JP3642144B2 - Reflective display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reflection type display device, and more particularly to an interference reflection type reflection type display device.
[0002]
[Prior art]
The liquid crystal display device has a large viewing angle dependency, and the display quality varies greatly depending on the viewing direction. Therefore, various methods have been considered for improving the viewing angle of a display device having a large viewing angle dependency such as a liquid crystal display device.
[0003]
For example, in JP-A-7-43703, JP-A-7-43704, and JP-A-7-120743, in a liquid crystal display device such as a TN system or STN system, a microlens array sheet is mounted on the observation surface side of the display element. By doing so, it is shown that the viewing angle is enlarged.
[0004]
Similarly, in JP-A-5-45644, JP-A-5-61032, and JP-A-5-61033, a large number of transparent thin plates made of acrylic resin or the like are stacked in a liquid crystal display device such as a TN mode or STN mode. It is shown that the viewing angle is expanded by arranging the combined viewing angle expansion plate on the display surface side of the display element.
[0005]
By the way, a small-sized information device, a portable information terminal, or the like uses a reflective display device that does not require a dedicated light source such as a backlight, consumes less power, and can be configured to be thin and light. In recent years, attention has been paid to a reflection type display device using an interference reflection type reflection type display element (light control element).
[0006]
An interference reflection type reflective display element uses a periodic change in the refractive index in the element, and is disclosed in U.S. Pat. No. 4,938,568, JP-A-4-355424, SID95Digest, p267, EuroDisplay. As shown in '93, p109, etc., it can be obtained by the following method.
[0007]
For example, a nematic liquid crystal having positive dielectric anisotropy is mixed with a mixture of a photopolymerizable monomer, a photopolymerization initiator and a sensitizer, and a pair of transparent substrates on which electrodes are formed are opposed to each other at a predetermined interval. It is injected into the formed cell, the cell is sealed, and a single laser beam is bisected and irradiated to the cell.
[0008]
At this time, due to the coherence of the laser beam, interference occurs between the divided laser beams, the intensity of the photoelectric field is generated in the liquid mixture, and photopolymerization is generated in a portion where the electric field is spatially strong. Rich portions are formed, and liquid crystal-rich portions are formed between the polymer-rich portions, and a striped refractive index distribution in the wavelength order of the laser beam is generated in the cell.
[0009]
In this case, the liquid crystal becomes a spherical droplet of 0.1 μm or less, and the refractive index of the portion becomes different from the refractive index of the surrounding polymer-rich portion. A structure of change is formed. And in the liquid crystal droplet part, the liquid crystal director is oriented in a random direction, and it is considered that there is no particular correlation between the droplets.
[0010]
When light is incident on the light control layer in which such polymer-rich portions and liquid crystal-rich portions are periodically formed, multiple interference occurs due to the periodic change of the refractive index, thereby satisfying the Bragg reflection condition. A reflected light of a specific wavelength is generated. This is the same phenomenon as interference reflection by the dielectric multilayer film.
[0011]
Further, when a voltage of a predetermined value or higher is applied between the electrodes, the liquid crystal directors in the liquid crystal droplets are uniformly arranged in the electric field direction. Therefore, by selecting the composition of the initial liquid mixture so that the refractive index no of the normal light of the liquid crystal is equal to the refractive index np of the polymer, the liquid crystal rich portion and the polymer rich portion can be obtained at this time. The difference in refractive index from the portion disappears, and all incident light is transmitted through the cell.
[0012]
According to the reflective display device using the reflective display element of the interference reflection system, since a polarizing plate is not used, light is not absorbed and a high reflectance is obtained by multiple interference, so that a bright display can be realized. Can do. However, in the interference reflection method, even if the incident light is white light, only light of a specific wavelength that satisfies the conditions of Bragg reflection is reflected with high reflectance as described above.
[0013]
[Problems to be solved by the invention]
However, in the reflective display element of the interference reflection system, the signal is transmitted only in the direction satisfying the Bragg reflection condition between the incident light that is external light and the signal light that is reflected light emitted from the element. Light is emitted. Therefore, the emission direction of the signal light is limited, the viewing angle dependency becomes very large, and the display becomes difficult to see.
