A Systematic Investigation into Printing Defects in Central Impression (CI) Flexographic Printing on Low-Density Polyethylene (LDPE) Substrates

Abstract

Printing quality in Central Impression (CI) flexographic printing on Low-Density Polyethylene (LDPE) substrates is strongly influenced by the interaction between substrate surface properties, ink behaviour, and press operating conditions. Despite its wide application in flexible packaging, maintaining consistent print quality remains challenging due to the frequent occurrence of various printing defects. The present investigation systematically examines common defects observed during CI flexographic printing on LDPE films, including ink smearing, dot gain, banding, pinholing, poor ink adhesion, and registration errors. The effects of key process parameters such as printing speed, impression pressure, anilox roller volume, ink viscosity, and substrate surface energy are critically analysed to understand their contribution to defect formation. Controlled printing trials were conducted using LDPE substrates with defined specifications to evaluate variations in print quality under different operating conditions.

Results indicate that defect formation is predominantly governed by the combined influence of low surface energy of LDPE, suboptimal ink rheology, and mechanical variations within the printing system. Inadequate wetting and adhesion behaviour leads to ink transfer issues, while improper balance between anilox selection and ink viscosity contributes to tonal inconsistency and print unevenness. Additionally, mechanical instabilities in CI flexographic systems are found to significantly affect registration accuracy and cause banding defects.

Findings highlight the necessity of optimizing substrate treatment, ink formulation, and press parameters to minimize defect occurrence and enhance overall print performance on LDPE materials used in flexible packaging applications.