KR20080017656A - Emi shield sheet and a method for manufacturing the same - Google Patents

Abstract

An EMI shield sheet and a method for manufacturing the same are provided to block EMI(ElectroMagnetic Interference) waves leaked from a housing of information technology equipment. An EMI(ElectroMagnetic Interference) shield sheet is composed of a fiber assembly(3) with conductive hairlines and an elastic resin(1) containing a conductive filler. At least a part of an end part of the fiber assembly is revealed from the outer surface of a shock-absorbing material, and the other part of the end part of the fiber assembly is buried in the shock-absorbing material. The elastic resin mixes the conductive filler uniformly, and has a number of cavities(2).

Description

EMI Shield Sheet And A Method For Manufacturing The Same}

1 is a schematic cross-sectional view showing the structure of a sheet of the present invention.

      ** Explanation of symbols on the main parts of the drawing **

1: Elastic resin in which conductive filler (particulates) is dispersed

2: joint

3: fiber aggregate (conductive thin wire)

The present invention relates to an electromagnetic wave shielding sheet having a high electromagnetic wave shielding effect and excellent flexibility, and more particularly, to a fiber aggregate and a cavity made of a conductive fine line, and a conductive filler dispersed therein. An electromagnetic wave shielding sheet containing an elastic resin and a method of manufacturing the same.

In recent years, as electronic technology advances, many electronic devices using electricity, electronics, radio waves, and the like have become widespread, and accordingly, rapid high frequency, digitalization, and high integration of electronic devices are progressing. Some of them radiate electromagnetic waves that have a harmful effect on humans, other devices, and the like, and these are particularly problematic in recent years, and their preventive measures have become a very important problem.

Various countermeasures against electromagnetic interference are present, but the most prominent countermeasures are conductive materials used as electromagnetic wave blocking materials having electromagnetic wave blocking performance. The electromagnetic wave blocking material refers to a material that prevents electromagnetic waves from entering the interior or blocks electromagnetic waves from the inside by covering electronic devices or buildings.

In general, the following four methods are typical and various methods have been proposed as a technique for imparting electromagnetic wave blocking performance or conductivity to a polymer material such as plastic or rubber.

(1) A technique for mixing and dispersing a conductive material in a polymer such as plastic, rubber, foam, or the like (for example, Japanese Patent Application Laid-Open No. H7-249890).

(2) Techniques for embedding conductors or conductive materials such as metals in a polymer matrix (see, for example, Japanese Patent Laid-Open Nos. 10-237184, 11-118376, and 2001-85888).

(3) A technique for forming a conductive route on the surface or the inside of a polymer by chemical plating or vapor deposition of a metal (for example, see Japanese Patent Application Laid-Open No. 2002-164684).

(4) A technique of adhering or laminating a highly conductive material to a polymer surface (see, for example, Japanese Patent Laid-Open No. 6-85488).

However, there are various problems with the conventionally proposed technique.

For example, the technique of mixing and dispersing the conductive material of the above (1) in the polymer is a conductive material. For example, when carbon black is used, a high concentration of filling is required. The filling rate lowers the mechanical properties of the material. On the other hand, expensive raw materials such as silver are required to lower the filling rate. Moreover, the manufacturing method by the impregnation method has a difficulty that the process is complicated.

In addition, the technique of embedding the conductive material of the above (2) in the polymer matrix is limited in their thickness when embedding mesh, metal foil, expanded metal, etc., that is, anisotropy occurs, that is, The isotropy may be lost, and in the case of embedding the conductive three-dimensional mesh state, the conductivity varies depending on the density of the mesh state in the polymer. In addition, high density filling (burying) is required to obtain high conductivity, which results in a loss of buffering properties.

Further, in the technique of chemically plating or depositing the metal of the above (3), the plating layer of the back contact surface portion of the housing exhibits stable performance over a long period of time since it is likely to fall off due to abrasion when buffering such as shock absorption. There is a difficulty.

In addition, the technique of adhering (or laminating) a material having high conductivity to the polymer surface on the surface of the polymer (4), when applying a fine metal mesh or the like, has no elasticity in the conductive layer, resulting in poor buffering of the entire system. . Moreover, the adhesiveness of the back contact part of a housing worsens, and there exists a difficulty that an electromagnetic wave leaks easily.

