JP2005283851A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semi-transparent liquid crystal display having enhanced luminance of a transmission mode. <P>SOLUTION: The semi-transparent liquid crystal display is mainly composed of: one member A; the other member B; and a nematic liquid crystal held by both members, and pixels are arranged in a matrix shape in the liquid crystal display. The one member A is formed with, on the inner side principal surface of a transparent substrate 4, a light reflection film 11 having a light transmitting hole on which a transparent electrode 8 and an alignment layer 9 are successively layered. The other member B is constituted by successively layering a transparent electrode 12 and an alignment layer 9 on the inner surface of a transparent substrate 4. A polarizing plate 1 is disposed on the other principal surface of the transparent substrate 4 on which the light reflection film 11 is formed and a quarter-wave birefringence layer is formed in only a reflection region of the light reflection film 11 at the upper part of the light reflection film 11, and a color filter layer straddling the reflection region and a transmission region is formed. In the above liquid crystal display, when the thicknesses of the color filter layer in the transmission region and in the reflection region are defined as Tt and Rt, respectively, the thickness of the quarter-wave birefringence layer 5 is set to be a value substantially obtained by Tt-Rt. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device having a reflective region and a transmissive region in one pixel region, and more particularly to a transflective liquid crystal display device with improved light use efficiency of transmitted light in the transmissive region.

  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 have them together, a semi-transmissive film of a half mirror is used (see Patent Document 1). 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 Patent Document 2).

  In addition, when such a semi-transmissive film of a half mirror is used, there is a problem that it is difficult to improve both the reflectance and transmittance functions. To solve this problem, light with a light transmitting hole is provided. A transflective liquid crystal display device that uses a reflective film instead of the transflective film has been proposed (see Patent Document 3).

  As a specific example, FIG. 4 is a schematic cross-sectional view showing an example of a transflective liquid crystal display device according to the prior art, and FIG. 5 is an enlarged view of a main part of one member A, schematically showing the polarization state of light. Is shown.

  Like the transflective liquid crystal display device 22 shown in FIGS. 4 and 5, the transmitted light X from the backlight (not shown) is only the linearly polarized light component in the transmission axis direction of the polarizing plate 1 in the polarizing plate 1. The linearly polarized light transmitted through the polarizing plate 1 is converted into left circularly polarized light at the λ / 4 plate 13. Then, the light passes through the light transmission hole 14, the color filter 6, the transparent electrode 8, and the alignment film 9 provided in the light reflection film 11 as left circularly polarized light, and enters the liquid crystal layer 10.

Further, the transmitted light Y from the backlight can transmit only the linearly polarized light component in the transmission axis direction of the polarizing plate 1 in the polarizing plate 1, and is converted into left circularly polarized light in the λ / 4 plate 13. Next, it is converted into right circularly polarized light when reflected by the light reflecting film 11. Next, the light is converted into linearly polarized light in the direction perpendicular to the transmission axis of the polarizing plate 1 in the λ / 4 plate 13. Since the direction of the linearly polarized light and the transmission axis direction of the polarizing plate 1 are perpendicular to each other, the light is absorbed by the polarizing plate 1. The brightness in the transmission mode of the transflective liquid crystal display device 22 is determined by the amount of light transmitted through the light transmission hole 14 from the backlight.
JP-A-8-292413 JP 7-318929 A Japanese Patent No. 2878231

  However, in the above-described transflective liquid crystal display device, in the structure in which the light transmission hole is formed in the light reflection film, only the light transmission hole part contributes to the transmission mode, and the backlight incident on the light reflection film part Since the light is reflected by the light reflecting film and then absorbed by the polarizing plate of one member, in the transmission mode, sufficient brightness cannot be obtained only with the light transmitted through the light transmitting hole.

  The present invention has been devised in view of the above circumstances, and the object thereof is a transflective type in which the brightness of the transmissive mode is improved by reusing light incident on the light reflecting film part in the transmissive mode. A liquid crystal display device is provided.

The liquid crystal display device of the present invention is a liquid crystal display panel in which one transparent substrate having a display electrode and an alignment film and the other transparent substrate having a display electrode and an alignment film are bonded together with liquid crystal interposed therebetween,
A light guide plate disposed on the outside of the other transparent substrate of the liquid crystal display panel and provided with a reflecting means on the outer main surface, and a backlight comprising a light source for supplying light to the light guide plate, and A reflective area formed with a reflective film on the inner main surface of one transparent substrate corresponding to a display pixel area where the display electrodes of both substrates intersect, and the light of the backlight without forming the reflective film In a liquid crystal display device comprising a transmissive region to transmit, a λ / 4 birefringent layer disposed on the reflective film, and a color filter layer straddling the reflective region and the transmissive region.
When the thickness of the color filter layer in the transmissive region is Tt and the thickness of the color filter layer in the reflective region is Rt, the thickness of the λ / 4 birefringent layer is set to a value substantially determined by Tt−Rt. It is characterized by being.

