JP2002062531A - Method for aligning liquid crystal molecule - Google Patents

Abstract

PROBLEM TO BE SOLVED: To align liquid crystal molecules while controlling alignment tilt angle. SOLUTION: In a method for aligning the liquid crystal molecules by coating a substrate with a coating liquid for an alignment layer and forming the alignment layer and by coating the alignment layer with a coating liquid containing the liquid crystal molecules and forming a liquid crystal layer, a quaternary ammonium salt is added to the coating liquid for the alignment layer and the tilt angle of the liquid crystal molecules are controlled by an action of the quaternary ammonium salt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for aligning liquid crystal molecules while controlling an alignment tilt angle.

[0002]

2. Description of the Related Art Since liquid crystal compounds exhibit both liquid-like fluidity and crystal-like regular molecular arrangement in a liquid crystal layer, they are expected to be applied in various fields. Control is indispensable for engineering application to liquid crystal devices represented by liquid crystal displays. In particular, control of the tilt angle including the pretilt angle is one of the important issues of the current liquid crystal alignment technology.

[0003] The molecular orientation of liquid crystal is a typical one.
1) homeotropic alignment, 2) homogeneous alignment,
Three types are known: 3) tilt alignment, 4) hybrid alignment, 5) twisted alignment, 6) planar alignment, and 7) focal conic alignment. For more details, "Basic and Application of Liquid Crystal", Industrial Research Institute Publishing (1991) Year).

In general, what kind of alignment can be obtained depends on what kind of alignment treatment is to be performed on the substrate surface if the liquid crystal to be used is determined. Various methods have been proposed for the alignment treatment, which are described in detail in "Basics and Applications of Liquid Crystals", published by the Industrial Research Institute (1991). For example,
Appl. Phy for vertical or parallel orientation
s. Lett., 27, 268 (1975), App
l. Phys. Lett., Vol. 29, p. 67 (1976),
Appl. Phys. Lett., Vol. 22, p. 111 (1973)
), A method of chemically adsorbing an aligning agent such as a chromium carboxylate complex or an organic silane onto a substrate surface, Journal of Applied Physics,
3, 18 (1974), Phys. Rev. Lett., Vol. 25, p. 67 (1976), and the like, a method of physically adsorbing an aligning agent on a substrate surface, Appl. Phys. Lett., 24th
Vol., 297 (1974), etc., a method of polymerizing a low molecular weight substance onto a substrate surface by plasma discharge, J. Appl. Phy.
s., 47, 1270 (1976) discloses a method of polymerizing a high molecular weight substance onto a substrate surface by the action of a high electric field. Next, as a method of tilting parallel alignment
Appl. Phys. Lett., 25, 479 (1974)
For example, the oblique deposition method of depositing an oxide such as silicon oxide on a substrate surface from an oblique angle is disclosed in Japanese Patent Application Laid-Open No. H11-146572. . As another method for oblique vertical alignment, an oblique vapor deposition method in which an oxide such as silicon oxide is vapor-deposited from an oblique angle while rotating the substrate surface is disclosed in the 6th Meeting of the Liquid Crystal Symposium, p. 96 (1980). Have been. According to this method, although stable orientation having a certain tilt orientation angle can be obtained, there are problems such as low productivity for industrial production and difficulty in increasing the area.

As a method of aligning molecules, there is a method of forming an organic film on the substrate surface, rubbing the surface with a cloth such as cotton, nylon, polyester or the like in a certain direction, and aligning the liquid crystal molecules in the rubbing direction. In this method, a stable orientation can be obtained relatively easily, and therefore, this method is exclusively used industrially. Examples of the organic film include polyvinyl alcohol, polyoxyethylene, polyamide, and polyimide. Among them, polyimide is most commonly used in terms of chemical stability, thermal stability, and the like. In such a liquid crystal alignment film, it is known that the tilt angle of liquid crystal molecules changes depending on the alignment film used. For example, JP-A-5-4
Nos. 3687, 8-12759 and 8-220541
Nos. 8-220542, 9-143196, 9-230354, 9-278724, and 10-
Nos. 45690 and 10-123532 disclose various alignment films capable of tilt alignment. However, the tilt angle depends on the properties of the alignment film itself, and the angle cannot be easily adjusted. A method of controlling the alignment of liquid crystal molecules by light is also known. For example, in Functional Materials, Vol. 17, p. 13 (1997), various alignment films whose tilt angle can be controlled by light are described.
However, these methods need to use polarized light irradiation or polarized ultraviolet light irradiation, need to change the incident angle of polarized light to adjust the inclination angle, and cannot always control the inclination angle easily. .

