JP2001123108A - Electromagnetic waves absorption paste and production method of electromagnetic waves-absorbing material using the paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide electromagnetic wave-absorbing paste that can be mechanically processed and can form structurally rigid, high-toughness, high-durability and incombustible electromagnetic wave-absorbing material and provide an simple and inexpensive method for producing complicated shapes, for example, of dome, parabola, pyramid, plate, angle, channel, cylinder, spiral and the like. SOLUTION: The objective electromagnetic wave-absorbing paste is used for forming electromagnetic wave-absorbing material and mainly comprises a formaldehyde resin precursor, an amide group-bearing polymer and an electromagnetic wave-absorbing filler. In this paste, the amount of the amide group- bearing polymer is 0.5-50 parts per 100 parts of the formaldehyde resin precursor in volume ratio and the total amount of the formaldehyde precursor and the amide group-bearing polymer is <=50 parts per 100 parts of the electromagnetic wave-absorbing material in volume ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an organic / inorganic composite material useful as an electromagnetic wave absorbing material and a method for producing the same.

[0002]

2. Description of the Related Art With the increasing interest in electronic application products, global electronic pollution is increasing more than ever. Of the methods available to overcome this contamination, shielding and absorbing electromagnetic waves seems to be one of the few promising methods in the future. Electromagnetic shielding shields the user from external electromagnetic interference, but impairs nearby by the reflection of electromagnetic waves. In view of this, electromagnetic wave absorption is the only method to be employed to prevent electromagnetic contamination.

In order to prevent the above-mentioned interference due to the reflection of electromagnetic waves, there is known an electromagnetic wave absorbing material prepared by dispersing ferrite or a mixture of ferrite and metal powder or ferrite and carbon powder in an organic polymer.
A commercially available UHF band electromagnetic wave absorbing material is produced by using a rubber material containing a magnetic powder or a resin material containing a magnetic powder such as ferrite and / or a conductive powder such as carbon. Rubber-ferrite absorbers have low weather resistance and soften under warm and humid conditions. Further, the rubber ferrite absorbent is not suitable as a partition wall of a building or a member having sufficient strength due to low rigidity.

Japanese Patent Application Publication No. 299971/93 discloses a resin composition for absorbing high-frequency electromagnetic waves, which is made of a thermoplastic resin and a fibrous alkaline earth metal titanate. It also discloses that it exhibits strength and has excellent absorption properties in the frequency range above 500 MHz.

The above patent applications disclose a number of thermoplastic resins including PPS (polyphenylene sulfide), PBT (polybutadiene terephthalate) and PA-66 (polyamide). Since these thermoplastic resins are all flammable, these absorbents are not preferable as wall materials for buildings.

Japanese Patent Application Publication No. 12904/96 discloses that
An electromagnetic wave absorbing paste composed of ferrite and a resol type phenol resin is disclosed. The technology of this patent application is
A method of treating an electronic component by dipping the electronic component into a paste containing ferrite and a phenolic resin is disclosed. The outermost ferrite / resin layer reduces and reduces electromagnetic interference by shielding and absorbing electromagnetic waves generated by the electronic device. However, this prior art does not disclose any method for forming an electromagnetic wave absorbing sheet.

Japanese Patent Application Publication No. 235417/86 discloses an electromagnetic wave absorbing material comprising a phenol formaldehyde oligomer, an isocyanate and a ferrite. Isocyanate is an essential component for achieving a predetermined mixing ratio that promotes generation of bubbles in the absorbent material. This material can be used to reduce the side lobe noise of parabolic antennas.
Since this material contains many air bubbles, its mechanical strength was weak and it could not be used as a wall material. Further, isocyanates have a strong pungent odor and are harmful to the human body.

[0008] A thin and flat electromagnetic wave absorbing material for the UHF band was developed by IEEETRANSACTI in December, 1994.
ONS ON BROADCASTING, 40th edition,
No. 4 is introduced. This multilayer type absorbent material is a wireless LA
It would be effective to use it on walls of ordinary homes and offices to protect the radio waves emitted from N and electronic devices. In this technique, a layer mainly composed of an epoxy resin containing carbonyl iron and ferrite has a thickness of 1.9 GHz, 2.45 GHz.
It is clarified that it absorbs 80% or more of the electromagnetic wave of z, 19 GHz. However, epoxy resins are very susceptible to fire, and this article does not disclose any useful manufacturing methods.

At present, a microwave band wireless communication system is used in many offices. These systems include industrial, scientific, and medical (ISM) 2.4 GHz
Includes band wireless LANs and 1.9 GHz band cordless phones. However, if the system is extensive, electromagnetic interference with other systems can occur. Therefore, in order for the wireless communication system to operate effectively, the indoor electromagnetic environment must be properly controlled. The selection of effective building materials has been shown to help control the electromagnetic environment. However, the problem with the prior art is that it does not disclose a material suitable for this or a method for effectively manufacturing a thinner and flatner electromagnetic wave absorber capable of effectively absorbing microwave band radio waves.

