Polyethylene runs on the same metallizers as PET and BOPP, and yet it exposes three limits at once. LDPE melts between 105 °C and 115 °C, its untreated surface energy sits near 31 dyn/cm, and a thin, low-modulus web folds under tension that other films simply ignore. Handle those three limits, and metallizing LDPE film produces a flexible, low-seal-temperature reflective layer; overlook them, and you get pinholes, wrinkles, drum contact marks and a web that stretches in the deposition zone.

This guide works through the three problems in the order they appear on the line — vacuum quality first, web behaviour second, thermal margin last — and finishes with a recipe you can build on your own machine.

Why Polyethylene Rewrites the Recipe

Polyethylene differs from polyester and polypropylene in ways that matter more inside a vacuum chamber than in a specification sheet:

• It holds almost no water in its bulk, so the classic “wet roll” mechanism changes character.
• Its additive package does the outgassing instead: slip and antiblock agents travel to the film surface by design.
• Its melting point is low — 105 °C to 115 °C for LDPE (LDPE material summary) — with published continuous service temperatures around 80 °C and short-term peaks near 95 °C (polyethylene property guide).
• It is non-polar and soft, with untreated surface energy around 31 dyn/cm (corona discharge treatment reference).

Each of those properties creates one of the three problems below.

Problem 1 — Outgassing: The Pressure Comes From the Additives

Ask most operators what causes pump-down problems, and they say “moisture”. Polyethylene breaks that reflex, because the resin itself takes on very little water. The outgassing load arrives from somewhere else:

1. Slip and antiblock agents. These additives work precisely because they migrate to the film surface and bloom there (slip additive behaviour). A bloomed surface layer releases volatiles in vacuum.
2. Low-molecular-weight fractions. They sit at the surface and leave it under heat and vacuum.
3. Surface condensation and handling residue. A wound roll stored in a cool, humid room collects moisture on exposed film faces, even when the polymer absorbs none of it.

Once that material enters the chamber, the symptoms look familiar: a longer pump-down, an evaporation rate that wanders, pinholes, and patchy adhesion where the bloomed layer behaves like a release agent.

What to change

• Ask your resin supplier for the slip type and loading before you quote a metallizing specification. You cannot tune a coating against an unknown surface.
• Store and stage rolls wrapped, at a stable temperature, for the shortest practical time.
• Establish a baseline pump-down curve with a full roll, then compare every batch against that curve.
• Skip aggressive drying. Polyethylene needs no moisture bake, and heat only damages a film this thin. Our outgassing and moisture control note explains how to read the pressure signal instead.

Problem 2 — Wrinkling: Thin PE Folds Before It Warns You

A wrinkle appears when compressive stress in the web passes a critical value, and researchers studying roll-to-roll coating lines describe exactly this transition from a flat web to a wrinkled one (study on web wrinkling in roll-to-roll coating). Because LDPE carries a low modulus, that critical point arrives at lower tension than it does for PET or BOPP.

The usual triggers stay the same across materials — machine misalignment, poor roller geometry, roller deflection and variations in incoming roll quality (web handling wrinkle causes) — yet thin PE punishes them sooner. A gauge band of a few micrometres, an idler that sits slightly out of parallel, or a sagging roller at the centre of a wide web will all show up as a fold line that then coats unevenly.

What to change

• Reduce tension and apply taper tension across the wound roll; copy the philosophy from our web tension control guide, then drop the setpoint further for PE.
• Check alignment and roller deflection across the full web width, not just at the edges.
• Add spreader or bowed rollers only after you fix the alignment problem; a spreader hides a fault rather than curing it.
• Control static electricity, because a migrating static charge drags the thin web sideways and creates its own wrinkle pattern. See static control in roll-to-roll metallizing.
• Inspect incoming rolls for gauge bands, blocked edges and telescoping before you load them. Our guide to wrinkles and curl covers the defect signatures.

Problem 3 — Heat Limits: The Narrowest Window in Your Recipe Set

Here the numbers do the talking. LDPE melts between 105 °C and 115 °C, and suppliers rate continuous service near 80 °C with short excursions to roughly 95 °C. Evaporation boats radiate heat into the chamber, and a thin PE web passes the deposition zone with very little thermal mass to absorb that energy. Therefore the margin between “coating” and “damage” is narrower than on any other common substrate.

When the web overheats, you see a predictable sequence:

• Gauge loss and stretch in the machine direction
• Drum-side embossing, where the chilled drum surface pattern transfers into the softened film
• Coating cracks as the web relaxes after the chamber
• Blocking in the wound roll, because the film still holds heat when it reaches the rewind
• Seal-layer damage on coextruded PE sealant films, which changes seal behaviour downstream

What to change

• Set the drum temperature deliberately and verify the wrap angle, so the drum removes heat before the web reaches the boats. Our analysis of chill roll temperature explains what the drum controls.
• Cap the deposition rate rather than the line speed alone. Radiant load from the evaporation sources drives the heat input, and a lower rate buys margin.
• Shorten the dwell time in the deposition zone where your optical density target allows it.
• Cool the web before the rewind, and check the wound roll with a hand test at the core.

