United States Patent
`Matsuo et al.
`[451 Nov. 30, 1976
`
`[111 3 3,994,567
`
`[19]
`
`ELECTRO-OPTICAL CELL FOR FIELD
`EFFECT TYPE LIQUID CRYSTAL DISPLAY
`Inventors: Makoto Matsuo; Takashi Toida,
`both of Chiba; Ichiro Tsunoda,
`Kawasaki, all of Japan
`
`Assignee: Dai Nippon Insatsu Kabushiki
`Kaisha, Tokyo, Japan
`Nov. 28, 1975
`
`Filed:
`
`Appl. No.: 635,880
`
`Foreign Application Priority Data
`Dec. 4, 1974
`Japan ............................ .. 49-139852
`
`U.S. Cl......................... .. 350/160 LC; 252/299;
`'
`428/1
`Int. Cl.’ .......................................... .. G02F 1/13
`Field of Search ................. .. 350/160 LC; 428/1
`
`[54]
`
`[75]
`
`[73]
`
`[22]
`[21]
`
`[30]
`
`[52]
`
`[51]
`[58]
`
`[56]
`
`References Cited
`UNITED STATES PATENTS
`350/160 LC
`2/1975
`Katagiri et al. ..,
`.. . .. 350/160 LC
`10/1975
`Sprokel . . .. . .
`
`3/1976 Harsch ..... ..
`. 350/160 LC X
`3/1976
`Saeva et al. ................ .. 350/160 LC
`
`3,864,021
`3,912,366
`3.941.901
`3,947,184
`
`3,955,881
`
`5/1976 Yaguchi et al.
`
`350/160 LC
`
`Primary Examiner—Edward S. Bauer
`Attorney, Agent, or Firm——Spensley, Horn, and Lubitz
`
`ABSTRACT
`[57]
`An electro-optical cell comprises, on an optical path,
`a pair of electrode base plates and a nematic liquid
`crystal material having a positive dielectric anisotropy
`and sandwiched between the electrode base plates,
`each of which comprises a transparent base plate hav-
`ing an inner surface, an electrode film provided on the
`inner surface, and a polyimide resin film orientated in
`one direction and provided on the inner surface over
`the electrode film, the electrode base plates being mu-
`tually disposed on opposite sides of the liquid crystal
`material with their respective polyimide resin films on
`their inner sides in mutually facing state with the ori-
`entated direction of one polyimide resin film intersect-
`ing that of the other as viewed along the optical path.
`An advantageous feature of this electro—optical cell is
`that the electrode base plates thereof has durable and
`heat-resistant orientation which can impart a uniform,
`initial alignment of ample strength to the liquid
`crystal.
`
`15 Claims, 2 Drawing Figures
`
`
`
`II~\\\\:s?
`K.\\\\//.\\(
`
`Page 1 of 10
`
`Tianma Exhibit 1021
`
`Page 1 of 10
`
`Tianma Exhibit 1021
`
`

`
`tHetaP.3U
`
`Név. 30-, 1976
`
`3,994,567
`
`Page 2 of 10
`
`

`
`‘ ELECTRO-OPFICAL CELL FOR FIELD EFFECT
`TYPE LIQUIDCRYSTAL DISPLAY ,
`BACKGROUND OF THE INVENTION
`
`5
`
`This invention relates to an electro-optical cell for
`liquid crystal display of (electric) field effect type (FE
`tYPe)-
`There are two principal types of display apparatus for
`converting electrical signals into visible information by
`utilizing the optical anisotropy of a liquid crystal. One
`of these is the DS type (for example, as disclosed in
`British Pat. No. l,l67,486) in which a dynamic scatter-
`ing phenomenon wherein a nematic liquid crystal mate-
`rial having negative dielectric anisotropy scatters light
`upon the application of an electric field is utilized for
`displaying. The other type is the FE type (for example,
`as disclosed in Japanese Laid Open Application No.
`l I737/l972) in which a nematic liquid crystal material
`having a positive dielectric anisotropy is interposed and
`clamped between a pair of electrode base plates whose
`surfaces have been orientated in mutually intersecting
`directions thereby to impart optical rotation (a helical
`structure beingiimparted to the liquid crystal mole-
`cules), and this optical rotation is caused to vary by the
`application of a suitable electric field and thus utilized
`for displaying.
