paste

Abstract

A paste containing a metal-containing powder, an epoxy-containing compound, and a hardener, exhibits a thermal weight reduction of less than 5% after heat curing at 180°C. The paste is preferably used, for example, as a material for the core of an inductor or as a material for filling the space between conductors in a coil, readily providing molded articles with excellent insulation properties.

Description

Technical Field

[0001] One embodiment of the present invention relates to a paste. More specifically, it relates to a paste that can suppress the degradation of properties in a hardened material after heat curing. Prior Technology

[0002] Materials containing metal powders with various physical properties are used depending on the characteristics required for industrial products. For example, materials containing magnetic powders are used in fields such as inductors, electromagnetic shields, and bonded magnets. In recent years, there has been an increasing demand for materials containing magnetic powders and resins that offer superior formability compared to sintered magnets. For example, Patent Documents 1 to 4 disclose magnetic pastes containing magnetic powders and resins. [Existing Technical Documents] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2004-31786 [Patent Document 2] Japanese Patent Application Publication No. 8-273916 [Patent Document 3] Japanese Patent Application Publication No. 1-261897 [Patent Document 4] Japanese Patent Application Publication No. 2014-127624 Summary of the Invention

[0004] [The problem that the invention aims to solve]

[0005] By molding and curing a metal powder paste (hereinafter sometimes referred to as paste) containing a curable resin, a molded body (cured product) containing metal powder can be formed. Generally, in order to improve the strength, electrical conductivity, thermal conductivity, and magnetic properties of the cured molded body, it is necessary to increase the proportion of metal powder in the paste and reduce the proportion of components other than metal powder. However, as the proportion of metal powder increases, the viscosity of the paste also increases, and its flowability tends to decrease. Therefore, the viscosity is usually adjusted by adding volatile components such as organic solvents to the paste.

[0006] However, if the amount of organic solvent in the paste is large, a drying step is required after the paste is coated, as the evaporation of the organic solvent causes environmental impact. In addition, due to volume shrinkage caused by the evaporation of organic solvent, the substrate may sometimes be partially exposed from the paste-coated surface. Furthermore, the use of organic solvents can easily lead to a decrease in the properties of the cured product. For example, due to volume shrinkage caused by the evaporation of organic solvents, stress and strain will accumulate inside the cured paste. In addition, when using organic solvents with a boiling point lower than the heating temperature during curing, the evaporation of organic solvents during heating can easily create voids in the cured product. If voids exist in the cured product, its mechanical strength and magnetic properties are likely to decrease. On the other hand, when using organic solvents with a boiling point higher than the heating temperature during curing, the organic solvent is difficult to evaporate during heating and remains directly in the cured product, which can easily lead to a decrease in the properties of the product. In particular, if organic solvents remain in the cured product, ionic components in the cured product are likely to migrate, and electrical insulation properties (hereinafter referred to as insulation) such as insulation resistance and insulation reliability are likely to decrease. Therefore, a metal paste that can reduce the amount of organic solvent used, suppress performance degradation caused by volatile components such as organic solvents in the cured product after heat curing, and easily obtain excellent insulation properties is desired. Furthermore, the coefficient of thermal expansion (CTE) of the cured metal paste is also an important characteristic. If the difference between the CTE of the cured metal paste and the CTE of the surrounding materials to which it is applied is large, the difference in expansion during heating can easily lead to the following adverse conditions: warping of the cured product, peeling at the interface with the surrounding materials, or easy cracking of the cured product. Therefore, for example, in the case of inductors, the CTE of copper coils and wiring board materials on which inductors are mounted is low; therefore, correspondingly, it is desirable for the CTE of the cured metal paste to also be low.

[0007] The present invention was made in view of the above circumstances, and provides a metal paste that can suppress the performance degradation caused by volatile components such as organic solvents in the hardened material after heat curing, and obtain excellent properties such as insulation in the hardened material. [Methods for solving problems]

[0008] That is, the embodiments of the present invention relate to the following. However, the present invention is not limited to the following embodiments and includes various embodiments.

[0009] One embodiment relates to a paste containing a metal-containing powder, an epoxy-containing compound, and a hardener, wherein the paste, after being cured by heating at 180°C, exhibits a thermal weight reduction rate of 5% or less. In one embodiment, it is preferable that the paste contains a metal-containing powder, an epoxy-containing compound, and a hardener, exhibits a thermal weight reduction rate of 5% or less after curing by heating at 180°C, and that the coefficient of thermal expansion of the cured product is 40 ppm / °C or less.

[0010] In the described embodiments, the curing agent preferably comprises at least one selected from the group consisting of amine-based curing agents and imidazole-based curing agents. The amine-based curing agent preferably comprises an aromatic amine.

[0011] In the embodiments described, it is preferable that the epoxy-containing compound is contained in an epoxy resin that is liquid at 25°C.

[0012] In the described embodiment, it is preferable that the hardener is a liquid hardener at 25°C.

[0013] In the above embodiment, it is preferable that the content of the metal-containing powder is 70% by mass or more, based on the total mass of the paste.

[0014] In the above embodiments, it is preferable that the powder containing metal elements includes magnetic powder.

[0015] In the embodiments described, it is preferable that the viscosity of the paste at 25°C is above 1 Pa·s and below 600 Pa·s.

[0016] Other embodiments relate to a paste used in screen printing of the embodiments described above. The disclosures in this application relate to the subject matter set forth in International Application No. PCT / JP2020 / 45278 filed on December 4, 2020, and all such disclosures are incorporated herein by reference. [The effects of the invention]

[0017] According to embodiments of the present invention, a metal powder paste that reduces the amount of volatile components such as organic solvents used can be provided. This provides a metal powder paste that can suppress performance degradation caused by volatile components such as organic solvents in the cured product after heat curing, and easily obtain excellent properties such as insulation in the cured product. According to the metal powder paste of the described embodiment, a cured product with low CTE can be easily obtained. Simple Explanation of the Diagram

[0018] none Implementation

[0019] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the embodiments described below. In this specification, the numerical range represented by "~" indicates the range of minimum and maximum values ​​recorded before and after "~". Within the numerical ranges described in stages in this specification, the upper or lower limit of a certain stage's numerical range can be arbitrarily combined with the upper or lower limit of another stage's numerical range. Unless otherwise specified, the materials illustrated in this specification may be used alone or in combination of two or more. In this specification, the content of each component in the composition, in the case of multiple substances equivalent to each component in the composition, refers to the total amount of such substances present in the composition, unless otherwise specified.

[0020] <Paste> The paste, as an embodiment of the present invention, comprises a powder containing a metal element, a compound containing an epoxy group, and a hardener. The paste can be hardened by heat treatment. The paste of this embodiment is characterized by its ability to suppress the increase in viscosity that occurs with an increase in the amount of powder containing the metal element, and to reduce the content of volatile components such as organic solvents, thus resulting in less mass reduction when the paste hardens.

[0021] Pastes with low levels of volatile components such as organic solvents exhibit excellent heat resistance, and the degradation of properties of the hardened product caused by the volatilization of volatile components during heating is suppressed. More specifically, the paste of the described embodiment is characterized in that, for example, when heat-treated at 180°C to form a hardened product, the rate of thermal weight reduction is 5% or less. More preferably, the rate of thermal weight reduction is 3% or less, and even more preferably 2% or less. The most ideal rate of thermal weight reduction is 0%. The rate of thermal weight reduction can be calculated using measurements taken with a thermogravimetric differential thermal analysis (TG-DTA) apparatus. When the rate of thermal weight reduction of the paste is 5% or less, desired properties such as insulation can be readily obtained in the hardened product after heat curing of the paste.

[0022] The coefficient of thermal expansion (CTE) of the cured paste is preferably small compared to the CTE of the surrounding materials. In one embodiment, for example, when the paste is applied to inductors, the CTE of the cured paste is preferably also low because the CTE of copper coils and wiring board materials is low. From this perspective, in one embodiment, the CTE of the cured paste is preferably 40 ppm / ℃ or less, more preferably 30 ppm / ℃ or less, and even more preferably 25 ppm / ℃ or less. When the CTE of the cured paste is 40 ppm / ℃ or less, the occurrence of defects such as warping, peeling at the interface with the surrounding materials, and cracking can be easily suppressed. Furthermore, the cured paste can be obtained by shaping the paste under vacuum conditions at 165°C and 2 MPa for 30 minutes, followed by heating to 180°C and maintaining the temperature for 1 hour. Pre-forming can also be performed before curing. Pre-forming can be carried out, for example, by heating the paste in a nitrogen atmosphere at 100°C for 1 hour, then heating to 150°C and maintaining the temperature for 20 minutes. The CTE value refers to the coefficient of linear thermal expansion in the region below the glass transition temperature, measured within a temperature range of 0°C to 250°C at a heating rate of 10°C / min.

