Patent GB-1020372-A (GB)
Title: Flexible cellulosic filamentary materials having ultra-violet light shielding properties
Inventor: BRADER WILBUR THOMAS
IPC: D06M11/49
Filed: 1963-10-14
Abstract: A fibrous cellulosic base sheet (e.g. of paper or cotton) is impregnated with a cellulosic hydrophilic film-forming material, e.g. regenerated cellulose, carboxy methyl cellulose and other cellulose ethers, and hydrophilic cellulose esters, and treated with an aqueous solution of an inorganic water-soluble ferric salt and then immersed in an aqueous solution maintained at a pH of at least 5, preferably at least 10, to precipitate ferric hydroxide in situ.  The ferric salt is preferably ferric chloride, suitably 0.01-0.2% by weight of the anhydrous salt, and the second aqueous solution may contain an alkali or alkaline earth metal basic salt or hydroxide, preferably 2% sodium hydroxide.  Sodium acetate, sodium carbonate, ammonium carbonate, potassium hydroxide and calcium hydroxide are also specified.  Immersion times may be 1-60 secs. in the ferric salt bath at room temperature, and 5-30 secs. in the alkaline bath at from room temperature to 40 DEG C. After removal from the alkaline bath and washing, the sheet may be plasticized in an aqueous bath containing e.g. glycerol, and also an anchoring agent, e.g. melamine-formaldehyde precondensates, urea-formaldehyde precondensates, polyalkylene-imines and epoxy resins, if it is desired subsequently to apply a polymeric film-forming coating. Water-insoluble anchoring agents may be applied to the sheet after drying.  Materials so treated show a substantially reduced transmission of ultra-violet light and are useful in packing foodstuffs (see Division A2).  For details of coatings which may be applied see Division B2.ALSO:A coated sheet material comprises a flexible, hydrophilic cellulosic filamentary material, for example a non-fibrous regenerated cellulose film, a carboxymethyl cellulose film, or a fibrous cellulosic base sheet (e.g. paper or cotton) impregnated with a hydrophilic cellulosic film-forming material, uniformly impregnated with ferric hydroxide or hydrated ferric oxide at least adjacent one surface thereof, and having a film-forming polymer coating on the surface thereof, for instance a copolymer of at least 50% of vinylidene chloride and at least one other monomer copolymerizable therewith.  Filamentary materials in general include fibrous and non-fibrous sheets, films, pellicles, and ribbons of regenerated cellulose, cellulose ethers, hydrophilic cellulose esters, cotton and paper.  Specified coating materials include also vinyl chloride-vinyl acetate copolymers, nitrocellulose and polyalkylenes such as polyethylene and polypropylene.  Coatings may be applied by melt-extrusion or from solutions, including lacquers and latices, to the coloured cellulosic base sheet.  In a preferred method, regenerated cellulose film, in the wet-gel state, is treated with an aqueous solution of an inorganic water-soluble ferric salt and then immersed in an aqueous solution maintained at a pH of at least 5, preferably at least 10, to precipitate ferric hydroxide in situ. The ferric salt is preferably ferric chloride, suitably 0,01-0,2% by weight of the anhydrous salt and the second aqueous solution may contain an alkali or alkaline earth metal basic salt or hydroxide, preferably 2% sodium hydroxide.  Sodium acetate, sodium carbonate, ammonium carbonate, potassium hydroxide and calcium hydroxide are also specified.  Immersion times may be 1-60 seconds in the ferric salt bath at room temperature, and 5-30 seconds in the alkaline bath at from room temperature to 40  DEG C.  After removal from the alkaline bath and washing, the film may be plasticized in an aqueous bath containing e.g. glycerol, and also an anchoring agent, e.g. melamine-formaldehyde precondensates, urea-formaldehyde precondensates, polyalkylene-imines and epoxy resins, if it is desired subsequently to apply a polymeric film-forming coating. Water-insoluble anchoring agents may be applied to the film after drying.  The film is then coated.  In an example, an impregnated, anchor-coated regenerated cellulose film is coated with "Saran" (Registered Trade Mark) dissolved in a mixture of tetrahydrofuran and toluene, and containing also small proportions of clay, wax and alkyd resin to improve surface characteristics.  Coated films so made show a substantially reduced transmission of ultra-violet light and are useful in packing foodstuffs (see Division A2).