| 1. |
- Barros, Gustavo Gil, 1976-
(författare)
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Influence of Substrate Topography on Ink Distribution in Flexography
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The printability of paper in flexography is largely dependent on the topographical characteristics of the substrate. Topography imaging instruments make it possible to obtain three-dimensional scans of paper surfaces that can be further used to calculate valuable quality parameters. The primary aim of the work described in this thesis has been to identify and isolate structural properties of the paper surface which significantly influence the ink distribution during printing and limit the subsequently attainable print quality.OptiTopo is an optical imaging technique which provides precise and fast topographic scans of both printed and unprinted paper surfaces. The potential and limitations of the technique have been evaluated. The optical requirements on the substrate for an accurate and precise topographic scan were determined. Detail-rendering was substantially improved using a custom-designed restoring filter, and a new enhanced spatial resolution range was established. A combination of further algorithm improvements made it possible also to obtain reflectance-factor-calibrated intensity images of scanned printed surfaces.Serious deficiencies affecting the quality of flexographic prints may appear in the form of local unprinted areas (UCA) in a full-tone print, generally caused by incomplete ink transfer. An algorithm detecting and quantifying local uncovered area was developed, tested and successfully integrated with the OptiTopo instrument. A UCA occurrence frequency distribution, indicating the percentage of the uncovered area at a certain topographical elevation, was calculated for different prints. The topographic characteristics of the uncovered areas clearly indicate that surface depressions are the primary cause of uncovered areas in flexographic printing.Four different predictive models based on topography thresholding were proposed and tested using two independent quality judgement criteria. These quality indices took into account both the amount and location of the predictions. A deeper understanding of the topographical features governing UCA occurrence was established with a proposed ink bridging effect. The total risk of non-ink-covered areas in flexography printing due to topographical features was estimated.The overall influence of paper topography on the flexography printability of full-tone areas was studied and its importance for the ink distribution assessed. The impacts of printing plate hardness, printing pressure, anilox cylinder volume and substrate roughness were quantified. Two typical flexography patterns were identified and their origin discussed: sub-millimetre elongated structures and millimetre-scale blotches.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Bohlin, Erik, et al.
(författare)
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Flexographic Ink-Coating Interactions : Effects of Porous Structure Variations of Coated Paperboard
- 2013
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Ingår i: Nordic Pulp & Paper Research Journal. - : AB Svensk papperstidning. - 0283-2631 .- 2000-0669. ; 28:4
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Tidskriftsartikel (refereegranskat)abstract
- Ink transfer and ink penetration into a coated surface, and variations thereof, influences the print density, mottling and dot gain, which affects the achievable print quality and visual appearance. The pressure in the printing nip and the porosity of the substrate are conditions and properties that will regulate the amount of ink that penetrates into a porous coating structure. The purpose of this study was to relate print quality aspects to ink penetration of water-based flexographic ink into calcium carbonate based coatings of differently engineered structures. Pilot-coated paper-boards with different coating porosities were printed in a laboratory flexographic printer. Results indicate that ink transfer distribution is strongly affected by the roughness and the porosity of the substrate. A coating layer of broad pigment particle size distribution resulted in a lower print density, compared to coatings of narrowly distributed particle sizes. A structure characterized by larger pore volume and greater dominating pore radius, showed a higher amount of z-directional ink penetration, which was supported by estimating the penetration using a physical model accounting for both capillary- and pressure driven penetration. A coating with narrow particle size distribution also showed a lower dot gain.
