What is Hologram Film Corona Treatment?
Hologram film corona treatment is a surface modification process that uses high‑frequency, high‑voltage electrical discharge to increase the surface energy of plastic films (such as PET, BOPP, or PVC) used as substrates for hologram embossing. The treatment creates a polarised surface layer, improving wettability and adhesion for subsequent processes such as printing (ink adhesion), coating (primer or top coat application), metalization (aluminium deposition), or lamination. Untreated holographic films have low surface energy (typically 28–30 dynes/cm), causing inks and coatings to bead up and fail to adhere. Corona treatment raises the surface energy to 38–44 dynes/cm, ensuring that printed barcodes, QR codes, and protective coatings bond permanently. The treatment is applied inline during film production or just before printing/coating. Holoseal works with film suppliers and converters who use precision corona treatment to guarantee that your hologram labels have excellent printability, durability, and metal adhesion.
🔬 How Hologram Film Corona Treatment Works (Step‑by‑Step)
The treatment is performed inline on a film production line or a converting machine (printer, coater). Here is the typical process:
1. Film Transport
The holographic film passes over a grounded metal roller (anodised or ceramic‑coated) at speeds ranging from 50 to 300 m/min.
2. High‑Voltage Discharge
A high‑frequency, high‑voltage electrode (typically 10–20 kV at 10–30 kHz) is positioned a few millimetres above the film surface. The electrical discharge creates a corona (ionised air plasma).
3. Surface Oxidation
The plasma bombards the film surface, breaking polymer chains and introducing polar functional groups (hydroxyl, carbonyl, carboxyl). This increases the surface energy and wettability.
4. Immediate Use or Storage
Treated film should be used within hours or days because the effect decays over time (hydrophobic recovery). Some films retain treatment longer, but for best results, printing or coating should follow soon after.
📦 Why Corona Treatment Is Essential for Hologram Labels
- Improves ink adhesion – Prevents smudging, scratching, or peeling of printed barcodes, QR codes, and brand graphics.
- Enhances coating bond – Primer coatings, protective top coats, and adhesives adhere more strongly.
- Ensures metalization quality – The aluminium layer in metalized holograms bonds more uniformly to treated film, reducing pinholes.
- Enables high‑speed printing – Consistent wetting allows flexo and gravure presses to run faster without ink defects.
- Critical for scannability – Well‑adhered barcodes and QR codes remain readable throughout the product’s life.
🛡️ Corona Treatment Parameters
- Surface energy target – 38–44 dynes/cm for most printing and coating applications. Measured with dyne pens or contact angle meters.
- Treatment level (power density) – Typically 2–10 W min/m². Higher for thicker films or more inert polymers.
- Electrode gap – 1–3 mm. Too close risks arcing; too far reduces treatment efficiency.
- Temperature control – The roller is often water‑cooled to prevent heat damage to the film.
🔐 Corona Treatment Decay (Hydrophobic Recovery)
The effect of corona treatment is not permanent. Over time, the polar groups migrate back into the bulk polymer, and the surface energy drops. Factors affecting decay:
- Storage conditions – High temperature and humidity accelerate decay. Store treated film in a cool, dry place (20–25 °C, <50% RH).
- Film type – PET retains treatment longer than BOPP or PE.
- Additives – Slip agents and antiblock additives migrate to the surface and reduce treatment effectiveness.
Practical rule: Use treated film within 3–6 months, or re‑treat before use. Holoseal ensures that film supplied for printing is treated just before shipment or we provide fresh treatment upon request.
⚙️ Corona Treatment vs. Other Surface Treatment Methods
| Aspect | Corona Treatment | Plasma Treatment | Flame Treatment |
|---|---|---|---|
| Method — | Electrical discharge in air— | Ionised gas (vacuum or atmospheric)— | Oxidising flame |
| Typical use — | Films, foils, paper— | 3D parts, intricate surfaces— | Large bottles, heavy profiles |
| Effect duration — | Temporary (weeks to months)— | Temporary— | Temporary |
| Cost — | Low – inline integration— | Higher— | Moderate |
| Suitability for holographic film — | Excellent – industry standard— | Possible but overkill— | Not recommended (heat damage) |
🌍 Holoseal’s Approach to Corona Treatment
Holoseal does not perform corona treatment in‑house. We source holographic film from suppliers who apply precision corona treatment to the embossing side (or both sides) of the film. For custom‑printed hologram labels, we work with converters who re‑treat the film inline before printing to guarantee optimal ink adhesion. We also provide dyne test reports upon request to verify that the surface energy meets your requirements.
❓ Frequently Asked Questions About Hologram Film Corona Treatment
- How can I test if my hologram film is properly treated? – Use a dyne pen (e.g., 38 dynes/cm). Draw a line on the film surface. If the line stays unbroken for 2 seconds, the treatment is adequate. If it beads up, the film needs re‑treatment.
- Can I over‑treat hologram film? – Yes – excessive corona treatment can degrade the film surface, causing “orange peel” texture, haze, or even pinholes. It can also oxidise the metalized layer if applied on the metal side. Follow manufacturer recommendations.
- Does corona treatment affect the hologram’s rainbow effect? – No – the diffraction grating is embossed before or after treatment; the treatment does not alter the optical structure. However, excessive treatment can cause surface haze that slightly reduces brightness.
- What happens if I print on untreated hologram film? – Ink will bead up, resulting in poor opacity, smudging, and low barcode scan grades. The print may rub off easily.
- How long does corona treatment last on holographic film? – Typically 3–6 months when stored in cool, dry conditions. PET holds treatment longer than BOPP. Always check with a dyne pen before printing.
- How to order corona‑treated hologram film or labels from Holoseal? – Specify that you need corona treatment on the printing surface. We will ensure the film is properly treated (and re‑treated if necessary) before printing. Contact us for a quote.
