Many people is asking the questions about color fastness. Some is asking why the clothes color bleeding when washing. and some is telling the color fades after long time hanging under the sun. All these questions are leading to today’s topic: color fastness.
Let’s talk about it from the very beginning.
Failure Factors and Control Solution of Color Fastness
There are many factors that affect the color fastness of dyed products, but they mainly depend on the chemical structure of the dye material, the physical state of the dye material on the fiber (the degree of dispersion of the dye material, the combination with the fiber), the concentration of the dye material, the dyeing method and the process conditions. The properties of fibers also have a great influence on the color fastness of dyeing. The same dyes often have different fastness on different fibers. For example, the color fastness to sunlight of indigo on cotton fiber is not high, but it is very high on wool.
1. Influencing Factors and Solutions of Color Fastness to Soaping
Color fastness to soaping refers to the degree of fading of dyed products after washing in soap solution under specified conditions. It includes the original fading and the staining of white cloth. Original fading refers to the fading of printed and dyed fabrics before and after soaping; white cloth staining is a situation where white cloth and dyed fabric are stitched together in a certain way, and after soaping, the white cloth is stained due to the fading of the dyed fabric. The soaping and fading of dyed products is the effect of external force and detergent on the dye on the fabric in the soap solution, which destroys the combination of the dye and the fiber, so that the dye falls off the fabric and dissolves into the washing liquid and fades.
First of all, color fastness to soaping relates to the solubility of dyes. Dyes with many hydrophilic groups and good water solubility have low soaping color fastness. On the contrary, insoluble dyes have high soaping color fastness. For example, acid dyes and direct dyes have low soaping color fastness because they contain more water-soluble groups, while insoluble dyes such as reduction, vulcanization, and dispersion have higher soaping color fastness.
Secondly, the color fastness to soaping relates to the combination of dyes and fibers. For example, acid mordant dyes and direct copper salt printing and dyeing product quality control dyes, due to the dye and metal chelation, the water solubility of the dye is reduced, the binding force between the dye and the fiber is increased, and the soaping color fastness is improved. The reactive dyes and cellulose fibers can be covalently bonded, so the soaping color fastness is better.
Third, the soaping color fastness of same dye material on different fibers is different. For example, the soaping colorfastness of disperse dyes on polyester is higher than that on nylon. This is because the structure of polyester is tighter than nylon and its hydrophobicity is stronger. In addition, the soaping colorfastness is also closely related to the dyeing process. Dye diffusion is not sufficient, most of it floats on the surface of the fiber, and it is easy to fall off from the fiber, and the soaping color fastness is poor; it is not washed after dyeing, and the floating color has residues, which will also cause the soaping color fastness to decrease; Temperature, pH value and stirring conditions all have an effect on soaping colorfastness; dye concentration generally has a small effect on soaping colorfastness, but the dye concentration is high, the combination of dye and fiber is super saturated, and the dye is easy to fall off by external force. This also affects the soaping color fastness.
In order to improve the soaping colorfastness, for different fibers, it is necessary to select different dyes according to the soaping colorfastness requirements, formulate a reasonable dyeing process, and operate strictly according to the process to fully combine the dye and fiber, and wash thoroughly after dyeing. For net floating color, appropriate fixing agent can be added to fix the color if necessary to improve the soaping color fastness.
2. Influencing Factors and Solutions of Color Fastness to Crocking/Rubbing
The color fastness to crocking/rubbing of dyed products is divided into dry rubbing color fastness and wet rubbing color fastness. The former is to rub the dyed fabric with a dry white cloth to observe the staining of the white cloth; the latter is to rub the dyed fabric with a white cloth containing 100% water to observe the staining of the white cloth. The friction fading of the fabric is caused by the dye falling off under the action of friction. In addition to the action of external force, wet friction also has the action of water. Therefore, wet friction is generally about one level lower than dry friction.
The rubbing color fastness of the fabric depends on the amount of floating color and the molecular weight of the dye, the combination of the dye and the fiber, the uniformity of the dye penetration, and the particle condition of the dye on the surface of the fabric. Such as reactive dyes, dyes and fibers are fully combined by covalent bonds, and their rubbing fastness is high; insoluble azo dyes and vat dyes are mechanically attached to the fibers, and their rubbing color fastness is low, such as floating color removal. , The rubbing colorfastness is lower; the dye molecule is large (such as sulfur black), and the dye is easy to form large particles of dye floating on the surface of the fiber after dyeing, and the dye concentration is generally too large, which reduces the crocking colorfastness; especially most dyes The binding force with the fiber is more easily destroyed in the presence of moisture, so the wet crocking color fastness is lower than the dry crocking color fastness.
