The binding force of water-based coatings is a factor

With the progress of water-based resin technology, water-based coating technology has been recognized and applied by more and more industries. While advocating environmental protection, water-based coatings with their special hydro-friendly structure may also lead to the early failure of the coating. We often attribute failure to resin performance defects, ignoring the combination of water-based coatings and construction substrates,

.the quality of the
binding force can be understood as whether the coating and substrate has established a good connection relationship, the experimenters through various methods to obtain the connection between the coating and the substrate, but before the coating is not fully moisturized substrate to form a solid liquid interface, the discussion of mechanical anchoring, Van der Huali or chemical bonds and other binding force factors will become impractical. Therefore, "wetting and spreading" has become a prerequisite for the production of binding force.
in everyday applications, it is generally accepted that relatively rough substrates are more conducive to the generation of binding forces. Theoretically, rough substrate pores have a larger surface area than flat substrates, and when the substrate is moistened by paint and air is removed, the two produce a larger contact area to obtain binding force. However, for water-based coatings, the surface temperature of 40-50dyn/cm is higher than that of most substrates, and applications often reduce the contact area between water-based coatings and substrates because they cannot be wet, resulting in the loss of binding force. For example, Figure 1 shows that the formation of a liquid solid interface is conducive to the generation of binding forces.
Figure 1: Water-based coatings are used in the actual and ideal form of porous substrates
water-based coatings come into contact with substrates, their gas-solid interface SG and gas-liquid interface SL are replaced by liquid-solid interface SGs, coatings and substrates begin to establish a partial connection relationship, when this phenomenon quickly spread to a certain extent, the coating entered the drying stage, and finally completed mechanical anchoring or chemical reaction. The formation of contact angle is related to the surface stress of the substrate and coating, the angle size is directly related to the degree of wetting of the substrate by the water-based coating, when the contact angle is >90, it is considered not to produce wetting, and when the contact angle is <90, the coating can quickly spread and penetrate the pores.
the formation of the ideal liquid solid interface, the increase of the contact area between the coating and the substrate will certainly promote the generation of binding force. However, due to the surface pressure difference (Figure 2), complete wetting can only be achieved in large aperture pores, while for pores with small apertures, the wetting process becomes quite slow and often cannot be completed before curing. When the tiny pores are dense enough, a micron-grade air film is formed between the surface of the un humide substrate and the coating, and the presence of the air film hinders the binding between the coating and the substrate. To solve this problem, it is often necessary to change the surface properties of the substrate to a greater extent or to find solutions in terms of water-based coatings for rapid wetting and spreading. As can be seen from Figure 3, the degree of wetting is related to capillary aperture.
: The formation of surface pressure difference
there are many ways to solve the wetting problem in water-based coatings. From emulsion polymerization began to add surfactants, to the finished formulation of solvents, there is no doubt that the surface strength of water-based coatings have a certain degree of impact. However, for capillary catheters or low surface pressure substrates, the most effective way is to promote water-based coatings to achieve the ideal wetting spread by adding a substrate wetting agent to the water-based coating formulation, so as to facilitate the production of binding forces. This method is widely used because of its ease of use and significantly improving the ability to wet and spread.
Figure III: 30dyn/cm water-based coating wetting results for different aperture substrates
Polysilane has less surface strength and hydrophobicity than most substrates, and the introduction of polyether chain links in polysilicae can effectively enhance the water solubility of polysilica and bring high surf activity. In the application process of water-based coatings, the substrate moisturizer tends to form a directed adsorption single subfilm at the gas-liquid interface, thus effectively reducing the surface pressure of water-based coatings and improving the wetting spread efficiency. Especially in recent years, the water-based coating process tends to thin multi-layer coating, coating construction time period is short, the rapid wetting and spreading of coatings has become particularly important.
Figure IV: Chemical structure of polysilioxane substrate wetting agent
The experimental results show that the addition of polysilioxane substrate wetting agent can effectively improve the wetting and spreading capacity of water-based coatings on substrates (Figure V) (Figure VI). From the fine catheter penetration of wood (Figure 7) can be shown that the addition of substrate wetting agent can help water-based coatings on the fine aperture substrate for good wetting penetration. When the air in most of the pores on the substrate surface is replaced by liquid, the coating shields the external water vapor and forms a mechanical anchorage or physical entanglement with the internal pores. In some coating systems, the resin can react with the active substrate on the substrate surface to further enhance the binding force of the coating and substrate. This conclusion can be proved in the results of the metal salt-resistant spray test (Figure 8).
Figure V: 0.3% SiFast ® series substrate moisturizers can significantly reduce the contact angle of water-based coatings
but in practical applications, the surface pressure of water-based coatings is not as low as possible, but depending on the nature of the substrate to choose an optimal addition and use scheme. This can promote the coating to effectively wet the substrate to achieve good combination at the same time, to prevent the substrate wetting agent improper use of the risk.
Figure VI: 0.1-0.3% SiFast ® Series substrate moisturizer water solution spread effect
The application experimental data of polysilicaxane moisturizer mentioned in this article are derived from the SiFast® series of water-based substrate wetting agent products developed and produced by Standard America. SiFast ® series of water-based substrate moisturizers is not limited to substrates, it can play a surface wetting role for a variety of materials. For example, for various structures of pigment wetting dispersion, dust residue caused by the dent defect wetting cover, water-compatible substances in the water system to help dissolve.
figure 7: Acrylic emulsion for the wetting of porous substrates to bring a good shielding effect
in conclusion
in the global environment of environmental revolution, compared to the more mature oily coating water-based coatings appear to have more potential, supporting the development of special functions of additive products become a trend. Based on materials science and organic chemistry research, the development of coatings and ink additives with higher market acceptance is the goal pursued by Peugeant.
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