A Brief Discussion on the Principles of Color Fixing Agents

The fixation process of most color fixing agents utilizes multiple fixation mechanisms to improve the color fastness indicators of dyed or printed fabrics, such as washing, sun exposure, friction resistance, acid and alkali resistance, and chlorine resistance, in order to achieve satisfactory fixation effects.
1、 The properties that color fixing agents should possess
1. Has strong fixation ability, which can significantly improve the color fastness indicators of dyed or printed textiles;
2. Dyes have wide adaptability, and the influence of dye structure on the fixation effect is relatively small;
3. Strong affinity with fibers and high absorption rate in fixed color bath;
4. After being fixed with a color fixing agent, the fabric will not or will rarely cause color changes;
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 texture of the fabric or yarn, and does not cause a decrease in the strength of the fabric or yarn.
2、 The principle of various color fixing agents
1. Ionic bonding of anionic and cationic groups
By utilizing the cationic groups in the fixing agent molecules to form ionic bonds with the anionic groups of the dye, insoluble color lakes are formed on the fabric, blocking the soluble groups of the dye, making it difficult for the dye on the fabric to dissolve and fall off in contact with water, and achieving the goal of improving wet treatment fastness. The stronger the cationic nature of the fixing agent, the better its color fastness. Direct dyes, acidic dyes, and unbound reactive dyes contain hydrophilic groups, which reduce the affinity between dyes and fibers when they come into contact with water. Using cationic compounds for fixation, it can combine with dyes to form insoluble salts. Water soluble dyes can also be regarded as anionic active colloidal electrolytes that undergo dissociation when exposed to water, generating high molecular weight anions. They can exchange ions with cationic surfactants on fibers, generating salts that are slightly soluble or insoluble in water.
2. Reactive groups in fixing agent molecules
By utilizing the reactive groups in the fixing agent molecules to react with the reactive groups on the dye molecules and the hydroxyl groups on the cellulose molecules, a highly diversified cross-linking system is formed, which tightly and firmly connects the dye and fiber, prevents the dye from falling off the fiber, and improves the dyeing fastness of the dye, thereby improving the wet treatment fastness. At present, the main method is to introduce active groups such as epoxy groups onto the fixing agent.
3. Film formation of fixing agents
By utilizing the film-forming properties of color fixing agents, a layer of mesh like film is generated on the surface of fibers, and the dye is coated on the fiber surface to prevent dye detachment and improve wet treatment fastness. All color fixing agents with good film-forming properties have good color fixing effects. Polymers formed by the polymerization of olefins, even without reactive or cationic groups, can improve dyeing fastness. This is because the polymer forms a film on the dye, reducing dye dissolution; After improving the molecular weight of polyamine color fixing agents, the color fastness can also be improved. If reactive or cationic groups are introduced into the film-forming material, it can better improve dyeing fastness.
4. Molecular attraction between fixing agents and fibers
By utilizing the molecular attraction between fixing agents and fibers, the fixation strength of dyes is increased, thereby improving the washing fastness of dyed fabrics. The intermolecular attraction referred to here is mainly hydrogen bonding attraction.
5. Sweat fastness enhancer
Utilize the buffering ability of fixatives to neutralize acidic substances in sweat

5. Sweat fastness enhancer
By utilizing the buffering ability of color fixing agents, acidic substances in sweat are neutralized, preventing covalent bonds between dyes and fibers from breaking, and achieving the goal of improving sweat fastness. Reactive dyes are not resistant to acid invasion. In acidic environments, the covalent bonds between reactive dyes and fibers will hydrolyze and break, leading to a decrease in sweat fastness. Sweat contains acidic substances, and in order to improve sweat fastness, the molecular structure of the fixing agent must have strong acid absorption ability, that is, good buffering ability. This is why most color fixing agents containing nitrogen atoms in their molecular structures have good acid resistance. The use of polyol amine condensates as fixing agents has better sweat fastness than fixing agents made from polyol acids or naphthalene diphenol condensates. After dyeing, anti shrink wool fibers are treated with fixing agents prepared by reacting formaldehyde with urea, thiourea, dicyandiamide or melamine, which can improve the wet treatment and sweat fastness, especially for complex dyes.

6. Wet friction fastness enhancing agent
By utilizing the smoothing effect of color fixing agents, the friction coefficient on the fiber surface can be reduced. By reacting with fibers and dyes, the dye and fibers can be tightly and firmly combined to prevent the dye from falling off the fibers; By combining fixing agents with dyes to form insoluble salts that are difficult to dissolve in water, the wet treatment fastness can be improved; The use of color fixing agents can form a three-dimensional network of water insoluble protective films on the surface of fibers, block the contact between dyes (reactive and non reactive) and water and other media, increase the smoothness of the fabric surface, reduce the friction coefficient, and further prevent dye swelling, hydrolysis, and detachment during friction, improving dry and wet friction fastness.
7. Sun fastness enhancer
Grafting UV absorbers into the fixing agent molecules, utilizing UV absorption groups to absorb UV rays in the same light, prevents UV damage to the dye structure, and thus improves the same light fastness.
8. Active chlorine resistant fixing agent
By utilizing the chlorine resistance or chlorine absorption properties of certain substances, the attack of reactive chlorine on dyes can be prevented, thereby improving the fastness of dyes to chlorine immersion and chlorine bleaching.