Minimizing setups and waste when printing labels of consumer goods

A real-world planning problem of a printing company is presented where different sorts of a consumer goods’ label are printed on a roll of paper with sufficient length. The printer utilizes a printing plate to always print several labels of same size and shape (but possibly different imprint) in parallel on adjacent lanes of the paper. It can be decided which sort is printed on which (lane of a) plate and how long the printer runs using a single plate. A sort can be assigned to several lanes of the same plate, but not to several plates. Designing a plate and installing it on the printer incurs fixed setup costs. If more labels are produced than actually needed, each surplus label is assumed to be “scrap”. Since demand for the different sorts may be heterogeneous and since the number of sorts is usually much higher than the number of lanes, the problem is to build “printing blocks”, i.e., to decide how many and which plates to design and how long to run the printer with a certain plate so that customer demand is satisfied with minimum costs for setups and scrap. This industrial application is modeled as an extension of a so-called job splitting problem which is solved exactly and by various decomposition heuristics, partly basing on dynamic programming. Numerical tests compare both approaches with further straightforward heuristics and demonstrate the benefits of decomposition and dynamic programming for large problem instances.

Determining the Print Quality Due to Deformation of the Halftone Dots in Flexography

This paper researches the issues related to the print quality in flexography, especially the influence of the print run and inadequate printing settings on dot deformation. Dot deformation can lead to inconsistencies in print quality, such as a loss of highlight tones or an unpredictable increase in tonal value. This research was conducted on two concrete examples of flexible packaging printed on transparent films. All significant parameters of dot deformation were evaluated, including dot coverage, dot sharpness and the uniformity of the ink density. The increase in the coverage values in the midtones was linear throughout the entire print run, while in the light tones, it was more logarithmic. The overall percentage deviations from the reference value were 6.3% in the midtones and 52.6% in the light area. The increase in dot coverage was due to the wear of the polymer plate, which caused the side shoulders of the dot to become a part of the printing surface. An analysis of the ink density showed a much more homogeneous shape of the dot at the beginning of the print run. The correct ratio of the anilox roller line screen to the line ruling of the printing plate is important in order to ensure a minimum dot size in print.

Assessment of the Condition of Anilox Rollers

To produce high-quality prints using flexographic printing technology, it is important, among other factors, how accurately and consistently the ink is delivered to the printing plate, and, from there, onto the printed material. This function is performed by anilox rollers. The aim of this research is to investigate the condition of anilox rollers in printing houses in the Baltic states. The study evaluated the wear and cell clogging of anilox rollers. The dependency of clogging on the cell size, as well as the dependency of wear on the cell size (i.e., change in cell volume) and quantity of doctor blades, was investigated. In addition, the uniformity of cell clogging and wear on the surface of the anilox roller was evaluated. Studies have shown that more than half of the anilox rollers in printing houses are not washed properly; higher line screen anilox rollers tend to become more clogged, and it is important to take measurements at more than three locations to assess the reliability of more worn rollers.

THE PHENOMENON OF INK DUSTING TAKING INTO ACCOUNT THE SURFACE ROUGHNESS OFFSET PRINTING PLATE

The paper investigates the influence of the mechanics of a friction printing pair on ink dusting in the printing process, taking into account the surface roughness of the printing plate. The aim of the study is to determine the influence of the surface roughness of the printing plate on the deformation of the deckle, as well as on the value of the total force in the area of the printed contact, the relative gear ratio and the relative speed of sliding of the deckle along the surface of the cylinder, which directly affects the dusting of the ink. It was found that when studying the mechanics of a printed pair, the influence of the microgeometry of the contacting surfaces on the parameters under study was not taken into account. The influence of microprotrusions of the surface roughness of the printing plate on the deformation of the deckle in the area of the printed contact has been substantiated and established. To determine the introduction of surface roughness irregularities, a discrete roughness model is used, presented as a set of identical spherical segments. To determine the influence of the surface roughness of the printing plate on the friction force arising in the contact zone, a calculation scheme is proposed that differs from analogs. A method is developed for calculating the parameters of a friction pair in the printing process, taking into account the roughness. Expressions are obtained for determining the total moment of tangential friction forces in the sliding sections when spherical irregularities are introduced. According to the proposed technique, the corresponding graphical dependences of the gear ratio on different parameters of the friction printed pair are shown. The advantages of this study in comparison with analogs are that at certain values of the parameters of the friction pair, taking into account the surface roughness of the printing plate, also at known values of the mechanical characteristics and thickness of the deckle, it is possible to determine the change in the length of the deckle of a given composition, which is necessary in the printing process. The proposed calculation method, which is carried out without taking into account the pressure in the printed contact zone, allows predicting the quality of printed impressions and the amount of ink involved in the formation of ink dusting, as well as correctly adjusting the printing press before the printing process.

