JP2001209046A - Planar display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar display device displaying with sufficient luminosity, brightness and saturation both in reflective and transmissive mode functions. SOLUTION: A selective reflection layer 18 and a color filter layer 50 are placed opposite to each other holding a liquid crystal layer 15 in between. The selective reflection layer is provided with plural selective reflection filters 18R, 18G, 18B arrayed in a specified pattern. The color filter layer is provided with plural color filters 50R, 50G, 50B placed opposite to the selective reflection filters respectively and with mutually different transmission wavelength regions. Each of the color filters is provided with one wavelength region with >=50% transmittance in the visible ray region and the other wavelength region with <50% transmittance in the visible ray region. Each of the selective reflection filters is provided with 50-90% reflectance with respect to the light in the wavelength region where the countering color filter has >=50% transmittance and with >90% reflectance with respect to the light in the wavelength region where the countering color filter has <50% transmittance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a flat display device such as a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as a flat panel display device, for example, a reflection type liquid crystal display device uses an external light to perform display, so that the display screen becomes dark due to insufficient illumination depending on the use environment. Cannot be used at all.

On the other hand, in a dark environment, a semi-transmissive reflector (half mirror) is used as a reflector for reflecting external light so that it can be used as a transmissive liquid crystal display device. A transflective type liquid crystal display device provided with is provided. However, since the transflective plate has a maximum utilization efficiency of 50% of the incident light, the brightness of the display screen is significantly inferior to that of a transmissive liquid crystal display device or a reflective liquid crystal display device.

In recent years, a transflective liquid crystal display device in which a pinhole corresponding to each pixel is provided on a reflection plate and a microlens corresponding to each pinhole is arranged has been studied to solve such a problem. In this liquid crystal display device, when using external light, external light reflected in a region excluding the pinhole of the reflector is used as a light source, and when using a backlight,
The light transmitted through the pin pole is condensed and used by a microlens, thereby increasing the light use efficiency.

[0005] However, even in such a liquid crystal display device, light loss corresponding to the pinhole occurs when external light is used. As a result, the frequency of use as a transmissive liquid crystal display device using a backlight increases, and power consumption increases.

[0006] Further, since the reflector provided with the pinhole has a complicated structure, it must be configured as a reflector external to the liquid crystal panel. As a result, parallax is generated and the display performance is significantly reduced.

Further, a so-called front light type display device in which a light guide plate is arranged on a reflection type liquid crystal display device and a linear light source is arranged on a side surface of the light guide plate has been studied. However, in this display device, the surface reflection on the front light surface is remarkable, and the light emitted from the linear light source leaks out of the light guide plate, so that the display quality such as contrast is significantly reduced. Further, the utilization efficiency of the light emitted from the linear light source is low.

A transflective liquid crystal display device as described above is
By providing a color filter layer, color display is possible. That is, a conventional transflective color liquid crystal display device is configured by sequentially stacking a polarizing plate, a front substrate, a color filter layer, a driving electrode, a liquid crystal layer, a back substrate, a semi-reflective plate, and a back light source. The color filter layer is provided in front of the reflector, that is, on the viewer side.

[0009]

When the above-mentioned liquid crystal display device functions as a reflection type, external light incident from the front substrate side passes through a color filter layer and a liquid crystal layer and is reflected by a reflection plate. Then, the light is emitted to the outside again through the liquid crystal layer and the color filter layer. That is, the optical path is transmitted twice through the color filter layer. On the other hand, when the liquid crystal display device is used as a transmission type, light emitted from the back light source passes through the color filter layer only once.

Therefore, when a color filter layer that provides sufficient saturation as a transmission type is used, when functioning as a reflection type, external light is transmitted twice through the color filter layer, so that light absorption in the color filter layer is reduced. Significantly, the reflection luminance is reduced. Conversely, when the density of the color filter layer is reduced so as to obtain sufficient luminance as a reflection type, that is, when the transmittance of the color filter layer is obtained so as to obtain a desired saturation when transmitted twice through the color filter layer. If the wavelength dispersion characteristic is designed and, for example, the Y value of the average transmittance is set to 40% or more, the light emitted from the rear light source passes through the color filter layer only once when the liquid crystal display device functions as a transmission type. Otherwise, the saturation will be insufficient.

As described above, in the conventional transflective color liquid crystal display device, the display brightness becomes extremely dark when functioning as a reflective type, or the display color density becomes extremely light when functioning as a transmissive type. Or only one of the optical characteristics was obtained.

[0012] The present invention has been made in view of the above points, and an object of the present invention is to provide a display having sufficient brightness and sufficient brightness and saturation both when it functions as a reflection type and when it functions as a transmission type. It is an object of the present invention to provide a flat panel display device which can perform the following.

