Otpornost termokromnih offsetnih boja prema otiranju

Rub resistance of thermochromic offset inks

Sonja Jamnicki Hanzer, Lana Šprem, Emilija Perica

Sveučilište u Zagrebu Grafički fakultet

sjamnick@grf.hr

Sažetak

U radu je provedeno ispitivanje otpornosti otisaka offsetnih termokromnih boja prema otiranju. Za dobru otpornost otisaka prema otiranju važan je optimalan izbor tiskarske boje i tiskovne podloge te njihov odgovarajući adhezioni odnos. Termokromne tiskarske boje su boje koje mijenjaju svoje obojenje pod utjecajem promjene temperature. One se često koriste u oblikovanju pametne ambalaže gdje najčešće dolaze u funkciji temperaturnih indikatora. No, budući da se u sastavu takvih boja koriste specijalno formulirani koloranti koji su mikrokapsulirani, otisci takvih boja jako su osjetljivi na otiranje. Cilj je ovog istraživanja dati smjernice o otpornosti takvih boja prema otiranju koje se najčešće javlja upravo kod ambalažnih otisaka. U eksperimentalnom dijelu rada, tri su offsetne termokromne boje (plava, vinsko crvena i zelena), otisnute na nekoliko papira koji su se razlikovali u svojstvima i obradi površine (premazani i nepremazani papiri). Prije samog otiskivanja, izvršena su ispitivanja glatkosti korištenih papira kako bi se mogao odrediti eventualan utjecaj tiskovne podloge na stupanj otiranja boje. Nakon otiskivanja i sušenja, otisci su izloženi definiranom otiranju. U ispitivanjima je korišten tribometar Hanatek RT4 Rub and Abrasion Tester. Ovakvom vrstom ispitivanja određuje se pogodnost tiskovne podloge prema određenoj tiskarskoj boji. Nakon provedbe testa, stupanj otiranja utvrđen je vizualnom metodom. Također su određene kolorimetrijske promjene nastale na otiscima nakon njihovog izlaganja otiranju. Termokromne boje analizirane u okviru ovog istraživanja pokazale su se najotpornijima na nepremazanim tiskovnim podlogama.
Ključne riječi: Termokromna boja, tisak ambalaže, otpornost prema otiranju, test otiranja

 

Abstract

This paper evaluates rub resistance of offset thermochromic inks. For good rub resistance of prints, it is essential to find optimum combination of printing ink and printing substrate in order to achieve adequate adhesion of the print with the chosen substrate. Thermochromic printing inks are special inks that exhibit color changes depending on changes in temperature. They are often printed on smart packaging applications where are mostly used as temperature indicators. Since the colorants in these inks are microcapsuled, the prints obtained with these inks are very sensitive to rubbing. The aim of this study is to provide guidance on rub resistance of such inks, more so as rubbing usually appears on prints applied on packaging. In the experimental part of the work, three offset thermochromic inks (blue, burgundy and green) were printed on several papers that differed in their surface properties (coated and uncoated papers). Prior to printing, smoothness of used papers was determined to see whether this property influences the degree of the rubbing. After printing and drying of the inks, prints were subjected to a standard rub test for which Hanatek RT4 Rub and Abrasion Tester was used. This type of test determines the suitability of the printing substrate to a particular printing ink. After the rub test was conducted, the degree of rubbing was assessed visually. The colorimetric changes on the prints after their exposure to rubbing were also determined. Thermochromic inks analyzed within this study showed best rub resistance on uncoated papers.
Key words: Thermochromic ink, packaging printing, rub resistance, rub test