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| 7. |
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| 8. |
- Bohlin, Erik, 1968-
(författare)
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Optics of coated paperboard : Aspects of surface treatment on porous structures
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Calendering of coated and uncoated paper is widely used to enhance optical properties such as gloss and print quality. The aim of this thesis is to characterize coatings and prints, and to validate models using experimental results from optical measurements of physical samples. Calendering of coated paper often leads to a brightness decrease. The mechanism for this is not altogether clear. One common explanation is that the porosity of the coating layer decreases and hence the scattering decreases. By comparing simulated and measured results it was shown that modifications of the surface properties account for the brightness decrease of ground calcium carbonate coated substrates with calendering. Monte Carlo light scattering simulations, taking into account the measured decrease of surface microroughness and increased effective refractive index, showed that surface modifications accounted for most of the observed brightness decrease of the ground calcium carbonate coated substrate, whereas the bulk scattering and absorption coefficients were not affected by calendering. It was also shown that the scattering coefficient is significantly dependent on the coat weight whereas the physical absorption coefficient is not. The penetration of ink in the z-direction of a substrate influences the quality of the print. The ink penetration affects print density, mottling and dot gain, common print effects that influence the preference of consumers. The pressure in the printing nip and the porosity of the substrate both affect the amount of ink that is pressed into the porous structure of a coating layer during printing. By printing pilot coated paperboard with different coating porosity and measuring the resulting optical properties of the prints, a basis for simulations of the different layers, that is to say the coating, the print and the mixed layer in between, was created. Results show that ink distribution is strongly affected by the roughness of the substrate. Fibres and fibre flocks underneath the two coating layers created an unevenly distributed coating thickness that affected the print quality. Differences in pore size and pore size distribution also affected the behaviour of the ink. A coating layer of broad pigment particle size distribution resulted in a relatively low print density, in comparison to coatings of narrowly distributed particle sizes. Comparison of dot gain showed that the coating layer of a narrow particle size distribution had a relatively low dot gain compared to others. In this work, these results are explained by the differences in ink distributions on and in the coating layers.
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| 9. |
- De Magistris, Federica, et al.
(författare)
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Effect of calendering on the compressibility of papers made with fibre of various properties
- 2010
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The surface and bulk compressibility of a given paper influence its calendering, coating, surface sizing and printing properties. This study aims at a deeper knowledge of which variable affects the compressibility of paper sheets and how calendering effect different sheet properties. The pulps were characterized by their chemical compositions and physical properties. The bulk compressibility, the surface compressibility and the thickness were evaluated both before and after calendering
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| 10. |
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| 11. |
- De Magistris, F., et al.
(författare)
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Influence of paper compressibility on flexographic printing quality
- 2008
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Ingår i: Progress in paper physics seminar 2008, proceedings, Espoo, Finland, 2-5 June 2008. - 9789512293919 ; , s. 243-245
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The compression ability of fibres and fibre networks were investigated. The surface and bulk compressions of paper influence calendering, coating, surface sizing ability and the penetration of ink in printing. Two kraft pulps (spruce) were produced in the laboratory to obtain pulps with different levels of xylan. Using those kraft pulps alone or mixed with 50% of a commercial TMP pulp, single-layer sheets were formed in a Formette Dynamique sheet former. The pulps and mixture levels were chosen to obtain papers with systematically altered property variation but with constant grammage. The papers were characterized according to both bulk and surface compressibility. The papers were printed in a flexo IGTF1 laboratory printing press and the transferred amount of ink, dot gain, and mottling were analyzed.
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| 12. |
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| 13. |
- Engquist, Isak, et al.
(författare)
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Hydrogen Bond Interaction between Self-Assembled Monolayers and Adsorbed Water Molecules and Its Implications for Cluster Formation
- 1995
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Ingår i: Journal of Physical Chemistry B. - : AMER CHEMICAL SOC. - 1520-6106 .- 1520-5207 .- 0022-3654 .- 1541-5740. ; 99:39, s. 14198-14200
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Tidskriftsartikel (refereegranskat)abstract
- Infrared spectroscopy is used to investigate the adsorption of D2O onto self-assembled monolayers of methyl 16-mercaptohexadecanoate on gold. The D2O molecules are shown to interact with the carbonyl oxygens of the monolayer, forming hydrogen bonds and causing a structural rearrangement of the CO2CH3 terminal group. The number of hydrogen bonds decreases as the amorphous-like, essentially flat (two-dimensional) ice overlayer that forms at 100 K changes into polycrystalline-like ice upon annealing at 140 K. This decrease is a consequence of the formation of three-dimensional ice clusters, which leaves a large fraction of the monolayer surface bare.
