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Improvements in or relating to the stabilization against rapid gelation of acidic, aqueous, colloidal solutions of partially polymerized unalkylated and alkylated melamine-formaldehyde condensation products
Improvements in or relating to the stabilization against rapid gelation of acidic, aqueous, colloidal solutions of partially polymerized unalkylated and alkylated melamine-formaldehyde condensation products
An acidic, aqueous, colloidal solution of partially polymerized unalkylated or alkylated melamine-formaldehyde condensation product or partially polymerized melamine-urea-formaldehyde co-condensation product initially containing between 12 and 40 per cent by weight of the condensation product is stabilized against gelation by adding thereto urea or thiourea in amount in excess of that required to combine with any free formaldehyde present in the solution. The solution gradually liberates formaldehyde and the period of stabilization depends upon the quantity of urea or thiourea added. From 5 to 50 per cent, preferably 20-40 per cent by weight, of the initial solution of urea or thiourea is added. To reduce the quantity of acid required and to assist the stabilization and prevent the formation of cloudiness a polyhydric alcohol may be added e.g. from 5-50 per cent, preferably 10-40 per cent, by weight of the total solution may be added. Alcohols specified are ethylene, propylene and butylene glycols, amyl and diethyl glycerol, pentitol and mannitol. Alternatively aromatic polyhydric compounds such as resorcinol, orcinol and tetra-hydroxy-benzene may be used. The acid present may vary from 2-3 per cent by weight of the entire solution. The condensation products may be prepared as described in Specifications 623,355 and 623,361. A large number of examples are given of colloidal solutions of various condensation products stabilized to various extents and gel times of various unstabilized solutions are also given. Specification 623,362 also is referred to.
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