JP7584551B2 - Photosensitive resin composition, photocured product of photosensitive resin composition, and printed wiring board having photocured film of photosensitive resin composition - Google Patents

Description

The present invention relates to a photosensitive resin composition suitable as a coating material, for example, an insulating coating material for coating a conductor circuit pattern formed on a printed wiring board having a rigid or flexible substrate, a photocured product of the photosensitive resin composition, and a printed wiring board having a photocured film of the photosensitive resin composition.

A conductor circuit pattern such as copper foil is formed on the substrate of a printed wiring board, electronic components are mounted on the soldering lands of the conductor circuit pattern by soldering, and the conductor circuit portion excluding the soldering lands is covered with an insulating film (solder resist film) as a protective film. In particular, in the case of a printed wiring board having a flexible substrate, the protective film is required to be flexible. The protective film may also be required to have a matte appearance.

Therefore, a thermosetting photosensitive resin composition has been proposed that contains (A) a thermosetting resin, (B) a resin having an acidic functional group and an unsaturated double bond, (C) a resin having an acidic functional group and no unsaturated double bond, (D) a compound having an unsaturated double bond, (E) a photopolymerization initiator, and (F) an organic filler (Patent Document 1). In Patent Document 1, the use of (F) an organic filler, in particular organic beads having urethane bonds, gives the protective film flexibility that can withstand repeated bending. In addition, the use of organic beads can give the protective film a matte appearance.

On the other hand, in the mounting process in which electronic components are mounted on the soldering lands of a conductor circuit pattern by soldering, the electronic components are placed on a printed wiring board on which a protective film has been formed, and the electronic components are soldered onto the printed wiring board by a heat treatment in a reflow furnace. In the above mounting process, solder containing flux components may be used. When solder containing flux components is used, the flux components may seep out of the solder and permeate into the protective film from the surface of the insulating coating or the openings in the conductor circuit pattern.

If flux components penetrate the protective film, the protective film may peel off from the printed wiring board or blister, causing problems with the insulating coating. Therefore, the protective film may be required to have flux resistance that can prevent the protective film from peeling off or swelling from the printed wiring board even if flux components seep out from the solder.

However, in the protective film formed from the photosensitive resin composition of Patent Document 1, the organic filler has low heat resistance, so when flux components seep out of the solder during heat treatment in a reflow furnace, the flux components permeate the protective film, causing the protective film to peel off from the printed wiring board or swell, leaving room for improvement in flux resistance.

In addition, by blending an inorganic filler into the photosensitive resin composition, the heat resistance of the protective film is improved, but flexibility is not obtained. Furthermore, when the particle size of the inorganic filler is reduced to impart flexibility, there is a problem that a matte appearance cannot be obtained.

JP 2022-017603 A

In view of the above circumstances, the present invention aims to provide a photosensitive resin composition that can form a protective film that has excellent insulation reliability, flux resistance, a matte appearance, and flexibility.

The gist of the configuration of the present invention is as follows.
[1] A composition comprising (A) a carboxyl group-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound;
The inorganic filler (B) is talc having a particle size D50 at a cumulative volume percentage of 50 volume% of 0.7 μm or more and 5.5 μm or less,
The photosensitive resin composition, wherein the (C) photopolymerization initiator contains at least one selected from the group consisting of (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator.
[2] The photosensitive resin composition according to [1], wherein the inorganic filler (B) is untreated talc that has not been surface-treated with an organic compound and has a particle diameter D50 at a cumulative volume percentage of 50 volume% of 0.7 μm or more and 5.5 μm or less.
[3] The photosensitive resin composition according to [2], wherein the inorganic filler (B) is the untreated talc having a particle diameter D50 at a cumulative volume percentage of 50 volume% of 1.3 μm or more and 2.3 μm or less.
[4] The photosensitive resin composition according to [1], wherein the inorganic filler (B) is a surface-treated talc having a particle diameter D50 at a cumulative volume percentage of 50 volume% of 0.7 μm or more and 5.5 μm or less, which has been surface-treated with an organic compound.
[5] The photosensitive resin composition according to [4], wherein the inorganic filler (B) is the surface-treated talc having a particle diameter D50 at a cumulative volume percentage of 50 volume% of 2.0 μm or more and 4.0 μm or less.
[6] The photosensitive resin composition according to [4] or [5], wherein the organic compound is at least one selected from the group consisting of epoxy silane compounds and (meth)acryl silane compounds.
[7] The photosensitive resin composition according to [1], containing 8 parts by mass or more and 80 parts by mass or less of the talc per 100 parts by mass of the (A) carboxyl group-containing photosensitive resin.
[8] The photosensitive resin composition according to [1], containing 30 parts by mass or more and 70 parts by mass or less of the talc per 100 parts by mass of the carboxyl group-containing photosensitive resin (A).
[9] The photosensitive resin composition according to [1], which does not contain an organic filler.
[10] The photosensitive resin composition according to [1], further comprising an organic filler.
[11] The photosensitive resin composition according to [1], wherein the (A) carboxyl group-containing photosensitive resin has a cresol novolac type epoxy resin skeleton.
[12] The photosensitive resin composition according to [1], wherein the (C1) α-aminoalkylphenone-based photopolymerization initiator contains 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone.
[13] The photosensitive resin composition according to [1], wherein the (C2) oxime ester photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime.
[14] A photocured product of the photosensitive resin composition according to [1].
[15] A printed wiring board having a photocured film of the photosensitive resin composition according to [1].

According to an embodiment of the photosensitive resin composition of the present invention, the composition contains (A) a carboxyl group-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound, and the (B) inorganic filler is talc having a particle diameter D50 of 0.7 μm to 5.5 μm at a cumulative volume percentage of 50 volume%, and the (C) photopolymerization initiator contains at least one selected from the group consisting of (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator, thereby making it possible to obtain a photosensitive resin composition that can form a protective film that has excellent flux resistance, matte appearance, and flexibility while maintaining insulation reliability.

