JPH11126030A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display high in the use efficiency of light and high in brightness. SOLUTION: A reflection oblique surface consisting of plural small projecting or small recessed parts is formed so that the light beams from the incident plane of a light transmission plate 2 are reflected to a transparent surface direction with a prescribed angle. Then, a display device is irradiated with the illuminating light beams having an appropriate angular distribution from the transparent surface. Note that the lowest value of the illuminating efficiency of the light beams, which arrive at a liquid crystal panel through an optical member, against the incident light beams of the plate 2 is defined as 60% and the lowest value of the illumination efficiency of the light beams passing through the panel to the light beams made incident on the plate 2 is defined as 1.8%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having improved light use efficiency and luminance.

[0002]

2. Description of the Related Art In recent years, miniaturization of personal computers has been promoted, and portable models called laptops have become widespread. In this laptop type, a liquid crystal device is usually used for display, but with the recent trend toward color display, a light source is arranged behind the liquid crystal display panel so that the entire display surface is illuminated from behind. Backlit display devices are becoming popular. A light source as a backlight of such a display device needs to have high luminance and to illuminate the entire plane without luminance unevenness. Increasing the brightness of the light source is easy to increase the brightness, but increasing the brightness of the light source is limited in laptop-type personal computers, etc., because a battery or the like is used as a drive source. There was no effective way.

[0003] JP-A-4-162002, JP-A-6-2002
No. 67004 is known as a known example. As a conventional edge light type lighting device for a liquid crystal display element,
As shown in FIG. 3, a lamp such as a cold-cathode tube or a hot-cathode tube is used as a light source 1 and is connected to a light guide plate 2 made of a transparent material.
And a diffusion sheet 3 made of a milky white synthetic resin having a light scattering effect for making the luminance of the illumination surface uniform over the entire surface on the light guide plate 2. Further, on the upper surface, a first prism sheet 4 and a second prism sheet 5 for converging the diffused light to some extent and improving the luminance in front of the display device are arranged.

A light scattering layer 6 for scattering light guided to the light guide plate 2 toward the diffusion sheet 3 is provided on the back surface of the light guide plate opposite to the light exit surface of the light guide plate 2. Here, in order to further uniform the luminance of the light emitted from the light scattering layer 6, the structure and manufacturing method of the light scattering layer are as follows.

FIG. 4 shows the structure of the light scattering layer. That is,
In the light scattering layer 6, a plurality of light scattering substances using titanium oxide or the like are formed on the back surface of the light guide plate 2 using a technique such as printing. The light intensity from the light source 1 decreases as the distance from the light source increases. Therefore, the area of the light scattering material of the light scattering layer 6 in the light guide plate 2 is formed so as to increase as the distance from the light source 1 increases. Further, in FIG. 3, a reflection sheet 8 is disposed on the lower surface of the light scattering layer 6.

Further, as disclosed in Japanese Patent Application Laid-Open No. 7-294745, a light guide plate of a type in which a grating groove is formed on the bottom surface of the light guide plate to reflect light incident on the light guide plate has been proposed.

[0007]

As described above, in the conventional lighting device, the light emitted from the light source 1 is guided to the light guide plate 2 and scattered by the light scattering material of the light scattering layer 6,
The scattered light is incident on the light guide plate 2 again by the reflection sheet 8, and thereafter, the diffusion sheet 3, the two prism sheets 4, 5
And irradiates the liquid crystal element through the liquid crystal element, and the configuration is complicated.

Since the light absorbing material of the diffusion sheet 3 is disposed on the upper surface of the light guide plate 2, the unevenness in luminance can be reduced, but there is a disadvantage that the luminance of the entire liquid crystal element is reduced. In the case of such a configuration, improvement in luminance is prevented, and contradictory problems of uniforming luminance and improving luminance cannot be solved. Also, in the case of a conventional light guide plate having a grating groove, although the luminance can be improved,
There is a problem that light emitted from the light guide plate by the grating grooves interferes with a member constituting the liquid crystal display element, for example, a regular pattern of a liquid crystal cell, and moire is generated. In order to solve this, there is a disadvantage that a sheet for diffusing light must be used together.

Further, in the conventional light guide plate 2, since heat is propagated by the light source 1, it is difficult to fix the reflection sheet 8 due to a difference in the coefficient of thermal expansion between the light guide plate 2 and the reflection sheet 8. There is also a problem that the distance from the back surface of the light guide 2 changes due to vibration, thermal deformation, and the like, and that dust is mixed between the reflection sheet 8 and the light guide plate 2, thereby changing the light use efficiency and causing uneven brightness. there were.

The present invention has been made to overcome such a situation, and provides a liquid crystal display device which can improve the luminance without increasing the luminance of the light source by improving the conventional disadvantages. The purpose is to:

[0011]

In order to achieve the above-mentioned object, a liquid crystal display device according to the present invention is provided for converting light from a light guide plate incident surface into a predetermined angle with respect to a transmission surface direction. Using a light guide plate having a reflection slope formed of a plurality of small projections or small depressions, and, if necessary, forming a reflection film along the reflection slope formed of the small projections or small depressions on its lower surface, or When a reflective sheet is arranged, and further a reflective sheet is used, a prism sheet having an appropriate prism apex angle is arranged so that illumination light having an appropriate angular distribution is emitted from the light transmitting surface toward the display element. With this configuration, the minimum value of the irradiation efficiency of the light that reaches the liquid crystal panel via the optical member with respect to the light incident on the light guide plate: 60%
Is realized. Further, the minimum value of the irradiation efficiency of the light transmitted through the liquid crystal panel with respect to the light incident on the light guide plate:
1.8% is achieved.

