GB213567A - Improved manufacture of condensation products from urea, or its derivatives, and formaldehyde - Google Patents

Abstract

In the manufacture of condensation products from urea and its derivatives with formaldehyde, the first stage of the reaction, viz. the formation of the initial water-soluble intermediate products, is conducted in two phases, the first in the absence of free hydrogen ions and the second in the presence of free hydrogen ions whose concentration exceeds 10-7 but does not attain 10-3. As regards the first phase, the absence of free hydrogen ions is secured either by adding a base to render the reaction mixture neutral or slightly alkaline or by using formaldehyde free from acid. The second phase is effected by further heating with the addition of an acid, acid salt, acid ester, or a compound such as an ammonium salt which generates acid, or after formic acid has been produced, e.g. by aeration, from the formaldehyde present. According to the concentration of the hydrogen ions present, different colloidal products are obtained. When only small quantities of acid are present, a viscous hydrophile product is formed; with greater quantities of acid, a tough, resinous, hydrophobe gel is precipitated on cooling. When, however, the hydrogen ion concentration exceeds 5 x 10-3, the reaction mixture sets to a brittle material which crumbles on drying. The hydrophobe gel is very suitable not only for producing a hard final working material but also for the manufacture of lacquers. For the production of hard materials, the hydrophobe gel is not necessarily separated, but the acid conditions are so chosen that the hydrophobe gel remains in pseudo-solution; in the case of lacquer manufacture, the hydrophobe gel may be dissolved in non-aqueous solvents such as epichlorhydrin to which non-aqueous softening agents may be added. According to the examples, urea and neutral or slightly alkaline formaldehyde are heated, and after short boiling, boric acid then added and the mixture further boiled; the viscous product, which comprises a hydrophile colloid, is poured into moulds and hardened by heat treatment. If the reaction mixture be further heated after the formation of the hydrophile colloid, it separates on cooling into two layers, the tough lower layer of which, comprising a hydrophobe gel, is dried in vacuo and then hardened. Alternatively the whole of the reaction mixture in which the colloid has become hydrophobe is evaporated in vacuo and then hardened in moulds after the free acid and formaldehyde have been fixed. In the above process, boric acid may be replaced by acetic-acid, ammonium acetate, benzoic acid, sulphuric acid, or even by formic acid produced by oxidation of a little of the free formaldehyde present. Specifications 151,016, 171,094, 187,605, and 201,906 are referred to.