Curable resin composition, cured object, printed wiring board, and method for producing printed wiring board

Abstract

To provide a curable resin composition capable of forming solder resists which combine long-lasting low glossiness and resultant long-term freedom from solder adhesion with withstand voltage on a high level.SOLUTION: A curable resin composition comprising a curable resin, barium sulfate, and a heat-curing catalyst, the barium sulfate having an oil absorption of 40-70 mL / 100 g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a curable resin composition, particularly to a curable resin composition suitable for use in forming a solder resist. The present invention also relates to a printed wiring board using the curable resin composition and a method for producing the same. [Background technology]

[0002] Adhesion of solder to solder resist that occurs during the flow soldering process in the manufacture of printed wiring boards can cause defects such as solder bridges (solder shorts), which can ultimately lead to defects in the printed wiring board. In recent years, with the advancement of finer wiring patterns on printed wiring boards, such solder bridges have become particularly likely to occur, and are considered to be one of the factors that hinder the efficient manufacture of printed wiring boards.

[0003] It has been known that making the surface of a solder resist matte (low gloss) can prevent solder from adhering to the solder resist. One method for making the surface of a solder resist matte has been to incorporate a component called a matting agent as a filler into a resin composition for forming the solder resist. For example, Patent Document 1 proposes forming a solder resist with a matte surface using a resin composition containing finely divided aluminum silicate as a filler, which has a matting effect. Other known matting agents include ultrafine anhydrous silica, talc, large-particle fused silica, clay, and aluminum hydroxide.

[0004] Meanwhile, with the growing trend toward carbon neutrality in recent years, the electrification of social infrastructure and daily necessities has progressed, and there is a growing need for electrically powering large machines such as automobiles. Many of these social infrastructures and daily necessities require operation in harsh environments and the passage of high voltages and large currents. Therefore, components for operating these machines, such as printed wiring boards, and ultimately the solder resists that make up printed wiring boards, are required to meet these needs. For example, Patent Document 2 proposes an electrically insulating resin composition that can form a solder resist that has excellent heat resistance and moisture resistance, higher voltage resistance (breakdown voltage) than conventional products, and can be used stably for long periods of time even in harsh environments. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-157574 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-314554 Summary of the Invention [Problem to be solved by the invention]

[0006] However, it has been difficult to achieve a high level of both low gloss over time and the resulting solder adhesion resistance over time, as well as high voltage resistance (dielectric breakdown voltage) in a solder resist. Therefore, a technical challenge exists to provide a solder resist that achieves a high level of both low gloss over time and the resulting solder adhesion resistance over time, as well as high voltage resistance, and a resin composition for forming such a solder resist.

[0007] Furthermore, since it is expected that printed wiring boards will be required to carry higher voltages and currents in the future than at present, it is also a technical challenge to provide a solder resist having voltage resistance at least as high as that of current printed wiring boards, and a resin composition for forming such a solder resist.

[0008] Therefore, an object of the present invention is to provide a curable resin composition capable of forming a solder resist that maintains low gloss over time and thereby achieves high levels of solder adhesion resistance and voltage resistance, which have been difficult to achieve together in the past, a cured product thereof, and a printed wiring board comprising the cured product. Another object of the present invention is to provide a method for producing a printed wiring board comprising a solder resist that maintains low gloss over time and thereby achieves high levels of solder adhesion resistance and voltage resistance, using the curable resin composition. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have discovered that the above-mentioned problems can be solved by adjusting the oil absorption of barium sulfate to 40 to 70 mL / 100 g in a curable resin composition containing a curable resin, barium sulfate, and a thermosetting catalyst. The present invention is based on this discovery. Specifically, the gist of the present invention is as follows.

[0010] [1] A curable resin composition comprising a curable resin, barium sulfate, and a thermosetting catalyst, A curable resin composition, wherein the barium sulfate has an oil absorption of 40 to 70 mL / 100 g. [2] The curable resin composition according to [1], wherein the barium sulfate comprises barium sulfate surface-treated with silica. [3] The curable resin composition according to [1] or [2], wherein the curable resin comprises one or more thermosetting resins selected from the group consisting of epoxy compounds, polyfunctional oxetane compounds, and oxazoline compounds. [4] The curable resin composition according to any one of [1] to [3], wherein the curable resin comprises a carboxyl group-containing photosensitive resin having one or more ethylenically unsaturated groups in one molecule. [5] The curable resin composition according to [4], further comprising a photopolymerization initiator. [6] The curable resin composition according to any one of [1] to [5], which is used for forming a solder resist. [7] The curable resin composition according to [6], wherein the solder resist is a matte solder resist. [8] A cured product of the curable resin composition according to any one of [1] to [7]. [9] A printed wiring board comprising the cured product according to [8].

[10] A method for producing a printed wiring board provided with a solder resist, the method comprising a step of forming a solder resist by curing the curable resin composition according to any one of [1] to [7]. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a curable resin composition capable of forming a solder resist that maintains low gloss over time and thereby achieves high levels of both solder adhesion resistance and voltage resistance over time, a cured product thereof, and a printed wiring board including the cured product.Furthermore, it is possible to provide a method for producing a printed wiring board including a solder resist that maintains low gloss over time, solder adhesion resistance, and voltage resistance over time at high levels using the curable resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Curable resin composition] The curable resin composition of the present invention contains a curable resin, barium sulfate, and a thermosetting catalyst as essential components. The curable resin composition of the present invention can be suitably used to form a solder resist during the manufacture of printed wiring boards, particularly a matte solder resist for printed wiring boards that require high voltage and large current conduction. The curable resin composition of the present invention contains barium sulfate having an oil absorption of 40 to 70 mL / 100 g, which allows the solder resist, which is a cured product of the curable resin composition, to maintain low gloss over time and thereby impart high levels of solder adhesion resistance and voltage resistance over time.

