World’s lightest and smallest PET hot fill bottles
Sidel’s Skyward and Curvy 0.5 l bottles weigh 18.9 g and their design is said to be a breakthrough for the shape of hot-fill bottles, which traditionally have six or eight panels and often look exactly like each other.
Bottle lightweighting has been made possible by redesigning the neck, body and base. The 28 mm amorphous (non-crystallised) neck has been made lighter and it accepts a standard cap for carbonated soft drinks. The base has also been revised, making it stiffer while also using less raw materials. The new geometric structure of the bottle body compensates for deformations due to vacuum absorption after cooling. The Skyward bottle has a square section over a cylindrical one, an antiovalisation waist and a rigid label area at the base. The rigidity of the Curvy bottle is obtained by an anti-ovalisation waist in the top third of the body, the heel and the base, the twisted shape that acts as support beams and the succession of curves that absorb the vacuum while also making the bottle easier to grasp. Good material distribution is ensured by optimisation of the bi-orientation rates and preform thickness ratios, which are suited to the bottle shape.
In addition, the company has upped the blow moulding speed to 1,800 bottles/hour/mould with a standard HR process has been obtained due to heating optimisation on its SBO Universal machine range. Apart from the speed, other benefits are the optimised cycle times, greater induced crystallinity due to the stretching rate, 100% heating regulation inside the inner walls ensuring perfect spherolitic crystallinity of the bottle, which at this speed remains in the oven for a shorter time. Sidel’s bell nozzle also enables the blowing of lighter, amorphous necks without deforming them (isobaric pressure around the neck). Finally, the heat conduction of F300 aluminium molds helps produce bottles at this high output.
Meanwhile, Amcor PET Packaging’s 2.5 oz PET bottle has been used for the first time by Hormel Health Labs for the launch of its healthy shot high-protein healthcare beverage.
Amcor adapted its proprietary hot fill technology, used primarily for large containers, to create a simple cylindrically-shaped bottle to meet the needs of the speciality healthcare beverage market. “Perhaps the most difficult part was getting heat set properties into a bottle that size,” explained Kirk Maki, Amcor Project Engineer. “Vacuum control in hot filling and cooling is the other critical issue, which also required considerable manipulation.”
According to Maki, equipment had to be modified with speciality machine controls. “We had to downsize and modify the tooling to create a scaled down version of how we would normally process the container in order to drive heat set properties to a level high enough to prevent deformation under the heat. The heat set testing has come back at levels equal to or better than some of our other larger heat set containers,” Maki said.
Maki acknowledged there were challenges with the overall bottle design relating to vacuum control. Testing and calculations based on container diameter were run up-front to ensure that speciality panelling wouldn’t be needed. The panelling was fine when initial hot-filling and cooling trials were run, but the panel rib design had issues,” Maki said. So the rib portion of the design was modified and a smooth area of labelling developed.
The mini bottle’s finish area also added to the complexity of this project. Whereas the standard finish recalls an earlier PET era, it is not the kind of heat set finish one typically finds on a store shelf today.
“When you have a relatively large 28 mm opening on a 2.5oz container, compared to a 43 mm opening on top of 500 ml bottle, you can’t simply transfer technology,” said Maki. “Although it is not as light in weight as some newer designs, it has a versatile finish. What allowed us to use it here is the fact that the bottle is small, so there’s relatively little heat capacity.”
Compared with other bottles on the market today, which have smaller 20 mm finish, the larger 28 mm finish on this bottle makes it easier for patients to drink from.
Because this hot fill bottle is so small compared to others on the market, it takes custom equipment to fill. Not many fillers are currently set up to do it because there hasn’t been a demand for hot fill in bottles this size. “We know it’s a little difficult to maintain the heat when filling small containers while also maintaining throughput,” said Chris Curtis, Amcor PET Account Manager, North East. “Most of the hot fill in the industry has been with much larger containers.”
Hormel Health Labs focuses primarily on speciality products for hospitals, nursing homes, and rehabilitation centers. One of the primary concerns in nursing homes is weight loss among ageing patients who do not consume enough protein. Many patients usually drink only half or less of an 8 oz milkshake type product that contains 9 g of protein. With the new 2.5 oz PET bottle, Hormel can pack 12 g of protein.
Amcor has also developed other similar 2.5 oz bottle applications with beverage suppliers including a natural energy drink supplier.