Principles of Flocculation in Coatings and Inks/Inkjet and Guidelines for Selecting Anti-Flocculation Dispersants
I、 First, clarify the core logic: the three major judgment criteria for flocculation
1. Charge neutralization flocculation: refers to the process in which particles with opposite charges (such as pigments and fillers, different metal oxide powders) attract each other in a dispersed system (such as coatings, inks, ceramic slurries), causing the double layer to be compressed or neutralized, thereby losing electrostatic repulsion stability and undergoing flocculation and agglomeration;
2. Solvent induced desorption flocculation: High content of ethylene glycol/propylene glycol, oily strong solvents, UV monomers in aqueous systems, incompatible solvents with resins/dispersants, cause the dispersants originally adsorbed on the surface of pigment particles to be "washed away", thereby losing steric hindrance or charge repulsion protection, ultimately causing pigment particles to re aggregate;
3. Storage/heating instability flocculation: Ordinary dispersants lose their electrostatic repulsion and have insufficient adsorption strength when subjected to high temperatures, long-term standing, and acid-base changes, resulting in particle settling and agglomeration.
Core standard for anti flocculation dispersant: strong anchoring+thick spatial resistance layer. Simple electrostatic additives cannot provide long-term anti flocculation.
II、 Four major categories of anti flocculation dispersants, applicable systems, advantages and disadvantages
1. Comb shaped block polycarboxylate type (water-based universal anti flocculation, preferred inorganic filler)
Structure: The particles are firmly adsorbed by the main chain carboxyl group, and the side chain long polyether forms a hydration barrier, synergistically achieving dual protection of electrostatic repulsion and spatial impedance aggregation
-Adaptation: Nano zirconia, alumina, silicon powder, titanium dioxide, various metal oxide water-based systems
-Anti flocculation features: multi-layer steric hindrance isolation, mixed inorganic powder is not easily charged and flocculated; Moderate tolerance to diols;
-Disadvantages: It is prone to flocculation when mixed with low polarity organic pigments and cationic resins; Insufficient stability of ultra-high alcohol inkjet system
-Representative: RK-4017F0, ammonium polyacrylate (specialized for electronic ceramics, free of metal impurities) RK-4008Y
-Applicable scenarios: water-based industrial coatings, ceramic slurries, color pastes, ordinary water-based inks
2. Bipolar block polyurethane type (versatile anti flocculation, optimal for complex mixed systems)
The strongest anti flocculation model in the industry, solving the vast majority of complex flocculation problems
Structure: The molecule contains anionic anchoring groups, amino polar groups, and ultra long polyether side chains, which strongly adsorb inorganic/organic powders, prevent particle flocculation and precipitation, and maintain particle dispersion stability;
1. Anti charge flocculation: Simultaneously encapsulating inorganic and organic pigments, by endowing particles with different charge properties with the same surface electrical properties (or forming strong steric hindrance), eliminating agglomeration caused by mutual attraction of positive and negative charges;
2. Anti solvent desorption flocculation: resistant to over 30% ethylene glycol and propylene glycol and stable. During the long-term flow, reflux, and storage of water-based inkjet ink in the circulation pipeline of the printing equipment, the pigment particles always remain in a nano dispersed state, without coarsening or settling, and without the risk of clogging the nozzle;
3. Anti high temperature storage flocculation: Ink, color paste, coating, etc., after accelerated aging at 50 ℃ for 30 days, did not undergo particle agglomeration or solid precipitation hardening (agglomeration), proving their excellent thermal storage stability;
4. -Suitable for: organic pigment+nano oxide composite ink, water-based digital inkjet, cationic system, multi filler mixed slurry
5. -Disadvantage: High price
6. -Recommended: RK-4039AC, RK-4057
3. Phosphate modified polymer dispersant (oil/alcohol solvent anti flocculation, metal oxide specific)
Using phosphonic acid groups to "anchor" molecules on the surface of inorganic metal oxide (zirconia, silicon nitride, zinc oxide) particles, and then using long carbon chains to construct a physical barrier in the oil phase, thereby achieving permanent stable dispersion of nano/micro particles in oily media and preventing sedimentation, flocculation, and stratification;
-Adaptation: PGMEA, ethanol, ester ketone solvents, electronic ceramic slurry, oil-based anti-corrosion coatings
-Advantages: Powder mixing without flocculation, high temperature without desorption, low impurities suitable for electronic materials
-Model: RK-4012, RK-4013, RK-4013A
4. Acrylic/polyamide super dispersant (oil-based ink, weak solvent inkjet anti flocculation)
1). Acrylic block: Its molecular structure is specifically designed for medium to high polarity pigments, providing steric hindrance through anchoring solvation mechanism to prevent pigment precipitation, coagulation and aggregation during solvent dilution or storage;
2). Polyamide: Refers to the modification of low polarity transparent organic pigments with polyamide as a dispersant/carrier, which inhibits pigment float and crystal re coagulation through steric hindrance stabilization mechanism, thereby improving the uniformity and transparency of the color paste;
-Adaptation: Weak solvent inkjet, oily UV ink, plastic baking paint;
-Model: RK-4036, RK-4020
Disabled: Dispersants that cannot prevent flocculation
Low molecular weight sodium polyacrylate, hexametaphosphate, small molecule surfactant, short chain fatty acid soap
Only pure electrostatic repulsion, no spatial hindrance, immediate coagulation upon contact with alcohol, heating, and mixing.
