Metallic stearates look deceptively simple on a price list: zinc stearate and calcium stearate, four mesh grades each, all one CAS number per metal. In practice the whole family is decided by three variables that never appear in the product name — particle fineness, metal content and free fatty acid — plus the company the two soaps keep in a formulation. A rigid PVC line can run perfectly on a 600-mesh calcium stearate and plate out badly on a 200-mesh one; a zinc-rich stabiliser package can hold colour for an hour and then go black in seconds. This guide works through those decisions with the grades we supply.
The two soaps do two different jobs — and that is why they are used together
PVC degrades by a self-catalysing chain: unstable chlorine sites split off HCl, and the HCl released accelerates further dehydrochlorination, taking the colour from white to yellow to brown to black. Both stearates interrupt this chain, but at different speeds, which is exactly why the Ca/Zn system works:
- Zinc stearate (CAS 557-05-1) reacts with HCl very fast, replacing it before it can attack the polymer. That gives excellent initial colour — but the zinc chloride formed is a strong Lewis acid that itself catalyses degradation. Push zinc too far or let the temperature run away, and the compound turns dark suddenly and catastrophically: the failure the industry calls zinc burning.
- Calcium stearate (CAS 1592-23-0) is a slower HCl scavenger with weaker initial colour protection, but it does two things zinc cannot: it mops up HCl over a long period, and it reacts with the ZnCl2 formed, regenerating zinc stearate and locking the chlorine up as CaCl2. In other words, calcium defuses the bomb that zinc plants.
A practical Ca/Zn package is therefore never just two soaps: commercial stabiliser blends typically run 20–25% zinc stearate and 20–25% calcium stearate on a carrier of hydrotalcite (15–20%, the main zinc-burning insurance), polyols, β-diketones or phosphites (co-stabilisers), PE wax and paraffin (lubricants) and 25–30% calcium carbonate for handling. Understanding that composition matters, because buying the soaps separately — which is what our catalogue lets you do — gives you control over exactly this ratio.
Mesh size: the number that decides where a grade can go
"Mesh" counts sieve openings per inch, so higher mesh means finer powder. The conversion is not intuitive, and the differences between adjacent grades are large enough to change behaviour on the line:
| Grade | Approx. particle size | Where it fits |
|---|---|---|
| 100–200 mesh | ≈ 75–150 µm | Rubber compounding and dusting, coarse plastic work, cost-sensitive filler roles |
| 325 mesh | ≈ 44–45 µm | General plastics and masterbatch, standard PVC stabiliser work, the workhorse fineness |
| 600 mesh | ≈ 23 µm | Rigid PVC profiles and SPC flooring, high-gloss surfaces, thin films |
| 800 mesh | ≈ 18 µm | Fine films, high-end coatings, primers and sanding sealers, anywhere specks are unacceptable |
The rule of thumb: finer dispersion, better surface, higher price. A 200-mesh powder dispersed in a clear film will read as a visible speck; the same chemistry at 800 mesh disappears. But for rubber dusting or a mould-release role, paying for 800 mesh buys nothing — the coarse grade spreads faster and costs less.
Working dosages
| Application | Typical level | Notes |
|---|---|---|
| Soft PVC (film, cable sheath, hose) | 1.0–2.5 phr total Ca/Zn soaps | Plasticisers lower the heat load; wide Ca/Zn ratio tolerance |
| Rigid PVC pipe | 2.5–3.5 phr | Balance with internal/external lubricants; watch fusion torque |
| Rigid profiles / SPC flooring | 4.0–6.0 phr full pack | High CaCO3 loading (200–300 phr) raises the stabiliser demand |
| Cable compounds | 3.0–6.0 phr | Insulation grades need volume-resistivity checks on the stabiliser |
| PVC foam | 2.0–4.0 phr | Over-stabilising causes local overheating and uneven cells |
| PE / PP (petrochemical grade) | trace–0.2% | Calcium stearate as halogen absorber / residue neutraliser in polymerisation |
| Masterbatch | 1–3% of carrier | Calcium stearate as dispersing aid and lubricant |
| Rubber | as needed | Zinc stearate as dusting/release agent and softener; soft, non-abrasive film |
Two warnings from the extrusion floor. First, the stearates are themselves lubricants — raising them without trimming the wax system changes fusion time and can either slip the screws or, if external lubrication runs short, overheat the melt at the die and trigger exactly the zinc burning you were avoiding. Second, plate-out (waxy die and roll deposits) usually traces to over-lubrication or incompatible low-molecular-weight components, not to the metal soap itself — but a coarse, high-free-acid grade makes it worse.
