Micom offers UV testing services as part of its accelerated aging testing. UV sun exposure can be done through direct exposure i.e.: outdoor exposure or the impact of sun exposure through glass i.e.: indoor exposure. There are many test methods and two main practices for this important type of ageing process. Among others, Micom offers UV testing services to the following test methods and practices as well as many others:
For a more elaborate list of available test methods, please see: Test methods requiring the use of a QUV and Test methods requiring the use of a Xenon Arc Tester.
Use and factors to be considered:
The ultimate goal is of UV testing is to “compress time” so that we know how a product will react to sunlight as it gets exposed more and more. To do so, we want to simulate the sun on an accelerated basis; this process is called “Accelerated weathering”. Just like for any other accelerated aging process, the goal is to have the best simulation possible with the fastest aging rate possible while not inducing reactions that would not occur under normal exposure conditions. The two prevalent UV aging type of equipment used nowadays are: Xenon arc and Fluorescent light . Each technique has pros and cons and each of them can also be used with a broad variety of test conditions that can drastically change the test outcome. Xenon arc testing is mainly used to assess color/appearance changes over time as a result of indoor/outdoor exposure to UV light either directly from the sun or through glass (indoor conditions). There is no fix algorithm that allows to predict accurately what is the actual ageing rate also called “time compression factor ”. However, with Xenon arc, reasonable assumptions can be made to at least approximate orders of magnitude. For more information on time compression factor and the test parameters required see:
Fluorescent light accelerated weathering testing is mainly used to assess mechanical properties retention through exposure. This technique is used for comparison/certification purposes. However, scientific literature is clear that this technique, despite its uses, is a poor time predictor. For more information on this test method please see: ASTM G-154.
Micom also offers UVc exposure for surfaces used in healthcare environments. UVc exposure is often used as a sanitation process in healthcare environments.
Post UV testing optical measurements:
What is of interest to most of our customers requiring UV testing is not so much how the exposed samples look upon test completion as much as how different from the unexposed sample they look. Typically gloss and color measurements a taken at different exposure intervals until the total planned exposure duration is completed. In some cases, even is the color and gloss are the same we can see significant discrepancies between samples exposed at different time intervals. This can be explained by the fact that the human eye sees more than gloss and color.
There are three types of reflections; specular, scattered, diffused. A good example of a high specular reflection object would be a mirror or a perfectly polished metal. Scattered reflection: most materials fall into that category; most of the light is reflected in the specular angle but surface defects will scatter the light creating a bell curve deflection. The bell curve shape will depend on the micro-topography of the surface. A good example of diffuse reflection would be white paper.
Standard Gloss meters (ASTM D523) measures the « shininess » / Brightness (quantity of the light directly reflected from the surface). However, in comparing gloss measurements with what our eye sees, it is important to be aware that the human eye evaluates much more than the shininess of the surface. Simply put; two products with a similar gloss can look very different.
This is explained by the fact that whereas a gloss meter can only measure the specular reflection at a specific angle, the eye can see the light scattering as well i.e. a diffuse reflection.
Nowadays, equipment with light sensor arrays can take measurements that mimic the light reflection on the human eyes cones. These new sensors allow us to measure additional parameters:
- - Haze
- - RIQ (Reflected Image Quality)
- - DOI (Distinctness of Image)
- - RSpec(Smoothness quantification)
Haze is produced by imperfections/irregularities on the surface that affect the light distribution around the specular angle. Haze is sometimes called « gloss haze » as both are related. Haze is actually the sum of the gloss around the specular angle (-3° to -1 ° and +1 ° to +3 °) and is sometimes compared to « turbidity ».
DOI (Distinctness Of Image) measures how clearly an image appears on a reflective surface. A low DOI indicates image distorsion amd a perfect mirror has a DOI of 100.
RIQ Reflected Image Quality is an improved version of the DOI. It provides a better response to orange peel effects on a wider range of materials and textures.
Rspec is the Peak Specular Reflectance at ± 0.0991° around the specular angle. This very precise measurement quantifies the surface texture as any wave or ripple on the surface will create light diffraction and therefore affect the «light response ». For a perfectly smooth surface, the RSpec value will be equal to the gloss value.
10 things to know for a successful UV testing project
UV testing is often required on carbon based materials and coatings as they react with UV radiations to which they are exposed either because of sunlight or artificial light exposure. UV aging can cause a wide range of damaged from color fading to depletion of material resistance depending on the radiation source, the intensity and other contributing environmental factors. Important factors to consider for getting the right answers while requiring UV testing are:
- 1. UV source
- a. Sun?
- b. Artificial light?
- 2. Indoor or outdoor exposure?
- 3. Ambient temperature? Aggravating factor.
- 4. Ambient relative humidity? Aggravating factor.
- 5. Rain cycle? Erosion & cooling effect promoting aging.
6. Dark cycle? In some cases this will promote chemical reactions that would not happen otherwise.
7. Sample size; shape, thickness
8. Which undesirable impacts do you expect and are you trying to prevent? Color change or loss of mechanical properties might dictate the use of a different test protocol.
9. Duration of the predictable real life exposure.
10. Do you need progressive sampling/measurements on your samples? This will limit your testing costs should the materials you are testing are not performing as expected.
Should you need help, our experts will be happy to recommend the proper test conditions: contact us.