GB 18581-2020 “Limit of Harmful Substances of Wood Coatings” is China’s mandatory national standard for coatings applied to wood furniture and woodware (putty, primer, topcoat, stain). Issued on 2020-03-04 and effective 2020-12-01, it merges the former solvent-borne GB 18581-2009 and waterborne GB 24410-2009 into one document covering solvent-borne, waterborne and radiation-curable (UV) coatings, and specifies limits, test methods and inspection rules for VOC, benzene, halogenated solvents, free isocyanate, free formaldehyde, APEO, glycol ethers, phthalates, polycyclic aromatic hydrocarbons and soluble heavy metals.
TL;DR
- Scope: an as-shipped gate for wood coatings, not the finished-furniture limit (that is GB 18584 / GB/T 3324).
- Tiers: solvent-borne / waterborne / radiation-curable, further split by clearcoat, colour coat, primer and putty — no single blanket value.
- Key limits: PU high-gloss topcoat VOC ≤ 550 g/L, NC ≤ 700 g/L; waterborne colour coat VOC ≤ 250 g/L; benzene ≤ 0.1% by mass; waterborne free formaldehyde ≤ 100 mg/kg; APEO ≤ 1000 mg/kg.
- Trend: limits tightened versus the old versions; waterborne, UV/radiation-curable and high-solids are the main compliance routes, while solvent-borne nitrocellulose is squeezed out of indoor site coating.
- Handling: separate factory (VOC, formaldehyde, etc.) from type (full) testing and back procurement, e-commerce and project acceptance with third-party reports.
Key figures at a glance
- VOC (g/L): solvent PU high-gloss ≤550 / low-gloss ≤650 / primer ≤600; nitrocellulose ≤700; alkyd ≤450; unsaturated polyester ≤420. Waterborne colour ≤250 / clear ≤300. UV waterborne ≤250 / non-waterborne ≤420.
- Benzene (by mass): solvent and non-waterborne UV ≤ 0.1%.
- Free isocyanate (TDI/HDI, by mass): moisture-cure PU ≤ 0.4%, other PU ≤ 0.2%.
- Free formaldehyde (mg/kg): waterborne coatings and putty ≤ 100.
- APEO (mg/kg): waterborne (incl. waterborne UV) ≤ 1000.
- Soluble heavy metals (mg/kg): for colour coats, putty and alkyd clearcoat — total lead ≤90, cadmium ≤75, chromium ≤60, mercury ≤60.
- Others: halogen total ≤0.1%; glycol ethers and esters ≤300 mg/kg; PAH ≤200 mg/kg; phthalates ≤0.2% (NC); methanol ≤0.3%.
Limit comparison across the three classes
Core limits by coating class for quick formulation and purchasing reference (“—” = no separate limit or not applicable; the standard text governs).
| Item (unit) | Solvent-borne | Waterborne | Radiation-curable (UV) |
|---|---|---|---|
| VOC (g/L) | PU gloss ≤550 / low ≤650 / primer ≤600; NC ≤700; alkyd ≤450 | colour ≤250 / clear ≤300 | waterborne ≤250 / non-waterborne ≤420 |
| Benzene (%) | ≤0.1 | — | non-waterborne ≤0.1 |
| Free isocyanate (%) | moisture-cure ≤0.4 / other ≤0.2 | — | — |
| Free formaldehyde (mg/kg) | — | ≤100 | — |
| APEO (mg/kg) | — | ≤1000 | waterborne ≤1000 |
| Halogen total (%) | ≤0.1 (some) | colour ≤0.1 | — |
| Glycol ethers (mg/kg) | PU ≤300 | — | — |
| PAH (mg/kg) | ≤200 | ≤200 | — |
| Soluble heavy metals (mg/kg) | lead ≤90 / Cd ≤75 / Cr ≤60 / Hg ≤60 — colour, putty, alkyd clear |
What each figure means and where it comes from
VOC — organics released while drying
VOC reflects the organic matter released to indoor air and atmosphere during coating and drying. Solvent-borne systems run high on aromatics/esters/ketones/alcohols; waterborne systems are water-dominated and lean on a few coalescents, so colour-coat VOC is capped at 250 g/L; radiation-curable systems contain almost no volatile solvent and their VOC comes from residual monomer.
Benzene, toluene/xylene and halogenated solvents
Benzene is a strictly controlled substance (≤0.1% for solvent and non-waterborne UV). Toluene, xylene and ethylbenzene are managed together with low-toxicity solvent substitution. Halogenated (chlorinated/brominated) solvents are limited to ≤0.1% over ozone and toxicity concerns; switch to halogen-free esters and glycol esters.
