Browsing by Author "Boeva R."
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Item Compensation effect in the kinetics of thermal aging of semi chemical pulp(2014-01-01) Boeva R.; Radeva G.The effect of thermal ageing of neutral sulfite semi-chemical pulp derived from poplar wood is followed on the ground of the comparative investigation of bleached and unbleached samples. The brightness reversion observed in the course of the process is studied at 90°C, 105°C and 120°C. The degree of brightness is determined at the 6-th, 12-th, 24-th and the 36-th hour of the process duration. The kinetic analysis carried out shows that the exponential kinetic equation valid for processes taking place on uniformly inhomogeneous surfaces describes the kinetics of the process investigated. The linear relation between the apparent pre-exponential factor and the apparent activation energy, as obtained from an Arrhenius analysis, indicates the existence of a compensation effect.Item Effect of bleaching procedure type on the aging resistance of chemical-mechanical pulp(2016-01-01) Boeva R.; Radeva G.Chemical-mechanical pulping methods are for producing pulp from high-yield fiber materials derived from poplar wood. The samples are subjected to a single-stage bleaching with H2O2 and a two-stage procedure combining the effect of H2O2 and Rongalyt C. A kinetic investigation of the bleaching pretreatment effect on the thermal ageing of chemical-mechanical pulp is presented. Comparative investigations are carried out with pulp chips which were not subjected to preliminary bleaching. The brightness reversion is followed within the interval from 6 to 48 hours at constant temperature. The ageing process is described by an exponential kinetic equation. The initial and the current rates of the process are determined. It is found that they decrease with increase of the extent of the process proceeding. Microscopic images of the samples are taken after preparation, bleaching and ageing, correspondingly.Item EVALUATION OF THE INFLUENCE OF ARTIFICIAL UV AGEING OF PRINTED IMAGES(2022-01-01) Spiridonov I.; Boeva R.The main problems encountered in the long storage of printed or painted images are associated with deterioration of color characteristics and loss of information from them. The changes, that occur are due to the processes of ageing of the inks and papers. Natural ageing is a rather slow process. Therefore a study of the changes occurring with the printed images over the time under artificial UV radiation has been carried out. For the purpose of this experiment, was designed specialized test form, containing thousands of control patches for estimating the spectral, color and optical density shifts during the artificial ageing. The main goals of this research are to investigate the influence of artificial UV ageing on the optical density, spectral and color characteristics of printed images. The experiment have been performed in real printing conditions on state of art offset printing presses. The printing media used in the experiment are matte coated and uncoated offset paper, which are chosen because they are wide used all over the world. The test images and all the thousands of color control patches have been submitted to UV artificial ageing. The spectral and color characteristics of the inks and paper were examined during the different UV ageing period. The obtained results shows changes in all of investigated parameters during artificial ageing. The results are important from scientific and practical point of view. They might be used for modeling of ageing processes and could be very useful for recovering of original color characteristics of aged images.Item Influence of Paper Properties and Printing Machines Properties on Optical Density in Electrophotography(2023-01-01) Kašiković N.; Jurič I.; Randjelović D.; Spiridonov I.; Żołek-Tryznowska Z.; Boeva R.; Petrović S.Electrophotography is affected by several parameters, including printing machines and paper type, which determine the final quality of reproduction. For the investigation of those effects, tests were done on the three types of electrophotography printing machines and eight types of uncoated paper with different properties of weight, surface roughness, whiteness, brightness and opacity. Samples were printed with cyan, magenta, yellow and black toner under the standard, identical conditions. The assessment of standard print quality parameter (optical density) was done using spectrodensitometer Techkon Spectro Dens. At the same time, the paper substrates were characterized using the atomic force microscopy (AFM) as well as by spectrophotometric measurements (X Rite Eye-One, i1). Obtained results showed that the reproducibility significantly depends on the type of printing machine rather than optical and mechanical properties of paper.Item Investigation of process colours variations of electrophotography colour production presses(2020-01-01) Spiridonov I.; Yordanov S.; Boeva R.; Milkov A.In this investigation is approached method for assessing and evaluation of colour repeatability and variation for digital electrophotography printing presses. Two of most popular midlevel electrophotography colour production presses were chosen. These presses are widely used in printing houses for the printing of book covers, posters, etc. in small circulations. The similar perception of quality of digital production to the offset printing quality (ISO 12647-2:2013 ) is required from most of the clients of printing houses, publishers, etc. One of the problems of midlevel electrophotography colour production presses are variations