JP7696515B2 - Photosensitive thermosetting resin composition, dry film, cured product and electronic parts - Google Patents

Description

The present invention relates to a photosensitive thermosetting resin composition, a dry film, a cured product, and an electronic component.

Light-emitting devices are known in which light-emitting diodes (hereinafter sometimes abbreviated as LEDs) are mounted on a printed wiring board. In order to efficiently utilize the light of the LEDs mounted on the printed wiring board, a highly reflective white solder resist film may be formed on the printed wiring board (see, for example, International Publication No. 2008/050768, JP 2008-134621 A, JP 2011-017010 A, and WO 2012/141124 A). In addition, JP 2013-210443 A proposes a photocurable thermosetting resin composition containing a photopolymerization initiator that does not contain a phosphorus atom in its molecular structure.

One aspect of the present invention aims to provide a photosensitive thermosetting resin composition that is capable of forming a solder resist film that has excellent surface curing properties and heat resistance even at low exposure doses and has high reflectivity.

The present invention includes the following aspects: [1] A photosensitive thermosetting resin composition comprising a carboxyl group-containing resin, a photopolymerization initiator, a white pigment, and a thermosetting resin,
The photopolymerization initiator includes an oxime ester-based photopolymerization initiator and a titanocene-based photopolymerization initiator,
the thermosetting resin includes an epoxy resin,
The photosensitive thermosetting resin composition has a b ^* value of 2.0 or less in the L ^* a ^* b ^* color system and a reflectance of 85% or more at a wavelength of 450 nm when the composition is thermally cured.

[2] The photosensitive thermosetting resin composition described in [1], in which the mass-based content ratio of the oxime ester-based photopolymerization initiator to the titanocene-based photopolymerization initiator is within the range of 1:10 to 10:1.

[3] A dry film having a resin layer obtained by applying the photosensitive thermosetting resin composition described in [1] or [2] to a first film and drying it.

[4] A cured product obtained by curing the photosensitive thermosetting resin composition described in [1] or [2].

[5] An electronic component comprising the cured product described in [4].

According to one aspect of the present invention, a photosensitive thermosetting resin composition can be provided that is capable of forming a solder resist film that has excellent surface curing properties and heat resistance even at low exposure doses and has high reflectivity.

In this specification, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In addition, the content of each component in the composition means the total amount of the multiple substances present in the composition when multiple substances corresponding to each component are present in the composition, unless otherwise specified. In addition, the solid content means the substance after removing volatile components (e.g., organic solvents). Furthermore, the upper and lower limits of the numerical ranges described in this specification can be arbitrarily selected and combined from the numerical values exemplified as the numerical ranges. Hereinafter, the embodiments of the present invention will be described in detail. However, the embodiments shown below are examples of photosensitive thermosetting resin compositions, dry films, cured products, and electronic parts for embodying the technical idea of the present invention, and the present invention is not limited to the photosensitive thermosetting resin compositions, dry films, cured products, and electronic parts shown below.

Photosensitive thermosetting resin composition The photosensitive thermosetting resin composition is composed of a carboxyl group-containing resin, a photopolymerization initiator, a white pigment, and a thermosetting resin. The photopolymerization initiator includes at least an oxime ester-based photopolymerization initiator and a titanocene-based photopolymerization initiator. The thermosetting resin includes at least an epoxy resin. The cured product of the photosensitive thermosetting resin composition after thermal curing has a b ^* value of 2.0 or less in the L ^* a ^* b ^* color system and a reflectance of 85% or more at a wavelength of 450 nm.

The photosensitive thermosetting resin composition contains a photopolymerization initiator having a specific structure in combination as a photopolymerization initiator, and thus can form a cured product having excellent surface curability and heat resistance and high reflectance even at a low exposure dose. In addition, discoloration of the cured product due to heat, light, etc. can be suppressed. Furthermore, a latent image can be formed with high sensitivity and excellent resolution. This can be considered to be due to the synergistic effect of the oxime ester photopolymerization initiator and the titanocene photopolymerization initiator, for example. The low exposure dose in the present invention specifically refers to 600 mJ/ ^cm2 or less.

Carboxy group-containing resin The carboxy group-containing resin may be a resin having a carboxy group in the molecule, and may or may not have a photosensitive functional group in the molecule. By including a carboxy group-containing resin in the photosensitive thermosetting resin composition, it is possible to impart alkali developability to the photocured product of the photosensitive thermosetting resin composition obtained by irradiating active energy rays. It is preferable that the carboxy group-containing resin has an ethylenically unsaturated double bond as a photosensitive functional group in the molecule from the viewpoints of photocurability, development resistance, and the like. The ethylenically unsaturated double bond in the molecule may be derived from acrylic acid or methacrylic acid or a derivative thereof. The photosensitive thermosetting resin composition may contain one type of carboxy group-containing resin alone, or may contain two or more types in combination. In addition, when the photosensitive thermosetting resin composition contains only a carboxy group-containing resin that does not have an ethylenically unsaturated double bond as the carboxy group-containing resin, the photosensitive thermosetting resin composition can be made photocurable by using a compound having a plurality of ethylenically unsaturated groups in the molecule, i.e., a photopolymerizable monomer, as described later. Specific examples of the carboxyl group-containing resin include the following compounds (which may be either oligomers or polymers): In the following, (meth)acrylate is a general term for acrylate, methacrylate, and mixtures thereof, and the same applies to other similar expressions.

(1) A carboxyl group-containing resin obtained by copolymerizing an unsaturated carboxylic acid such as (meth)acrylic acid with an unsaturated group-containing compound such as styrene, α-methylstyrene, lower alkyl (meth)acrylate, or isobutylene.

(2) Carboxy group-containing urethane resins obtained by polyaddition reaction of diisocyanates such as aliphatic diisocyanates, branched aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates with carboxy group-containing dialcohol compounds such as dimethylolpropionic acid and dimethylolbutanoic acid, and diol compounds such as polycarbonate-based polyols, polyether-based polyols, polyester-based polyols, polyolefin-based polyols, acrylic-based polyols, bisphenol A-based alkylene oxide adduct diols, and compounds having phenolic hydroxyl groups and alcoholic hydroxyl groups.

(3) Carboxy group-containing photosensitive urethane resins obtained by polyaddition reaction of diisocyanates with partial acid anhydride-modified products of reaction products of bifunctional epoxy resins such as bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bixylenol type epoxy resins, and biphenol type epoxy resins with monocarboxylic acid compounds having ethylenically unsaturated double bonds such as (meth)acrylic acid, carboxy group-containing dialcohol compounds, and diol compounds.

(4) A carboxyl group-containing photosensitive urethane resin having a terminal (meth)acrylation formed by adding a compound having one hydroxyl group and one or more (meth)acryloyl groups in the molecule, such as a hydroxyalkyl (meth)acrylate, during the synthesis of the resin (2) or (3) described above.

(5) A carboxyl group-containing photosensitive urethane resin having a terminal (meth)acrylation formed by adding a compound having one isocyanate group and one or more (meth)acryloyl groups in the molecule, such as an equimolar reactant of isophorone diisocyanate and pentaerythritol triacrylate, during the synthesis of the resin (2) or (3) described above.

(6) A carboxyl group-containing photosensitive resin obtained by reacting a difunctional or more polyfunctional (solid) epoxy resin with (meth)acrylic acid and adding a dibasic acid anhydride to the hydroxyl groups present in the side chains.

(7) A carboxyl group-containing photosensitive resin obtained by reacting a polyfunctional epoxy resin in which the hydroxyl groups of a bifunctional (solid) epoxy resin have been further epoxidized with epichlorohydrin with (meth)acrylic acid, and then adding a dibasic acid anhydride to the resulting hydroxyl groups.

(8) A carboxyl group-containing polyester resin obtained by reacting a dicarboxylic acid such as adipic acid, phthalic acid, or hexahydrophthalic acid with a bifunctional oxetane resin, and then adding a dibasic acid anhydride such as phthalic anhydride, tetrahydrophthalic anhydride, or hexahydrophthalic anhydride to the resulting primary hydroxyl groups.

