TWI899390B - Photosensitive resin composition - Google Patents

Abstract

The present invention is to provide a photosensitive resin composition that exhibits excellent dispersibility during storage, reduces water absorption, and forms a cured film with excellent flexural properties and insulation reliability. The present invention addresses this problem by providing a photosensitive resin composition comprising (A) a carboxyl-containing photosensitive resin, (B) an epoxy compound, (C) urethane beads, (D) a photopolymerization initiator, and (E) a reactive diluent. The urethane beads (C) are coated with silica, wherein at least 20% by mass of the 100% by mass silica is hydrophobic silica.

Description

Photosensitive resin composition

The present invention relates to a photosensitive resin composition suitable for use as a coating material, for example, for coating a conductive circuit pattern formed on a wiring board such as a flexible printed wiring board, a dry film having a coating of the photosensitive resin composition, and a wiring board having a light-curing film of the photosensitive resin composition.

Printed wiring boards are used to form a conductive circuit pattern on a substrate. Electronic components are soldered to the soldering lands of the pattern and mounted on the board. The circuitry outside of these lands is covered with an insulating protective film (such as a solder resist film). This insulating protective film can be formed by applying a photosensitive resin composition to the printed wiring board to form a coating, followed by light curing. This prevents solder from adhering to unwanted areas when soldering electronic components to the printed wiring board, and also protects the circuitry from corrosion caused by oxidation or humidity due to direct exposure to air.

Furthermore, in recent years, due to the miniaturization of electronic devices, flexible printed wiring boards with excellent bendability have been used. The insulating protective film applied to flexible printed wiring boards is particularly required to have flexibility (flexibility). Therefore, to impart flexibility (flexibility) to the insulating protective film applied to flexible printed wiring boards, urethane beads are blended into a photosensitive resin composition as an organic filler (Patent Document 1).

However, when urethane beads are mixed into a photosensitive resin composition, due to their low softening point, the solid components aggregate during storage, leading to a loss of dispersibility in the photosensitive resin composition. Therefore, by mixing urethane beads coated with silica into the photosensitive resin composition, it is possible to impart flexibility (flexibility) to the insulating protective film while also imparting dispersibility to the photosensitive resin composition.

However, if the silica coating of the silica-coated urethane beads is low, solid components may aggregate during storage of the photosensitive resin composition, resulting in a problem of poor dispersion of the photosensitive resin composition. Furthermore, the silica in the silica-coated urethane beads is untreated silica that has not undergone surface treatment. Increasing the silica coating of the silica-coated urethane beads to improve dispersion of the photosensitive resin composition may increase the silica-coated urethane beads' water absorption properties, potentially impairing the insulation reliability of the insulating protective film, particularly in high-temperature and high-humidity environments. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2017-201369

[The problem that the invention aims to solve]

In view of the above circumstances, the object of the present invention is to provide a photosensitive resin composition, a dry film coated with the photosensitive resin composition, and a wiring board having a photocurable film of the photosensitive resin composition. The photosensitive resin composition exhibits excellent dispersibility during storage, reduces water absorption, and forms a cured film with excellent flexural properties and insulation reliability. [Means for Solving the Problem]

The gist of the present invention is as follows. [1] A photosensitive resin composition comprising (A) a photosensitive resin containing a carboxyl group, (B) an epoxy compound, (C) urethane beads, (D) a photopolymerization initiator, and (E) a reactive diluent, wherein the urethane beads (C) are coated with silica, and 20% by mass or more of the 100% by mass of the silica is hydrophobic silica. [2] The photosensitive resin composition as described in [1], wherein 30% by mass or more of the 100% by mass of the silica is hydrophobic silica. [3] The photosensitive resin composition according to [1] or [2], wherein the coverage of the aforementioned silicon dioxide in the aforementioned urethane beads (C) is not less than 1.0 mass % and not more than 40 mass % [4] The photosensitive resin composition according to [1] or [2], wherein the coverage of the aforementioned silicon dioxide in the aforementioned urethane beads (C) is not less than 5.0 mass % and not more than 30 mass % [5] The photosensitive resin composition according to any one of [1] to [4], wherein the hydrophobic silica is at least one selected from the group consisting of monoalkylsiloxylated silica surface-modified with a monoalkylsilyl group, dialkylsiloxylated silica surface-modified with a dialkylsilyl group, trialkylsiloxylated silica surface-modified with a trialkylsilyl group, (meth)acrylsiloxylated silica surface-modified with a (meth)acrylsilyl group, silica surface-modified with a dialkylsiloxyalkyl group, and silica surface-modified with a dialkylpolysiloxyalkyl group. [6] The photosensitive resin composition according to any one of [1] to [4], wherein the hydrophobic silica is at least one selected from the group consisting of monoalkylsiloxylated silica surface-modified with a monoalkylsilyl group, dialkylsiloxylated silica surface-modified with a dialkylsilyl group, and (meth)acryloylsiloxylated silica surface-modified with a (meth)acryloylsilyl group. [7] The photosensitive resin composition according to any one of [1] to [6], wherein the urethane beads (C) coated with silica are contained in an amount of not less than 35 parts by mass and not more than 150 parts by mass per 100 parts by mass of the carboxyl group-containing photosensitive resin (A). [8] A dry film having a coating of the photosensitive resin composition described in any one of [1] to [7]. [9] A wiring board having a photocurable film of the photosensitive resin composition described in any one of [1] to [7].

Regarding the silica coverage of urethane beads, "silica coverage" refers to the ratio of the mass of silica covering the outer surface of the urethane beads relative to the mass of the silica-coated urethane beads. The silica coverage is determined by gravimetrically measuring the ash content of the silica-coated urethane beads after burning them at 600°C for 2 hours. [Effects of the Invention]

According to the present invention, by coating the urethane beads (C) with silica, wherein 20% by mass or more of the 100% by mass silica is hydrophobic silica, a photosensitive resin composition can be obtained that exhibits excellent dispersibility during storage and reduced water absorption. Furthermore, a photosensitive resin composition can be obtained that forms a cured film with excellent flexural properties and insulation reliability.

