JPH05281513A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device capable of being easily manufactured with excellent yields, providing adequate responsiveness and an excellent contrast display and at the same time adequately compensating the coloring of a display by making the thickness of the liquid crystal layer of a liquid crystal cell large and making the twist angle and the pre-tilt angle of a liquid crystal molecular small. CONSTITUTION:The thickness of the liquid layer of a liquid crystal display cell 10 is made to be 6 to 7mum, the twist angle of a liquid crystal molecular being made 200 to 220 deg., the prechilt angle of a liquid crystal molecular being made to be 3 to 4 deg. and the ratio of the retardation DELTAn1.d1 of a liquid crystal display cell 10 and the retardation DELTAn2.d2 of a color compensation liquid crystal cell 20 is made to be in the range of 0.80<=DELTAn2.d2/DELTAn1.d1<=0.90.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using an STN type liquid crystal cell.

[0002]

2. Description of the Related Art As a liquid crystal display device which displays an image using a liquid crystal cell, there is a liquid crystal cell which uses an STN type liquid crystal cell excellent in multiplex driveability.

In this liquid crystal display device, polarizing plates are respectively arranged on the light incident side and the light emitting side of an STN type liquid crystal cell, and the direction of the polarization axis (transmission axis or absorption axis) of one polarizing plate is set to the polarization direction. The direction of the polarization axis of the other polarizing plate is intersected with the orientation direction of the liquid crystal molecules on the surface of the liquid crystal cell substrate on the plate side, and the direction of the polarization axis of the other polarizing plate is also adjacent to this polarizing plate. The liquid crystal cell is crossed at an angle of 35 to 50 ° with respect to the liquid crystal cell, and a voltage is applied between the display electrodes on both substrate surfaces of the liquid crystal cell so that the liquid crystal molecules are vertically aligned due to the electric field. The optical change in the state where the molecules are twisted is used.

However, in the above-mentioned liquid crystal display device, linearly polarized light that has entered through the incident side polarization plate is changed to elliptically polarized light due to the birefringence of the liquid crystal of the liquid crystal cell, and the transmission side light is controlled by the emission side polarization plate. Since it is for displaying, the refractive index anisotropy for light of each wavelength in the liquid crystal layer of the liquid crystal cell is different, and therefore the transmittance of light in a specific wavelength range becomes large, which causes a problem that the display is colored. There is.

Therefore, in the liquid crystal display device using the STN type liquid crystal cell, the liquid crystal cell (hereinafter, referred to as a display liquid crystal cell) and a pair of polarizing plates arranged on the light incident side and the light emitting side of the liquid crystal cell. A color compensating element having a birefringence effect is arranged between either one of the polarizing plates to compensate for display coloring.

As the color compensation element, an STN type liquid crystal cell or a phase plate is used. A liquid crystal cell used for color compensation (hereinafter referred to as a compensating liquid crystal cell) does not have a display electrode, and has liquid crystal molecules twisted in opposite directions at almost the same twist angle as that of the display liquid crystal cell. It is said that.

A liquid crystal display device provided with the above-mentioned color compensation element is
The elliptically polarizing action in the liquid crystal layer of the display liquid crystal cell and the elliptically polarizing action in the color compensating element are canceled each other. Conventionally, the retardation (refractive index anisotropy of liquid crystal of the display liquid crystal cell is And the liquid crystal layer thickness) and the retardation of the color compensation element (the product of the refractive index anisotropy of the liquid crystal and the liquid crystal layer thickness in the compensating liquid crystal cell, and the refractive index anisotropy and the plate thickness of the phase plate). And the light is transmitted through the liquid crystal cell for display and the color compensation element in the initial state in which a voltage is not applied between the electrodes of the liquid crystal cell for display, and becomes almost linearly polarized light. By making the light incident on the plate, the leakage of light in a specific wavelength range is eliminated and the coloring of the display is eliminated.

By the way, in the conventional liquid crystal display device in which the retardation of the display liquid crystal cell and the retardation of the color compensation element are substantially equal to each other as described above, when the liquid crystal layer of the display liquid crystal cell is thick, a sufficient response is obtained. Is not obtained, and if the twist angle of the liquid crystal molecules is small, display with sufficient contrast cannot be obtained.

Therefore, in the above-mentioned conventional liquid crystal display device, the layer thickness of the liquid crystal layer of the liquid crystal cell for display is made smaller than 6 μm in order to increase the response speed, and the liquid crystal molecules are 240 ° or more in order to obtain a better contrast. In order to perform twist orientation with a large twist angle of, and to maintain the orientation of liquid crystal molecules even at a twist angle of 240 ° or more,
The pretilt angle of the liquid crystal molecules is increased to 5 ° or more.

