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D2067-97 – Standard Test Method Technical Guide
🔬 Scope and Significance
ASTM D2067-97 (Reapproved 2020) provides a standard test method for determining the weight concentration of coarse particles in printing ink dispersions via sieve retention. The method is specifically applicable to printing inks, flushed pigments, and other dispersions containing particles larger than 45 µm. With appropriate solvent selection, it accommodates both paste and liquid ink formulations.
The presence of coarse particles significantly reduces dispersion efficiency, necessitating extra milling passes and causing frequent pump filter blockages. In printing applications, these particles can lead to excessive plate wear, ink piling on blankets, water balance disruptions, and diminished color strength and gloss. This test is therefore a critical tool for quality control in ink manufacturing.
⚙️ Test Procedure and Key Apparatus
A 50 g specimen of the test dispersion is prepared and, if necessary, diluted with a reducing varnish. The sample is then combined with 200 g of mineral spirits (conforming to Specification D235) or a mutually agreeable solvent. This mixture is agitated in a paint shaker for exactly 30 minutes.
| 🔧 Parameter | 📏 Specification |
|---|---|
| Specimen Size | 50 g (plus reducing varnish as needed) |
| Washout Solvent | 200 g Mineral Spirits (D235) |
| Mixing Duration | 30 minutes (paint shaker) |
| Sieve Mesh Size | 325 mesh (45 µm openings, E11) |
| Sieve Diameter | 60.3 mm (disposable) or 75 mm (standard) |
| Drying | Oven per Specification E145 |
The slurry is then passed through a tared 325-mesh wire cloth sieve. The retained residue is thoroughly washed with solvent, dried, and weighed.
⚠️ Solvent Sensitivity: Strong washout solvents must be avoided. They can dissolve large resin particles from the ink vehicle, leading to artificially low retained residue values and invalid test results. Mineral spirits per D235 is the standard recommended solvent.
📊 Reporting Results and Precision
The mass of the residue retained on the sieve is used to calculate the concentration of coarse particles, reported as a percentage or in parts per million (ppm) relative to the original 50 g specimen. The nature of the retained particles can be qualitatively characterized using a magnet or through visual and microscopic examination.
| 🎯 Measured Value | ⚡ Unit | 📋 Key Notes |
|---|---|---|
| Coarse Particle Content | % or ppm (by weight) | Calculated from retained residue mass |
| Particle Size Threshold | 45 µm | Defined by the 325 mesh sieve cloth |
| Particle Identification | Qualitative | Magnet, visual, or microscopic exam |
| Precision Enhancement | N/A | Larger specimen sizes improve precision |
💡 Precision Best Practice: Disposable 60.3 mm diameter sieves are strongly preferred for this method. Because they weigh only approximately 0.5 g compared to roughly 70 g for a standard sieve, they drastically reduce the potential for weighing errors on the analytical balance.
❓ Frequently Asked Questions
🔍 Why is the 45 µm (325 mesh) threshold specifically chosen for this test?
This threshold directly targets the coarse particles known to cause processing issues like poor dispersion, filter clogging, and plate wear. For analyzing particle sizes significantly smaller than this (under 25 µm), the standard specifically recommends using Test Method D1316 (NPIRI Grindometer) for more appropriate characterization.
💡 How does the washout solvent affect the test results?
The solvent dilutes the ink so that fine particles pass through the sieve. The choice of solvent is critical; strong solvents will dissolve resin-based coarse particles, incorrectly indicating good dispersion quality. Mineral spirits (D235) is specified to ensure only the true coarse particles remain as residue.
⚡ Can the sensitivity of this quality control test be adjusted?
Yes, Section 4 of the standard explicitly states that the precision of the test may be improved by using a specimen size larger than the prescribed 50 g. Laboratories requiring tighter control over dispersion quality can scale the material sample up while following the standard procedure.
📌 How does this method relate to ASTM D1316 and D185?
D2067 is similar in principle to D185 (Coarse Particles in Pigments). The distinction is that D2067 is tailored for ink dispersions. For particles under 25 µm, D1316 (Fineness of Grind of Printing Inks) is the applicable standard. The interlaboratory precision for D2067 is established following Practice E691.