SOFT MAGNETIC FILM

Description

TECHNICAL FIELD

[0001] The present invention relates to a soft magnetic 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 mounted on a circuit board and thereafter, a reflowing process is performed. When the magnetic film is subjected to high temperature treatment of above 200°C such as a reflowing process, however, there is a disadvantage that magnetic properties such as relative magnetic permeability deteriorate.

[0007] An object of the present invention is to provide a soft magnetic film in which deterioration of magnetic properties is suppressed after a reflowing process.

MEANS FOR SOLVING THE PROBLEM

[0008] A soft magnetic film of the present invention contains flat soft magnetic particles, wherein the ratio E'₂₀₀/E'₂₃ of a tensile storage elastic modulus E'₂₀₀ at 200°C to a tensile storage elastic modulus E'₂₃ at 23°C in dynamic viscoelasticity measurement at a temperature increase rate of 10°C/min and a frequency of 1 Hz is 0.25 or more.

[0009] It is preferable that the soft magnetic film of the present invention has a tensile storage elastic modulus E'₂₀₀ at 200°C of 8.0 × 10⁸ Pa or more.

[0010] It is preferable that the soft magnetic film of the present invention is formed from a soft magnetic resin composition containing epoxy resin, phenol resin, and acrylic resin.

[0011] It is preferable that in the soft magnetic film of the present invention, a total of the epoxy resin content and the phenol resin content is 20 parts by mass or more and 99 parts by mass or less relative to 100 parts by mass of a soft magnetic particles-excluding component excluding the soft magnetic particles from the soft magnetic resin composition.

[0012] It is preferable that in the soft magnetic film of the present invention, the content ratio of the soft magnetic particles in the soft magnetic resin composition is 30% by volume or more and 70% by volume.

[0013] It is preferable that the soft magnetic film of the present invention is in a cured state.

EFFECT OF THE INVENTION

[0014] The soft magnetic film of the present invention suppresses deterioration of magnetic properties and has excellent magnetic properties after being subjected to high temperature treatment such as a reflowing process.

DESCRIPTION OF EMBODIMENTS

[0015] The soft magnetic film of the present invention is, for example, formed from a soft magnetic composition containing soft magnetic particles and a resin component into a film shape (sheet shape).

[0016] 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.

[0017] 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.

[0018] The soft magnetic particles are shaped flat (plate). That is, the soft magnetic particles are formed into a shape having a thin thickness and a wide surface. The aspect ratio thereof is, for example, 8 or more, preferably 15 or more, and for example, 80 or less, preferably 65 or less. The aspect ratio is, for example, 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.

[0019] 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.

[0020]  The mass ratio of the soft magnetic particles in the soft magnetic resin composition (and in 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 resin 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.

[0021] The resin component may contain either a thermosetting resin or a thermoplastic resin. Preferably, the resin component contains a thermosetting resin.

[0022] 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.

[0023] The epoxy resin, for example, used as an adhesive composition can be used. Examples thereof include 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. 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.

[0024] Of these epoxy resins, preferably, bisphenol epoxy resin is used, or more preferably, bisphenol A epoxy resin is used. Containing such an epoxy resin allows for excellent reactivity with phenol resin, and as a result, the soft magnetic film has excellent reflow resistance.

[0025] 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.

[0026] 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 reflow resistance.

[0027] 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, more preferably 45 parts by mass or more, and for example, 70 parts by mass or less, preferably, 50 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 25 parts by mass or less.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 film in a semi-cured state is excellent, and deterioration can be suppressed.

[0032] 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 in a cured state is produced by laminating a plurality of soft magnetic films in a semi-cured state and hot pressing the laminate, a soft magnetic film having a uniform laminated interface without unevenness and having excellent magnetic properties can be produced.

[0033] 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".

[0034] 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.

[0035] The acrylic-type polymer can be a copolymer of the alkyl (meth)acrylate ester and an additional monomer.

