1 Introduction
Nylon is a hydrophobic fiber, which contains amino and carboxylic groups [1]. It can be dyed with dispersed dyes, acid dyes, and especially weakly acidic dyes. Its dyeing has the characteristics of fast dyeing rate and high dyeing rate, but due to the different spinning process specifications, the fiber structure varies greatly, causing large differences in the dyeing performance, which makes it easy to produce color difference. Therefore, if you are negligent in formulating the sample process, it may cause uneven dyeing, resulting in defects such as color difference, color stains, color points, dark edges, strips, color differences and poor dyeing fastness. Therefore, when dyeing nylon, sample personnel must formulate reasonable dyeing processes and strictly control the entire process to reduce the defective rate and reduce the large production pressure.
The author summarizes common defects in nylon dyeing and prevention and technical remedies through more than ten years of practice in nylon dyeing and proofreading work.
2 Common defects and prevention and remedial measures
2.1 Contradiction causes color flowers to be inconsistent with color
This is caused by improper selection of dyeing materials. The dyeing saturation value of nylon is very low, so when dyeing thick colors, the competition between different dyes appears to be very prominent. If the dye selected has a large difference in dyeing rate and affinity, the color of the fiber dyeing will be very different within different dyeing times, resulting in poor color difference and reproducibility of the size and sample.
The prevention and remedial measures are to choose dyeing materials series with similar dyeing curves, good affinity, good compatibility, and suitable for production machines. Proofing personnel are required to fully grasp the dyeing properties of various dyes. When choosing dyeing materials, they should comprehensively consider the dyeing rate, dyeing curve, uniform dyeing properties, color fastness properties of the dyeing agent, as well as their sensitivity to temperature and dyeing agents. factors such as sex.
2.1.1 Fully consider the compatibility of dyes
When using several types of dyes to dye, choose appropriate dyes and control the amount of dyes. Generally, the same series of dyes from the same company should be selected as much as possible. Even if the dyes from different companies have to be used to combine, the dyes with similar dye curves, similar initial dye temperatures, and similar sensitivity to temperature and uniform dye agents should be selected. Avoid competition.
2.1.2 Pay attention to the differences in dye size and sample competition
Some dyes are not obvious when dyeing small samples, but are completely exposed in large-scale production. 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 turquoise blue is large and the dyeing curve is very different from the acidic yellow, which causes competitive dyeing. If the acidic green basket is used to combine with the yellow-light acidic green, the competitive dyeing problem will basically be solved.
2.1.3 Pay attention to the adaptability of the machine to dyes
Dyeing machines include jet, warp shaft and dyeing machine. The dye liquid in the jet dyeing machine has sufficient contact with the fabric, good uniformity, the product feels full, and has good reproducibility, and the cylinder difference is small, but its moisture-resistant and fastness is relatively poor. You can choose weak acid dyes with good fastness but slightly poor uniformity or 1:2 metal complex acidsSex dyes are stained. The product width control of the warp-shaft dyeing machine is easy to control and color fixation, but it is easy to cause problems such as dark and shallow layers and head-tail color difference. You can choose dyes with good uniformity and slightly poor fastness, and slightly increase the amount of uniform dye, and then strengthen the color fixation after dyeing.
2.2 Flaws caused by unreasonable process
Nylon dyeing requires extremely high technology. Process conditions are important factors that affect the color and uniformity of dyed products, such as temperature, bath ratio, pH value, etc., which will affect the quality of the product. Unreasonable processes are prone to defects such as uniform dyeing, color flowers, willows, color difference, and fastness.
2.2.1 Control the initial dyeing temperature and temperature increase rate
Temperature is an important factor in controlling the dyeing. The temperature will affect the degree of expansion of the fiber, the performance of the dye (solubility, dispersion, dyeing rate, chromogloss, etc.) and the performance of the additive. Nylon is a thermoplastic fiber. The dyeing rate is very slow when the temperature is low. When the temperature exceeds 50℃, the swelling of the fiber continues to increase with the increase of the temperature.
