Thermosetting resin composition, cover film, and flexible printed wiring board

Abstract

The thermosetting resin composition includes: a polyamideimide resin having an acrylonitrile butadiene rubber skeleton; epoxy resin which is non-solid at 25 DEG C; a particulate rubber dispersed in the non-solid epoxy resin; an inorganic filler; and a curing agent. The content of the non-solid epoxy resin is from 30 parts by mass to 70 parts by mass (inclusive) with respect to 100 parts by mass of the polyamide-imide resin. The content of the fine particle rubber is 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the polyamide-imide resin. The content of the inorganic filler is from 20 parts by mass to 40 parts by mass (inclusive) with respect to 100 parts by mass of the polyamide-imide resin.

Description

Technical Field

[0001] The present invention relates to a thermosetting resin composition, a cover film, and a flexible printed wiring board. Background Art

[0002] Patent Document 1 discloses a cover film having an adhesive layer that is supposed to be placed in a high-temperature environment for a long time, and a flexible printed wiring board including a substrate formed with wiring and a cover film covering the wiring. In addition, an adhesive resin composition that can be used for the adhesive layer of the cover film is disclosed. Specifically, an adhesive resin composition including a silicone-containing polyimide resin and a bisphenol type vinyl ester resin is disclosed.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-43925 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] The bisphenol type vinyl ester resin contained in the adhesive resin composition is liable to deteriorate due to heat and is liable to be oxidized. Therefore, when the cover film using the adhesive resin composition as an adhesive layer is placed in a high-temperature environment for a long time, the adhesive layer deteriorates, and the adhesive force between the adhesive layer and the adherend is liable to decrease.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide a cover film having excellent adhesiveness even when placed in a high-temperature environment for a long time, a flexible printed wiring board including the cover film, and a thermosetting resin composition that can be used for the adhesive layer of the cover film.

[0009] Means for Solving the Problems

[0010] The present invention is as follows.

[0011] [1] A thermosetting resin composition, comprising:

[0012] A polyamideimide resin having an acrylonitrile-butadiene rubber backbone;

[0013] An epoxy resin that is not in a solid state at 25°C;

[0014] A fine particle rubber dispersed in the non-solid epoxy resin;

[0015] An inorganic filler; and

[0016] A curing agent,

[0017] The content of the aforementioned non-solid epoxy resin is 30 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the aforementioned polyamideimide resin.

[0018] The content of the aforementioned particulate rubber is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the aforementioned polyamideimide resin.

[0019] The aforementioned inorganic filler is 20 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the aforementioned polyamideimide resin.

[0020] [2] The thermosetting resin composition as described in the above [1], wherein the aforementioned particulate rubber is composed of a core layer and a shell layer covering its surface.

[0021] [3] A cover film, which comprises:

[0022] A polyimide film having an oxygen permeability at 30 °C of 35.0×10 -6 m 3 / m 2 ·atm·24 hr or less; and

[0023] An adhesive layer composed of the thermosetting resin composition described in the above [1] or [2],

[0024] The aforementioned adhesive layer is laminated on at least one side of the aforementioned polyimide film.

[0025] [4] The cover film as described in the above [3], wherein a gas barrier layer for suppressing oxygen permeation is laminated on at least one side of the aforementioned polyimide film.

[0026] [5] The cover film as described in the above [4], wherein the polyimide film laminated with the aforementioned gas barrier layer has an oxygen permeability at 30 °C of 5.0×10 -6 m 3 / m 2 ·atm·24 hr or less.

[0027] [6] A flexible printed wiring board, which comprises the cover film described in any one of the above [3] to [5], and a substrate formed with wirings,

[0028] The aforementioned cover film is laminated on the aforementioned substrate in such a manner that the aforementioned adhesive layer is in contact with the aforementioned wirings.

[0029] Advantages of the Invention

[0030] According to the present invention, it is possible to provide a cover film having excellent adhesiveness even when placed in a high-temperature environment for a long time, a flexible printed wiring board having the cover film, and a thermosetting resin composition that can be used for the adhesive layer of the cover film. Detailed Embodiments

[0031] Hereinafter, the embodiments for implementing the present invention (hereinafter referred to as embodiments) will be described in detail. The embodiments are examples for explaining the present invention and are not intended to limit the present invention to the following content. The present invention can be appropriately modified and implemented within the scope of its gist. In addition, the parts by mass used in the present invention refer to, for example, the parts by mass of the resin after removing volatile components such as organic solvents contained in the resin, that is, the parts by mass of the non-volatile components. In addition, the semi-cured state (B stage) refers to a state in which the curing reaction of the thermosetting resin composition has proceeded halfway.

