| 摘要 |
PCT No. PCT/EP87/00691 Sec. 371 Date Jul. 13, 1988 Sec. 102(e) Date Jul. 13, 1988 PCT Filed Nov. 7, 1987 PCT Pub. No. WO88/03847 PCT Pub. Date Jun. 2, 1988.The binder serves to produce foundry moulds and comprises a solution (preferably an aqueous solution) of aldehyde reactive phenol substances and gaseous acetals (preferably dimethyl formal) as reaction partners and strong acids, e.g. sulphuric acid and sulphonic acids as a catalyst. The acetal is in this system hydrolysed by the acid, the basic aldehyde being formed, which will react with the aldehyde reactive phenol substance accompanied by cross-linking. The acid serves thereby simultaneously as a cross-linking catalyst. In principle, it is possible to regard as "aldehyde reactive phenol substances" any phenolic compounds which can in the acid range cross-link more or less spontaneously with aldehydes. Preferably, these are resorcinol or resorcinol products, e.g. resorcinol pitch or precondensates formed with a shortfall of aldehyde, e.g. based on resorcinol formaldehyde, phenol resorcinol formaldehyde or resorcinol melamine formaldehyde. To produce foundry moulds, a granular basic moulding material, e.g. sand, the solution of the aldehyde reactive phenol substance and the acid are used to produce a moulding mixture which is then caused to set by passing the gaseous acetal (formal) through it. The aldehyde cross-linking of the aldehyde raective phenol substance in the acid medium, the process which takes place thereby, produces duroplasts (resites), which combine a very good thermal resistance and a low pollutants emission during casting with a high strength and negligible sensitivity to moisture in the mouldings produced, features which make them extremely favorable. |