[0013] The reason why it has been difficult to maintain a low gloss level over time in a solder resist and thereby achieve high levels of both solder adhesion resistance and voltage resistance over time is presumed to be as follows. Specifically, to achieve a matte (low gloss) solder resist, a typical method involves blending a component called a matting agent as a filler into the resin composition used to form the solder resist. When silica or other commonly used matting agents are used, air bubbles adhere to the particles, resulting in the presence of air bubbles in the resin composition. As a result, air bubbles remain in the solder resist formed by curing the resin composition. Air bubbles adhered to silica or other such agents are difficult to separate and remove. For example, even when a large amount of an antifoaming agent is blended into the resin composition, a large number of air bubbles remain in the resin composition. Similarly, when hydrophilic fillers such as aluminum hydroxide and aluminum silicate, commonly used matting agents, are used, air bubbles adhere to the particles, resulting in a large number of air bubbles remaining in the solder resist. The presence of air bubbles in a solder resist significantly impairs the voltage resistance of the solder resist, and therefore it is thought that when conventional matting agents are used, it is not possible to achieve a high level of both a matte finish (low gloss) in the solder resist and the resulting solder adhesion resistance, as well as voltage resistance.

[0014] On the other hand, in the curable resin composition of the present invention, by using barium sulfate with a specific oil absorption as a matting agent, adhesion of bubbles to the barium sulfate matting agent is suppressed, and the remaining bubbles in the solder resist formed by curing the curable resin composition are suppressed. As a result, it is believed that the solder resist can be maintained at a low gloss level over time, and thereby be endowed with high levels of solder adhesion resistance and voltage resistance over time.

[0015] The curable resin composition of the present invention preferably has a 60° gloss of 20 or less, more preferably 15 or less, and even more preferably 10 or less when cured and formed into a 25 μm thick cured product (cured coating film) immediately after preparation. Furthermore, the curable resin composition of the present invention can form a cured product that maintains a low gloss comparable to that of the curable resin composition immediately after preparation, even after storage at 30°C for 6 months after preparation. That is, the curable resin composition of the present invention preferably has a 60° gloss of 20 or less, more preferably 15 or less, and even more preferably 10 or less when cured and formed into a 25 μm thick cured product (cured coating film) after storage at 30°C for 6 months after preparation. The gloss of the cured product of the curable resin composition can be measured as a 60° specular reflectance using a Micro Trigloss glossmeter manufactured by BYK-Chemie, for a cured product (cured coating film) of the curable resin composition formed by applying the curable resin composition to the entire surface of a 1.6 mm thick copper FR-4 substrate by screen printing so that the film thickness after curing is 25 μm, and then heating the composition at 150°C for 30 minutes in a hot air circulation drying oven.

[0016] The curable resin composition of the present invention has a withstand voltage value of a 50 μm-thick cured product (cured coating film) of preferably 5 kV (5 kV / 0.05 mm) or more, more preferably 5.5 kV (5.5 kV / 0.05 mm) or more, and even more preferably 6 kV (6 kV / 0.05 mm) or more. The withstand voltage value of the curable resin composition can be measured on a substrate having a 50 μm-thick cured product (cured coating film) using a withstand voltage tester TOS5101 manufactured by Kikusui Electronics Co., Ltd., by increasing the voltage at 0.5 kV / second in AC mode with electrodes of 10 mm diameter, and the voltage value is the voltage value at which the cured product breaks down.

[0017] Each component of the curable resin composition of the present invention will be described in detail below. (curable resin) The curable resin composition of the present invention contains a curable resin. The curable resin is not particularly limited as long as it is a resin that is cured by the action of heat, light, or the like. Specifically, the curable resin may be a thermosetting resin, a photocurable resin, or the like. One type of curable resin may be used alone, or two or more types may be used in combination. For example, a thermosetting resin or a photocurable resin may be used alone, or these may be used in combination.

[0018] The curable resin composition of the present invention can contain a thermosetting resin as the curable resin. Adding a thermosetting resin is expected to improve the heat resistance of the curable resin composition. The thermosetting resin may be used alone or in combination of two or more. Any known thermosetting resin can be used. Examples of known thermosetting resins that can be used include amino resins such as melamine resins, benzoguanamine resins, melamine derivatives, and benzoguanamine derivatives, isocyanate compounds, blocked isocyanate compounds, cyclocarbonate compounds, epoxy compounds, oxetane compounds, oxazoline compounds, episulfide resins, bismaleimides, and carbodiimide resins. Each of these thermosetting resins may be monofunctional or polyfunctional. Among these thermosetting resins, a thermosetting resin having a cyclic ether group or a cyclic thioether group in the molecule is preferably used. Examples of such thermosetting resins include epoxy compounds having an epoxy group in the molecule, oxetane compounds having an oxetanyl group in the molecule, oxazoline compounds having an oxazoline group in the molecule, and episulfide resins having a thioether group in the molecule. The thermosetting resin preferably contains one or more compounds selected from the group consisting of epoxy compounds, polyfunctional oxetane compounds, and oxazoline compounds, and particularly preferably contains an epoxy compound. By incorporating these compounds as the thermosetting resin in the curable resin composition, it is possible to impart particularly excellent heat resistance, chemical resistance, and adhesion to the curable resin composition.

