Screen Printing Emulsions Overview
Screen printing emulsions are applied directly to a cleaned and degreased screen using a scoop coater. After drying, the emulsion becomes light-sensitive and can be exposed to ultraviolet light.
This process transfers your design onto the screen: areas exposed to light become waterproof, while areas shielded by the film remain water-soluble and can be washed out, transferring your positive film to the screen.
Historical Context and Evolution
The development of screen printing emulsions has seen significant advancements over the decades. Diazo emulsions, introduced in the mid-20th century, provided a cost-effective solution but had limitations in terms of shelf life and exposure times. Dual-Cure emulsions emerged as a more versatile option, combining the benefits of Diazo and photopolymer technologies. The latest advancement, SBQ Photopolymer emulsions, offers unmatched speed and efficiency, reflecting the industry’s push towards faster production times and higher precision.
Three Types of Screen Printing Emulsions
- Diazo
- Dual-Cure
- SBQ Photopolymer
Diazo Emulsion
- Composition: Two-component system with a sensitizer and a non-sensitizer.
- Cost: Low.
- Shelf Life: 30-45 days after mixing.
- Usage: Becoming less common, replaced by dual cure and SBQ emulsions.
- Historical Note: Once the industry standard, Diazo emulsions are now less favored due to the availability of more advanced alternatives.
- Expert Opinion: “While Diazo emulsions are cost-effective, their shorter shelf life and longer exposure times make them less practical for high-volume production,” many say.
Dual Cure Emulsions
- Composition: Two-part system with sensitizer mixed into a base.
- Cost: More expensive than Diazo but less than SBQ.
- Shelf Life: Longer than Diazo.
- Benefits: Fast exposure, durability, sharp edge definition, wider exposure latitude, easier washing and development.
- Practical Example: In my Own Shop, switching to dual cure emulsions reduced exposure time by 40% and increased the clarity of fine details in complex designs.
SBQ Photopolymer Emulsions
- Composition: Pure photopolymer.
- Cost: Highest.
- Shelf Life: Up to one year.
- Benefits: Fastest exposure times, no mixing required, excellent mesh bridging, reduced stencil surface area (Rz).
- Case Study: I saw a 30% increase in production efficiency after switching to SBQ emulsions, thanks to their quick exposure times and high durability. “The transition to SBQ emulsions has been a game-changer for the workflow,”.
Comparative Analysis
| Feature | Diazo | Dual-Cure | SBQ Photopolymer |
| Cost | Low | Moderate | High |
| Shelf Life | 30-45 days | Longer than Diazo | Up to 1 year |
| Exposure Time | Moderate | Fast | Fastest |
| Durability | Good | Very Good | Excellent |
| Ease of Use | Moderate | Easier than Diazo | Easiest |
| Use Cases | General, Cost-Sensitive | Versatile, High Precision | High-Speed, High-Precision |
Using Emulsion for Screen Printing
- Preparation:
- Degrease and thoroughly dry the screens.
- Ensure screen tension is at least 20 N/cm for best results.
- Coating:
- Apply Emulsion to the Print Side first (side that will touch the garment).
- Use the blunt edge of the coater for maximum emulsion over mesh (EOM) or the sharp edge for a thin emulsion layer on the screen.
- Dry screens horizontally with the contact side down in a dust-free environment.
- Avoid using a fan directly on the coated screen to prevent pinholes.
- Apply a top coat to reduce Rz if needed.
- Dry at 30-40°C (86-104°F) without excessive heat to avoid premature sensitizer activation.
- Storage:
- Store coated and dry screens in a light-protected room at 30-50% relative humidity.
Emulsion Considerations for Inks
- Plastisol and Water-Based Inks: Check with your supplier for compatibility.
- Water-Based Inks: May require a hardener.
Advanced Tips for Optimal Results
- Screen Tension:
- Higher screen tension not only improves print quality but also extends screen life. Aim for tensions above 25 N/cm for critical jobs.
- Exposure Times:
- Conduct the 21 Step Wedge tests to determine optimal exposure times for your specific setup. This ensures precise exposure and better detail retention.
- Humidity Control:
- Maintain consistent humidity levels in your drying and storage areas. Fluctuations can affect emulsion consistency and performance.
- Retouching:
- When retouching your screen to close pinholes, you need then expose it again to UV light. This will ensure the retouched areas are fully hardened and durable.
Emulsion Over Mesh (EOM) and Scoop Coaters
Emulsion Over Mesh (EOM )
Emulsion over mesh (EOM) = Total stencil thickness minus mesh thickness.
EOM Emulsion over Mesh
Stencil Surface (Rz)
Scoop Coater: Sharp edge for thin layers, blunt edge for thick layers ideal for optimum EOM.
Capillary Film
- Advantages: Superior mesh bridging, no pinholes, excellent Rz value.
- Usage: Ranges from 10-50 microns for standard printing to 100-400 microns for high-density (HD) and special effects (SFX) printing.
By understanding these different emulsions and their applications, you can optimize your screen printing process and achieve the best possible results. Incorporating these insights, expert opinions, and advanced tips will ensure you get the most out of your screen printing emulsions, leading to higher quality prints and more efficient production.
Questions & Answer
What are the different types of emulsions used in screen printing?
Diazo, Dual-Cure, and SBQ Photopolymer.
How long can you leave photo emulsion on a screen?
The length of time you can leave photo emulsion on a screen before exposure depends on the type of emulsion and storage conditions. Generally, once a screen is coated with emulsion, it should be stored in a dark, cool, and dry place. For optimal results: Use it in some days, you don’t want to store it for months to come.
What is the shelf life of a diazo emulsion?
30-45 days after mixing. Dual Cure emulsions have a longer shelf life, and SBQ emulsions have the longest shelf life of up to one year.
What are the recommended exposure times for different types of emulsion?
Exposure times can vary based on factors such as light source intensity and mesh count. To determine the correct exposure time for your specific emulsion, refer to the Technical Data Sheet (TDS) provided by the manufacturer. Additionally, using an exposure calculator can help you find the optimal time based on your setup.
How should emulsions be stored to maximize their shelf life?
o extend the lifespan of your emulsions, store them in a cool, dark place. Sensitized emulsions can have their shelf life extended by refrigerating them. However, it’s important to allow the emulsion to return to room temperature before use to ensure proper application and performance.
What are some common issues with emulsions and how can they be resolved?
Common problems include pinholes, underexposure, and overexposure. Pinholes can be caused by contaminants or improper coating; ensure your screen is clean and apply the emulsion evenly. Underexposure may result in incomplete image development, making screens much harder to reclaim. Adjust your exposure time if this occurs. Overexposure can cause excessive hardening of the emulsion, making it difficult to wash out; reduce exposure time if this happens. Regularly test and adjust your exposure settings for best results.
What methods are recommended for removing emulsion from screens?
For effective emulsion removal, use a dedicated screen reclaiming solution or emulsion remover. Apply the remover to the screen, allow it to sit for the recommended time, and then scrub with a brush to remove the emulsion. Rinse thoroughly with water. Ensuring the emulsion is properly exposed helps make cleaning easier, as underexposed screens are much harder to reclaim.
Is there an environmentally friendly photo emulsion for screen printing?
Currently, there is no environmentally friendly photo emulsion that lasts through production. While some emulsions may claim to be more eco-friendly, none can maintain the durability required for consistent screen printing production.
How to Expose Emulsion Video
