Dyeing of nylon fabrics often causes problems such as “white spots” and “white stains”. If there is severe silicone oil back-staining, the “white spots” and “white stains” formed in this way cannot be removed and cause defective fabrics.
Since the amino and carboxyl groups at both ends of the nylon fiber macromolecule are sensitive to light, heat and oxygen, especially the amino group, the number of groups will decrease during the process of oxidation and thermal cracking. ． Nylon fibers will also yellow at the same time. In addition, the various oils used in the fiber spinning and weaving processes of nylon fabrics may also change their properties under the action of light and oxidation, causing oil stains that are difficult to remove on the fabric surface, which will also cause “white stains” , white spots” phenomenon occurs. Therefore, it is required that nylon fabrics should be packaged in opaque packaging materials after weaving.
1 Pre-treatment of nylon and elastic fabrics
Nylon and its Pre-treatment steps for elastic fabrics: smoothing → desizing → scouring
1. Desizing of nylon woven fabrics
Desizing agent 8 g/L
Chelating dispersant 1 g/L
Liquid caustic soda (30 %) 30g/L
Continuous open-width desizing, the vehicle speed is 40m/min, using the working fluid in the first two compartments, and overflow water washing one by one. Since nylon woven fabrics are prone to creases or chicken paw prints, it is best to use open-width equipment before the fabric is pre-shaped at high temperatures.
2. Example of scouring process:
Nylon scouring agent 1- 3g/L
Chelating dispersant 1-2g/L
About pH 5 (HAc adjustment), overflow machine dipping method 95℃×30min, liquor ratio 1:8. According to the dyeing factory’s own equipment, the open-width machine can be used to adjust the number of sections of the feeding box and the washing box to use the long car continuous refining and oil removal process.
3. Washing
Due to the increasing pressure on environmental protection, Many factories only pay attention to the removal of oil and impurities from the fabric, but do not pay attention to the subsequent washing work. This causes excessive accumulation of oil and impurities washed from the fabric, and the accumulated oil bundles cause back staining, thus forming There are “white spots and white stains” after dyeing, so the fabric cleaning after refining and oil removal is also a process detail that cannot be ignored. Alkaline cleaning often requires a large amount of water. It should be noted that if the oil stains cannot be completely removed under acidic conditions, an alkaline refining process can be added.
2 Dyeing of nylon and elastic fabrics
Can be used for nylon dyeing The dyes include acidic (weakly acidic) dyes, disperse dyes, reactive dyes, direct dyes, etc. Although reactive dyes have the advantages of bright colors, good light fastness, and no heavy metal ions, their dyeing depth and cover dyeing properties are poor. Disperse dyes can only dye light colors, so the dyes currently used for nylon dyeing are still mainly acidic or weakly acidic dyes.
The isoelectric point of nylon fiber is at pH 5-6. When the pH value of the solution is lower than the isoelectric point, the nylon fiber is positively charged, and the dye and fiber form ionic bonds. Combined with each other, the dye is mainly fixed on the terminal amino group of the fiber; when the pH value of the solution is higher than the isoelectric point, the nylon fiber is negatively charged, and the dye can only dye nylon through the combination of intermolecular attraction such as van der Waals force or hydrogen bonding. .
Problems such as “willows” and “rungs” often occur in the dyeing of nylon fabrics. The various influencing factors in the dyeing process are analyzed below.
1. The influence of pH value of dye liquor on dyeing
Industry It has always been believed that the control of the pH value of nylon dyeing is the key to success or failure. After years of production accumulation, we have found that if buffer system additives and the selection of good leveling agents are used in dyeing, it will play a decisive role in the success or failure of nylon dyeing.
When dyeing with acidic (or weakly acidic) dyes, the pH value of the dye solution tends to increase as the dyeing proceeds. For dyes with low affinity and sensitive to the pH value of the dye bath, the dyeing pH value should be controlled at around 5. In this way, the use of buffer system additives can achieve twice the result with half the effort in controlling the pH value of nylon dyeing. Stabilizing the pH value of the dye liquor is one of the key factors in achieving uniform dyeing.
The influence of different pH values on the adsorption of acid dyes onto nylon: Under certain temperature conditions, the dye adsorption capacity decreases significantly as the pH value of the dye liquor increases, but when dyeing When the liquid pH value reaches above 9, the dye adsorption capacity will drop sharply, seriously affecting the dyeing process. This is because when the pH value of the dye solution is higher than the isoelectric point of the nylon fiber, the negatively charged dyes on the nylon fiber are used to adsorb and color the nylon fiber mainly through intermolecular van der Waals forces and hydrogen bonds.
When the pH value of the dye solution is weakly alkaline, the dye will be dyed slowly and evenly, which can effectively improve the phenomenon of color flowers and color difference that are easy to occur during the heating process of dyeing. happened.
When the pH value of the dye solution is lower than the isoelectric point, the terminal amino groups of the nylon fiber absorb H+ and form positively charged -NH3 +, thereby making the fiber positively charged. At this time, the amount of dye adsorption increases sharply, and the dye and fiber are not only combined through van der Waals forces, but also mainly through ionic bonds. At this time, the dye is dyed very quickly. If not controlled, it can easily cause dyeing problems such as colored flowers and stripes. And when the pH of the dye solutionThe wet treatment fastness of medium and dark dyed varieties is poor, and color fixing treatment is required to improve the wet treatment fastness. The special color-fixing agent for nylon can react with nylon fiber, and the color-fixing agent molecules can be cross-linked with each other to form a three-dimensional network structure, which can effectively fix the acid dye molecules in the fiber to improve its wet processing fastness.
3 Finishing of nylon fabrics
1. Softness of nylon fabrics Finishing
With the diversification of people’s clothing requirements, nylon fabrics have not only undergone rich changes in fabric categories and clothing styles, but also the feel and style of nylon fabrics have also changed. There are endless variations, some require waxy and smooth, some require soft elasticity, some require strong drape, some require dry and fluffy, etc. Silicone softeners comply with the requirements of clothing trends and have gone through the development stages of methyl silicone oil, amino silicone oil, polyether modified silicone oil, and ternary copolymer silicone oil. Product performance has been continuously improved, and hand feel styles have emerged in endlessly.
2. Other functional arrangements
Due to market demand At present, there are many functional finishing requirements for the finishing of nylon fabrics, such as moisture wicking finishing, flame retardant finishing, mite removal and deodorizing finishing, sanding finishing, as well as pre-shaped anti-oxidation, storage anti-yellowing, etc., all of which are required The use of corresponding additives and processes will not be described in detail here.
4 Production Notes
1. The choice of nylon fabric pre-treatment technology directly affects the quality of nylon fabric dyeing and finishing products.
2. During the dyeing process, the control of the pH value of the dye liquor is one of the key factors for the success or failure of dyeing. The lower the pH value of the dye liquor, the faster the dyeing speed and the uniformity of the dye. The dyeability and covering ability of menstrual willow are worse.
3. Nylon leveling agent can improve the initial dyeing pH value of the dye solution and the charge of the nylon fabric, and can effectively prevent color flowers and warp threads caused by too low initial dyeing pH. , rungs and other issues. It has a very good leveling effect.
4. The wet treatment fastness of nylon fabrics not only requires the selected dyes to meet product requirements. Moreover, a good nylon color fixing agent has a good effect on improving the wet processing fastness.
5. The control of dyeing temperature is also one of the key factors in nylon dyeing. The dyeing heating curve and dyeing starting temperature should be determined according to the selected dyes, different colors, and different fabric structures. The heating curve generally adopts the ladder method.
6. The finishing process of nylon fabric should be determined according to different product requirements. </p
