Interior VOC and Odor: Low-Emission Coatings for Car Trim Parts

Interior volatile organic compounds (VOC) and odor — interior air quality, commonly called VIAQ in the industry — is the sum of the low-molecular-weight organics and semi-volatile organic compounds (SVOC) that plastics and rubber parts, foam layers, adhesives, textile and leather dressings and the interior coating itself give off inside the passenger compartment under the drive of temperature, and that then build up in a small sealed volume into a concentration level and an olfactory impression. Its technical definition rests on three layers of scope: the whole-vehicle air limit layer (e.g. the eight pollutant concentration requirements of GB/T 27630-2011), the component and material emission layer (e.g. GB/T 39897-2021, VDA 278 and the chamber / bag / thermal-desorption scopes of the ISO 12219 series), and the sensory and condensate layer (the 1–6 grade odor panel ratings of VDA 270, the fogging values of DIN 75201). For a trim coating, judging low-emission capability on a single TVOC number is not enough: the coating is at once an emission source (residual solvent, unreacted monomer, additives, and thermally driven release from insufficient crosslinking) and an emission path (the skin coat blocks or delays odor escaping from the foam and the carrier beneath it). These two identities are why formulation, process and acceptance criteria have to be designed separately.

The typical situation goes like this: a car that has just come off final assembly stands outside in the summer sun for two hours, the door opens, and the front occupant is hit by a harsh new-car smell; the instrument-panel skin feels tacky and the steering-wheel trim ring gives off a plastic odor. After the owner complains the OEM runs a whole-vehicle chamber test: benzene and formaldehyde are both inside the GB/T 27630-2011 limits and TVOC passes as well, yet the odor rating still lands at grade 4. The responsibility chain then starts to pull back and forth. The trim supplier produces a material-level VDA 270 report showing the skin at grade 3.0 and the foam at grade 2.5; the coating supplier says the product VOC is only 60 g/L, far below the ≤450 g/L waterborne-primer ceiling that GB 24409-2020 sets for coatings for interior parts; while the third-party report in the SQE's hands shows acetaldehyde and acrolein clearly rising under the 65 ℃ condition. All three sets of data are correct — they simply are not aligned to the same test conditions and the same decision scope. This article writes out, item by item, the mechanisms, limits, methods, formulation routes and acceptance wording along this chain, so that the argument comes back to numbers and standard numbers.

TL;DR: the conclusions first

• GB/T 27630-2011 covers only 8 substances and sets no TVOC. The standard was issued 2011-10-27 and implemented 2012-03-01. It specifies compartment-air limits of benzene ≤0.11, toluene ≤1.10, xylene ≤1.50, ethylbenzene ≤1.50, styrene ≤0.26, formaldehyde ≤0.10, acetaldehyde ≤0.05 and acrolein ≤0.05 mg/m³, with testing carried out per HJ/T 400-2007; TVOC ≤0.60 mg/m³ belongs to GB/T 18883-2022, the indoor air quality standard, and must not be quoted as a ninth requirement of the vehicle standard.
• The sampling conditions are themselves part of the verdict. HJ/T 400-2007 requires an ambient temperature of (25.0±1.0) ℃, relative humidity 50%±10% and air velocity ≤0.3 m/s, with the test vehicle 28 d±5 d off the line; doors and windows are opened and the car stands for no less than 6 h before a 16 h sealed soak and sampling, VOC on Tenax adsorption tubes at 100～200 mL/min for 30 min and carbonyls on DNPH tubes for 30 min. Change the soak duration or the temperature on the same car and the result can differ by several times, so temperature / time / loading have to be written into the technical agreement.
• A separate national standard exists at component level, but a passing part does not mean a passing vehicle. GB/T 39897-2021《Test methods for volatile organic compounds and aldehyde/ketone substances from non-metallic parts and components in automobiles》(issued 2021-03-09, implemented 2021-10-01) gives two routes, the bag method and the box method, on a publicly restated 65 ℃ condition (clearly stricter than the 25 ℃ whole-vehicle chamber scope); chamber volume, loading ratio and air-exchange rate differ from those of the passenger compartment, so material data cannot be linearly extrapolated and may only be used for tiered approval and for tracing abnormalities.
• Odor and instrument values follow two independent curves. VDA 270 scores 1–6 (grade 1 no odor, grade 6 unbearable) at the three temperature levels 23 ℃ / 40 ℃ / 80 ℃, with several trained assessors scoring independently and a statistic taken; OEMs commonly require an average of ≤3.0 or ≤3.5 grades. VDA 278 direct thermal desorption gives a VOC value desorbed at 90 ℃ (toluene equivalent, μg/g) and a FOG value further desorbed at 120 ℃ (n-hexadecane equivalent, μg/g). Longer baking or faster-drying solvents will not suppress the olfactory contribution of aldehydes and amines, and "low TVOC ≠ low odor" is a common misconception in acceptance.
• Fogging is a safety item, not merely an environmental one. The DIN 75201 system (sharing its origin with ISO 6452 and SAE J1756) reports a fogging value as a percentage by the reflectometric method and the condensate mass in mg by the gravimetric method, with the specimen side at about 100 ℃ and the condensation surface at about 21 ℃; in-house limits common in OEM specifications are gravimetric ≤1.5～2.0 mg and reflectance retention ≥85%～90%. The condensate deposits directly on the inside face of the windscreen as an oily film that reduces visibility at night and in rain, so fogging, odor and VOC are three independent mandatory items.
• Pick the formulation route by the price it pays in the emission spectrum, not by the VOC number. Waterborne 1K / 2K polyurethanes bring VOC down from several hundred g/L (solventborne) to double-digit or low triple-digit g/L, at the price of co-solvent residue and moisture lag; UV / LED-UV is essentially solvent-free (commonly <50 g/L on a public-data basis), at the price of residual (meth)acrylate monomer and the odor and migration risk of the photoinitiator system; powder coatings come close to zero solvent at application, but standard cure is 180～200 ℃ and even low-cure systems need 120～160 ℃, which — together with thermally sensitive interior substrates such as PP / TPO / leather and the available rework routes — keeps powder out of many part types.
• Supply-chain evidence has to come as data with conditions attached. At minimum the trim part maker should request from the coating supplier: the VOC spectrum and single-point values with method numbers; a VDA 270 odor report (grade + odor-type description + temperature level + number of assessors); the fogging value, stating gravimetric or reflectometric; SDS and REACH SVHC declarations; the hardener free di-isocyanate COA (GB 30981.2-2025 brings hardeners and other auxiliary materials under mandatory control for the first time); isocyanate sensitization and training notices; and the coating hazard marking (C / NC) required by GB 30981.2-2025.