(9) A carboxyl group-containing photosensitive resin obtained by reacting an epoxy compound having multiple epoxy groups in one molecule with a compound having at least one alcoholic hydroxyl group and one phenolic hydroxyl group in one molecule, such as p-hydroxyphenethyl alcohol, and an unsaturated group-containing monocarboxylic acid, such as (meth)acrylic acid, and then reacting the alcoholic hydroxyl groups of the resulting reaction product with a polybasic acid anhydride, such as maleic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, or adipic acid.

(10) A carboxyl group-containing photosensitive resin obtained by reacting a compound having multiple phenolic hydroxyl groups in one molecule with an alkylene oxide such as ethylene oxide or propylene oxide, reacting the reaction product obtained with an unsaturated group-containing monocarboxylic acid, and reacting the resulting reaction product with a polybasic acid anhydride.

(11) A carboxyl group-containing photosensitive resin obtained by reacting a compound having multiple phenolic hydroxyl groups in one molecule with a cyclic carbonate compound such as ethylene carbonate or propylene carbonate, reacting the reaction product obtained with an unsaturated group-containing monocarboxylic acid, and reacting the resulting reaction product with a polybasic acid anhydride.

(12) A carboxyl group-containing photosensitive resin obtained by further adding a compound having one epoxy group and one or more (meth)acryloyl groups in one molecule to the resins (1) to (11) described above.

Among these, from the viewpoints of suppressing warping in the cured product, heat resistance, reflectance, etc., the carboxyl group-containing resin is preferably a carboxyl group-containing urethane resin produced by a polyaddition reaction between a diisocyanate such as an aliphatic diisocyanate, a branched aliphatic diisocyanate, an alicyclic diisocyanate, or an aromatic diisocyanate, a carboxyl group-containing dialcohol compound such as dimethylolpropionic acid or dimethylolbutanoic acid, and a diol compound such as a polycarbonate-based polyol, a polyether-based polyol, a polyester-based polyol, a polyolefin-based polyol, an acrylic polyol, a bisphenol A-based alkylene oxide adduct diol, or a compound having a phenolic hydroxyl group or an alcoholic hydroxyl group, and the resin is preferably at least one type of carboxyl group-containing photosensitive urethane resin that is (meth)acrylated at the end by adding a compound having one hydroxyl group and one or more (meth)acryloyl groups in the molecule, such as a hydroxyalkyl (meth)acrylate, during the synthesis of the urethane resin. More preferably, the carboxy group-containing resin is a carboxy group-containing urethane resin obtained by a polyaddition reaction between an aliphatic diisocyanate such as an aliphatic diisocyanate, a branched aliphatic diisocyanate, or an alicyclic diisocyanate, a carboxy group-containing dialcohol compound, and a diol compound such as a polycarbonate-based polyol, a polyether-based polyol, a polyester-based polyol, a polyolefin-based polyol, or an acrylic polyol, and may include at least one type of carboxy group-containing photosensitive urethane resin that has been terminally (meth)acrylated by adding a hydroxyalkyl (meth)acrylate during the synthesis of the urethane resin.

From the viewpoint of heat resistance and reflectance of the cured product, it is also preferable that the carboxyl group-containing resin contains at least one type of carboxyl group-containing photosensitive resin obtained by reacting a compound having multiple phenolic hydroxyl groups in one molecule with an alkylene oxide such as ethylene oxide or propylene oxide, reacting the reaction product obtained with an unsaturated group-containing monocarboxylic acid, and reacting the resulting reaction product with a polybasic acid anhydride.

The acid value of the carboxyl group-containing resin may be, for example, 10 mgKOH/g or more and 150 mgKOH/g or less, and preferably 30 mgKOH/g or more and 120 mgKOH/g or less. When the acid value of the carboxyl group-containing resin is 10 mgKOH/g or more, the alkaline developability of the photosensitive resin composition becomes good. Also, when the acid value is 150 mgKOH/g or less, it is easy to draw a good resist pattern. The acid value of the carboxyl group-containing resin is a value measured in accordance with JIS K0070:1992.

The weight average molecular weight of the carboxyl group-containing resin may vary depending on the resin skeleton, and may generally be 2,000 to 150,000, and preferably 5,000 to 100,000. By having a weight average molecular weight of 2,000 or more, tack-free performance, resolution, etc. can be improved. In addition, by having a weight average molecular weight of 150,000 or less, the developability, storage stability, etc. of the photosensitive resin composition can be improved. Here, the weight average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography.

The content of the carboxyl group-containing resin in the photosensitive thermosetting resin composition may be, for example, 5% by mass or more and 40% by mass or less, preferably 10% by mass or more and 35% by mass or less, calculated as solid content. By having a carboxyl group-containing resin content of 5% by mass or more, the strength of the coating film can be improved. In addition, by having a carboxyl group-containing resin content of 40% by mass or less, the viscosity of the photosensitive resin composition becomes appropriate, and the processability is improved.

Photosensitive Compound The photosensitive thermosetting resin composition may further contain at least one photosensitive compound that does not have a carboxy group. The photosensitive compound may be, for example, a compound having an ethylenically unsaturated bond. The photosensitive compound may be a compound having a plurality of ethylenically unsaturated bonds.

Specific examples of compounds having an ethylenically unsaturated bond include the following compounds: hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate; acrylamides such as N,N-dimethyl (meth)acrylamide, N-methylol (meth)acrylamide and N,N-dimethylaminopropyl (meth)acrylamide; aminoalkyl (meth)acrylates such as N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate; di(meth)acrylates derived from alkylene glycols such as ethylene glycol, polyethylene glycol, propylene glycol and polypropylene glycol; hexanediol, trimethylolpropane, pentane, etc. Examples of the polyhydric (meth)acrylates include polyhydric alcohols such as pentaerythritol, dipentaerythritol, and tris-hydroxyethyl isocyanurate, or their ethylene oxide adducts, propylene oxide adducts, or ε-caprolactone adducts; aromatic group-containing polyhydric (meth)acrylates derived from ethylene oxide adducts or propylene oxide adducts of bisphenol A, bisphenol F, and these phenols; polyhydric (meth)acrylates derived from glycidyl ethers such as glycerin diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, and triglycidyl isocyanurate; and the like. In addition to the above, examples of the polyhydric (meth)acrylates include (meth)acrylates obtained by directly (meth)acrylating polyols such as polyether polyols, polycarbonate diols, hydroxyl group-terminated polybutadiene, and polyester polyols, or urethane (meth)acrylating them via a diisocyanate compound, and melamine (meth)acrylates.

Further examples include epoxy (meth)acrylate resins obtained by reacting (meth)acrylic acid with multifunctional epoxy resins such as cresol novolac epoxy resins, and epoxy urethane (meth)acrylate compounds obtained by reacting the hydroxyl groups of the epoxy (meth)acrylate resins with half urethane compounds of hydroxyacrylates such as pentaerythritol tri(meth)acrylate and diisocyanates such as isophorone diisocyanate. Such epoxy (meth)acrylate resins can improve photocurability without reducing tactile dryness.

The photosensitive compound may contain at least aromatic group-containing polyvalent (meth)acrylates derived from bisphenol A, bisphenol F, and ethylene oxide or propylene oxide adducts of these phenols. The photosensitive resin may contain one type of photosensitive compound alone or two or more types in combination.

When the photosensitive thermosetting resin composition contains a photosensitive compound, the content of the photosensitive compound may be, for example, 5 parts by mass or more and 100 parts by mass or less, and preferably 10 parts by mass or more and 80 parts by mass or less, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. When the content is 5 parts by mass or more, the photocurability is improved, and the pattern formability by alkaline development after irradiation with active energy rays tends to be further improved. Also, when the content is 100 parts by mass or less, sufficient solubility in an alkaline aqueous solution after irradiation with active energy rays is obtained, and the strength of the formed coating film tends to be further improved.

