Complete knowledge of color fastness
Color fastness, also known as color fastness or dye fastness. It refers to the resistance of the color of textiles to various effects during processing and use. Assess the fastness level based on the discoloration of the sample and the staining of the unstained lining fabric.
Textiles are subject to various external factors such as light exposure, washing, ironing, sweat stains, friction, and chemical agents during their use. Some printed and dyed textiles also undergo special finishing processes, such as resin finishing, flame retardant finishing, sand washing, and sanding, which require the color of printed and dyed textiles to maintain a certain degree of fastness.
Factors affecting color fastness
The so-called color fastness (abbreviated as color fastness) refers to the degree of color fading of dyed fabrics under external factors such as compression, friction, washing, rain, exposure, light, seawater immersion, saliva immersion, water stains, sweat stains, etc. during use or processing. It is an important indicator of fabrics* Commonly used are items such as washability, light resistance, friction resistance, sweat resistance, ironing resistance, and weather resistance.
In practical work, the testing items are mainly determined based on the end use and product standards of the product. For example, the wool textile product standards stipulate that the color fastness to sunlight must be tested, knitted underwear of course needs to be tested for sweat fastness, and outdoor textiles (such as sunshades, lightbox fabrics, and canopy materials) of course need to be tested for their color fastness to weather.
Including: color fastness to soap washing (sample), color fastness to friction, color fastness to chlorine water, color fastness to non chlorine bleaching, color fastness to dry cleaning, color fastness to actual washing (clothing, fabric), color fastness to sweat stains, color fastness to water, color fastness to light, color fastness to sea water, and color fastness to saliva.
How to test color fastness?
1. Color fastness to washing
Stitch the sample together with standard lining fabric, wash, wash, and dry under appropriate temperature, alkalinity, bleaching, and friction conditions to obtain test results in a shorter period of time. The friction between them is achieved through the rolling and impact of a small bath ratio and an appropriate number of stainless steel beads, which are rated using a gray card to obtain test results.
Different testing methods have different temperature, alkalinity, bleaching and friction conditions, and sample sizes, which should be selected according to testing standards and customer requirements. Generally, colors with poor washing fastness include emerald, bright orchid, dark red, navy blue, etc.
2. Dry cleaning color fastness
Same color fastness as washing, except that washing has been changed to dry cleaning.
3. Color fastness to friction
Place the sample on the rubbing fastness tester and rub it with a standard white cloth under a certain pressure for a certain number of times. Each group of samples needs to be tested for dry rubbing fastness and wet rubbing fastness. The color of the standard friction white cloth is rated using a gray card, and the resulting level is the measured color fastness to friction. Friction color fastness requires two tests: dry rubbing and wet rubbing, and all colors on the sample must be rubbed.
4. Sun color fastness
Textiles are usually exposed to light during use, which can damage dyes and cause well-known “fading”, causing colored textiles to change color, generally becoming lighter, darker, and some may also change color. Therefore, it is necessary to test the color fastness. Sun color fastness testing is to place the sample together with blue wool standard cloth of different fastness levels under specified conditions for sunlight exposure, compare the sample with the blue wool cloth, and evaluate the light fastness. The higher the level of blue wool standard cloth, the more light resistant it is.
5. Color fastness to sweat stains
Sew the sample together with standard lining fabric, treat it in sweat stain, clamp it on a sweat stain color fastness tester, place it in an oven at a constant temperature, then dry it, grade it with a gray card, and obtain the test results. Different testing methods have different sweat stain ratios, sample sizes, testing temperatures, and times.
6. Color fastness to water stains
Test the water treated sample as described above.
Color fastness to chlorine bleaching: After washing the fabric with chlorine bleaching solution under certain conditions, the degree of color change is evaluated, which is the color fastness to chlorine bleaching.
7. Non chlorine bleaching color fastness
After washing the fabric under non chlorine bleaching conditions, the degree of color change is evaluated, which is called non chlorine bleaching color fastness.
8. Color fastness to hot pressing
After covering the dry sample with cotton lining fabric, it is compressed in a heating device at a specified temperature and pressure for a certain period of time, and then the color change of the sample and the adhesion of the lining fabric are evaluated using a gray sample card. The color fastness of hot pressing includes dry pressing, wet pressing, and wet pressing, and the specific testing method should be selected according to different customer requirements and testing standards.
