JP4122808B2 - Liquid crystal display device and electronic device - Google Patents

Liquid crystal display device and electronic device Download PDF

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Publication number
JP4122808B2
JP4122808B2 JP2002087120A JP2002087120A JP4122808B2 JP 4122808 B2 JP4122808 B2 JP 4122808B2 JP 2002087120 A JP2002087120 A JP 2002087120A JP 2002087120 A JP2002087120 A JP 2002087120A JP 4122808 B2 JP4122808 B2 JP 4122808B2
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liquid crystal
light
display device
crystal display
polarizing plate
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JP2003279988A (en
JP2003279988K1 (en
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強 前田
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セイコーエプソン株式会社
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of securing a certain degree of visibility even under a bright use environment. <P>SOLUTION: This liquid crystal display device is provided with a liquid crystal cell 15 in which a liquid crystal layer 27 is clamped between a counter substrate 3 and an element substrate 2 and a backlight 18 arranged on the outer surface side of the liquid crystal cell 15. An upper polarizing plate 20 is provided on the outer surface side of the counter substrate 3. A lower polarizing plate 23, a forward scattering layer 28 and prism sheets 31 and 32 are provided in this order from a substrate side between the element substrate 2 and the backlight 18. Further, a reflector 29 is provided on the outer surface side of the light guide plate 16 of the backlight 18. The absolute value of the crossing angle of the extension direction of the light refraction surface 31a of the prism sheet 31 and the transmission axis of the lower polarizing plate is constituted to be less than 45 degrees. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device and an electronic apparatus, and particularly to a configuration of a liquid crystal display device mainly including a transmissive display provided with an illumination device.
[0002]
[Prior art]
As a liquid crystal display device that can display even in a dark place, an illuminating device (hereinafter sometimes referred to as a backlight) is provided on the back side of the liquid crystal cell, and a transmissive liquid crystal that performs display using light emitted from the illuminating device. There is a display device. The illuminating device used here generally has a light source composed of a cold cathode fluorescent lamp (CCFL), a light emitting diode (LED), and the like and a structure having a structure in which light incident from the light source is emitted to the liquid crystal cell side while propagating inside. And a light plate.
[0003]
An active matrix type liquid crystal display device is known as a liquid crystal display device with high definition and excellent display quality. As a display method of an active matrix liquid crystal device, a display method in a twisted nematic (hereinafter abbreviated as TN) mode is currently in use. The reason is that the TN mode liquid crystal device balances the basic characteristics required for display, such as bright, high contrast, relatively fast response speed, low drive voltage, and easy gradation display. It is because it is well equipped. In the case of a TN mode liquid crystal cell, the major axis direction of the liquid crystal molecules is twisted by 90 ° between the element substrate and the counter substrate, and polarizing plates are arranged on the outer surface sides of these substrates so that the transmission axes are orthogonal to each other. Has been placed.
[0004]
FIG. 11 shows a schematic configuration of the conventional liquid crystal display device. In this apparatus, an upper polarizing plate A, an upper substrate B, a liquid crystal layer C, a lower substrate D, a lower polarizing plate E, and a prism sheet F are arranged in this order from the front side (that is, the observation side), and further, a light source behind A backlight having G and a light guide plate H is disposed, and a reflector J is disposed behind the light guide plate H.
[0005]
Here, by arranging the prism sheet F between the liquid crystal cell and the backlight, light having a large emission angle with respect to the normal of the surface of the light guide plate H among the light emitted from the backlight is prism sheet F. Thus, the light can be condensed and the light amount of the backlight contributing to the display is increased.
[0006]
However, this type of liquid crystal display device takes out only polarized light having one vibration direction out of the unpolarized light Rb emitted from the backlight by the lower polarizing plate E and the upper polarizing plate A on the principle of display. The transmitted light Rt is used for display. In the case of the conventional liquid crystal display device, since the polarizing plates A and E disposed above and below the liquid crystal cell are absorption-type polarizing plates, the polarized light that is not used for display is absorbed by the polarizing plate. That is, the conventional liquid crystal display device has a problem that only about half of the light emitted from the backlight contributes to the display, and the use efficiency of the irradiation light of the backlight is low.
[0007]
In order to cope with this problem, a liquid crystal display device having a reflection type polarizing plate (hereinafter simply referred to as “reflection polarizing plate”) R indicated by a dotted line in FIG. 11 behind the lower polarizing plate E has been proposed. . In the case of this liquid crystal display device, the polarized light Rc that is not used for display among the light emitted from the light guide plate H is reflected by the reflective polarizing plate R, and the polarized light Rc is the reflective plate J installed on the outer surface of the light guide plate H of the backlight. For example, the light is reflected and returned to the reflective polarizing plate R again. However, even if some depolarization occurs in the meantime, the light returns almost in the polarization state reflected by the reflective polarizing plate R at first, so that it is transmitted through the reflective polarizing plate R and used for display. There was very little light, and the utilization efficiency of the light of the backlight could not be improved sufficiently. Generally speaking, the conventional transmissive liquid crystal display device has a display that is dark for the luminance of the backlight, and it has been required to realize a brighter transmissive display by increasing the light use efficiency of the backlight. .
[0008]
Therefore, as a method for increasing the light use efficiency of the backlight, a liquid crystal display device having a quarter-wave plate behind the reflective polarizing plate R has been proposed. When a quarter-wave plate is disposed behind the reflective polarizing plate R, when the linearly polarized light Rc in one polarization direction reflected by the reflective polarizing plate R passes through the quarter-wave plate, it is converted into, for example, clockwise circular polarized light. Is done. When this clockwise circularly polarized light is reflected by a reflecting plate or the like installed on the outer surface of the light guide plate of the backlight, it returns as counterclockwise circularly polarized light and passes through the quarter wavelength plate. After being transmitted through the / 4 wavelength plate, it is converted into linearly polarized light whose polarization axes are orthogonal to those before transmission. Then, since this linearly polarized light is transmitted through the reflective polarizing plate R, it can be used for display. As described above, when a quarter-wave plate is used, since a lot of light emitted from the backlight and reflected by the reflective polarizing plate R can be reused, a bright transmissive display can be obtained. This technique is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 10-162619 and 2000-98372.
[0009]
[Problems to be solved by the invention]
By the way, in recent years, this type of transmissive liquid crystal display device has also been adopted in an image display unit of a mobile phone, an image display unit of a digital camera, and the like. Widely used in the center. Since the light utilization efficiency of the backlight is improved by the above technique, the brightness of the transmissive display is also improved year by year. However, transmissive liquid crystal display devices have the following major drawbacks for application to portable electronic devices. In other words, depending on the usage environment of the portable electronic device, for example, outdoors in strong sunlight, the brightness of the backlight is much weaker than sunlight, so the image displayed on the liquid crystal screen is very dark and extremely difficult to see There was a problem.
[0010]
As a method for solving this problem, for example, increasing the output of the backlight that illuminates the liquid crystal panel can be considered. However, when the output of the backlight is increased, the power consumption of the backlight is increased, so that a large-capacity power supply device is required. This is not practical for electronic devices where portability is important.
