SI9210019A - Ferroelectric liquid crystal display cell, its method of manufacture and use - Google Patents
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Abstract
V feroelektrični tekočekristalni celici nahajajoči se orientiran feroelektričen tekoči kristal (1) v kiralni smektični lazi C s smektičnimi ravninami (11), pravokotnimi na mejni plošči (P) celice, je vpet med polimerne teksturine niti (2), ki utrdijo in zamrznejo urejenost tekočega kristala (1). Niti (2) so zlepljene druga z drugo in so prilepljene na polimerne mikrokapljice (31), ki so prilepljene vsakič na eni od obeh plošč (P). Skupna masa polimera v nitih (2) in v mikrokapljicah (31, 32) je največ od 1 % do 6 % mase tekočega kristala. Polimerizacijo v zmesi monomera in tekočega kristala se sproži, ko je tekoči kristal orientiran bodisi s pomočjo plasti OL in/ali prednostno s pomočjo magnetnega polja B in je v eni od faz, v kateri so tekočekristalne molekule vzporedne druga z drugo in so vzporedne s ploščama (P).In a ferroelectric liquid crystal cell is oriented ferroelectric liquid crystal (1) in chiral smectic lobe C with smectic planes (11) perpendicular on the boundary plate (P) of the cell, is enclosed by honey polymeric textural threads (2) that harden and freeze arrangement of the liquid crystal (1). The threads (2) are glued together with one another and glued to the polymeric micro-droplets (31), which are glued each time on one of the two plates (P). Total mass of polymer in filaments (2) and in microbeads (31, 32) are not more than 1% to 6% by weight of liquid crystal. Polymerization in a mixture of monomer and of liquid crystal is triggered when liquid crystal oriented either by means of an OL layer and / or preferably by magnetic field B and is in one of the phases, v which are liquid crystal molecules parallel to each other the other and are parallel to the plates (P).
Description
Institut Jožef Stefan'Jozef Stefan Institute '
Feroelektrična tekočekristalna celica, postopek njene izdelave in uporaba te celiceFerroelectric liquid crystalline cell, process for its production and use
Področje tehnikeThe field of technology
Izum spada v področje tekočekristalnih prikazalnikov.The invention falls within the field of liquid crystal displays.
Predmet izuma je po mednarodni klasifikaciji patentov uvrščen v razred G 02F 1/13.According to the international patent classification, the subject matter of the invention is classified in class G 02F 1/13.
Tehnični problemA technical problem
Glede na pomanjkljivosti dosedaj znanih feroelektričnih tekočekristalnih celic je tehnični problem izuma v tem, kako izdelati celico takšne vrste in razviti postopek njene izdelave, da bo v celici vgrajeni polimer zagotovljal volumsko stabilizacijo urejenosti molekul feroelektričnega tekočega kristala, pri čemer pa naj celica po izumu ohrani odlične lastnosti znanih feroelektričnih tekočekristalnih celic, in bo z vgrajenim polimerom dosežena očvrstitev medsebojne razdalje mejnih plošč celice.In view of the disadvantages of the known ferroelectric liquid crystal cells, the technical problem of the invention is how to make a cell of this type and develop a process for its production, so that the polymer embedded in the cell will provide volume stabilization of the ordering of the ferroelectric liquid crystal molecules, while maintaining the cell according to the invention properties of known ferroelectric liquid crystalline cells, and the embedded polymer will result in the solidification of the interfacial distance of the cell boundary plates.
Stanje tehnikeThe state of the art
Feroelektrične tekočekristalne celice so zaradi fizikalnih lastnosti feroelektričnih tekočih kristalov za tekočekristalne optične preklopnike oziroma prikazalnike mnogo primernejše kot celice z nematskimi tekočimi kristali. Krmiljenje je bistveno hitrejše, razen tega pa se s feroelektričnimi tekočimi kristali doseže spominski efekt zaradi njihove izrazito bistabilne urejenosti, s čimer pa se poenostavi krmiljenje. Zadošča namreč pasivna krmilna matrika za razliko od aktivne tankoplastne elektrodne krmilne matrike, ki obstoji iz tranzistorjev in diod in ki je potrebna pri nematskih tekočekristalnih celicah.Due to the physical properties of ferroelectric liquid crystals, ferroelectric liquid crystal cells are much better suited to cells with nematic liquid crystals for liquid crystal optical switches and displays. Steering is significantly faster, with the result that the ferroelectric liquid crystals achieve a memory effect due to their highly bistable arrangement, thus simplifying steering. A passive control array is sufficient, unlike the active thin-film electrode control array, which consists of transistors and diodes, which is required for nematic liquid crystal cells.
