Factors Affecting the Quality of Dry Lamination in Flexible Packaging
Selection of Adhesive Type
Many flexible packaging companies have a serious misconception when choosing adhesives. They often choose based on cost or simply follow the practices of other companies without considering their own product characteristics. Each company has its product features, and the choice of film materials varies. Therefore, when selecting adhesives, it's essential to consider customer requirements and product structure. For example, water-based adhesives may be suitable for lightweight packaging. Additionally, the adhesive should match the equipment capabilities, and consideration should be given to the product structure, such as the adhesive quantity for two-layer or three-layer structures.
Adhesive Ratio Method
Some companies still use wooden sticks to stir adhesives and casually mix them, lacking precision with electronic scales and specific procedures for adhesive mixing. Adhesive preparation should consider product structure, depth of web roller lines, adhesive quantity, composite and printing materials, etc. The formulation should be accurate, standard, and detailed to ensure product quality.
Adhesive Quantity
The adhesive quantity is the total amount of adhesive attached to the surface area when bonding substrates. Controlling the adhesive quantity is crucial for quality control in the entire composite process. Too low adhesive quantity results in low peel strength and potential delamination, while too high adhesive quantity leads to wrinkles, tunneling, hardening, and edge sticking. It is essential for cost control and solvent evaporation. Determining the appropriate adhesive quantity is crucial.
Correct Selection of Web Roller
Choosing the right web roller is critical, not only for controlling adhesive quantity but also for cost control. Some companies make mistakes in selecting web rollers, using, for example, a 120-line web roller for ordinary structures or a 150-line roller for boiling water products. Proper selection is crucial. Generally, for polyurethane two-component adhesives, a 140-170 line roller is suitable for standard products, 110-120 lines for boiling water products, and 90-100 lines for cooking-grade products.
Setting Drying Temperature
The drying temperature is determined by the solvent's boiling point, material temperature resistance, adhesive quantity, adhesive type, etc. It must match the composite production speed to allow complete solvent evaporation from the adhesive applied to the film. If the drying temperature is too low, the solvent evaporates slowly, resulting in poor bond strength and solvent residue. If the drying temperature is too high, the film may stretch, causing wrinkles and tunneling. It is crucial to set a gradient drying temperature and maintain cleanliness in the drying chamber.
Composite Roller Temperature and Pressure
Increasing the composite temperature and pressure helps improve the secondary flowability of the adhesive, promoting rapid wetting of the second substrate and entering the pores on the substrate surface, enhancing bonding strength. Typically, the composite temperature is 55-80°C, and the composite pressure is 4-6 kg/cm2.
Setting Composite Tension
Composite tension includes winding tension, unwinding tension, traction tension, and oven tension. Insufficient tension can lead to tunneling and wrinkling, while excessive tension may cause stretching, deformation, curling, and misalignment of pattern dimensions. During normal production, tension should be set according to the film's structure, considering the properties of BOPP, PET, PA, PE, CPP, and other materials.
Purity of Solvent
The solvents purchased by flexible packaging companies often come from distributors, and some companies lack equipment to test solvent purity. Solvent purity is crucial for composite processes.