JP7187136B2 - sheet - Google Patents

Description

The present invention relates to seats.

A sheet formed from a metal powder and a resin composition is used, for example, as an industrial product such as an inductor, an electromagnetic wave shield, or a bond magnet, or as a raw material thereof. (See Patent Documents 1 to 3 below.)

JP-A-2004-31786 JP-A-8-273916 JP-A-1-261897

When the sheet is used in an electronic device, it may be required that the sheet shield electromagnetic waves generated inside and outside the electronic device.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sheet having an excellent shielding effect against electromagnetic waves.

A sheet according to one aspect of the present invention is a sheet comprising a first powder containing iron, a second powder containing copper, and a binder, wherein the mass of the first powder contained in the sheet is expressed as _M1 . and the mass of the second powder contained in the sheet is expressed as _M2 , and 100× _M2 /( _M1 + _M2 ) is 0.1 or more and 50 or less.

In the sheet according to one aspect of the present invention, the binder may contain a resin composition.

In the sheet according to one aspect of the present invention, the binder may contain a thermosetting resin.

In the sheet according to one aspect of the present invention, the binder may contain an epoxy resin.

In the sheet according to one aspect of the present invention, the binder may contain a thermoplastic resin.

In the sheet according to one aspect of the present invention, the binder may contain an acrylic resin.

In the sheet according to one aspect of the present invention, the acrylic resin may have a weight average molecular weight of 500,000 or more and 1,500,000 or less.

In the sheet according to one aspect of the present invention, the acrylic resin may have a glycidyl group.

In the sheet according to one aspect of the present invention, the binder may contain a phenolic resin.

In the sheet according to one aspect of the present invention, the binder may contain a curing agent and a curing accelerator.

In the sheet according to one aspect of the present invention, the first powder may contain at least one of elemental iron and an iron-based alloy.

In the sheet according to one aspect of the present invention, the second powder may contain at least one of elemental copper and a copper-based alloy.

ADVANTAGE OF THE INVENTION According to this invention, the sheet|seat excellent in the shielding effect of electromagnetic waves is provided.

Preferred embodiments of the present invention are described below. However, the present invention is by no means limited to the following embodiments.

The sheet according to this embodiment includes a first powder containing iron, a second powder containing copper, and a binder. The mass of the first powder contained in the sheet is represented as _M1 mass %. The mass of the second powder contained in the sheet is expressed as _M2 mass %. 100×M ₂ /(M ₁ +M ₂ ) is 0.1 or more and 50 or less. The first powder containing iron may be a powder containing elemental iron, and may not necessarily be a powder containing elemental iron or an iron-based alloy. The second powder containing copper may be a powder containing elemental copper, and may not necessarily be a powder containing elemental copper or a copper-based alloy.

As will be described later, the sheet is obtained by forming a sheet-like compact from a paste containing a binder, first powder, second powder and an organic solvent, and removing the organic solvent from the compact. As the organic solvent is removed, the binder adheres to the surfaces of individual particles that constitute the first powder and the second powder. The binder binds together individual particles that constitute the first powder and the second powder. As a result, a sheet is formed that has sufficient mechanical strength to maintain the desired shape. The present inventors have surprisingly found that when 100×C ₂ /(C ₁ +C ₂ ) is 0.1 or more and 50 or less, the electromagnetic wave shielding effect increases compared to conventional sheets. Found it. The reason why the sheet according to this embodiment is excellent in shielding effect against electromagnetic waves is not clear. Moreover, the sheet has the characteristics of the first powder and the characteristics of the second powder by individually including the first powder and the second powder. For example, iron powder (iron simple substance) has excellent magnetic properties. Copper powder (copper simple substance) has a high thermal conductivity. By including both the iron powder and the copper powder, it is possible to obtain a sheet having excellent magnetic properties and high thermal conductivity.

100×M ₂ /(M ₁ +M ₂ ) is 1.7 or more and 50 or less, 1.7 or more and 17 or less, 1.7 or more and 10 or less, 1.7 or more and 5 or less, 5 or more and 50 or less, or 5 or more and 10 It may be below. When 100×M ₂ /(M ₁ +M ₂ ) is within the above range, the electromagnetic wave shielding effect tends to increase. If the content of the first powder in the sheet is expressed as C ₁ % by mass and the content of the second powder in the sheet is expressed as C ₂ % by mass, then 100×M ₂ /(M ₁ +M ₂ ) is 100 It may be equivalent to ×C ₂ /(C ₁ +C ₂ ).

