Photosensitive resin composition, photocured product of photosensitive resin composition, and printed wiring board having the photocured product

Abstract

To provide a photosensitive resin composition capable of forming a photocured product which is excellent in flexibility, resolution and adhesion while having a high reflectance.SOLUTION: The photosensitive resin composition contains (A) a carboxyl group-containing photosensitive resin, (B) a reactive diluent, (C) a photopolymerization initiator, (D) titanium oxide, and (E) an epoxy compound. The reactive diluent (B) contains (B1) polypropylene glycol diacrylate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a photosensitive resin composition, in particular a photosensitive resin composition useful as an insulating coating for circuit boards such as printed wiring boards, a photocured product of the photosensitive resin composition, and a printed wiring board having a coating obtained by photocuring the photosensitive resin composition. [Background technology]

[0002] Wiring boards, such as printed wiring boards using rigid or flexible substrates, are used to form conductor circuit patterns on the substrate and mount electronic components to the soldering lands of the pattern, with the circuit area excluding the soldering lands being covered with an insulating film (e.g., solder resist film). This prevents solder from adhering to unnecessary areas when soldering electronic components to the printed wiring board, and also prevents the circuit (conductor) from being corroded by oxidation or humidity due to direct exposure to air.

[0003] Printed wiring boards are also used as substrates for mounting light-emitting diode elements (LEDs) and the like, and the insulating coating formed on the mounting surface is required to have functions such as adhesion to the printed wiring board substrate and resolution. Furthermore, in applications requiring high reflectivity in printed wiring boards, photosensitive resin compositions containing a white colorant such as titanium oxide are mainly used as the photosensitive resin composition for forming the insulating coating.

[0004] However, photosensitive resin compositions containing white colorants such as titanium oxide can discolor due to light or heat, reducing the optical reflectance of the resulting insulating coating. Therefore, a solder resist composition capable of suppressing the reduction in optical reflectance due to discoloration has been proposed (Patent Document 1). Patent Document 1 discloses a photocurable and thermosetting solder resist composition containing a carboxyl group-containing resin without an aromatic ring, a photopolymerization initiator, an epoxy compound, rutile titanium oxide, and a diluent. Patent Document 1 claims that by using a carboxyl group-containing resin without an aromatic ring and rutile titanium oxide as a white pigment, discoloration of the photosensitive resin due to light, which is caused by the photoactivity of the aromatic rings and titanium oxide in the photosensitive resin, can be suppressed, and high reflectance can be maintained for a long period of time.

[0005] In recent years, due to the miniaturization of electronic devices in which printed wiring boards are mounted, the installation space for printed wiring boards has become narrower, and flexible printed wiring boards are sometimes used as printed wiring boards. The insulating coating of such flexible printed wiring boards is required to be flexible (flexible) so as not to impair the flexible performance of the printed wiring board.

[0006] On the other hand, conventional white photosensitive solder resists such as those disclosed in Patent Document 1 use, as a reactive diluent, an acrylic monomer (e.g., dipentaerythritol hexaacrylate) with a DPHA (dipentaerythritol hexaacrylate) skeleton, which reduces the decrease in reflectance. However, the use of an acrylic monomer with a DPHA skeleton leads to a decrease in flexibility and resolution, so there is room for improvement in maintaining these functions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-322546 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above circumstances, an object of the present invention is to provide a photosensitive resin composition that can form a photocured product having high reflectance and excellent flexibility, resolution, and adhesion. [Means for solving the problem]

[0009] A photosensitive resin composition according to an embodiment of the present invention contains (A) a carboxyl group-containing photosensitive resin, (B) a reactive diluent, (C) a photopolymerization initiator, (D) titanium oxide, and (E) an epoxy compound, and the (B) reactive diluent contains (B1) polypropylene glycol diacrylate.

[0010] In one embodiment of the present invention, the (B) reactive diluent further contains (B2) a caprolactone-modified (meth)acrylate.

