JP7563375B2 - Magnetic Film - Google Patents

Description

The present invention relates to a magnetic film having a resin composition layer containing magnetic powder and a cover film layer.

Inductors known as power inductors, high-frequency inductors, and common mode choke coils are used in large numbers in information terminals such as mobile phones and smartphones. Traditionally, independent inductor components were mounted on a circuit board, but in recent years, a method has come to be used in which coils are formed using the conductor pattern of the circuit board and the inductor is installed inside the circuit board.

For example, Patent Document 1 discloses that an inductor substrate is embedded in a core substrate of a circuit substrate in order to reduce the thickness of the circuit substrate, and discloses an inductor substrate in which an inductor is formed by a plurality of conductor patterns formed on an insulating layer. It also discloses an adhesive film in which magnetic powder is contained in a resin composition constituting the resin composition layer of a resin sheet with a support as a material for forming the insulating layer.

In order to meet the recent demand for thinner and smaller information terminals and to make inductor elements thinner and smaller, it is necessary to reduce the number of turns in the coil and the cross-sectional area of the wiring that makes up the coil. However, in an inductor composed of a conductor pattern on a magnetic layer formed from an adhesive magnetic film as described above, simply reducing the number of turns in the coil and reducing the cross-sectional area of the wiring that makes up the coil results in a decrease in inductance. On the other hand, if the magnetic permeability (μ') of the magnetic layer can be increased, the L value and Q value of the inductor element can be improved, so there is a demand for the development of a magnetic film that can form a magnetic layer with high magnetic permeability.

JP 2012-186440 A

Adhesive films used as insulating layers for printed circuit boards are generally produced by applying a varnish of a resin composition to a support and then heating and drying the resin composition to form a resin composition layer. A cover film layer may be provided on the surface of the resin composition layer opposite the support to prevent adhesion of foreign matter, etc. Biaxially oriented polypropylene film (OPP film) is usually used as the cover film.

However, as a result of intensive research by the present inventors, it was found that in a magnetic film, when a cover film layer is provided on a resin composition layer containing magnetic powder, the cover film layer tends not to adhere to the resin composition layer. In particular, the tendency becomes more pronounced as the content of magnetic powder in the resin composition is increased to achieve high magnetic permeability, etc. In an adhesive film used for insulating layers of printed circuit boards, which has a resin composition layer containing an inorganic filler such as silica, the cover film layer adheres relatively easily to the resin composition layer, and the above problem is a new problem that arises from the use of a resin composition layer containing magnetic powder.

If a cover film layer is not provided on the magnetic film, in the case of a sheet-form product, the risk of foreign matter adhering increases when preparing the film into sheet form or when packaging. On the other hand, in the case of a roll-form product, it is possible to reduce the risk of dust adhering compared to sheets. However, even in this case, there is a risk of foreign matter present on the support surface adhering when wound into a roll. Even in the case of a roll-form product, if the magnetic film is slit for use, the risk of foreign matter adhering still increases.

The objective of the present invention is to provide a magnetic film that can suppress adhesion of foreign matter to a resin composition layer containing magnetic powder by providing a cover film layer on the resin composition layer, and a method for manufacturing the same.

As a result of intensive research conducted by the inventors in order to achieve the above-mentioned objective, they discovered that a specified cover film layer can be easily attached even to a resin composition layer containing magnetic powder, and thus completed the present invention.

That is, the present invention includes the following.
[1] A support;
a resin composition layer formed from a resin composition provided on the support;
A cover film layer bonded to a surface of the resin composition layer opposite to the support,
The resin composition contains a magnetic powder,
A magnetic film, wherein the cover film layer is a self-adhesive film.
[2] The magnetic film according to [1], wherein the content of the magnetic powder is 75% by mass or more and 98% by mass or less, when the non-volatile content of the resin composition is 100% by mass.
[3] The magnetic film according to [1] or [2], wherein the minimum melt viscosity of the resin composition layer is 50,000 poise or more and 50,000,000 poise or less.
[4] The magnetic film according to any one of [1] to [3], wherein the resin composition is a thermosetting resin composition.
[5] The magnetic film according to any one of [1] to [4], wherein the resin composition contains an epoxy resin.
[6] The magnetic film according to any one of [1] to [5], wherein the resin composition contains at least one of a curing agent and a curing accelerator.
[7] The magnetic film according to any one of [1] to [6], wherein the resin composition contains a thermoplastic resin.
[8] The magnetic film according to any one of [1] to [7], wherein the adhesive strength of the cover film layer to the resin composition layer is 0.1 gf/cm or more and 10 gf/cm or less.
[9] The magnetic film according to any one of [1] to [8], wherein the magnetic powder is at least one selected from iron oxide powder and iron alloy metal powder.
[10] A method for producing a magnetic film according to any one of [1] to [9],
A method for producing a magnetic film, comprising: a step of applying a resin varnish containing a resin composition onto a support to form a resin composition layer; and a step of laminating a cover film layer onto the resin composition layer.

According to the present invention, it is possible to provide a magnetic film and a manufacturing method thereof that can suppress adhesion of foreign matter to a resin composition layer even when the film has a resin composition layer containing magnetic powder.

FIG. 1 is a schematic cross-sectional view showing an example of a magnetic film.

Below, an embodiment of the present invention will be described with reference to the drawings. Note that FIG. 1 merely shows the shape, size, and arrangement of the components in a schematic manner to the extent that the invention can be understood. The present invention is not limited by the following description, and each component can be modified as appropriate. In the drawings used in the following description, similar components are indicated with the same reference numerals, and duplicated descriptions may be omitted. Furthermore, the configuration according to the embodiment of the present invention is not necessarily manufactured or used according to the arrangement of the illustrated example.

[Magnetic film]
The magnetic film of the present invention has a resin composition layer formed from a resin composition provided on a support, and a cover film layer bonded to the surface of the resin composition layer opposite to the support, the resin composition containing a magnetic powder, and the cover film layer being a self-adhesive film. One or more arbitrary layers may be provided between the support and the resin composition layer.

Fig. 1 is a schematic cross-sectional view showing an example of the magnetic film of the present invention. In the magnetic film 1 shown in Fig. 1, a support 11, a resin composition layer 12, and a cover film layer 13 are laminated in this order.
Each layer constituting the magnetic film of the present invention will now be described in detail.

<Support>
The magnetic film has a support, which can be, for example, a film made of a plastic material, a metal foil, or a release paper, with a film made of a plastic material and a metal foil being preferred.

When a film made of a plastic material is used as the support, examples of the plastic material include polyesters such as polyethylene terephthalate (hereinafter sometimes abbreviated as "PET") and polyethylene naphthalate (hereinafter sometimes abbreviated as "PEN"), polycarbonate (hereinafter sometimes abbreviated as "PC"), acrylics such as polymethyl methacrylate (PMMA), cyclic polyolefins, triacetyl cellulose (TAC), polyether sulfide (PES), polyether ketone, polyimide, etc. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred, with inexpensive polyethylene terephthalate being particularly preferred.

When a metal foil is used as the support, examples of the metal foil include copper foil and aluminum foil, with copper foil being preferred. As the copper foil, a foil made of a single metal, copper, or an alloy of copper and another metal (e.g., tin, chromium, silver, magnesium, nickel, zirconium, silicon, titanium, etc.) may be used.

When the support and the resin composition layer are joined, the support may be subjected to a matte treatment or corona treatment on the surface that will be joined to the resin composition layer.

In addition, in cases where the support and the resin composition layer are bonded, a support with a release layer having a release layer on the surface of the support that is bonded to the resin composition layer may be used. Examples of the release agent used in the release layer of the support with a release layer include one or more release agents selected from the group consisting of alkyd resins, polyolefin resins, urethane resins, and silicone resins. The support with a release layer may be a commercially available product, such as "SK-1", "AL-5", and "AL-7" manufactured by Lintec Corporation, "Lumirror T60" manufactured by Toray Industries, Inc., "Purex" manufactured by Teijin Limited, and "Unipeel" manufactured by Unitika Limited, which are PET films having a release layer mainly composed of an alkyd resin-based release agent.

The thickness of the support is not particularly limited, but is preferably in the range of 5 μm to 75 μm, and more preferably in the range of 10 μm to 60 μm. When using a support with a release layer, it is preferable that the thickness of the entire support with the release layer is in the above range.

