Mercerisation of cellulosic fibres

Abstract

A process for mercerising unconstrained cellulosic fibres comprises transporting the fibres along a transit path through a mercerising zone in which the fibres are contacted with a mercerising liquid, followed by a rinsing zone, in which the fibres are rinsed, wherein the unconstrained cellulosic fibres are held to prevent longitudinal shrinkage during transportation through both zones. The fibres, such as cotton fibres in sliver form, may be held by being pressed between a pair of belts through the zones. Apparatus for conducting the process contains a mercerising zone and a rinsing zone, and a conveyor comprising a pair of surfaces such as belt surfaces for holding the fibres to prevent shrinkage. The belts may be slightly elastic and under tension to slightly stretch the fibres. The belts wind around rollers separated a short distance apart to maintain tension on the belt and on the fibres therebetween.

1 . A process for mercerising unconstrained cellulosic fibres comprising: transporting the unconstrained cellulosic fibres along a transit path through a mercerising zone, in which the unconstrained cellulosic fibres are contacted with a mercerising liquid followed by a rinsing zone, in which the unconstrained cellulosic fibres are rinsed; wherein the unconstrained cellulosic fibres are held to prevent longitudinal shrinkage during transportation through both zones.  
   
   
       2 . The process of  claim 1 , wherein the unconstrained cellulosic fibres are raw fibres, carded fibres, slivers or rovings.  
   
   
       3 . The process of  claim 1 , wherein the unconstrained cellulosic fibres are in the form of a sliver.  
   
   
       4 . The process of  claim 1 , wherein the fibres are held to retain the fibre length during the entire sequence of the mercerising step followed by the rinsing step, including the passage between the two steps.  
   
   
       5 . The process of  claim 1 , wherein the unconstrained cellulosic fibres are held by being compressed between two surfaces as they travel along the transit path.  
   
   
       6 . The process of  claim 5 , wherein the cellulosic fibres are transported along the transit path between a pair of belts which are pressed together in a plurality of positions through the transit path.  
   
   
       7 . The process of  claim 5 , wherein the fibres are stretched during transportation through the mercerising and rinsing zones.  
   
   
       8 . The process of  claim 7 , wherein the degree of stretching is about 4% or less.  
   
   
       9 . The process of  claim 7 , wherein the belt is slightly elastic and placed under tension through the mercerising and rinsing zones.  
   
   
       10 . The process of  claim 7 , wherein the unconstrained cellulosic fibres are oriented.  
   
   
       11 . The process of  claim 6 , wherein the transit path includes nip rollers at the beginning and end of the transit path, which place the belts under tension through the two zones therebetween.  
   
   
       12 . The process of  claim 6 , wherein the belts pass over guide means at a number of points along the transit path.  
   
   
       13 . The process of  claim 12 , wherein the straight path length between the points at which the belt is in contact with a guide means is in the range of the average length of the cellulosic fibres or less than this distance.  
   
   
       14 . The process of  claim 13 , wherein the straight path length is less than 2.8 cm.  
   
   
       15 . The process of  claim 12 , wherein the guide means are rollers.  
   
   
       16 . The process of  claim 15 , wherein the diameter of the rollers is less than two times the average length of the fibres being treated.  
   
   
       17 . The process of  claim 15 , wherein the diameter of the rollers is less than 1.5 times the average length of the fibres being treated.  
   
   
       18 . The process of  claim 15 , wherein the transit path is a circuitous path that winds around the rollers.  
   
   
       19 . The process of  claim 12 , wherein nip rollers are provided in the region between the mercerising zone and the rinsing zone to squeeze excess mercerising liquid out of the fibres and belts.  
   
   
       20 . The process of  claim 6 , wherein the belts are driven by a pad mangle at the end of the transit path which pulls the belt through the transit path.  
   
   
       21 . The process of  claim 1 , wherein the cellulosic fibres are transported through additional zones after rinsing.  
   
   
       22 . The process of  claim 21 , wherein the cellulosic fibres are conveyed through a neutralising zone in which the cellulosic fibres are neutralised with a neutralising liquid.  
   
   
       23 . An apparatus for mercerising unconstrained cellulosic fibres, the apparatus comprising: (i) a mercerising zone; (ii) a rinsing zone following the mercerising zone; (iii) a conveyor comprising a pair of surfaces for holding the unconstrained cellulosic fibres to prevent longitudinal shrinkage during transportation of the unconstrained cellulosic fibres along a transit path through the mercerising zone and the rinsing zone; (iv) driving means for driving the conveyor; and (v) pressure means for pressing the surfaces of the conveyor together in the mercerising zone and the rinsing zone to thereby hold the unconstrained cellulosic fibres so as to prevent longitudinal shrinkage of the fibres through the zones.  
   
   
       24 . The apparatus of  claim 23 , wherein the apparatus includes a neutralising zone following the rinsing zone.  
   
   
       25 . The apparatus of  claim 23 , wherein the conveyor is configured to enable the unconstrained cellulosic fibres to be held to prevent longitudinal shrinkage throughout the mercerising zone, the rinsing zone and the passage between these two zones.  
   
   
       26 . The apparatus of  claim 23 , wherein the conveyor comprises a pair of belts.  
   
   
       27 . The apparatus of  claim 26 , wherein the belts are under tension so that, in use, a compression force is maintained on the fibres to hold them firmly and thus prevent longitudinal shrinkage.  
   
   
       28 . The apparatus of  claim 27 , wherein the belt is slightly elastic so that, in use, an assembly of aligned, unconstrained cellulosic fibres fed between the belts are subjected to a stretching force by the belts in the mercerising and rinsing zones.  
   
   
       29 . The apparatus of  claim 26 , wherein the pressure means includes at least two pairs of nip rollers, one pair of nip rollers being located at the end of the mercerising zone, to squeeze out excess mercerising liquid, and the other pair being located at the end of or following the end of the rinsing zone.  
   
   
       30 . The apparatus of  claim 26 , wherein the straight distance between the points at which the belts come into contact with pressure means (“path length”) along the transit path is in the range of the average length of the cellulosic fibres to be treated in the apparatus, or less than this distance.  
   
   
       31 . The apparatus according to  claim 30 , wherein the path length is less than 2.8 cm.  
   
   
       32 . The apparatus of  claim 26 , wherein the pressure means includes a plurality of rollers located along the transit path in the mercerising zone and the rinsing zone.  
   
   
       33 . The apparatus of  claim 32 , wherein the diameter of the rollers is less than two times the average length of the fibres to be treated in the apparatus.  
   
   
       34 . The apparatus of  claim 32 , wherein the transit path is a circuitous path that winds around the rollers, and there are approximately equal numbers of left- and right-hand curves around the rollers in the transit path.  
   
   
       35 . The apparatus of  claim 26 , wherein the drive means is in the form of a mangle at or downstream of the end of the transit path.  
   
   
       36 . The apparatus of  claim 23 , wherein the mercerising zone includes a mercerising bath for containing a mercerising liquid, the rinsing zone including a rinsing bath for containing a rinsing liquid.  
   
   
       37 . An apparatus for treating fibres, comprising: a treatment zone; a conveyor comprising a pair of surfaces for holding the fibres to be treated to prevent shrinkage of the material through the treatment zone; driving means for driving the conveyor; and pressure means for pressing the surfaces of the conveyor together to hold the fibres to prevent shrinkage of the fibres.  
   
   
       38 . A product produced by the process of  claim 1.