(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2001/0046570 A1
`Gibbons et al.
`(43) Pub. Date:
`NOV. 29, 2001
`
`US 20010046570A1
`
`(54) PHOTOSENSITIVE POLYIMIDES FOR
`OPTICAL ALIGNMENT OF LIQUID
`CRYSTALS
`
`(76)
`
`Inventors: Wayne M. Gibbons, Bear, DE (US);
`Patricia A. Rose, Wilmington, DE
`(US); Paul J. Shannon, Exton, PA
`(US); Hanxing Zheng, Wilmington, DE
`US
`(
`)
`
`Correspondence Address:
`ELSICON, INC.
`DELAWARE TECHNOLOGY PARK
`5.100 INNOVATION WAY
`NEWARK, DE 19711 (US)
`
`(21) Appi. No;
`
`09/739,937
`
`(22)
`
`Filed:
`
`Dec. 19, 2000
`
`Related US, Application Data
`
`Continuation-in-part of application No. 09/618,193,
`filed on Jul. 18, 2000, Which is a division of appli-
`Cation No. 09/221,295, filed on Dec. 23, 1998, now
`Pat. No. 6,103,322.
`
`Publication Classification
`Int. Cl.7 ................................................... G02F 1/1337
`(51)
`(52) U.S. Cl.
`...................... .. 428/127; 428/126; 528/353
`
`ABSTRACT
`(57)
`The present invention provides novel polyamic acids and
`polyimide optical alignment layers for inducing alignment
`of a liquid crystal medium. The novel Compositions Com-
`prise reactive diamines containing a C3-C20 linear or
`branched hydrocarbon chains containing 1 to 4 carbon-
`carbon double bonds. The invention further describes liquid
`crystal displays comprising the novel polyimide optical
`alignment layers.
`
`.QZjz—g::DV.Q5zuQ'...Q"Z5Q§z"
`*cut.t§t»Lc.:m.‘-nn.:1u:u1$$In.
`
`Page 1 of 11
`
`Tianma Exhibit 1020
`
`Page 1 of 11
`
`Tianma Exhibit 1020
`
`

`
`Patent Application Publication Nov. 29, 2001
`
`US 2001/0046570 A1
`
`Page 2 of 11
`
`Page 2 of 11
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`

`
`US 2001/0046570 A1
`
`Nov. 29, 2001
`
`PHOTOSENSITIVE POLYIMIDES FOR OPTICAL
`ALIGNMENT OF LIQUID CRYSTALS
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`[0001] This application is a Continuation-in-Part of appli-
`cation Ser. No. 09/618,193, filed Jul. 18, 2000, which is a
`divisional of application Ser. No. 09/221,295, filed Dec. 23,
`1998 and issued as U.S. Pat. No. 6,103,322, Aug. 15, 2000.
`
`BACKGROUND OF INVENTION
`
`invention relates to photosensitive
`[0002] The present
`materials for aligning liquid crystals, liquid crystal displays,
`and other liquid crystal optical elements.
`
`[0003] Common to almost all liquid crystal based devices
`is a liquid crystal layer disposed between a pair of substrates
`coated with a polymeric alignment layer. The polymeric
`alignment layer controls the direction of alignment of the
`liquid crystal medium in the absence of an electric field.
`Usually the direction of alignment of the liquid crystal
`medium is established in a mechanical bufling process
`wherein the polymer layer is buffed with a cloth or other
`fiberous material. The liquid crystal medium contacting the
`buffed surface typically aligns parallel to the mechanical
`buffing direction. Alternatively, an alignment layer compris-
`ing anisotropically absorbing molecules can be exposed to
`polarized light to align a liquid crystal medium as disclosed
`in U.S. Pat. Nos. 5,032,009 and 4,974,941 “Process of
`Aligning and Realigning Liquid Crystal Media”.
`
`[0004] The process for aligning liquid crystal media with
`polarized light can be a noncontact method of alignment that
`has the potential to reduce dust and static charge buildup on
`alignment layers. Other advantages of the optical alignment
`process include high resolution control of alignment direc-
`tion and high quality of alignment.
`
`[0005] Requirements of optical alignment layers for liquid
`crystal displays include low energy threshold for alignment,
`transparency to visible light (no color), good dielectric
`properties and voltage holding ratios, long-term thermal and
`optical stability and in many applications a controlled uni-
`form pre-tilt angle. Most liquid crystal devices, including
`displays, have a finite pre-tilt angle, controlled, for instance,
`by the mechanical buffing of selected polymeric alignment
`layers. The liquid crystal molecules in contact with such a
`layer aligns parallel to the buffing direction, but
`is not
`exactly parallel to the substrate. The liquid crystal molecules
`are slightly tilted from the substrate, for instance by about
`2-15 degrees. For optimum performance in most display
`applications a finite and uniform pre-tilt angle of the liquid
`crystal is desirable.
