JPH11258598A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to secure a high reflection factor even in the case of a low backscattering ratio by arranging a specific optical means on the rear side of a liquid crystal display(LCD) panel. SOLUTION: A reflection type scattering LCD 11 is constituted of arranging a sheet-like prism array 13 on the rear side of the scatter type LCD panel 12 and sticking a glass plate 14 and a light absorbing plate 15 such as a black resin plate close to the lower surface of the array 13. The rear side of she array 13 is flately formed and prism patterns 16 having uniform isosceles trianglar cross sections in one direction are arrayed on the surface side of the array 13 in each fixed pitch. The array direction of the patterns 16 coincides with one pixel array direction of the panel 12. The prism array 13 has a function for transmitting light made incident at an incident angle smaller than a certain fixed incident angle through its lower face (a boundary with the glass plate 14) and totally reflecting light made incident at an incident angle larger than the certain fixed incident angle by the lower face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device using a scattering type liquid crystal.

[0002]

2. Description of the Related Art Since a reflection type liquid crystal display does not require a backlight, it is expected to be applied to portable information terminals with low power consumption. However, in a conventional reflective color liquid crystal display device of TN (twisted nematic) mode or STN (super twisted nematic) mode, the amount of reflected light is reduced by half because a polarizing plate is used, and sufficient luminance is obtained in principle. I couldn't do that. Therefore, in order to increase the reflectance of the reflection type liquid crystal display device, various liquid crystals and liquid crystal display devices using the same have been developed.

Among these liquid crystals, GH (guest / host) mode, PDLC mode, PC (phase change)
If a mode liquid crystal display device or the like is used, it is possible to improve the reduction in reflectance, which has been a problem of TN and STN. However, in the liquid crystal display devices of these modes, the performance of other specifications such as contrast and the number of colors is deteriorated in exchange for the improvement of the reflectance. This means that a liquid crystal display device with high specifications in all aspects of performance has not been realized, and future challenges will be to make use of the characteristics of the liquid crystal display device of each mode and to display the liquid crystal display of each mode. It is to improve the disadvantages of the device.

[0004] Under such a background, a reflection type liquid crystal display device (hereinafter referred to as a reflection type scattering LCD) using a scattering type liquid crystal (polymer dispersion type liquid crystal, phase transition type liquid crystal) has a high reflectance. In addition to these advantages, the liquid crystal display device is likely to be used in the future because of its simple structure and the absence of double reflection which is a problem peculiar to the reflection type liquid crystal display device. one of.

FIG. 1 schematically shows the structure of this reflection type scattering LCD.
(A) and (b). The reflective scattering LCD 1 has a PC or PD between glass substrates having a transparent electrode (ITO) or the like on the inner surface.
The light absorbing plate 3 is stacked on the back surface of a liquid crystal display panel 2 in which liquid crystal such as LC is sealed. Thus, in a certain pixel, when the driving voltage applied between the electrodes from the outside is off, the liquid crystal exhibits scattering characteristics as shown in FIG. 1A, and scatters the incident light R. At this time, the backscattered light (scattered in the direction opposite to the traveling direction of the incident light) returns to the direction of the observer, so that the pixel is in a reflection state. Conversely, when the drive voltage of a certain pixel is on, the liquid crystal completely transmits light as shown in FIG. Therefore, all the light is absorbed by the light absorbing plate 3 provided below the liquid crystal, and the pixel becomes dark.
As a result, switching between reflection and absorption of light is realized. In addition, since no polarizing plate is used, the reflectance, which is the biggest problem for the reflection type liquid crystal display device, can be improved.

As can be understood from the above principle, the reflectance of the reflective scattering LCD can be improved by increasing the backscattering rate in the scattering state (when the driving voltage is off). However, in order to sufficiently increase the scattering characteristics of the reflection-type scattering LCD, the thickness of the liquid crystal layer must be increased, so that an essentially high driving voltage is required. This is a factor that hinders the practical use of the reflection-type scattering LCD, and improvement is desired. In order to solve this, it is necessary to find a means that can obtain a high reflectance even at a low backscattering rate (that is, even at a low driving voltage).