In order to ensure the crocking color fastness, it is necessary to select suitable dyes and formulate a reasonable process to ensure that the dyes fully penetrate into the fiber and the floating color should be fully washed after dyeing. If necessary, a smoothing and fixing cross linking agent can be added to make the dye and fiber bond more firmly, reduce the friction on the surface of the fabric, and at the same time form a soft film covering the dye on the fiber surface, so that the dye is not easy to fall off during rubbing, and the color fastness to crocking is improved.
3. Influencing Factors and Solutions of Color Fastness to Sunlight
The fading and discoloration of dyed fabric after exposure to sunlight is a relatively complicated process. Under the action of sunlight, the dye material absorbs light energy, and the molecule is in an excited state. It is unstable. The energy must be released in different forms to become a stable state. One of the forms is that the dye material is directly decomposed after receiving sunlight energy, and the dye color system is destroyed and changed, and some dye molecules are oxidized or reduced under the action of sunlight to fade. For example, the fading of azo dyes on cellulose fibers is an oxidation process, while the fading on protein fibers is the result of reduction.
The colorfastness to sunlight of same dye material on different fibers is very different. The light fastness of disperse dyes on polyacrylonitrile and polyester fibers is higher than that on acetate fibers, and other dyes are similar. The dyes have different sunlight color fastness on cotton and viscose fibers at the same concentration, and the sunlight color fastness on viscose fibers is higher than that on cotton. Another example is the sunlight colorfastness of vat dyes on cellulose fibers, but poor on polyamide fibers. This is because the physical state of the dye on different fibers and the binding fastness to the fiber are different.
When the sunlight fastness of the dye material is related to its molecular structure. For example, the indigo dyes in the vat dyes are relatively poor in light fastness. While the anthraquinone dyes are mostly excellent; among other dyes, anthraquinone. The sunlight fastness of phthalocyanine and metal complex dyes is generally higher. For example, the direct sunlight colorfastness dye contains metal atoms in its molecule, and its sunlight colorfastness is higher than that of ordinary direct dyes. Another example is that the molecular structure of the dye contains more amino hydroxyl groups and other groups, which will promote the dye to absorb sunlight energy and oxidize and fade, and its sunlight colorfastness is low; and the introduction of nitro groups, halogens and other groups is not easy to fade, which will cause the dye to fade. The colorfastness to sunlight is improved.
The sunlight colorfastness also varies with the dyeing concentration. The same dye is on the same fiber, and the sunlight colorfastness of low dyeing concentration is generally worse than that of high concentration. This is because the same intensity of incident light when the dyeing concentration is low, the energy distributed to each dye molecule is high, and the dye reception is high. Intensity of light energy is easier to oxidize or reduce and fade.
When dyes with different colorfastness to sunlight are mixed together, they sometimes affect each other’s sunlight colorfastness, some reduce the sunlight colorfastness, and some increase the sunlight colorfastness.
Because some additives are added to the dyed fabric, it will affect the sunlight colorfastness of the dyed fabric. For example, some fixing agents make dyed fabric easy to absorb sunlight energy and fade and reduce the sunlight colorfastness, while ultraviolet light shielding agents make dyed products difficult to absorb sunlight energy and can improve the colorfastness to sunlight.
The colorfastness to sunlight is also related to the bonding state of the fiber and the dye. For example, reactive dyes, which are covalently bound to the fiber, are stable to sunlight and have high sunlight colorfastness, but when the fiber contains more hydrolyzed dyes, the sunlight colorfastness is low.
Dyes with good penetrability have good light fastness.
To ensure that the dyed fabric have good colorfastness to sunlight, the key is to choose the dye from the structure, and then formulate a reasonable dyeing process to dye specific fiber fabrics. In the finishing after dyeing, the additives added should also be selected to ensure that the additives will not significantly reduce the light fastness of the dye.
