How to improve dye fastness has become a research topic for engineering and technical personnel in the printing and dyeing industry. In particular, the light fastness of light-colored fabrics dyed with reactive dyes and the wet rubbing fastness of dark-colored fabrics; the decrease in wet processing fastness caused by post-dyeing thermal migration of disperse dyes; and high chlorine resistance, perspiration and light fastness There are many factors that affect color fastness, and there are many ways to improve color fastness. We have explored some methods and Measures have been taken to improve the dyeing fastness to a certain extent and basically meet the market demand.
Sunlight fastness of light-colored fabrics with reactive dyes
As we all know, dyeing on cotton fibers Reactive dyes are attacked by ultraviolet rays under sunlight, and the chromophores or auxochromophores in the dye structure will be damaged to varying degrees, resulting in discoloration or light color, which causes problems with light fastness.
National standards have already stipulated the light fastness of reactive dyes. For example, the GB/T411-93 cotton printing and dyeing cloth standard stipulates that the light fastness of reactive dye dyed cloth is 4-5 Level, the light fastness of printed fabrics is level 4; GB/T5326 standard for combed polyester-cotton blended printing and dyeing fabrics and FZ/T14007-1998 standard for cotton-polyester blended printing and dyeing fabrics stipulate that the light fastness of disperse/reactive dyeing fabrics is level 4, and the light fastness of printed fabrics is level 4. Cloth is also level 4. It is difficult to reach this standard when dyeing light-colored fabrics with reactive dyes.
The relationship between dye matrix structure and light fastness
Activity The light fastness of dyes is mainly related to the parent structure of the dye. 70-75% of the parent structure of reactive dyes is azo type, and the rest is quinone type, phthalocyanine type and A type.
Azo type has poor light fastness, while anthraquinone type, phthalocyanine type and azo type have better light fastness. The molecular structure of yellow reactive dyes is azo type, and the parent color bodies are pyrazolone and naphthalene trisulfonic acid, which have the best light fastness. The blue spectrum reactive dyes have anthraquinone, phthalocyanine, and toluene parent structures, and the sun fastness is the best. It has excellent light fastness and the molecular structure of the red spectrum reactive dye is azo type. Sunlight fastness is generally low, especially for light colors.
The relationship between dyeing concentration and light fastness
Dyeing test The light fastness of samples will vary with the change of dyeing concentration. For samples dyed with the same dye on the same fiber, the light fastness will increase with the increase of dyeing concentration, mainly because the dye is on the fiber. caused by changes in aggregate particle size distribution.
The larger the aggregate particles, the smaller the area of the dye per unit weight exposed to air and moisture, and the higher the light fastness.
The increase in dyeing concentration will increase the proportion of large particle aggregates on the fiber, and the light fastness will also increase accordingly. The dyeing concentration of light-colored fabrics is low, and the proportion of dye aggregates on the fiber is low. Most dyes are in a single-molecule state, which means the dye is highly decomposed on the fiber. Each molecule has the same chance of being exposed to light and air. , the effect of moisture, the light fastness also decreases accordingly.
ISO/105B02-1994 standard sunlight fastness is divided into 1-8 levels for evaluation. my country’s national standards are also divided into 1-8 levels for evaluation, AATCC16-1998 or AATCC20AFU standard Sunlight fastness is evaluated according to standards from 1 to 5. Therefore, we must first understand what standards the customer requires. The light fastness of dyed goods shown on the color cards provided by all dye manufacturers or companies, including the “Dye Index”, is measured at a dyeing depth of 1/1. The data is measured on medium-colored fabrics with a dye concentration of about 20-30g/L. Light-colored fabrics cannot reach this level.
Measures to improve light fastness
1. Dyes Selection
The most important factor affecting the light fastness of light-colored fabrics is the dye itself, so the selection of dye is the most important. When selecting dyes for color matching, the light fastness level of each component dye must be equivalent. As long as the light fastness of any one component, especially the component with the smallest amount, cannot reach the light fastness of light-colored dyes. If the requirements are met, the light fastness of the final dyed product will not meet the standard.
