JP3274365B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display element suitable for use in a projection type liquid crystal display device. The liquid crystal display device is, for example, a device in which a twisted nematic liquid crystal panel is disposed between two polarizing elements whose polarization axes are orthogonal to each other.

[0002]

2. Description of the Related Art A high-definition television (hereinafter abbreviated as HDTV) as a next-generation display device is characterized by its excellent display quality. In recent years, in the technical field of liquid crystal display devices, small and high-definition projection-type liquid crystal display devices for HDTV display have been actively developed.

A liquid crystal display element used in such a projection type liquid crystal display device has a liquid crystal alignment layer formed thereon.
The liquid crystal is sealed between two glass substrates.
As a material of the liquid crystal alignment layer, an organic material such as polyimide or an inorganic material such as SiO is used. In the case where an organic material such as polyimide is used, the forming method can be divided into a spin coating method and an offset printing method using a printing plate.

The spin coating method is a method in which after a substrate is adsorbed on a rotating stage, polyimide diluted with a solvent is applied to the substrate while rotating the substrate at a predetermined number of revolutions. However, this method requires a large amount of polyimide material when forming a liquid crystal alignment layer on a large substrate,
It is rarely used at present. On the other hand, the offset printing method is a method in which a polyimide material is once transferred to a roller, spread to a uniform film thickness, and then re-transferred to a printing plate and printed on a substrate. In this method, only a very small amount of polyimide material is required per substrate, and it is possible to cope with an increase in the size of the substrate.

Japanese Patent Application Laid-Open No. 61-177440 discloses a technique for suppressing so-called display roughness caused by a liquid crystal alignment layer by reducing the thickness of the liquid crystal alignment layer. This technique is intended to suppress display unevenness due to a difference in threshold voltage caused by an increase in screen size by setting the thickness of a liquid crystal alignment layer made of a polyimide film to 20 to 100 °. This liquid crystal alignment layer is formed using a spin coating method.

[0006]

As described above, in the process of manufacturing a liquid crystal display element, a liquid crystal alignment layer is usually provided to uniformly align liquid crystal molecules. The liquid crystal alignment layer is formed by an offset printing method using polyimide as a material. Specifically, the surface of the printing plate is several tens of microns.
m-shaped concave portions are formed in a mesh shape, and the alignment material diluted with a solvent is once scooped into the concave portions and transferred onto the substrate. However, at this time, traces of the mesh and the like remain on the transferred alignment material. The alignment material is baked at a high temperature after the transfer, but surface irregularities such as traces of the mesh remain as uneven film thickness.

After the alignment layer is formed, the panel is manufactured through a bonding step, a liquid crystal injection / sealing step, and the like. However, if the liquid crystal panel is turned on with uneven thickness, the following problems occur. . That is, even when the same level of voltage is applied to a certain picture element and an adjacent picture element, the voltage level applied to the liquid crystal layer differs due to the difference in the thickness of the liquid crystal alignment layer. As a result, there is a problem that the transmittance is different between adjacent picture elements. In particular, in a projection type liquid crystal display device, since an image is enlarged and projected, a transmittance difference in a pixel unit of a level which is not problematic in a direct view type is observed as display roughness. This is fatal for an HDTV that requires display quality.

In order to solve the above problem, Japanese Patent Laid-Open No.
When the technique disclosed in Japanese Patent Application Laid-Open No. 177440 is used, the following problem newly occurs. That is, since this technique uses the spin coating method, the productivity is low as described above. In addition, the thickness of the liquid crystal alignment layer is 20
Since it is very thin, ie, about 100 °, the liquid crystal alignment layer is easily peeled off when the alignment treatment is performed by rubbing, and as a result, the problem that the alignment of the liquid crystal is disturbed is caused.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to suppress a variation in transmittance caused by a variation in film thickness caused when a liquid crystal alignment layer is formed. It is an object of the present invention to provide a liquid crystal display element that realizes a uniform display image without display roughness even in a device or the like.

