How to avoid uneven phenomena during the printing and dyeing process is one of the important indicators of printing and dyeing process quality; Leveling agent is an auxiliary agent used to achieve uniform dyeing on the dyed material.

         One of the functions of a leveling agent is to allow the dye to be slowly adsorbed by the fibers. Secondly, when the dyeing is uneven, it causes the dark part of the dye to move towards the light part, ultimately achieving leveling. Therefore, slow dyeing and transfer dyeing are the two most important roles of leveling agents.

        In recent years, various new types of fibers have been widely applied in the printing and dyeing industry. At the same time, with the gradual improvement of people's environmental awareness, various leveling agents have made new developments. This article reviews the development of reactive dyes and leveling agents used in fiber rope dyes, in order to better promote the research work of leveling agents in China.

Leveling agents for reactive dyes

        The dyeing of cellulose fibers is currently dominated by reactive dyes, which are water-soluble dyes containing active groups and can chemically bind with macromolecules such as cotton, wool, and silk, resulting in high soap washing and friction fastness of dyed fabrics. The commonly used leveling agents generally include non-ionic surfactants. In addition to ionic surfactants, anionic leveling agents and combinations of non-ionic and anionic surfactants have also been frequently used in recent years.

1. Non ionic surfactants

The hydrophobic groups of commonly used 1F ion surfactants can be higher alcohols, higher fatty acids, higher alkylamines, etc. The hydrophobic groups are above C12, and the long-chain alkyl groups of C16 and C18 are ideal. This can form ether, ester, amine, and other forms of connection with the hydrophilic groups of polyoxyethylene.

Commonly used leveling agents such as Ping Ping Jia 0, leveling agent 102, and leveling agent OP have a certain leveling effect on the dyeing part of reactive dyes. Because the molecular long chain of such leveling agents contains polyoxyalkyl ethers, they can form loose oxygen bonds with hydroxyl (- OH), amino (- NH) and other functional groups in the dye molecules.

On the one hand, it will combine with the dye in the dyeing solution to form a relaxed complex, which hinders the adsorption and dyeing of the dye, thereby playing a slow dyeing role; On the other hand, it can enhance the interface transfer and full process transfer of dyes, further promoting the uniform adsorption of dyes. As a leveling agent for wool, WE is a non ionic/weakly cationic fatty amine polyoxyethylene ether. It is mainly used as a leveling agent for dyeing wool with reactive dyes, which can increase the color supply. It is beneficial for slow dyeing without affecting the dyeing percentage. It also has excellent leveling effects when used in media, neutral, weakly acidic, and metal complex dyes.

2. Anionic surfactants

Anionic dispersant leveling agents belong to dye affinity leveling agents. Anionic surface active agents have the same ion type as reactive dyes, and adopt the mechanism of occupying the dyeing mat first to slow down the dye uptake rate.

EDER, an anionic leveling agent, is a relatively new type of anionic leveling agent composed of a complex of aromatic polysulfonates. Its advantages include several points: (1) The leveling agent EDER has a certain chelating and dispersing regulation function on heavy metal ions such as calcium and magnesium, improving the quality of the dye; (2) In the dyeing and adsorption stage, it has excellent slow dyeing performance and controls the uniform dyeing and adsorption of dyes; (3) During the fixation stage, buffer the pH of the dyeing bath to ensure stable and uniform fixation of the dye, avoiding uneven fixation; (4) There is no adverse effect on the dyeing fastness of the fabric.

3. Complex of non-ionic and anionic surfactants

Non ionic surfactants achieve a slow dyeing effect by combining oxygen atoms on the polyoxyethylene bond with dye molecules through oxygen bonds. At present, most of the nylon leveling agents provided by auxiliary manufacturers are anionic/non-ionic composite leveling agents.

Leveling agents for dispersed dyes

1. Polyester fabric

Disperse dyes have good levelness and high dyeing fastness when dyeing polyester

At present, polyester dyeing and processing mostly use dispersed dyes for high-temperature and high-pressure dyeing, but it is difficult to color dark dyes and causes environmental pollution. Therefore, polyester simulation technology and product development have been the most active research topics in the textile industry in the past two decades. Ultra fine polyester fabric has a fast color absorption rate, and appropriate leveling agents should be added to the dyeing bath to enhance leveling.

2. Polyester ultrafine fiber

Due to the characteristics of smaller single fiber size, larger specific surface area, and higher content of amorphous zone compared to ordinary fibers, ultrafine fibers are prone to uneven dyeing. Therefore, it is very important to choose appropriate leveling agents.

Leveling agents can significantly reduce the initial adsorption percentage of dispersed dyes, improve the desorption and migration of dyes at initial and high temperatures, and increase the high-temperature dispersibility and compatibility of dyes. Traditional dispersed dyes can be used for dyeing ultrafine fibers in the presence of leveling agents.

In addition, β - cyclodextrin is also an effective leveling agent in the dispersion dyeing research of polyester ultrafine fibers. Cyclodextrin is a polycyclic glucose produced by the degradation of polysaccharide starch by cyclodextrin glucosyltransferase through biotechnology. The special circular structure of β - cyclodextrin can form inclusion complexes with most cationic dyes, causing it to be slowly released during the dyeing process, slowing down the E-dyeing rate and thus playing a leveling role. The use of β - cyclodextrin does not affect the final surface color depth and color fastness of the dye, but it is not suitable to be used together with surfactants. β - cyclodextrin ring has a moderate size, high solubility in water, biodegradability, and broad application prospects in printing and dyeing processing.

This article is excerpted from "Research progress on commonly used leveling agents for printing and dyeing dyes", Oriental Chemical Industry, Vol.9,37 (209)

Author: Liang Haomei

Transferred from printing and dyeing personnel