JP7009782B2 - Seat - Google Patents

Description

The present invention relates to a sheet.

Sheets formed from metal powders and resin compositions are used, for example, as industrial products such as inductors, electromagnetic wave shields, or bonded magnets, or raw materials thereof. (See Patent Documents 1 to 3 below.)

Japanese Unexamined Patent Publication No. 2004-31786 Japanese Unexamined Patent Publication No. 8-273916 Japanese Unexamined Patent Publication No. 1-261897

In the process of manufacturing an industrial product using the above-mentioned sheet, processing and handling of the sheet such as molding, cutting, laminating, moving and transporting are required. However, since the conventional sheet containing the metal element-containing powder does not have sufficient flexibility, it is easily damaged by processing and handling. Even when the sheet itself is used as an industrial product, the flexibility of the sheet is required to prevent damage.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sheet having excellent flexibility despite containing a metal element-containing powder.

The sheet according to one aspect of the present invention comprises a metal element-containing powder, an epoxy resin, and an acrylic resin.

In one aspect of the present invention, the weight average molecular weight of the acrylic resin may be 500,000 or more and 1.5 million or less.

In one aspect of the present invention, the specific gravity of the metal element-containing powder may be 7.0 or more and 10.0 or less.

In one aspect of the present invention, the metal element-containing powder may contain at least one of Fe simple substance and Fe-based alloy.

The sheet according to one aspect of the present invention may contain at least two kinds of metal element-containing powders having different specific gravities from each other.

In one aspect of the present invention, the difference in specific gravity between the two types of metal element-containing powder may be 3.0 or more and 5.0 or less.

The sheet according to one aspect of the present invention may be provided with a curing agent and a curing accelerator.

According to the present invention, a sheet having excellent flexibility is provided even though it contains a powder containing a metal element.

Hereinafter, preferred embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments.

The sheet according to this embodiment includes a metal element-containing powder, an epoxy resin, and an acrylic resin. The metal element-containing powder may be, for example, at least one powder selected from the group consisting of elemental metals, alloys and metal compounds. The sheet may include a curing agent and a curing accelerator. The sheet may include additives. In the following, the remaining components (nonvolatile components) excluding the organic solvent and the metal element-containing powder, which are components including an epoxy resin, an acrylic resin, a curing agent, a curing accelerator and an additive, are referred to as "resin composition". May be written as. The resin contained in the resin composition may be only an epoxy resin and an acrylic resin. The resin composition may contain yet another resin (for example, a phenolic resin) in addition to the epoxy resin and the acrylic resin. The additive is a component of the rest of the resin composition excluding the resin, the curing agent and the curing accelerator. The additive is, for example, a coupling agent, a flame retardant, or the like. The mass of the epoxy resin contained in the sheet is not limited, but may be, for example, 30 to 90 parts by mass with respect to 100 parts by mass in total of the total mass of the epoxy resin and the acrylic resin contained in the sheet. The mass of the acrylic resin contained in the sheet is not limited, but may be, for example, 10 to 70 parts by mass with respect to 100 parts by mass in total of the total mass of the epoxy resin and the acrylic resin contained in the sheet.

