JP2672628B2 - Liquid crystal optical element alignment method - Google Patents

Description

The present invention relates to a method for orienting a liquid crystal optical element, and more specifically, the present invention has a highly orientated ferroelectric liquid crystal and is used for a display device or the like. The present invention relates to a liquid crystal optical element alignment method which can be practically advantageously used as an alignment method of a liquid crystal material in the manufacturing process in manufacturing a liquid crystal optical element that can be suitably used as a liquid crystal display element, a liquid crystal recording element and the like.

[Conventional technology]

In recent years, a liquid crystal optical element that uses a ferroelectric liquid crystal material as a liquid crystal material, highly orientates the liquid crystal material, and sandwiches the liquid crystal material between two substrates on which electrodes are disposed It has attracted attention because of its excellent characteristics such as high-speed response to stimuli and excellent contrast ratio.
It has come to be widely used as a liquid crystal display device, a liquid crystal storage device, and the like.

In order to obtain such excellent characteristics, it is necessary to control the orientation of a liquid crystal material composed of a ferroelectric liquid crystal at a high level. Therefore, various alignment control methods have been proposed.

For example, when a low-molecular ferroelectric liquid crystal is used as the ferroelectric liquid crystal, a rubbing method, a shearing method, a temperature gradient method, an oblique vapor deposition method, and the like are conventionally used for controlling the alignment.

However, in the orientation control using these methods, there are drawbacks such as complicated operations and controls performed on the substrate in advance, and since a glass substrate is usually used as the substrate, it is necessary to keep the manufacturing apparatus extremely clean. Moreover, there are problems that continuous production is difficult and it is difficult to increase the area.

Recently, as an alignment control method using an improved method or a modified method of the conventional rubbing method, an alignment film such as a rubbing-treated polyimide or polyvinyl alcohol is provided on the surface of a glass substrate sandwiching a liquid crystal material so that liquid crystal molecules In contrast to the conventional rubbing method that realizes the alignment state, the above-mentioned alignment film is provided on the rotating drum in advance, the liquid crystal is aligned on the drum, and the liquid crystal is transferred onto the substrate. Alignment method for producing a device (Japanese Patent Laid-Open No. 63-14125), and in the conventional rubbing method, a thin film of polyimide, polyvinyl alcohol, or the like is rubbed with a cloth with flocked hair (rubbing), and the liquid crystal is aligned by this alignment film. So let's
A lot of dust is generated during rubbing, scratching the alignment film,
Although it is difficult to make a very thin cell, in order to prevent dust generation and keep the rubbing surface smooth, press or rub with a substance that has hardness equal to or higher than that of the alignment film (polyimide, etc.). Orientation treatment method (Japanese Patent Laid-Open No. 63-64,027)
In order to extend the rubbing material replacement cycle and perform rubbing over a large area more uniformly, an alignment treatment method is performed while shifting the relative position of the rubbing material and the substrate in the direction orthogonal to the rubbing direction during rubbing (Patent Document 1). 63-
Japanese Patent No. 66,534) has been proposed.

However, in the above method, (a) the liquid crystal must be set to an appropriate temperature and the viscosity adjusted in order to uniformly apply the liquid on the drum; (b) the application from the drum to the substrate. Since the liquid crystal must be oriented in the process leading to the transfer of the ink, a waiting time is required for cooling and the production speed is limited. (C) How to process the drum (type of polymer to be applied, drum Since the alignment state of the liquid crystal is greatly different depending on the groove shape, etc.), there is a problem that a complicated optimization process is required one by one. In the above method, (a) is almost as complicated as the normal rubbing method. (B)
It is difficult to obtain uniform orientation over a large area; (c)
A flexible substrate such as plastic may be deformed when pressed and may damage the thin electrode. (D) Like the normal rubbing method, the process of liquid crystal injection and slow cooling is required, which shortens the manufacturing time. There are problems such as difficulty, and in the above method, (a) the process is complicated and the manufacturing cost is high; (c) In the large area orientation treatment, the table and the rubbing roll with very high accuracy are used. (C) The manufacturing time is as long as the ordinary rubbing method.