Photopolymerization Initiator The photosensitive thermosetting resin composition contains at least an oxime ester-based photopolymerization initiator and a titanocene-based photopolymerization initiator as a photopolymerization initiator.

Oxime ester photopolymerization initiator The oxime ester photopolymerization initiator may be any photopolymerization initiator having an O-acyloxime structure in the molecule, and may be, for example, a photopolymerization initiator containing a partial structure represented by the following formula (I).

In the formula, R ¹ represents a hydrogen atom, a phenyl group which may have a substituent, an alkyl group having 1 to 20 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 8 carbon atoms, an alkanoyl group having 2 to 20 carbon atoms, or a benzoyl group which may have a substituent. R ² represents a phenyl group which may have a substituent, an alkyl group having 1 to 20 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 8 carbon atoms, an alkanoyl group having 2 to 20 carbon atoms, or a benzoyl group which may have a substituent. Examples of the substituent in the phenyl group represented by R ¹ or R ² include an alkyl group having 1 to 6 carbon atoms, a phenyl group, and a halogen atom. The number of substituents in the phenyl group may be 1 to 5. The alkyl group represented by R ¹ or R ² may be linear or branched, and may be substituted with one or more hydroxyl groups. At least one of the methylene groups constituting the alkyl group may be substituted with an oxygen atom or a carbonyl group. Examples of the substituent in the benzoyl group represented by ^R1 or ^R2 include an alkyl group having 1 to 6 carbon atoms, a phenyl group, etc. The number of the substituent in the benzoyl group may be 1 to 5.

Examples of compounds that can be substituted with the partial structure represented by formula (I) include diarylsulfane, 9H-carbazole, thioxanthen-9-one, fluorene, and derivatives thereof. The partial structure represented by formula (I) may be bonded by substituting a hydrogen atom of these compounds, or may be bonded via a carbonyl group.

Specific examples of oxime ester photopolymerization initiators containing the partial structure represented by formula (I) include compounds represented by the following formulas (I-1), (I-2), (I-3), etc.

In formula (I-1), R ¹¹ has the same meaning as R ¹ in formula (I), and R ¹² has the same meaning as R ² in formula (I). R ¹³ represents a hydrogen atom, a hydroxy group, a carboxy group, a hydroxyalkoxy group, a hydroxyalkoxycarbonyl group, or the like. The hydroxyalkoxy group in R ¹³ may have 1 to 20 carbon atoms. n represents 0 or 1.

In formula (I-2), R ²¹ has the same meaning as R ¹ in formula (I), and R ²² and R ²⁴ each independently represent a phenyl group which may have a substituent, an alkyl group having 1 to 20 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 8 carbon atoms, an alkanoyl group having 2 to 20 carbon atoms, or a benzoyl group which may have a substituent. Examples of the substituent in the phenyl group represented by R ²⁴ include an alkyl group having 1 to 18 carbon atoms and an organic group having an acetal bond. The organic group having an acetal bond may be, for example, a (2,2-dimethyl-1,3-dioxolan-4-yl)methoxy group. R ²³ represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms including the substituent, a phenyl group, a benzyl group, a benzoyl group, an alkanoyl group having 2 to 12 carbon atoms, an alkoxycarbonyl group having 2 to 12 carbon atoms, or a phenoxycarbonyl group. When the alkyl group constituting the alkoxycarbonyl group represented by ^R23 has 2 or more carbon atoms, it may be substituted with at least one hydroxyl group, and at least one methylene group constituting the alkyl group may be substituted with an oxygen atom.

In formula (I-3), R ³¹ has the same meaning as R ¹ in formula (I), and R ³² has the same meaning as R ² in formula (I). R ³³ represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms including a substituent, or the like.

Specific examples of oxime ester photopolymerization initiators containing the structural portion represented by formula (I) include 1-[4-(phenylsulfanyl)phenyl]-1,2-octanedione 2-(O-benzoyloxime), 1-{4-[4-(2-hydroxyethoxy)phenylsulfanyl]phenyl}propane-1,2-dione 2-(O-acetyloxime), 2-(acetyloxyiminomethyl)thioxanthen-9-one, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone 1-(O-acetyloxime), 1-[9-ethyl-6-(2-methyl- 4-tetrahydrofuranylmethoxybenzoyl)-9H-carbazol-3-yl]ethanone 1-(O-acetyloxime), 1-[9-ethyl-6-{2-methyl-4-(2,2-dimethyl-1,3-dioxolanyl)methoxybenzoyl}-9H-carbazol-3-yl]ethanone 1-(O-acetyloxime), 1-[4-[3-[4-[[2-(acetyloxy)ethyl]sulfonyl]-2-methylbenzoyl]-6-[1-[(acetyloxy)imino]ethyl]-9H-carbazol]-9-yl]phenyloctanone 1-(O-acetyloxime), etc. These oxime ester photopolymerization initiators may be used alone or in combination of two or more.

Commercially available oxime ester photopolymerization initiators include ADEKA ARCLES NCI-700, ADEKA ARCLES NCI-730, ADEKA ARCLES NCI-831, ADEKA ARCLES NCI-930; 1-4-[[4-(2-hydroxyethoxy)phenyl]thio]phenyl]-1,2-propanedione 2-(O-acetyloxime) (all manufactured by ADEKA Corporation), DFI-020, DFI-091 (all manufactured by Daito Chemistry Corporation), CGI-325, Irgacure OXE01, Irgacure OXE02; 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone 1-(O-acetyloxime), Irgacure OXE03, Irgacure OXE04 (all manufactured by BASF Japan Ltd.) can also be used.

The content of the oxime ester photopolymerization initiator in the photosensitive thermosetting resin composition may be, for example, 0.01 parts by mass or more and 10 parts by mass or less, preferably 0.02 parts by mass or more and 8 parts by mass or less, and more preferably 0.05 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. When the content of the oxime ester photopolymerization initiator is 0.01 parts by mass or more, sufficient photocuring can be achieved. Also, when the content is 10 parts by mass or less, there is a tendency for the balance between surface curing and bottom curing to be good. In one embodiment, the content of the oxime ester photopolymerization initiator may be 3 parts by mass or less, 2 parts by mass or less, or 1 part by mass or less.

Titanocene Photopolymerization Initiator Examples of the titanocene photopolymerization initiator include a compound represented by the following formula (II).

In the formula, R ⁹ and R ¹⁰ each independently represent a halogen atom, an aryl group, a halogenated aryl group, or a heterocycle-containing halogenated aryl group.

