Causes of Gloss Ghosting and Effect of Properties of the Paper on the Gloss Ghosting

抄録

Gloss ghosting is an undesirable phenomenon that occurs in the sheet-fed offset printing. An ink gloss differential on the reverse side imagery appears in the form of a ghosted image of the front side printing. As it gives a significant damage to the appearance of the printed product, the value as a commodity deteriorates. It was reported that oxidizing vapors released from the drying ink of the front side printing accelerate the drying of the reverse side ink film between adjacent sheets in the printed load. However, the detailed mechanism of gloss ghosting has many unclear points. We have investigated what is happening on the surface of the printed ink film, and the effect of the paper properties on the gloss ghosting.

In our study, it was confirmed that the condition of contact between the front side printing surface and the reverse side printing surface is important to determine whether the gloss ghosting occurs or not. It was found that the time interval between front side printing and reverse side printing greatly influences the gloss ghosting. We were able to clarify the mechanism of the gloss ghosting by tracking both the oxidizing vapors generation amount from the front side printing and the arithmetic average roughness Ra of the surface of the printed ink film. Gloss ghost appeared clearly as the difference in Ra value between the printed surface accelerated drying by oxidizing vapors and the surrounding area was larger. In conclusion, there was a tendency that gloss ghosting is less likely to occur in printing papers with smaller variations in Ra value over time on the printed surface.