[0010]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an electromagnetic wave absorber which is machineable and structurally strong, has high rigidity, high durability, is nonflammable and therefore can be easily manufactured as a long and wide sheet. To provide materials. Further, another object of the present invention is to provide an effective manufacturing method for producing an absorbent material, and a dome-shaped, parabolic-shaped, pyramid-shaped, plate-shaped, angle-shaped, channel-shaped, cylindrical-shaped, spiral-shaped by using the same. It is an object of the present invention to provide a method for manufacturing a material having a complicated shape such as the above.

[0011]

SUMMARY OF THE INVENTION The present invention is an electromagnetic wave absorbing paste used to form an electromagnetic wave absorbing material, the paste comprising a formaldehyde resin precursor, a polymer having an amide group, and (B) a highly dielectric powder; (c) a low conductive metal powder; and (d) at least one of electromagnetic wave absorbing fillers of the low conductive carbon powder. A paste, wherein the polymer having an amide group is mixed at a volume ratio of 0.5 to 50 parts with respect to 100 parts of the formaldehyde resin precursor, and further has the formaldehyde resin precursor and the amide group. An electromagnetic wave absorbing paste, wherein the total amount of the polymer is mixed in a volume ratio of 50 parts or less with respect to 100 parts of the electromagnetic wave absorbing filler (claim 1), The electromagnetic wave absorbing paste according to claim 1, wherein the formaldehyde resin precursor is one of a phenol resin precursor, a melamine resin precursor, and a urea resin precursor. The electromagnetic wave absorbing paste according to claim 1, wherein the formaldehyde resin precursor is an alcohol-soluble formaldehyde resin precursor, and the polymer having an amide group is any one of polyamide and polyacrylamide. The electromagnetic wave absorbing paste according to claim 1, wherein the electrical resistivity of the electromagnetic wave absorbing filler is 10 ⁻⁷ Ωm or more. electromagnetic wave absorption pastes (claim 5), the electrical resistivity of the complex permeability ceramic powder is characterized in that it is 10 ³ [Omega] m or more Electromagnetic wave absorption paste according to Motomeko 1 (claim 6), the complex permeability ceramic powder electric resistivity of 10 ^6, characterized in that at Ωm or more claims 1 to wherein the electromagnetic wave absorbing pastes (claim 7 2. The electromagnetic wave absorbing paste according to claim 1, wherein the complex magnetically permeable ceramic powder is ferrite, and an electromagnetic wave absorbing material is manufactured using the electromagnetic wave absorbing paste defined in claim 1. (A) mixing the paste with a Banbury mixer, a pressure kneader or a roll mill at a shear rate of 50 s ^-1 ; and (b) extruding the paste obtained in the step (a). A method for producing an electromagnetic wave absorbing material comprising: a step of supplying the paste to a calender roll to form the paste into a desired molded article; and (c) a step of heating and curing the molded article at a high temperature. (Claim 9) and the electromagnetic wave absorbing material has any one of a plate shape, a dome shape, a parabolic shape, a pyramid shape, an angle shape, a channel shape, a cylindrical shape, and a spiral shape. It is an object of the present invention to provide a method for producing an electromagnetic wave absorbing material according to the present invention.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The components of the composition of the present invention and the processing method will be described below.

(1) Polymer Matrix Material First, in the present invention, several mixing ratios of raw materials that can be used as an electromagnetic wave absorbing material after mixing, molding, heat curing and laminating with a conductive metal layer are disclosed. . First of the present invention
As an example of the present invention, the present inventors paid great attention to the selection of a resin suitable as a main binder of an electromagnetically active filler.

Among many reaction-curable polymers, formaldehyde resin is excellent in heat stability, solvent resistance, abrasion resistance and fire resistance, and is inexpensive. As the formaldehyde resin, a phenol resin, a urea resin, and a melamine resin are known, and they are used alone or in combination to form a molding material. One of the key features of phenolic resins is that they can withstand working temperatures in the range of 120-170 ° C. without significant degradation over time. Furthermore, phenolic moldings are inherently excellent in fire resistance. Phenolic moldings are considered quasi-noncombustible materials because of their low fire spread and low smoke generation.
This is a priority feature to be considered when obtaining approval in the construction field. Examples of phenol formaldehyde resins include phenol, resorcinol, o-cresol or p-cresol, m-cresol, pt-butylphenol, p-octylphenol, p-nonylphenol, p-phenylphenol, mixed xylenol, cashew nut shell liquid and the like. And phenols of the following formulas; reaction products with formaldehydes such as gasias, formalin, paraformaldehyde, trioxane and hexamethylenetetramine. Generally, other formaldehyde resins besides urea formaldehyde and melamine formaldehyde can be used, but it is more preferable to use phenol formaldehyde resin.

