JP2013250571A - Method for manufacturing liquid crystal alignment membrane, liquid crystal alignment membrane, liquid crystal display element - Google Patents

Abstract

A liquid crystal alignment film having good and stable alignment ability, a liquid crystal display element including the liquid crystal alignment film as a constituent element, and a method for producing the liquid crystal alignment film are provided.
The following steps: (1) a substrate pretreatment step, (2) a step of applying a photoalignment layer on the substrate, (3) a step of irradiating the photoalignment layer with light to impart a photoalignment function, (4) a liquid crystal alignment film comprising: a step of disposing an auxiliary layer made of a crosslinkable material on the photoalignment layer and imparting an alignment function by the photoalignment layer; and (5) a step of crosslinking the crosslinkable material. A liquid crystal alignment film manufactured by a manufacturing method, a method for manufacturing the liquid crystal alignment film, and a liquid crystal display element having the liquid crystal alignment film as a constituent element.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal alignment film, a liquid crystal display element including the liquid crystal alignment film as a constituent element, and a method for producing the liquid crystal alignment film.

Controlling liquid crystal alignment is one of the important issues of liquid crystal devices in recent years. Liquid crystal alignment is usually provided by a properly processed boundary substrate, and both the substrate material and the process affect the liquid crystal alignment.
A processing process mainly used in the liquid crystal device industry in recent years is rubbing. Rubbing provides a sufficiently high quality, planar and low pretilt orientation. However, the rubbing technique is known for several problems such as charging, dusting, fine non-uniformity, etc., and these drawbacks are mainly caused by the direct mechanical contact of the brush with the alignment surface. It is.
Moreover, when using the rubbing technique, it is very difficult to achieve a patterned alignment and a stable liquid crystal alignment with an appropriate pretilt angle (80 °>θ> 10 °).

Many new alignment techniques have been developed to overcome the essential challenges of rubbing. Among them, the so-called photo-alignment method is particularly promising. The photo-alignment method is based on the ability of several photosensitizers to align liquid crystals after irradiation with active energy rays such as ultraviolet rays and electron beams, and is based on Gibbons et al. (Patent Literature 1) and Chigrinov et al. (Patent Literature 2). ). Usually, this light is linearly polarized, but in some cases, good alignment is achieved even with irradiation of elliptically polarized light or non-polarized light obliquely directed to the alignment layer.
The photo-alignment material has a light-sensitive site having strong molecular absorption anisotropy, and is mixed or chemically combined with a host of a polymer compound, and is adsorbed or grafted onto a substrate. The active energy rays activate a photoreaction that is sensitive to polarized light, and as a result, the ordering of the alignment is induced by the disappearance and / or reorientation of the angle selectivity of the photoalignment site (Non-patent Documents 1 and 2). Possible photochemical reactions at these sites include isomerization (azobenzene, stilbene) (non-patent document 3), dimerization (cinnamate, chalcone, coumarin) (non-patent document 4, patent document 3), polymerization (free methacryloyl). Group-containing polymer) (non-patent document 5), photolysis (polyimide (non-patent document 6), silane (non-patent document 7)). The induced ordering of the orientation of the light-sensitive sites can cause partial ordering of the non-photosensitive units of the composite system. Further, the ordering of the alignment of the photo-alignment film may be propagated to the adjacent liquid crystal layer due to the anisotropic interaction between the liquid crystal molecules and the photo-alignment layer.

The photo-alignment technology minimizes mechanical damage and charging by preventing direct mechanical contact with the alignment layer, and easily provides excellent alignment uniformity, liquid crystal alignment control and patterned alignment . However, the photo-alignment technique has introduced new problems such as insufficient alignment stability, relatively weak anchoring force, and image sticking. Furthermore, since a photo-alignment material is used in the photo-alignment technique, it is required to have stability including meanings such as light stability, temperature stability, and durability. The best photo-alignment materials currently available on the market only partially overcome these challenges. For example, the best cinnamate-based materials have weaknesses that are still insufficient in terms of temperature resistance and orientation durability.
On the other hand, the photo-aligned azo dye disclosed by Yip et al. (Patent Document 4) has a strong anchoring force and a high temperature stability, but the light stability and stability over time are not sufficient, and it is weak against moisture. In order to improve the stability of the azo dye layer, new improvements of these azo dyes have also been developed that have polymerizable end groups that fix the light-induced orientational ordering. However, although the improved product has succeeded in improving the alignment stability, the quality of the alignment has deteriorated.
Therefore, improving the stability of photo-alignment has been a current issue in the technical field.