[0013]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a plurality of transparent substrates sandwiched between a pair of opposing transparent substrates on an observation side and a back side and arranged in a matrix. A light modulation layer that has liquid crystal pixels and modulates incident light according to an applied voltage; and a plurality of light modulation layers that are arranged at a predetermined period on the back side of the liquid crystal pixels and selectively partially reflect light of different wavelength bands from each other. A selective reflection layer having a selective reflection filter, and a color filter layer having a plurality of color filters that are disposed opposite to the front side of the selective reflection filter and have different transmission wavelength ranges in the visible light range, respectively, Each of the above color filters has a wavelength range in which the transmittance in the visible light range is 50% or more and a wavelength range in which the transmittance in the visible light range is less than 50%. The reflection filter has a transmittance of 50% to 90% for light in a wavelength region where the transmittance of the color filter provided opposite thereto is 50% or more, and the transmittance of the color filter is 50%. It is characterized by having a reflectivity of more than 90% for light in a wavelength range of less than 90%.

According to the flat display device having the above-described structure, each selective reflection filter has a transmittance of 50% or more in a visible light region of a color filter provided opposite to the filter in a wavelength region of 50% or more. Since the flat display device functions as a reflection type since it has a reflectance of 90% to 90%, a sufficient reflection luminance for display can be obtained. Further, even when a flat display device is made to function as a transmissive type by providing a back light source having a reflecting plate, the light quantity of the value obtained by subtracting the reflectance of each selective reflection filter from 100% and the reflectance of the reflectance are obtained. Only the amount of light reflected by the selective reflection filter and reused via the reflector of the flat light source contributes to the display luminance. That is, the above 2
When the two light amounts are combined, the polarization transmittance of the selective reflection filter becomes 50% to 90% in the wavelength band.
Therefore, a display having a sufficient reflection luminance can be obtained.

Conversely, for light in a wavelength range where the transmittance of the color filter in the visible light range is less than 50%, the selective reflection filter opposed thereto has a reflectance of more than 90%. When the flat panel display functions as a reflection type, external light passes through the color filter twice,
A display with sufficient saturation can be obtained. When the flat display device is made to function as a transmissive type, the selective reflection filter sufficiently reflects light in the above-mentioned wavelength range to the back light source side, so that it does not transmit through the opposing pixels and has sufficient saturation for display. Is obtained.

When the color filter layer is formed on the inner surface of the transparent substrate on the observation side, there is no parallax between colors, and sufficient saturation can be obtained. When the selective reflection layer is formed on the inner surface of the transparent substrate on the back side, the liquid crystal layer for driving and the reflection surface are adjacent to each other. Can be eliminated.

In the flat display device of the present invention, the selective reflection wavelength band of the selective reflection filter corresponds to a color pixel. Such a selective reflection filter is preferably constituted by a cholesteric liquid crystal thin film. It is known that the cholesteric liquid crystal layer selectively reflects light in a specific wavelength band according to the helical direction and helical pitch and transmits other light components, and is also applied as a polarizing element.

In this case, it is common to design the selective reflection characteristics to cover the entire visible light range and to design the polarization reflectance thereof to be 100%.
The helical pitch of the cholesteric liquid crystal layer may be set so as to set the wavelength band and the polarization reflectance for each pixel of (red), G (green), and B (blue). Therefore, an arbitrary selective reflection filter is manufactured such that the helical pitch, the number of layers, and the film thickness are different from any other selective reflection filter adjacent thereto.

The selective reflection layer is formed by applying a cholesteric liquid crystal to the inner surface of the transparent substrate on the back side, and irradiating ultraviolet rays to each selective reflection filter region while adjusting the irradiation time, thereby selecting different crosslinking pitches. It can be formed as one layer in which the reflection filters are arranged. The cholesteric liquid crystal thin film has a helical pitch different in the layer thickness direction as a laminated structure, and between adjacent selective reflection filters, a helical pitch different in the helical pitch depending on the spectral characteristics of the facing color filter, or a variety of film thicknesses. With such a structure, a selective reflection layer having a different polarization reflectance depending on the wavelength range can be obtained.

The selective reflection filter has a first wavelength range,
That is, if the wavelength region where the transmittance of the opposing color filter is 50% or more is designed so as to partially overlap the first wavelength region of any of the other selective reflection filters adjacent thereto, the selective reflection will not occur. In forming the layer pattern, a margin is obtained in the dimensional tolerance.

The average transmittance Y of the color filter layer
If the square value of the value (Y of the tristimulus value) is set to 40% or more, a flat display device capable of displaying sufficient luminance and saturation can be obtained, similarly to the conventional reflective flat display device.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A transflective color liquid crystal display device according to an embodiment of the present invention will be described below in detail with reference to the drawings. First, the basic configuration of the liquid crystal display device 10 according to the present embodiment will be described. As shown in FIGS. 1 to 4, the liquid crystal display device 10 includes a polarizing plate 11, a λ / 4 retardation plate 12, a color filter layer 50, and a vertical alignment type functioning as an optical phase modulation layer arranged in this order from the observation side. Liquid crystal layer 15, polymerizing cholesteric liquid crystal, selective reflection layer 1
8 and a back light source 21.

