JPH02925A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce the weight of the liquid crystal display device and to obtain sufficient brightness by adding 0.2-2.0wt.% dichroic pigment which absorbs at least one of red, green, and blue in supertwisted nematic (STN) liquid crystal. CONSTITUTION:The STN liquid crystal 8 which is twisted and oriented spirally while controlled by the orientation axes on orienting films 6 and 7 is charged in the space between glass substrates 1 and 2 and the dichroic pigment which absorbs at least one of red, green, and blue is added in the STN liquid crystal 8. This dichroic pigment absorbs light which can not be compensated by a phase difference plate 10 and the addition is performed within a 0.2-2.0wt.% range. Consequently, the response speed is not reduced and the brightness on the display screen at the time of displaying white is prevented from decreasing.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a dot matrix type liquid crystal display device used in personal computers, word processors, etc. The present invention relates to a liquid crystal display device capable of black and white display using super twisted nematic liquid crystal (hereinafter referred to as STN liquid crystal) larger than @.

(B) Conventional technology A liquid crystal display device capable of displaying black and white using a conventional STN liquid crystal has either compensated the amount of transmitted light for each color by stacking a phase plate on the STN display panel, or twisted the colors in the opposite direction. A two-layer system in which compensation liquid crystal cells are stacked, and a guest that incorporates dichroic dye into the STN liquid crystal to increase contrast.
The host system or the product of the refractive index anisotropy Δn of the liquid crystal and the cell gap d is reduced to lower the saturation, and the twist angle is set to 2201f or more to increase the contrast.
M[(Optical Mode Interfere
nce) method (NIKKEI).
ELECTRONICS 1987. fl, 2 (n.

433) p130-138, JP-A-62-13342
Publication No. 7, Appl.

Phys, Lett, 50(5), 2 February
y 1987 p326-238).

(c) Problems to be solved by the invention However, each of the above-mentioned methods had the following advantages.

(1) The 21 system uses two STN liquid crystal cells, which increases the weight and thickness of the display device, making it difficult to reduce its weight.

(2) In the guest-host method, the dye is 2. Owt%~3
The more 0W was added, the more the response speed slowed down, and in the case of white display, the display screen tended to become darker.

(3) In the OM1 system, since the display is basically a positive type display, there are problems with black display and clear color display.

This invention has been made in consideration of the above-mentioned circumstances, and is intended to provide a liquid crystal display device that is lightweight and can provide sufficient brightness.

(d) Means for Solving the Problems This invention provides that the angle change of the alignment axes on the alignment film attached to the two glass substrates constituting the liquid crystal cell is 180° or more.
In a liquid crystal display device in which the liquid crystal layer sandwiched between glass substrates at 270° is composed of super twisted nematic liquid crystal, a double layer that absorbs at least one color among red, green, and blue is used in the super twisted nematic liquid crystal. A liquid crystal display device is provided, in which a chromatic dye is added in a range of 0.2 to 2.0% by weight, and a retardation plate is disposed on the outside of at least one glass substrate.

As the dichroic dye in this invention, a dye that absorbs at least one of red, green, and blue is added. This type of dichroic pigment includes merocyanine and anthraquinone pigments that absorb red and have a blue display color.
Tetranon-based dyes that absorb green color can be used, and dyes that display a reddish-purple color can be used, and styryl- and azomethine-based dyes that absorb blue color, and have a yellow display color can be used.

Two types of these dichroic dyes or a mixture of 3N types may be added. And the total amount added is S T N
, & products, preferably within a range of 0.2 to 2.0% by weight (hereinafter referred to as wt%). That is, if the total amount added is less than 0.2 wt%, a sufficient color compensation effect cannot be obtained, and if it is more than 2.0 wt%, the light transmittance decreases and the response becomes poor.

Further, the N class dichroic dye to be added is determined by the retardation of the retardation plate used.

As the retardation plate in this invention, a uniaxial stretched organic film preferably made to have a thickness of 50 to 200 μm by stretching a polymer compound such as polycarbonate or polyvinyl alcohol can be used.

The retardation of the retardation plate is defined by the stretched organic film, and the value of this retardation is controlled by the stretching ratio when stretching the stretched organic film lengthwise or in the lengthwise and crosswise directions. In this invention, the retardation of the retardation plate is preferably 1100 nm to 600 nm.

The retardation plate may be provided on the outside of at least one glass substrate depending on its retardation value.

Super twisted nematic (S) in this invention
TN) Liquid crystals include nclohexane type, ester type,
Some of the well-known nematic liquid crystals, such as biphenyl-based and pyridimine-based liquid crystals, have chiral dopants added thereto, thereby increasing the twist angle of the liquid crystal molecules to 1.
At an angle of 80° to 270°, preferably 240°
A twisted one between the lower glass substrates is used.

At this time, cholesteric nonanoate is used as a typical levorotatory chiral dopant, and it is used in the above-mentioned nematic liquid crystal when the thickness of the S T N liquid crystal cell is 5 to 8 um.
In this case, by adding within the range of lit% to 3.5wt%, the molecular axis of the liquid crystal molecules can be controlled to 1800 to 270°. Preferred thicknesses of S T N liquid crystal cells are typically 6 μm and 7.5 μm.