[0019] Epoxy compounds include epoxidized vegetable oils, bisphenol A epoxy resins, hydroquinone epoxy resins, bisphenol epoxy resins, thioether epoxy resins, brominated epoxy resins, novolac epoxy resins, phenol novolac epoxy resins, biphenol novolac epoxy resins, bisphenol F epoxy resins, hydrogenated bisphenol A epoxy resins, glycidylamine epoxy resins, hydantoin epoxy resins, alicyclic epoxy resins, trihydroxyphenylmethane epoxy resins, bixylenol or biphenol epoxy resins, and Examples of epoxy resins include, but are not limited to, bisphenol S epoxy resins, bisphenol A novolac epoxy resins, tetraphenylolethane epoxy resins, heterocyclic epoxy resins, diglycidyl phthalate resins, tetraglycidyl xylenoylethane resins, naphthalene group-containing epoxy resins, epoxy resins having a dicyclopentadiene skeleton, glycidyl methacrylate copolymer epoxy resins, cyclohexylmaleimide and glycidyl methacrylate copolymer epoxy resins, epoxy-modified polybutadiene rubber derivatives, and CTBN-modified epoxy resins. These epoxy resins may be used alone or in combination of two or more.

[0020] As the oxetane compound, a polyfunctional oxetane compound having two or more oxetanyl groups in one molecule is preferably used. Examples of the polyfunctional oxetane compound include bis[(3-methyl-3-oxetanylmethoxy)methyl]ether, bis[(3-ethyl-3-oxetanylmethoxy)methyl]ether, 1,4-bis[(3-methyl-3-oxetanylmethoxy)methyl]benzene, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, (3-methyl-3-oxetanyl)methyl acrylate, (3-ethyl-3-oxetanyl)methyl acrylate, and the like. Examples of suitable oxetane compounds include polyfunctional oxetanes such as acrylate, (3-methyl-3-oxetanyl)methyl methacrylate, (3-ethyl-3-oxetanyl)methyl methacrylate, and their oligomers or copolymers, as well as ethers of oxetane alcohols with novolak resins, poly(p-hydroxystyrene), cardo-type bisphenols, calixarenes, calixresorcinarenes, or hydroxyl group-containing resins such as silsesquioxane. Other examples include copolymers of unsaturated monomers having an oxetane ring and alkyl (meth)acrylates.

[0021] Examples of oxazoline compounds include compounds having two or more oxazoline groups in one molecule. Examples of such oxazoline compounds include oxazoline group-containing polymers such as polymers of oxazoline group-containing monomers and copolymers of oxazoline group-containing monomers with other monomers. Examples of oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2-isopropenyl-2-oxazoline, and 2-isopropenyl-4,4-dimethyl-2-oxazoline.

[0022] The episulfide resin may be, for example, a compound in which an oxygen atom constituting an epoxy group in any epoxy compound is substituted with a sulfur atom. Examples of the epoxy compound include the same compounds as those described above. In addition, a conventionally known method can be used to substitute an oxygen atom constituting an epoxy group in an epoxy compound with a sulfur atom.

[0023] Examples of amino resins such as melamine derivatives and benzoguanamine derivatives include methylolmelamine compounds, methylolbenzoguanamine compounds, methylolglycoluril compounds, and methylolurea compounds.

[0024] The isocyanate compound may be a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, naphthalene-1,5-diisocyanate, o-xylylene diisocyanate, m-xylylene diisocyanate, and 2,4-tolylene dimer; aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, trimethylhexamethylene diisocyanate, 4,4-methylenebis(cyclohexyl isocyanate), and isophorone diisocyanate; alicyclic polyisocyanates such as bicycloheptane triisocyanate; and adducts, biuret compounds, and isocyanurates of the above-mentioned isocyanate compounds.

[0025] The blocked isocyanate compound can be an addition reaction product of an isocyanate compound and an isocyanate blocking agent. Examples of isocyanate compounds that can react with an isocyanate blocking agent include the polyisocyanate compounds described above. Examples of the isocyanate blocking agent include phenol-based blocking agents, lactam-based blocking agents, active methylene-based blocking agents, alcohol-based blocking agents, oxime-based blocking agents, mercaptan-based blocking agents, acid amide-based blocking agents, imide-based blocking agents, amine-based blocking agents, imidazole-based blocking agents, and imine-based blocking agents.

[0026] The amount of the thermosetting resin in the curable resin composition is not particularly limited as long as the effects of the present invention are achieved, and can be, for example, 3 to 50 mass % in terms of solid content relative to the total mass of the curable resin composition.

[0027] The curable resin composition of the present invention can contain a photocurable resin as the curable resin. Known and commonly used photocurable resins can be used as the photocurable resin. Among them, from the viewpoints of photocurability and development resistance, a photocurable resin that can be cured by a radical addition polymerization reaction with active energy rays is preferably used, and a photocurable resin having an ethylenically unsaturated group in the molecule is more preferably used. The ethylenically unsaturated group is preferably derived from acrylic acid, methacrylic acid, or a derivative thereof. One type of photocurable resin may be used alone, or two or more types may be used in combination. A carboxyl group-containing photosensitive resin, which will be described later, is preferably used as the photocurable resin.

[0028] Examples of photocurable resins having an ethylenically unsaturated group in the molecule include well-known and commonly used photopolymerizable oligomers and photopolymerizable monomers. Examples of photopolymerizable oligomers include unsaturated polyester oligomers and (meth)acrylate oligomers. Examples of (meth)acrylate oligomers include epoxy (meth)acrylates such as phenol novolac epoxy (meth)acrylate, cresol novolac epoxy (meth)acrylate, and bisphenol-type epoxy (meth)acrylate, as well as urethane (meth)acrylate, epoxy urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and polybutadiene-modified (meth)acrylate.

