How Can The Printing And Lamination Bond Strength of Aluminum-plastic Composite Films Be Improved? Corona Treatment Is An Effective Solution

A Batch of Pet Food Bags Thrown Away

Last month, a North American pet food client emailed us in a panic. He'd just received a batch of composite film packaging bags, and during printing, the ink peeled off in large sheets. After lamination, the peel strength was under 1.5 N/15mm — well below the industry standard of 3.5 N/15mm minimum. The entire shipment, nearly 3 metric tons, had to be scrapped. He went through every variable: ink formulation, adhesive ratios, workshop temperature and humidity. All checked out. It wasn't until our technical team examined the samples that the cause became clear — the film's surface energy was only 32 dynes/cm. The ink simply couldn't grip the surface, and the adhesive couldn't penetrate.

This kind of problem is depressingly common in the aluminum-plastic composite film industry. And more often than not, the root cause traces back to one overlooked step: corona pretreatment.

Surface Energy: Where All Adhesion Begins

To understand the problem, you need to understand surface energy. Simply put, the higher the surface energy of a solid, the better liquids — inks, adhesives — spread, penetrate, and form strong bonds. Untreated PE or PP film typically sits at around 30-32 dynes/cm. Untreated PET is maybe 38 dynes. Meanwhile, most inks and adhesives need a substrate surface energy of at least 38-44 dynes to adhere properly.

That gap is exactly where ink flaking and delamination come from.

The old-school fix was chemical priming — applying a primer containing something like chlorinated polypropylene to chemically bridge the low-energy surface and the ink. The problem? Solvent-based primers carry VOC emissions. Water-based primers dry slowly and drag down throughput. And either way, you're adding another process step and another cost.

Corona Treatment: A Physical Solution, Not a Chemical One

The idea behind corona treatment is refreshingly direct. A high-voltage, high-frequency electrical discharge bombards the film surface. Oxygen in the air gets ionized into ozone and free radicals, which break the polymer chains on the film surface. The exposed reactive chain ends combine with oxygen to form polar functional groups — carbonyls (C=O), hydroxyls (-OH), carboxylic acids (-COOH). These polar groups act like tiny chemical anchor points, giving inks and adhesives something to grip.

The results are immediate. PE film surface energy jumps from 30 dynes to 42-48 dynes. PET goes from 38 to 50-54 dynes. One real-world case showed peel strength leaping from under 0.5 N/15mm to over 2.1 N/15mm after corona treatment, with scrap rates dropping from 18% to below 1.5%.

No chemicals involved. No change to the base film properties. No added thickness. And it can be done inline, in real time, as part of the production process.

The Key Parameter: Power Density Determines Everything

Corona treatment isn't as simple as flipping a switch and walking away. The critical parameter is power density, measured in watt-minutes per square meter (W·min/m²). The formula looks roughly like this: Power = number of sides × line speed × film width × material factor.

Different substrates need very different treatment levels. LDPE for printing typically targets 38-40 dynes, which needs 1.5-2.5 W·min/m². PP or BOPP for lamination wants 40-44 dynes, requiring 2.0-3.0. PET before metallization needs 48-52 dynes, and you need to push power density up to 3.0-5.0.

Here's a trap many people fall into: you speed up the line but forget to increase the power proportionally. Power density drops, dyne level drops, and suddenly you've got an adhesion problem again. Running at 200 meters per minute requires roughly twice the power of 100 meters per minute for the same dyne gain. This is, not coincidentally, the most common reason quality varies between shifts.

One more detail that matters: the gap between the electrode and the film surface needs to stay at 3-5mm. Too far and the discharge is too weak to treat effectively. Too close and you risk electrical arcing that damages the film.

Dyne Levels Have a Shelf Life

Corona treatment doesn't last forever. Surface energy decays over time — and it decays faster in hot, humid conditions. A PE film treated to 42 dynes can drop below 36 within just a few days if storage conditions aren't ideal. That's why the industry standard is to print or laminate as soon as possible after treatment, ideally within 72 hours.

This is exactly why inline corona treatment keeps gaining popularity. You treat the film and immediately print or laminate it, leaving no window for decay.

VWIN's Corona Treatment Solution

At VWIN, our aluminum-plastic composite film production lines are equipped with inline corona treatment systems. We precisely control power density and electrode gap for different substrates — PE, PP, PET, nylon — making sure every roll hits its target dyne level before it goes to your press or laminator. We set application-specific parameters: films destined for printing are held to ≥42 dynes, lamination films to ≥44 dynes, and metallization-pretreatment films to ≥50 dynes.

Every shipment comes with a dyne level test report, peel strength data, and printability verification records. If you've been dealing with ink adhesion failures or lamination delamination in your aluminum-plastic composite film supply, reach out to us. We can help you solve the problem at the source — before it ever reaches your production line.