introduction
In the field of painting, the appearance characteristics of paint film is one of the important indicators to evaluate the quality of painting. In addition to gloss and color, fog shadow is also a key characterization property, especially for high-gloss coatings. This paper will introduce the definition of fog shadow, related standards, and the determination method of paint film fog shadow specified in ISO 13803 standard.

Purpose and significance of paint film mist shadow measurement
Fog shadow refers to the phenomenon of diffuse reflection caused by light irradiation on the surface of a high-gloss film. The ISO 13803 standard specifies the measurement range of fog shadows: applicable to coatings with a gloss value of 90 units (20° gloss) or more. The purpose of fog shadow measurement is to evaluate the surface diffuse reflection of high gloss coating and to evaluate the quality of coating on this basis.

Analysis of the importance of film mist shadow measurement for evaluating the quality of high gloss coatings

Relevant standard

ISO 13803:2000 specifies the method for determining the 20° fog shadow of paint and varnish film. The standard provides an accurate and repeatable method of determining fog shadows to ensure consistency and standardization of coating quality.

Method for determination of mist shadow in paint film
Test principle

The fog shadow measurement method described in ISO 13803 measures the fog shadow of the paint film by receiving the scattered light in the reflected light from both sides at an Angle close to 20°. This method can accurately evaluate the diffuse reflection of high gloss film at different angles.

Analysis of the importance of film mist shadow measurement for evaluating the quality of high gloss coatings

Operating essentials

Preparation of the test plate: Apply the color paint on the clean glass plate using a wet film preparation device with a specification of 150μm to ensure that the paint film is smooth.

Fog shadow determination: Three readings are measured at different positions of the test film parallel to the coating direction. If the error is less than 0.5 units, the average value is recorded as the linear fog shadow value. Otherwise, three more measurements are performed to record the average and limit values of all six values.

For coatings on non-glass substrates: After adjusting and calibrating the instrument, measure six times in different areas or directions on the template surface (excluding textured directions such as brush marks on the surface) and record its average value. If the error of six measurements is less than 1 unit value or 20% of the mean value, the mean value and the limit value are recorded. Otherwise, the test board is discarded.

Analysis of the importance of film mist shadow measurement for evaluating the quality of high gloss coatings

Result representation

According to ISO 13803, the average linear fog shadow value can be used to represent the fog shadow of the paint film. It may also be agreed to use the logarithmic mean of the fog shadow as a representation.

Significance and application

The measurement of mist shadow is of great significance in evaluating the quality of high gloss coatings. For coating with high decorative requirements, such as automobile coating, fog shadow is one of the important indicators to measure its appearance quality. The results of fog shadow determination can help to formulate a reasonable grinding dispersion time, select the appropriate additive and the concentration of the additive to ensure the high quality and consistency of the coating.

conclusion
In the field of coating, fog shadow, as an important characterization property, is very important for the appearance quality of high-gloss coatings. The ISO 13803 standard provides an accurate measurement method to assess the fog shadow of a film by measuring the scattered light in the reflected light from both sides at an Angle approaching 20°. The application of this method helps the coating industry to ensure the consistency and high quality of product appearance. At the same time, the film fog shadow measurement also provides a scientific basis for adjusting the process parameters and optimizing the formula, so as to improve the coating quality and customer satisfaction.