How much do you know about the various methods of knit wear pretreatment?

- 2021-10-18-

How much do you know about the various methods of knitwear pretreatment?

一、Pretreatment of knitted fabrics

Knitted fabric has soft feel, good air permeability, flexibility, comfortable to wear. Often used to make sweaters, cotton sweaters, sports shirts, gloves and socks, etc. Knitted fabrics are composed of coils, so the structure is loose, easy deformation under the action of external forces, can not withstand larger tension, so the fabric must be kept loose when processing, and the use of low tension processing equipment, at the same time should be as far as possible to shorten the processing process.

二、Pretreatment of cotton knitting

The main products of cotton knitting are sweat cloth, cotton wool cloth and so on. Knitting yarn is not starched before weaving, so there is no size on the fabric. In the pre-treatment process, there is generally no singing or desizing, but only scouring, bleaching and softening. Some varieties (such as sweatcloth) also need alkali shrinkage, in order to increase the density and elasticity of the fabric, cotton knitting material pretreatment process mainly has the following forms.

A. Bleaching process: grey cloth → alkali shrinkage → scouring → sodium hypochlorite bleaching → hydrogen peroxide bleaching → whitening → soft treatment → dehydration → drying

B. Dyeing process: grey cloth → alkali shrinkage → scouring → sodium hypochlorite bleaching → dyeing (printing) → finishing

C. Dyeing process: grey cloth → scouring → bleaching with sodium hypochlorite → dyeing (printing) → finishing

bleaching

Knitted fabrics can be bleached with sodium hypochlorite, hydrogen peroxide and sodium chlorite.Sodium hypochlorite bleaching effect is general, and easy to damage the fiber, has a great impact on the environment, but its low cost, simple equipment, so it is still widely used in cotton knitting bleaching, has been gradually replaced by hydrogen peroxide.

The hydrogen peroxide bleaching effect is good, the fiber damage is small, has a certain ability to remove impurities, it is not only suitable for cotton, but also can make other fibers get good bleaching effect, so it is especially suitable for cotton and synthetic fiber blended fabric bleaching.

三、 Pretreatment of polyester knitted fabric

The purpose of polyester knitted fabric pretreatment is to remove the oil and antistatic agent applied to the fiber during spinning and the oil stain during weaving. Any fabric that takes shape before dyeing should be pre-treated so as to avoid defects caused by oil stains and impurities sticking to the fabric during heat setting.For the pretreatment of polyester knitted fabric, 0.5%~1%(the weight of the fabric) soap or synthetic detergent solution can be used to add a small amount of soda, treated at 80~90℃ for about 30min, and then washed with hot water or cold water.

Pure polyester knitted fabric does not need to be bleached, because polyester itself is very white, even if it is extremely white, it can meet the whiteness requirements only by fluorescent whitening.


Sodium chlorite not only has good bleaching effect, but also has small damage to fiber and strong ability to remove impurities. It is an ideal bleaching agent with wide adaptability to fiber. However, its high cost, strong corrosive to the equipment, the release of toxic gases when bleaching, has a great impact on the environment, so the use of great restrictions. The bleaching process and conditions of knitted fabric are similar to those of cotton cloth. Products requiring high whiteness also need to be repeated bleaching and fluorescent whitening processing.

四、Pretreatment of medium and long chemical fiber fabrics

Medium length chemical fiber fabrics are mainly polyester viscose wave fabrics, and there are polyester and nitrile blended medium length fiber fabrics and polyester and nitrile blended medium length fiber fabrics. Long chemical fiber fabrics are wool-like fabrics. Thick fabrics require a plump, fluffy, elastic and thick wool-like style. The actor actor of these styles depends on the quality of dyeing and finishing processing.

Medium and long chemical fiber fabric does not contain natural impurities, and the scouring and bleaching process is simpler, requiring only singing, desizing and heat setting. In order to improve the wool - like effect, it is necessary to adopt loose processing technology before treating medium and long chemical fiber fabric.

singeing

Using less fire mouth, strong flame, fast speed of the process. The arrangement order of the singing process can be determined according to the factory conditions and the requirements of the varieties. For the varieties dyed with high temperature and high pressure, the singing should be carried out after dyeing to avoid affecting the evenness of dyeing.

desizing

Desizing is in loose, wet heat processing, so that the fabric can be desizing at the same time fully shrink, so as to obtain fluffy and plump hair style. Medium and long chemical fiber fabric size PVA as the main size, can use alkali desizing or oxidant desizing. After alkali desizing, the fabric feel is slightly rough and hard, and the color is slightly darker under the same hot melt condition. Can also use detergent desizing, desizing fabric feel soft, better elasticity, easy to pull. After desizing and washing, it is washed again on the loose washing machine and then dried on the loose dryer.

Heat setting

Setting temperature to 190℃ is appropriate. Setting before dyeing can ensure dimensional stability in dyeing process, reduce wrinkle and improve dyeing quality.