When dispersed scarlet and maroon (dark colors) are used for high-temperature and high-pressure dyeing, some color spots will appear if you are not careful. Since the dyeing process is a dynamic, complex and changeable process, which is affected by many factors (such as technology, equipment, operations, water, electricity, steam, etc.), this article only makes a simple analysis. Please correct me for any shortcomings. .
Disperse dye dyeing properties
Disperse dyes have three performance defects in dip dyeing:
1. There is thermal cohesion.
Disperse dyes have very little water solubility and rely almost entirely on dispersing (diffusion) agents to coat them to form hydrophilic dye colloidal particles so that they can be dispersed in water. However, during the process of heating, maintaining, and cooling, these dye colloidal particles are subject to the dual effects of high temperature and shear force of the dye liquor, and the “binding energy” between the dye and the dispersant will gradually decrease, and even partially break. The free dye crystal particles will aggregate with each other due to the repulsion of water, causing the tiny dye crystal particles to gradually turn into large dye aggregates. As a result, in mild cases, the brightness of the color and dyeing fastness will be reduced; in severe cases, it will gather together with suspended matter such as polyester oligomers and cilia in the dye liquor to form a tar-like substance that will adhere to the fabric and cause stains. Produces “tar spots” that cannot be removed.
Countermeasures: 1. According to testing, thermal cohesion is common in commonly used disperse dyes. But their severity is obviously different. Therefore, you should choose a dye with a small aggregation tendency. If it is an aggregate of dye, you should choose a dye that is easy to re-depolymerize over time. Dyes that are easy to aggregate and difficult to depolymerize should not be used in dip dyeing. For this reason, dyes are tested before use. 2. It is necessary to select and apply a dispersion leveling agent with good high-temperature dispersibility to improve the dispersion stability of the dye grains in the high-temperature dye bath.
2. Poor alkali resistance and stability.
In high-temperature and high-pressure dyeing, once the pH value of the dye bath is >6, significant or even serious color differences and depth differences will occur. The main reason is that in a high temperature (above 100°C) dye bath with pH > 6, some groups with poor alkali resistance and stability in the dye molecular structure, such as ester groups, cyano groups, amide groups, etc., will be hydrolyzed, causing the dye to develop. The color system was destroyed.
Countermeasures: The key countermeasure is to use a pH buffer system with strong buffering capacity and wide buffering range, such as sodium acetate-acetate. Keep the pH value of the dye bath stable in the weakly acidic range (pH=”4~5) from beginning to end for dyeing. Do not use ammonium sulfate or ammonium acetate as pH regulator. Because their pH value is >6 at 2~3g/L . If a single acetic acid is used to adjust the pH value, it is recommended to use a more appropriate amount. Glacial acetic acid 0.5ml/L (pH=4~4.2) can be used. Otherwise, it will be difficult to eliminate the influence of alkaline substances brought in from the outside on the pH value of the dye bath. , to keep the pH value of the dye bath stable.
3. It has thermal migration.
Thermal migration means that after polyester is dyed and then dried at high temperature During heat treatment, the dye originally dyed inside the polyester will migrate to the surface of the polyester. Thermal migration is a common physical property of disperse dyes. It is worth noting that the thermal migration behavior of different disperse dyes is different. Therefore During high-temperature dry heat finishing (such as soft setting, waterproof setting, resin finishing, etc.), due to the different thermal migration amount of the dye, while the dye fastness decreases, the color of the cloth surface also changes. Out of the vat occurs. When the color and light are consistent and the fastness is qualified, when entering the finished product, the color and light are “deviated” and the fastness is low, resulting in quality problems that require rework and color correction.
Countermeasures: 1. Key countermeasures It is to use dyes with low thermal migration and high washing fastness. Choose dyes with larger molecular weights and higher affinity for polyester, which are difficult to migrate from the inside of the fiber to the fiber surface even under high-temperature dry heat conditions above 150°C. . Therefore, the thermal migration is small, the washing fastness is high, and the color becomes lighter after finishing. 2. Since surfactants have different promotion effects on the thermal migration of disperse dyes, the use of surfactants during the dyeing process should be Adhere to “If you can’t use it, don’t use it; if you can use it less, use it less.” When it must be used, the variety should be selected and the water should be clean. 3. Silicone emulsion softeners contain a certain amount of non-ionic emulsifier. The presence of non-ionic emulsifier on the fiber has a negative impact on dispersion. Thermal migration of dyes has a serious impact. Therefore, white emulsion softeners without emulsifiers should be used instead of emulsion softeners.
Problems of dispersing dark and red colors
When dispersed red and maroon (dark colors) are used for high temperature and high pressure dyeing, the reasons for color spots are as follows:
1. The quality of dispersed red is poor, and sometimes the particle size is larger. Recrystallization of tiny particles occurs after chemical mixing. When the recrystallized particles gather together, they will precipitate from the dye and deposit on the fabric or machine wall, causing color spots.
2. Improper chemical mixing can easily lead to color spots. The dye forms large particles with high viscosity, especially in cold water. It is difficult to dissolve the sticky dye that forms “mud”. If the dye solution is poured into the dye vat, it will adhere to the fabric and form color. Spots and color spots.
3. The temperature rises too fast during dyeing, especially in the early stage of dyeing, if the steam volume is too large or the air pressure is too high, it can destroy the dispersion state of the dye bath, cause flocculation or aggregation of the dye, and lead to color spots. , the generation of color points.
