Shrinkproof finishing
refers to the finishing of clothing to prevent shrinkage. Among them, mechanical method is an effective way to solve the warp shrinkage, which is to make the original potential shrinkage in the fabric retract before it becomes the finished product. Mechanical anti-shrinkage can be accomplished using special equipment. In addition, there are chemical anti-shrink methods, which try to reduce the hydrophilicity of the fiber so that it cannot swell greatly in water, so that the fabric will not suffer serious shrinkage.
Shrinkage phenomenon
1. Shrinkage: When the dry fabric is wetted by water in a relaxed state, the size will shrink significantly. In production, the shrinkage rate is used to assess the degree of shrinkage of fabrics. Shrinkage: The length difference in the warp or weft direction of the fabric before and after washing according to the prescribed method, accounting for the percentage of the length before washing, which is the shrinkage rate in the warp or weft direction respectively.
2. Felt shrinkage: Some fabrics (such as wool fabrics) are washed under certain conditions At this time, in addition to the general shrinkage phenomenon, due to mechanical action, the fibers will undergo special peristalsis and become entangled with each other, causing the fabric to shrink into a tight state. This shrinkage is called felting, which is generally expressed as the percentage of area change.
Anti-shrink finishing
Fabrics with unstable dimensions (i.e. potential shrinkage) are shipped from the factory as finished products. It is difficult to make garments with stable shape (such as wrinkles at seams, pattern alignment). Inaccurate, poor forming effect, etc.), and the durability of the finishing effect during the use is very poor. It is necessary to improve the shrinkage of fabrics through physical and chemical methods. Different fibers cause fabrics to shrink in different ways. Not only does the initial shrinkage of wool fabrics be serious, but the subsequent shrinkage is also very prominent. The initial shrinkage of cotton fabrics is larger, but the subsequent shrinkage is not high; the shrinkage of synthetic fiber fabrics is smaller. In addition, the shrinkage of the fabric is also related to the yarn, fabric structure and processing process.
Fabric shrinkage mechanism
1 , Fibers with “drying and setting” deformation cause shrinkage due to internal stress relaxation, but this is not the main reason. 2. The anisotropic swelling effect increases the diameter of the yarn, and the stroke of the fiber in the yarn around the yarn axis increases, causing the yarn to shrink, but it is only 2 to 3.5%, which is still not the main reason. 3. Anisotropic swelling changes the fabric shrinkage before and after wetting, which is the main cause of shrinkage. Weaving shrinkage: The length of the yarn is shortened after weaving (that is, the difference between the yarn length and the fabric length accounts for the percentage of the fabric length). The above discussion is the shrinkage mechanism of cotton fabrics, and wool fabrics also have a similar phenomenon.
Shrink-proof finishing method
[Mechanical preshrinking]: It is an effective method to solve the warp shrinkage
Principle: Increase the weft density and warp shrinkage of the fabric to a certain extent, so that the fabric has a relaxed structure. In effect, the potential shrinkage that originally existed in the fabric is allowed to shrink before it becomes the finished product. The following equipment (pre-shrinking machine) is mainly used to achieve the purpose of pre-shrinking.
1. Overfeeding pin tenter: The overfeeding device is used to stretch the fabric in a relaxed state, allowing the fabric to retract in the warp direction when drying at a fixed width. conditions to achieve the purpose of improving meridional shrinkage.
2. Rubber blanket compression anti-shrinking machine. When the rubber blanket passes between the guide roller and the pressure roller, it is thinned and stretched. After leaving, it shrinks and returns to its original shape, forcing the fabric to Synchronous shrinkage occurs. It consists of cloth feeding device, moistening device, short cloth clip tenter, three-roller blanket compression device and blanket dryer. Features: The shrinkage rate can be reduced to less than 1%, the equipment structure is simple, and the fabric shrinks and shapes more fully due to the pressure between the guide roller and the pressure roller.
