Inkjet ink, ink set, cured film, method for manufacturing cured film, printed wiring board, and electronic device

Abstract

Provided is an inkjet ink or an ink set which can be used for forming a cured film through light irradiation and heat curing, and hardly causes delamination at a lamination interface. The present invention relates to a curable composition containing a compound having a (meth)acryloyl group and a compound having an epoxy group. The curable composition contains a material that may be present as a dispersed elastomer in a cured film. The curable composition may be a one-component inkjet ink or a multi-component inkjet ink set.

Description

Inkjet ink, ink set, cured film, method for manufacturing cured film, printed circuit board, and electronic device.

[0001] The present invention relates to inkjet ink, ink sets, cured films, methods for manufacturing cured films, printed circuit boards, and electronic devices.

[0002] Electric vehicles (EVs) and drones require power electronics, which are power supply devices that provide relatively high voltage or high current. Electronic devices that require power electronics use printed circuit boards (PCBs), which are made by etching copper from copper plates or copper-clad laminates to form wiring. Solder resist is then formed on the outermost layer of the PCB as an insulating protective layer.

[0003] For PCBs requiring high current, relatively thick copper wiring is used to reduce wiring resistance and thus the size of the PCB. To insulate and protect such wiring, a thick solder resist film needs to be formed.

[0004] Incidentally, the use of compositions possessing both photocuring and thermocuring properties has been proposed as materials for solder resists (Patent Documents 1 and 2, etc.). Such compositions enable rapid and precise pattern formation due to their photocuring properties. Furthermore, such compositions can enhance the heat resistance and mechanical strength of the cured film due to their thermocuring properties.

[0005] Incidentally, the use of inkjet compositions possessing both photocuring and thermocuring properties has been proposed as solder resist materials (Patent Documents 1 and 2, etc.). These compositions can be applied to a substrate by an inkjet method, and then rapidly and precisely patterned by light irradiation. Furthermore, by thermocuring these compositions after light irradiation, the heat resistance and mechanical strength of the cured film can be increased.

[0006] Japanese Patent Publication No. 2016-204453 Japanese Patent Publication No. 2018-203912

[0007] The inkjet compositions described in Patent Documents 1 and 2 are formed by repeatedly applying them to a substrate and irradiating them with light to create a pre-cured film, and then accumulating the pre-cured film to a predetermined thickness before being irradiated with light and heat-cured. However, the cured films formed in this way are prone to delamination at the layering interface.

[0008] The present invention has been made in view of the above circumstances and provides an inkjet ink or ink set that can be used to form a cured film by light irradiation and heat curing, and which is less prone to peeling at the lamination interface. The present invention also provides a method for manufacturing a cured film using the above inkjet ink or ink set. The present invention also provides a cured film manufactured by the above method, as well as a wiring board and electronic equipment having the cured film.

[0009] To solve the above problems, one aspect of the present invention relates to the following [1] to

[17] inkjet ink, ink set, cured film, method for manufacturing a cured film, printed circuit board, and electronic device. [1] An inkjet ink comprising a curable composition containing a compound having a (meth)acryloyl group and a compound having an epoxy group, wherein the material can exist as a dispersed elastomer in a cured film obtained by curing the curable composition. [2] The inkjet ink according to [1], wherein the elastomer exists in a dissolved state in the inkjet ink and exists in the dispersed state in the cured film after phase separation. [3] The inkjet ink according to [1] or [2], wherein the elastomer is a polymer particle with an average particle diameter of 50 nm or more and 1000 nm or less. [4] The inkjet ink according to any one of [1] to [3], wherein the elastomer is a core-shell type polymer fine particle. [5] The inkjet ink according to any one of [1] to [4], comprising silica surface-treated with a silane coupling material. [6] An ink set comprising: a first inkjet ink comprising a compound having a (meth)acryloyl group and not comprising a compound having an epoxy group; and a second inkjet ink comprising both a compound having a (meth)acryloyl group and a compound having an epoxy group, wherein at least one of the first inkjet ink and the second inkjet ink contains a material that can exist as a dispersed elastomer in a cured film obtained by curing a curable composition which is a mixture of the first inkjet ink and the second inkjet ink. [7] The ink set according to [6], wherein the elastomer exists in a dissolved state in the inkjet ink and exists in the dispersed state in the cured film after phase separation. [8] The ink set according to [6] or [7], wherein the elastomer is a polymer particle with an average particle diameter of 50 nm or more and 1000 nm or less. [9] The ink set according to any one of [6] to [8], wherein the elastomer is a core-shell type polymer microparticle.

[10] The ink set according to any one of [6] to [9], wherein at least one of the first inkjet ink and the second inkjet ink contains silica surface-treated with a silane coupling material.

[11] A method for manufacturing a cured film, comprising the steps of: applying the first inkjet ink and the second inkjet ink contained in the ink set according to any one of [1] to [5], or the ink set according to any one of [6] to

[10] , to a substrate; and curing the applied inkjet ink by light irradiation and heating.

[12] A cured film formed by the inkjet ink according to any one of [1] to [5], or the ink set according to any one of [6] to

[10] , wherein the cured film contains an elastomer in a dispersed state.

[13] The cured film according to

[12] , wherein the thickness is 50 μm or more and 1000 μm or less.

[14] The cured film according to

[12] or

[13] , wherein the glass transition temperature is 120°C or more and 300°C or less.

[15] A cured film according to any one of

[12] to

[14] , used as an insulating film.

[16] A printed circuit board having a cured film according to any one of

[12] to

[15] .

[17] An electronic device having a printed circuit board according to

[16] .

[0010] The present invention provides an inkjet ink or ink set that can be used to form a cured film by light irradiation and heat curing, and which is less prone to peeling at the lamination interface. The present invention also provides a method for manufacturing a cured film using the above inkjet ink or ink set. Furthermore, the present invention provides a cured film manufactured by the above method, as well as a wiring board and electronic equipment having the cured film.

[0011] Figure 1 is a schematic diagram showing the general configuration of the apparatus used in the example to apply the curable composition to the substrate and to irradiate the applied curable composition with light.

[0012] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0013] 1. Curable Composition One embodiment of the present invention relates to a curable composition that can be applied to a substrate by an inkjet method for forming a cured film by light irradiation and thermal curing. The curable composition may be a one-component composition (inkjet ink, hereinafter inkjet ink will also be simply referred to as "ink"). Alternatively, the curable composition may be a two-component (or more than two-component) composition (ink set) prepared by separating the materials contained in the curable composition into other compositions (all of which are inkjet inks).

[0014] The curable composition may include a photopolymerizable compound and a thermosetting compound, and further include a material that can exist as a dispersed elastomer in the cured film obtained by curing the curable composition (hereinafter also simply referred to as "elastomer material"). The curable composition may optionally include a photopolymerization initiator for polymerization and crosslinking of the photopolymerizable compound, and may further include a photosensitizer. The curable composition may also optionally include a thermosetting agent for crosslinking the thermosetting compound, and may further include a thermosetting accelerator. Furthermore, the curable composition may optionally include a filler for increasing the mechanical strength of the cured film.

