JP3962191B2 - Manufacturing method of light-reflective substrate and reflection type liquid crystal display device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal diffuse reflection type reflective liquid crystal display device, and more particularly to a light reflective substrate thereof.
[0002]
[Prior art]
A reflective liquid crystal display device or a transflective liquid crystal display device can be viewed without a backlight when there is external light, and thus can reduce power consumption and is suitable for portable use.
[0003]
When the liquid crystal display device is used as a reflection type, there are various methods. As a method for brightening the display, it is preferable to provide a light reflection layer and an uneven layer inside the liquid crystal cell.
[0004]
As a method of providing a light reflecting layer and an uneven layer inside a liquid crystal cell, a positive photosensitive polyimide film, which is a photosensitive material, is formed on one glass substrate used in a liquid crystal display panel, and a predetermined light transmission pattern is formed. A method has been proposed in which an infinite number of fine irregularities are formed by developing after exposure through a photomask, and the surface of the glass substrate is roughened. In this case, the light reflecting layer is formed on this rough surface.
[0005]
The light transmission pattern of the photomask used here has a periodic structure with one pixel being the minimum unit of the liquid crystal display unit as the maximum unit. In addition, the light transmission openings are irregularly arranged within the unit area. Therefore, the uneven layer formed on the glass substrate also has the above-described periodic structure, and unevenness is irregularly arranged within the unit area.
[0006]
FIG. 11 shows an example of the periodic structure of the light transmission pattern of the photomask. In this example, one pixel which is the minimum unit of the liquid crystal display unit is 305 μm × 95 μm, and the distance between the lines is 10 μm. Therefore, the period is 105 μm in the horizontal direction and 315 μm in the vertical direction. In the photomask 42, the light transmission ports 44 are irregularly arranged in the unit area of each period as described above.
[0007]
FIG. 12 shows an example of the position where the uneven layer is formed on the glass substrate. In FIG. 12, the uneven layer is formed with the periodic structure shown in FIG. 11 only in a region where pixels exist, that is, a portion corresponding to the liquid crystal display unit 46.
[0008]
The photomask 42 as described above is used because moire occurs when the pixel period and the photomask 42 period are different. Further, such a method is employed because it is not practical to create a mask pattern that can cover the entire surface of the glass substrate and has an irregular arrangement of the light transmission apertures 44, which requires a large amount of data.
[0009]
[Problems to be solved by the invention]
However, in the case of manufacturing a reflective liquid crystal display device and a transflective liquid crystal display device by the conventional method, the photomask 42 for forming irregularities is changed each time the pixel size is changed. Must. This is because the light transmission pattern of the photomask 42 has a periodic structure in which one pixel, which is the minimum unit of the liquid crystal display unit 46, is the maximum unit as described above. For this reason, there existed a problem that manufacturing cost will become high.
[0010]
Further, in order to eliminate the influence of the above-described uneven layer and improve the orientation of the liquid crystal, it is necessary to form a planarizing layer between the uneven layer and the liquid crystal layer, specifically on the light reflecting layer. . At this time, if the uneven layer is formed only on the liquid crystal display part, the thickness combined with the planarization layer is increased, and the transparent conductive film is formed between the liquid crystal display part and the other part where the uneven layer is not formed. There is a step in For this reason, there also existed a problem that a transparent conductive film will be cut | disconnected.
[0011]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a low-cost reflective liquid crystal display device that does not generate moire and a method for manufacturing a transflective liquid crystal display device. .
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for producing a light-reflective substrate used as one substrate of a reflective liquid crystal display device, wherein a photosensitive surface is formed on one surface of a transparent substrate having a smooth surface. The material is applied in the form of a film having a predetermined thickness, and the photosensitive material film is an area having a length of ½ or less of the long side and the short side of one pixel, which is the minimum unit of the liquid crystal display unit. By exposing and developing through a photomask having a light-transmitting pattern formed with a periodic structure with the maximum unit being baked at a predetermined temperature, the photosensitive material film is formed with irregularities having a curved surface shape. The surface of the transparent substrate is roughened, and a light reflection layer is formed on the rough surface.