As described above, since the proposed conventional electromagnetic wave shielding conductive material has various problems, there is a need for a conductive buffer material having excellent electromagnetic wave shielding ability which solves such a problem.

An object of the present invention is to solve the problems of the conventional conductive materials and to effectively block electromagnetic waves leaking from the housings of information devices such as mobile phones and to protect electronic components that are relatively susceptible to shock. It is to provide an electromagnetic wave shielding sheet having a function and a manufacturing method thereof that can be easily manufactured by a simple manufacturing process.

In order to achieve the above object, the present inventors impregnated a solution containing a polyurethane containing conductive carbon black in a solvent to impregnate a conductive metal thin sheet, and molded in a steam humidified hot air to produce an electromagnetic wave blocking sheet, The electromagnetic wave shielding sheet has not only a high electromagnetic wave shielding effect but also has a large number of cavities (bubbles) therein, so it has been found to have excellent flexibility and buffering effect. The present invention has been completed based on this finding.

Specifically, according to the first aspect of the present invention, there is provided an electromagnetic wave shielding sheet composed of an elastic resin (B) containing a fiber assembly (A) made of a conductive fine line and a conductive filler (C). At least a portion of the distal end of the c) is exposed to the outer surface of the buffer material, but the other part is buried in the buffer material, and the elastic resin (B) uniformly incorporates the conductive filler (C), An electromagnetic wave shielding sheet is provided having a cavity.

According to the second invention of the present invention, in the first invention, the elastic resin (B) is provided with an electromagnetic wave shielding sheet, characterized in that the polyurethane.

According to the third invention of the present invention, in the first or second invention, the fiber aggregate (A) has a weight per unit area in the range of 1 to 0.005 (kg / m ² ) Is provided.

According to the 4th invention of this invention, in the 3rd invention, the said fiber assembly (A) is provided with the electromagnetic wave shielding sheet characterized by consisting of a metal fine wire.

According to the 5th invention of this invention, in any one of the 1st-4th invention, the said electroconductive filler (C) is carbon black, The electromagnetic wave shielding sheet is provided.

According to the sixth invention of the present invention, in the fifth invention, the compounding amount of the carbon black is 20 to 40% by weight based on the total amount of the elastic resin (B) and the carbon black, the electromagnetic wave blocking sheet is provided. do.

On the other hand, according to the seventh invention of the present invention, a first step of obtaining an elastic resin solution in which an elastic resin (B) is dissolved in a solvent and a conductive filler (C) is mixed therein, and the elastic resin solution is made of conductive fine wire fibers. First to sixth inventions comprising a second step of impregnating the assembly A and a third step of forming a cavity in the elastic resin B while removing the solvent in the elastic resin solution under high temperature and high humidity. Provided is a method of manufacturing an electromagnetic wave shielding sheet according to any one of the inventions.

According to the eighth aspect of the present invention, in the seventh aspect, a fourth step of removing the solvent by immersing in water or hot water after the third step is provided.

According to the ninth invention of the present invention, in the seventh or eighth invention, in order to improve thickness adjustment and surface smoothness, a fifth step of forming the electromagnetic wave shielding sheet by pressing or hot pressing is added. Provided is a method of making a barrier sheet.

The present invention is an electromagnetic wave shielding sheet composed of an elastic resin (B) containing a fiber aggregate (A) made of a fine conductive wire and a conductive filler (C) as described above, wherein at least a portion of the end portion of the fiber assembly (A) is buffered. It is exposed to the outer surface of the material, but the other part is buried in the buffer material, the elastic resin (B) is characterized in that the conductive filler (C) uniformly mixed with a number of cavities therein Regarding a blocking sheet or the like, the following are included as a preferred embodiment thereof.

(1) In the first invention, the electrical conductivity is 50 (Ω / 3 cm) or less, the electromagnetic shielding performance is 45 (db) or more in the range of 100 to 1000 MHz, and the flexibility is Type A Durometer hardness. The electromagnetic wave shielding sheet which is 30 or less.

(2) The electromagnetic wave shielding sheet according to the third invention, wherein the fine metal wire is a brass fine wire.

(3) In the seventh invention, the high temperature and high humidity of the third step is a hot air atmosphere in which the steam is humidified.