Simulation of Shear-Thickening Liquid Transfer between U-Shaped Cell and Flat Plate

Based on the actual measurement of the shear-thickening properties of water-based inks, in order to improve the ink transfer rate, the PLIC (Piecewise Linear Interface Construction) interface tracking method and the VOF (Volume of Fluid) method are used to simulate the transfer process of the shear-thickening liquid between the U-shaped cell and the upwardly moving plate. The effects of substrate surface wettability, cell contact angle, and cell depth on liquid transfer were studied. The results showed that all can increase the liquid transfer rate, and the change of the cell contact angle also led to the difference in the breaking time of the liquid filament. In addition, the shallow plate effect was discovered in the study of cell depth. The shallow plate effect is a phenomenon by which the amount of liquid transferred and the liquid transfer rate are greatly improved when the depth of the cell decreases to a certain limit value. In addition, for the U-shaped cell, the optimization method combining the shallow printing plate effect and fillet can greatly improve the liquid transfer rate and solve the undesirable problems such as plate blocking. After optimization, a liquid transfer rate of about 85% can be achieved.

STUDY OF WETTING ON THE NON-IMAGE AREA OF OFFSET PRINTING PLATES BY AN ALTERNATIVE ISO-PROPYL ALCOHOL-FREE FOUNTAIN SOLUTION

In this study, an alternative aqueous isopropyl alcohol-free fountain solution for sheet-fed offset printing is prepared comprising 5 w/w% McIlvaine's buffer system for pH control, 0.3 w/w% Polysorbate 80 as a surfactant, 1 w/w% magnesium nitrate hexahydrate as a conductivity agent and 10 w/w% ethylene glycol mono-butyl ether as an additional wetting agent. The percentages of each composition are w/w% of active and then adjusted to 100 w/w% by adding distilled water. The contact angles of the obtained fountain solution on non-image areas of three common offset printing plates: CTP plate of Kodak, CTP plate of Huaguang Graphic Co. Ltd (China), and CTP plate of Mylan Printing Media Co. Ltd (Vietnam), range from 10° to 20°.The surface tension, conductivity, pH and viscosity were found to be 30.5 mN/m, 1.45 mS/cm, 4.8, and 1.05 x 10-2 g/cm.s, respectively. In comparison to the commercial fountain solution (KF – Trade Mark (China) containing isopropyl alcohol (IPA), the obtained fountain solution shows similar wettability on the non-image area of the offset printing plate whilst having similar physico-chemical parameters. The results indicate that ethylene glycol mono-butyl ether could be a potential substitute for IPA in fountain solution in offset printing, and the obtained fountain solution displays suitable properties for the offset printing process.

Statistical analysis of the influence of print run on surface roughness of digital flexo printing plates’ solid tone areas

In this study we have aimed to present statistical evaluation of changes in the surface roughness of the solid tone areas on CtP flexo printing plate in dependence of print run. Changes in flexo plate surface roughness is influenced by the plate-making process, printing pressure and speed, the interaction with the ink and printing substrate and by the wear of the printing plate due to long print-runs. Thus, the aim of this research was to evaluate the changes in the amplitude surface roughness parameters (Ra, Rp, Rv and Rz), between the printing plates used for different print runs. In the experiment, we have employed three sets of CtP flexo printing plates, for three colors-cyan, magenta and blue. The first set was not used for printing, the second was used to print 7 rolls of substrate and the third is used to print 11 rolls of printing substrate. The amplitude surface roughness parameters were compared by applying independentsamples t-test method using the software SPSS (Statistical Package for Social Science) with a 0.05 significance level. Statistical analysis revealed that the difference between the amplitude surface roughness parameters measured on CtP flexo printing plates are significant with a 95% confidence level, whereas the statistical significance pointed out that with the longer print runs, the difference will be strongly expressed.

Influence of Some Flexographic Printing Process Conditions on the Optical Density and Tonal Value Increase of Overprinted Plastic Films

The print quality of prints performed with flexographic printing technology is influenced by various parameters such as viscosity of the printing inks, printing substrates, plates, anilox rolls, etc. The aim of this work is to analyze the influence of ink viscosity, printing plate and printing base on selected properties of print quality, such as optical density of full tone area and the increase of tonal value (TVI). Additionally, the printed dots on 5, 15, 30, 50 and 75% of half tone area were investigated using digital microscopy. The least square fitting method in a matrix form was successfully used in order to confirm the influence of printing process parameters on print quality. The results obtained reveal the significant influence of the printing plate and printing substrate characteristics and the lesser influence of printing ink viscosity for 40–100% coverage area. The values of the optical densities of full tone areas are mainly influenced by the properties of the printing plate and the printing base. Furthermore, the optical density decreases when the value of flow time decreases, which is related to the lower thickness of dried ink film. The TVI on light tones (0 to 20%) is mainly influenced by the ink viscosity.

Mechanical Behaviour of 3D Printed PLA Hollow Spherical Parts Under Axial Compression

The form of the outer and inner surfaces of hollow spherical parts determines the developments of some particular categories of efforts during the compression tests. The overall purpose of the research presented in this paper was to study the behaviour of the hollow spherical parts under axial compression. The PLA hollow spherical parts were obtained by 3D printing and using distinct values for certain process input factors. The finite element method was used to theoretically investigate the behaviour of the parts and it highlighted the total plastic deformation of the test pieces. To experimentally verify the theoretical considerations, an L9 Taguchi orthogonal design was performed. The empirical mathematical model thus determined highlighted the stronger influence exerted by the printing plate temperature, printing speed, and part wall thickness.