`
`In a continuing effort to develop optical alignment
`[0006]
`materials for commercial applications U.S. Pat. No. 6,103,
`322 (Gibbons et al.) describes novel polyamic acids com-
`prising a dianhydride containing a diaryl ketone group, i.e.
`two aromatic rings linked by a carbonyl group, (e.g. ben-
`zophenonetetracarboxylic dianhydride) and an aromatic
`diamine containing an unsaturated alkyl side chain (e.g.
`geranyl or allyl group). Gibbons et al, recognized that
`polyamic acids combining these two structural units gave
`good quality alignment and better electrical properties (spe-
`cifically, voltage holding ratio, VHR) than similar materials
`that lacked the unsaturated alkyl side-chain.
`
`Page 3 of 11
`
`[0007] Herein are described new reactive side-chain poly-
`mers within the class of polyimides, polyamic acids and
`esters thereof, that give good quality alignment of liquid
`crystals and generate VHR properties superior to those
`previously achieved with optical alignment processing.
`
`SUMMARY OF INVENTION
`
`[0008] The present invention provides reactive side-chain
`polymers within the class of polyimides, polyamic acids and
`esters thereof, characterized in that they comprise identical
`or different repeat units selected from one or more of the
`formula
`
`0
`
`N
`
`M
`
`N*Aj
`
`X-111
`
`T
`
`O
`
`O
`
`—NH
`
`iM NH—A—
`
`/ \
`BOZC
`co2B
`
`|
`X_R1
`
`[0009] wherein A is a trivalent unsubstituted or optionally
`fluoro-, chloro-, cyano-, alkyl-, alkoxy-, fluoroalkyl- or
`fluoroalkoxy-substituted aromatic or cycloaliphatic group;
`R1 is a monovalent radical containing 1 to 4 carbon-carbon
`double bonds and is selected from the group of C3-C24 linear
`or branched aliphatic radicals, optionally interrupted by one
`to two 5- to 6-membered cycloaliphatic or aromatic radicals
`and optionally substituted with 1 to 3 heteroatoms selected
`from the group of oxygen, nitrogen and sulfur, wherein the
`carbon-carbon double bonds(s) are isolated from any other
`at system within the side-chain; X is selected from the group
`of covalent bond, —O—, —S—, and —NR—, wherein R is
`selected from H, R1, and C1-C4 hydrocarbon chain; B is
`hydrogen or a monovalent organic group derived from an
`alcohol after formal removal of the hydroxyl group; and M
`is a tetravalent organic radical of a tetracarboxylic acid
`dianhydride after formal removal of the two —CO—O—
`CO— groups, the four valencies of which are distributed
`between four different carbon atoms of the radical; wherein
`when M comprises two or more aromatic rings, said aro-
`matic rings are linked by one or two linkers, independently
`selected from the group of a covalent bond, —O—, —S—,
`—NR2—, straight-chain and branched-chain alkylenes rep-
`resented by
`(CH2)n
`,
`L2
`(CH2)n
`,
`(CH2)n L2,
`—L2(CH2)n—L3—, each optionally mono- or poly-substi-
`tuted by fluorine or chlorine and optionally chain interrupted
`by —O— or —NR2, wherein L2 and L3 are selected,
`independently, from the group of —O—, —S—, —NR2—,
`—O—CO—, —CO—O—; R2 is selected from H and C1-C4
`hydrocarbon chain and n is 1 to 20.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`[0010] FIG. 1 is a cross-sectional view of a liquid crystal
`display element.
`
`Page 3 of 11
`
`

`
`US 2001/0046570 A1
`
`Nov. 29, 2001
`
`DETAILED DESCRIPTION
`
`[0011] As used herein, the term “alignment layer” is the
`layer of material on the surface of a substrate that controls
`the alignment of a liquid crystal layer in the absence of an
`external
`field. A “conventional alignment
`layer” herein
`refers to an alignment layer that will only align a liquid
`crystal layer Via processing other than optical means. For
`example, mechanically buffed polyimides, evaporated sili-
`con dioxide, Langmuir-Blodgett films, have all been shown
`to align liquid crystals.
