JP4544908B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to the structure of a transflective liquid crystal display device.

  In recent years, liquid crystal display devices have been used for large-sized and high-definition monitors in addition to small or medium-sized portable information terminals and notebook computers. Furthermore, a technology of a reflective liquid crystal display device that does not use a backlight has been developed, and is excellent in thinness, light weight, and low power consumption.

  A reflective liquid crystal display device has a scattering reflection type in which an uneven light reflection layer is formed on the inner surface of a substrate disposed at the back, but the surrounding light is effectively used by not using a backlight. ing.

  In addition, a transflective liquid crystal display device has been developed in which a transflective film is formed in place of the light reflecting layer, a backlight is provided, and the reflective mode and the transmissive mode are selectively used.

  According to this transflective liquid crystal display device, it can be used as a reflective device by external illumination such as sunlight or fluorescent lamp, or it can be used as a transmissive device with a backlight attached. In order to provide this, a semi-permeable membrane is used (see JP-A-8-292413). In addition, it has been proposed to use a semi-transmissive film for the same purpose in an active matrix type semi-transmissive liquid crystal display device (see JP-A-7-318929).

  When such a semi-transmissive film of a half mirror is used, there is a problem that it is difficult to improve both functions of reflectance and transmittance. To solve this problem, a reflective film provided with a light transmitting hole is used. A transflective liquid crystal display device used in place of the transflective film has been proposed.

In addition, by forming an alkyl group having 1 to 6 carbon atoms and 12 to 22 carbon atoms on the surface of the spacer, it is excellent in wet dispersibility and prevents light leakage due to abnormal alignment of liquid crystal molecules at the interface between the liquid crystal and the spacer. Liquid crystal display element spacers and liquid crystal display devices have been proposed. (See JP2003-186025)
JP-A-8-292413 JP-A-7-318929 JP 2003-186025 A

  In conventional transmissive liquid crystal display devices, reflective liquid crystal display devices, and transflective liquid crystal display devices using a half mirror, display is performed using the entire pixels arranged in a matrix. On the other hand, since the effective pixel size is large, as described above, formation of an alkyl group having 1 to 6 carbon atoms and 12 to 22 carbon atoms on the surface of the spacer prevents the occurrence of light leakage due to orientation abnormality. I was able to.

  However, in a transflective liquid crystal display device using a reflective film provided with a light transmitting hole, only a part of the pixels contributes to transmissive display.

  Here, since the spacers disposed between the two substrates are randomly disposed by wet spraying or dry spraying, the number of spacers disposed on the light transmitting hole is also random.

  Therefore, when a conventional transparent spacer is installed between two substrates, white spots occur due to abnormal alignment of the transparent spacer itself and the surrounding liquid crystal during black display, and the degree of white spots in each pixel. Is dependent on the number of spacers arranged on the light transmission hole, so that white spots appear to be uneven as a whole.

  In addition, formation of an alkyl group having 1 to 6 carbon atoms and 12 to 22 carbon atoms on the spacer surface can prevent light leakage due to orientation abnormality, but the effective pixel size with respect to the spacer size. Therefore, when the orientation regulation force is too strong in white display, black unevenness is visible.

  The present invention has been devised in view of the above-described problems, and an object of the present invention is a transflective liquid crystal display device using a reflective film provided with a light transmissive hole, by a spacer mixed in a liquid crystal layer. An object of the present invention is to provide a transflective liquid crystal display device capable of eliminating display unevenness and capable of stable display.

The liquid crystal display device of the present invention is a liquid crystal display device having a plurality of pixel regions, and includes a first substrate on the display surface side and a second back surface side disposed opposite to the first substrate. A substrate, a liquid crystal layer interposed between the first substrate and the second substrate , a spacer disposed in the liquid crystal layer, and between the first substrate and the second substrate A reflective film having a light reflection region and a light transmission region for each pixel region , and disposed opposite to the second substrate and transmitting light to the second substrate. A backlight for supplying, and the spacer includes a black spacer and a transparent spacer having the same diameter as the black spacer, and the ratio of the black spacer to the transparent spacer is , 20: 80-80: 20 range der of is, the space When the radius of the service r, the area of the light transmitting region was S, the value of pi] r ² / S is in the range of 0.001 to 0.01.

