Paper and Fibre Science and Technology
Warren Batchelor, Australian Pulp and Paper Institute, Monash University
Afriana Sudarno-"Investigation of the effect of press and paper variables on linting during the offset printing of newsprint."
Afriana submitted her Masters by research thesis on the 6th of January, 2007. The thesis may be downloaded here.
Chapter 2 was the literature review and covered all of the main print and paper variables that affect linting.
Chapters 3 and 4 describe the experimental methods that were used and the work done to establish the new experimental methods and describes the printing trials. Two methods were used to measure lint- tape pulls and image analysis. For image analysis, the lint was washed off the blanket surface with iso-propyl alcohol. The lint suspension was then split and either filtered to measure the weight or to create as sample for optical microscope and image analysis. There was a linear relationship between lint weight per unit blanket area from the tape pulls method and the lint collected by washing, although the lint weight collected by washing was always less. There was also an overall linear relationship between the area of lint measured by microscopy and lint weight. A new method of measuring the percentage of fountain solution emulsion on the printing press, by printing a sheet of waterproof paper, was also developed.
Three major printing trials were done on a large fast web fed newspaper printing press (a Man Roland Uniset). An extended series of measurements were also done on a small single colour sheet fed press (a Heidelberg GTO-52).
Chapter 5 gives the results. Ink tack was found to have little effect on lint on the blanket, except at very high tacks. This was shown on both the large and small printing press trials. This results contradicts established wisdom in the area. Tack may not be be strongly correlated with lint as tack is measured from the torque required to turn a fixed configuration of rollers with a specified speed and ink weight. The ink film in the instrument is thicker and the shear rate applied to the ink lower than on a printing press. The apparent shear viscosity was measured for a number of inks up to shear rates of 200,000s-1. The inks were all shear thinning and their apparent viscosities tended to converge at high shear rates. Tack may not be a good indicator of lint because it is not measured under relevant conditions.
Take-off angle was found to have the greatest impact on linting. High take-off angles produced higher lint weights on the blanket and much larger particles. This was true independent of printing tone or ink tack. The effect of printing tone was to produce a maximum in lint at around 25% in the lint.
Measurements of lint particle size distributions on blanket and plate showed that larger particles tended to preferentially transfer from blanket to plate. This transfer was associated with a reduction in image quality.
An increase in fountain solution reduced the rate of accumulation of lint on the blanket.