JPH055882A - Display device - Google Patents

Abstract

PURPOSE:To present a display device which easily realizes a quick responsiveness and a high contrast and has advantages of wide visual field angle, etc. CONSTITUTION:The display device consists of an electrode 2, an optical waveguide 3 made of a transparent resin, a liquid crystal layer 4, a liquid crystal orienting film 5, a transparent electrode 6, and a transparent substrate 7 which are laminated on a substrate 1 and has a mechanism to lead in light from a prism coupler 8 and satisfies relations ne: max > np >ne: min where np is the refractive index of the optical waveguide and ne: max and ne: min are higher one and lower one of effective refractive indexes of liquid crystal before and after electric field switching respectively.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel display device,
Specifically, it relates to a novel flat display panel using liquid crystal.

[0002]

2. Description of the Related Art Currently, a cathode ray tube (CR) is used as a display device.
Although T) occupies the mainstream, it has a drawback that it is large and heavy, and therefore, the transition to a flat display panel (hereinafter sometimes simply referred to as a flat panel) is progressing. Examples of flat panels include liquid crystal displays, plasma displays, electrochromic displays, etc., but liquid crystal displays are becoming the mainstream. As liquid crystal displays, types using nematic liquid crystals such as twisted nematic type and super twisted nematic type, types using ferroelectric liquid crystal or anti-ferroelectric liquid crystal, etc. have been put to practical use or are being studied for development.

[0003]

However, in a type using a nematic liquid crystal, for example, a twisted nematic type display device, there is a limit in response speed, and it is difficult to increase the area and the definition. In addition, there is an essential problem that it is difficult to obtain a good contrast ratio and a wide viewing angle characteristic. On the other hand, recently, a method of driving a nematic liquid crystal using a thin film transistor has been intensively researched, but there is a problem in manufacturing the thin film transistor, and for example, it is still sufficient to supply a panel of about 8 to 10 inches at low cost. I haven't obtained any good results.

On the other hand, a display method using a ferroelectric liquid crystal,
For example, a surface-stabilized ferroelectric liquid crystal display device (hereinafter referred to as SSFL
In addition to its fast response speed, CD) has the potential for memory properties and good viewing angle characteristics, and is therefore receiving a great deal of attention. However, even in this method, high-speed response and a high contrast ratio can be expected in principle, but since the rotation of the polarization plane of the ferroelectric liquid crystal is used for switching, it is necessary to realize a high contrast ratio. , Guest −
In the method called the host method, it is necessary for the liquid crystal molecules to rotate 90 ° with respect to the plane of the substrate when an electric field is applied, and for the birefringence method to also rotate 45 °, which makes the response speed even faster. It seems to be an obstacle to doing. Therefore, in reality, it must be said that it is very difficult to achieve a response speed of, for example, 10 μs or less and to obtain a high contrast ratio.

An object of the present invention is to provide a display device using liquid crystal for easily realizing high-speed response and high contrast ratio.

[0006]

That is, the present invention provides, on a substrate, an electrode, an optical waveguide made of a transparent resin, a liquid crystal layer, a liquid crystal alignment film and a transparent electrode in this order, or an optical waveguide made of a transparent resin, a transparent electrode, A liquid crystal layer, a liquid crystal alignment film, and transparent electrodes are provided in this order, and a light introducing portion for introducing light to the end portion of the optical waveguide is provided, and the refractive index of the optical waveguide and the effective refractive index of the liquid crystal are n _e : max> n _p > n _e : min (where n _p is the refractive index of the optical waveguide, n _e : max is the larger value of the effective refractive indices of the liquid crystal before and after switching the electric field,
n _e : min indicates the smaller value of the effective refractive indices of the liquid crystal before and after switching the electric field. The present invention is to provide a display device characterized by satisfying the relationship (1).

As described above, in the present invention, since the change in the effective refractive index of the liquid crystal due to the change in the electric field is utilized instead of the conventional rotation of the plane of polarization by the liquid crystal, the liquid crystal molecules have a 90 ° or 45 ° angle. It is considered that rotation is not always necessary. That is, the optical response in the device of the present invention does not require the time of the whole process of the movement of liquid crystal molecules. Here, the response time is the time until the effective refractive index of the liquid crystal becomes larger or smaller than the refractive index of the optical waveguide. This point is essentially different from the conventional display device using liquid crystal.

