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Dear colleagues, we are extremely honoured to present to you the Proceedings of the international conference 19th Ružička Days, which was successfully held on September 21–23, 2022, in Vukovar, Croatia, in the hometown town of our famous Croatian scientist and first Nobel laureate, professor Leopold (Lavoslav) Ružička. The main goals of the Conference were to promote excellence, originality and innovation of interdisciplinary scientific research as well as the practical application of the obtained results through collaboration with industry, emphasizing thus the recognizable slogan of the Ružička Days conference: "Today Science – Tomorrow Industry". In addition, the Conference gave the opportunity for meetings, exchanging the ideas, opinions, experiences and cooperation among participants from different working surroundings. It is also important to point out that since 2008, within the international conference Ružička Days, Meeting of Young Chemists has also been held, where high school students, with the help of their mentors, present papers in the field of chemistry, with the aim to direct students and young people to the technical and natural sciences, especially chemistry. In its seventh issue (2011, 2013, 2015, 2017, 2019, 2021) the Proceedings publishes scientific and professional full papers of high quality in the following sections: Chemical analysis and synthesis (10), Chemical and biochemical engineering (3), Food technology and biotechnology (4), Chemistry in agriculture and forestry (1), Environmental protection (9) and 8th Meeting of Young Chemists (3). Full-length papers were subjected to an international review procedure done by eminent experts from the corresponding fields, to whom we express our gratitude, but they were not subjected to linguistic proofreading. On behalf of the Scientific and Organizing Committee of the 19th Ružička Days we cordially thank all the authors, reviewers, participants, lecturers, organizers, especially the international organizers EuCheMS and EHEDG, auspices and sponsors, and all the others who, in any way, supported the Conference and contributed to the preparation of the Proceedings, especially to our highly skilled and committed associates, who have put a lot of effort in the preparation of these Proceedings. At the very end, special thanks to our young, future scientists and their mentors who are faithful participants of the Meeting of Young Chemists of the Ružička Days conference. Enjoy the extremely interesting scientific and professional papers contained in these Proceedings, until the next 20th jubilee of Ružička Days in 2024! We are looking forward to meeting you again in Vukovar! Yours sincerely, Chief Editors Jurislav Babić Vesna Ocelić Bulatović Dajana Kučić Grgić

Customers are usually unaware of the process required to reproduce graphic products that are used on a daily basis. Manufacturers of graphic products and merchandise are aware that, regardless of the substrate they are printed, they must ensure consistent colour matching and print quality to attract attention on store shelves and ensure customer loyalty. Packaging, labels and publications are mostly printed using multicolour printing, whereby different colour shades are reproduced with the three standard process colours (cyan, magenta and yellow) in different ratios. The quality of the graphic product depends largely on the origin of the raw materials used for the printing substrate, the type of ink and the technology used for printing. The paper substrate most used for printing labels, packaging, or publications is generally made from cellulose fibres derived from wood, non-wood or non-plant sources. Nowadays, the use of non-wood lignocellulosic fibres resources plays an important role in optimizing raw materials for paper production. The aim of this research was to evaluate the usability and printability of paper substrates with the addition of non-wood fibres for graphic products printed by digital, flexographic, gravure, screen and offset printing process.

Nowadays, the paper industry is facing challenges in providing its main raw material – wood. Deforestation and the lack of reliable sources, as one concern, and transport issues as another, contribute to the rising research into new materials that can be used to partly replace wood as the main source of cellulose fibres needed for paper production. The latest research indicates that cereal straw has great potential as an additional source of cellulose fibres, due to its renewable nature and low cost. Paper substrates with added cereal straw pulp are mainly used for the secondary packaging purposes, and therefore they must show high mechanical resistance. Secondary packaging, almost always, contains printed information about the product that is exposed to various external conditions, and it is important that the print remains unchanged during transport and handling of the packaging. This research focuses on comparison of the mechanical resistance (or rub stability) of prints on papers to which straw pulp of three cereals abundant in Croatia have been added: wheat, barley, and triticale. Prints were made using UV curable inks and four different printing techniques (offset, gravure, flexographic, and digital printing). Mechanical resistance was determined by conducting the rub resistance tests and calculating the Euclidean colour difference based on measured colorimetric values of the prints before and after the tests. A comparison of the results was made to establish the best suited combination of printing technique and paper substrate containing cereal straw pulp that ensures the highest mechanical resistance of the print.

Soybean is an important industrial crop grown for oil and protein production. Soybean oil is the second most widely produced edible oil. Except as edible oil, soybean is widely used in human nutrition as flour, milk, cheese and sauces, while soy lecithin is an inevitable additive in many food products. It should be emphasized that soybean has become indispensable in the production of meat and dairy substitute products as the fastest growing trend in the food industry. In addition to human and animal nutrition, soybean is also important for the pharmaceutical, textile and chemical industries and in the production of biodiesel fuel. Many of the listed soybean products also require appropriate packaging that complies with environmental regulations. Due to the global trend of increasing consumption of soybean products, within the scope of this research, the impact of soybean oil on the print quality of paper packaging from alternative raw materials was monitored. The deterioration of the original quality of the print with black UV ink applied by digital, flexographic, gravure, screen and offset printing techniques was evaluated after 24 hours of contact with soybean oil based on measured spectrophotometric values.

