The deep processing of cotton and other cellulose fiber dyeing and finishing, its pre-treatment is good or bad, greatly related to the quality of the dyeing and finishing results. If the pre-treatment is bad, the light will affect the fiber base whiteness of the semi-products, penetration absorption index, dyeing and leveling performance, etc.; the heavy will make the fiber strength drop drastically, resulting in obvious brittle loss of semi-products, serious even make the fiber break (or fabric breakage). And once this fiber brittle damage, will not only be difficult to repair but also may lead to the textile being scrapped.
Since the on-site supervision of pre-treatment quality is not as easy as dyeing and finishing in the production line, the quality semi-inspection is usually limited to a certain percentage of random inspections. Moreover, some quality problems caused by poor pre-treatment are intertwined with the quality of dying, which makes it particularly complicated to find and analyze the causes. Some of these defects are very difficult and costly to repair, not to mention the more serious consequences of non-repairability after the fibers have been damaged.
01 Sudden quality problems in a mature process
In the initial trial dyeing of new textile products (or new varieties), if the process, the design of the formula is not mature and reasonable enough, including the choice of chemical raw materials does not meet the new requirements of new products, then the trial production still has the quality requirements on the lack of words, should be understandable and can be explained. At this point, the direction of further improvement, ideas, is also easier to clear and understand.
And once entering the regular mass production, after the batch production is confirmed to be a mature and stable process, the formula, usually does not happen again with many problems. Therefore, the production technology department of dyeing and finishing enterprises, in order to ensure the high stability of mass production, are very cautious about the pre-treatment link, and generally will not casually change the process and formula that has been confirmed to be mature and stable, as well as including the varieties of chemical materials and their supply enterprises.
However, sometimes it can be disturbed by a somewhat inexplicable and sudden defect, and there may be a more taboo fiber fragility (or even holes) problem. Since it has been determined that it is not the design of the process formula when such a situation arises, it is often suspected that it is the chemical raw materials first, especially if there is something wrong with the quality of the relevant additives, so it is also easy to cause disputes.
However, with the chemical raw materials such as additives for review and re-inspection, there may not be any problems. Detection of chemical materials such as auxiliaries, now generally has reached the initial scale of dyeing and auxiliaries enterprises, have been able to do quick response and clear detection. It is also necessary to mention that in the current additives market is basically supply is greater than demand, and credit sales after payment of the market climate, each chemical additives companies almost all will not, and dare not take the credibility and reputation of the survival of the enterprise, to be used as a child’s play.
At this point, the surface of this seems to be “not according to common sense” sudden fiber brittle loss phenomenon, even the direction of the cause is also very easy to find confusion. Although the probability of sudden fiber brittleness defect is not high, once it happens, it is often the event that makes the specific manager both busy and fearful, because it contains a large economic cost loss and its responsibility.
02 Factors influencing the sudden brittleness of fibers
The occurrence of fibrous defects without any reason is certainly not scientifically based and not objective. There is no doubt that there must be a hidden inevitable factor behind it, just maybe overlooked, or even ignored; in addition, also need to remind us not to exclude that there is a genus against the scope of common-sense requirements.
1, the fluctuation of water quality
Easy to be ignored, but the impact of the larger, and likely to suddenly appear in the impact of fluctuations in factors, first of all, the production of water iron ion content. As we all know, the calcium, magnesium, iron and other metal ions in water have a close impact on all aspects of dying and finishing production; and among them, the cellulose fiber in pretreatment can produce brittle damage in the first place, there is nothing better than iron ions.
Hydrogen peroxide is an indispensable basic chemical raw material in pretreatment nowadays. Hydrogen peroxide decomposes slowly at room temperature, but under the condition of heat and light, or after adding alkali, H2O2 activates and decomposes rapidly, as shown in the following formula.
The above reactions promote the formation of free radicals and subsequently radicalize the decomposition reaction.
As can be seen from the formula, increase the amount of caustic soda, then HOO increases, so that the bleaching effect, but with the increase in alkali concentration and the presence of metal ions, the decomposition rate of H2O2 rapidly accelerated, in the case of uncontrolled, not only a needless waste of hydrogen peroxide, and fabric whiteness decreased, and even cotton fiber bristle loss.