When a reflection film is formed along a reflection slope,
The cross-sectional shape of the reflection slope is determined so that the direction of light emitted from the light transmission surface of the light guide plate becomes highest in the direction perpendicular to the light guide plate surface.

On the other hand, when the reflection film is not formed on the bottom surface of the reflection slope, the traveling direction of light is changed mainly by using total reflection. The direction of the light beam emitted from the light transmission surface of the light guide plate is
The cross-sectional shape of the reflecting slope is determined so that the luminance becomes highest in the direction in which the center of the light flux is oblique to the vertical with respect to the light guide plate surface. In this case, by arranging the prism sheet on the light transmitting surface of the light guide plate, the light in the direction with the highest luminance of the light flux is vertical to the liquid crystal display element surface, that is, the user , A prism sheet having an appropriate apex angle is arranged so that the front luminance becomes highest.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Table 1 summarizes the embodiments of the present invention. The sectional inclination angle, depth or height, plane shape, size, dot arrangement, dot arrangement of dots (reflection slopes) are shown in Table 1. The density distribution and auxiliary materials indispensable for the light guide plate of the present invention are shown.

[0015]

[Table 1]

In the embodiments of the present invention, there are cases where a reflection film is formed on the back surface of the light guide plate and cases where it is not formed. The cross-sectional inclination angle of the dot composed of the small convex portion or the small concave portion is 20 to 5
0 °, preferably 35 ± 10 ° is suitable. In particular, when a reflective film is formed, 35 ° ± 10 ° is appropriate, and when no reflective film is formed, 35 ± 15 ° is appropriate. Specifying the dot cross-section inclination angle within the above range optimizes the emission angle distribution of light from the emission surface of the light guide plate, and simultaneously suppresses the amount of light emitted obliquely more than necessary to improve front luminance. To do that.

The depth or height of the dot is 2 to 40 μm
Is appropriate. The reason is that when the depth or height of the dots is larger than 40 μm, the brightness near the cold cathode tube as the light source becomes too high, resulting in uneven brightness distribution, This is because when forming, it is difficult for the plastic material to fill the small protrusions or small recesses of the dots of the stamper, which is a mold, and it is difficult to form a desired dot shape. On the other hand, if the dot depth or height is 2
If it is smaller than μm, the light reflection efficiency is reduced, and it becomes impossible to obtain a desired luminance.

Various shapes are effective for the planar shape of the dots, that is, the shape when the light guide plate is viewed from the front, but when a reflective film is formed, a circle or a substantially rectangular shape is particularly desirable. The term “substantially rectangular” refers to a shape including a rectangle, with rounded corners of the rectangle, and a shape close to a trapezoid in which one side of the rectangle is deformed. If there is no reflective film, a substantially rectangular shape is suitable. The reason is to reduce the scattered light in the light guide plate to improve the luminance.

The size of the dot is desirably φ200 μm or less when the plane shape is a circle, and the short side is desirably 200 μm or less when the plane shape is a substantially rectangular shape or another figure. The reason is that if the size of the dot is larger than this, when a user such as a personal computer looks at the liquid crystal display device, the shape of the dot formed on the light guide plate may be seen depending on characters and patterns (dot appearance). , Characters, and figures. The lower limit is desirably 10 μm. The reason for this is that if it is smaller than 10 μm, the number of dots will increase too much, making manufacture difficult.

The planar arrangement of dots needs to be random. The reason for this is that, since the dots of the present invention are fine, the moire generated by interfering with other members constituting the liquid crystal display device, for example, a regular pattern such as a liquid crystal cell, a color filter, a TFT pattern and a black stripe is prevented. That's why. When the plane shape of the dot is substantially rectangular, it is preferable that the long side of the rectangle is disposed substantially parallel to the light source. The reason is that it becomes easy to optimize the emission angle distribution.

As for the dot density, in order to make the luminance distribution uniform, the dot density is made smaller as it is closer to the light source.

Sub-materials indispensable for constituting the liquid crystal display device of the present invention include a reflection sheet and a prism sheet when there is no reflection film. These auxiliary materials are indispensable for improving the luminance and optimizing the emission angle.

Regardless of the presence or absence of the reflection film, the use of conventionally used auxiliary materials such as a prism sheet and a diffusion sheet as needed can improve the luminance, optimize the luminance distribution, and optimize the emission angle. It is effective for

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view of a backlight unit used in the liquid crystal display device of the present invention, and FIG. 2 is a perspective view showing a small convex portion 10 serving as a reflection slope of the light guide plate 2 of FIG. The backlight unit in this liquid crystal display device includes a light source 1, a light guide plate 2, a reflection film 1
Although not shown in FIG. 1 or FIG. 1 and FIG. 2, the reflection sheet 8 shown in FIG. 3 is a minimum component, and the light guide plate 2 has a crater-like reflection slope 10 (hereinafter referred to as a small convex portion) formed on the back surface. The reflection film 11 is formed along the small projections 10. The small protrusions 10 are basically randomly arranged.