According to an embodiment of the photosensitive resin composition of the present invention, the inorganic filler (B) is untreated talc that has not been surface-treated with an organic compound and has a particle diameter D50 at a cumulative volume percentage of 50 volume% of 1.3 μm or more and 2.3 μm or less, thereby making it possible to improve flux resistance, matte appearance, and flexibility in a well-balanced manner.

According to an embodiment of the photosensitive resin composition of the present invention, the inorganic filler (B) is a surface-treated talc having a particle diameter D50 of 0.7 μm or more and 5.5 μm or less at a cumulative volume percentage of 50 volume%, which is surface-treated with an organic compound, thereby reliably improving insulation reliability, matte appearance, and flexibility.

According to an embodiment of the photosensitive resin composition of the present invention, the inorganic filler (B) is a surface-treated talc having a particle diameter D50 of 2.0 μm or more and 4.0 μm or less at a cumulative volume percentage of 50 volume%, which is surface-treated with an organic compound, thereby further improving the insulation reliability, matte appearance, and flexibility.

According to an embodiment of the photosensitive resin composition of the present invention, the organic compound is at least one selected from the group consisting of epoxy silane compounds and (meth)acrylic silane compounds, which further improves the insulation reliability, matte appearance, and flexibility.

According to an embodiment of the photosensitive resin composition of the present invention, the talc is contained in an amount of 8 parts by mass or more and 80 parts by mass or less per 100 parts by mass of the carboxyl group-containing photosensitive resin (A), so that flux resistance, matte appearance, and flexibility can be obtained more reliably.

According to an embodiment of the photosensitive resin composition of the present invention, the talc is contained in an amount of 30 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the carboxyl group-containing photosensitive resin (A), thereby making it possible to improve flux resistance, matte appearance, and flexibility in a well-balanced manner.

According to the photosensitive resin composition of the present invention, the absence of an organic filler ensures improved flux resistance.

According to an embodiment of the photosensitive resin composition of the present invention, the (A) carboxyl group-containing photosensitive resin has a cresol novolac type epoxy resin skeleton, which more reliably improves insulation reliability and flux resistance.

According to an embodiment of the photosensitive resin composition of the present invention, the (C1) α-aminoalkylphenone-based photopolymerization initiator contains 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone, which contributes to further improving flux resistance.

According to an embodiment of the photosensitive resin composition of the present invention, the (C2) oxime ester photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime, which contributes to further improving flux resistance.

Next, the photosensitive resin composition of the present invention will be described below. The photosensitive resin composition of the present invention contains (A) a carboxyl group-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound, and the (B) inorganic filler is talc having a particle diameter D50 of 0.7 μm or more and 5.5 μm or less at a cumulative volume percentage of 50 volume%, and the (C) photopolymerization initiator contains at least one selected from the group consisting of (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator. In the photosensitive resin composition of the present invention, talc having a particle diameter D50 of 0.7 μm or more and 5.5 μm or less at a cumulative volume percentage of 50 volume% is blended as the (B) inorganic filler. In the photosensitive resin composition of the present invention, the inorganic filler (B) is made of talc having a particle diameter D50 of 0.7 μm or more and 5.5 μm or less at a cumulative volume percentage of 50 volume%, and does not contain other inorganic fillers such as barium sulfate, silica, mica, etc. The photosensitive resin composition of the present invention can form a protective film that has excellent insulation reliability, flux resistance, matte appearance, and flexibility.

<(A) Carboxyl Group-Containing Photosensitive Resin>
The carboxyl group-containing photosensitive resin, which is the component (A), is the base resin of the photosensitive resin composition. The structure of the carboxyl group-containing photosensitive resin is not particularly limited, and examples thereof include resins having one or more photosensitive unsaturated double bonds and free carboxyl groups. Examples of the carboxyl group-containing photosensitive resin include polybasic acid-modified radical polymerizable unsaturated monocarboxylated epoxy resins having a structure obtained by reacting at least a part of the epoxy groups of a multifunctional epoxy resin having two or more epoxy groups in one molecule with a radical polymerizable unsaturated monocarboxylic acid to obtain a radical polymerizable unsaturated monocarboxylated epoxy resin, and reacting the resulting hydroxyl group with a polybasic acid and/or a polybasic acid anhydride.

Multifunctional epoxy resin The multifunctional epoxy resin forms the skeleton of the carboxyl group-containing photosensitive resin. The epoxy equivalent of the multifunctional epoxy resin is not particularly limited, and for example, the upper limit is preferably 3000 g/eq, more preferably 2000 g/eq, further preferably 1000 g/eq, and particularly preferably 500 g/eq. On the other hand, the lower limit of the epoxy equivalent of the multifunctional epoxy resin is preferably 100 g/eq, and particularly preferably 200 g/eq. The chemical structure of the polyfunctional epoxy resin is not particularly limited, and examples thereof include rubber-modified epoxy resins such as biphenylaralkyl-type epoxy resins, phenylaralkyl-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, and silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, cresol novolac-type epoxy resins such as ortho-cresol novolac-type epoxy resins, bisphenol novolac-type epoxy resins, cyclic aliphatic polyfunctional epoxy resins, glycidyl ester-type polyfunctional epoxy resins, glycidyl amine-type polyfunctional epoxy resins, heterocyclic polyfunctional epoxy resins, bisphenol-modified novolac-type epoxy resins, and polyfunctional modified novolac-type epoxy resins. These polyfunctional epoxy resins may be used alone or in combination of two or more.

Among these polyfunctional epoxy resins, cresol novolac type epoxy resins are preferred because they more reliably improve insulation reliability and flux resistance, and therefore it is preferred that the carboxyl group-containing photosensitive resin has a cresol novolac type epoxy resin skeleton.