[0032] (Thermosetting resin composition)

[0033] The thermosetting resin composition of the embodiment contains: a polyamideimide resin having an acrylonitrile-butadiene rubber skeleton; an epoxy resin that is not in a solid state at 25°C; a fine particle rubber dispersed in the non-solid epoxy resin; an inorganic filler; and a curing agent.

[0034] The thermosetting resin composition of the embodiment has excellent heat resistance and adhesiveness by containing the above components. This thermosetting resin composition is suitable as a resin composition constituting the adhesive layer of the cover film.

[0035] Hereinafter, the components contained in the thermosetting resin composition will be described.

[0036] (Polyamideimide resin having an acrylonitrile-butadiene rubber skeleton)

[0037] The polyamideimide resin used in the embodiment is composed of the following components: component (a): a polycarboxylic acid derivative having an acid anhydride group; component (b): an isocyanate compound; and component (c): an acrylonitrile-butadiene rubber having carboxyl groups at both ends. Hereinafter, acrylonitrile-butadiene rubber will also be referred to as NBR.

[0038] (Component (a))

[0039] Examples of the polycarboxylic acid derivative having an acid anhydride group include trimellitic anhydride, pyromellitic dianhydride, ethylene glycol bisanhydrotrimellitate, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, etc. They can be used alone or in combination of two or more.

[0040] (Component (b))

[0041] As the isocyanate compound, for example, diphenylmethane-4,4'-diisocyanate, toluene-2,4-diisocyanate, m-xylylene diisocyanate, 2,2'-dimethylbiphenyl-4,4'-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, toluene-2,4'-diisocyanate, etc. can be cited. They can be used alone or in combination of two or more.

[0042] (c) component

[0043] An acrylonitrile-butadiene rubber having carboxyl groups at both ends imparts adhesiveness and flexibility to the thermosetting resin composition. From the viewpoint of imparting adhesiveness and flexibility to the thermosetting resin composition, the weight average molecular weight of the NBR having carboxyl groups at both ends is preferably 1000 or more and 4000 or less.

[0044] The polyamideimide resin used in the embodiment can be obtained by the isocyanate method. Specifically, the (a) component, (b) component, and (c) component are respectively added to a container in a manner that satisfies the following formula, and for example, heated to 100°C or more and 180°C or less to cause condensation. Organic solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and γ-butyrolactone can also be added during the condensation.

[0045] The number of isocyanate groups contained in the (b) component / {the number of acid anhydride groups contained in the (a) component + the number of carboxyl groups contained in the (c) component} = 0.8 or more and 1.2 or less

[0046] The polyamideimide resin obtained by the above method improves the film-forming property of the thermosetting resin composition of the embodiment.

[0047] In addition, the glass transition temperature of the obtained polyamideimide resin is 150°C or more and 200°C or less. This polyamideimide resin improves the heat resistance of the thermosetting resin composition of the embodiment. The glass transition temperature can be determined by measuring the dynamic viscoelasticity of the polyamideimide resin.

[0048] (Epoxy resin that is not in a solid state at 25°C)

[0049] The epoxy resin that is not in a solid state at 25°C has fluidity at 25°C. This epoxy resin has two or more epoxy groups in one molecule. The epoxy equivalent of this epoxy resin is preferably 100 g / eq or more and 400 g / eq or less, more preferably 150 g / eq or more and 350 g / eq or less. This epoxy resin can improve the dispersibility of the particulate rubber in the thermosetting resin composition and can also improve the adhesiveness between the substrate and the adhesive layer constituting the cover film.

[0050] Examples of the epoxy resin that is non-solid at 25°C include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol A Novolac type epoxy resin, phenol Novolac type epoxy resin, amine type epoxy resin, and alicyclic epoxy resin. From the viewpoint of heat resistance, the epoxy resin that is non-solid at 25°C is preferably bisphenol A type epoxy resin, more preferably bisphenol A Novolac type epoxy resin and phenol Novolac type epoxy resin. Two or more kinds of epoxy resins may be used in combination for the epoxy resin that is non-solid at 25°C.

[0051] From the viewpoint of improving the adhesiveness between the substrate and the adhesive layer constituting the cover film, the content of the epoxy resin that is non-solid at 25°C is 30 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the polyamideimide resin.

[0052] (Fine particle rubber)

[0053] The fine particle rubber may be a fine particle rubber dispersed in the epoxy resin that is non-solid at 25°C. From the viewpoint of improving dispersibility, a fine particle rubber composed of a core layer and a shell layer covering its surface is preferred.

