JPH11160687A - Display device and method of manufacturing optical diffusion layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sharpen display contrast by improving an optical diffusion layer arranged on an observer's side of a display device. SOLUTION: A display device consists of a transparent front substrate 1 arranged forwardly opposing an observer and a rear substrate 2 joined to the front substrate 1 from behind via a predetermined gap. A transparent electrode 5 is formed on the front substrate 1, and a reflecting electrode 7 is formed on the rear substrate 7. Liquid crystal 9 is held in the gap between both substrates 1, 2, and in response to voltages impressed on the electrodes 5, 7, incident light reflected from behind is optically modulated into forward beams for showing an image. An optical diffusion layer 10 is arranged on the front substrate l and diffuses the outgoing beams to widen a viewing angle of the image from an observer. The optical diffusion layer 10 consists of cylindrical regions 102 formed to be able to forwardly guide the outgoing light and a medium 103 filling the space between the cylindrical regions 102, and the cylindrical regions 102 and the medium 103 have different refractive indices from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a display device and a method for manufacturing a light diffusion layer. For example, the present invention relates to a reflective display device having a light diffusion layer on a front substrate and a mirror light reflection layer on a rear substrate.

[0002]

2. Description of the Related Art FIG. 5 is a schematic sectional view showing an example of a conventional reflective display device. The display device has a panel structure including a transparent front substrate 1 disposed in front of the viewer facing the viewer, and a rear substrate 2 joined to the front substrate 1 from the rear via a predetermined gap. A polarizing plate 11 is attached to the outer surface of the front substrate 1. A transparent electrode 5 is formed on the inner surface of the front substrate 1. A reflection electrode 7 is formed on the inner surface of the rear substrate 2. The reflection electrode 7 is made of a deposited film of aluminum or the like and also serves as a mirror-like light reflection layer. Liquid crystal is held in the gap between the front substrate 1 and the rear substrate 2 as an electro-optical material. The liquid crystal molecules 9m are oriented in a predetermined direction. In this example, 9 m of liquid crystal molecules are
Are vertically aligned and a white display is obtained. That is, the light incident from the front substrate 1 becomes linearly polarized light by the polarizing plate 11, passes through the vertically aligned liquid crystal as it is, is reflected by the reflective electrode 7, passes through the polarizing plate 11 again, and is emitted forward. On the other hand, when the voltage is applied (ON), the liquid crystal molecules 9m shift to horizontal alignment and switch to black display. The horizontally aligned liquid crystal has uniaxial anisotropy and its retardation is substantially λ /
The thickness of the liquid crystal is set to be 4. When the refractive index anisotropy of the liquid crystal is Δn and the thickness is d, the retardation is represented by Δn · d. D is set so that Δn · d = λ / 4. Here, λ is the wavelength of the incident light.
In other words, the liquid crystal functions as a quarter-wave plate when a voltage is applied. The incident linearly polarized light that has passed through the polarizing plate 11 is reflected by the reflective electrode 7, and reciprocates through the quarter-wave plate during this time, so that the polarization axis of the incident linearly polarized light is rotated by 90 °.
The reflected linearly polarized light is almost absorbed because it is orthogonal to the transmission axis of the polarizing plate 11. Therefore, the display becomes black. Incidentally, 4
In order to rotate the polarization axis of the linearly polarized light by 90 ° by the half-wave plate, the transmission axis of the polarizing plate 11 is set to form an angle of 45 ° with the uniaxial orientation direction of the liquid crystal.

[0003]

The reflective display device described above differs from a transmissive display device using a backlight in that an image is projected by utilizing the reflection of external light, so that power consumption is low. It is expected as a terminal display. In the reflection type display device, a light reflection layer of aluminum or the like is formed on the rear substrate to reflect incident light. Since this light reflecting layer is specularly reflected, incident light is reflected only in a certain direction (specular reflection direction), and a display having sufficient visibility cannot be obtained. Therefore, it is common to mount the light diffusion layer 10 on the outer surface of the front substrate 1. The light diffusion layer 10 diffuses a light beam emitted from the rear side to widen a viewing angle of an image viewed from an observer. FIG. 6 schematically shows the configuration of a conventional light reflecting layer. The light diffusion layer 10 is composed of a fine particle 10a and a medium 10b having different refractive indexes. The fine particles 10a are made of, for example, glass powder and are dispersed at a constant density in a medium 10b such as a transparent resin. However, in the light diffusion layer 10 having such a structure, a considerable portion of light incident from the front side is reflected at the interface between the fine particles 10a and the medium 10b and cannot reach the liquid crystal. That is,
Unnecessary reflection that does not contribute to image display occurs, and in particular, black display does not sink sufficiently, resulting in poor contrast.
In addition, the fine particles 10a are generally spherical and diffuse the emitted light in almost all directions. In other words, the conventional light diffusion layer 1
Numeral 0 is omnidirectional and generates unnecessary emitted light that is not directed to the observer. When a non-directional diffuse reflection layer is used, the intensity of reflected light in the regular reflection direction decreases, and a white display with sufficient brightness cannot be obtained.