According to the present invention, by providing hydrophobic silica at least 30% of the total 100% by mass of silica coating the urethane beads (C), the water absorption rate of the photosensitive resin composition can be further reduced, thereby forming a cured film with even better insulation reliability.

According to the present invention, by setting the silica coverage of the urethane beads (C) to 1.0% by mass and 40% by mass, a photosensitive resin composition having excellent dispersibility during storage can be obtained with greater certainty, and a photosensitive resin composition capable of forming a cured film with excellent bendability can also be obtained with greater certainty.

According to aspects of the present invention, by setting the silica coverage of the urethane beads (C) to 5.0% by mass or more and 30% by mass or less, a photosensitive resin composition having excellent dispersibility during storage can be obtained with greater certainty, and a photosensitive resin composition capable of forming a cured film with excellent bendability can also be obtained with greater certainty.

According to the present invention, the hydrophobic silica is selected from the group consisting of monoalkylsiloxylated silica surface-modified with a monoalkylsilyl group, dialkylsiloxylated silica surface-modified with a dialkylsilyl group, trialkylsiloxylated silica surface-modified with a trialkylsilyl group, (meth)acryloylsiloxylated silica surface-modified with a (meth)acryloylsilyl group, and the like. At least one of the group consisting of silicon oxide, silicon dioxide surface-modified with a dialkylsiloxyalkyl group, and silicon dioxide surface-modified with a dialkylpolysiloxyalkyl group can more reliably provide a photosensitive resin composition that exhibits excellent dispersibility during storage and reduced water absorption, and can also more reliably provide a photosensitive resin composition capable of forming a cured film with excellent flexural properties and insulating reliability.

According to aspects of the present invention, by using at least one hydrophobic silica selected from the group consisting of monoalkylsiloxylated silica surface-modified with a monoalkylsilyl group, dialkylsiloxylated silica surface-modified with a dialkylsilyl group, and (meth)acrylsiloxylated silica surface-modified with a (meth)acrylsilyl group, a photosensitive resin composition can be more reliably obtained that exhibits excellent dispersibility during storage and reduced water absorption. Furthermore, a photosensitive resin composition can be more reliably obtained that forms a cured film with excellent flexural properties and insulating reliability.

According to aspects of the present invention, by including 35 to 150 parts by mass of the silica-coated urethane beads (C) per 100 parts by mass of the carboxyl group-containing photosensitive resin (A), excellent coating properties can be imparted to the photosensitive resin composition. Furthermore, a photosensitive resin composition can be more reliably obtained that exhibits excellent dispersibility during storage and reduced water absorption. Furthermore, a photosensitive resin composition can be more reliably obtained that forms a cured film with excellent flexural properties and insulation reliability.

[Form of implementing the invention]

Next, the photosensitive resin composition of the present invention is described in detail. The photosensitive resin composition of the present invention comprises (A) a carboxyl group-containing photosensitive resin, (B) an epoxy compound, (C) urethane beads, (D) a photopolymerization initiator, and (E) a reactive diluent. The urethane beads (C) are coated with silica, and at least 20% by mass of the 100% by mass silica is hydrophobic silica.

<(A) Carboxyl-containing Photosensitive Resin> The structure of the carboxyl-containing photosensitive resin of component (A) is not particularly limited. Examples include resins having one or more photosensitive unsaturated double bonds and free carboxyl groups. Examples of carboxyl group-containing photosensitive resins include radically polymerizable unsaturated monocarboxylic acid-modified epoxy resins such as epoxy (meth)acrylates obtained by reacting at least a portion of the epoxy groups of a polyfunctional epoxy resin having two or more epoxy groups per molecule with a radically polymerizable unsaturated monocarboxylic acid such as acrylic acid or methacrylic acid (hereinafter sometimes referred to as "(meth)acrylic acid"), and polyacid-modified radically polymerizable unsaturated monocarboxylic acid-modified epoxy (meth)acrylates obtained by reacting the hydroxyl groups of the resulting radically polymerizable unsaturated monocarboxylic acid-modified epoxy resins with a polyacid and/or its anhydride.

As long as the polyfunctional epoxy resin is a bifunctional or higher-functional epoxy resin, its chemical structure is not particularly limited. Furthermore, the epoxy equivalent weight of the polyfunctional epoxy resin is not particularly limited. For example, the upper limit is preferably 4000 g/eq, more preferably 3000 g/eq, particularly preferably 2500 g/eq, and particularly preferably 2000 g/eq. On the other hand, the lower limit of the epoxy equivalent weight of the polyfunctional epoxy resin is preferably 100 g/eq, particularly preferably 200 g/eq.

Examples of the polyfunctional epoxy resin include biphenyl aralkyl epoxy resin, phenyl aralkyl epoxy resin, biphenyl epoxy resin, naphthalene epoxy resin, dicyclopentadiene epoxy resin, silicone modified epoxy resin, and other rubber modified epoxy resins, ε-caprolactone modified epoxy resin, bisphenol A epoxy resin, bisphenol F epoxy resin, and other phenol modified epoxy resins. Novolac-type epoxy resins, o-cresol novolac-type epoxy resins, cresol novolac-type epoxy resins, bisphenol A novolac-type epoxy resins, epoxy aliphatic polyfunctional epoxy resins, epoxy propyl ester-type epoxy resins, epoxy propyl amine-type epoxy resins, hybrid epoxy resins, bisphenol-modified novolac-type epoxy resins, polyfunctional modified novolac-type epoxy resins, etc. Furthermore, these epoxy resins may be further introduced with halogen atoms such as Br and Cl. These polyfunctional epoxy resins may be used alone or in combination.

The radically polymerizable unsaturated monocarboxylic acid is not particularly limited, and examples thereof include (meth)acrylic acid, crotonic acid, chamomile acid, angelic acid, and cinnamic acid. Among these, (meth)acrylic acid is preferred due to its availability and ease of handling. These radically polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more.

