JP2603580B2 - Surface light source device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent light guide plate in which a line light source is disposed on one side surface, a side reflection layer is disposed on the other side surface opposite to the line light source, and a light diffusion transmission portion is provided on the back surface of the light guide plate. The present invention relates to a thin surface light source device in which a white back reflection layer is disposed on the back surface of a light guide plate. The surface light source device according to the present invention includes:
It has stable quality characteristics, and is suitable, for example, for a backlight of a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, thin surface light source devices include a device in which a line light source is disposed only on one side surface of a light guide plate and a device in which a line light source is disposed on two opposite side surfaces. Among them, the former surface light source device has an advantage that it consumes less power and is lightweight because it has one line light source.
However, on the other hand, since the line light source is disposed only on one side of the light guide plate, the surface emission luminance of the light guide plate gradually decreases as the distance from the line light source increases, and a uniform light emitting surface cannot be obtained at all. There is.

[0003] This problem is extremely important in a surface light source device, and several inventions have been made to solve this problem. For example, a light diffusion / transmission portion is provided on the back surface of a light guide plate, and 2. Description of the Related Art A surface light source device is known which aims to obtain surface light as uniform as possible by diffusing the guided light through a light diffusion / transmission portion. Among them, JP-A-2-
The surface light source device disclosed in the specification of 269382 is particularly excellent.

The surface light source device disclosed in Japanese Patent Application Laid-Open No. 2-269382 discloses a light guide plate in which a line light source is disposed on one side of a transparent light guide plate and a side reflection layer is disposed on the other side opposite to the line light source. In a surface light source device in which a light diffusion transmission portion is provided on the back surface of the light guide plate and a white back reflection layer is disposed on the back surface of the light guide plate, the light diffusion transmission portion is configured with a large number of fine dot patterns by printing, and its area ratio is reduced. As shown in FIG. 6, in a region from the line light source side surface a ′ of the light guide plate to the point b ′ where the surface light emission luminance is least expected, the surface light emission luminance is gradually increased with increasing distance from the line light source side surface a ′. In the region from the least expected location b 'to the side surface c' of the light guide plate on the side of the side reflection layer, the size is gradually reduced.

In other words, in this surface light source device, not only the surface light emission luminance of the light guide plate gradually decreases as the light guide plate moves away from the side of the light source on the side of the line light source, but also the light reflected by the side reflection layer is affected by the light. The invention was invented based on the phenomenon that the surface emission luminance starts increasing from the place where the surface light emission luminance is the lowest and approaches the side surface of the side reflection layer. Therefore, as shown in FIG. 6, if the surface emission luminance change curve X ′ and the light diffusion / transmission area ratio change curve Y ′ can be completely inversely proportional, a uniform surface emission luminance curve Z ′ can be obtained over the entire surface of the light guide plate. An ideal surface light source device to be exhibited can be obtained.

[0006]

However, it is extremely difficult to industrially mass-produce this ideal surface light source device. Because, when manufacturing line light sources and light guide plates industrially, no matter how strict the quality control is, it is possible to obtain line light sources with the same brightness and light guide plates with the same light diffusion degree. It is impossible. For example, a line light source is composed of many parts such as a glass tube, an electrode, a fluorescent substance, mercury, and an inert gas, but in each of these parts, there is variation in quality characteristics for each product,
Since there are variations at the time of assembling these components, it is inevitable that the brightness of each line light source varies. Also, regarding the light guide plate, there are variations in the position, size, and thickness of the ink film of the dots in the light diffusion / transmission portion, and variations in the thickness, size, and cut surface of the light guide plate, based on the limit of printing accuracy. Therefore, the light diffusivity in each light guide plate must be different.