[0029] On the other hand, as the photopolymerizable monomer, a monomer having an ethylenically unsaturated group is preferably used, such as commonly known polyester (meth)acrylate, polyether (meth)acrylate, urethane (meth)acrylate, carbonate (meth)acrylate, epoxy (meth)acrylate, etc. Specific examples 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; and hexanediol, trimethylolpropane, pentaerythritol, ditrimethylolpropane, dipentaerythritol, and trishydroxyethyl isocyanurate. Polyhydric acrylates 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; glycidyl ether acrylates such as glycerin diglycidyl ether, trimethylolpropane triglycidyl ether, and triglycidyl isocyanurate; and acrylates and melamine acrylates obtained by directly or via diisocyanate urethane acrylate of polyols such as polyether polyols, polycarbonate diols, hydroxyl-terminated polybutadienes, and polyester polyols, as well as methacrylates corresponding to the above acrylates, can be appropriately selected and used. The photopolymerizable monomers can be used singly or in combination of two or more. Furthermore, the photopolymerizable monomers can also be used as reactive diluents.The term "photopolymerizable monomer" refers to a compound that is a monomer among photocurable resins.

[0030] The amount of the photocurable resin in the curable resin composition is not particularly limited as long as the effects of the present invention are achieved, and can be, for example, 10 to 50 mass % in terms of solid content relative to the total mass of the curable resin composition.

[0031] The curable resin may preferably contain a carboxyl group-containing resin in order to impart alkaline developability to the curable resin composition. As the carboxyl group-containing resin, various conventionally known resins having a carboxyl group in the molecule may be used. Specific examples of the carboxyl group-containing resin include the following compounds (which may be either oligomers or polymers):

[0032] (1) Carboxyl group-containing resins obtained by copolymerizing unsaturated carboxylic acids such as (meth)acrylic acid with unsaturated group-containing compounds such as styrene, α-methylstyrene, lower alkyl (meth)acrylates, and isobutylene.

[0033] (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.

[0034] (3) Carboxylic acid group-containing photosensitive urethane resins obtained by the 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 groups such as (meth)acrylic acid, partially acid anhydride-modified products thereof, carboxyl group-containing dialcohol compounds, and diol compounds.

[0035] (4) A carboxyl group-containing photosensitive urethane resin that is (meth)acrylated at the terminal 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).

[0036] (5) A carboxyl group-containing photosensitive urethane resin that has been (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 reaction product of isophorone diisocyanate and pentaerythritol triacrylate, during the synthesis of the resin (2) or (3).

[0037] (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 group present in the side chain.

[0038] (7) A carboxyl group-containing photosensitive resin in which the hydroxyl groups of a bifunctional (solid) epoxy resin are further epoxidized with epichlorohydrin to form a multifunctional epoxy resin, which is then reacted with (meth)acrylic acid, and a dibasic acid anhydride is added to the resulting hydroxyl groups.

[0039] (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.

[0040] (9) A carboxyl group-containing photosensitive resin obtained by reacting an epoxy compound having multiple epoxy groups in one molecule with a compound having at least one alcoholic hydroxyl group and one phenolic hydroxyl group in one molecule, such as p-hydroxyphenethyl alcohol, and an unsaturated group-containing monocarboxylic acid, such as (meth)acrylic acid, and then reacting the alcoholic hydroxyl groups of the resulting reaction product with a polybasic acid anhydride, such as maleic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, or adipic acid.

[0041] (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 resulting reaction product with an unsaturated group-containing monocarboxylic acid, and then reacting the resulting reaction product with a polybasic acid anhydride.

[0042] (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 resulting reaction product with an unsaturated group-containing monocarboxylic acid, and then reacting the resulting reaction product with a polybasic acid anhydride.

[0043] (12) A carboxyl group-containing photosensitive resin obtained by further adding a compound having one epoxy group and one or more (meth)acryloyl groups in one molecule to the resins (1) to (11). In this specification, (meth)acrylate is a general term for acrylate, methacrylate and mixtures thereof, and the same applies to other similar expressions.

[0044] Furthermore, as the photosensitive resin, a resin synthesized according to the procedure described in the examples below can also be used.

[0045] The acid value of the carboxyl group-containing resin is suitably in the range of 30 to 150 mgKOH / g, more preferably 50 to 120 mgKOH / g. If the acid value of the carboxyl group-containing resin is 30 mgKOH / g or more, alkaline development can be carried out appropriately, while if it is 150 mgKOH / g or less, dissolution of the exposed area by the developer does not proceed, so that the exposed area and the unexposed area can be dissolved and peeled separately by the developer, facilitating drawing of a normal resist pattern, which is preferable.

[0046] The weight-average molecular weight of the carboxyl group-containing resin varies depending on the resin skeleton, but is generally in the range of 2,000 to 150,000, and preferably 5,000 to 100,000. A weight-average molecular weight of 2,000 or more provides good moisture resistance to the coating film after exposure, prevents film loss during development, and facilitates the achievement of excellent resolution. On the other hand, a weight-average molecular weight of 150,000 or less facilitates the achievement of good developability and good storage stability. The weight-average molecular weight can be measured by gel permeation chromatography (GPC).

[0047] (barium sulfate) The curable resin composition of the present invention contains barium sulfate having an oil absorption of 40 to 70 mL / 100 g. By containing barium sulfate having such a relatively high oil absorption, the curable resin composition can be made into a solder resist that is a cured product of the curable resin composition, and can thereby be imparted with high levels of solder adhesion resistance and voltage resistance over time.

