JP2008090173A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device which has high brightness and can have its brightness viewing angle optionally controlled. <P>SOLUTION: The display device comprises a display panel, a backlight unit 4 which projects illumination light with high parallelism, a polarizer which has an axis of light absorption in a first direction d1 and an axis of light transmission in a second direction d2, a polarizing reflection plate which reflects first-directional linear polarized light of the illumination light and transmits second-directional linear polarized light of the illumination light, and a luminance viewing angle control liquid crystal panel 3 having a liquid crystal layer capable of controlling the diffusion state of incident illumination light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a display device.

  In recent years, liquid crystal display devices as display devices have been applied to various fields, and are used in electronic devices such as notebook computers, monitors, car navigation systems, scientific calculators, small and medium-sized TVs, large TVs, mobile phones, and electronic notebooks.

  Among these electronic devices, electronic notebooks, personal digital assistants (PDAs), mobile phones, tablet PCs (personal computers), notebook PCs, and the like are frequently used by being carried around due to their small and thin features. In addition, liquid crystal display devices used for POP (point of purchase) applications, ATM (automated teller machine) applications, and ticket vending machine applications are often used in public places.

  In these applications, it may be difficult for others to identify the display contents depending on the usage situation. For example, it is a case where private contents are displayed on a mobile phone, PDA, or tablet PC in a public place. In such a case, it is desirable that the viewing angle is narrow. However, since there are also opportunities for a plurality of people to observe an image, it is desired to have a function capable of controlling the viewing angle. The problem of viewing angle characteristics is a problem common to mobile devices and public information terminal devices.

  In recent years, a detachable louver sheet has been used as means for controlling the viewing angle of a liquid crystal display device or a cathode ray tube (CRT) (see, for example, Patent Document 1). In addition, in a liquid crystal display device using a polarizing plate, a system in which a polarizing plate on the viewer side is not provided and the display can be identified only when polarizing glasses are applied is also applied.

The conventional louver sheet is provided with a light shielding layer of about several millimeters in the normal direction of the sheet in order to make the viewing angle sufficiently narrow. For this reason, the method using the louver sheet has a problem of low light transmittance. The louver sheet manufacturing process is complicated and the manufacturing cost is high. There is also a problem that it takes time to attach and detach the louver sheet. Further, the method using polarized glasses has a problem that an image cannot be shown to an unspecified person. In order to solve the problem of viewing angle characteristics, a liquid crystal display device has been developed in which a viewing angle control liquid crystal panel for controlling the viewing angle is provided in the liquid crystal display device to control the viewing angle.
JP 2003-58066 A

  Among the liquid crystal display devices, liquid crystal display devices capable of controlling the viewing angle of luminance have been developed. Such a liquid crystal display device includes a liquid crystal display panel, a backlight unit having a lens sheet and a prism sheet, and a luminance viewing angle control liquid crystal panel provided between the liquid crystal display panel and the backlight unit for controlling the luminance viewing angle. And. The lens sheet and the prism sheet are disposed on the light emission surface of the light guide plate of the backlight unit.

  The lens sheet and the prism sheet narrow down the diffused illumination light emitted from the light emitting surface in the normal direction of the light emitting surface, and emit it as parallel light parallel to the normal direction. That is, the lens sheet and the prism sheet have a function of improving the directivity of illumination light. In other words, since the lens sheet and the prism sheet cannot obtain sufficient luminance in the direction inclined from the normal direction, the image in the inclined direction cannot be viewed. The luminance viewing angle control liquid crystal panel controls the luminance viewing angle of the backlight unit by causing the illumination light incident from the backlight unit to travel straight or diffuse and exit.

Further, in order to obtain sufficient directivity, it is necessary to provide a high refractive index medium in a fine pattern so that the pattern of the lens sheet and the prism sheet cannot be visually recognized. However, in practice, the fine pattern cannot be formed. As a result, sufficient directivity cannot be obtained, and in reality, it is impossible to disable visual recognition of an image in an inclined direction.
The present invention has been made in view of the above points, and an object of the present invention is to provide a display device having high luminance and capable of arbitrarily controlling the luminance viewing angle.

In order to solve the above-described problem, a display device according to an aspect of the present invention includes:
A display panel for displaying images,
A backlight unit disposed opposite to the display panel and emitting illumination light having high parallelism to the display panel;
The light is disposed between the backlight unit and the display panel, and is light in a first direction parallel to the plane of the display panel and in a second direction perpendicular to the first direction and parallel to the light absorption axis and the plane of the display panel. A polarizing plate having a transmission axis;
A polarizing reflector disposed between the backlight unit and the polarizing plate, which reflects the linearly polarized light in the first direction of the illumination light and transmits the linearly polarized light in the second direction of the illumination light;
A brightness viewing angle control liquid crystal panel having a liquid crystal layer disposed between the polarizing reflector and the polarizing plate and capable of controlling a diffusion state of the incident illumination light.

