Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
  • G02F1/133711—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films
  • G02F1/133723—Polyimide, polyamide-imide
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
  • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
  • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors

Definitions

• LCD Liquid Crystal Displays
• LCD technology offers widely known advantages over traditional display technologies such as cathode ray tubes. Among these advantages are low weight and low power consumption.
• Liquid crystal displays have previously been considered to provide a narrower field of view than traditional display technologies, such as the previously mentioned cathode ray tubes.
• Liquid crystal displays typically contain a plurality of liquid crystal cells.
• Each liquid crystal cell generally contains a liquid crystal material sandwiched between two substrates. Located on either side of the liquid crystal material is a set of electrodes which are typically indium-tin oxide (ITO) or tin oxide.
• ITO indium-tin oxide
• a pair of polarizing filters is located outside of the substrates, with each filter on an opposite side of the liquid crystal cell.
• the polarizers are oriented at right angles relative to each other. The orientation of the liquid crystal material in the cell determines whether light passes through each polarizer in the absence of external influence such as an electric field, thereby giving a transparent appearance, or whether light is blocked by one of the polarizers, thereby giving the cell a darkened appearance.
• the orientation of the liquid crystal material is changed by the application of an electric field by the electrodes to alter light transmission through the cell.
• the liquid crystal material is aligned such that the cell appears opaque or transparent absent an application of an electric field through the electrodes.
• an electric field is applied to such a cell, the orientation of the liquid crystal UA.388 2
• the orientation of a liquid crystal material at its surface is dependent on the orientation of material it comes in contact with. It is known to coat the surface of a substrate with an agent which influences the orientation of a liquid crystal material that comes in contact with the coated substrate. Such coating agents are known as alignment layers.
• Various materials and methods have been used in establishing an alignment layer of a desired orientation.
• an alignment layer may comprise anisotropically absorbing molecules which can be oriented by exposure to polarized light.
• Inorganic thin films, such as metal oxide films, which have been deposited on a substrate at an oblique angle can also be used as alignment layers as disclosed in U.S. Patent No. 5,638,197.
• a polymeric alignment layer which can be oriented by means of a mechanical buffing process.
• a polymer layer is applied to a substrate and is buffed with a cloth or other fibrous material. Liquid crystal material coming into contact with a surface treated in this way typically aligns itself parallel to the direction of buffing.
• Polyimides are frequently used as a polymeric alignment material for liquid crystal cells and for optical compensator layers including O-plate compensators. Polyimides generally display good chemical stability and are easily deposited on a substrate and rubbed. Polyimides are generally prepared by contacting a diamine with an acid anhydride, producing a polyamic acid. This polyamic acid may be coated onto a substrate and heat treated at about 150°- 230°C, converting the polyamic acid to a polyimide. The polyimide film is then mechanically rubbed as mentioned above.
• LCDs frequently have a narrow field of view. It is frequently desirable to increase this field of view especially in applications such as computer displays, avionic displays and televisions.
• the viewing zone of an LCD that is not equipped with an optical compensator is narrow UA.388 3
• Optical compensators have been used to increase the viewable angle of LCDs without negatively affecting image quality when viewed normal to the surface of the LCD.
• Optical compensators typically take the form of an additional layer of liquid crystal material located between a polarizer and the viewing area, on the outer surface of an LCD. This liquid crystal material may be given a specific orientation under the influence of an alignment layer material.
• O-plate compensation films, or O-plate compensators are one type of optical compensator. O-plate compensators generally minimize reversal of gray levels and improve overall gray scale stability.
• O-plate compensators have been previously described as comprising a positive birefringent material which has a principle optic axis oriented at an oblique angle relative to the surface of the liquid crystal layer.
• An oblique angle includes any angle between 0° and 90°.
• this angle has been provided in various ways.
• U.S. Patent No. 5,619,352 describes an O-plate compensator which includes an alignment layer, a liquid crystal pretilt layer, and a liquid crystal compensator layer.
• the described O-plate compensator depends on the liquid crystal pre-tilt layer to provide an adequate pre-tilt angle for the liquid crystal compensator layer because the alignment layer produces only a 1° to 10° liquid crystal pretilt angle at the alignment layer/liquid crystal pre-tilt layer interface.
• the described O-plate compensator therefore depends on multiple layers of liquid crystal material to provide an adequate angle of orientation of the liquid crystal material.
