Nylon fabric has become more and more popular in the market because of its unique wearing properties. However, nylon fabrics are susceptible to many dyeing and finishing problems such as “white stains”, “white spots”, color flowers, stripes, and poor wet treatment fastness during the dyeing and finishing process. This article briefly introduces the basic dyeing and finishing processes of nylon fabrics, focusing on analyzing the causes of common dyeing and finishing problems and corresponding solutions.
Basic knowledge of nylon
Nylon is the trade name of synthetic polyamide fiber, commonly known as nylon. Its basic composition is aliphatic polyamide linked by amide bonds – [NHCO] -.
The nylons commonly used in textile fabrics include nylon 6 and nylon 66. The nylon macromolecules are mainly composed of three parts, namely the hydrophobic methylene part and the hydrophilic amide group and the amino and carboxyl groups at the chain end. Although the amino content of nylon is low, its molecular chain has a large number of methylene groups that can form van der Waals forces and hydrogen bonds with dyes. Therefore, in addition to being able to combine with anionic dyes through ionic bonds, nylon can also be combined with anionic dyes through stronger Van der Waals forces interact with dyes to produce color. Although there are some small differences in molecular structure and dyeing properties between nylon 6 and nylon 66, their dyeing and finishing processes are the same.
Because of its good strength, excellent wear resistance, better hygroscopicity than polyester fiber, and better wearing comfort than polyester, nylon fiber has been widely used in clothing fabrics, high-end underwear, Sportswear and mountaineering clothing, etc. Due to the development of the market and the advancement of spinning technology, most nylon fabrics currently have elastic fibers (spandex yarns) added to enhance the wear resistance and resilience of nylon fabrics, which makes the dyeing and finishing of nylon fabrics more difficult.
The general dyeing and finishing production process of nylon fabrics:
Pre-treatment → (pre-formation) → dyeing → finishing → packaging
Pre-treatment
Nylon yarn and nylon yarn used in nylon and nylon elastic fabrics In the spinning process of polyurethane (spandex yarn), in order to improve the spinnability of the fiber, a large amount of spinning oil is needed. Generally, the oil used for spinning nylon fiber is an oil agent prepared from mineral oil (containing hydrocarbons with fewer carbon atoms) and anionic and nonionic surfactants in a certain compound ratio, while the spinning oil of polyurethane (spandex yarn) Silk oil agents generally contain more dimethylpolysiloxane or ethylsilane silicone oil components. Due to the large friction coefficient of polyurethane, the amount of oil agent is relatively high in order to meet the friction coefficient required for weaving. However, the addition of a large amount of oil will seriously affect the subsequent dyeing and finishing production. Therefore, during the dyeing and finishing process of nylon and its elastic fabrics, it is necessary to choose an effective degreaser and how to effectively and cleanly remove the spinning and weaving agents. Various oils and debris in the process are important factors related to the success of nylon dyeing and finishing processing.
There are two common pre-treatment methods for nylon fabrics:
One is dry cleaning machine extraction method,
A It is an open-width machine or dye vat scouring method.
Due to the large investment in dry cleaning machine extraction equipment, incomplete recovery of extraction solvents (tetrachlorethylene, etc.) can easily cause environmental problems, as well as the strong impact of organic solvents on spandex yarns. Due to various factors, most dyeing factories currently use the process methods and processes of open-width scouring and degreasing or dye vat overflow scouring and degreasing after flattening.
A good refining degreaser must not only have excellent oil and impurity removal capabilities, but also must have excellent anti-re-staining capabilities. In particular, in addition to mineral oil, nylon elastic fabrics also contain methyl and ethyl silicone oils that are more difficult to remove. The oil and dirt removed from the fabric will accumulate if they are not well emulsified and dispersed. Together they form oil spots, which cause serious contamination to fabrics or equipment, thus causing problems such as “white spots” and “white stains” after dyeing. If it is severe silicone oil back-staining, the “white spots” and “white stains” formed in this way will “White stains” 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, during the process of oxidation and thermal cracking, the number of groups will decrease, and the nylon fiber will also Yellowing occurs. 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, pending dyeing and finishing processing.
1. Pre-treatment of nylon and elastic fabrics
Smoothing→Desizing→Scouring
1.1 Continuous desizing process of nylon woven fabric:
Desizing agent 8 g/L
Chelating dispersant 2-4 g/L
Liquid alkali (30%) 20-30 g/L
Continuous open-width desizing, the vehicle speed is 40m/min, the first two compartments of working fluid are used, the temperature is 90-95℃, and the overflow water is washed 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.
1.2 Nylon knitted fabric scouring process
Nylon scouring agent 1- 3 g/L
Chelating dispersant 1-2 g/L
Around pH 5 (HAc adjustment)
The overflow machine dipping method is 95℃*30min, and the liquor ratio is 1:8. It can also be used according to the dyeing factory’s own equipment.The dyeability is better, but its wet processing fastness is poor. In order to improve the wet processing fastness of acid dyes, the proportion of organic groups will be increased to increase the relative molecular weight of the dye and reduce the proportion of water-soluble groups. However, the leveling and migration properties of the dye will be reduced. Therefore, it is necessary to control the dyeing process starting from the dyeing process to ensure the dyeing quality and prevent the occurrence of problems such as “color flowers” and “strips”.
