JP3298263B2 - Active matrix 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 an active matrix liquid crystal display for displaying a multicolor image.

[0002]

2. Description of the Related Art Conventionally, a TN type active matrix liquid crystal display device has been used. This T
The N-type active matrix liquid crystal display element has a first substrate on which a plurality of pixel electrodes and a plurality of active elements respectively corresponding to these pixel electrodes are provided, and a counter electrode on which the pixel electrodes face each other. And two substrates, with their electrode formation surfaces facing each other, a nematic liquid crystal layer provided between the two substrates, and a polarizing plate disposed on the outer surface side of each of the two substrates. A liquid crystal display element for displaying a color image includes a plurality of color filters (generally, three colors of red, green and blue) alternately provided on one of the two substrates so as to correspond to the respective pixel electrodes. It has a configuration provided side by side.

[0003] An alignment film for regulating the alignment direction of the liquid crystal molecules is provided on each of the electrode forming surfaces of the two substrates, and the liquid crystal molecules are twist-aligned at a twist angle of approximately 90 ° between the two substrates. ing. The pair of polarizing plates disposed on the outer surfaces of both substrates are provided with their transmission axes substantially parallel to each other.

[0004]

However, the above-mentioned TN type active matrix liquid crystal display element has a problem that it is difficult to obtain a multicolor display with sufficient brightness. This is because incident light from the outside is linearly polarized by one of the polarizing plates and is incident on the liquid crystal layer, and of the light passing through the liquid crystal layer, passes through an electric field-free region (a region where liquid crystal molecules are in a twisted arrangement state). Light is absorbed by the other polarizing plate, and only light that has passed through the electric field application region (region where liquid crystal molecules rise up) is transmitted and emitted through the other polarizing plate. Is large, and the color filter transmits only light in a specific wavelength range of visible light and absorbs light in other wavelength ranges. And therefore
The displayed multicolor image is considerably darker than the brightness of the light incident on the liquid crystal display element.

[0005] This is particularly remarkable in a reflection type liquid crystal display device in which a reflection plate is disposed on the back surface side. The reflection type device uses natural light or indoor illumination light to perform display. The light that enters from the front side, is reflected by the reflection plate on the back side, and exits to the front side passes through the pair of polarizers and the color filter twice each, resulting in a considerable loss of light quantity and extremely dark display image. Become.

[0006] In contrast to this reflective type element, in a transmissive type element used by disposing a backlight on the back side, light incident from the back side and emitted to the front side is formed by a pair of polarizing plates and a color filter. Since the light only passes through each one time, the light amount loss due to light absorption by the polarizing plate and the color filter is smaller than that of the reflective element, but still,
The brightness of the display image is considerably darker than the brightness of the illumination light from the backlight.

The present invention greatly reduces light loss,
It is an object of the present invention to provide an active matrix liquid crystal display device capable of displaying a very bright multicolor image.

[0008]

An active matrix liquid crystal display device according to the present invention is an active matrix liquid crystal display device for displaying a multicolor image.
An active matrix liquid crystal display device, comprising: a first substrate on which a plurality of pixel electrodes and a plurality of active elements respectively corresponding to the pixel electrodes are disposed; and a second substrate having a counter electrode facing the pixel electrodes. And a liquid crystal / polymer composite film in which liquid crystal is dispersed in a polymer layer is provided between the two substrates.
And, on the electrode formation surface of said first substrate, said pixel electric multiple color phosphor film that emits fluorescence of different colors from each other
Disposed below and corresponding to the pole, in front of the first substrate
A reflector is disposed on the outer surface side opposite to the electrode forming surface .

[0009]

In other words, the active matrix liquid crystal display device of the present invention displays an image by utilizing the scattering and transmission of light in a liquid crystal / polymer composite film. The liquid crystal molecules are oriented in various directions when no electric field is applied. In this state,
The light passing through the composite film is scattered, and the pixels are turned to a dark state.
Further, when an electric field is applied between the pixel electrode and the counter electrode on both substrates, the liquid crystal molecules rise and align, and light passing through the composite film is transmitted with almost no light scattering action, and the pixel is in a bright state. become.

