JP3019523B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in viewing angle characteristics of a twisted nematic liquid crystal display.

[0002]

2. Description of the Related Art A liquid crystal display device has a simple matrix type in which a plurality of stripe-shaped electrodes facing each other via a liquid crystal are arranged so as to intersect with each other, and a plurality of pixels are formed at a plurality of intersections. There has been proposed an active matrix type in which a plurality of pixel electrodes each connected to a driving thin film transistor are provided, and a plurality of pixels are formed at a portion where the pixel electrode and a counter electrode face each other. Among these liquid crystal display devices, a twisted nematic type (hereinafter, referred to as TN) liquid crystal display device having a thin film transistor (hereinafter, referred to as TFT) is used for a display such as a word processor or a personal computer. A TN type liquid crystal display device (hereinafter referred to as a TFT-LCD) provided with the TFT includes a TN liquid crystal cell provided with a driving TFT for each pixel electrode and a TN liquid crystal cell having a transmission axis of a substrate on the light incident side of the liquid crystal cell. A polarizer disposed on the light incident side of the liquid crystal cell so as to be parallel to the rubbing direction, and an analyzer disposed on the light exit side of the liquid crystal cell such that the transmission axis is substantially orthogonal to the transmission axis of the polarizer. It is composed of Since this conventional TFT-LCD can be driven statically, it has a high contrast and a relatively wide viewing angle.

FIG. 21 shows a viewing angle characteristic of such a conventional liquid crystal display device, FIG. 22 shows a voltage-luminance characteristic thereof, and FIG. 23 shows a change in display color. This FIG.
Indicates an iso-contrast curve, in which five concentric circles are inclined from the inside toward the outside at angles of 10 °, 20 °, 30 °, 40 °, and 50 ° with respect to the normal line of the liquid crystal display device. Indicates the direction. In addition, this isocontrast curve is based on the rubbing direction A of the substrate on the incident light side of the liquid crystal cell as a reference (0 °), and the clockwise direction (leftward in the figure) as viewed from the incident light side of the liquid crystal cell is positive. It represents the observed contrast. The dotted line indicates that the contrast is 10
0 indicates the contrast, the one-dot chain line indicates the contrast of 50, the solid line indicates the contrast of 10, and the two-dot chain line indicates that the contrast is less than 1, that is, the display brightness is reversed. In measuring the contrast, a C light source is used, and the value of the contrast is defined by the ratio of the Y value of the transmitted light.
The front contrast was set to about 100.

As shown by the isocontrast curve, in the conventional liquid crystal display device, the direction in which a high contrast is obtained (viewing angle direction) is 315 ° from the rubbing direction of the alignment film formed on the light incident side substrate. V. Therefore, in the TFT-LCD, the direction V is made to coincide with the vertical direction of the liquid crystal cell. This TFT-LCD has a relatively large area of contrast 50 or more surrounded by a dashed line,
Further, the region surrounded by the solid line and having a contrast of 10 or more is relatively wide, and has a better viewing angle characteristic than the conventional simple matrix type liquid crystal display device.

[0005]

However, in the above-mentioned conventional liquid crystal display device, as shown in FIG. 21, the display device has a relatively wide viewing angle in the left-right direction, but has a large viewing angle in the vertical direction. There was a disadvantage that it was narrow. Further, in the conventional liquid crystal display device, as shown in FIG. 21, a region having a contrast of less than 1 surrounded by a two-dot chain line exists in a relatively wide range in a direction in which the liquid crystal display device is observed from above. The region where the contrast is less than 1 is a region where the brightness of a displayed image is reversed (hereinafter, referred to as a reversed region). With this reversal area, it is 40 ° above the front of the liquid crystal display device.
When viewed from a direction inclined by about 50 °, the image looks like a negative image in which the density of the image is inverted, and the display quality of the liquid crystal display device is significantly reduced. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display device capable of improving a viewing angle.

[0006]

In order to achieve the above object, the present invention provides a twisted nematic liquid crystal cell in which the alignment of liquid crystal molecules is twisted approximately 90 ° counterclockwise in the light traveling direction. On one surface side and the other surface side, a pair of polarizing plates are provided with the polarizing axes substantially orthogonal to each other, and the polarizing axis of one of the pair of polarizing plates is one of the liquid crystal cells. In a liquid crystal display device arranged substantially in parallel with the orientation processing direction applied to the substrate on the surface side,
A first phase plate having a slow axis in a range of −15 ° to 15 ° with respect to the alignment processing direction between the pair of polarizing plates, and a slow axis of the first phase plate; And a second phase plate having a slow axis in a direction substantially perpendicular to the liquid crystal cell.
To the substrate adjacent to the first or second phase plate.
The orientation direction applied and the liquid crystal cell adjacent to the liquid crystal cell.
The liquid crystal cell is arranged so that the slow axis of the first or second phase plate is substantially orthogonal to the slow axis, the value of Δnd of the liquid crystal cell is in a range of 350 nm to 700 nm, and the value of Δnd of the first and second phase plates is value is equal to or and together equal Kushida in the range of 300nm to 600nm of