[0010]

In order to solve the above-mentioned problems, a liquid crystal display element according to the present invention is provided with a liquid crystal alignment layer on each of two opposing substrates. In addition, in a liquid crystal display element in which liquid crystal is sealed between these substrates and a liquid crystal layer is provided, the relative permittivity of the liquid crystal is set to ε.
_LC , the thickness of the liquid crystal layer is d _LC [m], the relative permittivity of the liquid crystal alignment layer is ε _AL , and the thickness of the liquid crystal alignment layer is d
_AL [m], ε _LC , d _LC , ε _AL and d _AL
It is characterized by satisfying a relationship of _LC d _AL / ε _AL d _LC ≦ 0.020.

According to the above configuration, the relative permittivity of the liquid crystal, the thickness of the liquid crystal layer, the relative permittivity of the liquid crystal alignment layer, and the thickness of the liquid crystal alignment layer are optimized. ΔT / Tmax, which is an index of variation, can be suppressed to within 6%. Therefore, there are almost no areas having different transmittances (brightness) in the display, and even when displaying a halftone using a general projection optical system, a uniform projected image without display roughness can be realized. .

According to a second aspect of the present invention, there is provided a liquid crystal display device according to the first aspect, wherein the thickness d _AL [m] of the liquid crystal alignment layer is 1.00. ×
It is characterized by being in the range of 10 ⁻⁸ ≦ d _AL ≦ 4.00 × 10 ⁻⁸ .

According to the above configuration, as described later, the variation in the thickness of the liquid crystal alignment layer is suppressed from increasing, and
It is possible to prevent the liquid crystal alignment layer from peeling off during the alignment treatment by rubbing and to suppress ΔT / Tmax within 6% under a wide range of manufacturing conditions.

Further, a liquid crystal display device according to a third aspect of the present invention provides a liquid crystal display device according to the first or second aspect.
Wherein the liquid crystal alignment layer is formed by an offset printing method using a printing plate.

According to the above configuration, since the liquid crystal alignment layer is formed by the offset printing method, a small amount of alignment material per substrate is required as compared with the spin coating method or the like.
It can respond to the enlargement of the substrate. Further, even when the liquid crystal alignment layer is formed by this method, the variation in transmittance can be reduced as described above, so that the display quality does not deteriorate.

Hereinafter, the operation of the liquid crystal display device of the present invention will be described in detail with reference to FIGS.

In general, the relationship between the difference in brightness that can be identified by a human and the absolute value of brightness is described in, for example, Reference 1 (JPConnor a).
nd REGanoung, J. Opt. Soc. Am., Vol. 25 P. 287 1935)
Is shown in Here, the difference in brightness that can be identified is
It can be represented by ΔT / Tmax described later. According to Document 1, for example, when the brightness is 0.1 ft-lamberts, the difference in brightness can be identified by about 3%. Therefore, if the variation in the transmittance due to the variation in the thickness of the liquid crystal alignment layer is suppressed to the discrimination limit or less, a uniform projected image without so-called display roughness can be obtained.

FIG. 3 shows a general example of a voltage-transmittance (VT) characteristic of a twisted nematic liquid crystal device.
This figure is a graph when the thickness of the liquid crystal layer is 4.0 μm. The display variation is caused by a transmittance near a halftone where the transmittance difference per unit voltage is large, for example, a transmittance 5 indicated by oblique lines in the drawing.
Appears remarkably in the range of ３０30%. For example, using a liquid crystal display device having VT characteristics as shown in FIG.
When the light is projected so as to have a transmittance of 5 to 30% using a general optical system, the screen luminance is about 1 ft-lamberts (applied voltage Vapp = 2.5 V). When the brightness is 1 ft-lamberts, the discrimination limit of the brightness is approximately ΔT / Tmax = 1%. However, when an HDTV image is projected experimentally, ΔT / T
Up to max = 6% is an acceptable level.

Therefore, when displaying a halftone image using a general projection optical system, a uniform projected image without display roughness can be realized by suppressing ΔT / Tmax to within 6%.

In a liquid crystal display device, a liquid crystal layer generally has a sandwich structure sandwiched between liquid crystal alignment layers, and is expressed by series connection of capacitors. The capacitance of the liquid crystal layer is applied to C _LC , the capacitance of one liquid crystal alignment layer of the substrate is C _AL1 , the capacitance of the other liquid crystal alignment layer of the substrate is C _AL2 , and applied between pixel electrodes (between electrodes provided on each substrate). Assuming that the applied voltage is Vapp [V], the voltage V _LC [V] applied to the liquid crystal layer is

[0021]

(Equation 1)

## EQU2 ## Usually, the liquid crystal alignment layers provided on each substrate are printed under the same conditions.

