Fiber Distribution
Optimizing the strength and smoothness of paperboard requires separating the raw pulp into distinct fiber length streams before papermaking. Using fractionated furnish allows mills to allocate long kraft fibers to the outer plies for high stiffness and short hardwood fibers to the inner plies for bulk. This spatial distribution reduces the total consumption of expensive virgin fiber while keeping sheet properties high.
Furnish Formulation
Pressure screens with specialized slotted plates divide the incoming pulp slurry into accept and reject streams. The accept stream contains mostly short, fine fibers that provide excellent printability, while the reject stream retains the long, flexible fibers that give the sheet its tear resistance. By recombining these fractions in precise ratios, papermakers can tailor the board to match the specific requirements of folding carton converters.
This selective blending avoids the over-refining of fibers, which can otherwise weaken the paper sheet.
Structural Performance
Multi-ply board machines deposit these different streams through separate headboxes to build a layered structure. The long-fiber fraction provides the bending stiffness needed for heavy detergent boxes or beverage carriers, while the short-fiber fraction provides the flat printing surface needed for high-fidelity graphics. This division maintains structural integrity while reducing the overall weight of the package.
