Photosensitive thermosetting resin composition, photosensitive coverlay, and flexible printed wiring board

Abstract

This photosensitive thermosetting resin composition contains a prepolymer, a photosensitive monomer, a thermosetting resin, and a polymerization initiator. The prepolymer contains a carboxylic acid-modified bisphenol epoxy (meth)acrylate. The photosensitive monomer contains a monofunctional monomer having a single (meth)acryloyloxy group per molecule and having a number average molecular weight (Mn) of 1,300-36,000.

Description

Photosensitive thermosetting resin composition, photosensitive coverlay, and flexible printed wiring board

[0001] The present invention relates to a photosensitive thermosetting resin composition, a photosensitive coverlay, and a flexible printed wiring board.

[0002] BACKGROUND ART Various techniques have been proposed in the past relating to photosensitive coverlays and photosensitive thermosetting resin compositions for producing the photosensitive coverlays.

[0003] For example, a photosensitive thermosetting resin composition for resist ink has been proposed, which produces a cured product with excellent folding resistance (flexibility) and the like (see, for example, Patent Document 1). Specifically, the proposed photosensitive thermosetting resin composition contains (A) a specific carboxy-modified epoxy (meth)acrylate resin, (B) a biphenyl-type epoxy resin, (C) a photopolymerization initiator, and (D) a diluent, and the acid value of the (A) carboxy-modified epoxy (meth)acrylate resin is within a specific range.

[0004] Furthermore, a photosensitive thermosetting resin composition for solder resist ink has been proposed (see, for example, Patent Document 2). Specifically, the proposed photopolymerizable thermosetting resin composition comprises (A) an active energy ray-curable resin, (B) a diluent, (C) a photopolymerization initiator, (D) a curing adhesion promoter, and (E) a compound having an epoxy group, wherein the active energy ray-curable resin (A) is selected from specific unsaturated resins.

[0005] Furthermore, a dry film resist has been proposed that aims to improve the peelability between a protective film and a photosensitive layer (see, for example, Patent Document 3). Patent Document 3 describes photosensitive prepolymers, photopolymerization initiators (including sensitizers), flame retardants, fillers, and the like that can be used in the dry film resist.

[0006] Furthermore, photosensitive compositions have been proposed that aim to improve performance related to the formation of photosensitive coatings, such as photosensitivity, developability, and shelf life (see, for example, Patent Document 4). Specifically, the proposed photosensitive composition contains a compound (A) having an ethylenically unsaturated group, an epoxy resin (B), a photopolymerization initiator (C), and an intercalation compound (D) in which a specific thermal polymerization catalyst is inserted into an inorganic layered compound.

[0007] Furthermore, a photosensitive thermosetting resin composition has been proposed that has a long shelf life, excellent storage stability at room temperature, solder heat resistance after curing, and is easy to handle while maintaining high adhesion (see, for example, Patent Document 5).

[0008] However, with photosensitive coverlays formed from conventional photosensitive thermosetting resin compositions, it has been difficult to improve bending properties while maintaining heat resistance and adhesion.

[0009] In view of the above problems, the present invention aims to provide a photosensitive thermosetting resin composition that can be used to prepare a photosensitive coverlay that has improved bending properties while maintaining heat resistance and adhesion, a photosensitive coverlay that uses the photosensitive thermosetting resin composition, and a flexible printed wiring board that uses the photosensitive coverlay.

[0010] As a result of intensive research conducted by the present inventors to solve the above problems, they discovered that it is possible to prepare a photosensitive coverlay that has improved foldability while maintaining heat resistance and adhesion by using a photosensitive thermosetting resin composition that contains a prepolymer containing a carboxylic acid-modified bisphenol-type epoxy (meth)acrylate, a photosensitive monomer containing a monofunctional monomer having one (meth)acryloyloxy group in each molecule and having a number average molecular weight (Mn) of 1,300 to 36,000, a thermosetting resin, and a polymerization initiator, and thus completed the present invention.

[0011] That is, the present invention is as follows: [1] A photosensitive thermosetting resin composition containing a prepolymer, a photosensitive monomer, a thermosetting resin, and a polymerization initiator, wherein the prepolymer contains a carboxylic acid-modified bisphenol-type epoxy (meth)acrylate, and the photosensitive monomer contains a monofunctional monomer having one (meth)acryloyloxy group per molecule and having a number average molecular weight (Mn) of 1,300 to 36,000. [2] The photosensitive thermosetting resin composition according to [1] above, wherein the monofunctional monomer contains a curable component obtained by a urethanization reaction between a polyoxyalkylene monool (1a) represented by the following formula (1a) and a compound (1b) represented by the following formula (1b): (In formula (1a), R １２ is an alkylene group having 2 to 4 carbon atoms, and R １３ is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms, and b is an integer of 20 to 600. In formula (1b), R １１is a hydrogen atom or a methyl group, and a is an integer of 1 to 4.) [3] The photosensitive thermosetting resin composition according to [1] or [2] above, wherein the photosensitive monomer further contains pentaerythritol ethoxy tetraacrylate. [4] The photosensitive thermosetting resin composition according to any one of [1] to [3] above, wherein the prepolymer further contains at least one of a carboxylic acid-modified cresol novolac epoxy (meth)acrylate and a carboxylic acid-modified urethane (meth)acrylate. [5] The photosensitive thermosetting resin composition according to [4] above, wherein the mass ratio of the carboxylic acid-modified bisphenol epoxy (meth)acrylate to the total of the carboxylic acid-modified cresol novolac epoxy (meth)acrylate and the carboxylic acid-modified urethane (meth)acrylate is 80:20 to 20:80. [6] The photosensitive thermosetting resin composition according to any one of [1] to [5] above, wherein the content of the photosensitive monomer per 100 parts by mass of the prepolymer is 5 parts by mass or more and less than 100 parts by mass. [7] The photosensitive thermosetting resin composition according to any one of [1] to [6] above, wherein the thermosetting resin is an epoxy resin having an epoxy group equivalent of 100 g / eq or more and less than 600 g / eq and containing two or more epoxy groups. [8] The photosensitive thermosetting resin composition according to any one of [1] to [7] above, further comprising a curing agent, wherein the content of the curing agent per 100 parts by mass of the thermosetting resin is 0.1 parts by mass or more and less than 1.0 part by mass. [9] The photosensitive thermosetting resin composition according to any one of [1] to [8] above, wherein the polymerization initiator consists of a nitrogen-free photopolymerization initiator and a photosensitizer.

[10] A photosensitive coverlay formed by forming the photosensitive thermosetting resin composition according to any one of [1] to [9] into a sheet.

[11] A flexible printed wiring board having the photosensitive coverlay according to

[10] provided on a metal foil on which a circuit is formed.

[0012] According to the present invention, there are provided a photosensitive thermosetting resin composition capable of producing a photosensitive coverlay that has improved bending properties while maintaining heat resistance and adhesion, a photosensitive coverlay using the photosensitive thermosetting resin composition, and a flexible printed wiring board using the photosensitive coverlay.

[0013] Fig. 1 is a schematic cross-sectional view showing one embodiment of the photosensitive coverlay of the present invention, and Fig. 2 is a schematic cross-sectional view showing the manufacturing and use steps of one embodiment of the flexible printed wiring board of the present invention.

[0014] Next, an embodiment of the present invention will be described. The following embodiment is an example for explaining the present invention, and is not intended to limit the present invention to this embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention.

[0015] The definitions and meanings of terms and notations used in this specification are as follows. "(Meth)acryloyloxy group" is a general term for acryloyloxy group and methacryloyloxy group. "(Meth)acrylate" is a general term for acrylate and methacrylate. Similarly, "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid. "Number of functional groups" means the number of (meth)acryloyloxy groups in one molecule, unless otherwise specified. "Average number of functional groups" means the average number of (meth)acryloyloxy groups per molecule, where the formula weight or number average molecular weight (Mn) obtained based on the chemical formula is one unit, unless otherwise specified. "Curable component" means a compound having a (meth)acryloyloxy group. "Index" in the reaction of an isocyanate group-containing compound and a hydroxyl group-containing compound is the value obtained by dividing the number of moles of isocyanate groups in the isocyanate group-containing compound by the number of moles of hydroxyl groups in the hydroxyl group-containing compound, multiplied by 100. The hydroxyl value of a hydroxyl-containing compound is obtained by measurement in accordance with JIS K1557 (2007 edition). The hydroxyl value-based molecular weight is calculated by applying the hydroxyl value to the formula "56100 / (hydroxyl value) × (number of active hydrogen atoms in the initiator)". The number average molecular weight (Mn) is the polystyrene-equivalent molecular weight obtained by measurement with gel permeation chromatography (GPC) using a calibration curve prepared using standard polystyrene samples of known molecular weight. The molecular weight distribution refers to the value obtained by dividing the weight average molecular weight (Mw) (polystyrene-equivalent molecular weight obtained by GPC in the same way as the number average molecular weight (Mn)) by the number average molecular weight (Mn). In addition, if a peak of unreacted low molecular weight components (monomers, etc.) appears in the GPC measurement, the peak is excluded to determine the number average molecular weight (Mn). Even if the number average molecular weight (Mn) is specified, if there is no molecular weight distribution, it is replaced by the molecular weight represented by the formula weight obtained based on the chemical formula.

