If you have an application that needs to be suitable for outdoor use or needs to be protected from UV radiation, you need to consider what is known as weather and light fastness.
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Important facts about light fastness
Lightfastness (or light resistance) describes the resistance of colours to prolonged exposure to light, especially sunlight with a high UV content. Chemical degradation (photooxidation) occurs: Cracking, deterioration of mechanical and physical properties as well as colour changes such as fading can be the result. There is no such thing as permanent lightfastness and the degradation process can never be stopped completely.
The general rule is: the higher the UV radiation, the higher should be the quality of the colourants.
Measurements with the blue wool scale
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If a (new) raw material or a specific recipe is to be checked, the most common method is the wool scale, also known as the blue wool scale. This measurement is carried out manually and visually. The wool scale ranges from level 1 (=low light fastness) to level 8 (=high light fastness). The eight blue wool strips fade differently when exposed to light due to their colouring agents. The scale is placed on the sample to be tested, covering a part of the sample and the wool strips. After irradiation, the samples and the wool strip are compared: The difference found determines the lightfastness.
Important information on weather resistance
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Weather fastness is also of decisive importance for quality and durability. It describes the resistance of materials to external weather and environmental influences (such as temperature, UV radiation, moisture, air constituents) - in other words, it encompasses more factors than light fastness and UV radiation. Lifocolor has a weathering machine for measurements under laboratory conditions.
The machine simulates all possible weather conditions such as heat, rain, frost, wind etc. for up to 3000 hours, customisable according to customer requirements. It complies with DIN EN ISO 4982-2, the international standard for quality testing.
A xenon arc lamp is used to measure the light resistance. In the weathering machine, moulded samples are clamped for different weathering times - if necessary with the enclosed wool scale. After weathering, the unweathered test specimens are visually compared with the weathered test specimens. The scale for assessing weather resistance generally ranges from 1 to 5 (5 = very high, 1 = very low).
