JP2024065105A - CURABLE RESIN COMPOSITION, METHOD FOR PRODUCING CURED PRODUCT OF THE CURABLE RESIN COMPOSITION, AND METHOD FOR PRODUCING PRINTED WIRING BOARD COMPRISING THE CURED PRODUCT - Google Patents

Abstract

[Problem] To provide a curable resin composition capable of forming a highly reliable cured product in which the occurrence of cracks due to changes in shape caused by the influence of temperature or stress is suppressed. [Solution] A curable resin composition containing a carboxyl group-containing resin, a thermosetting component, and a photopolymerization initiator, in which the tensile break elongation of the cured product at 20°C is A%, the tensile break elongation at 85°C is B%, and the tensile break elongation at 240°C is C%, is adjusted so as to satisfy all of the following formulas 1 to 3: 2A<B (Formula 1) 2A<C (Formula 2) 4<C<6 (Formula 3). [Selected Figure] None

Description

The present invention relates to a curable resin composition, and in particular to a curable resin composition that is suitable for use in forming a solder resist. Furthermore, the present invention also relates to a method for producing a cured product using the curable resin composition, and a production method that includes the cured product.

Conventionally, when mounting electronic components on printed wiring boards used in electronic devices, etc., solder resist is formed on the circuit patterned substrate in areas other than the connection holes in order to prevent solder from adhering to unnecessary areas. Currently, solder resist is mainly formed using a so-called photo solder resist, in which a curable resin composition is applied to a substrate, dried, exposed to light, and developed to form a pattern, and the patterned resin is then fully cured by heating or irradiating it with light.

However, in recent years, with electronic devices becoming lighter, thinner, shorter, and smaller, and with the increase in battery capacity resulting in a decrease in the area occupied by the board, there is a demand for printed wiring boards to be increasingly finer and thinner. In addition, with the diversification of electronic devices, the need for flexible printed wiring boards is increasing significantly.

When such a flexible printed circuit board is molded in one go, it is necessary to process the flexible printed circuit board having the solder resist formed by the photo solder resist by laser irradiation. However, such laser processing is accompanied by an increase in temperature and the generation of stress, which causes a problem that cracks occur in the solder resist in the part not irradiated with the laser due to the influence of these factors. Furthermore, since stress is also generated when mounting electronic components on the flexible printed circuit board, there is also a problem that the stress causes cracks in the solder resist. Therefore, a technology has been proposed to suppress the occurrence of cracks in the solder resist due to stress by forming a dummy pattern in a margin part where no wiring pattern is formed (for example, Patent Document 1). However, since the manufacturing process of the flexible printed circuit board is diverse and various stresses are generated during the process, the current situation is that further improvement is required in the technology to suppress the occurrence of cracks in the solder resist caused by such stress.

JP2006-196878A

Under these circumstances, a continuing technical challenge remains to provide a curable resin composition that can form a highly reliable cured product, particularly a solder resist, in which cracks are suppressed even when the shape is changed due to the effects of temperature or stress.

Therefore, an object of the present invention is to provide a curable resin composition capable of forming a highly reliable cured product, particularly a solder resist, in which the occurrence of cracks is suppressed even when the shape is changed due to the influence of temperature or stress. Another object of the present invention is to provide a method for producing a highly reliable cured product in which the occurrence of cracks due to changes in shape due to the influence of temperature or stress is suppressed by using the above-mentioned curable resin composition, and a method for producing a printed wiring board including the cured product.

As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by providing a curable resin composition containing a carboxyl group-containing resin, a thermosetting component, and a photopolymerization initiator, in which the tensile elongation at break of the cured product of the curable resin composition at 20°C, 85°C, and 240°C satisfy a specific relationship with each other. The present invention is based on this finding. That is, the gist of the present invention is as follows.

[1] A curable resin composition comprising a carboxyl group-containing resin, a thermosetting component, and a photopolymerization initiator,
The tensile elongation at break of the cured product of the curable resin composition at 20° C. is A%,
The tensile elongation at break of the cured product of the curable resin composition at 85° C. is B%, and the tensile elongation at break of the cured product of the curable resin composition at 240° C. is C%.
In this case, the following formulas 1 to 3 are satisfied:
2A<B (Equation 1)
2A < C (Equation 2)
4 < C < 6 (Equation 3)
A curable resin composition, characterized in that all of the above is satisfied.
[2] The curable resin composition according to [1], wherein the carboxyl group-containing resin contains a resin having a bisphenol skeleton.
[3] The curable resin composition according to [1], wherein the carboxyl group-containing resin further contains a copolymer resin.
[4] The curable resin composition according to [3], wherein the copolymer resin does not have a novolak skeleton and an aromatic ring.
[5] The curable resin composition according to [1], wherein the thermosetting component contains an epoxy resin having a bisphenol skeleton and a biphenyl-type epoxy resin.
[6] The curable resin composition according to [5], wherein the ratio of the epoxy equivalent of the epoxy resin having a bisphenol skeleton to the epoxy equivalent of the biphenyl-type epoxy resin in the thermosetting component is 1:0.5 to 1:5, and the ratio of the total carboxylic acid equivalent of the carboxyl group-containing resin to the total epoxy equivalent of the epoxy resin having a bisphenol skeleton and the biphenyl-type epoxy resin in the thermosetting component is 1:1.2 to 1:5.
[7] A method for producing a cured product of the curable resin composition according to [1], comprising the steps of exposing the curable resin composition to light and then thermally curing the composition.
[8] The method according to [7], further comprising a step of irradiating the curable resin composition with UV light after exposure of the curable resin composition and before thermal curing.
[9] A method for producing a printed wiring board provided with a solder resist, comprising the steps of exposing the curable resin composition according to [1] to light and then thermally curing the composition to form the solder resist.
[10] The method according to [9], further comprising a step of irradiating the curable resin composition with UV light after exposure of the curable resin composition and before thermal curing.

According to the present invention, it is possible to provide a curable resin composition capable of forming a highly reliable cured product, particularly a solder resist, in which the occurrence of cracks is suppressed even when the shape is changed due to the influence of temperature or stress, as well as a method for producing a cured product using the curable resin composition and a printed wiring board including the cured product. Furthermore, according to the present invention, it is possible to provide a method for producing a printed wiring board including a highly reliable cured product in which the occurrence of cracks due to changes in shape due to the influence of temperature or stress is suppressed by using the curable resin composition as described above.

FIG. 1 shows a schematic diagram of a Kapton (registered trademark) polyimide film substrate on which a copper circuit pattern is formed during the preparation of a sample for evaluating cracks caused by laser irradiation and cracks during mounting of electronic components. Fig. 2 shows a schematic diagram of a flexible substrate in which four Kapton (registered trademark) polyimide films on which copper circuit patterns have been formed are arranged in parallel in the preparation of a sample for evaluating cracks caused by laser irradiation and cracks when mounting electronic components. Fig. 2A shows a schematic diagram before printing with a curable resin composition, and Fig. 2B shows a schematic diagram after printing, exposing, and developing the curable resin composition to form a pattern. FIG. 3 shows a schematic diagram of an evaluation sample after being cut into pieces by a laser processing machine in the evaluation of cracks caused by laser irradiation and cracks during mounting of electronic components.

[Curable resin composition]
The curable resin composition of the present invention is characterized in that it contains a carboxyl group-containing resin, a thermosetting component, and a photopolymerization initiator as essential components, and the tensile elongation at break of a cured product of the curable resin composition at temperatures of 20° C., 85° C., and 240° C. satisfy specific relationships with each other. That is, the curable resin composition of the present invention satisfies the following formulas 1 to 3, where the tensile elongation at break of the cured product at 20° C. is A%, the tensile elongation at break at 85° C. is B%, and the tensile elongation at break at 240° C. is C%:
2A<B (Equation 1)
2A < C (Equation 2)
4 < C < 6 (Equation 3)
The curable resin composition of the present invention is characterized in that the tensile elongation at break at each temperature of the cured product of the curable resin composition satisfies the above-mentioned relationships, and therefore it is possible to form a highly reliable cured product, particularly a solder resist, in which the occurrence of cracks is suppressed even when the shape is changed due to the influence of temperature or stress.

