JPH1020310A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device equipped with a back light capable of emitting linearly polarized light whose polarization degree is high, without using a polarizing plate. SOLUTION: The device is provided with a light condensing sheet 6 for enhancing the directivity of a luminous flux emitted from a cold cathode fluorescent lamp and guiding the luminous flux to a light transmission plate 3, and the sheet 6 is installed on the light incident plane of the light transmission plate 3, and the device is also provided with a collimator lens sheet 10 for controlling the angle of the advancing direction of the luminous flux which is emitted toward a reflection sheet 12 after returning from the reflection polarizing plate 8 to the light transmission plate 3 so that the luminous flux may advance in a direction near the normal direction of a 1/4 wavelength plate 11. Thus, the light using efficiency is enhanced and a bright display is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various display devices such as a simple matrix type liquid crystal display device and an active matrix type liquid crystal display device provided with a backlight having high luminance and low power consumption, and more particularly, to a back surface of the display device. The present invention relates to a transmission type liquid crystal display device in which a surface light source device is disposed.

[0002]

2. Description of the Related Art With the spread of multimedia, it is desired to reduce the thickness and weight of a display device and to reduce power consumption in order to improve portable performance. In recent years, a so-called liquid crystal display device has been used as a thin and lightweight display device with low power consumption. It is becoming heavily used.

[0003] The liquid crystal display device has an illuminating device called a backlight installed on the back of the liquid crystal display element, and an image formed on the liquid crystal display element by illumination light from the backlight.
Visualize letters or numbers.

The backlight includes a light guide plate formed of a transparent substrate for transmitting light in a planar manner, a cold cathode fluorescent lamp provided along at least one side edge of the light guide plate, and a top surface of the light guide plate. A prism sheet inserted between liquid crystal display elements,
And a reflection sheet provided or formed on the back surface of the light guide plate.

FIG. 1 is an exploded perspective view for explaining an example of the entire configuration of a general liquid crystal display device.
Is a backlight, 3 is a light guide plate, 4 is a cold cathode fluorescent lamp, 5 is a lamp reflection sheet, 9 is a prism sheet, 12 is a reflection sheet, 13 is a diffusion sheet, 14 is an upper frame, 15 is a spacer, and 16 is a printed circuit board. , 17 are shading frames, 1
8 is an intermediate frame, 19 is a lower frame, and 20 is a lamp cover.

In FIG. 1, a liquid crystal display element 1 has a driving I
A printed circuit board 16 on which electronic components such as C are mounted is integrated, and the backlight 2 is stacked on the lower surface of the printed circuit board 16 and assembled to the intermediate frame 18, which is sandwiched and fixed between the upper frame 14 and the lower frame 19. You.

The backlight 2 has a light guide plate 3 having a spread covering at least an effective area of the liquid crystal display element 1.
A reflection sheet 12 provided on the lower surface of the light guide plate 3, a diffusion sheet 13 provided on the upper surface of the light guide plate 3, a prism sheet 9 provided between the diffusion sheet 13 and the liquid crystal display element 1, and a light guide plate 3. Cold cathode fluorescent lamp 4, lamp reflection sheet 5, and lamp cover 2 arranged along one edge
0.

A spacer 15 is interposed between the liquid crystal display element 1 and the upper frame 14, and light from the backlight 2 is interposed between the liquid crystal display element 1 and the backlight 2. A light-shielding frame 17 for preventing leakage outside the effective area is provided.

In such a structure, the liquid crystal display element 1
Is illuminated with the illumination light from the backlight 2,
Images, characters, numbers, and the like formed on the liquid crystal display element 1 are visually displayed.

FIG. 2 is a cross-sectional view of a main part of a conventional liquid crystal display device for explaining the structure of a backlight, wherein 1 is a liquid crystal display element, 2 is a backlight, 3 is a light guide plate, 4 is a cold cathode fluorescent lamp, 4a is a power supply cable of a cold cathode fluorescent lamp, 5 is a lamp reflection sheet, 9 is a prism sheet, 12 is a reflection sheet, 13 is a diffusion sheet, 14 is an upper frame, 16 is a printed board, and 16a is a drive IC mounted on a printed board. ,
18 is an intermediate frame, and 19 is a lower frame.

In FIG. 1, a cold cathode fluorescent lamp 4, a lamp reflection sheet 5, a reflection sheet 12, a light guide plate 3, a diffusion sheet 1
A backlight (illumination light source) 2 is constituted by 3 and the prism sheet 9.

The liquid crystal display element 1 is stacked above the backlight 2 which is the illumination light source, and is integrated with the upper frame 14 and the lower frame 19 together with the printed circuit board 16 on which the drive IC 16a is mounted to constitute a liquid crystal display device. .