As will be described later, the sheet is obtained by forming a sheet-shaped molded product from a paste containing a resin composition, a metal element-containing powder and an organic solvent, and removing the organic solvent from the molded product. With the removal of the organic solvent, the resin composition adheres to the surface of the individual particles constituting the metal element-containing powder. The resin composition then functions as a binder and binds the individual particles constituting the metal element-containing powder to each other. As a result, a sheet having enough mechanical strength to maintain the desired shape is formed. In the case of the conventional sheet containing no acrylic resin, it is difficult for the metal element-containing powder to be uniformly dispersed, the sheet becomes brittle at the portion where the metal element-containing powder is unevenly distributed, and the sheet cannot have sufficient flexibility. As a result, the sheet is liable to be damaged during processing and handling of the sheet such as molding, cutting, laminating, moving and transporting. In particular, when the content of the metal element-containing powder in the sheet is large or the specific gravity or the difference in specific gravity of the metal element-containing powder is large, the flexibility of the sheet is likely to be impaired due to the above-mentioned causes. On the other hand, the sheet according to the present embodiment contains not only an epoxy resin but also an acrylic resin having a higher molecular weight and a higher viscosity than the epoxy resin. Therefore, the movement of the metal element-containing powder due to factors such as specific gravity is suppressed by the high viscosity of the acrylic resin. As a result, the uneven distribution of the metal element-containing powder in the sheet is suppressed, and the metal element-containing powder is easily uniformly dispersed in the sheet. In other words, the composition of the sheet tends to be uniform. Even if the content of the metal element-containing powder is large or the specific gravity of the metal element-containing powder is large, the above mechanism suppresses the uneven distribution of the metal element-containing powder in the sheet, and the metal element-containing powder is contained in the sheet. Easy to disperse evenly within. Further, the viscosity of the resin composition containing the acrylic resin itself directly contributes to the flexibility of the sheet. For the above reasons, the flexibility and mechanical strength of the entire sheet are improved, and the sheet is less likely to be damaged during processing and handling. However, the action and effect according to the present invention are not limited to the above items.

The sheet according to the present embodiment may contain an uncured resin composition and a metal element-containing powder. The sheet according to this embodiment may contain a semi-cured resin composition and a metal element-containing powder. The sheet according to the present embodiment may contain a cured product of the resin composition and a metal element-containing powder bonded to each other by the cured product. By the heat treatment of the sheet, the resin composition (binder) is cured, and the metal element-containing powders are more firmly bonded to each other.

When the mass of the resin composition is expressed as M and the mass of the metal element-containing powder is expressed as m, m / (m + M) 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, the sheet can have sufficient flexibility and mechanical strength even if m / (m + M) is 0.95 or more. That is, according to the present embodiment, the sheet can have sufficient flexibility and mechanical strength even when the ratio of the metal element-containing powder in the sheet is high. It can be said that m / (m + M) · 100 is the space factor of the metal element-containing powder in the sheet. That is, according to the present embodiment, the sheet can have sufficient flexibility and mechanical strength even when the occupancy rate of the metal element-containing powder in the sheet is 95% or more.

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 resin, stillben type epoxy resin, diphenylmethane type epoxy resin, sulfur atom-containing epoxy resin, novolak type epoxy resin, dicyclopentadiene type epoxy resin, salicylaldehyde type epoxy resin, naphthols and phenol. Copolymerization type epoxy resin, aralkyl type phenol resin epoxide, bisphenol type epoxy resin, alcohols glycidyl ether type epoxy resin, paraxylylene and / or metaxylylene modified phenol resin glycidyl ether type epoxy resin, terpene modified phenol resin 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 resin, alicyclic epoxy resin, halogenated phenol novolac type epoxy resin, hydroquinone type epoxy resin, trimethylol propane type epoxy resin, and linear fat obtained by oxidizing an olefin bond with a peracid such as peracetic acid. It may be at least one selected from the group consisting of group epoxy resins. The epoxy resin may be liquid or semi-solid. The sheet may be provided with one of the above epoxy resins, and the sheet may be provided with a plurality of the above epoxy resins.

The acrylic resin is a polymer or copolymer having at least one of a structural unit derived from acrylic acid (acrylic monomer) and a structural unit derived from methacrylic acid (methacrylic monomer). The acrylic resin 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 1.5 million or less, and more preferably 600,000 or more and 1 million or less. The acrylic monomer may be at least one selected from the group consisting of, for example, acrylonitrile, ethyl acrylate, and butyl acrylate. The methacrylic monomer may be, for example, glycidyl methacrylate. The acrylic resin may have a glycidyl group. The sheet may be provided with one of the above acrylic resins, and the sheet may be provided with a plurality of of the above acrylic resins.

