KR101000973B1 - Electrically Conductive coating Liquid, Manufacturing Method of Electromagnetic wave absorber using the same and Electromagnetic wave absorber formed thereby - Google Patents

Abstract

The present invention relates to a conductive coating solution for absorbing electromagnetic waves, a method for producing an electromagnetic wave absorbing material using the same, and an electromagnetic wave absorbing material thereof, more specifically, 10-30% by weight of water-dispersed carbon black at 23-25 ° C, and a urethane binder 2-10. A conductive coating solution that absorbs electromagnetic waves is prepared by mixing the wt%, 10-35 wt% of the aqueous flame retardant, and 50-60 wt% of the solvent. In this case, the dispersant may further include 0.05-0.2 parts by weight, antifoaming agent 0.05-0.2 parts by weight, and pH adjuster 2.0-4.0 parts by weight based on 100 parts by weight of the conductive coating solution.

The conductive coating prepared in this way is 100-200 bar After spray-coating the substrate under pressure, the prepared substrate is dried at 110-125 ° C. for 25-35 minutes to prepare an absorber that absorbs electromagnetic waves.

Electromagnetic Waves, Absorbers, Carbon Black, Conductive Coatings

Description

Electrically conductive coating liquid, manufacturing method of electromagnetic wave absorber using the same and electromagnetic wave absorber formed thereby

The present invention relates to a conductive coating liquid, and more particularly, to a conductive coating liquid including carbon black and a urethane binder sprayed onto a substrate by coating with a conductive coating liquid capable of absorbing electromagnetic waves, and an electromagnetic wave absorbing material manufacturing method using the same. It relates to an electromagnetic wave absorber.

Recently, with the rapid development of the electric and electronic industry, information and communication technology, and the use of wireless communication services such as mobile communication and wireless LAN, modern people have enjoyed the convenience and richness in daily life.

However, the occurrence of unnecessary radio waves is sharply increased, resulting in deterioration of reliability of electronic devices, interference in communication, malfunction of home and industrial electrical and electronic devices, and harmful effects on human body by electromagnetic waves of these devices. Doing.

This phenomenon is a side effect of radio wave pollution that is serious due to the use of various electronic devices.

In order to avoid such electromagnetic waves, an absorber that absorbs electromagnetic waves reflected from a building wall, a building glass, an electromagnetic mat, etc., and prevents noise or radio wave interference is used. In particular, the electromagnetic wave absorber is used when a space without reflection propagation is required, such as when designing an antenna or measuring electromagnetic waves. However, it is difficult to shield the radio wave from the recently increasing radio wave pollution.

In general, the characteristics required for electromagnetic wave absorbers for electronic information and communication devices include ① large reflection attenuation coefficient (small reflection coefficient), ② wide band capable of absorbing electromagnetic waves, and ③ thin thickness. However, electromagnetic wave absorbers capable of satisfying all of the above characteristics have not yet been realized.

Recently, the electromagnetic wave absorber is manufactured by impregnating carbon material into urethane foam. When impregnation processing is performed by dipping urethane foam into an impregnation solution containing carbon material and squeezing out, carbon material is easily released and the urethane foam dipped in the impregnation liquid. It takes a considerable time to dry. In addition, the electromagnetic wave absorber is heavy in itself, and the moisture is introduced into the absorber as time passes due to the unique water absorption of carbon, and the weight is further increased. When the heavy electromagnetic wave absorber is installed on the wall, not only the wall is overwhelmed, but also the weight is not overcome, but the wall is separated from the wall. In addition, due to the complex impregnation process, there is a problem that the manufacturing process is long, cumbersome and not permanently conductive.

Accordingly, the present invention includes a carbon black, a urethane binder, and additives, and may use a spray coating method, and to provide a conductive coating liquid capable of absorbing a wide range of electromagnetic waves.

In addition, the present invention is to provide an electromagnetic wave absorber lighter weight by injecting a conductive coating liquid on the substrate.

In addition, the present invention is to provide an electromagnetic wave absorber capable of absorbing a wide band of electromagnetic waves to attenuate radio waves.