[0036] 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.

[0037] 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, heat resistance of the soft magnetic film is excellent.

[0038] 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.

[0039] 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 film with excellent adhesiveness and heat resistance can be achieved. The weight-average molecular weight is measured by gel permeation chromatography (GPC) based on a polystyrene standard calibration value.

[0040] 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 film in a semi-cured state is excellent. Meanwhile, when the glass transition temperature (Tg) is the above-described upper limit or less, handleability of the soft magnetic 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).

[0041] When the resin component contains the acrylic resin, the thermosetting resin content of the resin component is, for example, 20 mass% or more, preferably above 50 mass%, more preferably 60 mass% or more, further more preferably 65 mass% or more, and for example, 90 mass% or less, preferably 80 mass% or less, or more preferably 70 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 high temperature, and occurrence of a void in the soft magnetic film can be effectively suppressed, so that reflow resistance of the soft magnetic film is excellent.

[0042] The acrylic resin content of the resin component is, for example, 10 mass% or more, preferably 20 mass% or more, more preferably 30 mass% or more, and for example, 80 mass% or less, preferably less than 50 mass%, more preferably 40 mass% or less, further more preferably 35 mass% or less.

[0043] The resin component content of the soft magnetic resin 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.

[0044]  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 resin composition, is, for example, 20 parts by mass or more, preferably 40 parts by mass or more, more preferably above 50 parts by mass, further more preferably 60 parts by mass or more, most preferably 65 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, most preferably 70 parts by mass or less. By setting the thermosetting resin content in the above-described range, the soft magnetic film has excellent reflow resistance.

[0045] 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.

[0046] The resin component can contain an additional thermoplastic resin other than the thermosetting resin and the acrylic resin.

[0047] 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.

[0048] The soft magnetic resin composition (and the soft magnetic film) preferably contains a thermosetting catalyst.

[0049] 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.

[0050] 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.

[0051] The thermosetting catalyst has a shape of, for example, spherical or ellipsoidal.

[0052] 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 film in a semi-cured state can be cured by heating at low temperature and for a short period of time, and excellent reflow resistance can be achieved.

[0053] The soft magnetic resin composition (and the soft magnetic film) may contain another additive as necessary. Examples thereof include commercially available or known additives such as a dispersant, a cross-linking agent, and an inorganic filler.

[0054] The soft magnetic resin composition preferably contains a dispersant.

[0055] 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 resin composition to contain a dispersant, particularly polyether phosphate ester, coating properties of the soft magnetic resin composition can be improved and magnetic properties of the soft magnetic film can be further improved.

[0056] Examples of the polyether phosphate ester include polyoxyalkylene alkyl ether phosphate and polyoxyalkylene alkyl phenyl ether phosphate. Preferably, polyoxyalkylene alkyl ether phosphate is used.

[0057] 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.

[0058] 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.

[0059] Examples of the silane coupling agent include 3-methacryloxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0060] These dispersants can be used singly, or can be used in combination of two or more.

[0061] 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").

[0062] 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.

[0063]  The soft magnetic resin composition can be prepared by mixing the above-described components at the above-described content ratio.

[0064] The soft magnetic resin composition is prepared by mixing the above-described components at the above-described content ratio.

[0065] The soft magnetic film can be, for example, produced by a preparing step of preparing a soft magnetic resin composition solution by dissolving or dispersing the soft magnetic resin composition in a solvent, a drying step of producing a soft magnetic film in a semi-cured state by being applied to a surface of a release substrate to be dried, and a hot pressing step of laminating a plurality of soft magnetic films in a semi-cured state to be hot pressed.

[0066] First, a soft magnetic resin composition is dissolved or dispersed in a solvent (preparing step). In this manner, a soft magnetic resin composition solution is prepared.

[0067] 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.

[0068] The soft magnetic resin 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.

