CA2019652A1 - Ferroelectric liquid crystal components having high spontaneous polarization and low helical pitch - Google Patents
Ferroelectric liquid crystal components having high spontaneous polarization and low helical pitchInfo
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- CA2019652A1 CA2019652A1 CA002019652A CA2019652A CA2019652A1 CA 2019652 A1 CA2019652 A1 CA 2019652A1 CA 002019652 A CA002019652 A CA 002019652A CA 2019652 A CA2019652 A CA 2019652A CA 2019652 A1 CA2019652 A1 CA 2019652A1
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- spontaneous polarization
- flc
- helical pitch
- liquid crystal
- layer thickness
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K19/00—Liquid crystal materials
- C09K19/52—Liquid crystal materials characterised by components which are not liquid crystals, e.g. additives with special physical aspect: solvents, solid particles
- C09K19/58—Dopants or charge transfer agents
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K19/00—Liquid crystal materials
- C09K19/02—Liquid crystal materials characterised by optical, electrical or physical properties of the components, in general
- C09K19/0225—Ferroelectric
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K19/00—Liquid crystal materials
- C09K19/52—Liquid crystal materials characterised by components which are not liquid crystals, e.g. additives with special physical aspect: solvents, solid particles
- C09K19/58—Dopants or charge transfer agents
- C09K19/586—Optically active dopants; chiral dopants
- C09K19/588—Heterocyclic compounds
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
- G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
- G02F1/141—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent using ferroelectric liquid crystals
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- Organic Chemistry (AREA)
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Abstract
Ferroelectric liquid crystal components having a high spontaneous polarization and a small helical pitch Liquid crystal materials are becoming increasingly important in electro-optical switching and display devices. During recent times, ferroelectric liquid crystal mixtures have also been investigated to a particularly great extent and used in displays.
A physical quantity which is particularly important for the purpose of describing FLC mixtures is the spontaneous polarization (Ps). On the one hand, a high spontaneous polarization leads to short switching times, while on the other hand in the case of high Ps values an optical hysteresis occurs, which leads, inter alia, to so-called "ghost images".
In spite of high spontaneous polarization, the problem of the optical hysteresis may be overcome by the use of FLC
mixtures having a high spontaneous polarization (Ps 20 nC/cm2) and a natural helical pitch of less than one half of the layer thickness in an SSFLC display with a layer thickness of 1 to 10 µm.
FLC mixtures with Ps > 40 nC/cm2 can also be switched under these conditions.
A physical quantity which is particularly important for the purpose of describing FLC mixtures is the spontaneous polarization (Ps). On the one hand, a high spontaneous polarization leads to short switching times, while on the other hand in the case of high Ps values an optical hysteresis occurs, which leads, inter alia, to so-called "ghost images".
In spite of high spontaneous polarization, the problem of the optical hysteresis may be overcome by the use of FLC
mixtures having a high spontaneous polarization (Ps 20 nC/cm2) and a natural helical pitch of less than one half of the layer thickness in an SSFLC display with a layer thickness of 1 to 10 µm.
FLC mixtures with Ps > 40 nC/cm2 can also be switched under these conditions.
Description
2019~2 HOECHST AK~IENGESELLSCHAFT HOE 89/F 197 Dr. JA/1 Ferroelectric liquid crystal component~ having high spontaneou~ polarization and low helical pitch Switching and display components containing ferroelectric liquid crystal mixtures ("F~C displays"~ are known, for example, rom EP-B 0,032,362 t= US-A 4,367,924). They are constructed in such a manner that the FLC layer is enclosed on both sides by specific layer~, which are u~ually - in this sequence, starting from the FLC layer -at lea~t one electrically in~ulating layer, electrodesand a boundary plate (eg. of qlass~. Moreover, they include a polarizer, if they are operated in the ~gues~-host" mode or in the reflexive mode, or two polarizers if transmission by refringence is employed as the mode. One or preferably both electrically insulating layers are employed as the so-called orientation layer.
Such orientation layers bring ~ in con~unction with a spacing of the boundary plates which i5 selected t~ be sufficiently small - the FLC ln the FLC mixture into a configuration in which the molecules are arranged with their longitudinal axe~ parallel to one another and the smectic planes are disposed perpendicular or obliquely to the orientation layer. In this arrangement, as i8 known, the molecules have two equivalent orientations, between which they can be switched by pulsed application of an electxic field, i.e. FLC displays can be switched in a bistable manner and the switching times are in the ~s range, thase being inversely proportional to the spontaneous polarization of the FLC mixture.
The es6ential advantage of such FLC displays a~ compared with the LC displays which can still to date essentially be encountered in industrial practice is considered to be the attainable multiplzx ratio, i.e. the maximum number of targets which can be driven in the time-sequential process ("multiplex" process), which is significantly larger in the case of FLC displays. This elec~rical drive 20~9652 is essentially based on the above-described pulsed addressing.