1. Source breakdown: the coating plays three roles on the same chain

1.1 The four emission chains and their main species

VOC and odor in the passenger compartment never come from a single source, and engineering practice splits them into four chains. First, plastics and rubber parts — the skins of the instrument panel, door trim and pillar trim (PVC slush molding, TPO, PU synthetic leather, modified PP), the carriers (PP + EPDM-TD, glass-fiber-reinforced PP), the foam layer (molded polyurethane foam) and the seals (foamed EPDM); the main emitters are residual solvent, low-molecular-weight plasticisers, antioxidants and thermo-oxidative degradation products. Second, adhesives and laminating layers — flame-laminated or roller-coated adhesive in the headliner, carpet and door trim; mainly esters, ketones, aliphatic hydrocarbons and traces of aldehydes. Third, textile and leather dressings — dye carriers, fixatives, feel modifiers, fungicides and dressing resins; mainly amines, aldehydes and characteristic additive odors. Fourth, the interior coating itself — the soft-touch skin coat, the matte top clear, the UV coat on trim strips, and the painting of buttons and knobs. The first three chains set the vehicle's background emission; the fourth is both a controllable variable (with the same waterborne coating, a bake window 10 min different can double or halve the emission) and an interface valve (a dense coat delays small molecules leaving the foam, whereas an under-crosslinked one locks oligomers inside the film and releases them slowly).

1.2 The three mechanisms by which a coating contributes VOC

Broken down, coating release has only three origins, each with its own corrective action: (1) physical residue — solvent carried by the film-forming resin, the co-solvents and neutralizing amines of waterborne systems, the low-viscosity reactive diluents of UV systems; none of them react, they leave the coating by evaporation, they are governed by bake temperature × time × film thickness, and this is the fraction that can be removed in the short term; (2) chemical residue — unreacted monomers ((meth)acrylates, isocyanate monomer), resin-synthesis leftovers (end-group small molecules), catalyst not encapsulated in the dispersion, and low-molecular-weight components of defoamers and flow additives; this fraction needs raw-material specifications (e.g. a low-free-isocyanate hardener) and higher conversion; (3) reaction and degradation products — the small amine and urea molecules formed when isocyanate reacts with water in a 2K polyurethane, with CO₂ evolution; the ester-bond cleavage of a polyester polyurethane under hot and humid conditions, giving small carboxylic acids and diols; and the oxygen-inhibited uncured surface layer of a UV coat, which goes on oxidizing into aldehydes and ketones during high-temperature service. The third class is the usual root of high odor at low TVOC: the TVOC chromatographic integration window generally spans n-hexane to n-hexadecane (the FOG stage of VDA 278 continues to desorb the n-tetradecane to n-tritriacontane range at a higher temperature), it does not count the carbonyls trapped on the DNPH tube, and it frequently cannot turn ppb-level odor-active substances into a significant peak area.

1.3 Telling the mechanisms apart: "hot sun soak — drop after ventilation — rebound on reheating"

This is precisely the curve owners and after-sales staff describe: the smell is harsh after a summer bake, opening the windows for ten-odd minutes improves it, and the next day's sun brings it back. The three origins produce quite different curve shapes, and that is the lever for assigning responsibility:

• Residual-solvent escape (fast variable): diffusion-controlled initial burst release; the first hot cycle gives the peak, and ventilation plus later heating cycles make the peaks decay one after another (each rebound visibly smaller). Fix it on the process side: lengthen flash-off and bake, cut the share of high-boiling solvent and co-solvent, and avoid clear-coating over a primer that has not outgassed, which traps a sandwich residue.
• Thermally driven resin release and insufficient crosslinking (repeatable variable): the release rate is driven mainly by the exponential temperature term (roughly Arrhenius behavior, with the diffusion coefficient jumping above the glass-transition region); cooling does not change the inventory inside the coating, so every reheating to the same temperature gives a close odor grade and the rebound does not fall much with cycle count. Fix it on the formulation side: raise crosslink density and conversion, control the isocyanate index and the cure window, and move to a resin backbone with better heat and hydrolysis resistance.
• Plasticiser and additive migration (slow variable): mainly SVOC, migrating from the bulk of the substrate to the surface and then vaporizing, with time constants measured in weeks to months; ventilation can only suppress the air concentration and never removes the inventory — and this is also the main contributor to fogging (high-boiling esters still volatilize at the roughly 100 ℃ test temperature and condense on the cold face). Fix it in substrate selection: replace low-molecular-weight phthalates with high-molecular-weight or polymeric plasticisers, and control mold-release-agent and regrind blending.

On top of this there is an adsorption / re-release term: headliner fabric, carpet and acoustic felt adsorb VOC emitted by other parts and release them a second time when temperature and humidity change, so the whole-vehicle curve oscillates rather than falling monotonically. That is also why a single passing spot check on one vehicle cannot prove long-term stability.

2. Limits scope: the 8 substances GB/T 27630-2011 controls, and how far

GB/T 27630-2011《Guideline for air quality assessment of passenger car compartment》was issued jointly by the former environmental protection ministry and the former quality inspection authority (issued 2011-10-27, implemented 2012-03-01, first issue); it specifies concentration requirements for eight organic substances in compartment air, applies to the assessment of passenger-car interior air quality and mainly to newly produced cars offered for sale. Clause 5.1 states that the determination of organic concentrations in compartment air is carried out per HJ/T 400-2007, with the test vehicle stationary, doors, windows and the compartment fresh-air inlet dampers closed, and the engine, air conditioning and similar equipment off; clause 5.2 leaves conditions such as whether the interior state is altered and the interval between delivery and testing to be agreed between the parties — and that single sentence is where vehicle makers and trim makers most often diverge.

2.1 Standardization dynamics: the position as of this article's date

The direction of a mandatory revision of GB/T 27630-2011 leaves clear traces in public material: the ecology-and-environment ministry published a draft for comment in January 2016,《Guideline for air quality assessment of passenger car compartment (draft for comment)》(working number GB 27630, replacing GB/T 27630-2011), whose foreword lists four revision points — adding information disclosure and environmental conformity check content, adding a production-off-line rule for the conformity check, revising part of the limits, and turning a recommended standard into a mandatory standard — with the scope narrowed to the eight volatile substances in M1-category vehicle compartments. As of this article's date (2026-11-03) the national full-text standards disclosure system still lists GB/T 27630-2011 as current. The claims circulating online — that a new version has been issued, that formaldehyde drops to 0.05～0.06 mg/m³, that a 38 ℃ / 850 W/m² solar-exposure condition has been added — could not be confirmed against any officially issued text, so the body of this article does not quote such new limit values and marks them in the scope note as unconfirmed information instead. For formulation and purchasing decisions the steadier course is to feed tighter limits in as design margin (set the in-house line at half the current value) rather than writing a rumoured number into a technical agreement.

