Sizing Female Matrix Channels for Uncoated Folding Boxboard Grades
Uncoated folding boxboard requires matrix channel width equal to creasing rule thickness plus 1.8 times caliper to prevent top liner cracking during folding.
Uncoated Folding Boxboard
Substrate Grade
Multi-ply paperboard grades composed of mechanical pulp cores sandwiched between chemical pulp outer layers provide structural rigidity without synthetic surface coatings. The natural surface of uncoated folding boxboard offers high bulk and stiffness while allowing direct ink absorption into exposed top fibers. This grade designation applies to virgin fibre cartonboard structures lacking pigment coating layers, distinguishing it from coated folding boxboard and solid bleached board.
Fiber Architecture
Mechanical pulp layers inside the core create maximum caliper and bending resistance at minimal sheet weight. Bleached chemical pulp on outer surfaces provides tearing strength and clean creasing properties without surface cracking. Uncoated top layers absorb liquid inks and adhesives rapidly, accelerating drying times on sheet-fed offset presses while requiring higher ink film weights to achieve deep color saturation.
Absorbent surface fibres render the sheet susceptible to moisture fluctuations, which alters board stiffness and causes flat panel warping in high humidity environments. Converters choose this grade for rustic aesthetic designs and eco-friendly packaging applications where mineral coating pigments are undesirable.
Surface Boundary
Absence of pigment coating limits optical smoothness and fine-screen halftone print resolution. Surface strength limits must prevent linting or fibre picking under high tack printing inks. High moisture vapor transmission prevents use in moisture-barrier packaging without secondary lining materials.