Nylon is a hydrophobic fiber that contains amino and carboxyl groups on the fibers and can be stained with disperse dyes, acid dyes, and especially weakly acidic dyes. Its dyeing has the characteristics of fast dyeing rate and high exhaustion dyeing rate, but due to the different specifications of the spinning process, the fiber structure is very different, causing a large difference in dyeing performance, which is easy to produce color differences.
Therefore, if there is a slight negligence in the formulation of the small sample process, it may cause uneven dyeing, resulting in defects such as color difference, color stains, color spots, dark and light edges, strip flowers, color discrepancies and poor dyeing fastness.
(Pictured: Molecular formula of nylon 6 and nylon 66)
Common staining problems and preventive solutions
First, the color and color difference caused by competitive dyeing
This is due to improper selection of dyes. The dyeing saturation value of nylon is very low, so when the color is spelled out, the competition between different dyes is very prominent. If the dye selected varies greatly in terms of dyeing rate and affinity, the color of the fiber will be very different in different dyeing time, resulting in different color differences and repetition of the size sample.
The prevention and remedy is to select a series of dyes with similar upper dyeing curves and affinities, good compatibility, and suitable for production machines. Proofing personnel are required to fully grasp the dyeing performance of various types of dyes, and when selecting dyeing materials, they should comprehensively consider the dyeing rate, dyeing curve, leveling, color fastness performance, and sensitivity to temperature and leveling agent.
1. Fully consider the compatibility of dyes
When using several dyes for concoction, it is necessary to select the appropriate dye and control the amount of dye used. Generally, you should try to choose the same series of dyes from the same company, even if you have to choose dyes from different companies, you should try to choose dyes with similar dyeing curves, similar starting dyeing temperatures, and similar sensitivities to temperature and leveling agents, so as to avoid competitive dyeing.
2. Pay attention to the difference in dye size and sample dyeing
Some dyes are not obvious when dying small samples, but are completely exposed in large production. For example, in the production of lake green and peacock blue, if the acidic emerald blue and acid yellow are used together, a similar problem occurs. This is due to the large molecular structure of the acidic emerald blue, which is very different from the acid yellow dyeing curve, which causes competition. If you switch to an acidic basket and an acidic green with yellow light, you will basically solve the problem of competition dyeing.
3. Pay attention to the adaptability of the machine to the dye
Dyeing machines include jetting, warp shafts and coil dyeing machines. In the jet dyeing machine, the dyeing liquid is in full contact with the fabric, the leveling is good, the product feels plump, and the reproducibility is good, the cylinder difference is small, but its wet resistance and fastness are relatively poor. Staining can be performed with weak acid dyes with good fastness but slightly poor leveling or 1:2 metal complex acid dyes. The product width of the warp shaft dyeing machine is easy to control and the color fixation is easy, but it is easy to have problems such as dark and shallow layers and head and tail color differences. You can choose a dye with good leveling and slightly poor fastness, and slightly increase the amount of leveling agent, and then strengthen the fixation after dyeing.
Second, the defect caused by unreasonable process
Nylon dyeing places extremely high demands on the process. Process conditions are important factors that affect the color and light and leveling of dyeing products, such as temperature, bath ratio, PH value, etc., which will affect the quality of the product. Unreasonable processes are prone to flaws such as poor leveling, color flowers, color willows, color differences, and poor fastness.
1. Control the temperature of the first dye and the heating rate
Temperature is an important factor in controlling staining. The level of temperature will affect the degree of puffing of fibers, the performance of dyes (solubility, dispersibility, dyeing rate, color and light, etc.) and the performance of additives. Nylon is a thermoplastic fiber, the dyeing rate is very slow when the temperature is low, the temperature exceeds 50 ° C, and the swelling of the fiber increases with the increase of temperature.
The influence of temperature on the dye dye rate also varies depending on the dye, and the dyeing rate of the leveling dye gradually increases with the increase of temperature; The dyeing rate of the shrinkant dye should be increased rapidly with the increase of temperature after the dyeing bath temperature is higher than 60 °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 the control is improper, it will cause fast coloring, poor dyeing, easy to spend and difficult to repair the problem. If the use of shrink-resistant dye dyeing nylon, the initial dyeing temperature should be room temperature, in the 65 ~ 85 ° C temperature section, strictly control the heating rate of about 1 ° C / min, and add leveling agent, take the step heating method; Then heat up to 95 ~ 98 °C, insulation for 45 ~ 60 min. 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 shaping decreases significantly.
2. Determine the appropriate bath ratio
Due to the limitations of the equipment, the small sample bath ratio will be larger than the large production, but the bath will reduce the dyeing rate than the assembly, resulting in the color difference of the size sample. The light and thin tarf silk bath ratio is generally 1:50, and the thicker fabric bath ratio is 1:20, subject to the fact that the fabric can be fully immersed in the dyeing solution.
3. Control the PH value
The pH value of the dye bath has a great influence on the dyeing rate, and the dyeing rate will increase rapidly with the decrease of the PH value. When dyeing nylon with a weak acid dye, the PH value of dyeing light colors is generally controlled at 6 to 7 (usually adjusted by ammonium acetate), and the amount of leveling agent is increased to strengthen leveling and avoid dyeing, but the PH value cannot be too high, otherwise the color will be dim; Dyeing a dark color has a pH value of 4 to 6 (commonly used to adjust acetic acid and ammonium acetate), and an appropriate amount of acetic acid is added in the process of heat preservation to reduce the PH value and promote dye dyeing.
