SIPA's Holistic Approach to Neck Lightweighting

SIPA has developed innovations that allow a container with a lightweight neck to pass through all the stages of the production process without being damaged or deformed.

Nov 28 2011 --- Everybody wants a lighter bottle, but very few know how to make one. It requires an holistic approach that considers every aspect of design, development and engineering, preform injection molding, bottle blow molding, handling, filling and sealing. A lot has already been written about lightweighting the container body. Here, we consider SIPA’s approach to lightweighting PET bottle necks.

The neck is where the bottle wall is at its thickest. Taking blow molding to the extremes of its capability can yield optimum results in producing very light containers, but the neck is determined by the preform injection molding process. To design a lightweight neck requires a detailed study of the passage of the product all along the process chain. SIPA has developed innovations that allow a container with a lightweight neck to pass through all the stages of the production process without being damaged or deformed.

Design and development

When SIPA designs a new lightweight neck, it has several targets in its sites:
• keep all areas relating to function and neck seal unchanged, so that the same closure can be used;
• analyse how the design performs all along the line, to minimize the need to change the configuration of the existing production operation (blower, filling line, etc..);
• consider the existing injection mold so that only the neck-ring needs changing;
• analyse how the neck performs during the filling to see how much the wall thickness in the neck can be reduced - optimize where necessary the air vents and exhaust, and consider possible treatments on the mold surface;
• internal tests to validate the new neck against the standard (using the same closures);
• if possible, carry out industrial tests at the customer with the use of a single neck-ring installed on the existing mold.

Injection molding

Molding a lightweight neck is never simple. With a huge background as a packaging developer SIPA well understand all critical points. In this case, having a small quantity of PET resin this may cool too quickly inside the injection mold and not be able to fill the cavity all the way to the top of the neck, giving a “short shot.” During the development process, SIPA considers all factors, including the viscosity of the resin, that may affect this process and its thermal profile inside the hot runner. It then carries out several tests to guarantee the perfect neck injection: dimensional checks to verify the correct formation of the thread, various physical and mechanical tests – for example on pressure resistance or the proper opening of the thread – and tests on chemical and/or biological contamination.

Mold conversion

SIPA aims to provide the best results with the lowest investment for its customers. When it comes to converting the injection mold to a lightweight neck, the tendency is to change only the lip (for example when cutting the weight from 3.9 to 3.2 g). In these cases, reverse engineering is carried out to limit the risk of creating defects in the final product and to ensure the correct mechanical matching and duration of mechanical components of the mold. Whether the customer is in Asia, the Americas or Europe, it can always rely on SIPA’s most advanced tool shops, located on all three continents, to guarantee the finest results with the shortest lead times.

The thread

For flat water bottles, it has already been possible to reduce the weight of “Novembal 267” necks from 3.6 g to 2.6 g - that’s a saving of 27%. With special modifications on the line, the weight can now be halved, to 1.8 g. For non-carbonated drinks, a 3.9-g 30-25 thread is very widespread; a stripped-down version weighing 3.2 g has already been used in several different projects.
For carbonated soft drinks, apart from the now widespread PCO1881, which weighs 3.7 g compared to 5g for the PCO1810, SIPA is now validating an even lighter version weighing just 3.4 g. Again, by making appropriate changes to the line, it should be possible to go even further, and reach 2.5 g - a weight saving of 50%.
Excellent results are also being obtained with the lightweighting of the PCO 28 mm for hot fill: a materials saving of 41%, from 6.4 g to 3.8 g, has already been achieved.

Blow molding

SIPA’s rotary blow molding equipment now includes various innovations dedicated to ensuring proper processing of preforms with lightweight necks, including systems that enable the preform body to be reheated without deforming the neck. The innovations start at the very beginning, preform loading. This has been enhanced with the introduction of a system to expel preforms that have become lodged one inside the other - light preforms with small bodies do tend to stack together. The new system ejects them, enabling loading rates of up to 48,000 preforms/hour.
In the SFR rotary stretch-blow molding machine, the shape of the preform carrier has been improved in order to ensure the stability of the preform during heating and to keep the neck temperature as low as possible.
In the oven, in order to process very light necks, SIPA has modified the ventilation modules to improve the cooling of the neck while increasing the capacity to heat the preform. To further improve results, the configuration of the infrared lamps has also been suitably adjusted.
SIPA’s characteristic “crocodile style” vertical mold opening system keeps centrifugal forces on preforms and bottles at a very low level. This means that the grippers do not have to pinch the necks to maintain the preforms and bottles in the correct position. This is an important advantage when it comes to easily deformable lightweight necks.

Downstream

Filling and sealing procedures have to be carried out in a way that stresses the container as little as possible, whatever its design. But this is especially the case with bottles with lightweight necks. SIPA pays particular attention to the force applied by the lifting devices that raise the bottles during the filling process. What also has to be taken into consideration is that the contact force used for hot filling needs to be lower than for cold filling with carbonated soft drinks.
Some hot-fill systems operate without the bottle touching the filling valve, and this limits the time that the neck is being heated to around 30 seconds, while the bottle is tilted. At this point, the bottle has already been sealed and so has been subject to the axial load applied when the closure is attached to the bottle. Furthermore, a neck with the closure in place is stronger than an unsealed neck.
Lightweight necks need to be sealed using an axial load that may be as little as half that used for normal bottles. This issue needs to be addressed together with the manufacturer of the closures, as the load required depends on the interference between the warranty seal and the neck finish.

Integrated systems: SincroBloc and SincroTribloc

SIPA’s Sincro Bloc is a compact and integrated system for high-speed blow molding, filling and capping that guarantees high quality standards at an output at anywhere from 14,000 to 52,800 bottles per hour. Thanks to its direct connection between blowing and filling, Sincro Bloc provides a solution that is particularly suitable for processing of lightweight necks and bottles. The absence of air conveyors, in fact, eliminates the possibility of potential jams.
With Sincro Tribloc, which integrates bottle production, labelling, filling and sealing,the positive holding action using pincers helps even more, eliminating the air-assisted transport of the bottles between blowing and filling as well as the conveyor belt up to the labelling section. This has the potential to further increase the quality of the container.