JP2001042319A - Production of light-reflecting substrate and reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a surface having smooth recesses and projections without melting resin at a high temperature in the process of roughening a photosensitive resin applied on a substrate by exposure and development to form recesses and projections for diffusion of light. SOLUTION: In the production of a light-reflecting substrate 20 to be used for a reflection type liquid crystal display device using an inner diffusion and reflection method, a positive photosensitive polyimide resin 27 is applied in a film state on a glass substrate 21 having a smooth surface, then the resin film is partially exposed through a photomask, developed and baked at a specified temperature. Thus, recesses 27a are formed in the positive photosensitive polyimide resin to roughen the surface. Then a light-reflecting layer consisting of a metal film is formed all over the roughened surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device of an internal diffuse reflection type, and more particularly, to a light reflective substrate thereof.

[0002]

2. Description of the Related Art A reflection type liquid crystal display element requires a light source from external light, and therefore does not require a backlight unlike a transmission type or semi-transmission type liquid crystal display element. For this reason, power consumption can be reduced, and reduction in thickness and weight can be achieved.

In order to make a liquid crystal display element reflective, a light reflection plate is provided integrally with a polarizing plate outside the liquid crystal display panel, or a light reflection layer is formed inside the liquid crystal display panel by, for example, aluminum sputtering. Like that.
In particular, when a light reflection layer is provided inside the panel, a light diffusion layer is separately provided inside or outside the panel in order to increase the viewing angle and efficiently use the indoor / outdoor illumination light as a light source. I have.

The light diffusion layer is preferably provided inside the panel in view of display resolution (internal diffuse reflection system). As an example of this, conventionally, a negative photosensitive polyimide film is formed on one glass substrate used for a liquid crystal display panel, and is developed after being exposed through a photomask having a predetermined light transmission pattern. And countless fine projections are formed and roughened.

[0005] The projection thus obtained has a substantially rectangular cross-section and has poor light diffusion. Therefore, the polyimide resin is melted by applying high heat to form a cross-section with a gentle corner. However, this conventional technique has the following problems.

[0006]

That is, when the melting temperature of the negative photosensitive polyimide resin to be used is extremely high, the shape of the convex portion is stable, and the film is formed thereon in a later step. The effect on various films is small, but on the other hand, it is necessary to use expensive glass such as non-alkali glass for the substrate because melting is not performed unless the temperature is considerably high.

[0007] This problem can be solved by using a negative photosensitive polyimide resin having a low melting temperature. However, in the case of a resin having a low melting temperature, it is necessary to form various films thereon in a later step. This is not preferable because there is a possibility that the protrusions may be reduced in film thickness or peeled off due to deformation.

[0008]

The above object can be achieved by using a positive photosensitive polyimide resin instead of a negative photosensitive polyimide resin.

That is, the present invention relates to a method of manufacturing a light-reflective substrate used as one substrate of a reflection type liquid crystal display element, wherein a positive photosensitive polyimide resin is coated on one surface of a transparent substrate having a smooth surface. After being applied in the form of a film having a predetermined thickness, the positive photosensitive polyimide resin film is partially exposed and developed through a photomask having a light transmission pattern formed regularly or irregularly, and developed. Thereafter, by firing at a predetermined temperature, a concave portion is formed in the positive photosensitive polyimide resin to roughen the surface, and a light reflection layer made of a metal film is formed over the entire rough surface. I have.

According to the positive photosensitive polyimide resin, a desired waveform shape can be obtained by adjusting the exposure condition and / or the development condition, and it is not necessary to melt the resin at a high temperature as in the prior art. Absent.

The positive photosensitive polyimide resin used in the present invention is a solvent-evaporable (solvent-soluble) polyimide, which is applied on a substrate by a spinner or the like. Actually, the film thickness will be in the range of 0.5 to 10 μm. However, in consideration of workability at the time of coating and a difference in thermal expansion from the substrate, etc. The range is preferably from 0 to 5.0 μm.

In the case of a positive photosensitive polyimide resin,
Baking is performed to evaporate the solvent (solvent),
The firing temperature may be in the range of 300-350C.
This temperature range is equal to or lower than the soda glass compaction (strain) generation temperature, so that expensive glass such as non-alkali glass is not required.

Further, the reflection type liquid crystal display element of the present invention comprises a transparent electrode substrate having a transparent electrode formed on a metal film of a light reflective substrate obtained by the above-mentioned manufacturing method, with a surface smoothing layer interposed therebetween. It is characterized in that it is provided as one of the substrates.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an embodiment of the reflection type liquid crystal display element 1 of the present invention will be described with reference to the schematic sectional view of FIG.

