How to improve the dyeing fastness of printing and dyeing cloth to meet the increasingly fierce demand of textile market has become a research topic of printing and dyeing industry. For example, the light color fabric dyed with reactive dyes, the wet rub fastness of the dark color fabric; Wet treatment fastness of disperse dyes decreased due to thermal transfer after dyeing. And high chlorine fastness, sweat - light fastness, etc.

There are also many ways to improve the color fastness. Through years of production practice, the printing and dyeing practitioners have explored some methods and measures in the aspects of selecting the appropriate dye additives, improving the dyeing and finishing process, and strengthening the process control, which have improved and improved the color fastness to a certain extent and basically met the market demand.

Light fastness of fabric with reactive dyes

It is well known that the reactive dyes dyed on cotton fibers are attacked by ultraviolet rays in the sun, and the chromophore or chromophore in the dye structure will be destroyed to varying degrees, resulting in color change or light color, that is, the problem of sun fastness.

China's national standards have long stipulated the color fastness to light of reactive dyes. For example, GB/T411-93 standard of cotton printed and dyed fabrics provides that the light fastness of dyed fabrics with reactive dyes is 4-5 grade, and that of printed fabrics is 4-4 grade. According to the GB/T5326 standard for combed polyester/cotton blended printing and dyeing fabrics and FZ/T14007-1998 standard for cotton-polyester blended printing and dyeing fabrics, the light fastness of disperse/reactive dyeing fabrics is Grade 4, and that of printed fabrics is Grade 4. It is difficult to meet this standard for light-colored fabrics dyed with reactive dyes.

Light fastness of fabric with reactive dyes

The light fastness of reactive dyes is mainly related to the parent structure of the dyes. 70-75% of the parent structure of reactive dyes is azo type, and the rest are anthoquinone type, phthalocyanine type and A type. The azo type had poor light fastness, and the anthraquinone type, phthalocyanine type and A had better light fastness. The molecular structure of yellow reactive dyestuff is azo type. Pyrazolone and naphthalene trisulfonic acid have the best light fastness in their parent chromatids. The reactive dyestuff of blue chromatography has the best light fastness in their parent structures of anthraquinone, phthalocyanine and methyl.

Light fastness is generally low, especially light color.

Relationship between dye concentration and light fastness

The sun fastness of the sample will vary with the change of dyeing concentration. The sun fastness of the sample dyed with the same dye on the same fiber will increase with the increase of dyeing concentration, which is mainly caused by the change of aggregate particle size distribution of the dye on the fiber.

The larger the aggregate particles, the smaller the exposure area of dye to air - water and other effects per unit weight, and the higher the sun fastness.

The increase of dyeing concentration will lead to an increase in the proportion of large particle aggregates on the fibers and the corresponding increase in the sun fastness. The dyeing concentration of light-colored fabric is low, the proportion of dye aggregates on the fiber is low, most of the dye is single molecule state, that is, the decomposition degree of dye on the fiber is very high, each molecule has the same probability by the action of light, air and water, and the sun fastness is also decreased accordingly.

ISO/105B02-1994 standard sun fastness points 1-8 grade standard assessment, China's national standard is also points 1-8 grade standard assessment, AATCC16-1998 or AATCC20AFU standard sun fastness points 1-5 grade standard assessment.

Therefore, you must first find out the customer request is by what standard, all dye production enterprise or the company includes providing on the color of the dye index showed that the dyeing of sunlight fastness in dyeing depth of 1/1 of the cases, the measured data, and also is in dye concentration about 20-30 g/L at the fabric on measurement data, light color fabric is less than the horizontal.

Measures to improve light fastness

1. The selection of dyes affects light-colored fabrics

The most important factor in sun fastness is the dye itself, so the choice of dye is the most important.

When selecting dyes for color combination, it is necessary to make sure that the light fastness level of each component is the same. As long as the light fastness of any component, especially the component with the least amount, fails to meet the requirements of light-colored dyes, the light fastness of the final dye will not meet the standards.

2. Other measures

Effect of floating color dyes.

