A solder resist ink composition

Abstract: The photo-curable liquid solder resist ink composition of the present invention mainly comprises a photo-polymerizable resin having a sufficient molecular weight and (meth)acryloyl groups which are imparted by both the introduction of (meth)acryloyl groups into a novolak-type epoxy resin having 4 or more benzene nuclei and the polymerization using a chain-extension agent. The composition is useful for a photo-curable type resist, since it can produce a coated film excellent in tack free characteristic and resolution, and can produce a cured film excellent in heat resistance, adhesiveness, and chemical resistance. In addition, by reaction with an acid anhydride, development with alkalis becomes possible.

Description: The present invention relates to a photo-curable type liquid solder resist ink composition which can form a permanent protective film excellent in adhesiveness, heat resistance, chemical resistance and resolution oh a printed circuit board. Heretofore, in solder resists, there has been mainly adopted a method in which a thermo-curable or UV-curable type of solder resist is printed by screen printing to form patterns. However, the screen printing has a limitation in ability to form fine patterns, and therefore, can no longer keep abreast with the recent trend of fine patterning by higher integration in ultra LSI. As the result, the resist-forming method has been replaced with a method in which a photo-imaging is utilized with a tendency to increase high density and fineness of printed substrates. As a photo-solder resist utilizing photo-imaging, a dry film type had been initially used. Such photo-solder resist , however, tends to produce bubbles during compression bonding to the substrates. Therefore, nowadays, a liquid solder resist having no limitation in coating method has been highlighted In a pattern forming method using a photo-imaging liquid solder resist, the following serial process is adopted: 1. At first, applying a resist to a printed circuit board, followed by forming a film by heat-drying; 2. Laminating a patterning film to the coated film by applying pressure; 3. Exposing light to the resulting film to cure the exposed portion; and 4. Finally, removing the non-exposed portion of the film by developing. In this process, if the coated film stays tacky after heat-drying in said step 1, the pattern film cannot be removed or, if it can, a precise pattern cannot be reproduced because of sticking of a part of the resist to the pattern film. For these reasons, a tack free characteristic of a coated film given after heat-drying during the pattern formation process is an important required property. In addition, other properties to be required for a solder resist ink are solder heat resistance, chemical resistance, adhesiveness and resolution of the coated film. In order to improve such properties, the cross-linking density of the solder resist given after photo-setting should be raised. Consequently, the photo-sensitivity of the photo-polymerizable resin which is a main component of an ink composition before photo-polymerization should be increased. However, the simple increase of the photo-polymerizable double bonds causes a fragility and decrease of adhesiveness of the resist film after photo-curing. In addition, this further causes a decrease of tack free characteristic. Accordingly, it is required to design a polymer molecule of the photo-polymerizable resin so that the molecular weight of the photo-polymerizable resin is increased, and as many photo-polymerizable double bonds as possible according to the molecular weight are introduced into the molecule. In the actual molecular design mentioned above, in case where the photo-polymerizable resin is an epoxy acrylate, the introduction of the photo-polymerizable double bonds can be carried out by utilizing a reaction of epoxy groups. However, even if using a novolak-type epoxy resin which has most functional group and a larger molecular weight than aliphatic epoxy compounds, the photo-polymerizable double bonds which can be intoduced in one molecule is about 10, in which case both the molecular weight and the number of the double bonds are insufficient. The object of the present invention is to provide a photo-curing liquid solder resist ink composition which can form a coated film excellent in heat resistance, chemical resistance, adhesiveness and resolution, as well as in tack free characteristic, by synthesizing a photo-polymerizable resin having a sufficient molecular weight and photo-polymerizable double bonds in a novolak-type epoxy resin which is used as a starting material. The solder resist ink according to the present invention comprises a photo-polymerizable resin (A) a photo-polymerization initiator (B) and ' a diluent (C) which is characterized in that the photo-polymerizable resin (A) is preparable by: reacting a novolak-type epoxy resin (I) having 4 or more benzene nuclei with both (meth)acrylic acid (II) and a chain-extension agent (III) having two or more functional groups reactable which the hydroxyl groups and/or the epoxy groups wherein the reaction order of the novolak-type epoxy resin (I) with (meth)acrylic acid (II) and the chain-extension agent (III) is not particularly limited. When the above chain-extension agent (III) is a compound having two or more functional groups reactable with epoxy group (hereinafter, referred to as a chain-extension agent (IIIa)), it is preferably a compound selected from the group consisting of polyhydric phenols, polybasic acids, polyfunctional amines and polyhydric thiols. Among them, polyhydric phenols are more preferable. On the other hand, when the above chain-extension agent (III) is a compound having two or more of functional groups reactable with hydroxyl groups (hereinafter, referred to as a chain-extension agent (IIIb)), polyfunctional isocyanates are preferably used. In case