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Technical Bulletin TRM/95

Today's higher resolution lithographic plates require some understanding of how film edges, cut lines, and dust contribute to problems on the finished printing plate.

All three of these conditions have individual characteristics, but generally the greater the density of any of the items, and/or size of the item, the greater the problem it creates in the plate room or the press room.

In the Plate Room
The first area to work on is a clean plate room. This should be as clean as a film camera room, since you are working with photographic film and imaging it onto the printing plate. Areas to work on are:

*A clean airflow (a positive airflow moving into the room). The use of electrostatic air filters also help to control dust in the area.

*Anti-static devices help remove dust from the film or the glass areas.

*Clean the vacuum frame area and vacuum frame bladder. Ribbed areas on bladder collect dust and should be cleaned with a vacuum cleaner equipped with a filter.

*Clean the vacuum frame glass with good glass cleaner, preferably one containing an anti-static ingredient to retard further accumulation of dust.

*The vacuum frame glass should be free of nicks and scratches. (Do not use as a cutting board.) Replace damaged glass from the vacuum frame manufacturer, designed to transmit the maximum amount of ultraviolet (UV) light. Replacing with ordinary window glass can retard the UV light source and increase exposure time required.

*Maintain humidity at a level that reduces static.

*If the plate room is carpeted, spray the surface with anti-static material to reduce dust accumulation.

Working with Clean Film
*Use anti-static film cleaner and devices through which film can be drawn to reduce static.

*Use envelopes for storing or holding film to keep dust from contaminating the surfaces.

Film Stripping
*Strippers should use single sheet film composites whenever possible, to avoid trapping dirt between film layers and to avoid film edges.

*Avoid placing cut film edges in the image area. If film edges are un-avoidable, cut with a sharp razor blade perpendicular to the cut film line. This avoids angular cuts which increase the size of the cut edge.

*Avoid using table cutters to cut film being used in the flats. Table cutters usually place a scrap piece of stripping film between the masking sheet and the film before cutting the halftone windows. This will avoid cutting the halftones. When finished, remove the scrap film.

Plate Exposure (steps to correct the origin of the problem)
*Increase plate exposure slightly to "burn in" cutlines to fill them in, or to fill in dust specks or dirty areas. (Experiment, using a gray scale to avoid overexposure, which can cause halation problems. Good judgment is the rule in this area.)

*Cover the film edges on the flat with Scotch™ brand 811 tape, a matte surface, low adhesive tape.

*Cover the entire flat with diffusion film to reduce the effect of film edges, cutlines, dust specks, etc.

*Consult with the vacuum frame manufacturer, to determine if a more diffuse type of light source is available.

*In plate making inspection area, use Viking™ addition fluid to fill in pinholes and cutlines.

In general, good housekeeping practices and responsible craftsmanship will eliminate nearly all problems of this type, brought about by advanced image-making abilities of todays sharper, higher resolution printing plates.

Copyright 1996 Imation. All rights reserved.