KR19990072927A - Liquid crystal display - Google Patents

Abstract

The present invention relates to a liquid crystal display device using a member for a liquid crystal display device such as a back lighting device (back light), wherein irradiated light is applied to the liquid crystal display panel and the liquid crystal display panel in order to improve the brightness without increasing the brightness of the light source. A liquid crystal display device having a backlight, wherein the backlight is formed of a light guide plate having at least one light source and one side portion opposed to the light source, and has a small recess on the bottom surface of the light guide plate which is substantially parallel to the liquid crystal cell surface, and has a planar shape of the small recess. This substantially rectangular shape was comprised.

By such a configuration, a liquid crystal display device having a multifunctional, high performance, stable luminance with improved luminance and no luminance unevenness is obtained.

Description

Liquid Crystal Display {LIQUID CRYSTAL DISPLAY}

The present invention relates to a liquid crystal display device using a member for a liquid crystal display device such as a back lighting device (back light).

In recent years, miniaturization of personal computers has been promoted, and portable models called laptops have been widely used. In this laptop personal computer, a liquid crystal device is usually used for the display thereof. Background Art [0002] In recent years, liquid crystal devices have become popular with a back lighting device type display device in which a light source is arranged behind a liquid crystal display panel and the entire display surface is illuminated from the back side. The light source as a back lighting device of such a display device is required to illuminate the entire plane having high luminance and no luminance unevenness. In order to improve the luminance, it is easy to increase the luminance of the light source. However, in a laptop-type personal computer or the like, a battery or the like is used as a driving source, so increasing the luminance of the light source is limited and there is no conventional effective method.

Conventional etch light type lighting apparatuses for liquid crystal display devices include those described in Japanese Patent Application Laid-Open No. 4-162002 and Japanese Patent Application Laid-open No. 6-67004. The conventional lighting apparatus uses a wrap such as a cold cathode tube or a hot cathode tube as a light source 1, as shown in FIG. 2, and arranges it on the end face of the light guide plate 2 made of a transmissive material. The lower surface of the light guide plate 2 is provided with a light scattering layer 3 for scattering light and a reflecting plate 4 for reflecting light, and the upper surface of the light guide plate 2 is provided with light scattering for equalizing the luminance of the illumination surface over the entire surface. A diffusion plate 5 made of a milky white synthetic resin having an effect is provided. Further, a first light collecting plate 6 and a second light collecting plate 7 are arranged on the upper surface thereof to focus diffused light to some extent and to improve the brightness of the front of the display device. As the light scattering layer, as shown in Fig. 3, a plurality of ink dots 8 using light scattering materials such as titanium oxide on the surface of the light guide plate 2 are used. Since the light intensity in the light source 1 decreases as it moves away from the light source 1, the area of the ink dot 8 is formed to be larger as it moves away from the light source 1 as shown in FIG.

As described above, in the conventional lighting device, the light emitted from the light source 1 is guided to the light guide plate 2, scattered by the light scattering material 8 included in the light scattering layer, and then passes through the diffuser plate. Since the liquid crystal element is irradiated, there is a problem of a decrease in luminance due to light scattering loss.

In order to solve these problems, there is a light guide plate which does not use ink as disclosed in Japanese Patent Application Laid-open No. Hei 9-269489. This forms a small convex portion or a small concave portion on the light guide plate surface, thereby reflecting light to illuminate the liquid crystal element. However, its shape and distribution are not optimized and there is room for brightness enhancement.

In addition, one of the problems related to the improvement of the luminance of the liquid crystal display device is the transmittance of the polarization filter. The polarization filter is an element having a function of being disposed between the liquid crystal cell and the backlight to inject a predetermined polarized light into the liquid crystal cell. Generally, a polarizing filter can be produced by adsorbing a dichroic substance into a micelle tube of a polymer film in which micelles are arranged in a predetermined direction. Here, polyvinyl alcohol is used as the polymer film, and this is extended about 3 to 5 times in a predetermined direction between the rollers rotating at different speeds. The micelles of the extended PVA are arranged in the extending direction and the arranged films have strong birefringence. Examples of the substance for imparting dichroism include halogen substance dyes such as iodine, and polarization characteristics are expressed by adsorbing the substance on an extended film. The polarization filter easily obtains a polarization separation function, but since its transmittance is in principle used as a dichroic material, the polarization filter absorbs polarized light that is orthogonal to the polarized light that is transmitted. Therefore, 50% or more of the light energy is lost by the polarization filter, and the current state is that the brightness of the liquid crystal display device is significantly reduced.