4. Other Color Fastness Classification
The perspiration color fastness, chlorine bleaching color fastness, and sublimation color fastness mainly depend on the structure of the dye itself. For example, in reactive dyes, the bond between some dyes and fibers is easy to break under acidic conditions, and the perspiration fastness is poor. Reactive dyes based on pyrazolone have poor color fastness to chlorine bleaching, and phthalocyanine structure is better; reactive dyes with bromamine acid structure are prone to smoke fading; disperse dyes with strong binding force to fibers are sublimated high color fastness. Color fastness is also closely related to factors such as the color density of the dye material and the structural condition of the fiber, the physical state of the dye on the fiber, the dyeing process, and the fiber performance.
I think you may have a brief idea about the color fastness and its classification. So we may start our more detailed discussion now.
Color Fastness Definition
What is color fastness? Color fastness is one of the important internal quality indicators of dyed products. Different products and different uses have different requirements for color fastness. Dyed fabric must be tested for color fastness according to customer requirements, and those who do not meet the standards cannot leave the factory.
There are many factors that cause the dyed fabric fail to meet the color fastness test standard. The influencing factors of color fastness in different aspects are also different, and the measures to improve color fastness are also different. The following only analyzes and explains the reasons and improvement measures for several commonly used color fastnesses (soaping fastness, sunlight fastness, crocking/rubbing fastness, and sublimation fastness) that do not meet the standards.
1. Color Fastness to Soaping
Color fastness to soaping is the most commonly used index to measure the color fastness of dyed textiles, especially as a raw material for products that are frequently washed. For example, textiles for towels, tablecloths, underwear, jackets and other products are often washed. And various detergents such as soap are often used for washing. Affect its use effect and service life.
(1) Color Fastness to Soaping Failure Causes:
The factors affecting soaping color fastness have been mentioned in the second section of this chapter, and the possible reasons for unqualified soaping fastness will be summarized below.
① The selection of dyes is unreasonable. As mentioned earlier, the structure of the dye determines the fixation method and water solubility of the dye on the fiber, and the binding method of the dye and the fiber and the size of the water solubility are the most direct and critical reasons that affect the soaping fastness. Reactive dyes containing reactive groups react with fibers to form a covalent bond. When washing, the dyes are not easy to separate from the fibers and dissolve in the washing liquid, and the fastness is good. Non-reactive water-soluble dyes (such as direct dyes, acid dyes, etc.), if the solubility of the dyes is not changed after dyeing, the dyes dyed on the fabric can still be dissolved in water, so soaping The color fastness is generally poor. However, poorly water-soluble or non-water-soluble dyes (such as vat dyes, sulfur dyes, insoluble azo dyes, etc.), because of their poor solubility, are difficult to dissolve in the washing liquid during washing, and are not easily separated from the fiber, so the soaping color fastness is high. Therefore, when selecting dyes, if the dyed products have higher requirements for color fastness, and the non-reactive and soluble dyes are selected, the fastness of the dyed products will generally not meet the standard.
②The dyeing process is unreasonable. The dyeing temperature is too low and the fiber is not sufficiently expanded; the dyeing time is too short, and the amount of dyeing auxiliaries such as fiber bulking agent penetrants and dye accelerators is insufficient. The above reasons affect the penetration of the dye into the fiber, making it difficult for the dye to fully penetrate the fiber. Poor washing color fastness.
Low dyeing fixation temperature, insufficient time, and too small fixation aid concentration make dye fixation poor, which will lead to low soaping color fastness, especially the fixation process and fixation effect of reactive dyes will seriously affect the soaping color fastness of dyed products.
③Improper washing process after dyeing. After dyeing, different dyes and fibers should be washed with different washing methods to remove the floating color on the surface of the fiber. This is an important measure to ensure the soaping color fastness and some other color fastness standards. For example: direct dyes, acid dyes, etc. should be washed after dyeing, reactive dyes and vat dyes should be fully soaped after dyeing, and disperse dyes should be washed with reduced water after dyeing polyester fiber fabrics. The washing, soaping, and reduction cleaning after dyeing are all to remove the surface floating color that is not sufficiently dyed and fixed, so as to ensure a higher soap fastness. The improper processing conditions such as water washing, soaping, reduction and cleaning after dyeing, resulting in unclean removal of floating color is one of the important reasons for the substandard soaping colorfastness.
