JPH02216125A - Orienting method for liquid crystal optical element - Google Patents

Abstract

PURPOSE:To very simply and easily orient liquid crystal materials to a high degree by using the difference in thermal expansion between two flexible substrates to orient ferroelectric liquid crystal materials held between these substrates. CONSTITUTION:Two flexible substrates 3 on which electrodes 2 are arranged are put one over the other and ferroelectric liquid crystal is held between them to form a liquid crystal optical element A. At the time of producing this optical element A, a roll coater 6 is used to coat flexible substrates 4 having electrodes with ferroelectric liquid crystal materials 1 and they are stuck to each other by a prescribed laminator to quickly and continuously produce the optical element. This liquid crystal optical element A is allowed to pass between a pair of upper and lower rolls TH and TL different in temperature, and shearing stress is relatively given to liquid crystal materials by the difference in expansion to orient liquid crystal materials. Thus, elements of stable quality are continuously mass-produced though having a large area.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for aligning a liquid crystal optical element, and more specifically, the present invention relates to a method for aligning a liquid crystal optical element. The present invention relates to a method for aligning a liquid crystal optical element that can be practically advantageously used as a method for aligning a liquid crystal material in the manufacturing process when manufacturing a liquid crystal optical element that can be suitably used as a liquid crystal display element, a liquid crystal recording element, etc.

[Conventional technology]

In recent years, liquid crystal optical elements have been developed that use ferroelectric liquid crystal materials as liquid crystal materials, control the orientation of this material to a high degree, and sandwich this liquid crystal material between two substrates on which electrodes are provided. It has attracted attention because of its excellent properties such as high-speed response to stimuli and excellent contrast ratio, and has come to be widely used as liquid crystal display elements, liquid crystal memory elements, etc.

In order to obtain such excellent properties, it is necessary to highly control the alignment of a liquid crystal material made of ferroelectric liquid crystal, and for this purpose 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 evaporation method, etc. have been conventionally used to control its orientation.

However, orientation control using these methods has drawbacks such as complicated operations and controls to be performed on the substrate in advance, and because glass substrates are usually used as substrates, it is necessary to keep the manufacturing equipment extremely clean. Moreover, there are problems such as difficulty in continuous production and difficulty in increasing the area.

Recently, as an alignment control method using an improved or modified conventional rubbing method, liquid crystal molecules are In contrast to the conventional rubbing method, which achieves the alignment state of Orientation method for manufacturing optical elements
25 Publication), ■ In the conventional rubbing method, polyimide,
A thin film of polyvinyl alcohol, etc. is rubbed with a cloth with flocked hair (rubbing), and this alignment film aligns the liquid crystal, so a lot of dust is generated during rubbing, which can damage the alignment film or create very thin cells. However, in order to prevent the generation of dust and keep the rubbing surface smooth, an alignment treatment method (unexamined Japanese Patent Application Publication No. Showa 63
64, No. 027), ■ In order to extend the replacement cycle of the rubbing material and perform more uniform rubbing of a wide area,
An alignment treatment method (Japanese Patent Laid-Open No. 63-66534) has been proposed in which the relative positions of the rubbing material and the substrate are shifted in the direction perpendicular to the rubbing direction during rubbing.

However, in method (2) above, (a) in order to uniformly coat the drum, it is necessary to set the liquid crystal at an appropriate temperature and adjust the viscosity; (b) from the coating on the drum to the substrate. Since the liquid crystal must be oriented in the process leading to the transfer, it requires waiting time for cooling, which limits the reduction in manufacturing speed; (C) How to process the drum (type of polymer to be applied, Since the alignment state of the liquid crystal varies greatly depending on the shape of the drum grooves, etc., there are problems such as the need for complicated optimization processing. (b) Requires a somewhat complicated manufacturing process;
Difficult to obtain uniform orientation over a large area; (C)
Flexible substrates such as plastic may deform when pressed and may damage thin electrodes; (d) Similar to the normal rubbing method, a process of liquid crystal injection and slow cooling is required, reducing manufacturing time. In addition, in the method (2) above, (a) the process is complicated and the manufacturing cost is high; (C) the alignment treatment of large areas requires a highly accurate table and There were problems such as requiring a rubbing roll; and (C) the production time was as long as that of a normal rubbing method.