The formaldehyde resin is preferably a solution of water or alcohol, preferably methanol, ethanol,
It is used in a form dissolved in alcohols such as propanol, butanol, methyl ethyl ketone, cyclohexanol, phenol, cresol, ethylene glycol and trimethylene glycol. If the resin is used in solution, the non-volatiles should not be less than 30% by weight of the resin solution.

The present invention also discloses a polymer having an amide group as a molding aid. Formaldehyde resin alone cannot be easily formed as a sheet because of its low molecular weight. Therefore, the high molecular weight polymer having an amide group plays an important role as a molding aid and also reacts with a formaldehyde resin. Examples of the molding aid include polymers having an acid amide bond such as polyamide and polyacrylamide, for example, N-methoxymethyl nylon, nylon 6, nylon 66, nylon 610, nylon 12, and the like. When this molding aid is used as a solution, it is preferable that polyamide is dissolved in alcohol, and polyacrylamide is dissolved in water. Such an alcohol-soluble polyamide may be an amide bond -CONH- in which at least a part of hydrogen is substituted by a methoxymethyl group or an amide bond -CON (R)-generated from a secondary amine. The polymer having an amide group is added in a volume ratio of up to 50 parts per 100 parts of formaldehyde resin, and preferably 0.5 to 20 parts by volume per 100 parts of formaldehyde resin. If the volume ratio is less than 0.5 part, the moldability will not be improved. On the other hand, when the amount exceeds 50 parts, the mechanical strength of the absorbing material becomes low, and it becomes easy to burn and becomes expensive.

Other small amounts of raw materials such as plasticizers, curing agents, accelerators and coupling agents may be added to the electromagnetic wave absorbing paste, but are not essential components of the electromagnetic wave absorbing paste disclosed herein. Typical examples of the plasticizer include glycerol, glycerol triacetate, phthalic anhydride, furfural, alkylphenol, zinc stearate, magnesium stearate, and rosin. Examples of curing agents and accelerators include hexamethylenetetramine, acetic acid, citric acid, sulfuric acid, hydrochloric acid, sodium hydroxide and the like. Examples of the coupling agent include γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, and the like.

(2) Electromagnetic Wave Absorbing Filler The electromagnetic wave absorbing material used in the present invention comprises at least a) a complex magnetically permeable ceramic powder, b) a high dielectric powder, c) a low conductive metal powder, and d) a low conductive carbon powder. One selected from the group. In particular, a) complex magnetically permeable ceramic powder is most preferred.

According to the first embodiment of the present invention, the complex magnetically permeable ceramic powder is an essential component of the electromagnetic wave absorbing paste. The complex magnetically permeable ceramic powder includes hematite (Fe ₂ O ₃ ), magnetite (Fe ₃ O ₄ ), and a general formula MO. It is a ferrite represented by Fe ₂ O ₃ . Here, M is Mn, Co, Ni, Cu, Zn, Ba, M
g, Cd, Ba, Sr and the like. In order for the absorbent material to exhibit excellent absorption performance, the electric resistance of the complex magnetically permeable ceramic powder is 10 ³ Ωm or more, more preferably 10 ⁶ Ωm.
That is all. Generally, the electrical resistance of Mn-Zn ferrite is about 2 × 10 ³ Ωm, while the electrical resistivity of Mg—Zn ferrite and Ni—Zn ferrite is 10 ⁶ Ω.
m higher.

The high dielectric powder includes particles, fibers, whisker-like MO. TiO ₂ type titanate, MO. Zr
O ₂ type zirconates include. Where M is Ba,
La, Sr, Pb, Zr, and K. It is silicon carbide, silicon nitride, and its shape is particles, fibers,
It has a whisker shape.

The low conductive metal powder includes particles, fiber-like supermalloy, permalloy, sendust, carbonyl iron and ferromagnetic alloy. Especially A
Iron alloys composed of one or more elements such as 1, V, Co, Mo, Cr, Ni, Si and C are preferred. However, the electric resistivity of the low conductive metal powder is preferably 10 ⁻⁷ Ωm or more, and the initial magnetic permeability is preferably 200 or more.

The carbon mixed with the resin is preferably low conductive carbon, carbon fiber or the like. The electric resistance of the carbon powder or carbon fiber is preferably 10 ⁻⁷ Ωm or more.

The above-mentioned electromagnetic wave absorbing fillers (a) to (d) may be used alone or as a mixture of two or more at a desired ratio.