[0015] 1-1. Photopolymerizable Compounds Photopolymerizable compounds are compounds that polymerize or crosslink upon light irradiation, with the assistance of photopolymerization initiators or other agents as needed.

[0016] Photopolymerizable compounds enable rapid and precise pattern formation of curable compositions and improve the pattern accuracy of the cured film by suppressing bleeding. Furthermore, photopolymerizable compounds facilitate increasing the thickness of each layer of the pre-cured film formed by a single light irradiation. Additionally, because photopolymerizable compositions form a pre-cured film with high surface flatness upon light irradiation of the curable composition, the layer structure remains stable even after multiple applications of the curable composition and subsequent light irradiation.

[0017] The photopolymerizable compound may contain radical polymerizable compounds, cationic polymerizable compounds, or both. From the viewpoint of reducing the influence of humidity during photopolymerization, it is preferable that the photopolymerizable compound contains radical polymerizable compounds. Examples of radical polymerizable compounds include compounds having a (meth)acryloyl group, other compounds having vinyl groups, and compounds having maleimide gas. Examples of cationic polymerizable compounds include compounds having alicyclic epoxy groups and compounds having oxetane groups.

[0018] The photopolymerizable compound may include monofunctional compounds having only one functional group for polymerization or crosslinking within the molecule, or polyfunctional compounds having multiple such functional groups within the molecule, or both. From the viewpoint of the flexibility of the cured film, it is preferable that the photopolymerizable compound includes monofunctional compounds. Furthermore, from the viewpoint of the strength of the cured film, it is preferable that the photopolymerizable compound includes polyfunctional compounds.

[0019] For example, increasing the proportion of monofunctional compounds among the photopolymerizable compounds increases the flexibility of the cured film. On the other hand, increasing the proportion of polyfunctional compounds among the photopolymerizable compounds increases the strength of the cured film.

[0020] In this specification, (meth)acryloyl means acryloyl or methacryloyl, (meth)acrylate means acrylate or methacrylate, and (meth)acrylic means acrylic or methacrylic.

[0021] In this embodiment, the curable composition includes a compound having a (meth)acryloyl group as a photopolymerizable compound. The compound having a (meth)acryloyl group further improves the pattern accuracy of the cured film.

[0022] Examples of monofunctional compounds containing a (meth)acryloyl group include tetrahydrofurfuryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, phenoxyethyl (meth)acrylate, isobornyl (meth)acrylate, 3-methyl-1,5-pentanediol (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, ethoxylated-o-phenylphenol (meth)acrylate, and 2-(meth)acryloyloxyethyl succinic acid.

[0023] Examples of polyfunctional compounds containing a (meth)acryloyl group include diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate with more than one ethylene oxide group, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate with more than one propylene oxide group, 1,3-butylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-Decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, (meth)acrylic acid modified product of alkylene oxide adduct of bisphenol A, (meth)acrylic acid modified product of alkylene oxide adduct of bisphenol F, tricyclodecanedimethanol di(meth)acrylate, pentaerythritol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, (meth)acrylic acid modified product of alkylene oxide modified product of trimethylolpropane, pentaerythritol tri(meth)acrylate, dipentaerythritol This includes di(meth)acrylate, trimethylolpropane tri((meth)acryloyloxypropyl) ether, (meth)acrylic acid modified products of alkylene oxide modified isocyanuric acid, dipentaerythritol propionate tri(meth)acrylate, tri((meth)acryloyloxyethyl) isocyanurate, sorbitol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, sorbitol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, sorbitol penta(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, and acrylic acid modified products of alkylene oxide modified phosphazene, etc.

[0024] These photopolymerizable compounds may be used individually or in combination. The type and amount of photopolymerizable compounds can be determined according to the characteristics of the cured film.

[0025] The content of the photopolymerizable compound in the curable composition is preferably 10% by mass or more and 55% by mass or less based on the total mass of the curable composition. The content of the photopolymerizable compound includes the content of the photo / thermosetting compound described later. The higher the content of the photopolymerizable compound, the higher the accuracy of the pattern can be. On the other hand, the lower the content of the photopolymerizable compound, the higher the heat resistance and mechanical strength of the cured film can be. The content of the photopolymerizable compound is more preferably 15% by mass or more and 50% by mass or less, and even more preferably 18% by mass or more and 45% by mass or less.

[0026] 1-2. Photopolymerization Initiators The photopolymerization initiator may include a photoradical polymerization initiator, a photocationic polymerization initiator, or both. When the curable composition contains a radical polymerizable compound as the photopolymerizable compound, it is preferable to include a photoradical polymerization initiator as the photopolymerization initiator. When the curable composition contains a cationic polymerizable compound as the photopolymerizable compound, it is preferable to include a photocationic polymerization initiator as the photopolymerization initiator.

[0027] Photo-radical polymerization initiators are compounds that generate radicals upon irradiation with light, thereby initiating the polymerization and crosslinking of radical-polymerizable compounds.

[0028] Examples of photoradical polymerization initiators include benzoin compounds, alkylphenone compounds, acetophenone compounds, aminoacetophenone compounds, anthraquinone compounds, thioxanthone compounds, ketal compounds, acylphosphine oxide compounds, oxime ester compounds, and titanocene compounds.

[0029] Examples of benzoin compounds include benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether.

[0030] Examples of alkylphenone compounds include 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl-phenylketone, 2-hydroxy-2-methyl-1-phenylpropanone, 1-[4-(2-hydroxyethoxyl)-phenyl]-2-hydroxy-methylpropanone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropane-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, and 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, etc.

[0031] Examples of acetophenone compounds include acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, and 1,1-dichloroacetophenone, etc.

[0032] Examples of aminoacetophenone compounds include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, and N,N-dimethylaminoacetophenone, etc.

[0033] Examples of anthraquinone compounds include 2-methylanthraquinone, 2-ethylanthraquinone, and 2-t-butylanthraquinone, etc.

[0034] Examples of thioxanthone compounds include 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone, etc.

[0035] Examples of the ketal compounds include acetophenone dimethyl ketal, benzyldimethyl ketal, and the like.

[0036] Examples of the acylphosphine oxide compounds include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and the like.

[0037] Examples of the oxime ester compounds include 1,2-octanedione, 1-[4-(phenylthio)-2-(o-benzoyloxime)], and the like. Further, ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(o-acetyloxime), and the like are included. <00001​​​​​​​​​​​​​​​​​​​​​​​３ SO ３ － This includes salts, sulfonates that generate sulfonic acid, halides that photocatalyze hydrogen halides, and iron allene complexes.

[0041] The content of the photocationic polymerization initiator in the curable composition can be 1% by mass or more and 10% by mass or less based on the total mass of the cationic polymerizable compound.

