Multi-Layer Forming Technology: Achieving Uniform Coating Board Quality
Coating board production requires precise control across multiple layers, each with distinct fiber compositions and formation requirements. Multi-layer forming technology has evolved to deliver superior plybond strength, surface smoothness, and coating holdout while optimizing raw material costs.
Layer Composition and Fiber Selection
The top layer, typically 15-25% of total basis weight, uses high-brightness bleached kraft pulp at 25-35 SR freeness. The filler layer, representing 55-65% of total weight, incorporates lower-cost recycled fiber or mechanical pulp. The back layer uses unbleached or low-grade recycled fiber. This stratified approach reduces raw material costs by 20-30% compared to homogeneous board of equivalent surface quality.
Forming Section: Multi-Ply Headbox Technology
Modern multi-ply headboxes with individual slice lip controls per layer achieve basis weight uniformity within 1.5% across the machine width. Each layer jet is deposited at 0.5-0.8% consistency with independent jet-to-wire ratio control. For coating board grades at 200-450 gsm, the forming section typically operates at 350-800 m/min depending on basis weight and machine configuration.
Coating Application: Blade and Air Knife Systems
Pre-coating at 8-12 gsm with a bent blade coater seals the base sheet surface. The top coating at 12-18 gsm uses an air knife or soft blade coater for uniform coverage. Coating solids of 58-65% minimize drying energy while maintaining rheological properties suitable for uniform application.
Quality Control Parameters
Finished coating board targets: surface smoothness below 1.2 microns PPS, gloss at 65-80% at 75 degree angle, and plybond strength above 150 J/m2 Scott Bond. Internal sizing with AKD or ASA at 0.10-0.15% dosage provides edge wick resistance below 2 mm for packaging applications.
Zhengzhou Leizhan Technology offers complete coating board production lines including stock preparation, multi-layer forming, coating stations, and finishing equipment. Turnkey solutions from 100 to 600 TPD capacity.