(3) Manufacturing Method As a second example of the present invention, the inventor provides an inexpensive and effective manufacturing method for manufacturing an electromagnetic wave absorbing material. For example, the composition is premixed with an open kneader, a planetary mixer or a blender, and the inorganic component is mixed with the resin. This pre-mixing is usually simple and only serves as a partial mixing, which can be omitted in the next step if necessary as it can be carried out in the next step. The next step is high shear mixing on a twin roll mill, the most important step. The premixed paste or individual ingredients are fed to rolls for high speed shear mixing. For high-speed shear mixing, the speed ratio between the front and rear rolls is preferably adjusted to 5: 4. During high speed shear mixing, as the solvent in the paste evaporates, the paste becomes entangled around the two rollers, and after a few minutes of mixing, the paste becomes entangled around the faster roller. In low shear mixing, the speeds of the front and rear rollers are equal. During this time, the paste can be peeled off from the roller, so this paste is collected from the roll,
Roll it several times until it becomes a sheet.

In calendaring, the speeds of the front roll and the rear roll are both reduced to keep the speeds equal. Calendering can be divided into two parts: "fining" and "stretching". The thickness of the layer is reduced by fining to produce a uniform sheet with a fine surface. In this step, the sheet is folded several times until it is a fine and uniform sheet and rolled again. During "stretching", the sheet is fed to the rollers several times without folding. The sheet is then stretched to remove any defects contained within the sheet. After the roll milling is completed, the sheet is set at 135 ° C. to 250 ° C. as shown in Route 1 of FIG.
Cured directly in an oven for several hours in a temperature range of ° C.

The high-speed shearing mixing paste may be supplied to an extruder without performing the above-described calendering, and formed into a channel shape, an angle shape, a pipe shape, or the like. The molded body is cured by heating in the same manner as described above. Alternatively, the sheet is further densified by pressing between the impression cylinders of a hydraulic laminating press at the desired pressure and temperature of 40 ° C. to 180 ° C. to remove lamination defects (see route 2 in FIG. 1). Further, the obtained sheet can be formed into a complicated shape such as a dome shape, a parabola shape, a pyramid shape, or a spiral shape after calendering. Then, the obtained sheet or molded body is cured by heating in the same manner as described above.

Another manufacturing method includes a step of mixing with a Banbury mixer or a pressure kneader, which will be described below. For example, the composition is fed to a Banbury mixer or a pressure kneader, and the
Mix with static load of a or more. Mixing may use a pair of rotors rotating in opposite directions. The high speed rotor is rotated clockwise at a speed 1.5 times faster than the low speed rotor. The mixing time can be reduced by increasing the rotor speed, and the rotor speed is preferably kept above 10 rpm. The composition is mixed until the highest net torque level is at least 1.5 times the lowest net torque, at which point the paste is removed from the mixer. The paste can then be fed to an extruder, preferably a single or twin screw extruder, and extruded into a number of desired shapes, such as sheets or channels, pipes, and the like. Preferably, the screw speed is adjusted to give the desired feel and quality to the extruded material, and the extruder chamber temperature is controlled to be above room temperature. After the extrusion is completed, the extruded material is directly cured by heating in an oven at a temperature of 135 ° C. to 250 ° C. for several hours as shown by Route 1 in FIG. Alternatively, if the extruded material is a sheet, it is further densified by pressing between the impression cylinders of a hydraulic laminating press at the desired pressure and a temperature of 40 ° C. to 180 ° C. to remove lamination defects (route 2 in FIG. 2). reference). Further, after extrusion, the sheet can be in a desired shape. Alternatively, the paste can be subjected to high-speed shear mixing with a Banbury mixer or a pressure kneader, and then calendered with a twin roll mill.

The load torque during mixing can be measured by the method described below. The motor of the press kneader is connected via a load sensor to a computer and to an analog / digital transducer which measures the power required by a pair of rotors rotating in opposite directions at a constant mixing speed. Torque can be calculated using the following equation: T = (P.9550) / n where T is torque in units of N.P. m and P are power and unit k
W and n are rotor rotation speeds and are in units of rpm. Mixing torque and paste temperature can be monitored continuously during operation.

As described above, in the present invention, the inventor
Special mixing methods and molding techniques required to produce components with more fillers were employed. The content of the non-volatile organic substance in the electromagnetic wave absorbing material composition is desirably kept to a minimum level of 30% by volume of the electromagnetic wave absorbing filler. The reason for this is to improve the electromagnetic characteristics of the material. The magnetic permeability, the dielectric constant, the electric conductivity or the electric resistance depends on the content of the electromagnetic wave absorbing filler in the resin.

