GB2063287A - Liquid Crystal Materials Incorporating Benzoate Ester Derivatives and Liquid Crystal Devices Incorporating such Materials - Google Patents
Liquid Crystal Materials Incorporating Benzoate Ester Derivatives and Liquid Crystal Devices Incorporating such Materials Download PDFInfo
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- GB2063287A GB2063287A GB7934125A GB7934125A GB2063287A GB 2063287 A GB2063287 A GB 2063287A GB 7934125 A GB7934125 A GB 7934125A GB 7934125 A GB7934125 A GB 7934125A GB 2063287 A GB2063287 A GB 2063287A
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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
- C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
- C09K19/42—Mixtures of liquid crystal compounds covered by two or more of the preceding groups C09K19/06 - C09K19/40
- C09K19/44—Mixtures of liquid crystal compounds covered by two or more of the preceding groups C09K19/06 - C09K19/40 containing compounds with benzene rings directly linked
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Abstract
A liquid crystal mixture suitable for a multiplexed twisted nematic effect device comprises a nematic liquid crystal material having a high positive dielectric anisotropy and including at least one 4-n-alkyl- or 4- n-alkoxy-4-cyanobiphenyl together with at least one laterally substituted benzoate ester compound having a structure formula: <IMAGE> where X1 and X2 are H or F, at least one being F, and wherein R1 is either an n-alkyl or n-alkoxy group, and Z is either <IMAGE> where R2 is an alkyl group, or <IMAGE> where R3 is an alkyl, alkoxy, alkanoyloxy or alkoxycarbonyloxy group.
Description
SPECIFICATION
Liquid Crystal Materials Incorporating Esters of Substituted Phenols and Liquid Crystal Devices
Incorporating such Materials
This invention relates to liquid crystal materials incorporating esters of substituted phenols and to liquid crystal devices incorporating such materials.
Liquid crystal devices are commonly formed by sandwiching a layer typically 7 to 1 2,um thick, of a liquid crystal material between optically transparent electrically insulating substrates, eg glass slides.
Electrode structures on the substrates enable voltages to be applied across the layer and change the molecular arrangement of the liquid crystal molecules in selected regions. This causes an observable effect in those regions which can be used in displays of various types, for example, digital watches, small calculators, voltage meters, etc.
There are several different display effects which may be obtained from electrical re-arrangement of liquid crystal molecules. These depend on the liquid crystal material employed and the initial molecular alignment (if any). This invention is concerned particularly with the twisted nematic effect in which an essentially nematic material is arranged in its OFF state (zero or low applied voltage) in an arrangement in which the molecules gradually twist, usually through 900, from one substrate surface to the other as defined by fixed alignments at these surfaces. Such an arrangement is optically active, ie rotates the plane of polarised light in this state.An applied voltage greater than a threshold essentially causes the twist to be destroyed so that the molecular arrangement is no longer optically active. Thus, when placed between plane (linear) polarisers a twisted nematic effect device provides one or more optical shutters which are switchable from a light state to a dark state or vice versa depending on whether the polarisers are in a parallel or cross relationship.
Such shutters may in a single device form the component elements of a series of letters, words or numerals, ie in an information display, as defined by the electrode structures on the substrates and the applied volfages. An example of a twisted nematic effect device is further described in UK Patent
Number 1,478,592.
One method of arranging the electrodes and applying the voltages in a liquid crystal display is called multiplexing. This involves applying electric potentials to lines of electrodes connected in series, each region or display element, eg each individual shutter in a twisted nematic effect display, being defined by the intersection of the electrodes on the two substrates Examples of multiplexed displays are the matrix displays described in UK Patent Number 1 458,045.
One of the major problems concerned with multiplexed displays is that all electrodes in the display receive a non-zero electrical potential, even when they are in the OFF state. Consequently it is difficult to provide sufficient contrast between the ON and OFF states. The contrast can vary with viewing angle, temperature and liquid crystal material as well as applied voltage. As described in UK
Patent Application Number 36595/78 and 40580/73' a figure of merit which may be used to define the usefulness of any given material in a multiplexed twisted nematic effect display is the parameter
M20. This is the ratio, at 200 C, ol voltages V10(00); V,,(450) which are voltages which may be designated as necessary to achieve the ON and OFF states respectively.In fact V10(00) is the minimum voltage required to achieve along an axis normal to the display substrates 10% of the maximum light transmission along that axis for a twisted nemaric effect cell: the incident light is plane polarised parallel'to the surface alignment of the liquid crystal molecules upon which the light is first incident and the analyser is arranged with its polarising axis perpendicular to that alignment and parallel to the surface alignment of the molecules from which the light emerges.
