Recommendations for water-based paint ink anti flocculation dispersants
The coagulation essence of paint ink color paste: pigment or filler particle desorption dispersant, charge reduction, bridging aggregation, electrolyte destabilization, solvent competitive adsorption; The core requirements for anti flocculation are: firm anchoring without easy detachment, high electrostatic potential, sufficient stretching of steric hindrance chains, resistance to electrolytes, and resistance to interference from system additives. The following provides a complete explanation of the principles, classification, material matching, scene pain points, and screening methods for adapting pigments, carbon black, metal oxides, and inorganic fillers.
I、 Four common causes of flocculation in water-based systems (targeted avoidance of dispersants)
1. Weak anchoring force of dispersant
Ordinary short chain polyacrylic acid molecules have short molecular chains and low density of active anchoring groups (carboxyl COOH), resulting in few binding points (single or weak multi-point anchoring) with the surface of solid particles, and insufficient physical/chemical adsorption force; During the storage, heating, or addition of other additives after grinding, thermal motion intensifies or the polarity of the medium changes, breaking the fragile adsorption equilibrium and causing the dispersant to desorb and detach from the particle surface; The surface of particles that have lost the protection of dispersants is exposed, and van der Waals forces dominate between particles. Polar groups such as hydroxyl groups on the surface attract each other through hydrogen bonds, leading to irreversible aggregation (flocculation) of particles, sudden increase in system viscosity, or precipitation; This is a typical shortcoming of traditional polyacrylic acid with low molecular weight and linear structure, lacking the steric hindrance stabilization provided by long chains.
2. Electrolyte interference leads to flocculation
The main effects of film-forming aids and alcohol ethers on film-forming and wetting properties may exacerbate phase separation if compatibility is poor, but they are not directly the main cause of compressing the double layer; PH regulator, changing the pH value of the system may affect the surface charge density of pigments and fillers; If a large number of cations (such as amines) are introduced, they will directly participate in compressing the double layer; Anti corrosion and antibacterial agents, some of which contain metal ions or electrolyte components, may contribute to ion strength if added in excess; Metal ions/pigment fillers precipitate ions, which are key disruptors. Multivalent cations (such as Ca ² ⁺) compress the double-layer with much higher efficiency than monovalent ions, which can easily lead to the failure of electrostatic stability.
3. Competition between additives affects adsorption
Wetting agents, defoamers, leveling agents and resin lotion molecules also contain polar groups, which will spontaneously migrate to the surface of pigments with high surface energy. If the adsorption affinity of these substances is stronger than that of dispersants, or if the order of addition is improper and they occupy the site first, they will "replace" the already adsorbed dispersants (desorb).
4. Effects of temperature and concentration changes
During the storage process, as the ambient temperature increases, the tiny pigment particles that were originally evenly dispersed in the liquid weaken the "barrier" that protects them, causing a decrease in steric hindrance and resulting in coarse flocculation, ultimately leading to precipitation, abnormal viscosity, or printing/coating defects.
Anti flocculation dispersants must possess both strong anchoring, high Zeta potential, long hydrophilic solvation chains, and resistance to competition from additives
II、Structural classification of water-based dispersants (from weak to strong anti flocculation ability)
1. Ordinary small molecule polyacrylate (poor anti flocculation, use with caution)
-Structure: Short chain sodium polyacrylate and ammonium salt dispersant, with only scattered carboxyl anchoring and no hydrophilic side chains;
-Defects: It can cause reversible adsorption, easy replacement by additives, poor electrolyte resistance, and high temperature desorption; Only low activity inorganic powders can be temporarily dispersed, and flocculation will inevitably occur in the later stage of storage;
-Usage: Only suitable for temporary pulping, cannot be used as a storage ink coating color paste dispersant alone.
2. Linear polymer polycarboxylate (moderate anti flocculation dispersant)
Long chain linear ammonium/sodium salt dispersant with uniformly distributed carboxyl groups; Strong electrostatic stability, but without comb shaped side chains and lacking spatial hindrance;
It is prone to flocculation when encountering alcohol ether additives and electrolytes; Only suitable for inert titanium dioxide and calcium carbonate, not suitable for carbon black, iron oxide, or organic pigments.
