Anti-Graffiti UV Coatings: Materials, Principles and Application Formulations
A comprehensive technical guide covering UV coating fundamentals, curing mechanisms, silicone-based anti-graffiti additives, and validated formulation recipes.
1. Characteristics and Composition of UV Coatings
1.1 Key Characteristics of UV Coatings
UV-curable coatings have become a dominant force in the surface treatment industry due to their exceptional efficiency and environmental profile. The core advantages include:
- Broad substrate compatibility — applicable to wood, plastic, metal, paper, and composite materials.
- Low energy consumption — curing occurs at ambient or near-ambient temperatures, eliminating the need for thermal ovens.
- Ultra-fast curing — full cure can be achieved in as little as 0.05–0.1 seconds under optimal UV intensity.
- Low VOC emissions — traditional solvent-borne coatings contain 30–70% inert solvents, nearly all of which evaporate into the atmosphere during film formation. UV coatings use reactive diluents instead, dramatically reducing volatile emissions.
1.2 Composition Comparison: Conventional vs. UV-Curable Coatings
| Conventional Coatings | UV-Curable Coatings |
|---|---|
| Resin | Oligomer |
| Solvent | Reactive diluent |
| Catalyst | Photoinitiator |
| Pigments & fillers | Pigments & fillers |
| Additives | Additives |
The fundamental shift lies in replacing non-reactive solvents with reactive diluents that participate directly in the polymerization reaction, and replacing thermal catalysts with photoinitiators that generate reactive species upon UV exposure.
2. UV Curing Types, Light Sources and Basic Raw Materials
2.1 UV Curing Spectrum
UVA (315–400 nm, energy 3.2–3.9 eV) is the long-wave ultraviolet band and the most critical range for UV-curable coatings. It corresponds to the maximum absorption spectrum of the majority of photoinitiators. The commonly used mercury arc lamp emits its principal wavelength at 365 nm, which falls precisely within this band.
2.2 UV Irradiation Light Sources
Three primary light source types are used in industrial UV curing:
- High-pressure mercury lamp — A transparent quartz tube encapsulating mercury with electrodes at both ends. When electrified and heated, mercury vapor is excited to a higher energy state; upon returning to the ground state, it emits ultraviolet radiation.
- Metal halide lamp — Emissive elements combine with halogens to form metal halides, producing a broader and more tailored spectral output.
- UV-LED lamp — Light-emitting diodes that directly convert electrical energy into light and radiant energy, offering instant on/off, low heat generation, and long service life.
2.3 Basic Raw Materials for UV-Curable Coatings
UV coating formulations are built upon four foundational material classes:
- Photoinitiators (3–7% loading) — the decisive component governing curing speed.
- Reactive diluents — small organic molecules containing polymerizable functional groups; they reduce application viscosity and regulate curing rate and film properties.
- Oligomers — relatively low-molecular-weight photosensitive resins that form the backbone of the cured film.
- Additives — pigments, fillers, leveling agents, wetting agents, defoamers, and other performance modifiers.
2.4 Photoinitiators in Detail
A. Cleavage-Type Free Radical Photoinitiators
Common grades include 1173 / 184 (α-hydroxy ketone derivatives), 2959 (water-compatible), and TPO (acyl phosphine oxide).
- Darocur 1173 (HMPP) — abbreviated as 1173
- Irgacure 184 (HCPK) — abbreviated as 184
- Darocur 2959 (HHMP) — abbreviated as 2959, water-borne compatible
B. Hydrogen-Abstraction Free Radical Photoinitiators
Benzophenone and its derivatives, thioxanthones, and anthraquinones. Hydrogen donors are typically tertiary amine compounds.
C. Cationic Photoinitiators
The most common structures are diaryl iodonium salts and triaryl sulfonium salts, typically supplied as 50% solutions in propylene carbonate.