Hereinafter, the present invention will be described in detail by item.

The electromagnetic wave shielding sheet of the present invention is an electromagnetic wave shielding sheet composed of an elastic resin (B) containing a fiber aggregate (A) made of fine conductive wires and a conductive filler (C), wherein at least a portion of the end portion of the fiber assembly (A) is a buffer material. Although exposed to the outer surface of the other portion is buried in the buffer material, the elastic resin (B) is characterized in that the conductive filler (C) uniformly mixed with a plurality of cavities therein.

1. Fiber assembly (A)

In the electromagnetic wave shielding sheet of the present invention, the fiber assembly A is made of conductive fine wire. The conductive fine wire can be suitably used as long as the surface is electrically conductive, such as a fiber coated with a conductor, a fine coated metal wire, a carbon fiber, or carbon fiber.

Among these, since a thin metal wire has a small resistance, since favorable electroconductivity can be obtained, it is more preferable. Examples of such fine metal wires include brass, copper, aluminum, and stainless steel.

It is preferable that the diameter of an electroconductive thin wire is 100 micrometers or less from a viewpoint of the buffering property and electrical resistance value of an electromagnetic wave shielding sheet.

The weight per unit area of the fiber assembly is preferably in the range of 1 to 0.005 (kg / m ² ). If the weight of the fiber aggregate is less than 0.005 (kg / m ² ), the conductive effect or the electromagnetic wave shielding effect is not exerted. On the other hand, if the weight of the fiber aggregate is greater than 1 (kg / m ² ), it becomes difficult to impregnate the elastic resin solution, resulting in poor operability. Not desirable

The thickness of the fiber aggregate may vary depending on the thickness of the electromagnetic wave shielding sheet desired, but is preferably in the range of 0.2 to 5 mm at a fixed value.

2. Elastic resin (B)

The elastic resin (B) of the present invention can be suitably used as long as it is a resin having elasticity, and examples thereof include a polyurethane resin, a polyurethane urea resin, a silicone resin, and an unvulcanized rubber material.

Among these, polyurethane is preferable because it has excellent mechanical properties, low cost, and can easily change the desired physical properties, particularly hardness, by changing the blending ratio of its components. Moreover, polyurethane is preferable also in this point, since the range of solvent selection is wide. This is because there are many solvents in the solvent group that can dissolve polyurethane, so that water is also easy to dissolve.

When using an unvulcanized rubber material as an elastic resin, it is also preferable to add a vulcanizing agent, a vulcanization adjuvant, etc., and to perform a vulcanization reaction, removing a solvent at high temperature and high humidity.

3. Conductive Filler (C)

In the electromagnetic wave shielding sheet of the present invention, the conductive filler (C) is added to improve the conductivity of the elastic resin (B). It is preferable to use metal particles, carbon particles, or the like as the filler, but in terms of conductivity and price, acetylene black made of acetylene gas is preferable.

4. Electromagnetic wave shielding sheet and manufacturing method thereof

Not only the excellent electromagnetic wave shielding performance of the present invention, but also the electromagnetic wave shielding sheet having a buffer function can be obtained by the following manufacturing method. The manufacturing method of the electromagnetic wave shielding sheet is characterized by including the following 3 (I to III), 4 (I to IV), or 5 (I to V) process, the most important of which is the elastic resin After dissolving in a solvent and mixing the conductive filler in the solution to prepare an elastic resin solution, and then impregnated it in a fiber assembly, the solvent is removed under high temperature and high humidity to cure the elastic resin and to produce a cavity.

(I) The 1st process of obtaining the elastic resin solution which melt | dissolved elastic resin (B) in a solvent, and mixed conductive filler (C) in it.

(II) A second step of impregnating the elastic resin solution obtained from the first step into a fiber aggregate (A) made of conductive fine wire.

(III) A third step in which the elastic resin solution-impregnated fiber assembly (A) obtained from the second step is removed from the solvent in the elastic resin solution under high temperature and high humidity to cure the elastic resin and to form a cavity in the elastic resin (B). .

(IV) 4th process of removing a solvent by immersing the electromagnetic wave shielding sheet obtained from the 3rd process in water or hot water.