`
`“Optical alignment layer” herein refers to an align-
`[0012]
`ment layer that contains anisotropically absorbing molecules
`that will induce alignment of liquid crystals after exposure
`with polarized light. The optical alignment layer can be an
`isotropic medium or have some degree of anisotropy before
`optical alignment. Optical alignment layers may be pro-
`cessed by conventional means, such as mechanical rubbing,
`prior to or after exposure to polarized light. The anisotro-
`pically absorbing molecules of the optical alignment layers
`exhibit absorption properties with different values when
`measured along axes in different directions. The anisotropic
`absorbing molecules exhibit absorption bands between 150
`nm and about 2000 nm. Most preferable optical alignment
`layers for the present invention have absorbance maxima of
`about from 150 to 400 nm and especially about from 300 to
`400 nm.
`
`[0013] Polymers especially useful and preferred as optical
`alignment layers are polyimides. Polyimides are known for
`their excellent thermal and electrical stability properties and
`these properties are useful in optical alignment layers for
`liquid crystal displays. The preparation of polyimides is
`described in “Polyimides”, D. Wilson, H. D. Stenzenberger,
`and P. M. Hergenrother Eds., Chapman and Hall, New York
`(1990). Typically polyimides are prepared by the conden-
`sation of one equivalent of a diamine with one equivalent of
`a dianhydride in a polar solvent to give a poly(amic acid)
`prepolymer intermediate. Alternatively copolymer polyim-
`ides are prepared by the condensation of one or more
`diamines with one or more dianhydrides
`to give
`a
`copolyamic acid.
`
`[0014] An alternative intermediate to polyimides are
`poly(amic esters) that can be made by esterification of
`poly(amic acids) with alcohols. The poly(amic esters)
`undergo thermal imidization to form polyimides.
`
`[0015] Thus, poly(amic acids) and poly(amic esters) are
`considered to be closely related precursors to polyimides of
`the invention. Therefore,
`they are considered further
`embodiments of this invention. Furthermore, preimidized
`polyimides derived from chemical or thermal imidization of
`poly(amide acids) or poly(amide esters) are also considered
`an embodiment of the invention.
`
`[0016] The poly(amic acid) is typically formulated to give
`a 1 to 30 wt % solution. The condensation reaction is usually
`performed between room temperature and 150° C. The
`prepolymer solution is coated onto a desired substrate and
`thermally cured at between 180 and 300° C. to complete the
`imidization process. Alternatively, the poly(amic acid) pre-
`polymer is chemically imidized by addition of a dehydrating
`agent to form a polyimide polymer.
`
`1:1, but can vary between 0.821 to 1.221. The preferred ratio
`of diamine to dianhydride is between 0.9:1 and 1.121.
`
`[0018] The present invention provides reactive side-chain
`polymers within the class of polyimides, polyamic acids,
`and esters thereof,
`that are disclosed above. Within the
`disclosure, in defining the group A, the term “aromatic or
`cycloaliphatic group” includes one or more 5- and 6-mem-
`bered aromatic and heteroaromatic rings, 9- and 10-mem-
`bered fused aromatic and heteroaromatic rings, 4-, 5-, 6-,
`and 7-member saturated carbon rings, and 6- to 10-mem-
`bered fused or bicyclic saturated or partially unsaturated
`carbon rings. The term “optionally substituted with 1 to 3
`heteroatoms selected from the group of oxygen, nitrogen
`and sulfur” means that 1 to 3 carbon atoms in the aliphatic
`radical can be formally replaced by —O—, —NR— or
`—S—. The phrase “isolated from any other It-system within
`the side-chain” me ans that the carbon-carbon double bond(s)
`are not
`in direct conjugation to another at-system,
`for
`instance, an aromatic ring (e.g. stilbene), carbonyl group
`(e.g. acrylate) or combination of both (e.g. chalcone).
`
`[0019] Preferred side-chain polymers of the invention are
`those wherein M is selected from the group
`
`@r::©- @-
`
`IXETQQ
`
`><>@<a::
`
`[0020] wherein Z is said linker noted above and m=1 or 0.
`
`[0021] More preferred are polymers wherein M is
`
`In preparing polyamic acids for optical alignment
`[0017]
`layers the molar ratio of diamine to dianhydride usually is
`
`and Z is selected from the group of covalent bond,
`[0022]
`—O—, —NR2, and —(CH2)n—, and m=0. Also more
`
`Page 4 of 11
`
`Page 4 of 11
`
`

`
`US 2001/0046570 A1
`
`Nov. 29, 2001
`
`preferred are polymers of claim 2 wherein M is selected
`from the group
`
`[0023] A further preference is for polymers wherein A is
`selected from the group
`
`<3 ml *xT>f©‘
`
`[0024] wherein X1 is selected from the group of H, F, Cl,
`CN, alkyl, and alkoxy.
