Thermosetting resin composition, resin sheet, double-sided adhesive sheet, coverlay film, and flexible printed wiring board

Abstract

A thermosetting resin composition according to the present invention contains an epoxy resin, a curing agent, and a polyurethane resin derived from polycarbonate diol. The polyurethane resin has a storage modulus at 25°C of 1.0 GPa or more, and a weight average molecular weight of 60,000 or more, and when the total parts by mass of the epoxy resin is 100 parts by mass, the polyurethane resin content is 50-120 parts by mass, and the storage modulus at 25°C after curing is 1.0-5.0 GPa.

Description

Thermosetting resin composition, resin sheet, double-sided adhesive sheet, coverlay film, and flexible printed wiring board

[0001] The present invention relates to a thermosetting resin composition, a resin sheet, a double-sided adhesive sheet, a coverlay film, and a flexible printed wiring board.

[0002] One of the characteristics required for a flexible printed wiring board is flexural fatigue resistance, which means that the wiring is not easily broken even when repeatedly bent. A coverlay film that protects the wiring plays an important role in improving the flexural fatigue resistance.

[0003] For example, Patent Document 1 discloses a resin composition that can be used as the resin composition of the adhesive layer of a coverlay film, the resin composition containing an epoxy resin, a polyester urethane resin having an average molecular weight of 15,000 or less, a novolac type phenol resin, and a phosphoric acid ester amide.

[0004] Japanese Patent Application Laid-Open No. 2008-205374

[0005] However, the urethane resin contained in this resin composition is a polyester urethane resin and has an average molecular weight of 15,000 or less. Therefore, the storage elastic modulus of the cured resin composition at 25°C tends to be low. Further, in a flexible printed wiring board in which the wiring is protected by a coverlay film composed of this resin composition, when repeatedly bent, the wiring may be disconnected within several thousand times. That is, the flexural fatigue resistance of the flexible printed wiring board is inferior.

[0006] An object of the present invention is to provide a flexible printed wiring board having excellent flexural fatigue resistance and a coverlay film used for protecting the wiring of this flexible printed wiring board, to provide a resin sheet and a double-sided adhesive sheet used for this flexible printed wiring board, and to provide a thermosetting resin composition constituting the adhesive layer of the coverlay film, the resin layer of the double-sided adhesive sheet, and the resin sheet.

[0007] The present invention is as follows: [1] The thermosetting resin composition according to the present invention comprises an epoxy resin, a curing agent, and a polyurethane resin derived from polycarbonate diol, wherein the storage modulus of the polyurethane resin at 25°C is 1.0 GPa or more, the weight-average molecular weight of the polyurethane resin is 60,000 or more, when the total mass of the epoxy resin is 100 parts by mass, the content of the polyurethane resin is 50 parts by mass or more and 120 parts by mass or less, and the storage modulus of the cured material at 25°C is 1.0 GPa or more and 5.0 GPa or less.

[0008] [2] The epoxy resin may include an epoxy resin that is non-solid at 25°C, and when the total mass of the epoxy resin is 100 parts by mass, the content of the non-solid epoxy resin may be 5 parts by mass or more and 100 parts by mass or less.

[0009] [3] The thermosetting resin composition according to the present invention may contain rubber-elastic particles.

[0010] [4] The rubber-elastic particles may be core-shell polymer particles, which consist of a core portion and a shell portion that covers the surface of the core portion.

[0011] [5] The content of the rubber-elastic particles may be 30 parts by mass or less when the total mass of the epoxy resin is 100 parts by mass.

[0012] [6] The acid value of the polyurethane resin may be 10 mg KOH / g or more.

[0013] [7] The amount of the curing agent may be 0.3 equivalents or more and 0.8 equivalents or less per equivalent of epoxy groups in the epoxy resin.

[0014] [8] The thermosetting resin composition according to the present invention may have a storage modulus at 60°C after curing of 1.0 GPa or more and 5.0 GPa or less.

[0015] [9] The thermosetting resin composition according to the present invention may have a storage modulus at 80°C after curing of 1.0 GPa or more and 5.0 GPa or less.

[0016]

[10] The thermosetting resin composition according to the present invention may contain inorganic particles, and when the total mass of the epoxy resin is 100 parts by mass, the content of the inorganic particles may be 50 parts by mass or more and 80 parts by mass or less.

[0017]

[11] The resin sheet according to the present invention is composed of a thermosetting resin composition according to any one of [1] to

[10] .

[0018]

[12] The double-sided adhesive sheet according to the present invention is composed of a film and a resin layer formed on both sides of the film, wherein the resin layer is composed of a thermosetting resin composition according to any one of [1] to

[10] .

[0019]

[13] The coverlay film according to the present invention is composed of a film and an adhesive layer formed on one side of the film, wherein the adhesive layer is composed of a thermosetting resin composition according to any one of [1] to

[10] .

[0020]

[14] The flexible printed circuit board according to the present invention comprises the coverlay film described in

[13] and a substrate on which wiring is formed, wherein the coverlay film is arranged on the substrate such that the adhesive layer is in contact with the wiring.

[0021] According to the present invention, it is possible to provide a flexible printed circuit board with excellent bending resistance and a coverlay film used to protect the wiring of the flexible printed circuit board, a resin sheet and a double-sided adhesive sheet used in the flexible printed circuit board, and a thermosetting resin composition constituting the adhesive layer of the coverlay film, the resin layer of the double-sided adhesive sheet, and the resin sheet.

[0022] This is a schematic cross-sectional view of a resin sheet according to an embodiment. This is a schematic cross-sectional view of a double-sided adhesive sheet according to an embodiment. This is a schematic cross-sectional view of a coverlay film according to an embodiment. This is a schematic cross-sectional view of a flexible printed circuit board according to an embodiment. This is a schematic top view of the wiring formed on the substrate used in the bending test. This is a schematic cross-sectional view of a flexible printed circuit board used in the bending test. This is a schematic cross-sectional view of a flexible printed circuit board used in the bending test. This is a schematic cross-sectional view of a multilayer flexible printed circuit board used in the bending test. This is a schematic cross-sectional view of a test sample used for bending in the bending test. This is a schematic cross-sectional view showing a test sample for bending before bending in the bending test. This is a schematic cross-sectional view showing a test sample for bending after bending in the bending test.

[0023] The following describes in detail embodiments of the present invention, including a thermosetting resin composition, a resin sheet, a double-sided adhesive sheet, a coverlay film, and a flexible printed circuit board. These embodiments are examples for illustrating the present invention and are not intended to limit the invention to the following. The present invention can be implemented by modifying it as appropriate within the scope of its gist.

[0024] In the present invention, parts by mass refer to the mass of the resin only, excluding volatile components such as organic solvents contained in the resin, and the mass of non-volatile components.

[0025] [Thermosetting Resin Composition] The thermosetting resin composition of the embodiment comprises an epoxy resin, a curing agent, and a polyurethane resin derived from polycarbonate diol, as described below, and has a storage modulus of 1.0 GPa or more and 5.0 GPa or less at 25°C after curing. This thermosetting resin composition can be suitably used as the adhesive layer of a coverlay film, the resin layer of a double-sided adhesive sheet, and the resin composition constituting the resin sheet. In a flexible printed circuit board in which wiring is protected by a coverlay film using this thermosetting resin composition as the resin composition of the adhesive layer, the surface of the wiring is covered and fixed without gaps by the adhesive layer. For this reason, the wiring is less likely to break even when the flexible printed circuit board is bent. That is, such a flexible printed circuit board has excellent bending resistance. The components contained in the thermosetting resin composition of the embodiment will be described below.

[0026] (Epoxy Resin) The epoxy resin included in the thermosetting resin composition may be any epoxy resin that mixes uniformly with the polyurethane resin, and may be an epoxy resin that is solid at 25°C and / or an epoxy resin that is non-solid at 25°C. From the viewpoint of improving the adhesion of the thermosetting resin composition after curing, it is preferable that the epoxy resin includes an epoxy resin that is non-solid at 25°C. Furthermore, the inclusion of an epoxy resin that is non-solid at 25°C in the thermosetting resin composition improves the uniformity after mixing the thermosetting resin composition.

