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 the high chlorine fastness and sweat resistance—— Light fastness, etc.

There are many factors that affect color fastness, and there are many ways to improve color fastness. Through many years of production practice, I have explored some in choosing suitable dyeing and chemical additives, improving dyeing and finishing processes, and strengthening process control. The methods and measures have improved and improved the color fastness to a certain extent, basically satisfying the market demand.

1 Light fastness of light-colored fabrics with reactive dyes

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 The problem of light fastness.

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 the printed fabric is also level 4.

It is more difficult for reactive dyes to dye light-colored printed fabrics to achieve this standard.

• The 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, the light fastness of dyed samples will increase with the increase of dyeing concentration. 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, 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 high, and each molecule has the same probability of being exposed to light and air. , The effect of moisture, the light fastness is also reduced accordingly.

ISO/105 B02-1994 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, AATCC 16-1998 or AATCC 20AFU standard light fastness is divided into 1-5 grade standard assessment.

Therefore, we must first find out what standard the customer requires. All dye manufacturers or companies, including the color card provided by the "Dye Index", show the light fastness of the dyed material, which is measured under the condition of the dyeing depth of 1/1. The data is measured on medium-colored fabrics with a dye concentration of about 20-30g/L. Light-colored fabrics cannot reach this level.

• Measures to improve light fastness

1. The choice of dyes 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 light fastness of the final dyed product will not reach the standard.

2. Other measures

(1) The influence 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 products. 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.

(2) 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 choosing fixing agents and softeners, attention must be paid to their influence on the light fastness of dyed products.

(3) The influence of ultraviolet absorbers.

Ultraviolet absorbers are often used in light-colored dyeings 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.

2 Wet rubbing fastness of reactive dyes in wet processing

In recent years, it has been a difficulty in the use of reactive dyes and other dyes. Reactive dyes endow dyed products with excellent fastness through covalent bonding. However, dark dyed products often suffer from fading and staining. These phenomena occur in addition to part of the dye matrix structure due to light, heat, sweat, and acidity. The erosion of gases and oxidants, the decomposition of azo groups, the detachment of complex metal ions, and the oxidation of amino groups can cause discoloration and fading of dyed products.

The breaking of the dye-fiber bond can also cause fading and staining. The floating color on the dyed material is the washing fastness of the dark dyed material.

• Floating

Dyes All dyes will leave floating dyes on the fabric after dyeing. The floating dyes of reactive dyes include partially hydrolyzed dyes and dyes that are adsorbed on fibers without participating in a covalent reaction. The degree of removal of these floating dyes is related to them. It is related to the directness of fibers. Among them, the most direct is vinylsulfone based dyes, followed by hydrolyzed dyes. Unreacted dyes have the least directness to fibers due to the presence of sulfur ester water-soluble bases and are the easiest floating dyes to remove. Practice has proved that even after sufficient water (soaping) washing, there are still some floating dyes remaining on the fibers. The greater the directness of the reactive dyes, the more difficult the floating dyes will be removed from the fibers. At the same time, they are water-soluble. Water will dissolve down and stain other fabrics. They are the main reason for the unqualified fastness of reactive dyes to wet processing of deep and dense fabrics, including washing, soaping and wet rubbing fastness.

To remove floating dyes, consideration must be given to both dye selection and process rationalization.

• Dye selection

Printing and dyeing factories choose dyes based on the fastness performance and sample test provided by the dye color card to determine the wet processing fastness level of the dye.

Because the fastness provided on the color chart is dyed at a depth of 1/1 of the dye concentration, it can only be used as a reference, and the latter is the main one.

Therefore, the dyes for deep and concentrated dyeings must be optimized. Imported reactive dyes with better fastness should be selected, the fixation rate should be high, and the transmittance should be good.

• Process attention

1. Strengthen the quality control of pre-treatment The pre-treatment is mainly desizing, singeing, scouring and bleaching, mercerizing and other processes, and the quality of each process control directly affects the quality and color fastness of dyeing.

(1) Desizing

Desizing must fully remove the sizing inside the fiber. The poor de-sizing will affect the levelness and transmittance of dyeing, hinder the diffusion of the dye into the fiber, make the dye float on the surface of the fiber, and affect the color fastness.

(2) Singeing

The singeing should be burned cleanly. The singeing will directly affect the smoothness and smoothness of the fiber surface, increase the friction coefficient, generate a certain resistance, and reduce the friction fastness.

(3) Boiling, bleaching, scouring and bleaching should be cooked thoroughly, and reach the required whiteness, remove impurities and cottonseed hulls, and reach the standard wool effect of 8-10cm/30min or more. Failure to meet the requirements will directly affect the dyeing rate and fixation. Rate.