  Furthermore, in the liquid crystal display device of the present invention, the λ / 4 birefringent layer is made of a resin film containing oriented liquid crystal molecules, and the liquid crystal is interposed between the λ / 4 birefringent layer and the reflective film. An alignment layer for aligning molecules is interposed.

  The liquid crystal display device of the present invention is provided between one member formed by sequentially stacking a display electrode and an alignment film on a transparent substrate and the other member formed by sequentially stacking a display electrode and an alignment film on a transparent substrate. A transflective liquid crystal display device in which pixels are arranged in a matrix with a nematic liquid crystal interposed therebetween, and a backlight comprising a light guide plate having a reflecting means on the outer principal surface of the other transparent substrate and a light source And a light reflection film having a light transmission hole is formed on the inner main surface of the other transparent substrate, a λ / 4 birefringence layer is formed on the light reflection film, and the backlight and the other transparent substrate By arranging the polarizing plate between them, the backlight light that passes through the polarizing plate and is incident on the other transparent substrate is reflected by the light reflecting film formed on the inner surface of the other transparent substrate, and is the same as the transmission axis of the polarizing plate. Be absorbed by the polarizing plate in the direction of polarization. Returning to the backlight, and again enters into the other transparent substrate by the reflecting means of the backlight, it is possible to reuse the light, thereby improving the brightness of the liquid crystal display device in the transmissive mode.

  Further, by changing the thickness of the λ / 4 birefringent layer, the difference in thickness of the color filter layer in the transmissive region and the reflective region can be adjusted, and the color tone of each of the transmissive mode and the reflective mode can be optimized. .

  Hereinafter, a transflective liquid crystal display device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic sectional view of a liquid crystal display device according to the present invention, and FIG. 3 is an enlarged view of a main part of one member of the liquid crystal display device according to the present invention, showing the polarization state of light. FIG. 2 shows a process of the method for manufacturing one member of the liquid crystal display device according to the present invention.

  First, the structure of the liquid crystal display device 20 shown in FIG. 1 will be described.

  The liquid crystal panel of the liquid crystal display device 20 is mainly composed of one member part A including the glass substrate 4, the other member B including the glass substrate 4, and the liquid crystal layer 10 sandwiched between these members.

  On the other hand, for the member A, a light reflecting film 11 having a light transmitting hole 14 is formed on the inner surface side main surface of the glass substrate 4, and the λ / 4 birefringent layer 5 is formed only in the reflecting region where the light reflecting film 11 is formed. Is formed. An alignment film 15 for aligning the λ / 4 birefringent layer 5 is disposed between the light reflecting film 11 and the λ / 4 birefringent layer 5.

Further, a color filter 6, an overcoat layer 7 made of acrylic resin, a transparent electrode 8 which is a display electrode point light source made of ITO arranged in a plurality of stripes in parallel, and an orientation made of polyimide resin rubbed in a certain direction. Films 9 are sequentially stacked. Note that an insulating film made of resin, SiO ₂ or the like may be interposed between the transparent electrode 8 and the alignment film 9.

  The color filter 6 is formed by photolithography by applying a photosensitive resist previously prepared by a pigment dispersion method, that is, pigments (red, green, blue) onto a substrate.

As for the other member B of the liquid crystal display device 20, a transparent electrode 12 which is a display electrode made of ITO arranged in parallel and in stripes on the inner surface of the glass substrate 4, and an alignment film 9 made of polyimide resin rubbed in a certain direction. They are sequentially stacked. The alignment film 9 is formed directly on the transparent electrode 12, but an insulating film made of resin, SiO ₂ or the like may be interposed between the alignment film 9 and the transparent electrode 12.

  Then, the one member A and the other member B having such a configuration are bonded to each other by a seal member (not shown) through the liquid crystal 10 made of chiral nematic liquid crystal twisted at an angle of, for example, 0 ° to 180 °. In addition, a large number of spacers (not shown) are arranged between the members in order to make the thickness of the liquid crystal 10 constant.

