Causes and prevention methods of common problems in jet overflow dyeing

1. Key points of operation
1.1 Preparation before the gray cloth enters the machine

Check whether the machine is clean, whether the tools are fully prepared, whether all instruments, electrical appliances and machinery are complete, and whether the rubber rings are intact; check whether the gray cloth is consistent with the plan, and whether the process card matches the cylinder number; when the gray cloth enters the machine, stack it Push the gray cloth cart to the cloth inlet of the machine cylinder, and then put water into the machine to the predetermined water level; check whether the machine cylinder mouth, the cloth feeding frame and the edge of the gray cloth cart are smooth and clean, and only when the requirements are met can the cloth be fed.
1.2 Operations when gray fabric enters the machine

Tie a slip knot between the gray cloth head and the lead rope in the cylinder. Hold the gray cloth with one hand and press the main pump and lifting motor with the other hand. Hold the gray cloth with both hands to prevent it from being mopped and stained. During the cloth feeding process, scan the quality of the cloth surface with both eyes. If you find oil stains, holes, stains, etc. that were missed during the pre-inspection, record them on the process card in time; after feeding the fabric, press it flat, straight, neat, and secure, with four needles at both ends, and a needle density of 20-30 needles/ According to the requirement of 10cm, sew the head and tail of the gray fabric.

1.3 Chemical operation

Check whether the prepared dyeing materials are accurate according to the prescription sheet. When dispersing dyes are usually mixed with cold water (mixer stirs for about 20~30 minutes), dilute it with 40~45 °C warm water before use. Dissolve the dispersant and ammonium sulfate with warm water and mix well. Dissolve as needed.

For dyes that are difficult to dissolve, such as Disperse Red 3B and Yuhong S-2GFL, use alcohol or diluent solution to make a slurry, beat with cold water and stir evenly, and dilute with warm water.

When adding dyes, be sure to filter through a sieve. The small particles remaining in the sieve are dissolved with water and then filtered. 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.

1.4 Operations during 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 °C, disperse dyes dye slowly or hardly at all. Above 80 °C, the dyeing speed accelerates. Therefore, the temperature should not rise too fast between 80 and 130 °C.

Generally, graded heating and graded heat preservation are used to control the heating rate. This is especially important for red 3B, ruby S-2GFL, red S-BWGL, etc. that are prone to color stains. During the cooling stage, the cooling rate should not be too fast to avoid the formation of wrinkle marks, chicken paw marks and other defects. The heating and cooling speed is generally based on the principle that the temperature change does not exceed 1-1.5 °C for each revolution of the fabric (referring to the main heating and cooling sections).

The dyeing bath ratio depends on the equipment model and structure, and is preferably 1:8~20. The principle of controlling the nozzle spray pressure is: 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; the greater the thickness or weight of the fabric, the greater the nozzle pressure, and the larger the nozzle cross-section; Generally, the ratio of the cross-section diameter of the rope-like fabric to the cross-section diameter of the nozzle is 9:10. When cooling down, it is strictly prohibited to inject cold water into the machine to directly force the cooling when the temperature is high.

1.5 Color matching operation

After the fabric is dyed, the temperature should be cooled to 85°C (exhaust the steam, and the cover can be lifted only after the steam is exhausted. At 70-80°C, turn off the lifting motor, touch the head with a hook, and cut the sample within 10cm of the seam head. The size of the cut sample is 6cm, about 4cm wide. Wrap the sample cloth with a cloth on the steam pipe and iron it to dry.

Blow steam to make it regain moisture, and check the colors under the color matching light box. If you need to add color correction, you should immediately add materials and raise the temperature to 100°C (re-dyeing; if the color and light match, you can continue to cool down. After dyeing, light colors should only be washed with hot water, medium and dark colors, especially dark colors, must be restored and cleaned. In order to improve the dyeing brightness and fastness of fabrics. The reducing cleaning agent used should be melted and poured in from the feeding bucket, and should not be added directly through the operation window.
1.6 Clean the vat after dyeing

When the dyeing machine dyes dark colors and changes to light colors, brushing is required. Brushing generally uses 4-6kg of 98% caustic soda, 1-2kg of detergent, 2000L of liquid volume, temperature of 130°C, and time of 60-90°C. When scrubbing, open all valves in each pipeline to allow the fluid in the brush tank to flow smoothly. After the heat preservation is completed, drain the sewage at high temperature. When producing medium-long fiber fabrics, the filter screen is brushed once per shift; when producing polyester filament fabrics, the filter screen is brushed once a day; when producing whitening varieties such as polyester, light-colored cylinders are used and brushed.

