JP2003131215A - Reflection type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate glaring light in a reflection type display device and to obtain a display with preferable appearance. SOLUTION: An optical member 101 is disposed on the display screen side of an electric display element of a reflection type display device so that the light entering from the display face passes from the back face side of the optical member to the top face side. A first transparent medium 102 having a refractive index nH and a second transparent medium 103 having a refractive index nL (satisfying 0.40>=nH-nL>=0.10) are disposed to form an interface in such a manner that at least part of the interface is inclined to the display face and that the first transparent medium is disposed on the back face side of the interface inclined to the display face while the second transparent medium is disposed in the top face side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical member used in a reflective display device and a reflective display device.

[0002]

2. Description of the Related Art In a transmissive mode display device, a light source luminous flux emitted from a backlight provided on the back side is irradiated from the back side of the display element to obtain display light from the front side of the display element. Although a part of the light source luminous flux is lost due to scattering and absorption, most of the display light depends on the light source luminous flux from the backlight.

Conventionally, many of these transmissive mode display devices have been used. However, in a portable display device, from the viewpoint of size and weight reduction, a semi-transmissive reflective mode in which external light is used as a light source other than the backlight, There has been a demand for a reflection mode display device that uses only external light as a light source without using a backlight.

[0004]

A reflective mode or semi-transmissive reflective mode display device utilizing external light has already been put into practical use. However, when used under a fluorescent lamp or the like, glare light is generated on the surface of the display unit, and the display contrast ratio is considerably lowered. Therefore, there is a problem in that the appearance of the display is significantly deteriorated and the desired display quality cannot be obtained.

As a method for reducing the glare light, an anti-glare film having unevenness on the surface of the display surface, an anti-reflection film using a dielectric interference film, and the like have been proposed. However, the antireflection film has a drawback that scattered light is generated to lower the display contrast ratio as a whole. In the case of an antireflection film, it is difficult to completely eliminate glare light. Alternatively, a general-purpose display device has a problem that its constituent members are considerably expensive.

Further, there has been proposed a method for avoiding glare light by disposing a saw-toothed inclined reflection layer on the side opposite to the viewer of the display section. However, when the tilted reflection layer is arranged outside the pair of substrates that form the electronic display element, the manufacturing itself is easy. However, this method of installing the device outside the substrate causes a new problem that a strong shadow is generated on the display surface and a double image is visually recognized.

Further, instead of outside the substrate of the electronic display element,
A method has also been proposed in which a tilted reflection layer is arranged at a position near the display layer inside the substrate. However, in this case, there arises a problem that manufacturing becomes considerably difficult.

Further, there has been proposed a method of avoiding glare light by using a hologram technique to construct a hologram layer as a reflection layer or an optical path changing layer in combination with a display device.
However, the manufacturing of the hologram layer requires a highly accurate manufacturing technique, and it is generally difficult to match with the pixels of the display device. In addition, the price of the entire display device becomes expensive, which is not suitable for general-purpose use.

[0009]

That is, in Embodiment 1 of the present invention, a front side polarizing plate and a back side polarizing plate, an electric display element, an optical member, and a reflective layer are arranged, and the optical member comprises:
A first transparent medium is a refractive index _{n H,} the refractive index _n L _{(n H}
≠ n _L ) and a second transparent medium are provided so as to have an interface, and at least a part of the interface is arranged obliquely with respect to the display surface of the electric display element. The first transparent medium is placed on the back surface side and the second transparent medium is placed on the front surface side in the interface portion obliquely arranged on the display surface, and the light emitted from the display surface is directed from the back surface side to the front surface side of the optical member. In the reflection type display device which is passed through as follows, the refractive index n _H and the refractive index n _L are n _H −n _L ≧ 0.10
There is provided a reflection type display device characterized in that the optical member is provided between the front side polarizing plate and the display layer of the electric display element so as to satisfy the above relationship.

Aspect 2 of the present invention is 0.40 ≧ n _H −
A reflective display device according to aspect 1, which satisfies the relationship of n _L.

A third aspect of the present invention is the first or second aspect in which the interface is formed so as to have a sawtooth shape in the thickness direction of the reflective display device and is continuously formed with respect to the display surface. A reflective display device as described above is provided.