As described above, various orientation techniques have been proposed.
A technique for tilt-aligning a liquid crystal compound has also been disclosed.
However, none of them is sufficient from the viewpoint of controlling the tilt angle, and there has been a demand for the development of a method capable of easily controlling the tilt angle of the liquid crystal compound.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to easily control the tilt angle of the liquid crystal compound.

[0008]

The present invention provides the following (1) to
(7) A method for aligning liquid crystal molecules is provided. (1) A coating liquid for an alignment film is applied on a substrate to form an alignment film, and a coating liquid containing liquid crystal molecules is applied on the alignment film to form a liquid crystal layer and align the liquid crystal molecules. A method, wherein a quaternary ammonium salt is added to the coating liquid for the alignment film,
A method for aligning liquid crystal molecules, wherein the tilt angle of liquid crystal molecules is controlled by the action of a quaternary ammonium salt. (2) The method for aligning liquid crystal molecules according to (1), wherein the quaternary ammonium salt has a total number of carbon atoms of 7 to 44. (3) The method for aligning liquid crystal molecules according to (1), wherein the quaternary ammonium salt is represented by the following formula (I):

[0009]

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Wherein R ¹ has 4 to 20 carbon atoms.
R ² , R ³ and R ⁴ are each independently an aliphatic group having 1 to 8 carbon atoms or a nitrogen-containing group wherein R ² and R ³ are bonded to each other; Forming a heterocycle; and X is an anion]. (4) In the formula (I), R ¹ is an alkyl group having 4 to 20 carbon atoms or a halogen-substituted alkyl group having 4 to 20 carbon atoms; R ² , R ³ and R ⁴ are
(3) The method for aligning liquid crystal molecules according to (3), which is independently an alkyl group having 1 to 8 carbon atoms. (5) The method for aligning liquid crystal molecules according to (1), wherein the quaternary ammonium salt is used in a molar ratio to the liquid crystal molecules in the range of 1/1000 to 250/1000. (6) The method for aligning liquid crystal molecules according to (1), wherein the liquid crystal molecules are discotic liquid crystal molecules. (7) The method for aligning liquid crystal molecules according to (1), wherein the liquid crystal molecules have a triphenylene nucleus.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In this specification, a substrate refers to a material for mounting a liquid crystal layer or a material for sandwiching a liquid crystal layer which is a component of a liquid crystal cell. Specifically, a polymer film such as a triacetyl cellulose (TAC) film or a polyethylene naphthalate (PEN) film is used. In addition, a glass plate, an ITO substrate, a color filter substrate, a quartz plate, a silicon wafer, and a polarizing plate can be used as the substrate. The substrate may be provided with an alignment layer, a transparent electrode (ITO), a color filter layer, a black matrix, and a thin film transistor. Further, an alignment process such as the formation of an electrode pattern, the rubbing process described above, and the irradiation of polarized UB may be performed. A single substrate or a pair of substrates may be used. When a pair is used, a spacer, a sealant, or the like may be used as necessary. In this specification, the layer adjacent to the liquid crystal layer is preferably a layer closest to the liquid crystal layer among layers located between the substrate and the liquid crystal layer. The layer adjacent to the liquid crystal layer may have a function as an alignment film or a transparent electrode.

The liquid crystal layer is mainly composed of liquid crystal molecules. As the liquid crystal molecules, discotic liquid crystal molecules, rod-like liquid crystal molecules, and cholesteric liquid crystal molecules are preferable. Discotech liquid crystalline molecules are particularly preferred. The discotec liquid crystal molecules preferably have a triphenylene nucleus. Two or more liquid crystal molecules may be used in combination. Components other than liquid crystal molecules (eg, dyes, dichroic dyes, polymers, polymerizers, sensitizers, phase transition temperature lowering materials, stabilizers) may be added to the liquid crystal layer. As a method for providing the liquid crystal layer on the substrate, a known method is employed. As a method of applying, a known method,
For example, curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, and the like are employed. At this time, the substrate may be provided with necessary layers and portions including the necessary processing and alignment layers as described above. As a method of injecting liquid crystal molecules between the substrates, a general method such as a dispenser method or a bell jar method is employed. Further, a liquid crystal layer may be applied to a substrate, and another substrate or a substrate to which another liquid crystal layer is applied may be combined.

