Key points of dyeing operation of overflow jet dyeing machine
1. Key points of chemical operation should be based on the prescription list to check whether the prepared dye is accurate. When using disperse dye, Generally, beat it with cold water first (stir with a mixer for about 20-30 minutes), and then dilute it with 40-45℃ warm water before use.
Dispersing agent and leveling agent should be dissolved with warm water and stirred evenly. They should be dissolved as needed. When encountering difficult-to-treat dyes such as Disperse Red 3B and Disperse Ruby S-2GFL, beat with cold water and mix well, then dilute with warm water.
The feeding sequence is to add acetic acid at about 40°C, run for a while, adjust the pH value to 5-6, then add dye, run for 10 minutes, and dye according to the predetermined temperature rise curve. If too much foam is found in the machine after feeding, defoaming agent should be added in time to avoid damaging the circulation pump, reducing the lift, or even causing the fabric to float.
2. Key points in the dyeing process
When dyeing, close the machine cover before heating up , and observe the operation of the gray fabric in the machine through the glass viewing hole at any time, and check whether there are any abnormal sounds and phenomena in various parts of the machine.
At 50~60℃, disperse dyes dye very slowly or basically not at all. When above 80℃, the dyeing speed accelerates. Therefore, the temperature should not be raised too fast between 80~130℃. .
Graded heating and graded heat preservation are generally used to control the heating rate. This should be noted for dispersed red 3B, dispersed ruby S-2GFL, dispersed red, etc. that are prone to color stains.
When cooling down, the cooling rate should not be too fast to avoid defects such as wrinkle marks and chicken paw prints. Therefore, the cooling rate must be strictly controlled. Generally, the heating rate is based on the principle that the temperature of the fabric does not change more than 1 to 1.5°C per revolution (referring to the main stages of heating and cooling).
Principles for controlling the nozzle spray pressure:
1. When the fabric is put on the machine, the nozzle pressure can be larger, and when the operation is normal, the nozzle pressure can be smaller
2. The greater the thickness or weight of the fabric, the greater the nozzle pressure and the larger the nozzle diameter;
3. Generally, the ratio of rope fabric diameter to nozzle diameter is 9:10.
4. When cooling down, it is strictly prohibited to inject cold water into the machine to directly force the cooling when the temperature is high.
3. Key points for washing the vat after dyeing
When changing from dark to light color, The tank cleaning agent generally uses 4 to 6 kg of 98% caustic soda and insurance powder. Process conditions: liquid volume 2000L, temperature 130℃, time 60~90min. When washing the tank, open all valves in each pipe to allow the tank washing liquid to flow smoothly, and drain the sewage at high temperature after the heat preservation is completed. Pay attention to cleaning the filter frequently. When producing whitened varieties such as polyester, use light-colored cylinders, and pay special attention to replacing the filter.
After dyeing red products, the dyeing vat should be changed to dye blue products first, and then the vat should be washed before dyeing white varieties. Otherwise, the whitened fabric produced will not only have poor whiteness, but also have a red light. Even if the cylinder is brushed two or three times before producing the whitened variety, it will be ineffective. For seriously polluted dye vats, depending on the contamination situation, use a cleaning agent composed of highly permeable polymer detergent, hydrogen peroxide, ammonium bifluoride, oxalic acid and organic acid corrosion inhibitors for cleaning.
Common problems and prevention of disperse dyeing
1. Foam
Foam is the most common problem in high temperature and high pressure jet overflow dyeing. In high-temperature and high-pressure jet overflow dyeing machines, the occurrence of foam is the result of high-energy turbulence caused by the high-speed operation of the fabric and liquid circulation.
The main factor affecting foam formation is the performance and quantity of dyes and additives. Pre-refining with low-foaming additives or solvent methods can eliminate foam caused by possible contamination on the fiber; when selecting dyes, its foaming performance should be considered, and low-foaming dyes should be selected as much as possible. It’s best to avoid using defoaming agents as they can stain fabrics.
2. Wrinkles (wrinkles)
The wrinkles that appear when polyester fabrics are dyed on high-temperature and high-pressure jet overflow dyeing machines are often in the shape of chicken feet. This is due to the fabric being stacked in a folded shape in the stacking area for too long. Permanent wrinkles are most likely to occur if the fabric is folded and the fibers are cooled past the secondary glass transition temperature.
Prevention methods
Do not overload the machine, mainly to avoid tangle problems. The entire stacking area must be fully utilized; within the stacking area The turning speed and moving speed of the fabric should be quite high (the maximum recognized turning time is generally 2 to 3 minutes); the heating and cooling rates should not be too fast, the latter of the two factors is more important; when dyeing, the fabric should be relaxed and refined first , and then pre-shape the fabric. At the end of the dyeing cycle, do not cool it by introducing cold water at the beginning. Such treatment will cause the fabric to suffer a considerable impact; the fabric should be shipped out of the machine at room temperature; unless there are special needs, do not For centrifugal dehydration of fabrics, vacuum dehydration can be used; reduce the maximum dyeing temperature; use smoothing agents in the dye bath or pre-treatment.
3. Uneven color
Causes and prevention methods: The heating time is too fast, the heating time should be reasonably determined; the holding time If it is too short, the holding time should be determined reasonably; if the circulation speed of the cloth is too slow, the nozzle pressure should be readjusted, and the nozzle gap and conical tube should be re-selected to increase the cloth speed; if the dye adsorption is uneven, dyeing materials should be selected reasonably when color matching. If disperse dyes with large differences in dyeing rates are used, the amount of dispersant or dye should be appropriately increased; the cloth capacity far exceeds the standard capacity, and the cloth capacity should be moderate.