Therefore, C _AL1 = C _AL2 can be _satisfied , the relative permittivity of the liquid crystal is ε _LC , and the thickness of the liquid crystal layer is d.
_{Assuming that LC} [m], the relative permittivity of the liquid crystal alignment layer is ε _AL , and the thickness of the liquid crystal alignment layer is d _AL [m], the equation (1) becomes

[0024]

(Equation 2)

In this equation (2), C = ε ₀ ε _r (S / d) (where ε ₀ : vacuum permittivity, ε _r : relative permittivity, S: picture element area, d: layer thickness )

[0026]

(Equation 3)

Can be expressed as follows. That is, the voltage V _LC applied to the liquid crystal layer can be represented by a function of ε _LC , d _AL , ε _AL , and d _LC . V _LC can be calculated from equation (3), and the transmittance can be read from the VT characteristic.

Here, the parameter ΔT / Tmax for discussing the difference in brightness will be described with reference to FIG. Due to the film thickness variation occurring during the formation of the liquid crystal alignment layer, the thickest portion is dmax and the thinnest portion is dmin. The largest difference in the transmittance is due to the first substrates formed with dmax and dmax in both substrates on which the liquid crystal alignment layer is formed.
Between the area and a second area formed by dmin and dmin. Assuming that the transmittance when the incident light is transmitted through the first area is Tmax and the transmittance when the incident light is transmitted through the second area is Tmin, the transmittance difference ΔT caused by the thickness variation of the liquid crystal alignment layer is: ΔT = Tmax−Tmin.
Since the sensitivity of the human eye changes depending on the brightness, it is normalized by Tmax.

From FIG. 3 and equation (3), for example, a transmittance of 5
% (Vapp = 2.5V), a condition for ΔT / Tmax = 6% is derived. First, when ΔT / Tmax = 6%,
If the transmittance Tmax of the portion constituted by dmax is 5%, the transmittance Tmin calculated from dmin is 4.70%.
(Because ΔT / Tmax = (5.00−4.70) / 5
= 0.06 = 6%).

Next, ε when ΔT / Tmax = 6% is satisfied
_{Find LC} and _dAL . As a condition, the dielectric constant ε of the liquid crystal alignment layer
The _AL as a general value 3.4, similarly, 4.5 [mu] m thickness d _LC of the liquid crystal layer, ± 10% thickness variation of the orientation layer by offset printing, is applied between the pixel electrodes The voltage Vapp is 2.5V. The thickness of the alignment layer is 100-1000Å
ΔT that occurs with a film thickness variation of ± 10% in the range of
Ε _LC and d _AL when / Tmax becomes ΔT / Tmax = 6%
Is shown in Table 1 below and FIG.

[0031]

[Table 1]

From Table 1, it can be seen that when ΔT / Tmax = 6%, ε _LC d _AL / ε _AL d _LC = 0.020. That is, ΔT / Tma that can suppress display roughness
To make x ≦ 6%, ε _LC d _AL / ε _AL d _LC ≦ 0.0
It can be seen that ε _LC and d _AL should be designed to be 20. In the graph of FIG. 5, the setting may be made so as to be within the hatched portion.

Further, when the transmittance is 30%, ΔT / Tmax
= Request epsilon _LC and d _AL when the 6%. The conditions are the same as when the transmittance is 5%. However, the voltage Vapp applied between the pixel electrodes is 2.0 V. The thickness of the alignment layer is 100
Ε when ΔT / Tmax generated at ± 10% of film thickness becomes ΔT / Tmax = 6% in the range of up to 1000 °
Table 2 shows the relationship between _LC and _dAL .