  According to the present invention, it is possible to provide a display device having high luminance and capable of arbitrarily controlling the luminance viewing angle.

Hereinafter, embodiments in which a display device according to the present invention is applied to a liquid crystal display device will be described in detail with reference to the drawings.
As shown in FIG. 1, the liquid crystal display device includes a liquid crystal display panel 1 as a display panel for displaying an image, a phase control liquid crystal panel 2, a luminance viewing angle control liquid crystal panel 3, a backlight unit 4, and a first unit. A polarizing plate 5, a second polarizing plate 6, a polarizing reflection plate 7, and a drive unit 8 are provided.

  The plane of the liquid crystal display panel 1, the plane of the phase control liquid crystal panel 2, the plane of the luminance viewing angle control liquid crystal panel 3, the light emission surface of the backlight unit 4, the plane of the first polarizing plate 5, the plane of the second polarizing plate 6, The planes of the polarizing reflector 7 are parallel to each other.

  The liquid crystal display panel 1 is formed as a twisted nematic (TN) mode liquid crystal display panel. The liquid crystal display panel 1 includes an array substrate 11, a counter substrate 12, and a first liquid crystal layer 13.

  The array substrate 11 includes a rectangular glass substrate 14 as a transparent insulating substrate, a plurality of pixel electrodes 15 formed in a matrix on the glass substrate, and an alignment film 16 formed on the glass substrate and the pixel electrodes. And have. The array substrate 11 has various wirings (not shown) formed on the glass substrate 14, TFTs (thin film transistors) as switching elements, and the like. The array substrate 11 has a plurality of pixels. The plurality of pixels are provided in a matrix in a display region R1 described later, and each have a TFT, a pixel electrode 15, and the like.

  The counter substrate 12 includes a rectangular glass substrate 17 as a transparent insulating substrate, a common electrode 18 formed on the glass substrate, and an alignment film 19 formed on the glass substrate and the common electrode. Yes. The pixel electrode 15 and the common electrode 18 are formed of a transparent conductive material such as ITO (Indium Tin Oxide). The alignment film 16 and the alignment film 19 are rubbed.

  The array substrate 11 and the counter substrate 12 are arranged to face each other with a predetermined gap by a plurality of spacers 21. The array substrate 11 and the counter substrate 12 have a display region R1 in which the pixel electrode 15 and the common electrode 18 face each other and an image is displayed. The array substrate 11 and the counter substrate 12 are joined to each other by a rectangular sealing material 22 disposed on the outer peripheral portion of both substrates outside the display region R1. The first liquid crystal layer 13 is formed between the array substrate 11, the counter substrate 12, and the sealing material 22.

  In the display region R1, a color filter having a plurality of colored layers of red, green, and blue (not shown) is disposed on one of the array substrate 11 and the counter substrate 12. For this reason, the liquid crystal display panel 1 can perform color display.

  The phase control liquid crystal panel 2 is disposed to face the counter substrate 12. The phase control liquid crystal panel 2 includes a first substrate 41, a second substrate 42 disposed opposite to the first substrate with a predetermined gap, and a second liquid crystal layer 43. The first substrate 41 is formed of, for example, a rectangular first sheet 44a made of a polyester film or glass as a transparent insulating substrate, and a transparent conductive material such as ITO disposed on the first sheet. The first electrode 45 and a first alignment film 47a disposed on the first electrode.

  The second substrate 42 is formed as a transparent insulating substrate by a rectangular second sheet 44b made of, for example, a polyester film or glass, and a transparent conductive material such as ITO disposed on the second sheet. A second electrode 46 and a second alignment film 47b disposed on the second electrode. The outer surface side of the second sheet 44b functions as the display surface S.

  The first alignment film 47a and the second alignment film 47b are rubbed. In this embodiment, the glass substrate 17 and the first sheet 44a are integrally formed. For this reason, the counter substrate 12 of the liquid crystal display panel 1 and the first substrate 41 of the phase control liquid crystal panel 2 have a transparent common substrate 61, and are configured by the same substrate.

  The first substrate 41 and the second substrate 42 are arranged to face each other so that the first alignment film 47a and the second alignment film 47b face each other, and are held by a plurality of spacers 48 with a predetermined gap. The first electrode 45 and the second electrode 46 are maintained in an insulated state. The first substrate 41 and the second substrate 42 are regions where the first electrode 45 and the second electrode 46 are opposed to each other, and the phase control capable of controlling the phase state of the light transmitted between the first substrate and the second substrate. It has area | region R2. In this embodiment, the phase control region R2 overlaps the display region R1 described above.

