ISO 787-21:1979

Overview

ISO 787-21:1979 defines a general method for comparing the heat stability of pigments using a stoving medium. Published by the International Organization for Standardization (ISO) as part of the ISO 787 series covering test methods for pigments and extenders, this standard allows manufacturers and formulators to objectively evaluate and compare how pigments withstand heat exposure. While primarily intended for comparison by specifying heating temperatures and times, the method is also adaptable for determining a pigment's overall heat resistance.

The procedure serves as a reference for the coatings industry, supporting consistent quality control and formulation development across various sectors such as paints, varnishes, and plastics.

Key Topics

• Heat Stability Comparison
  The standard prescribes a process for side-by-side comparison of a test pigment’s heat stability versus an agreed reference pigment sample using controlled heating in a stoving medium.

• Test Procedure

  • Preparation of pigment dispersions in stoving mediums under agreed conditions
  • Application of consistent film thicknesses on metal panels
  • Curing samples at specific temperatures and timeframes
  • Cooling and visual (or instrumental) comparison of color changes after heating

• Result Evaluation
  Evaluation focuses on the degree of color change, categorizing the tested pigment as having less than, equal to, or greater heat stability compared to the reference.

• Documentation and Reporting
  Comprehensive reporting is required, including test conditions, reference materials, pigment concentrations, and results, ensuring transparent communication and reproducibility.

Applications

• Quality Control for Coatings
  Paint and coating manufacturers deploy this method to assess whether pigment batches meet thermal stability requirements, ensuring products perform reliably during industrial baking, curing, or stoving.

• Pigment Selection and Formulation
  R&D teams use the test to compare new pigment candidates with established references, optimizing formulations for high-temperature processing and end-use environments.

• Regulatory and Procurement Specifications
  The standard supports technical documentation in contracts and regulatory filings, establishing a common ground for thermal stability expectations and acceptance criteria.

• Cross-Industry Adaptability
  While tailored for paints and varnishes, its principles are extendable to plastics, inks, and other materials where pigment heat durability is critical.

Related Standards

• ISO 787 Series: The broader ISO 787 family provides standard methods for testing pigments and extenders, ensuring consistency in determining properties like color, solubility, oil absorption, residue, and more. Relevant parts include:

  • ISO 787-1: Comparison of color
  • ISO 787-2: Determination of matter volatile at 105°C
  • ISO 787-15: Resistance to light
  • ISO 787-22: Resistance to bleeding
  • ISO 842: Sampling of raw materials for paints and varnishes

• ISO 3668: Specifies the procedure for visual comparison of paint colors, useful for the assessment phase of heat stability testing.

Practical Value

Adopting ISO 787-21:1979 equips manufacturers, suppliers, and regulatory agencies with a standardized, internationally recognized framework for evaluating and specifying pigment heat stability. This promotes product reliability, facilitates communication across supply chains, and supports compliance with international quality standards in the pigments and coatings industry.

Keywords: ISO 787-21, pigment heat stability, stoving medium, thermal stability test, paint pigment testing, pigment comparison, coatings quality control, ISO pigment standards