ASTM D4141 涂層室外加速暴露試驗的實施方法

ASTM D4141發(fā)行信息

標準號ASTM D4141/D4141M-2014

中文名 涂層的黑箱和陽光集中暴露處理用標準操作規(guī)程

英文名 Standard Practice for Conducting Black Box and Solar Concentrating Exposures of Coatings

發(fā)布日期2014

實施日期

廢止日期無

中國標準分類號A29

國際標準分類號87.040 (Paints and varnishes)

發(fā)布單位US-ASTM

ASTM D4141適用范圍

5.1 As with any accelerated test, the increase in rate of weathering compared to in service exposure is material dependent. Therefore, no single acceleration factor can be used to relate two different types of outdoor weathering exposures. The weather resistance rankings of coatings provided by these two procedures may not agree when coatings differing in composition are compared. These two procedures should not be used interchangeably.

5.2 The procedures described in this practice are designed to provide greater degradation rates of coatings than those provided by fixed angle open-rack outdoor exposure racks. For many products, fixed angle exposures will produce higher degradation rates than the normal end use of the material.

5.2.1 The use of Procedure A (Black Box) instead of an open-rack direct exposure is a more realistic test for materials with higher temperature end use service conditions. For many coatings, this procedure provides greater rates of degradation than those provided by 5x00b0;, equator-facing, open-rack exposures because the black box produces higher specimen temperatures during irradiation by daylight and longer time of wetness. The black box specimen temperatures are comparable to those encountered on the hoods, roofs, and deck lids of automobiles parked in sunlight. The relative rates of gloss loss and color change produced in some automotive coatings by exposures in accordance with Procedure A are given in ASTM STP 781.4

5.2.2 The acceleration of Procedure C is produced by reflecting sunlight from ten mirrors onto an air-cooled specimen area. In the ultraviolet portion of the solar spectrum, approximately 1400 MJ/m2 of ultraviolet radiant exposure (295 to 385 nm) is received over a typical one-year period when these devices are operated in a central Arizona climate. This compares with approximately 333 MJ/m2 of ultraviolet radiant exposure from a central Arizona at-latitude exposure and 280 MJ/m2 of ultraviolet radiant exposure from a southern Florida at-latitude exposure over the same time period. However, the test described by Procedure C reflects only direct beam radiation onto test specimens. The reflected direct beam of sunlight contains a lower percentage of short wavelength ultraviolet radiation than global daylight because short wavelength ultraviolet is more easily scattered by the atmosphere, and because mirrors are typically less efficient at shorter ultraviolet wavelengths. Ultraviolet radiant exposure levels should not be used to compute acceleration factors since acceleration is material dependent.

5.3 The weather resistance of coatings in outdoor use can be very different depending on the geographic location of the exposure because of differences in ultraviolet (UV) radiation, time of wetness, temperature, pollutants, and other factors. Therefore, it cannot be assumed that results from one exposure in a single location will be useful for determining relative weather resistance in a different location. Exposures in several locations with different climates that represent a broad range of anticipated service conditions are recommended.

5.4 Because of year-to-year climatological variations, results from a single exposure test cannot be used to predict the absolute rate at which a material degrades.

Note 3x2014;Several years of repeat exposures are typically needed to get an x201c;averagex201d; test result for a g......

5.1與任何加速試驗一樣，與在役暴露相比，風化速率的增加取決于材料。因此，不能使用單一的加速系數(shù)來關聯(lián)兩種不同類型的室外風化暴露。當比較成分不同的涂層時，這兩種程序提供的涂層耐候性等級可能不一致。這兩種程序不應互換使用。


5.2本實施規(guī)程中描述的程序旨在提供比固定角度開放式機架戶外暴露機架更高的涂層降解率。對于許多產(chǎn)品，固定角度曝光將產(chǎn)生比材料正常最終用途更高的降解率。


5.2.1使用程序A（黑匣子）代替開架直接暴露，是對具有更高溫度最終使用條件的材料進行的更現(xiàn)實的試驗。對于許多涂層，該程序比5x00b0提供的降解率更高；，面向赤道的開放式機架暴露，因為黑匣子在日光照射期間產(chǎn)生更高的樣本溫度，且潮濕時間更長。黑盒樣本的溫度與停放在陽光下的汽車的發(fā)動機罩、車頂和甲板蓋上的溫度相當。ASTM STP 781.4中給出了根據(jù)程序A暴露在某些汽車涂料中產(chǎn)生的光澤度損失和顏色變化的相對速率


5.2.2程序C的加速是通過將陽光從十面鏡子反射到風冷試樣區(qū)域而產(chǎn)生的。在太陽光譜的紫外線部分，當這些設備在亞利桑那州中部氣候下運行時，在典型的一年時間內(nèi)接收到約1400 MJ/m2的紫外線輻射暴露（295至385 nm）。與此相比，在同一時間段內(nèi)，亞利桑那州中部緯度地區(qū)的紫外線輻射照射量約為333 MJ/m2，佛羅里達州南部緯度地區(qū)的紫外線輻射照射量約為280 MJ/m2。然而，程序C中描述的試驗僅將直射光束輻射反射到試樣上。由于短波紫外線更容易被大氣散射，而且鏡子在短波紫外線波長下的效率通常較低，因此反射的陽光直射光束所含短波紫外線輻射的百分比低于全球日光。紫外線輻射暴露水平不應用于計算加速度系數(shù)，因為加速度取決于材料。


5.3由于紫外線（UV）輻射、濕潤時間、溫度、污染物和其他因素的差異，戶外使用的涂料的耐候性可能因暴露的地理位置而大不相同。因此，不能假設單一位置的一次暴露結果將有助于確定不同位置的相對天氣阻力。建議在不同氣候條件下的多個位置進行暴露，這代表了廣泛的預期使用條件。


5.4由于年復一年的氣候變化，單次暴露試驗的結果不能用于預測材料降解的絕對速率。


附注3x2014；通常需要幾年的重復暴露才能獲得x201c；平均x201d；g……的測試結果。。。。。。