In the course of the further development of FLC displays during the last 10 years, a disadvantage has h~wever emerged, which resides in that the aforementioned pulsed addres~ing leads to a reproducible switching between the two stable states frequently only in the case of suffi-ciently small values for the spontaneou~; polarization. By way of ex~mple, it may be observed that in an FLC display which has been ~ituated for a relatively great length of time in one of the two stable states (~Istanding Lmage") switching over to the respecti~e other state can take place only with very great difficulty, ie. only with high amplitude or a very long pulse duration of the applied volt~ge. In the case of pictorial displays, this behaviox of an optical hysteresis leads to a situation in which an image which has been inscribed over a relatively great length of time can be recogni~ed in the following image, as a silhouette in the fonm of a ~ghost image". It appears that this observation of an optical hysteresis i8 the more marked, the greater is tha spontaneous polarization of the FLC mixture. In the case of particularly high value~ (P8 ~ 35 nC cm~23, it ia as a rule no longer possible to achieve any switching by means of pulsed addressing. One of the concepts as to the cause of this phenomenon of an optical hystere i~ i~ to the effect that ionic impurities in the FLC mixture could be responsible for this. The formerly known attemp~s at a solution; a) direct contact between FLC mixture and electrodes and b) intensive cleaning have not yet given satisfactory result~; the fir~t method i8 very costly in the avoidance of electrical short circuits, and the second requirQs a specific type of purification almost for each individual component of a mixture.
In the case of the hitherto known FLC di~plays, the starting point is, on a controlled basis, that the spacing of the boundary plates is chosen in such a manner 2019~52 that the development of the twist (~Ihelix~l) typical of ferroelectric phases is suppressed. This takes place in such a manner that - see the initially cited EP-B - the spacing of the plates is smaller than approximately five tLmes the natural helical pitch. However, on account of the optical switching behavior and for general tech-nological reasons, there is virtually no possibility of setting the spacing of the plates to be arbitrarily small, so that in practice a spacing of approximately 2 ~m is adopted. For this reason, efforts were hitherto made to develop FLC mixture~ having the greatest possible helical pitch; this has also recently been made subject to further demands (Gray et al., Thermotropic Liquid Crystals, 1987) according to which the spacing of the plates should be less than one quarter of the helical pitch.
The object of the present invention is to develop FLC mixtures which do not exhibit any optical hysteresi~, in spite of hi~h values in spontaneous polarization.
The invention proceeds from the known FLC dis-plays - by display and switching components using LC
mixtures, which exhibit a ferroelectric phase - which operate using SSF~C technology ("surface stabilized ferroelectric liquid crystal"), as is described, for example, in the aforementioned EP-B. These FLC displays have a layer thickness (ie. spacing of the boundary plates) of 1 to 10 ~m, and especially of 1.2 to 3 ~m.
According to the invention, in such F~C displays use is made of those F~C mixtures which exhibit a high spontaneous polari~ation of P5 > 20 nC cm~2 (measured at 25C), preferably of P~ > 35 nC cm 2, in particular oP
40 nC cm~2, and exhibit a natural helical pitch of less than one half of the layer thickness of the afore-mentioned SSFLC displays, in particular of more than 1/10 of this layer thickness. Preferably, such displays are subiected to pulsed addressin~.
In preferred embodLments, the ferroelectric phase is an SO phase and the phase sequence of the FLC mi~ture proceeds as follows:
Such orientation layers bring ~ in con~unction with a spacing of the boundary plates which i5 selected t~ be sufficiently small - the FLC ln the FLC mixture into a configuration in which the molecules are arranged with their longitudinal axe~ parallel to one another and the smectic planes are disposed perpendicular or obliquely to the orientation layer. In this arrangement, as i8 known, the molecules have two equivalent orientations, between which they can be switched by pulsed application of an electxic field, i.e. FLC displays can be switched in a bistable manner and the switching times are in the ~s range, thase being inversely proportional to the spontaneous polarization of the FLC mixture.
The es6ential advantage of such FLC displays a~ compared with the LC displays which can still to date essentially be encountered in industrial practice is considered to be the attainable multiplzx ratio, i.e. the maximum number of targets which can be driven in the time-sequential process ("multiplex" process), which is significantly larger in the case of FLC displays. This elec~rical drive 20~9652 is essentially based on the above-described pulsed addressing.
