Good pre-treatment is half of successful dyeing

1. Batch management of raw blanks (or yarns):

Some experts say: 30% technology, 70% management; some experts say: 20% technology, 80% management. In the dyeing and finishing industry of applied chemistry, when the technology develops to a certain level, the management level determines the technology and quality level of an enterprise.

Therefore, before talking about pre-treatment, we should emphasize the batch management of raw blanks (or yarns). The same batch is dyed according to the same process, and when changing batches, there must be a proofing and tracking procedure. After the batch of dyed objects is changed, 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 for sizing woven fabrics. In order to facilitate weaving, most woven fabrics need to be sizing before weaving. Speaking of desizing, we have to mention the three major sizings in the textile sizing industry: starch and derivatives, polyvinyl alcohol (PVA), and acrylic sizing. PVA has been gradually eliminated due to environmental protection issues, and most of the sizing used now is starch and acrylic sizing.

The four most commonly used desizing methods are hot water desizing, alkaline desizing, enzyme desizing, and oxidative desizing. Enzyme desizing and alkaline desizing are now more commonly used, and enzyme desizing (amylase) is mainly for starch sizing. The quality of desizing is generally evaluated by the desizing level. Among the three major sizings, acrylic sizing is easier to remove, while starch sizing and PVA both have simple and fast testing methods (such as iodine/potassium iodide method.) Insufficient desizing will affect the dyeing rate during dyeing, or cause the fabric to feel worse.

3. Degreasing:

Degreasing is mainly for chemical fiber fabrics (or yarns), such as polyester, nylon, etc. Incomplete degreasing will also affect the dyeing and cause oil spots, color spots and other problems. Degreasing is generally carried out under alkaline conditions with a degreasing agent at high temperature. The selection of a good degreasing agent helps to improve the degreasing effect. Now, 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.

Related reading: What oils should be removed in polyester pre-treatment degreasing?

4. Weight reduction:

Fiber opening is also for chemical fiber fabrics, such as polyester microfiber, sea 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 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 for natural fibers and regenerated cellulose fibers, the purpose is to remove impurities such as grease, wax, pectin, etc. on the fibers. Similarly, scouring is mostly alkali high-temperature scouring, and there are many methods such as cold pile, continuous long car, and intermittent. The main indicator for assessing scouring is the wool effect, and the wool effect directly affects the dyeing rate and uniformity. Pad dyeing (left, middle, right) and cheese yarn (inside, middle, and outside) dyeing have higher requirements for wool effect. For specific wool effect test methods, please refer to the article: Commonly used test methods for water absorption of textiles. Another indicator of scouring is weight loss. In principle, the higher the weight loss, the better the scouring effect, but excessive weight loss also leads to a decrease in the manufacturing rate and an increase in cost. .

6. Bleaching:

Bleaching is also for natural fibers and regenerated cellulose fibers. It is usually called bleaching with one-bath scouring. 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 (insurance powder). The indicator for measuring bleaching is whiteness. For sensitive colors and bright colors, the stability of bleaching whiteness is critical. The measurement of whiteness can be compared with the naked eye or tested by a whiteness meter.

7. Summary:

In order to improve the one-time success rate of dyeing, all indicators of pre-treatment need to be controlled, such as: desizing level, oil removal rate, fiber opening rate, gross effect, weight loss, whiteness and other indicators. Through the testing and control of indicators, the pre-treatment process can be formulated and corrected. After the current treatment indicators are stable, successful dyeing is half successful.