JP2003021708A - Reflective substrate, method of forming the same, and reflective display element using the same - Google Patents

Abstract

(57) [Summary] [Object] To realize a wide viewing angle while maintaining a bright display on a reflective substrate used for a reflective display element or the like. A reflection portion has a structure in which a reflection film and a transparent resin film in which a phosphor is dispersed are laminated, and a particle diameter of the phosphor dispersed in the transparent resin is 0.1 μm to 5 μm. I do.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display element, and more particularly to a reflective display element that displays by controlling reflection of light from an external light source in combination with a display medium having an optical shutter function such as liquid crystal. And a method for forming a reflective substrate.

[0002]

2. Description of the Related Art A reflective display device using an optical switch such as a liquid crystal does not require a backlight, and thus consumes less power and is smaller in size and weight than a backlight type transmissive display device. It is widely used as a display for small notebook personal computers, mobile terminals, mobile phones, etc., and it is expected that the application range will be further expanded and demand will be increased in the future.

FIG. 1 shows an example of a cross section of a reflective display element using a liquid crystal as a first conventional example. In FIG. 1, 1 is a front glass substrate, 2 is a reflection side substrate, and these two substrates are opposed to each other by a spacer (not shown) so as to maintain a predetermined distance. A liquid crystal 4 is enclosed as a display medium between the opposed substrates. The liquid crystal 4 is applied with a voltage between the transparent display electrode 11 formed on the front glass substrate 1 and the reflective display electrode 21 formed on the reflection-side substrate 2 to cause the state of liquid crystal molecules. Can be controlled, and in combination with the polarizing plate 13 provided on the surface of the front glass substrate, it can function as an optical switch for switching between transmission and absorption of external visible light that has passed through the front glass substrate 1 and is incident. it can. Further, on the front glass substrate 1, R, G, B color filters 12R, 1
2G and 12B are provided so as to correspond to the display electrode 11 for each pixel for each color, and by transmitting only the color component corresponding to each pixel from the incident external light, R
Color display can be performed according to the combination of GBs. In addition, 14 is a black matrix for blocking the leaked light at the boundary of the color filter to improve the contrast, and 15 and 22 control the alignment direction of the molecules of the liquid crystal 4 on the surface of each substrate. Is an alignment film for.

When the liquid crystal 4 is in the transmissive state, external light incident from the front glass substrate 1 side passes through the polarizing plate 13 and the front glass substrate 1, and the color filter 12 * (* indicates R / G /
In (B)), only the corresponding color component is selected, further passes through the display electrode 11, passes through the liquid crystal 4, and reaches the reflection side substrate 2. This light is reflected by the reflective electrode 21, and again the liquid crystal 4, the display electrode 11, and the color filter 12
*, Emitted through the front glass substrate 1 and the polarizing plate 13 to the front glass substrate surface side which is the observation surface, and color display light is obtained. By the way, in this reflective liquid crystal element, the light source is only ambient light, and a brighter display than the brightness of ambient light cannot be obtained. In reality, the color filter absorbs light other than the required wavelength and causes a large amount of attenuation.In addition, the required wavelength component that has passed through the filter is also attenuated at the stage of passing through each layer that constitutes the element, so ambient light However, only a fairly dark display can be obtained.

Therefore, according to Japanese Unexamined Patent Publication No. 7-110477 (conventional example 2), a reflecting plate having a daylight phosphor film 23 on the surface of the reflecting electrode 21 is used on the reflecting side as shown in FIG. A reflective display device without a color filter has been proposed. In this reflective display element, since the color filter is not used, not only the attenuation of the light by the color filter disappears, but also the light of the wavelength component absorbed by the color filter until now is converted into the light of the useful wavelength. Therefore, the display can be brighter than the ambient light.

[0006]

However, in the conventional reflective substrate using the phosphor as shown in FIG. 2, the viewing angle, which is a large performance factor of the display element, is not mentioned.

It is an object of the present invention to realize a wider viewing angle in a reflective substrate that uses a phosphor to obtain a bright display.

[0008]

The reflective substrate of the present invention has a reflective portion for reflecting incident light on the substrate, and at least a part of the reflective portion has a reflective layer for reflecting the incident light, Particles that emit fluorescence of a predetermined wavelength in response to the incident light is composed of a laminated structure with a transparent medium dispersed therein, the particles that emit fluorescence of the predetermined wavelength is an average of the transparent medium. The size is 0.1 μm or more and 5 μm or less, and more preferably, the weight ratio of the entire particles to the transparent medium is 10 wt% or more and 50 wt% or less.

