1 How many forms of spandex elastic fiber yarn are there?
Spandex elastic fiber is mixed with other fibers to form elastic yarn. There are currently three forms of yarn. Form: spandex core-spun yarn, spandex twisted yarn and spandex covered yarn. The three forms of yarn are essentially different in processing principles and structural properties. Therefore, their uses and weaving properties also vary greatly. The structural diagram of the three types of yarns is shown in the figure.
What is the origin of spandex fiber and its main properties?
Spandex fiber is a kind of elastic fiber. Elastic fiber is collectively called Spandex abroad. The product name in my country is spandex. In fact, spandex is only elastic fiber. A broad category. Spandex fiber (Polyurethane Fibre) is referred to as PU fiber. There are two varieties. One is a copolymer made of aromatic diisocyanate and polyester segments containing hydroxyl groups, which is referred to as polyester spandex. The other variety is made of aromatic diisocyanate and hydroxyl-containing polyester segments. Polyether segment-embedded copolymer of hydroxyl groups is referred to as polyether spandex. The representative trade name of polyester spandex is Vyrent, and the representative trade name of polyether spandex is Lyera.
The main properties of spandex fiber are: usually an elongation of 500% to more than 700%, and good elastic recovery performance. It retracts 97% at 200% elongation and over 99% at 50% elongation.
The relative density of various spandex has a small difference, generally 1.20~1.25, the breaking strength is 4.41~8.82cN/tex (0.5~1.0g/denier), polyester spandex The strength is lower, while the strength of polyether spandex is higher. The moisture absorption rate is generally 0.3%-1.2%. The moisture absorption rate of multifilament is slightly higher than that of monofilament. The heat resistance is generally between 95 and 150°C. Short-term storage will not damage the fiber. The safe ironing temperature is below 150°C.
Fiber burns slowly and forms a gelatinous residue after burning. It has excellent dyeing performance, can be dyed in a variety of colors, and has strong affinity for dyes. It has good acid and alkali resistance, can be bleached, and does not become moldy.
2 Spandex dyeing
Spandex can use disperse dyes and acid dyes Dyeing, but the fastness of these two dyes is too poor, and experiments have shown that nylon reactive dyes (dyed with nylon elastic fabric) and dispersed cationic dyes (dyed with CDP elastic fabric) basically do not stain spandex. Is this true? This shows that these two dyes are not suitable for spandex dyeing. In fact, this is not the case. Reactive dyes for nylon can be used to dye spandex with appropriate additives as a medium, and the fastness and depth are relatively good.
There are very few pure spandex fabrics on the market, so spandex dyeing is relatively unfamiliar. Pure spandex fabrics can be used together with low-elastic fabrics or non-elastic fabrics to increase the elasticity and recovery of the fabrics. force. And when the elastic fabric is stretched or pressed, if the color of the spandex is inconsistent with the filament, there will be a problem of color leakage of the spandex, which requires dyeing the spandex.
For spandex dyeing with light colors
It can be dyed with acid dyes or disperse dyes under acidic bath conditions, with the same dye dosage conditions Under the conditions, the fastness of disperse dyes on spandex is better than that of acid dyes, but the fastness of different disperse dyes to spandex is different. Generally, disperse dyes can be used for dyeing when the dye dosage is less than 0.5%.
Spandex is a highly elastic fiber. Considering that long-term dyeing under high temperature conditions will cause the spandex to lose elasticity, it is usually dyed below 100°C, and spandex is not resistant to alkali. Furthermore, disperse dyes and acid dyes are suitable for acidic dyes. For dyeing under acidic bath conditions, spandex is generally dyed under acidic bath conditions, and the pH is around 5.
Various dyes can be dyed with suitable additives as a medium. This type of additives is called spandex colorant or spandex colorant on the market. It is mainly used for reactive dyes and acid dyes for nylon. When dyeing spandex, it is generally zwitterionic in nature.
The working principle is roughly as follows: under acidic conditions, groups such as amide bonds in spandex are ionized and become positively charged, and the spandex coloring agent reacts with them, and the color-fixing agent is fixed on the spandex. The spandex coloring agent contains amino cations, so the dye can also combine with the spandex coloring agent.
Nylon reactive dyes
Rule of dyeing spandex (adding spandex coloring agent)
1 , the general rule of various fastnesses after spandex dyeing: washing>sweat (acid)>water immersion, and the wet rubbing fastness is much better than the dry rubbing fastness.