`‘
`'
`.
`The latter apparatus of FE type has such features as
`lower voltage operation,
`lower power consumption,
`and longer serviceable life compared with the former
`DS type and, for this reason, has wide utility in applica-
`tions such as various displays and optical shades. In a
`DS type display device, uniformity of the initial align-
`ment of the liquid crystal is not absolutely necessary
`from the point of view of operational principle, but in
`an FE type display device, according to its operational
`principle, the initial alignment ‘of the liquid crystal is
`controlled or realigned by the electric field, and the
`resulting variation of an optical property is utilized, and
`for this reason, the uniformity of the initial alignment of 40
`the liquid crystal (i.e., the uniformity of the—alignment
`when no electric field is applied) is especially impor-
`tant..
`,
`Heretofore, various attempts have been made to
`improve the uniformity of this initial alignment of a
`liquid crystal. These attempts, however, cannot be
`considered to have been completely successful in all
`cases. According to the results of -our research, this
`may be attributed to the reasons set forth below.
`First, as a measure known heretofore for obtaining
`uniformity of the initial alignment, of a liquid crystal,
`there isha method wherein_ the electrode base plates are
`rubbed in one direction by a material such as cloth, but
`by this method, alignments of liquid crystal molecules
`differ locally, and the uniformity of alignment is not
`sufiicient. Furthermore, the alignment is lost within a
`short time.
`
`50
`
`_
`55
`
`45
`
`According to another method intended to solve the
`above described problems, a surface-active agent (sur-
`factant) of a certain kind is additionally used, and the
`electrode base plates are rubbed in» one direction (as
`disclosed, for example in IBM Technical Disclosure
`Bulletin Vol. 13, N0. ll, Apr. l97l). While the uni-
`formity of alignment is improved to a certain extent by
`this method, the surfactant does not possess heat resis-
`tance and, furthermore, gives..rise to deterioration of
`the liquid crystal material. Then, when an electric field
`is applied, the surfactant decomposes because of the
`
`65
`
`1
`
`3,994,567
`
`2
`electric field and undergoes deterioration, and the ori-
`entation is destroyed. A further difficulty is that if, in
`the fabrication of an electro-optical cell after orienta-
`tion of the electrode base plates, a substance of high
`softening temperature such as, for example, polyvinyli-
`dene fluoride, is used as the sealing material for bond-
`ing the pair of electrode base plates, orientation will be
`lost by the heating temperature at the time of sealing.
`Furthermore, a method wherein, for example, the
`electrode base plates are inclined relative to an evapo-
`ration deposition material source, and a material such
`as silicon oxide or magnesium fluoride is deposited by
`evaporation thereby to accomplish orientation (re-
`ferred to as “inclined evaporation orientation method"
`for convenience).is known (as disclosed, for example,
`in U.S. Pat. No. 3,834,792) but is accompanied by the
`problem of weak alignment energy.
`With the object of obtaining an electro-optical cell in
`which the above described various difficulties accom-
`panying the known electro-optical cells for FE type
`liquid crystal displaying are overcome, we have carried
`out studies, as a result of which we have made certain
`findings as set forth below. This invention is based on
`these findings._
`
`SUMMARY OF THE INVENTION
`It is an object of this invention to provide an electro-
`optical cell provided with electrode base plates to
`which an orientation effect with an orientation agent of
`excellent durability and heat resistance has been af-
`forded for imparting a uniform, initial alignment of
`ample strength to the liquid crystal. ‘
`‘ As a result of our studies, we have found thata pair
`of electrodebase plates having an orientated polyimide
`resin film causes excellent initial alignment of the liquid
`crystal interposed therebetween, and, moreover, the
`polyimide resin film has excellent heat resistance, dura-
`bility, and dissolution resistance, whereby, by using
`these electrode base plates, an excellent electro-optical
`cell for FE type liquid crystal displaying can be pro-
`duced.