US Pat. No. 4,974,941 US Pat. No. 5,389,698 US Pat. No. 6,582,776 US Patent Application Publication No. 2005/0153274 US Pat. No. 6,157,427 US Pat. No. 6,201,588

M.M. Dumont et al. , "SPIE", 1774, 188 (1992) Yaroschuk et al. "J. Phys. Chem. B", 108, 4647 (2004). Eich, M.M. Wendorff, J .; H. Reck, B .; , & Ringsdorf, H. "Macromol. Chem. Rapid. Commun.", 8, 59 (1987). Jackson, P.M. R. & O'Neill, M .; , “Chem. Mater”, 13, 694 (2001). L. Vretik et al. "Mol. Cryst. Liq. Cryst.", 479, 121-134 (2007). J. et al. West et al. , "SID 95 Digest", XXVI, 703 (1995) O. Yaroshchuk & A. Kadashchuk, “Appl. Surf. Sci.”, 158, 3-4, 357-361 (2000) D. J. et al. Broer, H.C. Finkelmann, K.M. Kondo, “Macromol. Chem.”, 189, 185 (1988).

An object of the present invention is to provide an alignment film having improved alignment characteristics and alignment stability by a combination of a photo-alignment layer and a reactive mesogen layer, a liquid crystal display element having the alignment film as a constituent element, and the liquid crystal alignment It is to provide a method for manufacturing a film.
An object of the present invention is to provide a method for improving characteristics of liquid crystal alignment on a photo-alignment layer, such as light and temperature stability, alignment aging resistance, and alignment uniformity. Another object of the present invention is to provide a method for reducing the destructive chemical interaction between the liquid crystal, the environment, the adhesive and the photo-alignment layer.

In order to achieve the above object, the inventors of the present invention have studied photo-alignment films having various structures, and as a result, the present invention has been completed.
The present invention is
(1) 1. Substrate pretreatment process,
2. Applying a photo-alignment layer on the substrate;
3. Irradiating the photo-alignment layer with light to impart a photo-alignment function;
4). A step of disposing an auxiliary layer made of a crosslinkable material on the photo-alignment layer and provided with a liquid crystal alignment function by the photo-alignment layer;
5. Cross-linking step of cross-linkable material,
A method for producing a liquid crystal alignment film comprising:
(2) A liquid crystal alignment film manufactured by the method for manufacturing a liquid crystal alignment film according to (1),
(3) A liquid crystal display element comprising the liquid crystal alignment film according to (2) as a constituent element,
I will provide a.

Figure 2 is a structure of a prior art alignment layer (a) and alignment layers (b) and (c) made according to a preferred embodiment of the present invention. Pretilt angle as a function of cell storage time for an anti-parallel cell based on an SD1 orientation layer (curve 1) and an SD1 layer (curve 2) coated with an RMM256C layer. An anti-parallel cell based on a bare SD1 layer (a) and a layer (b) comprising an SD1 layer coated with an RMM256C layer has been seen between cross-polarizers. The liquid crystal cell was filled with E7 liquid crystal. The lower part of the cell was irradiated with visible light (450 nm, 24 mW / cm ² , 30 minutes) polarized along the alignment direction of the liquid crystal. It is clear that reorientation occurred only in cells based on bare photoalignment layers. It is the photograph of two cells seen between the cross polarizers. The alignment layers in cell (a) and cell (b) are a bare SD1 layer and an SD1 layer coated with reactive mesogen RMM256C, respectively. In both cells, one SD1 layer was irradiated with totally polarized light and then a polymerized RM layer was deposited in cell (b). Half of the other substrate was irradiated for the second time in the direction of light forming an angle of 90 ° with the polarization direction of the first irradiation step after the first irradiation. In the cell (b), the second irradiation was performed after placing the polymerized RM layer on the photo-aligned SD1 film. See Comparative Example 3 and Example 3 for details of cell adjustment conditions. It is clear that the RM auxiliary layer prevented easy axis light reorientation in cell (b). It is a TN cell having an alignment layer of only SD1 (a) and SD1 / RM (b), which was produced according to Comparative Example 4 and Example 4. It is clear that the RM coating prevents the formation of the reverse twist domain and the reaction between SD1 and the adhesive. FIG. 6 is a series of photographs of two anti-parallel cells based on bare PM2 only (a) and PM2 / RM (b) alignment layers made by Comparative Example 5 and Example 5. FIG. The photographs in each series correspond to different times for cells fired at 150 ° C. Numbers 1, 2, 3, and 4 correspond to 0, 0.5, 1.0, and 2.0 hours firing. 2 is a photograph of two anti-parallel cells fabricated according to Example 1 between cross-polarizers. Cells (1), (3) and cells (2), (4) are filled with E7 liquid crystal and MLC-12100-000 liquid crystal, respectively, based on the SD1 / RM alignment layer. Both cells showed high orientation uniformity. 7 is a photograph of a liquid crystal cell based on an SD1 / RM alignment layer produced according to Example 7. It is clear that the RM auxiliary layer does not limit the alignment patterning ability of the alignment film.