[0011]
The present invention has been made in order to solve the above-described problems, and a liquid crystal capable of obtaining a bright display by increasing the light use efficiency and ensuring a certain degree of visibility even in a bright use environment. An object is to provide a display device. In particular, the object is to obtain a bright display by increasing the substantial reflection efficiency of external light.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a liquid crystal display device of the present invention has a liquid crystal cell in which liquid crystal is sandwiched between a first substrate and a second substrate which are arranged to face each other, a light source and a light guide plate, A liquid crystal display device including a lighting device disposed on an outer surface side of a second substrate of the liquid crystal cell, wherein a first polarizing plate is provided on the outer surface side of the first substrate, and the second A second polarizing plate, a light scattering layer, a first prism sheet having an inclined light refracting surface, and an inclined light refracting surface from the second substrate side between the substrate and the illumination device. 2 prism sheets are provided in this order, a reflecting plate is provided on the surface of the light guide plate opposite to the side on which the liquid crystal cell is disposed, and is orthogonal to the optical axis of the light refraction surface of the first prism sheet. Intersection line to the virtual plane Is a first crossing line, and a crossing line with respect to a virtual plane perpendicular to the optical axis on the light refraction surface of the second prism sheet is a second crossing line, the first crossing line And the crossing angle θ between the second polarizing plate and the transmission axis of the second polarizing plate are set in a range of −45 ° <θ <45 °. The first intersection line and the second intersection line are orthogonal to each other. It is characterized by.
[0013]
In the conventional liquid crystal display device, as shown in FIG. 11, when the prism sheet F is arranged behind the liquid crystal cell after the external light Ro is incident and transmitted through the liquid crystal cell, the prism sheet F Since the light is scattered and does not return to the observation side, the brightness of the external light Ro cannot be used for display. Further, since the external light Ro is often incident obliquely at an angle from a direction different from that of the observer, the incident angle with respect to the display surface is increased, and the external light Ro is reflected by being disposed behind the light guide plate H. Since the reflected light Rr reflected by the plate J (that is, the light returning by regular reflection) is also inclined with respect to the display surface, it does not return to the viewer side and is not used for display. was there.
[0014]
On the other hand, in the present invention, as shown in FIG. 10, a light scattering layer S is provided behind a liquid crystal cell having an upper polarizing plate A, an upper substrate B, a liquid crystal layer C, a lower substrate D, and a lower polarizing plate E. Arranged. Further, the crossing angle θ between the crossing line of the light refracting surface f of the prism sheet F disposed on the backlight side of the light scattering layer S, and the plane orthogonal to the optical axis, and the transmission axis of the lower polarizing plate E is set. It is set within the range of −45 ° <θ <45 °. As a result, a part of the external light incident on the liquid crystal cell can be efficiently reflected on the surface of the prism sheet F, and the reflected light can be used for display, so that the contrast is improved particularly in a bright place. Has an effect.
[0015]
For example, in the above configuration, among the illumination light Rb emitted from the light source G, the illumination light irradiated obliquely from the light guide plate H is collected by the prism sheet F and then scattered through the light scattering layer S. After being received, it becomes the transmitted light Rt emitted from the liquid crystal cell toward the observation side, that is, along the optical axis. This is the same as the conventional structure except for the presence or absence of scattering by the light scattering layer S.
[0016]
Further, when external light is incident on the liquid crystal cell due to a bright place or the like, the external light Ro passes through the liquid crystal cell and is scattered by the light scattering layer S, and a part of the scattered light is transmitted through the prism sheet F. Then, the light is reflected by the reflection plate J through the light guide plate H, becomes reflected light Rr again, passes through the light guide plate H, the prism sheet F, and the light scattering layer S, then passes through the liquid crystal cell and is emitted as reflected light Rr1. . As described above, the external light reflected by the reflector J is less likely to be directed to the observation side in the conventional structure and is rarely used as a part of the display. A part of S contributes to display as reflected light Rr1.
[0017]
Further, a part of the scattered light generated when the incident external light Ro reaches the light scattering layer S is a virtual plane perpendicular to the optical refraction surface f of the prism sheet F and the optical axis with respect to the transmission axis of the lower polarizing plate E. Since the crossing angle θ of the crossing line with −45 ° <θ <45 ° is reflected on the surface of the prism sheet S, it is again transmitted through the liquid crystal cell as reflected light Rr2. This is because only the polarization component having the vibration direction parallel to the transmission axis of the lower polarizing plate E passes through the liquid crystal cell out of the external light Ro incident on the liquid crystal cell. When the intersecting line between the photorefractive surface f and the virtual plane orthogonal to the optical axis intersects the transmission axis of the lower polarizing plate E at an intersecting angle θ of −45 ° <θ <45 °, it is efficiently reflected, This is because the reflected light Rr2 can sufficiently contribute to display.
[0018]
For example, consider the case where the intersection line between the light refracting surface f of the prism sheet F and the imaginary plane orthogonal to the optical axis is parallel to the transmission axis of the lower polarizing plate E. The transmitted light is linearly polarized light having a vibration direction parallel to the transmission axis of the lower polarizing plate E, and is incident on the light refraction surface f of the prism sheet F after being scattered by the light scattering layer S. At this time, the linearly polarized light is s-polarized light incident on the photorefractive surface f, and thus is reflected more efficiently than the p-polarized light. And most of the reflected light passes through the lower polarizing plate E. Incidentally, if the incident angle of the linearly polarized light incident from the lower polarizing plate with respect to the light refraction surface f is Brewster's angle, the reflected light is only s-polarized light, and all the reflected light consisting of this s-polarized light is transmitted again through the lower polarizing plate E. To do. Therefore, under this condition, the light transmitted through the liquid crystal cell can be reflected by the light refracting surface f of the prism sheet F most efficiently.
[0019]
In addition, as described above, the intersection line between the light refracting surface f of the prism sheet F and the virtual plane orthogonal to the optical axis is not limited to being parallel to the transmission axis of the lower polarizing plate E. If the absolute value of the crossing angle θ is less than 45 degrees as described above, the s-polarized component of the polarized light incident on the prism sheet F from the observation side is larger than the p-polarized component, so that the reflected light Rr2 The strength of can be increased.
[0020]
In the present invention, the crossing angle θ is preferably set within a range of −30 ° ≦ θ ≦ 30 °.
[0021]
According to the present invention, since the intensity of the reflected light Rr2 is increased because the absolute value of the crossing angle θ is 30 degrees or less, the display in a particularly bright place can be brightened.
[0022]
In the present invention, it is preferable that the light refraction surface is provided on a surface of the prism sheet on the liquid crystal cell side.
[0023]
According to the present invention, the light refracting surface is provided on the surface of the prism sheet on the liquid crystal cell side, whereby the light caused by the external light can be more efficiently reflected on the surface.
[0024]
In the present invention, the prism sheet is preferably formed in a stripe shape in which a plurality of the light refracting surfaces extend in a predetermined direction, and is inclined in a direction orthogonal to the predetermined direction.
[0025]
According to the present invention, the plurality of light refracting surfaces are formed in a stripe shape extending in a predetermined direction, and are inclined in a direction orthogonal to the predetermined direction, whereby the light refracting surface and a virtual plane orthogonal to the optical axis are formed. Since the intersecting line extends in the predetermined direction, the intensity of the reflected light Rr2 can be further increased.
[0026]
In the present invention, the prism sheet is preferably arranged so that the light refracting surface extends left and right during use.
