6. How to improve the Color Fastness of textiles (general rules)
The dye fastness of the fabric is related to fiber, yarn structure, fabric structure, printing and dyeing method, dye type and external force.
The following are the general principles for improving the Color Fastness of textiles. When it comes to individual Color Fastness, there will be targeted improvement methods.
Start with the following three aspects:
6.1 Selection of dyestuff
How fast a product is heavily dependent on the choice of dyestuff. If the choice of dyeing materials is inappropriate, no matter how good the auxiliary agent and the best dyeing process are, there is no way to dye high-quality Color Fastness. Only by choosing the right dye can we talk about the next step.
(1) Choose dyes according to fiber characteristics. Different types of dyes and fibers have different binding forms, and the strength of the binding bonds is also different. After the type of dye is determined, select dyes with high dyeing performance. For example, when dyeing wool fabrics, they are also strong acid dyes. Domestically produced strong acid dyes are not as good as imported strong acid dyes. Not only are the former not good in color, but their bonding strength is not as good as the latter. Different dyes have different binding fastness to wool and dyeing vividness. For example, the Color Fastness of wool yarn dyed with weak acid dyes is higher than that of strong acid dyes. In the case of pure cotton fabrics or regenerated cellulose fiber fabrics, either direct dyes (the category of dyes that are directly applied to cellulosic fabrics) or reactive dyes (a group of dyes considered to be the most permanent dyes because of their character of attaching to textile fibers and forming covalent bonds) can be used. In addition to acid dyes and some reactive dyes, individual direct dyes can also be used.
(2) Choose dyes according to the color depth. After determining the type of dye, it is necessary to further determine which dye to use according to the dyed color’s color system and depth. Try to choose dyes with shades close to the desired color. If there is a deviation, use other dyes to color. Secondly, look at the Color Fastness index of the selected dye itself. If the dye’s color fastness is poor, then the process can improve the Color Fastness by half. Finally, see whether the saturation of the dye can reach the required color depth. Choose a dye with a very low dyeing rate, even if the desired high-depth color can be temporarily achieved after processing. The dye’s combination will not be firm, and it will fall off during use reprocessing.
(3) Select the dye according to its Color Fastness grade. In the introduction of each dye, the Color Fastness grade of the dye is also introduced. When choosing a dye, you must choose the dye according to the Color Fastness grade required by the product, and the dye fastness of the matching colors’ dyes should be similar. For example, the dye’s Color Fastness can only reach 2~3, or even 1~2, no matter how good the auxiliary and dyeing process are, a product with 4~5 Color Fastness cannot be dyed. Because the dye’s Color Fastness mainly depends on the binding force between the dye and the fiber, if the bond between the two is not strong enough, no external force can make them bond firmly, even when the color is improved. They also would not withstand the damage of external factors such as washing and friction.
(4) The dye uptake rate of the fiber. Different dyes will exhibit different dye uptake rates, and under different dyeing conditions, the dye uptake rate of the same dye is also different. Therefore, the dyeing rate must be considered when choosing dyes. Otherwise, there will be competition between dyes. One of the dyes occupies the fiber’s dyeing position in advance so that other dyes can only be dyed on the surface of the fiber, not evenly. It forms a strong bond with the fiber, which is first destroyed in the subsequent process or daily use. That is why some colors fade and show a completely different color system from the original color. Therefore, when selecting dyes, dyes with similar dyeing speeds under the same conditions must be selected, which is also very beneficial to the next step of the formulation process.
(5) There should be good compatibility between dyes. Different dyes in the same fabric have different compatibility—the greater the compatibility value, the better the ability of dyes to match colors. There must be good compatibility between the dyes that match the colors. It is best to use the three primary colors for colors that are not easy to fight. The three primary colors have the best compatibility among each type of dyes, and they are also the three dyes with the most complete and most positive color matching. Therefore, it is best to use the three primary colors to match some of the more difficult, strange colors, and try not to use other dyes to fight. It is prone to competing for dyeing and dyeing flowers. 2.1.6 To minimize the number of dyes needed, first choose dyes whose shades are similar to the required colors when choosing dyes, and then use one or two dyes to supplement the lack of shades in the main dyes. For dyes of the same color series, the color dyed in this way should be pure, smooth, gorgeous and full. Try not to use four or five kinds of dyes for coloring, as it is not easy to color, neither is it easy to handle mass dyeing. Moreover, although the color and luster are matched, the dyed shade is not bright and full, and the dye cannot be fully combined with the fiber, resulting in poor Color Fastness.