  Further, an iodine-based polarizing plate 1 is sequentially formed on the outer main surface of the glass substrate 4 of the one member A. Further, the polarizing plate 1 is sequentially formed on the outer main surface of the glass substrate 4 of the other member B. About these arrangement | positioning, it carries out by apply | coating the adhesive material which consists of an acryl-type material.

  Then, a backlight unit including a light source unit and a light guide plate is disposed in close contact with the polarizing plate 1.

  In the backlight, a light guide plate 31 made of a translucent material, a reflective layer 32 disposed on the back surface side (lower side in the figure) of the conductor plate 31, and a light source 33 are disposed on an end surface of the light guide plate 31. The light emitted from the light source unit 33 is reflected through the light guide plate 31 and the reflection layer 32 on the back surface of the light guide plate 31, and the polarizing plate 1 and the glass of the one member A of the liquid crystal display device 20. It will be guided to the substrate 4. The light guide plate 31 has a light scattering function in order to guide light uniformly to the one member A side of the liquid crystal display device 20. The reflective layer 32 is configured by depositing and forming a highly reflective metal layer on the light guide plate 31 or forming a reflective groove that physically reflects the back surface of the light guide plate 31.

  Here, the structure of FIG. 1 may be a panel structure in which an active element such as a passive drive or TFT or TFD is provided.

  Next, a method for manufacturing the liquid crystal display device 20 according to the present invention will be described.

  Since the other member B of the liquid crystal display device 20 according to the present invention is manufactured by the prior art, description of this manufacturing method is omitted.

  About the manufacturing method of the one member A of the liquid crystal display device 20 which concerns on this invention, as shown in FIG. 2, it manufactures using the (a)-(d) process. Details of the steps (a) to (d) will be described below.

(A) A metal film (for example, Al, Ag, or an alloy thereof) or the like is formed on the glass substrate 4 and then patterned (using a general photolithography technique or the like) to form the light reflecting film 11. Further, an alignment film 15 is formed by a printing method, and is rubbed to perform an alignment process. The rubbing cloth is YA20R manufactured by Yoshikawa Processing, the rotation speed is 1200 rpm, and the pushing amount is 0.5 mm.

(B) Next, a transparent photosensitive resist 5 mixed with a liquid crystal material having a birefringence (Δn = 0.138, λ = 589 nm) is applied to a thickness of 1 μm. Pre-bake at 80 ° C for 2 minutes to evaporate the solvent. Only a portion corresponding to the reflective region is exposed to 50 mj using a photomask. By this step, the liquid crystal molecules are uniaxially aligned in the direction subjected to the alignment treatment in the step (a).

(C) Development is performed to remove the unexposed portion, thereby patterning the λ / 4 birefringent layer 5 only in the reflective region. Then, it is cured by post-baking at 200 ° C for 30 minutes.

(D) A resist in which pigments made of red, green, and blue are uniformly dispersed is formed on each pixel by photolithography,
In order to further smooth the surface, the overcoat 7 may be performed with a transparent resin.

  Furthermore, the operation principle of the liquid crystal display device according to another embodiment of the present invention will be described with reference to FIG.

  First, the transmitted light X from the backlight (not shown) is transmitted through the polarizing plate 1 only through the linearly polarized light component in the transmission axis direction of the polarizing plate 1, and then transmitted through the light transmitting hole 14 and the color filter 6. The linearly polarized light component is incident on the liquid crystal layer 10 side.

  The transmitted light Y from the backlight can transmit only the linearly polarized light component in the direction of the transmission axis of the polarizing plate 1 in the polarizing plate 1, and is then reflected on the back surface of the light reflecting film 11. That is, the light is reflected by the light reflecting film 11 while being linearly polarized in the same direction as the transmission axis of the polarizing plate 1 and reflected to the backlight side. And since the direction of this linearly polarized light and the transmission axis direction of the polarizing plate 1 are the same direction, the reflected light is not absorbed by the polarizing plate 1 and is incident on the light guide plate 31 of the backlight. Further, the light is reflected again by the reflective layer 32 of the backlight. As a result, the light of the backlight reflected by the light reflecting film 11 is emitted from the light guide plate 31 again (reflected by the reflective layer 32) without being absorbed by the backlight side, so that this light is regenerated. Can be used.