N. A. Clark in S. T. Lagenvall sta v Appl. Phys. Lett. 36, 11 (1980) in v patentu US 4,367,924 opisala površinsko stabilizirano feroelektrično tekočekristalno celico. Urejenost tekočekristalnih molekul je dosežena s pomočjo orientacijskih plasti na vsaki od obeh mejnih plošč celice, razdaljo med mejnima ploščama pa določajo distančniki (steklena vlakna, granulati, polistirenske mikrokroglice in podobno), ki so razporejeni po vsej ploskvi celice. Kljub nadaljnjim izboljšavam (US 4,958,916; Ferroelectrics 59, 25 (1984); Molecular Crystals and Liquid Crystals 114, 151 (1984) in Phys. Rev. A 37, 3 1053 (1988)) so feroelektrične tekočekristalne celice zelo občutljive na mehanske motnje. Zaradi še vedno nestabilnega razmika mejnih plošč celice pride do pretakanja tekočega kristala po celici; pri tem pa se poruši dotedanja urejenost feroelektričnega tekočega kristala. Prav tako ta urejenost izgine v znanih feroelektričnih tekočekristalnih celicah ob znatnejših temperaturnih spremembah, sama od sebe pa se le s pomočjo orientacijskih plasti ne more vzpostaviti.N. A. Clark and S. T. Lagenvall are in Appl. Phys. Lett. 36, 11 (1980) and described in the patent US 4,367,924 a surface-stabilized ferroelectric liquid crystal cell. The arrangement of the liquid crystal molecules is achieved by means of orientation layers on each of the two boundary plates of the cell, and the distance between the boundary plates is determined by the spacers (glass fibers, granules, polystyrene microspheres, etc.), which are distributed throughout the cell surface. Despite further improvements (US 4,958,916; Ferroelectrics 59, 25 (1984); Molecular Crystals and Liquid Crystals 114, 151 (1984) and Phys. Rev. A 37, 3 1053 (1988)), ferroelectric liquid crystal cells are highly sensitive to mechanical interference. Due to the still unstable spacing of the cell boundary plates, the flow of liquid crystal throughout the cell results; in doing so, the orderliness of the ferroelectric liquid crystal is being destroyed so far. Also, this orderliness disappears in known ferroelectric liquid crystalline cells with significant temperature changes, and cannot be restored by itself through orientation layers.
S širšega področja stanja tehnike je uporaba kompozitnih materialov, kot je tekoči kristal v polimeru (US 4,688,900, US 4,685,711, US 4,994,204), sicer poznana. Vendar je tekočemu kristalu primešano mnogo polimera, tako da le-ta vključuje tekoči kristal v obliki mikrokapljic. Molekule tekočega kristala v mikrokapljicah so orientirane radialno ali bipolarno, z električnim poljem med mejnima ploščama celice pa se krmili sipanje svetlobe v kompozitnem materialu.The use of composite materials such as liquid crystal in polymer (US 4,688,900, US 4,685,711, US 4,994,204) is otherwise well known in the art. However, many polymers have been mixed with the liquid crystal so that the polymer includes microcapella liquid crystal. Liquid crystal molecules in micro beads are oriented radially or bipolar, and the electric field between the boundary plates of the cell controls the light scattering in the composite material.
Opis rešitve tehničnega problema s primerom izvedbeDescription of a solution to a technical problem with an example implementation
Navedeni tehnični problem je rešen s feroelektrično tekočekristalno celico po izumu, katere mejni plošči, ki sta medsebojno razmaknjeni za razdaljo, ki je manjša od periode vijačnice v zgradbi feroelektričnega tekočega kristala, sta npr. za uporabo celice za tekočekristalni prikazalnik na znan način opremljeni s prozornimi elektrodami in ki je značilna po tem, da je med tema ploščama nahajajoči se feroelektričen tekoči kristal orientiran tako, da so smektične ravnine pravokotne na mejni plošči, in je feroelektričen tekoči kristal vpet med polimerne teksturine niti, ki so pretežno vzporedne z mejnima ploščama in ki zamrzujejo njegovo urejenost, in da so teksturine niti mestoma zlepljene med seboj in s svojim delom prilepljene na majhne polimerne mikrokapljice, ki so prilepljene vsakič na eni od obeh mejnih plošč.This technical problem is solved by a ferroelectric liquid crystal cell according to the invention, whose boundary plates, which are spaced apart from each other by a distance less than the helix period in the ferroelectric liquid crystal structure, are e.g. for the use of a liquid crystal display cell in a known manner equipped with transparent electrodes, characterized in that the ferroelectric liquid crystal located between these plates is oriented so that the smectic planes are perpendicular to the boundary plate and the ferroelectric liquid crystal is interconnected between the polymer texture strands, which are substantially parallel to the boundary plates and which freeze its orderliness, and that the texture strands are in places glued to one another and glued to their work on small polymeric micro-droplets which are glued each time on one of the two boundary plates.