4. Pay attention to the selection and dosage of leveling agent
In view of the characteristics of nylon dyeing and poor coverage, a small amount of anionic or non-ionic leveling agent should be added to the dyeing bath, of which anionic surfactants are the mainstay. It can be used in the same bath with the dye during dyeing, or the nylon can be pre-dyed with a leveling agent. The anionic leveling agent dissociates into negative ions in the dyeing bath, enters the fiber, first occupies the limited dye seat on the nylon fiber, and then gradually replaces the dye with the increase of temperature during the dyeing process, reducing the binding speed between the dye and the fiber, and achieving the purpose of leveling; Non-ionic leveling agents bind to the dye in the dye bath, and then gradually decompose during the dyeing process to release the dye, and are adsorbed by the fibers.
Through the test, it was found that the addition of leveling agent can significantly improve the leveling and covering ability, but with the increase of the concentration of the auxiliary, the rate of dyeing decreases, resulting in different degrees of depletion of the dyeing rate, so the amount of leveling agent should not be too much. Because in addition to the leveling effect of the leveling agent in the dyeing process, it also has a staining blocking effect. Excessive amount of leveling agent will reduce the dyeing rate of acid dyes, increase the concentration of staining residues, and cause color differences and re-repetition of large and small samples. In general, the amount of leveling agent is larger when dyeing light colors; When dyeing dark colors, the amount of leveling agent is less.
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 found that after the introduction of the buffer system, the selection and dosage of leveling agent play a decisive role in controlling the color difference of large and small samples. The leveling agent should be used in conjunction with the corresponding dye class, but the dosage must be adjusted according to the actual situation. When producing small samples, the dosage of leveling agent is controlled at 0.2 ~ 1.5g / L, that is, under the premise of achieving a good leveling effect, if the residual liquid rate of light color is 2% to 3%, and the medium and dark color is 5% to 15%, the amount of the leveling agent is the required amount. Large production and then according to the amount of small samples to correct, can achieve good results.
Third, the size of the sample lofting color difference
When nylon is dyed, the reasons for the color difference between the size of the sample are manifold, such as the blank cloth used in the size sample, the dye material, and the different process conditions of the size sample. The prevention and remedy that can be taken include: reducing the impact of the environment and light source, standardizing proofing and color alignment operations; Analyze the differences between large and small samples, and correct the lofting of the data of small samples.
1. The color of the sample must be strict and precise
(1) The design of the laboratory color pairing and color matching environment should be used as much as possible to use a series of colors such as black and white gray, which can prevent the "residual image" caused by the environmental color on the eye physiology and affect the color. The illumination of the color environment must be sufficient to prevent hue changes due to the light source when the color is opposed, and a "conditional" fixed light source should be used, or equipped with a light box that meets international standards. If the probability of light source change is relatively high, such as the laboratory is open to the color environment, the light source outside the window will affect the color matching efficiency due to the change of different light sources at different times (such as different light sources in the morning and afternoon, and different light sources on cloudy and sunny days).
(2) Before confirming the sample, you should first find out the various requirements of the customer, such as the original color and light bias, whether there is a special finishing, and whether the dye for fiber dyeing is specified.
(3) The water used for small samples should be consistent with the production of large samples, and the water quality and its PH value should be tested daily, and adjusted to the process requirements to avoid color and light differences.
(4) The dyeing properties of nylon fibers also change with their heat history before dyeing. Different heat setting conditions will cause different fabric color absorption rates, resulting in color differences between fabric batches and batches. The process control of the pretreatment of nylon fabric also has a great impact on the dyeing effect, so the tissue specifications of the size of the sample should be the same, and the process conditions of the dyeing half of the product should be consistent, and it is best to use the same batch of half products.
(5) The small sample should be made of the same origin, the same factory, the same product name, and the same batch number of dye materials as the large sample. The compatibility value of the dye selected when matching color should be basically the same, so as to ensure the proportional relationship between each dye in the dyeing solution during the dyeing process, which is conducive to the stability and reproducibility of the dyeing color. When coloring, the main color dye should be fixed, and the dye for color and light should be adjusted to facilitate the consistency of color and light in size. Dyes that are easy to cause discoloration during dyeing processing are not used.
2. Standardize the color matching operation of the laboratory
(1) In general, the closer to the color of the gray series, the more difficult it is to judge the gray chroma, because the absorption hue it contains is more complex, and it often needs three dyes to be mixed, so it is close to the hue of the gray series, and the color matching can only be selected with the feeling of yellow, red and blue. The more colors have a strong sense of color, the more important the freshness and purity of the color are to judge the hue, so when matching colors, we must first make a correct judgment and choose the correct dye.
(2) When coloring, pay attention to the change of the angle of observation and light illumination to maintain consistency.
(3) Grasp the degree of drying of the sample cloth after dyeing. Excessive drying will cause irreversible redness of color and light; Insufficient drying affects the color and light saturation of the color sample. Both cases cause chromo-optical deviations.
(4) When color imitation, attention should be paid to the classification of varieties and color systems, and the sample should be retained, and the accumulation of data should be established to establish a color sample library (it is better to have the corresponding actual production sample).
3. Strictly control the consistency of the large and small sample process
(1) The PH value and heating process of the proofing and dyeing bath should be consistent with large-scale production as much as possible. Large sample production due to the cross use of water quality and direct steam or indirect steam, often boiler steam into alkaline and make the dyeing bath PH value is high, the use of buffers or equipped with PH value online monitor can solve this problem.
(2) The holding time of small sample dyeing should be consistent with that of large sample, so as not to cause color difference due to poor dyeing permeability.
(3) Because the fixing color will also affect the color light, therefore, after the small sample fixes the color, it is necessary to adjust the color light in order to enter the process of large-scale production.
epilogue
There are many factors affecting the quality of nylon dyeing products, mainly including equipment, process, dye material, color difference and operation. Production practice has proved that grasping the above links can improve the accuracy and stability of nylon dyeing, so that the success rate of small sample lofting can reach more than 90%.