JP6448892B2 - Liquid crystal display device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a liquid crystal display device using a direct type backlight unit and a manufacturing method thereof.

  Conventionally, as a backlight unit applied to a liquid crystal display device, an edge light type backlight unit in which a light source is arranged at an edge of a light guide plate and light emitted from the light source is incident on the liquid crystal panel via the light guide plate. Are known.

  However, since the edge light type backlight unit uses a light guide plate, the large liquid crystal display is particularly heavy, and the light source is arranged at the edge of the light guide plate. There was a problem that the design was reduced.

  On the other hand, a light source is arranged on the back surface of the liquid crystal panel with respect to the edge light type backlight unit described above, and the light emitted from the light source is diffused and collected by a combination of various optical films (diffusion sheet, prism sheet, lens sheet, etc.). A direct type backlight unit that emits light and enters a liquid crystal panel is known.

  The direct-type backlight unit includes a plurality of light sources and a plurality of optical lenses corresponding to the light sources, and each of the optical lenses has a central lens portion having a convex shape, a concave shape, and a central lens portion. There has been proposed a backlight assembly including a peripheral lens portion formed on the outside and a light guide portion extended from the peripheral lens portion (see, for example, Patent Document 1).

Japanese Patent No. 4959971

  However, the direct type backlight has a problem that the thickness of the display is increased because the light source is disposed on the back surface of the liquid crystal panel. In addition, as a common problem with liquid crystal displays, most of the light emitted from the light source is absorbed by the polarizing plate provided on the incident surface (the surface on the backlight unit side) of the liquid crystal panel, so the light use efficiency is low. There is a problem.

  As a means for reducing the thickness of the direct type backlight, a method using a lens material having a high refractive index has been proposed. However, a general high refractive index material has a refractive index of about 1.7, and more than that. When seeking improvement, it is necessary to use expensive special materials.

  On the other hand, in order to increase the light use efficiency of the liquid crystal display, the reflection component and the transmission component in the orthogonal axial direction installed in front of the incident side polarizing plate (polarizing plate provided on the backlight side surface) of the liquid crystal panel A light recycling structure composed of an optical film (polarizing optical film) having a separating ability and a reflecting plate that reflects light not transmitted through the optical film or light emitted from a light source to the film side is applied. The method is widely used. A typical example of the film is DBEF (Dual BRIGHTNESS ENHANCEMENT FILM) composed of multilayer thin films having different refractive indexes. However, the size of the DBEF needs to be approximately the same as the size of the liquid crystal panel, and since the DBEF is formed of a multilayer film, there is a problem that the cost is increased particularly when the screen is enlarged. is there. Further, since the conversion efficiency from S wave to P wave in DBEF is not 100%, a new breakthrough is necessary to achieve further light use efficiency at low cost.

  The present invention has been made to solve the above-described problems, and is a liquid crystal using a direct type backlight unit that can be realized at low cost, thinning, improvement of light utilization efficiency, and low power consumption. An object is to obtain a display device and a manufacturing method thereof.

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 is provided to face the liquid crystal panel. Provided between a plurality of light sources that emit light, a plurality of lenses that refract the light emitted from the plurality of light sources, and between the plurality of light sources and the plurality of lenses, and transmits only light in a specific vibration direction A first polarizing plate that reflects non-transmitted light, and a reflecting plate that reflects the light reflected by the first polarizing plate and the light emitted from the plurality of light sources to the liquid crystal panel side. A second polarizing plate is provided on the light unit side surface and transmits only light in a specific vibration direction, and the transmission axis direction of the first polarizing plate and the transmission axis direction of the second polarizing plate coincide with each other. Wait , The first polarizer, for each of the plurality of light sources are those provided with a plurality.

The liquid crystal display device manufacturing method according to the present invention is a method of manufacturing a liquid crystal display device including a liquid crystal panel and a backlight unit that irradiates light to the liquid crystal panel. Between a plurality of light sources that emit light and a plurality of lenses that refract light emitted from the plurality of light sources, and transmits only light in a specific vibration direction to one surface of the substrate and does not transmit light. forming a first polarizing plate for reflecting the light emitted from the light and a plurality of light sources reflected by the first polarizing plate and a step of constructing a reflector for reflecting toward the liquid crystal panel, the liquid crystal Forming a second polarizing plate that transmits only light in a specific vibration direction on a side surface of the backlight unit of the panel, the transmission axis direction of the first polarizing plate and the transmission of the second polarizing plate As the direction coincide with each other, comprising the step of forming a second polarizer, the first polarizer, for each of the plurality of light sources are those provided with a plurality.