Step 1: Select based on the system medium (water/oil/UV/inkjet)
1. Pure water-based system (paint, ceramic slurry) - single inorganic nano powder (zirconia/silicon/titanium dioxide): comb shaped ammonium polycarboxylate RK-4008Y (low-cost anti flocculation)
-Organic pigment+inorganic powder compound, containing a large amount of diols, inkjet system: amphoteric polyurethane dispersant
-Cationic lotion/cationic primer: only amphoteric polyurethane (RK-4059), ordinary anionic polycarboxylic acid can directly flocculate
2. Oil based system+alcohol ether solvent (electronic paste, oil-based casting)
Metal oxide filler preferred phosphate polymer dispersant (RK-4012); Organic pigments use acrylic/polyamide dispersant (RK-4035)
3. UV curing system
Select UV specific block super dispersant (RK-4013A) to avoid monomer dissolution and delamination of the dispersion layer, which may cause flocculation
4. Digital inkjet (water-based/weak solvent) - water-based inkjet: must use amphoteric polyurethane dispersant (RK-4061CF), polycarboxylate high alcohol environment is prone to flocculation and clogging
-Weak solvent inkjet: Oil soluble acrylic dispersants (RK-4031, RK-4035), completely incompatible with water-based additives
Step 2: Select based on powder combination (key points for anti flocculation core)
1. Single inorganic nano metal oxides (ZrO ₂, SiO ₂, Si ∝ N ₄)
Water based: ammonium polyacrylate dispersant; Oily: Phosphate dispersant, steric hindrance isolation, no charge flocculation
2. Single organic pigments (phthalocyanine, azo, carbon black)
Water based polyurethane dispersant; Oil based acrylic super dispersant to prevent pigment crystallization and flocculation
3. Mixing inorganic powder and organic pigment (most easily flocculated)
Unique universal solution: Amphoteric polyurethane dispersant (RK-4061CF), simultaneously coating two types of powders to neutralize charge conflicts
4. Compound of various inorganic fillers (zirconia+alumina+sintering aids)
Water based polycarboxylate ammonium dispersant, oil-based phosphate dispersant, fully oxide compatible, will not adsorb or agglomerate heterogeneous powders
Step 3: Strengthen anti flocculation selection in special circumstances
1. Long term high-temperature storage (40-60 ℃) is required: polyurethane dispersant, phosphate polymer dispersant (with the strongest anchoring force and no detachment at high temperatures)
2. High solvent system (ethylene glycol>25% inkjet ink): only amphoteric polyurethane dispersant, polycarboxylate dispersant will cause solvent desorption and flocculation
3. Electronic high-purity paste (MLCC, optical coating): Sodium free polycarboxylate ammonium dispersant, metal phosphate ester dispersant, to avoid ion induced flocculation
4. Low pH/high pH extreme acid-base system: Phosphate dispersants, polyurethane dispersants are acid and alkali resistant, and short chain polycarboxylates are prone to failure and flocculation
IV、 Optimization of anti flocculation supporting process (the right dispersant also needs to be selected)
1. Add quantity gradient test
Insufficient dosage of dispersant: incomplete coating, rapid flocculation; Excessive addition: free dispersant triggers system instability
Inorganic powder: 1%~4%; Organic pigments: 8%~22%; Inkjet system takes the middle high addition amount
2. Powder pretreatment
Surface modification of nano metal oxides with amino silane enhances the adsorption strength of dispersants and significantly reduces solvent flocculation
3. pH control (aqueous system)
Avoiding the isoelectric point of the powder, allowing the particles to carry sufficient same number charges, and providing dual protection to suppress flocculation;
The pH range of zirconia is 8.5-10, the pH range of silicon nitride is 9.5-11, and the pH range of general oxides is 8-9
4. Compound of auxiliary additives
Paired with a small amount of low foaming non-ionic wetting agent (RK-8005) to eliminate the aggregation of powder bubbles; Do not add small molecule electrolytes (salts can damage the electrostatic layer and cause flocculation)
V、Rapid screening and validation method (to determine the anti flocculation ability of dispersants)
1. Cold and hot cycle test: Cycle 5 times at -5 ℃~50 ℃, without layering, white flocs, or coarse particles;
2. High alcohol tolerance test: Add 35% ethylene glycol to the aqueous system and let it stand for 72 hours without flocculation or precipitation;
3. Compatibility testing of mixed materials: inorganic+organic pigment co grinding, no floating color, no particle agglomeration;
4. Particle size detection: There were no double peaks in the particle size curve and no significant increase in particle size before and after storage for 14 days.