As a means of improving this, the method of using a reflective polarizing film is proposed. The reflective polarizing film is a film having a property of passing a specific kind of polarizing component, such as a cholesteric liquid crystal film, and reflecting other polarizing components. That is, non-polarized natural light emitted through the light guide plate is incident on the reflective polarizing film to transmit only a specific polarization component and to reflect other polarization components. Thereafter, the reflected polarization component is reflected again by the reflector to change the polarization state and is incident again to the reflective polarizing film to transmit only a specific polarization component. By repeating this, almost all components of light can be used.

Specifically, a method of using a cholesteric liquid crystal film which is a reflective polarizing film as described in Japanese Patent Application Laid-open No. 3-45906 and Japanese Patent Application Laid-open No. Hei 6-281814 has been proposed. The cholesteric liquid crystal film is composed of an optically active layer of polymer material having cholesteric regularity. The cholesteric liquid crystal film transmits only the circular polarization component in the same direction as the spiral direction of the cholesteric layer in the unpolarized natural light emitted from the light source via the light guide plate and reflects the circular polarization component in the reverse direction. Therefore, in the configuration as shown in Fig. 16, the reflected circularly polarized light component is reflected and returned by the reflecting plate again, and returns to a state close to natural light and is incident again into the cholesteric liquid crystal film. By repeating this, almost all components of light can be used. When the 1/4 phase plate is superimposed on the light emitting surface of the cholesteric liquid crystal film, the circular polarization component is converted into linearly polarized light and can be used as a back light emitting device of the liquid crystal display device.

The luminance of the liquid crystal display device using the cholesteric liquid crystal film is theoretically twice that of the liquid crystal display device using the normal polarizing filter. However, in the case of combining the dominant ink-dot light guide plate and cholesteric liquid crystal film, the circularly polarized light reflected by the scattering loss or the cholesteric liquid crystal film and re-entered into the light guide plate as described above is ink dot. Diffuse reflection causes loss due to scattering, and the polarization state is also eliminated, making it difficult to use as re-emitting light. In addition, the printing dots are considerably large in size, and it is necessary to use a diffuser plate in order to prevent dot sight, so that the effect of improving luminance is further reduced. When combined with a prism sheet that improves the front luminance and optimizes the angular distribution of the emitted light, the luminance improvement effect is only about 10%.

On the other hand, as described in Japanese Patent Application Laid-Open No. Hei 9-102209, a method of combining a light guide plate and a cholesteric liquid crystal film having a lattice-shaped groove formed on the bottom surface of the light guide plate is proposed. In this method, the loss due to scattering is high and the luminance is high, and the luminance improvement effect is also higher than that of the printing dot.

However, the light guide plate in which the lattice groove is formed is difficult to control the luminance coating in the X direction, and it is expected that the problem of mold processing cost and delivery time is also large. In addition, due to the problem of roughness, a soft metal such as brass is often used as a mold material, and there is a concern that the productivity is low. It is also expected that moire is likely to occur between the periodically formed lattice groove and the liquid crystal cell. In addition, the lattice-shaped grooves have a very long period, and it is necessary to use a diffusion plate together, so that the effect of improving the brightness may be further reduced. When combined with a prism sheet that improves the front luminance and optimizes the angle distribution of the emitted light, the luminance improvement effect is only about 20%.

In the above-mentioned conventional apparatus, since light from a light source is irradiated to the liquid crystal element side using scattering by an ink dot, there is a limit in improving efficiency due to loss in scattering and absorption of light by ink. In addition, the shape and distribution of the light guide plate which does not use ink are not optimized, and there is room for luminance improvement.