[0027] The epoxy resin that is solid at 25°C preferably has two or more epoxy groups in one molecule and an epoxy equivalent of 150 g / eq to 500 g / eq, and more preferably 150 g / eq to 350 g / eq, from the viewpoint of increasing the reactivity of the epoxy resin and improving the electrical insulation reliability of the thermosetting resin composition after curing. The epoxy resin that is solid at 25°C is, for example, a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a bisphenol S type epoxy resin, a novolac type epoxy resin, an amine type epoxy resin, a biphenyl type epoxy resin, a biphenyl novolac type epoxy resin, a biphenyl aralkyl type epoxy resin, and an alicyclic epoxy resin, whose epoxy equivalent is within the aforementioned range. From the viewpoint of improving the electrical insulation reliability and flame retardancy of the thermosetting resin composition after curing, the epoxy resin that is solid at 25°C is preferably a biphenyl type epoxy resin, a biphenyl novolac type epoxy resin, and a biphenyl aralkyl type epoxy resin. The thermosetting resin composition may contain two or more epoxy resins that are solid at 25°C.

[0028] An epoxy resin that is non-solid at 25°C preferably has two or more epoxy groups in one molecule and an epoxy equivalent of 100 g / eq to 400 g / eq, and more preferably 150 g / eq to 350 g / eq. Examples of epoxy resins that are non-solid at 25°C and have epoxy equivalents within the aforementioned range include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, amine type epoxy resin, and alicyclic epoxy resin. From the viewpoint of heat resistance, bisphenol A type epoxy resin and phenol novolac type epoxy resin are preferred among non-solid epoxy resins at 25°C. The thermosetting resin composition may contain two or more non-solid epoxy resins at 25°C. Here, a non-solid epoxy resin at 25°C means an epoxy resin that is fluid at 25°C. The epoxy equivalent of the epoxy resin can be measured in accordance with JIS K7236 2001.

[0029] The content of non-solid epoxy resin at 25°C is 5 parts by mass or more and 100 parts by mass or less, when the total mass of epoxy resin contained in the thermosetting resin composition is 100 parts by mass. From the viewpoint of improving the adhesion of the thermosetting resin composition after curing, the content of non-solid epoxy resin at 25°C is preferably 5 parts by mass or more and 90 parts by mass or less, more preferably 10 parts by mass or more and 90 parts by mass or less, even more preferably 20 parts by mass or more and 90 parts by mass or less, and even more preferably 20 parts by mass or more and 70 parts by mass or less.

[0030] The epoxy resin, which is non-solid at 25°C, preferably contains rubber-elastic particles, as described later. Furthermore, it is preferable that the rubber-elastic particles are dispersed within the non-solid epoxy resin at 25°C. Adding such a non-solid epoxy resin at 25°C to a thermosetting resin composition allows for uniform dispersion of the rubber-elastic particles within the composition. Additionally, a thermosetting resin composition containing a non-solid epoxy resin at 25°C containing rubber-elastic particles exhibits improved adhesion of the cured resin composition. Examples of non-solid epoxy resins at 25°C containing rubber-elastic particles include MX-136, MX-153, MX-154, MX-170, MX-217, MX-257, MX-416, MX-451, MX-551, MX-960, and MX-965, manufactured by Kaneka Corporation.

[0031] (Particles with rubber elasticity) The thermosetting resin composition preferably contains particles with rubber elasticity. This can improve the adhesion of the thermosetting resin composition after curing. The particles with rubber elasticity are preferably core-shell polymer particles, which consist of a core portion and a shell portion that covers its surface. Core-shell polymer particles are also referred to as core-shell rubber (CSR) in this specification.

[0032] The core of the core-shell polymer particles is composed of a polymer with rubber elasticity. Examples of polymers with rubber elasticity include diene rubber, acrylic rubber, styrene rubber, and polysiloxane rubber. The core may be composed of two or more types of rubber.

[0033] The polymer constituting the shell portion of core-shell polymer particles is a polymer or copolymer obtained by polymerizing one or more components selected from (meth)acrylic acid ester monomers, aromatic vinyl monomers, vinyl cyanide monomers, unsaturated acid derivatives, (meth)acrylamide derivatives, and maleimide derivatives. Furthermore, the polymer of the shell portion is bonded to the polymer of the core portion by graft polymerization. As a result, part or all of the surface of the core portion is covered by the shell portion, making it difficult for the shell portion to peel off from the core portion. In addition, because the surface of the core portion is covered by the shell portion, aggregation between one core portion and another core portion is unlikely to occur. In other words, aggregation between core-shell polymer particles can be prevented.

[0034] From the viewpoint of dispersing core-shell polymer particles in a thermosetting resin composition, it is preferable that the polymer constituting the shell portion has functional groups that have high affinity with epoxy resin, polyurethane resin, or curing agent. Examples of functional groups include hydroxyl groups, carboxyl groups, and epoxy groups, with epoxy groups being preferred from the viewpoint of increasing reactivity.

[0035] From the viewpoint of improving dispersibility, the size of the rubber-elastic particles is preferably 0.05 μm or more and 1 μm or less in volume-average particle size.

[0036] The content of rubber-elastic particles is 30 parts by mass or less, preferably 10 to 20 parts by mass, when the total mass of the epoxy resin is 100 parts by mass. This improves the adhesion of the thermosetting resin composition after curing. Furthermore, in a flexible printed circuit board where the wiring is protected by a coverlay film using such a thermosetting resin composition as the resin composition of the adhesive layer, the surface of the wiring is covered and fixed without gaps by the adhesive layer. For this reason, the wiring is less likely to break even if the flexible printed circuit board is repeatedly bent.

[0037] The thermosetting resin composition may contain rubber-elastic particles as is, or it may contain a non-solid epoxy resin at 25°C in which rubber-elastic particles are dispersed. Furthermore, the rubber-elastic particles may consist of two or more core-shell polymer particles with different core polymers.

[0038] (Curing agent) The curing agent included in the thermosetting resin composition only needs to be able to cure the epoxy resin, and examples include diaminodiphenylmethane (DDM), diaminodiphenylsulfone (DDS), diaminodiphenyl ether (DDE), hexamethylenediamine, dicyandiamide, and phenol novolac. Among these, dicyandiamide and diaminodiphenylsulfone are preferred from the viewpoint of ease of controlling the curing reaction, and diaminodiphenylsulfone is more preferred. The thermosetting resin composition may contain two or more curing agents.

[0039] From the viewpoint of improving the electrical insulation reliability of the thermosetting resin composition after curing, the equivalent amount of the curing agent is preferably 0.3 equivalents or more and 0.8 equivalents or less, and more preferably 0.5 equivalents or more and 0.7 equivalents or less, relative to one equivalent of epoxy groups of the epoxy resin contained in the thermosetting resin composition.

[0040] (Polyurethane resin derived from polycarbonate diol) The polyurethane resin derived from polycarbonate diol contained in the thermosetting resin composition has at least one polycarbonate skeleton in each molecule. This suppresses the water absorption of the polyurethane resin. Furthermore, the cured product obtained from a thermosetting resin composition containing such polyurethane resin has excellent hydrolysis resistance and electrical insulation reliability in high temperature and high humidity environments. In addition, when a thermosetting resin composition containing polycarbonate diol-derived polyurethane resin is applied to a film substrate, it can be applied uniformly. Furthermore, the thermosetting resin composition after application has excellent film-forming properties, and the thermosetting resin composition after curing is less prone to cracking. Moreover, the adhesive layer of a coverlay film, the resin layer of a double-sided adhesive sheet, and the resin sheet made from such a thermosetting resin composition have excellent flexibility. Hereinafter, the polyurethane resin derived from polycarbonate diol will also be referred to as polyurethane resin.

[0041] Polycarbonate diol-derived polyurethane resins are obtained by reacting (a) a carboxyl group-containing polyester resin having hydroxyl groups at its termini with (b) a diisocyanate. The materials necessary for the synthesis of polyurethane resins are described below.

[0042] (a) Carboxyloid-containing polyester resin having hydroxyl groups at the terminals A carboxyloid-containing polyester resin having hydroxyl groups at the terminals is obtained by reacting (a-1) polycarbonate diol with (a-2) tetracarboxylic dianhydride. Hereinafter, the carboxyloid-containing polyester resin having hydroxyl groups at the terminals will also be simply called a carboxyloid-containing polyester resin.

