Overview
ISO 787-22:1980, titled General Methods of Test for Pigments and Extenders - Part 22: Comparison of Resistance to Bleeding of Pigments, is an international standard developed by ISO Technical Committee ISO/TC 35, which focuses on paints and varnishes. This standard specifies a practical and reliable method for comparing the resistance to bleeding of pigments with that of an agreed reference sample. Bleeding refers to the undesirable discoloration or staining caused by the migration of pigment color into adjacent paint layers during or after application.
The method outlined in ISO 787-22 prioritizes practical applicability over purely theoretical assessments. It ensures consistency and comparability when testing pigment stability, making it highly valuable for quality control and product development in the coatings industry.
Key Topics
-
Scope and Application
The standard applies to pigments and extenders used in paints and coatings, establishing a method to compare their resistance to bleeding in relation to an agreed sample. It is designed as a general method suitable for many types of pigments, with notes on possible modifications tailored to specific pigment properties.
-
Materials and Equipment
- Test panels made of light-gauge metal such as tinplate or aluminum, pre-cleaned and abraded
- Silicon carbide abrasive paper (grade 600) for optional panel surface preparation
- Agreed medium for pigment dispersion (drying or stoving methods)
- White overcoating composition agreed upon by testing parties
- Black and white reference charts for visual comparison
-
Test Procedure
- Prepare dispersions of the pigment under test and the agreed reference sample in the same medium.
- Apply the pigment dispersion on metal panels with a wet film thickness of 75 to 120 microns over two-thirds of the panel length.
- After drying or stoving as specified, optionally abrade the coated area lightly.
- Attach black and white charts to the uncoated panel section.
- Apply the white overcoating composition over the pigmented area, overlapping the reference chart and the uncoated part.
- Allow drying or stoving of the overcoating.
- Visually compare the degree of bleeding under diffuse daylight, or artificial daylight if necessary, immediately and after 24 hours, using ISO 3668 for color comparison.
- Optionally, utilize colorimeters for quantitative assessment if agreed upon.
-
Reporting
The test report must detail:
- Pigment identification and type
- Reference to ISO 787/22
- Test conditions including dispersion medium, pigment concentrations, film application method, curing conditions, and overcoating type
- Any agreed modifications to procedures
- Type of lighting used for evaluation
- Results specifying if bleeding resistance is greater than, equal to, or less than the reference sample
- Test date for record keeping
Applications
-
Paint Manufacturing Quality Control
Manufacturers can apply this method to ensure pigment batches perform consistently in terms of bleeding resistance, preventing discoloration and related quality issues in final coatings.
-
New Pigment Development and Benchmarking
Pigment developers use the test to benchmark new pigments against established standards, optimizing formulation and improving market acceptance.
-
Supplier and Vendor Evaluation
Comparing pigments from different suppliers for bleeding resistance supports procurement decisions and specification compliance.
-
Standardization in Coatings Specifications
ISO 787-22 provides a standardized and reproducible test that can be referenced in product datasheets, technical agreements, and regulatory documents related to coating durability and aesthetics.
Related Standards
ISO 787-22 is part of the broader ISO 787 series of general test methods for pigments and extenders, which includes:
- ISO 787-1: Comparison of Colour
- ISO 787-5: Determination of Oil Absorption Value
- ISO 787-9: Determination of pH Value of an Aqueous Suspension
- ISO 787-15: Lightfastness Testing of Coloured Pigments
- ISO 787-20: Comparison of Ease of Dispersion
- ISO 787-21: Comparison of Heat Stability of Pigments
These complementary standards help provide a comprehensive framework for testing the physical and chemical properties of pigments, ensuring reliable performance in coatings and related applications.
Keywords: ISO 787-22, resistance to bleeding, pigments testing, paint quality control, bleeding test method, pigments and extenders, coatings industry standards, pigment stability, paint discoloration prevention, ISO TC 35 standards.
Open preview (PDF)General methods of test for pigments and extenders — Part 22: Comparison of resistance to bleeding of pigments