Photosensitive resin composition, photocured product of the photosensitive resin composition, and printed circuit 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, particularly 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 Art

[0002] Wiring boards such as printed wiring boards using rigid substrates or flexible substrates are used to form a pattern of a conductor circuit on the substrate and mount electronic components on the soldering lands of the pattern. The circuit portions excluding the soldering lands are coated with an insulating film (for example, a solder resist film). This prevents solder from adhering to unnecessary portions when soldering electronic components to the printed wiring board, and also prevents the circuit (conductor) from being directly exposed to air and corroded by oxidation or humidity.

[0003] Also, printed wiring boards are used as mounting substrates for light-emitting diode elements (LEDs) and the like, and the insulating film formed on the mounting surface is required to have functions such as adhesion and resolution to the substrate of the printed wiring board. Further, in applications where a high reflectance is required for printed wiring boards, a photosensitive resin composition containing a white coloring agent such as titanium oxide is mainly used as the photosensitive resin composition for forming the insulating film.

[0004] However, in the case of photosensitive resin compositions containing white colorants such as titanium dioxide, discoloration due to light or heat can occur, reducing the light reflectivity of the resulting insulating film. Therefore, a solder resist composition that can suppress the reduction in light reflectivity due to discoloration has been proposed (Patent Document 1). Patent Document 1 discloses a photocurable and thermosetting solder resist composition comprising a carboxyl group-containing resin without aromatic rings, a photopolymerization initiator, an epoxy compound, rutile-type titanium dioxide, and a diluent. Patent Document 1 states that by using a carboxyl group-containing resin without aromatic rings and rutile-type titanium dioxide as a white pigment, discoloration of the resin due to light caused by the aromatic rings of the photosensitive resin and the photoactivity of titanium dioxide can be suppressed, and high reflectivity can be maintained for a long period of time.

[0005] Furthermore, in recent years, due to the miniaturization of electronic devices on which printed circuit boards (PCBs) are mounted, the installation space for PCBs has become smaller, and flexible PCBs are sometimes used as PCBs. The insulating coating of such flexible PCBs requires flexibility to avoid impairing the flexible properties of the PCB.

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

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-322546 [Overview of the project] [Problems that the invention aims to solve]

[0008] In view of the above circumstances, the present invention aims to provide a photosensitive resin composition that can form a photocurable product having high reflectivity while exhibiting excellent flexibility, resolution, and adhesion. [Means for solving the problem]

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

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

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

[0012] In one embodiment of the present invention, the content of (B1) polypropylene glycol diacrylate per 100 parts by mass of (A) carboxyl group-containing photosensitive resin 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-mentioned photosensitive resin composition.

[0014] Another aspect of the present invention is a printed circuit board comprising the above-mentioned photocured material. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a photosensitive resin composition that can form a photocured product having high reflectivity while exhibiting excellent flexibility, resolution, and adhesion, as well as a photocured product and printed circuit board made using the same. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described in detail below. 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 dioxide, and (E) an epoxy compound. In addition, in the photosensitive resin composition of the present invention, (B) the 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 free carboxyl groups, but examples include carboxyl group-containing resins having one or more photosensitive unsaturated double bonds. Specifically, as the carboxyl group-containing photosensitive resin, for example, a (meth)acrylic photocurable resin (hereinafter also referred to as (meth)acrylic resin) whose constituent unit is a monomer having a (meth)acryloyl group is preferred. The carboxyl group-containing photosensitive resin may be used alone or two or more may be used in appropriate combination.

[0018] Examples of (meth)acrylic resins include alkyl (meth)acrylate homopolymers and copolymers in which alkyl (meth)acrylate is the main monomer and a copolymer containing a co-monomer copolymerizable with the main monomer. Such copolymers may be (meth)acrylic polymers obtained by copolymerizing (meth)acrylate with an ethylenically unsaturated carboxylic acid, and other copolymerizable monomers having ethylenically unsaturated groups may be copolymerized into the polymer. Furthermore, from the viewpoint of improving photocurability, (meth)acrylic resins having (meth)acryloyl groups (preferably acryloyl groups) in the side chains may also be used.

[0019] (Meth)acrylates include, for example, 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, 2,2,3,3-tetrafluoropropyl (meth)acrylate, and the like.

[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, and their half esters can also be used. Among these, acrylic acid and methacrylic acid are particularly preferred.