[0004]

The following means have been taken in order to solve the above-mentioned problems of the prior art. That is, the display device according to the present invention has, as a basic configuration, a transparent front substrate disposed in front of the viewer facing the observer, and a rear substrate joined to the front substrate from behind through a predetermined gap. Have. An electrode is formed on at least one of the front substrate and the rear substrate. An electro-optical material such as a liquid crystal is disposed in a gap between the front substrate and the rear substrate, and in response to a voltage applied to the electrodes, an incident light from behind is optically modulated and converted into a forward emitting light. To project an image. A light diffusing layer is disposed on the front substrate and diffuses the outgoing light to widen the viewing angle of the image as viewed by an observer. As a feature, the light diffusion layer includes a columnar region formed so as to be able to guide the emitted light forward and a medium that fills a gap between the columnar regions that are discretely arranged in a plan view. The columnar region and the medium have different refractive indices. Preferably, the diameter of the columnar region is set to 1/10 or less of the thickness of the light diffusion layer. Preferably, the columnar regions are randomly distributed in a plan view. Preferably, the diameter of the columnar region decreases from the front to the rear. Preferably, a light reflecting layer is formed on the rear substrate to reflect an incident light beam supplied from the front, and the electro-optical material converts the incident light beam reflected by the light reflecting layer into an outgoing light beam.

The present invention includes a method for manufacturing a light diffusing layer incorporated in the above-mentioned display device, and comprises the following steps. First, a coating step of applying a mixture of a precursor of an ultraviolet-curable first transparent resin having a fast curing speed and a precursor of a second transparent resin having a different refractive index from the first transparent resin having a slow curing speed. I do. Next, a first irradiation step of selectively irradiating the applied mixture with ultraviolet rays to cure only the precursor of the first transparent resin and forming discrete columnar regions is performed. Finally, the applied mixture is again irradiated with ultraviolet rays to cure the precursor of the second transparent resin left uncured, and processed into a medium that fills between the discretely arranged columnar regions. Two irradiation steps are performed. In some cases, the first irradiation step irradiates the collimated ultraviolet light obliquely to form a columnar region inclined from the normal line of the display device. Further, the collimated ultraviolet rays may be simultaneously irradiated from two directions to form columnar regions inclined in two directions.

