Curable resin composition, dry film, cured product and printed wiring board

Abstract

To provide a curable resin composition that can form a cured product having excellent resolution, visibility, and concealability; a dry film; a cured product; and a printed wiring board.SOLUTION: The present invention provides a curable resin composition. In a cured product formed by placing and curing the curable resin composition on a substrate, a first transmittance of the substrate-side region is higher than a second transmittance of the region opposite the substrate side.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a curable resin composition, a dry film, a cured product, and a printed wiring board. [Background technology]

[0002] Printed wiring boards used in electronic devices are substrates on which electronic circuit patterns are printed using copper wires, and various components are mounted. When components are mounted on printed wiring boards with exposed copper wires, there is a possibility that the copper wires may break due to external forces, or that short circuits may occur due to solder sticking to areas other than the circuit patterns. Therefore, solder resist is formed to protect the circuit patterns and prevent short circuits.

[0003] The solder resist is formed, for example, by an alkaline development method using a photocurable resin composition (see, for example, Patent Document 1). The alkaline development method is a method in which a photocurable resin composition is applied to the entire surface of a substrate, dried to form a coating film, the dried coating film is exposed to light to partially cure, and the uncured photocurable resin composition is developed with an alkaline aqueous solution to form a pattern. The alkaline development method is used in the manufacture of printed wiring boards because it can also be used to form fine patterns. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-65942 A Summary of the Invention [Problem to be solved by the invention]

[0005] The solder resist is formed as the outermost layer of a printed wiring board, and is therefore required to not only protect the circuit, but also to provide high visual concealment of the circuit from the viewpoint of enhancing the design. However, colorants, particularly black colorants, have high light absorption properties, and photocuring during resist pattern formation may not proceed smoothly, making it difficult to obtain a desired pattern. On the other hand, if the amount of colorant is reduced, it becomes difficult to form a solder resist of a dark color such as black, and there is a problem of reduced visibility, such as characters written on the solder resist becoming invisible. In addition, a solder resist of a light color has a problem of reduced concealment of the circuit, such as making it difficult to form a design that covers and hides the circuit. Furthermore, if the content of the colorant is low, in forming a pattern when the photocurable resin composition is made into a coating film, the light applied for exposure is diffused in the coating film, and the pattern is formed with a line width thicker than desired, and the resist pattern may become blurred.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a curable resin composition capable of forming a cured product having good resolution, visibility and hiding power, a dry film, a cured product and a printed wiring board. [Means for solving the problem]

[0007] That is, the curable resin composition according to the present invention is In a cured product obtained by disposing a curable resin composition on a substrate and curing the composition, The first transmittance of the region on the substrate side is higher than the second transmittance of the region on the opposite side to the substrate side.

[0008] In a further embodiment of the present invention, the cured product preferably has a first layer having a first transmittance and a second layer having a second transmittance.

[0009] In an embodiment of the present invention, the second transmittance is preferably 1% to 45%.

[0010] In an embodiment of the present invention, the curable resin composition preferably contains at least one of a photopolymerization initiator and a colorant.

[0011] A dry film according to another aspect of the present invention is characterized by having a first film and a resin layer made of the above-mentioned curable resin composition formed on the first film.

[0012] A cured product according to another aspect of the present invention is characterized by being obtained by curing the above-mentioned curable resin composition or the above-mentioned resin layer.

[0013] A printed wiring board according to another aspect of the present invention is characterized by having the above-mentioned cured product. Effect of the Invention

[0014] According to the present invention, it is possible to provide a curable resin composition capable of forming a cured product having good resolution, visibility and hiding power, a dry film, a cured product and a printed wiring board. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view of an example of a cured product of the curable resin composition according to this embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of another example of the cured product of the curable resin composition according to the present embodiment. [Diagram 3] FIG. 3 is a schematic cross-sectional view of an example of the dry film according to the present embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view of another example of the dry film according to the present embodiment. [Diagram 5] FIG. 5 is a schematic cross-sectional view of a structure in an embodiment. [Figure 6] FIG. 6 is a schematic diagram of a forward tapered structure. [Figure 7] FIG. 7 is a schematic diagram of an undercut shape. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The curable resin composition, the dry film, the cured product, and the printed wiring board according to the present embodiment will be described below.

[0017] (Curable resin composition) When the curable resin composition according to this embodiment is disposed on a substrate and cured, the cured product has a first transmittance in a region on the substrate side that is higher than a second transmittance in a region opposite to the substrate side.

[0018] Here, the transmittance of the cured product will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view of an example of a cured product of the curable resin composition according to the present embodiment. In Fig. 1, a cured product 3 of the curable resin composition is disposed on a substrate 4. In the cured product 3, when the transmittance (first transmittance) of a region 1 on the substrate side is compared with the transmittance (second transmittance) of a region 2 on the opposite side to the substrate side, the transmittance (first transmittance) of the region 1 on the substrate side is higher. "High transmittance" also means "the color of the cured product is light." Therefore, a cured product having a first transmittance higher than a second transmittance means that the color of the cured product 3 becomes darker from the substrate 4 toward the upper part.

[0019] Fig. 2 is a schematic cross-sectional view of another example of the cured product of the curable resin composition according to the present embodiment. As shown in Fig. 2, the cured product 13 may have a first layer 11 having a first transmittance and a second layer 12 having a second transmittance. At this time, the boundary between the first layer 11 and the second layer 12 may be clear or unclear. 2, the first layer 11 has a lighter color than the second layer 12. Therefore, the cured product 13 has a darker color from the substrate 4 toward the top. When the cured product has two layers as in FIG. 2, the curable resin composition may be one type or two types, but it is preferable that the curable resin composition be two types.

