How to Fix Wash Boarding Defects in Corrugated Board

Wash boarding—also called corrugator shadow or flute show-through—occurs when the flute pattern becomes visible on the outer liner surface. This defect affects print quality and product appearance.

What Causes Wash Boarding:

1. Excessive Adhesive Application:

Too much adhesive creates wet spots that swell the liner unevenly over the flute tips, causing the pattern to show through.

2. Excessive Pressure:

Over-pressure at the double backer crushes the board, making flute tips more visible.

3. Moisture Imbalance:

When the liner has different moisture content than the medium, it can shrink or expand unevenly.

4. Thin or Low-Quality Liner:

Lightweight liners show flute patterns more readily than heavier papers.

5. High Hot Plate Temperature:

Excessive heat can cause rapid, uneven drying that accentuates the flute pattern.

Solutions and Adjustments:

Adhesive Optimization:

• Reduce glue application weight

• Ensure uniform glue film across the web

• Check doctor roll gaps and condition

• Use instant-setting adhesive to minimize moisture penetration

Process Adjustments:

• Reduce double backer pressure

• Lower hot plate temperature gradually

• Balance moisture between liner and medium

• Check and adjust wrap angles

Paper Selection:

• Use heavier liner basis weights

• Choose papers with good opacity

• Consider surface-treated liners for critical applications

Quality Verification:

Inspect board at multiple points along the web to identify where the defect originates. This helps target corrective actions effectively.