The method for reacting the polyfunctional epoxy resin with the free-radically polymerizable unsaturated monocarboxylic acid is not particularly limited. For example, a method of dissolving the polyfunctional epoxy resin and the free-radically polymerizable unsaturated monocarboxylic acid in a diluent such as an organic solvent and stirring the mixture while heating is exemplified.

The polyacid and/or polyacid anhydride introduces free carboxyl groups into the free-radically polymerizable unsaturated monocarboxylic acid epoxy resin by reacting the hydroxyl groups generated by the reaction of the polyfunctional epoxy resin with the free-radically polymerizable unsaturated monocarboxylic acid. The chemical structure of the polyacid and polyacid anhydride is not particularly limited; either saturated or unsaturated can be used. Examples of the polyacid include succinic acid, maleic acid, adipic acid, citric acid, phthalic acid, tetrahydrophthalic acid, 3-methyltetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, 3-ethyltetrahydrophthalic acid, 4-ethyltetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, methyl Examples of polybasic acid anhydrides include tetrahydrophthalic acids such as endomethylenetetrahydrophthalic acid, hexahydrophthalic acid, 3-methylhexahydrophthalic acid, 4-methylhexahydrophthalic acid, 3-ethylhexahydrophthalic acid, and 4-ethylhexahydrophthalic acid, trimellitic acid, pyromellitic acid, and diglycolic acid. Examples of polybasic acid anhydrides include anhydrides of the aforementioned polybasic acids. These polybasic acids and/or polybasic acid anhydrides may be used alone or in combination of two or more.

The method for reacting the free-radically polymerizable unsaturated monocarboxylic acid epoxy resin with the polyacid and/or polyacid anhydride is not particularly limited. For example, a method of dissolving the free-radically polymerizable unsaturated monocarboxylic acid epoxy resin and the polyacid and/or polyacid anhydride in a diluent such as an organic solvent and stirring the mixture while heating is exemplified.

The polyacid-modified unsaturated monocarboxylate epoxy resin can also be used as a photosensitive resin containing a carboxyl group. Alternatively, a polyacid-modified free radical polymerizable unsaturated monocarboxylate epoxy resin having a free radical polymerizable unsaturated group introduced therein can be used, which is obtained by subjecting a portion of the carboxyl groups of the polyacid-modified unsaturated monocarboxylate epoxy resin obtained above to an addition reaction with a compound having one or more free radical polymerizable unsaturated groups and an epoxy group. Polyacid-modified free radical polymerizable unsaturated monocarboxylate epoxy resins with further introduction of free radical polymerizable unsaturated groups. Due to the chemical structure of further introduction of free radical polymerizable unsaturated groups into the side chains of the polyacid-modified unsaturated monocarboxylate epoxy resins, compared to polyacid-modified unsaturated monocarboxylate epoxy resins, this is a photosensitive resin with carboxyl groups that further enhances photosensitivity.

Examples of compounds having one or more free-radically polymerizable unsaturated groups and epoxy groups include glycidyl compounds. Examples of glycidyl compounds include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, pentaerythritol triacrylate monoglycidyl ether, and pentaerythritol trimethacrylate monoglycidyl ether. The glycidyl group may be present in one or more glycidyl groups in a molecule. Furthermore, the compounds having one or more free-radically polymerizable unsaturated groups and epoxy groups may be used alone or in combination of two or more.

The method for reacting the polyacid-modified unsaturated monocarboxylic acid epoxy resin with a compound having one or more free radical polymerizable unsaturated groups and an epoxy group, such as a glyoxypropyl compound, is not particularly limited. For example, a method may be employed in which the polyacid-modified unsaturated monocarboxylic acid epoxy resin and the compound having one or more free radical polymerizable unsaturated groups and an epoxy group are dissolved in a diluent such as an organic solvent and stirred while heating.

The acid value of the carboxyl group-containing photosensitive resin is not particularly limited. For example, from the perspective of reliably imparting alkaline developability, the lower limit is preferably 30 mgKOH/g, and particularly preferably 40 mgKOH/g. On the other hand, from the perspective of preventing dissolution of the exposed portion (photocured portion) by alkaline developer, the upper limit of the acid value of the carboxyl group-containing photosensitive resin is preferably 200 mgKOH/g, and from the perspective of reliably preventing a decrease in the moisture resistance and insulation reliability of the photocured product, it is particularly preferably 150 mgKOH/g.

The mass average molecular weight of the carboxyl group-containing photosensitive resin is not particularly limited. For example, to ensure strong toughness and dryness to touch of the photocured product, the lower limit is preferably 6,000, more preferably 7,000, and particularly preferably 8,000. On the other hand, to ensure good alkali developability, the upper limit of the mass average molecular weight of the carboxyl group-containing photosensitive resin is preferably 200,000, more preferably 100,000, and particularly preferably 50,000. The term "mass average molecular weight" refers to the mass average molecular weight calculated in terms of polystyrene as measured by gel permeation chromatography (GPC) at room temperature.

A carboxyl group-containing photosensitive resin can be prepared using the above-mentioned components and the above-mentioned reaction steps. Commercially available carboxyl group-containing photosensitive resins can also be used. Examples of commercially available carboxyl group-containing photosensitive resins include "SP-4621" (Showa Denko Co., Ltd.), "KAYARAD ZAR-2000," "KAYARAD ZFR-1122," "KAYARAD FLX-2089," and "KAYARAD ZCR-1569H" (all from Nippon Kayaku Co., Ltd.), and "Cyclomer P(ACA)Z-250" (Daicel Allnex Co., Ltd.). These carboxyl group-containing photosensitive resins can be used alone or in combination.

