METHOD OF PREPARING UREA-FORMALDEHYDE BINDER FOR MANUFACTURING SAND MOLDS AND RODS IN LIGHT ALLOY MOLDING PROCESS Russian patent published in 2006 - IPC C08G12/12 B22C1/22 

FIELD: polymer production.

SUBSTANCE: invention, in particular, relates to binders used for manufacturing molding blends employed for molding profiled items from light alloys. Preparation of urea-formaldehyde binder comprises urea/formaldehyde condensation to achieve refractory index 1.4055-1.4072. Condensation is carried out at initial urea-to-formaldehyde molar ratio 1:(1.95-2.18), pH of mixture from 8 to (4.7-4.1) until viscosity of resin (using viscosimeter VS-4, nozzle 4 mm) 15.5-26.0 s, after which mixture is neutralized to pH 7.0-8.5, water is distilled off from boiling reaction mixture until refractory index achieves 1.4220-1.4230 followed by addition of polyvinyl alcohol solution at a rate of 1.2% solid substance based on initial weight of urea. Reaction mixture is then cooled and two further portions of urea are added to achieve final urea-to-formaldehyde molar ratio 1:(1.40-1.43). When second portion of urea is being charged, sodium decahydrotetraborate is simultaneously added in amount 0.35-0.7% based on the total weight of urea and then first and second post-condensation steps are conducted, each step being followed by ageing for 30-50 min.

EFFECT: reduced toxicity of resin, achieved controlled viscosity and gelation time, improved water resistance, and prolonged shelf time.

3 cl, 1 tbl, 4 ex