Radical polymerizable unsaturated monocarboxylic acid The carboxyl group of the radical polymerizable unsaturated monocarboxylic acid reacts with the epoxy group of the polyfunctional epoxy resin to form an ester bond, and thus a photosensitive unsaturated double bond derived from the radical polymerizable unsaturated monocarboxylic acid is introduced into the epoxy resin, imparting photosensitivity to the skeleton of the polyfunctional epoxy resin. Examples of radical polymerizable unsaturated monocarboxylic acids include acrylic acid, methacrylic acid (acrylic acid and/or methacrylic acid may be referred to as "(meth)acrylic acid"), crotonic acid, tiglic acid, angelic acid, and cinnamic acid. Among these, (meth)acrylic acid is preferred in terms of reactivity, availability, and handling. These radical polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more.

The method for reacting the polyfunctional epoxy resin with the radically polymerizable unsaturated monocarboxylic acid is not particularly limited, and an example of the method is to heat the polyfunctional epoxy resin and the radically polymerizable unsaturated monocarboxylic acid in an appropriate solvent (e.g., an inert organic solvent).

Polybasic acid and/or polybasic acid anhydride The polybasic acid and/or polybasic acid anhydride reacts with the hydroxyl group of the unsaturated monocarboxylated epoxy resin to form an ester bond, thereby introducing a free carboxyl group into the photosensitive resin. The polybasic acid and/or polybasic acid anhydride is not particularly limited, and either saturated or unsaturated may be used. Examples of polybasic acids include succinic acid, maleic acid, adipic acid, citric acid, phthalic acid, tetrahydrophthalic acid, 3-methyltetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, 3-ethyltetrahydrophthalic acid, 4-ethyltetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, and other tetrahydrophthalic acids, hexahydrophthalic acid, 3-methylhexahydrophthalic acid, 4-methylhexahydrophthalic acid, 3-ethylhexahydrophthalic acid, 4-ethylhexahydrophthalic acid, and other hexahydrophthalic acids, difunctional carboxylic acids such as diglycolic acid, trifunctional carboxylic acids such as trimellitic acid, and tetrafunctional carboxylic acids such as pyromellitic acid. Examples of polybasic acid anhydrides include the anhydrides of the polybasic acids described above. These polybasic acids and polybasic acid anhydrides may be used alone or in combination of two or more.

The method for reacting the radically polymerizable unsaturated monocarboxylated epoxy resin with the polybasic acid and/or polybasic acid anhydride is not particularly limited, and examples thereof include a method in which the radically polymerizable unsaturated monocarboxylated epoxy resin and the polybasic acid and/or polybasic acid anhydride are heated in a suitable solvent (e.g., an inert organic solvent).

In addition, instead of the polybasic acid-modified radically polymerizable unsaturated monocarboxylated epoxy resin, a carboxyl group-containing photosensitive resin having a chemical structure in which a compound having one or more radically polymerizable unsaturated groups and an epoxy group (e.g., a glycidyl compound) is further reacted with a part of the carboxyl group of the polybasic acid-modified radically polymerizable unsaturated monocarboxylated epoxy resin may be used as necessary. The carboxyl group-containing photosensitive resin in which a compound having a radically polymerizable unsaturated group and an epoxy group is further reacted has a chemical structure in which a radically polymerizable unsaturated group is further introduced into the side chain of the polybasic acid-modified radically polymerizable unsaturated monocarboxylated epoxy resin. Therefore, the carboxyl group-containing photosensitive resin having a chemical structure in which a compound having a radically polymerizable unsaturated group and an epoxy group is reacted has better photopolymerization reactivity and further improved photosensitive properties than the polybasic acid-modified radically polymerizable unsaturated monocarboxylated epoxy resin.

Examples of compounds having a radically polymerizable unsaturated group and an epoxy group include glycidyl acrylate, glycidyl methacrylate (acrylate and/or methacrylate are sometimes referred to as "(meth)acrylate"), allyl glycidyl ether, pentaerythritol tri(meth)acrylate monoglycidyl ether, etc. These compounds having a radically polymerizable unsaturated group and an epoxy group may be used alone or in combination of two or more kinds.

The method for reacting the polybasic acid-modified radically polymerizable unsaturated monocarboxylated epoxy resin with a compound having a radically polymerizable unsaturated group and an epoxy group is not particularly limited, and an example of the method is to heat the radically polymerizable unsaturated monocarboxylated epoxy resin with a compound having a radically polymerizable unsaturated group and an epoxy group in an appropriate solvent (e.g., an inert organic solvent).

The acid value of the carboxyl group-containing photosensitive resin is not particularly limited, and for example, the lower limit is preferably 30 mgKOH/g, and particularly preferably 40 mgKOH/g, from the viewpoint of reliably imparting alkaline developability. On the other hand, the upper limit of the acid value of the carboxyl group-containing photosensitive resin is preferably 200 mgKOH/g, from the viewpoint of reliably preventing dissolution of the exposed portion (photocured portion) by the alkaline developer, and is particularly preferably 150 mgKOH/g, from the viewpoint of more reliably improving insulation reliability.

The mass average molecular weight of the carboxyl group-containing photosensitive resin is not particularly limited and can be appropriately selected depending on the conditions of use as a protective film. For example, the lower limit is preferably 6,000, more preferably 7,000, and particularly preferably 8,000, from the viewpoint of contributing to improving the toughness and tackiness of the photocured product. On the other hand, the upper limit of the mass average molecular weight of the carboxyl group-containing photosensitive resin is preferably 200,000, more preferably 100,000, and particularly preferably 50,000, from the viewpoint of contributing to improving alkaline developability. The above "mass average molecular weight" means the mass average molecular weight measured at room temperature using gel permeation chromatography (GPC) and calculated in terms of polystyrene.

The carboxyl group-containing photosensitive resin may be prepared by the above reaction process using the above components, or a commercially available carboxyl group-containing photosensitive resin may be used. Examples of commercially available carboxyl group-containing photosensitive resins include "Lipoxy SP-4621", "Lipoxy SP-4785", and "Lipoxy SP-4785L" (all from Showa Denko K.K.), "ZAR-2000", "ZFR-1122", "ZFR-1887", "FLX-2089", "ZCR-1569H", and "ZCR-1601H" (all from Nippon Kayaku Co., Ltd.), and "Cyclomer P (ACA) Z-250" (Daicel Corporation). These carboxyl group-containing photosensitive resins may be used alone or in combination of two or more.