The first powder may be at least one powder selected from the group consisting of elemental iron, iron-based alloys, and iron compounds. The iron-based alloy may contain at least one selected from the group consisting of solid solutions, eutectics and intermetallic compounds. The iron compound may be an oxide such as ferrite. The first powder may contain elements other than the iron element. The first powder may contain, for example, oxygen, boron, or silicon. The first powder may be magnetic powder. The surface of the first powder may be covered with an insulating coating film (for example, resin composition).

The first powder may contain at least one of elemental iron and an iron-based alloy. Iron-based alloys include, for example, Fe—Si alloys, Sendust (Fe—Si—Al alloys), permalloys (Fe—Ni alloys, Fe—Cu—Ni alloys, etc.), permendur (Fe—Co alloys, etc.). alloy), stainless steel (Fe-Cr alloy, Fe-Ni-Cr alloy, etc.), soft magnetic alloys such as electromagnetic stainless steel (Fe-Cr-Si alloy), and Nd-Fe-B alloy, At least one selected from the group consisting of ferromagnetic alloys such as Sm--Fe--N alloys may be used. When the sheet contains at least one of an iron element and an iron-based alloy as the first powder, the electromagnetic wave shielding effect tends to increase.

The second powder may be at least one powder selected from the group consisting of simple copper, copper-based alloys and copper compounds. The copper-based alloy may contain at least one selected from the group consisting of solid solution, eutectic and intermetallic compounds. The copper compound may be, for example, copper oxide or the like. The second powder may contain an element other than the copper element. The second powder may contain oxygen, boron, or silicon, for example. The second powder may be magnetic powder. The surface of the second powder may be covered with an insulating coating film (for example, resin composition).

The second powder may contain at least one of elemental copper and a copper-based alloy. The copper-based alloy may be, for example, at least one selected from the group consisting of Cu--Sn-based alloys, Cu--Sn--P-based alloys, Cu--Ni-based alloys, and Cu--Be-based alloys. When the sheet contains at least one of copper and copper-based alloy as the second powder, the shielding effect against electromagnetic waves tends to increase.

The shape of each particle that constitutes each of the first powder and the second powder is not particularly limited. Individual particles may be, for example, spherical, flattened, or acicular. The average particle size (d50) of each of the first powder and the second powder may be, for example, preferably 20 μm or more and 300 μm or less, more preferably 40 μm or more and 250 μm or less. The sheet may contain multiple types of powders with different average particle sizes. Another powder with a small average particle size is filled in the gaps formed between the powders with a large average particle size, thereby increasing the space factor of the first powder and the second powder in the sheet. The particle size distribution of each of the first powder and the second powder is calculated, for example, based on weight measurement by sieving or analysis using a measuring instrument such as a laser diffraction/scattering device.

The binder may contain a resin composition. The binder may consist only of the resin composition.

The resin composition may contain a thermosetting resin. The resin composition may contain a thermoplastic resin. The resin composition may contain a curing agent and a curing accelerator. The resin composition may contain additives. Among the components contained in the sheet, the resin composition includes a thermosetting resin, a thermoplastic resin, a curing agent, a curing accelerator, and additives, and is composed of a solvent, a first powder, and a second powder. It may be the remaining components (non-volatile components). The thermosetting resin may be, for example, at least one selected from the group consisting of epoxy resins, phenolic resins, and polyamideimide resins. When the resin composition contains both an epoxy resin and a phenolic resin, the phenolic resin may function as a curing agent for the epoxy resin. The thermoplastic resin may be, for example, at least one selected from the group consisting of acrylic resin, polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate. The resin composition may contain epoxy resins and acrylic resins. The resin contained in the sheet may be only epoxy resin and acrylic resin. When the sheet contains an epoxy resin and an acrylic resin, the mass of the epoxy resin contained in the sheet is not limited. It may be parts by mass. When the sheet contains an epoxy resin and an acrylic resin, the mass of the acrylic resin contained in the sheet is not limited, but is, for example, 10 to 70 parts per 100 parts by mass of the total mass of the epoxy resin and the acrylic resin contained in the sheet. It may be parts by mass. The additive is the remaining component of the resin composition excluding the resin, the curing agent and the curing accelerator. Additives are, for example, coupling agents or flame retardants.