In the combination of the ink-dotted light guide plate and the cholesteric liquid crystal film, the luminance improvement effect is as low as 10%. In the combination of the light guide plate having the lattice groove and the cholesteric liquid crystal film, the brightness enhancement effect is as high as 20%, but it is difficult to control the brightness distribution or manufacture the light guide plate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device capable of improving such a brightness without improving the conventional defect and increasing the brightness of a light source.

1 is a perspective view of a rear lighting device used in the liquid crystal display device of the present invention;

2 is a cross-sectional view of a conventional dot printing method light guide plate,

3 is an explanatory diagram of conventional dot printing;

4 is an explanatory diagram of a cutting direction of a light guide plate;

5 is a view for explaining a light trace in the light guide plate of the light guide plate used in the present invention;

6 is an explanatory diagram of a dot shape of a light guide plate used in the present invention;

7 is an explanatory diagram of a cross-sectional tilt angle of a light guide plate used in the present invention;

8 is a relationship diagram between surface roughness Ra and front luminance of a light guide plate used in the present invention;

9 is a dot reflection effective area ratio distribution chart of a light guide plate used in the present invention;

10 is an explanatory diagram of a dot random arrangement of a light guide plate used in the present invention;

11 is an explanatory diagram of a cross-sectional tilt angle of a light guide plate used in the present invention;

12 is a relationship diagram between a cross-sectional tilt angle and a front luminance of the light guide plate used in the present invention;

13 is a dot reflection effective area ratio distribution chart of a light guide plate used in the present invention;

14 is a process chart showing a manufacturing method of the light guide plate used in the present invention;

15 is a configuration diagram of a liquid crystal display device of the present invention;

16 is an explanatory view of a principle of a liquid crystal display device using a cholesteric liquid crystal film;

17 is a configuration diagram of a liquid crystal display device using a cholesteric liquid crystal film;

18 is an explanatory view of the effect of the cholesteric liquid crystal film of Example 2 of the present invention;

19 is an explanatory diagram of the effect of the cholesteric liquid crystal film of Comparative Example 1;

20 is an explanatory diagram of the effect of the cholesteric liquid crystal film of Comparative Example 2. FIG.

In order to achieve the above object, in the liquid crystal display device of the present invention, a light guide plate having a plurality of small recesses (hereinafter referred to as dotras) for converting the traveling direction of the guided light in the light guide plate into a predetermined direction is used, and its planar shape. The cross section inclination angle is appropriately controlled. In addition, a reflecting plate is disposed on the lower surface of the light guide plate. Further, if necessary, a prism sheet having an appropriate prism angle is disposed, and illumination light having an appropriate angle distribution on the light exit surface can be irradiated toward the display element. In addition, in order to prevent the occurrence of moire, a member in which the arrangement of dots meets certain constraints and is arranged randomly is used. In addition, the luminance distribution of the emitted light is made uniform by making the density of the dot a predetermined density distribution. If necessary, a reflective polarizing film (such as a cholesteric liquid crystal film and a quarter-phase plate) is disposed between the light guide plate exit surface and the liquid crystal unit to improve luminance.

1 shows a perspective view of one embodiment of the present invention. In the light source device used in the present invention, dots 10, which are small recesses, are formed on the surface of the lower surface of the light guide plate 9 so as to convert the traveling direction of the light guide plate in the light guide plate into a predetermined direction. As shown in Fig. 1, the dot is a dot bottom portion that is present on the flat portion 11 (the surface having an angle of 5 ° or less with respect to the light guide plate light exit surface 13 except for the dot bottom portion 12) on the bottom surface of the light guide plate. And a small concave portion composed of a dot slope portion 14 (however, Fig. 1 is a small convex portion since it is seen from the inside of the light guide plate).

4 is a view for explaining a direction of the light guide plate 2 used in the following description. When the light source 1 is approximated to a linear light source, a plane perpendicular to the light source 1 is parallel to the light guide plate end surface 15, and a direction parallel thereto is perpendicular to the X direction 16 and to the light guide plate light exit surface 13. The direction parallel to the direction is set to the Y direction 17.