3. Comb/graft type polycarboxylate (mainstream anti flocculation universal dispersant)
Dense anchoring groups (carboxyl, phosphoric, sulfonic acid) in the backbone main chain, and multiple hydrophilic long chains of polyethylene oxide PEO with side linking branches;
Stability mechanism: dual stability of electrostatic repulsion and steric hindrance;
Advantages: There are multiple anchoring points that are not easily detached, and the hydrophilic side chains are fully stretched in water to form a hydration protection layer, which resists electrolyte compression and competition from additives, greatly improving the anti flocculation ability;
Water based inks and coatings are the preferred category for conventional anti flocculation.
4. Phosphate modified comb dispersant (special for high-strength anti flocculation and difficult to disperse pigments)
Introducing phosphate/phosphonic acid anchoring groups on the basis of comb shaped polycarboxylates;
The adsorption strength of phosphate groups on metal oxides (TiO ₂, iron oxide, Al ₂ O3, ZnO) is 3-5 times that of ordinary carboxyl groups, and irreversible adsorption is difficult to replace with alcohol ethers and additives;
Characteristics: It has extremely strong anti flocculation, anti alcohol, and high temperature resistance properties; Disadvantages Some phosphoric acid foam is high;
Applicable: Metal oxide color paste, inorganic oxide concentrated color paste, high alcohol system ink.
5. Sulfonic acid modified polycarboxylate (super salt resistant, electrolyte resistant, and anti flocculation)
Introducing sulfonic acid groups, strong ionization ability, thick double layer, not affected by metal ions and high electrolytes;
Suitable for: Inkjet inks and industrial water-based inks containing a large amount of alcohol ethers, polyols, fungicides, and high ion content in the system; Prevent ion induced flocculation.
6. Block copolymer super dispersant (high-end long-lasting anti flocculation)
AB block structure with strict separation of anchoring segment and hydrophilic solvation segment; The anchoring section concentrates on adsorbing the surface of particles, while the hydrophilic section extends outward; Almost not replaced by resin or wetting agent competition;
Used for: high pigment carbon black, phthalocyanine organic pigments, concentrated colorants, high solid content coatings, and long-term storage inks.
III、 Select targeted anti flocculation dispersants based on the type of pigment and filler
1. Metal oxides (TiO ₂, iron oxide, aluminum oxide, zinc oxide, most easily alcohol induced flocculation)
-Disadvantages: There are a large number of hydroxyl groups and alcohol ether film-forming agents on the surface, which easily compete for hydrogen bonds. Once the dispersant system is peeled off, flocculation and precipitation will occur;
-Select priority dispersants: phosphoric acid modified comb dispersants>sulfonic acid modified polycarboxylates>high carboxyl comb polycarboxylates;
-It is strictly prohibited to use ordinary linear polyacrylate alone;
-Ink systems with high alcohol content must use phosphoric acid modified anti flocculation dispersants.
2. Organic pigments (phthalocyanine blue-green, bright red, permanent pigment)
-Disadvantages: the polarity of the pigment surface is weak, the adsorption capacity of carboxyl group is insufficient, and it is easy to be replaced by resin lotion to generate flocculation;
-Choose dispersant type: styrene maleic anhydride SMA comb dispersant, block copolymer dispersant; Relying on hydrophobic anchoring of aromatic rings and synergistic adsorption of carboxyl groups; Simple fatty chain polycarboxylates are prone to flocculation and thickening.
3. Carbon black (pigment black, furnace black)
-Disadvantages: Large specific surface area, complex oxygen-containing functional groups, easy to agglomerate, thicken, and thicken;
-Choose dispersant type: aromatic modified comb shaped polycarboxylate, phosphoric aromatic dispersant; Long side chain PEO provides a thick hydration layer to prevent carbon black particles from overlapping and flocculation.