  The liquid crystal display device of the present invention includes a light reflection region and a light transmission region in one pixel region, and the ratio of the black spacer to the transparent spacer is set on the liquid crystal layer between the upper and lower substrates. They are mixed and arranged in the range of 20:80 to 80:20. As a result, a liquid crystal display device in which the unevenness of the spacer is not manifested during white display roughness, black display roughness or color display is obtained.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing a schematic structure of a liquid crystal display device of the present invention. FIG. 1 is a plan view of adjacent pixel portions.

On the other hand, the member is, for example, a second substrate, and is a member including the transparent substrate 4 on the lower side in the drawing. Specifically, a light reflection film 9 made of an aluminum metal material having a light transmission hole formed on the inner surface of a glass substrate which is a transparent substrate 4 is formed, and a color filter 8 and an overcoat made of an acrylic resin are formed thereon. A layer 7, a transparent electrode 5 made of ITO arranged in stripes in parallel, and an alignment film 6 made of polyimide resin rubbed in a certain direction are sequentially laminated. Note that an insulating film made of resin, SiO ₂ or the like may be interposed between the transparent electrode 5 and the alignment film 6. The color filter 8 is formed by photolithography by applying a photosensitive resist previously prepared by a pigment dispersion method, that is, a pigment (red, green, blue) onto a substrate.

The other member is, for example, a first substrate, and is a member including a transparent substrate 4 on the display surface side in the drawing. Specifically, a transparent electrode 5 made of ITO and a plurality of alignment electrodes 6 made of polyimide resin rubbed in a certain direction are sequentially laminated on the inner surface of a glass substrate which is a transparent substrate 4. The alignment film 6 is formed directly on the transparent electrode 5, but an insulating film made of resin, SiO ₂ or the like may be interposed between the alignment film 6 and the transparent electrode 5.

  Then, the one member and the other member having such a configuration are bonded to each other by a seal member via a liquid crystal composed of a chiral nematic liquid crystal 16 twisted at an angle of, for example, 200 ° to 260 °. In addition, a large number of spacers 10 are arranged between both members in order to keep the thickness of the liquid crystal (hereinafter simply referred to as the liquid crystal layer 16) constant.

  Further, a phase difference plate 11 made of polycarbonate or the like and an iodine-based polarizing plate 12 are sequentially formed outside the transparent substrate 4 as one member. Further, the first retardation plate 3, the second retardation plate 2, and the iodine-based polarizing plate 1 made of polycarbonate or the like are sequentially formed outside the transparent substrate 4 of the other member. About these arrangement | positioning, it performs by apply | coating the adhesive material which consists of an acryl-type material.

  The backlight unit BL including the light source unit and the light guide plate 17 is disposed in close contact with the polarizing plate 12 formed on the transparent substrate 4 on the lower side of the liquid crystal panel DP.

  In the liquid crystal panel DP having such a structure, when the two substrates 4 are opposed to each other, for example, in the case where a pixel formed by crossing a pair of transparent electrodes 5 is a TFT or a TFD, A plurality of pixels defined by the transparent electrode are arranged in a matrix.

  Here, although the STN structure is shown in FIG. 1, a liquid crystal panel DP in which a TFT and a TFD are provided and a switching transistor is connected to each pixel may be used. In FIG. 1, the color filter 8 is formed on the transparent substrate 4 on the lower side, but may be formed on the transparent substrate 4 on the display surface side.

  FIG. 2 is a plan view showing adjacent pixels.

