Galić, Eduard (2017) Kolorimetrija spotnih boja kod različitih postupaka lakiranja = Colorimetry of spot colours of different varnishing methods. Dissertation (PhD) thesis. Grafički fakultet. [Mentor: Zjakić, Igor].
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Abstract
Procesi lakiranja otisaka sveprisutni su u grafičkoj industriji. Osim u svrhu zaštite od mehaničkih oštećenja otiska te poboljšanja procesa sušenja, često su korišteni i u svrhu vizualnog unapređenja otisnutog proizvoda. Svoju primjenu, lakiranje pronalazi ponajprije u tisku ambalažnih grafičkih proizvoda, ali i u tisku drugih svakodnevno korištenih proizvoda kao što su katalozi, brošure, etikete, prospekti. Poznavanje utjecaja različitih postupaka lakiranja u međuovisnosti s hrapavošću tiskovne podloge na kolorimetrijske promjene spotnih boja, značajno je za reprodukcijski proces. Dosadašnje spoznaje upućuju na problematiku kolorimetrijskih promjena procesnih boja CMYK sustava, pod utjecajem različitih postupaka lakiranja, no područje promjena spotnih boja ostaje relativno neistraženo. U ovom je radu naglasak stavljen na utjecaj najčešće korištenih postupaka lakiranja u tehnici ofsetnog tiska, ali i termalnih laminacijskih postupaka na često korištene spotne boje, koje su u procesu grafičke proizvodnje prepoznate kao problematične. Istraživanje je usmjereno na definiranje graničnih vrijednosti kolorimetrijskih odstupanja koja mogu utjecati na kvalitetu reprodukcijskog procesa. Kako bi se provelo ispitivanje, otisnuti su uzorci u tehnici ofsetnog tiska, prema standardiziranim uvjetima. Uzorci su podvrgnuti laboratorijskim ispitivanjima hrapavosti tiskovne podloge, sjajnosti tiskovne podloge te mikroskopskoj analizi. Kolorimetrijska ispitivanja provedena su spektrofotometrijskim metodama u CIE L*a*b* prostoru. Denzitometrijska mjerenja su također provedena. Na osnovu provedenih objektivnih, laboratorijskih mjerenja, pristupilo se izračunima koji su pokazali u kojoj je mjeri došlo do kolorimetrijskih promjena spotnih boja, a uslijed raznovrsnih procesa lakiranja te uslijed termalnih laminacijskih postupaka. Ispitala se međuovisnost parametara hrapavosti i sjajnosti tiskovne podloge te su rezultati stavljeni u korelaciju s kolorimetrijskim promjenama na bojama. Definirala su se granična područja i uvjeti unutar kojih navedene promjene mogu utjecati na subjektivni doživljaj prosječnog promatrača – korisnika određenog grafičkog proizvoda. Ponuđene su nove znanstvene preporuke koje mogu biti iskoristive u svakodnevnoj grafičkoj reprodukciji te rezultirati uspješnijom kvalitetom tiska.
| Item Type: | Dissertation (PhD) thesis |
|---|---|
| Mentor name: | Zjakić, Igor |
| Thesis Committee: | Mrvac, Nikola and Bates, Irena and Barišić, Mario |
| Defence date: | 28 April 2017 |
| Abstract in english: | Processes of print varnishing are very common in the printing industry. Except for the purpose of protection against mechanical damage of prints, and improvement of the drying process, they are often used for improving the visual impression of a printed product. Varnishing is applied primarily in packaging printing products, but also in the other daily used products such as catalogs, brochures, labels, booklets. Understanding the impact of different methods of varnishing in interdependence with the printing surface roughness on colorimetric change of spot colors is important for the reproduction process. According to current knowledge, the issue of change of process colors in CMYK system under the influence of different varnishing methods is recognized, but the area of changes in spot colors remains relatively unexplored. In this paper, emphasis is placed on the impact of the most commonly used varnishing methods in offset printing, as well as thermal lamination processes on frequently used spot colors, which are identified as problematic in the process of graphic production. The research is aimed at defining the limits of colorimetric variations that may affect the quality of the reproduction process. To perform the research, the samples were printed in offset printing technique, according to standardized conditions. Samples were subjected to laboratory tests of printing substrate roughness, printing substrate gloss, and microscopic analysis. Colorimetric tests were conducted by spectrophotometric methods in CIE L*a*b* color system. Based on the objective, laboratory measurements and calculations were conducted, showing the extent to which there was a colorimetric change of spot colors under the influence of various varnishing methods and thermal lamination processes. The interdependence of printing substrate roughness and gloss parameters was examined, and the results were placed in correlation with colorimetric changes in colors. The border areas and conditions within which these changes may affect the subjective experience of the average spectator - user of specific printed products were defined. The research has yielded new scientific recommendations that may be usable in everyday graphic reproduction and that could result in improved print quality. Basic concepts of the printing industry are described at the beginning of this work, as well as other key concepts required to understand the entire process that needs to be implemented to achieve the required