Epoxy vs Polyester Metal Coatings for Can Manufacturing in Pakistan: When to Use Each

Why Coating Selection Is Not Arbitrary

In a modern Pakistani can manufacturing facility, the coating line is where raw metal becomes a functional packaging component. The coatings applied at this stage determine whether the finished can protects its contents for 2+ years on a shelf, whether printing adheres properly, and whether the entire product passes food-safety regulations.

Yet we regularly encounter factories running the wrong coating on the wrong surface — using exterior polyester as an interior lacquer, or applying interior epoxy too thin to provide adequate barrier protection. These mistakes lead to product recalls, failed export inspections, and costly rework.

Interior Coatings: Epoxy-Melamine (HF1625)

The inside surface of any food or beverage can must be coated with a system that creates a chemically inert barrier between the metal and the contents. Our Sewin HF1625 epoxy-melamine system is engineered precisely for this purpose.

The epoxy resin component provides exceptional chemical resistance — it withstands acidic products like tomato paste (pH 3.5–4.5), carbonated beverages, and aggressive cleaning chemicals used in retort processes. The melamine cross-linker enables the coating to fully cure at 200–210°C in 10–12 minutes, forming a dense, impermeable film.

Critical application parameters include dry film thickness of 4–7 g/m² depending on the aggressiveness of the food product, full cure verification via MEK (methyl ethyl ketone) rub test where a minimum of 30 double rubs without breakthrough indicates proper cure, and adhesion testing via cross-hatch method — Grade 0 or 1 is acceptable with Grade 0 being the target.

Exterior Coatings: Polyester (HF1632-1)

The exterior surface has completely different requirements. It needs to accept printing inks, survive the mechanical abuse of can forming and handling, and maintain visual appearance throughout the supply chain. Our Sewin HF1632-1 polyester system is optimized for these demands.

Polyester coatings offer superior flexibility compared to epoxy systems — critical because the exterior coating must stretch during can forming without cracking or delaminating. The coating provides excellent adhesion for both conventional offset inks and UV-curable inks used on modern high-speed printing lines.

White base coatings (HF220, HF2205, HF2206) are a special category within exterior coatings. Applied as the first exterior layer, they provide the opaque white background that makes printed colors appear vibrant and accurate. Without a proper white base, printing directly on the grey metal surface produces dull, washed-out graphics that damage brand perception.

Common Mistakes in Pakistani Factories

The four most common coating errors we encounter in Pakistani can manufacturing operations are as follows. First, using exterior polyester as an interior coating because it appears to work visually — however, polyester lacks the chemical resistance of epoxy and will fail under retort conditions, allowing corrosion and taste contamination. Second, under-curing the interior coating by running the bake oven too fast to increase throughput — this leaves the epoxy incompletely cross-linked, and it will fail migration testing. Third, applying the white base coat too thick, which causes orange-peel texture that ruins print quality and wastes expensive coating material. Fourth, failing to control the coating application roller gap, leading to thickness variation across the sheet width — thin areas become corrosion failure points.

Cure Temperature and Line Speed Optimization

Both coating systems cure in the 200–210°C range, but the critical variable is time at temperature, not just peak metal temperature (PMT). For HF1625, we recommend a minimum of 10 minutes at 200°C to achieve full cross-linking. For HF1632-1, 8 minutes at 200°C is typically sufficient due to the different cure chemistry.

Pakistani factories often measure only the oven set temperature, not the actual PMT of the coated sheet. We strongly recommend investing in a through-oven temperature profiler (data logger) that travels through the oven on a sample sheet, recording the actual metal temperature every second. This single investment prevents the majority of cure-related quality failures.

Sourcing Consistent Coatings in Pakistan

Synergy Solutions is the exclusive Pakistan supplier for Sewin industrial coatings. We maintain warehouse stock of HF1625, HF1632-1, HF220, and the full HF4xx overprint varnish range. All batches ship with Certificates of Analysis, and our technical team is available to assist with coating line setup, cure optimization, and troubleshooting. Contact us for trial quantities or full production supply pricing.