[0010]

However, when the liquid crystal layer thickness of the liquid crystal cell is smaller than 6 μm as described above, a very slight assembly error of the liquid crystal cell greatly affects the liquid crystal layer thickness. The accuracy is severely restricted, and difficult alignment treatment is required to increase the pretilt angle of the liquid crystal molecules to 5 ° or more.

Therefore, the liquid crystal cell is difficult to manufacture, and the yield is low. Therefore, the conventional liquid crystal display device using the liquid crystal cell has a problem that the manufacturing cost is high. ..

An object of the present invention is to increase the layer thickness of the liquid crystal layer of a liquid crystal cell and to reduce the twist angle and pretilt angle of liquid crystal molecules so that the liquid crystal cell can be manufactured easily and with high yield. Another object of the present invention is to provide a liquid crystal display device that can obtain a display with sufficient responsiveness and good contrast and can also sufficiently compensate for coloring of the display.

[0013]

According to the present invention, a polarizing plate is arranged on each of the light incident side and the light emitting side of an STN type liquid crystal cell for display, and the liquid crystal cell is disposed between the liquid crystal cell and one of the polarizing plates. In the liquid crystal display device in which the color compensating element is arranged in the liquid crystal cell, the thickness of the liquid crystal layer of the liquid crystal cell is 6 to 7 μm, the twist angle of the liquid crystal molecules is 200 to 220 °, and the pretilt angle of the liquid crystal molecules is 3 to 4 °, and , The ratio of the retardation Δn ₁ · d _{1 of the} liquid crystal cell and the retardation Δn ₂ · d ₂ of the color compensation element is 0.80 ≦ Δn ₂ · d ₂ / Δn
It is characterized in that the range is ₁ · d ₁ ≦ 0.90.

[0014]

As described above, the thickness of the liquid crystal layer of the liquid crystal cell is 6 to 7 μm.
If m is made large, the degree to which the assembly error of the liquid crystal cell influences the liquid crystal layer thickness becomes small, so that some error is allowed in the assembly accuracy of the liquid crystal cell, and the twist angle of the liquid crystal molecules is 200 to 220 °. If it is made smaller, the pretilt angle of the liquid crystal molecules required to maintain the alignment of the liquid crystal molecules may be 3 to 4 °, and the alignment treatment is facilitated, so that the liquid crystal cell can be manufactured easily and with high yield. be able to.

Even when the layer thickness of the liquid crystal layer of the liquid crystal cell is increased to 6 to 7 μm and the twist angle of the liquid crystal molecules is reduced to 200 to 220 ° as described above, the liquid crystal cell and the color compensation element are separated from each other. Retardation ratio 0.90 or less (Δn ₂ ·
When d ₂ / Δn ₁ · d ₁ ≦ 0.90), a display with sufficient responsiveness and good contrast can be obtained, and the retardation ratio is 0.80 or more (0.80 ≦ Δn ₂ ·.
With d ₂ / Δn ₁ · d ₁ ), the coloring of the display can be sufficiently compensated.

[0016]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIG. The liquid crystal display device of this embodiment uses an STN type liquid crystal cell as a color compensating element for compensating for display coloring.

First, the structure of the liquid crystal display device will be described.
In this liquid crystal display device, polarizing plates 31 and 32 are respectively arranged on the light incident side and the light emitting side of a STN type liquid crystal display cell (hereinafter referred to as a display cell) 10, and at least one of the display cell 10 and the display cell 10 is arranged. An STN type color compensating liquid crystal cell (hereinafter referred to as a compensating cell) 20 is arranged between the polarizing plate (in this embodiment, the lower outgoing polarizing plate in the drawing) 32.

The incident side polarizing plate 31 is adhered to the light incident surface of the display cell 10, and the emitting side polarizing plate 32 is the compensation cell 20.
The display cell 10 and the compensating cell 20 are bonded to each other on the surfaces facing each other.

The display cell 10 has a frame-shaped sealing material 11
The liquid crystal 1 between the pair of transparent substrates 12 and 13 bonded via
4, the transparent display electrodes 15 and 16 are formed on the opposing surfaces of the substrates 12 and 13, and the alignment films 17 and 18 are formed on the electrode forming surfaces.
And the molecules of the liquid crystal 14 are formed on both substrates 12, 1
Twist orientation is performed between the three.

The gap between the substrates 12 and 13 of the display cell 10, that is, the layer thickness d _{1 of the} liquid crystal layer is 6 to 7 μm,
The liquid crystal molecules have a twist angle of 200 to 220 °, the substrate 12,
The pretilt angle of liquid crystal molecules with respect to the 13th plane is 3 to 4 °.

