JP2796212B2 - 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 In a reflection type STN type liquid crystal display device provided with a phase difference plate as an optical compensator, a phase difference of one layer having a retardation value of about 560 nm is provided on the front side (display surface) side of the liquid crystal display element. Only one retardation plate composed of layers is provided, and d · Δn of the liquid crystal display element is 0.75 to 0.85.
It is. d is the thickness of the liquid crystal layer between the liquid crystal display element substrates, and Δn is the refractive index anisotropy of the liquid crystal display element.

[0003]

However, in the liquid crystal display device according to the above-described configuration and arrangement conditions, complete color correction is not performed, and the white color, which is the background color when no voltage is applied, is colored. Cannot be obtained, a large change in color tone due to temperature changes in the use environment, a stable contrast cannot be obtained with temperature changes, a large change in color tone with respect to variations in the thickness of the liquid crystal display element and retardation values of the retardation plate, and the like. Have a problem.

An object of the present invention is to provide a liquid crystal display device which can solve the above-mentioned problems and can obtain sharp and stable black-and-white display and stable contrast.

[0005]

SUMMARY OF THE INVENTION The present invention provides a first polarizing plate,
A first retardation plate, a second retardation plate, a liquid crystal display element having a super-twisted nematic liquid crystal interposed between a pair of translucent substrates, a second polarizer, and a reflector for reflecting incident light from the liquid crystal display element Are laminated in this order, the retardation values of the first and second retardation plates are both 400 nm to 470 nm, and the slow axis of the first retardation plate and the second retardation The angle of intersection with the slow axis of the plate is set at 35 to 55 degrees, and the product d · Δ of the liquid crystal layer thickness d of the liquid crystal display element and the refractive index anisotropy Δn.
A liquid crystal display device wherein n is set to 0.80 to 0.94.

[0006]

According to the present invention, the retardation values of the first and second retardation plates, the crossing angles of the slow axes of the first and second retardation plates, and d · Δn of the liquid crystal display element are optimized. As a result, in a super twisted nematic liquid crystal display device, the color tone of the background color when no voltage is applied can be made brighter and closer to achromatic, and a stable black-and-white display can be realized. Can be obtained. In general, in a liquid crystal display device, the retardation value of the phase difference plate, the intersection angle of the slow axis of the phase difference plate, and d · Δn of the liquid crystal display element work in relation to each other, and even one of them works in advance. If the value is out of the predetermined range, stable black and white display cannot be obtained, and the background color is colored and the display color does not become black. The present invention provides optimum installation conditions for solving these problems.

[0007]

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 is configured by laminating a first polarizer 2, a first retarder 3, a second retarder 4, a liquid crystal display element 5, a second polarizer 6, and a reflector 7 in this order. You. The first and second polarizing plates 2 and 6 are:
A neutral gray type polarizing plate having a single transmittance of 44.5% and a degree of polarization of 97.8% is used. For example, F-1205 DuN (trade name) manufactured by Nitto Denko Corporation is used.
The first and second retardation plates 3 and 4 are each composed of a single-layer uniaxially stretched polymer film such as polycarbonate.
The thickness is about 50 μm, and the retardation value is 400
nm to 470 nm. The crossing angle of the slow axis of each retardation plate is set to 35 degrees to 55 degrees.

The liquid crystal display element 5 comprises electrodes 10 and 11 made of ITO (indium tin oxide) and polyimide on the opposing surfaces of a pair of translucent 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) = 0.80 to 0.94. The electrode formation pattern is segment type, simple matrix type,
Any active matrix type may be used.

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 formed 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.
The angle β is the angle between the liquid crystal molecule alignment axis P2 of the light transmitting substrate 9 and the absorption axis P4 of the second polarizing plate 6, and the angle γ is the angle between the liquid crystal molecule alignment axis P1 of the light transmitting substrate 8 and the first retardation plate. 3 slow axis P5
Is the angle between the liquid crystal molecule alignment axis P1 of the translucent substrate 8 and the slow axis P6 of the second retardation plate 4,
The angle φ indicates the twist angle of the liquid crystal molecules.

In this embodiment, α = 45 degrees, β = 50 degrees,
γ = 115 degrees, θ = 70 degrees, and φ = 240 degrees. Therefore, the angle (= γ−θ) between the slow axis P5 and the slow axis P6 is 45 degrees.

