UV zářením vytvrzované inkousty pro inkjet tisk

Ing. Miroslav Tejkl

Doctoral thesis

UV curable inks for inkjet printing

Abstract:

Pojivove systemy inkjetovych inkoust. a lak. vytvrzovanych UV za.enim jsou nej.ast.ji zalo.eny na akrylatovych monomerech a oligomerech polymerujicich radikalovym mechanizmem. Na trhu men. usp..nou a malo roz.i.enou alternativou jsou inkousty a laky obsahujici epoxidove, oxetanove .i vinyletherove monomery polymerujici kationtovym mechanizmem. Oba mechanizmy polymerace maji jine vyhody a nevyhody. Radikalova polymerace je inhibovana kyslikem snadno difundujicim do tenke vrstvy nizkoviskozniho systemu ze vzduchu. Systemy polymerujici kationtovym mechanizmem podlehaji p.i skladovani pomale p.ed.asne polymeraci, ke ktere dochazi v d.sledku nedostate.ne stability oniovych soli b..n. u.ivanych jako fotoiniciatory. V teto praci jsou studovany p.ipravene laky a inkousty obsahujici sm.s radikalov. a kationtov. polymerujicich material. a fotoiniciator., ktere p.i expozici UV za.eni polymeruji sou.asn. a vytva.i interpenetrujici polymerni sit.. Experimentalni prace byla strukturovana do p.ti etap. V prvni etap. byly naformulovany sm.si radikalov. a kationtov. polymerujicich monomer. (a oligomeru) s dostate.n. nizkou viskozitou spl.ujici technologicke po.adavky dane typem pou.ite tiskove hlavy. Ve druhe etap. byl sledovan vliv n.kterych vybranych material. na rychlost kationtove polymerace iniciovane UV za.enim s cilem formulovat dostate.n. reaktivni kationtov. polymerujici system. T.eti etapa prace byla zam..ena na studium pr.b.hu UV za.enim iniciovane polymerace p.ipravenych bezpigmentovych lak., obsahujicich kationtov. a radikalov. polymerujici slo.ky v r.znych pom.rech, a hodnoceni mechanickych vlastnosti tenkych vytvrzenych vrstev p.ipravenych z t.chto lak.. Polymerace akrylatovych a oxetanovych funk.nich skupin byla sledovana pomoci FTIR za i bez p.istupu vzduchu. Vzorky tenkych vytvrzenych vrstev byly testovany v tahu pomoci dynamometru. Tvrdost vytvrzenych vrstev byla stanovena metodou Persoz. Ve .tvrte etap. byla studovana UV za.enim iniciovana polymerace experimentalnich inkoust. obsahujicich p.ipravenou pigmentovou preparaci ftalocyaninu a stejne podily radikalov. a kationtov. polymerujicich slo.ek. S experimentalnimi inkousty i laky byly provedeny tiskove testy na laboratornim tiskovem za.izeni s inkjetovou hlavou Xaar XJ500/80. V pate etap. byly provedeny testy dlouhodobe stability p.ipraveneho kapalneho laku obsahujiciho stejne podily radikalov. a kationtov. polymerujicich slo.ek. V pr.b.hu n.kolika tydn. tepelne expozice vzork. byl sledovan nar.st viskozity laku v d.sledku p.ed.asne polymerace. Experimentalni laky a inkousty obsahovaly radikalov. polymerujici nizkoviskozni akrylaty, kationtov. polymerujici epoxidove a oxetanove monomery, fotoiniciatory radikalove a kationtove polymerace (?ż-hydroxyketon, iodoniova s.l) a dal.i aditiva. Kationtov. polymerujici monomery a fotoiniciatory byly vybrany tak, aby jejich dostate.n. rychla polymerace mohla ovlivnit soub..n. probihajici radikalovou polymeraci akrylat.. Sou.asny pr.b.h radikalove a kationtove polymerace sm.snych system. ma p.iznivy vliv na pr.b.h radikalove polymerace obsa.enych akrylat. za p.istupu vzduchu. Rychlost radikalove polymerace se zvy.uje s rostoucim podilem kationtov. polymerujicich slo.ek ve sm.si. Vytvrzene tenke vrstvy lak. obsahujicich sm.s radikalov. a kationtov. polymerujicich slo.ek jsou pru.n.j.i a m.k.i ne. vrstvy lak. obsahujici slo.ky pouze jednoho typu. Experimentalni inkousty obsahujici pigmentovou preparaci bylo nutne vytvrdit v.t.i davkou oza.eni ne. bezpigmentove laky. Nep.iznivy vliv p.itomnosti pigmentu byl .aste.n. kompenzovan p.idavkem fotosenzibilizatoru absorbujiciho i v oblasti del.ich vlnovych delek vyza.ovanych Hg vybojkami pou.ivanymi jako zdroje UV za.eni. Tisk experimentalniho laku i inkoustu byl stabilni, tiskova kvalita byla srovnatelna s kvalitou tisku komer.n. dodavaneho inkoustu. P.ed.asna polymerace experimentalniho laku obsahujiciho stejne podily radikalov. a kationtov. polymerujicich slo.ek b.hem dlouhodobe tepelne exp