[0043] (a-1) Polycarbonate diols for obtaining a polyester resin containing polycarbonate diols are aliphatic polycarbonate diols and alicyclic polycarbonate diols. From the viewpoint of increasing the flexibility of the polyurethane resin, it is preferable that the polycarbonate diol is an aliphatic polycarbonate diol. Furthermore, by using an aliphatic polycarbonate diol and an alicyclic polycarbonate diol in combination, the flexibility of the polyurethane resin can be increased, the stickiness of the polyurethane resin can be suppressed, and the processability can be improved.

[0044] Polycarbonate diol can be obtained, for example, by reacting a dialkyl carbonate such as dimethyl carbonate with a diol compound having two hydroxyl groups in the molecule. Examples of the diol compound for obtaining an aliphatic polycarbonate diol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, and 2-methyl-1,8-octanediol. From the viewpoint of improving the flexibility of the polyurethane resin, the diol compound for obtaining an aliphatic polycarbonate diol is preferably 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, or 1,6-hexanediol. The diol compound for obtaining an alicyclic polycarbonate diol is 1,4-cyclohexanedimethanol.

[0045] (a-2) Tetracarboxylic dianhydride The tetracarboxylic dianhydride for obtaining a carboxy group-containing polyester resin preferably includes 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride. The carboxy group-containing polyester resin obtained from such a tetracarboxylic dianhydride can suppress water absorption and has excellent heat resistance. From the viewpoint of improving heat resistance, the tetracarboxylic dianhydride may include an aromatic tetracarboxylic dianhydride other than 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride. Examples of the aromatic tetracarboxylic dianhydride include 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, and 4,4'-oxydiphthalic anhydride.

[0046] (b) The diisocyanate for obtaining the diisocyanate polyurethane resin has two isocyanate groups in one molecule. The diisocyanate is, for example, an aromatic diisocyanate, an aliphatic diisocyanate, or an alicyclic diisocyanate. From the viewpoint of improving the heat resistance of the polyurethane resin, the diisocyanate is preferably an aromatic diisocyanate. From the viewpoint of improving the flexibility of the polyurethane resin, the diisocyanate is preferably an aliphatic diisocyanate. Two or more diisocyanates may be combined.

[0047] The aromatic diisocyanate is, for example, tolylene diisocyanate (TDI), 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, 2,4-diisocyanate diphenyl ether, diphenylmethane diisocyanate (MDI), durylene diisocyanate, xylylene diisocyanate, 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, and 4,4'-diisocyanate dibenzyl.

[0048] The aliphatic diisocyanate is, for example, methylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI), and 1,10-decamethylene diisocyanate.

[0049] The alicyclic diisocyanate is, for example, 1,4-cyclohexylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,5-tetrahydronaphthalene diisocyanate, isophorone diisocyanate (IPDI), hydrogenated diphenylmethane diisocyanate (HMDI), and hydrogenated xylylene diisocyanate.

[0050] From the viewpoint of improving the reactivity, heat resistance, flexibility, and solubility of the polyurethane resin, the diisocyanate is preferably at least one selected from the group consisting of diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), isophorone diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI), 1,5-pentamethylene diisocyanate (PDI), and hydrogenated diphenylmethane diisocyanate (HMDI). Diphenylmethane diisocyanate (MDI) and / or isophorone diisocyanate (IPDI) are more preferred.

[0051] Polycarbonate diol-derived polyurethane resin can be synthesized using the materials described above, for example, by the following method. First, (a-2) tetracarboxylic dianhydride, an excess amount of (a-1) polycarbonate diol, and an organic solvent are added to a container and mixed. Next, the mixture is reacted with stirring at 100°C to 150°C for 1 to 7 hours to obtain a carboxyl group-containing polyester resin having hydroxyl groups at its ends. Next, (b) diisocyanate is added to the obtained carboxyl group-containing polyester resin so that the molar ratio of hydroxyl groups (OH groups) to isocyanate groups (NCO groups) (OH groups / NCO groups) is about 1.0, and the mixture is reacted at 50°C to 120°C for 1 to 12 hours. After that, it is cooled to obtain a liquid polyurethane resin. Organic solvents may be added as appropriate while observing the reaction. Examples of organic solvents used in this synthesis are toluene, methyl ethyl ketone, and dimethyl carbonate.

[0052] The obtained polyurethane resin derived from polycarbonate diol has carboxyl groups in its molecular chain. It is particularly preferable that the carboxyl groups are present in the side chains. By adding such a polyurethane resin to a thermosetting resin composition, the reactivity with the epoxy resin can be increased, and the electrical insulation reliability and adhesion of the cured thermosetting resin composition can be improved.

[0053] The amount of carboxyl groups in the polyurethane resin described above can be indicated by its acid value. The acid value of the polyurethane resin is 10 mg KOH / g or more, preferably 10 mg KOH / g to 80 mg KOH / g, more preferably 10 mg KOH / g to 60 mg KOH / g, even more preferably 10 mg KOH / g to 50 mg KOH / g, even more preferably 10 mg KOH / g to 40 mg KOH / g, and even more preferably 10 mg KOH / g to 35 mg KOH / g. An acid value of 10 mg KOH / g or more of the polyurethane resin can improve the adhesion of the thermosetting resin composition after curing. Furthermore, an acid value of 80 mg KOH / g or less can improve the storage stability of the thermosetting resin composition. The acid value of the polyurethane resin can be measured in accordance with JIS K1157-5:2007.

[0054] The amount of polyurethane resin derived from polycarbonate diol contained in the thermosetting resin composition is 50 parts by mass or more and 120 parts by mass or less, preferably 60 parts by mass or more and 110 parts by mass or less, and more preferably 70 parts by mass or more and 100 parts by mass or less, when the total mass of epoxy resin is 100 parts by mass. This allows the thermosetting resin composition to be applied uniformly when applied to a film substrate. Furthermore, the thermosetting resin composition after application has excellent film-forming properties, and the thermosetting resin composition after curing is less prone to cracking. In addition, the adhesion of the thermosetting resin composition after curing can be improved.

[0055] The weight-average molecular weight of the polyurethane resin derived from polycarbonate diol is 60,000 or more, preferably 60,000 to 200,000, more preferably 60,000 to 150,000, even more preferably 60,000 to 134,000, even more preferably 70,000 to 120,000, and even more preferably 80,000 to 110,000. The inclusion of such a polyurethane resin in the thermosetting resin composition results in a thermosetting resin composition with a high storage modulus after curing. Furthermore, because the thermosetting resin composition contains the high molecular weight polyurethane resin described above, it exhibits excellent flexibility after curing. The weight-average molecular weight of the polyurethane resin derived from polycarbonate diol can be measured by gel permeation chromatography (GPC) using standard polystyrene with an average molecular weight of approximately 500 to 1,000,000.

[0056] The storage modulus at 25°C of the polyurethane resin derived from polycarbonate diol is 1.0 GPa or higher, preferably 1.0 GPa to 5.0 GPa, and more preferably 1.0 GPa to 3.0 GPa. The storage modulus at 25°C of the thermosetting resin composition after curing, which contains this polyurethane resin, is 1.0 GPa to 5.0 GPa.

[0057] In a flexible printed circuit board where the wiring is protected by a coverlay film using the aforementioned thermosetting resin composition containing polyurethane resin as the resin composition for the adhesive layer, the surface of the wiring is completely covered with the adhesive layer, and the surface of the wiring and the adhesive layer are firmly bonded. Therefore, such a flexible printed circuit board is less prone to wiring breakage even when repeatedly bent. In other words, such a flexible printed circuit board has excellent bending resistance.

[0058] (Other Components) In addition to the components described above, the thermosetting resin composition of the embodiment may also contain, for example, inorganic particles. By adding inorganic particles to the thermosetting resin composition of the embodiment, the storage modulus of the thermosetting resin composition after curing can be increased. Furthermore, flame retardancy and heat resistance can be exhibited in the thermosetting resin composition after curing. Examples of inorganic particles include aluminum hydroxide, aluminum hydroxide oxide, magnesium hydroxide, and silica. Among these, magnesium hydroxide is preferred, aluminum hydroxide is more preferred, and aluminum hydroxide oxide is even more preferred. This increases the storage modulus of the thermosetting resin composition after curing and improves flame retardancy and heat resistance. Furthermore, in a flexible printed circuit board in which wiring is protected by a coverlay film using a thermosetting resin composition containing inorganic particles as the resin composition of the adhesive layer, the resin composition of the adhesive layer can be filled without gaps between the wiring. That is, the resin filling between wiring can be improved. Note that the thermosetting resin composition may contain two or more types of inorganic particles.