The display cell 10 is of a simple matrix type, and the display electrode 15 on the surface of one substrate 11 is used.
Is a scanning electrode, and the display electrode 16 on the other substrate 12 surface
Is a signal electrode orthogonal to the scanning electrode 15.
The display cell 10 shown in FIG. 1 displays a black-and-white image, but in a display cell displaying a full-color image, red, green, and blue are provided on one of the substrate surfaces in correspondence with the respective electrodes. Color filters are provided.

On the other hand, the compensating cell 20 has a liquid crystal 24 sealed between a pair of transparent substrates 22 and 23 adhered via a frame-shaped sealing material 21, and a display is provided on the opposing surface of both substrates 22 and 23. There are no electrodes for use, and only the alignment films 25 and 26 are formed.

The gap between the substrates 22 and 23 of the compensation cell 20, that is, the layer thickness d ₂ of the liquid crystal layer is the same as the layer thickness d ₁ of the liquid crystal layer of the display cell 10 (6 to 7 μm). Furthermore, the molecules of the liquid crystal 24 of this compensation cell 20 are
Between the liquid crystal molecules, the liquid crystal molecules have the same twist angle (200 to 220 °) as the liquid crystal molecule twist angle of the display cell 10 and are twisted in the opposite direction to the liquid crystal molecule twist direction of the display cell 10, and the pretilt angle of the liquid crystal molecules. Display cell 1
The angle is the same as 0 (3 to 4 °).

The alignment directions of the liquid crystal molecules (alignment treatment directions of the alignment films 18 and 25) on the surfaces of the substrates 13 and 22 on the opposite sides of the display cell 10 and the compensation cell 20 are substantially orthogonal to each other. Further, the polarization axis (transmission axis or absorption axis) of one of the incident side polarization plate 31 and the emission side polarization plate 32 is oriented in the liquid crystal molecule alignment direction on the liquid crystal cell substrate surface on the polarization side. On the other hand, they intersect at an angle of 35 to 50 °, and the polarization axis directions of the incident side polarization plate 31 and the emission side polarization plate 32 are substantially orthogonal to each other.

Then, the retardation Δn ₁ · d _{1 of the} display cell 10 (the product of the refractive index anisotropy Δn ₁ of the liquid crystal 14 and the liquid crystal layer thickness d ₁ ) and the retardation Δ of the compensation cell 20.
n ₂ · d ₂ is the ratio (Δn ₂ · d ₂ / Δn ₁ ·
d ₁ ) is set to be in the range of 0.80 ≦ Δn ₂ · d ₂ / Δn ₁ · d ₁ ≦ 0.90. In this embodiment, the liquid crystal layer thickness d ₁ of the display cell 10 and the liquid crystal layer thickness d ₁ of the compensation cell 20 are set.
_The retardation ratio is set as described above by making ₂ different.

[0026] Incidentally, the liquid crystal 24 of the compensation cell 20, using what value of the refractive index anisotropy [Delta] n ₂ is smaller than the refractive index anisotropy [Delta] n ₁ of the liquid crystal 14 of the display cell 10, display cells 10 and compensation cell The retardation ratio with 20 may be set in the above range.

According to the liquid crystal display device of this embodiment, since the liquid crystal molecule twist angle of the display cell 10 is as small as 200 to 220 °, the pretilt angle of the liquid crystal molecules is 3 to 4 °.
However, the orientation of the liquid crystal molecules can be sufficiently maintained.

That is, the following [Table 1] shows 4 of A to D.
Regarding the liquid crystal of the kind, when the liquid crystal molecules are twist-aligned at a twist angle of 220 ° and when the twist alignment is at a twist angle of 240 °, the pretilt angle is 4 ° and the pretilt angle is 8 °. The d / P margin at the time of performing is shown. The d / P margin indicates the range of the layer thickness d of the liquid crystal layer in which the liquid crystal molecules are twist-aligned at a predetermined twist angle. The larger the value of this d / P margin, the more stable the alignment of the liquid crystal molecules. Will get better.

[0029]

[Table 1]

As shown in [Table 1], the d / P margin shows a large difference depending on the twist angle and the pretilt angle of the liquid crystal molecules, and the difference due to the liquid crystal is small. Further, in any of the liquid crystals A to D, the d / P margin at the twist angle of 220 ° and the pretilt angle of 4 ° is the twist angle of 240 °.
And the d / P margin in the case of a pretilt angle of 8 ° are substantially equal to each other. Therefore, if the twist angle of the liquid crystal molecules is made small, the orientation of the liquid crystal molecules can be sufficiently maintained even if the pretilt angle is small.

