Calcium Carbonate for White Masterbatch: Choosing a Grade and Extending Titanium Dioxide

In short: In white masterbatch, titanium dioxide is the expensive ingredient and calcium carbonate's job is to extend it — let you remove part of the TiO₂ while the product stays white and opaque. That only works with the right grade: fine (tight D97 top cut), high whiteness (≥98 / ISO brightness ≥95), low iron (Fe₂O₃ ≤0.05%), usually coated. Choose that grade and the TiO₂ you remove — often 15–35% of the loading — is usually worth far more than the filler costs. This guide covers grade choice, how far you can extend, and what to check, and it keeps white masterbatch separate from filler masterbatch, which is a different product.

These two products are often confused, and the calcium carbonate you want is different for each.

• White masterbatch is a colour masterbatch. Its job is to make the finished product white and opaque. Its main functional ingredient is titanium dioxide (TiO₂), the white pigment that provides hiding power. Calcium carbonate goes in as an extender — it lets you use less of the expensive pigment while holding the whiteness spec.
• Filler masterbatch (calpet) is a cost-down product. Its job is to replace part of the resin with cheap mineral, adding stiffness and lowering raw-material cost. Whiteness is secondary. (That product has its own guide: filler masterbatch / calpet.)

The rest of this guide is about white masterbatch — where the calcium carbonate is chosen to protect a whiteness spec and make a pigment budget go further, not simply to fill.

White masterbatch economics are dominated by one line: the titanium dioxide. TiO₂ is one of the most expensive routine ingredients in any white formulation, and a white masterbatch is mostly there to carry it. So anything that lets you use less TiO₂ per kilogram of finished product, without losing the white, lowers your cost directly.

That is what a high-whiteness calcium carbonate does — but only by extension, not replacement. TiO₂ hides because its refractive index (about 2.7) is far from the polymer's (about 1.5), so it scatters light strongly. Calcium carbonate's refractive index (about 1.6) is so close to the polymer's that it scatters almost nothing — it adds whiteness, not opacity. So calcium carbonate cannot take over TiO₂'s hiding job. What it can do is let you remove the part of the TiO₂ that is doing whiteness work rather than hiding work, and correct the base colour so the remaining TiO₂ goes further. (The full mechanism and the honest limits are in how much titanium dioxide calcium carbonate can replace.)

The lever that decides how far you can go is the filler's own whiteness. A dull 90–96 whiteness filler carries a yellow or grey cast — so as you load it, TiO₂ has to be spent correcting the filler, and you gain little. A clean ≥98 whiteness, low-iron filler is close to neutral in the compound, so more TiO₂ can come out before the white drops out of spec. That is the whole reason the grade matters.

White masterbatch usually ends up in thin film, sheet, and surface-critical products, and it runs a high mineral loading. Four properties decide the grade:

In the Kantor KC Series that points to KC-4 (D97 ~5.5 µm) for premium white masterbatch and fine film, or KC-6 (D97 ~6 µm) for general white masterbatch — both at whiteness ≥98 / ISO brightness ≥95 (R457/ISO 2470), CaCO₃ ≥98%, Fe₂O₃ ≤0.05%, coated or uncoated. Match the top cut to the thinnest product your masterbatch ends up in — the fuller grade-selection logic is in which grade for your application.

One point buyers often get wrong: whiteness is only comparable when measured the same way. "Whiteness 98" from two suppliers can mean different things on different scales; ISO brightness (R457) is the method-defined number you can compare. Ask for both, with the method named. (Explained in full: whiteness vs. ISO brightness.)

The extendable share is not a fixed number — it depends on your product, its thickness, its whiteness spec, and the filler's whiteness. Application work puts white masterbatch around 15–35% of the TiO₂ loading, with an ordinary 90–96 whiteness filler reaching only the low end and a ≥98 whiteness grade reaching the high end. Treat that as a starting point for a trial, not a promise.

The only figure that counts is the one you measure on your own line. Run a step-down trial: establish your baseline whiteness and opacity, then step the TiO₂ down in stages — with the calcium carbonate stepping in — and measure at each stage. The last step that still meets your spec is your ceiling. From there, the pigment you save is a real saving, and it is usually far larger than the filler cost — you can run the numbers on your own loading and prices with the filler economics calculator.

