Živko Pavlović

Evaluation of effective models of offset CTP plate aluminium oxide surface roughness characterisation

In this study, three different approaches for characterisation of printing plates non-printing elements surface structure and roughness were compared: stylus profilometric method, AFM, method and software (indirect), SEM image-based profilometry. The comparison was made to evaluate the possibility of utilising the different methods for characterisation of CTP offset printing plate surface roughness. The direct profilometric measurements involved the use of stylus profilometer visual analysis were made using AFM device and for the indirect approach, the Gwyddion software, for analysis of single and stereo SEM images and calculation of standard profilometric parameters, was used. The results of this study demonstrate that it is possible to obtain profilometric parameters from the analysis of AFM and SEM micrographs with appropriately calibrated grey scale intensity distribution and that the values of the parameters are comparable to those obtained by contact stylus profilometry. The results of this comparative study indicate that profilometric 2D direct stylus method is more applicable when larger areas tend to be measured, while the indirect image-based 3D profilometry is a valuable and efficient tool for characterisation of various surfaces topographies on micron scale sample areas.

13 – Offset Printing

Offset printing is an indirect printing method that is widely used for printing on polymer substrates. It is characterized by the fact that the selective ink adsorption in the printing process is achieved by opposite physical–chemical properties of printing and nonprinting areas on the printing plate. They mainly differ in printing plate construction, ink characteristics, and, most importantly, usage of dampening solution. In the wet offset printing process, it is inevitable to use a dampening solution to define printing and nonprinting areas on the printing plate. Waterless offset printing is a process that eliminates this. However, both technologies can be successfully used for printing on polymer substrates and offer certain advantages depending on the end use of the final printed product. Printing on polymer materials is influenced by certain, specific requirements that will direct the choice of the offset printing process (wet or waterless), printing plate, inks, etc.