[0034]

[Table 2]

ΔT / Tmax = 6% at a transmittance of 30%
It can be seen that ε _LC d _AL / ε _AL d _LC = 0.031 when That is, in order to satisfy ΔT / Tmax ≦ 6%, ε _LC and d _AL may be designed so that ε _LC d _AL / ε _AL d _LC ≦ 0.031. Where ε _LC d _AL / ε
Since ΔT becomes smaller the smaller the _AL d _LC, also in the transmittance of 30%, it can be effectively suppressed roughness displayed by the _{ε LC d AL / ε AL d} LC ≦ 0.020. Therefore, the transmittance 5 to make the display roughness more conspicuous
By setting ε _LC d _AL / ε _AL d _LC ≦ 0.020 at 30%, ΔT can be reduced and display roughness can be suppressed. However, in actual design, ε _LC ,
Of the d _AL , ε _AL and d _LC , ε _LC and ε _AL depend on the material, so the range of choice is limited. D _LC is Δ
Since there are restrictions on panel transmittance and color balance depending on nd _LC / λ (Δn: birefringence of liquid crystal, λ: wavelength of incident light), it cannot be largely changed. On the other hand, the thickness of the liquid crystal alignment layer can be easily changed because it is proportional to the solid content concentration of the liquid crystal alignment material diluted with the solvent. Therefore, in the design, d
Changing the _AL is most effective. FIG. 6 shows ΔT / Tmax at ± 10% and ± 15% of film thickness variation.
4 is a graph showing the dependence of the thickness of the liquid crystal alignment layer on the thickness of the liquid crystal alignment layer. Since ΔT / Tmax decreases as the liquid crystal alignment layer becomes thinner, it is most effective in the present invention to reduce the thickness of the liquid crystal alignment layer in order to realize ε _LC d _AL / ε _AL d _LC ≦ 0.020. It can be said that.

FIG. 7 is a graph showing the film thickness dependence of the film thickness variation when printing the liquid crystal alignment layer. The film thickness variation includes the printing pressure of the printing plate, the stage speed, the environmental temperature and humidity, the viscosity of the alignment material, and the like. Is controlled by However, the thickness of the liquid crystal alignment layer is
If the angle is less than 100 °, print sagging will occur due to low viscosity of the alignment material and the like, and the thickness variation will increase, and ΔT / T
max is also undesirably large. Even if the film can be thinned, there arises a problem that the alignment layer is peeled off when the alignment treatment is performed by rubbing, and the alignment of the liquid crystal runs off. In addition, there is a problem that ε _LC for satisfying ε _LC d _AL / ε _AL d _LC ≦ 0.020 exceeds 20 and is not realistic. Therefore, it is desirable that d _AL is 100 ° or more.

Also, the manufacturing conditions of the liquid crystal display element require a margin since the conditions may deviate from the optimum conditions. For example, when the printing condition of the liquid crystal alignment layer deviates from the optimum condition and increases from ± 10% to ± 15% of the film thickness variation, ΔT / Tmax ≦ 6% is satisfied as shown in FIG. At 15%, the film thickness is 400 mm or less. Therefore, it can be said that there is a margin as a manufacturing condition when the thickness of the liquid crystal alignment layer is 400 mm or less.

Therefore, the thickness of the liquid crystal alignment layer in the present invention is
Preferably it is between 100 and 400 mm.

It is known that the thickness d _LC of the liquid crystal layer is generally proportional to the response speed. A display element having a large number of scanning lines, such as an HDTV, is required to have a high response speed because the scanning time per line is short. For a general liquid crystal material, the thickness d _LC of the liquid crystal layer is desirably d _LC ≦ 4.5 μm. In general, the relative dielectric constant ε _AL of polyimide as a liquid crystal alignment material is 2.0 ≦ ε _AL ≦ 4.0. Therefore, the thickness of the liquid crystal layer in the present invention is d
_{Assuming that LC} [m], d _LC is preferably in the range of d _LC ≦ 4.5 × 10 ⁻⁶ , and when the relative permittivity of the liquid crystal alignment layer is ε _AL , ε _AL is 2. Preferably, it is in the range of 0 ≦ ε _AL ≦ 4.0.

Incidentally, in the offset printing method, which is a method of forming a liquid crystal alignment layer, the film thickness varies as described above. The thickness variation can be suppressed to about ± 10% by optimizing the printing conditions.