`
`[0025] Preferably, within the side-chain, X is selected
`from the group of —O—, and —NR— and R1 is selected
`from the group of allyl, geranyl, citronellyl, famesyl and
`3-methyl-2-butenyl.
`
`[0026] Amost preferred polymer comprises the repeat unit
`
`[0027] A wide Variety of dianhydrides may be used in
`forming preferred polymers of
`the invention. Specific
`examples of preferred tetracarboxylic dianhydride compo-
`nents include aromatic dianhydrides such as pyromellitic
`dianhydride,
`2,3,6,7-naphthalenetetracarboxylic
`dianhy-
`dride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,
`5,8-naphthalenetetracarboxylic dianhydride, 3,3‘,4,4‘-biphe-
`nyltetracarboxylic
`dianhydride
`(A2),
`2,3,2‘,3‘-
`biphenyltetracarboxylic
`dianhydride,
`bis(3,4-
`dicarboxyphenyl)ether
`dianhydride
`(A3),
`bis(3,4-
`dicarboxyphenyl)diphenylsulfone
`dianhydride,
`bis(3,4-
`dicarboxyphenyl)methane
`dianhydride,
`2,2-bis(3,4-
`dicarboxyphenyl)propane
`dianhydride,
`1,1,1,3,3,3-
`hexafluoro-2,2-bis(3,4-dicarboxyphenyl)propane
`dianhydride, bis(3,4-dicarboxyphenyl)dimethylsilane dian-
`hydride, 2,3,4,5-pyridinetetracarboxylic dianhydride; alicy-
`clic tetracarboxylic dianhydrides such as 1,2,3,4-butanetet-
`racarboxylic
`dianhydride,
`1,2,3,4-
`cyclobutanetetracarboxylic
`dianhydride
`1,2,4,5-
`
`(A1),
`
`Page 5 of 11
`
`dianhydride,
`cyclohexanetetracarboxylic
`dianhydride,
`acid
`tricarboxycyclopentylacetic
`dianhydride
`and
`bicyclooctanetetracarboxylic
`dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic
`dianhydride; and their acid and acid chloride derivatives.
`1,2,3,4-Cyclobutanetetracarboxylic dianhydride and 2,3,5-
`tricarboxycyclopentylacetic acid dianhydride are most pre-
`ferred for preparing polyimides of the invention.
`
`2,3,5-
`1,3,4,6-
`3,4-
`
`[0028] Examples of the diamines that are useful in form-
`ing polymers of the invention are listed in Table 1. The
`syntheses of these diamines is discussed in U.S. Pat. No.
`6,103,322 and is hereby incorporated by reference. These
`diamines are sensitive to air and easily undergo oxidation to
`give colored products. The diamines are stored and handled
`under inert conditions to avoid the formation of colored
`
`oxidation products.
`
`[0029] A variety of other diamines may be useful in the
`preparation of novel copolyamic acids of the invention
`including aromatic diamines such as are 2,5-diaminoben-
`zonitrile, 2-(trifluoromethyl)-1,4-benzenediamine, p-phe-
`nylenediamine, 2-chloro-1,4-benzenediamine, 2-fluoro-1,4-
`benzenediamine, m-phenylenediamine, 2,5-diaminotoluene,
`2,6-diaminotoluene, 4,4‘-diaminobiphenyl, 3,3‘-dimethyl-4,
`4‘-diaminobiphenyl, 3,3‘-dimethoxy-4,4‘-diaminobiphenyl,
`diaminodiphenylmethane, diaminodiphenyl ether, 2,2-di-
`aminodiphenylpropane,
`bis(3,5-diethyl-4-aminophenyl-
`)methane, diaminodiphenylsulfone, diaminonaphthalene,
`1,4-bis(4-aminophenoxy)benzene,
`4,4‘-diaminobenzophe-
`none, 3,4‘-diaminobenzophenone, 1,4-bis(4-aminophenyl-
`)benzene, 9,10-bis(4-aminophenyl)anthracene, 1,3-bis(4-
`aminophenoxy)benzene,
`4,4'-bis(4-
`aminophenoxy)diphenylsulfone,
`2,2-bis[4-(4-
`aminophenoxy)phenyl]propane,
`2,2-bis(4-
`and
`aminophenyl)hexafluoropropane
`2,2-bis[4-(4-
`aminophenoxy)phenyl]hexafluoropropane;
`alicyclic
`diamines such as bis(4-aminocyclohexyl)methane; and ali-
`phatic diamines such as tetramethylenediamine and hexam-
`ethylene diamine. Further, diaminosiloxanes such as bis(3-
`aminopropyl)tetramethyldisiloxane may be used. Such
`diamines may be used alone or in combination as a mixture
`of two or more of them.