FIG. 5 shows the ray trajectory of the light guide plate 12 traveling in the light guide plate 2 of FIG. In FIG. 5, the light emitted from the light source 1 enters the light guide plate 2 as the light guide plate incident light 9 at the left end face 7 of the light guide plate 2, and the light guide plate waveguide light 1
2 and progresses toward the other end surface (right end) while repeating total reflection on the light guide plate lower surface 13 and the light transmission surface 16. Of the guided light 12, the light incident on the small convex inclined surface 15 is reflected and hits the light transmitting surface 16, where it is refracted and emitted from the light transmitting surface 16 to enter the liquid crystal display element as illumination light. Further, of the guided light 12, the guided light incident on the small convex bottom surface 14 is reflected by the small convex bottom surface 14, and a part of the guided light is further incident on the small convex inclined surface 15, where it is reflected and reflected by the light transmitting surface 16, ie, exit from the light transmitting surface. Therefore, the small convex portion 1
By appropriately arranging 0 and the reflection film 11, the liquid crystal display device can be illuminated by gradually emitting the guided light 12 from the light guide plate 2.

FIG. 6 is a ray trajectory of the guided light and the reflected light in the light guide plate for explaining the exit angle of the light beam from the light guide plate 2 to the liquid crystal display element. In FIG. 6, the incident angle spread angle α of the light guide plate is an angle when light emitted from the light source 1 is incident on the light guide plate 2, that is, an angle of the left end face 7 of the light guide plate 2,
It is determined by the refractive index of the material constituting the light guide plate 2. As shown in FIG. 6, when the angle of the left end surface 7 of the light guide plate 2 is perpendicular to the light transmission surface 16 and the refractive index of the light guide plate 2 is a general plastic material such as acrylic resin, α is about ± 40 °. Note that considering geometrically, α
The light having a negative angle does not directly enter the small convex portion 10. Here, the small convex section cross-sectional inclination angle is θ,
The depth of the small protrusion is d. Also, the emission angle of the light reflected by the small convex portion inclined surface 15 is referred to as a small convex portion reflected light emission angle, which is δ, and the output angle of the light reflected by the small convex portion bottom surface 14 and the small convex portion inclined surface 15 is δ '.

FIG. 7 shows the relationship between α and δ, and the numerical value in the figure indicates θ. Here, when δ is negative, it means that the emitted light is emitted to the left side with respect to the perpendicular set on the light transmitting surface 16. From FIG. 7, it can be seen that, of the guided light, the light incident on the small convex inclined surface 15 is emitted from the light transmitting surface 16 with a certain angular distribution. For example, when θ is 35 °, δ is ± 30 °, and it can be seen that light having an appropriate angular distribution is emitted from the light transmitting surface 16 of the light guide plate 2. Similarly, FIG. 8 shows the relationship between α and δ ′. 8 that the light exits from the light transmitting surface 16 with a certain angular distribution, similarly to FIG. Here, FIG.
From FIG. 8, it can be seen that, by setting the appropriate value of θ to 20 to 60 °, and particularly to 35 ° ± 10 °, the emitted light illuminates the liquid crystal display element at an appropriate angle.

Therefore, according to the present invention, the rear lighting unit, which has conventionally been constituted by a number of components, that is, the light source 1, the light guide plate 2, the diffusion sheet 3, the prism sheets 4, 5, and the reflection sheet 8, is replaced by the light source 1 And the light guide plate 2 only,
As a result, it is possible to improve the luminance and reduce the cost of parts and the number of assembly steps. Furthermore, according to the present invention, the device has a stable characteristic without a change in light use efficiency due to dust being mixed between the reflection sheet 8 and the light guide plate 2 and the occurrence of uneven brightness, which is a problem in the configuration of the conventional device. A liquid crystal display device is obtained.

Next, various shapes of the small projections 10 of the light guide plate 2 will be described in more detail. FIG. 9 is a perspective view of a main part of the light guide plate 2 used in the present invention, and FIG. 10 is a partial sectional view of the small protrusion 10 of the light guide plate 2. In this embodiment, the small protrusion 1
The shape of 0 has a substantially conical shape, and a protective film 19 is formed on the back surface of the reflective film 11. The protective film 19 is effective for preventing the reflectance of the reflective film 11 from changing with time and preventing the reflective film 11 from being physically damaged.

FIG. 11 shows a ray trajectory of light guided by the light guide plate traveling in the light guide plate 2 shown in FIG. When the shape of the small convex portion 10 is conical, the small convex portion reflected light is only the guided light incident on the small convex portion inclined surface because there is no small convex portion bottom surface 14 in FIG. The light exits from the light transmitting surface 16 in the relationship shown. Therefore, the control of the emission angle distribution of the illumination light becomes easier.

