Abstract: Provided are a polyurethane and a curable composition capable of obtaining an overcoat film for a flexible wiring board that is excellent in low-warpage properties, flexibility, long-term insulation reliability, and wiring disconnection preventing properties. The polyurethane has: a structural unit of formula (1) (in formula (1), an n-number of R1 each independently represents a 1,2-phenylene group or a 1,2-phenylene group having a substituent, an (n+1)-number of R2 each independently represents a hydrocarbon group having 3-9 carbon atoms, and n represents an integer from 1 to 50); a structural unit of formula (2) (in formula (2). R3 represents a divalent organic group having 6-14 carbon atoms); and a structural unit of formula (3) (in formula (3), R3 represents a divalent organic group having 6-14 carbon atoms, and R4 represents a methyl or ethyl group).

Abstract: A curable composition for forming an overcoat film for flexible wiring boards, the curable composition being effective in improving adhesion to substrates, low warpage, flexibility, the property of inhibiting wire breakage, and long-term reliability. The curable composition according to the present invention comprises a polyurethane (component a) having carboxyl groups and an aromatic-ring concentration of 0.1-6.5 mmol/g and containing an organic residue derived from a polyisocyanate, a solvent (component b), and a compound (component c) having two or more epoxy groups in the molecule.

Abstract: There is disclosed a photo-imaging resist ink containing (A) an unsaturated group-containing polycarboxylic acid resin which is a reaction product of (c) succinic anhydride with an additive reaction product of (a) an epoxy resin with (b) an unsaturated group-containing monocarboxylic acid, wherein (a) the epoxy resin is represented by the following formula (1): ##STR1## wherein M stands for ##STR2## n is at least 1 on the average; and m is 1 to n on the average. The resist ink is excellent in developability and photosensitivity, while the cured product thereof is excellent in flex resistance and folding resistance, and well satisfactory in adhesion, pencil hardness, solvent resistance, acid resistance, heat resistance, etc.