where the chain-extension agent (IIIa) is used, it is preferable that the total of the functional groups of the (meth)acrylic acid (II) and the chain-extension agent (IIIa) is 0.9 to 1.1 chemical equivalent based on 1 chemical equivalent of epoxy groups in the novolak-type epoxy resin (I) and the amount of the chain-extension agent(IIIa) used is 0.2 to 0.8 moles based on 1 mole of the novolak-type epoxy resin (I). On the other hand, in case where the chain-extension agent (IIIb) is used, it is preferable that (meth)acrylic acid (II) is 0.9 to 1.1 moles based on 1 chemical equivalent of epoxy group in the epoxy resin (I) and the amount of the chain-extension agent (IIIb) used is 0.2 to 0.8 moles based on 1 mole of the epoxy resin (I). The increase of photo-sensitivity can be also achieved by reacting a polyfunctional (meth)acrylate (V) having one isocyanate group and two or more (meth)acryloyl groups in its molecule with hydroxyl groups in the photo-polymerizable resin (A). In the present invention, for the purpose of easy development with alkalis, it is also a preferable practical mode to react hydroxyl groups in the photo-polymerizable resin (A) with an acid anhydride (VI) to introduce carboxyl groups,by which water solubility is imparted. The solder resist ink of the present invention contains a photo-polymerization initiator (B) and a diluent (C) as components other than the photo-polymerizable resin (A). In the present invention, the photo-polymerization initiator (B) is preferably to be contained in an amount of 0.5 to 25 % by weight in the solder resist ink composition, and the diluent (C) is preferably to be contained in an amount of 5 to 500 parts by weight based on 100 parts by weight of the photo-polymerizable resin (A). The novolak-type epoxy resin (I) to be used in the present invention is, for example, a phenolnovolak-type epoxy resin, a brominated phenolnovolak-type epoxy resin, or a cresolnovolak-type epoxy resin, which can be prepared by reacting each novolak resin with epichlorohydrin. In general, such novolak-type resins are represented by the following general formula: wherein, R 1 represents a hydrogen atom or amethyl group; R 2 represents a hydrogen atom, a halogen atom or an alkyl group. In the general formula, when n is 2 or more, the number of benzene nuclei is 4 or more. Preferably, n lies in the range of 2 ≦ n < 10. A novolak-type epoxy resin (I) in which n is 10 or more is difficult to obtain for manufactural reasons. On the other hand, when the novolak-type epoxy resin (I) in which n is less than 2 is used, the resulting solder resist composition is inferior in curability and other properties, since not only an unreactant tends to occur during polymerization by the reaction with the chain-extension agent (III), but also the effect of increasing molecular weight can not be recognized. In the present invention, a photo-polymerizable resin (A) can be prepared by using said novolak-type epoxy resin (I) as a starting material. That is, a photo-polymerizable resin (A) having a high molecular weight and sufficient (meth)acryloyl groups can be obtained by reacting epoxy groups in the epoxy resin (I) with carboxyl groups in the (meth)acrylic acid (II) to introduce (meth)acryloyl groups which have photo-polymerizable double bonds into the epoxy resin (I); and polymerizing (i.e., chain-extension) the epoxy resin (I) using a chain-extension agent (IIIa) having two or more functional groups which can react with epoxy groups in the epoxy resin (I), or polymerizing the epoxy resin (I) using a chain-extension agent (IIIb) having two or more functional groups which can react with hydroxyl groups produced by epoxy-ring opening. In the present invention, the reaction order of the novolak-type epoxy resin (I) with (meth)acrylic acid (II), and the chain-extension agent (III) is not particularly limited. For example, these materials can be reacted with one another according to the following methods: (a) A method in which at first the novolak-type epoxy resin (I) is reacted with (meth)acrylic acid (II) [incorporated with the polyfunctional (meth)acrylate, as required], and then the reactant is further reacted with the chain-extension agent (III); (b) A method in which the novolak-type epoxy resin (I), (meth)acrylic acid [incorporated with the polyfunctional (meth)acrylate, as required] and the chain-extension agent (III) are reacted simultaneously; and (c) A method in which at first the novolak-type epoxy resin (I) is reacted with the chain-extension agent (III), and then the reactant is further reacted with (meth)acrylic acid (II) [incorporated with the polyfunctional (meth)acrylate, as required]. According to the kind of the chain-extension agent (III), the reaction method (order) to be used can be suitably selected from the above (a) to (c) or other reaction methods. As the chain-extension agent (III), there can be employed a chain-extension agent (IIIa) having two or more functional groups which can react with epoxy groups,and a chain-extension agent (IIIb) having two or more functional groups which can react with hydroxyl groups. In method (c), the chain-extension agent (IIIb) cannot be used singly since it essentially requires the presence of hydroxyl group. Therefore, in such case, the chain-extension agent (IIIb) is used in a combination with the chain-extension agent (IIIa). The amounts of the novolak-type epoxy resin (I), (meth)acrylic acid (II) and the chain-extension agent (III) to be used in order to give a photo-polymerizable resin (A) by a reaction thereof can vary adequately, according to the kind of the chain-extension agent or the use or non-use of the polyfunctional acrylate (V) and acid anhydride (VI), both described below. For example, in the reaction system in which the chain-extension agent (IIIa) is used and the polyfunctional acrylate (V) and the acid anhydride (VI) are not used, it is preferable that the total of the