[0020] The thickness of the first layer is not particularly limited and can be appropriately selected depending on the purpose, and is preferably, for example, 8 μm to 30 μm. The thickness of the second layer is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness is preferably from 2 μm to 20 μm, and more preferably from 4 μm to 15 μm. When the thickness of the first layer and the thickness of the second layer are within these numerical ranges, a cured product with better resolution can be formed.

[0021] The first transmittance is not particularly limited as long as it is higher than the second transmittance, and can be appropriately selected depending on the purpose, but is preferably 40% to 70%. When the first transmittance is higher than the second transmittance, the cured product has good resolution.

[0022] The second transmittance is preferably 1% to 45%, and more preferably 5% to 30%. When the second transmittance is within this range, a cured product with good hiding power can be formed.

[0023] The transmittance of the cured product of the curable resin composition according to this embodiment is defined as the average value of the transmittance in the range of 360 nm to 830 nm. Specifically, a cured coating film of the curable resin composition is formed on a glass plate so that the dried coating film has a thickness of 13±2 μm, and the transmittance of the formed coating film from a baseline in the range of 300 nm to 850 nm is measured using a UV-visible spectrophotometer and an integrating sphere device. During the measurement, the scanning speed is 400 nm / min and the scanning interval is 1 nm. The average value of the measured values ​​obtained in the range of 360 nm to 830 nm is regarded as the transmittance of the measured cured product of the curable resin composition.

[0024] The curable resin composition according to the present embodiment is not particularly limited as long as it has the property of being cured, and may be appropriately selected depending on the purpose. However, it is preferable that the curable resin composition contains at least one of a photopolymerization initiator and a colorant, and further contains other components as necessary.

[0025] <Photopolymerization initiator, colorant> The photopolymerization initiator and the colorant are contained in order to adjust the transmittance of the cured product of the curable resin composition. By adjusting the transmittance of the cured product, it is possible to improve the resolution and hiding power.

[0026] <<Photopolymerization initiator>> The photopolymerization initiator is not particularly limited as long as it is used in a normal curable resin composition, and can be appropriately selected according to the purpose, and any known photopolymerization initiator can be used. The photopolymerization initiator may be used alone or in combination of two or more kinds.

[0027] Examples of the photopolymerization initiator include bis-(2,6-dichlorobenzoyl)phenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, bis-(2,6-dimethoxybenzoyl)phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. bisacylphosphine oxides such as bis-(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide and bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylphenylphosphinic acid methyl ester, 2-methylbenzoyldiphenylphosphine oxide, pivaloylphenylphosphinic acid isopropyl monoacylphosphine oxides such as phenyl(2,4,6-trimethylbenzoyl)phosphinate, 1-hydroxy-cyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one, 2-hydroxy- Hydroxyacetophenones such as 2-methyl-1-phenylpropan-1-one; benzoins such as benzoin, benzil, benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether, and benzoin n-butyl ether; benzoin alkyl ethers; benzophenones such as benzophenone, p-methylbenzophenone, Michler's ketone, methylbenzophenone, 4,4'-dichlorobenzophenone, and 4,4'-bisdiethylaminobenzophenone;Acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, 1,2-(dimethylamino)-2-[(4-methylphenyl)methyl)-1-[4-(4-morpholinyl)phenyl]-1-butano acetophenones such as acetophenone, N,N-dimethylaminoacetophenone, etc.; thioxanthones such as thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2,4-diisopropylthioxanthone, etc.; anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone, 2 -Aminoanthraquinone and other anthraquinones; acetophenone dimethyl ketal, benzil dimethyl ketal and other ketals; ethyl 4-dimethylaminobenzoate, 2-(dimethylamino)ethyl benzoate, p-dimethylbenzoic acid ethyl ester and other benzoic acid esters; 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyl oxime esters such as bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium, bis(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(1-pyrrol-1-yl)ethyl)phenyl]titanium, and other titanocenes; phenyl disulfide 2-nitrofluorene, butyroin, anisoin ethyl ether, azobisisobutyronitrile, tetramethylthiuram disulfide, and the like.

[0028] The amount of the photopolymerization initiator other than the oxime ester photopolymerization initiator is preferably 0.01 to 30 parts by mass, calculated as solid content, relative to 100 parts by mass of the carboxyl group-containing resin. When it is 0.01 parts by mass or more, the photocurability of the curable resin composition is good, the cured product is less likely to peel off, and properties such as chemical resistance are also good. On the other hand, when it is 30 parts by mass or less, the light absorption at the surface of the resin layer is good, and the deep curability is less likely to decrease. More preferably, it is 0.1 to 20 parts by mass. The amount of the oxime ester photopolymerization initiator is preferably 0.01 to 5 parts by mass, calculated as solid content, relative to 100 parts by mass of the carboxyl group-containing resin. When the amount is 0.01 parts by mass or more, the photocurability of the curable resin composition is good, and properties such as heat resistance and chemical resistance are also good. On the other hand, when the amount is 5 parts by mass or less, light absorption at the surface of the resin layer is good, and deep curability is less likely to decrease. More preferably, the amount is 0.1 to 3.9 parts by mass.

[0029] <<Coloring agent>> The colorant is not particularly limited as long as it is one that is used in a typical curable resin composition and can be appropriately selected depending on the purpose. Conventional and well-known colorants such as black, red, blue, green, yellow, and white can be used, and any of pigments, dyes, and colorants can be used. Regarding the black color, only a black colorant may be used, or a colorant other than black may be mixed to produce the black color.