Paper is one of the most important materials for packaging and the demand for it is constantly increasing. The printing and packaging industries are researching alternative sources of fibre, to produce more environmentally friendly paper without compromising quality. As a packaging material, paper must meet high strength requirements, and it must have acceptable surface properties to preserve the printing quality. The production of paper made from pulp of recycled fibre reinforced with virgin straw fibre and the evaluation of the print quality on such papers are two objectives of this research. The straw pulp used for this purpose was obtained from three cereal crops: wheat, barley, and triticale. The paper produced was printed using five printing techniques. The rubbing stability was evaluated by the difference in colour and reflectance spectra before and after performing rub tests and a comparison was made for the best interaction of paper and ink determined by the printing technique. For the prints with the highest colour difference after the rub test, the surface of the rub test receptor (uncoated recycled paper) was examined for signs of ink transfer during the test and the areas of transferred ink coverage were calculated on their processed microscopic images.

Packaging is the material with which the product is wrapped or inside which the product is placed. The main function of packaging is to protect the packaged product, identify it and place it on the market, and to ensure the original shape of the packaged goods. The trend today is to reduce the global amount of packaging waste by recycling the same waste or reusing other available waste materials, while maintaining the required quality of the packaging thus produced. Cereal grains which include wheat, rye, barley, oats, rice, corn, millet, sorghum, wheat, spelt and others, are staple foods for human and animal consumption. Each year, large quantities of stalks are left in the fields after harvesting, and after drying in the sun is mostly treated as waste. Given the high availability of cereals worldwide, cereal straw could be more usefully utilized as an alternative source of fiber for secondary packaging. Therefore, the printing paper substrates were formed from the straw pulp of three different cereal species (wheat, barley and triticale) and mixed with recycled wood pulp in a 3:7 ratio. Since offset and gravure printing are used globally to print absorbent packaging, in this study we analyzed the black prints made by these two printing techniques. The usability of the printed papers with straw pulp for secondary packaging was observed based on the penetration of the ink into the printing substrate. It was found that the composition of the paper substrate has no effect on the depth of ink penetration into the printing substrate, so that cereal straw can be used as waste material for the production of secondary packaging. In general, prints with gravure inks have lower ink penetration compared to offset inks.

The overall quality of the graphic product depends largely on the origin of the raw materials for pulp and paper, the type of ink, the technology used to print the product, and the printing conditions. Each printing technology is more or less suitable for a particular type of printing substrate, depending on how the ink is transferred to the substrate. Although the Chinese used other raw materials for papermaking almost 2, 000 years ago, wood is now the most important raw material for the production of pulp and paper. As forest areas become smaller and fewer trees are available as raw material for cellulose fibers, the production of paper and graphic products has focused heavily on the use of alternative, non-wood raw materials. Alternative cellulose fibers for papermaking from agro-residues are the most cost-effective and environmentally friendly solution that aims to reduce the consumption of wood raw materials by replacing them with alternative plant biomass. The objective of this study was to evaluate the printability of paper substrates for a specific graphic product where wood fibers are partially replaced by alternative fibers from cereal straw. Papers with a straw fiber content of 30% were produced under laboratory conditions and printed using digital and conventional printing techniques. The evaluation of the printability of paper substrates with agro-residues was based on the determination of the quality of ink acceptance on the previously printed ink, which is the basis for multicolor reproductions in the graphic industry.

Compared to papers derived from virgin fibres, recycled papers possess somewhat limited optical, strength and printing properties. Strength properties are usually increased by blending recycled fibres with virgin fibres in pulp for paper production, while optical and printing properties are often improved by coating after the paper is being manufactured. In this study, the usability of virgin fibres derived from straw as the agricultural residue of wheat, barley and triticale crops for paper production was evaluated based on the stability of prints on laboratory-made paper. For that purpose, in laboratory conditions, the papers with the addition of straw pulp in the pulp of recycled fibres were formed and prior to printing they were coated with TiO2-based coating. Process inks, in full-tone, were applied on coated straw-containing papers by digital printing process. Optical properties of digital prints upon accelerated ageing were evaluated based on Euclidean colour difference calculated from spectrophotometric values measured on black and magenta prints before and after 48 h and 96 h of ageing. The obtained results were compared with those provided by printing substrates made only from recycled fibres with and without TiO2-based coating. It was observed that TiO2-based coating has no influence on the stability of black digital prints, while each layer of TiO2-based coating reduces deviations in magenta colour upon ageing.

Svijet je suočen sa smanjenom količinom šumskih površina uslijed djelovanja požara i klimatskih promjena, te ilegalnih i neodrživih sječa šuma i njihovih prenamjena u druge svrhe. Drveće je još uvijek glavni izvor celuloznih vlakanaca, zbog čega je industrija papira kontinuirano usmjerena na traženje novih izvora sirovina. Svijest o održivom razvoju i ekologiji zahtijeva korištenje novih rješenja, kao što su alternativni izvori celuloznih vlakanaca za proizvodnju papira od poljoprivrednih ostataka biljaka koje su brzo obnovljive i jeftine za proizvodnju. Žitarice poput slame pšenice, ječma i pšenoraži dokazale su se sa svojim povoljnim svojstvima prikladnima za dobivanje celuloznih vlakanaca. U ovom radu proizvedene su laboratorijske papirnate podloge iz recikliranih drvnih vlakana s dodatkom alternativnih nedrvnih vlakanaca u masenom udjelu od 30% te je analizirana kvaliteta reprodukcije na istim. Načinjene papirnate podloge otisnute su tehnikom bakrotiska kao tehnikom kojom se omogućuje najkvalitetnija reprodukcija u području tiska ambalaže. Analiza kvalitete reprodukcije provedena je na temelju parametra neravnomjerne pokrivenosti konvencionalnim te UV bojama na dobivenim laboratorijskim tiskovnim podlogama s nedrvnim vlakancima. Vrijednosti neravnomjerne pokrivenosti bojom laboratorijskih tiskovnih podloga određene su analizom slika u programu ImageJ. Utvrđeno je da su sve analizirane tiskovne podloge otisnute visokokvalitetnom tehnikom bakrotiska ostvaruju visoku pokrivenost boje u rasponu od 97% do 98%.

