Method for Dyeing Aramid Fibers and Dyed Aramid Fibers

Abstract

Methods for dyeing aramid fibers, and the dyed arimid fibers produced by these methods, which comprises a dye providing step in which a vat dye or a sulfur dye is provided to aramid fibers, a solvent treatment step in which the aramid fibers are treated by a treating solution containing a polar solvent, and after the solvent treatment step, a heat treatment step in which the aramid fibers are subjected to a heat treatment, if necessary, and having one or more dyeing operations comprising the combination of the respective steps dyeing operations. The dyeing methods can be applied to either of the para-type aramid fibers, the para-type copolymerized aramid fibers and the meta-type aramid fibers, which can be dyed to a practical color depth required for developing new applications of the aramid fibers. Colorfastness of the dyed product, in particular, colorfastness to light, is improved.

1 . A method for dyeing aramid fibers which comprises a dye providing step in which a vat dye or a sulfur dye is provided to aramid fibers, a solvent treatment step in which the aramid fibers are treated by a treating solution containing a polar solvent, and
 after the solvent treatment step, a heat treatment step in which the aramid fibers are subjected to a heat treatment, if necessary, and having at least one dyeing operation among the following four dyeing operations,   dyeing operation 1: dye providing step followed by solvent treatment step,   dyeing operation 2: solvent treatment step followed by dye providing step,   dyeing operation 3: dye providing step followed by solvent treatment step followed by heat treatment step,   dyeing operation 4: solvent treatment step followed by heat treatment step followed by dye providing step, once or more.   
     
     
         2 . The method for dyeing aramid fibers according to  claim 1 , wherein the polar solvent has a value of a solubility parameter (δ) within the range of 18 to 32 (MPa) 1/2 . 
     
     
         3 . The method for dyeing aramid fibers according to  claim 1 , wherein the polar solvent is at least one selected from the group consisting of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, benzyl alcohol, diethylene glycol, triethylene glycol, sulfuric acid, formic acid, lactic acid and oxalic acid. 
     
     
         4 . A method for dyeing aramid fibers which comprises the method for dyeing aramid fibers according to  claim 1 , and a pre-dyeing step which is carried out before the method for dyeing or a post-dyeing step which is carried out after the same,
 wherein the aramid fibers are dyed by a dye other than the vat dye and the sulfur dye in the pre-dyeing step or in the post-dyeing step.   
     
     
         5 . Dyed aramid fibers which are dyed by the method for dyeing aramid fibers according to  claim 1 . 
     
     
         6 . The dyed aramid fibers according to  claim 5 , wherein lightness (L* value) in an L*a*b* colorimetric system thereof is 38 or less. 
     
     
         7 . The dyed aramid fibers according to  claim 5 , wherein lightness (L* value) in an L*a*b* colorimetric system thereof is 30 or less. 
     
     
         8 . Dyed aramid fibers which are dyed by the method for dyeing aramid fibers according to  claim 4 . 
     
     
         9 . The dyed aramid fibers according to  claim 8 , wherein lightness (L* value) in an L*a*b* colorimetric system thereof is 30 or less.