The liquid crystal display device 10 includes a liquid crystal display element formed by sandwiching a liquid crystal layer 15 between two glass substrates 13 and 14 disposed opposite to each other. 13, a λ / 2 retardation plate 1
2, and a polarizing plate 11 are sequentially provided. Further, a λ / 4 retardation plate 25, a polarizing plate 26, and a back light source 21 are provided in this order in opposition to the outer surface of the other glass substrate 14. The retardation plate 12 functions as a fixed retarder layer, and the liquid crystal layer 15 functions as a variable retarder layer. These fixed and variable retarder layers constitute a variable retarder.

The glass substrate 13 on the observation side of the liquid crystal display element constitutes an array substrate, and a color filter layer 50 is provided on the inner surface of the glass substrate 13, and a large number of pixels made of transparent ITO are provided on the color filter layer. The electrodes 16 are provided in a matrix. Also, on the glass substrate 13,
The signal lines 32 and the scanning lines 34 including the gate electrodes 33 are provided in a matrix, and an auxiliary capacitance electrode (not shown) is provided as necessary. Further, a thin film transistor (hereinafter, referred to as TFT) 31 as a switching element is provided at an intersection of the signal line 32 and the scanning line 34, and is connected to the pixel electrode 16.

An oxide film 35 is formed over the signal line 32 and the scanning line 34. Each TFT 31 has an oxide film 3
5, a semiconductor film 36 made of amorphous silicon (a-Si) provided on the gate electrode 33 with a source electrode 41 and a drain electrode 39 provided on the semiconductor film with a low-resistance semiconductor film 37 provided therebetween. It is covered with a passivation film 38.

In a TFT having a bottom gate structure in which the gate electrode 33 is disposed below the semiconductor film 36, external light entering the TFT 31 from the array substrate 13 is shielded by the gate electrode 33. Does not enter. As a result, it is possible to prevent a decrease in contrast ratio due to a light leakage current generated by light when the display device is used outdoors.

Each pixel electrode 16 has a color filter layer 50.
Is connected to a source electrode 41 via a contact hole 40 of about 10 μm square formed in the above. The color filter layer 50 is disposed on the entire surface of the pixel portion. The color filter layer 50 is a color filter layer of three primary colors of red, green, and blue or three complementary colors of yellow, magenta, and cyan. The liquid crystal layer 15 is formed by the pixel electrodes 30 and the counter electrodes 17 arranged in a matrix. Color display by additive color mixture is performed by controlling the electric field in pixel units.

A signal line 32,
Any one of the scanning line 34 and the auxiliary capacitance line is arranged,
When the transmitted light from the back light source 21 is used, light from the back light source does not leak and the contrast ratio is not reduced.

On the other hand, the glass substrate 14 on the back side of the liquid crystal display element constitutes a counter substrate. On a surface of the glass substrate 14 facing the pixel electrode 16, a counter electrode 17 made of a transparent conductive film such as ITO is formed substantially over the front surface. Between the glass substrate 14 and the counter electrode 17, there is provided a selective reflection layer 18 which is in the form of a film formed by polymerizing cholesteric liquid crystal and functions as a transflective layer. It is preferable that film formation and patterning of the counter electrode 17 are simultaneously performed by a normal mask sputtering method. In this case, the cholesteric liquid crystal layer 60
Process load can be extremely reduced.

An alignment film (not shown) is formed on each of the surfaces of the array substrate 13 and the counter substrate 14 which are in contact with the liquid crystal layer 15. These alignment films have alignment directions such that liquid crystal molecules of the liquid crystal layer 15 are aligned perpendicular to the substrate. Thus, a large number of liquid crystal pixels arranged in a matrix are formed between the array substrate 13 and the counter substrate 14.

The array substrate 13 and the counter substrate 14 are bonded to each other by a sealing material 43 applied along a peripheral portion (seal portion) 42 of both substrates.
At this time, the sealing material 43 is used for the selective reflection layer 1 of the counter substrate 14.
It is desirable to apply to the area where 8 is not formed. When a sealing material is applied on the selective reflection layer 18, the adhesion of the sealing material is poor, and there is a possibility that the reliability may be deteriorated such that the substrates are peeled off when used for 10,000 hours or more.

Alternatively, when an overcoat agent having excellent adhesion of the seal material is applied on the selective reflection layer 18 and the seal material is applied on the selective reflection layer 18 via the overcoat agent, the reliability is high. Sex problems can be avoided. As the overcoat agent, for example, an acrylic resin used for an ordinary color filter can be used.

The back light source 21 provided on the back side of the glass substrate 14 includes a light guide 22 made of a light-transmitting flat plate made of, for example, acrylic, and a linear light source 24 disposed on the side of the light guide.
And a scattering reflection layer 23 provided on the back surface of the light guide.