Examples of the titanocene photopolymerization initiator represented by formula (II) include di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(1H-pyrrol-1-yl)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(3-(1H-pyrrol-1-yl)propyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((1H-pyrrol-1-yl)methyl)phenyl]titanium, bis(methylcyclopentadienyl)-bis[2,6-difluoro-3-((1H-pyrrol-1-yl)methyl)phenyl]titanium, and di(cyclopentadienyl)-bis[2,6-difluoro-3-((2,5-dimethyl-1H-pyrrol-1-yl)methyl)phenyl]titanium. )methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((2-isopropyl-5-methyl-1H-pyrrol-1,6-yl)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((2-(2-methoxyethyl)-5-methyl-1H-pyrrol-1-yl)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((3-trimethylsilyl-2,5-dimethyl-1H-pyrrol-1-yl)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((2,5-dimethyl-3-(bis(2-methoxyethyl)aminomethyl)-1H-pyrrol-1-yl di(cyclopentadienyl)-bis[2,6-difluoro-3-((2,5-bis(morpholinomethyl)-1H-pyrrol-1-yl)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((2,5-dimethyl-3-(1,3-dioxolan-2-yl)-1H-pyrrol-1-yl)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-4-((2,5-dimethyl-1H-pyrrol-1-yl)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-methyl-4-(2-(1H-pyrrol-1-yl)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-methyl-4-(2-(1H-pyrrol-1-yl)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((2,3,4,5-tetramethyl-1H-pyrrol-1-yl)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,3,5,6-tetrafluoro-4-(3-(1H-pyrrol-1-yl)propyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(1H-pyrrol-1-yl)propyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(1-methyl-2-(1H-pyrrol-1-yl)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(3-(2-isoindol-2-yl)propyl)phenyl]titanium , di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(4,5,6,7-tetrahydro-isoindol-2-yl)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(6-(9-carbazol-9-yl)hexyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(3-(2,3,4,5,6,7,8,9-octahydro-1-carbazol-9-yl)propyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(3-(4,5,6,7-tetrahydro-2-methyl-1-indol-1-yl)propyl)phenyl]titanium, di(cyclopentadienyl)-bis [2,6-difluoro-3-((acetylamino)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(propionylamino)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(3-(acetylamino)propyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(4-(pivaloylamino)butyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(2,2-dimethylpentanoylamino)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(3-(benzoylamino)propyl)phenyl]titanium di(cyclopentadienyl)-bis[2,6-difluoro-3-((2,2-dimethylpentanoylamino)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(2,2-dimethyl-3-chloropropanoylamino)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((2,2-dimethyl-3-ethoxypropanoylamino)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(lauroylamino)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(N-allylmethylsulfonylamino)ethyl di(cyclopentadienyl)-bis[2,6-difluoro-3-(3-(N-isobutylphenylsulfonylamino)propyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-((methylsulfonylamino)methyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(3-(ethylsulfonylamino)propyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(butylsulfonylamino)ethyl)phenyl]titanium, di(cyclopentadienyl)-bis[2,6-difluoro-3-(4-(trisulfonylamino)propyl)phenyl]titanium, bis(η ^5-2,4 -cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium, etc. These titanocene photopolymerization initiators may be used alone or in combination of two or more.

Commercially available titanocene photopolymerization initiators include JMT-784 (manufactured by Yueyang Jinmaotai Technology Co., Ltd.; di(η ⁵ -2,4-cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium).

The content of the titanocene-based photopolymerization initiator in the photosensitive thermosetting resin composition may be, for example, 0.01 parts by mass or more and 10 parts by mass or less, preferably 0.02 parts by mass or more and 8 parts by mass or less, and more preferably 0.05 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. When the content of the titanocene-based photopolymerization initiator is 0.01 parts by mass or more, sufficient photocuring can be achieved. Also, when it is 10 parts by mass or less, there is a tendency that uneven curing can be suppressed. In one embodiment, the content of the titanocene-based photopolymerization initiator may be 2 parts by mass or less, 1 part by mass or less, or 0.5 parts by mass or less.

The mass ratio of the oxime ester photopolymerization initiator and the titanocene photopolymerization initiator in the photopolymerization initiator may be, for example, 1:10 to 10:1 (oxime ester photopolymerization initiator: titanocene photopolymerization initiator), preferably 1:8 to 8:1, more preferably 1:5 to 5:1, and even more preferably 1:2 to 2:1. If the ratio is within the above range, the balance between surface curability and deep curability is good, and a good pattern can be formed.

The total content of the titanocene photopolymerization initiator and the oxime ester photopolymerization initiator in the photosensitive thermosetting resin composition may be, for example, 0.01 to 10 parts by mass, preferably 0.1 to 2 parts by mass, and more preferably 0.2 to 1 part by mass, in terms of solid content, per 100 parts by mass of the carboxyl group-containing resin. When the total content of the titanocene photopolymerization initiator and the oxime ester photopolymerization initiator is 0.01 parts by mass or more, sufficient photocuring can be achieved. Furthermore, when it is 10 parts by mass or less, there is a tendency that uneven curing can be suppressed.

In addition to the oxime ester photopolymerization initiator and the titanocene photopolymerization initiator, the photopolymerization initiator may further include other photopolymerization initiators other than the oxime ester and titanocene types. Examples of other photopolymerization initiators include benzophenone photopolymerization initiators, acetophenone photopolymerization initiators, aminoacetophenone photopolymerization initiators, benzoin ether photopolymerization initiators, benzyl ketyl photopolymerization initiators, oxime ether photopolymerization initiators, alkylphenone photopolymerization initiators, and acylphosphine oxide photopolymerization initiators.

When the photopolymerization initiator contains other photopolymerization initiators, in one embodiment, the content thereof may be, for example, 80% by mass or more and 99% by mass or less, and preferably 90% by mass or less and 97% by mass or less, calculated as solid content relative to the total mass of the photopolymerization initiator. In another embodiment, the content may be, for example, 10% by mass or less, preferably 1% by mass or less, and more preferably 0.1% by mass or less.

White Pigment The photosensitive thermosetting resin composition contains at least one type of white pigment. By containing a white pigment, the cured product can be whitened. Examples of white pigments include zinc oxide, potassium titanate, zirconium oxide, antimony oxide, white lead, zinc sulfide, and lead titanate. From the viewpoint of reflectance and discoloration suppression effect, the white pigment preferably contains at least titanium oxide. As the titanium oxide, those produced by the sulfuric acid method, the chlorine method, etc., rutile type titanium oxide, anatase type titanium oxide, or titanium oxide surface-treated with a hydrous metal oxide or an organic compound can be used. Among these titanium oxides, rutile type titanium oxide is preferred from the viewpoint of photocatalytic activity. By using rutile type titanium oxide, a more stable cured product (for example, a solder resist film) can be obtained. Specific examples of rutile titanium oxide include TR-600, TR-700, TR-750, and TR-840 (manufactured by Fuji Titanium Industry Co., Ltd.), R-550, R-580, R-630, R-820, CR-50, CR-60, and CR-90 (manufactured by Ishihara Sangyo Kaisha, Ltd.), and KR-270, KR-310, and KR-380 (manufactured by Titanium Industry Co., Ltd.). Among these rutile titanium oxides, it is particularly preferable to use titanium oxide whose surface is treated with hydrous alumina or aluminum hydroxide from the viewpoints of dispersibility in the composition, storage stability, and flame retardancy. The white pigment may be used alone or in combination of two or more kinds.

The volume average particle size of the white pigment may be, for example, 10 nm to 5 μm, and preferably 100 nm to 1 μm. The volume average particle size of the white pigment is measured as the particle size corresponding to 50% of the cumulative volume from the small diameter side in the cumulative particle size distribution based on volume measured, for example, using a laser diffraction particle size distribution measuring device.

The whiteness of the white pigment may be, for example, 80 or more, and preferably 85 or more. The whiteness is measured, for example, using a spectrophotometer (such as PF10 manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS P8148:2018 "Method of measurement of ISO whiteness (diffuse blue light reflectance)".

The content of the white pigment in the photosensitive thermosetting resin composition may be, for example, 200 parts by mass or more and 1000 parts by mass or less, and preferably 250 parts by mass or more and 800 parts by mass or less, per 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. When the content of the white pigment is 200 parts by mass or more, sufficient reflectance can be achieved in the cured product. Also, when the content is 1000 parts by mass or less, the viscosity increase of the composition can be suppressed, and the coating and moldability are good, and the brittleness of the cured product tends to be suppressed.

Thermosetting resin The photosensitive thermosetting resin composition contains at least one type of thermosetting resin. As the thermosetting resin, known and commonly used ones such as isocyanate compounds, blocked isocyanate compounds, amino resins, maleimide compounds, benzoxazine resins, carbodiimide resins, cyclocarbonate compounds, epoxy resins, polyfunctional oxetane compounds, and episulfide resins can be used. Among these, the thermosetting resin preferably has at least one type of cyclic ether group and cyclic thioether group (hereinafter abbreviated as cyclic (thio)ether group) in one molecule. There are many types of thermosetting components having these cyclic (thio)ether groups on the market, and various properties can be imparted depending on their structure.

Thermosetting resins having multiple cyclic (thio)ether groups in the molecule are compounds that have multiple 3-, 4-, or 5-membered cyclic ether groups or cyclic thioether groups in the molecule, and examples of such compounds include compounds having multiple epoxy groups in the molecule, i.e., polyfunctional epoxy compounds, compounds having multiple oxetanyl groups in the molecule, i.e., polyfunctional oxetane compounds, and compounds having multiple thioether groups in the molecule, i.e., episulfide compounds.

