JP3246014B2 - 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 a twisted nematic liquid crystal display device.

[0002]

2. Description of the Related Art As a liquid crystal display device used as a display of a word processor or a personal computer, a TFT-TN type liquid crystal display device is used.
This liquid crystal display device has a twisted nematic (TN) type liquid crystal cell in which a driving thin film transistor (TFT) is provided for each pixel, and a polarizer has a transmission axis on a light incident side of the liquid crystal cell. The liquid crystal cell is disposed so as to be perpendicular to the orientation processing direction of the incident side substrate, and the analyzer is disposed on the light emitting side of the liquid crystal cell so that the transmission axis is substantially perpendicular to the transmission axis of the polarizer. Since this conventional liquid crystal display device can be driven by applying a static voltage to each pixel, it has a higher contrast and a wider viewing angle than a simple matrix type liquid crystal display device.

[0003]

However, such a conventional TN type liquid crystal display device has a narrow viewing angle,
There is a drawback that a brightness reversal phenomenon occurs depending on the viewing angle at the time of halftone display, and the grayscale display is disturbed.

FIG. 5 shows the viewing angle characteristics of such a conventional TN type liquid crystal display device (a structure in which a liquid crystal cell is simply sandwiched between a polarizer and an analyzer). FIG. 5 shows an iso-contrast curve, in which five concentric circles are arranged in order from the inside to 10 °, 20 °, 30 ° with respect to the normal direction of the substrate of the liquid crystal display device.
Black, square (■) has a contrast of 10, white square (□) has a contrast of 50, black triangle (▲) has a contrast of 100, and white triangle (△) represents a viewing angle inclined at °, 40 °, and 50 °. A contrast of 150 and a star (★) represent a contrast of 200, respectively. As is clear from the isocontrast curve in FIG. 5, in the conventional liquid crystal display device, the azimuth angle which is the angle representing the azimuth of the display surface with respect to the upward direction (the orientation processing direction R of the incident side alignment film) is 1
It can be seen that the viewing angle at which a certain level of contrast or more can be obtained is narrow between the direction of 35 °) and the downward direction (direction of 315 ° azimuth).

FIGS. 6A to 6D show the viewing angle dependency of an L * -V curve representing the relationship between the luminance (light transmittance) L * and the drive voltage V. FIG. In FIG. 6A, the liquid crystal cell is directed upward (direction of azimuth 135 °), in FIG. 6B, leftward (direction of azimuth 225 °) of the liquid crystal cell, and in FIG. In FIG. 6D, the viewing angle (the angle of the line of sight with respect to the normal of the liquid crystal cell) is set to 0 in the right direction (direction of the azimuth angle of 45 °) and in FIG.
Each L * -V curve at the time of shaking from 〜 to 50 ° is shown. Among these figures, in particular, L * in the downward direction shown in FIG.
In the −V curve, in the halftone display area where the luminance change is large,
It can be seen that the curve rises once after sinking, and the brightness is inverted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a uniformly wide viewing angle, prevents a brightness inversion phenomenon at the time of halftone display, and stably displays a correct grayscale. It is an object of the present invention to provide a liquid crystal display device that can perform the above-described operations.

[0007]

In order to achieve the above object, the present invention provides a twisted nematic liquid crystal cell in which liquid crystal molecules are twisted at substantially 90 °, and a transmission axis on the light incident side of the liquid crystal cell. A first polarizing plate disposed substantially orthogonal to the incident side alignment processing direction of the liquid crystal cell; and a first polarizing plate disposed between the first polarizing plate and the liquid crystal cell; A first phase plate oriented in a direction substantially parallel or substantially perpendicular to the direction of alignment treatment on the incident side of the cell, and a transmission axis on the light exit side of the liquid crystal cell substantially orthogonal to the transmission axis of the first polarizing plate. A second polarizing plate disposed, a direction disposed between the second polarizing plate and the liquid crystal cell, the slow axis of which is substantially orthogonal to or substantially parallel to the slow axis of the first phase plate; and a second phase plate facing the first phase Refractive index anisotropy Δn and the thickness d of
The value of the product Δnd is arranged on the light emission side of the liquid crystal cell.
It is set to be larger than the value of [Delta] nd of the second phase plate .

