JPH0416928A - Compensating plate for liquid crystal display element and production thereof - Google Patents

Abstract

PURPOSE:To obtain the compensating plate which has the film thickness uniform over a large area and for which a liquid crystalline high polymer subjected to orientation control at a high degree is utilized by constituting the compensat ing plate of a pair of substrates subjected to an orientation treatment and a liquid crystalline high polymer film which is clamped between the substrates and is dispersed with fine particles for gap control. CONSTITUTION:This compensating plate is constituted of a pair of the substrates 1, 11 which are subjected to such orientation treatment as to orient the liquid crystalline high polymer in one direction and the liquid crystalline high polymer film dispersed with the fine particles 6 for gap control. Namely, the oriented liquid crystalline high polymer layer 3 is formed between the light transparent substrates 1 and 11 consisting of glass, plastic, etc., and the fine particles 6 for controlling the thickness of the layer 3 are dispersed in the liquid crystalline high polymer layer 3. Retardation is uniform in this way and the twist angle is controlled at the high degree and, therefore, the display of the liquid crystal display element is extremely uniformized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compensation plate for a liquid crystal display element using a liquid crystalline polymer and a method for manufacturing the same.

[Prior art and problems to be solved by the invention] The alignment state of liquid crystals changes depending on external fields such as electric fields, magnetic fields, and shear forces, and by utilizing the accompanying changes in optical properties, various optoelectronic devices can be used. used in the field.

Among these, liquid crystal polymers have higher viscosity in the liquid crystal state than low-molecular liquid crystals, so after being aligned in the liquid crystal state, the alignment state of the liquid crystal is fixed by cooling slightly below the glass transition point. It has a feature not found in low-molecular liquid crystals: the ability to Utilizing this, attempts are being made to apply it to optical electronics fields such as thermal writing optical memory and optical filters. To achieve these goals, it is necessary to highly control the desired molecular orientation as well as accurately control the film thickness. A color compensation plate for a super twisted nematic (STN) type liquid crystal display element, which is a type of optical filter, is inserted between the liquid crystal cell and the polarizing plate of the STN type liquid crystal display element, and converts the light that has become elliptically polarized light by the liquid crystal cell into a straight line. It is necessary to function to return the polarized light, but such a function is necessary to align the liquid crystal polymer horizontally and in a certain direction with a high degree of order and uniformity, and to adjust the optical anisotropy of the compensator. It is necessary to strictly control the retardation Δn−d, which is the product of the film thickness d and the film thickness d. Also,
For use in such display devices, uniformity of retardation over a large area is also required.

In the case of low-molecular liquid crystals, alignment control methods have almost been established, but in the case of liquid crystalline polymers, they have not been fully established.

As an example of controlling the orientation of liquid crystalline polymers, methods of applying an external force such as shear stress, and methods of applying an external field such as a magnetic field or electric field are known, but these methods do not allow orientation control over a large area. It cannot be said that it is possible or sufficient in terms of uniformity. If the method of injecting low-molecular-weight liquid crystal into the gap between substrates that has been subjected to alignment treatment is applied directly to liquid crystalline polymers, the liquid crystalline polymer will flow along the injection flow due to the high viscosity of liquid crystalline polymers. If the molecules become oriented and the desired orientation cannot be obtained, or if the area becomes large, even injection becomes difficult. In addition, in the case of low-molecular liquid crystals, there is a method in which fine particles for gap control are dispersed on one substrate, and the gap between the substrates is controlled by overlapping the opposing substrates, thereby controlling the thickness of the liquid crystal layer uniformly. is widely used, but even when this method is applied to liquid crystalline polymers, in addition to the difficulty of injection, the alignment of the liquid crystalline polymer being injected is disturbed by the fine particles, resulting in alignment defects. There is also the issue of marking.

The present invention has been made in view of the problems of the prior art as described above, and its purpose is to provide a liquid crystal display element using a liquid crystalline polymer that has a uniform film thickness over a large area and whose alignment is highly controlled. An object of the present invention is to provide a compensator for use in a vehicle and a method for manufacturing the same.