research. The human experience of color, the interaction of light with thesubject that it illuminates, and the human eye as a receptor of that experience is an extremely complicated system. As the most perfect "instrument", the human eye is able to experience and "see" very small color differences between the printed colors, but on the other hand - without a reference sample, the human eye "does not remember" and can easily be fooled. Metamerism, as a phenomenon during which the human eye sees two samples the same even though the two samples have different spectral characteristics, is an interesting phenomenon which indicates the necessity of objective and instrumental color measurement. In this context, the work presents the most commonly used methods of measuring color and colorimetry that predicts colors with respect to how they are experienced by the average observer. Colorimetric model shows the results of the same numerical values for two different samples in cases when the average observer sees the same color. Colorimetric model shows the different numerical values, and indicates the difference between two colors for the cases when the average observer sees the difference between the colors. Varnishing processes used in offset printing are diverse in terms of the effects they cause on the printed sheets, in terms of applications, but also in terms of technical and technological solutions which enable their application. Besides the mechanical protection achieved by various coating processes, they are also used for improvement of visual appearance of the printed products. Oil-based varnishes, water-based varnishes and UV varnishes are the most commonly used varnishes for the varnishing processes. Application of oil-based varnishes within the printing unit can be carried out by offset printing plate or directly by means of offset printing blanket, depending on the request. Oil-based varnishes have a similar chemical composition to the conventional offset printing inks, with the exception of pigment. Waterbased varnishing is a process that uses varnish based on water. Besides the packaging industry, with new constructions of printing machines and increased technical and technological capabilities, the water-based varnishes are used during the printing of other everyday graphic products. Water-based varnishes require a special varnishing unit, consisting of several rolls systems and the varnish is transferred directly by a prepared coating form of a coating cylinder. The biggest gloss effect is achieved by the process of UV varnishing, compared to oil-based varnish and water-based varnish. Besides the in-line mode of application with the technical and technological solutions that are part of the printing machine, UV varnishing can be applied by a screen printing technique. Applying gloss or matte lamination with thermallamination process is one of the first stages in the process of graphic finishing. This is a very common way of protecting printed products, used in matte or gloss version for book covers, magazines, brochures, folders, boxes, etc. Although the lamination film seems transparent, it still has a certain opacity and will retain a certain percentage of light that would otherwise be reflected by the print if it has not been laminated. For research purposes, it is necessary to consider occurrences and characteristics that occur on the surface of the printing substrate. Interaction of printing inks, varnish and printing substrate during the printing process significantly affects the colorimetric changes that may occur. The roughness of the printing substrate is one of the most important factors during the process of manufacturing paper. Printing substrate used during printing affects printing, as well as the realization of the required reproduction, achieving gamut, trapping, drying, and subsequent finishing processes. The various varnishing processes have different impacts on increasing or reducing the roughness of the printing substrate. This phenomenon was observed in all three printing substrates with respect to the experiment carried out: matte and gloss coated printing substrates and uncoated printing substrate. Glossiness and the roughness of the printing substrate are one of the main characteristics of the printing substrate that affects the reproduction chain of offset printing processes and standardization of the production flow. The various varnishing processes also influence the decrease or increase of the printing substrate gloss. The abovementioned properties of the printing substrates can be measured in the laboratory with special measuring equipment. The basis of this research are spot colors that are special for several reasons. Apart from providing the ability to increase reproduction gamut, spot colors also provide a very important repeatability of the printing process and reproduction chain. The various systems of spot colors used in the printing industry provide a variety of applications and benefits. One of the most commonly used system of spot colors in the printing industry is Pantone® color system. During the printing process, spot colors show a number of characteristics, which is important to recognize and understand in order to achieve a satisfactory reproduction process. Colorimetric change