[0011] In one embodiment of the present invention, the polypropylene glycol diacrylate (B1) is represented by the following formula (1): [ka] (In formula (1), n ​​is an integer of 10 to 15.)

[0012] In one embodiment of the present invention, the content of the polypropylene glycol diacrylate (B1) relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A) is 5 parts by mass or more and 40 parts by mass or less.

[0013] Another aspect of the present invention is a photocured product of the above photosensitive resin composition.

[0014] Another aspect of the present invention is a printed wiring board comprising the photocured product. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a photosensitive resin composition capable of forming a photocured product having high reflectance and excellent flexibility, resolution, and adhesion, as well as a photocured product and a printed wiring board produced using the same. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail. The photosensitive resin composition of the present invention contains (A) a carboxyl group-containing photosensitive resin, (B) a reactive diluent, (C) a photopolymerization initiator, (D) titanium oxide, and (E) an epoxy compound. In the photosensitive resin composition of the present invention, the (B) reactive diluent contains (B1) polypropylene glycol diacrylate.

[0017] (A) Carboxyl group-containing photosensitive resin The carboxyl group-containing photosensitive resin is not particularly limited in its chemical structure as long as it is a photocurable resin having a free carboxyl group, but examples thereof include carboxyl group-containing resins having one or more photosensitive unsaturated double bonds.Specific examples of the carboxyl group-containing photosensitive resin include (meth)acrylic photocurable resins (hereinafter also referred to as (meth)acrylic resins) whose constituent units are monomers having a (meth)acryloyl group.One type of carboxyl group-containing photosensitive resin may be used alone, or two or more types may be used in combination.

[0018] Examples of (meth)acrylic resins include homopolymers of alkyl (meth)acrylates and copolymers containing alkyl (meth)acrylates as the main monomer and sub-monomers copolymerizable with the main monomer. Such copolymers may be (meth)acrylic polymers obtained by copolymerizing (meth)acrylates with ethylenically unsaturated carboxylic acids, or may be copolymerized with other monomers having copolymerizable ethylenically unsaturated groups. Furthermore, from the viewpoint of improving photocurability, (meth)acrylic resins having (meth)acryloyl groups (preferably acryloyl groups) in the side chains may be used.

[0019] Examples of (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, lauryl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-(dimethylamino)ethyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate, and 2,2,3,3-tetrafluoropropyl (meth)acrylate.

[0020] As the ethylenically unsaturated carboxylic acid, monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid are preferably used, and dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid, as well as half esters thereof, can also be used. Of these, acrylic acid and methacrylic acid are particularly preferred.

[0021] Other copolymerizable monomers having an ethylenically unsaturated group include, for example, styrene, α-methylstyrene, p-methylstyrene, p-ethylstyrene, p-methoxystyrene, p-ethoxystyrene, p-chlorostyrene, p-bromostyrene, (meth)acrylonitrile, (meth)acrylamide, diacetone acrylamide, vinyl toluene, vinyl acetate, and vinyl-n-butyl ether.

[0022] The (meth)acrylic resin may contain a monomer unit derived from an acidic group-containing monomer having an acidic group. For example, in addition to a (meth)acryloyl group, such a (meth)acrylic resin may further contain at least one monomer unit selected from the group consisting of a phenolic hydroxyl group, a carboxyl group, a sulfo group, a phosphono group, and a boronic acid group. This effectively enhances the removability of uncured portions in the development step, thereby improving developability and shortening development time. The acidic group may be bonded to a carbon atom in the main chain or a carbon atom in the side chain.

[0023] The acid value of the carboxyl group-containing photosensitive resin is not particularly limited, but its lower limit is preferably 30 mgKOH / g, more preferably 40 mgKOH / g, and particularly preferably 50 mgKOH / g from the viewpoint of reliable alkaline development. On the other hand, the upper limit of the acid value is preferably 150 mgKOH / g from the viewpoint of reliable prevention of dissolution of the exposed area by the alkaline developer, and more preferably 120 mgKOH / g, and particularly preferably 100 mgKOH / g from the viewpoint of preventing deterioration of the moisture resistance and electrical properties of the photocured product.

