SOFT MAGNETIC THERMOSETTING FILM AND SOFT MAGNETIC FILM

Description

TECHNICAL FIELD

[0001] The present invention relates to a soft magnetic thermosetting film and a soft magnetic film obtained from the soft magnetic thermosetting film.

BACKGROUND ART

[0002] A position detection device having a pen-type position indicator for detecting a position by moving the pen on a position detection plane is called a digitizer, and is widely spread as an input device for computers. The position detection device includes a position detection flat plate, and a circuit board (sensor board) disposed therebelow and having loop coils formed on the surface of the board. Then, the position of the position indicator is detected by using electromagnetic induction generated by the position indicator and loop coils.

[0003] Patent Document 1 has proposed, for example, a method in which a soft magnetic film containing a soft magnetic material is disposed at a face (opposite face) opposite to the face of the position detection plane of the sensor board in a position detection device for efficient communication by controlling the magnetic flux generated at the time of electromagnetic induction.

[0004] Patent Document 1 discloses a soft magnetic film containing a soft magnetic powder, a binder resin composed of, for example, acrylic rubber, phenol resin, epoxy resin, and melamine, and a metal salt of phosphinic acid. The soft magnetic film has a high content of, for example, a metal salt of phosphinic acid and melamine, and therefore fire-retardancy is given to the circuit board without affecting reliability of an electronic device.

Citation List

Patent Document

[0005] Patent Document 1: Japanese Unexamined Patent Publication No. 2012-212790

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0006] A soft magnetic film is generally produced by curing a thermosetting resin containing a soft magnetic powder and a binder resin by heating. However, there is a disadvantage that when the soft magnetic film is stored for a long period of time under a high temperature and high humidity atmosphere after heating, magnetic properties such as relative magnetic permeability deteriorate.

[0007] An object of the present invention is to provide a soft magnetic thermosetting film and a soft magnetic film obtained from the soft magnetic thermosetting film in which deterioration of magnetic properties is suppressed after being stored for a long period of time under a high temperature and high humidity atmosphere.

MEANS FOR SOLVING THE PROBLEM

[0008] A soft magnetic thermosetting film of the present invention contains soft magnetic particles, wherein the ratio (µ1'/µ0') of a relative magnetic permeability µ1' at a frequency of 1 MHz at the time of curing the soft magnetic thermosetting film by heating to be allowed to stand under an atmosphere of 85°C and 85%RH for 168 hours to an initial relative magnetic permeability µ0' at a frequency of 1 MHz immediately after curing the soft magnetic thermosetting film by heating is 0.85 or more.

[0009] It is preferable that the soft magnetic thermosetting film of the present invention is formed from a soft magnetic thermosetting composition containing the soft magnetic particles at a ratio of 40% by volume or more.

[0010] It is preferable that in the soft magnetic thermosetting film of the present invention, the soft magnetic thermosetting composition contains epoxy resin, phenol resin, and acrylic resin.

[0011] A soft magnetic film of the present invention is produced by curing the above-described soft magnetic thermosetting film by heating to be brought into a cured state.

EFFECT OF THE INVENTION

[0012] The soft magnetic film of the present invention obtained by curing the soft magnetic thermosetting film of the present invention by heating suppresses deterioration of the magnetic properties and has excellent magnetic properties after being stored (allowed to stand) for a long period of time under a high temperature and high humidity atmosphere.

DESCRIPTION OF EMBODIMENTS

[0013] The soft magnetic thermosetting film of the present invention is, for example, formed from a soft magnetic thermosetting composition containing soft magnetic particles and a resin component.

[0014] Examples of the soft magnetic materials that form the soft magnetic particles include magnetic stainless steel (Fe-Cr-Al-Si alloy), Sendust (Fe-Si-Al alloy), permalloy (Fe-Ni alloy), silicon copper (Fe-Cu-Si alloy), Fe-Si alloy, Fe-Si-B (-Cu-Nb) alloy, Fe-Si-Cr-Ni alloy, Fe-Si-Cr alloy, Fe-Si-Al-Ni-Cr alloy, and ferrite. Among these, in view of magnetic properties, preferably, Sendust (Fe-Si-Al alloy) is used.

[0015] Among these, more preferably, a Fe-Si-Al alloy having a Si content of 9 to 15 mass% is used. In this manner, magnetic properties of the soft magnetic film can be improved.

[0016] The soft magnetic particles are preferably shaped flat (plate). The aspect ratio is, for example, 8 or more, preferably 15 or more, and for example, 80 or less, preferably 65 or less. The aspect ratio is calculated as an aspect ratio dividing the average particle size (average length) of the soft magnetic particles by an average thickness of the soft magnetic particles.

[0017] The soft magnetic particles have an average particle size (average length) of, for example, 3.5 µm or more, preferably 10 µm or more, and for example, 100 µm or less. The average thickness is, for example, 0.3 µm or more, preferably 0.5 µm or more, and for example, 3 µm or less, preferably 2.5 µm or less. By adjusting the aspect ratio, average particle size, and average thickness of the soft magnetic particles, demagnetization effects of the soft magnetic particles can be reduced, and as a result, magnetic permeability of the soft magnetic particles can be increased. To equalize the size of the soft magnetic particles, as necessary, those soft magnetic particles classified with, for example, a sieve can be used.

