The causes and improvement methods of edge interference (rainbow pattern) in PET coatings

The causes and improvement methods of edge interference (rainbow pattern) in PET coatings In the field of packaging materials, polyethylene terephthalate (PET) is widely used due to its excellent performance. However, in the actual production process, sometimes a phenomenon called “rainbow stripes” may appear at the edge of the PET coating. This phenomenon manifests as visual effects such as uneven color and changes in light and shadow on the surface of transparent or semi transparent coatings, which can seriously affect the overall aesthetics and quality of the product. This article will explore the causes of edge interference in PET coatings and possible solutions. What is PET coating edge interference? Edge interference of PET coating refers to a phenomenon in which the coating exhibits uneven color and decreased glossiness at the edges due to various factors during the PET film coating process. These issues usually distribute along the edges of the coating, forming patterns similar to rainbow stripes, and are therefore often referred to as “rainbow stripes”. 2. Analysis of the causes of edge interference in PET coatings a Coating equipment issue: Improper coating speed: Excessive coating speed may cause incomplete solvent evaporation, leading to poor coating drying. Insufficient pressure on the scraper: Insufficient pressure on the scraper may cause uneven coating thickness, especially at the edges, which can easily result in thin and uneven coating. Coating roller wear: The wear of the coating roller can cause changes in the gap between the coating head and the substrate, affecting the stability of the coating amount and the consistency of the coating. b. Uneven dispersion of pigments due to uneven particle size or insufficient grinding, resulting in uneven distribution of pigments in the coating and easy accumulation in edge areas. Unstable solvent system: The use of inferior or unsuitable solvents may cause abnormal chemical reactions during the coating curing process, leading to rainbow pattern phenomenon. Additive failure: Some additives such as leveling agents, defoamers, etc. may lose their intended function due to improper dosage or poor quality. c. Improper process control and pre-treatment: Improper cleaning and activation steps on the substrate may lead to inconsistent surface tension and affect coating adhesion. Inappropriate coating temperature: The ambient temperature during coating, whether too high or too low, may affect the film-forming process of the coating, leading to changes in the characteristics of the coating at the edges. Unreasonable drying conditions: Short drying time or high drying temperature may cause an increase in internal stress of the coating, leading to shrinkage and deformation of the coating. 3. Improvement measures for edge interference of PET coating a Adjust coating equipment and parameters to optimize coating speed: Reduce the coating speed appropriately according to the actual situation, ensuring that the solvent has enough time to evaporate. Adjusting the scraper pressure: By adjusting the angle and pressure of the scraper, the uniformity of the coating thickness is ensured. Regular maintenance of coating rollers: replace severely worn coating rollers in a timely manner to maintain the good condition of the coating head. b. Improving paint formulation and enhancing pigment dispersibility: Select high-quality pigments and thoroughly grind them to ensure uniform dispersion in the paint. Optimize solvent system: Select high-quality solvents with high stability to avoid using inferior products with excessive water content or other impurities. Reasonable addition of additives: Add leveling agents, defoamers, and other additives as needed to help the coating spread and smooth better. c. Strengthen process control and strictly control the pre-treatment process: ensure that the cleanliness and activity of the substrate surface meet the requirements. Monitor coating temperature and humidity: maintain a stable coating environment to prevent adverse consequences caused by excessive temperature and humidity. Reasonable setting of drying conditions: Based on the characteristics of the coating, set reasonable drying time and temperature to reduce the internal stress of the coating. By analyzing the edge interference phenomenon of PET coatings, we can take a series of measures to reduce or even eliminate the occurrence of this problem. These measures include but are not limited to adjusting coating equipment and parameters, optimizing coating formulations, and strengthening process control. Through continuous technological innovation and management optimization, we can continuously improve the quality and performance of PET coatings, meeting the market’s demand for high-quality packaging materials.