Plate problems, black plate only?!?

[Russ_G]

Getting lines from punch to tail on black screen plates, 175lpi @ 2400 dpi, 45 degree black screen angle. I know the platesetter doesn't know it's making a black plate vs any other, the 45 degree screen angle on the black plate being the only difference. Most noticeable at 50% and below. I couldn't see it on the plate at first and thought it was a press problem, but it can in fact be faintly seen on the plates before going on press, just becomes much more visible when inked up. Lines are narrow less than 1/8 of an inch and are in bands about an inch and half apart. Thought maybe processor but lines appear in the same direction regardless of the direction plates are ran through processor. We are running Fuji LHPJ's though a dartIII platesetter, Rampage workflow. Any ideas??

 

[Visualaid]

Getting lines from punch to tail on black screen plates, 175lpi @ 2400 dpi, 45 degree black screen angle. I know the platesetter doesn't know it's making a black plate vs any other, the 45 degree screen angle on the black plate being the only difference. Most noticeable at 50% and below. I couldn't see it on the plate at first and thought it was a press problem, but it can in fact be faintly seen on the plates before going on press, just becomes much more visible when inked up. Lines are narrow less than 1/8 of an inch and are in bands about an inch and half apart. Thought maybe processor but lines appear in the same direction regardless of the direction plates are ran through processor. We are running Fuji LHPJ's though a dartIII platesetter, Rampage workflow. Any ideas??

sounds like the laser is "off" on your plate processor. a tech had to adjust ours to correct it.
one other idea-when your sending the artwork to the rip make sure you don't have "print visible guides" checked; just thinking you might have a ruler on the document.

 

[Russ_G]

We have a tech coming in to check it, meanwhile I've changed the dot from the Rampage "RCS" dot to the standard dot and that has made it much less noticable. Thanks.

 

[jaed]

is it just a consistant 50% screen or is it a gradient screen? If it was me I would reburn the plates @ 150LPI and see if the problem is still there. 175LPI @ 2400 DPI gives about 170 gray levels which could potentially produce banding. 150LPI @ 2400 DPI gives 257 gray levels and would rule out the posibillity.
For some reading on the subject Halftones & Gray Levels
If you do try it let us know if it works or not.

JaeD

 

[Russ_G]

It's a consistent screen, a process color build of pms 5783 with 11% K. I've read a similar article and that is a very good point and even though it's not a grad it is less noticeable at 150lpi, but that didn't help as much as changing to Rampage's "standard" dot. I'm thinking it is some sort of problem with the platesetter that the RCS dot is exaggerating. I appreciate the reminder about banding at 175lpi, I will keep an eye out for it.

 

[rich apollo]

sounds like a lack of laser power from the platesetter. Could be dirty optics or aging laser(s).