According to the present invention, an improved light diffusion layer is mounted on an outer surface of a front substrate of a display device. The light diffusion layer is used to widen the viewing angle of the display device. The light reflection layer according to the present invention has a structure in which countless columnar regions formed along the thickness direction are embedded with a medium. The columnar region and the medium have different refractive indexes. Therefore, reflection occurs at the interface between the two. In other words, the columnar region functions as an optical fiber. Since the light passing through the optical fiber is diffused and emitted at the opening, the viewing angle of the display device can be widened. In addition, the columnar area is a medium (binder)
The structure solidified by functions as a stacked diffraction grating. Light that has passed through the light diffusion layer is diffracted and diffusely emitted. By appropriately setting the shape, dimensions, orientation, refractive index, etc. of the columnar regions, it is possible to obtain a light diffusion layer having a certain degree of directivity instead of non-directionality. Is obtained. Such a stacked diffraction grating,
For example, it can be easily prepared by forming a coating film in which two kinds of UV-curable transparent resins having different refractive indices and curing speeds (photopolymerization speeds) are mixed, and irradiating the coating film with ultraviolet rays through a mask.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a display device according to the present invention. (A) is a cross-sectional view of the display device in a state where no voltage is applied, (B) is a cross-sectional view of the display device in a state where a voltage is applied, and (C) is a schematic view of a light diffusion layer incorporated in the display device. FIG. As shown in FIG. 1A, the display device includes a transparent front substrate 1 disposed in front of the viewer facing a viewer, and a rear substrate 2 joined to the front substrate 1 from behind through a predetermined gap. And has a flat panel structure. A color filter 3, an antireflection film 4, a transparent electrode 5, and an alignment film 6 are sequentially formed on the inner surface of the front substrate 1. The color filter 3 is divided into RG
B is colored in three primary colors. The transparent electrode 5 is made of a transparent conductive film such as ITO. Since the color filter 3 has a relatively small refractive index and the transparent electrode 5 has a relatively large refractive index, if they are directly joined, unnecessary reflection occurs at the interface. In order to prevent this, in this embodiment, an antireflection film 4 having an intermediate refractive index is interposed between the color filter 3 and the transparent electrode 5. A light diffusion layer 10 and a polarizing plate 11 are mounted on the outer surface of the front substrate 1. The light diffusion layer 10 is used for diffusing an emitted light beam to widen a viewing angle of an image viewed from an observer. A reflective electrode 7 and an alignment film 8 are formed on the inner surface of the rear substrate 2. The reflection electrode 7 is made of, for example, a vacuum deposited film or a sputtered film of aluminum and also serves as a light reflection layer. This light reflection layer has a specular reflection surface. still,
In some cases, a light reflection layer may be provided separately from the electrode 7. A liquid crystal 9 is sealed in the gap between the front substrate 1 and the rear substrate 2 as an electro-optical material. The liquid crystal 9 is controlled to be vertically aligned by the upper and lower alignment films 6 and 8, and has a negative dielectric anisotropy. In this state, the incident light from the front side (observer side) becomes linearly polarized light by the polarizer 11, passes through the liquid crystal 9, is reflected by the reflection electrode 7, and is reflected by the liquid crystal 9.
The light beam passes through the polarizing plate 11 as it is without undergoing any modulation. Therefore, the display becomes white. However, in this embodiment, since the color filter 3 is interposed, each pixel is actually colored in RGB.

As shown in FIG. 1B, when a voltage is applied between the transparent electrode 5 on the front substrate 1 and the reflective electrode 7 on the rear substrate 2, the liquid crystal 9 has a negative dielectric anisotropy, so that the liquid crystal 9 has a horizontal alignment. Move to The liquid crystal 9 in a horizontal alignment state has a refractive index anisotropy of 4.
It functions as a half-wave plate. In this case, a black display is obtained as described with reference to FIG. The liquid crystal 9 optically modulates an incident light beam in response to a voltage applied between the transparent electrode 5 and the reflective electrode 7, and converts the incident light beam into a forwardly emitted light beam to project an image. The emitted light is diffused by the light diffusion layer 10, and the viewing angle of the image viewed from the observer can be widened. Although the present embodiment is a reflection type display device, the present invention is not limited to this, and is applicable to a transmission type display device. In the case of the transmission type, a backlight is mounted on the outer surface of the rear substrate 2. A rearward incident light beam emitted from the backlight is modulated by the liquid crystal 9 and converted into an outgoing light beam. The emitted light beam is directed to a viewer in front through the light diffusion layer 10. In the case of the reflection type, a light reflection layer is used in place of the backlight, and the incident light reflected from the rear is similarly modulated by the liquid crystal 9, converted into an outgoing light, and passes through the light diffusion layer 10. Will be. In addition, the present embodiment employs an EC using the birefringence of the liquid crystal 9.
Although the display device is of the B mode, the present invention is not limited to this. For example, a GH (guest-host) mode in which a dichroic dye is dispersed in a nematic liquid crystal can be used as the liquid crystal 9. Alternatively, a TN (twisted nematic) mode or STN (super twisted nematic) mode may be used.