(V) 5th process of shaping | molding the electromagnetic wave shielding sheet obtained from the 3rd or 4th process by press or hot press in order to improve thickness adjustment and surface smoothness.

In the electromagnetic wave shielding sheet of the present invention, the fiber assembly (A) is embedded in a buffer material, that is, in an elastic resin (B) containing a conductive filler (C) constituting the buffer material. At least a portion of the distal end thereof is preferably exposed to the outer surface of the buffer material, that is, the elastic resin B (see FIG. 1).

In addition, the electromagnetic wave blocking sheet of the present invention includes a plurality of cavities in the elastic resin in order to have a buffer. Among the cavities contained in the elastic resin, the shape and size of the cavities visible to the naked eye are almost spherical or tau spherical, and the diameter of the cavity is about 0.3 to 1 mm.

Such a cavity may be formed by adding a foaming agent, but in order to provide better buffering property, the above-described manufacturing method, that is, the elastic resin is dissolved in the solvent and the conductive filler is uniformly mixed therein to prepare the elastic resin solution. It is preferable to harden the elastic resin and to form a cavity by impregnating the fiber aggregate and then removing the solvent at high temperature and high humidity, that is, for example, steam humidified heat. Moreover, it is preferable to harden an elastic resin to some extent under high temperature, high humidity, and to impregnate in water or hot water, and to remove a solvent.

The solvent used in the method for producing an electromagnetic wave shielding sheet of the present invention can be suitably used without any particular limitation as long as it dissolves the elastic resin and is dissolved in water.

For example, when urethane is used as the elastic resin, it is suitable to use dimethylformamide (DMF), dimethylacetamide (DMAC), N-methyl-2-pyrrolidone (NMP), or the like. In addition, tetrahydrofuran (THF) etc. are used when silicone resin is used as an elastic resin, and acetone, methyl ethyl ketone (MEK), etc. are mentioned when unvulcanized rubber is used.

Moreover, the elastic resin solution which mixed the electrically conductive filler (C) obtained from the 1st process concerning the manufacturing method of the electromagnetic wave shielding sheet of this invention uses carbon black as an electrically conductive filler, and uses polyurethane as an elastic resin, for example. In this case, the solution concentration in which the carbon black and the polyurethane are dissolved depends on the aspect of the conductive fiber aggregate, but is preferably prepared at a stock solution concentration that is easily impregnated. If the concentration of the stock solution is too low, the fiber aggregates are exposed after solidification and the polyurethane layer containing carbon black is extremely thin, which is undesirable. On the other hand, when the concentration of the stock solution is too high, it is difficult to impregnate the conductive fiber assembly and the coating layer of the end portion of the conductive fiber assembly is peeled off, which is not preferable. Preferred stock solutions (solutions in which carbon black and polyurethane are dissolved) range in concentration from 7 to 12% by weight.

It is preferable to mix | blend the compounding quantity of carbon black as an electroconductive filler according to the electroconductivity of the desired electromagnetic wave shielding sheet, and it is not specifically determined. However, when the blending concentration of carbon black is too low, the conductivity is lowered, which is not preferable. On the other hand, when too high, it becomes difficult to disperse carbon black and raise the viscosity of the stock solution rapidly, so that it is difficult to obtain the expected performance, and there is a risk of impairing the operability and the appearance of the electromagnetic wave shielding sheet. Preferably 20 to 40% by weight, more preferably 25 to 40% by weight relative to the total amount of the elastic resin (B) and the carbon black can be obtained to obtain a buffer material having suitable performance and quality.

An example (summary) of the manufacturing method of a specific electromagnetic wave shielding sheet is demonstrated. In this production method, fine brass is used as the fiber assembly (A), polyurethane is used as the elastic resin (B), and carbon black is used as the conductive filler (C). However, the manufacturing method of the electromagnetic wave shielding sheet of this invention is not limited to this.

(1) Preparation of polyurethane solution (first half of first step)

A kneader is used to prepare a DMF (dimethyl formamide) solution (concentration 15% by weight) of ether-based polyurethane pellets. After dissolution is completed, DMF is added to prepare a 10% by weight polymer solution.

(2) Preparation of conductive carbon black dispersion (first half of first step II)

A 10 (wt%) DMF solution of conductive carbon black was prepared. A homogenizer is used for the dispersion processing.