[0024] The mass average molecular weight of the carboxyl group-containing photosensitive resin is not particularly limited, but the lower limit is preferably 5,000, particularly 10,000, from the viewpoints of toughness, mechanical strength, and dryness to touch of the photocured product. On the other hand, the upper limit of the mass average molecular weight is preferably 1,000,000, more preferably 50,000, particularly preferably 30,000, from the viewpoint of reliable alkaline development. The mass average molecular weight is measured at room temperature using gel permeation chromatography and calculated in terms of polystyrene.

[0025] The carboxyl group-containing photosensitive resin preferably includes a (meth)acrylic resin containing a (meth)acryloyl group and a carboxyl group, and more preferably includes a (meth)acrylic resin having an acidic group. Commercially available (meth)acrylic resins having an acidic group include Cyclomer P (registered trademark) ACA 200M, Z230AA, Z250, Z251, Z300, Z320, and Z254F manufactured by Daicel-Allnex Corporation. The content of the carboxyl group-containing photosensitive resin is not particularly limited, and is preferably 10% by mass or more and 70% by mass or less, and particularly preferably 20% by mass or more and 50% by mass or less, based on 100% by mass of the solid content of the photosensitive resin composition.

[0026] (B) Reactive diluent The photosensitive resin composition of the present invention contains, as a reactive diluent, a photopolymerizable monomer, which is a compound having at least one polymerizable double bond per molecule, and preferably two or more polymerizable double bonds per molecule. One of the reactive diluents contains (B1) polypropylene glycol diacrylate, and such polypropylene glycol diacrylate preferably has a structure represented by the following formula (1): In formula (1), n ​​is an integer of 10 to 15, and preferably an integer of 11 to 13.

[0027] [ka]

[0028] The content of polypropylene glycol diacrylate is not particularly limited, but from the viewpoint of improving flexibility, the lower limit is preferably 5 parts by mass, more preferably 10 parts by mass, and particularly preferably 15 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, while the upper limit is preferably 60 parts by mass, more preferably 55 parts by mass, and particularly preferably 50 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin.

[0029] The reactive diluent may further contain (B2) caprolactone-modified (meth)acrylate in addition to (B1) polypropylene glycol diacrylate. By using (B1) polypropylene glycol diacrylate and (B2) caprolactone-modified (meth)acrylate in combination as the reactive diluent, a photosensitive resin composition capable of forming a photocured product having excellent reflectance and flexibility can be obtained.

[0030] The caprolactone-modified (meth)acrylate is not particularly limited as long as it is a caprolactone-modified (meth)acrylate compound, and examples thereof include caprolactone-modified polyfunctional (meth)acrylates. Examples of caprolactone-modified polyfunctional (meth)acrylates include pentafunctional or higher (meth)acrylates such as caprolactone-modified dipentaerythritol hexa(meth)acrylate and caprolactone-modified dipentaerythritol penta(meth)acrylate, tetrafunctional (meth)acrylates such as caprolactone-modified pentaerythritol tetra(meth)acrylate, caprolactone-modified ditrimethylolpropane tetra(meth)acrylate, and caprolactone-modified dipentaerythritol tetra(meth)acrylate, and difunctional or trifunctional (meth)acrylates such as caprolactone-modified pentaerythritol tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, caprolactone-modified dipentaerythritol tri(meth)acrylate, and caprolactone-modified dicyclopentenyl di(meth)acrylate. These may be used alone or in combination of two or more.

[0031] Among these, pentafunctional or higher caprolactone-modified (meth)acrylates are preferred, hexafunctional caprolactone-modified (meth)acrylates are more preferred, and caprolactone-modified dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0032] The molecular weight (g / mol) of the caprolactone-modified (meth)acrylate is not particularly limited, but is preferably 1,000 or more and 5,000 or less, and from the viewpoint of further improving flexibility, is more preferably 1,300 or more and 2,500 or less, and particularly preferably 1,500 or more and 2,200 or less.

