JP7767341B2 - Photosensitive resin composition - Google Patents

Description

The present invention relates to a photosensitive resin composition that can be used as a coating material, for example, an insulating coating material for covering conductor circuit patterns formed on substrates such as printed wiring boards and flexible printed wiring boards; a cured product obtained by curing the photosensitive resin composition; a substrate such as a printed wiring board coated with the cured product; and a dry film having a coating formed by applying the photosensitive resin composition to a film.

A conductor circuit pattern made of a conductor (e.g., copper foil) is formed on substrates such as printed wiring boards and flexible printed wiring boards. Electronic components are mounted to the soldering lands of the circuit pattern by soldering, and the circuit portion excluding the soldering lands is covered with an insulating coating (e.g., solder resist film) as a protective film. A photocured film of a photosensitive resin composition containing a photosensitive resin and a photopolymerization initiator is sometimes used as the insulating protective film for the circuit portion.

A dry film may also be used as a method for forming the insulating protective film on a substrate. A dry film can be produced by forming a coating film of a photosensitive resin composition on a resin support film such as polyethylene terephthalate using a coating method such as a die coater, drying the coating film to form an insulating film (e.g., a solder resist film) on the support film, and then laminating a cover film on the formed insulating film. The cover film of the dry film is peeled off while bonding the insulating film to the substrate, forming an insulating film (e.g., a solder resist layer) on the substrate. The solder resist layer is then exposed to light from above the support film to photocure it, and then further heat-cured to form an insulating protective film on the substrate.

When forming an insulating protective film such as a solder resist film on a printed wiring board, flexible printed wiring board, or the like, an exposure process may be performed using a direct imaging exposure device that directly draws an image on the coating film of the printed wiring board, flexible printed wiring board, or the like, without using a photomask. Depending on the application of the printed wiring board, the insulating protective film such as a solder resist film may be made white to improve the reflectance of the insulating protective film. For white photosensitive resin compositions, an acylphosphine oxide-based photopolymerization initiator that is resistant to discoloration may be used as the photopolymerization initiator (Patent Document 1).

Electronic components are mounted by soldering to the soldering lands of the circuit pattern on a substrate having an insulating protective film. One method for mounting electronic components on soldering lands is reflow processing. However, in the high-temperature atmosphere used during reflow processing (e.g., an atmosphere of 150°C to 260°C), conventional insulating protective films such as those described in Patent Document 1 can harden and shrink due to the heat, resulting in the problem of warping of the substrate having the insulating protective film.

When a substrate with an insulating protective film warps, it becomes harder to handle and harder to incorporate into devices such as smartphones.

JP 2011-232402 A

In light of the above circumstances, the present invention aims to provide a photosensitive resin composition that can produce an insulating protective film that does not lose sensitivity even when exposed to direct writing exposure, and that can prevent cure shrinkage even in high-temperature atmospheres during reflow processing.

The gist of the configuration of the present invention is as follows.
[1] A photosensitive resin composition containing (A) a photosensitive resin, (B) a photopolymerization initiator, (C) a reactive diluent, (D) an epoxy compound, (E) a colorant, and (F) a latent antioxidant.
[2] The photosensitive resin composition according to [1], wherein the (F) latent antioxidant is an aromatic compound having a carbonate ester bond.
[3] The photosensitive resin composition according to [1], wherein the latent antioxidant (F) is an aromatic compound having a chemical structure of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- (wherein R ¹ , R ² , and R ³ each independently represent a hydrocarbon group having 1 to 5 carbon atoms, and Ar represents an aromatic hydrocarbon group having 6 carbon atoms).
[4] The photosensitive resin composition according to [1], wherein the latent antioxidant (F) is an aromatic compound having a chemical structure of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- (wherein R ¹ , R ² , and R ³ each independently represent a hydrocarbon group having 1 to 5 carbon atoms, and Ar represents an aromatic hydrocarbon group having 6 carbon atoms) in one molecule.
[5] The photosensitive resin composition according to [3] or [4], wherein R ¹ , R ² and R ³ are a hydrocarbon group having 4 carbon atoms represented by C(CH ₃ ) ₃ .
[6] The photosensitive resin composition according to any one of [1] to [4], wherein the colorant (E) is a white colorant.
[7] The photosensitive resin composition according to [6], wherein the white colorant is titanium oxide.
[8] The photosensitive resin composition according to any one of [1] to [4], further comprising 1.0 part by mass or more and 25 parts by mass or less of the latent antioxidant (F) relative to 100 parts by mass of the photosensitive resin (A).
[9] A cured product of the photosensitive resin composition according to any one of [1] to [4].
[10] A flexible printed wiring board comprising the cured product according to [9].
[11] A dry film comprising the photosensitive resin composition according to any one of [1] to [4].

In the above embodiment, a "latent antioxidant" is a compound in which the moiety that functions as an antioxidant is protected with a protecting group, and the protecting group is eliminated by heating at 100°C to 150°C or at 80°C to 150°C in the presence of an acid/base catalyst, causing the compound to function as an antioxidant upon elimination of the protecting group.

In one embodiment of the photosensitive resin composition of the present invention, the inclusion of (F) a latent antioxidant prevents sensitivity loss even when using direct imaging exposure, and prevents oxidation of the photosensitive resin composition forming the insulating protective film, even in the high-temperature atmosphere of reflow treatment, thereby producing an insulating protective film that is resistant to cure shrinkage.