Next, a more detailed structure of the liquid crystal display device 10 will be described together with its operation principle.

As shown in FIG. 6, the selective reflection layer 18 made of cholesteric liquid crystal selectively reflects only a left circularly polarized light component or a right circularly polarized light component of a certain wavelength band in incident light reaching one principal surface 18f. Transmits the right-handed circularly polarized light component or the left-handed circularly polarized light component that is opposite to the component that is selectively reflected, and reflects only the left-handed circularly polarized light component or the right-handed circularly polarized light component of the incident light that reaches the opposite main surface 18b. , Has the function of transmitting the right circularly polarized light component or the left circularly polarized light component. When this state is viewed from the one main surface 18f side, the rotation directions of the reflected light emitted to the one main surface side and the transmitted light from the back surface side are equal, and the rotation directions of the transmitted light and the reflected light emitted to the back surface side are also equal. equal. In FIG. 5, the rotation directions of the circularly polarized lights L1, L2, L1 ′, L2 ′ are
All the figures show the state observed from the main surface 18f side of the selective reflection layer 18.

It is assumed that the cholesteric liquid crystal forming the selective reflection layer 18 has an np value obtained by multiplying the twist pitch p of the liquid crystal molecules 19 and the average refractive index n equal to the wavelength λ of the incident light. When the liquid crystal molecules 19 have a helical structure counterclockwise when viewed from the observation side, of the external light Lf incident from the main surface 18f side, light of the left circularly polarized component is selectively reflected by the main surface 18f. The remaining polarized light component is transmitted to the other main surface 18b.

When the cholesteric liquid crystal has an np value equal to the wavelength λ of the incident light, ideally the circularly polarized light component in the direction (left-handed or right-handed) equal to the spiral direction (left-handed or right-handed) is 100%. Although it has the function of reflecting light, the reflectance or transmittance in the selective reflection wavelength range can be set to an appropriate value by forming the cholesteric liquid crystal to an appropriate thickness.

In the liquid crystal display device 10 provided with such a selective reflection layer 18, as shown in FIG. 4, a vertical alignment type liquid crystal layer 15 is turned on when a voltage is applied from a power supply 20.
To be precise, a state in which a voltage higher than the threshold of the liquid crystal is applied (Vo
At the time of n), the nematic liquid crystal molecules are in a homogeneous alignment arranged in a direction parallel to the substrate from the array substrate 13 to the counter substrate 14.

In this state, the light Lf entering from the upper side of the drawing passes through the polarizing plate 11 and the λ / 4 phase difference plate 12 which is a fixed retarder layer, and is converted into right-handed circularly polarized light. Incident on the liquid crystal layer 15 which is a layer. The light Lf is converted into counterclockwise circularly polarized light by the phase being delayed by λ / 2 by the liquid crystal layer 15 and reaches the selective reflection layer 18. Therefore, as described above, the left-handed circularly polarized light that has arrived is reflected by the selective reflection layer 18, and the phase is again delayed by λ / 2 by the liquid crystal layer 15.
The light is converted to clockwise circularly polarized light and output to the observation side. This light passes through the λ / 1 phase difference plate 12 again,
It becomes linearly polarized light along the polarization axis of the polarizing plate 11, and the polarizing plate 1
1 and output to the outside. Thus, a display in a bright state is obtained.

Further, as shown in FIG. 5, an off state (including zero voltage) in which a voltage lower than the threshold is applied to the liquid crystal layer 15.
At the time of (Voff), the liquid crystal layer 15 has the liquid crystal molecules arranged perpendicular to the glass substrates 13 and 14, so that the phase of the incident light is not modulated.

In this state, the light Lf incident from the information shown in FIG.
The liquid crystal layer 1 passes through the four phase difference plate 12 and turns as clockwise circularly polarized light.
5, the liquid crystal layer is not phase-modulated, and reaches the selective reflection layer 18 as clockwise circularly polarized light. Therefore, the clockwise circularly polarized light passes through the selective reflection layer 18 toward the back side, and is converted by the phase difference plate 25 into linearly polarized light having a vibration component along the absorption axis of the polarizing plate 26. As a result, the incident light Lf does not return to the observation surface, and a dark display is obtained.

Next, the operation when the back light source 21 provided on the back side of the selective reflection layer 18 is operated will be described. At the time of Von shown in FIG. 4, the light Lb output from the surface light source 21 becomes counterclockwise circularly polarized light by the polarizing plate 26 and the phase difference plate 25, and a predetermined ratio of the light Lb is selectively reflected by the selective reflection layer 1.
8 and the rest is reflected by the selective reflection layer.
The light that has passed through the selective reflection layer 18 is phase-modulated by the liquid crystal layer 15 and converted into clockwise circularly polarized light. Then, when this light passes through the λ / 4 retardation plate 12, it becomes linearly polarized light along the polarization axis of the polarizing plate 11, and is output to the observation surface side after passing through the polarizing plate 11. Thereby, a display in a bright state is obtained.

