| 摘要 |
<p>Paper sheets for the simultaneous production of an original and copies have on their two sides thin layers of different types. One layer is friable and micorporous so that when sheets are superposed and local pressure applied this layer is transferred at the areas pressed to the other sheet. The other retaining layer may be also microporous but has a greater strength than the transferable layer, or it may be slightly adhesive. In one embodiment, the transferable layer has a colour different from that of the paper, or that of a coloured non-transferable coating layer underlying the transferable layer, is that the local removal of donor layer leaves a legible mark. In a second embodiment, transferable layer overlies a coloured layer to which it adheres more strongly than the coloured layer adheres to the paper. On the application of pressure they are transferred together to form a legible mark on the retaining layer. In a third embodiment, the transferable and retaining layers differ in colour, so that the transferred portions of the transferable layer form a legible mark. The transferable layer may be of an organic film former e.g. polyvinyl acetate chloride, made friable by a non-crystalline filler, e.g. talc. Alternatively it may be made friable by deposition from a solution in a volatile solvent mixed with a less volatile non-solvent liquid. The retaining layer may be of a slightly plasticized resin e.g. an acrylic resin, polyvinyl acetate chloride, polyvinyl propionate, polyvinyl acetate or shellac, or of an adhesive wax doped with butyl rubber. The intercalated colouring layer, if any, may be of lamp black and a wetting agent, or black wax.</p> |