[0018] The mass ratio of the soft magnetic particles in the soft magnetic thermosetting composition (and in the soft magnetic thermosetting film and the soft magnetic film) is, for example, 70 mass% or more, preferably 80 mass% or more, more preferably 85 mass% or more, and for example, 95 mass% or less, preferably 92 mass% or less, more preferably 90 mass% or less. The volume ratio of the soft magnetic particles in the soft magnetic thermosetting composition is, for example, 30% by volume or more, preferably 40% by volume or more, more preferably 50% by volume or more, and for example, 80% by volume or less, preferably 70% by volume or less, more preferably 60% by volume or less. By setting the mass ratio and the volume ratio of the soft magnetic particles in the range of the above-described upper limit or less, excellent forming properties of the soft magnetic film can be achieved. Meanwhile, by setting the mass ratio and the volume ratio of the soft magnetic particles in the range of the above-described lower limit or more, the soft magnetic film having excellent magnetic properties can be achieved.

[0019] The resin component contains a thermosetting resin.

[0020] Examples of the thermosetting resin include epoxy resin, phenol resin, amino resin, unsaturated polyester resin, polyurethane resin, silicone resin, urea resin, melamine resin, thermosetting polyimide resin, and diallylphthalate resin. Preferably, epoxy resin and phenol resin are used, more preferably, epoxy resin and phenol resin are used in combination. These can be used singly, or can be used in combination of two or more.

[0021] The epoxy resin is not particularly limited as long as it is generally used as an adhesive composition, and for example, bifunctional epoxy resins and multifunctional epoxy resins such as bisphenol epoxy resin (particularly, bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, brominated bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin, bisphenol AF epoxy resin, etc.), phenol epoxy resin (particularly, phenol novolak epoxy resin, orthocresol novolak epoxy resin, etc.), biphenyl epoxy resin, naphthalene epoxy resin, fluorine epoxy resin, trishydroxyphenylmethane epoxy resin, and tetraphenylolethane epoxy resin are used. Furthermore, for example, hydantoin epoxy resin, trisglycidylisocyanurate epoxy resin, and glycidylamine epoxy resin are also used. These can be used singly, or can be used in combination of two or more.

[0022] Of these epoxy resins, preferably, bisphenol epoxy resin, novolak epoxy resin, orthocresol novolak epoxy resin, biphenyl epoxy resin, trishydroxyphenylmethane resin, and tetraphenylolethane epoxy resin are used, or more preferably, bisphenol epoxy resin is used. Containing such epoxy resins allows for excellent reactivity with phenol resin, and as a result, the soft magnetic film obtained by curing the soft magnetic thermosetting film by heating has excellent storage stability for a long period of time of the magnetic properties under a high temperature and high humidity atmosphere.

[0023] Phenol resin is a curing agent for epoxy resin, and for example, novolak-type phenol resins such as phenol novolak resin, phenol aralkyl resin, cresol novolak resin, tert-butyl phenol novolak resin, and nonylphenol novolak resin; resol-type phenol resin; and polyoxystyrene such as polyparaoxystyrene are used. These can be used singly, or can be used in combination of two or more. Of these phenol resins, preferably, novolak-type resin is used, more preferably, phenol novolak resin and phenol aralkyl resin are used, or further more preferably, phenol aralkyl resin is used. Containing these phenol resins allows for excellent reactivity with epoxy resin, and as a result, the soft magnetic film has excellent storage stability for a long period of time.

[0024] In a case where the resin component contains both of the epoxy resin and the phenol resin, when the hydroxyl equivalent of the phenol resin relative to 100 g/eq of the epoxy equivalent of the epoxy resin is 1 g/eq or more and less than 100 g/eq, the epoxy resin content relative to 100 parts by mass of the resin component is, for example, 15 parts by mass or more, preferably 30 parts by mass or more, and for example, 70 parts by mass or less, preferably, 50 parts by mass or less, more preferably 40 parts by mass or less; and the phenol resin content relative to 100 parts by mass of the resin component is, for example, 5 parts by mass or more, preferably 15 parts by mass or more, and for example, 30 parts by mass or less, preferably 20 parts by mass or less.

[0025] When the hydroxyl equivalent of the phenol resin relative to 100 g/eq of the epoxy equivalent of the epoxy resin is 100 g/eq or more and less than 200 g/eq, the epoxy resin content relative to 100 parts by mass of the resin component is, for example, 10 parts by mass or more, preferably 25 parts by mass or more, and for example, 50 parts by mass or less; and the phenol resin content relative to 100 parts by mass of the resin component is, for example, 10 parts by mass or more, preferably 25 parts by mass or more, and for example, 50 parts by mass or less.

[0026] When the hydroxyl equivalent of the phenol resin relative to 100 g/eq of the epoxy equivalent of the epoxy resin is 200 g/eq or more and 1000 g/eq or less, the epoxy resin content relative to 100 parts by mass of the resin component is, for example, 5 parts by mass or more, preferably 15 parts by mass or more, and for example, 30 parts by mass or less; and the phenol resin content relative to 100 parts by mass of the resin component is, for example, 15 parts by mass or more, preferably 35 parts by mass or more, and for example, 70 parts by mass or less.

[0027] The epoxy equivalent when two types of epoxy resins are used in combination is an epoxy equivalent of all epoxy resins in total calculated by multiplying the epoxy equivalent of each epoxy resin by the mass ratio of each epoxy resin relative to the total amount of the epoxy resin, and adding up these.