The present invention will be described in detail below. The display device of the present invention, switching of the electric field applied to the liquid crystal molecules formed on the optical waveguide (increasing or decreasing the electric field,
It means adding or removing an electric field, or reversing an electric field. Hereinafter, it may be simply referred to as switching. ), A part of the light traveling in the optical waveguide is extracted to the front (display surface side) of the flat panel to draw the brightness and darkness.
Specifically, use a combination of an optical waveguide and liquid crystal that satisfy the above refractive index relationship, let light travel in this waveguide, and control the amount of light extracted to the front surface of the panel by switching the electric field to the liquid crystal molecules described above. Is a novel display device that displays by. The flat panel mentioned here includes a curved panel having a gentle curvature.

The present invention will be described with reference to the drawings. Figure 1
Shows a schematic view of a cross section of a main part of an example of the device of the present invention. A transparent electrode 2, an optical waveguide 3, a liquid crystal layer 4, an alignment film 5, a transparent electrode 6, and a transparent substrate 7 are laminated in this order on the substrate 1. The transparent substrate 7 is not always necessary, but it is preferably provided in consideration of strength and manufacturing. A prism coupler 8 for introducing light into the optical waveguide 3 is provided at the end of the optical waveguide 3. This prism coupler 8 is not always necessary, and other means may be used as long as light can be introduced into the optical waveguide 3. The liquid crystal of the liquid crystal layer 4 is aligned by the alignment film formed above so that the major axis direction of the liquid crystal faces the optical axis direction. The light that has entered from the prism coupler 8 on the left side propagates while being totally reflected in the optical waveguide 3 made of a transparent resin film, and either proceeds in the optical waveguide 3 as it is due to the switching of liquid crystal or exits from the optical waveguide 3. To the front of the panel, that is, the display surface side. When traveling through the optical waveguide 3, there is almost no leakage of light to the front of the panel and the field of view is in a dark state. On the other hand, when light travels in front of the panel due to switching of liquid crystal molecules, the field of view in front of the panel is in a bright state.

Next, the principle of switching between the bright state and the dark state in the present invention will be described when a ferroelectric liquid crystal is used as the liquid crystal. 2 and 3 show schematic diagrams of the optical switching operation. Considering the TE wave propagating in the optical waveguide combined with the ferroelectric liquid crystal, when the liquid crystal molecules are oriented in the traveling direction of the light by the application of the electric field as shown in FIG. Since the refractive index n _e (n _e : min) is smaller than the refractive index n _p of the optical waveguide, light propagates in the optical waveguide. At this time, since the light is not scattered by the liquid crystal, the light propagates in the optical waveguide without being attenuated. At this time, the entire panel becomes dark. On the other hand, as shown in FIG. 3, when the electric field is reversed and the liquid crystal molecules are oriented symmetrically with respect to the layer normal, n _e (n _e : max)> n _p , and the light enters the liquid crystal layer. Then, it passes through the liquid crystal layer and propagates to the front surface of the panel. At this time, the entire panel is in a bright state. That is, the light to the display surface side can be controlled by changing the electric field.

The present invention will be described in more detail below. With respect to the material constituting the optical waveguide, the constituent requirements necessary for the optical waveguide used in the present invention are (1) sufficient characteristics as the optical waveguide, (2) effective refractive index of liquid crystal that changes with switching of liquid crystal molecules. It is preferable that the compound has a refractive index in the middle of (3) and that further functions as (3) an aligning agent for liquid crystal molecules. It is not particularly limited as long as it is a material having such characteristics, but for example, a film of an organic polymer material such as polyvinyl alcohol, polymethylmethacrylate, polycarbonate, or polystyrene can be used. It is important to properly combine with the liquid crystal so that the refractive index n _p falls between the effective refractive index n _e : max and n _e : min of Further, on the electrode 2 side below this resin, polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, trifluoroethylene-vinylidene fluoride copolymer, polymethacrylic acid trifluoropolymer having a smaller refractive index than the above resins. It is preferable to provide a thin film layer of a fluorine-based resin such as ethyl or an ethylene-vinyl acetate copolymer because light can be more efficiently totally reflected at the interface with the resin of the optical waveguide.

The thickness of the optical waveguide layer is not particularly limited, but is usually 1 μm to 1 mm, preferably 1 to 50 μm. When a thin film layer is provided, its thickness is 0.1
It is preferably about 10 μm.

The shape of the optical waveguide used in the present invention is not particularly limited, but for example, as one flat film corresponding to the entire panel surface, or a structure divided into several parts, for example, scanning lines. Can be used in a shape divided into parts corresponding to.