[0014]
In addition, since the interference reflection type reflective display element emits signal light in a specific direction in this way, the viewing angle is expanded by the viewing angle expansion plate in which the above-described microlens array sheet and a large number of transparent thin plates are superimposed. With this method, it is difficult to enlarge the viewing angle.
[0015]
In view of this, the present invention is an interference reflection type reflective display device that can reliably enlarge the viewing angle by a simple method.
[0016]
[Means for Solving the Problems]
In the reflective display device of the first invention, a prism is arranged for each pixel of the reflective display element of the interference reflection type, and one surface of the prism is used as an incident surface for taking in external light, and the other surface is used as By forming a concavo-convex shape on this, an observation surface on which reflected light from the pixel is scattered and emitted is used.
In the reflection type display device of the second invention, a prism is arranged for each pixel of the reflection type display element of the interference reflection type, and one surface of the prism is used as an incident surface for taking in external light, and the other surface is used. By providing a light scatterer in the vicinity thereof, an observation surface on which reflected light from the pixel is scattered and emitted is provided.
[0017]
In this case, the bottom surface of the prism is brought into close contact with the pixel surface of the reflective display element with an adhesive, and the refractive index of the prism and the adhesive is made equal to the refractive index of the pixel surface. Alternatively, the prism is formed integrally with the pixel surface of the reflective display element.
[0018]
It is desirable to form an antireflection film on the incident surface of the prism.
[0019]
[Action]
In the reflective display device of the present invention configured as described above, when external light is incident on the incident surface, which is one surface of the prism, the pixel of the reflective display element is defined by the conditions of Bragg reflection. Reflected light is emitted in a specific direction. However, the emitted signal light, which is reflected light, always illuminates the observation surface, which is the other surface of the prism, and is scattered by the observation surface. Therefore, as long as the observer views from the observation surface side, the signal light can be observed regardless of the viewing angle, and the viewing angle dependency of the reflective display device is greatly improved.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1A shows the basic configuration of a reflective display device according to the present invention, in which a minute prism 20 is arranged for each pixel P of an interference reflective reflective display element 10.
[0021]
As long as the reflective display element 10 is of an interference reflection type using a periodic change in the refractive index in the element, the polymer-rich part and the liquid crystal-rich part are not necessarily formed periodically as described above. It is not necessary to be formed, and it is not necessary to be formed by the method described above.
[0022]
Further, on the side opposite to the external light incident side of the reflective display element 10, that is, the side opposite to the side where the prism 20 is disposed, a light absorption layer that absorbs light transmitted through the reflective display element 10 is provided as necessary. In addition, in the case of a multicolor display device, for example, three display elements each having a red, green, and blue wavelength region as reflection wavelength regions are stacked as the reflective display element 10.
[0023]
The prism 20 is obtained by processing or forming a transparent material such as transparent glass or resin into a prism shape. As will be described later, the prism 20 is formed separately from the reflective display element 10 and its bottom surface is reflected by an adhesive. The pixel display device 10 is formed in close contact with the pixel surface or formed integrally with the pixel surface of the reflective display device 10.
[0024]
As shown in FIG. 1B, one surface of the prism 20 is an incident surface for taking in the external light 1, and the other surface is an observation surface from which reflected light from the pixels P is emitted as emitted light 2.
[0025]
In this case, as shown in FIGS. 2A, 2B, or 2C, the external light 1 is one surface of the prism 20 at an angle of θ1, θ2, or θ3 with respect to the pixel surface of the reflective display element 10. When the light enters the incident surface, the reflected light 3 is emitted from the pixels of the reflective display element 10 in a specific direction defined by Bragg reflection conditions.
[0026]
The emitted signal light that is the reflected light 3 always illuminates the observation surface, which is the other surface of the prism 20, but forms an uneven shape on the observation surface, as described later, or in the vicinity of the observation surface. Is provided with a light scatterer. Therefore, the signal light that illuminates the observation surface is scattered by the observation surface. Therefore, as long as the observer sees from the observation surface side, the observer can observe the signal light regardless of the viewing angle. That is, illumination light from various directions such as room light and outdoor light is effectively used.
