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D5326-22 – Standard Test Method Technical Guide
This standard, designated D5326-22, covers a procedure for measuring color development in tinted latex paints for determining the efficiency of colorants, the tintability of base paints (or color acceptance), and the potential for poor color uniformity of applied paint films.
💡 Standard Units: Per Section 1.2, the values stated in SI units are to be regarded as the standard. Values given in parentheses (inch-pound units) are mathematical conversions provided for information only and are not considered standard under this test method.
📐 Scope and Terminology of Color Development
Per the standard’s definitions in Section 3, color development is formally defined as the extent to which the colorant has achieved its full tinting potential, evidenced by the color change (or lack thereof) when the tinted paint is subjected to very strong shear stress. Tintability is the capability of a white or tint base paint to accept various colorants, as demonstrated by the color development achieved in the mixture. A deficiency in color development indicates poor tintability, often resulting in streaking or non-uniformity during brush or roller application.
⚙️ Test Procedure and Shearing Technique
The test method requires the application of the test paint by drawing it down on a striped black and white sealed chart. This substrate is critical for verifying that the applied film thickness is sufficient to obtain full hiding. Following the initial drawdown, a portion of the film must be subjected to strong shearing forces using a prescribed brushing procedure. This action physically breaks down undispersed colorant agglomerates, fully releasing the colorant’s tinting potential.
After the film has dried, the CIELAB color difference (ΔE*) between the undisturbed drawdown area and the sheared area is calculated and reported. This color difference acts as the primary measure of the deficiency in the color development of the test paint. A high ΔE* value indicates a significant deficiency, warning of potential application issues.
⚡ Critical Note on Shearing: The prescribed brushing procedure represents the core mechanism of the test. Inconsistent shearing force or technique will directly compromise the repeatability of the ΔE* result. Laboratories must validate their shearing procedure rigorously to achieve reliable data for colorant efficiency analysis.
📊 Key Referenced Standards and Measured Properties
The color difference calculation depends on several key ASTM standards. Practice D2244 governs the calculation of color differences from instrumentally measured coordinates. Data must be acquired using procedures from E1164 and a validated geometric condition, such as hemispherical (E1331) or bidirectional 45°:0° (E1349). Practice E1345 is followed to reduce measurement variability. All conditioning and testing must take place in a Standard Environment per Specification D3924 (typically 23 ± 2 °C, 50 ± 5 % RH).
| 🎯 Referenced Standard | ⚡ Function in D5326-22 |
|---|---|
| D2244 | Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates. |
| E1331 / E1349 | Test Methods for Reflectance Factor and Color by Spectrophotometry (Hemispherical or 45°:0° Geometry). Defines the optical measurement geometry. |
| E1345 | Practice for Reducing the Effect of Variability of Color Measurement by Use of Multiple Measurements. Ensures statistical reliability of the ΔE* data. |
| D3924 | Specification for Standard Environment for Conditioning and Testing Paint, Varnish, Lacquer, and Related Materials (23±2°C, 50±5% RH). |
| D16 / E284 | Terminology standards for Paint and Appearance, providing the foundational language for the test method. |
The final result is a single quantitative value: the CIELAB color difference (ΔE*ab) between the sheared and unsheared areas. A well-formulated base paint with high tintability will produce a very low ΔE*, confirming that the colorant has achieved its full tinting potential without the need for extreme post-application shear.
❓ Frequently Asked Questions
🔍 What does a high ΔE* value indicate?
A high CIELAB color difference between the sheared and unsheared drawdown areas indicates poor color development. The colorant failed to reach its full tinting potential during the initial drawdown and required high shear to develop. This is a direct warning of poor tintability in the base paint.
💡 Why is the striped black and white chart mandatory?
The chart is used to visually confirm full hiding. The film must be thick enough so that the contrast between the black and white stripes does not influence the measured reflectance. If the film lacks opacity, the substrate color will affect the CIELAB calculation, skewing the color development measurement.
⚡ Is this test method applicable to solvent-based paints?
No. The scope of D5326-22 is strictly limited to tinted latex paints. The rheology and dispersion dynamics of solvent-based systems differ significantly, and this specific shearing test procedure is calibrated for water-based architectural coatings.
📌 How is this test used to determine colorant efficiency?
The test method directly compares the color of a tinted paint before and after destructive shear. If a colorant requires intense shear to develop, its in-can efficiency is considered low. By testing different colorants in the same base, or one colorant across multiple bases, the relative efficiency and compatibility can be quantified by the resulting ΔE* values.