The reflection characteristics of colored anodic oxide film of aluminum and its alloys (hereinafter referred to as colored anodized aluminum surface) are different from those of other objects. Because the color of colored anodized aluminum has the characteristic of conditional color development, that is, when the two colors are observed at a certain angle or under a certain light source, they will show one color, and when the observation angle or light source changes, the two colors will no longer be the same. Therefore, the color difference estimated by visual observation will be seriously affected by the observer and lighting conditions, resulting in the instability of aluminum profile coloring quality. Developing an instrument to effectively evaluate and control the color difference of colored anodized aluminum is a problem to be solved by alloy aluminum profile manufacturers and decoration engineering.

At present, musnencolor system is widely used as a method of classification and calibration of surface color in the world. Any color can be calibrated with the three coordinates of hue, lightness and chroma in Munsell color space. Colorimeter is an instrument that simulates human eyes and quantitatively describes color. CIE1976 (L * a * b *) uniform color coordinate system is widely used. (L * is the lightness coordinate and a * b * is the chromaticity coordinate). However, due to the particularity of double-layer reflection of colored anodized aluminum film, there is no clear direct connection between the application of monselka's "visual observation method" and the commonly used "instrument test method".

Therefore, we have designed a spectrophotometer with reasonable photoelectric sensor, which can simply judge the depth and uniformity of coloring by measuring the surface brightness coefficient of colored anodized aluminum (different lightness is sensed by human eyes). The measurement results are expressed by coloring depth. In this way, it is possible to design the instrument to be practical, simple and reliable, low cost, and overcome the shortcomings of visual observation method at the same time.

A new spectrophotometer for aluminum color detection

Take the color difference measurement of copper plate with CS-650 as an example.

Table 1 color difference value and visual perception difference of human eyes measured by CS-650 spectrophotometer

Aluminum profiles in other colors, such as silver white, blue black, golden yellow, etc., also roughly conform to the above results. Only change the measurement selection key of the instrument accordingly.

Color difference is one of the two important indexes to evaluate colored anodized aluminum (commonly known as aluminum profile). Because the anodized aluminum surface has the double reflection characteristics of reflection from the metal substrate, there is no unified international standard for the "instrument test method" of aluminum profile color and color difference in the world. "Visual observation method" has been used until now. The successful development of CS-650 spectrophotometer will be a powerful tool for evaluating aluminum profiles and ensuring the coloring quality of aluminum profiles. The spectrophotometer is also suitable for testing the coloring depth and uniformity of other color coatings and other opaque color objects.