How to Choose the Right Dispersant for Curtain Coating Inks? — A Professional Selection Guide
Choosing the right dispersant for curtain coating inks requires a comprehensive consideration of pigment
characteristics, process conditions, and dispersant performance. The following is a systematic selection process:
1. Identify the pigment type and characteristics.
Inorganic pigments (such as titanium dioxide and carbon black):
Since their surfaces are often negatively charged, anionic dispersants (such as phosphates and sulfonates) are
preferred.
The addition level is typically 1%-5% of the pigment mass and requires experimental optimization.
Organic pigments (such as phthalocyanine blue and permanent red):
Since their molecular structures are complex, high-molecular-weight dispersants (such as polycarboxylates and
block copolymers) are recommended.
When adding higher levels (10%-30%), ensure that the dispersant molecular chains fully coat the pigment surface.
Mixed pigment systems (such as blue and white):
A general-purpose dispersant (such as modified polyacrylate) or a combination of inorganic and organic dispersants
can be used.
Performance and cost must be balanced to avoid competitive adsorption between dispersants, which can lead to
reduced performance.
2. Analyze Process Conditions
Solvent Type:
Water-based systems: Select a water-soluble dispersant (such as sodium polycarboxylate), paying attention to its
water resistance.
Oil-based systems: Select an oil-soluble dispersant (such as modified polyurethane), ensuring compatibility with
the resin.
Temperature and Shear:
High-temperature processes (such as oven curing): Select a dispersant with good thermal stability (such as
polyether-modified siloxane).
High-shear environments (such as high-speed flow coating): Select a dispersant with a higher molecular weight
(such as hyperbranched polyester) to enhance steric hindrance.
Flow Coating Speed:
High-speed flow coating requires a dispersant that quickly wets the pigment. Therefore, a low-viscosity dispersant
(such as sodium alkylbenzene sulfonate) can be selected.
3. Evaluate Key Performance Indicators of Dispersants
Viscosity Reduction:
Testing ink viscosity using a rotational viscometer reveals that a high-quality dispersant can reduce viscosity by
30%-50%.
For example: If the base ink viscosity is 1000 mPa·s, the viscosity should drop to 500-700 mPa·s after adding the
dispersant. Particle Size Control:
Use a laser particle size analyzer to measure the pigment particle size after grinding. The target particle size is
typically less than 2μm (for organic pigments) or 5μm (for inorganic pigments).
Example: A company reduced the particle size of phthalocyanine blue from 8μm to 1.5μm by optimizing the
dispersant, resulting in a 40% improvement in tinting strength.
Storage Stability:
Perform an accelerated aging test (storage at 50°C for 7 days) to observe whether the ink delaminates or
settles.
Acceptance Criteria: No delamination, less than 5% (by mass).
Compatibility:
Mix the dispersant with a resin (e.g., epoxy resin, acrylic resin) and observe for turbidity or gelation.
Acceptance Criteria: The mixed system is transparent, with no flocculation or precipitation.
4. Pilot and Pilot Verification
Planar Stage:
Add the dispersant at the theoretical dosage (e.g., 2% of the pigment weight) and grind to the target particle size.
Test the ink viscosity, leveling, and coating color difference (ΔE value should be less than 1.0). Pilot Phase:
Run the process on actual coating equipment to observe coating uniformity, equipment clogging, and production
efficiency.
Adjust dispersant dosage (e.g., ±0.5%) and optimize process parameters (e.g., coating speed and temperature).
5. Environmental and Cost Considerations
Environmental Performance:
Select low-VOC (volatile organic compound) dispersants that comply with local environmental regulations
(e.g., EU REACH, China GB 38508-2020).
For water-based dispersants, consider biodegradability (e.g., biodegradable polycarboxylates).
Cost-Effectiveness:
Balance dispersant price and performance, avoiding excessive pursuit of high-end products that lead to increased costs.
Example: One company reduced unit cost by 15% while maintaining performance by optimizing dispersant dosage.
Summary: Selection Flowchart
Determine pigment type → Analyze process conditions → Evaluate dispersant performance → Pilot test → Pilot optimization
→ Environmental and cost assessment → Final selection
Through these steps, you can systematically select the appropriate dispersant for curtain coating inks, ensuring ink stability,
coating quality, and production efficiency.
