GB552770A - Improvements in or relating to the manufacture of transparent alginate films - Google Patents

Abstract

552,770. Alginic films. CEFOIL, Ltd., and ROSE, R. C. Oct. 21, 1941, No. 13537 Drawings to Specification. [Class 2 (ii)] A solution of a soluble alginate is formed into a film and solidified by treatment with a salt which forms an insoluble alginate, and the film is at least partially dried and then converted into a film of alginic acid. A solution of sodium alginate may be subjected to compressed air pressure and extruded through a slot in the bottom of a hopper into a solution of calcium chloride or other alkaline-earth salt. The sodium alginate solution may be of a strength of 5 per cent. or more and may give a viscosity of 10-200 centipoises at 15‹ C. when diluted to a strength of 1 per cent. The coagulated film may be passed from the first coagulating bath into a second bath containing calcium chloride solution. It is then passed through nip rollers and through a washing bath continuously supplied with fresh water. It is passed through nip rollers and then round heated drying cylinders by which alternate sides of the film are exposed to the hot surfaces and. to the atmosphere. Drying may be carried out until the solid content of the film is 30 per cent. or more of the total weight. The partially dried film is passed into an acid conversion bath which may contain hydrochloric acid of 2 per cent. strength. The alginic acid film passes through a washing bath and then through a bath containing a solution of glycerol. It is dried and then passed over conditioning rollers located in a chamber containing air at a relative humidity of 65 per cent. The treatment results in an alginic acid film which is strong enough in wet condition to permit of rapid speed of production and which in finished condition is of improved toughness. Specifications 492,264 and 530,889 are referred to.