The improper process conditions of water washing, soaping and reduction cleaning after dyeing mainly refer to insufficient concentration of washing aids, too low temperature, too short time, too small bath ratio, and too few times. These reasons will lead to insufficient washing and stickiness. The dyes attached to the surface of the fiber are not cleanly washed, causing the soaping fastness to be substandard.
④The fixing process after dyeing is unreasonable. After the dyeing water washes off the floating color, when the soaping color fastness of some dyes is still not up to the standard, the fixing agent can be treated to reduce the solubility of the dye and improve the soaping colorfastness. For example, direct dyes, acid dyes, cationic dyes and other non-reactive, water-soluble dyes are washed to remove the floating color after dyeing, and then treated with a fixing agent to seal the water-soluble group, reduce the water solubility of the dye, and can significantly improve the soaping colorfastness Spend. However, if the fixing agent is improperly selected, the concentration of the auxiliary agent such as fixing agent is not enough, the temperature is not appropriate, and the time is too short will affect the fixing effect, making the soaping colorfastness still not up to the standard.
⑤Dyeing concentration. The dyeing concentration of textiles will also affect the soaping fastness, especially when dyeing with non-reactive water-soluble dyes, the fastness of densely colored products will be lower. As long as the dyeing and washing process of light-colored products is reasonable, it is generally not necessary to fix the color, and the soaping is fast. The degree will be up to the standard.
① Use dyes reasonably. The category structure of dyes is closely related to soaping color fastness, so when choosing dyes for dyeing, the soaping fastness requirements of the fabric, the structural properties of dyes and fibers should be considered to select the appropriate dyes. For example, towels, bath towels, underwear and other products that are frequently washed will have high soaping colorfastness requirements. It is necessary to choose vat dyes and reactive dyes with high color fastness instead of direct dyes with generally low color fastness. When choosing dyes, pay attention to the soaping colorfastness of similar dyes because of the difference in their molecular structure. The soaping colorfastness is also different.
②Reasonably formulate and control the dyeing process. The dye penetrates fully into the fiber and the surface color is less, which is conducive to the improvement of soaping color fastness. To ensure sufficient dye penetration, the following process factors should be considered.
Choose necessary and reasonable dyeing auxiliaries, including types and dosages. The auxiliaries that help dyes penetrate include fiber bulking agents and penetrants. Especially when the dye molecules are large, difficult to penetrate, and the fiber structure is tight and difficult to expand, there must be enough fiber bulking agent and dye penetrating agent to help fiber bulking and dye penetration.
Ensure proper dyeing temperature. Temperature is an important condition to ensure that the fiber gets enough energy to expand and the dye gets enough energy to penetrate into the fiber, so it is necessary to ensure a sufficiently high temperature.
Ensure enough dyeing time. The dye is absorbed and dyed faster on the surface of the fiber, but it diffuses and penetrates slowly into the fiber, and it takes a certain time. Therefore, the dyeing time should be subject to the full penetration of the dye. If the time is not enough, more floating colors will be produced, which will affect the soaping fastness and other color fastnesses.
③Reasonably formulate and control the dye fixation process. Reactive dyes must be covalently bonded to the fiber to ensure color fastness after dyeing the cellulose fiber. Therefore, the reactive fixation of the reactive dye to the fiber is very important. If the fixation is not good, the soaping color fastness must not meet the standard.
Controlling the fixing effect of reactive dyes mainly controls: the type and amount of fixing aids, fixing temperature and time.
④Strictly control the washing process and operation after dyeing. Improper washing after dyeing and excessive floating color are one of the important external reasons for the substandard soaping fastness. Therefore, the floating color cleaning after dyeing is an important link to ensure that the soaping color fastness reaches the standard. The measures to be implemented to ensure a good cleaning effect are:
Choose reasonable cleaning aids and methods. Generally, non-reactive, water-soluble and good dyes can be washed with hot or warm water. When dyeing cellulose with reactive dyes, all unreacted dyes are required to be washed out to ensure high soap fastness. The washing requirements are high and difficult. It is necessary to add enough soap or other detergents for washing to ensure the washing effect. The floating color of vat dyes is difficult to dissolve in water, and the floating color can only be removed by adding soap and other detergents and washing at a higher temperature. Disperse dyes are also difficult to clean when dyeing polyester because of the insoluble floating color, and the surface floating color can be removed by the action of reducing agent.
