Surface control technology of waterborne industrial coatings -- base material wetting agent

Due to the high surface tension of the coating itself and the complexity and diversity of industrial construction base materials, there are often many surface defects due to the insufficient wetting between the paint film and the base material As one of the important additives for surface control, the wetting agent of the base material can prevent the surface defects caused by the poor wetting of the coating base material and improve the film's resistance and appearance effect I what is base material wetting agent Base material wetting agent belongs to surfactant Base material wetting agent can achieve the purpose of wetting the construction base material by reducing the surface tension of paint and its special interface action mode It belongs to the same surfactant as pigment wetting, both of which have the property of surfactant, but focus on different functions Pigment wetting agent focuses on the wetting of pigment surface to improve pigment dispersion and Color development performance The wetting of substrate focuses on the wetting of industrial substrate, so as to avoid the problems of uneven coating, edge shrinkage, oil shrinkage and flow equality caused by insufficient wetting of substrate 2 Action mechanism of base material wetting agent: the traditional base material wetting theory is to reduce the dynamic and static surface tension of the paint to achieve the control ability of the surface of the paint film Generally speaking, the lower the static and dynamic surface tension is, the stronger the wettability of the base material is, and the phenomenon of oil shrinkage, edge shrinkage, pinhole and so on will be reduced However, according to the relevant experiments, the researchers of France cepstrum chemical company confirmed that although reducing the surface tension of liquid is one of the important factors affecting the wettability of substrate, the mode of substrate wetting at the interface can not be ignored The traditional substrate wetting is through the single-phase effect of the interface, while the cepstrum star like substrate wetting is through the principle of multi-phase action, which significantly increases the efficiency Strong Through this theory, the evaluation of substrate wetting agent becomes more scientific 3 The mechanism of anti foaming property of the base material wetting agent: due to the special hydrophobic structure of the starting end of the surfactant, the base material wetting agent has better anti foaming property for the water-based coating under the action of excellent dynamic surface tension What is dynamic surface tension? Description of dynamic surface tension: dynamic surface tension, also known as interfacial tension, is the value of surfactant containing liquid at a specific interface or surface period, which is different from the static equilibrium value (static surface tension) When the surfactant is absorbed by the liquid, the dynamic surface tension or the interfacial tension will decrease, which will continue to reach the static equilibrium value The decreasing time depends on the diffusion and absorption efficiency of surfactants Diagram of dynamic surface tension: IV requirements, types and how to optimize the selection of base material wetting agent for waterborne industrial paint The base material wetting agent currently used in waterborne industrial paint not only needs very good wetting force but also has better antifoaming performance The main chemical structures are polyether silicone, star shaped polyether and alkyne glycol ether Their contribution to defoaming and substrate wetting is different due to their different chemical structures The most important choice is to take into account the wettability of the substrate and the performance of foam suppression and defoaming Secondly, the compatibility, luster and durability of the resin are considered 4.1 the chemical structure of polyether organosilicon polyether organosilicon takes organosilicon as hydrophobic end polyether as hydrophilic end Chemical structure diagram At present, most of the successful applications in waterborne industrial paint are based on trisilane as the starting material, after a series of chemical treatment and then catalytic etherification Its performance is mainly to provide a better wettability of the substrate, but its antifoaming ability is insufficient On the basis of ordinary organosilanes, the Gemini organosiloxane polyether is expanded by reactive linking groups and then surface activated, which has a significant improvement in defoaming and substrate wettability However, both mono and Gemini organosilicon wetting agents use organosilicon with very low surface tension to form umbrella like structure, so as to reduce the surface tension rapidly At last, a strong hydrophobic micro interface will be formed on the surface of the coating, which has certain influence on the adhesion and repainting between layers The addition should be controlled in a proper range Typical model: sinpols 830 (static surface tension 20.4 0.1% concentration slight foam suppression), sinpols 850 (static surface tension 20.7 0.1% concentration foaming), sinpols 530 (static surface tension 23.4 0.1% concentration) 4.2 star polyether Polyether with star structure, chemical structure diagram, hydrophobic end selection is more diverse, without organic silicon structure, hydrophilic end ethoxylation There will be no problems of adhesion and recoating between layers Its wettability is mainly due to its excellent dynamic surface tension and multi-phase effect of star structure, and its antifoaming ability is due to its special star hydrophobic structure and superior dynamic surface tension Sepson chemical has a variety of patented star like polyether wetting agents Different specifications have different emphases on foam inhibition and substrate wetting Typical model: pag30 (focusing on defoaming, can be used as defoamer), pag33 (focusing on substrate wetting and antifoaming), pag40 (focusing on strong defoaming and antifoaming and substrate wetting), 4.3-alkynodiol ether The performance of polyether with alkynylene glycol structure is mainly influenced by the special structure of alkynylene glycol At present, decynylene glycol polyether is the main market, but the performance of dodecynylene glycol polyether is better Alkynylene glycol products mainly have good dynamic surface tension, fast diffusion speed in water, good foam breaking and inhibiting force, which does not affect recoating and adhesion between layers, but the wettability of substrate is relatively insufficient Antifoam additives are mainly used in waterborne industrial paints In order to achieve better wettability, polyether silicone or star polyether should be used Typical models: sinpols 465 sinpols 485 V, polyether organosilicon, star polyether alkyne glycol ether in the application of waterborne industrial paint VI common coating defects due to the influence of surface tension The surface defects of waterborne industrial paint are caused by the differences and changes in the surface tension of liquid paint, substrate and pollutants The main reasons are as follows 6.1 orange peel - a typical defective appearance that can only be observed after the spray process The three main factors influencing the defect include the viscosity of spraying liquid, spraying conditions such as temperature, pressure or air / liquid ratio, and surface tension of liquid The first two factors largely depend on the coating personnel The third factor can be controlled by the paint formulation designer Reducing the surface tension of the liquid can make the droplets smaller under the same spraying conditions and improve the fluidity of single droplet after spraying 6.2 Fisheye - fisheye is caused by insufficient moisture of the base material When the surface tension of the liquid coating is higher than that of the substrate, this phenomenon will occur The coating on the surface is not spread Spreading can be improved by reducing the surface tension of the liquid 6.3 edge shrinkage - edge shrinkage occurs at the edge of the substrate Because the surface of the coating at the edge is larger than that at other places, the solvent volatilization speed at the edge is faster, resulting in the increase of surface tension at the edge faster than that at other places Higher surface tension results in surface shrinkage as the film attempts to form a smaller total volume when cured This problem can be avoided by reducing the surface tension of the liquid 6.4 Florescence (Bernard pinhole) and streaks - florescence and streaks are related to the technological process of the liquid coating in the drying stage The difference in density and surface tension will cause turbulence from the bottom to the top of the coating In the colored system, the pigment will settle in different areas according to its fluidity On a horizontal surface, this hair flower presents a hexagonal pattern called a Bernard hole The same reason for stripes is that they appear as linear patterns on vertical surfaces This defect can be avoided by minimizing the difference in surface tension during drying.