Celica po izumu je nadalje značilna po tem, da polimorfizem feroelektričnega tekočega kristala poleg kiralne smektične faze C vključuje izotropno, kiralno nematsko in smektično fazo A.The cell of the invention is further characterized in that, in addition to the chiral smectic phase C, the ferroelectric liquid crystal polymorphism includes isotropic, chiral nematic and smectic phase A.
Celica po izumu je nadalje značilna po tem, da so naključno porazdeljene in od ene do druge mejne plošče segajoče velike polimerne mikrokapljice, na katere so prilepljene teksturine niti, prilepljene na obe mejni plošči.The cell of the invention is further characterized by the fact that large polymeric micro-droplets are randomly distributed and boundary plates extending from one boundary plate to which textural filaments adhered to both boundary plates are attached.
Celica po izumu je nadalje značilna po tem, da je skupna masa polimera v teksturinih nitih in v mikrokapljicah največ od 1 % do 6 % mase tekočega kristala.The cell of the invention is further characterized in that the total weight of the polymer in the textural filaments and in the micro-droplets is at most 1% to 6% by weight of the liquid crystal.
V variantni izvedbi je celica po izumu značilna po tem, da sta mejni plošči prevlečeni s plastjo za orientiranje feroelektričnega tekočega kristala.In a variant embodiment, the cell of the invention is characterized in that the boundary plates are coated with a layer to orient the ferroelectric liquid crystal.
Navedeni tehnični problem je rešen tudi s postopkom izdelave feroelektrične tekočekristalne celice, po katerem se zmes monomera in feroelektričnega tekočega kristala v izotropni fazi uvede med mejni plošči celice in ki je značilen po tem, da je v zmesi masa monomera v mejah od 1 % do 6 % mase feroelektričnega tekočega kristala in da se polimerizacijo v zmesi monomera in feroelektričnega tekočega kristala sproži, ko je feroelektričen tekoči kristal orientiran v eni takšnih tekočekristalnih faz, da so si molekule tekočega kristala vzporedne druga z drugo in so vzporedne z mejnima ploščama P.The said technical problem is also solved by the method of manufacturing a ferroelectric liquid crystal cell, by which a mixture of monomer and ferroelectric liquid crystal is introduced during the isotropic phase between the boundary plates of the cell, characterized in that the mixture has a mass of monomer in the range from 1% to 6 % by weight of ferroelectric liquid crystal and that polymerization in a mixture of monomer and ferroelectric liquid crystal is initiated when the ferroelectric liquid crystal is oriented in one such liquid crystal phase that the liquid crystal molecules are parallel to each other and parallel to the boundary plates P.
Nadalje je postopek po izumu značilen po tem, da je tekočekristalna faza, v kateri se sproži polimerizacijo, kiralno nematska faza sicer pa ena od smektičnih faz.Furthermore, the process according to the invention is characterized in that the liquid crystalline phase in which polymerization is initiated, and the chiral nematic phase is otherwise one of the smectic phases.
Postopek po izumu je nadalje značilen po tem, da se feroelektričen tekoči kristal orientira v magnetnem polju, vzporednem z ravninama mejnih plošč in z gostoto, katere vrednost je vsaj 2 T, in da se pri tem zmes monomera in feroelektričnega tekočega kri stala počasi ohlaja od izotropne faze do faze, v kateri se sproži polimerizacijo.The process of the invention is further characterized by the fact that the ferroelectric liquid crystal is oriented in a magnetic field parallel to the planes of the boundary plates and at a density of at least 2 T and the mixture of monomer and ferroelectric liquid crystal is slowly cooled from isotropic phase to the phase in which polymerization is initiated.
Polimerna tekstura prepreda tekoči kristal in s svojimi nitmi predstavlja površine, ki orientirajo feroelektričen tekoči kristal. S tem je njegova urejenost zamrznjena, torej prostorsko stabilizirana, še posebej, ker tekstura obenem otežuje pretakanje feroelektričnega tekočega kristala po celici, ohranijo pa se vse odlične lastnosti doslej znanih feroelektričnih tekočekristalnih celic. Razen tega se z večjimi mikrokapljicami polimera, ki so prilepljene hkrati na obe plošči celice in so po njej naključno porazdeljene, doseže fiksiranje medsebojne razdalje mejnih plošč celice tako na njuno medsebojno primikanje kot razmikanje, s čimer je dodatno preprečeno pretakanje tekočega kristala po njej. Normalni mehanski tresljaji torej ne razrušijo urejenosti feroelektričnega tekočega kristala.The polymer textures the liquid crystal and, with its filaments, represent surfaces that orient the ferroelectric liquid crystal. This keeps its orderliness frozen, ie spatially stabilized, especially since the texture makes it difficult to flow ferroelectric liquid crystal throughout the cell, while retaining all the excellent properties of the known ferroelectric liquid crystal cells. In addition, larger micro-droplets of polymer, which are glued simultaneously to both panels of the cell and are randomly distributed therefrom, achieve a fixation of the inter-spacing of the boundary plates of the cell both at their mutual displacement and spacing, which additionally prevents the flow of liquid crystal through it. Therefore, normal mechanical vibrations do not destroy the orderliness of the ferroelectric liquid crystal.