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| 14. |
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| 15. |
- Engquist, Isak, et al.
(författare)
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Microscopic wettability of ester- and acetate-terminated self-assembled monolayers
- 1997
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Ingår i: Langmuir. - : American Chemical Society. - 0743-7463 .- 1520-5827. ; 13:15, s. 4003-4012
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Tidskriftsartikel (refereegranskat)abstract
- Four different carbonyl-containing self-assembled monolayers (SAMs) of alkanethiolates on gold were studied to assess the impact of the functional group Linked to the carbonyl upon its hydrogen bond accepting capability. These SAMs (HS(CH2)(16)O(C=O)-X,X = CH3, CF3, or C6H5, and HS(CH2)(15)(C=O)OCH3) were thoroughly characterized with contact angle measurements, single wavelength ellipsometry, and infrared reflection-absorption spectroscopy (IRAS) prior to the studies of interaction with D2O. The first three monolayer compounds were introduced by reacting hydroxyl-terminated SAMs (HS(CH2)(16)OH) with either acetyl chloride, trifluoroacetic anhydride, or benzoyl chloride. The behavior of D2O ice on the SAMs was investigated at 100 K with IRAS and temperature programmed desorption (TPD). On all monolayers the D2O molecules were shown to interact with the carbonyl oxygen. The degree of interaction depended upon the termination of the thiol, where the size, structure, and electronegativity of the terminating groups in the molecules comprising the monolayer were found to be important factors. Indications of interaction with the C-O-C oxygen were seen for all compounds, as well as weak interaction between water molecules and the CF3 group of one of the investigated SAMs. Common behavior for all four monolayers with an adsorbed D2O overlayer was a decrease in the number of hydrogen bonds to the substrate when the overlayer was annealed from amorphous ice at 100 K to polycrystalline-like ice at 140 K. The spectral changes accompanying the structural transition were consistent with a change from a mainly flat overlayer to condensed three-dimensional clusters. The bulk-to-surface molecular ratio of adsorbed ice clusters could be assessed by IRAS and correlated to macroscopic wetting properties. Our results infer that microscopic ice clusters on these SAMs qualitatively mimic the shape of macroscopic water drops on the same SAMs. Results of TPD measurements are also consistent with this view.
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| 16. |
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| 17. |
- Govindarajan, Venkatesh, 1972-, et al.
(författare)
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An economic-environmental analysis of selected barrier coating materials used in packaging food products : A Swedish case study
- 2018
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Ingår i: Environment, Development and Sustainability. - Dordrecht : Springer. - 1387-585X .- 1573-2975. ; 20:4, s. 1483-1497
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of a barrier coating in food packaging is primarily to increase the shelf life of the foodstuff contained within the packaging, preserve its colour, odour, taste and quality, and thereby reduce food wastage (both at retail outlets and households). While most publications hitherto have compared packaging and barrier-coating materials on the basis of their environmental impacts alone, this paper adopts a more holistic approach by factoring in the economic aspect as well. Four barrier material alternatives—starch, polyethylene, EVOH + kaolin and latex + kaolin are analysed. Two well-defined end-of-life handling scenarios, relevant to Sweden, are: one in which everything except starch is recycled, with starch being composted, and the other in which everything is incinerated. Among the several environmental impact categories which can be analysed, this paper considers only global warming. Two approaches are tested to combine the economic and environmental aspects—normalisation, weighting and aggregating on the one hand, and using the carbon tax to internalise the externality caused by GHG emissions on the other. For the set of weighting factors obtained thanks to a survey conducted by the authors (40.6% for environmental and 59.4% for economic), starch emerges as the most sustainable alternative, followed by polyethylene for both the end-of-life handling scenarios. This tallies with the result obtained by using the carbon tax for internalisation of the externality. The case study, methodology and results presented in this paper, will hopefully be a springboard for more detailed studies of this nature, under the umbrella of sustainability.
