Effect of semi-finished grey fabric with alkali on dyeing and finishing

With today's energy saving and emission reduction requirements continue to improve, the cost of water gradually rise, cotton and other cellulosic fiber fabrics before coloring, after finishing before the more likely to occur on the semi-products of this color cotton with alkali phenomenon, even in the dyeing of finished products on the fabric PH value of 8 or more also happens, some even more than 9; which continuous long car rolling dyeing production line and more frequent than intermittent dip-dyeing method.

　　After coloring, post-processing before the semi-products of this color cotton with alkali phenomenon, will have a greater adverse effect on the post-processing, post-finishing more auxiliary varieties, and sometimes very far-reaching (such as some reactive dyestuff coloring fabrics that are not resistant to alkali hydrolysis, several months later will still occur due to the fabric with alkali and wind printing and other receding color problems).

　　Because often in the post-treatment, after the finishing defects only revealed, which brings difficulties to find the cause of the problem, simple misleading misjudgment, and focus attention on the post-treatment, after finishing additives.

　　A, the impact of some post-processing additives

　　Post-treatment refers to the completion of the coloring process after the washing, soaping, color fixing (or cross-linking agent treatment) and other process content. For the coloring of reactive dyestuff, the floating color must be fully removed by soaping to reveal the stable and real coloring color. Although some fixing agents may cause a definite shift in the color phase, this should be controlled in advance when releasing the sample, and the purpose of fixing is to increase the fastness of the dye.

　　However, some common important color fixing agent, cross-linking agent varieties, mostly for the appropriate working bath pH value in 5 ~ 6.5 weak acid, in alkaline media, the higher the pH value is the worse the effect, to a certain alkalinity will even precipitate precipitation.

　　Bad working bath conditions, will not get the proper effect, so that the dyeing fastness and other indicators can not get the desired improvement. At this time, even if the amount of color fixing agent or cross-linking agent is increased, the fastness is not synchronized, so the significance of increasing the amount of additives is lost.

　　Second, the impact of some additives on the finishing

　　After finishing for the dyeing and finishing project in the three major links in the latter part, it is of great significance for the expansion of the function of fabric products, the role of extension, grade enhancement.

　　After the finishing on some important varieties of additives, such as silicone softener, non-iron resin finishing agent, etc., and color fixing agent, cross-linking agent additives have a similar situation, also need to be processed in a weak acidic working bath to be more suitable. The difference is that the silicone softener taboo is not the alkali agent can directly destroy the silicone oil to make the fiber soft, but the emulsification of the softener can produce emulsion breaking effect. Pure silicone oil can not be used directly on the fabric, so we must use the emulsification method, made of silicone oil content is generally 10 ~ 15% of the emulsion (or microemulsion), in order to become the real available commercial softener.

　　Alkali agent to emulsify the softener can produce emulsion, so that the emulsifier failure and precipitation of silicone oil, with the advancement of time, respectively, and the precipitation of silicone oil points, after repeated re-aggregation, and the formation of a larger diameter, the naked eye can identify the oil droplets, severe when there will even be oil bleaching phenomenon. These separate precipitation of silicone oil, stained to the fabric, it will form a different size of oil spot oil spot defects. More serious is, silicone oil and fiber combined with firm, so that such defects are quite difficult to peel off and back to repair, so this only prevention is more important than treatment, to have positive practical significance.

　　Another important place in the finishing after the non-iron finishing resin, in the use of more acid catalytic conditions, so to ensure that the PH value of the working bath of the rolling bath in the prescribed range, also has a considerable criticality.

　　After finishing various items, basically adopt the continuous method of rolling car dipping and rolling, which has the advantage of high efficiency, high speed, and almost close to 100 percent raw material utilization. If the semi-products of this color cotton with alkali, it will have a cumulative effect on the working bath in the rolling bath, so that the pH value of the working solution gradually rise. Therefore, often there is no problem at the beginning of the first drive, after 2000 ~ 3000m, the problem appears by zhe, and more and more serious, which for the lack of field experience, simple illusion and misjudgment. Only from the surface phenomenon, from the auxiliaries alone to find the cause, not only make the problem is not solved, will also end up confused.

　　After finishing on a variety of finishing items, most of the firmness, durability are very good, few can be effectively used to peel off the supporting chemicals, which makes the defects once they occur, it is difficult to effectively repair, so compared with the post-treatment problems, the consequences are more serious.

　　Third, the cloth surface with alkali prone factors

　　4.1 Cellulose fiber in the pre-treatment and coloring, basically in the higher pH working bath. Due to the role of caustic soda, soda ash and other alkaline agents, cellulose fibers have great directness (affinity), coupled with the extremely good water absorption of cellulose fibers, so to fully penetrate the adsorption of alkali on the fiber for cleaning, a large amount of water is needed to clean, which in addition to a large amount of cold water, but also need to use hot water, and sometimes acid and alkali neutralization to give with. As the water consumption, energy consumption and removal efficiency of the alkali removal process is basically a proportional relationship, so the pretreatment and coloring is also the main link of water and energy consumption. This is cotton and other natural cellulose fibers and alkali performance characteristics, and its relationship between the decision, so far, the fabric dyeing and finishing can not be separated from the alkali agent.

