Patent GB-421279-A (GB)
Title: Process of developing fabrics printed with vat-dyestuffs
IPC: D06P1/22
Filed: 1933-06-12
Abstract: <PICT:0421279/IV/1> <PICT:0421279/IV/2> Printing; regenerated celluloses, dyeing.--Moist fabrics printed with vat dyestuffs and on which there are present, besides the dyestuff and a thickener, an alkali and a hydrosulphite or a derivative thereof, are developed by bringing the goods to a temperature, advantageously below 100 DEG C., e.g. 70--80 DEG  C., suitable for effecting reduction, by exposing them in a moist atmosphere to a source of heat of a higher temperature and removing them from the influence of the source of heat as soon as they have attained the reduction temperature, the fixation of the leuco compound on the fibre thus being effected at a temperature below the reduction temperature.  Difficulties arising from the decomposition of the hydrosulphites by heat are avoided by the process.  Fig. 1 shows apparatus suitable for use with those vat dyes which are advantageously fixed at room temperature.  The moist printed fabric passes at high speed over a roller R<1>, thence around a body H, heated to 150--200 DEG  C., mounted in an open tank K and out over a roller R<2>; the vat dye is thus reduced at about 100 DEG C. in the moist atmosphere in the tank and the leuco compound is fixed on the fibre during the subsequent passage through the air. Fig. 2 shows apparatus suitable for use with those vat dyes which are best fixed at 50--60 DEG  C.  The fabric passes over rollers mounted in a closed tank K containing a heating element B and a humidifier heated by elements A; it passes first over the element B and then traverses a relatively long path before leaving the tank.  The heat supplied by the element B may be regulated by a thermostat or by two thermostats, one being in the upper part of the tank and the other near the outlet slot. The humidifier may be hygrometrically controlled, e.g. in accordance with variations of the dielectric constant between condenser plates with varying humidity.  The following examples are specified.  (1) A cotton fabric is printed with an aqueous paste containing the dyestuff N-dihydro-1 : 2 : 1<1> : 2<1>-anthraquinoneazine, thiodiglycol and starch tragacanth thickening, dried, passed through an aqueous bath at 50 DEG  C. containing caustic soda and hydrosulphite, passed into a tank containing electric heating elements which heat the fabric to 80 DEG C. in about 10 seconds, passed through the tank for about a further 50 seconds while cooling to 65 DEG  C., and finished as usual to obtain a vivid blue pattern of good fastness.  (2) A fabric of viscose artificial silk is printed with a paste containing the dyestuff obtainable by carbazolation of a  : a -trianthrimide according to the process of Specification 296,758, [Class 2 (iii)], and methylcellulose thickening, passed through an aqueous bath at 40 DEG  C. containing caustic soda, hydrosulphite and Glauber's salt, well squeezed, passed through a tank as described in (1) and subsequently through the air whereby it is cooled to about 40 DEG C., and finished as usual to obtain a fast yellow print. (3) A cotton fabric is printed with a paste containing 3 : 4 : 8 : 9-dibenzpyrene - 5 : 10 - quinone and methylcellulose thickening, passed through an aqueous bath containing caustic soda, hydrosulphite and Glauber's salt, squeezed, passed for about 10 seconds over a steam-heated plate to heat it to 70 DEG  C., passed through the air for about 60 seconds, rinsed, oxidized, rinsed and soaped to obtain a vivid yellow-orange print.  (4) A linen fabric is printed with a paste containing dimethoxydibenzanthrone and methylcellulosestarch thickening, padded with an aqueous solution containing potassium carbonate, formaldehyde-sulphoxylate, thiodiglycol, Glauber's salt and a wetting agent, squeezed, passed through an apparatus similar to that of Fig. 2, wherein it is heated to about 100 DEG  C. in about 30 seconds and thereafter cooled to 60--70 DEG  C. in a further 60 seconds, and finished as usual to obtain a vivid, very fast green print.  (5) Fabrics of different weight and moisture content, e.g. heavy cloth and light voile are treated as in (1) with control of the humidity and thermostatic temperature regulation in the tank.  (6) A cotton-viscose fabric is printed with a paste containing dichloroisoviolanthrone, starch tragacanth, potassium carbonate, formaldehyde-sulphoxylate and glycerine and is passed through the apparatus used in (4) with control of the humidity therein to obtain a deep fast black print. (7) The process of (4) is performed with drying of the fabric carrying the vat dye, thickener, alkali and formaldehyde-sulphoxylate and a subsequent moistening immediately before its introduction into the fixing apparatus.