The reflection type liquid crystal display element 1 has a first electrode substrate 2 and a second electrode substrate 3, and the first electrode substrate 2 has a light-reflective substrate obtained by the manufacturing method of the present invention. 2
0 is used. The light-reflective substrate 20 has, as a base, a transparent glass plate 21 made of, for example, soda glass having a roughened surface 21a on one surface (the upper surface side in FIG. 1). Note that a plastic substrate may be used as long as it has heat resistance enough to withstand the firing temperature of the positive photosensitive polyimide resin.

A light reflection layer 23 made of a metal film is formed on the roughened surface 21a. In this embodiment, the light reflection layer 23 is made of an aluminum film formed by a sputtering method.
The film thickness is, for example, about 1000 °. The lower surface of the transparent glass plate 21 is smooth.

On the light reflecting layer 23, a surface smoothing layer 25 formed by applying, for example, an acrylic resin by a spinner is formed. In the case of a color display, a color filter layer is provided on the light reflection layer 23 by an electrodeposition method or the like.
The surface smoothing layer 25 is formed thereon.

The first electrode substrate 2 has the surface smoothing layer 2
5 is formed by sputtering ITO (Indium Tin Oxide), and its display portion has an ITO pattern 2a as a predetermined patterned display electrode.
Are formed.

The second electrode substrate 3 is made of a transparent glass substrate. In this case, a terminal portion 31 for forming an extraction electrode is continuously provided on the second electrode substrate 3 side. The display portion and the terminal portion 31 of the second electrode substrate 3 are formed with an ITO pattern 3a as a display electrode and an extraction electrode.

The first electrode substrate 2 and the second electrode substrate 3
These display portions are attached to each other via the peripheral seal material 4 with the display portions facing each other. In addition, an in-plane spacer (not shown) for keeping the cell gap constant between the display portions is arranged in advance, and a predetermined liquid crystal material 6 is sealed in the cell gap.

The peripheral sealing material 4 contains a transfer material 41 made of, for example, a conductive bead.
The O pattern 2a is connected to a lead electrode in the terminal portion 31 on the second electrode substrate 3 side. On the display surface side of the second electrode substrate 3, a retardation plate 7 and a polarizing plate 8 are attached, respectively.

Next, the light reflective substrate 20 will be described with reference to FIGS. To obtain the light-reflective substrate 20, a positive photosensitive polyimide resin 27 as a photoresist is applied to one surface (the upper surface side in FIG. 2) of the transparent glass plate 21 to a uniform thickness by a spinner or the like. .

The positive photosensitive polyimide resin 27 is a solvent-evaporable (solvent-soluble) polyimide, such as RN-901 manufactured by Nissan Chemical Industries, Ltd., for example. The coating thickness is 0.
5 to 10 μm is a practical range, but considering the ease of application and the difference in thermal expansion with the glass substrate, it is 1.0 to 10 μm.
A range of 5.0 μm is preferred.

Solvents contained after prebaking (solvents)
After volatilizing a part of the polyimide resin 27, a photomask M having a predetermined pattern for forming unevenness is formed.
It is set on the top, exposed with a batch exposure machine, and developed with a predetermined developer. Then, post baking is performed.

Since the polyimide resin 27 is of a positive type, the exposed portions are removed by development. Therefore, as illustrated in the enlarged sectional view of FIG. 3A and the enlarged plan view of FIG.
Are formed on the surface of the substrate. Finally, a light reflection layer 23 made of a metal film (FIG. 1)
) Is formed.

The depth RzD of the recess 27a depends solely on the exposure conditions and development conditions. Further, the pitch Sm and the size (opening area) of the concave portion 27a are determined by the light transmission pattern of the photomask M and the proximity gap. Therefore, by adjusting these conditions, the surface of the polyimide resin 27 can be approximated to an optimal waveform shape (ideally, a sine curve shape).

As described above, according to the positive photosensitive polyimide resin, an uneven shape having a smooth curve can be obtained without melting the resin at a high temperature as in the case of the negative photosensitive polyimide resin. Here, as shown in FIG. 3A, assuming that the angle between the tangent line at the edge of the concave portion 27a and the resin plane is an inclination angle θ, the inclination angle θ is also stable in each concave portion 27a. There is little variation. Therefore, uniform light diffusion over the entire surface can be obtained.