[Problem to be solved by the invention]

The present invention has been made based on the above-mentioned circumstances, and its purpose is to solve the above-mentioned problems and to improve the basic characteristics of liquid crystal optical elements such as high-speed response to external stimuli such as electric fields and contrast ratio. It is possible to mass-produce liquid crystal optical elements extremely easily and rapidly, which have excellent features such as excellent flexibility, sufficient flexibility, and easy expansion into large areas. An object of the present invention is to provide a method for aligning a liquid crystal optical element that is extremely advantageous in practice and has excellent advantages such as being able to easily obtain a high degree of alignment without performing specific pretreatment operations for alignment control. be.

[Means for Solving the Problems] As a result of extensive research in order to solve the above problems, the present inventors, for example, formed a film of a ferroelectric liquid crystal material on the surface of a plastic substrate with electrodes at high speed, and then Liquid crystal optics made of a ferroelectric liquid crystal material sandwiched between two flexible substrates with electrodes, which are fabricated in advance using a method such as high-speed lamination by overlapping opposing plastic substrates with electrodes. By using the extremely simple operation of orienting the device using the difference in thermal expansion of the substrates, it is possible to easily orient the ferroelectric liquid crystal material to a high degree without performing any specific pretreatment operations on the substrates. The present inventors have discovered new and important knowledge that it is possible to easily realize liquid crystal optical elements such as liquid crystal display elements with excellent high-speed response, contrast ratio, etc., and have completed the present invention based on these findings.

That is, the present invention utilizes the difference in thermal expansion of the substrates to produce a ferroelectric liquid crystal material of a liquid crystal optical element, which is made of a ferroelectric liquid crystal material sandwiched between two flexible substrates on which electrodes are disposed. The present invention provides a method for aligning a liquid crystal optical element, which is characterized by aligning the element.

In the present invention, when a ferroelectric polymer liquid crystal is used as the ferroelectric liquid crystal material, film forming properties are significantly improved by polymerization, and flexible substrates such as plastic can be suitably used as substrates. It is easy to increase the area from the point,
Become a highly productive person.

In the present invention, various materials can be used as the flexible substrate, but usually, from the viewpoint of productivity, versatility, processability, etc., strength, heat resistance, transparency, durability, etc. A substrate made of plastic having excellent properties is preferably used.

Specific examples of plastics having flexibility include crystalline polymers such as -axially or biaxially oriented polyethylene terephthalate, amorphous polymers such as polysulfone and polyethersulfone, polyolefins such as polyethylene and polypropylene, polycarbonates, Examples include polyamides such as nylon.

Among these, -axially oriented polyethylene terephthalate, polyether sulfone, and the like are particularly preferred.

In the present invention, the two substrates may be made of the same material or different materials, but usually at least one of the two substrates is It is used by making it optically transparent and providing a transparent electrode.

The shape of the substrate used in the present invention is not particularly limited, and various shapes can be used depending on the purpose of use, etc., but usually a plate, sheet, or film shape is used. It can be used suitably, and in particular, a film-form one can be suitably used because it is advantageous for continuous production.

The thickness of the substrate can be appropriately selected depending on the transparency of the substrate, the degree of flexibility, strength, workability, etc. of the material, the intended use of the device, etc., and is usually set within a range of about 20 to 1000 μm. .

In the present invention, various types of electrodes that are commonly used, such as metal films, conductive inorganic films such as conductive oxide films, and conductive organic films, can be used as the electrodes.

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

Specific examples of this transparent or semitransparent electrode include a tin oxide film called a NESA film, an indium oxide film mixed with tin oxide called an ITO film, an indium oxide film, a vapor-deposited film of gold or titanium, or other films. Examples include thin film metals or alloys. These electrodes can be fabricated using various known methods such as sputtering, vapor deposition, printing, coating, plating, adhesion, or an appropriate combination of these methods.
It can be provided on a predetermined surface such as a substrate or a liquid crystal layer.

There are no particular restrictions on the shape of these electrodes, and they may cover the entire surface of a predetermined surface of a substrate, etc., may be striped, or may have any other desired shape. Either can be used.

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, and includes a ferroelectric liquid crystal polymer, a ferroelectric low molecular weight liquid crystal compound, or a mixture thereof. and so on.

Examples of ferroelectric liquid crystal polymers include acrylate main chain liquid crystal polymers, methacrylate main chain liquid crystal polymers,
These include chloroacrylate main chain liquid crystal polymers, oxirane main chain liquid crystal polymers, siloxane main chain liquid crystal polymers, ester main chain liquid crystal polymers, and the like.

Examples of repeating units of the acrylate main chain liquid crystal polymer include (A) (B) (C) Hs (D).

Examples of the repeating unit of the chloroacrylate main chain liquid crystal polymer include (E) I and the like.

Examples of the repeating unit of the methacrylate main chain liquid crystal polymer include the following.