According to the present invention, between the pair of polarizing plates,
A first phase plate having a slow axis in a range of −15 ° to 15 ° with respect to the orientation processing direction, and a slow phase in a direction substantially orthogonal to the slow axis of the first phase plate; A second phase plate having an axis and the first or second phase of the liquid crystal cell.
The orientation treatment direction applied to the substrate on the side adjacent to the plate,
Slow phase of the first or second phase plate adjacent to the liquid crystal cell
When the value of Δnd of the liquid crystal cell is in the range of 350 nm to 700 nm, the value of Δnd of the first and second phase plates is 300 nm to 600 n.
Since the range of m, the phase difference of light first caused by the light of the liquid crystal cell is transmitted obliquely, is compensated by the second phase plate, in the horizontal direction and the vertical direction perpendicular thereto of the liquid crystal display device As the viewing angle increases, the inversion region appearing in the vertical direction becomes narrower, and the viewing angle characteristics are improved. In particular, the value of Δnd of the liquid crystal cell is 450 nm to 550.
nm, the value of Δnd of the phase plate is 300n
m to 400 nm, most preferably , the value of Δnd of the liquid crystal cell is 350 nm, and Δn of the phase plate is
The value of d is 400 nm. The first and second phase plates may be arranged on either the light incident side or the light emission side of the liquid crystal cell between a pair of polarizing plates, and may be arranged on both sides so as to sandwich the liquid crystal cell. You may. Particularly, when the two phase plates are arranged on either the light incident side or the light exit side of the liquid crystal cell, when the value of Δnd of the liquid crystal cell is 300 nm, the value of Δnd of the phase plate may be 300 nm to 400 nm. It is preferable that the value of Δnd of the liquid crystal cell is 51.
When it is 0 nm, the value of Δnd of the phase plate is preferably 350 nm. Furthermore, the value of Δnd of the liquid crystal cell is 375 nm, when the value of Δnd of the phase plate is 350 nm, when the value of the refractive index _{n 0} of ordinary light of the phase plate to 1.3, becomes wider high contrast region .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. In FIGS. 1 and 2, an upper substrate 1 and a lower substrate 2 made of transparent glass or the like are arranged to face each other with a predetermined interval. A transparent common electrode 3 is formed on a lower surface of the upper substrate 1, and a first alignment film 4 is formed on a surface of the common electrode 3 and a display region of the upper substrate 1. A plurality of transparent pixel electrodes 5 are arranged in a matrix on the upper surface of the lower substrate 2, and a thin film transistor (TFT) 6 formed on the lower substrate 2 is connected to each of the pixel electrodes 5. The TFT 6 has a source electrode connected to the pixel electrode 5, a gate electrode connected to a gate line formed on the lower substrate 2, and a drain electrode connected to a data line formed on the lower substrate 2. . These pixel electrodes 5, TFTs 6, gate lines and data lines are covered with a second alignment film 7, and the second alignment film 7 is formed at least in the display area of the lower substrate 2.

The second alignment film 7 of the lower substrate 2 and the first alignment film 7 of the upper substrate 1
As shown in FIG. 2, each of the alignment films 4 is subjected to an alignment process in a predetermined direction. The second alignment film 7 has been subjected to a rubbing process in a first alignment processing direction _Ao in the right front direction of the lower substrate 2, and the first alignment film 4 has a second alignment processing direction in the upper right direction of the upper substrate 1. The rubbing process is performed toward B. The first orientation direction _Ao and the second orientation direction B intersect at an angle of about 90 °.

The upper substrate 1 on which the common electrode 3 is formed and the substrate 2 on which the pixel electrode 5 is formed are joined to each other by a sealing material 8 at a predetermined interval. A region surrounded by the upper substrate 1, the lower substrate 2, and the sealant 8 is filled with a liquid crystal material 9. Thus, a liquid crystal layer is formed between the first alignment film 4 and the second alignment film 7, and a liquid crystal cell 10 is formed by the liquid crystal layer sandwiched between the lower substrate 2 and the upper substrate 1. I have.