In the present invention, the tensile elongation at break of the cured product of the curable resin composition is a value measured according to the following procedure using RSA-G2 manufactured by TA Instruments in accordance with JIS K 7127:1999, Plastics - Tensile Properties Testing Method.
First, a cured product of the curable resin composition for use in a tensile test is prepared. Specifically, the curable resin composition is printed by screen printing on a 100 mm long x 150 mm wide x 1.6 mm thick FR-4 substrate with copper foil attached, so that the thickness of the cured product is 35 μm. Next, the substrate is dried at 80° C. for 30 minutes using a hot air circulation drying oven, and exposed to UV (ultraviolet light) at an accumulated exposure of 50 mJ/cm ² using an exposure device equipped with a metal halide lamp. Next, the substrate is developed for 60 seconds using a developer for printed wiring boards using a 1% aqueous sodium carbonate solution at 30° C. as a developer, and the curable resin composition is exposed to UV at an accumulated exposure of 1000 mJ/cm ² using an exposure device equipped with a high-pressure mercury lamp. Next, the substrate is thermally cured at 150° C. for 60 minutes using a hot air circulation drying oven to obtain an FR-4 substrate equipped with a cured product of the curable resin composition. Next, the cured product and the copper foil are peeled off together from the obtained FR-4 substrate, and then the copper foil is peeled off from the cured product to obtain a cured product for tensile testing having a width of 3 mm, a length of 40 mm, and a thickness of 35 μm. Next, the obtained cured product for tensile testing is subjected to a tensile test under the conditions of a gripper distance of 10 mm and a tensile speed of 0.002 mm/sec (0.12 mm/min) to measure the elongation at break, and the tensile elongation at break percentage (%) of the cured product of the curable resin composition is measured based on the following formula. The elongation at break is the measured value of the maximum elongation (at break) that the cured product for tensile testing can withstand when pulled.

Below, each component of the curable resin composition of the present invention will be described in detail.

(Carboxyl group-containing resin)
In the curable resin composition of the present invention, the carboxyl group-containing resin may be any of various conventionally known resins having a carboxyl group in the molecule. By including a carboxyl group-containing resin in the curable resin composition, it is possible to impart alkali developability to the curable resin composition. In particular, a carboxyl group-containing resin having an ethylenically unsaturated double bond in the molecule is preferred in terms of photocurability and development resistance. The ethylenically unsaturated double bond in the molecule is preferably derived from acrylic acid or methacrylic acid or a derivative thereof. The carboxyl group-containing resin may be used alone or in combination of two or more types. In addition, when only a carboxyl group-containing resin not having an ethylenically unsaturated double bond is used as the carboxyl group-containing resin, the curable resin composition is 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).

(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) Carboxyl group-containing urethane resins obtained by polyaddition reaction of diisocyanates such as aliphatic diisocyanates, branched aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates with carboxyl group-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.

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

(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 hydroxyalkyl (meth)acrylate, during the synthesis of the resin (2) or (3) described above.

(5) A carboxyl group-containing photosensitive urethane resin that is (meth)acrylated at the end 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 are 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 group 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 then 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 then reacting the resulting reaction product with a polybasic acid anhydride.

(12) A carboxyl group-containing photosensitive resin obtained by adding a compound having one epoxy group and one or more (meth)acryloyl groups in one molecule to any of the resins (1) to (11) above.
In this specification, the term "(meth)acrylate" is a general term for acrylate, methacrylate, and mixtures thereof, and the same applies to other similar expressions.

From the viewpoint of improving the flexibility of the curable resin composition by reducing the number of crosslinking points in the carboxyl group-containing resin, the carboxyl group-containing resin used in the curable resin composition preferably contains a carboxyl group-containing resin having a bisphenol skeleton. Examples of such carboxyl group-containing resins include carboxyl group-containing resins having a bisphenol skeleton, such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin, which are used as the epoxy resins (6), (7), or (12) described above.

In addition, from the viewpoint of easiness in dispersing the curable resin composition uniformly and low gloss of the cured product, the carboxyl group-containing resin used in the curable resin composition of the present invention preferably contains a copolymer resin in addition to the above-mentioned carboxyl group-containing resin having a bisphenol skeleton. Examples of such copolymer resins include the above-mentioned copolymerized carboxyl group-containing resins (1) and (12). It is particularly preferable to use a copolymer resin that has neither a novolac skeleton nor an aromatic ring as the copolymer resin.

The acid value of the carboxyl group-containing resin is preferably 30 to 150 mgKOH/g, and more preferably 50 to 120 mgKOH/g. When the acid value of the carboxyl group-containing resin is 30 mgKOH/g or more, the alkaline developability of the curable resin composition is improved. Furthermore, when the acid value is 150 mgKOH/g or less, it becomes easier to draw a good resist pattern.

The weight average molecular weight of the carboxyl group-containing resin varies depending on the resin skeleton, but is generally preferably 2,000 to 150,000, and more preferably 2,000 to 50,000. A weight average molecular weight of 2,000 or more can improve tack-free performance and resolution. Furthermore, a weight average molecular weight of 150,000 or less can improve the developability and storage stability of the curable resin composition.

The amount of the carboxyl group-containing resin in the curable resin composition is preferably 10 to 40% by mass, more preferably 20 to 35% by mass, calculated as solid content. By having the amount of the carboxyl group-containing resin be 10% by mass or more, the strength of the coating film can be improved. Furthermore, by having the amount of the carboxyl group-containing resin be 40% by mass or less, the viscosity of the curable resin composition becomes appropriate, and the processability is improved.

(Photopolymerizable monomer)
The curable resin composition of the present invention may contain a photopolymerizable monomer as required. 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. Specific examples of the alkyl acrylate include 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, and trishydroxyethyl isocyanurate. Polyhydric alcohols such as polyhydric alcohols or their alkylene oxide adducts or ε-caprolactone adducts; phenols such as phenoxy acrylate and bisphenol A diacrylate or their alkylene oxide adducts; acrylates of glycidyl ethers such as glycerin diglycidyl ether, trimethylolpropane triglycidyl ether, and triglycidyl isocyanurate; and at least one of acrylates and melamine acrylates obtained by directly acridating polyols such as polyether polyols, polycarbonate diols, hydroxyl group-terminated polybutadienes, and polyester polyols or by urethane acridating polyols via diisocyanates, as well as methacrylates corresponding to the acrylates, can be appropriately selected and used. Such photopolymerizable monomers can also be used as reactive diluents. The photopolymerizable monomers may be used alone or in combination of two or more.

The amount of photopolymerizable monomer in the curable resin composition is preferably 10 to 100 parts by mass, calculated as solid content, per 100 parts by mass of the carboxyl group-containing resin. When the amount of photopolymerizable monomer is 10 parts by mass or more, the photocurability of the curable resin composition is good, and pattern formation is easy in alkaline development after irradiation with active energy rays. On the other hand, when the amount is 100 parts by mass or less, halation is less likely to occur and good resolution can be obtained.

The photopolymerizable monomer is effective when a non-photosensitive carboxyl group-containing resin that does not have an ethylenically unsaturated double bond is used as the above-mentioned carboxyl group-containing resin, since it is necessary to use a photopolymerizable monomer in combination to make the curable resin composition photocurable.