[0027]
According to the present invention, in normal use, external light incident from above is stronger than external light incident from other directions (for example, illumination and sunlight are irradiated from above). Scattered light generated in the light scattering layer S based on the strong external light Ro incident from above is concentrated on the observation side by the prism sheet F arranged so that the striped light refracting surface f extends left and right. Since an effect is acquired, visibility can be improved further.
[0028]
In this invention, it is preferable that the said prism sheet has a function which condenses the light irradiated from the said illuminating device to the observation side.
[0029]
According to this invention, it has the function which condenses the light irradiated from an illuminating device to the observation side, Therefore The utilization efficiency in the display of the illumination light of an illuminating device can be improved, and a display can be made bright. Here, the observation side refers to the normal direction (optical axis direction) of the display screen of the apparatus.
[0030]
In the present invention, it is preferable that another prism sheet having a light refracting surface inclined in a direction different from the light refracting surface of the prism sheet is further arranged on the illumination device side of the prism sheet.
[0031]
According to the present invention, by arranging another prism sheet having a light refracting surface inclined in different directions, the light emitted from the illumination device can be condensed in the different directions. The utilization efficiency of the irradiation light of the apparatus can be further increased. In addition, the effect of the reflected light Rr2 can be maintained by disposing another prism sheet on the illumination device side of the prism sheet.
[0032]
In the present invention, the light scattering layer is preferably a forward scattering layer that mainly produces forward scattering.
[0033]
According to this invention, since the light scattering layer is a forward scattering layer that mainly generates forward scattering, the reflected light Rr1 reflected by the reflector J, the reflected light Rr2 reflected by the light refracting surface of the prism sheet, In addition, since any of the irradiation light Rb from the light guide plate H of the lighting device can be scattered to the observation side, it is possible to suppress a decrease in display brightness and improve the contrast by increasing the whiteness of the display. .
[0034]
In the present invention, the haze of the forward scattering layer is preferably 60% or more.
[0035]
According to this invention, since the haze (cloudiness value) of the front scattering layer is 60% or more, the deviation of the emission angles of the reflected lights Rr1 and Rr2 based on external light can be reduced, which contributes to display. The light component can be increased to brighten the display, and the whiteness of the display can be further increased. Furthermore, any material having a haze of 60% or more can be easily obtained. In particular, it is desirable that the numerical value range of the haze be in the range of 60 to 80% because it is possible to ensure the availability and suppress the decrease in the light utilization efficiency.
[0036]
As used herein, “haze” is a measure of light transmission characteristics commonly referred to as haze or haze in the field of optics, excluding the region within a cone of 8 degrees around the normal of the material. It is a value expressed in% by dividing the diffuse transmittance at the angled portion by the total light transmittance. A larger haze value indicates more scattered light, and a smaller haze value indicates less scattered light. As a function of the forward scattering layer of the present invention, the larger the haze is, the higher the effect of reducing display unevenness caused by the light guide plate is, but on the other hand, the emitted light from the illumination device is scattered. The transmissive display becomes dark. Therefore, it is necessary to optimize the balance. If the haze value is 60% or more, display unevenness caused by the light guide plate can be sufficiently reduced without greatly reducing the brightness of the display.
[0037]
In addition, as this front scattering layer, it is desirable to have an adhesive and the particle | grains mixed in this adhesive and different in refractive index from an adhesive. In this way, since it functions as an adhesive layer that adheres the layers disposed before and after the front scattering layer to each other, it also has a front scattering function, so that it is possible to reduce the labor of manufacturing and to configure the apparatus Can be simplified.
[0038]
In the present invention, the retardation value of the light scattering layer is preferably 10 nm or less.
[0039]
According to the present invention, the retardation value of the light scattering layer, that is, the value of Δn · d (where Δn is the optical anisotropy and d is the thickness) is 10 nm or less, whereby the polarization due to the retardation of the light scattering layer. Since the change of the state is suppressed to a negligible level, the light loss in the external light reflection process due to the change of the polarization state by the light scattering layer can be reduced. For example, when the linearly polarized light generated after the external light Ro passes through the liquid crystal cell passes through the light scattering layer, if the polarization state of the scattered light generated by the light scattering layer changes, the light of the second polarizing plate correspondingly changes. Since the amount of transmitted light decreases, the amount of reflected light Rr1 and Rr2 decreases, but according to the present invention, a decrease in the amount of reflected light can be substantially suppressed.
[0040]
The light scattering layer is preferably a filler-type scattering material in which fillers having different refractive indexes are dispersed in a substrate. As a result, the forward scattering layer can be easily constructed, and the retardation value can be kept low.
[0041]
In this invention, it is preferable that the reflective polarizing plate is arrange | positioned between the said 2nd polarizing plate and the said illuminating device.
[0042]
According to the present invention, since the polarization component that is not directly used for display among the light emitted from the backlight can be reflected to the backlight side by the reflective polarizing plate, at least a part of the polarization component is somehow formed. It can be used for display.
[0043]
In this invention, it is preferable that the 1st phase difference plate is arrange | positioned on the opposite side to the side by which the said liquid crystal cell is arrange | positioned with respect to the said reflective polarizing plate.
[0044]
According to this invention, about the light emitted from the illuminating device, the polarization component in the direction orthogonal to the transmission axis of the reflective polarizing plate is reflected by the reflective polarizing plate, so that about half of it is transmitted to the observation side. However, by arranging the first retardation plate, the polarization state of the polarization component reflected by the reflective polarizing plate can be changed, so if the polarization component is reflected by the reflection plate Since it becomes possible to allow at least a part of the light to pass through the reflective polarizing plate, the brightness of the display can be further increased.
[0045]
In the present invention, it is preferable that the first retardation plate includes at least a quarter-wave plate.
[0046]
According to the present invention, in the process in which the polarization component reflected by the reflective polarizing plate is reflected by the reflective plate and returns to the reflective polarizing plate, the quarter-wave plate is added before and after reflection by the reflective plate. By passing twice, the polarization component can be rotated 90 degrees and converted into polarized light having a polarization direction that coincides with the transmission axis of the reflective polarizing plate, so that the reflective polarizing plate can be efficiently transmitted. It becomes like this.
[0047]
Furthermore, in the present invention, it is preferable that the first retardation plate includes a ¼ wavelength plate and a ½ wavelength plate. However, in this case, it is necessary to arrange a half-wave plate on the reflective polarizing plate side.
[0048]
According to the present invention, a wave plate in which a quarter wave plate and a half wave plate are combined is known as a broadband quarter wave plate. According to this configuration, illumination light can be emitted in a wide wavelength band. Can be reused.
[0049]
In the present invention, it is desirable that the retardation value of the first retardation plate is in a range of 100 nm to 180 nm.
[0050]
According to this configuration, most of the visible light band having a wavelength of 380 to 780 nm can be covered, and the function as the first retardation plate in the liquid crystal display device of the present invention can be achieved with respect to visible light. it can.
[0051]
In the present invention, it is desirable that the wavelength dispersion of the first retardation plate is 1 or less.
