The quality of pre-treatment (scouring and bleaching) is not only related to the quality of finished bleached products, but also directly affects the quality of dyeing, printing, finishing and other semi-finished products. Some experts say that 70% of quality problems in dyeing and finishing products are caused by poor pre-treatment. There is a certain reason for this. The quality of dyeing and finishing is related to gray fabrics, equipment conditions and operations, process technology and execution, and dyes. , it is also related to auxiliaries, we focus on the influence of auxiliaries.
1: Common quality issues in pre-processing and the selection of additives
1:1 Problems with poor whiteness and hair effect
Poor whiteness includes insufficient whiteness Pure, uneven and 3Omin wool effects cannot reach more than 8cm. This is related to the quality of the knitted fabric. If there is a lot of low-grade cotton, 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:
(l) The amount of H2O2 and NaOH must be sufficient:
H2O2 not only plays a bleaching role in pre-treatment It has the function of pigments and has the function of removing impurities (including removing cottonseed hulls). If the amount of H2O2 is insufficient (including decomposing too quickly), the whiteness cannot be guaranteed; NaOH not only provides the alkali (pH) required for H2O2 bleaching, but also cooperates with the scouring agent. , to achieve the greatest impurity removal effect. If the amount of NaOH is insufficient, impurity removal will be poor, and the gross effect will not meet the requirements first. Of course, the whiteness cannot meet the requirements, so the amount of H2O2 and NaOH can be said to be the primary factor in ensuring whiteness and wool effect.
(2) Select high-quality scouring agent:
The scouring agent must have excellent comprehensive effects such as cleaning, emulsification, dispersion, and penetration. , to ensure the removal of impurities and ensure whiteness and wool effect. However, 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 a consideration. One aspect.
(3) Oxygen bleach stabilizer and chelating dispersant:
These two additives are mainly used to improve the essence. It adsorbs and complexes metal ions such as Fe3+ in water to prevent the rapid and ineffective decomposition of H2O2 caused by metal ion catalysis. If H2O2 decomposes quickly and ineffectively, its whiteness and wool effect will not meet the requirements, and it will also cause brittleness and even holes in the fabric. . Therefore, in order to achieve whiteness and wool effect, excellent oxygen bleaching stabilizers must be selected, and the decomposition rate of H2O2 must 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 reach If not, the pigments and impurities will not be completely removed, and the whiteness and hair effect will not be achieved.
(5) Washing:
It is very important to wash after scouring and bleaching. It is necessary to clean and remove the impurities to ensure the whiteness and Gross effect.
1:2 Cottonseed husk removal is not complete
Cottonseed husk removal It mainly relies on NaOH to expand and swell the cottonseed hulls under certain conditions, and then remove the cottonseed hulls with a certain mechanical cleaning force. The incomplete removal is mainly caused by insufficient temperature and time, so it must be allowed sufficient time at a certain temperature to completely remove the cottonseed hulls. To remove cottonseed hulls, H2O2 and scouring agents are helpful in removing cottonseed hulls, so there must be a certain temperature and time in the pre-treatment to ensure the removal of cottonseed hulls. At the same time, NaHSO3 or anthraquinones can be added to help remove cottonseed hulls. Remove.
1:3 Holes and brittle damage
Holes and In addition to singeing holes, hooking during processing, and original holes in the gray cloth, the main reason for brittle damage is the presence of Fe3+, Cu2+ and other metal ions in the H2O2 bleaching bath or on the cloth surface; these metal ions catalyze H2O2 Decomposes rapidly, causing fiber brittleness. If metal ions (such as rust, etc.) are too concentrated in one place, the fibers and yarns will become brittle and form holes. Therefore, in H2O2 bleaching, high-quality oxygen bleaching stabilizers and chelating dispersants must be selected to complex and absorb the fabric and The metal ions in the bleach bath prevent H2O2 from decomposing too quickly and causing holes or brittle damage. If it is used during bleaching
Of course, the cloth surface will be brittle and damaged if it contains alkali (the alkali is removed and it is not clean) or acid (the acid is removed and it is not clean). At the same time, under high temperature and alkali conditions, the fabric will be brittle and damaged when there is air. This situation can be prevented by adding weak reducing agents such as NaHSO3.
In addition, moisture and mildew in fabrics are also one of the causes of brittleness and holes.
2: Common quality problems in dyeing and the selection of auxiliaries
2:1 Unsatisfactory color fastness
Color fastness includes light fastness, soaping fastness, perspiration fastness, rubbing fastness, bloom fastness, ironing fastness Fastness, etc. The key to these fastnesses lies in the structural properties of the dye, and is also closely related to the 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 Application of additives.
When producing a dyeing process certificate, it must be reasonably determined based on the dye, fiber and customer indicators, so that the dye, with the help of additives, can dye the fiber as firmly as possible under certain conditions. Let it set fully. For auxiliaries, one is to use good leveling agents and dye accelerators to make the dye slowly, evenly and fully dye the fibers; the other is to add chelating agents toThe softener adheres to the fabric;
(2) There is too much foam after the soft sheeting, and when the cloth comes out of the vat, the fabric will be stained with softener foam;
(3) The water quality is poor, the hardness is too high, and the impurities in the water combine with the softener and aggregate on the fabric. Some factories even use sodium hexametaphosphate or alum to treat water. These substances and impurities in the water form floc, which causes stains on the cloth after entering the softening treatment bath;
(4) The cloth surface contains anionic substances, which combine with the cationic softener to form stains when softened, or the cloth surface contains alkali, which causes the softener to agglomerate;
(5) Softness The structure of the softener is different, and some cause the softener to change from an emulsified state to a slag-like substance that adheres to the fabric at higher temperatures;
(6) The original tar-like state in the tank Substances such as softener fall off and stick to the fabric.