[0021] Examples of other monomers having a copolymerizable ethylenically unsaturated group include styrene, α-methylstyrene, p-methylstyrene, p-ethylstyrene, p-methoxystyrene, p-ethoxystyrene, p-chlorostyrene, p-bromostyrene, (meth)acrylonitrile, (meth)acrylamide, diacetone acrylamide, vinyltoluene, vinyl acetate, vinyl-n-butyl ether, and the like.

[0022] (Meta)acrylic resins may contain monomer units derived from acidic group-containing monomers having acidic groups. Such (meta)acrylic resins may contain, for example, in addition to the (meth)acryloyl group, at least one monomer unit selected from phenolic hydroxyl groups, carboxyl groups, sulfo groups, phosphono groups, boronic acid groups, etc. Thereby, the removability of the uncured portion in the development step can be effectively enhanced, the developability can be enhanced, and the development time can be shortened. The acidic group may be bonded to a carbon atom of the main chain or a carbon atom of the side chain.

[0023] The acid value of the carboxyl group-containing photosensitive resin is not particularly limited, but its lower limit value is preferably 30 mgKOH / g, more preferably 40 mgKOH / g, and particularly preferably 50 mgKOH / g from the viewpoint of reliable alkali development. On the other hand, the upper limit value of the acid value is preferably 150 mgKOH / g from the viewpoint of surely preventing the dissolution of the exposed portion by the alkali developer, more preferably 120 mgKOH / g, and particularly preferably 100 mgKOH / g from the viewpoints 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 its lower limit value is preferably 5000, and particularly preferably 10000 from the viewpoints of the toughness, mechanical strength, and touch dryness of the photocured product. On the other hand, the upper limit value of the mass average molecular weight is preferably 1000000, more preferably 50000, and particularly preferably 30000 from the viewpoint of reliable alkali 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 contains a (meth)acrylic resin containing a (meth)acryloyl group and a carboxyl group, and more preferably contains a (meth)acrylic resin having an acidic group. Examples of commercially available (meth)acrylic resins having an acidic group include Cyclomer P(registered trademark) ACA 200M, Z230AA, Z250, Z251, Z300, Z320, Z254F, etc., manufactured by Daicel Ornex. The content of the carboxyl group-containing photosensitive resin is not particularly limited, but for example, it is preferably 10% to 70% by mass, and particularly preferably 20% to 50% by mass, in 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 a photopolymerizable monomer, which is a compound having at least one polymerizable double bond per molecule, preferably two or more polymerizable double bonds per molecule, as a reactive diluent. 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 from 10 to 15, and preferably an integer from 11 to 13.

[0027] [ka]

[0028] The content of polypropylene glycol diacrylate 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 per 100 parts by mass of the carboxyl group-containing photosensitive resin, from the viewpoint of improving flexibility. On the other hand, the upper limit is preferably 60 parts by mass, more preferably 55 parts by mass, and particularly preferably 50 parts by mass per 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 a reactive diluent, a photosensitive resin composition capable of forming a photocurable product with excellent reflectivity and flexibility can be obtained.

[0030] Caprolactone-modified (meth)acrylates are not particularly limited as long as they are caprolactone-modified (meth)acrylate compounds, for example, caprolactone-modified polyfunctional (meth)acrylates. Examples of caprolactone-modified polyfunctional (meth)acrylates include 5- or more functional (meth)acrylates such as caprolactone-modified dipentaerythritol hexa(meth)acrylate and caprolactone-modified dipentaerythritol penta(meth)acrylate; 4-functional (meth)acrylates such as caprolactone-modified pentaerythritol tetra(meth)acrylate, caprolactone-modified ditrimethylolpropane tetra(meth)acrylate and caprolactone-modified dipentaerythritol tetra(meth)acrylate; and 2- to 3-functional (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 individually or in combination of two or more.

[0031] Among these, caprolactone-modified (meth)acrylates with five or more functionalities are preferred, caprolactone-modified (meth)acrylates with six functionalities are more preferred, and caprolactone-modified dipentaerythritol hexa(meth)acrylates are particularly preferred.

[0032] The molecular weight (g / mol) of the caprolactone-modified (meth)acrylate is not particularly limited, but is preferably between 1000 and 5000, more preferably between 1300 and 2500, and particularly preferably between 1500 and 2200, in order to further improve flexibility.

