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  • 1.
    Holmvall, Martin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Nip Mechanics, Hydrodynamics and Print Quality in Flexo Post-Printing2010Doctoral thesis, comprehensive summary (Other academic)
  • 2.
    Holmvall, Martin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Striping on flexo post-printed corrugated board2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Striping is the most common print non-uniformity on corrugated board. It is defined as periodic print density and/or print gloss variations parallel to the flutes. Corrugated boards are mainly printed with flexography, making striping a major concern for the flexographic post-printing industry. In spite of its long history, the basic mechanisms of striping have not been fully understood, and no concrete solution has been provided. The objective of this thesis is to obtain an understanding of the fundamental mechanisms behind and a solution to striping. Both experimental and numerical approaches have been taken in thiswork. Nonlinear finite element models have been constructed in both corrugated board and halftone dot scales to determine the pressure distributions in the printing nip. Ink transfer experiments have been performed to determine the print density vs. pressure relations. Parametric studies have been done for the effects of printing system variables and deformations. The results showed that striping is predominantly print density variations caused by pressure variations in the printing nip. The pressure variations are inherent to the corrugated board structure. Washboarding was shown to play a minor part in causing print density variations, but might contribute to gloss striping. A new printing plate design has been proposed to eliminate the pressure variations and hence the print density striping.

  • 3.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Drolet, Francois
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Lindström, Stefan
    Micro-fluidics in printing nip - Liquid transfer on random fibre network surface2011In: Progress in Paper Physics Seminar, Graz, Austria: Verlag der Technischen Universität Graz , 2011Conference paper (Other academic)
  • 4.
    Holmvall, Martin
    et al.
    SCA R&D Ctr, SE-85121 Sundsvall, Sweden.
    Lindström, Stefan
    Royal Inst Technol, Dept Fibre & Polymer Technol, S-10044 Stockholm, Sweden.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Simulation of two-phase flow with moving immersed boundaries2011In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 67, no 12, p. 2062-2080Article in journal (Refereed)
    Abstract [en]

    A two-dimensional 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. The immersed boundary method has been utilised to handle moving immersed objects and the phase-field boundary conditions have been adapted accordingly. Numerical stability and execution time was significantly improved by the use of a new boundary condition which implements minimisation of the free energy in a direct way. 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 two-phase flow problems with moving boundaries of complex geometry, such as the penetration of fluid into a deformable, porous medium.

  • 5.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Nip Mechanics of Flexo Post-Printing on Corrugated Board2006In: Euromech Colloquium 486, 2006Conference paper (Other academic)
  • 6.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Nip Mechanics of Flexo Post-Printing on Corrugated Board.2007In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 41, no 17, p. 2129-2145Article in journal (Refereed)
    Abstract [en]

    A finite element model of a flexo printing press has been developed and the material and geometrical properties of the sustem has been investigated. The results showed that it is the photopolymer and the top liner that have the biggest impact on the printing pressure variations.

  • 7.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Print Uniformity of Corrugated Board in Flexo Printing: Effects of Corrugated Board and Halftone Dot Deformations.2008In: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 21, no 7, p. 385-394Article in journal (Refereed)
    Abstract [en]

    Print non-uniformity problems are a major concern for flexo post-printers. Many of these non-uniformities 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 flexo post-printing. The problems were analysed by using finite element models to simulate deformed board and halftone dot compression 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 ridge and valley areas above the flute structure.

  • 8.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Striping of Corrugated Board in Flexo Post-Printing2006In: International Printing and Graphic Arts Conference proceedings 2006, 2006Conference paper (Other academic)
    Abstract [en]

    By doing ink transfer experiments and measuring reflectance variations on corrugated boards it was found that striping mainly consists of print density variations and not print gloss variations.

  • 9.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Striping of Corrugated Board in Full-tone Flexo Post-Printing2008In: Appita journal, ISSN 1038-6807, Vol. 61, no 1, p. 35-40Article in journal (Refereed)
    Abstract [en]

    Striping is a print defect that is often seen in flexo post-printing on corrugated board. It appears as lines parallel to the flutes of the corrugated medium (fluting). These lines are generally thought to be print density and/or print gloss variations. The objective of this Paper is to obtain fundamental understanding of the striping mechanism. Print density and print gloss have been determined as a function of printing pressure. Typical printing pressure variations have also been determined by a non-linear finite element method. A 2D reflectance mapping has been performed for printed corrugated boards. The results showed that striping is dominated by print density variations for uncoated board, and the print density variations are, in turn, caused by the printing pressure variations. The extent to which the pressure variations appear as print density variations depends on the ink transfer characteristics of the liner board.

  • 10.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Striping of Corrugated Board in Halftone Flexo Post-printing2007In: 61st Appita annual conference and exhibition, Gold Coast, Australia, 6-9 May 2007, 2007 International paper physics conference, 6pp, 2007Conference paper (Other academic)
    Abstract [en]

    A fintie element model has been used to simulate how halftone dots deform during printing. Another finite element model has also been used for simulating how the pressure distribution in the nip changes when the corrugated board is deformed before printing by e.g. moisture induced warp. The simulations showed that striping in halftone prints can be explained by the deformation of halftone dots leading to more "dot gain" above flute ridges than between. When the corrugated board is deformed over a few flutes, the pressure distribution is affected which might cause print non-uniformities.

  • 11.
    Holmvall, Martin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Drolet, Francois
    FPInnovations-Paprican, 570 boul. St-Jean, Pointe-Claire, Québec, Canada.
    Lindström, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Transfer of a microfluid to a stochastic fibre network2011In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 27, no 7, p. 937-946Article in journal (Refereed)
    Abstract [en]

    The transfer of a microscopic fluid droplet from a flat surface to a deformable stochastic fibre network is investigated. Fibre networks are generated with different levels of surface roughness, and a two-dimensional, two-phase fluid-structure model is used to simulate the fluid transfer. In simulations, the Navier-Stokes equations and the Cahn-Hilliard phase-field equations are coupled to explicitly include contact line dynamics and free surface dynamics. The compressing fibre network is modelled as moving immersed boundaries. The simulations show that the amount of transferred fluid is approximately proportional to the contact area between the fluid and the fibre network. However, areas where the fluid bridges and never actually makes contact with the substrate must be subtracted.

  • 12.
    Uesaka, Tetsu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Wiklund, Hanna
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Holmvall, Martin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Fluid-Structure Interactions in Random Fibre Networks2012Conference paper (Refereed)
1 - 12 of 12
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