Manufacturing bottles by thermoforming film material is not new. Thermoforming is a generic term for the manufacturing of plastic components through the vacuum and / or pressure forming processes. A simplistic overview of the single-sheet thermoforming process consists of heating extruded plastic sheet and forming the sheet over a male mould or into a female mould. (For a detailed explication of the thermoforming process see the end of this article).
The first attempts to create bottles by thermoforming were in the 1930s, but, although a number of projects has been pursued, they all were without commercial success.
The recent years, however, have seen successful developments in thermoforming bottles, closed with a pre-punched round aluminium seal, especially in the sector between 50 – 200 ml bottles used for yogurt, juice and isotonic drinks.
The Illig Technology
For this market segment Illig Maschinenbau GmbH & Co. KG, in Heilbronn / Germany introduced its Bottleform BF 70 process in 2008. The material is drawn from the reel, heated and deep drawn in the forming station, mechanically pre-stretched, and subsequently formed by using sterile pressure air. However, due to the bottle design with its significant undercuts, it is necessary to have movable tool parts to enable de-moulding of the bottles. In addition a forming procedure has to be found, which enables an absolutely uniform wall thickness distribution despite reduced initial area and high depth of draw. With the use of specific tools in combination with a servo plug assist and control of the forming air it is possible to deep draw bottles at a stability in line with market conditions even out of a material only 1.4 mm thick (top load)!
The stability of the bottle is a decisive feature for further procedures like filling, sealing and transport. This applies for both the vertical load and the stability of the side walls.
The bottle rims have always to be absolutely even round for sealing. The quality of the sealing rims is decisive for the exact sealing. The secure lock between round plate and bottle guarantees longer durability.
Products do not show a middle seam that is a typical characteristic of blow moulded bottles.
Illig claims that a comparable bottle made by blow moulding has an average weight up to 8.5 gram. A thermoformed bottle stays far below this weight, as the average weight is 4.5 gram.
The Agami ‘Roll N Blow’ Technology
It is obvious that this system has its limits in terms of dimensions (50 – 200 ml). Furthermore they have a sealed top and not a screw closure as blow moulded bottles have. But more recently we have seen the solution for both problems with the development of Agami in France by blow moulding / thermoforming plastic bottles from the reel. I wrote about this development in my article “Highlights of Interpack 2011 – The Second Day”.
The Bottle Thermoforming machine ‘Roll N Blow’ of French company Agami, is based on an innovative technology of tubular thermoforming from a plastic sheet in reel. This sheeting is cut into strips, and each strip is shaped into a tube around a blow pipe. Each strip is then welded lengthwise and the resulting plastic tube is heated and blown into a mould, in order to create the bottle. This technology authorizes high and round shapes for a volume from 100 to 500 ml.
The Hol-Pack Technology
The world of thermoforming bottles is getting much more interesting since a mainly unknown Rudolf Holzleitner, of Hol-Pack Verpackungen from Piberbach in Austria, patented (EP2091829) his invention.
Hol-Pack patented the thermoformed, welded plastic bottle for filling non-carbonated liquids for larger bottles, up to 1.25 litres. The Hol-Pack process involves thermoforming two sheet halves, joined in such a way that the parting line forms a flange-shaped undercut within the bottle. The flanges are welded together at the end of the bottle forming process. The parting line can be arranged along or across the bottle vertical axis.
The lengthwise version allows for production of multi-chamber bottles. Sleeves and labels can be used to conceal the weld line, which is visually unappealing but adds stiffness to finished bottles.
Bottling companies have the option whether to manufacture the entire bottle from a film reel, or buy pre-made semi-finished halves and only carry out the welding of the delivered items on their own machines.
As it is possible to thermoform such semi-finished products in a stackable version, the stackable semis also allow for a commercially interesting modular system. Easily changeable, various bottle shapes are achieved by the fusion of different parts. This technology allows bottlers to a great variety of options and flexibility in bottle shapes as well as in material.
Technically the welded sheet thermoformed bottles feature, compared with blow-moulded bottles, a higher stiffness, due to the welding of the undercuts.
Up till this moment the thermoformed, welded plastic bottles only are suitable for filling non-carbonated liquids, but I am sure that future development will eliminate this restriction and that we will see quite some new applications for this technology, due to its economic prizing, its flexibility in processing, the almost unlimited choice of material, and the almost unlimited free-hand of the designer.
What is Thermoforming?
For my readers who want to know in more detail about the thermoforming technology. Here are the principles.
Thermoforming is a generic term for the manufacturing of plastic components through the vacuum and / or pressure forming processes. A simplistic overview of the single-sheet thermoforming process consists of heating extruded plastic sheet and forming the sheet over a male mould or into a female mould. Depending on what type of mould a customer selects, the thermoforming process allows the customer the ability to receive a part with the same aesthetic properties as an injection-moulded part at a fraction of the tooling expense involved in injection moulding.
There are 4 basic processes in the Thermoforming Technology: Vacuum Forming, Pressure Forming, Mechanical Forming and Pressure Diaphragm Forming.
Vacuum Forming – The most common method with the simplest mould. The sheets adhere to the mould using atmospheric pressure. Various other versions of the process are available, using pre-blowing (balloon), negative forming (plug assisted), reverse blow moulding, etc.
Pressure Forming – A blowing bell is combined with the mould, in order to increase, through the use of compressed air, the adherence of the sheet onto the mould. Indispensable for tenacious materials and clearer definition on the surface of the sheet in contact with the mould.
Mechanical Forming – Pre-cutting negative forming (plug assisted) is combined to the base mould in order to obtain areas precise details on the surface of the sheet opposite that facing the mould.
Pressure Diaphragm Forming – The sheet adheres to the mould through the use of an elastic diaphragm which is compressed by a high pressure fluid. Indispensable for extremely tenacious materials.
Some of these same principles apply to another thermoforming processes: twin sheeting. Twin-sheeting is heating two sheets of plastic and forming simultaneously on two opposing half-moulds, and then welded together under high pressure. Cavities can also be created with materials of varying colour and type.
In some cases, the twin-sheeting process produces parts that resemble a blow-moulded part, but the twin sheeting process allows the customer to receive 1) a higher quality, more aesthetic part, 2) a two colour part, and 3) a part with an assembly device trapped inside as the part is being formed.
source: Kenplas Industry Ltd.