[0013]
In the above method for manufacturing a light-reflective substrate, the light transmission pattern of the photomask has a periodic structure with a maximum period of 50 microns or less.
[0014]
In the method for producing a light-reflective substrate, the photosensitive material is applied to one entire surface of the transparent substrate, and the entire surface of the photosensitive material film is exposed and developed with a photomask, and then baked at a predetermined temperature. As a result, irregularities having a curved shape are formed on the photosensitive material film to roughen the surface of the transparent substrate over almost the entire surface, and a light reflecting layer is formed on each portion corresponding to the liquid crystal display part on the rough surface. It is characterized by doing.
[0015]
Further, in the reflective liquid crystal display device, an electrode substrate on which a transparent electrode is formed on a light reflecting layer and a rough surface of the light reflecting substrate via a planarizing layer for planarizing the surface is provided on one side. It is provided as a substrate.
[0016]
Further, in the reflective liquid crystal display device, the liquid crystal display unit includes a liquid crystal cell in which a liquid crystal layer is inserted in a gap between the first and second substrates each having an electrode formed on the opposite surface side. Two or more retardation plates and a polarizing plate are arranged in this order on the outer side of one substrate, and a light reflecting layer is formed on the second substrate side in the liquid crystal cell. The liquid crystal layer retardation value indicated by the product of the refractive index anisotropy Δn1 of the liquid crystal layer and the thickness d1 of the liquid crystal layer is twist angle θ1 in the alignment direction of the liquid crystal molecules toward two substrates. Δn1 · d1 is 0.30 μm to 2.00 μm.
[0017]
In the transflective liquid crystal display device, the light reflecting layer is a transflective layer.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0019]
FIG. 1 shows a cross-sectional view of an embodiment of a reflective liquid crystal display device according to the present invention. In FIG. 1, electrodes 14 and 16 are formed on opposite sides of the first transparent substrate 10 and the second transparent substrate 12 made of glass or the like, respectively. Is a liquid crystal cell in which the liquid crystal layer 18 is inserted. Further, two retardation plates 20 and 22 and a polarizing plate 24 are arranged in this order on the outside of the first transparent substrate 10. The electrodes 14 and 16 are configured as transparent electrodes.
[0020]
A color filter 26 is disposed inside the first transparent substrate 10, and a planarizing layer 28 is provided to cover the color filter 26. On the other hand, an uneven layer 30 is formed on the inner surface of the second transparent substrate 12, and a light reflecting layer 32 is formed in a portion corresponding to the liquid crystal display portion thereon. A planarizing layer 28 is also provided on the light reflecting layer 32. As described above, the planarization layer 28 is provided to improve the alignment of the liquid crystal. The electrodes 14 and 16 described above are formed on the opposing surface side of each planarization layer 28, and an insulating layer 34 and an alignment layer 36 are formed on the inside thereof. Spacers 38 are disposed inside the two alignment layers 36, and the liquid crystal layer 18 is inserted into a space formed by the spacers 38. Thus, the liquid crystal cell is formed in the gap between the first transparent substrate 10 and the second transparent substrate 12. A seal 40 is provided on the side of the liquid crystal cell.
[0021]
In the liquid crystal layer 18 used in this embodiment, the twist angle θ1 in the alignment direction of the liquid crystal molecules from the first transparent substrate 10 toward the second transparent substrate 12 is 160 ° to 300 °. The retardation value Δn1 · d1 of the liquid crystal layer 18 indicated by the product of the refractive index anisotropy Δn1 and the thickness d1 of the liquid crystal layer 18 is 0.30 μm to 2.00 μm.
[0022]
In order to form the uneven layer 30 on the second transparent substrate 12, a film of a photosensitive material is applied with a predetermined thickness on one surface of the transparent substrate 12 having a smooth surface, and a predetermined light transmission pattern is formed. This is based on a method of forming innumerable fine irregularities, that is, a rough surface, by exposing through a photomask 42 having a color and developing and then baking at a predetermined temperature. In this case, for example, positive photosensitive polyimide is used as the photosensitive material. According to this method, a predetermined curved surface shape is given to the unevenness. A light reflecting layer 32 is formed on the rough surface on the transparent substrate 12 thus formed, and the light reflecting substrate according to the present invention is manufactured.