[0052]
For example, when the chromatic dispersion is represented by the ratio of the retardation value at a wavelength of 450 nm and the retardation value at a wavelength of 590 nm, a conventionally available retardation plate usually has a chromatic dispersion exceeding 1. On the other hand, in recent years, a phase difference plate having a wavelength dispersion of 1 or less has been provided. When this retardation plate is used, the fact that the wavelength dispersion takes a value of 1 or less means that the retardation value increases as the wavelength becomes longer. Even if the wavelength changes, it functions as a quarter-wave plate. Therefore, according to this structure, the function as the 1st phase difference plate of this invention with respect to the light of a different wavelength can be fulfill | performed.
[0053]
In the present invention, it is preferable that the first retardation plate is disposed closer to the lighting device than the prism sheet.
[0054]
According to the present invention, since the first retardation plate is disposed on the illuminating device side of the prism sheet, the prism sheet is formed without changing the polarization state of the light incident on the prism sheet from the second polarizing plate. Since the light can be reflected by the photorefractive surface, the effect of the present invention is not affected, and a decrease in the effect can be prevented.
[0055]
In the present invention, it is desirable that the reflecting surface disposed on the outer surface side of the light guide plate of the lighting device be in a mirror state.
[0056]
The reflector in the present invention not only guides the light emitted from the illumination device first to the liquid crystal cell side, but also functions to reuse the reflected light from the reflective polarizing plate in transmissive display. Further, the reflective display functions to reflect the amount of external light transmitted through the light diffusion layer. Therefore, it is required to reflect more light, and in that sense, it is desirable that the reflecting surface be in a mirror state.
[0057]
In addition, it is desirable to provide a second retardation plate between the first polarizing plate and the first substrate or between the second polarizing plate and the second substrate.
[0058]
According to this configuration, even when the display is colored, for example, when an STN (Super Twisted Nematic) liquid crystal is used, the coloring can be compensated.
[0059]
By the way, there are two possible relations between the transmission axis of the second polarizing plate and the transmission axis of the reflective polarizing plate.
[0060]
One is a configuration in which the transmission axis of the second polarizing plate is parallel to the transmission axis of the reflective polarizing plate. According to this configuration, since all the light transmitted through the reflective polarizing plate in the transmissive display can pass through the transmission axis of the second polarizing plate, the light use efficiency in the transmissive display can be maximized.
[0061]
On the other hand, the transmission axis of the second polarizing plate and the transmission axis of the reflective polarizing plate may be crossed in a plane, and the angle ψ formed may be arranged in the range of 0 ° <ψ <10 °. . In the case of this configuration, contrary to the above configuration, part of the light transmitted through the reflective polarizing plate in the transmissive display cannot pass through the transmission axis of the second polarizing plate. Slightly lower than the configuration. On the other hand, in the reflective display, part of the light transmitted through the transmission axis of the second polarizing plate is reflected by the reflective polarizing plate, so that the reflective display can be slightly brightened. The reason why the angle ψ between the transmission axis of the second polarizing plate and the transmission axis of the reflective polarizing plate is preferably in the range of 0 ° <ψ <10 ° will be described later.
[0062]
The display mode of the liquid crystal display device of the present invention is preferably a normally white mode.
[0063]
According to this configuration, a black display screen on a white background can be realized with low power consumption.
[0064]
The first polarizing plate and the second polarizing plate are preferably absorption-type polarizing plates.
[0065]
According to this configuration, a high contrast display can be obtained.
[0066]
An electronic apparatus according to the present invention includes the liquid crystal display device according to the present invention.
[0067]
According to this configuration, by providing the liquid crystal display device of the present invention, it is possible to realize a portable electronic device having a bright display screen suitable for use outdoors, for example, where sunlight is strong.
[0068]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
The first embodiment of the present invention will be described below with reference to FIGS. The liquid crystal display device of this embodiment is an example of an active matrix type transmissive liquid crystal display device using a thin film transistor (hereinafter abbreviated as TFT) as a switching element. FIG. 1A shows the liquid crystal display device. FIG. 1B is an enlarged view of one pixel in FIG. 1A, and FIG. 2 is a cross-sectional view of the liquid crystal display device. In all the drawings below, the film thicknesses and dimensional ratios of the constituent elements are appropriately changed in order to make the drawings easy to see. In FIG. 2, illustration of wiring on the inner surface side of each substrate, switching elements, electrodes, alignment films, and the like is omitted.
[0069]
As shown in FIG. 1A, the liquid crystal display device 1 of the present embodiment includes a liquid crystal cell 15, a backlight 18 (illumination device) having a light guide plate 16 and an LED 17 (light source) disposed on the outer surface side thereof. It is roughly structured. In the liquid crystal cell 15, the element substrate 2 (second substrate) on the side where the TFT is formed and the counter substrate 3 (first substrate) are arranged to face each other, and a liquid crystal layer (not shown) is disposed between the substrates 2 and 3. Is enclosed. On the inner surface side of the element substrate 2, a large number of source lines 4 and a large number of gate lines 5 are provided in a lattice shape so as to intersect each other. A TFT 6 is formed in the vicinity of the intersection of each source line 4 and each gate line 5, and a pixel electrode 7 is connected to each other through each TFT 6. That is, one TFT 6 and pixel electrode 7 are provided for each pixel arranged in a matrix. On the other hand, a common electrode 8 is formed on the entire inner surface of the counter substrate 3 over the entire display region in which a large number of pixels are arranged in a matrix. In this specification, the surface on the liquid crystal layer side of each substrate constituting the liquid crystal cell 15 is referred to as an “inner surface”, and the opposite surface is referred to as an “outer surface”.
[0070]
As shown in FIG. 1B, the TFT 6 includes a gate electrode 10 extending from the gate line 5, an insulating film (not shown) covering the gate electrode 10, and polycrystalline silicon, amorphous silicon, etc. formed on the insulating film. A semiconductor layer 11, a source electrode 12 extending from a source line 4 electrically connected to a source region in the semiconductor layer 11, and a drain electrode 13 electrically connected to a drain region in the semiconductor layer 11. Have. The drain electrode 13 of the TFT 6 is electrically connected to the pixel electrode 7. The pixel electrode 7 is formed of a transparent conductive film such as ITO, and the common electrode 8 on the counter substrate 3 side is also formed of a transparent conductive film such as ITO.
[0071]
Looking at the cross-sectional structure of the liquid crystal display device 1, as shown in FIG. 2, an upper polarizing plate 20 (first polarizing plate) is provided on the outer surface of the upper glass substrate 19 constituting the counter substrate 3, and R on the inner surface side. A color filter 21 having color material layers of (red), G (green), and B (blue) is provided. Although not shown, a common electrode and an alignment film are formed on the color filter 21.
[0072]
On the other hand, on the outer surface of the lower glass substrate 22 constituting the element substrate 2, a lower polarizing plate 23 (second polarizing plate), a front scattering layer 28, and prism sheets 31, 32 are provided in this order from the lower glass substrate 22 side. ing. Although not shown, the gate line 5, the source line 4, the TFT 6, and the pixel electrode 7 are formed on the inner surface side of the lower glass substrate 22, and an alignment film is formed. A liquid crystal layer 27 made of TN liquid crystal having a positive dielectric anisotropy is sealed between the substrates 2 and 3. Specifically, the upper polarizing plate 20 and the lower polarizing plate 23 are both constituted by absorption-type polarizing plates.