`-
`
`Accordingly, the electro-optical cell of this‘invention
`for achieving the above stated object is characterized
`by an organization wherein a pair of electrode base
`plates, ’each comprising a transparent base plate, an
`electrode- film provided on one surface of the base
`, plate, and an orientated polyimide resin film provided
`over the surface of the base plate having the electrode
`film, are so disposed on an optical path with their poly-
`imide resin films on their inner sides facing ‘each other
`that the directions of orientation of their polyimide
`resin films intersect as viewed along the optical path,
`and a nematic liquid crystal material having positive
`dielectric anisotropy is sandwiched between the elec-
`trode base plates.
`As a result of the provision of the polyimide film as
`described above as an orientation agent, the photoelec-
`tric cell of this invention has excellent optical charac-
`teristics such as visibility angle, contrast, and response
`and, at the same time, possesses durability and heat
`resistance. Moreover, an advantageous feature of the
`electro-optical cell of this invention is that almost any
`kind of nematic liquid crystal material having positive
`dielectric anisotropy can be used therewithin as a liquid
`crystal material for displaying. Accordingly, this inven-
`tion makes possible the use of biphenyl liquid crystal
`materials, which, while possessing excellent stability,
`could not be fully used heretofore because of their
`
`Page 3 of 10
`
`

`
`3
`properties of strong dissolving characteristic and diffi-
`culty in orientating. In this case, the excellent ability of
`achieving initial alignment of the liquid crystal and
`solvent resistance of the orientated polyimide resin film
`are remarkably exhibited, whereby a reliable electro-
`optical cell of high stability imparted thereto by the
`biphenyl liquid crystal material is obtained.
`The nature, utility, and further features of the inven-
`tion will be apparent from the following detailed de-
`scription, beginning with a consideration of general
`aspects of the invention and concluding with specific
`examples of practice illustrating preferred embodi-
`ments of the invention, when read in conjunction with
`the accompanying drawing.
`BRIEF DESCRIPTION OF THE DRAWING
`
`_
`
`3,994,567
`
`5
`
`4
`characters or a pictorial pattern. In these patterns, of
`course, the electrode film can beleft remaining in a
`part thereof or at the periphery thereof.
`Next, in accordance with this invention, a polyimide
`resin film is formed on one part including the electrode
`film or the entire surface of each base plate 5 (or 8)
`having the transparent electrode film.
`The term “polyimide resin” as herein used is in-
`tended to mean any polymers containing recurring
`imide bonds in the main chain thereof and include
`polyimides containing recurring imide bonds, polya-
`mide-imides containing recurring amide bonds and
`imide bonds, and polyesterimides containing recurring
`ester bonds and imide bonds.
`
`.
`In the drawing
`FIG. 1 is a simplified, exploded perspective showing
`diagrammatically the essential organization of the elec-
`Vtro-optical cell of this invention; and
`FIG. 2 is a fragmentary, longitudinal section showing
`the assembled structure of an electro-optical cell of the
`invention.
`
`DETAILED DESCRIPTION
`
`Referring first to FIG. 1 showing, in exploded per-
`spective view, the essential elements of the electro-op-
`tical cell according to this invention, the cell 1 of the
`invention comprises, basically, a pair of electrode base
`plates 2 and 3 and a liquid crystal material 4 interposed
`therebetween, all in parallelly stacked alignment. The
`electrode base plate 2 comprises a base plate 5, an
`electrode film 6 disposed on the inner surface of the
`base plate 5, and a polyimide resin film 7 disposed on
`the inner side of the electrode film 6, that is, between
`the electrode film 6 and the liquid crystal material 4.
`Similarly, the electrode base plate 3 comprises a base
`plate 8, an electrode film 9 on the inner surface of the
`base plate 8, and a polyimide resin film 10 on the inner
`side of the electrode film 9.
`.
`The polyimide resin films 7 and 10 are respectively
`orientated, and the electrode base plates 2 and 3 are so
`disposed that the orientated directions 11 and 12 of
`these polyimide resin films 7 and 10 intersect each
`other. At least one lead wire (not shown) is connected 45
`to each of the electrode films 6 and 9 for applying
`voltage thereto. While the orientated directions of the
`pair of electrode base plates may be any other than
`parallel directions, it is perferable that their angle of
`intersection be 90° from various considerations such as 50
`visibility angle, contrast, and response. It will be obvi-
`ous that the actual construction of the electro-optical
`cell, illustrated in exploded view of FIG. 1, is one in
`which the elements thereof are in closely laminated
`arrangement as illustrated by one example in FIG. 2.
