The visual manifestation of silicon spots on the surface of fabrics is as small as a needle tip or as large as a rice grain. The oil spots may become larger under extreme conditions. Sometimes the oil spots will have a certain color due to floating color. The spots are like small wet spots, soft and non-grainy to the touch, and are extremely difficult to find and remove before drying. The reason is caused by the demulsification and bleaching of silicone oil, which often occurs after finishing and washing.
The formation of silicon plaque
The mystery of silicone oil and waterproofing agent molecules Veil
1. Ordinary silicone oil molecular structure
2. Molecular structure of waterproofing agent
3. Effect diagram and schematic diagram of finishing agent on fabric surface
Causes of silicone oil spots
1. Alkaline problem
Cotton fabrics usually need to be treated with a higher concentration of alkali to remove fabric impurities (especially mercerizing alkali, which uses a larger amount). It is difficult to clean the fiber when alkali enters the interior. Alkali must also be added during dyeing (reactive vat dyes). , so the cloth surface may be alkaline during finishing.
Chemical fiber fabrics must be restored and cleaned after dyeing. Currently, printing and dyeing factories still use insurance powder and caustic soda for cleaning. If the subsequent cleaning is not clean, it will also cause softness on the front. The cloth contains alkali. Ordinary silicone oil is not resistant to alkali and will break emulsification under alkaline conditions. This is the reason why the factory will stick to the roll after several kilometers of padding. Therefore, before softening, the cloth surface must be washed with alkali or acetic acid added to the working fluid to keep the rolling groove pH 5-6.
2. Cohesion problem
On fabrics containing short fibers (cotton cloth, T/R cloth, velvet type), some short fibers will inevitably fall off during the processing. The short fibers falling off the cloth accumulate in the rolling groove, and will cohesion with ordinary silicone oil. The finishing liquid goes up to the roller and sticks to the silicone oil that is extruded and demulsified, forming sticky roller or silicon spots. When the water quality is relatively poor, it will also condense with ordinary silicone oil to produce sticky rollers. In addition, similar situations will also occur with velvet fabrics. Do a good job of cleaning before driving, and clean them at any time if you find any lint.
3. Charge stability issues
Dye and whitening used in cotton cloth Most of the agents are anionic, and cotton whitening is basically done on the setting machine. In addition, dyed fabrics need fine-tuning and color correction when the shade is wrong. Color correction usually involves adding a small amount of dye or paint when applying the softening agent. Factories generally use ordinary silicone oil (weak cations), which will produce negative and positive charge attraction reactions, causing agglomeration and sticky rollers. , and the softness of the anionic silicone oil did not meet the requirements, causing confusion in the factory. Charge consistency must be considered during processing.
4. Temperature problem
Fabrics dyed by long cotton machines All the fabrics must be dried in a drying drum and packaged in large rolls or stacked in cloth boxes. If the cloth is not cooled sufficiently, especially the cloth in large rolls, the surface temperature of the fabric may be high when it is soft, causing the temperature of the rolling tank working fluid to rise. High (especially in summer), sometimes reaching more than 60℃, and ordinary silicone oil may also cause roller sticking when its heat resistance is not good.
It is better that the temperature in the rolling tank does not exceed 40 ℃.
5. The issue of fixed vehicle speed
The factory is making some thin fabrics At this time, the setting speed is very fast, sometimes reaching a speed of 60 meters/minute. Due to the poor permeability of ordinary silicone oil, the silicone oil flows back on the roller, causing the roller to stick. Pay attention to changing the working fluid in the rolling groove and wiping the roll frequently.
6. Dip vat problem
Many factories are doing impregnation softening Ordinary silicone oil will stick to the cylinder wall. Over time, some black oil spots will form on the cylinder wall, and silicone oil spots will form on the cloth surface. Increase cleaning efforts.
7. Handle problem
Due to the current demand for fabrics in the market The requirements for hand feel are getting higher and higher, and various fabrics need to show various style requirements due to different seasons and different customer requirements. Some require smooth drape, smooth and flexible, fluffy and soft, and simple elasticity. etc. A kind of silicone oil can generally only reflect one style. As a result, many factories have to use many kinds of silicone oil, causing production confusion. Sometimes they cannot find the silicone oil that suits the customer’s requirements, so they have to give up business and cause losses. We can synthesize amino silicone oils with different ammonia values, viscosity and reactions to meet the softness, smoothness and elasticity requirements of various fibers by selecting amino silicone oil end groups with different ammonia values to control the molecular weight and molecular distribution.
8. Cost issue
The biggest concern for printing and dyeing factories at present The problem is cost. Since the prices of water, electricity and gas are rising, while the printing and dyeing processing fees are decreasing, many printing and dyeing factories have been busy for a year but have basically no profits. Therefore, cost control is a problem that printing and dyeing factories need to solve.
Removal of silicone oil spots
1. The fabric has not been set at high temperature
①Acetic acid washing
②High-temperature treatment with solvent-based degreaser.
2. The fabric has been set at high temperature
Specialized fluorine and silicon stripping The agent is treated under alkaline conditions.
