BOPP (Biaxially Oriented Polypropylene) is the most widely used film for self-adhesive labels in India. It is dimensionally stable, moisture resistant, and takes print well. But BOPP is also a low surface energy substrate, which makes adhesive selection and coating critical.
Why BOPP is Challenging
BOPP has a surface energy of approximately 30–36 mN/m in its untreated state. Most adhesives need adequate wetting of the substrate to bond properly — and low surface energy makes this harder. Corona treatment raises BOPP surface energy to 38–44 mN/m, but this decays over time. Adhesive coat weight, viscosity, and rheology all need to be matched to the specific BOPP film and coating line speed.
What to Look for in a BOPP PSA
For BOPP label stock, you need: good anchorage to the film (no delamination under peel), sufficient tack for automatic label application, and clean die-cutting without adhesive ooze. WB-3400, our dedicated BOPP grade, is formulated for high-speed coating lines at 50–150 m/min with minimal foaming and stable viscosity. For line speeds above 80 m/min, see our guide to high-speed BOPP coating.
Common Coating Problems and Causes
| Problem | Likely Cause | Fix |
|---|---|---|
| Edge lifting after die cutting | Insufficient adhesive anchorage or incorrect coat weight | Check corona treatment level, increase coat weight |
| Adhesive ooze at die-cut edges | Adhesive too soft or coat weight too high | Reduce coat weight or switch to harder grade |
| Uneven coat weight (chatter marks) | Metering rod pressure or viscosity drift | Check rod pressure, measure viscosity each run |
| Ghosting on clear BOPP | Adhesive too aggressive | Reduce coat weight or use lower tack grade |
| Foaming during coating | Air introduction in adhesive tank | Add defoamer 0.1–0.3%, check pump speed |
Coat Weight Recommendations
| Application | Coat Weight (gsm) |
|---|---|
| Standard paper labels | 18–22 |
| BOPP film labels | 20–25 |
| Aggressive permanent applications | 22–28 |
These are starting points — always run trials on your specific substrate and liner combination.
Request a WB-3400 Sample
Dedicated BOPP PSA emulsion for high-speed coating lines. Full TDS and coating recommendations included.