Ink composition for solder resist

Disclosed is an ink composition for solder resist that includes, as a binder polymer, a styrene-maleic anhydride copolymer of which the maleic anhydride group is partly esterified with a lower alcohol, the ink composition forming a solder resist film excellent in flexibility and hence soldering heat resistance as well as adherence.

EXAMPLE 1 (Preparation of solution A) 10,000 g of a styrene-maleic anhydride copolymer (M.W. 65,000) having a maleic anhydride group partly esterified with a lower alcohol and 100 g of an epoxy resin (EPN-1138, commercially available from Ciba-Geigy Co., Ltd.) were dissolved in 1.600 g of ethyleneglycol mono n-butylether. After adding 5 g of a photoinitiator (IRGACURE-907. commercially available from Ciba-Geigy Co., Ltd), the resulting solution was admixed at 3,000 rpm for one hour with a disc-type impeller. (Preparation of solution B) 200 g of a bisphenol A novolak epoxy resin, 600 g of dipentaerythritol pentacrylate and 60 g of an epoxy thermosetting agent,. dicyandiamide (commercially available from Ciba-Geigy Co., Ltd.) were dissolved in 150 g of propyleneglycol n-butylether. Subsequently, 200 g of phthalocyanine green and 1.500 g of aluminum oxide were dispersed in the resulting solution. Each 200 g of the solution A and the solution B were mixed at 2,000 rpm for one hour with a disc-type impeller to prepare an ink composition for solder resist. 
 EXAMPLE 2 (Preparation of solution A) 1,000 g of a styrene-maleic anhydride copolymer (M.W. 105,000) having a maleic anhydride group partly esterified with a lower alcohol and 100 g of an epoxy resin (EPN-201, commercially available from Nippon Kayaku) were dissolved in 1,600 g of ethyleneglycol mono n-butylether. After adding 5 g of a photoinitiator (IRGACURE-907. commercially available from Ciba-Geigy Co., Ltd.), the resulting solution was admixed at 3,000 rpm for one hour with a disc-type impeller. (Preparation of solution B) 200 g of a phenol novolak epoxy resin, 700 g of pentaerythritol triacrylate and 60 g of an epoxy thermosetting agent, dicyandiamide (commercially available from Ciba-Geigy Co., Ltd. ) were dissolved in 150 g of propyleneglycol n-butylether. Subsequently, 200 g of phthalocyanine green and 1,500 g of barium sulfate were dispersed in the resulting solution. 300 g of the solution A and 200 g of the solution B were mixed at 2,000 rpm for one hour with a disc-type impeller to prepare an ink composition for solder resist. 
 EXAMPLE 3 (Preparation of solution A) 10,000 g of a styrene-maleic anhydride copolymer (M.W. 180,000) having a maleic anhydride group partly esterified with a lower alcohol and 100 g of an epoxy resin (EPN-1138, commercially available from Ciba-Geigy Co., Ltd. ) were dissolved in 1,600 g of ethyleneglycol mono n-butylether. After adding 5 g of a photoinitiator (IRGACURE-907, commercially available from Ciba-Geigy Co., Ltd.), the resulting solution was admixed at 3,000 rpm for one hour with a disc-type impeller. (Preparation of solution B) 200 g of an epoxy resin., 600 g of tris(2-hydroxyethyl)isocyanulate triacrylate and 60 g of an epoxy thermosetting agent, dicyandiamide (commercially available from Ciba-Geigy Co., Ltd.) were dissolved in 150 g of propyleneglycol n-butylether. Subsequently, 200 g of phthalocyanine green and 1,500 g of barium sulfate were dispersed in the resulting solution. 300 g of the solution A and 200 g of the solution B were mixed at 2,000 rpm for one hour with a disc-type impeller to prepare an ink composition for solder resist. 
 EXAMPLE 4 (Preparation of solution A) 800 g of a styrene-maleic anhydride copolymer (M.W. 90,000) having a maleic anhydride group partly esterified with a lower alcohol. 200 g of a second styrene-maleic anhydride copolymer (M.W. 180,000) having a maleic anhydride group partly esterified with a lower alcohol, and 100 g of an epoxy resin (EPN-1138) were dissolved in 1,200 g of ethyleneglycol mono n-butylether. After adding 5 g of a photoinitiator (IRGACURE-907), the resulting solution was admixed at 3,000 rpm for one hour with a disc-type impeller. (Preparation of solution B) 200 g of a bisphenol novolak epoxy resin, 600 g of dipentaerythritol pentacrylate and 60 g of an epoxy thermosetting agent, dicyandiamide were dissolved in 150 g of propyleneglycol n-butylether. Subsequently, 200 g of a coloring agent, phthalocyanine green and 1,500 g of aluminum oxide were dispersed in the resulting solution. 300 g of the solution A and 200 g of the solution B were mixed at 2,000 rpm for one hour with a disc-type impeller to prepare an ink composition for solder resist. 
