JP2006293359A - Alignment layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alignment layer which induces uniform and stable alignment in a LC applied thereon, and in particular, which can be easily produced for mass-production and has no drawback of alignment layer or of the material of conventional technologies, and to provide a method and a material for manufacturing the alignment layer. <P>SOLUTION: The alignment layer is obtained by photopolymerization of a polymerizable cholesteric-material, containing one or more kinds of dichroic or liquid crystal photopolymerization initiators in the cholesteric phase. It also relate to a method and a material for manufacturing the alignment layer and to the use of the layer for aligning a liquid crystal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The invention relates to an alignment film obtained by photopolymerization in the cholesteric phase of a polymerizable cholesteric material comprising one or more dichroic or liquid crystal (LC) photoinitiators, a method for the production thereof And its use for materials and liquid crystal alignment.

  Liquid crystal (LC) materials are widely used in many display applications. In fact, it is often necessary to orient the LC material in a certain direction. This orientation is often achieved by rubbing the substrate (or polymer layer) with a velvet cloth. For example, various polyimide layers can be rubbed and used to align the liquid crystal material. Static electricity generated during the rubbing phase can attract dust from the atmosphere and thus cause defects in the alignment layer. In addition, the alignment film may be stretched and damaged during the rubbing process. If these elongations are severe, they interfere with the orientation direction of the liquid crystal material. Therefore, alternative alignment films are desirable. One possible alternative to overcome this problem is a photo-alignment film.

  The LC photo-alignment is a known technique in which anisotropy occurs in the film by exposure of the alignment film to polarized light, for example, UV light, and the LC can be aligned using this. In this way, rubbing is avoided. Various photo-alignment materials and methods are known in the prior art, such as photoisomerizable, photodegradable or photocrosslinkable materials.

1. Photoisomerizable material For example, upon exposure to polarized UV radiation, azobenzene materials undergo isomerization induced by selective light from the trans isomer to the cis isomer. Using this effect, the liquid crystal material can be aligned as described in Non-Patent Document 1 or Patent Document 1, for example. However, azo-containing alignment materials have the serious drawback that they are colored and have problems with their long-term stability due to configuration relaxation and photochemical sensitivity to visible light. In Patent Document 1, a dye having improved photochemical stability is reported. However, due to the other drawbacks listed above, these materials are still ideally not suitable for display applications. Other photoisomerizable materials, such as cinnamates, often have low thermal stability.

2. Photolytic materials Polyimides are widely used for conventional orientation of LC materials (by rubbing). One advantage of polyimide is that it typically has a high thermal stability. However, the disadvantage is the high temperature (typically above 150 ° C.) required to polymerize the material. In the photosensitive mode of the polyimide alignment film, the polyimide is irradiated with linearly polarized UV radiation as described, for example, in US Pat. This results in selective bond breaking (depolymerization), which can be used to orient the LC material. However, the decomposition process often has an adverse effect on LCD performance. For example, polar anchor energy can be 10 times lower compared to rubbed polyimides, and these alignment films can cause image sticking and display flicker in LCDs. See review article by Non-Patent Document 2.

3. Materials that can be photocrosslinked Some materials undergo light-induced crosslinking when irradiated with UV light. For example, polyvinyl-cinnamate (PVCi) films exposed to linearly polarized UV radiation are known to induce uniform LC orientation (perpendicular to the polarization direction of light) [eg, non-patent literature]. 3]. This process is believed to be due to a 2 + 2 cycloaddition reaction. Unfortunately, PVCi oriented films have the disadvantage of poor thermal stability, making them impractical to use. The problem is that (i) a blend of a photoactive (eg, coumarin or cinnamate) side chain polymer and a more inert material (eg, polyimides), eg, Patent Literature 3, Patent Literature 4, Patent Literature 5 or partially (ii) chemically combined with a photoactive polymer with an inert polymer, for example, see US Pat. . However, cycloaddition materials typically have process limitations, where the direction of uniform orientation relative to the plane of incident radiation can vary with exposure time.

  Accordingly, alternative photoalignment materials that do not have the problems listed above are desired.