[0073]
The front scattering layer 28 is a transparent base material in which transparent and minute particles having a refractive index different from that of the base material are dispersed, and thereby has a function of mainly scattering light forward. . That is, most of the scattered light generated by the forward scattering layer 28 becomes forward scattered light. The forward scattering layer 28 is made of, for example, an acrylic resin whose photocured state is changed in an acrylic resin (for example, light refractive index = 1.55) having a thickness of about 10 to 50 μm, preferably about 20 to 30 μm. A large number of fine particles of 2 to 3 μm or beads (for example, optical refractive index = 1.6) are dispersed.
[0074]
By disposing the forward scattering layer 28 as described above, external light transmitted through the liquid crystal cell 15 can be scattered toward the prism sheet 31. Therefore, the incident angle of external light with respect to the prism sheet 31 can be dispersed. In addition, by configuring the forward scattering layer with a filler-type scattering material as described above, forward scattering can be easily realized, and a retardation value described later can be suppressed to a small value.
[0075]
Further, it is desirable that the retardation value (Δn · d; Δn is optical anisotropy, d is thickness) of the front scattering layer 28 is 10 nm or less. Since the forward scattering layer 28 is disposed between the liquid crystal cell 15 and the prism sheet 31, if the retardation value is large, the linearly polarized state emitted from the liquid crystal cell 15 is canceled, and the effect of the present invention is reduced. Because.
[0076]
The haze (cloudiness value) of the front scattering layer 28 is preferably 60% or more. In particular, the practical haze range is 60 to 80%. If the haze is less than 60%, the effect of reducing display unevenness due to the light guide plate is reduced, and if it exceeds 80%, the amount of light that can contribute to the display is affected and the display becomes dark.
[0077]
The forward scattering layer 28 is preferably an adhesive layer. In this case, for example, an acrylic resin-based pressure-sensitive adhesive in which fine particles (beads) having a refractive index different from that of the pressure-sensitive adhesive, for example, having a particle diameter of 2 to 3 μm, is used. Since the front scattering layer 28 has adhesiveness, it can also serve as an adhesive that adheres members disposed on both sides of the front and back. For example, the liquid crystal cell 15 and the prism sheet 31 can be bonded.
[0078]
The prism sheets 31 and 32 include light refracting surfaces 31a and 32a on the surface on the observation side (upper side in the drawing). These light refracting surfaces 31a and 32a are inclined with respect to the optical axis (vertical direction in the figure), and are configured to refract light incident from the backlight 18 side and light incident from the observation side. ing. The outlines of the surfaces of the prism sheets 31 and 32 are formed in a sawtooth shape as a whole, and a plurality of light refracting surfaces 31a and 32a are provided in a stripe shape extending in a predetermined direction. That is, the strip-shaped light refracting surfaces 31a and 32a inclined to the opposite sides are alternately arranged to form a stripe shape as a whole.
[0079]
The light refracting surface 31a of the prism sheet 31 extends in a direction orthogonal to the paper surface of FIG. 2, and the light refracting surface 32a of the prism sheet 32 extends in a direction parallel to the paper surface of FIG. That is, the extending direction of the light refracting surface 31a and the extending direction of the light refracting surface 32a are orthogonal to each other.
[0080]
As shown in FIG. 3A, the extension direction of the light refracting surface 31a of the prism sheet 31, that is, the extension direction D of the intersecting line between the light refracting surface 31a and the virtual plane orthogonal to the optical axis is the lower polarizing plate 23. Intersects with the transmission axis T at an intersection angle θ. Here, the crossing angle θ is ideally 0, but may be in a range of −45 ° <θ <45 °. Among these, it is desirable that it is in the range of −30 ° ≦ θ ≦ 30 °. Here, the extension direction D is a direction in which an intersecting line between the light refracting surface 31a and a virtual plane orthogonal to the optical axis (that is, a plane parallel to the paper surface of FIG. 3A) extends.
[0081]
Returning to FIG. 2 again, the liquid crystal display device 1 will be described. The backlight 18 includes a light guide plate 16 and a light source 17 such as an LED disposed on an incident end surface of the light guide plate 16. A reflection plate 29 having a mirror surface is provided on the outer surface side of the light guide plate 16. ing. Here, the light guide plate 16 is disposed to overlap the liquid crystal cell 15 in a planar manner, and the light source 17 is disposed on the side of the light guide plate 16.
[0082]
In addition, regarding the axial arrangement of each polarizing plate, the upper polarizing plate 20 and the lower polarizing plate 23 are arranged so that the transmission axes are orthogonal to each other. The alignment films formed on the element substrate 2 and the counter substrate 3 are rubbed in a direction orthogonal to each other, and the liquid crystal layer 27 sandwiched between the alignment films takes a state of being twisted by 90 ° without applying a voltage. ing. Further, in the following description, the crossing angle θ = 0, that is, the extending direction of the light refracting surface 31a of the prism sheet 31, that is, the extending direction D of the intersecting line between the light refracting surface 31a and the virtual plane orthogonal to the optical axis. Are respectively described in the case of being configured parallel to the transmission axis T of the lower polarizing plate 23 and the case where θ is not 0 but within the above range.
[0083]
In the present embodiment, of the light emitted from the backlight 18, for example, linearly polarized light having a vibration direction perpendicular to the paper surface is transmitted through the lower polarizing plate 23 and is incident on the liquid crystal layer 27. When no voltage is applied, the light transmitted through the liquid crystal layer 27 has a polarization direction rotated by 90 °, converted into linearly polarized light having a vibration direction parallel to the paper surface, transmitted through the upper polarizing plate 20, and a white display is obtained (normally). White mode). On the other hand, in the voltage application state, even if it passes through the liquid crystal layer 27, the polarization direction remains perpendicular to the plane of the paper, so that this polarized light cannot pass through the upper polarizing plate 20, resulting in black display. In the present embodiment, by adopting the normally white mode, a black display screen on a white background can be realized with low power consumption.
[0084]
In this case, the light emitted from the backlight 18 is condensed in a direction along the optical axis by passing through the prism sheets 32 and 31, and thus is used for light that is visually recognized on the observation side, that is, for display. Light can be increased. Here, the prism sheet 31 has a function of condensing light inclined in the illustrated left-right direction (direction parallel to the drawing sheet), and the prism sheet 32 has a function of collecting light inclined in a direction orthogonal to the drawing sheet. Have
[0085]
Further, the light emitted from the backlight 18 passes through the prism sheets 31 and 32 and is then scattered forward (that is, the observation side) by the front scattering layer 28. This has an effect of reducing variations in brightness caused by light collection by the prism sheets 31 and 32.
[0086]
On the other hand, when the liquid crystal display device 1 is used in a bright place, from the upper side of the liquid crystal cell 15 (including the observation direction, usually, external light is incident mainly from a slightly inclined direction with respect to the observation direction). External light is incident. Of this incident light, linearly polarized light having a vibration direction parallel to the paper surface passes through the upper polarizing plate 20 and enters the liquid crystal layer 27. In the state where no voltage is applied, the light transmitted through the liquid crystal layer 27 has a polarization direction rotated by 90 degrees, converted into linearly polarized light having a vibration direction perpendicular to the paper surface, passed through the lower polarizing plate 23, and then scattered by the forward scattering layer 28. Receive. Then, the forward scattered light from the forward scattering layer 28 is incident on the surface of the prism sheet 31. FIG. 3B is an enlarged cross-sectional view of the prism sheet 31.
