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 screen printing emulsion should you use? Why would you use a pre-sensitized emulsion over a diazo emulsion?
The biggest factor in 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 screen printing emulsions are ready to go from the container, no need to mix or wait for use. Ecotex® emulsions that fall into this category are:
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-sensitized 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 emulsions are much different. Ecotex® emulsions included in this category are:
Ecotex® Dual Cure "DC" Pink Emulsion
Ecotex® Dual Cure "DC" Blue Emulsion
Ecotex® Water Resistant Blue Emulsion
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 it 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 the preferred route. Diazo emulsions hold up longer against water-based inks. A stencil's 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 Part 2 of " What Emulsion Do I Need?"
Click here for "What Emulsion Do I Need Part 2"
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