<Resin composition layer>
The magnetic film has a resin composition layer containing a resin composition. The resin composition layer is formed directly or indirectly on the support, and a cover film layer is provided on the surface opposite to the surface on the support side. The resin composition may contain magnetic powder, and the cured product usually has sufficient mechanical strength and relative magnetic permeability. For this reason, the resin composition is preferably a thermosetting resin composition containing magnetic powder. Examples of such thermosetting resin compositions include compositions containing magnetic powder and thermosetting resin. As the thermosetting resin, a conventionally known curable resin used when forming the magnetic layer of an inductor element can be used, and among them, an epoxy resin is preferable. Therefore, in one embodiment, the resin composition contains (a) magnetic powder and (b) epoxy resin. The resin composition may further contain (c) a curing agent, (d) a curing accelerator, (e) a thermoplastic resin, (f) an inorganic filler other than the magnetic powder, and (g) other additives, as necessary.

--(a) Magnetic powder--
The resin composition contains (a) a magnetic powder. When the cured resin composition layer is included in an inductor substrate, the (a) magnetic powder is preferably a soft magnetic powder. Examples of the (a) magnetic powder include soft magnetic powders such as pure iron powder, Mg-Zn ferrite, Fe-Mn ferrite, Mn-Zn ferrite, Mn-Mg ferrite, Cu-Zn ferrite, Mg-Mn-Sr ferrite, Ni-Zn ferrite, Ba-Zn ferrite, Ba-Mg ferrite, Ba-Ni ferrite, Ba-Co ferrite, Ba-Ni-Co ferrite, Y ferrite, iron oxide powder (III), and tetrahydrofuran. Examples of the iron oxide powder include iron oxide powder such as ferric oxide; iron alloy metal powders such as Fe-Si alloy powder, Fe-Si-Al alloy powder, Fe-Cr alloy powder, Fe-Cr-Si alloy powder, Fe-Ni-Cr alloy powder, Fe-Cr-Al alloy powder, Fe-Ni alloy powder, Fe-Ni-Mo alloy powder, Fe-Ni-Mo-Cu alloy powder, Fe-Co alloy powder, and Fe-Ni-Co alloy powder; and amorphous alloys such as Co-based amorphous alloys.

Among them, (a) the magnetic powder is preferably at least one selected from iron oxide powder and iron alloy metal powder. The iron oxide powder preferably contains ferrite containing at least one selected from Ni, Cu, Mn, and Zn. The iron alloy metal powder preferably contains iron alloy metal powder containing at least one selected from Si, Cr, Al, Ni, and Co.

(a) As the magnetic powder, commercially available magnetic powders can be used. Specific examples of commercially available magnetic powders that can be used include "M05S" manufactured by Powdertech Co., Ltd.; "PST-S" manufactured by Sanyo Special Steel Co., Ltd.; "AW2-08", "AW2-08PF20F", "AW2-08PF10F", "AW2-08PF3F", "Fe-3.5Si-4.5CrPF20F", "Fe-50NiPF20F", "Fe-80Ni-4MoPF20F" manufactured by Epson Atmix Corporation; "LD-M", "LD-MH", "KNI-106", "KNI-106GSM", "KNI-106GS", and "KNI-109" manufactured by JFE Chemical Corporation. ", "KNI-109GSM", "KNI-109GS"; Toda Kogyo Co., Ltd. "KNS-415", "BSF-547", "BSF-029", "BSN-125", "BSN-125", "BSN-714", "BSN-828", "S-1281", "S-1641", "S-1651", "S-1470", "S-1511", "S-2430"; Japan Metals and Chemical Industries Co., Ltd. "JR09P2"; CIK Nanotech Co., Ltd. "Nanotek"; Kinsei Matec Co., Ltd. "JEMK-S", "JEMK-H"; ALDRICH Co., Ltd. "Yttrium iron oxide" and the like. The magnetic powder may be used alone or in combination of two or more types.

(a) The magnetic powder is preferably spherical. The aspect ratio (the value obtained by dividing the length of the long axis of the magnetic powder by the length of the short axis) is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1.2 or less. In general, it is easier to improve the relative permeability if the magnetic powder is flat and not spherical. However, it is usually preferable to use spherical magnetic powder, in particular, from the viewpoint of reducing magnetic loss.

(a) From the viewpoint of improving the relative magnetic permeability, the average particle size of the magnetic powder is preferably 0.01 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. Also, it is preferably 8 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less.

(a) The average particle size of magnetic powder can be measured by a laser diffraction/scattering method based on Mie scattering theory. Specifically, a particle size distribution of the magnetic powder is created on a volume basis using a laser diffraction/scattering type particle size distribution measuring device, and the median diameter is taken as the average particle size. The measurement sample is preferably magnetic powder dispersed in water using ultrasonic waves. Examples of laser diffraction/scattering type particle size distribution measuring devices that can be used include the "LA-500" manufactured by Horiba, Ltd. and the "SALD-2200" manufactured by Shimadzu Corporation.

(a) From the viewpoint of improving the relative magnetic permeability and reducing the loss coefficient, the content (volume %) of the magnetic powder is preferably 10% by volume or more, more preferably 20% by volume or more, and even more preferably 30% by volume or more, assuming that the non-volatile components in the resin composition are 100% by volume. Also, it is preferably 85% by volume or less, more preferably 80% by volume or less, and even more preferably 75% by volume or less.

(a) From the viewpoint of improving the relative magnetic permeability and reducing the loss coefficient, the content (mass%) of the magnetic powder is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 84% by mass or more, when the non-volatile components in the resin composition are taken as 100% by mass. It is also preferably 98% by mass or less, more preferably 96% by mass or less, and even more preferably 95% by mass or less. In the present invention, the content of each component in the resin composition is the value when the non-volatile components in the resin composition are taken as 100% by mass, unless otherwise specified.

-(b) Epoxy resin-
The resin composition contains an epoxy resin as component (b). The epoxy resin (b) disperses and bonds the magnetic powder (a) in the resin composition, and can form a magnetic layer having sufficient mechanical strength.

Examples of epoxy resins include glycirol type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenol AF type epoxy resins, dicyclopentadiene type epoxy resins, trisphenol type epoxy resins, phenol novolac type epoxy resins, tert-butyl-catechol type epoxy resins, naphthol novolac type epoxy resins, naphthalene type epoxy resins, naphthol type epoxy resins, anthracene type epoxy resins, and other epoxy resins having a condensed ring structure; glycidylamine type epoxy resins, glycidyl ester type epoxy resins, cresol novolac type epoxy resins, biphenyl type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexane dimethanol type epoxy resins, trimethylol type epoxy resins, and tetraphenylethane type epoxy resins. The epoxy resins may be used alone or in combination of two or more. The epoxy resin is preferably at least one selected from bisphenol A type epoxy resins and bisphenol F type epoxy resins.

The epoxy resin preferably contains an epoxy resin having two or more epoxy groups in one molecule. The epoxy resin preferably has an aromatic structure, and when two or more epoxy resins are used, it is more preferable that at least one of them has an aromatic structure. The aromatic structure is a chemical structure generally defined as aromatic, and also includes polycyclic aromatics and aromatic heterocycles. The ratio of the epoxy resin having two or more epoxy groups in one molecule to 100% by mass of the non-volatile components of the epoxy resin is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

Epoxy resins include epoxy resins that are liquid at a temperature of 25°C (hereinafter sometimes referred to as "liquid epoxy resins") and epoxy resins that are solid at a temperature of 25°C (hereinafter sometimes referred to as "solid epoxy resins"). When an epoxy resin is contained as component (b), the epoxy resin may contain only liquid epoxy resin, may contain only solid epoxy resin, or may contain a combination of liquid epoxy resin and solid epoxy resin. However, from the viewpoint of improving the adhesive strength between the resin composition layer and the cover film layer, it is preferable to contain a combination of liquid epoxy resin and solid epoxy resin.

Preferred liquid epoxy resins are glycidylol type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AF type epoxy resins, naphthalene type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, phenol novolac type epoxy resins, alicyclic epoxy resins having an ester skeleton, cyclohexane dimethanol type epoxy resins, and epoxy resins having a butadiene structure, with glycidyl amine type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AF type epoxy resins, and naphthalene type epoxy resins being more preferred. Specific examples of liquid epoxy resins include "HP4032", "HP4032D", and "HP4032SS" (naphthalene type epoxy resins) manufactured by DIC Corporation; "828US", "jER828EL" (bisphenol A type epoxy resin), "jER807" (bisphenol F type epoxy resin), and "jER152" (phenol novolac type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "630" and "630LSD" manufactured by Mitsubishi Chemical Corporation; "ED-523T" (glycirol type epoxy resin (ADEKA glycirol)), "EP-3980S" (glycidylamine type epoxy resin), and "EP-4 088S" (dicyclopentadiene type epoxy resin); "ZX1059" (mixture of bisphenol A type epoxy resin and bisphenol F type epoxy resin), "EX-201" (alicyclic glycidyl ether), "ZX1658", "ZX1658GS" (liquid 1,4-glycidylcyclohexane) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "EX-721" (glycidyl ester type epoxy resin) manufactured by Nagase ChemteX Corporation; "Celloxide 2021P" (alicyclic epoxy resin having an ester skeleton) and "PB-3600" (epoxy resin having a butadiene structure) manufactured by Daicel Corporation. These may be used alone or in combination of two or more types.

