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Yantai Hailian Printing and Dyeing Machine Co., Ltd
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How to do fabric retraction well shared by pre shrinking machine manufacturers?
As we all know, clothing should shrink before processing, commonly known as "shrinkage" processing, belongs to the category of fabric finishing. Under normal circumstances, most clothing enterprises will not buy pre shrinking machine because of the requirement of "pre shrinking" in this process. The supplier only needs to finish the pre shrinkage process from the supplier.
But this is not the case. When there are higher requirements for clothing quality indicators; when fabrics are commonly used in products (such as elastic fabrics, easy to deform fabrics, etc.). ）In terms of dimensional stability, it is relatively strict (shrinkage and stretching); when there are many changes in styles and fabrics, and there are few batches, there will be fabric upgrading and the added value of clothing products will increase. For such a clothing factory (especially a suit factory), it is still necessary to buy a pre shrinking machine to "pre shrink" the fabric before cutting.
Shrinkage effect of fabric (pre shrinkage mechanism);
The reason why fabrics need pre shrinkage is that they have shrinkage effect. According to the research of textile materials, the shrinkage effect can be divided into three categories: natural shrinkage of elastic recovery of fiber; hydrophilic hygroscopic expansion and contraction of fiber in chemical structure; and thermal shrinkage of fiber. The specific methods are as follows:
1. Water absorption shrinkage
The anisotropic expansion of hydrophilic fibers is the main cause of fabric shrinkage. The better the hygroscopicity of hydrophilic fiber is, the greater the shrinkage of fabric is. The results show that the length and diameter of hydrophilic fibers increase when they are wetted by water, but the increase of diameter is far greater than that of length.
Compared with cotton fiber and viscose fiber, cellulose and protein fiber have better hygroscopicity and swelling property. After absorbing water, the fiber expands and coarsens, and the yarn diameter becomes larger and larger. After drying, the fiber and yarn almost return to the original thickness. As a result of this "one by one relaxation", the accumulated elongation deformation (also known as residual deformation) in the fabric is completely "released". At the same time, the original winding mode of longitude and weft changes and moves due to expansion. Therefore, after the hydrophilic fabric is dried in water, the area will be reduced, the thickness will be increased, and the surface will become uneven.
The design idea of the damp heat pre shrinking machine is to use the water absorption and shrinkage characteristics of the fabric, and the pre shrinking process is spray wet drying.
It is especially pointed out that viscose fiber has short molecular chain, many amorphous regions, loose structure, high swelling rate, low wet modulus and severe shrinkage. Even after mechanical pre shrinking, it may not be possible to solve the problem sometimes.
2. Natural contraction
The fabric is constantly stretched in the process of processing, resulting in accumulated elongation deformation of yarn and fiber. The greater the tension, the more stress and deformation accumulated. After the tension disappears, the elastic deformation in the accumulated deformation will be released, which will reduce the length and size of the fabric, resulting in natural shrinkage. In production, some fabrics (such as elastic fabrics) usually need to be placed for a period of time (usually 24 hours) before cutting, so as to give the fabric enough time for natural shrinkage. Natural shrinkage is also a pre contraction method.
3. Chemical thermal contraction
Synthetic fibers (e.g. polyester, etc.). ）Thermal shrinkage occurs during processing and use. The main reason is that when the fiber temperature exceeds the glass transition temperature, the orientation structure and crystal structure of the fiber will change. From the macroscopic point of view, the shrinkage of fiber length will directly reflect the change of fabric length and width. The "stretch setting and high temperature steaming" pre shrinkage of synthetic fabrics takes advantage of this property. When ironing polyester and other synthetic fabrics, the temperature should be strictly controlled to avoid heat shrinkage.
It is specially pointed out that due to the characteristics of strong water absorption and pile shrinkage of wool fabric, the mechanical pre shrinkage of wool fabric is usually carried out by "low temperature steam and cooling" under "no tension state", and the washing of wool fabric is also required to be carried out at room temperature.