　　4.2 mechanical equipment work, but also directly decision-making to the washing efficiency, different washing methods, such as immersion washing type, spray type, recoil overflow type, shock type (ultrasonic), etc., have their different varieties of adaptability, the effect of different types of equipment washing efficiency is the existence of differences. Production of water washing equipment requires both water and steam saving, and can have a good net washing effect, however, there is a definite contradiction between the two. For the net washing of fiber to alkali, to ensure product quality is its basic principle. Otherwise, the occurrence of defects and then repair, will not be worth the loss but cause greater consumption of water, energy, other raw materials and waste. To ensure the success of a time, is one of the fundamental measures to save water and energy.

　　4.3 Dyeing and finishing water and energy saving is a goal that has almost no end. First of all, the design of machinery and equipment must be considered, the starting point, purpose and goal of its design, the working principle of equipment operation, should be completely possible to meet the requirements of the dyeing and finishing process. The conclusion on the effectiveness of washing, water and energy saving can only be reliable after large production use. The process scheme of dyeing and finishing application must also be based on the performance characteristics of the equipment, to develop a suitable target process. Therefore, dyeing and finishing personnel need to understand the equipment in addition to the nature and properties of the relevant chemical raw materials. Reasonable process scheme and process, both to ensure cleaning efficiency, but also make it possible to reduce the number of washings and process time.

　　4.4 After testing, it can be found that the pH value of the cloth surface of the coloring semi-products (including the final dyed products) after coloring and before post-treatment, even in the same production line, is also showing fluctuating changes. Generally speaking, the defects in mechanical equipment and process design, once they occur, will be in bulk, while the problems in operation and site management will be dynamic changes. Therefore, this is also a governance on the concern that can not be missed. After a long period of viewing, it can also be found that the problems on the water washing and pre-treatment processes have similarities, with a definite seasonal cycle, in the climate temperature is lower in the winter, fluctuations are particularly frequent.

　　The water temperature of water washing, the dissolution of chemical raw materials such as alkali (including additives) have a significant impact, so the net washing work can not be missing the hot water cleaning. It can be seen that some liquid additives, there are many varieties in the summer is a very simple flow of thin solution, it is very simple to become a uniform working solution, but the same additives to the winter, it will become a high viscosity thick, the chemical material becomes more difficult. And this corresponds to the cleaning process, different water temperature of the cleaning water, the net washing efficiency will not be the same.

　　Soda ash even in summer, when using cold water at room temperature, it is easy to draw in crystalline water molecules and generate solid old alkali precipitation which is difficult to be dissolved by low temperature water, but when using hot water at 50-60℃ or above, it will dissolve very well and no old alkali will be generated. In winter, the water temperature of cold water is very low, if the water temperature and the number of times of washing can not be distinguished, the net washing efficiency will naturally decline accordingly. The permeability of hot water to cellulose fiber is much better than that of cold water, so there is a saying that "the cheap permeant is hot water". Since hot water can improve the solubility and also promote the permeability, it further enhances and strengthens the cleaning base of alkali agent. Therefore, it can be seen and similar to the pre-treatment defects, and bad chemical material and cleaning after the bad is often related, but also often in winter prone to more frequent.

　　Therefore, if a line of block operators do not know enough about the problem of washing, think that washing is not relevant to the big picture and treat casually, and even think that this does not have much impact on the color, in the water temperature, water, washing times, washing time and other process parameters can not pay enough attention to the aftermath of the bad effects will not be spared.

　　4.5 As the fabric in the pretreatment, coloring two major links in the work bath for a long time, alkali agent in the fiber penetration and draw adsorption, has been extremely thorough, in this color cotton cloth by the tension is very large continuous rolling dyeing line, there is also a simple occurrence of surface cleaning problems, very high density, heavy this color cotton cloth is particularly likely. In this regard, in addition to cleaning should be strengthened, and neutralization treatment is also a useful supplement.

　　Another thing to note is that, in addition to the color cotton, fiber type of variability, changes in water quality, equipment and supporting facilities on the failure, are often possible objective phenomena, coupled with the possibility of subjective aspects of the implementation of the process interference, resulting in semi-products of this color cotton with alkali is also dynamic, often with the possibility of high and low irregularity. For this reason, the site governance on the working bath of the rolling bath pH value of the regular detection and correction, should be set as a process protocol.

　　Fourth, concluding remarks

　　pH value is one of the key factors of chemical reaction, so it is also listed as one of the four process conditions on dyeing and finishing production. Coloring semi-products with alkali, for post-treatment, post-finishing, many of the negative effects of additives, although the mechanism of its impact varies, but will produce sequelae on this point is common.

　　The cause of semi-products with alkali on natural cotton, from the surface, of course, and washing-related, but different washing machinery, process measures and washing efficiency and effect are inextricably linked. This problem seems to be trivial, but the negative consequences are very wide, and many quality problems of dyed products are related to this, so we must pay full attention to it.