  The first substrate 41 and the second substrate 42 are joined to each other by a rectangular sealing material 49 disposed on the peripheral edge portions of the first electrode 45 and the second electrode 46 outside the phase control region R2. The second liquid crystal layer 43 is formed between the first substrate 41, the second substrate 42 and the sealing material 49.

  The layer thickness of the second liquid crystal layer 43 is 5.0 μm. A predetermined chiral material is added to the liquid crystal material constituting the second liquid crystal layer 43 so as to obtain the following characteristics. The refractive index anisotropy (Δn) of the liquid crystal material is 0.072 with respect to a wavelength of 590 nm. The twist angle of the liquid crystal molecules is 450 ° and the twist pitch is 3.92 μm. The twist of the liquid crystal molecules is counterclockwise.

  The second liquid crystal layer 43 described above has a function of controlling the phase state of light transmitted between the first substrate 41 and the second substrate 42. More specifically, the second liquid crystal layer 43 controls the viewing angle by controlling the arrangement of liquid crystal molecules. When the arrangement of the liquid crystal molecules in the second liquid crystal layer 43 is controlled, the drive voltage applied to the phase control liquid crystal panel 2 is controlled to control the potential difference between the first electrode 45 and the second electrode 46.

  The luminance viewing angle control liquid crystal panel 3 is disposed to face the array substrate 11. The luminance viewing angle control liquid crystal panel 3 includes a third substrate 51, a fourth substrate 52, and a third liquid crystal layer 53. The third substrate 51 includes a glass substrate 54a as a transparent insulating substrate, a third electrode 55a formed on the glass substrate, and an alignment film 56a formed on the glass substrate and the third electrode. Yes.

  The fourth substrate 52 includes a glass substrate 54b as a transparent insulating substrate, a fourth electrode 55b formed on the glass substrate, and an alignment film 56b formed on the glass substrate and the fourth electrode. Yes. The third electrode 55a and the fourth electrode 55b are formed of a transparent conductive material such as ITO. The alignment film 56a and the alignment film 56b are rubbed.

  The third substrate 51 and the fourth substrate 52 are arranged to face each other with a predetermined gap by a plurality of spacers 57. In the luminance viewing angle control liquid crystal panel 3, the third electrode 55a and the fourth electrode 55b are opposed to each other, and the diffusion state of light emitted from the backlight unit 4 transmitting through the luminance viewing angle control liquid crystal panel can be controlled. A light diffusion control region R3. In this embodiment, the light diffusion control region R3 overlaps the display region R1 and the phase control region R2 described above.

  The third substrate 51 and the fourth substrate 52 are joined to each other by a sealing material 58 disposed on the outer periphery of both substrates outside the light diffusion control region R3. The third liquid crystal layer 53 is formed between the third substrate 51, the fourth substrate 52 and the sealing material 58.

  Here, the third liquid crystal layer 53 according to this embodiment will be described. The third liquid crystal layer 53 is made of a liquid crystal material obtained by dissolving 2 wt% of a photocrosslinkable polymer in twisted nematic liquid crystal. The layer thickness d of the third liquid crystal layer 53 is 5 μm. The refractive index anisotropy (Δn) of the third liquid crystal layer 53 is 0.049. The liquid crystal material of the third liquid crystal layer 53 is a transparent liquid at room temperature. The twist angle of the liquid crystal molecules is 630 °. The third liquid crystal layer 53 is formed of polymer network liquid crystal (PNLC).

  When the liquid crystal is filled between the third substrate 51, the fourth substrate 52, and the sealing material 58, it can be filled by using a vacuum injection method or the like in the same manner as the conventional liquid crystal injection method. Therefore, the liquid crystal is filled in a liquid state. The filled liquid crystal is irradiated with ultraviolet rays to form a polymer (polymer network) and to deposit liquid crystal molecules. The arrangement of the liquid crystal molecules in the third liquid crystal layer 53 can be regarded as almost random.

  In a state where no voltage is applied to the third liquid crystal layer 53, the luminance viewing angle control liquid crystal panel 3 acts as a negative C plate having a retardation value of −250 nm, and when the liquid crystal display panel 1 having Δnd of about 450 nm is displayed in black. To compensate for the contrast viewing angle.

  In a state where a voltage is applied to the third liquid crystal layer 53, the luminance viewing angle control liquid crystal panel 3 acts as a positive C plate having a retardation value of +250 nm, and when the liquid crystal display panel 1 having a Δnd of about 450 nm is in black display. Deteriorates the contrast viewing angle.

  The backlight unit 4 is provided on the outer surface side of the third substrate 51 of the luminance viewing angle control liquid crystal panel 3. The backlight unit 4 includes a light guide 4a that is disposed to face the third substrate 51 and includes a light guide plate, and a light source 4b and a reflector 4c that are disposed to face one side edge of the light guide. Yes.