As described above, the metal element-containing powder may be, for example, at least one powder selected from the group consisting of elemental metals, alloys and metal compounds. The alloy may contain at least one selected from the group consisting of solid solutions, eutectic and intermetallic compounds. The alloy may be, for example, stainless steel (Fe—Cr based alloy, Fe—Ni—Cr based alloy, etc.). The metal compound may be, for example, an oxide such as ferrite. The metal element-containing powder may contain one kind of metal element or a plurality of kinds of metal elements. The metal element contained in the metal element-containing powder may be, for example, a base metal element, a noble metal element, a transition metal element, or a rare earth element. The metal elements contained in the metal element-containing powder include, for example, iron (Fe), copper (Cu), titanium (Ti), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), and aluminum ( Al), tin (Sn), chromium (Cr), barium (Ba), strontium (Sr), lead (Pb), silver (Ag), placeodim (Pr), neodym (Nd), samarium (Sm) and dysprosium ( It may be at least one selected from the group consisting of Dy). The metal element-containing powder may contain an element other than the metal element. The metal element-containing powder may contain, for example, oxygen (О), beryllium (Be), phosphorus (P), boron (B), or silicon (Si). The metal element-containing powder may be a magnetic powder. The metal element-containing powder may be a soft magnetic alloy or a ferromagnetic alloy. The metal element-containing powder is, for example, Fe-Si alloy, Fe-Si-Al alloy (Sendust), Fe-Ni alloy (Permalloy), Fe-Cu-Ni alloy (Permalloy), Fe-Co alloy. (Permenzur), Fe-Cr-Si alloy (electromagnetic stainless steel), Nd-Fe-B alloy (rare earth magnet), Sm-Fe-N alloy (rare earth magnet), Al-Ni-Co alloy It may be a magnetic powder consisting of at least one selected from the group consisting of (alnico magnet) and ferrite. The ferrite may be, for example, spinel ferrite, hexagonal ferrite, or garnet ferrite. The metal element-containing powder may be a copper alloy such as a Cu—Sn-based alloy, a Cu—Sn—P-based alloy, a Cu—Ni-based alloy, or a Cu—Be-based alloy. The metal element-containing powder may contain one of the above elements and compositions, and may contain a plurality of of the above elements and compositions.

The specific gravity of the metal element-containing powder may be 7.0 or more and 10.0 or less, or 7.0 or more and 9.0 or less. The metal element-containing powder having a specific gravity within the above range may be at least one selected from the group consisting of, for example, iron powder, copper powder, Fe-Cr-Si-based alloys, and Nd-Fe-B-based alloys. When the conventional sheet containing no acrylic resin contains a heavy metal element-containing powder having a specific gravity of 7.0 or more, the metal element-containing powder moves in the sheet due to its own weight and tends to be unevenly distributed locally. In other words, when the conventional sheet containing no acrylic resin contains a heavy metal element-containing powder having a specific gravity of 7.0 or more, the metal element-containing powder is difficult to be uniformly dispersed in the sheet, and the sheet is flexible. Is easily damaged. On the other hand, the sheet according to the present embodiment can have sufficient flexibility for the above-mentioned reason even when it contains a heavy metal element-containing powder having a specific gravity of 7.0 or more.

The metal element-containing powder may contain at least one of Fe simple substance and Fe-based alloy. The Fe-based alloy may be, for example, a Fe—Si—Cr based alloy or an Nd—Fe—B based alloy. A sheet containing at least one of Fe simple substance and Fe-based alloy as a metal element-containing powder has a high space factor and is excellent in magnetic properties.