3:1:8 Silicone oil stains
Silicon oil stains It is the most difficult type of stain to treat. The main reasons are:
(1) The pH value of the cloth surface is not neutral, especially with alkali, causing the silicone oil to break emulsification and float oil;
(2) The water quality of the treatment bath is too poor and the hardness is too high. Silicone oil can easily float in water with a hardness greater than 15Omg/L;
(3) Problems with the quality of silicone oil, including poor emulsification (poor emulsifier selection, poor emulsification process, too large emulsified particles, etc.), intolerance to shearing (mainly problems with the silicone oil itself, such as silicone oil quality, emulsification system , silicone oil varieties, silicone oil synthesis process, etc.).
You can choose silicone oil that is resistant to shear, electrolytes, and pH changes, but you should pay attention to the use method and environment of the silicone oil. You can also consider choosing hydrophilic silicone oil.
3:1:9 Poor fluffing
Poor fluffing It is closely related to the operation of the raising machine (such as tension control, raising roller speed, etc.). For raising, when applying softener (commonly known as waxing), controlling the dynamic and static friction coefficients of the fabric is the key, so the preparation of raising softener is the key. If the softener is not used properly, it will directly cause poor fluffing, and even cause tearing or door width changes.
3:2 Common quality problems in resin finishing
3:2:1 Formaldehyde problem
The formaldehyde content exceeds the standard due to the free formaldehyde in the resin or the formaldehyde decomposed from the resin with N-hydroxymethyl structure. Ultra-low formaldehyde resin or formaldehyde-free resin should be used.
Of course, formaldehyde problems come from a wide range of sources, such as color fixing agents Y and M, softeners MS-20 and S-l, waterproofing agents AEG and FTC, adhesives RF, and flame retardants. Additives such as THPC may sometimes cause formaldehyde to exceed the standard. At the same time, formaldehyde migration in the air may also cause formaldehyde on fabrics to exceed the standard.
3:2:2 Yellowing or discoloration problem
After resin finishing, yellowing will generally occur, so: Reduce yellowing and discoloration as much as possible.
3:2:3 strong drop problem
General resin finishing All will produce a decrease in strength, and fiber protective agents, such as oxidized polyethylene wax emulsions, can be added.
3:2:4 Handle problem
General resin finishing meeting If the hand feels hard, you can add soft ingredients, but be careful not to affect the quality of the resin finishing. The hand feel has improved, and the problem of power drop has also been greatly improved. However, problems such as a hard feel caused by surface resin are caused by the resin itself and drying, and need to be improved accordingly.
3:3 Other quality issues
3:3:1 Metal ions exceeding the standard
Metal ions Cu, Cr, Co, Ni, Zn, Hg, As, Pb, Cd, etc. need to be detected in export products. If they exceed the standard, it is also like formaldehyde exceeding the standard. It will also have serious consequences. Among the additives, there are relatively few metal ions of this type, but some additives can cause exceeding the standard. For example, the flame retardant antimony trioxide emulsion contains a large amount of mercury, and the waterproofing agent CR, phoboTexCR (Ciba), Cerolc (Sandoz), etc. chromium. When using mordant dyes on wool, the mordant dye used is potassium dichromate or sodium dichromate or sodium chromate, and Cr6+ will exceed the standard.
3:3:2 Color change problem
After menstruation After finishing, there are many problems with color changes. This requires attention to the selection of dyes during dyeing. During dyeing, corresponding finishing must be carried out according to the process to determine whether the selected dye will change color under the action of additives. Of course, it is ideal to choose a finishing agent that does not cause discoloration, but this often has limitations (for example, copper-containing antibacterial agents have colors themselves, and chromium-containing waterproofing agents also have colors, which can cause fabric discoloration. ), and factors such as light color and color change caused by dye sublimation during drying and baking of dyed fabrics, and yellowing caused by excessive temperature should also be taken into consideration.
3:3:3 APEO exceeds the standard
APEO as a The indicator is also strictly restricted by some countries. This indicator is related to the scouring agent and penetrating agent in pre-treatment, the cleaning agent and leveling agent in printing and dyeing, and the emulsifier in the softener during finishing. It is not yet available. When TX and NP series surfactants are widely used as raw materials for additives, it is difficult to prevent them. The only way is for printing and dyeing factories to insist on using environmentally friendly additives and strictly prevent additives containing APEO and toxic and harmful substances from entering the factory.
There are many common quality problems in dyeing and finishing products, and there are many reasons for them. Some quality problems cannot even be analyzed. Here we only discuss the relationship with auxiliaries. It is inappropriate to communicate with peers. If there are any errors, I would like to ask experts to correct me.
Regarding the relationship with auxiliaries and communication with colleagues, if there is anything inappropriate, I kindly ask experts and colleagues to correct me.
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