The liquid crystal material 9 has a dielectric constant ratio Δε / ε |
2.44, a liquid crystal having physical properties in which the value of elastic constant ratio K ₃ / K ₁ is 1.43 and the value of K ₃ / K ₂ is 2.50, and the product of its refractive index anisotropy Δn and layer thickness d The value of Δnd (retardation) is set in the range of 450 nm to 550 nm. In the liquid crystal material 9, the liquid crystal molecules near the first and second alignment films 4 and 7 are arranged in the first and second alignment processing directions, respectively, and the first alignment processing direction _Ao and the second alignment processing are performed. The direction B differs from the direction B by approximately 90 °. Therefore, the liquid crystal molecules toward the second alignment treatment direction B of the upper substrate 1 from the first alignment treatment direction A _o of the lower substrate 2, are arranged twisted approximately 90 ° counterclockwise. In this case, the value of d / p is set to about 0.05, and the pretilt angle of the liquid crystal molecules is about 1 °.

Outside the lower substrate 2 of the liquid crystal cell 10 (incident light side), a polarizer 11 composed of a linear polarizer is provided. Outside the upper substrate 1 of the liquid crystal cell 10 (outgoing light side), a linear polarizer 11 is provided. An analyzer 12 is provided. Liquid crystal cell 10
Between the first and second phase plates 13 and
14 are provided. Polarizer 11 has its polarization axis, for example, the transmission axis P ₁ is disposed substantially parallel to the rubbing direction A _o of the incident light-side substrate of the liquid crystal cell 10. Analyzer 12
Is disposed such that its polarization axis, for example, the transmission axis P ₂ is orthogonal to the transmission axis P ₁ of the polarizer 11. The first and second phase plates 13 and 14 are arranged such that their respective slow axes R ₁ and R ₂ are orthogonal to each other. These phase plates 1
3, 14 are formed so as to have the same phase difference, and the value of the phase difference Δnd is set in the range of 300 nm to 400 nm. The phase plates 13 and 14 are made of the same material, for example, polycarbonate (PC) or polyvinyl alcohol (PVA), and are sandwiched between protective films such as triacetyl cellulose. As shown in FIG. 3, a phase plate having a structure in which polyvinyl alcohol is interposed between protective films of triacetyl cellulose has almost no wavelength dependence of Re (retardation). On the other hand, in the phase plate made of polycarbonate, since the polycarbonate has a phenyl group, the wavelength dependence of Re is large as shown in FIG.

In this liquid crystal display device, the first phase plate 13
Since the slow axes R ₁ and R ₂ of the liquid crystal cell 10 and the second phase plate 14 are arranged orthogonal to each other, no phase difference occurs for light emitted in the normal direction of the liquid crystal cell 10. In addition, a phase difference occurs with respect to light incident obliquely with respect to the normal line of the liquid crystal cell 10. This phase difference compensates for the decrease in contrast caused by the difference in Δnd of the liquid crystal cell 10 between the light transmitted in the normal direction of the liquid crystal cell 10 and the light transmitted in the oblique direction, and lowers the contrast when observed from the oblique direction. And the viewing angle characteristic is improved.

By the way, in the liquid crystal display device having the above configuration, the value of Δnd of the liquid crystal cell 10 is set to 510 nm.
(Measured with light having a wavelength of 589 nm), phase plates 13 and 1
4 is 350 nm (a value measured with light having a wavelength of 589 nm), and the slow axis R ₁ of the _first phase plate 13 and the second
With the slow axis R ₂ of the phase plate 14
The slow axis R1 of the _first phase plate 13 is set to 0 °, ± 15 °, ± 3 °.
The contrast observed from each direction when arranged at each angle of 0 ° was measured. Here, the liquid crystal cell 10
Reference to the rubbing direction A _o of the lower substrate 2 of the incident light side (0
°) and clockwise as viewed from the incident light side was defined as positive. The results are shown by isocontrast curves in FIGS. In the isocontrast curves shown in FIGS. 5A to 5E, _Ao represents the first alignment processing direction, and five concentric circles extend from the inside to the outside, as in the case of the conventional example. In order to the normal of the liquid crystal display
The directions inclined at angles of 0 °, 20 °, 30 °, 40 °, and 50 ° are shown, and the dotted line represents the contrast 100, the one-dot chain line represents the contrast 50, the solid line represents the contrast 10, and the two points. The chain line indicates that the contrast is less than 1, that is, the brightness of the display is reversed. In addition,
In measuring the contrast, a C light source was used, the value of the contrast was defined by the ratio of the Y value of the transmitted light, and the front contrast was about 100.

