IL44425A - Nematic mixtures with positive dielectric anisotropy - Google Patents

Description

Nematic Mixtures with positive Dielectric The invention relates to mixtures with positive dielectric Nematic compounds are as dielectrics in devices in order to convert electrical potential pulses into optically perceptible in Λ preferred type of device which employs such nematic compounds is a liquid crystal cell with homogeneous for example a twisted nematic cell located between parallel or crossed such as described in Applied Physics Letters 10 197 pages 127 128 and in German Of t 2 202 For these nematic compounds or mixtures with positive dielectric are that is nematic compounds or mixtures for which the dielectric constant in the direction parallel to the direction of the molecular clusters is greater than that at angles Preferred nematic compounds or tures are those in which the difference between these two dielectric constants referred to as has a value of at least Nematic compounds or mixtures with positive dielectric anisotropy are German schrift 2 202 555 describes a nematic mixture with this which consists of from 3 to parts by weight of a and from 97 to 60 parts by weight of a mixture of from 20 to parts by weight of diamine and 20 to arts by weight of p The use of as nematic compounds with positive dielectric anisotropy is described in Applied Physics Letters volume 10 1971 pages Although at least some o these known nematic compounds with positive dielectric anisotropy form nematic within broad and advantageously located temperature that is at or below room their suitability for use in technical applications is very Being they are so sensitive to moisture that a partial hydrolysis takes place merely on handling in the sence of normal atmospheric The products of this lower the electrical of the dielectric and hence substantially impair the functioning of the devices produced Other known nematic compounds with dielectric anisotropy as described in German Of 2 234 522 certain acid Whilst these compounds possess sufficient chemical they only have a narrow temperature range for the nematic and this temperature range is so high that optical devices using these must be and thermostatically when in Nematic materials containing azoxybenzcnes benzoic acid phenyl esters are and excellent chemical stability and also nematic hases in broad and advantageously located tem these materials either have a or only a small dielectric sotropy 2 and be used as dielectrics in liquid crystal cells with homogeneous Bri tish In Patent Specification we have descriVjed and claimed compounds of the in which is a alkyl or alkoxy group with 1 to 7 carbons or a alkanoyloxy group to 7 carbon is a alkyl or alkoxy group with 1 to 7 carbon atoms and n is 0 1 or 2 provided that in the compounds which only contain two aromatic rings the radicals R and together contain at least carbon and the radical is not capronyloxy if is an Bri tish Patent alkoxy 1 have also described a nematic mixture which comprises at compound of formula as defined optionally together with one or more other nematic or nematogenic Reference shall be made Bri tish Patent for further We have now found that certain nematic tures which contain one or more benzoic acid phenyl esters of the formula wherein A is or carbonyloxy and and R are the same or different and are or alkoxy with from 1 to 8 carbon are and the position and breadth of the temperature range of the nematic of the mixture is not tially changed from that of the benzoic acid phenyl These mixtures display a distinct positive dielectric anisotropy can be used as dielectrics in liquid crystal cells with homogeneous According to the invention there is provided a neniatic mixture with positive dielectric which at least one nematic compound of the formula wherein A is azoxy or and which may be the same or are alkyl or alkoxy groups from 1 to 8 carbon and at least one compound of the X R Y wherein X is a alkyl group having from to 9 carbon or a dialkylamino group having cyano from 2 to carbon Y is a or trifluororaethyl group and R is a divalent group of the Binar mixtures consisting one compound of formula and one compound of formula or in a molar of or and ternary mixtur consisting in a molar ratio of two compounds of formula and one compound of formula or or of one compound of formula and two rounds of formula are disclosed German Offenlegungsschr 2024269 and not included in the present That enlegungsschrift 2024269 neither anticipate nor suggest the object of the present According to Offenlegungsschrift liquiu crystalline mixtures are wherein the position the breadth of the temperature range of the mesophase differs considerably from those properties of the In contrast in the mixtures according to the present vention the position and the breadth the temperature mixtures to at least one of the and which may be the or are or groups hav g 1 to 8 carbon The of one or of formula a mixture according to the invention reduces changes in the properties of the nematic of formula may be caused by of the mixture the in to the of tempera re of e nemat c Preferred nematic mixtures according to the invention contain to 99 more from to b weight of at least one nematic pound of formula