functional groups in (meth)acrylic acid (II) and the chain-extension agent (IIIa) is 0.9 to 1.1 chemical equivalents based on 1 chemical equivalent of epoxy groups in the novolak-type epoxy resin (I) and the amount of the chain-extension agent (IIIa) used is 0.2 to 0.8 mole, and preferably 0.3 to 0.7 mole based on 1 mole of the novolak-type epoxy resin (I). On the other hand, in the above reaction system in which the chain-extension agent (IIIb) is used instead of (IIIa), it is preferable that (meth)acrylic acid (II) is 0.9 to 1.1 chemical equivalents based on 1 chemical equivalent of epoxy groups in the novolak-type epoxy resin (I), and the amount of the chain-extension agent (IIIb) used is 0.2 to 0.8 mole, and preferably 0.3 to 0.7 mole based on 1 mole of the novolak-type epoxy resin (I). The chain-extension agent (III) is preferably caused to react so that the number of benzene nuclei in the resulting photo-polymerizable resin (A) is 10 or more, to give a photo-polymerizable resin (A) having a sufficient molecular weight. The chain-extension agent (IIIa) to be used in the present invention is a compound which contains two or more functional groups able to react with epoxy groupsin its molecule, such as a polyhydric phenol, a polybasic acid, a polyfunctional amine, a polyhydric thiol, and so on, as follows. The polyhydric phenol to be used is one which contains two or more of phenol groups in one molecule, such as bisphenol A, tetrabromobisphenol A, bisphenol F, bisphenol S, resolsinol, hydroquinone, etc. The polybasic acid to be used is one which contains two or more carboxyl groups in one molecule. Among such acids, a dibasic acid, which hardly causes gelation during polymerization process, is preferably used, such as succinic acid, adipic acid, sebacic acid, azelaic acid, fumaric acid, isophthalic acid, telephthalic acid, and so on. But in view of well-balanced impartment of hardness and stiffness to the resulting photo-curable film, it is especially preferable to use a long-chain dibasic acid having 18 or more of total carbon atoms other than those contained in the acidic group as a polybasic acid. Specific examples of such long-chain dibasic acids include dimer acids and hydrogenated dimer acids derived from 1,18-octadecanedicarboxylic acid, 1,16-(6-ethylhexadecane)-dicarboxylic acid, 1,18-(7,12-octadecadiene)-dicarboxylic acid, linoleic acid, etc. In addition, as a part of such long-chain dibasic acids, a liquid polybutadiene, a liquid butadieneacrylonitrile copolymer and a liquid polybutylacrylate, each containing carboxyl groups as both end groups, can also be used. The polyfunctional amine to be used is one which has two or more of amino groups in one molecule. Among them, a polyfunctional amine comprising secondary amino groups which hardly causes gelation during the polymerization process is preferably used, such as piperazine, 1,3-di-(4-piperidil)-propane, homopiperazine, and so on. The polyhydric thiol to be used is one which has two or more of thiol groups in one molecule, such as 2,2-dimercaptodiethylether, 1,2-dimercaptopropane, 1,3-dimercaptopropanol-2, bis(2-mercaptoethyl)sulfide, esters of thioglycolic acid and polyhydric alcohols, and so on. When the chain-extension agent (IIIa) to be used is a polybasic acid or a polyhydric phenol which exhibits poor reactability at relatively low temperatures,the reaction of the novolak-type epoxy resin (I) with the (meth)acrylic acid (II) and the chain-extension agent (IIIa) can be carried out by reacting the novolak-type epoxy resin (I) with (meth)acrylic acid (II) and the chain-extension agent (IIIa) simultaneously or stepwise at 80 to 130°C, in the presence or absence of a diluent mentioned below in said mixing ratio, and in the co-presence of a polymerization inhibitor such as hydroquinone and oxygen and a reaction catalyst such as a tertiary amine and a tertiary phosphine. On the other hand, when the chain-extension agent (IIIa) is a polyfunctional amine or a polyhydric thiol which exhibits good reactability at relatively low temperatures, the reaction of the novolak-type epoxy resin (I) with (meth)acrylic acid (II) and the chain-extension agent (IIIa) can be carried out by, at first, reacting the novolak-type epoxy resin (I) with the chain-extension agent (IIIa) at room temperature to 80°C in the presence of a diluent mentioned below and in the presence of a polymerization inhibitor such as hydroquinone and oxygen, and then reacting the resultant with (meth)acrylic acid (II) at 80 to 130°C in the presence of a reaction catalyst such as a tertiary amine and a tertiary phosphine. The chain-extension agent (IIIb) having two or more of functional groups which can react with hydroxyl group produced by reacting the novolak-type epoxy resin (I) with the (meth)acrylic acid (II) is, for example, a polyfunctional isocyanate. The polyfunctional isocyanate to be used is one which has two or more isocyanate groups in its molecule. Examples of such polyfunctional isocyanates include diisocyanates such as p-phenylene diisocyanate, 2,4- or 2,6-toluenediisocyanate (TDI), 1,5-naphthalenediisocyanate, hexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), tolylene diisocyanate, isophorone diisocyanate, etc.; triisocyanates such as triphenylmethane triisocyanate, 1,3,6-hexamethylene triisocyanate, etc. The chain-extension agent (IIIb) is preferably reacted with a (meth)acrylic-modified epoxy resin having hydroxyl groups, which can be produced by reacting the epoxy resin (I) with (meth)acrylic acid (II), since the chain-extension agent (IIIb) reacts with hydroxyl group. The reaction can be carried out in a manner, for example, that, at first, the novolak-type epoxy resin (I) is mixed with (meth)acrylic acid (II) in a mixing ratio so that (meth)acrylic acid (II) is 0.9 to 1.1 moles on 1 chemical equivalent of the epoxy resin (I), and then the compounds are reacted with each other at 80 to 130°C in the presence