Therefore, according to the invention disclosed in Japanese Patent Application Laid-Open No. 2-269382, the light diffusion / transmission portion area ratio change curve shown in FIG.
As shown as Y ', a surface which is industrially mass-produced despite the fact that the maximum area ratio portion B' of the light diffusion transmission portion must be located at the position b 'where surface emission luminance is least expected. In the light source device, as shown in the light diffusion transmission part area ratio change curve Y′1, the maximum area ratio part B ′ of the light diffusion transmission part reaches the point b ′ up to the point b ′ where the surface emission luminance is least expected. 1
Or the light diffusion transmission area ratio curve Y'2
As shown in (2), there is a shift to a location b'2 beyond the location b 'where the surface emission luminance is least expected. The surface emission luminance curve Z′1 in the former case is higher in parallel in the region from the line light source side surface a ′ to the point b′1, compared to the surface emission luminance curve Z ′,
In the area from point b'1 to point b ',
In a region from b ′ to the side surface c ′ on the side of the side reflection layer, a low curve is formed in parallel. Also, the surface emission luminance curve in the latter case
Z′2 is lower in parallel in the area from the line light source side surface a ′ to the point b ′ as compared with the surface emission luminance curve Z ′,
In the region up to b′2, the temperature rises significantly, and in the region from the point b′2 to the side surface c ′ on the side surface reflection layer, a high curve is formed in parallel. Therefore, the maximum area ratio portion B ′ of the light diffusion transmission portion is equal to the location b ′.
From the point b'1 or the point b'2, the gap between the high-luminance point H'1 and the low-luminance point L'1 in the surface-emission luminance curve Z'1 or the surface-emission luminance curve Z'2 , The gap between the high luminance point H'2 and the low luminance point L'2 becomes large, so that the quality characteristics between products become unstable. Of course, if the range in which the deviation of the maximum area ratio portion B 'is allowed is narrowed, the quality characteristics are stabilized, but the quality control of the line light source, the light guide plate, and the like must be stricter.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, the present inventor of the present invention has made it difficult to completely reverse the change in the surface emission luminance and the change in the area ratio of the light diffusion / transmission portion. Based on the point that this is not the case, based on the idea of obtaining a surface light source device as close as possible to an ideal surface light source device, the inventors conducted various studies, and as a result, completed the present invention.

That is, in the surface light source device according to the present invention, the line light source 2 is disposed on one side surface of the transparent light guide plate 1, and the side reflection layer 4 is disposed on the other side surface opposite to the line light source 2. In the surface light source device in which the light diffusion / transmission portion 3 is provided and the white back reflection layer 5 is disposed on the back surface of the light guide plate 1, the area ratio of the light diffusion / transmission portion 3 in the direction perpendicular to the axis of the line light source 2 is determined. ,
In the region from the light source side surface a of the light guide plate 1 to the point b where the surface light emission luminance is least expected, the area gradually increases as the distance from the line light source side surface a increases, and the light guide plate 1 is moved from the position b where the surface light emission luminance is least expected. It is characterized in that it is constant in the region up to the side surface c on the side reflection layer side.

Next, a surface light source device according to the present invention will be described in detail with reference to the drawings. In the surface light source device according to the present invention, in order to obtain a high-brightness surface light source device by efficiently utilizing the light emitted from the line light source 2 disposed on one side surface of the light guide plate 1, that is, the side surface a on the line light source side. The side reflection layer 4 is disposed on the other side facing the light source side side a, that is, on the side reflection layer side side c,
The light diffusion / transmission portion 3 is provided on the back surface of the light guide plate 1, and a white back reflection layer 5 is provided on the back surface of the light guide plate 1.

As the line light source 2, a cathode ray tube such as a hot cathode ray tube or a cold cathode ray tube is used. In addition, it is preferable to arrange the curved reflection plate 7 so as to cover the line light source 2 so that the light of the line light source 2 can be used efficiently.

The thickness, material, shape and the like of the light guide plate 1 are appropriately selected and used according to the application. For example, in the case of the light guide plate 1 applied to a backlight of a liquid crystal display device, the thickness is 1 to 8 mm, the material is acrylic resin, polycarbonate resin, polyvinyl chloride resin or glass, and the shape is rectangular or square. Things are used.