All the light entering the light entrance surface of the light guide plate 3 from the cold cathode fluorescent lamp 4 enters the light guide plate at a refraction angle of 42 ° or less with respect to the light entrance surface, as indicated by arrows in the figure. The liquid crystal display element 1 propagates through the light guide plate 3 while repeating reflection on the upper and lower surfaces of the light guide plate and scattering by the print pattern.
To illuminate the liquid crystal display element 1 from behind.

As described above, the backlight used in the liquid crystal display device transmits light from the cold-cathode tube provided along the side edge of the light guide plate made of a transparent plate preferably made of a resin plate to the light guide plate. In this way, they are distributed in a planar manner.

In recent liquid crystal display devices,
The backlight itself needs to have high brightness and low power consumption in order to achieve high brightness and low power consumption of the liquid crystal display device.

For this purpose, for example, as shown in ASIA DISPLAY '95, pages 731 to 734, polarized light can be made incident on a liquid crystal cell without using a polarizing plate. Possible light guide plates have been proposed.

FIG. 3 is a schematic sectional view showing a partial structure of a backlight having a light guide plate capable of emitting polarized light.

As shown in FIG. 1, a lenticular lens array 21 is provided on the upper surface of the light guide plate 3, and a titanium oxide film having a thickness of 1/4 wavelength is formed on the upper and lower surfaces thereof. A glass substrate 8 is disposed, and a prism sheet 9 is disposed thereon. In addition, a reflector 12 is disposed below the light guide plate via a １ ／ wavelength plate 11.

In the backlight having such a structure, the light generated from the cold cathode fluorescent lamp 4 is incident on the light guide plate 3 and is incident on the glass substrate 8 through refraction and transmission on the surface of the lenticular lens array 20. I do. Assuming that the paper surface is the incident surface and the refractive index of the titanium oxide is 2.3, of the light incident on the glass substrate 8, the light incident at an incident angle of 66.5 ° is formed on the surface of the titanium oxide film by air and oxidized light. The light is incident at an incident angle substantially equal to the Brewster angle at the medium boundary of titanium. At this time, with respect to the medium boundary between the air and the titanium oxide, the transmittance of the p-wave is 100% and the transmittance of the s-wave is about 53% among the polarization components constituting the light.

The light transmitted through the medium boundary between air and titanium oxide enters the medium boundary between titanium oxide and glass at an incident angle of about 23 °, and the p-wave transmittance at this boundary is about 98%.
The s-wave transmittance is about 95%.

Further, the light transmitted through the medium boundary between the titanium oxide and the glass is approximately 3
The light is incident at an incident angle of 5 °, and the p-wave transmittance at this interface is about 98% and the s-wave transmittance is about 95%.

Furthermore, the light transmitted through the medium boundary between glass and titanium oxide impinges on the medium boundary between titanium oxide and air by about 24 μm.
入射, and the p-wave transmittance at this interface is 10
0%, the s-wave transmittance is about 53%. The transmitted light here is emitted into the air at a refraction angle of 66.5 °.

When the transmittances at the boundaries of these four media are integrated, the light incident on the glass substrate 8 from the light guide plate 3 at the Brewster angle of 66.5 ° has a p-wave transmittance of about 97%. , S-wave transmittance is about 26%, so that a remarkable polarization splitting action occurs.

The s-wave reflected by the glass substrate is reflected by the light guide plate 3, is reflected by the reflector 12 via the quarter-wave plate 11, passes through the light guide plate, and returns to the glass substrate. At this time, since the s-wave has passed through the quarter-wave plate 11 twice, the plane of polarization of the light has been rotated by 90 ° and has been converted to a p-wave. The s-wave component re-enters the glass substrate as a p-wave and is transmitted. As a result, about 87% of the light emitted from the glass substrate 8 having the titanium oxide film formed on the upper and lower surfaces becomes a p-wave, and the glass substrate 8 can be used substantially as a substitute for the polarizing plate. The light beam emitted from the glass substrate 8 is subjected to angle control by the prism sheet 9 and emitted in the vertical direction (normal direction of the display surface) in the plane of incidence to illuminate the liquid crystal display element 1 (without the lower polarizing plate). It will be.

Thus, light close to linearly polarized light can be incident on the liquid crystal layer without using a polarizing plate. Therefore, if the possibility of multiple incident surfaces and its influence are not considered, the number of polarizing plates used Can be reduced from two to one, and there is an effect that the luminance can be improved correspondingly.