[0033] The content of the caprolactone-modified (meth)acrylate is not particularly limited, but from the viewpoint of further improving flexibility, the lower limit is preferably 5 parts by mass, more preferably 10 parts by mass, and particularly preferably 20 parts by mass relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, while the upper limit is preferably 100 parts by mass, more preferably 90 parts by mass, and particularly preferably 85 parts by mass relative to 100 parts by mass of the carboxyl group-containing photosensitive resin.

[0034] In addition, the mass ratio of (B1) polypropylene glycol diacrylate to (B2) caprolactone-modified (meth)acrylate is preferably 1:4 to 3:1 in terms of resolution, and more preferably 1:3 to 2:1.

[0035] In addition to (B1) polypropylene glycol diacrylate, (B3) a (meth)acrylate compound not modified with caprolactone may also be used as the reactive diluent. The (meth)acrylate compound not modified with caprolactone is not particularly limited, and examples thereof include 2-hydroxyethyl methacrylate, phenoxyethyl methacrylate, diethylene glycol monomethacrylate, 2-hydroxy-3-phenoxypropyl acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentyl glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and hydroxypivalic acid neopentyl glycol di(meth)acrylate. Examples of the acrylate include methylolpropane tri(meth)acrylate, ethylene oxide-modified phosphate di(meth)acrylate, allylated cyclohexyl di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, propionic acid-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc. These may be used alone or in combination of two or more.

[0036] The total content of the reactive diluent is not particularly limited, and the lower limit is preferably 5 parts by mass, more preferably 15 parts by mass, and particularly preferably 25 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, while the upper limit is preferably 130 parts by mass, more preferably 120 parts by mass, and particularly preferably 110 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin.

[0037] (C) Photopolymerization initiator The photopolymerization initiator is not particularly limited as long as it is a commonly used one, and specific examples thereof include 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime), and (Z)-(9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone. Examples of suitable oxime ester compounds include O-acetyloxime, 2-(acetyloxyiminomethyl)thioxanthen-9-one, 1,8-octanedione, 1,8-bis[9-ethyl-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyloxime), and 1,8-octanedione, 1,8-bis[9-(2-ethylhexyl)-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyloxime). Examples of suitable acetophenone compounds include acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, and 2,2-diethoxy-2-phenylacetophenone.Further, examples of photopolymerization initiators other than those mentioned above include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-methyl-4'-(methylthio)-2-morpholinopropiophenone, 2-(dimethylamino)-1-(4-morpholinophenyl)-2-benzyl-1-butanone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-t-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethyl ketal, acetophenone dimethyl ketal, p-dimethylaminobenzoic acid ethyl ester, etc. These may be used alone or in combination of two or more.

[0038] The content of the photopolymerization initiator is not particularly limited, but the lower limit is preferably 1.0 part by mass, more preferably 2.0 parts by mass, and particularly preferably 3.0 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, while the upper limit is preferably 12.0 parts by mass, more preferably 10.0 parts by mass, and particularly preferably 8.0 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin.

[0039] (D) Titanium oxide Titanium oxide is a white colorant for whitening a photocured product. Examples of titanium oxide include anatase titanium oxide and rutile titanium oxide. Anatase titanium oxide and rutile titanium oxide have different crystal structures. Either anatase titanium oxide or rutile titanium oxide can be used. Although anatase titanium oxide has a higher degree of whiteness than rutile titanium oxide, it has photocatalytic activity and may cause discoloration of the resin in the photosensitive resin composition over a long period of time. In contrast, rutile titanium oxide has almost no photocatalytic activity and can prevent discoloration of the photocured product over a long period of time. Therefore, from the viewpoint of preventing discoloration of the photocured product, it is preferable that the titanium oxide be rutile titanium oxide.