[0069] Then, the soft magnetic resin composition solution is applied to a surface of a release substrate (separator, core material, etc.) to be dried (drying step).

[0070] The application method is not particularly limited, and for example, doctor blades, roll coating, screen coating, and gravure coating can be used.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The separator or the core material has an average thickness of, for example, 1 µm or more and 500 µm or less.

[0075] In this manner, the soft magnetic film in a semi-cured state is produced.

[0076] The soft magnetic 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.

[0077] The soft magnetic film (in a semi-cured state) 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.

[0078] Next, a plurality of obtained soft magnetic films in a semi-cured state are prepared and the plurality of soft magnetic films are hot pressed in the thickness direction (hot pressing step). In this manner, the soft magnetic films in a semi-cured state (and the soft magnetic composition) are cured by heating. Also, the soft magnetic 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 film (in a semi-cured state) 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 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] The tensile storage elastic modulus E'₂₃ at 23°C is, for example, 8.0 × 10⁸ Pa or more, preferably, 1.0 × 10⁹ Pa or more, more preferably 1.0 × 10¹⁰ Pa or more, and for example, 1.0 × 10²⁰ Pa or less.

[0087] The tensile storage elastic modulus E'₂₀₀ at 200°C is, for example, 1.0 × 10⁸ Pa or more, preferably, 8.0 × 10⁸ Pa or more, more preferably 5.0 × 10⁹ Pa or more, and for example, 1.0 × 10²⁰ Pa or less. In this manner, further more excellent reflow resistance of the soft magnetic film can be achieved.

[0088] The ratio E'₂₀₀/E'₂₃ of E'₂₀₀ to E'₂₃ is, for example, 0.25 or more, preferably 0.40 or more, more preferably 0.42 or more, further more preferably 0.45 or more, and for example, 0.90 or less. In this manner, excellent reflow resistance of the soft magnetic film can be achieved.

[0089] The tensile storage elastic modulus (E'₂₃ and E'₂₀₀) is measured using a Dynamic Mechanical Analyzer under the conditions of temperature increase rate of 10°C/min and a frequency of 1 Hz.

[0090] In the soft magnetic film, preferably, the flat 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. In this manner, the soft magnetic 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 film is achieved.

[0091] The soft magnetic film has a relative magnetic permeability (before reflowing process) of, for example, 150 or more, preferably 160 or more, more preferably 180 or more, and for example, 500 or less.

[0092] 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.

[0093] In the above-described embodiment, a plurality of soft magnetic films in a semi-cured state are laminated and the laminate is hot pressed. Alternatively, for example, one piece (single layer) of soft magnetic film in a semi-cured state can be also hot pressed.

[0094] In the above-described embodiment, the soft magnetic film in a semi-cured state is hot pressed, but the hot pressing may not be performed. That is, the soft magnetic film in a semi-cured state can be also used. The soft magnetic film in a semi-cured state has adhesiveness in its surface, so that it can be directly laminated on a circuit board without using, for example, an adhesive. Thereafter, the soft magnetic film in a semi-cured state is cured by heating as necessary, so that a soft magnetic film in a cured state can be also produced.

[0095] 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.

[0096] Examples of a method for laminating the soft magnetic film on the circuit board include a method in which the soft magnetic film in a cured state is fixed to the circuit board via an adhesive layer and a method in which after the soft magnetic film in a semi-cured state is directly attached to the circuit board, the soft magnetic film in a semi-cured state is cured by heating to be fixed to the circuit board.

[0097] In view of unnecessity of an adhesive layer and miniaturization of an electronic device, preferably, a method in which after the soft magnetic film in a semi-cured state is directly attached to the circuit board, the soft magnetic film is cured by heating is used.

[0098] In view of insulation properties, preferably, a method in which the soft magnetic film in a cured state is fixed to the circuit board via the adhesive layer is used.

[0099] 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.