[Problems to be solved by the invention]

The present invention has been made based on the above circumstances, and an object thereof is to solve the above problems and to provide basic characteristics as a liquid crystal optical element such as high-speed response to an external stimulus such as an electric field and contrast ratio. It is possible to mass-produce liquid crystal optical elements, which are excellent, have sufficient flexibility, and are easy to increase in area, and to continuously mass-produce them at a high speed. To provide a practically remarkably advantageous liquid crystal optical element alignment method having excellent advantages such as easily obtaining a high degree of alignment without performing a specific pretreatment operation for alignment control on is there.

[Means for solving the problem]

The present inventors have conducted extensive studies to solve the above-mentioned problems, and as a result, for example, a ferroelectric liquid crystal material is formed at high speed on the surface of a plastic substrate with electrodes, and then plastic substrates with electrodes facing each other are superposed. A liquid crystal optical element made of a ferroelectric liquid crystal material sandwiched between two flexible substrates on which electrodes are arranged, which is prepared in advance using a method such as high-speed laminating, is used. It is possible to easily orient the ferroelectric liquid crystal material to a high degree without subjecting the substrate to a specific pretreatment by extremely simple operation of orienting the substrate. The present inventors have found new and important findings that a liquid crystal optical element such as an excellent liquid crystal display element can be easily realized, and have completed the present invention based on these findings.

That is, according to the present invention, the ferroelectric liquid crystal material of the liquid crystal optical element composed of the ferroelectric liquid crystal material sandwiched by the two flexible substrates on which the electrodes are arranged is utilized by utilizing the difference in thermal expansion of the substrates. The present invention provides a method for aligning a liquid crystal optical element, which is characterized by aligning.

In the present invention, when a ferroelectric polymer liquid crystal is used as the ferroelectric liquid crystal material, the film-forming property is remarkably improved by the polymerization, and a flexible substrate such as plastic can be suitably applied as the substrate. From this point of view, it is easy to increase the area and the productivity is excellent.

In the present invention, as the flexible substrate, various materials can be used, and usually, from the viewpoint of productivity, versatility, workability, etc., strength, heat resistance, transparency, durability, etc. A substrate or the like made of a plastic having excellent characteristics is preferably used.

Specific examples of this flexible plastic include:
Examples thereof include crystalline polymers such as uniaxially or biaxially oriented polyethylene terephthalate, non-crystalline polymers such as polysulfone and polyether sulfone, polyolefins such as polyethylene and polypropylene, polyamides such as polycarbonate and nylon.

Among these, uniaxially stretched polyethylene terephthalate and polyether sulfone are particularly preferable.

In the present invention, the two substrates may be made of the same material as each other or may be made of different materials, but at least one of the two substrates is usually used. Is optically transparent, and a transparent electrode is provided for use.

The shape of the substrate used in the present invention is not particularly limited, and various shapes can be used according to the purpose of use, etc., but usually a plate, a sheet or a film is used. Can be suitably used,
In particular, a film-shaped one can be preferably used because it is advantageous for a continuous production system.

The thickness of the substrate depends on the degree of transparency, flexibility, strength,
It can be appropriately selected depending on the material such as workability and the purpose of use of the element, and is usually set within the range of about 20 to 100 μm.

In the present invention, as the electrode, any of commonly used ones such as a metal film, a conductive inorganic film such as a conductive oxide film, and a conductive organic film can be used.

In the present invention, it is usually desirable to use an optically transparent or semitransparent electrode as at least one of the two electrodes. At least one transparent or semitransparent electrode is a transparent substrate. It is desirable to install it on the side.

Specific examples of the transparent or translucent electrode include, for example, a tin oxide film called a NESA film, an indium oxide film mixed with tin oxide called an ITO film, an indium oxide film,
Examples include vapor-deposited films of gold or titanium, or other thin film metals or alloys. These electrodes are
Various methods such as known methods, for example, sputtering method, vapor deposition method, printing method, coating method, plating method, bonding method,
Alternatively, it can be provided on a predetermined surface such as a substrate or a liquid crystal layer by using a method in which these are appropriately combined.

