| 1. |
- Johnson, Tomas, 1979, et al.
(författare)
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A Multi-Scale Simulation Method for the Prediction of Edge Wicking in Multi-Ply Paperboard
- 2015
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 30:4, s. 640-650
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Tidskriftsartikel (refereegranskat)abstract
- When liquid packaging board is made aseptic in the filling machine the unsealed edges of the board are exposed to a mixture of water and hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. To be able to make a priori predictions of the edge wicking properties of a certain paperboard material is therefore of great interest to the paper industry as well as to packaging manufacturers. In this paper an extended multi-scale model of edge wicking in multi-ply paperboard is presented. The geometric and physical properties of the paperboard are modeled on the micro-scale, and include fillers and fines. The absolute air permeabilities and pore size distributions are validated with experimental and tomographic values. On the macro-scale random porosity and sizing distributions, time and sizing dependent contact angles, and inter-ply dependence are modeled. Arbitrary shapes of the paperboard are handled through an unstructured 3D surface mesh. Stationary and transient edge wicking simulations are validated against experiments with excellent agreement. The simulations show that the diffusive menisci between the liquid and air phases together with the two-ply model is necessary to achieve good agreement with the transient edge wicking experiments.
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| 2. |
- Kettil, Gustav, 1990, et al.
(författare)
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Detailed Simulations of Early Paper Forming
- 2015
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Ingår i: COST FP1005 Fibre Suspension Flow Modelling Final Conference Trondheim 2015 June 9-11.
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Konferensbidrag (refereegranskat)abstract
- Computer simulations are important to increase the knowledge of the processes involved in paper making. Because of the complexity of the paper processes the development of simulation tools requires models and numerical methods which capture as much as possible of the real physical phenomena. In this paper a framework for simulation of fiber suspension flow is presented. The framework is founded on a fluid solver for the Navier-Stokes equations and a fiber model based on finite strain beam theory including shearing. Moreover, the coupling between fibers and fluid is resolved with the immersed boundary method and the interaction between the fibers is calculated using a model based on DLVO-theory.
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| 3. |
- Kettil, Gustav, 1990, et al.
(författare)
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Novel Contact Forces for Immersed Boundary Paper Forming Simulations
- 2015
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Ingår i: Online proceedings: http://tappi.sclivelearningcenter.com/; PF2 - The Past, Present and Future of CFD Papermaking; PaperCon 2015 Atlanta April 19-22.
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Konferensbidrag (refereegranskat)abstract
- To be able to simulate the different processes involved in paper machines, models, numerical methods and algorithms have to be developed which capture as much as possible of the real physical phenomena. In this paper a model for calculation of the chemical and physical interaction between objects included in a fiber suspension is presented. The contact force model is based on DLVO theory [1, 2] and uses so-called contact points distributed along the fiber suspension objects. The contact model has been used in an existing framework to simulate the build-up of low density paper webs. In the framework fibers are modeled as elliptical cylinders whose movements are described by finite-strain beam theory which includes shearing. The fluid flow is computed using a Navier-Stokes solver and immersed boundary methods are utilized to resolve the flow around each fiber. For validation, the air permeability and thickness of the paper webs have been measured and compared with simulated data. The result demonstrates that the software can be used to simulate paper forming.
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| 4. |
- Mark, Andreas, 1980, et al.
(författare)
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Modeling and Simulation of Paperboard Edge Wicking
- 2012
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:2, s. 397-402
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Tidskriftsartikel (refereegranskat)abstract
- When liquid packaging board is made aseptic in the filling machine the unsealed edges of the board are exposed to hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. To be able to make a priori predictions of the edge wicking properties of a certain paperboard material is therefore of great interest to paper industry as well as to packaging manufacturers. The aim of this paper is to present a new analytical theory for prediction of the edge wicking properties of paperboard. The theory is based on Darcy’s law and the ideal gas law to describe the physical behavior of water flow in paperboard. The theory is compared to a recently published multi-scale framework and with pressurized edge wick experiments. The agreement is very good for paperboard samples of different sizes. The conclusion from the work is that both analytical theory and detailed simulations are useful to predict edge wicking properties of paperboard material.
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| 5. |
- Rentzhog, Maria
(författare)
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Characterisation of water-based floxographic inks and their interacitons with polymer-coated board
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis comprises two parallel studies dealing with water-based flexographic inks on PE-coated liquid packaging board. The commercial waterbased inks that were used in both studies vary in type of pigment and acrylatepolymer vehicle, and in pigment/vehicle mixing proportions. One vehicle is solely based on emulsion polymer, another contains solution polymer, and the third is a 50/50 blend of these two. The first study presents results from characterisation of a matrix of these water-based inks with respect to their rheology, surface tension and wetting of PE-coated board. The rheological properties were measured over a wide range of shear rates relevant to various stages in the printing process. All inks represent shear thinning fluids, forming thixotropic structures. The plastic viscosity and yield stress are shown to increase strongly with content of solution polymers (at comparable solids contents). Measurements of static surface tension and drop spreading, on untreated as well as corona treated board, clearly display differences in interfacial properties for the vehicles. An increasing amount of solution polymer give lower surface tension values, while the equilibrium contact angles increase. The validity of a simple model for expressing the ink drop spreading dynamics was tested and could be applied to spreading on treated board. The rheology, surface tension and wetting properties are also shown to depend on the pigment type (cyan or black) in the ink and on the pigment/vehicle mixing proportion. In the second study, the print performance of this matrix of inks on the PE-coated board was evaluated. Changes in the ink formulation are shown to have significant influence on the ink amount transferred to the board and the print quality parameters. The 50/50 intermediate vehicle consistently gave the highest ink amounts, although the highest print density generally was obtained with the vehicle containing most solution polymer. High contents of solution polymer also resulted in more uniform prints and high print gloss. Mottling was most severe with the vehicle containing solely emulsion polymers. The transferred wet ink amount is demonstrated to correlate well with the plastic viscosity and static surface tension of the ink.
