Selection Principles of Dispersants for Epoxy Coating Inks
Epoxy systems can be divided into two main categories: waterborne epoxy and solvent-based epoxy. The dispersants used in the two are not interchangeable. Epoxy groups are prone to side reactions with the acidic/basic groups of the dispersant, which is the primary taboo in selection.
I. Waterborne epoxy systems can be divided into two main categories: emulsified epoxy and water-dispersible epoxy.
Core Constraints
The selection of dispersants in waterborne epoxy systems must match the pH range of the epoxy emulsion, typically controlled within the pH range of 7-9. Strongly acidic dispersants must be strictly avoided to prevent system instability issues such as epoxy emulsion demulsification and stratification. Dispersants containing free amine structures must also be excluded.
1. Carbon black and highly difficult-to-disperse organic pigments:
Acrylic block polymeric dispersants are preferred. Conventional small-molecule polycarboxylate dispersants have insufficient dispersion efficiency for carbon black, easily causing pigment coarsening and system sedimentation instability. Recommended models: RK-4010, RK-4017E, RK-4058.
2. Inorganic Pigments and Fillers
In the dispersant selection stage of waterborne epoxy coating systems, anionic polymeric dispersants are preferred, typically including phosphate ester and acrylate types. These dispersants effectively prevent the gravitational settling instability of pigment particles through the synergistic effect of electrostatic repulsion and steric hindrance. Reference models: RK-4008DH, RK-4047, RK-4058.
Special Note: The core prohibition in selecting waterborne epoxy dispersants clearly points out that the destructive effect targets the colloidal stability system of the epoxy emulsion. This fully complies with the professional terminology standards in the field of waterborne coating additives and aligns with the rigorous expression requirements of epoxy coating technical manuals.
II. Solvent-based epoxy resin systems are two-component systems, consisting of a main agent and a matching epoxy curing agent.
Core Constraints
A large number of primary and secondary amine groups in the dispersant must be strictly avoided. These active sites can undergo pre-crosslinking side reactions with epoxy groups, ultimately leading to abnormal viscosity increases, gelation, and decreased coating gloss during system storage.
1. Carbon black pigments and organic synthetic pigments: High molecular weight block copolymer dispersants are preferred; they possess sufficient steric hindrance to inhibit pigment particle flocculation and avoid coating surface discoloration. Reference models: RK-4031, RK-4036.
2. Inorganic pigments and functional fillers, including titanium dioxide, talc, barium sulfate, iron oxide, etc.: High molecular weight carboxylic acid esters and phosphate ester anchoring dispersants are preferred; phosphate ester anchoring groups have strong adsorption to inorganic powders, good compatibility with epoxy, and do not affect the curing reaction. Reference models: RK-4012, RK-4013A, RK-4013C.
3. Low molecular weight wetting and dispersing agents should be used with caution in epoxy coating systems. These agents are prone to molecular migration during film formation, which can negatively impact the water resistance and chemical resistance of the cured coating film.
Based on the total mass of pigment powder, the recommended addition amount of dispersant for inorganic pigments is 2%–5%; the recommended addition amount for carbon black is 8%–15%. These values are for reference only; the final addition amount needs to be confirmed through formulation experiments.
III. Key Technical Points for Epoxy Inks
Epoxy ink systems require high solids content and stringent grinding fineness, while also needing to consider compatibility stability with epoxy curing agents and leveling properties during printing.
1. In water-based epoxy ink systems, high-molecular-weight acrylic block dispersants compatible with the epoxy emulsion colloidal system should be selected. The proportion of low-molecular-weight additives should be strictly controlled to avoid their negative deterioration effects on ink adhesion and water resistance.
3. In solvent-based epoxy ink systems, high-molecular-weight phosphate ester dispersants are preferred. These additives can simultaneously achieve dual dispersion stabilization effects, including anti-flocculation and anti-gravity sedimentation of pigment particles.
IV. Selection Guidelines to Avoid Common Pitfalls
1. Ordinary latex paint dispersants cannot be directly applied to water-based epoxy paints, as this can easily lead to demulsification and instability.
2. Dispersants containing primary or secondary amine active groups are strictly prohibited from use in the main component system of two-component epoxy paints, as they will trigger pre-crosslinking side reactions.
3. After selecting a dispersant, a storage stability test must be conducted: After paint preparation, store at 50°C for 7 days and observe for thickening, coarsening, and sedimentation phenomena.