[0030] Examples of black colorants include carbon black, zirconium nitride, Pigment Black 1,6,7,8,9,10,11,12,13,18,20,25,26,28,29,30,31,32, and the like. Red colorants include monoazo-based, disazo-based, azo lake-based, benzimidazolone-based, perylene-based, diketopyrrolopyrrole-based, condensed azo-based, anthraquinone-based, and quinacridone-based. Blue colorants include phthalocyanine and anthraquinone types, and the pigment type can be a compound classified as a pigment. In addition to these, metal-substituted or unsubstituted phthalocyanine compounds can also be used. Green colorants include phthalocyanine-based, anthraquinone-based, and perylene-based compounds, and may also include metal-substituted or unsubstituted phthalocyanine compounds. Yellow colorants include monoazo, disazo, condensed azo, benzimidazolone, isoindolinone, anthraquinone, and the like. Examples of white colorants include rutile or anatase type titanium oxide, etc. In addition, purple, orange, brown, and other colorants may be added for the purpose of adjusting the color tone.

[0031] The content of the colorant is not particularly limited and can be appropriately selected depending on the purpose, but it is preferable that the content of the colorant in the region having the first transmittance and the region having the second transmittance is as follows. The content of the colorant in the region having the first transmittance is preferably 0.5 parts by mass to 100 parts by mass, more preferably 1 part by mass to 80 parts by mass, based on 100 parts by mass of the carboxyl group-containing photosensitive resin, calculated as solid content. When the content of the colorant falls within this range, a cured product with high hiding power is obtained. The content of the colorant in the region having the second transmittance is preferably 0 to 30 parts by mass, more preferably 0 to 20 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin, calculated as solid content. When the content of the colorant falls within this range, a cured product with good resolution is obtained.

[0032] <Other ingredients> The other components are not particularly limited as long as they are used in ordinary curable resin compositions and can be appropriately selected according to the purpose, and examples thereof include a thermosetting component, a carboxyl group-containing resin, a photopolymerizable monomer, a filler, other additives, etc. These may be used alone or in combination of two or more.

[0033] <<Thermosetting component>> The thermosetting component is not particularly limited as long as it is cured by heating, and can be appropriately selected according to the purpose. Examples of the thermosetting component include known and commonly used ones such as isocyanate compounds, blocked isocyanate compounds, amino resins, maleimide compounds, benzoxazine resins, carbodiimide resins, cyclocarbonate compounds, epoxy compounds, oxetane compounds, and episulfide resins. These may be used alone or in combination of two or more. Among these, epoxy resins are preferred.

[0034] Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, hydrogenated bisphenol A type epoxy resins, brominated bisphenol A type epoxy resins, bisphenol S type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, dicyclopentadiene type epoxy resins, and triphenylmethane type epoxy resins.

[0035] When the curable resin composition contains a carboxyl group-containing photosensitive resin described later, the content of the epoxy resin is preferably 0.3 to 2.5 equivalents, more preferably 0.5 to 2.0 equivalents, of the epoxy group relative to 1 equivalent of the carboxyl group of the carboxyl group-containing photosensitive resin in terms of solid content. By making the amount of the epoxy group 0.3 equivalents or more, no carboxyl group remains in the cured product, and heat resistance, alkali resistance, electrical insulation, etc. are improved. In addition, by making the amount 2.5 equivalents or less, no thermosetting component remains in the dried coating film, and the strength of the cured product is improved.

[0036] <<Carboxyl group-containing resin>> The carboxyl group-containing resin is a resin having a carboxyl group in the molecule, and various conventionally known resins can be used. The curable resin composition contains a carboxyl group-containing resin, so that the curable resin composition can be given developability (alkali developability). In particular, a carboxyl group-containing photosensitive resin having an ethylenically unsaturated double bond in the molecule is preferred from the viewpoint of photocurability and development resistance. The ethylenically unsaturated double bond is preferably derived from acrylic acid or methacrylic acid or a derivative thereof. In addition, when only a carboxyl group-containing resin having no ethylenically unsaturated double bond is used, in order to make the curable resin composition photocurable, it is necessary to use in combination a compound having a plurality of ethylenically unsaturated groups in the molecule, i.e., a photopolymerizable monomer, which will be described later.

[0037] Specific examples of the carboxyl group-containing resin include the following compounds (which may be either oligomers or polymers): These may be used alone or in combination of two or more.

[0038] (1) Carboxyl group-containing resins 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, isobutylene, etc.

[0039] (2) Carboxylic acid-containing urethane resins obtained by the polyaddition reaction of diisocyanates such as aliphatic diisocyanates, branched aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates with carboxyl-containing dialcohol compounds such as dimethylolpropionic acid and dimethylolbutanoic acid, and diol compounds such as polycarbonate polyols, polyether polyols, polyester polyols, polyolefin polyols, acrylic polyols, bisphenol A alkylene oxide adduct diols, and compounds having phenolic hydroxyl groups and alcoholic hydroxyl groups.

[0040] (3) Carboxylic acid-containing photosensitive urethane resins obtained by polyaddition reaction of diisocyanates with partially 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, carboxyl group-containing dialcohol compounds and diol compounds.

[0041] (4) A photosensitive urethane resin containing a carboxyl group, which is terminated with (meth)acrylation 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).

[0042] (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).

[0043] (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.

[0044] (7) A carboxyl group-containing photosensitive resin obtained by reacting a multifunctional epoxy resin with the hydroxyl groups of a bifunctional (solid) epoxy resin further epoxidized with epichlorohydrin, with (meth)acrylic acid, and then adding a dibasic acid anhydride to the resulting hydroxyl groups.

