JP2024068926A - Liquid crystal display device - Google Patents

Abstract

To provide a liquid crystal display device capable of achieving both the color reproducibility of transmissive display and the brightness of reflective display.SOLUTION: A liquid crystal display device includes: a backlight 3 which emits light; and a liquid crystal panel 2 which is arranged so as to receive the light from the backlight 3 and has a color filter with a red filter, a green filter, and a blue filter. The backlight 3 is configured so that the spectral intensity has peaks in red, green, and blue, respectively. If information about brightness in an XYZ color system is a Y value, the Y value of white display using the red filter, the green filter and the blue filter is 33 or more. The liquid crystal panel 2 is capable of transmissive display using the light of the backlight 3 and reflective display using light obtained by reflecting the external light by the backlight 3.SELECTED DRAWING: Figure 3

Description

The present invention relates to a liquid crystal display device.

Transmission/reflection type LCD devices have been developed that perform transmissive display using illumination light from a backlight arranged behind the LCD panel in dark places, and perform reflective display using external light incident from the front of the LCD panel in bright places. Some transmission/reflection type LCD devices divide each pixel into a transmission display area and a reflection display area, and provide a reflective film in the reflective display area of the pixel (Patent Document 1). Others enable both transmission display using light emitted by a backlight and reflective display using external light reflected on the backlight, without dividing each pixel into a transmission display area and a reflection display (Patent Document 2).

When a pixel is divided into a transmissive display region and a reflective display region, there is a trade-off between the transmissive display and the reflective display. If the transmissive display region is widened and the transmittance is increased, the reflectance decreases, and if the reflective display region is widened and the reflectance is increased, the transmittance decreases, so it is difficult to obtain good displays in both the transmissive display and the reflective display.

If the pixels are not divided into transmissive and reflective display regions, the same color filters are used for both transmissive and reflective displays, and increasing the color purity of the color filters increases the color reproducibility of the transmissive display, but the reflective display becomes darker (the reflectance drops significantly). Also, decreasing the color purity of the color filters increases the reflectance, but the color reproducibility of the transmissive display drops significantly. Therefore, it is difficult to achieve both the color reproducibility of the transmissive display and the brightness of the reflective display. Also, in the reflective display, external light is reflected on the backlight, and the light seen is that, but it is difficult to efficiently reflect external light on the backlight, resulting in low reflectance.

JP 2004-4494 A JP 2011-100051 A

The present invention provides a liquid crystal display device that can achieve both color reproducibility in transmissive display and brightness in reflective display.

According to a first aspect of the present invention, there is provided a liquid crystal display device comprising a backlight that emits light, and a liquid crystal panel that is arranged to receive light from the backlight and includes a color filter having a red filter, a green filter, and a blue filter, the backlight is configured so that the spectral luminance has peaks in red, green, and blue, respectively, and when information regarding brightness in the XYZ color system is taken as a Y value, the Y value of white display using the red filter, the green filter, and the blue filter is 33 or more, and the liquid crystal panel is capable of a transmissive display using the light from the backlight and a reflective display using external light reflected by the backlight.

According to a second aspect of the present invention, there is provided a liquid crystal display device according to the first aspect, further comprising a polarizing plate, a diffusing member, and a reflective polarizing plate arranged in this order on the backlight side of the liquid crystal panel, and the transmission axis of the reflective polarizing plate is parallel to the transmission axis of the polarizing plate.

According to a third aspect of the present invention, there is provided a liquid crystal display device according to the first aspect, in which the Y value of the red filter is 21 or more, the Y value of the green filter is 58 or more, and the Y value of the blue filter is 15 or more.

According to a fourth aspect of the present invention, there is provided a liquid crystal display device according to the first aspect, in which the x value in the whiteness (x, y) of the color filter is set in the range of 0.290 to 0.320, and the y value is set in the range of 0.280 to 0.350.

According to a fifth aspect of the present invention, there is provided a liquid crystal display device according to the second aspect, in which the haze value of the diffusing member is 40% or more and 90% or less.

According to a sixth aspect of the present invention, there is provided a liquid crystal display device according to the first aspect, in which the light source of the backlight includes a blue LED, a green phosphor, and a red phosphor.

According to a seventh aspect of the present invention, there is provided a liquid crystal display device according to the first aspect, in which the light source of the backlight includes a red LED, a green LED, and a blue LED.

According to an eighth aspect of the present invention, there is provided a liquid crystal display device according to the first aspect, in which the light source of the backlight includes a blue LED, the backlight is arranged to transmit blue light from the blue LED, and includes a quantum dot sheet that converts the blue light into green light and red light.

According to a ninth aspect of the present invention, there is provided a liquid crystal display device according to the first aspect, in which the pixels of the liquid crystal panel are not divided into areas for transmissive display and areas for reflective display.

The present invention provides a liquid crystal display device that can achieve both color reproducibility in transmissive display and brightness in reflective display.

FIG. 1 is a block diagram of a liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is a circuit diagram of the liquid crystal panel shown in FIG. FIG. 3 is a cross-sectional view of a liquid crystal panel. FIG. 4 is a plan view of the liquid crystal panel. FIG. 5 is a perspective view of the backlight according to the first embodiment. FIG. 6 is a cross-sectional view of the light-emitting element according to the first embodiment. FIG. 7 is a cross-sectional view of a light-emitting element according to a second embodiment. FIG. 8 is a perspective view of a backlight according to the third embodiment. FIG. 9 is a cross-sectional view of a light-emitting element according to the third embodiment. FIG. 10 is a diagram for explaining the display operation of the liquid crystal display device. FIG. 11 is a diagram for explaining the light dispersion of the backlight according to the first embodiment. FIG. 12 is a diagram illustrating the light dispersion of the backlight according to the second embodiment. FIG. 13 is a diagram illustrating the light distribution of the backlight according to the third embodiment. FIG. 14 is a diagram for explaining the dispersion of light by a color filter. FIG. 15 is a diagram illustrating the chromaticity of a color filter. FIG. 16 is a diagram illustrating the relationship between the Y value and the reflectance in white display. FIG. 17 is a diagram illustrating color filters and whiteness in a transmissive display. FIG. 18 is a diagram illustrating the characteristics of the diffusing member. FIG. 19 is a diagram illustrating the reflection and transmission characteristics of a liquid crystal display device. FIG. 20 is a cross-sectional view of a liquid crystal panel according to a second embodiment of the present invention. FIG. 21 is a cross-sectional view of a liquid crystal panel according to a third embodiment of the present invention. FIG. 22 is a cross-sectional view of a liquid crystal panel according to a fourth embodiment of the present invention. FIG. 23 is a perspective view of the backlight shown in FIG.

