Causes and Solutions of Bubbles in Coatings

In view of the causes of bubble formation in coatings during construction, this paper will discuss this problem in three steps in detail.
(1) How do the bubbles in the film come into being? Bubble is the phenomenon that the gas mixed into the coating is left on the surface of the coating to form bubbles.
A. Air entrainment caused by mechanical movement in the process of mixing and filtering of lacquer liquor, strengthening agent and blending agent.
B. During construction, a large amount of air will be entrained in the paint brush, and bubbles will be formed in the wet film when painting. The base material is not uniform, the base material is loose, the gap is filled by the paint liquid, and the air discharged will form bubbles.
C. Gases released from chemical reactions form bubbles, such as humidity, bad solvent containing moisture, water entrained in compressed air when spraying paint, and a small amount of acid, alcohol, amine contained in bad diluent. They react with curing agent and release carbon dioxide gas to form bubbles.
(2) Bubble rupture process:
A. In paint, the rising speed of bubbles: V = KX (r2/y)
(V: Bubble rising rate k: constant r: bubble radius y: paint viscosity)
It can be seen that the bigger the bubbles, the faster the speed of rising to the paint surface, the bigger the paint sticker, the slower the bubbles rise.
B. Vapor light drainage effect: When the bubbles rise to the surface of the paint, the liquid flows downstream of the bubbles, and the bubbles become thinner gradually. When the thickness of the bubbles is less than 10 nm, the bubbles will burst.
C. The surface tension of defoamer is very low. It will make the bubble wall thinner and cause the bubble to rupture more easily.
D. It is not easy to produce bubbles by using solvents with low surface tension.
E. During construction, the paint is sparse and the viscosity is low. The bubbles formed are easy to crack.
(3) Bubble avoidance:
A. Prepare the paint to be painted. After filtration, it must be stationary for more than 15 minutes to eliminate the small bubbles in the paint as far as possible.
B. Wet the brush in the blending agent beforehand, stir repeatedly, remove the bubbles entrapped in the hair, and then immerse in the prepared paint solution to further eliminate the bubbles until the brush stirs in the paint solution and does not exhaust the bubbles, so that another 15 minutes to brush the paint, this is particularly important.
C. No matter what kind of base material (furniture or floor), it must be coated with more than two closed primers to seal the wood grain holes of the base material, so as to prevent the paint from penetrating into the base material and discharging air to cause bubbles.
D. The prepared paint should be thinned properly to control the construction viscosity.
E. Controlling the thickness of wet film in each construction to facilitate leveling and defoaming.
F. Use high quality diluents to avoid bubbles from chemical reactions caused by water and other impurities.
G. Uneven base material will cause filling bubbles. Therefore, smooth and smooth base material is required for finish painting.
H. Pay attention to the difference of horizontal construction and vertical painting, along with the difference of wood grain and cross-grain painting, control the viscosity of paint and the thickness of paint film.
I. Paint is different, it is difficult to eliminate bubbles, but no matter what kind of paint, as long as the above aspects are not properly handled, it will produce.