[0054] The core layer constituting the fine particle rubber is composed of a polymer having rubber-like elasticity. Examples of the polymer having rubber-like elasticity include diene rubber, acrylic rubber, styrene rubber, and polysiloxane rubber. The core layer may also be composed of two or more kinds of polymers. The shell layer covering the surface of the core layer is composed of a copolymer obtained by copolymerizing one or more components selected from (meth)acrylate monomers, aromatic vinyl monomers, cyanated vinyl monomers, unsaturated acid derivatives, (meth)acrylamide derivatives, and maleimide derivatives.

[0055] The polymer constituting the core layer and the copolymer constituting the shell layer are bonded by graft polymerization. In addition, the shell layer covers a part or the whole of the surface of the core layer. In addition, the copolymer constituting the shell layer preferably has a functional group that reacts with the epoxy resin and the curing agent that are non-solid at 25°C. The fine particle rubber having such a structure has increased affinity with the epoxy resin that is non-solid at 25°C and improved dispersibility. Examples of the functional group that reacts with the epoxy resin and the curing agent that are non-solid at 25°C include a hydroxyl group, a carboxyl group, and an epoxy group. From the viewpoint of improving dispersibility, an epoxy group is preferred.

[0056] Regarding the size of the fine particle rubber, from the viewpoint of improving dispersibility, the average particle diameter is preferably 0.05 μm or more and 1 μm or less.

[0057] From the viewpoint of improving the adhesiveness between the substrate and the adhesive layer constituting the cover film, the content of the fine particle rubber is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the polyamideimide resin.

[0058] Compared with directly adding particulate rubber to the thermosetting resin composition, it is preferable to add an epoxy resin in which particulate rubber is dispersed and which is non-solid at 25°C to the thermosetting resin composition. Thereby, the particulate rubber can be uniformly dispersed in the thermosetting resin composition. Examples of the epoxy resin in which particulate rubber is dispersed and which is non-solid at 25°C include MX-136, MX-153, MX-154, MX-170, MX-217, MX-257, MX-416, MX-451, MX-551, MX-960, MX-965, etc. manufactured by Kaneka Corporation. Two or more kinds of epoxy resins in which particulate rubber is dispersed and which are non-solid at 25°C can also be used in combination.

[0059] (Curing agent)

[0060] The curing agent only needs to be able to cure the epoxy resin that is non-solid at 25°C. For example, diaminodiphenylmethane (DDM), diaminodiphenylsulfone (DDS), diaminodiphenylether (DDE), hexamethylenediamine, dicyandiamide, phenol novolac can be cited. Among them, from the viewpoint of ease of controlling the curing reaction, dicyandiamide is preferable, and diaminodiphenylsulfone is more preferable. Two or more kinds of curing agents can also be used in combination.

[0061] With respect to 1 equivalent of the epoxy group of the epoxy resin that is non-solid at 25°C, the equivalent of the curing agent is preferably 0.3 equivalent or more and 0.8 equivalent or less, and more preferably 0.3 equivalent or more and 0.6 equivalent or less. By setting the equivalent of the curing agent to be less than 1 equivalent of the epoxy group of the epoxy resin that is non-solid at 25°C in this way, the adhesiveness between the substrate and the adhesive layer constituting the cover film can be improved. In addition, the thermosetting resin composition can be spread to the gaps between the wirings formed on the substrate. Further, the insulation reliability of the cured thermosetting resin composition itself can be improved.

[0062] (Inorganic filler)

[0063] Examples of the inorganic filler include aluminum hydroxide, magnesium hydroxide, and silica. From the viewpoints of improving heat resistance and exhibiting flame retardancy, the inorganic filler is preferably aluminum hydroxide, and more preferably magnesium hydroxide. In addition, two or more kinds of inorganic fillers can also be used.

[0064] From the viewpoint of improving the adhesiveness between the substrate and the adhesive layer constituting the cover film, the content of the inorganic filler is 20 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the polyamideimide resin.

[0065] A predetermined amount of each of the above components, namely: polyamideimide resin, an epoxy resin that is not in a solid state at 25°C, particulate rubber dispersed in the non-solid epoxy resin, an inorganic filler, and a curing agent, is added to a container and mixed, whereby a thermosetting resin composition can be obtained. Such a thermosetting resin composition has excellent heat resistance and adhesiveness.