The effect of temperature on dyeing rate varies depending on the dye. The dyeing rate of uniform dyes gradually increases with the increase of temperature; the dyeing rate of shrink-resistant dyes must be in the dye bath The temperature will only increase rapidly with the increase of temperature after it is above 60°C. Especially in the temperature range of 65 to 85℃, controlling the heating rate is the key to the success or failure of nylon dyeing. If improper control, it will cause problems such as fast coloring, poor dyeing, and easy flowering and difficult to repair. If nylon is dyed with shrink-resistant velvet dye, the initial dyeing temperature should be room temperature, at the temperature range of 65 to 85℃, strictly control the heating rate of about 1℃min, and add a uniform dyeing agent, and adopt a step-by-step heating method; then increase the temperature to 95~ 98℃, insulation for 45~60min. In addition, the dyeing performance of this fiber also varies with the heat treatment conditions before dyeing, and the fiber dyeing rate after dry heat setting is significantly reduced.
2.2.2 Determine the appropriate bath ratio
Due to equipment limitations, the sample bath ratio will be larger than that of large production, but excessive bath ratio will reduce the dyeing rate, resulting in color difference between size and sample. The light and thin taffeta bath ratio is generally 1:50, and the thicker fabric bath ratio is 1:20, which is the basis for the fabric to be completely immersed in the dye solution.
2.2.3 Control pH
The pH value of the dye bath has a great impact on the dyeing rate of the dyeing rate, and the dyeing rate will increase rapidly with the decrease of the pH value. When dyeing nylon with weak acid dyes, the pH value of light dyeing is generally controlled between 6 and 7 (commonly adjusted by ammonium acetate), and the amount of uniform dyeing agent is increased to strengthen uniform dyeing and avoid dyeing, but the pH value cannot be exceeded. High, otherwise the color light will be darker; the pH value of dark dye is 4 to 6 (commonly used to adjust acetic acid and ammonium acetate), and add an appropriate amount of acetic acid to reduce the pH value during the insulation process to promote dyeing.
2.2.4 Pay attention to the selection and dosage of uniform dyeing agents
In view of the characteristics of nylon dyeing, poor uniform dyeing and covering properties, a small amount of anionic or nonionic uniform dyeing agent should be added to the dye bath, including anionic agents. surfactants are the main type. now thatIt can be used in the same bath as the dye during dyeing, or it can be used to dye nylon with a uniform dyeing agent before dyeing. Anionic homogenizing agent dissociates into negative ions in the dye bath and enters the fibers. First, it occupies a limited dyeing base on the nylon fibers. Then, during the dyeing process, it is gradually replaced by dyes as the temperature increases, reducing the bond between the dye and the fibers. The purpose of uniform dyeing is achieved; the non-ionic uniform dyeing agent will hydrogen bond with the dye in the dye bath, and then gradually distribute the dye during the dyeing process and be adsorbed by the fibers.
It was found through experiments that the addition of uniform dyeing agent can significantly improve uniform dyeing and covering dyeing ability, but as the concentration of auxiliary agent increases, the dyeing rate decreases, resulting in a decrease in the exhaustion rate to varying degrees. Therefore, the dosage of uniform dyeing agents is used. Not too much. Because in addition to having a uniform dyeing effect during the dyeing process, it also has a dye-proof effect. Too large amount of uniform dyeing agent will reduce the dyeing rate of acid dyes, increase the concentration of dye residues, resulting in color difference and poor repeatability of large and small samples. Generally, the amount of uniform dyeing agent is used for light colors; when dyeing dark colors, the amount of uniform dyeing agent is used for dark colors.
For a long time, the industry has believed that pH control is the key to the success or failure of nylon dyeing. After years of accumulation of production experience, we found that after the introduction of the buffer system, the selection and dosage of homogenizer play a decisive role in controlling the color difference of size and sample. The dye uniform agent should be used in conjunction with the corresponding dye category, but the dosage must be adjusted according to actual conditions. During sample production, the dosage of uniform dyeing agent is controlled at 0.2~1.5gL, that is, under the premise of achieving good uniform dyeing effect, if the light-colored residual liquid rate is 2%~3%, and the medium-dark color is 5%~15 %, then the amount of the uniform dyeing agent is the required amount. Large production and correction are made according to the small sample usage, which can achieve good results.