Even though most information is digitized today, paper as a printing substrate is still essential. The quality of the paper depends on whether it has the properties required for its intended use, which will fundamentally rely on the raw materials used. Nowadays, the production of paper and board is increasingly focused on alternative non-wood raw materials. In this context, the main objective of this research is to improve the quality of prints on laboratory-made papers with supplementary barley pulp by coating the surface of the papers with titanium dioxide coating. Since laboratory-made papers were not subjected to the bleaching process and no additional surface treatments were used, TiO2-based coating proved to be one of the ways to improve the quality of the prints on such substrates. In this study, it was concluded that TiO2-based coating did not affect the colorimetric values of the black prints to the extent that it affected the colorimetric values of the magenta prints. However, density of printed inks was increased up to 14% for prints on laboratory-made papers with higher amount of barley pulp and TiO2-based coating in two layers.

The final quality of a graphic product largely depends on the source of raw materials for pulp and paper, the type of printing ink, the technology of printing the product and the conditions under which the printing was performed. Each analog printing technology is suitable for a particular type of printing substrate depending on the transfer of printing ink from the printing plate to the printing substrate. In the last few years, due to the over-exploitation of forests as a natural resource on a global scale, there is a growing tendency to replace wood as a traditional raw material for the production of paper with fibres from non-wood sources. The use of other cellulose sources for paper production is a costeffective and environmentally friendly solution that reduces the consumption of virgin wood pulp. In this paper, the rub stability was analyzed on a printing substrate with non - wood fibers obtained from triticale straw printed with gravure and offset UV inks. By comparing the mechanical stability of prints made by these two analog technologies, direct and indirect, the usability of innovative printing substrates with non-wood fibers was assessed.

Traditional papermaking is based on the use of an aqueous suspension consisting of cellulose fibres obtained by processing wood, non-wood plants or waste paper. With growing environmental concerns regarding deforestation and CO2 production, the paper industry has been always looking for new sources of non-wood pulp that would produce papers of similar quality to those made from wood pulp. Cereal straw from wheat, barley or triticale crops that remains on fields as a residue after grain harvesting has proven to be a good substitute for virgin wood fibres needed in the production of recycled paper. In this study, the quality of printed text on recycled paper with added straw pulp is evaluated mainly based on the line and edge characteristics of the printed letters. For this purpose, three types of laboratory paper substrates were first prepared using recycled wood pulp with the addition of 30% wheat, barley, or triticale straw pulp. The same letter pattern was printed with black ink on each paper substrate at a standard size of 12 pt with two common typefaces: Arial and Times New Roman. The quality of the printed letters was assessed through the measured print quality parameters such as blurriness, raggedness, fill and contrast. The resulting measurements were compared with the results obtained on the reference and control samples made exclusively from recycled wood pulp as a substrate from laboratory and commercial production. In terms of fill and contrast values, the uniformity of lines printed on the recycled papers with added straw pulp is the same or very similar to the reference and control papers. Letters printed in Arial (sans-serif) typeface show slightly better reproduction quality than letters printed in Times New Roman (serif) typeface. The measured parameters blurriness and raggedness of all laboratory-made paper substrates (with and without straw pulp) had similar values between 0.17 mm and 0.20 mm, resulting in a very similar reproduction quality compared to the reference paper substrate.

