Patent GB-1067576-A (GB)
Title: Improvements in or relating to the production of a non-woven self-bonded fabric
IPC: D04H1/54
Filed: 1963-08-30
Abstract: A non-woven sheet comprises at least 75% by weight of randomly disposed, crystalline, synthetic, organic, polymeric filaments of denier 1-25.  The filaments are self-bonded throughout the sheet; the molecular orientation of the filaments, as measured by birefringence is substantially the same at the bonds as between them, and at least 40% of the calculated maximum birefringence; the average edge-bond count of the sheet is between 30 and 80 bonds per 100 filaments; and the average maximum cross-sectional dimension of an individual filament in the bond is less than twice that at the mid-point between bonds.  The filaments may be of isotactic polypropylene, linear polyethylene, polyethylene terephthalate, polyhexamethylene adipamide, polycaproamide, polytetrafluoroethylene and linear copolymers of propylene or ethylene with up to 25% of other copolymerisable monomers, and melt blends of said polymers and copolymers with up to 25% of other polymers e.g. atactic polypropylene branched polyethylene, polyisobutylene.  Oriented fibres of low crystallinity may be used for some applications, an example given being the fibre spun from a copolyester of ethylene glycol with a 90/10 mixture of terephthalic/isophthalic acids.  The remaining filaments in the web, i.e. up to 25%, may comprise glass, metal or other inorganic or organic filaments of a generally inert character.  Small amounts of fillers, delustrants, pigments and stabilisers may also be present.  The filamentary web may be a random structure of continuous filaments, or may be made by air-laying staple filaments, or may be made by cross-lapping of unidirectional filamentary webs.  The sheet may be bonded by exposure to a non-solvating fluid, e.g. steam, at a pressure at least atmospheric at a temperature within < 3% of the critical bonding temperature, for a time sufficient of self-bond the filaments at a plurality of spaced intersection points.  The temperature of the web is maintained constant within 5 DEG C. throughout its extent during the bonding, the web is restrained by light compressive forces to prevent filament shrinkage of more than 20% or loss of birefringence of more than 50%, and the web is cooled sufficiently before removing the restraint to prevent filament shrinkage.  The critical bonding temperature (Tx) lies within the range of 45 DEG C below the crystalline melting point of the polymer, and is determined by bonding identical samples of the web material at each 2 DEG C within this range.  The tongue-tear resistance of each sample after bonding is determined and plotted on a graph against temperature.  The bonding temperature at which tongue-tear resistance is a maximum is the critical bonding temperature. After bonding, the sheet may be calendered or embossed. The products may be used for clothing, hats, felts, heat, electrical and sound insulation, wallboards, roofs, filters, reinforcing tapes, moulded sheets, shoes, wallpaper, carpet backings, floor coverings, mattress pads, packaging, upholstery, curtains and draperies, tents, tarpaulins and book-binding.