Causes and prevention methods of whitening of coating film surface
Cause analysis: Volatile paints such as nitro and perchlorethylene often cause whitening during construction, and amino and other paints sometimes also appear whitening. The main reason is that the thinner volatilizes too fast, causing the surface temperature of the coating to drop sharply, and The other is the whitening caused by the decrease of the solubility of the resin caused by the imbalance of the true solvent and the thinner in the thinner, which is called whitening of the resin. Whitening occurs in daily construction, and the reasons are roughly as follows:
Construction in a climate or environment with high temperature and high humidity; the proportion of each component in the thinner is out of balance, such as the proportion of diluent in banana water is too large, and the proportion of true solvent is too small; the temperature of the construction site is too low and the ventilation is too strong; water is brought in during construction in paint.
Prevention and control methods: Avoid construction under high temperature and high humidity (temperature above 30°C, relative humidity above 80%); construction should also be avoided in heavy rain or morning foggy weather; hot air or heating can be used during the mildewy rainy season in the south Heating to reduce the relative humidity of the air, or heating the workpiece to 40 ℃, and reducing the gas pressure of the Spray Gun, or adding a mass fraction of 5% to 10% moisture-proof agent in the paint to solve the problem. For those that have begun to turn white, you can spray a layer of anti-whitening water; use a special thinner or increase the proportion of true solvents in the mixed thinner, such as butyl acetate or cyclohexanone, etc.; in winter construction sites, the ambient temperature should be raised to less than If it is lower than 16°C, reduce the ventilation appropriately to ensure the indoor temperature; abide by the process specifications and strictly prevent moisture from being brought into the paint.
Causes and prevention methods of bleeding of coating film
Analysis of the cause: The penetrating power of the topcoat solvent is strong, so that part of the pigment of the primer is dissolved and floated on the surface of the topcoat, so that the color of the topcoat is polluted; the paint contains pigments or organic dyes that are prone to bleeding, such as red primer. When applying white (or light) paint. The red is easy to float out, making the white pink, yellow or orange; the primer is not completely dry; there are other stains on the surface of the primer, such as words, numbers, etc. written in colored chalk, and dyeing such as dragon Dan purple; Spray Guns and other tools Soluble pigments remain unwashed and contaminate the paint.
Prevention and control methods: If bleeding occurs, the construction should be stopped immediately. After the sprayed paint is dried and smoothed, it can be isolated with a layer of shellac paint (this is only suitable for volatile paints). Shellac paint cannot be used for high-temperature baking paints such as amino, or coatings with high operating environment and working temperature, because it will foam when the temperature exceeds 80°C. It can be sprayed with aluminum powder paint or polyvinyl alcohol paint for isolation and then sprayed. Topcoat; the bottom layer is effectively dried before applying topcoat; other pollutants, such as colored chalk, dragon violet, etc., must be effectively cleaned and polished before applying topcoat; tools such as Spray Guns must effectively clean soluble pigments, and then reuse.
