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- 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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| 3. |
- Nestorson, Anna, et al.
(författare)
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Enzyme immobilization in latex dispersion coatings for active food packaging
- 2008
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Ingår i: Packaging technology & science. - : Wiley. - 0894-3214 .- 1099-1522. ; 21:4, s. 193-205
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Tidskriftsartikel (refereegranskat)abstract
- Carboxylated styrene acrylate latex samples have been functionalized by the immobilization and entrapment of the enzyme glucose oxidase (GOx), which can be used as an oxygen scavenger in food packaging. GOx was covalently immobilized both on the surface of already formed films and on the latex particles in dispersion, as well as entrapped within the polymer matrix. In the latter two cases, polymer films were formed after the enzyme had been added to the latex dispersion. The storage stability of the enzyme and the influence of adding clay were also studied. For a given amount of enzyme, the enzyme immobilized on the film surface showed an enzyme activity about 10 times higher than that of the enzyme present within the polymer matrix. This is probably due to the diffusion limitations of the substrate in the polymer matrix. The films with the enzyme present within the polymer matrix, however, showed a higher total oxygen-removal capacity than films with the enzyme immobilized on the surface. Entrapped enzyme showed a slightly higher activity than enzyme immobilized in the dispersion due to the negative effect of the activating chemicals used during the immobilization and on conformational constraints upon covalent bonding. Low amounts of clay added to the dispersion decreased the enzyme activity, but with higher amounts of clay the enzyme activity increased, probably because of the increased porosity and thus higher substrate accessibility. The most suitable storage condition for all the enzyme-containing films was +8°C, which is just above the glass transition temperature of the polymer used.
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- 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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