[0026]

In the backlight device shown in FIG. 3, the light emitted from the ordinary light guide plate has a diffusive property. It can be seen that the number of incident surfaces when light is incident on the surface is innumerable, not one. Therefore, at this time, even if a p-wave having a degree of polarization of 1 is obtained on each of the incident surfaces, the light transmitted through the glass substrate becomes a composite wave thereof. Light having different incident surfaces is light that has propagated through different light paths in the light guide plate 3 or light in which phase information is randomized by scattering. Instead, it becomes a partially polarized light in which natural light components are mixed. When light in such a state is incident on the liquid crystal display element 1 (without the lower polarizing plate), even if the pixels of the liquid crystal display element 1 (without the lower polarizing plate) are in the OFF state, the upper polarized light of the liquid crystal display element is turned off. There is a problem that a component that transmits through the plate is inevitably generated and the contrast is deteriorated as compared with a normal liquid crystal display device in which linearly polarized light is incident on a liquid crystal layer using a polarizing plate.

Further, s reflected by the glass substrate 8
Waves １ ／ through lenticular lens array
To enter the wave plate 11 at various angles, 1/4
There is a problem in that the phase shift effect received in the wave plate 11 differs for each incident angle, and an s wave having a specific incident angle is not correctly converted to a p wave.

An object of the present invention is to provide a liquid crystal display device having a backlight capable of emitting linearly polarized light having a high degree of polarization without using a polarizing plate.

[0029]

In order to achieve the above object, a liquid crystal display device to which the present invention is applied comprises: a light guide plate made of a transparent plate having a rear surface subjected to a light reflection treatment for avoiding total reflection; A cold cathode fluorescent lamp installed along the light incident surface with at least one side edge of the light guide plate as a light incident surface, and a lamp reflection installed around the cold cathode fluorescent lamp except for a portion facing the light incident surface. A sheet, a transparent plate with a high refractive index film installed on the upper surface of the light guide plate, a prism sheet installed on the upper surface of the transparent plate with the high refractive index film, and a 波長 wavelength plate installed on the lower surface of the light guide plate And at least a reflection sheet provided on the lower surface of the quarter-wave plate, and a liquid crystal display element provided on the upper surface of the prism sheet, between the cold cathode fluorescent lamp and the light incident surface of the light guide plate. The light emitted from the cold cathode fluorescent lamp is collected and It was installed a condensing sheet to be introduced into the light incident surface.

Further, a condensing sheet is provided between the side end surface of the light guide plate and the cold cathode fluorescent lamp, and a collimator lens sheet is provided between the light guide plate and the quarter-wave plate.

In the backlight of the present invention, since the light generated from the cold cathode fluorescent lamp is incident on the light guide plate in a state where the directivity is enhanced by the condensing sheet, the light is repeatedly reflected on the upper and lower surfaces of the light guide plate. The trajectory of the light beam propagating in the light plate is within one plane (for example, in the plane of the paper, that is, in the plane perpendicular to the cold cathode fluorescent lamp).
, And the incident surface of the group of light rays emitted from the upper surface of the light guide plate and incident on the glass substrate 8 can be made substantially the same. Thereby, the polarization planes of the group of rays (p-waves) transmitted through the glass substrate 8 can be made substantially the same, and linearly polarized light having a high degree of polarization can be emitted.

In the backlight of the present invention, the polarization planes of the group of light rays (s-waves) reflected by the glass substrate 8 are also substantially the same, and they pass through the light guide plate and are １ ／ of the lower part of the light guide plate. When entering the wave plate 11, the １ ／ wave plate 1
Collimator lens sheet 10 placed on top of 0
As a result, the trajectory of the incident light is corrected to approximately 0 degrees, so that a group of light beams (s-waves) emitted from the lower surface of the light guide plate at various emission angles undergo substantially the same phase shift action by the collimator lens sheet 10. Become. Thereby, when the light beam group (s-wave) reflected by the glass substrate 3 returns to the light guide plate side via the 波長 wavelength plate, any of the linearly polarized light whose polarization plane is rotated by 90 degrees (ie, (The p-wave for the original incident surface), the s-wave reflected by the glass substrate 3 can be re-incident on the glass substrate 3 as a p-wave having a high degree of polarization, and linearly polarized light having a high degree of polarization can be obtained. Can be emitted.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 is a schematic view of a main part of an embodiment of a liquid crystal display device according to the present invention, wherein 1 is a liquid crystal display element (without a lower polarizing plate), 2 is a backlight, 3 Is a light guide plate, 4 is a cold cathode fluorescent lamp, 5 is a lamp reflection sheet, 6 is a condensing sheet, 7 is a reflection tape, 8 is a transparent plate with a high refractive index film, 9 is a prism sheet, 10 is a collimator lens,
A sheet, 11 is a quarter-wave plate, and 12 is a reflection sheet.

