How to Select Matting Agents for UV Cure Coatings
100% solid UV systems impose unique constraints that standard silica cannot meet. This guide explains the critical parameters, common failure modes, and grade selection logic for UV wood, floor, and plastic coatings.
Why UV Cure Coatings Demand a Different Matting Agent
Most formulators start with the same silica matting agent across all coating systems. In solvent-based and waterborne coatings, this is often acceptable. In 100% solid UV systems, it leads to serious failures.
UV coatings are fundamentally different from solvent-based systems in three ways that directly affect matting agent performance:
No Solvent Evaporation
All components remain in the film. Silica particles are fully embedded — meaning you need slightly higher loading to achieve the same gloss reduction compared to solvent systems.
Very Low Viscosity
UV monomers and oligomers have viscosities far below conventional resins. Standard silica settles rapidly and forms hard, unredispersible cakes within days of storage.
Rapid Radical Curing
The curing reaction is near-instantaneous. Any wax treatment on the silica surface can migrate to the film surface during this process, creating a "weak boundary layer" that destroys inter-coat adhesion.
Key Parameters for UV Matting Agent Selection
When evaluating a silica matting agent for UV cure coatings, four technical parameters determine suitability:
1. Surface Treatment Chemistry
This is the most critical parameter in UV systems. The treatment must provide anti-settling performance without using migrating waxes. Look for proprietary organic treatments or specialized non-wax surface modifications that provide steric hindrance against settling while remaining chemically inert during UV cure.
2. Particle Size (D50)
Particle size must be matched to the dry film thickness (DFT) of the coating. A particle protruding above the film surface creates excessive surface roughness; a particle fully buried below the surface contributes little to gloss reduction.
| Dry Film Thickness | Recommended D50 | Typical Application |
|---|---|---|
| 15 – 25 µm (thin) | 7.0 – 7.5 µm | UV spray topcoat, OPV |
| 25 – 30 µm (medium) | 7.5 – 8.0 µm | UV wood topcoat (standard) |
| > 30 µm (thick) | 8.0 – 8.5 µm | UV roller coat, floor primer |
3. Oil Absorption
High oil absorption silica (>250 g/100g) drastically increases viscosity in 100% solid UV systems, making roller and spray application impossible. For UV formulations, target an oil absorption of 130 – 220 g/100g to balance matting efficiency with workable rheology.
4. Pore Volume
Pore volume (ml/g) governs how much UV monomer/oligomer is absorbed into the silica particle. Excessively high pore volume leads to monomer absorption, reducing cure efficiency at the particle surface and causing soft spots in the cured film. For UV systems, a pore volume of 1.4 – 1.8 ml/g is the appropriate range.
GMATT UV Grade Comparison
The GMATT UV Series is engineered specifically for 100% solid UV coatings. All grades use a proprietary organic treatment — no PE wax — ensuring zero inter-coat adhesion loss. Select grade based on your target DFT and application method.
| Grade | D50 (µm) | Oil Absorption (g/100g) | Pore Volume (ml/g) | Target DFT | Primary Use |
|---|---|---|---|---|---|
| GMATT U700 | 7.0 – 7.5 | 130 – 200 | ≥ 1.4 | 15 – 25 µm | UV spray, OPV, thin topcoat |
| GMATT U750 | 7.5 – 8.0 | 130 – 200 | ≥ 1.4 | 25 – 30 µm | UV wood topcoat (standard) |
| GMATT U800 | 8.0 – 8.5 | 170 – 220 | ≥ 1.4 | > 30 µm | UV roller coat, floor, heavy primer |
* Highlighted row indicates most commonly specified grade. All grades: SiO₂ ≥ 99.0%, pH 6.0–8.0, surface treatment: specialized organic (non-wax).
Grade Selection by UV Application
UV Wood Flooring (Roller Coat)
UV wood flooring is the most demanding application in this category. Roller coating lines operate at high speed with thick films (DFT 30–60 µm), and the coating must withstand heavy foot traffic after cure. The matting agent must provide strong matting power, excellent scratch resistance, and robust anti-settling during storage.
Recommended: GMATT U800. The larger D50 (8.0–8.5 µm) is well-matched to thick film DFT, and the controlled oil absorption (170–220 g/100g) prevents viscosity problems in roller coat viscosity ranges.
UV Wood Topcoat (Spray)
Furniture and cabinet UV spray topcoats typically run at DFT 20–30 µm. The key requirements are high transparency (no hazing over dark wood grain), efficient gloss control, and stable anti-settling in the low-viscosity spray formulation.
Recommended: GMATT U750 for standard DFT. For ultra-thin decorative coatings below 20 µm, consider GMATT U700 to avoid particles protruding above the film surface.
