After dyeing with reactive dyes, there are many factors causing poor wet rubbing fastness, such as dyes, water quality, auxiliaries, equipment, washing, fixation, and dyeing process design defects. It is manifested in the friction transfer between the reactive dye itself and the water-soluble floating color in the wet state, as well as the transfer of colored fiber fluff particles on the surface of the dyed object under mechanical friction. Improving the process can improve the wet rubbing fastness of reactive dyes.
1. Improve the pre-treatment process
At present, the pre-treatment process for cotton fabrics and yarns is generally direct oxygen bleaching. The traditional oxygen bleaching process uses caustic soda, hydrogen peroxide, stabilizers, penetrants and other additives at 98°C for 50-60 minutes. Caustic soda can easily damage cotton fibers during oxygen bleaching. Under high temperature and air conditions, the interaction between caustic soda and cotton fibers can cause oxidation of cotton fibers, resulting in a decrease in the degree of polymerization, resulting in brittle fiber damage and reduced strength. The wax on the cotton fiber undergoes a saponification reaction with the caustic soda solution, dissolves, and is then removed by washing with water, causing the fabric and yarn to have a high weight loss rate, a rough surface, and a rough feel. After dyeing, the wet rubbing fastness is affected because the friction coefficient of the fabric yarn surface increases.
In order to avoid weight loss, rough fabric surface, and rough hand feel during the oxygen bleaching process, a mild non-caustic soda oxygen bleaching process should be used. Using oxygen bleaching special additive 197 + hydrogen peroxide, it only takes 40-45 minutes at 98-100°C; if it is 110°C, it only needs to be kept warm for 15-20 minutes. Since the oxygen bleaching special additive is a compound additive that contains a variety of functional additives, it can penetrate, clean, and remove oil. The oil and wax on the gray cloth can be removed through emulsification and dispersion, and the wool effect is uniform. It is consistent, which is conducive to leveling and dyeing, and avoids uneven color absorption caused by uneven absorption of caustic soda in the process of using caustic soda. Using oxygen bleaching special additive 197, the fabric loses less weight. Compared with the caustic soda process, the cloth surface appears smoother and softer to the touch. The friction coefficient during wet friction is significantly lower than that of the alkali process.
2. Improve the dyeing process
2.1 Establishment and inspection of bleaching and dyeing water standards
When designing the bleaching and dyeing process, the standards for bleaching and dyeing water must be set, tested every day, and effectively controlled within the standards. High water hardness causes the water-soluble groups of floating dyes to form lakes that are insoluble in water during dyeing, affecting the removal of floating colors. For example, the Ca2+ and Mg2+ ions in hard water react with the sulfonate ions on the dye molecules and transform into water-insoluble calcium sulfonate and magnesium sulfonate, which weakens the hydrophilicity of the dye and makes it difficult for the dye to dissolve and diffuse when washed. Floating colors are difficult to clean, and the Ca2+ and Mg2+ ions in hard water react to generate CaCO3, MgCO3 and other insoluble substances that combine with dyes to form lakes and deposit on the surface of the fabric, causing the dyed object to feel rough and increasing the friction coefficient. Reduce wet rubbing fastness. It can be seen that standardized soft water must be used in the entire wet processing process from pre-treatment to dyeing and soaping. If the water quality temporarily fails to meet the standard requirements, sequestering agents can be added to the water to complex heavy metal ions such as Ca2+ and Mg2+.
2.2 Selection of dyes
There are many varieties of reactive dyes, and their quality varies greatly. It is crucial to choose dyes that meet the dyeing quality standards.
2.2.1 Choose dyes with dual reactive groups and multiple reactive groups
S-triazine reactive dyes react with fibers to form ester bonds and have poor acid resistance and stability. Vinyl sulfone dyes react with fibers to form ether bonds and have poor alkali resistance. Dyes with dual reactive groups have improved acid and alkali resistance.
2.2.2 Select dyes with suitable substantivity
If the directness of reactive dyes is too high (such as vinyl sulfone-based reactive dyes), the diffusion performance is poor, and the dyes are easy to gather on the surface of the fabric and difficult to diffuse and transfer into the fiber, which can easily cause…There are many colors and it is difficult to wash, but the directness cannot be too low to affect the fixation rate, so the directness of reactive dyes is preferably medium. The directness can be determined from the data provided by the dye supplier or from the dyeing characteristic values of reactive dyes. Measured in SERF and permeability circle tests.