In one embodiment of the photosensitive resin composition of the present invention, the latent antioxidant (F) is an aromatic compound having a carbonate ester bond, which more reliably prevents oxidation of the photosensitive resin composition forming the insulating protective film, even in the high-temperature atmosphere of reflow treatment, thereby enabling the production of an insulating protective film that more reliably prevents cure shrinkage.

According to one aspect of the photosensitive resin composition of the present invention, the (F) latent antioxidant is an aromatic compound having a chemical structure of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- (wherein R ¹ , R ² , and R ³ each independently represent a hydrocarbon group having 1 to 5 carbon atoms, and Ar represents an aromatic hydrocarbon group having 6 carbon atoms). This more reliably prevents oxidation of the photosensitive resin composition forming the insulating protective film, even in a high-temperature atmosphere during reflow treatment, and makes it possible to obtain an insulating protective film that is more reliably prevented from shrinking on cure.

According to one aspect of the photosensitive resin composition of the present invention, the (F) latent antioxidant is an aromatic compound having a chemical structure of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- (wherein R ¹ , R ² , and R ³ each independently represent a hydrocarbon group having 1 to 5 carbon atoms, and Ar represents an aromatic hydrocarbon group having 6 carbon atoms) in one molecule, thereby further improving the oxidation resistance of the photosensitive resin composition forming the insulating protective film, even in a high-temperature atmosphere during reflow treatment, and making it possible to obtain an insulating protective film that can more reliably prevent cure shrinkage.

According to one aspect of the photosensitive resin composition of the present invention, by containing 1.0 part by mass or more and 25 parts by mass or less of the latent antioxidant (F) per 100 parts by mass of the photosensitive resin (A), oxidation of the photosensitive resin composition forming the insulating protective film is more reliably prevented, even in the high-temperature atmosphere during reflow treatment, thereby obtaining an insulating protective film that more reliably prevents cure shrinkage.

Next, the photosensitive resin composition of the present invention will be described in detail. The photosensitive resin composition of the present invention contains (A) a photosensitive resin, (B) a photopolymerization initiator, (C) a reactive diluent, (D) an epoxy compound, (E) a colorant, and (F) a latent antioxidant. Details of the above-mentioned components (A) to (F) are described below.

(A) Photosensitive Resin The chemical structure of the photosensitive resin of component (A) is not particularly limited, and examples thereof include resins having one or more, preferably two or more, photosensitive unsaturated double bonds in one molecule. Examples of photosensitive resins include (A-1) a photosensitive resin (A-1 resin) obtained by reacting a radically polymerizable unsaturated monocarboxylic acid such as (meth)acrylic acid with at least a portion of the epoxy groups of a copolymer of an ester of a radically polymerizable unsaturated monocarboxylic acid such as acrylic acid or methacrylic acid (hereinafter sometimes referred to as "(meth)acrylic acid") and a compound having one or more radically polymerizable unsaturated groups and an epoxy group, (A-2) a photosensitive resin (A-2 resin) obtained by reacting an epoxy or alcohol with a carboxyl group of a radically polymerizable unsaturated monocarboxylic acid such as (meth)acrylic acid, and (A-3) a polymer of at least a portion of the carboxyl groups of a radically polymerizable unsaturated monocarboxylic acid such as (meth)acrylic acid or a radically polymerizable unsaturated monocarboxylic acid such as (meth)acrylic acid and (meth)acrylic acid. and (A-4) an acid-modified urethane-modified unsaturated monocarboxylated epoxy resin (A-4 resin (urethane-modified resin)) having a moiety obtained by reacting at least a portion of the epoxy groups of a polyfunctional epoxy resin having two or more epoxy groups in one molecule with a radically polymerizable unsaturated monocarboxylic acid to obtain an unsaturated monocarboxylated epoxy resin, then subjecting the resulting hydroxyl groups to an addition reaction with a polyisocyanate compound, and further subjecting the isocyanate groups of the resulting polyisocyanate compound to an addition reaction with a compound having a hydroxyl group and a carboxyl group.

Examples of radically polymerizable unsaturated monocarboxylic acids constituting the ester of radically polymerizable unsaturated monocarboxylic acid for Resin A-1 include (meth)acrylic acid, crotonic acid, tiglic acid, angelic acid, and cinnamic acid. Of these, (meth)acrylic acid is preferred due to its ease of availability and handling. These radically polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more. Furthermore, the alcohol constituting the ester of radically polymerizable unsaturated monocarboxylic acid is not particularly limited, but examples include aliphatic monoalcohols having 1 to 10 carbon atoms, such as methanol, ethanol, propanol, butanol, and hexanol. These alcohols may be used alone or in combination of two or more.

An example of a compound having one or more radically polymerizable unsaturated groups and an epoxy group is a glycidyl compound. Examples of glycidyl compounds include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, pentaerythritol triacrylate monoglycidyl ether, and pentaerythritol trimethacrylate monoglycidyl ether. One or more glycidyl groups may be present in one molecule. The above-mentioned compounds having one or more radically polymerizable unsaturated groups and an epoxy group may be used alone, or two or more types may be used in combination.

Examples of the radically polymerizable unsaturated monocarboxylic acid to be reacted with at least a portion of the epoxy groups of the copolymer include (meth)acrylic acid, crotonic acid, tiglic acid, angelic acid, and cinnamic acid, which are the same compounds as the radically polymerizable unsaturated monocarboxylic acids that form the esters of radically polymerizable unsaturated monocarboxylic acids. These radically polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more.