<< Method for producing liquid crystal alignment film >>
A method for forming an alignment layer for liquid crystal includes the following steps: depositing a layer of photo-alignment material on a substrate; irradiating the photo-alignment layer with actinic light to impart a liquid crystal alignment function; A thin layer of reactive mesogen (RM) (d <200 nm) is deposited on the top of the film, where the RM layer is oriented on the photo-alignment film; the RM layer is photopolymerized.
Also disclosed are liquid crystal devices containing a liquid crystal layer aligned between two alignment substrates; at least one of these substrates includes an alignment layer prepared by the disclosed method above.

[1. Substrate pretreatment process]
First, the substrate is pretreated.

The substrate used in the present invention is not particularly limited as long as it is a substrate normally used for a liquid crystal display element. A substrate in which an electrode such as ITO (indium tin oxide) is provided on glass, a silicon wafer, plastic, or the like. Can be used.
The substrate is preferably pretreated by a commonly used method. For example, cleaning using an ozone cleaning device can be used.

[2. Step of applying photo-alignment layer on substrate]
The photo-alignment layer material is applied on the substrate that has been subjected to the pretreatment in 1 to form a photo-alignment layer.

The material for the photo-alignment layer of the present invention is not particularly limited as long as it is a suitable material. For example, a dichroic dye (here, the dichroic dye means that the light absorption ability in the chromophore is a polarized electric A pigment having a different group depending on the direction of the vector), and those containing the above-mentioned known light-sensitive sites. Examples of the dichroic dye include anthraquinone, azo, quinophthalone, and perylene compounds. Especially, the material for photo-alignment layers of the present invention preferably contains a dichroic dye composed of an azo compound, and more preferably a compound represented by the following formula (A).
The photo-alignment layer material in the present invention can be used after being dissolved in a suitable solvent. The solvent is not particularly limited as long as the photo-alignment layer material exhibits good solubility, and a known solvent can be used. Moreover, you may add a well-known and usual additive in the range which does not impair the effect of this invention.

[3. Step of irradiating the photo-alignment layer with light to give a photo-alignment function
Next, light is irradiated to the substrate on which the photo-alignment layer obtained in 2 above is formed, and the photo-alignment layer is oriented in a certain direction. In this specification, the operation of aligning the photo-alignment layer with light is referred to as “giving a photo-alignment function”. The photo-alignment layer provided with the photo-alignment function can align other layers or liquid crystals.

The light used in the present invention is linearly polarized light or partially polarized light, or non-polarized light or elliptically polarized light irradiated from an oblique direction with respect to the substrate surface.
The light source is not particularly limited as long as it is suitable, and a high pressure mercury lamp, a medium pressure mercury lamp, a light emitting diode, or the like can be used.
Light irradiation conditions such as spectral composition, wavelength, type of polarized light, irradiation time, and incident angle may be arbitrarily adjusted according to the target orientation.
Moreover, it is preferable to perform light irradiation by making the said conditions the same with respect to all the layer surfaces of a photo-alignment layer, or performing it using different masks on different conditions.

[4. Step of disposing an auxiliary layer made of a crosslinkable material and having an alignment function provided by the photo-alignment layer on the photo-alignment layer]
An auxiliary layer made of a crosslinkable material is disposed on the photo-alignment layer provided with the photo-alignment function in 3 above. The arranged auxiliary layer is aligned in the same manner as the alignment of the lower photoalignment layer. Further, the orientation of the auxiliary layer is an amplified orientation compared to the orientation of the photo-alignment layer.

