JPH0412322A - Optical phase plate, manufacturing method thereof, and liquid crystal display element using the optical phase plate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical phase plate, and more particularly to an optical phase plate using a liquid crystalline polymer suitable as a color compensation plate for an STN type liquid crystal display element, and its use. The present invention relates to a manufacturing method and a liquid crystal display device using the optical phase plate.

[Conventional technology]

The display modes of liquid crystal display elements that have been mainly used in the past are:
It is called a twisted nematic (TN) type, and has a structure in which liquid crystal molecules are twisted approximately 90 degrees between a pair of upper and lower substrates, and utilizes the rotation of the plane of polarization by the liquid crystal and the disappearance of this effect when voltage is applied. There is. This display method has the advantage that it has an excellent shutter effect because it is a black and white display, and can relatively easily display multiple colors by providing a color filter for each pixel. This has the disadvantage that high-time division driving is difficult, and in large-capacity displays there are problems such as a decrease in contrast and a narrow viewing angle.

Therefore, in order to improve the steepness of the voltage-transmittance characteristic, a method was proposed in which the twist angle of the liquid crystal molecules was increased and the polarization axis of the polarizing plate was shifted from the alignment direction of the liquid crystal, thereby utilizing the birefringence effect of the liquid crystal. (supertwisted
birefringence effect) or STN (supertwisted nematic)
It's called a mode. This method has excellent threshold characteristics, so there is little decrease in contrast even in time-division driving, and it has a wide viewing angle. However, it uses the birefringence effect, which results in colored display, and further Colorization was also difficult.

Recently, in order to reduce the coloring phenomenon in STN mode, two liquid crystal cells with liquid crystal layers with opposite twist directions are stacked, one for driving and the other as a compensator, and the birefringence A two-layer STN liquid crystal display element that compensates for coloration and provides black and white display has been developed. However, this two-layer system displays black and white when viewed from the front;
When viewed from an angle, there are problems with coloration, the use of two liquid crystal cells makes the device thick and heavy, and productivity is poor.

These problems can be improved by replacing the compensation cell with a birefringent polymer film (phase plate type monochrome display STN liquid crystal display element). However, this phase plate method has the problem that it is not possible to obtain sufficient contrast, and that the viewing angle is further narrowed.

In a two-layer system in which two liquid crystal cells are stacked, a method has also been proposed in which a twistedly oriented liquid crystal polymer is used as a compensation plate instead of a compensation cell. This method uses a coated and oriented liquid crystalline polymer as the main component of the compensator. By cooling the liquid crystalline polymer to below the glass transition point, the alignment state in the liquid crystal state can be fixed. If a liquid crystalline polymer having a glass transition point higher than room temperature is twisted and oriented in a liquid crystal state and then cooled, compensation performance equivalent to that of a liquid crystal cell for compensation can be achieved. By utilizing the self-retention property in the same phase, only one substrate is required to hold the liquid crystalline polymer.
Not only can the compensator be made thinner, but the contrast is also comparable to that of the two-layer system, which has excellent characteristics.

However, the liquid crystalline polymer compensator plate constructed in this manner had the following problems. Since a liquid crystalline polymer becomes fluid when heated above its glass transition point, the glass transition temperature needs to be sufficiently higher than the operating temperature of the device. When such materials are used, the temperature at which the liquid crystalline polymers are aligned will inevitably rise, leading to a decrease in productivity, and cases where plastic films with low heat resistance are used as phase plate substrates, or when polarizing light is used. This is inconvenient when forming a phase plate on a plate. In addition, this optical phase plate can be used in liquid crystal cells.
When it is formed as a part, for example, when it is provided on the inner surface of a substrate of a liquid crystal cell, it is necessary to form a transparent conductive film or an alignment film on the liquid crystal polymer. In these steps, the optical phase plate itself is required to have high heat resistance since it is generally heated to 100° C. or higher. Furthermore, when the alignment film is composed of an organic polymer film, resistance to the solvent of the alignment agent is also required. Conventional optical phase plates using liquid crystalline polymers were not sufficient in these respects.

[Purpose of the invention]

The present invention has been made in view of the problems of the prior art as described above, and its purpose is to provide an optical phase plate that can be formed at low temperatures and has excellent heat resistance and solvent resistance, and a method for manufacturing the same. It's about doing. A further object of the present invention is to provide a liquid crystal display element that uses the optical phase plate as a compensator, has excellent display quality, is thin, and is capable of black-and-white display.