[0048] The oil absorption of barium sulfate is preferably 45 to 70 mL / 100 g, more preferably 45 to 65 mL / 100 g, and even more preferably 50 to 60 mL / 100 g. The oil absorption of barium sulfate can be measured in accordance with the method specified by Japanese Industrial Standards (JIS K5101-13-1).

[0049] The barium sulfate may be untreated or may be chemically and / or physically treated. Examples of such treated barium sulfate include surface-treated barium sulfate. Examples of materials for surface-treating barium sulfate include inorganic materials such as silica and alumina. It is particularly preferable to use barium sulfate that has been surface-treated with silica by multi-treatment (also referred to as "multi-treatment processing"). Multi-treatment refers to a process in which a surface-treating material (e.g., silica, alumina, etc.) is attached to the surface of the barium sulfate to be surface-treated so that it is present in a very thick layer. Commercially available barium sulfate that has been surface-treated with silica is, for example, PFS-701 manufactured by Ishihara Sangyo Kaisha, Ltd.

[0050] Barium sulfate, particularly barium sulfate surface-treated with silica, has superior matting performance compared to conventional matting agents, and a high matting effect can be achieved by incorporating a small amount of silica-surface-treated barium sulfate into a curable resin composition. This suppresses the problem of air bubbles being introduced into the curable resin composition, which can be a problem when incorporating a matting agent, and the persistence of air bubbles in the solder resist formed by curing the curable resin composition, thereby suppressing a decrease in the voltage resistance of the solder resist. Furthermore, since the viscosity of a resin composition generally increases when a matting agent is incorporated into the resin composition, the use of barium sulfate, particularly barium sulfate surface-treated with silica, which can achieve a high matting effect with a small amount of incorporation, suppresses the increase in viscosity of the curable resin composition, thereby suppressing a decrease in the printability of the curable resin composition on a substrate. Furthermore, barium sulfate, particularly barium sulfate surface-treated with silica, has high acid resistance (acid resistance). Therefore, by blending barium sulfate as a matting agent in a curable resin composition, the curable resin composition has high acid resistance, and as a result, has high resistance (tin plating resistance) to tin plating or the like that is carried out under strong acidic conditions.

[0051] In the curable resin composition, the amount of barium sulfate having an oil absorption of 40 to 70 mL / 100 g is not particularly limited as long as the effects of the present invention are achieved, and is, for example, preferably 30 to 74 mass%, more preferably 40 to 70 mass%, and even more preferably 45 to 67 mass%, calculated as solid content, relative to the total mass of the curable resin composition.

[0052] (Thermosetting catalyst) The curable resin composition of the present invention contains a thermosetting catalyst, such as imidazole derivatives such as imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 2-phenyl-4,5-dihydroxymethylimidazole; 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. Commercially available catalysts include, for example, 2MZ-A, 2MZ-OK, 2PHZ, 2PHZ-PW, 2P4BHZ, and 2P4MHZ (all trade names of imidazole-based compounds) manufactured by Shikoku Chemical Industry Co., Ltd., and U-CAT 3513N (trade name of a dimethylamine-based compound), DBU, DBN, and U-CAT SA 102 (all bicyclic amidine compounds and salts thereof) manufactured by San-Apro Co., Ltd. However, the catalyst is not particularly limited to these, and any catalyst that promotes the reaction of a heat curing catalyst for an epoxy resin or an oxetane compound, or at least one of an epoxy group and an oxetanyl group with a carboxyl group may be used, and they may be used alone or in combination of two or more. 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 these compounds that also function as adhesion promoters are preferably used in combination with a heat curing catalyst.The heat curing catalyst may be used alone or in combination of two or more.

[0053] The amount of the thermosetting catalyst to be added is preferably 2 to 30 parts by mass, more preferably 5 to 25 parts by mass, based on 100 parts by mass of the thermosetting resin.

[0054] (Photopolymerization initiator) When the curable resin composition of the present invention contains a photosensitive resin, the curable resin composition preferably contains a photopolymerization initiator. Any known photopolymerization initiator can be used. The photopolymerization initiator may be used alone or in combination of two or more.

[0055] Specific 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 acylphosphine 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-trimethylbenzoylphenylphosphinic acid methyl ester, 2-methylbenzoyldiphenylphosphine oxide, pivaloyl monoacylphosphine oxides such as phenylphosphinic acid isopropyl ester and 2,4,6-trimethylbenzoyldiphenylphosphine oxide; 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}-2-methyl-propan-1-one hydroxyacetophenones 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-butanone, N,N-dimethylamino acetophenones such as cetophenone; thioxanthones such as thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone; anthraquinones such as anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone, and 2-aminoanthraquinone; acetophenone di Ketals such as methyl ketal and benzyl dimethyl ketal; benzoic acid esters such as ethyl-4-dimethylaminobenzoate, 2-(dimethylamino)ethyl benzoate, and p-dimethylbenzoic acid ethyl ester; oxime esters such as 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime); bis(η5-2,4-cyclopentadien-1-yl)-bis( Examples of suitable compounds include titanocenes such as 2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium and bis(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(1-pyrrol-1-yl)ethyl)phenyl]titanium; alkylphenones such as 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholinophenyl)-butan-1-one; phenyl disulfide 2-nitrofluorene, butyroin, anisoin ethyl ether, azobisisobutyronitrile, and tetramethylthiuram disulfide.