[Means and effects for solving the problem] In order to achieve the above object, the present invention provides a pair of substrates that have been subjected to an alignment treatment that orients liquid crystalline polymers in one direction, and A compensating plate for a liquid crystal display element is provided, which is comprised of a liquid crystal polymer film in which fine particles for gap control are sandwiched between the liquid crystal polymer film and the liquid crystal polymer film in which fine particles for gap control are dispersed.

Further, according to the present invention, a liquid crystalline polymer film containing fine particles for gap control is formed on a first substrate that has been subjected to an alignment treatment that aligns liquid crystalline polymers in one direction. Provided is a method for manufacturing a liquid crystal display element compensator, which comprises orienting a polymer and then superimposing a second substrate that has been similarly oriented so that its oriented surface comes into close contact with the liquid crystal polymer. be done.

Next, the present invention will be explained in detail using the drawings.

FIG. 1 is a sectional view showing the structure of a compensator according to the present invention, in which an oriented liquid crystal polymer layer 3 is formed between transparent substrates 1.11 made of glass, plastic, etc. Fine particles 6 are included in the liquid crystal polymer layer 3 to control the thickness of the layer 3.
are distributed.

FIG. 2 schematically shows the manufacturing process of the compensator plate according to the present invention.
form. Orientation treatment methods include forming a polymer film of polyimide, polyetherimide, polyamideimide, polyesterimide, polyamide, polyester, polyvinyl alcohol, polyacrylonitrile, etc., followed by rubbing treatment, or using alkoxysilane, organic titanate, etc. Examples include a method of rubbing a coating film of an organometallic compound or a heat-treated film thereof, and an oblique vapor deposition method of silicon oxide. It is also possible to carry out the alignment treatment by directly rubbing the plastic substrate; in this case, the alignment treatment layer 2 becomes unnecessary.

Next, a liquid crystal polymer layer 3 is formed by applying a liquid crystal polymer to the alignment-treated surface. Fine particles 6 for gap control are dispersed in the liquid crystalline polymer. The fine particles 6 include polystyrene, polydivinylbenzene, and a copolymer of both;
Examples include spherical fine particles of a polymer compound such as benzoguanamine, spherical fine particles of silica, zirconium oxide, etc., and cut glass fibers. The particle size of the fine particles 6 varies depending on the desired film thickness, but is generally in the range of 2 to 10 tones.

The liquid crystalline polymer that can be used is a thermotropic liquid crystalline polymer, and its structure is not particularly limited. Chain type liquid crystal polymer knee e11-X”8A1-X2)-Xl, X2: -Cm-, -CONH-, -0CO-,
-# Isopolymer: A1: 4H2Th, -+c)12C82%, -(
CH, CH2 (h.

C) 13 M2 knee Ph-Ph-R3, -()Ph-Ph-R3,
-Ph-cOO-Ph-R', -0-Ph-CO[)
-Ph-R3゜↓ Represents an integer. ) Or a side chain type liquid crystal with the following structure having a liquid crystalline residue in the side chain using vinyl polymer, polysiloxane, etc. (However, R''
is an alkyl group, an alkoxy group, a halogen atom, a nitro group or a cyano group, and n represents an integer of 0 to 18. ) can be exemplified. Liquid crystalline polymers may be used alone or in combination. It is also possible to introduce an optically active group into the liquid crystalline polymer or add an optically active compound.

The coating method is to directly apply a liquid crystalline polymer mixed with fine particles at a temperature above the glass transition point, or to dissolve the liquid crystalline polymer in a solvent and apply or print a coating liquid in which fine particles are dispersed. A method can be used. The latter is particularly preferably used in terms of uniformity of film thickness, ease of control, and uniformity of dispersion. The solvent for the liquid crystalline polymer varies depending on the type of liquid crystalline polymer used, degree of polymerization, etc., but is usually selected from the following.

Chloroform, dichloroethane, tetrachloroethane,
Halogenated hydrocarbons such as trichlorethylene, tetrachlorethylene, and orthodichlorobenzene; phenolic solvents such as phenol, 0-chlorophenol, and cresol; aprotic polar solvents such as dimethylformamide, dimethylacetamide, and dimethylsulfoxide;
Ether solvents such as tetrahydrofuran and dioxane, and mixed solvents thereof.