[0028] The hydroxyl equivalent in the phenol resin per 1 equivalent of the epoxy group of the epoxy resin is, for example, 0.2 equivalent or more, preferably 0.5 equivalent or more, and for example, 2.0 equivalent or less, preferably 1.2 equivalent or less. When the amount of the hydroxyl group is in the above-described range, curing reaction of the soft magnetic thermosetting film is excellent, and deterioration can be suppressed.

[0029] The resin component preferably contains an acrylic resin in addition to the thermosetting resin. More preferably, acrylic resin, epoxy resin, and phenol resin are used in combination. Further more preferably, the resin component is formed from only epoxy resin, phenol resin, and acrylic resin. By allowing the resin component to contain these resins, when one piece of soft magnetic film is produced by laminating a plurality of soft magnetic thermosetting films and hot pressing the laminate, a soft magnetic film having a uniform laminated interface without unevenness and having excellent magnetic properties can be produced.

[0030] An example of the acrylic resin includes an acrylic-type polymer produced by polymerizing a monomer component of one, or two or more of straight chain or branched alkyl (meth)acrylate ester having an alkyl group. "(Meth)acrylic" represents "acrylic and/or methacrylic".

[0031] An example of the alkyl group includes an alkyl group having 1 to 20 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a n-butyl group, a t-butyl group, an isobutyl group, an amyl group, an isoamyl group, a hexyl group, a heptyl group, a cyclohexyl group, a 2-ethylhexyl group, an octyl group, an isooctyl group, a nonyl group, an isononyl group, a decyl group, an isodecyl group, an undecyl group, a lauryl group, a tridecyl group, a tetradecyl group, a stearyl group, an octadecyl group, and a dodecyl group. Preferably, an alkyl group having 1 to 6 carbon atoms is used.

[0032] The acrylic-type polymer can be a copolymer of the alkyl (meth)acrylate ester and an additional monomer.

[0033] Examples of another monomer include glycidyl group-containing monomers such as glycidylacrylate and glycidylmethacrylate; carboxyl group-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid; acid anhydride monomers such as maleic anhydride and itaconic anhydride; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methylacrylate; sulfonic acid group-containing monomers such as styrenesulfonic acid, allylsulfonic acid, 2-(meth) acrylamide-2-methylpropane sulfonic acid, (meth)acrylamidepropane sulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid; phosphoric acid group-containing monomers such as 2-hydroxyethylacryloyl phosphate; styrene monomer; and acrylonitrile.

[0034] Among these, preferably, a glycidyl group-containing monomer, carboxyl group-containing monomer, or hydroxyl group-containing monomer is used. When the acrylic resin is a copolymer of alkyl (meth)acrylate ester and an additional monomer of these, that is, when the acrylic resin has a glycidyl group, a carboxyl group, or a hydroxyl group, reflow resistance of the soft magnetic film is more excellent.

[0035] The mixing ratio of another monomer (mass) is, when a copolymer of the alkyl (meth)acrylate ester and another monomer is used, preferably 40 mass% or less relative to the copolymer.

[0036] The acrylic resin has a weight-average molecular weight of, for example, 1 × 10⁵ or more, preferably 3 × 10⁵ or more, and for example, 1 × 10⁶ or less. By setting the mixing ratio of another monomer (mass) in this range, a soft magnetic thermosetting film with excellent adhesiveness and reflow resistance can be achieved. The weight-average molecular weight is measured by gel permeation chromatography (GPC) based on a polystyrene standard calibration value.

[0037] The acrylic resin has a glass transition temperature (Tg) of, for example, -30°C or more, preferably -20°C or more, and for example, 30°C or less, preferably 15°C or less. When the glass transition temperature (Tg) is the above-described lower limit or more, adhesiveness of the soft magnetic thermosetting film is excellent. Meanwhile, when the glass transition temperature (Tg) is the above-described upper limit or less, handleability of the soft magnetic thermosetting film is excellent. The glass transition temperature is determined based on the maximum value of the loss tangent (tanδ) measured by using a dynamic viscoelasticity measuring apparatus (DMA, frequency of 1 Hz, temperature increase rate of 10°C/min).

[0038] When the resin component contains the acrylic resin, the thermosetting resin content of the resin component is, for example, 35 mass% or more, preferably above 50 mass%, more preferably 52 mass% or more, and for example, 90 mass% or less, preferably 80 mass% or less, or more preferably 60 mass% or less. When the thermosetting resin content is in the above-described range, particularly when the thermosetting resin is rich (above 50 mass%), expansion of the resin caused by water absorption or heat, and occurrence of a void in the soft magnetic film can be effectively suppressed, so that storage stability for a long period of time of the magnetic properties under a high temperature and high humidity atmosphere is excellent.

[0039] The acrylic resin content of the resin component is, for example, 10 mass% or more, preferably 20 mass% or more, more preferably 40 mass% or more, and for example, 65 mass% or less, preferably less than 50 mass%, more preferably 48 mass% or less.

[0040] The resin component content of the soft magnetic thermosetting composition is, for example, 5 mass% or more, preferably 8 mass% or more, more preferably 10 mass% or more, and for example, 30 mass% or less, preferably 20 mass% or less, more preferably 15 mass% or less. By setting the resin component content in the above-described range, the soft magnetic film having excellent film-forming properties and magnetic properties can be achieved.

