How to Prepare Ulano 145 Screen Printing Emulsion with Dichromate Sensitizer

Screen printing with Ulano 145 emulsion can be challenging due to limited information and unhelpful suppliers. This guide provides clear, practical steps to prepare Ulano 145 emulsion using dichromate sensitizer, based on real-world user experiences.

It covers sensitizer types, mixing ratios, safety precautions, and tips for handling this decades-old emulsion, particularly for users in regions like Pakistan where resources are scarce.

What is Ulano 145 Emulsion?

Ulano 145 is an older screen printing emulsion, likely 20-30 years old. If stored properly, it remains usable as long as it’s liquid and free of lumps. This emulsion requires a sensitizer to become light-sensitive for screen coating.

Without clear manufacturer instructions, users must rely on standard practices for similar emulsions. The two common sensitizers are diazo and dichromate, with dichromate being more accessible in some regions.

How to Choose the Right Sensitizer?

Dichromate sensitizer is often supplied as a colored liquid resembling Fanta or as a powder. It’s widely used due to its availability and effectiveness.

Diazo is an alternative but less common in some markets like Pakistan.

Dichromate is toxic and light-sensitive, requiring careful handling and storage. For Ulano 145, dichromate is a reliable choice if stored correctly.

How to Mix Dichromate Sensitizer with Ulano 145?

The standard mixing ratio for dichromate sensitizer is 100 ml per liter of Ulano 145 emulsion. For smaller batches, scale proportionally (e.g., 10 ml for 100 ml of emulsion). If using liquid dichromate, ensure it’s not degraded from light exposure. The liquid should be stored in a dark, opaque bottle to maintain its shelf life, which can last years if unexposed to light.

For powder dichromate, dissolve 12-15 grams per 100 ml of water to create the sensitizer solution. Some Indian suppliers recommend 12 grams per 100 ml, which aligns with typical 1-liter emulsion kits containing 900 ml of emulsion. The remaining 100 ml comes from the sensitizer solution (12 grams of powder dissolved in 88 ml of water). A 15-20% weight concentration is ideal for consistent results.

Step-by-Step Preparation Process

Check Emulsion Condition: Ensure Ulano 145 is liquid and lump-free. Stir gently to confirm consistency.
Prepare Sensitizer:
- For liquid dichromate, measure 100 ml per liter of emulsion.
- For powder dichromate, dissolve 12-15 grams in 100 ml of distilled water. Stir until fully dissolved.
Mix Sensitizer and Emulsion: Slowly add the sensitizer to the emulsion while stirring. Avoid introducing air bubbles.
Rest the Mixture: Let the sensitized emulsion sit for 1-2 hours in a dark place to remove air bubbles.
Store Properly: Transfer any unused sensitized emulsion to an opaque container. Use within 24-48 hours, as dichromate-sensitized emulsion has a short shelf life.

What are the Safety Precautions You Should Follow?

Dichromate is toxic and can cause skin irritation or respiratory issues. Always wear gloves, a mask, and protective eyewear when handling it.

Work in a well-ventilated area to avoid inhaling fumes. Dispose of dichromate waste according to local regulations, as it’s hazardous to the environment. Avoid exposing dichromate solutions to light, as this degrades their effectiveness.

How to Apply Ulano 145 to Screens?

Once sensitized, Ulano 145 can be applied to a degreased, clean screen using a scoop coater. Apply 1-2 thin, even coats on both sides of the screen in a darkroom to prevent premature exposure.

Dry the coated screen horizontally in complete darkness at room temperature. A fan can speed up drying but avoid heat sources that may damage the emulsion.

Exposure and Development

Expose the dried screen using a UV light source, following standard exposure times for your setup (typically 1-5 minutes, depending on light intensity). After exposure, rinse the screen with cool water to develop the image.

Unexposed areas will wash away, leaving the stencil. If the stencil washes out entirely, the emulsion may be under-exposed or the sensitizer degraded.

Challenges and Solutions

Degraded Sensitizer: If the dichromate liquid is stored in a clear bottle, it may be ineffective. Transfer it to an opaque container or use fresh powder.
Short Shelf Life: Sensitized Ulano 145 lasts only 24-48 hours. Mix small batches to avoid waste.
Availability Issues: In regions like Pakistan, dichromate powder may be hard to find. Import small sachets (e.g., 3-gram packs from India) and mix as needed.
Inconsistent Results: If the emulsion doesn’t harden, check the sensitizer concentration or emulsion age. Test with a small batch before coating large screens.

What are the Tips for Success?

Use distilled water for mixing to avoid impurities affecting the emulsion.
Store unsensitized Ulano 145 in a cool, dark place to extend its usability.
Keep a log of mixing ratios and exposure times to refine your process.
If dichromate is unavailable, source diazo sensitizer (50 ml per liter of emulsion) from international suppliers.

Conclusion

Preparing Ulano 145 emulsion with dichromate sensitizer requires careful attention to mixing ratios, storage, and safety. Use 100 ml of liquid dichromate or 12-15 grams of powder per 100 ml of water per liter of emulsion.

Handle dichromate with care due to its toxicity and light sensitivity. By following these steps, users in regions with limited resources can achieve reliable screen printing results. Always test small batches and store materials properly to maximize success.