KR20060108539A - Cholesteric film and homeotropic alignment layer - Google Patents

Abstract

The present invention relates to cholesteric films comprising low optical retardation polymerized cholesteric liquid crystal (CLC) materials, and their use as homeotropic array layers.

Description

Cholesteric film and homeotropic array layer {CHOLESTERIC FILM AND HOMEOTROPIC ALIGNMENT LAYER}

1 shows the delay results for the C2 / N2 combination.

2 shows the delay result for the C3 / N3 combination.

3 shows the delay results for the C1 / N1 combination.

4 shows the delay result for the C2 / N2 combination.

5 shows the delay results for the C3 / N3 combination.

FIG. 6 shows the decrease in off-axis delay for samples C1 / N1, C2 / N2 and C3 / N33 at 60 ° viewing angle.

7 shows the delay side of polymer films C5 to C7.

8 shows the delay side of the combination of C7 and C7 / N7.

9 shows the delay side of the C8 / N8 / glass combination.

10 shows the delay side of C8 / N8 at different time intervals.

FIG. 11 shows the decrease in the off-axis delay of C8 / N8 at 60 ° viewing angle.

12 shows the off-axis delay drop of C8 / N8 / glass at 60 ° viewing angle.

The present invention relates to cholesteric films comprising polymerized cholesteric liquid crystal (CLC) materials with low or no optical retardation and their use as homeotropic alignment layers.

Homeotropic polymeric films are disclosed in the prior art and are disclosed, for example, in WO 98/00475. These films are typically made by providing a polymerizable LC monomer or reactive mesogen (RM) on a substrate, arranging them in a homeotropic orientation, and fixing the oriented structure by polymerizing in situ. However, standard methods known in the art to promote homeotropic orientation, such as rubbing these substrates or applying an array such as alkyltrichlorosilane, lecithin, silica or thin layers of high tilt polyimide are satisfactory uniform. It does not provide an array.

Other methods of promoting homeotropic alignment have also been discussed in the art. For example, EP 1 376 163 A2 describes the preparation of homeotropic polymer films by coating a polymerized LC material on another polymerized LC material with a flat or spirally twisted orientation and serving as an alignment layer. However, linear or twisted LC films can themselves act as optical retarders, thus affecting the performance of homeotropic films. Therefore, in many applications, the homeotropic film needs to be delaminated from the array layer.

It is an object of the present invention to use in the production of homeotropic polymer films, which does not have the disadvantages of an array layer comprising a homeotropic arrangement, in particular a layer of the prior art, and which enables easy and economical production even on a large scale. To provide. Yet another object is to provide an improved method of making homeotropic polymer films. It is another object of the present invention to extend the pool of alignment layers and methods for facilitating homeotropic alignment available to those skilled in the art. Other objects of the present invention are immediately apparent to those skilled in the art from the following detailed description.

This object can be attained by the materials and films according to the invention and the production process.

It has been found that with the materials and methods according to the invention it is possible to produce CLC films with only low optical delay and which are very optically isotropic and still can be used as an alignment layer to promote homeotropic alignment. In addition, these array layers can be used to thermally stabilize the polymerized homeotropic arrayed film produced thereon. Homeotropic polymer films made on these alignment layers have excellent optical properties, much-reduced defect counts, and significantly better thermal stability properties compared to isotropic films made by prior art methods.

As used herein, the term “film” includes hard or flexible self-supporting or free standing films having mechanical stability as well as coatings or layers on or between support substrates.

The term "liquid crystal or mesogenic material" or "liquid crystal or mesogenic compound" refers to a substance or compound comprising one or more rod-like, plate- or disc-shaped mesogenic groups, ie groups capable of inducing liquid crystalline behavior. LC compounds of the rod or plate group are also known in the art as "calamitic liquid crystals". LC compounds of the discotic group are also known in the art as "discotic liquid crystals". Compounds or materials comprising mesogenic groups do not necessarily have to be LC phases themselves. It is also possible to exhibit liquid crystalline behavior only in mixtures with other compounds or only when the mesogenic compounds or substances or mixtures thereof are polymerized.

For the sake of brevity in the following, the term "liquid crystal material" is used as both mesogenic and LC material.

Also, polymerizable compounds having one polymerizable group are referred to as "monoreactive" compounds, compounds having two or more polymerizable groups are referred to as "direactive" compounds, and compounds having more than two polymerizable groups are referred to as "polyreactive" Is referred to as a compound. Compounds without polymerizable groups are also referred to as "non-reactive" compounds.