W. M. Gibbons et al, Nature, 351 49 (1991) US 2003/0072896 US Pat. No. 6,139,926 M. O'Neill & S. M. Kelly, J. Phys. D: Appl. Phys., 33 R67 (2000) M. Schadt, Japan J-Appl Phys., 31 2155 (1992) European Patent Application Publication No. EP-A-0 611 786 International Publication No. 99/49360 Pamphlet US Pat. No. 6,731,362 US Pat. No. 6,749,895 US Pat. No. 5,998,563 US Pat. No. 6,764,724

  One object of the present invention is to provide a uniform and stable orientation of the LC provided thereon, which is easy to manufacture, especially for mass production, and is suitable for the above-described prior art alignment films and materials. It is an object of the present invention to provide an alignment film and methods and materials for its manufacture that do not have drawbacks. Other aims of the present invention are immediately evident to the person skilled in the art from the following detailed description.

  The inventors have found that these objects can be achieved by using the materials and methods described in the present invention. In particular, photopolymerizing an alignment film having good alignment properties by exposing a polymerizable cholesteric mixture comprising a polymerizable LC compound and a dichroic or LC photoinitiator to linearly polarized light in this cholesteric phase. It has been found that can be obtained by:

  WO 03/054111 discloses a method of producing this from a cholesteric biaxial film having a deformed helix and an elliptical refractive index and a polymerizable cholesteric material having a dichroic photoinitiator. This use is not disclosed.

Definition of terms The terms “liquid crystalline or mesogenic material” or “liquid crystalline or mesogenic compound” are one or more rod-shaped or plate-shaped (calamitic) or disc-shaped (discotic) ) Means a material or compound containing a mesogenic group, ie a group having the ability to induce liquid crystal (LC) phase behavior. Compounds or materials that contain mesogenic groups need not necessarily exhibit LC phases themselves. They can also exhibit LC phase behavior only in a mixture with other compounds or when polymerizing mesogenic compounds or materials or mixtures thereof.

  A polymerizable compound having one polymerizable group is also referred to as a “monoreactive” compound, and a compound having two polymerizable groups is referred to as a “bireactive” compound and more than two. Compounds having polymerizable groups are referred to as “multi-reactive” compounds. Compounds that do not have a polymerizable group are also referred to as “non-reactive” compounds. The term “reactive mesogen (RM)” means a polymerizable mesogenic or liquid crystal compound.

  The term “polarization direction” of a linear polarizer means the direction of the plane of linearly polarized light transmitted by the polarizer, corresponding to the “transmission axis” of the polarizer. In the case of stretched plastic polarizer films, including, for example, dichroic iodine-based dyes, this is perpendicular to the stretch direction.

SUMMARY OF THE INVENTION The present invention provides an alignment film obtained by photopolymerizing a polymerizable cholesteric material using polarized light, comprising one or more dichroic or LC photoinitiators in this cholesteric phase. About.
The present invention further relates to a method for producing the alignment film described herein.

  The present invention further relates to the use of the alignment film described herein in a liquid crystal display (LCD) or other optical or electro-optical element or device for decorative or security applications.

Detailed Description of the Invention The alignment film of the present invention has a low helical pitch, contains a dichroic or LC photoinitiator, and is photopolymerized in the cholesteric phase using polarized light, preferably linearly polarized light such as UV light. A possible cholesteric material, preferably a polymer film made from an RM mixture.

  Instead of a cholesteric material, it is also possible to use circularly polarized light in a direction opposite to the twisted direction of the cholesteric helix in the polymerizable material. Instead of cholesteric materials, it is also possible to use chiral smectics, for example chiral smectic C, LC materials.

  The amount of chiral compound in the cholesteric material and the helical twisting power (HTP) are selected so that the material has a pitch well below the visible wavelength range, preferably less than 250 nm. As a result, the film transmits light having a visible wavelength. The reflection wavelength of the cholesteric material is preferably lower than 380 nm. This can be achieved by using a large amount of chiral compound and / or by using a chiral compound having a high HTP value.

The thickness of the alignment film of the present invention is preferably 0.01 to 2 microns, preferably 0.02 to 1 microns, and very preferably 0.02 to 0.07 microns.
The alignment layer of the present invention typically induces planar alignment in the layer of LC material applied thereon.

