About the printing and dyeing process of knitted fabrics
Regarding the printing and dyeing process of knitted fabrics 1, why knitted fabrics need to be printed and dyed, and what processes are required for printing and dyeing. Dyeing and finishing of knitted fabrics is one of the main processes in the production process of knitted fabrics. It plays an important role in improving the appearance and wearing performance of knitted fabrics, improving the intrinsic quality, and increasing the variety of designs and colors. The dyeing and finishing process of knitted fabrics starts with knitted fabrics, which undergo scouring, bleaching, and dyeing. , printing, finishing and other processing processes to make it into a product with bright colors and colorful flower shapes and good wearing properties, providing raw materials for the next level of sewing processing factories. Knitted fabric dyeing and finishing plant knowledge includes six parts: fiber, weaving, refining and bleaching, dyeing, printing and finishing. The basic knowledge of fiber processing includes the structure, composition, and physical and chemical properties of fiber materials. It mainly includes fiber——weaving——refining and bleaching——-bleaching——dying ——-Printing—–Finishing Someone has already talked about the above fibers and weaving. I mainly focus on refining and bleaching—– Bleaching—–Dyeing—-After finishing, in order to talk about the dyeing process, you must first know the commonly used textile fibers. The codes of commonly used textile fibers: Several commonly used textile fibers are generally represented by the following codes:– ——Cotton: C Wool: W Linen: L Silk: S Polyester: T or P Eyes: A Vinyl: V Viscose: R Polyester: T/C Polyester: T/R Wool: A /W etc. N: Nylon The fibers we often dye are: cotton – dyed with reactive dyes, polyester – dyed with disperse dyes, wool dyed with cationic dyes – dyed with acid dyes such as T/ C Polyester cotton fabrics such as single-dyed cotton are dyed with reactive dyes. The polyester will not be colored and the dyeing effect will be like ash. When single-dyed polyester is dyed with disperse dyes, the cotton will not be colored, and the dyeing effect will be like ash. For example, if T/C cloth is dyed polyester first and then cotton, the dyeing effect will be plain color without the gray effect. Similarly, T/R can be dyed with polyester T in one bath, or R in one bath. R can be dyed with reactive dyes, or it can be dyed in two baths, that is, dyeing both T and R. The dyeing effect will be plain color, without Ash effect. However, when dyeing single-bath polyester, there may be a little stain on the cotton, so the stain on the cotton must be washed away after one-bath dyeing. Washing methods include washing with soaping agent for light colors, and cleaning with insurance powder and caustic soda for dark colors. If the cotton is dyed by the one-bath method, there will be a little stain on the polyester, but the stain on the polyester must be washed off after dyeing the cotton. You can only use detergent to wash away the floating color, do not use insurance powder, or caustic soda to wash the floating color. , because after cotton is reactively dyed, all the colors will be stripped off when encountering insurance powder and caustic soda. 2. Let’s talk about each process in detail. Let’s talk about the cationic dyeing process first. 1. The basic principle of cationic dyeing. The dyeing of acrylic with cationic dyes is mainly due to the ionic bond generated between the acidic groups of the acrylic molecules and the pigment cations of the cationic dyes. At the beginning of dyeing, since the surface of acrylic has a high negative potential, the dye and pigment cations are quickly adsorbed on the surface of the acrylic, neutralizing the negative charges. This adsorption only occurs on the surface of the fiber and does not reach the interior of the fiber. As the temperature increases, when the temperature reaches the glass transition temperature of acrylic, the micro-gaps between the molecular chains increase due to the generation and intensification of the movement of the molecular chain segments. At this time, the dye diffuses into the fiber because of the acrylic structure. It is relatively close, and there is a large electrical attraction between the dye and the fiber, so the diffusion resistance of the dye inside the fiber is relatively large. Therefore, some people think that the dye diffuses one by one. The diffusion of some anti-ionic dyes in acrylic requires high energy, so dye migration is difficult. Temperature has a great influence on the diffusion rate of dyes. 2. Dyeing characteristics of cationic dyeing A: Cationic dyeing has a saturation value. What is the saturation phenomenon and saturation value of cationic dyeing? Dyeing acrylic with cationic dyes relies on the ionic bonding between the dye and the acidic groups on the fiber. Because one acidic group can only adsorb one dye cation, this sub-adsorption is positional adsorption. The content of the third monomer in acrylic is relatively low, so the content of acidic groups is limited. When all the acidic groups in the fiber are adsorbed by the dye cations (that is, the dye seats are full), increase the amount of acidic groups in the dye bath. Depending on the dye content, the dye cannot be adsorbed by the sub-fiber. This phenomenon is called the saturation phenomenon of dyeing. Acrylic can absorb a large amount of cationic dyes called the saturation value of dyeing. The radical saturation value is roughly equivalent to the acidic radical content on the fiber. When the dyeing reaches the saturation value, if the dye concentration in the dye bath is increased, the dye on the fiber will remain unchanged. Therefore, the saturation value of acrylic is an important indicator of acrylic dyeing. The saturation value of acrylic varies with different dyeings, and different dyes have different dyeing abilities for the same fiber. Therefore, different dyes have different saturation values for the same fiber. How to know the saturation value? Let’s talk about the soil method. The saturation value of domestic acrylic and the saturation value of imported acrylic. B: Level dyeing problem of cationic dyed acrylic: When cationic dyes are used to dye acrylic, due to their rapid adsorption, it is easy to cause uneven adsorption. In addition, when the glass transition temperature is above the glass transition temperature, the dyeing rate increases rapidly, and excessive temperature rise can easily cause dyeing. Uneven. In addition, cationic dyes and clear�Simple, so the intermolecular force is small, and sublimation is easy to occur at high temperatures, resulting in fading and staining after dyeing and setting. Sublimation fastness is an important indicator of disperse dyes. Large molecular weight and good sublimation fastness. 