[0056] A photoinitiator aid or sensitizer may be used in combination with the above-described photopolymerization initiator. Examples of the photoinitiator aid or sensitizer include benzoin compounds, anthraquinone compounds, thioxanthone compounds, ketal compounds, benzophenone compounds, tertiary amine compounds, and xanthone compounds. Thioxanthone compounds such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone are particularly preferred. The inclusion of a thioxanthone compound can improve deep curing properties. While these compounds may be used as photopolymerization initiators, they are preferably used in combination with a photopolymerization initiator. The photoinitiator aid or sensitizer may be used alone or in combination of two or more.

[0057] These photopolymerization initiators, photoinitiator assistants, and sensitizers absorb specific wavelengths, which can reduce sensitivity in some cases and function as ultraviolet absorbers. However, they are not used solely for the purpose of improving the sensitivity of the curable resin composition. They can absorb light of specific wavelengths as needed to increase the photoreactivity of the surface, change the line shape and opening of the resist to vertical, tapered, or reverse tapered, and improve the accuracy of the line width and opening diameter.

[0058] (filler) The curable resin composition of the present invention may contain fillers other than the above-mentioned barium sulfate as needed to increase the physical strength of the coating film, as long as the effects of the present invention are not impaired. Known inorganic or organic fillers can be used as such fillers, with various silicas (e.g., finely divided silica, spherical silica, etc.), hydrotalcite, and talc being particularly preferred. Furthermore, metal oxides and metal hydroxides such as aluminum hydroxide can be used as extender pigment fillers to achieve a white appearance and flame retardancy.

[0059] (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 curable resin composition or when applying it 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. These organic solvents may be used alone or in combination of two or more.

[0060] The organic solvent can be evaporated and dried using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, etc. (a method using an oven equipped with a heat source for air heating using steam, in which hot air in the dryer is brought into countercurrent contact, or a method in which hot air is blown onto the support from a nozzle).

[0061] (Other ingredients) The curable resin composition of the present invention may further contain, as necessary, components such as colorants, elastomers, mercapto compounds, urethanization 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 antifoaming agents and leveling agents, imidazole-based, thiazole-based, and triazole-based silane coupling agents, and flame retardants such as phosphinates, phosphate ester derivatives, and phosphorus compounds such as phosphazene compounds. These may be known in the field of electronic materials.

[0062] The curable resin composition of the present invention may be used in the form of a dry film or in a liquid form. When used in a liquid form, it may be a one-component type or a two-component or more-component type.

[0063] [Cured product] The cured product of the present invention is obtained by curing the curable resin composition of the present invention described above, and maintains low gloss over time, thereby achieving high levels of solder adhesion resistance and voltage resistance over time. The cured product of the present invention is, for example, a solder resist, particularly a matte solder resist, having a thickness of 1 to 150 μm.

[0064] [Printed wiring board] The printed wiring board of the present invention has a cured product obtained from the curable resin composition of the present invention described above. In the method for producing a 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 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 (pre-dried) at a temperature of 60 to 100°C to form a tack-free resin layer.

[0065] The substrates include printed wiring boards and flexible printed wiring boards with circuits already formed using copper or the like, as well as copper-clad laminates for high-frequency circuits made from 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, 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.

[0066] 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).

[0067] After forming a resin layer on a 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., a 0.3 to 3% by mass aqueous solution of sodium carbonate) to form a pattern of a cured product. Furthermore, the cured product is irradiated with active energy rays and then heat-cured (e.g., at 100 to 220°C), or is irradiated with active energy rays after heat-curing, or is heat-cured alone to form a final finish curing (main curing), thereby forming a cured coating film with excellent properties such as adhesion and hardness.

[0068] The exposure device used for the above-mentioned active energy ray irradiation may be a device 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 device (for example, a laser direct imaging device that directly draws an image with a laser based on CAD data from a computer) may also be used. The lamp or laser light source of the direct imaging device may have a maximum wavelength in the range of 350 to 450 nm. The exposure dose for image formation varies depending on factors such as the film thickness, but is generally 10 to 1,000 mJ / cm. 2 , preferably 20 to 800 mJ / cm 2 The range may be:

[0069] The developing method may be a dipping method, a shower method, a spray method, a brush method, or the like, and the developing solution may be an aqueous alkali solution such as potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, or an amine. [Example]

[0070] 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 by mass unless otherwise specified.

[0071] [Preparation of photocurable resin solution] A photocurable resin (aromatic ring-containing carboxyl group-containing resin) solution used in this example was prepared according to the following procedure. 600 g of diethylene glycol monoethyl ether acetate was charged with 1070 g of orthocresol novolac epoxy resin (EPICLON N-695, manufactured by DIC Corporation), 360 g (5.0 mol) of acrylic acid, and 1.5 g of hydroquinone. The mixture was heated to 100 °C while stirring until homogeneous. Next, 4.3 g of triphenylphosphine was added to the resulting solution, and the mixture was heated to 110 °C for 2 hours to react. The temperature was then raised to 120 °C and the reaction continued for another 12 hours to obtain a reaction solution. 415 g of aromatic hydrocarbon (Solvesso 150, manufactured by Ando Parachemie Co., Ltd.) and 456.0 g (3.0 mol) of tetrahydrophthalic anhydride were added to the resulting reaction solution, and the reaction continued for 4 hours at 110 °C. After cooling, a photosensitive carboxyl group-containing resin solution with an aromatic ring and an acid value of 89 mg KOH / g solids and a solids content of 65% by mass was obtained.

