ISO 2431-2019 PDF

Full title and description

ISO 2431:2019 — Paints and varnishes — Determination of flow time by use of flow cups. This International Standard specifies a standardized method and set of flow cups for determining the flow time (a quick, practical measure of kinematic viscosity expressed as seconds of flow) of paints, varnishes and related liquid coating materials to control consistency and production quality.

Abstract

The standard defines four calibrated flow cups (nominal orifice diameters 3 mm, 4 mm, 5 mm and 6 mm), details the test procedure (cup preparation, filling, temperature control, timing and report requirements), gives two methods for checking flow-cup wear (Annex A), and states exclusions and limitations (for example, replaceable-jet flow cups and commonly used dipping cups are excluded; the method is intended for materials for which a clear flow breakpoint can be determined).

General information

• Status: Published (International Standard); confirmed current after review in 2025.
• Publication date: June 2019 (Edition 6; published 2019-06 / 17 June 2019 in many catalogues).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 87.040 — Paints and varnishes.
• Edition / version: Edition 6 (2019).
• Number of pages: 14 pages (ISO published document).

Key bibliographic and lifecycle details above are taken from the ISO bibliographic record for ISO 2431:2019.

Scope

ISO 2431:2019 specifies a method for determining flow time by use of calibrated flow cups for paints, varnishes and related products that display a well-defined flow breakpoint. The standard covers cup dimensions and tolerances, permitted measurement ranges, test conditions (including temperature control), the procedure for performing determinations and reporting results, and methods to check flow-cup wear; it excludes flow cups with replaceable jets and commonly used dipping flow cups and notes limitations for non-Newtonian or strongly thixotropic materials.

Key topics and requirements

• Specification of flow-cup types and orifice diameters (ISO No. 3, 4, 5, 6) and manufacturing/finish tolerances.
• Procedure for cup preparation, sample conditioning, filling, temperature control and timing of flow.
• Measurement ranges and guidance on converting flow time to kinematic viscosity where applicable.
• Methods for checking flow-cup wear and ensuring equipment integrity (Annex A).
• Limits and exclusions (replaceable-jet cups and dipping cups excluded; caution for non‑Newtonian materials).
• Reporting requirements and guidance on repeatability/reproducibility and precision statements.

Typical use and users

Used by paint, varnish and coatings manufacturers, quality-control and production laboratories, formulation chemists, third‑party testing labs and instrument manufacturers for routine viscosity/consistency control and batch-to-batch verification where flow-cup testing is appropriate. Industry guidance and summaries (standards bodies and technical organizations) note the method’s suitability as a rapid screening technique for Newtonian or near‑Newtonian fluids.

Related standards

Standards commonly referenced alongside ISO 2431 include ISO 3219 (rotational viscometry for non‑Newtonian fluids), ISO 4618 (terminology for paints and varnishes), and various national/adopted versions such as EN ISO 2431:2019; the flow-cup method is also associated with comparable test methods (for example ASTM D5125) and country-specific equivalents (DIN, BS). These related documents are typically cited for complementary viscosity methods, terminology and laboratory practice.

Keywords

flow time, flow cup, viscosity, paints, varnishes, coatings, kinematic viscosity, ISO 2431, consistency control, QC testing

FAQ

Q: What is this standard?

A: ISO 2431:2019 is an International Standard that specifies a standardized flow‑cup method to determine the flow time of paints, varnishes and related products for consistency control and quality assurance.

Q: What does it cover?

A: It covers the design and tolerances of four specified flow cups (3, 4, 5 and 6 mm orifices), test procedure (sample and cup preparation, temperature control, filling and timing), measurement ranges and reporting, and methods for checking cup wear; it excludes replaceable‑jet and dipping flow cups and cautions about non‑Newtonian materials.

Q: Who typically uses it?

A: Quality-control technicians, formulation chemists, laboratory analysts, coatings manufacturers and instrument suppliers use this standard for routine viscosity/consistency checks where a rapid flow‑time method is suitable.

Q: Is it current or superseded?

A: ISO 2431:2019 is the current edition (Edition 6, published June 2019) and the ISO bibliographic record indicates the publication was reviewed and confirmed as current in 2025; earlier editions (e.g., 2011, 1993, 1984) have been superseded.

Q: Is it part of a series?

A: It forms part of the family of ISO standards on paints and varnishes (ISO/TC 35) and is commonly used alongside other test methods and terminology standards such as ISO 3219 and ISO 4618.

Q: What are the key keywords?

A: Flow cup, flow time, viscosity, paints, varnishes, consistency control, kinematic viscosity, QC.