(E) Effect The dichroic dye added to the STN liquid crystal absorbs light that cannot be compensated for by the retardation plate, and the amount added is 0.2 to 2.
．． Since it is within the range of Ovt%, it is possible to prevent the brightness of the display screen from decreasing in the case of white display without reducing the response speed.

In addition, the retardation plate is a retardation plate that measures the retardation produced in the STN liquid crystal layer, that is, the STN
It acts to cancel out the elliptical polarization of linearly polarized light caused by the optical rotation dispersion effect of liquid crystal.

(F) Examples Examples of carrying out the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to the following examples.

1 and 2 are a longitudinal sectional view and a plan view of a dot matrix type liquid crystal display device according to an embodiment of the present invention.

In FIGS. 1 and 2, reference numeral 1.2 denotes upper and lower glass substrates, which are bonded together with a sealing material 3 interposed therebetween. For example, [TO
A transparent electrode 4.5 made of a film (transparent conductive II) is formed, and a rubbed alignment film 6.7 is formed on each glass substrate 1.2 so as to cover each transparent electrode 4.5. It is pasted. The angle formed by the alignment axes 6a and 7a on each alignment film 6.7';! 180' ~ 27
In this embodiment, the angle is set to 24°.In the space between the glass substrates INI, 2, there is an S T which is oriented in a spiral manner defined by the orientation axes 6a and 7a. N liquid crystal 8 is sealed in. The STN liquid crystal 8 is a known nematic liquid crystal containing a levorotatory chiral dopant and a levorotatory chiral dopant.
For example, cholesteric nonanoate can be added to set the twist angle of liquid crystal molecules in the range of 180° to 270°, and in this example, 24°
Set to 0°.

Furthermore, as the S T N liquid crystal 8, a liquid crystal material having a refractive index anisotropy Δn of 0.109 at room temperature is preferable.
In this example, since the thickness of the liquid crystal layer is 6 μm, the product ΔnXd of the refractive index anisotropy Δn and the thickness d of the liquid crystal layer
is set to 0.654 μm.

Furthermore, a dichroic dye is added to the STN liquid crystal 8.

This dichroic dye uses a dye that has spectral characteristics that absorb light that cannot be compensated for by a retardation plate, which will be described later.

In this example, the dye G206 (product name,
1.0 wt% of the following 1), a dye CL D 506 manufactured by Sumitomo Chemical Co., Ltd. (Madhi) that absorbs red color and has a blue display color.
was added at 0.5 wt%.

A liquid crystal cell 9 is constituted by a glass substrate 1.2 provided with a transparent electrode 4.5 and an alignment film 6.7, and an S T N liquid crystal 8.

Reference numeral 10 denotes a retardation plate, which is made by stretching an organic stretched film such as polycarbonate, and is disposed on the outer upper surface of the upper glass substrate l.

Preferably, the retardation is in the range of 1100 nm to 600 nm, and the optimal setting angle is achieved, and in this embodiment, a retardation of 147.3 nm is used.

And a retardation plate! For example, the upper surface of 0 and the lower surface of glass groups Vi and 2 have a single transmittance of 42% and a polarization degree of 99%.
．． Polarization Ff7. with 99%. ll, 12 are arranged.

The direction of the alignment axes 6a, 7a on each alignment film 6.7, the direction of the optical axis 10a of the retardation plate 1O, and the direction of each polarizing plate 1
The relationship with the direction of the absorption axes 11a and 12a in 1.12 is expressed as the third
As shown in the figure. The orientation axis 6a and the orientation axis 7a intersect at 240 m, and the absorption axis 11a and the absorption axis 12a are perpendicular to each other. The absorption axis 11a has an angular shift of 60 degrees with respect to the orientation axis 6a, and the optical axis 10a of the retardation plate 10 is set at 45 degrees with respect to the absorption axis 11a.

In the above configuration, when driven at a duty of 1/200, a contrast ratio of 12 was obtained when the device was turned on directly above the device, and the background was sufficiently black with a response speed of 1400 m5ec.

Next, an embodiment of the pond of this invention will be described.

In this other example, the main difference from the above example is that the dichroic dye is red and/or green and/or
Or 3N pigments that absorb blue color, the total amount of which is 0.2
wt%~2. It is to be added within the range of Owt%.

In this other embodiment, since the retardation of the retardation plate 10 is set to 570 nm, Δn
Xd is set to 0.92 μm.

As shown in FIG. 4, the angle β between the alignment axis 6λ of the alignment film 6 and the absorption axis 11a of the polarizing plate 11 is +60°,
The angle γ between the orientation axis 7a of the orientation @7 and the absorption axis 12a of the polarizing plate 12 is 145@, and the orientation axis 6a of the orientation film 6 is
The angle θ between the optical axis 10a of the retardation plate 10 is +105
° respectively. In the same figure, the angle φ is S
The twist angle of the liquid crystal molecules of the TN liquid crystal 8 is set to 240°.

In addition, the sign of the above-mentioned angle is B with the clockwise rotation direction being positive.