As described above, in the liquid crystal display device in which the liquid crystal alignment layer is provided on each of the facing surfaces of the two substrates arranged to face each other, and the liquid crystal is sealed between these substrates and the liquid crystal layer is provided, The relative permittivity is ε _LC and the thickness of the liquid crystal layer is d.
_{Assuming that LC} [m], the relative permittivity of the liquid crystal alignment layer is ε _AL , and the thickness of the liquid crystal alignment layer is d _AL [m], ε _LC , d _LC , ε _AL and d _AL become ε _LC d _AL / By satisfying the relationship of ε _AL d _LC ≦ 0.020, even when magnified projection is performed, there is no difference in transmittance, especially in halftone, between pixel units or multiple pixel units. Images can be realized. Preferably, the thickness d _AL of the liquid crystal alignment layer
[M] is changed to 1.00 × 10 ⁻⁸ ≦ d _AL ≦ 4.00 × 10 ⁻⁸
And the thickness d _LC [m] of the liquid crystal layer and the relative dielectric constant ε _AL of the liquid crystal alignment layer are set to d _LC ≦ 4.5 × 10, respectively.
^-6 and 2.0 ≦ ε _AL ≦ 4.0.

The lower limit of ε _LC d _AL / ε _AL d _LC is desirably the following value. That is, assuming that the value of ε _LC d _AL / ε _AL d _LC is the minimum in the liquid crystal display device of the present invention, each value is “3” as the minimum value of the ε _LC.
, D _AL is "100Å" as a minimum value, and ε _AL is a maximum value as "
4 ", d _LC is the maximum value" considered when it is 4.5 [mu] m ", the value of this _{time, ε LC d AL / ε AL} d LC 0.002
Becomes Therefore, it is desirable that 0.002 ≦ ε _LC d _AL / ε _AL d _LC .

It is desirable that the lower limit of d _LC is as follows. That is, the liquid crystal panel generally has a transmittance,
From the relationship of the viewing angle and the like, assuming that the refractive index anisotropy of the liquid crystal is Δn, the thickness of the liquid crystal layer is d _LC , and the wavelength of the incident light is λ, 2d _LC Δn / λ = √3
Alternatively, a cell having d _LC Δn of √15 is optimal. Therefore, if 2d _LC Δn / λ = √3, then d _LC Δn
= 0.476. On the other hand, as for Δn, a liquid crystal having a characteristic of a high retention rate is currently used for the active matrix driving method, but the liquid crystal having a practical level is Δn.
n is about 0.14. The value of d _LC calculated from the above equation is 3.4 μm, and therefore, 3.4 μm ≦
d _LC is desirable.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram showing a schematic configuration of a liquid crystal display device 1 according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a projection type liquid crystal display device 2 using the liquid crystal display device 1. FIG. 3 is a diagram illustrating a configuration.

The liquid crystal display element 1 has a pair of substrates 3 and 4 facing each other, and a liquid crystal layer 5 is provided between the substrates 3 and 4.

On one substrate 3, an a-Si TFT element 3b, which is a thin film transistor having amorphous silicon, is provided on the surface of the glass substrate 3a as a base on the side of the liquid crystal layer 5, and an I-type TFT.
And a transparent electrode 3c made of TO (indium tin oxide). An alignment film (liquid crystal alignment layer) 3d is formed on the transparent electrode 3c. On the other substrate 4, a matrix-shaped light-shielding pattern 4b and a transparent electrode 4c made of ITO are provided on the surface of the glass substrate 4a serving as a base on the liquid crystal layer 5 side. Also, the transparent electrode 4c
An alignment film (liquid crystal alignment layer) 4d is formed thereon.
The displayable area of the a-Si TFT element 3b is 46.1.
mm × 27.2 mm.

In the liquid crystal display element 1, the transparent electrode 3c
A portion where the image and the transparent electrode 4c overlap is a picture element that contributes to display, and the picture elements are arranged in a matrix.
The alignment films 3d and 4d are subjected to an alignment process to regulate the alignment of the liquid crystal 5a included in the liquid crystal layer 5. Also, the substrate 3... Is formed so that the angle between the direction of the alignment treatment of the alignment film 3 d and the direction of the alignment treatment of the alignment film 4 d is 90 °.
4 are pasted together.

The liquid crystal layer 5 is filled with a liquid crystal 5a by a sealing material (not shown). The alignment of the liquid crystal 5a is regulated by the alignment films 3d and 4d, and the liquid crystal 5a is twisted at 90 °. When an electric field is applied, the orientation of the liquid crystal 5a changes.

