JPH0293622A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To allow black and white display which eliminates a background color by providing double refractiveness to a light transparent film. CONSTITUTION:This display device includes the light transparent film 8 and isotropic film 2 which crimp a liquid crystal layer 7 and are formed with electrodes 3a, 3b on the opposite surfaces and polarizing members. The film 8 has the double refractiveness. Namely, liquid crystal molecules are arranged in a light transmission direction when a voltage is impressed between the electrodes 3a and 3b and, therefore, the layer 7 allows the transmission of the elliptically polarized light from the film 8. This elliptically polarized light is made incident on a polarizing plate 1b. Since the axes of polarization of the polarizing plates 1a, 1b are shifted from each other, the incident light by the polarizing plate 1b is shut off and the black display is executed. The elliptically polarized light from the film 8 is twisted in the oscillation direction thereof by a prescribed angle in the layer 7 and is double-refracted, by which the light is converted to linearly polarized light when a voltage is not impressed. The linearly polarized light is outputted via the polarizing plate 1a to an arrow P2 direction. The black and white display having no background color is thus executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to, for example, super twisted nematic (
The present invention relates to a film-like liquid crystal display device in a mode called LJ, rsTNJ).

2. Description of the Related Art Liquid crystal display devices are used in a wide range of fields, including watches, calculators, computer terminals, word processor displays, and televisions. More recently,
There is a great demand for multi-color and full-color liquid crystal display devices, and they have already been put into practical use in the fields of graphic displays and image displays. Color display, which is currently in widespread practical use, is a method in which a color filter layer is provided inside a liquid crystal cell and light is switched by the liquid crystal cell to produce each color. The display mode at this time is twisted nematic, in which the axial direction of the liquid crystal molecules is twisted 90 degrees for contrast etc.
e+natic (hereinafter abbreviated as "TN") mode liquid crystal display devices are mainstream.

In addition, as the display area of liquid crystal display devices becomes larger and the number of display pixels increases, the contrast ratio between display and non-display (
The claw device has come to be used in the STN mode, which has an excellent ratio of the amount of transmitted light per unit area when voltage is applied and when no voltage is applied.

In an STN mode liquid crystal display device, the twist angle of liquid crystal molecules in the liquid crystal layer is set to 180 to 270 degrees, and the light transmittance changes sharply near the threshold of the applied voltage. Therefore, a high contrast ratio can be obtained even when the number of transparent electrodes is increased and high time division driving is performed.

Furthermore, film-like liquid crystal display panels are used in IC cards, watches, calculators, electronic memos, and the like, which have appropriate flexibility, excellent breakage resistance, and can be manufactured to be ultra-thin. A film-like liquid crystal display panel is made of an organic polymer material such as polycarbonate or polyether sulfonate, and is made of an IFJ3? A pair of optically isotropic films are used. A transparent electrode and an alignment film are formed on one side of the optically isotropic film, and this alignment film is subjected to an alignment treatment. After such a pair of films are pasted together with the alignment films facing each other, liquid crystal is sealed in the gap between them, and in this way, a film-like liquid crystal panel is manufactured.

Problems to be Solved by the Invention In the above-mentioned STN mode liquid crystal display device, in the non-display state, that is, when no voltage is applied, the display panel exhibits a yellow or green tone due to the birefringence effect in the liquid crystal layer. There is a problem that the background color appears. Particularly in film-type liquid crystal display devices, there is a problem in that subtle changes in the thickness of the liquid crystal layer change the tone of the background color, resulting in non-uniformity in the tone of the entire screen. Furthermore, since the background color is yellow or green, it is extremely difficult to perform color display. Moreover, in the field 6 where color display is performed, red, green, and blue filters are usually placed inside the liquid crystal cell, so a chemical reaction may occur between the liquid crystal and the filter, causing the liquid crystal to deteriorate. Unable to obtain stable display.

An object of the present invention is to provide a film-like liquid crystal display device that solves the above technical problems, improves the contrast ratio, has no display unevenness within the display area, and can easily perform color display. be.

Means for Solving the Problems The present invention involves sealing a liquid crystal between a pair of translucent films each having electrodes formed on their mutually opposing surfaces.
A liquid crystal display device in which 14 optical members are laminated on the side opposite to the liquid crystal layer of the light-transmitting filter, wherein the light-transmitting film on at least one side is made of a birefringent film. It is a display device.

