JP2002350849A - Front light of liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a front light of a liquid crystal display device, by which the contrast of the liquid crystal display device can be heightened by forming a reflection preventing film on the lower surface of a light guide plate to prevent the generation of whitening, in the light guide plate wherein a hologram is formed on the lower surface thereof and the hologram is used as a reflection surface. SOLUTION: The front light of the liquid crystal display device wherein the light guide plate consists of a light guide plate main body guiding and diffusing light from the end face opposed to a light source to the inner part and a film of a hologram polymer adhered to the lower surface of the light guide plate main body and which characteristically consists of a reflection surface downwardly reflecting light by the diffraction of light by the hologram, a protective film for protecting the film of the hologram polymer and the reflection preventing film disposed at the lower part of the protective film and preventing the reflection of light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source, and a light guide plate for illuminating a liquid crystal panel by introducing light from an end face facing the light source and diffusing the light inside, and reflecting the light downward at a reflection surface. More particularly, the present invention relates to a front light of a liquid crystal display device in which a hologram is formed as a reflection surface on a light guide plate and light is reflected downward by the hologram.

[0002]

2. Description of the Related Art Front lights of liquid crystal display devices are already known. The front light of this liquid crystal display device has a light source and a light guide plate facing the light source. Light is introduced into the inside from the end face of the light guide plate and diffused inside, and the light is reflected downward by the reflection surface. And illuminates the liquid crystal panel. In a normal front light, a prism such as a V-groove prism or a staircase prism is formed on the upper surface of a light guide plate, and the prism is used as a reflection surface to reflect light downward to illuminate a liquid crystal panel. FIG. 6 shows an example of the V-groove prism of the light guide plate, and FIG. 7 shows an example of the staircase prism. Here, the names of the V-groove prism and the staircase prism are names given depending on whether the shape of the prism formed on the upper surface of the light guide plate looks like a V-groove or looks like a staircase. It has no special significance in performance.

As shown in FIGS. 6 and 7, a light guide plate 31 is provided.
Are known, such as a V-groove prism 32 (FIG. 6) having a V-shaped groove formed as a reflection surface on the upper surface of the light guide plate 31 and a staircase prism 33 (FIG. 7) having a gentle wavy groove formed thereon. ing. These light guide plates 31 have a light source (not shown) on the left side in the figure, and light 34, 35 projected from this light source is
The light is introduced into the light guide plate 31 from the left end surfaces 32a and 33a, and is diffused into the light guide plate 31 by repeating total reflection on the upper and lower surfaces, and the left inclined surface 32b of the groove serving as the reflection surface in FIG. The light that hits the slope 33b on the right side in the figure of the mountain serving as the reflection surface in FIG. 7 is reflected downward,
The liquid crystal panels 36 and 37 are configured to be illuminated. Here, the illustrated liquid crystal panels 36 and 37 are reflection type color display liquid crystal panels, and light reflected downward to illuminate the liquid crystal panels 36 and 37 is reflected by the liquid crystal panels 36 and 37.
It is drawn to reflect off the surface.

FIG. 8 is a conceptual sectional view showing one example of a liquid crystal display device. The liquid crystal display device of the present embodiment is a liquid crystal display device of a color display,
A light source 42 and light projected from the light source 42
And a light guide plate 43 that is introduced into the inside from an end face 43a facing the front light 44 is disposed. The light guide plate 43 diffuses the light A introduced from the end face 43a into the light guide plate 43 by repeatedly reflecting the light A on the upper and lower surfaces, and a reflection surface (not shown) such as a prism provided on the upper surface. Illuminates the liquid crystal panel 45 by reflecting light downward.

When the surrounding environment is bright, external light B enters the light guide plate 43 and illuminates the lower liquid crystal panel 45. Therefore, in the liquid crystal display device 41 of this embodiment,
When the surrounding environment is sufficiently bright, it is possible to illuminate the liquid crystal panel 45 with only the light projected from the environment without using the light from the light source 42, and it is possible to save power consumption. .

Below the front light 44, there is disposed a liquid crystal panel 45 of various types already known. The liquid crystal panel 45 of this embodiment is a liquid crystal panel for a liquid crystal display device for color display, in which a polarizing / compensating plate 46 in which a polarizing plate and a compensating plate are integrated is disposed at the top. A liquid crystal cell 47 is disposed below. As is well known, the liquid crystal cell 47 includes an upper glass substrate 48, a color filter 49, a liquid crystal 50, and a reflection plate 5.
1. The lower glass substrate 52 is arranged in this order and integrated.