[0033] The content of caprolactone-modified (meth)acrylate is not particularly limited, but the lower limit is preferably 5 parts by mass, more preferably 10 parts by mass, and particularly preferably 20 parts by mass per 100 parts by mass of the carboxyl group-containing photosensitive resin, in order to further improve flexibility. On the other hand, the upper limit is preferably 100 parts by mass, more preferably 90 parts by mass, and particularly preferably 85 parts by mass per 100 parts by mass of the carboxyl group-containing photosensitive resin.

[0034] Furthermore, 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] The reactive diluent may also contain (B3) an unmodified (meth)acrylate compound in addition to (B1) polypropylene glycol diacrylate. The unmodified (meth)acrylate compound is not particularly limited and includes, for example, 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, hydroxypivalate neopentyl glycol di(meth)acrylate, dicyclop Examples include thinyl di(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, and dipentaerythritol hexa(meth)acrylate. These may be used individually or in combination of two or more.

[0036] The total content of the reactive diluent is not particularly limited, but its lower limit is preferably 5 parts by mass, more preferably 15 parts by mass, and particularly preferably 25 parts by mass, per 100 parts by mass of the carboxyl group-containing photosensitive resin. On the other hand, its upper limit is preferably 130 parts by mass, more preferably 120 parts by mass, and particularly preferably 110 parts by mass, per 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. Specifically, for example, 1,2-octanedione, 1-[4-(phenylthio)phenyl]-,2-(O-benzoyl oxime), ethanolone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-,1-(O-acetyl oxime), (Z)-(9-ethyl-6-nitro-9H-carbazole-3-yl)(4-((1-methoxypropane-2-yl)oxy)-2-methylphenyl)methanone Examples of oxime ester compounds include O-acetyloxime, 2-(acetyloxyiminomethyl)thioxanthene-9-one, 1,8-octanedione, 1,8-bis[9-ethyl-6-nitro-9H-carbazole-3-yl]-,1,8-bis(O-acetyloxime), 1,8-octanedione, 1,8-bis[9-(2-ethylhexyl)-6-nitro-9H-carbazole-3-yl]-,1,8-bis(O-acetyloxime). Also, examples of acetophenone compounds include acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, and 2,2-diethoxy-2-phenylacetophenone.Furthermore, other photopolymerization initiators 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, and 1-hydroxycyclohexyl Examples include 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-chlorthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyldimethyl ketal, acetophenone dimethyl ketal, and p-dimethylaminobenzoate ethyl ester. These may be used individually or in combination of two or more.

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

[0039] (D) Titanium oxide Titanium dioxide is a white coloring agent used to whiten photocured products. Examples of titanium dioxide include anatase-type titanium dioxide and rutile-type titanium dioxide. Anatase-type titanium dioxide and rutile-type titanium dioxide differ in their crystal structures. While either anatase-type or rutile-type titanium dioxide can be used, anatase-type titanium dioxide, although whiter than rutile-type titanium dioxide, possesses photocatalytic activity, which can cause discoloration of the resin in the photosensitive resin composition over time. In contrast, rutile-type titanium dioxide has almost no photocatalytic activity, thus preventing discoloration of photocured products over long periods. Therefore, from the viewpoint of preventing discoloration of photocured products, rutile-type titanium dioxide is preferred.

[0040] Titanium dioxide can exist in particulate form. The average particle size of titanium dioxide is not particularly limited, but for example, it is between 0.01 μm and 1.0 μm.

[0041] Examples of anatase-type titanium dioxide include "Typake A-100" and "Typake A-220" from Ishihara Sangyo Co., Ltd. Examples of rutile-type titanium dioxide include "TR-600", "TR-700", "TR-750", and "TR-840" from Fuji Titanium Industries Co., Ltd., and "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" from Ishihara Sangyo Co., Ltd., as well as "KR-270", "KR-310", and "KR-380" from Titanium Industries Co., Ltd.

[0042] The titanium dioxide content is not particularly limited, but its lower limit is preferably 100 parts by mass, more preferably 120 parts by mass, and especially preferably 140 parts by mass, in order to reliably obtain excellent light reflectance per 100 parts by mass of carboxyl group-containing photosensitive resin. On the other hand, its upper limit is preferably 500 parts by mass, more preferably 400 parts by mass, and especially preferably 300 parts by mass, in order to reliably obtain excellent alkali developability and prevent a decrease in coating properties.

