Water-powered car original paint "wet touch wet process" appearance improvement process

With the strengthening of national environmental protection requirements, the emission limits of volatile organic compounds (VOCs) in coating formulations are becoming more and more stringent, and the application of water-based coating formulations has made rapid progress in recent years.
However, due to the water-based formula with water as the medium, its drying speed relative to conventional organic solvents is slow, in order to improve the coating efficiency of water-based coatings in the original paint coating process, it is generally necessary to add pre-drying (flash drying) process to meet the needs of subsequent coating and overall paint coating appearance.
in recent years, however, the industry's requirements for energy conservation and environmental protection of the coating process have been increasing, and now has gradually developed a non-pre-drying process, that is, water-free BC1 and BC2 flash-free drying process - direct wet wetting process

.
But
due to differences in the physical parameters of BC1 and BC2 (e.g. rheumation performance, surface tension, etc.), wet wetting processes can lead to interaction between BC1 and BC2, resulting in poor final appearance of the paint film, such as poor leveling, etc.
, especially when the thickness of the paint film is high, it can even cause a slight crack in the dry paint film. As shown in Figure 1, BC1 and BC2 wet wet coating and completely dry, when the dry film thickness reaches 45 m, the paint film surface has obvious cracks, is due to BC1 and BC2 interaction caused.
Figure 1: BC1 and BC2 wet touch wet coating dry paint film appearance (dry film thickness 45 m, local magnification)
How to eliminate/reduce the interaction between
BC1 and BC2 in wet wet process?
experiments have shown that selecting the right surfactant/wetting agent can effectively reduce inter-layer interaction in wet-touch processes. The addition of wetting agents in water-based formulations can effectively reduce surface stress in water-based formulations, but experiments have shown that
does not reduce surface stress to a certain level to eliminate inter-layer interaction, but also need to consider the components of surface stress.
The surface stress of different surfactants is generally composed of polar and non-polar parts, as shown in Figure 2, in 0.1% aqueous solution, the figure shows that the ability of different surfactants to reduce surface stress (i.e., the absolute value of surface stress) is different, but also can be seen that the composition of different surfactant surface stress (polar and non-polar parts) are also different.
Figure 2: Surface stress values and polar/non-polar parts of different surfactants in aqueous solutions
The study found that in formulating the formulation of water-based BC1 and BC2, the appearance of wet-wetting process lacquer film was closely related to the surface stress of BC1 and BC2, not only to the absolute value of surface stress, but also to the components of BC1 and BC2's respective surface stress (i.e., polarity and non-polarity).The experimental results of
show that by adding a suitable surfactant to the water-based BC2 formula, the BC1/BC2 can get a relatively perfect appearance after wet and wet coating process when the polar and non-polar parts of the surface stress are infinitely close to the polar and non-polar parts of the water-based BC1 formula.
As shown in Figure 3, the addition of the wetting agent Dynol™607 (0.5% dosage) to the BC2 formulation by adjusting the BC2 formulation surface stress polarity and non-polarity part close to BC1, can completely eliminate the dry film thickness when the paint film surface cracking phenomenon. When the dry film thickness is moderate, Dynol™ 607 can significantly improve the smoothing performance of the wet-touch process paint film, as shown in Figure 4.
3: Wetting agent Dynol™ 607 to BC1/BC2 wet wet coating process paint film appearance improvement (dry film thickness 45 sm, local amplification)
Figure 4: wetting agent Dynol™ 607 to BC1/BC2 The improvement of the appearance of the paint film during the wet touch coating process (dry film thickness 25 m)
conclusion: Surface stress is very important to the application performance of water-based formulation, and it is more important for the wet-touch wetting process and the appearance of the paint film to require higher water-based automotive original paint, not only surface strength, but also the polarity and non-polarity of the surface stress of different coatings.