What are the factors that affect color fastness? The color fastness of textiles (color fastness for short) refers to the degree of fading of dyed or printed fabrics under the action of external factors (pressure, friction, washing, rain, sun exposure, light, seawater immersion, saliva immersion, water stains, sweat stains, etc.) during use or processing. It is an important indicator of fabrics. Good color fastness means that textiles are not easy to fade during post-processing or use; poor color fastness will result in fading, slight color change, or staining, causing many troubles.
　　1. Common problems of textile color fastness In daily spot checks and consumer complaints, the most common textile color fastness problems are as follows: 1) The light fastness is unqualified. In the wearing process of outerwear, the color of the parts exposed to sunlight becomes lighter or changes color (generally the back and shoulder parts), while the color of the parts not exposed or less exposed to sunlight remains unchanged or changes slightly, resulting in inconsistent colors of the originally consistent products, and it cannot be used again.
　　2) The water washing fastness, soap washing fastness and dry cleaning fastness are unqualified. High-grade silk garments, wool garments and pure cotton garments are most prone to this problem.
　　3) The rubbing fastness is unqualified. During the use of textiles, the degree of fading is different because the degree of friction on different parts of the product is different. For example, the elbows, collars and armpits of jackets and sleeves are the most prone to fading. In addition, the buttocks and knees of trousers are also prone to fading.
　　4) The perspiration fastness is unqualified. It mainly refers to summer clothes or close-fitting underwear fading when worn after being soaked in sweat.
　　2. Factors affecting color fastness and improvement methods Products with poor color fastness will fade during wearing, affecting other clothing worn on the body, or staining other clothes when washing with other clothes, affecting the appearance and wearing performance; on the other hand, good or bad color fastness is also directly related to human health and safety. Dye molecules and heavy metal ions on products with poor color fastness may be absorbed by the human body through the skin, harming the skin and even damaging health.
　　The factors affecting the color fastness of textiles are divided into internal factors and external factors. Internal factors refer to the degree of firmness of the combination of dyes and fibers, and external factors refer to the external forces or environmental conditions applied to the product by external factors during use. External factors cannot be controlled, so producers should strive to improve the color fastness of the products themselves. Below are some solutions based on personal practical experience for your reference.
　　2.1 Selection of dyes The choice of dyes is very important for the color fastness of a product. If the dyes are not chosen properly, no matter how good the auxiliaries or dyeing technology are, high-quality color fastness cannot be dyed. Only by choosing suitable dyes can the next step be discussed.
　　2.1.1 Selection of dyes according to fiber characteristics Different types of dyes have different binding forms with fibers, and the firmness of the binding bonds is also different. After the type of dye is determined, a dye with high dyeing performance is selected. For example, when dyeing wool fabrics, the domestic strong acid dyes are not as good as the imported strong acid dyes in terms of dyeing performance. Not only is the color not good, but the firmness of the combination is also not as good as the latter; or, for the same domestic strong acid dyes, different dyes have different bonding strength and dyeing brightness with wool. For example, the color fastness of wool yarn dyed with weak acid dyes is higher than that of strong acid dyes; while pure cotton fabrics or regenerated cellulose fiber fabrics can use direct dyes or reactive dyes; silk fabrics can use weak acid dyes, some reactive dyes, and some direct dyes.
　　2.1.2 Selection of dyes according to color depth After determining the general category of dyes, it is necessary to further determine which specific dye to use according to the color system and depth of the dyed color. First, try to choose dyes with color light close to the required color, and if there is a deviation, use other dyes to adjust the color; second, look at the color fastness index of the selected dye itself. If the color fastness of the dye itself is poor, the color fastness can be improved by half a grade at most through the process; third, see if the saturation of dye dyeing can reach the required color depth. If a dye with a very low dyeing rate is selected, even if the required high-depth color can be temporarily achieved after processing, the combination of the dye will not be firm and will fall off during use or reprocessing.