[0066] (Other components)

[0067] The thermosetting resin composition may further contain other additives and the like. As other additives, imidazole-based accelerators such as 2-methylimidazole, N-benzyl-2-methylimidazole, 2-undecylimidazole, Lewis acid complexes such as boron trifluoride monoethylamine, curing accelerators such as polyamines and melamine resins, dispersants, softeners, anti-aging agents, pigments, dyes, silane coupling agents, etc. can be cited. In addition, two or more kinds of additives and the like can also be used.

[0068] (Cover film)

[0069] The cover film of the embodiment is composed of, for example, a polyimide film and an adhesive layer laminated on one side thereof. The cover film of the embodiment is used to protect the wiring formed on the substrate. From the viewpoint of reducing the deterioration of the adhesive layer caused by oxygen when the adhesive layer is placed in a high-temperature environment for a long time, it is preferable that the oxygen permeability of the polyimide film is low. The oxygen permeability of the polyimide film at 30°C is preferably 35.0×10 -6 m 3 / m 2 / m·atm·24 hr or less. Thus, since the oxygen permeating through the polyimide film is reduced, the deterioration of the adhesive layer caused by oxygen is reduced, and the decrease in the adhesive force between the adhesive layer and the wiring is suppressed. In addition, since the glass transition temperature of the cured thermosetting resin composition is 130°C or higher and 200°C or lower, the adhesive layer also has excellent heat resistance. Therefore, the cover film has excellent adhesiveness even when placed in a high-temperature environment for a long time.

[0070] Regarding the thickness of the polyimide film, it only needs to have the function of a cover film. From the viewpoint of processability, for example, it is 2 μm or more and 75 μm or less. In addition, from the viewpoint of reducing oxygen permeability, the thickness of the polyimide film is preferably 12.5 μm or more.

[0071] The thickness of the adhesive layer only needs to protect the wiring formed on the substrate. For example, the thickness after drying is 5 μm or more and 50 μm or less. The curing state of the adhesive layer before being laminated on the substrate, that is, the curing state of the thermosetting resin composition, is a semi-cured state (B stage). It should be noted that the adhesive layer can also be formed on both sides of the polyimide film. According to the cover film having this configuration, since the adhesive layers are formed on both sides of the polyimide film, the wiring surfaces of one substrate and another substrate can be protected with one cover film, and the substrates can be multilayered.

[0072] Next, an example of the manufacturing method of the cover film will be described. First, prepare the thermosetting resin composition of the embodiment. Use a coating device to coat the thermosetting resin composition on one side of the polyimide film. Then, heat the film coated with the thermosetting resin composition until the thermosetting resin composition becomes a semi-cured state (B stage), and then cool it. In this way, a cover film with an adhesive layer laminated on one side of the polyimide film is obtained. The heating conditions are, for example, 100°C or more and 250°C or less, 5 seconds or more and 30 minutes or less, and can be adjusted according to the thickness of the adhesive layer. It should be noted that in order to improve the coatability, an organic solvent can also be added to the thermosetting resin composition.

[0073] As the organic solvent added to the thermosetting resin composition, a solvent that can adjust the viscosity of the thermosetting resin composition is sufficient. For example, glycols such as ethylene glycol and propylene glycol; glycol monoalkyl ethers such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; glycol dialkyl ethers such as ethylene glycol dimethyl ether and ethylene glycol diethyl ether; alkyl esters such as methyl acetate, ethyl acetate, propyl acetate, and methyl acetoacetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; aliphatic hydrocarbons such as hexane, cyclohexane, and octane; amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; cyclic ethers such as tetrahydrofuran and dioxane, etc. Two or more organic solvents can also be used in combination.

[0074] The coating device only needs to be a device that can laminate the thermosetting resin composition on the film with a specified thickness. As the coating device, for example, a die coater, a comma coater, an intaglio coater, etc. can be cited.

[0075] (Flexible printed wiring board)

[0076] The flexible printed wiring board of the embodiment includes a substrate on which wiring is formed and a cover film having an adhesive layer, and the cover film is laminated on the substrate in such a way that the wiring is in contact with the adhesive layer.

[0077] As the wiring formed on the substrate, for example, there can be cited wiring formed by etching the copper layer of a copper-plated laminate or a copper-clad laminate, wiring printed with conductive ink, etc. As the material constituting the wiring, it is a material having conductivity, for example, copper, silver, zinc, etc. From the viewpoint of making the flexible printed wiring board flexible, the thickness of the substrate constituting the flexible printed wiring board is, for example, 15 μm or more and 200 μm or less. Among them, the copper-plated laminate has a copper layer composed of copper plating. The copper-clad laminate has a copper layer composed of copper foil.