Now, as shown in FIG. 5A, when the installation angle of the slow axis R ₁ of the first phase plate 13 is 0 °, compared to the conventional example shown in FIG. A region surrounded by a dashed line and having a contrast of 50 or more is the vertical direction V _{o of the} liquid crystal display device.
Spread (viewing angle direction in the direction of 315 ° from the rubbing direction A _o), also is narrower inversion region surrounded by a two-dot chain line in the vertical direction V _o of the liquid crystal display device, the viewing angle characteristic is improved I have. As shown in FIG. 5B, when the installation angle of the slow axis R1 of the _first phase plate 13 is 15 °, it is surrounded by a one-dot chain line as compared with the conventional example shown in FIG. A region having a contrast of 50 or more extends below the liquid crystal cell, and the viewing angle characteristics are improved. FIG. 5 (C)
21, when the installation angle of the slow axis R ₁ of the first phase plate 13 is −15 °, the contrast surrounded by a dashed line is 50 or more compared to the conventional example shown in FIG. 21. Is expanded below the liquid crystal cell, and the inversion area surrounded by the two-dot chain line that appears above the liquid crystal cell is narrowed, and the viewing angle characteristics are improved. As shown in FIG. 5D, when the installation angle of the slow axis R1 of the _first phase plate 13 is 30 °, the first phase plate 13 is surrounded by a one-dot chain line as compared with the conventional example shown in FIG. contrast more than 50 regions are narrower in the vertical direction V _o of the liquid crystal cell and a substantially inverted region surrounded by a two-dot chain line appearing above the liquid crystal cell the same, the viewing angle characteristic is not improved. As shown in FIG. 5 (E), when the installation angle of the slow axis R1 of the _first phase plate 13 is −30 °, it is surrounded by a one-dot chain line as compared with the conventional example shown in FIG. The region where the contrast is 50 or more is the vertical direction V of the liquid crystal cell.
_o narrowed and appear above the liquid crystal cell
The inversion region surrounded by the dashed line is almost the same, and the viewing angle characteristics are not improved.

[0016] For this reason, the installation angle of the slow axis R ₁ of the first phase plate 13 relative to the alignment treatment direction A _o subjected to the lower substrate 2 of the incident light side of the liquid crystal cell 10, -15
If the angle is within the range of 15 ° to 15 °, the viewing angle with the highest contrast exists in the vertical direction V _o of the liquid crystal cell 10, and the range that can be observed with a high contrast is widened. Therefore, it is desirable that the installation angle of the slow axis R1 of the _first phase plate 13 be in the range of −15 ° to 15 °. In such a range of the installation angle of the slow axis R ₁ of the first phase plate 13, the phase difference of the light caused by the oblique transmission of the light through the liquid crystal cell 10 is caused by the first and second phase plates 13. , 14, the viewing angle in the vertical direction V _o of the liquid crystal display device and in the horizontal direction orthogonal thereto are wide, and the inversion region appearing upward can be narrowed, and the viewing angle characteristics are improved.

Next, a second embodiment of the present invention will be described with reference to FIGS. The same members as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
The second embodiment has a structure in which two phase plates are disposed between the polarizer 11 and the liquid crystal cell 10. That is, the first phase plate 1 is placed between the polarizer 11 and the liquid crystal cell 10.
3 together with its slow axis R ₁ is arranged to be either in the range from -15 ° to 15 ° to the rubbing direction A _o of the lower substrate 2 of the incident light side of the liquid crystal cell 10, the first Between the first phase plate 13 and the liquid crystal cell 10.
4 is disposed such that its slow axis R ₂ is substantially orthogonal to the slow axis R _{1 of} the first phase plate 13. Thus, even if the first and second phase plates 13 and 14 are arranged, the viewing angle characteristics are improved to substantially the same degree as in the first embodiment described above.

As shown in FIG. 6, two phase plates 13 and 14 are disposed between the polarizer 11 and the liquid crystal cell 10 so that their slow axes R ₁ and R ₂ are orthogonal to each other. The installation direction of the slow axis R1 of the _first phase plate 13 disposed on the side of the polarizer 11 was made coincident with the rubbing direction _Ao, and observation was performed from each direction under the same conditions as in the first embodiment described above. FIG. 7 shows the measurement results of the contrast. The isocontrast curve in FIG.
Compared to an equal contrast curve shown in FIG. 5 (A) described above, the plane connecting the direction of direction and 315 ° of 135 ° relative to the alignment direction A _o of the lower substrate 2 of the incident light side of the liquid crystal cell 10 Mirror-symmetrical.