In the case of a sheet containing no acrylic resin, the first powder and the second powder are difficult to disperse uniformly, the sheet becomes brittle at locations where the first powder or the second powder is unevenly distributed, and the sheet has sufficient flexibility. hard. As a result, the sheets are susceptible to breakage during processing and handling of the sheets, such as forming, cutting, stacking, moving and conveying. In particular, when the total content of the first powder and the second powder in the sheet is large, or when the specific gravity of each of the first powder and the second powder or the difference in specific gravity between the first powder and the second powder is large, the above causes The flexibility of the sheet is likely to be impaired due to the On the other hand, in the case of a sheet containing an acrylic resin having a higher molecular weight and a higher viscosity than an epoxy resin, the movement of the first powder and the second powder due to factors such as specific gravity is easily suppressed by the high viscosity of the acrylic resin. As a result, uneven distribution of the first powder and the second powder within the sheet is easily suppressed, and the first powder and the second powder are easily dispersed uniformly within the sheet. In other words, the composition of the sheet tends to be uniform. Even if the total content of the first powder and the second powder is large, or the specific gravity of each of the first powder and the second powder is large, the above mechanism allows the first powder and the second powder to be unevenly distributed within the sheet. is suppressed, and the first powder and the second powder tend to disperse uniformly within the sheet. Also, the viscosity of the resin composition containing the acrylic resin itself tends to directly contribute to the flexibility of the sheet.

The sheet may contain an uncured resin composition, a first powder, and a second powder. The sheet may contain a semi-cured resin composition, a first powder, and a second powder. The sheet may include a cured product of the resin composition, and a first powder and a second powder bound together by the cured product. By heat-treating the sheet, the resin composition (binder) hardens and binds the first powder and the second powder more firmly.

When the mass of the resin composition contained in the sheet is expressed as M _B , (M ₁ +M ₂ )/(M ₁ +M ₂ +M _B ) is, for example, 0.900 or more and less than 1.00, 0.900 or more It may be 0.998 or less, 0.900 or more and 0.996 or less, 0.950 or more and less than 1.00, 0.950 or more and 0.998 or less, or 0.950 or more and 0.996 or less. According to this embodiment, even if (M ₁ +M ₂ )/(M ₁ +M ₂ +M _B ) is 0.95 or more, the sheet can have sufficient flexibility and mechanical strength. That is, according to the present embodiment, the sheet can have sufficient flexibility and mechanical strength even when the ratio of the first powder and the second powder in the sheet is high. (M ₁ +M ₂ )/(M ₁ +M ₂ +M _B )·100 can be said to be the total space factor of the first powder and the second powder in the sheet. That is, according to the present embodiment, even when the total space factor of the first powder and the second powder in the sheet is 95% or more, the sheet has sufficient flexibility and mechanical strength. can be done.

The epoxy resin may be, for example, a resin having two or more epoxy groups in one molecule. Epoxy resins include, for example, biphenyl-type epoxy resins, stilbene-type epoxy resins, diphenylmethane-type epoxy resins, sulfur atom-containing epoxy resins, novolak-type epoxy resins, dicyclopentadiene-type epoxy resins, salicylaldehyde-type epoxy resins, naphthols and phenols. Copolymerized epoxy resins, epoxidized aralkyl-type phenolic resins, bisphenol-type epoxy resins, glycidyl ether-type epoxy resins of alcohols, glycidyl ether-type epoxy resins of para-xylylene and/or meta-xylylene-modified phenolic resins, terpene-modified phenolic resins glycidyl ether type epoxy resin, cyclopentadiene type epoxy resin, glycidyl ether type epoxy resin of polycyclic aromatic ring-modified phenol resin, glycidyl ether type epoxy resin of naphthalene ring-containing phenol resin, glycidyl ester type epoxy resin, glycidyl type or methyl glycidyl type epoxy resins, alicyclic type epoxy resins, halogenated phenol novolac type epoxy resins, hydroquinone type epoxy resins, trimethylolpropane type epoxy resins, and linear fats obtained by oxidizing olefin bonds with peracids such as peracetic acid. may be at least one selected from the group consisting of group epoxy resins. The resin composition may contain one type of epoxy resin among the above, and the resin composition may contain multiple types of epoxy resins among the above.

