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The main factors affecting the curing speed are coating type, coating thickness, curing method, curing conditions, curing equipment and specific curing procedures.
1, coating type
under the same curing conditions, the type of coating is different, curing speed is very different.
generally speaking, volatile paint cures fast, oily paint cures slowly
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of polymerized paint is very different. The photosensitive paint cures fastest in polymerized paints, while other polymerized lacquers are mostly between volatile and oily paints. Volatile paint and acid-cured amino alcohol paint are commonly used when using mechanized pipeline for decoration.
2, coating thickness
In the process of coating, the coating is basically not formed at once, usually using the method of multiple times thin coating (e.g. oily paint generally applied about 35 m at a time, nitro paint about 15 m, etc.).
Under the same curing conditions, when the thin coating is cured, the internal stress is small and the resulting coating defects are less, while when the coating is too thick, the internal stress is large, easy to produce wrinkles and other defects, and due to the volatile solvent, the coating shrinks, resulting in uneven gloss, internal non-curing, etc.
practice has proved that, in addition to polyester paint, other paints formed by multiple coatings, compared with the same thickness of paint film formed by a one-time coating, its physical properties are better.
3, curing conditions
1) curing temperature
the curing temperature plays a decisive role in the curing speed of most coating coatings.
when the curing temperature is too low, solvent volatilization and chemical reaction is slow, the coating is difficult to cure. Increased temperature accelerates solvent volatilization and water evaporation, accelerates coating oxidation and thermochemical reactions, and accelerates coating curing. However, the temperature cannot be increased indefinitely because the temperature is not directly related to the curing speed. When the curing temperature is too high, the curing speed does not increase significantly, but will make the paint film yellow or darken.
, temperature also affects the substrate during coating curing. The substrate is heated, causing changes in moisture content, shrinkage and deformation of the substrate, and even warping and cracking. Volatile lacquer coating, curing temperature of more than 60 degrees C, the solvent is fiercely volatile, the surface quickly dry solidified, the internal solvent vapor reached the surface easy to produce bubbles. Therefore, when using artificial curing method, the surface temperature generally does not exceed 60 degrees C.
2) Air humidity Air humidity should be appropriate.
temperature is too high, the evaporation rate of moisture in the coating decreases, and the solvent evaporation speed decreases, which slows down the curing speed of the coating. Most coatings are most suitable for curing in air with a relative humidity of 45% to 60%. If the air in the drying and curing site is humid, not only does it slow the curing process, but the resulting lacquer film is hazy and has other defects.
high relative humidity, the coating is prone to "whitening" phenomenon. Due to oily paint, when the relative humidity exceeds 70%, the effect on the curing speed of the coating is significant than the temperature. During the curing process, the internal stress produced by the coating is related to its relative humidity.
3) Ventilation conditions
coating curing should have appropriate ventilation measures, so that the coating surface has suitable air circulation, timely discharge of solvent vapor, increase air circulation can reduce curing time, improve curing efficiency, to ensure curing quality.
4) Air flow speed
air circulation is beneficial to the curing of the paint film itself. In closed, solvent vapor concentration of high environment, paint film curing slowly, or even dry. Ventilation facilitates the evaporation of paint film solvents and the removal of solvent vapors, and ensures the safety of natural curing sites.
forced air drying chamber is caused by ventilation to circulate hot air, its drying curing effect depends to a large extent on the air flow speed. The higher the air speed, the better the heat transfer. The better the heat transfer effect, hot air drying usually uses low air flow speed, generally 0.5 to 5m/s, temperature of 30 to 50 degrees C.
direction of air flow is also very important, air flow and coating direction in parallel and vertical forms, according to experiments, vertical air drying is better than parallel air delivery.
4, external conditions
used for polymerization into a film coating, the coating curing into a complex chemical reaction process.
curing speed is related to the properties of the resin contained, the curing agent and the amount of catalyst added. External conditions, such as temperature, infrared, ultraviolet, electron rays, etc., can often speed up this reaction. The size of the effect of external conditions depends on the degree to which the external conditions are suitable for the properties of the coating. If the photo-curing coating is exposed to strong ultraviolet light, it only takes a few seconds to cure into a film. If infrared or other heating methods are used, it is difficult to cure, or even not cure. Also such as electron-ray curing coating, its coating in the electron accelerator emitted by the electron ray exposure, faster than photosensitive paint curing, while other coatings do not respond well to the electron beam. Therefore, the coating curing method should be selected according to the nature of the coating used.