Comprehensive Selection Solution for Water-Based Titanium Dioxide Anti-Sedimentation Dispersants
I、 First, clarify the core logic of titanium dioxide settling and the underlying logic and basis for selecting titanium dioxide dispersants
Rutile and rutile titanium dioxide have a density of 4.2g/cm ³, while water only has a density of 1g/cm ³. The physical density difference is extremely large, and the particles are naturally prone to gravity settling, leading to layered settling; There are a large number of hydroxyl (- OH) groups on the surface of particles, and these particles in aqueous systems are prone to agglomeration and form hard precipitates.
Dispersant anti settling relies on two stabilization mechanisms:
1. Mechanism of electrostatic repulsion:By adsorbing the negatively charged groups of anionic dispersants onto the surface of titanium dioxide, the adsorption layer increases the net negative charge on the particle surface, the thickness or potential difference of the double layer increases, and the absolute value of Zeta potential increases. When particles approach, the electrostatic repulsion potential generated by the same charge is greater than the gravitational potential, and the system maintains a dispersed state;
2. Spatial hindrance principle: Polymer long chains adsorb onto the surface of particles and stretch to form a thick hydrophilic "protective layer". When particles approach, overlapping chain segments generate repulsive and osmotic pressure repulsion, physically blocking particle contact and preventing agglomeration and sedimentation.
The type of coating on the surface of titanium dioxide determines its surface charge properties (isoelectric point). If the dispersant cannot accurately match the four-dimensional conditions of "coating characteristics+environmental pH+resin medium+concentration", it will not be able to form effective electrostatic repulsion or steric hindrance, resulting in agglomeration, floating color, decreased gloss, and even system emulsification.
II、 Comparison of Four Types of Water based Dispersants (Classification of Anti settling Ability)
1. Inorganic polyphosphate dispersants (sodium hexametaphosphate, sodium tripolyphosphate)
-Mechanism: Pure electrostatic stability, low cost and anionic adsorption of titanium dioxide hydroxyl groups
-Features: Extremely low cost, fast adhesion reduction, low solid content of latex paint for interior walls, universal use
-Disadvantages: Poor long-term anti settling effect, high temperature/high pH/high solid content are prone to hydrolysis and failure, long-term storage is prone to delamination, leading to hard precipitation; Poor water resistance, industrial paint, inkjet, and high solid color paste are prohibited
-Applicable: Interior wall latex paint (titanium dioxide solid content<40%, short-term storage)
-Addition amount: Titanium dioxide 1.0% to 2.0%
2. Low molecular weight polyacrylate dispersant (maleic anhydride copolymer RK-4046) [cost-effective preferred, mainstream in architectural coatings]
Anionic type, strong anchoring of titanium dioxide metal hydroxyl groups with multiple carboxyl groups, electrostatic+weak steric hindrance, and superior anti settling performance compared to inorganic salts.
-Features: obvious viscosity reduction, high grinding efficiency, alkali resistance, suitable for acrylic architectural lotion, no hard precipitation after 1~3 months of storage
-Disadvantages: High solid titanium dioxide slurry (>50%), average stability under low temperature/cold/hot cycling; General compatibility with polyurethane and epoxy lotion
-Adaptation: Aluminum coated rutile titanium dioxide, interior and exterior latex paint, water-based putty, papermaking titanium dioxide slurry
-Addition amount: Titanium dioxide 1.2% to 2.5%
-Representative: RK-4008Y
3. Polymer comb shaped polycarboxylate dispersant (long-term anti settling main force, industrial paint/color paste)
High molecular weight block/comb type anionic dispersant RK-4057, with multiple anchoring sites and ultra long hydrophilic solvent chains, extremely strong steric hindrance, optimal anti settling, and minimal delamination during cold and hot cycling and high-temperature storage.
-Core advantages:
1. High solid titanium dioxide concentrated slurry (50%~70%) can be stored for 60 days without hard precipitation;
2. Suitable for silicon aluminum composite coating and silicon coated weather resistant titanium dioxide (exterior walls, automotive paint titanium dioxide);
3. Compatible with various resins such as acrylic, water-based PU, epoxy, and amino, with no color floating during color matching;
4. Improve coverage and glossiness, while suppressing the coarsening and settling of titanium dioxide
-Disadvantage: Higher price than low molecular weight polyacrylic acid dispersants
-Applicable: water-based industrial paint, exterior wall weather resistant paint, titanium white paste, plastic water-based paint, digital inkjet white ink
-Addition amount: Titanium dioxide 1.5% to 3.0%
-Reference models: RK-4017F0, RK-4057
4. Water based polyurethane polymer dispersant (universal versatile, multi pigment compound system)
Polyurethane type dispersant, with anionic charge or dual (containing both anionic and cationic groups) characteristics, multiple anchoring groups (such as amino, carboxylic acid, phosphate groups, etc.), relying on long polymer chains to form a thick adsorption layer (usually>10 nm) around pigment particles, generating strong steric hindrance effect, can be compatible with titanium dioxide+iron oxide/organic pigments at the same time, ensuring that all pigments can be uniformly dispersed in the mixed system, maintaining color consistency and storage stability.