If the original dyeing machine is a red type, it should be dyed from the red group to the blue group, gradually becoming lighter, and then whitening. Otherwise, the whitened fabric produced will have poor whiteness and a red light. Even if it is continuously dyed before producing the whitened variety, Brushing 2-3 times also has no effect. For seriously contaminated cylinders, depending on the contamination condition, use a cleaning agent composed of highly permeable polymer detergent, hydrogen peroxide, ammonium bifluoride, oxalic acid and organic acid corrosion inhibitors for cleaning.

2 Common problems and prevention methods

2.1 Bubble

In high-temperature and high-pressure jet overflow dyeing machines, foam is produced due to high-energy turbulence caused by high-speed operation and liquid circulation. Factors that influence foam formation include the type and amount of dye and standardization agent, the amount of fiber treatment agent on the fabric and the foaming properties of the dyeing auxiliaries used.

Prevention methods:

Pre-scouring with low-foaming additives or solvent methods can eliminate foam caused by contamination on the fiber. When selecting dyes, you should consider their foaming properties and choose low-foaming dyes and additives as much as possible. It is best to avoid the use of defoamer as it can stain fabrics and the amount required can be reduced if other additives are kept to a minimum. Of course, foaming is a common problem, so defoamers sometimes have to be added.

2.2 Wrinkles (wrinkles)

Polyester fabrics will wrinkle when dyed in high-temperature and high-pressure jet overflow dyeing machines. Wrinkles often take the shape of chicken feet, which is caused by fabrics being folded and stacked 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:

The machine should not be overloaded and the entire stacking chamber should be fully utilized as long as it does not cause tangle problems. In the stacking room, the turning speed and movement rate of the fabric should be quite high (the maximum acceptable turning time is generally 2-3 minutes). Do not heat or cool too quickly, the latter being more important. When dyeing, the fabric is first relaxed, refined and pre-shaped. When dyeing is completed, do not introduce cold water into the machine for cooling at the beginning, otherwise the fabric will be subject to considerable thermal shock. Do not put hot and humid fabrics out of the machine into boxes. The fabrics should be out of the machine at room temperature. Do not centrifuge the fabric to remove water (unless there is special need), you can use vacuum dehydration. Reduce the maximum dyeing temperature and use smoothing agents in the dyebath or pre-treatment.
2.3 Uneven color

The reasons for uneven color are that the temperature rises too fast, the holding time is too short, the circulation speed of the cloth is too slow, the dye adsorption is uneven, and the cloth capacity far exceeds the standard capacity.

Prevention methods:

Reasonably determine the heating time and holding time, readjust the nozzle pressure, and select the nozzle gap and conical tube to increase the cloth speed. Reasonably select dyeing materials. If disperse dyes with large differences in dyeing rates are used in color matching, the dispersant or dye should be appropriately added, and the cloth capacity should be moderate.
2.4 Oligomers

Oligomers are low molecular weight condensation polymers generated during polymerization. In polyester fiber products, most of the oligomers are derived from 3 ethyl pairs.

Cyclic compounds formed from phthalic acid esters. Oligomers dissolve in the dyebath at high temperatures and crystallize out of solution, then deposit onto machinery or fabric surfaces upon cooling, especially in low flow areas. Oligomer deposits on machinery, such as heat exchangers, can restrict the flow and cause it to lose heat exchange efficiency. Oligomers deposit on the fiber surface and appear as white spots.

Elimination of oligomers: The problem of oligomers can be overcome by scouring the fabric with solvent before dyeing. Oligomer control agents can also be added during dyeing to increase the solubility of the oligomers in the dye bath or to produce a stable oligomer dispersion. The cleaning action produced by using additives in post-processing can also help remove deposited grease and dyes.
2.5 Condensation of disperse dyes

The agglomeration of dye will cause color spots on the fabric, reduce the absorption of dye or extend the dyeing time, and reduce the rubbing fastness. The origin of agglomeration

Because there are too many electrolytes in the dye bath, the incompatibility of the additives causes the precipitation of both the additive and the dye. Non-ionic additives promote precipitation and agglomeration or prevent dyeing at high temperatures. The dyeing time is too long, the dyeing rate is too fast, the processing quality of the dye is poor, the concentration of the dye is too high, the dye bath is contaminated, etc.

