Migration after dyeing of disperse dyes
Polyester dyed with disperse dyes can produce a thermal migration phenomenon during high-temperature treatment (such as setting), that is, migration after dyeing.
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 the fiber surface.
Residual additives mainly come from the following two aspects:
(1) Antistatic agents added during spinning and weaving.
(2) Antistatic agents, penetrants, anti-pollution agents and softeners added during dyeing and post-processing. The additives added during spinning, weaving and dyeing should be basically washed during the production process, and the remaining additives 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, and reduced fastness to washing and perspiration. , dry cleaning and light fastness decrease, 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
(1) On the fiber before dyeing Residual additives, regardless of whether they can cause thermal migration of dyes, should be removed;
(2) Additives used in the dyeing process should be removed after dyeing;
(3) The additives 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;
(4) 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.
Check whether there is thermal migration in the dyed fabric. You can use dimethylformamide (DMF) as a solvent and put the fabric into the fabric for 3 minutes. Any dye that migrates to the fiber surface should be able to peel off on the dimethylformamide. In the amide, the dye in the fiber does not peel off; the colorimetric method can also be used to measure the migration amount, still using dimethylformamide as the solvent, and after treatment for 5-10 minutes in the boiling state, the dye stained on the fiber It will all peel off.
Causes of dispersed dyeing color spots and stains
High temperature and high pressure There are two types of color spots and spots produced when machine dyeing polyester knitted fabrics: 1. Color spots and spots caused by the agglomeration of dyes, which can be repaired with a repair agent or stripped and re-dyed; 2. Color spots and spots caused by dyeing in the fibers. Oligomers cause color spots and stains that are difficult to remove.
Causes of color spots and spots produced by oligomers
Oligomer, also known as oligomer, is a low molecular substance with the same chemical structure as polyester fiber that exists inside polyester fiber. It is a by-product in the spinning process of polyester fiber.
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.
Cause analysis
1. Preprocessing
When there are many operations , The pre-treatment of polyester dyeing is not paid enough attention, and inferior degreasing agents are used for slight treatment or direct dyeing 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
a. Improper selection of dyes
Generally, when dyeing dark colors, the chances of thermal collision of dye particles increase 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, a large number of fillers are used in dyes.Improper use will also cause stains and color spots.
b. Improper selection of auxiliaries
Poor-quality dispersants condense together with impurities inside the fiber and the dye vat at high temperatures to cause 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 gray fabric capacity
When dyeing in the same dyeing machine, high-gram weight knitted fabrics have a tight structure and the dye It is not easy to enter the inside of the fiber, and the gram mass 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 probability of thermal collision of dye particles in the high-temperature and high-pressure dyeing machine is relatively increased. It is easy to produce dye spots and colored flowers.
Measures to prevent color spots and stains
1. Strengthen dyeing Pre-treatment
Before dyeing, the gray fabric is treated with 100% NaOH 3% and surface active 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 achieve 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, the temperature is 100°C. It is easy to accumulate and precipitate on dyeing 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. After dyeing, wash with reducing agent, use 32.5% (38°Be) Na0H 3-5 mL/L, insurance powder 3-4g/L, treat at 70°C for 30 minutes, then cold wash, Hot washing and cold washing use acetic acid to neutralize, and the other uses acidic reducing cleaning aids to save energy and have high efficiency.
7. The liquor ratio for dyeing high-gram quality knitted fabrics is 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.
Summary
In production, although various high-quality additives and various dyes play a certain effective role, people are The first leading role is to establish quality awareness in operations. At the same time, the workshop must strengthen production site management and stipulate correct procedures for the use of dyes. Additives and dyes must be added one by one. It is strictly forbidden to mix dyes and additives without dilution. Together, the dye needs to undergo necessary filtration before entering the tank. </p
