Flash-cure units are essential in textile screen printing, playing a pivotal role regardless of a printer’s experience level. Understanding their function and the technical aspects of the flashing process can significantly enhance print quality and efficiency. Outside of automatic presses, no other equipment has influenced garment design and printing as profoundly as flash-cure units. Over 98% of dark garments undergo flashing, and even some white garments are flashed to achieve unique special effects that appeal to consumers.

Designing Artwork for Flashing

Flashing has transformed screen print artwork, enabling artists to create striking visual effects through strategic color separations. Modern designs account for flashing to ensure smooth production. Skilled artists craft separations that integrate flashes without slowing down the press, allowing print runs to achieve speeds of 55–65 dozen garments per hour, often with one or two flashes in the sequence. Advanced computer-based separation techniques and scanning technology have streamlined this process, minimizing the amount of ink that needs flashing. This efficiency reduces trial and error, with artists often perfecting separations in just one or two attempts, compared to the four or five tries required before digital tools were prevalent.

Flashing Solid Colors

While technology has improved flash-unit performance, printing solid color areas remains a challenge. Solid flashed areas tend to retain more tackiness after flashing compared to broken-up designs like halftones. To address this, printers should select high-opacity inks with low after-flash tack. Adding 5% puff additive to white ink can help, as puff inks dry thoroughly when flashed, reducing tackiness. Ideally, printers should use a white ink formulated for flashing, but the puff additive can serve as a temporary solution until the right ink is sourced.

Multiple Flashes

Complex designs with multiple colors or special effects often require several flashes. Each flash unit, paired with a cool-down station, occupies two printing heads, which can strain even large presses. Special-effect inks, typically applied last, often necessitate additional flash and cool-down stations. For example, let’s say we have a design that requires three flashes to incorporate an underbase, two metallic inks, and a highlight white. The sequence is:

  • Bleed-resistant clear (305 mesh)
  • White underbase (196 mesh)
  • Flash
  • Cool
  • Gray (305 mesh)
  • Red (305 mesh)
  • Navy (305 mesh)
  • Metallic blue (140 mesh)
  • Flash
  • Cool
  • Metallic silver (140 mesh)
  • Flash
  • Cool
  • Highlight white (196 mesh)

This design, despite using few colors, requires a 14-color press to maintain print clarity, as coarser meshes are avoided to preserve definition. A bleed-resistant clear layer is printed first to capture lint and prevent dye migration.

Flashing colors other than white can also be effective. Non-white underbases, like gray, offer high opacity due to their black content and absorb heat faster than white, reducing flash time and tackiness. Printing a black outline before the white underbase on dark garments can eliminate a post-flash screen, reducing the risk of mottling.

On-Press Factors

Screen Quality: High-tension screens are critical for efficient flashing. They allow finer mesh counts, depositing ink on the fabric’s surface rather than pushing it in, which reduces flash time. Low-tension screens require more squeegee pressure, embedding ink into the fabric and necessitating coarser meshes or multiple passes, increasing flash duration.

Flash Unit Setup: Optimal flash unit settings vary by equipment and application. The distance between the flash unit and ink film depends on the unit’s energy output (e.g., fused-quartz or infrared). Most units perform best 1–2.5 inches from the ink surface, but printers should consult the manufacturer’s guidelines. Placing the unit too close risks scorching the fabric, while excessive heat can cause issues like loss of ink adhesion or dye sublimation in polyester blends.

Temperature Control: Flash units often operate at 800–900° F, but setting them too high can overheat the ink or garment. Plastisol inks gel at 150–250° F, but reaching cure temperatures (320° F) or remelt temperatures (350° F) during flashing can compromise adhesion or durability. For 50/50 cotton/polyester garments, excessive heat may trigger dye sublimation (340–400° F), causing bleeding. Printers should aim for the lowest effective gel temperature, typically 550–700° F, to avoid scorching cotton or overheating platens.

Dwell Time: The time the ink spends under the flash unit (dwell time) should be minimized. Start with a 3-second dwell, increasing by 1-second increments until the ink gels sufficiently for overprinting. Alternatively, set a 4-second dwell at 500° F and raise the temperature in 50° F increments until the ink is ready. This approach prevents overheating while maintaining productivity.

Managing Heat in Production

After setting the flash unit’s distance, temperature, and dwell time, monitor the ink and garment temperature as they enter the dryer, which is typically set to 320° F. If the pre-dryer temperature is high (e.g., 280° F), the ink or garment may exceed safe thresholds, risking remelting or dye sublimation. As platens heat up during production, the ink gels faster, allowing printers to reduce flash temperature or dwell time. Regular temperature checks ensure consistent results and prevent issues like mottling or poor washability.

Conclusion

By mastering these aspects of flash curing, printers can optimize production, enhance design quality, and achieve vibrant, durable prints tailored to modern market demands.