On the other hand, at the time of Voff shown in FIG. 5, the counterclockwise circularly polarized light that has passed through the selective reflection layer 18 is output to the observation side as it is without being subjected to phase modulation by the liquid crystal layer 15. Then, this light passes through the λ / 4 phase difference plate 12, becomes linearly polarized light having a vibration direction orthogonal to the polarization axis of the polarizing plate 11, and is absorbed by the polarizing plate 11. Thus, a display in a dark state is obtained.

In the liquid crystal display device which operates as described above, the color filter (CF) layer 50 is formed on the inner surface of the glass substrate 13 on the observation side, and the selective reflection (Ch) layer 1 is formed.
Numeral 8 is formed on the inner surface of the glass substrate 14 on the rear side. Then, the color filter 50 and the selective reflection layer 18
Has a pattern corresponding to the arrangement pattern of the pixel electrodes constituting the liquid crystal pixels.

As schematically shown in FIG. 7, the color filter layer 50 has three color filters 50R, R, G and B, respectively.
50G and 50B, and these color filters are formed in stripes along the liquid crystal pixel columns, respectively.
They are arranged alternately by color. In addition, the selective reflection layer 18 has 3
There are various types of selective reflection filters 18R, 18G, and 18B. These selective reflection filters are formed in stripes along the liquid crystal pixel columns, and are arranged at a predetermined period. Then, the selective reflection filter 18R,
The color filters 18G and 18B are formed so as to selectively partially reflect light of different wavelength bands from each other, and are arranged to face the corresponding color filters 50R, 50G and 50B.

The color filter layer 50 has the spectral characteristics shown in FIG. Each G (green) color filter 50G
Has a transmittance of 50% or more in a wavelength region around 550 nm, and has a transmittance of less than 50% in other wavelength regions. Each B (blue) color filter 50B has 43
It has a transmittance of 50% or more in a wavelength region near 0 nm, and has a transmittance of less than 50% in other wavelength regions. The color filter 50R of each R (red) has 61
It has a transmittance of 50% or more in a wavelength region near 0 nm, and has a transmittance of less than 50% in other wavelength regions. As shown in FIG. 9, the square value of the Y value of the average transmittance (Y of the tristimulus values) of the color filter layer 50 is set to 40% or more.

On the other hand, in the selective reflection layer 18, the selective reflection filter 18R provided opposite to the color filter 50R is provided.
As shown in FIG. 10, the transmittance of the color filter 50R is 50 to 90% for polarized light in a wavelength range of 50% or more,
For example, it has a reflectance of 70% and a transmittance of 30%. The selective reflection filter 18R has a reflectance of greater than 90% for polarized light in a wavelength range where the transmittance of the color filter 50R is less than 50%.

The selective reflection filter 18G provided opposite to the color filter 50G has a transmittance of 50 to 90 with respect to polarized light in a wavelength region where the transmittance of the color filter 50G is 50% or more.
%, For example, 70%, and 30% transmittance. The selective reflection filter 18G has a reflectance of greater than 90% for polarized light in a wavelength range where the transmittance of the color filter 50G is less than 50%.

Similarly, the selective reflection filter 18B provided opposite to the color filter 50B has a transmittance of 5% or more for the polarized light in the wavelength range where the transmittance of the color filter 50B is 50% or more.
It has a reflectance of 0 to 90%, for example, 70%, and a transmittance of 30%. Also, the selective reflection filter 18B
Has a reflectance of greater than 90% for polarized light in a wavelength range where the transmittance of the color filter 50B is less than 50%. Each selective reflection wavelength range of the selective reflection filters 18R, 18G, and 18B partially overlaps with the selective reflection wavelength range of any other adjacent selective reflection filter.

The glass substrate 14 including the selective reflection layer 18 having the plurality of selective reflection filters 18R, 18G, and 18B having different selective reflection characteristics as described above is formed, for example, as follows.

(1) As shown in FIG. 11A, first,
After a polyimide film is applied to the entire one main surface of the glass substrate 14, a cholesteric liquid crystal material having a spiral pitch p (selective reflection wavelength λ / average refractive index n) of 620 / 1.54 is applied to a thickness of 2.0 μm. Then, the entire surface of the cholesteric liquid crystal material is irradiated with ultraviolet rays for 5 minutes and exposed, and solidified as a liquid crystal polymer to form a first cholesteric liquid crystal layer P1.

(2) Subsequently, a cholesteric liquid crystal material similar to that of (1) is applied to a thickness of 1.0 μm on the first cholesteric liquid crystal layer P1, and the regions corresponding to the selective reflection filters G and B are masked. After the light is shielded by 70, ultraviolet rays are irradiated for 5 minutes to expose an area corresponding to the selective reflection filter R.