[0023] The following is a detailed explanation of the components of the paste. (Powder containing metallic elements) Powder containing metallic elements may contain one or more metallic elements. For example, powder containing metallic elements may be at least one powder selected from the group consisting of elemental metals, alloys, and metal compounds. The metallic elements contained in powder containing metallic elements may be at least one selected from the group consisting of base metals, noble metals, transition metals, and rare earth elements. The metallic element may be at least one selected from the group consisting of iron (Fe), copper (Cu), titanium (Ti), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), niobium (Nb), aluminum (Al), tin (Sn), chromium (Cr), barium (Ba), strontium (Sr), lead (Pb), silver (Ag), ferroium (Pr), neodymium (Nd), samarium (Sm), and dysprosium (Dy).

[0024] In one embodiment, the powder containing the metallic element may be a single metallic element or an alloy containing two or more metallic elements. The alloy may contain at least one element selected from the group consisting of solid solutions, eutectics, and intermetallic compounds. For example, the alloy may be stainless steel such as Fe-Cr alloys and Fe-Ni-Cr alloys. Alternatively, it may be a copper alloy such as Cu-Sn alloys, Cu-Sn-P alloys, Cu-Ni alloys, and Cu-Be alloys.

[0025] In one embodiment, the powder containing the metal element may be a powder comprising a metal compound containing the previously exemplified metal element and an element other than the metal element. Examples of elements other than the metal element include at least one selected from the group consisting of carbon (C), oxygen (O), beryllium (Be), phosphorus (P), boron (B), and silicon (Si). The metal compound may be, for example, a metal oxide such as iron oxide. The metal compound may be a magnetic material formed by mixing and sintering metal elements such as cobalt, nickel, and manganese as the main component of a metal oxide. Ferrites may be an example of a magnetic material.

[0026] In one embodiment, the powder containing the metallic element may be a magnetic material powder. The magnetic material may be a soft magnetic alloy or a strong magnetic alloy. The magnetic material powder (hereinafter referred to as magnetic powder) may, for example, be at least one selected from the group consisting of Fe-Si alloys, Fe-Si-Al alloys (aluminum silicon iron), Fe-Ni alloys (permalloy), Fe-Cu-Ni alloys (permalloy), Fe-Co alloys (permendur), Fe-Cr-Si alloys (electromagnetic stainless steel), Nd-Fe-B alloys (rare earth magnets), Sm-Fe-N alloys (rare earth magnets), Al-Ni-Co alloys (AlNiCo magnets), and ferrites. The ferrite may, for example, be spinel ferrite, hexagonal ferrite, or garnet ferrite. Powder containing metallic elements may contain at least one selected from the group consisting of elemental, alloy, and compound metallic elements.

[0027] In a preferred embodiment, the powder containing the metallic element may include at least one powder selected from the group consisting of elemental Fe and Fe-based alloys. Fe-based alloys may be, for example, at least one selected from the group consisting of Fe-Si alloys, Fe-Si-Al alloys, Fe-Ni alloys, Fe-Cu-Ni alloys, Fe-Co alloys, Fe-Cr-Si alloys, Fe-Si-B alloys, and Fe-Si-BP-Nb-Cr alloys. The Fe-based alloy may be an amorphous Fe alloy. When the paste contains powder of at least one of elemental Fe and Fe-based alloys, a molded body with excellent magnetic properties can be easily obtained. In particular, when the paste contains Fe amorphous alloy powder, even better magnetic properties can be easily obtained.

[0028] Fe amorphous alloy powder is an amorphous powder obtained by rapidly cooling an alloy formed by melting Fe, the main component, together with other elements such as Si, at high temperature. It is also known as a metallic glass. Fe amorphous alloy powder can be manufactured according to methods well known in the art. Fe amorphous alloy powder is also available as a commercially available product. Examples include: Epson Atmix Co., Ltd.'s AW2-08 and KUAMET-6B2; Daido Special Steel Co., Ltd.'s DAPMS3, DAPMS7, DAPMSA10, DAPPB, DAPPC, DAPMKV49, DAP410L, DAP430L, and DAPHYB series; and Kobe Steel Co., Ltd.'s MH45D, MH28D, MH25D, and MH20D. One of these Fe amorphous alloy powders can be used, or a combination of two or more can be used.

[0029] The shape of the individual particles constituting the metal-containing powder is not particularly limited. Individual particles can be, for example, spherical, ellipsoidal, flat, plate-like, rod-like, or needle-like. From the viewpoint of the fill factor of the metal-containing particles in the hardened paste and the reduction of the paste's viscosity, spherical particles are preferred. From the viewpoint of the paste's thixotropic properties, a combination of flat and needle-like particles is also acceptable.

[0030] The average particle size of the metal-containing powder can be 0.05 μm to 200 μm, more preferably 0.5 μm to 100 μm, and even more preferably 1 μm to 50 μm. The "average particle size" described in this specification refers to the particle size at 50% (volume basis) of the cumulative value in the particle size distribution. As described later, in the case of powder coated with metal elements, the average particle size of the metal-containing powder, including the coating, can be within the range described.

[0031] In one embodiment, the paste may contain powders of various metal-containing elements with different average particle sizes (D50). For example, powders of two or more metal-containing elements with different average particle sizes may be used in combination. In this embodiment, the gaps formed between the metal-containing element powders with large average particle sizes can be easily filled with powders of other metal-containing elements with smaller average particle sizes. Therefore, the fill factor of the metal-containing element powder in the paste hardener can be easily increased. The particle size distribution of the metal-containing element powder can be calculated, for example, based on weight determination using sieving and analysis using measuring equipment such as laser diffraction and scattering devices.

[0032] In one embodiment, the entirety or a portion of the surface of the metal-containing powder may be coated with a surface treatment agent. The surface treatment agent may be, for example, inorganic oxides, phosphoric acid compounds and phosphate compounds, inorganic surface treatment agents such as silane coupling agents, organic surface treatment agents such as lignite wax, or resin curing agents. Coupling agents described later may also be used as surface treatment agents. In one embodiment, for example, the surface of the metallic magnetic powder, such as an Fe-based alloy, is preferably entirely or partially covered with an insulating material. Examples of insulating materials include silicon dioxide, titanium dioxide, calcium phosphate, lignite wax, and epoxy resin cured products.

[0033] In one embodiment, the powder containing metallic elements may include magnetic powder with its surface coated by an insulating material (hereinafter referred to as insulating coated magnetic powder). The paste containing the insulating coated magnetic powder can readily provide a cured material with excellent magnetic properties and insulation. The paste containing the insulating coated magnetic powder may contain two or more types of insulating coated magnetic powder, and the average particle sizes of the two or more types of insulating coated magnetic powder may be the same or different. In addition to containing the insulating coated magnetic powder, the paste containing the insulating coated magnetic powder may also contain magnetic powder without an insulating coating (hereinafter referred to as uncoated magnetic powder). The average particle size of the uncoated magnetic powder may be the same as or different from the average particle size of the insulating coated magnetic powder. For example, from the viewpoint of exhibiting insulation, the average particle size of the uncoated magnetic powder is preferably smaller than the average particle size of the insulating coated magnetic powder.

[0034] In one embodiment, the insulating-coated magnetic powder may be an Fe amorphous alloy powder with an insulating coating. For example, "KUAMET9A4" (Fe-Si-B alloy, D50: 20 μm, with insulating coating) manufactured by Epson Atmix Inc. and "SAP-2C" (Fe-Si-BP-Nb-Cr alloy, D50: 2.2 μm, with insulating coating) manufactured by Shin-Tung Industrial Co., Ltd. are preferred. In one embodiment, it is preferable to use both in combination. As a magnetic powder used in combination with the Fe amorphous alloy powder with an insulating coating, soft ferrite powder "BSN-125" (Ni-Zn alloy, D50: 10 μm, without insulating coating) manufactured by Uda Industrial Co., Ltd. is preferred.