FIG. 5 shows the light traces of the guided light of the light guide plate traveling in the light guide plate 2 of the present invention. The light from the light source 1 is incident on the light guide plate 2 as the light guide plate incident light 19 by the light guide plate light source side end face 18 to become the light guide plate waveguide 20, and toward the other end face 21. The whole reflection is repeated on the lower surface and the light guide plate exit surface 13. The light 23 incident on the dot slope 22 of the waveguide 20 is reflected and collided with the light guide plate exit surface 13 and refracted therefrom to be emitted as the output light 24 from the light guide plate exit surface 13. Then, the unreflected light becomes the dot slope transmitted light 25 and is reflected by the reflecting plate 4 to be incident again on the light guide plate 2, part of which is emitted from the light exit surface 13, and the rest of the light guide plate waveguide light again. It becomes (20). Therefore, the light guide 20 is gradually emitted from the light guide plate 2 so that the liquid crystal display device can be illuminated by appropriately disposing the dots.

Fig. 6 shows the shape of a suitable dot. The shape (hereinafter, referred to as planar shape) in which the dot bottom portion 12 of the present invention is accurately projected on the light guide plate light exit surface 13 is substantially rectangular or has a vertex bent portion 26 as shown in FIG. Substantial rectangles (hereinafter simply referred to as rectangles) are suitable. This is because the area of the dot reflecting surface 22 can be increased with respect to circles or squares having the same area of the dot bottom surface, so that the number of dots can be reduced. That is, the degree of freedom of dot distribution is also improved, and mask and dot coordinate data can be easily created. Further, the bent portion 26 of the apex is effective in reducing scattering and increasing front luminance. In addition, as shown in FIG. 6, the length of the long side at the time of approximating a rectangle of a dot bottom part is made into the dot length 28, and the length of the short side is made into the dot width 29. As shown in FIG.

The arrangement direction of the dots is arranged so that the long side slopes 30 of the dots are substantially parallel to the X direction 16. This arrangement is because the area of the long side slope 30 of the dot is larger than the slope 31 of the short side of the dot, so that light can be efficiently reflected from the light source 1.

It is preferable that the dot length is 80-800 micrometers in dot length. The reason is that when the length 28 is larger than 800 µm, 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 appears by letters or patterns (dot site). This is because it obstructs the discrimination of letters and patterns. If the length 28 is smaller than 80 mu m, the number of dots becomes too large, making it difficult to create masks and dot coordinate data. In consideration of the cost of manufacturing the mask, the optimum value is 100 µm or more, and considering the display quality, 300 µm or less is preferable.

It is preferable that the dot width 29 is 60 micrometers or less. The reason for this is that when the length 29 is larger than 60 mu m, the ratio of the dot slope portion 14 occupying the dot area decreases, making it difficult to obtain a sufficient reflection surface. Moreover, it is preferable to make the said length 29 into 45 micrometers or less in order to acquire sufficient luminance also in the 4 corners of the light guide plate 2. As shown in FIG. In addition, the lower limit is a problem of the luminance of the mask, the exposure device and the resist, but 20 µm or more in which an inexpensive mask or exposure device can be used is preferable. Moreover, Preferably it is 30 micrometers or more.

5-20 micrometers is suitable for the depth of a dot. The reason is that in order to obtain a depth of 20 µm or more, a resist having a high viscosity must be used, and the flatness of the flat portion of the dot-forming surface is lowered, or transferability is lowered when forming the light guide plate 2, making it difficult to form a desired dot shape. Because. On the other hand, if the depth of the dot is smaller than 5 占 퐉, the ratio of the dot slope portion 14 to the dot area is reduced, so that desired luminance cannot be obtained. In consideration of using a liquid resist, the thickness is optimally about 6 to 12 µm.

20-35 degrees are suitable for the cross-sectional tilt angle of this invention, and the optimum value is 28 +/- 4 degree. Here, the cross-sectional tilt angle is demonstrated using FIG. FIG. 7 is a view showing a dot cross-sectional shape by a dot cutting surface passing through the center of the dot and parallel to the light guide plate cutting surface 15 of FIG. 4. The cut surface is determined in this way because the slope 30 of the long side of the dot acts more effectively when the path of light is changed.