As solid epoxy resins, naphthalene-type tetrafunctional epoxy resins, cresol novolac-type epoxy resins, dicyclopentadiene-type epoxy resins, trisphenol-type epoxy resins, naphthol-type epoxy resins, biphenyl-type epoxy resins, naphthylene ether-type epoxy resins, anthracene-type epoxy resins, bisphenol A-type epoxy resins, and tetraphenylethane-type epoxy resins are preferred, with naphthalene-type tetrafunctional epoxy resins, naphthol-type epoxy resins, and biphenyl-type epoxy resins being more preferred. Specific examples of solid epoxy resins include "HP4032H" (naphthalene type epoxy resin), "HP-4700", "HP-4710" (naphthalene type tetrafunctional epoxy resin), "N-690" (cresol novolac type epoxy resin), "N-695" (cresol novolac type epoxy resin), "HP-7200", "HP-7200HH", "HP-7200H" (dicyclopentadiene type epoxy resin), "EXA-7311", "EXA-7311-G3", "EXA-7311-G4", "EXA-7311-G4S", "HP6000" (naphthylene ether type epoxy resin), manufactured by DIC Corporation; "EPPN-502H" (trisphenol type epoxy resin), "NC7000L" (naphthol novolac type epoxy resin), "NC3000H", "NC3000H" (naphthol novolac type epoxy resin), manufactured by Nippon Kayaku Co., Ltd. 00, "NC3000L", "NC3100" (biphenyl type epoxy resin); "ESN475V" (naphthalene type epoxy resin) and "ESN485" (naphthol novolac type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YX4000H", "YL6121" (biphenyl type epoxy resin), "YX4000HK" (bixylenol type epoxy resin), "YX8800" (anthracene type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "PG-100", "CG-500" manufactured by Osaka Gas Chemical Co., Ltd., "YL7760" (bisphenol AF type epoxy resin), "YL7800" (fluorene type epoxy resin), "jER1010" (solid bisphenol A type epoxy resin), "jER1031S" (tetraphenylethane type epoxy resin) and the like. These may be used alone or in combination of two or more.

When a liquid epoxy resin and a solid epoxy resin are used in combination as component (b), the ratio by mass (liquid epoxy resin:solid epoxy resin) is preferably 1:0.1 to 1:4, more preferably 1:0.3 to 1:3.5, and even more preferably 1:0.6 to 1:3.

The epoxy equivalent of the epoxy resin as component (b) is preferably 50 g/eq. to 5000 g/eq., more preferably 50 g/eq. to 3000 g/eq., even more preferably 80 g/eq. to 2000 g/eq., and even more preferably 110 g/eq. to 1000 g/eq. By being in this range, the crosslink density of the cured product is sufficient, and a magnetic layer with small surface roughness can be obtained. The epoxy equivalent can be measured according to JIS K7236 and is the mass of the resin containing one equivalent of epoxy groups.

The weight average molecular weight of the epoxy resin as component (b) is preferably 100 to 5000, more preferably 250 to 3000, and even more preferably 400 to 1500. Here, the weight average molecular weight of the epoxy resin is the weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

(b) From the viewpoint of obtaining a magnetic layer exhibiting good mechanical strength, the content of the epoxy resin is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, when the non-volatile components in the resin composition are taken as 100% by mass, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

--(c) Hardener--
The resin composition may contain a (c) curing agent as an optional component. By using the (c) curing agent, the curing of the epoxy resin can be effectively promoted, and the mechanical strength of the cured product can be increased. Examples of the (c) curing agent include active ester curing agents, phenolic curing agents, naphthol curing agents, benzoxazine curing agents, cyanate ester curing agents, and carbodiimide curing agents. As the (c) curing agent, active ester curing agents, phenolic curing agents, and naphthol curing agents are preferred from the viewpoint of heat resistance and mechanical strength of the cured product of the resin composition. The (c) curing agent may be used alone or in combination of two or more types.

As the active ester curing agent, a resin having one or more active ester groups in one molecule can be used. Among them, as the active ester curing agent, a resin having two or more highly reactive ester groups in one molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds, is preferred. The active ester curing agent is preferably one obtained by a condensation reaction between a carboxylic acid compound and/or a thiocarboxylic acid compound and a hydroxy compound and/or a thiol compound. In particular, from the viewpoint of improving heat resistance, an active ester curing agent obtained from a carboxylic acid compound and a hydroxy compound is preferred, and an active ester curing agent obtained from a carboxylic acid compound and a phenol compound and/or a naphthol compound is more preferred.

Examples of carboxylic acid compounds include benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and pyromellitic acid.

Examples of phenol compounds or naphthol compounds include hydroquinone, resorcin, bisphenol A, bisphenol F, bisphenol S, phenolphthaline, methylated bisphenol A, methylated bisphenol F, methylated bisphenol S, phenol, o-cresol, m-cresol, p-cresol, catechol, α-naphthol, β-naphthol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, phloroglucin, benzenetriol, dicyclopentadiene-type diphenol compounds, and phenol novolak. Here, "dicyclopentadiene-type diphenol compounds" refers to diphenol compounds obtained by condensing one molecule of dicyclopentadiene with two molecules of phenol.

Specific examples of preferred active ester-based hardeners include active ester-based hardeners containing a dicyclopentadiene-type diphenol structure, active ester-based hardeners containing a naphthalene structure, active ester-based hardeners containing an acetylated product of phenol novolac, and active ester-based hardeners containing a benzoylated product of phenol novolac. Among these, active ester-based hardeners containing a naphthalene structure and active ester-based hardeners containing a dicyclopentadiene-type diphenol structure are more preferred. The term "dicyclopentadiene-type diphenol structure" refers to a divalent structural unit consisting of phenylene-dicyclopentylene-phenylene.

Commercially available active ester curing agents include "EXB9451", "EXB9460", "EXB9460S", "HPC-8000-65T", "HPC-8000H-65TM", and "EXB-8000L-65TM" (manufactured by DIC Corporation) as active ester curing agents containing a dicyclopentadiene-type diphenol structure; "EXB9416-70BK" and "EXB-8150-65T" (manufactured by DIC Corporation) as active ester curing agents containing a naphthalene structure; and "EXB9416-70BK" and "EXB-8150-65T" (manufactured by DIC Corporation) as active ester curing agents containing an acetylated product of phenol novolac. Examples of such a hardener include "DC808" (manufactured by Mitsubishi Chemical Corporation); "YLH1026" (manufactured by Mitsubishi Chemical Corporation) as an active ester-based hardener containing a benzoyl compound of phenol novolac; "DC808" (manufactured by Mitsubishi Chemical Corporation) as an active ester-based hardener which is an acetylated product of phenol novolac; and "YLH1026" (manufactured by Mitsubishi Chemical Corporation), "YLH1030" (manufactured by Mitsubishi Chemical Corporation), and "YLH1048" (manufactured by Mitsubishi Chemical Corporation) as active ester-based hardeners which are benzoyl compounds of phenol novolac.

From the viewpoint of heat resistance and water resistance, phenol-based and naphthol-based hardeners are preferably those having a novolac structure. From the viewpoint of adhesion to the conductor layer, nitrogen-containing phenol-based hardeners are preferred, and triazine skeleton-containing phenol-based hardeners are more preferred.

Specific examples of phenol-based and naphthol-based curing agents include "MEH-7700", "MEH-7810", and "MEH-7851" manufactured by Meiwa Kasei Co., Ltd.; "NHN", "CBN", and "GPH" manufactured by Nippon Kayaku Co., Ltd.; "SN170", "SN180", "SN190", "SN475", "SN485", "SN495", "SN-495V", "SN375", and "SN395" manufactured by Nippon Steel Chemical & Material Co., Ltd.; and "TD-2090", "LA-7052", "LA-7054", "LA-1356", "LA-3018-50P", and "EXB-9500" manufactured by DIC Corporation.

Specific examples of benzoxazine-based curing agents include "JBZ-OD100" (benzoxazine ring equivalent 218), "JBZ-OP100D" (benzoxazine ring equivalent 218), and "ODA-BOZ" (benzoxazine ring equivalent 218) manufactured by JFE Chemical Corporation; "P-d" (benzoxazine ring equivalent 217) and "F-a" (benzoxazine ring equivalent 217) manufactured by Shikoku Kasei Corporation; and "HFB2006M" (benzoxazine ring equivalent 432) manufactured by Showa Polymer Co., Ltd.

