What are the factors that cause alkali on the cloth surface?

1 The pretreatment and dyeing of cellulose fibers are basically carried out in a working bath with a higher pH value. Due to the action of alkali agents such as caustic soda and soda ash, it has great directness (affinity) to cellulose fibers, and the cellulose fibers have extremely good water absorption properties. When cleaning, a large amount of clean water is required for washing, in addition to a large amount of cold water, hot water is also required, and sometimes acid-base neutralization is required for coordination. Since the water consumption, energy consumption and removal efficiency of the alkali removal process are basically in a proportional relationship, pretreatment and dyeing are also the main links of water and energy consumption. This is determined by the performance characteristics of natural cellulose fibers such as cotton and alkali agents, and their relationship with each other. So far, the dyeing and finishing of fabrics is inseparable from alkali agents.

2 The working method of mechanical equipment also directly determines the washing efficiency. Different washing methods, such as immersion, spray, backflush overflow, oscillating (ultrasonic), etc., have different varieties of adaptability. There are differences in the washing efficiency effect of different equipment types. In production, water washing equipment is required to save water and steam, and to have a good cleaning effect, but there is a certain contradiction between the two. For the net washing of fibers to remove alkali, ensuring product quality is the basic principle. Otherwise, repairing after the defect occurs, it will cause more consumption and waste of water, energy and other raw materials than the gain. To ensure the first success is one of the most fundamental measures to save water and energy.

3 Dyeing and finishing Water saving and energy saving is a goal with almost no end. First of all, the design of mechanical equipment must be considered. The starting point, purpose and goal of its design, and the working principle of equipment operation, should meet the requirements of the dyeing and finishing process as much as possible. For cleaning efficiency, water saving and energy saving effect, the conclusion is reliable only after large-scale production and use. The process plan for dyeing and finishing applications must also be based on the performance characteristics of the equipment, and a suitable targeted process must be formulated. Therefore, in addition to understanding the properties and performance of relevant chemical raw materials, dyeing and finishing personnel also need to understand equipment. A reasonable process plan and process can not only ensure the washing efficiency, but also make it possible to reduce the number of washings and process time.

4 After testing, it can be found that the pH value of the dyed semi-finished products (including the final dyed products) after dyeing and before post-processing shows fluctuations even on the same production line. Generally speaking, defects in mechanical equipment and process design, once problems occur, will be in batches, while problems in operation and on-site management will change dynamically. Therefore, this is also a concern that cannot be missed in management. After long-term observation, it can also be found that the problems in water washing are similar to those in the pretreatment process, and have a certain seasonal periodicity. In winter when the weather temperature is low, the fluctuations are especially frequent.

The water temperature of washing has a significant effect on the dissolution of chemical raw materials (including auxiliaries) such as alkali agents, so hot water washing cannot be lacking in cleaning work. You can see some liquid additives. Many varieties are thin solutions that are easy to flow in summer, and can be easily turned into a uniform working fluid, but the same additives will become thick and thick with high viscosity in winter. The difficulty of chemical materials has increased. Corresponding to this, when it comes to the cleaning process, the cleaning performance of different water temperatures will not be the same.

Even in summer, soda ash is easy to absorb crystal water molecules when using cold water at room temperature to dissolve the material, and the solid old alkali that is insoluble in low temperature water is precipitated and precipitated. The dissolution is very sufficient and there will be no old alkali generation. In winter, the water temperature of cold water is very low. If the water temperature and frequency of washing cannot be distinguished, the cleaning efficiency will naturally decrease accordingly. The permeability of hot water to cellulose fibers is much better than that of cold water, so there is a saying that "the cheapest penetrant is hot water". Since hot water can improve solubility and promote permeability, it further enhances and strengthens the cleaning basis for alkaline agents. Therefore, it can be seen that similar pre-treatment defects are often related to poor chemical materials and poor post-cleaning, and are often prone to occur frequently in winter.

Therefore, if the front-line vehicle operators do not have enough understanding of the water washing problem, they treat it casually because they think that the water washing has nothing to do with the overall situation, or even think that it has little effect on the color and luster, and cannot cause enough problems in terms of process parameters such as water temperature, water volume, water washing times, and water washing time. Pay attention to it, and the adverse effects will be difficult to avoid.

5 Due to the long-term treatment of the fabric in the working bath of the two major links of pre-treatment and dyeing, the penetration and absorption of the alkali agent on the fiber has been extremely thorough. There is also a problem of easy surface cleaning, especially for some high-density, heavy grey fabrics. In this regard, in addition to cleaning should be strengthened, neutralization treatment is also a useful supplement.

It should also be noted that, in addition to the variability of grey fabrics and fiber types, changes in water quality, and failures in equipment and supporting facilities are often possible objective phenomena, plus the possibility of subjective interference such as process execution. , so that the semi-finished grey cloth with alkali will also be dynamic, and it may be irregular at different levels. For this reason, the regular detection and correction of the pH value of the working bath of the rolling groove in on-site management should be set as a process specification.