2.3 Choose the right dyeing process
The dyeing process has a great influence on the color fastness of the dyed product. For example: Improper chemical materials, hydrolysis of dyes, and excessively hard water quality, resulting in dye aggregation and precipitation; improper color-fixing conditions, low color-fixing rate, poor washing and soaping after dyeing, and unfixed dyes cannot be removed cleanly; The increase of dye hydrolysis and bond breakage, etc., will result in an increase in floating color and a decrease in dye fastness. Therefore, choosing the correct dyeing process is an important part of improving dye fastness. The selection of dyeing process can be considered from the following aspects:
(1) Some colors should be dyed at a higher temperature as far as possible, and the dyeing temperature can be appropriately increased, and then cooled to 60°C-65°C, and then add alkali to fix the color;
(2) Using low temperature weak alkali to fix color;
(3) The fixing temperature is generally 60°C-65°C
(4) The fixing agent adopts a single soda ash;
(5) The pH value is stable at around 11;
(6) soda ash is added in stages;
(7) Use the correct water washing and soaping process. The purpose of soaping is to remove floating color, and the purpose of water washing is to remove the residual alkali agent on the fiber. Washing and soaping should prevent the bonded dyes from being broken and hydrolyzed and falling off the fibers.
To this end, pay attention to the following points: wash with water before soaping, choose a soaping agent with good washing ability, dispersing ability, emulsifying ability and dirt-carrying ability, and it is best to add an appropriate amount of chelating dispersant to the soaping liquid. Soaping must be carried out at higher temperature and under neutral conditions (pH=6-7).
2.4 Strengthen the color-fixing treatment
Although a covalent bond is formed between the reactive dye and the fiber by adding alkali to fix the color, under certain conditions, the bond will still be hydrolyzed and broken, resulting in a hydrolyzed dye. When the hydrolyzed dyes, unbonded dyes are not removed completely, or the conditions of the post-soap treatment are not appropriate, the wet fastness of the dyed products will decrease. Reactive dyes are soluble anionic dyes. Try to reduce the solubility of dyes on fibers, or increase the force between dyes and fibers, which can improve the washing fastness of dyes and resist the adverse effects of the atmosphere on the dyes. There are several methods for this.
(1) Use a metal salt fixing agent to fix the color.
This method is suitable for reactive dyes that can complex with metal ions, such as dyes with salicylic acid structure. After the dyes react with metal ions, insoluble stable complexes can be formed on the fibers, thereby reducing the water solubility of the dyes and improving the washing fastness and light fastness of dyed fabrics.
(2) Use a cationic fixing agent to fix the color.
The cationic fixing agent can be combined with the dye anion, the water-soluble group is blocked, and the larger insoluble compound is formed and precipitated on the fiber. Thus, the washing fastness of the dyed product is improved.
(3) Reactive color fixing agent is used.
Such fixatives can be divided into 2 categories. Type 1 molecules contain cross-linking groups, which can react with polar groups such as amino groups and carboxyl groups in dyes and fibers to form covalent bonds. After high-temperature baking, various reactive groups in the resin are cross-linked and condensed with each other. A three-dimensional network protective film is formed on the surface of the fiber, thereby improving the fastness to wet treatment. The second type of polycations with active groups in the molecule can not only chemically react with fibers to form covalent bonds, but also form insoluble salts with dye anions, which can significantly improve wet fastness and formaldehyde-free.
2.5 Adopt new dyeing technology
With the development of dyeing materials and equipment and the application of industrial Internet, dyeing technology has made great progress. New technologies for reactive dyeing include controlled dyeing, wet short steam dyeing, cross-linking dyeing, ecological dyeing, and non-aqueous dyeing. These dyeing technologies can not only improve dyeing fastness and dyeing uniformity, but also save energy and reduce consumption, clean production, reduce pollution and protect the environment.