bubbleDuring the coating process, the surface of the coating film is bubble-like bulging, or bubbles are generated in the coating film. This defect is prone to occur during the drying process.
bubble
The bubbles caused by stirring or the bubbles caused by the evaporation of the solvent remain in the coating film without disappearing during the coating film formation process, collectively referred to as bubbles.
blister
The defect that is absorbed by the bottom village or the bottom coating or contains water, solvent or gas, so that the coating arches in a bubble-like arch during the drying process (especially drying), and the blistering of the coating surface caused by the water under the coating film is called blistering.
Solvent bubbles or air bubbles
composedCoating filmThe traces of bubbles produced by the solvent or air on the coating surface are called solvent bubbles or air bubbles.
Substrate bubbles
Blistering of the coating surface caused by the substrate is called substrate bubbles
Electrophoresis bubbles
The phenomenon of air bubbles in the ED bath liquid adhering to the inner surface of the coated object (such as truck covers) and forming bubble traces on the electrophoresis coating film after drying is called electrophoretic bubbles.
1. Etiology
1) The thinner volatilizes quickly, and the viscosity of the coating is high.
2) The drying time is short, and the temperature rises too quickly when the coating is dried.
3) The substrate (e.g. wood, fiberglass), the undercoat (especially the putty layer) or the surface to be coated contain (or remain) solvents, moisture or gases.
4) Stir the gas mixed into the paint before it is released, or mix it with air when brushing or scraping.
5) Thickly applied putty layers, or broken crevices, fail to seal.
2. Prevention
1) Use the thinner specified by the paint factory, and the viscosity should be selected according to the coating method, and should not be too high.
2) Dry according to the specified time, and the temperature should not rise too fast when the coating is dried.
3) The substrate, bottom layer or coated surface should not contain moisture, solvents and gases, and should be dry and clean.
4) Wait for the air bubbles in the paint to be released before painting.
5) Inspect and re-seal the gaps and putty layers of the damaging car body.
Remedy
Air bubbles are a destructive disadvantage of the coating film, which can only be eradicated and re-prepared on the surface; Scrape putty and sprayLacquer.
Note: Example of substrate bubbles: Spray low aminoalkyd resin enamel on wooden truck cargo pieces at 90~150°CAfter baking and drying, a large number of medium and large air bubbles are generated on the coating surface, while there are no bubbles on the metal fasteners under the same process conditions. sickness
Cause:1) The wood parts are porous, and the moisture content is ≤15%; 2) The surface of the aminoalkyd paint dries quickly, the wood substrate heats up slowly, and absorbs solvents.
Blistering, prickly heat
A part of the coating film bulges from the surface or base coat to be applied, contains moisture or air inside, and is a size of 77 or $77 in diameter or in large bulks.
Bulging
It is smaller in diameter and has a prickly heat shape, which is called prickly heat. The coating film contains water and air inside, and the granular foaming is called bulging.
Contamination blistering
The phenomenon of large pieces of paint floating due to the contamination of the painted surface is called pollution blistering.
1. Etiology
Even a good paint film can still be penetrated by moisture. When moisture penetrates the paint film, it may form enough pressure to weaken the adhesion between the different coating films, or the adhesion of the overall coating to its bottom village, and as a result, bubble-like protrusions containing water may be formed.
1) The surface has been polluted before painting, especially in the coated surface residual sweat, fingerprints, salt alkali, sanding ash and other hydrophilic substances.
2) The water quality of the last water used to clean the surface to be coated is poor and contains impurity ions.
3) The coating film of the paint used has poor water resistance or moisture resistance.
4) The coating is not cured sufficiently. The paint surface is exposed to humid climates or high humidity before it is truly dry.
5) The thickness of the primer and topcoat coating is insufficient, and the thinner is used incorrectly.
6) Continuous exposure to severe humid climate and high humidity environment, such as in the rainy season, the coating film is easy to blister.
In addition, damage to the paint film that protects the upper surface, improper maintenance of the vehicle (residual surface detergent) and prolonged parking of the vehicle in poorly ventilated garages will accelerate the blistering of the coating.
Although the blistering is affected by external conditions (humidity, temperature), the prickly heat can disappear from time to time (difficult to see with the naked eye), but it has destroyed the integrity of the coating, and over time, some water vapor has caused rust under the coating, and there is no remedy but to remove the coating and recoat.
2. Prevention
On the basis of the selection of automotive coatings with excellent water resistance, in order to make the coating work can be greatly anti-foaming (orIt is important to observe the following points.
1) All surfaces should be clean and pollution-free, and no hydrophilic substances are allowed to remain.
2) The water used for grinding should be changed frequently, and all the grinding dirt has been removed, and the final washing should be done with deionized water or
Distilled water. If you use tap water for rinsing, be sure to wipe and blow dry with a clean cloth before drying.
3) When not wearing gloves, do not touch the surface of the coating with bare hands.
4) Keep the paint shop at the correct temperature. Before painting, the vehicle needs to reach the temperature in the paint booth.
5) The compressed air should be clean and not polluted.
6) The spraying primer and topcoat should reach the specified sufficient thickness.
7) There should be enough drying time between each layer, and the coating film should be dry thoroughly.
8) The coating needs to be fully dried before it can be exposed to high temperature and high humidity.
Example: In the 60s of the 20th century, before the adoption of electrophoretic primers, blistering was one of the common paint film defectsAt the beginning, alkyd resin primer and epoxy resin primer are used, and then paint pretreatment, only degreasing + washing, no phosphating treatment or phosphorusPoor management of chemical treatment, poor control of cleaning water quality (pollution degree), resulting in uneven phosphating film and water-soluble saline-alkali traces on the coated surface; Whenever the high temperature and humidity season (summer), the coating film of the car will produce flakes or streaks of "blistering" soon after leaving the factory (or in the warehouse). After the alkyd resin coating system, the phosphating treatment and electrophoretic primer (especially the cathodic electrophoresis primer in the century'" years), after adding a good amino topcoat and strengthening the coating management, the water resistance and moisture resistance of the coating have been significantly improved, and the "blistering" disadvantage has been basically eliminated.