In this liquid crystal display device, phosphor films of a plurality of colors emitting different colors of fluorescence are alternately arranged on at least one of the two substrates so as to correspond to the respective pixel electrodes. Therefore, the bright display color is the color of the fluorescent light emitted by the phosphor film, and therefore, the pixels can be colored without using a color filter.

Further, since this liquid crystal display element displays by utilizing the scattering and transmission of light in the liquid crystal / polymer composite film, a polarizing plate which is indispensable for a TN type liquid crystal display element is not required. In addition, since a pixel can be colored by the phosphor film, a color filter is not necessary, so that there is no light amount loss due to light absorption by the polarizing plate and the color filter.

Further, the above-mentioned phosphor film does not transmit only light in a specific wavelength range of visible light and absorb light in other wavelength ranges as colored light, as in a color filter.
Since the fluorescent light is emitted by the energy of the absorbed light, the intensity of the light colored by the phosphor film is much higher than the intensity of the colored light by the color filter. Therefore, according to this liquid crystal display device, it is possible to display a very bright multicolor image with significantly reduced light loss.

[0013]

EXAMPLES The following will be described with reference to the drawings an embodiment of the present invention. Figure 1 is Ri sectional view Der of a portion of the active matrix liquid crystal display device, the liquid crystal display device is of a reflective type arranged a reflector 30 on the back side thereof.

In FIG. 1, a lower substrate 1 is a rear substrate of the liquid crystal element, and an upper substrate 2 is a front substrate. The substrates 1 and 2 are transparent substrates made of a glass plate or the like, and the rear substrate 1 has a plurality of transparent pixel electrodes 3 arranged in a row direction and a column direction, and corresponds to each of the pixel electrodes 3. A plurality of active elements 4 are provided, and a transparent counter electrode 10 on which the pixel electrodes 3 of the back substrate 1 face is provided over substantially the entire surface of the front substrate 2.

The active element 4 is, for example, a TFT (thin film transistor). The TFT 4 has a gate electrode 5 formed on the surface of the back substrate 1, a gate insulating film 6 covering the gate electrode 5, and a gate insulating film. 6, a semiconductor film 7 made of a-Si (amorphous silicon) or the like formed opposite to the gate electrode 5, and a source electrode 8 and a drain electrode 9 formed on both sides of the semiconductor film 7. It is composed of

Although not shown, the rear substrate 1 has
A gate line (address line) for supplying a gate signal to the TFT 4 and a data line for supplying a data signal corresponding to image data to the TFT 4 are wired, and a gate electrode 5 of the TFT 4 is integrated with the gate line. The drain electrode 9 is formed and is connected to the data line.

Further, on the back side substrate 1, a plurality of phosphor films emitting different colors of fluorescence, for example, a red phosphor film 11a emitting red fluorescence and a green phosphor emitting green fluorescence are provided. The film 11b and the blue phosphor film 11c that emits blue fluorescent light are provided alternately so as to correspond to each of the pixel electrodes 3 disposed on the backside substrate 1.

Each of these phosphor films 11a, 11b, and 11c absorbs light and emits colored fluorescence.
The phosphor films 11a, 11b and 11c of this embodiment are different from those of FIG.
As shown in a partially enlarged manner in FIG. 1, a fluorescent substance 13 is mixed in a transparent substrate 12 in a dotted state.

The transparent substrate 12 is a transparent resin made of an acrylic resin, a vinyl chloride resin, an alkyd resin, an aromatic sulfonamide resin, a urea resin, a melamine resin, a benzoguanamine resin, and a copolycondensate thereof. is there.

