Characterization of ink adhesion failure; effect of pre-dampening of carbonate containing coatings

• To attain an improved knowledge about ink adhesion during offset printing we have developed a laboratory procedure to measure adhesion failure between ink and coated paper during ink setting. This paper describes the technique and a special case, where a normal coating and a coating with excess dispersing agent, in the form of sodium polyacrylate, have been printed. Characterization of the areas where the adhesion had failed at the pull-off points after tack testing was done by determining "white" spots in the retained print using image analysis. The "white" spots represent areas where ink has detached from the coating after contact with a rubber coated cylinder. This area is referred to as adhesion failure area (AFA). A minimum in AFA at the point of maximum in tack force was found for both coatings where the print was applied onto dried coating. When the coatings, however, were pre-damped, AFA increased on the normal coating over a short time period, independent of the dampening level. For the coating with excess dispersant, on the other hand, the higher dampening level strongly increased the AFA. The strong impact of excess dispersing agent in this work may be explained by a number of related effects, including increased polarity of the coating surface, and an associated moisture layer, and an effective reduction of fine pores due to water-swelling polyacrylate that blocks these pores.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Pappers-, massa- och fiberteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Paper, Pulp and Fiber Technology (hsv//eng)

Nyckelord

Adhesion

Image analysis

Ink

Lithography

Printing

Sodium

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