JP6401903B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device using an edge light type backlight unit.

  Conventionally, as a backlight unit applied to a liquid crystal display device, a light source is disposed at an edge of a light guiding plate (LGP), and light emitted from the light source is incident on the liquid crystal panel via the light guiding plate. An edge light type backlight unit is known. Hereinafter, a liquid crystal display device having an edge light type backlight unit will be described with reference to FIG.

  FIG. 2 is a schematic cross-sectional view showing a conventional liquid crystal display device 100. In FIG. 2, the liquid crystal display device 100 includes a backlight unit 110, a liquid crystal panel 120, and a DBEF (Reflective Polarizing Film: Dual BRIGHTNESS ENHANCEMENT FILM) 130.

  The backlight unit 110 includes a light source 111 that emits light, a light guide plate 112 that guides light from the light source 111 and extracts light from the surface, a reflective plate 113 that reflects light, a diffusion sheet 114 that diffuses light, and light. It is comprised from the prism sheet 115 which collects (condenses).

  Here, an LED (Light Emitting Diode) or a CCFL (Cold Cathode Fluorescent Lamp) is used as the light source 111. The light guide plate 112 is generally made of a material having birefringence.

  The liquid crystal panel 120 is provided on the surface of the liquid crystal cell 121 in which liquid crystal is sealed between two substrates, the backlight unit 110 side of the liquid crystal cell 121, and absorbs only light in a specific vibration direction. An absorptive polarizing plate (second absorption) that is provided on a surface opposite to the polarizing plate (first absorption polarizing plate 122) and the backlight unit 110 of the liquid crystal cell 121 and transmits only light in a specific vibration direction. Type polarizing plate 123).

  The DBEF 130 is provided between the backlight unit 110 and the liquid crystal panel 120, and is a reflecting plate for improving the light utilization efficiency. The DBEF 130 transmits only light in a specific vibration direction and reflects other light. The light reflected by the DBEF 130 changes its vibration direction due to reflection in the backlight unit 110, and part of the light is transmitted when reentering the DBEF 130, thereby improving the light utilization efficiency. The DBEF 130 is formed from multilayer thin films having different refractive indexes.

  In addition, the inventors of the present invention have proposed to increase the light utilization efficiency by using a zero / zero birefringent polymer that does not change the polarization state of incident light as a light guide plate (for example, Patent Document 1). reference). Hereinafter, a liquid crystal display device using a zero / zero birefringence polymer as a light guide plate will be described with reference to FIG.

  FIG. 3 is a schematic cross-sectional view showing a liquid crystal display device 200 using a zero / zero birefringent polymer as a light guide plate. In FIG. 3, the liquid crystal display device 200 includes a backlight unit 210 and a liquid crystal panel 220.

  The backlight unit 210 includes a light emitting unit 211 that emits polarized light, a light guide plate 212 that guides light from the light emitting unit 211, extracts light from the surface, a reflective plate 213 that reflects light, and a diffusion sheet 214 that diffuses light. And a prism sheet 215 that collects (collects) light. The diffusion sheet 214 and the prism sheet 215 have polarization maintaining characteristics that do not change the polarization state of incident light.

  The light emitting unit 211 transmits the light in a specific vibration direction among the light from the light source 211a and the light source 211a that emits light, and reflects the other light, and the reflective polarizing plate 211b. The reflection plate 211c reflects the light reflected at the light guide plate 212 side. The reflective polarizing plate 211b is a polarizing plate in which a laminated polarizing plate, WGP (Wire Grid Polarizer), a laminated film and a transmissive polarizing plate are combined. By combining these polarizing plates with the reflecting plate 211c, an optical recycling structure can be configured.

  Here, LED or CCFL is used as the light source 211a. Further, a semiconductor laser (laser diode (LD): Laser Diode) that emits polarized light can also be used as the light emitting unit 211.

  The light guide plate 212 is composed of a zero / zero birefringence polymer. The zero / zero birefringence polymer is a resin in which both the orientation birefringence index and the stress birefringence index are substantially zero, and can be emitted without changing the polarization state of incident light.

Specifically, in a zero-zero birefringence polymer, for example, the absolute value of in-plane retardation indicating orientation birefringence and the absolute value of thickness direction retardation are both 5 nm or less, and photoelasticity indicating stress birefringence. absolute value of the coefficient is less than 5.0 × ^10- 12 / Pa (e.g., see Patent Document 2).

  The liquid crystal panel 220 is provided on a surface of the liquid crystal cell 221 in which liquid crystal is sealed between two substrates, the backlight unit 210 side of the liquid crystal cell 221, and absorbs only light in a specific vibration direction. An absorptive polarizing plate (second absorption) that is provided on a surface opposite to the polarizing plate (first absorption polarizing plate 222) and the backlight unit 210 of the liquid crystal cell 221 and transmits only light in a specific vibration direction. Type polarizing plate 223).