As described above, if the liquid crystal layer thickness d ₁ of the display cell 10 is increased to 6 to 7 μm, the degree to which the assembly error of the display cell 10 influences the liquid crystal layer thickness is reduced, so that the display A certain degree of error is allowed in the assembling accuracy of the cell 10, and the twist angle of the liquid crystal molecules is set to 200.
If it is made as small as 220 °, the pretilt angle of the liquid crystal molecules required to maintain the orientation of the liquid crystal molecules may be 3 ° to 4 ° as described above, and therefore the alignment treatment is facilitated. Can be manufactured easily and with good yield.

This also applies to the compensating cell 20, and in the above embodiment, the thickness of the liquid crystal layer of the compensating cell 20 and the twist angle and pretilt angle of the liquid crystal molecules are the same as those of the display cell 10. The compensation cell 20 can be manufactured easily and with high yield.

In this embodiment, the retardation ratio between the display cell 10 and the compensation cell 20 is 0.90 or less (Δn
₂ · d ₂ / Δn ₁ · d ₁ ≦ 0.90),
As described above, the liquid crystal layer thickness of the display cell 10 is increased to 6 to 7 μm, and the twist angle of liquid crystal molecules is set to 200 to 220.
Even with a small value, the display with sufficient responsiveness and good contrast can be obtained.

[Table 2] below shows a comparison of the electro-optical characteristics of the conventional liquid crystal display device and the liquid crystal display device of the above-mentioned embodiment. The conventional liquid crystal display device in [Table 2] uses the liquid crystal of B shown in [Table 1], the liquid crystal layer thickness is 5 μm, the twist angle of liquid crystal molecules is 240 °, and the pretilt angle is 8 °. A liquid crystal cell is used as a display cell,
The liquid crystal display device of the embodiment has B and D shown in [Table 1] above.
A liquid crystal cell having a liquid crystal layer thickness of 6 μm, a liquid crystal molecule twist angle of 220 ° and a pretilt angle of 4 ° is used as a display cell.

[0035]

[Table 2]

As shown in [Table 2], the liquid crystal display device of the above-mentioned embodiment has the γ characteristic (when the light transmittance becomes 20%,
The ratio of the applied voltage when it becomes 0%) is slightly inferior to the conventional liquid crystal display device, but the response time (the sum of the rise time _Tr to the bright state and the fall time _Tf to the dark state) is It is as good as or better than the conventional liquid crystal display device, and thus has an apparently quick response.

The following [Table 3] shows the contrast value CR of the liquid crystal display device of the above embodiment in which the retardation ratio between the display cell 10 and the compensation cell 20 is 0.90 or less.
This is shown in comparison with the liquid crystal display device in which the retardation ratio is larger than 0.90. Here, the retardation ratio of the liquid crystal display device of the example is Δn ₂ · d ₂ / Δn ₁
・ D ₁ = 0.90, and the retardation ratio of the liquid crystal display device of the comparative example is Δn ₂ · d ₂ / Δn ₁ · d ₁ = 0.95. The contrast value CR in [Table 3]
Is the Y value at the time of OFF and ON (brightness that can be visually sensed) Y
_OFF and Y _ON were calculated and CR = Y _ON / Y _OFF .

[0038]

[Table 3]

As shown in [Table 3], the retardation ratio between the display cell 10 and the compensation cell 20 is Δn ₂ · d ₂ / Δn.
_The liquid crystal display device with ₁ · d ₁ = 0.90 has a much higher contrast than the liquid crystal display device of the comparative example with the retardation ratio Δn ₂ · d ₂ / Δn ₁ · d ₁ = 0.95. Indicates. The contrast value CR becomes higher as the retardation ratio is made smaller than 0.90.

If the retardation ratio is smaller than 0.80, the difference in retardation between the display cell 10 and the compensation cell 20 becomes too large, and the color compensation effect by the compensation cell 20 becomes small. , The retardation ratio is 0.80 or more (0.80 ≦ Δn ₂ · d ₂ /
Since Δn ₁ · d ₁ ), the coloring of the display can be sufficiently compensated.

(Second Embodiment) Although the STN type liquid crystal cell 20 is used as the color compensation element in the first embodiment, the color compensation element may be a phase plate.