(Photopolymerization initiator)
In the curable resin composition of the present invention, any known photopolymerization initiator can be used. 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-trimethylphenylphosphine oxide. bisacylphosphine oxides such as 2,6-dimethoxybenzoyldiphenylphosphine oxide, 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-trimethylbenzoylphenylphosphine acid methyl ester, and 2-methylbenzoyldiphenylphosphine oxide. monoacylphosphine oxides such as phenyl(2,4,6-trimethylbenzoyl)phosphinate, ethyl 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} 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; benzophenone, p-methylbenzophenone, Michler's ketone, methylbenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethyl Benzophenones such as aminobenzophenone; 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-mo acetophenones such as [(2-methylphenyl)phenyl]-1-butanone and N,N-dimethylaminoacetophenone; thioxanthones such as thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone; anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2- Anthraquinones such as amylanthraquinone and 2-aminoanthraquinone; ketals such as acetophenone dimethyl ketal and benzyl dimethyl ketal; benzoic acid esters such as ethyl-4-dimethylaminobenzoate, 2-(dimethylamino)ethyl benzoate and p-dimethylbenzoic acid ethyl ester; 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-( Examples of the photopolymerization initiator include oxime esters such as bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium and titanocenes such as bis(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(1-pyrrol-1-yl)ethyl)phenyl]titanium; phenyl disulfide 2-nitrofluorene, butyroin, anisoin ethyl ether, azobisisobutyronitrile, and tetramethylthiuram disulfide. One type of photopolymerization initiator may be used alone, or two or more types may be used in combination.

The amount of the photopolymerization initiator in the curable resin composition is preferably 1 to 20 parts by mass, more preferably 2 to 10 parts by mass, based on the solid content, for photopolymerization initiators other than oxime ester photopolymerization initiators, based on 100 parts by mass of carboxyl group-containing resin. When the amount is 1 part by mass or more, the photocurability of the curable resin composition is good, the coating is less likely to peel off, and the coating properties such as chemical resistance are also good. On the other hand, when the amount is 20 parts by mass or less, the effect of reducing outgassing is obtained, and furthermore, the light absorption on the surface of the solder resist coating film is good, and the deep curing property is less likely to decrease. In addition, in the case of an oxime ester photopolymerization initiator, the amount of the photopolymerization initiator in the curable resin composition is preferably 0.1 to 0.8 parts by mass, more preferably 0.4 to 0.7 parts by mass, based on 100 parts by mass of carboxyl group-containing resin, based on the solid content. When the amount is 0.1 part by mass or more, the photocurability of the curable resin composition is good, and the coating properties such as heat resistance and chemical resistance are also good. On the other hand, if the blending amount is 0.8 parts by mass or less, the light absorption of the solder resist film is good and the deep curing property is less likely to decrease.

The curable resin composition of the present invention may use a photoinitiator assistant or sensitizer in combination with the above-mentioned photopolymerization initiator. Examples of the photoinitiator assistant or sensitizer include benzoin compounds, anthraquinone compounds, thioxanthone compounds, ketal compounds, benzophenone compounds, tertiary amine compounds, and xanthone compounds. As the photoinitiator assistant or sensitizer, it is particularly preferable to use thioxanthone compounds such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone. By using a thioxanthone compound as a photoinitiator assistant or sensitizer, it is possible to improve deep curing properties. These compounds can be used alone as a photopolymerization initiator, but are preferably used as a photoinitiator assistant or sensitizer in combination with the above-mentioned photopolymerization initiator. The photoinitiator assistant or sensitizer may be used alone or in combination of two or more.

(Thermosetting component)
In the curable resin composition of the present invention, various conventionally known compounds and resins having thermosetting properties can be used as the thermosetting component. By including a thermosetting component in the curable resin composition, it is expected that the heat resistance of the composition can be improved. Examples of the thermosetting component used in the present invention include isocyanate compounds, blocked isocyanate compounds, amino resins, maleimide compounds, benzoxazine resins, carbodiimide resins, cyclocarbonate compounds, epoxy resins, oxetane compounds, and episulfide resins. The thermosetting component may be used alone or in combination of two or more. Among these, the preferred thermosetting component is an epoxy resin.

Epoxy resins include, for example, 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, novolac 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, triphenylmethane type epoxy resins, glycidylamine type epoxy resins, alicyclic epoxy resins, trihydroxyphenylmethane type epoxy resins, bixylenol type or biphenol type epoxy resins, tetraphenylolethane type epoxy resins, heterocyclic epoxy resins, diglycidyl phthalate resins, tetraglycidylxylenoylethane resins, glycidyl methacrylate copolymer epoxy resins, cyclohexylmaleimide and glycidyl methacrylate copolymer epoxy resins, CTBN modified epoxy resins, etc.

Commercially available epoxy resins include, for example, jER (registered trademark) 828, 806, 807, YX8000, YX8034, 834, and YX4000 manufactured by Mitsubishi Chemical Corporation, YD-128, YDF-170, ZX-1059, and ST-3000 manufactured by Nippon Steel Chemical & Material Co., Ltd., EPICLON (registered trademark) 830, 835, 840, 850, N-730A, N-695, N-860, and N-870 manufactured by DIC Corporation, and RE-306 manufactured by Nippon Kayaku Co., Ltd.

When an epoxy resin is used as the thermosetting component, the ratio of the total carboxylic acid equivalent of the above-mentioned carboxyl group-containing resin to the total epoxy equivalent of the epoxy resin having a bisphenol skeleton and the biphenyl type epoxy resin of the thermosetting component (total carboxylic acid equivalent of the carboxyl group-containing resin: total epoxy equivalent of the epoxy resin having a bisphenol skeleton and the biphenyl type epoxy resin of the thermosetting component) is preferably 1:1.2 to 1:5, more preferably 1:1.3 to 1:3, and even more preferably 1:1.5 to 1:2.5. By having the ratio of the total carboxylic acid equivalent of the above-mentioned carboxyl group-containing resin to the total epoxy equivalent of the epoxy resin having a bisphenol skeleton and the biphenyl type epoxy resin of the thermosetting component in such a range, it is possible to achieve a good balance between the developability and the coating properties of the curable resin composition. In addition, "total epoxy equivalent of the epoxy resin having a bisphenol skeleton and the biphenyl type epoxy resin" refers to the sum of the epoxy equivalent, which is the resin weight per epoxy group in the epoxy resin having a bisphenol skeleton and the biphenyl type epoxy resin contained in the curable resin composition, and is expressed in g/eq. Therefore, the number of epoxy groups of the epoxy resin having a bisphenol skeleton and the biphenyl type epoxy resin in the curable resin composition can be calculated from the value of the total epoxy equivalent of the epoxy resin having a bisphenol skeleton and the biphenyl type epoxy resin. In addition, "total carboxylic acid equivalent" refers to the total carboxylic acid equivalent, which is the resin weight per carboxyl group in each carboxyl group-containing resin contained in the curable resin composition, and is expressed in units of g/eq. Therefore, the number of carboxyl groups in the curable resin composition can be calculated from the value of the total carboxylic acid equivalent.

In a preferred embodiment, a combination of an epoxy resin having a bisphenol skeleton and a biphenyl type epoxy resin is used as the thermosetting component. When these epoxy resins are used in combination as the thermosetting component, the ratio of the epoxy equivalent of the epoxy resin having a bisphenol skeleton to the epoxy equivalent of the biphenyl type epoxy resin (epoxy equivalent of the epoxy resin having a bisphenol skeleton: epoxy equivalent of the biphenyl type epoxy resin) is preferably 1:0.5 to 1:5, more preferably 1:0.7 to 1:4, even more preferably 1:0.75 to 1:1.2, and particularly preferably 1:0.75 to 1:0.95. By having the ratio of the epoxy equivalent of the epoxy resin having a bisphenol skeleton to the epoxy equivalent of the biphenyl type epoxy resin in such a range, it is possible to achieve both good crack resistance and electrical insulation of the cured product of the curable resin composition. In particular, when the ratio of the epoxy equivalent of the epoxy resin having a bisphenol skeleton to the epoxy equivalent of the biphenyl type epoxy resin is in the range of 1:0.75 to 1:0.95, the cured product can have both good crack resistance and electrical insulation properties, as well as particularly good resolution.