When obtaining the cross section inclination angle, it is calculated by the following method. As shown in Fig. 7, the dot depth is divided into three, and the intersection of the three dividing line and the slope on the light source side is P1, P2, P3, and P4, respectively. Next, the angle formed by the straight line 32 passing through P2 and P3 and the dot bottom surface 12 is obtained, and this is taken as the cross-sectional tilt angle. As described above, the inclination angle of the cross section is defined because the angle is easily subject to variations in process conditions, which is easy to use for management, and this part greatly influences the light emission efficiency.

To define the cross-sectional inclination angle calculated in the above range in the above range to improve the front luminance by optimizing the angle distribution of light from the light guide plate light exit surface 13 and at the same time suppressing the amount of light emitted by tilting more than necessary. Because. That is, when the cross-sectional inclination angle exceeds 35 °, the ratio of light totally reflected on the dot slope decreases and the efficiency decreases. If the angle is smaller than 20 °, the angle formed between the light reflected from the dot slope and the light guide plate exit surface does not become large enough.

In this invention, it is preferable that the bottom part of the dot is substantially straight in the cross-sectional shape of the direction perpendicular | vertical to the light source of a dot. This is because the inclined slope can be reduced by making it a straight line, so that unnecessary reflection can be reduced to facilitate the design. By optimizing the dots of the small concave as described above, the luminance can be improved by 10% or more compared to the circular dot or square dot and the ink dot or the like.

In the present invention, light is guided to the outside of the light guide plate 2 by the reflection refraction caused by the slope of the dot, and light is diffused to every corner of the light guide plate 2 by using the specular reflection of the other part. Therefore, by reducing the surface roughness of the slope portion of the light guide plate, it is possible to reduce the loss at the time of reflection refraction and to improve the luminance. Since the surface roughness of the light guide plate flat portion is smaller than that of the slope portion, it is particularly important to suppress the surface roughness of the slope portion small. FIG. 8 is a diagram showing the relationship between the surface roughness and the front luminance of the slope portion (between P2 and P3) of the dot of the light guide plate. As such, Ra is preferably 0.4 µm or less.

In order to achieve uniform luminance distribution, the dot density is preferably made smaller as the light source 1 becomes smaller. Specifically, the length of the light guide plate Y direction 17 is 191 mm ± 20 mm, the thickness of the light incident part of the light guide plate 2 is 2.3 mm ± 0.5 mm, and the thickness of the part farthest from the light source 1 of the light guide plate 2 is In the case of 1.3 mm ± 0.3 mm, the Y-direction distribution in the center of the light guide plate is hatched in the range of 0.05 < Y < 0.95 when Y = distance from the light source / length in the light guide plate Y direction as shown in FIG. It is desirable to have a reflection effective area ratio in the range 33.

Specifically, in the range of 0.05 <Y <0.95, K ₁ Y ⁵ + K ₂ Y ⁴ + K ₃ Y ³ + K ₄ Y ² + K ₅ Y ¹ + K ₆ + C1 <reflective effective area ratio <K ₁ Y ⁵ The reflection effective area ratio is determined to satisfy + K ₂ Y ⁴ + K ₀ Y ³ + K ₄ Y ² + K ₅ Y ¹ + K ₆ + C2.

only,

K ₁ = -0.2330335, K ₂ = + 0.7497230,

K ₃ = -0.6375126, K ₄ = + 0.1875481,

K ₅ = -0.0011018, K ₆ = + 0.0298941,

C1 = -0.004, C2 = +0.004.

By setting the reflection effective area ratio to such a distribution, uniform luminance can be obtained from the entire liquid crystal display. At this time, the effective reflection area ratio is calculated using Equation 1. In this way, the dot density distribution is defined using the effective reflection area ratio. The long side slope, the dot bottom surface 12, and the short side slope 31 of the dot far from the light source 1 shown in FIG. This is because the design change is easy when the size or shape of the dot is changed compared to simply using the dot density or the dot dielectric constant because it has almost no light extraction function.

