Learn | Why do fibers still break or have holes in fabrics?

In the deep processing of dyeing and finishing of cellulose fibers such as cotton, the quality of the pre-treatment is greatly related to the quality of the dyeing and finishing results. If the pre-treatment is poor, it will affect the quality of the semi-finished products. The basic whiteness of the fiber, penetration absorption index, dyeing and leveling performance, etc.; in severe cases, the strength of the fiber will be greatly reduced, resulting in obvious brittleness of the semi-finished product, and in severe cases, the fiber will be broken (or the fabric will have holes). When this kind of fiber brittleness occurs, it will not only be difficult to repair, but may also cause the textile to be scrapped. section>

And once it enters regular large-scale production, it has been proven through mass production that it is mature and With stable processes and formulas, no major problems usually occur. Therefore, in order to ensure the high stability of large-scale production, the production technology departments of dyeing and finishing companies are very cautious about the pre-processing process, and generally will not casually change the processes and formulas that have been confirmed to be mature and stable, and Including varieties of chemical raw materials and their supply companies.

However, sometimes it is a bit inexplicable Sudden blemishes may interfere with the process, and there may also be taboo fiber brittleness (or even holes). Since it has been identified as a non-process formula design factor, when such a situation occurs, the first suspicion is that it is related to the chemical raw materials. In particular, attention is paid to whether there are any quality problems with the relevant additives, so it is easy to cause disputes.

1. Water quality fluctuations

Easy to be ignored, but it has a greater impact and is likely to appear suddenly among fluctuating factors, first of all, production water Iron ion content problem. As we all know, calcium, magnesium, iron and other metal ions in water have a close impact on all aspects of dyeing and finishing production; among them, the number one factor that can cause embrittlement damage to cellulose fibers during pre-treatment is iron ions.

Hydrogen peroxide is an indispensable basic chemical raw material in today’s pretreatment. Hydrogen peroxide is at room temperature It decomposes slowly under conditions of heat and light, or after adding alkali, H2O2 is activated and decomposes rapidly, as shown in the following formula:

The above reaction promotes the formation of free radicals, which in turn intensifies the decomposition reaction.

It can be seen from the formula that when the amount of caustic soda is increased, HOO increases, which improves the bleaching effect. However, with the increase in alkali concentration and the presence of metal ions, the decomposition rate of H2O2 accelerates rapidly. Without control, not only Hydrogen peroxide is wasted needlessly, and the whiteness of the fabric decreases, and the cotton fibers even become brittle.

The content of calcium, magnesium, and iron metal ions in water is, in principle, determined by the water supply Determined by the water source, we usually pay great attention to the quality of production water and testing and sampling work. However, iron ions are also greatly affected by the water supply pipe network in the production workshop, especially the iron water supply pipe network. After a long factory-wide holiday (such as the Spring Festival, etc.), or the whole factory shuts down. After a major overhaul, or after a production line in a certain area is shut down for a period of time, it is easy for a sudden increase in iron ion content to occur when the production line is resumed.

There are also steel-framed workshop roofs, or related aerial iron frames, After being corroded by steam, acidic gas, etc. for a long time, iron filings, rust particles, etc. are likely to naturally peel off, and will accelerate falling if exposed to strong winds. If the rusty material that falls on the rough white fabric to be treated is brought into the oxygen bleaching working bath, the rust will easily cause holes in the oxygen bleaching. Under normal circumstances, this type of roof structure and the production workshop of the iron water supply pipe network system must be vigilant after 8 to 10 years of use. The longer the service life, the more care and attention must be paid.

It should be said that the production technology department of dyeing and finishing enterprises generally has a problem with the water quality of production water. It is taken seriously, and there is usually a working system for regularly testing the water quality of water sources. The design and formulation of process recipes will also be formulated or adjusted based on the actual parameters after testing. But often after a period of time, when you see that the water quality parameters have not changed much, and the implementation of the production process formula is stable and calm, it is easy to feel paralyzed. In addition, most people don’t pay much attention to the actual water quality when entering the working machine, and then check whether there is any change.

Seriously, observe and pay attention to the front line of the production workshop at any time before entering the work The water quality of the machine water, especially after holiday shutdown or major overhaul, is both necessary and important. But in most cases, re-observation and re-checking of the incoming water conditions of the day, shift, and each machine are often underestimated or ignored.

2. Application issues of certain related additives

In order to reduce the COD index of the wastewater discharged after pre-treatment, the amount of caustic soda can be significantly reduced. Various types of scouring agents have become more and more popular. In the use of this kind of powdery scouring additives for pre-treatment, it is also based on the premise of mature process formulas. Sudden fiber brittleness may sometimes occur. The problem is due to quality issues with this batch of additives

From the essence Generally speaking, in the dyeing and finishing production system that has so far used water as the medium, it is best for commercial additives to be in liquid form within an appropriate concentration range, in order to be more in line with the actual operability of large-scale production required by the dyeing and finishing process. This is because the use of liquid additives in an appropriate concentration range makes it easy to achieve the two most basic requirements of uniformity and speed during material mixing in the workshop (which are closely related to dyeing and finishing quality and work efficiency).