`It is necessary that the above mentioned two base
`plates 5 and 8 have insulating property and be transpar-
`ent. Examples of materials suitable for these base plates
`are glass and transparent synthetic resins. On the inner
`surface of each of these plates, a transparent electrode
`film 6 (or 9) is formed by an ordinary process. For
`example, a transparent electro-conductive film such as
`a film composed principally of tin oxide, indium oxide,
`or the like can be formed by a process such as a spray-
`ing process or a vacuum evaporation deposition pro-
`cess. Each of these electrode films is worked by a pro-
`cess such as photo-etching to impart thereto a specific
`pattern such as, for example, one or more numerals or
`
`Polyimide resins as defined above are constituted by
`polymers having imide bonds and, in general, are insol-
`uble in solvents. For this reason, it is preferable,
`in
`order to form the polyimide resin film on a base plate in
`this invention, to resort to the process of dissolving a
`polyamic acid, which is a precursor of the polymers
`constituting the polyimide resins, in a solvent described
`hereinafter, applying the resulting solution as a coating
`on the base plate, and thereafter heat treating the film
`thereby to cause dehydration and ring closure and
`cause the film to acquire imide bonds.
`A polyamic acid as a precursor of the above men-
`tioned polyamide-imides is synthesized by polyaddition
`of a carboxylic acid anhydride and an oligodiamine
`obtained from an excessive diamine and a dicarboxylic
`acid.
`~
`
`A polyamic acid as a precursor of the above men-
`tioned polyester-imides is synthesized by polyaddition
`of a carboxylic acid dianhydride having an ester group
`and a diamine.
`'
`
`The above mentioned carboxylic acid dianhydride
`having an ester group is obtained from, for example,
`trimellitic acid and one of various diols.
`‘
`- A polyamic acid as a presursor of the above men-
`tioned polyimides in their narrower sense, is synthe-
`sized by polyaddition of a carboxylic acid dianhydride
`and a diamine.
`These polyaddition reactions are carried out under
`ordinary conditions, that is, under an anhydrous condi-
`tion and a temperature of 50° C or less.
`Examples of the above mentioned diamine are: m-
`phenylenediamine, p-phenylenediamine, m-xylenedia-
`mine,
`p-xylenediamine,
`.4,4’-diaminodiphenylether,
`4,4'-diaminodiphenylmethane,
`3,3’-dimethyl-4,45
`diaminodiphenylmethane, 3,3’, 5,5’-tetramethyl-4,45
`diaminodiphenylmethane, 2,2’-bis
`(4-aminophenyl)—
`propane-4,4’—methylenedianiline,
`benzidine,
`4,4'-
`diaminodiphenylsulfide, 4,4'—diaminodiphenylsulfone,
`1,5-diaminonaphthalene, 3,3’-dimethylbenzidine, 3,3’-
`dimethoxybenzidine, 2,4-bis(B-amino—tertbutyl)
`tolu-
`ene, bis(4-B-amino-tert—butylphenyl)ether, and 1,4-
`bis(2-methyl-4-aminopentyl)benzene.
`Examples of the above mentioned diols are: hydro-
`quinone, bisphenol A, dichlorobisphenol A,
`tetra-
`chlorobisphenol A, tetrabromobisphenol A, bisphenol
`F, bisphenol ACP, bisphenol L, bisphenol V, bisphenol
`S, and 4,4’-dihydrophenylether.
`Examples of the above mentioned carboxylic acid
`dianhydride are: pyromellitic anhydride, 2,3,6,7-naph-
`thalenetetracarboxylic anhydride, 3,3',4,4'-diphenyl-
`tetracarboxylic
`anhydride,
`1,2,5,6—naphthalenetet-
`racarboxylic
`anhydride,
`2,2’,3,3’-diphenyltetracar-
`boxylic anhydride,
`thiophene-2,3,4,5-tetracarboxylic
`anhydride,
`2,2—bis-
`(3,4—biscarboxyphenyI) propane
`
`Page 4 of 10
`
`

`
`5
`anhydride,
`3,4-dicarboxyphenylsulfone
`anhydride,
`perylene-3,4,9,10—tetracarb0xylic anhydride, bis(3,4-
`dicarboxyphenyl) ether anhydride, and 3,3’,4,4’-ben-
`zophenonetetracarboxylic anhydride.
