JP2009075296A - Liquid crystal display device and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device by which luminous reflection display can be obtained from any viewing angle. <P>SOLUTION: In the liquid crystal display 1, a reflection layer 6 reflecting light made incident from a second substrate 3 side via a liquid crystal layer 4 is provided on a first substrate 2, a circularly polarizing plate 11 or an elliptically polarizing plate 12 is provided on the side opposite to the liquid crystal layer 4 of the second substrate 3 and an optical compensation plate 10 is provided between the second substrate 3 and the polarizing plate 11 or 12. The optical compensation plate 10 satisfies two relations of (nz-(nx+ny)/2)×d>0 and nx=ny when a refractive index in an in-plane slow axis direction, a refractive index in an in-plane fast axis direction, a refractive index in a thickness direction and the thickness are defined as nx, ny, nz and d, respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device and an electronic apparatus, and more particularly to a liquid crystal display device excellent in brightness of reflection display.

  For example, a transflective liquid crystal display device that is one form of a liquid crystal display device has both a transmissive display and a reflective display. By switching between the transmissive display and the reflective display according to ambient brightness, power consumption can be reduced. Even when the surroundings are dark, the display can be clearly displayed. In this type of transflective liquid crystal display device, the present inventor has proposed an optimized liquid crystal twist angle and retardation (Δn · d, Δn: difference in birefringence of liquid crystal, d: liquid crystal layer thickness). (For example, refer to Patent Document 1).

In addition, the liquid crystal display device has a problem in that the retardation of the liquid crystal layer changes as the optical path length in the liquid crystal layer changes depending on the incident angle of light, and a desired contrast cannot be obtained depending on the viewing direction. It was. In view of this, a technique has been proposed in which an optically anisotropic layer is used to optically compensate for the difference in retardation to widen the viewing angle (see, for example, Patent Document 2).
JP 2003-344844 A JP 2003-195038 A

  Incidentally, in recent years, an electronic paper display (hereinafter abbreviated as EPD) has been in the limelight as a display device capable of realizing a high contrast like a printed matter on paper. EPD is a technology that uses a reflective display that does not require a backlight, and can be viewed under various lighting conditions including sunlight, and requires a lot of power to maintain the display. It has the advantage of not. For the EPD, for example, an electrophoretic display technique is often used, but a liquid crystal technique using a ferroelectric liquid crystal or a cholesteric liquid crystal may also be used.

However, as described above, in the field of EPD in which reflection display is effective, there has been no scene in which a conventional general reflection type liquid crystal display device is used. Reflective liquid crystal display devices that are often used in the present situation include a reflective layer in the liquid crystal panel, a circular (elliptical) polarizing plate is placed on the viewing side, and circular (elliptical) polarized light is used for the display principle. To do. The reason why this configuration is not used for EPD is that the brightness (reflectance) of white display decreases depending on the incident angle of light, and it cannot be said that it looks white like paper from any direction. It is.
This problem is common to reflective liquid crystal display devices and transflective liquid crystal display devices.
If the optically anisotropic layer of Patent Document 2 is used, the black display may be improved and the contrast may be improved, but it is difficult to increase the brightness of the white display.

  SUMMARY An advantage of some aspects of the invention is to provide a liquid crystal display device capable of obtaining a bright reflective display from any place, and an electronic apparatus using the liquid crystal display device.

In order to achieve the above object, a liquid crystal display device of the present invention is a liquid crystal display device in which a liquid crystal layer is sandwiched between a first substrate and a second substrate, and the first substrate includes: A reflective layer that reflects light incident through the liquid crystal layer from the second substrate side is provided; a circularly polarizing plate or an elliptically polarizing plate is provided on the opposite side of the second substrate from the liquid crystal layer; Between the second substrate and the circularly polarizing plate, or between the second substrate and the elliptically polarizing plate, the refractive index in the in-plane slow axis direction is nx, and the refraction in the in-plane fast axis direction When the rate is ny, the refractive index in the thickness direction is nz, and the thickness is d,
(Nz− (nx + ny) / 2) × d> 0
An optical compensator satisfying the above relationship is provided.
Furthermore, it is desirable that the refractive index nx of the optical compensation plate in the in-plane slow axis direction is substantially equal to the refractive index ny in the in-plane fast axis direction.

