1 Current status of color-coated board aging test
Due to its excellent formability, durability and decorative properties, color-coated sheets are widely used in construction, home appliances and furniture industries. The production and research of color-coated sheets abroad has a history of more than 50 years, while the history of domestic production of color-coated sheets is less than 20 years [1], and the research on the performance of color-coated sheets is very limited. This paper mainly studies the outdoor exposure and laboratory accelerated weathering test of color-coated panels and the correlation between them.
2 Outdoor exposure and laboratory accelerated weathering test methods
In order to study the outdoor exposure conditions in different regions, we conducted outdoor exposure tests on 12 kinds of color-coated panels with different resin systems commonly used at home and abroad in Baosteel Plant, Beijing, Guangzhou, Hainan, and Chongqing. The outdoor exposure time is 3 years in total, and the color change, loss of light, chalking and other properties of the samples are tested every 1 year. While carrying out outdoor exposure, we also conducted laboratory accelerated weathering tests. Expose for 1000 hours in the Q-Sun xenon lamp Test Chamber. The laboratory accelerated weathering test sets the test conditions according to the method in the national standard GB/T13448-2006. The specific parameters are shown in Table 1.
3. Analysis of the results of outdoor exposure and laboratory accelerated weathering test
3.1 Preliminary analysis of test results
After the outdoor exposure and laboratory accelerated weathering test, we selected and measured the color change, gloss loss, chalking and other values of 6 samples. During the measurement of these parameters, we found the following problems.
Outdoor exposure is greatly affected by the environment. In addition to the main effects of light, temperature, and humidity, outdoor factors such as acid rain, salt spray, mold, and industrial sediments also cause damage to materials. Due to the coastal climate conditions in Hainan and Guangzhou, the outdoor exposure of the samples will be affected by conditions such as salt spray and mold; the Chongqing area is greatly affected by acid rain; and the Baosteel test site is located in an industrial environment, and the settlement of various industrial pollutants The amount is large and the impact on the sample is also great. so only
The samples in Beijing area were less polluted, and the correlation between the laboratory accelerated weathering test results and the Beijing outdoor exposure results was better.
Since we have cleaned the samples before testing their properties such as color change, loss of light, chalking, etc., some test results cannot reflect the real aging results of the samples. For example, in the Beijing area, the color change in the third year is not as severe as that in the second year, mainly because when we cleaned the sample, the sample revealed a new surface layer that did not age, so the test described above appeared. result. Therefore, we only consider the results of the first and second year of outdoor exposure. Even outdoor exposures do not correlate well due to outdoor factors such as acid rain, salt spray, mold, and industrial fallout. In contrast, the correlation between accelerated laboratory tests and outdoor exposure was somewhat better. In the following sections we will focus on the relationship between the Q-Sun xenon arc Test Chamber and outdoor exposure.
3.2 Correlation between outdoor exposure and the color change of samples in the Q-Sun xenon arc Test Chamber test
3.2.1 Correlation between color changes of samples in outdoor exposure tests in various regions
For the color change of the samples, we first investigated how the outdoor exposure test results were correlated across regions. Table 2 below shows the correlation coefficient, rs [4] (spearman correlation coefficient), between color changes of samples in outdoor exposure tests in several different regions. The correlation coefficient refers to the correlation between the experimental results obtained by using two different test methods to test a group of samples. The formula for calculating the correlation coefficient rs is: rs=1-6∑di2/[n(n2-1)], where n refers to the number of samples, and di refers to the number of ranks in each group in the two-column sorting difference between. The closer rs is to 1, the better the correlation.
Looking at the data in Table 2, we found that the Spearman correlation coefficients between outdoor exposures were not very good. even the same
In other regions, the correlation between the test results of 1-year exposure and 2-year exposure is not all good. Among them, only the correlation coefficient between Baosteel 1-year and Baosteel 2-year is 1, and other correlation coefficients are less than 1, such as Hainan The correlation coefficient between 1 year and Hainan 2 years is only 0.66. The correlation coefficients between different regions are even more unsatisfactory, and some are even negative. For example, the correlation coefficients between Guangzhou 1 year, Guangzhou 2 years, Chongqing 1 year, Chongqing 2 years and Hainan 2 years are all negative.