`For the above specified diamines, diols, and carbox-
`ylic dianhydrides, aromatic compounds are preferable
`in all cases on the point of heat resistance.
`A polyamic acid prepared in this manner can be
`coated on a substrate base material by dissolving the
`polyamic acid in a solvent such as dimethylformamide,
`dimethylacetamide, dimethylsulfoxide, and N-methyl-
`pyrolidone to form a solution of from 0.0l- to 40-per-
`cent concentration and applying this solution by a
`method such as brush painting, dipping, spin coating,
`or- spraying. After coating, the coating film is heat
`treated and dried at a temperature of from 100° to 350°
`C, preferably from 200° to 300° C thereby to form a
`polyimide resin film on the substrate base material.
`The thickness of this polyimide resin film is con-
`trolled to be from 0.01 to 50 microns, preferably from
`0.1 to 5 microns. We have found that a film thickness
`less than 0.01 micron results in weak orientation power
`and a film thickness greater than 50 microns results in
`difficulty in producing a uniform coating and in deteri-
`oration of electrical response.
`The orientation processing of this polyimide resin
`film can be carried out by a method such as, for exam-
`ple, by rubbing in a constant direction by means of a
`material such as a cloth or a brush. This orientation can
`be carried out in any direction relative to the electrode
`pattern of each electrode in accordance with factors
`such as the visibility angle and is not limited to a direc-
`tion parallel to an edge of the electrode base plate as
`indicated in FIG. 1.
`
`In the forming of a film of an orientation processed
`polyimide resin film on the surface of a base plate con-
`taining the electrode film, infiltration of electric charge
`from the electrode part can be eliminated and the con-
`sumption of electrical power reduced by forming be-
`forehand a film of a thickness of 0.01 to 100 microns
`consisting of a polyorganosilane on the surface of the
`base plate containing the electrode film. In the forming
`of this film of a polyorganosilane on the electrode base
`plate surface containing the electrode film, the mono-
`mer or prepolymer of the organosilane is dissolved in a
`solvent such as n-hexane, benzene, toluene, or xylene
`thereby to prepare a solution of a concentration of
`from 0.1 to 20 percent. This solution is applied as a
`coating on the above mentioned base plate surface by
`any of the ordinary coating methods named above and
`then heated thereby to‘ polymerize the organosilane
`and, at the same time, to dry the coating film by evapo-
`rating off the solvent.
`An organosilane suitable for use according to this I
`55
`invention comprises one organosilane or a mixture of
`two or more organosilanes which is represented by the
`general formula RnSiX,,_,, (n=1,2,3).
`In this formula, X is a halogen such as chlorine, an
`alkoxy group such as a methoxy group or an ethoxy
`group, an acyloxy group such as an acetoxy group, or
`another hydrolyzable functional group. Furthermore,
`the group R in this formula is a saturated aliphatic
`hydrocarbon group such as methyl or ethyl, an unsatu-
`rated aliphatic hydrocarbon group such as vinyl or an
`alkenyl group, or an aromatic hydrocarbon group such
`phenyl. A hydrogen atom of these hydrocarbon groups
`may substituted by an unsaturated group such as vinyl
`or an alkenyl group, hydroxyl, carbonyl, a halogen
`
`65
`
`50
`
`3,994,567
`
`6
`. group such as chlorine, bromine, or fluorine, or an-
`other functional organic group. Examples of the groups
`thus substituted are chloromethyl, y,'y,y-trifluoropro-
`pyl, and -‘y-aminopropyl.
`In the above formula, the groups represented by X of
`the number (4-n)‘and the group represented by R of
`the number n may respectively be the same or differ-
`ent.
`
`In the above described manner, the pair of electrode
`base plates provided with orientated polyimide resin
`films are so disposed that their respective polyimide
`resin films are on their inner sides, and that they face
`each other with their orientated directions in mutually
`intersecting state. For example,
`the electrode base
`plates are maintained apart by a constant distance by
`means such as a spacer interposed therebetween, and
`the periphery is bonded and fixed by a sealing material
`comprising a spacer and/or an adhesive.
