating only one side. The following is an example.

A. The above-mentioned net alone is superimposed on a fabric material such as clothing, an interlining, a hot carpet, a lining of a building material board, or an existing product as a wallpaper, a curtain, or an exterior decorative sheet.

B. An electromagnetic wave shielding sheet is formed by laminating an adhesive or adhesive sheet on one side of the net (see FIG. 3). This sheet can be easily adhered to a synthetic resin or the like. Since it is simply pasted on other materials, handling is easy and cost performance is high. This seat is used for home electric appliances (TV, washing machine, dryer, microwave oven, etc.), telephone base, communication equipment such as mobile phones, electronic equipment such as personal computers and monitors, around the engine of a car, around the driver's seat, cockpit of an aircraft It can be used for lining around equipment, such as around the customer seat or inside and outside.

C. The net is insert-molded in the molding of plastic or rubber. In the same manner as above, insert-molded materials are used in home appliances (televisions, washing machines, dryers, microwave ovens, etc.), telephone bases, communication devices such as mobile phones, personal computers, monitors and other electronic devices requiring high-frequency noise suppression. It can be used as a housing or package for equipment, and can also be used for electronic equipment that requires high-frequency noise suppression, such as around the engine of an automobile, around the driver's seat, around the cockpit of an aircraft, or around the passenger seat.

D. By forming a rubber or resin into which a ferrite of a magnetic material is kneaded into a sheet and adopting a multilayer structure with the electromagnetic wave shielding net of the present invention, a material having high radio wave absorption efficiency can be developed.

E. The operation parts such as switches and keys of electronic equipment and the display parts such as displays, etc.
It is a necessary condition that the displayed contents can be visually recognized. When such transparency is required, a transparent and flexible electromagnetic wave shielding material can be provided by laminating a transparent and flexible sheet material of a soft polyvinyl chloride resin or the like by laminating or the like ( (See FIG. 4).

F. An electromagnetic wave shielding material is formed by laminating a base cloth made of a tricot fabric, such as synthetic leather, which has a small shrinkage ratio and is hard to expand (see FIG. 5). In this case, since the characteristics of the base fabric can be used as it is, the material can be provided with a sense of quality and decoration without losing its shape even if it is sewn in three dimensions.

[0043]

The electromagnetic wave shielding net of the present invention has the following characteristics as compared with a conventional cloth-shaped electromagnetic wave shielding material into which conductive fibers are kneaded or woven, and is applicable to any equipment. It has versatility that can be used as an electromagnetic wave shielding material with only simple processing.

The features are listed below. Electromagnetic Wave Blocking and Absorption Effect In a structure in which conductive fibers are in direct contact with each other, such as the electromagnetic wave blocking net of the present invention, the conductivity between the conductive fibers is well maintained, so that the entire net has high conductivity (electrical surface). Resistance value: 0.05Ω / sq.). Therefore, the electromagnetic wave shielding effect also increases accordingly. Further, when the conductive fiber is formed into a net shape, if the conductive fiber is formed into a coil shape (twist) as in the present invention, the surface area increases, and the effect of blocking and absorbing electromagnetic waves increases.

2. Effect of preventing static electricity (charge) The electric surface resistance is 0.05Ω / sq. Or less, and furthermore, the two fibers are made into a thread to form a coil to increase the body surface area, so that the effect of discharging static electricity into the air is great. Also,
The high conductivity of the surface makes it easy for static electricity to escape to ground,
Has antistatic effect. If the material is used for an electronic device, it is possible to prevent dust or cigarette smoke from being absorbed due to charging. The housing of the electronic device may be subjected to electroless plating or vapor deposition plating in order to prevent electromagnetic wave noise, but such plating does not have much antistatic effect.

3. Cost As the area to block electromagnetic waves increases like large electric appliances, it is necessary to use a large amount of electromagnetic shielding materials.
Therefore, a large cost is required for blocking the electromagnetic waves. When the electromagnetic wave shielding material is roughly woven into a mesh shape as in the present invention, the amount of the metal fiber material used can be greatly reduced, and the shielding material can be manufactured at low cost. The electromagnetic wave shielding net of the present invention does not require a special device, uses a general tricot knitting machine, reduces the amount of metal fiber material used, and succeeds in reducing the cost.

4. Antibacterial property The electromagnetic wave shielding net of the present invention has a metal coating of conductive fiber exposed on the surface, and it is known that metal (in the embodiment, silver) has an antibacterial effect. When the electromagnetic wave shielding net of the present invention is used for a portable telephone case or a curtain in a hospital or the like which can be touched, the surface of the case is effectively kept clean.

5. Heat resistance In some applications, heat is applied from equipment to which the electromagnetic wave shielding material is applied. Alternatively, it is conceivable to use it in a high-temperature place. The electromagnetic wave shielding net of the present invention is a material which does not melt or deform due to some heating and is strong against heat. For example, if nylon yarn is used as the basic fiber material, there is no problem if it is used at 180 degrees Celsius or less, and if it is Tetron yarn, there is no problem if it is 200 degrees or more. If a carbon fiber material is used, the material is more resistant to heat, but the conductivity of the metal fiber material is higher than that of the metal fiber material.

