company news about How is corrugated cardboard produced?

The production of corrugated cardboard is a continuous industrial process, usually completed on the automated production lines. The basic process is bond flat cardboard (face paper and inner paper) with corrugated core paper pressed into a wave shape, using the adhesive to complete several layer composite structure.

The following are the main production steps for common three-layer (single corrugated) and five layer (double corrugated) cardboard:
1、 Main raw materials
Box cardboard : used as the surface layer (face paper and inner paper) of cardboard, providing a flat printing surface and impact resistance, commonly seen as the cowhide hanging paper.
Corrugated core paper: a type of paper used for pressing into the wavy shapes, with good elasticity and compressive properties.
Adhesive: It's often made from corn starch or cassava starch, and other additives are sometimes added to adjust its properties.
Energy: mainly steam, used for heating and bonding processes.

2、 Basic production process (carried out sequentially in the corrugated cardboard production line)
A complete production line usually includes following steps:
Raw paper holder
Large roll shaped cardboard and corrugated core paper are placed on the unwinding rack, ready to enter the production line.
Single facer machine: this is the key process
Preheating: The core paper is the first heated by a preheating roller to make it flexible and easy to form.
Corrugated forming: The heated core paper is rolled by a pair of grooved corrugated rollers to form a continuous and uniform wavy pattern. Common types of ridges include A flute, B flute, C flute, E flute, etc. (with different wave heights and densities).
Glue application: Apply a certain amount of starch glue evenly on the top of the formed corrugated roof.
Bonding: The corrugated core paper coated with adhesive is immediately combined with a layer of cardboard (face paper or inner paper) from the original paper rack under pressure rollers, forming a single-sided corrugated cardboard (one side is flat paper and the other side is corrugated).
Double facer machine:
For three-layer boards: Place the corrugated surface of the single-sided corrugated cardboard upwards and attach it to another layer of cardboard (inner paper).
For five or seven layer boards: usually, two layers of single-sided corrugated cardboard (conveyed through a bridge) are combined with the middle box cardboard (intermediate paper) first, and then enter the double-sided machine together for multi-layer bonding.
In the double-sided machine, the paperboard passes through a hot plate (a flat plate heated by steam) and a pressure roller, and the starch adhesive gelatinizes, gelatum and solidifies under hot pressure to achieve firm adhesion. This process also removes some moisture from the cardboard.
Drying and cooling：
The bonded cardboard enters the drying unit (often connected to the hot plate section of the double-sided machine), further evaporating moisture and stabilizing the structure.
Subsequently, the cardboard enters the cooling section and is cooled down through the natural ventilation or a fan to thoroughly solidify the adhesive and restore the flatness of the cardboard.
Vertical and horizontal cutting:
Longitudinal cutting and creasing machine: According to the specification requirements, use a circular knife to cut the wide cardboard into the required width along the direction of travel, and press the crease line at the designated position.
Cross cutting machine (usually computer-controlled): Accurately cut continuous cardboard to a set length.
Stacking and packaging:
The cut single cardboard is automatically stacked into stacks, tied by a strapping machine, and then sent to a cardboard processing plant for subsequent printing, die-cutting, slotting, nailing, or bonding processes.

3、 Main types and layers of flutes
Single corrugated (three layers): surface paper+one layer of corrugated+inner paper. Common types of corrugations include B-corrugations (fine and adaptable to printing), C-corrugations (pressure balanced), and E-corrugations (fine corrugations with delicate texture).
Double corrugated (five layers): surface paper+one layer of corrugated+intermediate paper+another layer of corrugated+inner paper. Common combinations such as BC ribs, BE ribs, etc. can take into account the characteristics of different rib types (such as the flatness of B ribs and the buffering of C ribs).
Three corrugated (seven layers): used for heavy-duty packaging that requires extremely high strength.

4、 Basic principles
The core of corrugated structure is an engineering design: flat core paper is pressed into continuous arched waves, which can disperse the vertical pressure into the plane stress of the cardboard, they will improving the edge compression strength and cushioning performance of the cardboard, while maintaining the lightweight of the material.

In brief, corrugated cardboard production is an efficient and continuous automated process that transforms ordinary roll paper into packaging materials with excellent mechanical properties through heating, forming, gluing, pressing, and drying curing.