The Principle of Various Fixing Agents

The properties that color fixers should have:

1. Strong color fixation ability, which can significantly improve the color fastness index of dyed or printed textiles;

2. The dye has wide adaptability, and the dye structure has little effect on the color fixation effect;

3. Strong affinity with fibers, and high exhaustion rate in the color fixation bath;

4. After the fabric is fixed by the color fixer, it will not or rarely cause color change;

5. While improving a certain color fastness, other color fastness should not be reduced, and various color fastness indicators should be taken into account; 6. It does not affect the feel of the fabric or yarn, and does not cause the strength of the fabric or yarn to decrease.

The principles of various color fixers:

1. Ionic bond of anionic and cationic groups The cationic groups in the color fixer molecules are used to form ionic bonds with the anionic groups of the dyes to generate insoluble lakes on the fabrics, block the soluble groups of the dyes, and make the dyes on the fabrics difficult to dissolve and fall off when they come into contact with water, so as to achieve the purpose of improving wet treatment fastness. The stronger the cationicity of the color fixer, the better its color fastness. Direct dyes, acid dyes and unreactive dyes contain hydrophilic groups, which reduce the affinity between dyes and fibers when they come into contact with water. Cationic compounds are used for color fixation, which can combine with dyes to form insoluble salts. Water-soluble dyes can also be regarded as anionic active colloidal electrolytes, which dissociate when in contact with water to generate high-molecular anions, which can exchange ions with cationic surfactants on fibers to generate slightly soluble or insoluble salts.

2. Reactive groups in color fixative molecules

The reactive groups in the color fixative molecules are used to react with the reactive groups on the dye molecules and the hydroxyl groups on the cellulose molecules to form a highly diversified cross-linking system, so that the dye and the fiber are more closely and firmly connected together, preventing the dye from falling off the fiber, thereby improving the dye fastness, thereby improving the wet processing fastness. At present, the main method is to introduce reactive groups such as epoxy groups into the color fixative.

3. Film formation of color fixing agent Using the film-forming property of the color fixing agent, a layer of mesh film is formed on the fiber surface, and the dye is coated on the fiber surface to prevent the dye from falling off and improve the wet processing fastness. All color fixing agents with good film-forming properties have better color fixing effects. Polymers formed by olefin polymerization can improve color fastness even if they do not contain reactive groups or cationic groups. This is because polymers form films on dyes, reducing the dissolution of dyes; polyamine color fixing agents can also improve color fastness after increasing their molecular weight. If reactive groups or cationic groups are introduced into the film-forming material, the color fastness can be further improved.

4. Molecular attraction between color fixing agent and fiber Using the molecular attraction between color fixing agent and fiber, the fixing strength of dyes is increased, thereby improving the washing fastness of dyed fabrics. The molecular attraction here refers mainly to hydrogen bond attraction.

5. Sweat fastness enhancer uses the buffering capacity of the fixing agent to neutralize the acidic substances in the sweat, prevent the covalent bond between the dye and the fiber from breaking, and achieve the purpose of improving the sweat fastness. Reactive dyes are not resistant to acid attack. In an acidic environment, the covalent bond between the reactive dye and the fiber will be hydrolyzed and broken, resulting in a decrease in sweat fastness. Sweat contains acidic substances. To improve sweat fastness, the fixing agent molecular structure must have a strong acid absorption ability, that is, it must have good buffering capacity. This is why most fixing agents containing nitrogen raw materials in the molecular structure have good acid resistance. The use of polyol amine condensates as fixing agents has better sweat fastness than fixing agents made from polyacids or naphthalene diol condensates. After shrinkage-resistant fibers are dyed, they are treated with a fixing agent prepared by the reaction of formaldehyde with urea, thiourea, dicyandiamide or melamine to improve wet processing fastness and sweat fastness, especially for complex dyes.

6. Wet friction fastness enhancer uses the smoothing effect of the fixing agent to reduce the friction coefficient of the fiber surface: uses the fixing agent to react with the fiber and dye to make the dye and fiber more tightly and firmly combined together to prevent the dye from falling off the fiber; uses the fixing agent to combine with the dye to form a water-insoluble salt to make it difficult to dissolve in water to improve the wet processing fastness; uses the fixing agent to form a three-dimensional mesh, water-insoluble protective film on the fiber surface to block the contact of the dye (reacted and unreacted) with water and other media, increase the smoothness of the cloth surface, reduce the friction coefficient, and further prevent the swelling, hydrolysis and shedding of the dye during the friction process, and improve the dry and wet friction fastness.

7. Sunlight fastness enhancer grafts ultraviolet absorbers into the fixing agent molecules, uses the ultraviolet absorbing group to absorb ultraviolet rays in the same light, prevents ultraviolet rays from damaging the dye structure, and thus improves the same light fastness. 

8. Active chlorine-resistant color fixing agent uses the chlorine resistance or chlorine absorption of some substances to prevent active chlorine from attacking dyes, thereby improving the dye's chlorine fastness to chlorine immersion and chlorine bleaching.

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