The lowest shrinkage rate is synthetic fiber and blended textiles, followed by wool, hemp, cotton, silk fabric shrinkage is larger, and the largest is viscose fiber, artificial cotton, artificial wool fabrics. Objectively speaking, cotton fabrics more or less have the problem of shrinking and fading, the key is the finishing behind. Therefore, the general fabric of home textiles is preshrunk. It is worth noting that after pre-shrinkage treatment is not equal to no shrinkage, but refers to shrinkage rate control in the national standard 3%-4% clothing material, especially natural fiber clothing material will shrink. Therefore, in the choose and buy clothing material, in addition to the quality of the fabric, color, pattern selection, shrinkage rate of the fabric should also be understood.
The influence of fiber and weaving shrinkage fiber itself after absorbing water, will produce a certain degree of swelling. Usually the swelling of fiber is anisotropic (except nylon), that is, the length of shortening, the diameter of the increase. The length difference between the fabric before and after the water and the percentage of its original length is usually called shrinkage. The stronger the water absorption capacity, the more intense the swelling, the higher the shrinkage rate, the worse the dimensional stability of the fabric. The length of the fabric itself is different from the length of the yarn (silk) used, and the difference is usually expressed in terms of the shrinkage. Shrinkage (%) =[yarn (silk) thread length - fabric length]/ Fabric length After the fabric is in the water, due to the swelling of the fiber itself, the fabric length is further shortened, resulting in shrinkage rate. The shrinkage rate of the fabric is different, the size of the shrinkage rate is different. The fabric fabric structure and weaving tension are different, its shrinkage rate is different. The weaving tension is small, the fabric is tight and thick, the shrinkage rate is large, the shrinkage rate of the fabric is small; Weaving tension is large, the fabric is loose and thin, the shrinkage rate is small, the shrinkage rate of the fabric is large. In the dyeing and finishing process, in order to reduce the shrinkage rate of the fabric, the way of pre-shrinkage finishing is often used to increase the filling density and increase the shrinkage rate in advance, so as to reduce the shrinkage rate of the fabric.
The causes of shrinkage:
1. fiber during spinning, or yarn in weaving and dyeing and finishing, the fabric of the yarn fiber elongation by external force or deformation, stress in fiber yarn and fabric structure at the same time, in the static dry relaxation state, or static wet relaxation condition, or in a dynamic wet relaxation condition, total relaxation condition, different degree of internal stress release, Make the yarn fiber and fabric return to the initial state. 2. Different fibers and fabrics, the shrinkage degree is different, mainly depends on the characteristics of the fiber - hydrophilic fiber shrinkage degree is larger, such as cotton, hemp, viscose fibers; The shrinkage degree of hydrophobic fiber is less, such as synthetic fiber.
2. In the wetting state, the fiber expands due to the action of the immersion solution, which increases the diameter of the fiber. For example, on the fabric, the radius of the fiber curvature at the interleaved point of the fabric is forced to increase, resulting in the shortening of the fabric length. For example, cotton fiber expands under the action of water, and the cross-sectional area increases by 40~50%, and the length increases by 1~2%, while synthetic fibers shrink by heat, such as boiling water shrinkage, and so on, generally about 5%.
4. When the textile fiber is heated, the shape and size of the fiber change and shrink, and can not return to the initial state after cooling, which is called fiber thermal shrinkage. The percentage of length before and after thermal shrinkage is called thermal shrinkage rate, generally by boiling water shrinkage test, in 100℃ boiling water, the percentage of fiber length shrinkage as expressed; The percentage of shrinkage can also be measured in hot air above 100 ° C, or in steam above 100 ° C. Fiber performance is also different under different conditions due to internal structure and heating temperature and time. For example, the boiling water shrinkage rate of polyester staple fiber is 1%, the boiling water shrinkage rate of vinylon is 5%, and the hot air shrinkage rate of chloramide is 50%. There is a close relationship between fiber processing and dimensional stability of fabric, which provides some basis for the design of the following process.
The reasons affecting shrinkage rate:
1. The raw materials of raw materials are different, and the shrinkage rate is different. Generally speaking, the fiber with large hygroscopicity, after soaking in water, the fiber expands, the diameter increases, the length shortens, the shrinkage rate is large. If some viscose fiber water absorption rate as high as 13%, and synthetic fiber fabric hygroscopicity is poor, its shrinkage rate is small. 2, density fabric density is different, shrinkage is also different. If the warp and weft density is similar, the warp and weft shrinkage is also similar. The density of the fabric, the shrinkage will be large, conversely, the weft density is greater than the density of the fabric, the weft shrinkage will be large. 3, yarn thickness fabric is different, shrinkage rate is also different. The shrinkage rate of the fabric with thick yarn count is higher, and the shrinkage rate of the fabric with thin yarn count is lower. 4, production process fabric production process is different, shrinkage rate is different. Generally speaking, in the process of weaving and dyeing, the fiber should be stretched many times, the processing time is long, and the shrinkage rate of the fabric with larger tension is large, and vice versa. 5, fiber components of natural plant fiber (such as cotton, hemp) and plant regeneration fiber (such as viscose) compared with synthetic fiber (such as polyester, acrylic), easy to hygroscopic expansion, so the shrinkage rate is larger, and wool is due to the fiber surface of the scale structure and easy felt, affecting its dimensional stability. 6, fabric structure in general, the dimensional stability of woven fabric is better than knitted fabric; The dimensional stability of high-density fabrics is better than that of low-density fabrics. In woven fabric, the shrinkage rate of plain fabric is less than that of flannel fabric. In knitted fabric, the shrinkage of plain knitted fabric is smaller than that of ribbed fabric. 7. In the process of production and processing, the fabric will inevitably be stretched by the machine in the process of dyeing, printing and finishing, so that there is tension on the fabric. However, the tension of the fabric is easily relieved after being exposed to water, so we may find that the fabric shrinks after washing. In the actual process, we usually use pre-shrinkage to solve this problem. 8, washing care process washing care includes washing, drying, ironing, each of these three steps will affect the shrinkage of the fabric. For example, the dimensional stability of hand-washed samples is better than that of machine-washed samples, and the washing temperature will also affect the dimensional stability. Generally speaking, the higher the temperature, the worse the stability. The drying method of the sample also has a great influence on the shrinkage of the fabric. Commonly used drying methods are, drip drying method, metal mesh tiling method, hanging dry drying method and rotary drying method. Among them, drip drying method has the least effect on the fabric size, while rotary cylinder arch drying method has the greatest effect, and the other two methods are in the middle. In addition, choosing a suitable ironing temperature according to the composition of the fabric can also improve the shrinkage of the fabric. For example, cotton and linen fabrics can be ironed at a high temperature to improve their size reduction. But not the higher the temperature, the better, for synthetic fibers, high temperature ironing can not improve its shrinkage, but will damage its performance, such as fabric hair hard hair brittle.
