Nylon (polyamide fiber) has many excellent properties, such as high strength, good resilience and wear resistance, and light specific gravity. Knitted clothing made of nylon stretch yarn has the characteristics of good wear resistance, comfortable wearing, soft hand feel, good elastic recovery of fabric and elegant appearance, and is favored by consumers.
Dyeing process
Dye selection: Nylon is a hydrophobic fiber, but its macromolecules contain a large number of weakly hydrophilic groups (- CONH -), and there are – NH2 and – COOH hydrophilic groups at both ends of the molecule, so it can be dyed with a variety of dyes. Such as disperse dyes, neutral dyes, weak acid dyes, reactive dyes and direct dyes, etc., can all be used as dyes for nylon dyeing. After large and small sample tests, it was found that the ability of various dyes to cover warp and rung defects of nylon fabrics are: disperse dyes > acid dyes > reactive dyes > neutral dyes > direct dyes.
Although there are a variety of dyes that can be used to dye nylon products, each has its own pros and cons. At present, nylon dyeing is usually based on weak acid dyes. However, weak acid dyes are difficult to obtain level dyeing due to their fast coloring and poor dye transfer properties. They also require high operation requirements. If they are not used properly, they will cause color flowers and stains. Wait for dyeing defects. Nylon dyed with disperse dyes has the characteristics of good level dyeing, stable dyeing quality, good reproducibility and fewer dyeing defects. At the same time, disperse dyes can also be dyed in the same bath with weak acid dyes or neutral dyes to adjust the color light and improve level dyeing. In addition, most disperse dyes are easy to operate when dyeing light colors, have little fiber damage, have good compatibility between dyes, produce deep colors and have good color fastness. Its disadvantages are dark color and poor covering ability, so it is not suitable for dyeing light and colorful varieties.
The isoelectric point of nylon is 5 to 6. When the pH value is lower than this, it is conducive to dyeing. Generally, the lower the pH value, the faster the dyeing speed, but the levelness and defect covering ability will decrease. For this reason, the pH value of the dye solution must be controlled. If the pH value of the dye bath of acidic and neutral dyes is controlled below 5 to 6, the dye uptake rate and color fastness can be improved, and the color difference of warp and rungs can be reduced. Disperse dyes can be dyed in either neutral bath or acidic bath, but the dyeing effect is better when the pH value is 5 to 6. Reactive dyes are dyed in a neutral bath, and the dye uptake rate is extremely poor. However, under the condition of a pH value of 3 to 5, the dye uptake rate is increased and the color fastness is good.
After dye selection and analysis, our factory adopts two dyeing schemes for nylon dyeing, namely: light and medium colors are mainly dyed with disperse dyes; medium and dark colors are mainly dyed with neutral dyes, supplemented by weak acidic, reactive and other dyes. Make up for the incomplete chromatography to obtain a more satisfactory dyeing effect.
Dyeing process: Due to the high degree of orientation of nylon, the glass transition temperature is 40~60℃. If the dyeing temperature is too low, the dye migration property will be poor; and if the initial dyeing temperature is too high, it will be difficult for the dye to penetrate and level dye, which will inevitably cause color flowers and lead to warps and rungs. Most of the nylon fabrics produced by our factory are stretch knitted fabrics, and the dyeing is carried out on a high-temperature and high-pressure overflow dyeing machine. Stretch nylon knitted fabrics should be placed in a relaxed state for more than 6 hours before dyeing to restore the fiber curl and avoid uneven dyeing due to uneven tension during dyeing. After the fabric is put into the cylinder, the machine is run for a while, and auxiliary dyes are slowly added according to the prescribed process. If excessive foam is found in the machine during the feeding process, in order to avoid damaging the circulation pump and causing the fabric to float and clog, it is advisable to add defoaming agent in time. After the feeding is completed, let the fabric continue to run in the machine for a while, and then dye according to the prescribed temperature rise curve. An appropriate amount of glacial acetic acid can be added during dyeing to control the pH value of the dye solution within the process range to facilitate level dyeing and improve the dyeing rate, and reduce dyeing defects such as warp willows and rungs. The cooling rate should not be too fast to avoid the formation of wrinkle marks and chicken paw marks. Generally, the temperature change of the fabric does not exceed 1 to 1.5°C for each revolution, and the dye liquor liquor ratio is controlled at 18 to 112°C. Principle of adjusting the speed of the dyeing machine: the speed can be higher when the fabric is loaded on the machine, and the speed can be adjusted lower during normal operation (normally 180 ~ 190 r/min). The capacity of the fabric loading machine is 50% to 70% of the conventional dyeing capacity of the dyeing machine. It is strictly forbidden to discharge high-temperature sewage and exhaust when cooling down, and it is strictly forbidden to add cold water into the machine to force cooling under high-temperature conditions.
Examples of craftsmanship
1. Dyeing of medium and light color nylon knitted fabrics
For the dyeing of medium and light-colored stretch nylon knitted fabrics, disperse dyes are mainly used. Considering the various properties of the dye and the testing indicators of the dyed goods, dispersed blue 2BL N, yellow SE 2 3R, and red FB with good compatibility were finally selected as the basic three primary colors.