[0035] The content of the metal-containing powder in the paste, based on the total mass of the paste, can be 70% by mass or more. Preferably, the content of the metal-containing powder is 80% by mass or more, more preferably 90% by mass or more, and even more preferably 94% by mass or more. When the content of the metal-containing powder is 70% by mass or more, it is easy to obtain molded articles with excellent properties derived from the metal-containing powder. For example, when the metal-containing powder is magnetic powder, an inductor with excellent magnetic properties can be formed, and excellent mechanical strength can also be obtained.

[0036] The content of the metal-containing powder in the paste is based on the total mass of the paste, and may be less than 100% by mass, or 99.9% by mass. From the viewpoint of paste flowability and mechanical strength of the molded body, the content of the metal-containing powder is preferably 99.8% by mass or less, more preferably 98% by mass or less, and even more preferably 96% by mass or less. In one embodiment, the content of the metal element powder in the paste is based on the total mass of the paste, preferably 80% to 99.9% or more, more preferably 90% to 99.8% or more, and even more preferably 94% to 96% by mass.

[0037] (Compounds containing epoxy groups) Compounds containing epoxy groups are compounds that have one or more epoxy groups within their molecules. They can be monomers, oligomers, or polymers, which are structural units formed by the polymerization of monomers. Compounds containing epoxy groups can function as adhesive resins that are hardened by heat treatment, allowing metal-containing powders to be bonded together. Examples of epoxy-containing compounds include oligomers and polymers having two or more epoxy groups within a molecule, generally known as epoxy resins. Another example of epoxy-containing compounds includes compounds having one or more epoxy groups within a molecule but not containing structural units formed by polymerization (hereinafter referred to as epoxy compounds). Such epoxy compounds are generally known as reactive diluents. Preferably, epoxy-containing compounds comprise at least one selected from the group consisting of epoxy resins and epoxy compounds.

[0038] Epoxy resins can be, for example, selected from biphenyl-type epoxy resins, stilbene-type epoxy resins, diphenylmethane-type epoxy resins, sulfur-containing epoxy resins, phenolic varnish-type epoxy resins, dicyclopentadiene-type epoxy resins, salicol-type epoxy resins, copolymer epoxy resins of naphthol and phenol, epoxides of aralkyl-type phenolic resins, bisphenol-type epoxy resins, glycidyl ether-type epoxy resins of alcohols, glycidyl ether-type epoxy resins of p-xylene and / or m-xylene-modified phenolic resins, and glycidyl ether-type epoxy resins of terpene-modified phenolic resins. The epoxy resin comprises at least one of the following groups: epoxy resin, cyclopentadiene-type epoxy resin, glycidyl ether-type epoxy resin of polycyclic aromatic ring modified phenolic resin, glycidyl ether-type epoxy resin of phenolic resin containing naphthalene ring, glycidyl ester-type epoxy resin, glycidyl or methylglycidyl type epoxy resin, alicyclic epoxy resin, halogenated phenolic varnish-type epoxy resin, hydroquinone-type epoxy resin, trimethylolpropane-type epoxy resin, and linear aliphatic epoxy resin obtained by oxidizing olefin bonds with peroxy acids such as peracetic acid. The epoxy resin may be in liquid, semi-solid, or solid form, or a mixture thereof may exist.

[0039] The molecular weight of the epoxy compound is preferably 100 or higher, more preferably 150 or higher, and even more preferably 200 or higher. When using an epoxy compound with a molecular weight of 100 or higher, volatilization before reaction with the hardener can be suppressed by setting appropriate curing conditions. In addition, a lower molecular weight can reduce the occurrence of undesirable conditions such as short distances between crosslinking points after reaction, which can lead to easy cracking of the cured product. On the other hand, the molecular weight of the epoxy compound is preferably 700 or less, more preferably 500 or less, and even more preferably 300 or less. When using an epoxy compound with a molecular weight of 700 or less, a viscosity suitable for use as a diluent can be easily obtained.

[0040] In one embodiment, the molecular weight of the epoxy compound is preferably in the range of 100 to 700, more preferably in the range of 150 to 500, and even more preferably in the range of 200 to 300. When using an epoxy compound with a molecular weight within this range, adjusting the viscosity of the paste becomes easier. Unlike components such as organic solvents that volatilize upon heating, the epoxy compound undergoes curing upon heating and enters the cured product. Therefore, using an epoxy compound facilitates adjusting the viscosity of the paste and, on the other hand, helps to prevent a decrease in the properties of the cured product.

[0041] Epoxy compounds may contain one or more epoxy groups within their molecules. For example, an epoxy compound may be at least one selected from the group consisting of n-butyl glycidyl ether, neodecanoic acid glycidyl ether, styrene oxide, ethylhexyl glycidyl ether, phenyl glycidyl ether, butylphenyl glycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, diethylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether. The epoxy compound is preferably thoroughly purified to have a low content of ionic impurities. For example, in the epoxy compound, ionic impurities such as free Na ions and free Cl ions are preferably below 500 ppm.

[0042] The epoxy equivalent of the epoxy-containing compound is preferably 80 g / eq to 350 g / eq, more preferably 100 g / eq to 300 g / eq, and even more preferably 120 g / eq to 250 g / eq. When the epoxy equivalent is within the aforementioned range, the viscosity of the epoxy-containing compound itself decreases, thus making it easier to adjust the viscosity of the paste.

[0043] The epoxy-containing compound is preferably one that is liquid at 25°C. In this specification, "liquid at 25°C" means that the viscosity of the epoxy-containing compound at 25°C is 200 Pa·s or less. The viscosity is measured using a Type E viscometer at the following conditions: temperature: 25°C, rotor: SPP, rotation speed: 2.5 rpm. For example, a Type E viscometer such as the TV-33 viscometer manufactured by Toki Industries, Ltd. can be used.

[0044] When using epoxy-containing compounds that are liquid at 25°C, the amount of volatile components such as organic solvents typically used to achieve flowability can be significantly reduced. In one embodiment, a paste without organic solvents can also be formed. Furthermore, suitable flowability for a paste can be ensured, while easily increasing the content of metal-containing powders. From these perspectives, in one embodiment, the viscosity of the epoxy-containing compound is preferably 100 Pa·s or less, more preferably 50 Pa·s or less, and even more preferably 10 Pa·s or less. The viscosity of the epoxy-containing compound exceeds 0 Pa·s, and can be 0.001 Pa·s or more, or 0.01 Pa·s or more.

[0045] In the epoxy-containing compound, from the viewpoint of adjusting the paste viscosity, the viscosity of the epoxy compound is preferably lower than that of the liquid epoxy resin. The viscosity of the epoxy compound is preferably 1 Pa·s or less, more preferably 0.5 Pa·s or less, and even more preferably 0.1 Pa·s or less. The viscosity of the epoxy compound exceeds 0 Pa·s, and can be 0.001 Pa·s or more, or 0.01 Pa·s or more.

[0046] The epoxy-containing compound that is liquid at 25°C may include at least one selected from the group consisting of epoxy resins that are liquid at 25°C (hereinafter referred to as liquid epoxy resins) and epoxy compounds that are liquid at 25°C. Based on the total mass of the epoxy-containing compound, the content of the liquid epoxy resin is preferably 50% by mass or more, more preferably 70% by mass or more, more preferably 90% by mass or more, and may also be 100% by mass. However, the content of the liquid epoxy resin is not limited to the range described above.

[0047] The liquid epoxy resin may, for example, comprise at least one liquid epoxy resin selected from bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD ​​type epoxy resin, bisphenol S type epoxy resin, naphthol type epoxy resin, hydrogenated bisphenol A type epoxy resin, and amino glycidyl ether type epoxy resin. Preferably, at least one of liquid bisphenol A type epoxy resin, liquid bisphenol F type epoxy resin, and liquid amino glycidyl ether type epoxy resin is used.

[0048] Liquid epoxy compounds are also available as commercially available products. For example, liquid bisphenol A type epoxy resin and liquid bisphenol F type epoxy resin are sold by Nippon Steel Chemical Co., Ltd. For example, as a liquid bisphenol F type epoxy resin, the product name "YDF-8170C" (epoxy equivalent 165, viscosity 1,000 mPa·s~1,500 mPa·s) is preferred. As epoxy compounds, the series of Adeka glycyrol (product name) manufactured by ADEKA Co., Ltd. can be cited. For example, the product name "Adeka glycyrol ED-503G" (epoxy equivalent 135, viscosity 15 mPa·s) is preferred.

