Dycrothol in combinations with different dycrobases can give numbers of shades which gives a wide range of colors. The dyeing acquires very good fastness to light, soda, boil & chlorine. All these shades can also be produced on viscose & jute by necessary alteration in the dyeing.
Dycrothol are first applied to cotton in solution form. They form insoluble pigments on the fiber when coupled with diazo solutions of amino compounds which called "Dycrobases" in dyestuff.The dyeing of cotton with Dycrothol involves two operations which are impregnation and developing the impregnated material with diazotized Dycrobases or Dycrosalt solutions.
A) GREY YARN / FABRICS :
The material is boiled for 2-3 hours in the following solution using material to liquor ratio 1:20
0.35-0.75 gms/liter Suitable surface active Agent
1.50-3.00 gms/liter Caustic soda solid or Flakes
1.50-2.00 gms/liter Soda ash
B) BLEACHED YARN & FABRIC:
After that it is wetted out with a solution of 0.75 gm/liter of suitable wetting agent in hot using material oto liquor ration 1:10 and then it is rinsed in water.
Dycrothol solution is prepared by two methods:
1) By Hot Dissolving :
Dycrothol is pasted with Turkey Red Oil with little water and Caustic soda than added with boiling water with continuous stirring. If solution is not clear enough, boiling should be continued till it become clear. Allowed solution to be cool and then Formaldehyde added as necessary. Then add Salt before impregnation. In case Dycrothol AS-SW, Formaldehyde is not require to add.
2) By Cold Dissolving :
Dycrothol is pasted with industrial alcohol or methylated spirit and then Caustic Soda solution added with cold water containing 1 ml. of Caustic soda 620Tw per liter is added.
The dycrobase is pasted with hydrochloric acid with little cold water. Then hot or cold water is added with stirring. Allowed solution to cool at 100℃ with ice and then sodium nitrite solution (1:1) is added with stirring. Maintain temp. between 10-150℃. Keep solution for 20 minutes, the excess hydrochloric acid is neutralized with sodium acetate crystals. Then aluminum sulphate or acetic acid added. Then filter the solution and made as per requirement according to the concentration of Dycrobase required.
DYCROFAST Salts are always stored in a cool and dry places as they are very sensitive to heat and moisture and if they exposed to light, decomposition may occur.
DYCROFAST Salts are freely soluble in water. It is pasted with little water and further more water (5 ltrs.) is added maintaining temp. at 300℃. For Dycrofas Red B Salt, the powder is sprinkled slowly on water stirring. It is kept for 5-10 minutes and filtered through a fine mulmul fabric.
The dyeing process consists of two parts, in first part, the material is impregnated with Dycrothol solution and in second part it is developed with a diazotised Dycrobase or Dycrofast Salt solution. After that combines chemically with Dycrothol absorbed by the fiber to give an insoluble dye on the fiber.
Difference dyeing methods are used depending which type of equipment available like open beck, tub-dip, circulating liquor, jigger, padding methods, etc. These involve the use of different material to liquor ratio and therefore different concentration of the dyestuff is used to get the same shade.
The Dycrorapid Fast Dyes are stabilized Azoic dyes specially prepared for printing. They are applied to the fiber in one operations. when developed under acid condition bright full shades are obtained which possess very good fastness properties. Due to cross coupling which may occur between certain Dycrorapid Fast Dyes, proper care should be taken when using mixtures of Dycrorapid Fast Dyes as resultant shade obtained is un-predictable. Dyestuffs of others group may be used to supplement the colors range, particularly for greens and blues. As the Dycrorapid Fast dyes can be developed by either neutral or Acid ageing colors of Dycrorapid Fast, Dycrovat or Dycrosol dyes may be printed along side. In some cases Dycrosol can also be printed in admixture with Dycrorapid Fast dyes e.g. for producing Green shade Dycrorapid Fast Dyes are largely used in block and screen printing, some printers prefer particularly for dycrorapid Fast Lemon Yellow 3GH, Red RH, G.Yellow 2RA, G. Yellow IGK to expose undeveloped print to sunlight and then acid developed.
|Dycrorapid Fast Dyes (Powder)
|Caustic Soda Solution (1:2) 33% W/W
After printing, the material is dried and developed by one of the following processes.
The printed material is steamed for 2 to 4 minutes and then developed in following dye bath at 160 Dec. to 175 Dec. F.
40 CC Acetiv Acid - Per Liter
25 GMS Glauber Salt - Per Liter
The printed material is hang for 12 to 14 hrs. in moist and warm rood and then passed through following bath at 80 Dec. to 90 Dec.
30 GMS Sulphuric Acid - Per Liter
30 GMS Sodium Nitrite - Per Liter
The printed material is then washed immediately in cold water with little soda-ash, till all traces of acid neutralized.