As shown in FIG. 1C, a light diffusion layer 10 according to the present invention includes a columnar region 102 formed so as to guide outgoing rays forward and a columnar region discretely arranged in a plan view. The columnar region 102 and the medium 103 have different refractive indices. The columnar region 102 and the medium 103 constitute a stacked diffraction grating and are formed on the base 101. Preferably, the diameter of the columnar region 102 is set to 1/10 or less of the thickness of the light diffusion layer 10. With this setting, the columnar region 102 substantially functions as an optical fiber, and can diffuse the guided light from the opening. By regularly arranging the columnar regions 102 in a plan view, a stacked diffraction grating is obtained, and light from behind can be diffracted and emitted forward. However, the columnar region 102
If are precisely arranged at predetermined intervals, the wavelength dependence of the deposited diffraction grating becomes strong and chromatic dispersion may occur. Therefore, the columnar regions 102 may be randomly distributed to some extent in plan view. In some cases, the columnar region 10
2 may be formed in a conical shape whose diameter decreases from the front to the rear. The change in the diameter of the columnar region 102 in the thickness direction of the light diffusion layer 10 also has the effect of weakening the wavelength dependence of the diffused light. As described above, the light diffusion layer 10 according to the present invention forms the columnar region 102 made of a transparent resin having a high refractive index in a medium 103 made of a transparent resin having a low refractive index, for example. The direction is parallel to the normal. Note that a transparent resin having a high refractive index may be used for the medium 103, and a transparent resin having a low refractive index may be used for the columnar region 102. When light enters from the rear side of the light diffusion layer 10, the light is guided forward while being reflected at the interface between two kinds of transparent resins having different refractive indexes. Multiple reflection occurs in the course of the light traveling through the light diffusion layer 10, and the light changes in various directions, and a desired light diffusion characteristic is obtained. Further, the light is subjected to diffraction caused by the periodic structure of the columnar region 102 and diffused and emitted in various directions. The multiple reflection inside the light diffusion layer 10 is different from the conventional fine particle dispersion type light diffusion layer shown in FIG. 6 in that there are few interfaces perpendicular to the light traveling direction. Therefore, in the case of the reflective display device, most of the external light incident from the front side can enter the liquid crystal 9 without receiving unnecessary reflection by the light diffusion layer 10. Accordingly, black display due to unnecessary reflection by the light diffusion layer is not caused, and the contrast can be improved.

FIG. 2 is a process chart showing a method for manufacturing the light diffusion layer shown in FIG. First, the film forming step (A) is performed. Specifically, a mixture of a precursor of an ultraviolet-curable first transparent resin having a high curing speed and a precursor of a second transparent resin having a low curing speed and a refractive index different from that of the first transparent resin is used as a substrate 1
01 is applied. Such a mixture is, for example, OMNIDEX model number HRF manufactured by DuPont.
150 or HRF600 can be used. Next, a first irradiation step is performed as shown in FIG. In particular,
The coating film 104 of the applied mixture is selectively irradiated with ultraviolet rays 106 via a mask 105 to cure only the precursor of the first transparent resin, thereby forming discretely arranged columnar regions. The mask 105 has, for example, a pattern in which circular openings are arranged discretely and randomly. Only the precursor of the first transparent resin having a high curing speed is cured by the ultraviolet rays 106 passing through the circular openings, and columnar regions are obtained corresponding to the individual circular openings.

FIG. 1C shows a columnar region 102 formed after irradiation with ultraviolet rays. The diameter of each columnar region 102 decreases from the front to the rear. Such an inverted conical shape of the columnar region 102 can be automatically formed by an absorption process along the thickness direction of ultraviolet rays. Subsequently, a second irradiation step is performed to irradiate the coating film with the ultraviolet rays 107 again to cure the uncured second transparent resin precursor, thereby filling the space between the discretely arranged columnar regions 102. Medium 103
Process into As described above, the light diffusion layer 10 having a deposition-type diffraction grating structure can be formed on the substrate 101 by performing the ultraviolet irradiation twice.

FIG. 3 is a process chart showing a modification of the method for manufacturing the light diffusion layer. First, as shown in (A), a precursor of an ultraviolet-curable first transparent resin having a fast curing speed and a precursor of a second transparent resin having a slow curing speed and a different refractive index from the first transparent resin are used. The mixture is applied on the substrate 101 to form a coating film 104. Next, as shown in FIG.
4 is selectively irradiated with ultraviolet rays 106 via a mask 105 to cure only the precursor of the first transparent resin to form discrete columnar regions. At this time, the collimated ultraviolet rays 106 are irradiated obliquely to form the columnar region 102 inclined from the normal line of the display device. This inclined columnar region 10
2 is shown in (C). Thereafter, the coating film is again irradiated with ultraviolet rays 107 to cure the uncured precursor of the second transparent resin, which is then processed into a medium 103 that fills the space between the discretely arranged columnar regions 102. By inclining each columnar region 102 in this way, a light diffusion layer having a certain degree of directivity in a desired direction can be manufactured.

