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 years of production practice, printing and dyeing practitioners are selecting appropriate dyeing chemicals and additives and improving the dyeing and finishing process. In terms of strengthening process control and other aspects, some methods and measures have been explored to improve the dyeing 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 4-5. The fastness is level 4; the GB/T5326 standard for combed polyester-cotton blended printed and dyed fabrics and the 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 are also level 4. It is difficult to reach this standard when dyeing light-colored fabrics with reactive dyes.
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. 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.
The relationship between dyeing concentration and light fastness
Sunlight fastness of dyed samples It will vary with the change of dyeing concentration. For samples dyed with the same dye on the same fiber, its light fastness increases with the increase of dyeing concentration, mainly due to the size distribution of the aggregate particle size of the dye on the fiber. caused by changes.
The larger the aggregate particles, 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 at a dyeing depth of 1 /1, that is, the data 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 of light-colored fabrics
1. The selection of dyes has the most important influence on the light fastness of light-colored fabrics. The 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
The 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 dyes. of reactive dyes. The more complete the soaping is, the better the light fastness will be.
The influence of fixatives and softeners.
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 color fixing agents and softeners, attention must be paid to their impact on the light fastness of dyed materials.
The influence of UV 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.
The wet rubbing fastness of deep and concentrated reactive dyes in wet treatment
In recent years, it has been a difficulty in the use of reactive dyes and other dyes. . Reactive dyes impart excellent color fastness to dyed materials through covalent bonding, but dark and concentrated dyesFor 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 “use less if you can’t use it, use less if you can, and choose carefully when you have to 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 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 fibers by dyes 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-processed dyes should be small. </p