or absence of a diluent mentioned below, and in the co-presence of a polymerization inhibitor such as hydroquinone and oxygen and a catalyst such as a tertiary amine and a tertiary phosphine, to give a (meth)-acrylic-modified epoxy resin; and further, the chain-extension agent (IIIb) is reacted with the resulting epoxy resin in a ratio so that the chain-extension agent (IIIb) is 0.2 to 0.8 mole, and preferably 0.3 to 0.7 mole based on 1 mole of the epoxy resin, at room temperature to 130°C in the presence of a catalyst for urethanization such as a tin compound and/or a lead compound, to give a photo-polymerizable resin (A). The photo-polymerizable resin (A) according to the present invention has sufficient molecular weight and photo-polymerizable (meth)acryloyl groups, and can be used as a solder resist ink composition by blending with a photo-polymerization initiator (B) and a diluent (C), both described below, in a predetermined blending ratio. In the present invention, in order to improve the photo-sensitivity of the resulting photo-polymerizable resin (A), it is also possible to react a polyfunctional (meth)acrylate (V) having one isocyanate group and two or more of (meth)acryloyl groups in one molecule with hydroxyl groups in the photo-polymerizable resin (A). Such polyfunctional (meth)acrylate (V) can be produced by, for example, reacting a diisocyanate (IX) having two isocyanate groups, each having different reactivity, in one molecule with said polyfunctional (meth)acrylate (VII) having one hydroxyl group and two or more (meth)acryloyl groups in one molecule. The diisocyanate (IX) to be used is, for example, 2,4-toluene-diisocyanate, isophorone diisocyanate, hydorogenated 2,4-toluene-diisocyanate. As the polyfunctional (meth)acrylate (VII) having one hydroxyl group and two or more of (meth)acryloyl groups in one molecule to be used, there can be employed, for example, glycerine di(meth)acrylate, a di(meth)acrylate of tris(hydroxyethyl)isocyanate, trimethylolpropane di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, and so on. The reaction ratio of the polyfunctional (meth)acrylate (VII) to the diisocyanate (IX) is suitably 0.9 to 1.2 moles based on 1 mole of the diisocyanate (IX). Both components can be reacted with each other at the temperature range of room temperature to 130°C in the presence or absence of a diluent, and in the co-presence of a polymerization inhibitor such as hydroquinone and oxygen and a catalyst for urethanization such as a tertiary amine and a tin compound, to give a polyfunctional (meth)acrylate (V) having one isocyanate group and two or more (meth)acryloyl groups in one molecule. The reaction between the polyfunctional (meth)acrylate (V) and the photo-polymerizable resin (A) is a reaction for the introduction of more (meth)acryloyl groups into the photo-polymerizable resin (A) by utilizing urethane bonding between isocyanate groups in the polyfunctional (meth)acrylate (V) and hydroxyl groups in the photo-polymerizable resin (A). The reaction ratio of the polyfunctional (meth)acrylate (V) to the photo-polymerizable resin (A) is suitably 0.05 to 0.5 mole based on 1 chemical equivalent of hydroxyl groups in the photo-polymerizable resin (A). Both components can be reacted with each other under the same condition as those used in said reaction between the diisocyanate (IX) and the polyfunctional (meth)acrylate (VII). The photo-polymerizable resin (A) which can be provided by reacting the above polyfunctional (meth)acrylate (V) has a plenty of (meth)acryloyl groups and sufficient molecular weight, and consequently, can construct a solder resist ink composition having excellent properties. In the present invention, carboxyl groups can be introduced in the above photo-polymerizable resin (A) by reacting an acid anhydride (VI) with the hydroxyl group in the photo-polymerizable resin (A), by which water solubility can be imparted to the photo-polymerizable resin (A). Owing to this property, the non-exposed portion of the solder resist ink film can be dissolved and removed by an alkaline aqueous solution easily. Examples of such acid anhydrides (VI) include dibasic acid anhydrides such as phthalic anhydride, succinic anhydride, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, 3,6-endomethylenetetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, tetrabromophthalic anhydride, trimellitic acid, etc.; and aliphatic or aromatic tetracarbocylic dianhydrides such as biphenyltetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, diphenylethertetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic anhydride, benzophenonetetracarboxylic dianhydride, etc. These compounds can be used singly or in combination of two or more of them. The use amount of the acid anhydride (VI) is suitably 0.1 to 0.9 mole based on 1 chemical equivalent of hydroxyl groups in the photo-polymerizable resin (A). The acid anhydride (VI) and the photo-polymerizable resin (A) can be reacted with each other at 80 to 130°C in the presence or absence of a diluent, and in the co-presence of a polymerization inhibitor such as hydroquinone and oxygen and, as required, a catalyst for anhydride ring-opening reaction such as a tertiary amine. The acid anhydride (VI) can cause a ring-opening reaction by reacting with a hydroxyl group, by which an ester bond can be formed between the hydroxyl group existing in the photo-polymerizable resin (A) and one of the ring-opening groups in the acid anhydride (VI) and, at the same time, a carboxyl group is introduced into the photo-polymerizable resin (A). The photo-polymerizable resin (A) thus obtained, which has carboxylic groups, can be imparted with water solubility by neutralizing a part or all of the carboxylic groups with an alkali to give a salt. In addition, in such a photo-polymerizable resin (A), a development with an alkaline aqueous solution becomes possible. As the alkali to be used, there can be