A drive circuit (not shown) is connected to the transparent electrodes 3c and 4c, and the drive circuit supplies a display drive voltage to these electrodes. As a result, a voltage corresponding to the display content is applied to the liquid crystal 5a of each picture element,
The display is performed when the orientation of a changes and the light guided to the liquid crystal display element 1 is modulated and transmitted.

Further, polarizing plates 6 and 7 are provided on the sides of the substrates 3 and 4 opposite to the liquid crystal layer 5 side, respectively. The polarizing plates 6 and 7 are arranged so that their polarization axes are orthogonal to each other.

Next, the alignment film 3d of the liquid crystal display element 1
The manufacturing process of 4d will be described. The glass substrates 3a and 4a used were Corning's # 7059 glass (1.1 m thick).
m). The transparent electrodes 3 are provided on both substrates 3a and 4a, respectively.
After forming c.4c and the like, a liquid crystal alignment layer made of polyimide is laminated by an offset printing method.
By firing for 2 hours, the alignment films 3d and 4d are formed. As printing conditions, printing plate pressure, which is a parameter of the printing apparatus,
By optimizing the stage speed, the firing temperature, and the like, the film thickness variation was suppressed to about ± 10%.

After that, an alignment treatment by rubbing treatment is performed so as to obtain 90 ° TN (twisted nematic). The rubbing process is performed in the so-called + 45 ° to + 225 ° direction for the substrate 3 on which the TFT element 3b is provided, and the so-called + 315 ° to + 13 ° for the substrate 4.
Perform in 5 ° direction. After rubbing, the substrate 3
A thermosetting sealing material is printed on one of the substrates 4, and the in-cell spacers 8 are dispersed on the other substrate. Then, the two substrates 3 and 4 are bonded together and pressed at a high temperature of about 200 ° C.

After the press is completed, the panel is cut off, the liquid crystal 5a is vacuum-injected between the substrates 3 and 4, the injection port is sealed, and the panel fabrication is completed. The liquid crystal 5a was manufactured by Merck. The parameters of the liquid crystal 5a and the liquid crystal alignment layers 3d and 4d of the liquid crystal display element 1 were prepared as shown in Table 3 below.

[0055]

[Table 3]

Here, three samples were prepared as liquid crystal display elements, and the display quality of each sample was evaluated. The liquid crystal alignment material used for the three samples is a polyimide material manufactured by Nippon Synthetic Rubber Co., Ltd. In Samples 1 and 2 of the three samples, the liquid crystal alignment layer was formed thin and ε
_LC d _AL / ε _AL d _LC = 0.015. On the other hand, in the sample 3, the liquid crystal alignment layer is formed thick,
_LC d _AL / ε _AL d _LC = 0.031.

In evaluating the samples 1 to 3, each sample was applied to a projection type liquid crystal display device 2 as shown in FIG. 2 to evaluate the quality of the projected image. The projection type liquid crystal display device 2 includes three liquid crystal display elements (liquid crystal panels) 9a to 9c corresponding to red light, green light, and blue light, and a sample manufactured for each of the liquid crystal display elements 9a to 9c is applied. .

The projection type liquid crystal display device 2 comprises a light source 10, dichroic mirrors 11 a to 11 f and a projection lens 12.
And the light emitted from the light source 10 is reflected by the dichroic mirror 1 before entering the liquid crystal panels 9a to 9c.
The light is separated into red light, green light and blue light by 1a to 11c. The red light, the green light, and the blue light are incident on the liquid crystal display elements 9a to 9c that generate corresponding images, and are modulated. The modulated red, green and blue lights are synthesized again by the dichroic mirrors 11d to 11f,
The image is enlarged and projected on a screen 13 via a projection lens 12. In the projection type liquid crystal display device 2, H
A full-color moving image for DTV can be obtained. Table 4 shows the results of evaluation of the respective projected images when the samples manufactured for the liquid crystal display elements 9a to 9c were applied.