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a conventional reflective scattering LCD even with a low backscattering rate.
It is an object of the present invention to provide a reflective liquid crystal display device capable of ensuring the above-described reflectance.

[0008]

According to a first aspect of the present invention, there is provided a reflection type liquid crystal display device, wherein a liquid crystal display panel capable of switching incident light between a transmission state and a scattering state is disposed on a back side of the liquid crystal display panel. An optical means for transmitting light having an incident angle smaller than the incident angle and reflecting light having an incident angle larger than a predetermined incident angle, the optical means being capable of setting the predetermined incident angle, and a light absorbing element disposed on the back side of the optical means It is characterized in that it is made of a material having a characteristic.

In this reflection type liquid crystal display device, the light transmitted through the pixels of the liquid crystal display panel without being scattered is
Since the light is incident on the optical means at a relatively small incident angle, the light passes through the optical means and is absorbed by the light absorbing member. On the other hand, the light scattered by the pixels of the liquid crystal display panel is partially scattered (backscattered) in the original direction to illuminate the pixels, and the light scattered forward is relatively transmitted to the optical means. When the light is incident at a large incident angle, the light is reflected by the optical means and is reflected in the original direction to illuminate the pixel. Therefore, it is possible to manufacture a scattering type reflection type liquid crystal display device which can increase the contrast of an image without applying a high driving voltage to the pixel electrode in order to obtain a high back scattering ratio.

Further, in the optical means, a predetermined angle of incidence can be set as a boundary between transmitting and reflecting the incident light, so that the absorption and reflection of the incident light can be optimized, and the dark part and the dark part can be optimized. The contrast with the bright part can be increased.

According to a second aspect of the present invention, there is provided a reflection type liquid crystal display device.
The optical means, an optical element in which a prism pattern having a uniform cross section in one direction is arranged, an optical element in which a prism pattern having a uniform cross section is arranged in a direction substantially orthogonal to the direction, and both optical elements Are also formed of a transparent plate having a small refractive index.

When a prism pattern is used as the optical means, a predetermined incident angle can be set according to the base angle of the prism pattern. Further, in this embodiment, since the optical element having two prism patterns having different directions is used, the reflection / absorption of light in two-dimensional directions can be optimized.

According to a third aspect of the present invention, in the reflective liquid crystal display device according to the first aspect, the optical pattern of the optical unit is divided for each pixel.

In this embodiment, since the optical pattern of the optical element is divided for each pixel, light transmitted through a certain pixel and reflected by the optical means and returned is prevented from being emitted from an adjacent pixel. be able to. Therefore, blurring of an image and blurring of colors can be prevented.

[0015]

(First Embodiment) FIG. 2 is a perspective view showing the structure of a reflection type liquid crystal display device (hereinafter, referred to as a reflection type scattering LCD) 11 according to an embodiment of the present invention. The reflection type scattering LCD 11 is provided on the back side of a scattering type liquid crystal display panel 12 in which scattering type liquid crystals (polymer dispersion type liquid crystal, phase transition type liquid crystal, etc.) are sealed between glass substrates on which transparent electrodes are formed. A prism array 13 in the form of a sheet is placed, and a glass plate 14 and a light absorbing plate 15 such as a black resin plate are adhered to the lower surface thereof. Alternatively, instead of the light absorbing plate 15, a paint having a light absorbing property, for example, a black paint may be applied to the lower surface of the glass plate 14.

The prism array 13 is formed of a transparent optical resin, has a flat back surface, and has a prism pattern having a uniform isosceles triangular cross section in one direction on the front surface as shown in FIG. 16 are arranged at regular intervals. The prism array 13 is arranged such that the arrangement direction of the prism patterns 16 is oriented in a direction in which one of the pixel arrangement directions of the liquid crystal display panel 12 coincides.
2 is arranged on the back surface. Further, the arrangement pitch Lp of the prism patterns 16 is smaller than the pixel pitch of the liquid crystal display panel 12, and it is particularly preferable that the arrangement pitch Lp be 1 / n of the pixel pitch (where n is a positive integer and n ≧ 2). Or,
The arrangement of the prism patterns 16 may be uneven or random.

