Corrugated board - numerous advantages and the problem of curvature.

Corrugated board has numerous advantages as a sought-after material for packaging: Sustainable by nature, based on renewable raw materials and fully biodegradable. Packaging made from many other materials cannot offer this.

And that's not all. Often, no trees have to be felled for the production of corrugated board. Most of the raw paper required for the production of corrugated board comes from used corrugated board, waste paper and cardboard.

In a nutshell: corrugated board is an ideal circular product of a modern world. But it can also cause problems during production. Here, the focus is on the possible curvature of corrugated board sheets.

Corrugated board and the problem of curvature - the most important at a glance

• Curving of the arches can be done immediately after completion or a few days later.
• There are many different forms of curvature. The reason for the curvature often varies from shape to shape.
• To prevent or at least reduce curvature, the arches should always be stored in places with good climatic conditions after completion. In addition, the humidity of the ceiling sheets plays an important role.

Problems that can occur during the production of corrugated board

The production of corrugated board is more complex than one might think.

Regardless of the advantages corrugated board offers, problems can arise in the production of the material . These problems mainly concern the horizontal flute. The horizontal flute is an arrangement of the flutes that is not vertical, but horizontal - that is, perpendicular to the height of the box.

This is because it can sometimes cause difficulties when formats are processed during feeding. If the flute is not fed in exactly, this quickly leads to increased deviations with regard to the specified dimensions.

This forces manufacturers to produce more slowly. In addition, you have to reckon with a higher reject rate in this case. In addition, the horizontal flute has a significantly lower stacking capacity than the vertical flute .

In addition, the horizontal corrugations can lead to inaccurate folding of the vertical creasing during processing. Creases and folds are often unavoidable, especially in die-cut packaging, for design reasons.

The curvature of corrugated board

In addition to the problems around the horizontal flute , a curvature often causes difficulties. This curvature is called warp (here: to warp - in German: sich verformen, sich krümmen).

Curvature of corrugated board has traditionally been one of the most common problems encountered in the production of the material. In the first place, the problem of curvature always occurs within two different periods or phases of the production process:

1. Faulty or low-quality corrugated board base papers, defects in the processing machines or incorrect adjustment of the corrugator can lead to the so-called corrugator warp following production. "Corrugator" is the English term for corrugating machine.
2. Problems with curvature of the sheets can alternatively occur hours or even days after the end of production. In this case, the cause is unfavorable storage conditions and unfavorable climatic conditions. This is because the sheets usually leave the corrugator lying flat and in this case do not curl until later. This problem is known as "post corrugator warp".

The different forms of curvature at a glance

In addition to the classification according to time periods or points in time, the curvatures are also divided into different classes with regard to their shape. These six forms of cur vature exist:

Up-Warp
In the case of horizontal arcs, two or four edges lift. This deforms or curves the cross-section of the arcs almost into a U.

Down-Warp
In this case, the curvature is particularly noticeable in stacking, as the edges clearly point downwards. As a result, the stack takes on a hill-like shape instead of a straight one.

S-Warp
This curvature is characterized by its reversal of orientation exactly against the actual running direction of the machine. Possible causes include improper storage or local differences in the moisture content of ceiling webs.

Twist-Warp
In this type of curvature, the corrugated board takes the shape of a corkscrew. The reasons for the occurrence of this curvature are manifold.

Side-to-Side-Warp
If the ceiling webs have different moisture content, this can lead to sheet curvature, which then runs transverse to the machine running direction.

End-to-end warp
This term is used to describe curved sheets in the machine direction. End-to-end warp usually occurs when there are different web tensions or uneven moisture content of the ceiling webs.

Do you have further questions about corrugated board and the possibilities of its use? Then contact us!

How to avoid the curvature of corrugated board

In order to avoid the curvature of corrugated board, it is indispensable to make sure that the manufacturing machines are properly adjusted. In addition, regular checks should be made to see if there are any faults or defects in a machine, which can then be rectified before production starts.

The same applies with a look at the base papers used for production. Here, quality control should also take place in order to avoid curvatures.

To prevent post corrugator warp, the right climatic conditions during storage play a decisive role. In addition, it can be helpful to use intermediate layers for storage after production, for example in the form of boards.

Corrugated board offers these environmental benefits as a base material for packaging

However, corrugated board offers a whole range of advantages, which become apparent, among other things, when we take a look at sustainability. The raw material for the production of corrugated board is paper, which in turn is obtained from wood. With wood or wood fibers, many manufacturers rely on a renewable raw material from sustainable forestry.

The wood used for this purpose is a pure by-product of forestry and is accordingly referred to as deforestation wood. This ensures sustainable use of the natural resource.

Corrugated board that has already been used is also a valuable raw material. Disposed corrugated board packaging is recycled via the collection system in Germany. The recycling rate for corrugated board in Germany is well over 90 percent. By comparison, plastic only has a recycling rate of less than 60 percent.

Depending on the quality of the base materials, corrugated board can be recycled up to 20 times. This makes corrugated board an exemplary closed-loop product.

In addition, production is always close to nature. This becomes clear, among other things, when you look at the gluing process. Glue made from potato, corn or wheat starch is generally used to glue the individual paper webs. Glue made from these resources is completely biodegradable.

The corrugated board itself can also be completely biodegraded. The paper fibers consumed by multiple recycling passes are basically discharged from the manufacturing process. These can then be used for composting or energy generation, for example. Plastic, on the other hand, is not biodegradable.

Corrugated board packaging is always produced fresh by manufacturers and is therefore particularly hygienic. The base papers are manufactured by the respective producers with the aid of special paper machines at a temperature of around 140 degrees Celsius, while the corrugated board packaging is produced germ-free on a corrugator at a temperature of around 150 degrees Celsius.

That is why corrugated board is the material of the present and the future

The topic of recycling has long played a particularly important role with regard to packaging materials. The primary aim here is to realize the transition from a linear to a circular economy.

In view of environmental pollution, climate change, resource dependency and population growth, this change is urgently needed both ecologically and economically. The environmental impact of packaging and packaging materials currently in use is being scrutinized more than ever.

One thing is clear in this regard: the future belongs to recyclable packaging materials that are produced from natural, decomposable components and can be integrated into a circulating material flow. Corrugated board offers precisely these attributes.

This is because it is made from renewable raw materials (usually from sustainable forestry). In addition, the proportion of waste paper used in the production of corrugated board base paper is continuously increasing as a result of permanent improvements with regard to paper recycling.

Conclusion

Corrugated board offers many advantages as a material. These include comprehensive sustainability, stability and cost efficiency. During production, some problems can occur, which mainly include curvature. This can occur during the manufacturing process or during storage. So, in order to take full advantage of the material, it is essential that the smallest details are taken care of during production and storage. This includes a suitable setting and regular checks of the machines, as well as the right storage conditions.

FAQ

1. How do curvatures of corrugated board occur?
   Curvatures of corrugated board can be caused by errors during production as well as by incorrect storage. The former is referred to as currogator warp, the latter in turn as post-corrugator warp.

2. What are the types of curvature of corrugated board?
   There are six types of curvature of corrugated board in total: Up-warp, Down-warp, S-warp, Twist-warp, Side-to-Side-warp and End-to-End-warp.