Disc Printing - Screen Ghosting

"Ghosting" is commonly used to describe the residual image pattern on recycled screens. After recovery, many tiny hardened ink dots and emulsion particles adhere to the wire wall, affecting the ability of the next mesh ink to pass normally. In a bad situation, when the screen plate is reapplied and exposed to generate a new image, the hardened particles in the residual image portion will absorb the ink and thus appear a blurred pattern on the print.

Such ink/emulsion particles can generally be eliminated with strong cleaning chemicals such as defogging agents. The defogging agent decomposes the residual emulsion on the wire mesh wall and returns the mesh to a naturally stretched state.

There is another form of "ghosting" in which, when a new emulsion has been coated and subjected to a specific exposure, the fuzzy inconsistency pattern will also be partially contiguous when printing with this new screen image. Districts are presented. The cause of this problem can be traced back to the positive film itself.

There is a discontinuity in the continuous area of ​​the image, in other words, the image area should have enough opacity to block the passage of exposure light, but some areas will not reach the ideal density so that the light reaches the underlying emulsion layer. And a certain amount of actual exposure is generated. After development, the part of the mesh that should completely dissolve ink will be blocked and an unnecessary printing pattern will be produced on the printed product. The solution to this problem is to make full use of the density meter's function to use it to detect the highest density (Dmax) of the continuous tone zone of the positive film and the lowest density (Dmin) of the non-density transmission zone.

The third potential reason is the old and worn screen fabrics. In the long-term rolling, expansion and cleaning recovery process, the screen silk fabric will become more damaged flat plate, so that in the printing, this locally deformed thread brings changes in the ink transfer characteristics, compared with the intact part These areas will form additional pattern features on the prints. When this physical damage occurs, the only thing that can be done is to replace the screen screen.

Source: CD Encyclopedia