2. Other measures
(1) Floating dyes Influence. Incomplete dyeing and soaping, unfixed dyes and hydrolyzed dyes remaining on the cloth will also affect the light fastness of the dyed goods. Their light fastness is significantly lower than that of fixed reactive dyes. The more complete the soaping is, the better the light fastness will be.
(2) The influence of color fixing agent and softening agent. When cationic low-molecular or polyamine-condensed resin-based fixatives and cationic softeners are used in fabric finishing, the light fastness of dyed goods will be reduced. Therefore, when selecting fixatives and softeners, attention must be paid to their impact on the light fastness of dyed materials.
(3) The influence of ultraviolet absorbers. Ultraviolet absorbers are often used in light-colored dyed goods to improve the light fastness, but they must be used in large amounts to have any effect, which not only increases the cost, but also causes yellowing and strong damage to the fabric, so it is best not to use this method.
Wet processing wet rubbing fastness of deep and intense colors of reactive dyes
Reactive dyes impart excellent color fastness to dyed materials through covalent bonding. However, deep-concentrated dyed materials often suffer from fading and staining. These phenomena occur in addition to a part of the dye matrix structure that is exposed to light, heat, sweat, Erosion by acidic gases and oxidants,�Under the premise of �, the amount of dye should be appropriate. The fiber’s adsorption of each dye has a limit value, that is, the dyeing saturation value, which generally does not exceed about 10% of the saturation value. When the amount of dye greatly exceeds the saturation value, the excess dye cannot be dyed and fixed, and can only accumulate on the surface of the fabric, affecting the rubbing fastness of the fabric. Reactive dyes with high lifting power should be used to achieve a high dye uptake rate with a small amount. After testing the fabrics dyed by the above dyeing methods, it was found that the optimal color fastness is: dip dyeing > cold pad batch > wet short steaming > padding → drying → padding → steaming > padding → drying → steaming.
3. Washing treatment
The interior and surface of the fiber after dyeing There are impurities such as fixed dyes, floating dyes, residual alkali agents and electrolytes. Only by removing these impurities can the dyed goods achieve optimal dye fastness and color brightness. The method relies on water washing, soaping and mechanical external force. The purpose is to remove the hydrophilic floating color, wash away the electrolyte and alkali agent, reduce the electrolyte concentration to increase the electrostatic repulsion between the floating dye and the fiber, and make the floating dye more durable. It is easy to break away from the fiber; the alkali remover is to prevent the alkali agent from causing hydrolysis of the fixed dye during high-temperature soaping. Washing after soaping is to remove a large amount of floating dye that has been dispersed by the soaping agent. Water quality is very important in the post-treatment process. If the water hardness is high, there will be more heavy metal ions such as Ca2+ and Mg2+, which will change the color of the water-soluble sodium sulfonate salt into the insoluble calcium (magnesium) sulfonate salt. The water quality has a significant impact on the post-processing fastness of dyed materials.
4. Post-finishing
Congenital deficiencies must be made up for, and after dyeing The color fastness of the fabric cannot meet the requirements and can only be compensated and improved by using color fixing agents and enhancers in post-finishing. The special fixing agent can improve the wet rubbing fastness of deep and concentrated reactive dyes by 0.5-1.0 levels.
Chlorine fastness and sweat-light fastness of reactive dyes
Reactive dyes generally have poor chlorine resistance, which mainly depends on the molecular structure of the color body. There is a sulfonic acid group or carboxylic acid group in the ortho position of the diazo group of the dye, or in the ortho or para position of the hydroxyl group of the coupling component. When a sulfonic acid group or a carboxylic acid group exists, its steric hindrance effect reduces the ability of CI- to attack -NH- or -N-, thus improving the chlorine resistance fastness.