Production process examples
Stretch nylon knitted fabric 400 kg, 16 2 0613 TP bean green
Dye solution prescription (%,owf)
Disperse blue 2BL N (run soil) 0. 9
Disperse Yellow SE 2 3R (Open Source) 0. 12
Disperse red FB (Jihua) 0. 053
HAc(mL/ L) 0. 9
Treasures in the Bath 2～4
Leveling agent O 1 ~ 2
2. Dyeing of medium and dark nylon fabrics
Neutral dyes are mainly used for dyeing medium-dark stretch knitted fabrics. Neutral dyes have a complete chromatogram and can be selected according to different colors.
Dye solution prescription (%,owf)
Neutral dye x
Ammonium sulfate 1 ~ 2
Trisodium phosphate 0. 3 ~ 0. 5
Yuanming powder 20～40
Leveling agent O 0. 3 ~ 0. 4
pH value 5～6
When dyeing nylon with neutral dyes, the dye is more sensitive to water hardness and can easily cause color lakes, so soft water must be used and the water hardness should be less than 150ppm. When dissolving the dye, warm water at 40 to 50 ℃ should be used to make a thin slurry, and then diluted with hot or boiling water until the dye is fully dissolved. The dye should be filtered with a screen when entering the tank. Since the neutral dye solution is in colloidal form, precipitation will occur if left for too long, so it should be prepared as needed.
Dyeing defect analysis and solutions
When using a high-temperature and high-pressure overflow dyeing machine to dye nylon, dyeing defects such as wrinkles, slight uneven dyeing, and chicken paw prints may occur due to factors such as entanglement, blockage, overloading, or excessive spraying. For dyeing defects formed, the following methods can be used to solve them:
(1) How to repair wrinkles: Put the fabric back into the dye vat, raise the temperature to a slightly higher temperature than the original dyeing temperature, and then cool down slowly.
(2) Repair method for mild uneven dyeing: Generally, the migration property of dye is used for counter-dying. The process conditions are: start dyeing at room temperature, raise the temperature to 100~110°C at 1~1.5°C/min, keep it warm for 60min, and cool down.��.
Return prescription
Dyes (%) x
Leveling agent O (g/ L) 1 ~ 2
For dyes with poor dye migration properties, the dyeing temperature for repair can be appropriately increased and the holding time can be extended to improve the level dyeing properties of the fabric.
(3) For the repair of chicken paw prints, the process conditions are the same as (2).
Return prescription
Dyes (%) x
Leveling agent O (g/ L) 2 ~ 4
Repair agent L(%) 1～3
Bath treasure (g/ L) 2 ~ 4
pH value 5～6
Finishing
Nylon fabrics feel rough after dyeing, especially after color fixation, so they need to be softened. Light-colored fabrics can be softened and finished after dyeing, while dark-colored fabrics should be fixed first and then softened.
Fixation treatment
For dark-colored varieties, in order to further improve the washing fastness of the dyed finished product, the fabric should be fixed after dyeing.
Color fixing formula
Fixing agent AD 2 1(%) (Germany and the United States) 2 ~ 6
pH value (adjusted with glacial acetic acid) 5 ~ 6
Temperature (℃) 60～70
Time(min) 40
Preparation of fixing working solution: first dilute the fixing agent and then mix it with acetic acid. The fixing agent should not be in direct contact with concentrated acetic acid to avoid precipitation. If precipitation occurs, add a small amount of ammonia to dissolve it, and then adjust the pH value with dilute acetic acid. The fabric must be thoroughly washed before color fixation.
Soft finishing
In order to give the fabric a good feel, the dyed fabric is subjected to hydrophilic soft finishing.
Organize prescriptions
Hydrophilic softening agent (%) 2
Temperature (℃) 40
Time(min) 100
Setting temperature
Nylon’s heat resistance is not as good as polyester and it is easy to deform, but it has high resilience. Rising temperature will cause nylon to shrink. When it is close to the melting point, the shrinkage is serious and the fiber becomes yellow and brittle. Therefore, the setting temperature is generally controlled at 170 ~ 180 ℃, the machine speed is 40r/min, and overfeeding is appropriate.
Product quality inspection
After strict operation and management, the elastic knitted fabric produced has a soft color, smooth and smooth surface, smooth hand feeling, few dyeing defects, and the warp and rungs on the fabric are significantly reduced or eliminated. The dry and wet rubbing fastness of dyed fabrics is: medium light color dry rubbing fastness level 3 to 4, wet rubbing fastness level 3 to 4; medium dark color dry rubbing fastness level 3 to 4, wet rubbing fastness level 2 to 3 class. The above indicators all meet customer requirements.
Conclusion
Stretch nylon knitted fabric is a high value-added fabric. As long as the operating procedures are strict and the process requirements are paid attention to, common dyeing defects such as wrinkles, uneven dyeing and chicken paw prints during production can be avoided, and products that satisfy customers can be produced.
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