JPH02238435A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To allow bright and sharp black and white display by specifying the liquid crystal orientation angle of an STN liquid crystal and the relations between the product of the refractive index anisotropy of the liquid crystal and the thickness of a liquid crystal layer and the retardation of a phase difference and further specifying the angle formed by the optical axis of the phase difference plate and the orientation axis of the liquid crystal and the angle formed by 1st and 2nd polarizing plates and the orientation axis of the liquid crystal. CONSTITUTION:The STN (supertwisted nematic) liquid crystal has 200 deg.<=phi<=270 deg. liquid crystal twist angle phi and is set at lR2-R2l<=0.2mum in the product R1 of the refractive index anisotropy DELTAn of the liquid crystal and the thickness d of the liquid crystal layer and the retardation R2 of the phase difference. Further, the angle alpha formed by the optical axis of the phase difference plate 4 and the orientation axis of the liquid crystal in a 2nd glass substrate is set at +70 deg.<alpha<+110 deg., -110 deg.<alpha<-70 deg.. The 1st and 2nd polarizing plates 5, 6 are set at -70 deg.<alpha+beta<+110 deg., -110 deg.<alpha+beta<-70 deg. in the sum of the angle beta formed by the orientation axis of the liquid crystal of the 2nd glass substrate 2 and the absorption axis of the 2nd polarizing plate 5 and the angle alpha formed by the orientation axis of the liquid crystal of the 1st glass substrate 1 and the absorption axis of the 1st polarizing plate 6. The bright and sharp black and white display is obtd. in this way.

Description

Detailed Description of the Invention (a) Industrial Application Field This invention relates to a liquid crystal display device used in OAI11B of personal computers, word processors, etc.
More specifically, it relates to a liquid crystal display device (hereinafter referred to as LCD) capable of displaying black and white using super twisted nematic liquid crystal (hereinafter referred to as STN liquid crystal) in which the twist angle of twisted liquid crystal molecules is larger than 90°. .

(Example) Conventional technology Conventionally, LCDs using this type of STN liquid crystal are two-layer STN, which performs color correction using a two-layer cell structure, and one that has a single-layer cell structure, in which pigments are added to the liquid crystal and color correction is performed. There are two types of correction: guest-host type.

The former has two liquid crystal layers, as shown in FIG. 5, and the first layer lower substrate 23, the first liquid crystal layer 24, and A first cell in which a base plate 25 is arranged, and two cells are sequentially placed on top of the first cell.
It is composed of a second cell in which a lower layer substrate 26, a second liquid crystal layer 27, and an upper second layer substrate 28 are disposed, and an upper polarizing plate 29, whereby colored light generated in the first cell is transferred to a second cell. The color is corrected in the cell to make it achromatic.

On the other hand, in the latter case, as shown in FIG.
It is composed of a cell in which a lower substrate 33, a liquid crystal layer 34, and an upper substrate 35 are disposed, and an upper polarizing plate 36, and the liquid crystal layer 34 contains a dichroic dye that absorbs green, blue, and red, respectively. 2. Owt%~3. Color correction is performed by adding the amount within the range of Qwt%.

(c) Problems to be Solved by the Invention However, when a two-layer STN is used, since there are two liquid crystal layers, the LCD may be thicker and weigh more than a single-layer type.

In addition, when a guest-host type STN is used, IJ! without the above dye being mixed in! ! The response speed is slower than that of the conventional type, and the display screen tends to become darker when displaying white, and there is a risk that the display screen will be colored yellow-green.

An object of the present invention is to provide an LCD that is lighter in weight than when a two-layer STN is used, and which is brighter than when a guest-host STN is used and is capable of displaying clear black and white. be.