As the crosslinkable material in the present invention, it is preferable to use a reactive mesogen compound alone, which is a polymerizable liquid crystal material, or a mixture of the reactive mesogen and another composition. Other compositions miscible with reactive mesogens include photoinitiators, heat inhibitors, non-polymerizable mesogenic compounds, etc., and add known and commonly used additives and the like within a range that does not impair the effects of the present invention. May be.
Among the above, nematic liquid crystal is more preferable as the crosslinkable material. The nematic liquid crystal preferably has a wide temperature range as a nematic intermediate phase (5 ° C. or higher) and a low transition temperature to the nematic intermediate phase (10 to 90 ° C.).
The method of disposing the auxiliary layer on the photo-alignment layer is not particularly limited as long as it is a suitable method, and is a wet coating method such as a spin coating method, a deep coating method, a printing method, or a dry coating method such as a vapor deposition method. Can be used.
Moreover, in order to prevent the optical retardation by the reactive mesogen which comprises an auxiliary layer, it is preferable that the layer thickness of the auxiliary layer which a reactive mesogen comprises is 100 nm or less.
The thickness of the auxiliary layer may be a pattern or may not be a pattern.
The molecular orientation of the auxiliary layer may be a pattern or may not be a pattern.
The auxiliary layer is preferably a permanent layer. In the present invention, the permanent layer means that the auxiliary layer exists in at least a part of the liquid crystal alignment film according to the present invention. As shown in FIG. A part may be removed.

[5. Crosslinking process of crosslinkable material]
Next, the auxiliary layer made of the above-mentioned crosslinkable material 4 is crosslinked to obtain a liquid crystal alignment film comprising the photo-alignment layer and the auxiliary layer according to the present invention.

The method for crosslinking the auxiliary layer in the present invention is not particularly limited as long as it is a suitable method, and a photopolymerization method, a thermal polymerization method, an electron beam polymerization method and the like can be used, and among these, the photopolymerization method is preferable.
The crosslinking operation of the auxiliary layer may be performed on the entire auxiliary layer, or may be performed on only a part of the auxiliary layer by using a mask or the like. When only a part of the auxiliary layer is crosslinked, the auxiliary layer in the non-crosslinked part can be easily removed using a solvent or the like. Therefore, as shown in FIG. 1C, a liquid crystal alignment film consisting only of the photo-alignment layer and a liquid crystal alignment film consisting of the photo-alignment layer and the auxiliary layer can be mixed, and an alignment pattern having a plurality of pretilt angles is formed. Useful when doing.
The cross-linking operation of the auxiliary layer is preferably performed quickly before or after the liquid crystal filling, before or after the liquid crystal cell is manufactured.

  When the photopolymerization method is used, the auxiliary layer crosslinkable material contains a photopolymerization initiator. As a photoinitiator, if it is a suitable thing, it will not specifically limit, A well-known thing can be used. When using other polymerization methods, there is no particular limitation as long as it is a suitable method in each polymerization method, and a known and commonly used method can be used.

<Liquid crystal alignment film>
The liquid crystal alignment film of the present invention produced by the above << Method for producing liquid crystal alignment film >> has a good and stable alignment ability.

<Liquid crystal display element>
Using the << liquid crystal alignment film >> manufactured as described above, a liquid crystal display element can be manufactured by a known and conventional method. As an example, a manufacturing method of a TN type liquid crystal display element is shown below.
Two substrates on which the liquid crystal display film manufactured by the above << Liquid Crystal Alignment Film Manufacturing Method >> is formed, and the liquid crystal alignment film surfaces are opposed to each other through a spacer and perpendicular to each other. Let Next, liquid crystal is filled in the gap between the substrates on which the two liquid crystal display films are formed to manufacture a liquid crystal cell. A polarizing plate is attached to the outside of the obtained liquid crystal cell so that the transmission axis direction is parallel to the liquid crystal alignment direction of each substrate. As a result, a normally white type TN liquid crystal display element can be manufactured.

  An important idea of the present invention is that an intermediate layer made of reactive mesogen (RM) or polymerizable liquid crystal material is placed between the photo-alignment layer and the standard liquid crystal layer. In this case, the photo-alignment film functions as an alignment film for the reactive mesogen. Similarly, oriented and polymerized RM films are used to align standard liquid crystals. This means that the orientation function of the photo-alignment film is only required for a short time to orient the reactive mesogen. The RM layer reproduces and enhances the alignment function of the photo-alignment film and stabilizes the liquid crystal alignment.