[0023]
The positive photosensitive polyimide is applied to one whole surface of the transparent substrate 12, and the entire surface of the positive photosensitive polyimide film is exposed and developed by the photomask 42, and then baked and transparent in the same manner as described above. It is also preferable to roughen the surface of the substrate 12 over almost the entire surface. Thereby, the uneven layer 30 can be formed over the entire surface of the second transparent substrate 12. In this case, the light reflection layer 32 is formed only in a portion corresponding to the liquid crystal display unit.
[0024]
As described above, in the reflective liquid crystal display device according to the present embodiment, the planarizing layer 28 for planarizing the surface is formed on the light reflecting layer 32 and the rough surface on which the light reflecting layer 32 is not formed. The transparent substrate 12 on which the electrode 16 is formed via the planarizing layer 28 is provided as one electrode substrate.
[0025]
As described above, the light transmission pattern of the conventional photomask 42 has a periodic structure with one pixel being the minimum unit of the liquid crystal display unit 46 as the maximum unit. This is to avoid moire. However, moire can be avoided without having a periodic structure with one pixel being the minimum unit as the maximum unit. Therefore, in the present embodiment, the light transmission pattern of the photomask 42 is provided with a periodic structure that is 1/2 or less of one pixel, which is the minimum unit.
[0026]
The reason is as follows. Consider a wave that depends on the distance in the X direction. A wave having a pitch of a is cos ² ((1 / a) · X · π), and a wave having a pitch of b is cos ² ((1 / b) · X · π). Here, it is squared so as not to consider minus. These synthetic waves are
cos ² ((1 / a) · X · π) + cos ² ((1 / a) · X · π)
= Cos ((a + b) / (ab) · X · π) cos ((ab) / (ab) · X · π) +1
It becomes. This means that waves with a pitch of (ab) / (a + b) and (ab) / (ab) have been newly created. The moire in question is the pitch of (ab) / (ab). As the pitch of a and b approaches, (ab) / (ab) becomes a very large pitch. Even if a and b are small pitches that cannot be seen by humans, the pitch of (ab) / (ab) is invisible to the human eye.
[0027]
In order to avoid this, when a> b, the relationship b ≦ (1/2) · a should be satisfied. Desirably, the relationship b ≦ (1/3) · a may be satisfied. That is, a photo having a light transmission pattern formed of a periodic structure with an area having a length of ½ or less of the long side and the short side of one pixel, which is the minimum unit of the liquid crystal display unit, as a maximum unit If the mask 42 is used, the generation of moire can be eliminated. From this, it can be seen that the same photomask 42 can be used regardless of the size of the liquid crystal display portion having pixels with longer and shorter sides than twice the periodic structure of the photomask 42.
[0028]
In general, the minimum unit of pixels in the case of full dot color display is about 100 × 300 μm, so that the moire does not become a problem level if the period is 50 μm or less. Therefore, if a photomask 42 having a light transmission pattern with a period of 50 μm or less is created, the photomask 42 is compatible with any model. Thereby, since it is not necessary to prepare the photomask 42 for each model as in the prior art, the uneven layer 30 can be made at low cost. In addition, when the data necessary to create the photomask 42 is a small pattern repetition, the number of data required is reduced, and in this respect also, the photomask 42 can be created at low cost. However, if the period is too small, interference fringes of reflected light become a problem, so the period needs to be 10 μm or more.