Paper composition, from the aspect of the printing substrate, and especially its surface characteristics, are of immense importance for its printability and the achieved quality of the final graphic product. When we talk about print quality, the stability of printed papers under various influences such as time, chemical agents, transport, pressure, and others are also needed to consider them as quality prints. The ink rub resistance, as one of the most important properties of printed material during the shipping or handling processes, refers to the degree of removal of an ink layer under the action of rubbing. The quality of the printed product is determined not only by the printing substrate and the selected ink (which is defined by the printing technique) but also by their interaction. Therefore, it is particularly important to choose an adequate printing substrate to achieve a quality printing. Increased concern for the environment has led to the idea that wood fibres in the pulp and paper industry must be replaced, as much as possible, with non-wood fibres. Nowadays, more and more studies indicate that fibres of various non-wood raw material can be a good substitute for wood raw fibres in the paper industry. Wheat pulp is a by-product of crop production and it has been selected as an alternative source of fibre because it is available from the annually renewable crops and is produced abundantly in numerous regions all over the world. In laboratory paper production, the collected and purified wheat straw was first cut manually and processed by the soda pulping method. The obtained unbleached semi chemical wheat pulp was added into the pulp of recycled wood fibres in a ratio of 30% to wood fibres, and laboratory papers of approximately 42.5 g/m2 were formed by Rapid-Köthen sheet former (FRANK-PTI) according to standard EN ISO 5269- 2:2004. Laboratory paper made only from pulp of recycled wood fibres was used as a reference sample. For a better insight into the utilisation of wheat pulp in pulp and paper industry, a control sample of commercially produced newsprint paper made from the pulp of recycled wood fibres was used for comparison with laboratory-made samples. In this research, the emphasis was placed on laboratory papers made with the addition of wheat pulp and on stability of the prints after they were printed with cyan, magenta, yellow and black inks by offset printing technique. Offset is an indirect lithographic printing technology and is the main printing technique in various publications. The offset printing process depends on many chemical and physical characteristics of materials and components which are involved in the process. The full tone areas with cyan, magenta, yellow and black inks have been achieved with Suncure Starluxe UV curable ink (manufacturer Sun Chemical) by Prüfbau (Multi-purpose printability tester) which simulates offset printing. After printing and drying, the samples were subjected to a mechanical resistance test (i.e., rub resistance test) on a Hanatek T4 Rub and Abrasion Tester according to the standard BS 3110 with 20, 40 and 60 circular motions at a constant speed of one rotation per second. Evaluation of the rub resistance of the UV ink layer on papers with and without wheat pulp is based on the CIE L*a*b* colorimetric values. Colorimetric values were measured before and after performed rub resistance test. The Euclidean colour difference (ΔE00) was calculated to define the tolerance between changes in coloration, i.e., fading of the colour. As mentioned, the ink rub resistance strongly depends on the surface characteristics of printing substrate. It is important to emphasize that laboratory-made papers have not gone through the final stages of surface treatment as commercially produced papers. One of the most important surface characteristics that directly affects the rub stability is roughness of the paper. Laboratory papers have a far higher surface roughness than commercially produced ones due to the lack of surface treatment. Roughness profiles of the samples' surfaces was measured with a Mahr MarSurf PS 10 profilometer to study the correlation between surface characteristics of papers with wheat pulp and rub resistance after printing them with offset UV inks. As expected, commercial papers showed better rub resistance of all printed cyan, magenta, yellow and black offset inks compared to laboratory papers. Of all analysed offset inks on commercial paper, the black ink layer showed the lowest rub resistance (ΔE00 < 1.5), while the yellow ink layer showed the highest rub resistance (ΔE00 < 0.6). Compared to commercial papers, laboratory-made reference samples after printing with cyan, magenta and yellow ink showed lower rub resistance i.e., greater ΔE00 value, while black ink layer showed approximately the same rub resistance on both papers. Adding 30% wheat pulp into the pulp of recycled wood fibres, resulted with laboratory papers that provide lower rub resistance after printing. Observing all process inks, the cyan ink layer on papers with wheat pulp had the lowest rub stability. However, the calculated ΔE00 values of ink layers of all prints were within the tolerated range, according to the tolerance definition where ΔE00 ≤ 2 is classified as a very small noticeable difference for the standard observer. In this study, it is observed that the highest colour degradation occurs after only 20 rotations of the rubbing test, while further rubbing up to 60 rotations has a negligible impact on the colour degradation of the offset UV ink layers. This research contributes to the necessary knowledge about the possibility of using non-wood sources of cellulose fibres in the paper and graphic industry, given that wood sources are increasingly limited.

The fundamental raw material in the paper industry is cellulose. Cellulose fibers are traditionally obtained from wood and are used to produce a wide range of paper substrates. The recent significant increase in the consumption of wood resources is causing a global need for alternative non-wood cellulose fibers in paper production. The straw of various cereals is often used as a source of virgin cellulose fibers. Laboratory paper substrates made of recycled paper and triticale straw pulp are used in this research. This study aimed to explore the effects of artificial and natural aging processes on the optical deterioration of digitally printed laboratory substrates with variable triticale pulp content in recycled wood pulp. The goal was to assess the optical stability of UV inkjet cyan, magenta, yellow, and black prints after two aging process treatments. The optical stability was measured by observing the reflectance in the visible spectrum. The durability of UV inkjet prints and their reproduction quality play an important role in ensuring the accuracy of text and images in graphic products. The greatest optical stability after aging for a long period of time was observed for black prints on all test substrates.

Agriculture residues are one of the most abundantly available resources worldwide as millions of tons are produced globally. Wheat is a particularly cultivated species in Croatia, and after each harvest, huge amounts of straw remain in the fields. Efficient utilization of this residue to produce paper as a printing substrate offers advantages as reducing the use of primary wood fibres and thus reducing deforestation. In this research, printing substrates with wheat straw will be evaluated in terms of chemical stability of digital prints influenced by inorganic acids. For that purpose, printing substrates were formed on the Rapid Köthen device from pulp obtained by blending different proportions of wheat pulp and pulp of recycled fibres. Colour prints (C+M, M+Y, C+Y and C+M+Y) were made in full tone by digital printing technique and prints were treated with two inorganic acids under the conditions defined in the international standard ISO 2836:2004. Based on the measured spectrophotometric values of the untreated and acid-treated prints, changes in colorimetric values of L*a*b* and the Euclidean colour difference (ΔE00*) were calculated, and the colour stability of prints was assessed. Based on the obtained results it could be concluded that wheat pulp in printing substrates ensures equal or even better colour stability of prints than pulp from recycled fibres.