The solution concentration varies depending on the coating method, the viscosity of the polymer, the desired film thickness, etc., but is usually used in the range of 2 to 50 wt%, preferably in the range of 5 to 30 wt%. The amount of fine particles added depends on the coating method and the amount of dispersion. A preferable amount of dispersion is about several to 200 particles per square image, and a preferable addition amount when a spin code method is used as the coating method is about 20 to 300 particles per square image. As a coating method, a spin code method, a roll coating method, a gravure coating method, a dipping method, a screen printing method, etc. can be adopted. After coating the liquid crystalline polymer, the solvent is removed by drying, and the liquid crystalline polymer is aligned by heat treatment at a temperature at which the liquid crystalline polymer exhibits liquid crystallinity.

In this way, in the present invention, only one side of the liquid crystalline polymer is brought into contact with the alignment layer, and the other side is brought into contact with the outside air.

However, if both sides of the film are brought into contact with the alignment layer, sufficient alignment will not occur. This is because liquid crystal polymers have a higher viscosity than low-molecular liquid crystals, so when they come into contact with the alignment layer, the fluidity at the interface of the alignment film is greatly reduced, making it difficult for molecules to rearrange. it is conceivable that. In the present invention, since there is one alignment film interface, rearrangement easily occurs and uniform alignment is likely to occur. Further, the alignment of the liquid crystalline polymer is performed in a state in which the fine particles are dispersed, and at this time, the liquid crystalline polymer hardly flows. Therefore, orientation defects caused by fine particles hardly occur.

The temperature when orienting the liquid crystalline polymer needs to be higher than the glass transition point of the liquid crystalline polymer and lower than the transition temperature of the liquid crystalline polymer to an isotropic liquid. The lower the viscosity of the polymer, the better, in order to aid the alignment due to the interfacial effect of the alignment film, and therefore the higher the temperature, but if the temperature is too high, it will increase the cost and deteriorate workability, which is undesirable. −
For boat fishing, a temperature range of 50°C to 300°C is preferable.

The liquid crystalline polymer film obtained as described above has excellent monodomain orientation, but since it is a coating method, thickness distribution is unavoidable, and the desired thickness is 0.5%. 5
It is difficult to obtain a surface accuracy of less than %. In the present invention, after the liquid crystalline polymer is once aligned on the substrate, the first
By overlapping the second substrate 11 that has been subjected to another orientation treatment as shown in the figure, it is possible to control the gap with high precision, which is approximately equal to the particle size of the gap agent. In addition,
At this time, it is necessary that the particle size of the fine particles 6 and the thickness of the coating film are approximately equal. If the particle size is large, air bubbles will be mixed in, and if the particle size is small, the effect of mixing fine particles will be lost.

The second substrate 11 is made of a light-transmitting material such as glass or plastic, and the surface in contact with the liquid crystal polymer is subjected to an alignment treatment to align the liquid crystal polymer almost horizontally and in one direction. has been done. The method described for the first substrate 1 can be used for the alignment treatment. The direction of the alignment treatment is set approximately equal to the desired alignment direction of the liquid crystalline polymer in contact with the second substrate surface, which is determined by the desired twist angle ω.

After the second substrate 11 is superimposed, the liquid crystal polymer molecules in contact with the second substrate 11 are heated again to a temperature at which the liquid crystal polymer takes a liquid crystal phase and held for a certain period of time. It can be aligned in the orientation treatment direction of the substrate 11.

That is, even if the torsion angle has an in-plane distribution on the first substrate 1, a uniform torsion angle can be obtained over the entire surface by regulating the orientation of the second substrate 11. It is particularly preferable that ω and the angle formed by the orientation treatment direction of both substrates 1 and 11 are approximately equal, or the difference between them is approximately an integral multiple of 180°. If the deviation from this condition becomes large, it becomes difficult to rearrange the liquid crystal molecules, and domain division is likely to occur. The permissible deviation angle is approximately 45° or less, preferably 30° or less, particularly preferably 20' or less.

In the present invention, the liquid crystal polymer is first aligned in a state in which only one side is easily aligned with the alignment film, and then the interface from both sides is subjected to the condition that the movement necessary for rearrangement of the liquid crystal polymer is small. Because of the regulation, it is easy to obtain a monodomain orientation with a highly precisely controlled twist angle.

The obtained orientation state is maintained by rapid cooling below the glass transition point and is therefore extremely stable.

