Reasons for bubbles in the coating during construction

2021-08-29   Pageview:297

For the reason that the coating is easy to produce bubbles during the construction process, we discuss in three steps

(1) How does the vapor bubble in the coating film arise? Vapor bubble is the gas mixed into the paint, stay in the surface of the coating film, forming a small bubble phenomenon.

A.  In the process of preparing paint, adding curing agent and blending agent, stirring, air entrainment caused by mechanical movement in the process of paint filtration.

B.  During construction, a large amount of air will be entrained in the paint brush, which will stay in the wet film to form vapor bubbles when painting, the substrate is uneven, the substrate is loose, the void is filled by the paint, and the air will be discharged to form bubbles.

C. Chemical reactions released gas to form vapor bubbles, such as moisture, solvent bad contains water, spray paint when the compressed air entrained water, and bad thinner contains a small amount of acid, alcohol, amine, etc., they react with the curing agent, releasing carbon dioxide gas to form vapor bubbles.












(2) The rupture process of vapor bubble

A. In the paint, the vapor bubble rise speed: V = kx (r2 / y) (V: vapor bubble rise speed k: constant r: vapor bubble radius y: paint viscosity) It can be seen: the larger the vapor bubble, the faster the rise to the paint surface, the larger the paint viscosity store, the vapor bubble rise more slowly.

B. Effect of vapor bubble discharge: when the vapor bubble rises to the surface of the paint, the liquid will flow to the lower side of the vapor bubble, the vapor bubble wall gradually becomes thinner, when the thickness of the vapor bubble wall is less than 10nm, the vapor bubble will break.

C. The surface tension of defoamer is especially low, it will make the bubble wall thinner and cause the bubble to break more easily.

D. Use the solvent with low surface tension, it is not easy to produce vapor bubbles.

E. Construction, paint thin, low viscosity, the formation of vapor bubbles easy to rupture.

(3) Vapor bubble avoidance

A. Prepare the paint to be painted, after filtering, make sure to leave it for more than 15 minutes to try to eliminate the small vapor bubbles in the paint.

B. Pre-impregnate the brush in the mixer and wet it, stir it repeatedly for many times to exclude the vapor bubbles, and then dip it in the lacquer solution to further exclude the vapor bubbles until the brush is stirred in the lacquer solution without discharging the vapor bubbles, so that it will be painted for 15 minutes, this article is especially important.

C. No matter what substrate (furniture or floor wax supplier), must be coated with more than two closed primer to close the wood grain hole of the substrate, so as to avoid the vapor bubble caused by the paint of the top coat penetrating into the substrate and discharging air.

D. Prepare the paint to be properly diluted to control the construction viscosity.

E. Control the wet film thickness of each construction to facilitate leveling and defoaming.

F. Use high quality thinner to avoid water and other impurities caused by the chemical reaction of the vapor bubbles.

G. The unevenness of the substrate will cause filling vapor bubbles, so when constructing the top coat, the substrate is required to be flat and smooth.

H. Pay attention to the difference between horizontal construction and vertical painting, painting with the wood grain and across the wood grain, controlling the viscosity of the paint and the thickness of the paint film in one application.

I. Paint is not the same, the elimination of vapor bubbles is not the same difficulty, but no matter what paint, as long as the above aspects are not handled properly, it will produce the problem of vapor bubbles.


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