[0041] The thermosetting resin (preferably, thermosetting resin formed from epoxy resin and phenol resin) content relative to 100 parts by mass of the soft magnetic particles-excluding component, which is a composition excluding the soft magnetic particles from the soft magnetic thermosetting composition, is, for example, 20 parts by mass or more, preferably 30 parts by mass or more, more preferably 40 parts by mass or more, further more preferably above 50 parts by mass, most preferably 52 parts by mass or more, and for example, 99 parts by mass or less, preferably 90 parts by mass or less, more preferably 80 parts by mass or less, further more preferably 70 parts by mass or less, most preferably 60 parts by mass or less. By setting the thermosetting resin content in the above-described range, the soft magnetic film has excellent storage stability for a long period of time of the magnetic properties under a high temperature and high humidity atmosphere.

[0042] The soft magnetic particles-excluding component is a component consisting of the resin component, and a thermosetting catalyst (described later) and an additive (described later) that are added as necessary, and to be more specific, does not include the soft magnetic particles and a solvent.

[0043] The resin component can contain an additional thermoplastic resin other than the thermosetting resin and the acrylic resin.

[0044] Examples of the thermoplastic resin include natural rubber, butyl rubber, isoprene rubber, chloroprene rubber, an ethylene-vinyl acetate copolymer, a copolymer, polybutadiene resin, polycarbonate resin, thermoplastic polyimide resin, polyamide resin (6-nylon, 6,6-nylon, etc.), phenoxy resin, saturated polyester resin (PET, PBT, etc.), polyamide-imide resin, and fluorine resin. These resins can be used singly, or can be used in combination of two or more.

[0045] The soft magnetic thermosetting composition preferably contains a thermosetting catalyst.

[0046] The thermosetting catalyst is not limited as long as the catalyst accelerates curing of the resin component by heating, and examples thereof include a salt having an imidazole skeleton, a salt having a triphenylphosphine structure, a salt having a triphenylborane structure, and an amino group-containing compound. Preferably, a salt having an imidazole skeleton is used.

[0047] Examples of the salt having an imidazole skeleton include 2-phenylimidazole (trade name; 2PZ), 2-ethyl-4-methylimidazole (trade name; 2E4MZ), 2-methylimidazole (trade name; 2MZ), 2-undecylimidazole (trade name; C11Z), 2-phenyl-4,5-dihydroxymethylimidazole (trade name; 2-PHZ-PW), 2,4-diamino-6-(2'-methylimidazolyl (1)') ethyl-s-triazine isocyanuric acid adduct (trade name; 2MAOK-PW) (the above-described products are all manufactured by Shikoku Chemicals Corporation). These thermosetting catalysts can be used singly, or can be used in combination of two or more.

[0048] The thermosetting catalyst has a shape of, for example, spherical or ellipsoidal.

[0049] The mixing ratio of the thermosetting catalyst relative to 100 parts by mass of the resin component is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, and for example, 5 parts by mass or less, preferably 3 parts by mass or less. By setting the mixing ratio of the thermosetting catalyst in the above-described range, the soft magnetic thermosetting film can be cured by heating at low temperature and for a short period of time, and excellent storage stability for a long period of time of the magnetic properties under a high temperature and high humidity atmosphere and excellent reflow resistance can be achieved.

[0050] The soft magnetic thermosetting composition (and the soft magnetic thermosetting film and the soft magnetic film) may contain commercially available or known additives such as a dispersant, a cross-linking agent, and an inorganic filler.

[0051] The soft magnetic thermosetting composition preferably contains a dispersant.

[0052] Examples of the dispersant include polyether phosphate ester, a silane coupling agent, and a titanate coupling agent. Preferably, polyether phosphate ester is used. By allowing the soft magnetic thermosetting composition to contain a dispersant, particularly polyether phosphate ester, coating properties of the soft magnetic thermosetting composition can be improved and magnetic properties of the soft magnetic film can be further improved.

[0053] Examples of the polyether phosphate ester include polyoxyalkylene alkyl ether phosphate and polyoxyalkylene alkyl phenyl ether phosphate. Preferably, polyoxyalkylene alkyl ether phosphate is used.

[0054] The polyoxyalkylene alkyl ether phosphate has a structure in which one to three alkyl-oxy-poly(alkyleneoxy) groups are bonded to a phosphorus atom of phosphate. In the alkyl-oxy-poly(alkyleneoxy) group [that is, polyoxyalkylene alkyl ether portion], the number of repetition of alkyleneoxy related to the poly(alkyleneoxy) portion is not particularly limited, and can be appropriately selected from the range of 2 to 30 (preferably, 3 to 20). As the alkylene of the poly(alkyleneoxy) portion, preferably, an alkylene group having 2 to 4 carbon atoms is used. Specific examples thereof include an ethylene group, a propylene group, an isopropylene group, a butylene group, and an isobutyl group. The alkyl group is not particularly limited and preferably, an alkyl group having 6 to 30 carbon atoms is used, or more preferably, an alkyl group having 8 to 20 carbon atoms is used. Specific examples of the alkyl group include a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group. When the polyoxyalkylene alkyl ether phosphate has a plurality of alkyl-oxy-poly(alkyleneoxy) groups, the plurality of alkyl groups may be different or may be the same. The polyether phosphate ester may be a mixture with amine or the like.