The following describes the embodiments with reference to the drawings. However, the drawings are schematic or conceptual, and the dimensions and ratios of each drawing are not necessarily the same as those in reality. Even when the same parts are shown in different drawings, the dimensional relationships and ratios of each may be different. In particular, the following embodiments are examples of devices and methods for embodying the technical idea of the present invention, and the shape, structure, arrangement, etc. of the components do not specify the technical idea of the present invention. In the following description, elements having the same function and configuration are given the same reference numerals, and duplicate descriptions are omitted.

[1] First embodiment [1-1] Overall configuration of liquid crystal display device 1 The liquid crystal display device 1 according to this embodiment is a transmissive/reflective liquid crystal display device (also referred to as a semi-transmissive liquid crystal display device) capable of reflective display using external light and transmissive display using a backlight.

Figure 1 is a block diagram of a liquid crystal display device 1 according to a first embodiment of the present invention. The liquid crystal display device 1 includes a liquid crystal panel 2, a backlight (also called an illumination device) 3, a scanning line driving circuit 4, a signal line driving circuit 5, a common electrode driving circuit 6, a voltage generating circuit 7, and a control circuit 8.

The liquid crystal panel 2 comprises a number of pixels PX arranged in a matrix. The liquid crystal panel 2 is provided with a number of scanning lines GL1 to GLm each extending in the row direction, and a number of signal lines SL1 to SLn each extending in the column direction. "m" and "n" are each an integer greater than or equal to 2. Pixels PX are arranged in the intersection regions of the scanning lines GL and the signal lines SL.

The backlight 3 is a surface light source that irradiates light onto the back surface of the liquid crystal panel 2. For example, a direct-type or side-light type (edge-light type) LED backlight is used as the backlight 3. The backlight 3 emits white light. The specific configuration of the backlight 3 will be described later.

The scanning line drive circuit 4 is connected to the multiple scanning lines GL. Based on a control signal sent from the control circuit 8, the scanning line drive circuit 4 sends a scanning signal to the liquid crystal panel 2 to turn on/off the switching element included in the pixel PX. The scanning line drive circuit 4 includes a shift register circuit for sequentially scanning the multiple scanning lines GL. The shift register circuit shifts the scanning signal sequentially to the multiple scanning lines for each frame period.

The signal line drive circuit 5 is electrically connected to the multiple signal lines SL. The signal line drive circuit 5 receives control signals and display data from the control circuit 8. Based on the control signals, the signal line drive circuit 5 sends multiple grayscale signals (drive voltages) corresponding to the display data to the liquid crystal panel 2.

The common electrode driving circuit 6 generates a common voltage Vcom and supplies it to the common electrode in the liquid crystal panel 2. The voltage generating circuit 7 generates various voltages necessary for the operation of the liquid crystal display device 1 and supplies these voltages to the corresponding circuits.

The control circuit 8 controls the overall operation of the liquid crystal display device 1. The control circuit 8 receives image data DT and a control signal CNT from the outside. The control circuit 8 generates various control signals based on the image data DT and sends these control signals to the corresponding circuits.

Figure 2 is a circuit diagram of the liquid crystal panel 2 shown in Figure 1. The X direction in Figure 2 is the row direction in which the scanning lines extend, and the Y direction is the column direction in which the signal lines extend.

The liquid crystal panel 2 is provided with a number of scanning lines GL1 to GLm and a number of signal lines SL1 to SLn.

The pixel PX comprises a switching element (active element) 9, a liquid crystal capacitance (liquid crystal element) Clc, and a storage capacitance Cs. For example, a TFT (Thin Film Transistor) is used as the switching element 9, and an n-channel TFT is also used. Note that the source and drain of a transistor change depending on the direction of the current flowing through the transistor, but the following explanation will be given as an example of the connection state of the transistor. However, it goes without saying that the source and drain are not fixed as their names suggest.

The drain of the TFT 9 is connected to the signal line SL, its gate is connected to the scanning line GL, and its source is connected to one electrode of the liquid crystal capacitance Clc. The liquid crystal capacitance Clc as a liquid crystal element is composed of a pixel electrode, a common electrode, and a liquid crystal layer. A common voltage Vcom is applied to the other electrode of the liquid crystal capacitance Clc by the common electrode drive circuit 6.

One electrode of the storage capacitance Cs is connected to one electrode of the liquid crystal capacitance Clc. A common voltage Vcom is applied to the other electrode of the storage capacitance Cs by the common electrode drive circuit 6. The storage capacitance Cs has the function of suppressing potential fluctuations occurring in the pixel electrode and holding the drive voltage applied to the pixel electrode until the drive voltage corresponding to the next signal is applied. The storage capacitance Cs is composed of a pixel electrode, a storage capacitance line, and an insulating layer sandwiched between them. A storage capacitance voltage different from the common voltage Vcom may be applied to the other electrode (storage capacitance line) of the storage capacitance Cs.

[1-2] Configuration of the Liquid Crystal Panel 2 Next, we will explain the configuration of the liquid crystal panel 2. The liquid crystal panel 2 according to this embodiment is a FFS (fringe field switching) type liquid crystal display device. FFS is a method of switching homogeneously oriented liquid crystals by a fringe electric field.

Figure 3 is a cross-sectional view of the liquid crystal panel 2. Figure 3 is a cross-sectional view corresponding to three pixels PX. Figure 4 is a plan view of the liquid crystal panel 2. Figure 4 is a plan view corresponding to two pixels PX.

A backlight 3 is disposed on the opposite side of the liquid crystal panel 2 from the display screen at a predetermined distance from the liquid crystal panel 2. The backlight 3 includes light-emitting elements 30.

The liquid crystal panel 2 comprises a TFT substrate 10 on which switching elements and pixel electrodes are formed, a color filter substrate (referred to as a CF substrate) 11 arranged opposite the TFT substrate 10 and on which color filters are formed, and a liquid crystal layer 12 sandwiched and filled between the TFT substrate 10 and the CF substrate 11. Each of the TFT substrate 10 and the CF substrate 11 is composed of a transparent and insulating substrate (for example, a glass substrate or a plastic substrate).

