Overview
ISO 4625-1:2020 - Binders for paints and varnishes - Determination of softening point - Part 1: Ring-and-ball method - specifies standardized test methods for measuring the softening point of resins (including rosin) and similar binder materials using the ring-and-ball apparatus. The document defines both an automated (reference) method and a manual (alternate) method, sampling and specimen preparation procedures, bath media, calibration, test procedures across temperature ranges, and reporting requirements.
Key topics and technical requirements
- Definition and principle: Softening point is the temperature at which a sample disc in a horizontal ring is forced downward 25 mm by a steel ball under a prescribed heating rate.
- Sampling & specimen preparation: Guidance on representative sampling (per ISO 15528), pour method for melts, and a special procedure for low softening-point materials (≤ 35 °C) including cooling on dry ice or in a freezer.
- Methods specified:
- Automated ring-and-ball method - designated as the reference method; includes apparatus, calibration and procedures for different softening-point ranges.
- Manual ring-and-ball method - alternate method with its own apparatus, calibration and stepwise procedures.
- Heating-bath liquids: Recommended fluids by softening-point range:
- Distilled/deionized water for 35 °C–80 °C (use freshly boiled water)
- Glycerol (CAS 56-81-5) for 80 °C–150 °C (USP grade)
- Silicone oil (polymethylsiloxane) for >80 °C (stable to ≥200 °C)
- Calibration, precision & bias: Procedures for calibrating equipment and published precision data for both automated and manual methods to ensure reproducibility.
- Result expression and test report: Instructions for documenting the method used, conditions, and measured softening point.
Applications and users
ISO 4625-1 is used by:
- Laboratory technicians and quality control teams in the paints, coatings and varnishes industry
- R&D departments testing rosin-based resins and binders
- Manufacturers specifying softening behavior for formulation and processing
- Regulatory bodies and compliance testing (notably referenced in Title 21 CFR in regulatory contexts)
This standard supports product specification, batch acceptance, process control, and comparative testing between materials.
Related standards
- ISO 4625 series (other parts: Mettler cup-and-ball methods - ISO 4625-2 and forthcoming Mettler method without the ball)
- ISO 4618 (terms and definitions for paints and varnishes)
- ISO 15528 (sampling of paints, varnishes and raw materials)
- IEC 60751 (temperature sensors/prt requirements)
Keywords: ISO 4625-1, ring-and-ball method, softening point, binders for paints and varnishes, rosin, resins, test method, automated ring-and-ball, manual ring-and-ball.