In the figure, a backlight 2 comprises a light guide plate 3 made of a transparent plate having a rectangular cross section, a cold cathode fluorescent lamp 4 installed along one side edge thereof, and a light guide plate 3 of the cold cathode fluorescent lamp 4. Lamp reflecting sheet 5 installed around except for the facing side
A light-collecting sheet 6 provided along the one side edge of the light guide plate 3; a reflection tape 7 provided on a side edge of the light guide plate 3 opposite to the cold cathode fluorescent lamp 4; Side (top)
A transparent plate 8 with a high-refractive-index film placed thereon, a prism sheet 9 further placed thereon, a quarter-wave plate 11 placed on the lower surface of the liquid crystal display element 1, and a reflection sheet 12. Consists of

The light guide plate 3 has, for example, a length of 155 mm in the vertical direction (vertical direction), a length of 218 mm in the horizontal direction (horizontal direction), and
It is composed of a transparent plate such as an acrylic resin plate having a thickness of 4 mm and a refractive index of about 1.50 which has been subjected to a process of avoiding total reflection. There are two types of processing for avoiding total reflection, a processing mainly based on light scattering and a processing mainly based on regular reflection of light. Processing mainly based on light scattering includes:
Representative examples include a method of pattern printing an ink material having a light scattering property on the back surface of the transparent plate and a method of roughening the back surface of the transparent plate. A typical example of the processing mainly based on the regular reflection of light is a method of forming a prism array on the back surface of a transparent plate.

In applying the present invention, it is more desirable to use a prism array that performs regular reflection.

The light beam incident on the light entrance surface of the light guide plate 3 from the cold cathode fluorescent lamp 4 is condensed by the light condensing sheet 6 provided between the light entrance surface and the cold cathode fluorescent lamp 4.

The light beam condensed by the light condensing sheet 6 is
In the light guide plate 3, the reflection by the upper surface of the light guide plate 3 and the lower surface of the light guide plate including the reflection sheet 12 are repeated in the direction of the reflection tape 7, and substantially on the same plane (for example, on the paper surface, that is, on the surface perpendicular to the cold cathode fluorescent lamp). To propagate. At this time, by optimizing the process for avoiding total reflection performed on the back surface of the light guide plate 3, the light flux from the upper surface of the light guide plate 3 at an emission angle substantially equal to the Brewster angle on the surface of the transparent plate 8 with a high refractive index film. Is emitted. In this emitted light beam, a p-wave (the same plane, for example, a polarization component having an electric field vector parallel to the plane of the paper) transmits through the transparent plate 8 with a high refractive index film and is substantially parallel to the same plane (for example, the plane of the paper). The liquid crystal display element 1 (without a lower polarizing plate) is illuminated as linearly polarized light having a high degree of polarization consisting of only a polarized component.

In the liquid crystal display element 1 (without a lower polarizing plate), a predetermined pixel is made to be in a light transmitting state by a drive circuit (not shown), and illumination light from the backlight 2 passes through the pixel in the light transmitting state. To provide a visible display.

The s-wave (polarized light component having an electric field vector perpendicular to the plane of the drawing) of the light beam emitted from the upper surface of the light guide plate 3 is reflected by the transparent plate 8 with a high refractive index film. After passing through the light guide plate 3, the collimator
After being collimated by the lens sheet 10 in the normal direction of the quarter-wave plate 11, the light is reflected by the reflection sheet 12 via the quarter-wave plate 11, so that most of the light (s
(Wave) becomes a state of linearly polarized light whose polarization plane is rotated by 90 degrees, and returns to the light guide plate 3 side. Therefore, the light is re-incident on the transparent plate 8 with a high refractive index film as a p-wave having a high degree of polarization consisting of only a polarization component having an electric field vector substantially parallel to the same plane (for example, a paper surface). Illuminating the liquid crystal display element 1 (without a lower polarizing plate) as linearly polarized light having a high degree of polarization, which is transmitted only through the transparent plate 8 and has only a polarization component substantially parallel to the same plane (for example, paper). Become.

The reflection tape 7 has a function of returning the light that escapes from the light guide plate 3 to the light guide plate 3 again.

FIG. 5 is a partially broken plan view illustrating the installation state of the condensing sheet constituting the backlight in FIG.

As shown in the figure, the light-collecting sheet 6 is disposed close to the light entrance surface 3b of the light guide plate 3, that is, the side edge where the cold cathode fluorescent lamp 4 is installed. The light beam emitted from the light-collecting sheet 6 is condensed in a predetermined direction by passing through the light-collecting sheet 6, thereafter enters the light guide plate 3, and is emitted from the upper surface of the light guide plate 3 while repeating regular reflection and scattering.

FIG. 6 is an explanatory view of an example of a light-collecting sheet constituting a backlight according to the present invention.
(B) is a perspective view of the light-condensing sheet viewed from the light guide plate 3 side, (c) is a partial cross-sectional view cut along the line DD of (b), 6 is a light-collecting sheet of this example, 6a
Is a micro convex lens.