Free Radical vs. Cationic Curing Comparison:
| Parameter | Free Radical UV Curing | Cationic UV Curing |
|---|---|---|
| Oligomer | (Meth)acrylate resins, unsaturated polyesters | Epoxy resins, vinyl ether resins |
| Reactive diluent | (Meth)acrylates, vinyl monomers | Vinyl ethers, epoxy compounds |
| Active intermediate | Free radicals | Cations |
| Intermediate lifetime | Short | Long |
| Curing speed | Fast | Slow |
| Post-curing | Negligible | Strong (dark cure) |
| Volume shrinkage | 7%–15% | 3%–5% |
| Oxygen sensitivity | High | None |
| Moisture sensitivity | None | High |
| Alkali sensitivity | None | High |
| Odor | High | Low |
| Cost | Low | High |
2.5 Reactive Diluents
Reactive diluents (also called monomers or functional monomers) are small organic molecules containing polymerizable functional groups. They reduce application viscosity and regulate curing speed and film performance.
- Mono-functional — Acrylates such as 2-ethylhexyl acrylate, glycidyl methacrylate (GMA), styrene, isobornyl methacrylate.
- Di-functional — Polyethylene glycol diacrylate (PEG-200 DA), dipropylene glycol diacrylate (DPGDA), 1,6-hexanediol diacrylate (HDDA).
- Multi-functional — Trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETTA), di-trimethylolpropane tetraacrylate (DTMPTTA), dipentaerythritol pentaacrylate. Higher functionality reduces viscosity-lowering efficiency but increases crosslink density, yielding harder, more scratch-resistant films that may be more brittle.
- Vinyl ethers & low-molecular-weight aliphatic/cycloaliphatic epoxies — Triethylene glycol divinyl ether (DVE3), 1,4-cyclohexanedimethanol divinyl ether (CHVE), 4-hydroxybutyl vinyl ether (HBVE), 1,2-epoxy-4-vinylcyclohexane, oxetanes, and various low-molecular-weight epoxy or epoxy-vinyl ether hybrid materials.
2.6 Oligomers
Oligomers are relatively low-molecular-weight photosensitive resins that constitute the film-forming backbone. Major classes include:
A. Unsaturated Polyester (UPE)
The first-generation UV oligomer, paired with styrene. Contains C=C double bonds with relatively low reactivity. The abundant ester groups in the main chain result in poor alkali resistance. Currently used primarily in wood UV primer applications.
B. Epoxy Acrylate (EA)
Bisphenol-A epoxy acrylate is the fastest-curing oligomer. It delivers high film hardness, high gloss, excellent chemical and heat resistance. Side-chain hydroxyl groups improve adhesion to polar substrates. However, the aromatic ether bonds cause yellowing and chain scission/chalking under prolonged sunlight exposure. Modified versions include fatty acid, polyurethane, silicone, and anhydride-modified epoxy acrylates.
C. Polyurethane Acrylate (PUA)
One of the most important UV oligomers with the largest number of commercial grades, second only to epoxy acrylate in consumption. Urethane linkages form multiple hydrogen bonds between polymer chains, imparting excellent abrasion resistance and flexibility.
Silicone-modified polyurethane acrylates further enhance surface properties such as slip, anti-stain, and release characteristics.
D. Polyester Acrylate (PEA)
Low cost and low viscosity. Can serve as an oligomer or, in some cases, as a reactive diluent. Offers good flexibility and pigment wetting. Multi-functional and amine-modified grades reduce oxygen inhibition and increase curing speed.
E. Polyether Acrylate
Primarily polyethylene glycol and polypropylene glycol-based acrylates. Excellent flexibility, yellowing resistance, low viscosity, and good diluting power. However, mechanical strength, hardness, and chemical resistance are inferior; generally not used as the primary resin.
F. Pure Acrylic Resin
Acrylated polyacrylates or vinyl resins, produced by reacting polyacrylate copolymers with glycidyl acrylate or hydroxy acrylate to graft acryloxy groups. Excellent yellowing resistance and adhesion, but poorer mechanical strength and acid/alkali resistance. Not typically used as the main resin in practice.