[0016] [Photosensitive Thermosetting Resin Composition] The photosensitive thermosetting resin composition of the present invention contains a prepolymer, a photosensitive monomer, a thermosetting resin, and a polymerization initiator, and may further contain optional components such as a curing agent and a flame retardant, as necessary.

[0017] <Prepolymer> The prepolymer contains at least a carboxylic acid-modified bisphenol-type epoxy (meth)acrylate, and may further contain at least one of a carboxylic acid-modified cresol novolac-type epoxy (meth)acrylate and a carboxylic acid-modified urethane (meth)acrylate.

[0018] (Carboxylic Acid-Modified Bisphenol-Type Epoxy(meth)acrylate) The weight average molecular weight (Mw) of the carboxylic acid-modified bisphenol-type epoxy(meth)acrylate is not particularly limited, but from the viewpoints of adhesion, heat resistance, and developability, it is preferably 5,000 to 20,000, more preferably 6,500 to 16,500, and particularly preferably 8,000 to 13,000.

[0019] The carboxylic acid equivalent of the carboxylic acid-modified bisphenol epoxy (meth)acrylate is not particularly limited, but from the viewpoints of adhesion, heat resistance, and developability, it is preferably 300 g / eq or more and less than 1500 g / eq, more preferably 380 to 1220 g / eq, and particularly preferably 460 to 940 g / eq.

[0020] The carboxylic acid-modified bisphenol epoxy (meth)acrylate is not particularly limited, and examples thereof include compounds obtained by reacting a bisphenol epoxy resin with (meth)acrylic acid and then reacting with an acid anhydride. The bisphenol epoxy resin used as a raw material is not particularly limited, and examples thereof include bisphenol F epoxy resins and bisphenol A epoxy resins whose main skeleton is bisphenol F epoxy resins, and commercially available products can also be used. These may be used alone or in combination of two or more. Similarly, the acid anhydride used as a raw material is not particularly limited, and examples thereof include phthalic anhydride, succinic anhydride, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, itaconic anhydride, and methyl-end-methylenetetrahydrophthalic anhydride. These may be used alone or in combination of two or more.

[0021] In terms of improving the shelf life as well as the heat resistance and adhesion, the prepolymer preferably contains at least one of a carboxylic acid-modified cresol novolac epoxy (meth)acrylate and a carboxylic acid-modified urethane (meth)acrylate in addition to the carboxylic acid-modified bisphenol epoxy (meth)acrylate.

[0022] (Carboxylic Acid-Modified Cresol Novolac Epoxy (Meth)acrylate) The weight-average molecular weight (Mw) of the carboxylic acid-modified cresol novolac epoxy (meth)acrylate is not particularly limited, but is preferably 5,000 to 15,000, more preferably 6,500 to 14,000, and particularly preferably 8,000 to 13,000. When the weight-average molecular weight (Mw) is within the above range, the shelf life can be extended and good adhesion, heat resistance, and developability can be obtained.

[0023] The carboxylic acid equivalent of the carboxylic acid-modified cresol novolac epoxy (meth)acrylate is not particularly limited, but is preferably 300 g / eq or more and less than 1500 g / eq, more preferably 380 to 1220 g / eq, and particularly preferably 460 to 940 g / eq, in order to extend the shelf life and obtain good adhesion, heat resistance, and developability.

[0024] (Carboxylic Acid-Modified Urethane (Meth)acrylate) The weight-average molecular weight (Mw) of the carboxylic acid-modified urethane (meth)acrylate is not particularly limited, but is preferably 2000 to 15000, more preferably 2000 to 12500, and particularly preferably 2000 to 11000. When the weight-average molecular weight (Mw) is within the above range, the shelf life can be extended and good adhesion, heat resistance, and developability can be obtained.

[0025] The carboxylic acid equivalent of the carboxylic acid-modified urethane (meth)acrylate is not particularly limited, but is preferably 500 g / eq or more and less than 2000 g / eq, more preferably 700 to 1950 g / eq, and particularly preferably 900 to 1900 g / eq, in order to further extend the shelf life and obtain good adhesion, heat resistance, developability, and flexibility.

[0026] When a carboxylic acid-modified cresol novolac epoxy (meth)acrylate and a carboxylic acid-modified urethane (meth)acrylate are used as the prepolymer, the mass ratio (former:latter) of the carboxylic acid-modified bisphenol epoxy (meth)acrylate to the total of the carboxylic acid-modified cresol novolac epoxy (meth)acrylate and the carboxylic acid-modified urethane (meth)acrylate is preferably 80:20 to 20:80, more preferably 70:30 to 30:70, and particularly preferably 60:40 to 40:60. When the carboxylic acid-modified bisphenol epoxy (meth)acrylate is at or below the upper limit, shortening of shelf life can be prevented, while when the carboxylic acid-modified bisphenol epoxy (meth)acrylate is at or above the lower limit, deterioration of heat resistance and adhesion can be prevented.

[0027] The content of the prepolymer in the photosensitive thermosetting resin composition is not particularly limited, but from the viewpoint of imparting photosensitivity, it is preferably 10 to 80% by mass, more preferably 20 to 70% by mass, and particularly preferably 30 to 60% by mass. The total content of the carboxylic acid-modified bisphenol epoxy (meth)acrylate, carboxylic acid-modified cresol novolac epoxy (meth)acrylate, and carboxylic acid-modified urethane (meth)acrylate in 100% by mass of the prepolymer is not particularly limited, but from the viewpoint of good adhesion, solder heat resistance, and developability, it is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and particularly preferably 90 to 100% by mass. The total content of the carboxylic acid-modified bisphenol-type epoxy (meth)acrylate, the carboxylic acid-modified cresol novolac-type epoxy (meth)acrylate, and the carboxylic acid-modified urethane (meth)acrylate in 100% by mass of the photosensitive thermosetting resin composition is not particularly limited, but from the viewpoints of good adhesion, solder heat resistance, and developability, it is preferably 10 to 80% by mass, more preferably 20 to 70% by mass, and particularly preferably 30 to 60% by mass.

[0028] <Photosensitive Monomer> The photosensitive monomer is not particularly limited as long as it contains a monofunctional monomer (hereinafter simply referred to as "monofunctional monomer") having one (meth)acryloyloxy group per molecule and a number average molecular weight (Mn) of 1,300 to 36,000, and may or may not further contain a photosensitive monomer other than the monofunctional monomer. It is preferable that the photosensitive monomer is not carboxylic acid-modified and has a carboxylic acid equivalent of 0 g / eq.

[0029] The content of the photosensitive monomer relative to 100 parts by mass of the prepolymer is not particularly limited, but from the viewpoint of imparting flexibility, it is preferably 5 parts by mass or more but less than 100 parts by mass, more preferably 30 to 90 parts by mass, and particularly preferably 45 to 75 parts by mass. The content of the monofunctional monomer relative to the photosensitive monomer is not particularly limited, but from the viewpoint of imparting flexibility, it is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and particularly preferably 40 to 60% by mass.

[0030] From the viewpoint of developability and heat resistance, the photosensitive monomer preferably further contains pentaerythritol ethoxy tetraacrylate. When the photosensitive monomer further contains pentaerythritol ethoxy tetraacrylate, the content of pentaerythritol ethoxy tetraacrylate relative to 100 parts by mass of the prepolymer is not particularly limited, but is preferably 10 to 50 parts by mass, more preferably 15 to 45 parts by mass, and particularly preferably 20 to 40 parts by mass.

[0031] (Monofunctional Monomer) The monofunctional monomer has one (meth)acryloyloxy group per molecule, and preferably further has a polyoxyalkylene chain and a urethane bond derived from an isocyanate group-containing compound. When the photosensitive thermosetting resin composition of the present invention is ultraviolet-curable, the (meth)acryloyloxy group in the monofunctional monomer is preferably an acryloyloxy group.