When these fillers are increased to a necessary amount sufficient to keep the particles in contact with each other, the electromagnetic properties of the material are similar to solids consisting solely of electromagnetic wave absorbing fillers. For example, if the ferrite content of the ferrite resin composite material is very large, the ferrite resin composite material is almost the same as a fired ferrite tile in terms of electromagnetic wave absorption characteristics. However, when the content of the electromagnetic wave absorbing filler is large, the production becomes difficult and the mechanical strength is reduced, so that the content has an upper limit. Further, problems arise with the prior art, which does not disclose an accurate or specific manufacturing method to achieve this purpose.

Various methods are known for producing thermosetting plastics. Normally, these plastics contain very high amounts of resin, exceeding 50% by volume of the total volume of the final product. With such a high resin volume, hand lay-up, spray-up,
Pressure bag, autoclave molding, cold pressing, pressure molding, resin injection, pultrusion,
Molding by a method such as filament winding and injection molding is facilitated.

The extrusion molding and the calendering ring employed in the present invention are very widely used in the processing of thermoplastic resins because thermoplastic resins usually have appropriate fluidity and thermal properties. The inventor has appropriately utilized these features in processing a thermosetting formaldehyde resin by introducing a thermoplastic resin, that is, a polymer having an amide group, into the thermosetting formaldehyde resin. Further, another important requirement of the present invention is that the present invention discloses a predetermined shear rate applied to the paste during high shear mixing. We have found that the minimum shear rate is about 50 s- ¹ . In other words,
This level of shear rate provides the minimum energy required for the chemical reaction between the formaldehyde resin and the selected electromagnetic wave absorbing filler. This energy can only be provided by Banbury mixing, pressure kneaders and roll mills, as disclosed in the present invention.

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. In this example, “part” means “part in volume ratio”. The volume of a liquid type substance was calculated by dividing the mass of the liquid by the density. The density of the liquid type substance was measured according to JIS K5400-4.6.2. The volume of the solid type material was calculated by dividing the mass of the solid by the density. The density is calculated from the measured data of the specific gravity, and the specific gravity is calculated according to JIS K7112-
Measured according to 6.2.4.

[0034]

EXAMPLES (Example 1) Preparation of electromagnetic wave absorbing material 100 parts of Ni-Zn ferrite, phenol resin 31.
5 parts, solvent 31.5 parts, N-methoxymethyl 6-nylon (trade name, resin, manufactured by Teikoku Chemical Industry Co., Ltd.)
4.5 parts and 5.5 parts of glycerol were mixed with an open kneader to form a paste. Thereafter, this paste was supplied to a twin-roll mill to perform high-speed shear mixing. In high-speed shear mixing, the front and rear roll speeds were 250 mm / s and 200 mm / s, respectively, and the nip spacing between the rollers was 3 mm. After a few minutes of high-speed shear mixing, the paste was gradually converted into a sheet of rubber consistency in low-speed shear mixing to have a green strength sufficient for subsequent processing. The sheet was then peeled off, folded and fed several times through the desired nip interval until the sheet became a fine and uniform sheet, and roll forming was repeated. After the calendering was completed, the sheet was heated and cured in an oven at 200 ° C. for 18 hours to obtain an electromagnetic wave absorbing material. Note that the procedure described in this example is a summary including quantitative data, and the reader should follow the manufacturing method and the flowchart in FIG. 1 (route 1) for accurate details.

Note: The phenolic resin used in this example is Shaunol BRS330, a precursor of an alcohol-soluble phenolic resin manufactured by Showa Polymer Co., Ltd.
Shaunol BRS330 is available in liquid form as a solution of methanol and free phenol. The amount of the solvent in the mixture ratio is calculated by subtracting the amount of the non-volatile substance from the total amount of Shaunol BRS330. The amount of resin in the mixing ratio is Shaunol BRS330
Equal to the non-volatile content in

Shear rate Shear rate (γ) applied to the paste during mixing
Was calculated using the following known formula.

Γmax = [6U ₀ / h ₀ ]. [0.22
6+ (U ₁ −U ₂ ) / 6U ₀ ] where U ₁ and U ₂ are two roll speeds, U ₀ is an average speed, and h ₀ is a nip interval between rolls. Thus, the shear rate applied to the mixing paste is 118 s.
^-1 .

(Example 2) Preparation of electromagnetic wave absorbing material 78 parts of Ni-Zn ferrite, barium titanate 22
Parts, 30 parts of a water-soluble urea resin to which a phenol resin precursor (non-volatile substance content) was added, 33 parts of water as a solvent for the phenol resin precursor, and 4 parts of polyacrylamide were subjected to high speed shear mixing with a press kneader to form a paste. .
Thereafter, the paste was processed into an electromagnetic wave absorbing material as described in Example 1.