Specific examples of polyfunctional epoxy compounds include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, brominated bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, novolac type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, N-glycidyl type epoxy resins, bisphenol A novolac type epoxy resins, bixylenol type epoxy resins, biphenol type epoxy resins, chelate type epoxy resins, glyoxal type epoxy resins, amino group-containing epoxy resins, rubber-modified epoxy resins, dicyclopentadiene phenolic type epoxy resins, diglycidyl phthalate resins, heterocyclic epoxy resins, tetraglycidyl xylenoyl ethane resins, silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, etc. In addition, as polyfunctional epoxy resins, those in which halogen atoms such as chlorine and bromine, and atoms such as phosphorus have been introduced into their structures may be used. This can impart, for example, flame retardancy. The polyfunctional epoxy resin may be used alone or in combination of two or more kinds.

Examples of the polyfunctional oxetane compound include polyfunctional oxetanes such as bis[(3-methyl-3-oxetanylmethoxy)methyl]ether, bis[(3-ethyl-3-oxetanylmethoxy)methyl]ether, 1,4-bis[(3-methyl-3-oxetanylmethoxy)methyl]benzene, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, (3-methyl-3-oxetanyl)methyl acrylate, (3-ethyl-3-oxetanyl)methyl acrylate, (3-methyl-3-oxetanyl)methyl methacrylate, (3-ethyl-3-oxetanyl)methyl methacrylate, and oligomers or copolymers thereof, as well as ethers of oxetane alcohols with novolak resins, poly(p-hydroxystyrene), cardo-type bisphenols, calixarenes, calixresorcinarenes, or resins having a hydroxyl group such as silsesquioxane. Other examples include copolymers of unsaturated monomers having an oxetane ring and alkyl (meth)acrylates.

An example of an episulfide resin is YL7000 (bisphenol A type episulfide resin) manufactured by Mitsubishi Chemical Corporation. In addition, episulfide resins in which the oxygen atoms of the epoxy groups of novolac type epoxy resins are replaced with sulfur atoms using a similar synthesis method can also be used.

The content of the thermosetting resin in the photosensitive thermosetting resin composition may be, for example, 10 parts by mass to 100 parts by mass, and preferably 20 parts by mass to 80 parts by mass, per 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. If the content of the thermosetting resin is within the above range, the cured product of the photosensitive resin composition has good solder heat resistance, and also tends to have good properties, particularly electrical insulation, when used as an insulating protective film for printed wiring boards.

The photosensitive thermosetting resin composition may contain a thermosetting catalyst in addition to the thermosetting resin. Examples of the thermosetting catalyst include imidazole derivatives such as imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole; amine compounds such as dicyandiamide, benzyldimethylamine, 4-(dimethylamino)-N,N-dimethylbenzylamine, 4-methoxy-N,N-dimethylbenzylamine, and 4-methyl-N,N-dimethylbenzylamine; hydrazine compounds such as adipic acid dihydrazide and sebacic acid dihydrazide; and phosphorus compounds such as triphenylphosphine. Examples of commercially available compounds include 2MZ-A, 2MA-OK, 2PHZ-PW, and 2P4BHZ-PW (all manufactured by Shikoku Chemical Industry Co., Ltd.; all are trade names of imidazole-based compounds), DBU, DBN, U-CATSA102, and U-CAT5002 (all manufactured by San-Apro Co., Ltd.; all are bicyclic amidine compounds and salts thereof). The compound is not particularly limited to these, and may be a heat curing catalyst for an epoxy resin or an oxetane compound, or may be one that promotes the reaction of at least one of an epoxy group and an oxetanyl group with a carboxy group. Also usable are S-triazine derivatives such as guanamine, acetoguanamine, benzoguanamine, melamine, 2,4-diamino-6-methacryloyloxyethyl-S-triazine, 2-vinyl-2,4-diamino-S-triazine, 2-vinyl-4,6-diamino-S-triazine·isocyanuric acid adduct, and 2,4-diamino-6-methacryloyloxyethyl-S-triazine·isocyanuric acid adduct. The single thermal curing catalyst may be used alone or in combination of two or more.

When the photosensitive thermosetting resin composition contains a thermosetting catalyst, the amount of the catalyst may be, for example, 0.1 parts by mass or more and 20 parts by mass or less, and preferably 0.5 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of the thermosetting resin, calculated as solid content.

The photosensitive thermosetting resin composition may further contain at least one filler selected from the group consisting of inorganic fillers and organic fillers, if necessary, for the purpose of improving properties such as adhesion, hardness, and heat resistance. Examples of inorganic fillers include barium sulfate, calcium carbonate, silicon oxide, amorphous silica, talc, clay, hydrotalcite, and mica powder, and examples of organic fillers include silicon powder, nylon powder, and fluorine powder. Among the above fillers, silica is particularly excellent in terms of low moisture absorption and low volume expansion. Silica may be fused or crystalline, or may be a mixture of these, but silica surface-treated with a coupling agent or the like is preferable because it can improve electrical insulation. The average particle size of the filler is desirably 25 μm or less, more desirably 10 μm or less, and even more desirably 3 μm or less. When the photosensitive thermosetting resin composition contains a filler, the content of the filler may be, for example, 150 parts by mass or less, and preferably 50 parts by mass or less, per 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. When the content of the filler is in the above ratio, the folding resistance of the cured film is good.

The photosensitive thermosetting resin composition may contain additives other than the above components. Examples of additives include thickeners such as organic bentonite and montmorillonite, at least one of silicone-based, fluorine-based, and polymer-based defoamers and leveling agents, and fiber reinforcements such as glass fiber, carbon fiber, and boron nitride fiber. In addition, adhesion promoters, thermal polymerization inhibitors, peroxide decomposition agents, ultraviolet absorbers, silane coupling agents such as thiazole-based and triazole-based silane coupling agents, dispersants, defoamers, plasticizers, foaming agents, flame retardants, antistatic agents, antiaging agents, antibacterial and antifungal agents, etc. can be added as necessary.

The photosensitive thermosetting resin composition may further contain at least one of a radical scavenger and a peroxide decomposer as necessary. This can suppress functional deterioration in the cured product. The radical scavenger and the peroxide decomposer may be so-called antioxidants.

Examples of radical scavengers include phenolic compounds such as hydroquinone, 4-t-butylcatechol, 2-t-butylhydroquinone, hydroquinone monomethyl ether, 2,6-di-t-butyl-p-cresol, 2,2-methylene-bis(4-methyl-6-t-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, and 1,3,5-tris(3',5'-di-t-butyl-4-hydroxybenzyl)-S-triazine-2,4,6-(1H,3H,5H)trione; quinone compounds such as methaquinone and benzoquinone; and amine compounds such as bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate and phenothiazine.

The radical scavenger may be a commercially available product, such as ADK STAB (registered trademark) AO-30, ADK STAB AO-330, ADK STAB AO-20, ADK STAB LA-77, ADK STAB LA-57, ADK STAB LA-67, ADK STAB LA-68, ADK STAB LA-87 (all manufactured by ADEKA CORPORATION), Irganox (registered trademark) 1010, Irganox 1035, Irganox 1076, Irganox 1135, Tinuvin (registered trademark) 111FDL, Tinuvin 123, Tinuvin 144, Tinuvin 152, Tinuvin 292, Tinuvin 5100 (all manufactured by BASF Japan Ltd.).

The ultraviolet absorber may be a commercially available product, such as Tinuvin PS, Tinuvin 99-2, Tinuvin 109, Tinuvin 384-2, Tinuvin 900, Tinuvin 928, Tinuvin 1130, Tinuvin 400, Tinuvin 405, Tinuvin 460, Tinuvin 479 (all manufactured by BASF Japan Ltd.).