[0045] (8) Carboxyl group-containing polyester resins 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.

[0046] (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 group of the resulting reaction product with a polybasic acid anhydride, such as maleic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, adipic acid, or the like.

[0047] (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.

[0048] (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.

[0049] (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 any one of the resins (1) to (11).

[0050] In this specification, (meth)acrylate is a term that collectively refers to acrylate, methacrylate, and mixtures thereof, and the same applies to other similar expressions.

[0051] The acid value of the carboxyl group-containing photosensitive resin is preferably 40 mgKOH / g to 150 mgKOH / g, more preferably 50 mgKOH / g to 130 mgKOH / g. By making the acid value of the carboxyl group-containing photosensitive resin 40 mgKOH / g or more, the alkali developability becomes good. In addition, by making the acid value 150 mgKOH / g or less, the resolution can be improved.

[0052] The weight-average molecular weight of the carboxyl group-containing photosensitive resin varies depending on the resin skeleton, but is generally preferably 2,000 to 150,000, more preferably 5,000 to 100,000. By making the weight-average molecular weight 2,000 or more, it is possible to improve tack-free performance and resolution. In addition, by making the weight-average molecular weight 150,000 or less, it is possible to improve developability and storage stability. The weight average molecular weight can be determined from a standard polystyrene-equivalent value by gel permeation chromatography (GPC).

[0053] The content of the carboxyl group-containing photosensitive resin in the curable resin composition is preferably 20% by mass to 60% by mass, more preferably 30% by mass to 50% by mass, calculated as solid content. By making the content 20% by mass or more, the strength of the cured product can be improved. Also, by making the content 60% by mass or less, the viscosity becomes appropriate, and the printability is improved.

[0054] <<Photopolymerizable monomer>> The photopolymerizable monomer is a monomer having an ethylenically unsaturated double bond. Examples of such photopolymerizable monomers include commonly known polyester (meth)acrylates, polyether (meth)acrylates, urethane (meth)acrylates, carbonate (meth)acrylates, and epoxy (meth)acrylates. Specifically, alkyl acrylates such as 2-ethylhexyl acrylate and cyclohexyl acrylate; hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate; mono- or diacrylates of alkylene oxide derivatives such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol; acrylamides such as N,N-dimethylacrylamide, N-methylolacrylamide, and N,N-dimethylaminopropylacrylamide; aminoalkyl acrylates such as N,N-dimethylaminoethyl acrylate and N,N-dimethylaminopropyl acrylate; hexanediol, trimethylolpropane, pentaerythritol, ditrimethylolpropane, dipentaerythritol, trishydroxyethyl Examples of the polyhydric acrylates include polyhydric alcohols such as isocyanurate, or their alkylene oxide adducts or ε-caprolactone adducts; phenols such as phenoxy acrylate and bisphenol A diacrylate, or their alkylene oxide adducts; acrylates derived from glycidyl ethers such as glycerin diglycidyl ether, trimethylolpropane triglycidyl ether, and triglycidyl isocyanurate; and, without being limited to the above, acrylates and melamine acrylates obtained by directly acridating polyols such as polyether polyols, polycarbonate diols, hydroxyl-terminated polybutadienes, and polyester polyols, or by urethane acridating them via diisocyanates, and methacrylates corresponding to the above acrylates. These may be used alone or in combination of two or more. The photopolymerizable monomer can also be used as a reactive diluent.

[0055] The content of the photopolymerizable monomer is preferably 5 to 100 parts by mass relative to 100 parts by mass of the carboxyl group-containing resin. When the blending amount is 5 parts by mass or more, the photocurability is good, and pattern formation is easy in alkaline development after irradiation with active energy rays. On the other hand, when it is 100 parts by mass or less, halation is unlikely to occur and good resolution can be obtained.

[0056] <<Filler>> As the filler, known inorganic or organic fillers can be used, with barium sulfate, spherical silica and talc being particularly preferred. The content of the filler is not particularly limited and can be appropriately selected depending on the purpose.

[0057] <<Other additives>> The curable resin composition of the present invention may further contain, as necessary, components such as a photoinitiator assistant, a cyanate compound, an elastomer, a mercapto compound, a urethanization catalyst, a thixotropic agent, an adhesion promoter, a block copolymer, a chain transfer agent, a polymerization inhibitor, a copper inhibitor, an antioxidant, an anti-rust agent, a thickener such as organic bentonite or montmorillonite, at least one of silicone-based, fluorine-based, or polymer-based defoamers and leveling agents, imidazole-based, thiazole-based, or triazole-based silane coupling agents, phosphinates, phosphate ester derivatives, phosphorus compounds such as phosphazene compounds, and the like. These may be known in the field of electronic materials.

[0058] <Method for producing curable resin composition> The method for producing the curable resin composition is not particularly limited, and the composition can be produced, for example, by blending the above-mentioned components in a predetermined ratio and then kneading or mixing at room temperature with a kneading means such as a triple roll mill, a ball mill, a bead mill, a sand mill, or a stirring means such as a super mixer, a planetary mixer, etc. Furthermore, prior to the kneading or mixing, pre-kneading or pre-mixing may be performed as necessary.

[0059] The curable resin composition according to the embodiment may be used in the form of a dry film or in the form of a liquid, as described below. When used in the form of a liquid, the composition may be a one-component composition or a two-component composition.

[0060] (Dry film) The dry film according to this embodiment includes a first film and a resin layer, and further includes other members as necessary.

[0061] <Resin layer> The resin layer is formed on the first film described below and is made of a dried coating film of the curable resin composition described above. Here, the resin layer refers to a layer formed by applying and drying the curable resin composition, and is not laminated with other layers such as the first film described below or other members. The thickness of the resin layer is not particularly limited and can be appropriately selected depending on the purpose.