[Means and effects for solving the problems] In order to achieve the above object, according to the present invention, a light-transmitting substrate is formed on a transparent substrate,
An optical compensator whose main component is a substantially horizontally oriented polymer film is provided, in which the polymer film is made of a liquid crystalline polymer having a crosslinked structure within its molecules.

According to the present invention, there is also a step of applying a liquid crystalline polymer having a crosslinkable residue onto a substrate subjected to an alignment treatment, and aligning the liquid crystalline polymer in the direction of the alignment treatment. A method for producing an optical phase plate is provided, which includes the step of forming a crosslinked structure by reacting crosslinkable residues of a liquid crystalline polymer.

Further, according to the present invention, there is provided a pair of substrates having electrodes, which are sandwiched between the substrates, have positive dielectric anisotropy, are approximately horizontal when no voltage is applied, and are twisted with the helical axis directed perpendicular to the substrates. Consisting of a liquid crystal cell consisting of a liquid crystal layer, a polarizing plate placed on the outside of the substrate, and an optical phase plate whose main component is a liquid crystalline polymer layer arranged approximately horizontally between the liquid crystal layer and the polarizing plate. Provided is a liquid crystal display element in which the liquid crystal polymer layer is made of a liquid crystal polymer having a crosslinked structure within its molecules.

The optical phase plate of the present invention will be explained below according to a fabrication example shown in FIG.

(a) First, an alignment film 2 is formed on a substrate 1 to align the liquid crystalline polymer horizontally with respect to the substrate in a specific direction. Specifically, the alignment film 2 may be a conventionally known obliquely vapor-deposited film, or a film formed by forming an inorganic or organic film and then rubbing it with cotton cloth or the like. More specifically, it is preferable to use a polymer coating made of polyamide, polyimide, etc., which has been subjected to a rubbing treatment, or one which has been obliquely vapor-deposited with Sin, MgO1MgF2, or the like. Although glass, plastic, or the like is used as the substrate 1, the substrate 1 may be a substrate constituting a liquid crystal cell or a polarizing plate. Further, it is also possible to use the substrate by directly rubbing the substrate without providing an alignment film.

(b) Applying a liquid crystalline polymer having crosslinkable residues to the alignment-treated surface. Although the liquid crystalline polymer can be applied directly in a molten state, solution coating is preferably used from the viewpoint of uniformity of the film thickness. A solution 3'' in which a liquid crystalline polymer is dissolved in an organic solvent is applied onto the alignment film 2.The solvent for the liquid crystalline polymer varies depending on the type of liquid crystalline polymer used therein and the degree of polymerization. Generally, halogenated hydrocarbons such as chloroform, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, orthodichlorobenzene, phenolic solvents such as phenol, 0-chlorophenol, and cresol, and aprotic solvents such as dimethylformamide, dimethylacetamide, and dimethylsulfoxide are used. Examples include polar solvents, 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. The film thickness required for a compensation plate for a liquid crystal display element is generally about 2 to 10 layers, so it is usually about 2 to 10 layers.
Used in a range of 50wt%, preferably 5 to 30wt
Used in a range of %. As the coating method, a spin code method, a roll coating method, a gravure coating method, a dipping method, a screen printing method, a flexo printing method, etc. can be adopted.

The liquid crystalline polymers used here include polyacrylic esters, polymethacrylic esters, polysiloxane derivatives, etc. shown below, in which side chains exhibiting liquid crystallinity are introduced, since crosslinking groups can be easily introduced. Side chain type liquid crystalline polymers are particularly advantageously used.

(However, R3 is an alkyl group, an alkoxy group, a halogen atom, a nitro group, or a cyano group, and n represents an integer of θ to 18.) Vinyl polymers, polysiloxanes, etc. having the following.

The crosslinkable group is preferably a photocrosslinkable group, such as a cinnamoyl group, a cinnamylidene acetyl group, a benzalacetophenone group, a styrylpyridine group, an α-phenylmalenimide group, a phenyl azide group, a sulfonic acid azide group, and a carbonyl azide group. Examples include furyl acroyl group, pyrone group, anthracene group, and stilbene group. In order to introduce these crosslinking groups into a liquid crystalline polymer, it is necessary to copolymerize a vinyl monomer having these crosslinking groups during the polymerization of the liquid crystalline polymer, or after synthesizing the liquid crystalline polymer.
A crosslinkable group is introduced by a polymer reaction such as a transesterification reaction.