In the liquid crystal display device 41, the light A projected from the light source 42 is introduced into the inside of the light guide plate 43 from the end face 43a of the light guide plate 43, and is repeatedly reflected on the upper and lower surfaces, so that the inside of the light guide plate 43 is repeated. And the light reflected by a reflection surface (not shown) is projected downward to illuminate the liquid crystal panel 45. The reflected illumination light of the liquid crystal panel 45 projected downward is transmitted through the polarization / compensation plate 46 and the upper glass substrate 48, is transmitted only through a predetermined color through the color filter 49, and is transmitted through the liquid crystal 50 through a predetermined character. Alternatively, after transmitting only the portion where the shape is displayed, the light that has reached this point is reflected by the reflection plate 51 and emitted from the upper surface of the light guide plate 43 to the outside through the original path. Thus, the liquid crystal display device 41 of the present embodiment allows the user to recognize the predetermined character or shape. Illumination light is external light B
In the case of, the liquid crystal panel 45 is similarly illuminated.
Here, detailed description is omitted.

At this time, on the lower surface of the light guide plate 43, a part of the light is reflected upward and radiated to the outside from the upper surface of the light guide plate 43 as it is. This light is the liquid crystal panel 4
When the light is mixed with light that is transmitted upward through the liquid crystal 5, the contrast of the liquid crystal display device 41 is reduced, which causes a so-called white spot. In order to prevent this whitening, the light guide plate 4
An antireflection film formed by vacuum deposition, vacuum sputtering, application of a solution, or the like is arranged on the lower surface of the liquid crystal 3 to maintain a high contrast of the liquid crystal display device 41.

Conventionally, as an anti-reflection film disposed on the lower surface of the light guide plate, an anti-reflection film has been formed on the lower surface of the light guide plate. It is conceivable to attach the anti-reflection film on which the anti-reflection film is formed to the lower surface of the light guide plate. For example, a method of forming an anti-reflection film by attaching an anti-reflection film to the lower surface of the light guide plate has not been adopted as a method of forming the anti-reflection film because there is a problem that air bubbles remain in the light guide plate.

However, in a light guide plate in which a hologram is formed on the lower surface of the light guide plate as a reflection surface for reflecting the introduced light downward, the hologram is formed on the lower surface of the light guide plate. An antireflection film cannot be formed on the lower surface of the light guide plate, and a light guide plate employing a hologram on the lower surface as a reflection surface cannot prevent whitening due to light reflected on the lower surface of the light guide plate. Therefore, it was considered difficult to increase the contrast of the liquid crystal display device.

[0011]

SUMMARY OF THE INVENTION The present invention solves these problems of the prior art, and forms a hologram on the lower surface of a light guide plate. An object of the present invention is to provide a front light of a liquid crystal display device in which an anti-reflection film is formed on a lower surface to prevent the occurrence of whitening and to increase the contrast of the liquid crystal display device.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and includes a light source and light which is introduced from an end face facing the light source, diffuses the light, and reflects the light. A light guide plate having a light guide plate for illuminating the liquid crystal panel by reflecting light downward on a surface, wherein the light guide plate introduces and diffuses light from an end face facing the light source into the interior of the front light plate. A body, a hologram polymer film adhered to the lower surface of the light guide plate body, a reflection surface for reflecting light downward by diffraction of light by the hologram, a protection film for protecting the hologram polymer film, An object of the present invention is to provide a front light of a liquid crystal display device, comprising an anti-reflection film disposed below a film to prevent reflection of light.

Here, the protective film is preferably a TAC film, and an anti-reflection film is preferably formed on the surface of the TAC film, or the protective film is a highly transparent optical plastic film. Preferably, an antireflection film is formed on the surface of the optical plastic film. The optical plastic film is a PC film or PMMA.
It is preferable that an antireflection film is formed on the surface of the PC film or the PMMA film.

[0014] Alternatively, it is preferable that the protective film is a TAC film, and an antireflective film having an antireflective film formed thereon is adhered to the lower surface of the TAC film. It is preferable that the optical plastic film is high, and an antireflective film having an antireflective film formed thereon is adhered to the lower surface of the optical plastic film. And
The optical plastic film is a PC film or a PMMA film, and the PC film or the PMM
It is desirable that an antireflection film on which an antireflection film is formed is adhered to the lower surface of the A film.

