Guide to Screen Printing Emulsions Techniques and Tips

Imagine this: your carefully designed pattern develops pinholes, underexposure, or difficult stencil removal during screen printing, ruining your work. These issues often stem from improper emulsion selection or incorrect handling. As the core material in screen printing, photoemulsion directly impacts print quality and efficiency. This comprehensive guide explores emulsion principles, types, selection criteria, and application techniques to help you meet diverse printing needs.

Screen printing (also called silkscreen printing) is a versatile technique where ink is forced through a mesh stencil onto substrates. Photoemulsion plays a pivotal role as the light-sensitive material that creates the printing stencil on screens. Functioning similarly to photographic film, emulsion transfers designs onto screens for subsequent printing.

1. Coating: Liquid emulsion is evenly applied to the screen mesh.
2. Drying: The coated screen dries in darkness.
3. Exposure: A film positive is placed against the screen and exposed to specific light wavelengths (typically UV). Opaque areas block light while transparent areas allow exposure, chemically hardening the emulsion.
4. Development: Unexposed emulsion is washed away, leaving the stencil pattern.
5. Final Drying: The developed screen dries before printing use.

Screen printing emulsions are categorized by chemical composition and application characteristics:

This traditional type requires diazo sensitizer addition. While offering forgiving exposure times and beginner-friendliness, it has slower sensitivity and lower durability, making it unsuitable for high-precision or large-volume printing.

Combining diazo and photopolymer technologies, these emulsions balance user-friendliness with speed and durability. Compatible with water-based, solvent-based, and UV inks, they represent the most widely used emulsion type today.

Pre-mixed for convenience, these eliminate sensitizer measurement errors but have shorter shelf lives and higher costs.

Relying solely on photopolymerization, these offer fast exposure, high resolution, and excellent durability for precision work. However, they require precise exposure control and are prone to overexposure.

Specifically formulated for water-based inks, these feature high solids content for thick, durable stencils with superior opacity.

Engineered for LED exposure units, these deliver rapid exposure and exceptional resolution to maximize LED equipment efficiency.

Choosing the right emulsion requires evaluating multiple factors:

• Water-Based: Eco-friendly, easy-clean options for textiles and paper
• Solvent-Based: Vibrant, durable inks for plastics and metals
• Plastisol: High-opacity inks for textile printing
• UV: Fast-curing, high-gloss specialty inks
• Discharge: For dark fabrics, removing base colors while printing

Match emulsion sensitivity to your light system:

• UV fluorescent lamps (broad spectrum)
• Metal halide (high-intensity for production)
• LED (energy-efficient with precise wavelengths)

Consider resolution needs (photopolymers for fine detail), durability (long runs need robust emulsions), and user experience (beginners should choose forgiving formulations). Additional factors include viscosity, solids content, development time, and reclaimability.

1. Work under yellow safelights in darkrooms to prevent premature exposure
2. Thoroughly degrease screens before coating using specialized cleaners
3. Apply emulsion evenly with scoop coaters, adjusting thickness for mesh count and ink type
4. Dry coated screens in dark, ventilated spaces (controlled humidity prevents bubbling)
5. Calibrate exposure times using test calculators based on emulsion type and light intensity
6. Develop with gentle warm water spray, avoiding excessive pressure
7. Use compatible blockout fluids for pinhole repair
8. Remove stencils promptly after printing with appropriate reclaiming chemicals

Causes: Contaminated screens, uneven coating, or dust during drying. Solutions: Improve cleaning procedures, ensure consistent coating, maintain clean drying environments, and use blockout fluids.

Causes: Insufficient exposure time, weak light source, or low-density films. Solutions: Extend exposure, upgrade lighting, or use higher-quality films.

Causes: Excessive exposure duration or intensity, or expired emulsion. Solutions: Reduce exposure time, adjust light output, or use fresh emulsion.

Causes: Aged emulsion, depleted reclaim chemicals, or insufficient processing time. Solutions: Use fresh materials, replace reclaim solutions, and extend processing duration.

Causes: Uneven screen tension, film warping, or poor contact during exposure. Solutions: Maintain uniform tension, use dimensionally stable films, and ensure vacuum-sealed exposure.

The market offers specialized emulsions for various applications:

HXT Pre-Sensitized Hybrid Emulsion: Convenient pre-mixed formula with fast exposure characteristics. Requires careful light-protected storage.

TX-D Dual-Cure Emulsion: Versatile water/plastisol/discharge ink compatibility with excellent water resistance and durability.

WR-25 Diazo Emulsion: Forgiving exposure characteristics ideal for newcomers, though with slower speed and moderate durability.

DC-Plus Dual-Cure: Exceptional solvent resistance for aggressive inks including UV and plastisol types.

LXP Pre-Sensitized: Optimized for LED exposure units, delivering rapid processing and high resolution.

Complementary products include water-soluble blockout fluids for repairs, exposure calculators for precise timing, and various scoop coaters for professional-grade application.