[0042] 1-3. Photosensitizers: Photosensitizers absorb light of a different wavelength than the excitation wavelength of the photopolymerization initiator and propagate the energy from the absorbed light to the photopolymerization initiator. This allows the photosensitizer to increase the curing rate of the curable composition and to allow the photopolymerizable compound to react sufficiently even in deeper layers (on the substrate side). As a result, the photosensitizer can improve the adhesion and surface hardness of the cured film.

[0043] Examples of photosensitizers include amines such as triethanolamine, methyldiethanolamine, triisopropanolamine, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, (2-dimethylamino)ethyl benzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, and 2-ethylhexyl 4-dimethylaminobenzoate, as well as cyanines, phthalocyanines, merocyanines, porphyrins, spiro compounds, ferrocene, fluorene, fluged, imidazole, perylene, phenazine, and phenothiazine. This includes compounds such as polyenes, azo compounds, diphenylmethane, triphenylmethane, polymethine acridine, coumarin, ketocoumarin, quinacridone, indigo, styryl, pyrylium compounds, pyrometene compounds, pyrazolotriazole compounds, benzothiazole compounds, barbiturate derivatives, and thiobarbiturate derivatives, as well as compounds described in European Patent No. 568993, U.S. Patent No. 4508811, U.S. Patent No. 5227227, Japanese Patent Publication No. 2001-125255, and Japanese Patent Publication No. 11-271969, etc.

[0044] The amount of photosensitizer in the curable composition can be 0.01% by mass or more and 10% by mass or less, based on the total mass of the curable composition.

[0045] 1-4. Thermosetting Compounds Thermosetting compounds are compounds that polymerize or crosslink upon heating in the presence of a thermosetting agent or thermosetting accelerator. Thermosetting compounds enhance the heat resistance and mechanical strength of the cured film.

[0046] The thermosetting compound can be a known compound, such as a compound having an epoxy group.

[0047] Examples of thermosetting compounds having epoxy groups include bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, biphenyl type epoxy resins, aliphatic type epoxy resins, and glycidylamine type epoxy resins. Of these, epoxy resins having aromatic rings are preferred from the viewpoint of improving the heat resistance, insulation, mechanical strength, and thermal expansion coefficient of the cured film. More specifically, bisphenol type epoxy resins, phenol novolac type epoxy resins, and cresol novolac type epoxy resins are preferred.

[0048] Furthermore, thermosetting compounds may include compounds that do not have epoxy groups. Examples of thermosetting compounds that do not have epoxy groups include phenolic resins, unsaturated polyesters, cyanate esters, urea resins, and diallyl phthalates.

[0049] The content of the thermosetting compound in the curable composition is preferably 10% by mass or more and 70% by mass or less based on the total mass of the curable composition. The higher the content of the thermosetting compound, the higher the heat resistance and mechanical strength of the cured film can be. The content of the thermosetting compound is more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 40% by mass or less.

[0050] 1-5. Thermosetting Agents A thermosetting agent is a compound that promotes the curing of a composition by a thermosetting compound by reacting with epoxy groups, etc., that have been present in the thermosetting compound, thereby crosslinking the thermosetting compounds together.

[0051] The thermosetting agent can be a known compound such as an acid anhydride, amine compound, modified polyamine compound, phenol compound, and isocyanate compound.

[0052] Examples of acid anhydrides used as thermosetting agents include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, methylnadic anhydride, dodecyl succinic anhydride, chlorendic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, methylcyclohexenetetracarboxylic anhydride, trimellitic anhydride, and polyazelaic anhydride.

[0053] Examples of amine compounds used as thermosetting agents include aliphatic amines, alicyclic amines, aromatic amines, hydrazides, and guanidine derivatives.

[0054] Examples of modified polyamine compounds used as thermosetting agents include epoxy compound-added polyamines (reaction products of epoxy compounds and polyamines), Michael-added polyamines (reaction products of α,β unsaturated ketones and polyamines), Mannich-added polyamines (condensates of polyamines with formalin and phenol), thiourea-added polyamines (reaction products of thiourea and polyamines), and ketone-blocked polyamines (reaction products of ketone compounds and polyamines).

[0055] Examples of phenol compounds used as thermosetting agents include polyhydric phenols such as bis(4-hydroxyphenyl)-2,2-propane, 4,4′-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-tert-butyl-phenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, and 1,5-dihydroxynaphthalene, as well as polyfunctional phenols such as phenol novolac resins, bisphenol novolac resins, and cresol novolac resins.

[0056] Examples of isocyanate compounds used as thermosetting agents include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, phenylene diisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate, phenyl isocyanate, 2-methacryloyloxyethyl isocyanate, 2-acryloyloxyethyl isocyanate, and 1,1-bis(acryloyloxymethyl)ethyl isocyanate. From the viewpoint of improving the storage stability of the composition, these isocyanates are preferably so-called blocked isocyanates, which are protected by a blocking group.

[0057] Examples of the blocking agents mentioned above include carboxylic acid esters, active methylene compounds, oxime compounds, monohydric alcohols or their isomers, glycol derivatives, phenols or their isomers, hydroxyl group-containing esters, amine compounds, alcoholamines, lactams, mercaptans, imidazoles, acid amides, acid imides, and urea compounds.

[0058] The amount of thermosetting agent in the curable composition is preferably 0.1 equivalents or more and 1.5 equivalents or less in terms of equivalent ratio to the epoxy equivalent of the thermosetting compound, and more preferably 0.8 equivalents or more and 1.2 equivalents or less.

[0059] 1-6. Thermosetting accelerators Thermosetting accelerators are catalysts that adjust the curing rate without reacting with the thermosetting composition.

[0060] The thermosetting accelerator can be a known compound such as tertiary amines and their salts, imidazole derivatives, phosphine compounds and phosphonium hydrochloride anhydride, amine compounds, modified polyamine compounds, and phenol compounds. Of these, tertiary amines or their salts and imidazole derivatives are preferred due to their high solubility, reactivity, and latent properties in the composition.

[0061] Examples of tertiary amines and their salts include 1,8-diazabicyclo(5,4,0)-undecene-7 (DBU) and its organic acid salts, 1,5-diazabicyclo(4,3,0)-nonene-5 (DBN) and its organic acid salts, 2,4,6-tris(dimethylaminomethyl)phenol, piperidine, N,N-dimethylpiperazine, triethylenediamine, benzyldimethylamine, and 2-(dimethylaminomethyl)phenol. Examples of the above organic acids include 2-ethylhexanoic acid, phenol, formic acid, o-phthalic acid, and p-toluenesulfonic acid.

[0062] Examples of imidazole derivatives include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-phenylimidazole, 6-(2-(2-undecyl-1H-imidazole-1-yl)ethyl)-1,3,5-triazine-2,4-diamine, 6-[2-(2-methyl-1H-imidazole-1-yl)ethyl]-1,3,5-triazine-2,4-diamine, and 1-cyanoethyl-2-ethyl-4-methylimidazole.