[0059] From the viewpoint of improving storage modulus, flame retardancy, heat resistance, and resin filling between wiring, the inorganic particle content in the thermosetting resin composition is preferably 50 parts by mass or more and 80 parts by mass or less, and more preferably 55 parts by mass or more and 75 parts by mass or less, when the total mass of epoxy resin contained in the thermosetting resin composition is 100 parts by mass.

[0060] Additives may be added to the thermosetting resin composition as long as they do not impair the performance of the thermosetting resin composition described above. Additives include imidazole accelerators such as 2-methylimidazole, N-benzyl-2-methylimidazole, and 2-undecylimidazole; Lewis acid complexes such as boron trifluoride monoethylamine; curing accelerators such as polyamines and melamine resins; dispersants; softeners; antioxidants; pigments; dyes; and / or silane coupling agents.

[0061] From the viewpoint of improving the bending resistance of the flexible printed circuit board, the lower limit of the storage modulus at 25°C of the cured thermosetting resin composition is 1.0 GPa or higher, preferably 1.5 GPa or higher. Furthermore, from the viewpoint of improving the adhesion of the cured thermosetting resin composition, the upper limit of the storage modulus at 25°C of the cured thermosetting resin composition is 5.0 GPa or lower, preferably 4 GPa or lower.

[0062] Furthermore, the storage modulus at 60°C and 80°C of the cured thermosetting resin composition of this embodiment is preferably 1.0 GPa or more and 5.0 GPa or less, the same as the storage modulus at 25°C. As a result, the flexible printed circuit board of this embodiment also exhibits excellent bending resistance at high temperatures, for example, 80°C. In addition, the cured thermosetting resin composition of this embodiment also exhibits excellent adhesion at high temperatures, for example, 80°C. The storage modulus of the polyurethane resin derived from polycarbonate diol and the storage modulus of the thermosetting resin composition can be measured by a dynamic viscoelasticity measurement method.

[0063] The thermosetting resin composition of the embodiment is obtained by placing a predetermined amount of the above-mentioned materials into a container and mixing them. Furthermore, from the viewpoint of uniformly dissolving the components contained in the resin composition and adjusting the viscosity of the resin composition, an organic solvent may be added to the resin composition. Examples of organic solvents include alcohols such as methanol and ethanol; 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, methyl acetoacetate, 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; and cyclic ethers such as tetrahydrofuran and dioxane.

[0064] [Resin Sheet] Next, the structure of the resin sheet of the embodiment will be described. The resin sheet 10 of the embodiment shown in Figure 1 is composed of the thermosetting resin composition of the embodiment and has a sheet shape. Both sides of the resin sheet 10 are covered with release films 12 and 14. The resin sheet 10 is used after peeling off the release films 12 and 14. The resin sheet 10 is in a state in which the curing reaction is not yet complete, that is, in the B stage state.

[0065] The thickness of the resin sheet 10 in this embodiment is preferably, for example, 3 μm to 50 μm, more preferably 5 μm to 30 μm, and even more preferably 10 μm to 30 μm. Such a resin sheet 10 can, for example, bond one substrate such as a flexible printed circuit board to another substrate such as a flexible printed circuit board. After placing the resin sheet 10 on the wiring formed on the flexible printed circuit board, it is heated and pressurized. As a result, the wiring is completely covered with the resin sheet 10, protecting the wiring.

[0066] The resin sheet 10 is obtained, for example, by the following procedure. A predetermined amount each of epoxy resin, curing agent, and polyurethane resin derived from polycarbonate diol are added to a container and mixed. An organic solvent is added while observing the viscosity and dissolution state of the composition and mixed further to obtain the thermosetting resin composition of the embodiment. The obtained thermosetting resin composition is applied to a release film 14 using, for example, a coating device to form a resin layer composed of the thermosetting resin composition. Next, the formed resin layer is heated, for example, at a temperature of 80°C to 170°C for 30 seconds to 10 minutes. After cooling, the release film 14 is peeled off the resin layer to obtain the resin sheet 10.

[0067] The coating equipment used to form the resin layer is, for example, a die coater or a comma coater. The material of the release films 12 and 14 used to manufacture the resin sheet 10 is, for example, polyethylene, polypropylene, polyimide, polyamideimide, polyethylene naphthalate, or polyethylene terephthalate. The thickness of the release films 12 and 14 is preferably, for example, 12 μm to 100 μm, more preferably 25 μm to 75 μm, and even more preferably 25 μm to 50 μm, from the viewpoint of making it easy to peel the release films 12 and 14 from the resin sheet 10. Furthermore, from the viewpoint of making it easy to peel the release films 12 and 14 from the resin sheet 10, the surface of the release films 12 and 14 may be treated with a release agent. Examples of release agents include silicone-based agents, fluorine-based agents, alkyd-based agents, olefin-based agents, and melamine-based agents.

[0068] Alternatively, after forming the resin layer on the release film 14, another release film 12 may be attached to the side of the resin layer opposite to the side where the release film 14 is provided, while heating it. This allows both sides of the resin layer to be protected.

[0069] [Double-Sided Adhesive Sheet] Next, the configuration of the double-sided adhesive sheet of the embodiment will be described. The double-sided adhesive sheet 20 of the embodiment shown in Figure 2 consists of a film 21 as a core material and resin layers 22 and 23 formed on both sides of the film 21. The resin layers 22 and 23 are made of the thermosetting resin composition of the embodiment. The resin layers 22 and 23 of the double-sided adhesive sheet 20 are in a state in which the curing reaction is not yet complete, that is, in the B stage state.

[0070] The film 21 has heat resistance and hydrolysis resistance. The material of the film 21 is, for example, polyethylene, polypropylene, polyethersulfone, polyimide, polyamideimide, polyethylene naphthalate, polyetheretherketone, or polyphenylene sulfide. From the viewpoint of improving the heat resistance of the double-sided adhesive sheet 20, the material of the film 21 is preferably polyethersulfone, polyimide, polyamideimide, polyethylene naphthalate, polyetheretherketone, or polyphenylene sulfide.

[0071] The thickness of the film 21 is preferably, for example, 12 μm or more and 100 μm or less, more preferably 20 μm or more and 100 μm or less, and even more preferably 30 μm or more and 80 μm or less. Having the above-mentioned thickness of the film 21 provides the double-sided adhesive sheet 20 of the embodiment with excellent handling properties.

[0072] The thickness of the resin layers 22 and 23 is preferably, for example, 5 μm to 50 μm, more preferably 10 μm to 40 μm, and even more preferably 10 μm to 20 μm.

[0073] Such a double-sided adhesive sheet 20 can reliably bond substrates with uneven surfaces. Furthermore, similar to the resin sheet 10, the double-sided adhesive sheet 20 is placed on the wiring formed on the flexible printed circuit board, and then heated and pressurized. This ensures that the wiring is completely covered by the double-sided adhesive sheet 20, protecting it.

[0074] The double-sided adhesive sheet 20 can be obtained, for example, by the following procedure. Two resin sheets 10 with a release film attached to one side are prepared. Next, the resin sheets 10 are laminated on both sides of the film 21 so that the resin side is in contact with the film 21 to obtain a laminate. This laminate is heated and pressurized at a temperature of 100°C to 160°C, a pressure of 0.5 MPa to 3.0 MPa, and a time of 10 seconds to 30 seconds. After cooling, the release film is peeled off from the resin layers 22 and 23 to obtain the double-sided adhesive sheet 20.

[0075] Furthermore, the double-sided adhesive sheet 20 may also be provided with a release film to protect the surfaces of the resin layers 22 and 23.

[0076] [Coverlay Film] Next, the configuration of the coverlay film of the embodiment will be described. The coverlay film 30 of the embodiment shown in Figure 3 consists of a film 31 and an adhesive layer 32 formed on one side of the film 31. The adhesive layer 32 is made of the thermosetting resin composition of the embodiment. The adhesive layer 32 is in a state in which the curing reaction is not yet complete, that is, in the B stage state.