According to the liquid crystal display device and the method of manufacturing the same according to the present invention, the liquid crystal display device is provided between a plurality of light sources that emit light and a plurality of lenses that refract light emitted from the plurality of light sources, respectively. Provided on the surface on the backlight unit side of the liquid crystal panel, a first polarizing plate that transmits only light and reflects light that does not transmit, a recycling structure that reflects light reflected by the first polarizing plate to the liquid crystal panel side And a second polarizing plate that transmits only light in a specific vibration direction, and a transmission axis direction of the first polarizing plate and a transmission axis direction of the second polarizing plate coincide with each other.
Here, by providing the light recycling structure and the first polarizing plate, the light from the light source is ideally 100% of the second polarizing plate (the polarizing plate provided on the backlight unit side surface of the liquid crystal panel). Can penetrate.
Therefore, it is possible to obtain a liquid crystal display device using a direct-type backlight unit and a method for manufacturing the same, which can realize a reduction in thickness, an improvement in light utilization efficiency, and a reduction in 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 an expanded sectional view which shows the principal part of the liquid crystal display device which concerns on Embodiment 1 of this invention. It is another expanded sectional view which shows the principal part of the liquid crystal display device which concerns on Embodiment 1 of this invention.

  Hereinafter, preferred embodiments of a liquid crystal display device and a method for manufacturing the same 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 liquid crystal panel 10 and a backlight unit 20 that irradiates the liquid crystal panel 10 with light.

  The backlight unit 20 is provided to face the liquid crystal panel 10 and includes a plurality of light sources that respectively emit light and a plurality of lenses that refract the light emitted from the plurality of light sources. That is, the backlight unit 20 constitutes a direct type backlight unit.

  Here, an LED (Light Emitting Diode), a CCFL (Cold Cathode Fluorescent Lamp), a semiconductor laser, or the like is used as the light source. Here, a case where the light source is an LED will be described, but the same can be said for a CCFL.

  FIG. 2 is an enlarged cross-sectional view showing a main part of the liquid crystal display device 1 according to Embodiment 1 of the present invention. In FIG. 2, the liquid crystal panel 10 includes a liquid crystal layer 11 and a second polarizing plate 12 that is provided on the surface of the liquid crystal layer 11 on the backlight unit 20 side and transmits only light in a specific vibration direction. . The liquid crystal panel 10 also has a polarizing plate different from the plurality of substrates and the second polarizing plate 12, but illustration of these is omitted here.

  The backlight unit 20 includes a substrate 21, a lens 22, a first polarizing plate 23, an LED 24, and a reflection plate 25. The lens 22 is formed on the liquid crystal panel 10 side of the substrate 21. The detailed configuration of the lens 22 will be described later.

  The first polarizing plate 23 is formed between the lens 22 and the LED 24 on the surface of the substrate 21 opposite to the liquid crystal panel 10 and transmits only light in a specific vibration direction. The first polarizing plate 23 may be formed on the surface of the substrate 21 on the liquid crystal panel 10 side. At this time, the lens 22 is formed on the first polarizing plate 23. The role of the substrate 21 can also be used for the first polarizing plate 23. In that case, the lens 22 is formed on the surface of the first polarizing plate 23 on the liquid crystal panel 10 side, and the LED 24 is formed on the opposite surface.

  The first polarizing plate 23 is a reflective polarizing plate, and is preferably a wire grid polarizing plate. The wire grid polarizing plate is a polarizing plate in which metal wiring is arranged at a pitch of 50 to 100 nm, for example, and transmits light that vibrates in a direction perpendicular to the metal wiring and reflects light that vibrates in a direction parallel to the metal wiring. To do. In addition, it has high heat resistance and is suitable for use in the vicinity of LEDs that are exposed to high temperatures.

  A plurality of first polarizing plates 23 are provided corresponding to each of the plurality of LEDs 24 provided in the backlight unit 20. Specifically, as many first polarizing plates 23 as the number of LEDs 24 are provided in accordance with the sizes of the lenses 22 and the LEDs 24. That is, the 1st polarizing plate 23 is provided in a part of board | substrate 21, and is not provided in the whole surface.

  LED24 is being fixed to the surface on the opposite side to the lens 22 of the 1st polarizing plate 23 with resin. A phosphor, a quantum dot (QD: Quantum Dot), or the like for converting the wavelength of the LED 24 may be mixed in the resin. The reflection plate 25 is formed on the first polarizing plate 23 so as to cover the LED 24, and reflects the light reflected by the first polarizing plate 23 and the light emitted from the LED 24 toward the liquid crystal panel 10. A heat radiating plate (not shown) for radiating heat generated by the LED 24 may be provided around the reflecting plate 25.

  At this time, the 1st polarizing plate 23 and the reflecting plate 25 comprise an optical recycling structure. Note that the light recycling structure in the above-described conventional direct type backlight unit uses DBEF and a reflector that are approximately the same size as the liquid crystal panel, which increases the cost. In the first embodiment, the cost can be reduced by providing the first polarizing plate 23 according to the size of the lens 22 or the LED 24.