Examples of cyanate ester curing agents include bifunctional cyanate resins such as bisphenol A dicyanate, polyphenol cyanate, oligo(3-methylene-1,5-phenylene cyanate), 4,4'-methylenebis(2,6-dimethylphenyl cyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, 2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanate phenylmethane), bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanate phenyl-1-(methylethylidene))benzene, bis(4-cyanate phenyl)thioether, and bis(4-cyanate phenyl)ether; polyfunctional cyanate resins derived from phenol novolac and cresol novolac; and prepolymers in which these cyanate resins have been partially converted to triazine. Specific examples of cyanate ester-based curing agents include "PT30" and "PT60" (phenol novolac type multifunctional cyanate ester resin), "ULL-950S" (multifunctional cyanate ester resin), "BA230" and "BA230S75" (prepolymer in which part or all of bisphenol A dicyanate is converted to triazine to form a trimer), all of which are manufactured by Lonza Japan.

Specific examples of carbodiimide-based curing agents include Carbodilite (registered trademark) V-03 (carbodiimide group equivalent: 216), V-05 (carbodiimide group equivalent: 262), V-07 (carbodiimide group equivalent: 200), and V-09 (carbodiimide group equivalent: 200), all manufactured by Nisshinbo Chemical Co., Ltd.; and Stavaxol (registered trademark) P (carbodiimide group equivalent: 302), all manufactured by Rhein Chemie.

When an epoxy resin and a curing agent are contained, the ratio of the amount of epoxy resin to the curing agent is the ratio of [total number of epoxy groups in the epoxy resin]:[total number of reactive groups in the curing agent], and is preferably in the range of 1:0.01 to 1:5, more preferably 1:0.1 to 1:3, and even more preferably 1:0.5 to 1:2. Here, the "number of epoxy groups in the epoxy resin" refers to the total value obtained by dividing the mass of the non-volatile components of the epoxy resin present in the resin composition by the epoxy equivalent. In addition, the "number of active groups in the curing agent" refers to the total value obtained by dividing the mass of the non-volatile components of the curing agent present in the resin composition by the active group equivalent.

(c) The content of the hardener is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, based on 100% by mass of non-volatile components in the resin composition, from the viewpoint of obtaining a magnetic layer exhibiting good mechanical strength. The upper limit is not particularly limited as long as the effects of the present invention are achieved, but is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less.

-(d) Curing accelerator-
The resin composition may further contain a curing accelerator as an optional component (d). By using the (d) curing accelerator, the curing of the epoxy resin can be effectively promoted, and the mechanical strength of the cured product can be increased. Examples of the (d) curing accelerator include amine-based curing accelerators, imidazole-based curing accelerators, phosphorus-based curing accelerators, guanidine-based curing accelerators, and metal-based curing accelerators. As the (d) curing accelerator, an imidazole-based curing accelerator is preferred. The (d) curing accelerator may be used alone or in combination of two or more.

Examples of amine-based curing accelerators include trialkylamines such as triethylamine and tributylamine, 4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, 1,8-diazabicyclo(5,4,0)-undecene, etc., with 4-dimethylaminopyridine and 1,8-diazabicyclo(5,4,0)-undecene being preferred.

Examples of imidazole curing accelerators include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, 4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-furan Examples of the imidazole compound include imidazole compounds such as 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, and 2-phenylimidazoline, as well as adducts of imidazole compounds and epoxy resins. Of these, 2-ethyl-4-methylimidazole and 1-benzyl-2-phenylimidazole are preferred.

As the imidazole-based curing accelerator, commercially available products may be used, such as "2MZA-PW" and "2PHZ-PW" manufactured by Shikoku Chemical Industry Co., Ltd., and "P200-H50" manufactured by Mitsubishi Chemical Corporation.

Examples of phosphorus-based curing accelerators include triphenylphosphine, phosphonium borate compounds, tetraphenylphosphonium tetraphenylborate, n-butylphosphonium tetraphenylborate, tetrabutylphosphonium decanoate, (4-methylphenyl)triphenylphosphonium thiocyanate, tetraphenylphosphonium thiocyanate, butyltriphenylphosphonium thiocyanate, etc., with triphenylphosphine and tetrabutylphosphonium decanoate being preferred.

Examples of guanidine-based curing accelerators include dicyandiamide, 1-methylguanidine, 1-ethylguanidine, 1-cyclohexylguanidine, 1-phenylguanidine, 1-(o-tolyl)guanidine, dimethylguanidine, diphenylguanidine, trimethylguanidine, tetramethylguanidine, pentamethylguanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene. Examples of such biguanide include o-[4.4.0]dec-5-ene, 1-methylbiguanide, 1-ethylbiguanide, 1-n-butylbiguanide, 1-n-octadecylbiguanide, 1,1-dimethylbiguanide, 1,1-diethylbiguanide, 1-cyclohexylbiguanide, 1-allylbiguanide, 1-phenylbiguanide, and 1-(o-tolyl)biguanide. Of these, dicyandiamide and 1,5,7-triazabicyclo[4.4.0]dec-5-ene are preferred.

Examples of metal-based curing accelerators include organometallic complexes or organometallic salts of metals such as cobalt, copper, zinc, iron, nickel, manganese, and tin. Specific examples of organometallic complexes include organocobalt complexes such as cobalt (II) acetylacetonate and cobalt (III) acetylacetonate, organocopper complexes such as copper (II) acetylacetonate, organozinc complexes such as zinc (II) acetylacetonate, organoiron complexes such as iron (III) acetylacetonate, organonickel complexes such as nickel (II) acetylacetonate, and organomanganese complexes such as manganese (II) acetylacetonate. Examples of organometallic salts include zinc octylate, tin octylate, zinc naphthenate, cobalt naphthenate, tin stearate, and zinc stearate.

(d) From the viewpoint of obtaining a magnetic layer exhibiting good mechanical strength, the content of the curing accelerator is preferably 0.001% by mass or more, more preferably 0.003% by mass or more, and even more preferably 0.005% by mass or more, when the non-volatile components in the resin composition are taken as 100% by mass. The upper limit is preferably 1% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.05% by mass or less.

From the viewpoint of effectively promoting the curing of the epoxy resin and increasing the mechanical strength of the cured product, it is preferable for the resin composition to contain at least one of (c) a curing agent and (d) a curing accelerator, and it is more preferable for the resin composition to contain both (c) a curing agent and (d) a curing accelerator.

-(e) Thermoplastic resin-
The resin composition may contain (e) a thermoplastic resin as an optional component. By using the (e) thermoplastic resin, the stress of the resin composition layer can be reduced.

Examples of (e) thermoplastic resins include phenoxy resins, acrylic resins, polycarbonate resins, polyvinyl acetal resins, polyolefin resins, polyimide resins, polyamideimide resins, polyetherimide resins, polysulfone resins, polyethersulfone resins, polyphenylene ether resins, polyetheretherketone resins, polyester resins, etc. Among these, from the viewpoint of significantly obtaining the desired effects of the present invention, at least one selected from acrylic resins, polyvinyl acetal resins, and phenoxy resins is preferred, and phenoxy resins are more preferred. In addition, (e) thermoplastic resins may be used alone or in combination of two or more types.

As the polyimide resin, a resin having an imide structure can be used. Examples of such resins include modified polyimides such as linear polyimides obtained by reacting bifunctional hydroxyl-terminated polybutadiene, a diisocyanate compound, and a tetrabasic acid anhydride (polyimides described in JP-A-2006-37083), and polysiloxane skeleton-containing polyimides (polyimides described in JP-A-2002-12667 and JP-A-2000-319386, etc.).

Commercially available polyimide resins can be used. Examples of commercially available products include "Rikacoat SN20" and "Rikacoat PN20" manufactured by New Japan Chemical Co., Ltd.

As the polycarbonate resin, a resin having a carbonate structure can be used. Examples of such resins include hydroxyl group-containing carbonate resins, phenolic hydroxyl group-containing carbonate resins, carboxyl group-containing carbonate resins, acid anhydride group-containing carbonate resins, isocyanate group-containing carbonate resins, and urethane group-containing carbonate resins.

Commercially available carbonate resins can be used. Examples of commercially available products include "FPC0220" manufactured by Mitsubishi Gas Chemical Company, Inc., "T6002" and "T6001" (polycarbonate diol) manufactured by Asahi Kasei Chemicals Corporation, and "C-1090", "C-2090", and "C-3090" (polycarbonate diol) manufactured by Kuraray Co., Ltd.

