JP3941207B2 - Diffuse reflector, manufacturing method thereof, and reflective liquid crystal display using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reflective liquid crystal display used as a home, office, and portable information display terminal, a diffuse reflector, and a method for manufacturing the same.
[0002]
[Prior art]
A liquid crystal display (LCD) is widely used as a display unit of a notebook personal computer because it has features of low power consumption and space saving. In recent years, LCDs have been increasing in size and are expected to replace CRTs (Cathod Ray Tubes). These employ a transmission type in which a light source called a backlight is placed on the back of the LCD body and the transmitted light is viewed. The power consumption of the backlight occupies most of the power consumption of the LCD module, and has the disadvantages that the thickness of the backlight increases, is heavy, and generates heat.
[0003]
On the other hand, in the reflective LCD, the external light incident from the display surface side is reflected by the metal reflector and used for display, so the thickness is thin, light and does not generate heat. For this reason, it has been adopted as a display for small calculators, mobile phones, and the like that require battery life and portability. In recent years, with the development and popularization of portable information processing devices such as mobile phones and mobile computers with a large amount of information, a reflective LCD with high image quality, particularly full color display, has been demanded. However, the conventional reflective LCD is not suitable for a high-quality full-color LCD because the screen is not bright enough.
[0004]
The brightness of the reflective LCD screen is greatly affected by the diffuse reflector. Three types of diffuse reflectors have been proposed. The first is a method in which a diffuse reflector is provided on the back surface of the liquid crystal, which further includes a diffuse reflector 102 shown in FIG. 1A on the back surface of the LCD 101 and an LCD 101 shown in FIG. Divided into things. The second is the one in which the liquid crystal itself shown in FIG. 1 (c) diffuses, and the third is the one having the rear reflector 103 and the front diffuser 104 shown in FIG. 1 (d). In the case where the liquid crystal 105 itself diffuses, the liquid crystal layer becomes thick in order to obtain strong diffusion, and as a result, the driving voltage increases. An image having a back reflector and a front diffuser is blurred by diffusion at the front. On the other hand, such a problem does not occur in a case having a diffuse reflector. However, those having a diffuse reflector on the back of the LCD have a long optical path of the reflected light, which causes a parallax problem, resulting in a decrease in contrast and color bleeding. An LCD having a diffuse reflector in the LCD can avoid the parallax problem since the optical path of the reflected light is the shortest.
[0005]
Further, since the electrodes on the back substrate do not need to transmit light, a metal can be used. If this also serves as a diffuse reflector, the parallax can be minimized. Such a diffuse reflector is manufactured by forming a highly reflective metal thin film such as aluminum or silver having a high reflectance on a concavo-convex surface in a predetermined electrode shape. A cross-sectional view of this type of LCD is shown in FIG.
[0006]
In order to brighten the display on the reflective LCD, the reflectance of the diffuse reflector must be increased. However, simply increasing the reflectance of the diffuse reflector material does not solve the problem. Since the diffuse reflector is covered with high refractive index liquid crystal and glass, the incident angle causing total reflection at the interface between the air and the front substrate becomes relatively small, and most of the reflected light is confined in the panel. Because. Therefore, it is necessary to control the shape of the irregularities on the surface so that the amount of reflected light to the front surface of the diffuse reflector is increased. Moreover, in order to avoid coloring due to interference between reflected lights, the uneven shape needs to be somewhat messy.
[0007]
[Problems to be solved by the invention]
As a method for forming such a concavo-convex shape, a bead dispersion coating, an embossing method, a sputtering / vapor deposition method, and a photolithography method can be considered. A film obtained by coating beads having an appropriate shape dispersed in a binder requires a large amount of beads, but there is a problem that uniform application becomes difficult when the amount of beads is large. The embossing method has a problem that the unevenness is fine, the accuracy is high, and a large embossed plate is expensive. The sputtering / evaporation method has a problem that the equipment becomes large in order to obtain a high vacuum. Photolithography is a simple method compared to these methods, but it still requires a development process that uses a developer. Therefore, it is necessary to secure a space for the developing machine, separately require pure water equipment, and manage and discard the developer. There is a problem. Both have problems in industrial implementation. Alternatively, in order to make the uneven shape smooth, it is necessary to heat the pattern after forming it so that the shape becomes gentle. For this reason, there also exists a problem that the uneven | corrugated pitch is restrict | limited.
[0008]
The present invention has been made in view of the above problems, and it is an object of the present invention to provide a diffusive reflector that is extremely simple to manufacture, a manufacturing method thereof, and a reflective liquid crystal display using the same.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention
The diffusive reflector according to claim 1 has at least a photosensitive resin on which unevenness is formed by exposure and baking on a substrate, and a metal film.