Take measures
1. Strengthen dye quality inspection. The quality of dyes should be tested before they are put into production. Observe the dye particle size distribution and determine the fineness of the dye particles. During detection, the prepared 3% dye solution can be stirred thoroughly and 0.4 mL be drawn. Continuously drip into the small holes of the glass plate (use two glass plates, the upper one has a d=1mm hole drilled in the center, and a piece of filter paper is sandwiched between the two glass plates), and then continue to drip 0·2mL distilled water every 5 minutes. into the small hole (a total of 5 times, a total of 1.0 mL of distilled water was dropped), wait for it to spread around until the permeability circle is stable, take out the filter paper, dry it, observe its diffusion performance, and rate it. Level 4-5 is considered qualified (that is, a uniform colored bleeding circle is formed, and the middle spot circle is not obvious). You can also dip a glass rod into a small drop of glycerol and drop it on the slide. Use another slide to spread the glycerin into a thin layer. Then stir the prepared dye solution with a concentration of 0.5g/L and suck it up with a blood pipette. 0.1 mL, immediately drop it on the slide that has been coated with a thin layer of glycerol, cover the slide, place it on a 1000x microscope platform, let it sit for a while and observe the dye particles with a diameter equal to or greater than 2 μm within a field of view. number. If the diameter is 2 μm or more but within 5, and the maximum diameter is 3 to 5 μm, it is considered qualified.
2. Use cosolvent materials. Most disperse dyes only need to be hydrated at 40°C. However, a few disperse dyes such as dispersed scarlet BWFL and dispersed ruby H2GFL are easy to agglomerate in water, so the use of cosolvent materials can improve efficiency and reduce the generation of color spots. Commonly used co-solvents include ethanol, isopropyl alcohol, acetone, etc. Among them, ethanol is the most widely used. When making the dye, add ethanol to the dye at a ratio of 1:1, stir it into a slurry, and then rinse it with 10 times the water.
3. Control the heating speed. After fabric pre-treatment and cleaning, when the temperature reaches 60°C, pour the dye solution into the dye vat. After running for 5 minutes, turn on the steam to raise the temperature from 60°C to 100°C at a rate of 1.5-2°C/min. The dispersed red dye should be below 100°C. , only adsorbed on the fiber and not dyed, and 100~120℃ is the critical exhaustion zone of dye dyeing. At this time, the temperature should be raised slowly, preferably 1℃/min. After the temperature is raised to 130℃, the heat preservation dyeing should be carried out for 40 ~60min, because the dispersed red dye is slow to dye the fiber, the heat preservation time should not be too short, and it is also conducive to the migration of the dye. After the dyeing is completed, the temperature is lowered to 70°C, and the liquid is drained and restored for cleaning.
Other precautions
1. The circulation state of the dye liquor
The dyeing process of knitted fabrics is the penetration process of the dye liquor . Therefore, the requirements for the circulation state of the dye liquor are relatively high. The dye liquor must have strong penetrating power, which is the prerequisite for uniform dyeing. If the circulation pump is not strong enough or the valve is not properly controlled, the flow rate and flow rate of the dye liquor through the dyed material will be insufficient and uneven. Obviously, this can easily produce chromatic flowers, especially during the warming phase.
Countermeasures: The circulation state of the dye liquor must be good, and the flow and pressure of the dye liquor must be large. Because the flow and pressure of the dye liquor are large, it is conducive to the penetration and leveling of the dye liquor. For this reason, circulation pumps must be carefully selected and used. The flow rate of the pump should be 25~60 L/(kg·min).
2. Cleaning inspection of the dye vat
Disperse dyes are often prone to recrystallization due to repeated heating and cooling in high-temperature vats. The crystals are stained with It is attached to the cylinder wall and filter cover, causing poor friction fastness of the dyed material, and even clogging the filter of the high-temperature and high-pressure dyeing machine.
Preventive measures:
Clean the dye vat after dyeing for a period of time, clean the wall residue, and remove and wash the filter cover.
The number of dyeing times in the dye bath needs to be balanced. If recrystallized oligomers are produced in the dye bath, more dispersant must be added.
High-temperature dispersion leveling agents
High-temperature dispersing leveling agents commonly used in disperse dyeing can be roughly divided into three categories:
1. Anionic dispersing leveling agent. This type of dispersion leveling agent usually has two shortcomings:
The “binding energy” between it and the dye grains is low, so the dispersion ability is good at low temperatures, but it will As the dyeing temperature increases and thermal movement intensifies, the originally formed dye colloidal particles are easily broken and lose their dispersion stability;
The adsorption and coloring of dyes lacks the dyeing delay function. Lack of promotion effect on interface staining.
2. Non-ionic dispersing leveling agent.
This type of dispersion leveling agent lacks the repulsive force of the same charge on the outer layer of colloidal particles formed with the dye, so its ability to disperse dyes is not as good as that of anionic dispersing leveling agents. However, because it can combine with dyes to form unstable polymers that are slowly released during the dyeing process, this type of dispersing leveling agent has both a dispersion stabilizing effect and a dye-retarding dye migration function. The disadvantage is that when the dosage is too high, the color yield will be reduced.
3. Anionic/nonionic composite dispersion leveling agent. This type of dispersing leveling agent is a compound of anionic and nonionic surfactants, which has a good synergistic effect. Since the colloidal particles formed by the two and the dye have a double electric layer, they have a stronger protective effect on the dye crystal particles and the dispersion is more stable. It also has good dye retardation and dye transfer functions, and has a relatively small impact on the dye uptake rate.
Obviously, it is better to use anionic/nonionic composite high-temperature dispersing leveling agent. </p
