The reasons, preventive measures for paint film whitening in the super humid weather in South China
I. The main reasons of film whitening
Solvent evaporation is an important process in the drying process of solvent-based paint. When solvent evaporates, it will absorb lots of heat, cooling the sudden reduce of surrounding temperature. It's like the process we wipe hands with alcohol where the skin temperature will be lowered due to the heat absorption during alcohol evaporation. When the temperature is low, the steam in the air will condensate to small water drops, forming a white layer on the coat, which is called whitening.
II. The main factors causing whitening
From the whitening process, we can see that there are two important factors causing coat whitening:
1. Evaporation of solvent: the quicker the solvent evaporation is, the faster the temperature will be lowered and the larger will be the lower degree, thus, under the same humidity, the more serious is the whitening phenomenon.
2. Humidity of air. Similarly, the higher the air humidity is, the higher content of steam, thus under the same temperature, the more water drops are condensate, and the more the whitening phenomenon is.
Besides the volatile speed of solvent in each component and the weather, the coating quality and the application equipment condition (e.g. if there is filtration and drying equipment for compressed air and the equipment's effect) are also of great importance.
III. Whitening situations
Whitening affects the furniture quality. There are usually two whitening situations in paint application:
1. The paint film whitens immediately after application, some even like milk. Under such circumstance, the whitening many disappear partially or totally after the film dries, or the whitening still exists.
2. The other situation is that the film is not whitened during application but is whitened slowing during drying process.
IV. Influence of whitening
Whitening has great influence on the production and quality of furniture. If the whitening phenomenon cannot be eliminated after the coat dries, rework will be needed, which will affect production efficiency and waste large amount of manpower and material resources.
There is fierce competition in today's furniture industry and the profit is becoming lower and lower. High rework rate will increase production cost, reducing greatly the manufacturer's competitiveness. Even if the whitening phenomenon can disappear after the coat dries, there is still hidden problem of paint film quality. After a long time, the film may have whitening and peeling off problem, especially for PE series products.
Moreover, gloss loss usually accompanies whitening, which is also a big quality problem in coating application process. The existence of these hidden problems may increase after-sale services rendering and the reputation of the brand will also be affected.
V. Preventive measures of whitening
According to the main factors of whitening phenomenon, measures can be taken from aspects of paint drying speed adjustment and environment temperature and humidity adjustment to solve and prevent the whitening problem.
1. Lower the indoor humidity of application site and avoid application in environment of high humidity, for example, use dehumidifier to reduce humidity.
2. Use heating equipment like heater or infrared lamp to increase the temperature of work piece surface, so that the solvent can evaporate with the heat in the surrounding environment to stabilize the surface temperature of the coat to prevent whitening.
3. Pay attention to the cleaning and maintenance of surrounding environment and equipment, and avoid the product after application to have contact with environment with high humidity or steam.
4. Check the air compressor, install water filter and drain the water inside the filter regularly to avoid the moisture to mix into the compressor to cause whitening.
5. Avoid mixing water into the container and coating. Avoid to store the coating thinner in outdoor to avoid invasion of moisture.
6. When the humidity changes, the application thickness shall be also adjusted. When the humidity is high, avoid too thick coat.
7. Select proper coating variety. The formula of paint is different in different seasons, mainly in the drying speed. The paint designed for winter shall be dried faster, and will be easier to have whitening phenomenon.
8. Relatively speaking, under the same condition, nitrolacquer is easier to have whitening phenomenon. But the whitening phenomenon will disappear if you wipe the whitened paint film surface with cotton and alcohol after the film is fully dried.
9. Add a proper amount of BCS can reduce or eliminate the whitening phenomenon to some extent.
10. During on-site application, once the whitening phenomenon is found, the worker shall pay high attention to it and stop application immediately. Find the causes of the problem, correct and then apply again. Otherwise, it will be difficult to recover after the problem appears.