This makes it possible for the first time, to process materials that until now were difficult, or virtually impossible to process. For example, mono-materials, recyclates and bio-based compositions or films. The latest white paper from watttron provides further new sustainability drivers and reveals some ground-breaking process advantages.
Watttron explained to SPN the background technology to the cera2heat matrix heater and its advanced sustainability benefits: “With the signals of climate change getting ever stronger, the increasing environmental awareness and emerging protest against plastic pollution are major driving forces for creating plastic or plasticised packaging alternatives.
One of the sustainable options is the moulded fibre pack, as this is made of renewable, recyclable, and biodegradable paper fibres. The main challenge of any moulded fibre packaging is the lack of barrier protection against liquids, which makes them unsuitable for drink or food. Despite numerous research projects from reputable companies, there is still no adequate liquid barrier available for moulded fibre packaging.
However, there are different options available for creating a liquid barrier. These are mainly with the application of a layer of plastic film inside the cups. Another option is spraying a plastic coating inside the cup. However, this means that the coating and the cup cannot be separated after use, thereby making the cups unsuitable for recycling and also unbiodegradable.
Furthermore, the existing laminating processes can’t prevent the laminating film becoming unacceptably thin in the deep drawn process areas, allowing the fibres of the moulded pulp to puncture the film and creating a leak within the barrier. Using thicker film to compensate for these punctures is also not a consideration due to cost implications and would make the film extremely hard to separate for recycling purposes.
Production challenges
In addition, the following challenges connected with the existing production processes are worth noting:
- Heating of the thin film using radiation heating is ineffective as the heat is passing through the film.
- The machine complexity is increased due to the necessity of using plug assistance.
- Forming with a plug assistance is aggravated due to the small thermal mass of the film which results in cooling the film below the processing temperature or – in case of a heated plug – sticking to the plug itself.
With the recently developed cera2heat digital heating technology, it is possible to laminate a very thin (80 – 150 µm) layer of plastic film inside the cups during the production to provide the necessary barrier for liquids and food products. Due to the unique nature of the digital lamination, this plastic film has the same thickness in the whole cup and can therefore easily be separated by the consumer. The result is a fully recyclable cup with the additional advantage of the thermal insulation of the paper fibres against hot drinks, something which a standard plastic cup does not provide.
- Moreover, the cera2heat technology offers the following practical benefits:
- Perfect material distribution that allows adhesion up to the bottom corner- without plug assistance
- Greatly reduced heating times compared with existing radiation heating processes
- Less machine complexity, affording a simpler process-flow
- Allowing the processing of materials with small processing windows such as, (PP, rPP, rPET)
- Significant energy saving.
Individual programming and control
A cera2heat matrix heater consists of locally arranged and independently controllable heating pixels. The target temperature of each heating pixel can be individually programmed and controlled. Due to the operating principle, the cera2heat matrix heaters are characterised by both high-temperature precision and accuracy, thereby offering the possibility of processing materials that were previously knowingly difficult to process – such as mono-materials, recyclates, bio-based materials or films with layer-jumps.
By independently adjusting the temperature distribution, the visco-plastic behaviour of the thermoplastics to be processed, can be controlled perfectly as intended. This enables the physically controllable properties of the end-product or manufacturing process – such as air or liquid tightness, wall thickness distribution or heating time, can be achieved. In order to demonstrate the unique possibility to laminate a plastic film into a paper cup, the following settings were made:
- Two matrix-round-heaters in a sandwich mode with 61 independently controllable heating pixels (Figure1)
- Moulded fibre cup with a diameter of 70 mm and depth of 75 mm
- Heating times of approx. 500 ms
- Formed using vacuum-only applied through the cup
- Laminating film made of mono PE material with the thickness of 120 µm
- Temperature profile as depicted on Figure 2
An exemplary forming result is depicted on Figure 3. It can be seen that the forming of the polymer film is formed up to the bottom of the cup and it is firmly connected with the cup. The thinnest spot in the middle bottom part of the cup is 35 µm. When comparing with the homogenous heating and forming without stamp it is 3.5 times thicker.