Acrylic resins are polymers or copolymers having at least one of structural units derived from acrylic acid (acrylic monomer) and structural units derived from methacrylic acid (methacrylic monomer). The acrylic resin may have a glycidyl group. Acrylic resins may be formed, for example, by radical polymerization or living polymerization. From the viewpoint of improving the flexibility of the sheet, the polystyrene equivalent weight average molecular weight of the acrylic resin may be preferably 500,000 or more and 1,500,000 or less, and more preferably 600,000 or more and 1,000,000 or less. The acrylic monomer may be, for example, at least one selected from the group consisting of acrylonitrile, ethyl acrylate, and butyl acrylate. A methacrylic monomer can be, for example, glycidyl methacrylate. The resin composition may contain one acrylic resin among the above, and the resin composition may contain a plurality of acrylic resins among the above.

Curing agents are classified into curing agents that cure epoxy resins in the range from low temperature to room temperature, and heat curing type curing agents that cure epoxy resins with heating. Curing agents that cure epoxy resins in the range from low temperature to room temperature include, for example, aliphatic polyamines, polyaminoamides, and polymercaptans. Heat-curable curing agents include, for example, aromatic polyamines, acid anhydrides, phenol novolak resins, dicyandiamide (DICY), and the like.

When a curing agent that cures the epoxy resin is used in the range from low temperature to room temperature, the glass transition point of the cured epoxy resin tends to be low and the cured epoxy resin tends to be soft. As a result, the sheet tends to become soft. On the other hand, from the viewpoint of improving the heat resistance of the sheet, the curing agent may preferably be a heat curing type curing agent, more preferably a phenol resin, and still more preferably a phenol novolac resin. In particular, by using a phenol novolac resin as a curing agent, it is easy to obtain a cured product of an epoxy resin having a high glass transition point. As a result, the heat resistance and mechanical strength of the sheet are likely to be improved.

Phenolic resins include, for example, aralkyl-type phenol resins, dicyclopentadiene-type phenol resins, salicylaldehyde-type phenol resins, novolac-type phenol resins, copolymer-type phenol resins of benzaldehyde-type phenol and aralkyl-type phenol, para-xylylene and/or meta-xylylene-modified from the group consisting of phenolic resins, melamine-modified phenolic resins, terpene-modified phenolic resins, dicyclopentadiene-type naphthol resins, cyclopentadiene-modified phenolic resins, polycyclic aromatic ring-modified phenolic resins, biphenyl-type phenolic resins, and triphenylmethane-type phenolic resins It may be at least one selected. The phenolic resin may be a copolymer composed of two or more of the above. As a commercially available phenol resin, for example, Tamanol 758 manufactured by Arakawa Chemical Industries, Ltd. or HP-850N manufactured by Hitachi Chemical Co., Ltd. may be used.

Phenol novolak resins may be resins obtained by, for example, condensation or co-condensation of phenols and/or naphthols and aldehydes under an acidic catalyst. Phenols constituting the phenolic novolak resin may be, for example, at least one selected from the group consisting of phenol, cresol, xylenol, resorcinol, catechol, bisphenol A, bisphenol F, phenylphenol and aminophenol. Naphthols constituting the phenol novolac resin may be, for example, at least one selected from the group consisting of α-naphthol, β-naphthol and dihydroxynaphthalene. The aldehydes constituting the phenol novolac resin may be, for example, at least one selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde and salicylaldehyde.

A curing agent may be, for example, a compound having two phenolic hydroxyl groups in one molecule. The compound having two phenolic hydroxyl groups in one molecule may be, for example, at least one selected from the group consisting of resorcin, catechol, bisphenol A, bisphenol F, and substituted or unsubstituted biphenol.

The resin composition may contain one type of phenolic resin among the above, and the resin composition may contain a plurality of types of phenolic resins among the above. The resin composition may contain one curing agent among the above, and the resin composition may contain a plurality of curing agents among the above.

The ratio of the active group (phenolic OH group) in the curing agent that reacts with the epoxy group in the epoxy resin is preferably 0.5 to 1.5 equivalents, more preferably 1 equivalent of the epoxy group in the epoxy resin. may be 0.9 to 1.4 equivalents, more preferably 1.0 to 1.2 equivalents. If the ratio of active groups in the curing agent is less than 0.5 equivalents, the amount of OH per unit weight of the epoxy resin after curing is reduced, and the curing speed of the resin composition (epoxy resin) is reduced. If the ratio of the active groups in the curing agent is less than 0.5 equivalents, the glass transition temperature of the resulting cured product may be low, or a sufficient elastic modulus of the cured product may not be obtained. On the other hand, when the ratio of active groups in the curing agent exceeds 1.5 equivalents, the mechanical strength of the sheet after curing tends to decrease. However, even if the ratio of active groups in the curing agent is outside the above range, the effects of the present invention can be obtained.