The shape of these electrodes is not particularly limited, and may be the entire surface of a predetermined surface such as a substrate, the shape of stripes, or any other desired shape. It may be either.

As the ferroelectric liquid crystal material of the present invention, any material can be used as long as it takes a ferroelectric liquid crystal state, such as a ferroelectric liquid crystal polymer, a ferroelectric low molecular weight liquid crystal compound or a mixture thereof. There is.

Examples of the ferroelectric liquid crystal polymer include an acrylate main chain liquid crystal polymer, a methacrylate main chain liquid crystal polymer, a chloroacrylate main chain liquid crystal polymer, an oxirane main chain liquid crystal polymer, a siloxane main chain liquid crystal polymer, and an ester main liquid crystal polymer. It includes a chain type liquid crystal polymer and the like.

As the repeating unit of the acrylate main chain liquid crystal polymer, for example, And the like.

As the repeating unit of the methacrylate main chain liquid crystal polymer, for example, And the like.

As the repeating unit of the chloroacrylate main chain liquid crystal polymer, for example, And the like.

As the repeating unit of the oxirane main chain liquid crystal polymer, for example, And the like.

As the repeating unit of the siloxane main chain liquid crystal polymer, for example, And the like.

As the repeating unit of the ester main chain type liquid crystal polymer, for example, And the like.

In the repeating unit of the above-mentioned ferroelectric liquid crystal polymer, the side chain skeleton may be replaced with a biphenyl skeleton, a phenylbenzoate skeleton, a biphenylbenzoate skeleton, or a phenyl 4-phenylbenzoate skeleton. The benzene ring of may be replaced by a pyrimidine ring, a pyridine ring, a pyridazine ring, a pyrazine ring, a tetrazine ring, a cyclohexane ring, a dioxane ring, a dioxaborinane ring, or a halogen group such as fluorine or chlorine or a cyano group. Well, 1-methylalkyl group, 2-fluoroalkyl group, 2-chloroalkyl group,
2-chloro-3-methylalkyl group, 2-trifluoromethylalkyl group, 1-alkoxycarbonylethyl group, 2-alkoxy-1-methylethyl group, 2-alkoxypropyl group, 2-chloro-1-methylalkyl group ,
An optically active group such as 2-alkoxycarbonyl-1-trifluoromethylpropyl group, or an ether bond,
They may be replaced with these optically active groups through an ester bond, and the spacer length is such that the methylene chain length is 2
It may vary in the range of up to 30.

The ferroelectric liquid crystal polymer has a number average molecular weight of 1,
000 to 200,000 can be used.

As the ferroelectric low-molecular liquid crystal compound, for example, a Schiff base ferroelectric low-molecular liquid crystal compound, an azo and azoxy ferroelectric low-molecular liquid crystal compound, a vinylphenyl and aromatic ester ester ferroelectric low-molecular liquid crystal compound, a halogen,
Ferroelectric low-molecular liquid crystal compounds into which a ring substituent such as a cyano group is introduced, and ferroelectric low-molecular liquid crystal compounds having a heterocyclic ring are exemplified.

Examples of the Schiff base ferroelectric low-molecular liquid crystal compound include the following compounds (1) to (4).

Examples of the azo and azoxy ferroelectric low-molecular liquid crystal compounds include the following (5) and (6).

Examples of the biphenyl and aromatics ester-based ferroelectric low-molecular liquid crystal compounds include the following compounds (7) and (8).

Examples of the ferroelectric low-molecular liquid crystal compound into which a ring substituent such as a halogen or a cyano group is introduced include the following compounds (9) to (11).

As a ferroelectric low-molecular liquid crystal compound having a heterocyclic ring,
For example, the following compounds (12) and (13) can be mentioned.

The compound is a typical ferroelectric low-molecular liquid crystal compound, and the ferroelectric low-molecular liquid crystal compound of the present invention is not limited to these structural formulas.

A liquid crystal optical element composed of a ferroelectric liquid crystal sandwiched between two flexible substrates on which electrodes to be oriented according to the present invention are arranged [hereinafter, this may be referred to as a liquid crystal optical element (A). . There is no particular limitation on the manufacturing method of [], and it can be manufactured using a known manufacturing method. FIG. 1 is a cross-sectional view of a liquid crystal optical element for performing an alignment treatment of the present invention, in which 1 is a ferroelectric liquid crystal material, 2 is an electrode, and 3 is a flexible substrate.

