Quality problems may occur during production due to factors such as gray fabrics, semi-finished products, equipment, process level and execution, quality of dyeing materials, etc. Among them, the selection and use quality of auxiliaries directly affect the quality of dyeing and finishing products. , this article mainly talks about the relationship between the common quality problems of knitted fabric dyeing and finishing products and the selection of auxiliaries and equipment.
Common quality issues in pre-treatment and the selection of auxiliaries
The quality of pre-treatment (bleaching) is not only related to the quality of the finished bleaching product, but also serves as a Semi-finished products will also directly affect the quality of dyeing, printing, finishing and other aspects. Some experts say that 70% of quality problems in dyeing and finishing products are caused by poor pre-treatment, which makes sense. The quality of dyeing and finishing is related to gray fabrics, equipment conditions and operations, process technology and execution, dyes, and auxiliaries. We focus on the impact of auxiliaries.
1. Problems with poor whiteness and wool effect
Poor whiteness includes impure whiteness, uneven whiteness and poor hair effect of 8 to 10cm /More than 30 minutes, this is related to the quality of the knitted fabric. If the low-grade cotton content is high, the whiteness and wool effect are often difficult to achieve. Of course, the most critical issues are process formulation and additive selection.
In process formulation:
① The amount of H202 and NaOH must be sufficient
H202: after pretreatment, it not only plays the role of bleaching pigments, but also has the ability to remove Miscellaneous effects (including cottonseed hull removal), insufficient H202 dosage (including too rapid decomposition), and whiteness cannot be guaranteed. NaOH not only provides the alkalinity (PH) required for H202 bleaching, but also cooperates with the scouring agent to maximize the removal effect. If the amount of NaOH is insufficient, the impurity removal will be poor. The hair effect cannot meet the requirements first, and of course the whiteness cannot meet the requirements. Therefore, the amount of H202 and NaOH can be said to be the primary factor in ensuring whiteness and hair effect.
② Select high-quality scouring agents
The comprehensive effects of scouring agents such as cleaning, emulsification, dispersion, and penetration must be excellent to ensure that impurities are completely removed. The whiteness and wool effect are guaranteed, but the quality of scouring agents on the market is uneven. We must choose products with excellent comprehensive effects instead of just measuring penetration and solid content. Penetration is only one aspect to consider.
③ Oxygen bleaching stabilizer and chelating dispersant
These two additives are mainly used to improve water quality, adsorb and complex Fe3+ in water, etc. Metal ions prevent the rapid and ineffective decomposition of H202 caused by metal ion catalysis. If H202 decomposes quickly and ineffectively, its whiteness and wool effect will not meet the requirements, and it will cause brittleness and even holes in the fabric, so the whiteness and wool effect must be achieved. To be effective, oxygen bleaching stabilizers should be selected from excellent varieties, and the decomposition rate of H202 should be considered during the selection. The addition of chelating dispersant not only chelates iron, etc., but also chelates and disperses various impurities in the water, so that these impurities will no longer contaminate the fabric again and cause dark whiteness and graying. Therefore, chelating dispersant not only Both its chelating power for metal ions and its dispersion power should be considered.
④ Process conditions: It takes a certain amount of time and temperature for the additives to react with impurities. If the conditions are not met, the pigments and impurities will not be completely removed, and the whiteness and hair effect will not be achieved.
⑤ Washing: Washing after scouring and bleaching is very important. It is necessary to clean the removed impurities to ensure whiteness and wool effect.
2. The cottonseed hulls are not completely removed
The removal of cottonseed hulls mainly depends on the expansion and swelling of cottonseed hulls by NaOH under certain conditions, and then after a certain period of time Mechanical cleaning power removes cottonseed husks. Incomplete removal is mainly caused by insufficient temperature and time. Therefore, sufficient time must be provided at a certain temperature to completely remove cottonseed husks. H202 and scouring agents are helpful in removing cottonseed husks, so in There must be a certain temperature and time in the pretreatment to ensure the removal of cottonseed hulls. At the same time, sodium bisulfite (NaHS03) or anthraquinones can be added to help remove cottonseed hulls.
3. Holes and brittle damage
The causes of holes and brittle damage include singeing holes, scratches during processing, and original gray cloth In addition to holes and other causes, the main reason is the presence of Fe3+, Cu2+ and other metal ions in the H202 bleaching bath or on the cloth surface. These metal ions catalyze the rapid decomposition of H202, causing brittle fiber damage.
If metal ions (such as rust, etc.) are too concentrated in one place, the fibers and yarns will become brittle and form holes. Therefore, high-quality oxygen bleaching stabilizers and chelating dispersants must be selected for H202 bleaching to complex , adsorb metal ions on fabrics and in the bleach bath to prevent H202 from decomposing too quickly and causing holes or brittle damage. If mercerizing alkali is used for bleaching, it must be ensured that there are no impurities such as rust in the alkali.
Of course, alkali on the cloth surface (the alkali removal is not clean) or acid (the acid removal is not clean) will also cause brittle damage. At the same time, under high temperature and alkali conditions, the fabric will be brittle and damaged in the presence of air. This situation can be prevented by adding weak reducing agents such as NaHS03. In addition, moisture and mildew in fabrics are also one of the causes of brittleness and holes.