The term "reactive mesogen" (RM) means a polymerizable mesogenic or liquid crystalline compound.

The term "director" is a term well known in the art, in which the long molecular axis (for calamitic compounds) or the short molecular axis (for discotic compounds) of mesogens in liquid crystal materials Means a preferred orientation direction.

In films comprising uniaxial positive birefringent LC materials, the optical axis is given by the director.

The term "cholesteric structure" or "spiral twisted structure" refers to a film comprising LC molecules, where the director is spirally twisted about an axis parallel to the film plane and perpendicular to the film plane.

The term "homeotropic structure" or "homeotropic orientation" refers to a film whose optical axis is substantially perpendicular to the film plane.

The term "planar structure" or "planar orientation" refers to a film in which the optical axis is arranged substantially parallel to the film plane.

The present invention is characterized by having an optical retardation having an absolute value of less than 50 nm for light with a wavelength of 550 nm, preferably polymerized cholesteric liquid crystals having a thickness of less than 0.5 μm and in which the CLC material is polymerized in isotropic phase It relates to a film comprising a (CLC) material.

In addition, the present invention relates to the use of such films as homeotropic array layers for LC materials.

In addition, the present invention provides a polymerizable LC material on a CLC film according to the invention taking in the homeotropic direction, polymerizing the LC material to form a polymer film, and optionally a homeotropic polymer film from the CLC film. By removing, the present invention relates to a method for producing a polymerized homeotropic LC film.

The invention further relates to a multilayer comprising the polymerized homeotropic LC film and the CLC film according to the invention.

The present invention furthermore relates to the use of the CLC film or multilayer according to the invention as a component in decorative or safety optical or electro-optical devices.

The invention further relates to an optical component according to the invention, a retarder, a compensator, an arrangement, a liquid crystal display, a decorative image, or a device comprising a safety manufacturing or CLC film or multilayer.

The CLC films described in the present invention are very thin birefringent films or optically isotropic films. These can be used as homeotropic array layers that improve the thermal durability properties of the polymerized LC film arranged on the homeotropic array and provide excellent array quality.

Therefore, homeotropically arranged LC polymer films can be prepared directly on the CLC film, which serves as an alignment layer and optionally as a substrate. The homeotropic polymer film produced in this manner does not need to be delaminated or removed from the CLC film. Instead, a combination of homeotropic film and CLC film can be used for the manufacture of the optical element, for example it can be laminated on other films such as polarizers, adhesion layers or further retardation films or display panels. This can reduce the number of plastic substrates and the lamination steps, result in reduced process costs in the manufacture of displays or optical components and make mass production easier and cheaper.

When a homeotropic polymer film is produced on a CLC film according to the invention as an array layer, the durability of the homeotropic polymer layer is improved compared to a film made on a conventional substrate, such as polyimide coated glass. In particular, homeotropic polymer films exhibit less stability and higher stability of their optical retardation when exposed to high temperatures and / or humidity.

The CLC film according to the invention can also be used as an alignment layer to promote homeotropic alignment in other LC materials, such as low molar mass LC materials, or mixtures of low molar mass and polymerizable LC (or LC polymer gels). And it is used as an exchangeable medium in the LCD. In addition, the CLC films are applied, preferably as a solution, optionally dried on the CLC film, heated above their glass transition temperature or melting temperature, optionally sealed to a high temperature to improve alignment, and then cooled Or can be used to facilitate homeotropic alignment in magnetized, easily synthesized LC polymers to fix homeotropic orientation.

CLC films with low thickness are particularly suitable as alignment layers inside exchangeable LC cells of the display (“in-cell application”) to facilitate alignment in polymerized or unpolymerized LC media.

The CLC film preferably provides a polymerizable CLC material on a substrate that takes the orientation of its cholesteric helix axis substantially perpendicular to the plane of the layer, polymerizes the CLC material to form a polymer film, and optionally polymerizes the polymer film to the substrate. It is obtained by removing from. The arrangement and polymerization of the CLC material can be obtained by standard methods known and described in the literature.