[0029]
In the reflective liquid crystal display device according to the present embodiment described above, the uneven layer 30 is formed over the entire surface of the second transparent substrate 12, as shown in FIG. FIG. 2 shows a state where the uneven layer 30 and the liquid crystal display unit 46 are formed on the second transparent substrate 12. This shows an example of making 12 liquid crystal cells using this single glass substrate. As shown in FIG. 2, the uneven layer 30 is formed also on the part other than the liquid crystal display unit 46, and the light reflecting layer 32 is formed only on the part corresponding to the liquid crystal display unit 46, and then the second transparent substrate 12. When the planarizing layer 28 is formed on the entire surface, the gap control becomes easy. This is because etching is performed when the uneven layer 30 is formed, and the thickness of the portion where the uneven layer 30 is formed is relatively thinner than the portion where the uneven layer 30 is not formed. Therefore, if the uneven layer 30 is formed only on the liquid crystal display unit 46, a large difference in film thickness from other parts occurs, making gap control extremely difficult.
[0030]
The light reflection layer 32 can also be formed in a portion other than the liquid crystal display unit 46, and the planarizing layer 28 can be an insulating layer. However, when the light reflection layer 32 is exposed on the cut surface, the light reflection layer 32 is exposed. There is a risk of deterioration. Further, since alignment and the like at the time of manufacturing the liquid crystal display device are performed by transmission, it is not desirable to form the light reflection layer 32 on the entire surface of the transparent substrate 12.
[0031]
The reflective liquid crystal display device has been described above. However, if a transflective layer is formed instead of the light reflective layer 32, a transflective liquid crystal display device can be obtained. FIG. 3 shows an embodiment of a transflective liquid crystal display device according to the present invention. 3 differs from FIG. 1 in that a transflective layer 48 is formed instead of the light reflecting layer 32, and a λ / 4 plate 50 and a λ / 2 plate 52 are formed on the outer surface of the second transparent substrate 12. The circularly polarizing plate 56 composed of the polarizing plate 54 and the light source 60 are formed in this order. Instead of the polarizing plate, a reflective polarizing plate (for example, 3M DBEF) that substantially transmits one linearly polarized light and substantially reflects the other linearly polarized light may be used. Further, the circularly polarizing plate may be replaced with one using selective reflection.
[0032]
Hereinafter, specific examples of the above-described embodiment will be described as examples.
[0033]
[Example 1]
A reflective liquid crystal display device having a display portion size of about 5 cm and 120 × (160 × RGB) pixels was prepared as follows. The configuration is the same as that shown in FIG.
[0034]
The liquid crystal layer 18 is an STN having a twist of 240 degrees, the refractive index anisotropy Δn of the liquid crystal is 0.13, the gap is 5 μm, and Δnd is 0.65 μm. Further, Δnd of the phase difference plate 20 was 0.138 μm, and Δnd of the phase difference plate 22 was 0.385 μm. The light reflecting layer 32 and the uneven layer 30 were arranged as shown in FIG.
[0035]
In this embodiment, the minimum unit of the liquid crystal display unit is 305 μm × 95 μm, and the line spacing is 10 μm. Therefore, the period is 105 μm in the horizontal direction and 315 μm in the vertical direction.
[0036]
The uneven layer 30 is made by applying RN-901 manufactured by Nissan Chemical Co., Ltd. as a positive photosensitive polyimide resin to a thickness of 2.0 μm on a transparent substrate 12 (glass substrate) with a spinner, and in a batch furnace at 80 ° C. for 10 minutes. And prebaked. Next, a photomask was set on the film as shown in FIG. 4 and exposed with a proximity type batch exposure machine (wavelength 365 nm, exposure 40 mj, proximity gap 300 μm, exposure machine collimation angle 3). .4 °). In the photomask 42, holes having a size as shown in FIG. 5 (elliptical shape of 16 μm wide and 8 μm long) are arranged with a period of 40 μm in the horizontal direction and 100 μm in the vertical direction as shown in FIG. ing. However, in the rectangles of 40 μm and 100 μm, many holes are randomly arranged.
[0037]
Next, after developing for 20 minutes with an alkaline solvent NMD-3 (room temperature 30 ° C.) manufactured by Tokyo Ohka Kogyo Co., Ltd. and heating at 170 ° C. for 60 minutes, post baking was performed at 320 ° C. for 30 minutes. Thereby, the uneven layer 30 having a shape as shown in FIG. 7 was formed on the glass substrate, and the surface of the glass substrate was roughened. In this case, as shown in FIG. 2, the uneven layer 30 is formed on the glass substrate in all of the hatched portions.