The planar arrangement of the dots is preferably random. The reason for this is that the dots of the present invention are fine, and thus, to prevent moire generated from interfering with regular patterns such as liquid crystal cells, color filters, TFT patterns, black stripes, etc., which constitute the liquid crystal display device. Because.

The back lighting device that combines the light guide plate of the present invention and the reflective polarizing film (cholesteric liquid crystal film and quarter phase plate) is a combination of a light guide plate using an ink dot, a cholesteric liquid crystal film and a quarter phase plate. The luminance improvement effect is greater than that of the rear lighting apparatus which combines a light guide plate with a back lighting device or a lattice groove, a cholesteric liquid crystal film and a quarter-phase plate. In addition, the light guide plate of the present invention is easier to manufacture than a light guide plate having a lattice groove, and it is preferable to combine the light guide plate, the cholesteric liquid crystal film and the quarter-phase plate of the present invention.

Best Mode for Carrying Out the Invention Embodiments of the present invention will be described below with reference to the drawings.

(Example 1)

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a back lighting device used in the liquid crystal display device of the present invention, and Fig. 6 is a view for explaining the shape of a dot (small concave portion) of the embodiment. In the present embodiment, the dot length 28 is 200 mu m, the dot width 29 is 40 mu m, and the dot depth is 8 mu m. This back lighting device has a light source 1, a light guide plate 2, and a reflecting plate 4 as minimum components, and dots are formed on the bottom surface of the light guide plate 2. In addition, the dots are randomly arranged. A part of the dot arrangement is shown in FIG. By setting it as such, it can prevent generation | occurrence | production of moire. In addition, in this embodiment, a diffusion plate and two light collecting plates are used in addition to the minimum component.

Fig. 11 shows the dot cross-sectional shape of the light guide plate 2 produced in this embodiment. The cross section inclination angle is 28 degrees. Fig. 12 is a diagram showing the cross-sectional tilt angle and average luminance of the light guide plate of the embodiment. As can be seen from Fig. 12, the dot cross-sectional inclination angle is suitably 20 to 35 degrees, and the optimum value is 28 ± 3 degrees. Fig. 13 is a diagram showing the distribution of the effective reflection area ratio of dots.

(Example 2)

17 is a configuration diagram of a liquid crystal display device using a cholesteric liquid crystal film. In the case where the light guiding plate of the present invention is used for the light guiding plate in FIG. 17 (Example 2), when the light guiding plate of the ink dot method is combined (Comparative Example 1), or when the light guiding plate of the grating method is combined (Comparative Example 2) The luminance improvement effect was compared and examined.

Fig. 18 shows the luminance distribution in the X and Y directions in Example 2 and the luminance distribution in the X and Y directions when the cholesteric liquid crystal film and the λ / 4 plate are removed in the configuration of Example 2; One graph. In both X and Y directions, there is a 20% increase in luminance.

Fig. 19 shows the luminance distribution in the X and Y directions in Comparative Example 1 and the luminance distribution in the X and Y directions when the cholesteric liquid crystal film and the λ / 4 plate were removed in the configuration of Comparative Example 1; One graph. In both X and Y directions, there is a 10% increase in luminance.

FIG. 20 shows the luminance distribution in the X and Y directions in Comparative Example 2 and the luminance distribution in the X and Y directions when the cholesteric liquid crystal film and the λ / 4 plate were removed in the configuration of Example 1. FIG. One graph. In both X and Y directions, there is a 20% increase in luminance.

As described above, the light guide plate according to the present invention has a higher luminance improving effect by the cholesteric liquid crystal film than the ink dot light guide plate. In addition, there is an improvement in brightness equivalent to that of the grating type light guide plate. In addition, the luminance of the liquid crystal display device using the light guide plate according to the present invention is 10% or more higher than that of the ink dot method even when the cholesteric liquid crystal film is not used, and is equal to or higher than the lattice method. In addition, the lattice method has many manufacturing problems such as uniformity of in-plane luminance distribution and difficulty in manufacturing a mold, and thus is superior to the present invention.

