Title Termokromne tiskarske boje na bazi tekućih kristala Title (english) Liquid crystal-based thermochromic printing inks Author Maja Strižić Jakovljević Mentor Branka Lozo (mentor)Committee member Rahela Kulčar (član povjerenstva)Committee member Sonja Jamnicki Hanzer (član povjerenstva)Committee member Diana Gregor Svetec (član povjerenstva) Granter University of Zagreb Defense date and country 2018-4-9, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 655 - Graphic industries. Printing. Publishing. Book trade 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.
Abstract (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.
Keywords
termokromne tiskarske boje
mikrokapsulacija
optički efekt tekućih kristala
efekt "igre boja"
parametri tiska
spektroskopija i mjerna geometrija
Keywords (english)
thermochromic printing inks
microencapsulation
optical effect of liquid crystals
"color play" effect
printing conditions
spectroscopy and measurement geometry
Language croatian URN:NBN urn:nbn:hr:216:693382 Study programme Title: Graphic engineering and graphic product design Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2024-04-24 22:38:46