(Thermal curing catalyst)
In order to improve the thermosetting property of the above-mentioned thermosetting component, a thermosetting catalyst may be blended in the curable resin composition of the present invention, if necessary.

Examples of the thermosetting catalyst used in the present invention 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 thermosetting catalysts include 2MZ-A, 2MZ-OK, 2PHZ, 2P4BHZ, and 2P4MHZ (all trade names of imidazole-based compounds) manufactured by Shikoku Chemical Industry Co., Ltd., and U-CAT 3513N (trade name of dimethylamine-based compounds), DBU, DBN, and U-CAT SA 102 (all bicyclic amidine compounds and salts thereof) manufactured by San-Apro Co., Ltd. The thermosetting catalyst is not particularly limited to these, and may be a thermosetting catalyst for epoxy resins or oxetane compounds, or one that promotes the reaction of at least one of an epoxy group and an oxetanyl group with a carboxyl group. In addition, 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 can also be used, and preferably these compounds that also function as adhesion-imparting agents are used in combination with the heat curing catalyst. The heat curing catalyst may be used alone or in combination of two or more types.

The amount of the thermosetting catalyst in the curable resin composition is preferably 1 to 20 parts by mass, and more preferably 1 to 15 parts by mass, per 100 parts by mass of the carboxyl group-containing resin. When the amount of the thermosetting catalyst is 1 part by mass or more, the cured product of the curable resin composition has excellent heat resistance. On the other hand, when the amount of the thermosetting catalyst is 20 parts by mass or less, the storage stability of the curable resin composition is improved.

(Organic solvent)
The curable resin composition of the present invention may contain an organic solvent for the purpose of adjusting the viscosity when preparing the composition or when applying the composition to a substrate or film. Examples of the organic solvent include ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, diethylene glycol monomethyl ether acetate, and tripropylene glycol monomethyl ether; esters such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, petroleum naphtha, and solvent naphtha. Known and commonly used organic solvents can be used. The organic solvent may be used alone or in combination of two or more kinds.

The amount of organic solvent in the curable resin composition is preferably changed as appropriate depending on the components constituting the curable resin composition and their amounts, but for example, it can be 50 to 300 parts by mass, calculated as solid content, per 100 parts by mass of the above-mentioned carboxyl group-containing resin.

In the present invention, the volatilization and drying of the organic solvent 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 with the substrate using a heat source of an air heating method using steam, or a method in which hot air is blown onto the substrate from a nozzle).

(Filler)
The curable resin composition of the present invention may contain a filler as necessary in order to increase the physical strength of the coating film. As such a filler, known inorganic or organic fillers can be used, and barium sulfate, spherical silica, hydrotalcite, and talc are particularly preferably used. Furthermore, in order to obtain a white appearance and flame retardancy, titanium oxide, metal oxides, and metal hydroxides such as aluminum hydroxide can also be used as extender pigment fillers.

The amount of filler in the curable resin composition is preferably 40% by mass or less, calculated as solid content, based on the total mass of the curable resin composition. If the amount of filler exceeds 40% by mass of the total mass of the curable resin composition, the viscosity of the curable resin composition increases, its application and moldability decrease, and the formed cured product becomes brittle. More preferably, it is 5 to 40% by mass.

(Other added ingredients)
The curable resin composition of the present invention may further contain, as necessary, colorants, ion catchers, photoinitiator assistants, cyanate compounds, elastomers, mercapto compounds, urethane catalysts, thixotropic agents, adhesion promoters, block copolymers, chain transfer agents, polymerization inhibitors, copper inhibitors, antioxidants, rust inhibitors, thickeners such as organic bentonite and montmorillonite, at least one of silicone-based, fluorine-based, and polymer-based defoamers and leveling agents, silane coupling agents such as imidazole-based, thiazole-based, and triazole-based, and flame retardants such as phosphorus compounds such as phosphinates, phosphate ester derivatives, and phosphazene compounds. These may be known in the field of electronic materials.

The curable resin composition of the present invention may be used in liquid form or in the form of a dry film as described below. When used in liquid form, it may be a one-component composition or a two-component composition or more.

[Dry film]
The curable resin composition of the present invention can also be in the form of a dry film having a first film and a resin layer made of the curable resin composition formed on the first film. The first film in the present invention refers to a film that is at least adhered to the resin layer when a base material such as a substrate and a layer (resin layer) made of the curable resin composition formed on the dry film are laminated by heating or the like so that they are in contact with each other to form an integral mold. The first film may be peeled off from the resin layer in a process after lamination. In particular, in the present invention, it is preferable to peel off from the resin layer in a process after exposure. When forming a dry film, the curable resin composition of the present invention is diluted with the organic solvent to adjust the viscosity to an appropriate level, and applied 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, or the like, and usually dried at a temperature of 50 to 130 ° C. for 1 to 30 minutes to obtain a film. There is no particular restriction on the coating thickness, but it is generally selected appropriately in the range of 1 to 150 μm, preferably 10 to 60 μm, in terms of the thickness after drying.

As the first film, any known film can be used without particular limitation. For example, polyester films such as polyethylene terephthalate and polyethylene naphthalate, polyimide films, polyamideimide films, polypropylene films, polystyrene films, and other films made of thermoplastic resins can be suitably used. Among these, polyester films are preferred from the viewpoints of heat resistance, mechanical strength, ease of handling, and the like. A laminate of these films can also be used as the first film.

In addition, from the viewpoint of improving mechanical strength, it is preferable that the thermoplastic resin film described above is a film that has been stretched in a uniaxial or biaxial direction.

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

After forming a resin layer of the curable resin composition of the present invention on the first film, it is preferable to further laminate a peelable second film on the surface of the resin layer for the purpose of preventing dust from adhering to the surface of the resin layer. The second film refers to a film that is peeled off from the resin layer before lamination when laminating a base material such as a substrate and a layer (resin layer) of the curable resin composition formed on a dry film by heating or the like so that they are in contact with each other to form an integral structure. Examples of the peelable second film that can be used include polyethylene film, polytetrafluoroethylene film, polypropylene film, and surface-treated paper. The second film may be one in which the adhesive strength between the resin layer and the second film is smaller than the adhesive strength between the resin layer and the first film when the second film is peeled off.

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

The dry film may be prepared by applying the curable resin composition of the present invention to the second film and drying it to form a resin layer, and then laminating the first film on the surface of the resin layer. In other words, when producing a dry film in the present invention, either the first film or the second film may be used as the film to which the curable resin composition of the present invention is applied.

[Cured product]
The resin layer of the curable resin composition or dry film of the present invention described above can be cured to obtain a cured product of the curable resin composition. The cured product obtained using the curable resin composition or dry film of the present invention is prevented from cracking even when its shape is changed due to the influence of temperature or stress, and has high reliability required for a solder resist.

The cured product is not particularly limited as long as it is obtained by curing the curable resin composition of the present invention, but is preferably obtained by exposing the curable resin composition of the present invention to light and then thermally curing it, and particularly preferably obtained by exposing the curable resin composition of the present invention to light, irradiating it with UV light after exposure, and thermally curing it after UV irradiation. By exposing the curable resin composition of the present invention to light, irradiating it with UV light after exposure, and thermally curing it after UV irradiation, the occurrence of cracks in the obtained cured product when the shape changes due to the influence of temperature or stress can be particularly well suppressed. The reason why the occurrence of cracks in the obtained cured product can be effectively suppressed by exposing the curable resin composition of the present invention to light and then thermally curing it is not clear, but it can be inferred as follows. That is, by exposing the curable resin composition to light, the carboxyl group-containing resin is cured, and as a result, the crosslink density of the carboxyl group-containing resin increases. And, by increasing the crosslink density of the carboxyl group-containing resin, the subsequent thermal curing of the thermosetting component is moderately inhibited, and as a result, the obtained cured product has moderate hardness and toughness, and it is considered that the occurrence of cracks due to changes in shape due to the influence of temperature and stress can be particularly suppressed. Furthermore, by irradiating the curable resin composition of the present invention with UV light after exposure and before thermal curing, the carboxyl group-containing resin that was not completely cured by exposure (uncured carboxyl group-containing resin) is cured, and as a result, the crosslink density of the carboxyl group-containing resin becomes higher. And, by increasing the crosslink density, the subsequent thermal curing of the thermosetting component is more appropriately inhibited, and as a result, the obtained cured product has more appropriate hardness and toughness, and it is thought that the occurrence of cracks due to changes in shape caused by temperature and stress can be particularly suppressed.