Japanese Patent Application No. 2013-268999 JP2013-114198A

  However, in the conventional liquid crystal display device shown in FIG. 2, a little more than 50% of the light from the light source is absorbed by the first absorption type polarizing plate, so that the light utilization efficiency (the light emitted from the light source is the first). There is a problem that the ratio of transmitting through the absorption-type polarizing plate is low. Also, even when DBEF is used to increase the light utilization efficiency, the conversion efficiency from s-polarized light to p-polarized light by DBEF is not so high, so the light utilization efficiency is only about 51%. Does not improve.

  In addition, in the liquid crystal display device using the zero / zero birefringence polymer shown in FIG. 3 for the light guide plate, when the LED or CCFL is used as the light source of the light emitting unit, the polarized light from the light emitting unit diffuses to the light guide plate. Since the light enters, polarized light other than the predetermined polarization direction also enters the light guide plate. Note that, when a semiconductor laser is used as the light emitting portion, this problem is somewhat mitigated, but the problem is not completely solved.

  In addition, while the polarized light incident on the light guide plate is repeatedly reflected in the light guide plate, there arises a problem that a change in polarization state (polarization collapse) is promoted.

  Therefore, in a liquid crystal display device using a zero / zero birefringent polymer as a light guide plate, even when the optical conditions are adjusted, the light utilization efficiency is improved only to about 57%, and the light utilization efficiency is sufficient. There is a problem that it cannot be increased.

  The present invention has been made to solve the above-described problems, and is a liquid crystal display using an edge-light type backlight unit that can increase the light utilization efficiency and reduce the power consumption at a low cost. The object is to obtain a device.

  The liquid crystal display device according to the present invention is a liquid crystal display device including a liquid crystal panel and a backlight unit that irradiates light to the liquid crystal panel, and the backlight unit includes a light emitting unit that emits polarized light, and a zero unit. A light guide plate that is composed of a zero birefringent polymer, guides light from the light emitting section and extracts light from the surface, and a reflector that is provided on the surface opposite to the liquid crystal panel of the light guide plate and reflects light The liquid crystal panel is provided on a surface on the backlight unit side, and includes a liquid crystal panel-side reflective polarizing plate that transmits only light in a specific vibration direction and reflects other light.

According to the liquid crystal display device according to the present invention, the light guide plate is composed of a zero / zero birefringence polymer, the light guide plate is provided on the surface opposite to the liquid crystal panel, and the backlight unit of the liquid crystal panel is provided. On the side surface, there is provided a liquid crystal panel-side reflective polarizing plate that transmits only light in a specific vibration direction and reflects other light.
Therefore, it is possible to obtain a liquid crystal display device using an edge-light type backlight unit that can increase light utilization efficiency and reduce power consumption at low cost.

1 is a schematic cross-sectional view showing a liquid crystal display device according to Embodiment 1 of the present invention. It is a schematic cross section which shows the conventional liquid crystal display device. It is a schematic cross section which shows the liquid crystal display device which used the zero zero zero refraction polymer for the light guide plate.

  Hereinafter, preferred embodiments of a liquid crystal display device according to the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts will be described with the same reference numerals.

Embodiment 1 FIG.
FIG. 1 is a schematic cross-sectional view showing a liquid crystal display device 1 according to Embodiment 1 of the present invention. In FIG. 1, the liquid crystal display device 1 includes a backlight unit 10 and a liquid crystal panel 20.

  The backlight unit 10 includes a light emitting unit 11 that emits polarized light, a light guide plate 12 that guides light from the light emitting unit 11 and extracts light from the surface, a reflective plate 13 that reflects light, and a diffusion sheet 14 that diffuses light. And a prism sheet 15 that collects (collects) light.

  The light emitting unit 11 is a reflective polarizing plate (light emitting unit side reflective polarizing plate) that transmits only light in a specific vibration direction and reflects other light among the light from the light source 11a that emits light and the light source 11a. ) 11b and the reflection plate 11c that reflects the light reflected by the reflective polarizing plate 11b to the light guide plate 12 side.

  Here, LED or CCFL is used as the light source 11a. Here, a case where the light source 11a is an LED will be described, but the same can be said for a CCFL. Note that a semiconductor laser that emits polarized light can be used as the light emitting unit 11. In this case, although the cost is high, the configuration can be simplified.

  The reflective polarizing plate 11b and the reflective plate 11c constitute a light recycling structure for increasing the light utilization efficiency.

  The reflective polarizing plate 11b is a polarizing plate obtained by combining a laminated polarizing plate, WGP (Wire Grid Polarizer), a laminated film and a transmissive polarizing plate. By combining these polarizing plates with the reflector 11c, a light recycling structure can be configured.

  The WGP is a polarizing plate in which metal wirings are arranged at a pitch of, for example, 50 to 100 nm, and transmits light that vibrates in a direction perpendicular to the metal wirings and reflects light that vibrates in a direction parallel to the metal wirings. WGP has high heat resistance and is suitable for use in the vicinity of LEDs that are exposed to high temperatures.

The light guide plate 12 is composed of a zero / zero birefringence polymer. Specifically, in a zero-zero birefringence polymer, for example, the absolute value of in-plane retardation indicating orientation birefringence and the absolute value of thickness direction retardation are both 5 nm or less, and photoelasticity indicating stress birefringence. absolute value of the coefficient is less than 5.0 × ^10- 12 / Pa (e.g., see Patent Document 2).

