Dyeing of cellulose derivative textile materials with an acid dye in a swelling solution followed by washing with an aqueous salt solution

Claim 1

IN A PROCESS FOR THE COLORATION OF TEXTILE MATERIAL SELECTED FROM THE GROUP CONSISTING OF CELLULOSE ESTERS AND CELLULOSE ETHERS BY IMPREGNATING THE MATERIAL WITH A SOLUTION OF A DYE IN A LIQUID CONTAINING A SUBSTANTIAL PROPORTION OF A WATER MISCIBLE ORGANIC LIQUID, AND WHICH IS A SWELLING AGENT FOR THE CELLULOSE DERIVATIVE, THE SAID DYE BEING AN ACID DYE WHICH IS AGGREGATED IN WATER TO A SMALL DEGREE AT MOST HAS SUBSTANTIALLY NO AFFINITY FOR THE CELLULOSE DERIVATIVE WHEN APPLIED THERETO AS A SOLUTION IN WATER AND IS READILY REMOVED FROM THE WOLLEN MATERIAL BY WASHING WITH WATER, THE STEP OF DE-SWELLING THE DYE-IMPREGNATED MATERIAL AND FIXING THE DYE THEREIN BY WASHING THE IMPREGNATED MATERIAL WITH AN AQUEOUS SOLUTION OF AN INORGANIC SALT, THE SAID SALT BEING SUBSTANTIALLY WITHOUT SWELLING ACTION ON THE CELLULOSE DERIVATIVE AND BEING CAPABLE OF REDUCING THE SOLUBILITY OF THE ACID DYE IN WATER.