ISO 787-16:1986

Overview

ISO 787-16:1986 is an international standard published by the International Organization for Standardization (ISO) that specifies a general method for testing pigments and extenders. Specifically, Part 16 of this series defines the determination of relative tinting strength (or equivalent colouring value) and colour on reduction of coloured pigments using a visual comparison method. The standard outlines a procedure to compare the colour strength and undertone of a test pigment with an agreed reference pigment under controlled conditions.

This method plays an essential role in quality control and specification of coloured pigments, especially in paint and coating industries. It ensures reproducible results by standardizing the sample preparation, dispersion, and evaluation methods.

Key Topics

• Scope and Purpose: The standard aims to provide a reliable visual comparison method to assess the relative tinting strength and colour modification when coloured pigments are diluted or reduced with white pigments.

• Test Procedure:

  • Preparation of pigment dispersions using an automatic muller under defined conditions.
  • Mixing coloured pigment dispersions with white pigment paste at predetermined ratios.
  • Producing reduction pastes to compare tinting strength and colour visually.
  • Comparison against a standard reference pigment processed identically.

• Materials and Apparatus:

  • Use of specified white pigment pastes and binders compatible with the coloured pigment.
  • An automatic tri-roll mill (broyeuse automatique) for dispersion with controlled rotation speed, load, and temperature.
  • Tools including stainless steel spatulas, glass or plastic applicator blades, and consistent sample storage containers.

• Sample Preparation:

  • Determining optimal pigment-to-binder ratios based on pigment properties.
  • Grinding pigment particles to under 5 microns particle size to ensure uniform dispersion.
  • Preparing reduction mixtures maintaining precise mass ratios of coloured pigment to white pigment.

• Visual Comparison:

  • Assessing the resulting colour strength and undertone after reduction visually, with comparison to a reference pigment under identical conditions.
  • Expressing results as relative tinting strength or equivalent colouring value.

• Application Limits:

  • Mainly applicable to coloured pigments except for some yellow pigments where white paste evaluation is problematic.
  • The binder and white pigment paste must be agreed upon between testing parties to ensure consistency.

Applications

This ISO standard is widely applicable in industries and laboratories involved in:

• Paint and Coating Manufacturing: Ensures consistent pigment quality affecting colour accuracy and coverage.
• Pigment Quality Control: Routinely used for batch-to-batch consistency and supplier material evaluation.
• Research and Development: Formulating new pigments or assessing new formulations for colour strength and modification behaviour.
• Standardization and Specification Writing: Incorporated into technical specifications for pigments as a reference test method.
• Contractual Pigment Testing: Providing an agreed-upon visual comparison method between pigment producers and buyers.

The visual comparison method defined here supports rapid qualitative assessment without requiring advanced photometric instruments, though photometric methods are described in complementary standards like ISO 787-24.

Related Standards

ISO 787 Part series includes general test methods covering a wide range of pigment properties:

• ISO 787-1: Comparison of pigment colours
• ISO 787-24: Photometric method for determining relative tinting strength of coloured pigments
• ISO 591: Specifications for titanium dioxide pigments used in paints
• ISO 842: Sampling of raw materials for paints and varnishes
• ISO 1524: Determination of grinding fineness (applicable particle size measurement)
• Additional parts address volatile matter, oil absorption, pH, density, stability, and other functional tests essential for pigment characterization.

Benefits of Using ISO 787-16

• Provides a standardized and reproducible procedure to assess tinting strength across laboratories and industries.
• Facilitates objective comparison between pigments of similar types to ensure consistency.
• Supports quality assurance and regulatory compliance for paint and coating materials.
• Enables communication and agreement between pigment manufacturers and customers using a common reference method.
• Integrates seamlessly with other parts in the ISO 787 series for comprehensive pigment evaluation.

By adopting ISO 787-16:1986, companies and laboratories can reliably determine the relative tinting strength and reduced colour properties of coloured pigments, ensuring higher quality products and better control over visual characteristics in coatings and related applications.