Painting Polyethylene

Painting polyethylene, who would when there are so many difficulties involved?

For most rotomoulding companies, and indeed many rotomoulding customers, the answer to getting their logo, or design onto anything made of polyethylene has often been to use a sticker or vinyl.

This presents almost as many problems – in terms of permanence – to the end user as the process of painting the plastic does to the manufacturer.

The main problem when it comes to painting polyethylene is that the process is difficult, expensive and laborious. This is largely down to the fact that the surface of the plastic is not conducive to holding the paint. Historically, when paint was applied to the plastic it was known to flake and fall off … If it held long enough for it to dry at all.

More recently methods have been developed to allow for polyethylene to be painted successfully, however, there are only three that really work and the skills and facilities needed to carry them out correctly can often be hard to come by.

Mould-in Graphics

As early as the 1980s when successful painting of PE was completely unheard of Corilla Marine began working with an American company, by the name of Mold In Graphic Systems, to develop a more permanent option for affixing company logos and other graphics to PE than the traditional method of using a sticker.

The resulting mould-in graphics that Corilla Marine helped to develop were made from a similar polymer to the final part. The process involves applying the paint, or graphic, to the inside of the mould prior to the introduction of the PE powder for the product itself. The result is a coloured design that is permanently attached to the finished part and is as UV, scratch and chemically resistant as the moulded part itself.

Due to their involvement in the development of this process, for many years Corilla Marine was the only company in the UK with the ability to perform this process, and even today the number of rotational moulding companies that have the onsite capability is fairly small.

This method of ‘painting’ polyethylene is probably the most widely used and tends to be the most successful as it has fewer constraints than the other processes available. For example, its viability isn’t dependant on the thickness of the PE product and it creates a logo or design that is part of the final product.

Flame-on Graphics

When a product is large enough and thick enough, and needs a larger surface area painting – perhaps in stripes as with some of the marine buoys that Corilla Marine, produce – it is often best to paint the finished product. This process is often referred to as ‘flame-on’.

This is done by oxidising the surface of the PE with a propane torch to allow special PE compatible paints to be sprayed on and then adhere to the chosen surface area of the product. Using this method is perhaps more labour intensive than the mould-in method. However, it is also perhaps more versatile in that it allows for stripes and patterns etc. to be applied as well as logos and other graphic designs.

The special paints used are again made from a similar polymer to the PE product itself and the heat treating allows the graphic to partially melt into the surface and become permanently bonded to the product.

Adhesive Post-mould graphics

Finally, there is a screen printing method, otherwise known as ‘adhesive post-mould graphics’. This technique uses a similar premise to stick on tattoos for children. First, the requisite section of the moulded polyethylene product is polished to create a smooth surface for ease of application. Then a special ink is applied using an adhesive ‘vinyl’. Upon removal of the ‘vinyl’ section, the design will remain on the plastic part.

Using this method, although perhaps the easiest and least time consuming, is probably the least effective as the ink is exposed to the elements and remains secondary to the PE product itself. Therefore it doesn’t have the same resistance to UV, scratches and chemicals that the design would have using one of the other two methods.

Whichever process is the best for you and your specific needs, Corilla Marine has the expertise to ‘paint’ polyethylene to your exact requirements. Corilla Marine’s skilled craftsmen and state of the art machinery will ensure that we get your paint-job right first time, every time.

To find out more about these processes and if they could be beneficial to you, get in touch with us today.