What Is Fabric Color Fastness?
Color fastness is also called dyeing fastness or dyeing fastness. It refers to the resistance of the color of textiles to various effects during processing and use. The fastness grade is assessed based on the discoloration of the sample and the staining of the undyed adjacent fabric.
During their use, textiles will be exposed to various external effects such as light, washing, ironing, sweat, friction and chemical agents. Some printed and dyed textiles also undergo special finishing processes, such as resin finishing, flame retardant finishing, sand washing, sanding, etc., which requires the color of printed and dyed textiles to maintain a certain fastness.
Color fastness refers to the product's resistance to washing and friction.
The so-called color fastness (abbreviated as color fastness) refers to the degree of fading of dyed fabrics under the influence of external factors (extrusion, 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. The most commonly used are washing resistance, light resistance, friction resistance, sweat resistance, ironing resistance, and weather resistance.
In actual work, the test items are mainly determined according to the final use of the product and the product standard. For example, the wool textile product standard stipulates that the color fastness to sunlight must be tested, and the knitted underwear must of course be tested for perspiration fastness, while outdoor textiles (such as parasols, light box cloth, and canopy materials) must of course be tested for weather fastness.
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, actual washing color fastness (ready-made clothes, fabrics), color fastness to perspiration, color fastness to water, color fastness to light, color fastness to seawater, and color fastness to saliva.
How to test color fastness
1. Washing color fastness: Sew the sample together with the standard adjacent fabric, wash, clean and dry it, and wash it under appropriate temperature, alkalinity, bleaching and friction conditions to obtain the test results in a shorter time. The friction is achieved by rolling and impacting with a small bath ratio and an appropriate number of stainless steel beads, and the gray card is used for rating to obtain the test results. Different test methods have different temperatures, alkalinity, bleaching and friction conditions and sample sizes, which should be selected according to the test standards and customer requirements. The colors with poor water washing color fastness generally include emerald blue, bright blue, black red, navy blue, etc.
2. Dry cleaning color fastness: The same as water washing color fastness, except that water washing is changed to dry cleaning.
3. Rubbing color fastness: Place the sample on the friction fastness meter, and rub it with a standard friction white cloth for a certain number of times at a certain pressure. Each group of samples needs to be tested for dry friction color fastness and wet friction color fastness. The color stained on the standard friction white cloth is rated with a gray card, and the resulting grade is the measured friction color fastness. Rubbing color fastness requires two tests, dry and wet rubbing, and all colors on the sample must be rubbed.
4. Sunlight color fastness: Textiles are usually exposed to light when used. Light can destroy dyes and cause the well-known "fading", which causes colored textiles to change color, generally lighter or darker, and some will also change color. Therefore, it is necessary to test the color fastness. The sunlight color fastness test is to expose the sample to sunlight under specified conditions together with blue wool standard cloth of different fastness grades, compare the sample with the blue wool cloth, and evaluate the light fastness. The higher the grade of the blue wool standard cloth, the more light fast it is.
5. Perspiration color fastness: The sample is sewn together with the standard lining fabric, treated in sweat liquid, clamped on the sweat color fastness meter, placed in an oven at a constant temperature, and then dried. The gray card is used for rating to obtain the test results. Different test methods have different sweat liquid ratios, different sample sizes, and different test temperatures and times.
6. Water color fastness: The sample is treated with water as above.
7. Chlorine bleaching color fastness: After washing the fabric in chlorine bleaching solution under certain conditions, evaluate the degree of color change, which is the chlorine bleaching color fastness.
8. Non-chlorine bleaching color fastness: After washing the fabric under non-chlorine bleaching washing conditions, evaluate the degree of color change, which is the non-chlorine bleaching color fastness.
9. Pressing color fastness: After covering the dry sample with cotton adjacent fabric, press it in a heating device with specified temperature and pressure for a certain period of time, and then use the gray sample card to evaluate the color change of the sample and the staining of the adjacent fabric. Hot pressing color fastness includes dry pressing, damp pressing, and wet pressing. The specific test method should be selected according to different customer requirements and test standards.
