JP2000231102A - Surface light source device and liquid crystal display device utilizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device which can improve brightness, i.e., luminance of light emitted from a light-emitting surface of a light transmission body even when the same light source as conventional one is used, which has a simple structure and is easily manufactured, and a liquid crystal display device utilizing the same by utilizing light emitted from the light source arranged along the side end face of the light transmission body as efficiently as possible besides without damaging the lighting performance of the light source. SOLUTION: In the surface light source device, the light source 13 is arranged on the side end part 12 of a light transmission plate 11 of which the one surface is made to be a light-emitting surface 15 and besides on which an incident light scattering means 17 is provided and the light source 13 is covered by a reflector 14 to make light emitted from the light source 13 incident on the inside of the light transmission plate 11 from the end face 12 of the side end part. The reflector 14 is formed with a reflective plastic plate having a shape maintaining property.

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 and a surface light source device suitably used as a backlight of the liquid crystal display device and the like, and more particularly to a technique for improving the luminance performance, energy efficiency and the like of the surface light source device.

[0002]

2. Description of the Related Art In recent years, transmission type liquid crystal display devices have been frequently used as display devices for word processors, personal computers, and the like. Such a liquid crystal display device is generally configured by arranging a planar illumination device, that is, a backlight, on the back surface of a liquid crystal element. This backlight has a mechanism for converting a linear light source such as a cold cathode discharge tube into planar light.

[0003] Specifically, a conventional backlight has a light source disposed directly below the back surface of a liquid crystal element, or a light source provided on a side surface thereof, and a surface light source is obtained using a light guide such as an acrylic plate. Is typical (side light method),
In particular, in the case of the latter sidelight method, an optical element such as a prism array is arranged on the light emitting surface of the light guide plate to obtain desired optical characteristics.

[0004] Such a sidelight type backlight is disclosed in, for example, JP-A-61-99187 and JP-A-63-62104, and is already well known. In particular, in order to more effectively bring out the general characteristics of a liquid crystal display device that is lightweight and thin, it is preferable to use a sidelight method in which a backlight can be made thin, and it is suitable for a liquid crystal display device such as a portable personal computer. The backlight of the sidelight type is often used.

[0005]

The performance required of such a backlight has been increasing in recent years, and in particular, a portable personal computer or a TV monitor using a color liquid crystal display device has been developed. Then
Due to the extremely low light transmittance of the color liquid crystal cell itself, the luminance value required for the backlight light source is inevitably high.

For this reason, in the backlight of the sidelight type, there is a technique for providing an efficient illumination optical system with less energy loss by making effective use of light emitted from a cold cathode tube or the like as a light source as much as possible. The appearance has been awaited. This point will be described with reference to a typical mode seen in a conventional sidelight type backlight as an example.

Conventionally, in this type of surface light source device, as shown in FIG. 6, a tubular light source 13 is arranged along one side surface 12 of a light guide 11, and light emitted from the tubular light source 13 is effectively guided. The reflector 4 is arranged so as to cover the tubular light source 13 so that the light enters the inside from one side surface 12 which is the incident end surface of the body 11. A typical example of the reflector 4 is one in which a film is arranged to be wound around a cold cathode tube, or one in which a metal plate is subjected to sheet metal processing.

However, in a reflector wound with a film, it is difficult to say that the light emitted from the light source is always used sufficiently effectively due to the simplicity of the shape. In particular, the light emitted from the side opposite to the incident end face of the light guide is emitted. Ray component 5 is
There is a problem that the light is almost lost and the energy loss increases.

As another problem, in the reflector 4 wound with a film, it is difficult to remove the cold-cathode tube once the cold-cathode tube is mounted in the backlight module. When it becomes necessary, there is a problem that it becomes very difficult to repair the backlight module.

On the other hand, in a reflector formed by sheet metal processing of a metal plate, the gap between the cold-cathode tube and the reflector can be increased due to the degree of freedom in the shape design. It is possible to design an optically appropriate shape to utilize.

However, since the mounting space allowed for the reflector is not always large, even if an optically appropriate shape is designed, the reflector cannot be used because of the high electrical conductivity of the metal plate. Since it acts as an auxiliary capacitance of a circuit system, leakage occurs frequently in a complicated optimized shape, and the performance expected from an optical point of view is not always exhibited, resulting in a large energy loss.