Abstract:

UV curable inkjet inks and varnishes are generally based on acrylate monomers and oligomers which undergo photoinitiated radical polymerization. Inks and varnishes based on epoxide, oxetane or vinylether monomers which undergo photoinitiated cationic polymerization are less commercially successful alternative. Both of these polymerization mechanisms have different advantages and disadvantages. Radical polymerization is strongly inhibited by oxygen which easily diffuses into a thin layer of low viscosity system. Cationically polymerizable systems undergo slow premature polymerization during storage. This is a result of insufficient thermal stability of onium salts generally used as photoinitiators. Varnishes and inks studied in this work contained a mixture of radically and cationically polymerizable materials and photoinitiators of both polymerization types. As a result of the UV exposition, both types of the polymerization proceeded simultaneously. This experimental work proceeded in five stages. In the first stage, two mixtures of radically or cationically polymerizable monomers (and oligomer) with a required low viscosity for an inkjet printing was formulated. In the second stage, an influence of selected materials on a rate of cationic polymerization was tested with the aim to formulate a cationically polymerizable system with a required high reactivity. In the third stage, the process of the photopolymerization and mechanical properties of thin layers of the unpigmented experimental varnishes were studied. The varnishes contained different portions of the radically and cationically polymerizable components. The polymerization of acrylate and oxetane functional groups was studied by means of FTIR with and without air presence. The pull tests of the cured thin varnish layers were done using a dynamometer. The pendulum hardness of the cured thin varnish layers were measured by the Persoz method. In the fourth stage, the experimental UV curable inks containing a prepared pigment preparation and equal portions of the radically and cationically polymerizable components were studied. Their photopolymerization was studied by means of FTIR. The print tests of the selected experimental varnish and ink were done using the laboratory printing machine equipped with the inkjet printhead Xaar XJ500/80. In the fifth stage, the long-therm stability tests of the liquid varnish containing equal portions of the radically and cationically polymerizable components were done. During several weeks of the thermal exposition of the liquid samples, the increase of viscosity as result of premature polymerization was monitored. The experimental inks and varnishes consisted of radically polymerizable low viscosity acrylates, cationically polymerizable epoxide and oxetane monomers, photoinitiators of the radical and cationic polymerization (á-hydroxyketone, iodonium salt) and additives. The cationically polymerizable monomers and the photoinitiators were chosen to achieve the sufficiently fast cationic polymerization to affect the simultaneous radical polymerization of the acrylates. The simultaneous cationic polymerization positively affected the radical polymerization of the acrylates in air. The rate of the radical polymerization of the acrylates increased with the content of the cationically polymerizable components in the mixture. The cured thin layers of the experimental varnishes containing mixture of the radically and cationically polymerizable components were more plastic and less hard than the layers containing just one type of these components. The radiation dose needed to cure the experimental inks containing the pigment preparation was higher than in case of the unpigmented varnishes. An adverse effect of the pigment on the UV curing was partially compensated by an addition of a photosensitizer absorbing radiation of longer wavelengths emitted by a Hg lamp used as UV radiation source in printing machines. The process of inkjet printing of

Keywords

Inkjet tisk, inkjet inkoust, inkoust vytvrzovaný UV zářením, souběžná radikálová a kationtová polymerace, interpenetrující polymerní sítě.

Language used: Czech

Date on which the thesis was submitted / produced: 30. 4. 2012

Accessible from:: 31. 12. 2999

Thesis defence

• Date of defence: 28. 6. 2012

University of Pardubice

Faculty of Chemical Technology

Doctoral programme / field:
Chemistry and Technology of Materials / Technology of Macromolecular Compounds