From Novice to Expert: Ink Dispersant Usage Guide
Ink dispersants are key additives to improve pigment dispersibility, stability and printing effects. The correct use of
dispersants requires the combination of pigment characteristics, binder type and printing process. The following are
detailed usage methods and precautions:
1. Preparation before use
Choose a matching dispersant
Pigment type: organic pigments (such as phthalocyanine blue), inorganic pigments (such as iron oxide), carbon black,
etc. need to choose dispersants with corresponding anchor groups (such as acidic, alkaline, non-polar groups).
Binder compatibility: Ensure that the dispersant is compatible with the resin and solvent of the ink to avoid phase
separation or gelation.
Application requirements: Select a suitable dispersant according to the printing method (offset printing, gravure printing,
flexographic printing) and substrate (paper, plastic).
Pretreatment of pigments
Drying: Remove moisture from the pigment to prevent agglomeration.
Sieving: Use a 200~300 mesh screen to remove large particle impurities.
Determine the amount of dispersant
The general amount is 10%~50% of the pigment mass, and the specific amount needs to be optimized through experiments.
For example, carbon black usually requires 30%~50%, while organic pigments may only require 10%~20%.
2. Steps for using dispersants
Pre-dispersion stage
Mix dispersant and binder: Add dispersant to part of the binder and stir until completely dissolved.
Add pigment: Add pigment slowly to avoid agglomeration caused by pouring it all at once.
High-speed dispersion: Use a high-speed disperser (such as a sand mill, a three-roller mill) to stir at 1000~3000 rpm for
30~60 minutes to disperse the pigment preliminarily.
Grinding stage
Choose grinding equipment: Choose a ball mill, a bead mill or a nano grinder according to the pigment particle size
requirements.
Control grinding parameters:
Speed: 1000~3000 rpm (adjust according to the equipment).
Time: 2~8 hours (until the pigment particle size reaches the target value, such as 5~10 μm).
Temperature: ≤50℃ (avoid high temperature causing dispersant degradation).
Regular testing: Take samples to test the particle size distribution to ensure uniform dispersion.
Post-processing stage
Dilution and adjustment: Dilute the ink with the remaining binder and adjust the viscosity to 10~50 Pa·s (depending on
the printing method).
Filtration: Use a 100~200 mesh filter to remove large particles of impurities.
Stability test: Let the ink stand for 7 days to observe whether there is precipitation or stratification.
3. Precautions in use
Dispersant dosage control
Excessive use may lead to:
Increased ink viscosity, affecting printing adaptability.
Decreased water resistance, especially in outdoor printing, which is prone to frosting.
Excessive use will not effectively disperse the pigment, resulting in color difference, precipitation and other problems.
Interaction between dispersant and resin
Avoid chemical reactions between dispersant and resin (such as cross-linking and hydrolysis), which will lead to
deterioration of ink performance.
The compatibility of dispersant and resin can be verified by small sample experiments.
Environmental condition control
Temperature: Too high a temperature during grinding may cause dispersant degradation. It is recommended to use
a cooling system.
pH value: Some dispersants are sensitive to pH value (e.g. acidic dispersants fail under alkaline conditions), which
requires strict control.
Storage and stability
The dispersed ink needs to be stored in a light-proof and sealed condition to prevent dispersant migration or
pigment reaggregation.
Recommended storage temperature: 5~30℃, storage time not exceeding 6 months.
4. Common problems and solutions
Pigment agglomeration
Reason: Insufficient dispersant dosage or improper selection.
Solution: Increase dispersant dosage or replace matching dispersant.
Ink viscosity is too high
Reason: Excessive dispersant or improper resin selection.
Solution: Reduce dispersant dosage or replace resin.
Printing frosting
Reason: Dispersant migrates to the surface.
Solution: Select a dispersant with low migration or add a cross-linking agent.
Color difference
Reason: Uneven pigment dispersion.
Solution: Extend grinding time or increase grinding speed.
5. Example: Use of UV ink dispersant
Raw material preparation
Pigment: photoinitiator, active monomer, pigment (such as titanium dioxide).
Dispersant: polymer dispersant containing double bonds (can participate in UV curing reaction).
Binder: UV resin, active diluent.
Usage steps
Add dispersant to part of UV resin and stir to dissolve.
Slowly add pigment and pre-disperse with high-speed disperser for 45 minutes.
Grind with a bead mill for 4 hours until the pigment particle size is ≤10 μm.
Add photoinitiator and remaining diluent and adjust viscosity to 25 Pa·s.
Store after filtering and avoid light.
Precautions
Make sure the dispersant participates in the UV curing reaction to avoid residue.
Store away from light to prevent the photoinitiator from failing.
6. Summary
Accurate selection: Select matching dispersant according to pigment, binder and printing process.
Strict control: Parameters such as dosage, temperature, pH value, etc. need to be strictly monitored.
Experimental verification: Optimize dispersant dosage and process parameters through small sample
experiments.
Continuous improvement: Focus on new dispersant technologies (such as nano-dispersants and intelligent
responsive dispersants) to improve ink performance.
By using dispersants scientifically, the dispersibility, stability and printing quality of inks can be significantly
improved to meet the needs of different application scenarios.