[0077] The film 31 has heat resistance. The material of the film 31 is, for example, polyethersulfone, polyimide, polyamideimide, polyethylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyphenylene sulfide, or liquid crystal polymer. The surface of the film 31 may be subjected to corona treatment or plasma treatment. This modifies the surface of the film 31 and improves the adhesion between the film 31 and the adhesive layer 32.

[0078] The thickness of the film 31 is preferably, for example, 2 μm to 75 μm, more preferably 5 μm to 50 μm, and even more preferably 5 μm to 30 μm. This improves the handling of the coverlay film 30.

[0079] The thickness of the adhesive layer 32 is preferably, for example, 5 μm to 50 μm, more preferably 10 μm to 40 μm, and even more preferably 10 μm to 20 μm.

[0080] After placing the coverlay film 30 described above on the wiring formed on the flexible printed circuit board, it is heated and pressurized. This ensures that the wiring is completely covered by the coverlay film 30, protecting it.

[0081] The coverlay film 30 is obtained, for example, by the following procedure. A predetermined amount each of epoxy resin, curing agent, and polyurethane resin derived from polycarbonate diol are added to a container and mixed. An organic solvent is added while observing the viscosity and dissolution state of the composition and mixed further to obtain a thermosetting resin composition. The obtained thermosetting resin composition is applied to the film 31, for example, using a coating device, to form an adhesive layer 32 made of the thermosetting resin composition. Next, the formed adhesive layer 32 is heated, for example, at a temperature of 100°C to 250°C for 5 seconds to 30 minutes. A release film may be attached to the side of the adhesive layer 32 opposite to the side on which the film 31 is provided, while heating it. This protects the surface of the adhesive layer 32.

[0082] [Flexible Printed Wiring Board] Next, the configuration of the flexible printed wiring board of the embodiment will be described. The flexible printed wiring board 40 of the embodiment shown in Figure 4 comprises a substrate 42 on which wiring 41 is formed on one side, and a coverlay film 30 in which an adhesive layer 32 is arranged in contact with the wiring 41 of the substrate 42.

[0083] The wiring 41 formed on the substrate 42 may be formed, for example, by chemical etching (patterning) the copper layer of a copper-plated laminate or copper-clad laminate, which has a copper layer formed on one side of the substrate 42. Alternatively, the wiring 41 formed on the substrate 42 may be formed by inkjet printing using conductive ink. The material of the wiring 41 may be other metals such as silver or zinc instead of copper.

[0084] The thickness of the wiring 41 is 2 μm to 30 μm from the viewpoint of providing flexibility to the substrate 42. The thickness of the substrate 42 is 5 μm to 200 μm from the viewpoint of providing flexibility to the substrate 42.

[0085] The flexible printed circuit board 40 is manufactured by the following procedure. A substrate 42 with wiring 41 formed on one side and a coverlay film 30 according to the embodiment are prepared. Next, the coverlay film 30 is placed on the surface of the substrate 42 with the wiring 41 formed on it so that the adhesive layer 32 is in contact with it, and pressure is applied while heating. This gives rise to the flexible printed circuit board 40. The heating and pressurizing conditions are, for example, 120°C to 250°C, 5 seconds to 120 minutes, and 1 MPa to 10 MPa. The flexible printed circuit board 40 may also be manufactured by placing, for example, a resin sheet 10 or a double-sided adhesive sheet 20 between one flexible printed circuit board 40 and another flexible printed circuit board 40, and then applying pressure while heating. This allows for the layering of multiple circuit boards.

[0086] The present invention will be further described in detail by the following examples. The present invention is not limited in any way by the following examples.

[0087] The following materials were used as components in the thermosetting resin compositions of the examples and comparative examples. (Epoxy resin that is solid at 25°C) (S1) NC-3000H Manufactured by Nippon Kayaku Co., Ltd., biphenyl aralkyl type epoxy resin, epoxy equivalent 290 g / eq. (Epoxy resin that is not solid at 25°C) (L1) MX-257 Manufactured by Kaneka Corporation, bisphenol A type epoxy resin with a core-shell rubber content of 37%, epoxy equivalent 293 g / eq. MX-257 is a resin containing 63 parts by mass of bisphenol A type epoxy resin and 37 parts by mass of PBd as core-shell rubber in 100 parts by mass. The volume-average particle size of PBd is 0.1 μm or more and 0.2 μm or less. (L2) Epiclon 850 Manufactured by DIC Corporation, bisphenol A type epoxy resin, epoxy equivalent 190 g / eq. (L3) jER152 Manufactured by Mitsubishi Chemical Corporation, phenol novolac type epoxy resin, epoxy equivalent 177 g / eq. (Hardening agent) (H1) 3,3'-DAS Manufactured by Nippon Junryo Yakuhin Co., Ltd., diaminodiphenylsulfone, amine value 62 g / eq. (Inorganic particles) (P1) Alcube AlO(OH) Manufactured by Kamishima Chemical Industry Co., Ltd., aluminum hydroxide oxide.

[0088] (Polyurethane resin derived from polycarbonate diol) (U1) Polyurethane resin derived from polycarbonate diol (A) AR-902 Manufactured by Dainichi Seika Kogyo Co., Ltd., Mw 116208, acid value 24.0 mg KOH / g, storage modulus of 1.3 GPa (25°C) measured based on dynamic viscoelasticity measurement method. Mw represents the weight-average molecular weight. The same applies below. (U2) Polyurethane resin derived from polycarbonate diol (B) AR-902 Manufactured by Dainichi Seika Kogyo Co., Ltd., Mw 100454, acid value 24.0 mg KOH / g, storage modulus of 1.3 GPa (25°C) measured based on dynamic viscoelasticity measurement method. (U3) Polyurethane resin derived from polycarbonate diol (C) AR-902 Manufactured by Dainichi Seika Kogyo Co., Ltd., Mw 95720, acid value 26.4 mg KOH / g. Storage modulus of elasticity measured based on dynamic viscoelasticity: 1.5 GPa (25°C). (U4) Polycarbonate diol-derived polyurethane resin (D) AR-902 Manufactured by Dainichi Seika Kogyo Co., Ltd., Mw88791, acid value 25.0 mg KOH / g, storage modulus of elasticity measured based on dynamic viscoelasticity: 1.6 GPa (25°C). (U5) Polycarbonate diol-derived polyurethane resin (E) AR-902 Manufactured by Dainichi Seika Kogyo Co., Ltd., Mw62000, acid value 25.0 mg KOH / g, storage modulus of elasticity measured based on dynamic viscoelasticity: 1.6 GPa (25°C). (U6) Polycarbonate diol-derived polyurethane resin (F) AR-902 Manufactured by Dainichi Seika Kogyo Co., Ltd., Mw56822, acid value 25.0 mg KOH / g, storage modulus of elasticity measured based on dynamic viscoelasticity: 1.7 GPa (25°C). (U7) Polycarbonate diol-derived polyurethane resin (G) AR-902, manufactured by Dainichi Seika Kogyo Co., Ltd., Mw 134000, acid value 25.0 mgKOH / g, storage modulus of 1.4 GPa (25°C) measured by dynamic viscoelasticity testing. (U8) Polycarbonate diol-derived polyurethane resin (H) AR-902, manufactured by Dainichi Seika Kogyo Co., Ltd., Mw 101000, acid value 10.0 mgKOH / g, storage modulus of 1.0 GPa (25°C) measured by dynamic viscoelasticity testing.(U9) Polycarbonate diol-derived polyurethane resin (I) AR-902, manufactured by Dainichi Seika Kogyo Co., Ltd., Mw 72000, acid value 35.0 mgKOH / g, storage modulus of 2.4 GPa (25°C) measured by dynamic viscoelasticity measurement method.

[0089] The storage modulus of the polyurethane resin derived from polycarbonate diol, as described above, was measured using a sample for dynamic viscoelasticity measurement. The sample for dynamic viscoelasticity measurement was prepared in the following procedure. First, polyurethane resin was applied to the release surface of a 38 μm thick release PET (polyethylene terephthalate) film (PET3811, manufactured by Lintec Corporation) so that the thickness after pressing was 100 μm, and then covered with another release PET film. Subsequently, the laminate, consisting of release PET film, polyurethane resin, and release PET film, was heated under conditions of 180°C, 3 MPa, and 60 minutes while applying vertical pressure. After cooling, a polyurethane resin sheet with a thickness of 100 μm was obtained. The obtained polyurethane resin sheet was cut into rectangles with a length of 30 mm and a width of 4 mm to obtain a sample for dynamic viscoelasticity measurement. The apparatus used for measuring the storage modulus was an RSA-G2 (manufactured by T.A. Instruments Corporation). The measurement conditions were: temperature range -50°C to 100°C, heating rate 10°C / min, frequency 1 Hz, chuck distance 20 mm, and tensile mode.