Resin A-2 Examples of the radically polymerizable unsaturated monocarboxylic acid include the same compounds as those mentioned above, i.e., (meth)acrylic acid, crotonic acid, tiglic acid, angelic acid, cinnamic acid, etc. These radically polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more.

Examples of epoxy compounds to be reacted with radically polymerizable unsaturated monocarboxylic acids include compounds having an alicyclic or aromatic ring skeleton and an epoxy group, or resins having an epoxy group. The epoxy equivalent is not particularly limited, but is preferably 100 to 1,000, with 100 to 500 being particularly preferred. Examples of alicyclic compounds include cyclohexane and cyclopentane. Examples of alicyclic epoxy compounds include 3,4-epoxycyclohexenylmethyl-3',4'-epoxycyclohexenecarboxylate, vinylcyclohexene monoxide 1,2-epoxy-4-vinylcyclohexane, and 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol. The epoxy group-containing resin (epoxy resin) is not particularly limited, and examples include rubber-modified epoxy resins such as biphenylaralkyl epoxy resins, phenylaralkyl epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, dicyclopentadiene epoxy resins, and silicone-modified epoxy resins; ε-caprolactone-modified epoxy resins; phenol novolac epoxy resins such as bisphenol A epoxy resins and bisphenol F epoxy resins; cresol novolac epoxy resins such as ortho-cresol novolac; bisphenol A novolac epoxy resins; cycloaliphatic polyfunctional epoxy resins; glycidyl ester polyfunctional epoxy resins; glycidyl amine polyfunctional epoxy resins; heterocyclic polyfunctional epoxy resins; bisphenol-modified novolac epoxy resins; and polyfunctional modified novolac epoxy resins. These resins may also be further modified with halogen atoms such as Br or Cl. These epoxy resins may be used alone or in combination.

The alcohol to be reacted with the radically polymerizable unsaturated monocarboxylic acid is not particularly limited, and examples thereof include C 2 -C 6 alcohols such as ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, 3,3-dimethylolheptane, 2-ethyl-2-butyl- _1,3 -propanediol, 1,12-dodecanediol, and 1,18-octadecanediol. Examples of suitable alcohols include aliphatic diols such as alkanediol- ₂₂ , 2-butene-1,4-diol, and 2,6-dimethyl-1-octene-3,8-diol; alicyclic diols such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol; aliphatic triols such as glycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-hydroxymethylpentane, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-(hydroxymethyl)pentane, and 2,2-bis(hydroxymethyl)-3-butanol; and polyols having four or more hydroxyl groups such as tetramethylolmethane, pentaerythritol, dipentaerythritol, and xylitol. These alcohols may be used alone or in combination.

A-3 Resin Examples of monomers constituting a polymer of a radically polymerizable unsaturated monocarboxylic acid include the same compounds as those described above, i.e., (meth)acrylic acid, crotonic acid, tiglic acid, angelic acid, cinnamic acid, etc. These radically polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more. Furthermore, examples of esters of radically polymerizable unsaturated monocarboxylic acids constituting the copolymer include the esters used in synthesizing A-1 Resin. Examples of compounds having one or more radically polymerizable unsaturated groups and an epoxy group that are reacted with at least a portion of the carboxyl groups of a polymer of a radically polymerizable unsaturated monocarboxylic acid or at least a portion of the carboxyl groups of a copolymer obtained by reacting a radically polymerizable unsaturated monocarboxylic acid such as (meth)acrylic acid with an ester of a radically polymerizable unsaturated monocarboxylic acid such as (meth)acrylic acid, include glycidyl compounds. Examples of the glycidyl compound include the same compounds as those described above, i.e., glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, pentaerythritol triacrylate monoglycidyl ether, pentaerythritol trimethacrylate monoglycidyl ether, etc. Note that one or more glycidyl groups may be present in one molecule. The above-mentioned compounds having one or more radically polymerizable unsaturated groups and epoxy groups may be used alone or in combination of two or more.

A-4 Resin Examples of polyfunctional epoxy resins include the same compounds as those described above, i.e., rubber-modified epoxy resins such as biphenylaralkyl epoxy resins, phenylaralkyl epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, dicyclopentadiene epoxy resins, and silicone-modified epoxy resins; ε-caprolactone-modified epoxy resins; phenol novolac epoxy resins such as bisphenol A epoxy resins and bisphenol F epoxy resins; cresol novolac epoxy resins such as ortho-cresol novolac; bisphenol A novolac epoxy resins; cycloaliphatic polyfunctional epoxy resins; glycidyl ester polyfunctional epoxy resins; glycidyl amine polyfunctional epoxy resins; heterocyclic polyfunctional epoxy resins; bisphenol-modified novolac epoxy resins; and polyfunctional modified novolac epoxy resins. Furthermore, these resins may also be used with halogen atoms such as Br and Cl introduced therein. These polyfunctional epoxy resins may be used alone or in combination of two or more.

Radically polymerizable unsaturated monocarboxylic acids to be reacted with the epoxy groups of the polyfunctional epoxy resin include, for example, the same compounds as those listed above, i.e., (meth)acrylic acid, crotonic acid, tiglic acid, angelic acid, cinnamic acid, etc. These radically polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more.