In the course of the further development of FLC displays during the last 10 years, a disadvantage has h~wever emerged, which resides in that the aforementioned pulsed addres~ing leads to a reproducible switching between the two stable states frequently only in the case of suffi-ciently small values for the spontaneou~; polarization. By way of ex~mple, it may be observed that in an FLC display which has been ~ituated for a relatively great length of time in one of the two stable states (~Istanding Lmage") switching over to the respecti~e other state can take place only with very great difficulty, ie. only with high amplitude or a very long pulse duration of the applied volt~ge. In the case of pictorial displays, this behaviox of an optical hysteresis leads to a situation in which an image which has been inscribed over a relatively great length of time can be recogni~ed in the following image, as a silhouette in the fonm of a ~ghost image". It appears that this observation of an optical hysteresis i8 the more marked, the greater is tha spontaneous polarization of the FLC mixture. In the case of particularly high value~ (P8 ~ 35 nC cm~23, it ia as a rule no longer possible to achieve any switching by means of pulsed addressing. One of the concepts as to the cause of this phenomenon of an optical hystere i~ i~ to the effect that ionic impurities in the FLC mixture could be responsible for this. The formerly known attemp~s at a solution; a) direct contact between FLC mixture and electrodes and b) intensive cleaning have not yet given satisfactory result~; the fir~t method i8 very costly in the avoidance of electrical short circuits, and the second requirQs a specific type of purification almost for each individual component of a mixture.
In the case of the hitherto known FLC di~plays, the starting point is, on a controlled basis, that the spacing of the boundary plates is chosen in such a manner 2019~52 that the development of the twist (~Ihelix~l) typical of ferroelectric phases is suppressed. This takes place in such a manner that - see the initially cited EP-B - the spacing of the plates is smaller than approximately five tLmes the natural helical pitch. However, on account of the optical switching behavior and for general tech-nological reasons, there is virtually no possibility of setting the spacing of the plates to be arbitrarily small, so that in practice a spacing of approximately 2 ~m is adopted. For this reason, efforts were hitherto made to develop FLC mixture~ having the greatest possible helical pitch; this has also recently been made subject to further demands (Gray et al., Thermotropic Liquid Crystals, 1987) according to which the spacing of the plates should be less than one quarter of the helical pitch.
The object of the present invention is to develop FLC mixtures which do not exhibit any optical hysteresi~, in spite of hi~h values in spontaneous polarization.
The invention proceeds from the known FLC dis-plays - by display and switching components using LC
mixtures, which exhibit a ferroelectric phase - which operate using SSF~C technology ("surface stabilized ferroelectric liquid crystal"), as is described, for example, in the aforementioned EP-B. These FLC displays have a layer thickness (ie. spacing of the boundary plates) of 1 to 10 ~m, and especially of 1.2 to 3 ~m.
According to the invention, in such F~C displays use is made of those F~C mixtures which exhibit a high spontaneous polari~ation of P5 > 20 nC cm~2 (measured at 25C), preferably of P~ > 35 nC cm 2, in particular oP
40 nC cm~2, and exhibit a natural helical pitch of less than one half of the layer thickness of the afore-mentioned SSFLC displays, in particular of more than 1/10 of this layer thickness. Preferably, such displays are subiected to pulsed addressin~.
In preferred embodLments, the ferroelectric phase is an SO phase and the phase sequence of the FLC mi~ture proceeds as follows:
2~96~2 I N ~ S~ ~ Sc in this case in the entire temperature range of the N~
phase the helical pitch is no less than 8 ~m, preferably no less than 15 ~m. The ~tated properties (ie. high spontaneous polarization, a first speciiEied helical pitch in the smectic phase and a second specified helical pitch in the cholesteric phase) are in particular satisfied by non-chiral LC basic mixtures, to which two or more appropriate chiral dopants are added. Expediently, such chiral dopants contribute to the extent of at least 20 %
to the spontaneous polarization of the total mixture, pOS~QSS the same sign in the values of the ~pontaneous polarization; at the same time, they contribute to the extent of at least 20 % to the natural helical pitch in the smectic phase and have an identical sense of rotation in their twist capaci~y; in the ~* phase, two of the chiral dopants do moreover exhibit differing signs (non-identical sense of rotation) in their twist capacity.
The chemical compounds which sati~fy the a~ore-mentioned conditions in non-chiral LC basic mixtures include, in particular, tho~e of the general formulae (I) and (II) y R1 _ A - ~ L~ ~3 (I) R1 _ A - ~ R2 ~3 (II) where the symbols and indices have the following meaning:
Rl = straight-chain or branched-chain (Cl-Cl2)alkyl, in which one or two non-ad~acent -CH2-groups may be replaced by -O- and/or -S-, A = diazin-2,5-diyl or azin-2,5-diyl X, Y = O and/or S, and R2, R3, R4 = independently of one another H, straight-2 ~ 2 chain (C1-C1O)alkyl or branched-chain tC3-C1D)alkyl, in which R2, R3 and R4 are not simultaneously H.
