ISO 4625-3:2026

Binders for paints and varnishes — Determination of softening point — Part 3: Cup method (without a ball)

This document specifies the cup method (without ball) for determining the softening point of resins (including rosin) and can, under user-defined conditions, give results comparable to those obtained by ISO 4625-1 and ISO 4625-2.

Liants pour peintures et vernis — Détermination du point de ramollissement — Partie 3: Méthode de la coupe (sans bille)

General Information

• Status: Published
• Publication Date: 18-May-2026
• ICS: 87.060.20 - Binders
• Technical Committee: ISO/TC 35 - Paints and varnishes
• Drafting Committee: ISO/TC 35 - Paints and varnishes
• Current Stage: 6060 - International Standard published
• Start Date: 19-May-2026
• Due Date: 08-Jul-2027
• Completion Date: 19-May-2026

Overview

ISO 4625-3:2026 sets out the cup method (without a ball) for determining the softening point of resins, including rosins, commonly used as binders in paints and varnishes. This international standard, developed by ISO Technical Committee 35 (Paints and Varnishes), allows users to obtain results that can be comparable-under user-defined conditions-to those from other standardized softening point methods, such as those detailed in ISO 4625-1 and ISO 4625-2.

Understanding the softening point of resin binders is essential in quality control, formulation, and product evaluation processes within the paints and coatings industry. The method described in ISO 4625-3 is particularly valued for its efficiency, reproducibility, and suitability for European industry practices.

Key Topics

• Softening Point Determination: The standard specifies how to measure the temperature at which a sample of resin softens and flows a specified distance (19 mm) under controlled heating, using a cup without a ball.
• Apparatus and Calibration:
  • Describes equipment required, including temperature-controlled measuring cells and sample cup assemblies.
  • Outlines procedures for calibration using a primary reference material (e.g., benzoic acid) and secondary standards.
• Sample Preparation and Testing:
  • Provides procedures for preparing and filling sample cups, ensuring homogeneity and the absence of air bubbles.
  • Details the protocol for conducting the test, including temperature ramp settings and sample handling.
• Results and Reporting:
  • Explains how to calculate and report the mean softening point, including test parameters such as heating rate and any deviations from the standard method.
  • Specifies mandatory elements for the test report to support traceability and reproducibility.
• Precision Data:
  • Based on interlaboratory comparisons, repeatability and reproducibility limits are provided for low and high softening point resins.

Applications

ISO 4625-3:2026 is especially relevant for:

• Paints and varnishes manufacturers: Ensuring product consistency and meeting industry specifications for binder resins.
• Formulators of coating systems: Comparing resin properties for optimal performance in end-use environments.
• Quality control laboratories: Standardizing routine testing to monitor production batches or incoming raw materials.
• Research and development: Evaluating new resin types or formulations against established benchmarks.
• Resin suppliers: Demonstrating compliance with international standards when marketing products globally.

By adopting the cup method (without a ball), organizations benefit from a less time-consuming, user-friendly procedure that uses widely accessible laboratory equipment. This method is also more cost-effective than traditional ring-and-ball setups, while offering reliability across a broad range of resin types.

Related Standards

Organizations implementing ISO 4625-3:2026 should also consider the following related standards to ensure comprehensive quality and compatibility in softening point measurements:

• ISO 4625-1: Binders for paints and varnishes - Determination of softening point - Part 1: Ring-and-ball method
• ISO 4625-2: Binders for paints and varnishes - Determination of softening point - Part 2: Cup-and-ball method
• ISO 4618: Paints and varnishes - Vocabulary (for terminology and definitions related to coating materials)

These standards together establish a harmonized framework for evaluating softening points, vital for materials selection and quality assurance in the coatings industry.

Keywords: ISO 4625-3:2026, softening point, cup method, resins, paint binders, varnishes, quality control, calibration, interlaboratory comparison, standardization, coatings industry.

Standards Content (Sample)

International
Standard
ISO 4625-3
First edition
Binders for paints and varnishes —
2026-05
Determination of softening point —
Part 3:
Cup method (without a ball)
Liants pour peintures et vernis — Détermination du point de
ramollissement —
Partie 3: Méthode de la coupe (sans bille)
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
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Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Apparatus . 2
5.1 Softening point apparatus .2
5.2 Central processor .2
5.3 Measuring cell .2
5.4 Sample cup assembly .2
6 Calibration of apparatus using a primary standard . 2
6.1 General .2
6.2 Reagent .3
6.3 Procedure .3
6.3.1 Filling the sample cup .3
6.3.2 Heating .3
6.3.3 Cleaning .3
6.3.4 Interpretation .3
7 Instrument check of apparatus using a secondary standard . 3
8 Preparation of sample . 4
8.1 Preparation .4
8.2 Filling the sample cup .4
9 Procedure . 5
10 Expression of results . 5
11 Precision and bias . 5
11.1 General .5
11.2 Precision . . .5
11.3 Bias .5
12 Test report . 6
Annex A (informative) Details of the interlaboratory comparison for the estimation of precision . 7
Bibliography . 9

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
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ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
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For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes.
A list of all parts in the ISO 4625 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
The ISO 4625 series describes three widely used procedures for the measurement of the softening point of
rosin-based resins:
— ISO 4625-1 covers the ring-and-ball method which was the principal standard for many years;
— ISO 4625-2 covers the Mettler cup-and-ball method;
— this document adds a new method, the Mettler method without the ball.
ISO 4625-2 and this document are both called Mettler cup-and-ball methods. Although the recommended
testing conditions differ, the only difference between the equipment is that this document does not require
use of a ball. ISO 4625-2 is the most widely used in the US and the method described in this document is
most widely used in Europe. These methods are less time consuming than the ring-and-ball manual method
and the equipment is less expensive than the ring-and-ball automated method.
As a consequence of the thermoplastic nature of the test resins, the softening points obtained using the
recommended test conditions for all three methods are not the generally the same. Consequently, the test
method and the testing conditions used should be noted in the final report.

v
International Standard ISO 4625-3:2026(en)
Binders for paints and varnishes — Determination of
softening point —
Part 3:
Cup method (without a ball)
1 Scope
This document specifies the cup method (without ball) for determining the softening point of resins
(including rosin) and can, under user-defined conditions, give results comparable to those obtained by
ISO 4625-1 and ISO 4625-2.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 4618, Paints and varnishes — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
softening point
temperature at which the sample, suspended in a cylindrical cup with a 6,35 mm hole in the bottom and
without a stainless-steel ball, flows downward a distance of 19 mm, as the sample is heated at linear rate in
air
4 Principle
In general, with materials of these types, softening does not take place at a definite temperature. As the
temperature rises, these materials gradually change from brittle or exceedingly thick and slow-flowing
materials to softer and less viscous liquids. For this reason, the determination of the softening point shall be
made by a fixed, arbitrary, and closely defined method if the results obtained are intended to be comparable.
The disc of the test sample is placed in a cup and heated at a specified rate. The softening sample is forced
by its own weight downwards. The temperature at which
...