[Printed wiring board]
The printed wiring board of the present invention has a cured product obtained from the resin layer of the curable resin composition or dry film of the present invention. As a method for producing the printed wiring board of the present invention, for example, the curable resin composition of the present invention is adjusted to a viscosity suitable for the coating method using the organic solvent described above, and applied to 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) 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 contacts the substrate, and then the first film is peeled off to form a resin layer on the substrate.

The substrate for printed wiring boards includes printed wiring boards and flexible printed wiring boards with circuits already formed using copper or other materials, as well as materials such as paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth/non-woven cloth epoxy, glass cloth/paper epoxy, synthetic fiber epoxy, copper-clad laminates for high-frequency circuits using 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, and wafer plates.

The dry film is preferably bonded to 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, the dry film adheres closely to the circuit substrate even if the substrate has an uneven surface, preventing the inclusion of air bubbles and improving the filling of recesses in the substrate surface. The pressure conditions are preferably about 0.1 to 2.0 MPa, and the heating conditions are preferably 40 to 120°C.

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, etc. (a method in which hot air in the dryer is brought into countercurrent contact using a heat source of an air heating method using steam, or a method in which hot air is blown onto the support from a nozzle).

After forming a resin layer on the substrate, the resin layer is selectively exposed to active energy rays through a photomask with a predetermined pattern, and the unexposed areas are developed with a dilute alkaline aqueous solution (e.g., 0.3 to 3% by weight 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 properties 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 film with excellent 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 by heat curing alone to perform final finishing curing (main curing).

The exposure machine used for the 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 UV rays in the range of 350 to 450 nm, and further, a direct imaging machine (for example, a laser direct imaging machine that draws an image directly 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 can generally be within the range of 10 to 1000 mJ/cm ² , preferably 20 to 800 mJ/cm ² .

The development method can be a dipping method, a shower method, a spray method, a brush method, etc., and the developer can be an alkaline aqueous solution of potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, amines, etc.

According to the present application, the following inventions are provided.
[1] A curable resin composition comprising a carboxyl group-containing resin, a thermosetting component, and a photopolymerization initiator,
The tensile elongation at break of the cured product of the curable resin composition at 20° C. is A%,
The tensile elongation at break of the cured product of the curable resin composition at 85° C. is B%, and the tensile elongation at break of the cured product of the curable resin composition at 240° C. is C%.
In this case, the following formulas 1 to 3 are satisfied:
2A<B (Equation 1)
2A < C (Equation 2)
4 < C < 6 (Equation 3)
A curable resin composition characterized by satisfying all of the above.
[2] The curable resin composition according to [1], wherein the carboxyl group-containing resin contains a resin having a bisphenol skeleton.
[3] The curable resin composition according to [1] or [2], wherein the carboxyl group-containing resin further contains a copolymer resin.
[4] The curable resin composition according to [3], wherein the copolymer resin does not have a novolak skeleton and an aromatic ring.
[5] The curable resin composition according to any one of [1] to [4], wherein the thermosetting component contains an epoxy resin having a bisphenol skeleton and a biphenyl-type epoxy resin.
[6] The curable resin composition according to [5], wherein the ratio of the epoxy equivalent of the epoxy resin having a bisphenol skeleton to the epoxy equivalent of the biphenyl-type epoxy resin in the thermosetting component is 1:0.5 to 1:5, and the ratio of the total carboxylic acid equivalent of the carboxyl group-containing resin to the total epoxy equivalent of the epoxy resin having a bisphenol skeleton and the biphenyl-type epoxy resin in the thermosetting component is 1:1.2 to 1:5.
[7] A method for producing a cured product of the curable resin composition according to any one of [1] to [6], comprising a step of exposing the curable resin composition to light and then thermally curing the composition.
[8] The method according to [7], further comprising a step of irradiating the curable resin composition with UV light after exposure of the curable resin composition and before thermal curing.
[9] A method for producing a printed wiring board provided with a solder resist, comprising the steps of exposing the curable resin composition according to any one of [1] to [6] to light and then thermally curing the composition to form the solder resist.
[10] The method according to [9], further comprising a step of irradiating the curable resin composition with UV light after exposure of the curable resin composition and before thermal curing.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" are all based on mass unless otherwise specified.

[Preparation of each component of the curable resin composition]
In order to prepare each of the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3 shown in Table 1 below, the components shown in Table 1 below were prepared. Details of each component in Table 1 and the synthesis method are as follows.

(Synthesis of Carboxyl Group-Containing Resin 1)
Carboxyl group-containing resin 1 was synthesized according to the following procedure.
First, 456 parts of bisphenol A, 228 parts of water, and 649 parts of 37% formalin were charged into a flask equipped with a cooling tube and a stirrer, and 228 parts of 25% aqueous sodium hydroxide solution was added while maintaining the temperature below 40°C. After the addition was completed, the mixture was reacted at 50°C for 10 hours. After the reaction was completed, the mixture was cooled to 40°C, and 37.5% aqueous phosphoric acid solution was added until the pH reached 4 while maintaining the temperature below 40°C. Then, the mixture was left to stand to separate the aqueous layer, and 300 parts of methyl isobutyl ketone was added to the aqueous layer to dissolve it uniformly. The mixture was washed three times with 500 parts of distilled water, and the mixture was depressurized at a temperature below 50°C to remove water, solvent, etc., to obtain a polymethylol compound. The obtained polymethylol compound was dissolved in 550 parts of methanol to obtain 1230 parts of a methanol solution of the polymethylol compound. A part of the obtained methanol solution of the polymethylol compound was dried at room temperature using a vacuum dryer, and the solid content was 55.2%. Next, 500 parts of the resulting methanol solution of the polymethylol compound and 440 parts of 2,6-xylenol were charged into a flask equipped with a cooling tube and a stirrer, and were dissolved uniformly at 50° C. After the mixture was dissolved uniformly, the pressure was reduced at a temperature of 50° C. or less to remove the methanol. Next, 8 parts of oxalic acid was added, and the mixture was reacted at 100° C. for 10 hours. After the reaction was completed, the distillate was removed at 180° C. under reduced pressure of 50 mmHg, and 550 parts of novolak resin A was obtained.

Next, 130 parts of the novolak resin A obtained by the above procedure, 2.6 parts of a 50% aqueous sodium hydroxide solution, and 100 parts of toluene/methyl isobutyl ketone (mass ratio = 2/1) were charged into an autoclave equipped with a thermometer, a nitrogen introduction device/alkylene oxide introduction device, and a stirrer, and the inside of the system was replaced with nitrogen while stirring, and then heated to increase the temperature, and 45 parts of ethylene oxide were gradually introduced at 150 ° C. and 8 kg / cm ² to react. The reaction was continued for about 4 hours until the gauge pressure became 0.0 kg / cm ² , and then cooled to room temperature. 3.3 parts of a 36% aqueous hydrochloric acid solution were added to the obtained reaction solution and mixed to neutralize the sodium hydroxide. The obtained neutralized reaction product was diluted with toluene, washed with water three times, and desolvated using an evaporator to obtain an ethylene oxide adduct of novolak resin A with a hydroxyl value of 175 g / eq. The resulting ethylene oxide adduct of novolak resin A had an average of 1 mole of ethylene oxide added per equivalent of the phenolic hydroxyl group.

