Care-free, low-cost packaging with Steinemann

Switzerland represents enjoyable delicacies and high-quality foods. Impairments caused by foreign substances can besmirch this enjoyment. So, it's no wonder that Switzerland was one of the first countries to examine the issue of migration and the influence of packaging constituents on the taste of the packaged goods. The goal of Steinemann Technology AG is to continue this laudable tradition. Consequently, arriving at effective barriers to external influences that can be applied at low cost is a key field of research.

One undoubted source of undesirable influences on the packaged goods is the packaging, and the printing inks and varnishes applied to it. Suitable low-migration inks and varnishes reduce the risk of contamination. However, an additional barrier is also desirable in many cases. Only thick glass or aluminum provides an absolute barrier, but PET films also afford very good protection as a functional barrier.

The smell and the sensitivity to moisture of the packaged goods, the transport and storage conditions, or use as packaging for frozen foods, are other good reasons for using a composite consisting of folding-box material and a film. The attractiveness of the composite material can additionally be enhanced by using metallised or other special-effect foils.

Lamination after printing?
Packagings made of cardboard often have an internal PE coating as a functional barrier that is intended to fulfil technological demands, e.g. as a vapour barrier. At the same time, however, the functional barrier also prevents migration of constituents of the ink and varnish film into the packaged goods beyond the extent permitted by law. The functional barrier therefore serves purposes of food safety and to protect the packaged product against undesirable environmental influences.

Many cardboard manufacturers offer PE-coated board from the factory. A frequent disadvantage in this context is the large minimum purchase quantity, which impedes efficient use in the event of relatively short runs. In addition to which, printing pre-coated board also involves a slight residual risk of “invisible set-off”. In the delivery pile of the printing press, the freshly printed front side comes into contact with the barrier-coated back of the next sheet. Fresh ink and varnish films can bring about “invisible set-off”. This applies to UV ink and varnish films, because further curing in the pile is observed as a result of the post-curing effect. The drying energy applied, and the associated heat, give the ink and varnish films thermoplastic properties, this encouraging “set-off” on the back of the board.

This problem can be avoided very reliably by laminating a barrier film after printing. The curing process of the ink and varnish films has then been completed, and the risk of “invisible set-off” is almost zero. Consequently, lamination after printing affords maximum production reliability.

The Steinemann Lotus SF offers the least-cost method for this purpose.

Low-cost lamination with the Steinemann Lotus SF
The market is dominated by the water-based laminating method, where a dispersion adhesive is applied to the film and partially dried before the actual laminating operation. However, there are limits to the achievable speed in back lamination, because substantial quantities of dispersion adhesive are applied.

This automatically results in a high energy input for drying.

The low-cost alternative is lamination with polyurethane (PUR) adhesive. The PUR adhesive is generally more expensive than a dispersion adhesive, but the quantities required are considerably smaller. Another advantage is the significantly reduced energy input and the low contact pressure required.

Although the price of the adhesive is roughly 75% higher, “solvent-free” lamination with polyurethane adhesives nonetheless cuts the adhesive costs by half as a result of the smaller quantities required. In addition, the method offers further savings resulting from the lower energy input (approximately, 65% less than with water-based lamination) and better performance. Steinemann offers customers costing programs that can be used to calculate and compare the costs of the different methods.

Food-compatible PUR adhesives
Food-compatible polyurethane adhesives are available from Coim, Henkel, Pidilite and other adhesive suppliers. During production, too, the potential emission levels are very low owing to the low processing temperatures of the Lotus SF. Consequently, food-compatible polyurethane adhesives are optimally suited to the production of food packaging. Needless to say, the low consumption values are also reflected in the environmental balance of the Lotus SF. Moreover, the adhesive is based on solid, 100% solvent-free components.

Good gluing
Customers' doubts regarding the quality of gluing on the inside of cartons because of the thinness of the adhesive films applied were dispelled in extensive tests. The photo shows a GC2 board (300 g/m²) and a 2 mm thick kraft board. The inside of both boards was laminated with polyurethane adhesive and polyester or PE film. The fibre tears, and thus the good gluing quality even on the inside of the board, can be seen at first glance.

Patented hot-knife cutting technology – ideal for PE lamination
The heated, rotating cutting knife («hot knife») for tension-free cutting of all film types is particularly advantageous when using PE or polyester films. Tearing or scoring systems used for parting often fail when difficult film types are involved, whereas the hot knife reliably melts and severs the film material. The patented function for rear-edge detection before the actual laminating operation makes for precise cutting of slightly overlapping sheets.

Untapped potential
The sheets are transported absolutely straight on the Lotus SF, and the contact pressure during the actual laminating operation is also much lower than on water-based laminating machines. This permits new applications that can only be realised with difficulty by the classical sheet laminating process. In addition to kraft board with a thickness of 2 mm, corrugated F and E-flute board has also already been finished with metallised films.

Especially manufacturers of food packagings and primary packagings can make particularly good use of the potential of the Steinemann Lotus SF for cutting costs and expanding the range of applications.

This is a commissioned piece by PrintWeek India. The author is Rajesh Agarwal of SRK Technology who are the dealers of Steinemann in India.