Function In the present invention, a liquid crystal display device includes a pair of transparent films sandwiching a liquid crystal layer and having electrodes formed on opposing surfaces, and a pair of transparent films 11 laminated on the surface opposite to the liquid crystal layer. It includes a light-opening member and a pair of translucent films! , at least one of them has birefringence.

According to the present invention, the incident light is made into linearly polarized light by the polarizing member. This linearly polarized light is converted into elliptically polarized light by a liquid crystal layer, or into elliptically polarized light by a transparent film having birefringence. This elliptically polarized light is converted into linearly polarized light by a birefringent transparent film or liquid crystal layer. Therefore, changes in display hue caused by birefringence in the liquid crystal layer can be suppressed by using a transparent film with birefringence.
f2L-1 Stable black and white display can be performed. This makes it possible to eliminate undesirable background colors in the non-display state. Further, the wavelength dependence of transmitted light due to birefringence in the liquid crystal layer can be reduced, and transmission and/or blocking of light can be equally switched over the entire wavelength range of visible light. Moreover, since the liquid crystal display device of the present invention is in the form of a film and configured in #E3 type, for example, a color filter can be formed outside the liquid crystal layer, and a good color display can be easily realized.

Embodiment FIG. 1 is a sectional view showing the basic structure of a liquid crystal display panel 9 of a liquid crystal display device which is an embodiment of the present invention. This liquid crystal display panel is of a reflective type and includes a liquid crystal layer 7, a translucent film 8 having birefringence, and a reflecting plate 10. For example, light incident from the direction of arrow P1 has its optical characteristics converted by liquid crystal N7, is reflected by reflection plate 1o, and is again emitted in the direction of arrow P2 via liquid crystal N7.

Referring to FIG. 1, a light-transmitting film 8 is made of polycarbonate or diacetate, and is manufactured by a continuous process. One surface of the transparent film 8 is coated with ITO (Indium-Tin-Oxide).
) or a transparent conductive film such as wood film, for example,
Transparent type fi3 is made by evaporating ivy and etching.
a is patterned. Next, an inorganic film such as S i O 2 or a film made of polyimide, polyvinyl alcohol, urea resin film, nylon, acrylic, etc. is formed on the entire surface so as to cover the transparent electrode 3a. This film is subjected to an alignment treatment by rubbing with a cloth or the like to form an alignment film 4a. Further, on the other surface of the transparent film 8, a fa layer of the front plate 1a is provided.

On the other hand, an isotropic film 2 having light-transmitting properties is formed by molding an organic polymer such as polycarbonate or polyether sulfone in an isodirectional manner using a casting method or the like.

On one surface of this isotropic film 2, a transparent electrode 31) and an orientation v4
b is formed.

Further, on the other surface of the isotropic film 2, a polarizing plate 1b is laminated. A reflecting plate 10 is further formed on the lower surface of the polarizing plate 1b in FIG.

The above-mentioned translucent film 8 and isotropic film 2 are arranged at a predetermined distance apart so that the orientations [4a and 4b are opposed to each other, and are fixed by a sealing material 6. At this time, polarizing plates 1a, 1. The polarization axes of b are at a predetermined angle with respect to each other (they are arranged in a staggered manner, and transmit/block light polarized at a predetermined angle depending on the application/non-application of a voltage in the liquid crystal layer 7, which will be described later).

Furthermore, bead-shaped spacers 5 are interposed between the alignment films 4a and 4b in order to keep the thickness of the liquid crystal layer 7, which will be described later, constant. The gap between the transparent film 8 and the isotropic film 2 fixed at a constant interval d1 in this manner is filled with liquid crystal, thereby forming the liquid crystal layer 7.

The layer thickness d1 of this liquid crystal layer 7 is set to, for example, 5 μm to 9 μm. Further, as a liquid crystal material, for example, ZLI-
Various liquid crystal materials i+ for STN mode such as 2293 (manufactured by Merck & Co., Ltd.) can be suitably used. Depending on the type of liquid crystal material and the layer thickness of the liquid crystal layer 7 (, 11), the retardation R1 representing the birefringence in the liquid crystal layer 7 can be adjusted to 5 by appropriately selecting the inclination angle of the liquid crystal molecules in the liquid crystal layer.
It can be expressed as the following equation.