`
`[0030] Preferably the novel polyamic acids of the inven-
`tion comprise about from 1 to 100 mol % of structure Ib;
`more preferably from 5 to 50 mol % of structure Ib; and most
`preferably from 5 to 25 mol % of structure Ib. A higher mol
`% of structure Ib tends to give a higher degree of reactivity
`and improved electrical properties. However, improvement
`in voltage holding ratio (VHR) and the photosensitivity of
`the polyimide optical alignment layer is often observed at
`relatively low loading of structure Ib in a copolyamic acid.
`
`[0031] The term “reactive” is not meant to restrict the
`side-chain polymers to a specific mode of action. Rather, the
`term is meant to suggest to the artisian how the polymers
`may perform their function. To speculate, the double bonds
`may provide reactivity that allows a change in the chemical
`environment of the side-chain during and/or after exposure
`to polarized light. This change may be caused by bond
`forming, bond breaking, isomerization or some combina-
`tion. In any event, the invention is not restricted to a specific
`mechanism of action.
`
`the
`layers
`To prepare the optical alignment
`[0032]
`poly(amic acid) solutions or preimidized polyimide solu-
`
`Page 5 of 11
`
`

`
`US 2001/0046570 A1
`
`Nov. 29, 2001
`
`tions are coated onto desired substrates. Coating is usually
`accomplished with 2 to 30 wt % solids. Any conventional
`method may be used to coat the substrates including brush-
`ing, spraying, spin-casting, meniscus coating, dipping or
`printing. The preferred techniques for coating substrates
`demonstrated in the Examples are spinning and printing.
`However, the optical alignment materials of the invention
`are not limited to use in printing or spinning processes.
`
`[0033] The coated substrates are heated in an oven under
`air or an inert atmosphere, for instance nitrogen or argon, at
`elevated temperature usually not exceeding 300° C. and
`preferably at or below 200° C. for about from 1 to 12 hours,
`preferably for about 2 hours or less. The heating process
`removes the solvent carrier and may be used to further cure
`the polymer. For instance,
`the poly(amic) acid films are
`thermally cured to generate polyimide films.
`
`[0034] The concentration of polymer and choice of sol-
`vents can aifect the optical alignment quality, pretilt and
`VHR. For example, the optical alignment quality has been
`observed to improve under the same exposure conditions
`when the concentration of polymer is decreased in solution.
`In addition,
`the choice of solvent, co-solvents and cure
`conditions can also affect the alignment quality and electri-
`cal properties. A correlation between film thickness and
`alignment quality also is evident. In particular, the optical
`alignment quality improves with decreasing thickness. Simi-
`larly, VHR can increase with decreasing film thickness.
`
`[0035] The optical alignment layers are exposed to polar-
`ized light to induce alignment of liquid crystals. By “polar-
`ized light” is meant light that is elliptically polarized such
`that the light is more polarized along one axis (referred to as
`the major axis) versus the orthogonal axis (referred to as the
`minor axis). In this invention the polarized light has one or
`more wavelengths of about from 150 to 2000 nm and
`preferably of about from 150 and 1600 nm and more
`preferably about from 150 to 800 nm. Most preferably, the
`polarized light has one or more wavelengths of about from
`150 to 400 nm, and especially about from 300 to 400 nm. A
`preferred source of light is a laser, e.g., an argon, helium
`neon, or helium cadmium. Other preferred sources of light
`are mercury arc deuterium and quartz tungsten halogen
`lamps, xenon lamps, microwave excited lamps and black
`lights in combination with a polarizer. Polarizers useful in
`generating polarized light from nonpolarized light sources
`are interference polarizers made from dielectric stacks,
`absorptive polarizers, diffraction gratings and refiective
`polarizers based on Brewster reflection. With lower power
`lasers or when aligning small alignment regions, it may be
`necessary to focus the light beam onto the optical alignment
`layer.