[0049] In addition to the epoxy-containing compound, the paste may also contain other resins. These other resins may include at least one selected from the group consisting of thermosetting resins (excluding epoxy resins) and thermoplastic resins. The thermosetting resin may be, for example, at least one selected from the group consisting of phenolic resins, acrylic resins, polyimide resins, and polyamide-imide resins. In cases where phenolic resins are used in addition to those containing epoxy groups, the phenolic resin may also function as a curing agent for the epoxy-containing compound. Thermoplastic resins may be, for example, at least one selected from the group consisting of acrylic resins, polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate. In addition to containing epoxy-containing compounds, the resin composition may also include silicone resins.

[0050] When the paste contains resins other than epoxy-containing compounds, the content of other resins is preferably adjusted within a range that does not reduce the effect brought about by the epoxy-containing compounds. For example, the content of other resins, based on the total mass of the resins in the paste, is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less. However, the content of other resins is not limited to the ranges described above. In one embodiment, the mixing amount can be adjusted so that the viscosity of the mixture of the epoxy-containing compound and other resins is below 50 Pa·s at 25°C. The viscosity is a value obtained using an E-type viscometer under the following conditions: temperature: 25°C, rotor: conical plate, cone angle: 1°34', rotation speed: 2.5 rpm. For example, a TV-33 viscometer manufactured by Toki Industries, Ltd. can be used as an E-type viscometer.

[0051] (hardener) There are no particular limitations on the curing agent, as long as it is a compound that imparts appropriate viscosity to the paste and can react with the epoxy groups of epoxy-containing compounds to form a cured product. Well-known curing agents commonly used as curing agents for epoxy resins can be used. Examples of usable curing agents include phenolic curing agents, acid anhydride curing agents, and amine curing agents.

[0052] Curing agents are classified into curing agents that cure epoxy resins within a temperature range from low to room temperature, and heat-curing curing agents that cure epoxy resins with heating. Examples of curing agents that cure epoxy resins within a temperature range from low to room temperature include aliphatic polyamines, polyaminoamides, and polythiols. Examples of heat-curing curing agents include aromatic polyamines, acid anhydrides, phenolic varnish resins, and dicyandiamide (DICY). When using a curing agent that cures epoxy resin in a temperature range from low to room temperature, the cured epoxy resin tends to have a low glass transition point and be soft. Consequently, the molded body formed from the paste also tends to become soft. From the viewpoint of improving the heat resistance and mechanical strength of the molded body, the curing agent preferably includes a heat-curing type.

[0053] In heat-curing curing agents, from the viewpoint of reducing the viscosity of the paste, it is preferable to use a curing agent that is liquid at 25°C. As a liquid curing agent, for example, at least one selected from the group consisting of aliphatic or aromatic polyamines, amine curing agents such as aliphatic or aromatic amines, polythiols, acid anhydrides, and imidazole curing agents can be used. If the increase in paste viscosity can be suppressed, a hardener that is solid at 25°C can be used, or a combination of a liquid hardener and a solid hardener can be used. Examples of solid hardeners include dicyandiamine, tertiary amines, imidazole-based hardeners, and imidazoline-based hardeners. The exemplified solid hardeners are multifunctional or act as catalysts, thus allowing them to function effectively even in small quantities.

[0054] In one embodiment, the curing agent preferably comprises at least one selected from the group consisting of amine-based curing agents, imidazole-based curing agents, and imidazoline-based curing agents. More preferably, the curing agent comprises at least one selected from the group consisting of amine-based curing agents and imidazole-based curing agents. In one embodiment, the curing agent preferably comprises at least an amine-based curing agent. Amine-based curing agents (more specifically tertiary amines), imidazole-based curing agents, and imidazoline-based curing agents can also be used as curing accelerators in combination with other curing agents.

[0055] Amine curing agents can be compounds having at least two amino groups within a molecule. Amine curing agents include at least one selected from the group consisting of aliphatic amines and aromatic amines. As an aliphatic amine, it can be a compound with a straight-chain structure or a cyclic structure. Examples include: diethylenetriamine, triethylenetetramine, n-propylamine, 2-hydroxyethylaminopropylamine, cyclohexylamine, methylcyclohexylamine, isophorone diamine, 4,4'-diamino-dicyclohexylmethane, and diazabicycloundecene. As an aromatic amine, it can be a compound in which the amine is substituted on an aromatic compound, particularly a compound having a structure in which the hydrogen of the benzene ring is substituted with an amino group. Examples include: benzyl dimethylamine, tri-dimethylaminomethylphenol, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 2-methylaniline, diaminodiphenylamine, polyamide, amine compounds represented by formula (1) below, and amine compounds represented by formula (2) below. While there are no particular limitations, when using amine-based curing agents, it tends to be easier to adjust viscosity and the rate of decrease in thermal weight. In particular, when using aromatic amines, it tends to be even easier to adjust viscosity and the rate of decrease in thermal weight.

[0056] Imidazole-based curing agents are compounds with an imidazole skeleton, and can be imidazole compounds in which hydrogen atoms in the molecule are substituted with substituents. In one embodiment, the imidazole-based curing agent can be a compound with an imidazole skeleton, such as an alkyl-substituted imidazole. Examples of imidazole-based curing agents include imidazole, 2-methylimidazole, 2-ethylimidazole, and 2-isopropylimidazole. In one embodiment, "Curezol 2E4MZ" (2-ethyl-4-methylimidazole) manufactured by Shikoku Chemical Industries, Ltd. is preferably used. Imidazoline curing agents are compounds with an imidazoline skeleton, which can be imidazoline compounds in which hydrogen atoms in the molecule are substituted with substituents. They can be alkyl-substituted imidazolines or other compounds with an imidazoline skeleton. Examples of imidazoline curing agents include: imidazoline, 2-methylimidazoline, and 2-ethylimidazoline.

[0057] From the viewpoint of suitability for liquid epoxy resins and storage stability, the curing agent preferably contains at least an aromatic amine. The aromatic ring of the aromatic amine may also have substituents other than an amino group. For example, it may have an alkyl group with 1 to 5 carbon atoms, or an alkyl group with 1 or 3 carbon atoms. The number of aromatic rings in the aromatic amine may be one or more. When the number of aromatic rings is two or more, the aromatic rings may be linked to each other by single bonds or by linking groups such as alkyl groups.

[0058] In one embodiment, from the viewpoint of the viscosity of the paste, the hardener is preferably a liquid aromatic amine. For example, at least one selected from the group consisting of compounds represented by formula (1) and compounds represented by formula (2) may be used. Among the compounds represented by formula (2), compounds in which the methyl group is replaced by an ethyl group may also be used. In one embodiment, the compound represented by formula (1) may preferably be used.

[0059] [Chemistry 1]

[0060] [Chemistry 2]

[0061] Liquid aromatic amines that can be used as hardeners are also available as commercial products. For example, products manufactured by Mitsubishi Chemical Co., Ltd. with the product name "Grade: JER Cure WA" (the compound represented by formula (1), 2,6-diamino-3,5-diethyltoluene) and products manufactured by Nippon Kayaku Co., Ltd. with the product name "Kayahard AA" (3,3'-diethyl-4,4'-diaminodiphenylmethane) are examples.

[0062] While not particularly limited, when using at least one of the aromatic amines and imidazole compounds as a curing agent, there is a tendency to obtain a curing product with a lower CTE compared to curing products obtained using other curing agents. In this regard, in one embodiment, the curing agent is preferably at least one selected from the group consisting of 2,6-diamino-3,5-diethyltoluene, 3,3'-dimethyl (or diethyl)-4,4'-diaminodiphenylmethane, and 2-ethyl-4-methylimidazole.

[0063] There is no particular limitation on the content of the hardener in the paste. It can be set by considering the ratio of the equivalent number of epoxy groups in epoxy-containing compounds such as epoxy resin to the equivalent number of active groups in the hardener. For example, the ratio of the hardener to the equivalent number of epoxy groups in the epoxy-containing compound is preferably 0.5 to 1.5 equivalents, more preferably 0.9 to 1.4 equivalents, and even more preferably 1.0 to 1.2 equivalents.

[0064] When the ratio of active groups in the hardener is 0.5 equivalents or more, the decrease in the amount of OH groups per unit weight of the epoxy resin after heat curing and the resulting decrease in the curing rate of the epoxy resin can be suppressed. Furthermore, the decrease in the glass transition temperature and the decrease in the elastic modulus of the cured product can be suppressed. Moreover, the decrease in the insulation reliability of the cured product due to unreacted resin components in the adhesive resin can be suppressed. On the other hand, when the ratio of active groups in the hardener is 1.5 equivalents or less, the decrease in mechanical strength of the molded article formed by heat curing from the paste can be suppressed. Furthermore, the decrease in the insulation of the cured article due to unreacted hardener can be suppressed. In the above embodiments, the ratio of active groups in the hardener is not limited, and the effects of the present invention can be obtained even if it is outside the stated range.

