Introduction
Product defects are an important factor affecting the quality of dyeing and finishing products, and are also an important indicator of the production level and management level of an enterprise. Pretreatment is the front step of dyeing and finishing, and it is also a very important step. In daily production, if there are many defects in the pre-processed semi-finished products, it will not only cause a waste of manpower and material resources, but also reduce the quality of the finished products and affect the reputation of the factory. Therefore, it is necessary to improve the quality of the pre-processed semi-finished products and strive to reduce the defects of the pre-processed semi-finished products. It is an important task of the dyeing factory. This article describes common spot defects in the pretreatment process based on their shapes, causes, and overcoming solutions.
1. Common spot defects during pre-treatment
1. Macula; 2. Oil spots; 3. Plasma spots; 4. Whitening spots; 5. Alkali spots;6. Rust spots;7． Calcium plaque; 8. Air dry print.
2. Causes and solutions
1, macula
①.Cause analysis
The usual cause of yellow spots is the use of river water, especially during the rainy season. This is mainly due to the poor water quality of the river water. River water contains organic suspended solids. During the pre-treatment process, these organic suspended solids are not fully dispersed. During the pre-treatment process, these organic suspended solids re-agglomerate together with the impurities treated on the fabric and return to the fabric, causing yellow spots. During the post-finishing process, if the macular spots are whitened, they will produce whitening spots; if they are dyed, they will produce stains, etc.
②.Solution: For the macula caused by this reason, a chelating dispersant with good dispersion should be selected during the pre-treatment process. The chelating dispersant has a certain chelating power and can chelate metal ions in the water. , has excellent dispersing properties, is equivalent to a reactive dispersant, is highly targeted and has better effects.
2, oil spots
①.Cause analysis
Pre-treatment oil spots mainly appear as oily, almost transparent dot-like spots produced during the pre-treatment process. The general cause is that the fabric contains a large amount of chemical fiber oil and spandex oil such as dimethyl silicone oil on the spandex-containing fabric. After these oils were cleaned during the pre-treatment process, they were not fully emulsified and dispersed, causing agglomeration and back-staining on the fabric. Especially low-grade chemical fiber fabrics that use inferior chemical fiber oil or increase the amount of oil are prone to oil spots.
②.The solution is for chemical fiber oils and dimethyl silicone spandex oils. It is necessary to choose an emulsified degreasing agent with excellent dispersion of oils. The effect of combined use with degreasers is not heavy on oils. The fabric can be used alone.
3, plasma spots
①.Cause analysis
Mainly because the fabric contains a large amount of chemical slurry. Generally, chemical slurries are high-molecular polymers with relatively high degree of polymerization, high viscosity, and easy agglomeration. After being washed off during the pre-treatment process, it was not fully emulsified and dispersed, causing agglomeration and staining on the cloth surface. Its shape is similar to cloudy white or yellow patches. Some are similar to sticky substances or yellow gel-like substances, which stick to the fabric and form irregular dots.
②.Solution
In view of the above situations, a dispersant or desizing agent with excellent slurry dispersion performance should be selected during the desizing process. Emulsifying refining agent has excellent dispersion effect on slurry, decontamination effect, and emulsification effect on oil agent. The desizing agent focuses on the desizing effect and has a good dispersing effect on the slurry. They all belong to the surfactant type and achieve desizing and anti-staining prevention through penetration, emulsification and dispersion. Mostly used in continuous desizing and overflow machines.
In addition, especially PVA (polyvinyl alcohol) slurry, the solubility in water has a certain relationship with temperature. The temperature drops suddenly and the PVA in the desizing tank will re-agglomerate. This agglomerated particulate matter returns to the cloth surface and causes pulp spots. Therefore, the temperature of the desizing liquid cannot be high or low. In addition, the desizing fluid must be replaced regularly. During the desizing process, the slurry concentration in the desizing tank will gradually increase. When it reaches the saturation point, the slurry will re-agglomerate and become stained again. Therefore, the desizing fluid must be replaced in time.