In terms of volume, wood is the most available natural resource of cellulose fibres on earth. Although almost 2000 years ago the Chinese used other raw materials to make paper (bast, bark, hemp, rags and rice grass), today wood is still the most important raw material for pulp and paper production. As the forest area decreases daily, there are fewer trees as raw materials for cellulose fibres, the production of paper and paper products has significantly focused on the usability of alternative non-wood raw materials. The usage of these alternative cellulose fibres for paper production is the most cost-effective and environmental solution that aims to reduce the consumption of virgin wood pulp in paper production by replacing it with alternative plant biomass. The goal of this work was to assess the quality of offset prints on a substrate where wood fibres have been partially replaced by alternative fibres from triticale straw. For that purpose, laboratory-made printing substrate containing 30% triticale pulp was printed with UV low migration offset inks used for printing labels and non-food packaging. The assessment of the print quality on such substrates was based on the rub resistance according to the standard BS 3110:1959.

Each printing ink is formulated according to a specific printing technique in order to give the print a high degree of rub resistance to maintain equal quality during transport, storage and end use. Rub resistance is a very important parameter, which depends on the printing ink, printing substrate and printing conditions. In this paper, the rub resistance of laboratory substrates with variable content of wheat pulp printed with ink jet printing technique was analyzed. The ink jet printing technique is increasingly used for small print runs due to its variability and easy print preparation. Resistance to rubbing was evaluated according to BS 3110 standard on environmentally friendly laboratory substrates printed with magenta and cyan ink. The print stability was observed based on the color change of the prints shown through the Euclidean color difference. The analysis results showed greater rub resistance of prints on laboratory substrates with a lower share of wheat pulp with respect to all the analyzed samples. All samples printed with magenta ink show a higher degree of rub resistance than the samples printed with cyan ink.

Paper recycling is becoming increasingly important as the production of packaging and various printed products grows. As alternative to wood fiber that is the most common raw material in paper production this research examines the quality of paper which is made with addition of non-wood fibers derived from wheat straw. For this purpose, laboratory paper substrates were made by blending recycled newspaper pulp and wheat straw pulp in different proportions. In this study we analyse rub resistance of laboratory paper substrates with variable content of wheat pulp printed in full tone with black and yellow inks by digital ink jet printing technique. The main objective of this research is to determine whether this kind of print has necessary durability for carrying stable illustrations. One of the main characteristics of print quality is resistance to rubbing which is very important for packaging during transport, storage and the end use. Rub resistance test was executed according to BS 3110 standard. The print durability was assessed through the Euclidean color difference and the individual CIE L*a*b* differences before and after the rub tests. The analysis showed that the increase of wheat pulp content in paper substrates has affected the increase of color difference. Greater rub resistance was observed on substrates with lower share of wheat pulp. Samples printed with yellow ink showed overall greater durability than samples printed with black ink. In further analysis we observed that for the black prints the difference in lightness (ΔL') of the CIE L*a*b* color space was most affected as the prints became lighter with the number of rubbing cycles. In samples printed with yellow ink most affected was the color difference on yellow-blue axis (Δb') meaning that the yellowness of the prints was degrading with the number of rubbing cycles.

Flexographic and digital printing are currently the fastest growing branches in the printing industry. The selection of printing substrates for these printing techniques is large, but paper substrates are the most widely used. Paper manufacturing is based mainly on the use of renewable fibers, and the dominant fiber resource for the pulp and paper industry is wood which is accounting for 90% of the world's fiber utilization. As woods consumption for paper production is still high, there are various possibilities to reduce it. One way is by reducing the proportion of wood pulp in paper by adding straw pulp of various cereals such as wheat. Wheat straw has numerous advantages and can be used in pulp form as a source of primary fibers for paper production. As paper as a multi- component material, besides fibers composed of cellulose, hemicellulose and lignin also includes additives, minerals and synthetic polymers. Due to its complex nature it is prone to deterioration when exposed to elevated temperature, humidity and light. Paper ageing is irreversible change and is the best indicator of paper optical permanence. Objective of this study was to determine the optical stability of prints after undergoing aging treatment with elevated temperature and UV light for 48 and 96 hours. Laboratory papers containing wheat pulp were printed by two printing techniques with cyan and yellow inks to compare better optical stability: UV inkjet and flexographic technique. The optical stability of all prints was observed based on the difference in the reflection spectra (ΔR). The results indicated that all laboratory papers printed with cyan ink with flexographic technique show better optical stability than the ones printed with digital technique. Laboratory papers printed with yellow ink by both techniques show good optical stability.

Paper substrate, as the most common used substrate for printing labels or packaging, is traditionally produced from cellulose fibres derived from wood. The growth of a large number of industries has led to a significant increase in the use of such resource, which consequently led to a global awareness of the possibility of forest exploitation and the importance of reusing waste paper as a source of fibres. Hence, paper fibres can be recycled up to seven times and it is important to enrich paper pulp with virgin fibres during paper production. In such a way, the characteristics of the paper and the quality of the printed elements are improved. In this paper, cereal straw as an alternative resource of virgin fibres was turned into pulp and mixed with recycled wood pulp to conduct printing substrates using laboratory equipment. Since aging is an inevitable process of any printing substrates and prints, and the degradation of print quality due to aging largely depends on the properties of the printing substrate, ink and type of printing. This research was focused on analyzing optical stability of prints made on printing substrates with straw pulp by UV inkjet technique after natural and artificial aging. From a comparison of the aging processes based on the Euclidean difference results, it was observed that natural aging of UV inkjet prints yields less colour changes compared to artificial aging. Greater or equal optical stability after aging was perceived for prints on printing substrates with wheat, barley and triticale pulp compared to prints on substrates made with recycled wood pulp.

