JPH0922002A - Plastic substrate for liquid crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate having good visual angle characteristics without coloring. SOLUTION: This plastic substrate used for a display part of a liquid crystal display panel consists of a plastic film produced by continuous film forming process. The retardation R of the plastic film measured for 590nm wavelength visible rays is defined as R=(nx-ny)×d and a parameter K representing the three-dimensional refractive index anisotropy is defined as K=((nx+ny)/2-nz)×d, wherein (nx) is the refractive index in the direction of the lagging phase axis on the plane, (ny) is the refractive index in the direction of the advancing phase axis on the plane, nz is the refractive index in the film thickness direction, and d is the film thickness, and R and K satisfy R<=20nm and |K|<=100nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal plastic substrate used for a display portion of a liquid crystal display device having excellent optical characteristics, and particularly for a liquid crystal showing excellent visibility and excellent viewing angle characteristics. It relates to a plastic substrate.

[0002]

2. Description of the Related Art In recent years, liquid crystal display elements have been highly demanded to be thinner, lighter, larger, arbitrarily shaped, and capable of displaying curved surfaces. Especially with the expansion of the use of portable devices such as pagers, mobile phones, electronic notebooks, pen input devices, etc., liquid crystal display panels using plastic substrates instead of conventional glass substrates have been studied, and some of them have been put to practical use. It has started to be transformed.

Such a plastic substrate satisfies the demands of weight reduction and thinning in comparison with glass substrates.
However, when compared with a glass substrate, the plastic film used for the plastic substrate has refractive index anisotropy, and when used as a substrate for a liquid crystal display panel that visualizes linearly polarized light with a polarizing plate, the visibility is There was a problem that the viewing angle characteristics were inferior to the glass substrate.

[0004]

Generally, a plastic substrate is inferior to a glass substrate in terms of optical isotropy.

That is, the glass substrate is completely optically isotropic, and the fact that it is optically isotropic means that nx, ny, and nz, which are the refractive indices in the three-dimensional direction, are nx = ny = nz. Means that the liquid crystal plays a role of turning on / off the linearly polarized light and the polarizing plate visualizes the linearly polarized light, which means that it has no optical adverse effect when used as a substrate of a liquid crystal display element. ing. This is because the glass substrate has an amorphous structure and no optical anisotropy occurs.

However, in the case of a plastic substrate, there are anisotropy due to the molecular structure, anisotropy due to the structure, anisotropy due to molecular orientation and the like. In particular, in the case of a plastic film that is continuously formed, there is anisotropy in optical properties, retardation occurs in the in-plane direction due to retardation in the in-plane direction, and the refractive index in the thickness direction and surface Generally, a difference in refractive index in the inward direction occurs.

When such a plastic film is used as a substrate of a transparent electrode of a liquid crystal display panel, there are problems that the liquid crystal display panel is colored unnecessarily and the viewing angle characteristics are significantly deteriorated.

An object of the present invention is to provide a plastic substrate for liquid crystal which is free from such coloring and has good viewing angle characteristics.

[0009]

The above object is achieved by the present invention described below. That is, the present invention provides a plastic substrate for liquid crystal used in a display portion of a liquid crystal display panel, which is a plastic film having a positive refractive index anisotropy formed by continuously forming the plastic substrate, Assuming that the refractive index in the slow axis direction is nx, the refractive index in the in-plane fast axis direction is ny, the refractive index in the film thickness direction is nz, and the film thickness is d, it is a measured value at a wavelength of 590 nm of visible light. Let a certain retardation value be R = (nx-ny) * d and K = be a parameter showing three-dimensional refractive index anisotropy.
When ((nx + ny) / 2−nz) × d, R ≦ 2
It is a plastic liquid crystal substrate for liquid crystals, characterized by comprising a plastic film having a thickness of 0 nm and | K | ≦ 100 nm.

The details of the present invention will be described below along with the progress of the invention.

As a transparent electrode for a liquid crystal display device, a transparent conductive plastic obtained by laminating various barrier layers and solvent resistant layers on a plastic film as described above and then laminating transparent conductive layers. The substrate is being used.

