Pokanje premazov na specialnih grafičnih papirjih

Breskvar, Kaja (author), Možina, Klemen (mentor)

Pokanje premazov na pregibu je napaka, ki izkazuje negativen vpliv na končni izdelek. Proizvajalci papirja zato stremijo k odpravi pokanja premaza z namenom, da se izognejo reklamacijam in težijo k lastnosti raztezanja premaznega sloja na tiskovnem materialu s sočasno zadostno natezno odpornostjo papirja proti pregibu. Papirjem, ki izkazujejo nizko odpornost proti pregibu se pogosto pretrgajo vlakna in prekinejo medvlakenske povezave; njihova natezna odpornost se v primeru premazovanja poveča. Kakovost papirjev je povezana z dolžino in številčnostjo celuloznih vlaken, saj se ta ob pregibu ne pretrgajo, ampak le upognejo. Premazovanje papirjev je dodelavni postopek, pri katerem se izboljšajo optične in tiskovne lastnosti in poslabšajo fizikalno-mehanske lastnosti, kamor uvrščamo tudi prepogibanje papirja. Pokanje premazov je običajno posledica površinske masa surovega papirja, količine premaznega sloja, vplivov posameznih sestavin v premazni mešanici ter zunanjih okoljskih dejavnikov, kot sta temperatura in vlaga. Namen raziskave pokanja premazov specialnih grafičnih papirjev v magistrskem delu, ki je potekalo v sodelovanju s Papirnico Vevče, je bil preučiti lastnosti premazanih papirjev (osnovne, površinske in strukturne lastnosti), primerjava premaznih mešanic glede na njihovo sestavo, prepoznati vplive na pokanje premazov in določitev kombinacije sestavnih delov osnovnega papirja in premaza, ki bi izkazovala najnižjo tendenco pokanja. Preučevanih je bilo 5 različnih vzorcev specialnih grafičnih papirjev, tj. PackPro 7.1 (V1), NiklaPack (V2), Niklaselect (V3), NiklaPET (V4) in PackPro 7.5 (V5). Vsi vzorci so enostransko premazani in primerni za postopek oplemenitve papirja – kaširanje. V1, V2 in V5 so namenjeni izdelavi gibke embalaže, V3 in V4 pa sta namenjena izdelavi etiketnih papirjev. Rezultati raziskave pokanja premazov so pokazali, da ima na tendenco pokanja znaten vpliv debelina papirja in z njo posledično količina premaznega sloja. Vpliv je bil zaznan tudi zaradi višje količine vsebnosti vlage v vzorcu. Korelacija med tendenco pokanja premazov in sestavinami premazne mešanice je bila najbolj opazna pri vsebnosti višje količine veziv in izbrane vrste le-teh.

• Language: Slovenian
• Keywords: papir, premazovanje, pokanje premaza, pregibanje papirja
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2020
• PID: 20.500.12556/RUL-119385
• Publication date in RUL: 08.09.2020

Secondary language

• Language: English
• Title: Cracking of paper coatings on special graphic papers

Abstract

The cracking of coatings on the fold is a defect that harms the final product. Therefore, paper manufacturers strive to eliminate coating cracking to avoid complaints or objections and strive to achieve the elongation properties of the coating layer on the substrate while, at the same time, providing sufficient paper tensile strength against creasing. With papers with low crease-resistance, the fibers often tear and thus break the fiber bonds. Their tensile strength increases with the coating. The quality of the paper depends on the length and frequency of the cellulose fibers, since they do not break when folded, but only bend. The coating of paper is a finishing process in which the optical and printing properties are improved but the physical and mechanical properties are deteriorated, which includes folding the paper. Cracking during coating is usually due to the surface mass of the base paper, the number of coating layers, the effects of the individual components in the coating mixture, and external environmental factors, such as temperature and humidity. The aim of the investigations on cracking in coatings of special graphic papers in the master thesis which was carried out in cooperation with Papirnica Vevče was to investigate the properties of coated papers (base, surface, and structural properties), to compare coating mixtures according to their composition, to identify effects on cracking of coatings, and to determine combinations of base paper and coating components that would have the lowest tendency to crack. Five different samples of special graphic papers were examined, i.e. PackPro 7.1 (V1), NiklaPack (V2), Niklaselect (V3), NiklaPET (V4), and PackPro 7.5 (V5). All samples are coated on one side and suitable for the paper finishing process – laminating. V1, V2, and V5 are intended for the production of flexible packaging and V3 and V4 for the production of label papers. The results of the study on coating cracking showed that the tendency to cracking is significantly influenced by the thickness of the paper and consequently by the number of coating layers. The effect was also determined due to the higher moisture content in the sample. The correlation between the tendency to coat cracking and the components of the coating mix was most evident in the content of a higher amount of binders and the selected binder types.

• Keywords: paper, coating, coating cracking, paper folding