  The present inventor has found that the difference in retardation due to the incident angle of light for white display in a region where the angle between the major axis of the liquid crystal molecules and the substrate surface is small (the liquid crystal molecules are lying on the substrate surface). In order to compensate for this, it has been found that an optical compensator satisfying the above equation, that is, an optical compensator having a vertically long refractive index ellipsoid may be used, and the configuration of the present invention has been achieved. That is, according to this configuration, retardation due to liquid crystal molecules lying on the substrate surface can be effectively compensated by the optical compensator having the refractive index ellipsoid standing on the substrate surface. The angle range in which the reflectivity can be obtained can be widened, and a liquid crystal display device with less viewing angle dependency of white display in reflective display can be realized.

In the present invention, it is preferable that a light scattering uneven layer is formed on the liquid crystal layer side of the first substrate.
According to this configuration, visibility from directions other than the regular reflection direction can be further improved.

In the present invention, an optical compensation plate composed of a base material and a polymer liquid crystal layer formed on the base material can be used as the optical compensation plate.
As the optical compensator, for example, a uniaxially stretched resin film or the like can be used. However, if a polymer liquid crystal layer formed on a base material is used, the optical compensator is compared with a stretched resin film. The thickness of the liquid crystal display device can be reduced.

The present invention can be applied to a reflective liquid crystal display device that performs only reflective display, but can also be applied to a transflective liquid crystal display device having a reflective display region and a transmissive display region in one dot region.
According to this configuration, since the transmissive display is also provided, the visibility of the display can be ensured even in a dark place with little external light, and the quality of the white display during the transmissive display is ensured by the optical compensator. be able to.

An electronic apparatus according to the present invention includes the liquid crystal display device according to the present invention.
According to this configuration, it is possible to provide an electronic apparatus including a liquid crystal display unit capable of bright reflection display from any place.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic configuration of a liquid crystal display device (reflection type liquid crystal display device) of the present embodiment, and FIG. 2 shows a schematic configuration of another liquid crystal display device (transflective type liquid crystal display device) of the present embodiment. It is sectional drawing shown. 3 to 6 are diagrams showing reflection viewing angle characteristics of the liquid crystal display device of the present embodiment. FIG. 7 is a diagram showing the reflection viewing angle characteristic of the conventional example.
In each drawing, in order to make each component easy to see, the dimensional ratio, scale, etc. of each component are appropriately changed.

  As shown in FIG. 1, the reflective liquid crystal display device 1 according to the present embodiment includes a liquid crystal panel in which a liquid crystal layer 4 is sandwiched between a first substrate 2 and a second substrate 3. The back side as viewed from the user is the first substrate 2, and the front (viewing) side is the second substrate 3. The liquid crystal layer 4 is horizontally aligned when no voltage is applied, and is in a normally white mode. By applying a voltage to the liquid crystal layer 4, the liquid crystal molecules rise with respect to the substrate surface and display black. The twist angle of the liquid crystal layer 4 is desirably about 0 ° to 70 °. On the inner surface of the first substrate 2 (hereinafter, the surface on the liquid crystal layer side of each substrate is referred to as an “inner surface”, and the surface on the opposite side is referred to as an “outer surface”) The layer 6, the insulating layer 7, and the first transparent electrode 8 are formed in order. A second transparent electrode 9 is formed on the inner surface of the second substrate 3.

  On the outer surface of the second substrate 3, an optical compensation plate 10, a phase difference plate 11, and a polarizing plate 12 are sequentially arranged in this order from the substrate side. The two retardation plates 11 and the polarizing plate 12 function as a substantially circular polarizing plate that converts incident light into circular (or elliptical) polarized light. Specifically, in the case of circularly polarized light, the phase difference plate 11 has a quarter wavelength plate (having a phase difference of about 140 nm), and in the case of elliptically polarized light, it has a phase difference shifted from the quarter wavelength. The polarizing plate 12 is a normal linear polarizing plate.