Methods to prevent agglomeration:

Minimize electrolytes in the dye bath and choose additives with good compatibility. Shorten the dyeing time and do not dye up too fast. Carry out detection and analysis of dyes after entering the factory, and increase the amount of dispersant. The fabrics should be fully washed before dyeing, and the cleaning and maintenance of the equipment should be strengthened.
2.6 Tangle

Knotting of fabric bundles can cause downtime, especially on full-fill machines. Light fabrics tend to float, which is the most troublesome. There are some full-fill machines equipped with back-spray and control valves that control the stacking of fabrics in the stacking area. However, problems still arise because it is impossible to see how the fabric is stacked. Reducing tangles only relies on the experience and responsibility of the operator.
2.7 Dye spots and color spots

Dye spots and color spots are caused by dye agglomeration, oligomers in the dye bath.

Prevention methods: See methods to prevent agglomeration and elimination of oligomers.

2.8 Lining and abrasions

The causes of fluffing and scratches are that the diameter of the nozzle is too small, the cloth speed is out of proportion with the rotation speed of the cloth guide wheel, the gray cloth or semi-finished products are hit when transporting, and the cloth is scratched when opening the width.

Prevention methods:

Select a nozzle of appropriate diameter according to the unit weight of the dyed material to ensure a moderate spray pressure. The cloth speed should be commensurate with the rotation speed of the cloth guide wheel. When handling gray cloth or semi-finished products, handle it with care and use manual opening.

2.9 elongation

The reason for the elongation is that the fabric capacity is too low, which increases the transportation distance and increases the tension. The liquid level of the dye liquor is set too high, thereby increasing the resistance between the water and the fabric.

Prevention methods:

Control the moderate cloth volume and keep the liquid level as low as possible.
3. Repair measures for common defects

3.1 Severe uneven dyeing

When encountering serious uneven dyeing, you cannot use the migration property of the dye to correct it back and forth. You must decolorize before dyeing. If it is a light or medium color, it can be dyed into a dark or extremely dark color. Decolorization methods include oxidative decolorization and reduction decolorization, examples are as follows

(1) Examples of oxidative decolorization prescriptions:

Sodium chlorite 2~5g/L, acetic acid (98%) 2~3g/L, methylnaphthalene or chlorobenzene 3~5g/L, start treatment at 30°C, heat up to 93°C for 30min, boil for 60min and wash with water . If necessary, use bleaching powder and acetic acid to bleach at boiling temperature.

(2) Example of reduction depigmentation prescription:

Caustic soda (flakes) (1g/L,

Insulin powder 5g/L, chlorobenzene 5g/L, non-ionic active agent 2g/L, start processing at 30°C, heat to boiling at 30°C, heat preservation treatment for 60min, followed by cold water washing and hot water washing. If the decolorization is insufficient, process it again, or use oxidative decolorization again. Using the above methods may damage the feel of the fabric, so try to avoid it.

3.2 Wrinkles and mild uneven dyeing

The wrinkle treatment method is to put the fabric back into the jet dyeing machine, heat it to a slightly higher temperature than the original dyeing temperature, and then slowly cool it down. For fabrics that are slightly unevenly dyed, the migration property of the dye is generally used for counterdying. The process is to 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 X% disperse dye (confirmed after testing), leveling agent 1-2g/L, and use pH adjuster to adjust the pH value to 5~6. If dyes with poor migration properties are used, the dyeing temperature should be increased to 135~140°C, but this must be done on the premise that the mechanical properties are acceptable and the feel of the fabric is not affected.

3.3 Dyeing oil spots

To remove local oil spots or dead oil spots in small batches, organic solvents such as non-ionic detergent, carbon tetrachloride, and gasoline are usually used, sprayed with a spray gun and manually scrubbed, and then the fabric is washed.

To remove large-area oil spots, use 2-3g/L each of degreasing agent and non-ionic detergent, and treat it at 100°C for 20 minutes, or use 2-3g/L each of degreasing agent and non-ionic detergent and high-temperature dispersant 1-2g/L, treated at 130°C for 20min. For oil spots that are difficult to remove, consider dyeing them into colors with better coverage such as deep sapphire blue or black. Consider stripping and re-dying if necessary.

4. Energy saving methods
(1) Reduce heat dissipation loss, such as using composite silicate insulation materials to cover the dyeing machine and insulate it.

(2) Reuse the steam condensate. For example, connect the water outlet of the steam trap to the return water pipe and lead it back to the lower water tank of the boiler for reuse. Steam releases heat and condenses. Before being discharged from the steam trap, the temperature of the condensate water is equal to the steam temperature. If the return water pipe is properly insulated, the condensate water flowing back to the boiler's low water tank can reach more than %/0. Condensate water is clean distilled water, which does not require water treatment when reused in the boiler, eliminating water treatment costs, increasing the boiler inlet water temperature and reducing fuel consumption.