Technical Material · IndustryIn paints, PVC and plastics, the mineral filler defines cost, hardness, strength and processability. Understand what particle size (D50), oil absorption and surface treatment mean — and where dolomite wins and where calcite wins.
Mineral filler has an unfair reputation for being just "cheap bulk." In practice, the mineral powder that goes into a paint or a PVC compound is an engineering ingredient: it changes rheology, hardness, scratch resistance, processability and final cost. And the choice between calcitic calcium carbonate and dolomite is not a matter of indifference.
What each market demands of the powder
An architectural paint wants brightness, opacity and low oil absorption. A rigid PVC (pipe, profile) wants a fine, well-distributed particle, with surface treatment so it does not steal processability. A masterbatch wants dispersion and low abrasiveness so it does not wear the extruder screw. Each application translates into concrete specifications: D50 (mean diameter), top cut (largest particle), oil absorption, abrasiveness, brightness and, in many cases, a stearate coating.
Where dolomite wins
Dolomite is harder than calcite (higher Mohs hardness), which translates into scratch and scrub resistance in paints, and mechanical strength in compounds. It tends to have low oil absorption — good for carrying more without thickening the formulation too much — and a competitive cost. In glass, the MgO in dolomite is part of the formulation itself.
Where calcite wins — and we say so
For the premium white, where maximum brightness is what rules (high-grade white paints, cosmetics, printing paper), high-brightness calcitic carbonate holds the advantage. A 100% dolomitic line does not contest that maximum-brightness niche — and pretending it does would be a technical dishonesty that the formulation chemist dismantles in the first trial. The right positioning is to take dolomite to the markets where hardness, scrub, low oil absorption and cost are what decide.
Micronized, and why
Here the product is the rock ground to controlled finenesses (micronized/micropulverized), not calcined. What defines the grade is the D50 and the surface treatment: coarser grades for flexible PVC and construction; fine, coated grades for rigid PVC, plastic and masterbatch. The quality leap is in the classification — guaranteeing the top cut, without the out-of-range coarse particle that scratches a film or jams a screen.
Our micronized line is 100% dolomitic, with grades by D50 and stearate-treated versions, backed by our in-house XRF lab. We sell value-in-use: what the powder does in the customer's final product.
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