Reactive mesogens are low molecular weight liquid crystal compounds that have one, two, or more polymerizable groups (Non-Patent Document 8). A commonly used reactive mesogenic material is a single RM compound, or a mixture of complexes, in addition to the reactive mesogen, other compounds; for example, an initiator that causes polymerization of polymerizable groups, into the RM layer at both interfaces. And other compounds such as a surfactant, a chain transfer agent, a stabilizer, and a mesogen non-polymerized compound for preferred orientation.
The optical application of reactive mesogens is based on strong birefringence and angle selective absorption. Various variations of retardation plates, dichroic polarizers, and combinations thereof have been proposed using these bulk properties of RMs. These films are excellent in that they are easy to manufacture and easy to control optical parameters.
Patent Documents 4 and 5 disclose the ability of an RM retardation film for aligning liquid crystals, suggesting combining the retardation and alignment function of the RM layer with the application in the cell. In this case, however, the orientation of the liquid crystal is predetermined by the orientation of the reactive mesogen, which is not preferred for many applications. In order to separate the molecular orientation between the adjacent RM and the liquid crystal layer, the surface of the RM film needs to be appropriately treated.
Finally, Patent Document 6 suggests that the pretilt angle of the liquid crystal is controlled by using a reactive mesogen auxiliary layer on the alignment layer. In the disclosed method, a mixture of two reactive mesogens is used, in which a compound with two reactive groups affects the planar orientation, whereas a compound with only one terminal reactive group Affects the vertical alignment. Since the RM layer used is thin, the inherent retardation is minimal, so only the surface properties of the oriented RM film, ie the ability to align standard liquid crystals, are utilized.

The idea of using the reactive mesogen auxiliary layer to adjust the pretilt angle is to use the RM layer for the stability of the liquid crystal alignment on the photo-alignment layer and to protect the photo-alignment layer from the aggressive effects of the environment It was converted into the idea. At the same time, the RM auxiliary layer was found to improve the alignment uniformity and anchoring parameters of the photo-alignment layer at a high frequency.
The structure of the alignment layer according to a preferred embodiment of the present invention is shown in FIG. Compared to prior art photo-alignment layers, the present invention has an additional layer coated over the photo-alignment layer. This top layer is a layer of reactive mesogen, which is oriented on the photo-alignment film and then solidified by polymerization. This film is then used for liquid crystal alignment.
The photo-alignment layer is made of a suitable photo-alignment material, and includes azo, cinnamic ester, coumarin, chalcone, methacryloyl photosensitive group, photosensitive polyimide, and the like. The photo-alignment material is deposited by a suitable method, such as spin coating, deep coating, blade coating, Langmuir Blodget method, printing, vapor deposition, and the like. The substrate having the photo-alignment layer on the top may be any material that can be used for manufacturing a liquid crystal cell. Glass slides, silicon wafers, plastic pieces, etc., which are bare or covered with ITO electrodes or surface electronic elements can be used. The alignment ability of the photo-alignment film is introduced by irradiating these films with linearly polarized light that collides from any direction on the alignment substrate, or partially polarized light. The alignment function is also introduced by non-polarized light or elliptically polarized light obliquely on the alignment substrate. All locations of the photo-alignment film can be irradiated under the same conditions (spectral composition, intensity, polarization, angle of incidence), or different conditions using a suitable mask. The latter principle can be used to achieve a patterned orientation.
A suitable reactive mesogenic material is one RM compound or a mixture of complexes containing reactive mesogens, including photoinitiators, thermal inhibitors, mesogenic non-polymerized compounds, and the like. Preferred RM materials have a nematic mesophase. More preferred materials are those that have a wide temperature range of nematic liquid crystals (at least 5 ° C.) and a low transition temperature to this intermediate phase (between 10 ° C. and 90 ° C.). Reactive mesogens are deposited on the photo-alignment layer by a suitable method; solvent casting techniques such as spin coating, deep coating, printing, or dry casting techniques such as vapor deposition. The thickness of the RM layer is preferably 20 to 300 nm, more preferably 30 to 200 nm, and particularly preferably 50 to 100 nm. When it is thicker than 300 nm, the phase difference tends to be visually recognized, and when it is thinner than 20 nm, the stability of the alignment is deteriorated. Depending on the irradiation conditions of the photo-alignment substrate, spatial uniformity of the RM layer or patterned orientation is obtained.
The reactive mesogen layer is polymerized by an appropriate method, and examples thereof include photopolymerization, temperature polymerization, and electron beam polymerization. A preferred polymerization method is photopolymerization. In this case, the RM material necessarily contains a suitable photoinitiator. The photopolymerization of the RM layer can be performed before or after assembling the liquid crystal in the cell before assembling the liquid crystal cell.
In the preferred embodiment of the present invention, since the RM layer is photopolymerized entirely, the alignment layer has the structure shown in FIG. The direction of liquid crystal alignment on this alignment film is a film surface controlled by the irradiation conditions of the photo-alignment layer, and may not be patterned or may be patterned. In addition to the stability of liquid crystal alignment on the photo-alignment layer, this embodiment can also improve the stability of these layers, such as control of the pretilt angle and anchoring force on the photo-alignment layer.
In other embodiments, the RM layer is only partially polymerized using a suitable mask. The non-polymerized RM can be easily removed. For example, by removing by rinsing with an appropriate solvent, a portion of the alignment film having only the photo-alignment layer and a portion having both the photo-alignment layer and the RM layer are obtained ( FIG. 1). This principle is particularly useful when realizing alignment patterns having various pretilt angles.
The following examples illustrate the invention in more detail.