The polyisocyanate compound is not particularly limited, but examples include diisocyanates such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), methylene diisocyanate (MDI), methylene biscyclohexyl isocyanate, trimethylhexamethyl diisocyanate, hexane diisocyanate, hexamethylamine diisocyanate, methylene biscyclohexyl isocyanate, toluene diisocyanate, 1,2-diphenylethane diisocyanate, 1,3-diphenylpropane diisocyanate, diphenylmethane diisocyanate, and dicyclohexylmethyl diisocyanate. These polyisocyanate compounds may be used alone or in combination of two or more.

The compound having a hydroxyl group and a carboxyl group is not particularly limited, but examples include dialkanolalkanoic acids such as dimethylolalkanoic acids such as dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolpentanoic acid, and dimethylolheptanoic acid. These compounds having a hydroxyl group and a carboxyl group may be used alone or in combination of two or more.

In addition to the above-mentioned A-1 to A-4 resins, other photosensitive resins include polybasic acid-modified radically polymerizable unsaturated monocarboxylic acid-modified epoxy resins (A-5 resins) obtained by reacting a radically polymerizable unsaturated monocarboxylic acid such as (meth)acrylic acid with at least a portion of the epoxy groups of a polyfunctional epoxy resin having two or more epoxy groups per molecule to obtain a radically polymerizable unsaturated monocarboxylic acid-modified epoxy resin, and then reacting the resulting hydroxyl groups with a polybasic acid or its anhydride to introduce free carboxyl groups. The polyfunctional epoxy resins and radically polymerizable unsaturated monocarboxylic acids that make up A-5 resins can each be the various compounds listed above.

Examples of polybasic acids include succinic acid, maleic acid, adipic acid, citric acid, phthalic acid, phthalic acid derivatives (e.g., tetrahydrophthalic acid, 3-methyltetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, 3-ethyltetrahydrophthalic acid, 4-ethyltetrahydrophthalic acid, hexahydrophthalic acid, 3-methylhexahydrophthalic acid, 4-methylhexahydrophthalic acid, 3-ethylhexahydrophthalic acid, 4-ethylhexahydrophthalic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid, endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid), trimellitic acid, pyromellitic acid, and diglycolic acid. Furthermore, examples of polybasic acid anhydrides include the anhydrides of the polybasic acids listed above. These polybasic acids or their anhydrides may be used alone or in combination of two or more.

The above-mentioned A-1 resin to A-5 resin may be used alone or in combination of two or more types.

The weight average molecular weight of the photosensitive resin is not particularly limited, but the lower limit is preferably 3,000, and more preferably 5,000, from the viewpoints of toughness and dryness to the touch of the cured product of the photosensitive resin composition. On the other hand, the upper limit of the weight average molecular weight is preferably 200,000, and more preferably 50,000, from the viewpoints of preventing an increase in the viscosity of the photosensitive resin composition and achieving excellent coatability.

The double bond equivalent of the photosensitive resin is not particularly limited, but the lower limit is preferably 1000 g/eq, and more preferably 1300 g/eq, from the viewpoint of imparting excellent flexibility to the cured product of the photosensitive resin composition. On the other hand, the upper limit of the double bond equivalent of the photosensitive resin is preferably 3000 g/eq, and more preferably 2000 g/eq, from the viewpoint of imparting strength to the cured product of the photosensitive resin composition.

(B) Photopolymerization Initiator Examples of the photopolymerization initiator include oxime ester-based photopolymerization initiators and acylphosphine oxide-based photopolymerization initiators.

Examples of the oxime ester-based photopolymerization initiator include an oxime ester-based photopolymerization initiator having a diphenyl sulfide skeleton. Examples of the oxime ester-based photopolymerization initiator having a diphenyl sulfide skeleton include an oxime ester-based photopolymerization initiator represented by the following general formula (1):
(wherein R is H or a hydrocarbon group having 1 to 10 carbon atoms, ^R1 is H or a hydrocarbon group having 1 to 10 carbon atoms, and ^R2 is O—C _n H _2n —OH), and n is an integer of 1 to 10. Among these, R is preferably H or a chain hydrocarbon group having 1 to 5 carbon atoms, more preferably H or a chain hydrocarbon group having 1 to 3 carbon atoms, and particularly preferably H. Furthermore, ^R1 is preferably H or a chain hydrocarbon group having 1 to 5 carbon atoms, more preferably H or a chain hydrocarbon group having 1 to 3 carbon atoms, and particularly preferably H. Furthermore, n is preferably an integer of 1 to 5, more preferably an integer of 2 to 4, and particularly preferably 2.

Specific examples of the oxime ester photopolymerization initiator having a diphenyl sulfide skeleton include those represented by the following formula (1-1):
Examples of the compound include compounds represented by the following formula:

In addition, examples of oxime ester photopolymerization initiators other than those having a diphenyl sulfide skeleton include 1,2-octanedione, 1-[4-(phenylthio)-2-(O-benzoyloxime)], ethanone 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), 2-(acetyloxyiminomethyl)thioxanthen-9-one, 1,8-octanedione, 1,8-bis[9-ethyl-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyloxime), 1,8-octanedione, 1,8-bis[9-(2-ethylhexyl)-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyloxime), (Z) Examples include -(9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime.

Examples of acylphosphine oxide photopolymerization initiators include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide.

Examples of photopolymerization initiators (other photopolymerization initiators) other than oxime ester-based photopolymerization initiators and acylphosphine oxide-based photopolymerization initiators include α-aminoalkylphenone-based photopolymerization initiators such as 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy- Examples include 2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl) ketone, benzophenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethyl ketal, acetophenone dimethyl ketal, and p-dimethylaminobenzoic acid ethyl ester.