In order to improve the light diffusivity, FIG.
As shown in (a), a state in which the resin 27 is left at the bottom of the concave portion 27a, that is, a state in which the base glass surface is not exposed at the bottom is preferable. Further, in this example, as shown in FIG. 3B, each recess 27a is formed in an elliptical shape in plan view, but the present invention is not limited to this. The shape of each recess 27a can be arbitrarily selected.

[0029]

EXAMPLES Example 1 As a positive photosensitive polyimide resin, RN-901 manufactured by Nissan Chemical Co., Ltd. was applied to a glass substrate to a thickness of 2.0 μm by a spinner, and then placed in a batch furnace at 80 ° C. for 10 minutes. Prebaked. Next, a photomask (average opening diameter: 10 μm, average opening pitch: 13 μm) was set on the film, and exposure was performed by a proximity-type batch exposure machine (wavelength: 365 nm, exposure amount: 40 mj). Then, an alkaline solvent NMD-3 (liquid temperature 30) manufactured by Tokyo Ohkasha Co., Ltd.
C.) for 20 minutes, heated at 170.degree. C. for 60 minutes, and post-baked at 320.degree. C. for 30 minutes. The average inclination angle θ of each concave portion was 6.0 °. On this uneven surface, aluminum is formed as a reflective film by an evaporation method,
When the distribution of the reflected light with respect to the incident light of -30 ° was measured, a half value width of 32 ° was obtained. The light-diffusing film made of this positive photosensitive polyimide resin has a very small decrease in film weight at 400 ° C., and has not undergone a waveform forming step by melting, so that it has excellent shape stability after unevenness formation (post-bake). No change was observed in the average tilt angle and the half width of the reflected light even after the subsequent liquid crystal panel manufacturing process. Further, by adjusting the development time, the average inclination angle can be easily and reproducibly designed.

[0030]

As described above, according to the present invention,
By using a positive photosensitive polyimide resin as the resin that forms the uneven light diffusion layer on the substrate, it is possible to adjust the exposure conditions and development conditions, etc. Thus, a light-reflective substrate having a uniform light diffusion property over the entire surface can be obtained.

Further, according to the present invention, there is provided a reflection type liquid crystal display device having a good display resolution and a constant display quality without variation in brightness of a display surface.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of a reflection type liquid crystal display device according to the present invention.

FIG. 2 is a schematic view for explaining a method for manufacturing a light-reflective substrate used in the reflective liquid crystal display device.

FIG. 3 is an enlarged sectional view (a) and an enlarged plan view (b) of a concave portion formed on the light-reflective substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reflective liquid crystal display element 2, 3 Electrode substrate 2a, 3a Transparent electrode 20 Light reflective substrate 21 Transparent glass substrate 21a Roughened surface 23 Light reflective layer 25 Surface smoothing layer 27 Positive photosensitive polyimide resin 27a Depression 4 Peripheral Sealing material 6 Liquid crystal substance 7 Retardation plate 8 Polarizing plate M Photomask

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H025 AA00 AB17 AC01 AD03 BF29 BG00 FA03 FA17 FA29 2H042 DA02 DA11 DA12 DC02 2H091 FA16Y LA18 LA19 2H096 AA00 AA27 BA11 EA02 GA08 HA01 HA30 JA04

Claims (4)

[Claims] 1. A method of manufacturing a light-reflective substrate used as one substrate of a reflection-type liquid crystal display element, wherein a positive photosensitive polyimide resin having a predetermined thickness is coated on one surface of a transparent substrate having a smooth surface. After being applied in the form of a film, the positive photosensitive polyimide resin film is partially exposed and developed through a photomask having a light transmission pattern formed regularly or irregularly, and then developed at a predetermined temperature. Forming a concave portion in the positive photosensitive polyimide resin to roughen the surface thereof, and forming a light reflecting layer made of a metal film over the entire surface of the roughened surface. Substrate manufacturing method. 2. The method according to claim 1, wherein the thickness of the positive photosensitive polyimide resin applied on the substrate is in a range of 0.5 to 10 μm. 3. The method for producing a light-reflective substrate according to claim 1, wherein the sintering temperature of the positive photosensitive polyimide resin is 300 to 350 ° C. 4. A reflection type liquid crystal display comprising an electrode substrate having a transparent electrode formed on a metal film of a light reflective substrate according to claim 1 via a surface smoothing layer as one substrate. element.