FIG. 12 shows a cross-sectional shape of another embodiment of the small convex portion 10. FIG. 12A shows the small protrusion 10.
Is a trapezoidal cross section, and a protective film 19 is formed on the back surface of the reflective film 11.

FIG. 12B shows an example in which the cross-sectional shape of the small projection 10 is substantially trapezoidal and the edge has a smooth R-shape. This shape is an effective shape in consideration of variations in manufacturing conditions when the light guide plate 2 is actually formed. In forming the reflective film 11, the smooth R-shape of the edge is effective in improving the rotation of the reflective film 11. FIG.
2 (b) can be defined as shown.

FIG. 12C is an example in which the cross-sectional shape of the small convex portion 10 is asymmetric. Even if the small convex portion bottom surface 14 is present, reflection of guided light hardly occurs on the small convex portion bottom surface 14. There is an advantage that you can.

FIG. 12D shows an example in which the length of the bottom surface 14 of the small projection 10 is short. Similarly to FIG. 12C, there is an advantage that the reflection of the guided light can be made difficult to occur at the small convex portion bottom surface 14.

FIG. 12E shows an example in which a thick protective film 19 is formed. In practice, when the protective film 19 is formed by spin coating or roll coating, the protective film 19
Thickness improves workability.

It should be noted that the edge of FIG.
The shape is not limited to a trapezoidal cross-sectional shape, and can be applied to other shapes. The height D of the small protrusion 10 is not particularly limited, but in order to efficiently reflect the guided light, at least half of the small protrusion 10 has a height of 1 μm.
More preferably, the thickness is 5 μm or more. The reason is that if the height of the small convex portion 10 is low, the intensity of the reflected light is reduced, and the guided light is easily scattered, which is the same as simply making the lower surface of the light guide plate 2 rough. That's why. As for the size of the small convex portion, it is desirable that at least half of the size is 1 μm or more for the same reason. The size of the small protrusion,
An example of the height is specifically shown in the example of the conical small convex portion 10 in FIGS. 10 and 11, in the case of a cone, the diameter is about 50 μm, the angle θ is about 35 °, and the height D is about 18 μm. However, the above dimensions do not limit the present invention, but provide a guide.

The light intensity from the light source 1 is generally
As the distance from the light source 1 decreases, the density, height or size of the small projections 10 is changed accordingly, and the intensity distribution of the reflected light of the small projections 10, that is, the luminance, extends over the entire surface of the light guide plate 2. And make it even. In the present invention, in the case of a single light source, the density of the small projections 10 is
It is preferred that the light guide plate be formed so as to increase exponentially or exponentially toward the end face of the light guide plate. However, in consideration of the reflection of light at the light guide plate end face opposed to the light source side end face 7, near the end face of the opposing light guide plate, the closer the end face is to the end face, the more the brightness can be made more uniform. .

Next, the structure of the backlight unit of the liquid crystal display device of the present invention will be described with reference to FIG. FIG. 13A shows an example of a single light source and a wedge-shaped light guide plate. It is characterized in that the light guide plate 2 whose thickness is reduced in inverse proportion to the distance from the light source 1 is used, and is effective for making the intensity distribution of light emitted from the light guide plate uniform, reducing the thickness of the light guide plate, and reducing the weight. is there. FIG. 13B is an example in which a single light source is used and the end surface of the light guide plate opposite to the light source 1 is inclined. The angle of the guided light reaching the end face of the light guide plate is changed to facilitate guided light emission. Thereby, it is easy to make the intensity distribution of the light emitted from the light guide plate uniform, and the light loss can be reduced. FIG. 13 (c), (d)
Sets the light guide plate end face 7 on the light source 1 side to the light guide plate incident light spread angle α.
This is an example in which a concave shape and a convex shape are used to adjust. This is effective for controlling the angle distribution of light emitted from the light transmitting surface. FIG. 13 (e)
Is an example in which a two-light source type is used and a flat plate is used as the light guide plate 2. FIG. 13F shows an example in which the thickness of the light guide plate 2 is changed in order to compensate for uneven brightness due to a difference in the distance from the light source 1 with a two light source type.

The structure of the backlight unit is not limited to the one shown in the figure, but can be combined with each other.

Next, another embodiment of the present invention will be described. 14 and 15 show another embodiment of the present invention. Figures 14 and 1
The fifth embodiment is characterized in that a reflective sheet 8 is arranged instead of the reflective film 11 as compared with the embodiments shown in FIGS. A white sheet can be used as the reflection sheet 8, and the reflectance can be improved. FIG. 15 shows the cross-sectional shape of the small protrusion 10 and the arrangement relationship of the reflection sheet 8 in the embodiment of FIG.

FIG. 16 shows the ray tracing result of this embodiment. The light reflected by the reflection sheet 8 enters the light guide plate 2 again, the path is changed, and the light is emitted from the upper surface of the light guide plate 2. And works as illumination light for the liquid crystal display element.

FIGS. 17A to 17D show the shapes of the small projections 10 and correspond to the embodiment of FIGS. 12A to 12D. 2 functions as a backlight by being arranged on the bottom surface.