In this example, the light guide plate 3 is a transparent resin plate having the same thickness from the cold cathode fluorescent lamp installation side edge to the reflection tape 7 side. A prism array is formed on the back of the plate. The condensing sheet 6 located on the side edge of the cold cathode fluorescent lamp installation side has a large number of minute convex lenses 6a on the surface facing the cold cathode fluorescent lamp 4, and the light guide plate 3 side is a flat surface.

The condensing sheet 6 allows the cold cathode fluorescent lamp 4
The light emitted from the light guide plate 6a is condensed on the light guide plate 3 by the minute convex lens 6a on both surfaces in a plane parallel to the paper surface and in a plane perpendicular to the paper surface, and enters the light guide plate 3.

As a result, most of the luminous flux emitted from the cold cathode fluorescent lamp 4 is condensed with respect to the light incident surface of the light guide plate 3 in both a plane parallel to the paper and a plane perpendicular to the paper. Light is incident at a smaller incident angle than when there is no sheet. Taking into account the refraction effect on the light incident surface, the light flux entering the light guide plate 3 is condensed within a narrower angle range on both surfaces in a plane parallel to the paper and in a plane perpendicular to the paper. , And travels inside the light guide plate 3. The traveling direction of the light beam is controlled by specular reflection on the inclined surface of the prism array provided on the back surface of the light guide plate 3 so that the light beam is kept in a state parallel to the plane of the drawing. The light can be emitted from the upper surface of the light guide plate 3 at an emission angle substantially equal to the Brewster angle on the surface of the transparent plate 8 with a high refractive index film.

The plane of incidence when this emitted light beam enters the surface of the transparent plate 8 with a high-refractive-index film is equal to the plane of the paper. Therefore, of this emitted light beam, a polarized component having an electric field vector parallel to the incident plane, that is, the paper surface. Is transmitted through the transparent plate 8 with a high-refractive-index film, and the traveling direction of the p-wave is closer to the normal direction of the upper surface of the light guide plate 3 by a prism sheet provided on the upper surface of the transparent plate 8 with a high-refractive-index film. By controlling the angle, a linearly polarized light source having a high degree of polarization, which is composed only of the polarization component parallel to the paper surface, is realized.

The s-wave, which is a polarized component having an electric field vector perpendicular to the plane of incidence, out of the light flux emitted from the upper surface of the light guide plate 3, is reflected by the transparent plate 8 with a high-refractive-index film and guided. After passing through the inside of the light plate 3, it is collimated by the collimator lens sheet 10 in the normal direction of the １ ／ wavelength plate 11, and then the reflection sheet 1 is passed through the 波長 wavelength plate 11.
2, most of the light (s-wave) returns to the light guide plate 3 side in a state of linearly polarized light whose polarization plane is rotated by 90 degrees. Therefore, the light is re-incident on the transparent plate 8 with the high refractive index film as a p-wave having a high degree of polarization consisting of only a polarization component having an electric field vector substantially parallel to the same plane (for example, a paper surface). Through the transparent plate 8 with
By controlling the traveling direction to a direction close to the normal direction of the upper surface of the light guide plate 3 by a prism sheet provided on the upper surface of the transparent plate 8 with a high refractive index film, the prism sheet consists of only the polarization component parallel to the paper surface. It becomes linearly polarized light with a high degree of polarization.

As described above, the polarization component of both the p-wave and the s-wave constituting the light beam emitted from the upper surface of the light guide plate 3 while the trajectory of the light ray is kept in a plane parallel to the paper surface Contributes to the radiation intensity of a linearly polarized light source having a high degree of polarization and consisting only of the polarization component parallel to the paper surface. By illuminating the liquid crystal display element 1 (without the lower polarizing plate) using this, light emitted from the liquid crystal display element 1 is
Light loss due to absorption of radiant energy for the number of sheets can be avoided, and a high-luminance illumination light source is realized as a backlight for a liquid crystal.

FIG. 7 is a schematic view of a principal part for explaining another embodiment of the liquid crystal display device according to the present invention, wherein 1 is a liquid crystal display element (without a lower polarizing plate), 2 is a backlight, and 3 is a light guide plate. ,
4 is a cold cathode fluorescent lamp, 5 is a lamp reflection sheet, 6 is a condensing sheet, 7 is a reflection tape, 8 is a transparent plate with a high refractive index film, 9
Is a prism sheet, 10 is a collimator lens sheet, 1
1 is a 1/4 wavelength plate and 12 is a reflection sheet.