[0019] In the same manner, it arranged two phase plates 13 and 14 between the polarizer 11 and the liquid crystal cell 10, a first phase plate 13 that the slow axis R ₁ is in the rubbing direction A _o -15
° and + 15 °.
As shown in FIG. 7 described above, the liquid crystal cell 10 and the analyzer 1
2 as compared with the case where the two phase plates 13 and 14 is disposed between the direction of 135 ° from the rubbing direction A _o and 315 °
And a mirror-symmetric isocontrast curve is obtained with respect to a plane connecting the directions. Therefore, the polarizer 11 and the liquid crystal cell 10
When the two phase plates 13 and 14 are disposed orthogonal to each other between the first and second phase plates 13 and 14, the arrangement angle of the slow axis R ₁ of the first phase plate 13 disposed on the polarizer 11 side is set to −15. When the angle is in the range of 15 ° to 15 °, the viewing angle can be widened and the inversion region can be narrowed, so that the viewing angle characteristics are improved.

Next, in the liquid crystal display device having the structure shown in FIGS. 1 and 2, the value of Δnd of the liquid crystal layer of the liquid crystal cell 10 is set to 360 nm (value measured with light having a wavelength of 589 nm), and the value of Δnd of the phase plates 13 and 14 is set. Values of 300 nm and 350 nm
And 400 nm (measured with 589 nm wavelength light)
5 (A) to FIG. 5 (E), each direction when the slow axis R1 of the _first phase plate 13 is arranged so as to be at an angle of 0 ° and ± 15 °. The contrast observed from was measured. The measurement results are shown in FIGS. 8 (A) to 8 (C) show Δ of phase plates 13 and 14, respectively.
When the value of nd is 300 nm and the slow axis R ₁ of the first phase plate 13 is
9 (A) to 9 (C) show the first and second contrast plates when the setting angles of the phase plates are 0 °, 15 °, and −15 °, respectively. installation angle of the slow axis R ₁ of the phase plate 13 is 0 °, 15 °, -15
10 (A) to FIG. 10 (C), the values of Δnd of the phase plates 13 and 14 are 400 nm, and the installation angle of the slow axis R ₁ of the first phase plate 13 is shown in FIG. FIG. 4 is an isocontrast curve diagram in the case where is 0 °, 15 °, and −15 °. In this case, the physical characteristics of the liquid crystal are as follows: the value of the dielectric constant ratio Δε / ε | is 1.25, the value of the elastic constant ratio K ₃ / K ₁ is 1.57, and the value of K ₃ / K ₂ is 2.30. In addition, FIG.
In FIG. 10, the three-dot chain line represents the contrast 150.

As is apparent from these figures, as compared with the conventional example shown in FIG. 21, no inversion region appears in any case, and a region surrounded by a dashed line and having a contrast of 50 or more is a liquid crystal cell. Spread at V _o below 10. It is clear that a high contrast area appears below V _o of the liquid crystal cell 10. Therefore, the viewing angle is increased in the vertical direction of the liquid crystal cell 10, and the viewing angle characteristics are improved. Focusing on Δnd of the phase plates 13 and 14, the phase plate 1
The larger the value of Δnd of 3, 14 is, the lower V below the liquid crystal cell 10 is.
_The area with high contrast is widened with _o . Therefore, the value of Δnd of the phase plates 13 and 14 is preferably large, and the value is preferably in the range of 300 nm to 600 nm. The value of Δnd of the liquid crystal cell 10 is 350
It is preferably in the range of nm to 700 nm, and the smaller the value, the better the viewing angle characteristics. Therefore, the value of Δnd of the liquid crystal cell 10 is preferably 550 nm or less,
In particular, it is desirable to be about 360 nm. The same applies to a case where two phase plates are arranged between the polarizer 11 and the liquid crystal cell 10 so as to be orthogonal to each other.

For comparison, the set angles of the slow axis R ₁ of the first phase plate 13 are set to 45 °, 90 °, and 135 ° under the same conditions as in FIG. 8A of the second embodiment. 11 (A) to FIG.
It is shown in (C). As shown in FIG. 11A, when the set angle of the slow axis R ₁ of the first phase plate 13 is 45 °, a region having a contrast of 50 or more is obtained as compared with the conventional example shown in FIG. Although spread at the viewing angle 225 °, is narrower in the direction V _o that connects the viewing direction 135 ° and 315 °, and since the inversion region is widened in the place of the viewing angle direction 135 °, the viewing angle characteristic Not improved. As shown in FIG. 11B, the slow axis R of the first phase plate 13
_When the setting angle of ₁ is 90 °, the area where the contrast is 50 or more is almost the same as in the conventional example shown in FIG. 21, but the inversion area at the viewing angle of 135 ° is widened, The angular characteristics are not improved. FIG.
As shown in FIG. 11C, when the set angle of the slow axis R ₁ of the first phase plate 13 is 135 °, the _first angle is set to be smaller than the case where the set angle is 45 ° shown in FIG. , The second phase plate 1
FIG. 11 (A) corresponds to the case where 3 and 14 are interchanged.
As in the case of the setting angle 45 ° shown in FIG.
Although the region of 0 or more extends at the viewing angle direction of 225 °, the direction V connecting the viewing angle directions of 135 ° and 315 °
_O is narrow, and the reversal region at a viewing angle of 135 ° is wide, and the viewing angle characteristics are not improved.