Table 1 is a table summarizing the luminance change and the problem with or without the collector liquid crystal film for the liquid crystal display device of the present invention and the liquid crystal display device of the comparative example.

Comparison of each method LCD Display Example 2 Comparative Example 1 Ink Dot Method Comparative Example 2 Grid Type Reflective Polarizing Film * 1 radish U radish U radish U Front luminance * 2 111 135 100 108 110 132 Mass Production Problems radish radish radish radish Difficulties in manufacturing X-direction luminance distribution correction mold cost ◎ ○ ○ △ × ×× Judgment ○ ○ △ △ × ×

※ 1 cholesteric liquid crystal film is used

※ Relative value when we made brightness of 2 ink dot reflection polarization film nothing 100

As described above, the light guide plate according to the present invention has the same luminance as the liquid crystal display device using the cholesteric liquid crystal film in the conventional ink dot method, and is superior in cost. Moreover, when high brightness is required, the liquid crystal display device which combined the light guide plate and cholesteric liquid crystal film by this invention is the best. Moreover, the same effect can be acquired even if it uses reflective polarizing films other than a cholesteric liquid crystal film.

Next, the manufacturing method of the light guide plate for rear lighting apparatus of this invention is demonstrated.

As a manufacturing method of a light guide plate, a metal mold | die is produced and plastics is manufactured. Since the number of dots which consist of the small recessed part of a light-guide plate turns into a number which is 500,000-2 million in a 12.1-inch light-guide plate, it is good to apply the manufacturing method described below.

14 is a process diagram showing the manufacturing method thereof. In this manufacturing method, the photoresist 35 is formed on the substrate 34 of FIG. 14A, and the photomask 36 having the dot pattern of FIG. 14B is formed on the substrate 34. FIG. Disposed on the substrate 36 and irradiated with ultraviolet rays 37 from above the mask 36, and then developing a photoresist to form a pattern of dots on the substrate 34. Metal plating on the pattern of FIG. And a step of forming a stamper 39 made of the plating layer 38, and a step of plastic molding the light guide plate 2 using the stamper 39 shown in FIG. 14 (d).

As the substrate 34, a mirror polished glass substrate or the like is used. Before forming the photoresist 35, a silane-based adhesion improver may be applied in advance. As the photoresist material, a liquid or film-like positive or negative material can be used. As the formation method, there are a spin coating method and a roll coating method. It is possible to change the depth of the small recess by controlling the thickness of the photoresist. In addition, the cross-sectional tilt angle can be controlled by studying exposure, development, and annealing conditions. As the photomask 36, various masks such as a chrome mask, a film mask, and an emulsion (fluid) mask can be used, and data such as the size, number, and distribution of dots designed in advance are prepared and drawn by an electron beam, a laser beam, or the like. We can write by doing. If the conductive film is formed before the plating layer 38 is formed, the plating non-uniformity is eliminated, so that a good plating layer 38, that is, a stamper 39, can be formed. Although various metals can be used as a material of a conductive layer and a plating layer, Ni is an optimal material from a viewpoint of uniformity and mechanical performance. The obtained plating layer 38 can be physically easily peeled off from the substrate 34, and is polished as necessary to be used as the stamper 39.

The stamper 39 thus obtained is fixed to, for example, a model of an injection molding machine with a magnet, a vacuum channel, or the like, and the light guide plate 2 is plastic molded. In the above, the method of manufacturing the light guide plate 2 by the injection molding machine was explained, but the light guide plate 2 can be molded by discharge molding, compression molding, vacuum molding, etc. as another method.

As a material constituting the light guide plate 2, a transparent plastic material can be used. Specific examples include acrylic plastics, polycarbonate resins, polyacetal resins, polyurethane resins, and ultraviolet curing plastic materials. Among these, the acryl-based material is excellent in transparency, price, and moldability and is suitable for the present invention.

Next, the configuration of the liquid crystal display device will be described.