[0055] The polyether phosphate ester has an acid value of, for example, 10 or more, preferably 15 or more, and for example, 200 or less, preferably 150 or less. The acid value is measured by a neutralization titration method or the like.

[0056] Examples of the silane coupling agent include 3-methacryloxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0057] These dispersants can be used singly, or can be used in combination of two or more.

[0058] Specific examples of the dispersant include the HIPLAAD series manufactured by Kusumoto Chemicals, Ltd. ("ED152", "ED153", "ED154", "ED118", "ED174", and "ED251") and the KBM series manufactured by Shin-Etsu Chemical Co., Ltd. ("KBM303" and "KBM503").

[0059] The dispersant content relative to 100 parts by mass of the soft magnetic particles is, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and for example, 5 parts by mass or less, preferably 2 parts by mass or less.

[0060] The soft magnetic thermosetting composition can be prepared by mixing the above-described components at the above-described content ratio.

[0061] Next, description is given below of a method for producing a soft magnetic thermosetting film of the present invention.

[0062] To produce the soft magnetic thermosetting film, a soft magnetic thermosetting composition solution, in which the above-described soft magnetic thermosetting composition is dissolved or dispersed in a solvent, is prepared.

[0063] Examples of the solvent include organic solvents such as ketones including acetone and methyl ethyl ketone (MEK); esters such as ethyl acetate; ethers such as propylene glycol monomethyl ether; and amides such as N,N-dimethylformamide. Examples of the solvent also include water-based solvents such as water, and alcohols such as methanol, ethanol, propanol, and isopropanol.

[0064] The soft magnetic thermosetting composition solution has a solid content of, for example, 10 mass% or more, preferably 30 mass% or more, and for example, 90 mass% or less, preferably 70 mass% or less.

[0065] Then, the soft magnetic thermosetting composition solution is applied to a surface of a release substrate (separator, core material, etc.) to be dried. A soft magnetic thermosetting film is produced in this manner.

[0066] The application method is not particularly limited, and for example, doctor blades, roll coating, screen coating, and gravure coating can be used.

[0067] Examples of drying conditions include a drying temperature of, for example, 70°C or more and 160°C or less, and drying time of, for example, 1 minute or more and 5 minutes or less.

[0068]  Examples of the separator include a polyethylene terephthalate (PET) film, a polyethylene film, a polypropylene film, and paper. The surfaces of these examples of the separator are subjected to release treatment with, for example, a fluorine release agent, a long-chain alkylacrylate release agent, and a silicone release agent.

[0069] Examples of the core material include a plastic film (e.g., polyimide film, polyester film, polyethylene terephthalate film, polyethylenenaphthalate film, polycarbonate film, etc.), a metal film (e.g., aluminum foil, etc.), and a resin substrate, a silicon substrate, and a glass substrate reinforced with, for example, glass fiber and plastic nonwoven fiber.

[0070] The separator or the core material has an average thickness of, for example, 1 µm or more and 500 µm or less.

[0071] In this manner, the soft magnetic thermosetting film is produced.

[0072] The soft magnetic thermosetting film is in a semi-cured state (B-stage state) under room temperature (to be specific, at 25°C) and is a soft magnetic thermosetting adhesive film having excellent adhesiveness.

[0073] The soft magnetic thermosetting film preferably contains flat soft magnetic particles, and the flat soft magnetic particles are arranged in 2-dimensional in-plane direction of the soft magnetic thermosetting film. That is, the longitudinal direction (direction perpendicular to thickness direction) of the flat soft magnetic particles is oriented along the surface direction of the soft magnetic thermosetting film. In this manner, the soft magnetic thermosetting film is filled with the soft magnetic particles at a high proportion, and excellent magnetic properties are achieved. Also, film thinning of the soft magnetic thermosetting film is achieved.

[0074] The soft magnetic thermosetting film has an average thickness of, for example, 5 µm or more, preferably 50 µm or more, and for example, 500 µm or less, preferably 250 µm or less.

[0075] The soft magnetic thermosetting film of the present invention can be, for example, a single-layer structure of only a soft magnetic thermosetting film, a multi-layer structure in which a soft magnetic thermosetting film is laminated on one side or both sides of the core material, and a multi-layer structure in which a separator is laminated on one side or both sides of the soft magnetic thermosetting film.

[0076] Next, description is given below of a soft magnetic film of the present invention.

[0077] The soft magnetic film is formed of the above-described soft magnetic thermosetting film. To be specific, the soft magnetic film is produced by curing the above-described soft magnetic thermosetting film by heating.

[0078] Preferably, a plurality of soft magnetic thermosetting films are prepared and the plurality of soft magnetic thermosetting films are hot pressed in the thickness direction (hot pressing step). In this manner, the soft magnetic thermosetting film is filled with the soft magnetic particles at a high proportion, and magnetic properties can be improved.

[0079] Hot pressing can be performed using a known pressing machine. An example thereof includes a parallel flat plate pressing machine.

[0080] The number of lamination of the soft magnetic thermosetting film is, for example, 2 layers or more, and for example, 20 layers or less, preferably 5 layers or less. In this manner, the soft magnetic film can be adjusted to have a desired thickness.

[0081] The heating temperature is, for example, 80°C or more, preferably 100°C or more, and for example, 200°C or less, preferably 180°C or less.