Here, the prism array 13 is formed of a material having a higher refractive index than the glass plate 14. Further, the prism array 13 includes the liquid crystal display panel 12.
It is formed of a material having a higher refractive index than the medium (air layer in the case of this embodiment) between the prism array 13 and.

(Explanation of Function) Next, the function of the reflective scattering LCD 11 having such a structure will be described. Reflective scattering LC
In order to increase the backscattered light of D11, the same effect can be obtained not only by increasing the backscattering ability of the liquid crystal itself but also by inverting the forward scattered light in the original direction. However, in the method in which the forward scattered light is reflected by the mirror, the light is reflected even in the transmission state where the driving voltage is turned on, so that a complete black display cannot be performed. That is, an optical element that completely absorbs light in the transmission state and reflects light in the scattering state is required. In this embodiment, this optical element is realized by an optimally designed prism array 13.

That is, as shown in FIG. 4, the prism array 13 transmits the light R ₁ incident at an incident angle θ ₁ smaller than a certain incident angle θd through the lower surface (boundary surface with the glass plate 14). The light R ₂ incident at an incident angle θ ₂ larger than a certain incident angle θ _d has a function of being totally reflected at a lower surface (a boundary surface with the glass plate 14). Hereinafter, this incident angle θ _d is referred to as a separation angle of the prism array 13.

Therefore, if the separation angle θ _d of the prism array 13 is appropriately designed, the driving voltage is turned on as shown in FIG. 5B among the pixels of the liquid crystal display panel 12. Incident light R transmitted through the pixel in the transmission state
All light can pass through the lower surface of the prism array 13 and be absorbed by the light absorbing plate 15. Further, for the pixels in the scattering state the drive voltage is turned off, because the pixels of the transmission condition exists light R incident to the prism array 13 was not present angle, separation angle of the prism array 13 theta _d
5A, a part of the forward scattered light, which was conventionally absorbed by the light absorbing plate 15 and became a complete loss, is reflected toward the liquid crystal display panel 12 as shown in FIG. The light is then diffused again by the liquid crystal and exits to the front of the liquid crystal display panel 12 together with the backscattered light. Therefore, the prism array 1
3, and by appropriately designing the separation angle θ _d , the reflectance in the scattering state can be improved while maintaining the absorption rate in the transmission state. As a result, the reflection type scattering L
The reflectivity of a CD can be improved.

(Design of Optimal Separation Angle) Next, the light that has passed through the pixel in the transmission state is almost completely removed, or as much light as possible within a range that does not affect the image quality of the reflection type scattering LCD. And at the same time, a method of determining the separation angle θ _d that can reflect as much of the light in the scattering state as possible in the original direction. First, the maximum incident angle of light incident on the prism array 13 in the transmission state is θ
max. The maximum incident angle θmax is determined by the structure and material of the liquid crystal display panel 12, the refractive index of the medium between the liquid crystal display panel 12 and the prism array 13, and the like. 13 (that is, the liquid crystal display panel 1).
Assuming that the refractive index can be expressed by an equivalent refractive index nb, the maximum incident angle θmax can be expressed as θmax = Arcsin (1 / nb). As described above, all the light from the pixels in the transmission state reaches the light absorbing plate 15 and the light absorbing plate 1
5 is absorbed, to the pixels in the full black, the separation angle theta _d of the prism array 13 may be set greater than the maximum angle of incidence .theta.max.

On the other hand, since the light passing through the pixels in the scattering state is considered to be scattered in all directions, the reflection efficiency η _r of the light passing through the pixels in the scattering state by the prism array 13 is η _r = η _f ( 1−sin ² θ _d ). Here, η _f is the ratio of forward scattering by the liquid crystal. From this, in order to utilize the forward scattered light effectively, it can be seen the better to minimize separation angle theta _d of the prism array 13. However, when the separation angle theta _d below .theta.max, the reflected light also occurs in the transmission state.

From the above considerations, if the pixel in the transmission state is to be completely blackened, the separation angle θ of the prism array 13
_It can be seen that _d should be equal to the maximum incident angle θmax.

