The main factors affecting the curing of paint

The main factors affecting the curing of paint

2018-01-08

Factors affecting the curing speed are the main types of paint, coating thickness, curing methods, curing conditions, curing equipment and specific curing procedures.

1.The type of paint
Under the same curing conditions, the type of paint is different, the curing speed is very different.
Generally speaking, the volatile paint curing fast, oily paint curing is slow.
Polymeric paint is very different. Polymeric paint in the light-cured paint the fastest curing, and other polymer-based paint is more than between the volatile paint and oily paint. When use mechanized lines for finishing, the volatile paint, acid-cured amino acid alkyd paint is more commonly used.

2.Coating thickness

In the coating process, the coating is basically not formed once, usually using many times thin coating method (such as oil paint generally coated about 35μm, nitro paint 15μm, etc.).
Under the same curing conditions, the thin coating in the curing, the internal stress is small, the formation of less coating defects; and the coating is too thick, the internal stress is large, easy to produce wrinkles and other defects, and because of solvent evaporation , Coating shrinkage, resulting in uneven gloss, the internal non-curing and so on.
Practice has proved that, in addition to polyester paint, the other paint through the formation of multiple paint film, and a coating formed by the same thickness of the film compared to its physical properties is better.

3.Curing conditions

1)The curing temperature plays a decisive role in the curing rate of most coating coatings.
When the curing temperature is too low, the solvent evaporation and chemical reaction is slow, the coating is difficult to cure. Improve the temperature, can accelerate the evaporation of solvents and water evaporation, accelerated coating oxidation and thermal chemical reaction, coating curing speed. It cannot increase the temperature indefinitely, because the temperature and curing speed is not directly proportional relationship. Curing temperature is too high, the curing speed is not significantly improved, but will make the film yellow or darker color.
Not only that, the temperature in the coating curing process also has an impact on the substrate. Such as substrate heat, causing moisture content changes, the substrate shrinkage deformation, and even warping, cracking. Volatile paint coating, curing temperature exceeds 60 ℃, the solvent is volatile, the surface quickly dry, the internal solvent vapor to reach the surface when prone to bubbles. Therefore, the use of artificial curing method, the surface temperature is generally not more than 60 ℃.
2)Air humidity should be appropriate
The temperature is too high, the evaporation rate of the water in the coating decreases, the solvent evaporation rate slows down, which will slow down the curing speed of the coating. Most of the coating in the relative humidity of 45% to 60% of the air curing is most suitable. If the drying and curing sites are humid, not only the curing process is slow, but also the formation of the film is hazy and other defects.
When the relative humidity is high, the coating is easy to produce "whitening" phenomenon. Due to the oily paint, when the relative humidity is more than 70%, the impact of the curing rate of the coating than the temperature of its significant impact. During the curing process, the resulting internal stress is related to its relative humidity.

3)Ventilation conditions

Coating curing should have the appropriate ventilation measures, so that the surface of the coating has a suitable air circulation, timely discharge of solvent vapor, increase air circulation can reduce the curing time, improve curing efficiency, to ensure the quality of curing.
4) Airflow speed
Air circulation is beneficial to the film itself. In the environment which is closed and the solvent vapor concentration of high, the film curing is slow, or even dry. Ventilation is conducive to solvent solvent evaporation and solvent vapor removal, and to ensure the safety of natural curing sites.
Forced air drying chamber is caused by ventilation caused by circulating hot air, the drying curing effect depends to a large extent on the air flow rate. The greater the air speed, the better the heat transfer effect. Heat transfer effect is better, hot air drying is usually used low air velocity, usually 0.5 ~ 5m / s, the temperature is 30 ~ 50 ℃. b. Airflow direction.
The direction of air flow is also very important. The direction of airflow and coating is parallel and vertical. According to the experiment, the hot air drying of the vertical air supply is better than the parallel air supply.

4.External conditions

For the polymerization of curing film coating, the coating cured into a complex chemical reaction process.
The curing rate is related to the nature of the resin contained, the amount of curing agent and catalyst added. The external conditions, such as temperature, infrared, ultraviolet, electron beam, etc., can often accelerate the progress of this reaction. The size of the external conditions of the role, but also depends on the external conditions and the nature of the coating to adapt to the extent. Such as light-cured coating and then strong ultraviolet radiation, only a few seconds can be cured film. If the use of infrared or other heating methods, it is difficult to cure, or even not curing. Another example is the electron beam curing coating, the coating in the electron accelerator emitted by the electron beam irradiation, curing faster than the photosensitive paint, and other coatings on the electron beam response is not strong. Therefore, the coating curing method according to the nature of the paint used to choose a reasonable.