[0062] <First film> The first film has a role of supporting the resin layer of the dry film, and is a film onto which the curable resin composition is applied when the resin layer made of the curable resin composition is formed. In the present invention, when the dry film is laminated by heating or the like so that the resin layer side of the dry film contacts a base material such as a substrate to be integrally molded, the first film is at least adhered to the resin layer. The first film may be peeled off from the resin layer in a process after lamination. In particular, in this embodiment, it is preferable to peel off from the resin layer in a process after exposure.

[0063] As the first film, any known film can be used without any particular limitation, and for example, a film made of a thermoplastic resin such as a polyester film such as polyethylene terephthalate or polyethylene naphthalate, a polyimide film, a polyamideimide film, a polypropylene film, or a polystyrene film can be suitably used. Among these, a polyester film is preferred from the viewpoints of heat resistance, mechanical strength, handling, etc. A laminate of these films can also be used as the first film.

[0064] From the viewpoint of improving mechanical strength, the film made of a thermoplastic resin is preferably a uniaxially or biaxially stretched film.

[0065] When a thermoplastic resin film is used as the first film, a film having a specific surface morphology may be used by adding a filler to the resin when forming the film (kneading process), by matte coating (coating process), by subjecting the film surface to a blasting process such as sandblasting, or by hairline processing or chemical etching, etc.

[0066] The thickness of the first film is not particularly limited, but can be, for example, 10 μm to 150 μm.

[0067] Here, the dry film will be described with reference to the drawings. Fig. 3 is a schematic cross-sectional view of a dry film according to an embodiment. In Fig. 3, a resin layer 23, which is a layer made of a curable resin composition, is disposed on a first film 24. The layer 23 made of the curable resin composition becomes a cured product when cured. The dry film is disposed so that a region 21 on the opposite side to the first film is in contact with a substrate. The resin layer 23 has a first region 21 and a second region 22. In a cured product obtained by curing the dry film, the transmittance of the first region 21 (first transmittance) is higher than the transmittance of the second region 22 (second transmittance).

[0068] Fig. 4 is a schematic cross-sectional view of another example of the dry film according to the embodiment. In Fig. 4, the dry film may have a first layer 31 having a first transmittance when cured and a second layer 32 having a second transmittance when cured (these layers collectively form a resin layer 33) on a first film 24. In this case, the boundary between the first layer 31 and the second layer 32 may be clear or unclear.

[0069] <Other materials> The other members are not particularly limited as long as they are used in ordinary dry films and can be appropriately selected depending on the purpose. For example, a second film can be used.

[0070] <<Second film>> The second film is a film that is laminated for the purpose of preventing dust from adhering to the surface of the resin layer, etc. Specifically, when the dry film is laminated by heating or the like so that the resin layer side of the dry film is in contact with a base material such as a substrate to form an integral mold, the second film is a film that is peeled off from the resin layer before lamination.

[0071] The second film may be, for example, a polyethylene film, a polytetrafluoroethylene film, a polypropylene film, or surface-treated paper. The adhesive strength of the second film to the resin layer may be smaller than the adhesive strength between the resin layer and the second film. Since the adhesive strength of the second film is smaller than that of the first film, the second film can be peeled off without moving the first film.

[0072] The thickness of the second film is not particularly limited, but can be, for example, 10 μm to 150 μm.

[0073] <Method of manufacturing dry film> The dry film is prepared by diluting the above-mentioned curable resin composition with the above-mentioned organic solvent to adjust the viscosity to an appropriate level, applying the mixture to a uniform thickness on the first film using a comma coater, blade coater, lip coater, rod coater, squeeze coater, reverse coater, transfer roll coater, gravure coater, spray coater, applicator, or the like, and drying the mixture for 1 to 30 minutes at a temperature of 50° C. to 130° C. to obtain a film. There are no particular limitations on the coating film thickness, but the thickness after drying is generally appropriately selected within the range of 1 μm to 150 μm, preferably 5 μm to 60 μm.

[0074] When a dry film is produced by using layers made of two types of curable resin compositions with different compositions, the two layers may be produced simultaneously or one by one. The simultaneous production of two layers means that each curable resin composition is simultaneously applied to a first film. The layer-by-layer production means that the curable resin composition forming one layer is applied and dried, and then the curable resin composition forming the other layer is applied. Alternatively, the laminate may be produced by applying one layer each of two different types of curable resin compositions to obtain resin layers, and then laminating the resulting layers together using a laminator or the like.

[0075] (cured product) The cured product according to the embodiment is obtained by curing the above-mentioned curable resin composition or the resin layer of the above-mentioned dry film. The size and shape of the cured product are not particularly limited and can be appropriately selected depending on the purpose.

[0076] As a method for producing a cured product, for example, the curable resin composition of the present invention is adjusted to a viscosity suitable for the coating method using an organic solvent, and coated on a substrate by a method such as dip coating, flow coating, roll coating, bar coating, screen printing, or curtain coating, and then the organic solvent contained in the composition is evaporated and dried (temporarily dried) for 15 to 90 minutes at a temperature of 60 to 100° C. to form a tack-free resin layer. In addition, in the case of a dry film, the resin layer is attached to the substrate by a laminator or the like so that the resin layer is in contact with the substrate, thereby forming a resin layer on the substrate.