`Examples of materials suitable for use as the above
`mentioned sealing material are organic materials such
`as polyester’ resins, epoxy resins, polyamide resins,
`acrylic resins, polyimide resins, polyethylene, fluorore-
`sins, vinyl chloride resins, vinyl chloride-vinyl acetate
`copolymers, a-polyolefin resins, polyethylene waxes,
`microcrystalline waxes, and like single polymers, co-
`polymers, and mixtures thereof and inorganic materials
`such as low-melting—point glasses. In addition,
`if an
`electrical insulative layer is interposed, materials such
`as indium andvarious solder materials can be used.
`
`By dispersing beforehand in this sealing material, in a
`quantity of from 30 to 400 percent by weight relative to
`the sealing material, a drying agent such as silica gel,
`magnesia, activated alumina, or anhydrous copper sul-
`fate,
`infiltration of moisture into the interior of the
`electro-optical cell can be prevented, and the liquid
`crystal material thus sealed can exhibit its desirable
`characteristics over a long time.
`For installing the sealing material, a method such as
`that wherein a sealing material of frame skeleton film is
`installed or that wherein an ink composition containing
`the above mentioned material as its principal ingredi-
`ent is printed by a method such as the silk-screen print-
`ing method can be used.
`Of the sealing materials mentioned above, an inor-
`ganic material is one which has desirable features such
`as tight sealing performance and little effect on the
`liquid crystal. However, since a high temperature is
`required at the time of sealing, it has been difficult to
`use such an inorganic material as a sealing material of
`an electro-optical cell employing an electrode base
`plate to which a known orientation agent has been
`applied. However, a polyimideiresin used in this inven-
`tion, though depending on the kind thereof, is capable
`of withstanding a high temperature of the order of 300°
`to 450° C and does not lose its orientation effect even
`at high temperatures, whereby it has made possible the
`use of inorganic materials such as glass frit, which re-
`quire sealing at high temperature. For this reason, it is
`possible by thepractice of this invention" to fabricate an
`electro-opticalicell with excellent tight-sealing prop-
`erty.
`After the pair of electrode base plates have been
`caused to adhere and be fixed by way of the above
`mentioned sealing material by a measure such as heat
`pressure bonding of the pair of electrode plates, a ne-
`matic liquid crystal material having a positive dielectric
`anisotropy is poured through a pouring port provided
`beforehand, for example, in a part of a base plate or a
`
`Page 5 of 10
`
`

`
`3,994,567
`
`8
`
`R10-@—CN = N-©R2
`
`7
`sealing part. Then the pouring port is sealed by using a
`material such as a low melting point metal or a material’
`selected from those enumerated above as sealing‘mate-
`rials, whereupon the electro-optical cell of this inven-
`tion is obtained. Alternatively, the liquid crystal mate-
`rial is caused to drip onto one electrode base plate and
`is sandwiched between that electrode base plate and
`the other electrode base plate with a spacer interposed
`therebetween, and then the resulting laminate structure
`is sealed.
`The above mentioned liquid crystal material may be
`a single compound or a composition. A single com-
`pound or a composition which, as a whole, has a posi-
`.tive dielectric anisotropy (that
`is, a characteristic
`wherein the dielectric constant along the direction of
`the major axis of the molecules is greater than the
`dielectric constant in the direction perpendicular to the
`direction of the major axis of the molecules) is used.
`For this nematic liquid crystal material, a single ne-
`matic liquid crystal compound comprising one member
`of nematic liquid crystal compound having a positive
`dielectric anisotropy (referred to as Np liquid crystal
`compounds) or a composition comprising at least one
`member of Np liquid crystal compounds and at least
`one nematic liquid crystal compounds having a nega-
`tive dielectric anisotropy (referred to as Nn liquid crys-
`tal compounds) and, as a whole, exhibiting a positive
`dielectric anisotropy is used. In this connection, a liq-
`uid crystal material of a composition comprising two or
`more constituents gives a wide range of operational
`temperature of the display element, and is therefore
`desirable.
`Examples of Np liquid crystal compounds suitable for
`use as set forth above, are for example, as follows:
`anils:
`p-alkoxybenzylidene-p'-cyanoaniline
`repre-
`sented by the general formula
`
`5 R1: C,,,H2,,,+,, m = 1 to 6, R2: C,,,’Hz,,,+,, m’ = 3 to 7);
`biphenyls: p-alkyl-,p-alkoxy-,p-(p-alkylphenyl)-, or
`p-(p-alkoxy phenyl) -p’-cyanobiphenyl represented by
`the general formula
`
`"'-‘~<§>*@°N
`
`(A3 CmH2m+1s CmH2m+ 10.