To this end, the conductive coating solution according to the present invention comprises 10-30% by weight of water dispersion carbon black, 2-10% by weight of a urethane binder, 10-35% by weight of an aqueous flame retardant and 50-60% by weight of a solvent, and further 100 0.05-0.2 parts by weight of dispersant, 0.05-0.2 parts by weight of antifoaming agent and 2.0-4.0 parts by weight of pH adjuster, based on parts by weight.

The type of water-dispersed carbon black used at this time is selected from the group consisting of ketjen black, oil furnace black, thermal black, channel black, acetylene black, carbon nanotubes, the average particle diameter of 1-5㎛, solid content 15.5-17.5 %, pH 9.5.

The prepared conductive coating solution had a viscosity of 55-60 mPa · s and a surface resistance of (1.0-1.5) × 10 ⁴ dl / sq.

The method for producing an electromagnetic wave absorber using the conductive coating liquid according to the present invention is 10-30% by weight of water dispersion carbon black, 2-10% by weight of urethane binder, 10-35% by weight of aqueous flame retardant and solvent 50- under 23-25 ° C. In the first step of preparing a conductive coating solution by mixing 60% by weight, the conductive coating solution prepared in the first step of 100-200 bar A second step of spray coating the substrate at a pressure and a third step of drying the substrate prepared in the second step at 110-125 ° C. for 25-35 minutes.

At this time, the first step may further include 0.05-0.2 parts by weight of dispersant, 0.05-0.2 parts by weight of antifoaming agent and 2.0-4.0 parts by weight of pH adjusting agent based on 100 parts by weight of the conductive coating solution.

After the first step, the method may further include the step of immersing the substrate in a coating liquid corresponding to 40-50% by weight based on the total conductive coating liquid coated on the substrate. The impregnation method further includes a dehydration step for quick drying.

In addition, the electromagnetic wave absorber thus prepared has a surface resistance of (1.5-2.5) × 10 ⁴ Ω / sq.

In addition, the manufactured electromagnetic wave absorber absorbs and attenuates electromagnetic waves at 10 MHz or less at 80 MHz and 50 dB or less at 1 to 50 GHz.

As described above, since the conductive coating solution of the present invention has low surface resistance, it is effective in absorbing a wide band of electromagnetic waves and may have permanent conductivity. In addition, the electromagnetic wave absorber coated with the coating liquid not only has permanent conductivity, but also absorbs and attenuates electromagnetic waves at 10 MHz or less at 80 MHz and 50 dB or less at 1 to 50 GHz.

In addition, the conductive coating liquid of the present invention is excellent in the adhesion of carbon and excellent penetration into the substrate, so that the carbon does not bury the outside after spray coating and impregnation, spray coating.

In addition, the spray coating method used in the present invention can obtain the impregnated effect by spray coating the conductive coating solution, and can reduce the cost by reducing the amount of the coating solution as well as excellent electrical conductivity compared to the conventional impregnation method.

In addition, when the conductive coating liquid of the present invention is spray coated, the weight of the electromagnetic wave absorber is lighter, so that the workability is improved and the absorber is prevented from being separated from the wall.

In addition, the electromagnetic wave absorbing material of the present invention can be used for a long time because the moisture absorption is minimized.

The present invention manufactures a conductive coating liquid having permanent conductivity and coats the conductive coating liquid on a substrate to produce an electromagnetic wave absorbing material that facilitates electromagnetic wave absorption permanently.

EMBODIMENT OF THE INVENTION Hereinafter, the conductive coating liquid of this invention is demonstrated in detail.

The conductive coating solution of the present invention comprises 10-30% by weight of water-dispersed carbon black, 2-10% by weight of a urethane binder, 10-35% by weight of an aqueous flame retardant, and 50-60% by weight of a solvent. In this case, additives such as a dispersant, an antifoaming agent, and a pH adjusting agent may be additionally added to the conductive coating solution of the present invention. The dispersing agent is 0.05-0.2 parts by weight with respect to 100 parts by weight of the conductive coating solution, and the antifoaming agent is 0.05- with respect to 100 parts by weight of the conductive coating solution. 0.2 parts by weight and pH adjusting agent are included in an amount of 2.0-4.0 parts by weight based on 100 parts by weight of the conductive coating solution.

The water-dispersed carbon blacks include ketjen black, oil furnace black, thermal black, channel black, acetylene black, carbon nanotubes, and the like. Preferably, the ketjen black has an average particle diameter of 1-5 μm, a solid content of 15.5-17.5%, and pH. Use 9.5.

