Corrugated board is made up of one or more layers of corrugated paper. These corrugated layers are glued together with layers of straight paper. Corrugated board brings up the pros of solid boards and at the same time eliminates the cons. Physical characteristics of individual types of corrugated boards are defined based on requirements for the material. Corrugated board is fairly impact resistant because the impact tends to infract the corrugated parts and therefore minimizes the chances of destroying the packaged goods. The main attributes observed on boards are mainly so called bursting, disruptive breakdown and edge breaking point (the bigger the edge breaking point - the more you can stack the board - meaning you can stack higher volumes of boxes on each other).
Board is one of the most widely used materials in the packaging industry - around 75 % of all packages is made out of board. If the board isn’t treated than the disadvantage is definitely its low resistance to water and weight absorbing capabilities.
History of corrugated board
Corrugated board is over 150 years old. The first information about “paper or other material corrugating” may be found in a British patent by Edwarda G. Healyho and Edwarda E. Allena (1856). The manufacturing of corrugated board was patented in 1871 in US by Albert Jones. Rumor has it that the first corrugating machine was made from old cannon barrels from the Civil War. The inspiration was gained from pleated women skirts. His goal was to find an elegant and safe way to package glass bottles. Oliver Long improved his patent three years later by adding a solid board to the corrugated one - getting a two-ply board. In 1883 in London the first European corrugated board factory began operating. The 20th century brought the development of new machinery and techniques for making corrugated board.
Types of corrugated boards
Corrugated boards are made by a certain number of solid and corrugated boards. Corrugated board can be made from at least two and at maximum of seven layers. Board can be divided based on two criteria
- based on height of the rib/profile
- based on source material
Technical names of corrugated boards based on structures are as follows:
Two-ply corrugated board with an A type rib (one-ribbed) - can be delivered in rolls or sheets - board height: 4,4 mm and rib pitch: 8,6 mm
Three-ply corrugated board with a C type rib
board height: 3,5 mm and rib pitch: 7,3 mm
Three-ply corrugated board with a B type rib
board height: 2,7 and rib pitch: 6,1 mm
Three-ply corrugated board with an E type rib (micro-rib)
board height: 1,4 and rib pitch: 3,7 mm
Further more there are mini-ribs symbolized by letter F, these have a height of 0,8 mm. These ribs aren’t the smallest option. There are also microprofiles G and O that are only 0,3 mm high.
Production of a five-ply corrugated board
Basic materials for production on corrugated board
To create corrugated board a variety of papers of different characteristics, qualities and weights can be used. It depends on what is the end-use of the corrugated board. In order to create corrugated board, the solid board has to be layered with the corrugated paper. Typically in packaging industry the papers are divided based on quality:
Fluting – unbleached half-cellulosic paper made of leaf wood with minimum of 65 % primary fibers
Wellenstoff – predominantly made of recycled old paper
Šedák (Grayer) – paper made of a mix of collected papers such as print disposal, grey board, board tubes etc.
Kraftliner – sulfate, cellulosic paper made in natural brown or with a bleached treatment (white top) made of coniferous wood with minimum of 80 % primary fibers.
Testliner – mostly two-ply papers made of different types of papers. The covering paper may be out of quality fibrous materials. The fiber mix isn’t standardly set - therefore strength is given and guaranteed.
Šedák (Grayer) – paper made of a mix of collected papers
Surface density is given in g/m2. For covering paper 100-300g/m2 densities are used. For ribs 80 to 180 g/m2 surface density is used.
For production of corrugated board modified starch is used as glue. Also other types of glues such as dispersive adhesive are used - it depends on required qualities of the board (e.g. bigger resistance to water).
Production of corrugated board
The production process of corrugated board can be divided into several phases:
creating ribs and rib gluing
The basic machinery for production of corrugated board is the corrugator to which two belts of paper are fed. Paper intended for corrugating goes through a set of fluted valves (upper and lower fluted valve). These valves are heated to 180°C. Immediately after the corrugation process starch glue is applied to the ribs. Afterwards the corrugated paper is gently pressed with another layer of solid paper. This way one gets a two-ply corrugated board suitable for further conversion.
Corrugating on a corrugator
Marouflage, gluing and drying
Marouflage is a technique in which an upper treatment from a different material than the base material is applied. When the ribs are firmly connected to the solid base the lower part is marouflaged and glued to the other side of the board. This way single-ply or multi-ply boards are made. The drying process causes the starch to become a gel - this glues firmly together all layers.
Printing on corrugated board
Corrugated board is used for package production and therefore the surface has to be printable. Based on the place where it is printed we recognize so called preprint and postprint. In the case of preprint, the upper surface is being printed before it is glued to a layer of corrugated board. That means that a roll of paper for corrugated board is already printed. Or the paper is printed and than marouflaged to the corrugated cardboard. Both approaches have high quality printing, because virtually all printing techniques may be used: mostly off-set, gravure printing or flexoprint.