Further, it is preferable that the protective film is an anti-reflection film having an anti-reflection film formed thereon, and the protection of the hologram polymer and the formation of the anti-reflection film are performed by bonding the anti-reflection film.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings showing embodiments. 1 to 5 are cross-sectional views schematically showing an embodiment of a light guide plate of a front light of a liquid crystal display device according to the present invention. Here, the configuration other than the light guide plate of the front light, for example, the light source uses white light by a white diode or white light mixed with light from red, green, and yellow light emitting diodes as a luminous body as in the related art. It can be used as a linear light source using a light pipe if necessary,
Since the configuration is the same as that of the prior art, the description of the configuration other than the light guide plate of the front light is omitted here.

FIG. 1 shows a first embodiment of a light guide plate in a front light of a liquid crystal display device according to the present invention, in which a light source (not shown) and light introduced from an end face facing the light source are introduced. And a light guide plate 1 for illuminating a liquid crystal panel (not shown) by diffusing and reflecting light downward at the reflection surface. The light guide plate 1 according to the present embodiment reflects light by a hologram, and a hologram polymer is provided on the lower surface of a light guide plate main body 2 through which light is introduced and diffused from an end face facing a light source via an adhesive 3. The hologram polymer film 4 serves as a reflection surface that reflects light introduced into the light guide plate main body 2 and diffused downward by diffraction of light by the hologram. As a protective film for protecting the hologram polymer film 4, a generally used TAC film (triacetyl cellulose film, hereinafter referred to as TAC film) 6 is adhered via an adhesive 5.

As described above, the light guide plate body 2 repeats the reflection of the introduced light and diffuses and propagates the inside thereof.
When light introduced into the inside of the light guide plate main body 2 is incident on the surface of the thin film adhered to the lower surface of the light guide plate main body 2 on the surface of the film, the incident light is diffracted and reflected downward. A hologram is formed. As the hologram, a volume hologram can be preferably used.

The TAC film 6 is a transparent cellulose film, which is used to prevent and protect the hologram polymer when the hologram polymer film 4 is manufactured and stored. In this embodiment, the TAC film 6 used as the protective film is used as a base material for coating the anti-reflection film 7 by vacuum evaporation, vacuum sputtering or application of a solution, and the reflection is applied to the lower surface thereof. This is one in which the prevention film 7 is formed.

As described above, the anti-reflection film 7 is formed by vacuum evaporation, vacuum sputtering, application of a solution, or the like.
A thin film coating is applied to the surface of a base material such as an AC film 6, and MgF2, Al2 O2, ZrO2, and the like are known as materials for forming the antireflection film 7. The anti-reflection film 7 is formed by using these substances alone or in combination of several kinds. When the wavelength of light is λ, the thickness of the antireflection film 7 is λ / 4 or λ /
2 and λ / 4 according to the combination of the above-mentioned substances.
And λ / 2 are selected and combined.

Here, the TAC film 6 is replaced with an anti-reflection film 7.
When the base material is used, the cost can be reduced because the TAC film 6 used for moisture prevention and protection of the hologram polymer film 4 can be used as it is, but the TAC film 6 is formed on the TAC film 6 by vacuum evaporation or vacuum sputtering. The optical characteristics of the anti-reflection film 7 and the film properties of the anti-reflection film 7 due to the thermal stress of the anti-reflection film 7 and the substrate (TAC film 6) generated by the released gas, thermal expansion during vacuum deposition or vacuum sputtering, and subsequent cooling. There is a possibility that the adhesion strength is reduced and the reliability and yield of the product are deteriorated.

FIG. 2 shows a second embodiment of the light guide plate of the front light of the liquid crystal display device according to the present invention.
It is intended to prevent a decrease in the reliability and yield of the product caused by the release of gas and cooling after thermal expansion in the embodiment. In the second embodiment, the light guide plate 1 has the hologram polymer film 4 adhered to the lower surface of the light guide plate main body 2 via an adhesive 3, and the lower surface of the hologram polymer film 4 via an adhesive 5. The point that the TAC film 6 is adhered as a protective film is the same as in the first embodiment.

In this embodiment, a transparent antireflection film 9 on which an antireflection film is formed is adhered to the lower surface of the TAC film 6 with an adhesive 8 interposed therebetween. With this configuration, it is possible to prevent generation of outgassed gas generated by high temperature during vacuum deposition or vacuum sputtering, and to prevent reduction in optical characteristics and film adhesion strength due to thermal stress generated by subsequent cooling. In addition, since the antireflection film 9 is also commercially available, it can be easily obtained, and an optimum one can be selected from these commercially available antireflection films 9 and used. On the other hand, the light guide plate 1 has a disadvantage that the overall thickness is increased, and at the same time, generation of scratches generated when the anti-reflection film 9 is attached,
Yield may be reduced due to the generation of defective products due to dust or bubbles being included in the application surface.