<(B) Inorganic Filler>
The inorganic filler, which is the component (B), is talc having a particle diameter D50 (hereinafter sometimes simply referred to as "D50") at a cumulative volume percentage of 50 volume% of 0.7 μm or more and 5.5 μm or less. In the photosensitive resin composition of the present invention, the inorganic filler (B) is made of particulate talc having a D50 of 0.7 μm or more and 5.5 μm or less, and does not contain other inorganic fillers such as barium sulfate, silica, mica, etc. By using talc having a D50 of 0.7 μm or more and 5.5 μm or less as the inorganic filler (B), it is possible to obtain a photosensitive resin composition that can form a protective film that has excellent flux resistance, matte appearance, and flexibility while having insulation reliability.

Examples of talc include untreated talc that has not been surface-treated with an organic compound (hereinafter, simply referred to as "untreated talc") and surface-treated talc that has been surface-treated with an organic compound (hereinafter, simply referred to as "surface-treated talc").

As long as D50 is 0.7 μm or more and 5.5 μm or less, the particle size and particle size distribution of the talc are not particularly limited, whether it is untreated talc or surface-treated talc. In the case of untreated talc, the lower limit of D50 is preferably 0.9 μm, more preferably 1.1 μm, even more preferably 1.3 μm, and particularly preferably 1.5 μm, from the viewpoint of further improving flux resistance and matte appearance. On the other hand, the upper limit of D50 is preferably 5.0 μm, more preferably 4.0 μm, even more preferably 2.3 μm, and particularly preferably 2.1 μm, from the viewpoint of further improving flexibility. From the above, by having D50 of untreated talc within the range of the above-mentioned preferred upper and lower limits, it is possible to improve flux resistance, matte appearance, and flexibility in a well-balanced manner.

By using surface-treated talc, the insulation reliability, matte appearance, and flexibility are reliably improved. In the case of surface-treated talc, the lower limit of D50 is preferably 1.0 μm, more preferably 1.5 μm, and particularly preferably 2.0 μm, in order to further reliably improve insulation reliability, matte appearance, and flexibility. On the other hand, the upper limit of D50 is preferably 5.0 μm, and particularly preferably 4.0 μm, in order to further improve flexibility.

Examples of organic compounds used in the surface treatment of talc include silane compounds. Examples of silane compounds include epoxy-functional silane compounds, (meth)acrylic silane compounds, and phenyl silane compounds. Of these, (meth)acrylic silane compounds are preferred, and acrylic silane compounds are particularly preferred, in terms of further improving flux resistance.

The amount of talc having a D50 of 0.7 μm or more and 5.5 μm or less is not particularly limited, but the lower limit is preferably 8 parts by mass per 100 parts by mass (solid content, the same below) of (A) carboxyl group-containing photosensitive resin in order to more reliably obtain flux resistance and a matte appearance, and more preferably 30 parts by mass and particularly preferably 35 parts by mass in order to further improve flux resistance and a matte appearance. On the other hand, the upper limit of the content of talc having a D50 of 0.7 μm or more and 5.5 μm or less is preferably 80 parts by mass per 100 parts by mass of (A) carboxyl group-containing photosensitive resin in order to more reliably obtain flexibility, and more preferably 70 parts by mass and particularly preferably 60 parts by mass in order to further improve flexibility. From the above, by containing 8 to 80 parts by mass of talc having a D50 of 0.7 to 5.5 μm per 100 parts by mass of (A) carboxyl group-containing photosensitive resin, it is possible to more reliably obtain flux resistance, matte appearance, and flexibility, and by containing 30 to 70 parts by mass of talc having a D50 of 0.7 to 5.5 μm per 100 parts by mass of (A) carboxyl group-containing photosensitive resin, it is possible to improve flux resistance, matte appearance, and flexibility in a well-balanced manner.

<(C) Photopolymerization initiator>
By adding the photopolymerization initiator, which is component (C), the curing properties of the cured coating film are improved and the penetration of the flux component into the protective film is suppressed, making it possible to form a protective film with excellent flux resistance.

The photosensitive resin composition of the present invention contains at least one photopolymerization initiator selected from the group consisting of (C1) α-aminoalkylphenone-based photopolymerization initiators and (C2) oxime ester-based photopolymerization initiators.

（式（１）中におけるＲは、水素または炭素数１～５個のアルキル基を表す）で表される化合物を挙げることができる。これらのうち、保護膜の硬化性が確実に向上して耐フラックス性のさらなる向上に寄与できる点から、α－アミノアルキルフェノン系光重合開始剤として、１－(４－モルホリノフェニル)－２－(ジメチルアミノ)－２－(４－メチルベンジル）－１－ブタノン（式（１）中におけるＲがメチル基）が好ましい。これらのα－アミノアルキルフェノン系光重合開始剤は、単独で使用してもよく、２種以上を併用してもよい。 The α-aminoalkylphenone-based photopolymerization initiator, which is the component (C1), is, for example, a compound represented by the following general formula (1):

(in formula (1), R represents hydrogen or an alkyl group having 1 to 5 carbon atoms). Of these, 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone (in formula (1), R represents a methyl group) is preferred as the α-aminoalkylphenone photopolymerization initiator, since it reliably improves the curability of the protective film and contributes to further improving the flux resistance. These α-aminoalkylphenone photopolymerization initiators may be used alone or in combination of two or more kinds.

As the oxime ester photopolymerization initiator of component (C2), for example, (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime, 1,2-octanedione, 1-[4-(phenylthio)-2-(O-benzoyloxime)], ethanone 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), 2-(acetyloxyiminomethyl)thioxanthen-9-one, 1,8-octanedione, 1,8-bis[9-ethyl-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyloxime), 1,8-octanedione, 1,8-bis[9-(2-ethylhexyl)-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyloxime), and the like can be mentioned. Of these, (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime is preferred because it reliably improves the curing properties of the cured coating film and contributes to further improving flux resistance. These oxime ester photopolymerization initiators may be used alone or in combination of two or more types.

