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It is a phenomenon where the paint film on the inclined or vertical surface of the workpiece becomes locally thicker, wavy, or has a shallow single shape after application. Usually appearing in the vertical plane, we call it a vertical curtain like fluidization, which appears at the edges and corners.

It is a teardrop shaped flow, which can affect the appearance and performance of the paint film. This phenomenon does not occur on flat surfaces, only on vertical or inclined surfaces. Mainly the paint, due to gravity, it will flow downwards. The flow tank generated during coating construction may be caused by the following reasons.

Firstly, the paint film sprayed at once is too thick, or in areas where the spraying is uneven, the wet film is relatively thick and the surface dries slowly, making it easy for it to flow downwards.

Secondly, during our construction, the viscosity of the coating we adjusted was too low, and too much diluent was added, resulting in increased fluidity and easy sagging. Many of our oil brick and water engineers, as well as spray painters, use oil-based paint with a viscosity that usually lasts for more than ten seconds. The amount of diluent added can be 50% or even 100%, and even up to 200% at high levels. That water-based paint also follows this habit by adjusting its viscosity very low.

But we know that during the atomization of oil-based paint, most of the solvents actually evaporate. During the period from the nozzle to the machine, most of the containers have run away, but there is water vapor in the air, so our air has humidity. This water-based paint seriously affects the evaporation of moisture. So at the moment of spray atomization, water-based paint actually evaporates very little water. In this way, we will cause the viscosity of the wet film after spraying to be different from that of oil-based paint. So many people think that water-based paint is easier to stick.

Thirdly, it is due to improper construction. For example, the distance between our spray gun and the surface of the object being coated on the back is too close, or the speed of our spray gun is too slow, resulting in a pile of paint.

There are just a lot of them. Additionally, it is due to improper use of the spray gun. For example, if we spray a small board with a large caliber spray gun, and the spraying pressure is too low, the solvent evaporates less during atomization, which can cause the local paint film to become too thick and sulfide.

Fourthly, the diluent used is not compatible with the coating, resulting in slow evaporation and good solubility, which can also lead to lower viscosity of the coating and make it more prone to sticking. For example, using slow drying solvents in winter can also cause this phenomenon.

Fifth, when using the wet touch wet spraying process, the interval time is too short, and the bottom layer has not dried yet, and then the upper layer of paint film is applied. At this time, it is also more likely to cause our phenomenon of cheating.

Sixth, the temperature of the environment is inappropriate. The temperature of the construction environment is too high or too low, which affects the drying time and viscosity of the coating. Also, the surface temperature of the substrate is too low, which makes it prone to sagging. Therefore, for some substrates, we preheat them before construction, which is beneficial for preventing sagging.

Seventh, it is due to improper humidity in the environment, especially for water-based coatings. When the humidity is high, the water evaporates slowly during construction, and it cannot run away, which makes it relatively easier to hang on.

Eighth, it is the surface of the base color, which may have oil stains or be on some smooth old paint film, or on the smooth surface of this substrate. Directly spraying new paint can also easily cause oil stains, which is the last reason. It’s just that our paint formula design is unreasonable. If the formula itself is not good at preventing flow and hanging, then we definitely cannot come up with it. The effect of preventing greening is very good. So if we want to solve the problem of greening prevention, we still need to address the root cause. For example, if the construction is thinner, the construction viscosity should be higher, and attention should be paid to the environment or the temperature and humidity of the substrate.

By following standard operating procedures during construction, we can avoid the phenomenon of sagging. Additionally, adding appropriate dust-proof agents, anti flow plasticizers, low shear or medium low shear thickeners to coatings can effectively prevent sagging. For example, polyamide wax slurry, polyurea based anti sagging agents include bentonite, montmorillonite, magnesium aluminum silicate, lithium magnesium silicate, and the most commonly used cellulose alkali swelling agent in Mercury coatings.

This type of polyurethane thickener with a medium low point has a good anti flow effect on socks. In addition, we have special anti sagging resin, which is generally SCA modified resin, and micro gel resin, which can provide excellent anti sagging effect.

Also, we need to pay attention to the synergy and contradiction of some additives. For example, leveling agents can improve the leveling performance of our coatings. On the contrary, the streaming performance may deteriorate. In addition, we explain that coagulants can improve the dispersion effect.

However, at the same time, due to its smoke reducing effect, the flowability may also decrease. On the contrary, the coagulation state or controlled virtual state is beneficial for the anti flow tank. We need to find the right balance among them.