Reference Manual for Selection of Specialized Dispersants for Digital Inkjet Inks

Reference Manual for Selection of Specialized Dispersants for Digital Inkjet Inks

The core differences between digital inkjet ink and conventional coatings or screen printing ink: It must achieve a sub-200nm D90 particle size, narrow distribution, and low viscosity, suitable for piezoelectric/thermal bubble printheads, with no coarsening, clogging, or nozzle fouling during circulation storage. Direct application of conventional coating dispersants is strictly prohibited.

I、 Core Hard Judgment Criteria for Universal Inkjet Dispersants in the Whole System

1. Preferred: Dispersants with polymer block or comb like structures, and the use of small molecule dispersants is strictly prohibited. Such products are prone to detachment, causing particle aggregation and ultimately clogging the nozzle.

2. Molecular weight control requirements: The water-based system should be selected within the range of 5000-30000, while the solvent based and UV systems should be controlled within the range of 2000-8000; If the molecular weight is too small, the steric hindrance is insufficient, and if it is too large, the viscosity of the system will increase sharply, directly affecting the ink ejection performance.

3. Particle size control objective: The pigment D50 should be controlled within the range of 50-120nm, the D90 should be less than 200nm, and the absolute value of Zeta potential should not be less than 30mV to ensure the long-term stability of the colloidal system.

4. Impurity control requirements: Strictly control the content of free ions, completely remove chloride ions, and the thermal foaming nozzle is more sensitive to ions, which can easily cause electrode corrosion and nozzle scaling problems.

5. Compatibility requirements: It must be fully compatible with the solvents, monomers, moisturizers, and resins in the system, with no risk of precipitation throughout the process.

6. Rheological performance requirements: Maintain low viscosity and near Newtonian fluid characteristics, with no significant increase in viscosity under high shear conditions, and accurately adapt to the spray process window of the nozzle.

II、 Complete the selection of dispersant adaptation according to the four mainstream inkjet ink systems one by one

（1） Water based pigment inkjet categories covering desktop printing, textile coating printing, and indoor industrial printing scenarios

The system medium is composed of water and polyol moisturizing agents, rich in polar cosolvents such as ethylene glycol and diethylene glycol. Conventional polyacrylate dispersants are difficult to maintain a stable state in high alcohol environments.

1. Organic pigments, carbon black (colored, black main color)

-Preferred: Dispersants with multiple anchoring points, such as anionic comb type styrene maleic anhydride copolymers and amphoteric block waterborne polyurethanes, are resistant to high concentration diol environments and are not prone to detachment.

-Reference models: RK-4039ACB, RK-4039AC,RK-4059.

-Addition amount (pigment quality): 15-35% carbon black; Organic pigments account for 10-30%.

2. Inorganic pigments (titanium white ink, iron oxide)

-Preferred: Comb shaped polycarboxylate ammonium is used as a dispersant. If the proportion of alcohols in the system is high, switch to amphoteric polyurethane dispersant to avoid flocculation problems in the system.

-Addition amount: 3-8%.

3. Taboos

-Ordinary small molecule sodium polyacrylate dispersants are prone to losing stability and causing settling and clogging problems in inkjet systems with high alcohol content;

-In the vast majority of ink formulations, dispersants containing APEO components are prohibited..

（2） Suitable for outdoor photography and logo printing scenarios, solvent/weak solvent inkjet system with alcohol ether and ketone as core solvents

The medium is composed of a mixture of esters, alcohol ethers, and hydrocarbon solvents, and the system is completely free of moisture.

1. Oil soluble polyester polyamide block hyperdispersant suitable for organic pigment dispersion.

-Reference: RK-4016C, RK-4033

-Addition amount: 12-35% organic pigment; Carbon black accounts for 20-40%.

2. The most representative inorganic metal oxide pigments in ceramic inkjet scenes.

-Core main selection: Polymer phosphate ester dispersant, with strong anchoring ability of phosphate groups to metal oxides, excellent viscosity reduction performance, and minimal residual ash after high-temperature firing, ensuring stable color development.

-Reference: RK-4012, RK-4013A, RK-4013C

-Addition amount: 3-9% of powder mass.

（3） UV curable inkjet categories suitable for UV roll printing, white ink printing, glass and sheet printing scenarios

The system medium is solvent-free acrylic acid active monomer, and the dispersant cannot contain a large amount of primary amines, otherwise it will cause UV yellowing. It must be completely compatible with the monomer and cannot precipitate and interfere with the curing process.

1. Non free primary amine polyester block hyperdispersant suitable for organic pigment dispersion

-Reference: RK-4029, RK-4061CF, RK-4061CFB.

2. UV titanium dioxide ink uses amine free phosphoric acid anchored polyester dispersant. Titanium dioxide is more prone to settling compared to carbon black, and the solvation chain length of the dispersant is the core key factor affecting the stability of the system.

-Reference: RK-4013A, RK-4061C0.

-Addition amount: 4-8% titanium dioxide; Organic pigments account for 15-30%.

（4） Water based sublimation transfer ink with dispersed dyes as the core raw material

The system uses dyes instead of pigments, and requires the use of specialized dispersants for sublimation inks. Ordinary pigment dispersants cannot be directly applied, and RK-4010 and RK-4017E are typical representatives of such products.

III、Quick Selection Comparison Table

IV、 Selection of Ink Dispersants for Inkjet Ink: Exclusive Pit Avoidance Practical Guide

1. It is strictly prohibited to directly use ordinary paint dispersants. These products either have a high molecular weight or are structurally unsuitable, making it difficult to grind the pigment to within 120nm, which can easily cause nozzle blockage in the future.

2. It is crucial to control the amount of dispersant added: insufficient coverage can cause pigment coarsening, while excessive coverage can increase system viscosity and exacerbate nozzle scaling. Each type of pigment must undergo separate dose curve testing.

3. The mandatory core verification items include: particle size and particle size distribution testing, Zeta potential testing, 50 ℃ 14 day thermal storage stability verification, cyclic spray performance testing, nozzle scaling risk assessment, and compatibility verification of multi-stage filtration systems.

4. Correct feeding sequence: Mix the dispersant and medium thoroughly and evenly before adding the pigment for grinding. It is strictly prohibited to add dispersants during the later stage of paint mixing.