[0063] Examples of phosphine compounds and phosphonium salts include tributylphosphine, triphenylphosphine, benzyltriphenylphosphonium bromide, ethyltriphenylphosphonium methanesulfonate, tetraphenylphosphonium tetraphenylborate, and tetra-n-butylphosphonium tetraphenylborate.

[0064] The content of the thermosetting accelerator in the curable composition is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 2.0% by mass or less, based on the total mass of the thermosetting compound. Note that the total mass of the thermosetting compound includes the mass of the photo / thermosetting compound.

[0065] 1-7. Photo- / thermosetting compound curable compositions may contain compounds that react and cure the composition by either light irradiation or heating (hereinafter also simply referred to as "photo- / thermosetting compounds").

[0066] Photopolymerizable / thermosetting compounds can react with both photopolymerizable and thermosetting compounds. Therefore, photopolymerizable / thermosetting compounds can bond these polymers together, thereby increasing the toughness, mechanical strength, reducing delamination, and improving heat resistance of the cured product.

[0067] Photo- and thermosetting compounds can be compounds that contain both a vinyl group that reacts upon light irradiation and an epoxy group that reacts upon heating within their molecules. Preferably, photo- and thermosetting compounds are compounds that contain both a (meth)acryloyl group and a glycidyl group within their molecules.

[0068] Examples of compounds containing both a (meth)acryloyl group and a glycidyl group within their molecule include glycidyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether.

[0069] The photo- / thermosetting compound may be a partial (meth)acrylic compound of an epoxy compound or a urethane-modified (meth)acrylic epoxy compound. Examples of partial (meth)acrylic compounds of epoxy compounds include compounds obtained by reacting some of the epoxy groups of novolac-type epoxy compounds and bisphenol-type epoxy compounds with (meth)acrylic acid.

[0070] The content of the photo / thermosetting compound in the curable composition is preferably 0.5% by mass or more and 30% by mass or less, based on the total mass of the curable composition. The higher the content of the photo / thermosetting compound, the more pronounced the above-mentioned effect of the photo / thermosetting compound becomes. By limiting the content of the photo / thermosetting compound to 30% by mass or less, the cured film can be made harder and its heat resistance can be improved. More preferably, the content of the above-mentioned photo / thermosetting compound is 1% by mass or more and 30% by mass or less.

[0071] 1-8. Elastomers Elastomers are materials in which, in a cured film obtained by curing a curable composition, photopolymerizable compounds and thermosetting compounds are important and exist as dispersed elastomers, separated from the cured resin components.

[0072] In a laminated film formed by stacking pre-cured films cured by light irradiation, the first layer formed (closer to the substrate) receives a greater amount of accumulated light and exhibits a greater degree of curing shrinkage. Conversely, later layers formed (further from the substrate) receive less accumulated light and exhibit a smaller degree of curing shrinkage. Due to this difference in curing shrinkage, the laminated film and the cured film obtained by heat curing it are thought to have different residual stresses between layers. This difference in residual stress tends to result in insufficient adhesive strength at the laminated interface of the cured film. Therefore, the cured film is prone to delamination at the laminated interface.

[0073] In contrast, elastomers present as dispersed elements within the cured film tend to absorb stress within the film, thereby increasing the adhesive strength at the laminated interface. Therefore, cured films containing elastomers are less prone to delamination at the laminated interface.

[0074] Furthermore, cured films formed by light irradiation and heat curing are prone to cracking and delamination when subjected to repeated temperature changes, especially when the film thickness is increased or the glass transition temperature is raised. In contrast, cured films containing elastomers tend to have higher adhesive strength at the lamination interface, making them less susceptible to cracking and delamination due to the aforementioned temperature changes.

[0075] Furthermore, cured films formed by light irradiation and thermal curing tend to lose their insulating properties after moist heat storage, especially when the film thickness is increased. This is thought to be because the thicker the film thickness, the greater the shrinkage stress during thermal curing, making it easier for cracks and voids to occur in the cured film due to shrinkage. In contrast, elastomers that exist in a dispersed state in the pre-cured film during thermal curing are less likely to develop cracks and voids during thermal curing, and their insulating properties do not tend to decrease after thermal storage.

[0076] Elastomer materials may exist in a dissolved state in the ink, or in a dispersed state where polymer particles are dispersed as particulate matter. Elastomer materials that exist in a dissolved state in the ink but become dispersed after curing are less likely to reduce the ink ejection stability from the inkjet head and are less likely to generate satellites, etc. Elastomer materials that exist in a dispersed state in the ink are less likely to increase the viscosity of the ink and are less likely to reduce ejection stability, especially when ejecting ink at high frequencies.

[0077] Examples of elastomeric materials that exist in a dissolved state in ink but become dispersed after curing include materials that undergo phase separation by reaction-induced phase separation. Reaction-induced phase separation is a mechanism in which the polymerization reaction of a photocurable or thermosetting compound increases the free energy of mixing with the elastomer, thereby inducing phase separation. Examples of materials that undergo phase separation by reaction-induced phase separation include block copolymers with controlled compatibility balance with the cured polymer.

[0078] The elastomeric material present in a dispersed state preferably has an average particle diameter of 1 μm or less, and more preferably 300 nm or less. By setting the average particle diameter to 1 μm or less, it is possible to suppress the decrease in ejection stability from the inkjet head caused by the dispersed elastomeric material. The lower limit of the particle diameter of the elastomeric material is not particularly limited, but it is preferably 50 nm or more from the perspective of manufacturing stability of dispersed particles. In this specification, the average particle diameter of the elastomeric material dispersed in the ink is measured by dynamic light scattering and represents the particle diameter at 50% of the cumulative value in the particle size distribution based on volume. The average particle diameter can be measured, for example, by a laser scattering diffraction particle size distribution analyzer: Zetasizer Nano S90 (manufactured by Malvern).

[0079] Examples of elastomeric materials that exist in a dispersed state include styrene-butadiene rubber, butadiene rubber, isoprene rubber, acrylic rubber, chloroprene rubber, acrylonitrile-butadiene rubber, butyl rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, urethane rubber, silicone rubber, chlorosulfonated polyethylene rubber, epichlorohydrin rubber, and fluororubber.

[0080] The elastomeric material in a dispersed state is preferably a core-shell type dispersed particle in which a rubbery polymer is used for the core portion and a different polymer is used for the shell portion. By covering the rubbery core portion with the shell portion, aggregation and dissolution of the rubber layer into the photopolymerizable compound, thermosetting compound portion, and polymer formed by the polymerization of these can be suppressed. As a result, the dispersion state of the elastomeric material is kept stable in the ink or cured film, the viscosity of the ink does not increase easily, and the effects of the elastomer described above are well expressed.

[0081] The content of the elastomeric material in the curable composition is preferably 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the curable composition. The higher the content of the elastomeric material, the more pronounced the above-mentioned effect by the elastomer in the cured film. By setting the content of the elastomeric material to 0.3% by mass or less, the cured film can be made harder and its heat resistance can be improved. The content of the above-mentioned photo / thermosetting compound is more preferably 1.0% by mass or more and 10.0% by mass or less.