The diffusive reflector according to claim 2 is based on the diffusive reflector according to claim 1, wherein the unevenness is 10 μm or less and the maximum height is 500 mm or more. is there.
The method for producing a diffuse reflector according to claim 3 includes a step of applying a photosensitive resin on a substrate, a step of exposing with a predetermined photomask, a step of forming irregularities on the surface of the photosensitive resin by baking, the irregularities It includes at least a step of forming a metal film thereon.
According to a fourth aspect of the present invention, there is provided a reflective liquid crystal display in which the diffuse reflector is incorporated.
A reflective liquid crystal display according to a fifth aspect is based on the reflective liquid crystal display according to the fourth aspect, and is characterized in that the diffuse reflector also serves as an electrode.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The difference between the present invention and the method of forming irregularities by a photolithography method using a photosensitive resin is whether or not the development step is included. A feature of the present invention is that it does not include a development step. Hereinafter, a description will be given with reference to FIG.
[0011]
First, a photosensitive resin 202 is applied on the substrate 201 (see FIG. 2A). The required properties of the resin are that at least the film after firing should withstand the heating during the formation of a metal film (aluminum, chromium, silver, copper, etc.) and be chemically stable to the liquid crystal. It is. The phenomenon of the present invention is a phenomenon that appears in both negative and positive photosensitive resins. As a coating method, a spin coating method, a roll coating method, a printing method, or the like may be selected depending on the resin. After coating, the coating film is dried at an appropriate temperature.
[0012]
After drying, exposure is performed using a predetermined photomask 203 (see FIG. 2B). As for the pattern of the photomask, it is preferable that dot-like patterns are randomly distributed in position. The size of the dots is preferably about 10 μm to submicron in diameter. The exposure amount is set according to the photosensitivity of the resin. After exposure, without being developed, it is placed in an oven 206 and baked (see FIG. 2C). The firing condition may be a condition in which the resin is sufficiently thermoset. When baked, the unexposed part becomes lower than the exposed part, and as a result, irregularities 204 reflecting the pattern of the photomask are formed (see FIG. 2D).
[0013]
The reason why the relative height difference occurs between the exposed part and the unexposed part is considered to be that the reaction of the photosensitive resin proceeds in the exposed part, but there are many unreacted substances in the unexposed part, and this is evaporated by heating. In this method, the uneven cross-section is composed of a sinusoidal continuous curve according to SEM observation. The uneven step can be controlled to some extent by increasing the film thickness or increasing the amount of exposure, but can be generally controlled at 50 to 1 μm. A metal film 207 such as aluminum or silver is formed on the irregular surface by a regular sputtering method or vapor deposition method (see FIG. 2E).
[0014]
The average size of the uneven pattern is 10 μm or less, preferably 5 μm, and the height is 500 mm or more, preferably 2000 mm or more. When the pattern is larger or lower than this, the diffusion is weak and the specular reflection of the metal film cannot be eliminated.
[0015]
When multiple exposure is performed by changing the mask position and changing the exposure amount during exposure, it is possible to obtain a more complex uneven surface with mixed pitches and height differences.
[0016]
The diffusive reflector obtained in this way has a strong light diffusion property toward the front surface of the substrate due to the uneven surface while having a high reflectance by the metal film.
[0017]
In addition, it is possible to manufacture a diffuse reflector that also serves as an electrode by patterning a metal film in a stripe shape or an appropriate shape by mask patterning or photolithography.
[0018]
In this case, a reflective LCD 301 can be obtained by using a diffuse reflection plate 304 as a rear substrate, bonding the front substrate on which the color filter 302 is formed with a minute gap, and sealing the liquid crystal 303 in the gap. (See FIG. 3).
[0019]
【Example】
[Example 1]
390 g of epoxy resin (manufactured by Toto Kasei Co., Ltd .: “YDPN-601”) and 108 g of acrylic acid were dissolved in 750 g of 1,6-hexanediol acrylate, and in the presence of 0.5 g of hydroquinone and 3 g of methylethylammonium iodide. It was made to react at 100-150 degreeC for 2 hours. Subsequently, 279 g of anhydrous head acid was added and reacted at 100 to 150 ° C. for 2 hours to obtain a water-soluble photopolymerizable oligomer.
