Plate consistency

[Gianni_S]

Hi Forumers,
hope to find you well.
I am facing a strange problem and I would like to know if you faced something similar and if you have a possible solution.
I am ahving troubles with processless plates, while exposed and developed I am reading different values from plate to plate, here I have an example:

Vendor A with plate A exposed with linear curve
1st exposed at 50%K plate, read 48%,
2nd exposed plate at 50%K read 41%
3rd exposed plate at 50%, read 49%
4th,5th exposed at 50%K, read 55%
6th exposed at 50%K, read 49%
all happens randomly


Vendor B and C with plate B and C exposed with linear curve
1st to 10th plate exposed at 50%K, read 48-50%

I have tested several batches from vendor A, all having the same issue.
He says that the problem is in our RIP and CTP… but it sound strange.

Any suggestion?

(Unfortunately changing vendor is not an option for my boss, and a killer cost too much for my wage!)

 

[gordo]

It doesn't matter whether a linear curve was applied or not you should not see more than a 2% variation - if you're measuring correctly,The consistency of readings from vendor B and C suggests that vendor A's plates are the problem and not your RIP and CtP.
On a side note it's best to read a tone wedge instead of a single tone patch.

 

[maxon]

Gianni, in addition to what gordo said before :
- bear in mind these are almost certainly all negative working plates. As lasers write the image you would expect to read in the range 50 to 54 percent if energy is properly set because these negative plates have a bit of dot gain. Check the sensitivity spec for all these plate types. Most processless plates require 120 to 135 mJ/sqcm which is a lot
- you should ask the plate 'A' vendor to again demonstrate the cleaning procedure on-press because it seems that 'A' plates don't clean up completely (or correctly). Put a microscope in several places across the plate area and inspect all 'A' plates looking for residue between the dots. Might be a good idea to also measure the percentage in at least 20 places across the entire plate area to determine the cleaning performance. If uniformity is good but you still see plate to plate variation more than 2 percent, well, it may be that 'A' plates are simply bad - too old, incorrectly stored, or ... just bad.

 

[Magnus59]

Hi Forumers,
hope to find you well.
I am facing a strange problem and I would like to know if you faced something similar and if you have a possible solution.
I am ahving troubles with processless plates, while exposed and developed I am reading different values from plate to plate, here I have an example:

Vendor A with plate A exposed with linear curve
1st exposed at 50%K plate, read 48%,
2nd exposed plate at 50%K read 41%
3rd exposed plate at 50%, read 49%
4th,5th exposed at 50%K, read 55%
6th exposed at 50%K, read 49%
all happens randomly


Vendor B and C with plate B and C exposed with linear curve
1st to 10th plate exposed at 50%K, read 48-50%

I have tested several batches from vendor A, all having the same issue.
He says that the problem is in our RIP and CTP… but it sound strange.

Any suggestion?

(Unfortunately changing vendor is not an option for my boss, and a killer cost too much for my wage!)

Are you reading density from the plate or the printed sheet?
The latent image on a DoP (Develop on Press) plate may not accurately reflect the value of the image on the exposed emulsion.
Best practice is to read the image on a printed sheet with exactly the same paper and press conditions for each reading.
If you must read the plates, ensure you have a plate densitometer that is suitable for DoP plates and clean the surface with a finishing solution (gum) prior to measuring.

 

[Gianni_S]

Thanks for all your help.
Today I am going to discuss these problems with vendor A. Because those plates are the real problem.
To Gordo: thabks a lot, I totally agree with you, but to be certain that CTP laser is not the problem the CTP tech guy suggested me to do this. In real print environment is another reality. But with a plate that behave without sense… It is hard to achieve a good printed result!
To Maxon: all plates has been setted up by vendor's technician, so I assume that exposure power and focus are correct (On vendor C I'm not so convinced, but that's a nother story)
To MAgnus59: all 3 platesa has been imaged with 20% screen and printed on the same paper by the same press just to be sure that everything was good enough. Vendor A's plates have some serious problems, don't know why. From aour side everything is sotred perfectly in good condition. So I assume they have severe problems.
Thanks all for giving me a hand. I will let you know how it is going on in near future.