In this liquid crystal optical element (A), it is not necessary that the ferroelectric liquid crystal forming the liquid crystal optical element be subjected to the alignment treatment.

As a method for producing the liquid crystal optical element (A), for example,
A method of sandwiching the ferroelectric liquid crystal between two flexible substrates on which electrodes are arranged in advance can be preferably used.

As this method, various methods can be used, of which the coating method can perform the alignment treatment at the same time as the film formation, but the liquid crystal optical element (A) of the present invention does not need to be aligned, which is preferable. This method is advantageous in the present invention because it has a wide range of various operating conditions and film thickness.

The thickness of the ferroelectric liquid crystal layer in the liquid crystal optical element (A) is usually set in the range of 0.5 to 10 μm, preferably 0.5 to 4 μm.

In the present invention, as a coating method other than the above-mentioned coating method, for example, a method in which a ferroelectric liquid crystal is diluted with an appropriate solvent, and a film is formed by using a gravure coat, a roll coat or the like is also suitably used. be able to.

FIG. 2 is a schematic diagram showing an example of a method for forming a ferroelectric liquid crystal film by a coating method, which can be suitably used as a pre-process of the sandwiching process such as the alignment process and the laminating process of the present invention.

In FIG. 2, 4 is a flexible substrate with an electrode, 1 is a ferroelectric liquid crystal material, 5 is a laminated substrate composed of a flexible substrate 4 with an electrode coated with the ferroelectric liquid crystal material 1, and 6 is a roll coater. , 7 is an induction roll, 8 is a supply roll, and 9 is a doctor knife for scraping.

When the ferroelectric liquid crystal material is finished as a thin film, in order to prevent conduction between the substrates, an insulating spacer such as silicon oxide or insulating plastic is used between the substrates at the film forming or sandwiching step. A material may be provided, or an insulating film such as a thin polymer may be previously provided between the substrate and the ferroelectric liquid crystal material by a coating method or the like.

The thickness of the insulating film is not particularly limited, but is usually 1 μm or less, preferably 0.5 μm or less.

As a method of sandwiching and sandwiching the counter substrate with the ferroelectric liquid crystal material thus coated and formed, for example, an ordinary laminating method using a pressure roller or the like can be preferably used.

In addition, when performing this clamping, two substrates can be
For example, it may be fixed using an epoxy-based adhesive or the like.

In the present invention, as a method for producing the liquid crystal optical element (A) continuously and at high speed in mass production, for example, one of the flexible plastic substrates with electrodes is moved at high speed while the ferroelectric liquid crystal is added to the above. A method in which a film is continuously formed using a coating method or the like, and then plastic substrates with electrodes facing each other are superposed and continuously laminated can be particularly preferably used.

In the alignment method of the present invention, the ferroelectric liquid crystal in the liquid crystal optical element (A) is aligned by subjecting the liquid crystal optical element (A) produced as described above to an alignment treatment.

This orientation treatment is performed by shearing force due to the difference in thermal expansion of the flexible substrate with electrodes.

When the linear expansion coefficients of the flexible substrates are close to each other, this shearing force is preferably applied by passing the liquid crystal optical element through a pair of rollers having different temperatures of the upper and lower rollers. FIG. 3 is an explanatory view showing a state in which the liquid crystal optical element is passed between a pair of rollers in which upper and lower rollers are provided with a temperature difference, and the liquid crystal optical element is passed between three sets of rollers. In this case, it is preferable that the temperature of the rollers of the pair of adjacent rollers is reversed.