Examples of the repeating unit of the oxirane main chain liquid crystal polymer include (F).

Examples of the repeating unit of the siloxane main chain liquid crystal polymer include (G).

The repeating unit of the ester main chain liquid crystal polymer is as follows:
For example, (H) C1(3 (J) etc. are mentioned.

The repeating unit of the above ferroelectric liquid crystal polymer is
The side chain skeleton may be replaced with a biphenyl skeleton, a phenylhenzoate skeleton, a biphenylhenzoate skeleton, or a phenyl 4-phenylhenzuate skeleton, and the Hensen ring in these skeletons can be replaced with a pyrimidine ring, a pyridine ring, or a pyridazine ring. , may be substituted with a pyrazine ring, a tetrazine ring, a cyclohexane ring, a dioxane ring, a dioxaborinane ring, may be substituted with a halogen group such as fluorine or chlorine, or a cyano group, a 1-methylalkyl group, 2
-fluoroalkyl group, 2-chloroalkyl group, 2-chloro-3-methylalkyl group, 2-trifluoromethylalkyl group, l-alkoxycarbonylethyl group, 2-
With an optically active group such as alkoxy-1-methylethyl group, 2-alkoxypropyl L2-chloro-1-methylalkyl group, 2-alkoxycarbonyl-1-trifluoromethylpropyl group, or through an ether bond or ester bond. These optically active groups may be substituted, and the length of the spacer may vary within the range of 2 to 30 methylene chain lengths.

Further, the ferroelectric liquid crystal polymer has a number average molecular weight of i,
ooo to 200,000 can be used.

Examples of ferroelectric low-molecular liquid crystal compounds include Schiff base-based ferroelectric low-molecular liquid crystal compounds, azo and azoxy-based ferroelectric low-molecular liquid crystal compounds, biphenyl and aromatex ester-based ferroelectric low-molecular liquid crystal compounds, halogens, Examples include 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 heterocycle.

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

5-10, 7-10 Examples of the azo and azoxy ferroelectric low molecular weight liquid crystal compounds include the following (5) and (6).

For example, the following compound (9
) to (11).

As the biphenyl and hyaromatic ester-based ferroelectric low-molecular liquid crystal compound, for example, the following compound (7
) and (8).

(l 1) n=6, 8.10 H3 n= 8 n= 4, 6 Examples of the ferroelectric low-molecular liquid crystal compound having a heterocycle include the following compounds (12) and (Step 3). It will be done.

n=6, 8.11 The above compound is a typical compound of a 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 in any way. isn't it.

A liquid crystal optical element made of ferroelectric liquid crystal sandwiched between two flexible substrates on which t8ii to be aligned according to the present invention is disposed [hereinafter, this may be referred to as a liquid crystal optical element (A)] . ] There is no particular restriction on the manufacturing method, and any known manufacturing method can be used. FIG. 1 is a sectional view of a liquid crystal optical element subjected to the 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.

Note that in this liquid crystal optical element (A), the ferroelectric liquid crystal constituting it does not need to be subjected to alignment treatment.

As a method for manufacturing this liquid crystal optical element (A), for example, a method in which the ferroelectric liquid crystal is sandwiched between two flexible substrates on which electrodes are provided in advance can be used.

Various methods can be used for this,
Among these methods, the coating method allows alignment treatment to be performed at the same time as film formation, but the liquid crystal optical element (A) of the present invention does not require alignment and has the advantage of having a wide range of suitable operating conditions and film thickness. , is a preferred method in the present invention.

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

In the present invention, as a coating method other than the above-mentioned coating properties,
For example, ferroelectric liquid crystal diluted in an appropriate solvent,
A coating method using gravure coating, roll coating, etc. can also be suitably used.

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

In Fig. 2, 4 is a flexible substrate with electrodes, 1 is a ferroelectric liquid crystal material, 13 is a laminated substrate consisting of the flexible substrate 4 with electrodes coated with ferroelectric liquid crystal material 1, and 6 is a roll coater. -”N:
! : To! The roll, s represents a supply roll, and 9 represents a scraping doctor knife.

In addition, when finishing a ferroelectric liquid crystal material as a thin film, an insulating spacer such as silicon oxide or insulating plastic is placed between the substrates at the film forming or sandwiching stage to prevent conduction between the substrates. Alternatively, a thin insulating film such as a polymer may be provided in advance between the substrate and the ferroelectric liquid crystal material layer by a coating method or the like.

There is no particular limit to the thickness of this insulating film, but usually
It is appropriate that the thickness be 1 μm or less, preferably 0.5 μm or less.