[0032] The monofunctional monomer suppresses shrinkage during curing, reduces the elastic modulus after curing, and easily suppresses whitening when repeatedly bent. In addition, since it has one (meth)acryloyloxy group, it has better stability after curing and suppresses the occurrence of bleed-out.

[0033] The monofunctional monomer preferably has a polyoxyalkylene chain. Examples of the polyoxyalkylene chain include a polymer chain having an ethylene oxide unit, a polymer chain having a propylene oxide unit, a polymer chain having an ethylene oxide unit and a propylene oxide unit, a polymer chain consisting of an ethylene oxide unit, a polymer chain consisting of a propylene oxide unit, a polymer chain consisting of a butylene oxide unit, a polymer chain consisting of a tetramethylene oxide unit, a polymer chain consisting of an ethylene oxide unit and a propylene oxide unit, and a polymer chain consisting of a propylene oxide unit and a butylene oxide unit. A polymer chain having a propylene oxide unit, or a polymer chain having an ethylene oxide unit and a propylene oxide unit is preferred, with a polymer chain consisting of a propylene oxide unit being particularly preferred. When the monofunctional monomer has a polyoxyalkylene chain, the number of alkylene oxide units in one molecule is preferably 20 to 600, and more preferably 50 to 500.

[0034] The number of urethane bonds in one molecule of the monofunctional monomer is one or more, and is preferably one or two, more preferably one, because this inhibits shrinkage during curing and facilitates a reduction in the modulus of elasticity after curing. The concentration (abundance ratio) of urethane bonds in one molecule of the monofunctional monomer is not particularly limited, but from the viewpoint of obtaining better adhesiveness, it is preferably 0.35 to 1.9 mass%, more preferably 0.4 to 1.3 mass%, and particularly preferably 0.5 to 1.2 mass%. The concentration of urethane bonds can be calculated using the following formula, assuming that all of the isocyanate groups in the isocyanate group-containing compound used in producing the monofunctional monomer form urethane bonds: (number of moles of isocyanate groups in the isocyanate group-containing compound × molecular weight of urethane bonds (59) / mass of monofunctional monomer) × 100 (%)

[0035] The number-average molecular weight (Mn) of the monofunctional monomer is not particularly limited as long as it is 1,300 to 36,000, but is preferably 3,000 to 35,000, more preferably 4,000 to 20,000, and particularly preferably 5,000 to 18,000. When the number-average molecular weight (Mn) of the monofunctional monomer is within the above range, it is easy to adjust the viscosity of the photosensitive thermosetting resin composition. Furthermore, when the number-average molecular weight (Mn) of the monofunctional monomer is 3,000 or more, the cure shrinkage rate of the photosensitive thermosetting resin composition tends to be low. When the photosensitive thermosetting resin composition contains two or more monofunctional monomers, it is preferable that the number-average molecular weight (Mn) of each monofunctional monomer is within the above range.

[0036] In the production process of a monofunctional monomer, a by-product having a polyoxyalkylene chain other than the monofunctional monomer may be generated in the product. Examples of by-products having a polyoxyalkylene chain include compounds having two (meth)acryloyloxy groups, compounds having no (meth)acryloyloxy groups, and compounds having no urethane bonds. The content of the monofunctional monomer in the product is not particularly limited, but from the viewpoint of fully exhibiting the function as a monofunctional monomer, it is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and particularly preferably 90 to 100% by mass. When the product contains the monofunctional monomer in the above content, the function of the monofunctional monomer is fully exhibited, and the product can be considered a monofunctional monomer.

[0037] When the above product can be considered a monofunctional monomer, the average functionality calculated from the number average molecular weight (Mn) and the number of functional groups of the product can be considered the average functionality of the monofunctional monomer. In this case, the average functionality of the product is not particularly limited, but is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. A product having an average functionality within the above range is likely to fully exhibit the function of a monofunctional monomer. The average functionality can be adjusted to this range by adjusting the amount of impurities contained in the raw materials for producing the monofunctional monomer or by adjusting the index described below. Furthermore, in this specification, the average functionality can be calculated using the average functionality of the raw materials and the index described below.

[0038] Specific examples of the monofunctional monomer include reaction product (1), reaction product (2), and reaction product (3) shown below. These may be used alone or in combination of two or more. In particular, it is preferable that the monofunctional monomer in the photosensitive thermosetting resin composition contains one or more selected from the group consisting of reaction product (1) and reaction product (2). In particular, reaction product (1) is more preferable as the monofunctional monomer, since it has a lower content of by-products than other reaction products and can produce a photosensitive thermosetting resin composition excellent in flexibility and cure shrinkage.

[0039] The total content of reaction product (1) and reaction product (2) relative to the monofunctional monomer is not particularly limited, but is preferably 50% by mass or more, more preferably 80% by mass or more, and particularly preferably 100% by mass. When the total content of reaction product (1) and reaction product (2) is equal to or greater than the lower limit of the above range, flexibility and cure shrinkage rate are excellent. When the monofunctional monomer contains reaction product (1) and reaction product (2), the mass ratio thereof (reaction product (1):reaction product (2)) is preferably greater than 1:0 to 1:1.

[0040] Reaction product (1): An equimolar reaction product of a polyoxyalkylene monool and a compound having an isocyanate group and a (meth)acryloyloxy group. Reaction product (2): An equimolar reaction product of a polyoxyalkylene monool, a diisocyanate, and a compound having a group reactive with an isocyanate group and a (meth)acryloyloxy group. Reaction product (3): An equimolar reaction product of a polyoxyalkylene polyol and a compound having an isocyanate group and a (meth)acryloyloxy group.

[0041] The compound having an isocyanate group and a (meth)acryloyloxy group, which is the raw material for the reaction products (1) and (3), is preferably a (meth)acrylate having one isocyanate group, more preferably an isocyanate alkyl (meth)acrylate.

[0042] Examples of diisocyanates that are raw materials for the reaction product (2) include non-yellowing aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and various modified products of these diisocyanates (modified products having two isocyanate groups). These may be used alone or in combination of two or more. Among these, aliphatic diisocyanates and alicyclic diisocyanates are preferred because they have excellent light resistance, weather resistance, and heat resistance and can maintain transparency.

[0043] The non-yellowing aromatic diisocyanate is not particularly limited, and examples thereof include xylylene diisocyanate, tetramethylxylylene diisocyanate, etc. These may be used alone, or two or more types may be used in combination. The aliphatic diisocyanate is not particularly limited, and examples thereof include 1,6-hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, etc. These may be used alone, or two or more types may be used in combination. The alicyclic diisocyanate is not particularly limited, and examples thereof include isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,5-norbornane diisocyanate, 2,6-norbornane diisocyanate, etc. These may be used alone, or two or more types may be used in combination. The compound having a group reactive with an isocyanate group and a (meth)acryloyloxy group, which is a raw material for the reaction product (2), is not particularly limited, but is preferably a (meth)acrylate having one hydroxyl group, more preferably a hydroxyalkyl (meth)acrylate or a hydroxycycloalkyl (meth)acrylate, and particularly preferably a hydroxyalkyl (meth)acrylate having 8 or less carbon atoms in the hydroxyalkyl group.

[0044] The average number of hydroxyl groups per molecule of the polyoxyalkylene monool, which is the raw material for the reaction products (1) and (2), is not particularly limited, but is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. The hydroxyl value of the polyoxyalkylene monool is not particularly limited, but is preferably 1.6 to 18.1 mgKOH / g, more preferably 2.8 to 14 mgKOH / g, and particularly preferably 3.1 to 11.2 mgKOH / g, in order to obtain a monofunctional monomer having a urethane bond concentration within a predetermined range.

[0045] Polyoxyalkylene monool is a compound obtained by ring-opening addition polymerization of alkylene oxide with an initiator having an active hydrogen-containing group and one or more active hydrogens, and having an initiator residue, a polyoxyalkylene chain, and hydroxyl groups corresponding to the number of active hydrogens in the initiator.

[0046] The alkylene oxide is not particularly limited, and suitable examples include alkylene oxides having 2 to 4 carbon atoms, such as propylene oxide, ethylene oxide, 1,2-butylene oxide, and 2,3-butylene oxide. These may be used alone or in combination of two or more.

[0047] The active hydrogen-containing group of the initiator is not particularly limited, and examples thereof include a hydroxyl group, a carboxyl group, and an amino group having one hydrogen atom bonded to a nitrogen atom. These may be used alone or in combination of two or more. Among these, a hydroxyl group and a carboxyl group are preferred, and an alcoholic hydroxyl group is more preferred.

