Plastic containers (image courtesy of
Ropak)

A sidewall strengthening system for plastic containers is said to use 15-20% less source material and improves top load performance. The technology could increase storage space and reduce transport costs in rigid plastic shipping.

Ropak Packaging, Fountain Valley, USA, says its patented five-gallon square container, ‘employs a unique design that incorporates vertical grooves and horizontal reinforcing ribs in the corners of the container, where most of the load is carried’. This design is said to be optimised using finite element analysis, which gives a detailed visualisation of simulated stress points.

The developers say this reduces the wall thickness of the injection-moulded container, while maintaining stack strength performance.

Ropak Manager of New Products and Marketing, Pansy Leo, outlines the market need. ‘In North America, our customers have very stringent performance criteria when it comes to stack strength performance. They want to continue to stack containers in their warehouses two or three pallets high, sometimes under high heat and humidity conditions, without any containers buckling. They are not willing to compromise on these performance criteria, even if the price of the container is lowered’.

She notes that the top load performance of these containers has undergone, ‘extensive testing, such as dynamic compression and drop testing, according to the American Society for Testing and Materials standards’.

The container, she says, ‘has a better top load performance at 300lbs versus our other square containers, which range from 175-240lbs’.

The packs are made from polypropylene resin, as opposed to high-density polyethylene (HDPE). ‘Polypropylene is a stiffer resin than HDPE, offering about 20-25% better top load performance, and has a lower specific gravity. So, less material can be used to help achieve the same performance,’ Leo explains.

The product originally performed less favourably in frozen conditions compared to existing HDPE containers. However, she notes that the containers have now been manufactured from new grades of freezer grade polypropylene resin developed by their supplier to overcome this difficulty.

According to Leo, the containers have been successfully commercialised in various markets, including gardening, food, fasteners, chemicals and adhesives.  

Further information

www.ropakcorp.com