| abstract |
A new modified silicate compsn. is produced by reacting a silicate oligomer (1) with an active hydrogen cpd. (a) or (b). (1) is obtd. by hydrolysis-dehydration-condensn. polymerisation of tetraalkoxy silane using a hydrolysis coefft. of 0-65% (pref. 10-60%, esp. 40-60%). (a) has a mol. wt. between 80 and 500 and contains one functional gp. (b) has a mol. wt. of 500 or higher and has one or two functional gps.. The reaction is carried out with the ratio of the no. of alkoxy gps. to the no. of active H being 1-15 when (a) is the active H cpd. and 10-100 when (b) is the active H cpd.. A sand mould is produced by adding to moulding sand at least an organic binder, a hardener, and an isocyanate compsn. contg. this modified silicate compsn.. The isocyanate compsn. comprises a polyisocyanate and the modified silicate compsn. (1/9-9 times the wt. of polycyanate). The active H cpd. is a polyether or polyester alcohol. The organic binder is phenol resin, polyester resin, urea furan resin, phenol-furan resin, phenol-isocyanate resin or polyester-isocyanate resin. |