Organopolysiloxane resin, production method thereof, and curable organopolysiloxane resin composition using the same

A method of producing an organopolysiloxane resin having a number average molecular weight of at least 500 and a silanol group content of at least 5 weight %, and comprising units of formula R.sup.1 SiO.sub.3/2, wherein R.sup.1 represents a hydrogen atom or a monovalent substituted or unsubstituted hydrocarbon group having 1 to 18 carbon atoms, in a proportion of 30 to 100 mole %, said units of formula R.sup.1 SiO.sub.3/2 including 30-80 mole % of one silanol group-containing units of formula R.sup.1 Si(OH)O.sub.2/2,

• wherein said monovalent substituted or unsubstituted hydrocarbon group is selected from the group consisting of:
• a) unsubstituted alkyl groups, alkenyl groups and cycloalkyl groups,
• b) halo substituted alkyl groups and cycloalkyl groups,
• c) epoxy substituted alkyl groups, alkenyl groups and cycloalkyl groups,
• d) amino substituted alkyl groups, alkenyl groups and cycloalkyl groups,
• e) (meth)acrylic substituted alkyl groups, alkenyl groups and cycloalkyl groups,
• f) sulfur containing alkyl groups, alkenyl groups and cycloalkyl groups,
• g) alkyl ether substituted alkyl groups, alkenyl groups and cycloalkyl groups,
• h) carboxyl substituted alkyl groups, alkenyl groups and cycloalkyl groups, and
• i) alkyl, alkenyl and cycloalkyl groups substituted by quaternary ammonium salts, said method comprising:
• (1) a step of hydrolyzing an organosilicon compound represented by R.sup.1 SiX.sub.3, where R.sup.1 is as defined above and X is an alkoxy group, in a water solution having a pH value of 1-7 containing no organic solvent, and (2) a step of subjecting the organosilicon compound hydrolyzed in the step (1) to condensation reaction, wherein the amount of water used in step (1) is from 10 to 500 parts by weight per 10 parts by weight of the organosilicon compound.