How to improve the dye fastness of printed and dyed fabrics to meet the increasingly fierce textile market demand has become a research topic 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, sweat-light resistance Fastness etc.
There are many factors that affect color fastness, and there are many ways to improve color fastness. Through many years of production practice, I have selected appropriate dyeing and chemical additives and improved In terms of dyeing and finishing technology and strengthening process control, some methods and measures have been explored to improve the dye fastness to a certain extent, which basically meets the market demand.
Sunlight fastness of light-colored fabrics with reactive dyes
As we all know, reactive dyes dyed on cotton fibers will fade under sunlight. Under the attack of ultraviolet rays, 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. my country’s national standards have already stipulated the light fastness of reactive dyes. For example, the GB/T411-93 standard for cotton printing and dyeing fabrics stipulates that the light fastness of dyed fabrics with reactive dyes is level 4-5, and the light fastness of printed fabrics is level 4; GB /T5326 standard for combed polyester-cotton blended printed and dyed fabrics and FZ/T14007-1998 standard for cotton-polyester blended printed and dyed fabrics both stipulate that the light fastness of disperse/reactive dyed fabrics is level 4, and that of printed fabrics 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. Reactive dyes 70-75% of the parent structure is azo type, and the rest is quinone type, phthalocyanine type and A type. The azo type has poor light fastness, while the 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 two dyes on the same fiber, the light fastness increases as the dyeing concentration increases, mainly due to the change in the size distribution of the aggregate particles of the dye on the fiber. The larger the aggregate particles are, the smaller the exposure area of the dye per unit weight 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.
The ISO/105B02-1994 standard sun fastness is divided into 1-8 levels. my country’s national standards are also divided into 1-8 levels. The AATCC16-1998 or AATCC20AFU standard sun fastness is divided into 1 -Level 5 standard assessment. 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 the light fastness
1. The selection of dyes affects the light fastness of light-colored fabrics
The most important thing is the light fastness The biggest factor 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
(1) The influence of floating dyes: dyeing and soaping are not thorough, and unfixed dyes and hydrolyzed dyes remain on the cloth surface. It will also affect the light fastness of dyed materials, and 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) Effects of color-fixing agents and softening agents. Cationic low-molecule or polyamine-condensed resin-based color-fixing agents and cationic softening agents are used in fabric finishing, which will make the dyed materials less susceptible to sunlight. Fastness decreases. Therefore, when selecting fixatives and softeners, attention must be paid to their impact on the light fastness of dyed materials.
(3) The impact 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. This not only increases the cost, but also causes yellowing of the fabric. and strong damage, so it is best not to use this method.
The wet-process rubbing fastness of deep and concentrated reactive dyes
In recent years, it has been a difficulty in the use of reactive dyes and other dyes. . Reactive dyes give dyes excellent color fastness through covalent bonding. However, dark and dense dyes 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, and acid. Erosion by gases and oxidants, decomposition of azo groups, detachment of complex metal ions, oxidation of amino groups, etc.��Excessive 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. There are fixed dyes, floating dyes, residual alkali and electrolytes and other impurities inside and on the surface of the dyed fibers after washing treatment. Only these impurities can be removed. To achieve the best color fastness and bright color of dyed materials.
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, and reduce the electrolyte concentration to increase the static electricity between the floating dye and the fiber. The repulsive force makes floating dyes easier to separate from the fiber; the alkali cleaning agent prevents the alkali agent from causing hydrolysis of fixed dyes 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 is inherently deficient and must be compensated for later. The color fastness of dyed fabrics does not meet the requirements and can only be compensated by using color fixing agents and enhancers in post-finishing. and improvement. The special fixing agent can improve the deep and concentrated wet rubbing fastness of reactive dyes by 0.5-1.0 levels.
Chlorine fastness and sweat-light fastness of reactive dyes
Reactive dyes generally have poor chlorine fastness, which mainly depends on the color body In the molecular structure of the dye, when there is a sulfonic acid group or carboxylic acid group in the ortho position of the diazo group of the dye, or when 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, the It has the ability of CI- to attack -NH- or -N-, thus improving the chlorine resistance fastness.
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 the fading mechanism is different under the dual effects of sweat and sunlight. Because the amino acids or related substances in sweat chelate with the metal ions of metal complex dyes, they are separated from the dye matrix. The dye before complexing The light fastness of the matrix is 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 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 from the inside of the fiber through the fiber capillary at high temperatures and migrates to the fiber surface, causing the dye to accumulate on the fiber surface, causing a series of effects. , such as discoloration, contamination of other fabrics during ironing, resistance to friction, washing, sweat stains, dry cleaning resistance and reduced color fastness to sunlight.
Practice shows that the amount of thermal migration of dye 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 product. ; High-temperature treatment after dyeing has a greater impact on the thermal migration of disperse dyes. 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.
Amino silicone emulsion is currently the most commonly used softener as a softener, because to make a microemulsion, it is necessary to apply 40-50% of the total silicone content of fatty alcohol polyoxyethylene ether or alkyl phenol. Nonionic surfactants such as polyoxyethylene ethers serve 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 materials. Dyes attached to the fiber surface (floating colors) will aggravate the impact of thermal migration of dyes 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, in order to improve the color fastness of dyed goods, dye selection is very important and should be based on the color fastness requirements. To choose different dyes, light-colored fabrics with high requirements for light fastness should choose vat dyes and reactive dyes with high light fastness for dyeing; deep and dense colors can only use imported reactive dyes with high fixation rate and lifting power. Only in this way can the wet treatment 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. When using surfactants, we should adhere to the principle of “do not use it if you can, and use it less if you can.” “Use sparingly, and when you must use it, choose carefully.”
In the production management process, it is necessary to strengthen process control to ensure that the following process requirements are met: 1. The fiber surface must be smooth and clean with less hairiness. 2. The wool efficiency of the fiber should be high. 3. The color absorption ability of fiber should be strong. 4. The degree of leveling and dyeing of the fiber by the dye should be better. 5. The dye and fiber must be fully bonded and fixed. 6. Soap and wash thoroughly after dyeing. 7. The degree of bond breaking of post-processing dyes should be small.
It should be smooth and clean with less hairiness. 2. The wool efficiency of the fiber should be high. 3. The color absorption ability of fiber should be strong. 4. The degree of leveling and dyeing of the fiber by the dye should be better. 5. The dye and fiber must be fully bonded and fixed. 6. Soap and wash thoroughly after dyeing. 7. The degree of bond breaking of post-processing dyes should be small. </p
