| 摘要 |
<p>1,271,281. Freeze drying of coatings. ETHYL CORP. 23 July, 1969 [31 July, 1968], No. 37028/69. Heading B2E. [Also in Division Dl] A web e.g. of paper or plastic, is coated by applying to one or both sides a liquid vehicle containing at least one polymer reducing the temperature of the applied coating to freeze and solidify the coating, reducing the pressure to remove the liquid carrier by sublimation and returning the web to ambient temperature and pressure. The sublimation may be effected at 50-200 microns Hg pressure by infra red or microwave radiation, dielectric heating or by passing the web over a heated surface. Suitable polymeric materials include starch, oxidised starch, dextrin casein, soya protein, polyvinyl alcohol, styrene/butadiene or styrene/maleic anhydride copolymers, acrylic polymers or emulsified waxes and these may be employed in such vehicles as water or benzene at solids content of 5-60% wt. Pigments may also be included in the coating compositions. The coating may be strengthened by employing a mixture of polymers, by including thermoplastic emulsions in the coating and heating the web as it emerges from the vacuum chamber or by subjecting the coating to a reactive bond forming vapour after the coating has dried.</p> |