Common quality problems in dyeing and the selection of auxiliaries
1. Unqualified color fastness
Color fastness includes light fastness, soaping fastness, perspiration fastness, rubbing fastness, sublimation fastness, ironing fastness, etc. The key to these fastnesses lies in the structural properties of the dye, and also It is closely related to fiber, dye concentration, dyeing and finishing process, external conditions, etc. Therefore, the key to whether the color fastness reaches the standard is the selection of dyes, followed by the dyeing process and the application of auxiliaries.
When formulating the dyeing process, it must be reasonably determined based on the dye, fiber and customer indicators, so that the dye can be dyed with the help of additives.�Clean up promptly. The leakage of the airflow nozzle is related to the connection method, sealing structure and installation. If the installation is in place and there is still a large leakage, it means that the sealing and connection structure of the airflow nozzle are insufficient and should be improved and replaced. The airflow nozzle is a key component, and equipment manufacturers generally have their own patent protection.
Cylinder difference
Vat difference refers to the dyeing color difference caused by dyeing between different dyeing vats. The cause of pipe differences is between cylinders, which may also cause cylinder differences. In addition, there are other factors such as technology, equipment, operations, etc. that can cause cylinder differences.
(1) Cylinder arrangement and distribution.
When mass production of the same color occurs, issues such as cylinder arrangement and distribution volume will be involved. If the cylinder types are the same and the distribution volume of each cylinder is different, cylinder differences may occur. If there are several vat types, such as a two-tube dye vat and a four-tube dye vat, differences in vat types may also result in vat differences. Therefore, when arranging the vats, we should try our best to ensure that a batch of cloths of the same color are dyed in the same vat type dyeing vat. If the same vat type dyeing vat cannot be arranged, attention should be paid to the color mixing and color matching during the production process.
(2) Process consistency.
When a batch of cloth of the same color is dyed in different dyeing vats at the same time, if the liquor ratio, process design temperature, heating rate, holding time, cloth speed, adding method and adding time of dyestuffs If there is an obvious difference, it will cause cylinder difference. Therefore, the consistency of the process must be achieved to avoid cylinder differences caused by differences in process.
(3) Differences in the equipment itself.
It is inevitable that there are some differences in the equipment itself, such as the design and manufacturing tolerances of some parts, the sensitivity and accuracy differences between detection components, etc. Generally speaking, these differences are not enough to cause Dyeing vat is poor. However, if the manufacturing differences between some key components are too large, it may cause differences in the dyeing vat. For example, in the nozzle system, the gap between the airflow nozzle and the throat pipe is between the tubes in the same vat. The gap will be basically the same, but between different cylinders, there may be large differences in this gap during the equipment manufacturing process. Since this gap is related to the degree of atomization of the dye liquor and the spraying state of the dye liquor, if the difference is too large, it may cause cylinder differences.
There will objectively be some differences in accuracy and sensitivity between different manufacturers of components such as temperature gauges, pressure gauges, pressure sensors, platinum thermal resistors, liquid level gauges and various control valves. , when the difference is large or even malfunctions, dyeing vat differences are unavoidable.
There are vat type differences between vat types of different specifications. For example, there are objective differences between two-pipe cylinders and four-pipe cylinders in their capacity, structural dimensions, fan and main circulation pump performance, etc. The existence of these differences will lead to cylinder differences to a certain extent.
In order to avoid differences in dyeing vats due to the equipment itself, equipment manufacturers must use products from the same supplier for the same type of components in terms of design and manufacturing, and the quality must be guaranteed. ; The second is to ensure the manufacturing accuracy of key components in particular to avoid disadvantages caused by excessive manufacturing errors. For different cylinder types, pay attention to cylinder arrangement and distribution during dyeing processing. If necessary, process adjustments between cylinder types can be made to ensure the consistency of the dyeing results.
(4) Irregular or improper operation
is a factor that cannot be ignored that causes cylinder differences. Any type of dye vat, regardless of its degree of automation, should strictly follow the process to perform standardized operations, such as the order, frequency, time, heating rate, holding time, etc. of chemical and feeding materials, and the consistency of its execution should be ensured.
Pilling
Mainly occurs in some short fiber fabrics, such as polyester staple fiber or Polyester-cotton blend fabric. In the airflow dyeing process, the airflow drives the fabric through the airflow nozzle and exchanges with the dye liquor, and then runs through a section of cloth guide tube to the left and right cloth hopper and then falls into the cloth storage tank. Due to the effect of the airflow field and the change in the cross-sectional shape of the cloth guide tube, the fabric During this period of operation in the cloth guide tube, they are blown away laterally and constantly shaken. Under certain conditions of temperature, air pressure and air volume, some fibers are blown out and generate fluff on the surface of the fabric. Since the fabric inevitably interacts with the fabric during its operation, Friction occurs on the tube wall, so part of the blown fibers are stretched and curled into very fine balls and adhere to the surface of the fabric, resulting in pilling of the fabric. </p