In addition, the temperature of the high temperature side roller is T _H and the temperature of the low temperature side is
T _L, when the temperature of the entire system for performing the alignment treatment and T _O T _O is (T _H
+ T _L ) / 2 is preferable. The T _O is the isotropic phase and smectic A phase multiphase multiphase the isotropic phase and the chiral smectic C phase, smectic A phase, a chiral smectic C phase, is at a temperature in the temperature range taking liquid phase of the chiral nematic phase or the like Is desirable. _Regarding the temperature difference between T _H and T _L , since the linear expansion coefficient of PET film is usually 15 × 10 ⁻⁶ / ° C., T _H −T _L is preferably 3 ° C. or higher, more preferably 10 ° C.
C or higher. However, there is a temperature difference so that T _H is much higher than the isotropic phase of liquid crystal (about 20 ° C or more),
It is not preferable to set T _L to the temperature at which the liquid crystal crystallizes.

If the substrates have different linear expansion coefficients, T _H = T _L can also be used for orientation.

FIG. 4 is a cross-sectional view schematically showing the principle of orientation according to the present invention, and shows an example in which a temperature difference is provided between a pair of rollers and the difference in thermal expansion is utilized for orientation. Since there is a difference in expansion between the high-temperature roll side and the low-temperature roller side as shown in the figure, it is considered that shear stress is relatively applied to the liquid crystal material near the roller, and this shear force causes the liquid crystal molecules to be aligned.

The number of sets of free rotating rollers used is not particularly limited, but it is preferable to use two or more sets as shown in FIG.

As described above, the alignment method of the present invention can achieve a high degree of alignment with an extremely simple operation without necessarily requiring a complicated pretreatment on the substrate and the like, and is excellent in high-speed response, contrast ratio, and the like. It is a practically remarkably advantageous method for aligning liquid crystal optical elements, which has excellent advantages such as efficient production of liquid crystal optical elements and easy realization of high-speed continuous mass production processes. It can be suitably used as an alignment method in the manufacturing process of a ferroelectric liquid crystal optical element sandwiching a flexible substrate.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples,
The present invention is not limited to this.

Example 1 As a flexible substrate, a transparent polyethersulfone (PES) film having a thickness of about 100 μm was used, and a transparent conductive film as an electrode had a thickness of about 700 Å on one surface of the film.
A flexible substrate with an electrode is prepared by providing an ITO film, and a ferroelectric polymer liquid crystal having the following characteristics, which is composed of a repeating unit represented by the following formula, is formed on the electrode surface of the substrate. It was heated to ℃ and was applied in a state of isotropic phase by using a bar coater so that the thickness was about 2.5 μm.

Phase transition behavior [G: glass state, SmC ^* : chiral smectic C phase, S
mA: smectic A phase, Iso: isotropic phase] Next, a PES film having a thickness of about 100 μm was used as a counter substrate, and this was laminated on the surface of the coating film of the ferroelectric polymer liquid crystal described above, and a width of 10 cm, A liquid crystal optical element having a length of 60 cm was obtained.

In this state, the liquid crystal molecules are randomly aligned.

Next, the liquid crystal optical element (A) produced by the above method
Is passed through a heating device 10 as shown in FIG. 5 and heated to 80 ° C., and then three sets of rollers (11 to 16) as shown in FIG.
It was made to pass through between. The rollers 11, 14 and 15 were for high temperature (temperature T _H ), 12, 13, 16 were for low temperature (temperature T _L ), and were the temperature T _{O of the} entire system. The diameter of the adjacent rollers is 50.
mm, the distance between the rollers was 100 mm. The results are shown in Table 1.

v represents the moving speed of the flexible substrate, and A represents the degree of orientation.

The value of the degree of orientation A shown in Table 1 was determined according to a well-known general measuring method shown below.

That is, the liquid crystal optical element that has been subjected to the above alignment treatment is
When a crystal cell is formed by arranging parallelly between two polarizers whose polarization axes are orthogonal to each other, and the liquid crystal optical element is rotated around the light spot while the white light of the halogen lamp is incident on the liquid crystal cell. The change in intensity of transmitted light is measured, and the ratio of the maximum intensity (Imax) and the minimum intensity (Imin) at that time is A = Imax / Imi
The degree of orientation A was n.

As described above, it was found that the alignment process can be easily performed by passing the film sandwiching the non-aligned liquid crystal through the rollers having different temperatures.

