The growth in the use of PET bottles and containers has inevitably brought with it the demand for specific colours to correspond with the colour of the glass bottles which PET is replacing. This is, in part, to leave the marketer free to design new and attractive packages, but is also very much driven by tradition. Certain colours have, over a period of time, become associated in the mind of the consumer with different types of product. Bottle colours have taken on the role of product “markers”. A transparent blue bottle has become associated with mineral waters, especially in France; amber bottles mean beer; transparent yellow or red is frequently used for cooking oils. The bottle colour may also be closely linked to the product brand (e.g. a green bottle for Heineken beer, or for 7-Up) and in cases such as these a PET bottle of exactly the right colour will be absolutely essential to persuade the brand marketer to make the switch from glass. On the other hand it is clear that the choice of a wholly unsuitable bottle colour can have a negative influence when on the supermarket shelf -who buys cola in a blue bottle?
To meet the demands of product marketers the Wilson Color business of M.A.Hanna Company, has developed an extensive range of colours for PET. These include the traditional amber, blue and green, as well as a large number of transparent and opaque colours for cosmetics and toiletries. Of particular interest to product marketers looking to replace glass bottles with PET is Wilson’s FX ™ range of frosted colours which it is claimed successfully imitates frosted glass, and for which the manufacturer has developed a specific colour chart.

Trends in colouring technique

The PET market in Europe is growing at around 10 %per annum, with some bottlers using very large quantities, especially for filling beverages. In these cases, where production may exceed 300 milllion units p.a. the PET bottle will generally be produced in two stages: (a)the preform, and later (b) the blow-moulded bottle, which is produced just before filling to minimise volume storage requirements. Colour is usually added in the form of a masterbatch, with the trend being towards greater colour concentration to minimise coloration costs. The demand is also for smaller and smaller granulate size to facilitate the dispersion of the concentrated masterbatch in the polymer. For large scale product runs liquid concentrate is also used, for both transparent and opaque colours. The high pigment concentration in these liquid colours can result in significant coloration cost savings, but not without some disadvantage -principally in the area of dispensing the liquid, and above all in equipment cleaning. There is also a possibility of liquid pigment migrating through the bottle. Alternative solutions are offered by Wilson Color in the form of highly concentrated masterbatch in a very fine granulate form (micro-pellets), and which will be used at similar let down ratio as a liquid colorant. Due to the low melting point, high performance dispensing equipment is recommended.

Other developments

Bottles are coloured for marketing reasons rather than for functional reasons. However, under some circumstances, a UV barrier (screening) or stabilisation function is desired, this is why combined formulations including a colour +UV barrier or UV stabiizer are currently being developed. As well as producing colours for plastics M.A. Hanna Color +Additives Europe is currently working on an anti-static concentrate for blow moulded containers to facilitate the filling of powder products. This advance should open new application areas for PET. An “Anti Block” concentrate is also being developed which, when added to the PET, will prevent newly moulded warm bottles from sticking to each other during conveying and packing.