(3) Preparation of conductive carbon black-containing polyurethane solution (first step)

The polyurethane solution and the conductive carbon black dispersion are weighed and mixed to prepare a conductive carbon black-containing polyurethane solution. The mixing ratio is, for example, 30 parts by weight of the conductive carbon black dispersion based on 70 parts by weight of the polyurethane solution. After mixing and stirring, the mixture is allowed to stand for 1 hour to spontaneously deflate and proceed to the next step.

(4) Preparation of electromagnetic wave shield sheet (2nd, 3rd and 4th process)

Brass thin wire sheets were degreased and washed with methyl chloride as needed. After drying, the brass thin wire sheet is transferred to a vat, the conductive carbon black-containing polyurethane solution is charged, and the polymer solution is impregnated into the thin wire sheet (second step).

The vessel is then stored in steam humidified hot air (90 ° C. × 50 RH%). If desolvent and solidification proceed, remove the container and add water to promote desolvent. After immersing in water for about 12 hours, air is added to the contents and dried to obtain an electromagnetic wave shielding sheet (steps 3 and 4).

A cross-sectional schematic diagram of the electromagnetic wave shielding sheet thus produced is shown in FIG. 1. A fiber assembly made of conductive fine wire is embedded in a conductive fine particle (eg carbon black) dispersed polyurethane matrix, and at least a part of the fiber assembly is exposed to an external surface, and at high temperature and high humidity, that is, steam humidified heat. By shaping | molding in the air, a bubble, ie, a cavity, is formed. The presence of bubbles (cavities) contributes to the elasticity and synergistically cushioning of the polyurethanes.

The electromagnetic wave shielding sheet of the present invention has a hardness of about 20 to 30 in terms of type A durometer hardness. In addition, the conductive capability is 50 (Ω / 3 cm) or less in electrical resistance value, and the electromagnetic wave blocking performance has a performance of approximately 45 (db) in the range of 100 to 1000 MHz.

The electromagnetic wave shielding sheet of the present invention can have the mechanical properties of the fiber assembly by embedding the conductive fiber assembly in the buffer material, that is, the elastic resin constituting the buffer material, so that the FRP (U) [fiber-reinforced resin (urethane) Has improved mechanical properties. On the other hand, when the conductive additive is mixed with the elastic resin without using the fiber aggregate, it is necessary to increase the mixing ratio in order to exhibit sufficient conductivity, but in this case, the performance of the elastic resin is impaired.

In addition, the electromagnetic wave shielding sheet of the present invention has stable conductivity with respect to the surface, the thickness direction, and the longitudinal width direction, i.e., isotropic due to the structure in which the conductive fiber assembly in the elastic resin is three-dimensionally arranged. On the other hand, when embedding two-dimensional conductive materials, such as metal foil, for example, although it changes with the thickness of the final formation, the thickness of metal foil, and the number of lamination | stacking, sufficient electroconductivity with respect to the thickness direction cannot be ensured. In addition, there is a problem that not only the elastic performance is lost but also the manufacturing is difficult with this method.

Because of the above-mentioned performance, the electromagnetic wave shielding sheet of the present invention has a shock absorbing function that effectively blocks electromagnetic waves leaking from an information device housing such as a mobile phone and protects electronic components relatively susceptible to impact. For example, it can use suitably as a mobile phone liquid crystal protection buffer.

[Examples and Comparative Examples]

Hereinafter, examples and comparative examples of the present invention are listed and described in detail, but the present invention is not particularly limited to these examples.

The manufacturing method and performance evaluation method of the electromagnetic wave shielding sheet of Examples 1-17 and Comparative Examples 1-3 are shown below. However, fine brass is used as the fiber assembly (A), polyurethane is used as the elastic resin (B), and carbon black is used as the conductive filler (C).

1. Preparation of electromagnetic wave shielding sheet

(1) Preparation of polyurethane solution

 Kneader with a jacket of N, N-dimethyl formamide (DMF) 1983 (g) to 350 g of ether-based polyurethane pellets (trade name: Mobilon P-24TS) And dissolved for 2 hours at 50 ° C. The polymer concentration in the polymer solution is about 15 (% by weight). Then, DMF 2667 (g) was added and dissolved at 50 ° C. for 2 hours to obtain a polymer solution of 7 (% by weight). In the case of changing the polymer concentration in the polymer solution, a polymer solution of about 15 (% by weight) is prepared using the above method, and then the polymer solution is diluted to a total amount of 5000 (g) under the final polymer solution concentration. Got it.

