Characterization of composite flexographic printing plate carriers and their influence on cardboard packaging print quality


Flexography is a printing technique which is, like all the other printing techniques, dependant on the variety of parameters defining the process and the quality of the printed product. Apart from that, the development of technology is continuously contributing to the growth in quality and the productivity of flexography. Following the development of the technology is a need for characterization of the new or modified components of the process, especially if they are not thoroughly investigated in their previous iterations.

One of the variable parameters of flexography experiencing rapid development are the materials for mounting the plates on the sleeves, and the sleeves themselves. The sleeve technology currently being considered as the "cutting edge" bares the name Twinlock® sleeves.

Changes in most of the flexographic printing parameters, as well as the print quality, have been monitored in the scientific research conducted so far. However, the sleeve quality parameters have not been previously monitored, and neither were their changes brought into correlation with the quality of the printed product. The above facts point to the need for characterization of sleeves and monitoring their changes and the impact of the changes on the quality of the printed product.

Based on previous observations, the main objective of the research is to find parameters which can be used in the non-destructive method for determination of the sleeve condition. The results are expected to be applicable in practice at the industrial level, during the process quality control through measurements by standard devices on standard control patches.

Sleeves can be characterized by a number of terms directly affecting their properties and the quality of the process and the end product. The most important ones are the compressible layer and its mechanical properties, and in the case of Twinlock® sleeves, the adhesive layer and its adhesive properties. The main cause of the changes in the mechanical properties of the compressible polyurethane layer lies in the printing process, where the sleeves suffer the greatest stress and are exposed to the influence of various components from different sources. Mechanical changes relate to changes in compressibility, resilience, hardness, as well as the loss of energy through heat generation. The leading cause for the changes in adhesion properties, which are particularly significant in the case of the Twinlock® sleeve adhesive layer, lies in the mounting process of flexo printing forms, during which the composition of the adhesive layer may change.

All the above-mentioned changes can have a negative effect on the predictability and stability of the printing process. At the same time, the quality of the end product can be affected negatively or positively, depending on the parameter being observed. The impact on the stability of the printing process can be manifested through the occurrence of short-stops, permanent damage to printing forms, or changes in the temperature and viscosity of inks. On the other hand, product quality can undergo changes through tonal value increase, optical density, print uniformity, trapping, colour difference, slur, dot void, dot diameter and edge factor.

Characterization of changes of the previously mentioned mechanical, adhesion and print quality parameters was carried out through the research. Apart from that, the main causes were found for all of the changes. Bringing the results of the characterization of the changes of sleeve properties and print quality parameters into correlation enabled defining of the most reliable parameters and the trends and values of their changes, on the basis of which it is possible to establish the condition of the sleeves through non-destructive methods. In addition, the obtained results help in selecting adequate sleeves according to the type and level of exploitation, in relation to the printing requirements defined by the type of dominant printed motif.



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Faculty of Technical Sciences, Department of Graphic Engineering and Design

Graphic engineering and design