This paper aims to describe an in-plane detaching resistance of a white-coated paperboard subjected to a peeling deformation. Since the paperboard is composed of fibrous plies, its detaching mechanism seems to be different from a crack propagation of a fragile material. In this work, an internal breaking criteria and transient de-lamination of a weak-bonded layer of paperboard was experimentally investigated through a peel cohesion test (PCT), and its detaching resistance was estimated with a fluffing model using a finite element method (FEM) code to characterize the peeling deformation of the weak-bonded layer. A white-coated paperboard of 0.45 mm thickness (basis weight of 350 gm 2 ) was chosen for conducting a PCT and z-directional (out-of-plane) tensile test (ZDTT). The relationship between the pulling force and curvature of delaminated upper layer of the paperboard were discussed; moreover, the anaphase yielding resistance of detaching was analyzed through ZDTT. The peeled deformation of PCT was analyzed using the isotropic elasticity FEM model, which was developed through the ring crush test. The results were as follows: (1) The in-plane detaching resistance of whitecoated paperboard by PCT is experimentally characterized for observing with the maximum peak at early stage and the stationary line force. These line forces are almost independent of the paper-making direction. (2) A fluffing profile of the de-laminated layer and the thickness of the peeled upper layer experimentally depend on the pulling velocity. (3) Regarding the detaching resistance of peeled layer, a fluffing model was proposed in the developed simulation model. Equivalent fibers based fluffing model that were derived from a ZDTT experiment (approximated as discretely distributed nonlinear springs) well explains the existence of the peak point of peeling force and saturated peel resistance.

This study aims to develop a numerical simulation model of the folding process of a creased paperboard and to reveal the deformation characteristics of the creased paperboard. A cantilever type bending moment measurement apparatus was experimentally examined with a 0.43-mm thickness paperboard. To verify the folding mechanics of the creased part, the initial crease was varied within a certain range, and the lamination numbers were considered with 8 layers. A fluffing resistance model based on the z-directional (out-of-plane) tensile test was developed and simulated using isotropic elasto-plastic solid properties. However, because the fluffing resistance is restricted in the normal direction of the detached interface, in-plane shear resistance is not considered. When investigating the folding process of a creased part, the in-plane shear resistance and its breaking limit seem to be the primary characteristics. Therefore, in this work, in order to characterize the delamination and bulging deformation, an internal breaking criteria was numerically analyzed using a new combination model. A general purpose finite element method (FEM) code was applied to develop a combination model comprising the out-of-plane fluffing subroutine and the in-plane shear glue strength. Through the FEM simulation of the folding process of creased paperboards, the following results were revealed: (1) The simulated bulging profile of the creased part and its bending moment resistance well matched with the corresponding experimental result at the stationary folding state with a folding angle >20°. (2) The in-plane shear glue strength characterizes the pattern of the interlayer delamination in the folding process of the scored zone. (3) The initial delaminated span of the scored zone is estimated as >150% of the creasing width. (4) The initial gradient of the bending moment resistance is characterized by the scored depth.Keywords : Bending, Folding, Delamination, Bulging, In-plane shear strength, FEM, Fluffing, Scored depth IntroductionCoated paperboard is widely used in the packaging industry owing to its benefits such as a high strength-to-weight ratio, high surface smoothness, printability, sustainability and recyclability. In the production of packaging containers, wedge-pushed cutting, creasing by the flatbed die cutter and the folding of creased lines are inevitable and determine the quality of containers (Kirwan, 2013). In the formation of blank patterns made of paperboard, a suitable residual stiffness of the creased parts is necessary for processing the fold of the paperboard in an automatic folder-gluer machine, and the creased lines must be stably folded without any surface failures. Namely, the creaser indentation depth against the paperboard must be controlled to retain the folding strength of the creased lines and the appropriate bulge that forms in the fold's interior. These procedures were empirically managed by experts in the past. However, to process this formation automatically in the folder-gluer machine, an appro...

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This research work deals with the development of simple evaluation method of creasing characteristics of coated paperboard. The recent-developed testing device (CST, crease stress tester) is able to control the bending rotation speed of the creased part of a worksheet and its sleeping time at a specified angle position. Although the CST is a high grade equipment and useful for analyzing the bending characteristics, while the cost performance of equipment for simply having assurance of crease stiffness is another problem. The authors have developed a simple evaluation method for knowing the creasing characteristics on a folded line of paperboard, which is subjected to an in-plane compressive load by using a set of V-block fixtures. Through the bending experiment of creased paperboard, the proposed V-Block based estimation method has been compared with some analysis results based on the CST, and its effectiveness was revealed. The primary results were as follows: (1) The buckling strength as the maximum compressive load is characterized with respect to the nominal shear strain (normalized scoring depth of crease). (2) The transitional point as variation tendency of compressive load (by the V-Block) well coincides to the disappearance of peak bending moment of CST. (3) The equivalent bending moment of V-Block well coincides to the CST based bending moment resistance when choosing a certain large folding angle. (4) The proposed V-Block method can be effectively used for a certain large range of folding angle.

<abstract> <p>This study reveals the crease deviation behavior through the developed forming simulation. A combination resistance model was expanded and applied to simulate the 180° folding process of a creased paperboard, using the shear-yield detaching resistance and the out-of-plane fluffing resistance which were based on the isotropic elastro-plastic model. When varying the misalignment of the creasing rule against the groove, the eccentricity of the crease bulging of a white-coated paperboard was compared through the experiment and simulation of the 180° folding process. Comparing the experimental deformation and the simulation, it was explained that the deviation of <italic>e</italic> contributed to making the crease deviation <italic>c</italic>_d. At the folding test, the 180° folding was compared with the experiment and simulation. The rolling pass of the folded zone was considered to intensify the deviation state. The 180° folding simulation revealed that the crease deviation of <italic>c</italic>_d ≈ 2<italic>e</italic> was assessed as an ideal condition when using the rolling pass and non-rolling pass. In the case of some shallow indentation in the experiment, 2<italic>e</italic> &lt; <italic>c</italic>_{<italic>d</italic>} &lt; 4<italic>e</italic> was observed. The inside folded corners were quite different between the simulation and experiment, especially for a certain shallow indentation model. In the simulation, the local crushing was not performed under the assumption of any isotropic properties. In the simulation, the deviation of the creased position at the 180° folding was sufficiently predictable, when compared with experimental behavior.</p> </abstract>