The PE Recipe vs PET and BOPP: What Changes

How to Build an LDPE or Thin PE Recipe

1. Get the additive data first. Slip type and loading drive everything else on this list.
2. Stage the rolls correctly. Wrapped, stable temperature, no long storage in a humid room.
3. Baseline the pump-down with a full roll, and record it with the batch.
4. Cut the tension and apply taper tension; then raise it only until the web tracks flat.
5. Verify alignment and roller deflection across the full width before the first production roll.
6. Set the drum for the gauge and shorten the radiant exposure in the deposition zone.
7. Check the dyne level, then pull an adhesion test before you commit to the run.
8. Run an OD coupon, log the batch, and inspect the wound roll for blocking and gauge bands.

Equipment choice matters less than discipline here, although automatic tension control and a properly sized chilling system make thin PE far easier to hold. Tempo Machinery builds the roll-to-roll platform used for these recipes — see the fully automatic suspension vacuum coating machine — and the metallized PE film range that runs on it.

Where Metallized PE Film Wins

Polyethylene gives up some barrier to PET and BOPP, and it returns three things those films cannot match: flexibility, a low seal-initiation temperature, and low cost per square metre. Converters therefore choose metallized polyethylene film for:

• Reflective and insulation structures, where the aluminium layer does the work and the film only has to stay flexible — the mechanism behind emergency blanket film
• Lidding and sealant layers in laminates that need to seal below 100 °C
• Flexible packaging where the pack must survive folding without pinholes

Screen the application before you promise a barrier figure. A metallized PE structure protects against moisture and radiant heat well, while PET or BOPP structures carry the oxygen barrier in most high-barrier laminates. Our note on aluminium layer thickness and barrier performance shows how to set that target.

Quality Checks That Catch PE-Specific Problems

1. Pinhole count — the fastest indicator of an additive or vacuum problem
2. Drum-side inspection — look for contact marks and embossing under angled light
3. Optical density across the web width, not only at the centre
4. Adhesion, tested at the roll start and roll end
5. Wound roll quality — blocking, telescoping, gauge bands and edge damage

We describe the measurement side of the third and fourth checks in our notes on optical density and adhesion testing.

Frequently Asked Questions

1. Can I metallize LDPE on a machine that runs PET and BOPP? Yes. Expect a lower tension setpoint, a colder drum and a capped deposition rate, and baseline the pump-down curve separately for PE.

2. Why does my PE web outgas when polyethylene absorbs almost no water? The load comes from the additive package and the film surface: slip and antiblock agents bloom to the surface by design, low-molecular-weight fractions sit there too, and stored rolls collect surface moisture. Bulk moisture stays negligible.

3. What temperature limit applies to LDPE inside a metallizer? LDPE melts between 105 °C and 115 °C, with published continuous service ratings around 80 °C and short-term peaks near 95 °C. Keep the web well below those figures and use the drum to remove heat before the deposition zone.

4. Why does thin PE wrinkle so easily? A wrinkle starts when compressive stress passes a critical value, and a low-modulus film reaches that point at lower tension. Thin gauges also carry less bending stiffness, so small alignment and gauge errors show up as fold lines.

5. Does metallizing LDPE require corona treatment? Yes. Untreated polyethylene sits near 31 dyn/cm, which cannot wet out inks or adhesives reliably. Treat the web, target a surface energy comfortably above the adhesive or ink it must accept, and re-check stored rolls before use.

6. How do I stop blocking in the wound roll? Cool the web before the rewind, keep the rewind tension low, and confirm that the film leaves the deposition zone below its softening range.

7. What optical density can I expect on metallized PE film? Treat optical density as a recipe output rather than a material constant. Set the target from the application, then verify it across the web width and log the result per batch.

8. Which PE film grade should I choose for metallizing? Start with the additive package, not with the density. A grade with a low slip level and a clean surface coats more predictably than a high-slip film, and coex sealant structures need a metallizing recipe that protects the seal layer.

The Takeaway

Metallizing LDPE and thin PE films rewards a specific order of work: understand the additives, calm the web, and protect the heat margin. Polyethylene gives you flexibility, low seal temperatures and a low cost per square metre — and it gives you the narrowest process window in your recipe book. Build the recipe around those three facts, and thin PE runs as reliably as any other substrate on the line.

Working on a PE metallizing recipe or a thin-film line? Send us your film structure and gauge, and our engineers will map the coating recipe to your substrate.