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Correlation between xenon arc test and outdoor exposure test for automotive exterior paint

2022-12-29

The wording of the Automotive Non-metal Parts and Materials Xenon Arc Accelerated Aging Test Method and Automotive Non-metal Conduct outdoor aging exposure, because natural outdoor exposure is the basis of laboratory accelerated aging testing, and can be used as a guideline for accelerated aging tests in the laboratory.

Weathering test method for automotive exterior paint:

Outdoor exposure test:

Two typical exposure sites were selected. 59th Research Institute of China Ordnance Industry, which is a typical desert climate, the exposure site is at 94 ° 41 ′ east longitude, 40 ° 09 ′ north latitude, and an altitude of 1139.0 m, the total annual radiation is 6425MJ/m2, the annual average precipitation is 39 mm, the annual average relative humidity is 38% and the annual average temperature is 10.8°C, the mlocal average maximum temperature is 24.9 ℃ (July).

p> The other is the Qionghai exposure field, which is a typical sub istropic climate. The illumination field is located at 110°28′ east longitude, 19°15′ north latitude and an altitude of 20.0 m; the total annual radiation is 5400MJ/m2, the annual average precipitation is 2000 mm, the annual average relative humidity is 85% and the annual average temperature is 24.0°C. The monthly average maximum temperature is 28.4℃ (July).

Whether it is the Dunhuang exposure field or the Qionghai exposure field, the test samples are exposed in the exterior exposure box (Black Box) for automotive exterior parts. The illumination angle of the black box at the Dunhuang exposure site is 45° to the south, and the illumination angle of the black box at the Qionghai exposure site is 20° to the south.

Accelerated aging test in the laboratory:

There is a variety ofn xenon lamp aging test methods developed for automotive paint, as shown in Table 1. , Test Method 1 and Test Method 3 refer to the methods in the SAE J2527 standard A Perforated Technology Based Standard for Accelerated Exposure Testing of Automotive Exterior Trim Parts Using Xenon Lamp Equipment with Adjustable radiation. Test Method 2, Test Method 4 and Test Method 5 refer to the test methods of some major automotive OEMs.

Table 1 Xenon lamp aging test method

Test sample:

Participated in the development of this standard The unit provided a total of 40 kinds of paint samples, and the sample colors were black, white and red. Among them, there are 14 kinds of black models, 13 kinds of white and red models.

Weathering test results and analysis of automotive exterior paints:

Outdoor exposure results:

When evaluating test samples, gloss changes, color change,see if the sample is pulverized, foamed, cracked, oxidized, brittle, etc. This article mainly analyzes the gloss and color changes of the samples.

a. The evaluation of the gloss change of samples refers to ASTM D523 Specular Gloss Test Method

Lab

Method, measured with a reflectometer under geometric conditions of 85°.

b. The evaluation of the color change of the sample refers to ASTM D2244 Standard Specification for Calculation of Color Tolerance and Color Difference by the Method of Measuring Color Coordinates with Instruments, and selects CIEL*a*b* color space, D65 light source, 10° observer and specular reflectance include conditions to be measured. They were exposed for 18 months in the Dunhuang exposure field and the Qionghai exposure field, respectively.

Referring to GB/T 1766 Rating Method for Aging of Coatings and Varnishes, oNo matter in which illumination field most samples are light or very light lost, and only a small number of samples are obvious light loss and heavy light loss.

Referring to GB/T 1766 Grading Method for Aging of Paint and Varnish Coatings, regardless of the exposure field, most ampoules belong to slight discoloration, very slight discoloration, and only a small number of samples belong to obvious discoloration and greater discoloration.

Test results for accelerated aging in the laboratory:

According to the test method in Table 1, use the test chamber for accelerated aging of the xenon lamp

The color changes at different rates . For example, Test Method 1 changes more slowly than Test Method 3 because Test Method 1 uses a daylight filter and Test Method 3 uses an extended ultraviolet filter.

Laboratory accelerated aging test

Do accelerated test on the sample, the test time is 1200 hours, the loss ratedistribution and color change of the sample.

Correlation between laboratory accelerated weathering test and outdoor exposure test

Correlation between laboratory accelerated weathering test and outdoor exposure test and between two outdoor exposure fields The correlation study refers to the Spearman sorting method in ASTM G169 Guidelines for the Application of Basic Statistical Methods in Environmental Testing. The correlation coefficient rs refers to the correlation between the test results obtained by using two different test methods to test a group of samples. The calculation formula of rs is as follows: p>

rs=1-6∑di2/[n(n2-1)]

In the formula, di is the digit difference of two columns with paired variables , n is the number of samples

Sorting the test data from 18 months of outdoor exposure according to the percentage of light loss and color change △E* of the sample; The times to reach 3.0 are decreasingoddly sorted. Table 2 is the correlation coefficient of the sample's gloss change, and Table 3 is the correlation coefficient of the sample's color change.

Table 2 Correlation Coefficient of Specimen Gloss Change between Xenon Lamp Test and Outdoor Exposure Test

Table 2 shows that for the example, the gloss change is the correlation between xenon arc test and Qionghai is better than that between the xenon arc test and Dunhuang. The correlation between test method 1 and outdoor exposure is good, the correlation coefficient with Dunhuang is 0.76, and the correlation coefficient with Qionghai is 0.88.

Table 3 Correlation coefficient of sample color change between xenon lamp test and outdoor exposure test

Table 3 shows that for sample color change, xenon lamp The correlation coefficients between the test and the two outdoor exposure sites are relatively good. The Correlcoefficient of correlation between Test Method 1 and Dunhuang is 0.66, and the correlation coefficient between Test Method 1 and Qionghai is 0.95.


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