How to Choose an Ink Dispersant?
Choosing an ink dispersant requires comprehensive consideration of pigment characteristics, base
material type, application scenario, and the structure and performance of the dispersant. Here are
the key steps and precautions:
I. Clarify Core Needs and Scenario
Pigment Type and Characteristics
Inorganic Pigments (e.g., titanium dioxide, carbon black, iron oxide): Requires a dispersant with
high adsorption capacity (e.g., a polymeric dispersant containing carboxylic acid/phosphate groups) to
address dispersion stability on highly polar surfaces.
Organic Pigments (e.g., azo, xanthannaphthalene): Choose dispersants containing amine or ester groups
to balance adsorption and steric hindrance effects and prevent flocculation.
Functional Pigments (e.g., nanoparticles, metal powders): Requires a shear-resistant, low-viscosity
dispersant to prevent pigment agglomeration (e.g., superdispersants or specialized nanodispersants).
Ink System Type
Solvent-based Inks: Prioritize solvent-based dispersants (e.g., carboxylic acid/sulfonic acid, polyester),
which must have good compatibility with solvents (e.g., toluene, esters).
Water-based inks:
Choose water-based dispersants (such as ammonium polycarboxylate salts and polyethers) that are resistant
to salt spray and hard water, and avoid affecting the pH value of the system.
UV/EB curing inks: Require low-volatility, highly reactive dispersants (such as acrylates) to avoid residual odors
or affecting the curing speed.
II. Key Performance Indicators of Dispersants
Adsorption Capacity and Steric Hazard
Adsorption Capacity: The polar groups of the dispersant (such as -COOH, -NH₂) must be tightly bound to the
pigment surface (e.g., carbon black requires dispersants with aromatic ring structures).
Steric Hazard: Provide stable repulsive forces through high molecular chains (such as polyethers and polyesters)
to prevent pigment re-agglomeration (hyperdispersants with a molecular weight >1000 are recommended).
Compatibility and Dispersion Stability
Compatibility with Binder: The dispersant must be miscible with the binder (such as resins and oils) to avoid
"oil spots" or "haze" (e.g., polyester dispersants are selected for polyurethane inks).
Storage Stability: Prevent re-flocculation of dispersed pigments (assessed by measuring viscosity and particle size
changes).
Impact on Ink Performance
Viscosity Control: Select low-viscosity dispersants to avoid excessively high ink viscosity affecting coatability (e.g.,
flexographic inks require low-viscosity dispersants).
Gloss and Adhesion: The dispersant should not affect film gloss (e.g., amino resin inks require low-migration
dispersants) and should enhance the adhesion between pigments and the substrate.
III. Selection Methods and Experimental Verification
Matching Dispersants Based on Pigment Type
Inorganic Pigments: Dispersants containing phosphate esters or polycarboxylic acids are recommended (e.g.,
RK-4057, RK-4008).
Organic Pigments: Select dispersants containing amine or azo groups (e.g., RK-4020, RK-4030).
Nano Pigments: Use superdispersants (e.g., RK-4035 series) or dedicated nanodispersants to reduce particle size to
below 100nm.
Small-Scale Testing and Formulation Optimization
Dispersion Testing: Measure the particle size distribution (laser particle size analyzer), viscosity change (Ford cup 4),
and storage stability of the dispersed ink (centrifugation or observation of layering after standing).
Comparative Experiments: Test the dispersion efficiency of different dispersants (e.g., high molecular weight vs.
low molecular weight) and select the product with the best cost-performance ratio.
Industry Application Cases
Plastic Inks: Select solvent-based superdispersants (e.g., RK-4033) to improve pigment wettability and dispersion stability.
Paper Inks: Use polycarboxylic acid dispersants (e.g., RK-4019) to improve water resistance and printability.
Metallic Inks: Select phosphate ester-containing dispersants (e.g., EK-4013) to enhance adhesion and salt spray resistance.
IV. Precautions
Avoid Over-Dispersion: Over-dispersion may result in excessively small pigment particle size, affecting ink hiding power
(dispersion and performance must be balanced).
Dosage Control: Typically 5%~15% of the pigment dosage; excessive dosage may cause ink blooming or defoaming problems.
Environmental Protection and Regulations: Food contact inks must comply with FDA, GB 4806, and other standards,
selecting VOC-free and low-toxicity dispersants (such as water-based dispersants).
In summary, the core of selecting ink dispersants is to adhere to the matching principle of "pigment-dispersant-base
material," requiring a comprehensive evaluation considering pigment type, system medium, application performance
(such as weather resistance and adhesion), and cost. It is recommended to prioritize dispersants from reputable
companies and conduct small-scale tests to verify dispersion effects and ink stability before ultimately
optimizing the formulation.