of spot colors can be influenced by numerous parameters, including the various varnishing methods and laminating processes. The change of printed color is not necessarily immediately visible during printing, but it can also occur in a certain period of drying time, and even after a few weeks.Eight spot colors of contrasting wavelengths were selected for the implementation of the experiment. Samples were printed in standardized conditions in offset printing technique. The printed colors were subjected to various varnishing processes and a thermal lamination process. During the process of printing samples, part of prints remained uncoated, and the second part of the prints was coated with oil-based varnish in matte and gloss version, waterbased varnish in matte and gloss version, and UV gloss varnish, also under controlled conditions. Laboratory tests determined the parameters of roughness and gloss of the printed samples. Upon completion of samples, calculations were conducted that showed the extent to which there was a colorimetric change of spot colors, as well as to determine the interdependence of roughness and gloss properties of the printing substrate. Measurement of paper smoothness was carried out according to Bekk method. This exact method is based on the air flow between the paper and the smooth surface. Elcometer 407 was used for measuring the gloss of the printing substrate, which enables the measurement of three angles: 20°, 60° and 85°. Spectrophotometric measurements in the CIE L*a*b* color system were used for the purpose of defining and calculating colorimetric tolerances. The results of smoothness measurements showed that the greatest smoothness was achieved on samples with lamination. After that, the highest values were achieved on the samples with water-based gloss varnish, and then oil-based gloss varnish. Water-based matte varnish and oil-based matte varnish on matte and gloss coated printing substrates resulted in the reduction of surface smoothness relative to samples without varnish. Gloss and matte coated printing substrates reacted similarly influenced by different types of varnishing and laminating processes. On uncoated printing substrate, various types of varnishes, in contrast to gloss and matte thermal lamination processes, did not cause significant change in the surface roughness. Results of gloss measurement showed that various varnishing methods did not largely influence the change in glossiness of the samples printed on uncoated printing substrates. Initially, large surface roughness of uncoated printing substrate was not significantly changed by the application of coating, and therefore, the glossiness of the surface slightly changed in relation to the sample without varnish. On the gloss coated printing substrate, various varnishing methods significantly altered the gloss of the printing substrate. Different types of varnishing and lamination caused almost the same changes on the gloss coated printing substrates as on the matte coated printing substrates. For all measured samples, UV gloss varnish, and then water-based gloss varnish, caused the largest increase in gloss.Measurements of gloss and roughness of the printed samples confirmed the interdependence of these two parameters. In order to determine changes in the CIE L*a*b* values that different laminating and various varnishing methods caused to the individual samples, after the visual presentation of changes through 3D graphs, tabular calculation were made, and the overall results were presented for all printed samples. It is necessary to take into consideration that all the changes in which ∆E00 * > 2 are treated as changes that are visible to the average observer, and as such influence and/or may affect the quality and impression of finished printed products. The spectrophotometric measurement of color PANTONE Rubine Red showed that for all three types of printing substrate, it is common that at low values of raster tone (20 %) combined with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * > 3. In the field of medium raster tone values (50 % and 80 %), matte and gloss lamination, as well as UV gloss varnish, caused ∆E00 * > 3. With 100 % raster tone value, except for laminating, the color change is affected by both matte and gloss water-based varnishes. The spectrophotometric measurement of color PANTONE Warm Red showed that for all three types of printing substrate, it is common that at low values of raster tone (20 %) combined with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * > 3. In the field of medium raster tone values (50 %), matte and gloss lamination, as well as UV gloss varnish, caused ∆E00 * > 3. With 100 % raster tone value on matte and gloss printing substrates, ∆E00 * > 2 was noticed only under the influence of matte lamination process. The spectrophotometric measurement of color PANTONE Orange 021 showed that for all three types of printing substrate, it is common that at low values of raster tone (20 %) combined with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * > 3. This is especially visible on both matte and gloss coated printing substrates. In the field of medium raster tone values (50 %), gloss lamination, as well as UV gloss varnish, caused ∆E00 * > 3. At 80 % raster tone value, water-based