Calcium, magnesium, iron metal ion content in water, in principle, is determined by the water supply, so usually the production of water quality, testing sampling work is very important. However, iron ions in addition also greatly affected by the production plant water supply network, especially iron water supply network, in the encounter of a longer period of plant-wide holidays (such as Spring Festival, etc.), or plant-wide shut down for major maintenance, or a local area production line after a period of downtime, in the resumption of work, it is easy to appear the sudden rise in iron ion content.
In addition, there is a steel structure of the workshop roof, or the relevant air iron frame, in the long term by steam, acidic vapor erosion, iron chips, rust micro-particles, etc. is very likely to produce natural flaking, if the wind blowing after accelerated fall. If the rust chips that fall on the blank to be treated are brought into the oxygen bleaching bath, the rust staining will easily cause holes in the oxygen bleaching. Usually, this kind of roof structure, as well as the iron water supply network system of the production plant, must be alert after 8 to 10 years of use, and the longer the use, the more careful and attention should be paid.
It should be said that the production technology department of dyeing and finishing enterprises generally pays more attention to the water quality of production water, and usually has a working system of regular testing of water quality. The design of the process formula, it will also be made or adjusted according to the actual parameters after testing. But often after a period of time, see the water quality parameters do not change too much, in the implementation of the production process formula is also reflected in a stable and calm, it is easy to produce paralysis. In addition, most of them do not pay much attention to the actual water quality of the water into the machine when entering the work machine, whether there are changes in the situation and then gate-keeping.
Seriously, for the first line of the production plant site at any time to observe and pay attention to the water quality into the work machine, especially in the holiday shutdown or after a major overhaul, both necessary and important. But in most cases, for the day, when the shift, each machine into the water situation of the re-observation and once again gate-keeping, are often overlooked or ignored.
2、The application of some related additives
In order to reduce the COD index of the wastewater discharged after pretreatment, can significantly reduce the amount of caustic soda and other varieties of powdered refining agent, which has become popular. In the use of such powdered pre-treatment with refining additives, also under the premise of mature process formulations, sometimes due to the occurrence of sudden fiber brittleness, and blamed on the quality of the batch of additives out of the problem.
In essence, in the dyeing and finishing production system so far or water as the medium, the best commercial auxiliaries in the appropriate concentration range of liquid form, in order to better meet the requirements of the dyeing and finishing process of the actual operation of large-scale production use. This is because the use of liquid auxiliaries in the appropriate concentration range, it is easy to achieve the two most basic requirements of uniformity and speed in the workshop material (which is closely related to the quality and efficiency of dyeing and finishing).
Powdered material belongs to the solid-state, solubility is easy to block and granular solid material, but significantly lower than the liquid state; and the reason for the type of powdered commercial auxiliaries, there is an important reason is that the dissolution saturation of such powdered refining agent is relatively low, it is difficult to make the standard range of liquid commercial auxiliaries within the requirements, only in the form of powder is more appropriate and realistic.
This is because if the concentration is higher than the dissolution saturation point, it will make the commodity additives easy to produce precipitation, especially in winter; if you want to winter also does not produce precipitation, the content concentration becomes too low, resulting in packaging, transportation, storage, physical management and other aspects of production, operation and management costs increased significantly, thus not adapted to the marketing operation, and become the type of commodity additives not welcomed by the market. On the contrary, nowadays, some large-scale dyeing and finishing enterprises, based on the purpose of reducing production costs, the purchase of concentrated types of additives, has gradually become a tendency.
The physical and chemical properties of the powdered type of refining agent, the need to clearly understand the characteristics of the first line of the pre-treatment production staff for the correct use, do not dissolve incomplete phenomenon in the work of chemical materials, need to strictly avoid half-soluble products or even insoluble products not yet dissolved into the working bath, so as to stick to the fiber. This will make the locally high concentration of the refining agent, and lead to fiber damage, and in serious cases will also be broken holes.
Since the dissolution saturation often has a variable condition factor temperature, so the chemical material of this kind of additives is difficult, in summer and winter also become not the same. It can be seen that the first line of products in the blocking operation, the majority of the work of the material is very sloppy, often regardless of species, regardless of winter and summer, are using natural room temperature water to material, so the material is difficult to chemical additives varieties, in the winter should be used in the appropriate temperature of warm or hot water for chemical material. Each variety of specific material temperature requirements vary, can be known through a small test beforehand, which is also the enterprise technology department should do the basic work beforehand.
