In water-based ink systems where acrylic resin serves as the primary film-forming material, the selection of a dispersant requires comprehensive consideration of resin characteristics, pigment type, system pH, and final ink performance requirements. Below are the key points and recommended directions for choosing a dispersant:

1. Matching the Chemical Properties of the Acrylic Resin

● Charge Type: Water-based acrylic resins are typically anionic (pH 8-9). Anionic or non-ionic dispersants should be selected to avoid flocculation caused by charge conflict.

● Compatibility: The dispersant should be compatible with the acrylic resin solution to avoid abnormal viscosity or separation. Stability testing via mixing experiments (dispersant + resin solution + pigment) is recommended.

2. Selecting Dispersants Based on Pigment Type

● Organic Pigments (e.g., Phthalocyanine Blue, Permanent Red):Recommend high molecular weight polyurethane (e.g., BYK-190) or polycarboxylate dispersants, which stabilize pigments through steric hindrance.

○ For pigments with strong surface hydrophobicity, dispersants containing anchoring groups (e.g., phosphate ester, amine groups) can be selected.

● Inorganic Pigments (e.g., Titanium Dioxide, Carbon Black):Suitable for low molecular weight anionic dispersants (e.g., Tego Dispers 755W), which stabilize dispersions through electrostatic repulsion.

○ Pigments with high specific surface area like carbon black require highly adsorbent dispersants (e.g., EFKA-4580).

3. Molecular Weight and Dispersion Mechanism

● High Molecular Weight Dispersants (>5000 Da): Provide long-term stability through steric hindrance, suitable for highly polar or difficult-to-disperse pigments.

● Low Molecular Weight Dispersants (<3000 Da): Rely on electrostatic repulsion, suitable for easily dispersed pigments or systems requiring low viscosity.

4. Environmental and Regulatory Requirements

● Choose environmentally friendly dispersants free from APEO and low in VOC (e.g., BYK-2013), aligning with the eco-friendly positioning of water-based inks.

5. Recommended Dispersant Types and Products

6. Test Methods for Verifying Dispersion Effectiveness

1. Fineness Test: Use a grind gauge to detect the fineness of the milled paste (target ≤10μm).

2. Stability Test: Observe for separation, re-coarsening, or viscosity changes after storage.

3. Paste Fluidity: Excess dispersant may increase viscosity; optimize the dosage (typically 1-5% of pigment weight).

Summary

The core of selecting a dispersant lies in achieving a compatibility balance among the “Pigment-Dispersant-Resin” triad. It is advisable to first determine the dispersant type and dosage through small-scale trials, then optimize overall performance in combination with rheology additives (e.g., thickeners). For complex systems, consider using blended dispersants (e.g., anionic + non-ionic) to enhance stability.