Common dyeing problems of knitted fabrics include unqualified color fastness/brittleness/wrinkles/wind marks/color spots
1. Unqualified color fastness
Color fastness includes light fastness, soaping fastness, perspiration fastness, rubbing fastness, sublimation fastness, ironing fastness, etc. The key to these fastnesses lies in the structural properties of the dye, and is also related to the fiber, dye concentration, Dyeing and finishing processes, external conditions, etc. are closely related, so the key to whether the color fastness reaches the standard is the selection of dyes, followed by the application of dyeing processes and auxiliaries.
When formulating the dyeing process, 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 and fully fix it. For additives:
First, choose good leveling agents and dye accelerators to make the dye slowly, evenly and fully dye the fiber;
The second is to add chelating agents to overcome the floating color caused by the complexation of dyes with metal ions in the water, and reduce the hydrolysis of reactive dyes in water;
The third is to choose an excellent soaping agent to remove the floating color and prevent the floating color from re-staining the fabric;
The fourth is to choose an appropriate fixing agent. Currently, there is no ideal fixing agent for sublimation fastness, light fastness, etc. There are excellent fixing agents for soaping fastness, perspiration fastness, rubbing fastness and other indicators. Colorants are optional.
2. Brittle damage
Brittle damage is manifested by a decrease in strength. In addition to brittle damage or even holes caused by improper oxygen bleaching and other processes in pre-treatment, there are generally two reasons for brittle damage caused by the dyeing stage:
One is the photosensitive brittleness caused by dyes such as sulfur black, which needs to be improved with anti-brittle agents, and the brittleness of fibers caused by strong reducing agents and strong oxidants such as vat dyes;
The second is the improper use of acid in the dyeing stage or neutralization stage. The acid commonly used for neutralization is glacial acetic acid, and some substitute acids are currently available on the market. Some of these substitute acids are like BASF’s organic buffer acids, which do not contain sulfuric acid, hydrochloric acid, Strong inorganic acids such as phosphoric acid have even better performance than acetic acid. These buffer acids can also improve some of the disadvantages of glacial acetic acid (such as glacial acetic acid, which is inconvenient to use in winter, has a pungent smell, residual sour taste, and combines with metal ions in water (such as Ca2+, Mg2+) to remain on the fabric, causing the color to fade, etc.) . Some substitute acids containing H2S04, HCl, H3P04, etc. not only cause changes in dyeing shades, but also have a corrosive effect on dyeing and finishing equipment and pumps. The acid residue after neutralization can also cause brittle damage to fabrics under acidic conditions.
3. Wrinkle strips
The main reasons include equipment, the amount of cloth loaded, liquor ratio, processing operation, etc. The equipment is different, such as the amount of cloth loaded in a tube, the pressure and friction between cloths, pump force and strength. All affect the smoothness of the fabric surface. The liquor ratio will also affect the smoothness of the fabric surface. Too much additive foam in the process operation will cause the fabric to float and the sudden cooling and heating phenomenon in the heating and cooling during the process operation will cause fineness. wrinkle phenomenon. Current in-bath lubricating anti-wrinkle agents, in-bath treasures, and in-bath softeners can all improve the phenomenon of fine wrinkle lines. However, if the equipment is not improved and the process control is poor, adding in-bath lubricant alone cannot completely avoid fine wrinkle lines. generated.
4. Wind Seal
Wind printing has little to do with additives. The key is the performance of the dye itself (acid and alkali resistance) and the acidity and alkali of the fabric, the humidity and acid gas of the air, etc., such as light-fast green blue GC, frozen yellow in direct dyes G, etc. are prone to produce wind marks when exposed to acid gas. Active Cuilan KN-G, brilliant orange X-GN, etc. are sensitive to acid and alkali and are prone to produce wind marks. Disperse dyes such as yellow RGFL are sensitive to alkali and are prone to produce wind marks. , for additives, neutralization must be done well to make the cloth surface PH=7 as much as possible. Therefore, we must also pay attention to the types of acids and bases used during neutralization. Use glacial acetic acid or organic substitute acids as much as possible. Never use substitute acids containing strong inorganic acids such as H2S04 and HCl. The choice of base should also be as gentle as possible. .