Further, the reflection type display element of the present invention is characterized in that the reflection substrate having the above structure is used as the reflection side substrate.

Further, in the method for forming a reflective substrate of the present invention, polyhydric alcohol is used as a solvent for dissolving the transparent medium in the step of dispersing particles emitting fluorescence of a predetermined wavelength in the transparent medium. I am trying.

In realizing the reflective substrate of the present invention,
First, the inventors prepared a sample under the following conditions in order to evaluate the viewing angle characteristics of the reflective substrate shown in FIG.

First, an acrylic resin used as a transparent medium is diluted with acetone which is a general solvent, and the diluted product is a daylight fluorescent substance FZ-5005 manufactured by Sinlohi Co., which emits yellow-green fluorescence upon receiving visible light. The transparent medium was mixed and stirred so that the weight ratio was 20 wt%. This is applied onto a glass substrate having an aluminum reflective electrode 21 formed thereon by spin coating so that the film thickness after curing is 3 μm,
The phosphor film 23 was cured by heating. Hereinafter, the sample prepared under these conditions is referred to as Comparative Example 1.

3 and 4 show the reflection spectrum and viewing angle characteristics of the reflective substrate of Comparative Example 1, respectively. Here, θ represents the inclination with respect to the vertical line of the panel surface, and the light source is a parallel light beam from a direction inclined by −30 ° (θ = −30 °) from the vertical direction of the panel surface, and θ = for a standard white plate. The amount of reflected light at 0 ° is defined as 100% reflectance. As can be seen from FIG. 3 and FIG. 4, in Comparative Example 1, the reflectance decreases to 1/200 when deviating from the regular reflection direction of θ = 30 ° by ± 5 °, and the viewing angle becomes very narrow. There is.

As a result of investigating the cause of the narrowing of the viewing angle, the following has been found. Originally, fluorescent pigments have a particle size of several μm, which is sufficiently large for the wavelength of light.
Scatters incident light. However, when the fluorescent pigment is diffused in the resin dissolved in the solvent when forming the phosphor film, the fluorescent pigment dissolves in the solvent, and the undissolved particles are reduced to 0.1 μm or less. In this trial production condition,
The average particle size of the undissolved particles was 0.05 μm. As a result, the resin is colored by the melted pigment, and fine pigment particles are dispersed in the resin. This state is preserved as it is even after the solvent is evaporated to solidify the resin.

Here, when the particle diameter of the fluorescent pigment is smaller than 0.1 μm, the size becomes less than ¼ wavelength of visible light,
Scattering of light by the pigment particles hardly occurs. As a result, most of the incident parallel light is specularly reflected. Therefore, the viewing angle becomes extremely narrow.

As one method for solving this problem, it is conceivable that unevenness is provided on the base of the reflective electrode so that light is scattered on the surface of the reflective electrode. However, the unevenness is complicated. A process is required, which leads to an increase in cost.

As another method, it is conceivable to increase the particle size in the medium to a size at which light is scattered. In this method, a wide viewing angle can be obtained without using a complicated substrate structure. .

However, in the conventional general pigment dispersion method, it is difficult to increase the particle size because the pigment dissolves in the solvent.

Therefore, the inventors have studied the method of dispersing the pigment. As a result, it was found that when polyhydric alcohol was used as the solvent of the transparent medium, the dispersed fluorescent pigment maintained a relatively large particle size.

For example, as shown in Table 1, when polyhydric alcohol such as glycerin or ethylene glycol is used as a solvent, the average particle diameter of the phosphor in the transparent medium is 1 to 2 μm, and with diethylene glycol, Although the average particle size is greatly reduced, it becomes larger than 0.1 μm. On the other hand, when a solvent other than polyhydric alcohol such as acetone or methyl ethyl ketone is used, the particle size becomes smaller than 0.1 μm.

