Common Issues in Dry Lamination and Practical Solutions Many industry professionals have extensively discussed common challenges in dry lamination processes, and their insights have greatly benefited many companies in the flexible packaging sector. Based on frequent inquiries I’ve encountered while working with flexible packaging firms, this article outlines key issues, their underlying causes, and practical prevention strategies to help improve production quality and efficiency.
1. Surface Wrinkles on Bags Wrinkles on printed bags can occur at various stages—immediately after curing, after heat sealing, or even after boiling. A major cause is the improper use of curing agents in inks, especially with modern benzene-free and alcohol-based inks. These inks often use polyurethane binders, which are sensitive to solvents like alcohols. If the curing agent isn’t properly balanced, it can lead to incomplete drying and surface wrinkling. To address this, it’s essential to add a suitable hardener to the ink, as recommended by the manufacturer. If no hardener is used during printing, adding a small amount of curing agent (at least 20%) to the adhesive can help. However, recent experience shows that some inks may still not dry even with 50% curing agent added. Therefore, it's crucial to test compatibility between inks and adhesives before production.
2. High Solvent Residue High solvent residue is a critical concern in food packaging due to safety standards. While many factors contribute, equipment settings play a major role. Improper temperature, air flow, and pressure in drying tunnels can trap solvents, leading to high residual levels. To reduce this, ensure sufficient airflow at the tunnel outlet and maintain negative pressure throughout the system. Adjusting exhaust systems and avoiding excessive return air can also help. Additionally, keep drying temperatures moderate to prevent false drying, which can trap solvents inside the film.
3. Poor Opening After Aging Some films become difficult to open after aging, sometimes appearing damp or sticking together. This issue is often linked to over-tight rewinding or incorrect composite roll temperatures. To avoid this, adjust tension settings to keep the rewound film slightly loose. Lowering the composite roll temperature can also improve opening performance. However, it’s important to ensure the initial tack remains strong to prevent tunneling after aging. Proper cooling before bagging is equally essential.
4. Low Composite Strength Low adhesion strength is often caused by the precipitation of additives in heat-seal layers. If the seal layer becomes hazy and clears up when wiped, it’s likely due to additive migration. To resolve this, use adhesives resistant to such additives or increase the curing temperature by 5–10°C. The goal is to allow the adhesive to cure before the additives reach the interface. Also, ensure the adhesive is fully dried before initiating the curing process to minimize further additive movement.
5. Live Folds in Composite Films Live folds, typically found near the center of the roll, are a persistent issue. They appear after aging and are hard to flatten. This is usually due to weak initial tack, causing the film to shrink and form wrinkles around the core. To prevent this, use adhesives with higher initial tack and increase the temperature in the final section of the drying tunnel and the composite roller. This helps strengthen the bond and prevents blemishes from forming after aging.
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