Offset Press Research Articles

Deformation of the ink roller of an offset press based on a simplified model of ink-rubber viscoelasticity

Deformation of the ink roller of an offset press based on a simplified model of ink-rubber viscoelasticity

New Editions of The Great Gatsby

<i>New Editions of</i> The Great Gatsby

Aeroelastic instability of paper sheet in an offset printing press

Aeroelastic instability of paper sheet in an offset printing press

Dermatite de Contato Alérgica à Colofónia em operador de impressões gráficas- Caso Clínico

INTRODUCTION Colophony is a complex mixture of over one hundred compounds, resulting from the distillation of oleoresin, obtained from plants belonging to Pinaceae (mainly Pinus genus). The main allergens are the rosin oxidation products (unmodified and modified), as well as some of the new resin acids synthesized during their modification. It has numerous domestic or industrial applications, and exposure to these compounds is practically universal. We report a case of an occupational allergic contact dermatitis to colophony. CASE REPORT A 41-year-old caucasian male, graphic print operator for twenty one years, was referred to the Dermatology Department of Hospital de Braga, due to erythematodesquamative lesions, located on the back and lateral side of the hands, with aggravation during the professional activity. His personal history was negative for allergic rhinitis, asthma and allergy to particular foods or drugs. These lesions have evolved chronically for about ten years, yielding to the topical application of corticosteroids. In the workplace, he is responsible to makes ready and operates sheet-fed offset printing press, that is, calibrates the equipment, fills ink and dampening solution fountains, examines printed copy for ink density and makes adjustments, sometimes without the proper use of personal protective equipment. The patient reported improvement of symptomatology with prolonged withdrawal from the workplace. After resolution of symptoms, patch tests were carried out with the baseline standard Portuguese Contact Dermatitis Research Group series and a rubber series. A positive reaction was achieved to colophony (++) and abietic acid (++) at 72 and 96 hours. After checking the safety data sheets of printing inks and direct contact with their manufacturer, it was possible to confirm the presence of rosin derivatives. Later, the pathology was assumed as an Occupational Disease. DISCUSSION/CONCLUSION In printing ink industry, colophony and its derivatives are mainly used as colour carrier of the ink and to increase its adhesion to paper. In this worker, it was assumed a causal relationship between the exposure to the colophony present in the printing inks and the diagnosed of contact dermatitis. In this case, the implementation of collective protective measures as well as the use of personal protective equipment at work, its necessary to protect the user against health or the safety risk. It includes items such as nitrile gloves, protective clothing, a particle mask or respirator and the use of safety goggles. It is necessary to be aware of this etiology so that, in these workers, an early diagnosis can be made with the recommendation of appropriate protective measures.

A new technique for the measurement of show-through mottle of fine paper

Mottling within print-through and show-through is caused by the variability of the local optical properties of the sheet. This mottling is visually disturbing and a mark of poor paper quality. The ability to predict print-through mottle of printed paper by measuring show-through mottle on the unprinted sheet would be a valuable asset for paper machine control. We examined the relationship between print-through mottle and show-through mottle. We worked with nine samples of 60 lb. uncoated fine paper (90 g/m2), from various North American paper companies, that were printed on an offset press, 400K (400% Black), on both sides. A show-through mottle instrumental determination technique was developed using an existing Fast Fourier Transform-based algorithm. The nine samples examined were ranked similarly by the visual evaluation of print-through mottle and by the instrumental determination of show-through mottle. We thus established that show-through on the unprinted sheet can be used as a reliable predictor of print-through, therefore saving time and money for papermakers. We also found a significant two-sidedness in show-through for some of the samples.

Experimental and numerical investigations on dynamic characteristics of gear-roller-bearing system

In the present study, dynamic characteristics of gear-roller-bearing system is investigated by use of experimental test and theoretical modeling. In terms of experiment, a new test set-up dedicated to offset press is developed to measure the acceleration within a wide range of speed. After the completion of data acquisition, the vibration signals obtained from different conditions are analyzed both in time domain and frequency domain, thereby capturing the source of vibration excitation. For theoretical modeling, a novel dynamic model of gear-roller-bearing system including time-varying properties and contact nonlinearities is proposed based on the fundamental idea of finite element method, divided into the helical gear pair model, dynamic model of roller and shaft, bearing elements, shoulder iron and rubber contact elements. The unconditionally stable algorithm, known as Newmark-β method, is employed to solve the governing equations, and then the validity of mathematical model in predicting dynamic response is demonstrated by comparison with experimental results. Experimental and numerical results indicate that the proposed method can be utilized as a useful tool for parameter design and performance analysis of gear-roller-bearing system.