[0100] According to the soft magnetic film, the ratio (E'₂₀₀/E'₂₃) of the tensile storage elastic modulus E'₂₀₀ at 200°C to the tensile storage elastic modulus E'₂₃ at 23°C is 0.25 or more, so that when the soft magnetic film is subjected to reflowing treatment, deterioration of the relative magnetic permeability of the soft magnetic film can be suppressed. That is, reflow resistance is excellent. In this manner, when a reflowing process is performed in a mounted circuit board including the soft magnetic film, the soft magnetic film can surely develop excellent magnetic properties with respect to the mounted circuit board.

[0101] The temperature in the reflowing process is, for example, 200°C or more, preferably 250°C or more, and for example, 500°C or less, preferably 300°C or less.

[0102] The reflow storage time is, for example, 1 second or more, preferably 5 seconds or more, and for example, 10 minutes or less, preferably 5 minutes or less.

[0103] The soft magnetic film after the reflowing process has a relative magnetic permeability of, for example, 150 or more, preferably 160 or more, more preferably 180 or more, and for example, 500 or less.

Examples

[0104] 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

[0105] A soft magnetic resin composition was produced by mixing 500 parts by mass of soft magnetic particles, 59 parts by mass of an acrylate ester polymer, 8 parts by mass of bisphenol A epoxy resin ("Epikote 1004"), 4 parts by mass of bisphenol A epoxy resin ("Epikote YL980), 5 parts by mass of phenol aralkyl resin, 0.81 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 50% by volume relative to the soft magnetic resin composition.

[0106] The soft magnetic resin composition was dissolved in methyl ethyl ketone, thereby producing a soft magnetic resin composition solution having a solid content concentration of 43 mass%.

[0107] The soft magnetic resin 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. In this manner, a soft magnetic film in a semi-cured state (average thickness of only soft magnetic film was 90 µm) on which a separator was laminated was produced.

[0108]  Next, the soft magnetic 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 in a cured state.

Examples 2 and 3

[0109] Soft magnetic resin compositions were produced based on the materials and the mixing ratios shown in Table 1. Soft magnetic films in a cured state of Examples 2 and 3 were produced in the same manner as in Example 1, except that these soft magnetic resin compositions were used.

Comparative Example 1

(Soft magnetic film)

[0110] A soft magnetic resin 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 resin composition.

[0111] The soft magnetic resin composition was dissolved in toluene, thereby producing a soft magnetic resin composition solution having a solid content concentration of 40 mass%.

[0112] The soft magnetic resin 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. In this manner, a soft magnetic film in a semi-cured state (average thickness of only soft magnetic film was 90 µm) on which a separator was laminated was produced.

[0113] Next, the soft magnetic 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 Example 2

[0114] A soft magnetic resin composition was produced based on the materials and the mixing ratios shown in Table 1. A soft magnetic film of Comparative Example 2 was produced in the same manner as in Example 1, except that this soft magnetic resin composition was used.

(Measurement of tensile storage elastic modulus E'₂₃ and E'₂₀₀)

[0115] In each of the soft magnetic films of Examples and Comparative Examples, the dynamic viscoelasticity measurement was performed based on the following conditions, so that each of the tensile storage elastic modulus E'₂₃ at 23°C and the tensile storage elastic modulus E'₂₀₀ at 200°C was obtained.

[0116] Dynamic Mechanical Analyzer (MDA): trade name: "RSA III", manufactured by Rheometric Scientific, Inc.
Mode: tensile mode
Temperature increase rate: 10°C/min
Frequency: 1 Hz
Sample thickness: 90 µm
Distance between chucks: 20 mm
Strain: 0.1%
Measurement temperature range: 0°C to 210°C
The results and the ratio (E'₂₀₀/E'₂₃) are shown in Table 1.

(Magnetic properties)

[0117] The relative magnetic permeability of each of the soft magnetic films of Examples and Comparative Examples was measured by a one turn method (frequency of 1 MHz) using an impedance analyzer (manufactured by Agilent Technologies, "4294A"). The results are shown in Table 1.