  Also, the tilt angle that changes in the LC material layer applied on the alignment layer, i.e. from the surface of the LC layer facing the alignment layer ("first surface") to the opposite surface ("second surface"). It is also possible to induce a spray orientation with For example, as described in WO 98/12584 A1, for example, a spray orientation having a low tilt on the first surface of the LC layer and a high tilt on the second surface, the second surface being an “open” surface ( This can be achieved if the LC material contains polar molecules or polar RMs (ie it is not covered by a substrate and is in contact with air).

  In addition, an alignment film containing one or more additives that has an effect of lowering the surface energy (or surface energy component) of the RMM to be lower than the surface energy of the substrate is used for homeotropic alignment in the LC layer. It is also possible to guide. One or more compounds that can be added at a concentration sufficient to achieve this and / or have a high anisotropy of surface energy (eg, fluorocarbon based surfactants) For example, application of an LC compound comprising an LC compound or RM with polar end groups can be used. These techniques are described, for example, by S. Naemura Mol. Cryst. Liq. Cryst. 68 183 (1981).

Preferably, the method for producing an alignment film of the present invention comprises the following steps: a) providing a polymerizable cholesteric material containing one or more dichroic or LC photoinitiators as a thin layer on a substrate ,
b) optionally orienting a layer of polymerizable material;
c) polymerizing the polymerizable material or selected portions thereof by exposing to polarized light at a temperature at which the material exhibits a cholesteric phase; and d) optionally removing the polymerized film from the substrate.

  Alternatively, the photopolymerization (step c) is first performed with linearly polarized UV light (preferably with a short irradiation time and low power) and then with unpolarized UV light (preferably with a longer irradiation time). It is also possible to carry out in two stages (with higher power). Preferably, only one photopolymerization stage is used.

  In the method of the present invention, the alignment direction of the LC material is 45 ° with respect to the polarization direction of the polarized light. This provides several advantages.

  One advantage is that the alignment direction of the alignment film relative to the length and width directions can be easily determined by selecting a considerable irradiation direction. This can be done, for example, by producing a roll-to-roll stack of optical films, where a single film has its orientation direction or optical axes aligned with each other. Or preferably with a specific orientation, for example at 45 ° with respect to the processing (or laminating machine) direction.

  Another advantage is that it makes it possible to produce patterned alignment films with two or more regions or patterns of two or more regions having different alignment directions. It is. Such a patterned alignment film is another aspect of the present invention. This can be produced, for example, by the methods described herein, wherein selected regions of the polymerizable layer are separated in two or more separate stages, i.e. independent of each other. Then, photopolymerization is performed using polarized light having different irradiation directions. The areas not polymerized in the first (or previous) polymerization stage are covered, for example by a photomask, and the irradiation direction is changed in the second (or next) polymerization stage.

The polymerizable LC material includes one or more dichroic or LC photoinitiators.
The polymerizable LC material is preferably a mixture of two or more compounds, at least one of which is a polymerizable or crosslinkable compound. A polymerizable compound having one polymerizable group is hereinafter referred to as “monoreactive”. Crosslinkable compounds, i.e. compounds having two or more polymerizable groups, are also referred to below as "bi-reactive or multi-reactive".

Particularly preferred is
a) one or more achiral monoreactive, bireactive or polyreactive polymerizable mesogenic compounds,
b) one or more chiral compounds which may also be polymerizable and / or mesogenic,
c) one or more dichroic or LC photoinitiators,
d) optionally one or more monoreactive, direactive or polyreactive, polymerizable non-mesogenic compounds,
e) optionally one or more non-dichroic photoinitiators,
f) optionally, one or more dyes that exhibit an absorption maximum at the wavelength used to initiate photopolymerization,
g) optionally one or more chain transfer agents,
h) optionally one or more surfactant compounds,
i) A polymerizable material optionally containing one or more stabilizers.

More preferred is a polymerizable comprising one or more monoreactive polymerizable mesogenic compounds and one or more direactive or polyreactive polymerizable mesogenic compounds. Material.
More preferred include one or more monoreactive achiral polymerizable mesogenic compounds and one or more direactive or polyreactive achiral polymerizable mesogenic compounds. , A polymerizable material.

More preferred are one or more monoreactive, direactive or multireactive chiral polymerizable mesogenic compounds and one or more monoreactive, bireactive or multireactive. Polymerizable material comprising a chiral achiral polymerizable mesogenic compound.
Further preferred include one or more non-reactive chiral compounds and one or more monoreactive, direactive or polyreactive achiral polymerizable mesogenic compounds, Polymerizable material.