Incomplete soap-washing, unfixed dyes and hydrolyzed dyes remaining on the cloth will also affect the light fastness of the dyes, and their light fastness is significantly lower than that of fixed reactive dyes.

The more adequate the soaping, the better the fastness to light.

Effect of fixing agent and softener.

Cationic low molecular or polyamine condensation resin type fixing agent and cationic softener used in fabric finishing will make the color fastness to the sun decrease.

Therefore, attention must be paid to the influence of fixing agents and softeners on the fastness to sunlight of dyes.

Effect of ultraviolet absorbent.

Ultraviolet absorbent often is used at light color dye material to raise insolation fastness recently, but must dosage very big ability some effect, not only increase cost, and cause fabric yellowing and brute force damage, had better not use this method so.

Wet rubbing fastness of deep concentrated reactive dyes to wet treatment

In recent years, it has been difficult to use reactive dyes and other dyes. Reactive dyes dyeing by covalent bonds combined with excellent color fastness, but deep color dyeing thing often happens fade and stained with color phenomenon, the occurrence of these phenomena, in addition to the part of the dye matrix structure due to light, heat, sweat, acid gases and oxidant, azo matrix decomposition, complexation metal ions from, dyeing color and fade by amine oxide, etc.

The breakage of dye-fiber bonds can also cause discoloration and staining. The floating color on the stain is the wash fastness that causes the deep and concentrated color of the stain.

The floating color

Dye all the dyes will be left on the fabric after dyeing floating color dye, reactive dye floating color dye containing partially hydrolyzed dye adsorbed on the fiber, and did not participate in covalent reaction of the dye, the floating of dye removal degree related to them the immediacy of the fiber is one of the biggest direct was vinyl sulfone dye, followed by hydrolysis of dyes, Because of the existence of water-soluble groups of sulfur esters, the unreacted dyes have the least directness to the fibers and are the most easily removed floating dyes.

Practice has proved that even after sufficient water wash (soap), there are still some remaining floating color dyes on the fibers, the greater the reactive dye immediacy, floating of dye is not easily removed from the fiber down, with water soluble again at the same time, the water will fall, and contamination to other fabric, they are deep reactive dyes to dye color fastness to wet processing, fabric Including washing, soaping and wet rubbing fastness is not up to standard of the main reasons. The removal of floating dyes should be considered from two aspects: dye selection and process rationalization.

Dye selection

Dyeing plants select dyes according to the dye color card provided by the fastness performance and sample test to determine the level of wet treatment fastness of dyes. Because the color card provides the fastness is at the dye concentration of 1/1 depth, can only be used as a reference, and the latter is the main.

Therefore, the dyestuff of the deep concentrated color dyeing material must be optimized, and the imported reactive dyestuff with better fastness should be selected, and the color fixation rate should be high and the dye penetration is better.

Process Notes

1, strengthen the quality control of pretreatment pretreatment is mainly desizing, singeing, boiling bleaching, mercerizing and other processes, and the quality of each process control directly affects the quality and color fastness of dyeing.

(1) desizing must be fully removed from the pulp inside the fiber, the return will affect the evenness and penetration of dyeing, hinder the diffusion of dye to the fiber, so that the dye floats on the fiber surface, affecting the color fastness.

(2) singeing to be clean, singeing is not clean will directly affect the fiber surface smoothness and smoothness, increase the friction coefficient, produce a certain resistance, reduce the friction fastness.

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

The better the wool effect, the better the penetration and evenness, the higher the dyeing rate and fastness, the deeper the color, the less the floating color of the dye on the surface, the better the rubbing fastness and washing fastness, which can not only save the cost of dyeing materials, but also improve the dyeing fastness.

(4) is very important for dyed fabric mercerizing mercerization, mercerized fabric in addition to get stable width size, and can increase the dyeing depth, improve and smooth degree of the surface gloss of the fabric, and improve the wet rubbing fastness and stained with color fastness, especially dyeing dark fabric, silk is more important, so you must control the mercerizing alkali concentration, achieve the result of full mercerized.