(Reflow resistance)

[0118] Each of the soft magnetic films of Examples and Comparative Examples was laminated on a circuit board. A reflowing process was performed by allowing the obtained soft magnetic film laminated circuit board to pass through the inside of an IR reflow oven under the conditions of 260°C for 10 seconds.

[0119] The relative magnetic permeability of the soft magnetic film in the soft magnetic film laminated circuit board that was subjected to the reflowing process was measured by a one turn method (frequency of 1 MHz) using an impedance analyzer (manufactured by Agilent Technologies, "4294A"). The results are shown in Table 1.

[0120] [Table 1]

[Table 1]

				Ex. 1	Ex. 2	Ex. 3	Comp. Ex. 1	Comp. Ex. 2
	Soft Magnetic Particles	parts bv mass		500	500	500	500	500
		% bv volume		50	55	60	40	50
	Resin Component	Acrylic Resin	Paracron W197CM	59	22	25	-	74
		Epoxy Resin	Epikote 1004	8	19	13	-	-
Soft Magnetic Resin Composition			Epikote YL980	4	11	7	-	-
			TETRAD-C	-	-	-	-	1.2
		Phenol Resin	MILEX XLC4L	5	13	9	-	-
		Ethylene-Vinyl Acetate	EV170	-	-	-	106	-
	Thermosetting Catalyst	Imidazole	2PHZ-PW	0.81	0.66	0.53	-	-
	Dispersant	Polyether Phosphate Ester	ED152	2.5	2.5	2.5	-	2.5
	Tensile Storage Elastic Modulus E'23 at 23°C (Pa)			2.90 × 109	1.93 × 109	1.47 × 1010	5.25 × 109	3.47 × 109
	Tensile Storage Elastic Modulus E'200 at 200°C (Pa)			1.15 × 109	8.17 × 108	7.18 × 109	9.36 × 105	7.64 × 108
	E'200/ E'23			0.40	0.42	0.49	0.0018	0.22
	Relative Magnetic Permeability (before Reflowing)			160	174	200	120	157
	Relative Magnetic Permeability (after Reflowing)			158	174	200	78	130

[0121] 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 "Paracron W-197CM", acrylate ester polymer mainly composed of ethyl acrylate-methyl methacrylate, manufactured by Negami Chemical Industirial 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 ED 152", manufactured by Kusumoto Chemicals, Ltd., acid value of 20
• Ethylene acetate vinyl copolymer: trade name "EV170", manufactured by DU

PONT-MITSUI POLYCHEMICALS

[0122] 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

[0123] 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 film comprising flat soft magnetic particles, wherein
the ratio E'₂₀₀/F'₂₃ of a tensile storage elastic modulus E'₂₀₀ at 200°C to a tensile storage elastic modulus E'₂₃ at 23°C in dynamic viscoelasticity measurement at a temperature increase rate of 10°C/min and a frequency of 1 Hz is 0.25 or more.

2. The soft magnetic film according to claim 1, wherein
the soft magnetic film has a tensile storage elastic modulus E'₂₀₀ at 200°C of 8.0 × 10⁸ Pa or more.

3. The soft magnetic film according to claim 1, wherein
the soft magnetic film is formed from a soft magnetic resin composition containing epoxy resin, phenol resin, and acrylic resin.

4. The soft magnetic film according to claim 3, wherein
a total of the epoxy resin content and the phenol resin content is 20 parts by mass or more and 99 parts by mass or less relative to 100 parts by mass of a soft magnetic particles-excluding component excluding the soft magnetic particles from the soft magnetic resin composition.

5. The soft magnetic film according to claim 4, wherein
the content ratio of the soft magnetic particles in the soft magnetic resin composition is 30% by volume or more and 70% by volume.

6. The soft magnetic film according to claim 1, wherein
the soft magnetic film is in a cured state.