Paperboard - Common Terms

Common Terms

Basis Weight (US): Is the weight 1,000 square feet (93 m2) of paperboard.

Brightness: Brightness is a technical term that is defined as the amount of blue-white light that a paper reflects. This property is very subjective and individual to each buyer and end use, as skin colour and food are better reproduced on ‘warm’ (yellow) whites and not blue whites.

Grammage: The grammage of the paperboard is assessed in accordance ISO 536. Grammage expresses weight per unit area and is measured in g/m2.

PH: Surface pH is measured on a water extract and is on a scale of 0-14, 0 being acidic, 7 neutral and 14 alkaline.

Stiffness: Stiffness is one of the most important properties of paperboard as it affects the ability of cartons to run smoothly through the machine that erects, fills and closes them. Stiffness also gives strength and reduces the propensity of a carton to bulge under the weight of settling flowable contents such as cereals.

Although most paper strength properties increase with increasing sheet density, stifness does not. A rule of thumb is that stiffness is proportional to the 1.6 power of sheet caliper.

The species of fiber used has an effect on stiffness, other things being equal. Northern softwood species impart superior stiffness sompared to southern softwoods.

Other factors which affect board stiffness include coatings and moisture content.

Smoothness: Smoothness is particularly important when being used for printing, the smoother the paperboard, the better the image quality, because of better ink coverage. Smoothness is measured using air leak methods – the greater the rate of air leakage, at a specific air pressure, from under a cylindrical knife placed on the surface, the rougher the surface.

Caliper/Thickness: In the United States caliper is usually expressed in thousandths of an inch (0.001”) or points, where a sheet of paperboard with a thickness of 0.024” would be 24 points. In Europe it is often sold in g/m2, however the thickness of the board is measured in micron(μm) (1μm = 0.001mm) (also referred to as a micrometre)

Paperboard also tends to be referred to with thickness rather than weight.

Whiteness: It refers ideally to the equal presence of all colours, because a truly white sheet will reflect all wavelengths of visible light equally.