6. Shrinkability Since the electromagnetic wave shielding net of the present invention is a net woven in a tricot shape, the electromagnetic wave shielding net has a large shrinkage ratio and flexibility as compared with an electromagnetic wave shielding material manufactured using a woven fabric. Therefore, it is very easy to use it by superimposing it on other products and raw materials. Especially having complex shapes,
Ideal for small office automation equipment and communication equipment.

7. Shape stability In order to fix the conductive fibers in a grid (hexagon) at a certain level, it is best to knit them in a tricot shape. Tricot knitting can keep a certain grid, and a stable electromagnetic wave blocking effect can be obtained by keeping a certain grid.

8. Air permeability and heat conductivity Unlike ordinary woven and knitted fabrics, the electromagnetic wave shielding net of the present invention has a coarse net shape, so it has air permeability, high heat conductivity, and has a heat dissipation effect of electronic devices even when used for electronic devices. Do not spoil.

9. Lightweight Unlike ordinary woven or knitted fabrics, the electromagnetic wave shielding net of the present invention is a coarse net, so it is super lightweight (about 20 g /
m ² ).

10. Low Pollution / Energy Conservation Normally, housings of electronic devices are often made by electroless plating or vapor deposition plating on plastics to prevent electromagnetic noise, or made of metal plates themselves. Since electroless plating uses harmful chemicals (such as cyan), there is a problem of water pollution, and capital investment is not easy. In addition, increasing the amount handled has environmental problems. In addition, evaporation plating and metal plate formation use a lot of heat energy and
₂ is discharged, but the above problem does not occur if the net of the present invention is used.

[Brief description of the drawings]

FIG. 1 is an enlarged view of an electromagnetic wave shielding net of the present invention and an enlarged view of a twisted yarn used for the net.

FIG. 2 is a diagram showing an application example of the electromagnetic wave shielding net of the present invention.

FIG. 3 is a diagram showing another application example of the electromagnetic wave shielding net of the present invention.

FIG. 4 is an exploded structural view showing still another application example of the electromagnetic wave shielding net of the present invention.

FIG. 5 is an exploded structural view showing still another application example of the electromagnetic wave shielding net of the present invention.

FIG. 6 is a diagram showing an example of a product using the electromagnetic wave shielding net of the present invention.

FIG. 7 is a view showing another example of a product using the electromagnetic wave shielding net of the present invention.

FIG. 8 is a view showing still another example of a product using the electromagnetic wave shielding net of the present invention.

FIG. 9 is a diagram showing still another example of a product using the electromagnetic wave shielding net of the present invention.

FIG. 10 is a diagram showing experimental results of the electromagnetic wave shielding net of the present invention.

FIG. 11 is a diagram showing experimental results of the electromagnetic wave shielding net of the present invention.

FIG. 12 is a view showing an experimental apparatus used for the measurements in FIGS. 11 and 12;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Twisted yarn 2 Electromagnetic wave shielding net 3 Adhesive sheet 4 Sheet material 51,53 Soft sheet material 52 Electromagnetic wave shielding net 6 Base cloth 7,8 Electromagnetic wave shielding case for CD player 9,10 Mobile phone case

Claims (6)

[Claims] The present invention is characterized in that a plurality of yarns each having conductivity are twisted into a twisted yarn, and the yarn is knitted into a mesh having a stitch roughness of 1.5 mm or less using the twisted yarn. An electromagnetic wave shielding net with an electromagnetic wave shielding effect. 2. A twisted yarn obtained by twisting a plurality of yarns including at least one conductive yarn into a twisted yarn, and using the twisted yarn to form a mesh having a stitch roughness of 1.5 mm or less by tricot knitting. An electromagnetic wave shielding net having an electromagnetic wave shielding effect, characterized in that the knitted, stitched vertical and horizontal fibers restrain each other's movement to maintain a constant roughness. 3. An electromagnetic wave shielding effect in which a plurality of electrically conductive yarns are twisted into a twisted yarn, and the twisted yarn is woven in a mesh shape with a stitch roughness of 1.5 mm or less. An electromagnetic wave shielding board formed by thermally fusing an electromagnetic wave shielding net to a board. 4. A twisted yarn obtained by twisting a plurality of yarns including at least one conductive yarn into a twisted yarn, and using the twisted yarn to form a mesh having a stitch roughness of 1.5 mm or less by tricot knitting. The board is formed by heat-sealing an electromagnetic wave shielding net that has an electromagnetic wave shielding effect in which the vertical and horizontal fibers of the stitches restrain the movement of each other and the coarseness of the mesh is kept constant, to the board An electromagnetic wave shielding board characterized by the following. 5. The electromagnetic wave shielding net according to claim 1, wherein said conductive yarn is silver-plated nylon yarn. 6. The electromagnetic wave shielding board according to claim 3, wherein the conductive yarn is silver-plated nylon yarn.