V,,(450) is the maximum voltage which gives along an axis at a viewing angle of 450 to the alignment directions on the substrate surfaces 90% of the maximum transmission along that direction for the same cell for which Vl0I0 ) is measured. Of the four possible directions which are at 450 to the alignment directions the direction having the lowest value of V90(45 ) is chosen.
An ideal material would have M20 equal orjust greater than unity so that a very small change in applied voltage could be used to switch between the OFF and ON states. In practice, other liquid crystal properties, eg the temperature range of the nematic mesophase, have to be taken into account as well.
Materials based on the cyanobiphenyls and terphenyls as described in UK Patent Number
1,433,130 have found wide use in twisted nematic effect displays and have an excellent range of properties for many purposes. However, it is not easy to achieve multiplexing with such materials because they show relatively high values of M20. For example the well known material E7 marketed by
BDH Chemicals Limited of Broom Road, Poole, Dorset, has a value of 1.81 for M20.
UK Patent Application Nos 36595/78 and 40580/78 describes how the value of M20 may be reduced by the addition of benzoate esters of the form
R,R'=alkyl or alkoxy (..,.formula (I) (as described and claimed in USA Patent No 4,002,670) to mixtures of cyanobiphenyls and cyanoterphenyls or other compounds having similar properties.
According to the present invention in a first aspect a liquid crystal mixture suitable for a multiplexed twisted nematic effect device comprises a nematic liquid crystal material having a high positive dielectric anisotropy and including at least one 4'-n-alkyl- or 4'-n-alkoxy cyanobiphenyl together with at least one laterally substituted benzoate ester compound having a structural formula:
Where R, is an alkyl, preferably n-alkyl group;
Where Z is either
R2=Alkyl, preferably n-alkyl, or
R3=Alkyl, alkoxy, alkanoyloxy or alkoxycarbonyloxy, whose alkyl group is preferably an n-alkyl group
and where X1 and X2 represents H or F, at least one of X1 and X2 being F.
Preferably R, and R2 L or R, and R3 together contain less than 16 carbon atoms in total.
Preferably, the said cyanobiphenyl(s) contains 5 or less carbon atoms in its n-alkyl or n-alkoxy group.
The mixture may also contain one or more compounds analogous to cyanobiphenyls eg of the form
=bic/clo(2,2,2) octane), eg 0 to 50% by weight; R' and R"=n-alkyl.
The mixture may aiso include up to 25% by weight of one or more nematic compounds having at least three benzene or other rings as well as a terminal cyans group in their structure. The following compounds are suitable::
(preferably 0 to 10% by weight); R3=n-alkyl or n-alkoxy (preferably 0 to 15% by weight);
R4=n-alkyl (preferably 0 to 15% weight);
R5=n-alkyl (preferably 0 to 5% by weight); R6=n-alkyl or n-alkoxy (preferably O to 1 5% by weight);
R7-n-alkyl The fluoro-substituted ester or esters of formula (II) above preferably comprise from 10 to 90%, typically 40-50%, by weight of the mixture according to the first aspect although if the mixture also includes other compounds of low or negative dielectric anisotropy, eg one or more esters of formula (i) above, these figures relate to the total weight percentages of the compounds of formula IIIJ plus such other compounds.
It has been found that fluoro-substituted benzoate esters as defined in formula (ll) above can significantly reduce the value of M20 of high dielectric anisotropy cyanobiphenyls and terphenyls when added to them. Although the reduction obtained is similar in magnitude to that obtained by a similar addition of non-laterally substituted esters of formula (I) above the compounds of formula (II) (either alone or mixed with the compounds of formula (I) or other compounds having similar properties) are
superior in that generally they have a more negative dielectric anisotropy which usefully affects M20 in
mixtures.
According to the present invention in a second aspect a liquid crystal twisted nematic effect device includes two dielectric substrates at least one of which is optically transparent, electrodes on the inner surfaces of the substrates in an arrangement such as to provide a multiplexed display, a nematic liquid crystal material between the substrates with a twisted molecular arrangement and characterised in that the nematic liquid crystal material is a mixture according to the second aspect as defined above.
The device of the second aspect may be arranged between crossed, or parallel, linear polarisers.
A reflector may be located adjacent to one polariser so that the display may be observed by reflected light. The reflector may be only partly reflecting and a tungsten light (or other suitable light source) arranged to illuminate the display through the reflector as required.
Compounds of Formula II may be produced by methods as described in a copending UK patent application. One of these methods may be summarised as follows.