FIG. 18 is a perspective view of an embodiment in which a small concave portion is formed as a reflection slope on the bottom surface of the light guide plate 2. Small recess 1
A value of 0 ′ can change the path of the light that has entered the light guide plate 2 as in the case of the small protrusion 10 of the above-described embodiment. The small concave portion 10 ′ has the following features as compared with the small convex portion 10. (1) When the number and size of the dots are the same, the small recess 10 ′
Has a greater light-tracing effect. (2) In the case where the light guide plate 2 is obtained by injection molding using a material such as acrylic, a molded product having less molding defects is easily obtained in the small concave portion 10 '.

As the shape of the small concave portion 10 ', a rectangular shape shown in FIGS. 19 and 20 is desirable. Further, the reflection angle θ and the depth H of the small recess 10 ′ shown in FIG.
35 ± 15 °, preferably 35 ± 10 °, and 2 to 40 μm as in the case of the small projection 10 shown in FIG. FIG. 21 shows three examples of the cross-sectional shape. FIG.
It shows a ray trajectory when 0 'is formed. FIG. 23 shows a random planar arrangement of the small concave portions 10 '. In FIG. 22, the incident light is reflected by the side surface of the small concave portion 10 ', and the optical path is changed, so that the illumination light becomes effective illumination light.

The appropriate size and shape of the small projections and small recesses will be described below.

As for the size of the small projections 10 and the small recesses 10 ', when the shape is substantially square, the length of one side is desirably 200 μm, preferably 100 μm or less. When the shape of the small projections 10 and the small recesses 10 ′ is circular, the diameter is 200.
μm, preferably 190 μm or less. Similarly, when the shape of the small protrusions 10 and the small recesses 10 ′ is rectangular, the length of the short side is 200 μm, preferably 100 μm.
m or less. The reason is that if the small convex portion 10 and the small concave portion 10 'are larger than this, the small convex portion 10 and the small concave portion 10', which are bright spots of the backlight, are visually observed when the liquid crystal display panel is viewed closely. This is because it becomes possible to determine the characters and pictures indicated by the liquid crystal display, which hinders the determination.

On the other hand, the size of the small projections 10 and the small recesses 10 'is approximately 10 μm or more when the shape is substantially square, and the shape of the small projections 10 and the small recesses 10' is circular. In this case, the diameter is desirably 10 μm or more. Also,
When the shape of the small protrusions 10 and the small recesses 10 ′ is rectangular, the length of the short side is desirably 10 μm or more. The reason is that if the small projections 10 and the small recesses 10 'are made smaller than this, the number of dots formed on the entire surface of the light guide plate 2 becomes enormous, and it takes time and effort to manufacture the dots accurately. is there.

FIG. 24 shows a sectional shape of the prism sheet 4 which is effective when combined with a light guide plate having a small concave portion. FIG. 25 shows a backlight unit in which a light guide plate 2 having a small concave portion 10 ′, a reflection sheet 8 and a prism sheet 4 are arranged in combination. Here, the angles θp1 and θp2 of the prism sheet 4 are set to 35 ± 15 in order to maximize the intensity of light emitted from the light guide plate 2 in the vertical direction with respect to the panel. °, preferably 35 ± 10 °, 80-88 °, 2
0-40 ° is preferred.

In the backlight unit shown in FIG. 25, when the prism sheet 4 is not provided, the light incident on the light guide plate is reflected by the small recess 10 ', and is oblique to the light exit surface of the light guide plate (FIG. 2).
5, the emitted light with high brightness is emitted in the direction from the vertical direction to the oblique right direction. FIG. 26A shows the relationship between the emission angle and the luminance. In contrast, when the prism sheet 4 as described above is arranged,
The light emitted in the oblique direction is refracted by the prism, and the luminance in the vertical direction increases. This state is shown in FIG.
With such a configuration, it is possible to suppress the generation of scattered light and obtain a backlight unit having high front luminance. The angles θp1 and θp2 of the prism sheet 4 can be optimized by the angle of the small recess 10 ′ as described above.

Next, a method for manufacturing a light guide plate used for the back lighting unit of the liquid crystal display device of the present invention will be described.

The method of manufacturing the light guide plate is basically as follows.
A mold is manufactured and molded by plastic. As a method for manufacturing the mold, various machining methods, for example, methods such as drilling, cutting, and grinding can be used.
An electric discharge machining method is also an effective means. However, the number of the reflecting slopes composed of the small projections 10 or the small recesses 10 'of the present invention is 200 to 20,000 / square centimeter in a general design, and the light guide plate as a whole has an enormous number. A manufacturing method is preferably applied.

FIG. 27 is a process diagram showing one embodiment of a method of manufacturing the light guide plate 2. This manufacturing method includes (1) a step of forming a photoresist 21 on a substrate 20 as shown in FIG. 27 (a), and (2) a photomask 22 (FIG. 27 (b)) having an inverted pattern of the small projections 10. Then, as shown in FIG. 27 (c), the substrate is placed on the substrate 20 and irradiated with ultraviolet rays 23 from above the mask 22, then the photoresist 21 is developed, and as shown in FIG. Part 10
(3) A step of applying a metal plating 25 on the inverted pattern 21 to form a plastic molding stamper 26 composed of the plating layer 25 as shown in FIG. 27 (f), the light guide plate 2 is plastic-molded using the stamper 26.

