Nylon (nylon) is a hydrophobic fiber containing amino and carboxyl groups. As a basic material, it is widely used, especially in the textile industry. Nylon can be dyed with disperse dyes, acid dyes, especially weak acid dyes. Its dyeing has the characteristics of fast dyeing speed and high exhaustion rate. However, due to different spinning process specifications, the fiber structure is very different, resulting in large differences in dyeing performance and easy to produce color differences.
Common defects and preventive and remedial measures
Competition dyeing causes color flowers and colors not to match the sample This is caused by improper selection of dyeing materials. The dyeing saturation value of nylon is very low, so when dyeing strong colors, the competition between different dyes becomes very prominent. If the dyes selected have large differences in dye uptake and affinity, the fiber dyed colors will be very different at different dyeing times, resulting in color differences between large and small samples and poor reproducibility. The preventive and remedial measures are to choose a dye series with similar dyeing curves and affinity, good compatibility, and suitable for production machines. Sampling personnel are required to fully understand the dyeing properties of various dyes. When selecting dyeing materials, they must comprehensively consider the dye uptake rate, dye uptake curve, leveling properties, color fastness performance, and sensitivity to temperature and leveling agents. factors such as sex.
1. Fully consider the compatibility of dyes. When using several dyes for dyeing, you must choose appropriate dyes and control the amount of dyes. Generally, you should try to choose the same series of dyes from the same company. Even if you have to use dyes from different companies, you should try to choose dyes with similar dyeing curves, similar starting dyeing temperatures, and similar sensitivity to temperature and leveling agents. , try to avoid the occurrence of competitive contamination.
2. Pay attention to the differences in the dyeing of dye samples. Some dyes are not obvious when dyeing small samples, but they are completely different in large-scale production. exposed. For example, when producing lake green and peacock blue, if acidic emerald blue and acidic yellow are used to combine, similar problems will arise. This is because the molecular structure of acidic emerald blue is large and the dyeing curve of acidic yellow is very different, thus causing competitive dyeing. If the acid green basket is used instead of the acid green with yellow light, the problem of competing dyes will be basically solved.
3. Pay attention to the adaptability of the machine to dyes. Dyeing machines include jet, beam and jigger dyeing machines. In the jet dyeing machine, the dye liquor is in full contact with the fabric, resulting in good level dyeing, plump product feel, good reproducibility, and small cylinder difference, but its fastness to moisture treatment is relatively poor. You can choose weak acid dyes or 1:2 metal complex acid dyes that have good fastness but slightly poor leveling properties for dyeing. The product width of the beam dyeing machine is simple to control and the color is easy to fix, but it is prone to problems such as dark and shallow layers and head and tail color differences. You can choose dyes with good leveling properties but slightly poor fastness, slightly increase the amount of leveling agent, and then strengthen the color fixation after dyeing.
Defects caused by unreasonable processes. Nylon dyeing has extremely high process requirements. Process conditions are important factors that affect the color and levelness of dyed products, such as temperature, liquor ratio, pH value, etc., which will all affect the quality of the product. Unreasonable technology can easily produce defects such as poor level dyeing, color flowers, color willow, color difference, and poor fastness.
4. Controlling the initial dyeing temperature and heating rate. Temperature is an important factor in controlling dyeing. The temperature will affect the degree of puffing of the fiber, the performance of the dye (solubility, dispersion, dye uptake, color, etc.) and the performance of the additives. Nylon is a thermoplastic fiber. When the temperature is low, the dyeing rate is very slow. When the temperature exceeds 50’C, the swelling of the fiber continues to increase as the temperature increases. The effect of temperature on the dye uptake rate also varies with different dyes. The dye uptake rate of level dyeing dyes gradually increases as the temperature increases; the dye uptake rate of milling-resistant dyes must be maintained when the dye bath temperature is higher than 60°C. It starts to increase rapidly with the increase of temperature after “C. Especially in the temperature range of 65~85°C, controlling the heating rate is the key to the success or failure of nylon dyeing. If it is not controlled properly, it will cause fast coloring and poor dye migration. , the problem of easy flowering and difficult repair. If milling-resistant dyes are used to dye nylon, the starting dyeing temperature should be room temperature. In the temperature range of 65~85C, the heating rate should be strictly controlled to about 1’Cmin, and leveling agents should be added and steps should be taken. Heating method; then raise the temperature to 95~98C and keep it for 45~60 minutes. In addition, the dyeing performance of this fiber also changes with the heat treatment conditions before dyeing, and the dyeing rate of the fiber after dry heat setting decreases significantly.