FIGS. 3 and 4 show third and fourth embodiments of the light guide plate of the front light of the liquid crystal display device according to the present invention. The reliability and the yield of the product due to the thermal stress in the first embodiment are shown. In order to prevent deterioration of the film, a film of an optical plastic having high transparency, which is known to form various antireflection films, is used as a protective film. FIG. 3 shows a third embodiment in which a PC film (polycarbonate film, hereinafter referred to as PC film) is used as the optical plastic film, and a PMMA film (polymethyl methacrylate film, hereinafter referred to as PMMA film) is used. FIG. 4 shows a fourth example as a fourth embodiment.

In these embodiments, similarly to the first embodiment, the light guide plate 1 has the hologram polymer film 4 adhered to the lower surface of the light guide plate main body 2 via the adhesive 3.
A PC film 10 or a PMMA film 11 is adhered to the lower surface of the hologram polymer film 4 via an adhesive 5 instead of the TAC film 6 of the first embodiment. An anti-reflection film 7 is formed on the lower surface of 11 by vacuum evaporation, vacuum sputtering, application of a solution, or the like, as in the first embodiment.

PC film 10 or PMMA film 1
When the antireflection film 7 is formed by vacuum evaporation or vacuum sputtering, processing conditions such as temperature and pressure are more clarified as compared with the TAC film 6, so that it can be processed easily. Since vacuum deposition or vacuum sputtering can be performed at a lower temperature, generation of outgassing during vacuum deposition or vacuum sputtering and prevention of a decrease in optical properties and film adhesion strength due to thermal stress caused by subsequent cooling are prevented. be able to.

In the third and fourth embodiments,
As in the second embodiment, a PC film 10 or a PMMA film 11 is applied as a protective film instead of the antireflection film 7 formed by vacuum deposition or vacuum sputtering, and the antireflection is applied to the lower surface of the antireflection film via an adhesive 8. The transparent antireflection film 9 having the film formed thereon can be bonded. And, as described above, this antireflection film 9
Is commercially available, so that it can be easily obtained, and an optimum one can be selected from these commercially available antireflection films 9 and used. However, in this case, similarly to the second embodiment, the light guide plate 1 has a disadvantage that the entire thickness becomes large, and the antireflection film 9
There is a possibility that the yield may be reduced due to the generation of scratches generated when attaching the adhesive, or the occurrence of defective products due to the inclusion of dust or bubbles on the attaching surface.

FIG. 5 shows a fifth embodiment of the light guide plate of the front light of the liquid crystal display device according to the present invention.
The hologram polymer film 4 is bonded to the lower surface of the light guide plate main body 2 via an adhesive 3, and an antireflection film is formed directly on the lower surface of the hologram polymer film 4 via an adhesive 8. Transparent antireflection film 9
Is glued. In this embodiment, by configuring as described above, it is possible to prevent generation of outgassing generated by high temperature and subsequent cooling during vacuum deposition or vacuum sputtering, and to prevent reduction in optical characteristics and film adhesion strength due to thermal stress. Can be.

Further, since the antireflection film 9 is commercially available, it can be easily obtained, and an optimum one can be selected from these commercially available antireflection films 9 and used. In this embodiment, since the antireflection film 9 is directly adhered to the lower surface of the hologram polymer film 4, the entire thickness of the light guide plate main body 1 can be reduced. However, the yield may be reduced due to generation of scratches generated when the antireflection film 9 is applied, or generation of defective products due to inclusion of dust or bubbles on the application surface.

As described above, the front light of the liquid crystal display device of the present invention comprises the adhesive 3
The hologram polymer 4 is adhered through a TAC film 6 or a PC
An anti-reflection film 7 formed on the film 9 or the PMMA film 10 is disposed, or a TAC film 6 on which the anti-reflection film 7 is formed, or a PC via a protective film.
Film 9 or PMMA film 10 is affixed,
Alternatively, a transparent film on which an anti-reflection film is formed is adhered, but the present invention is not limited to the method described in the above-described embodiment and does not depart from the gist of the present invention. Of course, various changes and improvements can be made within the range.