Highly preferred polymerizable materials include the following:
-2 to 70% of one or more achiral direactive polymerizable mesogenic compounds,
-20 to 95% of one or more achiral monoreactive polymerizable mesogenic compounds,
-20 to 95% of one or more chiral monoreactive polymerizable mesogenic compounds and / or 1 to 25% of one or more which may also be mesogenic A chiral non-polymerizable compound,
-2 to 70% of one or more chiral direactive polymerizable mesogenic compounds and / or 1 to 25% of one or more which may also be mesogenic A chiral non-polymerizable compound,

-0.1-20% of one or more dichroic photoinitiators, preferably 0.5-15% of dichroic, very preferably liquid crystal photoinitiators,
From 0 to 10% of one or more chain transfer agents,
From 0 to 3% of one or more non-polymerizable or monoreactive, direactive or polyreactive polymerizable surfactants,
-1 to 8%, preferably 0 to 5% of one or more non-dichroic photoinitiators.

The polymerizable mesogenic or LC compound is preferably a monomer, very preferably a calamitic monomer. These materials typically have good optical properties, such as reduced chromaticity, and can be easily and quickly oriented to the desired orientation, especially on a large scale. It is important for the industrial production of polymer films. It is also possible for the polymerizable material to contain one or more discotic monomers.
The polymerizable material described herein is another aspect of the present invention.

  Polymerizable monoreactive, bireactive and polyreactive mesogenic or LC compounds suitable for the present invention are known per se and are standard academic books on organic chemistry, such as Houben-Weyl, Methoden der organischen Chemie, It can be produced by the method described in Thieme-Verlag, Stuttgart.

  Suitable polymerizable mesogenic or LC compounds for use as monomers or comonomers in a polymerizable LC mixture are, for example, WO 93/22397, EP 0 261 712, DE 195 04 224, WO 95/22586, WO 97/00600, US 5,518,652, US 5,750,051, US 5,770,107 and US 6,514,578.

Examples of suitable and preferred polymerizable mesogenic or LC compounds (reactive mesogens) are given in the list below.

Where
P is a polymerizable group, preferably an acrylic, methacrylic, vinyl, vinyloxy, propenyl ether, epoxy, oxetane or styrene group;
x and y are 1 to 12 identical or different integers;
A and D are 1,4-phenylene or 1,4-cyclohexylene, optionally monosubstituted, disubstituted or trisubstituted by L ¹ ;
u and v are independently 0 or 1,
Z ⁰ is —COO—, —OCO—, —CH ₂ CH ₂ —, —C≡C— or a single bond,

R ⁰ is one or more, preferably 1 to 12 C atoms, optionally fluorinated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy, or Y ⁰ ,
Y ⁰ is F, Cl, CN, NO ₂ , OCH ₃ , OCN, SCN, optionally fluorinated alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 4 C atoms. Or mono, oligo or polyfluorinated alkyl or alkoxy having 1 to 4 C atoms,
Ter is a terpenoid group, such as menthyl,
Chol is cholesteryl,
L ¹ and L ² are independently of each other H, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy having 1 to 5 C atoms. Or it is alkoxycarbonyloxy.

Suitable non-polymerizable chiral compounds include, for example, standard chiral dopants such as R or S-811, R or S-1011, R or S-2011, R or S-3011, R or S-4011, R or S-5011 or CB15 (all available from Merck KGaA, Darmstadt, Germany).
Suitable polymerizable chiral compounds are, for example, the compounds (R14) to (R23) listed above or the polymerizable chiral material Paliocolor® LC756 (BASF AG, Ludwigshafen, Germany). From).

  Highly preferred are chiral compounds with high HTP, in particular compounds containing a sorbitol group as described for example in WO 98/00428, such as compounds containing a hydrobenzoin group as described in GB 2,328,207, for example WO 02/94805 Chiral binaphthyl derivatives described in WO 02/34739, for example chiral binaphthol acetal derivatives described in WO 02/06347, for example chiral TADDOL derivatives described in WO 02/06265 and WO 02/06196 or WO 02 / Described in 06195 are chiral compounds having at least one fluorinated linking group and a terminal or central chiral group.

