All sunlight, both in the visible and invisible spectra, that is absorbed by an object will increase its temperature.
For humans the waveband of the visible spectrum is between 390 to 700nm. We refer to this as sunlight, daylight or more simply as just ‘light’, and it is this light that is responsible for the colours we see.
A colour that absorbs all these wavelengths appears black and conversely one that reflects them all appears white. A colour that absorbs some wavelengths but reflects the wavelength of a narrowband will appear coloured. The apparent colours are dependent on the wavelength of the reflected light.
Wavelengths lower than 380nm [ultra violet] and above 700nm [infra-red] are not visible to the human eye but will affect objects in exactly the same way as the visible. I.e. some are reflected and some are absorbed. This does not affect our perception of the colour
The more solar energy absorbed the greater the heat build-up. Items that are sitting in direct, intense sunlight will heat up more quickly and get hotter than those in shadow.
Colours utilising IRR pigments can offer up to 40% reduction in temperature profiles compared to that of a conventionally formulated colour, resulting in lower service temperatures. Two objects placed in direct sunlight, whose colour appears identical in the visible spectra, can be formulated to have completely different reflectance characteristics in the IR range. The colour designed to reflect the IR radiation will remain significantly cooler than its IR absorbing equivalent under the same environmental conditions
While this phenomenon might not appear very significant, we are probably all familiar with the noise produced by black PVC guttering on a hot day, where the expansion and subsequent contraction of the plastic leads to audible mechanical distortion at the joints and at worse, leaks. Conventional black PVC guttering can reach over 50°C in the sun in the South of England.
Blacks and colours made with IRR pigments typically only reach temperatures a few degrees above ambient and rainwater goods made using these do not experience the same thermal expansion and contraction.
This video demonstrates the difference in thermal performance and subsequent distortion of two conventional PVC blacks and an IRR black
White is a highly reflective colour and extensively used in the building industry but there is a demand for darker colours which are aesthetically more pleasing, especially with rainwater goods, soffits and cladding. Cooler plastics present a number of benefits, particularly in the building sector.
We know that exposure to heat accelerates the degradation of polymers. This manifests itself in a number of ways, typically, loss of gloss, yellowing, cracking and a reduction in physical properties.
By lowering the service temperature caused by solar energy absorption, the demands on the heat stabilisation package in the PVC is significantly reduced and hence the service life extended.
This can both enable savings to be made by reducing the amount of stabiliser in the compound and extend the working life of the PVC product as the demand on the stabiliser is now less.
Both useful benefits in the building industry where there is pressure to develop new products with a guaranteed longer life and to reduce maintenance and replacement costs.
Cool exterior cladding and roofing materials decrease the demand on interior building cooling. Heat generated by warm plastics is conducted into a building, raising its internal temperature. This is particularly relevant for buildings in warmer climates. Any reduction in exterior temperature reduces interior temperature and this improves the environment for users, as well as lowering the demand for air conditioning and hence the cost of keeping the interior cool.
There is no doubt the demand for ‘cool plastic’ is growing. Consumer awareness of global warming make the benefits of producing ‘greener’ products and meeting social responsibilities a positive marketing statement. We have touched on only a few areas of the industry where a ‘cool colours’ makeover can deliver positive benefits to the consumer.