`
`'—@>‘ Cm'H2m'+1’ '@ 0Cm'H2m'+1’
`
`m+4to 15. m'=2to 24)
`azoxybenzenes: p-alkyl-p’-alkylazoxybenzene repre-
`sented by the general formula
`
`: R1<§>g=N@R2
`
`(R1, R2-' n'CmH2m+la "1 = 4 to 7);
`benzoates: p—cyanophenyl—p’-n-alkylbenzoate repre-
`sented by the general formula
`
`R -@—cooN
`
`(R: C,,,H2,,,+,, m = 3 to 8); 13-Cyanophenyl-p'-alkox-
`ybenzoate represented by the general formula
`
`Rd-©-coo @—cN
`
`Ro<@-CH = N-@-cu
`
`to 7); p-alkoxyphenyl—p'-
`(R: C,,,H2,,,+,, m = 4
`cyanobenzoate represented by the general formula
`
`(R: n — C,,.H2,,,+,, m = 1 to 8); p-alkylcarboxybenzyli-
`dene-p’-cyanoaniline represented by the general for-
`mula
`O
`H
`RCO ._@—cH = N-@-CN
`
`to 6); p-alkylbenzylidene-p’-
`(R: n-C,,,H2,,,+1, m = 1
`cyanoaniline represented by the general formula
`
`R—@- CH = N@—CN
`
`(R: n — C,,,Hz,,,+,, m = 3 to 6); p—cyanobenzylidene-p’-
`alkoxyaniline represented by the general formula
`
`NC _©cH = ‘N—©-on
`
`(R: N—C,,,H2,,.+,, m = 1 to 8); p-cyanobenzylidene-p'-
`alkylaniline represented by the general fonnula
`
`NC-<‘:-)>-OH = N-<:)>-R
`
`(R: n — C,,.H2,,,...,, m = 3 to 6); and p-alkoxybenzyli-
`dene-p’-alkylaniline represented by the general for-
`mula
`‘
`’
`
`Nc—©—coo -@— OR
`(R: C,,.H2,,.+,, m = 4 to 7); and p-alkylphenyl-p’-
`cyanobenzoate represented by the general fonnula
`
`NC- COO©-R
`(R: C,,,H2,,.+,, m = 4 to 8); and
`azo-compounds: p-cyano-p'-alkoxyazobenzene rep-
`resented by the general formula
`
`Nc—©N = N—@oR
`(R: C,,,H2,,.+,, m = 4 to 7).
`,
`Examples of Nn liquid crystal compounds are p-
`methoxybenzylidene—p'-n—butylaniline
`and p-ethox-
`ybenzylidene-p’-n-butylaniline. These compounds are
`used in a liquid crystal composition having a positive
`dielectric anisotropy as a whole by adding thereto at
`least one Np liquid crystal compound which exhibits a
`great positive dielectric anisotropy.
`The uniformity of the initial alignment of this ne-
`matic liquid crystal material having a positive dielectric
`anisotropy can be further improved by adding thereto
`an optically active compound such as a cholesteryl
`
`Page 6 of 10
`
`

`
`3,994,567
`
`9
`compound, or a biphenyl derivative, phenylbenzoate
`derivative, benzylideneaniline derivative, or azoxyben-
`zene derivative having an optically active substituent in
`a quantity of from 0.01 to 5 percent by weight with
`respect to the nematic liquid crystal material. Desirably
`this additive quantity is of an order of from 0.0l to 2
`percent by weight which will not change the optical
`characteristics of the display device.