[0038]
On the uneven layer 30, as shown in FIG. 2, aluminum was deposited by vapor deposition as a light reflecting layer 32 in a portion corresponding to the liquid crystal display unit 46. On top of this, the reflection color was adjusted and the reflection intensity was controlled by making a laminated structure such as SiO ₂ or SiO ₂ / TiO ₂ / SiO ₂ . Thus, the light reflective substrate according to this embodiment was produced.
[0039]
A reflective liquid crystal display device according to this example was produced using the light reflective substrate produced as described above, and the angle of the reflected light with respect to -30 ° incident light in the evaluation system shown in FIG. Dependency was measured. The result is shown in FIG.
[0040]
For the display, a mode (negative mode) was adopted in which low reflection luminance was realized when no voltage was applied, and high reflection luminance was realized with voltage application. Further, a multiplex drive is used and a duty ratio of 1/120 is used. The characteristics of the used color filter 26 are such that the color purity of the reflective filter is lower than that of the transmissive filter, and the balance of each of the three RGB colors is adjusted to be achromatic under a C light source. The rate Y was 53%.
[0041]
In the reflective liquid crystal display device according to the present example, a bright display could be obtained without particularly feeling moire. According to the present embodiment, it has been proved that there is no problem even if the uneven layer is formed without using the period according to the pixel size.
[0042]
[Example 2]
In the configuration of the first embodiment, as the photomask 42, a large number of 16 μm wide and 8 μm long elliptical holes shown in FIG. 5 are randomly arranged in the 35 μm and 35 μm squares as shown in FIG. The same pattern was used in the vertical and horizontal directions with a period of 35 μm in the horizontal direction and 35 μm in the vertical direction.
[0043]
Even when the transparent substrate 12 on which the uneven layer 30 was formed using the photomask 42 was produced, a bright display could be obtained without feeling moire.
[0044]
[Example 3]
In the configuration of Example 1, a transflective layer 48 is disposed instead of the light reflecting layer 32, a broadband circularly polarizing plate 56 is laminated on the outer surface of the transparent substrate 12, and a backlight ( It was the same except that the light source 60) was arranged. This configuration is shown in FIG.
[0045]
As the transflective layer 48, a layer having little depolarization (polarization rotation) is preferable, and an Al half mirror is used. By making a laminated structure such as SiO ₂ or SiO ₂ / TiO ₂ / SiO _{2 on} top of Al, the reflection color was adjusted and the reflection intensity was controlled. The ratio of reflection to transmission was 7: 1.
[0046]
As in this example, a bright display could be obtained without feeling moire even when transflective. In addition, even when there is no outside light, since it is semi-transmissive, the display can be visually recognized by the effect of the backlight, and the application range is expanded.
[0047]
【The invention's effect】
As described above, according to the present invention, since it is possible to obtain a photomask that can be applied to any model without generating moire, it is not necessary to prepare a photomask for each model as in the past, and the cost is low. It becomes possible to produce an uneven layer.
[0048]
In addition, if a substrate using an uneven layer using this method is used, gap control is facilitated in a reflective liquid crystal display device and a transflective liquid crystal display device, and display with high uniformity and less unevenness can be realized. .
[0049]
Further, the transflective and reflective liquid crystal display devices of the present invention, particularly the transflective liquid crystal display device using a color filter, are portable electronic devices premised on outdoor use, such as mobile phones, Good visibility and expressiveness when used in electronic notebooks, electronic books, electronic dictionaries, personal digital assistants (PDAs), pagers, portable position detectors (GPS), portable fish finder, portable game machines, etc. Combined with the high functionality.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view illustrating an embodiment of a reflective liquid crystal display device according to the present invention.
FIG. 2 is an explanatory diagram of a place where an uneven layer is formed on a transparent substrate and a light reflection layer is formed when a large number of liquid crystal cells are formed from a single transparent substrate.