(3) The second cholesteric liquid crystal material is heated to about 100 ° C. to form a liquid, and the entire surface is irradiated with ultraviolet rays for 5 minutes to expose the cholesteric liquid crystal material P2. Form. In this case, in the second cholesteric liquid crystal layer, the region 72 corresponding to the selective reflection filter R is transparent. In the cholesteric liquid crystal layer composed of the first and second layers, a region corresponding to the selective reflection filter R has a reflectance of 70% for light in the R wavelength region, and a region corresponding to the selective reflection filters G and B. Is 100% reflectance for light in the R wavelength range.

(4) As shown in FIG. 11B, p = 5
Using a 50 / 1.54 cholesteric liquid crystal material, the second and fourth cholesteric liquid crystal layers P3 and P4 are formed by the same steps as in the above (1) to (3).
However, when the fourth cholesteric liquid crystal layer P4 is formed, the exposure is performed in a state where the regions corresponding to the selective reflection filters R and B are shielded from light by the mask 73. As a result, in the fourth cholesteric liquid crystal layer P4, the region 74 corresponding to the selective reflection filter G becomes transparent. In the cholesteric liquid crystal layer composed of the third and fourth layers, a region corresponding to the selective reflection filter G has a reflectance of 70% for light in the G wavelength region, and a region corresponding to the selective reflection filters R and B. Has a reflectance of 100% for light in the G wavelength range.

(5) As shown in FIG. 11C, p = 4
Using a 40 / 1.54 cholesteric liquid crystal material, fifth and sixth cholesteric liquid crystal layers P5 and P6 are formed by the same steps as in the above (1) to (3).
However, when forming the sixth cholesteric liquid crystal layer P6, exposure is performed in a state where the regions corresponding to the selective reflection filters R and G are shielded from light by a mask. As a result, in the sixth cholesteric liquid crystal layer P6, the region 76 corresponding to the selective reflection filter B becomes transparent. In the cholesteric liquid crystal layer composed of the fifth and sixth layers, the area corresponding to the selective reflection filter B has a reflectance of 70% for light in the B wavelength range, and the area corresponding to the selective reflection filters R and G. Has a reflectance of 100% for light in the B wavelength range.

Through the above steps, the selective reflection layer 18 having the plurality of selective reflection regions 18R, 18G, and 18B having different helical pitches is formed. Then, when the solidification of the cholesteric liquid crystal layer in all regions is completed, an overcoat layer such as an acrylic resin is formed on the cholesteric liquid crystal layer, a transparent electrode is formed on the entire surface, and further, an alignment film is formed. Thereby, the glass substrate 14 on the back side is obtained.

On the other hand, the glass substrate 13 on the observation surface side is provided with an active element such as a TFT, a liquid crystal drive electrode, and the like on an RGB color filter layer 50 formed by a known pigment dispersion method.
And an alignment film and the like are sequentially formed. Then, these glass substrates 13 and 14 are combined with the selective reflection layer 1.
The liquid crystal display element is obtained by arranging the pattern 8 and the pattern of the color filter layer 50 so as to face each other and sealing them together.

According to the liquid crystal display device configured as described above, the R, G, and B color pixels are formed by combining the selective reflection filter of the selective reflection layer 18 and the corresponding color filter of the color filter layer. Make up. Each of the selective reflection filters 18R, 18G, and 18B has a reflectance of 70% with respect to light in a wavelength range of 50% or more in a visible light range of a color filter provided opposed thereto. ing. Therefore, when the liquid crystal display device is made to function as a reflection type, as shown in FIG. 7, for example, of the light incident through the color filter 50R, the polarization in the R wavelength region is reflected 70% by the selective reflection filter 18R. And
Output through the color filter 50R. Therefore, a sufficient reflection luminance for display can be obtained.

When the liquid crystal display device is made to function as a transmissive type, for example, of the light incident on the selective reflection filter 18R from the back light source 21, the light amount of 30% of the polarized light in the R wavelength range is transmitted to the selective reflection filter 18R. Transmit and reflectivity 7
The polarized light of 0% is reflected by the reflection plate 23 of the back light source 21 and reused, and contributes to display luminance. That is, when the two light amounts are combined, the polarization transmittance of the selective reflection filter 18R is about 70% in the R wavelength band.
Therefore, a display having a sufficient reflection luminance can be obtained.

Conversely, each selective reflection filter 18R, 18R
G and 18B have a reflectance of almost 100% with respect to light in a wavelength region where the transmittance in the visible light region of the color filter provided opposite thereto is less than 50%. Therefore, when the liquid crystal display device is made to function as a reflection type, external light passes through the color filter layer 50 twice, and a display with sufficient saturation is obtained as shown in FIG. Also,
When the liquid crystal display device is made to function as a transmissive type, the light in the wavelength region where the reflectance is less than 50% is reflected toward the back light source 21 by the corresponding selective reflection filters 18R, 18G, and 18B and transmitted through the corresponding liquid crystal pixels. Output without Therefore, as shown in FIG. 12, sufficient saturation is obtained for display.