4. Oligomers
①The production and harm of oligomers: Oligomers are low-polymers produced during polymerization. Molecular weight condensation polymer,In polyester products, most of the oligomers are cyclic compounds formed by three ethyl terephthalates; oligomers can dissolve in the dye bath at high temperatures and crystallize out of the solution, and deposit when cooled to machinery or fabric surfaces, especially in low flow areas. The deposition of oligomers on the exchanger can restrict the liquid flow and reduce the heat exchange efficiency. Oligomers are deposited on the fiber surface, forming white spots or hoarfrost.
② Elimination of oligomers: Refining the fabric with solvent before dyeing can greatly reduce the production of oligomers. Oligomer control agents can also be added during dyeing, which can increase the solubility of oligomers in the dye bath or produce a stable oligomer dispersion. Using certain additives for cleaning in post-processing can also help remove deposited grease and dye.
5. Condensation of disperse dyes
The condensation of dyes can produce color spots on the fabric, reduce the dye uptake rate, and reduce the rubbing fastness. get worse.
Causes and prevention methods:
There are too many electrolytes in the dye bath, so the amount of electrolytes in the dye bath should be reduced as much as possible; Improper selection of additives can cause precipitation of both additives and dyes. Non-ionic additives can promote the precipitation and aggregation of dyes or prevent dyeing at high temperatures. Additives with good compatibility should be selected; if the dyeing time is too long, The dyeing time should be shortened; the dyeing rate is too fast, and the dyeing rate should be controlled not to be too fast; the processing quality of the dye is too poor, and the detection and analysis of the dye entering the factory should be done; the concentration of the dye is too high (the dye is easy to agglomerate at high concentrations) , but in high-concentration commercial dyes, the amount of dispersant can be increased to overcome agglomeration), the amount of dispersant should be increased; if the dye bath is contaminated, the fabric should be fully washed before dyeing, and the cleaning and maintenance of the equipment should be strengthened.
6. Tangles
Knotting of cloth bundles can cause downtime, especially when using full-fill equipment and dyeing light and thin fabrics. This kind of trouble maximum. Some full-fill machines are equipped with back-jet and control valves to control fabric stacking, but since it is impossible to see how the fabric is stacked, tangling is still possible. Reducing tangles can only rely on the experience and responsibility of the operator.
7. Dye spots and color spots
Cause: dye agglomeration; oligomers produced in the dye bath. Prevention methods: See the relevant content on dye agglomeration and oligomer prevention.
8. Pilling and scratches
Causes and prevention methods: The diameter of the nozzle is too small, so that the nozzle pressure is too large. Re-select a nozzle with a suitable diameter so that the spray pressure is moderate and should not be too high; the cloth speed and the rotation speed of the cloth guide wheel are out of proportion and the two should be proportional; scratches due to impact when transporting gray cloth or semi-finished products should be avoided when transporting gray cloth or semi-finished products. The product should be handled with care to prevent impact and scratches; if it is scratched when opening, it should be opened manually.
9. Causes of elongation and prevention methods: The cloth capacity is too low, which will lengthen the transportation distance of the cloth and increase the tension. The cloth capacity should be controlled appropriately; The liquid level of the dye liquor is set too high, thus increasing the resistance between the water and the cloth. The liquid level should be kept as low as possible.
Repair techniques for common dyeing defects
1. Dyeing Severe unevenness
In this case, the migration property of the dye cannot be used to repair it back and forth, and the color must be stripped before dyeing. If it is a light or medium color, it can be dyed into a dark color.
The peeling methods are:
① Oxidation peeling. Prescription example: sodium chlorite 2~5g/L, acetic acid (98%) 2~3g/L, methylnaphthalene or chlorobenzene 3~5g/L. The process is: start treatment at 30°C, raise the temperature to 98°C in 30 minutes, boil for 60 minutes, and wash with water. If necessary, use bleaching powder and acetic acid to bleach at boiling temperature.
② Restore color stripping. Process: Start treatment at 30°C, raise the temperature to boiling for 30 minutes, boil for 60 minutes, then wash with cold water and hot water. If the stripping is not sufficient, process it again, or use the oxidation stripping method again. Using the above methods may damage the feel of the fabric, so try to avoid it.
2. Wrinkles and mild uneven dyeing. Wrinkle treatment method: Put the fabric back into the jet dyeing machine and raise the temperature. The temperature should be higher than the original The dyeing temperature is slightly higher by a few degrees and then slowly cooled. For lightly dyed uneven fabrics, the migration property of the dye is generally used for counterdying. The process flow is as follows: start dyeing at 60°C, raise the temperature to 90°C in 15 minutes, then raise the temperature to 130°C in 40 minutes, keep it warm for 60 minutes, and then cool.
The repair formula is: disperse dye (determined after testing), leveling agent 1~2g/L, pH value adjusted to 5~6; when using dyes with poor dye migration, the dyeing should be The temperature is increased to 135~140℃, but it must be based on the mechanical properties and not affecting the feel of the fabric. The dispersion leveling agent includes a carrier (or repair agent).
3. Dyeing oil spots:
①Removal of local oil spots or dead oil spots in small batches. Usually non-ionic detergent, carbon tetrachloride, gasoline and other organic solvents are used, sprayed with a spray gun, washed manually, and then the fabric is washed.
②Removal of large-area oil spots. Use 2~3g/L of degreaser and non-ionic detergent each, and treat it at 100°C for 20 minutes, or use 2~3g/L of degreaser and non-ionic detergent, and 1~2g/L of high-temperature dispersant at 130°C. Process for 20 minutes.
③ Oil spots that are difficult to remove. If the oil spots are serious and difficult to remove, you can consider dyeing them into dark sapphire blue, black and other colors with better coverage.
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