The light diffusion transmission portion 3 is formed by a printing method such as gravure printing, offset printing, screen printing, or a transfer method, and has an area ratio in a direction perpendicular to the axis of the line light source 2. In the region from the line light source side surface a of the light guide plate 1 to the point b where the surface light emission luminance is least expected, the area gradually increases as the distance from the line light source side surface a increases, and
In the region from b to the side surface c of the light guide plate 1 on the side of the side reflection layer, it is constant. This change in the area ratio is achieved by using dots as shown in FIG. 1 or stripes as shown in FIG.
It is realized by changing it in a gradation form,
In FIG. 5, it is shown as a light diffusion transmission area ratio curve Y. The shape of the dot is not particularly limited, and may be an arbitrary shape such as a round dot, a square dot, or a chain dot.

The linear light source 2 has such characteristics that the central area is uniformly bright and only the both ends are gradually darkened. Accordingly, as shown in FIG. 3, the area ratio of the light diffusion / transmission portion 3 in the width direction of the light guide plate 1 is changed to the central portion of the light guide plate 1.
The area from d to the point e where the surface emission luminance starts to decrease is kept constant, and from the point e where the surface emission luminance starts to decrease to the right side f
By making the area up to the left side surface g larger quadratically, the entire surface of the light guide plate 1 can emit light more uniformly.

[0015] A having substantially the same or lower refractive index upon, light guide plate 1 to form a light diffusing transmitting unit 3
Runode using an ink containing a particulate transparent material such as acrylic or silica, can further improve the light diffusion properties. The portion where the area ratio of the light diffusion transmission part 3 is maximum means that the area ratio is the highest in the entire light diffusion transmission part 3 and that the area ratio is 100%. Not something.

The side reflection layer 4 is formed by attaching a white film or a metal plate to the side surface b of the light guide plate 1 on the side of the side reflection layer,
It is formed by applying white ink or depositing metal. The side reflection layer 4 may be disposed on another side surface other than the line light source side surface a.

The back reflection layer 5 is formed of a white film, a white plate, or the like, and is used by being superposed on the back surface of the light guide plate 1. Accordingly, in the portion of the light guide plate 1 where the light diffusion / transmission portion 3 is not formed, the light guide plate 1 and the back reflection layer 5 are formed.
Since a slight gap will be formed between
Light emitted from the linear light source 2 can be substantially totally reflected inside the light guide plate 1, and loss of light guided to the light guide plate 1 can be reduced.

The side reflection layer 4 or the back reflection layer 5
Can be replaced by a surface light source device case (not shown) whose inner surface is painted with white paint.

Although the essential components of the present invention have been described above, the light diffusing layer 6 may be arranged on the surface of the light guide plate 1 if necessary. In this case, the arrangement of the light diffusion layer 6 with an interval between the light diffusion layer 6 and the light guide plate 1 led to the light guide plate 1 rather than the close contact of the light diffusion layer 6 with the light guide plate 1. Light loss can be reduced.
As the light diffusion layer 6, a resin film coated with a light diffusion substance, a resin film or a resin plate in which the material itself has diffusibility can be used.

[0020]

According to the present invention, the light guide plate 1 has the above structure.
In the vicinity of the line light source side surface a, the area ratio of the light diffusion / transmission portion 3 is the smallest, so that most of the light emitted from the line light source 2 has an incident angle and a reflection angle within the light guide plate 1. The light is sequentially guided to the back of the light guide plate 1 while repeating equal total reflection. In addition, a part of the light emitted from the linear light source 2 is scattered by the light diffusion / transmission unit 3 and is directly guided to the surface of the light guide plate 1, or once passes through the light diffusion / transmission unit 3 and is reflected back. The light reaches the layer 5, is reflected by the back reflection layer 5, enters the light diffusion / transmission portion 3 again, and is then indirectly guided to the surface of the light guide plate 1. Further, a part of the light scattered by the light diffusion / transmission unit 3 shifts to total reflection inside the light guide plate 1.

Moving away from the side a of the light guide plate 1 on the line light source side,
The area ratio of the light diffusion / transmission portion 3 gradually increases as the position approaches the point b where the surface emission luminance is least expected.
The amount of light totally reflected inside the light guide plate 1 gradually decreases, and the amount of light scattered by the light diffusion / transmission unit 3 and guided directly or indirectly to the surface of the light guide plate 1 gradually increases.