Such carbon black is contained 10-30% by weight, preferably 15-20% by weight. In this case, when the carbon black content is less than 10% by weight, the conductivity of the coating liquid may be lowered. When the carbon black content is more than 30% by weight, it may be difficult to disperse the coating liquid by spraying and the manufacturing cost may be increased.

The urethane binder used in the present invention satisfies a solid content of 10 to 40%, a viscosity of 300 mPa.s, and a pH of 8, and in particular, a volatile organic compound (VOC) content of 5 g / L or less is used.

This urethane binder is used in 2-10% by weight, preferably 4-6% by weight. In this case, when the content of the urethane binder is less than 2% by weight, adhesion may be inferior to the base material when coating the prepared conductive coating solution. When the content is more than 10% by weight, the coating liquid of the present invention is made hard to make the absorber sprayed with elasticity. This can cause problems such as loss of quality and loss of coating.

Aqueous flame retardants are those containing from 10 to 35% by weight, preferably from 18 to 25% by weight, to protect the absorber, building and life from fire.

If the content of the water-based flame retardant is less than 10% by weight can not exhibit the flame retardant effect in the fire, when the content is more than 35% by weight may not only reduce the strength and durability of the coating film but also of the absorber sprayed coating of the present invention You can lose elasticity.

The solvent contains 50-60% by weight, but if the content is less than 50% by weight, the viscosity of the conductive coating prepared is high, making it difficult to paint with a spray.As a drying speed is slow even after the coating is formed, the coating may be peeled off and the conductivity may be decreased. In the case of more than 60% by weight, the viscosity of the conductive coating liquid is low and the coating liquid does not adhere to the coating when sprayed, resulting in uneven coating thickness, resulting in uneven conductivity and deterioration in the dispersibility of carbon black. have.

In this case, the solvent refers to a mixture of alcohol and distilled water in a ratio of 2: 1, and the alcohol used herein includes one or two or more selected from the group consisting of ethanol, methanol, isopropyl alcohol, diacetone alcohol, and isopropanol. It is preferably used isopropyl alcohol.

On the other hand, the dispersant which may be further included in the conductive coating liquid of the present invention may contain 0.05 to 0.2 parts by weight based on 100 parts by weight of the conductive coating liquid.

In this case, when the content of the dispersant is less than 0.05 parts by weight based on 100 parts by weight of the conductive coating liquid, agglomeration of carbon black occurs, resulting in low durability when forming a coating film, resulting in a rough coating surface and a drop in conductivity, and a content of the dispersant in excess of 0.2 parts by weight. In the case that the surface of the carbon black itself is coated can be reduced the ability to absorb electromagnetic waves when coating with a conductive coating liquid.

The dispersant used in the present invention is one or more materials selected from the group consisting of alkylalkoxysilane, siloxane, silane and polycarboxylic acid.

In addition, the antifoaming agent may contain 0.05-0.2 parts by weight with respect to 100 parts by weight of the conductive coating liquid, if the content of the antifoaming agent is less than 0.05 parts by weight with respect to 100 parts by weight of the conductive coating liquid, bubbles may occur on the surface of the absorbent material, the content is 0.2 parts by weight In the case of excessive excess, durability may be reduced when the coating liquid is applied.

The pH adjusting agent uses hydrated lime, soda ash, liquid caustic soda, ammonia water and at least one selected from among them, and the content of the pH adjusting agent is preferably an amount that can adjust the pH of the conductive coating solution to 7 to 8.5.

If the pH is less than 7 and if the pH is greater than 9, collision of materials in the coating solution may occur and the coating may not be formed. At this time, the content of the pH control material which can adjust the pH of the conductive coating solution to 7 ~ 8.5 is to contain 2.0 to 4.0 parts by weight based on 100 parts by weight of the conductive coating solution.

The conductive coating solution of the present invention thus made exhibits a viscosity of 55-60 mPa · s and a surface resistance of (1.0-1.5) × 10 ⁴ μs / sq.

Hereinafter, the method of manufacturing an electromagnetic wave absorber using the conductive coating liquid of this invention is demonstrated in detail.