<(B) Epoxy Compound> The epoxy compound in component (B) is used to increase the crosslink density of the cured photosensitive resin composition, thereby imparting sufficient strength to the cured product. Examples of epoxy compounds include epoxy resins. Examples of epoxy resins include the same polyfunctional epoxy resins used in the preparation of the aforementioned carboxyl group-containing photosensitive resin. Specifically, examples include biphenyl aralkyl epoxy resins, phenyl aralkyl epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, dicyclopentadiene epoxy resins, silicone-modified epoxy resins, and other rubber-modified epoxy resins, ε-caprolactone-modified epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, and other phenol novolac-type epoxy resins. , o-cresol novolac-type epoxy resins, cresol novolac-type epoxy resins, bisphenol A novolac-type epoxy resins, epoxy aliphatic polyfunctional epoxy resins, epoxypropyl ester-type polyfunctional epoxy resins, epoxypropylamine-type polyfunctional epoxy resins, heterocyclic polyfunctional epoxy resins, bisphenol-modified novolac-type epoxy resins, and polyfunctional modified novolac-type epoxy resins. These epoxy compounds may be used alone or in combination of two or more.

The content of the epoxy compound is not particularly limited, but, for example, from the perspective of obtaining a coating film of sufficient strength after curing of the photosensitive resin composition, it is preferably from 10 parts by mass to 100 parts by mass, and particularly preferably from 10 parts by mass to 50 parts by mass, per 100 parts by mass of the carboxyl group-containing photosensitive resin (solid content, the same shall apply hereinafter).

<(C) Urethane Beads> The urethane beads of component (C) are particulate materials with at least a portion of their outer surface coated with silica. Therefore, the urethane beads of component (C) have a core-shell structure, with the urethane beads forming a core and the silica forming a shell, at least in a portion of their outer surface. Furthermore, of the total silica coating the outer surface of the urethane beads, at least 20% by mass is hydrophobic silica. In other words, at least 20% by mass of 100% by mass of the silica is composed of hydrophobic silica.

By coating the (C) urethane beads with silica, 20% or more of the 100% silica being hydrophobic, the photosensitive resin composition exhibits excellent dispersibility during storage and reduces water absorption. Furthermore, by coating the (C) urethane beads with silica, 20% or more of the 100% silica being hydrophobic, the photosensitive resin composition forms a cured film with excellent flexural properties and insulation reliability.

The ratio of hydrophobic silica in the total silica coating the urethane beads is not particularly limited as long as it is 20% by mass or greater. However, from the perspective of further reducing the water absorption of the photosensitive resin composition and forming a cured film with even greater insulation reliability, it is preferably 30% by mass or greater, more preferably 40% by mass or greater, and particularly preferably 60% by mass or greater. The upper limit of the ratio of hydrophobic silica in the total silica coating the urethane beads is preferably higher, and an example of this is 100% by mass. By ensuring that the proportion of hydrophobic silica in the total silica coating the urethane beads is 100% by mass, i.e., the silica coating the urethane beads is composed entirely of hydrophobic silica, the water absorption of the photosensitive resin composition can be more reliably reduced, resulting in a cured film with further enhanced insulation reliability.

As silica other than hydrophobic silica that can be used as silica for coating the urethane beads, there can be exemplified untreated silica that has not been surface treated, that is, hydrophilic silica.

The coverage of the total silica including the hydrophobic silica in the urethane beads is not particularly limited, but from the perspective of more reliably obtaining a photosensitive resin composition with excellent dispersibility during storage, the lower limit is preferably 1.0 mass%. From the perspective of more reliably obtaining a photosensitive resin composition with excellent dispersibility during storage, the lower limit is more preferably 5.0 mass%, particularly preferably 8.0 mass%, and particularly preferably 12 mass%. On the other hand, the upper limit of the coverage of the entire silica of the urethane beads is preferably 40 mass % from the viewpoint of more reliably obtaining a photosensitive resin composition capable of forming a cured film having excellent bendability. From the viewpoint of more reliably obtaining a photosensitive resin composition capable of forming a cured film having excellent bendability, the upper limit is more preferably 30 mass %, particularly preferably 25 mass %, and particularly preferably 18 mass %.

The hydrophobic silica is not particularly limited as long as it is a silica having a hydrophobic substituent. For example, from the viewpoint of being able to more reliably obtain a photosensitive resin composition that has excellent dispersibility during storage and reduced water absorption, and also being able to more reliably obtain a photosensitive resin composition that can form a cured film with excellent flexural properties and insulation reliability, a silica surface modified with a monoalkylsilyl group is preferred. Monoalkylsiloxylated silica, dialkylsiloxylated silica surface-modified with a dialkylsilyl group, trialkylsiloxylated silica surface-modified with a trialkylsilyl group, (meth)acryloylsiloxylated silica surface-modified with a (meth)acryloylsilyl group, silica surface-modified with a dialkylsiloxyalkyl group, and silica surface-modified with a dialkylpolysiloxyalkyl group. Among these, monoalkylsiloxylated silica surface-modified with a monoalkylsilyl group, dialkylsiloxylated silica surface-modified with a dialkylsilyl group, and (meth)acryloylsiloxylated silica surface-modified with a (meth)acryloylsilyl group are particularly preferred from the viewpoint of more reliably obtaining a photosensitive resin composition that exhibits excellent dispersibility during storage and reduces water absorption, and more reliably forming a cured film with excellent flexural properties and insulating reliability.

The number of carbon atoms in each alkyl group in the dialkyl group and the trialkyl group is not particularly limited, but is preferably 1 to 10, more preferably 1 to 5, and particularly preferably 1 to 3. The number of carbon atoms in the monoalkyl group is not particularly limited, but is preferably 1 to 20, more preferably 3 to 15, and particularly preferably 5 to 10.

The above-mentioned hydrophobic silica may be used alone or in combination of two or more.

There is no particular limitation on the content of the silica-coated urethane beads. For example, the lower limit is preferably 35 parts by mass, more preferably 50 parts by mass, and particularly preferably 60 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, from the perspective of more reliably obtaining a photosensitive resin composition that exhibits excellent dispersibility during storage while reducing water absorption, and more reliably forming a cured film with excellent flexural properties and insulating reliability. On the other hand, the upper limit of the content of the silica-coated urethane beads is preferably 150 parts by mass, more preferably 120 parts by mass, and particularly preferably 90 parts by mass relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, from the perspective of imparting excellent coating properties to the photosensitive resin composition.

