Everyone uses corrugated boxes. You would be hard-pressed to exist in today’s society and not have some kind of contact with them. But have you ever thought about how they are made? To make corrugated boxes, you need three main materials: paper, steam, and adhesive. The process begins with paper.
Paper is used to make the two main components of corrugated fiberboard:
The linerboard—used as the outer facings
The medium—fluted paper that is attached to the linerboard to produce combined board in a continuous web
Multiple choices exist when it comes to paper types and thicknesses for corrugated board. Make sure you determine the goals for your package and work closely with your box plant and/or paper supplier to see the paper characteristics you need to reach those goals.
Once you have the paper, only two more raw materials are needed for a box plant to form the structural material used to make different types of corrugated packaging: steam and adhesive. Steam is vital to the corrugated box making process.
From making the adhesive that conditions the layers of paper to heating the pressure vessels that bond the fluted medium to the liners, steam generation is an invaluable process. Even though the condensed steam is reprocessed, the cost of boiler fuel is a large factor in packaging manufacturing. In addition to cost, another important factor to consider is the safety concerns of high steam-pressure environments.
You’ve got the paper and steam, now you need the adhesive—the liner must be affixed to the fluted medium. This is accomplished by the use of starch adhesive. Typically, this adhesive is a water-based, food-grade, corn starch combined with other additives. The adhesive is applied to the flute tips—the peaks on the fluted structure—of the corrugated medium, and then the liner is brought into contact with the tips, bonding all of the materials together.
Since we’ve learned about the ingredients needed to make corrugated board, let’s take a look at the machinery that combines them—the corrugating machine. This machine carries out a number of operations to bring the linerboard and medium together to form a rigid structure. Today’s corrugators can produce 1,000 feet per minute of combined board.
A basic breakdown of the process is as follows:
Rolls of paper are mounted on unwinding stands and pulled into the machine at the “wet end” of the corrugator.
The medium is treated with heat and steam, making it more flexible, so it can be formed into the fluted pattern at the corrugating rolls.
Corrugating rolls (gear-like cylinders) shape the medium into the fluted structure.
Glue is put on the flute tips, and the first liner (which may have also been treated with steam and heat) is pressed onto the adhesive on the fluted medium.
The heat, pressure, and steam cause the adhesive to form a gel which creates a bond between the two papers. This a called a single-face web.
The single-face web then travels through the corrugator to the double-back station, where a second liner is applied by adding adhesive to the fluted tips on the other side of the medium.
The bond with this layer is formed more gradually as the board passes over heated plates in a hot-plate section. Using significant pressure here would crush the flutes.
As the boards exit the hot-plate section, they are generally sheeted, or cut into manageable sheet sizes, then scored for folding.
The board is too stiff to be rolled at this point, so it is sheeted, where it can then be die-cut or slotted and folded into specific structures.
Boards are slit to width and cut, creating flat sheets to match customer requirements for a box.
Sheets are taken from the corrugator and stacked to allow time for the drying of fibers and curing of the adhesive.
During the manufacturing process, moisture is added to the papers with the application of starch adhesive and steam conditioning—it is also taken away by the heating and curing process. To avoid warping, these moisture changes must be closely controlled and balanced.
Wax or other chemicals may be added to one or more of the papers to give unique enhanced properties to the board.
Certain applications, especially fresh produce packaging, expose corrugated to excessive amounts of moisture from coolers, freezers, and water from cellular respiration of produce.
In these applications, it is common for the corrugated box to be coated with molten wax. This forms a highly water-resistant barrier once the wax absorbs into the paper fibers and dries.
With so many available options, it’s important to take the appropriate time upfront to determine the best corrugated paperboard for your application. Talk to your design team as well as your distribution team to see what corrugated possibilities will serve you the best.
Want to learn even MORE about the world of corrugated packaging? Head over to our course library where you’ll find our Corrugated Containers course, designed to show you a 360° view of the corrugated industry.