| 摘要 |
<p>The following polymeric compositions are coated onto a polyethylene glycol terephthalate backing to give a coating about 5.0 mils thick; (a) a polyvinylidene chloride/acrylonitrile copolymer, polymethyl methacrylate mixture in methylethyl ketone, containing ZnCl2 and a black dye (Ex. I and II) or (b) a formaldehyde, polyvinyl acetal, epoxy resin mixture in dioxane and acetonitrile containing a dye and either ZnCl2 (Ex. III, VI and VII), NaClO3 (Ex. IV), or Cu(NO3)2, (Ex. V). The coating is allowed to dry to produce a hard film. The coated backing is immersed in boiling water to render the coating opaque, and the subsequent application of pressure to the coating restores transparency, (see also Divs. B5 and B6).</p> |