2.2 The sampling and analysis method family: numbers, scope and detection limits

The compartment testing system is a two-layer structure of a limit standard plus method standards. The method backbone is HJ/T 400-2007《Methods for sampling and determination of volatile organic compounds and carbonyl substances in vehicle compartment》(issued 2007-12-07, implemented 2008-03-01, administered by the ecology-and-environment authority). It fixes the sampling points (one point for an M1 vehicle, at the intersection of the line joining the front-seat headrests and the vehicle center line, at occupant breathing height; no fewer than two points for M2 and no fewer than three for M3, laid out evenly along the center line), the requirements for the sampling environmental chamber, VOC sampling on Tenax-type adsorption tubes at 100～200 mL/min for 30 min, carbonyl sampling on DNPH tubes at 100～500 mL/min for 30 min, a total sampled gas volume not exceeding 5% of the compartment volume, background-concentration controls (e.g. toluene ≤0.02 mg/m³ and formaldehyde ≤0.02 mg/m³), plus the thermal-desorption / capillary gas-chromatography / mass-spectrometry method in annex B and the solid-sorbent high-performance liquid chromatography method in annex C (DNPH derivatives on a C18 reversed-phase column, eluted with acetonitrile/water 60:40, measured by ultraviolet detection at 360 nm). Quality-control elements include field blanks, flow calibration and a parallel-sample relative deviation ≤20%. The indoor-side method family serves as a comparison and arbitration backup: under GB/T 18883-2022 formaldehyde is measured by the AHMT spectrophotometric method (GB/T 16129), the phenol-reagent spectrophotometric method (GB/T 18204.2) or the high-performance liquid chromatography method of annex B; benzene compounds by solid-sorbent thermal-desorption gas chromatography (annex C); and TVOC by solid-sorbent thermal-desorption gas chromatography with mass spectrometry (annex D). One caution is needed: the adsorption-tube / thermal-desorption GC-MS methods of the ambient-air family and the purge-and-trap methods of the water family belong to different media systems and cannot be quoted as the normative basis for compartment sampling — which is why a fair number of test reports apply the wrong method, a point set out systematically in the on-site article coating VOC test methods: GB, ISO and ASTM standards compared.

3. From vehicle to part: chamber, bag and thermal-desorption scopes at component and material level

Whole-vehicle chamber testing feeds back too slowly (a sample car sealed for 16 h plus two to three more days of analysis), so development control and incoming-material control have moved almost entirely down to component and material level. The division of labour at that layer is: the chamber method gives comparable emission rates, the bag method gives a fast total screening, and thermal desorption gives high-throughput fingerprint comparison.

3.1 Why one and the same skin gives opposite conclusions under different methods

Three variables make cross-method data non-comparable: (1) temperature — a 25 ℃ chamber and a 65 ℃ bag probe completely different emission states, and published laboratory experience shows that for most non-metallic interior materials TVOC at 80 ℃ can be several times the value at 23 ℃; (2) the normalization basis — chamber methods give a volume concentration (μg/m³), micro-chamber methods a mass-specific emission rate (μg/(kg·h)), and thermal desorption an extraction per unit mass (μg/g); there is no general conversion factor between the three, only an approximate one through loading ratio and dwell time, which leaves the method difference intact; (3) conditioning and storage duration — the same material measured 24 h after molding and after 4 weeks in stock can differ several-fold, and HJ/T 400 and GB/T 27630 write 28 d±5 d off the line into the conditions precisely to pin that variable down. The engineering rule is: in a technical agreement one performance item is judged by one method and one set of conditions, and all other methods serve only as trend comparison.

4. Odor assessment: VDA 270 grades 1–6, assessor rules and the three temperature levels

VDA 270 (German Association of the Automotive Industry,《Determination of the odor characteristics of passenger-car interior materials》; the version published by testing institutes is marked VDA 270:2022-05) turns a subjective smell into a traceable grade. Scoring runs from grade 1 to grade 6: grade 1 no odor / hardly perceptible, grade 2 perceptible but not uncomfortable, grade 3 clearly perceptible yet not distracting, grade 4 objectionable / pungent, grade 5 strongly objectionable, grade 6 unbearable; the acceptance line OEMs commonly apply to interior parts is an average of ≤3.0 or ≤3.5. The test places a measured specimen in a clean sealed glass vessel, conditions it at the specified temperature for a defined time, and lets trained assessors smell and score it; the three temperature levels restated publicly are 23 ℃±2 ℃, 40 ℃±2 ℃ and 80 ℃±2 ℃ (the hot level corresponding to the real surface temperature of instrument panels and floor parts in the sun), and some versions also fix the assessment temperature after hot conditioning and the matching tiers of specimen amount to vessel volume. Assessor numbers reported across restatements range from 3～6 (most laboratories run independent scoring by 5 assessors and take a statistic), with outliers removed before an average and a range are reported.

4.1 Who is behind the amine, burnt and sweet notes

Odor type is a cheap diagnostic tool. Fishy and ammonia notes point to neutralizing amines and tertiary-amine catalyst residue in waterborne systems (ammonia solution, triethylamine, dimethylethanolamine types) and to the amines generated when isocyanate reacts with water in a 2K polyurethane (side-reaction mechanism and mix-ratio window: see the on-site article 2K polyurethane clear coat technology: HDI hardener, mix ratio, film thickness and VOC); pungent aldehyde notes point to aldehydes (acetaldehyde, acrolein) released by degradation or condensation; burnt and scorched-plastic notes point to free di-isocyanate monomer or thermal degradation from too high a molding temperature; sweet notes usually come from high-boiling ester plasticisers and certain cyclic-structure monomers (which carry a characteristic odor of their own, with tolerance varying widely between people). Such calls must be set alongside the GC-MS spectrum and the DNPH result; the nose alone cannot settle a case. Two neighbouring functional-coating chains are of the same origin: leather antifungal and flame-retardant coatings (antifungal flame-retardant nano coating for automotive interior leather) and oleophobic touchscreen coatings (anti-fingerprint oleophobic nano coating for interior touchscreens) also carry additive and monomer residue and should be logged on the same acceptance sheet.