UV Plastic Coating (3C Electronics)
UV coatings on mobile phone casings, laptop lids, and automotive interior panels require exceptional surface smoothness alongside gloss control. The formulation viscosity is typically very low (reactive diluent-heavy), making anti-settling the primary challenge.
Recommended: GMATT U700 or U750. The specialized organic treatment provides steric hindrance that keeps particles soft-settled — easily redispersed with gentle agitation — even in near-water-thin monomer blends.
UV Overprint Varnish (OPV) for Packaging
OPV applications run very thin (DFT 5–15 µm) and require absolute clarity to preserve print colour fidelity. The matting agent must not scatter light or cause haze over process colours.
Recommended: GMATT U700. Use at the lower end of the dosage range (3–5%) and optimise dispersion with high-shear mixing before letdown.
| UV Application | Recommended Grade | Key Reason |
|---|---|---|
| Wood flooring — roller | GMATT U800 | Large D50 matches thick DFT; high scratch resistance |
| Wood topcoat — spray | GMATT U750 | Balanced matting and transparency for medium DFT |
| Plastic / 3C — spray | GMATT U700 | Finest particle; superior anti-settling in low viscosity |
| OPV packaging | GMATT U700 | Minimum haze; low dosage sufficient for thin film |
| UV floor primer | GMATT U800 | High loading tolerance; robust suspension |
Dosage Guide for UV Matting Agents
Dosage in UV cure coatings is slightly higher than equivalent solvent-based systems because there is no film shrinkage during cure. In solvent systems, solvent evaporation concentrates the silica particles near the surface, enhancing gloss reduction efficiency. In 100% solid UV, the particles remain exactly where dispersed.
| Target Gloss (60°) | Finish Level | Suggested Dosage (UV) | Equivalent Solvent Dosage |
|---|---|---|---|
| 0 – 5 GU | Dead matte | 8 – 12% | 5 – 8% |
| 5 – 15 GU | Matte | 6 – 9% | 4 – 6% |
| 15 – 35 GU | Satin | 4 – 6% | 2 – 4% |
| 35 – 60 GU | Semi-gloss | 2 – 3% | 1 – 2% |
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Pre-disperse in reactive diluent
Disperse the matting agent in a portion of the reactive diluent (TPGDA, HDDA, or similar) at 2,000–3,000 rpm for 15–20 minutes before adding to the main resin blend. This prevents agglomeration.
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Add to resin blend at low shear
Add the pre-dispersion to the main oligomer/resin blend under gentle stirring (500–800 rpm). High shear at this stage can break down the silica particle structure and reduce matting efficiency.
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Check anti-settling before use
After 24 hours of storage, check for settling. The GMATT UV Series should form a soft, easily stirrable sediment — not a hard cake. If hard settling occurs, increase the fumed silica thixotrope loading by 0.2–0.5%.
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Measure gloss at correct angle
Always measure at 60° for matte and semi-gloss finishes. 85° measurement is appropriate only for near-dead-matte finishes below 5 GU. Cure the film fully before measurement — under-cured films give misleadingly low gloss readings.
Troubleshooting UV Matting Agent Problems
Problem: Hard cake settling after 1–2 weeks
Cause: Insufficient anti-settling treatment or formulation viscosity too low. Solution: Switch to GMATT UV Series (proprietary organic treatment) and/or add 0.3–0.5% hydrophobic fumed silica (SEMISIL R202) to build a thixotropic network.
Problem: Inter-coat adhesion failure
Cause: PE wax-treated matting agent migrating to film surface during UV cure. Solution: Replace immediately with GMATT UV Series — non-wax organic treatment does not migrate. No other fix is reliable.
Problem: Excessive viscosity increase
Cause: Oil absorption of matting agent too high for the 100% solid system. Solution: Switch to GMATT UV Series (oil absorption 130–220 g/100g). Reduce loading by 1–2% and compensate with a finer reactive diluent.
Problem: Surface roughness / sandy feel
Cause: Particle size D50 too large for the actual dry film thickness. Solution: Measure your actual DFT with a film thickness gauge and select grade accordingly — U700 for thin films, U750 for medium, U800 for thick.
Problem: Haze or cloudiness on dark substrates
Cause: Silica refractive index mismatch with resin, or particle size too large scattering visible light. Solution: Reduce dosage and switch to a finer grade (U700). Ensure full UV cure — under-cured films always appear hazy.
Problem: Inconsistent gloss batch-to-batch
Cause: Variable dispersion quality or inconsistent cure energy. Solution: Standardise pre-dispersion procedure. Check UV lamp energy output with a radiometer — degraded lamps give variable cure and variable gloss.