  Here, in FIG. 2, the transmission axis direction of the first polarizing plate 23 and the transmission axis direction of the second polarizing plate 12 coincide with each other. In such a liquid crystal display device 1, among the light emitted from the LED 24, the light reflected by the first polarizing plate 23 is reflected by the reflecting plate 25 and changes its polarization state. The light passes through the first polarizing plate 23 with an efficiency close to 100%.

  Further, since the transmission axis direction of the first polarizing plate 23 and the transmission axis direction of the second polarizing plate 12 coincide with each other, all the light transmitted through the first polarizing plate 23 passes through the second polarizing plate 12. To Penetrate. That is, by providing the first polarizing plate 23, the light absorbed by the second polarizing plate 12 can be significantly reduced. Therefore, it is possible to increase the light utilization efficiency and reduce the power consumption.

  Next, the detailed configuration of the lens 22 will be described. In the direct type backlight unit, the plurality of LEDs 24 are arranged at the lower part of the liquid crystal panel 10, so that the number of LEDs increases. Further, in order to reduce the number of LEDs, it is necessary to take a certain distance between the LED 24 and the liquid crystal panel 10 in order to diffuse the light emitted from the LED 24, and an edge light type backlight unit is used. The thickness of the liquid crystal display device 1 is thicker than that of the case.

  Therefore, it is conceivable to use a lens 22 having a high refractive index in order to reduce the number of LEDs and reduce the thickness of the liquid crystal display device 1. However, a general high refractive index material has a refractive index of about 1.7, and when further improvement is required, it is necessary to use an expensive material. Therefore, in order to form a lens with a relatively low cost and a high refractive index, each of the plurality of lenses 22 according to Embodiment 1 of the present invention includes a liquid crystal material that is uniaxially aligned, for example, a bis-biphenyl-diacetylene-based material. Or a dinaphthyl-diacetylene-based material or the like.

  Further, the uniaxial alignment of the liquid crystal material constituting the lens 22 is realized by any of a rubbing method, a photo alignment method, a shearing method, or a magnetic field alignment method. It is also conceivable to use a uniaxially oriented crystal instead of the uniaxially oriented liquid crystal material.

  In the lens 22 using the liquid crystal material described above, the difference Δn between the refractive index ne in the longitudinal direction of the liquid crystal and the refractive index no in the short direction is as large as about 0.4, and the refractive index ne is as high as about 2.0. Indicates the value. Therefore, by using the refractive index ne in the longitudinal direction of the liquid crystal material, it is possible to produce a lens with a relatively low cost and a high refractive index, to reduce the number of LEDs and to make the liquid crystal display device 1 thinner. Can do.

  Here, in FIG. 2, the optical axis (direction showing the refractive index ne) of the liquid crystal material constituting the lens 22 has a transmission axis direction of the first polarizing plate 23 and the second polarizing plate 12, and Are consistent with each other. In such a liquid crystal display device 1, the light transmitted through the first polarizing plate 23 is incident in parallel with the direction indicating the refractive index ne, and thus is refracted with the refractive index ne and transmitted through the second polarizing plate 12.

  That is, by making the direction of the refractive index ne of the liquid crystal material constituting the lens 22 coincide with the transmission axis directions of the first polarizing plate 23 and the second polarizing plate 12, a high refractive index can be utilized. A lens with a high refractive index can be produced at a relatively low cost, the number of LEDs can be reduced, and the liquid crystal display device 1 can be made thinner.

  In addition, along with the reduction in thickness, in the direct type backlight unit, the light source is arranged on the back surface of the liquid crystal panel, so it is necessary to secure a space for arranging the LEDs around the liquid crystal panel like the edge light type backlight unit. Furthermore, in the direct type backlight unit, since there is no light guide plate, it is not necessary to consider the expansion of the light guide plate due to high temperature or moisture absorption, and an ultra-narrow frame can be easily realized and the design can be improved. it can.

As described above, according to the first embodiment, only light in a specific vibration direction is provided between a plurality of light sources that emit light and a plurality of lenses that refract light emitted from the plurality of light sources. The transmission axis direction of the first polarizing plate that transmits light and the transmission axis direction of the second polarizing plate that is provided on the surface on the backlight unit side of the liquid crystal panel and transmits only light in a specific vibration direction are identical to each other. I'm doing it.
Here, the first polarizing plate is a reflective polarizing plate having a light recycling structure. By providing the first polarizing plate, the second polarizing plate (the polarizing plate provided on the surface of the liquid crystal panel on the backlight unit side). Can reduce the light absorbed.
Therefore, it is possible to obtain a liquid crystal display device using a direct type backlight unit and a method for manufacturing the same, which can significantly increase the light utilization efficiency and reduce power consumption at low cost.

