Patent GB-826570-A (GB)
Title: Improved process for the production of porous, highly absorptive surface structures
IPC: D04H1/68
Filed: 1956-02-15
Abstract: Porous highly-absorptive fleecy substances are produced by impregnating a fibrous fleece of cotton, ramie, regenerated cellulose or the like, or a mixture of such fibres with a foamlike dispersion of natural or synthetic rubber and/or thermoplastic synthetic resins, a finely-divided water-soluble pore-forming agent consisting of hexamethylene tetramine or carbamic or thiocarbamic acid derivatives or imino-urea derivatives such as dicyandiamide, urea, or thiourea and their derivatives, guanidine or urethane, being introduced into the fibrous fleece and dissolved out after the impregnant has hardened.  Additives such as (1) anionic or non-ionic emulsifying agents such as oxyethylation products of higher fatty alcohols, higher alkyl phenols or naphthols, protein-fatty acid condensation products, fatty alcohol sulphates, alkyl or alkyl-aryl sylphonates, carbohydrates and their derivatives, or polyvinyl alcohol, and (2) other known pore-forming agents such as common salt, Glauber's salt, alkali poly-phosphates or the sodium salt of nitrilo-triacetic acid or of ethylene-diaminetetra-acetic acid may also be present in the impregnating composition which is preferably applied in the form of a foam.  The material is heat-treated or vulcanized and the water-soluble pore-forming substances subsequently washed out.  The product is further improved by treatment with hot alkaline liquors. In examples: (1) a fleece of cotton fibres is impregnated with a foamed emulsion containing rubber, vulcanizing agents and urea, dried, again impregnated with a similar emulsion containing, in addition, the sodium salt of carboxymethyl cellulose, again dried, and vulcanized; the pore-forming ingredients are then washed out, the products treated with caustic soda solution, washed, neutralized with acetic acid, washed and dried; (2) a rayon fleece is impregnated with an emulsion containing synthetic rubber, vulcanizing agents, dicyandiamide, and wetting agents, dried, impregnated with a solution of Glauber's salt and dried, and finally impregnated with an emulsion containing rubber, methyl cellulose, hexamethylene tetramine and an oxyethylated fatty alcohol, dried, washed in water, dried, washed in caustic soda, dried, acidified with formic acid, washed and dried; (3) a cotton/ramie fleece is impregnated with an emulsion containing a copolymer of butadiene and styrene, vulcanizing agents, wetting agents and thiourea, dried, impregnated with a rubber dispersion containing polyvinyl alcohol, common salt and a wetting agent, dried, vulcanized, washed, dried, and treated with caustic soda as in (1); (4) a fleece of cotton, rayon and perlon fibres is impregnated with a foamed dispersion of a mixture of polyvinyl chloride and polyacrylic acid ester containing urea, dried, impregnated with a mixture of the same polymers and synthetic rubber containing dextrin and an emulsifying agent, dried, vulcanized, washed with water and again dried. A combination of different fibres may be used, part of the fibres being removed in the after-treatment with alkali.ALSO:Porous highly absorptive fleecy substances are produced by impregnating a fibrous fleece of cotton, ramie, regenerated cellulose or the like, or a mixture of such fibres with a foam-like dispersion of natural or synthetic rubber and/or thermoplastic synthetic resins, a finely-divided water-soluble pore-forming agent consisting of hexamethylenetetramine or carbamic or thio carbamic acid derivatives or imino-urea derivatives such as dicyandiamide, urea, or thiourea and their derivatives, guanidine or urethane, being introduced into the fibrous fleece and dissolved out after the impregnant has hardened.  Additives such as (1) anionic or non-ionic emulsifying agents such as oxyethylation products of higher fatty alcohols, higher alkyl phenols or naphthols, protein-fatty acid condensation products, fatty alcohol sulphates, alkyl or alkyl-aryl sulphonates, carbohydrates and their derivatives or polyvinyl alcohol, and (2) other known pore-forming agents such as common salt, Glauber's salt, alkali polyphosphates or the sodium salt of nitrilotriacetic acid or of ethylenediamine-tetraacetic acid may be present in the impregnating composition which is preferably applied in the form of a foam.  The material is heat-treated or vulcanised and the water-soluble pore-forming substances subsequently washed out.  The product is further improved by treatment with hot alkaline liquors. In Examples, (1) a fleece of cotton fibres is impregnated with a foamed emulsion containing rubber, vulcanising agents and urea, dried, again impregnated with a similar emulsion containing, in addition, the sodium salt of carboxymethyl cellulose, again dried, and vulcanised; the pore-forming ingredients are then washed out, the products treated with caustic soda solution, washed, neutralised with acetic acid, washed and dried; (2) a rayon fleece is impregnated with an emulsion containing synthetic rubber, vulcanising agents, dicyandiamide, and wetting agents, dried, impregnated with a solution of Glauber's salt and dried, and finally impregnated with an emulsion containing rubber, methyl cellulose, hexamethylene tetramine and an oxyethylated fatty alcohol, dried, washed in water, dried, washed in caustic soda, dried, acidified with formic acid, washed and dried; (3) a cotton/ramie fleece is impregnated with an emulsion containing a copolymer of butadiene and styrene, vulcanising agents, wetting p agents and thiourea, dried, impregnated with a rubber dispersion containing polyvinyl alcohol, common salt and a wetting agent, dried, vulcanised, washed, dried, and treated with caustic soda as in (1); (4) a fleece of cotton, rayon and perlon fibres is impregnated with a foamed dispersion of a mixture of polyvinyl chloride and polyacrylic acid ester containing urea, dried, impregnated with a mixture of the same polymers and synthetic rubber containing dextrin and an emulsifying agent, dried, vulcanised, washed with water and again dried.  A combination of different fibres may be used, part of the fibres being removed in the after treatment with alkali.