Press room problems and solutions – Series 3 – Horizontal Stripes

Posted: September 28, 2012 in horizontal stripes, ISO Press standardisation, issues in press room
Tags: , ,

A host of factors affect the quality of your printed products: in addition to the machine itself, there are the printing stock and inks, as well as external factors such as atmospheric humidity, and room temperature. Often, when problems arise in the pressroom, the root cause is not immediately apparent. Frequently, it takes time to filter out the underlying cause from among the many possible variables.

This series of blog with Professional Tips offers advice on tips in the most common problem cases. This handy guide should not be missing from any pressroom.

Horizontal Stripes

The problem in this case involves disturbances in the printed image, which are manifested as bright or dark stripes running horizontally to the direction of printing.

Horizontal stripes arise for a variety of reasons. Besides adjustment errors, errors in screen vignettes (prepress errors) may also play a role. Additionally, the formation of stripes may also be influenced by contamination from the build up of powder and coating, from damage to the printing blanket or the printing plate, or from the ink/dampening solution feeds, as well as from the quality of the ink. The machines themselves may also be causing the stripes, for example from an incorrect alignment of the ink and dampening units, or from rolling errors (too much pressure). Tone stripes can be caused by the relative lateral movement of the rollers on the printing plate.

remedy for stripe formation conditioned by machines

• When maintaining the rollers, only use appropriate cleansing agents; the weekly application of a wash paste removes lime deposits, and will regenerate the rollers.

• Adjust the rollers in accordance with the instruction manual; inspect the adjustment regularly.

• Change used rollers: the rubber surface of older rollers becomes glossy and over-smooth. At the same time, as their hardness increases, the edges bulge out in the shape of a trumpet. More pronounced abrasion becomes evident.

• Adjust reciprocation of the ink form rollers

• The dampening distributing cylinder must be kept clean and receptive to water.

• The roll bearings must be in fine working condition (no play, no sticking).

• Lubricate the roll bearings

• By setting the ink form rollers as gently as possible on the printing plate, impacts stemming from the run-on and run-off edges are reduced.

• The bearer ring should be kept clean and grease-free.

• The calibrated under packing should be clean, cut in a format to fit, and correctly inserted.

• Clamping between the plate and the blanket should range between 0.1 mm and a max. 0.13 mm. (0.004 in and 0.051 in).

• Clamping between the blanket and the counter pressure should be set in consideration of the surface of the printing stock; avoid clamping that is set too high.

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