4.2 Where execution bias in odor assessment comes from

Four places shift the result: residual odor in the vessel and its lid gasket (wash, then bake hot and run a blank); background odor in the assessment room and the assessors' condition (no perfume, avoid pungent food, ventilate the booths independently); whether the sample is in series-production state (material formula, production process and storage time all consistent); and the interval between hot conditioning and the smell test after uncapping (which decides the headspace concentration). For cross-laboratory comparison, assessor number, temperature level, specimen amount to vessel volume ratio and the assessment interval have to be fixed simultaneously before the numbers mean anything.

5. Fogging: the gravimetric and reflectometric methods of DIN 75201, and why it is a safety item

Fogging (condensable components) is the phenomenon in which the volatile and semi-volatile substances released by a heated interior material condense on a colder glass surface into micron-sized droplets or an oily film. It sits on the mandatory list because the condensation forms directly on the inner face of the windscreen: at night and in rain, oncoming headlights or street lighting create glare and reduce clarity of vision, and the air-conditioning defrost cycle does not clear an oily condensate film quickly — a functional-safety topic, not merely a comfort one. The backbone of the method family is Germany's DIN 75201 (determination of the fogging behavior of automotive interior materials, issued 1992), from which ISO 6452 and SAE J1756 derive; company specifications include Volkswagen PV 3015 and PV 3920, Toyota TSM0503G and General Motors GMW 3235, and China additionally has QB/T 2728 for leather materials. The division of work among the three methods is in the table below. A scope note is required here: in researching this article, DIN 75277 could not be confirmed as a current fogging test standard — neither its number nor its content could be verified — so that number is deliberately not cited, and the article uniformly uses the verifiable DIN 75201 / ISO 6452 / SAE J1756 scope.

5.1 Why gravimetric and reflectometric figures cannot be compared with each other

Published comparisons of the two methods show that for one and the same material the gravimetric deposit grows as test temperature rises, while the reflectometric method gives a lower reflectance retention because the temperature gap between specimen side and condensation surface widens — the two have no conversion relationship. Results also depend on plate flatness, cleanliness, conditioning time and gloss-meter calibration. The engineering rule therefore is: first fix the method number and the temperature–time combination in the OEM specification, then compare lot against lot; plotting values from different methods on one trend chart is bound to produce a false conclusion. For repeatability, foil wrinkling and elevated blank values (from vessel residue and earlier cross-contamination) must also be controlled, ultrasonically cleaning with chromatographic-grade solvent and baking hot where necessary.

5.2 How the coating side pushes fogging down

A coating contributes to fogging mainly through high-boiling co-solvents, low-molecular-weight flow additives and unreacted monomer. Four actionable measures: push the share of solvent and co-solvent fractions boiling above about 250 ℃ down to the floor (such fractions are both hard to remove in the bake and easy to deposit on the cold face); move to reactive additives (flow additives carrying hydroxyl or acryloyloxy groups, reactive diluents) so that the additive enters the network instead of remaining loose in the film; raise crosslink density and conversion (aliphatic polyisocyanate trimers as hardener, and UV dose matched to line speed); and avoid laminating before outgassing after coating — let the basecoat finish its main evaporation before the topcoat and the foam lamination follow.

6. Low-emission formulation routes: what each of five routes pays in the emission spectrum

Interior trim coatings have few viable routes, and each route changes not only how much is emitted but what is emitted. The table below first gives the mandatory product-side limits, then compares the routes.

GB 24409-2020 was issued 2020-03-04 and implemented 2020-12-01, with all technical content mandatory, and it states explicitly that the VOC limits of component coatings painted together with the body are those of the corresponding original-equipment coating product. Limits are counted in the applied state, and for waterborne systems the dilution water is not counted. The same standard also caps benzene content (solventborne ≤0.3%), total benzene compounds (solventborne ≤30%, waterborne ≤1%), total halogenated hydrocarbons (≤0.1%), total glycol ethers and their esters (waterborne ≤300 mg/kg) and heavy metals in color coats (lead ≤1000 mg/kg, cadmium ≤100 mg/kg, hexavalent chromium ≤1000 mg/kg, mercury ≤1000 mg/kg). GB 30981.2-2025《Limits of hazardous substances in coatings — Part 2: Industrial coatings》was issued 2025-05-30 and implemented 2026-06-01; it consolidates and replaces five standards — GB 18581-2020, GB 24409-2020, GB 24613-2009, GB 30981-2020 and GB 38469-2019 — and brings hardeners, thinners, putties and other auxiliary materials into mandatory control as well (publicly restated points: solventborne hardener VOC ≤500 g/L; total free di-isocyanate (TDI + HDI) in polyurethane hardener ≤0.5% in one restatement, with another restatement giving 0.1%); it adds SVOC content limits and a coating hazard marking (in a format such as GB 30981.2-W-Pb≤90-C, where C indicates the coating may be used where close body contact occurs). Transition-period practice note: as of 2026-11-03 the standard number on an acceptance sheet has to match the text the product actually complies with — a GB 24409-2020 report cannot be used to answer a GB 30981.2-2025 category split. The design-input logic behind regulations and limits is covered on this site in what VOC is: environmental regulation and the low-VOC trend in automotive coatings and industrial coating VOC regulations and limits.

6.1 Low-surface-energy parts: pre-treatment and a low-odor primer

PP / EPDM / TPO have low surface energy, high crystallinity and few polar groups, so general-purpose resins neither wet nor anchor well; the traditional answer is solvent etching or a chlorinated polyolefin (CPO) primer, combined with flame, plasma or corona activation. Once VOC comes down, this chain has to be re-laid. First, move the dependence on swelling for adhesion onto polar groups for adhesion — the on-site article automotive plastic-part painting process and adhesion mechanism: CPO, flame, plasma and primer quantifies activation depth and surface energy against CPO usage and interlayer peel. Second, choose a dedicated low-odor primer rather than reintroducing high-boiling aromatics for the sake of wetting. Third, write the interval between activation and painting into the work instruction, because surface energy decays with time and standing too long degrades adhesion and emission behavior at once. Fourth, for swelling-type formulations that skip flame treatment, verify what their solvent spectrum contributes to fogging and odor; checking the VOC total alone is not enough.