In particularly preferred e~bodLments, the following are applicable:
R1 = straight-chain (C5-C11)alkyl, in which a -CH2-group can be replaced by -O- or -S-;
~, Y = O;
R2, R3 = H and R4 = straight-chain or branched-cha:in ( C3-C7 )alkyl;
A = pyrimidin-2,5-diyl.
Surpriæingly, using the aforementioned F~C mixture it was even possible to suppres~ the - in the pre~ent ca~e undesired - development of a helix in the ferroelectric phase, if the layer thickness is greater than 10 timQ6 the natural helical pitch. Even in FLC mixtures having natural helical pitches of ~ 0.7 ~m in the ferroelectric phase, no optical hysteresis occurs at high P~ value~; at P~ values of ~ 100 nC cm~2, no ~ghost Lmages" were observe~ any longer. Further ad~antages of the invention reside in the retention of the short ~witching time6 and in the possibility of portraying grey gra~ations.
20~9~2 Examples:
In the examples ~et out below, two achiral LC basic mixtures A and B and various chiral dopants are used. In comparison therewith, the values of an hC basic mixture A with a combination of two chiral dopants which i~ not in accordance with the invention are investigated.
LC mixture A contains ~in % by weight) 11.06 N (Al) C8H17- O- ~ )~- C6~13 N
5.11 C8H17-O- C ~ ~ ~ C8H17 (A2) N
1011.67 C8H17-O- C~ ~ -O-C4Hg (A3) t~
9~28 C8H17-O- ~O ~ ~ -ClOH21 (A4) N
15.88 C8H17- C~ ) ~ O C8H17 (A5) N
17.50 C12H25- CO ~ _o-CO- ~ -C5Hll (A6) 2 ~ , 9 ~ ~ 2 N
17 7 0 C8EI17~~ O-C6H13 ~A7) rN /--\
11. 80 C8H17_~ ~~~~10H21 (A8 The miXtUre ShOWS the :EOllOWing Pha5e SeqUenCe:
LC mixture B contains ( in % by weight ) 13 . 33 Al (=B~) 4.4g A2 (=B2) 14 . 7 8 A3 ( =~3 ) 8.14 A4 (=B4) N
108 . 16 C8H17- O- CO ~--~ O- C6H13 ~ B5 ) 19 . 04 clOH21_C~) )~ O- CO~> C5Hll ( B~ ) N
12.00 C~H17-~)$ ~--C12H25 (B7) N
20.00 C8H17-~ ~o-cc~-c6~l3 (B8) ~, 2019~2 The mixture shows the following phase sequenceO
Examples of dopants which are suitable According to the in~ention are:
Dopant D 1 ~8H17- CO ~ --CH2~ Hg Dopant D 2 0 ClOH21- (C) >~3 O- CH2~4Hg N tS) (5~
Dopant D 3 C12H25- ~O ~ ~ -C~2 ~ C4Hg N (5~ tS) Dopant D 4 C8H17 ~ O ~ O-C~ ~ ~3H~
N (R) (~
Dopant D 5 C2Hs-CH(-cH2)7-~ ~ ~ O-CO ~ CH3 * N
(S) (R) (R) Dopant D 6 C8H17- ~ ~ ~ O-CO / \ ~H3 (R) (~) In detail, the listed dopants in the LC mixtures A and~or 2 ~ 5 2 g B show the following data at an ~dmixture rate of 10 (see Table I).
The following examples (FLC mixtures) accordin~ to the invention were produced from the aforementioned dopants and the likewise listed LC mixtu.res, having regard to the above data:
Example 1 The FLC mixture M1 possesses the following composition (in mol~) LC mixture A 65.6 Dopant Dl 11.4 D2 5.7 D3 11.4 " D5 5.9 and the phase sequence Sc 63 SA 74 78 ~ample 2 The FLC mixture M2 possesses the following composition LC mixture A 70.6 Dopant Dl 23.0 " D4 7.0 and the pha~e ~eguence Sc 64 SA 65 . 5 N~ 80 ~xample 3 The FLC mixture M3 posses3es the following compo~ition LC mixture B 72.0 Dopant D1 8.8 " D2 4.4 " D3 8.8 " D8 6.0 and the phase sequence Sc 68.5 SA 76 N 83.5 2~ ~6~2 _ . 0~ ~ ~O~t` O~U~OD d'O ~P
1 ~ 1 ~ 1 Lrl U~ d' ~ U~
++++ ++++ ~ ++ +~ ++
E~'~ o o o o o ~ o o ~ ~ V I V V V V A A I\
E~ __ _ .