G. Silicone Oligomers
Oligomers with a Si–O main chain, functionalized with acryloxy, vinyl, or epoxy groups at terminal or mid-chain positions. The cured film exhibits low surface energy, making it suitable for anti-fouling, moisture-proof, and anti-sticking coatings.
H. Epoxy Resins
Used as oligomers in cationic UV curing. Bisphenol-A epoxies have low cationic curing activity and high viscosity, so they are rarely used. Cycloaliphatic epoxies are preferred — low viscosity, low odor, high reactivity, low shrinkage, and good adhesion to plastics and metals. Applications include can coatings, plastics, electronics, and potting compounds.
I. Water-Based UV Oligomers
Predominantly water-based polyurethane acrylates, offering excellent flexibility and abrasion resistance across a wide range of applications. Other types include water-based epoxy acrylates and water-based polyester acrylates.
J. Other Oligomers
- Hyperbranched oligomers
- Dual-cure oligomers (free radical + cationic / moisture / hydroxyl / thermal)
- Self-initiating oligomers
- Low-viscosity oligomers (for UV inkjet printing)
- Polybutadiene acrylate oligomers (hydrolysis-resistant, high acid/alkali resistance)
- Oligomers for UV-curable powder coatings
- Metal-ion-containing hybrid oligomers
- Amino- or carboxyl-containing oligomers
3. Anti-Graffiti Materials: Structure and Working Principles
Silicone-based anti-graffiti additives leverage the low surface energy of Si–O backbones to create coatings that resist marker ink, paint, and common household stains. Below is a summary of key commercial grades:
| Grade | Chemical Structure | Recommended Applications |
|---|---|---|
| DPM-8244 | Hydroxyl polyether polysiloxane | Excellent compatibility, high transparency, water- and oil-compatible, superior anti-stain and leveling performance. |
| DPM-3869F3 | Multi-acrylate polysiloxane | Participates in free radical curing, excellent durability, designed for matte systems, strong anti-stain effect, pronounced skin-like feel. |
| DPM-3866F4 / 3866F7 | Silicone-modified polyurethane acrylate | 3866F4: excellent compatibility, high transparency, strong anti-stain. 3866F7: slightly lower compatibility, strong anti-stain, good hand feel. |
| DPM-7005 | Multi-functional water-based silicone-modified polyurethane acrylate resin | Outstanding anti-graffiti performance, high gloss, abrasion-resistant. |
| DPM-8586N / 8586 | Multi-epoxy polysiloxane | Recommended for matte systems, provides matting effect, highly efficient anti-stain, smooth slippery feel. |
| DPM-3598F7 | Multi-epoxy polysiloxane | Curable via UV cationic mechanism or conventional epoxy curing agents, excellent anti-stain, suitable for electronic potting and conformal coatings. |
| DPM-8550 / 8553 | Multi-hydroxyl polysiloxane | For water-based two-component PU systems, excellent anti-graffiti, good compatibility. |
| DPM-8554F | Reactive polysiloxane | Water- and oil-compatible in UV systems, suitable for matte systems. |
4. Application Formulations and Test Results
4.1 Solvent-Based UV Anti-Stain Test — Gloss System
Formulation:
| Component | Parts by Weight |
|---|---|
| Anti-graffiti additive | 2 |
| 6-functional resin (6145-100) | 45 |
| TMPTA | 31 |
| 2-functional resin (621-80) | 20 |
| Photoinitiator 184 | 4 |