[0027]
As shown in FIG. 3, the angle of the prism 20 is defined as α with respect to the bottom surface 23 of the observation surface 22 and β with respect to the bottom surface 23 of the incident surface 21.
[0028]
The outside light 1 can be effectively used up to light incident at an angle α with respect to the bottom surface 23. A part of light incident at an angle of α or more irradiates the observation surface 22, which causes a decrease in contrast. On the other hand, there is an advantage that the light reflected by the observation surface 22 enters the incident surface of the adjacent prism and is reused. Light incident at an angle of α or less can be effectively used except for reflection on the incident surface 21. Therefore, coupled with the high reflectivity of the interference reflection method, a high-brightness reflective display device can be obtained.
[0029]
The angle β determines the observation angle range of the observer. When the image is observed at an angle of β or more, the incident surface 21 that is the back surface can be seen, so that the image quality is deteriorated. Under normal use conditions, β should be around 45 degrees, and it is rare to look into it from directly above. The angles α and β may be determined according to the application.
[0030]
FIG. 1 shows the case where the angles α and β are the same for the prisms for the respective pixels, but the angle at which each pixel is desired by the observer is either in the orthogonal X or Y direction within the pixel plane. Therefore, the angles α and β may be slightly changed for each prism for each pixel.
[0031]
[Example 1]
FIG. 4 shows a first example of the reflection type display device of the present invention. A prism 20 is provided for each pixel P of the interference type reflection type display element 10, and its bottom surface is reflected by an adhesive 30. This is a case where the antireflection film 25 is formed on the incident surface 21 of the prism 20 while being arranged so as to be in close contact with the pixel surface of the element 10.
[0032]
The reflective display element 10 includes a light control layer 15 that periodically changes a refractive index between transparent substrates 11 and 12 made of glass or resin, respectively, on which transparent electrodes 13 and 14 made of ITO or the like are formed. Depending on whether or not a voltage is applied between the transparent electrodes 13 and 14, the external light 1 is transmitted as the transmitted light 4, or the light having a specific wavelength in the external light 1 is reflected as the reflected light 3. In addition, light having a wavelength other than that is transmitted as transmitted light 4.
[0033]
Although omitted in the figure, a light absorption layer that absorbs the transmitted light 4 is provided on the back side of the transparent substrate 12. In the case of a multicolor display device, as the reflective display element 10, for example, three display elements each having a red, green, and blue wavelength region as reflection wavelength regions are stacked.
[0034]
The prism 20 is obtained by processing a transparent material such as transparent glass or resin into a prism shape. The refractive index of the prism 20 and the adhesive 30 is equal to the refractive index of the transparent substrate 11.
[0035]
When an air layer is formed between the prism 20 and the transparent substrate 11, a difference in refractive index is generated and reflection occurs, and the amount of light incident on the reflective display element 10 through the prism 20 and observation through the prism 20 are observed. The amount of light emitted from the surface 22 decreases. The lower surface of the prism 20 is brought into close contact with the transparent substrate 11 with the adhesive 30, and the refractive index of the prism 20 and the adhesive 30 is made equal to the refractive index of the transparent substrate 11 to prevent such a decrease in the amount of light. it can.
[0036]
The antireflection film 25 is formed of, for example, a dielectric multilayer film. By forming the antireflection film 25 on the incident surface 21 of the prism 20 in this way, the incident efficiency of the external light 1 is increased and the external light 1 can be used more effectively.
[0037]
In this example, an uneven shape is formed on the observation surface 22, and the reflected light 3 is scattered on the observation surface 22.
[0038]
[Example 2]
FIG. 5 shows a second example of the reflective display device of the present invention, and the prism 20 is brought into close contact with the reflective display element 10 with an adhesive 30 as in the first embodiment of FIG. This is a case where a light scatterer 27 is provided in the vicinity of 22.
[0039]
As shown in the figure, the light scatterer 27 may be embedded in the prism 20 when the prism 20 is formed, or may be adhered to the observation surface 22 after the prism 20 is formed. Further, as the light scatterer 27, a white powder such as barium sulfate, which is as fine as the reflection wavelength, or a liquid crystal droplet can be used.
