Strength lies in lightness

The concept of lightweighting is now receiving a great deal of attention. The main reason for this is the EU Directive on Packaging and Packaging Waste, which has placed pressure on retailers to reduce the waste by weight, resulting in increased demand for lightweight packaging.

In addition to the legislation compliance issue, there are strong economic reasons why lightweighting of cartonboard is essential. Jürgen Schondelmayer, technical manager – global supply chain, Unilever, says: “As we use a large quantity of cartonboard, anything we do to reduce tonnage can translate into big money for us.”

What is lightweight board?

Lightweighting increases the yield obtained from a specific weight of cartonboard. When compared with standard boards, less raw materials are required for manufacturing, and a reduced amount of waste is produced during converting and packaging. Less post consumer waste is also produced. As the cartonboard is lightweight, greater amounts can be transported in one delivery, thereby reducing the costs and carbon footprint of transportation.

According to ProCarton, advances in lightweighting are due to developments in computer controlled processing and on-machine quality monitoring, resulting in productivity improvements and more consistent board quality.

The new forming and press section techniques have resulted in improved strength, facilitating grammage reduction. Many boards now incorporate middle layers of bleached mechanical pulp, reducing weight and enhancing brightness. Developments in surface coating methods, coating formulations and board machine techniques, including surface glazing and brushing, have also helped improve visual appearance and printability.

Talking to the board producers

Given the environmental concerns, manufacturers are continuously investing in the development of lightweight cartonboard. M-real, for example, has recently invested in lightweight board production at its Finnish plants in Aanekoski and Simpele, where the surface sizer and reeler on the board machine have been replaced, in addition to developments in the drying section

of the finishing department. M-real has also developed a new type of pulp, known as bleached chemi-thermo-mechanical pulp (CTMP), which permits greater stiffness to be derived from lower grammage board. Its Simcote 230 g/m² board is said to provide stiffness equivalent to WLC 300 g/m².

The boards have less variations – for example, a board with a thickness of 585 micron is said to have a tolerance of 3 per cent (36 micron). M-real claims that this enables die cutting machines to achieve outputs of 22 per cent more sheets per hour that when using WLC.

The stiff and bulky board structure for Stora Enso’s lightweight boards is achieved by the use of virgin fibres combined with multilayer techniques, where chemical pulps are enhanced with the strength of mechanically refined pulps. The company’s Natura Board comprises two outer layers of solid bleached sulphate (SBS) pulp with a middle layer of CTMP.

Stora Enso has been active in the development of liquid packaging board, and barrier coatings, and claims that this now permits the production of 1.5 times more one litre cartons from the same amount of wood material than was the case 30 years ago.

This year, Korsnäs modified its process equipment to mix different pulps in each of its four board layers. Each layer can be optimised, combining both chemical and mechnical pulp. During production, the virgin fibres can be treated in different ways, such as hard-sizing to produce a lightweight board that retains its stiffness in humid conditions. A typical example is Korsnäs White board, which comprises coating layers on both surfaces and two layers of bleached fibres which surround a layer of bleached strong fibres combined with CTMP.

Processing problems?

Bob Houghton, of Chesapeake, says: “There are no problems with processing lightweight boards, as the weight generally only drops by 20-50 g/m², so the board largely performs exactly the same. However, the reason that most cartons only drop a relatively small amount is due to the strength required to support the product’s weight. The majority of brands/ products are already using the optimal standard board, which is then lightweighted,”he confirms.