[0077] Substrates include printed wiring boards and flexible printed wiring boards with circuits already formed using copper etc., as well as materials such as paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / non-woven epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, copper-clad laminates for high frequency circuits using materials such as fluororesin-polyethylene-polyphenylene ether, polyphenylene oxide-cyanate, etc., including copper-clad laminates of all grades (FR-4 etc.), as well as metal substrates, polyimide films, polyethylene terephthalate films, polyethylene naphthalate (PEN) films, glass substrates, ceramic substrates, wafer plates, etc.

[0078] The dry film is preferably laminated onto the substrate under pressure and heat using a vacuum laminator or the like. By using such a vacuum laminator, when a circuit-formed substrate is used, even if the surface of the substrate is uneven, the dry film adheres closely to the substrate, so that no air bubbles are mixed in, and the filling of the recesses on the substrate surface is improved. The pressure condition is preferably about 0.1 to 2.0 MPa, and the heating condition is preferably 40 to 120°C.

[0079] The volatilization drying carried out after application of the curable resin composition of the present invention can be carried out using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, or the like (a method in which hot air in a dryer equipped with a heat source of an air heating method using steam is brought into countercurrent contact with the substrate, or a method in which hot air is blown onto the substrate from a nozzle).

[0080] After forming a resin layer on a substrate, the resin layer is selectively exposed to active energy rays through a photomask having a predetermined pattern formed thereon, and the unexposed portion is developed with a dilute alkaline aqueous solution (e.g., 0.3 to 3 mass% aqueous sodium carbonate solution) to form a pattern of the cured product. In the case of a dry film, after exposure, the first film is peeled off from the dry film and development is performed to form a patterned cured product on the substrate. Note that, as long as the characteristics are not impaired, the first film may be peeled off from the dry film before exposure, and the exposed resin layer may be exposed and developed. Furthermore, a cured product excellent in various properties such as adhesion and hardness is formed by irradiating the cured product with active energy rays and then heat curing (e.g., 100 to 220°C), or irradiating active energy rays after heat curing, or performing final finish curing (main curing) only by heat curing.

[0081] The exposure machine used for the above-mentioned active energy ray irradiation may be a machine equipped with a high pressure mercury lamp, an ultra-high pressure mercury lamp, a metal halide lamp, a mercury short arc lamp, or the like, and capable of irradiating ultraviolet rays in the range of 350 to 450 nm. Furthermore, a direct imaging machine (for example, a laser direct imaging machine that directly draws an image with a laser based on CAD data from a computer) may also be used. The lamp light source or laser light source of the direct imaging machine may have a maximum wavelength in the range of 350 to 450 nm. The exposure dose for forming an image varies depending on the film thickness, etc., but is generally 10 to 1000 mJ / cm. 2 , preferably 20 to 800 mJ / cm 2 The range may be:

[0082] The developing method can be a dipping method, a shower method, a spray method, a brush method, or the like, and the developing solution can be an aqueous alkali solution of potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, amines, or the like.

[0083] (Printed Wiring Board) A printed wiring board according to one embodiment of the present invention has a cured product of the above-mentioned curable resin composition. The size and type of the printed wiring board are not particularly limited and can be appropriately selected depending on the purpose. EXAMPLES

[0084] Next, tests carried out by the present inventors will be described, but the present invention is not limited to these.

[0085] <Preparation of Carboxyl Group-Containing Photosensitive Resin> An autoclave equipped with a thermometer, a nitrogen introducing device / alkylene oxide introducing device, and a stirrer was charged with 119.4 parts by mass of a novolac cresol resin (Shonor CRG951, manufactured by Aica Kogyo Co., Ltd., OH equivalent: 119.4), 1.19 parts by mass of potassium hydroxide, and 119.4 parts of toluene, and the atmosphere in the system was replaced with nitrogen while stirring, and the temperature was raised by heating. Next, 63.8 parts by mass of propylene oxide was gradually added dropwise, and the mixture was heated at 125°C to 132°C and 0 kg / cm 2 ~4.8kg / cm 2 The mixture was reacted at 40° C. for 16 hours. After that, it was cooled to room temperature, and 1.56 parts by mass of 89% phosphoric acid was added to the reaction solution to neutralize the potassium hydroxide, to obtain a propylene oxide reaction solution of a novolak cresol resin with a solid content of 62.1% and a hydroxyl value of 182.2 g / eq. This had an average of 1.08 moles of propylene oxide added per equivalent of phenolic hydroxyl group. 293.0 parts by mass of the resulting propylene oxide reaction solution of the novolac cresol resin, 43.2 parts by mass of acrylic acid, 11.53 parts by mass of methanesulfonic acid, 0.18 parts by mass of methyl hydroquinone, and 252.9 parts by mass of toluene were charged into a reactor equipped with a stirrer, a thermometer, and an air inlet tube, and the mixture was reacted at 110°C for 12 hours while blowing air at a rate of 10 mL / min and stirring. The water generated by the reaction was distilled as an azeotrope with toluene, and 12.6 parts by mass of water was distilled. After that, the mixture was cooled to room temperature, and the resulting reaction solution was neutralized with 35.35 parts by mass of a 15% aqueous sodium hydroxide solution, and then washed with water. After that, the toluene was distilled off while replacing it with 118.1 parts by mass of diethylene glycol monoethyl ether acetate in an evaporator, to obtain a novolac acrylate resin solution. Next, 332.5 parts by mass of the obtained novolac type acrylate resin solution and 1.22 parts by mass of triphenylphosphine were charged into a reactor equipped with a stirrer, a thermometer, and an air inlet tube, and air was blown in at a rate of 10 mL / min. While stirring, 60.8 parts by mass of tetrahydrophthalic anhydride was gradually added, and the mixture was reacted at 95°C to 101°C for 6 hours, cooled, and then removed. In this manner, a solution of a carboxyl group-containing photosensitive resin having a solid content of 65% and an acid value of the solid matter of 87.7 mgKOH / g (hereinafter, abbreviated as carboxyl group-containing photosensitive resin) was obtained.