[0082] The heating time is, for example, 0.1 hours or more, preferably, 0.2 hours or more, and for example, 24 hours or less, preferably 2 hours or less.

[0083] The pressure is, for example, 10 MPa or more, preferably 20 MPa or more, and for example, 500 MPa or less, preferably 200 MPa or less.

[0084] In this manner, the soft magnetic thermosetting film in a semi-cured state is cured by heating, thereby producing a soft magnetic film in a cured state (C-stage state).

[0085]  The soft magnetic film has an average thickness of, for example, 5 µm or more, preferably 50 µm or more, and for example, 500 µm or less, preferably 250 µm or less.

[0086] In the soft magnetic film, the relative magnetic permeability (initial relative magnetic permeability µ0') at a frequency of 1 MHz immediately after being cured by heating (to be specific, within 30 minutes after curing the soft magnetic thermosetting film by heating) is, for example, 100 or more, preferably 150 or more, more preferably 180 or more, and for example, 400 or less.

[0087] The relative magnetic permeability (relative magnetic permeability µ1') at a frequency of 1 MHz at the time of being allowed to stand under an atmosphere of 85°C and 85%RH for 168 hours after being cured by heating is, for example, 100 or more, preferably 150 or more, more preferably 180 or more, and for example, 400 or less.

[0088] The ratio (µ1'/µ0') of the relative magnetic permeability µ1' to the initial relative magnetic permeability µ0' is 0.85 or more, preferably 0.90 or more, more preferably 0.95 or more, further more preferably 0.96 or more, most preferably 0.97 or more, and for example, 1.00 or less. By setting the above-described ratio in the above-described range, the soft magnetic film has excellent storage stability for a long period of time of the magnetic properties under a high temperature and high humidity atmosphere.

[0089] The relative magnetic permeability (µ0' and µ1') is measured by a one turn method (frequency of 1 MHz) using an impedance analyzer (manufactured by Agilent Technologies, "4294A").

[0090] In the soft magnetic film, preferably, the soft magnetic particles contained in the soft magnetic film are arranged in 2-dimensional in-plane direction of the soft magnetic film. That is, the longitudinal direction (direction perpendicular to thickness direction) of the flat soft magnetic particles is oriented along the surface direction of the soft magnetic film. Thus, the soft magnetic film is thin and has an excellent relative magnetic permeability.

[0091] The soft magnetic film can be, for example, a single-layer structure of only a soft magnetic film, a multi-layer structure in which a soft magnetic film is laminated on one side or both sides of the core material, and a multi-layer structure in which a separator is laminated on one side or both sides of the soft magnetic film.

[0092] In the above-described embodiment, a plurality of soft magnetic thermosetting films are laminated and the laminate is hot pressed. Alternatively, for example, one piece (single layer) of soft magnetic thermosetting film can be also hot pressed.

[0093] The soft magnetic film can be preferably used as a soft magnetic film (magnetic film) to be laminated on, for example, an antenna, a coil, or a circuit board having these formed on the surface thereof. To be more specific, the soft magnetic film can be used for intended uses such as smart phones, personal computers, and position detection devices.

[0094] Examples of a method for laminating the soft magnetic film on the circuit board include a method in which the soft magnetic film is fixed to the circuit board via an adhesive layer and a method in which after the soft magnetic thermosetting film is directly attached to the circuit board, the soft magnetic thermosetting film is cured by heating to obtain the soft magnetic film and the obtained soft magnetic film is fixed to the circuit board.

[0095] In view of unnecessity of an adhesive layer and miniaturization of an electronic device, preferably, a method in which after the soft magnetic thermosetting film is directly attached to the circuit board, the soft magnetic thermosetting film is cured by heating is used.

[0096] In view of insulation properties, preferably, a method in which the soft magnetic film is fixed to the circuit board via the adhesive layer is used.

[0097] As the adhesive layer, a known adhesive layer usually used as an adhesive layer of a circuit board is used. The adhesive layer is, for example, formed by applying adhesives such as an epoxy adhesive, a polyimide adhesive, and an acrylic adhesive to be dried. The adhesive layer has a thickness of, for example, 10 to 100 µm.

[0098] According to the soft magnetic thermosetting film, the ratio (µ1'/µ0') of the relative magnetic permeability µ1' to the initial relative magnetic permeability µ0' is 0.85 or more, so that when the soft magnetic film obtained by curing the soft magnetic thermosetting film by heating is stored for a long period of time under a high temperature and high humidity atmosphere, deterioration of the relative magnetic permeability of the soft magnetic film can be suppressed. In this manner, excellent magnetic properties can be developed for a long period of time.

[0099] The resistance temperature under a high temperature and high humidity atmosphere is, for example, 50°C or more, preferably 80°C or more, and for example, 150°C or less, preferably 100°C or less.

[0100] The resistance humidity under a high temperature and high humidity atmosphere is, for example, 50%RH or more, preferably 80%RH or more, and for example, 100%RH or less, preferably 90%RH or less.

[0101] The storageable time under a high temperature and high humidity atmosphere is, for example, 96 hours or more, preferably 168 hours or more, more preferably 400 hours or more, further more preferably 700 hours or more.

Examples

[0102] While in the following, the present invention is described in further detail with reference to Examples and Comparative Examples, the present invention is not limited to any of them by no means. The numeral values in Examples shown below can be replaced with the numeral values shown in the above-described embodiments (that is, the upper limit value or the lower limit value).