[0065] The paste may further include curing accelerators as needed. In one embodiment, the paste may contain a powder containing a metal element, an epoxy-containing compound, a curing agent, and a curing accelerator. In other embodiments, in addition to the aforementioned components, the paste may also contain additives such as coupling agents and flame retardants. Detailed descriptions follow.

[0066] (hardening accelerator) The curing accelerator is not limited to any compound that can promote the curing reaction between the epoxy resin and the curing agent. Examples of curing accelerators include: tertiary amines, imidazole-based curing accelerators, imidazole-linen-based curing accelerators, and phosphorus compounds. Compounds previously exemplified as imidazole-based and imidazole-linen-based curing accelerators can also be used. In the case of liquid curing agents, it is preferable to use a combination of curing accelerators when using liquid acid anhydrides. The paste may contain one or more curing accelerators. Using curing accelerators can improve the mechanical strength of the molded body formed from the paste and also facilitates a decrease in the curing temperature of the paste.

[0067] The amount of curing accelerator is not particularly limited, as long as it is sufficient to achieve the curing accelerating effect. However, from the viewpoint of improving the curing properties and flowability of the paste when it absorbs moisture, the amount of curing accelerator is preferably 0.001 parts by weight or more, relative to 100 parts by weight of the total epoxy resin and curing agent. More preferably, the amount of curing accelerator is 0.01 parts by weight or more, and even more preferably, 0.1 parts by weight or more. On the other hand, the amount of curing accelerator is preferably 5 parts by weight or less, more preferably 4 parts by weight or less, and even more preferably 3 parts by weight or less.

[0068] When the amount of the curing accelerator is 0.001 parts by mass or more, a sufficient curing accelerator effect can be easily obtained. When the amount of the curing accelerator is 5 parts by mass or less, excellent storage stability can be easily obtained in the paste. Furthermore, the effects of this invention can be obtained even when the amount and content of the curing accelerator are outside the aforementioned ranges.

[0069] (Coupling agent) When using a coupling agent, it is easy to improve the dispersibility of the metal-containing powder in the paste and to control the paste viscosity. Furthermore, it is easy to improve the adhesion between the adhesive resin and the metal-containing powder. Consequently, it is easy to improve the adhesion, flexibility, and mechanical strength of the hardened product formed from the paste relative to the substrate. The coupling agent may be, for example, at least one selected from the group consisting of silane compounds (silane coupling agents), titanium compounds, aluminum compounds (aluminum chelates), and aluminum / zirconium compounds. The silane coupling agent may be, for example, at least one selected from the group consisting of epoxy silanes, mercaptosilanes, amino silanes, alkyl silanes, ureosilanes, anhydride silanes, and vinyl silanes. Particularly preferred are aminophenyl silane coupling agents. The paste may contain at least one of the aforementioned coupling agents. The paste may also contain two or more of the aforementioned coupling agents.

[0070] (Flame retardant) For environmental safety, recyclability, processability, and low cost, the paste may contain flame retardants. Flame retardants may be, for example, at least one selected from the group consisting of brominated flame retardants, phosphorus-based flame retardants, hydrated metal compound flame retardants, silicone-based flame retardants, nitrogen-containing compounds, hindered amine compounds, organometallic compounds, and aromatic engineering plastics. The paste may contain one or more of the flame retardants described above.

[0071] The adhesive required in the described embodiment may include an organic solvent. The organic solvent is not particularly limited. For example, an organic solvent capable of dissolving adhesive resins can be used. 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 a workability perspective, the organic solvent is preferably a liquid at room temperature (25°C). From a workability perspective, the boiling point of the organic solvent is preferably above 50°C and below 160°C.

[0072] On the other hand, when the paste contains organic solvents, a drying step is required after coating, generating an environmental burden due to volatile components. Furthermore, in the case of organic solvents with boiling points lower than the curing temperature, volatilization may occur during heating, creating voids in the cured paste. Conversely, in the case of organic solvents with boiling points higher than the curing temperature, the organic solvent may be difficult to volatilize during heating, remaining directly in the paste and degrading the properties of the cured product. For example, if voids exist in the cured product, properties such as mechanical strength and magnetic properties are prone to decrease. In particular, if organic solvents remain in the cured product, ionic components are easily mobile, leading to a decrease in insulation properties such as insulation resistance and insulation reliability.

[0073] In view of these points, when the paste of the described embodiment contains organic solvents, the content of such solvents, based on the total mass of the paste, is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. Ideally, the paste should not contain organic solvents. In this specification, "not substantially containing" means that no organic solvents are intentionally added to the paste. Therefore, the paste may, for example, contain organic solvents used in the manufacture of the resin and remaining in the resin.

[0074] The paste described in this embodiment can be adjusted to a suitable viscosity without using volatile components such as organic solvents, thus exhibiting fluidity. In one embodiment, from the viewpoint of coatability, the viscosity of the paste is preferably 1 Pa·s or higher, more preferably 10 Pa·s or higher, and even more preferably 100 Pa·s or higher. By adjusting the viscosity to 1 Pa·s or higher, liquid dripping after coating can be suppressed, and the collapse of the printed pattern shape can be easily prevented. In addition, the sedimentation of metal-containing powders in the paste can be suppressed, and the decrease in coatability caused by time after paste stirring can be easily improved. On the other hand, the viscosity of the paste is preferably below 600 Pa·s, more preferably below 400 Pa·s, and even more preferably below 200 Pa·s. By adjusting the viscosity to below 600 Pa·s, the paste becomes fluid, and good coatability can be easily obtained.

[0075] In one embodiment, when the paste is applied to screen printing, the viscosity of the paste is preferably 10 Pa·s to 400 Pa·s, more preferably 50 Pa·s to 300 Pa·s, and even more preferably 100 Pa·s to 250 Pa·s. When the viscosity is adjusted to the aforementioned range, the occurrence of the defect that the paste cannot pass through the opening of the screen during screen printing can be suppressed. The viscosity of the paste can be freely adjusted according to the structure and properties of the epoxy-containing compound, the structure and properties of the hardener, and the combination and proportion of these, as well as the structure and proportion of additives such as hardening accelerators and coupling agents. The paste may contain additives such as viscosity modifiers, thixotropic agents, and dispersing stabilizers.

[0076] Even with an increased content of metal-containing powder, the viscosity of the paste described in this embodiment can be easily adjusted to the preferred range without substantially using organic solvents. For example, a paste with a heat loss rate of less than 5% when heated to 180°C can suppress the performance degradation of the cured product caused by volatile components such as organic solvents, and can easily provide molded articles with excellent properties such as insulation.

[0077] (Preparation method of paste) The paste described in this embodiment can be prepared, for example, by uniformly mixing and kneading a powder containing a metal element, an adhesive resin containing at least an epoxy group compound, and a hardener. The mixing and kneading method is not particularly limited; for example, stirring blades, a rotary mixer, a roller mill, a disc mill, and a ball mill can be used.

[0078] (formed body) When a molded article is formed from the paste of the described embodiment, a B-type molded article can be produced by advancing the hardening of the paste through heat treatment. Further heat treatment of the B-type molded article can fully harden the resin in the molded article. Alternatively, a C-type molded article can also be rapidly produced from the paste. The electromagnetic properties or thermal conductivity of the molded body can be freely controlled according to the composition or combination of powders containing metal elements in the paste, and the molded body can be used in various industrial products or their raw materials. Industrial products manufactured using pastes include, for example, automobiles, medical devices, electronic devices, electrical equipment, information and communication equipment, home appliances, audio equipment, and general industrial equipment. For instance, a molded body (e.g., a sheet) formed from a paste containing magnetic powders such as Fe-Si-Cr alloys or ferrites can be used as a raw material (e.g., a magnetic core) for inductors such as electromagnetic interference (EMI) filters. A paste containing powders of permanent magnets can be used as a raw material for bonding magnets. A molded body (e.g., a sheet) formed from a paste containing iron and copper powders can be used as an electromagnetic wave shield. In one embodiment, the molded body (cured material) formed using the paste has a low CTE of 40 ppm / °C or less, thus making it more suitable for inductor applications. For example, when a paste is used and a cured material is applied to peripheral materials with low CTE, such as wiring board materials, it is easy to suppress defects such as warping, peeling at the interface with peripheral materials, and cracking caused by poor CTE, thereby improving reliability. [Example]

[0079] The present invention will now be described in more detail by way of examples and comparative examples, but the present invention is not limited to these examples in any way.