Of these photopolymerization initiators, it is preferable to use an oxime ester-based photopolymerization initiator having a diphenyl sulfide skeleton in combination with an acylphosphine oxide-based photopolymerization initiator in order to improve the discoloration resistance of the photosensitive resin composition.

The amount of photopolymerization initiator to be added is not particularly limited, but the lower limit is preferably 1.0 part by mass, more preferably 5.0 parts by mass, and particularly preferably 10 parts by mass per 100 parts by mass of photosensitive resin (solid content, the same applies hereinafter), in order to reliably improve sensitivity and resolution. On the other hand, the upper limit of the amount of photopolymerization initiator to be added is preferably 50 parts by mass, and particularly preferably 40 parts by mass, per 100 parts by mass of photosensitive resin in order to reliably reduce warping of the cured product of the photosensitive resin composition.

(C) Reactive Diluent The reactive diluent is, for example, 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. The reactive diluent reinforces the photocuring of the photosensitive resin composition, thereby contributing to the formation of a cured film having sufficient strength.

Examples of reactive diluents include monofunctional (meth)acrylate compounds and bifunctional or higher functional (meth)acrylate compounds. Examples of (meth)acrylate compounds include monofunctional (meth)acrylate compounds such as hydroxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, diethylene glycol mono(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and caprolactone-modified (meth)acrylate, as well as 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, and ethylene oxide. Examples of the (meth)acrylate compound include bifunctional (meth)acrylate compounds such as modified phosphoric acid di(meth)acrylate, allylated cyclohexyl di(meth)acrylate, and isocyanurate di(meth)acrylate, trifunctional (meth)acrylate compounds such as trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, and tris(acryloxyethyl)isocyanurate, and tetrafunctional or higher (meth)acrylate compounds such as ditrimethylolpropane tetra(meth)acrylate, propionic acid-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Examples of the (meth)acrylate compound include monofunctional or bifunctional or higher epoxy (meth)acrylate compounds. These (meth)acrylate compounds may be used alone or in combination of two or more.

The amount of reactive diluent added is not particularly limited, but is preferably 50 to 250 parts by weight, and particularly preferably 100 to 200 parts by weight, per 100 parts by weight of photosensitive resin.

(D) Epoxy Compound Epoxy compounds contribute to increasing the crosslink density of the cured product of the photosensitive resin composition and forming a cured film with sufficient strength. Examples of epoxy compounds include epoxy resins. Examples of epoxy resins include, but are not limited to, rubber-modified epoxy resins such as biphenylaralkyl epoxy resins, phenylaralkyl epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, dicyclopentadiene epoxy resins, and silicone-modified epoxy resins; ε-caprolactone-modified epoxy resins; phenol novolac epoxy resins such as bisphenol A epoxy resins and bisphenol F epoxy resins; cresol novolac epoxy resins such as ortho-cresol novolac; bisphenol A novolac epoxy resins; cyclic aliphatic polyfunctional epoxy resins; glycidyl ester polyfunctional epoxy resins; glycidyl amine polyfunctional epoxy resins; heterocyclic polyfunctional epoxy resins; bisphenol-modified novolac epoxy resins; polyfunctionally modified novolac epoxy resins; and dimer acid glycidyl ester epoxy resins. These epoxy compounds may be used alone or in combination of two or more.

The amount of epoxy compound is not particularly limited, but is preferably 20 to 100 parts by weight, and particularly preferably 30 to 80 parts by weight, per 100 parts by weight of photosensitive resin.

(E) Colorant By incorporating a colorant, a desired color can be imparted to the cured film of the photosensitive resin composition. The colorant is not particularly limited to pigments, dyes, etc., and any colorant can be used depending on the desired color, such as white colorants, blue colorants, green colorants, yellow colorants, purple colorants, black colorants, red colorants, orange colorants, etc. By incorporating a white colorant as the colorant, a white cured film can be formed, thereby improving the reflectance of the cured film. Examples of white colorants include titanium oxide. Examples of titanium oxide include anatase titanium oxide and rutile titanium oxide. Of these, rutile titanium oxide is preferred from the viewpoint of reflectance.

The amount of colorant used is not particularly limited. In the case of a white colorant, the amount is not particularly limited, but in order to improve reflectance and flexibility of the cured film, it is preferably 100 parts by weight or more and 800 parts by weight or less, and particularly preferably 300 parts by weight or more and 500 parts by weight or less, per 100 parts by weight of photosensitive resin.

(F) Latent Antioxidant By incorporating a latent antioxidant, it is possible to obtain an insulating protective film that is free from sensitivity loss even when exposed to a high-temperature atmosphere during reflow treatment (e.g., an atmosphere of 150°C to 260°C) and that is subject to the high-temperature atmosphere of reflow treatment, thereby preventing oxidation of the photosensitive resin composition that forms the insulating protective film and preventing shrinkage upon curing due to heat, even when used in an exposure method using direct imaging exposure. Thus, by incorporating a latent antioxidant, warping of a substrate having an insulating protective film formed from the photosensitive resin composition of the present invention can be prevented, preventing deterioration in the handleability of the substrate and preventing deterioration in the ease of incorporating the substrate into the main body of a device such as a smartphone.

As the latent antioxidant, an aromatic compound having a carbonate ester bond is preferred, as this more reliably prevents oxidation of the photosensitive resin composition that forms the insulating protective film, even in the high-temperature atmosphere of the reflow treatment and even after passing through the high-temperature atmosphere of the reflow treatment, thereby enabling the production of an insulating protective film that more reliably prevents cure shrinkage.