The polymerizable CLC materials and CLC polymer films according to the invention are preferably selected such that they have reflective wavelength lengths below the visible wavelength range, more preferably within the ultraviolet range or below the ultraviolet range, most preferably below 350 nm. to be. The cholesteric helix pitch in these CLC materials is preferably less than 275 nm. This can be achieved, for example, by using a CLC material comprising a large amount of chiral compound, or a chiral compound with high helical twisted power (HTP). Because the spiral pitch lowers the value below the visible wavelength length range, the Bragg reflection bands occur within the ultraviolet range, in order for the CLC film to be transparent to the visible wavelength length of light acting purely as these visible wavelength lengths.

The first preferred embodiment of the present invention relates in particular to a CLC film having a thickness of less than 0.5 μm which is advantageous for use as a homeotropic alignment layer for producing films comprising homeotropically arranged polymerized LC materials.

Since the CLC film is thin, it has low optical delay and its optical properties that do not interact strongly with or only to a small extent with that of the homeotropic film coated on the CLC film, which is durable for many optical applications. For example, the off-axis delay of CLC films is opposite to that of homeotropic films, but the magnitude of the delay from each film is significantly different, and the optical effect from the homeotropic film is predominant.

CLC films are typically made on a substrate, for example glass or transparent plastic film, which is preferably optically isotonic. After its manufacture, the CLC film remains on the substrate and can be used directly as an alignment layer for making homeotropic films. After polymerization, the homeotropic and CLC films may or may not be removed from this substrate together.

Especially preferred are 0.1 to 0.5 mu m thick, preferably 0.15 to 0.5 mu m thick; A thickness of less than 0.4 µm, preferably 0.1 to 0.4 µm, more preferably 0.15 to 0.4 µm; A thickness of less than 0.3 μm, preferably less than 0.2 μm; And a CLC film having a delay R _th of 0 to -50 nm.

The delay R _th is defined as:

Where

d is the film thickness;

n _x + n _y is the refractive index in the direction perpendicular to the film plane;

n _z is a refractive index in a direction perpendicular to the film plane.

A second aspect of the invention relates to a CLC film which can be obtained by polymerizing a polymerizable CLC material in its isotropic phase, ie, at a temperature above cholesteric-isotropic transition (isochronous point). This provides an optically isotropic polymer film that does not interact with the optical properties of the homeotropic film coated thereon.

Isotropic phases can be achieved by polymerizing at a given temperature and increasing the amount of chiral components in the polymerizable CLC material, or by increasing the polymerization temperature of a given CLC material to a temperature above the clearing point.

In addition, polymerization in isotropic phase obviates the requirement of achieving a uniform arrangement of CLC materials. Therefore, no special substrate treatment, such as scrubbing or the use of dispersants, is required. In addition, this has the advantage of reducing the number of defects in the film due to adhesion from the rubbing material to the substrate by the static electricity generated by the particles or by rubbing.

The polymerizable CLC material includes, for example, one or more chiral polymerizable mesogenic compounds, or one or more achiral polymerizable mesogenic compounds and one or more chiral compounds.

Preferably, the polymerizable CLC material comprises at least one achiral polymerizable mesogenic compound and at least one chiral compound. The chiral compound can be selected from the group consisting of polymerizable chiral compounds, conventional chiral dopants, polymerizable chiral non-mesogenic and polymerizable chiral mesogenic compounds.

Especially preferred are polymerizable CLC materials comprising:

At least one achiral polymerizable mesogenic compound having one polymerizer, at least one achiral polymerizable mesogenic compound having at least two heavy synthetic groups, and at least one chiral compound;

At least 5% of a chiral compound; And

At least one chiral compound having a helical twisted power (HTP) in an amount of -30 μm ⁻¹ or greater, preferably 8%.

Polymeric LC materials for making homeotropic films include one or more polymerizable mesogenic compounds having one polymerizable group, and one or more achiral polymerizable mesogenic compounds having two or more polymerizable groups. Especially preferred are polymerizable nematic mixtures.

The homeotropic film preferably provides a polymerizable LC material, preferably a polymerizable nematic LC material on a CLC film as described above and below taking homeotropic orientation, and polymerizing the LC material to polymer film And removing the homeotropic polymer film from the CLC film.

Especially preferred are homeotropics having:

A thickness of -0.8 to 2 mu m, preferably 1 to 1.4 mu m, more preferably 1.2 mu m;

Tilt angle of the optical axis relative to the film top of -88 to 90 °, preferably 90 °; And

A delay R _th of from -140 to 180 nm, preferably 160 nm.