[0090] (Example 1) (Preparation of thermosetting resin composition) In a container, 75 parts by mass of (S1) NC-3000H, 40 parts by mass of (L1) MX-257 containing 25 parts by mass of a non-solid epoxy resin at 25°C and 15 parts by mass of rubber-elastic particles, 16.2 parts by mass of (H1) 3,3'-DAS, 69 parts by mass of (P1) Alcube AlO(OH), 86 parts by mass of (U3) polyurethane resin (C) derived from polycarbonate diol, and 120 parts by mass of methyl ethyl ketone (hereinafter, MEK) as an organic solvent to adjust viscosity were added and stirred at room temperature for 90 minutes to obtain a thermosetting resin composition.

[0091] (Measurement of Storage Modulus) To measure the storage modulus of the obtained thermosetting resin composition, a sample for measurement was prepared. First, the thermosetting resin composition was applied to the release surface of a 50 μm thick release PET (polyethylene terephthalate) film (PET5011, manufactured by Lintec Corporation) so that the thickness after heating would be 100 μm, and then covered with another release PET film. Subsequently, the laminate, consisting of the release PET film, thermosetting resin composition, and release PET film in that order, was heated under conditions of 180°C, 3 MPa, and 60 minutes while applying vertical pressure. After cooling, a resin sheet with a thickness of 100 μm was obtained. The obtained cured resin sheet was cut into rectangles with a length of 50 mm and a width of 4 mm to obtain a sample for measuring the storage modulus.

[0092] The storage modulus was measured by dynamic viscoelasticity measurement using an RSA-G2 (manufactured by T.A. Instruments). The measurement conditions were a temperature range of -50°C to 150°C, a heating rate of 10°C / min, a frequency of 1 Hz, a chuck distance of 20 mm, and tensile mode. The storage modulus of the thermosetting resin composition (resin sheet after curing) of Example 1 was 2.9 GPa at 25°C, 2.2 GPa at 60°C, and 1.1 GPa at 80°C.

[0093] (Preparation of Coverlay Film) A film 31 (Kapton 30EN, manufactured by Toray DuPont), made of polyimide with a thickness of 7.5 μm, was coated with the prepared thermosetting resin composition using a bar coater to a thickness of 15 μm after heating. The film was heated at 150°C for 5 minutes to form an adhesive layer 32. Subsequently, the film was heat-pressed at 90°C together with a release PET film placed on the surface of the adhesive layer 32 to obtain a coverlay film 30 with a release PET film. The coverlay film 30 was used after the release PET film was peeled off.

[0094] [Evaluation of Bending Resistance] (Preparation of Bending Test Sample) To evaluate the bending resistance of the flexible printed circuit board 40 using the coverlay film 30 obtained above, a bending test sample 90 shown in Figure 9 was prepared as follows. First, a two-layer single-sided copper-clad laminate (manufactured by Arisawa Seisakusho Co., Ltd., PNS H0509RAC) comprising a polyimide layer and a copper layer formed on one side of the polyimide layer was prepared, and the copper layer was etched to obtain a rectangular substrate 42 on which the wiring 41 shown in Figure 5 was formed. The width (L) of the wiring 41 was 75 μm, and the spacing (S) between the wirings was 75 μm. Ends 43 for connecting the terminals of a resistance measuring device for measuring resistance values ​​are formed at both ends of the wiring 41. The thickness of the polyimide layer of the two-layer single-sided copper-clad laminate (manufactured by Arisawa Seisakusho Co., Ltd., PNS H0509RAC) is 12 μm, and the thickness of the copper layer is 9 μm.

[0095] Next, the substrate 42 and the coverlay film 30 were laminated so that the surface of the substrate 42 on which the wiring 41 is formed was in contact with the surface of the coverlay film 30 prepared as described above, and heated under vertical pressure at 185°C, 3.0 MPa, and 60 seconds. After that, it was heated in an oven at 160°C for 1 hour and then cooled to obtain the flexible printed circuit board 40 shown in Figure 6. The coverlay film 30 was bonded to the substrate 42 so that the ends 43 of the wiring 41 were exposed. Two more circuit boards identical to the obtained flexible printed circuit board 40 were also prepared.

[0096] Next, as shown in Figure 7, 25 μm thick adhesive sheets (Arisawa Seisakusho Co., Ltd., AU-25KA) were placed at two locations on the surface of the substrate 42 of the flexible printed circuit board 40 where the coverlay film 30 was not laminated, thereby creating a flexible printed circuit board 70 having adhesive layers 71 and 72. The bonding conditions for the substrate 42 and the adhesive sheets were 100°C, 0.4 MPa, and 1 m / min using a roll laminator. In addition, another circuit board with the same configuration as the flexible printed circuit board 70 was created.

[0097] Next, two flexible printed circuit boards 70 and flexible printed circuit board 40 were laminated as shown in Figure 8, and primary bonding was performed using a roll laminator under the conditions of 100°C, 0.4 MPa, and 1 m / min. Here, the flexible printed circuit boards 40 and 70 were laminated so that the coverlay film 30 of the flexible printed circuit board 40 and the adhesive layers 71 and 72 of the flexible printed circuit board 70 were in contact. After that, the boards were heated under vertical pressure at 180°C, 3.0 MPa, and for 60 minutes, and after cooling, a multilayer flexible printed circuit board 80 was obtained. The multilayer flexible printed circuit board 80 has gaps 81 between the flexible printed circuit boards 70 and between the flexible printed circuit boards 70 and 40.

[0098] Next, as shown in Figure 9, electromagnetic shielding film 91 (SF-PC8900-C, manufactured by Tatsuta Electric Wire Co., Ltd.) was laminated on both sides of the multilayer flexible printed circuit board 80, and primary bonding was performed using a roll laminator under the conditions of 100°C, 0.4 MPa, and 1 m / min. After that, it was heated under vertical pressure at 180°C, 3.0 MPa, and for 60 minutes, and after cooling, a bending test sample 90 was obtained. The bending test sample 90 was cut to a width of 10 mm and a length of 150 mm in order to be placed in the bending test apparatus described later. In addition, the terminals of the resistance value measuring device 110 shown in Figure 10A were soldered to the ends 43 of the wiring 41 of the flexible printed circuit board 40 that are positioned on the outermost side when bent. Here, the fixing part 95 shown in Figure 9 is the part sandwiched between the metal cover plate 101 for holding the sample and the sample fixing plate 103 for fixing the sample, as shown in Figure 10A. The non-fixed portion 97 shown in Figure 9 is a part that is not fixed between the cover plate 101 and the sample fixing plate 103.

[0099] (Bending Test) As shown in Figure 10A, the fixed portion 95 of the bending test sample 90 is sandwiched between the cover plate 101 and the sample fixing plate 103. The end portion 98 of the bending test sample 90 that is not fixed by the cover plate 101 and the sample fixing plate 103 is connected to the weight 109 via the connecting jig 106. The unfixed portion 97 of the bending test sample 90 is supported by the sample support stand 105, but is not fixed to the sample support stand 105.

[0100] As the sample fixing plate 103 moves in the direction of arrow 120 shown in Figure 10A, the fixing portion 95 sandwiched between the cover plate 101 and the sample fixing plate 103 is bent so that it overlaps the non-fixing portion 97. At this time, the non-fixing portion 97 moves on the sample support stand 105 in the direction of arrow 122 (left and right direction) in response to the bending of the bending test sample 90. The weight 109 continues to apply tension to the bending test sample 90 via the pulley 107 to prevent the bending test sample 90 from becoming loose during bending.

[0101] After the bending test sample 90 is bent, the sample fixing plate 103 moves in the direction of the arrow 130 shown in Figure 10B, and the bending test sample 90 moves from the folded state shown in Figure 10B to the 180° open state shown in Figure 10A. This movement was repeated to evaluate the bending resistance of the bending test sample 90.

