When acid dyes are used for warp dyeing of nylon warp knitted fabric, there is often a problem of color difference between the inner and outer layers. By using high-temperature pre shaping of the fabric (190 ℃, 20-30 S), selecting a roll density of 0.33 kg/m3, setting a flow rate of 220 m3/h, adding leveling agent M to the dyeing bath, and using organic acid releasing agent VS to control pH, the dyeing process can be optimized to effectively control the layer difference of nylon warp knitted fabric and achieve ideal dyeing results.
The warp dyeing machine, also known as the scroll dyeing machine, is a high-temperature and high-pressure dyeing machine composed of a dyeing pressure vessel, a hollow warp shaft filled with small holes, a secondary cylinder (batching bucket), a circulating pump, a heat exchanger, and a warp transport vehicle. During the dyeing process, the fabric is wound flat on a perforated core, and the fabric roll is fixed at both ends by an iron frame. A professional pump with high lift and high flow rate is used to force the dye solution to penetrate the fabric layer in the forward direction (from the core to the outside of the fabric roll) or in the reverse direction (from the outside of the fabric roll to the inside of the shaft). Because the fabric is not stretched, it is very suitable for dyeing lightweight and easily creased nylon warp knitted fabrics.
The advantages of a high-temperature and high-pressure warp dyeing machine are good dimensional stability of the fabric, resistance to wrinkling, and a flat surface. However, dyeing nylon warp knitted fabric with a warp dyeing machine is prone to problems such as dyeing patterns, layer differences, water ripples, and poor dyeing reproducibility. Through optimizing the density parameters of the roll fabric, pump flow rate, and dyeing process, I have solved these quality problems of nylon warp knitted fabric and conducted practical analysis through khaki dyeing.
Dyeing process and optimization
1. Dyeing process line
Fabric: Nylon warp knitted fabric (78% nylon+22% Lycra, 170 g/m2), with a width of 160 cm.
Dyes: Acidic NHF-S series
Auxiliaries: Organic acid releasing agent VS (Huntsman Textile Dyeing), acidic leveling agent M, fixing agent N.
Dyeing process curve.
2. High temperature predetermined shape
High temperature pre shaping can reduce or eliminate the uneven tension generated by nylon fibers during spinning, drawing, and weaving processes, providing a prerequisite for nylon warp knitted fabric to be uniformly and smoothly rolled onto the warp axis.
At the same time, it can avoid excessive shrinkage of the nylon fiber fabric, which may result in water leakage at both ends and dyeing of the rolled edges. However, if the temperature is too high, pre ordering the fabric will result in a loss of elasticity and damage to the coloring performance of nylon. Therefore, the pre order forming conditions should be reasonably controlled according to the fabric specifications and finished product elasticity requirements. It is advisable to choose a predetermined temperature of 190 ℃ and a duration of 20-30 seconds.
3. Optimization of dyeing process
The process of dye uptake refers to the transfer of dye from the dye solution to the fiber and its penetration into the fiber. Firstly, the dye solution enters the diffusion boundary layer of the fiber. After the dye approaches the fiber to a certain distance in the diffusion boundary layer, the dye molecules are quickly adsorbed on the fiber surface. The dye molecules form hydrogen bonds with the fiber surface and combine with van der Waals or Coulomb forces. After the dye is adsorbed on the fiber surface, a dye concentration difference is formed inside and outside the fiber, thus diffusing and fixing inside the fiber. The uptake process is the result of a large number of molecular movements.