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How does nylon dyeing prevent defects(2)?

Date:Mar 24, 2021

Defects caused by unreasonable technology Polyamide dyeing has extremely high technical requirements. Technical conditions are an important factor that affects the color and level of dyed goods, such as temperature, bath ratio, pH value, etc., which will affect the quality of the goods. Unreasonable techniques can easily cause defects such as poor level dyeing, stigma, color willow, chromatic aberration, and poor fastness.


1. Control the initial dyeing temperature and heating rate Temperature is an important element of dyeing control. The unevenness of temperature will affect the degree of fiber expansion, the function of dyes (solubility, dispersibility, dye uptake, shade, etc.) and the development of auxiliary functions. Nylon is a thermoplastic fiber. When the temperature is low, the dyeing rate is very slow, and the temperature exceeds 50°C. The swelling of the fiber is continuously added as the temperature rises. The effect of temperature on the dye uptake rate is also different due to different dyes. The dye uptake rate of level dyeing dyes increases with the temperature and the dye uptake rate of fulling-resistant dyes is gradually added. The bath temperature is higher than 60°C and will only be added quickly as the temperature rises. Especially in the temperature range of 65~85°C, the control of the heating rate is the key to the success or failure of nylon dyeing. If it is not properly controlled, it will cause problems such as fast coloring, poor dye migration, and easy flowers and difficult to repair. If you use fulling-resistant dye to dye nylon, the initial dyeing temperature should be room temperature. In the temperature range of 65 ~ 85C, the heating rate should be strictly controlled at about 1C/min, and the leveling agent should be added, and the step heating method should be adopted; then the temperature should be increased to 95 ~ 98'C, heat preservation 45 ~ 60m in. In addition, the dyeing function of this fiber also changes with the heat treatment conditions encountered before dyeing, and the dyeing rate of the fiber after dry heat setting is significantly reduced.


2.Determine the appropriate bath ratio. Because of the constraints of the equipment, the sample bath ratio will be larger than the larger one, but if the bath ratio is too high, the dye uptake rate will be reduced and the color difference of the size sample will be formed. The bath ratio of frivolous taffeta is usually 1:50, and the bath ratio of heavier fabrics is 1:20, subject to the fact that the fabric can be thoroughly immersed in the dye solution.


3.Controlling the pH value of the dye bath pH value has a great influence on the dye uptake rate, and the dye uptake rate will be added quickly as the pH value drops.3.  When dyeing nylon with weak acid dyes, the PH value of dyeing light colors is usually controlled at 6~7 (commonly used for ammonium acetate conditioning), and the amount of leveling agent is increased to enhance leveling and prevent dyeing, but the pH value cannot be exceeded. High, otherwise the color will become dark; the pH value of dyeing dark colors is 4~6 (usually adjusted by acetic acid and ammonium acetate), and appropriate acetic acid is used to reduce the pH value during the heat preservation process to promote dyeing.


 4. Pay attention to the selection and dosage of leveling agent. Regarding the characteristics of poor leveling and hiding of nylon dyeing, a few anionic or non-ionic leveling agents should be added in the dyeing bath, and anionic surfactants are the main ones. It can be used in the same bath with the dye during dyeing, and it can also be used for pre-dyeing nylon with a leveling agent. The anionic leveling agent dissociates into negative ions in the dye bath, enters the fiber, and firstly occupies the limited dye seat on the nylon fiber, and then gradually replaced by the dye as the temperature rises during the dyeing process, which reduces the relationship between the dye and the fiber. Speed reaches the purpose of level dyeing; non-ionic level dyeing agent is hydrogen-bonded with the dye in the dye bath, and then gradually differentiated during the dyeing process to release the dye and be absorbed by the fiber. Through experiments, it is found that the leveling agent can significantly improve the leveling performance and the ability to cover dyeing. However, with the addition of the auxiliary agent concentration, the dye uptake rate decreases, which causes the dye exhaustion rate to decrease to the same degree, so the leveling agent dosage Not too much. Because leveling agent in the dyeing process not only plays a role of leveling, but also has a blocking effect. Excessive amount of leveling agent will reduce the dye uptake rate of acid dyes, increase the concentration of dyeing residual liquid, and cause color difference and poor reproducibility of large and small samples. Generally, 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 always believed that the control of the p H value is the key to the success or failure of nylon dyeing. Through the accumulation of many years of production experience, we found that after the introduction of the buffer system, the selection and dosage of the leveling agent play a decisive role in controlling the color difference of the size and sample. The leveling agent should be used in conjunction with the corresponding dye types, but the amount used must be adjusted according to the actual situation. When the sample is produced, the dosage of the leveling agent is controlled at 0.2~1.5g/L, that is, under the premise of achieving an excellent leveling effect, if the residual liquid rate of the light color is 2% ~ 3%, the medium and dark color is 5% ~ 15%, the amount of the leveling agent is the required amount. Large-scale production and then make corrections based on the amount of small samples, which can achieve an excellent effect. The recommended alkaline dyeing auxiliaries for polyester 2J-RH98 are used here. When dyeing nylon with three large and small samples, there are many reasons for the color difference between large and small samples, such as the grey fabric used for the large and small samples, dyeing materials, and the technical conditions for the large and small samples. Different-all kinds of things. Adoptable prevention and compensation include: reducing the influence of environment and light source, standard proofing and color matching operations; analyzing the difference between large and small samples, and correcting and setting out the data of small samples.