The photosensitive thermosetting oil composition may further contain an organic solvent. By containing an organic solvent, each component can be easily dissolved or dispersed. In addition, the viscosity can be easily adjusted to a level suitable for the application method, such as coating. Examples of the organic solvent include aromatic solvents such as toluene, xylene, ethylbenzene, and nitrobenzene; aliphatic hydrocarbon solvents such as cyclohexane; ether solvents such as diethylene glycol dimethyl ether and ethylene glycol diethyl ether; ester solvents such as carbitol acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, dipropylene glycol methyl ether acetate, methyl methoxypropionate, ethyl methoxypropionate, methyl ethoxypropionate, ethyl ethoxypropionate, ethyl ethyl acetate, n-butyl acetate, isoamyl acetate, ethyl lactate, and γ-butyrolactone; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and isophorone; amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; sulfoxide solvents such as dimethyl sulfoxide; and halogenated hydrocarbon solvents such as chloroform and methylene chloride. The organic solvent may be used alone or in combination of two or more. The content of the organic solvent may be appropriately determined depending on the desired viscosity, etc.

The photosensitive thermosetting resin composition is obtained by dissolving or dispersing each of the above-mentioned components using a mixer, such as a disperser, kneader, three-roll mill, bead mill, etc.

In one embodiment, the photosensitive thermosetting resin composition includes a photosensitive resin, a photopolymerization initiator, a white pigment, and an epoxy resin, the photosensitive resin includes a carboxyl group-containing resin, the photopolymerization initiator includes an oxime ester photopolymerization initiator and a titanocene photopolymerization initiator, the mass ratio of the white pigment content to the photosensitive resin content may be 1.2 or more and 5 or less, and the mass ratio of the total content of the oxime ester photopolymerization initiator and the titanocene photopolymerization initiator to the white pigment content may be 0.0004 or more and 0.002 or less. By having the white pigment content within the above range and the photopolymerization initiator within the above range, excellent whiteness and high reflectance at a wavelength of 450 nm can be achieved.

Cured Product The cured product of the photosensitive thermosetting resin composition can exhibit high whiteness and excellent reflectance at a wavelength of 450 nm. The cured product of the photosensitive thermosetting resin composition can be obtained, for example, under the following curing conditions.

Curing conditions: The photosensitive thermosetting resin composition is applied to a substrate so that the film thickness after thermal curing is 55 μm, and then dried at 80° C. for 30 minutes. The composition is exposed to light at 400 mJ/cm ² using a high-pressure mercury lamp, and developed (30° C., 0.2 MPa, 1% by mass Na ₂ CO ₃ aqueous solution) for 60 seconds. Then, the composition is thermally cured at 150° C. for 60 minutes to obtain a cured product.

The cured product of the photosensitive thermosetting resin composition after thermal curing has a b ^* value of 2.0 or less in the L ^* a ^* b ^* color system. The b ^* value may be preferably 1.8 or less, more preferably 1.5 or less. The b ^* value in the L ^* a ^* b ^* color system is measured for a cured product having a thickness of 55 μm produced under the above-mentioned production conditions using a spectrophotometer (manufactured by Konica Minolta, Inc., model number: CM-5). When the b ^* value of the cured product is within the above range, yellowing due to heating tends to be suppressed.

The cured product also has a reflectance of 85% or more at a wavelength of 450 nm. The reflectance at a wavelength of 450 nm may preferably be 88% or more. The reflectance at a wavelength of 450 nm is measured for a cured product having a thickness of 55 μm produced under the above-mentioned curing conditions using a spectrophotometer (manufactured by Konica Minolta, Inc., model number: CM-5) with a measurement diameter of 8 mm using the SCI method. When the reflectance of the cured product is within the above range, the light extraction efficiency of the display improves, and reflected light tends to be utilized more effectively.

The cured product formed from the photosensitive thermosetting resin composition exhibits excellent heat resistance and can maintain whiteness and reflectance. Specifically, for example, ΔEab ^* after one heat treatment (reflow process) at a maximum temperature of 260°C for 10 seconds may be, for example, 2.0 or less, preferably 1.0 or less. Here, ΔEab ^* is a value calculated by the following formula (1) using ΔL ^* , Δa ^* , and Δb ^* , which are the differences between L ^* , a ^* , and b ^* before heat treatment and L ^* , a ^* , and b ^* after heat treatment, and is an index indicating the degree of discoloration.
ΔEab ^* = ((ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ) ^(1/2) ...(1)

The decrease in reflectance at a wavelength of 450 nm may be, for example, 5% or less, and preferably 2% or less. Here, the decrease in reflectance is calculated by subtracting the reflectance (%) measured in the cured product after heat treatment from the reflectance (%) measured in the cured product before heat treatment.

The photosensitive thermosetting resin composition can be applied to a printed circuit board by a method selected from commonly used application methods to form a resin composition layer. It can also be used in various forms and applications, such as dry films or prepregs. Various solvents can be used depending on the method of use and application, and in some cases, not only good solvents but also poor solvents can be used.

The photosensitive thermosetting resin composition can be adjusted to a viscosity suitable for the application method using, for example, the organic solvent, applied to a substrate, and the organic solvent contained in the composition is evaporated and dried (temporarily dried) at a temperature of about 60°C to 100°C to form a tack-free resin composition layer. Examples of application methods include dip coating, flow coating, roll coating, bar coater, screen printing, curtain coating, and spray coating. The photosensitive thermosetting resin composition can also be applied to a carrier film, dried, and rolled up as a film, which is then laminated onto a substrate to form a resin composition layer. Thereafter, the photosensitive thermosetting resin composition is selectively exposed to active energy rays through a photomask on which a pattern has been formed, or directly exposed to a pattern using a laser direct exposure machine, using a contact (or non-contact) method, and the unexposed parts are developed with a dilute alkaline aqueous solution (for example, a 0.3% to 3% sodium carbonate aqueous solution) to form a resist pattern (pattern image). The exposure conditions are as follows. Furthermore, by heating to a temperature of, for example, about 140° C. to 180° C. and thermosetting, the carboxy groups (or further the phenolic hydroxy groups) of the carboxy group-containing resin react with the cyclic (thio)ether groups of the thermosetting resin to form a white cured coating that achieves a high level of flexibility and high reflectance in a well-balanced manner in addition to properties such as adhesion to the substrate, folding resistance, low warping, resistance to electroless gold plating, solder heat resistance, and electrical insulation, and that suppresses deterioration in reflectance and deterioration in whiteness over time.

As substrates, printed wiring boards, flexible printed wiring boards, paper-phenolic resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass cloth/nonwoven cloth-epoxy resin, glass cloth/paper-epoxy resin, synthetic fiber-epoxy resin, copper-clad laminates of all grades (such as FR-4) using composite materials such as fluororesin, polyethylene, PPO, and cyanate ester, polyimide films, PET films, glass substrates, ceramic substrates, wafer plates, etc., can be used. Circuits may be formed on the above-mentioned substrates, and configurations such as transistors may be formed and mounted on them.

The volatilization drying carried out after application of the photosensitive resin composition can be carried out using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, etc. (a method in which hot air in the dryer is brought into countercurrent contact using a heat source that uses steam for air heating, or a method in which hot air is blown onto the support from a nozzle).

A photosensitive resin composition is applied to a substrate and dried by evaporation, and then the resulting resin composition layer is exposed to light (irradiated with active energy rays). The exposed areas of the resin composition layer (areas irradiated with active energy rays) are cured.

Examples of the exposure machine used for the above-mentioned active energy ray irradiation include a direct drawing machine (for example, a laser direct imaging machine that draws an image directly with a laser based on CAD data from a computer), an exposure machine equipped with a metal halide lamp, an exposure machine equipped with a (ultra) high pressure mercury lamp, an exposure machine equipped with a mercury short arc lamp, or a direct drawing machine using an ultraviolet lamp such as an (ultra) high pressure mercury lamp. The active energy ray may be a laser beam having a maximum wavelength in the range of 350 nm to 450 nm. The active energy ray may be irradiated using, for example, a gas laser, a solid laser, or the like. The exposure amount may be appropriately selected according to the film thickness, and may generally be within the range of 5 mJ/cm ² to 800 mJ/cm ² , preferably 5 mJ/cm ² to 500 mJ/cm ^2. The above-mentioned direct drawing machine may be, for example, a machine manufactured by Nippon Orbotech Co., Ltd., and any machine may be used as long as it emits laser light having a maximum wavelength of 350 nm to 450 nm.

