Good pre-treatment is half the success of dyeing

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Update time : 2024-06-12

Good pre-treatment is half the success of dyeing

1. Batch management of raw materials (or yarn):

Some experts say: three points of technology, seven points of management; some experts say: two points of technology, eight points of management. In dyeing and finishing, an industry that applies chemistry, when technology develops to a certain level, management level determines the technology and quality level of an enterprise.

Therefore, before talking about pre-processing, it is important to emphasize the batch management of raw materials (or yarns). The same batches are dyed according to the same process. When changing batches, there must be a proofing and tracking program. The dyed objects are changed in batches. Finally, the process must be adjusted in a timely manner based on the proofing comparison. Good batch management and control reflects the level of a dyeing factory.

2. Desizing:

Desizing is for sizing woven fabrics. In order to facilitate weaving, most woven fabrics need to be sized before weaving.
Speaking of desizing, we have to mention the three major sizing materials in the textile sizing industry: starch and derivatives, polyvinyl alcohol (PVA), and acrylic sizing. PVA has been gradually phased out due to environmental issues, and most of them are now used in combination with starch and acrylic slurry.

Four commonly used desizing methods: hot water desizing, alkali desizing, enzyme desizing, and oxidative desizing. Enzyme desizing and alkali desizing are currently used more frequently, and enzyme desizing (amylase) is mainly targeted at starch sizing. The quality of desizing effect is generally evaluated by the level of desizing. Among the three major slurries, acrylic slurry is easier to remove, while starch slurry and PVA both have simple and fast test methods (such as iodine/potassium iodide method.)
Insufficient desizing will affect the coloring rate of the dye during dyeing, or cause the fabric's feel to deteriorate.

3. Remove oil:

Oil removal is mainly targeted at chemical fiber fabrics (or yarns), such as polyester, nylon, etc. Incomplete oil removal will also affect the coloring of dyes and cause oil spots, stains and other problems. Degreasing is generally carried out under alkaline conditions with a degreaser and high temperature. Choosing a good degreaser will help improve the degreasing effect. Nowadays, in order to optimize the process flow, there are many degreasing and dyeing baths suitable for chemical fibers. When choosing, pay attention to the high temperature resistance and dispersion performance of the degreasing agent in the same bath.

4. Reduction:

Fiber opening is also for chemical fiber fabrics, such as polyester microfiber, island fiber, polyester-nylon blended fiber, etc. The fiber opening of polyester is also called alkali weight reduction. The excellent fiber opening affects the color fastness of dyeing and the color and light stability of dyeing. The fiber opening effect is generally controlled by the weight loss rate of fiber opening.

5. Refining:

Refining mainly targets natural fibers and regenerated cellulose fibers, with the purpose of removing impurities such as grease, wax, and pectin from the fibers. Similarly, refining is mostly alkali high-temperature refining, and there are many methods such as cold stack, continuous long car, and intermittent refining. The main index for assessing refining is wool efficiency, which directly affects the coloring rate and uniformity of the dye. Pad dyeing (left, middle and right) and cheese dyeing (inside, middle and outside) have higher requirements for wool effect. For specific wool effect testing methods, please refer to the article: Commonly used testing methods for textile water absorption

Another indicator of refining is weight loss. In principle, the higher the weight loss, the better the refining effect. However, excessive weight loss also reduces the production rate and increases the cost.

Good pre-treatment is half the success of dyeing(pic2)

6. Bleaching:

Bleaching is also targeted at natural fibers and regenerated cellulose fibers. The one-bath treatment with scouring is commonly referred to as scouring and bleaching. The purpose of bleaching is to remove pigments to achieve the whiteness required for dyeing. Common bleaching processes include oxidative bleaching (hydrogen peroxide, sodium hypochlorite, etc.) and reduction bleaching (safety powder). The indicator of bleaching is whiteness. For sensitive and bright colors, the stability of bleaching whiteness is critical. Whiteness can be measured with the naked eye or with a whiteness meter.

7. Summary:

In order to improve the one-time success rate of dyeing, various indicators of pre-treatment need to be controlled, such as: desizing level, oil removal rate, fiber opening rate, wool efficiency, weight loss, whiteness and other indicators. Through the testing and control of indicators, To formulate and revise the pre-treatment process, once the various indicators of the current treatment are stable, successful dyeing will be half successful.

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Good pre-treatment is half the success of dyeing

Good pre-treatment is half the success of dyeing

1. Batch management of raw materials (or yarn):

2. Desizing:

4. Reduction:

5. Refining:

6. Bleaching:

7. Summary:

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