Hereinafter, the present invention will be described in detail with reference to examples. However, the following examples are intended to illustrate the invention and not to limit it. Therefore, those skilled in the art can implement various modes different from the embodiments without departing from the technical scope and idea of the present invention. Unless otherwise specified, “%” is based on mass.
[Comparative Example 1]
As the photo-alignment material 1 (PM1), a diazo dye SD1 having the following chemical formula (A) was used.

The dye was dissolved in DMF at a concentration of 1% by mass, filtered through a 0.2 μm filter, and spin-coated on a glass slide having an ITO electrode at 800 rpm for 10 seconds and then at 3000 rpm for 60 seconds. Prior to coating, the substrate was cleaned with an ozone cleaner for 10 minutes. The substrate coated with SD1 was baked at 140 ° C. for 15 minutes in order to remove the residual solvent and enhance the adhesion of the azo dye molecules to the substrate.
The film was then irradiated in two steps with an Oriel medium pressure mercury lamp. First, cure by linear light incidence with linearly polarized light to the second stage, and irradiate the film obliquely with non-polarized light so that the projection of the light rays on the film is perpendicular to the polarization direction of the light of the first stage did.
The light intensity of each irradiation in emission line 365 nm, 3.3 mW / cm ² in the first irradiation step, was 9.2mW / cm ² in the second irradiation step. By the two-stage irradiation method, multiple degeneration of the pretilt angle of the liquid crystal can be prevented.
A liquid crystal cell (anti-parallel cell) was prepared using the two substrates prepared as described above so that the irradiation direction in the second irradiation stage was anti-parallel. The cell gap was held with a spacer of 18 μm. To adhere the cell with Noland's photo-curing adhesive NOA65 and prevent the azo dye molecules in the alignment film in the center part of the cell from becoming disordered during photocuring of the adhesive deposited on the edge of the cell Protected with a paper mask.
Two liquid crystal cells were produced by the method described above. Two cells were filled in the same manner with Merck nematic liquid crystal E7 and MLC-12100-000, respectively. Both cells showed high orientation quality.
The pretilt angles measured by the crystal rotation method were 3.0 ° for E7 liquid crystal and 4.6 ° for MLC-12100-000 liquid crystal.
Thereafter, the cell pretilt angle was observed while the cell was stored under environmental conditions. As is clear from FIG. 2 (curve 1), the pretilt angles of these cells gradually decreased with the storage time of the cells.

[Comparative Example 2]
An anti-parallel liquid crystal cell was prepared in the same manner as in Comparative Example 1, and filled with E7 liquid crystal. Thereafter, half of the cell was irradiated perpendicularly to the cell with polarized visible light (λ = 450 nm), with the polarization of the light forming an angle of 90 ° with the alignment direction of the liquid crystal. The light intensity was 24 mW / cm ² and the irradiation time was 15 minutes. It is clear from FIG. 3a that the light affects the liquid crystal alignment at the irradiated portion by the light realignment of the easy alignment axis on the alignment substrate.

[Comparative Example 3]
Two alignment layers were prepared in the same manner as in Comparative Example 1. After the first irradiation, a second polarized light irradiation (λ = 450 nm, 24 mW / cm ² , 10 minutes) was performed on a half portion of one substrate. The polarization direction in the second stage was perpendicular to the polarization direction in the first stage. The cell was manufactured so that the alignment directions formed in the first irradiation stage were parallel. The cell gap was 18 μm. The cell was bonded in the same manner as in Comparative Example 1 and filled with E7 liquid crystal. From the picture of the cell (FIG. 4a), two distinct patterns of parallel and twist director structures can be identified.
This result shows that the effective re-orientation of the easy axis of the alignment substrate and the resistance of the alignment layer to visible light are inferior.