  The light guide plate 12 is of an inverted prism type or a light scattering type. In the inverted prism type light guide plate 12, the prism is formed in parallel with the light incident surface of the light guide plate 12. Further, the diffusion sheet 14 and the prism sheet 15 have polarization maintaining characteristics that do not change the polarization state of incident light. Thereby, the utilization efficiency of light can further be improved.

  The liquid crystal panel 20 is provided on the surface of the liquid crystal cell 21 in which the liquid crystal is sealed between two substrates, the backlight unit 10 side of the liquid crystal cell 21, and transmits only light in a specific vibration direction. Is provided on a surface opposite to the backlight unit 10 of the liquid crystal cell 21 and reflects only light in a specific vibration direction. It is comprised from the type | mold polarizing plate (absorption type polarizing plate 23).

  Here, the reflective plate 13 provided on the light guide plate 12 and the reflective polarizing plate 22 provided on the liquid crystal panel 20 are a laminated polarizing plate, WGP (Wire Grid Polarizer), laminated film and transmission type. It is a polarizing plate combined with a polarizing plate, and together with the reflector 13 in the backlight unit 10, constitutes a light recycling structure for increasing the light utilization efficiency. That is, since the polarized light reflected without being transmitted through the reflective polarizing plate 22 due to the polarization breakage at the light guide plate 12 is reflected by the reflective plate 13 and changes its polarization state, it is reflected with high efficiency by repeating the reflection. It can be transmitted through the mold polarizing plate 22.

  In the liquid crystal display device 1 according to Embodiment 1 of the present invention, the transmission axis direction of the reflective polarizing plate 22 is such that polarized light incident on the light guide plate 12 from the light emitting unit 11 is emitted from the light guide plate 12. Are arranged so as to coincide with the polarization direction.

  In the liquid crystal display device 1 having such a configuration, it was confirmed that the light utilization efficiency, which was improved only to about 51% in the conventional liquid crystal display device 100 shown in FIG. 2, is improved to 60%. . Furthermore, this is higher than the light utilization efficiency (about 57%) in the liquid crystal display device 200 using the light guide plate 212 and the first absorption type polarizing plate 222 made of the zero / zero birefringence polymer shown in FIG. I understand that it is expensive.

As described above, according to the first embodiment, the light guide plate is formed of a zero / zero birefringence polymer, the reflection plate is provided on the surface of the light guide plate opposite to the liquid crystal panel, and the back of the liquid crystal panel is provided. The light unit side surface is provided with a liquid crystal panel-side reflective polarizing plate that transmits only light in a specific vibration direction and reflects other light.
Therefore, it is possible to obtain a liquid crystal display device using an edge-light type backlight unit that can increase light utilization efficiency and reduce power consumption at low cost.

  DESCRIPTION OF SYMBOLS 1 Liquid crystal display device, 10 Backlight unit, 11 Light emission part, 11a Light source, 11b Reflection type polarizing plate (Light emission part side reflection type polarizing plate), 11c Reflection plate, 12 Light guide plate, 13 Reflection plate, 14 Diffusing sheet, 15 Prism Sheet, 20 liquid crystal panel, 21 liquid crystal cell, 22 reflection type polarizing plate (liquid crystal panel side reflection type polarizing plate), 23 absorption type polarizing plate.

Claims (3)

A liquid crystal display device comprising a liquid crystal panel and a backlight unit for irradiating the liquid crystal panel with light,
The backlight unit is
A light emitting section for emitting polarized light;
A light guide plate that is composed of a zero-zero birefringence polymer, guides light from the light emitting section, and extracts light from the surface;
A first reflector that is provided on a surface of the light guide plate opposite to the liquid crystal panel and reflects light;
The liquid crystal panel is
Provided on the surface on the backlight unit side, including a liquid crystal panel side reflective polarizing plate that transmits only light in a specific vibration direction and reflects other light ,
The light emitting unit
A light source that emits light;
A light-emitting part side reflective polarizing plate that transmits only light in a specific vibration direction and reflects other light among the light from the light source;
A second reflector that reflects the light reflected by the light-emitting part side reflective polarizing plate toward the light guide plate,
The liquid crystal panel side reflective polarizing plate is composed of one of a wire grid polarizing plate, a laminated polarizing plate, and a polarizing plate combining a laminated film and a transmissive polarizing plate,
The light emitting part side reflective polarizing plate is a wire grid polarizing plate in which metal wirings are arranged at a pitch of 50 to 100 nm, transmits light that vibrates in a direction perpendicular to the metal wiring, and is parallel to the metal wiring. Reflects light oscillating in the direction,
Liquid crystal display device. The light source, a liquid crystal display device according to claim 1 is a LED or CCFL. The backlight unit is
It further has at least one of a diffusion sheet for diffusing light and a prism sheet for collecting light,
The diffusion sheet and the prism sheet, a liquid crystal display device according to claim 1 or 2 has a polarization maintaining characteristics that do not change the polarization state of the incident light.

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