When a plastic film is used as a transparent electrode of a liquid crystal display device, the R value has a wavelength of 550n.
The value of m is 50 nm or less.
It is disclosed in Japanese Patent No. 5568.

The reason why the R value, which is the in-plane retardation value of the plastic film, needs to be smaller than a specific value can be explained for the following reason. The liquid crystal display element adopts a display method of visualizing linearly polarized light. If the plastic film of the substrate material used while the polarizing plates are crossed has an R value of, for example, 100 nm, the upper and lower substrates are When the plastic film is used in the same slow axis direction, the R value is added to be 200 nm, and even when the liquid crystal display panel is viewed from the front,
It will give unfavorable coloring. In order to cancel the R value, if the slow axes are made orthogonal to each other in the upper and lower substrates and they are aligned with the optical axes of the respective polarizing plates, the R value of the substrates can be virtually zero. In this case, it is possible to prevent undesired occurrence of coloring in the front direction of the liquid crystal display panel.

However, by combining such plastic substrates in the orthogonal direction and aligning them with the optical axis of the polarizing plate, the effective utilization rate of the plastic film used for the substrate is remarkably reduced, and further the manufacturing process of the liquid crystal display element is considerably complicated. , The production efficiency will decrease.

Therefore, the R value of the plastic film used as the substrate needs to be smaller than a certain value. Further, it is preferable that the variation of the slow axis of the plastic film is small when controlling the optical properties of the upper and lower substrates and when the optical axes of the respective substrates and the polarizing plate are aligned with each other. If the R value is 10 nm or less, T
In the case of N type display, the axial variation is not a serious problem, but ± 20 degrees or less is preferable when the R value is 20 nm or less, and the R value when STN uses birefringence as the display mode. Is ± 10 degrees or less, and preferably ± 7 degrees or less until is less than 5 nm.

However, the size of the liquid crystal display device has been increased, and it is necessary to visually recognize the display panel from a direction other than the front. Even when a plastic film having a small R value is used as a substrate, when the display panel is viewed obliquely, the contrast may be significantly reduced or unnecessary coloring may occur, resulting in a significant reduction in visibility.

As a result of extensive studies on the cause, it was found that not only the in-plane R value of the plastic film but also the three-dimensional refractive index and the distribution of nx, ny and nz influence the viewing angle characteristics. Further, the variation of the slow axis is not more than ± 10 degrees in order to satisfy the basic preconditions such as optical axis alignment with the polarizing plate as well as the viewing angle dependence of the spatial optical axes of the two polarizing plates. .

Furthermore, the three-dimensional refractive index nx, ny, nz
As for the influence of the distribution of on the viewing angle characteristics, the K value indicating the three-dimensional refractive index anisotropy defined in the present invention is K =
In the case of ((nx-ny) / 2-nz) * d, the absolute value | K | is a parameter that influences the viewing angle characteristics of a liquid crystal display device using a plastic film as a substrate. It was found that when the value is 100 nm or less, the change in visibility depending on the viewing angle is reduced to such an extent that there is no practical problem, and the present invention has been completed.

That is, according to the present invention, the in-plane retardation value of the substrate is R ≦ 20 nm, which is a value that does not cause coloration in the display of the liquid crystal display device, and exhibits three-dimensional refractive index anisotropy. This is a plastic film having a K value of | K | ≦ 100 nm. By using this plastic film as a substrate, it is possible to obtain a liquid crystal display panel which is not colored and whose visibility is hardly changed depending on the viewing angle.

If the retardation value in the plane is 30 nm or less, almost no coloring can be ignored, but if it is 20 nm or less, coloring can be almost completely prevented. Not only for TN applications but also for STN applications, the R value is more preferably 15 nm or less in order to completely prevent coloring due to the R value of the substrate. Further, in this case, by adding a retardation plate of a uniaxially stretched plastic film, which is used for color compensation of STN liquid crystal display of a glass substrate, coloration due to birefringence of STN display is compensated, and white / black display is performed. It is also possible to obtain a liquid crystal display.