5. Color variations (including color difference, color without sample, etc.)
Color bloom is a common and common quality problem in the dyeing process. The causes are:
① Problems in process formulation and operation: Unreasonable formulation or improper operation will produce color flowers;
② Equipment problems: For example, after polyester is dyed with disperse dyes, the temperature in the oven of the heat setting machine is different, which can easily cause color differences and flowers. Insufficient pump power of the rope dyeing machine can also easily cause color flowers, etc.
③Dye problems: Dyes are easy to aggregate, have poor solubility, poor compatibility, are too sensitive to temperature and pH, and are prone to color flowers and color differences. For example, active green orchid KN-R is easy to produce colored flowers.
④ Water quality problems: Poor water quality causes dyes to combine with metal ions or dyes and impurities to agglomerate, resulting in colored flowers, light colors and no sample attached.
⑤Auxiliary issues:
Regarding the issue of additives, the additives related to color flowers mainly include penetrants, leveling agents, chelating dispersants, pH value control agents, etc. The penetrating agent’s penetrating power is not enough, which can easily lead to uneven penetration of the dye solution and color blooming, such as loose cotton dyeing, cheese dyeing, and heavy fabric dyeing. The role of the penetrating agent cannot be ignored. Some factories only believe in authentic JFC penetrating agents, but It is not considered that the cloud point of JFC is only 38-42°C. If it exceeds 42°C, its penetrating power will not be exerted, which will cause quality problems. Leveling agents include various types of leveling agents for polyester, cotton, wool, nylon, and acrylic fiber. The quality varies. Leveling agents must take into account the dispersion and solubilizing effect of dyes, the retarding dye migration effect, and the penetration aiding effect. It even has a complexing effect on metal ions in water, and factors such as its PH suitability and foamability that affect the coloring rate must be taken into consideration. Leveling agents are indispensable in improving phenomena such as color flowers and color spots. Some The factory’s leveling agent is just a solution of diffusing agent N, but I didn’t expect that the anti-dye aggregation effect of diffusing agent N is greatly reduced at high temperatures. Some factories use inappropriate non-ionic surfactants, which causes the non-ionic surfactants themselves to precipitate above the cloud point and adsorb dyes to form tar-like substances that stick to fabric equipment, causing quality problems. The quality of chelating dispersants is also related to leveling dyeing issues. At present, as the water quality is getting worse and worse, the help of chelating dispersing agents in leveling dyeing should be paid more attention to. PH control is an issue that factories do not pay much attention to. In some factories, the pH of each dyeing vat is different. In addition, the substitute acid used by some factories has different qualities. For example, it contains phosphoric acid. The pH generated by the third-level ionization of phosphoric acid is uniform. If there are differences, how can we control a uniform pH value? Some factories use pH slip agents.�But without understanding the relationship between temperature and time and the PH value generated by the slip agent, PH control is impossible, so color flowers and color differences continue to occur.
6. Color points (including white points)
There are many reasons for color spots, such as white spots, which may be due to immature cotton not being dyed, or solids such as soda ash staining the cloth, causing partial inability to be dyed. The main causes of color points are:
① Improper dye selection: the dye particles are too large or can easily agglomerate to form color spots;
② Poor dye dissolution: undissolved dye enters the dye solution and sticks to the fabric to form color spots;
③ Poor water quality: Poor water quality causes dye to condense:
④ The equipment is not clean: the tar-like material in the dye vat falls off causing color spots;
⑤ Reasons for additives: Additives added during dyeing sometimes cause the dye to agglomerate and produce color spots; the additive foam is too much, and the foam combines with the dye to form colored foam, which stains the fabric to form color spots; the additives precipitate and combine with the dye to stain the fabric. On fabrics and equipment, the agglomerates on the equipment will transfer to the fabrics and cause color spots.
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