JPH03179424A - Method for orienting liquid crystal - Google Patents

Abstract

PURPOSE:To improve the orientability of a ferroelectric liquid crystal and to obtain a good driving characteristic by using a specific orientation control means. CONSTITUTION:Photoirradiation is used as the orientation control means of the liquid crystal element constituted by forming electrodes 3, 4 and oriented layers 7, 8 for orienting a liquid crystal on the inner side of a pair of substrates 1, 2 facing each other and providing a liquid crystal layer 9 contg. a mesogene group to be photoisomerized therebetween. Namely, the liquid crystal contg. the mesogene group to be photoisomerized changes from the liquid state to an isotropic liquid state when this liquid crystal is irradiated with light of the wavelength changing from a trans body to a cis body. The liquid crystal changes from the isotropic liquid state to the liquid state when the liquid crystal is irradiated with the light of the wavelength changing from the cis body to the trans body. Thus, the liquid crystal element which exhibits the orientability of the uniform monodomain state and the large contrast ratio at the time of driving is obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for aligning liquid crystals.

[Prior Art] In recent years, research on liquid crystals as light modulation elements has become active, but the aim is for displays or optical shutters, and most of these are TN (Tvlsted Ne5at).
lc) type display system.

On the other hand, display systems [N, A] utilize ferroelectric liquid crystals, which are characterized by high-speed switching and memory properties.

C1arks et al; Applied Phys, Lett
, 38, 899 (1980)] has been proposed.

In these liquid crystal elements, it is necessary to preferentially align the liquid crystal in one direction. Since this alignment treatment has a great influence on the quality of these liquid crystal elements, much research has been conducted on it. The alignment state of liquid crystal on the substrate surface can be broadly divided into homogeneous alignment, which is aligned parallel to the substrate surface, and homeotropic alignment, which is aligned perpendicular to the substrate surface.

In actual liquid crystals, by applying an electric field or the like to the liquid crystals oriented in this way, the alignment state of the liquid crystals is changed, and the 0N-01''P of light is performed using birefringence, dichroism, etc.

Conventional methods for aligning liquid crystals include oblique vapor deposition of inorganic materials and rubbing of organic polymer coatings, but none of them are satisfactory. In particular, when trying to align a ferroelectric liquid crystal, it is much more oriented than a conventional nematic type, and it is difficult to achieve a uniform alignment using any method.

[Problems to be Solved by the Invention] The present invention provides a liquid crystal alignment method that improves the alignment of liquid crystals, particularly ferroelectric liquid crystals, and obtains good driving characteristics by using a specific alignment control means. It is to provide.

[Means for Solving the Problems] The present invention comprises a pair of opposing substrates each having an electrode and an alignment layer for aligning the liquid crystal on the inside thereof, and a liquid crystal layer containing a photoisomerizable mesogenic group provided therebetween. This is a liquid crystal alignment method characterized in that in a liquid crystal element, light@body-1 is used as an alignment control means.

The basic principle of the present invention will be explained by taking as an example a liquid crystal containing a mesogenic group that undergoes cis-trans photoisomerization.

In the first step, when a liquid crystal containing mesogenic groups to be photoisomerized is irradiated with light having a wavelength (λl) that changes the trans form to the cis form, the liquid crystal state changes to an isotropic liquid state. This is because the trans isomer is a long rod-shaped mesogenic group,
This is because the cis form has a bent structure and does not have the ability to form liquid crystals, and the coexistence of the cis form inhibits liquid crystal formation of mesogenic groups.

In the second stage, when the isotropic liquid state in which the cis isomer coexists is irradiated with light of a wavelength (λ2) that changes from the cis isomer to the trans isomer, the isotropic liquid state changes to a liquid crystal state.

This second step is used to orient the liquid crystal.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view of a liquid crystal element corresponding to an embodiment of the present invention, in which 1 and 2 are substrates, 3.4 are electrodes, 7.8 are alignment layers, 9 are liquid crystal layers, 10 are spacers, and 11 .12 is a polarizing plate.

As the substrate, glass, a synthetic resin film such as polyester, etc. can be used.

For example, ITO (indium tin oxide) is used for the electrodes provided on this substrate, and is formed on a substrate such as glass by vapor deposition, snowdropping, or the like. If necessary, a printing layer of 5iOz or the like may be provided between the glass substrate and the electrodes in order to prevent alkali ions from entering from the glass substrate. Further, the electrode thus provided can be formed into a desired shape by etching.

Next, an alignment film is formed on this electrode. Alignment film materials include polyimide, polyvinyl alcohol (PVA),
Organic polymer materials such as polyamide, polyvinylidene fluoride (PVDF), silane coupling agents, or Si
Oblique evaporation of oxides such as O is suitable. In the case of organic polymer materials, after the film is formed, the surface is subjected to a rubbing treatment to impart uniaxial anisotropy.

In the present invention, the mesogenic group to be photoisomerized is cis-
Mesogenic groups that undergo trans photoisomerization can be used. Examples of mesogenic groups that undergo cis-trans photoisomerization include compounds that undergo photoisomerization as described in "Technics of: Chemistry Vol. 3 Photoglomism" edited by Glenn H. Brown, pp. 471-556 (Wiley Interscience, 1971). residues can be used. Preferred examples include the group represented by general formula 1) and the residue of a thioindigo compound.