The bonding potential of pulp fibers is reduced by the paper recycling process. The most common technique for recovering this lost potential of secondary fibers involves upgrading the recycled pulp by blending it with virgin softwood pulps. In this research, we asses print stability on acid agents of UV inkjet prints when using straw pulp as reinforcing fibers in recycled papers. For that purpose, printing substrates were formed on the Rapid Köthen device from pulp obtained by blending different proportions of straw pulp and pulp of recycled fibers. Each printing substrate was printed in full tone with cyan, magenta, yellow, and black inks by digital technique of UV inkjet printing. Printed substrates were treated with various inorganic and organic acids under the conditions defined in the international standard ISO 2836:2004. Based on the measured spectrophotometric values of the untreated and acid-treated prints, the Euclidean color difference (ΔE00*) was defined and the stability of prints was assessed. The results of spectrophotometric measurements indicate small to medium color differences of the prints due to the effect of all acids (ΔE00max. * < 2.4) and it can be concluded that straw pulp in printing substrates from recycled fibers contributes to good chemical stability of prints. This research concludes that straw, as an annual renewable resource, can be used in conjunction with waste paper as an alternative to wood, which is currently the dominant raw material for graphic industry and producing paper.

Paper as cellulose based substrate is highly susceptible to photolytic damage caused by excessive exposure to light and temperature. Hence the focus of this research was to assess whether the wheat pulp used as a raw material for laboratory paper production can provide same or even better optical stability than papers from recycled wood pulp. For a better insight into the stability of the paper as printing substrate, study was expanded on prints made by digital technique on papers with different content of wheat pulp. Unprinted and printed papers were artificial aged using a xenon lamp with a daylight filter during 48 and 96 hours. Optical stability degradation of unprinted and printed papers was observed through Reflectance spectra (R) and by Euclidean colour difference (ΔE00). The results in this study indicated that addition of wheat pulp provide better optical stability of printed and unprinted laboratory papers.

Awareness of environmental issues has led to the increase in use of recycled printing papers or to the introduction of new alternative sources of cellulose fibres instead of virgin wood fibres. As recovered wood fibres cannot provide the same quality level of paper products as virgin ones, alternative sources of virgin cellulose fibres need to be identified. Therefore, the laboratory printing papers were produced using a wheat pulp in varying weight proportions and mixing with pulp from recycled paper. The print quality depends on the characteristics of the printing substrate, wherein the ink penetration is one of the important parameter. This study investigated ink penetration into laboratory papers made of different contents of pulp and their correlation with prints quality. The solid areas were printed on laboratory printing papers with cyan, yellow and magenta UV ink jet inks under standardized printing conditions. At last, the ink penetration inside laboratory papers were analyzed based on two methods (microscopic and spectroscopic) and their effect on rub resistance and print quality was also observed. Analyzed print quality parameters (ink optical density, mottling, colorimetric values) indicated that wheat pulp in the laboratory papers provides equal print quality compared to laboratory papers made from recycled pulp. The highest degradation of print quality was observed on laboratory papers with 30% of wheat pulp printed with cyan ink, as a result of the greatest measured average ink penetration depth.

Increased worldwide environmental awareness has led to a substantial increase in the use of recycled papers and new alternative sources of cellulose fibres to manufacture new paper. As recovered wood fibres do not provide the same level of paper quality as the virgin ones, alternative sources of cellulose fibers are continuously sought and researched. In this paper, the penetration profiles of UV inkjet inks within laboratory substrates formed with the addition of barley pulp in different weight proportions into pulp from recycled paper were observed. All the results have been compared to the control sample, respectively laboratory substrate produced only from recycled paper pulp. Penetration profiles were performed by observing and analyzing the microscopic images captured in the region of interest from a cross section of a pre-molded specimen into an epoxy resin. The aim of this paper is to examine whether the proportion of non-wood fibres effects the print quality, and to propose which fiber ratio is the most acceptable for paper production.

Topografske karakteristike površine papira bitno utječu na ukupnu kvalitetu otiska. Razvijeno je više metoda za mjerenje i numeričko karakteriziranje svojstava površine papira. Tri su osnovana pristupa mjerenjima glatkosti ili hrapavosti površine papira – optičke metode, profilometrijske metode i pneumatske metode. Premda te tri vrste metoda služe istoj svrsi, međusobno se razlikuju u načinu prikaza svojstava površine papira. Ovo istraživanje bazira se na dvije pneumatske metode, Bendtsen za mjerenje hrapavosti i Bekk za mjerenje glatkosti površine papira. Na temelju toga uspoređuju se dva spomenuta svojstva koja su mjerena na tri vrste ofsetnog papira (premazani, nepremazani i reciklirani papir).