[0082] 1-9. Fillers increase the mechanical strength of the cured film. In particular, fillers can reduce the coefficient of thermal expansion of the cured film, thereby improving its heat resistance.

[0083] On the other hand, according to the inventors' new findings, fillers are prone to cracking during thermal curing, and can reduce the adhesive strength at the lamination interface, making the cured film more susceptible to delamination. Therefore, when producing a cured film using a curable composition containing fillers, adjusting the physical properties of the pre-cured film to the above-mentioned range has a significant effect in reducing the likelihood of cracking and delamination.

[0084] The type of filler is not particularly limited. Examples of fillers include particles of silica, alumina, titanium oxide, aluminum hydroxide, zinc oxide, zirconium oxide, magnesium oxide, mica, bismuth oxychloride, talc, kaolin, barium sulfate, anhydrous silicic acid, calcium carbonate, magnesium carbonate, magnesium silicate, aluminum silicate, magnesium aluminum silicate, silicon carbide, silicon nitride, boron nitride, glass powder, metal oxides, and metals. Fillers may be hollow or solid particles.

[0085] The average particle size of the filler is preferably 0.1 μm or more and 2 μm or less, and more preferably 0.1 μm or more and 1 μm or less. Furthermore, the maximum particle size of the filler is preferably 2 μm or less. If the average particle size of the filler is 0.1 μm or more, the viscosity of the curable composition (or the composition that forms its material) is less likely to become high. Furthermore, if the average particle size and maximum particle size of the filler are 2 μm or less, ejection from the nozzle of the inkjet head is easy. Furthermore, if the average particle size and maximum particle size of the filler are 2 μm or less, filler sedimentation in the composition is less likely to occur.

[0086] In this specification, the average particle diameter of the filler is the particle diameter at 50% of the cumulative value in the volume-based particle size distribution, measured by laser diffraction / scattering. The average particle diameter can be the value measured by, for example, a laser scattering diffraction particle size distribution analyzer (Malvern, Zetasizer Nano S90).

[0087] The filler is preferably surface-treated, and more preferably surface-treated with a silane coupling material. In particular, when the filler is silica particles, surface treatment (especially surface treatment with a silane coupling material) is preferred. Surface-treated fillers have their surface functional groups sealed by the surface treatment agent (silanol groups in the case of a silane coupling material), making interparticle interactions less likely to occur in the composition. This facilitates ejection from the nozzle of the inkjet head when applying the composition by inkjet method. Furthermore, this makes aggregation less likely in the curable composition.

[0088] The filler content in the curable composition is preferably 3% by mass or more and 40% by mass or less based on the total mass of the curable composition. The higher the filler content, the higher the mechanical strength and heat resistance of the cured film can be. The filler content is more preferably 5% by mass or more and 30% by mass or less.

[0089] 1-10. Other components of the curable composition may include water, organic solvents, bonding aids such as coupling agents, pigments, dyes, leveling agents, defoamers, and polymerization inhibitors.

[0090] Furthermore, the photopolymerizable compounds and some thermosetting compounds mentioned above are themselves liquids and can act as reactive diluents. Therefore, the water content in the curable composition is preferably 0% to 1% by mass, more preferably 0% to 0.5% by mass, and even more preferably 0% to 0.2% by mass, based on the total mass of the curable composition. In addition, the water content in the curable composition is preferably 0% to 5% by mass, more preferably 0% to 1% by mass, and even more preferably 0% to 0.5% by mass, based on the total mass of the curable composition.

[0091] 1-11. Physical Properties The curable composition (when it is a two-component composition, each of composition A, composition B, etc.) preferably has a viscosity of 5 mPa·s or more and 100 mPa·s or less at the temperature during application. The lower the viscosity at the temperature during application, the easier it is to follow the irregularities of the substrate or the surface of the curable composition that has already been applied and irradiated with light, and the less likely it is to cause voids in the cured film due to the irregularities. In addition, the lower the viscosity at the temperature during application, the easier it is to apply by inkjet method, and the accuracy of the pattern can be improved. The viscosity of the curable composition at the temperature during application is more preferably 5 mPa·s or more and 30 mPa·s or less, even more preferably 5 mPa·s or more and 10 mPa·s or less, and particularly preferably 5 mPa·s or more and 10 mPa·s or less.

[0092] 1-12. One-component and multi-component compositions The curable composition may be a one-component ink containing the above-described components. Alternatively, the curable composition may be an ink set of two-component (or multi-component) inks, comprising ink A containing any of the above-described components and ink B (and further inks C, D, etc.) containing any of the others. The two-component or multi-component inks may be applied separately to the substrate and combined on the substrate, or they may be combined before being applied to the substrate (for example, before being introduced into the ink tank of an inkjet device).

[0093] Preferably, the multi-component ink comprises a first ink containing a compound having a (meth)acryloyl group but not a compound having an epoxy group, and a second inkjet ink containing both a compound having a (meth)acryloyl group and a compound having an epoxy group. By using such a combination of the first and second inkjet inks, the pot life of each ink can be extended.

[0094] In two-component or multi-component inks, the elastomer material only needs to be included in at least one of the inks. From the viewpoint of minimizing variations in the particle size of the elastomer material and improving the storage stability of the ink, it is preferable that the elastomer material be included in the second inkjet ink.

[0095] Furthermore, in multi-component compositions, it is preferable to include the thermosetting accelerator and the thermosetting compound in separate compositions. This prevents the thermosetting compound from reacting during storage of the composition, thereby extending the pot life of the composition.

[0096] Specifically, the multi-component composition is preferably a plurality of compositions comprising composition A containing the above-mentioned thermosetting agent or thermosetting accelerator, and composition B containing the above-mentioned thermosetting compound (particularly a compound having an epoxy group). In this case, it is preferable that composition B does not contain the thermosetting accelerator. Composition B may or may not contain the thermosetting agent. Furthermore, it is preferable that composition A does not contain the above-mentioned thermosetting compound (particularly a compound having an epoxy group), or that the content of the above-mentioned thermosetting compound (particularly a compound having an epoxy group) is less than that of composition B. This makes it possible to suppress the decrease in pot life due to the reaction of the thermosetting compound during storage of composition B.

[0097] Similarly, a photopolymerization initiator and a photopolymerizable compound may be included in a separate composition. In this case, the multi-component composition is preferably a plurality of compositions comprising composition A containing the above-mentioned photopolymerization initiator and composition B containing the above-mentioned photopolymerizable compound (particularly a compound having a (meth)acryloyl group). In this case, composition B shall not contain the photopolymerization initiator or shall contain less of the photopolymerization initiator than composition A. Furthermore, it is preferable that composition A shall not contain the photopolymerizable compound (particularly a compound having a (meth)acryloyl group) or shall contain less of the photopolymerizable compound (particularly a compound having a (meth)acryloyl group) than composition B.

[0098] These compositions can be prepared by mixing the components described above. Heating may be applied during the mixing process.

