JP2945573B2 - 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 super twisted nematic type (hereinafter referred to as STN type) liquid crystal display device provided with a retardation plate as an optical compensator.

[0002]

2. Description of the Related Art As a prior art, in a reflection type STN type liquid crystal display device provided with a retardation plate as an optical compensator, a single layer having a retardation value of about 560 nm is provided on the display surface side of the liquid crystal display element. And only one retardation plate composed of the retardation layers of the above. The product d · Δn of the liquid crystal layer thickness d and the refractive index anisotropy Δn of the liquid crystal display element was 0.75 to 0.85 μm.

[0003]

However, in the above-mentioned conventional liquid crystal display device, complete color correction is not performed, and white, which is the background color when no voltage is applied, is colored, and a sharp black-and-white display cannot be obtained. In addition, there are problems such as a large change in the color tone with respect to the temperature change in the use environment, a stable contrast cannot be obtained with respect to the temperature change, and a large change in the color tone with respect to the variation in the thickness of the liquid crystal display element and the retardation value of the retardation plate. Was.

Further, the inventors have disclosed in Japanese Patent Application No. Hei 4-91230 a first polarizing plate, a first retardation plate, a second retardation plate,
In a liquid crystal display device in which a liquid crystal display element having a super twisted nematic liquid crystal interposed between a pair of translucent substrates, a second polarizing plate, and a reflector for reflecting incident light from the liquid crystal display element are stacked in this order, The retardation values of the first and second retardation plates are both 400 nm to 470.
nm, the intersection angle between the slow axis of the first retardation plate and the slow axis of the second retardation plate is 35 to 55 degrees, the liquid crystal layer thickness d of the liquid crystal display element, the refractive index anisotropy Δn, The product d · Δn of 0.8
There has been a proposal to solve the above-mentioned drawbacks of the conventional liquid crystal display device by setting it to 0 to 0.94, but it cannot be said that the change in color tone when no voltage is applied with respect to a change in environmental temperature is not sufficient.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a liquid crystal display device capable of obtaining a sharp and stable black-and-white display with a small change in color tone with respect to a change in environmental temperature and a stable contrast. That is.

[0006]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal display device having a super-twisted nematic liquid crystal interposed between a pair of translucent substrates, and one polarizing plate disposed on each side of the liquid crystal display device. Two phase difference plates laminated between the polarizing plate and one of the upper surface and the lower surface of the liquid crystal display element; and a reflection plate for reflecting incident light from the liquid crystal display element. And the retardation values of the two retardation plates are both 400 nm to 470 nm, and the intersection angle of the slow axes of the two retardation plates is 35 ° to 55 °. The twist angle of the liquid crystal molecules of the liquid crystal display device is 240 to 260 degrees, the liquid crystal layer thickness d of the liquid crystal display device and the refractive index anisotropy Δ
The product d · Δn with n is 0.80 to 0.94 μm, and the liquid crystal layer has an amount of linear change in a threshold voltage at an ambient temperature of 0 ° C. to 50 ° C. of 5 mV / ° C. or less. Characterized by containing a four-ring compound of

Further, the present invention is characterized in that the above-mentioned linear four-ring compound comprises a benzene ring or a cyclohexane ring.

Further, the present invention is characterized in that the amount of the tetracyclic compound is at least 3% by weight or more based on the composition ratio of the liquid crystal compound forming the liquid crystal layer.

[0009]

According to the present invention, the retardation values of the first and second phase difference plates, the slow axis of the first phase difference plate and the second
The angle of intersection with the slow axis of the retardation plate, the twist angle of the liquid crystal molecules, the d · Δn of the liquid crystal display element are optimized, and the composition ratio of the liquid crystal compound forming the liquid crystal layer is further reduced from the benzene ring or the cyclohexane ring. Is set so as to contain at least 3% by weight or more of the following linear four-ring compound, so that the temperature change rate dV / dT of the threshold voltage Vth at an environmental temperature of 0 ° C. to 50 ° C. is 5 mV / ° C. or less. Therefore, in a super twisted nematic liquid crystal display device, it is possible to display with little change in color tone when no voltage is applied with respect to a change in environmental temperature, to achieve an achromatic color, to achieve stable black-and-white display, and to further change the temperature. , A stable contrast can be obtained.

