Analysis of Water-based Paint Adhesion Mechanism and Influencing Factors

The coating is well attached to the applied surface and is the prerequisite for the coating to play its protective role. Coating adhesion is one of the most important indicators in coating application.
the importance of adhesion
adhesion has long been known, but so far, the understanding of the adhesion of coatings is still insufficient to
The
. Most of the explanations for adhesion are based on experience and hypothesis, but we can still use this as a means of dialectics.
mechanical attachment
this attachment mechanism is mainly for uneven interface, containing holes, holes or fissures on the substrate coating.
When the paint liquid is applied to the substrate surface, the coating can wet and penetrate into these gaps, so that after the lacquer film is cured, these paint film into the crevice can play a nail-like role, thus grasping the substrate.
mechanism of mechanical attachment in such areas as wood, sand blasting treatment, mechanical polishing and so on have a certain performance.
codent key theory
co-price key theory refers to the coating film and substrate contact, the formation of some co-priced key, this type of link force is the most solid, the most durable.
the formation of the material requires that the coating film and substrate have a mutually matching chemical substrate, these groups close together, can form chemical bonds.
such as the increased adhesion of certain silicone to glass, metals and organic ores, and some substrates with links to hydroxyl, niobium and curing agents in coatings.
van der Worrhy theory
van der Wale is the most common force that provides conventional adhesion. When the coating film is in close contact with the substrate, the molecules are close to each other and become attractive.
this attraction is a short-range interaction that generally has a strong effect at 0.3-0.5nm. In addition, the greater the relative molecular mass of the molecule, the greater the deformation, the easier it is to be polarized, then the more powerful.
stration theory
coating and substrate surface have a certain amount of residual charge dispersion, when the coating and substrate close contact, these charges attract each other can promote the adhesion of the paint film.
Hydrogen Bond Theory
When hydrogen atoms form co-price bonds with electrons with large electron negatives (e.g. O, N, F, etc.), electrons tend to have large electron negative atoms, which in turn have positive electricity.
therefore, when the coating contains similar -OH, -COOH and other substrates, but also in the substrate contains negative electrical groups, it may form a hydrogen bond effect, thereby increasing the adhesion of the coating film.
this type of hydro-based group may affect the water resistance of the coating film.
diffusion theory
When the coating film is applied to the substrate, the two phases of the large molecules may be interlesed by diffusion, thereby increasing adhesion.
this force can only occur between the two-phase coating and substrate, so most of the effect is on inter-layer attachment, especially between the two coatings of the unified system.
above, which is a common explanation of the mechanism of adhesion formation. In fact, in the coating of coatings, the factors involved in adhesion are diverse and often contain a variety of forces.
factors of adhesion
from the above analysis of various factors, it can be seen that no matter what form of force to promote attachment, the close fit of the coating and substrate is the primary condition. By tightly bonding, a special attachment structure of the resin or additive can be reused to obtain a firm and tough paint film attached to the substrate.
can be seen that the performance of the resin itself, formula structure, coating and other aspects will have a certain degree of impact on adhesion.
water-based resin characteristics
every time we talk about performance factors, the first thing to talk about is the performance impact of water-based resin itself, adhesion is no exception. And the performance of water-based resin itself is characterized by adhesion as the most important factor.
moisture flow, particle size, special group and the surface energy and cohesion after the formation of dry film, etc. , will greatly affect the coating film adhesion.
to the excellent adhesion of SV-6145 as an example:
(1) the resin wetting flow is better, through good wetting, flow, spread, can make the paint film and substrate more close contact.
(2) the resin particle size is small, to prevent the formation of too large latex particles space bit resistance effect, affecting the effective contact between the paint film and the substrate, simply put, the film is more dense.
(3) itself contains special anchoring groups and low cohesion. Through the link effect of the special group, an excellent adhesion is formed, which is sufficient to offset the effect of its lower cohesion force on the coating film.
generally speaking, the softer resin has some advantages in adhesion, because with the change of environment, it is more able to adapt to the different degrees of deformation of the substrate.
and the SV-6145 still guarantee good adhesion with better hardness.
substrate treatment
substrate treatment - such as sanding, sand blasting, etc. - can effectively increase the roughness of the substrate. The increase of roughness can greatly enhance the contact area between the coating film and the substrate, and provide many effective anchoring points, which can help to enhance the adhesion of the coating film and substrate.
surface stress of the paint liquid
when the coating is applied to the substrate surface, the original interface disappears, forming a new interface. In the coating process, the degree of wetting of the coating on the substrate determines whether the coating film can form effective contact with the substrate.
water surface pressure is too high, wetting the cloth on the low surface energy substrate is very problem, which also leads to some problems. Therefore, how coatings or water-based resins can achieve low surface stress, excellent wetting and paving capacity is particularly important.
design, should also ensure that the substrate wetting agent added, to ensure that the coating can be effective, excellent wetting substrate.
the thickness of the coating
many experiments show that as the thickness of the coating film increases, the adhesion decreases gradually.
mainly because as the thickness of the coating film increases, its cohesion increases, and the adhesion remains the same;
from the point of view of the protective performance and fullness of the coating, the coating film should have a certain thickness, then, between these two aspects to do a balance. In addition, in the case of the same total film thickness, multiple coatings are better adhesive than one coating.
the drying process
the drying process, ambient temperature and humidity have a certain effect on adhesion.
above is to test a polyurethane water-based paint on the glass, temperature and humidity on its adhesion effects.
experiment, the maintenance conditions of higher temperature and lower humidity have a certain effect on adhesion.
the viscosity of the lacquer liquid
the viscosity of the lacquer liquid will also affect the adhesion of the coating film to a certain extent, one is from the effect on the wetting spread, the other is not suitable viscosity will form stress to weaken the adhesion.
adhesion promoters
certain adhesion promoters can significantly improve the adhesion of the coating, which is formed by a special chemical structure.
different substrate types, different additive effects are not the same, common types such as ethylene oxide.
pigment fillers
a small amount of pigment fillers can generally increase the adhesion of the coating, the principle is by reducing the system's cohesion energy. Different pigment effects are different, such as scale-like pigments to improve the effect is more obvious.
when the amount of pigment has reached a certain level, adhesion decreases with the increase of the addition.
solvent
sometimes, solvents can also have a significant impact on coating film adhesion, which is produced by surface stress, drying, and plasticization of the paint film.
most solvents have relatively low surface stress, which is helpful for the wetting of water-based paint on the substrate, which is conducive to improving the adhesion of the coating film.
also have solvents that evaporate more slowly and can take weeks or even months to evaporate clean. When the solvent remains inside the paint film, it weakens the attachment of the coating film itself.
addition, when the paint film cured after the solvent gradually volatile, the process of the paint film may have a certain degree of contraction, which produces a certain degree of internal stress, resulting in poor adhesion.
can be seen above, the formation of coating adhesion and the influence factors are many. When encountering adhesion problems, we should think about them in a comprehensive way.
source: Jiaye Tiancheng