FIG. 4 is a schematic view showing an application example of the manufacturing method shown in FIG. In this application example, collimated ultraviolet rays are simultaneously irradiated from two directions to form columnar regions 102 a and 102 b inclined in two directions in a medium 103. For example, one columnar region 102a is inclined in a direction substantially parallel to the observer 30, and the other columnar region 102b is inclined in a direction substantially parallel to the illumination light source 50. Thereby, the utilization efficiency of the illumination light emitted from the illumination light source 50 can be significantly improved.

[0014]

As described above, according to the present invention,
By attaching a light diffusion layer in which a columnar region having a different refractive index is formed in a transparent medium to the front side of the display device, it is possible to increase the viewing angle without lowering the display contrast. In addition, unnecessary reflection of incident light is reduced as compared with a conventional light diffusion layer in which fine particles are diffused, and it is possible to suppress floating of black display of a display device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a display device according to the present invention.

FIG. 2 is a process chart showing a method of manufacturing a light diffusion layer incorporated in the display device shown in FIG.

FIG. 3 is a process chart showing a method for manufacturing the light diffusion layer.

FIG. 4 is a schematic view showing an application example of the method for manufacturing the light diffusion layer shown in FIG.

FIG. 5 is a schematic diagram illustrating an example of a conventional display device.

6 is a schematic view showing a conventional light diffusion layer incorporated in the display device shown in FIG.

[Explanation of symbols]

Reference Signs List 1 front substrate, 2 rear substrate, 5 transparent electrode, 6 alignment film, 7 reflective electrode (light reflective layer),
8 alignment film, 9 liquid crystal (electro-optical material), 10
... Light diffusion layer, 11 polarizing plate, 101 substrate, 102 columnar region, 103 medium.

Claims (8)

[Claims] 1. A transparent front substrate disposed in front of an observer facing a viewer, a rear substrate joined to the front substrate from behind through a predetermined gap, and at least one of the front substrate and the rear substrate. An electrode formed on one side, and an electro-optical material that projects an image by optically modulating an incident light beam from the rear in response to a voltage applied to the electrode disposed in the gap and converting the light beam to a forward emitted light beam, A light diffusion layer disposed on the front substrate to diffuse the emitted light beam and widen the viewing angle of the image viewed by an observer, wherein the light diffusion layer forwards the emitted light beam It comprises a columnar region formed so as to be able to guide light, and a medium that fills the gap between the columnar regions that are discretely arranged in a plan view, wherein the columnar region and the medium have different refractive indexes from each other. Display device. 2. The display device according to claim 1, wherein the diameter of the columnar region is set to 1/10 or less of the thickness of the light diffusion layer. 3. The display device according to claim 1, wherein the columnar regions are randomly distributed in a plan view. 4. The display device according to claim 1, wherein the diameter of the columnar region decreases from the front to the rear. 5. The light-reflecting layer for reflecting an incident light beam supplied from the front on the rear substrate, and the electro-optic material converts the incident light beam reflected by the light-reflecting layer into an outgoing light beam. The display device according to claim 1, wherein: 6. A transparent front substrate disposed in front of the viewer facing the observer, a rear substrate joined to the front substrate from behind via a predetermined gap, and at least one of the front substrate and the rear substrate. An electrode formed on one side, and an electro-optic material that optically modulates incident light from behind and converts it to forward-emitting light in response to a voltage applied to the electrode disposed in the gap to project an image, thereby displaying an image. A method for producing a light diffusion layer, which is disposed on the front substrate and diffuses the emitted light beam to widen the viewing angle of the image viewed by an observer, wherein the curing speed is high. A film forming step of applying a mixture of a precursor of one transparent resin and a precursor of a second transparent resin having a different curing index from the first transparent resin and having a slow curing speed, and applying ultraviolet light to the applied mixture. Is selectively irradiated to cure only the first transparent resin precursor. And a first irradiation step of forming discretely arranged columnar regions, and again irradiating the applied mixture with ultraviolet rays to cure the precursor of the second transparent resin remaining uncured, And a second irradiation step of processing into a medium that fills the space between the columnar regions arranged in a specific manner. 7. The light diffusion layer according to claim 6, wherein in the first irradiation step, a collimated ultraviolet ray is obliquely irradiated to form a columnar region inclined from a normal line of the display device. Manufacturing method. 8. The method according to claim 7, wherein in the first irradiation step, the collimated ultraviolet rays are simultaneously irradiated from two directions to form columnar regions inclined in two directions. Method.