**Abstract**
The development of printing on knitted fabrics has experienced rapid growth over the past decade. However, due to their poor dimensional stability, it is challenging to control during the printing process, making it difficult to develop rotary screens for knitwear—especially for cotton knitted fabrics that contain spandex. These fabrics have a high degree of plasticity, and when fed through a drape weight and cloth rack tension, they are also affected by changes in speed, making it harder to maintain consistent pattern shape and size, particularly for geometric designs. Preserving the original design's spirit becomes more complex, and achieving satisfactory results can be tough without proper control throughout the entire production process.
**Printing Process of Spandex-Containing Knitted Fabrics**
The printing process includes several key stages: weaving, open-width printing, loose cloth preparation, steaming, pre-setting, pre-treatment, dyeing, printing, steaming, washing, dehydration, drying, and setting. Each step must be carefully managed to ensure quality and consistency.
**Color Separation and Design Drafts**
Computer color separation plays a crucial role in preparing the design drafts. Factors such as fabric type, elasticity, pattern return, number of colors, and printing method (direct, discharge, or anti-print) must be considered. The artwork must be scaled appropriately based on the spandex content to ensure accurate pattern reproduction.
**Printing Size Scaling**
Depending on the spandex percentage, the pattern must be scaled accordingly. For example, when spandex content is between 3% and 5%, the warp direction should be increased by 13–18%, while the weft direction can be reduced by about 3%. Higher spandex content (6–15%) requires a larger scale, up to 20–26% in the warp direction. Printing speed also affects pattern accuracy, with speeds below 40 m/min being easier to control.
**Pattern Discoloration in Different Printing Processes**
Knitted fabrics tend to be looser and more permeable than woven fabrics, which affects how patterns appear. Direct printing uses a good paste permeability, typically 8–16 silk, while discharge printing requires careful handling to avoid over-covering. Anti-print techniques require precise control of color layers to maintain clarity and vibrancy.
**Screen Preparation Methods**
Modern screen-making methods include inkjet and waxjet screens, though traditional film-based screens are still used. Inkjet screens may lack precision due to ink spreading, so maintaining consistent temperature and humidity is essential for accurate results.
**Nickel Mesh Selection**
Choosing the right nickel mesh is vital for achieving the desired print quality. Mesh sizes like 40, 60, 80, 105, 125, and 155 are commonly used, depending on the fabric’s thickness and the complexity of the pattern. Finer meshes are better for detailed prints, while coarser ones suit bulkier designs.
**Pre-Treatment of Spandex-Containing Fabrics**
Before printing, spandex-containing fabrics must be pre-treated to remove impurities and stabilize their structure. This includes relaxation, steaming, and setting to eliminate internal stress and prevent wrinkles. Proper pre-treatment ensures the fabric remains stable during printing.
**Setting of Semi-Finished Products**
The semi-finished product must be set according to the design specifications. Controlling shrinkage and width helps maintain the fabric’s shape. Adjustments are made to reduce weft twisting and ensure even tension during printing.
**Operation Method of Rotary Screen Printing**
Proper feeding and speed control are critical in rotary screen printing. The fabric’s elasticity and speed changes affect its elongation, requiring careful adjustment. Printing speed should ideally be between 30–40 m/min to maintain quality and pattern accuracy.
**Printing Pressure and Magnetic Bar Selection**
The pressure applied during printing and the choice of magnetic bar (scraper) depend on the pattern size and design complexity. Thinner areas use smaller bars, while larger surfaces require heavier ones. Adjustments ensure optimal ink transfer and print quality.
**Formulation of the Printing Process**
The printing formula varies depending on the fabric and dye type. Reactive dyes, for example, require specific amounts of alkali agents and urea to enhance dye absorption and color fastness. Formulas must be adjusted based on fiber properties and printing conditions.
**Discharge Printing Process**
Discharge printing involves preparing a special paste that removes color from the fabric. The formula depends on the desired whiteness level, with different concentrations of starch ether, sodium alginate, and other ingredients used to achieve the right effect.
**Drying After Printing**
Drying at the correct temperature is essential to prevent color bleeding and ensure proper fixation. The temperature range varies depending on the type of dye used, with reactive dyes requiring lower temperatures than disperse dyes.
**Steaming and Washing**
Steaming is a critical step in fixing the dye. Continuous steaming machines are preferred over steam tanks to avoid uneven heating and stretching. Washing after steaming helps remove excess dye and chemicals, ensuring clean and vibrant prints.
**Elastic Fabric Shaping**
After printing, elastic fabrics must be shaped to meet final dimensions. Careful control of temperature and speed during shaping prevents deformation and maintains the fabric’s elasticity.
**Conclusion**
Rotary screen printing on spandex-containing knitted fabrics, especially discharge printing, presents unique challenges. However, with proper control of each stage—from color separation to finishing—the process can produce high-quality, consistent results. Attention to detail at every step ensures that the final product meets all quality and dimensional requirements.
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