A Complete Methodology for Selecting General-Purpose Dispersants
A universal dispersant selection methodology covering three major scenarios: water systems, solvent systems, and UV systems. It can accurately match suitable products based on pigment properties and working conditions, ensuring dispersion efficiency and long-term system stability.
I. Before proceeding with the selection process, five key mandatory conditions must be verified, directly determining the overall direction of the subsequent selection:
1. Based on the type of pigment being dispersed:
1) For a variety of inorganic powder pigments including titanium dioxide, calcium carbonate, silica powder, zirconium oxide, silicon nitride, and alumina: Water-based systems are suitable for polycarboxylate dispersants, while solvent systems are suitable for polyester dispersants. Stable dispersion is achieved primarily through electrostatic repulsion.
2) For highly reactive metal powder materials including aluminum, zinc, and magnesium powders: Water-based systems should use neutral/weakly anionic dispersants without free acid. Strong acid dispersants are strictly prohibited to avoid hydrogen evolution and swelling problems.
3) For organic pigments and carbon black powder materials with high specific surface area and poor wetting properties: A high-molecular-weight anchoring dispersant is essential. Small-molecule dispersants only provide good short-term dispersion; long-term flocculation and coarsening problems will inevitably occur.
2. Dispersion medium is a priority factor in selection.
1) Solvent-based systems composed of xylene, esters, alcohol ethers, and ketones: Suitable dispersants include polyester, polyurethane, and modified polyacrylic acid polymers, relying on steric hindrance to achieve stable particle dispersion.
2) UV-curable resin systems: Preferred: UV-copolymerizable dispersants with double bonds. Dispersants with polymerization inhibitors, free amines, or high levels of saturated fatty acids are strictly prohibited to prevent incomplete curing.
3) Water-based coating and ink application systems: Suitable: Polycarboxylates, ammonium acrylates, nonionic grafted polymers, and organophosphates.
Prohibited: Dispersants containing oily long-chain fatty acids or high levels of solvent-based carriers.
3. Based on the type of base resin:
For epoxy, PU, acrylic, alkyd, and unsaturated polyester systems, it is essential to ensure good compatibility between the dispersant and the corresponding base resin and curing agent. Poor compatibility can lead to typical appearance and stability problems such as film cratering, loss of gloss, precipitation, reaction coking, and storage stratification.
4. Based on end-use requirements:
For dip coating/industrial coatings, use specialized dispersants that balance dispersion, anti-settling, low foaming, and no impact on adhesion. For inkjet applications, use specialized dispersants with low foaming, non-clogging, silicone-free, and non-precipitation properties. For electronic pastes, strict control of potassium and sodium impurities is required; choose dispersants with low residual carbon and complete decomposition under high-temperature conditions.
5. Based on system pH and electrolyte content:
For high-electrolyte, high-pH systems, ordinary small-molecule phosphates should be eliminated; use electrolyte-resistant polymeric dispersants.
II. Key Advantages, Disadvantages, and Precise Application Scope of Three Mainstream Dispersant Categories
1. Inorganic Small Molecule Dispersants, Represented by Sodium Hexametaphosphate and Sodium Tripolyphosphate: Advantages include low price and rapid viscosity reduction in the system. Disadvantages include poor water resistance, poor electrolyte resistance, and poor long-term storage stability.
Suitable for ordinary putty and inexpensive filler slurries; strictly prohibited for use in high-end coatings, electronic pastes, and inkjet systems.
2. Dispersants with Nonionic or Anionic Low-Molecular-weight Surfactants as Core Components:
Can only be used as wetting aids and cannot act as primary dispersants. Long-term dispersion and long-term stability are extremely poor.
3. Polymer-based dispersants that rely on multi-point anchoring groups to firmly adsorb onto the surface of pigment particles (e.g., RK-4035, RK-4036, RK-4031, RK-4017E, RK-4039AC, RK-4059).
The mechanism of action is that the anchoring groups firmly adsorb the powder particles, and the solvation chains create steric hindrance in the dispersion medium, effectively inhibiting particle agglomeration and sedimentation. Suitable for nanoparticles and ultrafine pigment systems.
These are preferred dispersants suitable for all scenarios; selection and adaptation are simply a matter of matching the corresponding dispersion medium and matrix resin.
III. The Simplest Practical Four-Step Selection Method
1. First, identify the dispersion medium (water/solvent/UV), then clarify the corresponding powder material – two core selection dimensions;
2. Select the core category of dispersants that precisely matches the chemical structure of the target system;
3. Define the fixed addition range: 0.2%–1.5% for inorganic powders, and 1%–5% for carbon black and organic pigments;
4. Conduct small-scale testing: verify the slurry viscosity stability, 7-day standing layering, paint film appearance, adhesion, and curing speed.
IV. Summary of General Taboos
1. All types of small molecule dispersants must be discarded in nanopowder applications;
2. High acid value dispersants are strictly prohibited in cross-linked resin systems (waterborne epoxy, two-component PU) to avoid premature gelation;
3. Acidic and strongly ionic dispersants should be avoided in metal powder applications.