[0048] Examples of initiators having one active hydrogen include monohydric alcohols, monohydric phenols, monovalent carboxylic acids, and amine compounds having one hydrogen atom bonded to a nitrogen atom. These may be used alone or in combination of two or more. Among these, monohydric aliphatic alcohols and monohydric aliphatic carboxylic acids are preferred. The number of carbon atoms in the monohydric aliphatic alcohol is not particularly limited, but is preferably 1 to 20, more preferably 1 to 14, and particularly preferably 2 to 8. The number of carbon atoms in the monohydric aliphatic carboxylic acid is not particularly limited, but is preferably 2 to 20, more preferably 2 to 14, and particularly preferably 2 to 8, including the carbon atoms of the carboxy group. In addition, a polyoxyalkylene monool having a lower molecular weight than the target polyoxyalkylene monool may be used as the initiator.

[0049] The oxyalkylene groups in the polyoxyalkylene monool preferably consist solely of oxypropylene groups or of a combination of oxypropylene groups and other oxyalkylene groups. The oxyalkylene groups other than oxypropylene groups are preferably oxyethylene groups. The proportion of oxypropylene groups relative to all oxyalkylene groups in the polyoxyalkylene monool is not particularly limited, but is preferably 50 to 100% by mass, more preferably 65 to 100% by mass, and particularly preferably 80 to 100% by mass. When the initiator is a polyoxyalkylene monool having a lower molecular weight than the target polyoxyalkylene monool, the oxyalkylene groups in the initiator are considered to be the oxyalkylene groups in the resulting polyoxyalkylene monool.

[0050] A low hydroxyl value (i.e., high molecular weight) polyoxyalkylene monool can be produced by ring-opening addition polymerization of an alkylene oxide having 3 or more carbon atoms (preferably propylene oxide) to an initiator in the presence of a composite metal cyanide complex catalyst. A low hydroxyl value polyoxyalkylene monool having an oxyethylene group can also be produced by ring-opening addition polymerization of an alkylene oxide having 3 or more carbon atoms (particularly propylene oxide) to an initiator in the presence of a composite metal cyanide complex catalyst. A high hydroxyl value polyoxyalkylene monool can also be produced using an alkali catalyst such as KOH.

[0051] In the production of polyoxyalkylene monools, initiators and alkylene oxides are typically introduced into the reaction system with low water content, typically obtained by removing water by vacuum degassing or the like. The water content of the initiator used in the production of polyoxyalkylene monools is not particularly limited, but the lower the content, the better. It is preferably 500 ppm by mass or less, more preferably 400 ppm by mass or less, and particularly preferably 300 ppm by mass or less. When the water content is within the above range, the amount of polyoxyalkylene diol produced from water is suppressed, thereby ultimately suppressing the amount of by-products produced due to the polyoxyalkylene diol, and making it easier to adjust the upper limit of the average number of hydroxyl groups in the resulting polyoxyalkylene monool to 1.2 or less. The water content of the polyoxyalkylene monool used as a raw material for reaction products (1) and (2) is not particularly limited, but the lower the content, the better. It is preferably 300 ppm by mass or less, more preferably 250 ppm by mass or less, and particularly preferably 50 to 200 ppm by mass relative to the polyoxyalkylene monool. When the water content is within the above range, the production of by-products, which are reaction products of water and the isocyanate group-containing compound, is reduced, improving the stability of the reaction products (1) and (2).Furthermore, it is easy to suppress changes in the appearance of the curable composition containing the reaction products (1) and (2) over time, and the elastic modulus of the cured product is easy to improve.

[0052] The polyoxyalkylene polyol used as the raw material for reaction product (3) is preferably a polyoxyalkylene diol. The average number of hydroxyl groups per molecule of the polyoxyalkylene polyol is not particularly limited, but is preferably 1.6 to 2.1, more preferably 1.7 to 2.0, and particularly preferably 1.8 to 1.96. That is, the polyoxyalkylene polyol used as the raw material for reaction product (3) is preferably a polyoxyalkylene diol. The content of oxypropylene groups relative to all oxyalkylene groups in the polyoxyalkylene polyol is not particularly limited, but is preferably 80 to 100% by mass. The hydroxyl value of the polyoxyalkylene polyol is not particularly limited, but is preferably 1.6 to 19 mgKOH / g, more preferably 2.2 to 16 mgKOH / g, and particularly preferably 2.8 to 14 mgKOH / g, from the viewpoint of obtaining a monofunctional monomer having a urethane bond concentration within a predetermined range.

[0053] [Reaction Product (1)] The reaction product (1) is an equimolar reaction product of a polyoxyalkylene monool and a compound having an isocyanate group and a (meth)acryloyloxy group. The compound having an isocyanate group and a (meth)acryloyloxy group is not particularly limited, and a suitable example is an isocyanate alkyl (meth)acrylate.

[0054] Because the polyoxyalkylene monool and the isocyanate alkyl (meth)acrylate each have one group capable of urethanization per molecule, it is easy to control the number of urethane bonds per molecule of the reaction product (1) to one. A low number of urethane bonds per molecule of the reaction product (1) tends to result in low viscosity. Therefore, it is preferable that the monofunctional monomer in the photosensitive thermosetting resin composition contains the reaction product (1), as this makes it easier to obtain a low-viscosity, cured product with excellent flexibility. Furthermore, because both the polyoxyalkylene monool and the isocyanate alkyl (meth)acrylate are compounds with one reactive group, they are less likely to produce by-products, making it easier to remove unreacted material and obtain a highly pure reaction product (1). If unreacted material remains, it is preferable that the unreacted material be a polyoxyalkylene monool from the perspective of the stability of the reaction product. To obtain a reaction product with minimal unreacted material, it is preferable to react the two at an index of 90 to 100, and more preferably at an index of 100. The average number of functional groups in the reaction product (1) is not particularly limited, but is preferably 0.9 to 1.1. A photosensitive thermosetting resin composition containing the reaction product (1) within the above range is likely to have reduced shrinkage during curing and a reduced elastic modulus after curing.

[0055] [Reaction Product (2)] Reaction product (2) is an equimolar reaction product of a polyoxyalkylene monool, a diisocyanate, and a compound having a group reactive with an isocyanate group and a (meth)acryloyloxy group. The diisocyanate is not particularly limited, and suitable examples thereof include aliphatic diisocyanates and alicyclic diisocyanates. The compound having a group reactive with an isocyanate group and a (meth)acryloyloxy group is not particularly limited, and suitable examples thereof include hydroxyalkyl (meth)acrylates in which the hydroxyalkyl group has 8 or less carbon atoms. Examples of reaction product (2) include (a) a reaction product obtained by reacting a polyoxyalkylene monol with a diisocyanate at an index of 200, and then reacting the resulting reaction product (a reaction product having an isocyanate group) with a hydroxyalkyl (meth)acrylate at an index of 100; and (b) a reaction product obtained by simultaneously reacting a polyoxyalkylene monol with an equimolar amount of hydroxyalkyl (meth)acrylate relative to the polyoxyalkylene monol, and a diisocyanate in an amount with an index of 100 relative to the total amount of the polyoxyalkylene monol and the hydroxyalkyl (meth)acrylate. Among these, reaction product (a) is preferred because it produces fewer by-products. When producing reaction product (a), the hydroxyalkyl (meth)acrylate may be used in excess, and the excess hydroxyalkyl (meth)acrylate may be incorporated into the photosensitive thermosetting resin composition together with the reaction product (a) as part of another photosensitive monomer, as described below. The average number of functional groups in the reaction product (2) is not particularly limited, but is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. A photosensitive thermosetting resin composition containing the reaction product (2) within the above range is likely to have reduced shrinkage during curing and a reduced elastic modulus after curing.

[0056] [Reaction Product (3)] The reaction product (3) is an equimolar reaction product of a polyoxyalkylene polyol and a compound having an isocyanate group and a (meth)acryloyloxy group. The polyoxyalkylene polyol is not particularly limited, and a suitable example thereof is a polyoxyalkylene diol. The compound having an isocyanate group and a (meth)acryloyloxy group is not particularly limited, and a suitable example thereof is an isocyanate alkyl (meth)acrylate. Note that the reaction product (3) is a reaction product having a hydroxyl group, and the number of hydroxyl groups is not limited to one. Therefore, as long as the compound having an isocyanate group and a (meth)acryloyloxy group is a compound having one isocyanate group and is an equimolar reaction product, the raw material polyoxyalkylene polyol may be a compound having more than two hydroxyl groups. The average number of functional groups in the reaction product (3) is not particularly limited, but is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. A reaction product (3) within the above range is likely to have reduced shrinkage during curing and a reduced elastic modulus after curing.