[0072] [Preparation of Curable Resin Composition] The components shown in Table 1 below were mixed in the amounts shown in the table, pre-mixed using a mixer, and then kneaded using a three-roll mill to prepare the curable resin compositions of Examples 1 to 6 and Comparative Examples 1 to 6. Details of each component in Table 1 are as follows: Thermosetting resin: phenol novolac epoxy resin (N-770, manufactured by DIC Corporation) Photocurable resin (photosensitive resin): A carboxyl group-containing resin solution having an aromatic ring prepared by the method described above. The amount is calculated as a solid content. Photocurable resin (photopolymerizable monomer): Dipentaerythritol hexaacrylate (manufactured by Nippon Kayaku Co., Ltd.) Blue colorant: Organic colorant Phthalocyanine Blue Yellow colorant: Organic colorant Chromophthalo Yellow Antifoaming agent: Polydimethylsiloxane (KS-66, manufactured by Shin-Etsu Chemical Co., Ltd.) Photopolymerization initiator 1: bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium (Irgacure 784, manufactured by BASF Japan Ltd.) Photopolymerization initiator 2: 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholinophenyl)-butan-1-one (Omnirad 379EG, IGM Resins) Heat curing catalyst 1: 2-phenyl-4,5-dihydroxymethylimidazole (2PHZ-PW, manufactured by Shikoku Chemicals Corporation) Heat curing catalyst 2: Melamine Aluminum silicate-based matting agent: Calcined kaolin (Satenton 5HB, manufactured by BASF Japan Ltd.) Aluminum hydroxide-based matting agent: Aluminum hydroxide (Hijilite H-42, manufactured by Showa Denko K.K.) Filler anti-settling agent: organic bentonite (BENTONE® 38, manufactured by Elementis Specialities) Finely divided silica matting agent: Finely divided silica (ACEMATT (registered trademark) 82, manufactured by EVONIK) Silica-alumina surface-treated barium sulfate (BARIACE® B-30, manufactured by Sakai Chemical Industry Co., Ltd.) (oil absorption: 18 mL / 100 g) Silica surface-treated barium sulfate (highly weather-resistant matte material PFS701, manufactured by Ishihara Sangyo Kaisha, Ltd.) (oil absorption: 56 mL / 100 g) Organic solvent 1: Diethylene glycol monoethyl ether acetate (carbitol acetate) Organic solvent 2: Petroleum-based solvent (SOLVESSO150, manufactured by Ando Parachemie Co., Ltd.)

[0073] [Printability evaluation] Each of the curable resin compositions of the Examples and Comparative Examples was printed on an IPC standard B-pattern substrate using a printing machine (manufactured by Ceria Corporation) with a Tetron 100-mesh screen. After curing each curable resin composition, the appearance of the coating film (cured coating film) was visually observed, and the printability of the curable resin composition was evaluated according to the following criteria. The evaluation results are shown in Table 1. ◯: Good printability (good leveling) △: Acceptable printability (mesh patterns are visible) ×: Unacceptable printability (pinholes present, and the base is visible)

[0074] Furthermore, the curable resin compositions of the Examples and Comparative Examples were stored at 30°C for 6 months after preparation, and then similar tests were carried out to evaluate the printability over time according to the same criteria. The evaluation results are shown in Table 1.

[0075] [Preparation of Evaluation Substrates (Examples 1 and 2 and Comparative Examples 1 and 2)] Each of the curable resin compositions of Examples 1 and 2 and Comparative Examples 1 and 2 was applied to the entire surface of a 1.6 mm thick copper FR-4 substrate by screen printing so that the film thickness after curing would be 25 μm, and the substrate was heated at 150°C for 30 minutes in a hot air circulation drying oven to prepare evaluation substrates having a cured product (cured coating film) of each curable resin composition.

[0076] [Preparation of Evaluation Substrates (Examples 3 to 6 and Comparative Examples 3 to 6)] Each of the curable resin compositions of Examples 3 to 6 and Comparative Examples 3 to 6 was applied to the entire surface of a 1.6 mm thick copper FR-4 substrate by screen printing so that the dried film thickness would be 25 μm, and the substrate was dried at 80°C for 30 minutes using a hot air circulation drying oven and allowed to cool to room temperature. The substrate was then exposed to 500 mJ / cm using an exposure device equipped with a high-pressure mercury lamp (short arc lamp). 2 The film was exposed to light at a temperature of 1000 mJ / cm 2 , and then developed by spraying a 1% by mass aqueous solution of sodium carbonate at 30°C at a spray pressure of 0.2 MPa for 90 seconds. 2 After irradiating with ultraviolet light under the conditions above, the substrate was heated at 160° C. for 60 minutes using a hot air circulation drying oven to prepare a substrate for evaluation having a cured product (cured coating film) of each curable resin composition.

[0077] [Gloss evaluation] The gloss of the cured product of each curable resin composition of the Examples and Comparative Examples formed on each evaluation substrate was measured as 60° specular reflectance using a BYK-Chemie Micro Trigloss glossmeter. The gloss evaluation was performed on five evaluation substrates, and the average gloss of the five evaluation substrates was rounded to one decimal place and expressed as a number. Based on the obtained values, the gloss was evaluated according to the following criteria. The gloss values ​​and evaluation results are shown in Table 1. ⊚: The gloss level is less than 10, which is extremely low. ◯: The gloss level is 10 or more and less than 20, and is sufficiently low. ×: The gloss level is 20 or more, and the gloss level is not low.

[0078] Furthermore, the curable resin compositions of the Examples and Comparative Examples were stored at 30°C for 6 months after preparation, and the same tests were then carried out on the prepared evaluation substrates, and the glossiness over time was evaluated according to the same criteria. The glossiness over time and the evaluation results are shown in Table 1.

