Lithographic Printing

The effectiveness of replacing organic solvents with vegetable oil-based cleaning agents (VCA) for cleaning offset lithographic printing presses has been evaluated at four print works. The occupational and environmental hazards and the technical performance of the organic solvents has been compared with the substitutes. The VCA have a lower environmental impact than the organic solvent cleaning agents, with lower VOC emissions and less waste produced. Occupational exposure to solvents vapours is, as expected, less with the non-volatile VCA. The main health effect is skin and mucous membrane irritation, and gloves are needed when using VCA. Slightly more physical effort is needed on the part of the operator and ergonomic risk is possibly increased. In addition, more attention needs to be paid to housekeeping, particularly in dealing with spillage due to an increased risk of slipping. No special storage facilities are required. VCA do not affect print quality or reduce machine speed, nor do they damage the machines, although compatibility trials are usually needed. Slightly more time is needed to use them and the direct costs can be up to 15% more for the VCA. Retraining operators in the use of the VCA is essential. The environmental and occupational hygiene benefits are clear but there are ergonomic and safety implications and, as direct costs may be higher and production time possibly slightly increased, management and trade union commitment is essential for successful substitution.

Two criteria for selecting ink sets for six-color lithographic printing are discussed. The first is the volume, in CIELAB space, of an approximation of the gamut. The second is the number of pixels within a digital image (or images) whose colors are contained within the approximate gamut. In order to obtain a balance between accuracy and efficiency, the different steps in the process are prioritized according to their impact on accuracy, their requirements for specialized measurements, and the computational load they create. Factors which have a first-order impact on accuracy are measured, while factors with higher-order, less controlling, impact are computed or estimated. Overprints of two or more colorants are estimated using a spectral model, rather than measured from printed samples. Combinations of inks on the gamut surface which contain intermediate amounts of inks are estimated using a spectrally-sharpened wideband model. The estimation is performed in a space in which subtractive colorants behave more linearly than density. A convex hull of the gamut is constructed in the linear space, using Computer Graphics routines. Through repeated bisection, the surface of the gamut is sampled in the linear space. The coordinates of the vertices are then transformed into CIELAB color space, for display, comparison, and analysis.

Small businesses frequently have inadequate in-house expertise to solve a variety of safety and health problems. The National Institute for Occupational Safety and Health (NIOSH) has therefore conducted a demonstration project in the commercial lithographic printing industry, which consists largely of small companies, in an effort to establish suitable control technology for airborne solvent vapors released primarily during press cleaning operations. These solvent vapors have a number of potential adverse health effects, including narcosis, kidney and liver damage, and cancer. Also, airborne anti-offset powder is a potential allergic sensitizer and cause of occupational asthma. As a means of controlling worker exposures to the vapors and dust, a local exhaust inlet was attached to the side of the press adjacent to the paper delivery point. Tempered outside air was introduced through ceiling outlets installed to make up for the exhausted air. Measurements of press operator exposure and area concentrations of solvent vapors and area concentration of anti-offset powder were made before and after installation of the new ventilation controls. Vapor concentrations were reduced by 73 percent for the press operators. Area concentrations of the vapors were reduced by 86 percent and dust concentration by 67 percent. The ventilation system was found to be suitable for vapor and dust control, although substitution of a cleaning solution containing non-carcinogenic solvents for solutions containing carcinogens was recommended.

AbstractHigh quality lithographic printing plates are made from electrolytically roughened aluminium sheets. A nitric or hydrochloric acid based electrolyte is normally used for the electro graining, and the substrate is most commonly commercial purity (CP) aluminium. Little is known about the relationship between the substrate microstructure and the pitting behaviour during electrograining in nitric acid solutions. The present work used three techniques to study the initiation and growth of surface pits responsible for the surface roughening of CP aluminium. A laboratory microcell simulated commercial graining but with the ability to interrupt the process and to rapidly clean and preserve the partially grained surface. Detailed scanning and transmission electron microscopy has been used to link substrate microstructure to pit initiation and growth morphology. The results demonstrate that the cold worked dislocation structure is an important feature whereas examination of simple binary alloys illustrates ...

The fundamental mechanisms of exposure by near-infrared pulses of multilayer films, which can be used as lithographic printing plates, are investigated using time-resolved optical microscopy. The films were developed by Presstek, Inc. (Hudson, NH) for use in the PEARL imaging system. Exposure by 10-μs duration Gaussian profile pulses is shown to occur with an extremely sharp fluence threshold of J th = 0.34 J/cm 2 . Exposure greatly alters the surface affinity for inks. Time-resolved microscopy shows the mechanism of surface alteration to involve thermochemical decomposition of the surface coating material, which results in its debonding from the film. Using threshold measurements and a theoretical thermal conduction model, debonding is shown to occur when the temperature in the film is about 500°C.

