In the dry lamination process for plastic packaging, adhesive preparation is one of the core steps that directly affects lamination quality. The preparation process involves mixing the main agent, hardener, and solvent in specified proportions following correct operational procedures to form a uniform adhesive suitable for machine coating. In actual production, quality incidents caused by improper adhesive preparation are common, such as insufficient hardening due to missing hardener, inadequate curing from imbalanced ratios, insufficient coating due to excessive solvent, reduced peel strength, and lamination defects from irregular use of leftover adhesive. Therefore, based on years of practical experience, Haide Packaging systematically outlines the preparation methods and key considerations for two-component solvent-based dry lamination adhesives, providing a reference for production personnel and management.
I. Emphasize Adhesive Technical Data and Establish Preparation Benchmarks
The technical data provided by adhesive manufacturers is an essential reference before preparation, clearly indicating standard ratios for different working concentrations. These ratios are typically based on thorough laboratory reaction tests, with an appropriate surplus of isocyanate groups in the hardener to account for consumption due to uncertain external factors. Companies should use this data to develop process sheets for specific products, specifying adhesive ratios, while also establishing internal Adhesive Preparation Operating Standards to solidify execution criteria.
Haide Packaging emphasizes that all adhesive preparation must be based on standard ratios. Any adjustments, especially to the ratio between the main agent and hardener, must be scientifically evaluated, and arbitrary changes based on personal experience are strictly prohibited.
Table: Relationship Between Solid Content and Diluent During Dilution
II. Determine Working Concentration Based on Production Process Requirements
The working concentration (solid content of the mixture) of the adhesive must be determined based on the coating weight and the anilox roller line count, strictly adhering to the process sheet or manual requirements. Different product structures (e.g., ordinary two-layer, aluminum foil-containing, or high-temperature retort) have varying requirements for adhesive type and coating weight, directly influencing the preparation ratio.
Haide Packaging reminds that production processes are systematic plans developed by integrating adhesive performance, product structure, environmental factors, and test data. Adhesive preparation must adhere to these plans, with technical data serving as an important reference.
III. Influence of Objective Conditions on Adhesive Ratios and Corresponding Measures
1. Product Peel Strength Requirements
For ordinary metallized products (non-specialized adhesives), the hardener may be appropriately reduced (by approximately 10%–20%) to minimize the risk of delamination. For high-temperature retort products, the hardener may be increased (by approximately 3%–5%) to enhance the adhesive layer's resistance to degradation. All adjustments must be validated through experiments and formalized into process standards. In ultra-high humidity environments (humidity >90%), it is not recommended to produce retort products even with increased hardener.
2. Anilox Roller Line Count Compatibility
When the anilox roller line count does not match the target coating weight, the working concentration of the adhesive can be adjusted for compensation: lower the concentration for finer lines and increase it for coarser lines. However, this approach may lead to increased costs (solvent loss) or quality risks (screen clogging, white spots). Haide Packaging recommends that companies rationally plan anilox roller configurations to avoid over-reliance on adhesive preparation adjustments.
3. Seasonal and Temperature-Humidity Variations
In high-temperature and high-humidity environments (e.g., humidity >85%, temperature >35°C), moisture intrusion and solvent evaporation can consume the hardener. It is advisable to increase the hardener by 5%–10% during preparation. In low-temperature environments, adhesive viscosity rises, and an appropriate amount of solvent (e.g., 10%) may be added to improve coating transfer. However, the actual coating weight must be verified through testing. Alternatively, adhesives with high solid content and low viscosity can be selected for low-temperature production.
4. Stable Viscosity Control
Viscosity directly affects the stability of the coating weight. Adhesive viscosity is influenced by the ratio, ambient temperature, and the degree of solvent evaporation. During production, viscosity must be maintained by manually adding solvent at regular intervals or using an automatic viscosity controller to ensure consistent adhesive concentration and viscosity, thereby achieving uniform coating.
5. Material Abnormalities and Property Influences
If it is known that alcohol solvent residues in printed films exceed standards (e.g., isopropanol >5 mg/m²) or if recycled ethyl acetate is used (purity <99.5%), the hardener ratio may be appropriately increased (by 1%–5%) to offset its consumption of the hardener. However, such measures are only temporary solutions, and material quality must ultimately be controlled at the source. For moisture-prone nylon films, it is recommended to increase the hardener by 3%–5% under normal humidity conditions and by 5%–10% in high-humidity environments (>85%).
6. Standardized Use of Leftover Adhesive
Leftover adhesive should not be stored for more than 48 hours (12 hours for fast-drying adhesives) and must show no signs of emulsification or discoloration. When reusing, it should be blended with fresh adhesive at a ratio of 5%–30%, stirred thoroughly, and the viscosity tested. Adjustments should be made by supplementing the main agent, hardener, or solvent to meet the required viscosity. Note that leftover adhesive should be used cautiously for ordinary products and is not recommended for high-temperature retort products. Additionally, leftover adhesive must only be mixed with fresh adhesive from the same manufacturer and of the same type.
IV. Establish a Standardized Adhesive Preparation Management System
Adhesive preparation is critical to quality stability and must be systematically managed. Companies should develop comprehensive Dry Lamination Adhesive Preparation Operating Standards covering all stages, including ingredient measurement, mixing, testing, and documentation, while strengthening personnel training and supervision. Haide Packaging effectively reduces the risk of human error and improves preparation consistency by implementing standardized operations and regular review mechanisms.
V. Conclusion
Adhesive preparation is a key control point in the dry lamination process. It must strictly adhere to process requirements, comprehensively considering factors such as product structure, environmental conditions, adhesive properties, and application scenarios. Simultaneously, human operational errors, such as arbitrary ratio adjustments, shortened mixing times, or omitted hardener, must be eliminated. Today, automated adhesive mixing systems provide higher-precision solutions for preparation. Haide Packaging is gradually introducing related technologies to enhance ratio stability while reducing solvent loss and quality risks, ensuring high quality and consistency for dry lamination products.