[0080] <Example 1-1> (1) Preparation of adhesive resin Weigh 40.00 g of Adeka glycyrol ED-503G liquid epoxy resin manufactured by ADEKA Corporation and 13.33 g of JER Cure WA (liquid aromatic amine) curing agent manufactured by Mitsubishi Chemical Corporation, and place these raw materials into a 250 ml ointment container. An adhesive was obtained by mixing all the raw materials in the ointment container using a rotary mixer. The rotary mixer used was an "ARE-500" manufactured by Thinky Corporation. The mixing was performed with the rotary mixer's rotation speed set to 2000 rpm for 1 minute. After stirring the adhesive resin with a spatula, the rotary mixer's rotation speed was again set to 2000 rpm for 1 minute to obtain adhesive resin I. (2) Preparation of paste 2.26 g of the adhesive resin I, 60.00 g of the iron amorphous alloy powder "KUAMET 9A4" (an insulating Fe-Si-B alloy, D50: 20 μm) manufactured by Epson Atmix Co., Ltd., which is a powder containing metal elements (hereinafter referred to as metal powder), 13.17 g of the metallic glass magnetic powder "SAP-2C" (an insulating Fe-Si-BP-Nb-Cr alloy, D50: 2.2 μm) manufactured by Shin-Tung Industrial Co., Ltd., and 0.22 g of the silane coupling agent "KBM-573" manufactured by Shin-Etsu Silicon Co., Ltd., were weighed and placed into a 50 ml ointment container. The ingredients in the ointment container were stirred using a rotary mixer at a speed of 2000 rpm for 45 seconds. After stirring the ingredients in the ointment container with a spatula, the mixture was stirred twice more using a rotary mixer at a speed of 2000 rpm for 45 seconds, thereby preparing paste 1-1. The metal powder content in the obtained paste 1-1 is 97% by mass. The metal powder content is calculated by setting the mass of the non-volatile components (solid components) other than the metal powder in the paste as "M" and the mass of the metal powder as "m", and then calculating the value based on m / (m+M).

[0081] <Examples 1-2> Except for changing the amount of adhesive resin I to 3.45 g, pastes 1-2 were prepared in the same manner as in Example 1-1. The metal powder content in the obtained pastes 1-2 was 95% by mass.

[0082] <Examples 1-3~Examples 1-6> Except for changing the amount of adhesive resin I, all pastes 1-3 to 1-6 with the metal powder content shown in Table 1 were prepared in the same manner as in Examples 1-1.

[0083] <Example 2-1> (1) Preparation of adhesive resin Weigh 40.00 g of Nippon Steel Chemicals' liquid epoxy resin "YDF-8170C" and 11.13 g of Mitsubishi Chemical Corporation's curing agent "jER Cure WA" (liquid aromatic amine). Place these as raw materials into a 250 ml ointment container. Adhesive resin was obtained by mixing all the raw materials in the ointment container using a rotary mixer. The rotary mixer used was an "ARE-500" manufactured by Thinky Corporation. The mixing was performed with the rotary mixer's rotation speed set to 2000 rpm for 1 minute. After stirring the adhesive resin with a spatula, the rotary mixer's rotation speed was again set to 2000 rpm for 1 minute to obtain adhesive resin II. (2) Preparation of paste 5.51 g of adhesive resin II, 60.00 g of Epson Atmix Co., Ltd.'s iron amorphous alloy powder "KUAMET 9A4" (an insulating Fe-Si-B alloy, D50: 20 μm) as metal powder, 13.17 g of Shin-Tung Industrial Co., Ltd.'s metallic glass magnetic powder "SAP-2C" (an insulating Fe-Si-BP-Nb-Cr alloy, D50: 2.2 μm) as metal powder, and 0.22 g of Shin-Etsu Silicon Co., Ltd.'s silane coupling agent "KBM-573" were weighed and placed into a 50 ml ointment container. The ingredients in the ointment container were mixed using a rotary mixer at 2000 rpm for 45 seconds. Then, the ingredients in the ointment container were stirred with a spatula, and then stirred twice more using the rotary mixer at 2000 rpm for 45 seconds to prepare paste 2-1. The metal powder content in the obtained paste 2-1 is 93% by mass. The metal powder content is calculated by setting the mass of the non-volatile components (solid components) other than the metal powder in the paste as "M" and the mass of the metal powder as "m", and then calculating the value based on m / (m+M).

[0084] <Examples 2-2~Examples 2-4> Except for changing the amount of adhesive resin II, all pastes 2-2 to 2-4 with the metal powder content shown in Table 1 were prepared in the same manner as in Example 2-1.

[0085] <Example 3> Weigh 3 g of adhesive resin I prepared in the same manner as in Example 1-1 and 7 g of adhesive resin II prepared in the same manner as in Example 2-1. Place these into an ointment container and mix them using a rotary mixer in the same manner as in Example 1-1 to obtain adhesive resins I-II. Subsequently, except for the use of adhesive resins I-II, paste 3 with a metal powder content of 94% by mass was obtained in the same manner as in Example 2-1.

[0086] <Example 4> 0.86 g of solid epoxy resin "NC-3000-H" manufactured by Nippon Kayaku Co., Ltd. and 0.14 g of curing agent "jER Cure WA" (liquid aromatic amine) manufactured by Mitsubishi Chemical Co., Ltd. were weighed separately. These were placed into an ointment container and mixed using a rotary mixer in the same manner as in Example 1-1 to obtain adhesive resin III. Next, 7 g of adhesive resin I prepared in the same manner as in Example 1 and 9 g of the previously prepared adhesive resin III were weighed. These were placed into an ointment container and mixed using a rotary mixer in the same manner as in Examples 1-1, thereby obtaining adhesive resins I-III. Furthermore, except for the use of adhesive resins I-III, paste 4 with a metal powder content of 94% by mass was obtained in the same manner as in Example 2-1.

[0087] <Example 5> 28.00 g of Nippon Steel Chemicals' liquid epoxy resin "YDF-8170C" and 12.00 g of Adeka glycyrol ED-503G's liquid epoxy resin "Adeka glycyrol" were weighed into 100 ml ointment containers. The mixture was stirred at 2000 rpm for 2 minutes using a rotary mixer. After stirring the ingredients in the ointment container with a spatula, it was stirred again at 2000 rpm for 2 minutes using a rotary mixer. 2.00 g of Shikoku Chemicals' liquid imidazole hardener "Curezol 2E4MZ" was added, and the mixture was stirred at 2000 rpm for 2 minutes using a rotary mixer to prepare adhesive resin IV. Subsequently, except for the use of the previously obtained adhesive resin IV, paste 5 with a metal powder content of 94% by mass was obtained in the same manner as in Example 2-1.

[0088] <Example 6> In the preparation of adhesive resin IV in Example 5, the hardener was changed to 13.08 g of 4,4'-diaminodiphenylmethane manufactured by Tokyo Chemical Industry Co., Ltd., thereby preparing adhesive resin V. Subsequently, except for the use of the previously obtained adhesive resin V, paste 6 with a metal powder content of 94% by mass was obtained in the same manner as in Example 2-1.

[0089] <Example 7> In the preparation of adhesive resin IV in Example 5, the hardener was changed to 6.44 g of triethylenetetramine manufactured by Tokyo Chemical Industry Co., Ltd., thereby preparing adhesive resin VI. Subsequently, except for the use of the previously obtained adhesive resin VI, paste 7 with a metal powder content of 94% by mass was obtained in the same manner as in Example 2-1.

[0090] <Example 8> In the preparation of adhesive resin IV in Example 5, the hardener was changed to 10.82 g of isophorone diamine manufactured by Tokyo Chemical Industry Co., Ltd., thereby preparing adhesive resin VII. Subsequently, except for the use of the previously obtained adhesive resin VII, paste 8 with a metal powder content of 94% by mass was obtained in the same manner as in Example 2-1.

[0091] <Example 9> In the preparation of adhesive resin IV in Example 5, the hardener was changed to 2.00 g of tri-dimethylaminomethylphenol manufactured by Tokyo Chemical Industry Co., Ltd., thereby preparing adhesive resin VIII. Subsequently, except for the use of the previously obtained adhesive resin VIII, paste 9 with a metal powder content of 94% by mass was obtained in the same manner as in Example 2-1.