Analyzing the reason, after the spandex is colored, the dye or the combination of the spandex coloring agent and the dye will migrate under wet conditions under the long-term action of external pressure, and it is a slow process (spandex It is a hydrophobic fiber, water molecules will not quickly enter the interior of the fiber, and dyes will not migrate quickly), so its washing fastness is better. Secondly, under sweat-stained acidic conditions, it is beneficial to the amide bonds on spandex or spandex colorants. Amino ionization can capture migrating dyes or spandex colorants and dye combinations, so the acidic perspiration fastness is better than the neutral water immersion color fastness. Under the action of friction, dry grinding will generate heat, causing the dye on the surface of spandex to thermally migrate, which does not occur under wet conditions.
2. Boil soda ash after dyeing spandex� will reduce its fastness by about 0.5 levels. This is because under alkaline conditions, the combination of spandex coloring agent with fibers and dyes will be destroyed, thus reducing the fastness. Secondly, after spandex is dyed, cationic fixatives are used to fix the color. The fastness improvement is greater than that of anionic fixatives. The cationic fixatives can react with the water-soluble groups (-SO3-) produced by the dye and block the water-soluble groups. The water solubility of the dye is reduced, and the fixing agent forms a film on the fiber surface, which can isolate the dye, and the dry rubbing fastness is accordingly improved.
3. The light fastness of spandex dyed with acidic, dispersed and nylon reactive dyes is worse than that of polyester or nylon filament dyed. The main reason is that spandex has low crystallinity and is in a highly elastic state at room temperature. Air can easily enter the fiber and change color under the influence of sunlight. Furthermore, spandex itself will yellow under the influence of sunlight, which is also Reasons for low light fastness.
When cotton elastic fabric is dyed black
The spandex will show white. Generally, a small amount of dispersed or acid black can be added to the dye bath. Let it be dyed with spandex, but be careful about the fastness.
Secondly, for the problem of polyester elastic and nylon elastic fabrics dyeing black spandex color, when dyeing polyester elastic fabrics, a small amount of spandex coloring agent of about 0.3% can be added to the dye bath, and nylon elastic fabrics can be dyed directly in the dye bath. Add spandex coloring agent to the bath for dyeing, so that the problem of color exposure of spandex can basically be solved. The problem of color exposure of spandex in other colors can be deduced according to the above analogy.
3 Why does denim and spandex lose elasticity?
In denim fabrics, low-elastic and high-elastic spandex core-spun yarn materials are becoming more and more common, and the elasticity of spandex directly determines the progress of the denim washing process. In addition to its poor quality and easy loss of elasticity, spandex elastic yarn is also affected by many external factors.
1. Enzyme powder in the enzyme washing process Since enzyme powder is a multi-component compound, the difference in its internal chemical components will affect the elasticity of spandex, especially the anti-dye powder component. The enzyme powder used basically does not have this phenomenon.
2. Sodium hypochlorite (bleach) Since spandex itself is not resistant to chlorine, the elasticity of spandex is greatly damaged during the chlorine bleaching process. The concentration of bleaching water, pH and other reaction speeds also play an important role in the elasticity damage of spandex. , heavy drift damage is serious.
The following are some suggestions for mitigating the elasticity loss of spandex: 1. For denim garments that require chlorine bleaching, use spandex chlorine bleaching anti-brittle agent 1-3g/L in advance ( 1/10 of the bleaching water) run in the water bath for 1-2 minutes, gradually raise the temperature to 40°C, add the bleaching water three times, add 1/5 of the total amount of bleaching water for the first time, and add 2/5 of the total amount of bleaching water for the second time. Add the remaining 2/5 of the bleaching water for the last time and operate according to the actual bleaching time.
2. After bleaching, drain water and add water at the same time. The water temperature will gradually drop. The reason for this is to prevent the spandex from becoming brittle and elastic due to a sharp drop in temperature.
3. Softness Due to the different formulas of softeners and silicone oils among various additive manufacturers, some softeners and silicone oils can damage the elasticity of spandex. This is mainly due to the small amount of solvents in their components, which have a negative impact on spandex. Elasticity has an impact. Some silicone oils and softeners basically do not contain this solvent and have no effect on the elasticity of spandex. Choose the appropriate silicone oil for softening.
4. Solvents Since the spandex weaving process contains silicone-containing oils, the oils need to be removed during the dyeing and finishing process, and many scouring agents contain solvents, which have a great impact on the elasticity of spandex.
5. Physical cutting. Because the characteristic of denim is nostalgia, many of them need to be physically damaged and cut. The damage will exert uneven force on the spandex elastic yarn, resulting in blistering of the spandex and the exposed parts. The yarn also breaks easily, causing loss of elasticity.
6. Drying temperature Generally, the drying temperature of denim fabrics containing spandex elastic yarn is lower than 60°C, so excessive temperature will cause great damage to the spandex elasticity. </p
