Extrusion International 2-2023

40 Extrusion International 2/2023 BLOWN FILM EXTRUSION – FROM THE RESEARCH Data-driven Prediction the Tensile Strength of Blown Film Due To Digital Shadows Prof. Dr-Ing. Ch. Hopmann, Daniel Gr ü ber, M.Sc. Institute for Plastics Processing (IKV) at RWTH Aachen University In addition to the optical and barrier properties, the mechanical properties are used as an important quality factor. The qualitative relationship between the influencing variables and the resulting film properties is largely known, but the findings are, depending on the model, highly machine-dependent. Ohlendorf [Ohl04] derives a property model through an empirical-statistical approach, which already allows a high prediction accuracy for the prediction of the Youngs’s modulus and the film shrinkage. However, a prediction of the tensile strength is not yet possible with sufficient accuracy. An extended modeling approach therefore provides for modeling which, in addition to the known parameters, also takes into account the stretching and cooling behaviour in the tube formation zone. A round 40% of the plastic processed throughout Europe is used in the production of packaging, of which plastic films make up a considerable amount [NN19c]. In Germany, too, the packaging sector repre- sents an important branch of industry with an annual consumption of around 4.4 million tonnes. In addition to packaging, films are also used in medical products, in the automotive and electrical industries, and in the agri- cultural and construction sectors [Nen06]. Because plas - tic films can be further processed into a wide variety of products, machine producers are faced with increasing challenges: Advancing globalisation and the associated worldwide price competition. To remain competitive in the long term, it is often necessary to position oneself in the market by means of unique selling points such as in- creasing productivity with high product quality [Dis13]. Next to flat film extrusion, blown film extrusion is the most important production process for plastic films [Nen06]. Compared to flat filmextrusion, the advantage of blown film extrusion is that the film width and thick- ness can be varied flexibly without having to modify the line or die technology. Biaxial properties of the film can also be adjusted in a targeted manner, which, howev- er, requires a high level of process knowledge [Lim13]. Therefore, non-knowledge-based process control, only using machine parameters like take-up ratio, blow-up ratio or frost line ratio, usually does not lead to the de- sired film properties, as the shape of the foil geometry is not included in the modelling. In addition to the op- tical and barrier properties, the mechanical properties are used as an important quality criterion. The quali - tative relationships between the influencing variables and the resulting film properties are largely known, but the findings are highly material-dependent and often machine-dependent, which means that a calculation of the mechanical properties without extensive, empirical investigation is only possible with reduced prediction quality [Ohl04]. Ohlendorf therefore developed a material-dependent calculation model which aims to predict the mechanical properties based on process parameters, thus enabling transferability to other machines [Ohl04]. However, a validation of the model shows that the transferability is only possible to a limited extent, which is due to an in- complete description of the process state, e.g. the ther- mal and stretching history of each segment of the film. Therefore, in the following an approach to increase the model quality is presented to increase the transferability of the empirical process model to other production ma - chines. For this purpose, it is first explained how the mechani- cal properties of blown films are influenced by pro- cessing. Subsequently, the process model according to Ohlendorf is explained and optimisation measures for increasing the model quality are shown. Determination of the mechanical properties of blown films The mechanical properties of blown films are set to a large extent in the tube formation zone between the die and the frost line. They can be qualitatively attribut -