[0059]

[Table 4]

As described above, when the samples 1 and 2 were applied, the projection type liquid crystal display device 2 was able to obtain a uniform and good full-color moving image without display roughness.
On the other hand, when Sample 3 not satisfying ε _LC d _AL / ε _AL d _LC ≦ 0.020 was applied, areas having partially different brightness were present, resulting in an uneven projection image.
As a result, when a liquid crystal panel satisfying ε _LC d _AL / ε _AL d _LC ≦ 0.020 is applied, it is confirmed that a uniform and full-color moving image without so-called display roughness can be obtained without impairing the essence of HDTV. Was done.

[0061]

According to the first aspect of the present invention, there is provided a liquid crystal display device comprising:
As described above, the relative permittivity of the liquid crystal is ε _LC , the thickness of the liquid crystal layer is d _LC [m], the relative permittivity of the liquid crystal alignment layer is ε _AL , and the thickness of the liquid crystal alignment layer is d _{Assuming that AL} [m], ε _LC , d _LC , ε _AL and d _AL are given by ε _LC d _AL / ε _AL d
_The configuration satisfies the relationship of _LC ≦ 0.020.

As a result, it is possible to suppress the variation in transmittance caused by the variation in film thickness that occurs when the liquid crystal alignment layer is formed.

Therefore, even in the projection type liquid crystal display device, there is an effect that a uniform projection image without display roughness can be realized.

As described above, in the liquid crystal display element according to the second aspect of the present invention, the thickness d _AL [m] of the liquid crystal alignment layer is 1.00 × 10 ⁻⁸ ≦ d _AL ≤ 4.0
The configuration is in the range of 0 × 10 ⁻⁸ .

As a result, it is possible to prevent the thickness variation of the liquid crystal alignment layer from becoming large, to prevent the liquid crystal alignment layer from peeling off during the alignment treatment by rubbing, and to obtain ΔT / T
Limiting max within 6% can be realized under a wide range of manufacturing conditions.

A liquid crystal display device according to a third aspect of the present invention has a structure in which the liquid crystal alignment layer is formed by an offset printing method using a printing plate in the structure of the first or second aspect. .

Thus, as compared with the spin coating method or the like,
Only a small amount of alignment material per substrate is required, and it is possible to cope with enlargement of the substrate. Also, in this case,
Since the variation in transmittance can be reduced, the display quality can be favorably maintained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a configuration diagram schematically showing a projection type liquid crystal display device to which the liquid crystal display element is applied.

FIG. 3 is a graph showing an example of a voltage transmittance (VT) characteristic of a twisted nematic mode liquid crystal display element.

FIG. 4 is an explanatory diagram showing a relationship between a film thickness variation generated when forming a liquid crystal alignment layer and ΔT / Tmax.

FIG. 5 is a graph showing the relationship between the thickness of the liquid crystal alignment layer required to satisfy ΔT / Tmax ≦ 6% and the relative permittivity of the liquid crystal.

FIG. 6 is a graph showing the relationship between ΔT / Tmax and the thickness of the liquid crystal alignment layer at film thickness variations of ± 10% and ± 15%.

FIG. 7 is a graph showing a relationship between a thickness variation of a liquid crystal alignment layer and a thickness variation generated when a liquid crystal alignment layer is formed by an offset printing method.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal display element 2 projection type liquid crystal display device 3.4 substrate 3a / 4a glass substrate 3ba a-Si TFT element 4b light shielding pattern 3c / 4c transparent electrode 3d / 4d alignment film (liquid crystal alignment layer) 5 liquid crystal layer 5a liquid crystal 6.7 Polarizer

Claims (3)

(57) [Claims] 1. A liquid crystal display device comprising: a liquid crystal alignment layer provided on each of opposing surfaces of two substrates arranged opposite to each other; and a liquid crystal layer filled with liquid crystal between the substrates. Ratio is ε _LC and the thickness of the liquid crystal layer is d
_LC [m], the relative permittivity of the liquid crystal alignment layer is ε _AL , and the thickness of the liquid crystal alignment layer is d _AL [m], ε _LC ,
A liquid crystal display device, wherein d _LC , ε _AL, and d _AL satisfy a relationship of ε _LC d _AL / ε _AL d _LC ≦ 0.020. 2. The liquid crystal alignment layer according to claim 1, wherein the thickness d _AL [m] is in the range of 1.00 × 10 ⁻⁸ ≦ d _AL ≦ 4.00 × 10 ^−8. Liquid crystal display element. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal alignment layer is formed by an offset printing method using a printing plate.