GB919500A - Improvements relating to bonded fibrous sheet material and its production - Google Patents

Abstract

919,500. Bonded fibrous material; coated bonded fibrous material. DU PONT DE NEMOURS & CO., E. I. Oct. 27, 1959, No. 36464/59. Addition to 914,712. Class 140. A flexible moisture permeable sheet material comprises a ligated fibrous met comprising at least 50%, based on weight of fibres in the mat, of in situ-retracted synthetic fibres, the said mat having been shrunk by 30% to 90% of its original planar area, and dispersed throughout the said mat 10% to 70% of a synthetic polymer binder based on the combined weight of fibres in the mat and of the binder, said binder being in such a form that in the absence of the fibres it would have a modulus of elasticity at 5% elongation of 5 to 150 pounds per square inch. The sheet material may be made by forming a mat or web of retractable synthetic staple fibres some of which are positioned substantially perpendicular to the plane of the mat, treating the mat so as to retract the fibres to effect a reduction in the surface area of the mat of from 30 to 90% and then impregnating the shrunken mat with from 10 to 70% of the binder based on the combined weight of the fibres in the mat and of the binder. The shrinking is done with hot water or other means capable of retracting the fibres without fusing or damaging them. The binder may be introduced into the mat in the form of a solution or aqueous dispersion, or as a dry powder or as a slurry of fibrils, after which it is coagulated by immersing the mat in a coagulant or other appropriate means and the mat is thereafter dried. By the term " ligated " and " ligating " is meant the binding together of adjacently disposed fibres lying substantially parallel to the plane of the mat by forcibly orienting sufficient fibres to a position substantially perpendicular to the plane of the mat so that a unitary dense coherent structure is formed. The required fibre orientation may be accomplished by punching the mat with fine barbed needles in a needle loom. Specified fibres and shrinking agents (the latter in brackets) are cellulose acetate (aqueous acetone), nylon (dilute nitric acid), polyethylene (hot water), polyethylene terephthalate (hot water or hot air), polystyrene, polytetrafluorethylene, copolymer of acrylonitrile and vinyl chloride, and copolymer of vinyl chloride and vinylidene chloride (hot air), viscose rayon and regenerated cellulose. A suitable binder is an elastomer formed by employing a compound having two active hydrogen atoms bonded to amino-nitrogen atoms to chain-extend the reaction product of a polyalkylene ether glycol and an organic diisocyanate. Preferred glycols are those of polypropylene ether and polytetramethylene ether, and a preferred diisocyanate is tolylene-2,4. A suitable chain extending compound is hydrazine. The binder may be dissolved in a solvent such as N,N-dimethyl formamide, dimethyl sulphoxide, tetrahydrofuran, tetramethyl urea, N,N-dimethyl acetamide. Non- retractable fibres employed may be natural or artificial, straight or crimped. The mat may be buffed, brushed dyed or pressed before or after impregnation and the product may be printed, stencilled, embossed, or dyed and coated on one or both sides with vinyl chloride polymers or copolymers, polyurethane elastomers, or synthetic rubbers, e.g. butadienestyrene or butadiene-acrylonitrile copolymers or neoprene. Specifications 712,950, 788,560, 849,154, 875,052, 914,711 and U.S.A. Specifications 2,336,797, 2,515,834, 2,758,908 and 2,910,763 also are referred to.