2. Preferred dyeing methods. Different dyeing methods will result in different color shades, leveling, transdyeing and fixation effects.

(1) Immersion dyeing method, the fabric can have sufficient time to react with the dye at a certain temperature, through adsorption → diffusion → dyeing, to achieve the full dyeing and penetration effect of the dye and fiber, and has a higher solid color rate, brightness and color fastness.

(2) Cold pad dyeing method Cold pad dyeing is the fabric through the room temperature dip pad dyeing solution and lye to roll, after a long time of slow rotation, the room temperature stack, unroll water washing, soap washing, to achieve the purpose of full dyeing. This method is the best method of energy saving, environmental protection and small batch production. In this method, dyes and fibers are fully absorbed for a long time to react, and have good dye-on rate, fastness, evenness and penetration, thus obtaining good color fastness.

(3) a wet short steaming process a wet short steaming dyeing is energy-saving method of dyeing fabric steaming through directly after the pad dyeing liquid, solid color in high temperature and high humidity conditions, so as to achieve the purpose of rapid dyeing, solid color, good dyeing rate and dye permeability, high color, bright color and good fastness to washing and rubbing fastness can be obtained.

(4) Pad-dyeing There are two processes for pad dyeing, one is rolling → baking → rolling → steaming, and the other is rolling → baking → steaming. The first is to roll the dye first and then roll the solid color liquid. Steam is wet steam, so as to achieve the purpose of dyeing and fixing the color.

The second is to steam after pad dyeing and solid color drying in the same bath, that is, dry steam. The latter dyeing depth is 20 percent deeper than the former, but the fastness is lower than the former, so the former is used more, but the depth of wet steaming can not be reached, you can consider using dry steaming, but after finishing to improve the dyeing fastness of the fabric with fixing agent.

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

The more the amount of dye, the more the floating color dye, so in the reference to the standard sample dyeing depth of the premise, the amount of dye should be appropriate, the fiber of each dye adsorption has a limit value, that is, dyeing saturation value, generally not more than about 10% of the saturation value. When the amount of dye greatly exceeds the saturation value, excessive dye can not be fixed, can only accumulate on the surface of the fabric, affecting the friction fastness of the fabric. Reactive dyes with high lifting power should be used to achieve high dyeing rate in the case of a small amount.

The color fastness of the fabric dyed by the above dyeing methods was found to be as follows: dip-dyeing > cold-rolling > wet short steam > rolling → baking → rolling → steamed > rolling → baking → steamed.

3. There are impurity such as fixed dyes, floating dyes, residual alkalics and electrolytes in the interior and surface of the fiber after washing treatment. Only when these impurities are removed can the dye achieve the best color fastness and brightness of color.

The method is to rely on water washing, soapwashing and mechanical external force, the purpose is to remove the hydrophilic floating color, wash away the electrolyte and alkali agent, reduce the electrolyte concentration to increase the electrostatic repulsion between the floating color dye and the fiber, so that the floating color dye is easier to detach from the fiber; Alkali-removing agents are used to prevent the hydrolysis of immobilized dyes caused by alkali-removing agents during high temperature soap-cooking.

Washing after soaping is to remove a large amount of floating dye that has been dispersed by soaping agent.

Post-treatment process of water quality is very important, if the water hardness is higher, there are more Ca2 +, magnesium 2 +, such as heavy metal ions, they are troubled sulfonic acid sodium salt change in soluble in water soluble in water of sulfonic acid calcium, magnesium salt lake, so as to weaken the hydrophilicity of floating color dye, so the water quality has distinct effect on the post-processing of fastness of dyed material.

4, after finishing congenital deficiency, the day after tomorrow to make up, dyed fabric color fastness can not meet the requirements, can only use fixing agent and enhancement agent after finishing to make up and improve. The wet rubbing fastness of deep concentrated reactive dyes can be increased by 0.5-1.0 grade by special fixing agent.

other

Reactive dyes is generally poor fastness to chlorine, mainly depends on the molecular structure of the hair color body, diazo dyes base of ortho sulfonic group, or carboxylic acid base, or in the coupled components of hydroxy ortho or para sulfonic group, or carboxylic acid base, because of its space steric effect, reduces the CI - attack - NH - or - N - ability, thus improves the resistance to chlorine fastness.

