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.
1 Sunlight fastness of light-colored fabrics with reactive dyes
We all know , the reactive dyes dyed on cotton fibers are attacked by ultraviolet rays under sunlight. The chromophores or chromophores in the dye structure will be damaged to varying degrees, resulting in color change or light color, that is, sunscreen. Sun fastness issue.
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 combed polyester-cotton blended printing and dyeing fabric standards and FZ/T14007-1998 cotton-polyester blended printing and dyeing fabric standards both 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.
1. The relationship between dyeing matrix structure and light fastness
The light fastness of reactive 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.
2. The relationship between dyeing concentration and light fastness
The light fastness of dyed 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 due to the increase of the dye concentration. Caused by changes in the particle size distribution of aggregates on the fiber.
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.
2 Measures to improve light fastness
1. Dyes Selection of dyes
The most important factor affecting the light fastness of light-colored fabrics is the dye itself, so the choice of dye is the most important. When selecting dyes for color combinations, the light fastness of each component of the dye must be at the same level. As long as the light fastness of any one of the components, 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
❶The influence of floating dyes. 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.
❷The influence of fixatives and softeners. 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.
❸The influence of ultraviolet absorbers. Recently, UV absorbers are often used to improve the light fastness of light-colored dyed fabrics, but they must be used in large amounts to be effective. This not only increases the cost, but also causes yellowing and strong damage to the fabric, so it is best not to use this method.
3 Reactive dye deep color wet treatment wet rubbing fastness
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 the fact that part of the dye matrix structure is exposed to light, heat, sweat, Erosion by acidic gases and oxidants causes decomposition of azo groups and metal complexes.o:p>
4 Chlorine fastness and sweat-light fastness
Reactive dyes generally have poor chlorine fastness, which mainly depends on the hair color. The molecular structure of the color body. When there is a sulfonic acid group or carboxylic acid group in the ortho position of the diazo group of the dye, or there is a sulfonic acid group or carboxylic acid group in the ortho or para position of the hydroxyl group of the coupling component, due to its steric hindrance effect , reducing 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.
5 Decreased fastness caused by thermal migration after disperse dyeing
Thermal migration phenomenon is a redistribution phenomenon of disperse dyes in two-phase solvents. Therefore, 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.
6 Postscript
In summary, it is necessary to improve the color fastness of dyed goods , the selection of dyes is very important. Different dyes should be selected according to the requirements of color fastness. Light-colored fabrics with high requirements for light fastness should be dyed with vat dyes and reactive dyes with high light fastness; dark and dense colors should be dyed. Only by choosing imported reactive dyes with high fixation rate and lifting power can the wet processing fastness be ensured; 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, and surfactants The principle of use should be adhered to: “If you can’t use it, don’t use it; if you can use it less, use it less; when you have to use it, choose it carefully”. </p
