"Whitening" — the milky, cloudy haze that appears on film-covered doors after membrane pressing — is the most common quality complaint we hear from new buyers. In almost every case it is a processing issue, not a film defect. Here are the seven settings our technical team tunes first.
1. Temperature curve, not a single setpoint
A sudden high heat shocks the film and traps moisture, which shows as white bloom. Use a ramped curve: pre-heat the silicone membrane, then ramp to working temperature gradually. For PVC we typically land at 110–130°C depending on thickness; PET runs hotter and needs tighter control.
2. Vacuum level & timing
Insufficient vacuum leaves micro-gaps that whiten under stress. Hold a steady vacuum (typically −0.6 to −0.9 bar) and let it fully seat the film into profiles before applying pressure. A slow, even pull is better than a hard, fast suck.
Membrane press with silicone membrane seating film into a profiled door
3. Dwell time
Too short and the adhesive is not fully activated; too long and the film over-softens. Find the minimum dwell that gives a clean edge fold — usually 30–60 seconds at temperature for standard MDF doors.
4. Glue activation
Whitening is often a glue problem. Ensure your PU or EVAC glue is fully cured-ready and applied at the right grammage. Under-glued edges lift and whiten; over-glued seams bleed. We supply a matched primer per substrate to stabilise this.
5. Pressure & membrane condition
A worn or punctured silicone membrane presses unevenly, leaving thin spots that haze. Inspect the membrane weekly and keep uniform pressure across the platen. Replace at the first sign of thinning.
6. Cooling under pressure
Releasing the door while it is still hot lets it relax and whiten at the edges. Cool to below 40°C under light pressure before demoulding for a stable, clear finish.
7. Film relaxation & storage
Cold film from storage presses poorly. Condition film to workshop temperature (20–25°C) for 24h before use, and keep it flat and dry. Moisture-laden film is the silent cause of bloom.
Need a press-parameter sheet?
Every BESUN film grade ships with a recommended processing window (temperature, vacuum, dwell, glue). If you are fighting whitening on a specific profile, send us the board, film thickness and press model — our engineers will return a tuned parameter sheet.
Sample parameter sheet / cured door cross-section