As a method for sandwiching the ferroelectric liquid crystal material coated in this manner by overlapping the opposing substrates, for example, a normal laminating method using a pressure roller or the like can be suitably used.

Note that when performing this sandwiching, the two substrates may be fixed using, for example, an epoxy adhesive or the like, if desired.

In the present invention, a continuous and high-speed mass-production method for liquid crystal optical elements (A) is adopted, for example, while moving one flexible plastic substrate with electrodes at high speed, ferroelectric liquid crystal is deposited on it as described above. Continuously form a film using a coating method, etc.
Particularly preferably used is a method in which the opposing electrically scratched plastic substrates are then stacked one on top of the other and continuously laminated.

In the alignment method of the present invention, for example, the liquid crystal optical element (A) produced as described above is subjected to alignment treatment to align the ferroelectric liquid crystal in the liquid crystal optical element (A).

This orientation process 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 whose upper and lower rollers have different temperatures. FIG. 3 is an explanatory diagram showing how a liquid crystal optical element is passed between a pair of rollers with a temperature difference between the upper and lower rollers, and the liquid crystal optical element is passed between three sets of rollers. In this case, it is preferable that the temperatures of the rollers in adjacent sets of rollers are opposite.

In addition, the temperature of the high temperature side roller is TH1 and the low temperature side is T.
L is the temperature of the entire system in which alignment treatment is performed.

Then, it is preferable to set To to about (T, +'rL)/2. This To is a mixed phase of Tokiyoshi phase and smectic A phase, a mixed phase of Tokiyoshi phase and chiral smectic C phase, smectic A phase, chiral smectic phase. The temperature is preferably within a temperature range in which a liquid crystal phase such as a C phase or a chiral nematic phase is taken. Since the linear expansion coefficient of PET film is usually 15 x 10-''/''C, the temperature difference between T and -TL is preferably 3°C or more, more preferably 10'C or more. . However, do not make too much of a difference in temperature.
It is not preferable to set H to a temperature that far exceeds the isobathic phase of the liquid crystal (about 20° C. or more) or to set TL to the temperature at which the liquid crystal crystallizes.

Furthermore, if the linear expansion coefficients of the substrates are different, alignment can be performed using TeeT.

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 orientation is performed using the difference in thermal expansion. As shown in the figure, there is a difference in expansion between the high-temperature roll side and the low-temperature roller side, so a relative shearing stress is applied to the liquid crystal material near the roller, and it is thought that this shearing force causes the liquid crystal molecules to become oriented.

Although there is no particular restriction on the number of sets of freely rotating rollers to be used, it is preferable to use two or more sets as shown in FIG.

As described above, the orientation method of the present invention can achieve a high degree of orientation with extremely simple operations without necessarily requiring complicated pretreatment of the substrate, etc., and has excellent high-speed response and contrast ratio. This is a method of aligning liquid crystal optical elements that is extremely advantageous in practice and has excellent advantages such as being able to efficiently obtain liquid crystal optical elements and easily realizing a high-speed continuous mass production process. It can be suitably used as an alignment method in the manufacturing process of a ferroelectric liquid crystal optical element with flexible substrates sandwiched therebetween.

〔Example〕

Hereinafter, the present invention will be explained in detail based on Examples, but the present invention is not limited thereto.

Example 1 A transparent polyethersulfone (PES) film with a thickness of about 100 μm was used as a flexible substrate, and a transparent conductive film with a thickness of about 70 μm was coated on one side of this film as an electrode.
A flexible substrate with electrodes was prepared by providing an ITO film of 100%, and a ferroelectric polymer liquid crystal consisting of a repeating unit represented by the following formula and having the following characteristics was applied to the electrode surface of this substrate. The mixture was heated to 100''C and coated in a uniform phase using a bar coater to a thickness of about 2.5 μm.

HMn=5000 [gniglass state, Sac'': chiral smectic C phase, SmA: smectic A phase, isotropic phase] Next, a PES film with a thickness of about 100 μm was used as a counter substrate, and this was coated with the above ferroelectric The liquid crystal optical element was laminated on the surface of the polymer liquid crystal coating film to obtain a liquid crystal optical element having a width of 10 cm and a length of 600 cm.

Note that in this state, the liquid crystal molecules are randomly oriented.

Next, the liquid crystal optical element (A) produced by the above method was passed through a heating device 10 as shown in FIG.
After heating to C, 3 navy blue rollers (11
to 16) were passed sequentially. The roller is 11.14
．． 15 was for high temperature (temperature TH), 12.13.16 was for low temperature (temperature TL), and the temperature of the entire system was T0. The diameter of the adjacent rollers was 50 an, and the distance between the rollers was 100 ffIIn. The results are shown in Table 1.