The better the hair effect, the better the dye penetration and leveling, the higher the dye uptake and fixation rate, the deeper the color, the less the floating color of the dye floats on the surface, the better the rubbing fastness and the washing fastness, which can save money The cost of dyeing and chemical materials can also improve the color fastness.

(4) Mercerized

Mercerizing is very important for dyeing fabrics. In addition to making the fabric obtain a stable width, mercerizing can increase the depth of dyeing, improve the gloss and smoothness of the fabric surface, and improve the wet rubbing fastness and staining fastness, especially the deep dyeing. For colored fabrics, mercerizing is more important, so the alkali concentration of mercerizing must be controlled to achieve the full mercerizing effect.

2. The preferred dyeing method. The dyeing method is different, and the effect of the color obtained is different in depth, level dyeing, penetrating dyeing, and fixing. Below, several different dyeing methods will be analyzed and discussed.

(1) Dip dyeing method

Dye dyeing, the fabric can have sufficient time to react with the dye at a certain temperature, through adsorption → diffusion → dyeing, the dye and fiber are fully dyed and penetrated, and it has a higher fixation rate and Brightness and color fastness.

(3) Cold rolled pile method

Cold pad-batch dyeing is to roll the fabric through room temperature pad dyeing solution and lye. After a long time of slow rotation, after stacking at room temperature, it is unrolled and washed with water and soaped to achieve the purpose of full dyeing.

This method is the best method for energy saving, environmental protection, and small batch production.

The method is that the dye and the fiber fully absorb and react for a long time, and it has good dye uptake, fixation, level dyeing and trans-dyeing properties, so as to obtain good color fastness.

(4) Wet short steaming method

The wet short steaming dyeing is an energy-saving dyeing method. The fabric is steamed directly after the padding liquor, and the fixation is carried out under high temperature and high humidity, so as to achieve the purpose of fast dyeing and fixation, and has a good dye uptake rate It has high color yield and bright color, and can obtain good washing and rubbing fastness.

(5) Pad dyeing method

There are two process methods for pad dyeing, one is rolling → drying → rolling → steaming, and the other is rolling → drying → steaming. The first is to pad the dye and then the color fixing solution. The purpose of dyeing and fixing. The second one is steaming after pad dyeing and fixing and drying in the same bath, that is, dry steaming.

The latter’s dyeing depth is 20% deeper than the former, but the various fastnesses are lower than the former, so the former is used more, but for depths that cannot be reached by wet steaming, dry steaming can be considered, but solid steaming should be used for finishing. To improve the color fastness of fabrics.

Fixation reaction is the most important stage of reactive dye dyeing. The entire process of dyeing must be controlled in a direction that is conducive to fixation reaction and inhibits hydrolysis reaction in order to obtain the highest fixation rate.

The more the amount of dye, the more floating dye. Therefore, the amount of dye should be appropriate on the premise of referring to the dyeing depth of the standard sample. The adsorption of each dye by the fiber has a limit value, that is, the dyeing saturation value, which generally does not exceed the saturation. Around 10% of the value.

When the amount of dye greatly exceeds the saturation value, the excess dye cannot be dyed and fixed, and can only accumulate on the surface of the fabric, which affects the rubbing fastness of the fabric.

Reactive dyes with high lifting power should be used to achieve a high dye uptake rate in a small amount.

After the fabrics dyed by the above several dyeing methods pass the test, it is found that the color fastness is preferably: dip dyeing>cold padding>wet short steaming>rolling→baking→rolling→steaming>rolling→baking→steaming.

3. There are fixed dyes, floating dyes, residual alkalis and electrolytes on the inside and surface of the dyed fiber after washing treatment. Only when these impurities are removed can the dyed material achieve the best color fastness and color brightness.

The method is to rely on water washing, soaping and mechanical external force to remove the hydrophilic floating color, wash away the electrolyte and alkali, reduce the electrolyte concentration to increase the electrostatic repulsion between the floating dye and the fiber, so that the floating dye is more It is easy to leave the fiber; the washing alkali agent is to prevent the alkali agent from causing the hydrolysis of the fixed dye during high-temperature soaping.

Washing after soaping is to remove a large amount of floating dyes that have been dispersed by the soaping agent.

Water quality is very important in the post-treatment process. If the water quality is high in hardness, there will be more heavy metal ions such as Ca2+ and Mg2+, which can transform the water-soluble sodium sulfonate into the insoluble calcium (magnesium) salt color. Lake, thereby weakening the hydrophilicity of floating dyes, so the water quality has a significant impact on the post-processing fastness of dyeings.