[0040] The titanium oxide may be in the form of particles, and the average particle size of the titanium oxide is not particularly limited, but is, for example, from 0.01 μm to 1.0 μm.

[0041] Examples of anatase titanium dioxide include "Tipake A-100" and "Tipake A-220" manufactured by Ishihara Sangyo Kaisha, Ltd. Examples of rutile titanium dioxide include "TR-600," "TR-700," "TR-750," and "TR-840" manufactured by Fuji Titanium Industries Co., Ltd.; "R-550," "R-580," "R-630," "R-820," "CR-50," "CR-60," "CR-63," "CR-80," "CR-90," "CR-93," "PF-671," "PF-690," "PF-691," "PF-711," "PF-726," "PF-728," and "PF-739" manufactured by Ishihara Sangyo Kaisha; and "KR-270," "KR-310," and "KR-380" manufactured by Titanium Industries Co., Ltd.

[0042] The content of titanium oxide is not particularly limited, but the lower limit is preferably 100 parts by mass, more preferably 120 parts by mass, and particularly preferably 140 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, from the viewpoint of reliably obtaining excellent light reflectance, while the upper limit is preferably 500 parts by mass, more preferably 400 parts by mass, and particularly preferably 300 parts by mass, from the viewpoint of reliably obtaining excellent alkaline developability and preventing a decrease in coatability.

[0043] (E) Epoxy compounds Epoxy compounds contribute to increasing the crosslink density of the photocured product, thereby achieving a photocured product with sufficient strength and hardness. Examples of epoxy compounds include epoxy resins. Examples of epoxy resins include rubber-modified epoxy resins such as biphenyl-type epoxy resins, bisphenol A-type epoxy resins, cresol novolac-type epoxy resins, biphenylaralkyl-type epoxy resins, phenylaralkyl-type epoxy resins, naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, and silicone-modified epoxy resins; ε-caprolactone-modified epoxy resins; phenol novolac-type epoxy resins; cycloaliphatic polyfunctional epoxy resins; glycidyl ester-type polyfunctional epoxy resins; glycidylamine-type polyfunctional epoxy resins; heterocyclic polyfunctional epoxy resins; bisphenol-modified novolac-type epoxy resins; polyfunctional-modified novolac-type epoxy resins; condensation-type epoxy resins of phenols and aromatic aldehydes having phenolic hydroxyl groups; and triisocyanurate-type epoxy resins. These epoxy compounds may be used alone or in combination of two or more.

[0044] The content of the epoxy compound is not particularly limited, but the lower limit is preferably 5 parts by mass, more preferably 10 parts by mass, and particularly preferably 15 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, while the upper limit is preferably 80 parts by mass, more preferably 70 parts by mass, and particularly preferably 60 parts by mass.

[0045] In addition to the components (A) to (E) described above, the photosensitive resin composition of the present invention may contain, as necessary, various other components, such as a flame retardant, a curing accelerator, an additive, a non-reactive diluent, etc. The amount of these other components added is not particularly limited as long as it does not impair the purpose and effects of the present invention, and they can be added in an appropriate amount depending on the purpose of addition.