6.2 Hardeners, catalysts and neutralizing amines: promoting odor from a formulation detail to a specification item

In two-component systems the hardener is the main entry point for free monomer. Control lines reported in public material are commonly: HDI trimer (isocyanurate type) with free HDI monomer no greater than 0.5% and NCO content about 19%～22%, with undiluted grades reaching 100% solids, which cuts solvent without sacrificing crosslink density; aromatic (TDI-type) adducts with free monomer typically about 1%～1.5%, clearly higher irritation and occupational sensitization risk, so aliphatic systems should be preferred for interior parts. Catalysts and neutralizing amines are the odor entry point of waterborne systems: ammonia solution volatilizes fast, decays pH noticeably and smells sharp; triethylamine volatilizes strongly and smells strongly; hydroxyl-bearing tertiary amines such as dimethylethanolamine (boiling point about 134～136 ℃) can be partly bonded into the molecular chain and leave less amine odor after film formation, but overdosing brings the amine note back and costs water resistance — and these amines are counted in the VOC determination (the calibrant list of the newer method standards includes triethylamine, dimethylethanolamine and 2-amino-2-methyl-1-propanol). Occupational health adds a hard constraint: EU regulation (EU)2020/1149 added entry 74 concerning di-isocyanates to Annex XVII of REACH, requiring industrial and professional use of mixtures at a concentration ≥0.1% (mass fraction) to be preceded by completed safety training from 2023-08-24. The practical recommendation is therefore to write three items into the coating purchase specification — free monomer content with COA attached, the identity and ceiling of the neutralizing amine, and the recommended bake window — instead of merely writing low VOC on a TDS. Quantified spray-booth ventilation and PPE requirements are covered on this site in isocyanate safety: sensitization mechanisms, PPE and spray-booth ventilation.

6.3 Bake temperature and time: the main switch for residual solvent, and the one limited by heat-sensitive substrates

Waterborne modification of the resin backbone likewise sets co-solvent usage and the odor of drying by-products; the mechanism is set out in the on-site article progress in waterborne alkyd resin modification and applications. The bake ceiling for interior parts is decided by the substrate: PP / TPO skins and foam laminates have a narrow dimensional-stability window, and PU synthetic leather and PVC slush-molded parts turn tacky or distort at temperature, so common drying schedules fall in the region of about 60～80 ℃ / 10～30 min (public-data basis), combined with flash-off and low-temperature dehumidification. The engineering point here is cumulative heat exposure rather than the set temperature: overshoot on the ramp, repeated bakes stacked over several coats, and sealed handling straight off the line without adequate cooling all change how much residual solvent is actually removed. In reverse, merely extending the bake does not solve thermally driven or migratory odor; with insufficient crosslinking, higher temperature accelerates degradation instead. The evidence should be paired data: the ratio between the 90 ℃ desorption VOC value and the 120 ℃ desorption FOG value for the same formulation, the difference in odor grade between the 40 ℃ and 80 ℃ levels, and the rebound after ageing retests.

7. Low TVOC ≠ low odor: four divergence mechanisms and a troubleshooting order

This is the one conclusion the article hopes readers take away, and it is the dividing line in many corrective programs that achieved nothing. At least four mechanisms drive the divergence: (1) the method window does not cover them — TVOC or a VOC value is a semi-quantitative total integrated over retention-time windows (the VOC stage of VDA 278 integrates up to about n-pentacosane as a toluene equivalent), whereas formaldehyde, acetaldehyde and acrolein have to be determined after DNPH derivatization by liquid chromatography and are simply not on the same curve; (2) odor thresholds span an enormous range — sulfur- and nitrogen-bearing compounds and some aldehydes are perceptible at ppb level, while alkanes can contribute considerable peak area and are almost odorless, so a material high in alkanes can smell faint; (3) SVOC are not counted in the conventional VOC scope — high-boiling esters, some siloxanes and antioxidant degradation products contribute mainly to odor and fogging, and before GB 30981.2-2025 brought SVOC under separate control the TVOC number could look very good; (4) a mixed odor is not a linear sum — synergy or masking between substances breaks any monotonic relation between grade and concentration, and covering the note with fragrance only adds a new emission source.

A workable troubleshooting order: first retest the odor grade of the same sample (three temperature levels, recording the odor type) → then add the carbonyl-specific analysis (DNPH-HPLC) and both the VOC and FOG stages of VDA 278 → then produce a GC-MS single-substance list (watching components ≥1 μg/g and the nitrogen- and sulfur-bearing peaks) → then separate solvent-residue from thermal-degradation / migration types using two heating cycles and thermogravimetric comparison → and only after that go back to formulation and process corrections. Measuring TVOC alone and then changing resin or extending the bake is the classic waste in these projects.

8. Key data

• Benzene ≤0.11 mg/m³, toluene ≤1.10 mg/m³, xylene ≤1.50 mg/m³, ethylbenzene ≤1.50 mg/m³, styrene ≤0.26 mg/m³, formaldehyde ≤0.10 mg/m³, acetaldehyde ≤0.05 mg/m³, acrolein ≤0.05 mg/m³ — the eight limits of table 1 in GB/T 27630-2011; the standard contains no TVOC item.
• (25.0±1.0) ℃, RH 50%±10%, air velocity ≤0.3 m/s, 16 h sealed, 30 min sampling (VOC flow 100～200 mL/min) — the compartment sampling scope of HJ/T 400-2007; the test vehicle is 28 d±5 d off the line and the total sampled gas volume does not exceed 5% of the compartment volume.
• Formaldehyde ≤0.08 mg/m³, benzene ≤0.03 mg/m³, TVOC ≤0.60 mg/m³, windows and doors closed 12 h, sampling for at least 45 min — the indoor scope of GB/T 18883-2022 (implemented 2023-02-01), used for comparison and arbitration backup.
• 90 ℃ / 30 min desorption (VOC), 120 ℃ / 60 min continued desorption (FOG), any single substance ≥1 μg/g listed — the two stages of VDA 278 direct thermal desorption, reported in μg/g as toluene and n-hexadecane equivalents respectively.
• (65±2) ℃, micro-chamber ≤1 L, 20 min equilibration, VOC 15 min@50 mL/min; small chamber about 1 m³, air-exchange rate 0.4 h⁻¹, equilibration ≥30 min, 4 h dwell — the publicly reported scope of ISO 12219-3 and ISO 12219-4.
• Grades 1～6, temperature levels 23 ℃ / 40 ℃ / 80 ℃, 3～6 assessors with a statistic taken, acceptance line ≤3.0～3.5 — the publicly reported range for VDA 270 odor assessment (version and assessor number to follow the current text).
• Specimen side about 100 ℃, condensation surface about 21 ℃, usually 3 h or 16 h, gravimetric in-house ≤1.5～2.0 mg, reflectometric retention ≥85%～90% — the conditions and limit range of the DIN 75201 / ISO 6452 / SAE J1756 fogging system.
• Coatings for interior parts: waterborne primer ≤450 g/L, basecoat ≤530 g/L, solid topcoat and clearcoat ≤420 g/L; solventborne primer ≤670 g/L, color coat ≤770 g/L — the mandatory limits of tables 1 and 2 in GB 24409-2020 (applied state).
• Hardener free di-isocyanate (TDI + HDI) total ≤0.5% (auxiliary-material scope, with a 0.1% restatement also in circulation), solventborne hardener VOC ≤500 g/L — publicly restated points of GB 30981.2-2025 (issued 2025-05-30, implemented 2026-06-01); the VOC / SVOC method cites GB/T 23986.2-2023 with a detection limit of 2 g/L.
• HDI trimer free monomer <0.5%, NCO 19%～22%; dimethylethanolamine boiling point 134～136 ℃; powder standard cure 180～200 ℃, low-temperature cure 120～160 ℃ — supplier and published-patent data basis.
• Industrial and professional uses of di-isocyanates at a concentration ≥0.1% must complete safety training, in force from 2023-08-24 — the restriction added by EU regulation (EU)2020/1149 as entry 74 of REACH Annex XVII.

