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How to Optimize Plate Finishing (it’s not just about time)

04/03/21

Optimizing the finish on your plates isn’t just a question of time. Print Applications Specialist Dan Magallanes shows how you can evaluate your plates before they head to the press.


So, your KODAK FLEXCEL NXH plate has been properly dried, cooled to room temperature, and is ready for finishing. But how do you confirm you’ve finished your plate for the correct amount of time to ensure you get the maximum plate life on press? It’s just about time…

Determining proper post exposure times is easy, because post-exposure/UVA times for FLEXCEL NXH plates are typically only two or three minutes, at the most.

Establishing the best finishing/UVC times is not so straightforward and tends to be subjective – if you show the same finished plate to three people, you can easily get three different opinions on the readiness of the plate for the press. Find out how to evaluate your finished FLEXCEL NXH plate for print readiness.

Determining proper finishing times

Typical light finishing/UVC times for FLEXCEL NXH plates range from 15-20 minutes. As you may guess, times will vary based on the age and light intensity of the UVC bulbs being used. Before starting, make sure ALL UVA and UVC lamps are functioning. During day-to-day platemaking, it’s easy to take for granted that lamps are working properly. However, this isn’t always the case, as over time the ballasts will eventually fail.

Even relatively new laps can fail prematurely. It’s always best to keep an eye on your lamp indicators that show you each lamp is on.

Note: Some older systems have LED indicators for each lamp in the system that come on when the lamp is on. The shortcoming of this type of indicator is that your lamps could be working fine but the monitoring system is failing, giving you a false negative. Newer finishing units have a fiber-optic tube above each lamp that connects to the front of the unit and glows when the lamp is on. This approach is analog and very reliable.

When to change bulbs

Since most shops don’t have a light meter to measure UVC output, there’s a general guideline that you can increase the UVC time approximately one minute for every 200 hours from the initial installation of the bulbs.

Another guideline is to change our either set of lamps when they reach 800 hours of use. Coincidentally, FLEXCEL NXH main exposure times tend to be similar to the finishing times. This means the main exposure and finishing lamps reach 800 hours close to the same time. Many customers will change both sets of lamps simultaneously.

With the short post-exposure times, the UVA lamps will last much longer. When you install new lamps, be sure to either reset your lamp hour counter or make a note of the current hours so you can monitor the lamp life.

Minimal timing and de-tack tests

When evaluating a finished plate, you should always use the minimal time needed. Excessive post-exposure (UVA) and/or finishing (UVC) may harm performance of the finished plate on press.

The plate will become harder as it received more UVA post exposure time. Too much UVA will cause the plate to become brittle and crack easily. UVC light finishing can also cause cracking, but it’s more of a surface cracking rather than the deep cracking that can happen from UVA.

In either case, solvent and inks can migrate into these cracks during and after a press run. To ensure optimal plate life, try not to overexpose plates in your post exposure and finishing process.

Another important method for optimizing plate finish is the de-tack test.

A common way to check that the plate is properly de-tacked:

  1. Post-expose the plate for two minutes using only the UVA lamps.
  2. Finish the plate for 12 minutes with the UVC lamps and allow the plate to cool to room temperature.
  3. With the plate facing up, place a clean coversheet on the plate and press it evenly onto the print surface. This can be tricky with plates that have very little coverage, so using a plate that has a larger coverage is best.
  4. Slowly remove the cover sheet and verify that the cover sheet no logner sticks to the plate.
  5. If the cover sheet sticks to the plate, the plate is tacky. Place the plate back in the finishing unit and expose with UVC ONLY for one minute and check tackiness again at room temperature. Repeat until the cover sheet no longer sticks to the print surface. With new UVC lamps, 15 minutes is a very common starting point.
  6. NOTE: Don’t worry if the floor is tacky. A tacky floor may be the result of an under-washed or under-dried plate or even a combination of the two. As tempting as it may be to increase the UVC/finishing time when your floors are tacky, you must remember that you don’t print with the floor. Increasing UVC finishing time to accommodate a tacky floor may result in over-finishing the print surface and cause problems at press or later in storage.
  7. If the floor is too shiny or has brush marks, it is likely under back-exposed and/or under-washed. Refer to this document for establishing proper back exposure and washout times:

For more processing speed and back exposure time, go to this document on Partner Place: Partner Place Answer ID 62382

Stick to optimized times

There are times when your pressroom may ask for plates that have been finished longer. If you find you are getting requests for plates that are less tacky, you should proceed carefully and take into consideration the entire platemaking process before making any knee-jerk changes to your finishing times.

At the same time, feedback from the pressroom can prompt you to evaluate your process to guarantee you are making the very best FLEXCEL NXH plates possible.

For more finishing FLEXCEL NXH plates, go to this document on Partner Place: Determining optimal light-finishing and post-exposure time: Partner Place Answer ID 66700

Once dried and cooled, the finishing process for FLEXCEL NXH Plates takes less than 30 minutes, but that’s not the whole story.

Knowing how the UVA and UVC lamps are functioning and if a plate is de-tacked are the ways to clear up uncertainty over an optimized finish.

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