Factors Influencing Lamination Quality in Packaging Printing
Thickness and Area of Ink Layers in Packaging Prints: Some packaging prints have extensive graphic areas, and some involve solid printing, resulting in relatively thick ink layers. Thick ink layers can pose challenges in adhering to plastic film, leading to delamination and bubbling shortly after bonding. This is because the thick ink layers alter the surface characteristics of porous paper, closing the paper fibers' capillaries and hindering the adhesive's penetration and spread. The adhesion's strength is significantly affected, and variations in ink layer thickness and area can alter surface tension, impacting bonding strength. Strict control over ink quantity and solid density values is crucial during packaging printing, with gravure printing achieving the thinnest ink layers (generally controlled at 2-3µm) for optimal lamination.
Ink Selection for Packaging Printing: For laminated products in packaging printing, fast-drying glossy offset printing inks are recommended. These inks, composed of synthetic resins, drying vegetable oils, and high-boiling-point kerosene, promote cross-linking, forming strong physical and chemical bonds conducive to lamination. Care must be taken not to use excessive kerosene, as it can lead to overly rapid ink drying, affecting lamination results. Additionally, when printing light colors, diluting agents should be added, with high-quality diluting agents being preferable.
Application of Printing Powder: To accommodate high-speed printing on multicolor machines and prevent paper backside soiling during printing, powdering processes are commonly employed in packaging offset printing. The powder, often composed of cereal starch and natural suspending agents, must be carefully controlled to avoid excessive application. Over-powdering can cause particles to float on the print surface, hindering uniform adhesive bonding during lamination and significantly impacting lamination quality.
Surface and Inner Drying Conditions of Printed Products: Poor drying of the surface or inner layers of printed products can significantly jeopardize lamination quality, leading to issues such as bubbling and delamination. Several factors, including ink type, drying agent quantity, paper structure, and workshop temperature and humidity, influence the drying of ink layers. Therefore, it is crucial to pay special attention to ink layer drying during printing. Strict control of ink-water balance, monitoring ink emulsification conditions, and controlling the acidity of fountain solution are essential. Maintaining optimal workshop temperature and humidity ensures both the surface and inner layers of packaging prints are adequately dried, guaranteeing the quality of lamination.