[0008]

According to the present invention, the first and second polarizers are arranged outside the TN type liquid crystal cell in which the liquid crystal molecules are twisted at substantially 90 ° so as to sandwich the TN type liquid crystal cell. Placed perpendicular to the orientation processing direction on the corresponding side,
A first phase plate whose slow axis is substantially parallel or substantially perpendicular to the liquid crystal cell incident side alignment processing direction is disposed between the first polarizer and the liquid crystal cell. slow axis thereof is arranged substantially orthogonal or second phase plate substantially parallel to the slow axis of the first phase plate between, and # 1
The value of Δnd which is the product of the refractive index anisotropy Δn of the phase plate and the thickness d
Is Δnd of the second phase plate arranged on the light emission side of the liquid crystal cell.
Since with the set value greater, first, the phase difference of light passing through the light obliquely transmitted through vertically crystal cell by the second phase plate is compensated, thereby together with the viewing angle characteristics are improved, the intermediate floor The brightness inversion phenomenon at the time of tonal display can be suppressed, and the correct gray scale can be stably displayed in the intermediate gray scale display regardless of the viewing angle.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described in detail with reference to FIG. 1 and 2 show a sectional view and an exploded perspective view of a liquid crystal display device. In this liquid crystal display device, a polarizer (first polarizing plate) 2 is provided on the light incident side of the twisted nematic liquid crystal cell 1, and an analyzer (second polarizing plate) 3 is provided on the light emitting side of the liquid crystal cell 1. A first phase plate 4 is provided between the liquid crystal cell 1 and the polarizer 2, and a second phase plate 5 is provided between the liquid crystal cell 1 and the analyzer 3.

The liquid crystal cell 1 includes a lower substrate 9 on which one electrode 6, a driving thin film transistor (TFT) 7 provided for each pixel of the electrode 6, and an alignment film 8 covering these electrodes are formed. The other electrode 10 orthogonally facing the one electrode 6 and the alignment film 1 covering the other electrode 10
The upper substrate 12 on which the substrate 1 is formed, a sealing material 13 for joining the upper and lower substrates 9 and 12 at a predetermined interval, and sealing in a region surrounded by the substrates 9 and 12 and the sealing material 13 Liquid crystal material 14. The liquid crystal cell 1 receives light from below in the drawing.
Hereinafter, the lower substrate is the incident side substrate 9 and the upper substrate is the emission side substrate 1.
Two.

The alignment films 8 and 11 formed on the opposing surfaces of the incident side substrate 9 and the outgoing side substrate 12, respectively, are subjected to an alignment treatment such as rubbing. When the liquid crystal cell 1 is observed from the front with the long side of the substrate aligned horizontally as shown in FIG. 2, the alignment film 8 of the incident side substrate 9 is oriented in the direction parallel to the long side along the horizontal direction. The orientation processing is performed in the direction 8a having an inclination of about 45 ° from the upper left to the lower right with respect to the reference. Emission-side substrate 1 facing incidence-side substrate 9
The alignment film 11 of the second direction is the alignment processing direction 8a of the incident side substrate 9.
The orientation processing is performed in a direction 11a that is rotated approximately 90 ° clockwise with respect to the emission side (hereinafter referred to as an incident side orientation processing direction). Due to such an alignment treatment, the liquid crystal molecules of the liquid crystal material 14 are rotated approximately 90 ° counterclockwise when viewed from the emission side.
(Φ) Twisted and arranged. The value of the product Δnd of the gap d and the refractive index anisotropy Δn of the liquid crystal cell 1 is set in a range of 350 to 400 nm (measurement wavelength: 589 nm).

The polarizer 2 has a transmission axis 2a whose liquid crystal cell 1
Are arranged so as to be substantially perpendicular to the incident side alignment direction 8a. The analyzer 3 is arranged such that the transmission axis 3a is substantially orthogonal to the transmission axis 2a of the polarizer 2.

