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Boxboard Definitions

Definitions for Boxboard

Basis Weight – A measure of the weight of boxboard in a given area. The greater the basis weight the stronger the boxboard. This is expressed either as grams per square meter (metric) or pounds per one thousand square feet (imperial).

Caliper – A measure of boxboard thickness. It is expressed as microns (metric) or points (imperial).

Density – A measure of the basis weight per single caliper unit. During printing, higher density boxboard will have improved color-to-color register as the sheet does not stretch when passing through press nip points. It may also permit the use of a more cost-effective lower caliper boxboard.

Machine Direction (MD) Stiffness – A measure of the force required to bend the sheet in the same orientation as the paper machine flow. MD stiffness is an important indicator of boxboard strength as it provides increased boxboard rigidity and fill line speeds for many manufacturers. It is expressed as milliNewton meters (metric) or Taber units (imperial).

Cross Direction (CD) Stiffness – A measure of the force required to bend the sheet in the cross direction orientation of the paper machine flow. When fed grain long during printing, a lower CD stiffness is advantageous. The sheets will contour around the cylinder, resulting in less scuffing and marking on the trailing edge of the sheet. In addition faster press speeds can be achieved. Expressed as milliNewton meters (metric) or Taber units (imperial).

MD/CD Ratio – A composite measure of boxboard performance based on strength characteristics. The higher the ratio, the better the on press and fill line performance of the board.

Smoothness – A measure of the surface smoothness characteristics of the boxboard expressed as micrometers. A lower result indicates a smoother sheet. A smoother sheet surface provides for enhanced colour laydown and improved press printing efficiency.

Brightness – A measure of the light reflected from the clay surface of the boxboard. The higher the brightness measurement, the more vibrant and precise the colour reproduction will be.

Plybond – A measure of the internal bond strength of the individual plies of boxboard. A higher result indicates higher strength. High plybond strength will ensure that the boxboard will not come apart during converting and will also help to ensure that the finished carton maintains its integrity throughout the supply chain. Expressed as kilograms per square centimetre (metric) or pounds per square inch (imperial).
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