JP3550771B2 - Backlight - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a backlight for illuminating a transmissive or transflective display panel from the back.
[0002]
[Prior art]
Recently, a liquid crystal display device having a thin and easy-to-see backlight mechanism has been used as a display device such as a laptop or notebook type word processor or computer. As such a backlight, an edge light system in which a linear light source 4 such as a fluorescent tube is provided at one end of a translucent light guide plate 1 as shown in FIG. 2 is often used. In particular, recently, in order to improve the performance of these word processors and personal computers, thinning, improvement of visibility, and improvement of power consumption-luminance conversion efficiency have been further desired. It has been proposed to arrange a light diffusion reflection sheet having a high diffuse reflectance or a mirror reflection sheet having a high specular reflectance (hereinafter, collectively referred to as a light source reflection sheet) and fix it to the end of the light guide plate with glue or the like. I have.
[0003]
For fixing the light source reflection sheet 5 to the light guide plate, a double-sided adhesive tape is often used in order to simplify the structure, but in the case of fixing with the double-sided adhesive tape, the adhesive of the adhesive tape is applied to the light guide plate surface. By directly affixing, the critical ray angle of the part becomes larger than that of the part without the adhesive, and the light leaked from the part, the inside of the double-sided adhesive tape or the double-sided adhesive tape and the light guide plate or the reflection sheet for the light source Because the light is scattered at the boundary, there is a problem that, in the vicinity of the portion where the light source reflection sheet is adhered with the double-sided adhesive tape, a portion which is generally called a bright line and is significantly higher in luminance than other portions is generated. Was. Since the portion where the bright line is generated is not regarded as an effective light emitting portion for illuminating the liquid crystal display element, the ratio of the effective light emitting portion to the outer dimensions is reduced, and some light is generated due to the generation of the bright line. Is leaked, so that there is a problem that the average luminance of the effective light emitting portion is reduced.
[0004]
[Problems to be solved by the invention]
In recent years, while devices using a backlight have been downsized, the required display surface has been made larger, low power consumption, high luminous efficiency, and the ratio of the effective light emitting portion to the external dimensions has been reduced. Large backlights are required. SUMMARY OF THE INVENTION It is an object of the present invention to provide a backlight having a high luminous efficiency, in which a ratio of an effective light emitting portion to an outer dimension is large.
[0005]
[Means for Solving the Problems]
The present inventors have conducted various studies on the luminance distribution near the linear light source of the edge light type backlight, and found that the end on the light emitting surface side of the light source reflective sheet covering the linear light source was In order to fix the light source on the light emitting surface, the stacked portions where the two are overlapped are overlapped so as to be as small as possible, and the outer surface of the light emitting surface side end of the light source reflecting sheet and the light guide plate adjacent thereto The present inventors have found that it is possible to prevent the generation of bright lines in the vicinity of the linear light source by adopting a structure in which the pressure-sensitive adhesive tape is covered over the light emitting surface, and the present invention has been accomplished.
[0006]
Hereinafter, the present invention will be described in more detail with reference to the drawings. First, an edge light type backlight to which the present invention is applied will be described. FIG. 2 is a perspective view showing an example of an edge light type backlight, and FIG. 1 is an enlarged view of a cross section near a linear light source of an example of the backlight of the present invention, which corresponds to a cross section taken along the line AA. . In FIG. 1, the thickness, width, and the like of some components are exaggerated in order to clearly show the structure.
[0007]
The light guide plate 1 is a plate for guiding the light emitted from the light source to the entire backlight, and may be any substance that allows light to pass therethrough efficiently, and is formed of a translucent natural or synthetic resin such as an acrylic resin. Have been.
[0008]
On one plate surface (the upper surface in FIG. 1) of the light guide plate, a light diffusion sheet 2 for diffusing light emitted with a component in a direction perpendicular to the plate surface and making it uniform is laminated. I have. Although FIG. 1 shows a case where one light diffusion sheet is used, a plurality of sheets having different properties can be used. Although not shown in FIG. 1, a sheet lens may be laminated on the light diffusion sheet as necessary, or a light diffusion sheet may be further laminated thereon. On the other hand, on the other plate surface (the lower surface in FIG. 1) of the light guide plate, a light diffuse reflection sheet 3 for diffusing and reflecting light leaked downward from the light guide plate and returning the light back into the light guide plate again is laminated. . In this specification, when the direction is indicated by the vertical direction, the plate surface of the upper surface of the backlight from which the light for illumination is emitted is referred to as a light emitting surface, and the upper side of the backlight is the light emitting surface side with reference to the arrangement of FIG. , The lower side is referred to as a reflection surface side. Further, for convenience, the plate surface on the light exit surface side of the light guide plate is also referred to as the light exit surface of the light guide plate, and the plate surface on the reflection surface side of the light guide plate is not a very appropriate term in a strict sense. It is referred to as the reflection surface of the light plate.