If the introduction rate of crosslinking groups is too large, liquid crystal formation will be inhibited,
Conversely, if the amount is too low, sufficient crosslinking reaction will not occur,
No improvement in heat resistance or solvent resistance was observed. Therefore, it is preferable to introduce it in a range of 0.1 to 20% based on the liquid crystalline residue.

When introducing a twisted structure into a liquid crystalline polymer, it is necessary to introduce an optically active group into the structure of the liquid crystalline polymer or add a low molecular or high molecular compound having an optically active group to the liquid crystalline polymer. Bye.

(c) After applying the liquid crystalline polymer, drying and removing the solvent,
The liquid crystalline polymer is aligned by heat treatment for a predetermined period of time at a temperature at which the liquid crystalline polymer exhibits liquid crystallinity (3''). The temperature must be lower than the transition temperature of the liquid crystalline polymer to an isotropic liquid.The lower the viscosity of the polymer, the better, in the sense that it aids alignment due to the interfacial effect of the alignment film. The higher the value, the better, but if it is too high, it increases costs and worsens workability, which is not desirable.
Numerically, a range of 30°C to 200°C is preferable. 50℃～
A range of 200°C is particularly preferred. Furthermore, in relation to the phase of the liquid crystalline polymer, the liquid crystalline polymer must be in a nematic phase or a cholesteric phase at this processing temperature, and uniform alignment cannot be obtained in the smectic phase due to its high viscosity. Alternatively, after heating to a temperature at which it becomes an isotropic liquid, it can be oriented by cooling to a temperature at which it exhibits the above-mentioned liquid crystal phase. The heat treatment time varies depending on the composition and molecular weight of the polymer, but is generally preferably in the range of 10 seconds to 60 minutes, particularly preferably in the range of 30 seconds to 30 minutes. If the treatment time is too short, orientation will be insufficient, and if it is too long, productivity will decrease, which is not preferred.

(d) After the liquid crystal alignment is completed, the liquid crystal polymer film can be cooled to a temperature below the glass transition point to fix the alignment. The cooling rate is not particularly limited, and it is sufficient to simply move from a heated atmosphere to an atmosphere below the glass transition point. If it is lower than this, the fixed alignment structure may collapse, which is not preferable. The film thickness of the liquid crystalline polymer 3' is preferably 1100 pm or less, particularly preferably 50 pm or less. If it is 100 μm or more, it becomes difficult to obtain uniform orientation.

(e) Irradiate the liquid crystal polymer with ultraviolet rays to crosslink the liquid crystal polymer (3). In the liquid crystalline polymer having a cinnamate group as exemplified above, the following crosslinking reaction occurs, and the alignment structure is completely fixed.

Crosslinked Structure of Polymer 2 - Crosslinking of liquid crystalline polymer can be carried out after cooling the liquid crystalline polymer to below the glass transition point to fix the liquid crystal structure, as in this example, or It can also be crosslinked in the state. However, when the film is crosslinked in a liquid crystal state, the crosslinking reaction causes a volume change, which may cause wrinkles in the film or destroy the alignment itself, so the former is particularly preferred.

Since the optical phase plate thus obtained has a crosslinked structure, it has improved heat resistance and solvent resistance.

Next, a case will be described in which the optical phase plate described above is used as a compensation plate for an STN type liquid crystal display element.

FIG. 2 is a sectional view showing the structure of an STN type liquid crystal display element according to the present invention. The first light-transmitting substrate 11 and the second light-transmitting substrate 21 are disposed apart and facing each other, and the open substrate 11.2
A liquid crystal is sealed in the space formed by the liquid crystal layer 1 and the outer peripheral seal 14 to form a liquid crystal layer 15, thereby forming a liquid crystal cell. Transparent electrodes 12 and 22 for applying voltage to the liquid crystal layer 15 and alignment films 13 and 23 for aligning the liquid crystal in a certain direction are formed on the inner surfaces of the substrates 11 and 21.

An optical phase plate 30 made of a liquid crystalline polymer having a crosslinked structure, which is a feature of the present invention, is arranged between the transparent electrode 22 of the substrate 21 and the substrate 21 . 17.27 is a polarizing plate, 3
3 is an alignment film.

