Overview
EN ISO 15715:2025 - Binders for paints and varnishes - Determination of turbidity specifies an instrumental method for objectively measuring the turbidity (loss of transparency) of clear liquids used in coatings. The standard applies to resins and resin solutions, solvents, clear coating materials, monomers and any other liquids where clarity is a specified property. It supersedes EN ISO 15715:2006 and aligns the method with current terminology and measurement practice (use of formazin nephelometric units (FNU)).
Key Topics and Requirements
- Measurement principle: Light scattering measured by a ratio-recording turbidimeter; readings reported directly in FNU, making results largely insensitive to colour when measured at recommended wavelengths.
- Instrument requirements:
- Incident light wavelength: (860 ± 30) nm
- Spectral bandwidth Δλ: ≤ 60 nm
- Non-divergent beam (convergence ≤ 1.5°)
- Measuring angle θ: (90 ± 2.5)°
- Aperture angle Ω: 20°–30°
- Measurement cells: Use manufacturer-specified optical cells or disposable cylindrical glass tubes with optical path length between 11.0 mm and 25.4 mm; instruments must allow centring of tubes.
- Calibration: Calibrate according to instrument manufacturer’s instructions; instrument standards are referenced to formazin (see Annex A for preparation and commercial standards are permitted).
- Reporting and precision:
- Results expressed in FNU; classes simplified and results reported to the nearest 1 FNU for specified ranges.
- Precision references linked to ISO 7027-1.
- Interferences: Colour (dissolved absorbers) is largely mitigated by near-infrared measurement; air bubbles and certain pigments (e.g., carbon black) can affect results and require careful handling or additional marginal conditions.
Applications and Users
- Quality control in coating and binder production - acceptance testing of raw materials (resins, solvents) and final clear formulations.
- Incoming goods inspection - suppliers and purchasers use turbidity to verify clarity specifications.
- R&D and formulation development - detect undissolved matter, flocculation, or phase separation in experimental batches.
- Instrument manufacturers and calibration labs - implement and validate turbidimeters per the standard.
- Typical users: paint and varnish manufacturers, QC laboratories, materials scientists, procurement teams, and standards bodies.
Related Standards
- ISO 7027-1 (precision and turbidity measurement practice)
- ISO 4618 (paints and varnishes vocabulary)
- EN ISO 15715:2025 includes normative and informative annexes (e.g., formazin standard preparation) and should be used alongside manufacturer guidance for turbidimeter setup.
Keywords: EN ISO 15715:2025, turbidity, binders for paints and varnishes, turbidimeter, FNU, formazin, clear coating materials, quality control, turbidity measurement.