Reactive dyes not only have the characteristics of bright color, complete chromatogram, low cost, convenient use, etc., but with the implementation of new environmental protection regulations in Germany, they can also replace many prohibited dyes, so their applications are becoming more and more extensive. In continuous pad dyeing, baking fixation and steaming fixation are commonly used, both of which have advantages and disadvantages, especially in dark dyeing. The curing method has a darker color, poor transmittance, and more neps on the cloth surface; the steam-setting method has a low fixation rate, and the dye loss is as high as about 30%, resulting in a large amount of dark wastewater and serious environmental pollution. Our factory tries to combine the two to maximize the strengths and avoid the weaknesses. The two-step fixing method of baking first and then steaming has achieved better results.

　　1 Fixing process analysis

　　1.1 First baking and fixing

When reactive dyes are dyed in dark colors, the conventional baking and fixing process is used. The amount of urea is generally above 80g/L, which not only causes great waste, but also decomposes urea under high-temperature baking conditions, releasing acidic substances and baking soda. It may also form highly toxic cyanic acid or isocyanate, which is not conducive to human health and environmental development requirements. The new process reduces the amount of soda ash and urea in the dyeing prescription by about 60%. After the fabric is dried by the pad dye solution, the curing rate can reach 50% to 60%, which can reduce the amount of additives. Reduce environmental pollution, and make the color bright and pure due to the decrease of the alkali dosage in the prescription.
1.2 Re-steaming and fixing

After the dyed fabric is baked, it is steamed by padding and fixing liquid (with an appropriate amount of alkali, urea and salt), which can greatly increase the fixation rate, and have good level and transmissive dyeing properties, and better remove the cotton Knot, improve the cloth surface finish and dye fastness.

This is because both urea and table salt can increase the dye fixation rate: table salt can promote dye adsorption and reduce desorption, thereby improving dye utilization; under high temperature conditions, urea and water or dyes form a eutectic mixture, which has a strong effect on dyes. The dissolving ability of the fiber also has a strong swelling ability to the fiber, so it can accelerate the dyeing and fixing of the dye and improve the fixing rate.
2 craft

　　2.1 Fabric specifications

　　119.5cm 28t/28t 435.2/228.3 /10cm cotton yarn card

　　119.5cm 15t/15t 523.6/283.5 /10cm cotton poplin

　　2.2 process flow

　　Padding liquid→pre-drying→drying→baking→padding fixing liquid→steaming→washing→soaping→washing→drying
2.3 Prescription

　　2.3.1 semi-finished products

　　 Singeing: Level 3 or higher

　　 hair effect: 9～10cm/30min

　　 Mercerized barium value: 140 or more

　　 cloth p H value: about 7

　　2.3.2 Dye solution prescription (g/L)

　　 Crimson yarn card black poplin reactive red K-2GN 50/

　　 active orange KGN 5 25

　　Reactive Blue K-R/6

　　Reactive Black KNB 2.5 46

　　 Soda Ash 10 12

　　 Urea 30 30

　　 Penetrant 219 1 1

　　 2.3.3 Fixing liquid prescription (g/L)

　　100%NaOH 5

　　 Urea 20

　　 table salt 30

　　2.4 Process conditions

　　Reduction rate (%): 70～75

　　Vehicle speed (m/min):

　　 Crimson yarn card 35～40

　　 black poplin 40～45

　　 Baking temperature (℃): 160～165

　　 Steaming temperature (℃): 100～102

　　After the fabric is steamed out of the steaming box, it is washed with cold running water in three compartments, washed in hot water at 60～70℃ in two compartments, and the soaping temperature is above 90℃