The K value indicating the anisotropy of the three-dimensional refractive index varies depending on whether the liquid crystal display panel display system is a reflection type or a transmission type, but | K | Is preferable as a standard for ensuring.
Further, when a viewing angle characteristic equal to or higher than that of a glass substrate is required, | K | is preferably 60 nm or less.

Although the detailed effect of the K value on the viewing angle characteristics of the liquid crystal display device is unknown, a remarkable difference is observed when the panel is actually assembled. Moreover, not only the refractive index of the substrate but also the film thickness and refractive index of the transparent conductive film, the type of liquid crystal, the degree of orientation, the cell gap setting and accuracy, the characteristics of the polarizing plate, the characteristics of the reflector, etc. Since there are various parameters, and their respective characteristics affect the display quality of the liquid crystal display panel including the viewing angle characteristics, sufficient consideration must be given to the design and assembly.

Strictly speaking, the K value of the substrate of the liquid crystal display cell has a K value which can maximize the viewing angle depending on the optical parameters of the liquid crystal cell used. However, there are variations in the K value due to fluctuations in the measurement accuracy of the refractive index of the plastic film, fluctuations in optical characteristics, and minute variations in the film thickness. In the case of a film substrate compared to a glass substrate, the thickness of the substrate is about 1/5 to 1/10, so
The visibility due to parallax is significantly improved. Considering these things, and considering the matching between the optical characteristics of the polarizing plate to be attached to the outside of the substrate and the optical characteristics of the pressure-sensitive adhesive of the polarizing plate, the lower limit of | K | I won't. From these facts, a particularly preferable range of the value of | K | is 10 nm to 60 nm.

Here, the three necessary values for determining the K value and the R value
The method for measuring the dimensional refractive index will be described. Although the three-dimensional refractive index can be measured by an Abbe refractometer or the like, it is preferably determined by a birefringence measuring device described later from the viewpoint of measurement accuracy.

Assuming that the plastic film is a three-dimensional index ellipsoid, it can be calculated from the incident angle dependence of the R value. That is, the refractive indices nx, ny,
When nz is used, the following two relational expressions hold.

[0026]

[Equation 1]

Therefore, after determining the average refractive index n = (nx + ny + nz) / 3 of the plastic film, the R (θ) value which is the retardation at the incident angle θ is measured by changing the incident angle θ, and the formula (1 ) And (2), the refractive index nx,
Determine ny and nz. Note that Δn (θ) is the birefringence at the incident angle θ, and d is the film thickness. Also, it is possible to use literature values for n.

The R value and K value can be easily determined by using a commercially available birefringence measuring device.
For example, KOBRA-21ADH manufactured by Shin Oji Paper Co., Ltd.
M-1 manufactured by JASCO Corporation that can measure wavelength and wavelength dispersion characteristics
It can be measured by 50. Since the measurement of the three-dimensional refractive index can be determined by the attached software, the K value can be determined from the measured value and the film thickness. The K value may take both positive and negative values according to the definition formula. In the present invention, the magnitude of the absolute value is larger than the positive and negative signs.
Since the influence on the viewing angle characteristics is great, the absolute value | K | is defined. In addition, for the sake of convenience, the determination of the R value and the K value is made from the value measured at a wavelength of 590 nm as a representative value of the wavelength of visible light.

The same measuring device can also measure the variation of the slow axis, but as the measurement accuracy, M-150 using the polarization modulation method is more preferable than KOBRA-21ADH using the rotation analyzer method. High measurement accuracy is obtained in the region of low R value.

The thickness of the plastic film can be easily measured by a contact type film thickness meter using a dial gauge.

As for the thickness of the plastic film used in the present invention, when the same birefringence is exhibited, the smaller the thickness is, the smaller the R value and the | K | value are. It is preferable to obtain a display without floating feeling, but it is a balance of various processing steps for processing the plastic film on the liquid crystal substrate and the handling point in the panel manufacturing process for assembling the liquid crystal display element. Therefore, it is preferably in the range of 50 μm to 500 μm.