and from 35 to 1 more preferably from to 5 weight of at least one compound of 2 When the mixtures according to the invention additionally contain a compound of formula 3 they preferably consist of from 20 to 95 more preferably from to 80 by weight of at least one compound of formula from 3 to 65 more preferably from 10 to by weight of a compound of formula 2 and from 2 to 27 more preferably from 10 to 25 by weight of at least one compound of formula The invention further comprises a method for preparing a nematic mixture of the which comprises mixing at least one nematic of formula with at least one compound of 2 with one or more compounds of formula 3 The nematic mixtures according to the invention are particularly suitable for use as dielectrics in liquid crystal cells with homogeneous Thus the invention comprises a method of preparing a liquid crystal cell with homogeneous which comprises introducing a nematic mixture according to the invention into a cell taining two electrodes spaced from to 25 microns The invention also com rises a li uid cr stal cell with homogeneous which comprises a liquid crystal layer from 8 to preferably from 10 to microns consisting of a nematic mixture according to the the nematic compounds of formula which inherently display a or only a very weakly positive dielectric form nematic mixtures with a markedly positive tric anisotropy and a advantageously nematic as a result of the addition of even a small amount of one or more compounds of formula The compounds of formula at most form an enantiotropic nematic within a very narrow temperature but in most cases are not crystalline or are only monotropically The nematic compounds of formula in the mixtures of the invention are Preferred compounds and mixtures of compounds of formula wherein Λ is an azoxy are for in German Offenlegungsschriften and Preferred compounds of wherein A is a carbonyloxy are for in British Patent German Offenlegungsschrift and Nematic mixtures with positive dielectric anisotropy which can be used particularly successfully as in twisted nematic cells contain at least one compound of formula in which at least one of the rou s is a alk rou Preferred mixtures according to the invention contain one or of the following yb and In the above mentioned azoxybenzene the term is used to include the structural elements and for also embraces the isomeric compound and any mixture these Further preferred compounds for use in a nematic mixture of the invention are as acid acid acid acid acid acid acid acid acid acid c V enyl cnzoic acid hen l ester acid acid acid acid acid ester acid ester acid acid acid acid tylphenyl acid acid l acid anisic acid anisic acid anisic acid anisic acid anisic acid anisic acid anisic acid anisic acid o acid acid oic acid acid acid ester acid acid acid 4 acid acid 4 acid 4 acid 4 acid ylphenyl acid 4 acid 4 acid 4 ester acid 4 acid acid 4 acid 4 and acid Particularly preferred nematic mixtures of compound of formula which are used to form a ture according to the by addition of one or more compounds of formula one or more compounds of formula and and and 4 4 and 4 4 and 4 and 4 and and and 4 4 anisic acid ester and acid acid ester and acid acid ester and acid anisic acid ester and anisic acid ester and acid compounds of formula are either described in the literature or can be prepared in a manner to that described in the literature for the preparation of analogous for the can be obtained from the corresponding lines by and reaction with aqueous potassium cupricyahide the benzoic acid phenyl esters are for by reaction of a benzoic acid halide with a substituted alkali and can be prepared by alkylation of or with a meth l halide ethyl are for reaction of acids with sulphur tetrafluoride biphonyls are for by reactio of acid with sulphur tetrafluoride to give followed by reduction of the latter to li which is then alkylated with methyl halides ethyl halideso of suitable compounds of formula for use in a mixture of the invention are as oic acid acid oic acid acid acid ester acid acid lphenyl acid acid acid acid acid acid acid acid acid acid acid acid luoromethylbenzoic acid acid acid acid acid 4 acid and acid lphenyl Preferred compounds of formula for use in the invent on are those in which X is dime th lamino or if has the structure or is with to 0 carbon and Y is C aminobenzoic acid acid and especially acid and acid butylphenyl ester are particularly The relative amounts of the components of the nematic mixtures according to the invention are determined by the sign and magnitude of the dielectric anisotropy of the of formula by the desired magnitude of the positive dielectric and by the desired melting points in by the desired clear points of the mixtures according to the when the compound of formula or a mixture of two or more already has a positive but small dielectric it occasionally sufficies to add from 1 to 3 by weight of a compound of formula in order to obtain a mixture with a usable tive dielectric Where the compound of formula or mixture thereof has a distinct negative dielectric a mixture according to the prepared may contain to 35 weight of a compound of formula In even larger amounts of the compounds of formula can be as a result of adding