Examples of developing methods include dipping, showering, spraying, brushing, etc. As a developing solution, an alkaline aqueous solution of potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, amines, etc. can be used.

In addition to being applied directly to a substrate in liquid form, the photosensitive thermosetting resin composition can also be used in the form of a dry film having a resin composition layer formed by applying the photosensitive thermosetting resin composition to a film such as polyethylene terephthalate and drying it. An example of using the photosensitive resin composition as a dry film is shown below.

Dry film The dry film has a resin composition layer obtained by applying the above-mentioned photosensitive thermosetting resin composition to a film and drying it. The dry film may have a structure in which a first film, a resin composition layer, and a peelable second film used as needed are laminated in this order. The resin composition layer is, for example, a layer obtained by applying and drying a photosensitive thermosetting resin composition to a first film or a second film. After forming a resin composition layer on a first film, a second film is laminated thereon, or a laminate obtained by forming a resin composition layer on a second film is laminated on the first film to obtain a dry film.

As the first film, a thermoplastic film such as a polyester film having a thickness of 2 μm to 150 μm is used. The resin composition layer is formed by uniformly applying a photosensitive thermosetting resin composition to the first film or the second film with a blade coater, lip coater, comma coater, film coater, etc., to a thickness of 10 μm to 150 μm, and drying the composition. As the second film, a polyethylene film, a polypropylene film, etc. can be used, but it is preferable that the adhesive strength with the resin composition layer is smaller than that of the first film.

To prepare a protective film (permanent protective film) on a substrate using a dry film, the second film is peeled off, the resin composition layer and the substrate on which a circuit is formed are superimposed, and laminated using a laminator or the like to form a resin composition layer on the substrate on which a circuit is formed. The formed resin composition layer can be exposed to light, developed, and heat cured in the same manner as above to form a cured coating film. The first film can be peeled off either before or after exposure.

Electronic Components The electronic components include the cured product of the above-mentioned photosensitive thermosetting resin composition. Examples of electronic components include printed wiring boards and light source modules. The printed wiring board includes a substrate having a pattern conductor and a cured product of the photosensitive thermosetting resin composition arranged on the substrate. The cured product arranged on the substrate may be patterned into a desired shape. The light source module includes a printed wiring board and a semiconductor light-emitting element arranged on the printed wiring board and connected to the pattern conductor. In the light source module, the semiconductor light-emitting element may be covered with a cured resin layer. The cured resin layer that covers the semiconductor light-emitting element may include, for example, a silicone resin.

In another aspect, the present invention also includes the use of the photosensitive thermosetting resin composition in the production of a dry film or electronic components, and the photosensitive thermosetting resin composition used in the production of a dry film or electronic components.

The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

The following materials were prepared as materials for preparing a photosensitive thermosetting resin composition.
Carboxy group-containing resin (Synthesis Example 1) Varnish A-1
Into a reaction vessel equipped with a stirrer, a thermometer, and a condenser, 2400g (3 moles) of polycarbonate diol derived from 1,5-pentanediol and 1,6-hexanediol (manufactured by Asahi Kasei Corporation, TJ5650J, number average molecular weight 800), 603g (4.5 moles) of dimethylolpropionic acid, and 238g (2.6 moles) of 2-hydroxyethyl acrylate as a monohydroxy compound were added. Next, 1887g (8.5 moles) of isophorone diisocyanate was added as a polyisocyanate, and the mixture was heated to 60°C with stirring and stopped. When the temperature in the reaction vessel started to decrease, the mixture was heated again and continued stirring at 80°C. The reaction was terminated by confirming that the absorption spectrum (2280 cm ^-1 ) of the isocyanate group had disappeared in the infrared absorption spectrum. Carbitol acetate was added so that the solid content was 50% by mass to obtain varnish A-1. The solid had an acid value of 50 mg KOH/g and a weight average molecular weight Mw of about 17,000.

(Synthesis Example 2) Varnish A-2
220 g of cresol novolac epoxy resin (EPICLON N-695, manufactured by DIC Corporation, epoxy equivalent: 220 g/eq.) was placed in a four-neck flask equipped with a stirrer and a reflux condenser, 214 g of carbitol acetate was added, and the mixture was dissolved by heating. Next, 0.1 g of hydroquinone as a polymerization inhibitor and 2.0 g of dimethylbenzylamine as a reaction catalyst were added. The mixture was heated to 95°C to 105°C, 72 g of acrylic acid was gradually added dropwise, and the mixture was reacted for 16 hours. The reaction product was cooled to 80°C to 90°C, 106 g of tetrahydrophthalic anhydride was added, the mixture was reacted for 8 hours, and the mixture was cooled and then taken out. The thus obtained carboxyl group-containing resin varnish A-2 had a solid content of 65%, an acid value of the solid matter of 100 mgKOH/g, and a weight average molecular weight Mw of about 3,500.

Photosensitive compound BPE-900: manufactured by Shin-Nakamura Chemical Co., Ltd.; ethoxylated bisphenol A dimethacrylate

Photopolymerization initiator oxime ester type ADEKA ARCLES NCI-930: manufactured by ADEKA CORPORATION; 1-4-[[4-(2-hydroxyethoxy)phenyl]thio]phenyl]-1,2-propanedione 2-(O-acetyloxime)
ADEKA ARCLES NCI-730: manufactured by ADEKA Corporation;
Irgacure OXE04: manufactured by BASF Japan Ltd.;
Irgacure OXE02: manufactured by BASF Japan Ltd.; 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone 1-(O-acetyloxime)

Titanocene-based JMT-784: manufactured by Yueyang Jinmaotai Technology Co., Ltd.; bis(η ⁵ -2,4-cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium)

Alkylphenone Omnirad 184: manufactured by IGM Japan LLC; 1-hydroxycyclohexyl phenyl ketone

α-Aminoacetophenone series Omnirad 379: manufactured by IGM Japan LLC; 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one Omnirad 907: manufactured by IGM Japan LLC; 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one

White pigment
CR-90: manufactured by Ishihara Sangyo Kaisha; rutile-type titanium dioxide

Thermosetting resin jER834: manufactured by Mitsubishi Chemical Corporation; bisphenol A type epoxy resin, epoxy equivalent 250 g/eq

Heat curing catalyst DICY7: manufactured by Mitsubishi Chemical Corporation; dicyandiamide wetting and dispersing agent Disperbyk-111: manufactured by BYK Japan Co., Ltd. Defoamer KS-66: manufactured by Shin-Etsu Chemical Co., Ltd.; silicone-based oil compound type defoamer

Preparation of Photosensitive Resin Composition Using each of the obtained varnishes A-1 and A-2, various components shown in Table 1 were blended in the indicated ratios (parts by mass), premixed with a stirrer, and then kneaded with a three-roll mill to prepare the photosensitive thermosetting resin compositions of Examples 1 to 13 and Comparative Examples 1 to 5. Values in the tables are parts by mass unless otherwise specified. In addition, "-" in Tables 1 and 2 indicates that not added or not evaluated (because evaluation is not possible).

The following evaluations were carried out on the photosensitive thermosetting resin compositions of Examples 1 to 13 and Comparative Examples 1 to 5 obtained in this manner. The results are shown in Tables 1 and 2.

