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Coloured Parts Conundrum

Colouring plastic parts has always been a touchy subject and even large automotive manufacturers usually like to paint parts instead of colouring them during the moulding process. This is because, in the past, colouring during the injection moulding process can produce colours that are not true reproductions of what was originally required or they can suffer from fading and discolouration during use and are thus not very hardwearing.


So, why do colours not behave as they should when introduced into the moulding process and how can we solve this problem? One of the main reasons colours do not work well in a lot of injection moulding jobs is that there is an incompatibility between the colour pigment and the resin itself being used to manufacture the part. This is especially problematic at high temperatures and can lead to leeching or bleeding of colours or colours that do not behave as they should and looking decidedly washed out or just plain wrong! Some of these issues can occur because of other compounds present in the resin pellets during manufacture, which can be dealt with by using the highest quality resins available from a known and trusted supplier and testing batches to ensure they meet quality control standards. Not all resins are the same and quality issues with these can cause many problems throughout the moulding process.


Moving onto the colours that you wish to add, it is also important to ensure that these are also high-quality and do not contain anything that is likely to react with the resins being used. It is also only sensible to check that the colour being used is stable up to the temperatures that it is likely to experience, both in use and during the moulding process, in order to reduce the likelihood of degradation. Certain colours are unable to be used with certain types of resin and this also can lead to dissatisfaction in the final product. It is very important to ensure that these aspects are verified during the sample production runs and that all parties are happy before proceeding with the manufacture of large quantities of coloured parts.


It is also worth noting that resins do not necessarily take kindly to any kind of additives, which can actually be viewed as a kind of contamination, even if we want this particular type of contamination there in the first place! Adding large amounts of colour may not be tolerated by the resin in certain circumstances and it might actually improve the end finish if a reduced amount of colour is added as a compromise. Finally, issues with added colour causing problems with quality can still be the case if you are using pre-coloured resin pellets and not only when adding colour itself into the mix during moulding.


At NICE Rapid, we are experts in ensuring you’re your next project goes as smoothly as possible – for any questions or to request a quote, please do not hesitate to contact us!   

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