Particularly preferred are chiral compounds having an HTP of 40 μm ⁻¹ or higher, very preferably 60 μm ⁻¹ or higher, most preferably 80 μm ⁻¹ or higher.

  Particularly preferred are polymerizable sorbitols such as those represented by formulas (R21) and (R22), and polymerizable hydrobenzoins such as those represented by formula (R23). Further preferred are non-polymerizable sorbitols and hydrobenzoins represented by the following formulas I and II. Further preferred are chiral binaphthols represented by the following formulas III and IIIb.

式中、Ｐ、Ｚ^０、Ａ、Ｌ^１、Ｌ^２、ｖおよびｘは、前に示した意味を有し、Ｒ^１は、前に示したＲ^０の意味の１つを有するか、またはＰ−Ｓｐであり、Ｒは、Ｒ^０の意味の１つを有し、ｍは、０、１、２または３であり、ｒ１およびｒ２は、０、１、２、３または４である。

In which P, Z ⁰ , A, L ¹ , L ² , v and x have the previously indicated meaning and R ¹ has ^one of the previously indicated meanings of R ⁰ , or P-Sp, R has one of the meanings of R ⁰ , m is 0, 1, 2 or 3, and r1 and r2 are 0, 1, 2, 3 or 4.

Highly preferred are compounds of formula III, wherein R ¹ is P-Sp. More preferably, m is 0 or 1, Z ⁰ is —COO—, —OCO— or a single bond, and A is optionally substituted by one or two groups L ¹ A compound of formula III which is 4-phenylene or trans-1,4-cyclohexylene.

As the dichroic photoinitiator, for example, the following compounds can be used.

Particularly preferred are dichroic or LC photoinitiators containing α-amino groups as disclosed in EP 1 388 538, for example of the formula

式中、Ｌ”は、ＨまたはＦであり、Ｒは、１〜１２個のＣ原子を有するアルキルまたはアルコキシであり、Ｒ’およびＲ”は、１〜６個のＣ原子を有するアルキルまたはアルコキシ、極めて好ましくはメチル、エチルまたはプロピルから選択されている、
で表されるものである。

Wherein L "is H or F, R is alkyl or alkoxy having 1 to 12 C atoms, and R 'and R" are alkyl or alkoxy having 1 to 6 C atoms. Very preferably selected from methyl, ethyl or propyl,
It is represented by

Unless otherwise stated, the general production of the polymer LC films of the invention can be carried out according to standard methods known from the literature.
Typically, a polymerizable LC material is applied or otherwise provided on a substrate, where it is aligned or is aligned and in situ. Polymerization by photopolymerization at a selected temperature, very preferably by UV photopolymerization, fixes the LC molecule orientation. If desired, uniform orientation can be promoted by additional means such as shearing and / or annealing of the LC material, surface treatment of the substrate or addition of a surfactant to the LC material.

  For example, a glass or quartz sheet or a plastic film can be used as the substrate. It is also possible to place the second substrate on top of the coated material before and / or during and / or after polymerization. The substrate can be removed or not removed after polymerization. In the case of curing with actinic radiation, when using two substrates, at least one substrate must be transparent to the actinic radiation used for the polymerization. Isotropic or birefringent substrates can be used. If the substrate is not removed from the polymerized film after polymerization, an isotropic substrate is preferably used.

  Suitable and preferred plastic substrates are, for example, films of polyester, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), polyvinyl alcohol (PVA), polycarbonate (PC) or triacetyl cellulose (TAC), very preferably PET or TAC film. As the birefringent substrate, for example, a uniaxially stretched plastic film can be used. PET films are commercially available, for example, from DuPont Teijin Films under the trade name Melinex®.

  The polymerizable material can be applied onto the substrate by conventional application techniques such as spin coating or blade coating. This is also applied to the substrate by conventional printing methods known to experts, such as screen printing, offset printing, open reel printing, letterpress printing, gravure printing, rotary gravure printing, flexographic printing, intaglio printing, pad printing, heat sealing. It can be applied by printing, ink jet printing, or printing with a size or printing plate.

