Multivariate Model for Characterising Physical Dot Gain, Chroma and Lightness in Offset Lithography

Bright print images help any product on the shelf stand out, attract the consumer, and add a unique value to the product. This research work is to empirically identify significant factors and optimize printing press parameters like press speed (x1: 5000, 7000, and 9000 sheets per hour), ink viscosity (x2: 15, 25, 35 Pa·s), and blanket rubber hardness (x3: 65, 70 and 75 shore A) to achieve prints with rich chroma yet with low dot gain in the lithography process, the most economical and widely used process today in the field of label and packaging industry. The parameters used during the printing process can affect the physical dot gain and the color of printed images. To study this, measurements were taken of the dot gain (y1) and color (measured in terms of lightness (y2) and chroma (y3)) at three different dot areas - highlight (25 %), middle tone (50 %), and shadow (75 %). Box-Behnken Design was used to test fifteen different print conditions. The second-order polynomial model’s fit quality was good concerning the responses. The optimum printing machine conditions determined to minimize dot gain and lightness and maximize chroma were a press speed of 5000 sheets per hour, 30 Pa·s ink viscosity, and blanket rubber having 70 A shore hardness. The optimized values agreed with the predicted responses were acceptable, considering the right balance of minimum dot gain, higher chroma, and lower lightness to give the vibrant yet controlled halftone dot area in print production.