4. Inorganic inert fillers (calcium carbonate, talc powder, kaolin)
Inert, with few hydroxyl groups, not easily flocculated; Ordinary comb shaped polycarboxylates are sufficient without the need for phosphoric acid modification, resulting in lower costs.
IV、Classification of anti flocculation selection based on system scenarios
① Water based industrial coatings (exterior wall paint, industrial topcoat, primer)
Features: many alcohol ether film forming aids, large amount of lotion resin, and many bactericide ions
✅ Preferred dispersant type: ordinary comb shaped polycarboxylate ammonium salt dispersant; Use phosphoric acid modified polycarboxylate dispersant instead of high alcohol addition; Do not use sodium salt dispersants (sodium ions increase electrolyte and promote flocculation), prioritize ammonium salts.
② Water based flexographic/gravure ink, ink wash
Features: High content of polyols, ethylene glycol, and propylene glycol, high system viscosity, multiple types of additives, easy to separate and flocculate during storage
✅ Preferred dispersant types: sulfonic acid modified comb shaped dispersant, phosphoric acid modified dispersant; Strengthen anti alcohol and anti flocculation measures; Try to use ammonium salt and less sodium salt.
③ Water based inkjet color paste, concentrated color paste (high color content)
Features: high solid content, ultra-fine particle size, long-term storage, harsh cold and hot cycles
✅ Preferred dispersant types: phosphoric acid+sulfonic acid binary modified comb shaped dispersant, block type super dispersant, long-lasting anti flocculation, non settling, and non clogging.
④ Wood water-based paint (with the highest amount of alcohol ether additives)
Characteristics: It is most prone to slight flocculation and a decrease in gloss after one week of storage
✅ Priority type: Must be phosphate anchored modified dispersant, resistant to alcohol hydrogen bond displacement, to avoid later flocculation from the root.
⑤ Latex paint interior walls (mild additives, low alcohol content)
Conventional comb shaped polycarboxylate ammonium salts are sufficient without the need for phosphate type cost control.
V、5 key usage points that are easily overlooked for causing flocculation
1. Selection of dispersant salt type
Sodium salt dispersant: ionizes Na ⁺, enhances the electrolyte of the system, and is prone to flocculation during long-term storage; Only suitable for on-site ready to use coatings;
Ammonium salt dispersant: with minimal ion influence, better storage resistance, and anti flocculation, ammonium salt is preferred for coating and ink storage.
2. Do not add too much or too little
-Insufficient dosage: The surface of the particles is not completely coated, resulting in mutual adsorption and flocculation of vacancies;
-Excessive dosage: Free dispersants form micelles in the system, bridging particles to cause flocculation and thickening;
Perform gradient addition for each material to find the appropriate coating amount.
3. The feeding sequence affects flocculation
Wrong way: add lotion resin first and then disperse pigment; Resin preferentially adsorbs pigments and directly flocculates;
Correct method: water → dispersant → wetting agent → pigment and filler are fully dispersed and ground → finally, lotion, film forming agent and bactericide are added.
4. PH control
The optimal stable pH range for polycarboxylate dispersants is 7.5 to 9.0; When the pH is too low, carboxyl ionization decreases and static electricity weakens, leading to flocculation; Excessive pH and strong alkalinity can damage the structure of dispersants. The pH of the oxide system should not exceed 9.5.
5. Do not add excessive wetting agents
Small molecule wetting agents have strong adsorption capacity, and excessive addition can cause competing pigments to replace dispersants on the surface, resulting in slow flocculation in the later stage; Wetting agents and dispersants should be added separately to avoid pre mixing.
VI、 Quick selection and simplified mnemonic
1. Oxide rich, alcohol ether rich, wood paint, ink wash ->phosphoric acid modified dispersant to prevent alcohol flocculation;
2. Ink, high content of polyols and ions → sulfonic acid modified dispersant resistant to electrolytes;
3. Organic pigments, carbon black → aromatic comb like, SMA copolymer dispersant to prevent resin competition flocculation;
4. Conventional latex paint and fillers as the main components → ordinary comb shaped polycarboxylate ammonium salt dispersant;
5. Pursuing stable storage for over a year → Block structured super dispersant.