  The backlight unit 4 includes an optical sheet 4d that is disposed to face the light emission surface of the light guide 4a. The optical sheet 4d can convert the light from the light guide 4a into light parallel to the normal direction of the light emission surface (hereinafter referred to as parallel light). As described above, the optical sheet 4d has a function of increasing the parallelism (directivity) of the illumination light emitted from the light guide 4a. As the optical sheet 4d, a BEF (light condensing sheet) manufactured by Sumitomo 3M Co., Ltd. or the like that has a very high degree of parallelism of emitted illumination light is used. For this reason, the backlight unit 4 can emit light with high parallelism.

  The first polarizing plate 5 is disposed between the array substrate 11 and the fourth substrate 52. More specifically, the first polarizing plate 5 is disposed on the outer surface of the array substrate 11. The first polarizing plate 5 may be bonded to the outer surface of the array substrate 11 via glue. The first polarizing plate 5 has a light absorption axis in a first direction d1 parallel to the plane of the liquid crystal display panel 1 and a light transmission axis in a second direction d2 that is parallel to the plane of the liquid crystal display panel and orthogonal to the first direction. Have.

  The second polarizing plate 6 is disposed on the opposite side of the first polarizing plate 5 with respect to the phase control liquid crystal panel 2. More specifically, the second polarizing plate 6 is disposed on the outer surface of the second substrate 42. The second polarizing plate 6 may be bonded to the outer surface of the second substrate 42 via glue. The outer surface of the second polarizing plate 6 functions as the display surface S. The second polarizing plate 6 has a light transmission axis in the first direction d1 and a light absorption axis in the second direction d2.

  The first polarizing plate 5 and the second polarizing plate 6 are arranged in crossed Nicols. For this reason, the liquid crystal display panel 1 becomes normally white display which becomes black display in a drive voltage application state.

  The polarization reflector 7 is disposed between the backlight unit 4 and the luminance viewing angle control liquid crystal panel 3. More specifically, the polarizing reflection plate 7 is disposed between the optical sheet 4 d and the third substrate 51. The polarization reflector 7 reflects the linearly polarized light in the first direction d1 of the illumination light and transmits the linearly polarized light in the second direction d2 of the illumination light. The linearly polarized light in the first direction d1 reflected by the polarization reflector 7 returns to the backlight unit 4 and is recycled. For this reason, a decrease in luminance level due to the provision of the polarizing reflection plate 7 can be suppressed. As the polarizing reflecting plate 7, DBEF manufactured by Sumitomo 3M Limited is used as the optical sheet 4d.

  The drive unit 8 controls the display state by applying a drive voltage to the liquid crystal display panel 1. The drive unit 8 applies a drive voltage to the phase control liquid crystal panel 2 and the luminance viewing angle control liquid crystal panel 3 in accordance with the display state of the liquid crystal display panel 1.

  In the liquid crystal display device described above, the backlight unit 4 is disposed to face the liquid crystal display panel 1. The first polarizing plate 5 is disposed between the backlight unit 4 and the liquid crystal display panel 1. The polarizing reflector 7 is disposed between the backlight unit 4 and the first polarizing plate 5. The luminance viewing angle control liquid crystal panel 3 is disposed between the polarizing reflector 7 and the first polarizing plate 5. The phase control liquid crystal panel 2 is disposed on the opposite side of the luminance viewing angle control liquid crystal panel 3 with respect to the liquid crystal display panel 1. The second polarizing plate 6 is disposed on the opposite side of the first polarizing plate 5 with respect to the liquid crystal display panel 1 and the phase control liquid crystal panel 2.

  Next, the principle that the luminance viewing angle control liquid crystal panel 3 can control the luminance viewing angle of the liquid crystal display device by controlling the diffusion state of the light transmitted through the luminance viewing angle control liquid crystal panel will be described with reference to FIGS. It explains using.

  As shown in FIG. 2, a voltage of 5 V is applied to the third liquid crystal layer 53 (between the third electrode 55a and the fourth electrode 55b). In a state where a sufficient driving voltage is applied to the luminance viewing angle control liquid crystal panel 3, the liquid crystal molecules 53m are arranged in the normal direction of the plane of the luminance viewing angle control liquid crystal panel. Δnd of the third liquid crystal layer 53 is a value for obtaining a phase difference of λ / 2 + n (n = 0, 1, 2,...) In the vicinity of Bdeg. Since the third liquid crystal layer 53 functions as a positive C plate, the phase of parallel light parallel to the normal direction does not change, but the phase of light in a direction inclined from the normal direction (hereinafter referred to as inclined light). Varies depending on the liquid crystal concentration LCwt%, Δn and layer thickness d of the third liquid crystal layer and the tilt angle of the tilted light from the normal direction. If the phase is shifted by λ / 2 in the visual field range that is desired to be invisible, the inclined light emitted from the luminance viewing angle control liquid crystal panel 3 becomes linearly polarized light in the first direction d1.

