Fraunhofer Institute for Process Engineering and Packaging IVV
Challenges presented by switching to monomaterials in the joining process
An increasing number of monomaterial packaging films are being developed to improve the recyclability of plastic packaging. However, monomaterial joining is severely limited by conventional heat contact welding, as the heat has to be conducted into the joining zone from the outside, resulting in complete melting of the seam area. In addition to impairing the seam quality and appearance, heat input over a wide area can cause damage to delicate packaged goods. Other disadvantages include high energy consumption and long sealing times.
Efficient joining technology for monomaterial film systems
High-frequency welding offers a promising alternative. Exciting the plastic molecules in a high-frequency alternating electrical field heats the film packaging material directly in the joining zone. The welding process is characterized by a high welding speed, lower energy consumption compared to conventional joining processes and very little structural impact on the joined materials. The process is cost-effective and low-wear. However, the use of high-frequency welding is limited to materials with suitable dielectric properties, such as PVC or PU, which are often not suitable for use in food or consumer products.
The aim of the research project is to take advantage of the benefits of high-frequency welding for industrial use with common recyclable monomaterials made of PE or PP. Chemical modifications are being developed to improve the dielectric properties of the monomaterials and make them suited to HF welding.
HF welding devices and systems that have been used up to now in the plastics sector operate at a fixed frequency of 27.12 MHz. In order to enable needs-based, dynamic adjustment of the performance parameters during the welding process, a HF generator is being developed that operates in a flexible frequency range from 27.12 to 150 MHz.
Development of a flexible joining demonstrator
As part of the research project, a joining demonstrator for the HF sealing of monomaterials is being constructed, integrating a newly developed sealing unit and the HF generator. The technical functionalities of the demonstrator take into account factors such as competitive process times, high seam strength, homogeneous heating of the entire joining zone and the avoidance of any temperature effects on the contents. The demonstrator has an operator interface and an innovative machine control system for clear process control and flexible adjustment of the sealing parameters.
The first step in the development of the demonstrator is to determine the input variables and boundary conditions. Based on these requirements, a test setup in the small signal range of 250 W is designed to determine the requirements for the subsequent HF equipment (tool arrangement, tool design, electrode geometry and material). The test rig is also used to carry out basic experimental investigations to determine the relevant material parameters of the films by means of numerical simulation.
Project information
| Project duration | Juli 1, 2022 to September 30, 2024 |
| Cooperation partners | Technische Universität Chemnitz (Professur für Umformendes Formgeben und Fügen), IMS Maschinenbau & Entwicklung GmbH, barthel HF-Technik GmbH, POLIFILM GmbH, Spano GmbH Spannsysteme und Normalien |
| Project sponsor/Grant authority: | Zentrales Innovationsprogramm Mittelstand (ZIM) / Bundesministerium für Wirtschaft und Klimaschutz |