On the other hand, if the separation angle theta _d smaller than the maximum angle of incidence .theta.max, as shown in FIG. 6, of the light passing through the pixels of the transmission state, the air separation angle theta _d (front surface of the liquid crystal display panel The light having an incident angle equal to or _larger than the angle θf converted in the above is reflected without being absorbed. This conversion angle θ _f is
It is expressed by the following equation. θ _f = Arcsin (nb · sin θ _d ) where nb is the equivalent refractive index of the optical structure between the air layer on the front surface of the liquid crystal display panel 12 and the prism array 13 as described above. In this case, as shown in FIG.
In the viewing angle of the above terms the angle theta _f, the contrast of the liquid crystal display panel 12 is reduced. Therefore, considering the contrary, if the contrast of the image is only to be obtained within the viewing angle theta _f is the use of the above equation, the separation angle theta _d of the prism array 13 is determined by the following equation. θ _d = Arcsin [(1 / nb) sin θ _f ] With this determination, the contrast of the image decreases when the incident angle is larger than θ _f, but the amount of reflected light increases in pixels in the scattering state.

(Design of Base Angle of Prism Array) When the separation angle θ _d of the prism array 13 is determined as described above, the base angle of the prism array 13 can be determined.
That is, as can be seen from FIG.
May be such that nc · sin (α−θ _d ) = np · sin (α−β). Here, nc is a medium between the liquid crystal display panel 12 and the prism array 13 (in this case, an air layer).
And np is the refractive index of the prism array material (for example, transparent resin). Β is prism pattern 1
6 is the critical angle of total internal reflection at the bottom surface of 6, and is represented by β = Arcsin (nk / np). Here, nk is the refractive index of the medium below the prism array 13 (a glass plate in this embodiment).
Therefore, the base angle α of the prism array 13 is calculated from the above equation as follows: α = Arctan [(γ · sin θ _d −sin β) / (γ · cos θ _d −c
osβ)]. Here, β = nc / np. For example, np =
Assuming that 1.6, nk = 1.2, nc = 1.2, and θ _d = 40 °, β = Arcsin (1.2 / 1.6) = 48.6 ° α = 72.0 °

(Second Embodiment) FIG. 9 is a perspective view showing a reflective scattering LCD 21 according to another embodiment of the present invention. In this embodiment, a space between the liquid crystal display panel 12 and the prism array 13 is filled with a transparent resin 22 (for example, an adhesive) having a different refractive index from that of the prism array 13. The liquid crystal display panel 12 is filled with the transparent resin 22.
And the prism array 13 can be joined and integrated. Or,
If the prism array 13 is filled with the transparent resin 22 before being assembled together with the liquid crystal display panel 12, the prism array 13 can be flattened, and the handling of the prism array 13 becomes easy. Further, by adjusting the refractive index of the transparent resin 22, the separation angle θ _d of the prism array 13 is adjusted.
Can be changed.

(Third Embodiment) FIG. 10 is a perspective view showing a reflection type scattering LCD 31 according to still another embodiment of the present invention. In the reflection type scattering LCD 31, the back surface of the liquid crystal display panel 12, the glass plate 14, and the light absorbing plate 15
, The two prism arrays 13 and 32 are sandwiched in a state where their directions are rotated by 90 degrees.

As in the first embodiment, even if only one prism array 13 is used, a part of the forward scattered light is reflected, so that the efficiency of the back scattering is improved. However, when one prism array 13 is used, the light R incident on the prism array 13 cannot be controlled in a plane substantially parallel to the long axis direction of the prism pattern 16. That is, as shown in FIG. 11 (a) (b) ( c), also the angle of incidence of FIG 11 (c)] light R as viewed from the short axis side of the prism pattern 16 is slightly greater than the separation angle theta _d , the incident angle [Figure 11 (b)] light R as viewed from the longitudinal direction is smaller than the separation angle theta _d, light R incident on the prism pattern 16 would be transmitted without being reflected.

Therefore, in this embodiment, the prism arrays 13 and 32 have two layers, and such light is reflected by the prism array 32 of the second layer, so that the separation angle θ _d is obtained in any direction. larger light incident angle is reflected by a prism array 13 or 32, the light of the small angle of incidence than the separation angle theta _d is so as to absorb by transmitting prism array 13, 32.