The liquid crystal layer 12 is enclosed within a display area surrounded by the TFT substrate 10, the CF substrate 11, and a sealant (not shown). The sealant is made of, for example, an ultraviolet curable resin, a thermosetting resin, or a combined ultraviolet and heat curable resin, and is applied to the TFT substrate 10 or the CF substrate 11 during the manufacturing process and then cured by ultraviolet irradiation, heating, or the like.

The liquid crystal material constituting the liquid crystal layer 12 has its optical characteristics changed by controlling the orientation of the liquid crystal molecules in response to the applied electric field. In this embodiment, a positive type (P type) nematic liquid crystal having positive dielectric anisotropy is used as the liquid crystal layer 12. In the initial state, the liquid crystal layer 12 is horizontally oriented (homogeneous orientation). The long axes of the liquid crystal molecules are horizontally oriented and aligned in one direction. When no voltage (no electric field) is applied, the liquid crystal molecules are oriented almost horizontally with respect to the main surface of the substrate. When a voltage (electric field) is applied, the long axes of the liquid crystal molecules rotate toward the electric field direction. The liquid crystal layer 12 is not limited to the positive type, and a negative type (N type) may also be used.

First, the configuration on the TFT substrate 10 side will be described. On the liquid crystal layer 12 side of the TFT substrate 10, a TFT 9 is provided for each pixel. FIG. 3 shows the TFT 9 diagrammatically. The TFT 9 includes a gate electrode that functions as a scanning line, a gate insulating film provided on the gate electrode, a semiconductor layer provided on the gate insulating film, and a source electrode and a drain electrode provided spaced apart from each other on the semiconductor layer. For example, the TFT 9 is disposed at the end of the pixel in the Y direction.

A pixel electrode 13 is provided on the TFT substrate 10. The pixel electrode 13 extends in the Y direction and is provided over almost the entire pixel region. The pixel electrode 13 is electrically connected to the source electrode of the TFT 9. Although not shown, a storage capacitance electrode is provided below the pixel electrode 13, with an insulating layer interposed between them. The storage capacitance electrode is provided in common to multiple pixels aligned in the X direction.

An insulating layer 14 is provided on the pixel electrode 13.

A common electrode 15 is provided on the insulating layer 14. The common electrode 15 is provided in common to all pixels. The common electrode 15 has a plurality of slits 16 for each pixel. In this embodiment, an example in which four slits 16 are provided for each pixel is shown. The number of slits 16 may be one or a number other than four. The plurality of slits 16 are arranged above the pixel electrode 13 so as to overlap the pixel electrode 13 in a plan view. The plurality of slits 16 are arranged at equal intervals. The slits 16 extend in the Y direction, like the pixel electrode 13, and have a rectangular shape. The slits 16 may be configured in a straight line or in a dogleg shape bent at the center of the pixel. The length of the slits 16 in the Y direction is set to be slightly shorter than the length of the pixel electrode 13 in the Y direction.

An alignment film 17 that controls the alignment of the liquid crystal layer 12 is provided on the common electrode 15. The alignment film 17 is rubbed so that the liquid crystal molecules are aligned horizontally during the initial alignment of the liquid crystal layer 12.

Next, the configuration of the CF substrate 11 side will be described. A color filter is provided on the liquid crystal layer 12 side of the CF substrate 11. The color filter includes a red filter 21R, a green filter 21G, and a blue filter 21B. A typical color filter is composed of the three primary colors of light, red (R), green (G), and blue (B). A set of three adjacent colors R, G, and B is a display unit (pixel), and a single color portion of R, G, or B in one pixel is the smallest driving unit called a subpixel. A TFT 9 and a pixel electrode 13 are provided for each subpixel. In the description of this specification, a subpixel is referred to as a pixel unless it is particularly necessary to distinguish between pixels and subpixels. In this specification, when there is no particular need to distinguish between the red filter 21R, the green filter 21G, and the blue filter 21B, they are referred to as color filters.

A light-shielding layer (also called a black matrix or black mask) 22 is provided on the liquid crystal layer 12 side of the CF substrate 11. The black matrix 22 is disposed at the boundaries of the pixels. The black matrix 22 is formed, for example, in a mesh shape so as to surround the pixels. The black matrix 22 has the function of blocking unnecessary light generated at the boundaries of the pixels and improving contrast.

An overcoat layer 23 is provided on the color filters and the black matrix 22. The overcoat layer 23 has the function of flattening the upper surfaces of the color filters and the black matrix 22. The overcoat layer 23 is made of, for example, a transparent resin.

An alignment film 24 that controls the alignment of the liquid crystal layer 12 is provided on the overcoat layer 23. The alignment film 24 is rubbed so as to align the liquid crystal molecules horizontally during the initial alignment of the liquid crystal layer 12. The alignment film 17 and the alignment film 24 are disposed opposite each other so that the directions of the rubbing treatment are antiparallel.

On the side of the TFT substrate 10 opposite the liquid crystal layer 12, a polarizing plate 18, a diffusing member 19, and a reflective polarizing plate 20 are laminated in this order.

The polarizing plate (also called a linear polarizer) 18 has a transmission axis and an absorption axis that are perpendicular to each other in a plane perpendicular to the direction of light propagation. The polarizing plate 18 transmits linearly polarized light (linearly polarized light components) that has a vibration plane parallel to the transmission axis among light that has a vibration plane in a random direction, and absorbs linearly polarized light (linearly polarized light components) that has a vibration plane parallel to the absorption axis.

The diffusion member 19 has the function of diffusing (scattering) the transmitted light in random directions to make the brightness of the transmitted light uniform. The diffusion member 19 is composed of a diffusion adhesive, a diffusion film, a diffusion plate, or the like. By using the diffusion member 19, the viewing angle can be improved. The haze value of the diffusion member 19 is set to be 40% or more and 90% or less.

The reflective polarizer 20 has a transmission axis and a reflection axis that are orthogonal to each other in the plane. The reflective polarizer 20 transmits linearly polarized light (linearly polarized light components) having a vibration plane parallel to the transmission axis among light having a vibration plane in a random direction, and reflects linearly polarized light (linearly polarized light components) having a vibration plane parallel to the reflection axis. The transmission axis of the reflective polarizer 20 is set parallel to the transmission axis of the polarizer 18. The reflective polarizer 20 has the function of reflecting external light in reflective display.