such a large amount of a or only monotropically the clear point is generally lowered to such an extent that the usefulness of the thus obtained is The clear points of the nernntic mixtures according to the have positive dielectric anisotropy and consist of at least one compound of formula and at least one compound of formula 2 are as a rule lower than the clear points of the or mixtures of of formula which are For mixtures in which the o clear point is stxll at least 10 C above room this generally has no adverse effect on the usefulness of the mixtures according to the if a higher clear point is the lowering of the clear point caused by the addition of compounds of formula 2 can be compensated by also adding to the mixture a compound of formula 3 13y this the effect of of formula 2 in lowering the clea point can be sufficiently pensated such that even mixtures with up to as much as 5 by weight of compounds of formula 2 are usable in technical The disubstituted benzoyloxybenzoic acid esters of formula 3 described in German Bri ti sh Patent Offenlegungsschri t 2 139 628 1 can be prepared analogously to other compounds of this the preparation of which is in these These compounds are clear points ally above possess a moderately high positive dielectric The following pounds of formula examples of suitable compounds for use in nematic mixtures according the acid 4 este acid 4 ester acid 4 ester acid 4 acid 4 acid 4 este benzoyloxy acid 4 acid 4 lphenyl acid 4 acid 4 acid 4 acid acid 4 acid 4 acid acid 4 ester l and ben o o o c ac d Preferred compounds of formula are those wherein at least one of the groups and is a preferably with from to 8 carbon especially The ing have been found to be particularly suitable compounds of formula acid acid and acid The compounds of formula can be added to a neinatic mixture consisting of at least one compound of formula and at least one compound of formula to raise the clear point of these as noted The amount required for this purpose depends primarily on the value of the clear of the mixture of compounds of formulae and and on the desired of the clear point of the final If the clear point is only to be raised it is as a rule sufficient to add a pound of formula in an amount of from 3 to 10 by weight of resulting to produce a greater shift in clear point it may be desirable to prepare a mixture with up to 27 by weight of one or more compounds of formula In even larger amounts of a compound of formula can be the upper limit determined by the solubility of the compound of formula in the of the compounds of the and as a the nematic mixture should contain not than 10 to 25 by weight of one or more compounds of since otherwise the viscosity of the mixture increases to such an extent that a liquid crystal cell with homogeneous containing such a mixture displays lengthened switch The nematic mixtures according to the invention may be used in a known manner as dielectrics in liquid crystal cells with homogeneous Since the liquid crystals possess a particularly steep characteristic transparency or opacity to as a function of the applied they are cularly suitable for use in electronic indicator elements in multiplex for example for matrix displays based on twisted nematic For this the mixtures accordin to the invention are introduced in a known for example by means of an injection into the filling orifice or orifices of suitable electrode Suitable electrode arrangements as a rule consist of two transparent electrodes arranged at a distance of from 8 to preferably from 10 to 20 microns from one which have been pretreated by rubbing with a polishing cloth or by with a grinding paste so that they impose an at least predominantly homogeneous orientation on adjoining nemutic These electrodes are connected in a but electrically insulating at the for example by so that they form a cell with at least one filling orifice for a After filling the cell with a nematic mixture according to the the filling orifice or orifices is or are sealed and a crystal cell with homogeneous orientation is thus Such cells can be used for the production of electronic indicator logic circuit ponents or optical If the electrodes are so arranged that the preferred direction of the molecule of the nematic material in the immediate vicinity of one electrode is twisted through relative to that in the immediate vicinity of the other the arrangement represents a twisted In the latter particular embodiment of a crystal cell with homogeneous the advantageous properties of the nematic mixtures according to the invention manifest themselves icularly In order that the be more fully the following examples of nematic mixtures according to the invention are given by way of illustration In the the tions are given as percentages by As well the the dielectric anisotropy the clear point and in some the thresho potential using the mixture in twisted cell with a layer thickness of microns at are also The points of all the mixtures in the Examples are below Exam 1 Example 2 Example 3 acid ester Δε Example 9 acid ester Δε Example 10 acid 4 ester Δε Example 11 acid 4 ester acid ester Δε Example anisic acid ester acid ester acid ester acid ester Δε Example anisic acid ester acid ester acid ester yl