Calculating Female Cavity Depth and Counter Clearance from Measured Paperboard Bulk
Female cavity depth equal to compressed bulk caliper and counter clearance matching substrate compressed thickness prevent fiber shear during embossing.
Solid Density
Material Compactness
Mass per unit volume of the solid phase of paperboard, excluding the air voids within the fibrous network, represents the theoretical upper limit of sheet compaction. The solid density of cellulose fibres remains relatively constant at approximately one point five grams per cubic centimetre. It serves as the baseline against which the bulk and porosity of various paper grades are calculated.
This property determines how much of the board’s volume consists of empty pore space.
Porosity Correlation
Calendering processes alter the overall sheet density but do not affect the internal solid density of the raw fibres themselves. Instead, the pressure compresses the pore structure, reducing the bulk and increasing the apparent density of the sheet. This changes the optical and absorbent qualities of the paper surface.
Highly calendered sheets have less void volume, which limits the absorption of printing inks and varnishes. Understanding this relationship helps mills design boards that achieve the required smoothness without using excess raw material.
Stiffness Tradeoff
High apparent density reduces the bending stiffness of the board for a given basis weight. Protective packaging designs rely on lower apparent density to maximize stiffness. The solid density determines the minimum possible weight for any solid structure.