[0057] The monofunctional monomer contributes to reducing shrinkage during curing and reducing the elastic modulus of the cured product, and since it has a (meth)acryloyloxy group as a curable functional group, the cured product has excellent stability and is less likely to bleed out.

[0058] A specific example of the monofunctional monomer is the monomer (IB-1).

[0059] Monomer (IB-1) Monomer (IB-1) contains a curable component having one curable functional group and represented by the following formula (1): The curable component represented by the following formula (1) is obtained by subjecting a polyoxyalkylene monool (1a) represented by the following formula (1a) and a compound (1b) represented by the following formula (1b) to a urethane reaction.

[0060]

[0061] In formulas (1), (1a), and (1b), R １１is a hydrogen atom or a methyl group, preferably a hydrogen atom. １２ is an alkylene group having 2 to 4 carbon atoms, and multiple R １２ may be the same or different. Two or more types of R １２ If there is -OR １２ The chain of - may be block or random. １２ is preferably an ethylene group or a propylene group. １３ is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms. The carboxylic acid residue is a monovalent group obtained by removing one hydrogen atom from a monocarboxylic acid having 1 to 20 carbon atoms, including the carbon atom in the carboxy group (—COOH). R １３ In terms of ease of reaction, a is preferably an alkyl group, more preferably an alkyl group having 2 to 8 carbon atoms. a is an integer of 1 to 4, preferably an integer of 1 or 2. b is an integer of 20 to 600, preferably an integer of 35 to 500, more preferably an integer of 65 to 250.

[0062] In producing the curable component represented by formula (1), the polyoxyalkylene monool (1a) represented by formula (1a) may be used in the form of a composition containing a diol as a by-product in addition to the polyoxyalkylene monool (1a) represented by formula (1a), which is produced as follows: The obtained curable component is used as monomer (IB-1).

[0063] Since the polyoxyalkylene monool (1a) represented by formula (1a) and the compound (1b) represented by formula (1b) each have one group capable of urethanization reaction present in one molecule, the number of urethane bonds in one molecule of the monomer (IB-1) is easily controlled to one on average. If the number of urethane bonds in one molecule of the monomer (IB-1) is small, the viscosity is likely to be low. Therefore, by including the monomer (IB-1), the photosensitive thermosetting resin composition has a low viscosity, and a cured product with excellent flexibility is easily obtained.

[0064] The hydroxyl value of the polyoxyalkylene monool (1a) represented by formula (1a) is not particularly limited, but is preferably 1.6 to 56.1 mgKOH / g, more preferably 2.8 to 14.0 mgKOH / g, and particularly preferably 3.5 to 12.5 mgKOH / g. The molecular weight calculated from the hydroxyl value of the polyoxyalkylene monool (1a) represented by formula (1a) is not particularly limited, but is preferably 1,000 to 35,000, more preferably 4,000 to 20,000, and particularly preferably 4,500 to 16,000.

[0065] The polyoxyalkylene monool (1a) component containing the polyoxyalkylene monool (1a) represented by formula (1a) can be obtained, for example, by ring-opening addition polymerization of an alkylene oxide with an initiator such as a monohydric alcohol or a carboxylic acid. The catalyst used in the ring-opening addition polymerization is not particularly limited, and examples thereof include alkali metal compound catalysts, composite metal cyanide complex catalysts (hereinafter also referred to as DMC catalysts), phosphazene compound catalysts, and boron-based cation catalysts which are Lewis acids. These may be used alone or in combination of two or more. Among these, DMC catalysts are preferred because they can reduce the contamination of low-molecular-weight bifunctional polyols, i.e., diols, which are by-produced using water as an initiator during ring-opening addition polymerization, and also because they facilitate the production of high-molecular-weight monools. The molecular weight calculated from the hydroxyl value of the polyoxyalkylene monool (1a) produced using a DMC catalyst is not particularly limited, but is preferably 1,000 to 35,000, more preferably 4,000 to 20,000, and particularly preferably 4,500 to 16,000.

[0066] The molecular weight of the by-produced low-molecular-weight diol is twice that of the polyoxyalkylene monool (1a). It is preferable to produce a polyoxyalkylene monool (1a) component containing the polyoxyalkylene monool (1a) represented by formula (1a) so that the amount of the low-molecular-weight diol is reduced. When the polyoxyalkylene monool (1a) component produced using a DMC catalyst is used, Zn and Co are present as residues in a total amount of 0.01 to 100 ppm by mass in the photosensitive thermosetting resin composition.

[0067] The polyoxyalkylene monool (1a) component thus obtained may contain, in addition to the polyoxyalkylene monool (1a) represented by formula (1a), a diol by-produced during the production, but the amount of the diol is preferably 30 mass% or less, more preferably 25 mass% or less, and even more preferably 18 mass% or less, based on the total amount of the polyoxyalkylene monool (1a) component produced. In the production of the polyoxyalkylene monool (1a) represented by formula (1a), the amount of the diol by-produced can be kept within the above-mentioned range by reducing the amount of water in the reaction system.

[0068] In the production of polyoxyalkylene monool represented by formula (1a), the total amount of water in the reaction system is not particularly limited, but is preferably 250 ppm by mass or less, more preferably 225 ppm by mass or less, and particularly preferably 200 ppm by mass or less. When the amount of water in the reaction system is within this range, the production of diol initiated by water, which is a by-product of polyoxyalkylene monool represented by formula (1a), is suppressed. In the production of monomer (IB-1), using a polyoxyalkylene monool (1a) component with a reduced diol content makes it easy to suppress the production of diol-derived bifunctional photosensitive monomers, and monomer (IB-1) containing a predetermined amount of curable component represented by formula (1) can be easily obtained.

[0069] To adjust the water content in the reaction system to the above range, water may be removed under reduced pressure after supplying the initiator to the reaction vessel. Alternatively, the water content in the reaction system can be adjusted by adjusting the water content of the alkylene oxide to be added to 200 ppm by mass or less. Therefore, the water content of the alkylene oxide to be added is preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less. When the ring-opening addition polymerization catalyst is an alkali metal compound catalyst, it is typically used as an aqueous solution containing the catalyst and having a solids content of 85% to 95% by mass. Since the water content in the reaction system tends to be high, water is removed under reduced pressure after alcoholating the hydroxyl groups of the initiator. DMC catalysts are preferred because they contain a low amount of water. Furthermore, the use of a DMC catalyst allows the production of a polyoxyalkylene monool (1a) represented by formula (1a) with a narrow molecular weight distribution.

[0070] The content ratio of the polyoxyalkylene monool (1a) represented by formula (1a) and the diol in the polyoxyalkylene monool (1a) component can be determined by GPC measurement of the produced polyoxyalkylene monool (1a) component. The average number of hydroxyl groups in the polyoxyalkylene monool (1a) represented by formula (1a) can be determined by GPC measurement of the produced monool (1a) component.

[0071] When the polyoxyalkylene monool (1a) represented by formula (1a) is reacted with the compound (1b) represented by formula (1b) using the polyoxyalkylene monool (1a) component, the compounding ratio of the compound represented by formula (1b) to the polyoxyalkylene monool (1a) component is not particularly limited, but is preferably an index (NCO / OH ratio) of 80 to 100, more preferably 90 to 100, and particularly preferably 100. By setting the index within the above range, the number of curable functional groups per molecule of the monomer (IB-1) can be brought close to one on average.

[0072] In particular, R present in one molecule of the curable component represented by formula (1) １２ It is preferable that the monomer (IB) contains a monomer (IB-1-PO) containing a monomer (1-PO) having a propylene group content of 50 to 100% by mass based on the total amount of the monomer (1-PO). １２ The proportion of propylene groups relative to the total amount of R is not particularly limited, but is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and particularly preferably 100% by mass. １２ Among these, the alkylene group other than the propylene group is preferably an ethylene group.

[0073] Furthermore, when the monomer (IB-1-PO) is used, the content of the monomer (IB-1-PO) relative to the monomer (IB) is not particularly limited, but is preferably 50 to 100% by mass, more preferably 65 to 100% by mass, and particularly preferably 80 to 100% by mass. When the content of the monomer (IB-1-PO) is equal to or greater than the lower limit of the above range, the viscosity is low and flexibility is excellent.

[0074] (Other Photosensitive Monomers) The other photosensitive monomers are not particularly limited, and examples thereof include polytetramethylene glycol di(meth)acrylate, ethoxylated 2-methyl-1,3-propanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-methyl-1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene ... Examples of suitable acrylates include methylisocyanuric acid tri(meth)acrylate, ethoxylated glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. These may be used alone or in combination of two or more. Among these, ethoxylated pentaerythritol tetra(meth)acrylate is preferred.