2.3 Color difference between size and size
When dyeing nylon, there are many reasons for color difference between size and size, such as the grey cloth, dyeing material, and different process conditions for size and size. The prevention and remedial can be taken to reduce the impact of the environment and light sources, standardize proofing and color operation; analyze the differences between sizes and samples, and correct the sample data.
2.3.1 The color matching of samples must be strictly and accurately
(1) When designing the color and color matching environment in the laboratory, black, white and gray should be used as much as possible to prevent the eye physiology due to environmental colors. The “afterimage” caused will affect the color. The lighting of the color environment must be sufficient to prevent the color change due to the light source when the color is in use. A fixed light source with “conditionality” should be used, or a light box that meets international standards should be equipped. If the chance of light source changes is relatively high, if the laboratory has an open color environment, the light source outside the window will affect the color matching due to the changes of different light sources at different times (such as the light source in the morning and afternoon, and the light source in the cloudy and sunny days). efficiency.
(2) Before checking the sample, you should first clarify the customer’s various requirements, such as the color deviation of the original color, whether there is special finishing, whether the dye for fiber dyeing is specified, etc.
(3) Water used for small samples should be consistent with large samples production, and the water quality and daily requirements should be madeIts pH value is tested and adjusted to process requirements to avoid chromoluminescence differences.
(4) The dyeing properties of nylon fibers also change with the history of heating before dyeing. Different heat setting conditions will cause different color absorption rates of fabrics, resulting in color difference between fabric batches. The process control of pretreatment of nylon fabrics also has a great impact on the dyeing effect, so the tissue specifications of the size and samples must be the same, and the process conditions of the first half-dyeing products must be consistent, so that the same batch of half-dyeing products should be used.
(5) The sample should be dyed materials of the same origin, same factory, same product name, and same batch number as the sample. The dye compatibility values selected during color matching must be basically the same, so as to ensure the proportional relationship of each dye in the dye solution during the dyeing process, which is conducive to the stability and reproducibility of the dyeing light. When color matching, the main color dye should be fixed, and the dye should be used to adjust the color light to make the color light consistent. Dyes that are prone to discoloration during dyeing processing will not be used.
2.3.2 Standardize laboratory color matching operations
(1) Generally speaking, the closer the color to the gray series, the harder it is to judge its gray color, because the absorption color it contains is relatively complex and often requires three The dyes are mixed together, so they are close to the color of the gray series. When matching the color, you can only choose the color bias of yellow, red and blue. The stronger the color feels, the more important the judgment of the color is, the freshness and pureness of the color is. Therefore, when matching colors, you must first make a correct judgment and choose the correct dye.
(2) When viewing colors, pay attention to the changes in the irradiation angle between the sample and the light to maintain consistency.
(3) Grasp the drying degree after dyeing the sample cloth. If excessive drying, the color light will be irreversible and reddish; if insufficient drying, it will affect the color light saturation of the color sample. Both cases will cause color deviation.
(4) When imitating colors, you should pay attention to the classification of varieties and color systems, and retain samples, accumulate data and establish a color sample library (it is better to have corresponding actual production samples).
2.3.3 Strictly control the consistency of large and small samples.
(1) The pH value and heating process of the sample dyeing bath should be consistent with the large production as much as possible. Due to the cross-use of water quality and direct steam or indirect steam, the boiler steam often brings alkaline to the dye bath pH, which can solve this problem by using buffers or equipped with an online pH monitor.
(2) The insulation time of dyeing small samples should be consistent with that of large samples to avoid color difference due to poor dyeing permeability.
(3) Because color fixation will also affect color light, the color light must be adjusted after the small sample is fixed to enter the process of large-scale production.
3 Conclusion
There are many factors that affect the quality of nylon dyeing products, mainly including equipment, technology, dyeing materials, color difference between size and sample and operation. Production practice has proved that by grasping the above links, the accuracy and stability of nylon dyeing can be improved, and the success rate of sample stakes can reach more than 90%.
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