[Abstract] The development of printing on knitted fabrics has accelerated significantly over the past decade. However, due to their inherent dimensional instability, controlling the printing process remains a challenge, particularly when it comes to creating rotary screens for knitwear—especially for cotton blends containing spandex. These fabrics are highly elastic and sensitive to tension, which complicates maintaining consistent pattern size and shape, especially for geometric designs. Ensuring the accuracy of floral motifs is also difficult, requiring precise control throughout the entire production cycle.
The rapid growth in the printing of knitted fabrics has brought many challenges, especially with materials like spandex-containing cotton knits. These fabrics have high elasticity, making them prone to distortion during processing. When fed into the printing machine, factors such as fabric weight, tension, and speed changes can affect the final pattern's dimensions. This makes it harder to maintain accurate shapes and sizes, especially for complex or geometric designs. To achieve good results, careful management of every step in the process is essential.
1. **Printing Process for Spandex-Containing Knitted Fabrics**
The general process includes: weaving, open-width printing, steaming, pre-setting, pre-treatment, dyeing, printing, steaming, washing, dehydration, drying, and setting. Each stage must be carefully managed to ensure the best outcome.
2. **Color Separation and Draft Design**
Computer color separation is crucial for achieving accurate prints. Factors such as fabric type, elasticity, pattern repeat, and printing method (direct, discharge, or anti-print) all influence the design. For example, when scaling patterns, adjustments are made based on spandex content. If the spandex percentage is between 3% and 5%, the warp direction may be stretched by 13–18%, while the weft is reduced by about 3%. For higher spandex percentages (6–15%), the warp is stretched more, up to 20–26%, and the weft is slightly reduced. Printing speed also plays a role; speeds above 50 m/min require more stretch, but most operations stay below 40 m/min for better quality control.
3. **Color Separation Adjustments**
Knitted fabrics are looser than woven ones, so color separation techniques differ. In direct printing, the paste penetrates well, and the number of screen layers depends on the desired detail. For discharge printing, reducing full-color coverage helps prevent excessive pressure. Anti-print methods involve using reactive or non-reactive coatings, depending on the design. Pull-printing requires careful attention to color overlap and edge clarity.
4. **Screen Preparation**
Screen types vary, including inkjet, waxjet, and film-based. Inkjet screens are less precise than waxjet systems, which offer better resolution. Temperature and humidity control are essential for maintaining print accuracy.
5. **Nickel Mesh Selection**
The choice of nickel mesh depends on the fabric’s texture and the desired print quality. For fine details, higher mesh counts (e.g., 155 mesh) are used, while coarser patterns may require lower mesh counts. The mesh must allow proper ink flow without causing blockages or uneven coverage.
6. **Pre-Treatment of Spandex-Containing Fabrics**
Pre-forming is critical to eliminate internal stress and prevent permanent creases. Steaming at around 80°C and adjusting feeding tension help stabilize the fabric. Setting at 185–190°C for 45–60 seconds ensures stability, but temperatures above 195°C can damage the fabric or reduce spandex performance.
7. **Washing and Drying**
After printing, the fabric must be washed thoroughly to remove excess dye and chemicals. Continuous washing machines are preferred for even results. Drying at controlled temperatures prevents discoloration and maintains fabric integrity.
8. **Steaming and Final Setting**
Steaming is essential for fixing dyes and ensuring colorfastness. The duration and temperature depend on the type of dye used. For example, K-type reactive dyes require 10–14 minutes at 102°C, while disperse dyes need 7 minutes at 175°C. Final setting at 135–160°C helps achieve the desired shape and dimension.
9. **Conclusion**
While printing on spandex-containing knits presents unique challenges, advances in technology and process control have made it possible to produce high-quality, consistent results. Attention to every step—from pre-treatment to final setting—is key to success. By managing tension, temperature, and speed effectively, manufacturers can overcome the difficulties associated with these elastic fabrics and deliver superior printed products.
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