We calibrated to new inks last week and I would like someone to explain to what causes a spike shown in the dot gain graph but, first I would like to explain my process.
After multiple iterations and manual moves, the spike never goes away.
What causes this spike? Are my plates truly not linear? I put screenshots of what our Image Control console shows when reading a sheet as attachments.
Is there any chance you are getting a double dot?
I have not heard the term double dot before. Could you please explain?
I had a client with an older press that had gripper issues. Because of this, he would print two dots, one right next to the other. Because they were so close to each other you could only see them in the highlight areas. (1-10%). A 2% dot would look like a figure 8. As the dots got larger they would blend into one another so you would not notice them.This is a rare occurance, but I thought I would throw it out there.
Its funny you mentioned not linearizing the plates. When I talked to Kodak, they mentioned with the plates we're using, some others do not create a plate curve as well.
My investigation is pointing to the linear plate curve being my issue.
Thank you for the detailed explanation. I greatly appreciate it!
Chiming in without adding any useful comments.
Thank you Don for your details on the futility of plate linearization. I always saw it as a "control point" in the process of getting ink on paper. Your explanation of post development emulsion left on the plate and plate reader inaccuracies finally made the light go off in my brain.
To ensure future plate verification, it is necessary to document the readings of non-linearized plates. If the accuracy of plate values is later questioned, it is crucial to verify that the same values are being imaged as when the G7 curves were created. A linearized plate simplifies the process of verifying 50% as it remains constant, but a non-linearized plate may show 48% instead of 50%.
I'd be surprised you are seeing a 15% increase at the 25% due to linearizing the plate. Are you using processless plates or processed plates?
Is this Flexo? It looks like the bump caused by a minimum dot setting. I don't have a ton of experience in flexo, but this would be somewhat normal in that case.
No, this is not flexo. Its an offset press, a Heidelberg CD74. Calibrating to 18pt C1S board.
I'd have to see the curve values to judge what's going on there.
Sorry, but I have to weigh in on the subject of not linearizing plates since it seems to be gaining traction. Plate linearization is the foundation on which you build all your curves to compensate for variables. Like press, substrate, UV or conventional inks and color aims. The benefit to incorporating a plate linearization curve is that if you change plate vendors or replace equipment, or even want to try out a new plate all you have to do is linearize that demo plate, new plate or new platesetter. All your "compensate for variables" curves will still be valid.Without a linearization curve in your process you have to recreate every single variable curve for every press every substrate and every ink set if you change plates or platesetting equpimentThat being said, you should be using a true plate reader to linearize your plates like an x-rite iCPlate2 and not a spectrophotometer. A spectro offers to read plates, but it is not designed to do that so it is inaccurate. therefor your plate linearization data will not be accurate
I 100% agree. We have had no issues doing G7 press calibrations from a linear plate using a plate reader.
I am leaving a site where we are doing a plate test and they did not have a linear plate curve and it is significantly more problematic and time-consuming.
you are correct. For every new plate iteration that I have to make I have to do a compensation curve on the CTP to match the uncalibrated plates. If they were linear, I would have one curve that would apply to all my press curves.
When I see a bump at the 25% like that I will always look at my pH and water balance. I would strongly recommend that the operator ensure that he looks at all the press variables because to me this looks like a press issue. Assuming that you validated your plate curve. Make sure that they check the blankets and the torque on the blankets to the appropriate specifications. Check the water balance, bring the water down until it's scumming and then bring it up enough to remove the scum.
is there any glazing on the rollers?
Did you verify registration?
How old are the rollers?
1800 Diagonal Road, Suite 320
Alexandria, VA 22314
Code of Conduct
© 2021 Idealliance