  In the present embodiment, the reflective film 9 formed on the transparent substrate 4 is made of a material mainly composed of Al, such as Al alone or an Al alloy (such as AlTi), and is formed with a thickness of 1200 mm. As other materials, Ag and an Ag alloy (AgPd, AgPdCu, AgCuAu, etc.) may be formed with a thickness of 1000 to 1500 mm.

  In the reflection mode, liquid crystal display is performed using external ambient light incident from the transparent substrate 4 on the display surface side. Specifically, the reflective film 14 in which ambient light constitutes a light reflection region of the pixel. Is reflected from the transparent substrate 4 on the display surface side and displayed on the liquid crystal. In the transmissive mode, display is performed using the light of the backlight BL arranged on the outer side of the lower transparent substrate 4, and specifically, the light of the backlight BL is formed in the reflective film 14 of the pixel. The liquid crystal is displayed from the transparent substrate 4 on the display surface side through the transmitted hole 15 (light transmission region).

  Next, the structure of the spacers arranged in the liquid crystal layer 16, that is, the spacers dispersed without being unevenly distributed in the light reflection region and the light transmission region of the pixel will be described.

  The spacer 10 is composed of at least two types of spacers. That is, the substantially transparent spacer 10 and the substantially black spacer. The transparent spacer substrate is formed by suspension polymerization of a monomer having an ethylenically unsaturated group under a radical polymerization agent. The black spacer can be obtained by mixing a black pigment with the above monomer or covering the periphery of a transparent substrate with a black film.

  Specifically, the radius r is set to 3 μm, for example, for both the black spacer and the transparent spacer. Here, the area of the transmission hole 15 (light transmission region) in one pixel is S.

In such a case, it is displayed as shown in FIG. 3 (A) or FIG. 3 (B). FIG. 3A shows a state in which scattering of the spacer is uniformly dispersed in the liquid crystal layer 16 and there is no display unevenness. On the other hand, in FIG. 3B, the dispersion of the spacers in the liquid crystal layer 16 is unevenly distributed, and the degree of influence that the light passing through the transmission hole 15 (light transmission region) receives from the spacer is different for each pixel. It appears as display unevenness.

  That is, unevenness occurs due to the difference in the number of spacers in adjacent pixels, particularly the number of spacers present in the light transmission region.

Here, assuming that the spacer radius is r, the area of the light transmission hole 15 (light transmission region) in the pixel is S, and the number of spacers present in the transmission hole regions A and B is N _A and N _B , the transmission hole regions A and B The area ratios of the spacers in are respectively N _A πr ² / S and N _B πr ² / S. Next, the difference is (N _A −N _B ) πr ² / S, and as this value increases, unevenness becomes more visible. Therefore, this numerical value decreases as the area S of the light transmission hole region increases, and unevenness becomes difficult to see.

Therefore, the value of πr ² / S when N _A −N _B = 1 is set (the transflective liquid crystal display device having the respective light reflection regions and light transmission regions described below is manufactured, and the value of S is calculated) and This is a result of comparing white spots in black display and black spots in white display.

For example, the values of πr ² / S in Table 1 are changed by adjusting the pixel size and the value of the transmission hole as follows. The pitch of each pixel (which actually corresponds to the area of one pixel) is 120 μm × 360 μm, and the area of the light transmission hole 15 (light transmission region) of the reflective film 14 is 100 μm × 269 μm. The area of the light transmission region was set to be 30:70 in the relationship of the area of the light reflection region: the area of the light transmission region. The πr ² / S value at this time is 0.0010.

Further, the pixel area was 100 μm × 300 μm, the area of the light transmission hole 15 of the reflection film 14 was 80 μm × 212 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 35:65. Πr ^{2 /} S at this time is 0.0017.

The pixel area was 80 μm × 240 μm, the area of the light transmission hole 15 of the reflection film 14 was 60 μm × 201 μm, and the area of the light reflection region: the area of the light transmission region was 25:75. At this time, πr ² /S=0.0003.

The pixel area was 90 μm × 270 μm, the area of the light transmission hole 15 of the reflection film 14 was 70 μm × 119 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 60:40. Πr ^{2 /} S at this time is 0.0034.