matte varnish caused ∆E00 * > 2 on matte and gloss coated printing substrates. With 100 % raster tone value on matte and gloss coated printing substrates, ∆E00 * > 3 was noticed only under the influence of matte lamination process and water-based matte varnish.The spectrophotometric measurement of color PANTONE Yellow showed that for all three types of printing substrate, it is common that at low values of raster tone (20 %) combined with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * > 3. In the field of medium raster tone values (50 %), matte and gloss lamination, as well as UV gloss varnish caused ∆E00 * > 3 on matte and gloss coated printing substrate, while on uncoated printing substrate caused ∆E00 * > 2. ∆E00 * > 2 changes were not noticed while measuring on matte and gloss coated printing substrate on 80 % and 100 % raster tone value. On uncoated printing substrate at 80 % and 100 % raster tone value, only the process of gloss lamination caused ∆E00 * > 2. The spectrophotometric measurement of color PANTONE Green showed that for all three types of printing substrate, it is common that at low values of raster tone (20 %) combined with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * > 3. An exception to the above represents matte coated printing substrate in combination with a matte lamination process. In the field of medium raster tone values (50 %), matte and gloss lamination, as well as UV gloss varnish, caused ∆E00 * > 3. With 100 % raster tone value on matte and gloss coated printing substrates, ∆E00 * > 2 was noticed only under the influence of matte lamination process. The spectrophotometric measurement of color PANTONE Reflex Blue showed that for all three types of printing substrate, it is common that at low values of raster tone (20 %) combined with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * > 3. With 100 % raster tone value on matte and gloss coated printing substrates, ∆E00 * > 3 was noticed only under the influence of matte lamination process and water-based matte varnish. Almost all methods of varnishing caused ∆E00 * > 2 on an uncoated printing substrate in certain situations. The spectrophotometric measurement of color PANTONE Violet showed that for all three types of printing substrate, it is common that at low values of raster tone (20 %) combined with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * > 3. With 100 % raster tone value on matte and gloss coated printing substrates, ∆E00 * > 3 was noticed only under the influence of matte lamination process and water-based matte varnish. On uncoated printing substrate at 100 % raster tone value, ∆E00 * > 2 was not measured only on the samples with oil-based matte and gloss varnish.The spectrophotometric measurement of color PANTONE Purple showed that for all three types of printing substrate, it is common that at low values of raster tone (20 %) combined with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * > 3. With 100 % raster tone value on matte and gloss coated printing substrates, ∆E00 * > 2 was noticed under the influence of matte lamination process. Water-based matte varnish on matte and gloss coated printing substrates also caused ∆E00 * > 2. On the matte coated printing substrate ∆E00 * > 2 was also caused by matte and gloss oil-based varnish. Considering all of the observed colors on uncoated printing substrate, under the influence of various varnishing methods and laminating processes, the most sensitive was PANTONE Violet, in which 79 % of the samples had ∆E00 * > 2 changes. After PANTONE Violet, PANTONE Reflex Blue followed with 68 % and PANTONE Rubine Red with 50 % of the samples that had changes ∆E00 * > 2. Considering all of the observed colors on matte coated printing substrate, under the influence of various varnishing methods and laminating processes, the most sensitive was PANTONE Purple, in which 49 % of the samples had ∆E00 * > 2 changes. PANTONE Reflex Blue and PANTONE Rubine Red followed with 39 % of the samples that had changes ∆E00 * > 2. Considering all of the observed colors on gloss coated printing substrate, the most sensitive was PANTONE Reflex Blue, PANTONE Violet and PANTONE Rubine Red in which 39 % of the samples had ∆E00 * > 2 changes. The smallest changes, as with an uncoated and matte coated printing substrate, occurred on PANTONE Green and PANTONE Yellow. Results presented in this research can be used as recommendations for achieving optimum results when printing spot colors in combination with the most commonly used varnishing methods and thermal processes, and on conventional printing substrates. |
| Uncontrolled Keywords: | lakiranje, hrapavost tiskovne podloge, sjajnost tiskovne podloge, spotne boje, kvaliteta otiska |
| Keywords in english: | varnishing, printing substrate roughness, printing substrate gloss, spot colors, print quality |
| Subjects: | TECHNICAL SCIENCES > Graphic Technology |
| Institution: | Grafički fakultet |
| City: | Zagreb |
| Number of Pages: | 185 |
| Callnumber: | 535.6 GAL k |
| Inventory number: | 10189 |
| Depositing User: | Nina Jelača |
| Status: | Unpublished |
| Date Deposited: | 11 May 2017 08:41 |
| Last Modified: | 11 May 2017 08:41 |
| URI: | http://eprints.grf.unizg.hr/id/eprint/2679 |
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