1、 Batch management of raw material (or yarn):
The batch management of raw material (or yarn) is very important. The same batch is dyed according to the same process. When changing the batch, there must be a proofing and tracking procedure. After the dye batch is replaced, the process should be adjusted in time according to the proofing comparison. Good batch management control reflects the level of a dyeing factory.
2、 Desizing:
Desizing is aimed at the starched woven fabric. In order to facilitate weaving, most woven fabrics need to be starched and woven.
When it comes to desizing, we have to mention the three major sizes in the textile size industry: starch and derivatives, polyvinyl alcohol (PVA) and acrylic size. PVA has been phased out due to environmental protection problems, and now most of the starch and acrylic size are used together. Four common desizing methods: hot water desizing, alkali desizing, enzyme desizing and oxidation desizing. At present, enzyme desizing and alkali desizing are widely used, and enzyme desizing (amylase) is mainly aimed at starch size. The desizing effect is generally evaluated by desizing level. Among the three sizes, acrylic size is relatively easy to remove, while starch size and PVA have simple and rapid test methods (such as iodine / potassium iodide method)
Insufficient desizing will affect the coloring rate of the dye or cause the hand feel of the fabric to deteriorate.
3、 Degreasing:
Degreasing is mainly aimed at chemical fiber fabrics (or yarns), such as polyester, nylon, etc. if the degreasing is not clean, it will also affect the coloring of dyes and cause oil spots, color spots and other problems. Degreasing is generally carried out at high temperature with degreasing agent under alkaline conditions. The selection of good degreasing agent will help to improve the degreasing effect. Now, in order to optimize the process flow, there are many same baths suitable for degreasing and dyeing of chemical fibers. When choosing, pay attention to the high temperature resistance and dispersion performance of the same bath degreaser.
4、 Decrement:
Fiber opening is also aimed at chemical fiber fabrics, such as polyester microfiber, sea island fiber, polyester nylon blended fiber, etc. the fiber opening of polyester is also known as alkali reduction. The excellent fiber opening affects the color fastness and color light stability of dyeing. Generally, the fiber opening effect is controlled by the weight loss rate of fiber opening.
5、 Refining:
Refining is mainly aimed at natural fiber and regenerated cellulose fiber, and the purpose is to remove impurities such as oil, wax and pectin on the fiber. Similarly, alkali high-temperature refining is the main refining method, including cold pile, continuous long car, intermittent and other methods. The main index for assessing scouring is wool effect, which directly affects the coloring rate and uniformity of dyes. Pad dyeing (left, middle and right) and bobbin dyeing (inside, outside and inside) have higher requirements for wool efficiency. For specific test methods of wool efficiency, please refer to article: Common test methods for water absorption of textiles
Another index of scouring is weight loss. In principle, the higher the weight loss, the better the scouring effect. However, excessive weight loss also leads to the reduction of production rate and the increase of cost..
6、 Bleaching:
Bleaching is also aimed at natural fibers and regenerated cellulose fibers. One bath treatment with scouring is commonly referred to as scouring and bleaching. The purpose of bleaching is to remove the pigment to achieve the whiteness required for dyeing. Common bleaching processes include oxidative bleaching (hydrogen peroxide, sodium hypochlorite, etc.) and reductive bleaching (insurance powder). The index to measure bleaching is whiteness. For sensitive and bright colors, the stability of bleaching whiteness is very important. The measurement of whiteness can be compared with the naked eye or tested with a whiteness meter.
7、 Summary:
In order to improve the one-time success rate of dyeing, various indicators of pretreatment need to be controlled, such as desizing level, degreasing rate, fiber opening rate, gross efficiency, weight loss, whiteness and other indicators. Through the test and control of indicators, the pretreatment process can be formulated and modified. After the current treatment indicators are stable, the successful dyeing will be half successful.
