Technical Guidelines for Dispersant Selection in Ink Systems
The core issues of the ink system: high pigment solid content, thin wet film thickness, and high shear strength during the printing process (including high-speed stirring/sand milling processes), requiring long-term stability in fineness, no flocculation, and no degradation in gloss, transparency, or interlayer adhesion. The performance boundaries of different ink sub-systems vary significantly.
I. Rapid filtering based on pigment type
1.For the dispersion scenarios of inorganic pigments such as titanium dioxide, iron oxide, fluorescent powder, and inert fillers, the use of small-molecule dispersants (RK-4006, RK-4013) can meet performance requirements, with the comprehensive cost advantages of this type of additive being particularly prominent.
2. For poorly dispersible organic pigments such as phthalocyanine, azo, and quinacridone, the highly compatible polymer super-dispersant (RK-4029) is selected, whose anchoring groups enable precise and selective adsorption onto the pigment crystal surface.
3. For difficult-to-disperse pigments such as high-pigment carbon black, a high-molecular-weight block copolymer dispersant (RK-4035) with strong adsorption aromatic anchoring groups is selected. Relying on its steric hindrance effect from high molecular weight, it can effectively inhibit the re-aggregation of carbon black particles, fundamentally avoiding the issue of system coarsening.
4. For the dispersion of functional powders such as ceramic/silicon nitride and zirconia in specialty inks, it is necessary to select a dedicated dispersant (RK-4035AB) with targeted phosphate and silane-based anchoring groups for modification.
II、 Select based on the major categories of ink systems
1. Solvent based ink categories (surface printing/inner printing gravure printing, screen printing solvent based ink)
-For the solvent based ink dispersion scenario of organic pigments and carbon black, polymer polyester and polyurethane hyperdispersants (RK-4033, RK-4031) are preferred. By anchoring groups, a strong adsorption layer is formed on the surface of the pigment, and the solvation chain segments are fully extended in the organic solvent medium to construct a high-strength steric hindrance stable barrier
-For the dispersion scenario of inorganic pigments in solvent based ink systems, small molecule carboxylic acid and phosphate ester dispersants (RK-4012, RK-4013A, RK-4013C) are preferred. These dispersants have a more prominent cost advantage in comprehensive use while meeting dispersion performance requirements.
Key selection points: It is necessary to accurately adapt to the ester/ketone/aromatic dispersion medium of solvent based ink. The solvation chain segment of the dispersant needs to have good compatibility with the ink solvent, otherwise it will directly cause pigment flocculation and ink layer loss.
2. Solvent free/high solid content ink system (represented by solvent-free epoxy ink)
Core selection requirements: Priority should be given to using polymer block type hyperdispersants (RK-4029), which are suitable for low VOC, high viscosity solvent-free/high solid ink systems. They can effectively suppress abnormal viscosity increase in the system, block pigment coagulation and aggregation pathways, and the auxiliary components must not contain free water or low boiling point volatile solvents.
3. UV curable ink system (covering sub application categories such as UV screen printing, UV offset printing, UV digital inkjet, etc.)
-The preferred UV curing ink system is acrylic based polymer hyperdispersants (RK-4028I, RK-4029HA), which can participate in UV free radical curing crosslinking reactions without the risk of free small molecule migration and will not degrade the light curing reaction rate of the system.
-Risk warning for UV curing ink selection: Ordinary solvent based dispersants are prone to free migration due to their lack of reactive functional groups, which can degrade the interlayer adhesion of the coating and reduce the hardness of the cured film; Partial amine dispersants can produce free radical polymerization inhibition effects, directly inducing incomplete photopolymerization of the system.
4. Water based ink system (covering four sub application categories: flexographic printing, gravure printing, digital inkjet printing, and water-based screen printing ink)
Suitable pigment categories: organic pigment series, carbon black, inorganic pigment series (titanium dioxide, iron oxide pigments)
-Priority selection categories for dispersion mechanism: ammonium/sodium polyacrylate, anionic polymer block copolymer
-The recommended dispersant category is polymer based water-based dispersants, whose molecular chain segments anchor aromatic and heterocyclic pigment affinity anchoring groups; For the dispersion system of organic pigments and carbon black, polymer block copolymer dispersants (RK-4019, RK-4010, RK-4017E) are preferred. Through the mechanism of steric hindrance stabilization, the system achieves anti flocculation, anti settling, and long-term thermal storage stability, and has excellent dispersion adaptability for low surface activity and difficult to disperse pigments such as high pigment carbon black and phthalocyanine blue.
-For the dispersion scenarios of titanium dioxide and organic filler inorganic pigments, low molecular weight polyacrylic acid salt dispersants are preferred. These additives have outstanding cost-effectiveness advantages and are suitable for the low steric hindrance stability requirements of this pigment system.
-Model selection risk tips: ordinary small molecule dispersants are easy to cause foam enrichment in the system, and the water resistance of the curing film deteriorates, and the pigment coarsening is easy to occur during high-temperature storage; Cationic dispersants should be carefully selected as they can easily undergo charge neutralization reactions with anionic additives (defoamers, thickeners) in the system, leading to compatibility failure of the system.
For digital inkjet ink systems, it is necessary to use exclusive polymer hyperdispersants with low viscosity, low foaming, and no macroscopic large particle impurities. It is prohibited to directly reuse conventional water-based ink dispersants to avoid production failures caused by excessive pigment particle size distribution and additive precipitation leading to nozzle blockage.
III、Exclusive key performance assessment indicators for ink system dispersants (mandatory for laboratory trials)
1. Evolution of rheological properties of ink system (most dispersants directly intervene in the rheological behavior of ink);
2. Compatibility with other additives in the system (defoamers, leveling agents, curing agents, to avoid shrinkage problems caused by interface conflicts);
3. Fineness index and thermal storage stability after sanding (accelerated storage at a constant temperature of 50 ℃, observing the phenomenon of pigment coarsening and layer settling);
4. Pigment coloring strength, color development efficiency, and ink layer glossiness;
5. Printing adaptability: ink layer transfer efficiency, substrate wetting and spreading properties, non deteriorating coating adhesion and multi-color overlay adaptability;
6. Residual control dimension: Water based ink needs to focus on assessing the water resistance and friction resistance of the ink layer; Food contact packaging ink must strictly control the amount of substance migration to meet relevant food safety compliance requirements
IV、Common commercial grade reference
Source: Official Product Manual
-Water based ink: RK-4010, RK-4017E
-Solvent ink: RK-4016C, RK-4033
-UV ink: RK-4028I, RK-4029HA