According to GB/T8433-1998 test method for water fastness of chlorinated swimming pools, the effective chlorine concentration can be divided into 20mg/L, 50mg/L and 100mg/L, and the special requirement is 200mg/L. With the increase of effective chlorine concentration, the fastness to chlorine decreases. Therefore, the selection of dye is very important, and the method of fixing agent can also be used in the post-finishing process to improve the chlorine fastness, but only by 0.5-1.0 grade.

The light fastness of reactive dyes has attracted much attention in recent years. Some reactive dyes have good light fastness but poor light fastness to sweat. Because under the dual action of sweat and sunlight, the fading mechanism is different, because the amino acids or related substances in sweat chelate with the metal ions of the metal complexing dye, so that it breaks away from the dye mother, the fastness to sunlight of the dye mother before complexing is not good, so it fades or changes in color.

Decreased fastness due to thermal migration after dispersion dyeing

Thermal transfer is a redistribution of disperse dyes in a two-phase solvent, so all the auxilaries that can dissolve disperse dyes can produce thermal transfer. Heat transfer phenomenon the reason is because the fiber outer additives at high temperature on the dye solution, dye through high temperature fiber capillary and broaden the migration from inside the fiber to fiber surface, make the dye on the fiber surface accumulation, a series of effects, such as color change, when ironing fouling other fabric, the friction resistance, resistance to water, perspiration, the fastness to dry cleaning and weather resistant.

Practice shows that the amount of dye heat transfer from inside to outside of the fiber is directly related to the dyeing depth. The deeper the dyeing depth of the fiber, the more the amount of dye heat transfer from inside to outside, and the greater the influence on the dye. The high temperature treatment after dyeing has a great influence on the thermal migration of disperse dyes, and the higher the temperature, the greater the influence. Therefore, try to use a gentle process when finishing dyed fabric.

The thermal migration of disperse dyes is related to the molecular structure of the dyes themselves. It is found that the widely used non-ionic surfactants are the main reason for the thermal migration of disperse dyes. Amino silicone emulsion as a softening agent is the most used softening agent at present, because to make microemulsion, it is necessary to add 40-50% of the total amount of silicone fatty alcohol polyoxyethylene ether or alkyl phenol polyoxyethylene ether and other non-ionic surfactants as emulsifier.

With the wide use of amino silicone emulsion, the heat transfer of disperse dyes becomes more serious after dyeing. The solution is to choose disperse dyes with high lifting power and absorption rate, especially those with good wet fastness after thermal fixation. The dye (float color) attached to the fiber surface will aggravate the effect of dye thermal transfer on the color fastness of dyed yarns. Therefore, after dyeing (especially for dark colors), reducing agents and alkalics should be used for reduction cleaning to completely remove floating colors.

To sum up, the selection of dyes is very important to improve the color fastness of dyes. Different dyes should be selected according to the requirements of color fastness. Vat dyes and reactive dyes with high sun fastness should be selected for the dyeing of light-colored fabrics with high sun fastness. Only the imported reactive dyes with high fastness and high lifting power can ensure the wet treatment fastness for deep and concentrated colors. Disperse dyes to choose less thermal mobility of dyes, especially dark should try to avoid reaching or exceeding the dyeing saturation value, the use of surfactants should adhere to the principle of "can not use, can use less, use less, must use, to choose carefully".

In the process of production management, the process control must be strengthened to ensure that the following process requirements are met:

(1) the fiber surface should be smooth and clean, and the hairiness should be less.

(2) The gross efficiency of the fiber is higher.

(3) fiber color absorption ability should be strong.

(4) Dye is better for fiber evenness and penetration.

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

(6) Soap and wash thoroughly after dyeing.

(7) The bond breaking degree of the post-treated dye is smaller.