The dye fastness of textiles (abbreviated as color fastness) refers to the way dyed or printed fabrics are subjected to external factors (squeezing, friction, washing, rain, exposure, light, seawater immersion, saliva immersion, etc.) during use or processing. The degree of fading caused by water stains, sweat stains, etc.) is an important indicator of fabrics. If the color fastness is good, the textile will not fade easily during post-processing or use; if the color fastness is poor, fading, slight discoloration, or staining will occur, causing a lot of trouble.
1. Frequently asked questions about color fastness of textiles
In daily random inspections and consumer complaints, common textile color fastness problems include the following aspects:
1) The sun fastness is unqualified. During the wearing process, the color of coats and garments will become lighter or discolored in areas exposed to more sunlight (usually the back and shoulders), while the color of areas not exposed to or exposed to less light will remain the same or change slightly, resulting in products with the same original color. The colors are different shades and can no longer be used.
2) The color fastness to washing, soaping and dry cleaning are unqualified. High-end silk clothing, wool clothing, and pure cotton clothing are prone to this problem.
3) The color fastness to rubbing is unqualified. During the use of textiles, because different parts of the product receive different degrees of friction, the degree of discoloration will be different. For example, the elbows of tops, sleeves, collars and armpits are prone to fading. In addition, the buttocks and knees of pants are also prone to fading.
4) The color fastness to perspiration is unqualified. It is mainly caused by the discoloration of summer clothes or underwear when they are soaked in sweat.
2. Factors affecting color fastness and improvement methods
Products with poor color fastness will fade during wearing, which will affect other clothes worn on the body, or contaminate other clothes when washed with other clothes, affecting the appearance and wearing performance; on the other hand, there is a direct relationship between good and bad color fastness. to human health and safety. The dye molecules and heavy metal ions on products with poor color fastness may be absorbed by the human body through the skin and harm the skin and even harm the health of the body.
Factors affecting the color fastness of textiles are divided into internal factors and external factors. Internal factors refer to the firmness of the combination of dye and fiber, and external factors refer to the external forces exerted on the product by external factors or the environmental conditions provided during the use of the product. External factors cannot be controlled, so manufacturers must work hard to improve the color fastness of the product itself. Here are some solutions based on personal practical experience for everyone to learn from.
2.1 Selection of dyes
How is the color fastness of a product? The choice of dyeing materials is very important. If the selection of dyeing materials is not appropriate, no matter how good the additives or the dyeing process are, it will not be possible to achieve high-quality color fastness. Only when you choose the right dye can you talk about the next step.
2.1.1Select dyes based on fiber characteristics
Different types of dyes have different binding forms with fibers, and the strength of the binding bonds is also different. After the dye type is determined, choose a dye with high dyeing performance. For example, when dyeing wool fabrics, it is also a strong acid dye, but the domestically produced strong acid dyes do not have as good a dyeing performance as the imported strong acid dyes. Not only is the color not good, but the bonding strength is not as good as the latter; or the same domestic strong acid dyes, Different dyes have different bonding fastness to wool and different dyeing brightness. For example, the color fastness of wool yarn dyed with weak acid dyes is higher than that of strong acid dyes; for pure cotton fabrics or regenerated cellulose fiber fabrics, either direct dyes or reactive dyes can be used; in addition to silk fabrics, weak acid dyes can be used In addition to dyes and some reactive dyes, individual direct dyes can also be used.
2.1.2 Select dyes according to color depth
After determining the major categories of dyes, it is necessary to further determine which dye to use based on the color system and depth of the dyed color. First, try to choose dyes whose color light is close to the desired color. If there is a deviation, use other dyes to adjust the color; second, look at the color fastness index of the selected dye itself. The color fastness of the dye itself is poor, and the color fastness can be improved by half a level through processing. Third, it depends on whether the saturation of the dye can reach the required color depth. If you choose a dye with a very low dye pick-up rate, even if it can temporarily achieve the required high depth of color after processing, the dye will not be firmly bonded and will fall off during use or reprocessing.
2.1.3 Select dyes based on their own color fastness levels
In the introduction of each dye, the dye fastness grade of the dye is introduced. When selecting dyes, be sure to select dyes based on the color fastness levels required by the product, and the dye fastnesses of matching color dyes should also be similar. For example, the color fastness of the dye itself can only reach level 2 to 3, or even level 1 to 2. No matter how good the additives and dyeing processes are, it cannot produce products with a color fastness of level 4 to 5. Because the color fastness of a dye mainly depends on the bonding force between the dye and the fiber. If the bond between the two is not strong, no amount of external force can make them bond firmly, even if it improves after fixation. , and cannot withstand damage from external factors such as washing and friction.