[0009]
The light guide plate 1 is provided with a light diffusing function (not shown) for giving a component emitted in a direction perpendicular to the light emitting surface to light emitted from the light source and traveling inside the light guide plate. In many cases, the light diffusion function is applied to the reflection surface of the light guide plate, but it may be applied to the light exit surface of the light guide plate, or may be applied to the inside of the light guide plate. As a method of providing the light diffusing function, any method may be used as long as it gives a component traveling in the light guide plate in a direction perpendicular to the light output surface, for example, the reflection surface or the light output surface of the light guide plate. , Partial coating with a light diffusing substance using screen printing, etc., formation of many fine holes on these surfaces, or uniform deposition of fine impurities inside the light guide plate. Has been done. Further, in order to make the luminance distribution uniform in the light emitting surface, the property of the light diffusion function at a certain point is changed according to the distance from the light source at that point.
[0010]
The linear light source 4 is installed close to at least one of the four side surfaces of the light guide plate 1 so that the center axis thereof is substantially parallel to the side surfaces. This linear light source may be installed on each of two opposing side surfaces of the light guide plate. Alternatively, an L-shaped or U-shaped light source may be used, and linear light sources may be installed on two or three adjacent side surfaces. Sometimes. Although a fluorescent tube is desirably used for the linear light source 4, a tungsten incandescent tube, an optical rod, an LED arrayed LED, or the like can be used.
[0011]
In order to effectively guide the light emitted from the linear light source 4 to the inside of the light guide plate 1, the linear light source 4 is provided around the linear light source 4 except for the portion facing the light incident end of the light guide plate 1. A light source reflection sheet 5 for covering is provided. The light source reflective sheet 5 is a light diffuse reflective sheet having a high light diffuse reflectivity or a specular reflective sheet having a high specular reflectivity, and any material that reflects light with high efficiency may be used. Silver, aluminum, platinum, nickel, Although a metal such as chromium is used, it is desirable to use a sheet in which silver, aluminum, or the like is coated on the surface of a plastic film substrate such as polyester by vapor deposition or sputtering.
[0012]
The light source reflection sheet 5 is attached to the backlight main body at both ends, and the state of the bright line generation near the linear light source changes depending on the attachment method. In this specification, the upper end 6 of the light source reflecting sheet 5 is referred to as an end on the light emitting surface side, and the lower end 7 is referred to as an end on the reflecting surface side. The upper surface is referred to as the outer surface of the end 6.
[0013]
Hereinafter, the present invention will be described in more detail with reference to FIG. In the present invention, as shown in FIG. 1, the light emitting surface side end 6 of the light source reflecting sheet 5 is superimposed on the light emitting surface of the light guide plate 1. Along the portion, the adhesive tape 8 is coated over the outer surface of the end 6 on the light emitting surface side of the light source reflecting sheet 5 and the light emitting surface of the light guide plate 1 adjacent thereto. The coating with the adhesive tape 8 is desirably applied over substantially the entire width of the light source reflection sheet 5 (substantially corresponding to the length of the linear light source 4). If a gap between the light source reflection sheet 5 and the light guide plate 1 can be prevented from being generated by interposing an elastic spacer between the light source and the element (not shown) or the like, the spacer does not necessarily extend over the entire length. There is no need to cover the adhesive tape.
[0014]
If the light emitting surface side end 6 of the light source reflecting sheet 5 and the light emitting surface of the light guide plate 1 are not overlapped with each other, the light will leak from that portion if they do not overlap. However, in order to enlarge the effective light-emitting portion, it is desirable that the width of the laminated portion of the two be as small as possible. In consideration of mechanical accuracy and workability when assembling as a backlight, the width of the laminated portion is desirably 1 mm or less, and more desirably 0.5 mm or less. Further, the lamination of the end portion 6 of the light source reflecting sheet 5 on the light emitting surface side and the light emitting surface of the light guide plate 1 is based on the change of the light critical angle as disclosed in, for example, JP-A-6-160849. In order to prevent leakage of the air, it is preferable that the layers are stacked via an air layer. Note that the thickness of the air layer referred to here may be at least a thickness in which air of a monomolecular layer is present, and if the air layer is simply laminated without using an adhesive or the like, this air layer is It is formed naturally.