A transparent conductive layer 25 and a polarizing plate 26 are laminated in this order on the side of the CF substrate 11 opposite the liquid crystal layer 12.

The transparent conductive layer 25 is provided on the entire surface of the CF substrate 11. The transparent conductive layer 25 is connected to the ground GND and has the function of discharging unnecessary charges, including static electricity.

The polarizing plate 26 has a transmission axis and an absorption axis that are perpendicular to each other in a plane perpendicular to the direction of light propagation. The polarizing plate 26 transmits linearly polarized light (linearly polarized light components) that has a vibration plane parallel to the transmission axis among light that has a vibration plane in a random direction, and absorbs linearly polarized light (linearly polarized light components) that has a vibration plane parallel to the absorption axis.

The relationship between the transmission axes of the polarizing plate 18 and the polarizing plate 26 is appropriately set according to the display mode (normally black mode or normally white mode) of the liquid crystal display device 1. The polarizing plate 18 and the polarizing plate 26 are arranged, for example, so that their transmission axes are perpendicular to each other, that is, in a crossed Nicol state.

(Examples of materials)
The gate electrode (scanning line) GL, the source electrode, the drain electrode, and the signal line SL are made of, for example, aluminum (Al), molybdenum (Mo), chromium (Cr), and tungsten (W), or an alloy containing one or more of these.

The pixel electrode 13, the common electrode 15, the transparent conductive layer 25, and the storage capacitance electrode are made of transparent electrodes, for example, ITO (indium tin oxide).

A transparent insulating material, such as silicon nitride (SiN), is used for the gate insulating film and the insulating layer 14.

Note that an FFS mode liquid crystal display device is not limited to the configuration shown in FIG. 3, and may be configured such that the common electrode is disposed on the lower side and the pixel electrode is disposed on the upper side, the common electrode is configured in a planar shape, and the pixel electrode has multiple slits.

[1-3] Configuration of the backlight 3 Next, the configuration of the backlight 3 will be described. In this embodiment, the backlight 3 is configured as a high color rendering backlight. The property that a light source has on how colors appear is called color rendering, and the closer the colors appear when viewed under natural light (sunlight), the better the color rendering of the light source is. Three examples (first to third examples) of high color rendering backlights will be described below.

(First embodiment)
In the first embodiment, a light-emitting element (light source) is configured using a blue LED (light-emitting diode), a green phosphor, and a red phosphor.

Figure 5 is a perspective view of the backlight 3 according to the first embodiment. The Z direction in Figure 5 is a direction perpendicular to the XY plane. In Figure 5, multiple components are shown spaced apart, but in reality, multiple components are stacked.

The backlight 3 includes a plurality of light-emitting elements 30, a reflective sheet 31, a light guide plate 32, a diffusion sheet 33, a first prism sheet 34, and a second prism sheet 35. The reflective sheet 31, the light guide plate 32, the diffusion sheet 33, the first prism sheet 34, and the second prism sheet 35 are laminated in this order.

Each of the multiple light-emitting elements 30 emits white light. The light-emitting elements 30 are composed of, for example, LEDs. In this embodiment, three light-emitting elements 30 are shown as an example, but the number of light-emitting elements 30 can be set as desired. The specific configuration of the light-emitting elements 30 will be described later. The multiple light-emitting elements 30 are arranged to face one side of the light guide plate 32, and emit light toward the side of the light guide plate 32.

The light guide plate 32 is an optical member for uniformly irradiating the light emitted from the light emitting element 30 onto the surface of the liquid crystal panel 2. The light guide plate 32 is made of a light-transmitting material such as acrylic resin or polycarbonate.

The reflective sheet 31 reflects the light leaking from the bottom of the light guide plate 32 back towards the light guide plate 32.

The diffusion sheet 33 has the function of making the brightness of the transmitted light uniform by diffusing (scattering) the transmitted light in random directions.

The first prism sheet 34 and the second prism sheet 35 have the function of concentrating light in the front direction (the direction toward the liquid crystal panel 2) and improving the brightness in the front direction. The first prism sheet 34 has a plurality of prisms each extending in the X direction and aligned in the Y direction. The second prism sheet 35 has a plurality of prisms each extending in the Y direction and aligned in the X direction. Each of the plurality of prisms is formed of a triangular prism. The first prism sheet 34 and the second prism sheet 35 are arranged so that the extension directions of the prisms are perpendicular to each other.

Figure 6 is a cross-sectional view of the light-emitting element 30 according to the first embodiment.

The light-emitting element 30 comprises a substrate 40, a blue LED chip 41B, a green phosphor 42, a red phosphor 43, a reflector 44, and a sealing resin 45.

The substrate 40 comprises an insulating substrate made of resin or the like, and a wiring layer provided on the upper surface and/or inside the insulating substrate. The substrate 40 may be a metal-based substrate with excellent heat dissipation properties. The metal-based substrate is formed by laminating a metal substrate, an insulating layer, and a wiring layer in this order.

A blue LED chip 41B is mounted in the center of the substrate 40. The blue LED chip 41B emits blue light.

A reflector 44 is provided on the periphery of the substrate 40 so as to surround the blue LED chip 41B. The reflector 44 has the function of reflecting light.

A green phosphor 42 and a red phosphor 43 are arranged above the blue LED chip 41B. The blue LED chip 41B, the green phosphor 42, and the red phosphor 43 are sealed with a sealing resin 45. The green phosphor 42 converts blue light into green light. The red phosphor 43 converts blue light into red light.

Second Example
In the second embodiment, a red LED, a green LED, and a blue LED are used to configure the light emitting element. The configuration of the backlight 3 other than the light emitting element 30 is the same as that shown in Fig. 5. Fig. 7 is a cross-sectional view of the light emitting element 30 according to the second embodiment.

The light-emitting element 30 includes a substrate 40, a red LED chip 41R, a green LED chip 41G, a blue LED chip 41B, a reflector 44, and a sealing resin 45.

A red LED chip 41R, a green LED chip 41G, and a blue LED chip 41B are mounted in the center of the substrate 40. The red LED chip 41R emits red light. The green LED chip 41G emits green light. The blue LED chip 41B emits blue light. The red LED chip 41R, the green LED chip 41G, and the blue LED chip 41B are sealed with sealing resin 45.