[0079] [Evaluation of solder adhesion resistance] Each evaluation board was subjected to solder flow in the atmosphere without application of flux using a flow soldering machine at a solder temperature of 260°C, double wave, and a conveyor speed of 1.4 m / min. The state of solder adhesion on the surface of the cured product of the curable resin composition on each evaluation board was then visually observed, and the solder adhesion resistance was evaluated according to the following criteria. The evaluation results are shown in Table 1. In this evaluation, evaluation boards were prepared in the same manner as in the preparation of the above evaluation boards, except that a copper circuit pattern board was used instead of the solid copper board, pattern printing was used instead of the full-surface screen printing in Examples 1 and 2 and Comparative Examples 1 and 2, and pattern exposure was used instead of the exposure in Examples 3 to 6 and Comparative Examples 3 to 6. ◯: No solder adhesion was observed on the surface of the cured product, and the solder adhesion resistance was good. ×: Thorny or spider web-like solder adhesion was observed, and the solder adhesion resistance was poor.

[0080] Furthermore, the curable resin compositions of the Examples and Comparative Examples were stored at 30°C for 6 months after preparation, and the same tests were then carried out on the evaluation substrates fabricated therefrom, and the solder adhesion resistance over time was evaluated according to the same criteria. The evaluation results are shown in Table 1.

[0081] [Evaluation of voltage resistance] For each evaluation substrate, a voltage was applied to a KIKUSUI Electronics Co., Ltd. TOS5101 withstand voltage tester at 0.5 kV / s in AC mode using 10 mm diameter electrodes to measure the voltage value (breakdown voltage) at which the cured product of the curable resin composition on each evaluation substrate experienced dielectric breakdown. The withstand voltage evaluation was performed on three evaluation substrates, and the average of the breakdown voltages of the three evaluation substrates was rounded to one decimal place. Evaluation was performed based on the obtained values ​​according to the following criteria. The breakdown voltage values ​​and the evaluation results of withstand voltage are shown in Table 1. The breakdown voltage (kV / 0.05 mm) values ​​in Table 1 are the breakdown voltage values ​​of each evaluation substrate having a cured coating film 25 μm (0.025 mm) thick, converted to 0.05 mm. ◯: The dielectric breakdown voltage is 5 kV / 0.05 mm or more, and the material has extremely high voltage resistance. ×: The breakdown voltage is less than 5 kV / 0.05 mm, and the voltage resistance is insufficient.

[0082] [Evaluation of acid resistance] Each evaluation substrate was tin-plated using a commercially available electroless tin plating bath under conditions of tin 1±0.2 μm. After plating, the cured product of the curable resin composition on each evaluation substrate was visually inspected, and then tape peeling was used to check for peeling of the cured product. Acid resistance was evaluated according to the following criteria. The evaluation results are shown in Table 1. In this evaluation, evaluation substrates were prepared in the same manner as in the preparation of the above evaluation substrates, except that a copper circuit pattern substrate was used instead of the solid copper substrate, pattern printing was used instead of the full-surface coating by screen printing in Examples 1 and 2 and Comparative Examples 1 and 2, and pattern exposure was used instead of the exposure in Examples 3 to 6 and Comparative Examples 3 to 6. ◯: Neither peeling nor whitening of the cured product was observed, and the cured product had sufficiently high acid resistance. ×: Peeling and whitening of the cured product were observed, and the acid resistance was insufficient.

[0083] [Table 1]

[0084] The evaluation results shown in Table 1 indicate that when the curable resin compositions of each Example were used, solder resists could be formed that maintained low gloss over time and thus achieved high levels of solder adhesion resistance and voltage resistance. Furthermore, it was also found that when the curable resin compositions of each Example were used, solder resists with high acid resistance could be formed. That is, a curable resin composition containing a curable resin, barium sulfate, and a thermosetting catalyst, in which the barium sulfate had an oil absorption of 40 to 70 mL / 100 g, was shown to be able to maintain low gloss over time and thus achieved high levels of solder adhesion resistance and voltage resistance, and to form solder resists with even higher acid resistance. On the other hand, when the curable resin compositions of each Comparative Example were used, it was shown that maintaining low gloss over time and thus achieved high levels of solder adhesion resistance and voltage resistance were not achieved.

Claims

1. A curable resin composition comprising a curable resin, barium sulfate, and a thermosetting catalyst, A curable resin composition characterized in that the oil absorption of the barium sulfate is 40 to 70 mL / 100 g.

2. The curable resin composition according to claim 1 , wherein the barium sulfate comprises barium sulfate surface-treated with silica.

3. The curable resin composition according to claim 1 , wherein the curable resin comprises one or more thermosetting resins selected from the group consisting of epoxy compounds, polyfunctional oxetane compounds, and oxazoline compounds.

4. The curable resin composition according to claim 1 , wherein the curable resin comprises a carboxyl group-containing photosensitive resin having one or more ethylenically unsaturated groups in one molecule.

5. The curable resin composition according to claim 4 , further comprising a photopolymerization initiator.

6. The curable resin composition according to claim 1 , which is used for forming a solder resist.

7. The curable resin composition according to claim 6 , wherein the solder resist is a matte solder resist.

8. A cured product of the curable resin composition according to claim 1.

9. A printed wiring board comprising the cured product according to claim 8.

10. A method for producing a printed wiring board provided with a solder resist, comprising the step of forming a solder resist by curing the curable resin composition according to claim 1.

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