Metallised Polyester Film Properties: Test Data and Grade Selection

Metallised polyester film properties come from the BOPET substrate, surface treatment, and vacuum-deposited aluminium. PET supplies most tensile strength, stiffness, dimensional stability, and thermal response. The treatment controls wetting and interfacial bonding. Aluminium changes optical density, reflectivity, electrical behaviour, and barrier. A workable specification therefore identifies thickness, treated side, metal side, OD, OTR and WVTR conditions, metal adhesion, COF, MD/TD shrinkage, winding direction, and performance after the intended converting process. It should also state whether reported values are typical or acceptance limits.

A TDS value belongs to a defined thickness, structure, method, environment, and specimen condition. Because lamination, creasing, heat, or storage can change performance, the final structure must be validated under the intended process.

Property Ownership Across the Film Structure

The aluminium deposit changes optical and barrier response but is not the main load-bearing layer. BOPET carries mechanical stress; treatment or primer controls wetting and bonding; aluminium controls opacity, reflectance, conductivity, and much of the permeation response. Coatings may add abrasion or oxidation resistance, while the laminate supplies heat sealing and package integrity.

A transparent BOPET base film may provide suitable stiffness but still lack the surface design required for stable metallising. Projects combining optical, thermal, and web-handling requirements should compare PET functional film grades by process route rather than nominal thickness alone.

Normalising TDS Data Before Comparison

Comparison rule: Values are comparable only when thickness, structure, method, temperature, relative humidity, units, direction, and conditioning match. ASTM D3985 is commonly used for oxygen transmission, ASTM F1249 for water-vapour transmission, ASTM D882 for tensile properties, and ASTM D1894 for friction. A lower result is not automatically better when one supplier tested bare film and another tested a coated laminate. Keep the full condition attached to every value through quotation, trial approval, and repeat-order control. This prevents misleading rankings between technically different constructions.

Metallized PET Film OTR and WVTR

Published TDS values are not universal. One 12 um high-barrier grade reports OTR about 0.24 cc/m2/day at 23 C and 0% RH and MVTR about 0.14 g/m2/day at 38 C and 90% RH. A coated 12.2 um grade reports about 0.078 under different humidity conditions and with a different structure.

For metallized polyester film barrier properties, state whether the specimen was bare, coated, laminated, aged, flexed, or taken from a finished pack.

COF Pairing and Shrinkage Conditions

The PET film coefficient of friction for converting affects unwinding, web tracking, blocking, and high-speed lamination. The result must identify the pairing, such as metal-to-metal or treated-to-plain. Thermal shrinkage of metallized PET film must also remain attached to temperature and time; a result measured at 105 C cannot be ranked beside one measured at 150 C without explaining the different exposure.

Why Similar OD Can Produce Different Barrier Results

Failure diagnosis: Metallized PET film optical density measures light attenuation and helps control deposition, but it does not reveal every pinhole, scratch, weakly bonded area, or fold crack. Two rolls may show similar OD while having different metal continuity or primer anchorage. Slitting, lamination, pouch forming, and flexing can enlarge defects into permeation paths. For barrier-critical structures, compare OD with OTR or WVTR after the process most likely to damage the aluminium layer. Visual silver appearance alone cannot prove converted-state barrier performance.

The Failure Chain to Check

A practical failure chain is: similar initial OD, different microscopic continuity, different converting damage, and different post-flex barrier. Map OD across the web, compare roll-start, middle, and end samples, and inspect bright points, scratches, metal pickoff, and aluminium transfer.

Flexible packaging may prioritise OTR, WVTR, metal bond, sealant compatibility, and post-flex performance. Reflective insulation needs reflectance, emissivity, corrosion protection, and fold durability. Electronic structures may prioritise controlled sheet resistance.

Three Substrate Routes Before Vacuum Metallising

Selection rule: Choose the base film by identifying what must bond to each side and the web’s thermal history. Transparent PET may suit a decorative laminate. Corona-treated PET provides an activated surface, while chemically primed PET may offer more durable anchorage. A heat-stable or low-shrink grade becomes important before hot drying, curing, or extrusion lamination. Validate the chosen route with the actual deposition, ink, adhesive, coating weight, cure, storage, and aging conditions. Confirm treated-side orientation before the roll enters production.