Aspect 4 of the present invention provides the reflective display device according to aspect 1, 2 or 3, wherein the optical member has a thickness of 50 to 500 μm.

Aspect 5 of the present invention satisfies the following equations 1 to 7 where the angle of inclination of the sawtooth shape of the optical member with respect to the display surface is α ° and the incident angle with respect to the display surface is θ _1. A reflective display device according to 1, 2, 3 or 4 is provided.

[0014]

[Equation 2]

Aspect 6 is the reflection type display device according to Aspect 1, 2, 3, 4 or 5, wherein a light diffusion layer is arranged between the front substrate of the reflection type display device and the back surface of the optical member. I will provide a.

Further, in each of the above aspects, it is more preferable that the front side retardation plate is disposed on the front side of the optical member.

In each of the above aspects, it is preferable that the optical member itself has diffusibility. Further, it is preferable that the pitch P of the continuous sawtooth shape is 100 to 300 μm. Further, it is preferable that the reflective layer of the reflective display device is a semi-transmissive reflective layer, and a backlight is provided on the back side of the semi-transmissive reflective layer. Further, it is preferable that a front light is arranged on the front surface side of the reflective display device.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of the basic configuration of a reflective display device of the present invention. Front side polarizing plate 1, twisted phase difference plate 2,
The light diffusion layer 3, the substrates 4 and 14, the transparent electrodes 5 and 10, the alignment films 6 and 9, the liquid crystal layer 7, the sealing material 8, the smoothing layer 11, the color filter 12, the semi-transmissive reflective layer 13, the retardation plate 15, Back side polarizing plate 16, backlight 17, optical member 101, first
The transparent medium 102 and the second transparent medium 103 are provided.

The pair of front polarizing plates 1 and 16 and the twist-aligned liquid crystal layer 7 cooperate to perform a switching operation for each pixel for display. The twisted phase difference plate acts so as to compensate for coloring of display light.

The color filter 12 is a so-called micro color filter, which corresponds to the three primary colors of RGB, and a full color display can be obtained. The semi-transmissive reflective layer 13 transmits the light source luminous flux of the backlight to the front side and reflects part of the external light incident from the front side to the front side.

The optical member is arranged between the front side polarizing plate 1 and the front side transparent substrate 4. With this configuration, the luminous flux component that contributes to the display can be effectively used, and the generation of stray light can be reduced. Also, the display device can be easily assembled,
Assembly can be performed by stacking planar members. In addition, it is preferable that the pixel pitch array PX of the electric display element and the sawtooth-shaped continuous pitch P of the optical member 101 are not substantially equal to each other.

Next, each part of the optical member 101 used in the reflection type display device of the present invention will be described with reference to FIG. The optical member 101 is configured by combining a transparent medium having a relatively high refractive index and a transparent medium having a relatively low refractive index. First transparent medium 1
02 has a refractive index n _H and has a sawtooth shape in a cross section in the thickness direction. Further, the second transparent medium 103 has a refractive index n _L and similarly has a sawtooth shape. The two concavo-convex surfaces are in close contact with each other so that an air layer does not enter between them. At that time, the saw-tooth shape has an inclination angle of α ° with respect to the display surface of the reflective display device.

In the present invention, a large value of (n _H -n _L ) is preferable because the inclination angle of the interface can be made smaller accordingly. Moreover, the thickness of the optical member can be reduced, and the interface portion between the first transparent medium and the second transparent medium which is perpendicular to the display surface can be reduced. In the present invention, n _H −n _L ≧
0.10 is required.

Light incident from the front side at an incident angle of θ ₁ from the direction perpendicular to the display surface is refracted at the surface of the transparent medium 103 and further at the sawtooth-shaped interface, and is placed on the back surface side of the electric display element. The light is reflected by the reflective layer, further refracted at the interface, and further refracted when the second transparent medium 103 exits to the air layer on the front side. The emission angle at this time is θ ₂ .

The light which is incident on the surface of the optical member 101 from the front side and is reflected is reflected at an angle of θ ₃ = θ ₁ . At this time, it is preferable to configure so as to satisfy the following expressions 2 to 8.