The analysis of the edge of the screen element is based on the selection of the linear sample on the paper – ink system in comparing models and reality. Although Yule and Nielsen suggested the Gaussian distribution for the description of the line spread function, our model, based on the stochastic approach of subsurface light scattering in paper, gives the complete description with the Lorentzian distribution. To determine which of the two proposed models, Gaussian or Lorentzian, gives a better approximation with respect to the measured data, Akaike information criterion has been used. As the observed profiles are asymmetric, both edges have been analyzed. It was not possible to distinguish which model better describes the resulting measurements, because of the extremely high value of the correlation coefficient for both models. Therefore the AIC method was applied using the routines in Origin 8.5 that was used to analyze the measured data. The Akaike weight demonstrates that the Lorentzian model better describes the LSF than the Gaussian model.

Modeliranje podpovršinskog raspršenja fotona pomoću Monte Carlo metode temelji se na nasumičnom generiranju uzoraka iz raspodjele vjerojatnosti koja opisuje udaljenosti koje foton prijeđe između dva događaja i kutova raspršenja. Pritom se gibanje fotona prikazuje propagacijom fotonskog paketa gdje se više ekvivalentnih fotona simultano propagira duž nekog puta. Put koji fotonski paket prijeđe između dvije interakcije je neuniformno raspodijeljena varijabla koja se iz uniformno raspodijeljene nasumične varijable dobiva s pomoću tehnike mapiranja. Fotonski paket lansira se kroz graničnu površinu u medij, pri čemu se putanja fotona određuje računanjem sukcesivnih raspršenja i apsorpcija unutar pojedinog sloja. Ovaj teorijski model računat je računalnim matematičkim programom u Mathcadu 11. Model omogućuje izračun lateralnog raspršenja svjetlosti u papiru, što omogućuje precizniji opis dot gaina.

Flexographic printing process is a fast growing printing technique, which has established itself as a very competitive printing method in the packaging production. Flexographic printing process is a quality and cost-effective printing technique used for a wide range of substrates such as foils, plastic films, corrugated boards, papers and even fabrics. Nowadays, when a more demanding printing has to be performed, it represents a strong competition to the gravure printing process. Every good quality printing technique, especially the one which pertains to the packaging, includes prints which must have good adherence to the printing substrate and the previously printed ink film. The key elements that cause uneven coverage of the ink are surface characteristics in relation to the surface tension. This research analysis was focused on testing the acceptance of cyan ink with various viscosities to the printing substrate and acceptance to the previously applied white ink. The research was performed with the use of six different polymer materials. The comparison of the cyan ink acceptance among analysed samples is based on spectrophotometric values and uneven reproduction of full tone.

Kvaliteta reprodukcija nastalih fleksografskom tehnologijom dostigla je visoku razinu, te je u današnje vrijeme postala jedna od vodećih tehnika tiska u ambalažnoj industriji. Pritom se najčešće kao tiskovne podloge koriste polimerni materijali. Za ostvarenje kvalitetnog otiska od velikog je značenja primanje tiskovnog bojila na tiskovnu podlogu. Zbog toga je ovo istraživanje usmjereno na ispitivanje primanja bojila (cijan fleksografskog bojila) na četiri transparentne tiskovne podloge: PVC, PP, PELD i PET, te dvije netransparentne (obojene) podloge: PELD i PP. Kvaliteta reprodukcije, odnosno kvaliteta primanja tiskovnog bojila na tiskovnu podlogu određivana je na osnovi spektrofotometrijskih vrijednosti bojila te usporedbom vrijednosti neravnomjerne reprodukcije punog tona.

Temeljem teorijskog opisa podpovršinskog raspršenja svjetlosti u papiru u okviru Monte Carlo simulacije, u radu je analizirana optička komponenta prirasta rastertonske vrijednosti. Rezultati pokazuju da je dobivena teorijska funkcija Lorentzovog oblika, koja opisuje podpovršinsko raspršenje, prepoznata kao funkcija razmazivanja točke, koja se koristi za konvolucijsko modeliranje reflektancijskih profila otisaka. Dobiveni rezultati analizirani su na otiscima koji su generirani na različitim papirima i digitalnim tiskarskim strojevima. Usporedbom mjerenih i računatih reflektancijskih profila otisnute linije i analizom primijenjenih teorijskih modela pokazano je da bolji opis daje funkcija razmazivanja točke koja ima Lorentzovu formu, nego do sada uobičajena Gaussova forma. Time je ujedno pokazana valjanost opisa korištenog u Monte Carlo simulaciji. Ovako dobivena funkcija razmazivanja ovisna je o samo jednom parametru – poluširini profila w. Utjecaji mnogih faktora (sastav papira, tehnika tiska, valna duljina svjetlosti, premaz, ...) detaljno su teorijski analizirani i uspoređeni s mjerenjima te se pokazuje superiornost opisa korištenjem Lorentzove funkcije. Provjera rezultata načinjena je usporedbom s rezultatima dobivenima gradijentnom metodom koji potvrđuju navedene pretpostavke. Dobiveni zaključci su dodatno potvrđeni analizom reflektancijskih profila u frekvencijskoj domeni.

