Why do yarns need sizing? What are the sizing requirements?

In weaving, the warp has to bear the action of various forces and undergo complex deformation. From the basic movement of the loom:

(1) When the opening movement occurs, the warp is bent into a broken line at the heald eye by the generally flat heald line, and elongation is proportional to the square of the shed height. At the same time, due to the asymmetry of the length of the front and back of the shed, the warp slips in the heald eye, resulting in friction. In the opening movement, when the upper and lower warp rises and falls alternately, violent friction occurs between each other.

(2) During the weft insertion movement, the shuttle of shuttle loom relies on the shed and frictions during the passage. Especially when entering and exiting the shed, the warp yarn at the edge is squeezed to a large extent, which causes bending, elongation and friction. The weft guide parts of shuttle-free loom also have considerable frictions on the warp yarn.

(3) During beating, the warp at the front of the shed is rubbed by the reciprocating reed teeth. Because of the shrinkage, the extrusion friction between the reed tooth and the edge warp is more intense. The friction between the warp and the heald eye will be increased by the forward and backward movement caused by each beating in the weft area.

(4) In the let-off and coiling movement, there is always a certain brake tension when the warp is sent out on the weaving shaft. Most of the existing let-off mechanisms belong to tension regulating let-off mechanisms which control the amount of let-off by the sensor feedback of warp tension. Therefore, when the warp with weak joints passes through the back beam, it begins to break. The coiling movement will also affect the warp tension, and form the elastic and plastic deformation system of warp with warp letting, filling beating and opening.

It can be seen that the forces and deformations of the warp yarn in the weaving process are mainly formed by tension (which is required not to cause breakage), elongation (which can be restored by cyclic deformation) and friction (which is not to cause pilling, pilling and grinding).

At the same time, it is worth paying attention to the hair problem. In the opening of the warp, the hair will be entangled with each other, making the opening unclear, resulting in defects such as yarn jumping, flower jumping and warp hanging that are difficult to eliminate. In filling insertion of air-jet loom, the filling blocking caused by unclear opening is the main factor affecting the efficiency. Therefore, reducing hairiness is an important index.

In view of the above situation, in order to improve the weaving performance of warp yarn, sizing is an effective method adopted in knitting preparation engineering. In other words, the slurry with adhesive material as the main body is applied to the warp yarn, which acts on the surface of the warp yarn to a certain depth, and forms the sizing structure of the pulp and yarn integrated after drying.

The improvement of warp performance after sizing should be to enhance, extend, wear resistance and stick hairiness. Through sizing, the single filament sticks to each other and has the ability of bunching, preventing the filament from flaring or breaking, and inhibiting the elasticity of the filament, making it easy to operate. Staple yarn meridian stretch yarn and strong twist yarn also need sizing to prevent retraction, in order to smooth production. The final purpose of sizing is: good pulp axis, less defects, low number of broken ends, high weaving efficiency, and improve the weavability of warp.

The specific requirements are:

(1) Increase yarn breaking strength. Appropriate increase in strength is necessary, but if excessive pursuit of size strength increase, is bound to make the yarn hard and brittle, lose elasticity, but easy to break. The strengthening rate of pure cotton yarn is generally controlled at 25% ~ 40%, polyester/cotton yarn L0% ~ 25%, pure polyester yarn 10% ~ 20%, polyester/viscose and pure viscose yarn >25%.

(2) Maintain yarn elongation at break. Cotton yarn elongation rate is generally 7%, sizing should be maintained at 4%-5%, in order to facilitate weaving, so elongation rate ≤30%, polyester/cotton, polyester/viscose yarn ≤25%, pure viscose yarn ≤35%.

(3) Improve wear resistance. Because the wear-resisting test has not been standardized, the wear-resisting rate of various slurry formulations is also very different.

(4) Hair reduction rate. Using YGl7lB yarn hairiness tester and BT 1 2 on-line hairiness tester, the advanced index of hairiness reduction rate before and after sizing is more than 75%.

(5) good axis rate of weaving shaft. It is required that the sizing yarn has no broken end, long head, sticking, twisted end, light pulp pilling, weaving has no defect such as pulling edge, and the advanced level of good shaft rate is above 60%.

(6) Number of warp breaks of loom. Shuttle loom should be 1 /(Taiwan •h) below, shuttless loom 100 000 weft broken number required 10-15 below.

As the grey cloth for printing and dyeing finishing, in addition to the requirements of weaving, it also requires easy desizing, and desizing waste liquid pollution-free to the environment. The selection and proportion of slurry must be considered.

As a finished fabric, it is required to give the fabric unique style and feel, and it must be adjusted appropriately in the types of sizing material, oil agent and sizing rate.