[0078] An example of the manufacturing method of the flexible printed wiring board will be described. First, a substrate formed with wiring and a cover film having an adhesive layer are prepared. Next, the cover film is laminated so that the adhesive layer is in contact with the wiring-formed surface of the substrate and heated and pressed. Thereby, a flexible printed wiring board is obtained. The conditions for heating and pressing are, for example, 120°C or more and 250°C or less, 5 seconds or more and 120 minutes or less, 1 MPa or more and 10 MPa or less, and can be adjusted according to the laminate structure.

[0079] In the above embodiment, a cover film having a polyimide film and an adhesive layer composed of a thermosetting resin composition and having the adhesive layer laminated on at least one surface of the polyimide film is cited, but the following modification examples are also included as one of the embodiments.

[0080] (Modification example of a cover film having a gas barrier layer)

[0081] The modification example further has a gas barrier layer that suppresses the permeation of oxygen. The gas barrier layer is laminated on at least one surface of the polyimide film constituting the cover film. The oxygen permeation rate of the polyimide film laminated with the gas barrier layer at 30°C is, for example, 5.0×10 - 6 m 3 / m 2 ·atm·24 hr or less.

[0082] The adhesive layer can be laminated on the polyimide film surface on the side opposite to the surface laminated with the gas barrier layer, or can be laminated on the gas barrier layer.

[0083] The gas barrier layer only needs to be able to suppress the permeation of oxygen. For example, there can be cited a gas barrier layer composed of silicon dioxide (SiO2), zinc oxide, etc. The thickness of the gas barrier layer is, for example, 10 nm or more and 100 nm or less. In the polyimide film laminated with the gas barrier layer, the permeation of oxygen is reduced. As a result, the contact between oxygen and the adhesive layer laminated on the film becomes less, the deterioration of the adhesive layer caused by oxygen, that is, the deterioration of the thermosetting resin composition caused by oxygen is reduced, and the decrease in the adhesive force between the adhesive layer and the wiring is suppressed.

[0084] Examples

[0085] The present invention will be described in more detail by the following examples. The present invention is not limited by any of the following examples.

[0086] As the respective components contained in the thermosetting resin compositions in the examples and comparative examples, the following substances were used.

[0087] (Polyamideimide resin)

[0088] (1) Polyamideimide resin: having an acrylonitrile-butadiene rubber skeleton and a glass transition temperature of 178 °C (manufactured by Toyobo Co., Ltd., HR-71DD). The glass transition temperature was measured using RSA-G2 manufactured by TA-instruments. The conditions were set to tensile mode, in air, 1 Hz, and heating at 10 °C / min.

[0089] (Epoxy resin that is not in a solid state at 25 °C)

[0090] (1) Epoxy resin EA: having an epoxy equivalent of 231 g / eq, phenol Novolac type, and containing 25 parts by mass of particulate rubber (polybutadiene rubber, average particle size 0.1 μm) in 100 parts by mass of epoxy resin EA (manufactured by Kaneka Corporation, MX-217)

[0091] (2) Epoxy resin EB: having an epoxy equivalent of 270 g / eq, bisphenol A type, and containing 33 parts by mass of particulate rubber (polybutadiene rubber, average particle size 0.1 μm) in 100 parts by mass of epoxy resin EB (manufactured by Kaneka Corporation, MX-153)

[0092] (3) Epoxy resin EC: having an epoxy equivalent of 270 g / eq, bisphenol A Novolac type, and containing 25 parts by mass of particulate rubber (styrene-butadiene rubber, average particle size 0.1 μm) in 100 parts by mass of epoxy resin EC (manufactured by Kaneka Corporation, MX-227M75)

[0093] (4) Epoxy resin ED: having an epoxy equivalent of 243 g / eq, bisphenol A type, and containing 25 parts by mass of particulate rubber (silicone rubber, average particle size 0.1 μm) in 100 parts by mass of epoxy resin ED (manufactured by Kaneka Corporation, MX-960)

[0094] (5) Epoxy resin EE: having an epoxy equivalent of 177 g / eq, phenol Novolac type (manufactured by Mitsubishi Chemical Corporation, jER (registered trademark) 152)

[0095] (6) Epoxy resin EF: having an epoxy equivalent of 190 g / eq, bisphenol A type (manufactured by DIC Corporation, EPICLON (registered trademark) 850).

[0096] (Curing agent)

[0097] Diaminodiphenyl sulfone: having an amine value of 62 g / eq (manufactured by Konishi Chemical Industry Co., Ltd., 3,3'-DAS).

