Cold foil on BOPP labels — press setup & adhesion

Why BOPP is different from paper for cold foil

BOPP (biaxially oriented polypropylene) has a native surface energy of 30–32 dyne/cm — too low for adhesive wetting. Paper stocks sit at 40–50 dyne/cm and accept free-radical acrylate cold foil adhesive directly. BOPP labels need three things paper does not: corona (or plasma) treatment, cationic adhesive chemistry, and tighter tension control.

• Surface energy: BOPP 30–32 dyne/cm native → 38–44 dyne/cm after inline corona.
• Adhesive: cationic epoxide (dark-cure) preferred over free-radical acrylate.
• Tension: 0.3–0.5 N/mm web width — BOPP stretches at higher tension, causing register drift.
• Static: BOPP builds triboelectric charge; ionising bars needed before the foil nip.

Recommended BOPP face stocks for cold foil

• Avery Dennison Fasson BOPP TC (topcoated clear) — the industry benchmark for cold foil PSL.
• UPM Raflatac PP TC50 — topcoated 50 µm BOPP for wine and craft beer labels.
• Herma 63Xpp / 62Xpp — topcoated BOPP for cosmetics and personal care.
• Face weight: 50–60 µm BOPP is standard; 40 µm requires slower press speeds (< 150 m/min).
• Topcoat: acrylic topcoat is required; untopcoated BOPP fails adhesion tests below 3B.

Step-by-step press setup on UV-flexo narrow-web

• 1. Corona: run the inline corona unit at 1.0–1.5 kW per meter web width; measure dyne with test inks (Sherman ACCU DYNE), target 38–44 dyne/cm.
• 2. Print the cold foil adhesive (e.g. Actega Colorpoint EB) through a 5–6 BCM 700-lpi anilox with a 1.14 mm 60 Sh A flat-top plate at 70 µm impression.
• 3. Nip the cold foil roll (19 µm PET carrier) against the wet adhesive at 150–250 m/min, foil tension 0.3–0.4 N/mm.
• 4. Cure under UV-LED 385 nm at 100–150 mJ/cm² (or UV-Hg 150 mJ/cm² if cationic-LED unavailable).
• 5. Peel the PET carrier at a 45° angle onto a waste rewinder — carrier tension 0.4–0.6 N/mm.
• 6. Allow 24 h dark-cure before die-cutting and matrix stripping; adhesion continues to build during this window.

Downstream converting — die-cut, laminate, overprint

• Die-cut: solid rotary tooling, +5 µm undercut vs paper stocks to avoid pulling foil off the edge.
• Overlaminate: UV or cast-and-cure clear PET/PP overlaminate is compatible after 24 h dark-cure.
• Overprint varnish: UV varnish only; solvent varnishes lift the metallising unless applied after the 24 h dark-cure window.
• Cold foil on BOPP survives autoclave / retort at 121 °C for 30 min when the adhesive is fully cured — verified by ASTM D3359 tape test post-autoclave.