Quick answer
Choosing a UV-curable chemistry family is choosing the end-properties — because the resin/oligomer backbone sets hardness, flexibility, chemical/thermal resistance, shrinkage and adhesion before the lamp is ever switched on. This is the substrate-side deep-dive to Selecting UV-Curable Adhesives & Coatings: End-Properties First — same lens: pick the family/oligomer by required properties, then gate on UV-curability.
Three families dominate: acrylate (fast free-radical; the oligomer type is the property dial), cationic epoxy (low shrinkage, strong metal adhesion, oxygen-insensitive, dark cure) and silicone (release/specialty, available as radical-acrylate or cationic-epoxy variants).
1. Acrylate family — the oligomer is the property dial
Acrylates cure fast by free radicals (oxygen-inhibited at the surface). The decisive end-property lever is the oligomer backbone. Coating hardness commonly spans Shore D 50–85.
| Acrylate oligomer | Hardness / strength | Flexibility | Resistance / notes |
|---|---|---|---|
| Urethane acrylate | tough; tensile 20–60 MPa | high; elongation 50–300 % | abrasion + weathering, low color; broad hard→soft range; carbamate H-bonding |
| Epoxy acrylate (bisphenol-A) | hard; tensile 40–80 MPa, pencil 4H–6H | low; elongation 5–20 % (brittle) | excellent adhesion + chemical resistance; hardcoat / overprint varnish |
| Polyester acrylate | balanced | good | low shrinkage, moderate reactivity, weatherability |
(Sources: PatSnap Eureka oligomer analysis; Bomar formulation overview; UV+EB urethane-acrylate; RadTech polyester-acrylate proceedings.)
Engineering takeaway: "acrylate" is not one property profile — urethane vs epoxy vs polyester acrylate is a hard-vs-tough-vs-balanced decision.
2. Cationic epoxy — low shrinkage, metal adhesion, dark cure
Cationic epoxy generates a strong acid on UV exposure that ring-opens the epoxy. Property profile (see also the foundation article):
- Low cure shrinkage → low internal stress → excellent adhesion (≈100 % reported on aluminium).
- Oxygen-insensitive (no inert-gas requirement, no tacky surface skin).
- Dark cure: polymerization continues after light-off, full properties developing up to ~24 h; often needs a post-thermal step.
- Slower than acrylate; cationic initiators cost more.
(Sources: EpoxySet; Meridian Adhesives; consistent across the foundation article's sources.)
3. Silicone — release liners & specialty
UV silicones come in two cure routes with different trade-offs:
| Silicone route | Cure | Oxygen | Adhesion / cost | Use |
|---|---|---|---|---|
| Silicone-acrylate | free-radical, very fast | sensitive → needs N₂ inerting | good shelf life with PI | fast release coatings |
| Epoxy-silicone | cationic | insensitive | excellent adhesion; cheaper to make, pricier initiator; post-cure ~24 h | durable/age-resistant release |
Key advantage of radiation-cured silicones for release liners: full cure without heat. Free-radical/cationic hybrids target age-resistant coatings.
(Sources: Adhesives & Sealants Industry; RadTech 2016 cationic-silicone paper; ACS I&ECR hybrid-silicone study (peer-reviewed); Incure industrial guide.)
4. Selection matrix (family → end-property)
| Family | Shrinkage / metal-adhesion | Oxygen | Hardness range | Flexibility | Speed |
|---|---|---|---|---|---|
| Acrylate – urethane | moderate | inhibited | mid | high | fast |
| Acrylate – epoxy | moderate | inhibited | high/brittle | low | fast |
| Acrylate – polyester | low | inhibited | mid | good | fast |
| Cationic epoxy | low / excellent | insensitive | high | low–mid | slow |
| Silicone (either route) | n/a (release) | route-dependent | low | very high | fast–mid |
5. Matching to the UV source (the gate)
Family/oligomer choice is property-first; the UV source then has to cure it. Carry over from the foundation article: align the photoinitiator absorption to the lamp peak (10–20 nm mismatch wastes photons), plan for oxygen-inhibition on radical systems (thin films, surface), and specify dose with the wavelength band.
Cross-references
- UV Curing - overview and how it works - the general topic this article supports.
- Selecting UV-Curable Adhesives & Coatings: End-Properties First — the selection-overview parent.
- (coming) Photoinitiator selection guide (Type-I/II, wavelength bands)
- (coming) Oxygen-inhibition engineering for thin-film coatings
Sources
- PatSnap Eureka — acrylate oligomer analysis (Shore D, MPa, elongation figures)
- Bomar — UV/EB oligomer formulation overview
- UV+EB Technology — urethane acrylate oligomers
- RadTech — polyester acrylate proceedings (industry standards body)
- Adhesives & Sealants Industry — UV silicone release coatings
- RadTech 2016 — cationic UV-curable silicone release coatings
- ACS Ind. & Eng. Chem. Research — free-radical/cationic hybrid silicone (peer-reviewed)
- EpoxySet / Meridian — cationic vs free-radical UV cure