 EXAMPLE 5 (Preparation of solution A) 900 g of a styrene-maleic anhydride copolymer (M.W. 65,000) having a maleic anhydride group partly esterified with a lower alcohol, 100 g of a second styrene-maleic anhydride copolymer (M.W. 105,000) having a maleic anhydride group partly esterified with a lower alcohol, and 100 g of an epoxy resin (EPPN-201) were dissolved in 1,200 g of ethyleneglycol mono n-butylether. After adding 5 g of a photoinitiator (IRGACURE-907), the resulting solution was admixed at 3,000 rpm for one hour with a disc-type impeller. (Preparation of solution B) 200 g of a phenol novolak epoxy resin, 700 g of pentaerythritol triacrylate and 60 g of an epoxy thermosetting agent, dicyandiamide were dissolved in 150 g of propyleneglycol n-butylether. Subsequently, 200 g of a coloring agent, phthalocyanine green and 1,500 g of aluminum oxide were dispersed in the resulting solution. 300 g of the solution A and 200 g of the solution B were mixed at 2,000 rpm for one hour with a disc-type impeller to prepare an ink composition for solder resist. 
 EXAMPLE 6 (Preparation of solution A) 600 g of a styrene-maleic anhydride copolymer (M.W. 30,000) having a maleic anhydride group partly esterified with a lower alcohol, 400 g of a second styrene-maleic anhydride copolymer (M.W. 150,000) having a maleic anhydride group partly esterified with a lower alcohol, and 100 g of an epoxy resin (EPN-1138) were dissolved in 1,200 g of ethyleneglycol mono n-butylether. After adding 5 g of a photoinitiator (IRGACURE-907), the resulting solution was admixed at 3,000 rpm for one hour with a disc-type impeller. (Preparation of solution B) 200 g of an epoxy resin, 600 g of tris(2-hydroxyethyl)isocyanulate triacrylate and 60 g of an epoxy thermosetting agent, dicyandiamide were dissolved in 150 g of propyleneglycol n-butylether. Subsequently, 200 g of phthalocyanine green and 1,500 g of barium sulfate were dispersed in the resulting solution. 300 g of the solution A and 200 g of the solution B were mixed at 2,000 rpm for one hour with a disc-type impeller to prepare an ink composition for solder resist. 
 COMPARATIVE EXAMPLE 1 The procedures were performed in the same manner as described in Example 1, excepting that no more than 1,000 g of a styrene-maleic anhydride copolymer (M.W. 3,000) having a maleic anhydride group partly esterified with a lower alcohol was used. 
 COMPARATIVE EXAMPLE 2 The procedures were performed in the same manner as described in Example 1, excepting that no more than 1,000 g of a styrene-maleic anhydride copolymer (M.W. 50.000) having a maleic anhydride group partly esterified with a lower alcohol was used. 
 EXPERIMENTAL EXAMPLE The ink compositions prepared in Examples 1 to 6 and Comparative Examples 1 and 2 were applied on a degreased, copper-plated laminate by screen printing and dried at 80° C. for 30 minutes with a hot air drier to form a film having a thickness of 15 &mgr;m. With a stopper 21-stepped tablet adhered to the film, a radiation of 400 mJ/cm 2 was applied on the film with a high-pressure mercury lamp. The film was then subjected to development using a 1% aqueous sodium carbonate solution at 30° C. with a pressure of 1.5 kg/cm 2 for 80 seconds. Subsequently, the film was heated at 150° C. for 30 minutes with the hot air drier and exposed to 1,000 mJ/cm 2 with the high-pressure mercury lamp. The film thus cured was then analyzed in regard to hardness, adherence and soldering heat resistance in the following procedures. The results are presented in Table 1. 1) Hardness The hardness of the film was measured according to the JIS K-5400 test method, in which the hardness was determined as the highest value when there is no crack in the film under a load of one kg with a pencil hardness tester. 2) Adherence The adherence of the film was measured according to the JIS D-0202 test method, in which the flaking state of the film was observed with naked eyes after a flaking test using an adhesive tape performed on the film provided with a checkered cross cut. &compfn;: No flake observed. &Dgr;: 1 to 5 flakes observed. ×: More than 6 flakes observed. 3) Soldering Heat Resistance The soldering heat resistance of the film was measured according to the JIS C-6481 test method, in which the film was immersed in a solder tank at 260° C. for 20 seconds and its apparent condition was evaluated. &compfn;: Normal. ×: Wrinkle, perforation or flake observed in the outer surface of the film. 1 TABLE 1 Comparative Examples Examples 1 2 3 4 5 6 1 2 Hardness 8H 7H 8H 8H 7H 8H 4H 6H Adherence &compfn; &compfn; &compfn; &compfn; &compfn; &compfn; &Dgr; &Dgr; Soldering heat resistance &compfn; &compfn; &compfn; &compfn; &compfn; &compfn; x &compfn; As seen from Table 1, the solder resist films of Examples 1 to 6 were excellent in hardness, adherence and soldering heat resistance. The properties of the solder resist pattern were superior when using a mixture of styrene-maleic anhydride copolymers having a different molecular weight, compared to using a styrene-maleic anhydride copolymer alone. Contrarily, the solder resist film containing the conventional binder polymer had a deteriorated flexibility and was thus poor in adherence and soldering heat resistance. As described above, the ink composition for solder resist comprising. as a binder polymer, a styrene-maleic anhydride copolymer of which the maleic anhydride group is partly esterified with a lower alcohol according to the present invention form a solder resist film excellent in flexibility and hence soldering heat resistance as well as adherence. In particular, the solder resist film had more excellent flexibility to provide good soldering heat resistance as well as good adherence, when using a mixture of a partly esterified styrene-maleic anhydride copolymer having a molecular weight of 12,000 to 100,000 and a partly esterified styrene-maleic anhydride copolymer having a molecular weight of 100,000 to 200,000.