As the aromatic compound having a carbonate bond, an aromatic compound having a chemical structure of R 1 -O-C(═O)-O-Ar(R 2 )(R 3 )- (wherein R ^{1 ,} R ² , and R ³ each independently represent a hydrocarbon group having ¹ to 5 carbon atoms, ^and Ar represents an aromatic hydrocarbon group having 6 carbon ^atoms ) is more preferred, from the viewpoint that oxidation of the photosensitive resin composition that forms the insulating protective film can be more reliably prevented even in the high-temperature atmosphere during reflow treatment and even after the high-temperature atmosphere during reflow treatment can be more reliably prevented, thereby obtaining an insulating protective film that can be more reliably prevented from shrinking on cure. An aromatic compound having a chemical structure of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- (wherein R ¹ , R ² , and R Particularly preferred are aromatic compounds having a plurality of chemical structures of the formula R 1 -O-C(═O)-O-Ar(R 2 )(R ³ )- per molecule, where R 1 is a C 1 to C 5 hydrocarbon group, and Ar is a C 6 aromatic hydrocarbon group. As the aromatic compound having a plurality of chemical structures of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- per molecule, aromatic compounds having 2 to 5 chemical structures of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- per molecule are preferred, and aromatic compounds having 3 to 4 structures per molecule are particularly preferred.

In the high-temperature atmosphere during reflow treatment, the chemical structure R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- undergoes decomposition at the -O-C(═O)-O- site, resulting in the elimination of the protective group and the generation of the chemical structure HO-Ar(R ² )(R ³ )-, forming a compound that functions as an antioxidant.

R ¹ , R ² , and R ³ are not particularly limited as long as they are each independently a hydrocarbon group having 1 to 5 carbon atoms. For example, R ¹ , R ² , and R ³ may all be a hydrocarbon group having 4 carbon atoms represented by C(CH ₃ ) ₃ .

Examples of aromatic compounds having a plurality of R ¹ —O—C(═O)—O—Ar(R ² )(R ³ )— chemical structures in one molecule include compounds of formula (2) and formula (3) below, but the compounds of formula (2) and formula (3) below are merely examples, and aromatic compounds having carbonate ester bonds are not limited to these compounds.

The amount of latent antioxidant to be added is not particularly limited, but the lower limit is preferably 1.0 part by mass, more preferably 2.0 parts by mass, and particularly preferably 4.0 parts by mass per 100 parts by mass of photosensitive resin, in order to more reliably prevent oxidation of the photosensitive resin composition that forms the insulating protective film, even in the high-temperature atmosphere of reflow treatment and after the high-temperature atmosphere of reflow treatment, and to obtain an insulating protective film that more reliably prevents cure shrinkage. On the other hand, the upper limit of the amount of latent antioxidant to be added is preferably 25 parts by mass, and particularly preferably 20 parts by mass, in order to reliably obtain excellent photosensitivity.

In addition to the components (A) to (F) described above, the photosensitive resin composition of the present invention may contain various additives, such as curing catalysts, flame retardants, elastomers, non-reactive diluents, and antifoaming agents, as needed.

Examples of curing catalysts include dicyandiamide (DICY) and its derivatives, melamine and its derivatives, boron trifluoride-amine complex, organic acid hydrazide, diaminomaleonitrile (DAMN) and its derivatives, guanamine and its derivatives, aminimide, and polyamines.

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

By blending an elastomer into a photosensitive resin composition, the cured film of the photosensitive resin composition can be imparted with flexibility, warp resistance, discoloration resistance, and high reflectivity. Examples of elastomers include silicone-based elastomers. Examples of antifoaming agents include silicone-based polymers, hydrocarbon-based polymers, and acrylic-based polymers.

Non-reactive diluents are used to adjust the viscosity, drying properties, coatability, etc. of the photosensitive resin composition. Examples of non-reactive diluents include organic solvents. Examples of organic solvents include ketones such as methyl ethyl ketone; aromatic hydrocarbons such as benzene, toluene, and xylene; alcohols such as methanol, n-propanol, isopropanol, and cyclohexanol; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; cellosolves such as cellosolve and butyl cellosolve; carbitols such as carbitol and butyl carbitol; and esters such as ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, diethylene glycol monomethyl ether acetate, and ethyl diglycol acetate. These non-reactive diluents may be used alone or in combination.

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

Next, we will explain an example of how to use the photosensitive resin composition of the present invention. First, we will explain an example of how to form a solder resist film on a flexible printed wiring board having a circuit pattern formed by etching copper foil on a substrate, using a dry film coated with the photosensitive resin composition of the present invention.

The dry film has a laminated structure comprising a support film (e.g., a thermoplastic resin film such as polyethylene terephthalate film or polyester film), a solder resist layer coated on the support film, and a cover film (e.g., a polyethylene film or polypropylene film) that protects the solder resist layer. The photosensitive resin composition of the present invention is applied to the support film using a known method such as a die coater method to form a coating film of the photosensitive resin composition having a predetermined thickness. If necessary, the formed coating film of the photosensitive resin composition is pre-dried by heating at a temperature of approximately 70 to 120°C for approximately 10 to 60 minutes to volatilize the non-reactive diluent in the photosensitive resin composition. The pre-drying process volatilizes the non-reactive diluent from the photosensitive resin composition, rendering the surface of the coating film tack-free, thereby forming a solder resist layer on the support film. A cover film is then laminated on the resulting solder resist layer to produce a dry film containing the photosensitive resin composition of the present invention.

