Coating solves a sticky packaging problem

Edited by the Engineeringtalk editorial team Dec 10, 2002

A specialised coating from Poeton Industries has helped solve a sticky packaging problem for Rexam, one of the world's top-ten consumer packaging suppliers.

A specialised coating from Poeton Industries has helped solve a sticky packaging problem for Rexam, one of the world's top-ten consumer packaging suppliers and a leading European supplier of thin wall plastic containers for the food industry.

At its factory in Yate near Bristol in the UK, Rexam has developed a proprietary process to mould high volume trays using PET, an advanced packaging material that is specified by major food brands because its clear finish allows consumers to see the product inside the pack.

However, although PET has obvious advantages for Rexam customers it can be difficult to process in high volume moulding machines, being both abrasive and sticky.

Its abrasive properties cause aluminium moulds to wear quickly and its stickiness makes it difficult to remove trays from moulds - problems that have a seriously affect on high volume production.

Also, because trays stick together when stacked, denesting is also difficult and slows down the customer's production lines.

Both problems were experienced recently at Rexam on a line producing trays for a major food product line.

To overcome the denesting problem Rexam had been grit blasting the mould to roughen the surface, and blending an expensive migrating wax additive with the PET.

Whilst this approach improved denesting it didn't solve the mould wear problem and, as the additive left a residue, the mould also needed regular cleaning.

At this stage the issue of pack clarity became secondary to the high volume needs of the customer and Paul Hawkins, technical manager at the Yate site, called in surface treatment specialist Poeton Industries to advise on coatings, primarily to improve the long-term wear characteristics of the moulds.

Poeton's engineers recommended a coating of Apticote 450 to reduce wear in the mould cavity; and bead blasting rather than grit blasting as a more effective pre-treatment for use with Apticote 450.

Initial trials were carried out on a 120-cavity drum mould with 20 cavities coated.

After six weeks of running 24 hours a day and seven days a week there were no signs of wear in the coated cavities and Rexam were sufficiently impressed to have the whole tool coated.

Although the result was good news for high volume production, the real surprise came when Rexam ran trials of the coated cavities with reduced amounts of the denesting additive in the PET.

With only half the amount of the expensive additive (the optimum result) denesting was significantly improved and additive costs reduced.

The process now produces 1.5 million of the twin-cavity trays each week to feed a production line that is operating every day of the week.

Commenting on the project, Paul Hawkins says: "Poeton coatings proved the ideal solution for the wear problems we encountered with this combination of long running, high-volume process and abrasive, sticky material.

The improvements in denesting and the reduction in additive use is a very welcome bonus".