The fluorescent substance 13 is provided on the substrate 12.
A fluorescent material obtained by dyeing the resin used in the above or another transparent resin with a fluorescent dye is pulverized into fine particles. The fluorescent material 13 has a specific wavelength range (wavelength range of a fluorescent color emitted by the fluorescent material 13). It has a wavelength conversion function of absorbing light other than the above and emitting light in the specific wavelength range by the energy of the absorbed light.

The red phosphor film 11a is made of a red fluorescent material that absorbs light outside the red wavelength range and emits light in the red wavelength range, and the green phosphor film 11b is a green phosphor film. A green fluorescent substance that absorbs light outside the wavelength range and emits light in the green wavelength range is used. The blue phosphor film 11c absorbs light outside the blue wavelength range and emits light in the blue wavelength range. A blue fluorescent material that emits light is used. Therefore, the red phosphor film 11a emits red fluorescent light emitted by the red fluorescent material, and the green phosphor film 11b emits green fluorescent light emitted by the green fluorescent material. And the blue phosphor film 11c emits blue fluorescence emitted from the blue phosphor.

The phosphor films 11a, 11b, 11c are
A mixture of a resin material serving as a base material 12 and a fluorescent substance 13 at a desired ratio is applied to the backside substrate 1 to a predetermined thickness by a printing method, a spin coating method, or the like, and then the resin material is applied. The phosphor films 11a, 11b, and 11c are covered with the gate insulating film 6 of the TFT 4 described above.

The gate insulating film 6 is a transparent film made of SiN (silicon nitride) or the like. The pixel electrode 3 is provided on the gate insulating film 6 and has a source electrode of the corresponding TFT 4 at one end. 8 is connected.

The back side substrate 1 and the front side substrate 2
Means that the liquid crystal / polymer composite film 20 is provided in a region between the substrates 1 and 2 surrounded by the sealing material, with a frame-like sealing material (not shown) interposed therebetween. ing.

The liquid crystal / polymer composite film 20 is obtained by dispersing liquid crystal in a polymer layer.
A liquid crystal is confined in each gap of the polymer layer 21 polymerized so as to have a cross section like a sponge. In FIG. 1, reference numeral 22 denotes a liquid crystal portion (portion where liquid crystal is confined) in the composite film 20.

In this embodiment, a nematic liquid crystal having a positive dielectric anisotropy is used as the liquid crystal, and a black dichroic dye is mixed in the liquid crystal. FIG. 3 shows the composite membrane 2
0 is an enlarged cross-sectional view of one liquid crystal unit 22 in an electric field-free state and an electric field applied state. In the figure, A indicates liquid crystal molecules, and B indicates the dichroic dye molecules.

In the liquid crystal display device, for example, after joining a pair of substrates 1 and 2 via a sealing material, the two substrates 1 and 2 are joined together.
Between the two, a mixed solution of a polymer material that undergoes a polymerization reaction by light and a liquid crystal to which a dichroic dye is added is injected by a vacuum injection method from an injection port formed by partially removing the sealing material. It can be manufactured by a method of filling and irradiating the filling solution with ultraviolet rays to photopolymerize the polymer material.
The inlet is sealed after filling with a solution or after photopolymerization of a polymer.

As described above, when the mixed solution filled between the substrates 1 and 2 is irradiated with ultraviolet rays, the polymer material in a monomer or oligomer state is radicalized by the dissolution of the double bond, and the radicals of adjacent molecules are released. Are formed into a polymer by a radical polymerization reaction in which the radicals are bonded to each other, and the liquid crystal undergoes phase separation by polymerization of the polymer material.

For this reason, the polymerized polymer layer 21 has a cross section like a sponge, and the liquid crystal is confined in each gap of the polymer layer 21 so that the liquid crystal / polymer composite film 20 having the above-described structure is formed. Is formed. This composite membrane 20
Is a method called a photopolymerization phase separation method.