3. Diffusion: Due to the tight structure of polyester and the small gaps between fibers, the diffusion of dyes within the fibers is very difficult, so the disperse dyes used for dyeing are required to have good diffusion properties. General disperse dyes have a simple molecular structure and small intermolecular forces, so they have good diffusion properties. However, diffusion properties and sublimation fastness are contradictory. Good diffusion properties have poor sublimation fastness. Poor diffusion properties have poor sublimation fastness. good. Therefore, when selecting disperse dyes, various factors must be considered to make a reasonable selection of dyes. 3. Dyeing methods with disperse dyes: Disperse dyeing methods; there are high temperature and high pressure methods, hot melt methods, and carrier methods. The first two methods use increased temperature to quickly coat the disperse dyes on polyester. The latter method is to add an additive to the dye bath that bulks the polyester, thus accelerating the dispersion of the dye and increasing the dye loading. Currently, high-temperature and high-pressure dyeing is used. High-temperature and high-pressure dyeing of disperse dyes is carried out at temperatures higher than 100 degrees, so it must be carried out in closed and pressure-resistant dyeing equipment. Dyeing, this method uses increased temperature to improve dispersion. The dye uptake rate is high, so not only the dye uptake rate is high, but also the covering effect is good. Most disperse dyes can be dyed using this method. Methods that affect high-temperature and high-pressure dyeing; 1. Temperature: Temperature is the key factor in high-temperature and high-pressure dyeing. Increasing the temperature can increase the dye uptake % of disperse dyes. But when the temperature reaches above 130 degrees, the dye uptake percentage of most disperse dyes no longer increases significantly. Excessive temperature will cause the hydrolysis of polyester ester bonds, resulting in a decrease in the elasticity and strength of the fiber and a difference in color and light. Therefore, high temperature and high pressure dyeing is generally limited to no more than 145 degrees. Generally, the dyeing temperature is controlled between 125-130 degrees. Dyeing at this temperature not only has good level dyeing and high color yield, but also the PH value of the dye bath is controlled within the weak acid range of 5-6. Most of the Disperse dyes are quite stable and therefore produce very bright colors. In order for the dye to be evenly adsorbed by polyester, the heating rate must be strictly controlled. When the temperature rises to the specified temperature, the dyeing should be kept warm for a period of time to ensure that the dye is fully diffused and penetrated. The heat preservation dyeing time is generally 30-60 minutes, which can be shorter for light colors and longer for dark colors. After dyeing, do not cool down too quickly, otherwise it will affect the feel and cause creases. 2. PH value; many disperse dyes will hydrolyze under high-temperature and alkaline conditions, so it is better to control the acidic conditions in high-temperature and high-pressure dyeing baths. 3. Application of additives, in order to stabilize the dye during high-temperature and high-pressure dyeing Dispersed in the dye bath, and in order to obtain a leveling effect, an appropriate amount of dispersant and leveling agent can be added to the dye bath. Commercial dyes are mixed with a large amount of dispersants. 4. Precautions for high-temperature dyeing. High-temperature and high-pressure dyeing often causes color flowers, color stains, color spots, and other defects due to improper process and poor operation. Therefore, you should pay attention to the dyeing process when dyeing. Pay attention to the following matters 1. Preparation of dye liquor: When preparing the dye liquor, you should first use a small amount of cold water to make the dye into a slurry, and then dilute it with room temperature water. Note that the dilution water temperature should not be too high, higher than 60 degrees, and the dispersed The dye quilt will be damaged and condensed. In addition to the above preparation, the dye can also be prepared by the dusting method, that is, slowly sprinkle the dye into cold water under high-speed stirring. It should not be left for a long time after the dye bath is prepared. It is necessary to stir slowly with a stirrer to prevent precipitation. 2. Selection of dyes: When dyeing, try to choose varieties with good diffusion and leveling properties. When color matching, you should choose dyes with relatively close dyeing properties. 3. Restoration cleaning; Restoration cleaning is an important part of removing floating colors. After restorative cleaning, the color faded slightly. At the same time, the rubbing fastness and light fastness are improved. 4. Prevention of tar spots: The so-called tar spots are viscous substances formed in the dye liquor. The main ingredients are dye dispersants and polyester oligomers. When polyester oligomer is polycondensed, it will seep out of the fiber and flow into the dye liquor to adhere to the surface of the fiber during the high temperature and long-term dyeing process. Measures to prevent tar spots include: 1. Strengthen fabric pre-treatment. 2. Increase the dyeing bath ratio. 3. Apply high temperature and high pressure dispersant. 4. Use high temperature drainage to avoid crystallization of the dye after cooling. 5. Shorten the equipment cleaning cycle. In addition to the above mentioned points of attention, when dyeing at high temperature and high pressure, the dyeing pH value should also be strictly controlled, the temperature rise speed should be controlled well, the circulation of the dye liquor should be accelerated, and the temperature distribution in the dye bath should be uniform to prevent color blooming and color difference
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