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| 18. |
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| 19. |
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| 20. |
- Hallberg Hofstrand, Erik, et al.
(författare)
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Dynamic Measurements of Nip Force Variations during Post-Printing of Corrugated Board
- 2006
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Ingår i: Nordic Pulp & Paper Research Journal, 21(1), 111-114 (2006).
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Tidskriftsartikel (refereegranskat)abstract
- A method has been developed in order to measure nip force variations during flexographic post-printing of corrugated board. This method can be used to study the influence of the nip mechanics on the final print quality
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| 21. |
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| 22. |
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| 23. |
- Hallberg Hofstrand, Erik, 1975-
(författare)
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Flexographic Post-Printing of Corrugated Board : Contact Mechanics and Print Quality
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the corrugated board industry strives to produce products with a higher print quality in the converting stage, there is a need for a greater understanding of the factors influencing the final print quality and how we perceive the print. In this work, a method for quantifying the print quality of printed corrugated board is presented as well as methods that quantitatively characterize the mechanical interaction between the printing form and the corrugated board in the printing nip. The results of investigations addressing the impact of the mechanical properties of the printing form on ink transfer are also presented. A band-pass image analysis method adapted to the spatial wavelength of B-flute corrugated board was used to quantify the print quality on the board in terms of print banding. The findings were substantiated by a perceptual evaluation which showed a high correlation to the instrumental quantification. The main cause of print banding is a higher local contact pressure on the fluting tips than in the fluting valleys, which leads to a higher ink transfer to the fluting tips. A greater difference between the local contact pressure on the fluting tips than in the fluting valleys generated a higher degree of banding. The difference in local contact pressure as well as nip force variations could be measured using the proposed methods to characterize the interaction between the printing form and the corrugated board. The difference in local contact pressure was highly dependent on the mechanical properties of the components of the printing form. An increase in the stiffness in compression mode and in the bending stiffness of the printing form led to a smaller contact area in the printing nip and consequently a higher external pressure on the ink, resulting in an overall higher ink transfer but also a higher degree of banding. The influence of the mechanical properties of the printing form components was supported by the results of numerical simulations of the contact between the printing form and the corrugated board. Contact area, pressure level and texture of the local contact pressure were compared with measurements of local contact pressures for different printing forms and the results showed a high degree of agreement. Numerical simulations could thus predict the print quality achieved with different printing forms under different printing conditions.
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| 24. |
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| 25. |
- Hämäläinen, Pyry, et al.
(författare)
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On the determination of transverse shear properties of paper using the short span compression test
- 2017
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Ingår i: Mechanics of materials. - : Elsevier. - 0167-6636 .- 1872-7743. ; 107, s. 22-30
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Tidskriftsartikel (refereegranskat)abstract
- The present paper explores the short span compression tester (SCT) as a means to experimentally determine the transverse shear moduli of paper. These moduli, which are known to be difficult to determine by any other means, are of importance for the behavior of paper during tissue manufacturing and in the converting and embossing of paperboard. Testing was conducted on paper of two different grammages both in MD and in CD. By applying the Timoshenko-Engesser theory for buckling of shear compliant materials, estimates of the transverse shear moduli were obtained through the measured SCT values and standard measurements of the Young's modulus and the thickness. These estimates were evaluated by detailed FE-analyses of the SCT setup incorporating initial geometrical imperfections representative for real test conditions. It was found that the Timoshenko-Engesser theory gives estimates of the transverse shear moduli that are within an accuracy well applicable for most engineering purposes. The results suggest that the method is at least as accurate as any other, more involved, method that could be used for the purpose.
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| 26. |
- Idris, Alamin, et al.
