In the latex paint of the building exterior wall, a bucket of white paint needs to evenly disperse 30 kg of titanium dioxide;
in the automobile painting workshop, the mirror effect of the metallic flash paint depends on the precise arrangement of
nano-level aluminum powder; on the photovoltaic panel production line, the anti-reflective coating requires the particle
size distribution of aluminum oxide particles to be controlled within the range of ±2nm... Behind these industrial scenes,
the scientific application of water-based inorganic pigment dispersants is indispensable.
1. Addition amount control: precise ratio from 1% to 50%
The addition amount of dispersant follows the "golden ratio law" - it is necessary to completely cover the surface of the
pigment to form a protective layer, and to avoid molecular chain entanglement caused by excessive amount. The specific
amount depends on the pigment type, particle size distribution and target system:
Inorganic pigment system
Conventional inorganic pigments such as titanium dioxide and iron oxide: the addition amount is 0.5%-5% of the pigment
mass. For example, the recommended dosage of Deqian Chemical W-511 dispersant in latex paint is 0.3%-0.5% of titanium
dioxide, which can prepare a high-concentration slurry with a solid content of 65%.
Nanoscale pigments (particle size <100nm): The dosage needs to be increased to 5%-20%. For example, when treating 30nm
alumina, the dosage of EEL.AD™ Dispersant 7338 needs to reach 15% of the pigment mass to form an effective steric hindrance
layer.
Difficult-to-disperse pigments (such as kaolin): The dosage of modified polycarboxylic acid sodium salt dispersants can reach
2% of the powder mass. A ceramic slurry case shows that when the dispersant addition amount is increased from 1.5% to 2%, the
slurry viscosity drops sharply from 12000mPa·s to 4500mPa·s.
Organic pigment system
Strongly hydrophobic pigments such as phthalocyanine blue and carbon black: require a higher dosage (20%-60%). When dispersant
W-20 is used to treat carbon black, the dosage must reach 40%-80% of the pigment mass to achieve particle size control of D50=35nm.
Composite pigment system: In water-based resin-free color paste, the dosage of dispersant is usually 10%-50% of the pigment mass.
A white color paste formula shows that when the titanium dioxide content is 35%, the amount of W-095 dispersant added must reach
18% of the pigment mass to ensure storage stability.
Scientific verification method: Determine the optimal dosage through the viscosity-addition curve. Measured by a Brookfield
viscometer, when the slurry viscosity reaches the lowest point, it means that the pigment surface has been completely covered
by the dispersant. A certain experimental data shows that when the amount of dispersant used in the iron oxide red slurry
reaches 4%, the viscosity drops from 18000mPa·s to 3200mPa·s, and the viscosity increases as the dosage continues to increase,
proving that there is an optimal ratio point.
2. Timing of addition: the golden window of 30 minutes before grinding
The timing of adding dispersants directly affects the dispersion efficiency and system stability, and must follow the three-stage
rule of "pre-dissolution-pre-dispersion-formal grinding":
Pre-dissolution stage
Prepare the dispersant into a 5%-20% aqueous solution, and use a high-speed disperser (1000-1500rpm) to stir for 30 minutes
to ensure that the molecular chain is fully extended. An experiment on a modified polyacrylate dispersant showed that extending
the pre-dissolution time from 15 minutes to 30 minutes can reduce the particle size distribution index (PDI) of the titanium
dioxide slurry from 0.35 to 0.18.
Pre-dispersion stage
Before adding the pigment, add 30% of the pre-dissolved dispersant solution to the system and stir at a speed of 500-800rpm
to form a "pre-adsorption layer". This step can increase the subsequent grinding efficiency by 40%. A case of automotive paint
production shows that the pre-dispersion process shortens the grinding time from 6 hours to 3.5 hours.
Formal grinding stage
The remaining 70% dispersant is added simultaneously with the pigment, and a sand mill is used for cyclic grinding. Key control
Parameters include:
Grinding media: zirconium oxide beads (diameter 0.3-0.8mm)
Linear speed: 8-12m/s
Temperature control: <50℃ (to prevent the molecular chain of the dispersant from breaking)
Grinding end point: stop when the particle size reaches the target value and does not change within 30 minutes
Special scene processing:
High solid content system (solid content>65%): Use the step-by-step addition method, first add 60% dispersant for preliminary
dispersion, and then add the remaining dispersant for deep grinding after the system viscosity drops below 10000mPa·s.
Low temperature environment (<10℃): The dispersant solution needs to be heated to 40℃ before adding to avoid uneven
dispersion due to excessively high solution viscosity. Winter production data of a northern paint factory showed that heating
treatment increased the dispersion efficiency by 25%.
3. Adding process optimization: technological leap from laboratory to production line
Equipment matching principle
Laboratory scale (<5L): Use ultrasonic disperser, power density controlled at 0.5-1.0W/cm², pulse time 2s/1s.
Pilot scale (5-500L): Use basket mill, grinding media filling rate 70%-80%, speed controlled at 1500-2000rpm.
Industrial production (>500L): Use horizontal sand mill, equipped with double-end mechanical seal, flow control at 300-500L/min.
pH value control technology
The ionicity of the dispersant determines the optimal pH range:
Anionic type (such as sodium polyacrylate): The dispersion effect is best at pH=8-10. An experiment shows that under pH=9,
the absolute value of the Zeta potential of iron oxide slurry increases from -35mV to -58mV.
Non-ionic (such as polyoxyethylene ether): pH application range is wide (5-10), but strong acid environment should be avoided to
cause molecular chain hydrolysis.
Synergy of composite additives
Compounded with wetting agent: Disponer W-18 wetting agent can reduce the pigment contact angle from 75° to 28°, and combined
with W-511 dispersant can increase the solid content of titanium dioxide slurry to 70%.
Synergy with defoamer: A case of water-based ink shows that adding 0.3% of silicone defoamer to the dispersant can reduce the
foaming height during grinding by 80%.
4. Analysis of typical application cases
Photovoltaic anti-reflective coating
A company used EEL.AD™ Dispersant 7338 to treat aluminum oxide nanoparticles. By precisely controlling the amount of dispersant
(12%), grinding time (4 hours) and pH value (9.2), the particle size distribution was successfully controlled at D50=35±1.5nm, which
increased the conversion efficiency of photovoltaic cells by 1.8%.
Automotive Metallic Flash Paint
The multifunctional dispersant FX600 developed by BASF achieves directional arrangement of aluminum powder particles through
molecular design. In a luxury brand coating line application, the dispersant increased the gloss of the paint film from 85GU to 92GU,
while reducing the orange peel index from 5.2 to 2.8.
3C Electronic Ceramic Coating
Zirconium oxide ceramic slurry was prepared using W-095 dispersant. By optimizing the addition process (pre-dissolution for 30
minutes + step-by-step grinding), the slurry viscosity was reduced from 22000mPa·s to 6800mPa·s, and the spraying line speed was
successfully increased from 80m/min to 150m/min.
From laboratory beakers to industrial production lines, the application of water-based inorganic pigment dispersants is an
interdisciplinary subject that integrates material science, rheology and process engineering. By accurately controlling the addition
amount, grasping the golden addition time, and optimizing the composite process, it can not only significantly improve the
performance of the coating, but also promote the entire color industry to develop in the direction of higher efficiency and lower
energy consumption. As the technical director of an international coatings giant said: "The scientific application of dispersants is
the bridge connecting pigment molecules and industrial aesthetics."