The curing accelerator is not particularly limited as long as it is a composition that reacts with the epoxy resin to accelerate curing of the epoxy resin. The curing accelerator may be, for example, an alkyl-substituted imidazole or imidazoles such as benzimidazole. The resin composition may contain one curing accelerator, or may contain multiple curing accelerators.

The amount of the hardening accelerator to be blended is not particularly limited as long as the hardening accelerating effect is obtained. However, from the viewpoint of improving the curability and fluidity of the resin composition when absorbing moisture, the amount of the curing accelerator is preferably 0.1 to 30 parts by mass, more than 100 parts by mass of the epoxy resin. Preferably, it may be 1 to 15 parts by mass. The content of the curing accelerator is preferably 0.001 parts by mass or more and 5 parts by mass or less with respect to a total of 100 parts by mass of the epoxy resin and the curing agent. When the amount of the curing accelerator is less than 0.1 part by mass, it is difficult to obtain a sufficient curing acceleration effect. If the amount of the curing accelerator is more than 30 parts by mass, the storage stability of the sheet tends to deteriorate. However, even if the blending amount and content of the curing accelerator are outside the above range, the effects of the present invention can be obtained.

The coupling agent improves the adhesion between the resin composition and the first powder and the second powder, and improves the flexibility and mechanical strength of the sheet. The coupling agent may be, for example, at least one selected from the group consisting of silane-based compounds (silane coupling agents), titanium-based compounds, aluminum compounds (aluminum chelates), and aluminum/zirconium-based compounds. The silane coupling agent may be, for example, at least one selected from the group consisting of epoxysilanes, mercaptosilanes, aminosilanes, alkylsilanes, ureidosilanes, acid anhydride-based silanes and vinylsilanes. In particular, an aminophenyl-based silane coupling agent is preferred. The resin composition may contain one of the above coupling agents, or may contain more than one of the above coupling agents.

For environmental safety, recyclability, moldability and low cost of the sheet, the resin composition may contain a flame retardant. The flame retardant is, for example, at least one selected from the group consisting of brominated flame retardants, bulb flame retardants, hydrated metal compound flame retardants, silicone flame retardants, nitrogen-containing compounds, hindered amine compounds, organometallic compounds, and aromatic engineering plastics. can be The resin composition may contain one of the above flame retardants, or may contain more than one of the above flame retardants.

The thickness of the sheet is not particularly limited since it is adjusted according to the application. The thickness of the sheet may be, for example, 0.03 mm or more and 2 mm or less, or 0.03 mm or more and 1 mm or less. As the thickness of the sheet increases, the electromagnetic wave shielding effect tends to increase. In order to reinforce the sheet, a sheet-like base material may adhere to a part or the whole of the sheet. The substrate may be in close contact with only one surface of the sheet, or may be in close contact with both surfaces of the sheet. That is, one sheet may be sandwiched between a pair of base materials.

The sheet may contain a resin other than the above resins. The sheet may contain, for example, a silicone resin or the like.

The sheet can be used for various industrial products or their raw materials. Industrial products in which the sheet is used may be, for example, automobiles, medical equipment, electronic equipment, electrical equipment, information communication equipment, home appliances, audio equipment, and general industrial equipment. For example, the sheets may be used as raw material (eg, magnetic cores) for inductors such as EMI filters. The sheet may be used as an electromagnetic shield.

The method for manufacturing a sheet according to this embodiment may include a first step, a second step and a third step. Details of each step are described below.

In the first step, a paste (varnish) is prepared by uniformly mixing a binder, a first powder, a second powder and an organic solvent. In other words, the paste is prepared by mixing the resin composition, the first powder, the second powder and the organic solvent. The paste may contain a curing agent and a curing accelerator. The paste may contain additives such as silane coupling agents and flame retardants. The organic solvent is not particularly limited as long as it dissolves each component of the sheet described above. The organic solvent may be, for example, at least one selected from the group consisting of acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, carbitol acetate, butyl carbitol acetate, cyclohexanone and xylene. From the viewpoint of workability, the organic solvent is preferably liquid at room temperature, and preferably has a boiling point of 60° C. or higher and 150° C. or lower.