The main principle is to hydrolyze the fluorosilicone chains by boiling under alkaline conditions, and then use the fluorosilicone stripping agent to The emulsification and dispersion ability can emulsify, disperse and seal the hydrolyzed fluorosilicone segments in time, thus completing the removal of silicone oil spots and waterproof spots.
Note that serious and difficult-to-remove cases can be removed with alkali , fluorine stripper by adding oil remover and hydrogen peroxide. In addition, the amount of stripper can be appropriately increased according to the severity of waterproof spots and silicone oil spots. If one treatment cannot completely remove it, the number of removal steps can be appropriately increased. To complete spot removal.
For regenerated cellulose fibers or protein fibers, due to their poor alkali resistance, it is recommended to use soda ash to adjust the PH value of the treatment bath to 8.5-9.5. Avoid strong damage or excessive protein loss.
Silicon oil bleach
When amino silicone oil emulsion is used together with color fixing agents, soft oils, etc., silicone spots sometimes occur, but not when used alone. Why?
Amino silicone oil and color fixing agents, Soft oil and other additives are incompatible, causing silicone oil to float.
Amino silicone oil emulsion is a cationic surfactant (or weak cation), and many chemicals are used in the dyeing process. They are anionic surfactants, such as dyes (some dyes are anionic), leveling agents, spreading agents, color fixing agents…, these chemicals are used after dyeing and finishing processing and before softening and finishing. Once they are not washed thoroughly, When the cationic amino silicone oil series softener reacts with the anionic substances in the dye bath, the amino silicone oil cationic emulsion will be demulsified and the bleached oil will appear soft spots (silicon spots). The effective method is to strengthen sufficient water washing before softening and finishing. It is best not to perform softening and finishing in the same dyeing machine. After dyeing and washing, pour out the fabric and perform softening and finishing in the padding car.
The special vat is too soft, which can effectively prevent Or reduce the formation of soft spots (silicone spots).
Common softness problems in printing and dyeing production
1. Decreased hydrophilicity of fabrics
Usually due to structural problems of the film used, the lack of water-absorbing genes after the silicone oil film is formed, and the blocking of hydroxyl groups like cellulose fibers , carboxyl groups, amino groups and other water-absorbing centers on wool cause a decrease in water absorption.
Treatment method: Anionic, nonionic film and hydrophilic silicone oil should be used as much as possible.
2. Dark spots
Causes:
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① The oil stain on the fabric was not removed during pre-treatment, and the color of the oil stain was darker during dyeing.
② There is too much foam in the dyeing bath, and the mixture of foam, floral sweaters, dyes, etc. stains the fabric.
③ Oil drifting from the defoaming agent causes dark oil spots.
④ Tar-like substance in the dye vat is stained on the fabric.
⑤ The dye agglomerates under different circumstances to form dark stains.
⑥ Excessive calcium and magnesium ions in the water combine with dyes and stain the fabric.
Processing method:
① Add degreaser for refining during pre-treatment.
② The dyeing auxiliaries use low-foaming and non-foaming auxiliaries.
③ Choose a defoaming agent that is not easy to float oil, add a chelating agent to improve the water quality, and add a solubilizing and dispersing agent to prevent dye aggregation. Use tank cleaning agent to clean and wash the tank promptly.
3. Light spots
Reasons:
① The pre-treatment is uneven, and the hair effect in some parts is not good, resulting in a certain degree of dye repellency and dye-repellent substances. During pre-treatment, the cloth contains calcium soap, magnesium soap, etc. or the mercerization is uneven.
② The semi-finished product is unevenly dried.
③ The cloth surface is stained with undissolved Yuanming powder, soda ash and other solids.
④ Add water to the dyed material before drying.
⑤ Stains caused by additives during finishing such as softening of dyed goods.
Treatment method: Strengthen pre-treatment. When selecting pre-treatment additives, it must be difficult to form calcium-magnesium soap. Pre-treatment must be uniform and thorough (this is related to scouring agents, penetrants, chelating and dispersing agents). agent, mercerizing penetrant, etc.). Yuanming powder, soda ash, etc. must be melted into the tank and production management must be strengthened.
4. Alkali spots
Causes: pre-treatment ( Such as bleaching, mercerization), the alkali removal is not clean or uneven, resulting in alkali spots.
Treatment method: The alkali removal process in the pre-treatment process must be strengthened.
5. Silicone oil stains
Cause: Cloth surface The pH value is not neutral, especially with alkali, causing the silicone oil to break emulsification and float oil. 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 of >150PPM. Silicone oil quality problems include poor emulsification (poor emulsifier selection, poor emulsification process, too large emulsified particles, etc.) and intolerance to shearing. Choose silicone oil that is resistant to shear, electrolytes, and pH changes, but pay attention to how the silicone oil is used and the environment. You can also consider choosing hydrophilic silicone oil.
Editor’s note
Currently, most dyeing factories rely on central control With the development of modernization, intelligence and science and technology, employees also operate according to factory processes and are extremely careful. Problems will inevitably occur. Production is no small matter and every production step is important.
, with the development of science and technology, employees also operate according to factory processes and are extremely careful, but problems will inevitably occur. There is no small matter in production, and every production step is important. </p