Izum bomo v nadaljnjem podrobno opisali na osnovi izvedbenega primera ter pripadajoče slike, ki prikazuje feroelektrično tekočekristalno celico po izumu, v katero je na shematičen način vrisan povečan prikaz mikroskopske zgradbe feroelektričnega tekočega kristala in polimerne teksture ter polimernih mikrokapljic med mejnima ploščama celice.The invention will now be described in further detail by way of an example example and an accompanying figure showing a ferroelectric liquid crystal cell according to the invention, in which a magnified view of an enlarged view of a microscopic structure of a ferroelectric liquid crystal and a polymeric texture and polymeric micro-droplets between the boundary plates of the cell.
V feroelektrični tekočekristalni celici po izumu se med njenima mejnima ploščama P, katerih razmik je manjši od periode vijačnice v zgradbi feroelektričnega tekočega kristala, nahajajo tekoči kristal 1 in polimer v obliki teksture z nitmi 2 ter v obliki mikrokapljic 31 in 32 (slika; zaradi jasnosti prikaza so popačena velikostna razmerja), pri čemer so mikrokapljice 31 v celoti vsakič le na eni od obeh plošč P in so nanjo prilepljene ter mikrokapljice 32 segajo od ene do druge plošče P in so prilepljene na obe plošči P. Struktura polimera je brez tekočega kristala izotropna. Teksturine niti 2 se mikrokapljic 31 in 32 dotikajo ali pa izhajajo iz njih. Plošči P sta na znan način opremljeni s prozornimi elektrodami E in sta prav tako na znan način medsebojno speti z obodnim lepilnim robom, v katerem so razmeščeni distančniki, npr. iz steklenih vlaken, debeline od 2 μτη do 7 μτη. Mikrokapljice 31, 32 polimera so po celici razporejene naključno. Z mikrokapljicami 32 sta plošči P medsebojno dodatno pritrjeni. Mikroskopska slika notranjosti celice prikazuje orientiran feroelektričen tekoči kristal 1, ki je ujet med teksturine niti 2 ter mikrokapljice 31 in 32, in sicer v smektični fazi. Smektične ravnine 11 tekočega kristala 1 so pravokotne na plošči P. Orientacija molekul tekočega kristala 1 in njegovih smektičnih ravnin 11 je homogena po vsej celici.In the ferroelectric liquid crystal cell of the invention, between its boundary plates P, whose spacing is less than the helix period in the structure of the ferroelectric liquid crystal, there is a liquid crystal 1 and a polymer in the form of textures with filaments 2 and in the form of micro droplets 31 and 32 (figure; for clarity The micro-droplets 31 are completely and only glued to one of the two plates P each time, and the micro-droplets 32 extend from one plate to another and are glued to both plates P. The structure of the polymer is free of liquid crystal. isotropic. Texture threads 2 touch or emerge from micro-droplets 31 and 32. The plates P are provided in a known manner with transparent electrodes E and are also connected in a known manner to a circumferential adhesive edge in which spacers are arranged, e.g. fiberglass, thickness from 2 μτη to 7 μτη. The micro-droplets 31, 32 of the polymer are arranged randomly throughout the cell. With the micro-droplets 32, the plates P are further attached to each other. A microscopic image of the cell interior shows an oriented ferroelectric liquid crystal 1 trapped between the texturine filaments 2 and the microbeads 31 and 32, respectively, in the smectic phase. The smectic planes 11 of liquid crystal 1 are perpendicular to plate P. The orientation of the molecules of liquid crystal 1 and its smectic planes 11 is homogeneous throughout the cell.
Skupna masa polimera v celici po izumu, torej polimera v teksturinih nitih 2 kot tudi polimera v mikrokapljicah 31 in 32, je enaka okoli 1 % do 6 % mase tekočega kristala 1 v celici, oziroma nekoliko manjša, Če je del molekul monomera ostal nepolimeriziran.The total weight of the polymer in the cell of the invention, that is, the polymer in the textural filaments 2 as well as the polymer in the microspheres 31 and 32, is equal to about 1% to 6% by weight of the liquid crystal 1 in the cell, or slightly less, if part of the monomer molecules remains unpolymerized.