Ensure that the washing temperature is high enough. Temperature can improve the solubility of the dye, and the washing temperature is high enough to ensure the effect of washing off the floating color.
Ensure proper washing time. It takes time for the dye to dissolve, so the washing time should be sufficient.
Ensure proper water bath ratio and frequency. If the bath ratio is too small and the number of washing times is not enough, the floating color will not be cleaned and the color fastness will not reach the standard.
⑤ Reasonable fixation. When the color fastness of non-reactive water-soluble dyes such as direct dyes, acid dyes, cationic dyes, etc. is not up to the standard, a suitable fixing agent can be used to fix the color to improve the color fastness. In order to ensure that the color fastness is improved to the standard level, a reasonable type and amount of fixing agent must be determined according to the dye concentration of the dye type, and the fixing liquor ratio, temperature and time and other process conditions must also be appropriate, and the operation process must be strict.
2. Color Fastness to Sunlight
colorfastness to sunlight is also one of the common colorfastness, especially when dyed textiles are used as products that are often exposed to the sun, the sunlight colorfastness is more important and more demanding.
(1) Color Fastness to Sunlight Failure Causes:
The factors affecting the sunlight colorfastness have been detailed in the second section of this chapter. The possible reasons for the unqualified sunlight colorfastness are summarized as follows:
① Improper selection of dyes. The molecular structure of the dye is an important internal factor that determines the sunlight colorfastness of the dye material, and the colorfastness to sunlight of dyes with different structures is sometimes very different. Generally speaking, anthraquinones, phthalocyanines, metal complexes, polyazo dyes and dyes containing more nitro and halogen groups have better light fastness. Dyes with structural groups that can promote the dye to absorb light energy have poor sunlight colorfastness, such as dyes containing benzidine structure, triarylmethane structure, indigo structure, and more amino groups, hydroxyl groups, etc., which are fast to light. Degree is poor. When dyeing textiles with high sunlight colorfastness requirements, if dyes with poor sunlight colorfastness are selected, the colorfastness to sunlight of the dyed fabric will not reach the standard no matter what measures are taken.
The sunlight colorfastness of the same dye materials on fibers of different properties can sometimes be very different. So when choosing dyes, we should also consider the influencing factors of fiber types.
When dyes are mixed and used, individual dyes will affect each other and reduce the sunlight colorfastness.
②The dyeing process is unreasonable. If the dyeing is uneven and the local dye concentration is larger, the colorfastness will be poor.
The dyeing temperature is not high enough, the time is too short, and the penetration aid is not enough, resulting in insufficient dye penetration of the dyed product, more dye on the outer surface of the fiber, incomplete washing after dyeing, and more dye on the fiber surface, which will make the sunlight color fastness significantly down.
When reactive dyes are dyed, the fixation process is unreasonable, which makes the dye and fiber bond insufficiently and also reduces the sunlight color fastness.
③The influence of additives. After dyeing, fixing agents and finishing auxiliaries, and some will have a significant impact on the sunlight color fastness of the dye. Some auxiliaries can hinder the absorption of light energy by the dye, thereby improving the light fastness; while some auxiliaries can promote the absorption of light energy by the dye and reduce the sunlight colorfastness.
① Use dyes reasonably. When selecting dyes, consider the requirements of dyed products for light fastness. For dyed products with high sunlight colorfastness requirements, try to choose anthraquinones, phthalocyanines, metal complexes, and polyazos. Structural dyes and dyes containing more nitro and halogen groups should avoid the use of dyes containing benzidine structure, triarylmethane structure, indigo structure and dyes containing more amino and hydroxyl groups.
When choosing dyes, the influence of fibers on the sunlight color fastness of dyes should also be considered.
When dyes are mixed and used, the mutual influence of the light fastness between the dyes should be considered
② Formulate a reasonable dyeing process and strict dyeing operation. Formulate a reasonable dyeing process and strict dyeing operating procedures to ensure uniform dyeing and sufficient dye penetration into the fiber. When dyeing with reactive dyes, attention is paid to the rationality of the fixation process, and the operation is strict to ensure sufficient bonding between the dye and the fiber.
