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D6336-11 – Standard Test Method Technical Guide
📐 Core Terminology and Equipment for Pigment Wetting
ASTM D6336-11 (Reapproved 2021) provides a standardized practice for the evaluation of flushing vehicles used in pigment dispersion. The process specifically applies to equipment known as a vacuum modified sigma blade mixer, or vacuum flusher. Understanding the specialized terminology defined within the standard is critical for effective application.
The technique of flushing is defined as the transfer of pigments from water-based dispersions (presscake) into oil-based vehicles by displacing the water. The flusher is a mixing device with two sigma-shaped blades rotating in opposing directions at different speeds to generate a kneading action. The vacuum cycle is the specific period during which the mixture is subjected to vacuum to remove entrapped water. A successful break (the separation of water from the pigment in a presscake) indicates an optimum vehicle-pigment interaction.
| 🟦 Term | 📐 Definition per ASTM D6336 |
|---|---|
| Flusher | Mixing device with two parallel sigma blades turning oppositely at different speeds for kneading. |
| Flushed Color | A color base in paste form prepared by the flushing process. |
| Vehicle | Liquid portion of the ink holding the pigment, providing workability, drying properties, and binding. |
| Pigment | Fine solid colorant particles substantially insoluble in both the vehicle and water. |
💡 Technical Note: The kneading action of the sigma blade mixer is the primary mechanism for displacing water from the presscake surface. An effective vehicle reduces surface tension to allow a rapid and complete “break” and efficient water removal during the vacuum cycle.
⚙️ Evaluation Guidelines for Flushing Vehicles
As a standard practice, D6336 provides guidelines rather than a single rigid test procedure. It directs users to evaluate the performance of the flushing vehicle based on the final properties of the flushed color. The standard heavily leverages an extensive suite of referenced ASTM methods to verify dispersion quality, rheology, and purity. The user is responsible for establishing appropriate safety and health practices (Section 1.3) before beginning any evaluation.
| 🎯 Evaluation Parameter | 📏 Referenced Standard | ⚡ Apparatus / Method |
|---|---|---|
| Fineness of Grind | D1316 | NPIRI Grindometer |
| Rheological Properties | D4040 | Falling-Rod Viscometer |
| Apparent Tack | D4361 | Three-Roller Tackmeter |
| Color Strength | D387 / D2066 | Mechanical Muller / Tinting Strength |
| Water Content | D4017 | Karl Fischer Titration |
| Coarse Particles | D2067 | Wash Sieve Method |
⚠️ Safety Considerations: The standard explicitly states (Section 1.3) that it does not address all safety concerns. Users must determine the applicability of regulatory limitations. Flushing operation involves significant heat generation from the mechanical kneading action and may require mitigation of volatile organic compounds from the vehicle.
📊 Key Measured Properties and Quality Control
The ultimate goal of D6336 is to determine if a vehicle is suitable for flushing a specific pigment. After the flushing process and vacuum cycle, the resulting flushed color must be characterized. A low water content measured by Test Method D4017 confirms effective water displacement. A high fineness of grind value per D1316 indicates excellent pigment wetting and dispersion. The rheological profile of the flushed color (D4040) provides vital data for subsequent ink formulation and printing performance. The color strength (D2066) and tack (D4361) of the flushed product must match the desired specifications for the final application.
📌 Best Practice: When conducting an evaluation, run a control sample using a known effective flushing vehicle. This comparative approach allows for clear differentiation of the candidate vehicle’s wetting efficiency and water rejection capabilities.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D6336?
It provides a standardized practice for evaluating flushing vehicles used to disperse pigments in a vacuum modified sigma blade mixer, ensuring consistent quality and performance in the ink manufacturing process.
💡 What defines a “break” in the flushing process?
The “break” is the specific action where water is physically separated from the pigment in the presscake as the vehicle wets the pigment particles during mixing in the flusher.
⚡ How does the vacuum cycle contribute to the flushed color quality?
The vacuum cycle removes residual water and entrapped air from the mixture. This is critical for achieving proper rheology, preventing defects in the final printed ink layer, and improving the color strength of the final dispersion.
📌 Which standards are used to determine the fineness of grind and tack of the flushed color?
Standard D1316 (NPIRI Grindometer) is used for fineness of grind, and standard D4361 (Three-Roller Tackmeter) is used for measuring the apparent tack. Both are critical metrics for the usability of the flushed color in printing inks.