How to improve the dyeing 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 reactive dyes to light-colored fabrics, the wet rubbing fastness of dark and dense fabrics; the decline in wet treatment fastness caused by the thermal migration of disperse dyes after dyeing; and high chlorine fastness, sweat-light fastness 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 have explored in the selection of suitable dyeing and chemical additives, improvement of dyeing and finishing processes, and strengthening of process control. Some methods and measures have been adopted to increase and improve the color fastness to a certain extent, which basically meets the market demand.

Light fastness of reactive dyes light-colored fabrics

As we all know, reactive dyes dyed on cotton fibers are attacked by ultraviolet rays under sunlight, and the chromophores or auxochromes in the dye structure will be damaged to varying degrees, resulting in color change or light color, which is Light fastness problem.

my country’s national standards have already stipulated the light fastness of reactive dyes. For example, the GB/T411-93 cotton printing and dyeing fabric standard stipulates that the light fastness of reactive dyes is 4-5, and the light fastness of printed fabrics is 4; GB /T5326 Combed polyester-cotton blended printing and dyeing fabric standard and FZ/T14007-1998 cotton-polyester blended printing and dyeing fabric standard both stipulate that the light fastness of dispersed/reactive dyed fabric is level 4, and printed fabric is also level 4. It is difficult for reactive dyes to dye light-colored printed fabrics to meet this standard.

Relationship between dye matrix structure and light fastness

The light fastness of reactive dyes is mainly related to the matrix structure of the dye. 70-75% of the matrix structure of reactive dyes is azo type, and the rest are anthraquinone type, phthalocyanine type and A type. The azo type has poor light fastness, and the anthraquinone type, phthalocyanine type, and nail have better light fastness. The molecular structure of yellow reactive dyes is azo type. The parent color bodies are pyrazolone and naphthalene trisulfonic acid for the best light fastness. The blue spectrum reactive dyes are anthraquinone, phthalocyanine, and a parent structure. The light fastness is excellent, and 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 density 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, its light fastness increases with the increase of dyeing concentration, mainly because the dye is in Caused by changes in the size distribution of aggregate particles on the fiber.

The larger the aggregate particles, the smaller the area per unit weight of the dye exposed to air-moisture, and the higher the light fastness.
The increase in dyeing concentration will increase the proportion of large aggregates on the fiber, and the light fastness will increase accordingly. The dyeing concentration of light-colored fabrics is low, and the proportion of dye aggregates on the fiber is low. Most of the dyes are in a single molecule state, that is, the degree of decomposition of the dye on the fiber is very high. Each molecule has the same probability of being exposed to light and air. , The effect of moisture, the light fastness also decreases accordingly.

ISO/105B02-1994 standard light fastness is divided into 1-8 grade standard assessment, my country’s national standard is also divided into 1-8 grade standard assessment, AATCC16-1998 or AATCC20AFU standard light fastness is divided into 1-5 grade standard assessment.

Measures to improve light fastness

1. The choice of dye affects light-colored fabrics
The most important factor in light fastness is the dye itself, so the choice of dye is the most important.
When selecting dyes for color matching, make sure that the light fastness level of each component dye selected is equivalent, as long as any one of the components, especially the component with the least amount, can not reach the light fastness of the light-colored dyed material The requirements of the final dyed material will not meet the light fastness standard.

2. Other measures
The effect of floating dyes.
Dyeing and soaping is not thorough, and the unfixed dyes and hydrolyzed dyes remaining on the cloth will also affect the light fastness of the dyed material, and their light fastness is significantly lower than that of the fixed reactive dyes.
The more thoroughly the soaping is done, the better the light fastness.

The influence of fixing agent and softener.
Cationic low-molecular-weight or polyamine-condensed resin type fixing agent and cationic softener are used in fabric finishing, which will reduce the light fastness of dyed products.
Therefore, when selecting fixing agents and softeners, attention must be paid to their influence on the light fastness of dyed products.

The influence of UV absorbers.
Ultraviolet absorbers are often used in light-colored dyed fabrics to improve the light fastness, but they must be used in a large amount to have some 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.