(Third Example)
In the third embodiment, a backlight is configured using a blue LED and a quantum dot sheet. Fig. 8 is a perspective view of a backlight 3 according to the third embodiment.

The backlight 3 comprises a plurality of light-emitting elements 30, a reflective sheet 31, a light guide plate 32, a quantum dot sheet 36, a first prism sheet 34, and a second prism sheet 35. The reflective sheet 31, the light guide plate 32, the quantum dot sheet 36, the first prism sheet 34, and the second prism sheet 35 are laminated in this order. The configurations of the reflective sheet 31, the light guide plate 32, the first prism sheet 34, and the second prism sheet 35 are the same as those in the first embodiment.

The multiple light-emitting elements 30 emit blue light.

The quantum dot sheet 36 has the function of converting blue light into red light and green light. The quantum dot sheet 36 is configured to include a plurality of quantum dots. The quantum dots are made of semiconductors. The quantum dot sheet 36 is configured to include a first quantum dot (e.g., with a particle size of about 7 nm) capable of converting blue light into red light, and a second quantum dot (e.g., with a particle size of about 3 nm) capable of converting blue light into green light.

Figure 9 is a cross-sectional view of a light-emitting element 30 according to the third embodiment. The light-emitting element 30 includes a substrate 40, a blue LED chip 41B, a reflector 44, and a sealing resin 45.

A blue LED chip 41B is mounted in the center of the substrate 40. The blue LED chip 41B emits blue light. The blue LED chip 41B is sealed with sealing resin 45.

[1-4] Operation Next, the operation of the liquid crystal display device 1 configured as above will be described.

First, we will explain the display operation of the liquid crystal display device 1. Figure 10 is a diagram explaining the display operation of the liquid crystal display device 1.

The off state is a state in which no electric field is applied to the liquid crystal layer 12, a common voltage Vcom is applied to the common electrode 15, and the same common voltage Vcom as the common electrode 15 is applied to the pixel electrode 13. The on state is a state in which an electric field is applied to the liquid crystal layer 12, a common voltage Vcom is applied to the common electrode 15, and a positive voltage different from the common voltage Vcom is applied to the pixel electrode 13. In practice, inversion driving (AC driving) is performed to invert the polarity of the electric field between the pixel electrode 13 and the common electrode 15 at a predetermined period. By performing inversion driving, it is possible to suppress deterioration of the liquid crystal. The period of the inversion driving can be set arbitrarily.

In the off state, the liquid crystal molecules are aligned in an initial state, i.e., the long axes of the liquid crystal molecules are horizontal and point, for example, in the Y direction. The Y direction is the same as the rubbing direction of the alignment film. In the off state, the liquid crystal display device 1 displays, for example, black.

In the on state, an electric field corresponding to the potential difference between the common electrode 15 and the pixel electrode 13 is applied to the liquid crystal layer 12. In a plan view, the liquid crystal molecules rotate in a direction oblique to the Y direction. This allows the liquid crystal display device 1 to control the amount of transmission of incident light. In other words, the transmittance of the liquid crystal display device 1 can be changed. In the on state, the liquid crystal display device 1 performs, for example, color display.

The liquid crystal display device 1 is capable of performing transmissive display and reflective display. In transmissive display, illumination light is emitted from the backlight 3. The illumination light from the backlight 3 passes through the liquid crystal panel 2 and is visible to the observer. The display light in transmissive display is called transmissive display light.

In reflective display, external light including sunlight enters the liquid crystal panel 2 from the display surface side of the liquid crystal panel 2. The external light is reflected by the components of the backlight 3 (reflective sheet 31, light guide plate 32, diffusion sheet 33, first prism sheet 34, and second prism sheet 35). The reflected light reflected by the backlight 3 enters the liquid crystal panel 2. The external light is also reflected by the reflective polarizer 20 of the liquid crystal panel 2. The reflected light passes through the liquid crystal panel 2 and is visually recognized by the observer. The display light in reflective display is called reflective display light. In reflective display, the backlight 3 may be off or on.

(Characteristics of Backlight 3)
Next, the characteristics of the backlight 3 will be described.

Figure 11 is a diagram explaining the spectrum (BL spectrum) of the backlight 3 according to the first embodiment. The horizontal axis of Figure 11 represents wavelength (nm), and the vertical axis represents relative spectral luminance. Generally, visible light is recognized as blue in the wavelength range of 435 to 480 nm, green in the wavelength range of 500 to 560 nm, and red in the wavelength range of 610 to 750 nm.

Figure 11 also shows the spectrum of the backlight in the comparative example. The comparative example is a commonly used backlight. The backlight in the comparative example is a backlight that uses a so-called pseudo-white LED. The pseudo-white LED is composed of a blue LED and a yellow phosphor. The spectral luminance of the backlight in the comparative example has a first peak at a wavelength of about 450 nm and a second peak at a wavelength of about 560 nm.

In the first embodiment, the spectral luminance of the backlight 3 has a first peak at a wavelength of about 450 nm, a second peak at a wavelength of about 530 nm, and a third peak at a wavelength of about 630 nm. The backlight 3 according to the first embodiment can generate white light by mixing red light, green light, and blue light. The backlight 3 according to the first embodiment has high color rendering properties.

Figure 12 is a diagram illustrating the light splitting of the backlight 3 according to the second embodiment. In the second embodiment, the spectral luminance of the backlight 3 has a first peak near a wavelength of 460 nm, a second peak near a wavelength of 520 nm, and a third peak near a wavelength of 640 nm. The backlight 3 according to the second embodiment can generate white light by mixing red light, green light, and blue light. The backlight 3 according to the second embodiment has high color rendering properties.

Figure 13 is a diagram explaining the light splitting of the backlight 3 according to the third embodiment. In the third embodiment, the spectral luminance of the backlight 3 has a first peak near a wavelength of 450 nm, a second peak near a wavelength of 530 nm, and a third peak near a wavelength of 630 nm. The backlight 3 according to the third embodiment can generate white light by mixing red light, green light, and blue light. The backlight 3 according to the third embodiment has high color rendering properties.

(Color filter characteristics)
Next, the characteristics of the color filters will be described.