[0098] (Inorganic filler)

[0099] (1) Filler FA: magnesium hydroxide (manufactured by Kyowa Chemical Industry Co., Ltd., KISUMA (registered trademark) 5P),

[0100] (2) Filler FB: aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., BF013),

[0101] (3) Filler FC: silica (manufactured by ADMATECHS Co., Ltd., SC2010-MB).

[0102] (Example 1)

[0103] (Preparation of thermosetting resin composition)

[0104] Add 100 parts by mass of polyamideimide resin, 52 parts by mass of epoxy resin EA, 8.4 parts by mass of curing agent, 30 parts by mass of filler FA, 100 parts by mass of methyl ethyl ketone as an organic solvent, and 260 parts by mass of toluene to a container, and stir at room temperature to obtain a thermosetting resin composition.

[0105] (Production of cover film)

[0106] Coat the thermosetting resin composition on one side of a 25-μm-thick polyimide film (manufactured by Du Pont-toray Co., Ltd., Kapton (registered trademark) 100EN) with a bar coater so that the thickness after heating becomes 30 μm, and heat at 150 °C for 5 minutes. Then, under the conditions of 100 °C, 1 MPa, and 10 seconds, bond a release PET film (manufactured by Toray Industries, Inc., Lumirror (registered trademark) #38-S10) to the film surface coated with the thermosetting resin composition to obtain a cover film with a release PET film. The oxygen transmission rate of the polyimide film used in Example 1 at 30 °C was 31.0×10 -6 m 3 / m 2 ·atm·24 hr. The oxygen transmission rate at 30 °C was measured according to ASTM D1434.

[0107] (Production of adherend)

[0108] The shiny surface of the copper foil (thickness: 35 μm) of a copper-clad laminate (manufactured by Arisawa Manufacturing Co., Ltd., LCSE1035EDH (T20)) with a thickness of 80 μm was softly etched with an aqueous sulfuric acid-based soft etching solution (manufactured by ADEKA Corporation, CL-8) to obtain an adherend with 1 μm of copper removed from the surface of the copper foil.

[0109] <Peel Strength (Adhesive Force)>

[0110] The adhesive force of the obtained cover film was measured by the following method.

[0111] (Sample for Measurement)

[0112] The release PET film was peeled off from the cover film, and the surface of the adhesive layer was bonded to the copper foil surface of the adherend, and heat pressing was performed under the conditions of 160 °C, 3.0 MPa, and 60 minutes to obtain a sample for measurement. When performing the measurement, the sample for measurement was cut into a width of 10 mm × a length of 100 mm.

[0113] (Measurement)

[0114] Using Autograph AGS-500 manufactured by Shimadzu Corporation, the peel strength in the 90° direction (perpendicular to the surface of the sample for measurement) was measured under the following measurement conditions.

[0115] (Peel Strength before Heat Treatment)

[0116] After storing the sample for measurement at 25 °C and a relative humidity of 50% for 24 hours, the peel strength for peeling off the cover film and the peel strength for peeling off the adherend were measured respectively. The test speed was set at 50 mm / min. It should be noted that "peeling off the cover film" means pulling the cover layer in the 90° direction (perpendicular direction) with respect to the surface of the sample for measurement. In addition, "peeling off the adherend" means pulling the adherend in the 90° direction (perpendicular direction) with respect to the surface of the sample for measurement. The same applies hereinafter.

[0117] The evaluation criteria are as follows.

[0118] Excellent: The peel strength is 7.0 N / cm or more,

[0119] Good: The peel strength is 3.4 N / cm or more and less than 7.0 N / cm,

[0120] Poor: The peel strength is less than 3.4 N / cm.

[0121] (Peel Strength after Heat Treatment)

[0122] The sample for measurement was placed in an atmosphere at 150 °C for 250 hours, and after being stored at 25 °C and 50% relative humidity for 24 hours, the peel strength of the peeled release film and the peel strength of the peeled adherend were measured respectively. The test speed was set at 50 mm / min.

[0123] The evaluation criteria are as follows.

[0124] Excellent: The peel strength is 7.0 N / cm or more.

[0125] Good: The peel strength is 3.4 N / cm or more and less than 7.0 N / cm.

[0126] Poor: The peel strength is less than 3.4 N / cm.

[0127] (Example 2) to (Example 11), (Comparative Example 1) to (Comparative Example 6)

[0128] (Preparation of thermosetting resin composition)

[0129] As shown in Table 1 and Table 2, the types and contents of the respective components were changed, and in addition, the thermosetting resin composition was prepared by the same method as in Example 1. The unit of the content in the table is parts by mass unless otherwise specified. It should be noted that in Example 11, only the polyimide film described later is different from that in Example 1, and the other configurations are the same as those in Example 1.