• a similar O- plate compensator is also described in U.S. Patent No. 5,986,734 and PCT Application No. WO 96/10770.
• the use of high pre-tilt alignment layers is also known in LCDs known as pi-cells.
• alignment layer for a liquid crystal layer has provided a pre-tilt angle greater than about 15°.
• the present invention provides a polyimide comprising a reaction product of at least one dianhydride and at least one diamine, wherein the at least one diamine contains a mesogenic group, with the proviso that when the at least one dianhydride is 2.2'-bis-(3,4-dicarboxyphenyl)-l, 1,1, 3,3,3- hexafluoropropane dianhydride (6FDA) or dibromo-biphenyltetracarboxylic dianhydride, the at least one diamine is not
• A is selected from the group consisting of O and COO.
• the present invention also provides a method for inducing a predetermined orientation of a liquid crystal material, the method comprising applying an alignment layer material to a substrate, and buffing the alignment layer material, thereby providing an alignment layer with a pre-tilt angle, wherein UA.388 5
• the alignment layer material is a reaction product of at least one dianhydride and at least one diamine, and wherein the at least one diamine contains a pendent mesogenic group.
• Figure 1 is a schematic summary of a method of preparing a mesogenic group of the present invention.
• Figure 2 is a graph showing the pre-tilt angles of the ⁇ polyimides 6FDA/C6CN and 6FDA/C6CN(ether) after heat treatment at various temperatures.
• Figure 3 is a graph showing the pre-tilt angles of the polyimides
• Figure 4 is a graph showing the pre-tilt angles of the polyimides 6FDA/C6CN and 6FDA/C11CN after heat treatment at various temperatures.
• Figure 5 is a graph showing the pre-tilt angles of polyimides containing varying amounts of diamines with mesogenic pendent groups (C6BP) and diamines with perfluorinated carbon pendent groups (PFMB).
• C6BP mesogenic pendent groups
• PFMB perfluorinated carbon pendent groups
• the present invention is directed toward polyimides which can be used to prepare liquid crystal display alignment layers for a liquid crystal device, such as an optical compensator, for example.
• the polyimides of the present invention contain mesogenic substituents and may optionally include functional substituents.
• Polyimides may be schematically represented by the structure
• A is one or more residues from an acid dianhydride group and B is one or more residues from a diamine compound and n is a positive number. It has been UA.388
• the properties of the polyimide may be altered by varying the components "A" and "B” as listed above.
• the use of polyimides containing mesogenic substituents to prepare high pre-tilt alignment layers has not been previously known.
• mesogenic groups are contributed to the structure of a polyimide by the diamine component.
• Any acid dianhydride useful in the synthesis of polyimides may be utilized in the present invention. Such acid dianhydrides are commercially available.
• polyimide polymers are prepared from diamines containing pendent mesogenic groups.
• the diamine contains a backbone portion, a methylene spacer, a linking group, and a pendent mesogenic group.
• the pendent mesogenic group is attached to the methylene spacer
• the methylene spacer is attached to the linking group
• the linking group is attached to the backbone portion.
• the linking group is selected from the group consisting of an ester and an ether.
• suitable diamines are represented by formulas I and II below.
• F-i is an ester or ether linking group
• R2 is a mesogenic group or a functional group as defined below
• x is a positive number.
• R3 is hydrogen or a halogen. In one embodiment, x is between 6 and 18. In another example, x is between 6 and 11. In one particular example, x is 6. In another example, R3 is bromine.
• Mesogenic groups are groups with a rod-like molecular structure. That is, mesogenic groups, or simply mesogens, are groups with a length to width ratio of at least 5:1.
• Functional groups are those groups which allow one polyimide molecule to react with another molecule.
• preferred functional groups are groups which permit the crosslinking of polyimide molecules within a layer.
• Especially preferred functional groups include molecules which allow the photopolymerization of polyimide molecules, such as acrylate and methacrylate groups.
• Suitable diamines include those containing a substituent selected from the group of compounds containing one or more of the subunits represented by formulas III, IV, V, and VI.
• X may be hydrogen or an organic group having from 1 to 20 carbon atoms
• R4 may be an organic group selected from the group consisting of esters, ethers, groups containing a methylene subunit, groups containing a crosslinking subunit and groups containing a combination of any of these subunits.