In the present invention, a light introducing means is provided at the end of the optical waveguide in order to introduce light into the optical waveguide. In the present invention, as an example, a means for directly injecting (introducing) light from the end face of the optical waveguide can be used, but since the thickness of the optical waveguide is usually thin, it is efficient to introduce the light by condensing it with a lens on the end face. is there. Further, as another example, it is also a preferable embodiment that a conventionally used prism coupler or grating is provided at an end portion of the optical waveguide to introduce light into the optical waveguide. By adopting these means, it becomes possible to introduce light into the optical waveguide by using, for example, a conventionally used laser light source or cold cathode tube as a light source.

Next, the liquid crystal layer provided on the optical waveguide will be described. As the liquid crystal used in the present invention,
Changes in the effective refractive index of liquid crystals caused by switching of liquid crystal molecules are important. That is, the main concept that constitutes the present invention is that the effective refractive index of the liquid crystal becomes larger or smaller than the refractive index of the material forming the optical waveguide by switching, and the light traveling through the optical waveguide is directed to the display surface side. It is to take it out or to proceed in the optical waveguide as it is. Therefore, the liquid crystal used in the present invention has an effective refractive index due to the switching of liquid crystal molecules,
It is an essential condition that the refractive index of the material forming the optical waveguide is larger or smaller than that of the material. That is, the refractive index of the optical waveguide and the effective refractive index of the liquid crystal are n _e : max> n _p > n _e : min (where n _p , n _e : max and n _e : min mean the same as above). It is an essential condition to use a combination of a liquid crystal and an optical waveguide so as to satisfy the relationship of. That is, since it is necessary to use a liquid crystal that satisfies the above relationship depending on the refractive index of the optical waveguide used, it is important to select an appropriate combination in consideration of the refractive index of the optical waveguide.

For example, as the liquid crystal, a bicyclic or tricyclic aromatic ester type or phenylpyrimidine type ferroelectric liquid crystal can be used. The thickness of the liquid crystal layer is approximately the same as the thickness of the liquid crystal used in the conventional liquid crystal display device, and is usually 0.5 to 20 μm, preferably 1 to 5 μm.

The response speed of switching between the bright state and the dark state in the display device according to the present invention is not the response speed of the liquid crystal molecules themselves as in the conventional liquid crystal panel, but the response speed corresponding to the change of the effective refractive index. is there. Therefore, the response speed of the display device according to the present invention has an advantage that it can exhibit an extremely high response speed.

Since the liquid crystal is used in the display device according to the present invention as described above, it is important to orient the liquid crystal uniformly over a wide range. In the present invention, it is preferable to provide a liquid crystal alignment film on the liquid crystal layer side of the transparent electrode above the liquid crystal layer. As the liquid crystal aligning agent for forming the alignment film, a liquid crystal aligning agent used in conventional liquid crystal display devices can be used. It is preferable to use a liquid crystal having an effective refractive index of about the same as or larger than n _e : max. When using an oriented organic polymer film such as an oriented polyvinyl alcohol film in the optical waveguide,
This optical waveguide is one of the preferred embodiments because it has a function as an aligning agent as well as a function as an optical waveguide.

The present invention requires a pair of electrodes for applying an electric field to the liquid crystal. The electrode provided on the substrate side of the optical waveguide does not necessarily need to be transparent, and is usually provided on the substrate and the optical waveguide is provided thereon.
As another aspect, a transparent electrode may be provided on the liquid crystal side of the optical waveguide. The other electrode provided on the upper side of the liquid crystal layer needs to pass light to the display side and is a transparent electrode. Normally, a transparent electrode is formed on a transparent substrate (panel) such as glass or transparent resin, which is the same as that used in conventional liquid crystal display devices, and then an alignment film is formed on the transparent electrode. It is preferable to use a liquid crystal layer sandwiched between the alignment film and the optical waveguide. IT as a transparent electrode
O, NESA glass, etc. A when transparency is not required
A film of u, Pt or the like may be used. Further, the electrodes can be arranged in a matrix as in the conventional liquid crystal display device and divided into a large number of pixels. The thickness of the electrode is similar to that in the conventional liquid crystal display device.

In the present invention, the light that has passed through the liquid crystal layer and traveled to the front surface is emitted obliquely with respect to the panel plane. Of course, even in this state, the function as a display device can be sufficiently fulfilled, but as in the known liquid crystal display device, a partition-shaped structure 9 is prepared for each pixel as shown in FIG. It is also possible to adopt a structure in which the pixels that do not leak light.