The dry film thus prepared is laminated onto the flexible printed wiring board while the cover film is peeled off, forming a solder resist layer on the flexible printed wiring board. The support film remains laminated on the solder resist layer. A negative film with a circuit pattern that is transparent except for the lands is then placed on the support film, and ultraviolet light (e.g., wavelengths in the range of 300 to 400 nm) is irradiated onto the negative film to photocure the solder resist layer. The support film is then peeled off, and the unexposed areas corresponding to the lands are removed with a dilute alkaline aqueous solution to develop the solder resist layer. Development methods include spraying and showering. Examples of dilute alkaline aqueous solutions include a 0.5 to 5% by weight sodium carbonate solution. After alkaline development, the solder resist layer is thermally cured (post-cured) for 20 to 80 minutes in a hot air circulation dryer at 130 to 170°C, forming a solder resist film on the flexible printed wiring board.

Next, as an example of a method for using the photosensitive resin composition of the present invention, we will explain the case where the photosensitive resin composition of the present invention is applied as a solder resist film to a flexible printed wiring board having a circuit pattern formed by etching copper foil on a substrate.

The photosensitive resin composition of the present invention is applied to a flexible printed wiring board to the desired thickness using a known coating method, such as screen printing, a spray coater, a bar coater, an applicator, a blade coater, a knife coater, a roll coater, or a gravure coater. After application, if a non-reactive diluent is incorporated into the photosensitive resin composition, the composition is pre-dried by heating at a temperature of approximately 70 to 120°C for approximately 10 to 60 minutes to volatilize the solvent in the photosensitive resin composition, forming a tack-free coating film. Next, the photosensitive resin composition is directly irradiated with active energy rays (e.g., ultraviolet rays) in a direct imaging device according to the desired pattern, photocuring the coating film in the desired pattern. The coating film is then developed by removing the unexposed areas with a dilute alkaline aqueous solution. Examples of the development method include a spray method and a shower method. An example of the dilute alkaline aqueous solution is a 0.5 to 5% by weight aqueous sodium carbonate solution. Next, the developed coating is thermally cured (post-cured) for 20 to 80 minutes in a hot air circulation dryer at 130 to 170°C, thereby forming a cured product of the photosensitive resin composition with the desired pattern on the flexible printed wiring board.

Next, examples of the present invention will be described, but the present invention is not limited to these examples as long as they do not depart from the spirit of the invention.

Examples 1 to 3, Comparative Examples 1 and 2
The components shown in Table 1 below were blended in the blending ratios shown in Table 1 below, and mixed and dispersed at room temperature using a three-roll mill to prepare photosensitive resin compositions used in Examples 1 to 3 and Comparative Examples 1 and 2. Unless otherwise specified, the blending amount of each component shown in Table 1 below means parts by mass.

Details about each component in Table 1 are as follows:

(A) Photosensitive resin FLX-2089: urethane-modified resin (A-4 resin), Nippon Kayaku Co., Ltd. (solid content 65% by mass)
Synthetic Resin An acrylic copolymer resin was synthesized as follows (referred to as "Synthetic Resin A" in Table 1).
A 3-liter separable flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen or air inlet tube was charged with 1500 g of propylene glycol monomethyl ether (Arcosolve PM, Sanyo Chemical Industries, Ltd.), and the temperature was raised to 105°C. A solution containing 142 g of glycidyl methacrylate (Blenmer GH, NOF Corporation), 1279 g of n-butyl methacrylate, 360 g of propylene glycol monomethyl ether, and 15.0 g of dimethyl 2,2'-azobis(2-methylpropionate) (V-601, Wako Pure Chemical Industries, Ltd.) was added dropwise over 3 hours. After the dropwise addition, the reaction was continued for 3 hours under a nitrogen atmosphere to allow maturation. Next, a solution containing 690 g of acrylic acid, 3 g of triphenylphosphine, and 3 g of methoxyphenol was added under an air atmosphere, and the mixture was allowed to react at 110°C for 10 hours. This resulted in a solution of synthetic resin A (solid content 65% by mass) having an acid value of 1.2 mg KOH/g, a double bond equivalent of 1500 g/eq, and a weight average molecular weight of 22000. Synthetic resin A corresponds to resin A-1.

(B) Photopolymerization initiator SPEEDCURE TPO: 2,4,6-trimethylbenzoyldiphenylphosphine oxide, LAMBSON; an oxime ester photopolymerization initiator having a diphenyl sulfide skeleton and a chemical structure shown in formula (1-1):

(C) Reactive diluent EBECRYL3708: Daicel Allnex Co., Ltd.

(D) Epoxy compound EPICRON 860: DIC Corporation EPICOAT 1003: Mitsubishi Chemical Corporation

(E) Colorant: CR-80: White colorant, Ishihara Sangyo Kaisha, Ltd.

(F) Latent antioxidant ADEKA ARCLES GPA-5001: an aromatic compound having a carbonate ester bond, ADEKA Corporation

Curing catalyst DICY-7: Mitsubishi Chemical Corporation, Melamine: Nissan Chemical Industries, Ltd. Flame retardant Exolit OP-935: Clariant Japan AG Elastomer EP-2601: Toray Dow Corning Co., Ltd. Non-reactive diluent EDGAC: Sanyo Chemical Industries, Ltd. Defoamer AC-2000HF: Kyoeisha Chemical Co., Ltd.

