Overview
EN ISO 8781-1:1995, titled Pigments and Extenders - Methods of Assessment of Dispersion Characteristics - Part 1: Assessment from the Change in Tinting Strength of Coloured Pigments, is an internationally recognized standard developed by CEN. It specifies a standardized method to evaluate the dispersion properties of colored pigments by measuring changes in their tinting strength during progressive dispersion stages.
This method is widely used to compare similar pigments-such as a test pigment against an agreed reference pigment-and assess their ease of dispersion within an agreed binder system. Tinting strength is a critical property influencing pigment performance in coatings, inks, and plastics, making this standard indispensable for quality control and product development in pigment manufacturing and related industries.
Key Topics
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Scope: Applies to colored pigments dispersed as defined in ISO 8780 series, focusing on tinting strength change as a measure of dispersion quality.
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Principle of Assessment:
- Pigments are dispersed in stages, following standardized conditions.
- After each stage, a sample of pigment dispersion is mixed with a white pigment to form a reduced paste.
- Tinting strength (K/S value) of this paste is measured using photometric methods described in ISO 787-24.
- The percentage increase in tinting strength between two dispersion stages quantifies the pigment’s dispersibility.
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Test Materials and Apparatus:
- Colored pigment paste and white pigment paste (preferably titanium dioxide as the white pigment).
- Binder system agreed between parties.
- Film applicator, spectrometer or photometer capable of measuring light reflectance between 400 nm and 700 nm.
- Automatic muller or other standard mixing devices for preparing the reduced paste.
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Test Procedure Highlights:
- Preparation of pigment dispersions under controlled conditions.
- Mixing colored pigment and white pigment paste to a precise reduction ratio.
- Application of reduced paste films on substrates and measuring tinting strength at each dispersion stage.
- Performing rub-out tests to ensure film uniformity and stability.
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Data Interpretation:
- Tinting strength increase (IS) calculated as a percentage difference between dispersion stages.
- Graphical plotting of tinting strength development can reveal overgrinding, flocculation, or recrystallization phenomena.
- Clear criteria define significant differences in ease of dispersion based on IS values.
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Reporting Requirements:
- Complete details including product ID, test conditions, materials used, dispersion stages, final IS values, and observed phenomena.
- Agreement on supplementary conditions such as white pigment type, reduction ratio, and film application method.
Applications
- Pigment Quality Control: Enables pigment manufacturers to objectively assess dispersion quality, ensuring consistent product performance.
- Product Development: Helps in comparing new pigment formulations against reference standards to optimize dispersion characteristics.
- Coatings, Inks, and Plastics: Provides reliable data on pigment performance which influences color strength, opacity, and stability in final products.
- Research and Testing Laboratories: Standardizes evaluation techniques to facilitate reproducibility and comparability of pigment dispersion assessments globally.
Related Standards
- ISO 8780 Series: Specifies various methods of dispersion including oscillatory shaking (Part 2), high-speed impeller milling (Part 3), bead milling (Part 4), automatic mulling (Part 5), and triple-roll milling (Part 6).
- ISO 787-24: Provides the photometric method for determination of relative tinting strength and scattering power of pigments.
- ISO 591: Defines technical requirements and classification of titanium dioxide pigments used as white pigments in these assessments.
- ISO 105-A01: Specifies general principles for color fastness testing relevant to pigment tinting strength evaluations.
By adhering to EN ISO 8781-1:1995, manufacturers and testers ensure accurate, reproducible, and internationally comparable results that optimize pigment dispersion processes and ultimately improve the performance and consistency of pigmented products.