[0020]
100 parts by weight of the obtained water-soluble photopolymerizable oligomer, 40 parts by weight of a phenol novolac type epoxy resin (manufactured by Toto Kasei Co., Ltd .: “YDCN-602”) as a water-insoluble photopolymerizable oligomer, and trimethyl as a photopolymerizable monomer 20 parts by weight of methylolpropane triacrylate (manufactured by Kyoeisha Yushi Co., Ltd .: “TMP-A”), 5 parts by weight as a photopolymerization initiator (manufactured by Ciba Geigy: “Irgacure-651”), diphenyl as a photocuring catalyst precursor A negative photosensitive resin material (1) was obtained by mixing 0.5 parts by weight of iodonium hexafluoroantimonate and 0.1 parts by weight of hydroquinone as a polymerization inhibitor in 1000 parts by weight of butyl cellosolve.
[0021]
A negative photosensitive resin material (1) was applied on a glass substrate by a spin coating method and dried at 70 ° C. for 30 minutes to obtain a resin film having a thickness of 1.6 μm. The resin film was exposed at 50 mJ / cm ² and baked at 150 ° C. for 1 hour using a photomask in which dot patterns with a diameter of 8 μm were randomly arranged on one surface. After firing, the resin film surface was observed with an SEM. As a result, dot-shaped irregularities having a height of 2000 mm were formed. On this unevenness, an aluminum film having a thickness of 1500 mm was formed by sputtering to obtain a diffuse reflector.
[0022]
In the obtained diffuse reflector, most of the reflected light gathered within 30 ° in the vertical and horizontal directions. Although the metal film itself was almost specular, the specular reflection was completely eliminated by diffusion due to rough irregularities.
[0023]
Next, a diffuse reflection plate was used as the back substrate, and the front substrate on which the color filter was formed was bonded with a fine gap, and liquid crystal was sealed in the gap to obtain a reflective LCD. The reflective LCD thus obtained had a small parallax and a good contrast.
[0024]
[Example 2]
A positive photosensitive resin material MP1400-31 (manufactured by Shipley Far East) was applied on a glass substrate by spin coating, and dried at 90 ° C. for 30 minutes to obtain a resin film having a thickness of 3 μm. The resin film was exposed at 50 mJ / cm ² and baked at 150 ° C. for 1 hour using a photomask in which dot patterns with a diameter of 10 μm were randomly arranged on one surface. After firing, the resin film surface was observed with an SEM. As a result, dot-shaped irregularities having a height of 2200 mm were formed. On this unevenness, 1500 mm of aluminum film was formed by vapor deposition to obtain a diffuse reflector.
[0025]
In the obtained diffuse reflector, most of the reflected light gathered within 30 ° in the vertical and horizontal directions. Although the metal film itself was almost specular, the specular reflection was completely eliminated by diffusion due to rough irregularities.
[0026]
Next, a diffuse reflection plate was used as a back substrate, and a front substrate on which a color filter was formed was bonded with a fine gap, and then liquid crystal was sealed in the gap to obtain a reflective LCD. The reflective LCD thus obtained had a small parallax and a good contrast.
[0027]
【The invention's effect】
According to the first and second aspects of the present invention, it is possible to obtain a diffusive reflector having high reflectivity and effective light diffusion characteristics toward the front surface. Further, according to the invention described in claim 3, in the production, the development process is not required and the production can be performed at low cost. Furthermore, according to the invention described in claim 4, it is possible to obtain a good reflective LCD. Furthermore, according to the invention described in claim 5, the parallax can be minimized by combining the functions of the electrodes. This makes it possible to obtain a bright and high-quality reflective LCD.
[0028]
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a setting format of a diffuse reflector in a reflective LCD.
FIG. 2 is an explanatory view explaining the manufacturing method of the present invention.
FIG. 3 is a cross-sectional view of a reflective LCD in which a diffuse reflector also serves as an electrode.
[Explanation of symbols]
101 LCD
102 Diffuse Reflector 103 Back Reflector 104 Front Diffuser 105 Liquid Crystal 106 Light 201 Substrate 202 Photosensitive Resin 203 Photomask 204 Irregularities 205 on Photosensitive Resin Film Exposure 206 Oven 207 Metal Film 301 Reflective LCD
302 Color filter 303 Liquid crystal 304 Diffuse reflector that also serves as an electrode

Claims (4)

It includes at least a step of applying a photosensitive resin on the substrate, a step of exposing with a predetermined photomask, a step of forming irregularities on the surface of the photosensitive resin by baking, and a step of forming a metal film on the irregularities. A manufacturing method of a diffuse reflector. 2. The method of manufacturing a diffuse reflector according to claim 1, wherein multiple exposure is used in the exposing step. Claim 1 or method of manufacturing a reflective liquid crystal display according to claim claim 2 in production that write set a diffuse reflector made free by the process. 4. The method of manufacturing a reflective liquid crystal display according to claim 3, wherein the diffuse reflector also serves as an electrode.

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