2.1.4 Dyeing rate of dyes on fibers
Different dyes will show different dyeing effects.The dye uptake rate of the same dye is also different under different dyeing conditions. Therefore, when selecting dyes, the dyeing rate must be considered, otherwise there will be a dyeing competition phenomenon between dyes, that is, one of the dyes occupies the dyeing position of the fiber in advance, causing the other dyes to only dye on the surface of the fiber and not evenly. It forms a strong bond with the fiber and is thus first destroyed in subsequent processes or daily use. This is why some colors fade to reveal a completely different shade than their original color. Therefore, when choosing dyes, you must choose dyes that have a similar fiber dyeing rate under the same conditions, which is also very beneficial to the next step of formulating the process.
2.1.5 The dyes must have good compatibility
Different dyes in the same type of dye have different compatibility. The greater the compatibility value, the better the ability of the dyes to match each other’s colors. There must be good compatibility between dyes that match colors. For colors that are difficult to match, use the three primary colors. The three primary colors are the three dyes with good compatibility among each type of dye, and they are also the three dyes that can be matched with complete and accurate colors. Therefore, for some strange colors that are difficult to dye, it is best to use the three primary colors to match the color. Try not to use other dyes to match the color, which is prone to competing dyeing and dyeing.
2.1.6 Minimize the number of dyes required
When choosing dyes, you should first choose a dye with a color that is similar to the desired color, and then use one or two dyes to supplement the color that the main dye lacks. Moreover, you should choose dyes with a color that is in the same color system, so that the color produced Pure, smooth, gorgeous and full. Try not to use four or five dyes for coloring. This is not only difficult to adjust the color, but also difficult to operate in large quantities. Moreover, although the color is correct, the dyed color is not bright and full, and the dye cannot fully combine with the fiber, resulting in poor color fastness.
2.2 Selection and use of additives
2.2.1Choose appropriate additives
After determining the type of dye, the choice of auxiliaries is also very important. Generally, try to choose additives that match the dye. If it is a commonly used ordinary dye, you should focus on the determination of the amount of additives and the method of use. For dark colors, the dye is not easy to absorb. The additives can be added in batches to increase the absorption rate. It can also improve the firmness of dye adsorption and play a role in color fixation.
2.2.2 Reduce the amount of dye retardant as much as possible
The amount of retarding agent that can retard dyeing should be reduced as much as possible, otherwise it will have a stripping effect. On the one hand, it will reduce the dye uptake rate, on the other hand, it will weaken the binding force between the dye and the fiber, making the color fastness worse. For colors that are easy to dye, the leveling effect can be achieved by blending dyes and heating speed.
2.2.3 Selection of fixing agent
The use of fixing agents will greatly improve the dye fastness of dyes, generally at least 0.5 to 1 level. However, when choosing a fixing agent, you must also consider the various fastnesses of the dye. Rather than just looking at individual projects. For example: after reactive dyes are treated with cationic low-molecular or polyamine fixatives, the washing fastness of the fabric will be level 4 to 5, but the light fastness will decrease. When fixing, the amount of fixing agent, fixing temperature, and fixing time must be strictly controlled.
2.2.4 Soaping and washing
When soaping and washing, be sure to wash thoroughly and ensure the washing temperature and time. Otherwise, the floating color on the surface of the fabric will fade during use.
2.2.5 Use of softener
In order to give the product a plump and soft feel, softeners should be added. Softeners are cationic, anionic, nonionic and silicone. Softening agent is a process that is carried out after the dyeing process. Further reaction between dye and softening agent may reduce the color fastness, especially if silicone softening agent is used after dyeing with acid dyes, part of the dye may even be removed during the softening process. , making the color slightly lighter. Therefore, the amount of softener used during softening treatment must be just right, otherwise, it will not only feel sticky but also affect the color.
3. Development of dyeing process
The dyeing process is a key link in dyeing. When formulating the process, the dyeing time, heating rate and holding time must be determined according to the dye and product. For light colors, the heating rate should be slow and the holding time can be shorter; for dark colors, the heating rate can be fast, but the holding time must be sufficient so that the dye and fiber can be fully combined to fix the color.
4. Conclusion
In short, there are many factors that affect the dye fastness of textiles. For internal factors, all production processes must be in place to ensure that the product has excellent color fastness indicators and meets the requirements for daily use and reprocessing; for external factors Generally speaking, you must follow the product’s usage requirements and pay attention to factors such as washing temperature, detergent and washing method, as well as friction intensity, exposure time and other factors that can reduce color fastness. Make the product better to use.
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