In general, in a liquid crystal display device, the retardation value of the phase difference plate, the angle of intersection of the slow axes of the phase difference plate, the twist angle of the liquid crystal molecules, and d · Δn of the liquid crystal display element are related to each other. However, if any one of them is out of this range, stable black-and-white display cannot be obtained, resulting in a problem that coloring of a color tone when no voltage is applied becomes large. The present invention is to provide an optimum arrangement condition for solving the above problem.

[0011]

FIG. 1 is a sectional view showing the structure of a liquid crystal display device 1 according to one embodiment of the present invention. The liquid crystal display device 1 has a first
A polarizing plate 2, a first retardation plate 3, a second retardation plate 4, a liquid crystal display element 5, a second polarizing plate 6, and a reflecting plate 7 for reflecting incident light from the liquid crystal display element 5 are laminated in this order. It is composed. The first polarizing plate 2 and the second polarizing plate 6 have a single transmittance of 4
A neutral gray type polarizing plate having 4.4% and a polarization degree of 97.8% is used. For example, Nitto Denko F
1225 DUN (trade name) is used. Each of the first retardation plate 3 and the second retardation plate 4 is made of a single-layer uniaxially stretched polymer film such as polycarbonate, and has a thickness of 50%.
μm and a retardation value of 430 μm. The crossing angle of the slow axis of each retarder is 35 degrees to 5 degrees.
Set to 5 degrees.

The liquid crystal display element 5 includes electrodes 10 and 11 made of ITO (indium tin oxide) and polyimide on the opposing surfaces of a pair of light-transmitting substrates 8 and 9 made of glass, plastic or the like. Alignment films 12 and 13 are formed, and liquid crystal 14 to which a levorotary chiral substance is added is sealed between these translucent substrates 8 and 9. The twist angle of the liquid crystal molecules is 240 degrees, and d · Δn
(D is the thickness of the liquid crystal layer 14, and Δn is the refractive index anisotropy of the liquid crystal 14.) = 0.84 μm. The electrode formation pattern may be any of a segment type, a simple matrix type, and an active matrix type.

The reflection plate 7 is a non-directional reflection plate, and is formed by forming a reflection film 16 made of aluminum or the like on the surface of the synthetic resin substrate 15 on the liquid crystal display element 5 side.

FIG. 2 is a diagram showing an arrangement condition of each component of the liquid crystal display device 1. In FIG. 2, an arrow P1 indicates a liquid crystal molecule alignment axis of the light transmitting substrate 8 forming the liquid crystal display element 5, and an arrow P2 indicates a light transmitting substrate 9 forming the liquid crystal display element 5.
, The arrow P3 indicates the absorption axis of the first polarizing plate, the arrow P4 indicates the absorption axis of the second polarizing plate 6, the arrow P5 indicates the slow axis of the first retardation plate 3, and the arrow P6 indicates The slow axis of the second retardation plate 4 is shown. The angle α is the angle between the liquid crystal molecule alignment axis P1 of the light transmitting substrate 8 and the absorption axis P3 of the first polarizing plate 2, and the angle β is the liquid crystal molecule alignment axis P2 of the light transmitting substrate 9.
And the angle γ is the angle between the liquid crystal molecule alignment axis P1 of the translucent substrate 8 and the slow axis P5 of the first retardation plate 3, and the angle θ Represents the angle formed between the liquid crystal molecule alignment axis P1 of the light transmitting substrate 8 and the slow axis P6 of the second retardation plate 4, and the angle φ represents the twist angle of the liquid crystal molecules.