The preparation route is:
Examples of devices and materials embodying the invention will now be described by way of
example only with reference to the accompanying drawings wherein:
Figure 1 is a sectional view of a digital display;
Figure 2 is a sectional view of Figure 1;
Figure 3 shows a rear electrode configuration for Figure 1;
Figure 4 shows a front electrode configuration for Figure 1;
Figures 5, 6, 7 show schematic views of the device of Figures 1 to 4 with typical addressing voltage.
The display of Figures 1 to 4 comprises a cell 1, formed of two, front and back, glass slides 2, 3
respectively, spaced 7 ,um apart by a spacer 4 all held together by an epoxy resin glue. In front of the
front glass slide 2 is a front polariser 5 arranged with its axis of polarisation axis horizontal. A reflector
7 is arranged behind a back polariser 6 behind the slide 3.
Electrodes 8, 9 of tin oxide typically 1 ooA thick are deposited on the inner faces of the slides 2,3 as a complete layer and etched to the shapes shown in Figures 3, 4. The display has seven bars per
digit 10 plus a decimal point 11 between each digit As shown in Figure 3 the rear electrode structure
is formed into three electrodes xç, x2, X3. Similarly the front electrode structure is formed into three
electrodes per digit and decimal point1, y2,y3.... Examination of the six electrodes per digit shows
that each of the eight elements can independently have a voltage applied thereto by application of
suitable voltage to appropriate x, y electrodes.
Prior to assembly the electrode clear slides 2, 3 are cleaned then dipped in a solution of 0.2% by
weight of polyvinyl alcohol (PEA) in water. When dry, the slides are rubbed in a single direction with a soft tissue then assembled with the rubbing direction orthogonal to one another and parallel to the optical axis of the respective adjacent polarisers. When a nematic liquid crystal material 12 is
introduced between the slides 2, 3 the molecules at the slide surfaces lie along the respective rubbing
directions with a progressive 90 twist between the slides.
When zero voltage is applied to the cell 1 light passes through the front polariser 5, through the cell 1 (whilst having its plane of polarisation rotated 90 ) through its rear polariser 6 to the reflector 7 where it is reflected back again to an observer, (shown at an angle of 450 to the axis Z normal to axes X
and Y in the plane of the slides 2, 3). When a voltage above a threshold value is applied between the electrode 8, 9 the liquid crystal layer 12 loses its rotary power, or optical activity, the molecules being
re-arranged to lie perpendicular to the slides 2, 3, ie along the axis Z. Thus light at that position does not reach the reflector 7 and does not reflect back to the observer who sees a dark display of one or
more bars of a digit 10.
Voltages are applied as fotlows as shown in Figures 5, 6 and 7 for three successive time intervals.
An electric potential of 3V/2 is scanned down each x electrode in turn whilst -V/2 is applied to the remaining x electrodes. Meanwhile3V/2 or V/2 is applied to the y electrodes. A coincidence of 3V/2 and -3V/2 at an intersection results in a voltage 3V across the liquid crystal layer 12. Elsewhere the voltage is V or-V. Thus by applying -2V/2 to appropriate y electrodes as 3V/2 is scanned down the x electrodes selected intersections are turned ON as indicated by solid circles. The electric voltage V is an ac signal of eg 100 Hz square wave, and the sign indicates the phase.
Each OFF intersection receives V for the entire scan period whilst each ON intersection receives 3
V for one third of the scan period and V for the rest of the scan period making an rms value of 1.91 V.
Thus the material of layer 12 preferably has M20 less than 1.91 to give a reasonable contrast between the ON and OFF states.
For similar displays having more than three rows of electrodes the figure of 1.91 V is reduced accordingly.
Suitable nematic mixtures for use to form the layer 12 in the above device are described below.
Small amounts of a cholesteric material may be added to the nematic material to induce a preferred twist in the molecules in the liquid crystal layer. This and the use of appropriate slide surface treatment removes the problems of display patchiness as taught in UK Patent Serial Number 1,472,247 and 1,478.592. Suitable cholesteric materials are:
C 15 about 0.1 to 0.5% by weight and CB 15 about 0.01 to 0.05% by weight.
The following mixtures are examples of nematic materials embodying the invention which may be used in the above device. In the properties of the mixtures
M20 is as defined above
M'20 is a similarly measured ratio but is the voltage required to give 50 XG transmission at an angle of 100 to the normai to the twisted nematic cell divided by the voltage
this is another figure of merit for the multiplexibility of a material in twisted nematic operation: a typical value for a mixture of cyancbiphenyls alone is 1.36 (for the material E7); n is the birefringence of the material measured at 20 C and at 589 nm;
1 (#V/#T) V is the percentage change of voltage V per CO over a temperature range in the range of OOC to 400 C; N
I is the nematic-to-isotropic liquid transition temperature; Tress is the time required to switch the twisted nematic cell ON (from 100 to 10% transmission) using the stated voltage; and Toeeay is the time required to switch the cell OFF (from O to 90% transmission) using the stated voltage.
