Building or upgrading a coating board production line involves coordination across multiple sub-systems — from pulping to coating. Each section must be sized and configured not in isolation, but as part of an integrated whole where upstream decisions cascade into downstream performance. This guide covers the major equipment categories that make up a modern coating board line.

Overall Line Architecture for Coating Board

A typical coating board production line producing 150–500 tonnes per day consists of these major sections:

1. Stock preparation system (one line per ply, or shared with fractionation)
2. Multi-ply wet end (multiple headboxes and forming sections)
3. Press section (shoe press or conventional roll press)
4. Pre-drying section (multi-cylinder)
5. Surface sizing or pre-coating station
6. Coating section (1–3 coating heads)
7. Post-drying and calendering
8. Reel and winder

Section 1: Multi-Ply Wet End Configuration

Coating board is almost always produced as a multi-ply sheet — typically 3 to 5 plies. The wet end must handle multiple furnish streams simultaneously:

• Top liner headbox: Hydraulic headbox with dilution profiling for CD basis weight control. Slice opening typically 4–8 mm, jet-to-wire ratio 0.98–1.02 for optimal formation
• Filler/middle ply headboxes: Air-padded or hydraulic, with wider slice openings (6–12 mm) since formation requirements are less stringent
• Back liner headbox: Same precision as top liner if board is two-side coated
• Forming section: Gap former or hybrid former for top ply; Fourdrinier or mini-Fourdrinier for middle plies. Wire mesh: 60–70 mesh for top liner, 40–50 mesh for filler

Section 2: Press Section — Dewatering and Ply Bonding

The press section serves dual purposes in coating board: dewatering and ply bonding. Key configurations:

• Shoe press: For grades above 250 g/m², a shoe press with nip width 150–250 mm achieves 48–55% solids leaving the press. This directly reduces steam consumption in drying by 15–25% compared to roll presses
• Double-felted first press: Optimizes water removal from both sides simultaneously, reducing two-sidedness
• Ply bonding: Nip pressure of 80–120 kN/m in the press ensures adequate internal bond strength for subsequent coating operations

Section 3: Drying Strategy — Managing Moisture for Coating

The moisture profile entering the coating section is critical. The target is typically 4–7% moisture content:

• Pre-dryer section: 30–45 drying cylinders, surface temperature gradually increasing from 60°C (first cylinders) to 130°C (last cylinders)
• Pocket ventilation: Maintains air temperature at 90–110°C and humidity at 0.18–0.25 kg H₂O/kg dry air for uniform CD moisture profile
• Moisture variation at coater inlet: Should be <1.5% across the web width — achieved through proper condensate removal and pocket ventilation

Section 4: Surface Sizing / Pre-Coating

Before the main coating application, most lines include a surface sizing or pre-coating station:

• Film press or size press: Applies starch solution (6–12% solids) at 1.0–2.5 g/m² dry pickup. This seals the surface, reduces porosity, and prevents excessive coating penetration
• Pre-coating: For high-quality grades, a bent blade or roll applicator coater applies a low-cost base coat (pigment + binder) at 8–15 g/m² per side to fill surface voids

Section 5: Coating Section — The Value-Adding Heart

Coating board lines typically use blade, curtain, or air-knife coating. Modern lines favor blade coating for its superior coverage and surface quality:

• Coating heads: 1–3 stations per side, each applying 8–15 g/m² (dry) per layer
• Coating color solids: 58–68% for blade coating; viscosity 800–1,500 cP (Brookfield, 100 rpm)
• Drying between coats: IR dryers (2–5 seconds dwell) followed by air flotation dryers (5–15 seconds) prevent binder migration and ensure layer adhesion
• Blade angle: 15–35° (bent blade) or 0–5° (stiff blade) depending on coat weight target

Section 6: Post-Coating Finishing

• Calendering: Soft-nip or multi-nip calenders at 80–160 kN/m line load and 100–160°C roll surface temperature achieve target smoothness (Bendtsen <50 mL/min after coating)
• Moisture control: After calendering, re-moisturizing system brings final moisture to 6–8% to prevent curl
• Reel and winder: Center-wind drums with tension control at 200–400 N/m prevent interlayer slip and maintain roll hardness uniformity

Integration: Why Equipment Sizing Must Be Holistic

A common mistake in coating board line design is sizing each section independently. The stock preparation capacity must match the paper machine’s maximum production rate plus 10–15% headroom. The drying section must be designed for the heaviest grade and highest speed combination. The coating section’s drying capacity determines the maximum coat weight and machine speed for premium grades.

Our engineering team can assist with complete line equipment specification, from pulper extraction plate sizing to dryer cylinder count and coating station configuration — ensuring every sub-system works in balance.

📧 Contact us at leizhanzhang@gmail.com for coating board production line equipment specifications.