[0015]
Since the light diffusion sheet 2 to be laminated on the light exit surface of the light guide plate 1 needs to be laminated so as to cover at least the entire surface of the effective light emitting portion, as shown in FIG. It is desirable to stack them on the light emitting surface in a state where they are brought close to each other to the extent that they come into contact. Since the light source reflection sheet 5 is opaque, it does not make much sense to cover the outer surface of the end portion 6 with the light diffusion sheet 2. However, for the portion where the adhesive tape 8 covers the light exit surface of the light guide plate 1, It may be covered with the light diffusion sheet 2 as needed.
[0016]
The adhesive tape 8 covering the outer surface of the light emitting surface side end 6 of the light source reflection sheet 5 and the light emitting surface of the light guide plate 1 adjacent thereto is a transparent adhesive using a transparent film as a base material. Desirably tape. If the adhesive tape 8 is colored, the spectrum of the light emitted from the light emitting surface is affected. Therefore, it is desirable that the transparent adhesive tape be as colorless and transparent as possible.
[0017]
When a black opaque tape is used as the adhesive tape 8, it is possible to prevent the generation of bright lines around the portion covered with the adhesive tape, but since the black tape absorbs some light, it is colorless. The average luminance may be lower than when a transparent tape is used. When an opaque tape of a color other than black is used, light leaked from the light guide plate is scattered by the tape, so that a bright line may be generated around a portion covered with the adhesive tape.
[0018]
The adhesive tape 8 covering the outer surface of the light emitting surface side end 6 of the light source reflecting sheet 5 and the light emitting surface of the light guide plate 1 adjacent thereto covers the light emitting surface of the light guide plate 1. Since the portion is often not regarded as an effective light emitting portion, it is desirable that the width of this portion be as small as possible. However, in consideration of mechanical strength and workability of assembly, the width of this portion is 5 mm or less. Desirably, it is more desirably 3 mm or less.
[0019]
The end portion 7 on the reflection surface side of the light source reflection sheet 5 only needs to be overlapped with the reflection surface of the light guide plate 1 or the light diffusion reflection sheet 3, and the order of lamination and the fixing method are not limited. For example, as shown in FIG. 1, the end of the light source reflection sheet, the light diffusion reflection sheet, and the light guide plate may be laminated in this order, or the light diffusion reflection sheet—the end of the light source reflection sheet—the light guide plate. May be laminated in this order. Alternatively, the light diffusion / reflection sheet 3 does not have to cover this laminated portion. Furthermore, a normal adhesive or a double-sided adhesive tape is applied to one or both of the upper and lower surfaces of the end portion 7 on the reflection surface side of the light source reflection sheet 5 on the light diffusion reflection sheet 3 or the light guide plate 1. It may be adhered and fixed via a cable, or may be fixed by covering with a single-sided adhesive tape. Also, the end portion 7 on the reflection surface side of the reflection sheet 5 for the light source is merely laminated on the reflection surface of the light diffusion reflection sheet 3 or the light guide plate 1, and the adhesive fixation with an adhesive or an adhesive tape need not be performed. Note that the degree of the effect of the present invention varies depending on the order of lamination and the method of fixing the end portion 7 on the reflection surface side of the light source reflection sheet 5 with the reflection surface of the light guide plate 1 and the light diffusion reflection sheet 3. However, in each case, the effects of the present invention can be obtained as such. In consideration of the degree of effect obtained and the workability at the time of assembling, as shown in FIG. 1, the end of the light source reflection sheet, the light diffusion reflection sheet, and the light guide plate are laminated in this order, and the light source reflection sheet 5 The end 7 on the reflection surface side may be adhered and fixed to the light diffusion / reflection sheet 3 via the double-sided pressure-sensitive adhesive tape 9, or may be simply laminated in this order, and not adhered by a pressure-sensitive adhesive tape or an adhesive. desirable.
[0020]
【The invention's effect】
INDUSTRIAL APPLICABILITY The present invention is small in size, has a sufficient effective light emitting area, a good luminance distribution, and can be used as a backlight having high power consumption-luminance conversion efficiency.
[0021]
【Example】
Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. First, a comparative example was tested by the following method. A cold cathode fluorescent tube (3 mm diameter normal tube manufactured by Harrison Electric Co., Ltd.) with a diameter of 3 mm, which is 7 mm longer than the end length, is disposed at a longitudinal end of a rectangular light guide plate (241 mm × 186 mm) having a thickness of 4 mm. Then, the outer circumference of the tube was covered with a silver-evaporated polyester sheet (thickness: 75 μm), and both ends were fixed to the ends of the light guide plate via a double-sided tape. The width of the laminated portion where the end of the silver-evaporated polyester sheet and the end of the light guide plate were overlapped was 3 mm.
