JP2007256697A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display, capable of reducing loss of light energy and improving the luminance of a screen by reducing light leakage from a gap between a reflection sheet on the rear-side of a light guide body and a printed board of a light source part. <P>SOLUTION: The liquid crystal display 1 is provided with a compact surface light source 6, arranged in a backlight 3, on the rear side of a liquid crystal display panel 2 and a light guide body 5 as a substantially rectangular plate which is arranged in the backlight 3 to radiate a light, emitted from the light source 6 from a light exit main surface 5a, to the liquid crystal display panel 2. The light guide body 5 has a surface-side inclined surface 10, where a side edge part is inclined at an inclination angle α so that thickness is thinned gradually, starting from a light-incidence side surface 5a to an opposite-side surface 5d and has a rear-side inclined surface 11, on the side of an opposite main surface 5c opposite to the surface side inclined surface 10, in parallel with the surface 10. If refractive index of the light guide body 5 is defined as n and the incident angle of light radiated from the light source 6 to the light incident side surface 5a at a radiation angle β upon the surface side inclined surface 10 is defined as γ, relations α< γ-β and γ=sin<SP>-1</SP>(1/n) holds. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transmissive or transflective liquid crystal display device in which a surface light source device is disposed on the back side of a liquid crystal display panel.

  In a transmissive or transflective liquid crystal display device such as an OA device, an information terminal device, or a personal computer, a surface light source device (backlight) is arranged on the back side of the liquid crystal display panel for clear display. . As a light source of such a backlight, for example, there is a light source using a small surface light source such as a light emitting diode (LED). Light from a small surface light source such as an LED having a small light emitting area is converted into a light guide, a reflection sheet, and a prism sheet. Are provided in the light path, so that a surface light source having required performance of a size suitable for the screen size of the display device can be obtained.

  As for the light in this light guide, the light in the LCD drive area and the vicinity thereof has a component in the direction parallel to the light emitting surface normal of the small surface light source, which contributes to improving the screen brightness. The component in the direction perpendicular to the light emitting surface normal perpendicular to this becomes a loss of light energy due to diffusion and absorption outside the light guide, and this is a factor of lowering screen brightness.

Therefore, the edge of the surface (light-emitting main surface) on the light incident side surface of the light guide is an inclined surface that is slanted so as to be thin in the direction of the opposite side surface that faces the light incident side surface. The incident light from the side surface is refracted to the outside of the light guide and becomes lost light, so that it is totally reflected by the inclined surface as an interface, thereby preventing the screen brightness from deteriorating. . (For example, see Patent Document 1)
For example, when an LED having a relative luminous intensity characteristic with respect to a radiation angle as shown in FIG. 5 is used as a small surface light source, most of the light energy is emitted light within a range of a radiation angle of 70 ° from the normal direction of the light emitting surface. Yes. Therefore, by using an inclined surface that totally reflects the emitted light within a range of a radiation angle of 70 °, the light directed toward the inclined surface is converted into the normal direction of the light emitting surface, and the screen brightness is Will improve.

  However, in the light guide provided with the inclined surface described above, absorption and diffusion at the interface between the reflection sheet disposed outside the opposing main surface of the light guide and the light guide are caused, so that light energy is reduced. Loss occurs.

On the other hand, the concave and convex lens-shaped fine processing is applied to the back surface (opposing main surface) of the light guide body provided with the inclined surface to reduce the energy loss of light emitted outward from the opposing main surface side of the light guide body. In addition to alleviating the brightness, the quality of the brightness unevenness of the entire screen is improved. However, in the light guide formed in this way, the light incident on the light incident side surface from the small surface light source is totally reflected by the inclined surface of the light guide and is subjected to microfabrication of an uneven lens shape. If it is directly propagated to the screen, it will be recognized as local unevenness with strong directivity on the screen, which causes a reduction in screen quality.
JP 2004-186131 A

The present invention has been made in view of the situation as described above.
Absorption and diffusion of light propagating inside the light guide due to total reflection cause interference between the printed circuit board of the light source unit and the reflective sheet, and the undulation of the reflective sheet caused by the interference occurs between the printed circuit board and the reflective sheet. An object of the present invention is to provide a liquid crystal display device in which light leakage from a gap is reduced and loss of light energy is reduced to improve screen luminance.

One is
The incident light is totally reflected by the inclined surface on the incident side surface, and light loss is reduced by the microfabrication of the concave-convex lens formed on the opposing main surface. An object of the present invention is to provide a liquid crystal display device that reduces local unevenness of strong directivity caused by directly propagating totally reflected light to a finely processed portion, and improves the screen luminance.

