Rotational Moulding Colouring P.1
In our previous blogs in this series on Rotational Moulding, we have covered Grade Selection, Melt Flow Index, the Effect of Comononer on Crack Resistance, Weather Resistance and Thermal Stability. We will now cover the importance of colouring in deciding on your poly water tank.
Pigments play a major role in many rotationally moulded articles. Indeed there would be a much lower demand for products if they could not be provided in a multitude of colours.
One of the benefits of polyethylene is that it can be readily pigmented to provide a very wide range of colours. Apart from aesthetic appeal, pigments can play a vital role by nature of their ability to absorb and reflect light and UV radiation from the sun. The ability to block light is essential for applications such as water tanks. A tank produced from unpigmented polyethylene would allow the transmission of light and provide a haven for algae to grow. Pigments added at sufficient levels can block light sufficiently to stop algae growth. As different pigments will allow different levels of light to pass through polyethylene, the quantity or loading of the pigment will need to be different to achieve the same level of blocking. This is true also when considering the absorption of UV radiation. Most pigments used in the colouration of polyethylene for rotational moulding will assist in resistance to weathering by absorbing UV radiation. It is UV radiation that attacks polyethylene and causes it to become brittle, leading to cracks. Some pigments can have quite a significant benefit. The best example of this is carbon black, the pigment typically used to colour polyethylene black. The right type of carbon black when added at a rate of 2 – 2.5% and well dispersed can enable UV life spans in polyethylene of greater than 20 years.
This blog post looked at the importance of pigments and their role in making poly tanks, and the next article will look at how to use (or not use) pigments optimally.