The average particle size of the silica-coated urethane beads is not particularly limited. For example, from the perspective of ensuring that the urethane beads are reliably coated with silica containing hydrophobic silica, ensuring dispersibility and insulation reliability in the photosensitive resin composition, and uniformly dispersing the silica-coated urethane beads in the photosensitive resin composition, the average particle size is preferably 1.0 μm to 10 μm, more preferably 2.0 μm to 7.0 μm, and particularly preferably 3.0 μm to 5.0 μm.

<(D) Photopolymerization Initiator> The photopolymerization initiator of component (D) is not particularly limited. Examples include 1,2-octanedione, 1-[4-(phenylthio)-2-(O-benzoyl oxime)], 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyl oxime)], 2-(acetyloxyiminomethyl)thiazol-9-one, 1,8-octanedione, 1,8-bis[9-ethyl-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyl oxime), 1,8-octanedione, 1,8-bis[9-(2 Oxime ester-based photopolymerization initiators include (Z)-(9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropane-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime, and α-aminoalkylphenone-based photopolymerization initiators such as 2-benzyl-2-dimethylamino-1-(4-oxolinylphenyl)-butanone-1 and 2-methyl-1-[4-(methylthio)phenyl]-2-oxolinylpropane-1-one.

In addition, examples of photopolymerization initiators other than oxime ester-based photopolymerization initiators and α-aminoalkylphenone-based photopolymerization initiators include benzoin-based initiators such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, and benzoin isobutyl ether; acetophenone-based initiators such as acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, and 2,2-diethoxy-2-phenylacetophenone; benzophenone-based initiators such as benzophenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, and dichlorobenzophenone; anthraquinone-based initiators such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, and 2-aminoanthraquinone; 2-methylthiazolinone, 2- Thiathione series such as ethylthiazonone, 2-chlorothiazonone, 2,4-dimethylthiazonone, and 2,4-diethylthiazonone; benzyl dimethyl ketal, acetophenone dimethyl ketal, ethyl p-dimethylaminobenzoate, 2,4,6-trimethylbenzyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzyl)phenylphosphine oxide, bis(2,6-dimethoxybenzyl)-2,4,4-trimethyl-pentylphosphine oxide, (2,4,6-trimethylbenzyl)ethoxyphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, and 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone. These photopolymerization initiators may be used alone or in combination of two or more.

The content of the photopolymerization initiator is not particularly limited, but is preferably from 0.1 to 10 parts by mass, and particularly preferably from 0.2 to 5.0 parts by mass, based on 100 parts by mass of the carboxyl group-containing photosensitive resin.

<(E) Reactive Diluent> The reactive diluent of component (E) is, for example, a photopolymerizable monomer, a compound having at least one, and preferably two or more, polymerizable double bonds per molecule. The reactive diluent enhances the photohardening of the photosensitive resin composition, contributing to imparting sufficient heat resistance, acid resistance, and alkali resistance to the cured product.

Examples of the reactive diluent include monofunctional (meth)acrylate compounds, bifunctional (meth)acrylate compounds, trifunctional (meth)acrylate compounds, and tetrafunctional or higher functional (meth)acrylate compounds. Examples of the (meth)acrylate compound include monofunctional (meth)acrylate compounds such as 2-hydroxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, diethylene glycol mono(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)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, hydroxytrimethylol neopentyl glycol di(meth)acrylate, dicyclopentyl di(meth)acrylate, and ethylene oxide-modified di(meth)phosphate. Examples include bifunctional (meth)acrylate compounds such as acrylate, allylated cyclohexyl di(meth)acrylate, and isocyanurate di(meth)acrylate; trifunctional (meth)acrylate compounds such as trihydroxymethylpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, epoxypropane-modified trihydroxymethylpropane tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate; and tetrafunctional or higher-functional (meth)acrylate compounds such as ditrihydroxymethylpropane tetra(meth)acrylate, propionic acid-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Examples also include monofunctional or bifunctional or higher-functional urethane (meth)acrylate compounds. These may be used alone or in combination of two or more.

The content of the reactive diluent is not particularly limited, but is preferably 5.0 parts by mass to 50 parts by mass, and particularly preferably 10 parts by mass to 30 parts by mass, based on 100 parts by mass of the carboxyl group-containing photosensitive resin.

In addition to the aforementioned components (A) to (E), the photosensitive resin composition of the present invention may further contain various other components, such as a base pigment, a curing accelerator, various additives, a flame retardant, a colorant, a non-reactive diluent, etc., as needed.

Examples of base pigments include talc, barium sulfate, aluminum oxide, aluminum hydroxide, and mica. Examples of curing accelerators include boron trifluoride-amine complexes, dicyandiamide (DICY) and its derivatives, organic acid hydrazides, diaminomaleonitrile (DAMN) and its derivatives, guanamine and its derivatives, melamine and its derivatives, aminoimide (AI), and polyamines. Examples of various additives include silicone-based, hydrocarbon-based, and acrylic-based defoamers, organic fillers such as (meth)acrylic polymers and organic bentonite, and thixotropic agents such as polycarboxylic acid amides.

Examples of the flame retardant include phosphorus-based flame retardants. Examples of the phosphorus-based flame retardant include halogen-containing phosphates 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; non-halogen-containing aliphatic phosphates such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, and tributoxyethyl phosphate; and triphenyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, tricresyl phosphate, tris(dicresyl) phosphate, dicresyl diphenyl phosphate, and tris(isopropyl) phosphate. Non-halogen aromatic phosphates such as tris(2-butylphenyl) phosphate, tris(3-methylphenyl) phosphate, tris(3-butylphenyl) phosphate, hydroxyphenyl diphenyl phosphate, and octyl diphenyl phosphate; metal salts of phosphonic acids such as tris(2-ethyl)phosphonate, tris(2-methyl)ethylphosphonate, tris(2-phenyl)phosphonate, zinc bis(2-ethyl)phosphonate, zinc bis(2-methyl)ethylphosphonate, zinc bis(2-phenyl)phosphonate, titanium bis(2-ethyl)phosphonate, titanium tetrakis(2-methyl)ethylphosphonate, titanium tetrakis(2-phenyl)phosphonate; and phosphine oxide compounds such as diphenylvinylphosphine oxide, triphenylphosphine oxide, trialkylphosphine oxide, and tris(2-hydroxyalkyl)phosphine oxide. Among them, organic phosphate-based flame retardants are preferred.

