Search

The requirements for embossing of cardboard for print and packaging applications are constantly increasing. High degrees of forming, richness of detail, and high shape accuracy are desired. However, current embossing technology can only fulfil these requirements to a limited extent. A loss of detail and moderate degrees of forming are typical defects in the embossing process. In previous research work, a positive effect on the forming behavior of cardboard could be observed by the application of ultrasound. Therefore, the influence of ultrasound was also investigated for embossing. In order to quantify the effects of ultrasound, conventional and ultrasonic-assisted embossing results were compared. New approaches for analysis and evaluation of embossing results and new characteristic values for describing the forming were applied for the comparison. Two exemplary embossing geometries and a range of ultrasonic parameters were used to characterize the impact of ultrasound and showed positive effects to the forming results. [ABSTRACT FROM AUTHOR]

Embossing is a commonly used design element on printed products and packaging. It enhances the product impression with optical and haptic effects. The material deformation during the embossing of cardboard is normally done using high mechanical pressure between two dies. The use of ultrasound in the embossing process leads to a noticeable reduction of the embossing pressure and a greater embossing precision. However, there is a noticeable heating of the cardboard during the ultrasonic-assisted embossing process. This work aimed to characterise the effects of heating and to understand the reasons for the greater precision with decreased force when ultrasound is used. Therefore, the effects of the thermal ultrasonic energy on the chemical composition and the morphological properties of the fibres were investigated. The findings showed that no noticeable changes occurred in the chemical composition or fibre geometry as a result of the embossing process with ultrasound. [ABSTRACT FROM AUTHOR]

During the embossing process, a fiber sandwich is compressed between embossing tools. The use of ultrasound causes a short-term increase in the material temperature in addition to causing plastic deformation. The combination of the material compression and an increase in material temperature leads to structural changes, which can be observed by the change in mechanical properties of the cardboard. This work investigated the influence of an ultrasonically induced temperature increase on the structural changes of cardboard. Using three-parameter combinations, different temperature levels were achieved with a material densification of less than 5%. Subsequently, the samples were subjected to selected physical and visual analyses to characterize the change in the fiber structure. With the increase of 124 °C material temperature there was a decrease of about 15% in the splitting resistance and 10% in the bending stiffness. [ABSTRACT FROM AUTHOR]