Abstract | U skladu sa sintagmom „održivi razvoj” istraživanja u ovom doktorskom radu usmjerena su na
dobivanje najznačajnijih kvalitativnih parametara novoga grafičkog proizvoda, izrađenog
korištenjem obnovljivih resursa koji odgovaraju standardu grafičkih proizvoda otisnutih
fleksografskom tehnikom tiska. Kvalitativna ispitivanja su provedena na fleksografskim
otiscima dobivenim s konvencionalnim bojama na bazi vode i modernim bojama koje se suše
UV zračenjem. Otisci su tiskani na laboratorijski izrađenim papirnim podlogama koje u
različitim omjerima sadrže celuloznu pulpu slame triju vrsta žitarica: pšenice, ječma, pšenoraži
te recikliranog papira. Istraživanje je podijeljeno na nekoliko faza: kvalitativnu evaluaciju
otiska, optičku stabilnost reprodukcije nakon standardnih metoda ispitivanja pri povišenoj
temperaturi i UV svjetlosti, te djelovanje pritiska i različitih kemijskih agensa. Cilj ovog rada
je definirati uporabljivost otisaka dobivenih fleksografskom tehnikom tiska na papirnim
tiskovnim podlogama s alternativnim nedrvnim vlakancima. Na temelju provedenih
istraživanja može se zaključiti kako laboratorijski proizvedeni papiri s dodatkom pulpe slame
svih žitarica postižu zadovoljavajuću kvalitetu reprodukcije, pri čemu laboratorijski papiri
otisnuti konvencionalnim bojama na bazi vode uglavnom pokazuju izvrsnu optičku stabilnost
nakon izlaganja povišenoj temperaturi, kemijskim agensima i pritisku, dok laboratorijski papiri
otisnuti UV sušećim fleksografskim bojama najveću otpornost pokazuju prema djelovanju
pritiska. Preporuka je da se papiri iz celulozne pulpe navedenih ekološki prihvatljivijih sirovina
izrade veće gramature kako bi se postigle manje vrijednosti euklidske razlike podtona i
penetracije boje u tiskovnu podlogu te da se uvedu završne faze površinske obrade papira.
Također, na temelju kvalitativnih analiza može se dati preporuka da se papiri s dodatkom pulpe
slame žitarica otisnuti konvencionalnim bojama na bazi vode trebaju izbjegavati samo kod
ambalaže proizvoda koji sadrže alkalne proizvode ili ulja. Papiri s dodatkom pulpe slame
žitarica nisu prikladni za otiskivanje primarne prehrambene ambalaže UV bojama, no zbog
svoje izuzetne mehaničke otpornosti mogu se upotrebljavati za tisak raznih publikacija,
sekundarne ambalaže i etiketa. |
Abstract (english) | In accordance with the term „sustainable development”, the research in this doctoral thesis is
focused on obtaining the most important qualitative parameters of a new graphic product made
by using renewable resources, which correspond to the standard of graphic products printed by
flexographic printing technique. Qualitative tests were carried out on flexographic prints
obtained with convencional water based inks and modern UV curing inks. The prints were
made on laboratory-made paper substrates containing cellulose pulp of straw of three types of
cereals in different proportions: wheat, barley, triticale, and recycled paper. The study is
divided into several phases: the qualitative evaluation of the print, the optical stability of the
print after standard methods of testing at high temperature and UV light and the stability on
various chemical agents and the pressure. The aim of this study is to define the usability of
printing substrates with alternative non wood fibers printed by flexographic printing technique.