  Since the light transmission axis of the polarizing reflector 7 and the light transmission axis of the first polarizing plate 5 are parallel, the parallel light emitted from the luminance viewing angle control liquid crystal panel 3 passes through the first polarizing plate 5 and controls the luminance viewing angle. The inclined light emitted from the liquid crystal panel 3 is absorbed by the first polarizing plate 5. As described above, the viewing angle is narrowed by shielding the inclined light and narrowing the luminance viewing angle. As a result, the light emitted from the first polarizing plate 5 has higher parallelism (directivity) than the light emitted from the optical sheet 4d.

  As shown in FIG. 3, no voltage is applied to the third liquid crystal layer 53 (between the third electrode 55a and the fourth electrode 55b). In a state where a sufficient driving voltage is not applied to the luminance viewing angle control liquid crystal panel 3, the arrangement of the liquid crystal molecules 53m is almost random. Since the third liquid crystal layer 53 functions as a negative C plate, the light incident on the luminance viewing angle control liquid crystal panel 3 is diffused and emitted. As a result, the light emitted from the first polarizing plate 5 has a lower degree of parallelism (directivity) than the light emitted from the optical sheet 4d. As described above, the viewing angle is widened by widening the luminance viewing angle. The visibility of an image can be improved in a wide visual field range.

Next, contrast viewing angle characteristics with and without applying a driving voltage to the phase control liquid crystal panel 2 will be described together with luminance viewing angle characteristics.
A wide viewing angle with high contrast (high luminance) can be obtained in a state where no driving voltage is applied to the second liquid crystal layer 43 (between the first electrode 45 and the second electrode 46). In a state where a driving voltage is applied to the second liquid crystal layer 43 (between the first electrode 45 and the second electrode 46), a narrow viewing angle having high contrast (high luminance) can be obtained.

Next, image visibility will be described.
As shown in FIG. 4, the visibility of an image depends on lightness (brightness) and contrast. The brightness is plotted on the x-axis and the contrast is plotted on the y-axis. The brightness depends on the illuminance of the illumination light emitted from the backlight unit 4 and the luminance viewing angle controlled by the luminance viewing angle control liquid crystal panel 3. The contrast depends on the luminance ratio and the hue ratio.

  The image visibility includes the first region D1 in which the image pattern cannot be determined, the second region D2 in which the image pattern is difficult to recognize, and the third region D3 that satisfies the readability and visibility of the image pattern. There are three main categories.

  It can be seen that if one or both of brightness and contrast is insufficient, the visibility of the image is impaired. From the viewpoint of preventing peeping, visibility of the first region D1 is required. Although depending on the directivity of the illumination light itself, in order to satisfy the visibility of the first region D1, it is better to control not only the luminance viewing angle but also the contrast viewing angle.

  In this embodiment, the contrast viewing angle can be controlled by arranging the phase control liquid crystal panel 2 that can control the functions of the positive C plate and the negative C plate between the first polarizing plate 5 and the second polarizing plate 6. It is said.

  The phase control liquid crystal panel 2 can control the phase difference and traveling direction of illumination light transmitted through the liquid crystal display panel 1, and can also control the viewing angle and the contrast viewing angle. From the above, in the narrow viewing angle display mode in which the driving voltage is applied to the luminance viewing angle control liquid crystal panel 3 and the phase control liquid crystal panel 2 to display an image, the normal direction (front direction of the plane of the liquid crystal display panel 1) ), The visibility of the third region D3 can be obtained, and the visibility of the first region D1 can be obtained in a direction (oblique direction) inclined from the normal direction of the plane of the liquid crystal display panel 1.

  In the wide viewing angle display mode in which an image is displayed without applying a driving voltage to the luminance viewing angle control liquid crystal panel 3 and the phase control liquid crystal panel 2, visibility of the third region D3 is obtained in the front direction and the oblique direction. It goes without saying that it can be done.

Next, a change in the brightness L ^* with respect to the viewing angle will be described.
As shown in FIG. 5, in the wide viewing angle display mode, high brightness is obtained over the entire viewing angle as indicated by the line L1. As indicated by the line L2, in the narrow viewing angle display mode, brightness higher than the wide viewing angle display mode is obtained in the vicinity of the front direction (0 °), and brightness lower than the wide viewing angle display mode is obtained in the oblique direction.

Next, a change in the product of the contrast ratio (CR) and the hue ratio with respect to the viewing angle will be described.
As shown in FIG. 6, as indicated by a line L3, the wide viewing angle display mode shows a high value in the entire viewing angle. As indicated by line L4, in the narrow viewing angle display mode, a high value is shown near the front direction (0 °), but a low value is shown in the oblique direction.

  As shown in FIGS. 5 and 6, in the narrow viewing angle display mode, in order to obtain the visibility of the first region D1 in an oblique direction, the luminance contrast is 2: 1 or less, or a color contrast equivalent thereto, and The brightness may be 30% or less of the brightness.

