| 摘要 |
<p>Multi-coloured signboards are produced by acid etching to remove parts of at least one coloured layer from a polyoxymethylene plate prepared by (a) doubling plates of different colours (i.e. joining the plates under pressure to form a laminate e.g. with polyethylene) or (b) dyeing the plate at the surface, the acid etching taking place at 40 DEG C to the melting range of the polyoxymethylene, and preferably 70 DEG -150 DEG C. Etching agents used include phosphoric acid, 5-sulphosalicylic acid and the ammonium salt of the sulphuric acid ester of caster oil. Thickening agents may be used e.g. titanium dioxide, barium sulphate, chromic oxide, and pyrogenically produced silicon dioxide. Disperse dyes are used. The term "polyoxymethylene" is defined.</p> |
