The Screen Print Column
Five most common screen exposure mistakes (and how to fix them)
Screen exposure can make or break a product with timing playing a huge role in the end result. In the column Beppe Quaglia, CEO and president of Virus Inks, explains a handful of helpful tips to enhance the screen print.
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n screen printing, the quality of the final print is determined long before the first squeegee stroke. Among all the pre-press stages, screen exposure plays the most decisive role. Even experienced printers can fall into subtle traps that compromise stencil durability, image definition, and ultimately print consistency. Exposure is not just about getting light onto the screen – it is a precise technical step, influenced by mesh geometry, emulsion thickness, lamp spectrum, and postprocessing. Misjudging any of these factors can mean wasted hours, reprints, and dissatisfied clients. Let’s look at the five most common exposure mistakes encountered in professional shops, and how to avoid them.
1. Under-tensioned mesh
This is the invisible enemy of print quality. When the mesh is too loose, the emulsion layer becomes inconsistent, leading to irregularities in stencil thickness and ink deposit. In high-resolution work, this can cause halftone dots to close, fine lines to blur, or details to wash away. Solution: Always monitor mesh tension with a calibrated tensiometer. For most textile applications, a stable range of 20-25N/cm is recommended. Where possible, use retensionable frames to maintain stability over time. Remember: a properly tensioned screen guarantees not only sharper prints but also longer stencil life.
2. Incorrect emulsion over mesh (EOM) EOM, defines the thickness of emulsion relative to the thread diameter. Too much emulsion leads to heavy ink deposits, loss of detail, and drying issues; too little emulsion results in fragile stencils that break down quickly on press. Solution: Measure EOM using a film gauge or spessimetro. For halftone printing, aim for 10-20% of thread diameter, while for blocky spot colours or high-density inks, a higher percentage may be required. Use conistent coating techniques dual-sided coating or controlled automatic coaters, to achieve reproducibility. The key is not guessing but measuring.
Insufficient spectrum Ideal spectrum 3. Wrong exposure time
Perhaps the most widespread mistake; assuming one-time fits all. Overexposure hardens the emulsion too much, making washout difficult and potentially reducing stencil resolution. Underexposure leaves unpolymerised emulsion, which softens during printing and collapses after a few runs. Solution: Calibrate exposure with a step wedge or exposure calculator. Every emulsion, mesh count, and coating thickness requires a different exposure time. Environmental factors – temperature, humidity, lamp age – also matter. Establish a standard operating procedure: record times, mesh data, lamp hours, and test results. Precision here saves frustration later.
4. Inadequate light source
Not all light is equal. Many shops switch to UV LED systems for energy efficiency but neglect to adapt exposure parameters. Conventional metal halide or fluorescent lamps emit broader spectra, while LEDs may lack penetration for certain emulsions or thick coatings. Poor lamp maintenance further reduces efficiency, leading to weak stencils. Solution: Match the emulsion to the light source. SBQ photopolymer emulsions are highly reactive to LED, but diazo-based emulsions often require broader UV spectra. Clean and recalibrate lamps regularly, monitor output with a radiometer, and replace aging bulbs before they cause quality loss. Exposure is chemistry meeting physics; light must be precise.
5. Poor washout and post-exposure practices Even after perfect exposure, mistakes during washout can destroy a stencil. Excessive water pressure can undercut edges, while insufficient rinsing leaves residue that clogs halftones. Skipping post-exposure reduces chemical resistance, making the stencil vulnerable to aggressive inks or cleaning agents. Solution: Standardise washout pressure and distance, ideally between two to three bar for textile screens. Always use clean, filtered water. After developing, dry completely and perform a short postexposure to increase hardness and solvent resistance. This step is often overlooked, yet it greatly extends stencil life.
Emulsion sensitivity
Emulsion sensitivity
Conclusion Radiation spectrum | 66 | November 2025
Exposure errors are not just technical inconveniences – they are profit killers. A stencil that collapses mid-run, or a halftone that prints inconsistently, forces reprints, wastes ink, and erodes customer trust. The solution is discipline: measure, calibrate, record, and repeat. Exposure is not guesswork; it is a controlled scientific process.
www.printwearandpromotion.co.uk
Halogen lamp
Halogen lamp
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