The glass substrate is usually 0.7 mm to 1.1 m
m thickness is used, in special cases about 0.4 m
m very thin substrate is used. When a plastic liquid crystal substrate is used, it is lightweight and does not break, and the thinner the substrate, the liquid crystal display panel with less floating feeling and parallax can be obtained. The upper limit is 500 μm, which is equivalent to that of the glass substrate, and 50 μm or more is preferable from the viewpoint of ease of handling. The thickness of the plastic film is preferably about 100 μm when the viewing angle characteristics are emphasized, and the film thickness is preferably 200 μm to 400 μm when the rigidity and handling characteristics of the substrate are emphasized.

The R value and the K value of the present invention include the thickness d of the plastic film in the defined formula,
The R value and the K value also change depending on the value of d. However, in order to achieve the object of the present invention, the above d is 50 μm to 500 μm.
In the range of μm, R value and K value are R ≦ 20 nm,
It is necessary that | K | ≦ 100 nm.

Most of the plastic films used in the present invention are transparent resins having a Tg (glass transition temperature) of 120 ° C. or more and can be continuously formed by a film forming method such as melt extrusion or solution film forming. Can be used. However, from the viewpoint of heat resistance, stability, mechanical strength and versatility, it is preferable that the polymer resin has at least one phenyl group in its main chain. Typical examples of these resins include polycarbonate resin, polyarylate resin, polycarbonate ester resin, polysulfone resin, and polyethersulfone resin. In order to improve the optical properties of these resins, especially in order to reduce the in-plane retardation value R, copolymerization and monomers
Substituents having various structures can be introduced into the side chain of the unit. In addition, by introducing a substituent having various structures into the side chain of the copolymer or monomer unit, | K |
The value can be reduced.

In any case, it is a plastic film containing a phenyl group in the main chain of a polymer resin, and the birefringence anisotropy is positive or negative. It is preferable to use a polymer resin having the following as a plastic film.

Further, as a method for forming a plastic film, there are a melt extrusion method and a solution film forming method, both of which can be used. However, it is easy to control the three-dimensional refractive index anisotropy, It is more preferable that the plastic film is formed by the solution film forming method in view of the small amount of visible foreign matter, the high uniformity of the film thickness, and the flatness of the film surface property.

The R value and K value can be controlled mainly by the structure of the monomer unit of the molecule constituting the plastic film and the film forming conditions. The R value and the K value can be reduced to some extent by making the molecular structure of the plastic film as random as possible or by increasing the symmetry, but in the end, the R film and K value can be reduced to a film during film formation. The reduction of the R value and the K value can be achieved by controlling the tension and heat history and controlling the solvent drying conditions and the tension in the case of solution film formation. In particular, in order to control the R value, which is the retardation value in the in-plane direction, to 20 nm or less and the K value to 100 nm or less, the control of the molecular orientation should be substantially uniform in the in-plane direction, and the polymer resin It is necessary to control the plane orientation of the phenyl group contained in the main chain, and it is necessary to precisely control the temperature and tension applied to the continuously flowing film. In order to obtain a plastic film having an R value and a K value within the target range of the present invention, a resin solution prepared by dissolving a polymer resin in a solvent was optically flatly polished. It is cast on a glass substrate and peeled off from the substrate when the residual solvent is about 10 wt%.
-50) to Tg ° C and pre-dried to obtain (Tg-10) to (Tg-10)
It can be obtained by performing main drying at g + 10) ° C. In this case, it is possible to suppress variations in the slow axis by applying a weak tension in one direction of the film.

As described above, the film forming method for reducing the R value can be achieved by forming the film in the in-plane direction of the plastic film as small as possible and under substantially equal tension in at least two orthogonal directions. At the same time, the method of reducing the K value can be achieved by incorporating a process of relaxing the plane orientation in the film forming process. Even in the case of continuous plastic film formation, by combining processes based on this principle, it is possible to form a plastic film in which the R value and the K value are controlled to be the same. , Control of solution concentration, solvent boiling point, solvent evaporation rate,
By controlling the tension and temperature applied to the film, the temperature and tension for orientation relaxation, and the cooling rate, it is possible to obtain a plastic film having an R value and a K value within the target range of the present invention.