以上已经提到，户外曝晒之间的相关系数不是很好，主要是因为户外曝晒受到酸雨、盐雾、霉菌、工业沉降物等户外因素的影响较大，我们甚至发现在宝钢试验点的样品表面出现黄斑或黑斑。
3.2.2 Q-Sun 氙灯试验箱与户外曝晒试验中样品颜色变化之间的相关性
在研究户外曝晒不同地区之间的相关性的同时， 我们也研究了 Q-Sun 氙灯试验箱与户外曝晒试验中样品颜色变化之间的相关性，具体相关系数如表 3 所示。
与表 2 相比较，表 3 中 Q-Sun 氙灯试验箱与户外曝晒试验中样品颜色变化之间的相关系数反而不是很差，一般都大于 0.60 。 Q-Sun 氙灯试验箱与北京试验点的相关系数都大于 0.80 ， 与北京 2年的相关系数高达 0.94 。
在户外复杂曝晒因素的影响下，我们能得到表3 所示的 Q-Sun 氙灯试验箱与户外曝晒试验中样品颜色变化之间的相关系数，已经说明它们之间的相关性较好了。 下面我们接着分析在 Q-Sun 氙灯试验箱中测试多长时间相当于户外曝晒多久的效果。
3.2.3 Q-Sun 氙灯试验箱与户外曝晒试验时间之间的对比
为了得到实验室加速耐候测试与户外曝晒试验结果之间的关系，也就是通常大家比较关心的一个问题—— — 对于材料的某种变化，如果加速测试与户外结果的相关性足够好， 那么在 Q-Sun 氙灯试验箱中测试多长时间相当于户外曝晒多久的效果。本文研究了在 Q-Sun 氙灯试验箱中测试 1000 小时分别相当于在北京、宝钢、广州、海南、重庆曝晒多少时间。
下面举例说明我们的分析方法，如当我们研究在 Q-Sun 氙灯试验箱中测试 1000 小时相当于在北京曝晒多少时间时，我们首先分别测量了样品在Q-Sun 氙灯试验箱中测试 1000 小时、在北京曝晒1 年和在北京曝晒 2 年后样品的颜色变化， 用 △E来表示，如表 4 所示。
本次试验由于我们的测量数值较少，只能大体知道在 Q-Sun 氙灯试验箱中测试 1000 小时，样品的颜色变化没有在北京曝晒 1 年的厉害，不过无法准确计算出到底相当于在北京曝晒几个月的结果。
所以我们建议，以后进行耐候试验时，应该多取几个时间段对样品进行测量。 在一个试验中，包括初始值在内至少要测量 5 次。 例如以上这个试验，对于 Q-Sun 氙灯试验箱测试，我们至少要测量初始值即 0 小时、 200 小时、 400 小时、 600 小时、800 小时及 1000 小时的结果， 而在北京曝晒 2 年的试验，至少要测量初始值即 0 个月、 6 个月、 1 年、18 个月及 2 年的结果。
通过观察表 4 ，我们同时发现， Q-Sun 氙灯试验箱测试时间不够长， 应该再多测试一些时间，如2000h 或 3000h 。
3.3 户外曝晒之间及与 Q-Sun 氙灯试验箱试验中样品失光率之间的相关性
3.3.1 各地区户外曝晒试验中样品失光率之间的相关性
对于样品的失光率，我们同样首先研究户外曝晒试验结果各地区之间的相关性如何。 下面的表 5是几个不同地区户外曝晒试验中样品失光率之间的相关系数。
通过观察表 5 中的数据，我们发现，户外曝晒之间的相关系数不是很好。 即使是同一地区，曝晒1 年和曝晒 2 年的试验结果之间的相关性也不全是好的，其中广州 1 年与广州 2 年之间的相关系数只有 0.17 。 不同地区之间的相关系数更是不称心，尤其是海南 1 年、海南 2 年与其它地区之间的相关系数。
3.3.2 Q-Sun 氙灯试验箱与户外曝晒试验中样品失光率之间的相关性
在研究户外曝晒不同地区之间的相关性的同时， 我们也研究了 Q-Sun 氙灯试验箱与户外曝晒试验中样品失光率之间的相关性，具体相关系数如表 6 所示。
与表 5 相比较，表 6 中 Q-Sun 氙灯试验箱与户外曝晒试验中样品失光率之间的相关系数反而不是很差，一般都大于 0.60 。 Q-Sun 氙灯试验箱与宝钢 1 年的相关系数高达 0.94 。
Under the influence of complex outdoor exposure factors, we can get the correlation coefficient between the Q-Sun xenon lamp Test Chamber and the sample light loss rate in the outdoor exposure test shown in Table 6, which has shown that the correlation between them is good. However, also because of the small number of measured values in this test, we can only roughly know that after testing in the Q-Sun xenon lamp Test Chamber for 1000 hours, the loss rate of the sample is equivalent to the result of Baosteel for 2 years, and it is impossible to calculate an accurate value. .
4. Conclusions and recommendations
This paper studies the outdoor exposure and laboratory accelerated weathering test of color-coated panels with different resin systems. Through this test, we realized that outdoor exposure is the basis of accelerated weathering tests in the laboratory, and it is very important to actively carry out outdoor aging tests. Outdoor exposure tests should be used to guide accelerated testing in laboratories. Due to the complexity of outdoor exposure factors, such as exposure samples are affected by acid rain, salt spray, mold, and industrial sediment, laboratory accelerated tests cannot completely simulate all aging phenomena that occur in outdoor tests.
Through reasonable evaluation and statistical analysis, we obtained a good correlation coefficient between the Q-Sun xenon lamp Test Chamber and outdoor exposure for the color change and light loss rate of the samples.
Through this experiment, we also noticed some areas for improvement during the experiment:
Before evaluating outdoor exposure samples, half of the samples should be washed instead of all, so as to avoid undocumented re-evaluation at a later time.
During the test, evaluate the sample at least 5 times, including the initial value, so as to avoid too little data and make it difficult to statistically analyze the test results.
The determination of the test end point is also very important. For example, in this test, some properties of the sample did not reach the aging degree of outdoor exposure in the laboratory accelerated test.
Another important point is the limitation of the existing laboratory accelerated test methods. For example, we can add acid rain simulation test (available in Q-Sun Xe-3HD model) to simulate the exposure environment in Chongqing, and add ultraviolet salt spray composite test [5] (available in QUV+Q-Fog) to simulate Hainan , Exposure environment in coastal areas of Guangzhou.
