JP2003233068A - Flat display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-quality flat display device in which sufficient contrast and improved reflectance are obtained by changing an order of lamination of cholesteric liquid crystal polymer layers while in a conventional translucent liquid crystal display device a polarized light reflection layer is constructed by laminating a plurality of cholesteric liquid crystal polymer layers so as to make the layer nearest to the display screen have the maximum pitch, however, obtaining poor reflection efficiency and only insufficient contrast. <P>SOLUTION: The polarized light reflection layer 23 consisting of the cholesteric liquid crystal polymer layers 22 laminated so as to make Y value (transmittance or reflectance of selective reflection) be minimum on the substrate 20 side and gradually get larger as going closer to the display screen side, is disposed on the substrate 20 placed opposite to an array substrate 18. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-transmissive flat panel display using a cholesteric liquid crystal polymer layer as a polarization reflection layer.

[0002]

2. Description of the Related Art As a current flat panel display device, an active matrix type liquid crystal display device is predominant because there is no crosstalk between adjacent pixels and a good display image can be realized. This active matrix type liquid crystal display device generally comprises a plurality of thin film transistors (TFTs) arranged in a matrix on a transparent substrate made of a glass material.
A transparent pixel electrode connected to the above is disposed, and further, an array substrate having an alignment film formed thereon, and a transparent counter substrate also made of a glass material and facing the array substrate are provided.

Such liquid crystal display devices are classified into a transmissive type using a backlight as a light source and a reflective type using external light as a light source. This reflective liquid crystal display device
Since the backlight is not used, the power consumption is greatly saved, and thus it is widely used for portable display devices such as mobile personal computers and mobile phones. However, when the surroundings of the portable display device are bright, outside light can be sufficiently taken in and bright display is possible, but when used in a dark surrounding such as at night, due to insufficient light rays introduced. It is difficult to obtain sufficient brightness, and this often impairs the display function during nighttime use.

Therefore, recently, a transflective flat panel display device having a reflection plate having a function of transmitting light from a backlight has been developed by taking advantage of the reflection type and the transmission type. It has become to.

As shown in FIG. 4, such a transflective liquid crystal display device has a transparent substrate 4 made of a glass material.
A drive line (not shown) for supplying a scanning signal, a video signal, and the like is provided on the main surface of No. 1, and a thin film transistor (TFT) 42 is provided near the intersection of these signal line and drive line. A three primary color filter 43 made of an acrylic material or the like is arranged on the TFT 42, and a black light shielding film 44 is provided on the outer periphery of the filter 43. A transparent pixel electrode 4 made of indium tin oxide (ITO) or the like is formed on the surface of the color filter 43.
5 are arranged in a matrix, and the pixel electrode 45 is connected to the TFT 42 through a through hole 46. An alignment film 47 made of polyimide or the like is further provided on the upper surface of the pixel electrode 45 to form an array substrate 48.

A counter substrate 49 facing the array substrate 48 is a transparent substrate 50 also made of a glass material, and a primary alignment on the main surface of the substrate 50 facing the array substrate 48. Polarization reflection layer 5 formed by laminating a plurality of cholesteric liquid crystal polymer layers 52 with a film 51 interposed therebetween.
3 is provided. A transparent common electrode 54 made of ITO or the like is provided on the polarization reflection layer 53, and an alignment film 55 made of polyimide or the like is further provided on the upper surface of the transparent common electrode 54 to form a counter substrate 49. is doing.

The array substrate 48 and the counter substrate 49 are arranged so as to face each other with a predetermined gap therebetween, and are adhered to each other via a seal material 56, and the liquid crystal layer 58 is sealed in the gap portion 57. The thickness of the liquid crystal layer 58 is defined by the spacer 59 interposed between the array substrate 48 and the counter substrate 49 to form the liquid crystal panel 60. On the outer surface of the liquid crystal panel 60 on the array substrate 48 side, a left circular polarizing plate 64 including a retardation plate 62 and a polarizing plate 63 is attached with an adhesive via a light diffusion film 61, and the counter substrate 49 side. The phase difference plate 65 is provided on the outer surface.
A right circularly polarizing plate 67 including a polarizing plate 66 and a polarizing plate 66 is attached with an adhesive.