As described above, according to the second embodiment, the two phase plates 1 are provided between the liquid crystal cell 10 and the polarizer 11.
3 and 14 are arranged such that their slow axes R ₁ and R ₂ are orthogonal to each other, and the set angle of the slow axis R ₁ of the first phase plate 13 provided on the polarizer 11 side is set to the liquid crystal. with any of the range of 15 ° from -15 ° to the rubbing direction a _o of the lower substrate 2 of the incident light side of the cell 10, it is possible to widen the viewing angle, also narrowing the reversal area And the viewing angle characteristics can be improved.

[0024] Here, ± 15 ° with respect to the first rubbing direction A _o of the lower substrate 2 set angle of incident light side of the phase plate 13
When the physical characteristics of the liquid crystal material 9 and the physical characteristics of the phase plates 13 and 14 were changed, the results of measurement of the viewing angle characteristics of the liquid crystal display device when the range was
As shown in FIG. In these isocontrast curves, the physical properties of the liquid crystal material 9 are as follows: the value of the dielectric constant ratio Δε / ε | is 1.25, the value of the elastic constant ratio K ₃ / K ₁ is 1.57, and the value of K ₃ /
The value of K ₂ is 2.30 and the value of Δnd of the liquid crystal layer is 360 n
m.

FIGS. 12 to 15 show isocontrast curves when a phase plate made of polyvinyl alcohol (PVA) is used. FIGS. 12A to 12C show the case where the value of Δnd of the phase plate is 300 nm and the set angles of the phase plate are −15 °, 0 °, and + 15 °, respectively. FIGS. 13A to 13C show the case where the value of Δnd of the phase plate is 400 nm and the set angles of the phase plate are −15 °, 0 °, and + 15 °, respectively. FIGS. 14A to 14C respectively show Δ of the phase plate.
The case where the value of nd is 500 nm, and the set angles of the phase plate are −15 °, 0 °, and + 15 °, respectively. FIG.
15 (A) to FIG. 15 (C) respectively show that the value of Δnd of the phase plate is 600 nm, the set angle of the phase plate is −15 °,
0 ° and + 15 ° are shown. 16 to 19 show isocontrast curves when a phase plate made of polycarbonate (PC) is used. FIG.
16A to 16C show that the value of Δnd of the phase plate is 300 nm, the set angle of the phase plate is −15 °,
0 ° and + 15 ° are shown. 17 (A) to 17 (C) show that the value of Δnd of the phase plate is 400 nm.
And the set angles of the phase plate are -15 °, 0 °, and +1 respectively.
5 ° is shown. 18 (A) to 18 (C)
Indicates a case where the value of Δnd of the phase plate is 500 nm and the set angles of the phase plate are −15 °, 0 °, and + 15 °, respectively. FIGS. 19A to 19C show the case where the value of Δnd of the phase plate is 600 nm and the set angles of the phase plate are −15 °, 0 °, and + 15 °, respectively.

As is clear from these isocontrast curves, in all cases, the viewing angle is a direction V _{o of} 315 ° with respect to the rubbing direction A _o of the lower substrate 2, that is, a high contrast area appears on the near side of the liquid crystal display device. The viewing angle in the direction is widened. Further, as a material of the phase plate, polyvinyl alcohol (PVA) or polycarbonate (P
When C) was used, good isocontrast characteristics were exhibited. Therefore, any of polyvinyl alcohol (PVA) and polycarbonate (PC) can be used as the phase plate. Further, when the value of Δnd of the liquid crystal cell 10 is 350 nm to 700 nm,
Desirably, it is 300 nm to 600 nm.