R1=d 1 ·Δn 1 - Here, Δr+ 1 is the difference between the refractive index of normal light and the refractive index of extraordinary light in the liquid crystal layer 7, and it depends on the type of liquid crystal material.

Liquid crystal molecules are usually organic molecules having rigid rod-like portions and are oriented in a direction, so that the liquid crystal layer exhibits optical anisotropy. That is, the refractive index in the liquid crystal layer has anisotropy, and the incident light ray is divided into normal light and extraordinary light due to the birefringence effect. Therefore, even if linearly polarized light is incident on the liquid crystal layer, the refractive index for normal light and the refractive index for extraordinary light are different in the liquid crystal layer, so a phase difference occurs between the normal light and the extraordinary light, and the light is emitted. becomes elliptically polarized light. Since such a birefringence effect depends on the wavelength of incident light, the emitted light causes interference, causing a so-called coloring phenomenon in the liquid crystal panel. Such an effect is particularly remarkable in the case of liquid crystal materials for STN mode. As a result, a normal STN mode liquid crystal panel exhibits a yellow or green background color when no voltage is applied between the electrodes, and is unable to perform black and white display without color.

In this embodiment, the above problem is solved by providing a transparent film 8 having birefringence. As mentioned above, the transparent film 8 is made of, for example, polycarbonate,
It consists of an organic polymer material fl such as diacetate or monoacetate. For manufacturing, such materials
By applying tension in a uniaxial direction and stretching, it is made into a film having anisotropy. In this way, the transparent film 8 is obtained. At this time, if necessary, the film can be stretched while being heated, for example.

In such a transparent film 8, its Ml\d
Express the retardation R2 using the following equation using 2 and the difference between the refractive index of normal light and the refractive index of extraordinary light.

R:2 = (12Δ[12 Retardation R2 is the retardation R1 of the liquid crystal layer 7
For example, a value of 0.200 to 0.650 μm is selected depending on the following. According to the inventor's experiments, the liquid crystal layer 7
The relationship between the retardation R1 and the retardation R2 of the translucent film 8 is R1-R2l = 0.20 to 0.3
If it is set to 0ttrn, particularly good black display can be performed and a good contrast ratio can be obtained. For example, when retardation R1=0.85 μm, retardation R2 may be approximately 0.57 μm.

Referring to FIG. 1, in such a liquid crystal display panel 9, light incident in the direction of arrow P1 is converted into linearly polarized light by the front plate 1a. This straight line II'M is made into an ellipse by the transparent film 8, and the transparent film fi3
a and the alignment film 4a.

When a voltage is applied between the transparent electrodes 3a and 3b, the liquid crystal molecules are aligned, for example, in the light transmission direction, so the liquid crystal layer 7 hardly exhibits birefringence and is a transparent film. Transmits elliptically polarized light from 8. This elliptically polarized light is
and I! via the transparent electrode 3b! The light is incident on the optical tip plate b. Since the polarization axes of the polarizing plates 1a and 1b are shifted, the incident light is blocked by the polarizing plate 1b. Therefore, in such a case, black display is performed.

Further, when no voltage is applied between the transparent electrodes 3a and 3b, the elliptically polarized light from the transparent filter 8 is transmitted to the liquid crystal layer 7.
The vibration direction of the light is twisted by a predetermined angle, and the light is birefringent, converted into linearly polarized light, and passes through the single-sided light plate 1b. The linearly polarized light here is actually elliptically polarized light that is very close to linearly polarized light. This straight line (shoulder tip is reflector 1
0 and is reflected by the liquid crystal layer 7 again via the polarizing plate 1b.
is incident on the The liquid crystal layer 7 converts the light into elliptically polarized light again, but the transparent film 8 converts it back into linearly polarized light, which is then output in the direction of arrow P2 via the polarizing plate 1a. As a result, white display is performed on the liquid crystal panel 9.

In this way, on the liquid crystal panel 9, black and white display without yellow-green coloring is possible. In addition, this transparent film 8
Since it also functions as a substrate on which the transparent electrode 3=t is formed, there is no need to provide a separate filter for the substrate. In addition, since the overall layer thickness does not increase compared to conventional film-like liquid crystal panels, the liquid crystal display panel 9
Do not worsen the visibility of

FIG. 2 is a sectional view showing the basic structure of a liquid crystal panel 22 of a liquid crystal display device that performs color display, which is another embodiment of the present invention. The liquid crystal display panels ↑ and 22 are transmissive type, and the arrows
Light from a light source (not shown) incident from the FP3 direction is
The light is emitted in the direction of arrow P4 via color filters 19 to 21, liquid crystal layer 17, transparent film 18, and the like.