Therefore, according to the liquid crystal display device configured as described above, in both the reflective display using external light and the transmissive display using the back light source, an image with high color purity and high luminance is displayed. be able to. In addition, the selective reflection layer 1
In No. 8, since the cholesteric liquid crystal pattern may be arranged so as to exhibit the required selective reflection characteristics corresponding to each color pixel, it is not necessary to form the cholesteric liquid crystal patterns so as to exhibit the selective reflection characteristics over the entire visible light range, thereby reducing the manufacturing cost. it can. Further, by forming the selective reflection layer 18 on the inner surface of the transparent substrate 14, parallax and the like can be eliminated and the display quality of the liquid crystal display device can be improved.

In the above-described embodiment, the selective reflection layer 18 may be configured as shown in FIG. That is, the selective reflection layer 18 is formed on the glass substrate 14.
Has a cholesteric liquid crystal layer A having a polarization reflectance of 70%. In the region corresponding to each selective reflection filter 18R, the cholesteric liquid crystal layer B1 having a reflectance of 30% for light in the blue (B) wavelength region.
And a cholesteric liquid crystal layer C1 having a reflectivity of 30% with respect to light in the green (G) wavelength region are sequentially laminated on the cholesteric liquid crystal layer.

In the region corresponding to each selective reflection filter 18G, the reflectance for light in the blue (B) wavelength region is 3%.
0% cholesteric liquid crystal layer B1 and cholesteric liquid crystal layer C having a reflectance of 30% for light in the red (R) wavelength range.
2 are sequentially stacked on the cholesteric liquid crystal layer.

Further, in the region corresponding to each selective reflection filter 18B, the reflectance for light in the green (G) wavelength region is 3%.
A 0% cholesteric liquid crystal layer B2 and a cholesteric liquid crystal layer C2 are sequentially laminated on the cholesteric liquid crystal layer. Even when the selective reflection layer configured as described above is used, the same operation and effect as those of the above-described embodiment can be obtained.

As shown in FIG. 14, the above-described liquid crystal display device employs an optical system 6 in order to increase the light utilization efficiency of the rear light source light.
0 may be provided. The optical system 60 includes the rear light source 2
It has a retardation plate 51 and a second cholesteric liquid crystal layer 52 provided between the first and the polarizing plates 26. Other configurations are the same as those of the above-described embodiment, and the details are omitted.

The optical system 60 converts a part of the light from the rear light source 21 into linearly polarized light along the polarization axis before the polarizing plate 26, and reflects the remaining light toward the rear light source 21 for recycling. The second cholesteric liquid crystal layer 52 includes the selective reflection layer 1
8 has a left-handed helical structure,
Has a slow axis parallel to the slow axis of the phase difference plate 25.

According to the liquid crystal display device having the above configuration, the clockwise circularly polarized light component of the light emitted from the back light source 21 passes through the second cholesteric liquid crystal layer 52, and the counterclockwise circularly polarized light component is the second circularly polarized light component. Most of the light is reflected by the cholesteric liquid crystal layer, but about 10 to 30% of the light passes through the second cholesteric liquid crystal layer 52. When the transmitted circularly polarized light enters the retardation plate 51, the clockwise circularly polarized light component is
Is converted into linearly polarized light having a vibration component parallel to the polarization axis. Therefore, only the counterclockwise circularly polarized light component transmitted through the polarizing plate 26 and converted by the phase difference plate 25 enters the selective reflection layer 18.

The counterclockwise circularly polarized light component is reflected by the selective reflection layer 1
The light is reflected at a predetermined ratio by 8, converted into linearly polarized light transmitted through the polarizing plate 26 by the phase difference plate 51, and further converted into circularly polarized light transmitted through the second cholesteric liquid crystal layer 52 by the phase difference plate 52. Then, the circularly polarized light reaches the reflecting plate 23 of the back light source 21 and the polarized light component is decomposed. By repeating this, the light reflected toward the rear light source 21 can be recycled, and the light source light utilization efficiency can be increased.

The optical system 60 is not limited to the above-described configuration. When a cholesteric liquid crystal layer having a swing in the opposite direction is used, the slow axis direction of the retardation
By rotating by an angle, an optical system having a similar function can be obtained.

In addition, the present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the present invention. For example, in the above embodiment, the liquid crystal display element is used as the variable retarder. However, the present invention is not limited to this. Any element that can control whether the phase of the incident light is shifted by a half wavelength or not modulated by an electric field is used. The same effect can be obtained. For example, a so-called ECB (Electrical
ly Controlled Birefringence mode) type liquid crystal can be used.

Further, a pixel electrode and a T
Although the configuration is such that the FT and the like are provided and the counter electrode is provided on the glass substrate on the back side, conversely, the configuration is such that the counter electrode is provided on the glass substrate on the observation side and the pixel electrode and TFT are provided on the glass substrate on the back side. Good.

