Lightweighting is a principle that all players in the paperboard packaging industry are implementing at all levels of the production chain. In a few words, lightweighting refers to any effort to save resources in packaging and transporting a product.
First, we should analyze the package looking for ways to reduce flap size, panel dimensions or the space between the product and the package walls. Secondly, the package shape may also be changed to make better use of materials and decrease final size. Reductions in size will lower the need for storage space, transport costs and less secondary packaging per unit. Transportation costs are directly related to
packaging cube and weight efficiency. Shrinking the package also implies less material used. Therefore lightweighting reduces resource usage and environmental impact.
Savings in materials not only comes from redesigning the package but also from utilizing lightweight paperboard grades that achieve comparable tear, tensile and compression strength at lower grammage.
A few examples of lightweight paperboard available in Europe and the US are:
M-real's Carta line of lightweight boards contains a middle layer of proprietary BCTMP pulp that helps reduce weight while preserving thickness. The company claims these paperboards offer the same stiffness. M-real has also reduced its board thickness tolerance to plus or minus 3%, compared to the 5% which is the industry standard. This brings more predictability, fewer stoppages, and waste.
Astir Pak C1S paperboard from MKD has a triple coated top surface with an uncoated natural white reverse side. Comparing this lightweight paperboard to the standard 18pt material, it weighs 16.66% less, reducing total raw material cost, transportation, and carbon footprint.
International Paper's Alaska Plus has a double coating on the top side and an uncoated manila back. It is their lightweight GC2 board version, with substantially lower basis weight than similar products.
WestRock's AngelCote® Low-Density CRB achieves superior stiffness than their regular Classic CRB, both in machine direction and cross direction, at the same basis weight. Or conversely, you can get the same stiffness for lower material weight.
Clearwater's Candesce CIS and Candesce Foldover Blister grades also claim to have advantageous stiffness-to-weight ratios.
How to Choose the Right Lightweight Paperboard
When choosing lightweight paperboard, designers, printers and folding carton manufacturers need to consider the performance characteristics of these new grades. Cutting, creasing, gluing and folding should not result in cracks or lessened package strength.
The cracks - a white line along the fold - are created in the folding process: the topmost layer suffers tension, and the bottom layer is compressed. When they appear, they denote a lesser quality carton.
The depth and width of the creasing grooves and the difference in height with the die cutting knives are based on the paperboard grade used in the folding carton, so using a lightweight paperboard changes the equation.
Luckily, most quality paperboard manufacturers supply product manuals that specify cutting and grooving parameters that deliver the best performance.
A miscalculation can cause cracks or prevent proper gluing. Flaps may spring back, generating jams, delays, and carton waste. That is why it is paramount to utilize all technical data about the lightweight paperboard stock to adjust the cutting dies and creasing elements.
The stretching force that breaks a strip of the paperboard is called the tensile strength. Although the paper is elastic to a certain extent, returning to its shape when the force is released, if it exerted beyond a given point, the paperboard ruptures. This property is higher in the MD (machine direction) compared with the CD (cross direction).
Stiffness and thickness
This property has major significance in printing, conversion, and use. Stiffness is characterized by the resistance to bending provoked by an external pressure. The exact resistance depends on the paperboard's manufacturing process, specifically how the fibers are aligned and stuck together. as well as with their length and density. MD stiffness is higher than in the cross direction. The exact proportion between both figures is part of the material's performance profile. When substituting the substrate for a lightweight paperboard, learning about its stiffness properties is crucial to confirm or make adjustments to the package.
Stiffness is not only related to compression strength, but also to creasability and foldability. One of the most important parameters that determine stiffness is thickness. As lightweight paperboard may not be as thick, feasibility studies and testing must be done to verify that the new lightweight paperboard - being thinner - withstands the same force.
Another dimension to analyze in lightweight paperboard is the way the layers are built. The creasing process creates a groove on the pressed side and a bulge on the opposite side. Both layers must withstand it without cracking, to preserve the crease as an effective hinge in the paper converting process.
The paperboard's inner layers also delaminate in the crease area. This depends on the strength of the ply bonds. If they separate too much when pressed by the crease, the material will lose strength. If they remain too tight, the flap may spring back. As multi-layer composition may differ from regular to lightweight paperboard grades, this needs to be verified before cutting and creasing the blanks.
One dimension that needs to be monitored in the printing and paper converting process is flatness, observed as twist or curl in the surface. This quality is inherent to the material and arises from its manufacturing method and its moisture content, which must be kept along the production chain. Otherwise, it may affect print speed and even sharpness. When switching to a lightweight paperboard, this parameter may or may not match with the original stock for which all printing and folding carton operations (and storage / production humidity levels) were set.
Another test to run on substitute lightweight paperboard is gluability. Adhesives should match the substrate they must bond. The quantity applied, surface glued, drying method and time are precisely chosen. If the carton has been well glued, the fibers will damage and break the inner plies of the paperboard when the seal is torn apart.
There is synergy between packaging cost reduction and lowering environmental impact. By lightweighting paperboard packaging, brands and folding carton printers and converters are achieving productivity goals thanks to reduced substrate volume, less transportation and storage costs. These three benefits have an additional "side effect" in that less natural resources are used to manufacture paperboard, less pollution, carbon footprint and fossil fuel utilization.
Balancing Packaging Functions with Weight and Strength
When evaluating lightweighting paperboard packaging such as folding cartons, the main functions of packaging should not be forgotten:
- Containment: holding the product and preventing spillage.
- Protection: keeping the product safe from accidental impacts
- Preservation: stopping or avoiding chemical and microbiological changes.
- Convenience: for the package handlers from factory to consumers in the household.
Exaggerating on the lightweighting side may compromise product protection across the distribution chain. Under-packaging is usually more detrimental to the environment than over-packaging. Every bit of product wasted contains much more energy and materials than its packaging. A damaged package also wastes the fuel that was used to transport it.