[0075] The number average molecular weight (Mn) of the other photosensitive monomer is not particularly limited, but in terms of obtaining good UV sensitivity and obtaining a fine pattern (fine pattern), it is preferably 150 to 1200, more preferably 150 to 1100, and particularly preferably 150 to 1000. The number of (meth)acrylic groups in the other photosensitive monomer is not particularly limited, but is preferably 2 or more, more preferably 3 or more, and particularly preferably 4 or more.

[0076] The content of the other photosensitive monomer is not particularly limited, but is preferably 10 parts by mass or more but less than 50 parts by mass, more preferably 15 to 45 parts by mass, and particularly preferably 20 to 40 parts by mass, relative to 100 parts by mass of the prepolymer.

[0077] <Thermosetting Resin> The thermosetting resin used in the present invention is not particularly limited, and examples thereof include epoxy resins such as biphenyl-type epoxy resins, bisphenol-type epoxy resins (e.g., bisphenol A-type, bisphenol F-type, bisphenol S-type, etc.), novolac-type epoxy resins (e.g., phenol novolac-type, cresol novolac-type, etc.), naphthalene ring-containing epoxy resins, and alicyclic epoxy resins. These may be used alone or in combination of two or more. Among these, biphenyl-type epoxy resins are preferred in terms of obtaining good adhesion and heat resistance.

[0078] The epoxy group equivalent of the thermosetting resin is not particularly limited, but is preferably 100 g / eq or more but less than 600 g / eq, more preferably 100 to 450 g / eq, and particularly preferably 100 to 300 g / eq, in order to obtain good adhesion, heat resistance, and developability. The number of epoxy groups in one molecule of the epoxy resin is not particularly limited, but is preferably 2 or more in order to obtain good adhesion, heat resistance, and developability.

[0079] The thermosetting resin is preferably blended in an amount such that the ratio of its epoxy group equivalent to the carboxylic acid equivalent of the prepolymer (former: latter) is in the range of 1: 1 to 1: 2. When this ratio is within this preferred range, good adhesion and heat resistance can be obtained.

[0080] The content of the thermosetting resin relative to 100 parts by mass of the prepolymer is not particularly limited, but from the viewpoint of obtaining good adhesion, solder heat resistance, and developability, it is preferably 10 to 70 parts by mass, more preferably 20 to 60 parts by mass, and particularly preferably 30 to 50 parts by mass.

[0081] <Polymerization Initiator> The polymerization initiator used in the present invention preferably comprises a nitrogen-free photopolymerization initiator and a photosensitizer, in that good UV sensitivity can be obtained.

[0082] The content of the photopolymerization initiator is not particularly limited, but is preferably 5 parts by mass or more and less than 15 parts by mass relative to 100 parts by mass of the prepolymer. The content of the photosensitizer is not particularly limited, but is preferably 0.5 parts by mass or more and less than 5 parts by mass relative to 100 parts by mass of the prepolymer.

[0083] (Photopolymerization initiator) The photopolymerization initiator is not particularly limited, and in terms of extending shelf life and improving room temperature storage stability, a photopolymerization initiator that does not contain a nitrogen atom, such as a photopolymerization initiator that does not contain a primary, secondary, or tertiary amine structure, is preferred. The photopolymerization initiator that does not contain a nitrogen atom is not particularly limited, and examples thereof include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide. These may be used alone or in combination of two or more. Among these, 2,2-dimethoxy-1,2-diphenylethan-1-one is preferred.

[0084] (Photosensitizer) The photosensitizer is not particularly limited, and from the viewpoint of extending the shelf life and improving storage stability at room temperature, preferred examples include photosensitizers that do not contain nitrogen atoms, such as photosensitizers that do not contain a primary, secondary, or tertiary amine structure. The photosensitizer that does not contain nitrogen atoms is not particularly limited, and examples include 2,4-diethyloxanthone, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. These may be used alone, or two or more may be used in combination. Of these, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide is preferred.

[0085] <Curing Agent> The curing agent used in the present invention is not particularly limited, and examples thereof include Lewis acid amine complexes, imidazole-based, phenol-based, amine-based, acid anhydride-based, and organic peroxide-based curing agents. These may be used alone or in combination of two or more. Among these, at least one selected from Lewis acid amine complexes is preferred in terms of extending shelf life, improving room temperature storage stability, and providing good adhesion and heat resistance. Examples of Lewis acid amine complexes include BF ３ , BCl ３ , TiCl ４ , SnCl ４ , SnCl ３ , ZnBr ２ , ZnCl ２ , Zn(CH ３ COO) ２ , AlCl ３ , AlBr ３ , SiCl ４ , FeCl ３ and the like, and complexes of Lewis acids such as monoethylamine, n-hexylamine, benzylamine, triethylamine, aniline, piperidine, and the like. These may be used alone or in combination of two or more. Among these, BF ３ BF complex with monoethylamine ３ Complexes are preferred.

[0086] The content of the curing agent is not particularly limited, but is preferably 0.1 part by mass or more but less than 1.0 part by mass, and more preferably 0.2 to 0.9 parts by mass, relative to 100 parts by mass of the thermosetting resin. When the content is within the above range, good adhesion, heat resistance, and migration properties can be obtained.

[0087] <Flame Retardant> A flame retardant can be blended into the photosensitive thermosetting resin composition of the present invention to achieve good flame retardancy. Flame retardants are not particularly limited, and examples include inorganic fillers such as aluminum hydroxide, silica, and barium sulfate; and organic phosphorus compounds such as phosphate esters. These may be used alone or in combination of two or more. The content of the inorganic filler is not particularly limited, but is preferably 30 to 70 parts by mass per 100 parts by mass of the prepolymer. The incorporation of an inorganic filler can improve adhesion in addition to flame retardancy. The content of the organic phosphorus compound is not particularly limited, but is preferably 20 to 70 parts by mass per 100 parts by mass of the prepolymer. When the phosphorus content is 8 to 9% by mass relative to the total mass of the organic phosphorus compound, the content of the organic phosphorus compound is preferably 20 to 50 parts by mass per 100 parts by mass of the prepolymer.

[0088] In addition, the photosensitive thermosetting resin composition of the present invention may contain additives that are commonly used in photosensitive thermosetting resin compositions, as needed.

[0089] <Method for forming a film from a photosensitive thermosetting resin composition> The method for forming a film from a photosensitive thermosetting resin composition is not particularly limited. For example, the photosensitive thermosetting resin composition is applied to a PET film to a thickness of 20 to 100 μm, and then the composition is applied to a PET film at a dose of 500 to 1000 mJ / cm ２ and then peeling it off from the PET to form a film.

[0090] The photosensitive thermosetting resin composition of the present invention is preferably used mainly for applications such as photosensitive coverlays, flexible printed wiring boards, etc. The photosensitive thermosetting resin composition of the present invention can also be used for multilayer printed wiring boards, flex-rigid printed wiring boards, etc.

[0091] [Photosensitive Coverlay] The photosensitive coverlay of the present invention is formed from the photosensitive thermosetting resin composition of the present invention described above. Because the photosensitive coverlay of the present invention is composed of such a resin composition, it can be formed into a sheet, has a long shelf life (usable period), excellent storage stability at room temperature, has heat resistance after curing, can maintain high adhesion, and is easy to handle. Furthermore, the photosensitive coverlay of the present invention may have a release film provided on at least one side of the sheet made from the photosensitive thermosetting resin composition of the present invention described above, and is used by appropriately peeling off the release film during processing. The method for forming the photosensitive thermosetting resin composition into a sheet is not particularly limited, and examples thereof include a molding method in which the photosensitive thermosetting resin composition is applied to a thickness of 20 to 60 μm on a release-treated surface of a PET (polyethylene terephthalate) film, a PP (polypropylene) film, a PE (polyethylene) film (thickness: 10 to 50 μm), or the like, at least one side of which has been subjected to a release treatment, using a comma coater, die coater, gravure coater, or the like, and the applied photosensitive thermosetting resin composition is cured under predetermined curing conditions (temperature: 150 to 300° C., time: 10 to 180 minutes).

[0092] The photosensitive coverlay of the present invention is provided to protect a metal foil circuit (conductor pattern) in a flexible printed wiring board, for example, by providing the photosensitive thermosetting resin composition of the present invention in a single layer or in a multilayer laminate state on an electrically insulating synthetic resin film by means of photolithography or the like. The release film in the photosensitive coverlay of the present invention is peeled off before use.