Polarizing plate 6 attached to this array substrate 48
3 and the phase difference plate 62 are configured as the left circularly polarizing plate 64 by adjusting the axial angle of bonding, and the bonding angle to the liquid crystal panel 60 is set to the angle at which the brightness of black in reflective display is the lowest. Has been done. Further, the polarizing plate 66 and the retardation plate 65 on the side of the counter substrate 49 are configured as a right circular polarizing plate 67 by adjusting the axial angle of bonding. Further, a backlight 68 is arranged outside the polarizing plate 66 on the side of the counter substrate 49 to form a liquid crystal display device.

In the liquid crystal display device having such a structure, the backlight 68, which serves as a light source, is turned on together with the external light, and the TF
By driving T42 to control the switching of the pixel electrode 45, the liquid crystal layer 58 on each pixel electrode 45 is controlled by the potential difference between the voltage of the pixel electrode 45 and the voltage supplied to the opposing common electrode 54. As a result, a predetermined image is displayed.

By the way, the cholesteric liquid crystal polymer layer 52 is one in which the orientation direction continuously changes in a spiral shape from the orientation direction of the underlying alignment film 51 to the thickness direction, and cholesteric liquid crystal silicon is overlaid to obtain a uniform thickness. It is made to have. The spiral period of the cholesteric liquid crystal polymer layer 52 that constitutes the polarized light reflection layer 53 is determined by the content ratio of the chiral material contained in the cholesteric liquid crystal before crosslinking and the wavelength at the time of photocrosslinking. The selective reflection wavelength λ is expressed as λ = nP, where n is the refractive index of P and P is the pitch length. The pitch is continuously changed, and cholesteric liquid crystal polymer layers 52 having different pitches are printed on the base alignment film 51 on the substrate 50. The base alignment film 51 is laminated in this order from the layer with the smallest pitch, and the display surface side is The polarization reflection layer 53 is formed by stacking layers in order so that the largest pitch is positioned.

This cholesteric liquid crystal polymer layer 52
According to the alignment direction formed on the upper surface in the thickness direction, both the light incident from above and the light incident from below are separated into circularly polarized light of either left or right polarity, one of the polarities is transmitted, and the opposite polarity is applied. It has a polarization function of reflecting light. By providing the polarization reflection layer 53 composed of the cholesteric liquid crystal polymer layer 52, either the left or right circularly polarized light is selectively reflected, and the circularly polarized light of the opposite polarity is transmitted, whereby the array substrate 48 is transmitted. External light introduced from the side is reflected by the polarized reflection layer 53, and the irradiation light from the counter substrate 49 side by the backlight 68 is transmitted through the polarized reflection layer 53 to increase the display light amount, It can be used in dark places.

Such a polarized reflection layer 53 has a thickness of USP5.
As disclosed in Japanese Patent Publication No. 825,444, as shown in FIG. 5, a laminate of a plurality of layers in which the pitch is continuously changed so that the light source has a minimum pitch and the opposite side has a maximum pitch. Is configured as. This cholesteric liquid crystal polymer layer 52 is provided with a base alignment film 51 on a counter substrate 49, an alignment film is printed on the base alignment film 51, and a cholesteric liquid crystal is aligned through a rubbing process to polymerize while changing the chiral pitch (helical pitch). It is formed by that.
Therefore, in the visible broadband wavelength, the reflection and transmission functions can be simultaneously performed.

[0013]

However, the polarization reflection layer 53 formed in this manner has a higher alignment control force as the upper layer is formed as a plurality of cholesteric liquid crystal polymer layers 52 are sequentially laminated. It tends to be weakened, causing disorder in the orientation of the liquid crystal molecules constituting the polarized reflection polymer.

For this reason, the selective reflection light from the polarization reflection layer 53 has the least polarization destruction when selectively reflected by the uppermost layer, and the selective reflection light from the cholesteric liquid crystal polymer layer 52 arranged on the side opposite to the display surface. Light is most likely to undergo polarization destruction because it passes through the interfaces of a plurality of layers.