SUMMARY OF THE INVENTION An object of the present invention is to solve such a conventional problem. The object of the present invention is to utilize light emitted from a light source arranged along a side end face of a light guide as effectively as possible. The structure is simple and easy to produce so as not to hinder the lighting performance of the light source and to improve the brightness, that is, the brightness of the light emitted from the light exit surface of the light guide even when using the same light source as before. An object of the present invention is to provide a surface light source device and a liquid crystal display device using the same.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a surface light source device and a liquid crystal display device using the same, and is configured as follows to solve the above-mentioned technical problems. That is, the surface light source device of the present invention includes a light guide having one surface as a light exit surface and provided with incident light scattering means, a light source provided at a side end of the light guide, and And a reflector for covering the light source so that the emitted light is made to enter the inside of the light guide from the end face of the side end portion, wherein the reflector is formed of a reflective plastic plate having shape maintaining properties.

<Specific Configuration of the Present Invention> The surface light source device of the present invention is composed of the above-mentioned essential components. However, the present invention is established even when the components are specifically as follows. The concrete component is that a test piece having a size of 1.0 × 100.0 mm is cut out from the reflective plastic plate, one end of the test piece is fixed on a vertical surface, and the other end of the test piece is removed. When measuring the amount of sag of the side end from the one side end fixed position, the amount of sag is 20.0
mm.

Further, in the surface light source device of the present invention, the reflective plastic plate is made of a white material having a reflectance of 80% or more, or the surface of the reflective plastic plate has a reflectance of 80% or more. An embodiment in which a metal layer is provided is preferable. Further, it is preferable that a cross-sectional shape of the reflector made of the reflective plastic plate is a polygonal shape.

In addition, in the surface light source device of the present invention, the reflector made of the reflective plastic plate is formed by bending a grooved flat reflective plastic sheet, or The reflector made of a conductive plastic plate is obtained by molding a flat reflective plastic sheet.

Further, in the surface light source device according to the present invention, it is preferable that the reflector is fixed by a lamp holder covering the reflector, and it is more preferable that the material forming the lamp holder is an insulating material. Further, as a more preferred aspect of the present invention, the reflection direction of the light source is prevented from being reflected on the reflection surface of the reflector positioned on a virtual axis passing through the center of the light source and substantially perpendicular to the end surface of the side end portion of the light guide. Means, and light from the light source passing through a center of the light source and exiting from an angle range around an imaginary axis substantially parallel to a light exit surface normal of the light guide, the light source It is preferable to use one provided with at least one parallel light reflecting means formed on the reflecting surface of the reflector so as to reflect in the avoiding direction.

Further, the present invention is a liquid crystal display device, and the liquid crystal display device can be constituted by using a surface light source device having the above-mentioned features as a backlight optical system.

According to the surface light source device of the present invention having such features, the light emitted from the light source disposed along the side end face of the light guide is utilized as effectively as possible, and the lighting performance of the light source is improved. In this case, the brightness of the light emitted from the light exit surface of the light guide, that is, the brightness can be improved even when the same light source as in the related art is used.

Further, in the surface light source device according to the present invention, since the light source including the reflector can be easily taken out from the backlight module, it is possible to obtain an excellent maintenance property that the cold cathode tube can be easily replaced. .

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a surface light source device and a liquid crystal display device of the present invention will be described in more detail with reference to the embodiments shown in the drawings. FIG. 1 shows a surface light source device 10 according to one embodiment of the present invention. The surface light source device 10 of this embodiment includes a substrate made of a translucent flat plate, that is, a light guide 11.
A tubular light source 13 is provided at one end of the light guide 11 along the side end surface 12.

A reflector 14 is attached to one end 12 of the light guide 11 so as to cover the tubular light source 13.
The direct light by the tubular light source 13 and the reflected light reflected by the reflector 14 enter the light guide 11 from one side end surface 12 which is a light incident end surface.

The light guide 11 is, for example, a rectangular thin plate having a thickness of about 4 mm, and one surface, which is the upper surface as viewed in FIG. 1, is a light exit surface 15 for emitting light. The other surface on the side is a surface 16 facing the light emitting surface. The light guide 11 is provided with various incident light scattering / reflecting means 17 as a mechanism for emitting incident light to the light exit surface side. Typical examples include a mode in which white ink or a rough surface is patterned in a dot shape, a mode in which light scattering fine particles are dispersed, a mode in which graining is performed, and the like. However, in the present invention, this mechanism, that is, the incident light scattering / reflecting means is not particularly limited.

