Basic Characteristics and Application Key Points of Flexible Packaging Polyurethane Laminating Adhesives

Flexible packaging polyurethane adhesives are the core materials in the dry lamination process, widely used in the composite of flexible packaging films in fields such as food, cosmetics, and medicine. They rely on the cross-linking reaction between the main agent and the curing agent to form a gel layer with both toughness and adhesion, suitable for the bonding of various types of plastic films and aluminum foil and other substrate requirements.

 

These adhesives are divided into two main categories: solvent-based and solvent-free. The solvent-based polyurethane adhesives have mature development and excellent wetting performance, are widely compatible with PET, BOPP, nylon, and aluminum foil, and can meet the production requirements of ordinary packaging as well as high-temperature sterilization packaging. The solvent-free polyurethane adhesives do not contain ethyl acetate and are more environmentally friendly, with lower production energy consumption, which is in line with the development direction of the packaging industry to reduce solvents. However, they require higher accuracy in mixing the adhesives and higher temperature control requirements for the equipment.

In actual production, the performance of soft packaging polyurethane adhesives is affected by multiple factors. The mixing ratio must be strictly controlled. Insufficient addition of the curing agent will result in incomplete cross-linking, and the cured adhesion strength will be low and the medium resistance will be poor; excessive addition of the curing agent will make the gel layer brittle and prone to membrane cracking. At the same time, environmental temperature and humidity have a significant impact on the construction. In high-humidity environments, water vapor will consume the curing agent, causing the gel layer to turn white and not dry.

 

When selecting materials, it is necessary to match the product's end-use scenarios. General snack packaging can use general-purpose polyurethane adhesives; while steam sterilization packaging requires a high-performance polyurethane system that is resistant to hydrolysis and high-temperature, to ensure that it does not delaminate or bubble after high-temperature sterilization. Daily storage should be sealed and protected from light to avoid moisture absorption and deterioration. After mixing the adhesives, follow the expiration date requirements to prevent the viscosity of the adhesive from continuously rising, which will affect the coating and composite quality.