FIGS. 3 and 4 are graphs showing measurement results of the viewing angle characteristics of the liquid crystal display device 1. FIG. FIG. 3 shows the viewing angle characteristics of the liquid crystal display device in the direction of 12: 00-6: 00, and FIG.
Indicates viewing angle characteristics of the liquid crystal display device in the direction of 9: 00-3: 00. The viewing angle characteristic is a change in contrast with a change in viewing angle. The viewing angle is the inclination angle of the line of sight from the normal direction of the display surface of the display device. In FIG. 3, a solid line L1 shows the viewing angle characteristics of the liquid crystal display device 1, and a broken line L2 shows the viewing angle characteristics of the conventional liquid crystal display device. In FIG. 4, a solid line L3
Indicates the viewing angle characteristic of the liquid crystal display device 1, and the broken line L4 indicates the viewing angle characteristic of the conventional liquid crystal display device. The liquid crystal display device has a measurement environment temperature Ta = 25 ° C., a duty of 1/200,
Driven at a / 13 bias.

As can be seen from FIGS. 3 and 4, the liquid crystal display device 1 of the present embodiment has very good contrast and good viewing angle characteristics as compared with the conventional liquid crystal display device.

Table 1 below shows the results of comparison of the brightness of the background color between the liquid crystal display devices of this embodiment and the prior art.

[0016]

[Table 1]

Here, the brightness of the background color (L *) is defined as CI
E1976L * a * b * display system (JIS Z8729-
(1980)) is a uniform perceived color space and is defined by the following equation.

[0018]

L * = 116 (Y / Yo) ^1/3 -16

[0019]

A * = 500 [(X / Xo) ^1/3 − (Y / Yo) ^1/3 ]

[0020]

B * = 200 [(Y / Yo) ^1/3 − (Z / Zo) ^1/3 ] 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, and L * is a quantity representing lightness.

As described above, the liquid crystal display device 1 of the present embodiment
It can be seen that the lightness is higher and the background color is brighter than the conventional liquid crystal display device. That is, sharp black and white display is obtained.

In this embodiment, two retardation plates each composed of one retardation layer are laminated, but one retardation plate composed of two retardation layers may be used.

[0023]

As described above, according to the present invention, in a reflection type super twisted nematic liquid crystal display device, the white color tone, which is the background color when no voltage is applied, is rendered achromatic. It is possible to provide a liquid crystal display device realizing a certain 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 1 according to an embodiment of the present invention.

FIG. 2 is a diagram showing conditions for disposing each component of the liquid crystal display device 1;

FIG. 3 is a graph showing measurement results of viewing angle characteristics of the liquid crystal display device 1.

FIG. 4 is a graph showing measurement results of viewing angle characteristics of the liquid crystal display device 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 1st polarizing plate 3 1st retardation plate 4 2nd retardation plate 5 Liquid crystal display element 6 2nd polarizing plate 7 Reflecting plate 8, 9 Translucent substrate 10, 11 Electrode 12, 13 Alignment film 14 Liquid crystal P1 Liquid crystal molecule alignment axis of light-transmitting substrate 8 P2 Liquid crystal molecule alignment axis of light-transmitting substrate 9 P3 Absorption axis of first polarizer P4 Absorption axis of second polarizer P5 Slow axis of first retardation plate P6 Slow axis of second retardation plate α Angle between liquid crystal molecule orientation axis P1 and absorption axis P3 β Angle between liquid crystal molecule orientation axis P2 and absorption axis P4 γ Liquid crystal molecule orientation axis P1 and first retardation plate 4 Slow axis P5
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

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-304422 (JP, A) JP-A-2-47625 (JP, A) JP-A-3-51414 (JP, U) (58) Field (Int.Cl. ⁶ , DB name) G02F 1/1335 510

Claims (1)

(57) [Claims] 1. A first polarizing plate, a first retardation plate, a second retardation plate, a liquid crystal display element having a super twisted nematic liquid crystal interposed between a pair of translucent substrates, a second polarizing plate, and the liquid crystal display. In a liquid crystal display device configured by laminating reflectors that reflect incident light from an element in this order, the first and second retardation plates each have a retardation value of 400 nm to 470 nm, and the first retardation plate The intersection angle between the slow axis of the second phase difference plate and the slow axis of the second retardation plate is set to 35 degrees to 55 degrees, and the product d · of the liquid crystal layer thickness d of the liquid crystal display element and the refractive index anisotropy Δn is set. A liquid crystal display device wherein Δn is set to 0.80 to 0.94.