[Comparative Example 4]
Similar to Comparative Example 1, an oriented film was produced on a glass / ITO substrate. Each of the two substrates was used to manufacture a liquid crystal cell so that the irradiation direction in the second irradiation stage was vertical (90 ° twist cell). The cell gap was held with a 5 μm spacer. The cell is bonded with Noland's photo-curable adhesive NOA65, so that during the photo-curing of the adhesive deposited on the edge of the cell, the central part of the cell prevents disordering of the light-sensitive fragments in the alignment film. Protected with a paper mask.
Two liquid crystal cells were prepared in the same manner as described above, and filled with a nematic liquid crystal mixture E7 made by Merck and MLC-12100-000. When the azimuth anchoring energy in these cells was measured, they were (3.2 ± 0.6) 10 ⁻⁵ J / m ² and (2.8 ± 0.6) 10 ⁻⁵ J / m ² , respectively. there were.
A photograph of these cells is shown in FIG. It is clear that these cells have a reverse twist domain. Also, a defect (red part) at the edge, possibly caused by the chemical reaction between the adhesive and the azo dye, was confirmed.

[Comparative Example 5]
A photo-alignment material PM2 having a structure represented by Formula B was used as the photo-alignment material.

The material was dissolved in DMF at a concentration of 1% by weight. The PM2 film was spin coated on a glass / ITO plate and baked according to the procedure described in Comparative Example 1. The film was irradiated with linearly polarized light from an Oriel high pressure mercury lamp with normal light incidence for 20 minutes. The overall intensity of light was 28 mW / cm ² . Using these two substrates, an anti-parallel cell was manufactured in the same manner as in Comparative Example 2, and filled with nematic liquid crystal ZLI2293 manufactured by Merck Taiwan. From FIG. 6a, it can be seen that the liquid crystal has excellent alignment in this cell.
The prepared cells were then stored stepwise at 150 ° C., with the liquid crystal alignment after storage at different steps as a control. From FIG. 6a, it can be seen that the liquid crystal alignment of the cell has completely disappeared after 1 hour storage.

Improved orientation durability
[Example 1]
A photo-alignment layer was prepared in the same manner as in Comparative Example 1.
Merck's reactive mesogen mixture RMM256C for planar alignment was dissolved in toluene at 2.5% by mass and filtered through 0.2 μm. The prepared solution was spin-coated on the photo-alignment layer at a spin speed of 3000 rpm and a spin time of 30 seconds. Thereafter, the RM film was polymerized by irradiation with non-polarized UV light from a medium pressure mercury lamp (the intensity of the bright line 365 nm was 9.2 mW / cm ² and the exposure time was 3 minutes).
Two anti-parallel cells were produced by the same method as in Comparative Example 1, and filled with E7 liquid crystal and MLC-12100-000 liquid crystal. From FIG. 7, it can be said that the quality of the liquid crystal alignment in these cells is as high as that of the cell without the RM layer (see Comparative Example 1).
The pretilt angles measured by the crystal rotation method were 3.05 ° for the E7 liquid crystal and 4.4 ° for the MLC-12100-000 liquid crystal. The pretilt angle in the cell was observed along with the cell storage time at environmental conditions. According to FIG. 2, the cell with RM showed higher durability than the control with only the photo-alignment film.

Improved alignment light stability: storage of filled cells [Example 2]
An anti-parallel cell filled with E7 liquid crystal was prepared in the same manner as in Example 1. Thereafter, half of the cell was irradiated with visible light as in Comparative Example 2. FIG. 3b shows that no reorientation occurs in the cell and is in strong contrast with the intrinsic reorientation of the cell without the RM coating described in Comparative Example 2. Thus, the RM coating on the photo-alignment layer dramatically improved the alignment light stability.

Improvement of alignment light stability: preservation of alignment layer [Example 3]
A liquid crystal as in Comparative Example 3 was used except that a reactive mesogen RMM256C layer was deposited and polymerized between the first and second irradiation stages on the substrate subjected to the two irradiations in the same manner as in Example 1. A cell was prepared. FIG. 4 shows that the cell does not form an alignment pattern, in contrast to a cell having no RM layer on the photo-alignment substrate (see Comparative Example 3). Thus, the RM layer on the photo-alignment film stabilizes the initial orientation direction of the photo-alignment film.