The tubular light source 1 used in the present embodiment
The reflector 14 that reflects the light emitted from 3 and makes it incident on the light guide 11 is made of a reflective plastic plate having a shape maintaining property, that is, a thermoplastic resin or a thermosetting resin having an appropriate thickness.
What was shape | molded by the shape is used. This shape maintaining property is necessary from the viewpoint that the clearance between the annular light source 13 and the reflector 14 is appropriately maintained, and the function of guiding the light emitted from each position of the light source to the side end surface 12 of the light guide 11 without loss is required. Is to secure a high rigidity.

More specifically, a test piece 30 having a size of W × L (W = 1.0 mm, L = 100.0 mm) is cut out from the reflective plastic plate used for the reflector 14 as shown in FIG. One end 31 of the test piece 30
Is fixed to a vertical surface 32, and when the amount of droop 33 of the other side end of the test piece 30 is measured with reference to the fixing position of one side end 31, the amount of droop 33 is 20.0.
Use is made of a reflective plastic plate having a thickness of within mm, preferably within 10.0 mm, more preferably within 5.0 mm. As a specific example, a reflector made of an engineering plastic plate represented by polyester or the like having a thickness of 200 μm or more is preferably used.

In addition, the reflector 14 used in the present invention has a reflectivity of 80% or more from the viewpoint of maintaining the above-mentioned shape maintaining property and guiding the light emitted from the tubular light source 13 to the light guide 11 without loss. It is preferable to use a white material of 85% or more, more preferably 90% or more. In particular, a white plastic sheet typified by a white plastic sheet kneaded with a foamable plastic and a white pigment such as titania is preferably used because it is easy to produce and has excellent optical characteristics.

In addition, from the viewpoint of increasing the reflection efficiency, the material is not necessarily limited to a white material. It is also possible to increase the reflection efficiency by forming a metal layer on the surface of the reflector 14 having shape maintaining properties. At this time, the reflectance required for the metal layer is 80% as in the case of the white material.
Or more, preferably 85% or more, more preferably 90%
It is preferable to make the above. The means for providing the metal layer is not particularly limited, but vacuum deposition, sputtering, plating, bonding of metal foil, and the like are preferably used.

The reflector 14 used in the present invention
Is not particularly limited as long as the light emitted from each position of the tubular light source 13 can be efficiently guided to the side end surface 12 of the light guide 11. The shape is preferably polygonal from the viewpoint of ease of mounting.

Further, as illustrated in FIGS. 3 (a), 3 (b) and 3 (c), the end face of the side end 12 of the light guide 11 passes through the center of the light source 13 and A light source direction reflection avoiding means 19 is provided on a reflecting surface located on an orthogonal virtual axis 18.
4A and FIG.
As shown in (b), the light from the light source 13 that passes through a center of the light source 13 and exits from a certain angle range around an imaginary axis 21 substantially parallel to the normal 20 of the light exit surface 15 of the light guide 11. A reflector 14 having at least one parallel light reflecting means 22 formed on a reflecting surface so as to reflect light in a direction avoiding the light source 13 is preferably used.

The method for manufacturing the reflector 14 used in the present invention is not particularly limited, and various plastic molding methods such as injection molding can be used. However, from the viewpoint of easiness of production, it is preferable to obtain a flat reflective plastic sheet on which a groove is formed by bending. That is, as illustrated in FIG.
By using the foamable white polyester sheet 25 or the like to which the No. 4 has been applied, it can be easily processed into a desired shape.

Also, the shape can be easily imparted and the mass can be produced by molding a flat reflective plastic plate, that is, by vacuum forming, blow molding, pressing or hot pressing. Is preferred. In particular, in a mode in which the surface layer is a metal vapor-deposited layer, it is difficult to perform a vapor deposition process after imparting a shape, and therefore, a molding method by molding a flat plastic plate is preferable.

The reflector 14 used in the present invention
As a preferred mounting mode, as shown in FIG.
That is, the reflector 14 is fixed by the lamp holder 26. Thereby, the positioning accuracy of the reflector 14 is remarkably improved, and the positional relationship with the light guide 11 is stably maintained, so that the inherent performance of the reflector 14 can be maximized.