[0087]
Here, the scattered light Rs is linearly polarized light parallel to the transmission axis of the lower polarizing plate 23. If the crossing angle is θ = 0, the surface of the prism sheet 31, that is, the light refracting surface 31a. Since it is s-polarized light Ps, at least a part of it is mainly reflected by the light refracting surface 31a, passes through the liquid crystal cell 15 again, and returns to the observation side. In this case, since almost all of the scattered light Rs is s-polarized with respect to the light refracting surface 31a, it is efficiently reflected by the light refracting surface 31a. Here, if the incident angle of the scattered light Rs with respect to the light refracting surface 31a coincides with the Brewster angle, only the s-polarized light Ps reflects the light refracting surface 31a, so that all the reflected light passes through the lower polarizing plate 23.
[0088]
When the crossing angle θ is not 0, the scattered light Rs includes not only the s-polarized light Ps but also the p-polarized light Pp with respect to the photorefractive surface 31a, but the crossing angle θ is within the above range (absolute value is 45 degrees). If the value is less than half), more than half of the value is s-polarized light Ps, so that the amount of reflected light at the photorefractive surface 31a increases compared to when the crossing angle θ is outside the above range, and the lower polarizing plate. The amount of light that passes through 23 also increases. Here, the point that the reflected light of the scattered light Rs whose incident angle with respect to the light refracting surface 31a coincides with the Brewster angle is only s-polarized light Ps is the same as described above.
[0089]
The reflected light generated by the light reflection by the light refracting surface 31 a of the prism sheet 31 is based on the scattered light that is scattered by the forward scattering layer 28 and is angularly dispersed. Therefore, for example, even when most of the external light is incident from a direction inclined to some extent with respect to the optical axis, the reflected light includes many components emitted in the direction along the optical axis. Therefore, the display becomes bright, and it is possible to suppress the display from becoming difficult to see even in a bright place with strong external light.
[0090]
In the present embodiment, as shown in FIG. 3A, a plurality of light refracting surfaces 31 a are arranged in a stripe pattern on the surface of the prism sheet 31. In this case, the liquid crystal display device 1 is preferably configured such that the extending direction D of the light refracting surface 31a of the prism sheet 31 is the left-right direction of the display screen. This is because, when the left-right direction of the display screen is the extension direction D, when the external light is incident obliquely from above the display screen (that is, when the external light is obliquely incident from the left side in the drawing), the prism sheet 31 By the light collecting action, the reflected light from the surface of the prism sheet 31 based on the external light can be efficiently emitted to the observation side (the optical axis direction, that is, the normal direction of the display surface). This is because the sun and the lighting fixture are arranged above, and the light is incident obliquely from above the display screen, so that the strongest external light can be used as reflected light contributing to display.
[0091]
As described above, according to the liquid crystal display device 1 of the present embodiment, a large amount of external light having a high incident angle can be returned to the observation side, so that a certain degree of visibility is ensured even in a bright usage environment. It is possible to realize a color liquid crystal display device that can be used.
[0092]
Moreover, in this embodiment, since the light is scattered by disposing the front scattering layer 28, the brightness of the display can be increased and the contrast can be improved. In particular, since the forward scattering layer 28 mainly uses forward scattering, light can be used efficiently for display. Further, when the haze of the front scattering layer 28 is set to 60% or more as described above, the contrast improving effect can be particularly enhanced.
[0093]
Further, as the color filter 21, the spectral characteristics of G having the highest visibility for human eyes are such that the minimum transmittance in the visible light region is 10% or more, and the average transmittance of R, G, B3 colors is 40% or more. Both a bright transmissive display and a reflective display can be realized by using a light filter having a relatively high transmittance and a light color.
[0094]
[Second Embodiment]
Next, a second embodiment according to the present invention will be described with reference to FIG. In this embodiment, the upper polarizing plate 20, the upper glass substrate 19, the color filter 21, the lower glass substrate 22, the lower polarizing plate 23, the front scattering layer 28, the prism sheets 31, 32, the light source 17, and the light guide plate shown in FIG. 16 and the reflector 29 are exactly the same as those in the first embodiment, and the structure not shown in FIG. 4 is also exactly the same as in the first embodiment. These descriptions are omitted.
[0095]
In the present embodiment, the reflective polarizing plate 24 is disposed between the front scattering plate 28 and the prism sheet 31. For this reflective polarizing plate 24, for example, what is called DBEF (trade name, manufactured by 3M) is used. The reflective polarizing plate 24 transmits a polarization component having a vibration direction in the direction of the transmission axis and reflects a polarization component having a vibration direction in a direction orthogonal to the transmission axis.
[0096]
Here, it arrange | positions so that the transmission axis of the lower polarizing plate 23 and the reflective polarizing plate 24 may become parallel. By disposing the reflective polarizing plate 24, the polarized light component having the vibration direction parallel to the paper surface of the drawing in the light emitted from the backlight 18 is reflected without being absorbed. The reflected light is reflected on the surface of the prism sheet 31, passes through the prism sheets 31 and 32, returns to the light guide plate 16, and is reflected by the reflecting plate 29. If the polarization state of the reflected light changes due to refraction or reflection by the prism sheets 31 and 32, a part of the reflected light eventually passes through the lower polarizing plate 23 and the reflective polarizing plate 24. It can be light that contributes as part of the display.
[0097]
In the present embodiment, the transmission axis of the lower polarizing plate 23 and the transmission axis of the reflective polarizing plate 24 are parallel, but the transmission axis of the lower polarizing plate 23 and the transmission axis of the reflective polarizing plate 24 are crossed in a plane, You may arrange | position so that the angle | corner (psi) made may become the range of 0 degree <(psi) <10 degree. In the case of this configuration, a part of the light transmitted through the reflective polarizing plate 24 in the transmissive display cannot pass through the transmission axis of the lower polarizing plate 23, and the light use efficiency in the transmissive display is slightly reduced. Since a part of the light transmitted through the transmission axis of the lower polarizing plate 23 is reflected by the reflective polarizing plate 24, the reflection display can be made slightly brighter.
[0098]
In the present embodiment, either the front scattering layer 28 or the reflective polarizing plate 24 may be disposed on the prism sheet 31 side.
[0099]
[Third Embodiment]
Next, a third embodiment according to the present invention will be described with reference to FIG. In this embodiment, the upper polarizing plate 20, the upper glass substrate 19, the color filter 21, the lower glass substrate 22, the lower polarizing plate 23, the front scattering layer 28, the reflective polarizing plate 24, the prism sheets 31, 32 shown in FIG. The light source 17, the light guide plate 16, and the reflection plate 29 are exactly the same as those in the second embodiment, and the structures not shown in FIG. 5 are also exactly the same as those in the second embodiment. Reference numerals are assigned and description thereof is omitted.
[0100]
In the present embodiment, as shown in FIG. 5, a quarter-wave plate 26 (first retardation plate) is disposed further on the backlight 18 side of the reflective polarizing plate 24. In particular, it is preferable to be disposed closer to the backlight 18 than the prism sheet 31. More specifically, in the present embodiment, the ¼ wavelength plate 26 is disposed closer to the backlight 18 than the prism sheets 31 and 32.