[0099] 2. Method for producing a cured film The curable composition described above can be used to produce a cured film by applying it to a substrate using an inkjet method, followed by light irradiation and thermal curing.

[0100] The type of substrate is not particularly limited and should be selected according to the application of the cured film. For example, printed circuit boards (PCBs) made by etching copper from a copper plate or copper-clad laminate to form wiring, as well as aluminum substrates, ceramic substrates, and flexible substrates based on plastic film can be used as substrates.

[0101] The curable composition only needs to be applied to the surface of the substrate (or the surface of a curable composition that has already been irradiated with light) when light is irradiated. As described above, a one-component curable composition containing the above-mentioned components may be applied. Alternatively, a composition A containing any of the above-mentioned components and a composition B (and further, compositions C, D, etc.) containing any of the others may be applied separately to prepare a mixture of these, and a curable composition containing the above-mentioned components may be prepared on the surface.

[0102] When forming a thick cured film, the process of applying the curable composition to the substrate and then irradiating the applied curable composition with light to form a pre-cured film is repeated multiple times. Specifically, the curable composition is applied to the surface of the substrate (or the surface of a curable composition that has already been irradiated with light). Then, the applied curable composition is irradiated with light. By repeatedly applying the curable composition and irradiating with light, a pre-cured film with a thickness corresponding to the thickness of the cured film to be formed is created.

[0103] Light irradiation should be carried out under conditions that allow the photopolymerizable compounds contained in the curable composition to polymerize and crosslink. The light used for irradiation is not particularly limited, and ultraviolet light and electron beams can be used. Of these, ultraviolet light, particularly ultraviolet light having a peak wavelength of 360 nm to 410 nm, is preferred.

[0104] The illuminance of the light being emitted is 50 W / cm². ２ More than 4000W / cm ２ Preferably, it is 300 W / cm². ２ More than 3000W / cm ２ It is more preferable that the following conditions are met: Illuminance of 50 W / cm² ２ As described above, the photopolymerizable compound can be sufficiently polymerized and crosslinked, effectively suppressing bleeding. Furthermore, higher illuminance allows the photopolymerizable compound to react more thoroughly, making it easier to raise the glass transition temperature (Tg) of the cured film. Moreover, higher illuminance shortens the irradiation time required to reach the necessary light level, thus increasing productivity.

[0105] The light intensity per irradiation is 100 mJ / cm². ２ More than 4000mJ / cm ２Preferably, it is 300 mJ / cm². ２ More than 3000mJ / cm ２ The following is more preferable: Light intensity of 100 mJ / cm ２ As described above, the photopolymerizable compound can be sufficiently polymerized and crosslinked, effectively suppressing bleeding. Furthermore, higher illuminance allows the photopolymerizable compound to react more thoroughly, making it easier to raise the glass transition temperature (Tg) of the cured film.

[0106] Subsequently, the formed pre-cured film is heat-cured.

[0107] The conditions for thermal curing are not particularly limited and can be determined according to the composition of the curable composition. For example, it may be carried out at a temperature of 120°C to 250°C for a period of 10 minutes to 5 hours. Alternatively, pre-baking at a lower temperature (around 80°C) may be performed before thermal curing.

[0108] 3. Cured Film A cured film can be produced by curing the curable composition using the method described above. The cured film has a structure in which an elastomer is dispersed in a resin phase formed by polymerization and crosslinking of a photopolymerizable compound (a compound having a (meth)acryloyl group) and a thermosetting compound (a compound having an epoxy group).

[0109] The smaller the size of the phase-separated and dispersed elastomer, the more likely it is to exhibit the aforementioned effects due to stress relaxation. Specifically, the size of the elastomer is preferably 1 μm or less in terms of the diameter as a sphere, more preferably 300 nm or less, and even more preferably 200 nm or less. There is no particular lower limit to the size of the elastomer, but from the viewpoint of forming a stable phase-separated state, it is preferably 30 nm or more.

[0110] The presence or absence of phase-separated elastomers, as well as their size, can be confirmed by electron microscopy or atomic force microscopy (AFM) observation of hardened film sections.

[0111] In the method described above, even when a cured film is formed with a thick film thickness, delamination at the lamination interface is less likely to occur, cracks and film peeling when subjected to repeated temperature changes are less likely to occur, and the insulating properties do not deteriorate easily after storage in moist heat. Therefore, a thick cured film can be efficiently formed. For example, even if the film thickness of the cured film is 50 μm or more, a cured film in which the above problems are less likely to occur can be formed. The film thickness of the cured film can be adjusted by the amount of curable composition applied each time, the number of times application and light irradiation are repeated, etc. The film thickness of the cured film is preferably 50 μm to 1000 μm.

[0112] In the method described above, thermosetting compounds can be sufficiently reacted with each other to form a crosslinked structure, thus enabling the formation of a cured film with a high Tg and high heat resistance. The Tg of the cured film is preferably 120°C to 300°C, more preferably 125°C to 250°C, and even more preferably 130°C to 200°C. The Tg of the cured film can be adjusted by the materials of the thermosetting compound and the photopolymerizable compound, and the conditions for forming the pre-cured film.

[0113] The cured film formed by the method described above can be used in insulating materials (especially insulating protective films for printed circuit boards), electronic components sealed with the cured film, etc. In particular, even when the cured film is formed to be thick, delamination at the lamination interface is less likely to occur, and temperature changes due to temperature fluctuations, film peeling, and deterioration of insulating properties after storage in humid heat are less likely to occur. Therefore, it can be suitably used as an insulating film between wiring in thick copper PCBs where a thick cured film is required. The cured film may be used as a planarizing film for the inner layer thick copper circuits of a thick copper PCB, or as an insulating protective film (solder resist) for the outer layer copper wiring.

[0114] For example, wiring boards used in electronic components for power electronics are expected to carry large currents through the wiring. Therefore, thick copper substrates such as 140 μm or more, 210 μm or more, or 300 μm or more are used. The cured film used on such substrates also needs to be thicker than the cured film formed on ordinary copper substrates. The cured film according to this embodiment is particularly suitable for these applications because, even when formed to a thick film, delamination at the lamination interface is less likely to occur, and temperature changes, film peeling, and deterioration of insulation after storage in humid heat are less likely to occur.

[0115] The printed circuit board having a cured film according to this embodiment can be used in various electronic devices. Examples of such electronic devices include information devices such as mobile phones, personal computers, and smartphones; household appliances such as refrigerators, washing machines, and microwave ovens; medical devices; and industrial robots.

[0116] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to the examples.

[0117] 1. Preparation of Curable Compositions The following materials were mixed and filtered through a 3 μm membrane filter of ADVANTEC Teflon ("Teflon" is a registered trademark of Zakemars Company) to obtain inks A1 to A3 and inks B1 to B11. The viscosity of inks A and B was determined in advance by checking the relationship between temperature and viscosity using a rheometer "MCR302" (manufactured by Anton Paar Corporation), and heating was controlled so that the viscosity of the ink in the ink tank and inkjet head was in the range of 5 to 100 mPa·s.

