| 摘要 |
<p>A make-ready comprises a layer of material adapted to be printed with an ink which acts as a resist in a subsequent etching step so as to form a relief design, and a supporting backing layer of synthetic plastics material which is resistant to attack by the etching agent. The etchable layer contains inorganic constituents such as calcium carbonate or kaolin, and a binder such as glue. The backing layer may consist of a sheet of polyester, polyvinyl chloride, polycarbonate, polyamide, polystyrene, a polyolefine, or a cellulose derivative or a sheet of paper impregnated or coated with a synthetic resinous materials &c. to render it weather resistant &c. Two intermediate layers may be located between the backing layer and the etchable layer of chalk &c., the first layer containing the inorganic constituents of the layer to be etched together with a synthetic plastics binder which is unsoluble in water, and the second layer containing in addition a water-soluble adhesive which can be attached by the etching agent. A dye may be added to at least one intermediate layer to indicate the end of the etching process. The agent may be a hypochlorite solution. In an example the first intermediate layer comprises the following parts by weight:- .China clay.70 - 100 parts .barium sulphate.10 - 20 parts .water.25 - 80 parts .vinyl isobutyl ether-methyl.15 - 50 parts .acrylate copolymer. .scum-removing agent.0.1 - 0.3 .wetting agents.0.15 - 0.4 .organic colouring matter.0.2 - 0.6 A suitable composition for the second intermediate layer is also given.</p> |