FIG. 2 shows a second embodiment of the present invention, in which the liquid crystal display device of this embodiment has polarizing plates 31, respectively on the light incident side and the light emitting side of the STN type liquid crystal cell 10 for display.
32 is disposed, and two color compensation phase plates 40a and 40b are disposed between the liquid crystal cell 10 and the emission side polarizing plate 32 as color compensation elements for compensating for display coloring. Since the liquid crystal cell 10 is the same as the display cell of the first embodiment described above, the description thereof will be omitted by giving the same reference numerals to the drawings.

Also in this embodiment, the liquid crystal layer thickness of the liquid crystal cell 10 is 6 to 7 μm, and the twist angle of the liquid crystal molecules is 200.
~ 220 °, pretilt angle of liquid crystal molecules is 3 ~ 4 °,
In addition, the retardation Δn ₁ · d _{1 of} the liquid crystal cell 10 and the retardation of the color compensation element (two phase plates 40a, 40
The total retardation of b) Δn ₂ · d ₂ is 0.80 ≦ Δn ₂ · d ₂ / Δn ₁ · d ₁ ≦ 0.90
It is in the range of.

The total retardation Δn ₂ · d ₂ of the two phase plates 40a and 40b is equal to that of both phase plates 40a and 40b.
When the retardations Re of a and 40b are the same, Δn ₂
・ D ₂ = {(Re +40 nm) × 2} (40 nm
Is the experimental value).

Also in the liquid crystal display device of this embodiment, the liquid crystal layer thickness of the liquid crystal cell 10 is as large as 6 to 7 μm as in the case of the above-mentioned first embodiment, so that an assembly error of the liquid crystal cell 10 is not caused. The degree of influence on the thickness of the liquid crystal layer is reduced, and therefore, some error in the assembling accuracy of the liquid crystal cell 10 is allowed, and the twist angle of the liquid crystal molecules is set to 200 to 2.
Since the pretilt angle of the liquid crystal molecules required to maintain the orientation of the liquid crystal molecules is set to 3 ° to 4 ° by making it as small as 20 °, the alignment process is facilitated, so that the liquid crystal cell 10 can be easily and easily walked. It can be manufactured easily.

Further, the retardation Δn of the liquid crystal cell 10
The ratio of ₁ · d ₁ to the retardation Δn ₂ · d ₂ of the color compensation elements (phase plates 40a and 40b) is 0.80 ≦ Δn ₂
Since the range of d ₂ / Δn ₁ · d ₁ ≦ 0.90 is set, the thickness of the liquid crystal layer of the liquid crystal cell 10 is as large as 6 to 7 μm, and the twist angle of the liquid crystal molecules is as small as 200 to 220 °. However, a display with sufficient responsiveness and good contrast can be obtained, and coloring of the display can be sufficiently compensated. Although two phase plates 40a and 40b are used as color compensation elements in this embodiment, the number of phase plates may be arbitrary.

[0047]

According to the liquid crystal display device of the present invention, the thickness of the liquid crystal layer of the liquid crystal cell is 6 to 7 μm, the twist angle of the liquid crystal molecules is 200 to 220 °, and the pretilt angle of the liquid crystal molecules is 3 to 4.
The liquid crystal cell can be manufactured easily and with a high yield because of the above-mentioned value, and the retardation Δn _{1 of the} liquid crystal cell can be increased.
.D ₁ and the retardation of the color compensation element Δn ₂ .d ₂
And the ratio is 0.80 ≦ Δn ₂ · d ₂ / Δn ₁ · d ₁ ≦
Since the range is 0.90, it is possible to obtain a display with sufficient responsiveness and good contrast, and it is also possible to sufficiently compensate the coloring of the display.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display device showing a first embodiment of the present invention.

FIG. 2 is a sectional view of a liquid crystal display device showing a second embodiment of the present invention.

[Explanation of symbols]

10 ... Display cell (display liquid crystal cell), 20 ... Compensation cell (color compensation liquid crystal cell), 31, 32 ... Polarizing plate, 40a,
40b ... Phase plate for color compensation.

Claims (1)

[Claims] 1. A liquid crystal in which a polarizing plate is arranged on each of a light incident side and an emitting side of an STN type liquid crystal cell for display and a color compensation element is arranged between the liquid crystal cell and one of the polarizing plates. In the display device, the liquid crystal layer of the liquid crystal cell has a layer thickness of 6 to 7 μm, a liquid crystal molecule twist angle of 200 to 220 °, a liquid crystal molecule pretilt angle of 3 to 4 °, and a retardation Δn _{1 of the} liquid crystal cell. .D ₁ and the retardation Δn of the color compensation element
The ratio of ₂ · d ₂ is 0.80 ≦ Δn ₂ · d ₂ / Δn ₁ ·
A liquid crystal display device, wherein d ₁ ≦ 0.90.