In the present invention, the tilt angle of the liquid crystal molecules is controlled by adding a quaternary ammonium salt to the coating solution for the alignment film and by the action of the quaternary ammonium salt. When a quaternary ammonium salt is added to a coating solution for an alignment film, the tilt angle of liquid crystal molecules generally increases. As a result, the tilt angle of the liquid crystal molecules can be controlled. The pyridinium ring of the quaternary ammonium salt preferably has a total carbon number of 7 to 44. It is preferable that four aliphatic groups are bonded to the nitrogen atom of the quaternary ammonium structure. Aliphatic groups include alkyl groups, substituted alkyl groups, alkenyl groups, substituted alkenyl groups, alkynyl groups, and substituted alkynyl groups. The aliphatic group may have a cyclic structure. The chain aliphatic group may have a branch. Examples of the substituent of the aliphatic group include an aryl group, an alkoxy group, an alkylthio group, an amide group, an acyl group, an acyloxy group, an alkoxycarbonyl group, a carboxyl, a halogen atom, an alkoxyalkyl group, an alkyloxyoxycarbonylalkyl group,
2,2,3,3,4,4,5,5,6,6,7,7,
8,8,8-Pentadecafluorooctyloxycarbonylethyl is included. Examples of the anion serving as the counter ion of the quaternary ammonium salt include a fluorine ion, a chloride ion,
Includes bromide, iodine, benzenesulfonium and paratoluenesulfonium ions.
A quaternary ammonium salt represented by the following formula (I) is preferred.

[0014]

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In the formula (I), R ¹ is an aliphatic group having 4 to 20 carbon atoms. Aliphatic groups include alkyl groups, substituted alkyl groups, alkenyl groups, substituted alkenyl groups, alkynyl groups, and substituted alkynyl groups.
The aliphatic group may have a cyclic structure. The cycloaliphatic group includes a group having a steroid structure. The chain aliphatic group may have a branch. Examples of the substituent of the aliphatic group include an aryl group, an alkoxy group, an alkylthio group, an amide group, an acyl group, an acyloxy group, an alkoxycarbonyl group, a carboxyl, a halogen atom, an alkoxyalkyl group, an alkyloxyoxycarbonylalkyl group,
2,2,3,3,4,4,5,5,6,6,7,7,
8,8,8-Pentadecafluorooctyloxycarbonylethyl is included.

In the formula (I), R ² , R ³ and R ⁴
Is independently an aliphatic group having 1 to 8 carbon atoms, or R ² and R ³ are combined to form a nitrogen-containing heterocyclic ring. Aliphatic groups include alkyl groups, substituted alkyl groups, alkenyl groups, substituted alkenyl groups, alkynyl groups, and substituted alkynyl groups. A chain aliphatic group is preferred over a cyclic aliphatic group. R ² , R ³ and R ⁴ are
Each independently, preferably an alkyl group, a substituted alkyl group, an alkenyl group or a substituted alkenyl group,
It is more preferably an alkyl group or a substituted alkyl group, and most preferably an alkyl group or a halogen-substituted alkyl group. The number of carbon atoms of R ² , R ³ and R ⁴ is preferably 1 to 7, more preferably 1 to 5, and most preferably 1 to 4. Examples of aliphatic groups include methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, se.
Includes c-butyl, t-butyl, cyclobutyl, cyclopropylmethyl, n-pentyl, neopentyl, n-hexyl, cyclohexyl and n-heptyl. R
^The nitrogen-containing heterocyclic ring formed by combining ² and R ³ is preferably a 5- or 6-membered ring.

In the formula (I), X is an anion. Examples of anions include chloride, bromine, iodine, p-toluenesulfonium and benzenesulfonium. Below, the example of a quaternary ammonium salt is shown.

[0018]

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[0019]

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The quaternary ammonium salt is added to the coating solution for the alignment film. The addition amount is 1/1 in a molar ratio to the liquid crystal molecules.
It is preferably in the range of 000 to 250/1000.