9. Supply-chain acceptance and compliance communication: writing the test conditions into the technical agreement

9.1 The nine categories of data a trim-part maker should request from the coating supplier

9.2 The four condition elements and the decision line in a technical agreement

An enforceable clause has to give all of the following at once: the method number and version; the test conditions (temperature, time, chamber or bag volume, loading or loading factor, air-exchange rate, sampling-port position and adsorption-tube type, sampling flow and volume); conditioning and sample handling (aluminium-foil sealing, sealing within a defined time after production, storage below 23 ℃, storage duration before the test); and the decision rule (limit or grade line, permitted parallel-sample deviation, retest and arbitration route). If any one of them is missing, data across lots or across laboratories are not comparable. The decision line is preferably built as three descending tiers: a material-level in-house line (e.g. odor ≤2.5 grades, VDA 278 VOC no higher than an agreed μg/g) → a component level (bag or box method, single substances and totals) → a vehicle level (the eight limits plus odor grades at both the ambient and the hot level), with every tier keeping an ageing or hot-retest item so that freshly made samples alone never release a part.

9.3 A passing component is not a passing vehicle, and parts cannot be summed linearly

There are three physical reasons. (1) The compartment volume, the total interior surface area and the ventilation condition form a definite chamber equivalence, whereas component testing uses a different loading ratio; converting between them would require assuming no internal mass-transfer resistance and no chamber-wall adsorption, while in reality skins and textile parts visibly adsorb both polar and non-polar fractions and release them late. (2) Release is a kinetic process, so the same part under different thermal histories (time off the line, stock rotation, number of sun exposures) emits at wildly different instantaneous rates, and adding up several 65 ℃ bag results to predict a compartment concentration after 16 h sealed at 25 ℃ has no basis. (3) Odor is a mixture effect with synergy and masking, and several grade-2.5 parts can stack into a grade-4 vehicle. Responsibility therefore has to be settled by tiered elimination: first locate the dominant contributor in the whole-vehicle chamber test (by zone sampling or by removing and retesting a part), then retest that part by the same method, then go back to material and coating data. Skipping the vehicle-level location and demanding a reformulation from the supplier usually ends in rework.

9.4 Four common points of dispute and how to decide them

• Lot-to-lot difference: retest first in one laboratory with sampling and desorption conditions fixed, then use GC-MS characteristic peak-area ratios (for instance the share of a marker additive in total peak area) to judge whether the raw material or the additive package changed, instead of looking only at the difference in totals.
• Sampling-temperature difference: make no conversion between 25 ℃ and 65 ℃; require both levels to be judged side by side. Write a "not below" floor for the hot level into the agreement so that an ambient pass cannot mask a hot rebound.
• Storage time and ageing: the vehicle scope is 28 d±5 d off the line, while interior parts should be grouped by days after coating; if the values rise rather than fall with time, the source is thermal degradation or migration, and longer ventilation will not help.
• Residual solvent or thermal degradation: run two heat-soak-cool cycles and compare the second peak with the first as a ratio — a ratio close to 1 indicates inventory migration or degradation, a clearly falling ratio indicates solvent escape; cross-check with the FOG / VOC ratio (the high-boiling share) and with fogging data.

Kexin New Materials (Guangdong) Co., Ltd. supplies this class of interior-part coating on a B2B wholesale and OEM customized basis; every shipment is accompanied by VOC test data carrying the method number, odor and fogging test reports, SDS, and the hardener free-monomer COA, and sampling and retesting can be aligned with the four condition elements of the customer's technical agreement (trade-terms basis EXW / FOB). For release decisions before formal series production, the result of a third-party retest under identical conditions should govern.

10. Frequently asked questions

Q1 The customer says the compartment formaldehyde limit is 0.06 mg/m³ — which number should I take as design input?

Comply with the current text, and use the rumoured number only as margin. What can be confirmed is formaldehyde ≤0.10 mg/m³ in table 1 of GB/T 27630-2011 (eight substances, no TVOC) and indoor formaldehyde ≤0.08 mg/m³ in GB/T 18883-2022. A draft for comment that would turn the standard mandatory and tighten the limits was published in 2016, but as of this article's date the officially issued text has not landed, and the online claims of formaldehyde at 0.05～0.06 mg/m³ or of a new 38 ℃ solar-exposure condition remain unconfirmed. The steadier course is to set the in-house line at 50% of the current limit (formaldehyde ≤0.05 mg/m³), require dual-track verification by material-level DNPH-HPLC data and a whole-vehicle retest, and write into the agreement a version-switch clause that defers to the formally issued text.

Q2 Our coating has only 60 g/L VOC — why did the interior part still score grade 4 on odor?

Because coating VOC and part odor are not the same curve. g/L describes the mass of volatiles in the liquid as supplied or as applied (GB 24409-2020 judges in the applied state, and dilution water is not counted for waterborne systems), while odor assessment (VDA 270) probes the headspace reaction of the cured coating together with the substrate and the adhesive at 23 / 40 / 80 ℃. Three classes of substance can still appear in a low-VOC formulation: neutralizing amine and tertiary-amine catalyst residue, carbonyls (acetaldehyde, acrolein), and high-boiling SVOC and degradation by-products. The corrective order should be to add DNPH carbonyl analysis, the FOG stage of VDA 278 and a single-substance list, pin down the chemical class behind the odor type, and only then decide whether to change the neutralizing amine, the hardener specification or the bake — rather than overturning the resin selection.

Q3 Both waterborne and UV bring VOC down — how should an interior part choose between them?