  In addition, the polymerizable material can be dissolved in a suitable solvent. This solution is then applied or printed onto the substrate, for example by spin coating or printing or other known techniques, and the solvent is removed by evaporation prior to polymerization. In many cases, it is preferred to heat the mixture to facilitate evaporation of the solvent. As the solvent, for example, a standard organic solvent can be used. Solvents such as ketones such as acetone, methyl ethyl ketone, methyl propyl ketone or cyclohexanone; acetate esters such as methyl acetate, ethyl or butyl or methyl acetoacetate; alcohols such as methanol, ethanol or isopropyl alcohol; aromatic solvents such as It can be selected from toluene or xylene; halogenated hydrocarbons such as di or trichloromethane; glycols or esters thereof such as PGMEA (propyl glycol glycol monomethyl ether), γ-butyrolactone, and the like. It is also possible to use binary, ternary or quaternary or higher mixtures of the aforementioned solvents.

  Alignment film by initializing the polymerized LC material (eg planar orientation) by annealing the material prior to polymerization, for example by rubbing the substrate, by shearing the material during or after coating Can be achieved by applying a magnetic or electric field to the applied material or by adding a surface active compound to the material. A review of orientation techniques can be found, for example, by I. Sage in “Thermotropic Liquid Crystals”, edited by GW Gray, John Wiley & Sons, 1987, pp. 75-77; and by T. Uchida and H. Seki, “Liquid Crystals -Applications and Uses Vol. 3 ", edited by B. Bahadur, World Scientific Publishing, Singapore 1992, pages 1-63. An overview of alignment materials and techniques is given by J. Cognard, Mol. Cryst. Liq. Cryst. 78, Addendum 1 (1981), pages 1-77.

Particularly preferred are polymerizable materials comprising one or more surfactants that promote specific surface orientation of the LC molecules. Suitable surfactants are described, for example, in J. Cognard, Mol. Cryst. Liq. Cryst. 78 , Addendum 1, 1-77 (1981). Preferred aligning agents for planar alignment are, for example, nonionic surfactants, preferably fluorocarbon surfactants, such as commercially available Fluorad FC-171® (from 3M Co.) or Zonyl. ) FSN® (from DuPont), a multiblock surfactant as described in GB 2 383 040 or a polymerizable surfactant as described in EP 1 256 617.

  It is also possible to apply an alignment film on the substrate and provide a polymerizable material on the alignment film. Suitable alignment films are known in the industry, for example, rubbed polyimide or alignment films manufactured by photo-alignment described in US 5,602,661, US 5,389,698 or US 6,717,644.

  It is also possible to induce or improve the orientation by annealing the polymerizable LC material at elevated temperatures, preferably at this polymerization temperature, prior to polymerization.

  Polymerization is accomplished by exposing the polymerizable material to polarized light such as UV light, IR light or visible light, preferably UV light. As a source of actinic radiation, for example, a single UV lamp or a set of UV lamps can be used. When using high lamp power, the curing time can be reduced. Other possible light sources are lasers, for example UV, IR or visible lasers.

  In addition to dichroic or LC photoinitiators, standard photoinitiators can be used. Typical radical photoinitiators are, for example, commercially available Irgacure® or Darocure® (Ciba Geigy AG, Basel, Switzerland).

  The polymerizable material may also contain one or more stabilizers or inhibitors, such as commercially available Irganox® (Ciba Geigy), to prevent unwanted spontaneous polymerization. AG, Basel, Switzerland).

  Curing time depends inter alia on the reactivity of the polymerizable material, the thickness of the applied layer, the type of polymerization initiator and the output of the UV lamp. The curing time is preferably ≦ 5 minutes, very preferably ≦ 3 minutes, most preferably ≦ 1 minute. For mass production, a short curing time of ≦ 30 seconds is preferred.

Preferably, the polymerization is carried out in an inert gas atmosphere such as nitrogen or argon.
The polymerizable material can also be one or more dyes, in particular UV dyes such as 4,4 "-azoxyanisole or Tinuvin, having an absorption maximum tuned to the wavelength of radiation used for the polymerization. (Registered trademark) dye (from Ciba AG, Basel, Switzerland).

  In another preferred embodiment, the polymerizable material comprises one or more monoreactive polymerizable non-mesogenic compounds, preferably in an amount of 0-50%, very preferably 0-20%. . Typical examples are alkyl acrylates or alkyl methacrylates.