Here, the polarizing reflection layer 5 that selectively reflects a wide visible region, for example, 400 nm to 800 nm.
3, in the layer that selectively reflects or transmits the wavelength of the selective reflection or the reflectance (referred to as Y value), for example, the wavelength of 550 nm, the polarized reflection layer 53 is formed in the pitch order as shown in FIG. Therefore, it is arranged in the substantially central portion of the polarization reflection layer 53. Therefore, when the external light F in the wavelength range having a large Y value of the selective reflection enters the polarization reflection layer 53,
As shown in FIG. 3, the light is selectively reflected at the central portion of the polarized light reflection layer 53, the optical path length inside the polarized light reflection layer 53 becomes long, and since it passes through a plurality of layers, the number of times of passing through the interface also increases. Therefore, the external light F in the wavelength range having a large Y value, which is selectively reflected by the polarization reflection layer 53, is largely affected by the polarization destruction, and cannot be sufficiently utilized as reflected light. It led to a decrease in contrast and a decrease in reflectance.

The present invention has been made to address these problems, and an object of the present invention is to provide a flat panel display device which improves the reflection efficiency of external light and suppresses the deterioration of contrast. .

[0017]

According to the present invention, there is provided a first substrate having a pixel electrode, and a reflection-transmission type second substrate which is arranged to face the first substrate with a predetermined gap therebetween. In a flat panel display device having a polarization reflection layer composed of a plurality of cholesteric liquid crystal polymer layers arranged on the second substrate and a light modulation layer sealed in a gap, the polarization reflection layer is sequentially selected from the display surface side. It was configured to be laminated from a layer having a high reflectance.

With this structure, light in the wavelength range having a large Y value can be selectively reflected by the upper layer of the polarization reflection layer, so that the effect of polarization destruction can be minimized and the light can be efficiently used as reflected light. Therefore, it is possible to suppress a decrease in contrast.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail by taking a liquid crystal display device as an example.

FIG. 1 is a cross-sectional view showing the overall structure of a liquid crystal display device, in which a drive line for supplying a scanning signal, a video signal and the like is provided on the main surface of a transparent substrate 11 made of a glass material. (Not shown) is provided, and a thin film transistor (TFT) 12 is provided near the intersection of these signal line and drive line. A three primary color filter (13) made of an acrylic material or the like is arranged on the TFT 12, and a black light shielding film 14 is provided on the outer periphery of the filter 13. Transparent pixel electrodes 15 made of indium tin oxide (ITO) or the like are arranged in a matrix on the surface of the color filter 13, and the pixel electrodes 15 are connected to the TFTs 12 through through holes 16. Has been done. An alignment film 17 made of polyimide or the like is further provided on the upper surface of the pixel electrode 15 to form an array substrate 18.

The counter substrate 19 facing the array substrate 18 is a transparent substrate 20 also made of a glass material, and the substrate 20 has a primary orientation on the main surface facing the array substrate 18. Polarization reflection layer 2 constituted by laminating a plurality of cholesteric liquid crystal polymer layers 22 with a film 21 interposed therebetween.
3 is provided. The cholesteric liquid crystal polymer layer 22 is one in which the orientation direction continuously changes in a spiral shape from the orientation direction of the underlying alignment film 21 to the thickness direction, and is formed by applying cholesteric liquid crystal silicon repeatedly to give a uniform thickness. ing. A transparent common electrode 24 made of ITO or the like is provided on the polarization reflection layer 23, and an alignment film 25 made of polyimide or the like is further provided on the upper surface of the transparent common electrode 24 to form the counter substrate 19. is doing.

The array substrate 18 and the counter substrate 19 are arranged so as to face each other with a predetermined gap therebetween, and are adhered to each other via a sealing material 26. In this gap portion 27, a liquid crystal layer 28 is sealed. The thickness of the liquid crystal layer 28 is defined by the spacer 29 interposed between the array substrate 18 and the counter substrate 19 to form the liquid crystal panel 30. On the outer surface of the liquid crystal panel 30 on the array substrate 18 side, a left circular polarizing plate 34 including a retardation plate 32 and a polarizing plate 33 is attached with an adhesive via a light diffusion film 31, and the counter substrate 19 side. On the outer surface, the phase difference plate 35
A right circularly polarizing plate 37 composed of the above and the polarizing plate 36 is attached with an adhesive.