  Further, as shown in FIG. 2D, a color filter is formed over the transmissive region and the reflective region. By changing the thickness of the λ / 4 birefringent layer formed in the reflective region, the color filter thickness Tt in the transmissive region and the reflective region are reflected. The thickness Rt of the color filter in the region can be adjusted, and the thickness of the λ / 4 birefringent layer is substantially in the relationship of Tt−Rt. The transmissive area transmits the light from the backlight once through the color filter thickness Tt, and the reflective area once when the color filter thickness Rt is incident from the upper side from the outside, once after being reflected by the light reflecting film, twice in total. Although light passes, the thickness of Tt and Rt can be changed to adjust the color tone of each of the transmission region and the reflection region, and there is a difference in color tone in both the transmission mode and the reflection mode display. You can see the display without any discomfort even if you change the mode.

  Next, an optical property evaluation method will be described.

  In the reflection mode, as shown in FIG. 6, the reflectance and color gamut of reflected light in the vertical direction when light (C light source) is incident from an oblique upper part 15 ° of the liquid crystal display device and the liquid crystal display device is driven. The area was measured. In addition, in order to improve the visibility of reflected light, a scattering plate is disposed on one substrate display surface side of the transflective liquid crystal display device (for example, IDS: manufactured by Sumitomo Chemical Co., Ltd .: not shown).

  In the case of the transmission mode, as shown in FIG. 7, the transmittance and color gamut of transmitted light in the vertical direction when light (C light source) is incident from the bottom of the liquid crystal display device and the liquid crystal display device is driven. The area was measured.

  FIG. 8 is a definition diagram of the color gamut area. The color gamut area indicates the ratio of the area surrounding each RGB chromaticity point to NTSC. The larger this area, the higher the color reproducibility and the higher the color purity of the panel display.

Table 1 summarizes the transmittance, reflectance, and color gamut area of the prior art and the transflective liquid crystal display device according to the present invention. The data of the present invention is shown as a relative value when the prior art data is set to 1.00.

  In the above data, since the color filter thickness Tt in the transmission region of the device of the present invention is about twice as large as that of the conventional liquid crystal display device, the transmittance tends to decrease. Due to the utilization effect, the color gamut area is doubled while suppressing the decrease in transmittance slightly compared to the prior art, and the color filter thickness Rt of the reflective area is almost the same as that of the prior art device. Compared to the prior art, the reflectance is almost unchanged, and the color gamut area is hardly changed.

Therefore, the device of the present invention has improved display characteristics in the transmissive mode.

1 is a schematic cross-sectional view of a liquid crystal display device according to the present invention. (A)-(d) is schematic which shows the process of the manufacturing method of the one member of the liquid crystal display device which concerns on this invention. It is a principal part enlarged view of one member of the liquid crystal display device which concerns on this invention. It is a schematic sectional drawing of the liquid crystal display device in a prior art. It is a principal part enlarged view of one member of the liquid crystal display device in a prior art. It is a schematic diagram which shows the optical characteristic evaluation method in the reflection mode of a liquid crystal display device. It is a schematic diagram which shows the optical characteristic evaluation method in the transmissive mode of a liquid crystal display device. It is a figure which shows the definition figure of a color gamut area.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Polarizing plate 2 ... 2nd phase difference plate 3 ... 1st phase difference plate 4 ... Glass substrate 5 ... 1/4 birefringent layer 6 ... Color filter 7 ... Overcoat 8 ... transparent electrode 9 ... alignment film 10 ... liquid crystal 11 ... light reflecting film 12 ... transparent electrode 13 ... λ / 4 plate 14 ... light transmission hole 15 ...・ Alignment film

Claims (2)

A liquid crystal display panel in which one transparent substrate having a display electrode and an alignment film and another transparent substrate having a display electrode and an alignment film are bonded together with a liquid crystal interposed therebetween;
A light guide plate disposed outside the other transparent substrate of the liquid crystal display panel and having a reflecting means on the outer principal surface; and a backlight comprising a light source for supplying light to the light guide plate. A reflective area formed with a reflective film on the inner main surface of one transparent substrate corresponding to a display pixel area formed by intersecting display electrodes of the substrate, and transmitting the light of the backlight without forming the reflective film In a liquid crystal display device comprising a λ / 4 birefringent layer on the reflective film and a color filter layer straddling the reflective region and the transmissive region.
When the thickness of the color filter layer in the transmissive region is Tt and the thickness of the color filter layer in the reflective region is Rt, the thickness of the λ / 4 birefringent layer is set to a value substantially determined by Tt−Rt. A liquid crystal display device.   The λ / 4 birefringent layer is composed of a resin film containing aligned liquid crystal molecules, and an alignment layer for aligning the liquid crystal molecules is disposed between the λ / 4 birefringent layer and the reflective film. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is interposed.

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