(2) Preparation of Conductive Carbon Black Dispersion

Conductive carbon black [manufactured by Electrochemical Industry. DMF 664.3 (g) was added to 50 g, and then dispersed in a homogenizer for 15 minutes to prepare a carbon black solution having a concentration of 7 (% by weight). The concentration of the carbon black solution was used in accordance with the polymer solution concentration used for preparing the composite.

(3) Preparation of conductive carbon black-containing polyurethane solution

To a 500 (ml) separation flask was added 60 (g) of carbon black solution to 140 (g) of 7 (wt%) polymer solution and stirred at room temperature for 15 (min). After the end of stirring, the air bubbles in the carbon black-containing polymer solution were naturally removed by leaving it for about 60 minutes.

(4) Manufacture of electromagnetic wave blocking sheet

Brass wire assemblies (hereinafter referred to as brass sheets) were degreased or washed with methylene chloride as needed to prepare buffer materials. The brass sheet has a diameter (hereinafter referred to as wire diameter) of about 50 (μm) of the brass wire constituting the sheet, and a weight of the brass sheet per meter per square meter (hereinafter referred to as a unit amount) of about 400 (g / m ^2). ) Was used. Brass sheets were cut at approximately 50 (mm) angle and placed in a tray made of polypropylene (size 300 mm × 210 mm). Subsequently, 100 (g) of the carbon black-containing polymer solution was weighed into the tray, and the bubbles formed from the sheet were removed while shaking the thin wire sheet with tweezers.

Then, a polypropylene tray containing a brass sheet and a carbon black-containing polymer solution was placed in a stainless steel tray (size 600 mm X 300 mm X 120 mm) filled with hot water 3 (1) of about 60 (° C), It was humidified and heated to about 60 (min) in the state of relative humidity 50 (RH%), desolvation, and solidified. The solidified electromagnetic wave shielding sheet was immersed in water for at least about 12 (hours), and then naturally dried. In this way, an electromagnetic wave shielding sheet was prepared.

2. Evaluation method

(1) Appearance and presence of cavity

The appearance of the electromagnetic wave shielding sheet was evaluated by visual evaluation. The evaluation criteria are as follows. In addition, the presence or absence of a cavity in the electromagnetic wave shielding sheet was visually determined.

(Double-circle): Brass fine wire is exposed and the polyurethane part containing carbon black is substantially flat cross section.

(Circle): Brass fine wire is exposed and is generally a flat cross section except that there is some recessed part in the polyurethane part containing carbon black.

(Triangle | delta): A brass thin wire is exposed and is generally a flat cross section except that the recessed part is prominent to the polyurethane part containing carbon black to some extent.

X: The brass fine wire has a part without carbon part (uncoated part) containing carbon black.

(2) hardness

The hardness of the electromagnetic wave shielding sheet was measured by the "durometer hardness test method of plastics" of JIS K7215.

As a rough acceptance criterion, the Type A durometer hardness of the low hardness, hot press free buffer material is on the order of 20-30.

(Double-circle): It is 30 or less by A-type hardness.

* (Circle): It is more than 30 and less than 40 by A-type hardness.

(Triangle | delta): It is more than 40 and 50 or less by A-type hardness.

X: A type | mold hardness exceeding 50.

(3) Conductivity (Electrical Resistance)

The open surface of the electromagnetic shielding sheet (the surface which does not come into contact with the container when preparing: referred to as the surface below) and the container contact surface (the surface that comes into contact with the container: referred to as the following surface) are respectively digital multimeters (CDM made by custom). -11HD type] electrical resistance was measured. The buffer material used for the measurement was the sample cut | disconnected at 50 (mm) angle, and what was marked on every 10 (mm) periphery of 10 (mm) inner part from the outer periphery was used. The test leads were placed near any mark, the test leads in the other direction were placed on opposite sides (in this case the measurement interval was 30 mm) and then the resistance was read. Subsequently, 8 points in total were measured according to one sample performed in the vicinity of a display part and the surface which faced it sequentially, and the average value was evaluated. In addition, the samples were recorded separately by measuring both sides of the front and back surfaces.