In addition, the present invention relates to a multilayer comprising a polymerized CLC film and a polymerized homeotropic LC film according to the invention. The multi-layer may comprise an additional layer, for example an optical layer of additional polymerized LC material with uniform orientation, or one or more glass or plastic substrates supporting the CLC film, or covering the CLC and / or homeotropic film. It may further comprise one or more protective or adhesion layers. This multilayer can be prepared as described above by coating and curing the homeotropic film onto the CLC film. Multilayers can be used as components, for example, in optical or electro-optical devices for decorative or safety purposes.

For example, the multilayered homeotropic polymer layer can be used as a compensator or retarder in LC displays having a compensating effect because of its birefringent off-axis properties, and the CLC polymer layer can be characterized by its low thickness and / or optically isotropic behavior. It has no or negligible effect. In addition, multiple layers may be used as the alignment layer to induce homeotropic alignment in the additional LC layer coated on the homeotropic layer side or the CLC layer side. In addition, multilayers can be used, for example, in safety manufacturing requiring birefringent films.

In general, polymerizable LC materials as described above and below preferably have at least one polymerizable compound having one polymerizable group (mono-reactive) and a polymer having at least two polymerizable groups (bi- or polyfunctional). At least one sex compound.

The polymerizable mesogenic or LC compound is preferably a monomer, more preferably a calamitic monomer. These materials typically have good optical properties, such as reduced chromaticity, and can be easily and quickly arranged in the desired orientation, which is particularly important for the industrial manufacture of large scale polymer films.

Polymeric mesogenic mono-, di- and multifunctional compounds suitable for the present invention are known per se and are described, for example, in the standard of organic chemistry in Houben-Weyl, Methoden der organischen Chemie, Thieme-Verlag, Stuttgart. Is described in the work.

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

Particularly useful and preferred chiral and achiral polymerizable mesogenic or LC compounds (reactive mesogens) are shown below:

Where

P is a polymerizable group, preferably an acrylic, methacryl, vinyl, vinyloxy, propenyl ether, epoxy or styrene group;

x and y are the same or differently an integer from 1 to 12;

A and D are 1,4-phenylene mono-, di- or trisubstituted by L ¹ or 1,4-cyclohexylene;

u and v are each independently 0 or 1;

Z ⁰ is —COO—, —OCO—, —CH ₂ CH ₂ — or a single bond;

Y is F, Cl, CN, NO ₂ , OCH ₃ , OCN, SCN, optionally fluorinated alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy, or carbon atom number of 1 to 4 carbon atoms 1 to 4 mono-, oligo- or polyfluorinated alkyl or alkoxy;

R ⁰ is optionally fluorinated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms;

Ter is a terpenoid radical 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 or alkoxycarbonyloxy having 1 to 5 carbon atoms.

Monoreactive achiral compounds are preferably selected from compounds of the formulas R1 to R8, in particular R1 and R5, wherein v is 1.

The direactive achiral compounds are preferably selected from compounds of the formulas R18 and R19, in particular compounds of the formula R18.

Suitable chiral dopants are, for example, standard 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 CB 15 (all manufactured by Merck KGaA, Darmstadt, Germany). Very preferred are chiral compounds of high helical twisted power (HTP), in particular compounds comprising sorbitol groups as described in WO 98/00428, compounds comprising hydrobenzoin groups as described in GB 2,328,207 , Chiral binaphthyl derivatives as described in International Publication No. WO 02/94805, chiral binaphthol acetal derivatives as described in International Publication No. 02/34739, as described in International Publication No. 02/06265. Such chiral tadol derivatives, and chiral compounds having at least one fluorinated linking group and a terminating or central chiral group as described in WO 02/06196 and 02/06195.

Unless stated otherwise, the general preparation of polymer LC films according to the invention can be carried out according to standard methods known from the literature. Typically, the polymerizable LC material is applied onto a substrate that is coated or arranged in a uniform orientation, for example by exposure to heat or actinic radiation, preferably photopolymerization, more preferably ultraviolet photopolymerization. The LC is polymerized in situ to fix the arrangement of LC molecules. If desired, a uniform arrangement can be facilitated by further methods, such as shearing the LC material, surface treatment of the substrate, or adding a surfactant to the LC material.

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

Suitable and preferred plastic substrates include, for example, films of polyester, such as polyethylene terephthalate (PET) or polyethylene-naphthalate (PEN), polyvinyl alcohol (PVA), polycarbonate (PC) or triacetylcellulose (TAC). ), More preferably PET or TAC film. As a birefringent substrate, for example, a uniaxial stretched film can be used. PET film is commercially available under the tradename Mellinex® from DuPont Teijin Films.

