The aim of this project was to use plastics in an innovative way to create an improved lunch box. The design team consisted of Tony Larsson, Fanny Odland, Johanna Österström and Andreas Lindegren.
Research showed that a good lunchbox, regardless of material, should be easy to clean, not leak food when in your bag and also be stackable to save space.
Further the following material requirements would need to be fulfilled to withstand normal use and live up to the high standard that the product was aiming for.
The New Lunch Box
The New Lunch Box consists out of three modules: one small and one big module for holding the food, and one middle module for joining the top and bottom by screwing into it. By having two separate compartments in the lunch box it is easy for the user to divide the food that should be microwaved from the food that should not. For example a user could bring cold meatloaf in one compartment and a salad in the other. When the time comes to heat the food the user simply screws off the compartment with the salad and puts the meatloaf into the microwave.
By having the storage modules be of two different sizes a customisability is allowed for in the lunch box. A person that eats a lot might choose to have two large compartments, while one that eats a little might use two small ones. If the food does not need to be separated it is even possible to only use one food storage module.
The material used in the small and large modules is Polyvinylidene Fluoride (PVDF). This high end plastic material has excellent properties that will ensure a long product life and make it a premium product. PVDF has the following properties which make it a great material for the food compartments:
- Excellent chemical resistance
- Service temperature up to 150°C
- Translucent to show food
To achieve a tight closing mechanism that does not allow food to spill out into the users bag, threads have been added to the food compartments and the middle module. While this mechanism for closing gives the user complete confidence that the food will not spill out it also adds a potential safety hazard.
If the user puts the lunch box into the microwave in a sealed state pressure will start building up as there is no way for the air and vapour to escape. This is a serious problem that could lead to the user being burnt by hot pressurised vapours when opening the lunch box.
To account for this potential safety hazard the middle lid has been made out of low density Polyethylene, a material with a significantly higher thermal expansion coefficient than the food containers made out of PVDF. This means that when the temperature starts rising the middle will expand more from the heat than the food containers. After a certain point the difference in expansion will have made the threads of the screwing mechanism lose grip, thus letting the excess pressure and vapours escape and removing the danger for the user.
When this safety mechanism is engaged the lid will most likely be deformed from the heat to an extent that it cannot be used again. But since the middle lid is made out of one of the cheapest plastics available, low density Polyethylene, this will not be a big loss for the user, and much preferred to the alternative of being badly burnt.
Unlike safety valves this solution does not create spaces that are hard to clean where bacteria can flourish. It is also advantageous to safety valves as the mechanism is not made more complicated from this solution.
Because the food compartments have slanted sides they can easily be stacked into each other, making compact storing possible.
In order to validate the manufacturing process of injection moulding the product was analysed with Autodesk Simulation Moldflow 2014. The CAD model was imported and the injection location was set to the center bottom of the piece. After the analysis, the model was checked for sink marks and cooling quality. No inconsistencies were found.
The final design of The New Lunch Box is friendly, carefully considers the users needs, and elegantly accommodates them. Simply put, it is a product that will bring you joy for many years.