Example 2 A biaxially stretched PET (polyethylene terephthalate) with an ITO film having a thickness of 125 μm (ITO thickness of about 1000Å) was used as a flexible substrate with electrodes, and the following polyoxirane-based ferroelectric polymer liquid crystal was formed as shown in FIG. Applied.

Phase transition behavior [Cry: crystalline state] That is, the liquid crystal is dissolved in a solvent (dichloromethane) at 10% by weight.
The diluted solution was applied to a thickness of about 15 μm with a roll coater as shown in FIG. 2, and then the solvent was evaporated to form a non-aligned liquid crystal film with a thickness of 1.5 μm.

Next, a 125 μm thick counter substrate with an ITO film made of the same biaxially oriented PET as described above was laminated on the above liquid crystal film, and then an alignment treatment was performed using the apparatus shown in Example 1.
Note that T _H = 90 ° C., T _L = 60 ° C., T _O = 75 ° C., and v = 3 cm / sec. The degree of orientation A is about 100 and is 50 when the width of the substrate is 10 cm.
It has a value of ~ 120 and is well oriented. Further, since the alignment treatment can be performed subsequent to the apparatus shown in FIG. 2, the productivity is very excellent.

Example 3 Using the same substrate and apparatus as in Example 2, a liquid crystal optical element was produced using the following liquid crystal composition containing a ferroelectric polymer liquid crystal.

In addition, T _H = 110 ° C., T _L = 80 ° C., T _O = 95 ° C., and v = 3 cm / sec. The degree of orientation A was about 110, and good orientation was obtained.

Example 4 In the same manner as in Example 2, low-molecular liquid crystal DOBAMBC was used for alignment.

In addition, T _H = 120 ° C., T _L = 100 ° C., T _O = 110 ° C., v = 3 cm /
Seconds. The orientation degree A was about 70, and the orientation could be performed without any practical problems.

As shown in the above examples, the method according to the present invention was found to be an effective method for aligning a ferroelectric polymer liquid crystal optical element, a ferroelectric low molecular liquid crystal, or a mixed liquid crystal thereof. It was It was also found to be more effective for a liquid crystal composition containing a polymer liquid crystal that is easily aligned by shear stress.

〔The invention's effect〕

According to the present invention, a high degree of alignment can be achieved in a liquid crystal optical element by a very simple and easy operation without subjecting the substrate to complicated specific pretreatment.

Further, high-speed and continuous orientation is possible, the efficiency of the continuous production process including the film forming process, the sandwiching process such as laminating, etc. can be remarkably enhanced, and high-speed mass production can be easily realized. .

Furthermore, since a ferroelectric liquid crystal is used as the liquid crystal material and a high degree of alignment can be obtained, a liquid crystal optical element excellent in high-speed response, contrast ratio and the like can be easily and stably obtained.

Further, since a flexible substrate such as plastic is used as the substrate, it is easy to increase the area.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal optical element, in which 1 is a liquid crystal material, 2 is an electrode, and 3 is a flexible substrate. FIG. 2 is a schematic view showing an example of a method for forming a ferroelectric liquid crystal film by a coating method, which can be preferably used as a pre-process of the sandwiching process such as the alignment process and the laminating process of the present invention. In the figure, 4 is a flexible substrate with an electrode, 5 is a laminated substrate comprising the flexible substrate 4 with an electrode coated with a ferroelectric liquid crystal material, 6 is a roll coater, 7 is an induction roll, 8 is a supply roll, 9 represents a doctor knife for scraping. Third
FIG. 4, FIG. 5 and FIG. 5 are cross-sectional explanatory views showing a state in which the alignment treatment of the present invention is performed between rollers. In the figure, 11 ~
16 is a roller, and 10 is a heating device.

Claims (2)

(57) [Claims] 1. A ferroelectric liquid crystal material of a liquid crystal optical element made of a ferroelectric liquid crystal material sandwiched between two flexible substrates on which electrodes are arranged by utilizing a difference in thermal expansion of the substrates. A method for orienting a liquid crystal optical element, which comprises orienting. 2. The liquid crystal optical element according to claim 1, wherein two flexible substrates having close linear expansion coefficients are used and the liquid crystal optical element is oriented by passing through at least a pair of rollers having different temperatures. Orientation method.