(författare)
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Oxygen Barrier Performance of Poly (Vinyl Alcohol) Coating Films with Different Induced Crystallinity and Model Predictions
- 2021
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Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 11, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The presence of the crystalline regions in poly(vinyl alcohol) coating films acts as barrier clusters forcing the gas molecules to diffuse in a longer pathway in the amorphous region of the polymer, where diffusivity and solubility are promoted in comparison. Evaluating the influence of crystalline regions on the oxygen barrier property of a semi-crystalline polymer is thus essential to prepare better coating films. Poly(vinyl alcohol) coating films with varying induced crystallinity were prepared on a polyethylene terephthalate (PET) substrate by drying at different annealing temperatures for 10 min. The coating films were first delaminated from the PET substrate and then characterized using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) techniques to determine and confirm the induced percentage of crystallinity. The barrier performance of the coating films, i.e., the oxygen transmission rate (OTR), was measured at room temperature. Results showed a decrease in the OTR values of poly(vinyl alcohol) film with an increase in the degree of crystallinity of the polymer matrix. Tortuosity-based models, i.e., modified Nielsen models, were adopted to predict the barrier property of the semi-crystalline PVOH film with uniform or randomly distributed crystallites. A modified Nielsen model for orderly distributed crystallites with an aspect ratio of 3.4 and for randomly distributed crystallites with an aspect ratio of 10.4 resulted in a good correlation with the experimental observation. For the randomly distributed crystallites, lower absolute average relative errors of 4.66, 4.45, and 5.79% were observed as compared to orderly distributed crystallites when the degree of crystallinity was obtained using FTIR, DSC, and XRD data, respectively.
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| 27. |
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| 29. |
- Johnson, Johanna, 1970-
(författare)
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Aspects of Flexographic Print Quality and Relationship to some Printing Parameters
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Flexographic printing is a common printing method in the packaging field. The printing method is characterized primarily by the flexible printing plate and the low viscosity inks which make it suitable for use on almost any substrate. The object of this study was to obtain further knowledge of the some important mechanisms of flexographic printing and how they influence the print quality. The thesis deals with printing primarily on board and liner but also on newsprint with water-borne ink using a full-scale flexographic central impression (CI) printing press. Several printing trials have been performed with a focus on the chemical interaction between the ink and substrate and the physical contact between the ink-covered printing plate and the substrate. Multicolour printing exposes the substrate to water from the water-containing ink. The emphasis was to investigate the relation between print quality and water-uptake of the paper surface with heat and water. Printing trials was carried out on substrates possessing a hydrophobic, and also a rather hydrophilic surface using a regular commercial water-borne ink. The favorable effect which water or surfactant solution had on the hydrophobic substrate with regard to print mottle could depend on its surface compressibility in combination with the hydrophobic nature of its surface that could affect the wetting properties. Conventional printing involves physical contact between plate and ink and between ink and substrate. A method for measuring the dynamic nip pressure using thin load cells is presented. Print quality was influenced by the plate material. A correction procedure taking into account the size of the sensor was developed in order to estimate the maximum dynamic pressure in the printing nip. An attempt was made to identify essential mechanical and chemical parameters, and also geometrical properties of the plate that affected print quality. Laboratory printing trials were carried out and a multivariate analysis was applied for evaluation of print quality data. The impact of the plate properties on print quality was evident. The essential properties of the plate that influence print quality were the small-scale roughness and long-scale roughness.
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| 30. |
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- Johnson, Johanna, et al.
(författare)
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Measuring the Dynamic Nip Pressure in a Flexographic CI-Printing Press
- 2004
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Ingår i: Nordic Pulp and Paper Journal, vol.19,2004,pp 84-88.