Next, 175 parts of the ethylene oxide adduct of the obtained novolak resin A, 50 parts of acrylic acid, 3.0 parts of p-toluenesulfonic acid, 0.1 parts of hydroquinone monomethyl ether, and 130 parts of toluene were charged into a reactor equipped with a stirrer, a thermometer, and an air inlet tube, and the mixture was stirred while blowing in air, and the temperature was raised to 115°C to react. The reaction was continued for another 4 hours while the water produced by the reaction was distilled off as an azeotrope with toluene, and then the mixture was cooled to room temperature. The resulting reaction solution was washed with a 5% aqueous NaCl solution, and the toluene was removed by distillation under reduced pressure, after which diethylene glycol monoethyl ether acetate was added to obtain an acrylate resin solution with a solid content of 68%.

Next, 312 parts of the obtained acrylate resin solution, 0.1 parts of hydroquinone monomethyl ether, and 0.3 parts of triphenylphosphine were charged into a four-neck flask equipped with a stirrer and a reflux condenser, the mixture was heated to 110°C, 45 parts of tetrahydrophthalic anhydride was added, and the mixture was reacted for 4 hours, cooled, and then removed. In this way, an alkali-soluble resin was obtained with a solid content of 72%, a solid acid value of 65 mg KOH/g, a weight average molecular weight of 12,000, and a carboxylic acid equivalent of 863 g/eq. The obtained alkali-soluble resin was designated as carboxyl group-containing resin 1.

(Synthesis of Carboxyl Group-Containing Resin 2)
Carboxyl group-containing resin 2 was synthesized according to the following procedure.
First, 220 g of cresol novolac epoxy resin (EPICLON (registered trademark) N-695 manufactured by DIC Corporation, epoxy equivalent: 220) was charged into 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 resulting mixture was heated to 95 to 105°C, 72 g of acrylic acid was gradually added dropwise, and the mixture was reacted for 16 hours. The resulting reaction product was cooled to 80 to 90°C, 106 g of tetrahydrophthalic anhydride was added, the mixture was reacted for 8 hours, and the mixture was taken out after cooling. In this way, an alkali-soluble resin having a solid content of 65%, an acid value of the solid content of 100 mgKOH/g, a weight average molecular weight of about 3,500, and a carboxylic acid equivalent of 561 g/eq. was obtained. The resulting alkali-soluble resin was designated as carboxyl group-containing resin 2.

(Synthesis of Carboxyl Group-Containing Copolymer Resin 3)
Carboxyl-containing resin 3 was synthesized according to the following procedure.
First, methyl methacrylate, ethyl methacrylate and methacrylic acid were charged in a flask equipped with a thermometer, a stirrer, a dropping funnel and a reflux condenser so that the molar ratio was 1:1:2, dipropylene glycol monomethyl ether was added as a solvent, and AIBN was added as a catalyst, and the mixture was stirred at 80°C for 4 hours under a nitrogen atmosphere to obtain a resin solution. The obtained resin solution was cooled, and glycidyl methacrylate was reacted with the carboxyl group of the resin solution at 95 to 105°C for 16 hours using methyl hydroquinone as a polymerization inhibitor and tetrabutylphosphonium bromide as a catalyst, at a rate of 20 mol%, and the resin solution was taken out after cooling. In this way, an alkali-soluble resin having both an ethylenically unsaturated bond and a carboxyl group with a solid content of 65%, a solid acid value of 120 mgKOH/g, a weight average molecular weight of about 20,000, and a carboxylic acid equivalent of 467 g/eq. was obtained. The obtained alkali-soluble resin was designated as carboxyl group-containing copolymer resin 3.

(Synthesis of Carboxyl Group-Containing Copolymer Resin 4)
Carboxyl-containing resin 4 was synthesized according to the following procedure.
First, 900 g of diethylene glycol dimethyl ether as a solvent and 21.4 g of t-butylperoxy 2-ethylhexanoate (Perbutyl (registered trademark) O manufactured by NOF Corp.) as a polymerization initiator were added to a 2-liter separable flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping funnel and a nitrogen inlet tube, and the mixture was heated to 90° C. After heating, 309.9 g of methacrylic acid, 116.4 g of methyl methacrylate and 109.8 g of lactone-modified 2-hydroxyethyl methacrylate (Placcel FM1 manufactured by Daicel Corp.) were added dropwise over 3 hours together with 21.4 g of bis(4-t-butylcyclohexyl)peroxydicarbonate (Perloyl (registered trademark) TCP manufactured by NOF Corp.) as a polymerization initiator, and the mixture was allowed to react for another 6 hours to obtain a carboxyl group-containing copolymer resin. The reaction was carried out under a nitrogen atmosphere. Next, 363.9 g of 3,4-epoxycyclohexylmethyl acrylate (Cyclomer A200 manufactured by Daicel Corporation), 3.6 g of dimethylbenzylamine as a ring-opening catalyst, and 1.80 g of hydroquinone monomethyl ether as a polymerization inhibitor were added to the obtained carboxyl group-containing copolymer resin, and the mixture was heated to 100°C and stirred to carry out a ring-opening addition reaction of epoxy. After 16 hours, a reaction solution containing a carboxyl group-containing resin having no aromatic ring and having a solid content of 53.8 mass%, a solid content acid value of 108.9 mgKOH/g, a weight average molecular weight of 25,000, and a carboxylic acid equivalent of 515 g/eq. was obtained. The obtained reaction solution was designated as carboxyl group-containing copolymer resin 4.

Details of each component other than the carboxyl group-containing resin are as follows.
Photopolymerizable monomer: dipentaerythritol hexaacrylate (DPHA)
Photopolymerization initiator: 2-[4-(methylthio)benzoyl]-2-(4-morpholinyl)propane (Omnirad (registered trademark) 907 manufactured by IGM Resins Co., Ltd.)
Filler 1: Barium sulfate (B-30 manufactured by Sakai Chemical Industry Co., Ltd.)
Filler 2: Surface-treated precipitated silica (ACEMATT® OK 412 from Evonik)
Filler 3: Surface-untreated precipitated silica (ACEMATT® 82 from Evonik)
Filler 4: Talc Thermosetting component 1: Bisphenol A novolac type epoxy resin (EPICLON (registered trademark) N-870 manufactured by DIC Corporation, epoxy equivalent: 200 g/eq)
Thermosetting component 2: Bisphenol A type epoxy resin (EPICLON (registered trademark) N-860 manufactured by DIC Corporation, epoxy equivalent: 245 g/eq)
Thermosetting component 3: Tetramethylbiphenyl type epoxy resin (YX-4000 manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 186 g/eq)
Thermosetting component 4: Triglycidyl triisocyanurate (TGIC, epoxy equivalent: 100 g/eq)
Heat curing catalyst: Melamine Defoaming/leveling agent: Silicone-based defoaming agent (KS-66 manufactured by Shin-Etsu Chemical Co., Ltd.)
Ion catcher: Synthetic hydrotalcite (DHT-4A manufactured by Kyowa Chemical Industry Co., Ltd.)

[Preparation of Curable Resin Composition]
The components shown in Table 1 below were mixed in the amounts shown in the table, pre-mixed with a mixer, and then kneaded with a three-roll mill to prepare the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3. The amounts shown in Table 1 indicate parts by mass of solids, unless otherwise specified.