The substrate 20 has a thickness of 2 to 1
A mirror-polished glass plate of about 0 mm is used. Before forming the photoresist 21, a silane-based adhesiveness improver can be applied in advance. As the photoresist material, a liquid or film-like positive or negative material can be used. FIG. 27 shows a process in the case where a positive-type material is used. As a forming method, there are a spin coating method and a roll coating method. By controlling the thickness of the photoresist 21, the height of the small projection 10 can be changed. By adjusting the exposure and development conditions, the inclination angle of the small projection 10 can be controlled. Photomask 22
A chrome mask, a film mask, an emulsion mask can be used, and data such as the size, the number, and the distribution of the small projections 10 designed in advance are created and drawn by an electron beam, a laser beam, or the like. Can be created. If the conductive film 24 is formed before the formation of the plating layer 25, the plating step becomes uniform, and a good plating layer 25, that is, a stamper 26 can be formed. Conductive layer 2
4. As the material of the plating layer 25, various metals can be used, but Ni is the most suitable material in terms of uniformity and mechanical performance. The obtained plating layer 25 can be easily peeled off physically from the substrate 20, and can be polished and used as a stamper 26 as necessary.

The obtained stamper 26 is fixed to, for example, a matrix 27 of an injection molding machine with a magnet 28, a vacuum chuck 29 and the like. FIG. 27 shows a method of manufacturing the light guide plate 2 by using an injection molding machine. However, as another method, the light guide plate 2 can be formed by extrusion molding, compression molding, vacuum molding, or the like.

As a material constituting the light guide plate 2, any transparent plastic material can be used. Specific examples include acrylic plastics, polycarbonate resins,
There are polyacetal resins, polyurethane resins, and ultraviolet-curable plastic materials. Among them, acrylic materials are excellent in transparency, cost and moldability, and are suitable for the present invention.

As a method of forming the reflection film 11 on the surface of the obtained light guide plate molded product on which the small projections 10 are formed, a vacuum evaporation method,
There are spin coating method and roll coating method, of which resistance heating, sputtering, CV
A vacuum deposition method such as D is suitable for the present invention. As a material of the reflection film 11, various metal films and conductive films are preferable, but aluminum is suitable in terms of price and reflectance. The reflective film 11 can also be formed on the side surface of the light guide plate 2 during vacuum evaporation. In this case, it is needless to say that the light guide plate end face 7 for introducing the light from the light source 1 needs to be covered with a film or the like so that the reflection film 11 is not formed.

Various plastic films can be used as the protective film 19 for the reflection film. Specific examples thereof include a paraffin wax and an ultraviolet curable resin. The paraffin-based wax is preferably of a hot-melt type, and the protective film 19 can be formed by a technique such as roll coating.

FIG. 28 is a process diagram showing another embodiment of the method of manufacturing the light guide plate 2. This manufacturing method
(1) As shown in FIG.
Forming a photoresist 21 film on the substrate, (2) FIG.
As shown in (b), a photomask 22 having a pattern of small projections is arranged on the stamper master 30 and the mask 2
2 irradiating ultraviolet rays 23 from above, and developing to form a pattern 21 of small projections on the stamper master 30;
(3) A step of forming a stamper by etching the stamper master 30 using the inversion pattern 21 as a mask as shown in FIG. 28C, and (4) As shown in FIG. (Pattern 21) is removed to form a stamper 26, and (5) as shown in FIG. 28 (e), a step of plastic molding using the stamper 26.

This step is different from the step of FIG. 27 in that the stamper 26 is processed directly without using a plating step. Here, the stamper master 30 is a mirror-finished metal plate such as Ni. As a method of etching the stamper master 30 using the photomask pattern as a mask, various dry etching methods can be used in addition to wet etching. In particular, the ion milling method, in which the ion beam is incident from a predetermined angle and the inclination angle of the small convex portion 10 can be controlled, is a method suitable for this.

It should be noted that a mold can be directly manufactured by the above-described manufacturing method using a generally used mold material instead of the stamper master 30.

FIG. 29 is a process diagram showing still another embodiment of the method of manufacturing the light guide plate 2. This manufacturing method
(1) A step of forming a photoresist 21 film on a substrate 20 as shown in FIG. 29 (a), and (2) A photomask 22 having a pattern of small projections as shown in FIG. 20 and UV light 2 from above the mask 22.
3 and then developing to form the original shape of the pattern of the small projections on the substrate 20. (3) As shown in FIG. 29C, the pattern is dry-etched so that the pattern has a desired sectional shape. 29 (d), forming a plastic molding stamper 26 by applying metal plating 24, and (5) forming the stamper 26 as shown in FIG. 29 (e). And plastic molding.

This process is a method in which a photomask pattern is formed into a predetermined shape by a dry etching method, and then a stamper 26 is formed by a plating process. The feature is that the original shape of the dot formed by the small concave portion can be shaped into a desired sectional shape.

