Overview
ISO 20566:2020 - Paints and varnishes: Determination of the scratch resistance of a coating system using a laboratory-scale car‑wash - specifies a laboratory test method to assess the scratch resistance (car‑wash resistance) of organic paint coatings, particularly those used in the automotive sector. The method simulates machine‑based washing with a rotating polyethylene brush and synthetic dirt (silica micro‑powder) under controlled conditions that mimic real car‑wash action. The procedure can also be adapted for protective plastic films and plastic components when test parameters are agreed.
Key topics and requirements
- Apparatus and setup
- Rotating washing brush: diameter (1 000 ± 40) mm, bristle thickness (0.8 ± 0.2) mm, visible bristle length (440 ± 20) mm, rotation speed (127 ± 5) min⁻¹.
- Test panel holder feed speed: (5.0 ± 0.2) m/min; brush/profile and nozzle arrangement specified to replicate back‑and‑forth car‑wash movement.
- Spray nozzles: stainless steel, 65° jet spread, flow (2.2 ± 0.2) L/min at (300 ± 50) kPa.
- Washing suspension
- Silica micro‑powder suspension: (1.50 ± 0.05) g silica per litre of tap water (mean particle size ~24 µm). Continuous stirring and reuse guidance provided.
- Test specimens and conditioning
- Flat test panels, agreed substrate and dimensions (preferably 0.5–5 mm thick); conditioning, spraying and curing parameters to be agreed by parties.
- Procedure
- Preliminary runs, determination of optimum test area using a reference panel, 10 washing operations (10 double passes), rinsing and solvent cleaning, then drying prior to evaluation.
- Evaluation and metrics
- Visual assessment (ISO 13076 / ISO 4628‑1), plus instrumental measurement of gloss (ISO 2813), haze (ISO 13803) and colour (ΔE) (ISO 18314‑1). Mean of three readings across the damage area; report differences or percent change relative to initial values.
- Precision and calibration
- Repeatability for gloss: r = 14 units; reproducibility: R = 20 units (95% probability).
- Equipment verification and calibration procedures are specified in Annex A; regular reference‑panel checks required.
- Limitation
- Results are comparative and sensitive to brush wear (aging); tests are comparable only for runs with similar brush condition.
Applications and users
- Primary users: automotive OEMs, automotive paint and clearcoat manufacturers, coating formulators, independent testing laboratories, quality assurance teams, and suppliers of protective films.
- Use cases: comparative product development, quality control of car‑wash resistance, coating specification verification, performance benchmarking, and research into reflow/self‑repairing effects of clearcoats.
Related standards
Normative and referenced standards include: ISO 1513, ISO 2813, ISO 4618, ISO 4628‑1, ISO 13076, ISO 13803, ISO 15528, and ISO 18314‑1 - for sample preparation, gloss/haze/colour measurement, terminology and visual assessment procedures.
Keywords: ISO 20566:2020, scratch resistance, car‑wash test, paints and varnishes, laboratory‑scale car‑wash, automotive coatings, washing suspension, rotating brush, gloss ΔE, coating evaluation.
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