:~
~ ~` ~1 r~ ~ O ~ r- ~ r~ o E~l t) _ a~ 0~ ~0 01) 10 Ul ~-:p N _I O
~ t o + + ~ ~ + ~ + ~ + + A
~
~ _ ~X 0000 0000 OOC O 00 00 00 ,~ ~ ~ ~ _~ ~1~ _~
C--_ _ _ ~ ~cm~4 ~mm ~P4m ~ ~ ~p:
_ ~P.
.o _~ ~ ~ d' U~ ~D
,¢ a a_ r~. a ~ c~
2nls~2 Reference e~ample ~1 The FLC mix~ur~ VM 1 possesses the followin~ composition LC mixture A 77.7 Dopant D7 10.3 ~ D8 5.0 ~ D4 7.0 Dopant D7 C8H17- ~ 0 CH2~ ~0 DOPant D8 O
C3H7 "/ ~ - C O- r~O )~ O C- C5H11 N
(R) (R) and the PhaSe 8eqUenCe SO 58 SA 67 N 78 I.
At a temperature of 15C, this FLC mixture VMl exhibits a value of P3 of + 55 nC-cm~2. In the Sc phase the dopant~
D7 and D8 possess a different sign in their twîst capacity and give in total a pitch which is large as compared with the cell thickne6s (layer thickness).
The measurement result~ of Examples 1 to 3 according to the invention are presented in Table II. For all measured temperstures, the pitch of Ml to M3 in the chale~teric phase is greater than 8 ~m. In the case of a pulsed addressing at 15 DC~ bipolar pulses of a total width of 400 ~s and a height of 3 V/~m are generated (with Ml), and the gaps between the pulses amount to 20 ms. A
co~parison with VMl does not lead to the pulse heights of the mixtures according to the in~ention, but to the optical hysteresis described in the introduction. The optical contrast (in exposed units) was determined as the di~ference in transmission between the two bistable 20~9652 states in a tes~ cell (of ~hickness as indicated~ (see Table II ) .
Table II
_ _ . _ . ~
FLC mixture Measurement Pitch Z in P~ Contrast temperature S~ (~m) (nC cm~2) CR
(C) _. _ ___ _ , _ ___ Ml ~Test 10 + 0.25 -~ 66 0.~0 cell 2.6 ~m) 15 ~ 0.32 + 66 0.35 + 0.39 -~ 55 0.33 + 0.46 + S0 0.31 M2 (Test 10 + 0.38 + 79 0.64 cell 2.04 ~m) 15 + 0.45 + 7~ 0.35 + 0.52 + 65 0.17 ~ 0.59 + 58 0.08 M3 (Test 10 + 0.38 + 77 2.36 cell 2.06 ~m) 15 + 0.46 + 70 1.98 ~0 + 0.55 ~ 62 1.50 L _ 25 + 0.63 -~ 55 l.lO
phase the helical pitch is no less than 8 ~m, preferably no less than 15 ~m. The ~tated properties (ie. high spontaneous polarization, a first speciiEied helical pitch in the smectic phase and a second specified helical pitch in the cholesteric phase) are in particular satisfied by non-chiral LC basic mixtures, to which two or more appropriate chiral dopants are added. Expediently, such chiral dopants contribute to the extent of at least 20 %
to the spontaneous polarization of the total mixture, pOS~QSS the same sign in the values of the ~pontaneous polarization; at the same time, they contribute to the extent of at least 20 % to the natural helical pitch in the smectic phase and have an identical sense of rotation in their twist capaci~y; in the ~* phase, two of the chiral dopants do moreover exhibit differing signs (non-identical sense of rotation) in their twist capacity.
The chemical compounds which sati~fy the a~ore-mentioned conditions in non-chiral LC basic mixtures include, in particular, tho~e of the general formulae (I) and (II) y R1 _ A - ~ L~ ~3 (I) R1 _ A - ~ R2 ~3 (II) where the symbols and indices have the following meaning:
Rl = straight-chain or branched-chain (Cl-Cl2)alkyl, in which one or two non-ad~acent -CH2-groups may be replaced by -O- and/or -S-, A = diazin-2,5-diyl or azin-2,5-diyl X, Y = O and/or S, and R2, R3, R4 = independently of one another H, straight-2 ~ 2 chain (C1-C1O)alkyl or branched-chain tC3-C1D)alkyl, in which R2, R3 and R4 are not simultaneously H.
In particularly preferred e~bodLments, the following are applicable:
R1 = straight-chain (C5-C11)alkyl, in which a -CH2-group can be replaced by -O- or -S-;
~, Y = O;
R2, R3 = H and R4 = straight-chain or branched-cha:in ( C3-C7 )alkyl;
A = pyrimidin-2,5-diyl.