[0040]
By thus Ru provided a light scattering member 27 in the vicinity of the observation plane 22, scattering of the random directions occurs efficiently, it is possible to realize a display exhibiting an appearance as printed matter.
[0041]
Also in this example, it is desirable to form an antireflection film on the incident surface 21 of the prism 20.
[0042]
Example 3
FIG. 6 shows a third example of the reflective display device of the present invention, in which the prism 20 is formed integrally with the pixel surface of the reflective display element 10, that is, the transparent substrate 11.
[0043]
Thus, by forming the prism 20 integrally with the transparent substrate 11 from the same material as the transparent substrate 11, the refractive index of the prism 20 becomes equal to the refractive index of the transparent substrate 11, and the prism 20 and the transparent substrate 11 An air layer is not formed between the two, and a decrease in the amount of light incident on the reflective display element 10 via the prism 20 and the amount of light emitted from the observation surface 22 via the prism 20 can be prevented. it can.
[0044]
In this case, the transparent substrate 11 and the prism 20 are integrally formed, the transparent electrode 13 is formed on the surface of the transparent substrate 11 opposite to the side on which the prism 20 is formed, and the transparent electrode 14 is formed on one surface of the transparent substrate 12. The transparent substrates 11 and 12 are made to face each other at a predetermined interval, the mixed liquid as described above is injected between them, and a single laser beam is divided into two, and one of them is separated from the incident surface 21 of the prism 20. By irradiating the mixed liquid through the prism 20 and the transparent substrate 11 and irradiating the mixed liquid through the transparent substrate 12 on the other side, it is possible to obtain the reflective display element 10 in which the prism 20 is integrally formed. it can.
[0045]
Also in this example, an uneven shape is formed on the observation surface 22 of the prism 20, or a light scatterer is provided in the vicinity of the observation surface 22. Further, it is desirable to form an antireflection film on the incident surface 21 of the prism 20.
[0046]
【The invention's effect】
As described above, according to the present invention, it is possible to reliably expand the viewing angle of the interference reflection type reflection type display device by a simple method, the reflection type display device having high contrast and low viewing angle dependency. Can be realized. In addition, since even light incident at an angle α with respect to the pixel surface can be used effectively, a high-brightness reflective display device can be obtained in combination with the high reflectivity of the interference reflection system. In addition, since only a prism is arranged for each pixel, the structure is simple, and weight reduction as a reflective display device is not impaired.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of a reflective display device according to the present invention.
FIG. 2 is a diagram showing a relationship between incident light and outgoing light in the reflective display device of the present invention.
FIG. 3 is a diagram showing an incident light usable range and an observable range depending on the angle of the prism in the reflective display device of the present invention.
FIG. 4 is a diagram showing a first example of a reflective display device according to the present invention.
FIG. 5 is a diagram showing a second example of the reflective display device of the invention.
FIG. 6 is a diagram showing a third example of the reflective display device of the invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Reflective display element 11, 12 Transparent substrate 13, 14 Transparent electrode 15 Light control layer 20 Prism 21 Incident surface 22 Observation surface 23 Bottom surface 25 Antireflection film 27 Light scatterer

Claims (5)

A prism is arranged for each pixel of the reflective display element of the interference reflection system, and one surface of the prism is used as an entrance surface for taking in external light, and the other surface is formed with an uneven shape on the pixel. A reflection-type display device characterized in that a reflection surface from which the light is scattered is emitted. A prism is arranged for each pixel of the reflective display element of the interference reflection system, and one surface of the prism is used as an incident surface for taking in external light, and the other surface is provided with a light scatterer in the vicinity thereof. A reflection-type display device characterized in that an observation surface on which reflected light from a pixel is scattered and emitted is used. The reflective display device according to claim 1 or 2 ,
A reflective display device, wherein a bottom surface of the prism is adhered to a pixel surface of the reflective display element with an adhesive, and a refractive index of the prism and the adhesive is made equal to a refractive index of the pixel surface. The reflective display device according to claim 1 or 2 ,
A reflective display device, wherein the prism is formed integrally with a pixel surface of the reflective display element. In the reflective display apparatus in any one of Claims 1-4,
A reflection type display device, wherein an antireflection film is formed on the incident surface of the prism.

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