Verfahren und Vorrichtung zur Herstellung von mikroporösen Filterfilmen

摘要

Films useful as microporous filters are made from a solution of a cellulose ester in an organic solvent by applying a film of said solution to the surface of a carrier and moving said carrier through a gelation zone through which moist air flows in countercurrent and then drying the film by heating it to about the beginning of its thermoplastic range. The air flow may be heated and humidified prior to its contact with the film, and the drying may be effected by causing a stream of heated and less moist air to flow past the film. The gelation and drying steps may take place successively using a common conveyer belt to support the film carrier, and the air stream may move at different speeds in different regions of the gelation zone. Apparatus as shown comprises means 13 for applying a film of the solution to the surface of a carrier member 10, a conveyer 11, 12 on which the carrier member may be placed and advanced horizontally, a conduit 14 disposed about the conveyer and through which the conveyer and film move, a blower 38 blowing air through the conduit in countercurrent, heating means 42 and humidifying means 45 for the air flow, a second conduit 15 disposed about the conveyer beyond conduit 14 and through which the conveyer and film move, a blower 58 blowing air through conduit 15 in countercurrent, and heating means 59 for heating this second flow of air. The film is stripped from the carrier member 10 after leaving the conduit 15. In the apparatus of Fig. 7, the upper limiting wall of the gelation zone is disposed at varying heights above the conveyer belt so that varying speeds are imparted to the air stream. The apparatus of Fig. 6 is suitable for applying a film forming solution to a backing of porous paper or cloth 64. The backing material is first moistened by a liquid-feeding apparatus 164 with a suitable aqueous solution (e.g. a mixture of water, acetone and/or methyl alcohol) and is then pressed on to the glass plate 10a by spring-loaded roller 65 prior to receiving a film of solution. U.S.A. Specification 1,421,341 and German 805,039 are referred to.ALSO:Microporous films are made by applying a solution of a cellulose ester in an organic solvent to a carrier which moves through a gelative zone through which moist air flows in countercurrent, the film finally being dried by heating to near its thermoplastic range. The cellulose ester is gradually precipitated by replacement of the solvent by water, pores then being formed by evaporation of the solvent. Suitable apparatus is described (see Group IV(a)).