[0031]

According to the front light of the liquid crystal display device of the present invention, as described above, the hologram polymer film 4 is bonded to the lower surface of the light guide plate main body 2 with the adhesive 3 interposed therebetween. 4 directly or on the TAC film 6, PC film 9 or P
Since the anti-reflection film 7 is provided through the protective film of the MMA film 10 or a transparent film on which the anti-reflection film is formed is bonded, a hologram is formed on the lower surface of the light guide plate, and the hologram is formed. Also, in the light guide plate having the reflection surface as the reflection surface, an anti-reflection film is disposed on the lower surface of the light guide plate to provide a front light of the liquid crystal display device in which whitening is prevented.

Further, the yield may be reduced due to generation of scratches generated when the TAC film 6 on which the antireflection film 7 is formed as a protective film, and generation of defective products due to inclusion of dust and bubbles on the bonding surface. However, in order to protect the hologram of the hologram polymer 4, it is necessary to attach a protective film to the lower surface, so that the TAC film 6, PC film 9 or PM
Even if the MA film 10 or the anti-reflection film 9 is attached, the occurrence of scratches due to the attachment of the protective film for protecting the hologram and the occurrence of dust and bubbles included in the attachment surface are not particularly different. Since there is no particular change in the incidence of defective products, there is no practical problem.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a first embodiment of a light guide plate of a front light of a liquid crystal display device according to the present invention.

FIG. 2 is a sectional view schematically showing a second embodiment of the light guide plate of the front light of the liquid crystal display device of the present invention.

FIG. 3 is a sectional view schematically showing a third embodiment of the light guide plate of the front light of the liquid crystal display device of the present invention.

FIG. 4 is a sectional view schematically showing a fourth embodiment of the light guide plate of the front light of the liquid crystal display device of the present invention.

FIG. 5 is a sectional view schematically showing a fifth embodiment of the light guide plate of the front light of the liquid crystal display device of the present invention.

FIG. 6 is a sectional view showing an example of a V-groove prism of the light guide plate.

FIG. 7 is a sectional view showing an example of a staircase prism of the light guide plate.

FIG. 8 is a conceptual cross-sectional view illustrating one example of a liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Light guide plate main body 3 Adhesive 4 Hologram polymer film 5 Adhesive 6 TAC film 7 Antireflection film 8 Adhesive 9 Antireflection film film 10 PC film 11 PMMA film

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/1335 G09F 9/00 324 5G435 G09F 9/00 324 336C 336 G02B 1/10 A F term (Reference) 2H038 AA55 BA06 2H042 BA01 BA12 BA20 2H049 CA05 CA07 CA09 CA11 2H091 FA19X FA23X FA37X FA41X FD14 GA16 LA03 LA17 2K009 AA04 BB14 BB24 BB28 CC03 CC06 DD02 DD03 DD04 5G435 AA02 AA03 BB12 FF16

Claims (8)

[Claims] 1. A front surface of a liquid crystal display device having a light source and a light guide plate for introducing and diffusing light from an end surface facing the light source and illuminating a liquid crystal panel by reflecting light downward at a reflection surface. In the light, the light guide plate comprises: a light guide plate main body for introducing and diffusing light into the inside from an end face facing the light source; and a hologram polymer film adhered to a lower surface of the light guide plate main body. A reflection surface that reflects light downward by diffraction; a protective film that protects the hologram polymer film; and an antireflection film that is disposed below the protective film and that prevents light reflection. Front light for liquid crystal display. 2. The front light according to claim 1, wherein the protective film is a TAC film, and an anti-reflection film is formed on a surface of the TAC film. 3. The liquid crystal according to claim 1, wherein the protective film is a highly transparent optical plastic film, and an antireflection film is formed on a surface of the optical plastic film. Display front light. 4. The optical plastic film is P
4. The front light according to claim 3, wherein the PC film or the PMMA film is a C film or a PMMA film, and an anti-reflection film is formed on a surface of the PC film or the PMMA film. 5. The liquid crystal display device according to claim 1, wherein the protection film is a TAC film, and an antireflection film having an antireflection film is adhered to a lower surface of the TAC film. Front light. 6. The protective film is a highly transparent optical plastic film, and an antireflection film on which an antireflection film is formed is adhered to a lower surface of the optical plastic film. Claim 1
A front light of the liquid crystal display device described in the above. 7. The optical plastic film is made of P
7. The front light according to claim 6, wherein an anti-reflection film on which an anti-reflection film is formed is bonded to a lower surface of the PC film or the PMMA film. . 8. The anti-reflection film having an anti-reflection film formed on the protective film, wherein the protection of the hologram polymer and the formation of the anti-reflection film are performed by bonding the anti-reflection film. The front light of the liquid crystal display device according to claim 1.