The amount of at least one photopolymerization initiator selected from the group consisting of α-aminoalkylphenone-based photopolymerization initiators and oxime ester-based photopolymerization initiators is not particularly limited, but the lower limit is preferably 0.50 parts by mass, more preferably 1.0 parts by mass, and particularly preferably 1.5 parts by mass, relative to 100 parts by mass of (A) carboxyl group-containing photosensitive resin, from the viewpoint of reliably improving the curing properties of the cured coating film and reliably obtaining excellent flux resistance. On the other hand, the upper limit of the amount of at least one photopolymerization initiator selected from the group consisting of α-aminoalkylphenone-based photopolymerization initiators and oxime ester-based photopolymerization initiators relative to 100 parts by mass of (A) carboxyl group-containing photosensitive resin, from the viewpoint of preventing a decrease in developability and halation, is preferably 8.0 parts by mass, more preferably 6.0 parts by mass, and particularly preferably 4.0 parts by mass.

<(D) Reactive Diluent>
The reactive diluent, which is the component (D), is, for example, a photopolymerizable monomer, and is a compound having at least one polymerizable double bond per molecule, preferably two or more polymerizable double bonds per molecule. The reactive diluent reinforces the photocuring of the photosensitive resin composition, and contributes to imparting sufficient strength, heat resistance, acid resistance, alkali resistance, etc. to the cured coating film of the photosensitive resin composition.

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

The amount of reactive diluent is not particularly limited, but is preferably 5.0 parts by weight or more and 70 parts by weight or less, and particularly preferably 15 parts by weight or more and 40 parts by weight or less, per 100 parts by weight of (A) carboxyl group-containing photosensitive resin.

<(E) Epoxy Compound>
The epoxy compound (E) is used to increase the crosslink density of the cured product of the photosensitive resin composition to impart sufficient hardness to the cured product. The increased crosslink density of the epoxy compound contributes to the formation of a protective film with excellent flux resistance by suppressing the penetration of flux components into the protective film.

Epoxy compounds include, for example, epoxy resins. Epoxy resins include, for example, the same epoxy resins as the polyfunctional epoxy resins that can be used to prepare the carboxyl group-containing photosensitive resins described above. Specific examples include rubber-modified epoxy resins such as biphenylaralkyl-type epoxy resins, phenylaralkyl-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, and silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, cresol novolac-type epoxy resins such as ortho-cresol novolac-type epoxy resins, bisphenol novolac-type epoxy resins, cyclic aliphatic polyfunctional epoxy resins, glycidyl ester-type polyfunctional epoxy resins, glycidyl amine-type polyfunctional epoxy resins, heterocyclic polyfunctional epoxy resins, bisphenol-modified novolac-type epoxy resins, and polyfunctional modified novolac-type epoxy resins. In addition, examples of epoxy compounds other than epoxy resins include, for example, triglycidyl isocyanurate. These epoxy compounds may be used alone or in combination of two or more. As the epoxy compound, the same type of epoxy resin as the type of multifunctional epoxy resin used in the preparation of the above-mentioned carboxyl group-containing photosensitive resin can be used.

The amount of epoxy compound is not particularly limited, but is preferably 5.0 parts by mass or more and 60 parts by mass or less, and particularly preferably 10 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of (A) carboxyl group-containing photosensitive resin.

In the photosensitive resin composition of the present invention, talc having a D50 of 0.7 μm or more and 5.5 μm or less is blended as the inorganic filler (B), and therefore a protective film having excellent matte appearance and flexibility can be formed, and therefore an organic filler does not need to be included. By not including an organic filler, the flux resistance is improved more reliably. On the other hand, if necessary, an organic filler may be further included as an optional component. By including an organic filler, the flux resistance is slightly reduced compared to the case where no organic filler is included, but the flexibility is improved.

Examples of organic fillers include polymers such as urethane resins (polymers of isocyanate and polyol), acrylic resins, polyethylene, copolymers of styrene and butadiene such as styrene-butadiene rubber, and silicone resins such as silicone rubber. These organic fillers may be used alone or in combination of two or more. The shape of the organic filler is not particularly limited, but particulate form is preferred.

The average particle diameter of the particulate organic filler is not particularly limited, but the lower limit is preferably 0.1 μm, and more preferably 0.5 μm, from the viewpoint of improving the matte appearance. On the other hand, the upper limit of the average particle diameter of the particulate organic filler is preferably 20 μm, and more preferably 10 μm, from the viewpoint of imparting excellent flexibility.

The upper limit of the amount of organic filler to be blended is preferably 20 parts by mass, and more preferably 15 parts by mass, per 100 parts by mass of (A) carboxyl group-containing photosensitive resin, in order to obtain flux resistance. On the other hand, the lower limit of the amount of organic filler to be blended when an organic filler is blended is preferably 1.0 part by mass, and more preferably 5.0 parts by mass, per 100 parts by mass of (A) carboxyl group-containing photosensitive resin, in order to further improve flexibility.

In the photosensitive resin composition of the present invention, in addition to the above-mentioned components (A) to (E), (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) another photopolymerization initiator other than the oxime ester-based photopolymerization initiator may be further blended as an optional component, if necessary. Other photopolymerization initiators include, for example, benzoin-based initiators such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, and benzoin isobutyl ether; acetophenone-based initiators such as acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, and 2,2-diethoxy-2-phenylacetophenone; benzophenone-based initiators such as benzophenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, and dichlorobenzophenone; anthraquinone-based initiators such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tertiary butylanthraquinone, and 2-aminoanthraquinone; 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, and the like. Examples of the thioxanthone-based initiators include thioxanthone, 2,4-dimethylthioxanthone, and 2,4-diethylthioxanthone; benzyl dimethyl ketal, acetophenone dimethyl ketal, p-dimethylaminobenzoic acid ethyl ester, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, and 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone. These other photopolymerization initiators may be used alone or in combination of two or more.

