Antimony Trioxide in Flame‑Retardant Systems
1 Why Sb₂O₃ is used
| Function | Mechanism |
|---|---|
| Synergist with halogens | Sb₂O₃ reacts in‑situ with HBr/HCl from brominated or chlorinated FRs → volatile antimony halides that scavenge flame‑propagating radicals (H·, OH·). |
| Smoke suppression | Reduces dripping and insulates char, lowering total smoke release 10–40 %. |
| Cost‑effectiveness | Allows 50–70 % less brominated FR to meet UL‑94 V‑0, cutting cost & density. |
2 Typical formulations
| Polymer | Brominated FR | Sb₂O₃ phr | Notes |
|---|---|---|---|
| HIPS TV housing | DecaBDE 9 phr | 3 phr | V‑0 @ 1.6 mm; gloss needs TiO₂. |
| PP cable compound | Br‑masterbatch 17 phr | 6 phr | UL‑94 V‑2, LOI 26 %. |
| PVC flexible sheet | None (Cl source intrinsic) | 3 phr | Boosts LOI from 24 → 30 %. |
| TPU conveyor belt | BrDP 12 phr | 4 phr | Retains 80 % tensile. |
phr = parts per hundred resin (weight).
3 Grade selection
| Parameter | FR grade | Why it matters |
|---|---|---|
| Purity (Sb₂O₃ %) | ≥ 99.5 % | Trace Pb/As limits for RoHS. |
| Particle size (D₅₀) | 0.8–1.2 µm film/cable; 2–3 µm moulding | Smaller → better dispersion, less bloom. |
| Surface treatment | Silane‑coated for PP/HIPS; untreated for PVC | Improves polymer wet‑out, reduces moisture pick‑up. |
| Whiteness (Ry) | 95 min for light‑coloured parts | Avoids yellow cast. |
Our in‑house grades
| Grade | D₅₀ | Surface | Typical use |
|---|---|---|---|
| SB‑110 | 1.0 µm | Silane | PP fibres, cables |
| SB‑300 | 2.5 µm | None | HIPS, ABS mouldings |
| SB‑320WS | 1.2 µm | Wax‑steeped | Low‑dust masterbatch feed. |
4 Regulatory snapshot (2025)
| Region | Status |
|---|---|
| EU CLP | Classified Aquatic Chronic 2 (H411); no REACH restriction but CSR required >10 t yr. |
| EU RoHS | Allowed; trace Pb, Cd, Hg, Cr⁶⁺ limits apply. |
| USA TSCA | Workplan chemical; no ban—EPA risk evaluation due 2026. |
| Prop 65 | Listed for cancer; requires warning in California consumer goods. |
Mitigation: enclose Sb₂O₃ in polymer matrix; provide SDS Section 15 statement.
5 Processing tips & pitfalls
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Dry‑blend first: add Sb₂O₃ with main FR, then feed masterbatch.
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Shear window: too high shear can re‑agglomerate; keep melt temp ≤ 230 °C for PP.
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Moisture: < 0.1 % to prevent voids; use dryer 80 °C / 2 h.
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Corrosion: Antimony halides at processing temp can attack steel; use bimetallic screws if > 15 phr.
6 Alternatives & reduction strategies
| Option | Trade‑off |
|---|---|
| Zinc stannate | Adds smoke suppression but costs 3–4×; higher loading needed. |
| BrFR + Al(OH)₃ (ATH) | Halogen level down, but ATH raises water absorption, drops HDT. |
| Non‑halogen (P‑N) | No Sb₂O₃ required; needs 20–30 phr → density & cost rise. |
7 Quick design checklist
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Target Sb₂O₃ : BrFR ratio 1 : 3 by weight for V‑0.
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Verify heavy‑metal panel (Pb < 5 ppm) for RoHS.
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Include antimony trioxide GWP data in LCA if OEM requests.
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Keep respirable dust control during compounding—OEL 0.5 mg m⁻³ (EU).
(Updated June 2025)