In a second step, the paste is applied to the surface of the substrate. Then, the paste applied to the substrate is dried to remove the organic solvent, thereby forming a B-stage sheet on the surface of the substrate. A B-stage sheet may be used as the finished product.

The substrate may be a polyethylene terephthalate (PET) film or a resin film such as a polyimide film. The substrate may be a resin film that has been subjected to mold release treatment. The substrate may be Sepanium (aluminum foil with release treatment).

The method of applying the paste may be, for example, a bar coater, a comma coater, or a dip coater.

The drying temperature of the paste applied to the substrate may be appropriately adjusted according to the type of organic solvent. The drying temperature may be, for example, 60° C. or higher and 160° C. or lower, preferably 70° C. or higher and 140° C. or lower, more preferably 80° C. or higher and 130° C. or lower. If the drying temperature is less than 60°C, it takes a long time to dry. If the drying temperature is lower than 60° C., the organic solvent may remain in the sheet, which may impair the mechanical strength of the sheet, cause wrinkles in the sheet, or cause voids in the third step. On the other hand, if the drying temperature exceeds 160° C., voids may occur in the second step due to rapid volatilization of the organic solvent, or curing of the resin composition may proceed excessively.

In the third step, the sheet (B-stage sheet) is cured by heat treatment to obtain a C-stage sheet. A C-stage sheet may be used as the finished product. The heat treatment temperature may be any temperature at which the resin composition in the sheet is sufficiently cured. The heat treatment temperature may be, for example, preferably 150° C. or higher and 300° C. or lower, more preferably 175° C. or higher and 250° C. or lower. In order to suppress oxidation of the first powder and the second powder in the sheet, it is preferable to perform the heat treatment in an inert atmosphere. If the heat treatment temperature exceeds 300° C., the trace amount of oxygen inevitably contained in the atmosphere of the heat treatment oxidizes the first powder and the second powder, or deteriorates the cured resin. In order to sufficiently cure the resin composition while suppressing the oxidation of the first powder and the second powder and the deterioration of the cured resin material, the holding time of the heat treatment temperature is preferably several minutes to 4 hours, more preferably 4 hours or less. may be from 5 minutes to 1 hour.

Although the preferred embodiments of the present invention have been described above, the present invention is not necessarily limited to the above-described embodiments. Various modifications of the present invention are possible without departing from the gist of the present invention, and these modifications are also included in the present invention.

For example, the effect of the present invention obtained by the sheet according to the present invention is provided with a first powder, a second powder, and a binder, and 100×M ₂ /(M ₁ +M ₂ ) is 0.1 or more and 50 or less. Some moldings are also obtained.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by these examples.

(Example 1)
<First step>
252.72 g of acrylic resin, 44.94 g of 2-butanone solution of epoxy resin, 17.88 g of 2-butanone solution of phenol novolak resin, and 4.51 g of 2-butanone solution of curing accelerator were weighed out, and 650 ml of these raw materials were added. ointment container.

As the acrylic resin, "HTR-860-P3" manufactured by Nagase ChemteX Corporation was used. NV (content of non-volatile matter) of the acrylic resin was 12.5% by mass. The polystyrene-equivalent weight average molecular weight of the acrylic resin was 800,000.

As the epoxy resin, "NC3000-H" manufactured by Nippon Kayaku Co., Ltd. was used. The NV (content of non-volatile matter) of the 2-butanone solution of the epoxy resin was 50.2% by mass.

As the phenol novolac resin (curing agent), "HP850N" manufactured by Hitachi Chemical Co., Ltd. was used. The NV (content of non-volatile matter) of the 2-butanone solution of the phenol novolac resin was 50.5% by mass.

As the curing accelerator, "2PZ-CN" manufactured by Shikoku Kasei Co., Ltd. was used. The NV (content of non-volatile matter) of the 2-butanone solution of the curing accelerator was 5.0% by mass.

A resin varnish was obtained by stirring and mixing all the raw materials in the ointment container with a revolutionary stirrer. “ARE-500” manufactured by THINKY CORPORATION was used as the rotation-revolution stirrer. In the stirring/mixing step, the revolution speed of the rotation-revolution stirrer was maintained at 1000 rpm for 5 minutes, and then the revolution speed was maintained at 2000 rpm for 1 minute.