Preparation of Evaluation Substrate The photosensitive thermosetting resin compositions of Examples 1 to 13 and Comparative Examples 1 to 5 were printed twice on a copper solid substrate by screen printing to form a coating film with a total thickness of 55 μm after thermal curing. Specifically, the composition was applied to the entire surface of the copper solid substrate by screen printing, dried for 10 minutes in a hot air circulation drying oven at 80 ° C. to form a first layer, and then further applied to the entire surface of the first layer by screen printing, dried for 20 minutes in a hot air circulation drying oven at 80 ° C. to form a second layer. The formed coating film was exposed to an optimal exposure amount using an exposure device (Mms60: manufactured by Oak Manufacturing Co., Ltd.) equipped with a high-pressure mercury lamp, and developed (30 ° C, 0.2 MPa, 1 mass% Na ₂ CO ₃ aqueous solution) for 60 seconds. Thereafter, the composition was thermally cured in a hot air circulation drying oven at 150 ° C. for 60 minutes to form a resin layer, and an evaluation substrate was prepared. The optimal exposure dose was determined by exposing the dried coating film through a Stouffer 41-step step tablet using an exposure device equipped with a high-pressure mercury lamp (Mms60: manufactured by Oak Manufacturing Co., Ltd.) and developing for 60 seconds with a 1% by mass _{Na2CO3 aqueous} solution at a spray pressure of 0.2 MPa and a liquid temperature of 30°C, at which the remaining step tablet pattern was 15 to 20 steps.

Evaluation of surface curability: Except for changing the exposure dose from the "optimum exposure dose" to "400 mJ/cm ² ," the evaluation substrate was prepared in the same manner as above, from development to thermal curing, and the substrate surface was visually observed. The evaluation criteria for surface curability were as follows:
a: The surface was not rough and was in good condition.
b: Roughness was observed on part of the surface.
c: Roughness was observed over the entire surface.

The reflectance and b ^* at 450 nm of the resin layer formed on each of the evaluation substrates obtained by the above-mentioned preparation of the evaluation substrate were measured by the SCI method of a spectrophotometer (manufactured by Konica Minolta, Inc., model number: CM-5) with a measurement diameter of 8 mm. The measurement results are shown in the "Reflectance" and b ^* rows in Table 1.

The evaluation board was subjected to a reflow process once at a maximum temperature of 260°C for 10 seconds using a reflow machine (NIS-20-82C manufactured by Atec Techtron Co., Ltd.). Thereafter, the reflectance and b ^* were measured in the same manner as above. The measurement results are shown in Table 1 as the reflectance after heat resistance test and b ^* after heat resistance test.

Evaluation of ΔEab ^* ΔEab ^* is an index showing the degree of discoloration, and is a value calculated by the following formula (1) using L ^* , a ^* , b ^* before reflow and L ^* , a ^* , b ^* after reflow. It was measured with a spectrophotometer (manufactured by Konica Minolta, Inc., model number: CM-5). The calculation results are shown in the row of ΔEab ^* in Table 1.
ΔEab ^* = ((ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ) ^(1/2) ...(1)

Evaluation of solder heat resistance Each evaluation board obtained above was coated with rosin-based flux and immersed in a solder bath previously set at 260° C. for 10 seconds. Next, the flux was washed off with denatured alcohol, and the resin layer was visually evaluated for swelling and peeling. The evaluation criteria for heat resistance were as follows:
a: After immersion for 10 seconds, the resin layer was not blistered or peeled off.
b: After immersion for 5 seconds, the resin layer was not blistered or peeled off.
c: After immersion for 5 seconds, the resin layer was clearly blistered and peeled off.

Evaluation of deep curing (undercut) The photosensitive thermosetting resin compositions of Examples 1 to 13 and Comparative Examples 1 to 5 were printed twice on a copper solid substrate by screen printing to form a coating film with a total film thickness of 55 μm after thermal curing. Specifically, the composition was applied to the entire surface of the copper solid substrate by screen printing, dried for 10 minutes in a hot air circulation drying oven at 80 ° C. to form a first layer, and then further applied to the entire surface of the first layer by screen printing, dried for 20 minutes in a hot air circulation drying oven at 80 ° C. to form a second layer. The formed coating film was exposed to a pattern at 400 mJ / cm ² using an exposure device (Mms60: manufactured by Oak Manufacturing Co., Ltd.) equipped with a high-pressure mercury lamp, and developed (30 ° C, 0.2 MPa, 1 mass % Na ₂ CO ₃ aqueous solution) for 60 seconds. The cross-section of the opening of the obtained pattern was observed, and the lengths of the upper part (air side) and the lower part (substrate side) were measured. The undercut was calculated using the following formula to evaluate deep hardening.
Undercut = (Top length - Bottom length)/2

As described above, it is understood that the present invention can provide a photosensitive resin composition that is less likely to discolor after a heating process and can maintain a high reflectance. In particular, Examples 2 and 4, which contain a small amount of oxime ester photopolymerization initiator and titanocene photopolymerization initiator and a larger amount of white pigment than Example 3, have high reflectance and are excellent in b ^* value, surface curing property, and solder heat resistance. This can be considered to be due to the synergistic effect of the oxime ester photopolymerization initiator and the titanocene initiator, which allows the desired characteristics to be expressed even with a small amount of initiator.

In Comparative Example 1, a coating film was formed, but a pattern that was not solid enough to evaluate undercutting after development was not left, so deep curing properties could not be evaluated. In Comparative Example 2, a coating film could not be formed, so all evaluation items could not be evaluated. In Comparative Examples 4 and 5, a resin layer could not be formed at the exposure dose used to evaluate surface curing properties and deep curing properties, so evaluation was not possible.

The disclosure of Japanese Patent Application No. 2023-055267 (filing date: March 30, 2023) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims (6)

A photosensitive thermosetting resin composition comprising a carboxyl group-containing resin, a photopolymerization initiator, a white pigment, and a thermosetting resin,
The carboxyl group-containing resin has an ethylenically unsaturated double bond in the molecule,
The photopolymerization initiator includes an oxime ester-based photopolymerization initiator and a titanocene-based photopolymerization initiator,
The oxime ester photopolymerization initiator has a structure in which a partial structure represented by the following formula (I) is substituted with a compound selected from the group consisting of diarylsulfane, 9H-carbazole, thioxanthen-9-one, fluorene, and derivatives thereof:

(In the formula, ^R1 represents a hydrogen atom, a phenyl group which may have a substituent, an alkyl group having 1 to 20 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 8 carbon atoms, an alkanoyl group having 2 to 20 carbon atoms, or a benzoyl group which may have a substituent. ^R2 represents a phenyl group which may have a substituent, an alkyl group having 1 to 20 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 8 carbon atoms, an alkanoyl group having 2 to 20 carbon atoms, or a benzoyl group which may have a substituent.)
The titanocene-based photopolymerization initiator is a compound represented by the following formula (II):

(In the formula, ^R9 and ^R10 each independently represent a halogen atom, an aryl group, a halogenated aryl group, or a heterocycle-containing halogenated aryl group.)
The white pigment includes titanium oxide,
the thermosetting resin includes an epoxy resin,
a total content of the oxime ester photopolymerization initiator and the titanocene photopolymerization initiator is, in terms of solid content, 0.01 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the carboxy group-containing resin;
The photosensitive thermosetting resin composition is exposed to light at 400 mJ/ ^cm2 using a high-pressure mercury lamp and thermally cured at 150°C for 60 minutes to obtain a cured product having a film thickness of 55 μm, which has a b ^* value of 2.0 or less in the L ^* a ^* b ^* color system and a reflectance of 85% or more at a wavelength of 450 nm. The photosensitive thermosetting resin composition according to claim 1, wherein the content of the white pigment is 200 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. The photosensitive thermosetting resin composition according to claim 1, wherein the photopolymerization initiator is an oxime ester-based photopolymerization initiator and a titanocene-based photopolymerization initiator in a mass ratio ranging from 1:10 to 10:1. A dry film having a resin layer obtained by applying the photosensitive thermosetting resin composition according to any one of claims 1 to 3 to a first film and drying it. A cured product obtained by curing the photosensitive thermosetting resin composition according to any one of claims 1 to 3. An electronic component comprising the cured product according to claim 5.