Silica reaches a given 60 degree gloss at a lower addition rate than polymethylurea, and it costs less per kilogram. Deuteron's own comparison in a solventborne nitrocellulose coating shows fumed and surface-modified silica taking gloss down faster per percent added than Deuteron MK. Polymethylurea (PMU, a urea-methanal thermoset, not a polyurethane or a polymer-modified urethane) needs a slightly higher dosage to reach the same gloss, and at that gloss the formulation has significantly lower viscosity, a harder and more polish-resistant surface, and a softer feel. Which of those the specification pays for decides the choice.
What both particles do to the film
Every particle matting agent works the same way. As the wet film loses solvent or water and shrinks, particles that were suspended in it stand up through the surface, the surface gets rough, and rough surfaces scatter light. Particle size sets roughness and roughness sets gloss. Within one chemistry the matting effect is proportional to particle size, and the particle size has to be matched to the dry film thickness: a 13.8 micron dv90 that reads as texture in a 10 micron film disappears in a 40 micron one.
Precipitated and fumed silica are inorganic and porous, and they build gloss reduction efficiently because a small mass of silica carries a large surface area into the film. Polymethylurea is an organic duromer, a urea-methanal polycondensate synthesized so that the particle comes out highly amorphous, with a comparatively high BET surface area and an oil absorption of 325 g per 100 g for the standard grade. Deuteron's leaflet states that the two are not directly comparable and that every application should be tested for the material in it.
Viscosity is the cost that arrives before gloss does
Silica builds viscosity quickly. In a published study of matting agents in UV coatings, the silica reference showed viscosity that "builds up quickly" while the organic alternatives had "low influence on coating viscosity (compared to standard silica)" and a gloss that stayed essentially stable across the film thicknesses tested, where the silica-matted gloss tracked film thickness almost linearly.
That viscosity is paid for off the additive invoice: in the solvent added to bring the coating back to application viscosity, in the VOC that solvent carries, in the solids given up, and in the application window that narrowed. Deuteron's leaflet states the trade: to reach a similar gloss level a slightly higher dosage of a PMU matting agent is needed, and the viscosity is still significantly lower.
Compare at the same gloss, never the same dosage
Run both ladders to the target gloss, then read viscosity, solids and burnish at that point. Tell us the system and the gloss and we will say where to start the PMU ladder.
Request a SampleDurability: hardness, burnish and the isocyanate bond
A matted surface is a rough surface, and rough surfaces polish. Rubbing a low-gloss film with a cloth, a fingertip or a cardboard carton flattens the peaks and brings the gloss back in patches, which is the defect the coatings trade calls burnishing.
Polymethylurea is a duromer with no melting point, a hardness of about 3.5 Mohs, and long-term temperature stability to 200 degrees C with short-term stability to 300. Deuteron lists outstanding mechanical resistance to scratches and polishing among the properties of the range, along with high anti-blocking and good recoatability. The particle also carries about 0.25 percent free hydroxyl groups. In a two-pack polyurethane, those hydroxyls react with the isocyanate, so the matting particle is bonded into the film instead of sitting in it, which is where the further gain in resistance comes from in 2K systems. A study of organic matting agents for UV coatings made the same point from the other direction: when the matting develops inside the film, the surface does not burnish.
Feel and slip
The finer the PMU grade, the more intensive the smoothing, gliding and slip effect at the surface. Deuteron MK-F and MK-F6 give a smoother, almost waxy appearance, and MK-F7 at 2.5 microns is described for very low friction values. Deuteron names the fine grades for soft-touch coatings, and the effect comes from the matting particle itself, without a fluoropolymer and often without a separate wax. A silica-matted film gets its feel from whatever wax or surface additive is added to it.
Film thickness and consistency on the line
The published UV study found the organic matting agents held an essentially stable gloss across the film thicknesses tested, where the silica-matted gloss changed almost linearly with film thickness. On a spray or roller line where the dry film varies from part to part, a silica-matted gloss varies with it.
Where silica stays
Thick, pigmented, cost-driven films. An industrial primer or a flat wall paint with no feel or polish requirement, applied at a film thickness that hides any particle, and bought on cost per gloss unit, is silica's home and PMU does not improve it. Some systems suit neither on its own: without volume shrinkage there is no roughness to develop, so in 100 percent UV, solvent-free polyurethane and epoxy, and powder coatings, a particle matting agent is often not sufficient by itself.
Combining the two chemistries is normal practice. Deuteron builds silica-modified PMU compounds for the purpose: MM 659 for UV systems with low viscosity impact, MM 680 for two-pack polyurethane, and MM 682 and MM 684 for coil coatings and DIY systems. They are the halfway house for a formulator who wants part of silica's efficiency with the viscosity and feel of PMU.
Where PMU pays
Wood and furniture finishes where the specification says soft touch or deep matte and the part will be handled. Coil and can coatings that take a bake. Printing inks and overprint varnishes where a fine particle has to disappear into a thin film and the print has to survive rub. Two-pack polyurethane topcoats where the hydroxyl bond adds resistance. UV overprint and inkjet, with the sub-micron MM 100 and MM 110 dispersions. And any low-gloss finish that has burnished in service.
Working out the cost per gloss unit honestly
Set the gloss target and read it at 60 degrees, adding 85 degrees below 10 units. Run both matting agents up a ladder to that gloss. At the target, record the addition level, the viscosity, the solvent needed to return to application viscosity, the solids, and whether the wax or slip additive in the silica version is still required with the PMU version. Then burnish both panels and recoat both. The additive line on the costing will favor silica; the other lines decide the total. A ladder for the PMU powders runs from 1 to 15 percent; the finer the grade, the higher the level a given gloss needs.
One handling note applies to both chemistries and matters more for PMU: incorporate with a high-speed dissolver and never through a bead mill. The particle size distribution is the product, and milling grinds it away.
Grades from US stock
Deuteron MK, MK-F and MK-F6 ship from our US warehouse in 10 kg bags, with MM 677 in drums for waterborne auto-dosing. Finer grades, the UV dispersions and the compounds are supplied to order.
See the matting agents rangeFrequently asked
Is a PMU matting agent a one-for-one replacement for silica?
No. Expect a somewhat higher addition level for the same gloss and a lower viscosity at that gloss, so rebalance the solvent down before adjusting anything else, and trial without the wax first. Cross-references to specific silica grades are available on request; the panel decides.
Does polymethylurea contain formaldehyde?
Polymethylurea is a fully reacted urea-methanal polycondensate. The safety data sheet lists the polymer under CAS 9011-05-6 with residual formaldehyde below 0.1 percent. We do not describe it as formaldehyde-free; the SDS and regulatory information sheet carry the figures a qualification review needs.
Which PMU grade do I start with?
Deuteron MK at 6.3 microns dv50 for the majority of coatings above about 15 microns dry. MK-F at 4.6 or MK-F6 at 3.5 microns for thinner films and a smoother feel. PMH C when viscosity is the constraint, since it has the lowest viscosity impact of the organic matting agents. MM 100 or MM 110 for thin UV films and inkjet.
Can silica and PMU be used together?
Yes, and Deuteron sells the combination pre-made in the MM 659, MM 680, MM 682 and MM 684 compounds. A formulator can also blend a silica grade with a PMU grade to tune efficiency against viscosity and feel.