V posebnem izvedbenem primeru sta plošči P feroelektrične tekočekristalne celice prevlečeni s plastjo OL, ki omogoča ali pa vsaj prispeva k orientiranju feroelektričnega tekočega kristala 1.In a specific embodiment, the panels P of the ferroelectric liquid crystal cell are coated with an OL layer that enables or at least contributes to the orientation of the ferroelectric liquid crystal 1.
Opisano feroelektrično tekočekristalno celico se izdela z naslednjim postopkom po izumu. Celico se na znan način v vakuumu napolni s feroelektričnim tekočim kristalom, kateremu je primešanega okoli 1 % do 6 % (utežno) monomera. Zmes obeh komponent se je predtem intenzivno zmešalo pri temperaturi, pri kateri je feroelektričen tekoči kristal v izotropni fazi. Polimerizacijo monomera v tej zmesi se sproži, na primer z ultra violično svetlobo, šele potem ko se je feroelektričen tekoči kristal ohladil prednostno do kiralno nematske faze ali pa do ene od smektičnih faz. V nematski fazi so molekule feroelektričnega tekočega kristala pod vplivom plasti OL in/ali prednostno magnetnega polja B orientirane vzporedno druga z drugo in vzporedno s ploščama P. V smektični fazi A ali C pa je feroelektričen tekoči kristal pri tem orientiran, kot je razvidno iz dosedanjega opisa celice po izumu. V vsakem od obeh primerov se oblikuje stabilna ravninska zgradba, ki ostane tudi po nadaljnji ohladitvi tekočega kristala do kiralne smektične faze C. Pri faznem prehodu iz kiralno nematske faze v smektično fazo A se molekule premaknejo znotraj ravnin, vzporednih s ploščama P, tako da se stvorijo smektične plasti, ki so pravokotne na plošči P.The described ferroelectric liquid crystal cell is made by the following method according to the invention. The cell is filled in a known manner in vacuo with a ferroelectric liquid crystal to which about 1% to 6% (w / w) of the monomer is mixed. The mixture of the two components was previously vigorously stirred at a temperature at which the ferroelectric liquid crystal is in the isotropic phase. The polymerization of the monomer in this mixture is triggered, for example, by ultraviolet light only after the ferroelectric liquid crystal has cooled down preferably to the chiral nematic phase or to one of the smectic phases. In the nematic phase, the ferroelectric liquid crystal molecules under the influence of the OL layer and / or preferably the magnetic field B are oriented parallel to each other and parallel to the plates P. In the smectic phase A or C, the ferroelectric liquid crystal is oriented in this way, as seen in the present cell description according to the invention. In each of the two cases, a stable planar structure is formed, which remains after further cooling of the liquid crystal to the chiral smectic phase C. During the phase transition from the chiral nematic phase to the smectic phase A, the molecules move within planes parallel to the plates P such that create smectic layers perpendicular to the P plate.
Izvedba postopka po izumu zavisi od vrste polimorfizma feroelektričnega tekočega kristala. Za izdelavo celice po izumu se prednostno izbere tak feroelektričen tekoči kristal, da njegov polimorfizem poleg kiralne smektične faze C obsega še izotropno, kiralno nematsko in smektično fazo A. Tedaj se zmes feroelektričnega tekočega kristala in monomera počasi ohlaja od izotropne faze vsaj do kiralno nematske tekočekristalne faze, ko se prednostno sproži polimerizacijo monomera. Kadar sta plošči P opremljeni s plastjo OL za orientiranje feroelektričnega tekočega kristala in predvsem kadar ima ta le malo primešanega monomera, torej se zmes obnaša podobno kot čisti feroelektričen tekoči kristal, ta postopek zadošča za izdelavo celice po izumu. Majhna primes monomera namreč ne vpliva znatno na interakcijo tekočekristalnih molekul s plastjo OL in se feroelektričen tekoči kristal uredi le pod vplivom plasti OL.The implementation of the process according to the invention depends on the type of polymorphism of the ferroelectric liquid crystal. Preferably, such a ferroelectric liquid crystal is selected for the manufacture of the cell according to the invention such that its polymorphism comprises, in addition to the chiral smectic phase C, an isotropic, chiral nematic and smectic phase A. Then the mixture of the ferroelectric liquid crystal and monomer is slowly cooled from the isotropic non-crystalline non-crystalline phase phases when the polymerization of the monomer is preferably initiated. When the panels P are provided with an OL layer to orient the ferroelectric liquid crystal, and especially when it has only a small amount of monomer impurity, the mixture behaves similarly to pure ferroelectric liquid crystal, this process is sufficient to produce a cell according to the invention. The small admixture of the monomer does not significantly affect the interaction of the liquid crystal molecules with the OL layer, and the ferroelectric liquid crystal is regulated only under the influence of the OL layer.