[0118] • Epoxy compounds (thermosetting compounds) Bisphenol A type epoxy resin (EP-4300E, manufactured by ADEKA Corporation) • Thermosetting agents Acid anhydride-based thermosetting agents (YH306 (methylbutenyltetrahydrophthalic anhydride), manufactured by Mitsubishi Chemical Corporation) Amine-based thermosetting agents (Fujicure 7002, manufactured by T&K TOKA Corporation) • Thermosetting accelerators Imidazole compounds (2PZ-CN (1-cyanoethyl-2-ethylimidazole), manufactured by Shikoku Chemicals, Inc.) • Compounds having glycidyl groups and (meth)acryloyl groups (photo- / thermosetting compounds) 4-hydroxybutyl acrylate glycidyl ether (4HBAGE, manufactured by Mitsubishi Chemical Corporation) • Compounds having (meth)acryloyl groups (photopolymerizable compounds) A1: Dipropylene glycol diacrylate (M222, manufactured by Miwon) A2: Acryloylmorpholin (ACMO, manufactured by Kj Chemicals Co., Ltd.) - Photopolymerization initiator IGM Resins Omnirad 819 (phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide) - Elastomer materials E1: PMMA-PBA-PMMA block copolymer (Nanostrength M22, manufactured by ARKEMA) E2: PMMA-PBA block copolymer (Nanostrength D51N, manufactured by ARKEMA) E1: PMMA-PBA-PMMA block copolymer (Nanostrength M65N, manufactured by ARKEMA) E4: 1,E5: Homopolymer of 2-butadiene (Nippon Soda Co., Ltd., Nisso-PB B-1000) E6: Silicone-based core-shell particles dispersed in bisphenol A type epoxy resin (core-shell particle content: 25% by mass) (Kaneka Corporation, Kaneace MX-962) E7: Polybutadiene-based core-shell particles dispersed in bisphenol A type epoxy resin (core-shell particle content: 40% by mass) (Kaneka Corporation, Kaneace MX-150) E8: Acrylic core-shell particles (core-shell particle content: 100% by mass) (Mitsubishi Chemical Corporation, Metabren W450A) E9: Acrylic particles (particle content: 100% by mass) (Soken Chemical Co., Ltd., MX-30BD) Filler S1: Silica particles surface-treated with a silane coupling agent, prepared by the method described below (Admatex Co., Ltd., 5SP-C3) S2: Untreated silica particles (AdmaFineSO-C2, manufactured by Admatex Co., Ltd.)

[0119] Furthermore, elastomer materials E1 to E4 are materials that are dissolved in the ink but become dispersed after curing. Also, elastomer materials E1 to E4 are materials that are dispersed in particulate form in the ink.

[0120] (Method for preparing silica particles S1) 1 g of trimethoxyphenylsilane was added to 200 mL of ethanol and dissolved. 40 g of silica particles (AdmafineSO-C2, manufactured by Admatex Co., Ltd.) were added to the solution while stirring. This mixture was stirred at room temperature for 12 hours. After washing with ethanol, the silica particles were centrifuged and dried to obtain surface-treated silica.

[0121] The compositions of inks A1 to A3 are shown in Table 1, and the compositions of inks B1 to B11 are shown in Tables 2 and 3, respectively. The units of the numerical values ​​for each material shown in Tables 1 to 3 are parts by mass.

[0122]

[0123]

[0124]

[0125] 2. As a substrate for fabricating the cured film, a copper foil laminate substrate was prepared by laminating 35 μm thick copper foil on both sides of a 1.6 mm thick FR-4 (Flame Retardant Type 4, glass epoxy substrate).

[0126] Using the apparatus whose schematic configuration is shown in Figure 1, one of inks A1 to A3 and one of inks B1 to B11 were applied to the substrate. Furthermore, the applied curable inks were irradiated with light.

[0127] Both inkjet heads 112 and 114 were Konica Minolta KM1024i series (nozzle pitch 360 npi, 1024 nozzles, standard droplet size 30 pL, built-in heater). Ink was supplied from ink tanks (not shown) connected to each inkjet head and applied to the substrate. The flow path, including the ink tanks, was controlled by back pressure control to ensure that an appropriate meniscus was formed at the nozzles of the inkjet heads. The amount of ink applied to the substrate was controlled by the voltage applied to each inkjet head, the droplet volume controlled by drop gradation, the resolution (dpi) of the dots formed on the substrate, and the number of scans.

[0128] Light sources 122 and 124 were placed on either side of the carriage 110. Both light sources 122 and 124 used UV-LED irradiators manufactured by Phoseon Technology, which utilize 395 nm UV-LEDs.

[0129] The distance between inkjet head 112 and inkjet head 114 was 4 cm, and the distance between each inkjet head and each light source was 10 cm.

[0130] On the printer stage 100, the carriage 110 and the substrate 200 were moved so that the carriage 110 scanned the substrate 200 in both directions. Then, one of inks A1 to A3 was ejected from the inkjet head 112, and one of inks B1 to B11 was ejected from the inkjet head 114. The liquid volume ratios of each ink were as shown in Tables 4 and 5 (by mass).

[0131] After each inkjet head ejected ink, it was UV exposed from a following light source for each back-and-forth scan. The UV exposure conditions were an exposure intensity of 2000 mW / m². ２ , the cumulative light intensity is 2000 mJ / cm² ２ That's what I decided.

[0132] In this manner, a rectangular pre-cured film measuring 1 cm wide x 4 cm long, and a linear pre-cured film with a target width of 1 mm, formed parallel to the rectangular film in the longitudinal direction, were created. Both of these pre-cured films were formed so that the longitudinal direction was the scanning direction of the inkjet head. Furthermore, by adjusting the resolution and the number of scans, each pre-cured film was manufactured so that the thickness of the cured film was ±10 μm of the thickness to be formed (listed in Tables 4 and 5).

[0133] The obtained pre-cured film was heated at 80°C for 1 hour, and then heated at 170°C for 2 hours to form a hardened film.

[0134] Furthermore, a rectangular cured film for measuring the glass dislocation temperature was formed in the same manner, except that the substrate was changed to a Teflon substrate in order to allow the cured film to be peeled off.

[0135] Furthermore, the substrate was changed to one in which 35 μm thick copper wiring was patterned in a comb-like manner so that the line / space width (L / S) was 1 mm / 1 mm. Except for adjusting the coating thickness so that it was 50 μm in the space areas and 15 μm on the copper wiring, a cured film for evaluating insulation performance was formed in the same manner as before.

[0136] 3. Evaluation and Measurement of Cured Film 3-1. Measurement of Elastomer Particle Size The cured film was cut in the thickness direction, and the mechanical properties of the cross-section were mapped using an atomic force microscope (AFM). Then, the diameter of the elastomer was determined by approximating the image of the area where the phase-separated elastomer could be confirmed with a circle. The atomic force microscope used was a BRUKER DIMENSION iCON.