(2) Means for Solving the Problems This invention provides a pair of first . a second glass substrate; and a second glass substrate supported by these glass substrates. 1 a liquid crystal layer made of super twisted nematic liquid crystal, and first and second glass substrates facing each other on opposite sides of the first and second glass substrates from which the liquid crystal layer is located;
between a polarizing plate, a backlight disposed on a side opposite to the side where the liquid crystal layer is located with respect to the first polarizing plate facing the first glass substrate, and the second polarizing plate and the second glass substrate; and a retardation plate for color compensation of colored light generated in the liquid crystal layer by irradiation from the backlight, and the super twisted nematic liquid crystal has a liquid crystal twist angle φ of 200@≦φ. ≦270°, and the product of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer (Δ(I X d = R + ) and the retardation R2 of the phase difference is R, −R , ≦0.2μa+, and furthermore, the angle θ between the optical axis of the retardation plate and the liquid crystal alignment axis in the second glass substrate is +70°<θ.
<+llO゜ (in case of levorotatory liquid crystal) - tio” <
θ<-70° (in the case of dextrorotatory liquid crystal), and the above 1. The second polarizing plate is the sum of the angle β formed by the liquid crystal alignment axis in the second glass substrate and the absorption axis in the second polarizing plate and the angle α formed by the liquid crystal alignment axis in the first glass substrate and the absorption axis in the first polarizing plate. This is a liquid crystal display device characterized in that α+β<+110"-110"<α+β<-70°.

That is, the present invention uses a retardation plate (for example, a uniaxial polymer film) to correct the color of colored light generated in a super twisted nematic (STN) liquid crystal by irradiation from a backlight in a super twisted type liquid crystal display element. It is something to do. At this time, for STN with a liquid crystal orientation angle (liquid crystal twist angle) of 200° to 270°,
±70゜<α＋β±110', ±70゜〈θ〉±11
0@ (clockwise is positive), and Rl (d・
Δn) and the retardation R of the retardation plate, as lR1 R
It is set to tl≦0.2um.

However, θ is the angle between the optical axis of the retardation plate and the coaxial axis of the STN liquid crystal on the second glass substrate disposed opposite to the retardation plate. α is the STN in the first glass substrate
An angle formed between a liquid crystal alignment axis and a first polarizing plate disposed facing the first glass substrate. β is an angle between the coaxial alignment of the STN liquid crystal on the second glass substrate and a second polarizing plate disposed facing the second glass substrate via a retardation plate.

Examples of the retardation plate in the present invention include a stretched organic film having an axial property and preferably having a thickness of 50 to 200 μm by stretching a polymer compound such as polycarbonate or polyvinyl alcohol. The retardation R, of the retardation plate is defined by the stretched organic film, and the value of R is controlled by the difference in the stretching ratio (stretching rate) in the longitudinal direction and the transverse direction.

Super twisted nematic (S) in this invention
TN) Liquid crystals include cyclohexane type, ester type,
Among well-known nematic liquid crystals such as biphenyl-based and pyridimine-based liquid crystals, chiral agents are added, thereby changing the molecular axis of the liquid crystal molecules from 200 to 27.
04, preferably twisted at an angle of 240@ between the upper and lower glass substrates. In this case, cholestepric nonanoate is used as a typical levorotatory chiral dopant, and it is added to the nematic liquid crystal in a range of 1.2 wt% to 1.91% for a liquid crystal cell with a cell thickness of 7.5 μm. As a result, the liquid crystal twist angle φ can be controlled to 200°, φ, and 270°.

And STN's R. is defined by the product d×Δn of the cell thickness d and the refractive index anisotropy Δn of the nematic liquid crystal, and since each nematic liquid crystal has a different refractive index anisotropy, R,
varies depending on each nematic liquid crystal used.

In this invention, R. , R, can be controlled as described above, and lR. -R. R. so that l≦0.2μm is satisfied. ,R, are set.

(e) Operation In an LCD equipped with a retardation plate for color compensation of colored light generated in the STN liquid crystal layer, ■ the orientation angle of STH (
When the liquid crystal twist angle) φ is 200 degrees and φ <270'', the relationship between R l of the STN (d x Δnod is the cell thickness, Δn is the refractive index anisotropy) and the retardation plate R, is Set lR.-R.l≦0.2μm, ■+700
<θ< + 110°, or -110° θ< -T
O', +70° α+β<+110''', or -110° α+β<-70' (where θ is the optical axis in the retardation plate and the second glass disposed opposite the retardation plate) Angle formed with the STN liquid crystal alignment axis in the substrate.α is the ST in the first glass substrate
An angle between the N liquid crystal alignment axis and the first polarizing plate disposed facing the first glass substrate. Since β is set to the angle formed by the STN liquid crystal alignment axis on the second glass substrate and the second polarizing plate disposed facing the second glass substrate through the retardation plate, the retardation plate has the same effect as the compensation temporary as a non-voltage side panel when using a two-layer STN, and as a result, it can be made lighter and thinner than an LCD using a two-layer STN. Type ST
It is possible to prevent coloring to yellow-green and improve color compensation of colored light generated in STN compared to an LCD using N.
Good normally black black and white display can be obtained.

