| 摘要 |
<p>1463063 Moulding expanded urea formaldehyde products IMPERIAL CHEMICAL INDUSTRIES Ltd 26 July 1974 [6 Aug 1973] 37196/73 Headings B5A and B5N A process for producing moulded expanded urea formaldehyde products comprises the steps of incorporating in a urea formaldehyde resin solution an acidic catalyst which causes gelling and curing of the resin solution, casting the mixture into an open top mould to gel, partially drying and curing the resulting gel at a temperature less than 70‹ C. to produce a preform, and subsequently heat treating the preform at a temperature above 120‹ C. in a closed restraining mould and allowing expansion of the preform therein. The resin solution may incorporate a foaming agent, and melamine formaldehyde resin may be used in addition to urea formaldehyde. The gel may be produced in a first, open, mould and then transferred to a second mould which is then positioned between the platens of a flat plate hot press having a closing pressure of about 50-300 and a platen temperature of 140- 155‹ C. Alternatively, the whole process may be carried out in the same mould, the mould being closed by a lid after the gel casting stage and being placed in a press, as described above, for the expansion process. The panels produced may be surfaced with synthetic resin skins, metal sheets, or paper skins to make sandwich boards. A laminated product may be obtained by casting a sheet-like preform which may then be cut up and stacked in a mould for the heat-pressure treatment. In an example, a mould is lined with a polyester film and a urea formaldehyde resin, which may contain plaster of Paris, is cast in a layer on it. After drying, the sheet formed is cut up, stacked in a mould and heated under pressure to give a laminated product.</p> |
