Overview
ISO 4625-2:2004 specifies the cup-and-ball method for determining the softening point of resins (including rosin) using a cup-and-ball apparatus. The method defines sample preparation, apparatus calibration and the test procedure so results can be reproducible and, under user-defined conditions, comparable with the ring-and-ball method in ISO 4625-1.
This part is harmonized with ASTM D6090 and was prepared by ISO/TC 35/SC 10. It is intended primarily for quality control, instrument verification and inter-laboratory comparison of binder materials used in paints and varnishes.
Key Topics
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Principle: A resin sample is placed in a cylindrical cup with a stainless-steel ball centred on top. As the assembly is heated at a controlled rate, the ball forces the softened sample downward; the softening point is the temperature at which the sample flows downward by a set distance and interrupts a light beam.
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Apparatus details:
- Cup orifice: 6.35 mm (standard test cup)
- Ball: stainless steel, 8.7 mm diameter, mass (2.77 ± 0.22) g
- Measuring cell and controller capable of linear heating and 0.1 °C detection precision
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Calibration and checks:
- Primary standard: benzoic acid (calibration check at 123.5 ± 0.5 °C) using a special cup (2.8 mm orifice)
- Secondary standards: materials with dropping points similar to the resin under test (table of examples provided in the standard)
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Procedure essentials:
- Typical heating rates: 1.0 °C/min to 2.5 °C/min
- Reference laboratory conditions for comparability: cup 6.35 mm, heating rate 1.6 °C/min, start 20 °C below expected softening point
- Mean of two determinations reported, rounded to the nearest 1.0 °C
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Precision:
- Repeatability (within-lab, 95%): about 0.5 °C to 1.3 °C
- Reproducibility (between-lab, 95%): about 1.4 °C to 2.1 °C
Applications
- Quality control of binder resins and rosin used in paints, coatings and varnishes
- Instrument calibration and performance verification using primary and secondary standards
- Cross-method correlation and research when comparing cup-and-ball results with ring-and-ball (ISO 4625-1)
- Batch acceptance testing and supplier qualification where a defined softening point specification is required
Related Standards
- ISO 4625-1: Determination of softening point - Ring-and-ball method (for comparison and correlation)
- ISO 5725-1: Accuracy (trueness and precision) of measurement methods and results - Principles used to report repeatability and reproducibility
Practical notes
- Follow specified cleaning and handling procedures to avoid altering cup orifice dimensions.
- Record deviations, test dates and full product identification in the test report as required by Clause 12 of the standard.
Keywords: cup-and-ball softening point, resins, rosin, ISO 4625-2, softening point test, cup-and-ball apparatus, calibration, QC.
Open preview (PDF)Binders for paints and varnishes — Determination of softening point — Part 2: Cup-and-ball method