Surpriæingly, using the aforementioned F~C mixture it was even possible to suppres~ the - in the pre~ent ca~e undesired - development of a helix in the ferroelectric phase, if the layer thickness is greater than 10 timQ6 the natural helical pitch. Even in FLC mixtures having natural helical pitches of ~ 0.7 ~m in the ferroelectric phase, no optical hysteresis occurs at high P~ value~; at P~ values of ~ 100 nC cm~2, no ~ghost Lmages" were observe~ any longer. Further ad~antages of the invention reside in the retention of the short ~witching time6 and in the possibility of portraying grey gra~ations.
20~9~2 Examples:
In the examples ~et out below, two achiral LC basic mixtures A and B and various chiral dopants are used. In comparison therewith, the values of an hC basic mixture A with a combination of two chiral dopants which i~ not in accordance with the invention are investigated.
LC mixture A contains ~in % by weight) 11.06 N (Al) C8H17- O- ~ )~- C6~13 N
5.11 C8H17-O- C ~ ~ ~ C8H17 (A2) N
1011.67 C8H17-O- C~ ~ -O-C4Hg (A3) t~
9~28 C8H17-O- ~O ~ ~ -ClOH21 (A4) N
15.88 C8H17- C~ ) ~ O C8H17 (A5) N
17.50 C12H25- CO ~ _o-CO- ~ -C5Hll (A6) 2 ~ , 9 ~ ~ 2 N
17 7 0 C8EI17~~ O-C6H13 ~A7) rN /--\
11. 80 C8H17_~ ~~~~10H21 (A8 The miXtUre ShOWS the :EOllOWing Pha5e SeqUenCe:
LC mixture B contains ( in % by weight ) 13 . 33 Al (=B~) 4.4g A2 (=B2) 14 . 7 8 A3 ( =~3 ) 8.14 A4 (=B4) N
108 . 16 C8H17- O- CO ~--~ O- C6H13 ~ B5 ) 19 . 04 clOH21_C~) )~ O- CO~> C5Hll ( B~ ) N
12.00 C~H17-~)$ ~--C12H25 (B7) N
20.00 C8H17-~ ~o-cc~-c6~l3 (B8) ~, 2019~2 The mixture shows the following phase sequenceO
Examples of dopants which are suitable According to the in~ention are:
Dopant D 1 ~8H17- CO ~ --CH2~ Hg Dopant D 2 0 ClOH21- (C) >~3 O- CH2~4Hg N tS) (5~
Dopant D 3 C12H25- ~O ~ ~ -C~2 ~ C4Hg N (5~ tS) Dopant D 4 C8H17 ~ O ~ O-C~ ~ ~3H~
N (R) (~
Dopant D 5 C2Hs-CH(-cH2)7-~ ~ ~ O-CO ~ CH3 * N
(S) (R) (R) Dopant D 6 C8H17- ~ ~ ~ O-CO / \ ~H3 (R) (~) In detail, the listed dopants in the LC mixtures A and~or 2 ~ 5 2 g B show the following data at an ~dmixture rate of 10 (see Table I).
The following examples (FLC mixtures) accordin~ to the invention were produced from the aforementioned dopants and the likewise listed LC mixtu.res, having regard to the above data:
Example 1 The FLC mixture M1 possesses the following composition (in mol~) LC mixture A 65.6 Dopant Dl 11.4 D2 5.7 D3 11.4 " D5 5.9 and the phase sequence Sc 63 SA 74 78 ~ample 2 The FLC mixture M2 possesses the following composition LC mixture A 70.6 Dopant Dl 23.0 " D4 7.0 and the pha~e ~eguence Sc 64 SA 65 . 5 N~ 80 ~xample 3 The FLC mixture M3 posses3es the following compo~ition LC mixture B 72.0 Dopant D1 8.8 " D2 4.4 " D3 8.8 " D8 6.0 and the phase sequence Sc 68.5 SA 76 N 83.5 2~ ~6~2 _ . 0~ ~ ~O~t` O~U~OD d'O ~P
1 ~ 1 ~ 1 Lrl U~ d' ~ U~
++++ ++++ ~ ++ +~ ++
E~'~ o o o o o ~ o o ~ ~ V I V V V V A A I\
E~ __ _ .
:~
~ ~` ~1 r~ ~ O ~ r- ~ r~ o E~l t) _ a~ 0~ ~0 01) 10 Ul ~-:p N _I O
~ t o + + ~ ~ + ~ + ~ + + A
~
~ _ ~X 0000 0000 OOC O 00 00 00 ,~ ~ ~ ~ _~ ~1~ _~
C--_ _ _ ~ ~cm~4 ~mm ~P4m ~ ~ ~p:
_ ~P.