The liquid crystal display device of the present invention is
A liquid crystal display panel and a surface light source device disposed on the back side of the liquid crystal display panel are provided. The surface light source device has a light source and a light incident side surface facing the light source so that light from the light source is liquid crystal from the light output main surface. A liquid crystal display device configured to include a substantially rectangular flat plate-shaped light guide body that radiates toward a display panel,
The light guide has a surface-side inclined surface in which the edge portion of the light output main surface is inclined at a predetermined inclination angle α so as to gradually become thinner from the light incident side surface toward the opposite side surface facing the side surface, and Opposite main surface facing the light output main surface is opposed to the front side inclined surface, and has a back side inclined surface parallel thereto, the refractive index of the light guide is n, and the radiation angle from the light source toward the light incident side When the incident angle to the surface side inclined surface of the light emitted at β is γ,
α <γ-β
γ = sin ⁻¹ (1 / n)
It is a device characterized by being,
In addition, the liquid crystal display panel includes a surface light source device disposed on the back side of the liquid crystal display panel. The surface light source device has a light source and a flat light output from the light source with a light incident side surface facing the light source. A liquid crystal display device configured to include a substantially rectangular flat light guide that radiates from a main surface toward a liquid crystal display panel,
The light guide has a surface-side inclined surface that is inclined at a predetermined inclination angle α so that the light guide gradually becomes thinner from the light incident side surface to the light output surface, and on the opposite main surface facing the light output main surface of the light guide. , Having a prism pattern, t is the thickness of the light exit main surface, d is the difference between the thickness of the light incident side surface and the thickness t of the light exit main surface, and the radiation angle of the light emitted from the light source in the direction of the inclined surface on the surface side Is β
The distance L from the incident light side to the installation position of the prism pattern is
L ≧ d / tan α + t / tan {α + β}
It is the apparatus characterized by being.

According to the present invention,
Light leakage from the gap provided so as to avoid interference due to thermal expansion can be reduced between the reflection sheet provided on the back side of the light guide and the printed circuit board of the light source unit, and the loss of light energy is small. Can improve the screen brightness,
In addition, the incident light is totally reflected by the inclined surface on the light incident side surface, reducing the energy loss of light due to the finely processed irregularities formed on the opposing main surface, and reducing local luminance unevenness with strong directivity. And the screen luminance quality can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, a first embodiment will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a schematic configuration of a transmissive or transflective liquid crystal display device, and FIG. 2 is a cross-sectional view showing a light incident side surface portion of a light guide.

  1 and 2, a transmissive or transflective liquid crystal display device 1 includes a backlight (surface light source device) on the back side of a liquid crystal display panel 2 in which a liquid crystal layer is interposed between the opposing array substrate and the opposing substrate. 3 and the liquid crystal display panel 2 and the backlight 3 are housed in a case made up of an outer frame 4 and a back plate 4a.

  The backlight 3 includes a substantially rectangular flat plate-shaped light guide 5 made of a transparent synthetic resin material and the like, and a light emitting surface 6a with a predetermined gap with respect to a light incident side surface 5a of the light guide 5. And a small surface light source 6 such as a light emitting diode (LED) disposed opposite to each other. The small surface light source 6 constitutes a light source unit by being mounted on the printed circuit board 7.

  Further, the backlight 3 includes an optical sheet 8 such as a diffusion sheet or a prism sheet provided between the light output main surface 5b substantially orthogonal to the light incident side surface 5a of the light guide 5 and the back surface of the liquid crystal display panel 2, and a light guide. And a reflection sheet 9 disposed on the outer side of the opposing main surface 5c facing the light output main surface 5b of the light body 5.

  Further, the light guide 5 has an edge on the light incident main surface 5b so that the light guide 5 gradually becomes thinner from the light incident side surface 5a toward the opposite side surface 5d in the middle on the light incident side surface 5a side. A surface-side inclined surface 10 is formed in which a portion is inclined downward in the direction of the opposing main surface 5c by a predetermined inclination angle α. Further, an optical prism shape portion 12 having a back-side inclined surface 11 parallel to the front-side inclined surface 10 is provided on the side edge of the opposing main surface 5c facing the surface-side inclined surface 10 on the light incident side surface 5a side. ing.

  The light guide 5 is formed so that the thickness of the light guide 5 on the light incident side surface 5a and the height of the light emitting surface 6a of the small surface light source 6 arranged opposite to each other are substantially equal. The light exit main surface 5b is formed flat so as to be parallel to the surface of the liquid crystal display panel 2 from the intermediate portion to the opposite side surface 5d through the surface-side inclined surface 10. The flat light output main surface 5b is disposed so as to substantially face the display effective surface of the liquid crystal display panel 2, and the surface-side inclined surface 10 portion is positioned on the non-display surface portion side of the liquid crystal display panel 2. .