The polymerizable material may be applied onto the substrate by conventional coating techniques such as spin-coating or blate coating. In addition, conventional printing techniques known to those skilled in the art such as screen printing, offset printing, reel-to-reel printing, letter press printing, gravure printing, rotogravure printing, flexographic printing , Intaglio printing, pad printing, heat-sealing printing, inkjet printing or printing by a method of stamp or printing plate.

It is also possible to dissolve the polymerizable material in a suitable solvent. This solution is then coated or printed onto the substrate, for example by spin-coating or printing or other known techniques, and the solvent is evaporated off prior to polymerization. In most cases, it is suitable to heat the mixture to promote the evaporation of the solvent. As the solvent, for example, standard organic solvents can be used. The solvent may be a ketone such as acetone, methyl ethyl ketone, methyl propyl ketone or cyclohexanone; Acetates such as methyl, ethyl or butyl acetate or methyl acetoacetate; Alcohols such as methanol, ethanol or isopropyl alcohol; Aromatic solvents such as toluene or xylene; Halogenated hydrocarbons such as di- or trichloromethane; Glycols or esters thereof, such as PGMEA (propyl glycol monomethyl ether acetate), γ-butyrolactone, and the like. Binary, ternary or more mixtures of the above solvents may also be used.

The initial arrangement of the polymerizable LC material (e.g. planar arrangement) may be, for example, by rubbing the substrate, shearing the material during or after coating, applying the array layer, applying an electric or magnetic field to the coated material, or It can be achieved by the addition of surface-active compounds to. A review of the alignment technique is described, for example, in I. Sage in "Thermotropic Liquid Crystals", edited by G. W. Gray, John Wiley & Sons, 1987, pages 75-77; And in T. Uchida and H. Seki in "Liquid Crystals-Applications and Uses Vol. 3", edited by B. Bahadur, World Scientific Publishing, Singapore 1992, pages 1-63. A review of array materials and techniques is described in J. Cognard, Mol. Cryst. Liq. Cryst. 78, Supplement 1 (1981), pages 1-77.

Particularly preferred are interpolated materials that include one or more surfactants that promote specific surface alignment of the LC molecules. Suitable surfactants are described in J. Cognard, Mol. Cryst. Liq. Cryst. 78, Supplement 1, 1-77 (1981). Preferred arrangements for planar arrangements are, for example, nonionic surfactants, preferably fluorocarbon surfactants such as the commercially available Fluorad FC-171® (3M Co.). 1) or Zonyl FSN® (Dupon), or surfactants described in GB 238040.

It is possible to apply an array layer on a substrate and to provide a polymeric material on this array layer. Suitable arrangement layers are known in the art and there are arranged layers prepared by, for example, rubbed polyimide or photoarrays as described in US 5,602,661, US 5,389,698 or US 6,717,644.

Polymerization is achieved, for example, by exposing the polymeric material to heat or actinic radiation. Irradiation with radiation means irradiation with light, for example ultraviolet light, infrared light or visible light, irradiation with X-rays or gamma rays, or irradiation with high energy particles such as ions or electrons. Preferred polymerization is carried out by ultraviolet light. As a source for actinic radiation, for example, a single ultraviolet lamp or a set of ultraviolet lamps can be used. If high lamp power is used, the curing time can be reduced. Other possible sources for actinic radiation include lasers, for example ultraviolet, infrared or visible lasers.

The polymerization is preferably carried out in the presence of an initiator which absorbs at the wavelength of actinic radiation. For example, when polymerized by ultraviolet light means, photoinitiators that decompose under ultraviolet irradiation can be used to produce free radicals or ions that initiate the polymerization reaction. In order to polymerize acrylate or methacrylate groups, radical photoinitiators are preferably used. In order to polymerize vinyl, epoxide or oxetane groups, cationic photoinitiators are preferably used. It is also possible to use thermal polymerization initiators that decompose when heated to produce free radicals or ions that start the polymerization. Typical radical photoinitiators include, for example, Irgacure 907, Irgacure 651, Irgacure 184, Darocure 1173 or Darocure 4205 (manufactured by Cibaa Geigy AG). Typical cationic photoinitiators include, for example, UVI 6974 (Union Carbide).