  In another preferred embodiment, the polymerizable material comprises one or more direactive or multireactive polymerizable non-mesogenic compounds, direactive or multireactive polymerizable mesogenic compounds. Alternatively or in addition, it is preferably contained in an amount of 0 to 50%, very preferably 0 to 20%. Typical examples of direactive non-mesogenic compounds are alkyl diacrylates or alkyl dimethacrylates having an alkyl group with 1 to 20 C atoms. Typical examples of multireactive non-mesogenic compounds are trimethylpropane trimethacrylate or pentaerythritol tetraacrylate.

  It is also possible to modify the physical properties of the polymer film by adding one or more chain transfer agents to the polymerizable material. Particularly preferred are thiol compounds such as monofunctional thiols such as dodecane thiol or multifunctional thiols such as trimethylpropanetri (3-mercaptopropionate). Highly preferred are mesogenic or LC thiols as disclosed, for example, in WO 96/12209, WO 96/25470 or US 6,420,001. By using a chain transfer agent, the length of the free polymer chain and / or the length of the polymer chain between two crosslinks in the polymer film can be controlled. In increasing the amount of chain transfer agent, the length of the polymer chain in the polymer film decreases.

  The polymerizable material can also include one or more monomers and / or one or more dispersing aids that can form a polymer binder or polymer binder. Suitable binders and dispersion aids are disclosed, for example, in WO 96/02597. Preferably, however, the polymerizable material does not contain a binder or dispersion aid.

  The polymerizable material further comprises one or more additional components such as catalysts, sensitizers, stabilizers, inhibitors, chain transfer agents, co-reacting monomers, surfactant compounds, lubricants, wetting agents. , Dispersants, hydrophobing agents, adhesives, flow improvers, antifoaming agents, degassing agents, diluents, reactive diluents, adjuvants, colorants, dyes or pigments.

  The polymer film of the present invention can be used as an alignment film for LC materials. For example, it can be used in an LCD to induce or improve the orientation of a switchable LC medium or to orient subsequent layers of polymerizable LC material applied thereon. In this way, a stack of polymerized LC films can be produced.

  The polymer film of the present invention can be applied to conventional LC displays such as vertical alignment, eg DAP (deformation of alignment phase), ECB (electrically controlled birefringence), CSH (color super homeotropic), VA (vertical alignment). , VAN or VAC (vertical alignment nematic or cholesteric), display with MVA (multi-domain vertical alignment) or PVA (patterned vertical alignment) mode; bent or hybrid alignment, eg OCB (optically compensated bent cell or Display with optically compensated birefringence, R-OCB (reflective OCB), HAN (hybrid oriented nematic) or pi-cell (π-cell) mode; twisted orientation, eg TN (twisted nematic), HTN (high) Twisted nematic), Display with TN (super twisted nematic), AMD-TN (active matrix driven TN) mode; display with IPS (in-plane switching) mode or display with switching in optically isotropic phase, eg in WO 02/93244 It can be used in what is described.

  Particularly preferred are TN, STN, VA and IPS displays, especially active matrix type displays. Further preferred is a transflective display.

Above and below, all temperatures are given in degrees Celsius, and all percentages are by weight unless otherwise stated. The following abbreviations are used to illustrate LC phase behavior: C, K = crystalline; N = nematic; S = smectic; N ^* , Ch = chiral nematic or cholesteric; I = isotropic. The number between these symbols indicates the phase transition temperature in degrees Celsius. Furthermore, mp is the melting point and cp is the clearing point (at ° C).

The HTP of the chiral dopant in the LC host material is shown as HTP = (p * c) ⁻¹ (in μm ⁻¹ ), where p is the pitch of the molecular helix (in μm) and c is the host The concentration of the chiral compound in (in weight%) (for example, a concentration of 1% by weight corresponds to c = 0.01). Unless otherwise stated, the specific HTP values given herein relate to a dopant concentration of 1% in the LC host mixture MLC-6260 (Merck KGaA, Darmstadt, Germany) at 20 ° C.

Unless stated otherwise, the percentages of components of the polymerizable mixture shown herein refer to the total amount of solids in the mixture polymerizable mixture, i.e. free of solvent.
The following examples illustrate the invention without limiting it.