8.5 g of the above resin varnish, 59 g of iron powder (first powder), 1 g of copper powder (second powder), and 0.18 g of silane coupling agent were weighed and placed in a 150 ml ointment container. The specific gravity of the iron powder was 7.8. The specific gravity of the copper powder was 8.9. As the silane coupling agent, "KBM-573" manufactured by Shin-Etsu Silicone Co., Ltd. was used. The raw material in the ointment container was stirred for 40 seconds at a revolution speed of 1000 rpm using a revolution stirrer. Subsequently, 2 g of cyclohexanone was introduced into the ointment container for viscosity adjustment. Furthermore, a paste was obtained by stirring the raw materials in the ointment container five times in total with a revolutionary stirrer. The portion of the paste excluding the iron powder, copper powder and organic solvent (2-butanone etc.) corresponds to the binder.

<Second step>
Using a bar coater manufactured by Yoshimitsu Seiki Co., Ltd., the above paste was applied to the surface of the substrate. A release-treated polyethylene terephthalate (PET) film was used as the substrate. A B-stage sheet was formed on the surface of the substrate by drying the paste applied to the substrate at 130° C. for 12 minutes. The thickness of the dried sheet was 200 μm. A hot air circulation dryer manufactured by Tabai Espec Co., Ltd. was used in the drying process.

<Third step>
The B-stage sheet was pressed at 2 MPa by sandwiching it between a pair of release-treated SUS plates. The sheet was cured by heating at 180° C. for 20 minutes while pressing the sheet. The sheet of Example 1 (C-stage sheet) was produced by the above procedure. The thickness of the sheet of Example 1 was 0.25 mm. Table 1 shows 100×M ₂ /(M ₁ +M ₂ ) for the sheet of Example 1.

[Electric field shield value]
An electric field shield value SE (unit: dB) defined by the following formula A was obtained by the Kansai Electronic Industry Development Center (KEC) method.
SE = 20 x _log10 ( _E0 / _E1 ) (A)
In Equation A, _E0 is the electric field strength of the electromagnetic wave (unit: V/m) when there is no sheet. _E1 is the electric field intensity (unit: V/m) of the electromagnetic wave transmitted through the sheet. A network analyzer 37247C manufactured by Anritsu Corporation was used to measure E ₀ and E ₁ . The frequency of electromagnetic waves used for the measurement was 1 MHz. The larger the SE, the better the shielding effect against electromagnetic waves.

(Examples 2 to 6, Comparative Examples 1 and 2)
In Examples 2 to 6 and Comparative Examples 1 and 2, the paste of the composition shown in Table 1 was used instead of the paste of Example 1. Sheets of Examples 2 to 6 and Comparative Examples 1 and 2 were produced in the same manner as in Example 1 except for the composition of the paste. Table 1 shows 100×M ₂ /(M ₁ +M ₂ ) for each sheet.

By the same method as in Example 1, the electric field shield values SE of the sheets of Examples 2 to 6 and Comparative Examples 1 and 2 were determined. Table 1 shows the results.

As shown in Table 1, the electric field shielding values of all examples were greater than the electric field shielding values of all comparative examples. It was confirmed that according to the present invention, a sheet having an excellent shielding effect against electromagnetic waves is provided.

A sheet according to the present invention is used, for example, as an electromagnetic wave shield.

Claims (10)

a first powder containing iron;
a second powder containing copper;
a binder;
A seat comprising
the first powder is at least one of an iron element and an iron-based alloy,
the second powder is at least one of a copper element and a copper-based alloy,
The mass of the first powder contained in the sheet is represented by _M1 ,
The mass of the second powder contained in the sheet is represented by _M2 ,
100 × M ₂ / (M ₁ + M ₂ ) is 1.7 or more and 5 or less,
sheet. wherein the binder comprises a resin composition;
A sheet according to claim 1 . wherein the binder comprises a thermosetting resin;
A sheet according to claim 1 or 2. the binder comprises an epoxy resin;
The sheet according to any one of claims 1-3. wherein the binder comprises a thermoplastic resin;
The sheet according to any one of claims 1-4. wherein the binder contains an acrylic resin;
The sheet according to any one of claims 1-5. The weight average molecular weight of the acrylic resin is 500,000 or more and 1,500,000 or less,
A sheet according to claim 6 . The acrylic resin has a glycidyl group,
A sheet according to claim 6 or 7. wherein the binder comprises a phenolic resin;
The sheet according to any one of claims 1-8. the binder comprises a curing agent and a curing accelerator;
The sheet according to any one of claims 1-9.