(Example 3) Preparation of electromagnetic wave absorbing material 100 parts of Mg-Zn ferrite, phenol resin 31.
5 parts, solvent 31.5 parts, N-methoxymethyl 6-nylon (trade name, resin, manufactured by Teikoku Chemical Industry Co., Ltd.)
4.5 parts were subjected to high-speed shear mixing with a press kneader to form a paste. The static load was 0.5 Mpa and the rotor speed was 64 rpm. The rotor diameter is 148mm,
The average spacing between the rotor and the kneader wall was 2 mm. After mixing the composition for 220 minutes, the highest net torque level reached 1.6 times the lowest net torque (the relationship between net torque and mixing time for this run is plotted and shown in FIG. 3). Thereafter, the paste was removed from the press kneader. Next, this paste was supplied to a single screw extruder and extruded into a sheet having a thickness of 5 mm. After the extrusion is completed, the sheet is heated to 200 ° C.
For 18 hours to obtain an electromagnetic wave absorbing material cured in an oven. Note that the procedure described in this example is an outline including quantitative data, and the reader wants the reader to follow the processing method and the flowchart in FIG. 2 (route 1) for accurate details.

Note: The phenolic resin used in this example is a brand name of Shaunol BRS330, an alcohol-soluble phenolic resin precursor manufactured by Showa Polymer Co., Ltd. Shaunol BRS330 is available in liquid form as a solution of methanol and free phenol. And the amount of solvent in the mixing ratio is Shaunol BRS
It is calculated by subtracting the amount of nonvolatile matter from the total amount of 330. The amount of resin in the mixing ratio is Shaunol BRS
Equivalent to a non-volatile content of 330.

Shear rate Shear rate (γ) applied to the paste during mixing
Was calculated using the following known formula.

Γmax = (πDR) / t where D is the diameter of the rotor, R is the rotational speed of the rotor, and t is the distance between the rotor and the wall of the kneader. And the shear rate applied to the paste during mixing is 248 s
^-1 .

Comparative Example 1 Preparation of Electromagnetic Wave Absorber 60 parts of Ni-Zn ferrite and 100 parts of epoxy-modified urethane rubber were mixed in an open kneader to form a paste. Thereafter, the paste was supplied to a twin-roll mill and subjected to high-speed shear mixing. For high speed shear mixing, the forward and backward roller speeds are 250 mm / s and 200 mm, respectively.
mm / s, the nip spacing between the rollers was 3 mm.
After a few minutes of high shear mixing, the paste was gradually turned into a sheet in low shear mixing. The sheet was then peeled through the desired nip interval, folded and rolled several times until a fine, uniform sheet was obtained. After the calendering was completed, the sheet was hot-pressed at 60 ° C. between the impression cylinders of a hydraulic laminating press to obtain an electromagnetic wave absorbing material.

Shear rate Shear rate (γ) given to the paste during mixing
Was calculated using the following known formula.

Γmax = [6U ₀ / h ₀ ]. [0.22
6+ (U ₁ −U ₂ ) / 6U ₀ ] where U ₁ and U ₂ are the speeds of the two rolls, U ₀ is the average speed, and h ₀ is the nip interval between the rolls. in this case,
The shear rate applied to the paste during mixing was 118
s- ¹ .

Comparative Example 2 The experiment of Example 1 was repeated without using N-methoxymethyl 6 nylon in the composition.
This composition was mixed with an open kneader to form a paste. Thereafter, this paste was supplied to a twin-roll mill to perform high-speed shear mixing. In high-speed shear mixing, the front and rear roller speeds are each 250 mm / s.
And 200 mm / s, and the nip interval between the rollers was 3 mm. The paste hardness did not increase after high shear mixing and also low shear mixing. Therefore, the paste did not become a sheet. The desired electromagnetic wave absorbing material could not be obtained.

Shear Rate The shear rate (γ) applied to the paste during mixing was calculated using the following known equation:

Γmax = [6U ₀ / h ₀ ]. [0.22
6+ (U ₁ −U ₂ ) / 6U ₀ ] where U ₁ and U ₂ are the speeds of the two rolls, U ₀ is the average speed, and h ₀ is the nip interval between the rolls. in this case,
The shear rate applied to the paste during mixing is 118 s ^-1.
Met.

Comparative Example 3 The composition used in Example 1 was mixed with an open kneader to form a paste. Thereafter, the paste was fed into a pair of rollers of a manual noodle machine having the same rotation ratio of the rollers. Maximum speed is 80mm / s
The nip interval between the rollers was 3 mm. After high and low shear mixing, the hardness of the paste did not increase. Therefore, the paste did not become a sheet. The desired electromagnetic wave absorbing material could not be obtained.

Shear Rate The shear rate (γ) applied to the paste during mixing was calculated using the following known equation:

Γmax = [6U ₀ / h ₀ ]. [0.22
6+ (U ₁ −U ₂ ) / 6U ₀ ] where U ₁ and U ₂ are the speeds of the two rolls, U ₀ is the average speed, and h ₀ is the nip interval between the rollers. At this time,
The shear rate applied to the paste during mixing was 36 s- ¹ .

