Mechanical Pulp Distribution in Folding Boxboard Core Layers
Core layer mechanical pulp distribution controls folding boxboard bulk and bending stiffness, enabling weight reduction while preserving box structural integrity.
PGW
Pressure Grade Weight
Grammage measures the mass of paper or paperboard per unit area, typically expressed in grams per square meter. The pgw designation identifies a specific subset of newsprint and mechanical papers produced using stone groundwood pulp. This material relies on the physical abrasion of logs against a rotating stone to separate fibres, resulting in high bulk and opacity at the cost of lower mechanical strength.
Manufacturers select this stock for high volume printing where cost efficiency outweighs the requirement for long term archival stability or high surface gloss.
Production Consistency
Converting equipment sets the tension and draw speed according to the basis weight of the incoming web. A pgw stock exhibits distinct elasticity compared to chemical pulps, requiring precise control over the dryer section temperatures during the papermaking process. Variations in density across the roll width cause uneven ink absorption, creating visual mottling during the offset printing cycle.
Converting lines manage these properties by calibrating the nip pressure on calendar rolls to flatten the surface without crushing the fibre structure.
Structural Performance
Fibres sourced from mechanical grinding retain lignin, which contributes to a stiff and resilient sheet profile. The pgw composition supports the high speed mechanical demands of web fed presses by providing sufficient internal bonding to withstand rapid acceleration and stop sequences. Moisture levels within the sheet dictate the final print quality, as these fibres swell and contract significantly when exposed to the dampening solutions used in lithographic processes.
Final sheets deliver the opacity required for double sided printing without excessive show through.