Strižić Jakovljević, Maja (2018) Termokromne tiskarske boje na bazi tekućih kristala = Liquid crystal-based thermochromic printing inks. Dissertation (PhD) thesis. Grafički fakultet. [Mentor: Lozo, Branka].
|
PDF
Doktorski rad Strižić Jakovljević Maja.pdf Download (10MB) | Preview |
Abstract
Cilj predloženog istraživanja je cjelovita karakterizacija optičkih efekata termokromnih tiskarskih boja na bazi tekućih kristala. Temperaturno ovisni optički efekt ove vrste tiskarskih boja razlikuje se od konvencionalnih tiskarskih boja, ali i od termokromnih tiskarskih boja na bazi leuko bojila. Selektivna refleksija upadnog svjetla od specifične spiralne strukture termokromnih tekućih kristala u definiranim uvjetima uzrokuje postupnu promjenu obojenja kroz cijeli vidljivi spektar. Mehanizam termokromnog efekta bazira se na temperaturnoj promjeni unutar radnog područja funkcionalnog materijala, a spomenuti efekt ispitivanih boja detaljno je prikazan i objašnjen u predloženoj disertaciji. U provedenom istraživanju definirani su posebni uvjeti stupnjevitog zagrijavanja i hlađenja uzoraka za provedbu mjerenja temperaturno ovisnog optičkog efekta. Otisnuta tiskarska boja podvrgnuta je spektroskopskim mjerenjima primjenjujući različite geometrije mjerenja. Dokazano je da se potpuna optička analiza termokromnog efekta tiskarskih boja na bazi tekućih kristala može postići sfernom geometrijom mjerenja (8°:di), uređajima s različitim promjerima integracijskih sfera. Kolorimetrijskom obradom podataka dobivenih mjerenjima provedena je karakterizacija termokromnih tiskarskih boja na bazi tekućih kristala. Dokazano je da se termokromni efekt tiskarskih boja na bazi tekućih kristala detaljno može prikazati pomoću (a*b*) i L*(T) dijagrama. Kolorimetrijske vrijednosti promjene obojenja i svjetline termokromnih tiskarskih boja na bazi tekućih kristala u ovisnosti o temperaturi prikazane u navedenim dijagramima pokazuju dinamiku optičkog efekta boje unutar i izvan njenog aktivacijskog područja. Istražen je utjecaj vrste i tona tiskovne podloge, te uvjeta tiska na optički efekt ispitivanih boja. Dokazano je da na termokromni efekt ispitivanih tiskarskih boja na bazi tekućih kristala utječu površinska svojstva papirne tiskovne podloge, na način da je termokromni efekt otisnute ispitivane boje jače izražen na nepremazanom papiru u odnosu na sjajno premazani papir. Ovakav efekt uzrokovan je mehanizmom sušenja tiskarske boje i upojnošću tiskovne podloge. Istražen je i utjecaj tona tiskovne podloge na optički efekt ispitivanih boja. Rezultati istraživanja pokazuju da optička gustoća crne tiskovne podloge mora iznositi minimalno 0,72 za razvoj optimalnog termokromnog efekta tiskarskih boja na bazi tekućih kristala. Temeljem rezultata istraživanja i specifikacije sustava temperaturno ovisnog efekta konstruiran je komunikacijski mehanizam karakterističan isključivo za termokromne boje na bazi tekućih kristala. Opisani mehanizam omogućava analizu samog termokromnog materijala bez utjecaja tiskovne podloge ili debljine nanosa boje na otisku. Otisnuta tiskarska boja podvrgnuta je ispitivanju svjetlostalnosti sa i bez primjene zaštitnog UV laka. Dokazano je da termokromnetiskarske boje na bazi tekućih kristala imaju nisku svjetlostalnost, koja se primjenom zaštitnog UV laka na otisnutu boju neznatno poboljšava. Iz tog se razloga termokromna tiskarska boja na bazi tekućih kristala ne preporuča za vanjske aplikacije i aplikacije u zatvorenim prostorima koje zahtijevaju neprekidno izlaganje svjetlu s komponentom UV zračenja kratkih valnih duljina u periodima duljim od dva tjedna. Predloženo istraživanje obuhvaća i područje mogućih aplikacija koje je uz primjere primjene temperaturnih indikatora detaljno razrađeno.
