1 Migration of disperse dyes after dyeing
Polyester dyed with disperse dyes can produce a thermal migration phenomenon during high-temperature treatment (such as setting), that is, after dyeing migration.
The phenomenon of thermal migration is that there are residual additives in the outer layer of the fiber. Under high temperature or long-term storage conditions, the additives can attract and dissolve the dye, and move the dye to fiber surface.
Residual additives mainly come from the following two aspects:
❶Antistatic agents added during spinning and weaving, etc.
❷Antistatic agents, penetrants, anti-pollution agents and softeners added during dyeing and post-processing.
The auxiliaries added during spinning, weaving and dyeing should be basically washed during the production process, and the remaining auxiliaries on the fiber during post-processing are the main ones. Thermal migration of disperse dyes can cause a series of effects, such as color change, staining other fabrics during ironing, reduced rubbing fastness, reduced fastness to washing and perspiration, reduced fastness to dry cleaning and light fastness, etc. Thermal migration is related to the processing temperature and time. Thermal migration phenomenon has no absolute relationship with the sublimation fastness of the dye.
Thermal migration phenomenon is a redistribution phenomenon of disperse dyes in two-phase solution (fiber and additives). Therefore, all additives that can dissolve disperse dyes, regardless of their ionicity and chemical structure, can produce thermal migration. If there is no second phase solution, there will be no thermal migration phenomenon; if the second phase solution is weakly soluble in the dye , the thermal migration phenomenon will also weaken accordingly.
It has been found from production practice that non-ionic surfactants, which are widely used, are the cause of thermal migration of dyes. Usually disperse dyes present in non-ionic surfactants Instability is closely related to temperature, but the different chemical structures of various dyes are also related to stability. For example, Disperse Blue 58 can be completely decomposed in nonionic surfactants at 130°C in 5 minutes, while Disperse Blue 58 can be completely decomposed in 5 minutes at 130°C. Under the same conditions, Orange 20 only decomposes 10% in 30 minutes.
Methods to prevent thermal migration of disperse dyes
❶Any additives remaining on the fibers before dyeing, whether they can be treated or not Any thermal migration of dyes should be removed;
❷Auxiliaries used in the dyeing process should be removed after dyeing;
❸Auxiliaries used in post-dyeing treatment, such as softeners, penetrants, antistatic agents, antifouling agents, etc., should be carefully selected. Only those products that will not cause thermal migration can be used;
❹ When finishing the resin, not only the sublimability of disperse dyes must be considered, but also the commonly used penetrant JFC must be washed away after finishing.
2 Causes of color spots and spots in disperse dyeing
High temperature and high pressure dyeing machine-dyed polyester knitted fabrics There are two types of color spots and stains caused by dyeing:
1. Color spots and stains caused by the agglomeration of dyes can be repaired with a repair agent or stripped and repainted. Dyeing;
2. Color spots and stains that are difficult to remove due to the production of oligomers in the fiber.
Cause of color spots and stains produced by oligomers: Oligomers, also known as oligomers, are a type of polyester fiber with the same chemical structure that exists inside the polyester fiber. Low molecular weight substances, which are by-products in the spinning process of polyester.
Generally, polyester contains 1‰~3% oligomers. Most of the oligomers are cyclic compounds formed by three ethyl terephthalates. When the temperature exceeds 120°C, oligomers can dissolve in the dye bath and crystallize out of the solution, combine with the condensed dye, and deposit on the surface of machinery or fabrics when cooled to form dye spots, color spots and other defects.
Disperse dye dyeing is generally incubated at 130°C for 30 minutes to ensure the dyeing depth and fastness. Therefore, light colors can be incubated at 120°C for 30 minutes, while dark colors must be incubated at 120°C for 30 minutes. Pre-treatment is required before dyeing. In addition, dyeing under alkaline conditions is also an effective method to solve oligomers.