Examples of the phenoxy resin include phenoxy resins having one or more skeletons selected from the group consisting of bisphenol A skeleton, bisphenol F skeleton, bisphenol S skeleton, bisphenolacetophenone skeleton, novolac skeleton, biphenyl skeleton, fluorene skeleton, dicyclopentadiene skeleton, norbornene skeleton, naphthalene skeleton, anthracene skeleton, adamantane skeleton, terpene skeleton, and trimethylcyclohexane skeleton. The terminal of the phenoxy resin may be any functional group such as a phenolic hydroxyl group or an epoxy group.

Specific examples of phenoxy resins include Mitsubishi Chemical's "1256" and "4250" (both phenoxy resins containing a bisphenol A skeleton); Mitsubishi Chemical's "YX8100" (phenoxy resin containing a bisphenol S skeleton); Mitsubishi Chemical's "YX6954" (phenoxy resin containing a bisphenol acetophenone skeleton); Nippon Steel Chemical & Material's "FX280" and "FX293"; Mitsubishi Chemical's "YL7500BH30", "YX6954BH30", "YX7553", "YX7553BH30", "YL7769BH30", "YL6794", "YL7213", "YL7290", "YL7553BH30", and "YL7482".

From the viewpoint of obtaining the effects of the present invention more prominently, the acrylic resin is preferably a functional group-containing acrylic resin, and more preferably an epoxy group-containing acrylic resin having a glass transition temperature of 25°C or less. Examples of the functional group of the functional group-containing acrylic resin include a phenolic hydroxyl group and an epoxy group.

The number average molecular weight (Mn) of the functional group-containing acrylic resin is preferably 10,000 to 1,000,000, and more preferably 30,000 to 900,000.

The functional group equivalent weight of the functional group-containing acrylic resin is preferably 1,000 to 50,000, and more preferably 2,500 to 30,000.

As the epoxy group-containing acrylic resin having a glass transition temperature of 25°C or less, an epoxy group-containing acrylic ester copolymer resin having a glass transition temperature of 25°C or less is preferred, and specific examples include "SG-80H" manufactured by Nagase ChemteX Corporation (epoxy group-containing acrylic ester copolymer resin (number average molecular weight Mn: 350,000 g/mol, epoxy value 0.07 eq/kg, glass transition temperature 11°C)) and "SG-P3" manufactured by Nagase ChemteX Corporation (epoxy group-containing acrylic ester copolymer resin (number average molecular weight Mn: 850,000 g/mol, epoxy value 0.21 eq/kg, glass transition temperature 12°C)).

Examples of polyvinyl acetal resins include polyvinyl formal resins and polyvinyl butyral resins, with polyvinyl butyral resins being preferred. Specific examples of polyvinyl acetal resins include Denka Butyral "4000-2", "5000-A", "6000-C", and "6000-EP" manufactured by Denka Co., Ltd., and S-LEC BH series, BX series (e.g. BX-5Z), KS series (e.g. KS-1), BL series, and BM series manufactured by Sekisui Chemical Co., Ltd.

Specific examples of polyamide-imide resins include "Viromax HR11NN" and "Viromax HR16NN" manufactured by Toyobo Co., Ltd. Specific examples of polyamide-imide resins include modified polyamide-imides such as "KS9100" and "KS9300" (polysiloxane skeleton-containing polyamide-imide) manufactured by Hitachi Chemical Co., Ltd.

A specific example of polyethersulfone resin is "PES5003P" manufactured by Sumitomo Chemical Co., Ltd.

A specific example of a polyphenylene ether resin is the oligophenylene ether styrene resin "OPE-2St 1200" manufactured by Mitsubishi Gas Chemical Company, Inc.

Specific examples of polysulfone resins include polysulfones "P1700" and "P3500" manufactured by Solvay Advanced Polymers.

(e) The weight average molecular weight (Mw) of the thermoplastic resin is, from the viewpoint of significantly obtaining the desired effects of the present invention, preferably 8,000 or more, more preferably 10,000 or more, and particularly preferably 20,000 or more, and is preferably 1,000,000 or less, more preferably 750,000 or less, and particularly preferably 500,000 or less.

(e) In order to significantly obtain the desired effect of the present invention, the content of the thermoplastic resin is preferably 1 mass% or more, more preferably 2 mass% or more, and even more preferably 3 mass% or more, based on 100 mass% of the non-volatile components in the resin composition, and is preferably 25 mass% or less, more preferably 20 mass% or less, and even more preferably 15 mass% or less.

-(f) Inorganic fillers other than magnetic powder-
The resin composition may contain (f) an inorganic filler other than the magnetic powder (hereinafter, simply referred to as "(f) inorganic filler") as an optional component. By including (f) an inorganic filler other than the magnetic powder in the resin composition, it is possible to impart other functions possessed by the inorganic filler, such as improved insulation, to the resin composition layer.

(f) The material of the inorganic filler is an inorganic compound, and is not particularly limited. Examples of the inorganic filler include, but are not limited to, silica, alumina, glass, cordierite, silicon oxide, barium sulfate, barium carbonate, talc, clay, mica powder, zinc oxide, hydrotalcite, boehmite, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, boron nitride, aluminum nitride, manganese nitride, aluminum borate, strontium carbonate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, titanium oxide, zirconium oxide, barium titanate, barium zirconate titanate, barium zirconate, calcium zirconate, zirconium phosphate, and zirconium tungstate phosphate. Among these, silica is particularly suitable. Examples of silica include amorphous silica, fused silica, crystalline silica, synthetic silica, and hollow silica. Spherical silica is also preferred as the silica. (f) component may be used alone or in combination of two or more.

(f) Commercially available inorganic fillers include, for example, "UFP-30" manufactured by Denka; "SP60-05" and "SP507-05" manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YC100C", "YA050C", "YA050C-MJE", and "YA010C" manufactured by Admatechs; "Silfil NSS-3N", "Silfil NSS-4N", and "Silfil NSS-5N" manufactured by Tokuyama Corporation; "SC2500SQ", "SO-C4", "SO-C2", and "SO-C1" manufactured by Admatechs.

(f) The average particle size of the inorganic filler is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.1 μm or more, or 0.3 μm or more, from the viewpoint of significantly obtaining the desired effect of the present invention. Also, it is preferably 5 μm or less, more preferably 2.5 μm or less, even more preferably 1.5 μm or less, or 1 μm or less. The average particle size of the inorganic filler can be measured by a method similar to the method for measuring the average particle size of the magnetic powder (a).

(f) It is preferable that the inorganic filler is treated with a surface treatment agent from the viewpoint of improving moisture resistance and dispersibility. Examples of the surface treatment agent include a fluorine-containing silane coupling agent, an aminosilane coupling agent, an epoxysilane coupling agent, a mercaptosilane coupling agent, a silane coupling agent, an alkoxysilane, an organosilazane compound, and a titanate coupling agent. In addition, the surface treatment agent may be used alone or in any combination of two or more types.

Examples of commercially available surface treatment agents include Shin-Etsu Chemical Co., Ltd.'s "KBM403" (3-glycidoxypropyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM803" (3-mercaptopropyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBE903" (3-aminopropyltriethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM573" (N-phenyl-3-aminopropyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "SZ-31" (hexamethyldisilazane), Shin-Etsu Chemical Co., Ltd.'s "KBM103" (phenyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM-4803" (long-chain epoxy-type silane coupling agent), and Shin-Etsu Chemical Co., Ltd.'s "KBM-7103" (3,3,3-trifluoropropyltrimethoxysilane).

From the viewpoint of improving the dispersibility of the inorganic filler, the degree of surface treatment with the surface treatment agent is preferably 0.2 to 5 parts by mass of the surface treatment agent per 100 parts by mass of the inorganic filler, more preferably 0.2 to 3 parts by mass, and even more preferably 0.3 to 2 parts by mass.

The degree of surface treatment by the surface treatment agent can be evaluated by the amount of carbon per unit surface area of the inorganic filler. From the viewpoint of improving the dispersibility of the inorganic filler, the amount of carbon per unit surface area of the inorganic filler is preferably 0.02 mg/m ² or more, more preferably 0.1 mg/m ² or more, and even more preferably 0.2 mg/m ² or more. On the other hand, from the viewpoint of suppressing the increase in the melt viscosity of the resin varnish and the melt viscosity in the sheet form, it is preferably 1 mg/m ² or less, more preferably 0.8 mg/m ² or less, and even more preferably 0.5 mg/m ² or less.