• Groups containing acrylate or methacrylate subunits may be crosslinked such as by photopolymerization, for example.
• X is an organic group containing between 1 and 16 carbon atoms.
• X is an organic group containing between 1 and 12 carbon atoms.
• X is a methyl group.
• the substituent is not represented by formula V.
• a mesogenic group shown in VI may be synthesized by the following method as described below with reference to Figure 1.
• Ethyl 4-hydroxybenzoic ester is alkylated with 6-chlorohexanol to produce intermediate (1) .
• Intermediate (1) was used in two different reactions. In the first reaction, the hydroxyl group of intermediate (1) was protected using 3,4- dihydro-2-pyran (DHP) forming intermediate (2). Intermediate (2) was then hydrolyzed to form a THP-benzoic acid derivative (4). In the second reaction, intermediate (1) was hydrolyzed to generate a hydroxy terminated benzoic acid (3) .
• DHP 3,4- dihydro-2-pyran
• the hydroxy terminated benzoic acid (3) is contacted with CH2CH2COCI in an organic solvent to form a intermediate (5).
• Tert-butyl dimethylsilyl chloride (TBDMS) was used to protect methyl hydroquinone.
• the major isomer was isolated by chromatography and then reacted with the THP-benzoic acid derivative (4) forming intermediate (6) .
• This reaction product was then selectively deprotected using tert-butylamonium fluoride (TBAF) in tetrahydrofuran (THF) to form intermediate (7) .
• TBAF tert-butylamonium fluoride
• THF tetrahydrofuran
• Mesogenic group (9) may be contacted with dinitro diphenic acid followed by tin (II) chloride reduction in ethanol to form a diamine of formula I.
• a diamine may be used to prepare a polyimide of the present invention.
• mesogens may be used to produce mesogen-containing diamine compounds of formula I by coupling the mesogen with a dinitro diphenic acid using the standard dicyclohexylcarbodiimide (DCC)/DMAP procedure to produce a dinitro intermediate compound.
• dinitro diphenic acid may be converted to 4,4'-dinitro-2,2'-biphenyl-carbonyl chloride by refluxing with thionyl chloride.
• the mesogen may be contacted with 4,4'-dinitro-2,2'-biphenyl-carbonyl chloride in an organic solvent such as triethylamine or methylene chloride to produce a dinitro intermediate.
• the dinitro intermediate may be reduced to form a diamine by stannous chloride reduction or by reduction using hydrazine in an organic solvent at 80 °C.
• Mesogens of the present invention may also be coupled to brominated biphenylcarboxylic acids to produced brominated diamines of formula I.
• Cyanuric acid is contacted with bromine and the resulting compound is used to brominate 4,4'-dinitro-2,2'-biphenyl-carboxylic acid yielding 6,6'-dibromo-2,2'- biphenylcarboxylic acid.
• This brominated carboxylic acid may be coupled with a mesogen and reduced as described above to produce a brominated diamine.
• Diamines of formula II may be synthesized by the following technique.
• 3,5-dinitrobenzoic acid is esterified with n-octadecanol to afford n-octadecyl 3,5- UA.388 10
• Diamines of the present invention may be purified by chromatography on deactivated silica gel and subsequent recrystalization. Purified diamines may then be contacted with acid dianhydrides to produce polyimides. The synthesis of polyimides is known in the art.
• polyimide precursors maybe synthesized from dianhydrides and diamines by either a 2-step or a 1-step method.
• a soluble polyimide precursor i.e., a polyamic acid
• the polyimide precursor is cyclodehydrated to form the corresponding polyimide either by thermal or chemical methods.
• the 2-step method gives high molecular weight polyimides if the diamine is highly reactive. However, when the diamine contains electron withdrawing groups such as CF3, CN and NO2, for example, the reactivity of the diamine is reduced and low molecular weight products result. When such electron withdrawing groups are present, the 1-step method is preferred.
• polymerization is carried out by heating the dianhydride and diamine at 180°-220°C in high boiling solvents, such as m-cresol and p-chlorophenol for example, in the presence of a tertiary amine catalyst. Under these conditions, polymerization and imidization occur essentially simultaneously. The water generated from imidization is continuously removed, such as by distillation for example.
• the pre-tilt angle of the alignment layer may be altered by varying the composition of various substituents of mesogen-containing polyimides.