Improvement of alignment uniformity and chemical stability of alignment layer [Example 4]
A photo-alignment layer was prepared on a glass / ITO slide as in Comparative Example 1, and an RM layer was coated as in Example 1. Two TN cells were manufactured and filled with E7 liquid crystal and MLC-12100-000 liquid crystal as in Comparative Example 4. The azimuthal anchoring energies in these cells were measured as (3.0 ± 0.6) 10 ⁻⁵ J / m ² and (2.5 ± 0.6) 10 ⁻⁵ J / m ² , respectively. .
From FIG. 5, it was found that these cells do not have the reverse twist domain and adhesive edge defects caused by the cell without the RM layer (Comparative Example 4). Therefore, it was found that the RM layer improves the alignment uniformity and prevents the reaction between the adhesive and the photo-alignment material.
[Example 4 ']
Similar to Comparative Example 1, a photo-alignment layer on a glass / ITO slide was prepared. A reactive mesogen mixture UCL017 for planar alignment manufactured by DIC Corporation was dissolved in toluene at 3% by mass and filtered through 0.2 μm. The prepared solution was spin-coated on the photo-alignment layer at a spin speed of 3000 rpm and a spin time of 30 seconds. Thereafter, the RM film was polymerized in the same manner as in Example 1.
Using two substrates of this type, a 90 ° TN liquid crystal cell having a cell gap of 5 μm was prepared in the same manner as in Comparative Example 4, and filled with E7 liquid crystal. Similar to Example 4, no reverse tilt domain and edge defects were found. This confirmed the results given in Example 4.

Improvement of alignment temperature stability [Example 5]
A cell was prepared in the same manner as in Comparative Example 5 except that the PM2 photo-alignment layer was coated with an RM material as in Example 5. The cell was stored stepwise at 150 ° C., with the liquid crystal orientation after storage at different steps as a control. From FIG. 6b it can be seen that the liquid crystal alignment of the cell is not affected even after storage for 2 hours. This was significantly different from the result of a cell based on a bare PM2 alignment layer; the cell was completely destroyed in liquid crystal alignment after 1 hour storage at 150 ° C. (Comparative Example 5).

Increase of pretilt angle [Example 6]
Similar to Comparative Example 1, two photo-alignment layers were prepared on a glass / ITO slide. A reactive mesogen mixture UCL017 (DIC, Japan) dissolved in toluene at 1.5% by mass and filtered at 0.2 μm was spin-coated on the photo-alignment layer at a spin speed of 3000 rpm and a spin time of 30 seconds. Thereafter, the RM film was polymerized in the same manner as in Example 1.
Using these substrates, an antiparallel liquid crystal cell was prepared in the same manner as in Comparative Example 1 and filled with E7 liquid crystal. The pretilt angle of this cell was found to be close to 90 °. Thus, the RM layer can dramatically change the pretilt angle and switch from the low pretilt orientation to the tilted vertical orientation.

Ease of orientation patterning [Example 7]
Similar to Comparative Example 1, an SD1 photo-alignment layer was deposited on two glass substrates. The alignment layer was irradiated with polarized visible light (λ = 450 nm) from a set of light emitting diodes. The light intensity was 24 mW / cm ² and the irradiation time was 5 minutes. Thereafter, one alignment layer was irradiated with polarized light forming an angle of 90 ° with the polarization direction of the first irradiation through a mask. The irradiation time in the second irradiation stage was 10 minutes. After irradiation, the alignment layer was coated with reactive mesogen RMM256C as in Example 1 and then polymerized. The cell was manufactured so that the alignment directions induced in the first irradiation stage were parallel. The cell gap was held with a 15 μm spacer. E7 liquid crystal was filled into the cell. FIG. 8 shows an excellent orientation pattern in the cell. Thus, the RM auxiliary layer on the photo-alignment substrate does not hinder alignment patterning.

Claims (9)

  (1) Pretreatment step of substrate, (2) Step of applying photo-alignment layer on substrate, (3) Step of irradiating the photo-alignment layer with light to impart photo-alignment function, (4) Photo-alignment layer A method for producing a liquid crystal alignment film comprising: a step of disposing an auxiliary layer made of a crosslinkable material and provided with an alignment function by the photoalignment layer; and (5) a step of crosslinking the crosslinkable material.   The method for producing a liquid crystal alignment film according to claim 1, wherein the photo-alignment layer is composed of a dichroic dye. The dichroic dye is represented by the formula (A)
The method for producing a liquid crystal alignment film according to claim 2, wherein the compound is represented by the formula:   The method for producing a liquid crystal alignment film according to claim 1, wherein the crosslinkable material is a polymerizable liquid crystal material.   The method for producing a liquid crystal alignment film according to claim 1, wherein the auxiliary layer is a permanent layer.   The method for producing a liquid crystal alignment film according to claim 1, wherein the auxiliary layer has a pattern thickness.   The method for producing a liquid crystal alignment film according to claim 1, wherein the molecular orientation of the auxiliary layer is a pattern.   The liquid crystal aligning film manufactured by the manufacturing method of the liquid crystal aligning film in any one of Claims 1-7.   The liquid crystal display element which uses the liquid crystal aligning film of Claim 8 as a component.