The curing time depends in particular on the polymerizable material, the thickness of the coated layer, the type of polymerization initiator, and the power of the ultraviolet lamp. The curing time is preferably 5 minutes or less, more preferably 3 minutes or less, and most preferably 1 minute or less. For mass production, short cure times of up to 30 seconds are preferred.

The polymerizable material can also be a dye having a maximum absorption at the wavelength of the radiation used for the polymerization, in particular ultraviolet dyes, such as 4,4'-azoxyniazole or Tinuvin® dyes (Basel, Switzerland) Or one or more of Ciba AG).

In another preferred embodiment, the polymerizable material comprises at least one monofunctional polymerizable non-mesogenic compound in an amount of preferably 0 to 50%, more preferably 0 to 20%. Typical examples are alkylacrylates or alkylmethacrylates.

In another preferred embodiment, the polymerizable material comprises at least one di- or multifunctional polymerizable non-mesogenic compound in an amount of preferably 0 to 50%, more preferably 0 to 20%, optionally or additionally Low- or multifunctional polymerizable mesogenic compounds. Typical examples of difunctional monomers are alkyldiacrylates or alkyldimethacrylates having 1 to 20 carbon atoms. Typical examples of polyreactive monomers are trimethylpropanetrimethacrylate or pentaerythritol tetraacrylate.

It is also possible to add one or more chain transfer agents to the polymerizable material to modify the physical properties of the polymer film. Especially preferred are thiol compounds, for example monofunctional thiols such as dodecane thiol, or polyfunctional thiols such as trimethylpropane tri (3-mercaptopropionate). Very 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 can be adjusted. When the amount of chain transfer agent is increased, the polymer chain length in the polymer film decreases.

In addition, the polymerizable material may include a polymerizable binder, or at least one monomer capable of forming a polymerizable binder, and / or at least one dispersion aid. Suitable binders and dispersing aids are disclosed, for example, in WO 96/02597. However, it is preferred that the polymerizable material does not contain a binder or dispersion aid.

The polymerizable material may include one or more additional components such as catalysts, photosensitizers, stabilizers, inhibitors, chain-transfer agents, co-reactive monomers, interfacial-active compounds, lubricants, wetting agents, dispersants, hydrophobic agents, adhesives, flow improvers, antifoams, Degassers, diluents, reactive diluents, adjuvants, colorants, dyes or pigments.

The polymer films of the present invention are conventional LC displays, such as displays having a vertical arrangement, such as DAP (array deformation), ECB (electrically controlled birefringence), CSH (colour super homeotropic) , VA (vertical array), VAN (vertical array nematic) or VAC (vertically arranged cholesteric), MVA (multi-domain vertical array) or PVA (patterned vertical array) mode; Displays with bent or hybrid arrangements, such as OCB (optically compensated curved cells or optically compensated birefringence), R-OCB (reflective OCB), HAN (hybrid arranged nematic) or π-cell mode; Displays with a twisted arrangement, such as TN (twisted nematic), HTN (high twisted nematic), STN (ultra twisted nematic) or AMD-TN (active matrix driven TN) mode; It can be used as an arrangement layer, a delay or compensation film in a display in IPS (in-plane switching) mode or in a display of optically isotropic switching as described in WO 02/93244.

Above and below, unless otherwise indicated, all temperatures are in degrees Celsius and all percentages are by weight. The following abbreviations are used to describe LC phase behavior: C, K = crystallinity; N = nematic; S = smectic; N ^* , Ch = chiral nematic or cholesteric; I = isotropic. Numbers between the abbreviations are expressed in phase transition temperature in degrees Celsius. In addition, mp is the melting point and cp is the clearing point in ° C.

The HTP of the chiral dopant in the LC host material is represented by Equation 2:

Where

p is the pitch of the molecular helix in micrometers;

c is the concentration (in weight percent) of the chiral compound in the host (e.g., c corresponds to a concentration of 1 weight percent is 0.01).

Unless otherwise indicated, the specific HTP values given above and below relate to a dopant at a concentration of 1% in LC host mixture MLC-6260 (Merck KGaA, Darmstadt, Germany) at 20 ° C.

The invention is illustrated by the following examples, but is not limited thereto.

Example

Example 1

Homeotropic film made on CLC film

1A) Preparation of CLC Film

The polymeric cholesteric mixture CM was formulated as follows:

The mixture CM has a cholesteric phase with a clear point (Ch-I phase transition temperature) of 63.8 to 64.1 ° C. and reflects light in the ultraviolet range.

