In PE screen printing, the leveling properties of the ink directly affect the smoothness and gloss of the printed surface, and are one of the key factors determining the final print quality. Due to its low surface energy and strong chemical inertness, PE material places higher demands on the wetting and spreading properties of the ink. Insufficient ink leveling can easily lead to defects such as orange peel, pinholes, and edge shrinkage after printing, affecting not only the product's appearance but also potentially reducing its functionality. Therefore, comprehensive optimization from multiple dimensions, including ink formulation design, additive selection, printing process control, and environmental conditioning, is necessary to improve the leveling properties of PE screen printing ink.
Ink formulation design is fundamental to improving leveling properties. PE screen printing ink typically consists of resin, pigment, solvent, and additives. Among these, the molecular structure of the resin and the evaporation gradient of the solvent significantly influence leveling properties. Selecting a low-viscosity, high-flexibility resin system, such as a composite of vinyl chloride resin and acrylic resin, can enhance the ink's wetting ability on the PE surface and reduce spreading resistance caused by surface tension differences. Simultaneously, by adjusting the polarity and evaporation rate of the solvent, a "fast at first, slow later" evaporation gradient is created, allowing the ink to spread rapidly in the initial stage and dry slowly in the subsequent stage. This avoids uneven surface tension caused by excessively rapid solvent evaporation, thus reducing the orange peel effect.
The appropriate addition of additives is a key means to improve leveling properties. Leveling agents promote uniform spreading of the ink on the PE surface by reducing its surface tension. Common leveling agents include silicone, acrylate, and fluorocarbon agents, among which silicone leveling agents are widely used due to their good compatibility and significant effects. The siloxane segments in their molecular structure can form an oriented arrangement on the ink surface, significantly reducing surface tension without affecting the ink's drying speed and adhesion. Furthermore, the selection of dispersants is also crucial; they prevent pigment particle aggregation, ensure uniform ink dispersion, and avoid a decrease in leveling properties due to pigment sedimentation.
Precise control of printing process parameters has a direct impact on leveling properties. The mesh count of the screen printing mesh must be matched with the ink viscosity. Too low a mesh count will lead to excessive ink transfer, making it difficult to control film thickness; too high a mesh count may result in incomplete printing due to poor ink flow. Generally, 80-120 mesh screen printing is used for PE, ensuring sufficient ink transfer while controlling film thickness within a reasonable range. Adjusting the squeegee hardness and angle is equally important. Hard squeegees (e.g., 70-75 degrees) are suitable for high-viscosity inks, providing sufficient pressure to promote ink spreading; soft squeegees (e.g., 60-65 degrees) are suitable for low-viscosity inks, reducing damage to the PE surface. The squeegee angle is recommended to be controlled between 65-75 degrees to balance ink transfer and spreading effect.
The influence of ambient temperature and humidity on ink leveling cannot be ignored. High temperatures accelerate solvent evaporation, causing premature curing of the ink surface and the formation of orange peel; low temperatures may increase ink viscosity, leading to spreading difficulties. Therefore, it is recommended to control the printing workshop temperature at 20-25℃ and the humidity at 50-65% to maintain suitable ink flow. Furthermore, the surface treatment of PE materials must be coordinated with environmental conditions. For example, corona treatment can increase surface energy, enhancing ink wettability; however, printing should be done as soon as possible after treatment to avoid decreased leveling properties due to surface energy decay.
Ink storage and usage specifications also affect leveling properties. Long-term storage may cause the migration of additives or solvent evaporation in the ink, leading to viscosity changes. Therefore, ink should be sealed and stored in a cool, dry place. Before use, it should be thoroughly stirred and the viscosity should be checked to ensure it meets requirements. If the viscosity is too high, a special thinner can be added to adjust it, but excessive addition should be avoided to prevent a decline in ink performance. In addition, the screen and squeegee should be cleaned regularly during printing to prevent ink drying and affecting leveling properties.
Optimizing post-processing can further consolidate leveling effects. For example, slow drying of the ink through hot air circulation or infrared heating can avoid uneven surface tension caused by localized overheating. For printed materials requiring high gloss, adding an appropriate amount of matting agent to the ink or adjusting curing conditions can achieve precise control over gloss. Furthermore, allowing the ink to stand for a period after printing before stacking or packaging can reduce surface damage caused by incomplete ink curing.
Improving the leveling properties of PE screen printing ink requires synergistic optimization across multiple aspects, including formulation design, additive selection, process control, environmental conditioning, and post-treatment. By scientifically matching resin and solvent systems, rationally adding leveling and dispersing agents, precisely controlling printing parameters and environmental conditions, and standardizing ink storage and use, the smoothness and evenness of the printed surface can be significantly improved, meeting the high-quality printing requirements of PE materials in packaging, labeling, and other fields.
