Guide to the use of dispersants for floor coatings: the secret of scientific formula and efficient construction
Guide to the use of dispersants for floor coatings: the secret of scientific formula and efficient construction
In the preparation process of floor coatings, dispersants are like an "invisible engineer". Through precise control of the molecular scale, solid particles such as pigments and fillers are evenly suspended in the resin system, and finally present a coating with uniform color and stable performance. This article will systematically analyze the scientific use of dispersants from the principle of action, formula design, construction process to quality control.
1. The core role of dispersants: breaking the "physical code" of particle agglomeration
Floor coatings are composed of resins, pigments, fillers, solvents and additives. The dispersion state of pigments (such as titanium dioxide, carbon black) and fillers (such as calcium carbonate, talcum powder) directly affects the performance of the coating. These solid particles carry electric charges on their surfaces and are easily attracted to each other through van der Waals forces in liquids to form agglomerates. If not fully dispersed, the coating will have problems such as floating color, reduced hiding power, poor leveling, and even cracking or peeling of the coating in severe cases.
Dispersants solve this problem through a dual mechanism:
Chemical anchoring: One end of the dispersant molecule carries an anchoring group such as carboxylic acid or phosphate, which can form a chemical bond or hydrogen bond with the pigment surface and firmly adsorb on the particle surface. For example, the acidic anchoring group can react with the hydroxyl group on the surface of titanium dioxide to form a stable chemical bond.
Steric hindrance: The solvated chain segments such as polyether and polyester at the other end of the dispersant stretch in the medium to form a protective layer several nanometers thick. When the particles approach, the chain segments compress to generate entropy repulsion, preventing agglomeration. This mechanism is particularly critical in solvent-based floor coatings, which can ensure long-term suspension of pigments.
2. Formulation design stage: the "golden rule" of dispersant selection
1). System compatibility is prioritized
Solvent-based system: polyphosphate esters or high molecular weight polyurethane dispersants are preferred. Its molecular weight (5000-50000 g/mol) has excellent compatibility with solvent-based resins such as epoxy resin and polyurethane. It can increase the pigment filling amount by more than 30% and reduce the grinding viscosity through the dual effects of chemical anchoring and steric hindrance.
Water-based system: Anionic (such as sodium carboxylate) or non-ionic dispersant (such as glycol ether) must be selected. In water-based epoxy flooring, the carboxylic acid group is ionized to form a double electric layer. With the steric hindrance of the polyether chain segment, the color development of carbon black can be improved by 30%, and the uniformity of the coating blackness can reach ΔE≤1.5.
2). Pigment property matching
Inorganic pigments (such as titanium dioxide, iron oxide): Select dispersants with acidic anchoring groups (phosphate, carboxylic acid) and firmly adsorb them through ionic bonds. For example, the adsorption strength of multivalent carboxylic acid dispersants on titanium dioxide is 85mN/m, which can prevent the pigment from coarsening during grinding.
Organic pigments (such as phthalocyanine blue, carbon black): alkaline anchoring groups (amines, quaternary ammonium salts) or hydrogen bond donors (polyhydroxy compounds) are required. For medium and low-pigment carbon black, amine dispersants can react with the acidic groups on the surface of carbon black and cooperate with the steric hindrance of polyester chain segments to increase grinding efficiency by 40% and reduce energy consumption by 25%.
3). Construction process adaptation
High shear construction (spraying, roller coating): select dispersants with lower molecular weight (5000-10000). Its short chain structure can reduce the entanglement of chain segments under shear force and avoid the decrease of leveling.
Low shear construction (scraping, self-leveling): high molecular weight (20000-50000) dispersants are required to provide strong steric stabilization to maintain the pigment suspension for 12 months without sedimentation, meeting long-term storage requirements.
3. Construction process stage: "key control points" for the use of dispersants
1). Optimization of addition order
Pre-dispersion stage: pre-mix the dispersant and pigment for 10-15 minutes, and use the wetting effect of the dispersant to reduce the surface energy of the pigment. For example, when preparing carbon black slurry, the dispersant can shorten the wetting time from 30 minutes to 5 minutes, and the pigment dispersion efficiency is improved by 80%.