2.2.3 Choose dyes with high color fixation rate
Dyes with a high fixation rate have less floating color, with a fixation rate of >80%. The amount of floating color after dyeing is relatively small, which is beneficial to removing floating color; the fixation rate is The floating color of 15% reactive dye is difficult to remove and is not suitable for dyeing medium and dark colors.
2.2.4 The effect of using dye sub-softeners with high lifting power is worse than that of anionic softeners. Weak cationic softeners and microsilicone emulsion softeners can be used in dyed products.
In the softening process, the effect of using a soft pad dryer is better than softening in the dyeing machine. The moisture content of the rolled fabric is about 80%. If a dehydrator is used, the moisture content will be around 65% and the softener will be thrown out, resulting in poor effect. The drying equipment uses a loose tension-free dryer for good results.
2.3 Selection of additives
2.3.1 Selection of penetrant
Adding a penetrating leveling agent during dyeing can promote the diffusion and penetration of the dye, making it easier for the dye to enter the dyed object through the diffusion boundary layer, and avoid excessive accumulation of dye molecules on the surface of the dyed object to cause floating color. For example, adding 1~ With 2g/L penetrating leveling agent 121, the amount of dye can be reduced by 10% to 15%, while the dyeing depth is the same. The lower the amount of dye used, the better the wet rubbing fastness.
2.3.2 Selection of anti-wrinkle agents
Adding anti-wrinkle agent 173 at a dosage of 1% during dyeing can effectively reduce the friction coefficient between the gray fabric and the dyeing machine and reduce the phenomenon of sanding.
2.3.3 Selection of soaping agent
The soaping agent should be selected with good penetrating power: it is easy for the dye to be compatible and form micelles, which will reduce the affinity between the dye and the dyed object, and form a core to make the dye micelles disperse stably in the soaping liquid. Choose a soaping agent with good penetrating and dispersing functions. Chelating and reducing soaping agent 1546, which has chelating and reducing effects, is good at removing floating colors.
2.3.4 Selection of polishing enzyme
In order to improve the surface smoothness of the dyed objects, some products can be polished with biological enzymes. Reduce the fluff on the cloth surface, improve the smoothness, and improve the wet rubbing fastness. For example, use biopolishing enzyme 1535, 1%-2% dosage, and process at 50°C for 30-40 minutes.
2.3.5 Selection of fixing agent
Excellent formaldehyde-free color fixing agent can improve the wet rubbing fastness of fabrics dyed with reactive dyes by 0.5-1 level. The performance of the fixing agent is: a polymer compound that can form a film, polyurethane or silicone with -OH, -NH2, and a cross-linking agent and high resolution.��Polymer cross-linking makes it durable and fast film-forming, does not change color, does not turn yellow, and does not reduce light fastness. It can make the dyed object feel smooth, reduce the surface friction coefficient, and keep the dyed object breathable. , moisture-permeable wearing performance.
2.3.6 Selection of softener
In order to improve the wet rubbing fastness, the dyed fabric is fully softened and finished to make the surface soft and smooth, which can greatly reduce the friction coefficient and effectively improve the wet rubbing fastness. Generally, anionic softeners are used in whitening products for better results, as they are soft and non-yellowing.
2.3.7 Electrolyte requirements
It is required that the electrolyte does not contain Ca2+ and Mg2+ ions. The detection method of electrolyte content is as follows: prepare 90g/L deionized solution containing salt or Yuanming powder (use 25℃ water for salt and 40℃ water for Yuanming powder), apply 20g /L of soda ash (solid), if the solution is turbid or precipitates, it indicates the presence of Ca2+ and Mg2+ impurities.
2.3.8 Requirements for pH value
The alkali agent used to fix the color of reactive dyes must meet the purity quality requirements. After adding alkali for 10 minutes, measure the pH value. The solid pH value should be 10.8-11.0 (cool to 20°C for measurement). At the end of dyeing, the final pH value of the dye bath is 10.6 to 11.0.
3. Summary
The process design to improve the wet rubbing fastness of knitted fabrics dyed with reactive dyes is a comprehensive task. The design of the pre-treatment process should simplify the process, shorten the time, and achieve efficient oxygen bleaching; the design of the dyeing process should use qualified dyes and auxiliaries to shorten the time, and strengthen detection and effective control of process parameters.
In the design of the dyeing process, the amount of dye should generally not exceed 10% of the dyeing saturation value. Excessive dye cannot be dyed and fixed, and will adhere to the surface of the dyed object, affecting the wet rubbing fastness of the dyed object. When dyeing dark colors, be sure to use high exhaustion rates. , dyes with high fixation rate and high lifting power, such as reactive dyes with double reactive groups and multi-reactive groups.
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