Patent GB-749132-A (GB)
Title: A process for improving the dimensional stability of cellulose derivative fabrics and apparatus for use therein
IPC: D06C7/02
Filed: 1953-11-12
Abstract: <PICT:0749132/IV(a)/1> <PICT:0749132/IV(a)/2> Knitted fabrics of cellulose derivative yarns are treated, while wet, with a gaseous medium at an elevated temperature while maintaining the moisture content of the fabric above its saturation regain value so as to swell the wetted yarns and release internal stresses therein, the fabric being held during the treatment to a definite width and being supported across its whole width at frequent intervals or continuously along its length, whereafter the fabric is cooled.  The fabric may be of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate-propionate or cellulose acetate-butyrate and, prior to the treatment, may contain from 20 to 120 per cent of its dry weight of water.  The saturation regain value is defined as the amount of water retained upon the fabric when in contact and in equilibrium with an atmosphere of 100 per cent relative humidity at the temperature of treatment.  At 100 DEG  C. this may be from 14 to 16 per cent by weight of the dry fabric.  After cooling, the fabric may be dried.  The fabric may be wet from a prior finishing treatment and, prior to the gaseous treatment, may be stretched by 5 to 30 per cent to a definite width and may be heated.  During the treatment the fabric may retain any softening or antistatic finish applied in a previous operation.  The gas may be superheated steam at a temperature of 230 DEG  to 250 DEG  F.  An apparatus for effecting the treatment comprises a chamber 16, Fig. 1, through which the fabric 11 is conveyed by tenter chains 12, Fig. 2.  The fabric may be supported during its passage through the chamber and for a short space beyond by rollers 22, drive at the same peripheral speed as the tenter chains from a motor 23.  The fabric may be preheated by a heater 15 and cold air is prevented from entering the chamber with the fabric by directing curtains of heated air on to the fabric from conduits 45, 451.  The chamber is filled with steam which is directed on to the fabric from distributers 28, 29.  The chamber has a double wall 19 through which steam is circulated to avoid condensation within the chamber.  Waste steam may be exhausted by means of ducts mounted at the side of the chamber.  The upper distributers 29 comprise channels 35 provided with perforated portions 38 and outlet slots defined by pairs of conduits 41 through which steam is passed to minimize condensation on the distributers.  The lateral spacing of the tenter chains may be adjusted by hand wheels 14.  The tenter chains convey the fabric through a cooling section 48 and through a drier 49.  The cooling may be effected by atmospheric air, which may be directed on to the fabric and may be refrigerated.  Means may be provided for preventing sagging of the fabric in the drier 49. Instead of rollers, moving screens or belts may support the fabric in its passage through the chamber 16.ALSO:<PICT:0749132/IV(c)/1> <PICT:0749132/IV(c)/2> Knitted fabrics of cellulose derivative yarns are treated, while wet, with a gaseous medium at an elevated temperature while maintaining the moisture content of the fabric above its saturation regain value so as to swell the wetted yarns and release internal stresses therein, the fabric being held during the treatment to a definite width and being supported across its whole width at frequent intervals or continuously along its length, whereafter the fabric is cooled.  The fabric may be of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate-propionate or cellulose acetatebutyrate and, prior to the treatment, may contain from 20 to 120 per cent of its dry weight of water.  The saturation regain value is defined as the amount of water retained upon the fabric when in contact and in equilibrium with an atmosphere of 100 per cent relative humidity at the temperature of treatment.  At 100 DEG C. this may be from 14 to 16 per cent by weight of the dry fabric.  After cooling, the fabric may be dried. The fabric may be wet from a prior finishing treatment, and prior to the gaseous treatment, may be stretched by 5 to 30 per cent to a definite width and may be heated.  During the treatment the fabric may retain any softening or antistatic finish applied in a previous operation.  The gas may be superheated steam at a temperature of 230 DEG  to 250 DEG F.  An apparatus for effecting the treatment comprises a chamber 16 (Fig. 1) through which the fabric 11 is conveyed by tenter chains 12 (Fig. 2).  The fabric may be supported during its passage through the chamber and for a short space beyond by rollers 22, driven at the same peripheral speed as the tenter chains from a motor 23.  The fabric may be preheated by a heater 15 and cold air is prevented from entering the chamber with the fabric by directing curtains of heated air on to the fabric from conduits 45, 451.  The chamber is filled with steam which is directed on to the fabric from distributers 28, 29.  The chamber has a double wall 19 through which steam is circulated to avoid condensation within the chamber.  Waste steam may be exhausted by means of ducts mounted at the side of the chamber.  The upper distributer 29 comprise channels 35 provided with perforated portions 38 and outlet slots defined by pairs of conduits 41 through which steam is passed to minimize condensation on the distributers.  The lateral spacing of the tenter chains may be adjusted by hand wheels 14.  The tenter chains convey the fabric through a cooling section 48 and through a drier 49.  The cooling may be effected by atmospheric air, which may be directed on to the fabric and may be refrigerated.  Means may be provided for preventing sagging of the fabric in the drier 49.  Instead of rollers, moving screens or belts may support the fabric in its passage through the chamber 16.