Nylon is a hydrophobic fiber containing amino and carboxyl groups [1], which can be dyed with disperse dyes, acid dyes, especially weak acid dyes. Its dyeing has the characteristics of fast dye uptake and high dye uptake. However, due to different spinning process specifications, the fiber structure is very different, which leads to great differences in dyeing properties and is prone to color difference. Therefore, if we are careless in the process of making samples, it may cause uneven dyeing, resulting in color difference, color stains, color spots, dark and shallow edges, stripes, color mismatch and poor dyeing fastness. Therefore, when dyeing nylon, the sample worker must formulate a reasonable dyeing process and strictly control the whole process, so as to reduce the defective rate and relieve the pressure of mass production.

Based on more than ten years' experience in nylon dyeing and proofing, the author summarizes the common defects in nylon dyeing, as well as the methods of prevention and technical remedy.

2 Common defects and preventive and remedial measures

2. 1 Competitive dyeing causes color difference between flowers and colors.

This is caused by improper selection of dyes. The dyeing saturation value of nylon is very low, so when it is mixed with dyes with strong colors, the competition between different dyes is very prominent. If the dye uptake and affinity of the dyes used are quite different, the color of the fiber will be very different at different dyeing time, resulting in poor color difference and reproducibility of the sample.

The preventive and remedial measures are to choose the dyeing material series with similar dyeing curve and affinity, good compatibility and suitable for production machines. Proofing personnel are required to fully grasp the dyeing properties of various dyes. When selecting dyes, the factors such as dye uptake, dye uptake curve, levelness, color fastness, sensitivity to temperature and leveler should be considered comprehensively.

2. 1. 1 Fully consider the compatibility of dyes.

When using several dyes for mixed dyeing, it is necessary to choose the appropriate dyes and control the dosage of dyes. Generally, try to choose the same series of dyes from the same company. Even if we have to choose dyes from different companies, we should try to choose dyes with similar dye uptake curve, similar initial dyeing temperature and similar sensitivity to temperature and leveler to avoid competitive dyeing.

2. 1.2 Pay attention to the difference of competitive dyeing of dye samples.

Some dyes are not obvious in small sample dyeing, but they are completely exposed in large production. For example, in the production of Lake Green and Kong Quelan, if acid turquoise blue and acid yellow are used together, similar problems will occur. This is because the molecular structure of acid turquoise blue is large, and the dyeing curve is quite different from that of acid yellow, which leads to competitive dyeing. If acid green and yellow light are matched with acid green basket, the problem of competitive dyeing will be basically solved.

2. 1.3 Pay attention to the adaptability of the machine to dyes.

Dyeing machines include jet, warp beam and jig dyeing machines. In the jet dyeing machine, the dye liquor is in full contact with the fabric, with good levelness, full hand feeling, good reproducibility and small cylinder difference, but the fastness to wet treatment is relatively poor. Weak acid dyes with good fastness but poor levelness or 1∶2 metal complex acid dyes can be used for dyeing. The product width control of warp beam dyeing machine is simple, and it is easy to fix color, but it is easy to have problems such as deep and shallow layers and head-tail color difference. Dyes with good levelness and poor fastness can be selected, and the dosage of leveler can be slightly increased, and then the fixation can be strengthened after dyeing.

2.2 Defects caused by unreasonable process

Nylon dyeing requires extremely high technology. Process conditions are important factors that affect the shade and levelness of dyed products, such as temperature, bath ratio and pH value, which will affect the quality of products. Unreasonable process is easy to produce defects such as poor levelness, flower, willow color, color difference and poor fastness.