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| 6. |
- Rentzhog, Maria, et al.
(författare)
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Correlations between properties of water-based flexographic inks and their print uniformity on PE-coated board
- 2006
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 21:3, s. 403-410
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Tidskriftsartikel (refereegranskat)abstract
- Uniformity of fulltone flexographic prints on PE-coated board was investigated for a large matrix of aqueous inks with varying acrylic-based vehicles and pigment concentrations, and with their applied amounts varied using a wide range of anilox volumes. Print mottle was characterised by coefficient of variation of reflectance, and partitioned into different feature-size classes. For all prints the mottle was caused by the residual pattern of white (poorly-covered) stripes originating from the anilox ruling, and subsequently distorted and redistributed to both finer and coarser length scales during transfer to, and flow on, the print substrate. Accordingly, mottle was largest on the sub-millimetre scales encompassing these stripe features, and generally increased with anilox volume, approximately proportionally so on above-millimetre scales. While greater pigmentation naturally increased both print density and mottle, the vehicle also exerted a strong influence, with mottle decreasing with increased content of soluble (versus emulsion) polymers. The latter was principally due to the associated increase in low-shear viscosity and decreased surface tension, both serving to reduce substrate dewetting. Empirical relations accurately correlating mottle to these two ink properties, and anilox volume and print density, were established.
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| 7. |
- Rentzhog, Maria, et al.
(författare)
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Effect of corona treatment of PE-coated board on water-based flexographic print resistance
- 2006
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 21:2, s. 202-210
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Tidskriftsartikel (refereegranskat)abstract
- The effect of corona treatment of Polyethylene-(PE-) coated liquid packaging board on its surface chemistry was quantified using surface energy determination by drop spreading and dyne-liquids, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The increase in total surface energy, due to its polar component, with increasing corona dosage, and its decrease on aging and washing, was strongly correlated to surface oxidation fraction from XPS. A fine structure of nano-mounds formed by oxidised material was revealed by AFM, with size and substrate coverage increasing with corona dosage, but no longer visible after washing. Resistance properties of water-based flexographic prints on these treated PE substrates were tested, with only wet rub resistance exhibiting a significant dependence on corona dosage. This property first increased at lower dosages before decreasing at higher levels, presumably due to worsened water resistance from soluble oxidised material dissolved in the ink film.
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| 8. |
- Rentzhog, Maria, et al.
(författare)
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Influence of formulation and properties of water-based flexographic inks on printing performance for PE-coated board
- 2005
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 20:4, s. 410-417
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Tidskriftsartikel (refereegranskat)abstract
- In this study the flexographic printing of lowdensity polyethylene- (LDPE-) coated liquid packaging board is analysed for a range of water-based inks, varying in type of pigment and acrylate-polymer vehicle and pigment/vehicle mixing proportions. One vehicle is solely based on emulsion polymer, another contains solution polymer, and the third is a 50150 blend of these two. Vehicle type and relative amount are shown to have a strong and systematic bearing on the absolute amount of ink transferred and its corresponding print density, gloss, and uniformity. For both ink colours (cyan and black), transferred amount increases with pigment content and is highest for the 50150 intermediate vehicle. Print density and homogeneity are generally highest for the vehicle containing highest content of solution polymer, at least with the lower anilox volumes, and this vehicle also gives highest print gloss. The wet amount of ink transferred is shown to be well correlated to its surface tension and viscosity.
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| 9. |
- Rentzhog, Maria, et al.
(författare)
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Print quality and resistance for water-based flexography on polymer-coated boards: Dependence on ink formulation and substrate pretreatment
- 2006
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Ingår i: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 57:3, s. 183-194
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Tidskriftsartikel (refereegranskat)abstract
- The performance of water-based acrylic flexographic inks laboratory printed on three different polymer-coated boards, namely coated with LDPE, OPP and PP, have been analysed and interpreted. The print quality and resistance properties obtained were related to varying ink formulation, in particular choice of emulsion polymer and presence of silicone additive in the vehicle, as well as varying levels of corona pretreatment. Print mottle and adhesion were worst on PP, while wet (water) rub and scratch resistance were worst on OPP and PE, respectively. However, these properties could be greatly influenced by the ink formulation, more so than corona level. In general addition of silicone improved scratch resistance, due to reduction in polar energy component of the print surface, but at the expense of worsened wet rub resistance. The emulsion polymer giving best resistance performance was generally found to give poorest optical properties, presumably due to more limited resolubility on press.
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| 10. |
- Rentzhog, Maria, et al.
(författare)
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Rheology and surface tension of water-based flexographic inks and implications for wetting of PE-coated board
- 2005
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 20:4, s. 399-409
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Tidskriftsartikel (refereegranskat)abstract
- This study systematically characterises a matrix of water-based flexographic inks with respect to their rheology, surface tension and wetting of liquid packaging board, to provide a basis for interpretation and prediction of their printing performance. For all pigment and acrylate polymer vehicles and mixing proportions the inks were shown to be shear thinning and thixotropic, with plastic viscosity, yield stress and storage and loss moduli increasing strongly with content of solution polymer (at comparable solids contents). The solution polymer decreases the static surface tension of the inks, but generally leads to an increase in their equilibrium drop contact angle oil the polyethylene- (PE-) coated board due to increase in the ink-board interfacial energy. The solution polymer also decreases the drop spreading rate, and a simple model is tested to express the spreading dynamics in terms of equilibrium contact angle and a rate parameter given by the effective ratio of surface tension to viscosity.
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