[0092] <Example 10> In the preparation of adhesive resin IV in Example 5, the hardener was changed to 8.97 g of m-phenylenediamine manufactured by Tokyo Chemical Industry Co., Ltd., thereby preparing adhesive resin IX. Subsequently, except for the use of the previously obtained adhesive resin IX, paste 10 with a metal powder content of 94% by mass was obtained in the same manner as in Example 2-1.

[0093] <Example 11> In Example 5, 60.00 g of "KUAMET 9A4" (an Fe-Si-B alloy with an insulating coating, D50: 20 μm) manufactured by Epson Atmix Inc. as the metal powder and 13.17 g of "BSN-125" (a Ni-Zn soft ferrite powder without an insulating coating, D50: 10 μm) manufactured by Toda Kogyo Inc. were used. Otherwise, paste 11 with a metal powder content of 94% by mass was obtained in the same manner as in Example 5.

[0094] <Comparative Example 1> (1) Preparation of adhesive resin X Weigh out 71.37 g of "Teisan Resin HTR-860-P3" (a cyclohexanone solution with an acrylic resin content of 12.6% by weight) manufactured by Nagase Chemtex Co., Ltd., 15.00 g of "NC-3000-H" solid epoxy resin manufactured by Nippon Kayaku Co., Ltd., 6.00 g of "HP850N" (phenolic varnish resin) curing agent manufactured by Showa Denko Materials Co., Ltd. (formerly Hitachi Chemical Co., Ltd.), 0.15 g of "2E4MZ" curing accelerator manufactured by Shikoku Chemical Industry Co., Ltd., and 21.30 g of "cyclohexanone" manufactured by Fujifilm and Wako Pure Chemical Co., Ltd. Place these raw materials into a 250 ml ointment container. Adhesive resin varnish X was obtained by mixing all the raw materials in the ointment container using a rotary mixer. The rotary mixer used was an "ARE-500" manufactured by Thinky Corporation. The mixing was performed twice, with the rotary mixer set to a revolution speed of 2000 rpm and a duration of 20 minutes. The NV (non-volatile content) of the obtained adhesive resin varnish X was 26.49% by mass. The adhesive resin varnish X, excluding organic solvents (such as cyclohexanone), consists of adhesive resin X. (2) Preparation of paste 8.54 g of adhesive resin varnish X, 60.00 g of "KUAMET 9A4" (an insulating Fe-Si-B alloy with a 20 μm D50) manufactured by Epson Atmix Co., Ltd., as a metal powder, 13.17 g of "SAP-2C" (an insulating Fe-Si-BP-Nb-Cr alloy with a 2.2 μm D50) manufactured by Shin-Tung Industrial Co., Ltd., and 0.22 g of "KBM-573" (a silane coupling agent manufactured by Shin-Etsu Silicone Co., Ltd.) were weighed separately and placed into a 50 ml ointment container. The ingredients in the ointment container were mixed using a rotary mixer at 2000 rpm for 45 seconds. Then, the ingredients in the ointment container were stirred using a spatula. Next, the mixture was stirred twice more using the rotary mixer at 2000 rpm for 45 seconds each time, thereby preparing paste 12. The metal powder content, based on the total solids content of the obtained paste 12, is 97% by mass. The metal powder content is calculated by setting the mass of the non-volatile components (solids) other than the metal powder contained in the paste 12 as "M" and the mass of the metal powder as "m", and then calculating the value based on m / (m+M).

[0095] <Comparative Example 2> Except for changing the amount of adhesive resin varnish X, paste 13 containing 84% by mass of metal powder was prepared in the same manner as in Comparative Example 1.

[0096] <2> Evaluation of the properties of paste Various properties of the pastes obtained in the examples and comparative examples were evaluated according to the methods described below. <Viscosity Evaluation> For each paste obtained in the examples and comparative examples, the viscosity was measured using a TV-33 viscometer manufactured by Toki Industries, Ltd., at a temperature of 25°C, a rotor of SPP, and a rotation speed of 2.5 rpm. The measured values ​​were evaluated according to the following criteria. The results are shown in Table 1. In the case of envisioned screen printing, good coatability can be easily obtained if the coating is divided into 2, 3, and 4. Among these, 3 is the best. (Viscosity distinction) 1: Viscosity less than 1 Pa·s 2: Viscosity above 1 Pa·s and below 10 Pa·s 3: Viscosity above 10 Pa·s and below 400 Pa·s 4: Viscosity above 400 Pa·s and below 600 Pa·s 5: Viscosity exceeding 600 Pa·s

[0097] <Reduction in thermal weight> The calorific value loss of the paste was measured using a differential thermogravimetric analysis (TG-DSC) device, "NEXTA STA200RV," manufactured by Hitachi High-Tech Science Co., Ltd. Specifically, in a nitrogen atmosphere, 15 mg of the paste was heated from 25°C to 100°C at a rate of 10°C / min and held at 100°C for 1 hour. Then, the temperature was increased from 100°C to 180°C at a rate of 3°C / min, and the calorific value loss after simultaneous heating at 180°C for 1 hour was measured. The heat loss rate is calculated as the percentage (reduction rate) of the weight reduction of the paste after heating to 180°C, based on the weight of the paste at 25°C (before heating) as 100%. The content of volatile components in the paste can be evaluated based on the heat loss rate. Regarding the heat loss rate of the paste, a low content of volatile components in the paste is considered good if the following criteria "AA", "A", or "B" are met. The results are shown in Table 1. (Evaluation Criteria) AA: The rate of decrease in thermal weight is greater than 0% and less than 1.0%. A: The rate of decrease in thermal weight is greater than 1.0% and less than 3.0%. B: The rate of decrease in thermal weight is greater than 3.0% and less than 5.0%. C: The rate of decrease in thermal weight is greater than 5.0%.

[0098] <Insulation Resistance> Eight sheets of polyimide tape (125 μm thick) manufactured by Uniontape were overlapped and attached to copper foil to create a 7 cm square quadrilateral frame. Paste was poured into the frame, and the paste layer was heated at 100°C in a nitrogen atmosphere for 1 hour. Next, the temperature was raised to 150°C and maintained for 20 minutes. Next, other copper foils are covered onto the paste layer, and a vacuum press (manufactured by Igen Manufacturing Co., Ltd., manual hydraulic vacuum heating press, 1A31) is used to maintain the pressure at 165°C and 2 MPa for 30 minutes under vacuum conditions. Then, the temperature is raised to 180°C and maintained for 1 hour to harden the paste layer. Next, the copper foil on both sides is peeled off to obtain a sample plate containing the hardened paste. The film thickness of the sample plate (hardened paste) is 1 mm. The volume resistivity of the sample plate is calculated based on the surface resistivity measured using a four-terminal pin resistivity meter and the film thickness determined by a micrometer. The insulation resistance (insulation performance) is evaluated according to the following criteria. The results are shown in Table 1. Good insulation performance is indicated when either "A" or "B" in the following criteria is met. (Evaluation Criteria) A: Volume resistivity above 1.0 × 10¹² μΩ·cm B: Volume resistivity of 1.0 × 10¹¹ μΩ·cm or higher but less than 1.0 × 10¹² μΩ·cm C: Volume resistivity less than 10 11 μΩ·cm

[0099] (Evaluation of insulation reliability) Using a metal scraper manufactured by Taku Giken Co., Ltd., the paste obtained in the examples and comparative examples was coated onto a comb-shaped wiring substrate with a 200 μm / 200 μm line and space pattern using the thickness of polyimide tape as a spacer. The paste layer was then heated at 100°C for 1 hour in a nitrogen atmosphere. Subsequently, the paste was cured in a vacuum dryer (Yamato Scientific Co., Ltd., square vacuum constant temperature dryer, DP32) by raising the temperature from room temperature to 180°C over 50 minutes under vacuum conditions and maintaining the temperature for 60 minutes, thereby forming a 100 μm thick cured layer (insulating magnetic layer) on the wiring substrate. A wiring board having the hardened layer obtained as described was used as a sample, and the initial insulation resistance value and the insulation resistance value after a migration test were measured. In the migration test, the sample was placed at a temperature of 85°C, a humidity of 85%, and an applied voltage of 12 V for 500 hours. For the five samples with an initial insulation resistance value of 10⁶ Ω or higher, the proportion of samples with an insulation resistance value of 10⁶ Ω or higher after the migration test was investigated to evaluate the insulation reliability between wirings. Specifically, the insulation reliability was evaluated according to the following criteria. The results are shown in Table 1. Insulation reliability is good if either "A" or "B" in the following criteria is met. (Evaluation Criteria) A: The proportion of samples with an insulation resistance value of 10⁶ Ω or higher was found in all five samples. B: The proportion of samples with an insulation resistance value of 10⁶ Ω or higher was four out of all five samples. C: The proportion of samples with an insulation resistance value of 10⁶ Ω or higher was less than three out of all five samples.