[0027] Next, the refractive index n _o of the ordinary light and extraordinary light in the phase plate, the results of examining the effect on the contrast characteristics of n _e in FIG. 20 (A) ~ FIG 20 (F).
20 (A) to 20 (F) show the first embodiment shown in FIG. 2 in which the set angle of the phase plate is 0 °, the Δnd of the liquid crystal layer of the liquid crystal cell 10 is 375 nm, and the Δn of the phase plate is
3 shows an isocontrast curve when d is fixed at 350 nm and the absolute values of the refractive indices of ordinary light and extraordinary light of the phase plate are changed. Figure 20 (A) is the refractive index n _o of the ordinary light is 1.2, Figure 2
0 (B) has a refractive index n _o of 1.3 normal light, FIG. 20 (C) has a refractive index n _o of the ordinary light is 1.4, Figure 20 (D) has a refractive index n _o of the ordinary
1.5, FIG. 20 (E) has a refractive index n _o of the ordinary light is 1.55, FIG. 20
(F) denotes a refractive index n _o of the ordinary light represents the case of 1.6, respectively. According to FIG. 20 (A) ~ FIG 20 (F), when the refractive index n _o of the ordinary light is 1.3, the near side of the liquid crystal display device, i.e. contrast downward V _o in the drawings are spread region of high I have. Therefore, in Δnd of the liquid crystal layer is 375 nm, when Δnd of the phase plate is 350 nm, it is preferable that the value of the refractive index n _o of the ordinary light of the phase plate to 1.3.

[0028]

As described above, according to the present invention, the first and second phase plates are disposed between a pair of polarizers so that their slow axes are orthogonal to each other, and the first phase plate is disposed. The setting angle of the slow axis of the plate is set in the range of -15 ° to 15 ° with respect to the rubbing direction of the incident light side substrate of the liquid crystal cell, and the value of Δnd of the liquid crystal cell is set to 350 nm to 700 nm.
Δnd of the first and second phase plates.
Are in the range of 300 nm to 600 nm and equal to each other, so that the viewing angle can be widened, the inversion region can be narrowed, and the viewing angle characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram illustrating the liquid crystal display device of FIG.

FIG. 3 is a diagram showing the wavelength dependence of retardation Re of a phase plate made of polyvinyl alcohol used in the present invention.

FIG. 4 is a diagram showing the wavelength dependence of retardation Re of a phase plate made of polycarbonate used in the present invention.

FIGS. 5A to 5E are iso-contrast curves showing respective viewing angle characteristics in the case where the setting angle of the slow axis of the phase plate is different.

FIG. 6 is a schematic configuration diagram illustrating a liquid crystal display device according to a second embodiment.

7 is an isocontrast curve diagram showing viewing angle characteristics of the liquid crystal display device of FIG.

FIGS. 8A and 8B show Δnd in the second embodiment.
FIG. 9 is an iso-contrast curve diagram showing viewing angle characteristics when a phase plate with a value of 300 nm is used and the installation angle of a slow axis of the phase plate is different.

FIGS. 9A and 9B show Δnd in the second embodiment.
FIG. 7 is an iso-contrast curve diagram showing viewing angle characteristics when a phase plate having a value of 350 nm is used and a slow axis of the phase plate is installed at a different angle.

FIGS. 10A and 10B show Δn in the second embodiment.
FIG. 11 is an isocontrast curve diagram showing viewing angle characteristics when a phase plate having a value of d of 400 nm and a slow axis of the phase plate are installed at different angles.

FIGS. 11A and 11B are view angle characteristics of the second embodiment in the case where the setting angle of the slow axis of the phase plate is further different from FIGS. 5A to 5E. FIG.

FIGS. 12A and 12B show a liquid crystal display device according to the second embodiment in which the values of Δnd of the liquid crystal cell and the phase plate are different from those of FIG. 8, and a phase plate made of polyvinyl alcohol having a value of Δnd of 300 nm is used. FIG. 4 is an isocontrast curve diagram showing viewing angle characteristics when the phase plate has a different slow axis setting angle when used.

13A and 13B are liquid crystal display devices according to the second embodiment, in which the values of Δnd of the liquid crystal cell and the phase plate are different from those of FIG. 8, and a phase plate made of polyvinyl alcohol having a value of Δnd of 400 nm is used. FIG. 4 is an isocontrast curve diagram showing viewing angle characteristics when the phase plate has a different slow axis setting angle when used.

FIGS. 14A and 14B show a liquid crystal display device according to the second embodiment in which the values of Δnd of the liquid crystal cell and the phase plate are different from those of FIG. 8, and a phase plate made of polyvinyl alcohol having a value of Δnd of 500 nm is used. FIG. 4 is an isocontrast curve diagram showing viewing angle characteristics when the phase plate has a different slow axis setting angle when used.

FIGS. 15A and 15B show a liquid crystal display device in which the value of Δnd of the liquid crystal cell and the phase plate is different from that of FIG. 8 in the second embodiment, and a phase plate made of polyvinyl alcohol having a value of Δnd of 600 nm is used. FIG. 4 is an isocontrast curve diagram showing viewing angle characteristics when the phase plate has a different slow axis setting angle when used.