Figure 14 is a diagram explaining the spectrum of a color filter (CF spectrum). The horizontal axis of Figure 14 represents wavelength (nm), and the vertical axis represents transmittance (%). In Figure 14, "R: embodiment" represents the spectrum of the red filter 21R according to the embodiment, "G: embodiment" represents the spectrum of the green filter 21G according to the embodiment, and "B: embodiment" represents the spectrum of the blue filter 21B according to the embodiment.

Figure 15 is a diagram explaining the chromaticity of color filters (CF chromaticity). In Figure 15, "red" represents the chromaticity of red filter 21R, "green" represents the chromaticity of green filter 21G, and "blue" represents the chromaticity of blue filter 21B. "White" in Figure 15 represents the chromaticity of a white display generated by mixing red filter 21R, green filter 21G, and blue filter 21B. The measurement light source used is C light source (a standard light source defined by the CIE). For the sake of convenience of measurement, the chromaticity is a value including ITO (film thickness 1200 Å) as a transparent electrode.

Figures 14 and 15 also show the spectrum of a color filter in a comparative example. The comparative example is a commonly used color filter.

In FIG. 15, "x" and "y" are values on the xy chromaticity diagram. The xy chromaticity diagram represents color (hue and saturation) in plane coordinates of (x, y). The xy chromaticity diagram does not include information on lightness. "Y" is the Y value of the XYZ color system. The Y value of the XYZ color system is one of the tristimulus values X, Y, and Z, and is information related to lightness. The XYZ color system is a system for representing color using the tristimulus values X, Y, and Z. The three elements Yxy can represent information on lightness, hue, and saturation. Hue, saturation, and lightness are called the three attributes of color.

In Figure 15, the color filters are evaluated using the NTSC ratio. The NTSC ratio (unit: %) is the area ratio obtained by comparing the triangle obtained by connecting the chromaticities of the single colors red, green, and blue of the image display device with the triangle connecting the three standard primary colors red (0.67, 0.33), green (0.21, 0.71), and blue (0.14, 0.08) defined by the National Television Standards Committee in terms of chromaticity (x, y) of the XYZ color system. This area ratio is defined as the color reproduction range, and the higher the ratio, the higher the color reproduction is determined to be.

As shown in FIG. 14, the peak transmittance of the blue filter 21B is 85% or more, which is higher than that of the comparative example. The peak transmittance of the green filter 21G is 85% or more, which is higher than that of the comparative example. The peak transmittance of the red filter 21R is 85% or more, which is equivalent to that of the comparative example.

The Y value of the red filter 21R is called the "R-Y value", the Y value of the green filter 21G is called the "G-Y value", the Y value of the blue filter 21B is called the "B-Y value", and the Y value of white display is called the "W-Y value". The W-Y value is calculated as the average of the R-Y value, the G-Y value, and the B-Y value. In this embodiment, the W-Y value is set to 33 or more. However, if the W-Y value is 44 or more, the effect of improving the color rendering properties (color reproducibility of the transmissive display) by the backlight is reduced, so it is preferable that the W-Y value is 44 or less. In other words, the W-Y value is set to 33 or more and 44 or less. Furthermore, the W-Y value is preferably 38 or more, and more preferably 40 or more.

Regarding the Y value conditions, R and G, whose color purity is easily improved with high color rendering BL, are set to a relatively high Y value (i.e., relatively low color purity), while B, whose color purity does not increase with high color rendering BL, is set to a relatively low Y value (i.e., relatively high color purity). It is desirable to adjust the Y values of each of RGB so that R-Y value ≧21, G-Y value ≧58, and B-Y value ≧15. It is even more desirable to adjust the Y values of each of RGB so that R-Y value ≧25, G-Y value ≧65, and B-Y value ≧18.

Figure 16 is a diagram explaining the relationship between the Y value (WY value) of white display and reflectance. The horizontal axis of Figure 16 represents the WY value, and the vertical axis represents the reflectance (%). The reflectance is the reflectance in the reflective display of the liquid crystal display device 1. The example of Figure 16 uses a liquid crystal panel in FFS mode with a resolution equivalent to 150 ppi.

To improve visibility in reflective display, it is desirable to set the reflectance to 1% or more. From FIG. 16, it is clear that to achieve a reflectance of 1% or more, the W-Y value must be set to 33 or more. In this embodiment, the W-Y value is set to 33 or more, which makes it possible to improve visibility of the reflective display in the liquid crystal display device 1.

Figure 17 is a diagram explaining the whiteness (chromaticity of white color) in color filters and transmissive display. The horizontal axis of Figure 17 is the x value of xy chromaticity (x axis), and the vertical axis is the y value of xy chromaticity (y axis). In Figure 17, the solid line squares represent the whiteness range of the color filters (CF whiteness range), and the dashed line squares represent the whiteness range of the transmissive display (transmissive display whiteness range). The area inside the squares in Figure 17 is the range where white display is good. The deviation between the dashed line squares and the solid line squares is due to the wavelength dispersion of the liquid crystal and the hue of the polarizing plate.

It is desirable for the whiteness of the transmissive display to fall within the range of the dashed lines in FIG. 17, and in order to satisfy this condition, it is necessary for the whiteness of the CF to fall within the range of the solid lines in FIG. 17. In other words, the x value of the whiteness of the color filter is set in the range of 0.290 to 0.320, and the y value is set in the range of 0.280 to 0.350.

(Characteristics of Diffusion Member 19)
Fig. 18 is a diagram for explaining the characteristics of the diffusing member 19. The horizontal axis of Fig. 18 represents the haze value (%) of the diffusing member 19, and the vertical axis represents the reflectance (%). The reflectance is the reflectance in reflective display of the liquid crystal display device 1. The embodiment of Fig. 18 uses a liquid crystal panel in FFS mode with a resolution equivalent to 150 ppi.

To improve visibility in reflective display, it is desirable to set the reflectance to 1% or more. From FIG. 18, to achieve a reflectance of 1% or more, it is desirable to set the haze value of the diffusing member 19 to 40% or more. This makes it possible to improve visibility of the reflective display in the liquid crystal display device 1. However, since a haze value of 90% or more results in a significant decrease in transmittance, it is desirable to keep it at 90% or less. In other words, the haze value of the diffusing member 19 is set to 40% or more and 90% or less.