Grinding stage: add the dispersant after the pigment is pre-dispersed and before the resin is added to ensure that it is fully adsorbed on the pigment surface. Experiments show that this sequence can reduce the amount of dispersant by 20%, and shorten the time to grind to less than 10μm by 40%.
2). Precise control of dosage
Theoretical calculation method: Dispersant dosage = pigment surface area × adsorption per unit area. Taking titanium dioxide (specific surface area 10m²/g) as an example, if the dispersant adsorption is 1mg/m², 0.1g of dispersant needs to be added for every 100g of titanium dioxide.
Experimental optimization method: determine the optimal dosage through the dosage curve method. When the amount of dispersant added increases from 1% to 2%, the viscosity of the system decreases by 50%; but when it exceeds 2%, the free dispersant causes the gloss of the coating to decrease by 15%, so the optimal amount is 1.8%-2.0%.
3). Process parameter coordination
Temperature control: When the water-based system is dispersed, the dispersant adsorption rate increases by 2 times for every 10°C increase in temperature, but exceeding 60°C may cause pigment desorption. It is recommended that the dispersion temperature of water-based epoxy flooring be controlled at 40-50°C.
Shear rate matching: High shear grinding (such as sand mill) requires low molecular weight dispersant. When the shear rate reaches 5000-10000rpm, the pigment particle size distribution D90 can be reduced from 50μm to 10μm; low shear stirring (such as self-leveling construction) requires high molecular weight dispersant to maintain stability.
4. Quality control stage: "Evaluation method" of dispersant effect
1). Stability test
Accelerated sedimentation test: Place the paint sample in a 50°C oven for 7 days to observe the pigment sedimentation. High-quality dispersants can make the pigment sedimentation volume ≤5%, meeting the long-term storage requirements.
Freeze-thaw cycle test: After the water-based paint has been cycled at -18℃/23℃ for 3 times, the dispersant can make the paint viscosity change rate ≤10%, without agglomeration or stratification.
2). Performance characterization
Leveling evaluation: The waviness of the coating surface is measured by a leveling meter. The leveling time of the coating with the addition of dispersant is shortened from 8 minutes to 3 minutes, and the waviness is ≤5μm.
Gloss test: The gloss at a 60° angle is measured using a gloss meter. The dispersant can increase the gloss of the coating from 75 to 85, which is close to the mirror effect.
3). Long-term durability
Abrasion resistance test: According to the standard test, the floor coating with the addition of dispersant has an abrasion resistance from 0.05g to 0.02g, and the service life is extended to more than 8 years.
Weathering resistance evaluation: Through the QUV accelerated aging test, the dispersant can make the coating color difference ΔE≤3.0 and the light retention rate ≥85%, meeting the needs of outdoor use.
5. Future Trends: Engineering Application of Intelligent Dispersants
With the development of materials science, intelligent dispersants are becoming a research hotspot:
pH-responsive dispersants: such as polyacrylic acid-polyethylene glycol block copolymers, the chain segments stretch in alkaline environments to provide steric stability, and the chain segments shrink under acidic conditions to reduce viscosity, which is suitable for the dual-stage construction and storage requirements of self-leveling floors.
Temperature-responsive dispersants: Poly N-isopropylacrylamide (PNIPAM) dispersants, the chain segments hydrate and expand to stabilize the pigment at low temperatures, and dehydrate and shrink at high temperatures to reduce viscosity, which can solve the contradiction between leveling in summer construction and storage stability in winter.
Nanocomposite dispersants: Introducing silica nanoparticles into the dispersant structure can provide a dual stabilization mechanism of chemical anchoring and physical isolation at the same time, so that the pigment filling amount of high-solid content coatings (solid content ≥70%) is increased to more than 60%.
Conclusion
From laboratory formulation to construction site, the scientific use of dispersants runs through the entire life cycle of floor coatings. Through the three-dimensional synergy of system adaptation, process optimization and quality control, dispersants can not only improve the performance of coatings, but also reduce the overall cost by more than 30%. With the engineering application of intelligent dispersants, floor coatings will achieve more precise molecular design in the future, providing material support for green buildings and intelligent manufacturing.