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, perspiration and light fastness Degree 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.
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.
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 4- Level 5, the light fastness of printed fabrics is level 4; GB/T5326 combed polyester-cotton blended printed and dyed fabric standards and FZ/T14007-1998 cotton-polyester blended printed and dyed fabric standards both stipulate that the light fastness of disperse/reactive dyed fabrics is level 4, Calico 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 the yellow reactive dye is azo type. The parent color body is pyrazolone and naphthalene trisulfonic acid, which has the best light fastness and blue spectrum activity. The dye is based on anthraquinone, phthalocyanine and acetyl parent structure and has excellent light fastness. The molecular structure of the red spectrum reactive dye is azo type.
The light 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 fibers is low. Most of the dyes are in a single-molecule state, which means that the degree of decomposition of the dyes on the fibers is very high. , each molecule has the same chance of being affected by light, air, and moisture, and the sunlight 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 find out what standards the customer requires. All dye manufacturers or companies include the light fastness of dyed goods shown on the color card provided by the “Dye Index” The data are all measured when the dyeing depth is 1/1, that is, the data are 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. The selection of dyes affects the light fastness of light-colored fabrics
The most important factor in the light fastness is the dye itself, so the selection of dyes is the most important.
When selecting dyes for color matching, the light fastness level of each component of the dye must be equivalent. As long as any one of the components, especially the one with the smallest amount, is If the light fastness of the components does not meet the requirements of light-colored dyes, the light fastness of the final dyed goods will not meet the standards.
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 dyes. of reactive dyes.
The more fully soaping is carried out, the better the light fastness will be.
(2) The influence of color fixing agent and softening agent.
Cationic low-molecular or polyamine-condensed resin-based fixatives and cationic softeners used in fabric finishing will reduce the light fastness of dyed goods.
Therefore, when selecting fixing agents and softening agents, 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 to improve the light fastness of light-colored dyed fabrics, but they must be used in large amounts to have any effect, which not only increases the cost, but also causes yellowing and strength of the fabric. damage, so it is best not to use this method.
As a softener, liquid is the most commonly used softener at present, because to make a microemulsion, it is necessary to apply non-ionic surfactants such as fatty alcohol polyoxyethylene ether or alkylphenol polyoxyethylene ether with 40-50% of the total amount of silicone. As an emulsifier.
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.
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.
5 Conclusion
To sum up, in order to improve 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 high-quality fabrics should be selected. Reactive dyes with light fastness are used for 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 low thermal migration should be selected, especially for dark applications. Try to avoid reaching or exceeding the 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.”
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 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 level dyeing and dyeing degree of dyes on fibers should be better.
(5) The dye and fiber must be fully bonded and fixed.
(6) Wash thoroughly with soap and water after dyeing.
(7) The degree of bond breaking of the post-treatment dye should be small.
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