[0026]

[Equation 3]

An observer does not look at the glare light from the surface,
It is preferable to view at an angle at which the reflection intensity of the display light of the reflective display device is maximized. For that purpose, the angle of (θ ₃ −θ ₂ ) is set in a numerical range of a certain degree or more. Specifically, (θ ₃ −θ ₂ ) is preferably set to 5 ° or more. Furthermore, it is preferable to set it to 10 ° or more.

In the present invention, two types of transparent media having different effective refractive indexes are required. Any isotropic optical material having high transparency and exhibiting no birefringence may be used. As a general-purpose optical material often used together with liquid crystal display elements,
Examples include polycarbonate, polyalate, polysulfone, and the like. Regarding the types and physical properties of optical materials,
For example, the column of optoelectronic polymer materials in the New Polymer Handbook (published by Maruzen Publishing Co., Ltd., Polymer Society of Japan) (87-
Page 90), and an optical material satisfying the conditions of the present invention may be selected. The configuration of the optical member will be described below.

First, polymethylmethacrylate (PMMA), which is an acrylic resin, is selected as the low refractive index material. A material having a refractive index of about 1.49 is used. Further, the inclination angle α is set to 3 by using PMMA having a refractive index of 1.67 as the high refractive index material.
Set to 0 °. In this case, when the incident angle θ ₁ is 30 °, θ ₂ is about 16 ° and θ ₃ is 30 °. Therefore,
(Θ ₃ −θ ₂ ) is 14 °, and bright display can be seen by avoiding glare light.

When the inclination angle α is 20 °, (θ ₃ −θ
₂ ) is about 9 °. When (θ ₃ −θ ₂ ) satisfies 5 ° or more, α needs to be about 11 ° or more. Table 1 shows these angular relationships. Therefore, in the present invention, it is preferable to satisfy θ ₁ = 10 to 30 °.

[0031]

[Table 1]

Next, the case where the refractive index difference (n _H −n _L ) between the low refractive index material and the high refractive index material is 0.30 or more will be described. A polymer material having a refractive index of about 1.34 is adopted. For example, there is Cytop manufactured by Asahi Glass Co., Ltd. PMMA with a refractive index of 1.67 is adopted as the high refractive index material, and the inclination angle α is 30.
Set to °. Then, when the incident angle θ ₁ is 30 °, θ ₂ becomes about 4.9 ° and θ ₃ becomes 30 °. Therefore,
The magnitude of (θ ₃ −θ ₂ ) is 25.1 °, and the observer can sufficiently avoid glare light and can see a bright display. Details are shown in Table 2.

[0033]

[Table 2]

As the low refractive index material, the refractive index is about 1.3.
4 transparent polymer (Asahi Glass Co., Ltd .: Cytop) is adopted,
PMMA with a refractive index of 1.49 is adopted as the high refractive index material.
It When the tilt angle α is set to 30 °, the incident angle θ
₁Is 30 °, θ _TwoIs about 18 °, θ_ThreeIs 30
It becomes °. Therefore, (θ_Three−θ_Two) Is 12 °
Yes Observers can avoid glare and see brighter displays
it can. Details are shown in Table 3.

[0035]

[Table 3]

In the present invention, the sawtooth-shaped pitch P when continuously formed on the display surface may be set to a size such that the observer looks at the display surface and does not notice the stripes in the surface. preferable. Specifically, the pitch P is 300 μm
The following is preferable. Further, when the thickness is 50 μm or less, the streaks on the display surface are hardly visible, which is preferable.

Further, it is necessary to take measures against moire by the sawtooth pitch P and the pixel pitch PX. Generally, the pixel size of a direct-view type reflective liquid crystal display device is 150 to 50.
It is about 0 μm. If the pitch P is set to 45 μm or less, which is far from the pixel size value of this degree, the occurrence of moire is reduced.

As described above, the numerical range of the sawtooth-shaped pitch may be changed with respect to the numerical range of the pixel pitch so that moire does not occur. However, adjusting and manufacturing the optical member for each model of the reflective display device having different uses and display specifications increases the production cost. Therefore, as another technique for avoiding moire, it is possible to dispose a light diffusion layer between the viewer-side substrate and the sawtooth-shaped transparent medium. By providing this light diffusion layer, it is possible to avoid the occurrence of moire.

