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color fastness

2019-05-22

Dyeing fastness refers to the ability of dyes or pigments to maintain their original color state under the influence of various external factors during the use of dyed fabrics or in subsequent processing.


Dyeing fastness is one of the important quality indicators to measure dyeing products of dyestuff factories. The dyeing fastness which is easy to fade is low, and the dyeing fastness which is not easy to fade is high. Dyeing fastness depends largely on its chemical structure. In addition, the physical state of dyes on fibers, the degree of dispersion, the combination of dyes and fibers, dyeing methods and technological conditions also have great influence.


Dyeing fastness is multifaceted, for consumers, generally the main fastness includes: sunshine, soaping, sweat stain, friction, brushing, ironing, smoke and so on. In addition, the fastness requirements of textiles vary with their uses or processing processes. In order to inspect the quality of products, textile and commercial departments have formulated a set of testing methods and standards for dyeing fastness in the light of the use of textiles, which are briefly introduced below.


1. Solar fading of fastness dyed fabrics is a complicated process. Under the action of sunlight, the dyes absorb light energy, and the molecules become extremely unstable in the state of excitation. Some chemical reactions easily occur, which make the dyes decompose and fade, resulting in a larger fading phenomenon of dyed fabrics after sunshine. The fastness to sunlight varies with dyeing concentration, and the fastness to sunlight at low concentration is worse than that at high concentration. The fastness to sunlight of the same dye on different fibers is also quite different. For example, the fastness to sunlight of indigo on cellulose fibers is only 3 grades, but on wool is 7-8 grades. The fastness to sunlight is also related to the aggregation of dyes on fibers, dyeing process and other factors.


The fastness to sunlight is divided into 8 grades, the worst is grade 1, and the best is grade 8.


2. Soap fastness is the degree of fading of dyed fabrics after soaping in soap solution under specified conditions, including original fading and white cloth staining. The fading of the original fabric is the fading of the dyed fabric before and after soaping. The staining of white cloth is the case where the white cloth is sewn together with the dyed material, and after soaping, the dyed material fades and the white cloth is stained.


The soaping fastness is related to the chemical structure of dyes and the binding state of dyes and fibers. In addition, soaping fastness is also related to dye concentration, dyeing process and soaping conditions.


The test conditions of soaping fastness vary with the fabric types. The commonly used soaping temperatures can be divided into 40 ~C, 60 ~C and 95 ~C (each dyeing factory has its own specific soaping temperature). After testing, washing and drying, the test samples are graded according to the national standard by "gray fading sample card". The soaping fastness is divided into five grades and nine grades, among which the first grade is the worst, the fifth grade is good, and the staining is also divided into five grades and nine grades. The first grade is the most serious staining and the fifth grade is non-staining.


3. Friction fastness of dyed fabrics can be divided into dry friction fastness and wet friction fastness. The former is used for rubbing white cloth to see the staining of white cloth, while the latter is used for rubbing and dyeing white cloth with 100% water content to see the staining of white cloth. Wet friction is caused by external friction and water action, and its wet friction fastness is generally lower than dry friction fastness.


The rubbing fastness of fabrics mainly depends on the number of floats, the combination of dyes and fibers, and the uniformity of dye penetration. If covalent bonding occurs between dyes and fibers, the rubbing fastness of dyes is higher. The concentration of dyes used in dyeing often affects the rubbing fastness. High dyeing concentration can easily cause floatation, but the rubbing fastness is low. The rubbing fastness was rated by "stained grey sample card" according to the five-grade and nine-grade system. The first grade was the worst and the fifth grade was the best.


The perspiration fastness and chlorine bleaching fastness were graded according to five grades and nine grades system.


In order to evaluate the dyeing fastness of dyes, it is necessary to dye the textiles into the prescribed color concentration to compare. This is because different dyeing concentration will make the measured fastness different. The test methods of dyeing fastness of dyed fabrics should be carried out according to the methods prescribed by the state, and the standards of fastness should also be based on the national standards.


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