The sheet may contain at least two kinds of metal element-containing powders having different specific densities from each other. The combination of the two types of metal element-containing powders having different specific gravity may be, for example, iron powder and copper powder, iron powder and aluminum powder, iron powder and titanium powder. The difference in specific gravity between the two types of metal element-containing powder may be 3.0 or more and 5.0 or less. The combination of the two types of metal element-containing powder having a difference in specific gravity of 3.0 or more and 5.0 or less may be, for example, a combination of iron powder and aluminum powder, or a combination of iron powder and titanium powder. When a conventional sheet containing no acrylic resin contains two or more types of metal element-containing powders having different specific densities, it is difficult for the metal element-containing powders to be uniformly dispersed in the sheet due to the difference in specific densities, and the powders are unevenly distributed locally. Easy to do. For example, in the process of producing a sheet, the metal element-containing powder having a large specific gravity may move due to its own weight and may be unevenly distributed locally on the sheet. As a result, the flexibility of the sheet is easily impaired, and it is difficult to uniformly impart the physical characteristics derived from each of the two or more kinds of metal element-containing powders over the entire sheet. On the other hand, the sheet according to the present embodiment contains not only an epoxy resin but also an acrylic resin having a higher molecular weight and a higher viscosity than the epoxy resin. Therefore, even when the difference in specific gravity between two or more kinds of metal element-containing powder is large, the movement and localization of the metal element-containing powder are suppressed by the viscosity of the acrylic resin, and each metal element-containing powder is uniform in the sheet. Easy to disperse. As a result, the flexibility and mechanical strength of the entire sheet containing two or more kinds of metal element-containing powders having different specific densities are likely to be improved. Further, the composition of the entire sheet containing two or more types of metal element-containing powder is likely to be uniform, and the desired physical properties derived from each of the two or more types of metal element-containing powder are likely to be uniformly imparted to the entire sheet. From the above, the sheet according to the present embodiment can contain, for example, a plurality of types of metal powders that are difficult to alloy with in a desired compounding ratio. Further, even when the sheet according to the present embodiment contains a plurality of types of metal powders in which the physical properties derived from the individual metal simple substances are impaired by alloying, the physical properties derived from the individual metal simple substances are impaired. It can be combined without any problems.

Depending on the composition or combination of the metal element-containing powder contained in the sheet, various properties such as electromagnetic properties or thermal conductivity of the sheet can be freely controlled, and the sheet can be used for various industrial products or their raw materials. can. The industrial product in which the sheet is used may be, for example, an automobile, a medical device, an electronic device, an electric device, an information / communication device, a home electric appliance, an audio device, and a general industrial device. For example, when the sheet contains a magnetic powder such as a Fe—Si—Cr alloy or ferrite as the metal element-containing powder, the sheet may be used as a raw material (for example, a magnetic core) for an inductor such as an EMI filter. When the sheet contains the powder of a permanent magnet as the powder containing a metal element, the sheet may be utilized as a bonded magnet. When the sheet contains iron powder and copper powder as the metal element-containing powder, the sheet may be used as an electromagnetic wave shield.

The shape of the individual particles constituting the metal element-containing powder is not particularly limited. The individual particles may be, for example, spherical, flat, or needle-shaped. The average particle size of the metal element-containing powder may be, for example, preferably 20 to 300 μm, more preferably 40 to 250 μm. The sheet may contain a plurality of types of metal element-containing powders having different average particle sizes. By filling the gaps formed between the metal element-containing powders having a large average particle size with another metal element-containing powder having a small average particle size, the space factor of the metal element-containing powders in the sheet is increased. The particle size distribution of the metal element-containing powder is calculated based on, for example, weight measurement by sieving or analysis using a measuring device such as a laser diffraction / scattering device).

The curing agent is classified into a curing agent that cures the epoxy resin in the range of low temperature to room temperature and a heat-curing type curing agent that cures the epoxy resin with heating. The curing agent that cures the epoxy resin in the range of low temperature to room temperature is, for example, aliphatic polyamines, polyaminoamides, and polymercaptans. The heat-curable curing agent is, for example, aromatic polyamine, acid anhydride, phenol novolac resin, dicyandiamide (DICY) and the like.