③ Reasonable selection of additives. Especially after dyeing, fixing agent and finishing auxiliaries should consider the influence of auxiliaries on the sunlight color fastness of dyes. Avoid using additives that can promote the absorption of sunlight energy by the dye and reduce the color fastness to sunlight.
3. Color Fastness to Crocking/Rubbing
Color fastness to crocking/rubbing is also one of the common indicators of dyeing color fastness. Especially when dyed textiles are used as products that are frequently rubbed, the requirements for rubbing color fastness are higher. For example, when making pants and other outer clothing color fabrics, higher friction is required.
① The dyeing process is unreasonable. The dyeing temperature is not high enough, the time is too short, and the penetration aid is not enough, resulting in insufficient penetration of the dyeing, more dye on the outer surface of the fiber, and incomplete removal of surface floating color after dyeing, resulting in floating color on the fiber surface. These are the main factors of rubbing color fastness failure.
②When using reactive dyes, the fixing process is unreasonable, which makes the dye and fiber bond insufficient, and the soaping after dyeing is not thorough. Hydrolyzed dyes are not thoroughly washed away, which will cause the rubbing colorfastness of the dyed textiles to not meet the standard.
③The state of the dye on the fiber is inappropriate. The dyes are distributed in molecular state on the fiber, and the rubbing colorfastness is better. If they exist on the fiber in the form of larger molecular aggregates, the rubbing colorfastness is poor.
① Formulate a reasonable dyeing process. In particular, the dyeing temperature and dyeing time should be appropriate, and the selection and dosage of penetration aids should be appropriate to ensure sufficient dye penetration of the dyed textiles.
After dyeing, it is necessary to select appropriate methods and process conditions such as water washing, soaping, reduction, and cleaning according to different fiber dyes to remove the floating color on the textile surface.
②When dyeing with reactive dyes, pay attention to the rationality of the fixation process and strictly operate to make the dyes fully bond with the fiber. After dyeing, perform sufficient soaping to remove the unbonded hydrolyzed dyes.
③Control the particle size of the dye and the state of existence of the dye on the fiber. The particle size of the dye should be as small as possible, and try to ensure that the dye is distributed in a molecular state on the fiber, which is beneficial to improve the rubbing colorfastness.
4. Sublimation Fastness
Sublimation fastness is also one of the common indexes of dyeing color fastness. Especially for dyed textiles that have to undergo high-temperature finishing and frequent ironing during use, the requirements for sublimation fastness are even higher. For example, when polyester is dyed with disperse dyes and subjected to heat setting treatment, if the sublimation fastness is poor, the dye sublimation will cause problems such as incorrect dyeing, color stains, and pollution of the setting equipment. use.
(1) Failure Causes:
① The dye selection is unreasonable. The sublimation fastness is mainly determined by the structure and molecular weight of the dye. Disperse dyes basically have no binding force with fibers. When the dye molecules are small, they are easy to sublime when heated, and the sublimation fastness is poor.
②The dyeing process is unreasonable. The dyeing temperature is not high enough, the time is too short, and the penetration aid is not enough, resulting in insufficient dye penetration of the dyed product, more dyes on the outer surface of the fiber, and incomplete removal of surface floating color after dyeing, resulting in floating color on the fiber surface. These factors will also cause The sublimation fastness is not up to standard.
③The state of existence on the fiber is inappropriate. Dyes are distributed on the fiber in a molecular state, and the rubbing fastness is better. If it exists on the fiber in the form of larger molecular aggregates, its sublimation fastness is poor.
① Choose dyes reasonably. The dye should be selected correctly according to the different uses of the dyed product and the post-treatment process conditions. The sublimation year of the dye on the fabric can be detected by consulting related materials or experiments. For dyeing products that need to be processed at high temperature and dyeing products that need to be ironed frequently, choose dyes with high “dry heat fastness” or choose high-temperature disperse dyes. Perform dyeing.
② Formulate a reasonable dyeing process, and strictly follow the process to ensure that the dye can penetrate and diffuse well on the fiber, and perform sufficient water washing and reduction cleaning after dyeing. For dyed products that require high sublimation fastness, they are treated at high temperature after dyeing and then aligned.
After this post I think you may have a general idea about the color fastness and the reason of its failure. Also you may have a specific knowledge about how to improve it in daily production. Check more knowledge about textile in my other posts.