Based on research, it can be concluded that laboratory-produced papers with the addition of
straw pulp of all cereals meet the quality of reproduction, while laboratory papers printed with
conventional water-based inks generally show excellent optical stability after exposure to
elevated temperature, chemical agents and pressure. Laboratory papers printed with UV
flexographic inks show the greatest resistance to pressure. It is recommended that the cellulose
pulp papers of these environmentally friendly raw materials be made of higher weight to
achieve lower values of Euclidean undertone differences and color penetration within the
printing substrate and to introduce the final stages of paper surface treatment. Also, based on
qualitative analysis, it can be recommended that papers with the addition of cereal straw pulp
printed with conventional water-based paints should be avoided only when packaging is
containing alkaline products or oils. Although papers with the addition of cereal straw pulp are
not suitable for printing with UV curing inks for use in primary food packaging, due to their
good mechanical resistance they are excellent for printing various publications and labels.
Experimental part was conducted in the following order: forming of laboratory papers by
mixing straw pulp from three types of cereals, wheat, barley or triticale in different mass ratios
with the pulp of commercial paper made from recycled wood pulp. The mass ratios for the
straw pulp of each type of cereal are: 10 % straw pulp and 90 % recycled commercial paper
pulp, 20 % straw pulp and 80 % recycled commercial paper pulp and 30 % straw pulp and 70
% recycled commercial paper pulp. Laboratory papers were then printed on a flexographic
printing simulators with two types of ink: conventional water-based and UV ink. All printingsubstrates are printed with both types of flexographic inks in monochrome (cyan, magenta,
yellow, black) and multichrome (yellow + magenta, yellow + cyan, cyan + magenta, yellow
+ cyan + magenta) prints. Usability of the prints made on paper with addition of straw pulp
were observed based on qualitative mesaurements: spectrophotometric values of color,
graininess, mottling, optical density, total amount of color on the print (undertone), trapping
and ink penetration within printing substrates. Optical stability of prints was analysed based on
elevated temperature and UV light, the effect of various chemical agents and pressure. Changes
in the prints were determined based on the colorimetric difference, i.e. the Euclidean difference
in the color of the prints before and after the treatment. Synthesis of results provides insight
and guidelines on which laboratory papers are most acceptable for a particular graphic product,
taking into account the type of ink.
Based on the qualitative analysis, it can be concluded that satisfactory quality of reproduction
of monochromatic and multichromatic colors obtained by flexographic printing technique was
achieved on laboratory papers with the addition of wheat, barley and triticale straw pulp. It is
recommended that the paper is made of a higher grammage in order to achieve lower values of
Euclidean difference of undertones and ink penetration within the printing substrate and to
carry out the final stages of paper production.
Flexographic prints on laboratory papers with cereal straw pulp printed with conventional
water-based inks have very good optical stability after exposure to elevated temperature and
UV radiation for 48 hours. After a period of 96 hours changes that are not optimal show
laboratory papers printed with cyan and yellow ink. Also, most laboratory papers printed with
conventional water-based inks have optimal chemical stability. Lower optical stability is
caused by alkali on all printed substrates, where the most stable laboratory papers are printed
in yellow and black inks, while all flexographic prints showed poor resistance to soybean oil.
Flexographic prints also showed excellent stability, i.e. resistance to pressure except laboratory
papers printed with three layers of ink.
Laboratory papers with the addition of straw pulp of all cereals are not equally good for printing
with UV inks and conventional water-based inks. Both inks used on laboratory papers with the
addition of straw pulp of all cereals shows advantages or disadvantages in various situations.
It is the same, of course, with commercial papers used in the industry for the production of
various graphic products. It is important to plan very well which ink will be printed on which
paper in order for the purpose of the final product to be fulfilled. Since most laboratory papers
with the addition of wheat, barley or triticale straw pulp printed with conventional water-based
inks have good resistance to elevated temperature, chemical agents and pressure, withadditional finishing stages and increasing the weight of such newly formed papers with nonwood fibers could be used for various purposes: for a certain type of food packaging that does
not contain oils or alkaline products, tobacco packaging, crates, bags, folders, office paper,
books and various publications. Laboratory papers with the addition of straw pulp of all cereals
printed with UV inks showed the best stability in the case of printing with yellow and black
and excellent mechanical stability. Although not recommended for use in primary food
packaging, they could be used to print a variety of publications and labels. |