Colorants are pigments, dyes, and the like, and are not particularly limited. Furthermore, the color of the colorant can be any color, such as white, blue, green, yellow, orange, red, purple, or black. Among the aforementioned colorants, inorganic colorants include, for example, titanium oxide for white colorants, carbon black and acetylene black for black colorants, and the like. Furthermore, organic colorants include, for example, phthalocyanine green for green colorants, phthalocyanine blue and Lionol blue for blue colorants, and diketopyrrolopyrrole colorants such as chromium phthalo orange for orange colorants.

Non-reactive diluents are components used to adjust the viscosity, coating properties, and drying properties of photosensitive resin compositions. Examples of non-reactive diluents include organic solvents. Examples of organic solvents include ketones such as methyl ethyl ketone, aromatic hydrocarbons such as toluene and xylene, alcohols such as methanol, n-propanol, isopropyl alcohol, cyclohexanol, and propylene glycol monomethyl ether, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, solvents such as solvent and butyl solvent, carbitols such as carbitol and butyl carbitol, ethyl acetate, butyl acetate, solvent acetate, butyl solvent acetate, carbitol acetate, butyl carbitol acetate, diethylene glycol monomethyl ether acetate, ethyl diglycol acetate, and propylene glycol monomethyl ether acetate. The content of the non-reactive diluent is not particularly limited, but is preferably 2.0 parts by mass to 50 parts by mass, and particularly preferably 5.0 parts by mass to 20 parts by mass, based on 100 parts by mass of the carboxyl group-containing photosensitive resin.

The method for producing the photosensitive resin composition of the present invention is not limited to a specific method, and well-known methods can be used. Specifically, for example, the above-mentioned components are blended in a specified ratio and then kneaded or mixed at room temperature (e.g., 25°C) using a kneading method such as a three-roll mill, ball mill, sand mill, bead mill, or kneader, or a stirring method such as a super mixer, planetary mixer, or three-arm mixer. Furthermore, prior to the kneading or mixing, preliminary kneading or preliminary mixing may be performed as needed.

Next, examples of how the photosensitive resin composition of the present invention can be used are described. First, the example involves applying the photosensitive resin composition of the present invention to a printed wiring board having a circuit pattern formed by etching a conductor such as copper foil, and using the resulting dry film to form an insulating protective film (e.g., a solder resist film).

A dry film is a laminate structure consisting of a support film (e.g., a thermoplastic resin film such as polyethylene terephthalate film or polyester film), a solder resist layer applied to the support film, and a cover film (e.g., polyethylene film or polypropylene film) to protect the solder resist layer. The photosensitive resin composition of the present invention is applied to the support film using a known method such as roll coating or rod coating to form a coating having a specific film thickness. The resulting photosensitive resin film is then dried to form a solder resist layer on the support film. Then, by laminating a cover film on the formed solder resist layer, a dry film having a coating of the photosensitive resin composition of the present invention can be produced.

The dry film produced as described above is then laminated to a printed wiring board (PCB) such as a flexible printed wiring board while the cover film is peeled off, forming a solder resist layer on the PCB. Furthermore, a support film is laminated on the solder resist layer. If necessary, a preliminary drying step is performed at approximately 60-100°C for 5-30 minutes to evaporate the non-reactive diluent (organic solvent) in the photosensitive resin composition, rendering the solder resist surface non-sticky. Next, a negative film (photomask) with a light-transmitting pattern is placed on the support film, outside the circuit pattern area. Ultraviolet light (e.g., in the wavelength range of 300-400 nm) is irradiated from above the negative film to photoharden the solder resist layer. The support film is then peeled off, and the non-exposed areas corresponding to the aforementioned areas are removed using a dilute alkaline aqueous solution to develop the solder resist layer. The development method can be a spraying method or a showering method, and the dilute alkaline aqueous solution used can be, for example, a 0.5-5% by mass sodium carbonate aqueous solution. After alkaline development, the solder resist layer is heat-cured (post-cured) for 20 to 80 minutes in a hot air circulation dryer at 130 to 170°C, thereby forming a solder resist film as a light-curable film on the printed wiring board.

As an example of a method for using the photosensitive resin composition of the present invention, a method for applying the photosensitive resin composition of the present invention to a printed wiring board to form an insulating protective film (such as a solder resist film) is described.

The photosensitive resin composition of the present invention is applied to a printed wiring board (PCB), such as a flexible PCB, to a desired thickness to form a coating film by a known method such as screen printing, rod coating, squeegee coating, doctor blade coating, knife coating, roll coating, gravure coating, or spray coating. The coating film is then pre-dried by heating at approximately 60-100°C for approximately 5-30 minutes to evaporate the non-reactive diluent (organic solvent) in the photosensitive resin composition, rendering the coating film non-tacky. Next, a negative film (photomask) with a light-transmitting pattern is placed in close contact with the coating outside the circuit pattern area. Ultraviolet rays (e.g., in the wavelength range of 300-400 nm) are irradiated from above to photocure the coating. The non-exposed areas corresponding to the aforementioned areas are then removed with a dilute alkaline aqueous solution, and the coating is developed. The development method can be a spraying method or a showering method. For example, a 0.5-5% by mass sodium carbonate aqueous solution can be used as the dilute alkaline aqueous solution. After alkaline development, the coating is thermally cured (post-cured) for 20-80 minutes in a hot air circulation dryer at 130-170°C, thereby forming a solder resist film as a photocurable film on the printed wiring board. [Example]

Next, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments as long as it does not exceed the scope of the present invention.

