Published: 2026-10-16 · Category: Process
Unimpregnated paper is weak, deforms when wet and will not hold a pleat. Impregnation creates bonds between fibres so the sheet gains stiffness, strength and resistance to water and heat while keeping its pore structure. The step is invisible in the finished element, but it decides whether the element reaches its design life.
What impregnation delivers
- Stiffness: pleat shape retention - no crushing, even pleat spacing;
- Strength: higher tensile and burst values, fewer crease cracks;
- Water resistance: less strength loss after moisture uptake;
- Heat resistance: structural stability in hot oil or hot air.
Resin content is a band, not a maximum
More resin means more stiffness and strength, but also less open area, lower permeability and greater brittleness. At the high end the sheet cracks when pleated or creases, and elements can fracture under pressure pulses. Production therefore holds resin content inside a band rather than pushing to the top of the range.
Cure level matters just as much
After impregnation the sheet must be dried and cured so the resin cross-links to the right degree. Under-cured paper is soft and tacky, misses its stiffness target and may bleed in service. Over-cured paper is brittle and cracks. The window depends on the resin system and on the temperature profile, dwell time and airflow - and it has to stay stable batch to batch.
Control points seen in production
| Control point | Symptom when it drifts |
|---|---|
| Resin concentration and pick-up | Resin content varies; stiffness comes and goes |
| Drying temperature and line speed | Under-cure (soft) or over-cure (brittle) |
| Web moisture before impregnation | Uneven resin uptake, hard and soft patches |
| Ambient humidity | Incomplete cure and performance decay in storage |