Finally, the structure of the liquid crystal display will be described.
FIG. 30 is a schematic sectional view of the liquid crystal display device of the present invention.
On the upper surface of the light guide plate 2 as a back lighting unit, a deflecting plate 31,
A TFT 32, a liquid crystal cell 33, a common electrode 34, a color filter 35, and a polarizing plate 31 are provided. This configuration shows a general example of a liquid crystal display device, and various configurations including a backlight unit may be considered depending on the use of the display device.

For example, a desktop-type liquid crystal display device or a television monitor of a personal computer requires a particularly wide viewing angle. In this case, a diffuser for scattering the illumination light and expanding the viewing angle is newly provided. 16 can be arranged at an appropriate position in FIG. In addition, the prism sheet 4 is disposed to illuminate the liquid crystal cell 3 with higher directivity.
After irradiating 3, a sheet having a light diffusion effect can be arranged to widen the viewing angle, or the light transmission surface can be processed to have a light scattering function to widen the viewing angle.

Specific examples of the light source include a cold cathode tube, a hot cathode tube, a tungsten lamp, a xenon lamp, and a metal halide lamp. Usually, a low-temperature light source such as a cold-cathode tube is desirable.

The liquid crystal element or liquid crystal cell used in the present invention is not particularly limited, and known elements and panels can be used. Examples of general liquid crystal cells include a twisted nematic type, a super twisted nematic type, a homogeneous type, a thin film transistor type, an active matrix driving type, a simple matrix driving type, and the like.

A brightness uniforming mask (not shown) used as necessary is used to compensate for uneven brightness caused by a difference in distance from a light source. For example, a sheet having a changed light transmittance is used. The brightness uniforming mask can be arranged at an arbitrary position on the light guide plate.

In the liquid crystal display device according to the present invention, the irradiation efficiency of the light reaching the liquid crystal panel with respect to the light incident on the light guide plate from the light source can be improved to 60% or more as compared with the conventional product. Table 2 shows a specific example in which the light use efficiency of the backlight is compared with a conventional product (printed dots) and the method of the present invention.

[0070]

[Table 2]

The “incidence efficiency of the light guide plate” in Table 2 means
The efficiency of light incident on the light guide plate 2 from the light source 1 is 0.85, that is, 85% in both the method of the present invention and the conventional product. Next, the “light guide plate transmittance” is a ratio of light emitted from the light emitting surface of the light guide plate to light incident on the light guide plate.
%, The system of the present invention can emit 90% because of low absorption and scattering. The “diffusion sheet transmittance” is a ratio of light that can pass through the diffusion sheet, out of the light emitted from the light guide plate emission surface. In the present invention, the same diffusion sheet is used in contrast to 91% of the conventional product. Despite the use, it shows an extremely high value of 97%. Further, the “prism sheet transmittance” is a ratio of light that can pass through the prism sheet, out of the light that has passed through the diffusion sheet, and is 93% in the conventional product and 95% in the method of the present invention. Indicates a high value. It is considered that the reason for this is that when the light guide plate of the present invention is used, the component of light in the direction perpendicular to the light guide plate surface becomes large, and the reflection loss at the time of incidence on the diffusion sheet and prism sheet is reduced. .

The total emission efficiency of the backlight (the irradiation ratio of the light emitted from the light source to the liquid crystal panel), which is the sum of the above efficiencies, is 47% in the conventional product, whereas in the case of the present invention, The value was as high as 67%.

Further, when the present invention is used, the irradiation efficiency of the light transmitted through the liquid crystal panel with respect to the light incident on the light guide plate is set to 1.
It can be improved to 8% or more. An example will be specifically described below.

FIG. 31 is a schematic diagram showing a detailed configuration of the liquid crystal display device in a sectional view. 30 shows the configuration in more detail than FIG. 30 described above. Table 3 is a table summarizing the light use efficiency of the liquid crystal panel of FIG. 31, and shows a comparison between a conventional product (printed dots) and the present invention.

[0075]

[Table 3]

The individual values in Table 3, that is, the transmittances of the respective constituent members, indicate the individual emission efficiencies and the respective transmittances when passing through the respective constituent members. For example, “the total emission efficiency of the backlight” is the value shown in Table 2 above. The “polarizer 1 transmittance” in Table 3 is the transmittance of the polarizer 1 disposed above the backlight in FIG. 31, which is 0.42 (42%) for the conventional product (printed dots). ,
In the case of the method using the present invention, the value is as high as 0.45. The values of the individual “transmittances” are as shown in Table 3, and the detailed description is omitted. The light use efficiency obtained by multiplying all the efficiencies, that is, the light use efficiency when the energy of the light source of the backlight is set to 1, is 0.0147 for the conventional product, whereas the liquid crystal display of the present invention is not used. The device shows a high value of 0.0224. In other words, the conventional light use efficiency of 1.47% is greatly improved to 1.5% of 2.24%. This indicates that a liquid crystal display device with high luminance can be obtained.

[0077]

As described above in detail, according to the liquid crystal display device of the present invention, it is possible to improve the light use efficiency and the luminance. When the luminance is kept constant, it means that the power consumption is reduced, and the environmental effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a perspective view of a backlight unit used in a liquid crystal display device of the present invention.

