At present, the more popular dyeing process is: roving → pickling → sub-bleaching → oxygen bleaching → washing → dyeing → washing → wet spinning → drying → winding. This process not only has lower cost, saves energy and reduces pollution, but also the production process is easy to control and the product quality is stable.
1 Characteristics of flax fiber Flax is a natural fiber. The fiber itself contains a lot of impurities. Cellulose only accounts for about 70%, while impurities such as pectin, lignin, wax, and ash account for about 30%. Due to the presence of the above impurities, the binding process of reactive dyes and cellulose is seriously hindered, resulting in the dyeing reaction not being able to diffuse from the high level with high dye concentration to the low level with low dye concentration, resulting in color flowers, opaque dyeing, and uneven dyeing. and other phenomena. Because flax fiber is a bundle fiber, it must be split to a count suitable for spinning. Impurities such as pectin and lignin affect the spinning performance, so the above impurities must be removed to increase the fiber count and make the fiber roots in the spun yarn section The number is increased, thereby achieving the purpose of improving fiber spinning performance. With the removal of impurities, the wool effect and whiteness of the fiber increase, making the color of the linen yarn more vivid and bright.
2. Design and control of roving and boiling and bleaching processes. When dyeing rovings, the process control of the pre-spinning roving process is as follows: fixed weight management is required between pots, and the net weight of each pot of roving before bleaching is controlled between 380kg-390kg. The winding density is controlled at 0﹒37-0﹒38, and the roving must be screened before bleaching. First of all, it is necessary to control poor forming and bread yarns, loose yarns, loose yarns, soft and hard edges, etc. to ensure that the above defective yarns are not used; secondly, strictly control the boiling and bleaching loss rate within 10%. Taking the above measures can ensure that The color difference between pots, within one pot, and between the inner and outer layers of the roving is controlled to a minimum range, and the dyeing color of the roving can be guaranteed to be consistent and uniform, without color streaks and color flowers. The roving boiling and bleaching process should be specifically adjusted based on comprehensive factors such as the origin of the flax, the color of the dye, and the count of the spun yarn. The alkalinity is controlled at (14±0﹒1)mL, the fire alkali is 5﹒8g/L, the pure alkali is 5﹒4g/L, the temperature is 100℃, and the time is 60min. The structure and chemical composition of flax fiber are hydrolyzed by pectin under the action of strong alkaline, and part of the lignin fixed on the fiber surface undergoes sulfonation degradation, and its degradation products are cracked during the decomposition.
3. The purpose of pickling is to neutralize the residual alkali remaining on the roving and remove impurities such as ash produced during the retting process. At the same time, hemicellulose and pectic polysaccharides are sensitive to acid and are easily hydrolyzed into pectic acid; removing fiber Iron and other metal ions simultaneously react with alkali to degumming, keeping the hydrogen peroxide stable and improving the bleaching effect. By properly controlling various influencing factors, the degree of reaction can be controlled. Flax fiber can be treated with concentrated sulfuric acid 2g/L, temperature 30℃, and time 20min without significant decrease in fiber strength.
4. Chlorine bleaching: Flax fiber contains a large amount of lignin and other impurities. In order to remove lignin while causing little damage to the fiber, sodium chlorite is used to bleach the fiber. Sodium chlorite selectively attacks flax fibers and only oxidizes aldehyde groups into carboxyl groups, which not only achieves the purpose of bleaching but also reduces the weight loss and damage of the fiber. Improper controlled process conditions will seriously damage the fiber, so the process conditions are determined based on the origin of the raw materials and the roughness and hardness of the hemp: acidity H2SO4 2﹒3g/L, penetrant Laonil2R 0﹒6g/L, NaClO2 2﹒7g/ L-3﹒4g/L, NaNO31﹒6g/L, heat preservation at 50℃ for 40min. Through the control of the above process conditions, part of the fiber impurities can be removed, and the wet strength of the roving can be controlled to a certain extent before dyeing.
5 Oxygen bleaching Oxygen bleaching process of roving: H2O2 concentration 1﹒8ｇ/L, alkali liquid 3﹒6g/L (its formula: sodium hydroxide﹕sodium carbonate=1﹕2), pH value between 11-11﹒5, silicon Sodium acid acid 4﹒8ｇ, and the silicone-free hydrogen peroxide stabilizer SOF is 0﹒3g, which can reduce heavy metal ions in the silicate complex, prevent catalytic oxidation and premature decomposition of hydrogen peroxide, improve hydrogen peroxide utilization, reduce costs, and maintain a certain degree of polymerization degree and reduce fiber damage. After scouring and bleaching, the fiber has a higher whiteness value, and impurities such as lignin, fatty waxes, and nitrogen-containing inorganic salts can be removed in large quantities, which improves the situation of poor dyeing uniformity and unfavorable dyeing.
6. Selection of dyes. In the development process of flax loose fiber dyeing, we selected Swiss Clariant reactive dyes and auxiliaries – S-type dyes, which have good dye uptake and dye-through properties and excellent cost performance, that is, ethylene type as well as salt, pure alkali, Fixing agent E-50 and other additives.
7 Dyeing equipment and process formula (1) Use CCA-140A Hong Kong Lixin boiling and bleaching pot. (2) Process formula:
8 Precautions during the dyeing process (1) First, the dye is stirred and dissolved in the auxiliary material tank and metered in linearly. At the same time, the salt and alkali are added linearly according to the preset procedure. For example, when adding salt for the first dyeing, add it all at once or in several batches. The one-time addition not only greatly speeds up the dyeing process and causes uneven dyeing, but also causes dye accumulation and even precipitation. For the second dyeing after adding alkali, the dyeing speed and color fixation degree are controlled by the pH value in the dye bath. Adding a large amount of alkaline agent will cause the pH value to rise rapidly. Not only will the hydrolyzed dye increase, but a large amount of dye will be fixed, making it difficult to transfer the dye. Causes poor level dyeing and dyeing through, so the dosage and addition method of salt and alkali should be reasonably programmed to affect the dyeing (adsorption) stage and color fixation (reaction) stage to ensure the best dyeing effect and prevent dyeing and blooming. Showthrough dyeing and color difference, etc. (2) When soaping colored yarn, detergent RSK with efficient wetting and cleaning functions should be used as the soaping liquid. This stage includes washing temperature, water flow speed, pH value, etc. It is mainly to remove electrolytes and unreacted dyes. Therefore, it is necessary to use a detergent with high temperature (90℃-95℃), fast water flow speed and strong cleaning function.
Conclusion The pre-dyeing treatment of flax roving dyeing is the key and foundation, and the selection of reactive dyes plays a decisive role. It can reduce pot differences and batch differences, improve level dyeing, dyeing through and dye fastness and other indicators, and effectively control Unfavorable factors that affect dyeing are eliminated to fully ensure product quality.