15 shows the configuration of main parts of the liquid crystal display device of the present invention. On the upper surface of the rear lighting device, a deflection plate, a liquid crystal cell, a common electrode, a color filter, and a polarizing plate are installed. This configuration shows a general example of the liquid crystal display device, and various configurations, including a back lighting device, are considered depending on the use of the display device. For example, a disc top type liquid crystal display device or a television monitor of a personal computer requires a particularly wide viewing angle. In this case, a diffuser plate for scattering illumination light to enlarge the viewing angle can be disposed at an appropriate position. Further, after the prism sheet is disposed to irradiate the liquid crystal cell with more direct illumination light, the sheet having the light diffusing effect may be disposed to widen the viewing angle, or the light exit surface may be processed to give a light scattering function to increase the viewing angle. As a specific example of the light source 1, a cold cathode tube, a hot cathode tube, a tungsten lamp, a xenon lamp, a metal halogen lamp etc. are mentioned.

Although it does not specifically limit about the liquid crystal element to liquid crystal cell used for this invention, A well-known element and a panel can be used. Typical liquid crystal cells are twist mnematic, super-twist mnematic, homogenous, thin film transistor type, active matrix drive type or simple matrix drive type. Etc. can be mentioned.

Although it does not specifically limit about the reflective polarizing film used for this invention, Well-known films, such as a cholesteric liquid crystal film, can be used. Specifically, DBEF (trade name) manufactured by 3M Corporation, Transmax (trade name) manufactured by Meruk Corporation, and the like can be used.

As described above, the liquid crystal display device of the present invention provides a liquid crystal display device having multi-function, high performance, stable luminance without luminance unevenness, and high brightness.

Claims (11)

A liquid crystal display device comprising a liquid crystal display panel and a backlight for irradiating irradiated light to the liquid crystal display panel. The backlight comprises at least a light source and a light guide plate having one side portion opposed to the light source, the backlight having a small recess on the bottom surface of the light guide plate substantially parallel to the liquid crystal cell surface, and the planar shape of the small recess is substantially rectangular. A liquid crystal display device. The method of claim 1, The bottom of the small concave portion has a length in a direction parallel to the light source in a range of 80 to 800 mu m, and a length in a direction perpendicular to the light source is 60 mu m or less. The method according to claim 1 or 2, The depth of the said small recessed part exists in the range of 5-20 micrometers, The liquid crystal display device characterized by the above-mentioned. The method according to claim 1 or 2, A cross-sectional inclination angle of the small concave portion is in the range of 20 to 35 degrees. The method according to claim 1 or 2, And the surface roughness of the slope of the small concave portion is Ra &lt; 0.4 mu m. The method according to claim 1 or 2, When the distribution of the small concave portion is a reflection effective area ratio, Y = distance from the light source / length of the light guide plate Y direction, K ₁ Y ⁵ + K ₂ Y ⁴ + K ₃ Y ³ + in the range of 0.05 <Y <0.95. K ₄ Y ² + K ₅ Y ¹ + K ₆ + C1 <Reflective effective area ratio <K ₁ Y ⁵ + K ₂ Y ⁴ + K ₃ Y ³ + K ₄ Y ² + K ₅ Y ¹ + K ₆ + C2 A liquid crystal display device. (K ₁ = -0.2330335, K ₂ = + 0.7497230, K ₃ = -0.6375126, K ₄ = + 0.1875481, K ₅ = -0.0011018, K ₆ = + 0.0298941, C1 = -0.004, C2 = +0.004.) The method according to claim 1 or 2, And the arrangement of the small recesses is random. The method according to claim 1 or 2, And the bottom portion of the small concave portion is substantially straight in a cross-sectional shape in a direction perpendicular to the light source of the small concave portion. The method according to claim 1 or 2, And at least a reflective polarizing film on the light guide plate exit face side of the light guide plate. The method according to claim 1 or 2, And at least a cholesteric liquid crystal film on the light guide plate exit surface side of the light guide plate. The method according to claim 1 or 2, And at least a cholesteric liquid crystal film and a quarter-phase plate on the light guide plate exit surface side of the light guide plate.