When a curing agent that cures the epoxy resin in the range of low temperature to room temperature is used, the glass transition point of the cured product of the epoxy resin is low, and the cured product of the epoxy resin tends to be soft. As a result, the sheet also tends to be soft. On the other hand, from the viewpoint of improving the heat resistance of the sheet, the curing agent may be preferably a heat-curing type curing agent, more preferably a phenol resin, and further 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.

The phenol resin is, for example, an aralkyl type phenol resin, a dicyclopentadiene type phenol resin, a salicylaldehyde type phenol resin, a novolak type phenol resin, a copolymerized phenol resin of a benzaldehyde type phenol and an aralkyl type phenol, a paraxylylene and / or a metaxylylene modification. From the group consisting of phenol resin, melamine-modified phenol resin, terpen-modified phenol resin, dicyclopentadiene-type naphthol resin, cyclopentadiene-modified phenol resin, polycyclic aromatic ring-modified phenol resin, biphenyl-type phenol resin, and triphenylmethane-type phenol resin. It may be at least one of the choices. The phenol resin may be a copolymer composed of two or more of the above. As the commercially available phenol resin, for example, Tamanol 758 manufactured by Arakawa Chemical Industry Co., Ltd., HP-850N manufactured by Hitachi Chemical Co., Ltd., or the like may be used.

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

The 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 at least one selected from the group consisting of, for example, resorcin, catechol, bisphenol A, bisphenol F, and substituted or unsubstituted biphenol.

The sheet may be provided with one of the above phenol resins, and the sheet may be provided with a plurality of the above phenol resins. The sheet may be provided with one of the above-mentioned curing agents, and the sheet may be provided with a plurality of of the above-mentioned curing agents.

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 0.5 to 1.5 equivalents with respect to 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. When the ratio of the active group in the curing agent is less than 0.5 equivalent, the amount of OH per unit weight of the cured epoxy resin is small, and the curing rate of the resin composition (epoxy resin) is lowered. Further, when the ratio of the active group in the curing agent is less than 0.5 equivalent, the glass transition temperature of the obtained 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 cured sheet tends to decrease. However, even when the ratio of the active group in the curing agent is out of the above range, the effect according to the present invention can be obtained.

The curing accelerator is not limited as long as it is a composition that reacts with the epoxy resin to accelerate the curing of the epoxy resin, for example. The curing accelerator may be, for example, an alkyl group-substituted imidazole or an imidazole such as benzimidazole. The sheet may be provided with one type of curing accelerator or may be provided with a plurality of types of curing accelerator.

The amount of the curing accelerator to be blended is not particularly limited as long as it can obtain the curing promoting effect. However, from the viewpoint of improving the curability and fluidity of the resin composition during moisture absorption, the amount of the curing accelerator is preferably 0.1 to 30 parts by mass with respect to 100 parts by mass of the epoxy resin. It may be preferably 1 to 15 parts by mass. The content of the curing accelerator is preferably 0.001 part by mass or more and 5 parts by mass or less with respect to the total mass of the epoxy resin and the curing agent. When the blending amount of the curing accelerator is less than 0.1 parts by mass, it is difficult to obtain a sufficient curing promoting effect. When the blending amount of the curing accelerator exceeds 30 parts by mass, the storage stability of the sheet tends to decrease. However, even when the blending amount and content of the curing accelerator are out of the above range, the effect according to the present invention can be obtained.

The coupling agent improves the adhesion between the resin composition and the metal element-containing 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 a silane compound (silane coupling agent), a titanium compound, an aluminum compound (aluminum chelate), and an aluminum / zirconium compound. The silane coupling agent may be at least one selected from the group consisting of, for example, epoxysilane, mercaptosilane, aminosilane, alkylsilane, ureidosilane, acid anhydride-based silane and vinylsilane. In particular, an aminophenyl-based silane coupling agent is preferable. The sheet may be provided with one of the above-mentioned coupling agents, and may be provided with a plurality of of the above-mentioned coupling agents.

