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With the rapid development of the coating industry, the varieties and grades of coatings are continuously upgraded, and people have put forward higher requirements for the protective and decorative properties of the coatings.
(Paint hole)
Characteristics and classification of bubbles
In the paint production process, air bubbles appear as an interference factor, causing surface defects in the application of the paint product, which not only damages the appearance, but also affects the anti-corrosion and weather resistance of the coating film.
Bubbles have sizes, and the bubbles can contain liquid, steam, other gases or crystals.
(Bubble on the metal surface after coating)
Causes of bubbles
Blistering usually occurs with the aging process of the coating.
PART1.
Substances such as oxides and soluble salts on the surface of the substrate are the inducing points for coating blistering.
PART2.
In the wet film formed by painting, about 10% of the volatile solvents remain, and about 90% of the other solvents have been volatilized into the atmosphere during the coating process.
PART3.
Residual gas in porous substrate
Solvents can also cause the coating film to foam on porous substrates (such as cement, wood).
Generally, organic coatings are coated on inorganic substrates, and blistering is prone to occur when the surface temperature is high.
At this time, the bubble generation speed is extremely fast, and it is easy to break and expose the substrate.
Such bubbles can be eliminated by applying a penetrating primer.
Penetrating primers usually have low viscosity, thin films, can dry quickly, and have enough time to penetrate.
Avoiding high temperature time construction can also avoid such bubbles.
PART4.
Adsorption of gas or liquid on the surface of pigment or filler
Soluble fillers in coatings are the cause of many bubble defects.
The soluble pigment absorbs the moisture that penetrates the coating and becomes a solution.
Due to osmosis, water will be drawn through the coating to the concentrated solution.
In addition, if the soluble pigment contaminates any surface between the substrate or the coating, the same phenomenon will occur.
Therefore, as long as the coating contains soluble substances, blistering is inevitable.
After understanding the causes of drumming and pinholes, find a suitable solution.
(Paint drumming)
Solve from two aspects: strengthening construction management and correct painting method of paint
1.
Avoid bad weather such as high temperature and humidity during construction, keep the surface humidity of the substrate above 3℃, and the relative humidity not higher than 85%;
2.
The substrate is treated thoroughly, the surface is kept clean, and there is no residual electrolyte, dust, oil and other impurities that affect the adhesion of the coating;
3.
(Key points) When brushing the paint, use multiple thin coatings to increase the brushing time, so that the solvent between the layers is fully volatilized, and the residual amount is reduced;
4.
Brushing with cross method to ensure uniform paint film thickness;