[1-5] Advantages of the First Embodiment According to the first embodiment, the brightness (reflectance) of the reflective display can be improved by using a color filter with low color purity and high lightness. At the same time, the color reproducibility of the transmissive display can be improved by using a backlight 3 with high color rendering. In other words, a liquid crystal display device 1 that can achieve both color reproducibility of the transmissive display and brightness of the reflective display can be realized.

In addition, a diffusing member 19 and a reflective polarizing plate 20 are arranged on the rear side of the liquid crystal panel 2. This makes it possible to improve the reflectance of the liquid crystal display device 1. Specifically, this has the effect of improving the reflectance by more than 40% compared to a display in which a diffusing member and a reflective polarizing plate are not arranged. As a result, the brightness of the reflective display can be further improved.

In addition, it is possible to realize a liquid crystal display device 1 that can perform both transmissive and reflective display without dividing pixels into transmissive and reflective display regions.

Figure 19 is a diagram for explaining the reflection and transmission characteristics of the liquid crystal display device 1. Figure 19 shows the characteristics of a comparative example and first to third examples as samples. The comparative example uses a conventional product using a pseudo-white LED as the backlight, and the comparative example of Figure 15 as the color filter. The first example uses the first example (blue LED + green phosphor / red phosphor) of Figures 5 and 6 as the backlight, and the embodiment of Figure 15 as the color filter. The second example uses the second example (red LED + green LED + blue LED) of Figures 5 and 7 as the backlight, and the embodiment of Figure 15 as the color filter. The third example uses the third example (blue LED + quantum dot sheet) of Figures 8 and 9 as the backlight, and the embodiment of Figure 15 as the color filter. The reflectance and transmittance are based on the comparative example.

Compared to the comparative example, the first embodiment has a 20% increase in reflectance and a 25% increase in transmittance. The NTSC ratio of the transmissive display is 50%, which is equivalent to the comparative example.

Compared to the comparative example, the second embodiment has a 20% increase in reflectance and a 25% increase in transmittance. The NTSC ratio of the transmissive display is 55%, which is an improvement over the comparative example.

Compared to the comparative example, the third embodiment has a 20% increase in reflectance and a 25% increase in transmittance. The NTSC ratio of the transmissive display is 50%, which is equivalent to the comparative example.

[2] Second Embodiment The second embodiment is another example of the configuration of the liquid crystal panel 2.

Figure 20 is a cross-sectional view of a liquid crystal panel 2 according to a second embodiment of the present invention.

The liquid crystal panel 2 is a VA mode that uses vertical alignment (VA) type liquid crystal. Negative type (N type) nematic liquid crystal with negative dielectric anisotropy is used for the liquid crystal layer 12. The liquid crystal layer 12 is vertically aligned in the initial state. When no voltage (no electric field) is applied, the liquid crystal molecules are aligned almost perpendicular to the main surface of the substrate. When a voltage (electric field) is applied, the long axes of the liquid crystal molecules are tilted toward the horizontal direction (parallel to the main surface of the substrate).

Pixel electrodes 13 are provided on the TFT substrate 10. The pixel electrodes 13 extend in the Y direction and are provided over almost the entire pixel region.

An alignment film 17 that controls the alignment of the liquid crystal layer 12 is provided on the pixel electrodes 13. The alignment film 17 aligns the liquid crystal molecules vertically in the initial alignment of the liquid crystal layer 12.

A common electrode 15 is provided on the color filters (including red filter 21R, green filter 21G, and blue filter 21B). The common electrode 15 is formed in a planar shape over the entire display area.

An alignment film 24 that controls the alignment of the liquid crystal layer 12 is provided on the common electrode 15. The alignment film 24 aligns the liquid crystal molecules vertically in the initial alignment of the liquid crystal layer 12.

On the side of the TFT substrate 10 opposite the liquid crystal layer 12, a retardation film 27, a polarizing plate 18, a diffusing member 19, and a reflective polarizing plate 20 are laminated in this order.

The retardation plate 27 has a refractive index anisotropy, and has a slow axis and a fast axis that are perpendicular to each other in a plane perpendicular to the direction of light propagation. The retardation plate 27 has a function of providing a predetermined retardation (a phase difference of λ/4, where λ is the wavelength of light) between light of a predetermined wavelength that is transmitted through the slow axis and the fast axis, respectively. In other words, the retardation plate 27 is composed of a quarter-wave plate (λ/4 plate). The slow axis of the retardation plate 27 is set to form an angle of approximately 45° with respect to the transmission axis of the polarizing plate 18.

A retardation plate 28 and a polarizing plate 26 are laminated in this order on the side of the CF substrate 11 opposite the liquid crystal layer 12.

The retardation plate 28 is composed of a quarter-wave plate (λ/4 plate). The slow axis of the retardation plate 28 is set to form an angle of approximately 45° with respect to the transmission axis of the polarizing plate 26.

The relationship between the transmission axes of the polarizing plate 18 and the polarizing plate 26 is appropriately set according to the display mode (normally black mode or normally white mode) of the liquid crystal display device 1. The polarizing plate 18 and the polarizing plate 26 are arranged, for example, so that their transmission axes are perpendicular to each other, that is, in a crossed Nicol state.

The angles that define the polarizing plate and retardation plate described above include an error that allows the desired operation to be achieved, and an error that occurs during the manufacturing process. For example, the aforementioned approximate 45° includes a range of 45°±5°. For example, the aforementioned perpendicular angle includes a range of 90°±5°.

The second embodiment can achieve the same effect as the first embodiment.

[3] Third Embodiment The third embodiment is another example of the configuration of the liquid crystal panel 2.

Figure 21 is a cross-sectional view of a liquid crystal panel 2 according to a third embodiment of the present invention.

The liquid crystal panel 2 is in a TN mode using TN (twisted nematic) type liquid crystal. Positive (P-type) nematic liquid crystal with positive dielectric anisotropy is used for the liquid crystal layer 12. In the initial state, the liquid crystal molecules are aligned horizontally and twisted 90 degrees along the thickness direction of the liquid crystal layer 12. The liquid crystal molecules are in their initial state when no voltage (no electric field) is applied. When a voltage (electric field) is applied, the long axes of the liquid crystal molecules tilt toward the vertical direction (perpendicular to the main surface of the substrate).

Pixel electrodes 13 are provided on the TFT substrate 10. The pixel electrodes 13 extend in the Y direction and are provided over almost the entire pixel region.

