Digital Magazine

A Communication from the PLACE Div. of TAPPI

Providing practical information to the converting and packaging industries…

New Terpolymer For Al-Based Peel Lids By Extrusion Coating Of A Mono-Layer
by Yves Trouilhet, DuPont de Nemours International S.A.

Application: A newly developed grade of ethylene/methylacrylate/methacrylic acid terpolymer combines flexibility given by the acrylate component with polarity from the acidic component. The two properties combined into one resin allow converters to produce aluminum based peel lids by extrusion coating of a single layer.

The heat seal/peel resins introduced more than ten years ago replaced the partially seal/peel lacquers widely used in food and non-food packaging. When compared with lacquers, the resins have lower seal initiation temperature. The resins therefore have use with thicker substrates in a lid or with substrates having low heat diffusivity such as paper, board, or films. The resins give a shorter seal time that means faster packaging and processing on filling machines. A lower seal temperature allows sealing of thinner containers without risk of deformation with resulting leaks. It also allows sealing of heat sensitive products without damage to the products. Finally, lower seal temperatures also provide lower energy consumption and less maintenance of the sealing jaw. Seal resins do not contain solvents. They are environmentally friendly at the level of lid production and have no risk of explosion. No residual solvents are possible at the consumer level.

A new heat seal/peel grade uses a terpolymer of ethylene/methylacrylate/methyl acrylic acid. The methylacrylic acid component gives polarity and therefore a high adhesion to aluminum foil that must be higher than the seal/peel strength. The methylacrylate component gives the flexibility and the seal/peel strength to a variety of polymers used as containers. The peel resin has a melt index of 3 dg/min at 190°C at 2.16 kg, a melt temperature of 96°C, and complies with direct food contact applications in Europe and in the United States.

The paper demonstrates the possibility for producing functional heat seal/peel lids with extrusion coating of a single layer of a peel resin directly on aluminum foil. The resin can be coated between 15 and 25g/m2 with sufficient adhesion to aluminum for this application at a line speed of 120 m/min. The seal/peel strength is between 7 and 12 N/15mm to polystyrene, polypropylene, polyvinyl chloride, and polyester with a temperature window between 160 and 200°C. The low seal initiation temperature and a technology omitting solvent are advantages favoring seal/peel lacquers.

Laminating Adhesives State-of-the-Art And Future Technologies
by Holger Eichelmann, Henkel KgaA

Lamination of flexible materials in use for contact with food commonly uses polyurethane laminating adhesives. The adhesive systems fall into two classes identified by their curing mechanisms—conventional systems and smart curing systems.

Smart curing systems offer fast physical curing and fast chemical curing. These systems have also a much broader scope of possible films to adhere.

The future will see use of radiation curing (UV or EB), isocyanate free systems, materials that provide additional values, and new polyurethane technology improvements. Radiation curing works as a switch to activate groups by energy introduction into the adhesive layer. The systems can cure immediately. So-called dual cure systems cure in a two-step mechanism that requires more hours for complete cure.

Additional value systems might include incorporation of an additional barrier to protect against oxygen. This would lead to a complexity reduction in the complete process generating the laminate.

Current state-of-the art systems have smart curing mechanisms as they meet more demands of customers and comply with legislative limits in a shorter time frame. This will lead to extended use of these systems. Future technologies will use radiation curing for instant or near-instant curing. In all areas, systems will give additional values and benefits besides adhesion to customers.

For information about the PLACE Division of TAPPI, access the TAPPI web page at tappi.org. To obtain the complete papers whose expanded summaries appear in this section, go to the TAPPI web site at tappi.org., then click on "the PLACE" in the section designated Journals.

Telephone inquiries are welcome at the TAPPI Service Line by calling 800/332-8686 in the United States, 800/446-9431 in Canada, or 770/446-1400 in other countries. Send FAX to 770/446-6947. Address mail to TAPPI, 15 Technology Parkway South, Norcross, GA, 30092.

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