Free isocyanate
Free HDI/TDI left in two-component polyurethane hardeners is a strong sensitiser; the standard tiers it at ≤0.4% (moisture-cure) or ≤0.2% (other PU). Low-free hardeners plus thin-film stripping are the main controls.
Formaldehyde, APEO, heavy metals, phthalates, PAH
In waterborne systems formaldehyde comes from resin/hardener hydrolysis and preservation, capped at 100 mg/kg; APEO (nonyl/octylphenol ethoxylates) once used as emulsifiers is capped at 1000 mg/kg and is replaced by alcohol ethoxylates, phosphates or reactive macromolecular emulsifiers. Heavy metals enter through pigments and driers and are limited on a soluble-migration basis.
How to read the test methods
- VOC: solvent systems use a difference/density method (GB/T 23985 family); radiation-curable systems use the dedicated method.
- Benzene and BTEX: gas chromatography (GB/T 23990 family) for benzene plus toluene/ethylbenzene/xylene totals.
- Free formaldehyde (waterborne): acetylacetone spectrophotometry or HPLC.
- Soluble heavy metals: digestion then AAS / ICP-OES / ICP-MS.
- Halogen, glycol ethers, phthalates, PAH: GC-MS separation and mass detection.
Formulation and waterborne compliance routes
Solvent-borne: high solids, benzene- and halogen-free
Keep solvent-borne hand and levelling while meeting limits by raising resin solids, replacing aromatics with acetates and propylene-glycol esters, stripping free isocyanate, and moving to lead/mercury-free pigments and zirconium/calcium driers.
Waterborne: coalescent and emulsion synergy
The crux is dosing the coalescent, which contributes VOC yet sets MFFT. Efficient coalescents, core-shell or self-crosslinking emulsions and low-temperature film-forming resins hold hardness, water resistance and the open/re-block window within VOC ≤250/300 g/L.
Radiation-curable: low monomer plus LED
UV/UV-LED is inherently low-VOC; control residual monomer and diluent volatility, choose low-odour epoxy/aliphatic polyurethane acrylates and match lamp power to dose (see the UVLED wood-coating power article).
Line and compliance management
The standard splits inspection into factory testing (key items such as VOC and formaldehyde, per batch) and type testing (all items, at least every six months in normal production and on new product, major raw-material or process change, restart after shutdown, or regulator request). Practical actions: archive raw-material SDS/compliance statements, verify supplier third-party reports, keep retain samples and batch release records, keep label claims consistent with the actual system, and map export differences to target-market rules.
FAQ
Is low-VOC waterborne automatically compliant?
No. Waterborne systems must also meet free formaldehyde ≤100 mg/kg, APEO ≤1000 mg/kg, and colour-coat halogen/PAH limits, and over-dosed coalescent can still breach VOC — judge on the full set.
Which solvent tier is tighter, PU or nitrocellulose?
PU high-gloss ≤550 g/L and primer ≤600 g/L versus NC ≤700 g/L. NC has a higher numeric ceiling but is being replaced by waterborne and UV in indoor site work due to restrictions and odour.
Why cap free isocyanate separately?
Free HDI/TDI in two-component hardeners is a strong sensitiser affecting application and cured-film safety; it is tiered at ≤0.4%/≤0.2% and controlled with low-free hardeners and stripping.
Why are heavy metals limited only for colour coats, putty and alkyd clear?
Metals come mainly from pigments and some additives; transparent clears contain almost no pigment, so limits apply to colour coats, putty and alkyd clear (lead ≤90, Cd ≤75, Cr ≤60, Hg ≤60 mg/kg).
Do test reports cover e-commerce and project acceptance?
Yes, but match lab accreditation, report format and sample class to the use case; storefront entry, procurement, acceptance and factory audits each impose different method and wording requirements.
Last updated: 2026-10-12. Prepared by the technical team of Kexin New Materials (Guangdong) Co., Ltd. for B2B formulation, procurement and coating-compliance reference; not a basis for test adjudication. All limits and methods are subject to the GB 18581-2020 text and its referenced files.
Sources: GB 18581-2020 “Limit of Harmful Substances of Wood Coatings” (issued 2020-03-04, effective 2020-12-01, superseding GB 18581-2009 and GB 24410-2009); public standard interpretations and third-party testing-house compilations; illustrative VOC figures drawn from published wood-coating testing data.