  On the other hand, the opposing main surface 5c is formed so as to be a substantially flat surface, and the portion facing the surface-side inclined surface 10 is substantially parallel to the surface-side inclined surface 10 and in the same direction as the side surface of the opposing side surface 5d. A plurality of back-side inclined surfaces 11 formed as described above are formed on the surface of the opposing main surface 5c, and each back-side inclined surface 11 is connected by a reverse inclined surface 13 to form a plurality of wedge-shaped optical prisms that are continuous as a whole. Forming.

Furthermore, regarding the inclination angle α formed by the flat surfaces of the light output main surface 5b and the opposing main surface 5c of the front side inclined surface 10 and the rear side inclined surface 11, the refractive index of the light guide 5 is n, and the small surface light source 6 is used. The emission range angle of light emitted from the light emitting surface 6a of the light guide 5 in the plane orthogonal to the light output main surface 5b is 2β, and the light incident surface 5a of the light guide 5 from the light emitting surface 6a of the small surface light source 6 When the incident angle of the light emitted at the radiation angle β toward the surface side inclined surface 10 is γ of the critical angle,
α <γ-β
γ = sin ⁻¹ (1 / n)
It has the relationship of.

  That is, since the light guide 5 is formed as described above and the light source 6 is arranged on the side edge of the light incident side 5 a of the light guide 5, the light is emitted from the light emitting surface 6 a of the small surface light source 6. Of the light emitted at the range angle 2β, the light directed toward the back-side inclined surface 11 of the outgoing light main surface 5b at the emission angle β is incident on the front-side inclined surface 10 at the incident angle γ. Here, the radiation range angle 2β is a radiation range angle set within a range in which the light energy supplied from the small surface light source 6 does not significantly affect the screen quality and screen brightness. Is an LED and the relative luminous intensity characteristic is the characteristic shown in FIG. 5, the radiation range angle 2β is 2 × 80 ° or less, particularly practically about 2 × 70 °.

  The light having the incident angle γ is totally reflected at the interface of the surface-side inclined surface 10 because the incident angle γ is a critical angle, and further totally reflected by the back-side inclined surface 11 parallel to the surface-side inclined surface 10. Thus, light is propagated in the direction of the opposing side surface 5d through the portion of the light guide 5 where the light output main surface 5b and the opposing main surface 5c are parallel to each other, so that the light loss can be greatly reduced.

  Further, the light emitted from the small surface light source 6 in the plane having the radiation angle β and incident on the light incident side surface 5a of the light guide 5 and directed toward the rear surface side inclined surface 11 is also back surface. Similarly, while being totally reflected by the side inclined surface 11, the inside of the portion where the light output main surface 5 b and the opposed main surface 5 c of the light guide 5 are parallel surfaces is transmitted in the direction of the opposed side surface 5 d.

  In this way, even the light having the radiation angle β from the small surface light source 6 is propagated into the light guide 5 while being totally reflected in the direction of the opposite side surface 5d, and the light incident side surface of the light guide 5 Since less light is emitted as refracted light outside the 5a edge, the loss of light energy can be very small, and the screen brightness can be improved.

  Further, since the printed circuit board 7 and the reflection sheet 9 of the light source portion on which the small surface light source 6 is mounted have a small amount of light that goes out of the light guide 5, the temperature rise is greatly reduced. Therefore, there is less risk of mutual interference due to thermal expansion, and the gap between them can be narrowed. As a result, light leakage from the gap between the printed circuit board 7 and the reflection sheet 9 can be reduced, the loss of light energy here can be reduced, and a decrease in screen brightness can be suppressed.

  Next, a second embodiment will be described with reference to FIGS. FIG. 3 is a cross-sectional view showing a schematic configuration of a transmissive or transflective liquid crystal display device, and FIG. 4 is a cross-sectional view showing a light guide. In addition, the same code | symbol is attached | subjected to the same part as 1st Embodiment, description is abbreviate | omitted, and the structure of this embodiment different from 1st Embodiment is demonstrated.

  3 and 4, the transmissive or transflective liquid crystal display device 21 is configured by arranging a backlight (surface light source device) 22 on the back side of the liquid crystal display panel 2. The backlight 22 has a substantially rectangular flat light guide 23 formed of a transparent synthetic resin material or the like, and is a small surface in which LEDs are linearly arranged with respect to a light incident side surface 23a of the light guide 23. A light source 6 is disposed opposite to the light emitting surface 6a with a predetermined gap.