It is desirable that the above-mentioned filling solution is irradiated with ultraviolet rays from the front substrate 2 on which the counter electrode 10 is formed, and the counter electrode 10 is a single film formed over almost the entire surface of the front substrate 2. When the surface side substrate 2 is irradiated with ultraviolet light, the entire filling solution is irradiated with ultraviolet light almost uniformly, and a uniform liquid crystal / polymer composite film 20 can be obtained.

After the liquid crystal / polymer composite film 20 is formed, the reflection plate 30 is bonded to the outer surface (back surface) of the back substrate 1 to complete the liquid crystal display device. The reflecting plate 30 is obtained by applying a reflecting film 32 on the surface of a base sheet 31 made of a resin film. The reflecting film 32 is formed of an Al (aluminum) reflecting film having a roughened surface, Ba Examples include a white reflective film having a light scattering surface made of SO ₄ (barium sulfate), a specular reflective film made of Ag (silver), and the like.

The active matrix liquid crystal display element displays an image by utilizing light scattering and transmission in the liquid crystal / polymer composite film 20.
The molecules A of the liquid crystal of the liquid crystal part 22 dispersed in one layer are oriented in various directions as shown in FIG. 3A when no electric field is applied. Since the molecules B are also oriented in various directions, in the absence of an electric field, when light incident from the surface side of the liquid crystal display element passes through the composite film 20, an interface between the liquid crystal part 22 and the polymer layer 21 is formed. In addition, the light is scattered by the light scattering action of the liquid crystal of the liquid crystal part 22, and most of the scattered light is absorbed by the dichroic dye.

Therefore, in the absence of an electric field, the composite film 2
0, the phosphor films 11a, 11b,
The amount of light reaching the reflector 11c and the reflector 30 on the rear surface is extremely small, and therefore, the phosphor films 11a, 11b, 1
Since the amount of fluorescence emitted by 1c and the amount of reflected light from the reflector 30 are small, and these lights are scattered and absorbed when passing through the composite film 20 again as described above,
There is almost no light emitted to the front side, and the display pixels are almost black and dark.

When an electric field is applied between the pixel electrode 3 and the counter electrode 10 of the substrates 1 and 2, as shown in FIG. Are uniformly oriented so as to be substantially perpendicular to the surfaces of the substrates 1 and 2, and the molecules B of the dichroic dye are also oriented so as to rise. The incident light passes through the composite film 20 with little light scattering effect on the composite film 20 and little absorption by the dichroic dye.

Therefore, when the electric field is applied, the incident light passes through the composite film 20 and the phosphor film 11 on the back substrate 1 is formed.
a, 11b, 11c and the phosphor film 1
The light reaches the back reflector 30 of the element through 1a, 11b, and 11c.

The light that has reached the reflector 30 is reflected by the reflector 30 to form the phosphor films 11a, 11b, 11c.
Reaches the phosphor film 12 to generate fluorescent light, the light reflected by the reflector 30 and the phosphor films 11a, 11
The fluorescent light emitted by b and 11c passes through the composite film 20 again and exits to the front surface side, and the display pixels are in a bright state.

In this liquid crystal display device, a red phosphor film 11 for emitting red fluorescence is provided on the backside substrate 1.
a, a green phosphor film 11b that emits green fluorescence, and a blue phosphor film 11c that emits blue fluorescence are alternately arranged in correspondence with each pixel electrode 3, so that the bright display color is These are the colors of red, green, and blue fluorescent light emitted by the phosphor films 11a, 11b, and 11c. Therefore, the display pixels are colored without using a color filter, and
Multicolor display can be performed by combining blue pixels.

The coloring of the pixel will be described. In the above liquid crystal display device, light transmitted through the liquid crystal / polymer composite 20 reflects the phosphor film 11a, as shown by the solid line arrow in FIG.
After passing through 11b and 11c, the light is reflected by the reflector 30 on the back surface of the device, and the reflected light is again reflected by the phosphor films 11a, 11b and 11
c, and some of the light impinges on the fluorescent material 13 dispersed in the phosphor film when passing through the phosphor film.

