Ionomers are transparent thermoplastic elastomers of glass-like clarity, high toughness and outstanding flexibility. They consist of both electrically neutral and ionized repeat units that are randomly and or regularly distributed along the polymer backbone. The concentration of ionic groups in ionomers is typically no more than 10 to 15 percent. One important characteristic of ionomers is the strong molecular aggregation of the ion-carrying groups to ion rich domains or ion clusters which act as physical crosslinks. When heated, the ionic bonds and clusters dissolve and when cooled, they reform. This gives ionomers a unique structure and behavior. At low temperatures, they behave like crosslinked polymers (elastomers) whereas at elevated temperatures they behave like ordinary thermoplastics. These resins are frequently used as a tie-layer and as an adhesive resin which provides excellent adhesion to aluminum and other polar substrates as well as outstanding sealing properties.
Kraft Paper is the strongest and most useful paper for packagaging applications. This type of coarse paper is typically made from southern softwoods by the sulfate process. It is produced in various weights ranging from 16-lb basis weight up to 90-lb basis weight and can have a rough or smooth finish. For many packaging applications natural-color Kraft paper is preferred, but it is also sold as white (bleached) or semi-white (semi-bleached) paper. However, bleaching reduces the strength of the paper.
Laminating adhesives: Flexible films in packaging often consist of several film/foil layers with different characteristics to attain the desired features for each individual package. The different layers are bonded with a broad range of laminating adhesives, including solvent-based and solvent-free polyurethane adhesives, water-based acrylic adhesives, hotmelts, as well as heat seal and cold seal lacquers. These adhesives are used in the packaging industry for laminating flexible packaging for food, medications, medical supplies, and cosmetics.
Low density polyethylene is a low cost, clear and flexibile thermoplastic. It is by far the most important type of plastic used in the packaging industry. The two most important grades are low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). These two resins are often thought to be the same because they have very similar properties. For example, both have good to fair clarity, excellent chemical resistance, good moisture barrier but poor gas barrier properties. Both types can be heat-sealed and are strong, tough and highly flexible. LDPE is often chosen for its higher clarity, ease of processing and higher gloss, whereas LLDPE is selected for its higher tensile and impact strength and better heat sealability. Both LDPE and LLDPE are used for similar applications, including stretch-wraps, shrink-wraps, bags, liners, and packaging films.