Patent GB-948619-A (GB)
Title: Improvements in or relating to a process for treating films before coating the filmswith gelatine containing light-sensitive substances
Inventor: BRATRING KURT
IPC: B29C71/00
Filed: 1960-02-02
Abstract: 948,619. Surface treatment of films. H. RUTGERS. Feb. 2, 1960, No. 3624/60. Drawings to Specification. Heading B5B. [Also in Division G2] Films consisting of hydrophobic polymeric organic thermoplastic material which is either a cellulose ester or a fully synthetic polymeric material is treated on one or both sides with an aqueous solution of an alkali metal hydroxide or of a highly ionisable inorganic acid, the solution in either case also containing an oxidizing agent or a reducing agent and being capable of forming on the surfaces of the films reaction products which are in part soluble and in part insoluble in water, the latter being capable of promoting the adhesion of light-sensitive gelatine coatings to the films which function as supports or substrates for the coatings. The water soluble reaction products are removed from the films by washing with water and the films are then dried. When the film consists of a polyester, concentrated aqueous solutions of sodium or potassium hydroxide containing oxidizing agents are preferably used. When the film consists of an oxygen-free material, such as polystyrene, polyethylene or polypropylene, aqueous solutions of highly ionisable inorganic acids are used. The acids used are preferably those having an oxidizing action on the film material. Films consisting of oxygen-containing polymers may also be treated with aqueous solutions of acids such as sulphuric acid and nitric acid. The oxidising agents present in the solution may be hydrogen peroxide and its derivatives, chlorine, bromine, or particularly, chromic acid with addition of sulphuric acid. The preferred oxidizing agents for alkaline treating solutions are hydrogen peroxide and more particularly its inorganic derivatives such as sodium or potassium peroxide, ammonium persulphate, percarbonates, perborates, especially the ammonium salts thereof, chlorites, hypochlorites, chlorates and perchlorates. Organic peroxides such as benzoylperoxide, and toluene sulphochloramide may also be used. Reducing agents such as formaldehyde, formic acid, hydrazine, sulphites, dithionites, thiosulphates, sulphoxalic acid and metal salts such as ferrous sulphate and stannous chloride may be used in alkaline treating solutions. Films treated with alkaline solutions containing oxidizing agents may be exposed to ultra-violet rays for a short time. Wetting agents and detergents such as fatty acid and fatty alcohol sulphonates, aromatic sulphonates and condensation products of fatty alcohols with alkoxides, e.g. ethylene oxide, may be used in the treating solutions and/or the water used for washing the films after treatment. Acid treating solutions for polyester films may advantageously contain reducing agents such as ferrous sulphate, stannous chloride or hydrazine. Low molecular weight mono- or polyvalent alcohols may be added to the treating solutions. The treated films while still wet may be treated with a dilute aqueous solution of a protein, such as casein or gelatine hardened with chromium-aluminium sulphate, and thereafter dried. In an example, a polyethylene terephthalate film is treated at 70 to 75‹ C. with an aqueous 25% potassium hydroxide solution containing 4-5% of potassium persulphate. The solution may contain sodium pyrophosphate to reduce the rate of oxygen evolution. In a second example, a cellulose acetate film is treated for ¢ to 5 minutes at about 60 to 70‹ C. with a mixture of 2 parts by volume of 40% aqueous sodium hydroxide solution and 3 parts by volume of aqueous sodium hypochlorite solution containing 150 grams per litre of active chlorine.