As the liquid crystal display element, a horizontal alignment type nematic liquid crystal display element in which a nematic liquid crystal is aligned parallel to the surface of a glass substrate, or a twisted nematic liquid crystal display element in which a nematic liquid crystal is twisted may be used. When the retardation plate is arranged so that the slow axis is approximately 45 ° counterclockwise from the polarization axis, the same operation as described above can be achieved by setting the twist direction of the cholesteric liquid crystal clockwise.

In the above liquid crystal display device, halftone display can be performed by applying an intermediate voltage between Von and Voff as a voltage applied to the variable retarder layer. In a medium to large liquid crystal display device having a diagonal screen size of 8 inches or more, a light diffusion film may be provided on the outer surface of the array substrate 13 to increase the viewing angle.

[0074]

As described above in detail, according to the present invention, a display having a sufficient brightness and a sufficient luminance and saturation can be realized both when functioning as a reflection type and when functioning as a transmission type. A flat display device can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a color liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing an array substrate of the color liquid crystal display device.

FIG. 3 is a plan view schematically showing the array substrate.

FIG. 4 is a diagram schematically showing a state where a first voltage is applied to a liquid crystal layer of the color liquid crystal display device.

FIG. 5 is a diagram schematically showing a state where a second voltage is applied to a liquid crystal layer of the color liquid crystal display device.

FIG. 6 is a diagram schematically showing the operation principle of a selective reflection layer in the color liquid crystal display device.

FIG. 7 is a sectional view showing an arrangement relationship between a color filter of a color filter layer and a selective reflection filter of a selective reflection layer in the color liquid crystal display device.

FIG. 8 is a graph showing spectral characteristics of the color filter layer.

FIG. 9 is a graph showing the square value of the transmittance of the color filter layer.

FIG. 10 is a graph showing spectral characteristics of the selective reflection layer.

FIG. 11 is a cross-sectional view showing a step of manufacturing the selective reflection layer.

FIG. 12 is a graph showing the total transmittance of the selective reflection layer and the color filter layer.

FIG. 13 is a view schematically showing a modification of the selective reflection layer.

FIG. 14 is a sectional view showing an embodiment in which an optical system is provided between a rear light source and a liquid crystal display element.

[Explanation of symbols]

 Reference Signs List 10 liquid crystal display device 11 polarizing plate 12 λ / 4 wavelength plate 13, 14 transparent substrate 15 liquid crystal layer 16, 17 transparent electrode 18 selective reflection layer 18R, 18G, 18B selective reflection filter 21 back light source 50: color filter layer 50R, 50G, 50B: color filter 60: optical system

Claims (9)

[Claims] 1. A light modulation layer sandwiched between a pair of transparent substrates on the observation side and the back side, having a plurality of liquid crystal pixels arranged in a matrix, and modulating incident light in accordance with an applied voltage. Are arranged at a predetermined period on the back side of the liquid crystal pixels, respectively.
A selective reflection layer having a plurality of selective reflection filters for selectively partially reflecting light in mutually different wavelength bands; and a transmission wavelength band in a visible light region, which is disposed to face the front side of the selective reflection filter, respectively. And a color filter layer having a plurality of color filters different from each other, wherein each of the color filters has a transmittance of 5 in a visible light region.
It has a wavelength range of 0% or more and a wavelength range where the transmittance in the visible light range is less than 50%. It has a reflectance of 50% to 90% for light in a wavelength range, and the transmittance of the color filter has a reflectance of more than 90% for light in a wavelength range of less than 50%. Characteristic flat display device. 2. The flat display device according to claim 1, wherein the color filter layer is provided on an inner surface of the transparent substrate on the observation side. 3. The flat display device according to claim 1, wherein the selective reflection layer is provided between the light modulation layer and the rear transparent substrate. 4. A flat display device according to claim 1, wherein each of said plurality of selective reflection filters is formed of a cholesteric liquid crystal layer. 5. The cholesteric liquid crystal layer has a structure in which a plurality of layers having different helical pitches are stacked in a layer thickness direction, and helical pitches are different between adjacent selective reflection filters. The flat panel display according to claim 4. 6. The liquid crystal display device according to claim 1, wherein each of said selective reflection filters and each of said color filters have a stripe shape extending along a column of said liquid crystal pixels. Item 2. The flat panel display according to item 1. . 7. Each of the selective reflection filters has a wavelength band partially overlapping the wavelength band of any other adjacent selective reflection filter with respect to the wavelength band of the light having the transmittance of 50% or more. The flat display device according to any one of claims 1 to 6, wherein: 8. The flat display device according to claim 1, further comprising a surface light source provided on the back side of the selective reflection layer. 9. The color filter layer according to claim 1, wherein the average transmittance is Y.
9. The flat panel display according to claim 1, wherein a square value of the value is 40% or more.