`
`is
`that polarized light
`[0036] By “exposing” is meant
`applied to the entire optical alignment layer or to a portion
`thereof. The light beam may be stationary or rotated. Expo-
`sures can be in one step, in bursts, in scanning mode or by
`other methods. Exposure times vary widely with the mate-
`rials used, etc., and can range from less than 1 msec to over
`an hour. Exposure may be conducted before or after con-
`tacting the optical alignment layer with the liquid crystal
`medium. Exposing can be accomplished by linearly polar-
`ized light transmitted through at least one mask having a
`pattern or with a beam of linearly polarized light scanned in
`a pattern. Exposing also may be accomplished using inter-
`
`Page 6 of 11
`
`ference of coherent optical beams forming patterns,
`alternating dark and bright lines.
`
`i.e.,
`
`[0037] Exposure energy requirements vary with the for-
`mulation and processing of the optical alignment layer prior
`and during exposure. A preferred range of exposure energy
`is about from 0.001 to 100 J/cm2 and most preferred range
`of exposure energy is about from 0.001 to 5 J/cm2. Lower
`exposure energy is most useful in large scale manufacturing
`of optical alignment layers and liquid crystal display ele-
`ments. Lower exposure energy also minimizes the risk of
`damage to other materials on the substrates.
`
`[0038] The efliciency of the alignment process, and the
`exposure energy required, may be further impacted by
`heating, beyond that inherent in the “exposing” step. Addi-
`tional heating during the exposing step may be accom-
`plished by conduction, convection or radiant heating, or by
`exposure to unpolarized light. Additional heating may
`increase the mobility of the molecules during exposure and
`improve the alignment quality of the optical alignment layer.
`Additional heating is not a requirement of the process of the
`invention but may give beneficial results.
`
`[0039] The quality of alignment and electrical properties
`of the liquid crystal cell assembled from exposed substrates
`can be improved by heating the substrates after exposure but
`prior to assembly of the cell. This additional heating of the
`substrates is not a requirement of the process but may give
`beneficial results.
`
`[0040] Exposing also can consist of two or more exposure
`steps wherein the conditions of each step such as angle of
`incidence, polarization state, energy density, and wavelength
`are changed. At least one of the steps must consist of
`exposure with linearly polarized light. Exposures can also be
`localized to regions much smaller than the substrate size to
`sizes comparable to the entire substrate size. A preferred
`method of dual exposing comprises a two step process of:
`
`least one optical alignment
`(a) exposing at
`[0041]
`layer to polarized light at a normal incidence, and
`
`(b) exposing the optical alignment layer to
`[0042]
`polarized light at an oblique incidence.
`
`[0043] Applying a liquid crystal medium to the optical
`alignment can be accomplished by capillary filling of a cell,
`by casting of a liquid crystal medium onto an optical
`alignment layer, by laminating a preformed liquid crystal
`film onto an optical alignment layer or by other methods.
`Preferred methods are capillary filling of a cell, injection
`filling and casting of a liquid crystal medium onto an optical
`alignment layer. Optical alignment layers are pre-exposed to
`polarized light or they are exposed after contacting the liquid
`crystal medium.
`
`[0044] A cell can be prepared by using two coated sub-
`strates to provide a sandwiched layer of liquid crystal
`medium. The pair of substrates can both contain optical
`alignment layers or a conventional alignment layer (e.g.,
`mechanically buffed) can be used as the second alignment
`layer comprising the same or a different polymer.
`
`[0045] As liquid crystal substances used for liquid crystal
`optical elements, nematic liquid crystal substances, ferro-
`electric liquid crystal substances, etc. are usable. Useful
`liquid crystals for the invention described herein include
`positive dielectric liquid crystals including 4-cyano-4'-alky-
`
`Page 6 of 11
`
`

`
`US 2001/0046570 A1
`
`Nov. 29, 2001
`
`light modulators,
`displays. These include electro-optical
`all-optical light modulators, erasable read/write optical data
`storage media; diffractive optical components such as grat-
`ings, beamsplitters,
`lenses (e.g., Fresnel
`lenses), passive
`imaging systems, Fourier processors, optical disc and radia-
`tion collimators; binary optical devices formed by combin-
`ing refractive and diffractive optics including eyeglasses,
`cameras, night vision goggles, robotic vision and three-
`dimensional
`image viewing devices;
`and holographic
`devices such as heads-up displays and optical scanners.
`
`[0050] Voltage Holding Ratio (VHR) is a critical electrical
`parameter for liquid crystal displays. VHR is a measure of
`the LCDS ability to retain a voltage during the time between
`pixel updates (frame time). The type of liquid crystal,
`alignment layers and cell geometry can all affect the mea-
`sured VHR value. In the examples to follow, liquid crystal
`test cells comprising soda-lime substrates with patterned
`indium-tin-oxide (ITO) transparent electrodes are described.
