The interweaving of cotton and nylon can be divided into two types: “cotton brocade cloth” with cotton as warp and brocade as weft, and “nylon cotton cloth” with brocade as warp and cotton as weft. This type of fabric has a large shrinkage rate under hot and humid conditions and is prone to deformation and wrinkling. This is especially the case with cotton nylon fabrics. Therefore, most of them currently use jigger dyeing machines and jet flow machines for exhaust dyeing.
The problem with the dye fastness of this type of fabric is: the washing fastness when dyed with dark colors often fails to reach ISO105-C02 (50℃, 45min) standard level 3 or above Export sales requirements. The light fastness when dyeing light colors often fails to meet the requirements of ISO105-BO2 (xenon arc lamp) standard level 5 or above.
The reason is that the color fastness of this type of fabric is poor, which involves not only the color fastness of cotton fiber, but also the color fastness of nylon. Obviously, in order to improve the color fastness of this type of fabric, we must study both cotton fiber and brocade silk. Production practice shows that correct selection of dyes and rational formulation of processes are the keys to improving the color fastness of cotton fiber and brocade silk.
Figure 1 Cotton brocade fabric
1. Selection of cotton dyes
At present, in the dyeing of cotton-nylon interwoven fabrics, the dyed cotton is generally dyed with double-reactive group reactive dyes and vinyl sulfone-type reactive dyes. These reactive dyes have high color yield and brightness. However, not all of these reactive dyes can be used for dyeing cotton and nylon fabrics. The main problems are the staining of nylon and the light fastness when dyeing medium and light colors.
1.1 Staining problem of nylon
Practice shows that commonly used medium-temperature reactive dyes have different staining phenomena on nylon under conventional dip-dyeing conditions. Commonly used medium-temperature reactive dyes contaminate nylon in four ways.
(1) In the exhaust dyeing of cotton and brocade fabrics, some reactive dyes have serious dyeing competition for cotton and brocade fibers. That is, when dyeing cotton under conventional dyeing conditions, the dye mainly dyes nylon, and the cotton fiber is rarely dyed, and the dyeing effect is completely reversed. Therefore, these reactive dyes cannot be used.
(2) In the exhaust dyeing of cotton and nylon fabrics, the staining shade of some reactive dyes on nylon is completely different from the dyeing shade on cotton fiber, and the shade variation is serious. Mainly mixed black reactive dyes. These dyes stain cotton fibers in black or blue-gray, while when stained on nylon, they are reddish-brown or brown, and the staining is very heavy, so they cannot be used in the dyeing of cotton and nylon fabrics at all.
Figure 2 Cotton Nylon Fabric
(3) In the exhaust dyeing of cotton and nylon fabrics, some reactive dyes stain nylon It is heavy, and the staining dye has poor light fastness, so these reactive dyes should be used with caution.
(4) In the exhaust dyeing of cotton and nylon fabrics, some reactive dyes contaminate nylon to a relatively minor extent and have relatively little impact on the color light and color fastness, so they can be used.
If the cotton nylon fabric needs to be dyed with a flash white effect (only cotton is dyed, leaving the brocade white), or a two-color effect (cotton and nylon two-phase colors are different), the nylon is not allowed to have obvious staining, then, Almost all commonly used medium-temperature reactive dyes cannot be used. Alkali-free reactive dyes dyed at high temperatures under neutral conditions must be used.
The biggest features of this type of dye are:
(1) No alkali is needed to fix the color. It is only required to dye under neutral conditions. The dye bath pH>7 or pH<7 will affect the depth and brightness of the color obtained. Therefore, when dyeing, a buffer with pH=7 must be added to keep the pH value of the dye solution in a neutral range from beginning to end.
(2) Excellent heat resistance and stability. It is suitable for dip dyeing at 100~130℃ under neutral conditions, and has little effect on the depth and brightness of the color.
(3) The conventional process of medium-temperature reactive dyes can also be used for dyeing. That is, 60~65℃ neutral color absorption, 60~65℃ soda ash fixation, the difference in color depth and color fastness is not obvious.
(4) When dyeing cotton and nylon interwoven fabrics, no matter whether it is neutral boiling temperature dyeing or conventional medium temperature dyeing, the nylon will not stain. However, in addition to yellow dyes that have good light fastness, other dye varieties also have light fastness problems.
