What are the influencing factors in the nylon dyeing process

1. The effect of pH value of dye solution on dyeing

The industry has always believed that the control of the pH value of nylon dyeing is the key to success or failure. After years of production accumulation, we found that if the buffer system auxiliaries and the selection of good leveling agents are used in dyeing, it will play a decisive role in the success or failure of nylon dyeing. .

When acid (or weakly acidic) dyes are dyed, the pH value of the dye solution tends to increase as the dyeing proceeds. For dyes with low affinity and sensitive to the pH value of the dye bath, the pH value of dyeing should be controlled at about 5, so that the use of buffer system auxiliaries can achieve a multiplier effect on the pH value control of nylon dyeing. Stabilizing the pH of the dye solution is one of the key factors to achieve uniform dyeing.

2. The influence of dyeing temperature on nylon dyeing

Temperature is an important factor in controlling the dyeing of dyes. The temperature will affect the swelling degree of the fiber, the performance of the dye and the effect of the auxiliary agent. Nylon is a thermoplastic fiber, and the dyeing is very slow at low temperature.

The glass transition temperature of nylon 6 is 30~50℃, while the glass transition temperature of nylon 66 is 47~50℃. Generally, the initial dyeing temperature of nylon 66 can be controlled at about 40℃, while the initial dyeing temperature of nylon 6 is lower. . When the temperature of the dye bath reaches 70°C, the fiber expands sharply, and the dye uptake rate increases linearly. In the subsequent heating process, the heating rate should be strictly controlled. Of course, the effect of temperature on the dyeing rate is also different depending on the dyes. The dyes with smaller molecular weight and better levelness gradually increase with the increase of temperature, while those with larger molecular weight, levelness and migration Poor dyestuffs, only when the temperature of the dye bath is higher than 60%, begin to gradually increase with the increase of temperature, especially in the range of 65-85 °C, the heating rate should be strictly controlled. Dyed too quickly and caused colored flowers.

Therefore, the heating rate has a great influence on the dyeing, and the heating rate depends on the choice of dye, the shade of dyed color and the structure of the fabric. Step heating can be used to ensure the levelness of dyeing. The main function of the heat preservation stage is to obtain a certain migration of the dye, so the appropriate extension of the heat preservation time is helpful for the leveling and cover dyeing of the dye.

3. The influence of dye selection on nylon dyeing

The selection of dyes mainly depends on factors such as the type, hue, color depth and color fastness requirements of the dyed object. The selected dyes must have reasonable compatibility.

As far as the acid dye itself is concerned, its application performance is determined by the molecular structure itself. The simpler the molecular structure and the smaller the relative molecular mass, the greater the proportion of water-soluble groups contained, and the better the levelness, but the poorer the wet fastness. In order to improve the wet fastness of acid dyes, the proportion of organic groups will be increased to increase the relative molecular weight of the dyes and reduce the proportion of water-soluble groups, but the levelness and migration of the dyes will decrease. Therefore, it is necessary to start from the dyeing process and control the dyeing process to ensure the dyeing quality and prevent the occurrence of problems such as "colored flowers" and "willows".

The dyeing saturation value of nylon is very low, so the phenomenon of "competitive dyeing" among different dyes is very prominent when dyeing dark colors. If the selected dyes have a large difference in affinity and dyeing rate, the color of the fibers will be very different in different dyeing times, which is very easy to cause color patterns and poor color reproducibility.

In general, try to use 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 initial dyeing temperatures, and similar sensitivity to temperature and leveling agent. In order to minimize the "race dyeing" phenomenon between dyes.

4. The influence of the choice of leveling agent on nylon dyeing

Weak acid dyes have less water-soluble groups than strong acid dyes, have a higher affinity for nylon fibers, and have poorer solubility in aqueous solution than strong acid dyes. The dyeability and levelness are poor.

In the process of fiber spinning and weaving of nylon and its elastic fabrics, the physical and chemical structures of the fibers themselves are not uniform, including differences in fineness, internal stress, molecular structure orientation, etc., or differences in fiber chemical properties, such as fiber ends. The difference in the number of amino groups will also cause dyeing problems such as the formation of color bars and rungs during the dyeing process. In addition, operational problems in the dyeing process will affect the levelness of nylon dyeing. Therefore, the selection of a good leveling agent can effectively prevent or reduce the occurrence of the above problems.

There are many kinds of leveling agents for nylon dyeing, such as fiber-friendly anionic type, dye-friendly polymer type, and amphiphilic zwitterionic type. The zwitterionic leveling agent has a large molecular weight, has excellent leveling effect on weak acid dyes with large molecular weight, has a high dye migration ability, and has the ability to level the dyeing rate of different types of acid dyes.