• the linking group Ri in formulas I and II greatly influences the pre-tilt angle generated by the resulting polyimide. UA.388 11
• An alignment layer material made from the polyimide of the present invention provides a high pre-tilt angle.
• the alignment layer provides a pre-tilt angle between about 5° and about 90°.
• the alignment layer provides a pre-tilt angle between about 10° and about 80°.
• the polyimide layer provides a pre-tilt angle between about 20° and about 80°.
• the polyimide layer provides a pre-tilt angle between about 40° and about 70°. It will be appreciated that the pre-tilt angle described herein relates to the use of one single alignment layer with one single liquid crystal layer and not a plurality of layers to obtain the above mentioned angles. A greater thickness of liquid crystal material is not required.
• the dianhydride used to synthesize a mesogen-containing polyimide also affects the pre-tilt angle.
• the dianhydride 2,2'-bis-(3,4-dicarboxyphenyl)-l,l,l,3,3,3-hexafluoropropane dianhydride (6FDA) provides a polyimide with a greater pre-tile angle than a similar polyimide based on 3, 3 ',4 A -biphenyltetracarboxylic dianhydride (BPDA) .
• BPDA 3, 3 ',4 A -biphenyltetracarboxylic dianhydride
• the present invention is not limited to the dianhydrides 6FDA and BPDA.
• Any acid dianhydride suitable for generating traditional polyimides for alignment layers may also be used in the polyimide of the present invention.
• acid dianhydrides are 2,2'-bis[4-(3,4 dicarboxyphenoxy)phenyl] propane dianhydride (BisA-DA), pyromellitic diahydride (PMDA), dibromo- biphenyltetracarboxylic dianhydride, 3,6-diphenylpyromellitic dianhydride, 3, 6-bis(trifluoromethyl) pyromellitic dianhydride, 3, 6 -bis (methyl) pyromellitic dianhydride, 3,6-diidopyromellitic dianhydride, 3,6-dibromopyromellitic dianhydride, 3 , 6-dichloropyromellitic dianhydride, 3, 3', 4,4'- benzophenonetetracarboxylic acid dianhydride, 2 , 3 , 3 '
• tetracarboxylic acid dianhydride bis(2,3-dicarboxyphenyl)methane dianhydride, bis(2,5,6-trifluoro-3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis (3,4- dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride (4,4'-oxydiphthalic anhydride), bis (3,4-dicarboxyphenyl) sulfone dianhydride, (3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride), 4,4'-[4,4'-isopropylidene-di(p-phenyleneoxy)]bis(phthalic anhydride), N,N-(3,4-dicarboxyphenyl)-N-methylamine dianhydride, bis (3,4-dicarboxyphenyl) diethylsilane dian
• Substituents in the diamine component other than the mesogenic group also affect the pre-tilt angle of the resulting polyimide.
• a polyimide with a greater pretilt angle results compared to similar polyimides containing a diamine component which contain bromine substituents as well as mesogenic substituents.
• the pre-tilt angle of a polyimide can also be varied by co-polymerization of a mixture of diamines with a dianhydride.
• a diamine containing pendent mesogen groups may be mixed with a diamine containing perfluorinated carbon atoms and polymerized with a diamine such as 6FDA.
• polyimides containing pendant mesogen groups contributed by a diamine were synthesized and tested for the pre-tilt angle they produced.
• one or more diamines and an acid dianhydride were polymerized in refluxing m-cresol, UA.388 3
• the polymers were isolated by precipitation in methanol and dried under reduced pressure at about 200°C for 6-8 hours. The resulting polyimides were dissolved in an organic solvent such as cyclop entanone and N-methylpyrrolidone (NMP) at 1.5 weight percent and filtered through 1.0 ⁇ m filters.
• Alignment layers were formed by spin coating on an indium-tin oxide (ITO) glass substrate at 2,000 rpm. The layers were heat treated at 150°C, 200°C, 225°C, or 250°C before mechanical rubbing.
• ITO indium-tin oxide
• the rubbing was carried out on a LCBM4 liquid crystal buffing machine.
• Liquid crystal displays were then constructed via a standard procedure.
• ZLI2293 liquid crystal molecules (available from Merck) were added to the cells at room temperature.
• the pretilt angles provided by the polyimides were determined by either the crystal rotating method or the magnetic null method.