1.2 The problem of light fastness when dyeing medium-light colors
Production practice shows that when dyeing medium-light colors of cotton with commonly used medium-temperature reactive dyes, its Sunlight fastness usually does not reach level 5 or above of the ISO105-BO2 standard, which has a great impact on the quality of dyed fabrics.
As we all know, the main factor affecting the light fastness of reactive dyes is the structure of the dye. For example, blue reactive dyes, including dark blue, navy blue and black dyes, are usually mixed with KN-B black. Its main structure is a disazo structure. Since the azo group (-N=N-) is easily decomposed under the action of light, the light fastness is low. Most blue dyes such as brilliant blue and emerald blue belong to anthraquinone structure, formazan structure and phthalocyanine structure. The light fastness of the anthraquinone structure is better than that of the azo structure, so dyes with anthraquinone structure have higher light fastness.
Figure 3�It can form salt bonds with the amino cations at the end of the nylon macromolecule chain in the form of dye anions. At the same time, the dye molecules can also combine with the nylon macromolecules through hydrogen bonds and van der Waals forces. Therefore, neutral dyes have a high affinity for nylon and can absorb and color with super equivalent weight. Due to the high dyeing saturation value of neutral dyes for nylon, it is easy to dye darker colors and the dyeing fastness is also very good. In addition, due to the high dyeing rate of neutral dyes on nylon, the dyeing reproducibility is also better, and the contamination of the cotton component is also lighter.
The disadvantages are: the dye has poor brightness and cannot be dyed with bright colors; it dyes quickly and is easy to dye flowers; the difference in the microstructure of nylon results in different color absorption properties and lack of hiding properties , it is easy to expose the warp, willow and weft files.
In actual production, cotton and nylon fabrics can be dyed with light-colored monodisperse dyes with good light fastness, because there is no wet fastness problem with light colors, but when dyeing with medium-dark colors, there is no wet fastness problem. Neutral dyes alone cannot be used for dyeing, because although the dyeing fastness of single neutral dyes is good, the leveling properties of the fabric surface are often poor, and the warp, willow and weft rails are easily exposed. Therefore, neutral dyes must be used in conjunction with disperse dyes. The darker the color, the greater the proportion of neutral dyes. The lighter the dyeing color, the greater the proportion of disperse dyes should be, even without neutral dyes. Because only in this way can we achieve a win-win effect of good level dyeing and good dye fastness on the fabric surface.
Figure 6 Cotton nylon fabric
2.3 Acid dye dyeing nylon
The biggest advantage of dyeing nylon with acid dyes is good vividness and bright color.
The disadvantages are:
(1) Many weak acid dyes have poor light fastness. The light fastness mentioned here refers to two aspects: First, it refers to the poor light fastness of the dye dyed on the nylon. The second refers to the poor light fastness of the dye attached to the cotton fiber.
(2) Many weakly acidic dyes are highly dependent on the pH value of the dye bath.
(3) Since the molecules of nylon are linear molecules and there are no branches or large side chains on the molecular chain, the dye molecules are easy to get close to the nylon molecular chain, so more dye-fiber interactions can occur. Hydrogen bonds and large van der Waals forces, coupled with the positive ionization of nylon under acidic conditions, can produce salt bonds with dye anions. Therefore, weakly acidic dyes have high affinity for nylon, fast coloring, and even dye transfer. The dyeability is poor and the warp and weft files lack coverage.
(4) Due to the limited terminal amino content of nylon, competitive dyeing is easy to occur when dyes with different dye uptake rates and different diffusion rates are used for dyeing. That is, as the dyeing time prolongs, the dyeing color light will continue to change, making it difficult to obtain a stable color matching effect.
(5) The wet fastness of weakly acidic dyes on nylon is poor, especially when dyeing dark colors. Therefore, when used for dyeing cotton and nylon fabrics, it is only suitable for the two-bath overdying process of dyeing cotton first and then dyeing cotton, so as to prevent the color on the nylon from changing in depth and light during the soda ash fixation and high-temperature soaping process of reactive dyed cotton. Significant changes occur, causing color and light inconsistencies.
In the actual dyeing of cotton and nylon fabrics, due to the above shortcomings, weak acid dyes are only used as a supplement to special chromatography when the brightness of disperse dyes and neutral dyes cannot be achieved. Such as bright red, bright purple, bright blue, etc., should not be used as common main colors.
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