The pixel area was 70 μm × 210 μm, the area of the light transmission hole 15 of the reflection film 14 was 50 μm × 120 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 50:50. Πr ^{2 /} S at this time is 0.0047.

The pixel area was 60 μm × 180 μm, the area of the light transmission hole 15 of the reflection film 14 was 40 μm × 128 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 40:60. Πr ^{2 /} S at this time is 0.0055.

The pixel area was 70 μm × 210 μm, the area of the light transmission hole 15 of the reflection film 14 was 50 μm × 84 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 65:35. Πr ^{2 /} S at this time is 0.0067.

The pixel area was 70 μm × 210 μm, the area of the light transmission hole 15 of the reflection film 14 was 50 μm × 72 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 70:30. Πr ^{2 /} S at this time is 0.0079.

Further, the pixel area was 80 μm × 240 μm, the area of the light transmission hole 15 of the reflective film 14 was 60 μm × 54 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 80:20. Πr ^{2 /} S at this time is 0.0088.

The pixel area was 60 μm × 180 μm, the area of the light transmission hole 15 of the reflection film 14 was 40 μm × 70 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 67:33. Πr ^{2 /} S at this time is 0.0101.

The pixel area was 60 μm × 180 μm, the area of the light transmission hole 15 of the reflection film 14 was 40 μm × 64 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 33:67. At this time, πr ² /S=0.110.

The pixel area was 70 μm × 210 μm, the area of the light transmission hole 15 of the reflective film 14 was 50 μm × 48 μm, and the relationship of the partial area of the light reflection region: area of the light transmission region = 80: 20 was established. At this time, πr ² /S=0.117.

The pixel area was 60 μm × 180 μm, the area of the light transmission hole 15 of the reflection film 14 was 40 μm × 53 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 75:25. At this time, πr ² /S=0.133.

The pixel area was 60 μm × 180 μm, the area of the light transmission hole 15 of the reflection film 14 was 40 μm × 47 μm, and the relationship of the area of the light reflection region: the area of the light transmission region was 78:22. At this time, πr ² /S=0.150.

The pixel area was 60 μm × 180 μm, the area of the light transmission hole 15 of the reflection film 14 was 40 μm × 43 μm, and the relationship between the area of the light reflection region and the area of the light transmission region was 80:20. At this time, πr ² /S=0.0164.

Further, the pixel area is 60 μm × 180 μm, the area of the light transmission hole 15 of the reflection film 14 is 40 μm × 34 μm, and the relationship of the area of the light reflection region: the area of the light transmission region is 84:16. At this time, πr ² /S=0.0207.

As shown in Table 1, in the liquid crystal display device in which transparent spacers are arranged at a density of 200 pieces / mm ² , both white display and black display are possible in the range of πr ² / S of 0.001 to 0.01. No roughness or display unevenness is observed at all, whereas when πr ² / S is larger than 0.01, no roughness is observed in white display, but roughness or display unevenness is observed in black display.

Next, as shown in Table 1, in a liquid crystal display device in which black spacers are arranged at a density of 200 pieces / mm ² , black display is also possible in white display when πr ² / S is in the range of 0.001 to 0.01. In the display, no roughness is observed at all. On the other hand, when πr ² / S is larger than 0.01, no roughness is observed in the black display, but roughness and display unevenness are observed in the white display.

The reason why the roughness and display unevenness in white display and the roughness and display unevenness in black display are different depending on the value of πr ² / S will be described.

When πr ² / S is large, since the ratio of the spacer to the light transmission region is large, display unevenness that makes it easy to visually recognize the roughness caused by the spacer occurs.

When πr ² / S is small, since the ratio of the spacer to the light transmission region is small, it is difficult to be visually recognized.