The light diffusion level of the light diffusion layer is as follows. When expressed as a haze value, it is preferably from 15 to 80%. Furthermore, 40 to 65% is preferable. If the light diffusivity is weak, the moire will not be completely eliminated, and if the diffusivity is too high, the reflection intensity will be low and the display will be dark. Here, the haze value is a value defined by diffuse transmittance / total light transmittance.

The present invention can also be used in a reflective display device that operates in a semi-transmissive reflection mode by combining a backlight and a semi-transmissive reflective layer. As the semi-transmissive reflective layer, a method of using a metal thin film such as Al or Ag as the reflective layer, or a method of using Al or Ag
There is a method of partially providing a transmissive portion on the reflective layer. Further, it may be a semi-transmissive reflective layer formed by forming a multilayer of an inorganic substance or an organic substance other than a metal. Further, as a method of illuminating the electric display element, a front light may be used instead of the backlight.

[0041]

EXAMPLES Example 1 Next, examples will be described with reference to the drawings. FIG. 1 is a schematic sectional view of a transflective color liquid crystal display device which is an example of the reflective display device of the present invention. Two polarizing plates are provided, and a color filter is provided near the liquid crystal layer. The liquid crystal cell used as the electric display element of this example was formed as follows.

The ITO transparent electrode 5 provided on the glass substrate 4 having a thickness of 0.5 mm was patterned in a stripe shape, and an insulating film was formed thereon. Further, a polyimide alignment film 6 was formed, and this was rubbed to form an alignment control film on the substrate to form one substrate.

An uneven layer is provided on the other glass substrate, a semi-transmissive reflective layer 13 is formed on the uneven layer, and striped red, green, and blue color filters 12 are provided thereon, and the striped ITO is formed thereon. The transparent electrode 10 is formed by patterning, the insulating film is formed, and the polyimide alignment film 9 is formed.
This was rubbed to form an alignment control film, and the other substrate was formed.

The periphery of these two substrates was sealed with a sealing material 8 to form an empty cell, then chiral nematic liquid crystal was injected into the empty cell, and the injection hole was sealed with a sealing material.

The liquid crystal layer 7 is a 240 ° twisted STN liquid crystal, and its Δn · d is 0.76 μm. The twisted phase difference plate 2 is rotated 180 degrees in the direction opposite to the twist direction of the liquid crystal layer 7.
It has a twisted orientation and its Δn · d is 0.642.
μm, and Δn · d of the retardation plate 15 was 0.135 μm.

The front side polarizing plate 1 and the back side polarizing plate 16 were arranged so as to have a desired crossing angle. For display, we adopted a negative mode that realizes low brightness when no voltage is applied and high brightness when voltage is applied.

A sidelight type backlight 17 is installed behind the backside polarizing plate 16 and is used as an auxiliary light source when the reflection by external light is weak. The backlight can be turned off depending on the usage environment.

The minimum unit pixel of the display unit is 305 μm
The size is × 95 μm. The distance between the lines was 10 μm. Therefore, the pixel array period is 105 μm in the horizontal direction and 315 μm in the vertical direction. The first transparent medium and the second transparent medium forming the optical member 101 are set to α = 30 °, a low refractive index n _L = 1.34, and a high refractive index n _H = 1.49.
Was used. Sawtooth pitch P of about 50
It was set to 0 μm.

As the light diffusion layer 3, a bead type light diffusion layer having a haze value of 45% was used. When the light diffusing layer was not provided, the observer visually recognized the moire, but by disposing the light diffusing layer 3, the occurrence of the moire was reduced, and the display quality had no problem in normal use.

Light was incident on the reflection type display device of the present example having the above-mentioned requirements so that the incident angle θ ₁ was about 30 °. Then, the observer was able to avoid the glare light sufficiently and see a sufficiently bright display.

Example 2 In this example, the sawtooth shape of the optical member is set to α = 30 °, and n = 1.4 as the low refractive material.
A second transparent medium was formed using the optical material of No. 9. As shown in FIG. 3, a high refractive index material has a high refractive index of 1.67.
A first transparent medium was formed by incorporating particles having a refractive index of 1.49 into the optical material of (1) to develop a diffusion function. Therefore, in the reflective display device of the present example, the light diffusing layer 3 employed in Example 1 is not provided, and the diffusing function can be exhibited inside one transparent medium of the optical members. Also,
The sawtooth pitch was about 153 μm.

