Polyurethane adhesives are widely used in the field of flexible packaging, mainly due to their excellent bonding strength, flexibility, resistance to media and process adaptability. The following are the main application fields of polyurethane adhesives:
1. Composite Membrane structure
Polyurethane adhesives are the core materials of dry lamination processes and are suitable for interlayer lamination of various films. Common structures include:
(1)Outer layer and middle layer composite: such as the composite of polyester film, nylon film, etc. with aluminum foil, which is used for packaging that requires high barrier properties and mechanical strength, such as milk powder, medicine, and high-end snacks.
(2)The combination of the middle layer and the inner layer heat-sealing layer: such as the combination of aluminum foil, aluminum-coated film and polyethylene, polypropylene heat-sealing film. This type of structure requires that the adhesive not only bond firmly but also withstand the high temperature of heat sealing during the bag-making process of the inner layer material.
(3)All-plastic film composites: such as combinations of polyester/polyethylene, nylon/polypropylene, etc., are widely used in liquid packaging, sauce packaging, retort packaging, etc. Among them, high-temperature resistant retaming packaging (such as above 121℃) must use special polyurethane adhesives.
2. Specific application packaging types
(1)Medium resistant packaging: It is used for packaging foods containing oil and spicy and sour components (such as oilseeds, marinated foods, condiments). The adhesive can effectively prevent delamination caused by oil penetration.
(2)Boiling and steaming packaging: By choosing specific polyurethane adhesives, it can withstand high-temperature sterilization treatment and is used for packaging meat, dishes, ready-to-eat rice, etc.
(3)Spout bags and stand-up bags: They are used for packaging composite liquids (such as fruit juice and beverages), and the adhesive must ensure that it does not delaminate after long-term immersion in the liquid.
(4)Pharmaceutical and medical device packaging: It is used for blister aluminum foil, medicine bags, etc. The adhesive should be pure, odorless and meet relevant hygiene standards.
3. Applications on Special Substrates
Polyurethane adhesives exhibit excellent effects on many difficult-to-bond materials, such as:
(1)Aluminum-coated film composite: It can effectively prevent the transfer of the aluminum-coated layer, maintaining the luster and barrier properties of the packaging.
(2)Films with lower surface treatment: It still has good adhesion to some polyolefin films with insufficient corona treatment.