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

Figure 1 shows a double matrix type LCD, and Figure 2 shows an L
It is a figure for explaining each predetermined angle in CD.

In FIG. 1, reference numeral 1.2 denotes a pair of lower and upper glass substrates that are arranged opposite to each other, and these two sheets are bonded together with a sealing material 12 interposed therebetween.

The inner surfaces of the glass substrates 1.2 are each coated with, for example, an IT
A transparent electrode (not shown) made of an O film (transparent conductive film) is formed, and a rubbed alignment film (not shown) is formed on each glass substrate 1.2 so as to cover each transparent electrode. ) is attached. The liquid crystal twist angle φ formed by the alignment axes 1a, 2& on each alignment film is 200
In this example, 1.6 wt% of cholesteric nonanoate, which is a levorotatory chiral dopant, was added to the nematic liquid crystal described later, and
Obtain an STN liquid product with a 40° twist. That is, the STN liquid crystal layer 3 consists of the nematic liquid crystal filled in the space between the glass substrates 1.2 and a chiral agent added thereto, thereby aligning the alignment axes 1a. 2
S T N twisted in a spiral as defined by a
It is filled with liquid crystal.

The STN liquid crystal used in this example has a transfer point (T,1,) of 8
It can be stored at 5°C, -25°C to 60°C, and the refractive index anisotropy Δn at room temperature is 0. It is a night item material with a value of 123.

Further, in this embodiment, the thickness d of the liquid crystal layer 3 is 7.5
.mu.m, the product .DELTA.nXd of the refractive index anisotropy .DELTA.n and the thickness d of the liquid crystal layer is set to 0.92 .mu.m.

4 is a retardation plate, which is a uniaxial polymer film of polycarbonate stretched to a thickness of 100 μm by a known method. This is arranged on the outer upper surface of the glass substrate 2, and the retardation R is set according to the thickness.

That is, in the present invention, ΔnXd and R are set so as to satisfy the range of 1ΔQXd−Rl≦0.2 μm.

In this example, a polycarbonate film having a retardation layer of R-800 nm was used.

As a result, the angle θ between the retardation absorption axis (stretching direction) 4a and the liquid crystal alignment axis 2a in the upper glass substrate is set, and in the case of levorotatory liquid products, +70°<θ<+110@ is preferable, and in the case of dextrorotatory liquid crystals, the angle θ is set. -110@<θ>-10' is preferred. In this embodiment, θ is set to +85°.

Further, polarizing plates 5.6 are disposed on the upper surface of the retardation plate 4 and the lower surface of the glass substrate 1, respectively. The polarizing plate used is, for example, RANO, which has a single transmittance of 42% and a polarization degree of 99.99%.

At this time, the angle β formed by the liquid crystal alignment axis 2a in the upper glass substrate 2 and the absorption axis 5 in the upper polarizing plate 5,
The sum β+α of the angle α formed by the liquid crystal alignment axis 1a in the lower glass substrate it and the absorption axis 6a in the lower polarizing plate 6 is +70"<β+α+llO゜.-ILQ"<
It is preferable to set β+a<-70', and in this embodiment, β=35°, α=45°, and β+α=80°.
It was set to 0.

On the other hand, 7 is a cold cathode fluorescent lamp as a backlight.
This means that its emission spectrum has an X component of 0.34<X
<0.36+. :, Y component (1.38<Y<
It is preferable to set the value to 0.40, and in this embodiment,
=0.3448 and Y=0.3901 were used.

In the above configuration, when the LCD is driven at l/200 duty, the colored light generated by the STN can be completely corrected, and the contrast when lit directly above the device is colored yellow-green. It should be possible to obtain a sufficient black/white display with sufficient prevention and sufficient background blackness.

