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.
1 Dyeing process
Dye selection, nylon is a hydrophobic fiber , but the macromolecule contains a large number of weak 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 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 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 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 increased 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.
2 Dyeing process
Due to nylon It has a high degree of orientation and a glass transition temperature of 40 to 60°C.
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 the 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 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 coloring 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. Principles for 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.
3 Process Example
1. Dyeing of medium and light color nylon knitted fabrics
For the dyeing of medium and light color elastic nylon knitted fabrics, disperse dyes are mainly used. Considering the various properties of the dyes and the testing indicators of the dyeing products, dispersed blue 2BLN, yellow SE23R, and red FB with good compatibility were finally selected as the basic three primary colors.
Examples of production process
Stretch nylon knitted fabric 400kg, bean green
Dye prescription (%, owf)
Disperse blue 2BLN 0.9
Disperse yellow SE3R 0.12
Disperse Red FB 0.053
HAc (mL/L) 0.9
Yuzhongbao 2～4
Leveling agent 1～2
2. Medium and dark nylon fabrics Dyeing
The dyeing of medium and dark elastic knitted fabrics mainly uses neutral dyes. 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, the dye has a relatively high water hardness It is sensitive and can easily cause color lakes, so you need to use soft water, 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 diluted with hot water or boiling water until the dye is dissolved.The dye is fully dissolved, and the dye should be filtered with a screen when entering the tank. Since the neutral dye solution is in colloid form, precipitation will occur if left for too long, so it should be prepared as needed.
4 Dyeing defect analysis and solutions
Using high temperature and high pressure overflow dyeing machine to dye nylon Dyeing defects such as wrinkles, slight uneven dyeing, and chicken paw marks may occur due to factors such as tangles, blockages, overloading, or excessive spraying.
For the dyeing defects formed, the following methods can be used to solve them:
1. Repair method of wrinkles: remove the fabric Put it back into the dye vat, raise the temperature to a temperature slightly higher than the original dyeing temperature, and then cool it down slowly.
2. Repair method for mild uneven dyeing: Generally, the migration property of the 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 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
5 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
Color-fixing agent (%) 2～6
pH value 5～6
Temperature (℃) 60～70
Preparation of solid color 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.
6 Other production details
After dyeing of nylon fabric, especially After solidification, the hand feels rough, so it needs to be softened. Light-colored fabrics can be softened and finished after dyeing, while dark-colored fabrics should be fixed first and then softened.
1. Softening finishing
In order to give the fabric a good feel, the dyed fabric is hydrophilized Soft finish.
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℃, the machine speed is 40r/min, and overfeeding is appropriate.
3. Product quality testing
After strict operation, management, The produced elastic 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: dry rubbing fastness of medium and light colors is 3~4, wet rubbing fastness is 3~4; medium and dark colors are dry rubbing fastness The strength is level 3 to 4, and the wet rubbing fastness is level 2 to 3. The above indicators all meet customer requirements.
About the causes of creases
1. It is knitted fabric The organizational structure is made of coils, which are subject to tension during the weaving process and produce large tensile deformations or artificial pulling during the production process;
2. It is the fabric’s Folding and squeezing in the dye vat, when the temperature rises and falls too quickly, the shrinkage difference of the fibers in a short period of time will lead to the displacement and deformation of the coil;
3. It is the shaping of the finished product The temperature of the cloth surface is still very high, and the cooling is not enough, causing the hot pressing deformation in the cloth car;
4. Because the elastic recovery rate of spandex is higher than that of other fibers, once it is pulled, other fibers will be affected. The fibers shrink together, causing changes in the fabric structure, and then are formed by folding and extrusion.
7 Postscript
Stretch nylon knitted fabric is high-added 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 in production can be avoided, and products that satisfy customers can be produced. </p
