Reasons for Color Inconsistency in Steel Barrel Coating
The impact of painting construction environment on topcoat color difference
During the process of spray painting, the temperature and humidity of the spraying environment have a significant impact on the color difference of the paint. In other words, when the same bucket of paint is sprayed in different temperature and humidity environments and measured for color difference after drying, there will be significant differences in ΔE. This is because the temperature and humidity of the environment affect the volatilization rate of paint solvents. With high temperature, solvents evaporate quickly; with low temperature, solvents evaporate slowly, thus affecting the drying time of the paint film. Similarly, if the humidity is high, solvents evaporate slowly, while if the humidity is low, solvents evaporate quickly, which will also affect the drying time of the paint film and result in color difference.
The influence of paint film thickness on color difference
During the spraying process, the thickness of the paint film is greatly affected due to differences in spraying distance, paint volume, gun speed, or operator skills. Some areas may have thicker paint film, some areas may have thinner paint film, and in some areas, the bottom may even be exposed. The areas with thicker paint film appear full and glossy, while the areas with thinner paint film are not shiny and have poorer gloss, resulting in color difference.
The influence of compressed air pressure
During the coating process, the difference in compressed air pressure has a significant impact on the color difference of the paint film. This is because the size of paint atomization particles is affected by the magnitude of air pressure. The smaller the compressed air pressure, the worse the atomization effect, and the larger the atomized paint particles. As a result, the paint film sprayed on the substrate is not smooth, but rough and dull. If the compressed air pressure is relatively high, although finer atomized particles can be formed, the paint mist will be scattered everywhere, which not only affects the quality of the paint film, but also affects the paint application rate and causes color difference.
The influence of drying temperature
During the drying process of the paint film, the temperature has a certain influence on the color difference of the paint film. This is because the drying process is a physical and chemical process from quantitative change to qualitative change, and the temperature and time greatly affect this process of physical and chemical change. With low temperature, the crosslinking reaction proceeds slowly. If the temperature is below the specified range, the paint film cannot dry completely, thus affecting the performance of the paint film. With high drying temperature, the crosslinking reaction process is accelerated, but due to the fast formation of the paint film, the leveling effect of the paint film will be compromised, resulting in a rough surface.
The influence of solvent evaporation rate
The evaporation rate of the solvent is directly related to the boiling point of the solvent. The higher the boiling point of the solvent, the slower its evaporation; the lower the boiling point of the solvent, the faster its evaporation. If the same paint is sprayed with solvents of different boiling points under the same process conditions, the resulting paint films will have color difference. This is because the evaporation rate of the diluent affects the drying time of the paint film, and thus affects the leveling of the paint film.
The influence of uneven mixing during construction on coating color difference
Before construction, the paint needs to be mixed evenly. The purpose of mixing is to stir up the sediment at the bottom of the bucket and mix it thoroughly. If the paint is not stirred, the colored dyes at the bottom of the bucket will settle and cannot be evenly dispersed in the paint, which will affect the covering power of the coating and also result in color difference.
The influence of other factors
Different batches of colored paints and varnishes may cause color difference in paint coatings due to differences in paint production process conditions and raw material factors. In addition, the interval between the wet-on-wet spraying process of paints and screen printing inks will also have an impact on the paint coatings. The vertical wind speed in the spray booth also affects the color difference of the topcoat.
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