Analysis of temperature characteristics of ink fluid based on power law model in microchannel

In the offset press, ink flows in the microchannel made of two rotating rollers that are in the state of squeezing and contacting. The ink flow characteristics are not only influenced by the viscous dissipation effect, but also change with the heat transfer. First, by summarizing the common viscosity–shear rate models of non-Newtonian fluid, the power law model was chosen for describing offset ink through rheometer measuring. Combined with the experimental data, the viscosity–temperature relationship of the offset ink was described by the Arrhenius’s law. Then, the temperature characteristics of the offset ink fluid in the microchannel were studied using the fluid simulation software FLUENT. The ink fluid temperature field model considering viscous dissipation and heat transfer was established, and the temperature distributions of the ink fluid inside the microchannel and at the exit and entrance were obtained. The influence of the feature size on the ink temperature was also researched. Finally, the ink temperature and flow characteristics were compared with that under the condition without heat transfer. We got the influence of feature size and heat transfer on the ink temperature characteristics. As the feature size is smaller, the ink temperature increase from the microchannel entrance to the exit, increases first and then decreases, and keeps invariant at last. The heat transfer makes the viscous dissipation weaken relatively and then the ink temperature decreases. In a word, the heat transfer enhances as the feature size decreases. The results provide reference for improving the printing quality of offset press.

Vibration and Noise Source Positioning Method of Printing Equipment Based on Transfer Path Analysis

Excessive vibration affects the register accuracy and the noise is harmful to the operators. This paper aims at the sources and their excitation. For positioning the sources quickly, the transfer path analysis model was established, and the vibration-acoustic transfer function of printing equipment was derived by using operational transfer path analysis (OTPA). Through the comprehensively testing of vibration and noise synchronization for four-color offset printing press, a decoupling of the transfer function through singular value decomposition (SVD) of the input matrix was achieved, and furthermore vibration-acoustic contribution rate of each path to identify the main vibration &amp; noise source was obtained. The result shows that main vibration &amp; noise source of the printing machine is the gripper opening and closing mechanism subsystem. The conclusions can be used for vibration and noise reduction design of the printing machine.

A finite line contact tribo-dynamic model of a spur gear pair

Abstract Dynamics and tribology are vital to gear transmission device mainly because of relating to noise, vibration, lubricating performance and durability. A novel method for predicting dynamic characteristics and lubricating property in spur gear of ink vibrator is proposed in this paper by means of integration technology. Unlike the ordinary spur gears, the spur gears of ink vibrator used in offset press not only have rotatory movement, but also possess axial motion. Consequently, a unified tribo-dynamic model bridged the two branches of spur gear, a multiple degrees of freedom (DOFs) discrete dynamic model and a finite line contact elastohydrodynamic lubrication (EHL) model with axial velocity, is built up to investigate the interactive mechanism and the influence of axial velocity on pressure distribution. To this end, an iterative calculation program integrated the Runge-Kutta method and the multigrid method is utilized to solve the governing equations. Obvious differences of simulation results between the tribo-dynamic and quasi-static conditions are found by making a comparison, demonstrating the necessity of establishing the proposed model. Numerical results indicate that the proposed model can be utilized as a useful tool for gear design and performance analysis.

Дослідження параметрів якості друкованого відбитка при двобічному друкуванні на аркушевих офсетних машинах

The quality parameters of printed impressions obtained via duplex printing on a sheet-fed offset press were studied in the article. The efficiency improvement of a sheet-fed offset press is achieved by using turning pages devices.The quality of a printed impression is affected by many factors, one of which is the duplex printing press construction, such as printing cylinder, on which, when turning, a metal plate is mounted to protect the printed image. Disability and accelerated failure during operation are the result of processes that occur in the surface layers. Thus the analysis of the research of the printed impressions’ parameters is relevant considering the application of the finishing-strengthening treatment by rolling vibration and the followed chrome coverage of an impression cylinder, which increases the performance properties due to the formation of a regular microrelief of the chrome surface of an impression cylinder and maintaining the quality of a printed impression within the standardized values.The results of the research allow us to analyze the influence of the complex technological process of processing the printing cylinder in pairs with the anti-mackling metal plate, to dot gain in particular and the quality of the imprint as a whole. The results of the research of the parameters of the quality of the imprint, testify to the high level of indicators and the stability of the printing process, which is explained by the direct relationship between the complex technological process and the parameters of the quality of printing products.The results of the parameters of the quality of the imprint, namely, the indexes of optical density in the percentage to the normative indicators, are in the range from 0.3 % to 4 %, the percentage distribution of the spread to the average values — from 1.4 % to 3 %; the points of dot gain in comparison with the normalized are within 0.9–3 %.