The optical compensator 10 of this embodiment has a refractive index in the in-plane slow axis direction of nx, a refractive index in the in-plane fast axis direction of ny, a refractive index in the thickness direction of nz, and a thickness of d.
(Nz− (nx + ny) / 2) × d> 0 (1)
nx = ny (2)
It satisfies the relationship of the two equations. Note that nx and ny do not have to be completely equal, and may have a relationship of nx≈ny. This optical compensation plate 10 is an optical compensation plate having a vertically long refractive index ellipsoid in a state of being placed on the outer surface of the second substrate 3 and standing with respect to the substrate surface, and is called a so-called positive C plate. It is. As a configuration of the optical compensation plate 10, for example, a uniaxially stretched resin film such as polycarbonate may be used, or a polymer liquid crystal layer formed on a base material such as triacetyl cellulose (TAC) is used. May be. In the case of using a substrate in which a polymer liquid crystal layer is formed on a substrate, the optical compensator 10 can be thinned to, for example, several tens of micrometers, and the entire liquid crystal display device can be thinned.

  The present invention can be applied not only to the reflective liquid crystal display device 1 shown in FIG. 1, but also to the transflective liquid crystal display device 21 shown in FIG. As shown in FIG. 2, the transflective liquid crystal display device 21 of the present embodiment has a reflective display region R and a transmissive display region T in one dot region. On the inner surface of the first substrate 22, in the reflective display region R, a light scattering uneven layer 23, a reflective layer 24, a liquid crystal layer thickness adjusting layer 25, and a first transparent electrode 26 are sequentially formed from the substrate side. ing. In the transmissive display region T, a light scattering uneven layer 23 and a first transparent electrode 26 are sequentially formed from the substrate side. That is, the reflective layer 24 is not formed in the transmissive display region T, and light from a backlight described later enters the liquid crystal layer 27 through the opening of the reflective layer 24. A color filter layer 29, a black matrix 30, and a second transparent electrode 31 are formed on the inner surface of the second substrate 28.

  On the outer surface of the first substrate 22, a retardation plate 32, a polarizing plate 33, and a backlight 34 are sequentially arranged from the substrate side. On the outer surface of the second substrate 28, an optical compensation plate 35, a phase difference plate 36, and a polarizing plate 37 are sequentially arranged in this order from the substrate side. The retardation plates 32 and 36 and the polarizing plates 33 and 37 on the outer surface side of both the substrates 22 and 28 function as a substantially circular polarizing plate that converts incident light into circular (or elliptical) polarized light. The configuration of the optical compensation plate 35 is the same as that described above.

Next, a simulation result of the reflection viewing angle characteristic performed by the present inventor will be described on the premise of the reflective liquid crystal display device 1 having the above configuration.
The observation position was fixed on the normal line (directly in front) passing through the center of the screen of the liquid crystal display device, and this position was set to a polar angle of 0 °. And the reflectance (reflected light quantity / incident light quantity) when the incident direction of light was changed in the azimuth angle range of 0 ° to 360 ° and the polar angle range of 0 ° to 60 ° was determined. 3 to 6 show equireflectance curves when the phase difference of the optical compensator is changed. Reflectance = 98%, 95%, 92%, 90% in order from the innermost curve in the figure. This is an equal reflectivity curve. 3 shows a case where the phase difference of the optical compensator is 100 nm, FIG. 4 shows a case where the phase difference of the optical compensator is 110 nm, FIG. 5 shows a case where the phase difference of the optical compensator is 150 nm, and FIG. Respectively. The twist angle of the liquid crystal layer was 60 °. The definition of “phase difference” here is phase difference = (nz− (nx + ny) / 2) × d.

  On the other hand, FIG. 7 shows a simulation result of the reflection viewing angle characteristics of the liquid crystal display device of this conventional example, with the configuration obtained by removing the optical compensation plate 10 from the configuration of FIG. 1 as a conventional example.

