As an opaque object, when visible light shines on it, the coating will absorb part of the light and reflect part of the light. The color of the film as we perceive it. According to the classification of colorimetry, it belongs to the category of "surface color".
If the coating film reflects all the visible light of all wavelengths irradiated on it (in fact, the reflectance rate is 80%~90%), the coating film will appear white. On the contrary, if Tumo absorbs all the visible light of all wavelengths irradiated on it (in fact, the reflectivity should be less than 4%), the coating film will be black. However, if all wavelengths of light in visible light are evenly absorbed by the coating film and partly reflected at the same time, the coating film will appear gray. The greater the amount of light absorbed, the darker the gray; the greater the amount of reflected light , the lighter the gray. In this way, a series of colors from white-light gray-medium gray-dark gray-black constitute a type of coating color - non-color.
If visible light is selectively absorbed and reflected when irradiated on the coating film, that is, light of certain wavelengths is absorbed and light of other wavelengths is reflected, the coating film will show the color of partially reflected light. For example: the coating film selectively reflects the light of 480~56Cnm wavelength, and relatively absorbs the light of other wavelengths, then the coating film will appear green. When the object reflects the long- wavelength light of the visible spectrum and absorbs most of the short-wavelength light below 580nm, the coating will appear red. The result of selective absorption and reflection of visible light by the coating film constitutes another type of coating film color—color.
The color of the coating film is not its own property, but is affected .
(1) Influence of light source
We know that the coating film reflects and absorbs the light that shines on it, and the light waves that actually enter the human eye in different colors are always determined by the composition of the incident light. Therefore, the same film will display different colors depending on the light source. For example, the coating film that is purple under sunlight has a blue tint under moonlight; and it has a red tint under incandescent light; therefore, the color that looks satisfactory under night light may not necessarily look satisfactory under daylight. . This is the reason why the saying "don't look at the color under the lamp" is usually said . Usually when we use the method of visual inspection to compare the color, the color of the paint film refers to the color of the film under natural sunlight (that is, white light). Different (such as A, C, D, D50, F65, F7, F11, F12 and other light sources), the values of the measured color characteristics are also different. Therefore, when we compare the color difference of the two coating films, we need to do it under the same light source. When discussing or studying the color of a coating film, it is necessary to take into account the specified incident light source in order to arrive at a correct assessment.
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(2) The influence of color contrast
The interaction of different colors in adjacent regions of the field of view is called color contrast. For example, if a small piece of yellow is projected on a dark background, in the eyes of the observer, it is undoubtedly yellow; but when the eyes look at a large area of strong red light for a period of time, and then look at the original yellow light, the yellow light will appear at this time. After a period of time, the eyes will recover , the green will gradually fade, and after a few minutes, it will become the original yellow again. Therefore, if there are other colors of light in the surrounding , the influence of these lights on the observed color should also be considered.
Because of the influence of the light source and color contrast factors on the observation of the color of the coating film, the national standard GB3181-82 of the People's Republic of CHINA "Coating Film Color Standard Sample" stipulates that "the light when observing the color of the coating film needs to be "natural day Light", and pointed out that the natural daylight system uses diffuse sunlight, and the light of the northern sky with some clouds is not allowed to have strong reflected light (such as red brick walls, green trees, etc.) around the colorimetric field of view. .The illuminance should be uniform around the sample board to be compared , and the illuminance at the colorimetric position should not be less than 1000lx, and direct sunlight should be avoided."
(3) The influence of the observer's physical and psychological conditions
Color science is a multidisciplinary field, not only related to physics (light), but also related to physiology and psychology. The eyes of normal people can distinguish more than 2000 kinds of colors. It can also sharply . However, different observers have different perceptions of the same color, and the same observer has different feelings and reflections on the same color due to different psychological states. Therefore, for the "manual visual inspection" method of color comparison , it is often difficult to rule out the human interference to the correct evaluation of the color. It is precisely for this reason that it is necessary to develop a new color measurement method.