.o _~ ~ ~ d' U~ ~D
,¢ a a_ r~. a ~ c~
2nls~2 Reference e~ample ~1 The FLC mix~ur~ VM 1 possesses the followin~ composition LC mixture A 77.7 Dopant D7 10.3 ~ D8 5.0 ~ D4 7.0 Dopant D7 C8H17- ~ 0 CH2~ ~0 DOPant D8 O
C3H7 "/ ~ - C O- r~O )~ O C- C5H11 N
(R) (R) and the PhaSe 8eqUenCe SO 58 SA 67 N 78 I.
At a temperature of 15C, this FLC mixture VMl exhibits a value of P3 of + 55 nC-cm~2. In the Sc phase the dopant~
D7 and D8 possess a different sign in their twîst capacity and give in total a pitch which is large as compared with the cell thickne6s (layer thickness).
The measurement result~ of Examples 1 to 3 according to the invention are presented in Table II. For all measured temperstures, the pitch of Ml to M3 in the chale~teric phase is greater than 8 ~m. In the case of a pulsed addressing at 15 DC~ bipolar pulses of a total width of 400 ~s and a height of 3 V/~m are generated (with Ml), and the gaps between the pulses amount to 20 ms. A
co~parison with VMl does not lead to the pulse heights of the mixtures according to the in~ention, but to the optical hysteresis described in the introduction. The optical contrast (in exposed units) was determined as the di~ference in transmission between the two bistable 20~9652 states in a tes~ cell (of ~hickness as indicated~ (see Table II ) .
Table II
_ _ . _ . ~
FLC mixture Measurement Pitch Z in P~ Contrast temperature S~ (~m) (nC cm~2) CR
(C) _. _ ___ _ , _ ___ Ml ~Test 10 + 0.25 -~ 66 0.~0 cell 2.6 ~m) 15 ~ 0.32 + 66 0.35 + 0.39 -~ 55 0.33 + 0.46 + S0 0.31 M2 (Test 10 + 0.38 + 79 0.64 cell 2.04 ~m) 15 + 0.45 + 7~ 0.35 + 0.52 + 65 0.17 ~ 0.59 + 58 0.08 M3 (Test 10 + 0.38 + 77 2.36 cell 2.06 ~m) 15 + 0.46 + 70 1.98 ~0 + 0.55 ~ 62 1.50 L _ 25 + 0.63 -~ 55 l.lO
Claims (12)
1. A method of using FLC mixtures having a high spontaneous polarization of Ps > 20 nC?cm-2 and a natural helical pitch of less than one half of the layer thickness in an SSFLC display with a layer thickness of 1 to 10 µm.
2. The method as claimed in claim 1, wherein the layer thickness is 1.2 to 3 µm.
3. The method as claimed in claim 1, wherein the helical pitch is greater than l/10 of the layer thickness.
4. The method as claimed in claim 2, wherein the helical pitch is greater than 1/10 of the layer thickness.
5. The method as claimed in claim 1, wherein the FLC mixture exhibits a spontaneous polarization of Ps > 35 nC?cm-2.
6. The method as claimed in claim 2, wherein the FLC mixture exhibits a spontaneous polarization of Ps > 35 nC?cm-2.
7. The method as claimed in claim 3, wherein the FLC mixture exhibits a spontaneous polarization of Ps > 35 nC?cm-2.
8. The method as claimed in claim 1, wherein the FLC mixture exhibits a spontaneous polarization of Ps > 40 nC?cm-2.
9. The method as claimed in claim 2, wherein the FLC mixture exhibits a spontaneous polarization of Ps > 40 nC?cm-2.
10. The method as claimed in claim 3, wherein the FLC mixture exhibits a spontaneous polarization of Ps > 40 nC?cm-2.
11. An FLC display for SSFLC technology having a layer thickness of 1 to 10 µm, containing an FLC mixture having a high spontaneous polarization of Ps > 20 nC?cm-2 and a natural helical pitch of less than one half of the layer thickness of the FLC display.