The approximate acceptance criterion is that the surface electrical resistance is low and the electrical resistance on both sides is 50 (Ω / 3 cm) or less. The best low values are 1 to 3 (Ω / 3 cm).

(Double-circle): Electrical resistance value is 10 ((ohm) / 3cm) or less.

(Circle): Electrical resistance value is more than 10 (ohm / 3cm), and is 50 or less (ohm / 3cm).

(Triangle | delta): Electrical resistance value exceeds 50 ((ohm) / 3cm) and is 1000 ((ohm) / 3cm) or less.

X: electrical resistance is more than 1000 (Ω / 3 cm).

(4) electromagnetic wave blocking performance

First, the electronic cutoff measurement tester was installed in a state without anything inside, and the reference level (EO) was measured. Subsequently, the blocking material cut | disconnected at 150 (mm) angle was installed in the electronic cutoff measurement tester, and the reception level (E1) was measured (KEC method).

The blocking effect S was calculated by the following formula.

Blocking Effect (S) = (EO)-(E1): Unit (db)

The measurement was performed at a frequency between 0.15 and 1000 (MHz). The electronic cutoff meter was measured using ANRITSU's MA8602, and the spectrum analyzer was measured using ADVANTEST's TR4173.

The electromagnetic wave blocking performance as an approximate acceptance criterion is assumed to have a performance of approximately 45 (db) between 100 and 1000 (MHz).

(Double-circle): Blocking effect is 45 (db) or more.

(Circle): Blocking effect is 15 (db) or more and less than 45 (db).

(Triangle | delta): Blocking effect is 5 (db) or more and less than 15 (db).

X: The blocking effect is less than 5 (db).

Example 1 is the same as described above, but in Example 13, the kind and compounding amount of the raw materials are in accordance with Table 3, and the preparation method was prepared in the same manner as in Example 1, was processed by hot press.

In the processing method by the hot press, the electromagnetic shielding sheet was hot pressed by an iron. The heating surface set temperature of the iron was 210 ° C., and was pressed horizontally with respect to the electromagnetic wave shielding sheet at a 50 (mm) angle for about 30 seconds.

In Comparative Example 1, an electromagnetic wave shielding sheet was prepared by vacuum heating, and the types and blending amounts of the raw materials are as shown in Table 3. The preparation method including the preparation of the polymer solution, the preparation of the carbon black solution, and the preparation of the carbon black-containing polymer solution was prepared in the same manner as in Example 1. And the preparation of the next electromagnetic wave shielding sheet was performed by the following method.

The brass sheet was degreased or washed with methyl chloride as needed to prepare a buffer material. As for the brass sheet, the diameter of the brass wire which comprises a sheet was about 50 (micrometer), and the weight of the brass sheet per square meter used 100 (g / m <^2> ). The brass sheets were cut at an angle of about 50 (mm) and placed in a polypropylene tray (size 300 mm X 210 mm X 37 mm). Subsequently, 100 (g) of the carbon black-containing solution was weighed and administered into the tray, and bubbles generated from the sheet were removed while shaking the brass sheet with tweezers. Then, the polypropylene tray containing the preparation was placed in a vacuum drier and left for 18 hours under a vacuum of 50 ° C. 76 (cmHg) to volatilize the solvent DMF.

In the other examples and comparative examples, the kind and the blending amount of the raw materials are according to Tables 1 to 3, and the preparation method was prepared in the same manner as in Example 1. The structure and the physical property evaluation result of the obtained electroconductive material are shown to Tables 1-3.

As is clear from the results of Tables 1 to 3, the electromagnetic wave shielding sheet according to Examples 1 to 17 is excellent in hardness, conductivity, electromagnetic wave shielding performance and good appearance.