CLC polymer films C1, C2 and C3 having different thicknesses shown in the table below were mixed from the mixture CM at different rotational speeds (3000 or at different concentrations in toluene / cyclohexanone (7: 3) on the melted polyimide coated glass surface. Solution of the mixture for 30 seconds at 5000 rpm). The coating was then sealed on a hot plate for 1 minute at 61 ° C. to align the LC material and polymerize by exposure to ultraviolet light to yield a CLC polymer film.

1B) Preparation of Homeotropic Film

The polymerizable nematic mixture NM was formulated as follows:

The homeotropic nematic polymer film was coated on a substrate for 30 seconds at 3000 rpm by coating a 25% solution of the mixture NM in toluene / cyclohexanone (7: 3), evaporating the solvent and exposure to ultraviolet light to polymerize the mixture. Prepared. The thickness of the homeotropic film was about 1 μm.

Homeotropic nematic films N1, N2 and N3 were prepared on CLC films C1, C2 and C3 provided on glass as substrates, respectively. For comparative purposes, a homeotropic polymer film N4 was prepared as a substrate on a glass substrate without any surface treatment instead of the CLC film.

The delay of the CLC film and the nematic film was measured at different viewing angles to establish the delay side. The table below shows the retardation (in nm) at different viewing angles for a single substrate and a combination of homeotropic films with these substrates:

It is shown that nematic film N1 made on CLC film C1 (1.21 μm) has a much lower deaxial delay than nematic film N2 made on CLC film C2 (0.37 μm). Nematic film N3 prepared on CLC film C3 (0.12 μm) has a retardation side that is almost similar to nematic film N4 coated directly on glass.

This shows that thin CLC films can be used as the alignment layer to promote homeotropic alignment.

Example 2

Durability test

The durability of the cholesteric and homeotropic films prepared according to Example 1 was tested.

2A) Durable at 80 ℃

Samples of the film were exposed to a temperature of 80 ° C. and 90% relative humidity (RH). The delay of the sample was measured before exposure and at different time intervals.

1 shows the results for the C2 / N2 combination. 2 shows the results for the C3 / N3 combination.

As shown, no significant change in delay was observed. In addition, no crack was detected in the film after exposure.

2B) high temperature durability

Samples of the film were placed in an oven at 180 ° C. Delays were measured at start time and at different time intervals.

3 shows the results for the C1 / N1 combination. 4 shows the results for C2 / N2. 5 shows the results for C3 / N3.

As shown, the smallest delay in the off-axis delay was observed in sample C2 / N2 (film thickness 0.37 μm). No crack was detected in any sample at any time.

FIG. 6 shows the reduction in off-axis delay for samples C1 / N1, C2 / N2 and C3 / N33 at 60 °. All initial delays are expressed as 100% and represent residual% after heat treatment. Sample C2 / N2 is shown to exhibit the lowest delay reduction. Sample N4 of Example 1, directly spin-coated on flat glass, is shown for comparison.

These results show that CLC films have the effect of establishing homeotropic films and that homeotropic films coated on CLC films have improved thermal stability and resistance to cracking.

Example 3

Homeotropic film prepared on CLC film polymerized on isotropic phase

A polymerizable cholesteric mixture of CM 2 and CM4 was prepared. Compared to the mixture CM of Example 1, CM2 contained twice the amount of chiral dopant 6 and CM4 contained four times. % Of single components are shown below:

The transition temperatures for these mixtures are as follows:

The mixture was dissolved in toluene / cyclohexanone (7: 3) at 30% concentration to form solutions S, S2 and S4, respectively.

Polymer films C5, C6 and C7 were prepared from solutions S, S2 and S4, respectively, by spin-coating on the melted polyimide coated on the glass side at 2000 rpm for 30 seconds. The coating was sealed at 61 ° C. for 1 minute and cured at 20 mW / cm ² for 1 minute to obtain a polymer film. All samples provided a very clean film.

7 shows the delay side of polymer films C5 to C7. C7 is isotropic while C6 and C5 are cholesteric with C6 having a low delay.

Polymer film C7 was then coated with a 25% solution of polymerizable nematic mixture NM of Example 1 in toluene / cyclohexanone (7: 3) at 2000 rpm. After evaporation of the solvent, the nematic mixture was polymerized under ultraviolet light to give a homeotropic polymer film N7.

8 shows the delay side of the combination of C7 and C7 / N7.