In the figure, a backlight 2 comprises a light guide plate 3 made of a transparent plate having a wedge-shaped cross section in a direction perpendicular to the longitudinal direction of the cold cathode fluorescent lamp 4, and a cold cathode fluorescent lamp installed along one side edge thereof. 4, a lamp reflection sheet 5 provided around the cold cathode fluorescent lamp 4 except for a side facing the light guide plate 3, a light collection sheet 6 provided along the one side edge of the light guide plate 3, and a light guide plate. 3, a reflective tape 7 installed on the side edge opposite to the cold cathode fluorescent lamp 4, a transparent plate 8 with a high refractive index film mounted on the liquid crystal display element 1 side (upper surface), and further thereon. The prism sheet 9 is arranged, a quarter-wave plate 11 provided on the lower surface of the liquid crystal display element 1, and a reflection sheet 12.

The light guide plate 3 has a vertical direction (vertical direction) of 155 mm, a horizontal direction (horizontal direction) of 218 mm,
The thickness of the cold cathode fluorescent lamp side is 4 mm, the thickness of the reflective tape side is 2 mm, and the refractive index is about 1.50. It is configured by processing that avoids reflection. There are two types of processing for avoiding total reflection, a processing mainly based on light scattering and a processing mainly based on regular reflection of light. Typical examples of the process mainly based on light scattering include a method of pattern printing an ink material having a light scattering property on the back surface of the transparent plate and a method of performing roughening on the back surface of the transparent plate. . The processing mainly based on the specular reflection of light includes:
A typical example is a method of forming a prism array on the back surface of a transparent plate.

A light beam incident on the light entrance surface of the light guide plate 3 from the cold cathode fluorescent lamp 4 is condensed by the light condensing sheet 6 provided between the light entrance surface and the cold cathode fluorescent lamp 4.

The light beam condensed by the light condensing sheet 6 is
In the light guide plate 3, the reflection by the upper surface of the light guide plate 3 and the lower surface of the light guide plate including the reflection sheet 12 are repeated in the direction of the reflection tape 7, and substantially on the same plane (for example, on the paper surface, that is, on the surface perpendicular to the cold cathode fluorescent lamp). To propagate. At this time, by optimizing the process for avoiding total reflection performed on the back surface of the light guide plate 3, the light flux from the upper surface of the light guide plate 3 at an emission angle substantially equal to the Brewster angle on the surface of the transparent plate 8 with a high refractive index film. Is emitted. In this emitted light beam, a p-wave (the same plane, for example, a polarization component having an electric field vector parallel to the plane of the paper) transmits through the transparent plate 8 with a high refractive index film and is substantially parallel to the same plane (for example, the plane of the paper). The liquid crystal display element 1 (without a lower polarizing plate) is illuminated as linearly polarized light having a high degree of polarization consisting of only a polarized component.

In the liquid crystal display element 1 (without a lower polarizing plate), a predetermined pixel is made to be in a light transmitting state by a drive circuit (not shown), and illumination light from the backlight 2 passes through the pixel in the light transmitting state. To provide a visible display.

An s-wave (a polarized component having an electric field vector perpendicular to the plane of the drawing) of the light beam emitted from the upper surface of the light guide plate 3 is reflected by the transparent plate 8 with a high refractive index film. After passing through the light guide plate 3, the collimator
After being collimated by the lens sheet 10 in the normal direction of the quarter-wave plate 11, the light is reflected by the reflection sheet 12 via the quarter-wave plate 11, so that most of the light (s
(Wave) becomes a state of linearly polarized light whose polarization plane is rotated by 90 degrees, and returns to the light guide plate 3 side. Therefore, the light is re-incident on the transparent plate 8 with the high refractive index film as a p-wave having a high degree of polarization consisting of only a polarization component having an electric field vector substantially parallel to the same plane (for example, a paper surface). Illuminating the liquid crystal display element 1 (without a lower polarizing plate) as linearly polarized light having a high degree of polarization, which is transmitted only through the transparent plate 8 and has only a polarization component substantially parallel to the same plane (for example, a paper surface). Become.

The reflection tape 7 has a function of returning the light that escapes from the light guide plate 3 to the light guide plate 3 again.

FIG. 8 is an explanatory view of a second example of a light-collecting sheet constituting a backlight according to the present invention, in which 6 is a light-collecting sheet as in FIG. 7, and 6a is a minute convex lens.

In this example, the light guide plate 3 is a wedge-shaped transparent resin plate having a thickness that gradually decreases from the side edge of the cold cathode fluorescent lamp to the reflection tape 7 side. As a process for avoiding reflection, a prism array is formed on the back surface of the transparent resin plate. The condensing sheet 6 located on the side edge of the cold cathode fluorescent lamp installation side has a large number of minute convex lenses 6a on the surface facing the cold cathode fluorescent lamp 4, and the light guide plate 3 side is a flat surface.

The condensing sheet 6 allows the cold cathode fluorescent lamp 4
The light emitted from the light guide plate 6a is condensed on the light guide plate 3 by the minute convex lens 6a on both surfaces in a plane parallel to the paper surface and in a plane perpendicular to the paper surface, and enters the light guide plate 3.

