What is Solvent Based Hologram Coating?
Solvent based hologram coating is a liquid coating formulation that contains organic solvents (e.g., toluene, methyl ethyl ketone, ethyl acetate, or alcohol) to dissolve resins, additives, and adhesion promoters. The coating is applied to holographic film (PET or BOPP) to serve as primers for printability, protective top coats, or pressure‑sensitive adhesives (PSAs). After application, the coated film passes through a long hot‑air drying oven (typically 10–30 metres) where the solvents evaporate, leaving a solid, dry coating layer. Solvent‑based coatings have been the industry standard for decades because they offer excellent adhesion to low‑surface‑energy substrates (like PET and BOPP), high chemical and abrasion resistance, and relatively low raw material cost. However, they release volatile organic compounds (VOCs) during drying, require energy‑intensive ovens, and pose fire and health hazards unless properly ventilated. Solvent‑based coatings are still widely used for high‑performance hologram labels requiring extreme durability or chemical resistance, and for applications where UV curing is impractical. Holoseal works with converters who use solvent‑based coating lines, ensuring proper solvent recovery and worker safety.
🔬 How Solvent Based Hologram Coating Works (Step‑by‑Step)
The coating is applied inline on a converting machine. Here is the typical process:
1. Coating Application
The liquid solvent‑based coating is applied to the holographic film using a gravure, reverse‑roll, or slot‑die coater. The coating thickness is controlled (typically 2–30 µm).
2. Drying (Solvent Evaporation)
The coated film enters a long hot‑air drying oven (10–30 m length, 60–120 °C). Heated air flows over the film, evaporating the organic solvents. The solvent vapours are extracted, and often recovered via condensation or thermal oxidisers.
3. Solidification
As solvents evaporate, the resin and additives coalesce into a solid, continuous film. The coating is now dry and ready for rewinding or further processing.
4. Optional Solvent Recovery
To reduce VOC emissions and recover expensive solvents, many modern lines include solvent recovery systems (e.g., carbon adsorption or condensation).
📦 Types of Solvent Based Coatings for Hologram Labels
- Solvent primers – Improve ink adhesion on holographic film. Contain chlorinated polyolefins, acrylics, or polyurethanes. Excellent for PET and BOPP.
- Solvent protective top coats – Clear, hard coatings that protect the metalised layer and inks from scratches, chemicals, and UV. Often acrylic or polyurethane based.
- Solvent pressure‑sensitive adhesives (PSAs) – High‑tack, high‑shear adhesives used for permanent labels. Provide excellent adhesion to a wide range of surfaces, including low‑energy plastics.
- Solvent varnishes (overprint varnishes) – Glossy or matte finishes applied over printed areas for aesthetics or protection.
🛡️ Advantages of Solvent Based Coatings for Holograms
- Excellent adhesion – Solvents swell the polymer surface, promoting mechanical interlocking and strong bond to PET/BOPP.
- High durability – Solvent‑based coatings offer superior scratch, chemical, and solvent resistance compared to water‑based alternatives.
- Low cost – Raw materials are generally cheaper than UV coatings.
- Wide formulation latitude – Many resin types (acrylic, polyurethane, rubber‑based) can be used.
- Good gloss and flow – Solvent coatings level well, providing smooth, high‑gloss finishes.
🔐 Disadvantages and Limitations
- VOC emissions – Organic solvents released during drying are harmful to the environment and human health. Strict regulations require costly abatement systems.
- Energy intensive – Long drying ovens consume significant energy (gas or electricity).
- Fire and explosion risk – Solvent vapours are flammable; ovens and coating lines must be explosion‑proof.
- Slow line speeds – Drying time limits line speed (typically 30–150 m/min, slower than UV).
- Solvent recovery cost – Installing and operating solvent recovery adds expense.
⚙️ Solvent Based vs. UV Curable vs. Water‑Based Coatings
| Aspect | Solvent‑Based | UV Curable | Water‑Based |
|---|---|---|---|
| VOC content | High (50–80%) | 0% | Low (5–15% coalescing solvents) |
| Drying/curing | Minutes (hot air oven) | Instant (UV lamp) | Minutes (hot air oven) |
| Energy consumption | Very high | Low | High |
| Adhesion to PET/BOPP | Excellent | Good (requires primer) | Moderate |
| Scratch/chemical resistance | Excellent | Excellent | Good |
| Line speed (m/min) | 30–150 | 50–300 | 30–150 |
| Capital equipment cost | High (ovens, solvent recovery) | Moderate (UV lamps) | High (ovens) |
🔬 Solvent Recovery and Environmental Compliance
To comply with environmental regulations (e.g., EPA, EU Solvent Emissions Directive), solvent‑based coating lines must include:
- Carbon adsorption systems – Activated carbon beds capture solvents, which are then desorbed with steam and recovered for reuse.
- Thermal oxidisers (incinerators) – Burn solvent vapours at high temperature (700–1000 °C), converting them to CO₂ and water. May include heat recovery to preheat incoming air.
- Condensation recovery – Cool the exhaust gas to condense and recover solvents.
These systems add significant capital and operating costs but are often mandatory.
🌍 Holoseal’s Use of Solvent Based Coatings
Holoseal does not apply solvent‑based coatings in‑house. We partner with converters who operate compliant solvent coating lines with proper recovery and safety systems. We specify the coating type (primer, top coat, adhesive) based on your performance requirements (adhesion, durability, chemical resistance) and advise on the trade‑offs between solvent, UV, and water‑based technologies. Our 15+ years of experience ensure that the coating is correctly formulated and applied for optimal label performance.
❓ Frequently Asked Questions About Solvent Based Hologram Coating
- Are solvent‑based coatings still legal? – Yes, but they are strictly regulated. Facilities must obtain permits, install abatement equipment, and monitor emissions. Many converters have switched to UV or water‑based to avoid these costs.
- Can solvent‑based coatings be used on heat‑sensitive holographic film? – Yes, because the drying ovens use hot air (60–120 °C), not direct contact heat. However, UV curing is even cooler (LED‑UV).
- Which offers better outdoor durability – solvent or UV? – Both can be formulated for excellent outdoor durability. Solvent‑based polyurethane top coats are particularly UV‑resistant.
- Are solvent‑based coatings more expensive than UV? – Raw materials are cheaper, but the cost of ovens, energy, and solvent recovery often makes them more expensive overall for small to medium runs. For very high volumes, solvent can be cost‑effective.
- Can I use solvent‑based adhesive on hologram labels for food packaging? – Yes, but only if the adhesive is formulated to be food‑contact compliant and the final product meets migration limits. Most solvent PSAs are not suitable for direct food contact without special approval.
- How to order hologram labels with solvent‑based coatings from Holoseal? – Specify your performance needs (adhesion, durability, chemical resistance) and volume. We will recommend the appropriate coating technology – solvent, UV, or water‑based – and produce samples. Contact us for a quote.
