The ink absorption performance of coated paper labels directly affects printing quality. Excessive absorption can lead to over-penetration, resulting in problems like bleed-through and pale colors; insufficient absorption can cause poor drying, smudging, or ink buildup. By optimizing surface treatment processes, the ink absorption characteristics of coated paper labels can be precisely controlled to meet different printing needs.
The surface coating structure of coated paper labels is a core factor affecting ink absorption. Traditional coatings with excessively high porosity, while quickly absorbing binders, tend to cause pigment particles to settle, resulting in dull or even powdery prints. Conversely, excessively low porosity prevents effective binder penetration, significantly reducing drying speed. Modern processes utilize microporous technology to create uniformly distributed nanoscale pores in the coating, accelerating binder absorption while retaining pigment particles on the surface to form a full ink layer. For example, using diatomaceous earth or hollow sphere pigment-filled coatings can optimize the pore structure without compromising smoothness, achieving a balance between absorption and color retention.
Surface energy regulation is another key method for improving ink absorption. The surface energy of coated paper labels needs to match the surface tension of the ink: if the label surface energy is too high, the ink will easily spread excessively, resulting in blurred edges; if it is too low, the ink will not be able to wet the surface, forming pinholes or poor adhesion. Polar groups can be introduced into the label surface through corona treatment, plasma treatment, or chemical coating, increasing its surface energy. For example, corona treatment ionizes air through high-voltage discharge, generating ozone and free radicals, which react with the polymer chains on the label surface to form polar groups such as carboxyl and hydroxyl groups, significantly increasing surface energy and enhancing ink wetting and adhesion.
Coating thickness and uniformity are crucial to the uniformity of ink absorption. If the coating thickness is uneven, areas that are too thin are prone to color differences due to excessively rapid absorption, while areas that are too thick may cause smudging due to insufficient drying. High-precision coating equipment, such as blade coaters or slot die coaters, can achieve precise control of coating thickness, with errors controlled at the micrometer level. Meanwhile, employing multi-roll coating or reverse coating processes can further eliminate microscopic undulations on the coating surface, ensuring uniform ink absorption. For example, reverse coating, by adjusting the speed ratio of the coating roller to the back roller, allows the coating to form a denser surface structure under pressure, reducing absorption differences.
Surface roughness and texture design can directionally control the ink penetration path. Through molding or laser engraving techniques, micron-level textures can be formed on the label surface, guiding ink penetration along specific directions and optimizing absorption efficiency. For example, fine mesh textures can accelerate the lateral diffusion of the binder, preventing localized accumulation; while directional groove structures can guide ink flow along the groove direction, forming a uniform ink layer. Furthermore, matte coatings, by adding matting agents, form micron-level particles on the surface, increasing roughness, reducing gloss, and simultaneously controlling the ink penetration depth to prevent bleed-through.
Post-processing plays a decisive role in the curing and stabilization of ink absorption performance. UV curing technology uses ultraviolet light to decompose photoinitiators, generating free radicals that rapidly polymerize monomers and prepolymers in the ink, forming a cross-linked network structure. This curing method not only dries quickly but also forms a dense ink layer, reducing binder penetration and improving abrasion and chemical resistance. Thermal curing, on the other hand, melts the thermoplastic resin in the ink through heating, allowing it to combine with pigment particles before cooling and solidifying to form a stable ink layer. The choice between these two processes depends on a comprehensive consideration of the ink type and label material.
Environmental factors also significantly impact ink absorption. High temperature and humidity accelerate binder absorption, leading to excessively rapid ink drying and cracking; low temperature and low humidity may delay drying, causing smudging. Therefore, printing workshops must strictly control temperature and humidity, typically maintaining a temperature of 20-25℃ and a relative humidity of 50%-65%. Furthermore, dust and oil in the air can adhere to the label surface, hindering ink wetting; therefore, an air purification system is necessary to maintain a clean environment. By optimizing the coating structure, regulating surface energy, controlling coating thickness and uniformity, designing surface roughness and texture, selecting post-processing techniques, and managing environmental factors, the ink absorption performance of coated paper labels can be systematically improved. These techniques not only solve common problems such as bleed-through, light color, and poor drying, but also endow labels with higher printing precision and durability, meeting the stringent requirements of food packaging, logistics labels, and anti-counterfeiting marking.