[0130] (Production of release film)

[0131] In Examples 2 to 10 and Comparative Examples 1 to 6, the same polyimide film with a thickness of 25 μm (manufactured by Du Pont-toray Co., Ltd., Kapton (registered trademark) 100EN) was used as in Example 1. In Example 11, a film having a gas barrier layer with a thickness of 30 nm composed of SiO2 laminated on one side of a polyimide film with a thickness of 25 μm (manufactured by Du Pont-toray Co., Ltd., Kapton (registered trademark) 100EN) was used. The oxygen transmission rate of the polyimide film laminated with the gas barrier layer used in Example 11 at 30 °C was 5.0×10 -6 m 3 / m 2 ·atm·24 hr or less, and was 2.5×10 -6 m 3 / m 2 ·atm·24 hr. The release film was produced by the same method as in Example 1. The oxygen transmission rate at 30 °C was measured according to ASTM D1434 in the same manner as in Example 1. The peel strength was measured by the same method as in Example 1. The measurement results are shown in Table 1 and Table 2.

[0132] [Table 1]

[0133]

[0134] [Table 2]

[0135]

[0136] Regarding Examples 1 to 11, it can be seen that the cover film composed of a polyimide film with low oxygen permeability and an adhesive layer has a high peel strength after heat treatment, and the aforementioned adhesive layer is composed of a thermosetting resin composition containing an inorganic filler and having high heat resistance. Specifically, it can be seen that in the thermosetting resin composition constituting the adhesive layer, the content of the epoxy resin that is not in a solid state at 25°C is 30 parts by mass or more and 70 parts by mass or less, the content of the fine particle rubber is 5 parts by mass or more and 20 parts by mass or less, and the content of the inorganic filler is 20 parts by mass or more and 40 parts by mass or less, thus having excellent adhesiveness.

[0137] In addition, as evidence of the high peel strength, the interface between the polyimide film and the adhesive layer after the measurement of the peel strength was observed, and cohesive failure of a part of the adhesive layer remaining on the surface of the polyimide film was confirmed. In addition, cohesive failure was also confirmed at the interface between the adherend and the adhesive layer in the same manner as at the interface between the polyimide film and the adhesive layer.

[0138] In addition, it can be seen that by making the oxygen permeability of the polyimide film constituting the cover film at 30°C be 35.0×10 -6 m 3 / m 2 ·atm·24 hr or less, the contact between oxygen and the adhesive layer laminated on the film becomes less, the deterioration of the adhesive layer caused by oxygen is reduced, and the decrease in the adhesive force between the adhesive layer and the adherend such as wiring is suppressed.

[0139] Regarding the sample of Example 11, the time placed in a high-temperature atmosphere was further extended, and the peel strength thereafter was further measured. Specifically, the peel strength after being placed in a 150°C atmosphere for 500 hours and stored at 25°C and 50% relative humidity for 24 hours, and the peel strength after being placed in a 150°C atmosphere for 1000 hours and stored at 25°C and 50% relative humidity for 24 hours were measured respectively. The results are as follows.

[0140] (Example 11)

[0141] (1) 150°C, 500 hours

[0142] The peel strength for peeling off the cover film is 10.5 N / cm,

[0143] The peel strength for peeling off the adherend is 9.8 N / cm.

[0144] (2) 150 °C, 1000 hours

[0145] The peel strength for peeling off the cover film is 9.5 N / cm,

[0146] The peel strength for peeling off the adherend is 8.5 N / cm.

[0147] As the reason for exhibiting high peel strength, the following can be cited: by virtue of a cover film having a polyimide film with a gas barrier layer laminated thereon, oxygen permeation is reduced, and deterioration of the adhesive layer caused by oxygen is decreased; and the presence of an inorganic filler in a thermosetting resin composition having high heat resistance. As the basis for the high peel strength, in the sample of Example 11, cohesive failure was also confirmed at the interface between the adherend and the adhesive layer after measuring the peel strength, and at the interface between the polyimide film and the adhesive layer after measuring the peel strength.

[0148] As described above, the cover film having an adhesive layer composed of the thermosetting resin compositions of Examples 1 to 11 has excellent adhesiveness in both peeling off the cover film and peeling off the adherend even when placed in a high-temperature environment for a long time. In addition, for Example 11, even when placed in a high-temperature environment for 500 hours and 1000 hours, it has excellent adhesiveness in both peeling off the cover film and peeling off the adherend. Such a cover film is suitable as a cover film for in-vehicle electronic devices.