The area ratio of the light diffusion / transmission portion 3 is highest in the portion b where the surface light emission luminance is least expected, and the light diffusion / transmission portion 3 from the portion b where the surface light emission luminance is least expected to the side surface c on the side reflection layer side. In this area, most of the light radiated from the linear light source 2 is scattered by the light diffusion / transmission portion 3 and is directly or indirectly guided to the surface of the light guide plate 1 in the region between them. I will In addition, a part of the light emitted from the linear light source is sequentially guided to the back of the light guide plate 1 while repeating total reflection inside the light guide plate 1. In this region, the area ratio of the light diffusion transmission portion 3 does not change.
As compared with the case where the area ratio of the light diffusion / transmission portion 3 is gradually reduced as in the surface light source device disclosed in the specification of 2-269382, the amount of light reflected by the light diffusion / transmission portion 3 is increased,
Light reaching the side reflection layer 4 is reduced. That is, the reflected light from the side reflection layer 4 is reduced. Therefore, in the surface light source device according to the present invention, in combination with the fact that the back reflection layer 5 is white, the action of the side reflection layer 4 gradually reduces the area ratio of the light diffusion / transmission portion 3. It will be smaller than that.

[0023]

Next, a surface light source device according to the present invention will be described based on an embodiment. As a line light source, tube length 145mm, diameter 4m
m, cold cathode ray tube (Matsushita Electric Industrial Co., Ltd.) with a tube luminance of 12,000 nt, and as a light guide plate, 220 mm long and 150 m wide
A transparent acrylic resin plate having a thickness of 2 mm and a thickness of 2 mm was prepared.

A change in the surface light emission luminance of the line light source is examined to obtain a surface light emission luminance change curve X. On the basis of the surface light emission luminance change curve, a number of dots are printed on the back surface of the light guide plate to form a light diffusion transmission portion. Provided. The light diffusion transmitting portion was provided by screen printing using a mat ink containing a pigment composed of a mixture of calcium carbonate and silica, a methyl methacrylate resin and a ketone-based solvent.

The area ratio of the light diffusion transmission portion gradually increases in inverse proportion to the surface emission luminance change curve in a region from the side surface on the side of the line light source to the portion where the surface emission luminance is least expected. In the region up to the layer side surface, the area ratio of the light diffusion / transmission portion was kept constant.

A white film (manufactured by Toray Industries, Inc.) was attached to the side surface of the light guide plate on the side of the reflective layer.

A back reflection layer made of a white polyethylene terephthalate resin plate is disposed in the surface light source device case,
A light guide plate is disposed thereon, and a light diffusion layer formed of a milky white polyethylene terephthalate resin plate is further disposed thereon, and the line light source is disposed on the side of the light source side of the light guide plate so as to be covered with a curved reflection plate. A surface light source device was used.

When the surface light emission luminance of this surface light source device was examined, high luminance and almost uniform luminance (350 nt) were obtained over the entire light emitting surface.

[0029]

In the surface light source device according to the present invention, in particular,
The area ratio of the light diffusion transmission part 3 is determined by the side a of the light guide plate 1 on the line light source side.
From the point b, where the surface emission luminance is least expected, to the area b, where the surface emission luminance is the least expected, and gradually increases as the distance from the line light source side surface a is increased. Since the present embodiment employs a constant configuration, the following effects are achieved.

In the case where the surface light source device according to the present invention is industrially mass-produced, the maximum area ratio portion B of the light diffusion / transmission portion 3 is shifted to a position b1 up to a position b where the surface emission luminance is least expected. Even if the surface light emission luminance shifts to a position b2 beyond the position b where the surface light emission luminance is least expected, a surface light source device with stable quality characteristics as close as possible to an ideal surface light source device can be obtained.

