Strength Index and Test Methods of Corrugated Paper

Corrugated paper is widely used to make packaging products like cartons and so on.  Since its quality and strength has significant influence on the quality of the carton boxes themselves, the corrugated paperboard should be closely monitored since its acceptance in the factory. And the requirements on its quality and strength is restricted by the productions techniques and operations, but also guided by its application purpose. In this case, it is quite important to monitor the strength index of the corrugated paper during printing and manufacturing, which is of great significance to ensure the quality and performance of boxes.

There are several indexes and methods to test its strength. Before strength testing, sampling should be done which has to represent the performance of the whole shift of the corrugated paperboards and has to be as few as possible. Generally speaking, 3% ~ 5% sampling should be selected according to different production scale or situations.

a. Ring crush strength of the paperboard is an important index for corrugated paper strength. However, it is not quite easy to measure the compressive strength of its base paper or paperboard along the width direction, because of its small thickness which makes it difficult to apply pressure on a flat paper along the direction while maintaining  It is difficult to measure the compressive strength of base paper or paperboard along the width direction (perpendicular to the thickness of the paper). Because the thickness of paper or paperboard is very small, it is difficult to apply pressure on a flat paper along the direction perpendicular to its thickness, while maintaining the shape stability of the base paper or paperboard. The ring crush pressure is generated by enclosing the base paper or paperboard into ring shape. In this way, the measurement can be carried out on a tiny pressure testing tool.

b. Flat compressive strength of corrugated core is another index for corrugated paper strength. The corrugated core is to keep a certain thickness of the board when the corrugated board is compressed and deformed, so that a larger moment of inertia could be obtained. The corrugated paper core should be able to bear the pressure, and form uniform equal height corrugation at high speed, and firmly fit with the surface paper. The performance of corrugated core can be measured by the flat compression strength of corrugated core. The determination of flat compression strength of corrugated core is that the corrugated base paper is first pressed into a certain shape of corrugated by groove tester under certain temperature and pressure. Then, the bearing capacity is measured by flat compression test on a small testing machine and represented by KN (KGF).