When automobile maintenance enterprises carry out paint repair, even if the color matching is carried out according to the standard formula provided by the coating supplier, the color guide plate after spraying by technician often has obvious color difference with the standard color plate provided by the coating supplier. Fig. 1). According to the different types of coatings, the differences are mainly reflected in the following aspects.
(1) For plain paint, the main difference lies in the hue, lightness and chroma (the three attributes of color).
(2) For metallic paints, it mainly depends on the structure and mixing ratio of aluminum pigment, the gloss at three observation angles (direct angle, intermediate angle and indirect angle) and the difference between colored pigments.
(3) For pearl paint, the differences among pearl particles (size, shape, flicker), coating times of nacre layer, color and three observation angles are mainly analyzed.
2. Problem analysis
First of all, there may be slight color difference in the paint of new cars produced by automobile manufacturers, mainly due to the following reasons.
(1) Different batches of OEM high temperature paint have different colors.
(2) The influence of coating viscosity, solid content, spraying site size, number of coating machines, coating efficiency, environmental wind speed and other factors.
(3) During the transportation and storage of new cars, the color changes slightly due to environmental factors.
However, generally speaking, the gap between the standard color plate provided by the coating supplier and the actual vehicle should be controlled.
However, there is a color difference between the color palette after spraying and the standard color palette provided by the coating supplier. There are the following reasons.
(1) Different coating suppliers have different requirements for the construction process, including four spraying elements (angle, moving speed, distance, spraying range), spray gun setting, spraying layer number and dry wet spraying. The technician's spraying operation did not meet the coating supplier's construction process requirements.
(2) The color mixing technician did not adjust the self-regulation.
(3) The temperature, humidity and wind speed of the spray booth do not meet the requirements, which will affect the color.
(4) The same gray value of color plate as standard plate is not used.
(5) The storage temperature of the color masterbatch of water-based paint does not meet the requirements, and the color masterbatch appears anti coarseness after the service life.
(6) The color masterbatch was not stirred evenly, and the new masterbatch was not stirred manually, and then the mixing cover was installed.
(7) The remaining coating cured at the injection port of paint tank was not treated in time.
8) The electronic paint mixing scale is not placed horizontally, too much paint scale affects the accuracy, or the electronic paint mixing scale has fault.
(9) The amount of coating is too little, which leads to the weight deviation of each color masterbatch.
(10) When spraying the shade guide, the shade guide is not fixed, but sprayed randomly in the hand.
(11) There is no blower (Venturi type) when spraying the shade guide plate with water-based paint, which results in that the surface coating of the paint film is not completely dry and the varnish is sprayed.
(12) There is no color separation plate to determine the spraying method and the number of layers of the color guide plate.
(13) The technician used a color masterbatch other than the standard formula for color matching.
(14) The color comparison between the color guide plate after spraying and the standard color plate was not carried out under the standard light source.