Characterisation of Lint Particle Removal in Offset Printing with Weibull Statistics

Linting is the process where small particles are removed from the surface of newsprint during offset printing. The buildup of these particles on the offset printing blanket is one of the major quality issues in offset printing. In this study, we apply Weibull statistics to particle size distribution of lint collected after both sheet-fed, printing either 1500 or 3000 copies, and web-fed printing trials, printing 23 000 copies. Weibull statistics has previously been applied successfully to the distribution of strength of paper samples. The lint data were obtained by washing lint from the blanket, filtering, imaging using a microscope and then analysing the images to measure the particles. To analyse the data we used the lint particle size as the independent variable. The results showed that particle size distribution of lint collected after printing 1500 or 3000 sheet-fed copies could be very well fitted with a Weibull distribution, with R 2 values 0.98 or higher. The Weibull distribution power term ranged from 1.52 to 1.26. The Weibull distribution power term gives the shape of the distribution of bonding strength of lint particles to the sheet surface as well as the response of the surface to a change in the force applied by the ink to remove particles as lint. The fits were much poorer for the lint collected after the web-fed trials, with Weibull power term ranging from 1.17 to 0.47. The differences between the sheet and web-fed trials were due to the preferential movement of smaller lint particles off the blanket during the much longer runs of the web-fed trials.