Curable composition

A curable composition, comprising:

• (A) an organopolysiloxane having an average composition formula of Formula 1, which is a reaction product of a mixture comprising a compound of Formula 5 and an organopolysiloxane represented as an average composition formula of Formula 6 or 7, and which has an acid value obtained by KOH titration of 0.05 mgKOH/g or less;
• and
• (B) an organopolysiloxane that has an alkenyl group and an epoxy group, that does not have an aryl group, and that does have an average composition formula of Formula 9:
• (R1R22SiO1/2)a(R3R4SiO2/2)b(R5SiO3/2)c(SiO2)d [Formula 1]
• where R1 is a monovalent hydrocarbon group having 2 or more carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms, R3 and R4 are each independently an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms or an aryl group having 6 to 25 carbon atoms, R5 is an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 25 carbon atoms, with the proviso that at least one of R1, R3 and R4 is an alkenyl group;
• a is a positive number, b is a positive number, c is a positive number, d is 0 or a positive number, b/a is 5 or more, and b/c is 5 or more;
• [ReSiO3/2] [Formula 6]
• [RaRb2SiO1/2]p[ReSiO3/2]q [Formula 7]
• where Ra is a monovalent hydrocarbon group having 2 or more carbon atoms, Rb is an alkyl group having 1 to 4 carbon atoms, Rc to Re are each independently an aryl group having 6 to 25 carbon atoms, an alkyl group having 1 to 20 carbon atoms or a monovalent hydrocarbon group having 2 or more carbon atoms, o is 3 to 6, p is 1 to 3, and q is 1 to 10, wherein at least one of Formula 6 or Formula 7 is a caged or partially caged structure;
• (R3SiO1/2)l(R2SiO2/2)m(RSiO3/2)r(SiO4/2)s [Formula 9]
• where the Rs are each independently an epoxy group or a monovalent hydrocarbon group excluding an aryl group, with the proviso that at least one of the Rs is an alkenyl group and at least one of the Rs is an epoxy group;
• and m, r and s are each 0 or a positive number, 1 is a positive number, (r+s)/(l+m+r+s) is 0.2 to 0.7, r/(r+s) is 0.8 or more, and when the sum of molar ratios of l, m, r and s is converted into 1, l is 0.01 to 0.3, m is 0 to 0.7, r is 0 to 0.7, and s is 0 to 0.7.