An alignment film 17 that controls the alignment of the liquid crystal layer 12 is provided on the pixel electrodes 13. The alignment film 17 aligns the liquid crystal layer 12 horizontally so that the long axes of the liquid crystal molecules are oriented in one direction during the initial alignment of the liquid crystal layer 12.

A common electrode 15 is provided on the color filters (including red filter 21R, green filter 21G, and blue filter 21B). The common electrode 15 is formed in a planar shape over the entire display area.

An alignment film 24 that controls the alignment of the liquid crystal layer 12 is provided on the common electrode 15. The alignment film 24 aligns the liquid crystal layer 12 initially so that the long axes of the liquid crystal molecules face in one direction, resulting in horizontal alignment. The alignment direction of the alignment film 24 is perpendicular to the alignment direction of the alignment film 17.

On the side of the TFT substrate 10 opposite the liquid crystal layer 12, a polarizing plate 18, a diffusing member 19, and a reflective polarizing plate 20 are laminated in this order.

A polarizing plate 26 is provided on the side of the CF substrate 11 opposite the liquid crystal layer 12.

The relationship between the transmission axes of the polarizing plate 18 and the polarizing plate 26 is appropriately set according to the display mode (normally black mode or normally white mode) of the liquid crystal display device 1. The polarizing plate 18 and the polarizing plate 26 are arranged, for example, so that their transmission axes are perpendicular to each other, that is, in a crossed Nicol state.

The third embodiment can achieve the same effect as the first embodiment.

[4] Fourth Embodiment In the fourth embodiment, a reflective polarizing plate used for reflective display is incorporated into the backlight 3.

Figure 22 is a cross-sectional view of a liquid crystal panel 2 according to a fourth embodiment of the present invention. Only a polarizing plate 18 is provided on the side of the TFT substrate 10 opposite the liquid crystal layer 12. The rest of the configuration is the same as in the first embodiment.

Figure 23 is a perspective view of the backlight 3 shown in Figure 22. In Figure 23, multiple components are shown spaced apart, but in reality, multiple components are stacked.

A reflective polarizer 20 is provided on the second prism sheet 35. The transmission axis of the reflective polarizer 20 is set parallel to the transmission axis of the polarizer 18. The reflective polarizer 20 has the function of reflecting external light in reflective display.

A diffusion member 19 is provided on the reflective polarizer 20. The haze value of the diffusion member 19 is set to 40% or more and 90% or less. The other configurations are the same as those of the first embodiment.

The fourth embodiment can achieve the same effect as the first embodiment. The fourth embodiment can also be applied to the second and third embodiments.

In this specification, the terms plate and film are used to exemplify the material, and are not limited to their configuration. For example, the retardation plate is not limited to a plate-shaped material, but may be a film or other material having the functions described in the specification. The polarizing plate is not limited to a plate-shaped material, but may be a film or other material having the functions described in the specification.

The present invention is not limited to the above-described embodiments, and can be modified in various ways in the implementation stage without departing from the gist of the invention. The embodiments may also be implemented in appropriate combination, in which case the combined effects can be obtained. Furthermore, the above-described embodiments include various inventions, and various inventions can be extracted by combinations selected from the multiple constituent elements disclosed. For example, if the problem can be solved and an effect can be obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiments, the configuration from which these constituent elements are deleted can be extracted as an invention.

1...Liquid crystal display device, 2...Liquid crystal panel, 3...Backlight, 4...Scanning line driving circuit, 5...Signal line driving circuit, 6...Common electrode driving circuit, 7...Voltage generating circuit, 8...Control circuit, 9...Switching element, 10...TFT substrate, 11...CF substrate, 12...Liquid crystal layer, 13...Pixel electrode, 14...Insulating layer, 15...Common electrode, 16...Slit, 17...Alignment film, 18...Polarizing plate, 19...Diffusion member, 20...Reflective polarizing plate, 21R...Red filter, 21G...Green filter, 21B...Blue filter, 22...Black Matrix, 23...overcoat layer, 24...alignment film, 25...transparent conductive layer, 26...polarizing plate, 27...phase difference plate, 28...phase difference plate, 30...light-emitting element, 31...reflective sheet, 32...light guide plate, 33...diffusion sheet, 34...first prism sheet, 35...second prism sheet, 36...quantum dot sheet, 40...substrate, 41B...blue LED chip, 41G...green LED chip, 41R...red LED chip, 42...green phosphor, 43...red phosphor, 44...reflector, 45...sealing resin.

Claims (9)

A backlight that emits light;
a liquid crystal panel arranged to receive light from the backlight and including a color filter having a red filter, a green filter, and a blue filter;
Equipped with
the backlight is configured to have a spectral luminance having a peak in each of red, green, and blue;
When the information regarding lightness in the XYZ color system is a Y value, the Y value of white displayed using the red filter, the green filter, and the blue filter is 33 or more;
The liquid crystal panel is capable of performing a transmissive display using light from the backlight and a reflective display using external light reflected by the backlight. The liquid crystal display further includes a polarizing plate, a diffusing member, and a reflective polarizing plate arranged in this order on the backlight side of the liquid crystal panel,
The liquid crystal display device according to claim 1 , wherein the transmission axis of the reflective polarizer is parallel to the transmission axis of the polarizer. 2 . The liquid crystal display device according to claim 1 , wherein the red filter has a Y value of 21 or more, the green filter has a Y value of 58 or more, and the blue filter has a Y value of 15 or more. 2. The liquid crystal display device according to claim 1, wherein the x value in the whiteness (x, y) of the color filter is set in the range of 0.290 to 0.320, and the y value is set in the range of 0.280 to 0.350. The liquid crystal display device according to claim 2 , wherein the haze value of the diffusing member is equal to or greater than 40% and equal to or less than 90%. The liquid crystal display device according to claim 1 , wherein the light source of the backlight includes a blue LED, a green phosphor, and a red phosphor. The liquid crystal display device according to claim 1 , wherein the backlight light source includes a red LED, a green LED, and a blue LED. the backlight light source includes a blue LED;
The liquid crystal display device according to claim 1 , wherein the backlight includes a quantum dot sheet disposed to transmit blue light from the blue LED and converting the blue light into green light and red light. The liquid crystal display device according to claim 1 , wherein the pixels of the liquid crystal panel are not divided into a region performing transmissive display and a region performing reflective display.