Polarizing plate 3 attached to this array substrate 18
3 and the phase difference plate 32 are configured as a left circularly polarizing plate 34 by adjusting the axial angle of bonding, and the bonding angle to the liquid crystal panel 30 is an angle at which the black brightness of the reflective display is the lowest. Has been done. The polarizing plate 36 and the phase difference plate 35 on the side of the counter substrate 19 are configured as a right circular polarizing plate 37 by adjusting the axial angle of bonding. Further, a backlight 38 is arranged outside the polarizing plate 36 on the side of the counter substrate 19 to form a liquid crystal display device.

In the liquid crystal display device having such a structure, the backlight 38 as a light source is turned on together with the external light, and the TF
By driving T12 to control the switching of the pixel electrode 15, the liquid crystal layer 28 on each pixel electrode 15 is controlled by the potential difference between the voltage of the pixel electrode 15 and the voltage supplied to the opposing common electrode 24. As a result, a predetermined image is displayed.

Here, the above-mentioned polarization reflection layer 23 is such that the pitch of the cholesteric liquid crystal polymer layer 22 is continuously changed, and layers having different pitches are formed on the underlying alignment film 21 printed on the substrate 20 with a pitch of Regardless of size, a total of eight layers were laminated in order from a layer having a small Y value of selective reflection, and the thickness of each layer was set to a thickness at which incident left circularly polarized light was selectively reflected by 70%. With this configuration, wavelength 40
The polarization reflection layer 23 having a thickness of 0 nm to 800 nm is formed.

A semi-transmissive display by the polarization function of the polarization reflection layer 23 composed of the cholesteric liquid crystal polymer layer 22 will be described. As shown in FIG. 2, a liquid crystal having a liquid crystal layer 28 having a phase difference of R = λ / 2. For example, a left-handed cholesteric liquid crystal polymer layer 22 that is a polarized light-reflecting polymer layer that reflects left-handed circularly polarized light and transmits right-handed circularly polarized light of opposite polarity is formed on a reflective / transmissive substrate (not shown) on the backlight 38 side of the panel 30. A polarization reflection layer 23 is provided. On the image display side of the liquid crystal panel 30, the retardation plate 3 with R = λ / 4
2 and a polarizing plate 33 are provided, and on the backlight 38 side,
A retardation plate 35 of R = λ / 4 and a polarizing plate 36 are provided.

As a result, in the cholesteric liquid crystal display device, in the white display area shown in the left half of FIG. 2, the external light A from the image display side passes through the polarizing plate 33 and the retardation plate 32 and rotates to the right. When the light enters the liquid crystal panel 30 as circularly polarized light, is converted into left-handed circularly polarized light while passing through the liquid crystal panel 30, and is irradiated to the polarization reflection layer 23 composed of the left-handed cholesteric liquid crystal polymer layer 22, the left-handed circularly polarized light is reflected. The light is reflected by the polarized light reflection layer 23, is converted to right-handed circularly polarized light while passing through the liquid crystal layer 28, and passes through the retardation plate 32 and the polarizing plate 33 to perform bright display by reflected light.

At the same time, the light B from the backlight 38 passes through the polarizing plate 36 and the phase difference plate 35 and is applied to the polarization reflection layer 23 as right-handed circularly polarized light. Since the light is incident on 28 and is converted to left-handed circularly polarized light while passing through the liquid crystal layer 28, bright display by transmitted light is performed thereafter via the retardation plate 32 and the polarizing plate 33.

On the other hand, in the case of black display shown in the right half of the figure, the external light C from the image display side enters the liquid crystal panel 30 as right-handed circularly polarized light through the polarizing plate 33 and the phase difference plate 32. However, the light passes through the liquid crystal layer 28 without being rotated, and is irradiated onto the polarized light reflection layer 23. Then, the external light C is transmitted through the polarization reflection layer 23 that transmits right-handed circularly polarized light, passes through the phase difference plate 35, and is absorbed by the polarizing plate 36 to perform dark display.

