To work in a flexible packaging factory, it's essential to understand the printing techniques for six common flexible packaging film substrates. Let’s go through them together:
1. BOPP is one of the most widely used materials in flexible packaging. Its printing process typically involves gravure printing. It is best to use polyamide or chlorinated polypropylene inks. Proper tension and embossing force are important, and drying temperature should be kept below 80°C for optimal results.
2. When printing on BOPET, keep in mind that PET is usually thin and prone to wrinkling. This requires higher tension during printing. The ink must be carefully selected, as general inks may not adhere well. Static electricity can be an issue, leading to dust accumulation and scratches. Maintaining a slightly humid environment in the workshop can help reduce these problems.
3. BOPA is a moisture-sensitive material that can easily deform. During printing, the humidity in the printing area should not be too high. The unprinted film should be kept in its original aluminum packaging until ready to print. Before printing, the nylon film needs to be preheated to around 50–80°C. Adjust the printing tension and pressure accordingly. Choose inks that are compatible with the product structure—especially for cooking bags, where heat-resistant inks are necessary. After printing, store the products in a dry, ventilated area and compound them as soon as possible.
4. Printing on K-coated films (KOP, KPA, KPET) presents unique challenges. These films are often coated using roller or spray methods, resulting in uneven thickness and a rough surface. The PVDC coating is brittle, so excessive tension or embossing pressure should be avoided. Overprinting can be difficult due to poor ink transfer. When printing shallow screens, a flower-like pattern may appear. A harder pressure roller is recommended. Also, solvents need to be chosen carefully, as some may damage the coating. Residual solvents can cause blocking, so proper drying and cooling are crucial. Matte films can be printed on their glossy side with OPP, but the matte layer is sensitive to high temperatures, so drying temperature must be controlled carefully.
5. Pearlescent films are typically printed using surface inks with good transparency. For heat-shrinkable films, low-temperature drying and special heat-shrinkable inks are required. If using PVC heat-shrinkable film, consider the solvent’s compatibility with the material to avoid any adverse effects.
6. Unstretched PP and PE films have very low printing tension, making overprinting more challenging. When designing samples, it's important to account for potential deformation during the process.
By understanding these key points, you can improve your efficiency and quality when working with different flexible packaging materials. Whether you're a new employee or looking to refine your skills, mastering these techniques will make a big difference in your workflow.
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