SKEW in plates from HB CTP

[MxPrepress]

Hi
Recently I having a lot of problems with press, because the dots in plates not correspond exactly in position along the entire sheet, however the register marks it does.
It is possible that the plates have a skew in diferent directions?
That happens mostly between CMYK and direct inks.
The traps disappears in some parts and plenty enought in others.
I have a Prinect workflow, Suprasseter A105 (new in 2009, 20,000 expositions) well treated, a eliptical dot, 175 dpi, 2400)

How I could giving them a proof or evidence of my plates are OK?

Any help?

 

[gordo]

Hi
Recently I having a lot of problems with press, because the dots in plates not correspond exactly in position along the entire sheet, however the register marks it does.
It is possible that the plates have a skew in diferent directions?
That happens mostly between CMYK and direct inks.
The traps disappears in some parts and plenty enought in others.
I have a Prinect workflow, Suprasseter A105 (new in 2009, 20,000 expositions) well treated, a eliptical dot, 175 dpi, 2400)

How I could giving them a proof or evidence of my plates are OK?

Any help?

I'm not sure what you mean by "the dots in plates not correspond exactly in position along the entire sheet" Can you clarify?

Is your rosette structure the same across the sheet or does it vary from clear centered to dot centered?

gordo

 

[MxPrepress]

Thanks gordo
The rosette structure vary from clear centered to dot centered in the direction the press rolls go, And in the left part of the sheet ask to move in one direction and viceversa in the right part of the sheet.
I pretty segure it is press control issue, but how give them the evidence that all the separations (CMYK & 2 direct inks) are ok?

 

[gordo]

Thanks gordo
The rosette structure vary from clear centered to dot centered in the direction the press rolls go, And in the left part of the sheet ask to move in one direction and viceversa in the right part of the sheet.
I pretty segure it is press control issue, but how give them the evidence that all the separations (CMYK & 2 direct inks) are ok?

My confusion is that you say that the register marks are correct. If they were also skewed then it would suggest a plating issue e.g. plate imaging, plate bending, or plate mounting on press.
If it was a paper stretch issue then the register marks would not register.
So, your description sounds like a prepress issue. Perhaps "Bottling" (which skews the page content) is somehow being applied to one or more separations?
Most screening keeps the rosette structure clear centered across the diagonal of the largest plate size the CtP is expected to output. If your rosette structure varies from clear centered to dot centered over a short distance but the register marks line up then it suggests that the screening engine is not set up correctly. You can measure the transition from clear centered to dot centered rosettes with a ruler. If the distances of the transition repeat with a frequency (e.g. every 6 inches) then that also suggests a screening problem.
It would be easier to figure out if the register marks weren't in register.

 

[Deleted member 16349]

If it was a paper stretch issue then the register marks would not register.
.

What if the register marks are near the grippers and not the tail?

 

[gordo]

What if the register marks are near the grippers and not the tail?

Then you'd look at which color was hanging beyond the others. It's direction would tell you if it was back sheet flare (on a sheetfed press)

 

[Green Printer]

Does the problem occur on various stock calipers or just those below 8 point?

 

[MxPrepress]

Gordo
I check out the rosseta with 25X microscope, and CMYK is in register ( the roseta and the register marks), its the direct inks that invade the clear center, and the dot seems blurring and not like a circle, there are white edges between direct inks and CMYK.
The distorsion are in register marks of direct inks vs CMYK.

It Occurs in several calipers from 8 to 16 points.

I´d appreciate very much yours comments

 

[gordo]

Is it a moiré pattern?

 

[MxPrepress]

YEAH, look like that in some parts. in the direction of de press rolls in the right part of sheet tail. The angles are: C 165 M45 Y0 K105 U30 Z60
And across the sheet at left ask to move to righ and in the right ask to move to left in both direct inks.

 

[gordo]

YEAH, look like that in some parts. in the direction of de press rolls in the right part of sheet tail. The angles are: C 165 M45 Y0 K105 U30 Z60
And across the sheet at left ask to move to righ and in the right ask to move to left in both direct inks.

I feel like a dentist pulling teeth.
“u” @ 30° conflicts with m @ 45° and with k at 105°
“z” @ 60° conflicts with c @ 75° and m @ 45°

So lots of opportunity for moiré if your spot colours are printing with your process colors.
If the spot colours are printing with your process colors as in a spot color simulation, Hex, or hi-fi situation then I think your only option is to use the screen angle for u and z (whatever they are) that is the same as the screen angle of the process colour that will not be printed with that spot color.
For example. Orange is never printed with Cyan, so you can use the Cyan angle for the Orange plate. Green is never printed with Magenta so you can use the Magenta angle for the Green plate.
Your alternative, if the “u” and/or “z” spots are light enough (light like a Yellow) is to use a coarse FM screen (35 micron) for the spots.

gordo

 

[MxPrepress]

Ok That explain the moiré BUT the distorsion of the spot colors, when a half of the boxes at left ask for move the plate of the spot color to right and the other half ask to move the plate to the left, What I can doing? There are a distorsion, It is about moiré too? AT first look with a manifying glass 5X, That used by press operator, the register mark of the spot colors register with CMYK, but when look carefully with 25X you be able to see that not such register.
Till now I learned about angles for prevent moiré but the interest thing for me its how I demonstrate to the press guy it there are not distorsion in the plate.

thanks very much, I admire a Prepres Spirit that you have!