The photosensitive resin composition of the present invention may further contain other optional components, such as colorants, additives, defoamers, flame retardants, non-reactive diluents, etc., as necessary.

The colorant is not particularly limited to pigments, dyes, etc., and any colorant can be used depending on the desired color, such as white colorant, black colorant, blue colorant, green colorant, yellow colorant, purple colorant, orange colorant, red colorant, etc. In addition, by containing a colorant, it is possible to impart hiding power to the protective film. Examples of the colorant include inorganic colorants such as titanium dioxide, which is a white colorant, acetylene black, carbon black, which are black colorants, phthalocyanine-based colorants such as phthalocyanine green, which is a green colorant, phthalocyanine blue, lyonol blue, which are blue colorants, and diketopyrrolopyrrole-based colorants such as chromophthalic orange, which is an orange colorant. These colorants may be used alone or in combination of two or more.

Additives include, for example, mercaptobenzoxazal and its derivatives, dicyandiamide (DICY) and its derivatives, melamine and its derivatives, boron trifluoride-amine complex, organic acid hydrazide, diaminomaleonitrile (DAMN) and its derivatives, guanamine and its derivatives, aminimide (AI), latent curing agents such as polyamines, and heat curing catalysts such as aliphatic dimethylurea.

Examples of antifoaming agents include silicone-based polymers, hydrocarbon-based polymers, and acrylic-based polymers.

The flame retardant is intended to impart flame retardancy to the cured coating film of the photosensitive resin composition. Examples of the flame retardant include phosphorus-based flame retardants, and organic phosphate-based flame retardants are preferred. Examples of phosphorus-based flame retardants include halogen-containing phosphate esters such as tris(chloroethyl)phosphate, tris(2,3-dichloropropyl)phosphate, tris(2-chloropropyl)phosphate, tris(2,3-bromopropyl)phosphate, tris(bromochloropropyl)phosphate, 2,3-dibromopropyl-2,3-chloropropylphosphate, tris(tribromophenyl)phosphate, tris(dibromophenyl)phosphate, and tris(tribromoneopentyl)phosphate; trimethyl phosphate, triethyl phosphate, etc. non-halogenated aliphatic phosphate esters such as tributyl phosphate, trioctyl phosphate, and tributoxyethyl phosphate; triphenyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, tricresyl phosphate, trixylenyl phosphate, xylenyl diphenyl phosphate, tris(isopropylphenyl)phosphate, isopropylphenyl diphenyl phosphate, diisopropylphenyl phenyl phosphate, tris(trimethylphenyl)phosphate, and tris(t-butylphenyl)phosphate. non-halogen-based aromatic phosphate esters such as hydroxyphenyl diphenyl phosphate and octyl diphenyl phosphate; aluminum trisdiethylphosphinate, aluminum trismethylethylphosphinate, aluminum trisdiphenylphosphinate, zinc bisdiethylphosphinate, zinc bismethylethylphosphinate, zinc bisdiphenylphosphinate, titanyl bisdiethylphosphinate, titanium tetrakisdiethylphosphinate, titanyl bismethylethylphosphinate, titanium tetrakismethylethylphosphinate, bisdiphenylphosphinic acid These include metal salts of phosphinic acid such as titanyl and titanium tetrakisdiphenylphosphinate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (hereinafter referred to as HCA), HCA-modified compounds such as the addition reaction product of HCA and acrylic ester, the addition reaction product of HCA and epoxy resin, and the addition reaction product of HCA and hydroquinone, and phosphine oxide compounds such as diphenylvinylphosphine oxide, triphenylphosphine oxide, trialkylphosphine oxide, and tris(hydroxyalkyl)phosphine oxide.

The non-reactive diluent is a component for adjusting the viscosity, coatability and drying property of the photosensitive resin composition. Examples of the non-reactive diluent include organic solvents that are inactive to the components blended in the photosensitive resin composition. Examples of the organic solvent include ketones such as methyl ethyl ketone, aromatic hydrocarbons such as benzene, toluene and xylene, alcohols such as methanol, ethanol, n-propanol, isopropanol and cyclohexanol, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, petroleum solvents such as petroleum ether and petroleum naphtha, cellosolves such as cellosolve and butyl cellosolve, carbitols such as butyl carbitol, ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, ethylene glycol acetate, ethylene diglycol acetate, diethylene glycol monoethyl ether acetate, and other esters. These may be used alone or in combination of two or more.

The photosensitive resin composition of the present invention may also contain an extender pigment such as aluminum hydroxide as a flame retardant.

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

Next, an example of a method for using the photosensitive resin composition of the present invention will be described. Here, a method for forming an insulating protective film (e.g., a solder resist film, etc.) by applying the photosensitive resin composition of the present invention to a printed wiring board will be described.

The photosensitive resin composition obtained as described above is applied to a desired thickness on a printed wiring board (a printed wiring board having a rigid or flexible substrate, etc.) having a circuit pattern formed by etching a copper foil, for example, by using a known coating method such as screen printing, a spray coater, a bar coater, an applicator, a blade coater, a knife coater, a roll coater, a gravure coater, etc. Next, an exposure process is performed in which active energy rays (for example, laser light) are directly irradiated onto the applied photosensitive resin composition according to a desired pattern using a direct imaging device, and the coating film is photocured in the pattern. Examples of the exposure amount include 50 mJ/cm ² to 2000 mJ/cm ^2. Next, the coating film is developed by removing the non-exposed region with a dilute alkaline aqueous solution. Examples of the development method include a spray method, a shower method, etc., and examples of the dilute alkaline aqueous solution include a 0.5 to 5% by mass aqueous sodium carbonate solution. Next, the developed coating film is thermally cured by performing a post-cure (thermal curing treatment) for 20 to 80 minutes in a hot air circulation dryer or the like at 130 to 170°C, thereby forming a photocured film (photocured product) having a desired pattern on the printed wiring board.