Examples 1-8, Comparative Examples 1-4 The components listed in Table 1 below were blended in the proportions shown in Table 1 and mixed at room temperature using a three-roll mill to prepare the photosensitive resin compositions used in Examples 1-8 and Comparative Examples 1-4. The prepared photosensitive resin compositions were then applied to substrates as follows to produce test specimens. The blending amounts of the components listed in Table 1 below are expressed as parts by mass unless otherwise specified. Blank columns indicating blending amounts in Table 1 indicate no blending.

The details of the components in Table 1 are as follows. (A) Carboxyl-containing photosensitive resin KAYARAD ZAR-2000: Nippon Kayaku Co., Ltd. (B) Epoxy compound EPICRON 850-S: DIC Corporation

(C) Urethane Beads ・Urethane Beads A: 10g of dimethylsiloxylated silica (trade name "Aerosil R974," manufactured by AEROSIL Co., Ltd., Japan, average primary particle size 0.012μm) was uniformly dispersed in 100g of solvent. An emulsion containing polyurethane spheres, obtained by reacting 20g of an isocyanate compound with 20g of an alcohol, was then uniformly dispersed using a homogenizer and dried to prepare Urethane Beads A (average particle size 3μm) with a silica coverage of 10% by mass. The silica coverage was determined from the ash content after complete combustion at 600°C for 2 hours. Urethane Beads B: Prepare urethane beads B (average particle size 3 μm) with a silica coverage of 15% by mass as in Urethane Beads A. Urethane Beads C: Prepare urethane beads C (average particle size 3 μm) with a silica coverage of 20% by mass as in Urethane Beads A. Urethane Beads D: Prepare urethane beads D (average particle size 3 μm) with a silica coverage of 15% by mass as in Urethane Beads A, except that octylsiloxylated silica (trade name "Aerosil R805," manufactured by AEROSIL Co., Ltd., Japan, average primary particle size 0.012 μm) was used instead of dimethylsiloxylated silica. Urethane Beads E: Prepared in the same manner as Urethane Beads A, with a silica coverage of 15% by mass (average particle size 3 μm), except that methacryloylsiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxy) (trade name "Aerosil R711," manufactured by AEROSIL Co., Ltd., Japan, average primary particle size 0.012 μm) was used instead of dimethylsiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxysiloxane) as described above.

Urethane Beads F: Urethane Beads F (average particle size 3 μm) were prepared in the same manner as Urethane Beads A, with a silica coverage of 15% (50% by mass of hydrophobic silica) except that the dimethylsiloxylated silica and untreated silica (trade name "Aerosil 200," AEROSIL Co., Ltd., Japan, average primary particle size 0.012 μm) used in Urethane Beads A were used in a 1:1 mass ratio. Urethane Beads G: Prepared in the same manner as Urethane Beads A, with a silica coverage of 15% (33% by mass) and an average particle size of 3 μm, using the same method as Urethane Beads A, except using the dimethylsiloxylated silica and untreated silica in a 1:2 mass ratio. Urethane Beads H: Prepared in the same manner as Urethane Beads A, with a silica coverage of 15% (25% by mass) and an average particle size of 3 μm, using the same method as Urethane Beads A, except using the dimethylsiloxylated silica and untreated silica in a 1:3 mass ratio.

Urethane Beads I: Prepared in the same manner as Urethane Beads A, except using untreated silica in the preparation of Urethane Beads F. Urethane Beads I (average particle size 3 μm) were prepared with a silica coverage of 10% by mass. Urethane Beads J: Prepared in the same manner as Urethane Beads A, except using untreated silica in the preparation of Urethane Beads F. Urethane Beads J (average particle size 3 μm) were prepared with a silica coverage of 15% by mass. Urethane Beads K: Prepared in the same manner as Urethane Beads A, except using untreated silica in the preparation of Urethane Beads F. Urethane Beads K (average particle size 3 μm) were prepared with a silica coverage of 20% by mass.

(D) Photopolymerization Initiator ・OXE-02: Oxime ester photopolymerization initiator, BASF (E) Reactive Diluent ・EBERCRYL 8405: DAICEL-CYTEC Co., Ltd.

Physical Pigments ・Higilite H42M: Showa Denko Co., Ltd. Flame Retardant ・Exolit OP-935: Clarion Japan Co., Ltd. Hardening Accelerator ・Melamine: Nissan Chemical Industries, Ltd. ・DICY-7: Mitsubishi Chemical Corporation Additives ・AC-303: Organic Filler, Shin-Etsu Chemical Co., Ltd. Colorants ・Cromofutal DPP Oriange TR: CIBA Specialty Chemicals Non-Reactive Diluents ・EDGAC: Sanyo Chemicals Co., Ltd.

Test specimen preparation steps: Substrate: Flexible printed wiring board (polyimide film, PANASONIC Co., Ltd., film thickness 25μm, conductor (Cu foil) thickness 12.5μm) Surface treatment: 5% sulfuric acid aqueous solution Coating: Screen printing Pre-drying: BOX furnace, 80°C, 20 minutes Exposure: 100mJ/ ^cm2 on photosensitive resin composition (main wavelength 365nm, OAK Co., Ltd. direct drawing (DI) UV exposure equipment "Mms 604B" (light source: high-pressure mercury lamp) Alkaline development: 1% _{Na2CO 3.} Aqueous solution, liquid temperature 30℃, spray pressure 0.2MPa, development time 60 seconds after curing (formal curing heat treatment): BOX furnace, 150℃, 60 minutes after curing. Film thickness: 20-23μm

The evaluation items are as follows. (1) Dispersibility (agglomeration) 200 g of the photosensitive resin composition was placed in a 300 ml plastic container and sealed. The container was placed in a 30°C heat preservation bath for 72 hours and visually observed. Evaluation was performed using the following criteria. The viscosity of the photosensitive resin composition was measured using a Brookfield B-type viscometer. ◎: The viscosity of the photosensitive resin composition after standing changed by 10% or less relative to the initial value, and no aggregated particles (agglomerates) were observed. ○: The viscosity of the photosensitive resin composition after standing changed by more than 10% and less than 20% relative to the initial value, and no aggregated particles (agglomerates) were observed. △: The viscosity of the photosensitive resin composition after standing has changed by more than 20% and less than 30% relative to the initial value, and no aggregated particles (lumps) are observed. ×: The viscosity of the photosensitive resin composition after standing has changed by more than 30% relative to the initial value, or aggregated particles (lumps) are observed in the photosensitive resin composition.