(Preparation of a sample for tensile test of the cured product of the curable resin composition of Example 1)
For the curable resin composition of Example 1, a sample for a tensile test was prepared according to the following procedure.
First, the components shown in Table 1 were mixed in the amounts (solid content) shown in the table, and kneaded and dispersed to obtain a curable resin composition of Example 1. Next, the curable resin composition of Example 1 was printed by screen printing on a 100 mm long x 150 mm wide x 1.6 mm thick FR-4 substrate with copper foil attached, so that the film thickness was 35 μm. Next, 1) it was dried at 80 ° C. for 30 minutes in a hot air circulation drying oven, and then 2) it was exposed to UV at an accumulated exposure amount of 50 mJ / cm ² using an exposure device equipped with a metal halide lamp. Next, 3) it was developed for 60 seconds with a printed wiring board developer using a 1% sodium carbonate aqueous solution at 30 ° C. as a developer, 4) it was exposed to UV at an accumulated exposure amount of 1000 mJ / cm ² using an exposure device equipped with a high-pressure mercury lamp, and then 5) it was thermally cured at 150 ° C. for 60 minutes in a hot air circulation drying oven to obtain a cured product of the curable resin composition of Example 1. Furthermore, the copper foil on the FR-4 substrate on which the cured product was formed was peeled off, and then the copper foil was peeled off from the cured product to obtain a sample for a tensile test.

(Preparation of samples for tensile test of cured products of curable resin compositions of Examples 2 and 3)
Tensile test samples of the cured products of the curable resin compositions of Examples 2 and 3 were obtained according to the same procedure as for preparing the tensile test sample of the cured product of the curable resin composition of Example 1 described above, except that the components were replaced with the components shown in Table 1.

(Preparation of a sample for evaluating cracks in the cured product of the curable resin composition of Example 1)
For the curable resin composition of Example 1, samples for evaluating cracks caused by laser irradiation and cracks during mounting of electronic components were prepared according to the following procedure.
First, a flexible substrate was obtained by forming four patterns (copper circuit thickness 18 μm) as shown in FIG. 1 in parallel as shown in FIG. 2A on a Kapton (registered trademark) polyimide film manufactured by DuPont Toray Co., Ltd., which is 100 mm long x 150 mm wide x 25 μm thick. The pattern shape in FIG. 1 is a pattern in which 30 (3 × 10) copper pads of 2000 μm × 2000 μm are arranged at 4 mm intervals, and the center of the copper pad is connected with a line width of 150 μm. Next, similar to the preparation procedure of the tensile test sample described above, the curable resin composition of Example 1 was printed and cured on the obtained flexible substrate by screen printing so that the film thickness was 35 μm, to obtain a crack evaluation sample. In addition, in the exposure process using the metal halide lamp described above in 2), a negative pattern of 2100 μm × 2100 μm was used for exposure and development so that the copper pads on the flexible substrate were completely exposed, and a curable resin composition layer with exposed copper pads as shown in FIG. 2B was formed, and then cured to produce a cured coating film.

(Preparation of samples for evaluating cracks in cured products of the curable resin compositions of Examples 2 and 3)
Except for replacing the components with those shown in Table 1, the same procedure was followed as in the preparation of the crack evaluation sample of the cured product of the curable resin composition of Example 1 described above. Crack evaluation samples of the cured products of the curable resin compositions of Examples 2 and 3 were obtained.

(Preparation of a sample for tensile test of the cured product of the curable resin composition of Comparative Example 1)
For the curable resin composition of Comparative Example 1, a sample for a tensile test was prepared according to the following procedure.
First, the components shown in Table 1 were mixed in the amounts (solid content) shown in the table, and kneaded and dispersed to obtain a curable resin composition of Comparative Example 1. Next, the curable resin composition of Comparative Example 1 was printed by screen printing on a 100 mm long x 150 mm wide x 1.6 mm thick FR-4 substrate with copper foil attached, so that the film thickness was 35 μm. Next, 1) after drying at 80 ° C. for 30 minutes in a hot air circulation drying oven, 2) UV exposure was performed at an accumulated exposure amount of 75 mJ / cm ² using an exposure device equipped with a metal halide lamp. Next, 3) development was performed for 60 seconds with a developer for printed wiring boards at 30 ° C. using a 1% sodium carbonate aqueous solution as a developer, 4) after thermal curing for 60 minutes at 150 ° C. in a hot air circulation drying oven, 5) the curable resin composition of Comparative Example 1 was irradiated with UV at an accumulated exposure amount of 1000 mJ / cm ² using an exposure device equipped with a high pressure lamp to obtain a cured product of the curable resin composition of Comparative Example 1. Furthermore, the copper foil on the FR-4 substrate on which the cured product was formed was peeled off, and then the copper foil was peeled off from the cured product to obtain a sample for a tensile test.

(Preparation of samples for tensile test of cured products of curable resin compositions of Comparative Examples 2 and 3)
Tensile test samples of the cured products of the curable resin compositions of Comparative Examples 2 and 3 were obtained according to the same procedure as for preparing the tensile test sample of the cured product of the curable resin composition of Comparative Example 1 described above, except that the components were replaced with the components shown in Table 1.

(Preparation of a sample for evaluating cracks in the cured product of the curable resin composition of Comparative Example 1)
For the curable resin composition of Comparative Example 1, a sample for evaluating cracks caused by laser irradiation and cracks during mounting of electronic components was prepared according to the following procedure.
First, a flexible substrate was obtained by forming four patterns (copper circuit thickness 18 μm) as shown in FIG. 1 in parallel as shown in FIG. 2A on a Kapton (registered trademark) polyimide film manufactured by Toray DuPont Co., Ltd., which is 100 mm long x 150 mm wide x 25 mm thick. The pattern shape in FIG. 1 is a pattern in which 30 (3 × 10) copper pads of 2000 μm × 2000 μm are arranged at 4 mm intervals, and the center of the copper pad is connected with a line width of 150 μm. Next, similar to the preparation procedure of the tensile test sample of Example 1 described above, the curable resin composition of Comparative Example 1 was printed and cured on the obtained flexible substrate by screen printing so that the film thickness was 35 μm, to obtain a crack evaluation sample. In addition, in the exposure process using the metal halide lamp described above in 2), a negative pattern of 2100 μm × 2100 μm was used for exposure and development so that the copper pads on the flexible substrate were completely exposed, and a curable resin composition layer with exposed copper pads as shown in FIG. 2B was formed, and then cured to produce a cured coating film.

(Preparation of samples for evaluating cracks in cured products of curable resin compositions of Comparative Examples 2 and 3)
Except for replacing the components with those shown in Table 1, the same procedure was followed as in the preparation of the sample for crack evaluation of the cured product of the curable resin composition of Comparative Example 1 described above, to obtain samples for crack evaluation of the cured products of the curable resin compositions of Comparative Examples 2 and 3.

(Preparation of Samples for Evaluating Resolution of Cured Products of Curable Resin Compositions of Examples 1 to 3 and Comparative Examples 1 to 3)
For the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3, samples for evaluating resolution were prepared according to the following procedure.
First, the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were printed by screen printing on a 100 mm long x 150 mm wide x 1.6 mm thick FR-4 substrate with copper foil attached, so that the film thickness was 35 μm. Then, after drying for 30 minutes at 80 ° C. in a hot air circulation drying oven, a negative capable of forming a pattern with an opening diameter of 80 μm was used, and an exposure device equipped with a metal halide lamp was used to UV expose the negative with an integrated exposure dose of 100 mJ / cm ^2. Then, using a 1% aqueous sodium carbonate solution as a developer, the developed product was developed for 90 seconds at 30 ° C. in a developer for printed wiring boards, and thermally cured for 60 minutes at 150 ° C. in a hot air circulation drying oven to obtain a sample for evaluating resolution.

[Measurement of tensile elongation at break and tensile strength]
The tensile elongation at break of the cured products of the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3 obtained by the above-mentioned procedure for preparing samples for tensile testing was measured according to the following procedure in accordance with the test method for plastics - tensile properties of JIS K 7127:1999. In order to measure stable tensile properties from low temperature to high temperature ranges, RSA-G2 manufactured by TA Instruments was used. Specifically, first, the cured products of the curable resin compositions were cut into test pieces of width 3 mm x length 40 mm x thickness 35 μm. The obtained test pieces were subjected to tensile tests at temperatures of 20°C, 85°C, and 240°C, with a gripping distance of 10 mm and a pulling speed of 0.002 mm/s (0.12 mm/min). As for the tensile elongation at break, the maximum elongation (at break) that the tensile test sample could withstand when pulled was measured, and the tensile elongation at break (%) was calculated by the following formula. The tensile strength was measured as the maximum stress that the tensile test sample could withstand when pulled (the stress at break). The results of the tensile elongation at break (%) and the tensile strength are shown in Table 1.