The amount of carbon per unit surface area of the inorganic filler can be measured after the surface-treated inorganic filler is washed with a solvent (e.g., methyl ethyl ketone (MEK)). Specifically, a sufficient amount of MEK as a solvent is added to the inorganic filler that has been surface-treated with a surface treatment agent, and ultrasonic cleaning is performed at 25°C for 5 minutes. After removing the supernatant and drying the solids, the amount of carbon per unit surface area of the inorganic filler can be measured using a carbon analyzer. An "EMIA-320V" manufactured by Horiba, Ltd., or the like, can be used as a carbon analyzer.

(f) The content (mass%) of the inorganic filler is preferably 1 mass% or more, more preferably 1.5 mass% or more, and even more preferably 2 mass% or more, based on 100 mass% of the non-volatile components in the resin composition. Also, it is preferably 10 mass% or less, more preferably 8 mass% or less, and even more preferably 5 mass% or less.

(f) The content (volume %) of the inorganic filler is preferably 1 vol% or more, more preferably 3 vol% or more, and even more preferably 5 vol% or more. The upper limit is preferably 20 vol% or less, more preferably 15 vol% or less, and even more preferably 10 vol% or less.

--(g) Other additives--
The resin composition may further contain (g) other additives as necessary, such as flame retardants, thickeners, defoamers, leveling agents, adhesion promoters, and colorants.

The resin composition can be produced, for example, by a method in which the blended components are stirred using a stirring device such as a three-roll mill, a rotary mixer, or a high-speed rotary mixer. The resin composition may be degassed after production, etc. Examples of degassing methods include degassing by leaving the composition to stand, degassing by centrifugation, vacuum degassing, degassing by stirring, and combinations of these.

As mentioned above, in order to increase the relative permeability of the magnetic layer formed by the magnetic film, it is possible to increase the content of the magnetic powder contained in the resin composition layer of the magnetic film. Increasing the content of the magnetic powder tends to increase the minimum melt viscosity of the resin composition layer. In addition, when forming a magnetic layer by a magnetic film, if the magnetic layer is formed by heat pressing, it is possible to increase the magnetic powder density in the magnetic layer, so that the relative permeability of the magnetic layer can be increased. Generally, adhesive films used to form insulating layers of circuit boards are laminated with a vacuum laminator or the like and then heat cured to form an insulating layer, so that the minimum melt viscosity is set relatively low, but it is preferable to set the minimum melt viscosity of the resin composition layer in the magnetic film of the present invention relatively high so as to be suitable for forming a magnetic layer by heat pressing. From the above viewpoint, the minimum melt viscosity of the resin composition layer is preferably 50,000 poise or more, more preferably 100,000 poise or more, and even more preferably 500,000 poise or more, and preferably 50,000,000 poise or less, more preferably 30,000,000 poise or less, and even more preferably 10,000,000 poise or less. The minimum melt viscosity of the resin composition layer can be measured by the method described in the examples below.

From the viewpoint of thinning, the thickness of the resin composition layer is preferably 250 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. The lower limit of the thickness of the resin composition layer is not particularly limited, but can usually be 5 μm or more.

<Cover film layer>
The magnetic film has a cover film layer, and the cover film layer is provided on the resin composition layer. As described above, the present inventors have found that the cover film layer tends to be difficult to adhere to the resin composition layer containing magnetic powder, and further, have found that the higher the content of magnetic powder, the more difficult the cover film layer is to adhere to the resin composition layer. In addition, when the minimum melt viscosity of the resin composition layer is set to a high range as described above so as to be suitable for forming a magnetic layer by heat pressing, the cover film layer is further difficult to adhere to the resin composition layer. In the present invention, by using a self-adhesive film as the cover film layer, it is possible to provide a cover film layer on the resin composition layer even in these cases. This makes it possible to suppress adhesion of foreign matter to the resin composition layer. In addition, when a magnetic film without a cover film layer is used, in addition to the problem of adhesion of foreign matter to the surface of the resin composition layer, when the magnetic film is slit, cracks and chips of the resin composition layer tend to occur easily at the film end. The present invention makes it possible to provide a cover film layer on a resin composition layer containing magnetic powder, which usually makes it possible to suppress adhesion of foreign matter to the resin composition layer and the occurrence of cracks or chips in the resin composition layer when slitting.

As mentioned above, the cover film layer is a self-adhesive film. The term "self-adhesive film" refers to a film having an adhesive surface formed by co-extruding a base resin and an adhesive resin, and which has adhesive power even without being coated with an adhesive.

The adhesive strength of the self-adhesive film is preferably 0.1 gf/cm or more, more preferably 0.2 gf/cm or more, even more preferably 0.5 gf/cm or more, and preferably 20 gf/cm or less, more preferably 15 gf/cm or less, even more preferably 10 gf/cm or less, against a slide glass under conditions of 23°C. The adhesive strength of the self-adhesive film can be measured by the method described in the examples below.

Examples of adhesive resins include ethylene-vinyl acetate copolymers; polyolefin resins such as linear low-density polyethylene; styrene-based elastomers, etc.

Examples of base resins include polyethylene, polypropylene, etc.

Commercially available products can be used for the cover film layer. Commercially available cover films that can be used include, for example, "R025" and "R033KS" manufactured by Toray Film Processing Co., Ltd., "FSA-300M" and "FSA-150M" manufactured by Futamura Chemical Co., Ltd., and "MS300" manufactured by Toyobo Co., Ltd.

The thickness of the cover film layer is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less. The lower limit is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more.

As for films with an adhesive surface, there are also adhesive-coated films formed by applying an adhesive to a base resin layer. However, when the cover film layer is peeled off, the adhesive remains on the resin composition layer, which may reduce the adhesion between the magnetic layer and other layers and make it difficult to achieve high magnetic permeability, and therefore these are not suitable for the cover film layer of the present invention.

[Magnetic film manufacturing method]
As described above, the magnetic film of the present invention has a support, a resin composition layer containing a resin composition provided on the support, and a cover film layer provided on the resin composition layer.
The method includes: (1) applying a resin varnish onto a support to form a resin composition layer; and (2) laminating a cover film layer onto the resin composition layer.
Each step will be described below.

<(1) Process>
The step (1) is a step of applying a resin varnish onto a support to form a resin composition layer, and the resin composition layer is formed on the support by this step. The details of the step (1) are as follows: a resin varnish containing a resin composition in an organic solvent is prepared, the resin varnish is applied onto the support, and the support is further dried to form a resin composition layer.

Resin varnish is a resin composition dissolved or dispersed in an organic solvent. The resin composition is as described above.

Examples of organic solvents include ketone solvents such as acetone, methyl ethyl ketone (MEK) and cyclohexanone; acetate ester solvents such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate and carbitol acetate; carbitol solvents such as cellosolve and butyl carbitol; aromatic hydrocarbon solvents such as toluene and xylene; amide solvents such as dimethylformamide, dimethylacetamide (DMAc) and N-methylpyrrolidone. The organic solvents may be used alone or in combination of two or more.

The resin varnish can be applied by a method capable of forming a coating film having a uniform thickness. For example, the resin varnish can be applied onto the support using a coating device such as a die coater, a comma coater, a gravure coater, or a bar coater.
After the resin varnish is applied onto the support, the resin varnish is dried to form a resin composition layer.

Drying may be carried out by known methods such as heating or blowing hot air. The drying conditions are not particularly limited, but the content of organic solvent in the resin composition layer is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and even more preferably 1% by mass or less.

Drying conditions vary depending on the boiling point of the organic solvent in the resin varnish, but for example, when using a resin varnish containing 30% to 60% by mass of organic solvent, a resin composition layer can be formed by drying at 50°C to 150°C for 3 to 10 minutes.

<(2) Process>
In the step (2), a cover film is laminated on the resin composition layer, and a cover film layer is formed on the resin composition layer by this step. In detail, after forming the resin composition layer, a cover film is further laminated on the surface of the resin composition layer that is not bonded to the support (i.e., the surface opposite to the support).

The resin composition layer and the cover film are preferably joined, for example, by laminating the cover film to the resin composition layer by roll compression or press compression, etc.

The lamination process may be performed under heating conditions. The heating temperature is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher, and is preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower.

The pressure and time for lamination are not particularly limited as long as the desired adhesive strength is obtained, and may be appropriately determined. For example, the pressure may be in the range of 0.1 kgf/cm ² to 18 kgf/cm ² (0.0098 MPa to 1.77 MPa), and the time may be in the range of 5 seconds to 400 seconds. The lamination may be performed under reduced pressure conditions (for example, 26.7 hPa or less).

The lamination process can be carried out using a commercially available vacuum laminator. Examples of commercially available vacuum laminators include the vacuum pressure laminator manufactured by Meiki Seisakusho Co., Ltd. and the vacuum applicator manufactured by Nikko Materials Co., Ltd.