Each of the first and second phase plates 4 and 5 is made of polycarbonate, and the value of the product Δnd of each thickness d of the phase plates 4 and 5 and each refractive index anisotropy Δn is different. I have. That is, the value of Δnd of the first phase plate 4 is 580 to
620 nm (measurement wavelength: 589 nm), and the value of Δnd of the second phase plate 5 is 160-200 nm (measurement wavelength: 589 nm). Then, the first phase plate 4
Indicates that the slow axis 4a of the liquid crystal cell 1
They are arranged so as to be substantially parallel (or substantially orthogonal) to a. The second phase plate 5 is disposed such that its slow axis 5a is substantially orthogonal to (or substantially parallel to) the slow axis 4a of the first phase plate 4.

In such a TN type liquid crystal display device, the first phase plate 4 is connected between the liquid crystal cell 1 and the polarizer 2 by the slow axis 4a.
Are arranged so as to be substantially parallel 8 or substantially orthogonal 9 to the incident side alignment processing direction 8a of the liquid crystal cell 1, and the second phase plate 5 is connected between the liquid crystal cell 1 and the analyzer 3 by the slow axis 5a.
The first phase plate 4 is disposed so as to be substantially orthogonal (or substantially parallel) to the slow axis 4a of the phase plate 4 and the value of Δnd of the first phase plate 4 is 58
0nd to 620 nm, Δnd of the second phase plate 5
Is set in the range of 160 to 200 nm, the first and second phase plates 4 and 5 cancel out the phase difference between the light vertically transmitted through the liquid crystal cell 1 and the light transmitted obliquely,
As a result, it is possible to suppress the brightness inversion phenomenon at the time of displaying the intermediate gradation, and to stably display the correct gradation even when the viewing angle changes.

Next, a specific measurement result of such a TN type liquid crystal display device will be described in comparison with a conventional one. In this liquid crystal display device, Δnd of the liquid crystal cell 1
Is 380 nm and the value of Δnd of the first phase plate 4 is 600 n
At m, the value of Δnd of the second phase plate 5 is 180 nm.

FIG. 3 shows an isocontrast curve of the liquid crystal display device. Also in this figure, five concentric circles are arranged in order from the inside toward the normal direction of the substrate of the liquid crystal display device.
°, 20 °, 30 °, 40 °, and 50 ° represent viewing angles, where a black square (■) has a contrast of 10, a white square (□) has a contrast of 50, a black triangle (▲) has a contrast of 100, The white triangle (△) has a contrast of 150,
The black star (★) represents a contrast of 200, respectively. In the isocontrast curve of FIG. 3, an area where the contrast can be obtained at a predetermined level or more in a downward direction (direction of azimuth angle of 315 °) is wider than the isocontrast curve of the conventional liquid crystal display device shown in FIG. It can be seen that the viewing angle has been improved.

[0017]

According to the present invention, almost 90 liquid crystal molecules are formed.
The first and second polarizers are arranged outside the TN type liquid crystal cell twist-aligned at an angle such that their transmission axes are perpendicular to the alignment processing direction on the corresponding side of the liquid crystal cell. A first phase plate whose slow axis is substantially parallel or substantially perpendicular to the direction of the alignment treatment on the incident side of the liquid crystal cell between the first polarizer and the liquid crystal cell; And a second phase plate whose slow axis is substantially orthogonal to or substantially parallel to the slow axis of the first phase plate, and
Δn which is the product of the refractive index anisotropy Δn of the first phase plate and the thickness d
the value of d in the second phase disposed on the light exit side of the liquid crystal cell
Since it is set to be larger than the value of Δnd of the plate , the first and second phase plates compensate for the phase difference between the light transmitted vertically and the light transmitted obliquely through the liquid crystal cell, thereby improving the viewing angle, and It is possible to suppress the brightness reversal phenomenon at the time of the halftone display, and it is possible to stably display the correct tone in the halftone display regardless of the viewing angle.