In the first step, the conductive coating solution is prepared by adding and stirring carbon black, a urethane binder, an aqueous flame retardant, and a solvent at 23-25 ° C. On the other hand, in order to further improve the physical properties of the conductive coating liquid may further comprise a dispersant, antifoaming agent pH adjusting agent.

In the second step, the coating solution prepared in the first step is sprayed to the inside of the substrate by spraying the prepared substrate at a pressure of 100-200 bar using a spray for 3-6 minutes. In this case, when the coating liquid is sprayed with a spray sprayed at a high pressure, the substrate made of an open cell may have excellent electrical conductivity by infiltrating the coating liquid into the open cell to obtain a dipping effect. However, when the pressure of the spray is less than 100 bar, the hardness of the formed coating film may be weakened and the adhesion with the substrate may be reduced, and when the pressure is more than 200 bar, the substrate may be dropped. In addition, when the conductive coating liquid is sprayed in less than 3 minutes, the impregnated effect of infiltrating the coating liquid into the open cell of the substrate cannot be obtained. In the case of spraying for more than 6 minutes, the thickness of the coated coating film becomes thick and excessive coating effect is prevented. The drying takes a long time, and the coating film may fall off.

The third step is to dry the substrate coated with the conductive coating solution for 25-35 minutes at 110-125 ° C to produce an electromagnetic wave absorber coated with the conductive coating solution.

Between the first step and the second step may further comprise the step of impregnating the substrate, wherein the conductive coating liquid used for the impregnation is 40-50% by weight of the conductive coating liquid corresponding to the entire conductive coating liquid required to coat the substrate Immersion of the substrate into the impregnation of only a portion of the substrate. When the impregnation method and the spray method are used continuously, the electromagnetic wave absorption is more excellent.

When adding the impregnation step may further include the step of dehydrating at 1000-2000 rpm for quick drying after spray coating on the substrate.

Here, the substrate means not only a foam containing a resin and a conductive material, but also a cell phone, an electric mat, a wall of a building, a building glass, etc. Polyurethane foam with open cell properties, more preferably flexible, containing conductive material and having open cell properties, in the form of a pyramidal, wedge, triangular prism, circular cone, V-shaped section or plate shape Polyurethane foam.

The electromagnetic wave absorber thus manufactured absorbs and attenuates electromagnetic waves at 10 MHz or less at 80 MHz and 50 dB or less at a range of 1 to 50 GHz, and has a moisture absorption rate of 1-6%.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the appended claims.

Example  1. Conductive Coating Solution

17 wt% water-dispersible carbon black (W-311N, Lion), 5 wt% urethane binder (FWD-2000, Mammsys), water-based flame retardant (MS-1020, Universal Chemtech, melamine cyanurate content 40 wt%) 20 wt% and 58 wt% of a solvent were added thereto and mixed to prepare a conductive coating solution.

Example  2. Preparation of conductive coating liquid

Water Dispersed Carbon Black (W-311N, Lion) 16% by weight, Urethane Binder (FWD-2000, Mammsys) 5% by weight, Water-Based Flame Retardant (MS-1020, Universal Chemtech, Melamine Cyanurate Content 40% by weight) 20 wt%, 0.1 wt% of dispersant, 0.1 wt% of antifoam, 2.8 wt% of pH adjuster, 56 wt% of solvent were added and mixed to prepare a conductive coating solution.

Comparative example  1. Conductive Coating Solution

Water Dispersed Carbon Black (W-311N, Lion) 8% by weight, Urethane Binder (FWD-2000, Mammsys) 5% by weight, Water-Based Flame Retardant (MS-1020, Universal Chemtech, Melamine Cyanurate Content 40% by weight) 35 wt% and 52 wt% of a solvent were added thereto and mixed to prepare a conductive coating solution.

Comparative example  2. Preparation of conductive coating liquid

17 wt% water-dispersible carbon black (W-311N, Lion), 18 wt% urethane binder (FWD-2000, Mammsys), water-based flame retardant (MS-1020, Universal Chemtech, melamine cyanurate content 40 wt%) 10 wt% and 55 wt% of a solvent were added thereto to prepare a conductive coating solution.

Comparative example  3. Manufacture of conductive coating solution

17 wt% water-dispersible carbon black (W-311N, Lion), 18 wt% urethane binder (FWD-2000, Mammsys), water-based flame retardant (MS-1020, Universal Chemtech, melamine cyanurate content 40 wt%) 10 wt%, 0.1 wt% of dispersant, 0.1 wt% of antifoam, 2.8 wt% of pH adjuster, and 52 wt% of solvent were added and mixed to prepare a conductive coating solution.