In the liquid crystal layer 15, the liquid crystal is a nematic or cholesteric liquid crystal having positive dielectric anisotropy, and the alignment film 13,
23, it is oriented substantially parallel to the substrate surface when no voltage is applied. It is preferable that the liquid crystal has a twisted orientation between the upper and lower substrates with the helical axis perpendicular to the substrate surface, and the twist angle is preferably 160" to 360°. If the twist angle is small, the voltage - The steepness of the transmittance characteristic decreases, and the time-division drive characteristic decreases.As shown in FIG. The retardation RL of the liquid crystal layer 15 can be easily controlled by controlling the alignment treatment direction (R2) of the alignment film 23, the pitch of the liquid crystal, and the thickness of the liquid crystal layer 15.The retardation RL of the liquid crystal layer 15 is determined by the refractive index anisotropy of the liquid crystal. It is defined as the product ΔnL - dL of ΔnL and the thickness dL of the liquid crystal layer 15.RL is 0 to obtain good contrast.
．． It is preferably in the range of 4 to 2.0 voices, and 0.5 to 2.0 voices.
A range of 1.5 voices is particularly preferred. An alignment film 33 is provided on the surface of the substrate 21 that comes into contact with the liquid crystalline polymer to align the liquid crystalline polymer parallel to the substrate and in a specific direction. The polymer is oriented in the direction (R3) of the alignment treatment of the alignment film 33. The liquid crystalline polymer is twisted at a twist angle determined by its pitch and film thickness, and is oriented in the direction D4 on the surface adjacent to the liquid crystal layer 15. It is necessary that D4 and R2 are substantially perpendicular to each other, and if this condition is not met, the compensation effect will be degraded, resulting in a decrease in contrast and coloration. In terms of specific angles, the intersection angle δ between the two is 60° to 12
It is necessary that the angle is in the range of 0°, and more preferably in the range of 70° to 110°. The retardation Rc of the liquid crystal polymer layer 30 is determined by the refractive index anisotropy Δn of the liquid crystal polymer.
It is defined by the product Δnc-dc of c and the thickness dc of the liquid crystalline polymer layer 30. Rc needs to be approximately equal to the retardation RL of the liquid crystal layer 15 in order to obtain good contrast. In such an arrangement, the light that passes through the polarizing plate 17 as linearly polarized light and becomes elliptically polarized light that varies depending on the wavelength by the liquid crystal layer 15 becomes linearly polarized light without wavelength dependence again by the liquid crystal polymer layer 30, and then passes through the polarizing plate 17. 27, and black and white display is performed. In general, the polarizing plate 17 is arranged such that its transmission axis P1 is shifted from the orientation treatment direction R1 of the substrate 11 by an angle α. The preferred range of α is 206 to 70″. The transmission axis P2 of the polarizing plate 27 is set at an angle β of 206 to 70° with respect to the alignment direction R3 of the liquid crystal polymer on the top surface of the liquid crystal polymer layer 30. Note that the above discussion was based on the transmission axis of the polarizing plate, but due to the characteristics of the polarizing plate, even if the transmission axis is replaced by the absorption axis, the effect will not change at all.

In the above configuration, after forming the liquid crystalline polymer layer, it is necessary to configure a transparent conductive film or alignment film made of indium oxide or the like on the liquid crystalline polymer layer. Since a liquid crystal polymer film in which the liquid crystal polymer is completely fixed is used, no deterioration in alignment of the liquid crystal polymer due to heat during formation, that is, deterioration in compensation performance, is observed.

In this configuration example, the increase in the thickness and weight of the element due to the provision of the compensation plate is negligible, and since the compensation plate has a twisted structure, ideal compensation performance is achieved, and high contrast black and white display is achieved. can be done.

The liquid crystalline polymer layer can be formed outside the substrate of the liquid crystal cell, or can be formed on the polarizing plate. It can also be formed on a completely different substrate and inserted between the polarizing plate and the liquid crystal cell. It is also possible to employ two or more liquid crystalline polymer layers, and the effect remains the same even if the vertical relationship in FIG. 1 is reversed. It is also possible to provide a reflective plate and use it as a reflective display element.

〔Example〕

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples illustrated here.

Example 1 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 dimethylformamide solution of a nematic acrylic liquid crystal polymer having a cinnamate group represented by the following formula (A) is applied onto the alignment film, dried, and then heated to 115° C. at which the liquid crystal polymer exhibits a nematic liquid crystal phase. oriented polymers. Then, when it was rapidly cooled to room temperature, a monodomain-aligned liquid crystalline polymer layer with a twist angle of 220° and Δnede=0.82 was obtained. This sample was irradiated with ultraviolet light using an ultra-high pressure mercury lamp to crosslink the liquid crystalline polymer. The sample after crosslinking also has a uniform orientation of monodomains, and 1
No structural change was observed even after heating at 40°C.