Kadar pa se želi doseči zaželjeno orientacijo tekočekristalnih molekul in s tem smektičnih ravnin 11 feroelektričnega tekočega kristala v izdelani celici ne glede na to, ali sta plasti OL za orientiranje prisotni, saj njun orientacijski vpliv pri večjih koncentracijah monomera z globino v tekočem kristalu hitro zamira in pri prehodu v kiralno smektično fazo C rado pride do defektov v orientaciji smektičnih ravnin 11, in ne glede na delež dodanega monomera, se ohlajanje zmesi tekočega kristala in monomera vrši v magnetnem polju B, ki je usmerjeno vzporedno z ravninama plošč P, in z gostoto, katere vrednost je vsaj 2 T. Da se zagotovi makroskopska homogenost urejenosti, se tekoči kristal v kiralni smektični fazi C za nekaj minut izpostavi približno 100 ms trajajočim impulzom izmeničnega električnega polja EA, ki je pravokotno na plošči P in ima jakost vsaj okoli 10 MV/m ter frekvenco okoli 3 Hz. S tem se izboljša prozornost in kontrast celice po izumu.However, when the desired orientation of the liquid crystal molecules and thus the smectic planes of the 11 ferroelectric liquid crystal in the fabricated cell is desired, regardless of whether the OL layers are present for orientation, as their orientation influence at higher concentrations of the monomer with the depth in the liquid crystal rapidly dies, and when transitioning to the chiral smectic phase C, defects in the orientation of the smectic planes 11 are glad to occur, and regardless of the proportion of the added monomer, the liquid crystal-monomer mixture is cooled in a magnetic field B oriented parallel to the planes of the plates P and with a density , whose value is at least 2 T. To ensure macroscopic homogeneity of orderliness, the liquid crystal in the chiral smectic phase C is exposed for a few minutes to approximately 100 ms continuous pulses of alternating electric field E A perpendicular to plate P and having a strength of at least about 10 MV / m and frequency around 3 Hz. This improves the transparency and contrast of the cell according to the invention.
Ob ohlajanju zmesi tekočega kristala in monomera se le-ta zaradi svoje nižje topnosti v tekočem kristalu pri nižji temperaturi pa tudi vsled spreminjanja strukture tekočega kristala ob faznih prehodih začne izločati sprva v obliki majhnih mikrokapljic 31 na celičinih ploščah P, preko katerih se ohlaja notranjost celice. Ko se sproži polimerizacijo, se od tekočega kristala fazno separira še večina preostalega raztopljenega dela monomera. Ta del monomera se pri nižjih koncentracijah monomera v tekočem kristalu in predvsem, kadar se prednostno v kiralno nematski fazi sproži polimerizacijo, izloči in nato polimerizira v obliki teksturinih niti 2, ki prepredejo ves tekoči kristal 1 in se nekatere od njih zlepijo med seboj oziroma se nekatere od njih s svojim delom prilepijo ob mikrokapljice 31. Pri višjih koncentracijah in predvsem, kadar se sproži polimerizacijo v smektični fazi A ali pa v kiralni smektični fazi C, pa se ta del monomera izloči in nato polimerizira v obliki mikrokapljic 32, ki segajo od ene do druge celičine plošče P in se nanju prilepijo, kot tudi v obliki teksturinih niti 2, ki pa se sedaj vežejo na mikrokapljice 31 in 32. Mikrokapljice 32 torej dodatno povežejo obe plošči P in zato po izvršeni polimerizaciji delujejo kot distančniki, ki preprečujejo tako medsebojno približevanje kot razmikanje mejnih plošč P.Upon cooling of the liquid crystal and monomer mixture, due to its lower solubility in the liquid crystal at lower temperature, as well as by changing the structure of the liquid crystal, phase excretions begin to excrete initially in the form of small micro droplets 31 on the cell plates P, through which the interior of the cell is cooled. . When polymerization is initiated, most of the remaining dissolved moiety is phase-separated from the liquid crystal. This part of the monomer, at lower concentrations of the monomer in the liquid crystal, and especially when polymerization is initiated in the chiral nematic phase preferably, is separated out and then polymerized in the form of textural filaments 2, which permeate the entire liquid crystal 1 and some of them adhere to one another or bond to one another. some of them attach to their microbeads 31. At higher concentrations, and especially when polymerization occurs in smectic phase A or in chiral smectic phase C, this part of the monomer is separated and then polymerized in the form of microspheres 32 extending from and then adhere to each other of the plate P, as well as in the form of textural filaments 2, which now bind to micro-droplets 31 and 32. The micro-droplets 32 therefore additionally bind both panels P and therefore act as spacers after polymerization, which prevents approaching each other as the spacing of the boundary plates P.
