Introduction to Coating Color Detection

The national standard stipulates that the color of the paint film is evaluated by comparing the color and appearance of the paint film with the standard color plate and standard sample. Its determination method is as follows:

1. Standard sample method

According to GB1727-79 "General Preparation Method of Paint Film", the test sample and the standard sample are respectively prepared on the tin plate. Check under light, the distance between the eyes and the sample is about 30cm, and the viewing angle is about 120°~140°. Check the color and appearance according to the product standard. The color should be within the technical tolerance range; the appearance is flat and smooth.

2. Standard color plate method

Make a test sample of the product to be tested according to the regulations, after drying, overlap the standard color plate by 1/14 area, check under natural scattered light, the distance between the eyes and the sample is about 30cm, and the angle is 120°~140° (standard color). For details, please refer to Chapter 4 Paint Toning). If the color is between two standard color plates or close to one standard color plate, it is considered to be within the technical tolerance range.

Compared with the standard swatches, the method of distinguishing whether the color of the paint film meets the requirements by eyes is effective and convenient, but it can only do qualitative analysis. If the difference in color is not represented by data, it is impossible to transmit and store; In addition, the observation results are closely related to the observer's experience and psychological quality, and the naked eye is imperceptible to subtle color differences. 3. Color measuring instrument-color difference meter

It calculates the color data by measuring the reflection or projection spectrum of the standard color plate and the sample plate in the visible spectrum, and then can accurately judge the deviation degree between the sample plate and the standard color plate (knowing from the content of paint coloring, color matching can only be very close, not exactly the same),. At present, there are many types of color difference meters such as desktop and portable.

GB1186.1.2-89 and GB1186.1.3-89 "Measurement method of paint film color" stipulate that the color of paint film is measured by Spectrophotometer , filter Spectrophotometer and tristimulus value Colorimeter, which is the above-mentioned The photoelectric color difference meter is used to express the feeling of paint film color in numbers.

The portable multi-angle Colorimeter and multi-functional color matching software can make the angle-dependent heterochromaticity of automotive metallic glitter paint meet the requirements of no visual color difference at all angles for paint color matching. Now the new color difference meter can measure the color difference from five angles of 15°, 25°, 45°, 75°, and 110° respectively. The color matching software can edit, store, exchange and print the measurement results, etc. Some software can also design color recipes for certain swatches.

Figure 8_2l is an American X-Rite five-angle dynamic measuring instrument suitable for automotive metallic flash paint and pearlescent paint. Its characteristics are:

① Five-angle color measurement: 45° lighting, l5°, 25°, 45°, 75°, 110° five-angle measurement, angle accuracy ±0.15°, optical fiber signal transmission, can completely and accurately test metal, pearlescent and special effect coatings Color changes from different angles.

② Measurement data: Lab, △L△a△b, F1opIndex (dynamic index), Lch, △L△c△h, △F1opIndex.

③Dynamic rotation measurement: X-Rite's dynamic rotation measurement technology adopts a more accurate and durable optical system, which can measure all angles at the same time and enhance spectral resolution performance, durable, high precision, and good stability.

④ It can be used in conjunction with X-Rite professional quality control software to draw L*, a*, b*, C* or h·* value changes at different angles, and quickly determine the chromaticity value that deviates from the tolerance.

⑤ Inter-instrument difference: within 0.18ΔE, measure the average value of BCRA series plates; 0.35△E* maximum, measure any color plate; 0.15△E* maximum, measure gray color plate.

This instrument has been adopted by Shanghai GM, FAW-Volkswagen, Jinbei, Chongqing Isuzu, Zhuzhou Yamaha, Kansai Paint, Daqiao Chemical, etc.

In places where there is no photoelectric Colorimeter, in order to quickly evaluate the color change of the paint film, the "color fastness fading sample card" researched and recommended by the International Organization for Standardization, that is, the 5-level gray standard sample card method can also be used for testing. The specific method is: five pairs of gray standard samples are divided into five grades, which respectively represent the relative change degree between the original sample and the functional sample. After the paint sample is tested, it is compared with the standard sample and the gray sample card to observe the degree of discoloration and the grade of the gray sample card. The specific evaluation is shown in Table 8-2.