In addition, instead of the exposure treatment in which active energy rays are directly irradiated according to the desired pattern using the direct imaging device described above, an exposure treatment may be performed in which after applying the photosensitive resin composition, a coating film is pre-dried by heating at a temperature of about 60 to 100°C for about 15 to 60 minutes to make it tack-free, a negative film (photomask) having a pattern in which the circuit pattern lands are made transparent is adhered to the coating film, and active energy rays (e.g., ultraviolet rays with a wavelength of 300 to 400 nm) are irradiated from above to photocure the coating film.

Examples 1 to 12, Comparative Examples 1 to 5
The components shown in Table 1 below were blended in the ratios shown in Table 1 below and mixed at room temperature using a three-roll mill to prepare photosensitive resin compositions used in Examples 1 to 12 and Comparative Examples 1 to 5. The prepared photosensitive resin compositions were then applied to substrates as described below to prepare test specimens. The blending amount of each component shown in Table 1 below is shown in parts by mass unless otherwise specified. Note that blank spaces in the blending amounts in Table 1 below mean that no blend was used.

Details of each component in Table 1 below are as follows.
(A) Carboxyl group-containing photosensitive resin Lipoxy SP-4785: polybasic acid-modified unsaturated monocarboxylated epoxy resin having a glycidyl methacrylate-modified cresol novolac structure, solid content (resin content) 65% by mass, Showa Denko K.K. ZCR-1601H: polybasic acid-modified unsaturated monocarboxylated epoxy resin having a bisphenol novolac structure, solid content (resin content) 65% by mass, Nippon Kayaku Co., Ltd. ZFR-1887: polybasic acid-modified unsaturated monocarboxylated epoxy resin, solid content (resin content) 65% by mass, Nippon Kayaku Co., Ltd.

(B) Inorganic filler FG-20: untreated talc, D50 is 2.0 μm, Nippon Talc Co., Ltd. FG-15: untreated talc, D50 is 1.5 μm, Nippon Talc Co., Ltd. SG-95: untreated talc, D50 is 2.1 μm, Nippon Talc Co., Ltd. SG-2000: untreated talc, D50 is 0.9 μm, Nippon Talc Co., Ltd. FH-105: untreated talc, D50 is 5.0 μm, Fuji Talc Co., Ltd. FG-20 with 3% epoxy silane surface treatment: surface-treated talc with 3% epoxy functional silane compound by mass, D50 is 2.5 μm, Nippon Talc Co., Ltd. FG-20 with 5% acrylic silane surface treatment: surface-treated talc with 5% acrylic silane compound by mass, D50 is 3.0 μm, Nippon Talc Co., Ltd.

(C) Photopolymerization initiator/Omnirad379: IGM Resins B. V. company

(D) Reactive diluent: KAYARAD DPCA-20: Nippon Kayaku Co., Ltd.

(E) Epoxy compounds YX-4000: biphenyl type epoxy resin, Mitsubishi Chemical Corporation N-695: cresol novolac type epoxy resin, DIC Corporation

Colorant Carbon black: Toyo Ink Mfg. Co., Ltd. Additive DICY-7: Mitsubishi Chemical Corporation U-CAT 3513N: San-Apro Co., Ltd. Melamine: Nissan Chemical Industries, Ltd. Defoamer AC-2300C: Shin-Etsu Chemical Co., Ltd. Flame retardant Exolit OP-935: Aluminum trisdiethylphosphinate, Clariant Japan Co., Ltd. Aluminum hydroxide Non-reactive diluent EDGAC: Sanyo Chemical Industries, Ltd.

Inorganic fillers other than talc B-30: barium sulfate, D50 is 0.1-0.2 μm, Sakai Chemical Industry Co., Ltd. SO-C2: silica, D50 is 0.5 μm, Admatechs Co., Ltd. Minusil 5 micron: D50 is 5 μm, Air Brown Co., Ltd. Organic fillers Urethane beads: D50 is 3.5 μm, Dainichiseika Chemicals Co., Ltd.

Test Specimen Preparation Step The photosensitive resin compositions of the Examples and Comparative Examples prepared as described above were applied onto a substrate in the manner described below to prepare test specimens having a cured coating film on the substrate.
Substrate: 2-layer FCCL (flexible copper clad laminate) (Cu foil: thickness 12.5 μm, polyimide film thickness: 25 μm)
Surface treatment: Soft etching treatment Coating method: Screen printing Pre-drying: In an oven, 80°C, 20 minutes Dry film thickness (20±3 μm)
Exposure: 100 mJ/cm ² on the coating film, exposure device: direct imaging (DI) exposure device "Nuvogo1000R" manufactured by Orbotech (light source: laser)
Post cure (thermal curing): 150°C in oven for 60 minutes

Evaluation Items (1) Flux Resistance A frame with polyimide tape laminated (thickness 150 μm) was placed on the pattern with openings in the cured coating on the Cu foil, and the inside of the frame was filled with rosin-based flux. The lid was then placed on the frame, and reflow was performed using a reflow furnace (product name: TNP-538EM, manufactured by Tamura Corporation) under the following conditions: preheat temperature 150°C to 180°C for 80 seconds, peak temperature 240°C for 40 seconds. After reflow, the lid was removed, and the condition of the cured coating was visually observed and evaluated as follows. A rating of △ or higher was determined to be acceptable.
⊚: The cured coating film is free of peeling or blistering, and the surface of the cured coating film is free of abnormalities.
◯: There is no peeling or blistering of the cured coating film, but there are traces of penetration on the surface of the cured coating film.
△: The cured coating film has some peeling or swelling.
×: The cured coating film exhibits significant peeling or blistering.

(2) Gloss value (matte appearance)
The 60-degree specular reflectance (%) of the cured coating surface of the test specimen was measured using a gloss meter VG-2000 (manufactured by Nippon Denshoku Industries Co., Ltd.) A gloss value of 30% or less was judged to have a matte appearance and to pass.