As a result, most of the luminous flux emitted from the cold cathode fluorescent lamp 4 is condensed on the light incident surface of the light guide plate 3 on both surfaces parallel to the paper surface and within a surface perpendicular to the paper surface. Light is incident at a smaller incident angle than when there is no sheet. Taking into account the refraction effect on the light incident surface, the light flux entering the light guide plate 3 is condensed within a narrower angle range on both surfaces in a plane parallel to the paper and in a plane perpendicular to the paper. , And travels inside the light guide plate 3. The traveling direction of the light beam is controlled by specular reflection on the inclined surface of the prism array provided on the back surface of the light guide plate 3 so that the light beam is kept in a state parallel to the plane of the drawing. The light can be emitted from the upper surface of the light guide plate 3 at an emission angle substantially equal to the Brewster angle on the surface of the transparent plate 8 with a high refractive index film.

Since the incident surface when this emitted light beam enters the surface of the transparent plate 8 with a high refractive index film is equal to the paper surface, the polarized light component having an electric field vector parallel to the incident surface, that is, the paper surface, of the emitted light beam. Is transmitted through the transparent plate 8 with a high-refractive-index film, and the traveling direction of the p-wave is closer to the normal direction of the upper surface of the light guide plate 3 by a prism sheet provided on the upper surface of the transparent plate 8 with a high-refractive-index film. By controlling the angle, a linearly polarized light source having a high degree of polarization, which is composed only of the polarization component parallel to the paper surface, is realized.

In the light flux emitted from the upper surface of the light guide plate 3, the s-wave, which is a polarization component having an electric field vector perpendicular to the incident surface, that is, the paper surface, is reflected by the transparent plate 8 with a high-refractive-index film. After passing through the light guide plate 3, the light is collimated by the collimator lens sheet 10 in the normal direction of the 波長 wavelength plate 11, and then reflected by the reflection sheet 12 via the 波長 wavelength plate 11. So most rays (s-waves)
Becomes a state of linearly polarized light whose polarization plane is rotated by 90 degrees, and returns to the light guide plate 3 side. Therefore, the light is re-incident on the transparent plate 8 with the high refractive index film as a p-wave having a high degree of polarization consisting of only a polarization component having an electric field vector substantially parallel to the same plane (for example, a paper surface). Through the transparent plate 8 with
By controlling the traveling direction to a direction close to the normal direction of the upper surface of the light guide plate 3 by a prism sheet provided on the upper surface of the transparent plate 8 with a high refractive index film, the prism sheet consists of only the polarization component parallel to the paper surface. It becomes linearly polarized light with a high degree of polarization.

As described above, the polarization component of both the p-wave and the s-wave constituting the light beam emitted from the upper surface of the light guide plate 3 while the trajectory of the light ray is kept in a plane parallel to the paper surface is considered. Contributes to the radiation intensity of a linearly polarized light source having a high degree of polarization and consisting only of the polarization component parallel to the paper surface. By illuminating the liquid crystal display element 1 (without the lower polarizing plate) using this, light emitted from the liquid crystal display element 1 is
Light loss due to absorption of radiant energy for the number of sheets can be avoided, and a high-luminance illumination light source is realized as a backlight for a liquid crystal.

[0066]

As described above, the liquid crystal according to the present invention comprising a combination of a transparent plate with a high refractive index film and a condensing sheet, or a combination of a transparent plate with a high refractive index film, a condensing sheet and a collimator lens sheet. According to the display device, linearly polarized light having a high degree of polarization can be incident on the liquid crystal layer without using a polarizing plate, and while maintaining the same contrast as in the case where a polarizing plate is used, the amount of one polarizing plate is eliminated. Only the brightness of the front surface of the liquid crystal display element is improved, and the power consumption of the surface light source device can be reduced.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view illustrating an example of the entire configuration of a liquid crystal display device.

FIG. 2 is a cross-sectional view of a principal part for explaining a structure of a backlight in a conventional liquid crystal display device.

FIG. 3 is a schematic sectional view showing a partial structure of a backlight having a light guide plate capable of emitting polarized light.

FIG. 4 is a schematic view of a main part for explaining one embodiment of a liquid crystal display device according to the present invention.

FIG. 5 is a partially broken plan view illustrating an installation state of a light-collecting sheet constituting the backlight in FIG. 4;

FIG. 6 is an explanatory diagram of a light-collecting sheet constituting a backlight according to the present invention.

FIG. 7 is a schematic diagram of a main part for explaining another embodiment of the liquid crystal display device according to the present invention.

