Method of preparing a birefringent polymer film
09663718 · 2017-05-30
Assignee
Inventors
- Graham Smith (Chilworth, GB)
- Owain Llyr Parri (Ringwood, GB)
- Sarah Whitehouse (Southampton, GB)
- Tara Perrett (Bournemouth, GB)
Cpc classification
C09K19/54
CHEMISTRY; METALLURGY
G03F7/2002
PHYSICS
C09K2019/3433
CHEMISTRY; METALLURGY
G03F7/0005
PHYSICS
C09K2019/0448
CHEMISTRY; METALLURGY
C09K2219/03
CHEMISTRY; METALLURGY
International classification
C09K19/54
CHEMISTRY; METALLURGY
Abstract
The invention relates to a method of preparing a polymer film and to the use of such polymer film as in liquid crystal displays (LCDs) or other optical or electro optical devices, for decorative or security applications, as alignment layer or optical retardation film.
Claims
1. A method of preparing a patterned polymer film comprising: a) providing a layer of a polymerizable liquid-crystalline material comprising at least one dichroic photoinitiator, and at least one chiral compound, onto a substrate, b) adjusting the temperature of the polymerizable liquid-crystalline material to a temperature, where the polymerizable liquid-crystalline material is in its nematic or isotropic phase, c) polymerizing and orientating by irradiating the polymerizable liquid-crystalline material with linear polarized actinic radiation, varying the angle between the layer of the polymerizable liquid-crystalline material or the direction of the electric field vector of the linear polarized actinic radiation, thereby causing the polymerizable liquid-crystalline material to form a polymer film, and d) optionally removing the polymer film from the substrate.
2. The method according to claim 1, wherein in c), the liquid-crystalline material is irradiated, while being in the nematic phase.
3. The method according to claim 1, wherein c) is performed while continuously or stepwise rotating the substrate with the layer of a polymerizable liquid-crystalline material.
4. The method according to claim 1, wherein c) is performed by continuously or stepwise rotating a photo mask or a linear polarizer or both, each located between the substrate and a light source.
5. The method according to claim 1, wherein the polymerizable liquid-crystalline material comprises at least one mono-, di- or multireactive polymerizable mesogenic compound, at least one chiral compound, and at least one dichroic photoinitiator.
6. The method according to claim 1, wherein the polymerizable liquid-crystalline material comprises at least one monoreactive polymerizable mesogenic compound, at least one di- or multireactive polymerizable mesogenic compound, at least one chiral compound, and at least one dichroic photoinitiator.
7. The method according to claim 1, wherein the polymerizable liquid-crystalline material comprises at least one monoreactive chiral polymerizable mesogenic compound, at least one mono-, di- or multireactive achiral polymerizable mesogenic compound, and at least one dichroic photoinitiator.
8. The method according to claim 1, wherein the polymerizable liquid-crystalline material comprises at least one di- or multireactive chiral polymerizable mesogenic compound, at least one mono-, di- or multireactive achiral polymerizable mesogenic compound, and at least one dichroic photoinitiator.
9. The method according to claim 1, wherein the polymerizable liquid-crystalline material comprises at least one non-polymerizable chiral compound, at least one mono-, di- or multireactive achiral polymerizable mesogenic compound and at least one dichroic photoinitiator.
10. The method according to claim 1, wherein the dichroic photoinitiator is a compound of formula I, ##STR00039## wherein P is a polymerizable group, Sp is a spacer group or a single bond, A.sup.11 is in case of multiple occurrence independently of one another an aryl-, heteroaryl-, aliphatic or heterocyclic group optionally being substituted by one or more identical or different groups L, Zis in each occurrence independently from each other, O, S, CO, COO, OCO, SCO, COS, OCOO, CONR.sup.01, NR.sup.01CO, -NR.sup.01CONR.sup.02, NR.sup.01COO, OCONR.sup.01,OCH.sub.2, CH.sub.2O, SCH.sub.2, CH.sub.2S, CF.sub.2O, OCF.sub.2, CF.sub.2S, SCF.sub.2, CH.sub.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CH.sub.2, CH.sub.2CF.sub.2, CF.sub.2CF.sub.2, CHN, NCH, NN, CHCR.sup.01, CY.sup.01CY.sup.02, CC, CHCHCOO, OCOCHCH,or a single bond, m is 0, 1, 2 or 3, r is 0, 1, 2, 3 or 4, L is, in case of multiple occurrence independently of one another, H, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1 to 5C atoms, R.sup.11 is H, halogen, CN, NO.sub.2, NCS, SF.sub.S, P-Sp-; or straight chain or branched alkyl with 1 to 20 C-atoms that is optionally mono- or polysubstituted by F, Cl, Br, I or CN, and wherein one or more non-adjacent CH.sub.2 groups are optionally replaced, in each case independently from one another, by O, S, NR.sup.01, SiR.sup.01R.sup.02, CO, COO, OCO, OCOO, NR.sup.01CO,CONR.sup.01, NR.sup.01CONR.sup.02, SCO, COS, CY.sup.01CY.sup.02 or CCin such a manner that O and/or S atoms are not linked directly to one another; or R.sup.14 R.sup.12-13 are independently of each other H, or straight chain or branched alkyl with 1 to 20 C-atoms that is optionally mono- or polysubstituted by F, Cl, Br, I or CN, and wherein one or more non-adjacent CH.sub.2 groups are optionally replaced, in each case independently from one another, by O, S, NR.sup.01, SiR.sup.01R.sup.02, CO, COO, OCO, OCOO, NR.sup.01CO, CONR.sup.01,NR.sup.01CONR.sup.02, SCO, COS, CY.sup.01CY.sup.02 or CC in such a manner that O and/or S atoms are not linked directly to one another, R.sup.14 denotes OH, NR.sup.01R.sup.02, or ##STR00040## Y.sup.01 and Y.sup.02 each, independently of one another, denote H, halogen or CN, and R.sup.01 and R.sup.02 are in dependently of each other H, or straight chain or branched alkyl with 1 to 5 C-atoms.
11. The method according to claim 1, wherein the proportion of the dichroic photoinitiator in the liquid-crystalline material as a whole is in the range from 1 to 25% by weight.
12. The method according to claim 1, wherein the chiral compound has a helical twisting power (HTP)25 m.sup.1.
13. The method according to claim 1, wherein the proportion of the chiral compound in the liquid-crystalline material as a whole is in the range from 2 to 20% by weight.
14. The method according to claim 1, wherein c) is performed by exposing the polymerizable liquid-crystalline material to linear polarised UV radiation.
15. The method according to claim 1, wherein the polymerizable liquid-crystalline material is has planar orientation concerning the substrate main plane after the irradiation c).
16. The method according to claim 1, wherein the polymerizable liquid-crystalline material has a tilted orientation (>0<90) concerning the substrate main plane, after the irradiation c).
17. The method according to claim 1, wherein the irradiation in c) is performed at an oblique angle (>0<90) concerning the substrate main plane.
18. A polymer film obtainable by the method of production according to claim 1.
19. In liquid crystal displays (LCDs) or other optical or electro optical devices, decorative or security applications, or window applications, comprising an alignment layer or optical retardation film, the improvement wherein the layer or film is a polymer film according to claim 18.
20. An optical or electro optical device comprising at least one polymer film according to claim 18.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1)
(2) Using an example, the principal of method of the present invention can be illustrated. At the same time, the example also shows a first preferred embodiment of the method according to the invention, without limiting the scope of the invention to this particular example.
(3) Preferably, the liquid-crystalline molecules in the polymer film are aligned into planar orientation concerning the substrate main plane. This planar orientation of the liquid-crystalline molecules in the resulting polymer film can be achieved, if the radiant source in curing step is located at an angle perpendicular to the substrate main plane.
(4) A typical setup for the method of production in accordance with the present invention is depicted in
(5) By adjusting the orientation of the wire grid polarizer with respect to the slit mask (cf.
(6) Using another example, the principal of method of the present invention can be illustrated. At the same time, this example also shows a second preferred embodiment of the method according to the invention, without limiting the scope of the invention to this particular example.
(7) Another typical setup for the method of production in accordance with the present invention is depicted in
(8) Following one of the above- described procedures, it is possible to produce a polymer film wherein the liquid-crystalline material is generally aligned into a tilted radial orientation (>0<90) concerning the substrate main plane (
(9) Preferably, the irradiation angle is between >0 and <90, more preferable between >10 and <80, or even more preferable between >20 and <70, especially between >30 and <60, and in particular about 45.
(10) The present invention also relates to a polymer film obtainable or obtained by the method described above and below.
(11) However, it is likewise preferred that the oriented polymer films of the present invention are used as retardation or compensation films, for example in LCDs to improve the contrast and brightness at large viewing angles and reduce the chromaticity. They can be used outside the switchable liquid-crystalline cell in an LCD, or between the substrates, usually glass substrates, forming the switchable liquid-crystalline cell and containing the switchable liquid-crystalline medium (incell application).
(12) Various types of optical retarders are known. For example, an A film (or A-plate) is an optical retarder utilizing a layer of uniaxially birefringent material with its extraordinary axis oriented parallel to the plane of the layer. In this connection, an C film (or C-plate) is an optical retarder utilizing a layer of uniaxially birefringent material with its extraordinary axis perpendicular to the plane of the layer. However also patterned or tilted variants of the above described retarders are in accordance with the with the present invention
(13) Depending on the irradiation angle described above, the polymer film obtainable or obtained by the method according to the present invention can either be used as an patterned A-plate (at least two different planar orientations of the director of the liquid-crystalline molecules of the polymer film), if the radiant source in the curing step is located at an angle perpendicular to the substrate main plane, or as an patterned O-plate (at least two different tilted orientations of the director of the liquid-crystalline molecules in the polymer film) if the radiant source is located at an oblique angle (>0<90) with regards to the substrate main plane.
(14) In another preferred embodiment, the polymer film obtainable or obtained by the method according to the present invention can also be used as a flat surface lens, exhibiting both concave or convex type director orientations, or gradient refractive index lens (GRIN), which both can be used for autostereoscopic display devices.
(15) The optical retardation (()) of a polymer film as a function of the wavelength of the incident beam () is given by the following equation (6):
()=(2n.Math.d)/(6)
(16) wherein (n) is the birefringence of the film, (d) is the thickness of the film and is the wavelength of the incident beam.
(17) According to Snellius law, the birefringence as a function of the direction of the incident beam is defined as
n=sin /sin (7)
(18) wherein sin is the incidence angle or the tilt angle of the optical axis in the film and sin is the corresponding reflection angle.
(19) Based on these laws, the birefringence and accordingly optical retardation depends on the thickness of a film and the tilt angle of optical axis in the film (cf. Berek's compensator). Therefore, the skilled expert is aware that different optical retardations or different birefringence can be induced by adjusting the orientation of the liquid-crystalline molecules in the polymer film.
(20) The birefringence (n) of the polymer film according to the present invention is preferably in the range from 0.01 to 0.30, more preferable in the range from 0.01 to 0.25 and even more preferable in the range from 0.01 to 0.16.
(21) The thickness of the polymer film obtained by the method according to the present invention is preferably in the range from 3 to 30 m, more preferable in the range from 3 to 20 m and even more preferable in the range from 3 to 10 m.
(22) In a preferred embodiment, the thickness of the polymer film is such that a phase change of /2 is introduced, then the resulting exiting beam will be circularly polarized. Since /2 is equivalent to a quarter of a wave, this retarder is referred to as a quarter waveplate. The quarter waveplate as previously explained will change linear polarization to circular and vice-versa.
(23) In a likewise preferred embodiment, the thickness of the polymer film is such that a phase change of is introduced, which corresponds to a half waveplate. Halfwaveplates keep linear polarization linear, however it will be rotated through an angle of 2; where is the angle between the incident polarization direction and the materials fast axis.
(24) In another preferred embodiment, the thickness of the polymer film is such that a change in retardance of one wave (2) is equivalent to no change in retardance and entrance beam.
(25) The polymer film of the present invention can also be used as alignment film for other liquid-crystalline or RM materials as described, for example, in WO 2006/039980 A1. For example, they can be used in an LCD to induce or improve alignment of the switchable liquid-crystalline medium, or to align a subsequent layer of polymerizable liquid-crystalline material coated thereon. In this way, stacks of polymerized liquid-crystalline films can be prepared.
(26) The polymer films of the present invention can be used in various types of liquid-crystalline displays, for example displays with vertical alignment like the DAP (deformation of aligned phases), ECB (electrically controlled birefringence), CSH (colour super homeotropic), VA (vertically aligned), VAN or VAC (vertically aligned nematic or cholesteric), MVA (multi-domain vertically aligned) or PVA (patterned vertically aligned) mode; displays with bend or hybrid alignment like the OCB (optically compensated bend cell or optically compensated birefringence), R-OCB (reflective OCB), HAN (hybrid aligned nematic) or pi-cell (-cell) mode; displays with twisted alignment like the TN (twisted nematic), HTN (highly twisted nematic), STN (super twisted nematic), AMD-TN (active matrix driven TN) mode; displays of the IPS (in plane switching) mode, or displays with switching in an optically isotropic phase.
(27) The present invention is described above and below with particular reference to the preferred embodiments. It should be understood that various changes and modifications might be made therein without departing from the spirit and scope of the invention.
(28) Many of the compounds or mixtures thereof mentioned above and below are commercially available. All of these compounds are either known or can be prepared by methods which are known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for said reactions. Use may also be made here of variants which are known per se, but are not mentioned here. Unless the context clearly indicates otherwise, as used herein plural forms of the terms herein are to be construed as including the singular form and vice versa.
(29) Throughout this application, unless explicitly stated otherwise, all concentrations are given in weight percent and relate to the respective complete mixture, all temperatures are given in degrees centigrade (Celsius) and all differences of temperatures in degrees centigrade. All physical properties have been and are determined according to Merck Liquid Crystals, Physical Properties of Liquid Crystals, Status November 1997, Merck KGaA, Germany and are given for a temperature of 20 C., unless explicitly stated otherwise. The optical anisotropy (An) is determined at a wavelength of 589.3 nm.
(30) Throughout the description and claims of this specification, the words comprise and contain and variations of the words, for example comprising and comprises, mean including but not limited to, and are not intended to (and do not) exclude other components. On the other hand, the word comprise also encompasses the term consisting of but is not limited to it.
(31) Throughout the description and claims of this specification, the words obtainable and obtained and variations of the words, mean including but not limited to, and are not intended to (and do not) exclude other components. On the other hand, the word obtainable also encompasses the term obtained but is not limited to it.
(32) It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Alternative features serving the same, equivalent, or similar purpose may replace each feature disclosed in this specification, unless stated otherwise. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
(33) All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).
(34) It will be appreciated that many of the features described above, particularly of the preferred embodiments, are inventive in their own right and not just as part of an embodiment of the present invention. Independent protection may be sought for these features in addition to or alternative to any invention presently claimed.
(35) The invention will now be described in more detail by reference to the following working examples, which are illustrative only and do not limit the scope of the invention.
EXAMPLES
(36) 1. Mixture Examples
(37) 1.1 Mixture M1
(38) The following polymerizable liquid-crystalline material is prepared
(39) TABLE-US-00001 Amount Compound [% w/w]
(40) 1.2. Mixture M2
(41) The following polymerizable liquid-crystalline material is prepared
(42) TABLE-US-00002 Amount Compound [% w/w]
(43) 1.3. Mixture M3
(44) The following polymerizable liquid-crystalline material is prepared
(45) TABLE-US-00003 Amount Compound [% w/w]
(46) 2. Cell Production
(47) 5 m spacer beads are mixed with Norland81 UV glue. The cell is created by placing drops of glue/beads mixture onto corners of raw glass slide, providing a second raw glass slide down on top, and then curing for 60 seconds with UV light (25 mW).
(48) 3. Radial Alignment
(49) Mixture M3 is flow-filled in to the cell on a hotplate at 80 C. The temperature is then adjusted to 60 C. for 60 seconds. The cell is placed on the motorized rotation stage and the rotation speed is set to 3 per seconds. For a radial alignment, the WGP is set to be parallel with respect to the slit of the slit mask (
(50) In the same manner clear, transparent polymer films with good radial orientation can be prepared from the mixtures M1 and M2.
(51) 3.1 Radial Alignment
(52) Mixture M3 is spin-coated onto raw glass at 1000 rpm for 30 sec. The film is placed on a hotplate at 56 C. for 60 seconds. The film is then placed into a nitrogen chamber at 34 C. for 60 seconds while the chamber is purged with nitrogen. The chamber is is placed on the motorized rotation stage and the rotation speed is set to 3 per seconds. For a radial alignment, the WGP is set to be parallel with respect to the slit of the slit mask (
(53) 4. Concentric Alignment
(54) Mixture M3 is flow-filled in to the cell on a hotplate at 80 C. The temperature is then adjusted to 60 C. for 60 seconds. The cell is placed on the motorized rotation stage and the rotation speed is set to 3 per seconds. For a radial alignment, the WGP is set to be perpendicular with respect to slit of the slit mask (
(55) In the same manner clear, transparent polymer films with good concentrical orientation can be prepared from the mixtures M1 and M2.
(56) 5. Tilted Radial Alignment
(57) Mixture M3 is flow-filled in to the cell on a hotplate at 80 C. The temperature is then adjusted to 60 C. for 60 seconds. The cell is placed on the motorized rotation stage and the rotation speed is set to 3 per seconds. The UV lamp is set at an oblique angle of 45 with regards to the cell main plane. The WGP is set to be parallel with respect to the slit of the slit mask (
(58) In the same manner clear, transparent and flat types lenses film with a good orientation in form of a convex orientation can be prepared from the mixtures M1 and M2.