Rank by substrate, cycle time and sensory risk. Waterborne 2K polyurethane suits PP / TPO skins and foam laminate systems and dries at about 60～80 ℃, but its co-solvent boiling spectrum and amine neutraliser must be controlled to prevent ammonia notes and loss of water resistance. UV / LED-UV has almost no solvent and a short cycle, at the price of residual monomer and photoinitiator-related odor and migration risk, plus a strong dependence of deep cure on dose, wavelength band and line speed, and low-surface-energy parts still need a dedicated primer. The verifiable basis: run both routes on the same part type, compare the 90 ℃ / 30 min VOC value against the 120 ℃ / 60 min FOG value, then add odor grades at the 40 ℃ and 80 ℃ levels and gravimetric fogging data — and close the case on those four data sets rather than on the lower VOC number.

Q4 Is powder coating not zero-VOC? Why is it so rarely seen on interior parts?

Zero solvent is not zero emission, and certainly not zero constraint. The main barrier for powder is cure temperature: standard systems cure at about 180～200 ℃ and low-cure systems still need 120～160 ℃, whereas PP / TPO skins, PVC slush layers, polyurethane foam and leather-type substrates distort, shrink or go tacky at those temperatures. Next come appearance and hand feel (matte uniformity, orange peel) and the difficulty of color changes and spot rework, which require dedicated booths and recovery systems. The applicable zone is metal brackets, small heat-resistant plastic parts and high-volume lines with ovens. For heat-sensitive interior parts the more practical route is a waterborne base with a UV topcoat, or powder on carrier parts outside the non-metallic trim, with the bake window and substrate heat distortion costed together in the design.

Q5 Fogging passes but odor is bad, or the reverse — can the two substitute for each other?

They cannot. Fogging probes condensable components (mostly SVOC and high-boiling esters) and reports mg gravimetrically or a reflectance percentage; odor probes the low-threshold components a nose can detect (aldehydes, amines, sulfur compounds, monomers), whose concentrations may be far below anything fogging can detect. The two overlap on one dimension only: a large share of high-boiling components gives a large deposit. Give the criteria in pairs — a fogging result per the OEM specification (with method number, temperature and time stated) plus an odor grade with temperature levels, and add the VDA 278 VOC / FOG ratio to judge the high-boiling share. Releasing a part on one of them alone will very likely be judged insufficient evidence later.

Q6 Is "tested per VDA 270, grade ≤3.0" enough inside a technical agreement?

It is not; four elements are missing. Write out in full: the method and version (e.g. VDA 270:2022); the temperature levels and conditioning times (23 ℃ / 40 ℃ / 80 ℃, the hot-conditioning duration and the assessment temperature); the specimen amount and vessel volume (or the corresponding specimen-amount tier referenced in the specification); and the assessor number with the statistical rule (independent scoring, outliers removed, average taken, verdict average ≤3.0). Add sample state and submission requirements (series-production state, aluminium-foil sealing, delivery within a defined time after production, and the range of days between coating and testing). Without these conditions, two laboratories returning 2.8 and 3.4 is not abnormal, and arbitration has nothing to stand on.

Q7 One passing vehicle spot check — does that prove long-term lot stability?

It does not. A single result is simultaneously affected by time off the line (the standard requires 28 d±5 d), storage and transport thermal history, the materials of that lot (new supplier, new pigment paste, new adhesive) and the turnaround after final assembly — it is one sample of a multi-variable system. Workable stability practice is a set of three: tiered sampling frequency (material: retain every lot and measure VOC / FOG and odor; component: bag or box per a sampling plan; vehicle: chamber tests by program phase and by quarter) + a change-notification mechanism (any change of formulation, resin or additive supplier, hardener specification or bake schedule must be sampled and confirmed first) + trend management (plot time series under one method and one set of conditions, catching anomalies through single-substance characteristic peak-area ratios rather than totals). The regulatory drift toward environmental conformity of production and information disclosure is moving in exactly this direction.

Q8 Does extending the bake bring the odor down? And at what price?

It works for the residual-solvent type and usually does not work — or works in reverse — for thermal-degradation and migration types. The test is a cumulative-heat-exposure record plus a two-cycle comparison: if the second peak is clearly below the first, the inventory is removable and a longer or hotter bake helps; if the second peak is close to the first, the source is continuous generation or migration inside the bulk, and the formulation must change (conversion, crosslink density, heat- and hydrolysis-resistant backbone, low-free-monomer specifications, lower-boiling additive spectrum). Count the price as well: distortion and hand-feel change on heat-sensitive substrates, weaker interlayer adhesion where the basecoat is already over-crosslinked, energy and cycle-time losses, and the false impression of a temporary suppression — passing at end of line and rebounding after a summer sunbake usually means a fast variable was treated as a slow one.