[0046] Printed wiring boards are often equipped with light sources and electronic components that generate a large amount of heat. Therefore, by incorporating a flame retardant into a photosensitive resin composition, flame retardancy can be imparted to a photocured product of the photosensitive resin composition. Examples of flame retardants include phosphorus-based flame retardants such as organic phosphates.Examples of phosphorus-based flame retardants include halogen-containing phosphorus compounds such as tris(chloroethyl)phosphate, tris(2,3-dichloropropyl)phosphate, tris(2-chloropropyl)phosphate, tris(2,3-bromopropyl)phosphate, tris(bromochloropropyl)phosphate, 2,3-dibromopropyl-2,3-chloropropyl phosphate, tris(tribromophenyl)phosphate, tris(dibromophenyl)phosphate, and tris(tribromoneopentyl)phosphate. Phosphate esters; non-halogenated aliphatic phosphate esters such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, and tributoxyethyl phosphate; triphenyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, tricresyl phosphate, trixylenyl phosphate, xylenyl diphenyl phosphate, tris(isopropylphenyl) phosphate, isopropylphenyl diphenyl phosphate, and diisopropyl phosphate. Examples of suitable phosphine compounds include non-halogen aromatic phosphate esters such as propylphenylphenyl phosphate, tris(trimethylphenyl)phosphate, tris(t-butylphenyl)phosphate, hydroxyphenyldiphenylphosphate, and octyldiphenylphosphate; metal salts of phosphinic acid such as aluminum trisdiethylphosphinate, aluminum trismethylethylphosphinate, aluminum trisdiphenylphosphinate, zinc bisdiethylphosphinate, zinc bismethylethylphosphinate, zinc bisdiphenylphosphinate, titanyl bisdiethylphosphinate, titanium tetrakisdiethylphosphinate, titanyl bismethylethylphosphinate, titanium tetrakismethylethylphosphinate, titanyl bisdiphenylphosphinate, and titanium tetrakisdiphenylphosphinate; and phosphine oxide compounds such as diphenylvinylphosphine oxide, triphenylphosphine oxide, trialkylphosphine oxide, and tris(hydroxyalkyl)phosphine oxide.

[0047] Examples of the curing accelerator include dicyandiamide (DICY) and its derivatives, melamine and its derivatives, boron trifluoride-amine complex, organic acid hydrazide, diaminomaleonitrile (DAMN) and its derivatives, guanamine and its derivatives, amine imide, and polyamine.

[0048] The additive may include an acrylic polymer.

[0049] The non-reactive diluent is a component that is blended to appropriately adjust the viscosity, drying property, coatability, etc. of the photosensitive resin composition. Examples of non-reactive diluents include organic solvents. Examples of organic solvents include ketones such as methyl ethyl ketone; aromatic hydrocarbons such as benzene, toluene, and xylene; alcohols such as methanol, n-propanol, isopropanol, and cyclohexanol; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; cellosolves such as cellosolve and butyl cellosolve; carbitols such as carbitol and butyl carbitol; and esters such as ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, and ethyl diglycol acetate. These organic solvents may be used alone or in combination.

[0050] The method for producing the photosensitive resin composition of the present invention is not limited to a specific method, but can be, for example, produced by blending the above components in a predetermined ratio and then kneading, stirring, and mixing at room temperature (e.g., 25°C) using a kneading means such as a triple roll mill, ball mill, sand mill, bead mill, or kneader, or a stirring or mixing means such as a super mixer or planetary mixer. Furthermore, prior to the kneading, stirring, and mixing, pre-kneading or pre-mixing may be carried out using a stirrer, if necessary.

[0051] Next, an example of a method for using the photosensitive resin composition of the present invention will be described. Here, a method is described in which the photosensitive resin composition of the present invention is applied as an insulating film (e.g., a solder resist film) onto a flexible printed wiring board having a circuit pattern formed by etching copper foil on a substrate.

[0052] The photosensitive resin composition of the present invention is applied to a flexible printed wiring board to a desired thickness using a known coating method, such as screen printing, bar coating, blade coating, knife coating, roll coating, gravure coating, or spray coating, to form a coating film. After application, if the photosensitive resin composition contains a non-reactive diluent, the composition is pre-dried by heating at a temperature of approximately 60 to 90°C for approximately 15 to 60 minutes to volatilize the non-reactive diluent, forming a tack-free coating film. Next, a negative film (photomask) having a pattern that makes the circuit pattern transparent except for the lands is adhered to the coating film, and the coating film is photocured by irradiating it with active energy rays (e.g., ultraviolet rays with a wavelength of 300 to 400 nm) from above to form a photocured film. The coating film is then developed by removing the unexposed areas corresponding to the lands with a dilute alkaline aqueous solution. Examples of development methods include spraying and showering. Examples of dilute alkaline aqueous solutions include a 0.5 to 5% by weight sodium carbonate aqueous solution. Next, the developed photocured film is thermally cured by performing a heat curing treatment (post-cure) for 20 to 80 minutes in a hot air circulation dryer or the like at 130 to 170°C, and a photocured product of the photosensitive resin composition having the desired pattern can be formed on the flexible printed wiring board. [Example]

[0053] Examples of the photosensitive resin composition of the present invention will be described below, but the present invention is not limited to these examples as long as they do not depart from the spirit of the invention.