However, the light that passes through the first-layer prism array 13 and reaches the second-layer prism array 32 has a large incident angle at the first-layer prism array 13. If the separation angle theta _d1 and the second layer of the prism array 32 separation angle [theta] d ₂ are equal, there is a case where the pixel is reflected by the second layer of the prism array 32 in the transmission state. In order to prevent this, the separation angle θd ₂ of the second-layer prism array 32 is set to the first-layer prism array 13.
Needs to be slightly larger than the separation angle θ _d1 .

FIG. 12 shows the relationship between the reflectance of the reflective scattering LCD on the vertical axis and the backscattering ratio η on the horizontal axis. Curve C1 is when there is no prism array (conventional example), curve C2 is when there is one prism array 13 (first embodiment), and curve C3 is when prism array 1 is used.
This is a case where there are two sheets 3 and 32 (third embodiment). FIG. 13 shows a sample used as the third embodiment. In the first embodiment, the one excluding the second-layer prism array is used. As a conventional example, one excluding the first and second layer prism arrays was used. From these results, it can be seen that one or two prism arrays are provided with higher reflectivity than the conventional one. Comparing the ratio of the back scattering with η = 0.7, the reflectance according to the third embodiment is increased by about 33% as compared with the related art. Further, in the embodiment using two prism arrays, the reflectance obtained at η = 0.7 in the conventional device can be obtained at η = 0.45. Driving is also possible.

(Fourth Embodiment) FIG. 14 is a perspective view of a reflective scattering LCD 34 according to still another embodiment of the present invention. In this reflective scattering LCD 34, a transparent resin 35 having a different refractive index from the prism array 13 is filled between the liquid crystal display panel 12 and the prism array 13, and the prism array 32 is also provided between the prism array 13 and the prism array 32.
And a transparent resin 36 having a different refractive index.

In this embodiment, the prism array 13,
Regardless of the apex angle (or base angle) of 32, both transparent resins 35,
By varying the refractive index of 36, it can be optimized each with different separation angle theta _d of the first layer and the second layer. If the refractive indices of the two transparent resins 35 and 36 are different, the same prism array 13 and prism array 32 can be used, and the prism array 13 may be of one type and the number of parts can be reduced. Further, the reflection efficiency at the interface with the prism arrays 13 and 32 can be effectively utilized by the transparent resins 35 and 36, and the reflection efficiency can be improved.

(Fifth Embodiment) FIG. 15 is an exploded perspective view showing a reflective scattering LCD 37 according to still another embodiment of the present invention. In this reflective scattering LCD 37,
A prism array 38 in which polygonal pyramid prism patterns 39 such as quadrangular pyramids, triangular pyramids or the like are two-dimensionally arranged between the back surface of the liquid crystal display panel 12 and the glass plate 14 and the light absorbing plate 15.
Is sandwiched.

As described above, the polygonal pyramid prism pattern 39
Is used, the prism patterns 13 and 32 in which the prism pattern 16 is continuous in one direction are used.
Can be obtained by using one prism array 38.

As shown in FIG. 16, a prism array 38 in which conical prism patterns 40 are two-dimensionally arranged may be used. According to the prism array 38 having the conical prism pattern 40, the prism array 3
8 can be made more isotropic.

(Sixth Embodiment) FIG. 17 is a sectional view showing a reflection type scattering LCD 41 according to still another embodiment of the present invention. In this reflective scattering LCD 41, the back surface of the liquid crystal display panel 12, the glass plate 14, and the light absorbing plate 15
, The prism array 13 is interposed therebetween, and a resin film 42 is formed between the prism array 13 and the glass plate 14 with a transparent adhesive or the like.

If the resin layer 42 is provided on the back surface of the prism array 13 as described above, the total reflection angle on the bottom surface of the prism array 13 can be controlled by adjusting the refractive index of the resin layer 42. Therefore, the prism array 13
The separation angle theta _d not only the base angle of the prism 16, can be controlled by the refractive index of the resin layer 42.