X-Y-Z-(II) (wherein, at least one of X1Z is an aromatic ring residue,
Y is -N-N-1-C1l-C1l- or -〇 II-
It is a group represented by N-. ) The aromatic ring X1z includes, in addition to a benzene ring, fused rings such as naphthalene and anthracene, and heterocycles such as furan and pyridine.

Specific examples of mesogenic groups that undergo cis-trans photoisomerization include residues of compounds such as azobenzene, stilbene, stilbazole, benzylideneaniline, indigo, thioindigo, and the like.

These can be substituted with a group such as a nitro group, a nitrile group, a halogen group, an alkoxy group, a dimethylamino group, etc., if necessary, in order to shift the wavelength at which photoisomerization occurs. Furthermore, in order to increase the chemical stability of the mesogenic group to be photoisomerized, it is also possible to substitute it with a similar group.

As the mesogenic group that photoisomerizes, in addition to cis-trans photoisomerization, if it causes a geometrical structural change when exposed to light, it may be combined with a known liquid crystal material.
Similar liquid crystal optical elements can be made. Spirobenzopyrans, which are isomerized as such,
Examples include fulgide residues.

As the material having a mesogenic group that photoisomerizes, known materials can be used, and examples include, but are not limited to, the following materials (* represents optically active carbon) CH3 COC) I2 CHC2Hs * (* represents optically active carbon) (8) Optically active liquid crystal compound of general formula (I) (R is an alkoxy group having 20 or less carbon atoms, n is an integer of 1 or 2, R* represents an optically active group ) These materials are mixed with I11 or other liquid crystals to form a liquid crystal layer as a liquid crystal composition.

The optically active compound shown in the general formula (1) [exemplary compound (
8)] can be obtained, for example, according to the following reaction formula.

The light source used for aligning the liquid crystal of the present invention may be any light source as long as it can change the structure of mesogenic groups, and known light sources such as laser xenon lamps and mercury lamps can be used. Furthermore, it is possible to separate the light and use only a specific wavelength, if necessary.

Light modulation in a liquid crystal element using ferroelectric liquid crystal can be performed as follows.

When an electric field is applied to liquid crystal molecules that are homogeneously aligned with respect to the substrate using electrodes that sandwich the liquid crystal layer, the liquid crystal molecules change their orientation within the plane relative to the direction of the electric field due to the interaction of spontaneous polarization and the electric field (Figure 2). ).

Therefore, by using birefringence or dichroism, the light becomes 0N-O
FF, that is, optical modulation becomes possible. However, at this time, the thickness of the liquid crystal layer needs to be so thin that the helix of the liquid crystal disappears.

Now, as stated above, 1: In order to increase the contrast when performing light modulation, the liquid crystal must be aligned uniformly.

The structure of the cell is shown in FIG. 1, and alignment of the liquid crystal is performed by an alignment film. Ferroelectric liquid crystals are difficult to align compared to nematic types, but in the present invention, in a liquid crystal element provided with a liquid crystal layer containing photoisomerizable mesogenic groups, good alignment can be achieved by using light irradiation as an alignment control means. Orientation can be obtained.

[Example] Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Liquid crystal material having a mesogenic group to be pre-initialized, 4-n-octyloxy-4°-[(S)-2-methylbutoxycarbonyl]stilbene [an optically active liquid crystal compound of general formula (T) with R= A compound of n-CaHry113 0-1n-1, R* -C2Hs C11Cl+2-, *The phase transition temperature ("C) is shown below.

(Cryst is a crystalline state, Iso is an isotropic liquid, S^
is smectic A phase, 80 is chiral smectic C
Transparent substrate...Glass plate (thickness 1.1l111) Transparent electrode...ITO (thickness 50oX, patterning after vapor deposition) Alignment layer Polyimide resin J IB-1 (manufactured by JSR) solution printed After forming a film with a thickness of 500 mm, it was fired, and then 100 mm thick.
Circumferential rubbing treatment was performed at a pressure of g1c2.

Spacer: 5P-202 made by Katsumi Fine Chemicals
(Average particle size 1.8μg+) Sealing agent: Photorec A manufactured by Building Block Fine Chemicals
-704 (Ultraviolet curable type) A liquid crystal element as shown in FIG. 1 was prepared using the above materials.

Next, this liquid crystal element was kept at 85°C and irradiated with monochromatic light of 313n for 10 minutes to make it into an isotropic liquid state, and then monochromatic light of 438ns was irradiated for 30 minutes to align the ferroelectric liquid crystal. I let it happen.

When the liquid crystal element thus prepared was driven under a polarizing microscope by applying a voltage of 20 Vpp to the electrode layer with light of 400 nm or less cut off by a filter, the response speed was 2.
30tlsec (0-90%), contrast ratio 4
It was 5.