[0043] (E) Epoxy compounds Epoxy compounds contribute to increasing the crosslinking density of photocured products, thereby obtaining photocured products with sufficient strength and hardness. Examples of epoxy compounds include epoxy resins. Examples of epoxy resins include biphenyl-type epoxy resins, bisphenol A-type epoxy resins, cresol novolac-type epoxy resins, biphenyl aralkyl-type epoxy resins, phenyl aralkyl-type epoxy resins, naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, rubber-modified epoxy resins such as silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, phenol novolac-type epoxy resins, cyclic aliphatic 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, condensate-type epoxy resins of phenols and aromatic aldehydes having phenolic hydroxyl groups, triisocyanurate-type epoxy resins, and the like. These epoxy compounds may be used individually or in combination of two or more.

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

[0045] In addition to the above-described components (A) to (E), the photosensitive resin composition of the present invention may optionally contain various other components, such as flame retardants, curing accelerators, additives, and non-reactive diluents. The amount of these other components is not particularly limited as long as it does not hinder the purpose or effect of the present invention, and can be added in appropriate amounts according to the purpose of formulation.

[0046] Printed circuit boards sometimes have light sources and high-heat-generating electronic components mounted on them. Therefore, by incorporating a flame retardant into the photosensitive resin composition, flame retardancy can be imparted to the 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-based 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, diiso Examples include non-halogenated aromatic phosphate esters such as propylphenylphenyl phosphate, tris(trimethylphenyl) phosphate, tris(t-butylphenyl) phosphate, hydroxyphenyldiphenyl phosphate, and octyldiphenyl phosphate; metal salts of phosphinic acids such as aluminum trisdiethylphosphinate, aluminum trismethylethylphosphinate, aluminum trisdiphenylphosphinate, zinc bisdiethylphosphinate, zinc bismethylethylphosphinate, zinc bisdiphenylphosphinate, titanyl bisdiethylphosphinate, titanium tetrakisdiethylphosphinate, titanium bismethylethylphosphinate, titanium tetrakismethylethylphosphinate, titanyl bisdiphenylphosphinate, and titanium tetrakisdiphenylphosphinate; and phosphin oxide compounds such as diphenylvinylphosphinate, triphenylphosphinate, trialkylphosphinate, and tris(hydroxyalkyl)phosphinate.

[0047] Examples of curing accelerators include dicyandiamide (DICY) and its derivatives, melamine and its derivatives, boron trifluoride-amine complex, organic acid hydrazides, diaminomaleonitrile (DAMN) and its derivatives, guanamine and its derivatives, amineimides, and polyamines.

[0048] Acrylic polymers can be cited as an example of an additive.

[0049] Non-reactive diluents are components added to appropriately adjust the viscosity, drying properties, coating properties, etc., of a 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, 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 individually or in combination of two or more.

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

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

[0052] The photosensitive resin composition of the present invention is applied to a flexible printed circuit 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, pre-drying is performed by heating at a temperature of about 60-90°C for about 15-60 minutes to volatilize the non-reactive diluent and form a tack-free coating film. Next, a negative film (photomask) having a pattern in which areas other than the lands of the circuit pattern are translucent is placed in close contact with the coating film, and the coating film is photocured by irradiating it with active energy rays (for example, ultraviolet rays in the wavelength range of 300-400 nm) to form a photocured film. After that, the coating film is developed by removing the unexposed areas corresponding to the lands with a dilute alkaline aqueous solution. For example, a spray method or a shower method can be used as the development method. For example, a 0.5-5% by mass aqueous solution of sodium carbonate can be used as the dilute alkaline aqueous solution. Next, by performing a post-curing treatment in a hot air circulating dryer at 130-170°C for 20-80 minutes, the developed photocured film is heat-cured, and a photocured photosensitive resin composition having the desired pattern can be formed on a flexible printed circuit board. [Examples]

[0053] Examples of the photosensitive resin composition of the present invention are described below, but the present invention is not limited to these examples unless it exceeds the spirit of the invention.

