UV cold foil adhesive — chemistry, cure energy & anilox setup

How UV cold foil adhesive works, in order

• 1. Adhesive image printed on substrate through UV-flexo or UV-offset unit.
• 2. Cold foil roll (metallised PET) nipped against the wet adhesive at 150–450 m/min.
• 3. UV lamp (Hg medium-pressure or UV-LED 385/395 nm) cures the adhesive through the transparent PET carrier at 80–250 mJ/cm².
• 4. PET carrier peeled off — the metallising stays bonded to the cured adhesive image, everything else strips away with the carrier.
• 5. Waste carrier rewound; residual metallising = 0 outside the adhesive image (unlike hot foil, where the die footprint = 100 % of the metallising consumed).

Adhesive chemistries — what to use where

Three families dominate: free-radical acrylate, cationic epoxide, and hybrid. Choice is driven by substrate energy, cure system (Hg vs LED), oxygen inhibition tolerance and downstream converting (overprint varnish, lamination).

Free-radical acrylate (e.g. INX AF-2110, Sun SunCure UFCA): fast cure, high gloss, best on coated paper and SBS board. Sensitive to oxygen inhibition on thin coats — needs 150–200 mJ/cm² UV-Hg or nitrogen inertion for UV-LED. Overprint with UV varnish only; solvent inks may lift the metallising.

Cationic epoxide (e.g. Actega Colorpoint EB): dark-cure continues after lamp exit, giving better bond on low-surface-energy films (BOPP, PET, PP). Runs at 80–150 mJ/cm², tolerates UV-LED without nitrogen. Cure completion in 24 h; can be overprinted with solvent or water-based inks after that window.

Hybrid (radical + cationic): compromise; used when the same press must switch between paper and film without changing adhesive.

Anilox, plate and press setup

• Anilox volume: 5.0–8.0 BCM (7.7–12.4 cm³/m²) for UV-flexo. Below 5 BCM — coverage voids in solids. Above 8 BCM — squeeze-out on halftones.
• Anilox screen: 500–800 lpi for solids; 800–1,000 lpi for halftone/vignette foil.
• Photopolymer plate: 1.14–1.70 mm, 60–65 Shore A hardness, flat-top dot preferred to reduce dot gain in the adhesive image.
• Impression: 60–90 µm engagement between plate and substrate — over-impression causes adhesive squeeze-out and haloing.
• UV lamp: Hg medium-pressure 120–160 W/cm, or UV-LED 385/395 nm at 12–24 W/cm². Peak irradiance ≥ 1.5 W/cm² for cationic; ≥ 2.0 W/cm² for free-radical.

QC tests to confirm the adhesive is working

• Adhesion — ASTM D3359-22 tape test, target 4B or higher (≤ 5 % detachment).
• Cure — MEK double-rub, 100 rubs no film breakdown; or Raman spectroscopy for acrylate C=C consumption > 85 %.
• Coating weight — 1.5–3.0 g/m² measured by pick weight on 100 cm² sample.
• Colour ΔE — spectrophotometer D65/10° vs master swatch, target ΔE ≤ 1.5.
• Coverage/waste rate — image area ÷ metallising consumed; well-tuned line runs at 92–96 %.