employed, for example, alkali metal compounds such as sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, etc.; ammonia; water-soluble organic amines such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dimethylpropylamine, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, diethylenetriamine, dimethylaminoethyl methacrylate, polyethyleneimine, etc. These alkalis can be used singly or in combination of two or more. It is preferable to use the alkali in an amount of 0.2 to 1.1 moles based on 1 chemical equivalent of carboxyl groups in the photo-polymerizable resin (A). The photo-polymerizable resin (A) according to the present invention not only has an extremely larger molecular weight, but also contains a remarkably larger amount of (meth)acryloyl groups in one molecule than a conventional photo-polymerizable resin having a novolak skeleton. Consequently, the photo-polymerizable resin (A) can give a photo-curable solder resist ink composition which can form a cured film excellent in resolution even with a slight amount of light radiation. Further, in such photo-polymerizable resin (A), the probability of the occurence of a reaction to a 3-dimensional structure becomes higher. Therefore, the resulting cured film has excellent heat resistance, adhesiveness and chemical resistance, as well as good tack free characteristic. The solder resist ink composition of the present invention can be prepared by adding a photo-polymerization initiator (B) and the diluent (C) to a photo-polymerizable resin (A). As photo-polymerization initiator (B), known ones can be employed. Specific examples of such known photo-polymerization initiators include benzoins and alkyl ethers thereof such as benzoin, benzoin methyl ether, benzoin ethyl ether, etc.; acetophenones such as acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, etc.; anthraquinones such as 2-methylanthraquinone, 2-amylanthraquinone, 2-t-butylanthraquinone, 1-chloroanthraquinone, etc.; thioxanthones such as 2,4-dimethylthioxanthone, 2,4-diisopropylthioxanthone, 2-chlorothioxanthone, etc.; ketals such as acetophenone dimethylketal, benzyl dimethylketal, etc.; benzophenones such as benzophenone, etc.; 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-on, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1; acylphosphine oxides; and xanthones; and so on. These photo-polymerization initiators can be used singly or as mixtures of two or more. It is preferable that such photo-polymerization initiator (B) is contained in the solder resist ink composition in an amount of 0.5 to 25 % by weight. If the content of the photo-polymerization initiator (B) is less than 0.5 % by weight, the light irradiating time must be elongated, or the polymerization by light radiation becomes difficult, resulting in inadequate surface hardness. On the other hand, if the content is over 25 % by weight, not only no merit can be obtained, but also there is no meaning in such a high photo-sensitization of the photo-polymerizable resin (A). From these reasons, both conditions are not preferable. As the diluent (C), solvents or diluent monomers which can participate in photo-polymerization reactions can be used singly or as mixtures of two or more. It is preferable that such a diluent is blended in an amount of 5 to 500 parts by weight based on 100 parts by weight of the photo-polymerizable resin (A), adjusted to the optimum viscosities in various applying methods. When diluent monomers are used singly or as a mixture as the diluent (C), they are preferably blended in an amount of 5 to 100 parts by weight based on 100 parts by weight of the photo-polymerizable resin (A) in view of properties of the resulting solder resist. Examples of the solvents to be used as the diluent (C) include hydrocarbons such as toluene, xylene, etc.; cellosolves such as cellosolve, butyl cellosolve, etc.; carbitols such as carbitol, butyl carbitol, etc.; esters such as cellosolve acetate, carbitol acetate, etc.; ketones such as methylethyl ketone, etc.; ethers such as diethylene glycol dimethyl ether, etc.; and so on. Examples of the diluent monomers to be used as the diluent (C) include diethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, β-hydroxyethyl (meth)acrylate, (2-oxo-1,3-dioxolane-4-yl)-methyl(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and so on. In addition to the components described above, the solder resist ink composition of the present invention may contain a filler such as talk, clay, barium sulfate, a coloring pigment, a defoaming agent, a coupling agent, a leveling agent, an epoxy resin, an epoxy-curing agent, and the like. EXAMPLES The present invention is illustrated more in detail by the following practical examples. All parts and percentages (%) are by weight, unless otherwise stated. <Synthesis of Polyfunctional Acrylate (V)> Synthesis Example 1 To 222 parts of isophorone diisocyanate, a mixture of 596 parts of a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (mixing ratio 1:1 by weight), 1.6 parts of dibutyltin dilaurate and 0.2 part of benzoquinone was added dropwise over 1 hour while maintaining the reaction temperature at 50°C. The resultant was reacted for 3 hours at 50°C and further reacted for 2 hours at 100°C, to give a mixture of a polyfunctional acrylate (V) having one isocyanate group and two or more acryloyl groups in one molecule with pentaerythritol tetraacrylate, which contained 64 % of the polyfunctional acrylate (V) (referred to as a mixture (V-1)). <Synthesis Examples 2 to 8 of Mixtures A-1 to A-7 Containing Photo-polymerizable Resin (A) and Diluent> Synthesis Example 2 To 322 parts of cresolnovolak-type epoxy resin "EOCN-104S" (produced by NIPPON KAYAKU; epoxy equivalent 220; n = 7 to 8), 94 parts of acrylic acid, 58 parts of dimer acid "Versadyme 228" (produced by HENKEL HAKUSUI; acid value 194), 104 parts of ethyl carbitol acetate, 104 parts of toluene, 2 parts of triphenylphosphine and 