Coating Board Production: Pulp Preparation and Sheet Formation Essentials
Coating Board Production: Pulp Preparation and Sheet Formation
Coating board — used for premium packaging, graphical displays, and consumer goods — combines a multi-ply substrate with pigmented coating layers. The quality of the base board directly determines coating holdout, surface smoothness, and final printability. Stock preparation for coating board focuses on producing clean, well-refined fiber fractions across multiple furnish layers.
Multi-Ply Pulp Preparation
Coating board typically uses 3–5 plies with different fiber compositions: a top liner of bleached chemical pulp for brightness, middle plies of mechanical or recycled fiber for bulk, and a back liner of unbleached or recycled fiber. Each ply requires dedicated stock preparation lines. Hydraulic pulpers with 200–400 TPD capacity handle the bulk middle-ply recycled fiber, while smaller 50–150 TPD pulpers prepare the premium top-liner pulp.
Screening Requirements by Ply
Top liner stock passes through 0.10–0.15 mm slotted pressure screens to eliminate all visible contaminants. Middle plies can tolerate 0.20–0.30 mm slots, trading slightly lower cleanliness for higher yield. Reject thickening screens recover fiber from the tailings stream, reducing overall fiber loss to below 3%. Multi-stage screening with intermediate consistency regulation ensures stable operation across furnish variations.
Refining Strategy for Multi-Ply Board
The top liner undergoes intensive refining at 100–150 kWh/ton to develop surface smoothness and coating holdout. Middle plies receive lighter refining at 40–70 kWh/ton to maintain bulk and stiffness. Double disc refiners with independent motor control (132–400 kW per unit) allow precise energy input per ply. Disc diameter selection (660–910 mm) depends on throughput and specific energy targets.
Forming and Press Section
Multi-fourdrinier or cylinder mould formers build up the board layer by layer, with individual plies at 20–80 g/m² each. Starch spray or size press application between plies ensures adequate inter-ply bonding. Press sections achieve 46–50% dryness before coating, critical for coating color absorption uniformity. Board caliper ranges from 200–600 µm at 300–600 m/min machine speeds.
Coating Kitchen Integration
While coating formulation is separate from stock preparation, base stock properties directly affect coating performance. Smoothness (Bendtsen < 300 ml/min) and porosity (Gurley > 100 s) targets must be met through proper refining and wet pressing. On-machine measurement systems provide real-time feedback to stock preparation adjustments.
Operational Efficiency Data
A 3-ply coating board line producing 400 TPD consumes approximately 420–520 kWh/ton total energy. Steam consumption in the dryer section ranges from 1.6–1.9 tons per ton of board. Optimized refining with VFD-controlled disc refiners reduces specific energy by 15–18% compared to fixed-speed operation. Disc savealls recover 96%+ of fiber from white water, returning it to the appropriate ply system.
Maintenance Schedule
Top liner pressure screen baskets (0.10–0.15 mm slots) need inspection every 6 weeks due to tighter tolerances. Middle ply screens at 8–10 weeks. Refiner plate changes: top liner plates every 800–1000 hours, middle ply plates every 1200–1500 hours. Cylinder mould wire replacement at 12–18 month intervals depending on abrasion from filler content. Forming fabric life is 45–90 days for top wire positions.
For technical specifications and project proposals on coating board production equipment, contact Leizhan Technology at leizhanzhang@gmail.com.