Influence of pre-creasing on the 3D formability of paperboard in the thermoforming process

Abstract

This thesis investigates how pre-creasing influences the three-dimensional formability of paperboard in fixed-blank thermoforming. Thermoforming of paperboard is a viable method for producing fibre-based packaging as a sustainable alternative to plastic, but its forming performance is limited by low stretchability, anisotropy, and moisture sensitivity. While pre-creasing has been studied in press-forming of paperboard, their effect in fixed-blank thermoforming has not been systematically investigated. The objective of this work is to examine how pre-creasing affects deformation behaviour, forming depth and draft angle by 3D shape analysis. Experiments were conducted using systematically designed pre-creasing patterns with increasing density, applied to two commercial grades of PET and PE coated paperboard under controlled thermoforming conditions. A reference pattern without creases and four pre-creased patterns were tested. The formed samples were evaluated using three-dimensional optical profilometry. The results show that pre-creasing mainly redistributes deformation within the sheet. However, its effect on the total deformation capacity depends on the paperboard material. Increasing crease density shifts deformation between directions depending on the elongation capacity of the paperboard. For paperboard with higher elongation capacity, the total deformation area remains nearly constant, while for paperboard with lower elongation capacity, pre-creasing enables additional deformation by reducing stiffness-related strain localisation.

Overall, in the case of the studied paperboard materials, pre-creasing improves forming consistency and strain distribution without significantly increasing the total deformation area, but its effectiveness depends on the elongation properties of the paperboard material.