<Physical properties of magnetic film>
The adhesive strength between the resin composition layer and the cover film layer is preferably 0.1 gf/cm or more, more preferably 0.2 gf/cm or more, and even more preferably 0.3 gf/cm or more, from the viewpoint of obtaining the effects of the present invention remarkably. The upper limit of the adhesive strength is preferably 10 gf/cm or less, more preferably 8 gf/cm or less, and even more preferably 6 gf/cm or less, from the viewpoint of suppressing peeling of the resin when peeling off the cover film layer. The adhesive strength is measured under the condition of room temperature (23°C) and can be measured by the method described in the examples described later.

[Method of manufacturing the magnetic layer]
When the magnetic film of the present invention is used to produce a magnetic layer in an inductor element or the like, the magnetic layer can be produced, for example, by a method including the following steps (A) and (B).
(A) a step of peeling off a cover film layer of a magnetic film; and (B) a step of laminating the magnetic film onto an inner layer substrate such that the resin composition layer is bonded to the inner layer substrate to form a magnetic layer.

<Step (A)>
Step (A) is a step of peeling off the cover film layer of the magnetic film. Step (A) may include a step of preparing a magnetic film. The magnetic film is as described above.

The method for peeling off the cover film layer can be the same as the method for peeling off the cover film layer in an adhesive film having a resin composition layer that does not contain magnetic powder and is used for insulation purposes. Peeling may be performed manually or mechanically. If the magnetic film is in a roll form, the cover film layer may be peeled off while the magnetic film is being transported, and if the magnetic film is in a sheet form, the cover film layer may be peeled off using a peeling device for peeling off the cover film layer.

<Step (B)>
Step (B) is a step of laminating the magnetic film onto the inner layer substrate so that the resin composition layer is bonded to the inner layer substrate to form a magnetic layer. In one embodiment of step (B), the magnetic film is heat-pressed onto the inner layer substrate so that the resin composition layer is bonded to the inner layer substrate, and the resin composition layer is heat-cured to form the magnetic layer.

The heating temperature of the heat press is preferably 130°C or higher, more preferably 150°C or higher, and preferably 250°C or lower, more preferably 200°C or lower.

The pressing time of the heat press is preferably at least 1 minute, more preferably at least 2 minutes, and is preferably at most 24 hours, more preferably at most 2 hours.

The pressure of the heat press is preferably 0.1 MPa or more, more preferably 1 MPa or more, even more preferably 10 MPa or more, and is preferably 200 MPa or less, more preferably 100 MPa or less.

After the magnetic layer is formed, the support is usually peeled off in the same manner as the cover film layer. The magnetic film of the present invention can be suitably used to form the magnetic layer of an inductor substrate. Such an inductor substrate can be used as a wiring board for mounting electronic components such as semiconductor chips, and can also be used as a (multilayer) printed wiring board using such a wiring board as an inner layer substrate. In addition, such a wiring board can be used as an individualized chip inductor component, and can also be used as a printed wiring board on which the chip inductor component is surface-mounted.

In addition, such wiring boards can be used to manufacture semiconductor devices of various types. Semiconductor devices including such wiring boards can be suitably used in electrical products (e.g., computers, mobile phones, digital cameras, and televisions) and vehicles (e.g., motorcycles, automobiles, trains, ships, and aircraft).

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following description, the terms "parts" and "%" used to express amounts refer to "parts by mass" and "% by mass", respectively, unless otherwise specified.

<Preparation of Resin Composition 1>
14 parts by mass of "ZX1059" (a mixture of bisphenol A type epoxy resin and bisphenol F type epoxy resin, manufactured by Nippon Steel Chemical & Material Co., Ltd.), 14 parts by mass of "HP-4700" (a naphthalene type tetrafunctional epoxy resin, manufactured by DIC Corporation), 35 parts by mass of "YX7553" (phenoxy resin, non-volatile content 30% by mass, manufactured by Mitsubishi Chemical Corporation), and 23 parts by mass of "KS-1" (a polyvinyl acetal resin, manufactured by Sekisui Chemical Co., Ltd.) were dissolved by heating with stirring in 10 parts by mass of MEK, 10 parts by mass of cyclohexanone, 30 parts by mass of ethanol, and 30 parts by mass of toluene. To this were added 28 parts by mass of "LA-7054" (triazine skeleton-containing phenolic curing agent, non-volatile content 60% by mass, manufactured by DIC Corporation), 0.1 parts by mass of "2E4MZ" (curing accelerator, manufactured by Shikoku Chemical Industry Co., Ltd.), and 1,010 parts by mass of "AW2-08PF3F" (magnetic powder, Fe-Cr-Si alloy (amorphous), average particle size 3.0 μm, manufactured by Epson Atmix Corporation), and the mixture was uniformly dispersed using a high-speed rotating mixer to prepare Resin Composition 1.

<Preparation of Resin Composition 2>
To the resin composition 1, 35 parts by mass of an inorganic filler ("SO-C2" (silica, average particle size 0.5 μm, manufactured by Admatechs) treated with "KBM-573" (aminosilane coupling agent, manufactured by Shin-Etsu Chemical Co., Ltd.)) was added. Resin composition 2 was prepared in the same manner as resin composition 1 except for the above.

<Preparation of Resin Composition 3>
7 parts by mass of "ZX1059" (mixture of bisphenol A type epoxy resin and bisphenol F type epoxy resin, manufactured by Nippon Steel Chemical & Material Co., Ltd.), 7 parts by mass of "HP-4700" (naphthalene type tetrafunctional epoxy resin, manufactured by DIC Corporation), 135 parts by mass of "YX7553" (phenoxy resin, non-volatile content 30% by mass, manufactured by Mitsubishi Chemical Corporation) were heated and dissolved while stirring. 14 parts by mass of "LA-7054" (triazine skeleton-containing phenolic hardener, non-volatile content 60% by mass, manufactured by DIC Corporation), 0.1 parts by mass of "2E4MZ" (curing accelerator, manufactured by Shikoku Chemical Industry Co., Ltd.), and 850 parts by mass of "AW2-08PF3F" (magnetic powder, Fe-Cr-Si alloy (amorphous), average particle size 3.0 μm, manufactured by Epson Atomics Corporation) were mixed and uniformly dispersed with a high-speed rotating mixer to prepare resin composition 3.

<Preparation of Resin Composition 4>
In Resin Composition 3, 850 parts by mass of "AW2-08PF3F" (magnetic powder, Fe-Cr-Si alloy (amorphous), average particle size 3.0 μm, manufactured by Epson Atmix) was changed to 600 parts by mass of "M05S" (magnetic powder, Fe-Mn ferrite, average particle size 3.0 μm, manufactured by Powdertech Co., Ltd.). Resin Composition 4 was prepared in the same manner as Resin Composition 3 except for the above.

<Preparation of Resin Composition 5>
In Resin Composition 3, 850 parts by mass of "AW2-08PF3F" (magnetic powder, Fe-Cr-Si alloy (amorphous), average particle size 3.0 μm, manufactured by Epson Atmix Corporation) was changed to 850 parts by mass of "PST-S" (magnetic powder, Fe-Si-Al alloy, average particle size 25 μm, manufactured by Sanyo Special Steel Co., Ltd.). Resin Composition 5 was prepared in the same manner as Resin Composition 3 except for the above.

Example 1: Preparation of magnetic film 1
A polyethylene terephthalate (hereinafter referred to as "PET") film (thickness 38 μm) was prepared as a support. Resin composition 1 was uniformly applied onto the PET film using a die coater so that the thickness of the resin composition layer after drying was 100 μm, and dried at 65° C. to 120° C. for 8 minutes so that the amount of residual solvent in the resin composition layer was 0.9 mass%. Next, a cover film "R205" (self-adhesive film, manufactured by Toray Film Processing Co., Ltd., thickness 40 μm) was laminated on the surface of the resin composition layer at 60° C. to obtain a magnetic film 1.

Example 2: Preparation of magnetic film 2
In Example 1, the cover film "R205" (self-adhesive film, manufactured by Toray Advanced Film Co., Ltd., thickness 40 μm) was changed to the cover film "R033KS" (self-adhesive film, manufactured by Toray Advanced Film Co., Ltd., thickness 45 μm). Magnetic film 2 was produced in the same manner as in Example 1 except for the above points.

Example 3: Preparation of magnetic film 3
In Example 1, the cover film was changed from "R205" (self-adhesive film, manufactured by Toray Film Processing Co., Ltd., thickness 40 μm) to "FSA-300M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm). Magnetic film 3 was produced in the same manner as in Example 1, except for the above points.

