A finite element model of a flexo post-printing press for corrugated board has been developed to determine the principal causes for local variations of printing pressure. It is the first, full-structure model of the flexo post printing system, including liners and medium boards of corrugated board as well as printing plate and backing materials. A parametric study has been performed to investigate how the properties and dimensions of these materials used in the printing system affect the printing pressure variations. It showed that the liner board and the photopolymer properties had the greatest impact on the local variations of printing pressure. However, `washboarding', defined as a periodic geometric imperfection of the corrugated board structure, had a limited impact on the pressure variations. It has been demonstrated that alleviating the printing pressure variations is possible through the optimization of printing plate materials within a realistic range of constitutive parameters.

SUMMARYA two-dimensional multi-phase model for immiscible binary fluid flow including moving immersed objects is presented. The fluid motion is described by the incompressible Navier-Stokes equation coupled with a phase-field model based on van der Waals' free energy density and the Cahn-Hilliard equation. A new phase-field boundary condition was implemented with minimization of the free energy in a direct way, to specifically improve the physical behavior of the contact line dynamics for moving immersed objects. Numerical stability and execution time were significantly improved by the use of the new boundary condition. Convergence toward the analytical solution was demonstrated for equilibrium contact angle, the Lucas-Washburn theory and Stefan's problem. The proposed model may be used for multi-phase flow problems with moving boundaries of complex geometry, such as the penetration of fluid into a deformable, porous medium.

Predicting how long time a corrugated board box can be stored with a constant load stacked on top of it without failing is an everyday challenge for a box designer. This is a basic step in corrugated board box material design which is usually resolved by utilizing so-called stacking factors. A stacking factor is the ratio between the compression strength of the box and the stacking load. Higher stacking factors are used to accommodate for longer storing times or high relative humidity conditions. Utilizing stacking factors in the way commonly done today can be a good first approximation. However, this method often neglects or overcompensates for the inherent nonnormal distribution statistical behaviour associated with corrugated board box lifetimes. A higher precision in predicting box lifetimes enables material optimization and, thus, a more efficient use of resources. This work presents a convenient way of predicting lifetimes of both containerboards and corrugated board boxes. The approach additionally introduces the concept of reliability into lifetime prediction.The prediction is made directly from material or structural parameters and the applied load. This is accomplished by relating two different parameter sets for the Weibull distribution. It is shown that lifetime is indeed dependent not only on a stacking factor but also on durability and the variations associated with the material or box.

Print non-uniformity is a major concern for fl exo post-printers. Many of these nonuniformities are suspected to be caused by the corrugated board structure itself. Striping is the most obvious one, but also other print quality problems might be structure-related. This work focuses on how deformations of the board might lead to print non-uniformities, and if the deformation of halftone dots is the mechanism behind striping in halftone fl exo post-printing. Finite element models were used to analyse the effects of deformations of corrugated boards and compressed halftone dots in the printing nip. Distortions of the board due to non-uniform hygro-thermal strains were shown to be a potential cause of print non-uniformities. Striping in halftone prints was found to be caused by differences in dot gain between areas above ridges and valleys of the fl ute structure.

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