PU Adhesive compositions are useful for a wide variety of purposes. For instance, some adhesives are used to adhere two or more film layers of substrates together thereby forming composite films, i.e., laminates comprising the two or more film layers. Example of substrates typically include polyethylenes, polyporpylenes, polyesters, polyamides, metas, papers and the like. The use of adhesives in laminating applications is generally known.
For example, adhesives, are generally applied between laminating films, can be used in the manufacture of film/film and film/foil laminates used in the flexible packaging industry for packaging of foodstuffs, pharmaceuticals, and industrial consumables, especially laminating adhesives for food packaging. Laminating adhesives can be classified generally into three categories:
1. Solvent-based laminating adhesives, 2. solventless laminating adhesive, and 3. water-based laminating adhesives. The performance of an adhesive varies by category and by the application in which the adhesive is applied. Within the solvent-based category of laminating adhesives, solvent-based polyurethane has been widely used to achieve relatively good heat, moisture, and chemical resistance. Solvent-based adhesive compositions can be used in high-performance laminate applications (e.g. retort, hot-fill, boil-in-bag,etc.)
For example, in retort flexible packages application, the retort flexible packaging offer several benefits, such as consumer convenience, a long shelf life of food packed in the packages, and preservation of the original flavor of the packed food. Retort flexible packages such as retort pouches are commonly constructed with multilayer lamination structures, such as a three-ply structure or a four-ply structure. The three-ply structure generally includes, for example, an outside layer of PET, a middle layer of a metal foil (e.g. aluminum), and an inside layer of casted PP (CPP), is generally indicated as PET/Alu foil/CPP. The laminating adhesives used for retort flexible packaging applications PET/Alu foil/CPP must not only meet the extreme performance requirements at high temperature in the presence of highly acidic and fatty food, such as at a temperature of 121 degrees celsius for 1 hour or 135 degrees celsius for 30 minutes.