• the composition of the various polyimides tested, an abbreviation of each polyimide, the pre-tilt angle provided by each polyimide and comments regarding the observed uniformity of the alignment layer are summarized in Tables 1-4.
• a prior art polyimide (6FDA-PFMB) is also included in Table 1 for comparison purposes.
• Pre-tilt angles after heat treatment at 225°C are listed in Table 1.
• pre-tilt angles were measured after heat treatment at 250°C, except as noted otherwise.
• pre-tilt angles were measured after heat treatment at 200°C, except as noted otherwise, and pre-tilt angles after heat treatment at 150°C are listed in Table 4.
• a number of different factors affect the pre-tilt angle provided by the polyimide of the present invention.
• the type of linkage between the mesogen and the aromatic portion of the diamine is one such factor.
• 6FDA/C6CN provides a pre-tilt angle of 42°
• 6FDA/C6CN (ether) provides a pre-tilt angle of 20°.
• These polyimides differ from each other only in the type of linkage between the mesogen and the aromatic group. It is apparent, therefore that the ester linkage of 6FDA/C6CN provides a greater pre-tilt angle than the ether linkage of 6FDA/C6CN (ether).
• the use of a cyano-substituted mesogen gives a polyimide which provides a slightly higher pre-tilt angle than a non-substituted mesogen.
• the pre-tilt angle provided by 6FDA/C6CN is greater than the pre-tilt angle provided by 6FDA-C6Biph.
• the dianhydride used in the polyimides of the present invention also affect the pre-tilt angle.
• 6-FDA provides a greater pre-tilt angle than BPDA when linked to BrC6CN.
• 6FDA-BrC6CN provides a pre-tilt angle of 20°
• BPDA-BrC6CN provides a pre-tilt angle of 1.5°.
• Substituents in the diamine component other than the mesogenic group also affect the pre-tilt angle of the resulting polyimide.
• a diamine component that contains only mesogenic substituents, such as 6FDA/C6CN provides a polyimide with a greater pre-tilt angle than a similar polyimide such as 6FDA-BrC6CN, which contains a diamine component having bromine substituents as well as mesogenic substituents.
• the pre-tilt angle of 6FDA/C6CN is 42°, while the pre-tilt angle of 6FDA-BrC6CN is 20°.
• heat treatment temperature influences the pre-tilt angle provided by the polyimide.
• the pre-tilt angles of 6FDA/C6CN and 6FDA/C6CN (ether) after heat treatment at 150°C, 175°C, 200°C, and 225°C are compared graphically in Figure 2.
• the pre-tilt angles of 6FDA/C6CN and 6FDA/C6BP are compared in Figure 3 and the pre-tilt angles of 6FDA/C6CN and 6FDA/C11CN are compared in Figure 4 after similar heat treatments.
• the pre-tilt angles provided by 6FDA/C6CN, 6FDA/C6CN (ether), and 6FDA/C6BP are UA.388 28 relatively similar over the heat treatment temperatures tested as shown in Tables 1 and 2.
• the pre-tilt angle provided by 6FDA/C11CN decreases as the heat treatment temperature increases, as seen in Figure 5.
• the pre-tilt angle provided by 6FDA/C11CN is about 90° at a heat treatment temperature of 150°C. At a heat treatment temperature of 200°, the pre-tilt angle drops to about 40°.
• a mixture of diamines may also be used to synthesize a polyimide for use as an alignment layer.
• the pre-tilt angle can be varied.
• Figure 5 is a graph showing the pre-tilt angles of polyimides containing diamines with mesogenic pendent groups (C6BP), diamines with perfluorinated carbon pendent groups (PFMB), or mixtures thereof.
• C6BP mesogenic pendent groups
• PFMB perfluorinated carbon pendent groups
• Figure 5 illustrates that the pre-tilt angle provided by a polyimide obtaining its diamine component only from PFMB is 1.5°.
• the pre-tilt angle of a polyimide obtaining its diamine component from a mixture of PFMB and C6BP increases as the percentage of C6BP increases relative to PFMB.
• the pre-tilt angle increases to about 40°.

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• 2002
  • 2002-01-02 CA CA002433747A patent/CA2433747A1/en not_active Abandoned
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  • 2002-01-02 AU AU2002237753A patent/AU2002237753A1/en not_active Abandoned
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