[0018]

According to the present invention, almost 90 liquid crystal molecules are formed.
The first and second polarizers are arranged outside the TN type liquid crystal cell twisted at an angle between the first polarizer and the liquid crystal cell, and the slow axis is aligned between the first polarizer and the liquid crystal cell. A first phase plate substantially parallel or substantially perpendicular to the processing direction is arranged, and a slow axis between the second polarizing plate and the liquid crystal cell is substantially orthogonal or substantially perpendicular to the slow axis of the first phase plate. Since the second phase plate that is substantially parallel is arranged and the values of Δnd of the first and second phase plates are different from each other, the first and second phase plates obliquely intersect light vertically transmitted through the liquid crystal cell. The phase difference of the transmitted light is compensated, which improves the viewing angle and suppresses the brightness reversal phenomenon in the halftone display, so that the correct grayscale in the halftone display is stable regardless of the viewing angle. Can be displayed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a TN type liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a schematic configuration of the liquid crystal display device of FIG.

FIG. 3 is an isocontrast curve diagram of the liquid crystal display device of the present invention.

FIG. 4 shows an L * -V curve of the liquid crystal display device of the present invention. FIG. 4 (a) shows the L * -V curve when the viewing angle is changed from 0 ° to 50 ° in the upward direction (135 ° azimuth angle) of the liquid crystal cell. * -V curve diagram, (b) is an L * -V curve diagram when the viewing angle is swung from 0 ° to 50 ° in the left direction (direction of azimuth 225 °) of the liquid crystal cell, and (c) is the liquid crystal cell. Right direction (45 ° azimuth direction)
L * -V curve diagram when the viewing angle is changed from 0 ° to 50 °,
(D) is an L * -V curve diagram when the viewing angle is shifted from 0 ° to 50 ° in the lower side direction of the liquid crystal cell (direction of azimuth angle of 315 °).

FIG. 5 is an equal contrast curve diagram of a conventional liquid crystal display device.

FIG. 6 shows an L * -V curve of a conventional liquid crystal display device,
(A) is an L * -V curve diagram when the viewing angle is shifted from 0 ° to 50 ° in the upward direction (direction of azimuth angle of 135 °) of the liquid crystal cell,
(B) is an L * -V curve diagram when the viewing angle is shifted from 0 ° to 50 ° in the left direction (direction of azimuth 225 °) of the liquid crystal cell,
(C) is an L * -V curve diagram when the viewing angle is shifted from 0 ° to 50 ° in the right direction (direction of azimuth angle of 45 °) of the liquid crystal cell, (d)
FIG. 3 is an L * -V curve diagram when the viewing angle is changed from 0 ° to 50 ° in the lower side direction of the liquid crystal cell (azimuth angle is 315 °).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal cell 2 Polarizer 3 Analyzer 4 First phase plate 4a Slow axis of first phase plate 5 Second phase plate 5a Slow axis of second phase plate 6, 10 Electrode 8, 11 Alignment film 8a Alignment on incident side Processing direction 9 Incident side substrate 12 Outgoing side substrate 13 Sealing material 14 Liquid crystal material

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/13363 G02F 1/1335 G02F 1/137 G02F 1/133 500

Claims (2)

(57) [Claims] 1. A twisted nematic liquid crystal cell in which liquid crystal molecules are twisted at an angle of about 90 °, and a transmission axis on the light incident side of the liquid crystal cell is made substantially perpendicular to the alignment processing direction on the incident side of the liquid crystal cell. A first polarizing plate, which is disposed between the first polarizing plate and the liquid crystal cell;
A first phase plate whose slow axis is oriented in a direction substantially parallel or substantially perpendicular to the direction of alignment treatment on the incident side of the liquid crystal cell; and a transmission axis on the light exit side of the liquid crystal cell, the first polarizing plate. A second polarizer disposed substantially orthogonal to the transmission axis of the second polarizer, and disposed between the second polarizer and the liquid crystal cell;
And a second phase plate whose slow axis is oriented in a direction substantially perpendicular or substantially parallel to the slow axis of the first phase plate , wherein the refractive index anisotropy Δn and the thickness of the first phase plate are provided. by the product of d
The second .DELTA.nd is arranged on the light emission side of the liquid crystal cell.
A liquid crystal display device characterized by being set to be larger than the value of Δnd of the phase plate . 2. The value of Δnd of the first phase plate is 580
2. The liquid crystal display device according to claim 1, wherein a value of Δnd of the second phase plate is 160 nm to 200 nm.