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic pressure in a flexographic printing press was measured and the influence of impression, speed and choice of printing plate on the dynamic pressure was analysed. The measurements were complemented by measurements to assess the ink transfer to the substrate
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| 35. |
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| 36. |
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| 38. |
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| 39. |
- Korin, Christer, 1970-
(författare)
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Mechanical Behaviour of Adhesive Joints in Cartonboard for Packaging
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A cartonboard package is often sealed and closed with an adhesive – either a hot-melt adhesive (adhesives that are applied in a molten state on the cartonboard) or a dispersion adhesive (adhesives that are applied as water-based dispersions). This thesis focuses on the process of hot-melt gluing, and how material properties and process conditions affect the performance of the adhesive joint. Requirements vary depending on how the package is to be used. A package that is only supposed to protect the product during transport differs from one that is supposed to attract consumers and facilitate their use of the product. If a package has been opened, due to external or internal forces that cause a fracture in the adhesive joint, the consumer may choose another package instead. A fracture of the adhesive joint may occur in several different ways; for example, a cohesive fracture in the adhesive, an interfacial fracture between the adhesive and one of the cartonboard surfaces, and a cohesive fracture in the cartonboard. The traditional way of testing the adhesive joint is to subjectively evaluate the fibre tear after manually tearing the joint apart. The primary interest of this study has been to find an objective method that can characterise the adhesive joint – that is, its strength and joint characteristics. The work has principally concentrated on physical experiments where the Y-peel method has been evaluated and further developed, including the construction of a laboratory adhesive applicator. Adhesive joint failure is analysed and correlated to the force-elongation curve during Y-peel testing in order to explore various mechanisms of the failure. The force versus elongation curves are transformed into a force versus inelastic deformation curve for the adhesive joint. The inelastic deformation of the adhesive joint is defined as the inelastic opening of the adhesive joint perpendicular to the cartonboard surface. The dissipative descending energy has been used to characterise the adhesive joint. High descending dissipative energy showed high resistance against final failure of the joint. This correlates very well with the manual fibre-tear test. Characteristic force-elongation curves in Y-peel testing – that is, the shape of the curve – have been analysed, and four main failure modes have been identified. The finite element method has been used to predict mechanical behaviour in the ascending part of the force-elongation curve. When it comes to local behaviour, a high stiffness adhesive results in bending behaviour while a low results in shearing, but on a global scale, no big difference was detected on the ascending part of the force-elongation curve. The new laboratory adhesive applicator and finite element method can be used to objectively design the interaction between the adhesive and the cartonboard for a specific application. This can be achieved by modifying the cartonboard, the adhesive or the process parameters.
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| 46. |
- Lestelius, Magnus, 1968-, et al.
(författare)
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Fiberförstärkta polymerer för 3D-utskrivna laminat, ES3D
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Projektet Fiberförstärkta polymerer för 3D-utskrivna laminat (ES3D) var ett samarbete mellan Karlstads universitet och The Wood Region. Syftet var att åstadkomma nya metoder och öka kunskapen kring 3D-utskrivna strukturer med blandningar av termoplaster och sågspån. Genom att öka styrkan i det 3D-utskrivna biobaserade och nedbrytbara materialet kan hållbarhetsmässiga fördelar uppnås. Den enskilda trådens styrka avsågs ökas genom att använda längre spån och rikta dem i utskriftsriktningen. Adhesionen mellan de utskrivna lagren skulle förbättras genom kontrollerad temperatur och s.k. coronabehandling.ES3D har resulterat i en metod för att kunna testa 3D-utskrivna prov i dragprovare för mekanisk karakterisering, som sedankan användas för att jämföra olika materialsammansättningar och tillverkningssätt.Sortering av sågspån, i olika storleksfraktioner, har genomförts med både maskinell rotationssorterare och sållning. Resultatet av den maskinella sorteringen var inte tillräckligt precis för att producera sågspånsfraktioner som kunde användas för ovanstående mål.Ökad adhesion mellan lager med temperaturkontroll eller coronabehandling, har ej kunnat prövas ordentligt, p.g.a. otillräcklig temperaturkontroll, samt att en teknisk lösning för coronabehandling ej fanns.
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