Mixture 1
Component Weght Yo c2H5 +( FCN 15 c4H9( CN 23 n-C5H%CN 10 C2H5 X c0o Thffoo CN 12 n-C4H9 4}OGX CO CH2C5H11-n 40 F Properties of Mixture 1 I N-l=560C (54.6580C) ii M20=1 .69 iii M'20=1 .29 iv #n=0.146 1 #V v ( ) from 0-30 C=0.53% per C for V90(45 ); 0.67% per
V #T C for V50 (10 ) and 0.65% per C for V10(0 ) as defined above
vi #RISE=194 msec for a voltage of 2V and 75msec for a
voltage of 3 V at 20 C
vii #DECAY=57 msec for a voltage of 2 V and 67msec for a voltage of 3 V at 20 C
Properties (ii) to (vii) were measured in a twisted nematic cell having an average liquid crystal layer thickness of 6.6 Fm.
Mixture 2
Component Weight % C2H5 ffThOOCN 15 n-C49ffThQ0 CN 23 n-C5+) < C N 10 C2H5IH ThffOOCN 12 n-HC0O CgHlln 40 Properties of Mixture 2 i N-I=39 C (37.5-41.0 C)
ii M20=1.66 iii M'20=1.29 1 #V iv ( )=0.67% per C for V90 (45 )0.79% per C for V50(10 );; and
V #T 0.87% per C for V10(0 ) from 0#20 C v #RISE=179 m secs at 2 volts rms at 20 C and
79 m secs at 3 volts rms at 20 C
vi #DECAY=88 m sec at 2 volts rms at 20 C and
103 m secs at 3 volts rms at 20 C
Properties (ii) to (vi) were measured in a twisted nematic cell having an average liquid crystal layer thickness of 6.2, m.
Mixture 3
Component Weight % Weight % C2H5 X CN 15 n- C4H9 EN 23 Mixture 3 (cont.).
Component Weight % n-C5 nflMŏo C N 10 C2H5{i}COO XCN 12 n-HC0 CH1fn 40 Properties of Mixture 3
i N-I=61 C (59.8#62.0 C) 1 #V ii ( )=0.46 for V90(45 )0.63 for V50(10 ) and
V #T 0.65 forV10(0 ) in units of % per C over the range 0"40 C
iii M20=1.74 iv M'20=1.33 v #TRISE=132 msec at 3 V rms at 20 C and 360 msec at 2 V rms at 20 C
vi #DECAY=98 msec at 2 V rms at 20 C and
118 msec at 3 V rms at 20 C Properties (ii) and (vi) were measured in a twisted nematic cell having a liquid crystal average layer thickness of 6.6 m.
The values of M20 and M'20 obtained for Mixtures 1 to 3 illustrate the improvement in multiplexibility achieved by the addition of compounds of formula (II) to cyanobiphenyls.
Mixture 4
Weight % C2Hs XCN 15 n- C4H9mȮQ CN 23 (OCN COO XCN 12 n-C5#mC 10 F n-CSH11- C3H7 40 Properties of Mixture 4 N-l=57 C (54.4 59.0)
ii M2o=1.72 iii M'20=1 .32 v iv ( )=0.7 1 for V,0 (00); 0.66 for V50 (100) and
V AT 0.58forV90(450)from 100C-1300C v ThISE=68 msec; zDECAy=69 msec; at 200 C; 3 V TRISE=1 79 msec zDEcAY=55 msec; at 200C; 2 V
Claims (7)
1. A liquid crystal mixture suitable for a multiplexed twisted nematic effect device comprises a nematic liquid crystal material having a high positive dielectric anisotropy and including at least one 4n-alkyl- or 4-n-alkoxy- 4-cyanobiphenyl together with at least one laterally substituted benzoate ester compound having a structure formula
where X, and X2 are H or F, at least one being F, and wherein R, is either an n-alkyl or n-alkoxy group and Z is either
where R2 is an alkyl group or
where R3 is an alkyl, alkoxy, alkoxycarbonyloxy or alkanoyloxy group.