Mathematical modeling and optimization of cam mechanism in delivery system of an offset press

This paper presents a new method for cam profile design and optimization by integrating a single objective optimization procedure with a dynamic model of cam-follower mechanism in delivery system of an offset press. The proposed approach based on a new strategy mainly includes two parts, a single objective optimization procedure for the kinematic characteristics of the follower and a dynamic model for the cam-follower mechanism. For the first part, the follower acceleration profile is described by modified trapezoidal curve, thereby deriving the velocity, jerk and displacement functions, respectively. Then sequential quadratic programming (SQP), which deals well with equality and inequality constrains, is adopted as the single objective optimized algorithm in this part. In the second part, a two degrees of freedom lumped parameter model taking into account the torsional flexibility and damping of the grippers, the contact compliance at the cam/roller and grippers/block interfaces, is established to investigate the dynamic behavior of the force-closed cam-follower mechanism. In order to improve the kinematic and dynamic characteristics of cam-follower mechanism synthetically, an optimization cycle, known as iterative process, is introduced to implement the procedure of single objective optimization and dynamic simulation alternately. The example illustrated in this paper, sufficiently demonstrates the effectiveness of the new method. Ultimately, the proposed approach gives cam designers a useful tool to design and optimize the cam profile, so as to reduce residual vibration.

Process color watermarking: the use of visual masking and dot gain correction

Subtractive-Color-Reproduction is the fundamental mechanism in 4-color process printing, which employs CMYK (cyan, magenta, yellow and black) dots for color reproduction. Watermarks embedded in RGB images are distorted when the image is transformed from what to process color for printing usage. Based on the feature of CMYK color space and human visual system, this paper presents a robust CMYK watermarking algorithm for printing images, which embeds an informative watermark and a structure template signal in DCT domain of the Yellow information channel and DFT domain of the black information channel respectively. The embedded template enables robustness against geometric distortions in the print-scanning process. Another spatial visual mask is proposed to reshape the embedded energy after it is inverted to the spatial domain, which significantly improves the color fidelity and the image quality. In addition, a dot gain compensation model is put forward for color correction. A series of proof tests have been carried out on an offset press, which show that the watermark preserves the fidelity of the image and can be extracted with a high quality; moreover, a remarkable fidelity of color and tones on printed copies is well preserved.

Cam profile optimization for the delivery system of an offset press

In this paper, a relatively new strategy known as unified optimization is applied to the cam profile optimization for the delivery system of an offset press by integrating the procedure of single objective optimization with ADAMS software. The proposed approach mainly consists of two parts that includes a single objective optimization procedure and a multibody dynamic model of cam–follower mechanism. For the procedure of single objective optimization, the design process starts from defining the follower acceleration profile by using a modified trapezoidal curve, then genetic algorithm is adopted to determine the evaluating indexes for the kinematic behavior of cam–follower mechanism in multiobjective optimization. Subsequently, sequential quadratic programming, which deals well with equality and inequality constrains, is selected as single objective optimized algorithm in this part. On the other hand, the dynamic simulation developed by ADAMS software is carried out to investigate the dynamic characteristics of cam–follower mechanism. Finally, an optimization cycle, also known as iterative process, is proposed to implement the procedure of single objective optimization and dynamic simulation alternately to improve the kinematic and dynamic characteristics of cam–follower mechanism fully. The cam profile optimization method presented in this paper provides a new tool for cam designers to avoid the undesirable impact and follower jump.

Investigation the Print Quality of Web Offset Colour Prints on Newsprint Paper

Paper and printing press plays important role for deviations in offset print quality. To retain a constant quality press operators need to explore, assess and investigate the print quality during production. Assessment of print quality mainly done by manually. Random forests based modelling is used to assess and predict the value for print quality attributes. Also the system utilises the double grey bar system of print mark for assessing. The sensors used here to assess the print quality attributes on the image of the double grey bar. Systematic analysis and categorisation of work relate to paper and press parameter on quality of colour images printed on newsprint paper by web offset printing press are detailed in this paper.

Dynamic Analysis of Offset Printing Press Gear-Cylinder-Bearing System under Time-Varying Meshing Stiffness Effect

This study propose a new nonlinear model for offset printing press gear-cylinder-bearing system by the lumped parameter approach. The multi-DOF model consists of helical gear pairs and spur gear pairs with time-varying meshing stiffness. Bearing and shaft flexibilities are include in the model as well. The equations of motion are obtained by Darren Bell principle and Runge-Kutta numerical method is used to slove the equations of motion. The results show that meshing stiffness and bearing stiffness significantly affect critical speed, vibration acceleration and meshing force. Multi-body dynamics software are applied to compare with lumped parameter model. The results show that there are many similarities in different aspects. Results of experimental study on offset printing press are also presented for validation of different models. After Discrete Fourier Transform, the graphics display that acceleration peaks frequencies are an integer multiple of the gear mesh frequency. It demonstrate that mechanical vibration is mainly from gear transmission system at high printing speed and gear transmission system lead to nonlinear vibration. This work provide a foundation for further improvement of the dynamics of gear system.