  As shown in FIGS. 3 to 6, although the shape of the iso-reflectance curve changes according to the value of the phase difference of the optical compensator, a region where a reflectivity of 98% or more is obtained (shown by shading in the figure) It was found that (part) was greatly expanded compared to the case of FIG. 7 without the optical compensator. As can be seen from FIGS. 3 to 6, since the shape of the equal reflectance curve does not have symmetry, the azimuth direction where the high reflectance region of the equal reflectance curve spreads matches the direction in which the viewing angle is desired to be expanded. Thus, the optical compensation plate may be rotated as appropriate.

  As described above, according to the liquid crystal display device including the optical compensator of the present invention, the retardation of the liquid crystal layer can be effectively compensated by the optical compensator made of the positive C plate. A liquid crystal display device that can be widened and has less viewing angle dependency of white display in reflective display can be realized.

[Electronics]
FIG. 8 is a perspective view showing a mobile phone which is an embodiment of the electronic apparatus according to the present invention. A cellular phone 1300 in the figure includes the liquid crystal display device of the above embodiment as a small liquid crystal display unit 1301, and includes a plurality of operation buttons 1302, an earpiece 1303, and a mouthpiece 1304. The liquid crystal display device of the above embodiment is not limited to the above mobile phone, but an electronic book, personal computer, digital still camera, liquid crystal television, viewfinder type or monitor direct view type video tape recorder, car navigation device, pager, electronic notebook A liquid crystal display that can be suitably used as an image display means for devices such as calculators, word processors, workstations, videophones, POS terminals, touch panels, etc., and capable of bright reflection display from any electronic device. An electronic device including a display portion can be realized.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the specific configuration of each part of the liquid crystal display device shown in FIGS. 1 and 2 is not limited to this, and can be changed as appropriate.

It is sectional drawing which shows schematic structure of the liquid crystal display device of one Embodiment of this invention. It is sectional drawing which shows schematic structure of the other liquid crystal display device of this embodiment. It is a figure which shows the reflective viewing angle characteristic (phase difference = 100 nm) of the liquid crystal display device of this embodiment. It is a figure which shows the reflective viewing angle characteristic (phase difference = 110 nm) of the liquid crystal display device of this embodiment. It is a figure which shows the reflective viewing angle characteristic (phase difference = 150 nm) of the liquid crystal display device of this embodiment. It is a figure which shows the reflective viewing angle characteristic (phase difference = 200 nm) of the liquid crystal display device of this embodiment. It is a figure which shows the reflective viewing angle characteristic of a prior art example. It is a perspective view which shows an example of the electronic device of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,21 ... Liquid crystal display device, 2,22 ... 1st board | substrate, 3,28 ... 2nd board | substrate, 4,27 ... Liquid crystal layer, 6,24 ... Reflective layer 10, 35 ... Optical compensator, 11, 32, 36 ... retardation plate, 12, 33, 37 ... polarizing plate.

Claims (6)

A liquid crystal display device in which a liquid crystal layer is sandwiched between a first substrate and a second substrate,
The first substrate is provided with a reflective layer that reflects light incident from the second substrate side through the liquid crystal layer,
A circularly polarizing plate or an elliptically polarizing plate is provided on the opposite side of the liquid crystal layer of the second substrate,
Between the second substrate and the circularly polarizing plate, or between the second substrate and the elliptically polarizing plate, the refractive index in the in-plane slow axis direction is nx, and the refraction in the in-plane fast axis direction When the rate is ny, the refractive index in the thickness direction is nz, and the thickness is d,
(Nz− (nx + ny) / 2) × d> 0
A liquid crystal display device comprising an optical compensator satisfying the relationship of the above formula.   2. The liquid crystal display device according to claim 1, wherein a refractive index nx in the in-plane slow axis direction of the optical compensator is substantially equal to a refractive index ny in the in-plane fast axis direction.   The liquid crystal display device according to claim 1, wherein a light scattering uneven layer is formed on the liquid crystal layer side of the first substrate.   4. The liquid crystal display according to claim 1, wherein the optical compensation plate is an optical compensation plate composed of a base material and a polymer liquid crystal layer formed on the base material. apparatus.   5. The liquid crystal display device according to claim 1, further comprising a reflective display region and a transmissive display region in one dot region.   An electronic apparatus comprising the liquid crystal display device according to any one of claims 1 to 5.

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