[0054] <Examples 1 to 6, Comparative Examples 1 to 3> The components shown in Table 1 below were blended in the proportions shown in Table 1 below, and mixed and dispersed using a three-roll mill at room temperature (approximately 25°C) to prepare the photosensitive resin compositions used in Examples 1 to 6 and Comparative Examples 1 to 3. Unless otherwise specified, the numbers in Table 1 below indicate parts by mass. Also, blank spaces in Table 1 below mean that no blend was used.

[0055] The details of each component in Table 1 are as follows: <(A) Carboxyl group-containing photosensitive resin> (ACA) Z251: Manufactured by Daicel Allnex <(B) Reactive Diluent> M400: Toagosei M270: Toagosei KAYARAD DPCA-60: Manufactured by Nippon Kayaku Co., Ltd. KAYARAD DPCA-120: Manufactured by Nippon Kayaku Co., Ltd. <(C) Photopolymerization initiator> Omnirad 819: Manufactured by IGM Resins BV DETX: Manufactured by DKSH Japan Omnirad TPO: Manufactured by IGM Resins BV <(D) Titanium oxide> CR-80: Ishihara Sangyo Kaisha <(E) Epoxy Compound> EPICLON 850: DIC <Curing accelerator> Melamine: Nissan Chemical Co., Ltd. <Flame retardant> Exolit® OP-935: Clariant Japan <Non-reactive diluent> ·EDGAC: Manufactured by Sanyo Kaseihin Co., Ltd.

[0056] <Preparation of test specimens for evaluation> Substrate: FCCL (adhesiveless copper clad laminate) "ESPANEX (registered trademark)" manufactured by Nippon Steel Chemical & Material Co., Ltd. Polyimide resin thickness: 25 μm, conductor (copper foil) thickness: 12 μm Substrate surface treatment: Dilute sulfuric acid treatment (5% by mass) Coating method: Screen printing, dry film thickness 30μm Pre-drying: 80°C, 20 minutes Exposure (light curing): 250 mJ / cm on the coating 2 Oak D exposure device "MMs-640B" Light source: Metal halide lamp Alkaline development: 1% by weight sodium carbonate aqueous solution, solution temperature 30°C, Spray pressure: 0.2 MPa, development time: 60 seconds Post-cure (heat curing): 150°C, 60 minutes

[0057] <Evaluation of test specimens> (1)Reflectance Initial value The reflectance of the cured coating film immediately after preparation of the test piece was measured at a wavelength of 450 nm using a spectrophotometer (CM-700d, manufactured by Konica Minolta). After N2 reflow The test pieces were subjected to a reflow treatment in a reflow furnace at a reflow temperature of 240°C for 30 seconds, and then the reflectance at a wavelength of 450 nm was measured using a spectrophotometer (CM-700d, manufactured by Konica Minolta) and evaluated based on the following criteria. ◎: Reflectance after reflow is 90% or more Good: Reflectance after reflow is 85% or more and less than 90% △: Reflectance after reflow is 80% or more and less than 85% ×: Reflectance after reflow is less than 80%