Beyond the two workhorses
- Calcium stearate in polyolefins. Its oldest large-volume job is the one nobody sees: neutralising catalyst residues and stray halogens in PE and PP, and it doubles as a lubricant in UPE/SMC moulding compounds.
- Zinc stearate as an emulsion. A 40% zinc stearate emulsion (CAS 557-05-1) brings the same hydrophobic, lubricating film to waterborne systems — textile waterproofing, coating flatting, paper and concrete treatments — where a dry powder would not disperse.
- Barium stearate (CAS 6865-35-6) is a high-temperature PVC stabiliser with excellent heat-holding, but barium chemistry is restricted in many export markets; treat it as a regional or industrial-only option and confirm the destination market's rules before specifying it.
- Zinc laurate (CAS 2452-01-9), the C12 analogue, melts lower and lubricates earlier in the fusion curve — a useful trimming tool when a Ca/Zn system fuses late.
- Wax partners. The stearates run best with a lubricant carrier: PE Wax 9038A (CAS 9002-88-4) and Fischer-Tropsch wax (CAS 8002-74-2) are the standard external-lubrication partners in rigid PVC.
The COA lines that matter
Because every grade of a given metal soap shares one CAS number, the specification sheet — not the CAS — is what distinguishes a usable lot from a problem lot. Insist on these lines:
- Metal content: zinc stearate typically 10.3–11.5% Zn; calcium stearate 6.5 ± 0.5% Ca; barium stearate 20 ± 1.5% Ba. Low metal content means the product is cut with free stearic acid — it will lubricate but not stabilise.
- Melting point: zinc stearate ≈ 118–130 °C; calcium stearate ≈ 149–155 °C. A low or broad melting range signals an off-ratio soap or high free acid.
- Free fatty acid: ≤ 0.5–1.0%. Free acid causes odour, plate-out and colour drift.
- Volatiles / moisture: ≤ 1.0% for zinc, ≤ 2.0% heating loss for calcium; water in the powder means fisheyes in film.
- Fineness: state the sieve (e.g. 99% through 325 mesh) rather than accepting "fine powder" — this is the line buyers forget, and the one the mesh table above turns into money.
Selection quick answers
Rigid white PVC with high filler, surface quality critical? 600-mesh calcium stearate, zinc added as the minor soap, hydrotalcite in the pack. Transparent or thin film? 800-mesh grades only; verify free acid on the COA. Rubber dusting and release? 200–325-mesh zinc stearate, coarse is fine. Waterborne textile or coating? The 40% emulsion, not powder. Masterbatch carrier lubrication? 325-mesh calcium stearate. PE/PP plant residue control? Calcium stearate, food-contact-compliant grade if the polymer is food-packaging destined.
Shanghai Better Chemical supplies the complete metallic stearate line — Zinc Stearate 200 Mesh, 325 Mesh, 600 Mesh and 800 Mesh (all CAS 557-05-1), Calcium Stearate 100 Mesh, 200 Mesh, 325 Mesh and 600 Mesh (all CAS 1592-23-0), Zinc Stearate Emulsion 40%, plus Barium Stearate (CAS 6865-35-6), Zinc Laurate (CAS 2452-01-9) and the wax partners Fischer-Tropsch Wax and PE Wax 9038A. Every lot ships with a COA covering metal content, melting point, free fatty acid, volatiles and sieve residue, with TDS/MSDS and samples for line trials. Tell us the polymer, the process and the surface you are selling, and we will match the mesh and confirm current pricing.