Overview
ISO 787-23:1979 specifies a general method for determining the density of pigments and extenders using a centrifuge to remove entrained air. This international standard from ISO Technical Committee 35 (Paints and varnishes) provides a precise technique ideal for quality control and product specification in the coatings and pigments industries. The method employs displacement liquids with known densities, ensuring accurate measurement of the true density by eliminating air bubbles trapped within the sample.
The centrifuge technique described is particularly useful for measuring pigments and extenders that may contain occluded air, which can affect density readings in other methods. By removing this air, the standard ensures reproducible and consistent measurements critical for industrial and research applications.
Key Topics
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Density Determination Principle
The method involves weighing a dried pigment or extender sample mixed with a displacement liquid. Under centrifugation, entrained air is removed, and the density is calculated from the difference in masses before and after immersion.
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Displacement Liquids
High-boiling aromatic or aliphatic hydrocarbons with low evaporation rates under vacuum are recommended. The liquid must be insoluble with respect to the test material and provide good wetting properties.
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Temperature Control
Temperature directly influences the density of the displacement liquid. All measurements must be performed at a constant temperature, ideally using a temperature-controlled environment or by noting the precise temperature for correction.
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Equipment Requirements
Key apparatus includes a laboratory centrifuge, centrifuge tubes (glass or inert material), fine wire suspension cradle, precise balance (accuracy to at least 1 mg), and a sieve for sample preparation.
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Procedure Highlights
- Dry and sieve the sample.
- Weigh the empty tube and rod, then weigh after immersion in displacement liquid at temperature.
- Add sample and displacement liquid, centrifuge to remove air.
- Fill tube fully with displacement liquid and weigh again.
- Density is calculated using the formula provided in the standard.
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Precision and Repeatability
The method exhibits high repeatability with an absolute difference of 0.03 g/ml expected under controlled conditions and reproducibility between labs within 0.05 g/ml.
Applications
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Quality Control in Pigment Manufacturing
Ensuring accurate density measurements of pigments and extenders supports consistent product performance and adherence to specifications.
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Product Specification Compliance
Many pigment and extender specifications reference ISO 787 methods for standardizing test results globally.
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Research and Development
Facilitates the characterization of new pigment materials by providing reliable density data, essential for formulating paints, coatings, and related products.
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Coatings and Paint Industry
Accurate density influences formulation, mixing ratios, and application properties, making this method valuable for production and lab settings.
Related Standards
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ISO 787-10:1978 – Density determination using the pyknometer method, an alternate density measurement technique applicable for pigments and extenders.
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ISO 842 – Sampling of raw materials for paints and varnishes to ensure representative test specimens.
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ISO 787 series – A comprehensive suite of standardized tests for pigments and extenders including color comparison, oil absorption, matter soluble in water, pH determination, and resistance tests.
By adhering to ISO 787-23:1979, laboratories and manufacturers benefit from a robust, temperature-controlled, centrifuge-based density measurement method, enabling enhanced accuracy in pigment and extender density reporting. This method helps eliminate errors due to entrained air, a common issue in pigment density tests, thus ensuring quality and consistency essential for industrial applications worldwide.
Open preview (PDF)General methods of test for pigments and extenders — Part 23: Determination of density (using a centrifuge to remove entrained air)