Further, if necessary, this obliquely emitted light can be emitted perpendicularly to the panel surface, or the viewing angle can be widened. For example, a method for installing a structure for scattering light for each pixel, for example, a method for installing a structure such as a minute lens 10 on the entire panel surface for each pixel as shown in FIG. 4 to change the traveling direction of light, Alternatively, for example, as shown in FIG. 5, a fluorescent layer 11 coated with a substance such as a fluorescent substance is provided on the front surface of the panel, and the emitted light is used as primary light to emit light when molecules excited by this light return to the ground state. A method of using the next light, or a method of providing a scattering film 12 for scattering and transmitting the light on the transparent electrode or the upper substrate as shown in FIG.

[0022]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 A test cell having the structure shown in the schematic plan view and the side view in FIGS. 7 and 8 was produced. This cell is composed of two upper and lower glass substrates 1 and 7 made of Pyrex having transparent electrodes 2 and 6, respectively. Polyvinyl alcohol was used as the optical waveguide 3 on the transparent electrode of the lower substrate. This refractive index is about 1.5. On the transparent electrode 6 of the upper substrate 7, a thin film of polyvinylidene fluoride subjected to rubbing treatment was used as the liquid crystal alignment film 5. As the liquid crystal layer 4, an aromatic ester-based ferroelectric liquid crystal represented by the following structural formula was used.

[0024]

[Chemical 1]

The liquid crystal has n _e : max of about 1.6 and n _e : min.
Is about 1.4. Spacer 1 between the upper and lower two substrates
A polyimide film having a thickness of 4 μm was used as 1. The liquid crystal is uniformly aligned by the polyvinylidene fluoride film on the upper substrate so that the layer normal of the liquid crystal has an angle of 30 ° with the optical axis. At the left end of the cell, a prism coupler 8 is configured to make light enter the optical waveguide 3. Using this prism coupler, monochromatic light of 632.8 nm was made incident on the optical waveguide from a helium-neon laser. The incident light traveled while being totally reflected in the waveguide 3.

In this example, the response of the emitted light when a square wave was applied between the transparent electrodes was detected by a photomultiplier tube. FIG. 9 shows a response waveform when an electric field of ± 30 V and 10 kHz is applied. A clean waveform close to a square wave is obtained. 10%
The response time corresponding to -90% is very fast at 4.5 μs when changing from the dark state to the bright state and 2.8 μs when changing from the bright state to the dark state. The contrast ratio was about 50, which is a very good result.

Example 2 Using a test cell having the same structure as described in Example 1, the applied voltage was changed and the response time was measured. The measurement results are shown in FIG.

[0028]

The display device of the present invention has advantages that a high-speed response and a high contrast ratio can be easily realized and that the viewing angle is large.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section of an example of a display device of the present invention.

FIG. 2 is a schematic diagram for explaining the operation principle of the present invention.

FIG. 3 is a schematic diagram for explaining the operation principle of the present invention.

FIG. 4 is a schematic view of a cross section of an example of a display device of the present invention.

FIG. 5 is a schematic view of a cross section of an example of a display device of the present invention.

FIG. 6 is a schematic view of a cross section of an example of a display device of the present invention.

FIG. 7 is a schematic view of an embodiment of the display device of the present invention seen from above.

FIG. 8 is a schematic view of a cross section of an embodiment of a display device of the present invention.

FIG. 9 shows an optical response waveform of the device of the example.

FIG. 10 shows the relationship between the response time and the applied voltage of the device of the example.

[Explanation of symbols]

1 ... Substrate, 2 ... Transparent electrode, 3 ... Optical waveguide,
4 ... Liquid crystal layer, 5 ... Liquid crystal alignment film, 6 ... Transparent electrode, 7 ... Translucent substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayoshi Minai 2-10-1 Tsukahara, Takatsuki City, Osaka Prefecture Sumitomo Kagaku Kogyo Co., Ltd.

Claims (1)

1. An order of an electrode, an optical waveguide made of a transparent resin, a liquid crystal layer, a liquid crystal alignment film and a transparent electrode on a substrate, or an optical waveguide made of a transparent resin, a transparent electrode, a liquid crystal layer, A liquid crystal alignment film and transparent electrodes are provided in this order, and a light introducing portion for introducing light is provided at an end portion of the optical waveguide, and the refractive index of the optical waveguide and the effective refractive index of the liquid crystal are n _e : max> n _p > n _e : min (where n _p is the refractive index of the optical waveguide, n _e : max is the larger value of the effective refractive indices of the liquid crystal before and after switching the electric field,
n _e : min indicates the smaller value of the effective refractive indices of the liquid crystal before and after switching the electric field. ) The display device characterized by satisfying the relationship of.