In-line monitoring of printing processes in an offset printing press by NIR spectroscopy: Correlation between the conversion and the content of extractable acrylate in UV-cured printing inks

Near-infrared (NIR) reflection spectroscopy was used for in-line monitoring of the conversion in printed layers of a UV-curable cyan printing ink at an offset printing press. Quantitative analysis of the spectra was based on the calibration of the method with chemometric approaches using reference data for the conversion obtained by FTIR/ATR spectroscopy. In this way, the conversion in ink layers with a thickness of 0.8 g m−2 was determined with a precision of 5%. Moreover, it was shown that the specific migration of the acrylate components in the binder of the printing ink was linearly dependent on the conversion in the studied range between about 80% and 100%, which allowed an estimation of the specific migration from conversion data. The strict linear relation between both parameters was used for indirect in-line monitoring of the acrylate migration during the printing process by predicting it from the conversion data derived from the NIR spectra. For comparison, off-line measurements on random samples by HPLC were carried out. The error of the predicted migration data in comparison with the results of the analytic measurements was found to be about 0.03 mg dm−2. The proposed indirect prediction of the migration will allow a better and more direct control of technical printing processes.

The influence of paper surface energy on multicolor offset print mottling

An evaluation of a series of commercial uncoated, semimatte, and glossy coated woodfree papers for the multicolor sheet-fed offset press is presented. This study is aimed at better understanding of mutual influences of surface free energy, paper surface roughness, and fountain solution on print mottling occurring in full-scale printing conditions. Each paper has unique structure in terms of surface roughness, porosity, and surface energy that are the result of manufacturing technology. At the point of contact of liquid with paper, the surface dynamic process of liquid absorption by paper occurs, involving phenomena such as wetting, penetration, diffusion, and swelling. Mottling of colored surface printed by cyan, magenta, yellow, and black inks copied the surface roughness of coated paper. Mottling in the second, third, and fourth printing units showed deviation from mottling in the first printing unit, depending on surface free energy of paper and on the frequency of paper-surface wetting by fountain solution before and after printing.

In-line monitoring of the conversion in UV-cured printed layers by NIR spectroscopy in an offset printing press

In this study, it was demonstrated that the conversion in printed layers of UV-cured printing inks and varnishes can be determined in-line in a printing press by NIR reflection spectroscopy supported by chemometric methods. Layers were printed with a thickness of ∼1.2 g m−2 for a printing ink and ∼2.8 g m−2 for a printing varnish. Quantitative analysis of the spectral data was carried out with calibration models based on the partial least squares (PLS) algorithm. In-line monitoring tests were performed at a large-scale sheet-fed offset printing press in order to evaluate the predicting performance of the calibration models under process conditions. Different conversions in the layers were induced by variation of the irradiation dose. The predicting errors were 4.5% for the ink and 4.0% for the varnish. The printing speed was found to have no significant influence on the precision of the measurements.

Transport of Immiscible Vapor Pressure Contrasting Liquids in Multiple Nip Impressions: Application to Heatset Offset Printing of Paper

A multistation heatset offset printing press was studied here to exemplify the transport of immiscible liquids into a porous substrate under dynamic rolling nip conditions. In offset printing, oil-based ink and a water-based fountain solution are used to define the image and nonimage areas according to the respective surface energy of the printing plate. The fountain solution and ink inevitably form an emulsion after the press has run sufficiently to reach equilibrium. It is this emulsion that is transported via a rubber blanket to the paper and forms the printed image. The emulsification degree depends on the ink properties and the printing process at the equilibrium ink–fountain solution balance, which, in turn, supports stable continuous running of the press in order to achieve a good print quality. Focus is given to the transfer of fountain solution to both nonimage areas of paper as well as to the inked areas carried in the emulsion. In order to monitor the amount transferred, each of two tracing ele...

Shaftless Driving Development Research on Sheet-Fed Offset Press

shaftless driving is a kind of advanced and new drive way which can solve the high precision of printing synchronism, mainly used in gravure printing, soft printing and wheel transformation printing equipment but less used in sheet-fed offset press at present. Based on sheet-fed offset press as the research object, the author analyzed the transmission characteristics of sheet-fed offset press, designs a scheme of shaftless driving used in sheet-fed offset press and set up the hardware and software platform, verified the scheme by experiments.