The reason why the surface emission luminance curve Z1 when the maximum area ratio portion B is shifted to the point b1 is the surface emission luminance curve Z1.
Compared with Z, it is parallel high in the region from the line light source side a to the point b1, but slightly lower in the region from the point b1 to the point b, and completely in the region from the point b to the side reflection layer side c. Therefore, the curve between the high luminance point H1 and the low luminance point L1 is a small curve. Therefore, even if the maximum area ratio portion B of the light diffusion transmission portion is shifted from the point b to the point b1, the gap between the high luminance point H1 and the low luminance point L1 is described in JP-A-2-269382. This is only half the gap between the high luminance point H'1 and the low luminance point L'1 in the disclosed surface light source device. The surface emission luminance curve Z2 when the maximum area ratio portion B is shifted to the location b2 is a surface emission luminance curve.
Compared with Z, it is low in parallel in the region from the side a of the linear light source side to the point b, but slightly rises in the region from the point b to the point b2, and completely increases in the region from the point b2 to the side reflection layer side c. , A curve having a small gap between the high luminance point H2 and the low luminance point L2 is obtained. Therefore, even if the maximum area ratio portion B of the light diffusion transmission portion is shifted from the point b to the point b2, the gap between the high luminance point H2 and the low luminance point L2 is described in JP-A-2-269382. This is only half the gap between the high luminance point H'2 and the low luminance point L2 in the disclosed surface light source device.

As described above, when the surface light source device according to the present invention is mass-produced industrially, the same strict quality control as that of the surface light source device disclosed in Japanese Patent Application Laid-Open No. 2-269382 is performed. If so, the stability of the quality characteristics will be doubled. In other words, if the stability of the quality characteristics of both is the same, the range in which the maximum area ratio portion B can be shifted is widened, and the strictness of the quality control of the line light source, the light guide, and the like is one. / 2 is sufficient.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a surface light source device according to the present invention.

FIG. 2 is a sectional view showing one embodiment of the surface light source device according to the present invention.

FIG. 3 is a plan view showing another embodiment of the surface light source device according to the present invention.

FIG. 4 is a plan view showing another embodiment of the surface light source device according to the present invention.

FIG. 5 is a model diagram showing a relationship among a surface light emission luminance change curve X, a light diffusion / transmission area ratio curve Y, and a surface light emission luminance curve Z in the surface light source device according to the present invention.

FIG. 6 shows a surface light emission luminance change curve X ′ and a light diffusion transmission part area rate curve Y ′ in a surface light source device in which the change in the surface light emission luminance of the light guide plate and the change in the area ratio of the light diffusion transmission part are completely inversely proportional. FIG. 4 is a model diagram showing a relationship between the surface emission luminance curve Z ′.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light guide plate 2 line light source 3 light diffusion / transmission section 4 side reflection layer 5 back reflection layer 6 light diffusion layer

Claims (4)

(57) [Claims] 1. A line light source (2) is arranged on one side of a transparent light guide plate (1), and a side reflection layer (4) is arranged on the other side opposite to the line light source (2). In a surface light source device provided with a light diffusion transmission portion (3) and a white back reflection layer (5) on the back surface of the light guide plate (1), a light diffusion transmission portion is provided.
(3) The refractive index of the light guide plate (1) is substantially equal to or less than
The light-transmitting plate (1) is made to contain a particulate transparent substance, and the area ratio of the light diffusion / transmission portion (3) in the direction perpendicular to the axis of the linear light source (2) is determined from the linear light source side (a) of the light guide plate (1). In the region up to the point (b) where the light emission luminance is least expected, the area gradually increases as the distance from the side surface (a) on the line light source side increases, and the side reflection layer of the light guide plate (1) starts from the point (b) where the surface light emission luminance is least expected. A surface light source device characterized by being constant in a region up to the side surface (c). 2. The area ratio of the light diffusion / transmission portion (3) in the width direction of the light guide plate (1) from the central portion (d) of the light guide plate (1) to a point (e) at which surface emission luminance starts to decrease. 2. The surface according to claim 1, wherein the surface is made to be constant in the region, and is increased quadratically in the region from the point (e) where the surface emission luminance starts to decrease to the right side surface (f) and the left side surface (g). Light source device. 3. The surface light source device according to claim 1, wherein a light diffusion layer is disposed on a surface of the light guide plate. 4. The light diffusing transmitting unit (3) is a surface light source device according to any one of claims 1 to 3 formed by dots.