White masterbatch runs a high mineral loading, and at high loading dispersion is what decides whether quality holds. A stearic-acid coating makes the calcium carbonate organophilic, so it disperses cleanly in the PP or PE carrier, picks up less moisture, and agglomerates less. Fine grades benefit most, because fine particles agglomerate more without a coating. Uncoated can work at lower loadings or where your compounding line disperses well on its own. (The full decision: coated vs. uncoated calcium carbonate.)

Loading depends on your formulation and the whiteness you must hold — there is no single right number, and pushing the mineral up to cut cost can quietly cost you more through dispersion defects and rejects. Set the loading on your line, at your whiteness spec, not on a target percentage.

Before you add a white-masterbatch grade to your formula, check the per-lot certificate of analysis against the technical data sheet — with these parameters first:

• Whiteness and ISO brightness, with the method stated — the number that sets your extension ceiling.
• The D97 top cut — the coarse tail causes the specks and tears that show up in thin film.
• Iron (Fe₂O₃) — the parameter that predicts whether lot 14 stays as white as lot 1.
• Coating level and moisture — dispersion in your carrier depends on them.

The full method for reading the certificate and running a sample-then-trial qualification is in how to qualify a new calcium carbonate supplier.

One note for food-contact white masterbatch (white bottles, caps, and closures): the qualifying gate there is not whiteness — it is an accredited heavy-metals panel (lead, arsenic, cadmium, mercury) and a food-contact declaration. Ask for it specifically if your white masterbatch ends up in food packaging.

The right grade for your white masterbatch is settled where it runs, not on a spec sheet. Send your application, the whiteness spec you hold, and your current TiO₂ loading, and we will recommend a KC grade and send a free sample (under a tonne) with its per-lot COA — so you can run the step-down and confirm the whiteness and dispersion on your own line before you commit to anything. Start from the product page.

One honesty note: the KC Series COA today reports whiteness, brightness, and particle size (on a Malvern analyser) to our current spec; a heavy-metals panel at an accredited laboratory is in progress and will be supplied with the COA once complete, which matters if your white masterbatch is for food-contact use.

What calcium carbonate grade is best for white masterbatch?

A fine, high-whiteness, low-iron grade — KC-4 (D97 ~5.5 µm) or KC-6 (~6 µm) in the KC Series. White masterbatch goes into thin, surface-critical products, so the top cut must be fine; whiteness must be high (≥98 / ISO brightness ≥95) so the filler does not pull the base colour down; and iron must be low (Fe₂O₃ ≤0.05%) so whiteness holds lot to lot. Coated helps dispersion at high loadings.

Does calcium carbonate replace titanium dioxide in white masterbatch?

It extends it, not replaces it. TiO₂ provides the opacity that makes a product white and solid; calcium carbonate provides almost none. A high-whiteness grade lets you remove part of the TiO₂ — often 15–35% of the loading — while the product holds its whiteness and opacity spec. The pigment removed is usually worth far more than the filler difference.

How much titanium dioxide can I save in white masterbatch with calcium carbonate?

Your lab's number, not a supplier's promise. Application work puts white masterbatch at 15–35% of the TiO₂ loading, depending on your product, thickness, whiteness spec, and the filler's whiteness. Confirm it with a step-down trial on your own line.

What is the difference between white masterbatch and filler masterbatch?

White masterbatch is a colour masterbatch — its job is to make the product white, and TiO₂ is its main ingredient, with calcium carbonate as an extender. Filler masterbatch (calpet) is a cost-down product — its job is to replace resin with cheap calcium carbonate, with whiteness secondary. Same mineral, different role and different grade.

Should the calcium carbonate for white masterbatch be coated?

Usually yes — white masterbatch runs a high mineral loading, and a stearic-acid coating makes the calcium carbonate disperse cleanly, absorb less moisture, and agglomerate less, which matters for thin film. Fine grades especially benefit. Uncoated can work at lower loadings or where your line disperses well on its own.