FIG. 2 is a perspective view showing a small convex portion of the light guide plate of FIG.

FIG. 3 is a perspective view showing a backlight unit of a conventional liquid crystal display device.

FIG. 4 is a schematic view showing a light scattering layer and a light scattering substance formed on the back surface of the light guide plate of FIG.

FIG. 5 is a diagram for explaining ray trajectories in the light guide plate in the embodiment of the light guide plate of FIG. 1;

FIG. 6 is a view for explaining ray trajectories in the light guide plate in the embodiment of the light guide plate of FIG. 1;

FIG. 7 is a diagram illustrating a relationship between an incident light spread angle of a light guide plate and an emission angle of reflected light of a small convex portion.

FIG. 8 is a diagram showing a relationship between a light guide plate incident light divergence angle and a small convex portion reflected light emission angle.

FIG. 9 is a perspective view of another embodiment of the light guide plate of the backlight unit used in the liquid crystal display device of the present invention.

FIG. 10 is a cross-sectional view of a small projection of the light guide plate of the embodiment of FIG. 9;

FIG. 11 is a diagram for explaining ray trajectories in the light guide plate of the embodiment of FIG.

FIG. 12 is a perspective view of another five embodiments of the light guide plate of the backlight unit used in the liquid crystal display device of the present invention.

FIG. 13 is a sectional view of six embodiments of a backlight unit used in the liquid crystal display device of the present invention.

FIG. 14 is a perspective view of another embodiment of the backlight unit used in the liquid crystal display device of the present invention.

FIG. 15 is a sectional view of a main part of the embodiment of FIG. 14;

FIG. 16 is a diagram for explaining ray trajectories in the light guide plate of the embodiment of FIG.

FIG. 17 is a cross-sectional view of another four embodiments of the backlight unit used in the liquid crystal display device of the present invention.

FIG. 18 is a perspective view of another embodiment of the light guide plate of the backlight unit used in the liquid crystal display device of the present invention.

FIG. 19 is a perspective view of another embodiment of the light guide plate of the backlight unit used in the liquid crystal display device of the present invention.

FIG. 20 is a view showing the shape of a small concave portion of the light guide plate of the embodiment shown in FIG. 19;

FIG. 21 is a cross-sectional view of three embodiments of a backlight unit used in the liquid crystal display device of the present invention.

FIG. 22 is a diagram for explaining ray trajectories in the light guide plate of the embodiment of FIG. 21 (b).

FIG. 23 is a diagram showing an arrangement of dots in an embodiment of the light guide plate of the present invention.

FIG. 24 is a sectional view of a prism sheet used in an example of the present invention.

FIG. 25 is a cross-sectional view around a light guide plate according to an embodiment of the present invention using a prism sheet.

26 is a luminance characteristic diagram showing the effect of the embodiment in FIG.

FIG. 27 is a process chart of one embodiment of a method for manufacturing a light guide plate of the present invention.

FIG. 28 is a process diagram of another embodiment of the method of manufacturing the light guide plate of the present invention.

FIG. 29 is a process chart of still another embodiment of the method of manufacturing the light guide plate of the present invention.

FIG. 30 is a schematic sectional view of the liquid crystal display device of the present invention.

FIG. 31 is a schematic cross-sectional view illustrating a detailed configuration of a liquid crystal display device.

[Explanation of symbols]

 1: light source 2: light guide plate 4, 5: prism sheet 8: reflective sheet 9: light guide plate incident light 10: small convex portion 10 ': small concave portion 11: reflective film 12: light guide plate guided light 13: light guide plate lower surface 14: Small convex portion bottom surface 15: Small convex portion inclined surface 16: Light transmitting surface 18: Light guide plate emission light 19: Protective film 25: Plating layer 26: Stamper 31: Polarizing plate 32: TFT 33: Liquid crystal cell 34: Common electrode 35: Color filter

Continued on the front page. (72) Inventor: Kie Kodera 4-6, Kanda Surugadai, Chiyoda-ku, Tokyo Hitachi, Ltd. Home Appliances and Information Media Business Unit

Claims (2)

[Claims] 1. A light source comprising: a liquid crystal panel; a light guide plate disposed on a rear surface of the liquid crystal panel; and a light source disposed on a side surface of the light guide plate, wherein light emitted from the light source includes the light guide plate. A liquid crystal display device adapted to reach the liquid crystal panel via a transmission member, wherein a minimum value of an irradiation efficiency of light reaching the liquid crystal panel via the light member with respect to light incident on the light guide plate is reduced. A liquid crystal display device characterized by being 60%. 2. A light source comprising: a liquid crystal panel; a light guide plate disposed on a back surface of the liquid crystal panel; and a light source disposed on a side surface of the light guide plate, wherein light emitted from the light source includes the light guide plate. A liquid crystal display device configured to reach the liquid crystal panel via a transmission member, wherein a minimum value of an irradiation efficiency of light transmitted through the liquid crystal panel with respect to light incident on the light guide plate is 1.8%. A liquid crystal display device characterized by the above-mentioned.