The use of water-based carbon black dispersants involves formula design, process control and performance optimization,
which requires a combination of theoretical guidance and practical operation experience. The following is a systematic
guide to use, analyzing the key links and precautions step by step:
1. Dispersant selection and matching verification
Anchor group adaptability
Carbon black contains oxygen-containing functional groups such as carboxyl and phenolic hydroxyl groups on the surface,
and the dispersant must have anchor groups (such as carboxylic acid, phosphoric acid, polyamine, etc.) that bind to them.
For example:
High-color carbon black (such as Mitsubishi MA series) has few surface functional groups, so it is necessary to select a
multi-anchor point dispersant (such as a polymer containing multiple carboxyl groups).
Furnace carbon black (such as Degussa Color Black FW200) contains more polycyclic aromatic hydrocarbons on the surface,
and it is appropriate to use a dispersant containing an aromatic ring structure to enhance adsorption.
Solvation chain and system compatibility
Polarity of water-based system: The solvation chain of the dispersant (such as polyether, polyester) needs to match the polarity
of the water-based resin (acrylic acid, polyurethane, etc.). For example, a polyurethane system requires a dispersant containing
a carbamate structure to enhance compatibility.
pH tolerance: If the system pH>9, it is necessary to select an alkali-resistant dispersant (such as a polymer containing sulfonic
acid groups); when pH<5, the carboxylic acid dispersant may not dissociate completely and the dosage needs to be adjusted.
Synergy between dispersant and resin
The competitive adsorption between dispersant and resin will affect the dispersion effect. Suggestion:
Preferably select dispersants with similar structures to resins (such as acrylic acid) to reduce competitive adsorption.
Through the "dispersant-resin" mixed adsorption experiment, determine the adsorption amount ratio of the carbon black surface
(such as XPS analysis) to ensure that the dispersant occupies the dominant adsorption position.
2. Pretreatment and dispersion process optimization
Carbon black pre-wetting technology
Method: Pre-mix carbon black with 5%-10% water (or solvent), add 0.5%-1% wetting agent (such as fatty alcohol polyoxyethylene
ether), and stir at 500-800 rpm for 10 minutes to form a uniform paste.
Function: Reduce the contact angle of the carbon black surface (from >120° to <60°) and promote the penetration of the dispersant.
Dispersant addition strategy
Step-by-step addition method: Under high-speed dispersion (1000-1500 rpm), add the diluted dispersant (concentration 10%-20%)
to the carbon black slurry at a rate of 0.5-1 mL/min to avoid flocculation caused by excessive local concentration.
Pre-adsorption method: Pre-mix the dispersant and carbon black in a 1:1 mass ratio, let it stand for 12 hours, and then add the
remaining water and resin to improve the dispersion efficiency by more than 30%.
Grinding process parameter control
Sand mill parameters:
Zirconium bead filling rate: 70%-80% (such as zirconium beads with a diameter of 0.3-0.5 mm).
Flow rate: 2-5 L/min (adjusted according to the volume of the sand mill).
Temperature: ≤40℃ (using cooling jacket or ice water circulation).
End point judgment:
Particle size monitoring: Laser particle size analyzer detects D50≤100 nm, D90≤200 nm.
Viscosity inflection point: Grind until the slurry viscosity no longer decreases (as measured by a rotational viscometer, the viscosity
is ≤500 mPa·s at 25°C).
3.Performance control and stability assurance
Dispersant dosage optimization
Dosage range: Usually 15%-30% of the carbon black mass (high-structure carbon black requires a higher dosage).
Determination method:
Draw a "dispersant dosage-viscosity" curve and take the dosage corresponding to the lowest viscosity point.
Combined with potential test (dispersion is stable when the absolute value of ζ potential is >30 mV).
System stability control
pH adjustment:
Acidic system (pH 4-6): Add ammonia or organic amine (such as triethanolamine) to avoid protonation of carboxylic acid dispersants.
Alkaline system (pH 8-10): Adjust with sodium hydroxide or potassium hydroxide, and monitor the hydrolysis of the dispersant (such
as polyester dispersants are easily hydrolyzed when pH>10).
Ionic strength control:
Use deionized water (conductivity <5 μS/cm) to avoid Ca²⁺ and Mg²⁺ in hard water from chelating with dispersants.
If electrolytes (such as thickeners) need to be added, a flocculation experiment must be performed first (such as determining the
critical flocculation concentration by turbidity method).
Long-term storage stability
Anti-corrosion treatment: Add 0.1%-0.3% of BIT/MIT composite preservatives (such as Clariant Acticide MBS) to inhibit the growth
of bacteria and mold.
Anti-sedimentation measures:
Add 0.5%-1% of thixotropic agents (such as fumed silica or polyamide wax) to form a three-dimensional network structure.
Verify the sedimentation rate (should be <5%) through a centrifugal test (3000 rpm, 30 minutes).
4.common problems and solutions
The slurry becomes coarse after dispersion
Reason: dispersant desorption or insufficient grinding.
Solution:
Detect the adsorption amount of dispersant on the carbon black surface (such as thermogravimetric analysis, the adsorption
amount should be ≥5 mg/g).
Extend the grinding time by 20%-30%, or increase the linear speed of the sand mill (such as from 8 m/s to 10 m/s).
Insufficient blackness of the coating
Reason: Carbon black agglomerates cover the light path or dispersant residues cause light transmission.
Solution:
Optimize the dispersion process to make the primary particle size of carbon black reach 20-30 nm (such as TEM observation).
Select dispersants that are easy to desorb (such as short-chain polymers with a molecular weight of <5000) to reduce residues.
Viscosity surges after storage
Reason: Dispersant cross-links with resin or microbial reproduction.
Solution:
Detect changes in system pH (if the drop is >1, add alkali solution).
Detect the number of colonies by plate counting method (should be <100 CFU/mL), and replace the preservative if it exceeds
the standard.
