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 elastic 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 molecules, 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 be used as dyes for nylon dyeing.
Through large and small sample tests, it was found that the covering abilities of various dyes on warp and rail 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 shade and improve level dyeing. In addition, most disperse dyes are easy to operate when dyeing light colors, have little fiber damage, good compatibility between dyes, deep color and 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 liquor must be controlled. If the dye bath pH value 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 neutral baths or acidic baths, but the dyeing effect is better when the pH value is 5 to 6. When reactive dyes are dyed in a neutral bath, the dye uptake rate is extremely poor, but under the condition of a pH value of 3 to 5, the dye uptake rate is improved and the color fastness is good.
The dyeing of nylon usually adopts two dyeing schemes, namely: light and medium colors are mainly dyed with disperse dyes; medium and dark colors are mainly dyed with neutral dyes, supplemented by weak acid, Reactive and other dyes can be used to make up for the incomplete chromatography, thereby obtaining 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 will be poor; 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, resulting in warp and horizontal stains. files.
Generally, nylon fabrics are mostly stretch knitted fabrics, and dyeing is carried out on high-temperature and high-pressure overflow dyeing machines. 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 the auxiliary dyeing materials are slowly added according to the prescribed process. If too much 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 become clogged, 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 before dyeing 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 leveling 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 appropriately controlled. The 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 180~190r/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.
Process Example
1. Dyeing of medium-light color nylon knitted fabric to medium-light elasticity The dyeing of nylon knitted fabrics mainly uses disperse dyes. Considering the various properties of the dye and the testing indicators of the dyed goods, we finally selected dispersed blue 2BLN, yellow SE23R, and red FB as the basic three primary colors with good compatibility.
Example of production process: stretch nylon knitted fabric 400kg,
Bean green dye solution prescription (%, owf)
Disperse Blue 2BLN 0.9
Disperse Yellow SE23R0.12
Disperse Red FB0.053
HAc(mL/L)0.9
Yuzhongbao 2～4
Leveling agents 1~2
2. Dyeing of medium-dark nylon fabrics Neutral dyes are mainly used for the dyeing of medium-dark stretch knitted fabrics. Neutral dyes have a relatively 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 0.3～0.4
pH value 5～6
When dyeing nylon with neutral dyes , dyes are sensitive to water hardness and can easily cause color lakes, so soft water is required and the water hardness should be less than 150ppm. When the dye is dissolved, warm water at 40-50℃ should be used to make a thin slurry, and then usedDilute the dye with hot or boiling water until the dye is fully dissolved. Use a screen to filter the dye into 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 high-temperature and high-pressure overflow dyeing machines to dye nylon, due to tangles, blockages, Factors such as overloading or excessive spraying may cause wrinkles, slight uneven dyeing, and chicken paw prints.
For the dyeing defects formed, the following methods can be used to solve them:
1. Repair method for wrinkles: Put the fabric back into the dye vat and raise the temperature to a higher temperature than the original dyeing The temperature is slightly higher and then cooled slowly.
2. Repair method for mild uneven dyeing: Generally, the migration property of the dye is used for counterstaining. 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 60 minutes, and cool.
Repair prescription
Dye chemical (%) x
Even Dye (g/L) 1～2
For dyes with poor dye migration, the dyeing temperature for repair can be appropriately increased and the holding time can be extended to improve the level dyeing of the fabric.
3. The process conditions for repairing chicken paw prints are the same as (2).
Repair prescription
Dye chemical (%) x
Even Dye (g/L) 2～4
Repair agent L (%) 1～3
Yuzhongbao (g /L)2～4
pH value 5～6
Color-fixing treatment
For dark-colored varieties, in order to further improve the washing fastness of the dyed finished product, the fabric should be subjected to color-fixing treatment after dyeing.
Color-fixing formula
Color-fixing agent (%) 2～6
pH value 5～6
Temperature (℃) 60～70
Preparation of solidification working solution: first The fixing agent should be diluted and then mixed 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.
Other production details
After dyeing nylon fabrics, especially solid After coloring, the hand feels rough, so it needs to be softened and finished. Light-colored fabrics can be softened and finished after dyeing, while dark-colored fabrics should be solidified first and then softened.
1. Softening finishing
In order to give the fabric a good feel, dyed fabrics are subjected to hydrophilic softening finishing.
2. Setting temperature
The heat resistance of nylon is not as good as polyester. Easy to deform, but 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°C, the machine speed is 40r/min, and overfeeding is appropriate.
3. Product quality testing
After strict operation, management, The produced stretch knitted fabric has a soft color, smooth and smooth surface, smooth hand feel, and few dyeing defects. The warp and rungs on the fabric are significantly reduced or eliminated.
The dry and wet rubbing fastness of dyed fabrics is: the dry rubbing fastness of medium and light colors is level 3 to 4, and the wet rubbing fastness is level 3 to 4; the dry rubbing fastness of medium and dark colors is level 3 to 4, and the wet rubbing fastness is level 3 to 4. Level 2~3. The above indicators all meet customer requirements.
About the causes of creases
1. The organizational structure of knitted fabrics is made of coils and loops. It is subject to tension during the weaving process and produces large tensile deformation or artificial pulling during the production process;
2. It is the folding and extrusion of the fabric in the dye vat. When the temperature rises and falls too quickly, the shrinkage difference of the fibers in a short period of time leads to the displacement and deformation of the coil;
3. The temperature of the cloth surface is still very high after the finished product is set, and insufficient cooling causes hot pressing deformation in the cloth car;
4. This is because the elastic recovery rate of spandex is higher than that of other fibers. High, once pulled, other fibers will shrink together, causing changes in the fabric structure, and then formed by folding and extrusion.
Postscript
Elasticity Nylon knitted fabrics are high value-added fabrics. As long as the operating procedures are strictly followed 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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