-Advantages:1. Co grinding and coexistence of titanium dioxide and colored inorganic/organic pigments without color floating or layering;
2. Resistant to alcohol, cold and hot shock, long-lasting anti settling for inkjet and leather ink;
3. Compatible with cationic resin system (ordinary polycarboxylates may lose stability and cause flocculation)
-Disadvantages: High addition amount, highest cost
-Applicable: water-based inkjet white ink, leather ink, two-component PU industrial paint, cationic primer, multi pigment compound color paste
-Addition amount: Titanium dioxide 2.0% to 3.5%
-Reference models: RK-4039AC, RK-4059
5. Cationic/non-ionic dispersants (rarely used alone for titanium dioxide)
-Cation: Only suitable for use with cationic resin systems. In ordinary systems, it neutralizes the negative charge of titanium dioxide and directly coagulates and settles. It is prohibited to use it alone;
-Non ionic: Can only be used as an auxiliary wetting agent, lacks sufficient electrostatic repulsion, causes severe settling when used alone, and is only used in conjunction with anionic dispersants.
III、 Selection based on titanium dioxide coating
1. Aluminum coated rutile (universal interior wall/industrial titanium dioxide, weak negative surface charge, pH 7-9)
Preferred: Low molecular weight polycarboxylate RK-4046, ordinary sodium polyacrylate; Upgrading high solid slurry with polymer comb like polycarboxylate
2. Silicon aluminum composite coating/silicon coated weather resistant titanium dioxide (exterior walls, automotive paint, strong negative surface charge)
Prohibition of low molecular weight inorganic salts; Polymer comb shaped polycarboxylic acid is required, with long chain hindrance to resist the aggregation and sedimentation of silicon hydroxyl groups RK-4017E
3. Sharp titanium dioxide (papermaking, matte paint, large specific surface area, faster settling)
Increase the dosage of dispersant+polymer polycarboxylate, combined with a small amount of non-ionic wetting agent to synergistically prevent sedimentation
IV、Accurate selection based on application scenarios
1. Interior wall latex paint (low solid content below 40%, short-term storage, low cost)
Solution: Compound of sodium hexametaphosphate and polyacrylic acid, balancing cost and short-term anti settling performance
2. Exterior wall weather resistant/water-based industrial paint (silicon coated titanium dioxide, stored for more than 3 months)
Solution: Polymer comb shaped polycarboxylate dispersant (RK-4017F0), a single component can provide long-lasting anti delamination
3. High concentration titanium white paste (60%~70% solid content, long-term storage)
Only option: Polymer polycarboxylate dispersant, phosphate is prohibited (high solid content viscosity surges, later settling)
4. Water based digital inkjet white ink (ultrafine nano titanium dioxide, with a large density difference that is prone to precipitation)
Solution: Anionic polyurethane dispersant RK-4039AC, with extremely strong steric hindrance effect, alcohol resistance, non clogging circulation, and anti settling properties
5. Cationic water-based resin system (cationic primer)
Special: Cationic compatible polyurethane dispersant, ordinary polycarboxylates will flocculate and stratify
6. Multi pigment co grinding (titanium dioxide+iron red/carbon black/organic blue)
Polyurethane dispersant RK-4059 prevents co coagulation and sedimentation caused by charge conflicts of different pigments
V、Optimization plan for anti settlement matching (selecting only the right dispersant is not enough)
1. PH control method
The isoelectric point of titanium dioxide is pH 6-7, and the stable pH of the system is adjusted to 8-9. The surface of titanium dioxide carries a strong negative charge, and the anionic dispersant adsorbs more firmly, greatly reducing sedimentation; The sedimentation rate of acidic systems doubles.
2. Compound efficiency enhancement (significantly reducing sedimentation)
Main dispersant (polycarboxylate/PU)+a small amount of non-ionic wetting agent to enhance powder wetting and reduce agglomeration precursors; High storage requirements are combined with water-based associative thickeners to construct a thixotropic system and physically suspend titanium dioxide.
3. Taboo on dosage - too little: incomplete coating, rapid particle aggregation and settling;
-Excessive: Free dispersants disrupt the charge balance of the system and instead cause coagulation and hard precipitation. Gradient tests must be conducted to find suitable addition points.
4. Simple testing method for settlement effect
Seal with 50% titanium dioxide slurry and store at 50 ℃ for 7 days. Observe for any hard sediment at the bottom; Inverted shaking can easily mix well, and qualified anti settling indicates successful selection of dispersant; The bottom clumps cannot be dispersed, indicating a failure in selecting the dispersant.