In order to introduce a twisted structure into a liquid crystalline polymer in the present invention, it is sufficient to use a liquid crystalline polymer exhibiting a cholesteric liquid crystal phase. A liquid crystalline polymer exhibiting a cholesteric liquid crystal phase may be obtained by introducing an optically active group into a liquid crystalline polymer exhibiting a nematic phase as described above, or by adding an optically active substance to the liquid crystalline polymer exhibiting a nematic phase. In this case, the liquid crystalline polymer is aligned in the direction of the alignment treatment on the alignment film surface, and has a twist angle corresponding to the natural pitch in the thickness direction, that is, when the natural pitch is Po, the film thickness is d, and the twist angle is ω. ω: 360 x d/P
.

Forms a torsion angle of (°).

[Examples] Next, the present invention will be described in detail, but the present invention is not limited to the examples illustrated herein.

(Example) Polyimide varnish PIQ manufactured by Hitachi Chemical was coated on a glass substrate to a thickness of about 1,000 mm using a spin code method, and then baked at 270'C to form a polyimide film.

Next, the polyimide film was rubbed in one direction with a Tetron flocked cloth to perform a rubbing treatment.

A nematic liquid crystal polysiloxane liquid crystal polymer having a repeating unit of the following formula a and a polysiloxane liquid crystal polymer having an optically active group having a repeating unit of the following formula a were mixed in a mixed solvent of phenol/tetrachloroethane (weight ratio 50
: 50) to a weight of 25% and 2% by weight. The ratio of polymer a to polymer s was 3:l (weight ratio). Further, divinylbenzene spheres having a particle size of 4.5 μm were added to this solution at a rate of 0.2 μm per 1 μm of the solution, and ultrasonic dispersion was performed.

(ch: Cholesteryl) This solution was applied onto the above alignment film by a spin code method, and then vacuum dried at 70'C, followed by heat treatment at 170C for 30 minutes at which polymer a exhibits a nematic phase. In this state, the liquid crystalline polymer film was rapidly cooled to room temperature, and a liquid crystalline polymer film having a film thickness of 4.6R and a fixed orientation twisted by about 220° was obtained. The dispersion density of divinylbenzene spheres was approximately 10 per square meter.

Then, a second glass substrate that had been subjected to the same orientation treatment was
Layer the alignment films in vacuum so that the rubbing direction makes an angle of 220° and the surface of the alignment film is in contact with the liquid crystal polymer.
Heat treatment was performed at ℃ for 30 minutes. The compensator plate of the present invention was then rapidly cooled to room temperature. When the orientation structure of this compensator was observed, it was found to be a monodomain uniform orientation, the twist angle was 22°, and the helical axis was perpendicular to the substrate. Retardation Δn-d is 0.82/Ia
Met.

In the compensating plate of 150 mm x 150 nn, there was no distribution of torsion angle at all, and the distribution of film thickness was 0.2 pm or less, showing extremely excellent uniformity.

〔Effect of the invention〕

Since the compensation plate for liquid crystal display elements of the present invention has uniform retardation and highly controlled twist angle, it is possible to make the display of the liquid crystal display element extremely uniform. Also,
High reliability because the liquid crystal polymer film is sandwiched between the substrates.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a compensating plate for a liquid crystal display element according to the present invention, and FIG. 2 is a diagram showing the manufacturing process of the compensating plate of FIG. 1. 1. First substrate 3. Liquid crystalline polymer layer 6, fine particles 11 Second substrate patent applicant Rico Co., Ltd.

Claims (2)

[Claims] (1) It is composed of a pair of substrates that have been subjected to an alignment treatment that orients liquid crystal polymers in one direction, and a liquid crystal polymer film that is sandwiched between the substrates and has fine particles for gap control dispersed therein. Compensation plate for liquid crystal display elements. (2) A liquid crystal polymer film containing fine particles for gap control was formed on a first substrate that had been subjected to an alignment treatment to align the liquid crystal polymer in one direction, and the liquid crystal polymer was aligned. A method for manufacturing a compensating plate for a liquid crystal display element, which comprises: thereafter superimposing a second substrate that has been similarly oriented so that its oriented surface is in close contact with the liquid crystal polymer.