The Improving of the fastness to wet rubbing of the deeper color fabric dyed with reactive dye is one of the methods to enhance the fabric's quality and overcome the export barrier.
The reasons that cause the bad fastness to wet rubbing is the transfer of water-soluble dye and mechanical friction transfer of colored fiber particle(10-40μm). The test fabric's fastness to wet rubbing process is: rubbing the fabric with the white cloth in stipulated conditions, compare the stain on the white cloth with the Greyscale for staining, that is the transfer from the dye molecule and colored fiber particle to white cloth. Under same fabric, same dye, same preliminary treatment and dyeing process, the deeper the color is, the worse the fastness to wet rubbing is.
The water-soluble groups in the reactive dye are good for the dye dissolution and up-taking, but it is the main reasons for bad wet fastness. Because of the water on the white cloth, it is impossible for the reactive dye to drop off itself and dissolve in the water. So for the reactive dye fabric, its fastness to dye rubbing is up to 4-5 grades, but only 2-3 grade to fastness to wet rubbing.
2.1 Choose the reactive dye with less unfixed dye The unfixed dye is the main reason for the unqualified fastness to wet rubbing of deeper color fabric.
The unfixed reactive dye includes the nonreactive dye that is adsorbing on the surface of the fiber, the dissolved dye and the ethylene dye removing sulfate. The unfixed dye quantity is written as E-F(E is dye-up-taking rate, F is fixation rate in SERF value)
So we must choose the reactive dye with less unfixed dye, that is the lower value got by E minus F, in order to remove the unfixed dye. If the dye fixation rate is high, the dye will be fixing on the fiber, the quantity of unfixed dye will decrease.
For example, the fixing rate of reactive dye, like Cibacron C type, F types, Procion H-EXL is up to 80%. And the quantity of unfixed dye is small. It is good for remove the unfixed dye.
But there are certain relations between final up-taking fixation rate and once up-taking fixation rate. So the reactive dye’s substantivity should not be too high. If the dye with F value less than 70% and E-F value large than 15%, it unfixed color is not easy to remove. So it is not suitable to dye deeper color.
2.2 Choosing the dye with high enhanced reactive dye
The deeper fabric uses the high concentration dye with more unfixed dye. The adsorb of fiber to dye have a saturation value. The concentration of the dye should no large than 10% of the saturation value. The excess dye can not be up-taken and fixed, it will pile up on the surface of the fabric and influence on the fabric’s fastness to wet rubbing. We must choose the reactive dye with good enhance power.
New developed Multi-reactive dye, such as Cibacron dark red S-B, whose enhance power is the 3 times of that of the common red reactive dye(such as, CI reactive red 239195). Other trio-reactive dyes, such as Cibacron red C-2G(CI reactive 228)have two sulphones and one chlorotriazine. Cibacron Red FN-3G(Cl reactive red 266)contain one chlorotriazine, one fluorine triazine base, and one ethylene, Remazol Red BS contain two sulphones and one chlorotriazine. All of them have the good adsorbing ability, high fixation ability, and high enhanced force. And its hydrolyzing dye is easy to be removed.
2.3 Proper dyeing and finishing process
Besides the correct choose of dye, the proper dyeing and finishing process will help to improve the fastness to wet rubbing. The smooth the fabric surface is, the higher the fastness to wet rubbing. So cleaning the floating hair in the singing and reducing the colored fiber particle is necessary. The semi-production of dyeing influence the dyeing penetration in the process of up-taking. If the dyeing penetration is good, the extension of the dye to the inner of the fiber is better. It will reduce the pile of the dye on the surface to the fabric. Moreover, the addition of penetration and mercerization will help to improve the fastness to the wet rubbing.
The washing difficulty of the unfixed dye related with its substantivity to fiber. The large substantivity vinyl sulfone is most different from washing, the second is hydrolysis dye.
The nonreactive β-sulphate vinyl sulfone dye contains sulfate water-soluble group. And its substantivity is small. And it is the dye that is easy to remove the unfixed dye. By water washing and soap washing, the unfixed dye, electrolyte, and alkali can be removed. The auxiliary using in soaping process should be penetrated, it will combine with dye and form into the micelle. And decrease the affinity between dye and fiber. It will form into the core and make the dye micelle disperse in the water evenly. We should choose the anionic or non-ionic surfactant with good penetrating and disperse function form into auxiliary. Or the cleaning of floating dye effect will not be reached.
Water quality is a very important factor. If the water hardness is high, the water-soluble groups in the unfixed dye will form into the insoluble color lake, and influence the removal of the unfixed dye.
The drying method is also important. The transfer of dye molecule in Contact type drying is large than non-contact type drying.
2.4 The PH value control of the fabric surface
In reactive dye deeper color fabric dyeing process, the alkali consumption is high, so we need to pay attention to the water washing process. The fabric surface PH value should be among 6.5-7.5(Oeko-Tex standard 100 technical standard PH value is 4.0-7.5 and 4.0-9.0)in order to prevent the broken of ether bond between vinyl sulfone and fiber in the alkaline medium.
2.5 The fabric's surface smooth
The rougher the fabric surface is, the larger the friction coefficient between testing white cloth and the cloth is. And the larger the effective contact is. So the fastness to wet rubbing declines. According to a stipulation in Eco-Label, the fastness to wet rubbing should not be less than 2 -3 grade. The mate is allowed to be 2 grade. Because compared to plain cloth, the material's coefficient is large than plain cloth’s. Under the same conditions, the fastness to wet rubbing is: Satin drill fabric.
2.6 The damage to the fabric's strength
Some finishing agent improves the functions of the fabric, but at the same time, damage the strength of the fabric. Such as the during easy-care resin shrinkage, fire retardant and sanitary finish agent will cause the cotton fiber polymerization degree (DP)decline, and increase the colored fiber particle, and causes the decline of the fastness.
2.7 Special dye-fixing agent
The special dye-fixing agent will increase the fastness to wet rubbing of deeper color reactive dye by 0.5-1.0 grade. Its requirement is as follows: (1)the phagemid high-molecular compound usually is polyurethane or organic silicone containing functional groups(-OH<, -NH2). It will crosslink with cross-linking agent and high-molecular polymer, and make it durable and easy to form film. (2)no discoloration, no yellowing, no decrease on the light fastness. (3)decline the friction coefficient of fabric, and improve the fabric’s hand feeling. (4) keep the fabric’s ventilation and moisture permeable property.
Besides the above improving measures, an auxiliary manufacturing company produces auxiliary which improves the fabric’s fastness to wet rubbing. This auxiliary is the compound containing the functional groups like -OH, -NH2, it will combine with the cross-linking agent which contains ethylene oxide, and from film quickly and covers on the fabric, and separate the contact between piled dye on the surface of the fabric and testing white cloth. This compound also functions as a softener, it will cause the decline of the film coefficient. When we test friction fastness, it will decrease the friction between testing cloth and fabric, thus, it will improve the fastness to wet rubbing. Such as the organic silicone high- molecular compound with the following molecular structure.
This auxiliary will form a durable film on the surface of fabric, and it will not decrease the light fastness and no discoloration. And it also functions as a softener.
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