The liquid crystal display panel 22 has a structure basically similar to the above-mentioned liquid crystal display panel, and has polarizing plates 11a, ll.
b, transparent film 18, liquid crystal layer 17, transparent electrode 13a
, t3b, an alignment film 14a14b, an isotropic film 12, a sealing material 16, and the like.

In this liquid crystal display panel 22, the isotropic film 1
One red color filter in the specified position on the bottom of Figure 2 of 2,
Green color filter 20 and blue color filter 21
is formed. A shoulder plate 11b is provided to cover the color fills 19 to 21. Also, a plurality of electrodes 13a are provided.

13[) are formed at positions corresponding to each of the color filters 19 to 21 individually.

In the liquid crystal display panel 22, the light incident from the direction of arrow P3 is converted into linearly polarized light by the polarizing plate 1.1b, and is incident on the liquid crystal layer 17 via each color filter 19-21. When a voltage is applied between the electrodes 13a and 13b, linearly polarized light that has passed through the liquid crystal layer 17 is incident on the transparent film 18 and converted into elliptically polarized light. This elliptically polarized light is blocked by the wide end plate 11a.

When no voltage is applied between the electrodes 13a and 13b, the vibration direction of the incident light is twisted by the liquid crystal layer 17, and the incident light is converted into an elliptical 1-shaped light and emitted to the transparent film 18. . The transparent film 8 is shaped like this ellipse (
I! Convert the light into linearly polarized light and pass through the polarizing plate 1 to the arrow P4
emits in the direction. Therefore, a plurality of transparent electrodes 13a, 1
Color display is realized by selectively applying a voltage between 3b.

In this way, in the liquid crystal display panel 22, color display can be realized simply by providing the color filters 19 to 21 between the isotropic film 12 and the polarizing plate 11b. Moreover, since the liquid crystal display panel 22 is constructed in the form of a film, there is no need to form the color filters 19 to 21 close to the liquid crystal layer 17, and deterioration of the liquid crystal due to chemical reaction between the liquid crystal and the filter is prevented. It will be resolved.

In this example, the case where a birefringent transparent film is used as the 10th and 2nd (2I upper transparent films 8.18) of the liquid crystal layer 7.17 has been described. It is also possible to oval the optical film 8.18 with an optically isotropic film, and use a translucent film with birefringence instead of the isotropic film 2.12. It is also possible to use a pair of translucent films having the following properties.

In addition, in this example, the perturbation direction of the incident linear IN light is twisted by the liquid crystal layer and the birefringent transparent film when no voltage is applied, and the incident linear IN light is converted into elliptically polarized light that is extremely close to linearly polarized light. Although a case has been described in which linearly polarized light is converted into circularly polarized light by a liquid crystal layer and a birefringent transparent film when no voltage is applied.

As described in detail, according to the present invention, in a film-type liquid crystal display device, it is possible to maintain the characteristics, improve the contrast ratio, and perform black-and-white display without undesirable background colors. . Therefore, non-uniform gray color tone caused by uneven thickness of the liquid crystal layer and changes in background color due to temperature changes are reduced. Furthermore, stable color display can be easily realized. Furthermore, since there is no need to increase the number of laminated films, bright display can be achieved without increasing loss due to scattered light at the interface between each filter.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic structure of a liquid crystal display panel 9 of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing the basic configuration of a liquid crystal display panel 22. FIG. 1 a, 1 b, 11 FL, 1 l b-
fJi optical plate tip plate, 12... Isotropic film, 3a, 3
1:l, 13a, 13b-transparent electrode, -4a, 4b, 1
4a, 14b-alignment film, 7.17...liquid crystal layer, 9,2
2...Liquid crystal display panel, 19-21...Color filter agent Patent attorney Keibu Saikyo Figure 2

Claims (1)

[Claims] A liquid crystal display in which a liquid crystal is sealed between a pair of translucent films each having electrodes formed on surfaces facing each other, and a polarizing member is laminated on the opposite side of the pair of translucent films from the liquid crystal layer. 1. A liquid crystal display device, wherein the light-transmitting film on at least one side is made of a birefringent film.