Even when an indium oxide film was formed by sputtering on the liquid crystalline polymer surface of the obtained sample, no similar change was observed. Indium oxide was patterned by the fetolitho method, and then polyimide-based alignment agent J manufactured by Japan Synthetic Rubber Co., Ltd.
IB was applied to a thickness of 1,000 mm, dried at 120° C., and then rubbed in a direction perpendicular to the liquid crystal alignment direction on the surface of the liquid crystalline polymer. Even in the alignment agent application process, the alignment of the liquid crystalline polymer did not change at all, confirming excellent solvent resistance.

Another substrate coated with alignment agent JIB and subjected to rubbing treatment and the substrate coated with the liquid crystalline polymer film are bonded together via a spacer so that the rubbing direction forms an angle of 220°, and Merck Co., Ltd. Manufactured nematic liquid crystal ZLI2
A liquid crystal cell was prepared by injecting a mixed liquid crystal of 293 and chiral nematic liquid crystal 5811. ΔnL-
The dL was 0.87 tones, and the twist direction was opposite to that of the liquid crystalline polymer.

This cell was sandwiched between two polarizing plates to produce a liquid crystal display element. α=β: 45°.

When this liquid crystal display element was driven by time division driving with a duty of 1/200, the result was as shown in FIG.

Excellent black and white display was achieved.

[Effects of the Invention] Since the optical phase plate of the present invention uses twisted oriented liquid crystalline polymers, when combined with an STN type liquid crystal display element, it exhibits excellent compensation performance and provides high-contrast achromatic display. can be made to do so. Furthermore, since the optical phase plate of the present invention has a crosslinked structure, it has excellent solvent resistance and heat resistance. Therefore, it is easy to form a transparent conductive film or an alignment film on the phase plate, the phase plate can be provided on the inner surface of the substrate of the liquid crystal cell, and the device can be made thin. In addition, although it ultimately has high heat resistance,
Since the phase plate can be formed at a low temperature, it can also be formed on a plastic film, and the compensator can be made thin.

The optical phase plate of the present invention is particularly suitably used as a color compensation plate for STN type liquid crystal display elements as described above, but it is also extremely useful as a numerical optical element.

[Brief explanation of drawings]

Figure 1 is a diagram showing the manufacturing process of the optical phase plate of the present invention, Figure 2 is a diagram showing the manufacturing process of the optical phase plate of the present invention.
3 is a cross-sectional view showing the structure of the STN liquid crystal display element according to the present invention, FIG. 3 is a diagram showing the angular relationship of each element in the liquid crystal display element of FIG. 2, and FIG. FIG. 3 is a diagram showing wavelength dependence of transmittance. 11.21... Substrate 12.22... Transparent electrode 13.23.33... Alignment film 14... Outer seal 15... Liquid crystal layer 17.27... Polarizing plate 30... High Molecular liquid crystal layer (compensator)

Claims (3)

[Claims] (1) In an optical compensator whose main component is a substantially horizontally oriented polymer film formed on a transparent substrate, the polymer film is composed of a liquid crystalline polymer having a crosslinked structure within its molecules. Features an optical phase plate. (2) A step of applying a liquid crystalline polymer having a crosslinkable residue on a substrate subjected to an alignment treatment, a step of orienting the liquid crystalline polymer in the direction of the alignment treatment, and a step of crosslinking the liquid crystalline polymer. 1. A method for producing an optical phase plate, comprising a step of reacting chemical residues to form a crosslinked structure. (3) A liquid crystal cell consisting of a pair of substrates having electrodes, and a liquid crystal layer sandwiched between the substrates, which has positive dielectric anisotropy and is twisted and oriented approximately horizontally when no voltage is applied, with the helical axis perpendicular to the substrates. In a liquid crystal display element consisting of a polarizing plate placed on the outside of a substrate, and an optical phase plate whose main component is a liquid crystalline polymer layer provided between the liquid crystal layer and the polarizing plate and aligned approximately horizontally, the liquid crystal 1. A liquid crystal display element, wherein the liquid crystal polymer layer is made of a liquid crystal polymer having a crosslinked structure within its molecules.