Example 1

(Soft magnetic thermosetting film)

[0103] A soft magnetic thermosetting composition was produced by mixing 500 parts by mass of soft magnetic particles, 22 parts by mass of an acrylate ester polymer, 45 parts by mass of bisphenol A epoxy resin ("Epikote 1004"), 26 parts by mass of bisphenol A epoxy resin ("Epikote YL980), 32 parts by mass of phenol aralkyl resin, 1.26 parts by mass (1.0 part by mass relative to 100 parts by mass of resin component) of 2-phenyl-4,5-dihydroxymethylimidazole ("2PHZ-PW", thermosetting catalyst), and 2.5 parts by mass (0.5 parts by mass relative to 100 parts by mass of soft magnetic particles) of polyether phosphate ester (dispersant) so that the soft magnetic particles were 40% by volume relative to the soft magnetic thermosetting composition.

[0104] The soft magnetic thermosetting composition was dissolved in methyl ethyl ketone, thereby producing a soft magnetic thermosetting composition solution having a solid content concentration of 43 mass%.

[0105] The soft magnetic thermosetting composition solution was applied on a separator (average thickness of 50 µm) composed of a polyethylene terephthalate film subjected to silicone release treatment, and thereafter, dried at 130°C for 2 minutes.

[0106] In this manner, a soft magnetic thermosetting film (average thickness of only soft magnetic thermosetting film was 90 µm) on which a separator was laminated was produced.

(Soft magnetic film)

[0107] Next, the soft magnetic thermosetting films were laminated in four layers and by hot pressing, the obtained laminate was cured by heating under the conditions of 175°C for 30 minutes at 20 MPa, thereby producing a soft magnetic film.

Examples 2 to 4

[0108] Soft magnetic thermosetting compositions were produced based on the materials and the mixing ratios shown in Table 1. Soft magnetic thermosetting films and thermosetting films of Examples 2 to 4 were produced in the same manner as in Example 1, except that these soft magnetic thermosetting compositions were used.

Comparative Example 1

(Soft magnetic thermosetting film)

[0109] A soft magnetic thermosetting composition was produced by mixing 500 parts by mass of soft magnetic particles and 106 parts by mass of an ethylene vinyl acetate copolymer so that the soft magnetic particles were 40% by volume relative to the soft magnetic thermosetting composition.

[0110] The soft magnetic thermosetting composition was dissolved in toluene, thereby producing a soft magnetic thermosetting composition solution having a solid content concentration of 40 mass%.

[0111] The soft magnetic thermosetting composition solution was applied on a separator (average thickness of 50 µm) composed of a polyethylene terephthalate film subjected to silicone release treatment, and thereafter, dried at 130°C for 2 minutes.

[0112] In this manner, a soft magnetic thermosetting film (average thickness of only soft magnetic thermosetting film was 90 µm) on which a separator was laminated was produced.

(Soft magnetic film)

[0113] Next, the soft magnetic thermosetting films were laminated in four layers and by hot pressing, the obtained laminate was cured by heating under the conditions of 175°C for 30 minutes at 20 MPa, thereby producing a soft magnetic film of Comparative Example 1.

Comparative Examples 2 and 3

[0114] Soft magnetic thermosetting compositions were produced based on the materials and the mixing ratios shown in Table 1. Soft magnetic thermosetting films and soft magnetic films of Comparative Examples 2 and 3 were produced in the same manner as in Example 1, except that these soft magnetic thermosetting compositions were used.

(Measurement of initial relative magnetic permeability (µ0'))

[0115] In each of the soft magnetic films produced in Examples and Comparative Examples, the relative magnetic permeability immediately after hot pressing (after 30 minutes) was measured by a one turn method (frequency of 1 MHz) using an impedance analyzer (manufactured by Agilent Technologies, "4294A"). The obtained value was defined as an initial relative magnetic permeability (µ0'). The results are shown in Table 1.

(Measurement of relative magnetic permeability (µ1'))

[0116] After measurement of the initial relative magnetic permeability was performed, each of the soft magnetic films produced in Examples and Comparative Examples was stored under an atmosphere of 85°C and 85%RH for 168 hours. The relative magnetic permeability of the soft magnetic film at the time of being stored for 168 hours was measured by a one turn method (frequency of 1 MHz) using an impedance analyzer (manufactured by Agilent Technologies, "4294A"). The obtained value was defined as a relative magnetic permeability (µ1'). The results are shown in Table 1.

(Relative magnetic permeability after being stored for long period of time under high temperature and high humidity)

[0117] After measurement of the relative magnetic permeability (µ1') was performed, the measurement of the relative magnetic permeability u' after a lapse of 400 hours and after a lapse of 700 hours under an atmosphere of 85°C and 85%RH was performed in the same manner as that described above. The results are shown in Table 1.

[0118] As clear from Table 1, in the soft magnetic films of Examples 1 to 4, even after a lapse of 400 hours and after a lapse of 700 hours, based on the initial relative magnetic permeability at the time of producing the soft magnetic film, the relative magnetic permeability at a high proportion was kept, that is, a reduction in relative magnetic permeability was suppressed. Meanwhile, in the soft magnetic films of Comparative Examples 1 to 3, after a lapse of 400 hours and after a lapse of 700 hours, based on the initial relative magnetic permeability at the time of producing the soft magnetic film, the relative magnetic permeability was substantially reduced. In the soft magnetic films of Comparative Examples 2 and 3, after a lapse of 400 hours and after a lapse of 700 hours, a reduction in relative magnetic permeability was progressed.