Test specimen preparation process Substrate: Polyimide film (film thickness 25 μm, copper foil thickness 12 μm, Nippon Steel & Sumikin Chemical Co., Ltd. "ESPANEX")
Surface treatment: 5% by mass sulfuric acid treatment Printing method: screen printing Dry film thickness: 20 μm
Pre-drying: 80°C, 20 minutes Exposure: 300 mJ/cm ² on the photosensitive resin composition (direct imaging exposure device "Nuvogo1000R" (light source: laser, main wavelength 375 nm, 405 nm), manufactured by Orbotech)
Alkaline development: 1% by weight _{Na2CO3 aqueous} solution, liquid temperature 30°C, spray pressure 0.2 MPa, development time 60 seconds Heat treatment for main curing (post-cure): 150°C, 60 minutes

Evaluation items (1) Sensitivity (direct imaging exposure (LDI exposure) sensitivity)
A step tablet for measuring sensitivity (Kodak, Stouffer 21 step) was placed on the coating of a substrate that had been subjected to the preliminary drying step of the above test specimen preparation process, and the substrate was irradiated through this step tablet with ultraviolet light of wavelengths of 375 nm and 405 nm ^at 300 mJ/cm2 using a direct imaging exposure device "Nuvogo 1000R" to prepare a test piece. This test piece was developed in the same manner as in the above test specimen preparation process. The exposed portion that was not removed after development was represented by a number (step number). A larger step number indicates better sensitivity.

(2) Warpage Resistance After cutting the test specimen prepared in the above test specimen preparation process into a size of 3 cm x 3 cm, the cut test specimen was gently placed on a horizontal table with the top concave, and without applying any external force, the vertical distance between the four corners of the test specimen and the table was measured with a ruler. The maximum value was used and evaluated on the following four-point scale, with a rating of △ or higher being considered a pass.
◎: Less than 1 mm
○: 1 mm or more and less than 3 mm
△: 3 mm or more and less than 5 mm
×: 5 mm or more

The evaluation results are shown in Table 1 below.

As can be seen from Table 1 above, in Examples 1 to 3, which contained a latent antioxidant, the substrate was able to resist warping even after heat treatment at 150°C for 60 minutes without impairing direct imaging exposure (LDI exposure) sensitivity. Therefore, it was found that in Examples 1 to 3, oxidation of the photosensitive resin composition forming the insulating protective film was prevented even in the high-temperature atmosphere of reflow treatment, making it possible to obtain an insulating protective film that prevents cure shrinkage.

On the other hand, as can be seen from Table 1 above, in Comparative Examples 1 and 2, which did not contain a latent antioxidant, the substrate warped after heat treatment at 150°C for 60 minutes, and it was not possible to obtain an insulating protective film that could prevent cure shrinkage.

The photosensitive resin composition of the present invention can prevent substrate warping even in high-temperature environments, making it particularly useful in the field of forming cured insulating coatings on flexible printed wiring boards.

Claims (12)

(A) a photosensitive resin, (B) a photopolymerization initiator, (C) a reactive diluent, (D) an epoxy compound, (E) a colorant, and (F) a latent antioxidant;
the colorant (E) is a white colorant,
The photosensitive resin composition of claim 1, wherein the content of the reactive diluent (C) is 50 parts by mass or more relative to 100 parts by mass of the photosensitive resin (A). (A) a photosensitive resin, (B) a photopolymerization initiator, (C) a reactive diluent, (D) an epoxy compound, (E) a colorant, and (F) a latent antioxidant;
the (E) colorant is a white colorant, and the content of the (E) colorant is 300 parts by mass or more relative to 100 parts by mass of the (A) photosensitive resin composition. 2. The photosensitive resin composition according to claim 1, wherein the content of the colorant (E) is 300 parts by mass or more per 100 parts by mass of the photosensitive resin (A). The photosensitive resin composition according to claim 1, wherein the (F) latent antioxidant is an aromatic compound having a carbonate ester bond. 2. The photosensitive resin composition according to claim ¹ , wherein the latent antioxidant (F) is an aromatic compound having a chemical structure of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- (wherein R 1 , R ² , and R ³ each independently represent a hydrocarbon group having 1 to 5 carbon atoms, and Ar represents an aromatic hydrocarbon group having 6 carbon atoms). 2. The photosensitive resin composition according to claim ¹ , wherein the latent antioxidant (F) is an aromatic compound having a chemical structure of R ¹ -O-C(═O)-O-Ar(R ² )(R ³ )- (wherein R 1 , R ² , and R ³ each independently represent a hydrocarbon group having 1 to 5 carbon atoms, and Ar represents an aromatic hydrocarbon group having 6 carbon atoms) in one molecule. 7. The photosensitive resin composition according to claim 5, wherein ^R1 , ^R2 , and ^R3 are each a hydrocarbon group having 4 carbon atoms represented by C( _CH3 ) ₃ . 7. The photosensitive resin composition according to claim 1, wherein the white colorant is titanium oxide. The photosensitive resin composition according to any one of claims 1 to 6, comprising 1.0 part by mass or more and 25 parts by mass or less of the latent antioxidant (F) per 100 parts by mass of the photosensitive resin (A). A cured product of the photosensitive resin composition described in any one of claims 1 to 6. A flexible printed wiring board comprising the cured product according to claim 10 . A dry film comprising the photosensitive resin composition according to any one of claims 1 to 6.