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

[0055] Further details regarding each component in Table 1 below are as follows: <(A) Carboxyl group-containing photosensitive resin> • (ACA)Z251: Manufactured by Daicel Ornex Co., Ltd. <(B) Reactive Diluent> • M400: Manufactured by Toagosei Co., Ltd. • M270: Manufactured by Toagosei Co., Ltd. • 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 Co., Ltd. Omnirad TPO: IGM Resins BV Co., Ltd. <(D) Titanium Oxide> • CR-80: Manufactured by Ishihara Sangyo Co., Ltd. <(E) Epoxy Compounds> • EPICLON 850: Manufactured by DIC Corporation <Curing accelerator> • Melamine: Manufactured by Nissan Chemical Corporation <Flame retardant> • Exolit (registered trademark) OP-935: Manufactured by Clariant Japan Co., Ltd. <Non-reactive diluent> ·EDGAC: Manufactured by Sanyo Kaseihin Co., Ltd.

[0056] <Preparation of test specimens for evaluation> • Substrate: FCCL (Adhesive-free 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 • Surface treatment of the substrate: Dilute sulfuric acid treatment (5% by mass) • Coating method: Screen printing, DRY film thickness 30μm Pre-drying: 80°C, 20 minutes • Exposure (photocuring treatment): 250 mJ / cm² on the coating film 2 Oak Corporation's D exposure system "MMs-640B" Light source: Metal halide lamp • Alkaline development: 1% by mass sodium carbonate aqueous solution, solution temperature 30°C, Spray pressure: 0.2 MPa, Development time: 60 seconds • Post-curing (heat curing): 150°C, 60 minutes

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

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

[0059] (3) Adhesion In accordance with JIS-K-5600-5-6, 100 grid patterns (10 x 10) of 1 mm squares were placed on a test specimen, and a peeling test (peel test) was performed using cellophane tape. The peeling state of the grid patterns was observed visually and evaluated based on the following criteria. ◎: No peeling observed in 95 out of 100 items. ○: No peeling observed in 90 to 95 out of 100 samples. △: No peeling observed in 50 to 90 out of 100 pieces. ×: Less than 50 out of 100 showed no peeling.

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

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

[0062] [Table 1]

[0063] As shown in Table 1 above, in Examples 1 to 6, which contain polypropylene glycol diacrylate as a reactive diluent in the photosensitive resin composition, all showed high reflectivity and received a rating of "△" or higher in all tests for flexibility, resolution, and adhesion. Therefore, it was found that the photosensitive resin compositions of Examples 1 to 6 can produce photocured products with high reflectivity while also exhibiting excellent flexibility, resolution, and adhesion.

[0064] Furthermore, in Examples 1 to 3, which included polypropylene glycol diacrylate and caprolactone-modified (meth)acrylate with a molecular weight of 1900 to 2000 as reactive diluents, high reflectivity was observed, along with improved flexibility. In particular, Examples 1 and 2 received an "◎" rating in all tests for reflectivity, flexibility, resolution, and adhesion. Moreover, a comparison of Examples 1 to 5 and Example 6 showed that in Examples 1 to 5, where the polypropylene glycol diacrylate content was 10 to 20 parts by mass per 100 parts by mass of carboxyl group-containing photosensitive resin, all exhibited a high reflectivity of 90% or more.

[0065] In contrast, Comparative Examples 1 to 3, which did not contain polypropylene glycol diacrylate as a reactive diluent in the photosensitive resin composition, all exhibited inferior flexibility. [Industrial applicability]

[0066] The photosensitive resin composition of the present invention can form a photocured product that has high reflectivity while also exhibiting excellent flexibility, resolution, and adhesion. Therefore, it is highly valuable for applications such as insulating coatings (e.g., solder resist films) applied to wiring boards.

Claims

1. (A) a carboxyl group-containing photosensitive resin, (B) a reactive diluent, (C) a photopolymerization initiator, (D) titanium dioxide, and (E) an epoxy compound. The (B) reactive diluent comprises (B1) polypropylene glycol diacrylate, A photosensitive resin composition characterized in that the (B) reactive diluent further comprises (B2) caprolactone-modified (meth)acrylate.

2. The photosensitive resin composition according to claim 1, wherein the (B1) polypropylene glycol diacrylate is represented by the following formula (1). 【Chemistry 1】 (Equation (1), where n is an integer between 10 and 15.)

3. The photosensitive resin composition according to claim 1 or 2, wherein the content of (B1) polypropylene glycol diacrylate per 100 parts by mass of (A) carboxyl group-containing photosensitive resin is 5 parts by mass or more and 60 parts by mass or less.

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

5. A printed circuit board comprising the photocured material described in claim 4.

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