[0022]
On the other hand, the light diffusion function of the light guide plate was provided by partially covering the reflection surface of the light guide plate with a light diffusion material containing silica. In order to partially cover the reflecting surface, a circular dot pattern made of a light diffusing material was screen-printed on the reflecting surface. The screen printing was made by CAD under the following conditions. Using. The plot was made such that the coverage of the light-diffusing substance was 7% at the minimum point and 80% at the maximum point, and it increased exponentially in the middle.
[0023]
The luminance when the alternating current of 30 KHz was applied to the cold cathode tube from the inverter and driven at a constant current was measured by a luminance meter (Topcon BM-8). FIG. 3 shows the measurement results near the linear light source among the results of the luminance measurement at the measurement points on a line passing substantially near the center of the linear light source and perpendicular to the linear light source. The vertical axis indicates the luminance (cd / m ² ) of the measurement point, and the horizontal axis indicates the position of the measurement point as a distance (mm) measured from the light source side end of the light guide plate.
[0024]
Next, as an example of the present invention, as shown in FIG. 1, the periphery of the linear light source is covered with a silver-evaporated polyester sheet having a thickness of 75 μm, and the end on the light emitting surface side is placed on the light emitting surface of the light guide plate. Silver vapor deposition covering the linear light source by overlaying and covering a transparent adhesive tape over the outer surface of the light emitting surface side end portion and the light emitting surface of the light guide plate adjacent thereto along this laminated portion. A backlight in which the end on the light emitting surface side of the polyester sheet was fixed on the light emitting surface of the light guide plate was produced. In addition, the width of the laminated portion of the light emitting surface side end of the silver-evaporated polyester sheet and the light guide plate was 0.3 mm, and a commercially available transparent adhesive tape having a thickness of 70 μm and a width of 6 mm was used. Was coated such that the coating width was 3 mm.
[0025]
As shown in FIG. 1, the end of the silver-evaporated polyester sheet on the reflection surface side is bonded to a light diffusion reflection sheet via a commercially available double-sided adhesive tape having a thickness of 70 μm and a width of 3 mm, and the light diffusion reflection sheet is guided. It was laminated on a light plate.
[0026]
A backlight was produced in exactly the same manner as in the comparative example, except for the method of fixing both ends of the silver-evaporated polyester sheet to the light guide plate, and the results of measuring the luminance by the same method as in the comparative example are shown in FIG.
[0027]
As can be seen from both figures, in the embodiment of the present invention, even in the vicinity of the linear light source, there is no occurrence of a bright line, which is a portion with extremely high brightness, and the average brightness in the effective light emitting portion is also comparable to the comparative example. A backlight improved by about 5% was obtained.
[Brief description of the drawings]
FIG. 1 is an enlarged view of the vicinity of a linear light source in a cross section taken along a plane perpendicular to a central axis of the linear light source as an example of the backlight of the present invention.
FIG. 2 is a perspective view of an edge light type backlight.
FIG. 3 is a diagram illustrating a luminance distribution near a linear light source in a comparative example.
FIG. 4 is a diagram showing a luminance distribution in the vicinity of a linear light source in an example.
[Explanation of symbols]
1: Light guide plate 2: Light diffusion sheet 3: Light diffusion reflection sheet 4: Linear light source 5: Reflection sheet for light source 6: Light emitting surface end of reflection sheet for light source 7: Reflection surface side of reflection sheet for light source End 8: Adhesive tape 9: Double-sided adhesive tape

Claims (3)

A light source reflecting sheet that covers the linear light source in an edge-light type backlight having a linear light source disposed close to at least one side surface of the light guide plate made of a translucent material and substantially parallel to the side surface. The light emitting surface side end of the light guide plate is superimposed on the light emitting surface of the light guide plate via an air layer, and the outer surface of the light emitting surface side end of the light source reflection sheet and the light emitting surface of the light guide plate adjacent thereto And a light-emitting surface of the light-source reflecting sheet is fixed on the light-emitting surface of the light guide plate by being covered with the adhesive tape. The backlight according to claim 1, wherein the outer surface of the light-emitting surface side end of the light-source reflecting sheet and the adhesive tape that is coated over the light-emitting surface of the light guide plate adjacent thereto have a transparent film and a base material. A backlight characterized in that the adhesive is a transparent adhesive tape. The width of the laminated portion where the light emitting surface side end of the light source reflecting sheet and the light emitting surface of the light guide plate are superimposed , that is , the length of the laminated portion in the direction perpendicular to the linear light source is 1 mm or less. 3. The backlight according to claim 1, wherein the backlight is a backlight.

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