Results:
- Compatibility: 8244 ≈ 3866F4 > 3869F3 ≈ 8586N
- Anti-stain performance: 8244 = 3866F4 = 3869F3 > 8586N
- Hand feel style:
- 8244 — oily-smooth
- 3866F4 — astringent-smooth
- 3869F3 — skin-like smooth
- 8586N — oily-smooth
4.2 Solvent-Based UV Anti-Stain Test — Matte System
Formulation:
| Component | Parts by Weight |
|---|---|
| Anti-graffiti additive | 2 |
| 6-functional resin (6145-100) | 45 |
| TMPTA | 31 |
| 2-functional resin (621-80) | 20 |
| Photoinitiator 184 | 4 |
| Matting agent 1011 | 8 |
Results:
| Grade | Hand Feel Style | Gloss (60°) |
|---|---|---|
| 8244 | Oily-smooth | 5.4 |
| 3866F4 | Astringent-smooth | 4.2 |
| 3869F3 | Skin-like smooth | 3.8 |
| 3866F7 | Dry-smooth | 4.2 |
Anti-stain ranking: 8244 = 3866F7 ≥ 3866F4 > 3869F3
4.3 Water-Based UV Anti-Stain Test — Gloss System
Formulation (WIN-7005 based):
| Component | Parts by Weight |
|---|---|
| WIN 7005 | 80 |
| Neutralizing agent DMEA | 0.1 |
| DPM | 5 |
| Water | 5 |
| Photoinitiator 1173 | 1 |
| Photoinitiator TPO-L | 1 |
| Leveling agent DPM-8244 | 0.5 |
| Wetting agent DPM-8022 | 1 |
| Water | 6.4 |
| Total | 100 |
4.4 Water-Based UV Anti-Stain Test — Matte System
Formulation (WIN-7005 based):
| Component | Parts by Weight |
|---|---|
| WIN 7005 | 75 |
| Neutralizing agent DMEA | 0.1 |
| DPM | 10 |
| Water | 4.8 |
| Photoinitiator 1173 | 1 |
| Photoinitiator TPO-L | 1 |
| Leveling agent SILOK-8244 | 0.5 |
| Wetting agent SILOK-8022 | 1 |
| Matting agent 1011 | 5 |
| 299 | 0.3 |
| 2020 | 0.3 |
| SILOK-3869F3 | 1 |
| Total | 100 |
4.5 WIN-7005 Coating Test Results
Gloss System
| Test Item | WIN-7005 Coating Result |
|---|---|
| Adhesion (cross-cut, PC/ABS) | Grade 0 |
| Hardness (pencil hardness tester) | >1H |
| Abrasion resistance (1 kg, eraser, 500 cycles) | Slight scratches |
| Oil-based marker resistance (red/blue/black, dry wipe with tissue) | Slight residual marks |
| Water-based red/black ink (1h / 24h, wet wipe) | — |
| Coffee (1h / 24h, wet wipe) | — |
| Vinegar (1h / 24h, wet wipe) | — |
Matte System
| Test Item | WIN-7005 Coating Result |
|---|---|
| Adhesion (cross-cut, PC/ABS) | Grade 0 |
| Hardness (pencil hardness tester) | >1H |
| Abrasion resistance (1 kg, eraser, 500 cycles) | Slight scratches |
| Oil-based marker resistance (red/blue/black, dry wipe with tissue) | Completely removable |
| Water-based red/black ink (1h / 24h, wet wipe) | 1h: completely removable / 24h: completely removable |
| Coffee (1h / 24h, wet wipe) | 1h: completely removable / 24h: completely removable |
| Vinegar (1h / 24h, wet wipe) | 1h: completely removable / 24h: completely removable |
Conclusion
UV-curable anti-graffiti coatings represent a high-performance, low-VOC solution for surface protection. The selection of photoinitiator, reactive diluent, and oligomer system determines the base film properties, while silicone-based additives — particularly the SILOK and WIN series — provide the low-surface-energy functionality essential for anti-graffiti and anti-stain performance. Formulators can choose between solvent-based and water-based systems, and between gloss and matte finishes, depending on substrate, application method, and performance requirements.
For product inquiries and technical support, contact the Deep-Polymer team.