When the usage environment is assumed to be 300 lx, the front luminance for obtaining sufficient visibility is about 150 cd / m ² . In order to set the luminance to 30% of the brightness, it is necessary to reduce the luminance to about 15 cd / m ² .

Here, the brightness and brightness will be described. The brightness of 100% is expressed by the luminance of illuminance / π. Therefore, at 300 lx, (300 lx ÷ π) × 0.3 = 28 cd / m ² . The relationship between the luminance Y and the lightness L is expressed as L = 116 × (ratio of the relative luminance Y to Y0 with 100% lightness) ^ (1/3) −16. Therefore, at 300 lx, (300 lx ÷ π) × (((30−16) / 116) ^ 3) = about 15 cd / m ² .

  The viewing angle required to prevent peeping is 45 ° or more. However, since the image itself is distorted at a viewing angle of 70 ° or more, the image pattern cannot be viewed regardless of the display performance. Therefore, in practice, it is only necessary to obtain the visibility of the first region D1 with a viewing angle in the range of 45 ° to 70 °. Then, the luminance at a viewing angle in the range of 45 ° to 70 ° may be 30% or less of the front luminance.

  Next, the change in light transmittance with respect to the viewing angle will be described. FIG. 7 shows the total light transmission of the polarizing reflector 7, the luminance viewing angle control liquid crystal panel 3, and the first polarizing plate 5 when ΔndLC is 1850 nm, 1900 nm, 1950 nm, 2000 nm, 2050 nm, 2100 nm, 2150 nm and 2200 nm. It is the figure which showed the measured value of the rate with the graph. ΔndLC is a value obtained by multiplying the refractive index anisotropy Δn of the third liquid crystal layer 53 with respect to the wavelength of 550 nm, the layer thickness d of the third liquid crystal layer, and the liquid crystal concentration LCwt% of the third liquid crystal layer.

  As shown in the figure, when ΔndLC is 2100 nm, the light transmittance is about 30% at a viewing angle in the range of 45 ° to 70 °. As a result, the luminance in the oblique direction of the liquid crystal display device is about 30% of the front luminance. Thus, the requirements for the visibility of the first region D1 are satisfied. Even if ΔndLC is varied, the effect of narrowing the luminance viewing angle can be obtained. However, in order to obtain a sufficient effect (visibility of the first region D1), ΔndLC may be set to 2000 to 2200 nm.

  According to the liquid crystal display device configured as described above, the polarizing reflector 7, the luminance viewing angle control liquid crystal panel 3, and the first polarizing plate 5 are disposed between the backlight unit 4 and the liquid crystal display panel 1. The backlight unit 4 emits illumination light with high parallelism by the optical sheet 4d. The polarization reflector 7 transmits linearly polarized light in the second direction d2 and reflects linearly polarized light in the first direction d1 among the incident illumination light.

  The luminance viewing angle control liquid crystal panel 3 to which the driving voltage is applied maintains the polarization direction of the linearly polarized light in the second direction d2 having a high degree of parallelism, advances straight, and enters the inclined second incident light. The linearly polarized light in the direction d2 is caused to reverse the polarization direction in the first direction d1 and go straight. The brightness viewing angle control liquid crystal panel 3 to which no driving voltage is applied causes the incident linearly polarized light in the second direction d2 to be diffused and emitted while maintaining the polarization direction. The first polarizing plate 5 transmits linearly polarized light in the second direction d2 and absorbs linearly polarized light in the first direction d1.

  The liquid crystal display device including the backlight unit 4, the polarizing reflector 7, the luminance viewing angle control liquid crystal panel 3, and the first polarizing plate 5 can have higher directivity than the liquid crystal display device including only the backlight unit 4.

  As described above, the luminance viewing angle control liquid crystal panel 3 can control the luminance viewing angle. The phase control liquid crystal panel 2 can control the illumination light phase difference and the traveling direction, and can also control the viewing angle and the contrast viewing angle.

  The value Δn · d · LC obtained by multiplying the layer thickness, refractive index anisotropy and liquid crystal concentration of the third liquid crystal layer 53 is 2000 to 2200 nm. Thereby, the visibility of the 1st field D1 can be obtained in the slanting direction, and sufficient peeping prevention effect can be acquired.

  From the above, even when using in a public place such as a mobile PC, a mobile phone, a PDA, an electronic notebook, and a tablet PC, the viewing angle (brightness) is displayed when it is difficult for others to identify the display contents. The viewing angle (brightness viewing angle) can be widened when the viewing angle is narrowed and the display image is observed by a plurality of observers. As a result, it is possible to eliminate the worry of others looking into the display contents. It is also possible for a plurality of observers to view the display screen simultaneously and satisfactorily. At this time, the viewing angle can be easily controlled by controlling the driving voltage applied to the third liquid crystal layer 53 and the second liquid crystal layer 43. When controlling such display characteristics, it is possible to control without substantially increasing power consumption. When controlling the display characteristics of the liquid crystal display device, it can be controlled by a switch or a single volume.