DOI: 10.1002/admi.201400080 which was responsible for these dynamic adhesion behaviors. Moreover, dynamic adhesion between oil fi lms and droplets of viscous water-based polymer solutions was also studied. These results are of signifi cance in lithographic printing to control liquid transfer for high printing quality and a novel inverse lithographic printing method. To study the dynamic adhesion of the water/oil interfaces, we designed an experimental model to observe the adhesion between a liquid fi lm and another immiscible liquid droplet. To obtain the liquid fi lm, rough alumina was used as substrates (Figure 1 c). [ 16 ] Alumina is a good candidate for the testing substrate because of its superamphilicity (as shown in the top panel of Figure 1 c, the water and oil contact angle of the substrate are 4.3° ± 0.4°and 3.9° ± 0.2°, respectively). Water and oil on the rough surface would be in the Wenzel state, where the liquids penetrate and get locked in surface asperities. [ 16 ]

This paper reports progress in the development of strain sensors fabricated using the conductive lithographic film (CLF) printing process. Strain sensitive structures printed via an unmodified offset lithographic printing press using a silver-loaded conductive ink have been deposited concurrently with circuit interconnect, to form an electronic smart packaging system. A system populated with surface mount technology (SMT) components has proven successful in interpreting and logging deformation incidences subjected to a package during testing. It is proposed that with further development such a system could be printed synchronously with packaging graphics using a single printing process to form an integrated time–strain monitoring system.

In this case study, the effect of water, a cationic polymer, an anionic surfactant and a proprietary surfactant mixture on the surface of non-image area of a lithographic printing plate was studied. Contact angle data was measured and analysed in terms of surface energy components; surface chemistry was monitored with XPS and surface topography was observed with SEM imaging. Surface energy of various treated plate was calculated from contact angle using Fowkes's Geometric Mean, Wu's Harmonic Mean and Good van Oss' Acid-Base approaches. Although the theoretical considerations behind these approaches are different, and they yield different values of surface energy components, they reflect changes of the non-image area of the plate after various treatments. Some discrepancies among these models are discussed. XPS and SEM results showed that cationic polymers absorbed onto the non-image area of the plate, leading to changes in both the surface topographic and energetic characteristics. The influence of the adsorbed cationic polymer to the surface energetics of the plate's non-image area is mainly through a reduction in the polar component of its non-image area. The wettability of the non-image area by water is more sensitive to the change in its polar component than dispersive component. Plate surface analysis showed that a correlation between the adsorption of cationic substances and scumming can be established.

The objective of this thesis is to provide methods for print quality enhancements in an offset lithographic printing process. Various parameters characterising the print quality are recognised, however, in this work print quality is defined as the deviation of the amount of ink in a sample image from the reference print. The methods developed are model-based and historical data collected at the printing press are used to build the models. Inherent in the historical process data are outliers owing to sensor faults, measurement errors and impurity of the materials used. It is essential to detect and remove these outliers to avoid using them to update the process models. A process model-based outlier detection tool has been proposed. Several diagnostic measures are combined via a neural network to achieve robust data categorisation into inlier and outlier classes. To cope with the slow variation in printing process data, a SOM-based data mining and adaptive modelling technique has been proposed. The technique continuously updates the data set characterising the process and the process models if they become out-of-date. A SOM-based approach to model combination has been proposed to permit the creation of adaptive -data dependent-committees. A multiple models-based controller, which employs the process models developed, is combined with an integrating controller to achieve robust ink feed control. Results have shown that the robust ink feed controller is capable of controlling the ink feed in the newspaper printing press according to the desired process output. Based on the process modelling, techniques have also been developed for initialising the printing press in order to reduce the time needed to achieve the desired print quality. The use of the developed methods and tools at a print shop in Halmstad, Sweden, resulted in higher print quality and lower ink and paper waste.

This paper presents a method to forecast ink flow characteristics of Lithographic Printing. As the movement of the vibrator rollers of the ink system, the output ink from one ink zone of the fountain roller will spread to multiple ink zones on paper. The ink distribution on the printing paper is not only influenced by image coverage of the current zone but also the nearby zone. This paper collects sample data of ink distribution on the paper which is produced by computer simulation method when one ink zone output a unit quantity ink to train BP neural network. After reading the actual image coverage of the digital files we can use the trained BP neural network to build a matrix which reflects ink flow characteristics. By this matrix model we can predict the distribution of ink on paper when a certain output ink is given. It is significant for accurately adjusting and controlling the output of ink amounts in each ink zone.