Comparative Example 1 A liquid crystal element prepared in the same manner as in Example 1 was heated to 110° C. with light of 400 rv or less cut off by a filter.
Thereafter, the ferroelectric liquid crystal was oriented by slow cooling at a rate of 0.2° C./min. When driven under the same conditions as Example 1 (85°C), the response speed was 250μ5ec (0 → 90%)
, and the contrast ratio was 15.

Example 2 A liquid crystal material containing a mesogenic group that is photosensitive at 5° C. Exemplary compound (11
) is mixed with 5 wt% of the pigment.

Transparent substrate...Glass plate (thickness 1.1+n+n) Transparent electrode...ITO (thickness 500mm, patterning after vapor deposition) Alignment layer Polyimide resin After forming a film to a certain thickness, it is fired, and then 100%
Rubbing treatment was performed five times at a pressure of g/cm'.

Spacer: 5P-202 manufactured by Building Blocks Fine Chemicals
(Average particle size 1.8 μm) Sealing agent: Photorec A manufactured by Building Blocks Fine Chemicals
-704 (ultraviolet curing type) The above materials were laminated as shown in Figure 2 to create a liquid crystal element.

Next, while keeping this liquid crystal element at 40°C,
The liquid crystal was irradiated with 111 color light of 100 nm for 10 minutes to turn it into an isotropic liquid state, and then 500 nm of JP color light was irradiated for 30 minutes to align the ferroelectric liquid crystal.

When the liquid crystal element thus prepared was driven under a polarizing microscope in guest-host mode under a polarizing microscope with light of 40 On1 or less cut off by a filter, a voltage of 20 Vpp was applied between the electrodes, and the response speed was 600 μsec (0-”9
0%), and the dichroic ratio was 8:1 (wavelength: 500 nm).

Comparative Example 2 A liquid crystal element prepared in the same manner as Example 2 was heated to 95°C,
Thereafter, it was slowly cooled at a rate of 0.2° C./min to orient the ferroelectric liquid crystal.

When driven under the same conditions (40°C) as in Example 2,
Response speed 600μsec (0-90%), dichroic ratio 5
21 (wavelength: 500 cm).

Example 3 Liquid crystal material containing a mesogenic group that exhibits photoλ property: A composition in which 10 wL% of the dye of the exemplary compound (2) was mixed with nematic liquid crystal Z L I-1132 manufactured by Merck & Co., Ltd.

Transparent substrate...Glass plate (thickness 1.1am) Transparent electrode/
...ITO (thickness 500λ, patterning after vapor deposition) Orientation layer Polyimide resin J IB-1 (manufactured by JSR) solution was formed into a film with a thickness of 500 μm by printing, then baked, and then 100 μm thick.
Rubbing treatment was performed five times at a pressure of g/c+g'.

Spacer: 5P-202 manufactured by Building Blocks Fine Chemicals
(Average particle size 7.0μ) Sealant: Anti-water Fine Chemical Photoretsu A
-704 (ultraviolet curing type) The above materials were laminated as shown in Figure 2 to create a liquid crystal element.

Next, this liquid crystal element was irradiated with 365 nm monochromatic light for 10 minutes at room temperature to make it into an isotropic liquid state, and then 470 nm
The liquid crystal was irradiated with 111 colors of na+ light for 30 minutes to align the liquid crystal.

When the thus produced liquid crystal element was cut with an optical filter of 400 r+m or less and driven under a polarizing microscope by applying a voltage of 1OVpp between the electrodes, the contrast ratio was 4Ω.

[Effects of the Invention] The 7t-' invention is remarkable in that it is possible to obtain a liquid crystal element that exhibits uniform monodomain state orientation and has a large contrast ratio during driving using a very simple method of using light beams 1 in the liquid crystal layer. This has the following effects.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal element showing an example of the present invention, and FIG. 2 is a diagram showing the action of liquid crystal molecules when an electric field is applied to the liquid crystal layer. In the figure, 1.2 is a substrate, 3.4 is an electrode, an alignment layer, and 9 is a liquid crystal layer. 5.6, 7.8 are

Claims (1)

[Scope of Claims] (1) A liquid crystal element comprising a pair of opposing substrates, each having an electrode and an alignment layer for aligning liquid crystal on the inside thereof, and a liquid crystal layer containing a photoisomerizable mesogenic group provided therebetween. A method for aligning a liquid crystal, characterized in that light irradiation is used as an alignment control means. (2) The method for aligning a liquid crystal according to claim 1, wherein the mesogenic group that undergoes photoisomerization is a mesogenic group that undergoes cis-trans photoisomerization. (3) A claim in which the liquid crystal layer containing a photoisomerizable mesogenic group is composed of an optically active liquid crystal compound of the following general formula (I).
1) The liquid crystal alignment method described above. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I) (R is an alkoxy group with 20 or less carbon atoms, n is an integer of 1 or 2, R^* is an optically active group) (4) Mesogen that photoisomerizes Claim (1) wherein the group is a residue of a photoisomerizable dye.
) The method for aligning liquid crystals described in ). (5) The alignment layer for orienting the liquid crystal is made of an inorganic oxide film or an organic polymer film, and the inorganic oxide film or organic polymer film is subjected to oblique vapor deposition or rubbing treatment. liquid crystal alignment method.