[0021]

[Table 1]

FIG. 5 shows the reflection spectrum characteristics when the particle diameter is 1 μm, using the angle as a parameter. Further, FIG. 6 shows the angle dependence of the reflectance measured with the particle size as a parameter. Here, the preparation and measurement conditions of the sample in FIGS. 5 and 6 are the same as those of Comparative Example 1 except that the type of the solvent of the transparent medium was changed in order to control the particle size of the pigment. Compared to Comparative Example 1, the peak reflectance is reduced, but the viewing angle is significantly improved. For a particle size of 1 μm, the reflectance of 70% or more of the peak value is ± 30 °. I know there is. FIG. 7 shows the relationship between the particle diameters of the yellow-green and red phosphors and the reflection characteristics (ratio of reflectance at θ = 0 ° and θ = 30 °). It means that the closer the reflection characteristic is to 1, the smaller the viewing angle dependence is, and it is understood that the reflection characteristic is as good as 0.6 or more in the range of the particle diameter specified in the present invention.

On the other hand, the upper limit of the particle size is dominated by the restriction due to the thickness of the resin film. This is because if the phosphor particles are thicker than the resin layer, the control of the cell thickness of the liquid crystal is affected, so that the particle diameter larger than the film thickness is not desirable. As the thickness of the resin film increases, the attenuation of light increases and the reflectance decreases. Further, since stress due to thermal expansion / contraction when temperature changes becomes large and problems such as peeling occur, the film thickness is preferably about 5 μm or less, and the particle size must be suppressed to be less than that.

Next, the relationship between the weight ratio of the phosphor to the transparent medium and the reflectance was investigated. FIG. 8 shows the change in reflectance when the weight ratio of the yellow-green phosphor having a particle diameter of 1 μm was changed, and FIG. 9 shows the change in reflectance when the weight ratio of the red phosphor was changed. Are shown respectively. As can be seen from the figure, each color exhibits a reflectance of 70 to 80% at 10 wt%, reaches a peak at 20 to 30 wt%, and gradually decreases below that. The flatness of the resin film surface is
In particular, this is a problem when the display electrode is formed on the resin film, but from this viewpoint, it is desirable to make the weight ratio of the phosphor to the transparent medium as small as possible. Therefore, it can be said that the optimum weight ratio of the phosphor to the transparent medium is 10 wt% or more and 50 wt% or less, especially about 20 to 30 wt%. Further, FIG. 10 shows the change in chromaticity when the weight ratio of the phosphor that emits yellow-green fluorescence is changed, and FIG. 11 shows the change when the weight ratio of the phosphor that emits red fluorescence is changed. The changes in chromaticity are shown respectively. In addition, in both figures,
For comparison, the chromaticity of RGB of a color filter type reflective liquid crystal panel mounted on a commercially available mobile terminal is plotted. As can be seen from the figure, in the reflective substrate of the present invention, the color purity increases as the weight ratio of the phosphor to the transparent medium increases, but it is almost saturated at about 30 wt%,
Almost no difference from the case of 50 wt%. That is, from the viewpoint of color purity, it is desirable to increase the weight ratio of the phosphor to the transparent medium, but even if 30 wt% or more is added, a large effect cannot be obtained. From these results, the weight ratio of the phosphor to the transparent medium is 10 to 50w.
It was found that t% is good, and it is particularly desirable to set it in the range of 20 to 30 wt%.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION [Embodiment 1] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
In each drawing, the same parts as those in the conventional example are designated by the same reference numerals and the description thereof will be omitted.

FIG. 12 shows an example of the structure of the reflective substrate according to the first embodiment of the present invention. In the figure, 3 is a substrate such as glass, 31 is a reflective film, and 32R / G are transparent resin films in which red / green daylight fluorescent pigments having an average particle diameter of about 1 μm are dispersed. The reflective portion corresponding to B is configured to use the colored reflective film 33 containing a pigment that reflects only blue light and absorbs light of other wavelengths.

This is because the blue light has a short wavelength and the excitation energy is high, so that the conversion efficiency of the blue phosphor is low in visible light, and when the daylight phosphor reflection film is used for all red / green / blue. This is because there is a problem that the color balance of the display is deteriorated because only the blue color becomes extremely dark. Therefore, the configuration is used in which the deterioration of the color balance is alleviated by using the reflection of the incident light instead of the fluorescence of the blue color only.

Since the blue pigment such as phthalocyanine used this time has high transparency, scattering of reflected light hardly occurs. Therefore, when only the pigment is dispersed in the medium, there is a problem that the viewing angle becomes narrow. Therefore, in order to cause scattering, white particles such as titanium oxide having an average particle diameter of about 0.1 to 2 μm are mixed. There is.