Potpovršinsko raspršenje svjetlosti u papiru (tekstilu ili drugim transparentnim materijalima) ovdje je izračunato u okviru Monte Carlo simulacije, što je kao rezultat dalo funkciju razmazivanja točke (PSF) Lorentzove forme. Papir je bio modeliran s obzirom na različite parametre opisa papira: premazanost, sastav i komponente papira te valne duljine svjetlosti kojom je papir obasjavan. S obzirom na to da je Lorentzova raspodjela parametarska, izračunate su ovisnosti parametra w Lorentzove raspodjele o debljini premaza papira o faktoru asimetrije celuloznih vlakana kao sastavnica papira, te o valnoj duljini svjetlosti koja pada na papir. Pokazalo se da osim celuloznih vlakana ostale komponente papira nemaju utjecaj na parametar w. Rezultati su pokazali da je parametar w manji za premazani papir, za manje asimetrične sastavnice papira i za manju valnu duljinu svjetlosti, što je u ovisnosti koeficijenata apsorpcije, odnosno raspršenja svjetlosti u papiru, i valne duljine svjetlosti.

The article deals with Monte Carlo modeling of uncoated printing paper surface based on light reflectance from the surface and on subsurface scattering. The paper surface was simulated using randomly oriented microfacets characterized by a specific parameter, critical azimuthal angle ϑc. Determination of the value of ϑc was based on the idea that the standard deviation of the light reflected from a paper surface is not equal to zero, and can be recognized as noise. Noise, i.e. standard deviation of the reflectance measured on actual paper samples, was used for calculating ϑc and, consequently, for obtaining theoretical surface models. The results show a satisfactory agreement with the real paper surfaces and indicate that ϑc can be one of the important parameters in future simulations of this kind.

U dizajnu i analizi sustava za obradu slike često se zahtijeva matematički opis slike koju želimo obraditi. Ovaj rad daje pregled funkcija koje se najčešće koriste prilikom obrade slike i pokazuje da je aproksimacija koja opisuje definiciju ruba na otisnutim rasterskim elementima bazirana na Lorentzovoj funkciji. Dobivenu raspodjelu u okviru Monte Carlo opisa raspršenja svjetlosti u papiru prepoznali smo kao funkciju razmazivanja točke (PSF) koja ima Lorentzov analitički oblik. Pokazano je da takva funkcija bolje opisuje problem definicije ruba od dosadašnjeg pristupa opisom Gaussovom funkcijom.

Za bolje razumijevanje porijekla optičkog prirasta rastertonske vrijednosti i realističniji opis medij u kojem dolazi do raspršenja svjetlosti uveli smo metodu baziranu na Monte Carlo modelu raspršenja svjetlosti u papiru. S obzirom da raspodjela svjetlosti u papiru (općenito bilo koja homogena ili nehomogena podloga) ovisi o njegovim optičkim svojstvima, pokušali smo utvrditi distribuciju svjetlosti unutar papira s poznatim optičkim svojstvima i njihov utjecaj na raspodjelu. Zbog činjenice da je papir složen medij, u našem prikazu bilo je potrebno uključiti i površinsku strukturu koju smo modelirali pomoći mikrofaceta. Numerički je ispitivan utjecaj tako modelirane površine substrata na optička svojstva papira prilikom podpovršinskog raspršenja svjetlosti.

U radu je dat kratki pregled neuralnih mreža te mogućnosti njihove primjene kao alata za generiranje rješenja o širokom aspektu kompleksnih problema koji se javljaju u procesima reprodukcije grafi čkog proizvoda. Optimiziranje pojedinih procesa kao što je na primjer proizvodnja papira1, 2, recikliranje ili proces tiska zbog svoje kompleksnosti i međusobne zavisnost velikog broja parametara i varijabli, te fi nih efekata međudjelovanja koji se za sada samo naslućuju, idealno je polje za primjenu neuralnih mreža.

Razvoj znanstvenih interesa i metoda proučavanja doveo je do toga da je promišljanje o pristupu i dizajnu eksperimenta krucijalna stvar u eksperimentalnom radu. Riječ eksperiment koristi se u strogom smislu, što znači da je sustav koji istražujemo pod potpunom kontrolom samog istraživača. Prihvaćajući činjenicu da naša osobna i kulturološka uvjerenja utječu istovremeno i na percepciju i interpretaciju prirodnih fenomen, pokušavamo te utjecaje svesti na najmanju moguću mjeru služeći se standardnim postupcima. Znanstvena metoda zasniva se na nekoliko koraka koji nakon opažanja i opisa fenomena ili grupe fenomena formuliraju hipotezu koja omogućuje predviđanja tako da iz teorije dobijemo više nego što je uloženo u nju. Ipak, često se kaže da se znanstvene teorije nikad ne dokazuju, već ruše, što znači da možemo uvijek očekivati da će neko novo opažanje ili eksperiment biti u suprotnosti od prihvaćene teorije. U radu su razmatrani osnovni principi eksperimentalnog pristupa u istraživanjima u grafičkoj tehnologiji.

Primjena holograma i ostalih difraktivnoih optički varijabilnih sustava u zaštitnom tisku danas je opće prihvaćena metoda protiv krivotvorenja visokorizičnih tiskovina. Sve više se primjenjuju kompjuterski generirani hologrami zbog posebnih mogućnosti koje pružaju. Naime, kako za izradu CGH nije potreban konkretan fizički objekt čija se slika generira, moguće izabrati bilo kakav, stvaran ili imaginaran objekt, čija se trodimenzionalna slika može matematički modelirati. Osim toga, takva metoda izrade holograma omogućuje dodatne elemente zaštite.