The fluorescent substance 13 is the fluorescent substance 1
3, light in a specific wavelength range, that is, light in the same wavelength range as the fluorescent color emitted by the fluorescent substance 13 is transmitted or reflected, and light in other wavelength ranges is absorbed and reflected. With this energy, light (fluorescence) in the specific wavelength range is emitted.

The fluorescence emitted from the fluorescent substance 13 is shown in FIG.
As shown by the dashed arrow in FIG. 2, some of the fluorescent light is emitted to the back side of the phosphor film, but this fluorescent light is reflected by the reflecting plate 30 and again emitted from the fluorescent material 13. The light is emitted to the surface through the body membrane. The same applies to light transmitted through the fluorescent substance 13 and light reflected by the fluorescent substance 13.

Therefore, the phosphor films 11a, 11
Light emitted to the surface side of b, 11c is light transmitted through the phosphor film without hitting the fluorescent substance 13, fluorescence emitted from the fluorescent substance 13, and transmitted or reflected by the fluorescent substance 13. Light (light in the same wavelength range as the fluorescent color emitted by the fluorescent substance 13), and the light transmitted through the phosphor film without hitting the fluorescent substance 13 is white light.
The color of the light emitted to the surface side of b, 11c, that is, the color of the displayed pixel is the color of the fluorescent light emitted by the fluorescent substance 13. The color density of this pixel is determined by the amount of the fluorescent substance 13 mixed in the phosphor film.

As described above, the above-mentioned liquid crystal display element has a liquid crystal /
Since the display is performed by utilizing the scattering and transmission of light in the polymer composite film, a polarizing plate which is indispensable for a TN type liquid crystal display element is not required, and the phosphor films 11a, 11b, 1 are not required.
Since the pixel can be colored by 1c, a color filter is not necessary, and therefore, there is no light amount loss due to light absorption by the polarizing plate and the color filter.

The phosphor films 11a, 11b, 11
c does not transmit only light in a specific wavelength range of visible light and absorbs light in other wavelength ranges into colored light as in a color filter, but emits fluorescence by the energy of the absorbed light. Therefore, the phosphor films 11a, 11
The intensity of the light colored by b and 11c is much higher than the intensity of the colored light by the color filter. Note that the fluorescent substance 13 in the phosphor films 11a, 11b, 11c emits fluorescence not only with visible light but also with wavelength light outside the visible light band, and therefore, the fluorescence emitted from the phosphor films 11a, 11b, 11c. Is high-brightness light.

Therefore, according to the above liquid crystal display device,
A very bright multicolor image can be displayed with significantly reduced light loss. In the above embodiment,
Since a black dichroic dye is mixed in the liquid crystal of the liquid crystal / polymer composite film 20, the color of the dark display is black. Therefore, the displayed multicolor image is a high-contrast image. is there.

Note that the phosphor film 11 in the above embodiment was used.
a, 11b, and 11c are obtained by mixing only the tendency material 13 into the transparent base material 12, and as shown in FIG. By adding a coloring pigment (pigment used for a color filter) 14 that transmits light in the wavelength range corresponding to the color and absorbs light in other wavelength ranges, the phosphor films 11a, 11
The color purity of the light colored by b and 11c can be improved.

In this case, a red pigment is added to the red phosphor film 11a, a green pigment is added to the green phosphor film 11b, and a blue pigment is added to the blue phosphor film 11c. When a color pigment is added to the phosphor films 11a, 11b and 11c, the light passing through the phosphor films 11a, 11b and 11c is absorbed to a certain extent by the pigment, and the intensity of the reflected light is reduced accordingly. By appropriately selecting the amount of the pigment to be added, it is possible to obtain colored reflected light having good color purity and sufficient intensity.