Types of color fastness tests and fastness analysis
The nature or degree of dyeing state variation can be expressed by dyeing fastness.
The dyeing fastness of fabrics is related to the type of fiber, yarn structure, fabric organization, printing and dyeing method, type of dye and the size of external forces.
Color fastness tests generally include color fastness to light, color fastness to weather, color fastness to washing, color fastness to friction, color fastness to perspiration, etc. Sometimes there are some special color fastness requirements according to different textiles or different use environments.
Usually, when color fastness tests are carried out, the degree of discoloration of the dyed fabric and the degree of staining on the lining are graded. Except for the color fastness to light, which is graded at grade eight, the rest are graded at grade five.
The higher the grade, the better the color fastness.
1. Sunlight fastness: Sunlight fastness refers to the degree of discoloration of colored fabrics under the action of sunlight. The test method is to compare the fading degree of the sample after simulating sunlight with the standard color sample, which is divided into 8 grades, grade 8 is the best score, and grade 1 is the worst. Fabrics with poor sunlight fastness should not be exposed to the sun 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 the dyed fabric after washing with detergent. Usually, the gray grading sample card is used as the evaluation standard, that is, the color difference between the original sample and the sample after fading is used for evaluation. Washing fastness is divided into 5 levels, with 5 being the best and 1 being the worst. Fabrics with poor washing fastness should be dry-cleaned. If wet-cleaned, extra attention should be paid to the washing conditions, such as the washing temperature should not be too high and the time should not be too long.
3. Friction fastness: Friction fastness refers to the degree of discoloration of the dyed fabric after friction, which can be dry friction and wet friction. Friction fastness is based on the degree of staining of white cloth as the evaluation principle, and is divided into 5 levels. The larger the value, the better the friction fastness.
4. Sweat fastness: Sweat fastness refers to the degree of discoloration of the dyed fabric after a small amount of sweat.
5. Ironing fastness: refers to the degree of discoloration or fading of the dyed fabric during ironing.
6. Sublimation fastness: refers to the degree of sublimation of the dyed fabric during storage. Normal fabrics generally require a color fastness of 3-4 to meet the needs of wearing.
Methods to improve dye color fastness
Although some dyes can produce brighter colors, due to the water-soluble groups on the dyes, the wet fastness is poor, and the fading and staining phenomena are serious, which not only makes the textiles themselves look old, but also the dyes fall off and stain the white or other colored fibers, resulting in staining and color matching.
In addition, although reactive dyes can form covalent bonds with cellulose fibers, if there are hydrolyzed dyes or the unbonded dyes are not soaped sufficiently during dyeing, the wet fastness will also decrease; in addition, reactive dyes that have formed covalent bonds with fibers may also decompose and break bonds under acidic or alkaline conditions, as well as problems such as insufficient chlorine fastness, perspiration fastness, and sunlight fastness.
In order to improve the color fastness of fabrics, color fixation treatment can be carried out. These auxiliaries that can improve various types of color fastness are called color fixatives.
Fixing agent fixing principle
1. Generate insoluble color lakes on the fabric, block soluble groups, make the dye on the fabric difficult to dissolve and fall off when in contact with water, and achieve the purpose of improving wet treatment fastness. However, after these fixing agents fix the color, it is easy to change the color of the fabric or cause the light fastness to decrease.
2. Generate a mesh film on the fabric to prevent the dye from falling off.
3. Use the reactive groups in the fixing agent molecules to cross-link with the reactive groups on the dye molecules and the hydroxyl groups on the cellulose molecules to improve the fixing effect of the dye on the fiber.
4. Use the molecular attraction between the fixing agent and the fiber to increase the fixing strength of the fixing agent, thereby improving the color fastness.