　　2.1.3 Selection of dyes according to the color fastness grade of the dye itself The introduction of each dye introduces the color fastness grade of the dye. When selecting dyes, you must select dyes according to the color fastness grade required by the product, and the color fastness of the matching dyes should also be similar. For example, if the color fastness of the dye itself can only reach grade 2-3, or even grade 1-2, even the best auxiliaries and dyeing processes cannot dye products with grade 4-5 color fastness. Because the color fastness of the dye mainly depends on the binding force between the dye and the fiber, if the binding bond between the two is not firm, no matter how great the external force is, it cannot make them firmly combined. Even if the color is improved after fixation, it cannot withstand the destruction of external factors such as washing and friction.
　　2.1.4 Dyeing rate of dyes on fibers Different dyes will show different dyeing rates, and the dyeing rate of the same dye is also different under different dyeing conditions. Therefore, when choosing dyes, the dyeing rate should be considered, otherwise, competition dyeing will occur between dyes, that is, one dye will occupy the dyeing position of the fiber in advance, causing other dyes to only dye on the surface of the fiber and cannot evenly form a firm binding bond with the fiber, thus being destroyed first in the later process or daily use. This is why some colors fade and show a completely different color system from the original color. Therefore, when choosing dyes, dyes with similar dyeing rates on fibers under the same conditions must be selected, which is also beneficial to the next step of process formulation.
　　2.1.5 Good compatibility between dyes Different dyes in the same type of dye have different compatibility. The larger the compatibility value, the better the ability of dyes to match colors. The matching dyes must have good compatibility. The colors that are not easy to match are best made with three primary colors. The three primary colors are the three dyes with the best compatibility in each type of dye, and the most complete and correct color light can be matched. Therefore, for some difficult-to-dye strange colors, it is best to use three primary colors to match the colors, and try not to use other dyes to forcefully match, which is easy to cause competitive dyeing and easy to dye flowers.
　　2.1.6 Minimize the Number of Dyes Required When selecting dyes, prioritize those with hues closest to the desired color. Supplement the main dye with one or two others to fill in missing hues, selecting dyes within the same color family for pure, bright, vibrant, and rich results. Avoid using four or five dyes, as this complicates color mixing, large-batch dyeing, and may result in dull, unsaturated colors with poor dye-fiber bonding and low colorfastness.
　　2.2 Selection and Use of Auxiliaries 2.2.1 Selecting Appropriate Auxiliaries After determining the dye type, proper auxiliary selection is crucial. Prioritize using dye-matched auxiliaries. For common dyes, focus on precise auxiliary quantity and application method. For dark colors where dye uptake is difficult, adding auxiliaries in batches can improve absorption and dye fixation, enhancing colorfastness.
　　2.2.2 Minimizing Retarder Use Retarders should be used sparingly, as excessive amounts can cause stripping. This reduces dye uptake and weakens dye-fiber bonding, diminishing colorfastness. For colors prone to uneven dyeing, adjust dye composition and heating rate to achieve uniformity.
　　2.2.3 Selection of Fixing Agents Fixing agents significantly improve colorfastness, typically by 0.5-1 grade. However, consider all colorfastness aspects when selecting a fixing agent, not just individual properties. For instance, cationic low-molecular or polyamine fixing agents with reactive dyes may achieve a 4-5 grade wash fastness but reduce lightfastness. Strictly control fixing agent quantity, temperature, and time.
　　2.2.4 Soaping and Washing Thorough soaping and washing are essential, ensuring correct temperature and time to prevent surface color loss during use.
　　2.2.5 Use of Softeners To achieve a full and soft hand feel, add softeners such as cationic, anionic, non-ionic, or silicone types. Applied after dyeing, softeners may react further with dyes, potentially reducing colorfastness, especially with acid dyes and silicone softeners, which might even lighten the color. Therefore, use softeners judiciously to avoid a sticky hand feel and color issues.
　　3 Dyeing Process Formulation Dyeing process formulation is critical. Determine dyeing time, heating rate, and holding time based on the dye and product. For light colors, use a slow heating rate and shorter holding time; for dark colors, a faster heating rate but sufficient holding time ensures proper dye-fiber bonding and colorfastness.
　　4 Conclusion In summary, numerous factors influence textile colorfastness. For intrinsic factors, ensure each production step is performed correctly to achieve optimal colorfastness, meeting everyday wear and further processing requirements. For extrinsic factors, consider the product's use, noting washing temperature, detergents, washing methods, friction intensity, and sun exposure, all of which can reduce colorfastness. These considerations improve product performance.