of colours in the printing run and variations of colours during the time – weeks, months, years. The variation degree depends on many factors like – the precision of internal calibration method and types of sensors during the printing run, quality of used materials, calibration precision made by press operator, temperature and humidity variation, etc. (Kachin, Spiridonov, 2000) Specially designed for experiment test forms have been printed on two of most widely used materials for book covers, business cards, etc. – 300 g/m2 matt-coated board and 300 g/m2 offset uncoated board. The evaluation method is based on colorimetrical and densitometrical measurements (Kachin, Spiridonov, 2004) of 100 continuous printed sheets. The experiment was repeated in different time periods-between 6 hours and 4 months, to collect data for colour variation between reprinting the same test images in the time.Item INVESTIGATION OF THE COLOUR REPRODUCTION QUALITY OF INKJET DIGITAL PRINTING MACHINES(2022-01-01) Yordanov S.; Spiridonov I.; Boeva R.Industrial digital inkjet printing machines are increasingly entering commercial printing, label, packaging, etc. The quality of printing and the speed of inkjet printing machines are constantly increasing, but in a number of industries such as packaging, labels, etc. there are increased requirements for colour reproduction quality, which requires additional and in-depth research. The main purpose of this article is to study the different quality indicators of the most widely used digital inkjet systems. For the purposes of the experiment were used from the most commonly used in practice materials such as – regular matte and glossy coated paper, uncoated white paper, Jetcoat paper, photo paper-gloss, self-adhesive film-gloss, etc. with standard colour profiles FOGRA 39 and FOGRA 51 and offset uncoated paper with standard colour profiles FOGRA 29 and FOGRA 52. Several test forms with a large number of test charts and various control elements are printed on the aforementioned digital printing presses on different media. Colour gamut (2D and 3D), colour volumes, colour differences, etc. were studied. ICC profiles for the specific printing systems and materials have been generated and 2D visualization and comparison of the colour gamut of the studied media at different values of L and 3D visualization and comparison of the colour gamut of the studied media with standard ICC profile FOGRA.Item STUDY OF THE COLOUR GAMUT VOLUMES AND OTHER REPRODUCTION QUALITY PARAMETERS OF ELECTROPHOTOGRAPHICAL DIGITAL PRINTING SYSTEMS(2022-01-01) Spiridonov I.; Yordanov S.; Boeva R.; Kalchev K.The main purpose of this article is to study the various quality indicators of industrial electrophotographical digital printing systems. Several test forms with a large number of test charts and various control elements were printed on the aforementioned digital printing and media systems. For the purpose of the study, one of the most common print media was used-mat and glossy coated papers, uncoated papers, Brigh foil gold, Martele Blanc paper, MC Primecoat, PP Silver, etc. with standard colour profiles FOGRA 39 and FOGRA 51 and offset uncoated paper with standard colour profiles FOGRA 29 and FOGRA 52. Colour gamut (2D and 3D), colour volumes, colour differences, etc. were studied. ICC profiles for specific printing systems and materials have been generated and their 3D volumes, 2D areas of different sections in light, medium and dark tones have been studied. Other indicators of the quality of reproduction have been studied, such as-achieved colour differences in relation to the set / desired colour and ISO standards, accuracy of reproduction-colour and geometric, grey balance TVI, etc.Item STUDY OF THE INFLUENCE OF CONSERVATION TREATMENT ON THE CHROMATIC CHARACTERISTICS OF ARABIC MANUSCRIPTS(2024-01-01) Ivanova I.; Spiridonov I.; Boeva R.In the present experiment, a study was conducted to investigate the effect of conservation treatment of an Arabic manuscript on its chromatic characteristics. For this purpose, extremely valuable, unrestored manuscripts (18 - 19th century) were selected from the archives of the National Library “St. St. Cyril and Methodius”, on which spectrophotometric chromatic characteristics were measured. The research was conducted at the restoration center of the National Library. The following processes were applied to the manuscript: mechanical cleaning and deacidification. Measurements of color characteristics were taken indifferent parts of the manuscript after each stage of the treatment: before treatment, after mechanical cleaning, after deacidification. The following parameters - CIE Lab, CIE Lch, ΔEab, ΔE2000, ΔL, Δc, Δh was calculated. Based on the results obtained, the changes and effects of each of the chromatic parameters were determined.Item THE HEAT TREATMENT EFFECT ON THE PRINT QUALITY OF INKJET PRINTED TEXTILE MATERIALS(2020-01-01) Kasikovic N.; Spiridonov I.; Juric I.; Vladic G.; Pal M.; Dedijer S.; Boeva R.This paper presents the research of the heat treatment effect on printed textile substrates. The samples used in the experiment are printed employing Epson Stylus Pro 4880 inkjet printing machine and Epson Ultrachrome inks. Two different types of textile materials are used as printing substrates. The composition of the materials is identical, but they differ in respect to their fabric weight and thread count. The samples are exposed to two heat treatments after printing. The results obtained provide the conclusion that the heat treatment affects the color change, while the print uniformity remains unchanged to some extent.