  Liquid crystal that controls the liquid crystal molecules of nematic liquid crystal from substantially vertical to horizontal alignment, tilted alignment, and twisted alignment, such as MVA mode, twisted nematic mode (TN mode), homogeneous mode (HOMO mode), and hybrid aligned nematic mode. In the display device, the first polarizing plate 5 and the second polarizing plate 6 are arranged so as to display black in a state in which the liquid crystal molecules of the nematic liquid crystal are aligned substantially vertically. In this state, the first liquid crystal layer 13 can be regarded as a substantially positive uniaxial crystal when viewed optically. Accordingly, since a phase difference occurs in the oblique direction of the display screen, the contrast ratio becomes lower than that observed from the front of the display screen.

  In the second liquid crystal layer 43, the refractive index anisotropy (Δn) of the liquid crystal material is small, the twist pitch of the liquid crystal molecules is short, and the twist angle of the liquid crystal molecules is 450 °. The second liquid crystal layer 43 is sufficiently low in optical rotation even when compared with the first liquid crystal layer 13. For this reason, in a state where no voltage is applied between the first electrode 45 and the second electrode 46, the second liquid crystal layer 43 is a retardation plate that can be regarded as a negative uniaxial crystal.

  Therefore, in this state, the second liquid crystal layer 43 compensates for the phase difference of the first liquid crystal layer 13 in a state where the liquid crystal molecules are arranged substantially vertically, so that a decrease in contrast in an oblique direction can be suppressed. In addition, by making the twist directions of the first liquid crystal layer 13 and the second liquid crystal layer 43 coincide with each other, the second liquid crystal layer 43 acts to expand the left and right viewing angle of the liquid crystal display panel 1 (TN mode).

  The effect described above is effective when the twist angle of the liquid layer molecules of the second liquid crystal layer 43 is controlled as follows. In a state where a voltage is applied between the first electrode 45 and the second electrode 46, a plurality of liquid crystal molecules are arranged substantially perpendicular to the planes of the first substrate 41 and the second substrate 42, and no voltage is applied. When aligning a plurality of liquid crystal molecules with a twist angle of 270 ° or more.

  Alternatively, in a state where no voltage is applied between the first electrode 45 and the second electrode 46, a plurality of liquid crystal molecules are arranged substantially perpendicular to the plane of the first substrate 41 and the plane of the second substrate 42, and a voltage is applied. In this state, a plurality of liquid crystal molecules are arranged at a twist angle of 270 ° or more.

  By providing both the phase control liquid crystal panel 2 and the luminance viewing angle control liquid crystal panel 3, the contrast viewing angle and the luminance viewing angle can be controlled simultaneously. These controls can be performed between the widest viewing angle state and the narrowest viewing angle state by controlling the driving voltage applied to both liquid crystal layers. In a state where the luminance viewing angle is controlled to be narrow by the luminance viewing angle control liquid crystal panel 3, the emitted light can be concentrated in the front direction of the display screen. In this case, since sufficient luminance can be obtained even if the illumination light intensity is weakened, power consumption can be reduced.

  The alignment of the liquid crystal molecules in a state where no driving voltage is applied to the third liquid crystal layer 53 is random, and alignment control by the alignment films 56a and 56b is not necessary. However, it is desirable to provide the alignment films 56a and 56b in order to protect the third electrode 55a and the fourth electrode 55b and to improve the retention characteristics of the third liquid crystal layer 53. However, in this case, alignment treatment such as rubbing is not necessary.

  The phase control liquid crystal panel 2 is disposed between the liquid crystal display panel 1 and the second polarizing plate 6. Thereby, the 2nd polarizing plate 6 plays the role of a polarizer. In this case, it is desirable that the outer surface of the second sheet 44b on the display screen side is pasted with a paste (not shown). If not attached, an air interface exists between the phase control liquid crystal panel 2 and the second polarizing plate 6, and if the gap is narrow, Newton ring fringes are visually recognized. Conversely, if the gap between the phase control liquid crystal panel 2 and the second polarizing plate 6 is wide, a spacer or the like for maintaining the gap is required, and the thickness of the entire liquid crystal display device is increased.

  Similarly, it is desirable that the phase control liquid crystal panel 2 and the liquid crystal display panel 1 are bonded together without providing a gap. When the first sheet 44a and the second sheet 44b of the phase control liquid crystal panel 2 are made of flexible plastic or thin glass, the phase control liquid crystal panel is attached to the liquid crystal display panel 1 via a paste (not shown). It ’s fine.