Various constitutions have been disclosed as prior arts regarding constitution examples for forming such a plastic film as a substrate material into a transparent conductive plastic substrate used for a transparent electrode. In JP-A-5-309794, a transparent conductive layer / active energy ray curable resin cured layer /
The air-permeable resin layer / anchor coating layer / plastic film substrate layer / anchor coating layer / air-permeable resin layer / crosslinkable resin cured product structure is disclosed in Japanese Patent Publication No. 5-520.
No. 02 publication, transparent conductive layer / metal oxide layer / polyvinyl chloride
Lu-alcohol resin layer / urethane resin layer / plastic film substrate layer / (transparent conductive layer) construction is disclosed in JP-A-6-
Japanese Patent No. 251631 discloses a structure of transparent conductive thin film / inorganic barrier-thin film / transparent film substrate.

The plastic film can be used as a plastic liquid crystal substrate by performing the processing as shown in the above configuration example. Depending on the processing conditions during these processing, the R value and K of the plastic film of the substrate
It is necessary to select processing conditions and materials so that the polymer resin coating layer to be coated does not maintain the optical characteristics such as the R value and K value of the plastic film without impairing the value characteristics. Is.

When a transparent conductive plastic substrate is not obtained by continuous processing but is processed by a single-wafer processing method such as solution dipping, drying is performed in a tensionless environment and the plastic material of the substrate is used. By performing the orientation relaxation treatment near the glass transition temperature Tg of the film, the R value and the K value can be controlled in the processing step.

Examples of the present invention will be described below.

[0043]

【Example】

[Example 1] Polycarbonate resin C manufactured by Teijin Chemicals Ltd.
-1400 (average molecular weight 37,000) was dissolved in methylene chloride at 18 wt%. Then, this solution was continuously cast on a stainless steel belt by a die-coating method, dried until the residual solvent was 15 wt%, and then peeled from the belt. After peeling, the residual solvent is 1.2 at 140 ° C.
After drying to wt%, relax treatment under low tension at 152 ℃, residual solvent 0.4% and thickness 100 ± 2μ
m polycarbonate film was obtained.

The retardation value of the obtained film was 12 nm when measured at a wavelength of 590 nm,
The variation in the direction of the slow axis was within ± 8 degrees. Also, |
The K | value was 55 nm as a result of calculation from the measured values of the three-dimensional refractive index at a wavelength of 590 nm.

Next, an anchor coat layer having a thickness of 2 .mu.m and a gas barrier layer having a thickness of 6 .mu.m are formed on one surface of the polycarbonate film, and a solvent resistant layer having a thickness of 8 is formed on both surfaces of the laminate.
A laminated film was prepared by sequentially forming the following in the following manner.

The anchor coat layer is a cured phenoxy resin, specifically, a phenoxy resin manufactured by Tohto Kasei Co., Ltd.
After mixing 20 parts of Phenototo YP-50 manufactured by Mitsui Chemical Co., Ltd. with 50 parts of methyl ethyl ketone and 30 parts of 2-ethoxyethyl acetate, 20 parts of A3 manufactured by Takeda Pharmaceutical Co., Ltd. as an isocyanate component was added to 100 parts of this mixture. The mixed solution was coated on the polycarbonate film using a Mayer bar, and heat-treated at 130 ° C. for 15 minutes to form a film.

The gas barrier layer is a polyvinyl alcohol.
As a resin, Kuraray Co., Ltd. PVA-HC was used,
PVA-HC contained 2.15 wt% of sodium acetate in ICP analysis, and was used after purification. The purification method was carried out by adding 50 parts of ultrapure water to 1 part of PVA-HC, stirring for 1 hour, discarding the washing water, and washing with ultrapure water 6 times, and then 100 ° C. 24
The resin was dried for an hour. Sodium acetate in the resin after purification
As a result of quantifying the amount of soda by ICP, it was found that the amount of soda acetate was reduced to 0.036 wt%.

15% of such polyvinyl alcohol resin is used.
Parts and 85 parts of ultrapure water are heated and mixed to completely dissolve the polyvinyl alcohol resin, and then the above anchor coat layer is coated with a Mayer bar at 110 ° C. for 20 minutes. It was formed by heat treatment.