4, whitening spots
①.Analysis of causes1) It is caused by water quality. High water hardness and many impurities can cause whitening spots during whitening;
2) Due to the re-staining of the slurry, whitening spots will occur when the areas where the slurry spots appear are whitened;
3) Whitening spots will appear when the oily cloth surface is whitened due to the re-staining of oil stains.
②.Solution
1) For whitening spots caused by water quality, water treatment should be strengthened during pre-treatment, and chelating dispersants should be added to improve water quality.
2) If it is caused by slurry back-staining, add emulsifying desizing agent during desizing to improve emulsification and dispersion. After desizing, strengthen water washing to prevent slurry back-staining.
3) If the oil is stained back, strengthen the oil-removing lotion.For chemical properties, use an emulsifying degreaser.
5, alkali spots
①.Cause analysis
The scouring liquid contains a lot of impurities, which causes the alkali-containing impurities to stick to the fabric; the scouring liquid is not dried in time after desizing and mercerization, resulting in air-drying marks and alkali spots.
②.Solution
1) Wash and dry in time after desizing and mercerizing;
2) If the scouring liquid contains many impurities, add chelating dispersant to the scouring liquid to improve the water quality and prevent the occurrence of alkali spots; 3) Repair of alkali spots. If it is confirmed to be an alkali plaque, it can be removed by washing with dilute hot hydrochloric acid.
6, rust spots
①.Cause analysis
Rust spots are caused by rust on the gray cloth itself, raindrops when storing the cloth, and leakage from the iron roof; rust on cloth trucks and equipment, and rust and rot in water pipes may all cause rust spots.
②.Solution1) When the water is stopped or the production is stopped for a long time before production, it is necessary to drain the water for a while and then add water for production or wrap gauze at the water pipe mouth and filter the water before production.
2) The gray fabric itself has rust, which can be washed away with warm oxalic acid and then pre-treated. Note that fabrics treated with oxalic acid must be washed with clean water to prevent the fabric from becoming brittle and causing a decrease in strength. Methods for cleaning rust spots, for reference only: grass
Acid
20g/L
Acetic acid (98%) 30ml/L
7, Calcium Plaque①.Cause Analysis
Mainly caused by the hardness of water. Due to the high hardness of water, there are more calcium and magnesium ions in the water. During scouring, insoluble calcium and magnesium substances will precipitate, which will adhere to the fabric and cause calcium spots. In addition, during bleaching, due to the residual calcium on the fabric (such as the number of times the bleach is used) Calcium chlorate, the lime decomposed in the bleach), if not washed, can easily cause calcium spots.
②.Solution
If the water used for printing and dyeing is hard, some water softeners, sodium hexametaphosphate, CT powder, etc. should be added during pre-treatment to soften the water; in addition, the calcium remaining on the fabric during bleaching Pay attention to washing.
If calcium spots are found before dyeing, they can be removed by washing with dilute hot hydrochloric acid.
8. Analysis of the causes of air-drying printing①.This kind of air-drying printing mainly occurs after desizing and before oxygen bleaching. The shapes of defects include dots and irregular horizontal strips. After such defects occur, they cannot be covered up in subsequent processes such as whitening and dyeing. These defects are mainly caused by the slurry not being completely washed after desizing, the wet cloth being stored for too long, and the stains caused by partial drying of the fabric exposed to the air surface.
②.Prevention and solutions1) Preventive measures
Reasonably control the production progress. The fabrics after desizing and in front of the oxygen bleaching machine cannot be stacked too much, and the stacking time cannot be too long; strengthen the cleaning of fabrics after desizing. If there are too many fabrics after desizing, plastic can be used The film covers the fabric to prevent parts of the fabric from being blown dry and causing air drying marks. 2) Solution
After air-drying marks appear, the fabric that produced the air-drying marks should be desized again and then oxygen-bleached. The air-drying marks can be removed.
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