This is because if the concentration is higher than the dissolution saturation point, commercial additives will easily precipitate, especially in winter; If precipitation does not occur in winter, the content concentration becomes too low, resulting in a significant increase in production, operation and management costs in packaging, transportation, storage, property management and other aspects, making it unsuitable for marketing operations and becoming A type of commercial additive that is not popular in the market. On the contrary, it has gradually become a tendency for some large-scale dyeing and finishing companies to purchase concentrated auxiliaries for the purpose of reducing production costs.

The physical and chemical properties of powdery scouring agents need to be clarified by front-line employees in pre-processing production Understand its characteristics and use it correctly. Avoid incomplete dissolution during chemical processing. Strictly avoid semi-soluble or even undissolved additives from entering the working bath and sticking to the fibers. This will cause the local high concentration of scouring agent to exist, causing fiber damage, and in severe cases, holes.

Since solution saturation often has a variable condition factor temperature, this type of helper The chemical composition of the agent is difficult and becomes different in summer and winter. It can be seen that in the car blocking operations on the front line of production, most people are very sloppy about the chemical work. They often use water at natural room temperature regardless of the variety, regardless of winter or summer.Therefore, for the types of additives that are difficult to dissolve, warm or hot water of a suitable temperature should be used for compounding in winter. The specific chemical material temperature requirements of each variety are different, which can be known through prior small tests. This is also the basic work that the company’s technical department should do in advance.

Due to the problem of solubility saturation, the minimum amount of water required when mixing materials is also not acceptable. Another basic point overlooked. Full stirring when mixing materials is a common sense requirement.

3. Other process execution issues that are easily overlooked

3.1 Dilution, measurement and standardized operation issues of inorganic acids used for neutralization

The neutralization method is used to reduce the PH value of the cloth surface. It is one of the commonly used methods in dyeing and finishing process design. Its advantage is that it can Reduce the number of washes and get quick results.

Due to the use of inorganic acids, there is some risk, but it is far greater than the use of organic acids The cost is low, and if the operation can be strictly controlled, safety can be guaranteed. First of all, the diluted solution with the ratio specified by the first-level enterprise standard must be prepared in advance, and the distribution must be strictly implemented; secondly, when used in the workshop, the dilute solution should be further diluted according to the ratio specified by the second-level workshop standard, stir evenly, and then add to the machine. When adding materials into the machine, it is forbidden to have direct contact between the dilute acid solution and the cloth surface; thirdly, carefully conduct online testing of the PH value of the cloth surface.

It should be highly noted that during the actual on-site operation on the front line of the production workshop , it may also happen that some truck operators (especially some new employees who still lack experience and lessons), because they have seen nothing serious for a long time, become careless and relaxed, and no longer strictly implement the operating procedures, especially During shifts such as in and out of shop management, late night shifts when there are fewer technicians.

3.2 Insufficient strength of water washing after oxygen bleaching and its impact

The pre-treatment of some types of gray fabrics and printed products will be included in the process after oxygen bleaching. A drying step. tenWhat is very simple and clear is whether there is sufficient water washing (including hot water washing and cold water washing) after oxygen bleaching. It is extremely important and direct to whether the chemical residues such as alkali agent, hydrogen peroxide and other chemical residues during oxygen bleaching on the gray fabric can be completely removed. The more thoroughly it is removed, the better it can ensure the quality requirements for future dyeing or printing, as well as finishing.

Neutralization treatment can certainly hedge the alkali on the gray fabric and reduce the PH on the fabric. value, but it will be converted into salt and may not have a reliable effect in removing residual hydrogen peroxide and other additives. Therefore, water washing cannot replace water washing but can only be used as a supplement to water washing because it can reduce the number of water washings and thus play a certain role in saving water.

Because washing is a process that is easier to omit in process execution, but is not easy to detect. process, and it is difficult to conduct effective review afterwards, so it is also one of the key contents in on-site management. If the washing intensity is insufficient or even reduced, during the drying process, the residual alkali and hydrogen peroxide on the gray cloth will become more concentrated on the cloth due to the rapid evaporation of water. Increase, once it is higher than the critical point, the decomposition of the remaining hydrogen peroxide will become uncontrolled under the high temperature environment of the dryer. From the chemical reaction formula between the above alkali agent and hydrogen peroxide, it can be known that this will inevitably lead to the decomposition of cellulose fibers. The problem of brittle damage occurs in this link.

Enterprises always hope to recruit skilled employees, but the current reality may not be able to meet the employment requirements of the enterprise. And even some The so-called “skilled” employees may also be a relative term. Due to differences in the forms and methods of dyeing and finishing caused by differences in textile types, although the basic principles of dyeing and finishing are the same, the specific processes, The formulas, production processes, car operations, etc. are quite different. For example, a skilled worker for long car pad dyeing may not be proficient in dip dyeing or jig dyeing methods and operating procedures, and certainly not vice versa. Those who have only worked in other industries are unskilled workers who are not in this major.

Current The turnover of employees in various enterprises is both frequent and common, and the objective reality of the recruitment and employment market means that dyeing and finishing companies often have to accept even unskilled employees. Therefore, whether on-the-job training and on-site management are in place has a significant and direct impact.