Example 4: Preparation of magnetic film 4
In Example 1, the cover film was changed from "R205" (self-adhesive film, manufactured by Toray Film Processing Co., Ltd., thickness 40 μm) to "FSA-150M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm). Magnetic film 4 was produced in the same manner as in Example 1, except for the above points.

Example 5: Preparation of magnetic film 5
In Example 1, the cover film was changed from "R205" (self-adhesive film, manufactured by Toray Advanced Film Co., Ltd., thickness 40 μm) to "MS300" (self-adhesive film, manufactured by Toyobo Co., Ltd., thickness 40 μm). Magnetic film 5 was produced in the same manner as in Example 1 except for the above points.

Example 6: Preparation of magnetic film 6
Resin composition 2 was uniformly applied onto a PET film using a die coater so that the thickness of the resin composition layer after drying was 100 μm, and then dried for 8 minutes at 65° C. to 120° C. so that the amount of residual solvent in the resin composition layer was 0.8 mass %. Next, a cover film "R033KS" (self-adhesive film, manufactured by Toray Advanced Film Co., Ltd., thickness 45 μm) was laminated onto the surface of the resin composition layer at 60° C. to obtain a magnetic film 6.

Example 7: Preparation of magnetic film 7
In Example 6, the drying time was changed from 8 minutes to 10 minutes, and the amount of the residual solvent in the resin composition layer was changed from 0.8% by mass to 0.5% by mass. Magnetic film 7 was produced in the same manner as in Example 6 except for the above.

Example 8: Preparation of magnetic film 8
In Example 6, the cover film was changed from "R033KS" (self-adhesive film, manufactured by Toray Film Processing Co., Ltd., thickness 45 μm) to "FSA-150M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm). Magnetic film 8 was produced in the same manner as in Example 6 except for the above points.

Example 9: Preparation of magnetic film 9
Resin composition 3 was uniformly applied onto a PET film using a die coater so that the thickness of the resin composition layer after drying would be 100 μm, and then dried for 8 minutes at 65° C. to 120° C. so that the amount of residual solvent in the resin composition layer would be about 1.3% by mass. Next, a cover film "FSA-150M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm) was laminated onto the surface of the resin composition layer at 60° C. to produce magnetic film 9.

Example 10: Preparation of magnetic film 10
Resin composition 4 was uniformly applied onto a PET film using a die coater so that the thickness of the resin composition layer after drying would be 100 μm, and then dried for 8 minutes at 65° C. to 120° C. so that the amount of residual solvent in the resin composition layer would be about 1.9% by mass. Next, a cover film "FSA-150M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm) was laminated onto the surface of the resin composition layer at 60° C. to produce magnetic film 10.

Example 11: Preparation of magnetic film 11
Resin composition 5 was uniformly applied onto a PET film using a die coater so that the thickness of the resin composition layer after drying would be 100 μm, and then dried for 8 minutes at 65° C. to 120° C. so that the amount of residual solvent in the resin composition layer would be about 1.2% by mass. Next, a cover film "FSA-150M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm) was laminated onto the surface of the resin composition layer at 60° C. to produce magnetic film 11.

Comparative Example 1: Preparation of Magnetic Film 12
In Example 1, the cover film "R205" (self-adhesive film, manufactured by Toray Film Processing Co., Ltd., thickness 40 μm) was changed to the cover film "MA-411" (OPP film, manufactured by Oji F-Tex Co., Ltd., thickness 15 μm). Aside from the above, the magnetic film 12 was produced in the same manner as in Example 1.

Comparative Example 2: Preparation of Magnetic Film 13
In Example 6, the cover film "R033KS" (self-adhesive film, manufactured by Toray Film Processing Co., Ltd., thickness 45 μm) was changed to the cover film "MA-411" (OPP film, manufactured by Oji F-Tex Co., Ltd., thickness 15 μm). A magnetic film 13 was produced in the same manner as in Example 6 except for the above points.

Comparative Example 3: Preparation of Magnetic Film 14
In Example 9, the cover film "FSA-150M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm) was changed to the cover film "MA-411" (OPP film, manufactured by Oji F-Tex Co., Ltd., thickness 15 μm). Apart from the above, the magnetic film 14 was produced in the same manner as in Example 9.

Comparative Example 4: Preparation of Magnetic Film 15
In Example 10, the cover film "FSA-150M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm) was changed to the cover film "MA-411" (OPP film, manufactured by Oji F-Tex Co., Ltd., thickness 15 μm). Magnetic film 15 was produced in the same manner as in Example 10 except for the above points.

Comparative Example 5: Preparation of Magnetic Film 16
In Example 11, the cover film "FSA-150M" (self-adhesive film, manufactured by Futamura Chemical Co., Ltd., thickness 30 μm) was changed to the cover film "MA-411" (OPP film, manufactured by Oji F-Tex Co., Ltd., thickness 15 μm). A magnetic film 16 was produced in the same manner as in Example 11 except for the above points.

<Measurement of Minimum Melt Viscosity of Resin Composition Layer>
The melt viscosity of the resin composition layers of magnetic films 1 to 16 was measured using a dynamic viscoelasticity measuring device (Rheosol-G3000 manufactured by U.B.M. Co., Ltd.). For 1 g of the resin composition, a parallel plate with a diameter of 10 mm was used to raise the temperature from a starting temperature of 60° C. to 180° C. at a heating rate of 5° C./min, and the dynamic viscoelasticity was measured under the measurement conditions of a measurement temperature interval of 2.5° C., a vibration frequency of 1 Hz, and a strain of 0.1 deg., and the lowest value among the complex viscosities was determined as the minimum melt viscosity (poise).

<Measurement of adhesive strength of cover film>
Each cover film was cut to a width of 24 mm and a length of 70 mm, and laminated to a slide glass ("S1112" manufactured by Matsunami Glass Industry Co., Ltd.) at 40°C to obtain a measurement sample. One end of the cover film layer was peeled off and gripped with a gripper, and the protective film was peeled off 15 mm in the vertical direction at room temperature (23°C) at a speed of 50 mm/min, and the load was measured to determine the peel strength (adhesion strength). A tensile tester ("AC-50" manufactured by TSE Corporation) was used for the measurement.

<Measurement of Adhesion Strength Between Resin Composition Layer and Cover Film Layer>
Each of the magnetic films 1 to 16 was cut to a width of 27 mm and a length of 70 mm, and the support was peeled off to obtain a measurement sample. A copper-clad laminate was cut to a width of 27 mm and a length of 100 mm, and a double-sided tape ("Nicetack" manufactured by Nichiban Co., Ltd.) was attached to the surface of the resin composition layer of the measurement sample up to 70 mm from the end. One end of the cover film layer was peeled off and held with a gripper, and the load when the protective film was peeled off 15 mm in the vertical direction at room temperature (23°C) at a speed of 50 mm/min was measured to determine the peel strength (adhesion strength). A tensile tester ("AC-50" manufactured by TSE Co., Ltd.) was used for the measurement.
The measured adhesion strength was evaluated according to the following criteria.
A: The cover film was attached to the resin composition layer.
×: The cover film was not attached to the resin composition layer.

1 Magnetic film 11 Support 12 Resin composition layer 13 Cover film layer

Claims (9)

A support;
a resin composition layer formed from a resin composition provided on the support;
A cover film layer bonded to a surface of the resin composition layer opposite to the support,
The resin composition contains a magnetic powder,
The cover film layer is a self-adhesive film that is not coated with an adhesive ,
A magnetic film , wherein the adhesive strength of the cover film layer to the resin composition layer is 0.1 gf/cm or more and 10 gf/cm or less . The magnetic film according to claim 1, wherein the content of the magnetic powder is 75% by mass or more and 98% by mass or less, when the non-volatile content of the resin composition is 100% by mass. The magnetic film according to claim 1 or 2, wherein the minimum melt viscosity of the resin composition layer is 50,000 poise or more and 50,000,000 poise or less. The magnetic film according to any one of claims 1 to 3, wherein the resin composition is a thermosetting resin composition. The magnetic film according to any one of claims 1 to 4, wherein the resin composition contains an epoxy resin. The magnetic film according to any one of claims 1 to 5, wherein the resin composition contains at least one of a curing agent and a curing accelerator. The magnetic film according to any one of claims 1 to 6, wherein the resin composition contains a thermoplastic resin. 8. The magnetic film according to claim 1, wherein the magnetic powder is at least one selected from the group consisting of iron oxide powder and iron alloy metal powder. A method for producing a magnetic film according to any one of claims 1 to 8 , comprising the steps of:
A method for producing a magnetic film, comprising: a step of applying a resin varnish containing a resin composition onto a support to form a resin composition layer; and a step of laminating a cover film layer onto the resin composition layer.

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