5. Determine the appropriate liquor ratio. Due to equipment limitations, the liquor ratio of small samples will be larger than that of large-scale production. However, excessive liquor ratio will reduce the dye uptake rate, resulting in Color difference between large and small samples. The liquor ratio of light and thin taffeta is generally 1:50, and the liquor ratio of thicker fabrics is 1:20, whichever is required when the fabric can be completely immersed in the dye liquor.
6. Control the pH value of the dye bath. The pH value of the dye bath has a great influence on the dye uptake rate. The dye uptake rate will increase rapidly as the pH value decreases. When dyeing nylon with weak acidic dyes, the dyeing will be light. The pH value of the color is generally controlled at 6~7 (commonly adjusted with ammonium acetate), and the amount of leveling agent is increased to enhance leveling and avoid staining, but the pH value cannot be too high, otherwise the color will fade; dyeing is dark The pH value of the color is 4~6 (commonly used for adjustment with acetic acid and ammonium acetate), and an appropriate amount of acetic acid is added during the heat preservation process to reduce the pH value and promote dyeing.
7. Pay attention to the selection and dosage of leveling agents. In view of the poor leveling and coverage characteristics of nylon dyeing, a small amount of anionic or nonionic leveling agents should be added to the dye bath, among which anionic surfactants are used. ���Mainly. It can be used in the same bath with dyes during dyeing, or it can be used as a leveling agent to pre-dye nylon. The anionic leveling agent dissociates into negative ions in the dye bath, enters the fiber, and first occupies a limited dye seat on the nylon fiber. Then it is gradually replaced by the dye as the temperature increases during the dyeing process, reducing the bond between the dye and the fiber. Speed, to achieve the purpose of leveling; non-ionic leveling agent hydrogen bonds with the dye in the dye bath, and then gradually decomposes to release the dye during the dyeing process, and is adsorbed by the fiber. Through experiments, it was found that the addition of leveling agent can significantly improve the leveling property and covering ability. However, as the concentration of the additive increases, the dyeing rate decreases, resulting in a decrease in the exhaustion rate to varying degrees. Therefore, the amount of leveling agent should not be too much. Because leveling agents not only have a leveling effect during the dyeing process, they also have a dye-blocking effect. Excessive dosage of leveling agent will reduce the dyeing rate of acid dyes, increase the concentration of dyeing residue, and cause color difference between large and small samples and poor reproducibility. Generally, when dyeing light colors, a larger amount of leveling agent is used; when dyeing dark colors, a smaller amount of leveling agent is used. For a long time, the industry has believed that the control of pH value is the key to the success or failure of nylon dyeing. After years of accumulation of production experience, we have found that after the introduction of a buffer system, the selection and dosage of leveling agents play a decisive role in controlling the color difference between large and small samples. The leveling agent should be used in conjunction with the corresponding dye category, but the dosage must be adjusted according to the actual situation. When producing small samples, the amount of leveling agent should be controlled at 0.2~1.5gL. That is, on the premise of achieving good leveling effect, if the residual liquid rate is 2%~3% for light colors and 5%~15% for medium and dark colors, %, then the amount of leveling agent is the required amount. For large-scale production, corrections can be made based on the sample dosage, which can achieve good results.
Color difference between large and small samples When dyeing nylon, there are many reasons for the color difference between large and small samples, such as the difference in gray fabrics, dyeing materials, and process conditions for large and small samples. Possible prevention and remedial measures include reducing the impact of the environment and light sources, standardizing proofing and color matching operations, analyzing the differences between large and small samples, and correcting the data of small samples.