4. The congenital deficiencies of the finishing process can be compensated by the day after tomorrow. The color fastness of the dyed fabric is not up to the requirements, and the fixing agent and enhancer can only be used in the finishing process to make up and improve it.

The special fixing agent can improve the wet rubbing fastness of reactive dyes by 0.5-1.0 level.

3 Chlorine fastness and sweat fastness of reactive dyes-light fastness

Reactive dyes generally have poor chlorine fastness, which mainly depends on the molecular structure of the color body. There are sulfonic or carboxylic acid groups at the ortho position of the diazo group of the dye, or there are sulfonates at the ortho or para position of the hydroxyl group of the coupling component. In the case of acid groups or carboxylic acid groups, due to its steric hindrance, the ability of CI- to attack -NH- or -N- is reduced, thus improving the chlorine fastness.

According to the GB/T8433-1998 test method for water fastness to chlorine-containing swimming pools, the available chlorine concentration is divided into three types: 20mg/L, 50mg/L and 100mg/L, with 200mg/L for special requirements.

As the concentration of available chlorine increases, the fastness to chlorine decreases.

Therefore, the choice of dye is very important, and the method of fixing agent can also be used in the finishing process to improve the chlorine fastness, but it can only be improved by 0.5-1.0 level.

The perspiration-light fastness of reactive dyes has received great attention in recent years. Some reactive dyes have good light fastness but poor perspiration light fastness.

Because under the dual action of sweat and sunlight, the fading mechanism is different. The amino acid or related substances in sweat chelate with the metal ion of the metal complex dye to separate it from the dye matrix. The light fastness of the dye matrix before complexation is originally Not good, so it fades or discolors.

4 Decrease in fastness caused by thermal migration of disperse dyes

Thermal migration is a redistribution phenomenon of disperse dyes in two-phase solvents. Therefore, all additives that can dissolve disperse dyes can produce thermal migration.

The reason for the phenomenon of heat migration is that the additives in the outer layer of the fiber dissolve the dye at high temperature. The dye moves from the inside of the fiber through the high temperature of the fiber capillary to expand and migrate to the surface of the fiber, causing the dye to accumulate on the surface of the fiber, causing a series of effects. , Such as discoloration, staining other fabrics when ironing, resistance to friction, washing, perspiration, dry cleaning and sunlight, the color fastness decreases.

Practice has shown that the thermal migration of dyes from the inside of the fiber to the outside of the fiber is directly related to the depth of dyeing. The deeper the dyeing depth of the fiber, the greater the amount of dye thermally migrated from the inside to the outside, and the greater the impact on the dyed product; The thermal migration of disperse dyes has a greater impact, and the higher the temperature, the greater the impact.

Therefore, try to use a gentle process when finishing dyed fabrics.

The thermal migration of disperse dyes is related to the molecular structure of the dye itself. The widely used non-ionic surfactants found in production practice are the main reason for the thermal migration of disperse dyes.

Amino silicone emulsion as a softener is currently the most used softener, because to make a microemulsion, it is necessary to apply 40-50% of the total amount of silicone nonionic such as fatty alcohol polyoxyethylene ether or alkylphenol polyoxyethylene ether Surfactants act as emulsifiers.

With the widespread use of amino silicone emulsions, the thermal migration of disperse dyes after dyeing becomes more serious.

The solution is to choose high lifting power and exhaustion rate, especially disperse dyes with good wet fastness after dyeing heat-set.

The dye (floating color) attached to the fiber surface will aggravate the effect of dye thermal migration on the color fastness of the dyed fabric.

Therefore, after dyeing (especially for dark colors), reducing agent and alkali agent should be used for reduction cleaning to completely remove floating color.

5 Conclusion

In summary, to improve the color fastness of dyed products, the choice of dyes is very important. Different dyes should be selected according to the requirements of color fastness. Light-colored fabrics with high requirements for light fastness should choose vat dyes and have high Reactive dyes with light fastness are used for dyeing; for deep and dense colors, only imported reactive dyes with high fixing rate and high lifting power can be used to ensure wet processing fastness; for disperse dyes, dyes with less thermal migration should be selected, especially for dark applications. Try to avoid reaching or exceeding the saturation value of dyeing. The use of surfactants should adhere to the principle of Use with caution

In the production management process, it is necessary to strengthen process control to ensure that the following process requirements are met:

(1) The fiber surface should be smooth and hairy should be less.

(2) The hair efficiency of the fiber should be high.

(3) The fiber has strong color absorption ability.

(4) The level and penetration degree of the dye to the fiber is better.

(5) The bonding and fixing of the dye and fiber should be sufficient.

(6) Soap and wash thoroughly after dyeing.

(7) The bond breaking degree of the post-treatment dye should be small.