In the production of flexible packaging composite materials (such as food and medicine packaging bags), adhesives are the key to determining the packaging performance. Compared with traditional adhesives (such as solvent-based rubber adhesives, ester-soluble acrylic adhesives, etc.), polyurethane adhesives have taken the leading position due to their outstanding comprehensive performance.
The main differences and outstanding advantages of polyurethane:
1. Outstanding bonding universality
Ordinary adhesives often have poor bonding effects on specific materials such as polyethylene and polypropylene, especially when dealing with plastic films with low surface energy. The molecular structure of polyurethane adhesives contains highly polar urethane bonds (-NH-COO-), which can generate powerful van der Waals forces and hydrogen bond interactions with the surfaces of various substrates. This enables it to firmly bond common plastic films (such as BOPP, CPP, PE), aluminum foil, aluminum-coated film, nylon (PA), polyester (PET), and other dissimilar or the same materials simultaneously, almost "sticking to everything", solving the most core problem in the composite packaging industry.
2. Excellent resistance to media and temperature
Flexible packaging often needs to hold contents containing oil, acid, spicy food, salt and other components. Ordinary adhesives are prone to degradation, stickiness or delamination under the long-term penetration of these media or high-temperature steaming. After curing, polyurethane adhesives form a three-dimensional network structure with high cross-linking density, which is chemically stable and can effectively resist the erosion of oils and chemical substances. More importantly, it can produce products that meet the requirements of high-temperature cooking at 121℃ or even 135℃, ensuring that the packaging does not delaminate or deform during the sterilization process. This is crucial for aseptic packaging of meat, medical devices, etc.
3. Outstanding flexibility and durability
Flexible packaging needs to be frequently bent and squeezed during use. Some brittle adhesives are prone to fatigue cracks under long-term dynamic stress, resulting in a decrease in composite strength. The film formed after the curing of
Polyurethane Adhesive itself has excellent elasticity and toughness, which can well absorb and disperse stress, deform synchronously with the flexible film without cracking, ensuring the structural integrity and sealing performance of the packaging throughout its life cycle.
4. Excellent process adaptability
Polyurethane adhesives (especially two-component types) can precisely "customize" their initial viscosity, operation time, curing speed and final performance by adjusting the proportion of soft and hard segments in the formula, to meet the requirements of different coating equipment (such as dry lamination, solvent-free lamination) and different application scenarios. The flexibility of this design is unmatched by many traditional adhesives.