3. Blanket compression anti-shrinking machine When the thick blanket bypasses the cloth guide roller with a smaller diameter, the outer layer expands and returns to its original shape when leaving, making the blanket stretch. The fabric on the surface shrinks synchronously to eliminate potential shrinkage. It consists of five parts: cloth feeding, moistening, whole fabric, shrinking cloth and drying and shaping (without tension). Features: The shrinkage rate can be reduced to less than 2%, the hand feels plump and soft, and it has good wearing properties.
Chemical methods
After pre- The structure of the shrink-finished fabric becomes loose and the weave shrinks greatly. Although there is no shrinkage problem, it is easily stretched. Especially for viscose fabrics, chemical methods need to be used to achieve dimensional stability.
The basic principle of the chemical method: Try to reduce the hydrophilicity of the fiber so that it cannot swell greatly in water, so that the fabric will not shrink seriously. It is mainly treated with resin primary shrinkage or cross-linking agent, that is, after the fabric is anti-wrinkle finished, it also has anti-shrinkage effect.
Wool fabric finishing
【 Pre-shrunk finishing]
1. Strengthen the shaping effect in post-finishing (1) During drying, it is carried out on an overfeed pin tenter; (2) During drying, try to reduce the warp direction tension.
2. Relaxation and pre-shrinking (1) Humidify the fabric and leave it in a relaxed state for a certain period of time, and then dry slowly. (2) Adopt forced pre-shrinking method. Forced retraction can be obtained by exposing the fabric to steam in a tension-free state, oscillating or shaking it, and then maintaining high-speed cooling without tension.
【Anti-felting finishing】
1. The significance and method of anti-shrinking (1) Eliminating the shrinkage of wool fabrics is of great significance to pure wool worsted fabrics and knitted fabrics. It not only allows the fabrics to obtain true dimensional stability, but also reduces fluffing. ball effect. (2) Reasons for felt shrinkage: D, F, E caused by the scale layer structure of wool, and the high stretchability (elasticity) of wool. The scales fix the displaced wool in a new position (braking factor), and the contraction drives the wool to move against each other (dynamic factor). Eliminating one of these factors will reduce shrinkage. (3) The method to eliminate the shrinkage of wool is: A. Change the friction properties of wool B. Change the stretch properties of wool. No matter which method is used, the reaction should be strictly controlled and limited to a certain area of the fiber.
2. Advantages of the “subtractive” anti-felting process: uniform treatment, no yellowing, no impact on fiber strength, and the process is easier to control.
3. “Additional” anti-felting treatment: The polymer is deposited on the surface of wool fibers. The fibers are bonded together and cannot move at will, thereby obtaining the anti-felting effect. The resin should meet the following conditions: ① The formed condensation polymer should be soft and its chemical properties should be close to those of wool. ②It can be adhered to the surface, and the dosage is small and even. ③It is best to combine it with wool through chemical bonds.
4. Protease treatment method and chlorination method: Industrial treatment is relatively mature, but labor protection is poor, environmental pollution is serious, and it affects human health. With the improvement of human health requirements and environmental awareness, Enhanced, easily biodegradable protease methods are attracting attention. This method belongs to the smoothing treatment of wool surface (surface denaturation). The principle is to use protease to extract the parts of the inner layer of scales that are easily digested by enzymes. However, the middle layer above the inner layer of the scales contains high sulfur and is highly resistant to enzymatic decomposition. The sulfur bridge must be oxidized with an oxidant first to reduce its resistance to enzymatic decomposition and make it easier to digest and remove. In order to prevent the inner cuticle of wool from being enzymatically decomposed , add enough neutral salt during enzyme treatment. The treated wool not only improves its anti-shrinking properties, but also properly destroys the cross-linking of the wool due to enzyme treatment, reducing the rigidity of the fiber, making it easy to stretch but not easy to shrink, the hand feels relatively soft, and the wool becomes smooth and fine. , rich in cashmere feel.
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