Paper & Packaging
Paper and Board
Adhesives are used in a wide variety of paper bonding and converting applications ranging from corrugated box construction and the lamination of printed sheets to packaging material used for all types of consumer products to the production of large industrial tubes and cores. They can also be found in everyday consumer products such as bathroom tissue, paper towels, and books.
Packaging is one of the largest markets for adhesives.
A high proportion of all industrial products are sold in packaging – either due to sta¬bility requirements for storage and transport or for aesthetic reasons. Although normal envelopes and paper bags consist of just a single layer of material, most packaging materials used nowadays are in fact different materials laminated together.
Laminated films can be manufactured from polyester (PETP, PBTP), polyamides, polyethylene, polypropylene, cello¬phane, paper, polyvinyl chloride, polyvinylidene fluoride, polyimides, aluminium and a few other materials. Metallic foils are also often used. Solvent-containing adhesives based on polyure¬thane are used for laminating films; the most recent developments in this area however involve solvent-free systems, so-called high-solid products and adhesives based on aqueous polyurethane disper¬sions. For application using automatic packaging machinery, high requirements are put on the con¬stancy of the adhesive properties, especially with regards to its viscosity stability. Dispersion adhes¬ives and hot melts are used to seal packaging (e.g. folding cartons, packets).
Only adhesives make frozen food possible. They provide a reliable seal for the packaging and ensure that the low temperatures in the freezer remain constant and that energy costs are minimized.
The range of application is enormous. The modern systems of distribution, self-service, ready-meals and frozen foods are unimaginable without adhesives to produce impermeable packaging materials such as laminating foil or to hermetically seal packaging (e.g. packets of coffee). The smallest amounts of laminating adhesive (approx. 1 to 3 g/m) are added to laminating foils at rates of up to 1640 ft/min. Adhesives that are resistant to high and low temperatures allow packaging to be made for frozen and microwavable foods. Of course it goes without saying that adhesives used to make packaging for food conform to all of the strict regulations governing food production.
Invisible, tasteless and odourless – adhesives hold the very fabric of our supermarkets together and even play their part at home. Where would a kitchen be without a fridge or freezer? Luckily adhesives ensure that the cold stays where it belongs and reliably protects ice cubes and other frozen foods. How is a fridge sealed? Inside there is a particularly cold-resistant layer of thermoplastic synthetic material, so called HIPS (High Impact Polystyrene). Equally resistant to cold is the adjacent thick, insulating layer of polyurethane (PU) rigid foam, used to fill the housing and door cavities. The PU-mix is injected and reacts inside to form polyurethane rigid foam. The secret of polyurethane rigid foam lies in the network of polymers with a predominantly closed cell structure. Each cell has a sealed cell membrane which causes the movement of gas within the material to be greatly delayed – to put it simply, the cold stays in the fridge.
Foaming agents are used to create this cell structure. CFCs were used until it was discovered that they were harmful to the environment. Nowadays fridges and freezers are CFC-free. Instead, cyclopentane and carbon dioxide are used; even the addition of water can help the cells to form.
A second property of polyurethane is that – thanks to a low density – it is very light. As it is also impervious to mould and rotting and does not attract pests, the fridge stays hygienic.