The electromagnetic wave absorbing materials of Examples 1 to 3 and Comparative Example 1 were subjected to an electromagnetic wave absorbing effect test, a bending strength test, and a flammability test as described below.

Electromagnetic Wave Absorbing Effect Measurement Method Using an HP 8722D network analyzer,
Μ and ε were evaluated by measuring S parameters in a frequency range of 50 MHz to 4 GHz. Measurement sample is 2
Place on the 0D coaxial sample holder and set the material constants μ and ε
And were measured. The reflection loss at four different frequencies commonly used in mobile phones and the electromagnetic wave reflectance at each reflection loss for a predetermined thickness of the sample were calculated using material constants. The results are shown in Table 1.

[0054]

[Table 1]

Method of Measuring Bending Strength of Electromagnetic Wave Absorbing Material The electromagnetic wave absorbing sheet was cut into sheet pieces having a width of 20 mm and a length of 120 mm. This sample was subjected to a three-point bending test using the plate thickness as the beam depth. The test is JIS
K 6911 (test method for thermosetting plastics). Table 2 shows the results of Examples 1, 2, and 3 and Comparative Example 1.

[0056]

[Table 2]

Method for Measuring Flammability of Electromagnetic Wave Absorbing Material The flammability of the electromagnetic wave absorbing material was measured according to ASTM D1692-68.
Was measured according to Dimensions 152 × 50 × 12.5m
m samples were placed horizontally on top of a standard wire gauge. A 50 mm wide propane flame was applied to one end of the sample for 60 seconds, and the burning distance, burning speed, and burning time were measured. If the flame tip did not reach 127 mm to the mark along the sample, it was classified as "self-extinguishing" in this test. Otherwise, it was classified as "flammable" in this test. Table 3
Shows the results of Examples 1, 2, and 3 and Comparative Example 1.

[0058]

[Table 3]

As is clear from the results of Examples 1 to 3,
The electromagnetic wave absorbing material of the present invention has a low electromagnetic wave reflectance and a wide effective absorption band. As is clear from the results of Comparative Example 1, Comparative Example 1 shows that the effective absorption band is narrow. The electromagnetic wave absorbing material described in Comparative Example 1 is flammable and does not have sufficient rigidity to be used as a wall material or the like. As is evident from the results of Comparative Example 2, N-methoxymethyl 6-nylon, a polymer having an amide group, is an essential component in the mixing ratio for processing the paste into a sheet.

Comparative Example 3 shows that the composition used in Example 1 was processed with a manual noodle machine, and it was impossible to process the paste into a sheet. As is evident from Comparative Example 3, there is a minimum energy level that should be substantially applied to the paste by high speed shear mixing to form a sheet as described in Example 2.

The effective absorption band can be freely moved to a desired frequency range by adjusting the content and thickness of the electromagnetic wave absorbing filler. In this example, 50M
An electromagnetic wave absorption effect in a frequency range of Hz to 4 GHz was observed. However, this extends its effective frequency range to 50 MHz.
It is not limited to z to 4 GHz. This material can be adjusted to 4 GHz by adjusting the mixing ratio within the range of the present invention.
Obviously, it can be modified to absorb electromagnetic waves in the higher frequency range.

According to the test results, the radio wave absorber of the present invention shows that the radio wave absorber of the wireless LAN system, the UHF level radio wave, the radio wave generated from the mobile telephone, and the radio wave absorption material sufficient for use as the radio wave absorbing material for the wall of the anechoic chamber Has absorption properties.
Furthermore, it can be used as a fireproof electromagnetic wave absorption case for any combustible absorber. This material is essential to prevent radar crashes in automotive collision warning systems. In particular, since it has a high degree of freedom in forming a desired shape, it can be used as a shell of a military stealth aircraft that absorbs radar waves in order to hinder enemy search operations.

It will be understood by those skilled in the art that the above embodiments can be modified without departing from the broad inventive concept thereof. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed, but to encompass modifications within the spirit and scope of the invention as defined by the appended claims. .

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method of manufacturing an electromagnetic wave absorbing material according to one embodiment of the present invention.

FIG. 2 is a flowchart illustrating a method of manufacturing an electromagnetic wave absorbing material according to another embodiment of the present invention.

FIG. 3 is a graph showing the relationship between net torque (N · m) and mixing time by plotting.

