In-Vacuum Flexo Top-Coating on Metallized Film: An Update on the State of the Art

Introduction

Celplast has presented at multiple AIMCAL conferences on its patented single-pass in-line metallizing and top-coating technology. The process applies flexo coating immediately after metallizing within a vacuum chamber, followed by E-beam curing in one pass. This approach locks in the metallized layer's barrier properties while minimizing coating defects.

The process achieves a Barrier Improvement Factor (BIF) of 6–8x over typical metallized substrates. Laminations made with this top-coated metallized PET film demonstrate equivalent or superior performance compared to the highest barrier metallized PET currently available.

Objectives

The study evaluates:

• Performance of 3-ply structures containing top-coated metallized films in retort packaging applications
• Bond strength and barrier properties of 3-ply structures with different adhesive systems
• Commercial viability of scaling the process to production speeds and widths

Experimental – Retort Study

Two alternatives to standard 4-ply retort structures were tested:

• Structure with top-coated metallized OPA film
• Structure with top-coated metallized PET film

Both aimed to replace two layers (foil and OPA) with a single top-coated metallized layer.

Adhesive Application: Henkel Loctite Liofol LA3649:LA6055 system at 3.4 g/m² dry weight was applied at the Henkel Research Center in Cary, NC.

Bond Strength Results:

• Uncoated film to CPP: >10 N/25 mm (stock split failure)
• PET/top-coat (OPA structure): 0.5 N/25 mm (delamination at metal-to-OPA surface)
• PET/top-coat (PET structure): 8.1 N/25 mm (clear PET stock split)

Retort Performance: Four-sided pouches filled with de-ionized water were subjected to 121°C for 60 minutes with water spray cooling.

Results showed:

• OPA-based structure: metallized layer disappeared; OPA/CPP delaminated from clear PET
• PET-based structure: metal layer remained intact; no noticeable shrinkage or delamination

The top-coated metallized PET structure proved suitable for retort applications.

Experimental – Lamination Study

Two new 3-ply structures were evaluated:

1. Clear PET / top-coated metallized PET / CPP sealant
2. Clear PET / top-coated metallized PET / LDPE sealant

Adhesive System: COIM Novacote NC 825A : CA 26 at ~3 g/m² dry weight, applied at Fraunhofer IVV in Freising, Germany.

Testing: After 5-day cure at 50°C, 90° peel tests and barrier testing were conducted. Oxygen transmission rate (OTR) was measured at 23°C/50% RH; water vapor transmission rate (WVTR) at 37.8°C/90% RH.

Performance Summary:

The 3-ply metallized PET-based structures showed slightly lower barrier and bond strength compared to 4-ply foil-based laminates, yet "for the purposes of the vast majority of food packaging applications, including hot-fill, retort and other high barrier applications, these structures are very capable."

Direct Food Contact Evaluation

The EB-cured top-coat contains no photoinitiators or substances of concern. High-vacuum curing conditions evaporate residual volatile species in situ, resulting in extremely clean chemical migration profiles.

Migration testing revealed "literally no detectable species attributed to the coating during migration studies at a 10 or 20 ppb detection limits" using 95% ethanol extraction at 40°C for 10 days (FDA Condition of Use E). Testing has been repeated numerous times at accredited laboratories across various processing windows.

Scale-Up

Previously, production occurred solely on a pilot line in Toronto at 2 m/s and 1320 mm width—insufficient for large-volume food packaging.

Scale-up objectives:

• Production speed: 6 m/s
• Maximum width: 2450 mm

The company acknowledged technical challenges but remained confident in eventual success. Celplast will soon commission "the first ever commercial scale machine with these capabilities."

Conclusion

What began as a concept has matured into a commercially viable technology. The in-vacuum flexo top-coated metallized film demonstrates:

• Proven barrier and lamination bond properties across multiple adhesive systems
• Suitability for demanding applications like retort packaging
• Clean chemical migration profiles appropriate for direct food contact
• Commercially viable production at scale

The expanded production capacity positions this product for adoption across flexible packaging applications.