Table 1 T++, TL,,To: ”Cv
: cm/sec ■ represents the moving speed of the flexible substrate, and A represents the degree of orientation.

Note that the values of the degree of orientation A shown in Table 1 were determined according to the well-known general measuring method shown below.

That is, a liquid crystal optical element subjected to the orientation treatment described below is arranged in parallel between two polarizers whose polarization axes are orthogonal to each other to form a crystal cell, and white light from a halogen lamp is incident on the liquid crystal cell. While rotating the liquid crystal optical element around the light spot, the intensity change of the transmitted light was measured, and the ratio of the maximum intensity (1 max) to the minimum intensity (I min ) at that time was calculated as A = I max / r m i n was defined as the degree of orientation A.

It has been found that it is possible to orient the tube by passing the film sandwiching the unoriented liquid crystal through rollers with a temperature difference.

Example 2 With ITO film 125 μm thick (ITO thickness approx. 1000 μm)
Biaxially stretched PET (polyethylene terephthalate) was used as a flexible substrate with electrodes, and the following polyoxirane-based ferroelectric polymer liquid crystal was coated as shown in FIG.

A solution diluted to 0% by weight was applied to a thickness of about 15 .mu.m using a roll coater as shown in FIG. 2, and then the solvent was evaporated to form an unoriented liquid crystal film of 1.5 .mu.m thick.

Next, a 125 μm thick ITO film-attached counter substrate made of the same biaxially stretched PET as above was laminated on the above liquid crystal film, and then an alignment treatment was performed using the apparatus shown in Example 1. In addition, TH=90°C5T+, =60"c, To
= 75° (:, v = 3 cm/sec. The degree of orientation A is about 100, and in the width direction of the substrate 10 cm, it is 50 to 120
This value indicates good orientation. Furthermore, since the orientation treatment can be performed following the apparatus shown in FIG. 2, productivity is very high.

(Cry: crystalline state) In other words, using a liquid crystal in a solvent (dichloromethane), Example 3 Using the same substrate and equipment as in Example 2, a liquid crystal optical element was manufactured using a liquid crystal composition containing the following ferroelectric polymer liquid crystal. Created.

CHff Example 4 In the same manner as in Example 2, alignment was performed using the low-molecular liquid crystal DOBAMBC.

30.4 mol% H3 n 20 mol% Note that TM = 110°C, TL = 80″c, To = 9
The temperature was set at 5°C and V=3CI/sec. The degree of orientation A was about 110, and good orientation was obtained.

Note that T,=120"(:,TL=100°C,T.

= 110''C, V = 3 (?11/sec). The degree of orientation A was about 70, and orientation without any practical problems could be achieved.

As shown in the above examples, the method according to the present invention has been found to be an effective method for aligning ferroelectric polymer liquid crystal optical elements, ferroelectric low molecular liquid crystals, or mixed liquid crystals. Ta. It was also found that this method is more effective for liquid crystal compositions containing polymeric liquid crystals that are easily oriented by shear stress.

(Effects of the Invention) According to the present invention, a high degree of alignment can be achieved in a liquid crystal optical element by an extremely simple and easy operation without performing any complicated specific pretreatment on the substrate.

In addition, high-speed and continuous orientation is possible, and the film forming process
The efficiency of the continuous production process including the clamping process by lamination etc. can be significantly increased, and high-speed mass production can be easily realized.

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

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

1 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-step to a clamping step by a worker or the like. In the figure, 4 is a flexible substrate with electrodes, 5 is a laminated substrate consisting of the flexible substrate 4 with electrodes coated with a ferroelectric liquid crystal material, 6 is a roll coater 17 is an induction roll,
8 represents a supply roll, and 9 represents a doctor knife for scraping. FIG. 3, FIG. 4, and FIG. 5 are cross-sectional explanatory views showing a state in which the orientation treatment of the present invention is performed between rollers. In the figure, ti to 16 represent rollers, and 10 represents a heating device.

Claims (1)

[Claims] 1. The ferroelectric liquid crystal material of a liquid crystal optical element is made of a ferroelectric liquid crystal material sandwiched between two flexible substrates on which electrodes are disposed, by adjusting the difference in thermal expansion of the substrates. 1. A method for aligning a liquid crystal optical element, the method comprising: 2. The method for aligning a liquid crystal optical element according to claim 1, wherein the two flexible substrates have similar coefficients of linear expansion, and the liquid crystal optical element is aligned by passing between at least a pair of rollers having different temperatures.