[0093] One embodiment of the photosensitive coverlay of the present invention is a photosensitive coverlay 100, which comprises a sheet 10 formed from the photosensitive thermosetting resin composition of the present invention as described above, and a release film 20 made of an electrically insulating synthetic resin film (e.g., a PET (polyethylene terephthalate) film, a PP (polypropylene) film, a PE (polyethylene) film, etc.) provided on one side of the sheet 10, as shown in Figure 1. Figure 1 is a schematic cross-sectional view showing one embodiment of the coverlay of the present invention.

[0094] In the photosensitive coverlay 100 of the embodiment shown in FIG. 1, the thickness of the sheet 10 is preferably 20 to 60 μm, and the thickness of the release film 20 is preferably 10 to 50 μm.

[0095] [Flexible Printed Wiring Board] The flexible printed wiring board of the present invention comprises the above-described photosensitive coverlay of the present invention provided on a metal foil on which a circuit is formed.

[0096] The flexible printed wiring board of the present invention may be, for example, a flexible printed wiring board in which the above-described photosensitive coverlay of the present invention is provided on a metal foil portion of a metal-clad laminate for flexible printed wiring boards, etc., on which a circuit is provided. Here, the metal-clad laminate for flexible printed wiring boards is a laminate in which a film and a metal foil are laminated together, if necessary, via an adhesive, and corresponds to a substrate when used for a flexible printed wiring board.

[0097] The film used here is not particularly limited, and examples thereof include polyimide film, polyester film, polyamide film, etc. These may be used alone or in combination of two or more. Among these, polyimide film is preferred in terms of flame retardancy, electrical insulation, heat resistance, elastic modulus, etc. Films made of other materials may also be used. Furthermore, the metal foil is not particularly limited, and examples thereof include conductive materials such as copper foil and silver foil.

[0098] The flexible printed wiring board of the present invention can be produced, for example, as shown in FIG. 2, by laminating a photosensitive coverlay 100 having a release film 20 made of a PET film provided on one side of a sheet 10 made of the photosensitive thermosetting resin composition of the present invention, and a substrate 40 having a metal foil 30 such as a patterned copper foil.

[0099] That is, in the lamination process, the photosensitive coverlay 100 is roll-laminated onto the substrate 40 provided with the metal foil 30 so that the surface of the sheet 10 is bonded to the surface of the metal foil 30 of the substrate 40. At this time, the lamination temperature, lamination line pressure, lamination speed, etc. are appropriately adjusted. In this manner, the flexible printed wiring board 200 can be formed.

[0100] As shown in FIG. 2, after the lamination step, the flexible printed wiring board of the present invention is used after undergoing steps of UV (ultraviolet) exposure, development and thermal curing.

[0101] In the UV exposure process, a UV irradiator using an ultra-high pressure mercury lamp light source is used to irradiate the photosensitive coverlay 100 on the substrate 40 having the metal foil 30 with UV light from above the release film 20 through a photomask 50 having light-transmitting portions 50a and light-non-transmitting portions 50b and formed with a predetermined pattern. In the development and thermal curing process, the release film is peeled off, and the unexposed portions are developed by spraying an alkaline aqueous solution adjusted to an appropriate temperature at an appropriate pressure, followed by a heat treatment at an appropriate temperature to form a pattern. This hardens the photosensitive portions of the sheet 10 due to the UV light, and the non-photosensitive portions can be developed with the alkaline aqueous solution. The lamination, UV exposure, and development and thermal curing processes can be automated.

[0102] Furthermore, the use of the photosensitive coverlay of the present invention described above offers the following advantages over the use of a coverlay (conventional coverlay) in which an adhesive layer is provided on a polyimide film: (1) Fine patterning is possible. (2) Hole drilling and positioning work using a mold are no longer necessary in the manufacturing process, making automation using photolithography possible. (3) There is no seepage into the land portion. (4) Dimensional change is small.

[0103] The thickness (total) of the flexible printed wiring board of the present invention can be arbitrarily set depending on the application.

[0104] The flexible printed wiring board of the present invention is suitably used, for example, as a chip-on-flex flexible printed wiring board for mounting IC chips.

[0105] Furthermore, the flexible printed wiring board of the present invention is not limited to the above embodiment, and may be a multilayer printed wiring board in which several layers having the above-described configuration are stacked.

[0106] The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples, and various modifications are possible within the scope of the gist of the present invention.

[0107] <Number Average Molecular Weight (Mn) and Weight Average Molecular Weight (Mw)> The number average molecular weight (Mn) and weight average molecular weight (Mw) of each sample are polystyrene-equivalent molecular weights obtained by gel permeation chromatography (GPC) measurement under the following conditions using a calibration curve prepared using standard polystyrene samples of known molecular weights. <<GPC Measurement Conditions>> Model used: HLC-8320GPC (manufactured by Tosoh Corporation) Columns used: G7000HXL+GMHXL+GMHXL (manufactured by Tosoh Corporation) Column size: each 7.8 mmφ×30 cm, total 90 cm Column temperature: 40°C Flow rate: 0.8 mL / min Injection volume: 100 μL Eluent: tetrahydrofuran Detector: differential refractometer (RI) Standard sample: polystyrene

[0108] (Examples 1 to 16) Photosensitive thermosetting resin compositions containing the components shown in Table 1 (composition amounts in parts by mass) were prepared. Then, a photosensitive coverlay was produced by forming this photosensitive curable resin composition into a sheet and providing a release film on at least one side of the sheet. The photosensitive thermosetting resin composition was formed into a sheet by applying the photosensitive thermosetting resin composition to a thickness of 25 μm onto a release PET film (thickness: 25 μm) using an applicator, and then drying the applied photosensitive thermosetting resin composition under specified curing conditions (temperature: 150°C, time: 60 minutes). Of Examples 1 to 16, Examples 2 to 4, 7 to 9, and 12 to 14 are working examples, and Examples 1, 5, 6, 10, 11, 15, and 16 are comparative examples.

[0109] The details of each component in Table 1 are as follows: Prepolymer (A): carboxylic acid-modified bisphenol-type epoxy acrylate (bisphenol A-type epoxy resin), weight-average molecular weight (Mw) = 10,000, carboxylic acid equivalent 560 g / eq Prepolymer (B-1): carboxylic acid-modified cresol novolac-type epoxy acrylate, weight-average molecular weight (Mw) = 10,000, carboxylic acid equivalent 560 g / eq Prepolymer (B-2): carboxylic acid-modified urethane acrylate, weight-average molecular weight (Mw) = 10,000, carboxylic acid equivalent 1,400 g / eq Photosensitive monomer 1: monomer containing four or more acryloyloxy groups and having a molecular weight of 150 to 2,000, pentaerythritol ethoxytetraacrylate (EO 5 mol): EBECRYL50 manufactured by Daicel Allnex Corporation Photosensitive monomer 2 (urethane acrylate): manufactured by Nippon Kayaku Co., Ltd. UX-0937 (number average molecular weight (Mn) 2000 to 8000, bifunctional) Photosensitive monomer 3 (urethane acrylate): monofunctional monomer (1) produced by the following Production Example 1-1 and Production Example 2-1 Photosensitive monomer 4 (urethane acrylate): monofunctional monomer (2) produced by the following Production Example 2-2 Photosensitive monomer 5 (urethane acrylate): monofunctional monomer (3) produced by the following Production Example 2-3 Photosensitive monomer 6 (acrylate): monofunctional acrylate AM-230G, molecular weight approximately 1000, manufactured by Shin-Nakamura Chemical Co., Ltd. Curing agent: BF ３MEA (boron trifluoride monoethylamine) (Lewis acid amine complex) Photopolymerization initiator: 2,2-dimethoxy-1,2-diphenylethan-1-one Photosensitizer: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide Thermosetting resin: epoxy group equivalent weight 270 g / eq, biphenyl skeleton type epoxy resin

[0110] <Production Example 1-1: Production of Monool (1)> A pressure-resistant reactor equipped with a stirrer and a nitrogen inlet tube was charged with 0.2 g of zinc hexacyanocobaltate-tert-butyl alcohol complex (hereinafter referred to as "DMC-TBA"), which is a composite metal cyanide complex catalyst, and 59 g of n-butanol, which is an initiator, and a nitrogen atmosphere was set at 130 ° C. 3941 g of propylene oxide (hereinafter also referred to as "PO") was added at a constant rate over 7 hours. After confirming that the internal pressure of the pressure-resistant reactor had stopped decreasing, 4000 g of the product was extracted. The main component of the product, excluding by-products and catalyst-derived metals, was polyoxypropylene monool (monool (1)) with a hydroxyl value of 11.2 mg KOH / g (hydroxyl value-based molecular weight: 5008), an average number of hydroxyl groups of 1.03, and a water content of 120 ppm by mass. The resulting product contained 8 ppm by mass of Zn and 2 ppm by mass of Co.