12. The FLC display as claimed in claim 11, which display is subjected to electrical pulsed addressing.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3920625.4 | 1989-06-23 | ||
| DE3920625A DE3920625A1 (en) | 1989-06-23 | 1989-06-23 | FERROELECTRIC LIQUID CRYSTAL ELEMENTS WITH HIGH SPONTANEOUS POLARIZATION AND LOW HELIXGANGHOEHE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2019652A1 true CA2019652A1 (en) | 1990-12-23 |
Family
ID=6383436
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002019652A Abandoned CA2019652A1 (en) | 1989-06-23 | 1990-06-22 | Ferroelectric liquid crystal components having high spontaneous polarization and low helical pitch |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0404081B1 (en) |
| JP (1) | JP2825318B2 (en) |
| KR (1) | KR0176700B1 (en) |
| CA (1) | CA2019652A1 (en) |
| DE (2) | DE3920625A1 (en) |
| NO (1) | NO902795L (en) |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE59009675D1 (en) * | 1989-06-29 | 1995-10-26 | Hoffmann La Roche | Bistable ferroelectric liquid crystal display. |
| US5539555A (en) * | 1990-07-20 | 1996-07-23 | Displaytech, Inc. | High contrast distorted helex effect electro-optic devices and tight ferroelectric pitch ferroelectric liquid crystal compositions useful therein |
| DE4143139A1 (en) * | 1991-12-28 | 1993-07-01 | Hoechst Ag | CHIRAL OXIRANYLMETHYL ETHER AND THEIR USE AS DUTIES IN LIQUID CRYSTAL MIXTURES |
| JPH05297375A (en) * | 1992-04-20 | 1993-11-12 | Hoechst Japan Ltd | Ferroelectric liquid crystal mixture and display element constituted by using this mixture |
| JPH05297376A (en) * | 1992-04-20 | 1993-11-12 | Hoechst Japan Ltd | Ferroelectric liquid crystal display element |
| JPH06123888A (en) * | 1992-10-09 | 1994-05-06 | Canon Inc | Liquid crystal element |
| DE69522494T2 (en) * | 1994-04-14 | 2002-04-25 | Canon K.K., Tokio/Tokyo | Liquid crystal composition, display device and method using the same |
| US6022492A (en) * | 1995-12-28 | 2000-02-08 | Hoescht Research & Technology Deutchland Gmbh & Co. | Difluorophenyl pyrimidyl pyridine derivatives and the use thereof in liquid crystal mixtures |
| DE59706003D1 (en) * | 1996-11-21 | 2002-02-21 | Rolic Ag Zug | Bistable ferroelectric liquid crystal cell |
| DE19652252A1 (en) * | 1996-12-16 | 1998-06-18 | Hoechst Ag | 1,3-difluoronaphthalene derivatives and their use in liquid crystalline mixtures |
| DE19652247A1 (en) * | 1996-12-16 | 1998-06-18 | Hoechst Ag | 5,7-difluoro-1,2,3,4-tetrahydronaphthalene derivatives and their use in liquid-crystalline mixtures |
| DE19653009A1 (en) * | 1996-12-19 | 1998-06-25 | Hoechst Ag | 6-fluorophenanthridine derivatives and their use in liquid-crystalline mixtures |
| DE19748440B4 (en) * | 1997-11-03 | 2006-01-19 | Aventis Research & Technologies Gmbh & Co Kg | 6,7-Difluoro-1,2,3,4-tetrahydronaphthalene derivatives and their use in liquid-crystalline mixtures, liquid-crystal mixtures containing them and ferroelectric switching and / or display devices |
| DE19748819A1 (en) | 1997-11-05 | 1999-05-06 | Hoechst Ag | Fluorinated derivatives of phenanthrene and their use in liquid crystal mixtures |
| CN100343365C (en) * | 2002-12-07 | 2007-10-17 | 默克专利股份有限公司 | Liquid crystal medium and liquid crystal display with a highly twisted structure |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6463931A (en) * | 1987-03-20 | 1989-03-09 | Hitachi Ltd | Liquid crystal optical modulation device |
| EP0283916B1 (en) * | 1987-03-20 | 1993-12-29 | Hitachi, Ltd. | Liquid crystal light-modulating device imparted with memory effect and display unit utilizing same |
| EP0309774B1 (en) * | 1987-09-18 | 1992-11-19 | F. Hoffmann-La Roche Ag | Ferroelectric liquid-crystal cell |
-
1989
- 1989-06-23 DE DE3920625A patent/DE3920625A1/en not_active Withdrawn
-
1990
- 1990-06-20 DE DE59010096T patent/DE59010096D1/en not_active Expired - Fee Related
- 1990-06-20 EP EP90111598A patent/EP0404081B1/en not_active Expired - Lifetime
- 1990-06-21 KR KR1019900009125A patent/KR0176700B1/en not_active IP Right Cessation
- 1990-06-22 NO NO90902795A patent/NO902795L/en unknown
- 1990-06-22 CA CA002019652A patent/CA2019652A1/en not_active Abandoned
- 1990-06-25 JP JP2166543A patent/JP2825318B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0404081A2 (en) | 1990-12-27 |
| JPH0338623A (en) | 1991-02-19 |
| KR910001431A (en) | 1991-01-30 |
| KR0176700B1 (en) | 1999-05-01 |
| EP0404081A3 (en) | 1991-09-18 |
| EP0404081B1 (en) | 1996-01-31 |
| NO902795D0 (en) | 1990-06-22 |
| DE3920625A1 (en) | 1991-01-03 |
| NO902795L (en) | 1990-12-27 |
| DE59010096D1 (en) | 1996-03-14 |
| JP2825318B2 (en) | 1998-11-18 |
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