Due to the environmental safety, recyclability, moldability and low cost of the sheet, the sheet may contain a flame retardant. The flame retardant is at least one selected from the group consisting of, for example, a brominated flame retardant, a scale flame retardant, a hydrated metal compound flame retardant, a silicone flame retardant, a nitrogen-containing compound, a hindered amine compound, an organic metal compound and an aromatic empra. May be. The sheet may be provided with one of the above flame retardants, and may be provided with a plurality of of the above flame retardants.

The thickness of the sheet is not particularly limited as it is adjusted according to the intended use. 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. In order to reinforce the sheet, a sheet-like base material may be in close contact with a part or the whole of the sheet. The base material may be in close contact with only one surface of the sheet, or both surfaces of the sheet may be in close contact with each other. That is, one sheet may be sandwiched between a pair of base materials.

The sheet may be further provided with other resins in addition to the epoxy resin and the acrylic resin. The sea may include, for example, at least one selected from the group consisting of silicone resin, polyamide-imide resin, polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate. The resin contained in the sheet may be only an epoxy resin and an acrylic resin.

The sheet manufacturing method according to the present embodiment may include a first step, a second step, and a third step. Hereinafter, the details of each step will be described.

In the first step, a paste is prepared by uniformly mixing an epoxy resin, an acrylic resin, a powder containing a metal element, and an organic solvent. In other words, the paste is prepared by mixing the above-mentioned resin composition, metal element-containing powder and 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 is a liquid that dissolves each component of the above-mentioned sheet. 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 a liquid at room temperature, and the boiling point of the organic solvent is preferably 60 ° C. or higher and 150 ° C. or lower.

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

The base material may be, for example, a polyethylene terephthalate (PET) film or a resin film such as a polyimide film. The base material may be a resin film that has undergone a mold release treatment. The base material may be sepanium (aluminum foil that has been subjected to a mold 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 the 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, and 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. Further, when the drying temperature is less than 60 ° C., the organic solvent remains in the sheet and the mechanical strength of the sheet is impaired, the sheet is wrinkled, and voids are generated in the third step. On the other hand, when the drying temperature exceeds 160 ° C., voids are generated in the second step due to the rapid volatilization of the organic solvent, or the resin composition is excessively cured.

In the third step, the sheet (B stage sheet) is cured by heat treatment to obtain a C stage sheet. The C stage sheet may be used as a finished product. The temperature of the heat treatment may be any temperature as long as the resin composition in the sheet is sufficiently cured. The temperature of the heat treatment may be, for example, preferably 150 ° C. or higher and 300 ° C. or lower, and more preferably 175 ° C. or higher and 250 ° C. or lower. In order to suppress the oxidation of the metal element-containing powder in the sheet, it is preferable to carry out the heat treatment in an inert atmosphere. When the heat treatment temperature exceeds 300 ° C., the metal element-containing powder is oxidized or the cured resin product is deteriorated by a small amount of oxygen inevitably contained in the heat treatment atmosphere. In order to sufficiently cure the resin composition while suppressing oxidation of the metal element-containing powder and deterioration of the cured resin product, the heat treatment temperature holding time is preferably several minutes or more and 4 hours or less, more preferably 5 minutes. It may be 1 hour or less.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these examples.

(Example 1)
<First step>
Weigh 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 novolac resin, and 4.51 g of 2-butanone solution of curing accelerator, and 650 ml of these raw materials. Placed in an ointment container.

As the acrylic resin, "HTR-860-P3" manufactured by Nagase ChemteX Corporation was used. The NV (nonvolatile content) 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 (nonvolatile content) 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 Kasei Co., Ltd. was used. The NV (nonvolatile content) 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 (nonvolatile content) of the 2-butanone solution of the curing accelerator was 5.0% by mass.