Med polimerizacijo pa se molekule monomera nahajajo v urejeni okolici orientiranega feroelektričnega tekočega kristala. Zato je polimerna tekstura z nitmi 2, ki prepredejo ves tekoči kristal 1, izrazito anizotropna in je usmerjena pretežno vzporedno z mejnima ploščama P. Teksturine niti 2 predstavljajo nove površine, s katerimi se pozneje v izdelani celici utrjuje orientacija molekul feroelektričnega tekočega kristala in se zamrzuje urejenost molekul feroelektričnega tekočega kristala, kot je bila pred sprožitvijo polimerizacije. Takšna urejenost se ohrani tudi po segrevanju celice čez fazni prehod v izotropno fazo.During polymerization, however, the monomer molecules are located in the ordered environment of the oriented ferroelectric liquid crystal. Therefore, the polymeric texture with the filaments 2, which interrupt all the liquid crystal 1, is highly anisotropic and oriented substantially parallel to the boundary plates P. The textural filaments 2 represent new surfaces that later strengthen the orientation of the ferroelectric liquid crystal molecules in the fabricated cell and freeze orderliness of ferroelectric liquid crystal molecules, as it was before the initiation of polymerization. Such orderliness is maintained even after heating the cell over the phase transition to the isotropic phase.
Da se olajša urejanje feroelektričnega tekočega kristala, naj ima le-ta pozitivno anizotropijo diamagnetne susceptibilnosti, za krmiljenje celice po izumu pa je ugodno, da ima negativno anizotropijo dielektrične susceptibilnosti. Vendar pa v celici po izumu, v kateri je debelina sloja tekočega kristala 1 manjša od periode vijačnice v kiralni nematski oziroma kiralni smektični fazi C, lahko orientiranje tekočega kristala 1 z magnetnim poljem B in izmeničnim električnim poljem EA uspešno izvedemo tudi, če je njegova anizotropija diamagnetne susceptibilnosti negativna in anizotropija dielektrične susceptibilnosti pozitivna. Anizotropija dielektrične susceptiblnosti ne glede na svoj predznak bistveno ne vpliva na delovanje celice, saj je njen vpliv znatno manjši od sklopitve električnega polja in električne polarizacije tekočega kristala.In order to facilitate the regulation of a ferroelectric liquid crystal, it should have a positive anisotropy of diamagnetic susceptibility, and it is advantageous for the control of a cell of the invention to have a negative anisotropy of dielectric susceptibility. However, in a cell according to the invention in which the thickness of the liquid crystal layer 1 is less than the helix period in the chiral nematic or chiral smectic phase C, orientation of the liquid crystal 1 with magnetic field B and alternating electric field E A can be successfully performed even if its diamagnetic susceptibility anisotropy negative and dielectric susceptibility anisotropy positive. The anisotropy of the dielectric susceptibility, regardless of its sign, does not significantly affect the function of the cell, since its influence is much smaller than the coupling of the electric field and the electric polarization of the liquid crystal.
Opisani postopek torej obstoji v orientiranju feroelektričnega tekočega kristala in v stabiliziranju dosežene homogene orientacije njegovih molekul in njegovih smektičnih ravnin, pri čemer se to urejenost zamrzne, s tem da se sproži polimerizacijo monomera, potem ko je bila dosežena vsaj željena orientacija molekul.The process described thus consists in orienting the ferroelectric liquid crystal and in stabilizing the homogeneous orientation of its molecules and its smectic planes obtained, freezing this order by initiating the polymerization of the monomer after at least the desired orientation of the molecules has been achieved.
V nadaljnjem je opisan izvedbeni primer postopka po izumu. Uporabljena sta bila večkomponentna mešanica tekočih kristalov ZLI 4237-100 (proizvajalec E. Merck) in monomer D044 (proizvajalec DSM Resins International). Tekoči kristal je v širokem temperaturnem intervalu od + 20 °C do t 61 °C v feroelektrični fazi, pri višji temperaturi se pojavijo še smektična faza A, kiralna nematska in izotropna faza. Nadalje ima pozitivno anizotropijo diamagnetne susceptibilnosti in negativno anizotropijo dielektrične susceptibilnosti.The following is an embodiment of the process of the invention. A multicomponent mixture of liquid crystals ZLI 4237-100 (manufactured by E. Merck) and monomer D044 (manufactured by DSM Resins International) were used. The liquid crystal is in the wide temperature range from + 20 ° C to t 61 ° C in the ferroelectric phase, with smectic phase A, chiral nematic and isotropic phase appear at higher temperature. It further has a positive anisotropy of diamagnetic susceptibility and a negative anisotropy of dielectric susceptibility.