0.2 part of methyl hydroquinone were added, and the resulting mixture was reacted at 110°C for 14 hours. After confirming the acid value of the reactant showing 3.7, the reactant was cooled to 50°C, and then 186 parts of the mixture (V-1) given by Synthesis Example 1 was added dropwise thereto at 50°C over 1 hour. The resulting reaction mixture was reacted at 50°C for 2 hours and further reacted at 100°C for 2 hours, and confirmed the complete disappearance of isocyanate groups by infrared absorption spectrum, to give a mixture of a photo-polymerizable resin with ethyl carbitol acetate, toluene and pentaerythritol tetraacrylate, which containing 68 % of the photo-polymerizable resin (referred to as a mixture (A-1)). Synthesis Example 3 To 400 parts of a mixture (A-1) given by Synthesis Example 2, 78 parts of tetrahydrophathalic anhydride and 37 parts of ethyl carbitol acetate were added. The resulting mixture was reacted at 100°C for 6 hours to give a mixture of a photo-polymerizable resin with ethyl carbitol acetate, toluene and pentaerythritol tetraacrylate, which contained 68 % of the photo-polymerizable resin having an acid value of 82 (referred to as mixture (A-2)). Synthesis Example 4 To 234 parts of phenolnovolak-type epoxy resin "EPPN-201" (produced by NIPPON KAYAKU; epoxy equivalent 187; n = 5), 92 parts of acrylic acid, 0.3 part of hydroquinone, 2.0 parts of triphenylphosphine, 50 parts of pentaerythritol tetraacrylate and 97 parts of butyl cellosolve acetate were added, and the resulting mixture was then reacted at 110°C for 14 hours. After confirming the acid value of the reactant showing 6.4, the reactant was cooled to 50°C, and then 23 parts of hexamethylene diisocyanate and 0.5 part of dibutyltin dilaurate were added thereto. The resulting reaction mixture was reacted at 50°C for 3 hours and further reacted at 100°C for 2 hours, and confirmed the complete disappearance of isocyanate groups by infrared absorption spectrum, to give a mixture of a photo-polymerizable resin with pentaerythritol tetraacrylate and butyl cellosolve acetate, which containing 70 % of the photo-polymerizable resin (referred to as a mixture (A-3)). Synthesis Example 5 To 200 parts of the mixture (A-3) given by Synthesis Example 4, 53 parts of tetrahydrophathalic anhydride and 23 parts of butyl cellosolve acetate were added. The resulting mixture was reacted at 110°C for 4 hours to give a mixture of a photopolymerizable resin with butyl cellosolve acetate and pentaerythritol tetraacrylate, which contained 70 % of the photo-polymerizable resin having an acid value of 102 (referred to as mixture (A-4)). Synthesis Example 6 To 114 parts of cresolnovolak-type epoxy resin "ECN1280" (produced by CIBA GEIGY; epoxy equivalent 227; n = 4.1), 36 parts of acrylic acid, 0.6 part of dimethylbenzylamine, 0.1 part of methylhydroquinone, 44 parts of toluene and 44 parts of ethyl carbitol acetate were added, and the resulting mixture was reacted at 110°C for 13 hours. After confirming the acid value of the reactant showing 3.0, the reactant was cooled to 30°C, and then 13 parts of toluene diisocyanate, 41 parts of the mixture (V-1) given by Synthesis Example 1 and 0.2 part of dibutyltin dilaurate were added thereto. The resulting reaction mixture was reacted at 40°C for 2 hours and further reacted at 100°C for 3 hours, and confirmed the complete disappearance of isocyanate groups by infrared absorption spectrum. Subsequently, 42 parts of tetrahydrophthalic anhydride was added to the resulting reactant, followed by further reacting at 100°C for 5 hours, to give a mixture of a photo-polymerizable resin with ethyl carbitol acetate, toluene and pentaerythritol tetraacrylate, which contained 69 % of the photo-polymerizable resin having an acid value of 67 (referred to as a mixture (A-5)). Synthesis Example 7 To 220 parts of a cresolnovolak-type epoxy resin used in Synthesis Example 2, 36 parts of tetrabromobisphenol A, 62.5 parts of acrylic acid, 65 parts of ethyl carbitol acetate, 65 parts of toluene, 1.4 parts of trimethylbenzylammonium bromide and 0.1 part of benzoquinone were added, and the resulting mixture was reacted at 110°C for 15 hours. After confirming the acid value of the reactant showing 3.8, 91 parts of tetrahydrophthalic anhydride were added to the resultant, and further reacted at 100°C for 5 hours, followed by adding 45 parts of pentaerythritol tetraacrylate, to give a mixture of a photo-polymerizable resin with ethyl carbitol acetate, toluene and pentaerythritol tetraacrylate, which contained 70 % of the photo-polymerizable resin having an acid value of 82 (referred to as a mixture (A-6)). Synthesis Example 8 To 220 parts of a cresolnovolak-type epoxy resin used in Synthesis Example 2, 36 parts of tetrabromobisphenol A, 75 parts of methacrylic acid, 80 parts of ethyl carbitol acetate, 80 parts of toluene, 1.8 parts of triethylamine and 0.2 part of benzoquinone were added, and the resulting mixture was reacted at 110°C for 18 hours. After confirming the acid value of the reactant showing 3.5, the resultant was cooled to 50°C, and 0.7 part of dibutyltin dilaurate was added thereto. Subsequently, 164 parts of a mixture (V-1) given by Synthesis Example 1 was added dropwise to the resulting reaction mixture at 50°C over 1 hour, and reacted at 50°C for 2 hours and further reacted at 100°C for 2 hours. After confirming the complete disappearance of isocyanate groups by infrared absorption spectrum, 50 parts of succinic anhydride was added to the resulting reactant, followed by further reacting at 100°C for 5 hours, to give a mixture of a photo-polymerizable resin with ethyl carbitol acetate, toluene and pentaerythritol tetraacrylate, which contained 70 % of the photo-polymerizable resin having an acid value of 58 (referred to as a mixture (A-7)). <Synthesis Examples 9 to 12 of Mixtures E-1 to E-4 Containing Comparative Photo-polymerizable Resin and Diluent> Synthesis Example 