On the other hand, the electromagnetic wave shielding sheet of Comparative Example 1, which was formed by vacuum heating instead of steam humidification, did not have a cavity, and as a result, the hardness was high, resulting in lack of flexibility (bufferability). In addition, in Comparative Example 2 of the brass thin wire sheet alone, the brass thin wire was scattered and could not be used. Further, in Comparative Example 3 in which the amount of undiluted solution was applied, all of the brass fine wires were embedded in the buffer, and the electrical resistance did not meet the acceptance criteria. The reason is not clear, but it can be inferred as follows. Fully buried conductive brass fibers means that the elastic resin layer containing the conductive filler (carbon black) on the surface of the electromagnetic wave shielding sheet is thickened. In other words, the electrical resistance is relatively low in the conductive route during the electrical resistance measurement. It is assumed that the high path is long. As a result, the root length of the fine metal wire closest to the electrical resistance of the elastic resin layer containing the conductive filler (i.e., the content of the carbon black content) (i.e. the coating thickness of the elastic resin containing the carbon crack in the fine metal wire) It is thought to be controlled by. That is, when the electrical resistance of the elastic resin layer containing the conductive filler is low and the coating thickness on the thin metal wire is thin, there is a preferable tendency that the electrical resistance as the electromagnetic wave shielding sheet is lowered. In the comparative example 3, since these requirements were not satisfied, it is thought that the acceptance criteria were not satisfied.

The electromagnetic wave shielding sheet of the present invention is characterized in that the conductive fiber assembly is three-dimensionally disposed in the buffer material (i.e., in the elastic resin), provided that at least a portion of the distal end of the fiber assembly is exposed to the outer surface of the buffer material. As a result, the mechanical properties of the fiber assembly can be obtained together, so that not only the mechanical properties are excellent, but also the conductivity and the electromagnetic wave blocking performance are excellent. Moreover, it has stable conductivity (that is, isotropic conductivity) in the surface, the thickness direction, and the longitudinal width direction. In addition, there is little fear that the conductivity will be lost by external force such as impact or friction.

In addition, the method for imparting conductivity according to the present invention can provide conductivity that satisfies the purpose of use by combining materials (fiber aggregate and carbon black) which are used in a wide range of industries. In addition, in the method for producing an electromagnetic wave shielding sheet of the present invention, an elastomeric resin solution containing a conductive filler is applied onto a carrier using a commercially available coating machine or the like, and then the electromagnetic wave shielding sheet precursor on the carrier is subjected to high temperature and high humidity. By passing through the state and the water washing process, the electromagnetic wave shielding sheet can be continuously and inexpensively produced and the production method is easy and economical.

Claims (9)

An electromagnetic wave shielding sheet composed of an elastic resin (B) containing a fibrous assembly (A) made of fine conductive wire and a conductive filler (C), wherein at least a portion of the distal end portion of the fibrous assembly (A) is exposed to the outer surface of the buffer material. And the other part is embedded in the buffer material, and the elastic resin (B) uniformly mixes the conductive filler (C) and has a plurality of cavities therein. The electromagnetic wave shielding sheet according to claim 1, wherein the elastic resin (B) is polyurethane. The electromagnetic wave blocking sheet of claim 1, wherein the fiber aggregate (A) has a weight per unit area in the range of 1 to 0.005 (kg / m ² ). The electromagnetic wave shielding sheet according to claim 3, wherein the fiber assembly (A) is made of fine metal wires. The electromagnetic wave shielding sheet according to any one of claims 1 to 4, wherein the conductive filler (C) is carbon black. The electromagnetic wave shielding sheet according to claim 5, wherein the compounding amount of the carbon black is 20 to 40% by weight based on the total amount of the elastic resin (B) and the carbon black. A first step of dissolving the elastic resin (B) with a solvent and incorporating the conductive filler (C) therein to obtain an elastic resin solution, a second step of impregnating the elastic resin solution into a fiber assembly (A) made of fine conductive wires; And a third step of forming a cavity in the elastic resin (B) while removing the solvent in the elastic resin solution under high temperature and high humidity. 8. The method for producing an electromagnetic wave shielding sheet according to claim 7, wherein the method for manufacturing an electromagnetic wave shielding sheet further comprises a fourth step of removing the solvent by immersion in water or hot water after the third step. 9. The method of manufacturing the electromagnetic wave shielding sheet according to claim 7 or 8, further comprising a fifth step of forming the electromagnetic wave shielding sheet by pressing or hot pressing to improve thickness adjustment and surface smoothness. Method of manufacturing electromagnetic wave shielding sheet.

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