Business & Industry
May 1, 2016
Most items at the supermarket, discount store, or shopping mall were delivered in boxes made of corrugated cardboard, and many are displayed in the same boxes. Learn more about the feedstock used in its production, the manufacturing process and future trends in the sector
Corrugated cardboard is a stiff, strong, and light-weight material made up of three, five or seven layers of brown Kraft paper. The rolls of Kraft paper are transported from the factory to a corrugating facility, where layers of Kraft paper are crimped and glued to form corrugated cardboard, which is then cut, printed, folded, and glued to make boxes. This process happens in a corrugator, a machine made especially for this purpose.
Some rolls of Kraft paper are used as the corrugating medium, and others are used as liners, gluing layers of Kraft paper onto each side of the medium. After being heated, glued, and pressed to form corrugated cardboard, the continuous sheet of cardboard is cut into wide box blanks that then go to other machines for printing, cutting, and gluing. Finally, the finished boxes are banded together into batches, and shipped to the thousands of businesses in the most varied sectors that depend on corrugated cardboard packaging.
Pine trees provide the primary raw material used to make corrugated cardboard, because it's a fast-growing tree. The largest packaging companies own thousands of acres of land where trees are matured, harvested, and replaced with seedlings. The largest packaging companies also own the mills where trees are converted to kraft paper.
At the mill, the harvested tree trunks are subjected to the kraft process, also known as "sulfate process", because of the chemicals used to convert the wood into fibrous pulp. After pulping and other processing, the fibres are sent directly to the paper machine where they are moulded, pressed, dried, and rolled into the wide, heavy rolls of kraft paper sent to corrugating plants to be made into cardboard.
At the corrugating plant, only a few other raw materials are needed to make a finished box, one of them being corn starch glue. It is used to bond the corrugated medium to the liner sheets. Because so much glue is used, rail cars or large tanker trucks deliver it in the form of a dry powder, which will then be stored in huge silos at the corrugating plant until it is needed.
Drawn from the silo, the dry corn starch is mixed with water and other chemicals and pumped into the corrugator to be spread on the corrugated medium, at the same time as the layers of liner are added.
Using powerful fork-lifts, skilled equipment operators select, move, and load rolls of kraft paper at one end of the corrugator.
One roll of medium is loaded to run through the corrugating rolls, and a roll of liner is fed into the corrugator to be joined with the corrugated medium. Liner from another roll travels up over the corrugating rolls along a flat structure called the bridge. This liner will later be glued to the corrugated medium. The medium to be corrugated is fed into the machine, it is electrically driven through the rollers of the corrugator, first through the preheating rollers and then into the corrugating rolls.
The medium then travels to a set of rollers called the single-facer glue station. Here, one layer of liner is glued to the medium. From the single-facer, the medium and liner go to the double-backer glue station where the other layer of liner from the bridge is added, following the same procedure. Continuing through the corrugator, the cardboard passes over steam-heated plates that cure the glue.
In the future, instead of using tree, corrugated cardboard will be manufactured using recycled packaging, because also in this industry, the importance of recycling and other environmentally friendly processes will continue to grow.