For the reason of dissolution saturation, the minimum amount of water required for the chemical material is also another basic point that cannot be ignored. The full stirring of the material is a common-sense requirement.
3、Some other process execution problems that are easily ignored
3.1 Dilution, measurement, and standard operation of inorganic acid for neutralization
The use of the neutralization method to reduce the PH value of the cloth is one of the common means of dyeing and finishing process design, which has the advantage of reducing the number of washings and quick results.
Since there is some risk in using inorganic acid, but it is far less costly than organic acid, it is safe if the operation is strictly controlled. Firstly, we should configure the diluted solution of the first level of enterprise standard regulation ratio beforehand, and strictly implement the measurement and distribution; secondly, when using it in the workshop site, we should further flush the diluted solution again according to the second level of workshop standard regulation ratio, stir it well and then add it to the machine, and prohibit the direct contact between the diluted acid solution and the cloth surface when adding the material into the machine; thirdly, we should carefully carry out the online testing of the PH value of the cloth surface.
It should be highly noted that in the actual operation of the first line of the production plant, it may also happen that some blocking operators (especially some new employees who still lack experience and lessons), because of the day-long see no big deal, so carelessness and relaxation, no longer strictly implement the operating procedures, especially in the late night shift when the management and technical staff in and out of the workshop is less.
3.2 Insufficient strength of washing after oxygen bleaching and its impact
Certain varieties of grey fabric and printing products pretreatment will be in the oxygen bleaching process after the placement of a drying link. It is very simple and clear, after oxygen bleaching there is no sufficient water washing (including hot water washing and cold water washing), for the blank fabric on the oxygen bleaching when the alkali, hydrogen peroxide, and another chemical residue removal can be complete, extremely important and direct. The more thorough the removal, the more we can ensure the quality requirements of dyeing or printing, and finishing later.
Neutralization treatment can certainly hedge the alkali agent on the blank fabric and reduce the PH value on the fabric, but it will be converted to exist in the form of salt, and may not have a reliable effect with the removal of residual hydrogen peroxide and other additives, etc. Therefore, it does not replace the water washing and cancel the water washing, but only as a supplement to the water washing, because it can reduce the number of water washing, thus playing a certain role in water saving.
As the water washing is easier to cut in the implementation of the process, but not easy to be detected in the process, and afterward it is difficult to make an effective review, so it is also one of the key elements of site management. If the strength of the water washing is lacking or even cut, then in the drying process, the residual alkali and hydrogen peroxide on the blank cloth, etc., will become the unit concentration on the cloth due to the rapid evaporation of water, once higher than the critical point, in the high-temperature environment of the dryer, the decomposition of the remaining hydrogen peroxide will become uncontrolled, from the above chemical reaction formula of alkali and hydrogen peroxide, etc., it is inevitable that this will lead to cellulosic fibers to produce brittle damage problem in this link.
03 The importance and necessity of job training
Enterprises always hope to recruit skilled employees, but the current reality may not be able to meet the employment requirements of enterprises. And even some so-called “skilled” employees may be relative. Although the differences in dyeing and finishing methods caused by the differences in textile varieties are the same in terms of the basic principles of dyeing and finishing, the specific processes, formulas, production procedures, blocking operations, etc., are very different. For example, a skilled worker for a long car rolling and dyeing may not be skilled in the way and method of dip-dyeing or roll-dyeing and its operation procedures, and vice versa. Of course, it is not necessary to mention the unskilled workers who have only been in other industries and who are not specialized in this field.
The current flow of employees in each enterprise is both frequent and common, as well as the objective actual situation of the recruitment and employment market, so that dyeing and finishing enterprises may even accept non-skilled employees, so the impact of job training and on-site management is both significant and direct.
04 Editor’s Note
In view of the above analysis of the situation of these influencing factors, including the staff of even the first line of production, should be corresponding to the use of each chemical raw materials in the physical and chemical knowledge of the special properties. In particular, for new product additives, or the plant’s new use of additives, its nature, performance, role, characteristics, safety requirements, and other aspects, as well as the resulting new production process and its operating procedures. Enterprises in charge of production technology, the staff should do a good job training, clear regulations, and strengthen the site management to regulate the operation, and to “prevention is better than cure” concept to guide the production of large.