(3) Flexibility: A test specimen having a cured coating film formed thereon was bent by a mandrel test, and the state of cracking in the cured coating film at that time was observed visually and with an optical microscope at ×200 to evaluate whether or not cracking occurred. A rating of △ or higher was judged to be acceptable.
⊚: No cracks were generated even when bent 10 times at a diameter of 2 mm.
◯: No cracks were generated even when bent once at a diameter of φ2 mm, but cracks were generated after bending 10 times.
Δ: Cracks occurred when bent once at φ2 mm, but no cracks occurred when bent once at φ3 mm.
×: Cracks occurred when bent once at φ3 mm.

(4) Insulation reliability: A test specimen was prepared using a comb-shaped electrode (line width/space = 30 μm/30 μm) instead of a two-layer FCCL substrate according to the above test specimen preparation process, and the insulation resistance was measured by applying DC 32 V using a HAST device after humidifying the specimen at 110°C and 85% R.H. for 24 hours. The evaluation criteria were as follows, and a rating of △ or higher was determined to be a pass.
⊚: The insulation resistance value is 1.0×10 ⁹ Ω or more.
◯: The insulation resistance value is 1.0×10 ⁸ Ω or more and less than 1.0×10 ⁹ Ω.
Δ: The insulation resistance value is 1.0×10 ⁷ Ω or more and less than 1.0×10 ⁸ Ω.
×: The insulation resistance value is less than 1.0×10 ⁷ Ω.

The evaluation results are shown in Table 1 below.

As shown in Table 1 above, in Examples 1 to 12 in which the inorganic filler was talc with a D50 of 0.7 μm or more and 5.5 μm or less, a protective film was formed that had excellent flux resistance, a matte appearance, and flexibility while maintaining insulation reliability.

In particular, Examples 1, 4, and 5 in which the inorganic filler is talc having a D50 of 1.3 μm or more and 2.3 μm or less were able to improve flux resistance, matte appearance, and flexibility in a well-balanced manner compared to Examples 6 and 7 in which the inorganic filler is talc having a D50 of 0.9 μm and 5.0 μm. Also, Example 1 in which about 50 parts by mass of talc having a D50 of 0.7 μm or more and 5.5 μm or less was blended with 100 parts by mass of carboxyl group-containing photosensitive resin was further improved in flux resistance and matte appearance compared to Example 2 in which about 20 parts by mass of talc having a D50 of 0.7 μm or more and 5.5 μm or less was blended. Also, Example 1 in which the carboxyl group-containing photosensitive resin has a cresol novolac type epoxy resin skeleton was further improved in insulation reliability and flux resistance compared to Examples 8 and 9 in which the carboxyl group-containing photosensitive resin does not have a cresol novolac type epoxy resin skeleton.

In Example 3, which further contained urethane beads as an organic filler, the flux resistance was slightly decreased compared to Example 1, but the flexibility was further improved. In Examples 10 and 11, which used surface-treated talc, the insulation reliability, matte appearance, and flexibility were reliably improved, and in particular, Example 11, which used surface-treated talc that had been surface-treated with an acrylic silane compound, exhibited excellent flux resistance. In Example 12, which used surface-treated talc and further contained urethane beads as an organic filler, the flexibility was improved while maintaining the flux resistance, matte appearance, and insulation reliability.

On the other hand, in Comparative Example 1, where the inorganic filler was barium sulfate with a D50 of 0.1 to 0.2 μm, flexibility and a matte appearance were not obtained. In Comparative Example 2, where the inorganic filler was silica with a D50 of 0.5 μm, a matte appearance was not obtained. In Comparative Example 3, where the inorganic filler was silica rather than talc, even though the inorganic filler had a D50 of 5 μm, flexibility and insulation reliability were not obtained. In Comparative Example 4, where urethane beads, an organic filler rather than an inorganic filler, were blended even though the D50 was 3.5 μm, flux resistance and insulation reliability were not obtained. In Comparative Example 5, where neither inorganic nor organic filler was blended, a matte appearance was not obtained.

INDUSTRIAL APPLICABILITY The photosensitive resin composition of the present invention can form a protective film that is excellent in insulation reliability, flux resistance, matte appearance and flexibility, and is therefore highly useful in the field of insulating protective films provided on printed wiring boards using flexible substrates.

Claims (10)

(A) a carboxyl group-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound;
the (A) carboxyl group-containing photosensitive resin is a polybasic acid-modified unsaturated monocarboxylated epoxy resin having a glycidyl methacrylate-modified cresol novolac structure, the (B) inorganic filler is untreated talc that has not been surface-treated with an organic compound and has a particle diameter D50 at a cumulative volume percentage of 50 volume% of 1.3 μm or more and 2.0 μm or less, or surface-treated talc that has been surface-treated with an organic compound and has a particle diameter D50 at a cumulative volume percentage of 50 volume% of 2.0 μm or more and 4.0 μm or less,
The photosensitive resin composition, wherein the (C) photopolymerization initiator contains at least one selected from the group consisting of (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator. 2. The photosensitive resin composition according to claim 1 , wherein the organic compound is at least one selected from the group consisting of epoxysilane compounds and (meth)acrylsilane compounds. The photosensitive resin composition according to claim 1, which contains 8 parts by mass or more and 80 parts by mass or less of the talc per 100 parts by mass of the (A) carboxyl group-containing photosensitive resin. The photosensitive resin composition according to claim 1, which contains 30 parts by mass or more and 70 parts by mass or less of the talc per 100 parts by mass of the (A) carboxyl group-containing photosensitive resin. The photosensitive resin composition according to claim 1, which does not contain an organic filler. The photosensitive resin composition according to claim 1 further contains an organic filler. The photosensitive resin composition according to claim 1, wherein the (C1) α-aminoalkylphenone-based photopolymerization initiator contains 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone. The photosensitive resin composition according to claim 1, wherein the (C2) oxime ester photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime. A photocured product of the photosensitive resin composition according to claim 1. A printed wiring board having a photocured film of the photosensitive resin composition according to claim 1.