According to the chlorine-resistant swimming pool water fastness test method of GB/T8433-1998, the available chlorine concentration is divided into three types: 20mg/L, 50mg/L and 100mg/L. Special requirements There are 200mg/L. As the available chlorine concentration increases, the chlorine fastness decreases. Therefore, dye selection is very important. Color fixing agents can also be used to improve the chlorine resistance fastness during the post-finishing process, but it can only increase by 0.5-1.0 levels. The perspiration-light fastness of reactive dyes has received great attention in recent years. Some reactive dyes have good light fastness, but poor perspiration and light fastness. Because under the dual effects of sweat and sunlight, the fading mechanism is different. Since the amino acids or related substances in the sweat chelate with the metal ions of the metal complex dye, they are separated from the dye matrix. The light fastness of the dye matrix before complexation is originally Not good, so it fades or changes color.
The decrease in fastness caused by thermal migration of disperse dyes after dyeing
Thermal migration phenomenon is a phenomenon of disperse dyes in two-phase solvents. This is a redistribution phenomenon, so all additives that can dissolve disperse dyes can produce thermal migration.
The reason for the thermal migration phenomenon is that the additives in the outer layer of the fiber dissolve the dye at high temperatures. The dye expands and migrates from the inside of the fiber to the surface of the fiber through the fiber capillary at high temperatures. The dye accumulates on the surface of the fiber, causing a series of effects, such as discoloration, staining other fabrics during ironing, resistance to friction, washing, sweat stains, dry cleaning resistance and reduced color fastness to sunlight. Practice has shown that the amount of thermal migration of dyes from the inside of the fiber to the outside of the fiber is directly related to the dyeing depth. The deeper the dyeing depth of the fiber, the greater the amount of dye that thermally migrates from the inside to the outside, and the greater the impact on the dyed goods; high temperature treatment after dyeing has a greater impact on the dyeing. The thermal migration of disperse dyes has a greater impact, and the higher the temperature, the greater the impact.
Therefore, try to use gentle processes when finishing dyed fabrics. Thermal migration of disperse dyes is related to the molecular structure of the dye itself. Nonionic surfactants widely used in production practice are the main reasons for the thermal migration of disperse dyes.
As a softener, amino silicone emulsion is currently the most commonly used softener, because to make a microemulsion, it is necessary to apply 40-50% of the total silicone content of fatty alcohol polyoxygen. Nonionic surfactants such as vinyl ether or alkylphenol polyoxyethylene ether are used as emulsifiers. With the widespread use of amino silicone emulsions, the post-dye thermal migration of disperse dyes is more serious. The solution is to choose disperse dyes with high lifting power and exhaustion rate, especially disperse dyes with good wet fastness after heat fixation of dyed goods.
Dye (floating color) attached to the fiber surface will aggravate the impact of thermal migration of dye on the color fastness of dyed fabrics. Therefore, after dyeing (especially dark colors), reducing agents and alkali agents should be used for reduction cleaning to completely remove floating colors.
Editor’s note:
In summary, it is necessary to improve For the color fastness of dyed goods, dye selection is very important. Different dyes should be selected according to the color fastness requirements. For light-colored fabrics with high requirements for light fastness, vat dyes and reactive dyes with high light fastness should be selected. Dyeing; for deep and dense colors, only imported reactive dyes with high fixation rate and lifting power can ensure wet processing fastness; for disperse dyes, dyes with less thermal migration should be selected, especially for dark colors, try to avoid reaching or exceeding dyeing saturation value, the use of surfactants should adhere to the principle of “do not use it if you can, use it less if you can, and choose carefully when you must use it.”
; For deep and dense colors, only imported reactive dyes with high fixation rate and lifting power can ensure the wet processing fastness; for disperse dyes, dyes with small thermal migration should be selected, especially for dark colors, try to avoid reaching or exceeding the dyeing saturation value. When using surfactants, we should adhere to the principle of “do not use it if you can, use less if you can, and choose carefully when you must use it.” </p