  The phase control liquid crystal panel 2 and the luminance viewing angle control liquid crystal panel 3 are easy to manufacture. It is also easy to configure the luminance viewing angle control liquid crystal panel 3 using a plastic substrate or thin glass instead of the glass substrates 54a and 54b. In this case, the entire thickness and weight of the luminance viewing angle control liquid crystal panel 3 can be further reduced.

The first substrate 41 and the counter substrate 12 have a common substrate 61, and are configured by the same substrate. For this reason, the thickness and weight of the entire liquid crystal display device can be reduced.
From the above, it is possible to obtain a display device having high luminance and capable of arbitrarily controlling the luminance viewing angle.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  For example, as shown in FIG. 8, the liquid crystal display device may be formed without providing the phase control liquid crystal panel 2. Since the polarizing reflector 7, the luminance viewing angle control liquid crystal panel 3 and the first polarizing plate 5 are disposed between the backlight unit 4 and the liquid crystal display panel 1, even in this liquid crystal display device, the viewing angle (luminance viewing field) Angle) can be controlled well.

The luminance viewing angle control liquid crystal panel 3 (the third liquid crystal layer 53) is not limited to the polymer network liquid crystal, but is also a polymer dispersed liquid crystal (PDLC), a polymer stabilized cholesteric texture (PSCT), What is necessary is just to form by dynamic scattering (DS) etc.
The present invention is not limited to a liquid crystal display device, and can be applied to any display device provided with a display panel, a luminance viewing angle control liquid crystal panel 3 and a polarizing reflector 7.

1 is a cross-sectional view of a liquid crystal display device according to an embodiment of the present invention. FIG. 4 is a diagram for explaining a cross-sectional structure of a third liquid crystal layer and an optical path of illumination light from a backlight unit in a state where no voltage is applied to the luminance viewing angle control liquid crystal panel shown in FIG. 1. FIG. 4 is a diagram for explaining a cross-sectional structure of a third liquid crystal layer and an optical path of illumination light from the backlight unit in a state where a voltage is applied to the luminance viewing angle control liquid crystal panel shown in FIG. 1. The xy coordinate diagram for demonstrating the visibility of an image. The figure which showed the change of the brightness with respect to a viewing angle by the graph. The figure which showed the change of the product of contrast ratio and hue ratio with respect to a viewing angle by the graph. The figure which showed the change of the light transmittance with respect to a viewing angle by the graph. Sectional drawing which shows the modification of the said liquid crystal display device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display panel, 2 ... Phase control liquid crystal panel, 3 ... Luminance viewing angle control liquid crystal panel, 4 ... Backlight unit, 4d ... Optical sheet, 5 ... 1st polarizing plate, 6 ... 2nd polarizing plate, 7 ... Polarization Reflector, 8... Driving unit, 11... Array substrate, 12. Counter substrate, 13... First liquid crystal layer, 43... Second liquid crystal layer, 53. d2 ... second direction, R1 ... display area, R2 ... phase control area, R3 ... light diffusion control area, LC ... liquid crystal concentration, Δn ... refractive index anisotropy.

Claims (6)

A display panel for displaying images,
A backlight unit disposed opposite to the display panel and emitting illumination light having high parallelism to the display panel;
The light is disposed between the backlight unit and the display panel, and is light in a first direction parallel to the plane of the display panel and in a second direction perpendicular to the first direction and parallel to the light absorption axis and the plane of the display panel. A polarizing plate having a transmission axis;
A polarizing reflector disposed between the backlight unit and the polarizing plate, which reflects the linearly polarized light in the first direction of the illumination light and transmits the linearly polarized light in the second direction of the illumination light;
A luminance viewing angle control liquid crystal panel having a liquid crystal layer disposed between the polarizing reflector and the polarizing plate and capable of controlling a diffusion state of the incident illumination light. When the layer thickness of the liquid crystal layer is d, the refractive index anisotropy with respect to the wavelength of 550 nm of the liquid crystal layer is Δn, and the liquid crystal concentration of the liquid crystal layer is LCwt%,
2. The display device according to claim 1, wherein a value Δn · d · LC obtained by multiplying the layer thickness, refractive index anisotropy, and liquid crystal concentration is 2000 nm to 2200 nm.   A phase control liquid crystal panel having another liquid crystal layer disposed on the opposite side of the luminance viewing angle control liquid crystal panel with respect to the display panel and capable of controlling a phase state of the incident illumination light. The display device according to 1.   The display device according to claim 3, wherein the other liquid crystal layer has a molecular arrangement in which liquid crystal molecules are twisted by 270 ° or more.   The display device according to claim 1, further comprising another polarizing plate disposed on the opposite side of the polarizing plate with respect to the display panel.   The display device according to claim 1, wherein the liquid crystal layer is formed of a polymer network liquid crystal or a polymer dispersed liquid crystal.

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