A binder resin varnish was obtained by stirring and mixing all the raw materials in the ointment container with a revolution stirrer. As the self-revolving stirrer, "ARE-500" manufactured by Shinky Co., Ltd. was used. In the stirring / mixing step, the revolution speed of the self-revolving 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 binder resin varnish, 60 g of iron powder, and 0.18 g of the silane coupling agent were weighed and placed in a 150 ml ointment container. The specific gravity of iron powder was 7.8. As the silane coupling agent, "KBM-573" manufactured by Shinetsu Silicone Co., Ltd. was used. The raw material in the ointment container was stirred at a revolution speed of 1000 rpm for 40 seconds using a self-revolution stirrer. Subsequently, 2 g of cyclohexanone was introduced into the ointment container for adjusting the viscosity. Further, the raw material in the ointment container was stirred with a revolution stirrer a total of 5 times to obtain a paste.

<Second step>
The above paste was applied to the surface of the base material using a bar coater manufactured by Yoshimitsu Seiki Co., Ltd. As the base material, a polyethylene terephthalate (PET) film that had undergone a mold release treatment was used. The paste applied to the substrate was dried at 130 ° C. for 12 minutes to form a sheet of the B stage of Example 1 on the surface of the substrate. The thickness of the dried sheet was 200 μm. A warm air circulation type dryer manufactured by Tabai ESPEC Co., Ltd. was used for the drying process.

<Third step>
The sheet of the B stage was pressed by 2 MPa by sandwiching the sheet of the B stage between a pair of SUS plates subjected to the mold release treatment. The sheet was cured by heating it at 180 ° C. for 20 minutes while pressurizing the sheet. By the above procedure, the C stage sheet of Example 1 was prepared. The space factor of iron powder (metal element-containing powder) in the sheet of Example 1 was 95% or more.

(Examples 2 to 6)
In Examples 2 to 6, one kind of powder shown in Table 1 below was used as the metal element-containing powder instead of iron powder. Sheets of Examples 2 to 6 were prepared in the same manner as in Example 1 except for the composition of the metal element-containing powder.

(Examples 7 to 10)
In Examples 7 to 10, as the metal element-containing powder, two kinds of metal element-containing powders having different compositions were used instead of iron powder. The composition, specific gravity and mass of each metal element-containing powder used in Examples 7 to 10 are shown in Table 1 below. Sheets of Examples 7 to 10 were prepared in the same manner as in Example 1 except for these matters.

(Comparative Example 1)
The sheet of Comparative Example 1 was prepared by the same method as in Example 1 except that the acrylic resin was not used.

[Evaluation of flexibility]
The flexibility of each of the sheets of Examples 1 to 10 and Comparative Example 1 was individually evaluated by the following tests.

The B-stage sheet formed on the entire surface of the PET film was wound around the plastic tube along the length direction of the PET film together with the PET film. At the time of winding, the PET film was placed inside. The dimensions of the PET film were 10 cm x 20 cm. The diameter of the plastic tube was 10 cm. The state of the sheet wrapped around the plastic tube was visually observed. Since all of the sheets of Examples 1 to 10 were excellent in flexibility, the sheets of Examples 1 to 10 did not peel off from the PET film, and no cracks were found in the sheets of Examples 1 to 10. rice field. That is, the states of the sheets and PET films of Examples 1 to 10 did not change with winding. On the other hand, in the case of Comparative Example 1, the sheet was peeled off from the PET film during the winding process, and the sheet of Comparative Example 1 was cracked. That is, in the case of Comparative Example 1, the sheet could not be wound around the plastic tube without being damaged while being in close contact with the PET film. As described above, it was confirmed that the sheets of Examples 1 to 10 were superior in flexibility to the sheets of Comparative Example 1.

The sheet according to the present invention is used, for example, for an inductor or the like.

Claims (3)

Equipped with metal element-containing powder, epoxy resin, and acrylic resin,
It contains at least two kinds of the metal element-containing powders having different specific densities from each other.
The difference in specific gravity between the two types of the metal element-containing powder is 3.0 or more and 5.0 or less.
Sheet. The acrylic resin has a weight average molecular weight of 500,000 or more and 1.5 million or less.
The sheet according to claim 1. Equipped with a curing agent and a curing accelerator,
The sheet according to claim 1 or 2 .