| 摘要 |
1,061,431. Web coating apparatus. GEVAERT PHOTO-PRUDUCTEN N. V. July 9, 1964 [July 16, 1963; (2)], Nos. 28048/63 and 28049/63. Heading D1L. In a method of coating a liquid composition on to a web, the liquid is caused to move upwardly on to the web at a zone extending laterally of the web while the web is advanced through said zone and while maintaining an electrical potential difference between the lipuid composition passing to the zone and a member or part which is close to or in contact with the opposite side of the web. The liquid composition may be supplied to a position below and spaced from the web such that either a meniscus can be maintained between the liquid and the web by surface tension effects alone or is dependent for its maintenance on the electrostatic field. The said member or part may be in the form of an electrode-forming roller having an inculated outer layer in contact with the web, the potential difference may be maintained by a D.C. or an A.C. source and the field may be confined within lateral limits which exclude marginal portions of the web. In the embodiment shown in Fig. 1, film 11 is passed over roller 12 to a backing roller 13 which is mounted in an insulated manner above bath 16 of a photographic emulsion 16 in a pan 17, means (not shown) being provided to maintain a constant level. The coating on the web is metered by an air-knife 18, variation in air volume, pressure and angle of incidence being used to control coating thickness. The film is then conducted over further rollers 19, 20 to a drying section. Pan 17 and thereby the coating emulsion therein are earthed whilst roller 13 is connected to one terminal of a potential source the other terminal of said source being also earthed so that an electrostatic field can be maintained between the roller 13 and the coating emulsion. In this embodiment the meniscus can be maintained by surface tension alone but by placing the pan 17 further from the roll 13 an embodiment in which the meniscus is maintained only with the aid of the electrostatic field is produced. A doctor roller may be used instead of the air knife 18. In another embodiment (Fig. 5 not shown) the coating roller is partly emmersed in the bath of liquid emulsion and the film is led in contact with the top of the roller there being a conductive member on the remote side of the web connected to a potential source, the bath of liquid again being earthed. In a further embodiment (Fig. 8, not shown) the meniscus is formed between the web, travelling around a backing roller, and a roller which carries emulsion upwardly as a layer from the bath to the coating zone. |