[0149] (Supplementary Note)

[0150] Hereinafter, various aspects of the present invention will be summarized and described in the form of supplementary notes.

[0151] (Supplementary Note 1)

[0152] A thermosetting resin composition, comprising:

[0153] A polyamideimide resin having an acrylonitrile-butadiene rubber backbone;

[0154] An epoxy resin that is not in a solid state at 25 °C;

[0155] A fine particle rubber dispersed in the aforementioned non-solid epoxy resin;

[0156] An inorganic filler; and

[0157] A curing agent,

[0158] With respect to 100 parts by mass of the aforementioned polyamideimide resin, the content of the aforementioned non-solid epoxy resin is 30 parts by mass or more and 70 parts by mass or less,

[0159] The content of the aforementioned particulate rubber is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the aforementioned polyamideimide resin.

[0160] The aforementioned inorganic filler is 20 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the aforementioned polyamideimide resin.

[0161] (Supplementary Note 2)

[0162] The thermosetting resin composition as described in Supplementary Note 1, wherein the aforementioned particulate rubber is composed of a core layer and a shell layer covering its surface.

[0163] (Supplementary Note 3)

[0164] A covering film, which has:

[0165] An oxygen transmission rate at 30 °C of 35.0×10 -6 m 3 / m 2 ·atm·24 hr or less of a polyimide film; and

[0166] An adhesive layer composed of the thermosetting resin composition described in Supplementary Note 1 or Supplementary Note 2,

[0167] The aforementioned adhesive layer is laminated on at least one surface of the aforementioned polyimide film.

[0168] (Supplementary Note 4)

[0169] The covering film as described in Supplementary Note 3, wherein a gas barrier layer for suppressing oxygen transmission is laminated on at least one surface of the aforementioned polyimide film.

[0170] (Supplementary Note 5)

[0171] The covering film as described in Supplementary Note 4, wherein the polyimide film laminated with the aforementioned gas barrier layer has an oxygen transmission rate at 30 °C of 5.0×10 -6 m 3 / m 2 ·atm·24 hr or less.

[0172] (Supplementary Note 6)

[0173] A flexible printed wiring board, which has the covering film described in any one of Supplementary Notes 3 to 5 and a substrate formed with wirings,

[0174] The aforementioned covering film is laminated on the aforementioned substrate in such a manner that the aforementioned adhesive layer is in contact with the aforementioned wirings.

[0175] In the context of the present invention, various embodiments and modifications are possible without departing from the broad spirit and scope of the present invention. Additionally, the above-described embodiments are used to illustrate the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is not represented by the embodiments but by the claims. Moreover, various modifications implemented within the scope of the claims and within the meaning of equivalent inventions are considered to be within the scope of the present invention.

[0176] This application is based on Japanese Patent Application No. 2022-201801, filed on December 19, 2022. The entire specification and claims of Japanese Patent Application No. 2022-201801 are incorporated herein by reference.

Claims

1. A thermosetting resin composition comprising: a polyamideimide resin having an acrylonitrile-butadiene rubber backbone; an epoxy resin that is not in a solid state at 25°C; a particulate rubber dispersed in the non-solid epoxy resin; an inorganic filler; and a curing agent, wherein, based on 100 parts by mass of the polyamideimide resin, the content of the non-solid epoxy resin is 30 parts by mass or more and 70 parts by mass or less, wherein, based on 100 parts by mass of the polyamideimide resin, the content of the particulate rubber is 5 parts by mass or more and 20 parts by mass or less, wherein, based on 100 parts by mass of the polyamideimide resin, the inorganic filler is 20 parts by mass or more and 40 parts by mass or less.

2. The thermosetting resin composition according to claim 1, wherein, The particulate rubber is composed of a core layer and a shell layer covering its surface.

3. A cover film comprising: a polyimide film having an oxygen transmission rate of 35.0×10 -6 m 3 / m 2 ·atm·24 hr or less at 30°C; and an adhesive layer composed of the thermosetting resin composition according to claim 1 or 2, wherein the adhesive layer is laminated on at least one surface of the polyimide film.

4. The cover film according to claim 3, wherein, A gas barrier layer that inhibits oxygen permeation is laminated on at least one surface of the polyimide film.

5. The cover film according to claim 4, wherein, The oxygen transmission rate of the polyimide film laminated with the gas barrier layer at 30 °C is 5.0×10 -6 m 3 / m 2 ·atm·24 hr or less.

6. A flexible printed wiring board comprising the cover film according to any one of claims 3 to 5 and a substrate on which wirings are formed, wherein the cover film is laminated on the substrate such that the adhesive layer is in contact with the wirings.

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