Adhesion, also known as blocking, refers to the unwanted sticking between layers of plastic films. This issue can occur in two main forms: first, when printed surfaces stick together, making it difficult for users to open packaging and leading to dissatisfaction; second, when the ink layer adheres to another surface, causing damage to the print or contamination of the contact area. These problems can result in product rejection or even scrapping in severe cases.
To prevent internal adhesion, slip agents and opening agents are often added to the resin during the manufacturing process. These additives improve the film's release properties, ensuring smooth handling and reducing the risk of sticking. In high-speed production environments, this is especially important for maintaining efficiency and product quality.
The second type of adhesion occurs when the roll material cannot be unrolled smoothly, which can lead to printing defects, ink peeling, and damage to the printed image. In extreme cases, the films may become permanently stuck together, making them unusable. Therefore, controlling and improving the anti-blocking properties of ink during the gravure printing process is crucial for both performance and cost-effectiveness.
Anti-blocking products should meet specific requirements to ensure optimal performance. They must allow for smooth unwinding of the material, support high-speed production, and provide a clean, easy-to-open surface. Additionally, the material must have good printability, strong ink adhesion, and efficient solvent release to prevent blocking during storage and use.
When selecting substrates for anti-blocking applications, factors such as surface slip, ink adhesion, solvent evaporation rate, environmental conditions, and printing speed must all be considered. Common materials include BOPP, BOPET, aluminum foil, and PET films. The choice of ink, solvent, and printing parameters should be carefully matched to the substrate to achieve the desired anti-blocking effect.
In gravure printing, improving anti-blocking properties typically involves optimizing the ink formulation. This includes selecting appropriate binder resins, controlling residual solvent levels, and adjusting printing equipment settings. The design of the ink must take into account these variables to ensure effective blocking resistance.
During the printing process, special attention should be given to several key aspects. For instance, using inks with high softening point resins can help reduce blocking. Solvents should be chosen based on their ability to dissolve and release from the resin effectively. It is also essential to ensure that the ink layer is fully dry before winding, as residual solvents can increase the risk of adhesion. After printing, the material should be cooled thoroughly before being rewound to minimize blocking.
Testing the anti-blocking properties of gravure-printed materials follows specific standards, such as GB/T 13217.8-2009. The test involves folding the printed surface and applying pressure under controlled temperature and time conditions. The degree of adhesion is then evaluated by observing how much ink remains on the surface versus how much is lifted off.
The test procedure includes preparing the sample by printing ink on the substrate or using a wire rod to apply the ink. If water-based ink is used, the sample must be dried at 59–61°C for five minutes before cooling. The sample is then folded and placed in an oven at 49–51°C with a 2000g weight applied for two hours. After removal, the fold is opened, and the adhesion is visually assessed.
The results are calculated by covering the pressed area with translucent millimeter paper and counting the number of grids occupied by the remaining ink (B1) and the number of grids where ink has been removed (B2). The adhesion level is then determined using the formula:
B (%) = B1 / (B1 + B2) × 100
This method provides a quantitative measure of the ink’s anti-blocking performance, helping manufacturers ensure consistent quality and reliability in their printed products.
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