Tips for Trimming the PVB Interlayer
To maximize laminating line productivity and protect critical equipment, proper PVB trimming techniques must be followed. Improper trimming can result in damage to the oven emitters, press rollers, and conveyor rollers within the heat and press sections. In addition, poor trimming can cause production delays and negatively impact the quality of the finished laminates.
Leaving Too Little Interlayer
Leaving too little PVB interlayer can cause a condition called “snap back,” where the interlayer edge shrinks behind the glass edge. When this occurs, the laminate may not seal properly, allowing air to seep between the glass and the interlayer during autoclaving.
Common results include:
- Air bubbles along the glass edge
- Poor bonding between the glass and the interlayer
- Improper edge sealing
- Rejection of the laminate after autoclaving
Leaving Too Much Interlayer
Leaving excessive PVB beyond the glass edge will cause the interlayer to melt in the laminating ovens. Melted PVB can drip onto heating elements, conveyor rolls, and press rolls, leading to serious and costly equipment issues, reduced production, and compromised laminate quality.
Examples of Problems Caused by PVB Drips
- PVB Dripping onto Heating Elements – Melted PVB causes uneven heating and eventually requires costly and time-consuming cleaning or replacement of the heating elements.
- PVB Dripping onto the Conveyor Rolls – PVB buildup on the conveyor rolls can transfer to the glass surfaces as the glass passes over the rollers. This requires operators at the unload end of the line to scrape and clean marks off the glass before autoclaving. The line may need to be stopped to remove hardened PVB from the rollers.
- PVB Tracking on Press Rolls – When PVB contaminates the press rolls, the resulting marks become compressed into the glass surface and are more difficult to remove. Cleaning press rolls is labor-intensive and can be hazardous if proper safety procedures are not followed.
Recommended PVB Overhang
A common industry rule of thumb is to leave no more than 5 mm (0.197 in) of PVB extending beyond the glass edge after trimming. It is best to consult with your PVB interlayer supplier for their specific recommendations, as interlayer formulations may vary.
If you have any questions, please contact Billco Service at 724.452.7390 or service@billco-mfg.com.