9 To 227 parts of a cresolnovolak-type epoxy resin used in Synthesis Example 6, 72 parts of acrylic acid, 1.1 parts of dimethylbenzylamine, 0.2 part of methylhydroquinone, 60 parts of ethyl carbitol acetate and 60 parts of toluene were added, and the resulting mixture was reacted at 110°C for 12 hours. The resulting reactant had an acid value of 3.0. Subsequently, 91 parts of tetrahydrophthalic anhydride were added to the reactant, and the resulting mixture was reacted at 100°C for 6 hours. After cooling, 44 parts of pentaerythritol tetraacrylate was added to the resultant, to give a mixture of a comparative photo-polymerizable resin with ethyl carbitol-acetate, toluene and pentaerythritol tetraacrylate, which contained 70 % of the comparative photo-polymerizable resin having an acid value of 86 (referred to as a comparative mixture (E-1)). Synthesis Example 10 To 176 parts of phenolnovolak-type epoxy resin "D.E.N. 431" (produced by DOW CHEMICAL; epoxy equivalent 176; n = 0.2), 72 parts of acrylic acid, 1.1 parts of dimethylbenzylamine, 0.2 part of methylhydroquinone, 45 parts of ethyl carbitol acetate and 45 parts of toluene were added, and the resulting mixture was reacted at 110°C for 12 hours. After confirming the acid value of the reactant showing 3.5, 44 parts of toluene diisocyanate and 0.4 part of dibutyltin dilaurate were added the the reactant, followed by reacting at 40°C for 2 hours and further reacting at 100°C for 2 hours. After confirming the complete disappearance of isocyanate groups by infrared absorption spectrum, 76 parts of tetrahydrophthalic anhydride was added to the reactant, and the resulting mixture was reacted at 100°C for 6 hours, followed by adding 38 parts of pentaerythritol tetraacrylate to give a mixture of a comparative photo-polymerizable resin with ethyl carbitol acetate, toluene and pentaerythritol tetraacrylate, which contained 74 % of the comparative photo-polymerizable resin having an acid value of 76 (referred to as a comparative mixture (E-2)). Synthesis Example 11 To 227 parts of the cresolnovolak-type epoxy resin used in Synthesis Example 6, 72 parts of acrylic acid, 1.1 parts of dimethylbenzylamine, 0.2 part of methylhydroquinone, 43 parts of pentaerythritol tatraacrylate and 85 parts of toluene were added. The resulting mixture was reacted at 110°C for 12 hours, followed by confirming the acid value of the reactant showing 3.3, to give a mixture of a comparative photo-polymerizable resin with toluene and pentaerythritol tetraacrylate, which contained 70 % of the comparative photo-polymerizable resin (referred to as a comparative mixture (E-3)). Synthesis Example 12 To 200 parts of a comparative mixture (E-3) given by Synthesis Example 11, 76 parts of a mixture (V-1) given by Synthesis Example 1 was added dropwise at 50°C over 1 hour. The resulting reaction mixture was reacted at 50°C for 2 hours and further reacted at 100°C for 2 hours, followed by confirming the complete disappearance of isocyanate groups by infrared absorption spectrum, to give a mixture of a comparative photo-polymerizable resin with toluene and pentaerythritol tetra-acrylate, which contained 68 % of the comparative photopolymerizable resin (referred to as a Comparative mixture (E-4)). Examples 1 to 7 and Comparative Examples 1 to 4 Solder resist ink compositions were prepared according to the blending compositions shown in Table 1, and their properties were evaluated by the methods described below. The results are shown in Table 2. The components such as epoxy resins, epoxy-curing agents, fillers, defoaming agents and pigments are additives used as required. In the practical examples, additives shown in Table 1 were used. <Evaluation in Exposure> A coated film for the tests was prepared by applying a solder resist ink composition of a thickness of 20 to 30 µm on a defatted copper-plated laminate having a thickness of 1.6 mm, and then drying at 80°C for 30 min. in a hot air-circulation type dryer oven. (1) Dryness of Coated Film (Tack Free Characteristic) The dryness of a coated film was evaluated according to a test method of JIS K-5400 based on the following scale. ○ : no perceivable tack being observed Δ : slightly perceivable tack being observed × : remarkably perceivable tack being observed (2) Exposure Sensitivity A step tablet of Stoffer 21 steps was closely adhered to the coated film for the test, and 500 mJ/cm 2 of light amount was irradiated thereon using a 1 kw of ultra high-voltage mercury lamp. Subsequently, the resulting coated film was subjected to a developing test, and the number of residual steps of the step tablet on the copper foil was checked. In the evaluation, the developing in Example 1 and 3 and Comparative Examples 3 and 4 was carried out by modified trichloroethane as described under (3) below, whereas the developing in Examples 2, 4, 5, 6 and 7 and Comparative Examples 1 and 2 was carried out by 1 % sodium carbonate aqueous solution, which was carried out in the same manner as the above developing by modified trichloroethane. (3) Developability The test sample films of Examples 1 and 3 and Comparative Examples 3 and 4 were developed by using modified trichloroethane at 20°C under a pressure of 2.1 kg/cm 2 for 80 sec. The test samples of Examples 2, 4, 5, 6 and 7 and Comparative Examples 1 and 2 were also developed in the same manner as the above method, except using 1% sodium carbonate aqueous solution instead of modified trichloroethane and employing the developing temperature of 30°C instead of 20°C. The resulting films were checked for states of the residual resins visually, and the developability thereof were evaluated based on the following scale. ○ : good developability ---- no residual resist being observed on the copper-plated face × : bad developability ---- a little residual resist being observed on the copper-plated face <Evaluation of Cured Coated Film> The coated films given in (1) were exposed