At the same time, the light D from the backlight 38 passes through the polarizing plate 36 and the phase difference plate 35, passes through the polarization reflection layer 23 that transmits right-handed circularly polarized light as right-handed circularly polarized light, and is transmitted to the liquid crystal layer 28. The light enters, passes through the liquid crystal layer 28 without optical rotation, is absorbed by the polarizing plate 33 through the phase difference plate 32, and dark display is performed.

By using the polarization reflection layer 23 in this way, semi-transmissive display is performed.

Therefore, as shown in FIG.
The cholesteric liquid crystal polymer layer 22 constituting No. 3 is laminated on the underlying alignment film 21 side in order from the one having a smaller Y value of selective reflection, and is arranged so that the cholesteric liquid crystal polymer layer 22 having a larger Y value is located on the display side. Then, when the external light E in the wavelength range having a large Y value of the selective reflection enters the polarization reflection layer 23, it is selectively reflected by the upper layer portion of the polarization reflection layer 23. This upper layer cholesteric liquid crystal polymer layer 2
The reflection at 2 reduces the number of times the light passes through the interface of the plurality of laminated cholesteric liquid crystal polymer layers 22 in the polarization reflection layer 23, so that the influence of polarization destruction is reduced. Therefore, the polarization ability of the selective reflection light of the polarization reflection layer 23 can be improved.

Next, Table 1 shows a performance comparison comparing the front contrast and the transmittance of the product to which the present invention is applied and the conventional product.

[Table 1] As can be seen from Table 1, in the transmissive display, the front contrast of the conventional product was 100: 1, but in the implementation product, it was improved to 120: 1. In the reflective display, the front contrast was also improved. Is 10: 1, the actual product is significantly improved to 30: 1, and the reflectance is also improved by 1%. Particularly in the reflective display, the embodied product exerts an excellent effect, and it has become possible to realize a high-quality reflective display.

[0034]

According to the present invention, it is possible to greatly improve the reflective display quality, particularly the reflective contrast and the reflectance, in a semi-transmissive flat panel display device having a polarization reflective layer.

[Brief description of drawings]

FIG. 1 is a sectional view showing a flat panel display device according to the present invention.

FIG. 2 is an explanatory view for explaining a light transmitting / reflecting state of the flat panel display device.

FIG. 3 is an explanatory diagram for explaining the configuration of a polarization reflection layer that also constitutes the flat panel display device.

FIG. 4 is a cross-sectional view showing a conventional flat panel display device.

FIG. 5 is an explanatory diagram for explaining the configuration of a polarization reflection layer that also constitutes the flat panel display device.

[Explanation of symbols]

11: First substrate 15: Pixel electrode 18: Array substrate 19: Counter substrate 20: Second substrate 22: Cholesteric liquid crystal polymer layer 23: Polarized reflective layer 27: Gap 28: Light modulation layer (liquid crystal layer) 38: Backlight

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuzo Kubu             2 shares, 1-9-1 Harara-cho, Fukaya City, Saitama Prefecture             Company Toshiba Fukaya Factory F-term (reference) 2H049 BA02 BA05 BA07 BA16 BA42                       BA43 BB03 BB62 BB63 BC22                 2H091 FA02Y FA08X FA08Z FA11X                       FA11Z FA12X FA12Z FA41Z                       FD06 GA03 GA13 HA06 LA17

Claims (2)

[Claims] 1. A first substrate having a pixel electrode, a reflection-transmission type second substrate which is arranged to face the first substrate with a predetermined gap, and a second substrate which is disposed on the second substrate. In a flat display device having a polarized light reflection layer composed of a plurality of cholesteric liquid crystal polymer layers, and a light modulation layer enclosed in the gap, the polarized light reflection layer is a layer having a larger selective reflection reflectance than the display surface side. A flat-panel display device, which is configured by being laminated from. 2. The flat panel display device according to claim 1, wherein a backlight is arranged at a position facing the polarized reflection layer with the second substrate interposed therebetween.