The sample color matching must be strict and accurate
1. Laboratory color matching and color matching environment design, A series of colors such as black, white, and gray should be used as much as possible to prevent the “afterimage” caused by environmental colors on eye physiology from affecting color matching. The lighting in the color matching environment must be sufficient to prevent hue changes due to light sources during color matching. A “conditional” fixed light source should be used, or a light box that meets international standards should be equipped. If the probability of light source change is relatively high, for example, the color matching environment of the laboratory is open, the light source outside the window will change due to different light sources at different times (such as different light sources in the morning and afternoon, different light sources on cloudy days and sunny days), which will affect the color matching. efficiency.
2. Before printing the confirmation sample, you should first clarify the various requirements of the customer, such as the original color light direction, whether there is special finishing, whether the dye used for fiber dyeing is designated, etc.
3. The water used for making small samples should be consistent with the production of large samples, and the water quality and pH value need to be tested daily and adjusted to process requirements to avoid color and light differences.
4. The dyeing performance of nylon fiber also changes with its heating history before dyeing. Different heat setting conditions will cause different color absorption rates of fabrics, resulting in color differences between fabric batches. The process control of nylon fabric pre-treatment also has a great influence on the dyeing effect. Therefore, the tissue specifications of large and small samples should be the same, and the process conditions of semi-finished products before dyeing should be consistent. It is best to use the same batch of semi-finished products.
5. The small sample should use dyeing materials from the same origin, the same factory, the same product name, and the same batch number as the large sample. The compatibility values of the dyes selected during color matching should be basically consistent, so as to ensure the proportion of each dye in the dye liquor during the dyeing process, which is beneficial to the stability and reproducibility of the dyeing shade. When color matching, the main color dye should be fixed, and the dye used to adjust the color light should be changed so that the color light of the large and small samples is consistent. Dyes that easily cause discoloration during the dyeing process shall not be used.
Standardize laboratory color matching operations
1. Generally speaking, the closer the color is to the gray series , the gray chroma is more difficult to judge, because it contains more complex absorption hues, and often requires mixing of three dyes, so it is close to the hue of the gray series. When color matching, you can only choose the color preference based on the feelings of yellow, red, and cyan. . The stronger the color perception, the more important the freshness and purity of the color are to the judgment of hue. Therefore, when color matching, you must first make a correct judgment and choose the correct dye.
2. When comparing colors, pay attention to the changes in the sample and the angle of light exposure to maintain consistency.
3. Understand the degree of drying of the sample fabric after dyeing. Excessive drying will cause the color to become irreversibly reddish; insufficient drying will affect the color saturation of the color sample. Both situations will cause color light deviation.
4. When dithering, attention should be paid to the classification of varieties and color systems, and samples should be retained to accumulate data and establish a color sample library (it is better to have corresponding actual production samples).
Strictly control the consistency of large and small sample processes
1. Proofing The pH value and heating process of the dye bath should be as consistent as possible with large-scale production. Due to the cross-use of water quality and direct or indirect steam in large-scale production, boiler steam often brings alkalinity into the dye bath, causing the pH value of the dye bath to be high. This problem can be solved by using buffers or equipping with online pH value monitors.
2. The heat preservation time of small sample dyeing should be consistent with that of large sample to avoid color difference due to poor dyeing penetrability.
3. Because color fixation will also affect the color light, the color light must be adjusted after the sample is fixed before entering into the process development for mass production.
Conclusion
There are many factors that affect the quality of nylon dyeing products, mainly including equipment, technology, dyeing Chemical materials, color difference between large and small samples and operation. Production practice has proved that by grasping the above-mentioned links, the accuracy and stability of nylon dyeing can be improved, so that the first-time success rate of sample lofting can reach more than 90%.
Color difference is caused by poor dyeing penetrability.
3. Because color fixation will also affect the color light, the color light must be adjusted after the sample is fixed before entering into the process development for mass production.
Conclusion
There are many factors that affect the quality of nylon dyeing products, mainly including equipment, technology, dyeing Chemical materials, color difference between large and small samples and operation. Production practice has proved that by grasping the above-mentioned links, the accuracy and stability of nylon dyeing can be improved, so that the first-time success rate of sample lofting can reach more than 90%. </p