[0102] The bending test was conducted under the following conditions: (1) It was conducted at room temperature (25°C). (2) The radius of curvature of the bending center 99 when the bending test sample 90 shown in Figure 10B was folded was set to 0.6 mm. The radius of curvature of the bending center 99 corresponds to the radius of curvature (101r) of the end of the cover plate 101. (3) The folded state (closed state) was set to 0°, and the open state to 180°, and this was repeated. The opening and closing speed was set to 30 rpm. (4) The weight 109 was set to 100 g. (5) While the bending test of the bending test sample 90 was being conducted, the resistance value of the wiring 41 was measured using a resistance value measuring device 110. The resistance value before starting the bending test was set to the initial resistance value, and the number of repetitions until the resistance value increased by 10% from the initial resistance value after starting the bending test was measured and evaluated according to the following criteria: Excellent: More than 250,000 repeated bending cycles. Good: Repeated folding count between 200,000 and 250,000. Poor: Repeated folding count less than 200,000.

[0103] The evaluation results for Example 1 using the method described above were excellent. From these results, it was found that the flexible printed circuit board of Example 1 has excellent bending resistance. Furthermore, since the storage modulus of the thermosetting resin composition of Example 1 after curing is 2.9 GPa at 25°C, the stress generated inside the flexible printed circuit board during the bending test is relieved by the adhesive layer, improving bending resistance. In addition, since the storage modulus at 60°C is 2.2 GPa and the storage modulus at 80°C is 1.1 GPa, it is expected that the bending resistance of the flexible printed circuit board will improve even in a high-temperature atmosphere.

[0104] [Peel Strength] (Preparation of Measurement Samples) Using the coverlay film 30 prepared as described above, measurement samples were prepared to measure the peel strength. First, the release PET film was peeled off the coverlay film 30, and the adhesive layer side was bonded to the copper layer side of a two-layer single-sided copper-clad laminate (manufactured by Arisawa Seisakusho Co., Ltd., PNS H0509RAC). The two layers were heated under vertical pressure at 185°C, 3.0 MPa for 60 seconds. After that, the samples were heated in an oven at 160°C for 1 hour, cooled, and then cut to a width of 10 mm x length of 100 mm to obtain measurement samples. Before bonding the two-layer single-sided copper-clad laminate (manufactured by Arisawa Seisakusho Co., Ltd., PNS H0509RAC) to the coverlay film 30, a mixture of sulfuric acid and hydrogen peroxide was applied to the surface of the copper layer to perform a soft etching treatment.

[0105] (Measurement) The peel strength in the 90° direction (direction perpendicular to the surface of the sample for measurement) was measured using a Shimadzu Autograph AGS-500 under the following measurement conditions. The measurement conditions were copper layer stripping and a test speed of 50 mm / min. The evaluation criteria were as follows: Excellent: Peel strength of 5 N / cm or more. Good: Peel strength of 3.4 N / cm or more and less than 5 N / cm. Poor: Peel strength less than 3.4 N / cm.

[0106] The evaluation results for Example 1, using the method described above, showed a peel strength of 6.8 N / cm, which was excellent. From these results, it was found that the thermosetting resin composition of Example 1 has excellent adhesive properties.

[0107] [Solder Heat Resistance] (Preparation of Measurement Samples) The release PET film was peeled off the coverlay film 30, and the adhesive layer side was bonded to the copper layer side of a two-layer single-sided copper-clad laminate (manufactured by Arisawa Seisakusho Co., Ltd., PNS H0509RAC). The samples were heated at 185°C, 3.0 MPa for 60 seconds while applying pressure in the vertical direction. After that, they were heated in a 160°C oven for 1 hour, cooled, cut into 20 mm x 20 mm pieces, and dried in a dryer maintained at 135°C for 1 hour to obtain measurement samples. Before bonding the two-layer single-sided copper-clad laminate (manufactured by Arisawa Seisakusho Co., Ltd., PNS H0509RAC) to the coverlay film 30, the copper layer surface was subjected to soft etching by applying a mixture of sulfuric acid and hydrogen peroxide.

[0108] (Measurement) The copper layer of the measurement sample was floated in a solder bath set to 288°C so that it was in contact with the solder bath. This state was maintained for 10 seconds or more, and the presence or absence of blistering and peeling was visually checked. Excellent: No blistering or peeling. Poor: Some blistering and / or peeling.

[0109] The evaluation results for Example 1 using the method described above were excellent. From these results, it was found that the thermosetting resin composition of Example 1 has excellent heat resistance.

[0110] As described above, the thermosetting resin composition of Example 1 has excellent adhesion and heat resistance, making it suitable for use as a resin composition constituting the adhesive layer of a coverlay film, the resin layer of a double-sided adhesive sheet, and the resin sheet itself. Furthermore, it was found that a flexible printed circuit board with wiring protected by a coverlay film using this thermosetting resin composition as the resin composition for the adhesive layer exhibits excellent bending resistance. In addition, since the storage modulus of the thermosetting resin composition of Example 1 at 80°C after curing is 1.0 GPa or higher, this flexible printed circuit board is expected to have excellent bending resistance even in a high-temperature atmosphere.

[0111] Tables 1 and 2 show the types and content of each component in the thermosetting resin compositions of each example and comparative example, as well as the storage modulus at each temperature and the results of the bending test. The thermosetting resin compositions of Examples 2 to 18 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the types and content of each component were changed, and evaluation samples for each test were made. The evaluation tests were also conducted using the same procedure as the evaluation test in Example 1.

[0112]

[0113]

[0114] As shown in Table 1, in the bending tests of flexible printed circuit boards in which wiring was protected by coverlay films using the thermosetting resin compositions of Examples 2 to 11 as the resin composition of the adhesive layer, Examples 2 to 9 and 11 were excellent, and Example 10 was good. From these results, it was found that Examples 2 to 11, like Example 1, have excellent bending resistance. The bending test results for Comparative Examples 1 to 3 were poor.

[0115] As shown in Table 2, the bending test results for the flexible printed circuit board made from the thermosetting resin composition of Example 12, which used, for example, a polyurethane resin derived from (U8) polycarbonate diol (acid value: 10.0 mg KOH / g), and the flexible printed circuit board made from the thermosetting resin composition of Example 13, which used a polyurethane resin derived from (U9) polycarbonate diol (acid value: 35.0 mg KOH / g), were excellent. Furthermore, the bending test results for the flexible printed circuit board made from the thermosetting resin composition of Example 15, which had a curing agent equivalent of 0.30 eq, and the flexible printed circuit board made from the thermosetting resin composition of Example 16, which had a curing agent equivalent of 0.80 eq, were also excellent. In addition, Examples 14, 17, and 18 were found to have excellent bending resistance, similar to Example 1.

[0116] Solder heat resistance tests were conducted on Examples 2-18 and Comparative Examples 1-3, and all results were excellent. These results indicate that the thermosetting resin compositions of Examples 2-18 and Comparative Examples 1-3 possess excellent heat resistance.

[0117] The peel strength measurements for Examples 2-18 and Comparative Examples 1-3 are as follows: Example 2 had a peel strength of 4.3 N / cm, which was Good. Example 3 had a peel strength of 4.0 N / cm, which was Good. Example 4 had a peel strength of 2.4 N / cm, which was Poor. Example 5 had a peel strength of 6.4 N / cm, which was Excellent. Example 6 had a peel strength of 7.5 N / cm, which was Excellent. Example 7 had a peel strength of 6.8 N / cm, which was Excellent. Example 8 had a peel strength of 6.6 N / cm, which was Excellent. Example 9 had a peel strength of 6.3 N / cm, which was Excellent. The peel strength of Example 10 was 5.8 N / cm, which was Excellent. The peel strength of Example 11 was 5.3 N / cm, which was Excellent. The peel strength of Example 12 was 3.9 N / cm, which was Good. The peel strength of Example 13 was 5.2 N / cm, which was Excellent. The peel strength of Example 14 was 4.3 N / cm, which was Good. The peel strength of Example 15 was 6.1 N / cm, which was Excellent. The peel strength of Example 16 was 6.6 N / cm, which was Excellent. The peel strength of Example 17 was 4.6 N / cm, which was Good. The peel strength of Example 18 was 3.8 N / cm, which was Good. Comparative Example 1 had a peel strength of 5.6 N / cm, which was excellent. Comparative Example 2 had a peel strength of 6.0 N / cm, which was excellent. Comparative Example 3 had a peel strength of 7.9 N / cm, which was excellent.