In this embodiment, since the light source 13 including the lamp holder 26 can be easily taken out of the backlight module, the maintenance of the backlight module is greatly improved when the lamp is out. It is possible to do. In particular, in order to maximize the luminous efficiency of the cold-cathode tube, it is desirable that the holder 26 is also made of an insulating material, and a molded body made of various general-purpose plastics and engineering plastics is preferably used. Is done.

As a preferred embodiment of the surface light source device according to the present invention, as shown in FIG. 1, a sheet 100 having an appropriate dimming function is arranged on the light emitting surface 15 of the light guide 11. Specifically, a mode in which a micro prism array composed of a triangular prism array is arranged is suitably used. Further, in order to obtain desired optical characteristics, a diffusion sheet 101 having various hazes is used in combination.

In the present invention, a liquid crystal display device refers to a device which applies an electric field or conducts electricity to an arbitrary display unit by utilizing the electro-optic effect of liquid crystal molecules, ie, optical anisotropy (refractive index anisotropy), orientation, and the like. It refers to a device that performs display by using a liquid crystal cell, which is an array of optical shutters, driven by changing the alignment state of liquid crystal and changing light transmittance and reflectance.

Specifically, there are liquid crystal display devices of a transmission type simple matrix drive super twisted nematic mode, a transmission type active matrix drive twisted nematic mode, and the like. By configuring the liquid crystal display device by using it as a light source, it is possible to provide high brightness, excellent energy efficiency, and excellent maintainability, and suitable characteristics as a liquid crystal display device.

[0037]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. (Embodiment 1) FIG. 1 shows an embodiment of the present invention. As the reflector 14, a foamed polyethylene terephthalate sheet having a thickness of 400 μm and a surface reflectance of 95% and having excellent shape retention characteristics is used, and a groove is cut at each position where the sheet is to be bent, and the sheet is bent as shown in FIG. A cross-sectional shape was formed.

Further, the reflector 14 is fixed in a lamp holder 26 obtained by processing a stainless steel plate, and the cold cathode tube 13 having a tube diameter of 2.6 mm is mounted on the reflector 14.
Into a lamp unit. At this time, the cold cathode tube is positioned and fixed in the reflector 14 by an O-ring made of silicone rubber.

The light guide 11 has a thickness of 12 inches and a thickness of 4 inches.
mm acrylic resin and the incident light scattering / reflecting means 17
Are printed on the light guide 11 by a conventional screen printing method, and the dot patterns are transferred to the light guide 11 by patterning white ink patterned so that the area becomes relatively large as the distance from the light source 13 increases. Light guide 11 so that the side opposite to the side on which light is emitted is the light exit surface.
Was disposed, and a reflection sheet 102 made of white foamed polyester and having a light reflectance of 95% was disposed on the surface facing the light emission surface.

A diffusion sheet 101 having a haze of 80% is provided on the light exit surface 15, and a thickness 12
A prism sheet 100 having a prism apex angle of 90 degrees and a pitch of 50 μm using polyethylene terephthalate of 0 μm as a base film was installed to obtain a surface light source device 10. The cold-cathode tube 13 is lit through a dedicated inverter unit, and measures the luminance value near the center with a luminance meter (BM-7 manufactured by Topcom).
It measured using. Table 1 shows the results.

Example 2 A reflector having a thickness of 500
Ag using a plastic plate made of polyethylene terephthalate having a thickness of at least 92%.
After the vapor deposition processing, it was processed into a shape shown in FIG. 4A by plastic molding processing by vacuum molding. Further, a luminance value near the center was measured using a luminance meter (BM-7, manufactured by Topcom) in the same manner as in Example 1, except that the reflector 14 was a lamp holder 26 obtained by injection molding of polycarbonate. . Table 1 shows the results.

[0042]

Comparative Example 1 Comparative Example 1 was repeated in the same manner as in Example 1 except that a flexible white film-like reflector having a thickness of 120 μm was wound around a cold cathode tube 13 to form a lamp unit.
The luminance value near the center was measured using a luminance meter (BM-7 manufactured by Topcom). Table 1 shows the results. (Comparative Example 2) A luminance value near the center was measured using a luminance meter (in the same manner as in Example 1 including the cross-sectional shape) except that an Ag vapor-deposited layer was formed on the surface of a brass reflector having a thickness of 230 µm to form a reflector. It was measured using Topcom BM-7). Table 1 shows the results.

