The wonderful world of emulsions can be pretty tricky for a new screen printer to understand, there are so many different kinds! There are different colors, types, abbreviations, and all kinds of things that can make choosing overwhelming and a bit tricky. Which emulsion should you use? Why would you use a pre sensitized emulsion over a diazo emulsion?
The biggest factor to indicating the right emulsion is choosing which type of ink you are going to print with. From there you can decide whether you need a “Pre sensitized emulsion” or “Diazo based emulsion.”
Pre sensitized emulsions are ready to go from the container, no need to mix or wait for use. Ecotex emulsions that fall into this category are AP Blue, PWR, Tex-Red, Tex-blue, Tex-red HV, Tex-blue HV and LED. They can be exposed very quickly which is nice, however this means you do not have room to overshoot or under shoot your exposure time. Doing so can result in an under or over exposed screen. When a screen is under-exposed the emulsion will wash away along with the image. When a screen is over-exposed nothing will wash off and you will have a tough time reclaiming.
Another characteristic of the pre-sensitized emulsions is that you can have a shelf life of up to 12 months which is awesome for those that do not print consistently.
Pre-sensistized sounds great and efficient, right? Yes, but if you print high volume runs with water-based inks you should consider a 2 part emulsion that requires the addition of diazo.
Pros: Ready to use, Long shelf life, Shorter exposure window.
Cons: Not as water resistant, exposure times have to be spot on.
Diazo based emulsion
Diazo based emulsions are much different. Ecotex emulsions included in this category are DC-Pink, DC-Blue and WR-Blue. For starters you need to mix the diazo sensitizer into your emulsion. It's a simple step, add the required water to the diazo and then mix into the emulsion. When you mix diazo into emulsion it is going to give the emulsion a slower exposure time. This might sound like a negative however it does give you a little more flexibility in exposure time compared to pre-sensitized emulsions.
Unlike the pre-sensitized emulsions these diazo emulsions are going to have a much shorter shelf life. Once mixed you can expect a diazo emulsion to last you a month, give or take a bit, depending on how you store it.
Don't let the short life deter you away. If you are going to be printing with water based inks consistently then this is preferred route. Diazo emulsions hold up longer against water-based inks. A stencils life span will hold up much longer when using water based ink compared to a pre-sensitized emulsion.
Pros: Wider exposure window. Water-resistant more durable stencil
Cons: Short shelf life once mixed, Longer exposure time
This should give you a good idea of what the main differences are between the two types of emulsion. Stay tuned for a Part 2 of "What emulsion do I need?"
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