Browsing by Author "Yordanov S."
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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 The influence of nd and sm on the structure and properties of sol-gel-derived tio2 powders(2021-07-01) Bachvarova-Nedelcheva A.; Yordanov S.; Iordanova R.; Stambolova I.; Stoyanova A.; Georgieva N.; Nemska V.TiO2 nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300◦C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400◦C). The TiO2 (rutile) was not detected up to 700◦C in the presence of both modified oxides. TiO2 (anatase) crystals found at about 400◦C in the Sm-modified sample exhibited an average crystallite size of about 25–30 nm, while doping with Nd resulted in particles of a lower size—5–10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240–350◦C. Photocatalytic tests showed that the samples heated at 500◦C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.