Two UV wood lines running the same gloss target, the same resin and the same cure conditions will not take the same matting agent. The application method changes what the silica has to do, and a grade that performs on a roller coater can produce a visibly rough or hazy panel through a spray gun.
The difference is not subtle. Across the Vistamatt UV range, the grades built for roller application run 5.5–8.5 µm at D50; the grades built for spray run 3.8–4.2 µm. That is roughly a two-fold gap, and it exists for reasons that have nothing to do with gloss.
Why the application method sets the particle size
Roller coating lays down a thicker, more uniform film. On a typical UV roller line the wet film is heavy enough that a 7–8 µm particle sits comfortably below the surface until the film shrinks during cure. The particle then creates the micro-roughness that reduces gloss, and it does so without protruding far enough to be felt. Coarser particles also reach a given gloss at lower loading, which matters on a line where every extra percent of silica is extra cost per square metre.
Spray lays down a thinner, less even film. The wet film is lighter, and it varies across the panel depending on gun distance, overlap and edge effects. A particle sized for roller application will protrude through the thin areas — the result is a panel that reads as gritty under the hand even when the gloss meter is happy. Spray systems also have to atomise cleanly: a coarse tail in the particle distribution increases the chance of nozzle wear and spitting on long runs.
This is why the two ranges do not overlap. It is not that one set of grades is better; it is that the constraint is different.
The roller range: choosing along the particle size gradient
Three grades cover the roller line, and they sit at deliberately separated points.
VS3550U at 5.5–6.0 µm is the fine end of the roller range, with the highest structure of the three (BET 125 m²/g, oil absorption 170 g/100 g). It is the first screen on most roller lines because it preserves the most surface uniformity — the finer particle produces a more even texture across the panel, which shows up when the panel is viewed at a glancing angle under line lighting.
VS370U at 7.0–7.3 µm is the middle position. Structure drops to 105 m²/g BET and 155 g/100 g oil absorption, which means it thickens the formulation less at the same loading — useful when viscosity headroom on the roller is tight.
VS6907 at 8.0–8.5 µm is the coarse end, and its dosage range reflects that: 1–2 % against 1–3 % for the finer two, reaching 3–10 GU rather than 5–15 GU. It is held for deep matte targets where the lower loading is worth trading some surface uniformity for.
The pattern is consistent across the three: as particle size goes up, structure comes down, matting efficiency per unit added goes up, and surface uniformity goes down. Nothing about that ordering is unique to this range — it is the standard trade-off — but knowing the specific values lets you predict which direction to move when a screening round fails.
The spray range: two grades, a narrow window
VS141S and VS641 are close in D50 (3.8–4.0 µm and 3.8–4.2 µm) and close in structure (165 and 160 m²/g BET; 205 and 200 g/100 g oil absorption). Both run 1–3 % to 5–15 GU.
The difference is in the distribution rather than the midpoint. VS141S runs D10 3.0 / D90 4.9 µm; VS641 runs D10 2.9 / D90 5.3 µm. VS141S therefore has the tighter distribution, and its narrower coarse tail is what makes it the first screen where spray appearance is being judged closely — fewer particles at the top end means fewer opportunities for a visible defect on a thin film.
VS641 has a slightly broader spread, which in some systems produces a marginally more forgiving surface at the cost of that tightness. Where a line has variable film build across the panel, the broader distribution sometimes reads better.
When a grade crosses over — and when it should not
Formulators occasionally use a roller grade on a spray line because it is already in the plant, or a spray grade on a roller line because it was the last thing sampled. Both work in the sense that gloss comes down. The failure mode is different in each direction.
Roller grade on a spray line: the panel feels rough where the film is thin, usually at the edges and in overlap zones. Gloss readings can be within specification while the panel is rejected on touch.
Spray grade on a roller line: the surface is smooth, but reaching the gloss target takes materially more silica. Viscosity rises, the formulation may need reworking, and the cost per square metre goes up. This crossover is less damaging than the other, and it is sometimes the right choice when a single grade must cover both lines.
If you do have to run one grade across both processes, the spray range is the safer starting point — it is the direction that fails on cost rather than on appearance.
Screening both lines in one round
If your plant runs both roller and spray, screen for each separately rather than looking for a compromise grade first. Run VS3550U on the roller line and VS141S on the spray line in the same round, both against your own control, both adjusted to your gloss target.
Compare at matched gloss, not matched loading. Because these grades differ in efficiency, running both at the same percentage will produce different gloss readings and tell you nothing useful. Find the loading that meets your target on each line first, then compare surface uniformity, hand feel and cure behaviour at that loading.
What you learn from that round is whether one grade can cover both processes at an acceptable cost, or whether the two lines genuinely need different grades. Either answer is useful; guessing at it is not.
What to send with a sample request
For a UV wood line, the useful information is: application method and line speed, wet and dry film thickness, lamp configuration and cure energy, resin system and its reactivity, target gloss and the angle it is measured at, substrate type, and whether the finished surface is handled in use.
Two details matter more than most: film thickness relative to particle size determines whether a grade will feel rough, and line speed determines how much time the film has to level before cure locks the surface. A grade recommendation made without those two is a guess dressed as advice.