(2) Bendability The prepared test piece was folded and bent once 180° in a direction perpendicular to the length of the conductor pattern line. The presence of microcracks in the hardened coating was observed using a ×500 optical microscope to determine whether microcracks had occurred. Microcracks are defined as cracks with a length of less than 100 μm. The measurement results were evaluated using the following criteria. ◎: No microcracks occurred. ○: Microcracks occurred in 1 to 3 locations. △: Microcracks occurred in more than 3 locations, and only occurred around the conductor pattern line. ×: Microcracks occurred throughout the hardened coating.

(3) Water absorption (D-24/23) Measure the water absorption (%) according to JIS C6481. A water absorption of less than 2.50% is considered acceptable.

(4) Insulation reliability (Insulation reliability in the thickness direction (Z-axis direction) of the coating) For the test piece produced in the above test piece production step, an electromagnetic wave shielding film (TAC Cable Co., Ltd., "SF-PC5000") was attached to the hardened coating and connected to the anode, and the copper conductor of the test piece was connected to the cathode. Then, in a constant temperature and humidity bath at 60°C and 95% humidity, 50V was applied and the resistance value was continuously measured using an ion migration tester (IMV, "MIG-8600B/128"). The insulation reliability in the thickness direction (Z-axis direction) was evaluated based on the following criteria: The time from the start of the measurement to the point at which the resistance value dropped to less than 1.0E+6 (1.0×10⁶) Ω was measured, starting with the application of 50V. ◎: Insulation failure time 1500 hours or longer. ○: Insulation failure time 1000 hours or longer but less than 1500 hours. △: Insulation failure time 500 hours or longer but less than 1000 hours. X: Insulation failure time less than 500 hours.

The results of the above evaluation are shown in Table 1 below.

As shown in Table 1 above, the photosensitive resin compositions of Examples 1 to 8, which contain (A) a carboxyl group-containing photosensitive resin, (B) an epoxy compound, (C) urethane beads, (D) a photopolymerization initiator, and (E) a reactive diluent, wherein the urethane beads (C) are coated with silica, and wherein 20% by mass or more of 100% by mass of the silica is hydrophobic silica, exhibit excellent dispersibility even after 72 hours of storage, reduce water absorption, and form cured films with excellent flexural properties and insulation reliability. In particular, Examples 1-5, in which the silica coating the urethane beads is entirely composed of hydrophobic silica, exhibit lower water absorption and improved insulation reliability compared to Examples 6-8, in which the hydrophobic silica ratio in the total silica is 25-50 mass%. Furthermore, Example 2, with a 15 mass% silica coverage, exhibits further improved dispersibility compared to Example 1, with a 10 mass% silica coverage, and further improved bendability compared to Example 3, with a 20 mass% silica coverage.

Furthermore, Example 2, in which urethane beads are coated with dimethylsiloxylated silica, exhibits further improved dispersibility and flexibility compared to Example 4, in which urethane beads are coated with octylsiloxylated silica, and Example 5, in which urethane beads are coated with methacryloylsiloxylated silica. Furthermore, Examples 6-8 demonstrate that a greater proportion of hydrophobic silica in the total silica content reduces water absorption.

On the other hand, in Comparative Example 1, which did not incorporate urethane beads, no bendability was achieved. Furthermore, in Comparative Example 2, which did not incorporate hydrophobic silica and had a silica coverage of 10% by mass, no dispersibility was achieved and the water absorption rate increased. In Comparative Example 3, which did not incorporate hydrophobic silica and had a silica coverage of 15% by mass, and in Comparative Example 4, which did not incorporate hydrophobic silica and had a silica coverage of 20% by mass, the water absorption rate increased and insulation reliability was not achieved. [Possible Industrial Applications]

The present invention exhibits excellent dispersibility during storage, reduces water absorption, and forms a cured film with excellent flexural properties and insulation reliability. Therefore, it has high utility in areas such as flexible printed wiring boards provided with insulating protective films such as solder resist films.

Claims (5)

A photosensitive resin composition comprising (A) a photosensitive resin containing a carboxyl group, (B) an epoxy compound, (C) urethane beads, (D) a photopolymerization initiator, and (E) a reactive diluent, wherein the urethane beads (C) are coated with silica, wherein 20% by mass or more of 100% by mass of the silica is hydrophobic silica, and the hydrophobic silica is selected from monoalkylsiloxylated silica surface-modified with monoalkylsilyl groups, dialkylsiloxylated silica surface-modified with dialkylsilyl groups, and hydrophobic silica surface-modified with dialkylsilyl groups. At least one of the group consisting of surface-modified dialkylsiloxylated silica and (meth)acryloylsiloxylated silica surface-modified with (meth)acryloylsilyl groups; the coverage of the urethane beads (C) with the silica is from 1.0% to 40% by mass; and the urethane beads (C) coated with silica contain from 35 parts by mass to 150 parts by mass per 100 parts by mass of the carboxyl group-containing photosensitive resin (A). The photosensitive resin composition of claim 1, wherein at least 30% by mass of the 100% by mass of the aforementioned silicon dioxide is hydrophobic silicon dioxide. The photosensitive resin composition of claim 1 or 2, wherein the coverage of the silicon dioxide in the urethane beads (C) is not less than 5.0% by mass and not more than 30% by mass. A dry film having a coating of the photosensitive resin composition according to any one of claims 1 to 3. A wiring board having a photocurable film of the photosensitive resin composition according to any one of claims 1 to 3.