| 摘要 |
<p>Films of hydroxyethylcellulose and of regenerated cellulose are coated with a thermoplastic, hydrophobic resin by applying an aqueous emulsion of the resin to the film, evaporating off in less than 4 seconds the water before it can substantially penetrate the film by heating with infra-red radiation say in the range 3 to 4 microns, and then applying to the residual resin more intense infra-red radiation in the range 6 to 9 microns to fuse the resin and bond it to the film. The hydroxyethylcellulose may contain ethylene oxide and a glycerine softener. The resins may be copolymers of vinylidene chloride, vinyl chloride, acrylonitrile or methyl methacrylate, polyethylene, and polyamides together with organic solvent and surfactants, and in some cases toluene and/or isopropanol. Surfactants include polyoxyethylene-polyoxypropylene block copolymer; alkylarylpolyether derivative, nonyl phenol polyglycol ether alcohol; polyoxyethylene sorbitan monoleate. The aqueous coating emulsions may include polyethylenamine as anchoring agent. The coating may be heated to /sB 20 DEG C of the fusion point of the resin to bond the resin to the film. Suitable emulsions contain 10 to 50% resin in water. In the Figure (not shown) hydroxyethylcellulose base film having 4% of ethylene oxide is continuously passed from roll 1 through tank 3 containing the aqueous emulsion, between the rolls 4 to remove excess emulsion and then over rolls 5 to smooth the applied emulsion. The coated film then passes through infra-red section 6 and heated with 3 and 4 microns radiation, the residence time being less than 4 seconds. Water vapour is vented to the atmosphere in section 7. The film then enters infra-red section 8 where 6 to 9 microns radiation is applied to fuse the resin and effect chemical bonding, the residence time being 1 second, and finally cooled in an air chamber or by passing over chilled rolls before it is wound on roll 2. The film is coated on both sides with the aqueous emulsion, or two contacting base films may be passed through the system in face-to-face contact to coate only one surface of each base film.</p> |