Light was incident on the reflective display device of this example so that the incident angle θ ₁ was about 30 °. Then, the observer could avoid the glare light and see a bright display.

[0053]

In the reflection type display device of the present invention, since the predetermined optical member is arranged between the front side polarizing plate and the electric display element, the display contrast ratio is dramatically improved.
Particularly, since the backscattering due to stray light can be suppressed, the appearance of the display is good. Further, it is possible to prevent a display defect (display blur) in which pixels on the display surface cannot be clearly visually recognized.

Therefore, it is possible to provide a bright, high-quality display which has a better contrast ratio and is easy to see. Then, it is possible to prevent the generation of glare light in a display device that employs the reflection mode. Further, the optical member used in the present invention is easy to manufacture. Further, since the optical member can be incorporated by using a conventionally known reflection type display device manufacturing technique, the manufacturing is easy.

The reflection type liquid crystal display device of the present invention, particularly the reflection type color liquid crystal display device of the transflective mode using a color filter, is a portable electronic device which is supposed to be used outdoors, such as a mobile phone or an electronic device. A notebook, an electronic book, an electronic dictionary, a personal digital assistant (PDA), a pager, a mobile position detector (GPS), a portable fish finder, a portable game machine,
When used for such purposes, it exhibits high functionality combined with its good visibility and expressiveness.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of Example 1 of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating the function of an optical member used in the present invention.

FIG. 3 is a schematic cross-sectional view of an optical member with a diffusion function used in the present invention.

[Explanation of symbols]

1: Front polarizing plate 2: Twisted phase plate 3: Light diffusion layer 4, 14: transparent substrate 5, 10: transparent electrode 6, 9: Alignment film 7: Liquid crystal layer 8: Seal material 11: Smoothing layer 12: Color filter 13: Semi-transmissive reflective layer 15: Retardation plate 16: Back side polarizing plate 17: Backlight 101: Optical member 102: first transparent medium 103: Second transparent medium

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09F 9/00 313 G09F 9/00 313 9/35 9/35 F term (reference) 2H042 AA02 AA03 AA07 AA26 BA02 BA12 BA20 CA14 CA17 2H091 FA08X FA08Z FA14Y FA14Z FA41Z GA01 KA01 KA10 LA17 5C094 AA01 AA11 EB04 ED14 FA04 JA13 5G435 AA02 BB12 BB16 DD13 FF02 FF04 FF05 FF06 HH03 HH04

Claims (6)

[Claims] 1. A front polarizing plate and a back polarizing plate, an electric display element, an optical member, and a reflective layer are arranged, and the optical member has a first transparent medium having a refractive index n _H and a refractive index. n
_L (n _H ≠ n _L ) is provided so as to have an interface with the second transparent medium, and at least a part of the interface is arranged obliquely to the display surface of the electric display element, The first transparent medium at the interface portion obliquely arranged with respect to the display surface is placed on the back surface side, the second transparent medium is placed on the front surface side, and the light emitted from the display surface is fed from the back surface side of the optical member. In a reflective display device which is made to pass toward the front surface side, the refractive index n _H and the refractive index n _L are provided so as to satisfy the relationship of n _H −n _L ≧ 0.10, and A reflective display device comprising an optical member arranged between the electric display element and a display layer. 2. The reflective display device according to claim 1, wherein the relationship of 0.40 ≧ n _H −n _L is satisfied. 3. The reflective display device according to claim 1, wherein the interface is formed so as to have a sawtooth shape in the thickness direction of the reflective display device, and is formed continuously with respect to the display surface. . 4. The reflective display device according to claim 1, wherein the optical member has a thickness of 50 to 500 μm. 5. When the inclination angle of the sawtooth shape of the optical member with respect to the display surface is α ° and the incident angle on the display surface is θ ₁ ,
The reflective display device according to claim 1, 2, 3, or 4, which satisfies the following expressions 1 to 7. [Equation 1] 6. A light diffusion layer is disposed between the front substrate of the reflective display device and the back surface of the optical member.
The reflective display device according to 3, 4, or 5.