[0101]
In this embodiment, of the light emitted from the backlight 18, linearly polarized light having a vibration direction parallel to the paper surface reflected by the reflective polarizing plate 24 passes through the quarter wavelength plate 26, for example, clockwise. Converted into circularly polarized light. The clockwise circularly polarized light is reflected by the reflecting plate 29 and then returned as the counterclockwise circularly polarized light and passes through the quarter-wave plate 26. Therefore, after passing through the quarter-wave plate 26, it is perpendicular to the paper surface. It is converted into linearly polarized light having a vibration direction. Since this linearly polarized light can pass through the reflective polarizing plate 24 and the lower polarizing plate 23, it can be used for display. Thus, by reusing the reflected light from the reflective polarizing plate 24, the transmissive display can be brightened. In particular, in the case of the present embodiment, since the transmission axis of the lower polarizing plate 23 and the transmission axis of the reflective polarizing plate 24 are parallel, all light transmitted through the reflective polarizing plate 24 can be transmitted through the lower polarizing plate 23 in transmissive display. The light use efficiency in transmissive display can be maximized.
[0102]
In addition, in order to show said effect, the quarter wavelength plate 26 may be arrange | positioned rather than the prism sheet 31 at the liquid crystal cell 15 side. However, when the quarter-wave plate is disposed on the liquid crystal cell 15 side with respect to the prism sheet 31, external light is incident on the liquid crystal cell 15 and the linearly polarized light transmitted through the liquid crystal cell 15 is 1/4. Since the polarization state changes, such as circularly polarized light by the wave plate 26, the amount of reflected light reflected by the light refracting surface 31a of the prism sheet 31 may decrease, and the effects unique to the present invention may be impaired. Therefore, it is preferable that the quarter-wave plate 26 is disposed at least on the backlight 18 side with respect to the prism sheet 31.
[0103]
The quarter wave plate 26 may be a normal one made of polycarbonate or the like, but preferably has a wavelength dispersion of 1 or less. Alternatively, a half-wave plate may be further inserted on the inner surface side of the quarter-wave plate 26. The retardation value of the quarter-wave plate 26 is desirably in the range of 100 nm to 180 nm. In that case, the function as a quarter-wave plate can be achieved for all visible light.
[0104]
In the above embodiment, the first retardation plate is described as being a quarter wavelength plate. However, as the first retardation plate, for example, a half wavelength plate such as a 3/4 wavelength plate is used. Various types of retardation plates can be used. However, it is desirable to include at least a quarter wave plate.
[0105]
That is, even if the first retardation plate is not necessarily a quarter wave plate, the first retardation plate is reflected when the polarized light once reflected by the lower surface of the reflective polarizing plate is reflected by the reflecting plate on the outer surface of the illumination device and returned. Because the polarization conversion occurs in the retardation plate and some component that can be transmitted through the reflective polarizing plate is generated, the effect of reusing the reflected light is always greater than when there is no first retardation plate, apart from the magnitude of the effect. Will occur. However, as described above, when the first retardation plate is a quarter wave plate, when the polarized light once reflected by the lower surface of the reflective polarizing plate is reflected again and returned, theoretically, The polarized light can be transmitted through the 100% reflective polarizing plate, and all can contribute to the display. Therefore, the reuse efficiency can be maximized, and a brighter transmissive display can be obtained as compared with the case where other retardation plates are used.
[0106]
[Fourth Embodiment]
Next, a fourth embodiment according to the present invention will be described with reference to FIG. In this embodiment, the upper polarizing plate 20, the upper glass substrate 19, the color filter 21, the lower glass substrate 22, the lower polarizing plate 23, the reflective polarizing plate 24, the quarter wavelength plate 26, and the forward scattering layer 28 shown in FIG. The prism sheets 31, 32, the light source 17, the light guide plate 16, and the reflection plate 29 are exactly the same as in the third embodiment, and the structure not shown in FIG. 6 is also exactly the same as in the third embodiment. These same parts are denoted by the same reference numerals, and description thereof will be omitted.
[0107]
This embodiment is different from the third embodiment in that the front scattering layer 28 is disposed on the backlight 18 side with respect to the reflective polarizing plate 24. However, this embodiment is the same as the third embodiment in that the forward scattering layer 28 is disposed closer to the liquid crystal cell 15 than the prism sheet 31. In the present embodiment, only the scattering position by the forward scattering layer 28 is different, and the polarization state is not different from that in the third embodiment. Therefore, the liquid crystal display device of the present embodiment can achieve the same effect as described above that a liquid crystal display device that can ensure a certain degree of visibility even in a bright use environment can be realized.
[0108]
Further, in this embodiment, similarly to the second embodiment, a phase difference plate (¼ wavelength plate 26) may not be interposed.
[0109]
[Electronics]
Finally, an example of an electronic apparatus provided with the liquid crystal display device of each of the above embodiments will be described. FIG. 7 is a perspective view showing an example of a mobile phone. In FIG. 7, reference numeral 1000 denotes a mobile phone body, and reference numeral 1001 denotes a display unit using the liquid crystal display device.
[0110]
FIG. 8 is a perspective view showing an example of a wristwatch type electronic apparatus. In FIG. 8, reference numeral 1100 indicates a watch body, and reference numeral 1101 indicates a display unit using the liquid crystal display device.
[0111]
FIG. 9 is a perspective view showing an example of a portable information processing apparatus such as a word processor or a personal computer. In FIG. 9, reference numeral 1200 denotes an information processing apparatus, reference numeral 1202 denotes an input unit such as a keyboard, reference numeral 1204 denotes an information processing apparatus body, and reference numeral 1206 denotes a display unit using the liquid crystal display device.
[0112]
Since the electronic apparatus shown in FIGS. 7 to 9 includes the liquid crystal display device of the above-described embodiment, it is a portable type including a bright (color) liquid crystal display unit suitable for use outdoors where the sunlight is strong. An electronic device can be realized.
[0113]
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, a retardation plate (second retardation plate) may be provided between the upper polarizing plate and the upper glass substrate, or between the lower polarizing plate and the lower glass substrate. In the above embodiment, the TN liquid crystal is used. However, even when the display is colored, particularly when the STN liquid crystal is used, the coloring can be compensated by providing the retardation plate.
[0114]
[Example]
Next, the inventor actually prototyped the TFT transmissive color liquid crystal display device of the first embodiment shown in FIG. 2 and observed the display to verify the effect of the present invention. The value obtained by dividing the brightness of the white display by the brightness of the black display). The results are reported below. Here, the contrast was measured by changing the crossing angle θ between the groove direction of the prism sheet 31 (the above-described extension direction D) and the transmission axis T of the lower polarizing plate 23 as follows.
[0115]
In this liquid crystal display device, a filler-type scattering plate having a haze value of 80% and a retardation value of 10 nm or less was used as the forward scattering layer 28. The brightness of the backlight 18 is 2000 [cd / m. 2 Further, the luminance of this liquid crystal display device was 200 [cd / m 2], and the display contrast in the dark room was 200. In addition, with the groove direction of the prism sheet 31 aligned with the horizontal direction of the display screen, the contrast was measured at a place (about 100,000 lux) having the same brightness as the outdoors on a sunny day. The results are shown in Table 1 below.
[0116]
[Table 1]
[0117]
As described above, in a bright place, the display can be recognized when the crossing angle θ is −45 ° <θ <45 °, but the display cannot be recognized beyond this range. In addition, when the crossing angle θ is in the range of −30 ° <θ <30 °, a contrast sufficient for display quality was obtained.