[0021]

[Example 1] (Evaluation of liquid crystal tilt angle controllability) 0.3% by weight of a quaternary ammonium salt was added to a commercially available coating liquid for an alignment film (San Ever SE-610, manufactured by Nissan Chemical Industries, Ltd.). did. The coating solution to which the quaternary ammonium salt (3) was added was applied on a glass substrate using a # 4 bar coater, dried, and rubbed to form an alignment film. The following discotic liquid crystal compound (DLC) 1 was added to 400 parts by weight of methyl ethyl ketone.
Then, 00 parts by weight and 1 part by weight of cellulose acetate butyrate were dissolved to prepare a liquid crystal layer coating solution. Apply the coating solution
After being applied on the alignment film by a spin coating method, it was dried at room temperature. After heating the formed liquid crystal layer to 200 ° C.,
Then, the liquid crystal compound was aligned, and in that state, the substrate was rapidly cooled to room temperature to fix the alignment state. The liquid crystal layer was observed with a polarizing microscope, and it was confirmed that the discotic liquid crystalline compound was aligned parallel to the rubbing direction and uniformly (monodomain). When the average tilt angle with respect to the substrate was determined by the crystal rotation method, it was confirmed that the addition of the quaternary ammonium salt (3) increased the alignment tilt angle of the liquid crystal molecules.

[0022]

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Examples 2 to 8 In the same manner as in Example 1 except that the kind and amount of the quaternary ammonium salt added to the coating solution for the alignment film were changed as shown in Table 1, The orientation tilt angle was measured. The results are shown in Table 1.

[0024]

[Table 1] Table 1 ──────────────────────────────────── Sample Quaternary ammonium salt addition amount Average tilt angle Example 1 (3) 0.3% by weight 10 degrees Example 2 (3) 0.5% by weight 12 degrees Example 3 (4) 0.3% by weight 12 degrees Example 4 (4) 0.5% by weight 16 degrees Example 5 (5) 0.3 % By weight 11 degrees Example 6 (5) 0.5% by weight 13 degrees Example 7 (6) 0.3% by weight 11 degrees Example 8 (6) 0.5% by weight 15 degrees ─────────────────────────────

[Comparative Example 1] (Evaluation of liquid crystal tilt angle controllability) A commercially available coating liquid for an alignment film (Sanever SE-610, manufactured by Nissan Chemical Industries, Ltd.) was applied on a glass substrate using a # 4 bar coater. Then, the resultant was dried and subjected to a rubbing treatment to form an alignment film. 100 parts by weight of the discotic liquid crystal compound (DLC) used in Example 1 and 1 part by weight of cellulose acetate butyrate were dissolved in 400 parts by weight of methyl ethyl ketone to prepare a liquid crystal layer coating solution. The coating liquid was applied on the alignment film by spin coating, and then dried at room temperature. 200 ° C. for the formed liquid crystal layer
Then, the liquid crystal compound was aligned at 130 ° C., and in that state, the substrate was rapidly cooled to room temperature to fix the alignment state. Observation of the liquid crystal layer with a polarizing microscope revealed that the discotic liquid crystal compound had dual domains and was not in a uniform alignment state.

Claims (7)

[Claims] An alignment film is coated on a substrate to form an alignment film, and a coating solution containing liquid crystal molecules is coated on the alignment film to form a liquid crystal layer. A method for aligning liquid crystal molecules, comprising adding a quaternary ammonium salt to a coating liquid for an alignment film, and controlling the tilt angle of the liquid crystal molecules by the action of the quaternary ammonium salt. 2. The method for aligning liquid crystal molecules according to claim 1, wherein the quaternary ammonium salt has a total number of carbon atoms of 7 to 44. 3. The method for aligning liquid crystal molecules according to claim 1, wherein the quaternary ammonium salt is represented by the following formula (I): [Wherein, R ¹ is an aliphatic group having 4 to 20 carbon atoms; R ² , R ³ and R ⁴ are each independently an aliphatic group having 1 to 8 carbon atoms. Or R ²
And R ³ combine to form a nitrogen-containing heterocyclic ring;
Is an anion. 4. In the formula (I), R ¹ is an alkyl group having 4 to 20 carbon atoms or 4 to 2 carbon atoms.
^{4. The} method for aligning liquid crystal molecules according to claim 3, wherein R ² , R ³ and R ⁴ are each independently an alkyl group having 1 to 8 carbon atoms. 5. The method for aligning liquid crystal molecules according to claim 1, wherein the quaternary ammonium salt is used in a molar ratio to the liquid crystal molecules in the range of 1/1000 to 250/1000. 6. The method according to claim 1, wherein the liquid crystal molecules are discotic liquid crystal molecules. 7. The method according to claim 1, wherein the liquid crystal molecules have a triphenylene nucleus.