[0086] (Examples 1 to 4, Comparative Examples 1 to 2) <Preparation of Curable Resin Composition> The materials were mixed in the ratios shown in Table 1, premixed with a mixer, and then kneaded with a three-roll mill to prepare a curable resin composition. The values ​​in the table are the amounts mixed in a solution containing a solvent. The units in the table are parts by mass.

[0087] [Table 1]

[0088] Details of each component in Table 1 other than the carboxyl group-containing photosensitive resin are as follows. Photopolymerizable monomer: Dipentaerythritol hexaacrylate (manufactured by Nippon Kayaku Co., Ltd.) Thermosetting component (epoxy resin): EPICLON N-770 (DIC Corporation) Photopolymerization initiator 1: TOE-04-A3 (manufactured by Nippon Chemical Industry Co., Ltd.) Photopolymerization initiator 2: 2,4,6-trimethylbenzoyl-diphenylphosphine oxide Filler: B-30 (manufactured by Sakai Chemical Industry Co., Ltd.) Melamine: (Nissan Chemical Co., Ltd.) Colorant 1: MA-100 (carbon black, manufactured by Mitsubishi Chemical Corporation) Colorant 2: See below Colorant 3: NITRBLACK UB-2 (Mitsubishi Materials Corporation) Solvent: Propylene glycol monomethyl ether acetate

[0089] <<Preparation of Colorant 2>> A blue colorant (CI Pigment Blue 15:3), 0.8 parts by mass of a yellow colorant (CI Pigment Yellow 147), 0.3 parts by mass of a red colorant (Paliogen Red K3580, manufactured by BASF Japan Ltd.), and 50 parts by mass of a carboxyl group-containing photosensitive resin were blended and premixed in a stirrer, and then kneaded in a three-roll mill to prepare the composition.

[0090] <Determining the optimal exposure> The optimum exposure dose for the resin layer in the examples was determined by carrying out the following experiment. A copper solid substrate with a copper thickness of 18 μm was pretreated using an etching agent (CZ-8100, manufactured by MEC Co., Ltd.) to prepare a substrate. Next, the obtained curable resin composition was applied onto a substrate so that the thickness after curing was 10 μm, and dried at 80° C. for 20 minutes to prepare a resin layer. The resin layer was then exposed through a Stouffer 41-step step tablet using an exposure device equipped with a high-pressure mercury short arc lamp, and the exposure amount at which the remaining step tablet pattern was 15 when developed for 60 seconds at a spray pressure of 0.2 MPa using a 1 wt % sodium carbonate aqueous solution at 30°C was determined as the optimal exposure amount (mJ / cm) for that resin layer. 2 ) was decided.

[0091] The optimum exposure dose for the dry film or structure of the embodiment was determined by carrying out the following experiment. In the case of the dry film, the obtained dry film was laminated using a vacuum laminator so that the first layer (L1) was in contact with the substrate, to produce a structure as shown in FIG. The structure was then exposed through a Stouffer 41-step step tablet using an exposure apparatus equipped with a high-pressure mercury short arc lamp, the first film was peeled off, and development was performed for 60 seconds with a 1 wt % aqueous solution of sodium carbonate at 30°C at a spray pressure of 0.2 MPa, giving an exposure amount at which the remaining step tablet pattern was 15, which was determined as the optimal exposure amount (mJ / cm 2 ) was decided.

[0092] <Transmittance measurement> Each of the obtained curable resin compositions was applied to a 0.5 mm thick glass plate as a substrate using an applicator so that the thickness after curing would be 13±2 μm, and then dried at 80° C. for 10 minutes. The dried resin layer was exposed to light at an optimal exposure dose using an exposure device equipped with a high-pressure mercury short arc lamp, and then developed with a 1 wt % aqueous sodium carbonate solution at 30° C. under a spray pressure of 0.2 MPa for 60 seconds. The resulting composition was then dried in a UV conveyor furnace with an integrated exposure dose of 1,000 mJ / cm. 2After irradiating with ultraviolet light under the above conditions, the glass plate was heated at 150°C for 60 minutes to cure, and a cured product was obtained. Using an ultraviolet-visible spectrophotometer and an integrating sphere device (UV / VIS / NIR spectrometer V-570, JASCO Corporation), a baseline was measured at 300 nm to 850 nm using the same glass plate as the glass plate on which the curable resin composition was applied. The transmittance of the cured product of each curable resin composition from the baseline at wavelengths of 360 nm to 830 nm was measured at a scanning speed of 400 nm / min and a scanning interval of 1 nm, and the average value of the transmittance in this wavelength range was taken as the transmittance of the cured product of the curable resin composition. The measurement results are shown in Table 2.

[0093] <Preparation of dry film> Using the obtained curable resin compositions A to E, dry films were produced in the combinations shown in Table 2. On a 38 μm-thick polyester film, which is the first film 24 in Fig. 4, a curable resin composition for forming the L2 layer 32 was applied with an applicator to a thickness of 13 ± 2 μm after drying, and dried for 10 minutes at 80° C. Thereafter, a curable resin composition for forming the L1 layer 31 was applied on the L2 layer 32 to a thickness of 20 ± 2 μm after drying, and dried for 10 minutes at 80° C. to produce a dry film.