Types of Color Fastness Testing and Fastness Analysis
The nature or degree of color state variation can be represented by color fastness.
The color fastness of fabrics is related to the type of fibers, yarn structure, fabric structure, printing and dyeing methods, dye types, and external forces.
The testing of color fastness generally includes color fastness to light, color fastness to weather, color fastness to washing, color fastness to friction, color fastness to sweat stains, etc. Sometimes there are special requirements for color fastness according to different textiles or different usage environments.
When conducting color fastness tests, the degree of discoloration of the dye and the degree of adhesion to the substrate are usually evaluated. The color fastness rating is five, except for the light fastness rating of eight. The higher the level, the better the color fastness.
1. Sun fastness
Sun fastness refers to the degree to which colored fabrics change color under the influence of sunlight. The testing method is to simulate the degree of fading of the sample after exposure to sunlight and compare it with the standard color sample. It is divided into 8 levels, with level 8 being * good score and level 1 being * poor. Fabrics with poor sun fastness should not be exposed to sunlight for a long time and should be placed in a ventilated place to dry in the shade.
2. Washing fastness
Washing or soaping fastness refers to the degree of color change of dyed fabrics after being washed with detergent. Usually, grey grading cards are used as evaluation criteria, which rely on the color difference between the original sample and the sample after fading for evaluation. The washing fastness is divided into 5 levels, with 5 levels being good and 1 level being poor. Fabrics with poor washing fastness should be dry cleaned. If wet washing is performed, double attention should be paid to washing conditions, such as not using too high a washing temperature and not using too long a washing time.
3. Friction fastness
Friction fastness refers to the degree of color fading of dyed fabrics after friction, which can be achieved through both dry and wet friction. The rubbing fastness is evaluated based on the degree of white cloth staining, and is divided into 5 levels. The higher the value, the better the rubbing fastness.
4. Sweat fastness
Sweat fastness refers to the degree of color fading of dyed fabrics after being lightly soaked in sweat.
5. Ironing fastness
It refers to the degree of discoloration or fading of dyed fabrics during ironing.
6. Sublimation fastness
It refers to the degree of sublimation that occurs during the storage of dyed fabrics. The color fastness of normal fabrics generally requires a level of 3-4 to meet the needs of wearing.
Methods to improve color fastness
The factors that affect the color fastness of textiles are mainly divided into internal and external factors. Internal factors refer to the degree of adhesion between dyes and fibers, while external factors refer to the external forces or environmental conditions applied to the product during use. External factors cannot be controlled, so producers need to strive to improve the color fastness of the product itself.
Selection of dyeing materials
The color fastness of a product depends on the choice of dyeing materials. If the selection of dyeing materials is not appropriate, even the best additives and dyeing processes cannot achieve high-quality color fastness. Only by selecting the appropriate dye can we discuss the next steps.
(1) Choose dyes based on the characteristics of the fibers. Different types of dyes have different binding forms with fibers, and the degree of bond strength also varies. After determining the type of dye, choose a dye with high dyeing performance. For example, when dyeing wool fabrics with strong acidic dyes, domestically produced strong acidic dyes do not have as good dyeing performance as imported ones. Not only is the color poor, but the bonding strength is also not as good as the latter; Alternatively, using domestically produced strong acid dyes, different dyes have varying degrees of adhesion and vividness when combined with wool. 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, both direct dyes and reactive dyes can be used; Silk fabrics can be dyed not only with weak acidic dyes and certain reactive dyes, but also with individual direct dyes.
(2) Choose dyes according to the depth of color. After determining the major categories of dyes, it is necessary to further determine which dye to use based on the color scheme and depth of the dyed color, Try to use dyes with colors that are close to the desired color, and if there is a deviation, use other dyes to adjust the color. Secondly, check the color fastness index of the selected dye itself. The color fastness of the dye itself is poor, and it can be improved to half degree color fastness through various processes. Thirdly, check if the saturation of the dye can reach the required depth of color. If a dye with a very low dyeing rate is selected, even if it can temporarily achieve the desired high depth color through processing, the binding of the dye will not be strong and will fall off during use or reprocessing.