Route A: Corona-Treated PET

A corona-treated PET film for metallizing may be suitable when the process needs an active surface for aluminium, ink, primer, or adhesive. A treated-side reference around 50-52+ dyn/cm may be useful, but the required level should be confirmed with the production chemistry. Initial dyne level is not proof of final metal adhesion because treatment can change during storage and heat exposure.

Route B: Chemically Primed PET

A chemically treated PET film for metallizing can be considered when primer-assisted anchorage is required. The metal adhesion of metallized PET film should be verified with a defined peel structure that records adhesive, coating weight, cure, peel width, speed, and whether aluminium stays on PET or transfers to the mating web.

Route C: Heat-Stable or Low-Shrink PET

Record MD and TD shrinkage at the expected drying or lamination condition. A result at 105 C cannot be ranked directly against one at 150 C. Web tension, oven profile, and cooling may also affect curl and registration.

Pilot Validation From Incoming Roll to Finished Laminate

Validation rule: Incoming-roll data describes film before coating, drying, nip pressure, slitting, sealing, folding, and aging. These operations can alter COF, weaken the metal-to-PET interface, or create microcracks. Approval should include the original film and a specimen from the intended production route. For barrier-critical work, repeat OTR or WVTR after forming or controlled flexing and inspect metal transfer during peel testing. The converted specimen is usually more relevant than an untouched strip. Use production-speed samples whenever laboratory preparation changes adhesive coverage.

1. Record thickness, OD, treatment, metal side, width, core, winding, and batch.
2. Measure required initial COF, adhesion, shrinkage, barrier, reflectance, or resistance.
3. Run the production adhesive, coating weight, speed, temperature, nip, and cure.
4. Apply expected folding, sealing, humidity, heat, storage, or aging.
5. Retest roll-start, middle, and end specimens.
6. Inspect pinholes, scratches, metal pickoff, and transfer.
7. Set limits from the approved structure and define revalidation triggers.

The metallized PET film after lamination should represent the production laminate, not a hand-made sample with different adhesive coverage. Trial-roll discussions should also fix slit width, edge quality, roll length, joints, metal-side orientation, and metallized PET film winding direction. When slitting, metallising, printing, or lamination produces off-spec rolls and process trim, the metallized PET scrap recycling guide explains how to distinguish PET-rich material from printed, adhesive-bearing, or multilayer waste before recycler qualification.  PET film converting capabilities can support discussions about custom dimensions and precision slitting; any vacuum-metallising or barrier-testing capability should be confirmed separately.

Metallised Polyester Film Properties in the Release Specification

Release rule: Separate typical TDS values from agreed acceptance limits. The RFQ defines the need, the trial proves whether the grade and process can meet it, and the CoA records agreed batch controls. A complete specification should not stop at “12 um silver PET.” Define layer orientation, OD range, test conditions, adhesion method, COF pairing, thermal exposure, roll geometry, finished-laminate tests, sampling frequency, and change control for repeat production. Record which values must appear on each batch certificate of analysis.

Common errors include comparing barrier values without matching conditions, using OD as proof of post-forming barrier, approving metal adhesion without a method, running the wrong surface, assuming every grade is heat sealable, and turning typical values into rejection limits.

Frequently Asked Questions

Does Higher Metallized PET Film Optical Density Mean Better Barrier?

Not always. Higher OD may support barrier when the metal is continuous, but pinholes, scratches, folds, and weak anchorage can reduce converted performance. Verify OTR or WVTR on the finished structure.

How Should Metallized PET Film OTR and WVTR Be Compared?

Match method, temperature, relative humidity, units, thickness, structure, and conditioning. Confirm whether the sample was bare, coated, laminated, aged, or flexed.

What Is the Difference Between Metallized Polyester Film and Aluminum Foil?

Metallised PET uses deposited aluminium on a polymer substrate; foil is a continuous metal sheet. PET is lighter and flexible but is not a universal replacement. Validate shelf life, forming, sealing, puncture, and finished-package performance.

Which Values Belong on a Batch CoA?

Include agreed, measurable items such as batch ID, thickness, OD, roll dimensions, and selected barrier, adhesion, COF, or shrinkage results. State the method and conditions.