acid ester Δε Example 14 acid ester acid ester ester acid 4 ester acid ester acid 4 ester Δε Ug Example 16 anisic acid ester xybenzoic acid ester acid ester acid acid ester Δε Ug Example 17 anisic acid ester y acid ester acid ester acid ester acid ester Δε Example 18 anisic ester acid ester acid ester acid ester acid 10 0 19 35 anisic acid acid ester 13 acid 4 ester acid ester 15 acid 4 ester Δε Example 20 17 anisic acid ester acid ester acid 4 ester acid 4 ester acid ester 10 Δε 12 Example 21 31 anisic acid ester 15 acid ester 15 acid ester acid ester acid 10 acid ester Δε Example 22 anisic acid ester acid ester acid 4 ester acid 4 ester acid ester Δε 1 Example 23 anisic acid 21 acid ester acid ester 15 acid ester Δε Example 24 anisic acid ester 21 ester 15 15 acid ester 5 acid ester Δε U Example acid ester Δε Example 26 acid ester Δε Example 27 acid ester Δε Example 28 acid ester acid ester acid 4 ester acid butylphenyl Ug E β 5ί acid ester acid 4 ester acid 4 phenyl ester acid phenyl ester Ug Example 30 acid ester acid 4 ester acid phenyl ester acid phenyl ester The Example which follows illustrates the use of a nernatic according to the invention as a dielectric in a liquid crystal cell homogeneous Two 1 thick glass plates of size 1 10 x 100 which were both covered on one in the longitudinal with an micron thick strip pattern of tin dioxide 2 wide strips at intervals of 5 from one each 3trip being provided with an electrical lead at the upper were with a soft cotton cloth on the coated from the electrical leads in the direction of the Λ plate pretreated in this way was then placed oh a with the coated and rubbed side facing upwards A 100 x 100 of 20 microns thick and 2 mm wide polyethylene strips was then placed on the plate so that the edge with the electrical leads remained The second glass plate was then with the coated side facing on to the first plate carrying the mask so that the strips on the second plate were at right angles to on the first The with the mask located between were glued leaving a filling orifice for the dielectric open on each o two opposite The outer faces of the plates were covered with a polarisation trie direction of polarisation of which was parallel to the strips on the particular plate and thus the two directions of polarisation were at right angles to one After the adhesive had the arrangement was by means of an injection with ml of a nctnatic mixture according to one of tho preceding Examples Λ display based on the nernatic cell thus obtained was transparent so long as no potential If a potential of about 3 volts was applied to the individual leads of the two the section points of the corresponding strips became dark when viewed by transmitted insufficientOCRQuality

Claims (1)

1. WHAT CLAIM Λ ncmatic mixture with positive dielectric which at least one nematic compound of tho wherein A is or carbonyloxy arid which be the or different are alkyl or alkoxy groups having from 1 to 8 carbon atoms and at least one compound of the X Y wherein X is a alkyl group having from to or a dialkylamino group having cyano from 2 to carbon Y is a nitro or group and is a divalent group of the A nematic mixture according claim which consists of from to by weight of at least one nematic compound of formula from 10 to by weight of at least one compound of formula and from 10 to by weight of at least one compound of formula A nematic mixture according to any one of claims 1 to which contains at least one compound of formula in which X is dimethylamino if has the structure or X is with from to 8 carbon and Y is A nematic mixture according to claim in which the at least one compound of formula is one or more of acid ester and butylphenyl mixture according to any one of claims 1 to which contains at least one nematic compound of formula wherein at least one of the groups R and ll is a alkyl A nematic mixture according to claim wherein the nematic compound of formula is 11 A nematic mixture according to claim wherein the nematic compound of formula is anisic ester acid Λ netnatic mixture according to any of claims 1 to which contains at least one compound formula wherein at least one of the groups and is a alkyl group from to 8 carbon nematic mixture according to claim wherein the compound of formula is yl benzoic acid acid acid or two or more Λ method for preparing a nematic mixture as claimed in claim which comprises least one nematic compound of formula at least one compound o formula Λ method according to claim for preparing a nematic mixture as claimed in claim wherein one or more compounds of formula are mixed with the compounds of formula and formula Λ method of preparing a liquid crystal cell with homogeneous which comprises ducin a nematic as claimed in any one of claims 1 to into a cell containing two transparent electrodes spaced 8 to microns Λ liquid crystal cell with homogeneous which contains a layer from 8 to microns thick of a nematic mixture according to any one of 1 to A liquid crystal cell according to claim wherein the liquid crystal layer is from 10 to 20 microns Λ nematic mixture according to claim substantially as herein described in any of Examples 1 to A liquid crystal substantially as herein described in insufficientOCRQuality