FIG. 3 is a schematic cross-sectional view illustrating an embodiment of a transflective liquid crystal display device according to the present invention.
FIG. 4 is a schematic diagram for explaining a method for producing a light reflective substrate.
FIG. 5 is a diagram showing a dimension of one hole of a photomask substrate.
FIG. 6 is a diagram showing an example of the irregularity of the photomask substrate.
FIG. 7 is a schematic perspective view of convex and concave portions created on a transparent substrate.
FIG. 8 is an explanatory diagram of an evaluation system for measuring the angle dependence of the reflected light intensity of the uneven reflection layer.
FIG. 9 is a diagram showing the angle dependence of the reflected light intensity of the reflective liquid crystal display device produced according to the example.
FIG. 10 is a diagram showing another example of the periodicity of the unevenness of the photomask substrate.
FIG. 11 is a diagram showing the irregularity periodicity of a photomask substrate as a conventional example.
FIG. 12 is a diagram showing a place where a textured layer is created on a transparent substrate as a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 1st transparent substrate, 12 2nd transparent substrate, 14, 16 electrodes, 18 liquid crystal layer, 20, 22 phase difference plate, 24 polarizing plate, 26 color filter, 28 planarization layer, 30 uneven surface, 32 light reflection Layer, 34 insulating layer, 36 alignment layer, 38 spacer, 40 seal, 42 photomask, 44 light transmission port, 46 liquid crystal display, 48 transflective layer, 50 λ / 4 plate, 52 λ / 2 plate, 54 polarization Plate, 56 circularly polarizing plate, 60 light source.

Claims (6)

A method of manufacturing a light reflective substrate used as one substrate of a reflective liquid crystal display device,
On one surface of a transparent substrate with a smooth surface, a photosensitive material is applied in the form of a film with a predetermined thickness,
The photosensitive material film is a light formed by a periodic structure whose maximum unit is an area having a length of 1/2 or less of the long side and the short side of one pixel, which is the minimum unit of the liquid crystal display unit. Exposure and development through a photomask having a transmission pattern,
Thereafter, by baking at a predetermined temperature, the surface of the transparent substrate is roughened by forming irregularities having a curved shape on the photosensitive material film,
A method for producing a light reflective substrate, comprising forming a light reflective layer on the rough surface. 2. The method of manufacturing a light-reflective substrate according to claim 1, wherein the light transmission pattern of the photomask has a periodic structure having a period of 50 microns or less as a maximum. The photosensitive material is applied to one entire surface of the transparent substrate,
By exposing and developing almost the entire surface of the photosensitive material film with the photomask, followed by baking at a predetermined temperature, irregularities having a curved shape are formed on the photosensitive material film, and the surface of the transparent substrate is formed. Roughened almost over the entire surface,
The method of manufacturing a light reflective substrate according to claim 1, wherein the light reflective layer is formed in a portion corresponding to the liquid crystal display portion on the rough surface. An electrode in which a transparent electrode is formed on the light reflective layer and the rough surface of the light reflective substrate according to any one of claims 1 to 3 via a planarizing layer for planarizing a surface. A reflective liquid crystal display device comprising a substrate as one substrate. The liquid crystal display unit has a liquid crystal cell in which a liquid crystal layer is inserted in the gap between the first and second substrates each having an electrode formed on the opposite surface side, and two cells are disposed outside the first substrate of the cell. The above retardation plate and polarizing plate are arranged in this order, and the light reflection layer is formed on the second substrate side in the liquid crystal cell,
In the liquid crystal layer, the twist angle θ1 in the alignment direction of liquid crystal molecules from the first substrate toward the second substrate is 160 ° to 300 °,
5. The retardation value Δn1 · d1 of the liquid crystal layer indicated by the product of the refractive index anisotropy Δn1 of the liquid crystal layer and the thickness d1 of the liquid crystal layer is 0.30 μm to 2.00 μm. The reflective liquid crystal display device described. 6. A transflective liquid crystal display device according to claim 4, wherein the light reflecting layer is a transflective layer.

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