FIG. 3 shows the chromaticity retention in this example.

That is, the chromaticity is the chromaticness index a', b
Represented by the value of a book. In FIG. 3, when the effective voltage value of the selected point is changed as a parameter, the hue at ON and OFF'F is 2. l5V, 2.03
It appears near V, and it is possible to obtain a display with a small color change. In addition, a'x. The closer the wood gets to O, the more achromatic the color becomes.

Further, FIG. 4 shows the brightness index characteristics in this example.

That is, it can be seen that the value of LX indicates the lightness index, and the lightness index increases in value as the effective value within the voltage character increases.

(g) Effects of the Invention As described above, according to the present invention, in an LCD equipped with a retardation plate for color compensation of colored light generated in the STN liquid layer,
In the range of 200° (nocturnal twist angle) and φ<270°, the relationship between R+ of STN (dxΔn: d is cell thickness, Δn is refractive index) and retardation R of the retardation plate is expressed as lR,
Set Rtl≦0.2μm, ■+70°<φ<+tt
o", or -110° and θ<-70°, +70°<α+β<+110°-llO°, or -1
10゜α+β<-70''' (where θ is the angle between the optical axis in the retardation plate and the STN liquid crystal alignment coax on the second glass substrate disposed opposite to the retardation plate. α is , ST in the first glass substrate
An angle between the N liquid crystal alignment axis and the first polarizing plate disposed facing the first glass substrate. Since β is set to the angle between the STNt & crystal orientation axis in the second glass substrate and the second polarizing plate disposed facing the second glass substrate via the retardation plate, the retardation plate has the same effect as the compensation temporary panel on the non-voltage side panel when using a two-layer STN, and as a result, it can be made lighter and thinner than an LCD using a two-layer STN. Type S
Compared to LCDs using TN, it is possible to prevent yellow-green coloration, improve color compensation of colored light generated in STN, and have the effect of obtaining bright and clear white/black display.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing one embodiment of the present invention, FIG. 2 is an explanatory diagram for explaining each predetermined angle in the above embodiment, and FIGS. 3 and 4 are color changes in the above embodiment, respectively. Characteristic diagrams showing characteristics and brightness characteristics, and FIGS. 5 and 6 are configuration explanatory diagrams showing conventional examples, respectively. 1...Lower glass substrate, 2...Upper glass substrate, 3...Super twisted nematic liquid crystal layer, 4...Retardation plate, 5... ...Upper polarizing plate, 6...Lower polarizing plate, 7...Backlight. Figure 3 Figure 1 Figure 2 Figure 4 Voltage (V) Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. A pair of first and second glass substrates facing each other, a liquid crystal layer sandwiched between these glass substrates and made of super twisted nematic liquid crystal, and the first and second glass substrates. first and second polarizing plates disposed facing each other on opposite sides to the side on which the liquid crystal layer is located;
A backlight is inserted between the second polarizing plate and the second glass substrate, and the backlight is disposed on the side opposite to the side where the liquid crystal layer is located with respect to the first polarizing plate facing the first glass substrate. , and a retardation plate for color compensation of colored light generated in the liquid crystal layer by irradiation from the backlight, and the super twisted nematic liquid crystal has a liquid crystal twist angle φ of 200°≦φ≦270°. , and the product of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer (Δn×d=R_1) and the retardation R_2 of the phase difference are set to |R_1−R_2|≦0.2 μm Furthermore, the optical axis of the retardation plate (stretching direction)
and the liquid crystal orientation axis in the second glass substrate, the angle θ is +70°<θ<+110° (in the case of levorotatory liquid crystal) -11
0°<θ<-70° (in the case of a dextrorotatory liquid crystal), and the first and second polarizing plates are arranged so that the alignment axis of the liquid crystal in the second glass substrate and the absorption axis in the second polarizing plate form The sum of the angle β and the angle α formed by the liquid crystal alignment axis in the first glass substrate and the absorption axis in the first polarizing plate is set to −70°<α+β<+110° −110°<α+β<−70°. A liquid crystal display device featuring: