JP2007304215A - Photo-alignment material and method for manufacturing optical element and liquid crystal alignment film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for suitably providing an optical element with controlled molecular orientation, such as a retardation film or a polarization diffraction element, and a liquid crystal alignment film. <P>SOLUTION: The optical element with controlled molecular orientation, such as the retardation film or the polarization diffraction element is manufactured by a process including photoirradiation, heating and cooling of a photo-alignment material having photoreactive groups in side chains, which form a dimer through at least one hydrogen bond moiety. The liquid crystal alignment film and the method for manufacturing those are also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical alignment material suitable for the production of an optical element or a liquid crystal alignment film in which molecular alignment is controlled, such as a retardation film or a polarization diffraction element.

The present inventor disclosed in Japanese Patent Application Laid-Open No. 2002-202409, Japanese Patent Application Laid-Open No. 2003-307618, etc. on a side-chain liquid crystal polymer (hereinafter referred to as a photo-alignment material) that induces birefringence by light irradiation or light irradiation and heating and cooling. A retardation film produced by a process including an operation of irradiating with light or an operation of irradiating with light and heating and cooling, and a method for producing the same, and Japanese Patent Application Laid-Open No. 2002-90750 include a liquid crystal alignment film provided with liquid crystal alignment ability by light irradiation and The manufacturing method has been proposed. In these materials, anisotropy can be imparted by an axis-selective photocrosslinking reaction of a polymer side chain when irradiated with linearly polarized ultraviolet light after being applied to a substrate and formed into a film. Further, when such a film is heated, since the material itself has liquid crystallinity, the unreacted side chain is aligned along the side chain that has been photocrosslinked selectively, so that the entire film can be molecularly aligned. Such a film can be used as a retardation film because it exhibits birefringence due to molecular orientation. Further, when liquid crystal molecules are brought into contact with the film surface, the liquid crystal molecules are aligned, so that the film functions as a liquid crystal alignment film.
Thus, these materials can be used in various applications due to the property of molecular orientation by light irradiation and heating. However, it cannot be said that these proposed materials have sufficient photoreactivity, which is not preferable in production such as a longer irradiation time.
In view of such problems, Japanese Patent Application No. 2006-53086 also proposes a method of enhancing the photoreaction rate by adding a photosensitizing component.
However, in the method of adding such a photosensitizing component, it is necessary to separately manufacture a material suitable for photosensitization of the photosensitive group of the photoalignment material. For this reason, when manufacturing a material, cost increases and it is unpreferable. Moreover, it is needless to say that it is suitable to improve the photoreaction rate more industrially.
JP 2002-202409 A JP 2003-307618 A JP 2002-90750 A Japanese Patent Application No. 2006-53086

  The present invention relates to a conventional technique for producing an optical element or liquid crystal alignment film in which molecular alignment is controlled, such as a retardation film or a polarization diffraction element, produced by a process including light irradiation and heating / cooling operations on a photo-alignment material. The present invention intends to solve the above-mentioned problem which becomes a problem in providing industrially using the.

  The above-mentioned problem can be solved by using a photo-alignment material having a structure represented by Chemical Formula 1 in at least one kind in the side chain.

Details of the present invention will be described below.
The materials proposed by the present inventors in the above-mentioned prior art for inducing birefringence by light irradiation or light irradiation and heating and cooling are biphenyl, terphenyl, phenylbenzoate, tolan, which are used as mesogenic groups of liquid crystal compounds. A liquid crystalline polymer having a side chain having a structure in which a rigid substituent such as azobenzene is bonded to a photosensitive group such as a cinnamoyl group or a derivative thereof. In such a material, since the mesogenic group described above has a relatively large conjugated system, it absorbs light having a wavelength that contributes to the photoreaction of the photosensitive group, so that the photoreaction efficiency is lowered. there were.
The photo-alignment material of the present invention is a liquid crystalline polymer having a carboxyl group at the end of the side chain. This photo-alignment material is a material that develops a liquid crystal phase even if the structure does not contain a mesogenic group as in the prior art material by forming a dimer by hydrogen bonding of the carboxyl group at the end of the side chain. FIG. 2 is a schematic diagram showing formation of a dimer by hydrogen bonding in a representative material of the present invention. In such a material, since the mesogenic group is not included in the structure, it does not absorb light having a wavelength that promotes the photoreaction of the photosensitive group. Thus, the irradiated light is consumed only for absorption of the photosensitive group, and the photoreaction is promoted. As a result, the photoreaction efficiency can be greatly improved.
Such a photo-alignment material may be a single polymer composed of the same repeating unit or a copolymer of units having side chains with different structures, or a unit having side chains not containing a photosensitive group may be copolymerized. Is also possible.
Furthermore, it is possible to add a crosslinking agent for improving heat resistance to the extent that liquid crystallinity is not impaired, or to copolymerize a monomer that does not exhibit liquid crystallinity without impairing liquid crystallinity with a photosensitive polymer. It doesn't matter.

