| 摘要 |
1,188,325. Papermaking, non woven fabric. DOW CHEMICAL CO. 24 Feb., 1967 [26 July, 1966], No. 47025/69. Divided out of 1,188,322. Headings D1R, D2A and D2B. A dry non-woven fibrous sheet is made from a web of selfbonding gel fibres (defined as in the parent specification) of thermoplastic, fibre-forming polymers of acrylonitrile, by subjecting it to drying conditions between two spaced barriers that limit the physical movement of the web in its thickness direction while providing substantially no restraint to movement in other directions. The barriers may be solid screens or platens or heat barriers, but are preferably hot bodies such as platens that will serve both as solid barriers and as heat barriers. The barriers may be applied throughout the drying period, or only in its earlier part (when most of the movement would otherwise take place). The fibres may be fibrillated by beating and may first be crushed to induce longitudinal splitting and so to facilitate this fibrillation. The crushing is preferably carried out before cutting to staple length, and may be applied by crush rollers, serrated-belt crimpers, gear crimpers or a stuffing-box crimper. The web may be formed by a scattering mechanism, distribution by a stream of air or water, or deposition by filtering from a liquid. Staple fibres, are preferably formed into a web by papermaking technique and continuous filaments also from suspension in water. The rate of drainage of aqueous slurries may be controlled by the process of Specification 1,188,323. The gel fibres may be toughened before sheetformation by subjecting them while free of restraint to a hot aqueous medium, but they must then be cooled before subjecting them to stress. The web may be first pressed as in the parent specification and then dried by the process of the present invention. Various textures can be produced by varying the conditions; mild pressing will give a fluffy product; pressing at higher temperature and pressure will give a leathery product of higher tensile strength; drying between heated surfaces spaced apart by two to five times the thickness of the web before drying will give a product with a straight core and crimped surfaces. The dried web may subsequently be annealed at a temperature at least 30‹C above the glass-transition temperature of the fibres. The specification also describes by way of comparison similar sheets dried with no restraint at all. |