The solvent resistant layer was a cresol-novolak type epoxy resin cured product. After mixing 100 parts of Cresol-novolak resin EOCN-104S manufactured by Nippon Kayaku Co., Ltd. and 150 parts of methyl ethyl ketone as a solvent, 74 parts of methylhexahydrophthalic anhydride and 1,8-diazabicyclo (5,4,0) were mixed. A mixture obtained by adding 5 parts of undecene and uniformly mixing was applied onto the gas barrier layer using a Mayer bar, and heat-treated at 100 ° C. for 5 minutes. Then, the same mixture was directly coated on the surface of the polycarbonate board film opposite to the coated surface with a Mayer bar, followed by heat treatment at 100 ° C. for 5 minutes and then at 135 ° C. for 30 minutes. Solvent resistant layers were formed on both sides of the polycarbonate film.

The gas barrier performance of the obtained laminated film was measured by the following measuring device manufactured by MOCON.
The oxygen transmission rate was measured by OXTRAN 2/20, the measurement result was 0.03 cc / square meter.day.atm, and the water vapor transmission rate was measured by PERMATRAN-W1A. The measurement result was 15 g / square meter. -Torr / day / atm. The visible light transmittance of this laminated film is 89.
%, And the haze value was 0.5%. The haze value is a value measured using COH-300A manufactured by Nippon Denshoku.

Polyvinyl alcohol of this laminated film
An ITO film, which is a transparent conductive film, was formed on the solvent-resistant layer on the surface on which the resin was formed as a gas barrier layer by a sputtering method as described below to prepare a transparent conductive laminated film.

As the sputtering target, a tin oxide-indium oxide target having a composition by weight ratio of 90/10 = indium / tin and a packing density of 95% was used. Ar / O ₂ = 98.5 / 1.5 was set after the laminated film was set in the sputtering device and exhausted to a pressure of 1.3 mPa.
A mixed gas having a volume ratio of 1 was continuously introduced, and sputtering was performed at a sputtering pressure of 0.27 Pa and a DC power density of 1.2 W / cm ² applied to the target.

The thickness of the laminated ITO film was 25 nm, and the surface resistance value was 250 Ω / □. The surface resistance value Ω / □ is a value measured by a square measurement in which electrodes are arranged on opposite sides of a unit square.

When the crystallinity of this ITO film was evaluated by a transmission electron microscope, it was found that most of the ITO films were amorphous ITO thin films with spherical crystals scattered in the amorphous structure.

The visible light transmittance of this transparent conductive laminated film was 85%, and the haze value was 0.6%. R
Both the value and the | K | value were almost the same as the initial characteristics of the original fabric within the measurement error range.

7 cm from the above transparent conductive laminated film
Two corner sample substrates were cut out, and a liquid crystal display element using this sample substrate as a transparent electrode was prepared as follows.

Liquid crystal alignment films "STX-24" manufactured by Hitachi Chemical Co., Ltd. on each substrate were diluted and dissolved in N-methylpyrrolidone and spin-coated, and then cured at 140 ° C. for 2 hours. Then, a uniform polyimide film having a film thickness of about 50 nm was formed, and then a rubbing roll of polyamide was set on a rubbing machine (RM-50 manufactured by Kawaguchiko Seimitsu Co., Ltd.) and rubbed 20 times each.

Further, after spraying "Micropar" manufactured by Sekisui Fine Chemical Co., Ltd., X8008 / EP001 manufactured by Cemedine Co., Ltd. was printed on one substrate by a screen printing method so as to surround the periphery. After that, the two substrates are attached so that the rubbing directions are different by 90 degrees, and 100
Both substrates were bonded while applying a uniform pressure at 2 ° C. for 2 hours.

The cell gap of the obtained empty cell for liquid crystal was 7.6 μm as measured by capacitance. A liquid crystal mixture obtained by adding "ZLI-2293" manufactured by Merck Ltd. as a liquid crystal material and "S-811" manufactured by Merck Ltd. as a minor additive was vacuumed through a part of the openings of this empty cell for liquid crystal. After injecting the liquid crystal, the liquid crystal was heated to the phase transition temperature of the liquid crystal material and then gradually cooled to room temperature to complete the alignment.