[0094] <Concealment> A single-sided printed wiring board with a 15 μm thick copper circuit formed thereon was used as the substrate. The printed wiring board was pretreated using an etching agent (CZ-8100, manufactured by MEC Co., Ltd.), and the resulting dry films were bonded together using a vacuum laminator so that the L1 layer was in contact with the substrate, to produce the structure shown in FIG. 5. As shown in FIG. 5, the structure is one in which the L1 layer 31, the L2 layer 32, and the first film 24 are laminated in this order on the substrate 4. The fabricated structure was exposed to a solder resist pattern at an optimal exposure dose using an exposure device equipped with a high-pressure mercury short arc lamp, and then the first film was peeled off and development was performed for 60 seconds using a 1 wt% sodium carbonate aqueous solution at 30°C under a spray pressure of 0.2 MPa to obtain a solder resist pattern. The structure on which the pattern was formed was then exposed in a UV conveyor furnace for an integrated exposure dose of 1,000 mJ / cm. 2 After irradiating with ultraviolet light under the above conditions, the coating was cured by heating at 150° C. for 60 minutes to obtain an evaluation substrate.

[0095] For the obtained evaluation board, the L * a * b * L in color space * Specifically, the L value was measured using a color difference meter (Konica Minolta, Inc., CM-2600d) in the total internal reflection (SCI) mode from above the cured product (opposite the substrate) that was made by laminating and curing the L1 and L2 layers in the circuit area of ​​the evaluation substrate. * The values ​​were measured. The area on the circuit here refers to the part on the evaluation board where copper of the same thickness as the circuit is laminated (formed) in an area of ​​4cm x 1.5cm or more. This is because a certain amount of area is necessary for color difference meter measurements, and the results obtained from this measurement can be considered as the measurement results on the circuit (on the copper) for the width of the actual circuit. The measurement results are shown in Table 2. Furthermore, the hiding power was evaluated based on the following evaluation criteria. The evaluation results are shown in Table 2. -Evaluation criteria- 〇:L * Value is 32 or less ×:L * Value is over 32

[0096] <Resolution> A plated copper substrate was used as the substrate. The substrate was pretreated using an etching agent (CZ-8100, manufactured by MEC Co., Ltd.), and the resulting dry films were bonded together using a vacuum laminator so that the L1 layer was in contact with the substrate, to produce the structure shown in Fig. 5. As shown in Fig. 5, the structure is one in which the L1 layer 31, the L2 layer 32, and the first film 24 are laminated in this order on the substrate 4. A negative mask for evaluating resolution with a solder resist dam width of 100 μm was placed on the fabricated structure, and the solder resist pattern was exposed to light at the optimum exposure dose using an exposure device equipped with a high-pressure mercury short arc lamp. The first film was then peeled off, and development was performed for 60 seconds using a 1 wt% sodium carbonate aqueous solution at 30°C under conditions of a spray pressure of 0.2 MPa to obtain a solder resist pattern. The structure on which the pattern was formed was then exposed in a UV conveyor furnace with an integrated exposure dose of 1,000 mJ / cm. 2 After irradiating with ultraviolet light under the above conditions, the coating was cured by heating at 150° C. for 60 minutes to obtain an evaluation substrate. The cross-sectional shape of the formed solder resist in the obtained evaluation board was visually confirmed, and the resolution was evaluated based on the following evaluation criteria. The evaluation results are shown in Table 2. In addition, in the case of an undercut shape, there is a risk that the solder resist will peel off and cause a short circuit, and therefore it can be said that the resolution is poor. -Evaluation criteria- ○: Straight shape (the length of the upper and lower sides are the same) or forward tapered structure (the top of the trapezoid is thinner. Figure 6) ×: Undercut shape (Fig. 7)

[0097] [Table 2]

[0098] The curable resin compositions of Examples 1 to 4 were applied onto a substrate, and the cured products were obtained by curing the substrate. The transmittance of the region on the substrate side (L1 layer) was higher than the transmittance of the region on the opposite side to the substrate side (L2 layer). These cured products were found to have excellent resolution and hiding power. In addition, the surface of the cured products was dark in color, so the visibility was good. In contrast, the cured products obtained by applying the curable resin compositions of Comparative Examples 1 and 2 onto a substrate and curing them have the same transmittance in the region on the substrate side (L1 layer) as in the region on the opposite side to the substrate side (L2 layer). These cured products were evaluated as "x" for either resolution or hiding power, revealing that they cannot achieve both resolution and hiding power. For the above reasons, a curable resin composition that gives a cured product in which the transmittance of the region on the substrate side is higher than the transmittance of the region on the opposite side to the substrate can provide a cured product that has excellent resolution, visibility, and hiding power.

[0099] Although the embodiment of the present invention has been specifically described above, the present invention is not limited to this embodiment, and various modifications are possible without departing from the spirit and scope of the present invention.

Claims

1. A curable resin composition comprising: In a cured product obtained by disposing the curable resin composition on a substrate and curing the composition, A curable resin composition, characterized in that a first transmittance in a region on the substrate side is higher than a second transmittance in a region on the opposite side to the substrate side.

2. The curable resin composition according to claim 1 , wherein the cured product has a first layer having the first transmittance and a second layer having the second transmittance.

3. The curable resin composition according to claim 1 or 2, wherein the second transmittance is 1% to 45%.

4. The curable resin composition according to claim 1 or 2, further comprising at least one of a photopolymerization initiator and a colorant.

5. A dry film comprising a first film and a resin layer formed on the first film and comprising the curable resin composition according to claim 1.

6. A cured product obtained by curing the curable resin composition according to claim 1 or the resin layer of the dry film according to claim 5.

7. A printed wiring board comprising the cured product according to claim 6.

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