Further, 34 is a resin film 32R / G and 33.
A pixel electrode formed of a transparent electrode formed on the above, 35 is an area for one pixel, 36 is a TFT for one pixel forming a active matrix for controlling liquid crystal (schematic), 381 is TF
Reference numeral 382 denotes a contact hole between T36 and the reflective film 31, and 382 denotes a contact hole for electrically connecting the reflective film 31 and the pixel electrode 34, respectively.

The reflective film 3 is formed on the substrate 3 as described above.
1, a resin film 32R / G containing a fluorescent substance, a resin film 33 containing a blue pigment, a pixel electrode 34, a TFT 36, etc. are referred to as a front side or a reflection side "assembly substrate". To distinguish. This reflective side assembly substrate was prepared as follows.

First, an active matrix using the TFTs 36 is formed on the glass substrate 3, an interlayer insulating film (not shown) is formed on the entire surface, and then the interlayer insulating film in the first contact hole 381 is formed by a photo process and dry etching. Removed. Next, an aluminum film having a film thickness of 0.1 μm was formed on the entire surface by sputtering, and patterned so as to be separated at least in each pixel region to form a reflective film 31. Next, in the acrylic resin diluted with ethylene glycol, the red / green phosphors were mixed and stirred so that the weight ratio was 30 wt% with respect to the weight of the resin component, and the paste and the blue paste were mixed. A paste prepared by mixing a pigment and fine particles of titanium oxide for scattering (average particle diameter 0.3 μm) with a resin component in an amount of 7 wt% and 0.4 wt%, respectively, and stirring the mixture,
Printing was carried out by a screen printing method so that they would not overlap. At this time, the coating thickness was adjusted so that the thickness after resin curing was 3 μm. Then, the resin was heat-cured to form resin films 32R / G and 33. Further, the resin in the second contact hole 382 portion was removed by a photo process and dry etching, and then a transparent electrode film of indium oxide was formed to a thickness of 0.2 μm by sputtering, and the pattern of the pixel electrode 34 was etched.

In the above example, the reflective film 31 is separated for each pixel and connected to the transparent pixel electrode 34, but it is not always necessary to separate for each pixel. In this case, the contact hole 381 is arranged so that the pixel electrode 34 is directly connected to the source electrode of the TFT, and the contact hole 3 is arranged so that the reflective film 31 does not make electrical contact with the pixel electrode 34.
It is necessary to form a pattern in which the peripheral portion of 81 is removed.

FIG. 13 shows a plot on the chromaticity diagram of each color of this substrate in comparison with a commercially available reflective liquid crystal panel (Comparative Example 2). It can be seen that in the case of blue that does not use fluorescence, the color purity is almost the same as in Comparative Example 2, and that in the cases of red and green that use phosphors, the color purity is high.

In this embodiment, a pigment that does not show fluorescence is used for the blue film. However, in the case where the incident light contains a lot of short-wavelength components such as ultraviolet rays, blue fluorescence is efficiently emitted. Since a material that emits well can be selected, a phosphor may be used as in the case of red and green.

Further, it is needless to say that the coloring is not limited to the combination of three colors of red / green / blue, and any number of various colors can be combined according to the application.

[Embodiment 2] FIG. 14 is a block diagram of the first embodiment shown in FIG.
The schematic diagram at the time of applying the board | substrate of this invention shown in 2 to a reflective liquid crystal panel is shown.

A reflection side assembly substrate shown in FIG.
Liquid crystal alignment films 15 and 37 are formed by applying polyimide to a thickness of 0.1 μm on each of the front assembly substrates having the transparent electrodes 11 formed on the glass substrate 1, heating and curing, and rubbing the surfaces. And

A sealing material for sealing is printed on one of the front and reflection side assembly substrates, spacers made of, for example, resin beads are scattered on the surface of the other substrate, and then two assembly substrates are attached. In addition, the guest-host liquid crystal 4 in which the black dichroic dye was dispersed was sealed in the gap to complete the reflective liquid crystal display panel.

As a result of full-color display with this element,
The brightness is 1.5 to 2 times that of Comparative Example 2, the color purity is high,
It was confirmed that high quality images could be obtained.

In these examples, the substrate of the present invention is applied to an active matrix type liquid crystal display device using a TFT, but a combination with a simple matrix type liquid crystal, PLZT, electrochromic or the like is used. It is also possible to use it in combination with another display medium, or further as a sign or a signboard without combining with the display medium.

