Paper, including both paper and cardboard, is made from plant fibers, fillers, pigments, and adhesives. In packaging printing, to ensure high-quality printed products, five key factors must be considered: people, machines, materials, methods, and environment. As a primary material, the quality of paper has a significant impact on printing. Its effects are as follows:
1. Impact of Poor Paper Smoothness
Smoothness refers to the flatness of the paper surface, reflecting its surface structure. The quality of printed products is closely related to paper smoothness. The degree of contact between the paper surface and the printing blanket directly affects ink transfer and image clarity.
Poor smoothness can cause uneven ink distribution, inconsistent ink film thickness on the blanket, resulting in uneven colors, enlarged dots, and mechanical dot gain.
Poor smoothness reduces ink adhesion, causing images to appear blurry or mottled, and severe cases may result in dot loss.
2. Impact of Paper Compression and Deformation Characteristics
Printing paper should have good compressibility and the ability to recover quickly after pressure is released. During printing, paper deforms under pressure, and appropriate compression ensures good contact with the blanket, allowing even ink transfer. If paper has high compressibility but poor elastic recovery, repeated color printing can cause paper to expand or shrink, seriously affecting registration accuracy.
3. Impact of Poor Paper Surface Strength
Surface strength refers to the bonding between fibers, adhesives, fillers, or between coating particles and the paper base. Poor surface strength can cause fiber or coating particles to be pulled away with the ink, resulting in a phenomenon called "picking." Its main effects are:
Image contamination: (i) white spots from detached paper particles, (ii) contamination from fine coating particles or paper dust.
Increased cleaning frequency: Poor surface strength leads to frequent blanket and roller cleaning, reducing printing efficiency.
4. Impact of Paper Acidity and Alkalinity
During printing, the pH of the fountain solution is usually controlled between 4.8–5.2. The paper’s acidity or alkalinity affects printing:
Acidic paper may corrode the plate or cause set-off, accelerating ink drying but potentially inhibiting oxidation and surface film formation.
Alkaline paper can neutralize the fountain solution, disrupting pH control and causing ink emulsification, resulting in localized contamination and reduced print quality.
Therefore, when using printing paper, it is crucial to carefully check smoothness, compressibility, surface strength, and acidity/alkalinity to avoid negative effects on printed product quality.