  Further, in the first embodiment, the light guide 23 is gradually thinned from the light incident side surface 23a toward the opposite side surface 23d direction intermediate portion at the edge portion on the light incident side surface 23a side. The light-emitting main surface 23b on which the surface-side inclined surface 10 having the height difference d formed at the predetermined inclination angle α described above is formed passes through the surface-side inclined surface 10 and extends from the intermediate portion to the opposing side surface 23b. The flat plate portion 24 is formed so as to be parallel to the two surfaces. The light output main surface 23b formed by the flat flat plate portion 24 is disposed so as to substantially face the display effective surface of the liquid crystal display panel 2, and the surface side inclined surface 10 portion is a non-display surface portion of the liquid crystal display panel 2. It is made to be located on the side. On the other hand, the opposing main surface 23c is formed to be a substantially flat surface. Thereby, in the light guide 23, the thickness of the thin flat plate portion 24 facing the display area rear surface of the liquid crystal display panel 2 is t, and the thickness of the light incident side surface 23a is (t + d).

  Further, on the opposing main surface 23c of the light guide 23, a prism pattern 25 having a minute uneven shape is formed at a distance L from the light incident side surface 23a, for example, forming a predetermined distribution pattern finely processed into a minute convex lens shape. ing.

This distance L is
L ≧ d / tan α + t / tan {α + β}
Is set to Here, β corresponds to β described in the first embodiment. When the small surface light source 6 is, for example, an LED having a relative luminous intensity characteristic shown in FIG. 5, the radiation angle β is 80 ° or less, particularly about 70 ° practically.

  Since it is configured as described above, the inclination angle α is set so that the light traveling from the small surface light source 6 toward the surface-side inclined surface 10 having the radiation angle β takes a critical angle at the interface of the surface-side inclined surface 10. Because it is totally reflected. Further, the light reflected by the surface-side inclined surface 10 is not directly incident on the prism pattern 25 because the inclination angle α of the surface-inclined surface 10 and the distance to the prism pattern 25 are set to a predetermined value L. Propagated into the light body 23.

  As a result, since highly directional light emitted from the light emitting surface 6a of the small surface light source 6 is reflected by the surface-side inclined surface 10 and then does not directly enter the prism pattern 25, luminance unevenness on the screen is reduced. Thus, the screen brightness quality is improved.

It is sectional drawing which shows schematic structure of the liquid crystal display device which is the 1st Embodiment of this invention. It is sectional drawing which shows the light-incidence side part of the light guide in the 1st Embodiment of this invention. It is sectional drawing which shows schematic structure of the liquid crystal display device which is the 2nd Embodiment of this invention. It is sectional drawing which shows the light guide in the 2nd Embodiment of this invention. It is a characteristic view which shows the relative luminous intensity characteristic with respect to the radiation angle in LED of a small surface light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,21 ... Liquid crystal display device 2 ... Liquid crystal display panel 3,22 ... Backlight 5,23 ... Light guide 5a, 23a ... Light-incidence side surface 5b, 23b ... Light emission main surface 5c, 23c ... Opposite main surface 5d, 23d ... Opposing side surface 6 ... Small surface light source 6a ... Light emitting surface 10 ... Front side inclined surface 11 ... Back side inclined surface 24 ... Plate portion 25 ... Prism pattern

Claims (4)

A liquid crystal display panel, and a surface light source device disposed on the back side of the liquid crystal display panel. The surface light source device has a light source and a light incident side surface facing the light source, and emits light from the light source from a light output main surface. A liquid crystal display device configured to include a substantially rectangular flat light guide that radiates toward the liquid crystal display panel,
The light guide has a surface-side inclined surface in which the edge portion of the light-emitting main surface is inclined at a predetermined inclination angle α so as to gradually become thinner from the light incident side surface toward the opposite side surface facing the side surface. And having a back side inclined surface facing the front side inclined surface on the opposite main surface side facing the light output main surface, and having a refractive index n of the light guide from the light source When the incident angle to the surface-side inclined surface of the light emitted at the radiation angle β toward the light incident side surface is γ,
α <γ-β
γ = sin ⁻¹ (1 / n)
A liquid crystal display device characterized by the above.   The liquid crystal display device according to claim 1, wherein a plurality of the back side inclined surfaces are provided. A liquid crystal display panel, and a surface light source device disposed on the back side of the liquid crystal display panel. The surface light source device has a light source and a flat light output from the light source. A liquid crystal display device configured to include a substantially rectangular plate-shaped light guide body that radiates toward the liquid crystal display panel from a surface,
The light guide has a surface-side inclined surface inclined at a predetermined inclination angle α so as to gradually become thinner from the light incident side surface to the light output surface, and faces the light output main surface of the light guide. The opposite main surface has a prism pattern, the thickness of the light output main surface is t, the difference between the thickness of the light incident side surface and the thickness t of the light output main surface is d, and the surface side is inclined from the light source. When the emission angle of light emitted in the plane direction is β,
The distance L from the light incident side surface to the installation position of the prism pattern is
L ≧ d / tan α + t / tan {α + β}
A liquid crystal display device characterized by the above.   4. The liquid crystal display device according to claim 1, wherein the radiation angle [beta] is approximately 70 [deg.].

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