to 500 mJ/cm 2 of light, developed, and then heated at 150°C for 30 min. The completely cured film thus prepared was evaluated for the following items. (4) Hardness of The Coated Film The biggests hardness values by which the sample films can not be scratched were measured when a load of 1 kg was applied by a pencil hardness tester according to a test method of JIS K-5400. (5) Adhesiveness The test films were cross-cut in checkerboard patterns, and then subjected to a peeling test with a cellophane adhesive tape according to a test method of JIS D-0202. The separation state after peeling of each sample film was checked visually, and the adhesiveness was evaluated based on the following scale. ○ : 100/100 (that is, absence of change) Δ : 80/100 to 99/100 × : 0/100 to 79/100 (6) Solder Heat Resistance The test films were dipped in a solder bath of 260°C for 20 sec. according to a test method of JIS D-0202. The solder heat resistance was evaluated by observation of the changing state in the films after dipping, based on the following scale. ○ : no change being observed in appearance of the film × : blister, melting and/or separation being observed in appearance of the film (7) Non-electrolytic Gold Plating Resistance The test films were subjected to gold plating by using "Autoronex CI" (a gold plating liquid; produced by Sel-Rex Corp., USA) at a current density of 1 A/dm 2 for 15 min. to apply gold thereon of a thickness of 2 µm. The resulting plated films were then subjected to a peeling test by an adhesive tape. The gold plating resistance of each test film was evaluated by visual observation of the state of the gold-plated surface of the film, based on the following scale. ○ : no separation being observed Δ : a slight separation being observed × : separation being observed over 20 % or more of the whole surface area As mentioned above, the present invention is characterized in using a photo-polymerizable resin given according to a polymer molecular design which imparts larger molecular weight and a larger amount of double bonds than those of conventional photo-polymerizable resins having a novolak skeleton. Such photo-polymerizable resins can be caused to be cured easily with a small degree of a photo-polymerization reaction, and have a high probability to react to 3-dimensional structures. Therefore, by using such photo-polymerizable resins, there can be provided a photo-curable liquid solder resist ink composition which can form a coated film excellent in tack free characteristic and resolution, and can form a cured film excellent in heat resistance, adhesiveness, and chemical resistance, even by a small amount of light radiation or short irradiation time. In addition, the solder resist ink composition prepared by using a photo-polymerizable resin into which carboxyl groups are introduced, can be developed with alkaline aqueous solutions.

Claims: A solder resist ink composition comprising a photo-polymerizable resin (A) a photo-polymerization initiator (B) and a diluent (C) which is characterized in that the photo-polymerizable resin (A) is preparable by: reacting a novolak-type epoxy resin (I) having 4 or more benzene nuclei with both (meth)acrylic acid (II) and a chain-extension agent (III) having two or more functional groups reactable with the hydroxyl groups and/or the epoxy groups wherein the reaction order of the novolak-type epoxy resin (I) with (meth)acrylic acid (II) and the chain-extension agent (III) is not particularly limited. The solder resist ink composition according to Claim 1, in which the chain-extension agent (III) is a compound having two or more functional groups reactable with epoxy groups, which is selected from the group consisting of polyhydric phenols, polybasic acids, polyfunctional amines and polyhydric thiols. The solder resist ink composition according to Claim 1 or 2,in which the chain-extension agent (III) is a polyhydric phenol. The solder resist ink composition according to Claim 1. in which the chain-extension agent (III) is a polyfunctional isocyanate having two or more of functional groups reactable with hydroxyl groups. The solder resist ink composition according to Claim 2 or 3, in which the total of functional groups in the (meth)acrylic acid (II) and the chain-extension agent (III) is 0.9 to 1.1 chemical equivalents based on 1 chemical equivalent of epoxy groups in the novolak-type epoxy resin (I), and the amount of the chain-extension agent (III)used is 0.2 to 0.8 moles based on 1 mole of the novolak-type epoxy resin (I). The solder resist ink composition according to Claim 4, in which the amount of (meth)acrylic acid (II) is 0.9 to 1.1 moles based on 1 chemical equivalent of epoxy groups in the novolak-type epoxy resin (I), and the amount of the chain-extension agent (III) used is 0.2 to 0.8 moles based on 1 mole of the novolak-type epoxy resin (I). The solder resist ink composition according to Claim 1, in which the photo-polymerizable resin (A) is prepared by further reacting a polyfunctional (meth)acrylate (V) having one isocyanate group and two or more (meth)acryloyl groups in its molecule. The solder resist ink composition according to Claim 1, in which the photo-polymerizable resin (A) is prepared by a further reaction with an acid anhydride (VI). The solder resist ink composition according to Claim 1, in which the photo-polymerization initiator (B) is contained in an amount of 0.5 to 25 % by weight. The solder resist ink composition according to Claim 1, in which the diluent (C) is contained in an amount of 5 to 500 parts by weight based on 100 parts by weight of the photo-polymerizable resin (A).

Inventors: ARAKAWA MOTOHIRO, AWAJI TOSHIO, OTSUKI NOBUAKI, TANAKA HIROMICHI, ARAKAWA, MOTOHIRO, AWAJI, TOSHIO, OTSUKI, NOBUAKI, TANAKA, HIROMICHI
Applicants: NIPPON CATALYTIC CHEM IND, NIPPON SHOKUBAI CO., LTD.
Application year: 1993
Main classification: C09D163
IPC codes: G03F7, C08G59, C08F290, H05K3