[0100] Coefficient of thermal expansion (CTE) Eight sheets of polyimide tape (125 μm thick) manufactured by Uniontape were overlapped and attached to a copper foil, forming a 7 cm square quadrilateral frame. The paste from this embodiment was poured into the frame to pre-form a paste layer. Pre-forming was performed by heating the paste at 100°C for 1 hour in a nitrogen atmosphere, followed by maintaining the temperature at 150°C for 20 minutes. Next, copper foil was placed over the paste layer and maintained under vacuum at 165°C and 2 MPa for 30 minutes using a vacuum press (manufactured by Igen Manufacturing Co., Ltd., manual hydraulic vacuum heating press, 1A31). Then, the temperature was raised to 180°C and maintained for 1 hour to harden the paste layer (1 mm thick). On the other hand, regarding the paste of the comparative example, since it contains organic solvents, it was carried out as follows. First, paste was applied to the demolded surface of the PET film using a plastering tool and heated at 120°C for 20 minutes to form a dried paste layer with a thickness of approximately 50 μm. This paste layer was peeled off from the PET film and overlapped or laminated using vacuum lamination to pre-shape it into a 7 cm square with a thickness of approximately 1.2 mm. Next, eight sheets of polyimide tape (125 μm thick) manufactured by Uniontape Co., Ltd. were overlapped and attached to the copper foil to form a 7 cm square quadrilateral frame. The previously pre-shaped paste layer was placed inside the frame, and the copper foil was covered from above. A vacuum press (manufactured by Imoto Manufacturing Co., Ltd., manual hydraulic vacuum heating press, 1A31) was used to maintain the pressure under vacuum conditions at 165°C and 2 MPa for 30 minutes. Subsequently, after heating to 180°C, the temperature was maintained for 1 hour to harden the paste layer (film thickness 1 mm). Next, the copper foil on both sides of the hardened paste layer as described above was peeled off to obtain sample plates containing the hardened pastes of the examples and comparative examples. 10 mm square sample pieces were cut from these sample plates. The CTE (coefficient of thermal expansion) of the sample pieces was measured using a TMA (TA Instruments, Thermomechanical Analysis Apparatus, TMA-Q400). The measurement was performed at a heating rate of 10 °C / min within the range of 0 °C to 250 °C, and the linear expansion coefficient α1 (ppm / °C) in the region below the glass transition temperature was calculated. Based on the obtained α1 value, the CTE was evaluated according to the following criteria. The results are shown in Table 1. A good CTE is achieved when "AA", "A", and "B" are met in the following criteria. (Evaluation Criteria) AA:α1 is below 25 ppm / ℃ A: α1 exceeds 25 ppm / ℃ but is below 30 ppm / ℃ B: α1 exceeding 30 ppm / ℃ and below 40 ppm / ℃ C:α1 exceeds 40 ppm / ℃

[0101] [Table 1] The composition of paste Evaluation of the properties of paste project paste (Adhesive resin) Metal powder content (mass %) Viscosity distinction thermal weight reduction rate Insulation resistance Insulation reliability CTE Example 1-1 Paste 1-1 (Resin I) 97 5 AA B B AA Example 1-2 Paste 1-2 (Resin I) 95 4 AA A A AA Example 1-3 Paste 1-3 (Resin I) 94 3 AA A A AA Example 1-4 Paste 1-4 (Resin I) 90 3 AA A A A Example 1-5 Paste 1-5 (Resin I) 85 3 A A A B Example 1-6 Paste 1-6 (Resin I) 80 2 A A A B Example 2-1 Paste 2-1 (Resin II) 93 4 AA A A AA Example 2-2 Paste 2-2 (Resin II) 90 3 AA A A A Example 2-3 Paste 2-3 (Resin II) 80 3 AA A A B Example 2-4 Paste 2-4 (Resin II) 70 2 A A A B Example 3 3 Paste (Resin I-II) 94 3 AA A A AA Example 4 4 (Resin I-III) 94 3 AA A A AA Example 5 5 pastes (Resin IV) 94 4 AA A A AA Example 6 6 (Resin V) 94 4 AA A A A Example 7 7 (Resin VI) 94 3 B A A A Example 8 8 (Resin VII) 94 3 B A A A Example 9 9. (Resin VIII) 94 4 AA A A A Example 10 10 pastes (Resin IX) 94 4 AA A A A Example 11 11 (Resin IV) 94 4 AA A A AA Comparative example 1 12 Paste (Resin X) 97 3 C C C A Comparative example 2 13 (Resin X) 84 3 C C C C

[0102] As shown in Table 1, the thermal weight loss rate of the pastes in the examples is all below 5%, resulting in excellent insulation resistance and insulation reliability in the cured product. Furthermore, it can be seen that the thermal weight loss rate of the pastes in the examples is all below 5%, with low content of volatile components such as organic solvents (virtually no organic solvents are present), while maintaining moderate fluidity and excellent coatability. Therefore, from a CTE perspective, the pastes in the examples are also satisfactory.

[0103] On the other hand, regarding the comparative examples of paste, the results showed that the heat loss rate exceeded 5%, and the insulation resistance and insulation reliability were poor. This is believed to be because the comparative examples of paste contained a large amount of organic solvent, which remained in the hardened product after heating and hardening, making it prone to short circuits in insulation reliability tests. Furthermore, while the reason for obtaining low CTE in the hardened products of the examples of paste is unclear, it is speculated that at least the heat loss rate of the paste is related to the use of the hardener. As can be seen in the examples and comparative examples, it is known that when aromatic amines or imidazoles are used as hardeners, there is a tendency for better CTE results compared to hardened products obtained using other hardeners. It is generally believed that the coefficient of thermal expansion is large when a liquid vaporizes or when a gas becomes hot, but according to the paste based on the present invention, organic solvents are difficult to remain in the hardened product, and voids caused by volatile components are less likely to form, thereby obtaining a low CTE.

[0104] Based on the above results, it can be seen that by constructing a paste containing powders with metal elements, compounds containing epoxy groups, and a hardener, and by achieving a heat weight reduction rate of less than 5% after heat curing, a paste capable of forming a hardened material with excellent properties such as insulation can be achieved. [Industrial Applicability]

[0105] As an embodiment of the present invention, the paste can be preferably used as a material for the core of an inductor or as a material for filling the space between conductors of a coil, and can easily provide a molded product with excellent insulation properties.

[0106] none

Claims

1. A paste comprising a metal-containing powder of Fe amorphous alloy powder with an insulating coating, an epoxy-containing compound, and a hardener, wherein the Fe amorphous alloy powder with an insulating coating comprises at least one selected from the group consisting of Fe-Si-B alloys and Fe-Si-BP-Nb-Cr alloys, and the hardener comprises at least one selected from the group consisting of 2,6-diamino-3,5-diethyltoluene, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 3,3'-diethyl-4,4'-diaminodiphenylmethane, wherein the paste exhibits a heat weight reduction rate of less than 5% after heat curing at 180°C.

2. The paste as claimed in claim 1, wherein the epoxy-containing compound comprises an epoxy resin that is liquid at 25°C.

3. The paste as claimed in claim 1, wherein the content of the metal-containing powder is 70% by mass or more, based on the total mass of the paste.

4. The paste as claimed in claim 1, wherein the content of the metal-containing powder is 90% to 96% by mass based on the total mass of the paste.

5. The paste as claimed in claim 1, wherein the viscosity at 25°C is 1 Pa·s or more and 600 Pa·s or less.

6. The paste as claimed in claim 1, wherein the viscosity at 25°C is 10 Pa·s or more and 400 Pa·s or less.

7. The paste as claimed in claim 1, wherein the Fe amorphous alloy powder with insulating coating comprises Fe-Si-B alloys and Fe-Si-BP-Nb-Cr alloys.

8. The paste as claimed in claim 1, wherein it further comprises a coupling agent.

9. The paste as claimed in claim 1, wherein the coefficient of thermal expansion of the hardened product formed by the paste is less than 40 ppm / °C.

10. The paste as described in any one of claims 1 to 9, used in screen printing.