[0118]
Next, the crossing angle θ was set to 0, and a plurality of forward scattering layers having different hazes were replaced, and the contrast was measured in the same manner as described above. The results are shown in Table 2.
[0119]
[Table 2]
[0120]
As shown in Table 2, when the haze value of the forward scattering layer was 60 or more, a contrast capable of visually recognizing the display was obtained.
[0121]
In the embodiment described above, the active matrix type liquid crystal display device is exemplified, but the present invention can be similarly applied to a passive matrix type liquid crystal display device.
[0122]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to realize a liquid crystal display device that can ensure a certain degree of visibility even in a bright usage environment such as outdoors where sunlight is strong.
[Brief description of the drawings]
FIG. 1 is a diagram showing a liquid crystal display device according to a first embodiment of the present invention, in which FIG. 1 (a) is a perspective view showing the overall configuration of the liquid crystal display device, and FIG. 1 (b) is FIG. It is an enlarged view of one pixel.
FIG. 2 is a sectional view showing the liquid crystal display device.
FIG. 3 is an enlarged cross-sectional view (a) showing an enlarged cross-sectional structure of a prism sheet used in the liquid crystal display device, and a plan view (b) showing a structure of the prism sheet and the back side thereof.
FIG. 4 is a cross-sectional view schematically showing a liquid crystal display device according to a second embodiment of the present invention.
FIG. 5 is a cross-sectional view schematically showing a liquid crystal display device according to a third embodiment of the present invention.
FIG. 6 is a cross-sectional view schematically showing a liquid crystal display device according to a fourth embodiment of the present invention.
FIG. 7 is a perspective view illustrating an example of an electronic apparatus using the liquid crystal display device of the present invention.
FIG. 8 is a perspective view illustrating another example of an electronic device.
FIG. 9 is a perspective view showing still another example of an electronic device.
FIG. 10 is a schematic explanatory diagram for explaining the display principle of the liquid crystal display device of the present invention.
FIG. 11 is a schematic explanatory diagram for explaining a display principle of a conventional liquid crystal display device.
[Explanation of symbols]
1. Liquid crystal display device
2 ... Element substrate (second substrate)
3 ... Counter substrate
15 ... Liquid crystal cell
16 ... Light guide plate
17 ... Light source
18 ... Backlight (lighting device)
20 ... Upper polarizing plate (first polarizing plate)
21 Color filter
23 ... Lower polarizing plate (second polarizing plate)
24 ... Reflective polarizing plate
26 ··· 1/4 wavelength plate (first retardation plate)
27 ... Liquid crystal layer
28: Forward scattering layer
29 ... reflector
31, 32 ... Prism sheet
31a, 32a ... Photorefractive surface
D: Extension direction of the light refracting surface of the prism sheet
T: Transmission axis of lower polarizing plate

Claims (23)

  1. A lighting device having a liquid crystal cell having a liquid crystal sandwiched between a first substrate and a second substrate disposed opposite to each other, a light source and a light guide plate, and disposed on the outer surface side of the second substrate of the liquid crystal cell A liquid crystal display device comprising:
    A first polarizing plate is provided on the outer surface side of the first substrate, and a second polarizing plate, a light scattering layer, and an inclined surface are provided from the second substrate side between the second substrate and the lighting device. A first prism sheet having a light refracting surface and a second prism sheet having an inclined light refracting surface are provided in this order, and the light is reflected on the surface opposite to the side on which the liquid crystal cell is disposed. A board is provided,
    An intersection line with respect to a virtual plane orthogonal to the optical axis in the light refraction surface of the first prism sheet is defined as a first intersection line, and a virtual plane orthogonal to the optical axis in the light refraction surface of the second prism sheet is defined. When the crossing line is the second crossing line, the crossing angle θ between the first crossing line and the transmission axis of the second polarizing plate is set within a range of −45 ° <θ <45 °. The liquid crystal display device , wherein the first intersection line and the second intersection line are orthogonal to each other .
  2.   2. The liquid crystal display device according to claim 1, wherein the intersection angle θ is set in a range of −30 ° ≦ θ ≦ 30 °.
  3.   The liquid crystal display device according to claim 2, wherein the light refraction surface is provided on a surface of the first prism sheet on the liquid crystal cell side.
  4.   4. The first prism sheet according to claim 1, wherein the first prism sheet is formed in a stripe shape in which a plurality of the light refracting surfaces extend in a predetermined direction, and is inclined in a direction orthogonal to the predetermined direction. The liquid crystal display device according to any one of the above.
  5.   5. The liquid crystal display device according to claim 4, wherein the first prism sheet is disposed such that the light refraction surface extends left and right during use.
  6.   6. The liquid crystal display device according to claim 1, wherein the first prism sheet has a function of condensing light emitted from the illumination device toward an observation side.
  7. The liquid crystal display device according to any one of claims 1 to 6, wherein the light scattering layer is forward scattering layer mainly produce forward scattering.
  8. The liquid crystal display device according to claim 7 , wherein the forward scattering layer has a haze of 60% or more.
  9. The liquid crystal display device according to any one of claims 1 to 8, wherein the retardation value of the light scattering layer is 10nm or less.
  10. The liquid crystal display device according to any one of claims 1 to 9, characterized in that the reflective polarizer is disposed between the second polarizing plate and the lighting device.
  11. The liquid crystal display device according to claim 10 , wherein a first retardation plate is disposed on a side opposite to the side on which the liquid crystal cell is disposed with respect to the reflective polarizing plate.
  12. The liquid crystal display device according to claim 11 , wherein the first retardation plate includes at least a quarter-wave plate.
  13. The liquid crystal display device according to claim 11 , wherein the first retardation plate includes a quarter-wave plate and a half-wave plate.
  14. The liquid crystal display device according to claim 11, wherein a retardation value of the first retardation plate is in a range of 100 nm to 180 nm.
  15. The liquid crystal display device according to claim 11, wherein the wavelength dispersion of the first retardation plate is 1 or less.
  16. The liquid crystal display device according to any one of claims 11 to 15 wherein the first phase difference plate is characterized in that it is arranged on the lighting device side than the first prism sheet.
  17. The liquid crystal display device according to any one of claims 1 to 16, characterized in that the reflecting surface of the reflector is a mirror surface state.
  18. The second retardation plate is provided between the first polarizing plate and the first substrate or between the second polarizing plate and the second substrate. The liquid crystal display device according to claim 1 .
  19. The liquid crystal display device according to any one of claims 1 to 18 transmission axis of the reflective polarizer and the transmission axis of the second polarizing plate is equal to or parallel.
  20. The transmission axis of the second polarizing plate and the transmission axis of the reflective polarizing plate intersect in a plane, and an angle ψ formed by the transmission axis is in a range of 0 ° <ψ <10 °. The liquid crystal display device according to claim 1 .
  21. The liquid crystal display device according to any one of claims 1 to 10 , wherein the display mode is a normally white mode.
  22. The liquid crystal display device according to any one of claims 1 to 21 wherein the first polarizing plate and the second polarizing plate is characterized in that it is a polarizing plate absorption type.
  23. An electronic apparatus comprising the liquid crystal display device according to any one of claims 1 to 22 .
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