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2024-12-17
Spraying paint on a car can not only increase the beauty of the car, but also attract the attention of consumers. If there is color difference in the car paint, it will not only affect the consumer's choice, but also reduce the competitiveness of the car product and affect the brand's reputation. So, what is the matter with the color difference of car paint? How to detect the color difference of car paint?
Car paint
1. Influence of paint materials
According to the different types of paint used, automotive paint can be divided into monochrome paint, metallic paint and pearlescent paint. The color difference of monochrome paint is the easiest to control, while the color difference of metallic paint and pearlescent paint is relatively difficult to control. For metallic paint, its reflection is mainly achieved by flaky aluminum powder. When the aluminum powder is arranged parallel to the substrate, the metallic color and sparkle will vary with the change of the viewing angle.
2. Impact of spraying environment
The temperature and humidity of the spray booth have a certain impact on the color difference of the paint on the exterior of the car. When the temperature rises, the paint film dries faster, and the color difference of the paint on the exterior of the car may be slightly affected. When the humidity is on the rise, the humidity of the paint film is higher, and the color difference of the paint on the exterior of the car will be greatly affected.
3. Human factors
Manual spraying is difficult to ensure the stability of color difference, so automobile manufacturers will use automated spraying equipment for paint spraying. During the spraying process, color difference will occur due to the influence of spraying parameter settings and measurement pressure.
4. Equipment factors
The influence of the spraying equipment status on the color is worth paying attention to, and the color changing valve and metering pump of the automatic paint spraying equipment are particularly important. During the paint spraying process, the color changing valve may get stuck, resulting in failure to close completely, causing color cross-talk. In addition, the deviation of the paint spraying metering pump will cause the deviation of the actual spraying flow of the paint, thereby affecting the paint film thickness and causing color difference problems.
Car paint color difference detection
Due to the different exterior substrates and the different types of paint used, the colors of the two parts must be completely matched, and the evaluation of color difference has many subjective factors. Therefore, high requirements are placed on the control and evaluation of color consistency. Good color difference evaluation and control methods can guarantee the color matching of the whole vehicle. The detection of color difference of traditional automobile body paint is visually evaluated by human eyes under a specific light source. This evaluation method is affected by many factors and can easily lead to inaccurate evaluation results. Therefore, in order to improve the accuracy and objectivity of color difference detection, professional color measuring instruments can be used, and multi-angle colorimeter is undoubtedly the best choice.
The angle displayed by the multi-angle colorimeter is the angle formed by the light reflected from the surface of the object and the observer's line of sight on the surface of the product. In the instrument, sensors are arranged at different observer positions. The light signals are received by the sensors and converted and calculated to obtain specific values. Therefore, the measurement values of multiple angles can be obtained through one measurement. The commonly used angles are 15°, 25°, 45°, 75° and 110°. At present, most automotive paints use metallic paints. When observed from different angles, there are different degrees of color differences. Therefore, for metallic paints, a multi-angle colorimeter is needed to measure multiple angle values. For positive solid color paints, a single angle of 45° is sufficient. The specific measurement steps are as follows:
1. Define the measurement points and select the same points as the visual evaluation points for measurement. The multi-angle colorimeter has requirements for the angle of incident light, so the direction of incident light needs to be defined during measurement;
2. Calibrate the instrument, mainly the black and white standard plates; ensure that the instrument measurement error is minimized.
3. Take the standard value on the standard color plate. The method of taking the value is: take the average value after multiple measurements. Measure the same point on the standard plate 20 times, measure 5 values each time, and take the average value as the standard value. Note that among the 100 data, if the difference is too large and the fluctuation is greater than 0.2, it is necessary to remove the unqualified points or re-measure and take the average value.
4. Measure and record the data. If only △E is tested, then only the △E value needs to be recorded. In order to more accurately reflect the actual deviation, the △L, △a and △b values can be tested separately, and the values at different angles can be recorded.
5. Result analysis. If only △E value is evaluated, the range of 0-0.5 is generally selected as the qualified limit. 0.5-1.0 is a small difference, which is somewhat acceptable. 1.0-2.0 is a moderate difference, which is specifically accepted. 2.0-4.0 is a difference, which is a significant difference, which is specifically accepted. Above 4.0, it is not accepted. You can also calculate the △L, △a and △b values of each angle, and calculate the qualified rate by comparing the acceptance limit to determine whether it is qualified.