Test Example  One.

Viscosity: Measure the viscosity using an LV viscometer (Brookfield).

Surface resistance: Measured by ASTM D 257 method.

Table 1 below compares the physical properties of the conductive coating solution prepared in Examples 1-2 and Comparative Examples 1-3.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Viscosity (mPa.s) 55 56 120 80 80 Surface resistance (/ sq) 1.5X10 ⁴ 1.0X10 ⁴ 9.0X10 ⁵ 5.0 X 10 ⁴ 5.0 X 10 ⁴

Looking at Table 1, the conductive coating liquid prepared in Example 1-2 is easy to spray with a spray, and the surface resistance is low compared to the coating liquid prepared in Comparative Examples 1-3 is effective in absorbing electromagnetic waves.

In addition, the conductive coating liquid prepared in Comparative Example 2-3 is not coated so that the coating liquid penetrates into the substrate due to the use of excess urethane binder, the substrate becomes hard and the elasticity is lost.

Example  3.

The conductive coating liquid prepared in Example 2 was sprayed on the surface of the substrate with a spray for 5 minutes, and then the substrate to which the coating liquid was applied was dried and cured for 25 minutes at 110 ° C. to prepare an electromagnetic wave absorber. The spray injection pressure at this time was 170 bar.

Example  4.

The substrate is impregnated with the conductive coating solution prepared in Example 2, wherein the substrate is immersed in 45% by weight of the conductive coating solution relative to the total conductive coating solution coated on the substrate so that only a part of the substrate is impregnated. The conductive coating solution is sprayed onto the surface of the impregnated substrate for 5 minutes with a spray and then dewatered at a speed of 1500 rpm. Thereafter, the substrate to which the coating liquid was applied was dried at 110 ° C. for 25 minutes to cure to prepare an electromagnetic wave absorber. The spray injection pressure at this time was 170 bar.

Comparative example  4.

The conductive coating liquid prepared in Example 2 was sprayed on the surface of the substrate with a spray for 5 minutes, and then the substrate to which the coating liquid was applied was dried and cured for 25 minutes at 110 ° C. to prepare an electromagnetic wave absorber. The spray injection pressure at this time was 90 bar.

Comparative example  5.

The conductive coating liquid prepared in Example 2 was sprayed onto the surface of the substrate with a spray for 2 minutes, and then the substrate to which the coating liquid was applied was dried at 110 ° C. for 25 minutes and cured to prepare an electromagnetic wave absorber. The spray injection pressure at this time was 170 bar.

Comparative example  6.

The conductive coating solution prepared in Comparative Example 3 was sprayed on the surface of the washed substrate for 5 minutes with a spray, and then the substrate coated with the coating solution was dried at 110 ° C. for 25 minutes and cured to prepare an electromagnetic wave absorber. The spray injection pressure at this time was 170 bar.

Comparative example  7.

The washed substrate is impregnated with the conductive coating liquid prepared in Comparative Example 3, wherein the substrate is immersed in 50% by weight of the conductive coating liquid relative to the total conductive coating liquid coated on the substrate so that only a part of the substrate is impregnated. The conductive coating solution is sprayed onto the surface of the impregnated substrate for 5 minutes with a spray and then dewatered at a speed of 1500 rpm. Thereafter, the substrate to which the coating liquid was applied was dried at 110 ° C. for 25 minutes to cure to prepare an electromagnetic wave absorber. The spray injection pressure at this time was 170 bar.

Comparative example  8.

Subsequently, the substrate was immersed in the coating solution prepared in Example 1 (impregnation method), squeezed, dried at 110 ° C. for 60 minutes, and cured to prepare an electromagnetic wave absorber.

Test Example  2.

end. Surface resistance: Measured by ASTM D257 method.

I. Coating adhesion measurement:

According to Test Method B of ASTM D3359, the dried coating film was scraped with a knife so as to cross each other at 6 by 2 cm intervals, and 25 cells were made. Evaluate in six steps according to. Here, six steps are shown below.