The experiment was repeated, but the cholesteric film was prepared and rubbed on the glass side pre-coated with polyimide to facilitate planar alignment. To ensure that no melted polyimide is required, the cholesteric coating was repeated again on the flat glass. The same result was obtained.

This shows that homeotropically arranged films can be produced on an isotropic CLC polymer film in the presence or absence of the rubbing substrate from which the CLC film was made.

Example 4

Homeotropic film prepared on CLC film polymerized on isotropic phase

A 15% solution of the polymerizable cholesteric mixture CM of Example 1 in toluene / cyclohexanone (7: 3) was spun-coated for 30 seconds at 5000 rpm on a coated glass surface with melted polyimide. The coated side was placed on a hot plate set at 80 ° C. and coated for 90 seconds to bring the temperature above the clearing point of the cholesteric mixture. Thereafter, the coating was cured at 25 mW / cm ² for 1 minute while maintaining the temperature at 80 ° C. to obtain polymer film C8 as a 0.49 μm clean film.

Thereafter, a 25% solution of the polymerizable nematic mixture NM of Example 1 in toluene / cyclohexanone (7: 3) was spin-coated on polymer film C8 for 30 seconds at 2000 rpm. After removal of the solvent, the coating was cured at 20 mW / cm ² for 1 minute to obtain a nematic polymer film as a clean film without homeotropic arrangement.

9 shows the delay side of the C8 / N8 / glass combination.

The durability of the C8 / N8 / glass combinations was tested by placing them on the face in an oven set at 200 ° C., the delays were measured at different time intervals, and the percent reduction in delay was calculated. 10 shows the delay side of C8 / N8 at different time intervals. FIG. 11 shows the decrease in the off-axis delay of C8 / N8 at 60 ° viewing angle. As shown, after the off-axis delay drops significantly from the first, the rate of decrease decreases. No crack in the film was observed.

Samples were prepared as described above and placed in an oven set at 250 ° C., and delays measured at different time intervals. On-axis delay showed little change. The off-axis delay drop of C8 / N8 / glass at 60 ° viewing angle is shown in FIG. 12. After 120 minutes, discoloration of the film appeared, but no crack was observed.

Cholesteric films comprising the low optical retardation of polymeric cholesteric liquid crystal (CLC) materials according to the present invention have superior optical properties, much-reduced defect counts, and prominence compared to isotropic films made by methods of the prior art. To have good thermal stability characteristics.

Claims (13)

A film comprising a polymerized cholesteric liquid crystal (CLC) material, characterized by having an optical delay having an absolute value of less than 50 nm for light at a wavelength of 550 nm. The method of claim 1, A film characterized by a thickness of less than 0.5 μm. The method according to claim 1 or 2, A film characterized by the CLC material polymerizing in isotropic phase. The method according to any one of claims 1 to 3, A film characterized by having a spiral pitch of less than 275 nm. The method according to any one of claims 1 to 4, Film characterized in that the thickness is 0.1 to 0.4㎛. The method according to any one of claims 1 to 5, A film characterized in that it is obtained by polymerizing a CLC mixture comprising at least one achiral polymerizable mesogenic compound and at least one chiral compound in an isotropic phase of the mixture. The method according to any one of claims 1 to 6, Obtained by providing a polymerizable CLC material on a substrate having an orientation of the cholesteric helix axis substantially perpendicular to the plane of the layer, polymerizing the provided CLC material to form a polymer film, and selectively removing the formed polymer film from the substrate. Characterized in that the film. The method according to any one of claims 1 to 7, A film characterized in that the polymerized CLC material comprises at least 5% chiral compounds. The method according to any one of claims 1 to 8, A film characterized in that the polymerized CLC material comprises at least one chiral compound having a helical twisted power (HTP) of at least 30 μm ⁻¹ . The method according to any one of claims 1 to 9, Film used as homeotropic alignment layer for LC material. A polymerizable LC material is provided on a CLC film according to any one of claims 1 to 10 taking homeotropic orientation, polymerizing the provided LC material to form a polymer film, and the formed polymer film is optionally selected from the CLC film. A method for producing a polymerized homeotropic LC film, which is removed by means of a polymer. 12. A multilayer comprising a CLC film according to claim 1 and a homeotropic polymerized LC film. The method according to any one of claims 1 to 12, Multilayers used as components of an optical or electro-optical device or for decorative or safety purposes.

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