Example 1
The following polymerizable mixture is blended:
Compound (1) 5.42%
Compound (2) 40.00%
Compound (3) 40.00%
Compound (4) 4.00%
Compound (5) 0.50%
Paliocolor (registered trademark) LC756 10.00%
Irgacure (registered trademark) 1076 0.08%

  Compounds (1) to (3) are known from the prior art. A dichroic photoinitiator (4) is disclosed in EP 1 388 538. Surfactant (5) is disclosed in GB 2 383 040. The mixture has a clearing point of 40 ° C.

A slide having an alignment film is manufactured as follows. The aforementioned mixture is dissolved in methyl ethyl ketone to obtain a 10 wt% solution. This solution is spin coated onto a clean glass substrate (5000 RPM, 30 seconds). The resulting film was photopolymerized with 5 mWcm ⁻² linearly polarized UV-A radiation for 2 seconds at room temperature in a nitrogen atmosphere to achieve the preferred orientation, and secondly, 20 mWcm ⁻² UV-A. Using radiation (unpolarized), photopolymerization is performed at room temperature in a nitrogen atmosphere for 30 seconds to obtain a hard film.

Various combinations of irradiation conditions can be used, and it is also possible to perform both orientation and polymerization in one stage with increased polarized UV power (eg 10-60 mWcm ⁻² ).
The final film thickness is measured (using an alpha-step profilometer) and is about 100 nm thick.

Example 2
A commercially available polymerizable nematic RM solution RMS03-001 (from Merck KGaA, Germany) is spin coated onto the film prepared in Example 1 and photopolymerized. The film is inspected at various angles between crossed polarizers as shown in FIG. The analysis of FIG. 1 shows that the alignment film works and induces good quality alignment in the RMS03-001 film.

FIG. 2 shows a layer of a standard polymerizable nematic LC mixture coated on the orientation of Example 1 between crossed polarizers. The sample is shown rotated 45 ° in (a) bright (or delayed) state and (b) dark state.

Claims (15)

  An alignment film obtained by photopolymerizing a polymerizable cholesteric material containing one or more dichroic or liquid crystal (LC) photoinitiators in the cholesteric phase using polarized light.   The alignment film according to claim 1, wherein the polarized light is linearly polarized light.   The alignment film according to claim 1, wherein the polarized light is UV light.   The alignment film according to claim 1, wherein the polymerization is performed in an inert gas atmosphere.   The polymerizable material comprises one or more monoreactive and one or more direactive or polyreactive polymerizable mesogenic compounds. The alignment film in any one of 1-4. Polymerizable material
a) one or more achiral polymerizable mesogenic compounds,
b) one or more chiral compounds which may also be polymerizable and / or mesogenic,
c) one or more dichroic or LC photoinitiators,
d) optionally one or more monoreactive, direactive or polyreactive, polymerizable non-mesogenic compounds,
e) optionally one or more non-dichroic photoinitiators,
f) optionally, one or more dyes that exhibit an absorption maximum at the wavelength used to initiate photopolymerization,
g) optionally one or more chain transfer agents,
h) optionally one or more surfactant compounds,
i) The alignment film according to claim 1, which optionally contains one or more stabilizers.   The alignment film according to claim 1, wherein the alignment direction is 45 ° with respect to the polarization direction of polarized light.   The alignment film according to claim 1, wherein the alignment direction is controlled by appropriately selecting the irradiation direction of polarized light.   The alignment film according to claim 1, which has a thickness of 0.05 to 1 micron.   The alignment film according to claim 1, wherein the alignment film has two or three or more regions having different alignment directions or a pattern of two or three or more regions.   A method for producing an alignment film as defined in claim 1. The following steps a) providing a polymerizable cholesteric material comprising one or more dichroic or liquid crystal (LC) photoinitiators as a thin layer on a substrate;
b) optionally orienting a layer of polymerizable material;
c) polymerizing the polymerizable material or selected portions thereof by exposing the material to polarized light at a temperature at which the material exhibits a cholesteric phase; and d) optionally removing the polymerized film from the substrate. The method of claim 11, characterized in that   13. A method according to claim 11 or 12, characterized in that different parts of the polymerizable material are photopolymerized separately from one another with polarized light having different irradiation directions.   Use of the alignment film according to any one of claims 1 to 10 in a liquid crystal display (LCD), an optical or electro-optical device, decoration or security applications.   An LCD, optical or electro-optical element, decoration or security marking comprising the alignment film according to claim 1.

Images