`The overlap of the electrodes was about 1 cm2 after the test
`cell was assembled. Approximately 2-3 inch wire leads were
`attached to the patterned ITO electrodes using an ultrasonic
`solder iron after the test cell is assembled but prior to filling.
`The leads were attached to a VHR measurement system
`(Elsicon VHR-100 Voltage Holding Ratio Measurement
`System, Wilmington, Del.) using test clips after the cell was
`filled and annealed. The VHR for the examples was mea-
`sured for a 20 msec frame time, which is typically used for
`measuring VHR, with an applied voltage of 1 volt. The VHR
`measured at 75° C. for the various exposure conditions is
`summarized in Table 2.
`
`[0051] Comparison of Examples 3, 4, and 5 indicate that
`cells fabricated with polyimides of the invention have sub-
`stantially higher VHR than a cell fabricated with polyimides
`that
`lack the reactive double bonds in the side chains.
`
`Comparison of Example 6 with 7 and 8 indicate that VHR
`can be improved by substituting a portion or all of a
`commonly used diamine with a reactive diamine of the
`invention.
`
`TABLE 1
`
`Crosslinking Diamines.
`
`Dia-
`mine
`No. Structure
`
`1
`
`lbiphenyls, 4-cyano-4‘-alkyloxybiphenyls, 4-alkyl-(4‘-cy-
`anophenyl)cyclohexanes,
`4-alkyl-(4'cyanobiphenyl)cyclo-
`hexanes, 4-cyanophenyl-4"alkylbenzoates, 4-cyanophenyl-
`4'alkyloxybenzoates,
`4-alkyloxyphenyl-4‘cyanobenzoates,
`4-alkylphenyl-4’alkylbenzoates, 1-(4'-alkylphenyl)-4-cyan-
`opyrimidines,
`1-(4‘-alkyloxyphenyl)-4-cyanopyrimidines
`and 1-(4-cyanophenyl)-4-alkylpyrimidines. Other useful liq-
`uid crystals are new superfluorinated liquid crystals avail-
`able from EM Industries, (Hawthrone N.Y.) including the
`commercial materials: ZLI-5079, ZLI-5080, ZLI-5081, ZLI-
`5092, ZLI-4792, ZLI-1828, MLC-2016, MLC-2019, MLC-
`6252 and MLC-6043. Other useful nematic materials for
`practicing the invention include the commercial liquid crys-
`tals available from Lodic Co., Ltd, (Tokyo, Japan) including
`the DLC series: 22111, 22112, 22121, 22122, 23070, 23170,
`23080, 23180, 42111, 42112, 42121, 42122, 43001, 43002,
`43003, 63001, 63002, 63003, 63004, and 63005.
`
`[0046] The invention is not limited to the use of liquid
`crystals defined above. One skilled in the art will recognize
`that the invention will be of value with many diverse liquid
`crystal structures and formulations containing mixtures of
`liquid crystals.
`
`[0047] A liquid crystal display element of the invention is
`composed of an electrode substrate having at
`least one
`polyimide optical alignment layer derived from a polyamic
`acid of Structure Ib (above), a voltage-impressing means and
`a liquid crystal material. FIG. 1 illustrates a typical liquid
`crystal display element, comprising a transparent electrode
`2 of ITO (indium-tin oxide) or tin oxide on a substrate 1 and
`optical alignment
`layers 3 formed thereon. The optical
`alignment layers are exposed to polarized light of a wave-
`length or wavelengths within the absorption band of the
`anisotropically absorbing molecules. A spacer concurrently
`with a sealing resin 4 is intervened between a pair of optical
`alignment layers 3. A liquid crystal 5 is applied by capillary
`filling of the cell and the cell is sealed to construct a liquid
`crystal display element. Substrate 1 may comprise an over-
`coat film such as an insulating film, a color filter, a color
`filter overcoat, a laminated polarizing film etc. These coat-
`ings and films are all considered part of the substrate 1.
`Further, active elements such as thin film transistors, a
`nonlinear resistant element, etc. may also be formed on the
`substrate 1. These electrodes, undercoats, overcoats, etc. are
`conventional constituents for liquid crystal display elements
`and are usable in the display elements of this invention.
`Using the thus formed electrode substrate, a liquid crystal
`display cell is prepared, and a liquid crystal substance is
`filled in the space of the cell,
`to prepare a liquid crystal
`display element in combination with a voltage-impressing
`means.
`
`[0048] Optical alignment layers of the invention are com-
`patible with all liquid crystal display modes. A liquid crystal
`display element of the invention can comprise a variety of
`display configurations including twisted nematic, super
`twisted nematic,
`in-plane-switching, vertical alignment,
`active-matrix, cholesteric, polymer dispersed, ferroelectric,
`anti-ferroelectric and multi-domain liquid crystal displays.