[0137] The particle size of the elastomer in the ink was measured using a dynamic light scattering particle size analyzer "Zetasizer Nano S90" (Malvern Corporation) for inks containing all materials except silica particles. The final ink with added silica particles was also measured similarly, and it was confirmed that no new peaks due to elastomer aggregation were detected. Ink B4 and the cured film 4 prepared using it did not show any dissolved or dispersed elastomer material E4.

[0138] 3-2. Measurement of Glass Transition Temperature A rectangular pattern (cured film) formed on a Teflon substrate was peeled off the substrate, and the glass transition temperature (Tg) of the cured film was measured using a thermal analyzer (SII TMA / SS7100) manufactured by Hitachi High-Tech Solutions Co., Ltd. under the following measurement conditions. <Measurement Conditions> Starting temperature for heating: 30°C Ending temperature for heating: 250°C Heating rate: 10°C / min Atmosphere: Under nitrogen

[0139] 3-3. Measurement of Heat Cycle Resistance The hardened film formed on the copper foil laminate substrate was evaluated using a thermal shock device (ESPEC TSE-11) by repeatedly performing cycles of high-temperature exposure at 125°C for 30 minutes and low-temperature exposure at -50°C for 30 minutes. The number of cycles until cracks or delamination occurred was determined according to the following criteria. Criteria "A", "B", and "C" below are considered to be without practical problems. A: No cracks or delamination occurred even after 3000 cycles or more B: Cracks or delamination occurred between 1000 and 3000 cycles C: Cracks or delamination occurred between 100 and 1000 cycles D: Cracks or delamination occurred in less than 100 cycles

[0140] 3-4. Evaluation of Peel Strength Each cured film formed on a copper foil laminated substrate was stored for 100 hours at a temperature of 85°C and a relative humidity of 85%. After that, a grid pattern of cuts was made according to the cross-cut method of JIS K5600-5-6:1999, and adhesive tape was applied to the cut areas and peeled off. The peel state of the cured film after peeling was observed, and the ratio of the number of squares remaining after tape removal to the number of squares created by the cuts (adhesion retention rate) was determined. Based on the obtained adhesion retention rate, the peel strength of the cured film obtained from each ink was evaluated according to the following criteria. Note that for cured films in which peeling was observed, there was no peeling at the interface between the copper foil laminated substrate and the cured film, and it is thought that the peeling occurred at the lamination interface of the cured film. Criteria "A" and "B" below are considered to be without practical problems. A: Adhesion and residue rate of 95% or more B: Adhesion and residue rate of 90% or more but less than 95% C: Adhesion and residue rate of less than 90%

[0141] 3-5. Evaluation of Insulation Performance (Ion Migration Resistance) Using a substrate on which a cured film for evaluating insulation performance was formed, a DC 100V voltage was continuously applied to the metal wiring in an environment of 85°C and 85% relative humidity, and the time until a short circuit due to ion migration occurred was measured. Criteria "A" and "B" below are considered to be acceptable for practical use. A: No short circuit after 1000 hours of application B: Short circuit occurs between 500 hours and 1000 hours C: Short circuit occurs in less than 500 hours

[0142] 3-6. Evaluation of Ink Ejection Stability Using the above inkjet head, ink was continuously ejected (driven) from all nozzles under the conditions of droplet volume of 30 pl, droplet velocity of 7 m / sec, and ejection frequency of 20 kHz. The number of nozzles that were not ejecting was counted after 1 minute, 5 minutes, and 10 minutes from the start of operation and evaluated according to the following criteria. Criteria "A" and "B" below are considered to be without practical problems. A: The number of missing nozzles is less than 2. B: The number of missing nozzles is 2 or more but less than 10. C: The number of missing nozzles is 10 or more.

[0143] Table 4 shows the fabrication conditions, evaluation, and measurement results for each cured film.

[0144]

[0145] As is clear from Tables 1 to 4, by using a material that can exist as a dispersed elastomer in the cured film, we were able to obtain a cured film with high heat cycle resistance, less delamination at the lamination interface, and high insulation durability after storage in high temperature and humidity.

[0146] This application claims priority to Japanese Patent Application No. 2025-025204, filed on 19 February 2025. All disclosures in the specification, claims, drawings, and abstract contained in the above Japanese application are incorporated herein by reference.

[0147] This invention enables the production of high-performance cured films by light irradiation and heat curing.

[0148] 100 Printer stage 110 Carriage 112, 114 Inkjet head 122, 124 Light source 200 Substrate

Claims

1. An inkjet ink comprising a curable composition containing a compound having a (meth)acryloyl group and a compound having an epoxy group, wherein the composition contains a material that can exist as a dispersed elastomer in a cured film obtained by curing the curable composition.

2. The inkjet ink according to claim 1, wherein the elastomer exists in a dissolved state in the inkjet ink and exists in a dispersed state after phase separation in the cured film.

3. The inkjet ink according to claim 1, wherein the elastomer is polymer particles with an average particle diameter of 50 nm or more and 1000 nm or less.

4. The inkjet ink according to claim 1, wherein the elastomer is a core-shell type polymer particle.

5. The inkjet ink according to claim 1, which contains silica surface-treated with a silane coupling material.

6. An ink set comprising: a first inkjet ink containing a compound having a (meth)acryloyl group and not containing a compound having an epoxy group; and a second inkjet ink containing both a compound having a (meth)acryloyl group and a compound having an epoxy group, wherein at least one of the first inkjet ink and the second inkjet ink contains a material that can exist as a dispersed elastomer in a cured film obtained by curing a curable composition which is a mixture of the first inkjet ink and the second inkjet ink.

7. The ink set according to claim 6, wherein the elastomer exists in a dissolved state in the inkjet ink and exists in a dispersed state after phase separation in the cured film.

8. The ink set according to claim 6, wherein the elastomer is polymer particles with an average particle diameter of 50 nm or more and 1000 nm or less.

9. The ink set according to claim 6, wherein the elastomer is a core-shell type polymer particle.

10. The ink set according to claim 6, wherein at least one of the first inkjet ink and the second inkjet ink contains silica surface-treated with a silane coupling material.

11. A method for manufacturing a cured film, comprising the steps of: applying the inkjet ink described in claim 1, or the first inkjet ink and the second inkjet ink included in the ink set described in claim 6, to a substrate; and curing the applied inkjet ink by light irradiation and heating.

12. A cured film formed by the inkjet ink described in claim 1 or the ink set described in claim 7, wherein the cured film contains an elastomer in a dispersed state.

13. The cured film according to claim 12, wherein the thickness is 50 μm or more and 1000 μm or less.

14. The cured film according to claim 12, wherein the glass transition temperature is 120°C or higher and 300°C or lower.

15. The cured film according to claim 12, which is used as an insulating film.

16. A printed circuit board having the cured film described in claim 12.

17. An electronic device having a printed circuit board as described in claim 16.

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