It should be noted that, as in the embodiment shown in FIG.
Even when the prism arrays 13 and 32 are used, a resin layer may be provided between the prism array 32 and the glass plate 14 (not shown).

(Seventh Embodiment) FIG. 18 is an exploded perspective view showing a reflective scattering LCD 43 according to still another embodiment of the present invention. In the reflective scattering LCD 43, a groove 45 for each pixel width is provided in the prism array 44 to separate the prism pattern 16 of the prism array 44 for each pixel. That is, the prism array 44 is formed by arranging the prism patterns 16 having a uniform triangular cross section in one direction. In the direction having the uniform cross section, the prism array 44 is provided for each pixel width of the liquid crystal display panel 12. Pattern 16
Is partially cut to form a groove 45. Then, the reflective scattering LCD 43 is assembled such that the grooves 45 of the prism array 44 are located between the pixels of the liquid crystal display panel 12 (black matrix area).

According to this embodiment, the liquid crystal display panel 1
In the area facing between the two pixels, the prism array 4
Since the groove 45 is provided in the pixel 4, it is necessary to prevent a certain pixel from passing through the prism array 44, being totally reflected at the boundary between the prism array 44 and the glass plate 14, and then being emitted from an adjacent pixel. Can be. Therefore, it is possible to prevent blurring of an image and blurring of colors.

[Brief description of the drawings]

FIGS. 1A and 1B are schematic diagrams illustrating the structure and operation of a conventional reflective scattering LCD.

FIG. 2 is a perspective view illustrating a reflective scattering LCD according to an embodiment of the present invention.

FIG. 3 is a perspective view of the same prism array.

FIG. 4 is a diagram illustrating a separation angle of a prism array.

FIGS. 5A and 5B are explanatory diagrams of the operation of the reflective scattering LCD of the above.

FIG. 6 is a diagram illustrating a method of setting a separation angle of a prism array.

FIG. 7 is a diagram showing the relationship between the viewing angle and the contrast of the reflective scattering LCD of the above.

FIG. 8 is a diagram showing how to determine the base angle of the prism pattern.

FIG. 9 is a reflective scattering LCD according to another embodiment of the present invention.
It is a perspective view of.

FIG. 10 is a perspective view of a reflective scattering LCD according to still another embodiment of the present invention.

FIGS. 11A, 11B, and 11C are diagrams illustrating a problem in the case where the number of prism arrays is one.

FIG. 12 is a diagram showing the relationship between the ratio of backscattering and the reflectance of a reflective scattering LCD.

FIG. 13 is a partially broken perspective view showing a sample used for collecting the data of FIG. 12;

FIG. 14 is a perspective view of a reflective scattering LCD according to still another embodiment of the present invention.

FIG. 15 is an exploded perspective view of a reflective scattering LCD according to still another embodiment of the present invention.

FIG. 16 is an exploded perspective view of a reflective scattering LCD according to still another embodiment of the present invention.

FIG. 17 is a front view of a reflective scattering LCD according to still another embodiment of the present invention.

FIG. 18 is an exploded perspective view of a reflective scattering LCD according to still another embodiment of the present invention.

[Explanation of symbols]

 12 Liquid crystal display panel 13, 32 Prism array 14 Glass plate 15 Light absorbing plate 16 Prism pattern 22, 35, 36 Transparent resin

Claims (3)

[Claims] 1. A liquid crystal display panel capable of switching incident light between a transmission state and a scattering state, and disposed on the back side of the liquid crystal display panel, transmitting light having an incident angle smaller than a predetermined incident angle, and A reflection type reflecting light having an incident angle larger than the incident angle, an optical unit capable of setting the predetermined incident angle, and a light-absorbing member disposed on the back side of the optical unit. Liquid crystal display. 2. An optical element having a prism pattern having a uniform cross section in one direction, and an optical element having a prism pattern having a uniform cross section in a direction substantially orthogonal to the direction. 2. The reflection type liquid crystal display device according to claim 1, comprising a transparent plate having a smaller refractive index than both optical elements. 3. The optical pattern of the optical means,
2. The image forming apparatus according to claim 1, wherein each pixel is divided.
3. The reflection type liquid crystal display device according to item 1.