Computer Direct Imaging Plate Quality Control

Mr. Ulrich Schmidt, FOGRA Printing Institute, said:
The control of tone value transmission during laser plate imaging is a complicated task because the value of this tone is determined by microscopy, density measurement and image analysis. Some of its printing plates are different from commonly accepted ink printing (note that those that cannot be printed are particularly highlights), so if you must compare the results of laser imaging with those of film-based printing, you will need to The plate is compared with the traditional plate for a comparative test. This test result is used to correct the RIP tone value of the platesetter. The image analyzer and densitometer measurements are only used for the consistency of the hue values ​​on the plate. The author agrees to use the Yule-Nielsen formula to convert the actual hue value determined by the printing plate to the actual print hue value. This method also restricts the instrument from being used for other purposes, which could easily lead to major errors in the final result. Recommendations for measuring laser imaging plates:
● Geometry 45/0 or 0/45
● sampling area at least 10mm = lateral 130mil
● Remove the polarizing filter as much as possible in the light path ● Measure the color of the light source to be complementary to the color of the printing plate coating ● The tone value will advance at 5% or less ● The density value below 1 should retain 3 decimal places ● Cylindrical dimensionally stable concave tools are used. The printers hope to guarantee that the printing plate will be produced using new technologies as if it were made of film.
• Densitometers should have a measurement mode that allows continuous measurement of background, solid patches, and halftones.
For a negative-to-contrast printing format, it should have the function of automatically converting X% to 100-X%. The density meter should be able to automatically switch channels during the tone measurement period.
This conclusion is based on the analysis of the results of the use of different substrates, photosensitive layers, and methods of operation. It is also applicable to printing plates marketed after the completion of this work.
Work should pay attention to the following points:
Samples for printing plate samples should not be glued but can be cleaned. The sample should be protected from light and abrasion before measurement.
The main purpose of setting the laser intensity and focal length is to equally and accurately set the positive and negative line patterns of the control device. For some plates that have been directly cross-linked (hardened) in the platesetter, their exposure is measured to determine if they are over-exposed to meet the high volume requirements. This will reduce the image resolution of the positive linear target relative to the negative target.
Finding the right color tone transmission value Printers working in a non-enclosed environment want to ensure that computer-based plate making is the same as traditional printing plates. It is unlikely that the actual printing tone values ​​of the two printing plates can be directly compared because a clearly visible laser spot can be partially printed, so that one can always print out all the plate points. Such a printed comparison test should be performed in the same way in film output (1:1) and laser printing plates. Then use the film to make traditional plates. Both types of plates will be continuously printed in exactly the same units and in exactly the same material. Create a measurement and use the color between the two prints.
Find the table and load it into the RIP. The printing results of the two printing plates should be the same. Visually check the consistency of the surface of the direct plate (in the Digital Plate Wedge's Visual? Reference Steps section) and measure the midtones with the instrument.