| Item Type: | Dissertation (PhD) thesis |
|---|---|
| Mentor name: | Lozo, Branka |
| Other mentors: | Klanjšek Gunde, Marta |
| Thesis Committee: | Kulčar, Rahela and Jamnicki Hanzer, Sonja and Gregor Svetec, Diana |
| Defence date: | 9 April 2018 |
| Abstract in english: | Thermochromic printing inks change color in dependence of surrounding temperature. This color change occurs inside the microcapsules containing thermo-responsive materials. There are two basic types of thermo-responsive materials; leucodye-based composites and thermochromic liquid crystals. Liquid crystal thermochromic printing inks start a color change at the defined activation temperature (TA), but the color change occurs in several degrees wide region above the TA. The color change temperature range is called activation region but can also be called "the color play interval". Outside the activation region this kind of printing ink is colorless. Within the activation region the color changes throughout the whole visible spectrum from red, orange, yellow, green, blue to violet, the effect known as "color play". Within "the color play interval", the spectral color with given wavelength λ appears when the elongated molecules of the active material inside the microcapsules develop a helical superstructure with pitch equal to λ. As the temperature raises the helical pitches shrink causing the shift of the peak in the reflectance spectra towards shorter wavelengths, therefore the color of the material changes towards blue shades. Thermochromic effect of liquid crystal thermochromic printing inks is a result of temperature dependent helical pitch. Temperature dependent optical effect achieved by liquid crystals is quite different from conventional printing inks and thermochromic leucodye-based printing inks and is explained in detail in this research. Special conditions are needed to observe and measure the colors of printed liquid crystal thermochromic ink samples. The presented research is focused on optical properties of water-based liquid crystal printing inks, screen-printed in several ink layers on various types and colors of printing substrates. The characterization of optical properties is determined by spectroscopic measurements. The "color play" effect was quantified by spectral reflectance applying (45°:0°) and (8°:di) geometries. The measured temperature dependent iridescent colors were calculated and presented as CIELAB colorimetric values, showing the "color play" effect throughout the visible spectra. The results show that liquid crystal thermochromic printing inks reflect incident light in a rather narrow spectral region. The temperature dependent iridescent colors are seen very clearly when the ink is printed over black background, while on the white substrate is hardly visible.This research shows that thermochromic liquid crystal printing inks reflect the light by spreading it in a way that the (45°a:0°) measurement geometry cannot capture the entire color play effect. This is an important practical message as this geometry is commonly used for spectrometric evaluation of samples with no angular dependent effects, i.e. for samples whose color is based on the absorption of light. The problem was solved by integrating sphere accessories, which collect (spatially integrate) the radiant flux reflected by the sample. The best results were obtained by larger diameter integration sphere. Communication mechanism has been designed specifically for liquid crystal thermochromic printing inks based on their temperature dependence. The proposed mechanism enables the analysis of the active thermochromic material without any colorimetric influence of printing substrate or applied printing ink layers. In the research special attention is devoted to stability of the samples printed with liquid crystal thermochromic printing inks. According to the available literature, the stability of this kind of printing inks has not been evaluated yet. The samples were exposed to daylight for varying time periods. The samples were also exposed to defined light and temperature conditions in a special laboratory climate chamber. The changes of the dynamic color due to light exposure were measured resulting with poor dynamic color stability. Temperature dependant optical properties of liquid crystal thermochromic printing inks enable their usage in various fields of application. The presented application examples, in conjunction to performed measurements can contribute to faster development of new kinds of indicators based on liquid crystal thermochromic printing inks, in the areas of functional packaging, security printing and others. |
| Uncontrolled Keywords: | termokromne tiskarske boje, mikrokapsulacija, optički efekt tekućih kristala, efekt "igre boja", parametri tiska, spektroskopija i mjerna geometrija |
| Keywords in english: | thermochromic printing inks, microencapsulation, optical effect of liquid crystals, "color play" effect, printing conditions, spectroscopy and measurement geometry |
| Subjects: | TECHNICAL SCIENCES > Graphic Technology |
| Institution: | Grafički fakultet |
| City: | Zagreb |
| Number of Pages: | 136 |
| Callnumber: | 667.5 STR t |
| Inventory number: | 10223 |
| Depositing User: | Nina Jelača |
| Status: | Unpublished |
| Date Deposited: | 18 May 2018 08:51 |
| Last Modified: | 18 May 2018 08:51 |
| URI: | http://eprints.grf.unizg.hr/id/eprint/2848 |
Actions (login required)
 |
View Item |
Download Statistics
Download Statistics