In Table 2, for example, a 3.8-inch transflective STN liquid crystal display device is used (the pixel area (pitch) is 80 μm × 240 μm, the number of pixels is 240 RGB × 320 dots), and the light transmission of the reflective film 14 The area of the hole 15 is 50 μm × 96.6 μm, the light reflection area: the light transmission area = 70: 30), the transparent spacer, the black spacer, the white display roughness when the spacer density is changed, and the black display This compares the uniformity of the roughness and the panel GAP (the thickness of the liquid crystal layer 16).

  In both the transparent spacer and the black spacer, if the dispersion density of the spacers 10 is reduced, the thickness uniformity (GAP uniformity) of the liquid crystal layer 16 is lowered.

  In a transparent spacer, white display roughness does not occur at all spacer densities, whereas black display roughness decreases as the spacer density decreases.

  In black spacers, black display roughness does not occur at all spacer densities, whereas white display roughness decreases as the spacer density decreases.

Next, Table 3 shows the roughness in white display, roughness in black display, and liquid crystal layer when the ratio of black spacers to transparent spacers is changed in a structure in which black spacers and transparent spacers are mixed. 16 is a comparison of thickness uniformity (panel GAP uniformity). The spacer density is kept constant at 200 / mm ^{2 in} order to maintain the panel GAP uniformity. The size of the light transmission hole 15 of the reflection film is 50 μm × 96.6 μm, and the light reflection region area: light transmission region area = 70: 30.

  In the range of the number of black spacers: the number of transparent spacers = 0: 100 to 10:90, the roughness in black display is not seen, but the roughness in white display becomes worse.

  Moreover, in the range of black spacer: transparent spacer = 90: 10 to 100: 0, the roughness in white display is not seen, but the roughness in black display becomes worse.

  In the range of black spacer: transparent spacer = 20: 80 to 80:20, there is a tendency that the roughness in white display and the roughness in black display tend to be improved. Black spacer: transparent spacer = 50: 50 Get the best.

  As described above, in a transflective liquid crystal display device having a light reflection region and a light transmission region in one pixel and performing liquid crystal display using ambient external light and backlight light, the upper and lower two liquid crystal display devices By arranging the ratio of the black spacer and the transparent spacer between 20%: 80% and 80%: 20% between the transparent substrates, the gap between the two substrates 4 and 4 can be reduced. A liquid crystal display device that maintains uniformity and has no display unevenness such as roughness in black display and white display can be obtained.

It is a fragmentary sectional view of the liquid crystal display device concerning the present invention. It is a schematic plan view explaining the structure of the reflecting film used for the liquid crystal display device of this invention. (A) is a plan view of a pixel portion of a liquid crystal display device in which the spacer is not unevenly distributed, and (B) is a plan view of a pixel portion of the liquid crystal display device in which the spacer is unevenly distributed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ...... Polarizing plate 2 ... Second retardation film 3 ... First retardation film 4 ... Transparent substrate 5 ... Transparent conductive film 6 ... Orientation film 7 .... Overcoat 8 ... Color filter 9 ... Metal reflective film 10 ... Spacer 11 ... Third retardation film 12 ... Polarizing plate 13 ... Black matrix 14 ... Reflective film 15: Light transmission hole 16 ... Liquid crystal layer BL ... Backlight

Claims (1)

A liquid crystal display device having a plurality of pixel regions,
A first substrate on the display surface side;
A second substrate on the back side disposed opposite the first substrate;
A liquid crystal layer interposed between the first substrate and the second substrate;
A spacer disposed in the liquid crystal layer;
A reflective film provided between the first substrate and the second substrate and having a light reflection region and a light transmission region for each pixel region;
A backlight arranged to face the second substrate and for supplying light to the second substrate,
The spacer includes a black spacer and a transparent spacer having the same diameter as the black spacer,
The ratio of the spacer and the transparent spacer of the black, 20: 80 to 80: Ri 20 range der of
A liquid crystal display device in which the value of πr ² / S is in the range of 0.001 to 0.01, where r is the radius of the spacer and S is the area of the light transmission region .

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