In the embodiment of the present invention, α = 45 degrees and β = 5
0 degree, γ = 115 degrees, θ = 70 degrees, and φ = 240 degrees. Therefore, the slow axis P5 of the first retardation plate 3
The intersection angle (γ-γ) between the second phase difference plate 4 and the slow axis P6.
θ) is 45 degrees.

Here, the color change when no voltage is applied is represented by a temperature change rate dV at an environmental temperature of 0.degree.
/ DT tends to increase as the ratio increases, and in practice, d
It is said that V / dT should be 5 mV / ° C. or less.

(Equation 1) dV / dT = [Vth (0 ° C.) − Vth (50 ° C.)] / (50 ° C.-0 ° C.) where Vth (0 ° C.) and Vth (50 ° C.) are 0 And the threshold voltage Vth at 50 ° C.

Therefore, how to make dV / dT 5 mV /
As a result of examining whether the temperature can be lowered below ℃, the liquid crystal layer injected with super twisted nematic liquid crystal has
For example, it was found that a linear four-ring compound consisting of a benzene ring or a cyclohexane ring may be added.

FIG. 3 shows the relationship between the amount of the four-ring compound and the dV / dT. From the figure, it can be seen that the amount of the four-ring compound added to the composition ratio of the liquid crystal compound forming the liquid crystal layer. Is added at least 3% by weight, dV / dT is 5 m
It can be seen that V / ° C. or less can be achieved.

Therefore, in the present embodiment, two examples, namely, specific example 1 in which the 4-ring compound was added at 5 wt% and specific example 2 in which 10 wt% was added, were prepared. And characteristics were compared.

Table 1 shows that the threshold voltages Vth at the ambient temperature of 0 ° C. and 50 ° C. and the ambient temperature of 0 ° C. to 50 ° C. for the liquid crystal display devices of the first and second examples and the liquid crystal display device of the comparative example.
The temperature change rate dV / dT at 50 ° C. and the content ratio of the 4-ring compound of the liquid crystal material are shown.

[0022]

[Table 1]

Chromaticity L *, a *, b * when no voltage is applied at an environmental temperature of 0 ° C. and 50 ° C .;
Table 2 shows the color difference ΔE * at ° C. by comparing the liquid crystal display devices of the specific examples 1 and 2 with the liquid crystal display device of the comparative example.

[0024]

[Table 2]

Next, the a * and b * chromaticity diagrams showing the chromaticity change at an ambient temperature of 0 ° C. to 50 ° C. are compared between the liquid crystal display devices of the first and second embodiments and the liquid crystal display device of the comparative example. Fig. 4
Shown in In FIG. 4, the solid line 17 shows the chromaticity change when no voltage is applied at the environmental temperature of 0 ° C. to 50 ° C. in the specific example 1. The dashed line 18 indicates the chromaticity change when no voltage is applied at the environmental temperature of 0 ° C. to 50 ° C. in the specific example 2. An alternate long and short dash line 19 indicates a change in chromaticity when no voltage is applied at an environmental temperature of 0 ° C to 50 ° C in the comparative example.

Here, chromaticity L *, a *, b *, color difference ΔE
* Means CIE1976L * a * b * color system (JIS
Z8729- (1980)) is a uniform perceived color space, and is defined by the following equation.

(Equation 2) L * = 116 (Y / Yo) ^1/3 -16 (Equation 3) a * = 500 [(X / Xo) ¹ /3-(Y / Yo) ^1/3 ] (Equation 2) 4) b * = 200 [( Y / Yo) 1/3 - (Z / Zo) 1/3] ( equation 5) ΔE * = (ΔL * 2 + Δa * 2 + Δb * 2) 1/2 here, Xo , Yo, and Zo are tristimulus values of standard light used for illumination, X, Y, and Z are tristimulus values of the target object, L * is lightness, and a * and b * are chroma. The amount to represent.

As described above, in Examples 1 and 2, the change in chromaticity with respect to the ambient temperature is smaller than that in the comparative example, and the change occurs near an achromatic color (a * = b * = 0). .