11. References and scope notes

• GB/T 27630-2011《Guideline for air quality assessment of passenger car compartment》(issued 2011-10-27, implemented 2012-03-01, first issue; eight concentration limits; test methods cited from HJ/T 400-2007 and GB 7258; listed as current in the national full-text standards disclosure system).
• 《Guideline for air quality assessment of passenger car compartment (draft for comment)》 (working number GB 27630, replacing GB/T 27630-2011, published by the ecology-and-environment authority in January 2016; the foreword records the change from a recommended standard to a mandatory one, the revision of part of the limits, and the addition of information disclosure and environmental conformity checks; the specific limit values follow the formally issued text).
• HJ/T 400-2007《Methods for sampling and determination of volatile organic compounds and carbonyl substances in vehicle compartment》(issued 2007-12-07, implemented 2008-03-01; sampling-point layout, (25.0±1.0) ℃ / RH 50%±10% / air velocity ≤0.3 m/s, a preparation phase ≥6 h and a 16 h seal, the sampling flows and times for VOC and carbonyls, sampled volume not exceeding 5% of the compartment volume, annex B thermal-desorption GC-MS and annex C DNPH-HPLC, and a parallel-sample relative deviation ≤20%; detailed parameters from publicly restated testing-laboratory versions).
• GB/T 18883-2022《Indoor air quality standard》(issued 2022-07-11, implemented 2023-02-01, replacing the 2002 edition; formaldehyde 0.08, benzene 0.03, toluene 0.20, xylene 0.20, TVOC 0.60 mg/m³; 12 h closed; annexes B / C / D and their correspondence to GB/T 16129 and GB/T 18204.2).
• GB/T 39897-2021《Test methods for volatile organic compounds and aldehyde/ketone substances from non-metallic parts and components in automobiles》(issued 2021-03-09, implemented 2021-10-01, administered by the national automotive standardization technical committee; applies to non-metallic parts in the compartments and boot spaces of M1 / N1 category vehicles; the bag and box routes, with condition values from publicly restated testing-laboratory courseware).
• GB 24409-2020《Limits of harmful substances in paints for motor vehicles》(issued 2020-03-04, implemented 2020-12-01, replacing GB 24409-2009, all technical content mandatory; VOC limits for interior-part coatings in tables 1 and 2, radiation-cured limits in table 3, benzene and benzene compounds / halogenated hydrocarbons / glycol ethers / heavy metals in table 4; methods cited from GB/T 23985, GB/T 23986, GB/T 23990, GB/T 23992, GB/T 30647, GB/T 34675, GB/T 6750, GB/T 1725).
• GB 30981.2-2025《Limits of hazardous substances in coatings — Part 2: Industrial coatings》(issued 2025-05-30, implemented 2026-06-01, consolidating and replacing GB 18581-2020, GB 24409-2020, GB 24613-2009, GB 30981-2020 and GB 38469-2019; adding SVOC limits, control of auxiliary materials and the coating hazard marking; VOC / SVOC method GB/T 23986.2-2023, di-isocyanate monomer GB/T 18446).
• The ISO 12219 series (interior air of road vehicles: Part 1 whole-vehicle chamber, Part 2 screening bag method, Part 3 micro-chamber, Part 4 small chamber, Part 5 static chamber, Part 11 thermal desorption, 2025 edition) together with ISO 16000-3 and ISO 16000-6; condition values taken from SAE J3233-2026《Recommended practice for measurement of VOC emissions from polyurethane foams for automotive interiors》(first issued 2026-09, also citing SAE J2989 on sample handling, packaging and conditioning) and its publicly reported interpretation.
• VDA 270 (determination of odor characteristics of passenger-car interior materials, public version marked 2022-05), VDA 275 (improved bottle method for formaldehyde), VDA 276 (chamber total hydrocarbons), VDA 278 (thermal-desorption analysis of organic emissions from non-metallic interior materials: VOC stage 90 ℃ / 30 min as toluene equivalent, FOG stage 120 ℃ / 60 min as n-hexadecane equivalent); with the companion company specifications PV 3900, PV 3938, PV 3015, PV 3920, GMW 3205, GMW 3235, TSM0503G, SAE J1351, SAE J1756.
• DIN 75201《Fogging behavior of automotive interior materials》(issued 1992) and the derived ISO 6452, SAE J1756 and QB/T 2728《Leather — physical and mechanical tests — determination of fogging behavior》; the specimen-side temperature (about 100 ℃), condensation-surface temperature (about 21 ℃), durations (3 h / 16 h) and result expressions of the gravimetric and reflectometric methods follow equipment-maker and testing-laboratory public material, and the OEM limits (gravimetric ≤1.5～2.0 mg, reflectance ≥85%～90%) are company-specification figures. As for the other fogging number, DIN 75277, this article could not confirm through public search that it is a current fogging test standard — neither its number nor its content — and therefore does not cite it.
• EU Commission regulation (EU)2020/1149 amending Annex XVII of REACH to add entry 74 on di-isocyanates: industrial and professional uses of mixtures at a concentration ≥0.1% (mass fraction) require completed safety training, with the placing-on-the-market requirement applicable from 2022-02-24 and the use requirement from 2023-08-24; together with the European Chemicals Agency classification change for TMPTA (listed as a category 2 carcinogen from 2023-12-01) and other publicly notified regulatory items.
• Materials and formulation data on a public basis: HDI trimer free monomer <0.5%, NCO 19%～22%, and 100% solids for undiluted grades; TDI-type adduct free monomer about 1%～1.5%; dimethylethanolamine boiling point 134～136 ℃ and pKa about 9.2～9.7; powder standard cure 180～200 ℃ and low-temperature cure 120～160 ℃ as stated in published patents and technical literature; a published patent formulation replacing a solventborne layer with a corona-treated TPO skin plus waterborne polyurethane base and topcoat; and the publicly restated companion items for interior parts under GB 8410《Burning characteristics of automotive interior materials》and the prohibited-substance scope of GB/T 30512.
• Chinese industry material: restated surveys by the Chinese Research Academy of Environmental Sciences and other bodies showing that far more VOC species are actually detected in vehicles than the current eight; public reporting that China Automotive Technology and Research and the group-standard system (e.g. T/CSAE 247-2023《Healthy cockpit evaluation specification》) have introduced odor comfort; and local-standard leads such as Guangdong DB44/T 2356-2023《Specification for healthy evaluation of vehicle cabin air quality》. These items are used for trend judgement only and are not quoted as limits.

Scope note: the standard numbers, years, limits and method parameters in this article are taken from published standard information, government release pages, the national full-text standards disclosure system, technical-body material and the restated technical documents of third-party testing laboratories and equipment makers; they are intended for engineering selection, test commissioning and acceptance communication, and they do not replace the original standard text. Four divergences and uncertainties deserve particular mention. First, the assessor number, vessel specification and conditioning times of VDA 270 differ between versions and between restatements; the article therefore speaks in ranges, and formal commissioning should follow the current text and the laboratory's method verification sheet. Second, on the free di-isocyanate limit for polyurethane hardeners in GB 30981.2-2025, public restatements give two readings, ≤0.5% (auxiliary-material scope) and ≤0.1%; both are listed side by side here and the discrepancy is marked. Third, the specific temperature, humidity and air-exchange values of the box and bag methods in GB/T 39897-2021 are taken from publicly restated testing-laboratory courseware and may differ editorially from the standard text. Fourth, the mandatory new edition of GB/T 27630 and the tightened values circulating online (formaldehyde 0.05～0.06 mg/m³, a new 38 ℃ high-temperature solar-exposure condition) had not been confirmed by officially issued text before this article's date, and are nowhere quoted as limits — only discussed as a trend. The limits in OEM company specifications (PV / GMW / TSM / JASO and similar) are all on a publicly restated basis, and the original specification text should be requested for any concrete item; for fogging the article uniformly uses the verifiable DIN 75201 / ISO 6452 / SAE J1756 numbering. The formulations, bake windows and VOC ranges given here are illustrative ranges on a public-data basis; they vary with resin lot, substrate formulation, application conditions and cure history, and release before formal series production should be based on third-party retest data under identical conditions.

Last updated: 2026-11-03　｜　Attribution: Kexin New Materials (Guangdong) Co., Ltd.　(B2B technical literature, trade-terms basis EXW / FOB)