Water-based multifunctional paints are a key development in the coatings industry due to their excellent environmental performance and wide application. However, their production process is prone to foaming due to their formulation characteristics and process conditions. If not promptly controlled, this can lead to reduced leveling, craters or pinholes on the coating surface, and even compromise equipment efficiency and product quality stability. Therefore, a systematic foam control solution is necessary, encompassing formulation design, raw material selection, process optimization, and defoamer application.
Foaming in water-based multifunctional paints primarily stems from two factors: First, surfactants in the formulation, such as wetting agents, dispersants, and leveling agents, function by reducing the system's surface tension but also stabilize the bubble structure, making it difficult for the foam to collapse naturally. Second, mechanical forces in the production process, such as high-speed mixing, grinding, and pumping, can introduce air into the coating system, forming a large number of tiny bubbles. Furthermore, the application temperature and substrate surface conditions (such as porosity) can exacerbate foaming. For example, when applying to wood or cement substrates, paint seeps into the pores, squeezing out air and trapping it within the coating.
Formulation optimization is the foundation of foam control. First, reduce the amount of foaming ingredients. For example, choose low-foaming wetting agents or dispersants. These additives, through molecular design, maintain wetting and dispersing properties while reducing their stabilizing effects on bubbles. Second, introduce defoaming ingredients. For example, some leveling agents, through their specialized structures, promote film leveling while suppressing foaming. Furthermore, adjust the particle size distribution of pigments and fillers to avoid excessive viscosity due to excessively fine particles, thereby minimizing air entrainment during stirring.
Precise control of process parameters is crucial for foam control. Stirring speed and time are key factors: While high-speed stirring improves dispersion efficiency, it also increases air entrainment. Therefore, the speed should be set appropriately based on the paint viscosity and equipment characteristics, and the stirring time should be controlled to avoid excessive shear. A staged grinding process should be employed, starting with coarse grinding at a low speed and then gradually increasing the speed for fine grinding. This ensures uniform pigment dispersion while minimizing foaming. When pumping materials, choose a low-shear pump, such as a screw pump or gear pump, to avoid foaming caused by high shear.
The selection and addition of defoamers are crucial for foam control. Water-based multifunctional paints require a dedicated water-based defoamer compatible with the paint system to prevent reactions with resins or additives, leading to defects such as craters and oily spots. Defoamers work by breaking and suppressing bubbles: Breaking defoamers reduce the surface tension of the bubble membrane, causing bubbles to collapse quickly; suppressing defoamers prevent bubble formation by forming a hydrophobic layer at the air-liquid interface. In practice, defoamers and suppressors are often combined and added in stages: the suppressor is added during the grinding stage to suppress foaming; the defoamer is added during the letdown stage to eliminate any foam that has already formed. The addition rate must be strictly controlled, generally between 0.1% and 0.3% of the total paint volume. Excessive addition may lead to surface defects in the coating.
Application environment and substrate preparation also influence foam control effectiveness. Before application, ensure the substrate surface is clean and dry to avoid dust, oil, or moisture that can cause poor contact between the paint and the substrate, leading to bubbles. For porous substrates, a sealer primer can be pre-applied to reduce air displacement when the paint penetrates the pores. Application temperature and humidity also need to be controlled. High temperatures and high humidity accelerate paint drying, trapping bubbles in the coating before they have time to escape. Therefore, an appropriate application temperature range should be set based on the paint's characteristics, and application in environments with excessive humidity should be avoided.
Foam control in water-based multifunctional paints requires a coordinated approach across multiple dimensions, including formulation design, process optimization, defoamer application, and construction environment management. By selecting low-foaming raw materials, precisely controlling process parameters, and strategically selecting and optimizing defoamer addition methods, combined with substrate pretreatment and application environment regulation, foam generation can be effectively suppressed, improving paint performance and coating quality, and driving the development of water-based multifunctional paints towards higher performance and more environmentally friendly solutions.
