The multitool of flame retardant synergists: zinc borate suppresses smoke, promotes char, kills afterglow — and since the antimony price shock, it has become the standard way to formulate antimony-lean. Supplied as fine powder and in pre-balanced packages for PVC cable, brominated systems, LSZH compounds and engineering plastics.
Fig. ZB01 — zinc borate powder at incoming QCFine white zinc borate powder checked before formulation.
Zinc borate is a hydrated inorganic borate (the workhorse grade is the 2ZnO·3B₂O₃·3.5H₂O type) that holds its water of hydration past ~290 °C — high enough to survive PVC, polyolefin and most engineering-plastic processing. It is rarely the star of a formulation; it is the additive that makes the star perform — and cost — better.
In PVC and brominated systems, zinc borate replaces up to ~75% of the antimony trioxide while holding the flame rating — the formulation answer to antimony’s price volatility and SVHC scrutiny.
Antimony boosts flames retardancy but worsens smoke; zinc borate pulls the other way — sealing char and trapping carbon in the condensed phase instead of releasing it as soot.
In engineering plastics and rubber, zinc borate suppresses afterglow (the smolder after flame-out) and improves arc and tracking behavior — small doses that fix specific test failures.
Mostly condensed-phase action — which is exactly why it complements gas-phase halogen systems instead of competing with them.
Above ~290 °C the borate dehydrates and boron oxide flows into a glassy film that seals the char, insulates the polymer and blocks fuel release.
Bound water leaves endothermically — a small heat-sink effect — while zinc species catalyze crosslinking and char formation, keeping carbon out of the smoke plume.
In halogenated systems, zinc borate forms volatile zinc halides that supplement the gas-phase radical quenching — the chemistry behind partial antimony replacement.
Almost always as a partner — to antimony, to bromine, to ATH/MDH. The dose is small; the effect on smoke, cost and specific test clauses is not.
| Application | Partner System | Typical Dose | What It Fixes | Related Page |
|---|---|---|---|---|
| Flexible PVC cable & sheet | Sb₂O₃ + plasticized PVC | 2–8 phr | Smoke density; antimony-lean cost; LOI support | PVC flame retardant |
| Brominated systems (PE, PP, ABS) | Brominated FR + Sb₂O₃ | Replaces up to ~75% of Sb₂O₃ | Antimony exposure; smoke; char strength | Brominated additives |
| LSZH / halogen-free compounds | ATH or MDH mineral base | 2–10 phr | Char sealing; smoke; drip behavior | Mineral FR (MDH & ATH) |
| Engineering plastics (PA, PBT) | Brominated or phosphinate systems | 1–5 phr | Afterglow; CTI / arc tracking | FR PBT guide |
| Rubber, coatings & epoxy | System-dependent | 3–15 phr | Smolder suppression; char quality | — |
Not rivals — teammates with different strengths. The practical question since the 2024–2025 antimony price shock is not “which one” but “what ratio”.
Smoke, cost stability or antimony scrutiny are pushing the formulation.
Raw flame efficiency per kilogram is the binding constraint.
Grade and ratio are formulation decisions, not catalog picks — the right split between zinc borate, antimony and minerals depends on which test clause is hardest in your spec.
We supply zinc borate as fine powder and — more usefully — inside pre-balanced packages: antimony-lean PVC systems, brominated packages and LSZH boosters, each burn-verified in-house at the substitution ratio we quote.
Fig. ZB02 — burn verification in our labEvery substitution ratio is burn-tested before we quote it.
Fig. ZB03 — export packagingBags, big bags and palletized supply for overseas buyers.Direct answers for formulators and procurement evaluating zinc borate before sampling.
As a multifunctional synergist: suppressing smoke, promoting and sealing char, stopping afterglow, improving arc tracking — and, most prominently since the antimony price shock, replacing a large share of antimony trioxide in PVC and brominated systems.
Usually not fully. Substitution up to ~75% of the Sb₂O₃ holds flame performance in most PVC and brominated systems with better smoke as a bonus; going to 100% typically costs LOI and rating margin. Most antimony-lean packages keep a reduced antimony core.
Yes — as a char and smoke booster alongside ATH or MDH in LSZH-type compounds, typically at 2–10 phr. It is itself halogen-free and antimony-free, so it fits either side of the halogen divide.
PVC cable: 2–8 phr alongside a reduced antimony core. Brominated polyolefins: begin by substituting a third of the Sb₂O₃ and ladder from there. Afterglow/CTI fixes in engineering plastics: 1–5 phr. We burn-test the ladder before recommending a final ratio.
Tell us the host system (PVC, brominated or halogen-free), the hardest clause in your spec, and your current antimony loading if the goal is substitution. We will design the ratio and prove it in our burn lab before you commit a trial.