`Although the display modes demonstrated in this specifica-
`tion are primarily twisted nematic, the optical alignment
`layers of the invention are not limited to use in twisted
`nematic liquid crystal displays.
`
`[0049] Optical alignment layers of the invention are useful
`in many other liquid crystal devices other than liquid crystal
`
`Page 7 of 11
`
`Page 7 of 11
`
`

`
`US 2001/0046570 A1
`
`Nov. 29, 2001
`
`TABLE 1-continued
`
`Crosslinking Diarnines.
`
`TABLE 1-continued
`
`Crosslinking Diarnines.
`
`Dia-
`mine
`No. Structure
`
`9 O
`
`Dia-
`rnine
`N0. Structure
`
`3
`
`10
`
`NH2
`
`Me
`/N
`
`NH2
`
`Page 8 of 11
`
`Page 8 of 11
`
`

`
`US 2001/0046570 A1
`
`Nov. 29, 2001
`
`[0052]
`
`TABLE 2
`
`Optical Alignment of Polyimide Compositions.
`
`Lamp Exposure Alignment
`2
`
`J/cm
`
`>>>>O>OO>>
`
`Example
`
`PolyimideComposition
`
`Dianhydride
`A
`
`Diamine(s)
`1
`
`2
`
`15
`
`16
`
`No.
`3
`
`4
`
`5
`compar.
`6
`compar.
`
`7 8 9
`
`10
`
`11
`
`12
`
`C Excellent alignment, no flow effects, high uniformity.
`0 Good alignment, low flow e ects, uniform.
`A Fair alignment, flow effects, some nonuniformity (mottled or cloudy background).
`X Poor alignment, severe flow effects, nonuniform.
`+Levels of improvement, A < A+ < A++ < 0.
`A1 = 1,2,3,4-cyclobutanetetracarboxylic dianhydride
`A2 = 3,4,3',4'—biphenyltetracarboxylic dianhydride
`A3 = bis(3,4-dicarboxyphenyl)ether dianhydride
`Diamine 15 = 4-(N,N-dipropylamino)-1,3-benzenediamine
`Diamine 16 = oxy(dianiline)
`
`[0053] The following examples are me ant to exemplify the
`embodiments and are not to limit the scope of the invention
`EXAMPLE 1
`
`[0054] This example illustrates the synthesis of diamine
`13.
`
`[0055] N-(3-methyl-2-butenyl)-N-methyl amine was first
`prepared by addition of 4-Bromo-2-methyl-2-butene (15.0
`g) to a stirred solution of 40% aqueous methyl amine (100
`mL), diethyl ether (110 mL) and methanol (50 mL). The
`mixture was extracted and the extracts dried over potassium
`carbonate and distilled to give the N-(3-methyl-2-butenyl)-
`N-methyl amine (5.25 g, bp 80-89 C).
`
`[0056] N-(3-methyl-2-butenyl)-N-methyl amine (5.20 g)
`was stirred with 3-fluoro-4-nitroaniline (3.12 g),
`triethyl
`amine (6.2 mL) and N-methylpyrrolidinone (NMP, 30 mL)
`at 80-85° C. for 10 hr. The mixture was extracted with water
`and diethyl ether. The extract was purified by chromatog-
`raphy on silica gel to give 3-[N-(3-methyl-2-butenyl)-N-
`methyl]amino-4-nitroaniline.
`
`3-[N-(3-methyl-2-butenyl)-N-methyl]amino-4-ni-
`[0057]
`troaniline (4.55 g) was treated with tin (II) chloride dihy-
`drate (18.0 g) in ethanol (100 mL) and 10 N hydrochloric
`acid (16 mL, added last) at ambient temperature for 9 hr. The
`mixture was basified with chilled 20 wt % potassium
`hydroxide (160 g), extracted with diethyl ether and the
`extract purified by chromatography on silica gel to give
`diamine 13 (1.0 g) as a light amber oil.
`
`EXAMPLE 2
`
`[0058] This example illustrate the synthesis of diamine 14.
`
`[0059] Amixture of 4,4‘-dinitro-2-biphenylamine (10.0 g),
`allyl bromide (20 mL), potassium carbonate (16 g) and NMP
`(100 mL) was heated to 90-95° C. for 90 hr. The mixture was
`extracted with tetrahydrofuran -ethyl acetate-water
`and purified by crystallization from ethyl