When the colour change of the tested parts was compared to those of untested products, the Grey Scale value obtained for all parts was 4/5 or 5. That means that the colour of the product did not change appreciably during the UV stress. The pulling strength (tensile force) of the plastic chain became halved after 250 hr stress and stabilised to this value for the duration of the rest of the test.
The testing examined colour and gloss changes, due to the effect of solar radiation and moisture, in the plastic parts of the Venetian blinds. For some of the parts, also mechanical resistance changes were measured in addition.
The product was aged by causing it stress by UV radiation. The total duration time of the test was 1 000 hours. The UV radiation dose for the samples when under stress was 90kWh/m2. A product in Northern Europe will be subjected to a comparable dose of solar radiation during a time span of 1.7 years on average when outdoors and approximately 3 years when behind a window glass. The product’s colour coordinates and sheen were measured before subjected to stress: under stress, in 250 hr intervals and after stress. The Grey Scale value describing visual colour change was measured after the stress by visually comparing the colour difference between the UV-stressed product and non-stressed product to the Grey Scale reference values (ISO 105-A02:1993). In addition, the tensile strength of the plastic chain of the samples subjected to UV radiation was measured at 250 hr, 500 hr, 750 hr and 1 000 hr.