ISO 12137:2011

Overview

ISO 12137:2011 - Paints and varnishes - Determination of mar resistance - defines a laboratory test method to assess the mar resistance of a single coating or the upper layer of a multicoat system using a curved (loop-shaped or ring-shaped) stylus. The standard is intended for comparative testing and provides relative ratings for coatings that show significant differences in susceptibility to mar. It complements, but does not replace, pointed-stylus methods described in ISO 1518‑1 and ISO 1518‑2.

Key Topics and Requirements

• Test principle: A loop- or ring-shaped stylus mounted at a 45° angle is pressed onto a coated test panel while the panel is moved beneath the stylus. Load is increased in steps until marring occurs.
• Instrument and stylus:
  • Balanced-beam mar-resistance instrument with capacity up to 5 kg and step resolution typically 0.5 kg (0.25 kg or 0.1 kg allowed for higher accuracy).
  • Loop stylus: chromium-plated steel, 1.6 mm rod bent into U-shape, outside radius (3.25 ± 0.05) mm, hardened to Rockwell HRC56–58, surface roughness < 0.05 µm.
• Test conditions:
  • Conditioning: coat panels as per ISO 1514; dry/age and condition at (23 ± 2) °C and (50 ± 5) % RH for ≥16 h.
  • Test stroke: push sliding table at about 3–6 mm/s for a distance of ≥75 mm.
• Defect classification: plastic deformation, surface blemish, surface scratch, cohesive fracture, or combinations.
• Determination of critical load: repeat tests around the approximate mar point (five repeats at critical, ±0.5 kg) and define the minimum load causing marring when at least two of five tests show marring.
• Reporting: include product ID, reference to ISO 12137:2011, panel prep, coating thickness (ISO 2808), apparatus and stylus type, increments used, inspection method/magnification, detailed results, deviations and test date.
• Precision: no precision data currently available.

Applications and Users

ISO 12137 is valuable for:

• Coating manufacturers comparing mar resistance across formulations and topcoats.
• Quality control laboratories performing routine comparative tests on batches.
• Automotive, furniture, architectural and industrial coatings R&D evaluating surface durability and finish performance.
• Specification writers and procurement teams requiring a standardized relative ranking of scratch/mar performance.

Practical benefits include straightforward instrumentation, repeatable comparative results, and guidance for test panel preparation and reporting that facilitate consistent mar-resistance evaluation.

Related Standards

• ISO 1518‑1 / ISO 1518‑2 - pointed-stylus scratch resistance methods (alternative approaches)
• ISO 1513 - Examination and preparation of test samples
• ISO 1514 - Standard panels for testing
• ISO 2808 - Determination of film thickness
• ISO 15528 - Sampling of paints and varnishes

Keywords: ISO 12137, mar resistance, paints and varnishes, loop-shaped stylus, ring-shaped stylus, coating testing, critical load, test panels, scratch resistance.