There are essentially 3 methods of processing or washing out photopolymer plates.
These processes include solvent wash, thermal removal, and water wash processing. The water wash plates of the past were not known necessary to be the best printing plate but they were known to resist ink swell and last a long time. In the last 5 - 10 years, there have been significant advancements to water wash photopolymer plates. Because of the significant improvements to these polymer formulations we see many printers gravitating to water wash plates. Whether you are currently processing water wash plates or if you are considering this technology, one often overlooked area to consider is water hardness.
Why do we not want hard water in our water-wash plate processor?
Not unlike washing dishes, cleaning your clothes, or yourself, hard water does not effectively break down and remove unwanted material from a surface. The same holds true with removing unpolymerized monomers from unexposed areas of the photopolymer plate during processing (washout). Soft water makes it easier to release unwanted material by decreasing the surface energy allowing for release. Soap or detergent acts in the same way in that it makes the surface or water itself more slippery and cleaning or in this case monomer removal is enhanced. This is also the reason we use hot water in the processors because as H20 molecules get hotter they become excited which results in the movement of the molecules which breaks down the unwanted material faster and more effectively, again not unlike cleaning household items.
What makes water hard?
When testing for H20 hardness, you should be measuring only water with no additives. Typically hard water is water that has high mineral content which is collected as the water filters through areas of gypsum, limestone, and chalk. These materials are primarily made up of calcium, magnesium, bicarbonates, sulfates, and carbonates. Hard water is measured in PPM (parts per million) and when something is added to the water, in a case like this it could be polymer particulate or granular detergent, the PPM can soar through the roof. Think of it this way, your water at home could be classified as soft (< 17.1 PPM), but by adding Kool-Aid the water hardness could indicate an increase in GPG. The customer only needs to be concerned with the water hardness entering the plate processor.
I have hard water; can this be fixed?
Absolutely, but remember just because your water is hard does NOT mean plates cannot be made; they will just not wash out as fast or effectively as they would with softer water. TSG has also found that hard water can diminish plate life and make the plate more brittle and slightly increasing durometer, making screens and fine lines more susceptible to damage. The most effective solution is a simple apartment size water softener for just a few hundred dollars. Remember, you don’t have to make the water soft for the entire facility, only the water being supplied to the plate processor which will likely consume <100 gallons per week.
If you want to learn more about this subject, please feel free to reach out to us by calling 1-800-445-4017, or by e-mail at [email protected].
All Printing Resources has formed our Technical Solutions Group (TSG) to encompass our full range of expertise in all critical areas of the flexo process. This team is made up of industry professionals dedicated to being up-to-date on new technologies along with best practices. They are armed with the latest in diagnostic tools and are experienced in problem-solving that can achieve sustainable results. The TSG has walked in your shoes, and have felt your pain.