Production of cotton warp yarns having inverse denim effect

Abstract

The present invention relates to a process for producing cotton warp yarns having an inverse denim effect, which comprises using an indigo dyeing range to perform a dyeing step whereby the cotton warp yarn is through-dyed with indigo in one pass at a dyeing temperature of 30 to 90° C. and an indigo concentration of 5-500 g/l and a subsequent bleaching step whereby the indigo is selectively decolorized on the surface of the cotton warp yarn.

1 . A process for producing cotton warp yarns having an inverse denim effect, which comprises using an indigo dyeing range to perform a dyeing step whereby the cotton warp yarn is through-dyed with indigo in one pass at a dyeing temperature of 30 to 90° C. and an indigo concentration of 5-500 g/l and a subsequent bleaching step whereby the indigo is selectively decolorized on the surface of the cotton warp yarn.  
     
     
         2 . A process according to  claim 1  that utilizes indigo in the form of a solution of leuco indigo.  
     
     
         3 . A process according to  claim 2 , wherein the leuco indigo has been produced from indigo by catalytic hydrogenation.  
     
     
         4 . A process according to  claim 1  wherein the process is further carried out in the presence of a wetting agent.  
     
     
         5 . A process according to  claim 4 , wherein the wetting agent is used in amounts of 5 to 50 g/l.  
     
     
         6 . A process according to  claim 1 , wherein the bleaching step is effected by means of a bleaching bath which contains potassium permanganate as bleaching agent.  
     
     
         7 . A process according to  claim 1 , wherein the bleaching step is effected by means of a bleaching bath which contains a thickener.  
     
     
         8 . A process according to  claim 1 , wherein the through-dyeing of the cotton warp yarn in the dyeing step is followed by rinsing with water, bleaching with permanganate, another rinse and a subsequent treatment with a bisulfite solution and the cycle of bleaching, rinsing and treating with bisulfite is repeated at least once.  
     
     
         9 . A process according to  claim 1 , wherein the bleaching step is followed by a third step whereby the cotton warp yarn surface decolorized in the bleaching step is treated with a pigment suitable for cotton.  
     
     
         10 . A textile article comprising cotton warp yarns dyed by a process according to  claim 1 .  
     
     
         11 . A process according to  claim 3 , wherein the process is further carried out in the presence of a wetting agent.  
     
     
         12 . A process according to  claim 11 , wherein the wetting agent is used in amounts of 10 to 25 g/l.  
     
     
         13 . A process according to  claim 1 , wherein said indigo concentration is 10-50 g/l.  
     
     
         14 . A process according to  claim 1 , wherein said indigo is a pre-reduced indigo.  
     
     
         15 . A process according to  claim 14 , wherein the pre-reduced indigo is produced from an indigo without the use of a reducing agent.  
     
     
         16 . A process according to  claim 2 , wherein the temperature is from 50 to 70° C.  
     
     
         17 . A process according to  claim 1 , wherein the dyeing is conducted at a pH from 10.5 to 13.5.  
     
     
         18 . A process according to  claim 12 , wherein the wetting agent is fatty alcohol ethoxylate, alkanesulfonate, sulfonsuccinate, alkyl phosphate, paraffin, hydrocarbon or mixtures thereof.  
     
     
         19 . A process according to  claim 12 , wherein the wetting agent is a salt of phosphoric esters.  
     
     
         20 . A process according to  claim 6 , wherein said potassium permanganate is used in an amount from 20 to 50 g/l.