Offset Litho Barring Effect

[Francis.Drake]

We operate Nilpeter offset litho presses MP330s both servo and line shaft. We have always suffered, when laying down large areas of ink, from barring. I have just heard a remark that occasionally this can be made worse by the screen angle.
Have any of you knowledgable people out there heard of screen angles for spot colours affecting barring.
generally we apply the following angles. Cy 165º MG 45º Y 90º with K and or spots on 105º
Many thanks in hope.

 

[gordo]

We operate Nilpeter offset litho presses MP330s both servo and line shaft. We have always suffered, when laying down large areas of ink, from barring. I have just heard a remark that occasionally this can be made worse by the screen angle.
Have any of you knowledgable people out there heard of screen angles for spot colours affecting barring. generally we apply the following angles. Cy 165º MG 45º Y 90º with K and or spots on 105º
Many thanks in hope.

By "barring" do you mean banding?

Screen angle can affect the appearance of banding if you are using a directional dot shape e.g. elliptical. What dot shape are you using?

Your screen angles:
Cy 165º MG 45º Y 90º with K and or spots on 105º

Are the same as:
Cy 75º MG 45º Y 90º with K and or spots on 105º

The screen angle for spot colors depends on how they're used. If the spot color is printed by itself it is usually run at 45° - the same as the black printer. If the spot color is printed with CMYK then it is run at the angle of the missing color. E.g. A green spot ink would be run using the Magenta angle since Green does not print with Magenta.

best, gordo