2. A mixture as claimed in claim 1 and wherein the said ester compound is
3. A mixture as claimed in claim 1 and wherein the said ester compound is
4. A mixture as claimed in claim 1 and wherein the said ester compound is
5. A mixture as claimed in claim 1 and wherein the said ester compound is
6. A mixture as claimed in claim 1 and substantially the same as any one of Mixtures 1 to 4 as hereinbefore described.
7. A liquid crystal twisted nematic effect device including two dielectric substrates at least one of which is optically transparent, electrodes on the inner surfaces of the substrates in an arrangement such as to provide a multiplexed display, a nematic liquid crystal material between the substrates with a twisted molecular arrangement and characterised in that the nematic liquid crystal material is a mixture as claimed in any one of claims 1 to 6.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7934125A GB2063287A (en) | 1979-10-02 | 1979-10-02 | Liquid Crystal Materials Incorporating Benzoate Ester Derivatives and Liquid Crystal Devices Incorporating such Materials |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7934125A GB2063287A (en) | 1979-10-02 | 1979-10-02 | Liquid Crystal Materials Incorporating Benzoate Ester Derivatives and Liquid Crystal Devices Incorporating such Materials |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2063287A true GB2063287A (en) | 1981-06-03 |
Family
ID=10508226
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7934125A Withdrawn GB2063287A (en) | 1979-10-02 | 1979-10-02 | Liquid Crystal Materials Incorporating Benzoate Ester Derivatives and Liquid Crystal Devices Incorporating such Materials |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2063287A (en) |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4357078A (en) * | 1980-01-30 | 1982-11-02 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | Liquid crystal compounds containing an alicyclic ring and exhibiting a low dielectric anisotropy and liquid crystal materials and devices incorporating such compounds |
| US4368135A (en) * | 1979-07-18 | 1983-01-11 | Bbc, Brown, Boveri & Company, Ltd. | Anisotropic compounds with negative or positive DC-anisotropy and low optical anisotropy |
| US4400061A (en) * | 1980-01-30 | 1983-08-23 | Her Majesty's Government of the UK. | Liquid crystal ester compounds exhibiting a low or negative dielectric anisotropy and liquid crystal materials and devices incorporating such compounds |
| US4406814A (en) * | 1981-04-10 | 1983-09-27 | Eaton Corporation | Liquid crystalline materials and optical displays utilizing same |
| US4548731A (en) * | 1982-05-17 | 1985-10-22 | Chisso Corporation | 2,4-Difluorobenzene derivatives |
| US4551280A (en) * | 1982-10-30 | 1985-11-05 | Dainippon Ink And Chemicals, Inc. | Nematic liquid crystalline compounds |
| US4551264A (en) * | 1982-03-13 | 1985-11-05 | Merck Patent Gesellschaft Mit Beschrankter Haftung | Polyhalogenoaromatic compounds for liquid crystal compositions |
| US4664840A (en) * | 1979-05-28 | 1987-05-12 | E. Merck | Liquid crystal compounds |
| GB2193839A (en) * | 1986-04-14 | 1988-02-17 | Thermalloy Inc | Heat sink clip assembly |
-
1979
- 1979-10-02 GB GB7934125A patent/GB2063287A/en not_active Withdrawn
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4664840A (en) * | 1979-05-28 | 1987-05-12 | E. Merck | Liquid crystal compounds |
| US4368135A (en) * | 1979-07-18 | 1983-01-11 | Bbc, Brown, Boveri & Company, Ltd. | Anisotropic compounds with negative or positive DC-anisotropy and low optical anisotropy |
| US4357078A (en) * | 1980-01-30 | 1982-11-02 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | Liquid crystal compounds containing an alicyclic ring and exhibiting a low dielectric anisotropy and liquid crystal materials and devices incorporating such compounds |
| US4400061A (en) * | 1980-01-30 | 1983-08-23 | Her Majesty's Government of the UK. | Liquid crystal ester compounds exhibiting a low or negative dielectric anisotropy and liquid crystal materials and devices incorporating such compounds |
| US4406814A (en) * | 1981-04-10 | 1983-09-27 | Eaton Corporation | Liquid crystalline materials and optical displays utilizing same |
| US4551264A (en) * | 1982-03-13 | 1985-11-05 | Merck Patent Gesellschaft Mit Beschrankter Haftung | Polyhalogenoaromatic compounds for liquid crystal compositions |
| US4548731A (en) * | 1982-05-17 | 1985-10-22 | Chisso Corporation | 2,4-Difluorobenzene derivatives |
| US4551280A (en) * | 1982-10-30 | 1985-11-05 | Dainippon Ink And Chemicals, Inc. | Nematic liquid crystalline compounds |
| US4673756A (en) * | 1982-10-30 | 1987-06-16 | Dainippon Ink And Chemicals, Inc. | Nematic liquid crystalline compounds |
| GB2193839A (en) * | 1986-04-14 | 1988-02-17 | Thermalloy Inc | Heat sink clip assembly |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |