Disperse bright red and maroon (dark series) when used for high temperature and high pressure dyeing. If you are not careful, there will be some Color points are generated. Since the dyeing process is a dynamic, complex and changeable process, it is affected by many factors (such as(technology, equipment, operation, water, electricity, steam, etc.), this article only makes a simple analysis. Please correct me for any shortcomings.
01
Dyeing properties of disperse dyes
dispersion The dye has three performance defects in dip dyeing:
1. It has 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, the thermal cohesion of commonly used disperse dyes is ubiquitous in . 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 dispersing 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 stability
That is, in high-temperature and high-pressure spell dyeing, once the pH value of the dye bath> 6. Significant or even serious color difference and depth difference 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 measure to deal with it is to use a pH buffer system with strong buffering capacity and wide buffering range, such as sodium acetate monoacetate. 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 a pH adjuster. 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 larger 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. Hot migration
Thermal migration means that after polyester is dyed and then subjected to high-temperature dry 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 amounts of dyes, while the dye fastness decreases, the color of the fabric surface also changes. When it comes out of the vat, the color and lightness are consistent and the fastness is acceptable, but when it comes to the finished product, the color and lightness are “off” and the fastness is low, resulting in quality problems that require rework and color correction.
Countermeasures:
1. The key measure is to use dyes with low thermal migration and high washing fastness. Choose a dye with a larger molecular weight and higher affinity for polyester, which will be difficult to migrate from the inside of the fiber to the fiber surface even under high temperature and dry heat conditions above 150°C. Therefore, it has small thermal migration, high washing fastness, and lighter color after finishing.
2. Since surfactants have varying effects on the thermal migration of disperse dyes, the use of surfactants should be consistent during the dyeing process. “If you can’t use it, don’t use it; if you can use it less, use it less. When you have to use it, you should choose the variety and the water should be clean.”
3. Silicone emulsion-type softeners contain a certain amount of non-ionic emulsifiers. The presence of nonionic emulsifiers on fibers has a serious impact on the thermal migration of disperse dyes. Therefore, white emulsified softeners without emulsifiers should be used instead of emulsion-type softeners.
02
Disperse dark colors, red Related issues
When dispersed scarlet 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 large. After the material is mixed, recrystallization of tiny particles occurs, and the recrystallized particles gather together. It will precipitate from the dye and deposit on the fabric or machine wall, causing color spots.��
2. Improper chemical materials can easily cause dye formation It is in the form of large particles with high viscosity, especially in cold water. It is difficult to dissolve the sticky dye that has formed into “mud”. If the dye solution is poured into the dye vat, it will adhere to the fabric and form stains. color point.
3. The temperature rises too fast during dyeing, especially when dyeing Excessive steam volume or excessive air pressure in the initial stage can destroy the dispersion state of the dye bath, causing flocculation or aggregation of dyes, resulting in color spots and color spots.
Take action
1. Strengthen dye quality inspection
Dye quality should be tested before the dye is 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. 0.1mL, immediately drop it on the slide that has been coated with a thin layer of glycerin, cover the slide, place it on a 1000x microscope platform, let it stand 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, while a few disperse dyes such as dispersed red BWFL and dispersed ruby H2GFL are easy to dissolve in water. agglomeration, and the use of co-solvent 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 is raised to 60°C, the dye solution is poured into Dyeing vat, after running for 5 minutes, turn on the steam and heat it up from 60°C to 100°C at a rate of 1.5-2°C/min. The dispersed red dye is only adsorbed on the fiber below 100°C and is not dyed, while at 100-120°C ℃ is the critical exhaustion zone for dye dyeing. At this time, the temperature should be raised slowly, preferably 1 ℃/min. After the temperature is raised to 130 ℃, heat preservation dyeing should be carried out for 40 to 60 minutes. Because the dispersed red dye is slow to dye the fiber, the heat preservation time is not suitable. If it is too short, it is also conducive to dye migration. After the dyeing is completed, the temperature is lowered to 70°C, and the liquid is drained and restored for cleaning.
03
Other notes
1. The circulation state of the dye liquid
The dyeing process of knitted fabrics is the penetration process of 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 solution must be good. Make sure that the flow and pressure of the dye liquor are large because the flow and pressure of the dye liquor are large, which 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 repeated in high-temperature tanks Recrystallization is prone to occur due to excessive heating and cooling. The crystals adhere to the cylinder wall and filter cover, resulting in poor friction fastness of the dyed material, and even clogging of the filter of the high-temperature and high-pressure dyeing machine.
Prevention measures:
After dyeing the dye vat for a period of time, wash the vat and clean the wall residues Remove and wash the filter cover.
Dyeing times of the dye vat A balance is required. If recrystallized oligomers are produced in the dye bath, more dispersant must be added.
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