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[Procedure amendment]

[Submission date] January 30, 2001 (2001.1.3)
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

[0011]

SUMMARY OF THE INVENTION The present invention is an electromagnetic wave absorbing paste used to form an electromagnetic wave absorbing material, the paste comprising a formaldehyde resin precursor, a polymer having an amide group, and (B) a highly dielectric powder; (c) a low conductive metal powder; and (d) at least one of electromagnetic wave absorbing fillers of the low conductive carbon powder. A paste, wherein the polymer having an amide group is formed in a volume ratio of the formaldehyde resin precursor 10
0 to 50 parts by weight, and the total amount of the formaldehyde resin precursor and the polymer having an amide group is the volume ratio of the electromagnetic wave absorbing filler 100
The electromagnetic wave absorbing paste (Claim 1), wherein the formaldehyde resin precursor is a phenol resin precursor, a melamine resin precursor, and a urea resin precursor The electromagnetic wave absorbing paste according to claim 1, wherein the formaldehyde resin precursor is an alcohol-soluble formaldehyde resin precursor. The electromagnetic wave absorbing paste according to claim 1, wherein the polymer having an amide group is any of polyamide and polyacrylamide. 4. The electric resistivity of the electromagnetic wave absorbing filler is 10 ⁻⁷ Ω
2. The electromagnetic wave absorbing paste according to claim 1, wherein the electric resistivity of the complex magnetically permeable ceramic powder is 10 ³ Ωm or more. The electromagnetic wave absorbing paste according to claim 6, wherein the complex magnetically permeable ceramic powder has an electric resistivity of 1
0 ⁶ wave absorption paste according to claim 1, characterized in that at Ωm or more (claim 7), the electromagnetic wave absorption paste according to claim 1, wherein the complex permeability ceramic powder characterized in that it is a ferrite (Claim 8), Claim 1
(A) mixing the paste at a shear rate of 50 s ^-1 or more by a Banbury mixer, a pressure kneader or a roll mill.
Process and that; (c) heating the molded article at high temperatures; (b) the paste obtained in step (a) above was supplied to an extruder or calender roll, process and of forming the paste into a desired shaped article A method of manufacturing an electromagnetic wave absorbing material comprising a step of curing and wherein the electromagnetic wave absorbing material has a plate shape, a dome shape, a parabolic shape,
The method for manufacturing an electromagnetic wave absorbing material according to claim 9, wherein the shape is any one of a pyramid shape, an angle shape, a channel shape, a cylindrical shape, and a spiral shape.
It is to provide.

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Claims (10)

[Claims] 1. An electromagnetic wave absorbing paste used for forming an electromagnetic wave absorbing material, the paste comprising a formaldehyde resin precursor, a polymer having an amide group, and (a) a complex magnetically permeable ceramic powder; And (c) a low-conductivity metal powder; and (d) a paste mainly containing at least one of electromagnetic-wave-absorbing fillers of the low-conductivity carbon powder, wherein an amide group is contained. The polymer having a volume ratio of 0.5 to 50 with respect to 100 parts of the formaldehyde resin precursor.
Parts, and the total amount of the formaldehyde resin precursor and the polymer having an amide group is 100 parts by mass of the electromagnetic wave absorbing filler in a volume ratio, and is mixed at a ratio of 50 parts or less. Electromagnetic wave absorbing paste. 2. The electromagnetic wave absorbing paste according to claim 1, wherein the formaldehyde resin precursor is one of a phenol resin precursor, a melamine resin precursor, and a urea resin precursor. 3. The electromagnetic wave absorbing paste according to claim 1, wherein the formaldehyde resin precursor is an alcohol-soluble formaldehyde resin precursor. 4. The electromagnetic wave absorbing paste according to claim 1, wherein the polymer having an amide group is one of polyamide and polyacrylamide. 5. An electromagnetic wave absorbing filler having an electric resistivity of 1
0 ^-7 wave absorption paste according to claim 1, characterized in that at Ωm or more. 6. An electric resistivity of the complex magnetically permeable ceramic powder is not less than 10 ³ Ωm.
The electromagnetic wave absorbing paste according to 1. 7. The complex magnetically permeable ceramic powder having an electrical resistivity of 10 ⁶ Ωm or more.
The electromagnetic wave absorbing paste according to 1. 8. The electromagnetic wave absorbing paste according to claim 1, wherein the complex magnetically permeable ceramic powder is ferrite. 9. A method for producing an electromagnetic wave absorbing material using the electromagnetic wave absorbing paste defined in claim 1, wherein: (a) the paste is sheared at a shear rate of 50 s ⁻¹ using a Banbury mixer, a pressure kneader or a roll mill. (B) supplying the paste obtained in the above step (a) to an extruder or a calender roll to form the paste into a desired molded product; and (c) heating the molded product to a high temperature. And a step of heating and curing at a temperature. 10. The electromagnetic wave absorbing material according to claim 9, wherein the electromagnetic wave absorbing material has one of a plate shape, a dome shape, a parabola shape, a pyramid shape, an angle shape, a channel shape, a cylinder shape, and a spiral shape. Method for producing an electromagnetic wave absorbing material.