5B: no peeling of coating

4B: less than 5% of coating peeling

3B: 5%-15% peeled off

2B: coating film peeling 5% -15%

1B: 5% -15% peeled off

0B: coating film peeling 65% or more

All. Water absorption rate measurement: The absorbent material is tested for 24 hours in a thermo-hygrostat at 30 ° C and 80% in HH conditions, and then left at room temperature for 30 minutes to measure the weight before and after the test.

Table 2 below compares the physical properties of the electromagnetic wave absorbers prepared in Examples 3-4 and Comparative Examples 4-6.

Example 3 Example 4 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Surface resistance (/ sq) 2.0 X 10 ⁴ 1.5X10 ⁴ 1 X 10 ⁵ 1.5X10 ⁵ 5X10 ⁵ 4X10 ⁵ 1 X 10 ⁵ Coating film adhesion measurement 5B 5B 4B 2B 1B 1B - Water absorption rate (%) 4 5 7 7 10 15 35

Looking at Table 2, the electromagnetic wave absorber prepared in Example 3-4 is lower in surface resistance than the electromagnetic wave absorber prepared in Comparative Example 4-6, it is effective in the absorption of electromagnetic waves, and excellent adhesion of the coated coating film. In addition, the electromagnetic wave absorbing material prepared in Example 3-4 has a lower water absorption than the comparative examples, and this water absorption is maintained even after 24 months has elapsed, thus extending the life of the product.

In addition, it can be seen that Example 4, which uses the impregnation method and spraying method continuously, has a slightly lower surface resistance than Example 3.

In addition, as a result of 12 months of testing with the electromagnetic wave absorber of the present invention, it was found that the surface resistance value did not change, and this indicates that the electromagnetic wave absorber prepared by the conductive coating liquid of the present invention is permanently conductive. there was.

Claims (11)

100 parts by weight of a liquid containing 10-30% by weight of carbon black, 2-10% by weight of a urethane binder, 10-35% by weight of an aqueous flame retardant, and 50-60% by weight of a solvent mixed with alcohol and distilled water in a ratio of 2: 1. Conductive coating liquid comprising 0.05-0.2 parts by weight of dispersant, 0.05-0.2 parts by weight of antifoaming agent and 2.0-4.0 parts by weight of pH adjuster. delete The method of claim 1, The water-dispersible carbon black is a conductive coating liquid selected from the group consisting of ketjen black, oil furnace black, thermal black, channel black, acetylene black, carbon nanotubes. The method of claim 1, The conductive coating solution has a viscosity of 55-60 mPa · s and a surface resistance of (1.0-1.5) × 10 ⁴ μs / sq. 10-30% by weight of water-dispersed carbon black, 2-10% by weight of urethane binder, 10-35% by weight of aqueous flame retardant and 50-60% by weight of solvent mixed with alcohol and distilled water at a ratio of 2: 1 at 23-25 ° C A first step of preparing a conductive coating liquid by mixing 0.05-0.2 parts by weight of a dispersant, 0.05-0.2 parts by weight of an antifoaming agent and 2.0-4.0 parts by weight of a pH adjusting agent with respect to 100 parts by weight of the mixed solution; The conductive coating solution prepared in the first step of 100-200 bar A second step of spray coating the substrate under pressure and Method for producing an electromagnetic wave absorber coated with a conductive coating liquid comprising a third step of drying the substrate prepared in the second step at 110-125 ℃ 25-35 minutes. delete The method of claim 5, The method of claim 1 further comprising the step of impregnating the substrate with the conductive coating liquid between the first step and the second step. The method of claim 5, The substrate is a polyurethane foam material, electromagnetic wave absorber manufacturing method of the form selected from pyramidal, wedge, triangular prism, circular cone, V-shaped section and plate-like. The method of claim 7, wherein The conductive coating liquid used for the impregnation is an electromagnetic wave absorbing material manufacturing method of 40-50% by weight based on the total conductive coating liquid. 10. Electromagnetic wave absorber having a surface resistance of (1.5-2.5) X10 ⁴ dl / sq and a water absorption of 1-6%, prepared by the process according to any one of claims 5 and 7-9. The method of claim 10, The electromagnetic wave absorber is an electromagnetic wave absorber that absorbs electromagnetic waves at 10 MHz or less at 80 MHz and 50 dB or less at a range of 1 to 50 GHz.