`An electro-optical cell of this invention fabricated as
`described above not only has excellent durability and
`heat resistance but, as a result of remarkably improved
`initial alignment of the liquid crystal, has particularly
`excellent electro-optical characteristics such as con-
`trast, visibility angle, and response
`Because of the use therein of a polyimide resin film as
`an orientation agent, the above described electro-opti-
`cal cell of this invention possesses the advantageous
`feature of not being limited in the kind of liquid crystal
`material for displaying. For this reason it is also possi-
`ble to use, as a liquid crystal material for displaying,
`biphenyl lieuqi crystal materials comprising or contain-
`ing one or more biphenyl
`liquid crystal compounds
`selected from p-alkyl-, p-alkoxy-, p-(p-alkylphenyl)—,
`and p-(p—a|koxyphenyl)-p’-cyanobypenyls represented
`by the general fomiula
`
`A@@°“
`(where A: c,.H.,..+..c..H.m+.o.
`
`‘
`
`or .@>. ocm.
`.©_cm-Hm+1 .
`H 2,,.:+,; m = 4 to 15 (preferably m = 5 to 9); and
`m’ = 2 to 24).
`The use of these biphenyl liquid crystals materials has
`been desired because they are compounds having very
`high stability when compared with other nematic liquid
`crystal materials. However, because of their high dis-
`solving power, these biphenyl liquid crystal easily im-
`pair the orientation agent or cause difficulty in align-
`ment by the aforementioned method of rubbing each
`electrode base plate in one direction with a material
`such as cloth or the aforementioned inclined evapora-
`tion orientation method. For these and other reasons,
`these biphenyl liquid crystals heretofore could not be
`fully utilized.
`On the basis of the characteristics possessed by the
`polyimide resin film used therein, particularly the sol-
`vent resistance, and excellent ability of aligning the
`liquid crystal, the electro-optical cell of this invention
`makes possible the use of biphenyl liquid crystal mate-
`rials as liquid crystal materials for displaying. In the use
`of biphenyl liquid crystals as liquid crystals materials
`for displaying in accordance with this invention, com-
`positions containing one or more kinds of the above
`mentioned biphenyl compounds and, in addition, Np
`and/or Nn liquid crystal compounds other than biphe-
`nyl compounds or compositions comprising one or
`more of these biphenyl compounds are used. In all
`cases, it is desirable that an optically active compound
`be added similarly as described hereinbefore. Further-
`more, when, within the above mentioned biphenyl
`compound, a triphenyl compound (which is classified
`in biphenyl compounds herein) is addedias one part
`thereof in a quantity of the order of less than 5 percent
`by weight relative to the entire nematic liquid crystal
`
`10
`material, the nematic region becomes wider, particu-
`larly nematicisotropic transition temperature being
`raised, which is a desirable result.
`‘
`» The electro-optical cell of this invention as described
`-above can be effectively used in combination with a
`, polarizer such as a linear polarizing plate or a circular
`polarizing plate, a reflecting plate, and the like to con-
`stitute a liquid-crystal displaying device of field effect
`type and thereby advantageously applied to a wide
`variety of displaying apparatuses such as electronic
`desk-top calculators, various time pieces, and counter
`display panels.
`In order to indicate more fully the nature and utility
`of this invention, the following examples of practice
`constituting preferred embodiments of this invention
`together with comparison examples are set forth,
`it
`being understood that these examples are presented as
`illustrative only and that they are not intended to limit
`the scope of the invention. Throughout these examples
`and comparison examples, quantities expressed in
`“parts" are parts by weight.
`EXAMPLE 1 .
`
`’
`
`An aromatic carboxylic acid dianhydride obtained
`from trimellitic acid and hydroquinone, and 4,4’-
`diaminodiphenylether were polyadded to produce a
`polyamic acid which is a precursor of polyester-imide.
`A 2-percent solution of this polyamic acid in me-
`thylacetamide was prepared. Pieces of glass for elec-
`trode base plates which had electroconductive films of
`indium oxide were etched with specific patterns and
`then washed by an ordinary method thereby to produce
`two pairs of electrode base plates, which were then
`immersed in the above mentioned solution. After this
`
`these electrode base plates were heat
`immersion,
`treated at 200° C for 1 hour and caused to undergo
`dehydration and ring closure, and a polyester-imide
`film was thus formed on each electrode base plate.
`Then each of this electrode base plates provided with
`the polyester-imide film was orientated by rubbing in
`one direction with a cloth. Thereafter, the two plates of
`each pair of these plates thus orientated were bonded
`and fixed with their surfaces coated with the polyester-
`imide film on the inner sides and facing each other and
`with their respective orientated directions at right an-
`gles to each