6.2 Selection and use of additives
(1) Choose suitable additives. After determining the type of dye, the choice of additives is also very important. Generally, try to choose the auxiliary agent that matches with the dyestuff; if it is the common dyestuff used routinely, the determination of the auxiliary agent amount and usage method should be emphasized. For dark colors, the dye is not easy to be exhausted. The auxiliary agent can be added in batches to increase the exhaustion rate and improve the fastness of dye adsorption to play a role in fixing the color.
(2) Minimize the amount of retarder. The amount of retarding agent that plays the role of retarding dyeing should be reduced as much as possible. Otherwise, it will have the undesirable effect of stripping. On the one hand, it will reduce the dye uptake, and on the other hand, it will weaken the dye’s binding force and the fiber, making the Color Fastness worse. For colors that are easy to dye, the leveling effect can be achieved through the deployment of dyes and the heating speed.
(3) Selection of fixing agent. The use of a fixing agent will greatly improve the dye’s Color Fastness, generally at least 0.5~1 level, but the choice of fixing agent should also be based on the dye’s fastness, rather than just the individual items. For example, after reactive dyes are treated with cationic low-molecular-weight or polyamine-type fixing agents, the washing fastness of the fabric is 4~5, but the lightfastness will decrease. Furthermore, when fixing, the amount of fixing agent, fixing temperature and fixing time must be strictly controlled.
(4) Soaping and washing. When soaping and washing, you must wash thoroughly and pay attention to the washing temperature and time; otherwise, the floating color on the fabric’s surface will fade during use.
(5) Use of softener. To make the product plump and soft, it is necessary to add a softener. Softeners are categorically cationic, anionic, nonionic and silicone. Softening is the last process after the dyeing process. The dye and softener react furtherly, reducing the Color Fastness especially when the acid dye is dyed with organic silicon softener. Some of the dye will even be removed during the softening process. To lighten the color slightly. Therefore, the amount of softener used in softening treatment should be just right; otherwise, it will feel sticky and affect dyeing.
6.3 Next is to improve the dyeing and finishing process
Fully reduce the crystallinity of the crystalline part of the fiber macromolecular structure and increase the non-crystalline area’s crystallinity. The crystallinity of the various areas inside the fiber tends to be consistent. This is so that after the dye enters the fiber, the fiber’s combination is more-so evenly.
This can not only improve the level of dyeing but also improve the fastness to sublimation. If the crystallinity of the various parts inside the fiber is not balanced enough, most of the dye stays in the amorphous area with a relatively loose structure. After the extreme state of the external conditions, the dye will be more easily separated from the amorphous area inside the fiber and sublimated to the fabric’s surface, thereby reducing the sublimation fastness of textiles.
The scouring and mercerizing of cotton fabrics and the pre-shrinking and pre-sizing of polyester fabrics are all processing procedures that balance the fibers’ crystallinity. After scouring and mercerizing cotton fabrics and pre-shrunk and pre-shaped polyester fabrics, the dyeing depth and Color Fastness can be significantly improved.
Strengthening the post-treatment and washing and removing more surface floating colors can also significantly improve the fabric’s sublimation fastness. Appropriately lowering the set temperature during the setting process can significantly improve the sublimation fastness of the fabric. Reduced fabric dimensional stability due to cooling can be compensated by appropriately reducing the setting speed. When choosing finishing agents, attention should also be paid to the influence of additives on Color Fastness. For example, after using cationic softeners for the soft finishing of polyester fabrics, the thermal migration of the disperse dyes may result in the sublimation fastness test of the disperse dyes failing. From the perspective of the temperature type of disperse dyes, high-temperature disperse dyes have better sublimation fastness.
To sum up:
Many factors affect the dyeing fastness of textiles. For internal factors, all production processes are in place to ensure that the product can have excellent Color Fastness indicators to meet the requirements of daily use and reprocessing; for external factors, We must pay attention to the washing temperature, detergent and washing method, friction strength, exposure time and other factors that can reduce the Color Fastness according to the use requirements of the product, so that the product can be used better.