Uniformity of dot

[Guest]

Hi all,

Would like to know the uniformity of the dot percentage ( say 50%) over the full exposure area (of a Pano plate of size like 568mm x 695mm) of different makes of CTP, especially Agfa Polaris XTV and Agfa Advantage 3850 DL. Is there a specification from the manufacturers for this?

Is this screen dependant? Is it resolution dependant?

Thanks in advance

Regards

Siva

 

[maxon]

Is this screen dependant? Is it resolution dependant?

Neither of these. It depends on other factors like platesetter optics alignment, dust contamination, plate, plate processing conditions.

 

[gordo]

Hi all,

Would like to know the uniformity of the dot percentage ( say 50%) over the full exposure area (of a Pano plate of size like 568mm x 695mm) of different makes of CTP, especially Agfa Polaris XTV and Agfa Advantage 3850 DL. Is there a specification from the manufacturers for this?

Is this screen dependant? Is it resolution dependant?

If you're trying to test the platesetter to see if it is able to image consistently across the plate then here are a few suggestions:

1- make a small test patch say 1" x 1" it should contain 8 patches: 1%,2%,3%,50%,97%,98%,99%,100%. Step and repeat this oatch across the entire surface of the plate.
2- put a strip of scotch tape/cellotape diagonally on the back of the plate from one corner to the other. This is to simulate the impact of a dust particle or some other contaminate when the plate is exposed.
3- expose two plates - but only pricess one.
4- take the exposed unprocessed plate and put it in a protective envelope.
5- one or two days later take the second unprocessed plate and image it a second time - then process that plate. This is to test the device's ability to remake a plate that is consistent with previously imaged plates despite changes in the environment. I.e. If one plate gets damaged will you have to image just one or all four?

Now examine the two plates. Note the dots on the single exposure plates. Are all %s imaged consistently? Are all dot %s imaged or do some fail to image. Look at the dots left and right side, corners and center. If you can see a line caused by the scotch tape then the imager may be subject to hotspots. If certain dot %s are not imaged then that shows you the limitation of the imager.
Look at the plates that was exposed twice. Can you see if dots are doubled? If so, where does this occur. That will help you see if the imager consistent day to day and if the dot doubling is directional, where it occurs and what may be the cause.

Gordo

 

[maxon]

Gordo, if I may, these tests do not apply to violet flatbed machines like Polaris and Advantage. Step 2 raising the plate emulsion by scotch tape won't change anything as violet machines are usually long depth of focus the image will still be ok, except perhaps internal drums using vacuum. Then I referred to dust contamination in the sense of affecting optics and spinner mirrors, rather than dust on plate. Step 4, image latency is maximum half an hour for violet photopolymer plates all flavors including chemfree certainly cannot process an exposed plate next day.

 

[Guest]

Thanks Gordo for your guidance. Will do the tests and come up with the results.

We have done a test with a 50% tint covering the whole area of the plate. When we read the dot values all over the plate we are getting a minimum value of 48% and a maximum value of 52%. Can I assume that my CTP is OK as I have been told by the CTP supplier that the tolerance is + or - 2 %? Or is there some ISO specs for this?

Thanks in advance

Regards

Siva

 

[Guest]

Dear maxon What are the parameters I will need to check on the Plate setter and the plate processor to see if they are causing any distortion on the Dot percentage?

We are using Violet Photopolymer

Normally we check the Developer Brush Pressure and the Preheat temperature uniformity in the plate peocessor. In the Plate setter we check the Laser power using a UGRA film strip.

Thanks in advance

Regards

Siva

 

[maxon]

You should be ok within 2%. Make sure the plate processor is within specifications, worn out parts have been replaced - brushes, roller bushings, bearings - and all adjustments done properly. Have the platesetter optics inspected every six months for dust contamination especially the spinner/polygon this is a very common problem causing beam energy variation across the plate. Expose two plates 50% tint, let the first one enter the plate processor, feed the second one by hand rotated 180 degrees.
With proper maintenance and good quality plates you should be able to run within 1-1.5% consistently. What plate processor do you use, what type of plate ?