[0111] <Production Example 2-1: Production of Monofunctional Monomer (1)> In a reaction vessel equipped with a stirrer and a nitrogen inlet tube, 928.1 g of the monool (1) obtained in Production Example 1-1 and 26.8 g of 2-acryloyloxyethyl isocyanate (Karenzu AOI, product name of Showa Denko K.K.) were charged and reacted at 70°C for 3 hours in the presence of 0.0955 g of dioctyltin distearate (DOTDS) to obtain a monofunctional monomer (1). The number average molecular weight (Mn) of the obtained monofunctional monomer (1) was 7660. The content of 2-acryloyloxyethyl isocyanate relative to the monool (1) was 100 in terms of index (NCO / OH ratio).

[0112] <Production Example 2-2: Production of monofunctional monomer (2)> Monool (2) was produced in the same manner as in Production Example 1-1, except that the amount of propylene oxide added was changed, and monofunctional monomer (2) was obtained in the same manner as in Production Example 2-1. The number average molecular weight (Mn) of the obtained monofunctional monomer (2) was 10,000. The content of 2-acryloyloxyethyl isocyanate relative to monool (2) was 100 in terms of index (NCO / OH ratio).

[0113] <Production Example 2-3: Production of monofunctional monomer (3)> Monool (3) was produced in the same manner as in Production Example 1-1, except that the amount of propylene oxide used was changed, and monofunctional monomer (3) was obtained in the same manner as in Production Example 2-1. The number average molecular weight (Mn) of the obtained monofunctional monomer (3) was 15,000. The content of 2-acryloyloxyethyl isocyanate relative to monool (3) was 100 in terms of index (NCO / OH ratio).

[0114] [(1) Solder Heat Resistance Test Method] A photosensitive coverlay (thickness 25 to 50 μm) was laminated onto a copper-clad board, irradiated with UV light, developed, and cured by heating. The solder bath was then set to 260°C and 288°C, respectively, and the specimen was dipped in each bath for 30 seconds. Visual inspection was performed to check for peeling, swelling, etc. The solder heat resistance was then evaluated according to the following criteria. The evaluation results are shown in Table 1. <Evaluation Criteria> A: No peeling or swelling after dipping at 288°C for 30 seconds B: No peeling or swelling after dipping at 260°C for 30 seconds, and peeling and swelling after dipping at 288°C for 30 seconds C: Peeling and swelling after dipping at 260°C for 30 seconds

[0115] [(2) Adhesion Test Method] The photosensitive coverlay was laminated onto a copper-clad plate, irradiated with UV light, and heat-cured. Then, slits were made in the photosensitive coverlay with a cutter to create 100 (10 x 10) 1 mm or 2 mm square grids. Cellophane adhesive tape was adhered to the grids, and one end of the tape was held perpendicular to the coverlay surface and instantly peeled off. The number of remaining grids was counted, and if 100 remained according to the following criteria, the test was deemed to have passed. The above test method complies with JIS D 0202 (1988) General Rules for Coating Films of Automotive Parts 4.15. The evaluation results, evaluated according to the following criteria, are shown in Table 1. <Evaluation Criteria> A: 100 / 100 clear B: 0 / 100 to 99 / 100 clear

[0116] [(3) Flexibility Test Method] After laminating a photosensitive coverlay on one side of a 25 μm thick polyimide film, the film was exposed to UV light (250 to 500 mj / cm ２ ), and then heat curing at 150°C for 30 to 60 minutes was carried out to prepare a test sample. The photosensitive coverlay surface was placed on the outside and folded 180 degrees in a mountain fold. At this time, a load of 300 gf / cm was applied using a rubber roller. The photosensitive coverlay surface was visually checked for cracks, and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation criteria> A... No cracks B... Cracks present

[0117] [(4) Repeated Bending Test Method] Using a U-shaped planar bending tester (DLDM111LH, manufactured by Yuasa Systems Co., Ltd.), the test sample obtained in (3) was repeatedly bent at approximately halfway along its length. Specifically, the test sample was bent into a U-shape so that the bending radius was 1.5 mm and the Kapton film was facing inward, and then the bending force was released (180° release). This operation was repeated 100,000 times at a rate of 60 times per minute. The appearance of the test sample after the test was visually observed and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation Criteria> A: No whitening, peeling, lifting, or cracking occurred, and there was no change in appearance. B: One or more of whitening, peeling, lifting, or cracking occurred, but the degree was slight and did not pose a practical problem. C: One or more of whitening, peeling, lifting, or cracking occurred significantly, posing a practical problem.

[0118]

[0119] Table 1 shows that when a monofunctional monomer having one (meth)acryloyloxy group per molecule and a number average molecular weight (Mn) of 1,300 to 36,000 is used as the photosensitive monomer, it is possible to produce a photosensitive coverlay that has improved bending properties while maintaining heat resistance and adhesion.

[0120] The present invention has industrial applicability as a photosensitive thermosetting resin composition capable of producing a photosensitive coverlay that has improved foldability while maintaining heat resistance and adhesion, a photosensitive coverlay using the photosensitive thermosetting resin composition, and a flexible printed wiring board using the photosensitive coverlay.

[0121] REFERENCE SIGNS LIST 10 Sheet made of photosensitive thermosetting resin composition 20 Release film 30 Metal foil 40 Substrate 50 Photomask 50a Light-transmitting portion 50b Light-non-transmitting portion 100 Photosensitive coverlay 200 Flexible printed wiring board UV Ultraviolet light

Claims

1. A photosensitive thermosetting resin composition comprising a prepolymer, a photosensitive monomer, a thermosetting resin, and a polymerization initiator, wherein the prepolymer comprises a carboxylic acid-modified bisphenol-type epoxy (meth)acrylate, and the photosensitive monomer comprises a monofunctional monomer having one (meth)acryloyloxy group per molecule and having a number average molecular weight (Mn) of 1,300 to 36,000.

2. The photosensitive thermosetting resin composition according to claim 1, wherein the monofunctional monomer contains a curable component obtained by a urethane reaction between a polyoxyalkylene monool represented by the following formula (1a) and a compound represented by the following formula (1b): (In formula (1a), R １２ is an alkylene group having 2 to 4 carbon atoms, and R １３ is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms, and b is an integer of 20 to 600. In formula (1b), R １１ is a hydrogen atom or a methyl group, and a is an integer of 1 to 4.

3. The photosensitive thermosetting resin composition according to claim 1 or 2, wherein the photosensitive monomer further contains pentaerythritol ethoxytetraacrylate.

4. The photosensitive thermosetting resin composition according to claim 1 or 2, wherein the prepolymer further contains at least one of a carboxylic acid-modified cresol novolac epoxy (meth)acrylate and a carboxylic acid-modified urethane (meth)acrylate.

5. The photosensitive thermosetting resin composition according to claim 4, wherein the mass ratio of the carboxylic acid-modified bisphenol-type epoxy(meth)acrylate to the sum of the carboxylic acid-modified cresol novolac-type epoxy(meth)acrylate and the carboxylic acid-modified urethane(meth)acrylate is 80:20 to 20:

80.

6. The photosensitive thermosetting resin composition according to claim 1 or 2, wherein the content of the photosensitive monomer relative to 100 parts by mass of the prepolymer is 5 parts by mass or more and less than 100 parts by mass.

7. The photosensitive thermosetting resin composition according to claim 1 or 2, wherein the thermosetting resin is an epoxy resin having an epoxy group equivalent of 100 g / eq or more and less than 600 g / eq and containing two or more epoxy groups.

8. The photosensitive thermosetting resin composition according to claim 1 or 2, further comprising a curing agent, wherein the content of the curing agent per 100 parts by mass of the thermosetting resin is 0.1 parts by mass or more and less than 1.0 part by mass.

9. The photosensitive thermosetting resin composition according to claim 1 or 2, wherein the polymerization initiator comprises a nitrogen-free photopolymerization initiator and a photosensitizer.

10. A photosensitive coverlay, which is formed into a sheet from the photosensitive thermosetting resin composition according to claim 1 or 2.

11. A flexible printed wiring board in which the photosensitive coverlay according to claim 10 is provided on a metal foil on which a circuit is formed.

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