It was confirmed by polarization microscope observation that the obtained liquid crystal display element was a TN cell in which liquid crystal was oriented at a twist angle of 90 degrees. The color tone of the obtained liquid crystal cell is uniform,
Even when the display of the cell was viewed at a viewing angle of 60 degrees, coloring was not seen, indicating that the cell has high visibility.

[Comparative Example 1] Using the same polycarbonate resin as in Example 1 (C-1400 manufactured by Teijin Chemicals Ltd.), a polycarbonate film was prepared as follows.

20 wt% of the polycarbonate resin was dissolved in methylene chloride as a solvent. This solution was continuously cast on a polyester film having a thickness of 175 μm by a die coating method, dried until the residual solvent became 13 wt%, and then peeled from the polyester film. After peeling 1
While balancing the vertical and horizontal tensions at 20 ° C, dry until the residual solvent becomes 0.08wt%, thickness 100 ± 2μm
To obtain a polycarbonate film.

The retardation value of the obtained film was 16 nm when measured at a wavelength of 590 nm.
The variation in the direction of the slow axis was within ± 10 degrees. Also,
The | K | value was 180 nm as a result of calculation from the measured values of the three-dimensional refractive index at a wavelength of 590 nm.

Using this polycarbonate film, a transparent conductive laminated film having the same structure as that of Example 1 was manufactured except for this, and the transparent conductive laminated film was used as a transparent electrode in the same manner as in Example 1. A liquid crystal display device was prepared.

The color tone of the obtained liquid crystal display device was uniform, but strong reddish coloring appeared from around a viewing angle of 45 °, and the visibility was remarkably reduced.

Comparative Example 2 A polyarylate film having a thickness of 80 μm, manufactured by Kaneka Kagaku Co., Ltd. under the trade name of Elmec, had an R value of 19 nm and a K value of 230 nm. In the same manner as in Example 1 except that this polyarylate film was used, a transparent conductive laminated film having the same structure and a liquid crystal display device using this as a transparent electrode were prepared.

The color tone of the obtained liquid crystal display device was uniform, but strong reddish coloration appeared from around a viewing angle of 40 °,
The visibility was significantly reduced.

[0068]

As described above in detail, according to the present invention, the plastic substrate used for the transparent electrodes of the liquid crystal display device is a plastic film having specific R and K values, so that the thickness of the plastic substrate is thin. The present invention provides a liquid crystal display element that is free from the floating feeling of the display due to a problem and is comparable to a liquid crystal cell on a glass substrate in a wide viewing angle, and that has excellent visibility without coloring or the like. This greatly contributes to the improvement of the display performance of the liquid crystal display device.

Claims (5)

[Claims] 1. A plastic substrate for liquid crystal used in a display portion of a liquid crystal display device, wherein the plastic substrate is a continuous plastic film having a refractive index in the in-plane slow axis direction of nx, When the refractive index in the in-plane fast axis direction is ny, the refractive index in the film thickness direction is nz, and the film thickness is d, the retardation value, which is a measured value at a wavelength of visible light of 590 nm, is R = (nx -Ny) xd and K = a parameter showing three-dimensional refractive index anisotropy.
When ((nx + ny) / 2−nz) × d, R ≦ 2
A plastic liquid crystal substrate for liquid crystal, comprising a plastic film having a thickness of 0 nm and | K | ≦ 100 nm. 2. The plastic substrate for liquid crystal according to claim 1, wherein the plastic film has a variation of the slow axis in the plane of ± 10 degrees or less. 3. The plastic film is a monomer
The plastic substrate for liquid crystal according to claim 1 or 2, which is a plastic film having a positive refractive index anisotropy and having at least one phenyl group in the main chain of the molecular structure of the unit. 4. The plastic film, wherein the plastic film is continuously solution-cast.
3. The plastic substrate for liquid crystal according to any one of 3 above. 5. The plastic substrate for liquid crystal according to claim 3, wherein the plastic film is a polycarbonate film.