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D2745-00 – Standard Test Method Technical Guide
🔬 Test Method Overview
This test method describes the procedure for determining the relative tinting strength of white pigments by reflectance measurements of black tints. It is applicable only when comparing a test pigment with a reference standard of the same type and grade. The Y tristimulus values (green-filter reflectance) of opaque drawdowns are measured to calculate the tinting strength.
⚙️ Apparatus and Materials
Key equipment includes an automatic muller with a total force of 445 N (100 lbf), flexible spatulas, and precision balances. The following table summarizes the specifications:
| 🔧 Equipment | 📏 Specification |
|---|---|
| Muller | 220 N (50 lbf) permanent + 220 N (50 lbf) additional, total 445 N (100 lbf) |
| Spatula (flexible) | Chromium-plated or plastic blade, 75 mm to 150 mm (3 in. to 6 in.) |
| Spatula (tapered) | 75 mm (3 in.) tapered blade |
| Balance (1) | Sensitive to 20 mg |
| Balance (2) | Sensitive to 0.4 mg |
| Vehicle | Solvent-free, agreed upon by purchaser and seller |
📊 Calculation and Significance
The relative tinting strength is calculated directly from the Y tristimulus reflectance values of the wet films. This test method is a referee method for quality control of white pigments. However, results obtained with a muller may not necessarily agree with industrial situations where different dispersing conditions exist.
💡 Tip: Keep muller glass plates sharp by grinding with No. 303 optical emery and water to ensure accurate and consistent dispersion.
⚠️ Note: The choice of vehicle may affect test results. Ensure it is solvent-free and agreed upon by both the purchaser and the seller.
❓ Frequently Asked Questions
🔍 What is the purpose of this test method?
To determine the relative tinting strength of white pigments by reflectance measurements of black tints, essential for quality control.
💡 How is the test performed?
The pigment is dispersed in a vehicle, let down with a tinted vehicle, and applied as opaque drawdowns. The Y tristimulus reflectance of the wet films is measured.
⚡ What is the recommended muller specification?
An automatic muller should exert a permanent 220 N (50 lbf) and an additional 220 N (50 lbf), for a total of 445 N (100 lbf).
📌 Why are specific spatulas required?
Flexible spatulas with chromium-plated or plastic blades of specified lengths are necessary for consistent dispersion during sample preparation.