(3) Choose the dye based on its own color fastness level. In the introduction of each dye, the color fastness level of the dye is described. When choosing a dye, it is necessary to select the dye according to the required color fastness level of the product, and the color fastness of the matching dyes should also be similar. For example, the dye itself can only achieve a color fastness of 2-3 levels, or even 1-2 levels, and even the best additives and dyeing processes cannot produce products with a color fastness of 4-5 levels. Because the color fastness of dyes mainly depends on the bonding force between dyes and fibers. If the bonding bond between the two is not strong, no amount of external force can make them firmly bonded. Even if there is some improvement after fixation, they cannot withstand external factors such as washing and friction.
(4) The dyeing rate of dyes on fibers. Different dyes exhibit different dyeing rates, and under different dyeing conditions, the dyeing rate of the same dye is also different. So when choosing dyes, the dyeing rate should be considered, otherwise there will be competitive dyeing 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, unable to uniformly form a strong bond with the fiber, and thus be destroyed first in the subsequent process or daily use. That’s why some colors appear completely different from their original colors after fading. Therefore, when selecting dyes, it is necessary to choose dyes with similar dyeing rates on fibers under the same conditions, which is also very beneficial for the next step of developing the process.
(5) There should be good compatibility between dyes. Different dyes within the same class have different compatibility, and the larger the compatibility value, the better the ability of dyes to match each other. Dyes that match colors must have good compatibility. The colors that are not easy to assemble are best used with the three primary colors. The three primary colors are the most compatible among all types of dyes, and they are also the most versatile and positive dyes for color matching. Therefore, for some difficult to dye strange colors, it is best to use the three primary colors for color matching, and try not to use other dyes for hard splicing, which can easily lead to competitive dyeing and flower dyeing. 2.1.6 Minimize the number of required dyes as much as possible. When selecting dyes, first choose dyes with colors similar to the desired color, and then use one or two dyes to supplement the missing color of the main dye. Moreover, choose dyes with colors belonging to the same color system, so that the dyed color is pure, smooth, bright, and full. Try not to use four or five types of dyes for coloring, as it is not easy to mix colors and handle large-scale dyeing. Moreover, although the color matches, the dyed light is not bright or full, and the dye cannot fully bond with the fiber, resulting in poor color fastness.
Selection and use of additives
(1) Choose appropriate additives. After determining the type of dye, the selection of additives is also important. Generally, it is advisable to choose additives that are compatible with the dye. If using regular dyes, it is important to focus on determining the amount of additives and the method of use. For dark colors, dyes are not easily absorbed. Adding additives in batches can improve the absorption rate and enhance the firmness of dye adsorption, playing a role in fixing the color.
(2) Try to minimize the amount of dye retardants used. The amount of dye retardants that have a slow dyeing effect should be minimized as much as possible, otherwise they will have a stripping effect. On the one hand, it will reduce the dye uptake rate, and on the other hand, it will weaken the binding force between the dye and the fiber, resulting in poor color fastness. For colors that are easy to dye, uniform dyeing can be achieved by adjusting the dye and heating rate.
(3) Selection of fixing agents. The use of fixing agents can greatly improve the color fastness of dyes, generally by at least 0.5 to 1 level. However, when choosing a fixing agent, it is necessary to consider all aspects of the dye’s color fastness, rather than just individual items. For example, when reactive dyes are treated with cationic low molecular weight or polyamine fixing agents, the washing fastness of the fabric is at level 4-5, but the sun fastness may decrease. When fixing, it is necessary to strictly control the amount of fixing agent, fixing temperature, and fixing time.
(4) Soap washing and water washing. When soap washing and water washing, it is necessary to wash thoroughly and ensure the washing temperature and time, otherwise, the floating color on the surface of the fabric will fade during use.
(5) The use of softener. In order to give the product a full and soft feel, a softener treatment should be added. Softeners come in cationic, anionic, nonionic, and organosilicon forms. Softener is a process that is carried out after the dyeing process is completed. The further reaction between dye and softener may reduce the color fastness, especially when using organic silicon softener after acid dye dyeing. During the softening treatment, some of the dye may even be removed, making the color slightly lighter. Therefore, the amount of softener used during softening treatment should be just right, otherwise, not only will it feel sticky, but it will also affect dyeing.
summary
There are many factors that affect the color fastness of textiles. For internal factors, it means that all production processes are done properly to ensure that the product has excellent color fastness indicators and meets the requirements of daily use and reprocessing; For external factors, it is necessary to pay attention to the washing temperature, detergent, washing method, friction force, exposure time, and other factors that can reduce color fastness according to the product’s usage requirements, so that the product can be used better.