[0058] (2)Flexibility Test pieces were cut into 2.5cm widths and subjected to bending tests at curvature radii of 1, 2, 3, 4, 5, 6, 8 and 10mm diameter with the cured coating facing outwards. The occurrence of cracks in the cured coating was then observed visually and under a microscope at 5-200x magnification, and the occurrence of cracks was evaluated according to the following criteria: ◎: No abnormalities in the cured coating film after bending with a diameter of 1 mm ○: No abnormalities in the cured coating film after bending with a diameter of 2 mm △: No abnormalities in the cured coating film after bending with a diameter of 3 mm ×: Cracks occur in the cured coating when bent with a diameter of 4 to 10 mm

[0059] (3) Adhesion According to JIS-K-5600-5-6, 100 1mm grids (10 x 10) were made on the test piece, and a peeling test (peel test) was carried out using cellophane tape. The peeling state of the grids was visually observed and evaluated based on the following criteria. ◎: No peeling was observed in 95 or more out of 100 pieces ○: No peeling was observed in 90 to 95 out of 100 pieces △: No peeling observed in 50 to less than 90 out of 100 pieces ×: Less than 50 out of 100 pieces were peeled off

[0060] (4) Resolution (dimensional accuracy) The remaining line width of the exposed portion of the photosensitive resin composition formed on Cu foil through a photomask (line width 50 to 200 μm) was visually confirmed and evaluated based on the following criteria. ◎: Line width 50μm or more and less than 80μm ○: Line width 80μm or more and less than 100μm △: Line width 100 μm or more and less than 120 μm ×: Line width 120 μm or more

[0061] The evaluation results of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0062] [Table 1]

[0063] As can be seen from Table 1, Examples 1 to 6, in which polypropylene glycol diacrylate was contained as a reactive diluent in the photosensitive resin composition, all exhibited high reflectance and were evaluated as "Fair" or better in the tests for flexibility, resolution, and adhesion. Therefore, it was found that the photosensitive resin compositions of Examples 1 to 6 were capable of producing photocured products that had high reflectance and excellent flexibility, resolution, and adhesion.

[0064] Furthermore, Examples 1 to 3, which contained polypropylene glycol diacrylate and caprolactone-modified (meth)acrylate having a molecular weight of 1900 to 2000 as the reactive diluent, exhibited high reflectance and further improved flexibility. In particular, Examples 1 and 2 were rated as "Excellent" in all tests of reflectance, flexibility, resolution, and adhesion. Furthermore, a comparison between Examples 1 to 5 and Example 6 revealed that all of Examples 1 to 5, in which the content of polypropylene glycol diacrylate per 100 parts by mass of the carboxyl group-containing photosensitive resin was 10 parts by mass or more and 20 parts by mass or less, exhibited high reflectance of 90% or more.

[0065] In contrast, in Comparative Examples 1 to 3, in which polypropylene glycol diacrylate was not contained as a reactive diluent in the photosensitive resin composition, all of the compositions were poor in flexibility. [Industrial Applicability]

[0066] The photosensitive resin composition of the present invention can form a photocured product that has high reflectance and excellent flexibility, resolution, and adhesion, and is therefore highly useful in the field of insulating coatings (e.g., solder resist films) applied to wiring boards, for example.

Claims

1. (A) a carboxyl group-containing photosensitive resin, (B) a reactive diluent, (C) a photopolymerization initiator, (D) titanium oxide, and (E) an epoxy compound; A photosensitive resin composition, characterized in that the (B) reactive diluent contains (B1) polypropylene glycol diacrylate.

2. The photosensitive resin composition according to claim 1, wherein the reactive diluent (B) further contains a caprolactone-modified (meth)acrylate (B2).

3. 3. The photosensitive resin composition according to claim 1, wherein the polypropylene glycol diacrylate (B1) is represented by the following formula (1): 【Chemical 1】 (In formula (1), n ​​is an integer of 10 to 15.)

4. 3. The photosensitive resin composition according to claim 1, wherein the content of the polypropylene glycol diacrylate (B1) relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A) is 5 parts by mass or more and 60 parts by mass or less.

5. A photocured product of the photosensitive resin composition according to claim 1 or 2.

6. A printed wiring board comprising the photocured product according to claim 5 .

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