Mešanici tekočih kristalov se pri temperaturi okoli 100°C, tekoči kristal je tedaj v izotropni fazi, doda med 1 % in 6 % (utežno) monomera. Zmes tekočega kristala in monomera se v magnetnem polju z gostoto B > 2 T kontrolirano ohlaja skozi različne faze. Pod vplivom magnetnega polja B se ob prehodu iz kiralne nematske faze v smektično fazo A vzpostavi urejena smektična ravninska struktura tekočega kristala. Tedaj se z ultra violično svetlobo sproži polimerizacijo. V praktični izvedbi postopka po izumu se osvetlitev z ultra violično svetlobo lahko izvede izven magnetnega polja pri sobni temperaturi, saj se smektična struktura ohrani do feroelektrične faze. Glede na fazo, v kateri se sproži polimerizacija monomera, pa se spreminjata deleža polimera v teksturi in v mikrokapljicah 31, 32. Večje mikrokapljice 32 pa se pojavljajo pri koncentracijah monomera nad 3%.At a temperature of about 100 ° C, the liquid crystal mixture is then in the isotropic phase, between 1% and 6% (w / w) of the monomer. The mixture of liquid crystal and monomer is cooled through various phases in a magnetic field with a density of B> 2 T. Under the influence of magnetic field B, an ordered smectic plane structure of a liquid crystal is established upon the transition from the chiral nematic phase to the smectic phase A. Then ultra-violet light initiates polymerization. In a practical embodiment of the method of the invention, ultraviolet light can be externally generated at room temperature, since the smectic structure is maintained up to the ferroelectric phase. However, depending on the phase in which the polymerization of the monomer is initiated, the proportions of the polymer in the texture and in the microspheres 31, 32 change. Larger microspheres 32 occur at monomer concentrations above 3%.
Urejenost molekul tekočega kristala v smektičnih plasteh se lahko izboljša tako, da se v kiralni smektični fazi C pravokotno na mejni plošči celice za nekaj minut v pulzih po 100 ms vzpostavi izmenično električno polje z jakostjo 15 MV/m ter s frekvenco okoli 3 Hz.The ordering of the liquid crystal molecules in the smectic layers can be improved by establishing an alternating electric field of 15 MV / m at a frequency of about 3 Hz in a chiral smectic phase C perpendicular to the cell boundary plate for a few minutes in 100 ms pulses.
Feroelektrična tekočekristalna celica po izumu ustreza zahtevam za uporabo v televizijskem prikazalniku visoke ločljivosti in z internim spominom oziroma v zelo hitrem optičnem preklopniku. Krmilno električno polje v celici prikazalnika je vzporedno smektičnim ravninam feroelektričnega tekočega kristala v celici, saj so lete pravokotne na mejni plošči P. Negativna dielektrična anizotropija feroelektričnega tekočega kristala nekoliko olajša krmiljenje celice po izumu, saj se njen prispevek prišteje k prispevku električnega dipolnega momenta molekul tekočega kristala. Hitrost preklopa je za red velikosti večja od celic, ki so izdelane iz nematskih kompozitov. Krmiljenje celice po izumu pa se tudi poenostavi zaradi bistabilnosti v orientaciji molekul feroelektričnega tekočega kristala v tej celici, kar ji omogoča spominski učinek. Celica po izumu se odlikuje po visoki prozornosti in dobrem kontrastu.The ferroelectric liquid crystal cell according to the invention meets the requirements for use in a high definition television display and with an internal memory or a very fast optical switch. The control electric field in the display cell is parallel to the smectic planes of the ferroelectric liquid crystal in the cell, since the flights are perpendicular to the boundary plate P. crystals. The switching speed is an order of magnitude greater than cells made of nematic composites. The control of the cell according to the invention is also simplified because of the bistability in the orientation of the ferroelectric liquid crystal molecules in that cell, which gives it a memory effect. The cell according to the invention is characterized by high transparency and good contrast.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1996007123A1 (en) * | 1994-08-31 | 1996-03-07 | The Secretary Of State For Defence | Ferroelectric liquid crystal devices |
| EP0750213A3 (en) * | 1995-06-22 | 1998-01-07 | Sharp Kabushiki Kaisha | Ferroelectric liquid crystal display device |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1996007123A1 (en) * | 1994-08-31 | 1996-03-07 | The Secretary Of State For Defence | Ferroelectric liquid crystal devices |
| GB2306498A (en) * | 1994-08-31 | 1997-05-07 | Secr Defence | Ferroelectric liquid crystal devices |
| GB2306498B (en) * | 1994-08-31 | 1999-03-24 | Secr Defence | Ferroelectric liquid crystal devices |
| EP0750213A3 (en) * | 1995-06-22 | 1998-01-07 | Sharp Kabushiki Kaisha | Ferroelectric liquid crystal display device |
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