[0043]

[Table 1]

[0044]

As described above, according to the surface light source device of the present invention, since the reflector covering the light source is formed of a reflective plastic plate having a shape maintaining property, the brightness and energy effect as the surface light source device are obtained. Not only can excellent characteristics be obtained, but also maintainability can be improved. These features are recently becoming increasingly sophisticated for personal computer LCD monitors and LCD TVs.
It responds to the demand for a liquid crystal display backlight used in a liquid crystal display.

That is, according to the liquid crystal display of the present invention, high brightness and excellent energy efficiency can be obtained by using the above-mentioned surface light source device as a backlight light source for a liquid crystal display element. Maintainability can also be significantly improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a main part of a surface light source device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a state in which the amount of sag of a test piece cut from the reflective plastic plate is measured to specify the rigidity of the reflective plastic plate used in the reflector used in the surface light source device of the present invention.

FIG. 3 is a schematic cross-sectional view showing, on an enlarged scale, a portion to show various aspects of the reflector used in the present invention.

FIG. 4 is a schematic cross-sectional view showing a part of the reflector used in the surface light source device of the present invention in an enlarged manner to show various aspects.

FIG. 5 is a perspective view schematically showing a foamable white polyester sheet that has been subjected to groove processing to form a reflector used in the surface light source device of the present invention.

FIG. 6 is a perspective view schematically showing a main part of a conventional surface light source device.

[Explanation of symbols]

 Reference Signs List 10 surface light source device 11 light guide plate 12 one side end surface (incident light side surface) 13 tubular light source 14 reflector 15 light emitting surface 16 surface facing light emitting surface 17 incident light scattering / reflecting means 18 virtual axis 19 light source direction reflection avoiding means 20 Normal line of light emitting surface 21 Virtual axis line 22 Parallel light reflecting means 23 Grooving 24 Grooving 25 Foamable white polyester sheet 26 Lamp holder 27 Dot pattern made of white ink 28 Dot pattern made of white ink 29 From white ink Dot pattern 30 Test piece 31 One end 32 Vertical plane 33 Hanging amount 100 Light control function sheet (micro prism array) 101 Diffusion sheet 102 Reflection sheet

Claims (12)

[Claims] 1. A light guide having one surface as a light emitting surface and provided with incident light scattering means, a light source provided at a side end of the light guide, and a light emitted from the light source. A reflector for covering the light source so that the light enters the light guide from an end face of a side end, wherein the reflector is formed of a reflective plastic plate having shape maintaining properties. 2. A test piece having a size of 1.0 × 100.0 mm is cut out from the reflective plastic plate, one end of the test piece is fixed to a vertical surface, and the other end of the test piece is cut. 2. The surface light source device according to claim 1, wherein when measuring the amount of sag from the one side end fixing position, the amount of sag is within 20.0 mm. 3. 3. The reflective plastic plate has a reflectivity of 80.
The surface light source device according to claim 1, wherein the surface light source device is formed using a white material of not less than%. 4. The surface light source device according to claim 1, wherein a metal layer having a reflectance of 80% or more is provided on a surface of the reflective plastic plate. 5. The surface light source device according to claim 3, wherein a cross-sectional shape of the reflector made of the reflective plastic plate is polygonal. 6. The surface light source device according to claim 5, wherein the reflector made of the reflective plastic plate is formed by bending a grooved flat reflective plastic sheet. . 7. The surface light source device according to claim 5, wherein the reflector made of the reflective plastic plate is formed by molding a flat reflective plastic sheet. 8. The surface light source device according to claim 6, wherein the reflector is fixed by a lamp holder that covers the reflector. 9. The surface light source device according to claim 8, wherein a material forming the lamp holder is an insulating material. 10. A light source direction reflection avoiding means is formed on a reflection surface of said reflector which is located on an imaginary axis passing through a center of said light source and substantially perpendicular to an end face of said side end portion of said light guide. The surface light source device according to any one of claims 6 to 9, wherein: 11. A direction in which light from the light source, which passes through a center of the light source and exits from an angle range about an imaginary axis substantially parallel to a light exit surface normal of the light guide, is avoided by the light source. The surface light source device according to any one of claims 6 to 9, further comprising at least one parallel light reflecting means formed on a reflecting surface of the reflector so as to reflect light. 12. A liquid crystal display device, wherein the surface light source device according to claim 1 is used in a backlight optical system.