The most common knowledge of shrinking textile fabrics!
The smallest shrinkage is synthetic fiber and mixed textiles, followed by wool, hemp, cotton, and silk fabric shrinkage, and the largest is viscose, rayon, artificial wool fabric.
Objectively speaking, there are some problems in shrinking and fading of cotton fabrics. The key is the finishing behind. Therefore, the fabrics of general home textiles are pre-shrinked.
It is worth noting that the pre-shrinking treatment does not mean that it does not shrink, but that the shrinkage rate is controlled at 3%-4% of the national standard. The underwear material, especially the natural fiber, will shrink. Therefore, in the purchase of clothing, in addition to the selection of fabric quality, color, pattern, the shrinkage rate of the fabric should also be known.
1. The influence of fiber and weaving
When the fiber itself absorbs water, it will have a certain degree of swelling. Generally, the swelling of the fibers is anisotropic (except for nylon), that is, the length is shortened and the diameter is increased. The percentage difference between the length of the fabric before and after the water is taken and its original length is usually referred to as the shrinkage rate. The stronger the water absorption capacity, the more intense the swelling, and 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 (filament) used, and the difference in the weaving ratio is usually used to indicate the difference between the two.
Knitting ratio (%) = [yarn (silk) thread length - fabric length] / fabric length
After the fabric is launched, the length of the fabric is further shortened due to the swelling of the fibers themselves, resulting in shrinkage. The shrinkage rate of the fabric is different, and the shrinkage rate is different. The fabric structure and the weaving tension of the fabric itself are different, and the weaving rate is different. The weaving tension is small, the fabric is tight and thick, the weaving rate is large, and the shrinkage rate of the fabric is small; the weaving tension is large, the fabric is loose and light, the weaving rate is small, and 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 pre-shrinking finishing method is often used to increase the weft density, and the weaving rate is increased in advance, thereby reducing the shrinkage rate of the fabric.
2. Reasons for shrinkage:
(1) When the fiber is spun, or when the yarn is woven and dyed, the yarn fiber in the fabric is stretched or deformed by an external force, and the yarn fiber and the fabric structure generate internal stress, and the static dry state is relaxed. , or static wet relaxation state, or in the dynamic wet relaxed state, full relaxation state, the release of different degrees of internal stress, the yarn fiber and the fabric return to the initial state.
(2) Different fibers and their fabrics have different degrees of shrinkage, mainly depending on the characteristics of the fibers - the hydrophilic fibers have a greater degree of shrinkage, such as cotton, hemp, viscose and the like; and the shrinkage of hydrophobic fibers Lesser, such as synthetic fibers.
(3) When the fiber is in a wet state, it is puffed by the action of the immersion liquid, so that the fiber diameter becomes large. For example, on the fabric, the fiber radius of curvature of the interlaced point of the fabric is forced to increase, resulting in a shortened fabric length. For example, cotton fiber puffs under the action of water, the cross-sectional area is increased by 40~50%, the length is increased by 1-2%, and the synthetic fiber is heat-shrinkage, such as boiling water shrinkage, etc., generally about 5%.
(4) Under the heating condition of textile fiber, the shape and size of the fiber change and shrink, and it cannot return to the initial state after cooling, which is called fiber heat shrinkage. The percentage of length before and after heat shrinkage is called the heat shrinkage rate. Generally, it is tested by boiling water shrinkage. In 100 °C boiling water, the percentage of fiber length shrinkage is expressed. It is also useful for hot air, hot air at over 100 °C. The percentage of shrinkage measured in the middle is also determined by the vapor method, and the percentage of shrinkage is measured in steam exceeding 100 °C. Fibers behave differently due to internal structure and heating temperature and time. For example, the boiling water shrinkage of processed polyester staple fiber is 1%, the shrinkage of vinylon boiling water is 5%, and the shrinkage ratio of colloidal silica is 50%. Fiber has a close relationship with the dimensional stability of textile processing and fabrics, providing some basis for the design of the post-process.
3. The shrinkage rate of general fabrics:
Cotton 4% -10%;
Chemical fiber 4% - 8%;
Cotton polyester 3.5% - 5 5%;
The natural white cloth is 3%;
Blue cloth is 3-4%;
Poplin is 3-4.5%;
Flower cloth is 3-3.5%;
Twill is 4%;
Labor cloth is 10%;
Artificial cotton is 10%.
4. Reasons for the impact of shrinkage rate:
1. Raw materials
The raw materials of the fabric are different and the shrinkage rate is different. In general, a fiber having a large hygroscopicity expands after immersion in water, has an increased diameter, a shortened length, and a large shrinkage rate. If the viscose fiber has a water absorption rate as high as 13%, and the synthetic fiber fabric has poor hygroscopicity, the shrinkage rate is small.
The density of the fabric is different and the shrinkage rate is also different. If the latitude and longitude density are similar, the warp and weft shrinkage rate is also close. The fabric with high density has a large shrinkage in the warp direction. On the contrary, the weft density is larger than that of the dense fabric, and the weft shrinkage is also large.
3, the thickness of the yarn
The yarn thickness of the fabric is different, and the shrinkage rate is also different. The shrinkage rate of the coarse yarn is large, and the shrinkage of the fine fabric is small.
4, production process
The fabric production process is different and the shrinkage rate is also different. Generally, in the weaving and dyeing process of the fabric, the fiber is stretched a plurality of times, the processing time is long, and the shrinkage rate of the fabric with a large applied tension is large, and vice versa.
5, fiber composition
Natural plant fibers (such as cotton and hemp) and plant regenerated fibers (such as viscose) are more hygroscopic and expandable than synthetic fibers (such as polyester and acrylic), so the shrinkage rate is higher, while wool is due to the scale structure of the fiber surface. It is easy to felt and affect its dimensional stability.
6, fabric structure
In general, the dimensional stability of woven fabrics is superior to that of knitted fabrics; the dimensional stability of high-density fabrics is better than that of low-density fabrics. In the woven fabric, the shrinkage ratio of the plain woven fabric is generally smaller than that of the flannel fabric; in the knitted fabric, the shrinkage ratio of the plain stitch structure is smaller than that of the rib fabric.
7, production and processing
Since the fabric is in the process of dyeing, printing, and finishing, it is inevitably stretched by the machine, so that tension exists on the fabric. However, the fabric is easily relieved of tension after it has been exposed to water, so we will find that the fabric shrinks after washing. In the actual process, we generally use pre-shrinkage to solve this problem.
8, washing care process
Washing care includes washing, drying, and ironing. Each of these three steps affects the shrinkage of the fabric. For example, hand-washed samples are more dimensionally stable than machine-washed samples, and the temperature of the wash also affects dimensional stability. In general, the higher the temperature, the worse the stability. The drying method of the sample has a relatively large influence on the shrinkage rate of the fabric.
Commonly used drying methods include drip drying method, metal mesh tiling method, hanging dry drying method and drum drying method. Among them, the drip drying method has the least influence on the size of the fabric, and the drum arching method has the greatest influence on the size of the fabric, and the other two are in the middle.
In addition, the selection of a suitable ironing temperature depending on the composition of the fabric can also improve the shrinkage of the fabric. For example, cotton and linen fabrics can be improved in size by high temperature ironing. But the higher the temperature, the better. For synthetic fibers, high-temperature ironing can not improve its shrinkage, but it will damage its performance, such as hard and brittle fabrics.