What is Hologram Film Adhesion Promotion Technology?
Hologram film adhesion promotion technology refers to the methods and materials used to increase the surface energy and chemical compatibility of holographic films (PET, BOPP, PVC) so that inks, coatings, primers, adhesives, and metalised layers bond strongly and durably. Untreated holographic films have low surface energy (typically 28–32 dynes/cm) and are chemically inert, causing liquids to bead up and coatings to peel or scratch easily. Adhesion promotion technologies – including corona treatment, atmospheric plasma, flame treatment, and wet chemical primers (adhesion promoters) – modify the film surface to create polar groups, increase wettability, and provide chemical anchoring sites. These treatments are essential for ensuring that printed barcodes, QR codes, protective top coats, and pressure‑sensitive adhesives remain intact throughout the product’s life. Holoseal works with converters who apply appropriate adhesion promotion to guarantee that your hologram labels meet durability, scannability, and environmental resistance requirements.
🔍 Why Adhesion Promotion Is Critical for Hologram Labels
- Ink adhesion for barcodes and QR codes – Prevents smudging, scratching, or delamination during shipping and handling, ensuring scannability.
- Protective top coat durability – A properly adhered top coat resists abrasion, chemicals, and UV degradation.
- Pressure‑sensitive adhesive (PSA) bond – Ensures the label stays on the product and doesn’t lift at edges.
- Metalisation quality – The vacuum‑deposited aluminium layer (for reflective holograms) adheres more uniformly, reducing pinholes.
- Resistance to environmental stress – Labels remain intact under humidity, heat, cold, and chemical exposure.
🛡️ Types of Adhesion Promotion Technologies
The choice of technology depends on the film polymer (PET, BOPP, PVC), the coating to be applied, and the production line speed.
1. Corona Treatment (Electrical Discharge in Air)
Corona treatment is the most common method for inline adhesion promotion. A high‑voltage, high‑frequency discharge ionises air, creating plasma that oxidises the film surface. It introduces polar groups (hydroxyl, carbonyl) and increases surface energy to 38–44 dynes/cm. Treatment is applied just before printing or coating. Advantages: low cost, high speed (up to 300 m/min). Limitations: effect decays over hours/days; not effective on heavily filled or very inert polymers.
2. Atmospheric Plasma Treatment
Plasma treatment uses ionised gas (air, nitrogen, or argon) to clean and activate the surface at the molecular level. It produces a more uniform and longer‑lasting activation than corona. Excellent for challenging substrates (e.g., polypropylene with high slip additives). However, equipment cost is higher than corona, and it may require specialised gas supplies.
3. Flame Treatment (Oxidising Flame)
A gas flame oxidises the surface, increasing surface energy. Used for thick films, profiles, and some polyolefins. Not common for thin holographic films because heat can distort the film or damage the diffraction grating. Limited to heat‑resistant substrates.
4. Wet Chemical Primers (Adhesion Promoters)
A thin liquid primer layer (e.g., polyethylenimine, chlorinated polyolefin, or acrylic‑based) is applied by gravure, flexo, or slot‑die, then dried. The primer acts as a tie layer between the inert film and the subsequent coating. Primers provide excellent and durable adhesion, are effective on a wide range of polymers, and are less dependent on immediate processing. However, they add an extra coating step and require drying/curing, increasing cost.
5. Co‑extruded Tie Layers (In‑line Adhesion Promotion)
During film extrusion, a thin layer of a specially formulated polymer (e.g., maleic anhydride‑grafted polyolefin) is co‑extruded onto the surface. This layer is designed to be chemically receptive to inks and coatings. It provides permanent adhesion without post‑treatment, but only available for films manufactured with co‑extrusion – not for pre‑made films.
🔐 Adhesion Testing Methods
To verify that adhesion promotion is effective, converters use standardised tests:
- Dyne pen / dyne solution test – Measures surface energy (dynes/cm). Target values: printing >38, metallisation >42, adhesive lamination >40.
- Cross‑hatch tape test (ASTM D3359) – A grid is cut into the coating, tape is applied and removed. Adhesion is rated 0B (poor) to 5B (excellent). For security holograms, 4B or 5B is required.
- Scratch resistance (pencil hardness) – The coating’s resistance to scratching.
- Rub test (ASTM D5264) – Simulates abrasion during shipping.
⚙️ Practical Considerations for Hologram Film Adhesion Promotion
- Treatment decay – Corona and plasma treatments degrade over time (hours to days). Primers and co‑extruded tie layers provide permanent activation. Holoseal recommends primer or co‑extruded layers for long‑life security products.
- Backside treatment – For two‑sided coatings (e.g., printing on one side, adhesive on the other), both surfaces may need treatment.
- Compatibility with holographic diffraction gratings – Adhesion promotion must not damage the embossed pattern. Corona and plasma are safe at correct power levels. Flame treatment is not recommended.
- Additive migration – Films containing slip agents (amide waxes) or antiblock additives may lose treatment effectiveness as additives migrate to the surface. Primers or co‑extruded layers are preferred for such films.
🌍 Holoseal’s Adhesion Promotion Capabilities
Holoseal does not perform adhesion promotion in‑house. We partner with converters who apply the appropriate treatment based on your film type and end‑use. We help clients specify:
- Required surface energy (dynes/cm) for their inks/coatings.
- Whether a primer coating is needed for extreme durability (e.g., outdoor labels, chemical exposure).
- Acceptable test methods and pass/fail criteria (e.g., cross‑hatch rating).
With 15+ years of experience, we ensure that your hologram labels have the proper adhesion for reliable scannability and long‑term performance.
❓ Frequently Asked Questions About Hologram Film Adhesion Promotion
- Can I print on untreated holographic film? – You can, but the ink will bead up, and the print will scratch off easily. Barcodes will fail verification. Always treat or prime the surface.
- How long does corona treatment last on holographic film? – Typically 3–6 months in cool, dry storage. However, for guaranteed results, treat inline just before printing or coating.
- What is the best adhesion promotion method for PET holographic film? – Corona treatment is standard for most applications. For long‑life security labels requiring maximum durability, a wet primer (e.g., polyethylenimine or acrylic) is recommended.
- Does adhesion promotion affect the hologram’s rainbow effect? – No – the diffraction grating is embossed first; adhesion promotion modifies only the surface chemistry, not the optical structure. Over‑treatment (excessive corona) can cause haze, but proper treatment is optically neutral.
- What is the target dyne level for printing QR codes on holograms? – 38–42 dynes/cm. For metallisation, 42–44 dynes/cm. We can test with dyne pens on sample rolls.
- How to order hologram labels with adhesion promotion from Holoseal? – Specify your printing or coating method, required durability (indoor/outdoor, chemical exposure), and any previous adhesion issues. We will recommend the appropriate treatment or primer and produce samples for adhesion testing. Contact us for a quote.
