Multi-Layer Coating Board Machine Technology: Achieving Superior Surface Quality and Bulk

Introduction to Multi-Layer Coating Board Production

Modern packaging demands for premium graphics and structural integrity have driven the widespread adoption of multi-layer forming technology in coating board production. A typical 4-layer board machine produces base sheets with basis weights of 200-450 gsm, combining a top layer of bleached chemical pulp for print surface quality, an under-top layer of mechanical or deinked pulp, a middle layer of OCC or mixed waste for bulk and stiffness, and a back layer of selected recycled fiber for balanced curl characteristics.

Headbox Technology for Multi-Layer Forming

The heart of multi-layer board production lies in the headbox configuration. Modern multi-layer headboxes with dilution profile control deliver precise cross-machine basis weight profiles with 2-sigma variation below 1.5%. Key specifications:

• Number of layers: 3-5 independent channels with individual stock supply systems
• Slice opening: 6-12mm, hydraulically adjustable with 0.01mm precision
• Consistency per layer: 0.3-0.8% for top layer, 0.5-1.2% for middle layers
• Jet-to-wire ratio: 0.97-1.03, adjustable per layer for optimal formation
• Dilution control zones: 50-60mm spacing for precise CD profile management

Forming Section Design Parameters

The forming section configuration varies by board grade and production speed. For coating board at 300-500 m/min, a hybrid former with a fourdrinier base and top wire dewatering unit provides excellent formation and plybond strength. Critical operating parameters include:

• Wire width: 3200-4800mm depending on deckle requirements
• Forming length: 12-18 meters for adequate dewatering time
• Dewatering elements: Hydrofoil blades with 0.5-3.0 degree attack angles gradually increasing
• Vacuum levels: Low-vacuum boxes at 2-5 kPa, high-vacuum at 15-25 kPa, couch roll at 40-60 kPa
• Top wire unit: Inverted suction box system for gentle top-side dewatering

Press Section and Drying Optimization

The press section heavily influences board density, surface smoothness, and energy consumption. A triple-nip press configuration (suction pickup, double-felted first press, and shoe press) achieves 48-52% dry content before the dryer section, reducing steam consumption by approximately 15% compared to roll-press-only configurations. Shoe press technology with 800-1200 kN/m linear load and extended nip length of 200-250mm provides superior bulk preservation while achieving high post-press dryness. Steam consumption for the complete dryer section typically ranges from 1.5-1.8 tons of steam per ton of board at 300-350 gsm.

Coating Section Capabilities

Coating technology determines the final printability and visual appeal of the board. Modern coating lines for premium packaging board feature:

• Pre-coating station: Blade coater applying 8-12 gsm of pigment coating
• Top coating station: Air knife or curtain coater for 6-8 gsm of final coat
• Coating solids: 62-68% for blade application, 55-60% for curtain coating
• IR drying and air flotation drying: Non-contact drying preserves coating uniformity
• Supercalendering: 2-4 nips at 150-250 kN/m and 100-140 degrees C surface temperature

Consultation

Multi-layer coating board production demands integrated engineering across forming, pressing, drying, and coating sections. Zhengzhou Leizhan Technology provides turnkey solutions for coating board lines from 100 to 500 TPD. Contact the engineering team for a customized technical proposal.

leizhanzhang@gmail.com | www.pulprefining.com