In the embodiment, a first polarizing plate, two retardation plates, a liquid crystal display device having a super-twisted nematic liquid crystal interposed between a pair of translucent substrates, and a reflection device for reflecting incident light from the liquid crystal display device Although the liquid crystal display device in which the plates are stacked in this order has been described, the liquid crystal display device in which the first polarizing plate, the liquid crystal display element, the two retardation plates, the second polarizing plate, and the reflecting plate are stacked in this order is also applicable. The same can be said above.

[0030]

As described above, according to the present invention, in a reflection type super twisted nematic type liquid crystal display device, a change in color tone when no voltage is applied to a change in environmental temperature is reduced, and the color tone is close to an achromatic color. Accordingly, it is possible to provide a liquid crystal display device that realizes uniform and stable black and white display and high contrast.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display device according to the present invention.

FIG. 2 is a diagram showing conditions for disposing each component of the liquid crystal display device according to the present invention.

FIG. 3 shows an ambient temperature of 0 ° C. to 5 ° C. of the liquid crystal display device according to the present invention.
Temperature change rate dV / d of threshold voltage Vth at 0 ° C.
It is a figure which shows the relationship between T and the content rate of a linear 4-ring compound.

FIG. 4 is a diagram showing a chromaticity change of the liquid crystal display device according to the present invention and a comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 1st polarizing plate 3 1st phase difference plate 4 2nd phase difference plate 5 Liquid crystal display element 6 2nd polarizing plate 7 Reflection plate 8, 9 Transparent substrate 10, 11 Electrode 12, 13 Alignment film 14 Liquid crystal 17 Chromaticity change with respect to environmental temperature change in Example 1 18 Chromaticity change with respect to environmental temperature change in Example 2 19 Chromaticity change with respect to environmental temperature change in Comparative Example P1 Liquid crystal molecule orientation axis of light-transmitting substrate 8 P2 Light-transmitting Liquid crystal molecule orientation axis of the transparent substrate 9 P3 absorption axis of the first polarizing plate P4 absorption axis of the second polarizing plate P5 slow axis of the first retardation plate P6 slow axis of the second retardation plate α liquid crystal molecule orientation axis P1 The angle between the liquid crystal molecule alignment axis P2 and the absorption axis P4, the angle between the liquid crystal molecule alignment axis P2 and the absorption axis P4, and the slow axis P5 of the first retardation plate 4.
The liquid crystal molecule alignment axis P1 and the slow axis P6 of the second retardation plate 4
Φ Angle of twist of liquid crystal molecules

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/133 500 G02F 1/13 500 G02F 1/1335 G02F 1/1335 510 G02F 1/139

Claims (3)

(57) [Claims] 1. A liquid crystal display device having a super-twisted nematic liquid crystal interposed between a pair of translucent substrates, one polarizing plate disposed on both sides of the liquid crystal display device, and an upper surface of the liquid crystal display device A liquid crystal comprising: two retardation plates laminated between the polarizing plate and either one of the surfaces on the lower surface side or the lower surface side; and a reflector that reflects incident light from the liquid crystal display element. In the display device, the retardation values of the two retardation plates may both be 400 nm to 4 nm.
70 nm, the intersection angle of the two retardation plates with the slow axis is 35 to 55 degrees, the twist angle of the liquid crystal molecules of the liquid crystal display element is 240 to 260 degrees, and the liquid crystal of the liquid crystal display element is The product d · Δn of the layer thickness d and the refractive index anisotropy Δn is set to 0.
80 to 0.94 μm, and the liquid crystal layer has an ambient temperature of 0 ° C.
The temperature change rate of the threshold voltage at ~ 50 ° C is 5 mV /
A liquid crystal display device comprising a linear four-ring compound in an amount of not more than ° C. 2. The liquid crystal display device according to claim 1, wherein the linear four-ring compound comprises a benzene ring or a cyclohexane ring. 3. The liquid crystal display device according to claim 1, wherein the amount of the tetracyclic compound added is at least 3% by weight or more in a composition ratio of the liquid crystal compound forming the liquid crystal layer.