  In the production of an optical element or liquid crystal alignment film in which the alignment of molecules such as a retardation film and a polarization diffraction element, which are produced by a process including an operation of light irradiation and heating / cooling to a photo-alignment material, is produced according to the present invention, In addition to shortening the light irradiation process with excellent properties, the material can be provided at low cost. Thereby, the problems of the prior art can be solved.

  A synthesis method relating to the raw material compound of the photo-alignment material used in the examples of the optical element of the present invention is shown below.

(Monomer 1)
4- (6-Hydroxyhexyloxy) cinnamic acid was synthesized by heating p-coumaric acid and 6-chloro-1-hexanol under alkaline conditions. A large excess of methacrylic acid was added to this product in the presence of p-toluenesulfonic acid for esterification to synthesize monomer 1 represented by Chemical Formula 2.

(Monomer 2)
4- (6hydroxyhexyloxy) benzaldehyde was synthesized from 6-bromohexanol and 4-hydroxybenzaldehyde by Williamson synthesis. This was reacted with a Bittig reagent synthesized from triphenylphosphine 4-bromomethylbenzoate to synthesize stilbene 4- (6-hydroxyhexyloxy) -4′-carboxylate. This was reacted with methacrylic acid chloride to synthesize monomer 2.

(Monomer 3)
4-Hydroxy-4 ′-(2-bromoethyloxy) biphenyl was synthesized by heating 4,4′-biphenyldiol and 1,2-dibromoethane under alkaline conditions. This product was reacted with lithium methacrylate to synthesize 4-hydroxy-4 ′-(2-methacryloyloxyethyloxy) biphenyl. Finally, p-methoxycinnamic acid chloride was added under basic conditions to synthesize monomer 3 represented by Chemical Formula 4.

(Polymer 1)
The monomer 1 was dissolved in tetrahydrofuran, and polymerized by adding AIBN (azobisisobutyronitrile) as a reaction initiator and polymerizing. The polymer 1 exhibited liquid crystallinity in the temperature range of 135 ° C. to 187 ° C. In addition, no absorption was observed in the visible light region.

(Polymer 2)
The monomer 2 was dissolved in tetrahydrofuran, and AIBN was added as a reaction initiator for polymerization to obtain a photosensitive polymer 2. This polymer 2 also exhibited a liquid crystal phase.

(Polymer 3)
The monomer 3 was dissolved in tetrahydrofuran, and AIBN was added as a reaction initiator for polymerization to obtain a photosensitive polymer 3. This polymer 3 also exhibited a liquid crystal phase.

Example 1 Polymer 1 was dissolved in tetrahydrofuran and applied to a quartz glass substrate with a thickness of 0.1 μm using a spin coater. The application surface of the substrate was irradiated with light from a high-pressure mercury lamp converted into linearly polarized light by a Grand Taylor prism, followed by heat treatment at 150 ° C. for 10 minutes, and then cooled to room temperature. The molecular orientation of the sample thus prepared can be confirmed by measuring a polarized UV-vis absorption spectrum. FIG. 1 shows a polarized UV-vis absorption spectrum of the prepared sample. In this figure, the solid line a is the polarized UV-vis absorption spectrum of the sample after application (before irradiation), and the broken line b is the polarized UV-perpendicular to the irradiation light electric field oscillation direction after irradiation with linearly polarized ultraviolet light. The vis absorption spectrum, solid line b ′ is a polarized UV-vis absorption spectrum parallel to the irradiation light electric field vibration direction after irradiation with linearly polarized ultraviolet light, and the broken line c is the irradiation light electric field vibration direction after the subsequent heat treatment. In addition, the polarized UV-vis absorption spectrum in the vertical direction and the solid line c ′ show the measurement results of the polarized UV-vis absorption spectrum in the direction parallel to the irradiation light electric field vibration direction after the heat treatment. By the heat treatment after irradiation, the absorbance (A _// ) at a wavelength of 315 nm in the direction parallel to the electric field oscillation direction of the irradiated linearly polarized ultraviolet light is greatly reduced. Since the absorbance (A _の ) at a wavelength of 315 nm in the direction perpendicular to the electric field oscillation direction is greatly increased, it can be seen that molecular orientation is induced.
Here about orientation of the sample orientation degree calculated from the polarization UV-vis absorption spectra (S) _{[S = (A // -A ⊥)} / (A larger +2 Asmaller), wherein, A _Larger is _{A //} or a larger absorbance of _⊥, a _smaller is smaller absorbance of a _// or a _⊥. ] Can be evaluated. FIG. 2 shows the relationship between the irradiation energy amount of the irradiated linearly polarized light and the degree of orientation (S). In polymer 1, the degree of orientation became maximum at an irradiation energy amount of 10 mJ / cm ² and the value was 0.61. The birefringence was 0.15.
It has been confirmed that the material exhibits a large orientation even with a low irradiation energy amount as compared with a material of a comparative example which has been conventionally proposed.

(Example 2) Polymer 1 was dissolved in tetrahydrofuran and applied to a quartz glass substrate with a thickness of 0.3 µm using a spin coater. The substrate was heated to 165 ° C., and light from a high-pressure mercury lamp was converted into linearly polarized light by a Grand Taylor prism on the coated surface, irradiated with 10 mJ / cm ² and cooled to room temperature. The sample thus prepared had an orientation degree (S) of 0.62 and a birefringence of 0.15.

  (Example 3) The polymer 2 was dissolved in tetrahydrofuran and applied to a quartz glass substrate with a thickness of 0.1 µm using a spin coater. The coated surface of the substrate was irradiated with light from a high-pressure mercury lamp converted into linearly polarized light by a Grand Taylor prism, followed by heat treatment, and then cooled to room temperature. Anisotropy was confirmed when the thus prepared sample was observed with a polarizing microscope.

(Example 4) Polymer 1 was dissolved in tetrahydrofuran and applied to a glass substrate with a thickness of 0.1 µm using a spin coater. The substrate was heated to 165 ° C., and light from a high-pressure mercury lamp was converted into linearly polarized light by a Grand Taylor prism on the coated surface, irradiated with 10 mJ / cm ² and cooled to room temperature. Two glass substrates prepared in this manner were prepared, 12 μm polyimide spacers were sandwiched between them, the coating surfaces were placed facing each other, and a low-molecular liquid crystal ZLI4792 (Merck) was injected between the glass substrates to produce parallel type liquid crystals. A cell was produced. When the liquid crystal cell thus prepared was observed with a polarizing microscope, it was confirmed that the low-molecular liquid crystals were well aligned.

(Comparative example 1) The polymer 4 which is a conventional material is dissolved in dichloromethane and applied to a quartz glass substrate with a thickness of 0.1 μm using a spin coater in the same manner as in the examples, and light from a high-pressure mercury lamp is granulated. Irradiation was carried out after conversion to linear polarization with a Taylor prism, followed by heat treatment at 190 ° C. for 10 minutes and then cooling to room temperature. In FIG. 3, the relationship between the irradiation energy amount and the degree of orientation (S) of the irradiation linearly polarized light in the sample produced using the polymer 4 is shown. The degree of orientation becomes maximum at 0.52, and the irradiation energy amount at that time is 150 mJ / cm ² , and it was confirmed that a larger amount of irradiation energy was required as compared with the Examples.

  From Example 1 to Example 5 and Comparative Example 1 using conventional materials, control of the orientation of molecules such as retardation films and polarization diffractive elements produced by processes including light irradiation and heating and cooling operations on the photo-alignment material A photoalignment material characterized by having a photoreactive group in a side chain and forming a dimer by at least one hydrogen bonding site in the method for producing an optical element or a liquid crystal alignment film. It has been proved that an optical element, a liquid crystal alignment film, and a method for producing the same, which have solved the conventional problems, can be obtained by using.

The figure which shows the change of the polarization UV-vis absorption spectrum of the sample produced in Example 1. Schematic diagram showing dimerization by hydrogen bonding in the material of the present invention Relationship between irradiation energy amount of linearly polarized light and degree of orientation (S) in Example 1 using the material of the present invention Relationship between irradiation energy amount of linearly polarized light and degree of orientation (S) in Comparative Example 1 using materials of the prior art

Explanation of symbols

a ... Result of measurement of polarized UV-vis absorption spectrum of sample after application (before irradiation) b ... Polarized UV-vis absorption perpendicular to irradiation light electric field vibration direction after irradiation with linearly polarized ultraviolet light Spectrum b ′: Polarization UV-vis absorption spectrum parallel to irradiation light electric field vibration direction after irradiation with linearly polarized ultraviolet light c—Perpendicular to irradiation light electric field vibration direction after heat treatment Polarized UV-vis absorption spectrum of c ′: polarized UV-vis absorption spectrum parallel to the direction of electric field vibration of irradiated light after heat treatment d—hydrogen bond

Claims (4)

   A photoalignment material having a photoreactive group in a plurality of side chains of a polymer structure, wherein the side chains are hydrogen-bonded to each other to form a dimer. 2. The photo-alignment material according to claim 1, wherein the side chain having the photoreactive group includes at least a structure represented by Chemical Formula 1. 3.

Here, m = 0, 1, n = 1-3, c = 0, 1, X = none, O, CH ₂ , N = N, C = C, C≡C, COO, OCO, R ₁ , R ₂ represents H or an alkyl group, an alkyloxy group and a halogen, respectively.    3. The method according to claim 1, further comprising a step of irradiating the photo-alignment material according to claim 1 with light containing a linearly polarized light component and a step of heating the photo-alignment material after irradiation with light containing the linearly polarized light component. A method for manufacturing an optical element.   A method for producing a liquid crystal alignment film, wherein the photo-alignment material according to claim 1 or 2 is irradiated with light containing a linearly polarized light component to impart liquid crystal alignment ability.

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