Further, the phosphor film 11 in the above embodiment is used.
Reference numerals a, 11b, and 11c denote transparent substrates 12 mixed with a tendency substance 14, and the fluorescent films 11a, 11b,
11c may be formed by depositing a transparent substrate on a substrate and dyeing the transparent substrate with a fluorescent dye.

Further, in the liquid crystal display device of the above embodiment, the reflection plate 30 is provided on the outer surface of the back substrate 1, but instead of the reflection plate 30, a reflection film is provided on the inner surface of the back substrate 1. Or the phosphor films 11a, 11b, 11c
May be provided so as to overlap the pixel electrode 3.

[0049]

[0050]

[0051]

[0052]

Further, in the above embodiment, the nematic liquid crystal is used as the liquid crystal of the liquid crystal / polymer composite film 20, but this liquid crystal may be a cholesteric liquid crystal. Since the array structure has a spiral structure, the light scattering property is high, so that the dark display can be made darker and the display contrast can be further increased.

Further, in the above embodiment, the liquid crystal / polymer composite film 20 has a dichroic dye mixed in the liquid crystal. However, the composite film 20 has a dichroic dye mixed in the liquid crystal. The display may be performed by scattering light in an electric field-free state and transmitting light in an electric field applied state. The active element is a TFT
Not limited to this, MIM or the like may be used.

[0055] In the real施例described above, the rear substrate 1
Are provided with phosphor films 11a, 11b, and 11c, but the phosphor films 11a, 1b are provided on both the back -side substrate 1 and the front-side substrate 2.
1b and 11c may be provided. Note that both substrates 1 and 2
When the phosphor films 11a, 11b and 11c are provided on the substrate, the phosphor films of the same color are formed to face each other.

[0056]

[0057]

[0058]

Since the active matrix liquid crystal display device of the present invention utilizes the scattering and transmission of light in a liquid crystal / polymer composite film to display an image, it is indispensable for a TN type liquid crystal display device. Since a polarizing plate is not required and a color filter is not required because pixels can be colored by the phosphor film, there is no loss of light amount due to light absorption by the polarizing plate and the color filter. Therefore, according to this liquid crystal display device, it is possible to display a very bright multicolor image with significantly reduced light loss.

[Brief description of the drawings]

Sectional view of a portion of the liquid crystal display device showing an embodiment of the present invention; FIG.

FIG. 2 is an enlarged sectional view of a part of a phosphor film.

FIG. 3 is an enlarged cross-sectional view of one liquid crystal portion of the liquid crystal / polymer composite film in an electric field-free state and an electric field applied state.

FIG. 4 is a cross-sectional view of a part of a phosphor film to which a coloring pigment is added.

[Explanation of symbols]

 1, 2 ... substrate 3 ... pixel electrode 4 ... active element (TFT) 10 ... counter electrode 11a ... red phosphor film 11b ... green phosphor film 11c ... blue phosphor film 12 ... transparent substrate 13 ... phosphor material 14 ... coloring Pigment 20: Liquid crystal / polymer composite film 21: Polymer layer 22: Liquid crystal part A: Liquid crystal molecule B: Dichroic dye molecule

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-173122 (JP, A) JP-A-5-241143 (JP, A) JP-A-63-15221 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G02F 1/1335

Claims (1)

(57) [Claims] 1. An active matrix liquid crystal display element for displaying a multicolor image, comprising: a first substrate provided with a plurality of pixel electrodes and a plurality of active elements respectively corresponding to the pixel electrodes; A liquid crystal / polymer composite film in which a second substrate provided with a counter electrode facing a pixel electrode is disposed with their electrode forming surfaces facing each other, and a liquid crystal is dispersed in a polymer layer between the two substrates. And, on the electrode forming surface of the first substrate,
In front of phosphor films of multiple colors that emit fluorescence of different colors
It is arranged below the pixel electrode in correspondence with the pixel electrode, and the first
A reflector is provided on the outer surface of the substrate opposite to the electrode forming surface.
An active matrix liquid crystal display device characterized by being placed .