[0118] Examples 2 to 18, like Example 1, had a storage modulus of 1.0 GPa or higher at 60°C. Furthermore, the storage modulus of 1.0 GPa or higher at 80°C was the same for all examples from Examples 2 to 18 except for Examples 3, 6, 11, and 15. From this, it can be expected that a flexible printed circuit board in which wiring is protected by a coverlay film using the thermosetting resin composition of Examples 2 to 18 (excluding Examples 3, 6, 11, and 15) as the resin composition of the adhesive layer will have excellent bending resistance even in a high-temperature atmosphere.

[0119] From the above results, it was found that the thermosetting resin composition of the example has excellent adhesion and heat resistance, and is suitable for use as a resin composition constituting the adhesive layer of a coverlay film, the resin layer of a double-sided adhesive sheet, and the resin sheet. Furthermore, it was found that a flexible printed circuit board in which wiring is protected by a coverlay film using this thermosetting resin composition as the resin composition of the adhesive layer has excellent bending resistance.

[0120] This invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Furthermore, the embodiments described above are for illustrative purposes only and do not limit the scope of the invention. In other words, the scope of the invention is indicated by the claims, not by the embodiments. Various modifications made within the scope of the claims and the equivalent meaning of the invention are considered to be within the scope of this invention.

[0121] This application is based on Japanese Patent Application No. 2024-195270, filed on 7 November 2024. The entire specification, claims, and drawings of Japanese Patent Application No. 2024-195270 are incorporated herein by reference.

[0122] (Note) (Note 1) A thermosetting resin composition comprising an epoxy resin, a curing agent, and a polyurethane resin derived from polycarbonate diol, wherein the storage modulus of the polyurethane resin at 25°C is 1.0 GPa or more, the weight-average molecular weight of the polyurethane resin is 60,000 or more, when the total mass of the epoxy resin is 100 parts by mass, the content of the polyurethane resin is 50 parts by mass or more and 120 parts by mass or less, and the storage modulus of the cured material at 25°C is 1.0 GPa or more and 5.0 GPa or less.

[0123] (Note 2) The thermosetting resin composition according to Note 1, wherein the epoxy resin comprises a non-solid epoxy resin at 25°C, and when the total mass of the epoxy resin is 100 parts by mass, the content of the non-solid epoxy resin is 5 parts by mass or more and 100 parts by mass or less.

[0124] (Note 3) A thermosetting resin composition according to Note 1 or Note 2, comprising particles having rubber elasticity.

[0125] (Note 4) The thermosetting resin composition according to Note 3, wherein the rubber-elastic particles are core-shell polymer particles composed of a core portion and a shell portion covering the surface of the core portion.

[0126] (Note 5) The thermosetting resin composition according to Note 3 or Note 4, wherein the content of the rubber-elastic particles is 30 parts by mass or less when the total mass of the epoxy resin is 100 parts by mass.

[0127] (Note 6) The thermosetting resin composition according to any one of Notes 1 to 5, wherein the acid value of the polyurethane resin is 10 mg KOH / g or more.

[0128] (Note 7) The thermosetting resin composition according to any one of Notes 1 to 6, wherein the amount of the curing agent is 0.3 equivalents or more and 0.8 equivalents or less per equivalent of epoxy groups of the epoxy resin.

[0129] (Note 8) A thermosetting resin composition according to any one of Notes 1 to 7, wherein the storage modulus at 60°C after curing is 1.0 GPa or more and 5.0 GPa or less.

[0130] (Note 9) A thermosetting resin composition according to any one of Notes 1 to 8, wherein the storage modulus at 80°C after curing is 1.0 GPa or more and 5.0 GPa or less.

[0131] (Note 10) A thermosetting resin composition according to any one of Notes 1 to 9, wherein the composition contains inorganic particles, and when the total mass of the epoxy resin is 100 parts by mass, the content of the inorganic particles is 50 parts by mass or more and 80 parts by mass or less.

[0132] (Note 11) A resin sheet comprising the thermosetting resin composition described in any of Notes 1 to 10.

[0133] (Note 12) A double-sided adhesive sheet comprising a film and resin layers formed on both sides of the film, wherein the resin layers are composed of a thermosetting resin composition as described in any of Notes 1 to 10.

[0134] (Note 13) A coverlay film comprising a film and an adhesive layer formed on one side of the film, wherein the adhesive layer is composed of a thermosetting resin composition as described in any of Notes 1 to 10.

[0135] (Note 14) A flexible printed circuit board comprising a coverlay film as described in Note 13 and a substrate on which wiring is formed, wherein the coverlay film is arranged on the substrate such that the adhesive layer is in contact with the wiring.

[0136] 10 Resin sheet, 20 Double-sided adhesive sheet, 30 Coverlay film, 40, 70 Flexible printed circuit board, 12, 14 Release film, 21, 31 Film, 22, 23 Resin layer, 32 Adhesive layer, 41 Wiring, 42 Substrate, 43 Edge, 71, 72 Adhesive layer, 80 Multilayer flexible printed circuit board, 81 Gap, 90 Bending test sample, 91, 92 Electromagnetic shielding film, 95 Fixed part, 97 Unfixed part, 98 Edge, 99 Bending center, 101r Radius of curvature, 101 Cover plate, 103 Sample fixing plate, 105 Sample support stand, 106 Connecting jig, 107 Pulley, 109 Weight, 110 Resistance value measuring device.

Claims

1. A thermosetting resin composition comprising an epoxy resin, a curing agent, and a polyurethane resin derived from polycarbonate diol, wherein the storage modulus of the polyurethane resin at 25°C is 1.0 GPa or more, the weight-average molecular weight of the polyurethane resin is 60,000 or more, the content of the polyurethane resin is 50 parts by mass or more and 120 parts by mass or less when the total mass of the epoxy resin is 100 parts by mass, and the storage modulus of the cured material at 25°C is 1.0 GPa or more and 5.0 GPa or less.

2. The thermosetting resin composition according to claim 1, wherein the epoxy resin comprises a non-solid epoxy resin at 25°C, and when the total mass of the epoxy resin is 100 parts by mass, the content of the non-solid epoxy resin is 5 parts by mass or more and 100 parts by mass or less.

3. The thermosetting resin composition according to claim 1 or 2, comprising particles having rubber elasticity.

4. The thermosetting resin composition according to claim 3, wherein the rubber-elastic particles are core-shell polymer particles composed of a core portion and a shell portion covering the surface of the core portion.

5. The thermosetting resin composition according to claim 3 or 4, wherein the content of the rubber-elastic particles is 30 parts by mass or less when the total mass of the epoxy resin is 100 parts by mass.

6. The thermosetting resin composition according to any one of claims 1 to 5, wherein the acid value of the polyurethane resin is 10 mg KOH / g or more.

7. The thermosetting resin composition according to any one of claims 1 to 6, wherein the amount of the curing agent is 0.3 equivalents or more and 0.8 equivalents or less per equivalent of epoxy groups of the epoxy resin.

8. The thermosetting resin composition according to any one of claims 1 to 7, wherein the storage modulus at 60°C after curing is 1.0 GPa or more and 5.0 GPa or less.

9. The thermosetting resin composition according to any one of claims 1 to 8, wherein the storage modulus at 80°C after curing is 1.0 GPa or more and 5.0 GPa or less.

10. A thermosetting resin composition according to any one of claims 1 to 9, wherein the composition contains inorganic particles, and when the total mass of the epoxy resin is 100 parts by mass, the content of the inorganic particles is 50 parts by mass or more and 80 parts by mass or less.

11. A resin sheet comprising a thermosetting resin composition according to any one of claims 1 to 10.

12. A double-sided adhesive sheet comprising a film and a resin layer formed on both sides of the film, wherein the resin layer is composed of a thermosetting resin composition according to any one of claims 1 to 10.

13. A coverlay film comprising a film and an adhesive layer formed on one side of the film, wherein the adhesive layer is made of a thermosetting resin composition according to any one of claims 1 to 10.

14. A flexible printed circuit board comprising a coverlay film according to claim 13 and a substrate on which wiring is formed, wherein the coverlay film is arranged on the substrate such that the adhesive layer is in contact with the wiring.

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