| 摘要 |
<p>501,031. Urea - formaldehyde resins. MAZZA, G. May 11 1937, Nos. 13410 and 13411. Void. Convention dates, May 12, 1936 and Sept. 12, 1936. [Class 2 (iii)] A flexible transparent product permeable to infra-red and ultra-violet rays, which can be worked by cutting and like tools, is made by mixing urea-formaldehyde condensates with traces up to 2 per cent of metals or metalloids and with ammonium derivatives, and hardening by heat. In the example, 1 mol. of urea or thiourea is condensed with 6 to 2 mols. of formaldehyde in the presence of ammonium hydroxide and traces of powdered aluminium or zinc. After baking for 2 hours at about 100‹C., the pasty mass is filtered, cast and moulded, then hardened by baking twice for some hours at about 80‹ C. The pasty mass may be coloured with soluble materials, or with insoluble pigments or fillers. It may be hardened in the mould which is heated in a pressure chamber for about 20 hours, and the product may be dried by heating in vacuum or in formaldehyde vapour in the same chamber. The surface of the hardened product can be plasticized by immersion in water or heated formaldehyde solution, and may be tinted by boiling in colouring solutions. The plasticized mass may be moulded under pressure at 60‹ C. between glass or metal plates.</p> |