[Measurement of Elastic Modulus]
The elastic modulus of the cured products of the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3 obtained by the above-mentioned procedure for preparing samples for tensile tests was calculated in accordance with JIS K 7161-1:2014, Method for Determining Tensile Properties of Plastics. The elastic modulus was calculated from the following formula using the stress values at two points of strain of 0.05% and 0.025% in the stress and strain measurement data at each temperature obtained by the above-mentioned tensile measurement. The results are shown in Table 1.

[Evaluation of cracks by laser irradiation]
The cured products of the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3 obtained by the above-mentioned procedure for preparing the crack evaluation samples were evaluated for cracks caused by laser irradiation according to the following procedure. Specifically, first, the crack evaluation samples of Examples 1 to 3 and Comparative Examples 1 to 3 were cut into the shape shown in FIG. 3 (length 650 mm x width 200 mm) by a laser processing machine. The cutting of each crack evaluation sample was performed using a laser with a wavelength of 1064 nm and a laser diameter of 50 μm. Next, the cured coating film at the cut portion was observed from above the coating film at a measurement magnification of 100 times or 200 times using a digital microscope (VHX-6000, Keyence Corporation), and the cracks caused by laser irradiation were evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.
◎: No cracks were observed (when observed at a measurement magnification of 200 times)
○: No cracks were observed (when observed at a measurement magnification of 100 times)
×: Cracks were observed (when observed at a measurement magnification of 100 times)

[Evaluation of cracks during electronic component mounting]
The cracks during electronic component mounting were evaluated for the cured products of the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3 obtained by the above-mentioned procedure for preparing the crack evaluation samples, according to the following procedure. First, a solder paste (M705-ULT369 manufactured by Senju Metal Industry Co., Ltd.) was applied by screen printing to the copper pads of 180 μm×180 μm of each of the crack evaluation samples of Examples 1 to 3 and Comparative Examples 1 to 3. Next, each crack evaluation sample was placed on a transport jig, and solder reflow was performed three times using a reflow oven (NIS-20-82C, manufactured by Atec Techtron Co., Ltd.) according to a temperature profile conforming to IPC/JEDEC J-STD-020. Each crack evaluation sample was returned to room temperature after each solder reflow.
●Reflow conditions ・Atmosphere: In air ・Conveyor speed: 0.9 m/min ・Preheating: 150-200°C within 180 seconds ・Main heating: 255°C or higher within 30 seconds ・Peak temperature: 260°C within 10 seconds ・Cooling

After three reflows, the corners of the curable resin composition at the openings of the copper pads to which the solder had adhered were observed at a measurement magnification of 100x or 200x using a digital microscope (VHX-6000, Keyence Corporation), and the cracks occurring during mounting of the electronic components were evaluated according to the following criteria. The evaluation results are shown in Table 1.
◎: No cracks were observed (when observed at a measurement magnification of 200 times)
○: No cracks were observed (when observed at a measurement magnification of 100 times)
×: Cracks were observed (when observed at a measurement magnification of 100 times)

[Evaluation of Resolution]
The undercut shape of the openings of the cured products of the curable resin compositions of Examples 1 to 3 and Comparative Examples 1 to 3 obtained by the above-mentioned procedure for preparing samples for evaluating resolution was evaluated. Specifically, the shapes of the openings of the evaluation samples of Examples 1 to 3 and Comparative Examples 1 to 3 were observed at an oblique angle of 45° at a magnification of 1000 times using a scanning electron microscope (JSM-6610LV, manufactured by JEOL), and the resolution was evaluated according to the following criteria. The evaluation results are shown in Table 1.
◎: A slight hem shape is observed at the bottom. ○: The bottom is observed. ×: The bottom is not observed.

From the evaluation results shown in Table 1, it can be seen that the curable resin compositions of Examples 1 to 3, which contain a carboxyl group-containing resin, a thermosetting component, and a photopolymerization initiator, and in which the tensile elongation at break of the cured product at 20°C, 85°C, and 240°C satisfy a specific relationship with each other, can form a highly reliable cured product in which the occurrence of cracks due to changes in shape caused by temperature and stress is suppressed. In particular, Example 2, in which the ratio of the epoxy equivalent of the epoxy resin having a bisphenol skeleton to the epoxy equivalent of the biphenyl type epoxy resin is in the range of 1:0.75 to 1:0.95, was evaluated as "◎" for both the occurrence of cracks due to laser irradiation and the occurrence of cracks during electronic component mounting. In other words, when the ratio of the epoxy equivalent of the epoxy resin having a bisphenol skeleton to the epoxy equivalent of the biphenyl type epoxy resin is in the specific numerical range as described above, it can be seen that a highly reliable cured product can be formed in which the occurrence of cracks due to changes in shape caused by temperature and stress is particularly suppressed. On the other hand, in the curable resin compositions of Comparative Examples 1 to 3, in which the tensile elongation at break of the cured product at 20°C, 85°C, and 240°C does not satisfy a specific relationship, the occurrence of cracks due to changes in shape caused by temperature and stress is not sufficiently suppressed, and a highly reliable cured product cannot be formed. It is also found that the cured products of each of the curable resin compositions of Examples 1 to 3 all exhibit high resolution. On the other hand, it is found that the cured products of each of the curable resin compositions of Comparative Examples 1 and 3 do not exhibit sufficient resolution.

Claims (10)

A curable resin composition comprising a carboxyl group-containing resin, a thermosetting component, and a photopolymerization initiator,
The tensile elongation at break of the cured product of the curable resin composition at 20° C. is A%,
The tensile elongation at break of the cured product of the curable resin composition at 85° C. is B%, and the tensile elongation at break of the cured product of the curable resin composition at 240° C. is C%.
In this case, the following formulas 1 to 3 are satisfied:
2A<B (Equation 1)
2A < C (Equation 2)
4 < C < 6 (Equation 3)
A curable resin composition, characterized in that all of the above is satisfied. The curable resin composition according to claim 1, wherein the carboxyl group-containing resin includes a resin having a bisphenol skeleton. The curable resin composition according to claim 1, wherein the carboxyl group-containing resin further contains a copolymer resin. The curable resin composition according to claim 3, wherein the copolymer resin does not have a novolac skeleton or an aromatic ring. The curable resin composition according to claim 1, wherein the thermosetting component includes an epoxy resin having a bisphenol skeleton and a biphenyl-type epoxy resin. The curable resin composition according to claim 5, wherein the ratio of the epoxy equivalent of the epoxy resin having a bisphenol skeleton to the epoxy equivalent of the biphenyl-type epoxy resin in the thermosetting component is 1:0.5 to 1:5, and the ratio of the total carboxylic acid equivalent of the carboxyl group-containing resin to the total epoxy equivalent of the epoxy resin having a bisphenol skeleton and the biphenyl-type epoxy resin in the thermosetting component is 1:1.2 to 1:5. A method for producing a cured product of the curable resin composition according to claim 1, comprising the steps of exposing the curable resin composition to light and then thermally curing the composition. The method according to claim 7, further comprising a step of irradiating the curable resin composition with UV light after the curable resin composition is exposed to light and before the curing is performed by heat. A method for manufacturing a printed wiring board having a solder resist, comprising the steps of exposing the curable resin composition according to claim 1 to light and then thermally curing the composition to form the solder resist. The method according to claim 9, further comprising a step of irradiating the curable resin composition with UV light after the curable resin composition is exposed to light and before the curing is performed by heat.