Each of the plurality of lenses is made of a uniaxially oriented liquid crystal material, and the optical axes having higher refractive indices of the lenses coincide with the transmission axes of the first polarizing plate and the second polarizing plate.
Therefore, a lens having a high refractive index can be formed at a relatively low cost, the number of light sources can be reduced, and the liquid crystal display device can be thinned.

  In the first embodiment, the case where the first polarizing plate 23 is a reflection-type polarizing plate has been described with reference to FIG. 2, but the first polarizing plate may be an absorption-type polarizing plate. Good. Hereinafter, the case where the first polarizing plate is an absorption-type polarizing plate will be described with reference to FIG.

  FIG. 3 is another enlarged cross-sectional view showing the main part of the liquid crystal display device 1 according to Embodiment 1 of the present invention. In FIG. 3, the first polarizing plate is an absorptive polarizing plate, and includes an absorptive polarizing plate 26 and a polarizing optical film 27 provided on the LED 24 side of the absorptive polarizing plate 26. The polarizing optical film 27 is a film having a multilayer thin film structure with different refractive indexes, such as DBEF.

  Here, the transmission axis direction of the absorption-type polarizing plate 26 and the transmission axis direction of the polarizing optical film 27 coincide with each other. In such a first polarizing plate, all the light transmitted through the polarizing optical film 27 passes through the absorption-type polarizing plate 26 without being absorbed, and thus functions similar to those of the first polarizing plate 23 shown in FIG. Have

  DESCRIPTION OF SYMBOLS 1 Liquid crystal display device, 10 Liquid crystal panel, 11 Liquid crystal layer, 12 2nd polarizing plate, 20 Backlight unit, 21 Substrate, 22 Lens, 23 1st polarizing plate, 24 LED, 25 Reflector, 26 Absorption type polarizing plate, 27 Polarizing optical film.

Claims (8)

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 plurality of light sources provided facing the liquid crystal panel, each emitting light;
A plurality of lenses for refracting light emitted from the plurality of light sources;
A first polarizing plate that is provided between the plurality of light sources and the plurality of lenses and transmits only light in a specific vibration direction and reflects light that does not transmit;
A reflection plate that reflects the light reflected by the first polarizing plate and the light emitted from the plurality of light sources to the liquid crystal panel side,
The liquid crystal panel is
A second polarizing plate that is provided on the surface of the backlight unit and transmits only light in a specific vibration direction;
The transmission axis direction of the first polarizing plate and the transmission axis direction of the second polarizing plate coincide with each other,
A plurality of the first polarizing plates are provided corresponding to each of the plurality of light sources. The liquid crystal display device according to claim 1, wherein the first polarizing plate is a reflective polarizing plate. The liquid crystal display device according to claim 2, wherein the reflective polarizing plate is a wire grid polarizing plate. The liquid crystal display device according to claim 1, wherein the first polarizing plate is an absorptive polarizing plate. The absorption-type polarizing plate is
An absorption polarizing plate;
A polarizing optical film provided on the light source side of the absorption-type polarizing plate;
The liquid crystal display device according to claim 4, wherein a transmission axis direction of the absorptive polarizing plate and a transmission axis direction of the polarizing optical film coincide with each other. The said reflecting plate is provided in the opposite side to the said liquid crystal panel of these light sources, and reflects the light reflected by the said 1st polarizing plate to the said liquid crystal panel side. Any one of Claim 1-5 2. A liquid crystal display device according to item 1. The plurality of lenses are each composed of a uniaxially oriented liquid crystal material, and the optical axes of the liquid crystal material having a higher refractive index coincide with the transmission axis directions of the first polarizing plate and the second polarizing plate. The liquid crystal display device according to any one of claims 1 to 6. A method of manufacturing a liquid crystal display device comprising a liquid crystal panel and a backlight unit for irradiating the liquid crystal panel with light,
About the backlight unit, light in a specific vibration direction is provided between a plurality of light sources that emit light and a plurality of lenses that refract light emitted from the plurality of light sources, on one surface of the substrate. Forming a first polarizing plate that transmits only light and reflects light that does not transmit;
Constructing a reflector that reflects the light reflected by the first polarizing plate and the light emitted from the plurality of light sources to the liquid crystal panel side, and
Forming a second polarizing plate that transmits only light in a specific vibration direction on a side surface of the backlight unit of the liquid crystal panel, the transmission axis direction of the first polarizing plate and the transmission of the second polarizing plate; Forming the second polarizing plate so that the axial directions coincide with each other;
The said 1st polarizing plate is provided with two or more corresponding to each of these light sources. The manufacturing method of a liquid crystal display device.

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