High Intensity UV, Is More Always Better?
It seems to be a common theme that the UV intensity continues to increase in exposure units. It was just a few years ago when we thought 18-20mw/cm2 was high output. Now we are seeing exposure units come in at 30-35mw/cm2 from the factory. To get more intensity out of older units, we have seen high definition bulbs and upgraded ballasts. So why is it that we want more UV intensity in our exposure frames? Let’s take a quick look at how high intensity UV output can be both good and bad.
The first reason to consider higher output is to decrease exposure times. Some polymer blends and calipers require very long main-exposure times, so a higher UV output can decease exposure times. This will decrease the overall access time to a finished plate and free up the exposure frame to expose more plates. However, when it comes to back-exposure time, decreasing the time narrows the window for the exact time needed to hit the target relief. As the back-exposure time becomes very short, it is critical that the bulbs are prewarmed to the same temperature for each plate. Speaking of temperature, the higher UV units will produce more heat so make sure cooling fans and chilled table are working properly to keep the plate cool.
It is common knowledge that using a low UV intensity on the main-exposure can make it difficult to form small highlight dots even when using long exposure times. So, in theory a high UV intensity main-exposure will allow you to form better highlight dots. This is good when you are really pushing the limit of what the plate can hold, but you must be careful not to over expose the plate. Over exposing the plate with the high intensity UV can create a whole new world of problems including but not limited to the following:
• bulging shoulders on dots causing ink build up
• reverse text fill-in
• poor ink transfer from hardening the print surface
• polymer becoming brittle and cracking often resulting in missing dots
• reduced plate life.
As you can see there are both pros and cons to using high intensity UV exposure frames. Before pulling the trigger on upgrading your equipment to achieve high intensity UV output, take the time to make sure your current plate type works well with it. DuPont has close ties to the leading equipment manufacturers, and the equipment that is part of our portfolio has been optimized to work with the DuPont™ Cyrel® plates. As always, DuPont is here to assist you in this testing and optimization process.
DuPont has designed a Cyrel® 2000 EC UVi Exposure unit, where the user can custom select the desired UV intensity. The exposure unit, through its patented monitoring and calibration system can keep this intensity constant. This not only improves the consistency of the exposure process, but also improves the reliability of the platemaking. This is a unit that balances cost, performance and productivity. “Click here to learn how the Cyrel® 2000EC-UVi exposure frame allows you to select and maintain the UV intensity that works best for you.”