[0119] [Table 1]

[Table 1]

				Ex. 1	Ex. 2	Ex. 3	Ex. 4	Comp. Ex. 1	Comp. Ex. 2	Comp. Ex. 3
	Soft Magnetic Particle	parts by mass		500	500	500	500	500	500	500
		% by volume		40	50	60	50	40	50	60
	Resin Component	Acrylic Resin	Paracron W197CM	22	29	25	44	-	74	44
		Epoxy Resin	Epikote 1004	45	23	13	15	-	-	3
Soft Magnetic Thermosetting Composition			Epikote YL980	26	13	7	9	-	-	1
			TETRAD-C	-	-	-	-	-	1.2	-
		Phenol Resin	MILEX XLC4L	32	16	9	11	-	-	2
		Ethylene-Vinyl Acetate	EV170	-	-	-	-	106	-	-
	Thermosetting Catalyst	Imidazole	2PHZ-PW	1.26	0.81	0.53	0.79	-	-	0.5
	Dispersant	Polyether Phosphate Ester	ED152	2.5	2.5	2.5	2.5	-	2.5	2.5
	Initial Relative Magnetic Permeability µ0'			120	160	200	158	120	157	170
	Relative Magnetic Permeability µ1'			114	154	194	140	78	130	142
	Ratio(µ1'/µ0')			0.95	0.96	0.97	0.89	0.65	0.83	0.84
	Relative Magnetic Permeability (after 400 hours)			114	154	194	139	74	127	142
	Relative Magnetic Permeability (after 700 hours)			115	154	194	139	75	125	140

[0120] The numeral values for the components in Table represent parts by mass unless otherwise noted. Details of the components shown in Table are shown below.

• Fe-Si-Al alloy:trade name "SP-7", soft magnetic particles, flat, average particle size of 65 µm, manufactured by Mate Co., Ltd.
• Acrylate ester polymer: trade name "Paracrom W-197CM", acrylate ester polymer mainly composed of ethyl acrylate-methyl methacrylate, manufactured by Negami Chemical Industrial Co., Ltd.
• Bisphenol A epoxy resin: trade name "Epikote 1004", epoxy equivalent of 875 to 975 g/eq, manufactured by JER
• Bisphenol A epoxy resin: trade name "Epikote YL980", epoxy equivalent of 180 to 190 g/eq, manufactured by JER
• Tetrafunctional aminoglycidyl epoxy resin: trade name "TETRAD-C", epoxy equivalent of 105 g/eq, manufactured by MITSUBISHI GAS CHEMICAL COMPANY, INC.
• Phenolaralkyl resin: trade name, "MILEX XLC-4L", hydroxyl equivalent of 170 g/eq, manufactured by Mitsui Chemicals
• 2-phenyl-4,5-dihydroxymethylimidazole: thermosetting catalyst, trade name "CUREZOL 2-PHZ-PW", manufactured by Shikoku Chemicals Corporation
• Polyether phosphate ester: dispersant, trade name "HIPLAAD ED152", manufactured by Kusumoto Chemicals, Ltd., acid value of 20
• Ethylene acetate vinyl copolymer: trade name "EV170", manufactured by DU

PONT-MITSUI POLYCHEMICALS

[0121] While the illustrative embodiments of the present invention are provided in the above description, such is for illustrative purpose only and it is not to be construed as limiting in any manner. Modification and variation of the present invention that will be obvious to those skilled in the art is to be covered by the following claims.

Industrial Applicability

[0122] The soft magnetic thermosetting film and the soft magnetic film of the present invention can be applied in various industrial products and, for example, can be used for a position detection device such as a digitizer.

Claims

1. A soft magnetic thermosetting film comprising soft magnetic particles, wherein
the ratio (µ1'/µ0') of a relative magnetic permeability µ1' at a frequency of 1 MHz at the time of curing the soft magnetic thermosetting film by heating to be allowed to stand under an atmosphere of 85°C and 85%RH for 168 hours to an initial relative magnetic permeability µ0' at a frequency of 1 MHz immediately after curing the soft magnetic thermosetting film by heating is 0.85 or more.

2. The soft magnetic thermosetting film according to claim 1, wherein
the soft magnetic thermosetting film is formed from a soft magnetic thermosetting composition containing the soft magnetic particles at a ratio of 40% by volume or more.

3. The soft magnetic thermosetting film according to claim 2, wherein
the soft magnetic thermosetting composition contains epoxy resin, phenol resin, and acrylic resin.

4. A soft magnetic film produced by curing a soft magnetic thermosetting film by heating to be brought into a cured state, wherein
the soft magnetic thermosetting film comprises soft magnetic particles, and
the ratio (µ1'/µ0') of a relative magnetic permeability µ1' at a frequency of 1 MHz at the time of curing the soft magnetic thermosetting film by heating to be allowed to stand under an atmosphere of 85°C and 85%RH for 168 hours to an initial relative magnetic permeability µ0' at a frequency of 1 MHz immediately after curing the soft magnetic thermosetting film by heating is 0.85 or more.