The impact of non-uniform ink absorption on flexographic print mottle
Sofia Thorman1,2, Li Yang1, Anni Hagberg1and Göran Ström1
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1 RISE Bioeconomy, Box 5604, 114 86 Stockholm, Sweden
2 Karlstad University, Department of Engineering and Chemical Sciences, 651 88 Karlstad, Sweden
Absorption non-uniformity and surface roughness of coated packaging boards are believed to have an impact on flexographic print mottle. Yet, their respective contributions are not well recognised due to their co-existence. Therefore, we propose a method that can solely study the effects of absorption non-uniformity on print mottle. This is achieved by artificially introducing uneven absorption, through well-controlled barrier patterns. The barrier patterns were added onto board surfaces using flexographic printing. By applying barrier patterns of several area coverages on board substrates of different intrinsic surface roughness it is possible to create a property-matrix, absorption non-uniformity versus for example surface roughness. With this matrix, the impact on print mottle from either of the properties can be studied independently. The results showed that surface roughness had a dominant effect on the print mottle, but mainly when comparing samples that spanned a broad roughness range. On the other hand, within a limited range of surface roughness, uneven ink absorption governed print mottle instead. This may explain why printing problems are sometimes encountered despite smooth board surfaces. Although the impact of absorption non-uniformity on print mottle differed from one board to another, the results indicated that a change towards more uneven absorption will have a negative impact on the print quality for most of the coated boards. The results give a better understanding of flexographic print quality and thereby can enable more reliable print mottle predictions.
Keywords: liquid packaging board, coated board, surface free energy, surface roughness, image analysis
JPMTR 104 | 1804 Original scientific paper
Biopolymer films from glucomannan: the effects of citric acid crosslinking on barrier properties
Glucomannan extracted from konjac root is used to form biodegradable films with gas and grease barrier properties for food packaging application. Nano-fibrillated cellulose (NFC) and plasticizers were used to improve the strength properties of the films. Citric acid and sodium hypophosphite (SHP) were used as crosslinking agent and catalyst, respectively, to improve the barrier property of the films against moisture. The film samples were prepared from glucomannan and NFC using a dispersion-casting method. The moisture barrier properties were characterized by the moisture vapor transmission rates (MVTR) and showed a significant decrease of 49.7 % (with 0.35 g citric acid in formulation, cured; marked as CA35-C). The crosslinked glucomannan films were calibrated with increasing mean tensile strength, modulus and elongation.
Keywords: packaging material, composite film, nano-fibrillated cellulose, air permeability, mechanical property
JPMTR 105 | 1802 Research paper
Analysis of the relationship of quality factors in the solventless lamination process
Vyacheslav Repeta, Yurii Kukura and Valentyna Kukura
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Faculty of Publishing and Printing Information Technology, Ukrainian Academy of Printing, 19, Pidholosko St., Lviv, 79020, Ukraine
The paper presents the necessity of establishing the priority ranking of factors which influence the solventless lamination process. The quality factors in the lamination process have been determined through the questionnaire survey of specialists experienced in the lamination of flexographic prints. To establish the priority of the quality factors in the flexographic prints lamination process, a ranking methodology was used which is based on the fact that the importance of the factor is determined by numerical indicators related to the number of influences and dependencies between the factors and their respective weight coefficients. The interconnections between the factors in the lamination process have been established and the model of the importance of quality factors in the solventless lamination process of flexographic prints was constructed with the help of the ranking method. In accordance with the obtained results, the following factors are of the highest priority: the construction of the section for adhesive supply, the type of adhesive, the complexity of the printed image, the type of material, web width, and the temperature. By the set terms, the fuzzy knowledge base of parameters in the solventless lamination process with the performance of the condition “if–then” has been formed. Based on this knowledge base, fuzzy logic equations for the calculation of the quality factors in the lamination process options have been built and defuzzification by the “center of gravity” method to get the quantitative quality parameters of the lamination technological process and to optimize the process.
Keywords: flexible packaging, factor analysis, process parameters, fuzzy logic
JPMTR 106 | 1806 Case study