[0041]

INDUSTRIAL APPLICABILITY By dispersing a phosphor in a reflective film, incident light is converted into fluorescent light of a required wavelength to obtain bright reflected light. Particle size of phosphor to be dispersed is 0.1μ
By setting m to 5 μm, the viewing angle of reflected light can be expanded and the display brightness can be secured at the same time without using a complicated process.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a reflective liquid crystal panel of Conventional Example 1.

FIG. 2 is a cross-sectional view of a reflective substrate of Conventional Example 2.

FIG. 3 is a reflection spectrum of the reflective substrate of Comparative Example 1.

FIG. 4 is a view angle characteristic of a reflective substrate of Comparative Example 1.

FIG. 5: Reflection spectrum of the reflection substrate when the particle size is 1 μm

FIG. 6 shows the relationship between the viewing angle characteristics of the phosphor reflection film and the particle size of the phosphor.

FIG. 7: Relationship between fluorescent pigment particle size and reflection characteristics

FIG. 8 shows the relationship between the weight ratio of yellow-green phosphor and the reflectance.

FIG. 9 shows the relationship between the weight ratio of red phosphor and the reflectance.

FIG. 10: Relationship between the weight ratio of yellow-green phosphor and chromaticity

FIG. 11 shows the relationship between the weight ratio of red phosphor and chromaticity.

FIG. 12 is a cross-sectional view of a reflective substrate of Example 1 of the present invention.

FIG. 13 is a chromaticity plot of the reflective substrate of Example 1 of the present invention.

FIG. 14 is a sectional perspective view of a reflective display element according to a second embodiment of the present invention.

[Explanation of symbols] 1 ... Front (glass) substrate 11 ... (Transparent) display electrode 12R, 12G, 12B ... Color filter 13 ... Polarizing plate 2, 3 ... (Glass) substrate 21 .. Reflective electrodes 23, 32R, 32G ・ ・ Phosphor-containing resin film 31 .. Reflective film 33..Blue resin film 34 .. (Transparent) pixel electrode 35 ... 1 pixel area 36 ... TFT 4 ... Liquid crystal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09F 9/30 G09F 9/30 349D 349Z 9/35 9/35 (72) Inventor Shinji Tadaki Kanagawa 4-1-1 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Fujitsu Limited (72) Inventor Tetsuya Makino 4-1-1, Kamiodanaka, Nakahara-ku, Nakahara-ku, Kawasaki-shi (72) Inventor, Yoshinori Kiyota Kanagawa 4-1-1 Kamitadanaka, Nakahara-ku, Kawasaki-shi F-term within Fujitsu Limited (reference) 2H042 BA02 BA12 BA20 DA01 DA12 DA14 DA17 DA21 DA22 DE04 2H091 FA14Z FA43Z FB02 FC13 GA01 GA13 KA10 LA16 LA17 LA19 5C094 AA08 AA10 BAA32 A32 BA43 CA19 CA24 DA13 EA04 EA05 EA06 EB04 ED02 ED13 ED20 FA01 FB01 GB10 JA01 JA08

Claims (5)

[Claims] 1. A substrate has a reflection portion for reflecting incident light, at least a part of the reflection portion reflecting layer for reflecting the incident light, and fluorescent light having a predetermined wavelength upon receiving the incident light. A reflective substrate having a structure in which a transparent medium in which particles that emit light are dispersed is laminated, and the particles that emit fluorescence of the predetermined wavelength have an average size of 0.1 μm in the transparent medium. A reflective substrate having a thickness of 5 μm or less. 2. The weight ratio of the entire particles that emit fluorescence of the predetermined wavelength to the transparent medium is 10 wt% or more and 50 w.
It is t% or less, The reflective substrate of Claim 1 characterized by the above-mentioned. 3. The reflection part is at least separately coated into two regions that emit red and green fluorescence and a region that absorbs light of red and green wavelengths and reflects light of blue wavelengths. The reflective substrate according to claim 1, wherein the reflective substrate is provided. 4. A reflection type display device using the reflection substrate according to claim 1 as a reflection side substrate. 5. A substrate has a reflecting portion for reflecting incident light, at least a part of the reflecting portion reflecting layer for reflecting the incident light, and fluorescent light having a predetermined wavelength upon receiving the incident light. A method of forming a reflective substrate having a structure in which a transparent medium in which particles that emit are dispersed is laminated, wherein when the particles that emit fluorescence of the predetermined wavelength are dispersed in the transparent medium, the transparent A method for forming a reflective substrate, wherein a polyhydric alcohol is used as a solvent for dissolving the medium.