16A and 16B show a liquid crystal display device in which the values of Δnd of the liquid crystal cell and the phase plate are different from those of FIG. 8 in the second embodiment, using a polycarbonate phase plate having a value of Δnd of 300 nm. FIG. 8 is an iso-contrast curve diagram showing the viewing angle characteristics of the case where the retardation axis of the phase plate is installed at a different angle.

17A and 17B are liquid crystal display devices in which the values of Δnd of the liquid crystal cell and the phase plate are different from those of FIG. 8 in the second embodiment, using a polycarbonate phase plate having a value of Δnd of 400 nm. FIG. 8 is an iso-contrast curve diagram showing the viewing angle characteristics of the case where the retardation axis of the phase plate is installed at a different angle.

FIGS. 18A and 18B show a liquid crystal display device according to the second embodiment in which the values of Δnd of the liquid crystal cell and the phase plate are different from those of FIG. 8, and using a polycarbonate phase plate having a value of Δnd of 500 nm. FIG. 8 is an iso-contrast curve diagram showing the viewing angle characteristics of the case where the retardation axis of the phase plate is installed at a different angle.

19A and 19B show a liquid crystal display device in which the value of Δnd of the liquid crystal cell and the phase plate is different from that of FIG. 8 in the second embodiment, using a polycarbonate phase plate having a value of Δnd of 600 nm. FIG. 8 is an iso-contrast curve diagram showing the viewing angle characteristics of the case where the retardation axis of the phase plate is installed at a different angle.

[20] (A) ~ (F) in the second embodiment, equal contrast curve diagrams representing respective viewing angle characteristics when the value of n _o of liquid crystal cell and the phase plate are different.

FIG. 21 is an equal contrast diagram showing viewing angle characteristics in a conventional liquid crystal display device.

FIG. 22 is a voltage-luminance characteristic diagram of the liquid crystal display device of FIG.

FIG. 23 is a CIE chromaticity diagram showing a change in display color of the liquid crystal display device of FIG. 21.

[Explanation of symbols]

 Reference Signs List 9 liquid crystal material 10 liquid crystal cell 11 polarizer 12 analyzer 13 first phase plate 14 second phase plate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-125224 (JP, A) JP-A-1-254917 (JP, A) JP-A-1-304422 (JP, A) JP-A-2- 19834 (JP, A) JP-A-2-35416 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/13363

Claims (7)

(57) [Claims] 1. A twisted nematic liquid crystal cell in which the alignment of liquid crystal molecules is twisted approximately 90 ° counterclockwise in the direction of light propagation, the polarization axes of the liquid crystal molecules are arranged on one side and the other side. A pair of polarizing plates are provided substantially orthogonal to each other, and the polarization axis of one of the pair of polarizing plates is arranged substantially parallel to the alignment processing direction applied to the substrate on one surface side of the liquid crystal cell. In the liquid crystal display device, a first phase plate having a slow axis in a range of −15 ° to 15 ° with respect to the alignment processing direction, between the pair of polarizing plates, a second phase plate having a slow axis in a direction substantially perpendicular to the slow axis of the phase plate, the liquid crystal cell
To the substrate adjacent to the first or second phase plate.
The orientation direction applied and the liquid crystal cell adjacent to the liquid crystal cell.
The liquid crystal cell is arranged so that the slow axis of the first or second phase plate is substantially orthogonal to the slow axis, the value of Δnd of the liquid crystal cell is in a range of 350 nm to 700 nm, and the value of Δnd of the first and second phase plates is Is in the range of 300 nm to 600 nm and equal to each other. 2. The value of Δnd of the liquid crystal cell is 450 nm.
2. The liquid crystal display device according to claim 1, wherein the values of Δnd of the first and second phase plates are equal to each other within a range of 300 nm to 400 nm. 3. 3. The value of Δnd of the liquid crystal cell is approximately 350
2. The value of Δnd of each of the first and second phase plates is approximately 400 nm.
3. The liquid crystal display device according to 1. 4. The liquid crystal display device according to claim 1, wherein the first and second phase plates are arranged on a light emission side of the liquid crystal cell. 5. The liquid crystal display device according to claim 1, wherein the first and second phase plates are arranged on a light incident side of the liquid crystal cell. 6. The value of Δnd of the liquid crystal cell is approximately 510.
6. The liquid crystal display device according to claim 4, wherein each of the first and second phase plates has a value of approximately 350 nm. 7. The value of Δnd of the liquid crystal cell is approximately 375
It is nm, the first, the fourth aspect value of Δnd of the second phase plate at approximately 350nm respectively, and wherein the value of the refractive index n _o of the ordinary light of these phase plate is approximately 1.3 6. The liquid crystal display device according to 5.