3 Cause Analysis
1. Preprocessing
In many operations, insufficient attention is paid to the pre-treatment of polyester dyeing. Poor quality degreasers are used to lightly treat or dye directly without treatment at all. When dyeing quality problems occur, the operator is suspected of improper operation. In fact, polyester by-products in raw material production and oils in the weaving process can easily cause dyeing quality problems, such as color flowers, color differences, color spots, stains, etc., so pre-treatment must be carried out before dyeing, and appropriate dyeing must be selected. Heat the degreaser to 90°C and keep it warm for 10 minutes, then cool down and wash with water.
2. Selection of dyes and auxiliaries
①Dye selection Improper selection
Generally, when dyeing dark colors, the chance of thermal collision of dye particles increases under high-temperature dyeing conditions, and the dye molecules are prone to re-agglomeration, resulting in dye spots and color spots. At the same time, improper use of fillers used in dyes can also cause stains and color spots.
②Improper selection of auxiliaries
Poor quality dispersants will condense together with impurities inside the fiber and the dye vat at high temperatures. Causes color spots and stains on the surface of the fabric. Mixing different ionic additives can easily lead to conflicts and demulsification, which can lead to precipitation on the fabric, resulting in color spots and stains.
3. Fabric weight and blank� Capacity
When dyeing in the same dyeing machine, the knitted fabric with high gram weight has a tight structure and the dye cannot easily enter the inside of the fiber, and the gram weight is 300g/m2. The above knitted fabrics are more likely to produce dye spots and color spots than sparse and light knitted fabrics of about 200g/m2. When there are too many gray fabrics in the cylinder, it will cause poor operation and produce dye spots and color spots.
4. Liquor ratio
The dyeing bath ratio is small and the dye particles In high-temperature and high-pressure dyeing machines, the probability of thermal collision is relatively increased, which easily produces dye spots and color flowers.
4 Measures to prevent color spots and stains
1. Strengthen Pre-dyeing treatment
Before dyeing, the gray fabric is treated with 100% NaOH 3%, surfactant detergent 1%, at 130°C for 60 minutes, with a liquor ratio of 1: 10 to 1: 15. The pre-dyeing treatment method has a certain corrosive effect on polyester fibers, but is extremely beneficial for removing oligomers. For polyester filament fabrics, “aurora” can be reduced, and for short fibers, the pilling phenomenon can be improved.
2. Control the dyeing temperature below 120°C and use appropriate carrier dyeing methods to reduce the production of oligomers and obtain the same dyeing depth.
3. Adding dispersing protective colloid additives during dyeing can not only produce a level dyeing effect, but also prevent oligomers from settling on the fabric.
4. After dyeing, the dye liquor is quickly discharged from the machine at high temperature. The drainage time is up to 5 minutes, because the oligomers are evenly distributed in the dye liquor at a temperature of 100 to 120°C. When the temperature is below 100℃, it is easy to accumulate and precipitate on the dyed materials. The disadvantage is that some heavy fabrics are prone to wrinkles.
5. Dyeing under alkaline conditions can effectively reduce the formation of oligomers and remove residual oil on the cloth surface. But the disadvantage is that you must use dyes suitable for dyeing under alkaline conditions.
6. Clean with reducing agent after dyeing, then cold wash, hot wash, cold wash, neutralize with acetic acid, and use Telijie acidic reduction cleaning aid. Save energy consumption and have high efficiency.
7. The liquor ratio for dyeing high-gram mass knitted fabrics should be above 1:10, and an overflow dyeing machine with a larger feed pipe diameter should be selected for dyeing. If it is necessary to dye in a small liquor ratio dyeing machine due to machine constraints, appropriately reduce the fabric capacity to ensure the running speed of the fabric.
8. For some dyes that are sensitive to metal ions, such as red 3B (red 60), soft water must be used for production to prevent color spots and stains.
5 Postscript
In production, although various high-quality Auxiliaries and various dyes play a certain effective role, but people are the first and leading role. Quality awareness should be established during operation. At the same time, the workshop must strengthen production site management and stipulate correct dyeing material usage procedures. Additives and dyes must be added one by one. , it is strictly prohibited to mix dyes and additives together without dilution. The dye needs to be filtered before entering the tank. </p
