Al from Murakami
Pure Photopolymers - Ok we introduced SBQ to the industry and pure photopolymers have some significant advantages. Long shelf life, over a year, good in any temperature found in a shop, 100+ degrees doesn't phase it, much longer coated screen life in good light safe dark rooms. Fast exposures, almost too fast on LED. You can post expose the emulsion for added strength or weak exposure systems, for dual cures and diazo it just helps dry it with very little additional exposure benefit. Great for all types of printing. No additives needed, comes ready to coat. Know your emulsion over mesh percentage to control halftones or to increase ink deposit for athletic printing. There are photopolymers for graphics as well as textile. Washout is typically with a pressure washer, hard to see unexposed image after exposure, shows up when wet. Pressure washer speeds up development. Available for all ink systems
Dual Cures - described as the best of both worlds. SBQ is fast, diazo has great resolution, combined you have the qualities of Pure Photopolymer and diazo. Latitude of exposure is wider and more forgiving. Halftones are easier to produce, washout is easier. Screen life and pot life of the emulsion are in the diazo range, 4-6 weeks (2-3 months at 70 degrees) Coated screens use within 2 weeks. Graphics uses Dual Cures quite often for wide lattitude exposure where precision halftone capture is needed. While not impossible with dual cures or diazo pure photopolymers are typically used for electronic printing where mesh bridging is crucial. Available for all ink systems
Diazo Emulsion - Diazo has a 4-6 week shelf life and 2 week screen life. These 'pot and shelf life' are always quoted to represent emulsion at it's peak of sensitivity. With proper storage you can extend the life a little. Good resolution of halftones, longer exposures, but LED is quickly changing that. Melts out of the screen during development. Requires hardeners for agressive ink systems. Diazo can be durable if coated and exposed well, but too many underexpose to get max halftones, brand dependent, some can be exposed completely and develop well for more durable screens. Available for all ink systems.
Bi-chromate - This was used a long time ago and hopefully is illegal to use in any area. High cancer risk, many horror stories about this stuff, kills downstream aquatic life when discharged. Tough as nails but so dangerous it should never be used again. Sad to say I have countries I go to where it isn't outlawed yet and it wreaks major ecological damage.