FIG. 8 is an explanatory diagram of a second example of the light-collecting sheet constituting the backlight according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display element, 2 ... Backlight, 3 ... Light guide plate, 4
... Lamp reflection sheet, 6 ... Condenser sheet, 7 ... Reflection tape, 8 ... Transparent plate with high refractive index film, 9 ... Prism sheet,
10: Collimator lens sheet, 11: 1/4 wavelength plate,
12: reflection sheet, 13: diffusion sheet.

Claims (11)

[Claims] 1. A liquid crystal display device comprising a liquid crystal display element and a backlight device disposed on the back of the liquid crystal display element, wherein the liquid crystal display element has a polarizing plate on an observation side, and The light device includes a transparent light guide plate having a rear surface subjected to light reflection processing for avoiding total reflection, and a linear light source installed along the light incident surface with at least one side edge of the light guide plate as a light incident surface. And a polarization separation plate installed on the observation side of the light guide plate for transmitting a predetermined polarization component of light from the light guide plate and reflecting other polarization components, and installed on the back surface of the light guide plate A polarization rotator to rotate the polarization direction of the light, a reflection sheet installed on the back of the polarization rotator,
A light-condensing sheet disposed between the linear light source and the light incident surface of the light guide plate to condense light emitted from the linear light source and to introduce the light into the light incident surface. Liquid crystal display device. 2. A liquid crystal display device comprising: a liquid crystal display element; and a backlight device disposed on the back of the liquid crystal display element. The light device is a transparent light guide plate that has been subjected to light reflection processing on the back surface to avoid total reflection, and is disposed on the observation side of the light guide plate and transmits a predetermined polarization component of light from the light guide plate, And, a polarization separation plate for reflecting other polarization components, a polarization rotation plate installed on the back of the light guide plate to rotate the polarization direction of light, and a reflection sheet installed on the back of the polarization rotation substrate And a lens sheet disposed between the light guide plate and the polarization rotation plate to correct light from the light guide plate in a direction substantially normal to the polarization rotation plate. . 3. A liquid crystal display device comprising a liquid crystal display device and a backlight device disposed on the back of the liquid crystal display device, wherein the liquid crystal display device has a polarizing plate on an observation side, and The light device includes a transparent light guide plate having a rear surface subjected to light reflection processing for avoiding total reflection, and a linear light source installed along the light incident surface with at least one side edge of the light guide plate as a light incident surface. And a polarization separation plate installed on the observation side of the light guide plate for transmitting a predetermined polarization component of light from the light guide plate and reflecting other polarization components, and installed on the back surface of the light guide plate A polarization rotator to rotate the polarization direction of the light, a reflection sheet installed on the back of the polarization rotator,
A light-condensing sheet disposed between the linear light source and the light incident surface of the light guide plate for condensing light emitted from the linear light source and introducing the light to the light incident surface; A liquid crystal display device comprising: a lens sheet disposed between the light guide plate and the light guide plate to correct light from the light guide plate in a direction substantially normal to the polarization rotation plate. 4. The light reflection process performed on the light guide plate is a process of printing an ink material having a light scattering property, a rough surface processing process, or a process of forming a prism array. Claim 1, Claim 2 or Claim 3
The liquid crystal display device according to any one of the above. 5. The liquid crystal display device according to claim 1, wherein the light guide plate has a greater thickness on the light incident surface side than on a surface facing the light incident surface. 6. The liquid crystal display device according to claim 1, wherein said linear light source is a cold cathode fluorescent lamp. 7. The liquid crystal according to claim 1, wherein said polarization separation plate is a translucent plate in which a high refractive index film is bonded to a glass substrate. Display device. 8. The apparatus according to claim 1, wherein said polarization rotating plate is a substantially quarter-wave plate of light having a predetermined wavelength passing through said light guide plate. Liquid crystal display device. 9. The liquid crystal display device according to claim 1, wherein a plurality of minute convex lenses are formed on the light-collecting sheet. 10. A transparent light guide plate having a rear surface subjected to a light reflection treatment for avoiding total reflection, and a cold cathode disposed along the light entrance surface with at least one side edge of the light guide plate being a light entrance surface. A fluorescent lamp, a lamp reflecting sheet provided around the cold cathode fluorescent lamp except for a portion facing the light incident surface, a transparent plate with a high refractive index film provided on an upper surface of the light guide plate, and A prism sheet installed on the upper surface of the transparent plate with a refractive index film, a 波長 wavelength plate installed on the lower surface of the light guide plate, a reflection sheet installed on the lower surface of the 波長 wavelength plate, and an upper surface of the prism sheet. A light-collecting device having at least an installed liquid crystal display element, and condensing light emitted from the cold-cathode fluorescent lamp between the cold-cathode fluorescent lamp and the light-entering surface of the light guide plate and introducing the light into the light-entering surface. A liquid crystal display device comprising a sheet. 11. A liquid crystal display device according to claim 10, wherein a collimator lens sheet is provided between said light guide plate and said quarter wavelength plate.