The dyeing saturation value of nylon is very low, so when dyeing deep and dense colors, the phenomenon of “dying competition” between different dyes becomes very prominent. If the selected dyes have large differences in affinity and dye uptake, the fiber dyed colors will be very different during different dyeing times, which can easily cause color blooms and poor color reproducibility. Generally, try to use the same series of dyes from the same company. Even if you have to use dyes from different companies, try to choose dyes with similar dyeing curves, similar initial dyeing temperatures, and similar sensitivity to temperature and leveling agents to minimize the number of dyes. The phenomenon of “dying competition” between dyes.
The influence of leveling agent selection on nylon dyeing
Weak Acid dyes have fewer water-soluble groups than strong acid dyes, and have a higher affinity for nylon fibers. Their solubility in aqueous solutions is worse than that of strong acid dyes. Their solubility and aggregation are moderate, so their wet processing fastness is better, but their dye migration The properties and leveling properties are poor. During the fiber spinning and weaving process of nylon and its elastic fabrics, the physical and chemical structure of the fiber itself is uneven, including differences in fineness, internal stress, molecular structure orientation, etc., or differences in fiber chemical properties, such as fiber ends. Differences in the number of amino groups can also cause dyeing problems such as color bars and rungs during the dyeing process. In addition, operational problems during the dyeing process will affect the levelness of nylon dyeing. Therefore, the selection of a good leveling agent can effectively prevent or reduce the occurrence of the above problems.
There are many kinds of leveling agents used for nylon dyeing, including fiber-friendly anionic type, dye-loving polymer type, amphiphilic type zwitterionic type, etc. Zwitterionic leveling agents have a larger molecular weight and have excellent leveling effect on weakly acidic dyes with larger molecular weights. They have higher dye migration capabilities and the ability to even out the dyeing rates of different types of acidic dyes.
Improvement of wet treatment fastness of nylon fabric after dyeing
Nylon After the fabric is dyed, because the acid dye has a water-soluble group and the dye and fiber are not combined with a strong covalent bond, the wet processing fastness of the medium and dark varieties of nylon dyed is poor and needs to be fixed. To improve wet processing 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.
Finishing
1. Softening and finishing of nylon fabric
With With the diversification of people’s requirements for clothing, nylon fabrics not only have rich changes in fabric categories and clothing styles, but also the feel and style of nylon fabrics have also changed. Some require waxy and smooth, some require soft and elastic, and some require soft and elastic. Some require strong drape, some require dry and fluffy texture, 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 finishing
Due to market demand, there are also many functional finishing requirements for nylon fabrics, such as moisture absorption. Sweat-wicking finishing, flame retardant finishing, mite removal and deodorizing finishing, sanding finishing, pre-formed antioxidant, storage anti-yellowing, etc. all require the use of corresponding additives and processes, which will not be described here.
Examples of large-scale production processes for dyeing and finishing nylon fabrics
Fabric specifications:
100D/96F semi-gloss nylon 6+40D spandex knitted jersey, 165cm*170 G/m2, color: brown
1. Process flow
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Cylinder pre-shrinking (oil removal and scouring) → slicing → low-temperature tenter → overflow cylinder scouring → high-temperature reservation → dyeing → final product shaping
2. Process flow description
Cylinder pre-shrinking: loose cylinder water passing equipment, 95℃, The vehicle speed is 55m/min. The purpose is to make the fabric fully shrink under the action of hot water, eliminate the internal stress during spinning and weaving, and make the fabric obtain a certain level of flatness and dimensional stability. During the pre-shrinking process, nylon scouring agent M-118 2-4g/L needs to be added to basically remove surface oil and impurities under acidic conditions.
Low temperature tenter: in order to better remove fine wrinkles and chicken paw prints on the cloth surface. The weight of the unloaded machine can be slightly heavier than the weight of the finished product, and the operating parameters can be 165℃×50m/s.
Dye vat scouring: Since the scouring in the first step of cylinder preshrinking is not very effective in removing impurities, if after high-temperature setting, especially the silicone oil component in spandex is cross-linked After the film is formed, it will have a great impact on the subsequent dyeing, and it is easy to cause problems such as color flowers and stains, so further refining is carried out in the dye vat.
M-118 0.8 g/L
Liquid soda 2 g/L
Liquor ratio: 1:8 105℃×25 min
High temperature pre-setting: The purpose of pre-setting is to completely remove wrinkles and chicken paw prints on the fabric surface and stabilize the fabric size.
3. Dyeing formula and curve
Erionyl Yellow A-R 0.52%
Erionyl Red A-3B 0.21%
Erionyl Blue A-B 0.37%
Leveling agent 1.5 g/L
Dyeing stabilizer 0.6 g/L
Chelating dispersant 0.5 g/L
Liquor ratio: 1:4 (air flow machine) 95℃*30 min
4． Finished product styling
Fluffy silicone oil 20 g/L
Smooth silicone oil 8 g/L
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3. Dyeing formula and curve
Erionyl Yellow A-R 0.52%
Erionyl Red A-3B 0.21%
Erionyl Blue A-B 0.37%
Leveling agent 1.5 g/L
Dyeing stabilizer 0.6 g/L
Chelating dispersant 0.5 g/L
Liquor ratio: 1:4 (air flow machine) 95℃*30 min
4. Finished product styling
Fluffy silicone oil 20 g/L
Smooth silicone oil 8 g/L</ p
