The intuitive manifestation of silicon spots on the fabric surface is the appearance of oil spots as small as a pin tip or as large as a rice grain. Under extreme conditions, the area may be larger. Sometimes the oil spots have a certain color due to floating color. The spots are like small Wet spots, soft and non-grainy to the touch, are extremely difficult to spot and extremely difficult to 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
1. The molecular structure of ordinary silicone oil
2. Molecular structure of waterproofing agent
3. Effect diagram and schematic diagram of finishing agent on fabric surface
Causes of the formation of silicone oil spots
1. Alkaline problem
When cotton fabrics are pre-treated, a higher concentration of alkali treatment is usually used to remove fabric impurities (especially The amount of alkali used in mercerization is larger). The alkali enters the inside of the fiber and is not easy to clean. When dyeing (reactive vat dye), alkali is also added, 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 the soft front fabric surface to be stained with 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, T/R cloth, velvet), it is inevitable during processing Some short fibers will fall off, and the short fibers falling off the cloth will accumulate in the rolling groove and cohere with ordinary silicone oil. As the finishing fluid moves up to the roller, it will bond with the extruded and demulsified silicone oil. Sticky rolls or silicon spots form. 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 problem
Most of the dyes and whitening agents used in cotton 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 a 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 issues
The cloth dyed by the long cotton machine must be dried in a drying drum and packaged in large rolls or piled in cloth boxes. If it is not cooled sufficiently, especially for large rolls of cloth, the surface temperature of the fabric may be high when it is soft, causing the temperature of the rolling tank working fluid to rise (especially in summer), sometimes reaching more than 60°C, while ordinary silicone oil is resistant to If the heat resistance is not good, it will also cause the roller to stick. It is better that the temperature in the rolling groove does not exceed 40 ℃.
5. The problem of shaping speed
When the factory is making some thin fabrics, the shaping speed is very fast, sometimes reaching a speed of 60 meters/minute. Normally Due to poor permeability of silicone oil, silicone oil flows back on the roller, causing roller sticking. Pay attention to changing the working fluid in the rolling groove and wiping the roll frequently.
6. The problem of cylinder sticking
When many factories are doing impregnation and softening, ordinary silicone oil will stick to the cylinder wall. Over time, the cylinder wall will Some black oil spots will form, which will form silicone oil spots on the cloth. Increase cleaning efforts.
7. Handle problem
As the market now has higher and higher requirements for the feel of fabrics, and various fabrics have different customer requirements due to different seasons. , need to show a variety of different style requirements, some require smooth drape, smooth and flexible, fluffy and soft, pure elasticity, etc. A kind of silicone oil can generally only reflect one style. Therefore, 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 most confusing issue for printing and dyeing factories at present is the cost issue. Since the prices of water, electricity and gas are constantly rising, printing and dyeing However, processing fees are decreasing, causing many printing and dyeing factories to be busy for a year but making almost 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 exposed to high temperatures Styling ① Acetic acid washing ② High temperature treatment with solvent-based degreaser.
2. The fabric has been set with high-temperature fluoropolymer��Silicon stripper is processed under alkaline conditions. The main principle is to hydrolyze the fluorosilicone chains by boiling under alkaline conditions, and then use the emulsification and dispersion capabilities of the fluorosilicone stripper to emulsify, disperse and seal the hydrolyzed fluorosilicone segments in time. This completes the removal of silicone oil spots and waterproof spots.
Note that for severe cases that are difficult to remove, you can add oil remover and hydrogen peroxide to alkali and fluorine strippers. In addition, the amount of stripper can be appropriately increased according to the severity of waterproof spots and silicone oil spots. Dosage, if one treatment cannot completely remove it, you can increase the number of removal steps appropriately to complete the 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 to avoid strong damage or excessive protein loss.
3. Silicone oil drift
Silicone spots sometimes appear when amino silicone oil emulsion is used at the same time as color fixing agent, soft oil, etc. This phenomenon does not occur when used alone. Why? Amino silicone oil is incompatible with color fixing agents, soft oils and other additives, causing the silicone oil to float. Amino silicone oil emulsion is a cationic surfactant (or weak cation), and many chemicals used in the dyeing process are anionic surfactants, such as: dyes (some dyes are anionic), leveling agents, spreading agents, color fixing agents agent. . . Once these chemicals are not washed thoroughly after dyeing and finishing and before softening, when the cationic amino silicone oil series softener reacts with the anionic substances in the dye bath, the amino silicone oil cationic emulsion will break and the bleached oil will appear soft. For spots (silicone spots), the effective way is to strengthen sufficient washing before softening and finishing. It is best not to perform softening and finishing in the same dyeing machine. After dyeing and washing, the fabric is poured out and softened in a padding car.
Note: The special cylinder is too soft, which can effectively avoid or reduce the formation of soft spots (silicone spots).
Common softness quality
1. The decrease in hydrophilicity of fabrics is generally caused by the structure of the soft film used, the lack of water-absorbing genes after the silicone oil film is formed, and the sealing Water-absorbing centers such as the hydroxyl groups of cellulose fibers, carboxyl groups, and amino groups on wool cause a decrease in water absorption. Treatment method: Anionic, non-ionic film and hydrophilic silicone oil should be used as much as possible.
2. Reasons for dark spots: ① The oil stains on the fabric were not removed during pre-treatment, and the oil stains were darker in color 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 The defoaming agent drifts oil and causes dark oil spots. ④ The 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. Treatment method: ① Add degreaser for refining during pre-treatment. ② Use low-foaming and non-foaming auxiliaries as dyeing 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 dispersant to prevent dye aggregation. Use tank cleaning agent to clean and wash the tank promptly.
3. Light stains
Causes: ① Uneven pre-treatment, poor hair effect in some parts, resulting in a certain degree of dye repellency. Contains 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 post-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, and pre-treatment must be uniform and thorough (this is related to the selection of scouring agent, penetrating agent, chelating dispersant, mercerizing penetrating agent, etc.). Yuanming powder, soda ash, etc. must be melted into the tank and production management must be strengthened.
4. Alkali spots
Cause: Alkali removal after pre-treatment (such as bleaching, mercerization) is not clean or uniform, resulting in alkali spots. . Treatment method: The de-alkali process of the pre-treatment process must be strengthened.
5. Silicone oil stains
Cause: The PH value of the cloth surface is not neutral, especially with alkali, causing the silicone oil to break and float. . 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 the use method and environment of the silicone oil. You can also consider choosing hydrophilic silicone oil.
Editor’s Note
At present, most dyeing factories are developing towards centralized control, intelligence and technology. Employees also operate according to factory processes, so be careful. Even if you are careful, problems will inevitably occur. Production is no small matter and every production step is important. </p
