GB724972A - Improvements in or relating to the manufacture of etherified melamine-formaldehyde resins - Google Patents

Abstract

An etherified melamine-formaldehyde resin is made by condensing melamine with aqueous formaldehyde, or a substance yielding formaldehyde, in presence of an alkaline catalyst which is calcium, barium or strontium hydroxide and condensing the product, preferably after removal of most of the water, with an aliphatic monohydric alcohol containing 3-5 carbon atoms in the presence of an acidic catalyst which is provided by passing a stream of carbon dioxide through the reaction mixture. The alkaline catalyst of the first stage is precipitated as carbonate in the second stage and may be filtered off. Preferably 3.5-7 moles of formaldehyde and 4.5-7 moles of alcohol are employed per mole of melamine. In examples: (1) melamine and formaldehyde are heated to 80 DEG C. in a solution adjusted to pH 7.7-8.0 with barium p hydroxide. When a sample retains its clarity when cooled to 25 DEG C. and is completely miscible with cold water, the pH is adjusted to 7.7 with further barium hydroxide and most of the water distilled off. Butanol is then added and the mixture heated whilst passing carbon dioxide through it, the butanol distilling off being returned to the reaction vessel. Heating is continued till the product is completely miscible with xylene; (2) and (3) as in (1) but using strontium or calcium hydroxide instead of barium hydroxide; (6) as in (1) but using isobutanol instead of n-butanol; (7) as in (1) but using amyl alcohol instead of butanol and stopping the etherification when the miscibility with xylene reaches a maximum value; (4) and (5) melamine and formaldehyde are heated to 80 DEG C. in a solution adjusted to pH 7.7-8.0 with barium hydroxide until a sample of the product shows an acetone tolerance of 3.5-4. After adjusting the pH to 7.7 with further barium hydroxide, most of the water is removed, n-butanol is added and the mixture heated whilst passing carbon dioide through it and returning butanol to the reaction vessel. Heating is continued until the miscibility of the resin with xylene reaches a maximum value; (8) melamine is condensed with formaldehyde as in example (1). n-Propanol and xylene are added to the condensate and the mixture heated whilst passing a stream of carbon dioxide through it. The distillate separates into two layers and the upper propanol-rich layer is returned to the reaction vessel. Heating is continued until the miscibility of the resin with xylene reaches a maximum value.