In this example, three types of dichroic dyes are added: red,
Use materials that absorb green and blue respectively. As a dichroic dye that absorbs red, for example, 0.3 wt% of dye 5HP564 (trade name, the same applies hereinafter) manufactured by Japan Photosensitive Color Research Institute (Aji), and as a dichroic dye that absorbs green, the same dye G202 is used. Similarly, 0.3 wt% of the dye G206 is added as a material that absorbs blue light. All of these display colors that are complementary to the color they absorb.

With the above configuration, it is possible to compensate for the coloring that occurs in the STN liquid crystal 8, and when driven at l/200 duty, the contrast ratio is 15 and the response speed is 380m5ec.
I was able to obtain the above black and white display.

Note that - numerically, dichroic dyes have weak absorption power for long wavelength light, so in addition to the three types of dichroic dyes in Ike's example above, a fourth dye that absorbs red color is added. It may also be a configuration.

An embodiment of the pond of this invention will be described.

The retardation of the retardation plate 10 is set to 550 nm,
Corresponding to this, ΔnXd is set to 0.85 μm.

As shown in FIG. 4, the angle β between the alignment axis 6a of the alignment film 6 and the absorption axis 11a of the polarizing plate 1 is +50°.
The angle γ between the alignment axis 7a of the alignment film 7 and the absorption axis +2a of the polarizing plate 12 is 150@, and the alignment axis 6a of the alignment @6 is
The angle θ between the optical axis 10a of the retardation plate ■0 is +100
° respectively. In the same figure, the angle is S
The twist angle of the liquid crystal molecules of the TN liquid crystal 8 is set to 240°.

Note that the sign of the above angle is such that the clockwise direction is positive.

As the dichroic dye to be added, in this example, 0.2 wt % of one type, for example, blue-absorbing dye G 206 manufactured by Nippon Kanko Shiki Kenkyusho (Mai) is added.

With the above configuration, it is possible to compensate for the coloring that occurs in the STN liquid crystal 8, and when driven at l/200 duty, the contrast ratio is 12 and the response speed is 250 m5ec.
I was able to obtain a black and white display of

Further, embodiments of the pond of this invention will be explained.

The retardation of the retardation plate 10 is set to 570 nm,
Corresponding to this, ΔnXd is set to 0.92. Then, as shown in FIG. 4, the alignment axis 6a of the alignment film 6 is
The angle β between the absorption axis 11a of the polarizing plate 11 is +50"
, the alignment axis 7a of the alignment film 7 and the absorption axis 12a of the polarizing plate 12.
The angle γ between the two is 160°, and the angle θ between the orientation axis 6a of orientation @6 and the optical axis 10a of the retardation plate IO is +1
00” respectively. In the figure, the angle φ
is the twist angle of the liquid crystal molecules of the STN liquid crystal 8 and is set to 24°. Note that the sign of the above angle is such that the clockwise direction is positive.

In this example, three types of dichroic dyes are added, which absorb red, green, and blue, respectively. As a dichroic dye that absorbs red color, for example, dye S HP 564 (trade name, hereinafter the same) manufactured by Japan Photosensitive Color Research Institute (MAI) is used at 0.6 wt%, and as a dye that absorbs green color, dye G202 is used at 0.6 wt%. , 6wt%, and 0.6wt% of the dye G206 as a substance that absorbs blue light.
Add each.

With the above configuration, it is possible to compensate for the coloring that occurs in the STN liquid crystal 8, and when driven at l/200 duty, the contrast ratio is 18 and the response speed is 400 ms.
I was able to obtain a black and white display of ec.

Furthermore, in each of the above embodiments, a cold cathode fluorescent lamp or an EL (electro l) lamp is used as a backlight.
uminescent) is available.

Furthermore, depending on the emission spectrum of the backlight used, a retardation plate may be provided on the glass substrate on the backlight side, that is, on the lower glass substrate side.

(g) Effects of the invention According to this invention, for example, the number of pixels is 640 x 40
Even if the liquid crystal display device is of a large capacity type such as 0, it is possible to obtain a liquid crystal display device that is lightweight, thin, capable of high contrast display with sufficient brightness and good black and white level, and has improved response speed.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, FIG. 2 is a plan view, and FIG. 3 is a diagram showing the direction of the alignment axis on each alignment film, the direction of the alignment axis of the retardation plate, and each polarizing plate. FIG. 4 is a diagram corresponding to FIG. 3 in another embodiment. 1.2...Glass substrate, 6.7...Alignment films 6a, 7a...Alignment axis, 8...Super twisted nematic liquid crystal 9
...Liquid crystal cell, 10...Retardation plate. fence map

Claims (1)

[Claims] 1. The angle formed by the alignment axes on the alignment film attached to the two glass substrates that make up the liquid crystal cell is 180° to 270°.
In a liquid crystal display device in which the liquid crystal layer sandwiched between glass substrates is made of super twisted nematic liquid crystal, red,
A dichroic dye that absorbs at least one color among green and blue is added in a range of 0.2 to 2.0% by weight, and a retardation plate is disposed on the outside of at least one glass substrate. LCD display device.