JPH07261030A - Back light device - Google Patents

Abstract

PURPOSE:To provide a superior back light device which is reduced in the volume of a light guide body required to constitute a light guide plate and lightweight and low in cost, and can efficiently irradiate even a liquid crystal display panel with large screen size. CONSTITUTION:A light source 3 is arranged along an end part of the light guide plate 1, a diffuse reflecting layer which diffuses and reflects light guided into the light guide plate 1 is provided on the bottom surface 2e of the light guide plate 1, and a diffusion plate 6 which diffuses light projected from the light projection end surface 2d of the light guide plate 1 is arranged above the light projection surface 2d facing the bottom surface 2e of the light guide plate 1. The light guide plate 1 has the section almost in an L shape and an air layer 5 for propagating the light from the light source 3 up to a part distant from the light source 3 is formed between the diffusion plate 6 and light guide plate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device provided for a liquid crystal display device or the like and provided with a light guide plate for illuminating a liquid crystal display panel from the back side.

[0002]

2. Description of the Related Art In recent years, as a backlight device which is mounted on a liquid crystal display device and illuminates a liquid crystal display panel from the back side, a tubular light source such as a cold cathode fluorescent lamp (CCFT) is used because it can be easily thinned. It is attached along the side edge of a flat light guide plate made of acrylic such as polymethylmethacrylate (PMMA) resin, which is a light guide with excellent light transmission, and guides the light from the light source into the light guide plate and guides it. The so-called edge light type, in which light is emitted from the light emitting surface on the upper surface of the light plate, is the mainstream.

As an edge light type backlight device, for example, as shown in FIGS. 9 (a) and 9 (b), a light source 103 in which a light source 103 is arranged along one end of a light guide plate 101 having a parallel plate shape is used. There are two types, one is a light source and the other is a two-lamp type in which the light sources 103 are arranged along both ends of the light guide plate 101, as shown in FIGS.

On the end surface of the light guide plate 101 where the light source 103 is provided, the light emitted from the light source 103 is
A reflecting mirror 104 for preventing the light from leaking to other than 01 is provided, and a diffuser plate for effectively diffusing light emitted from the upper surface of the light guide plate 101 is provided on the upper surface side of the light guide plate 101. 106 is provided. On the other hand, the light guide plate 1
On the lower surface of 01, a diffuse reflection layer (not shown) that diffuses / reflects the light guided inside the light guide plate 101 in the normal direction is formed. This diffuse reflection layer is formed, for example, by a rough surface treatment or a white paint applied in a predetermined pattern. Further, on the lower surface side of the light guide plate 101, a reflection plate 107 for reflecting light leaking from the light guide plate 101 to the inside of the light guide plate 101 is provided.

In this case, the light emitted from the light source 103 is directly or as shown in FIG.
Through the end surface of the light guide plate 101 on the side where the light guide plate 101 is provided.
Incident on the inside. The light that has entered the light guide plate 101 is
The refractive index of the light guide body that constitutes the light guide plate 101, and the light guide plate 10
1 is repeatedly propagated inside the light guide plate 101 by repeating total reflection caused by a difference between the refractive index of the air layer existing around the light guide plate 101 and the normal line of the light guide plate 101 by the diffuse reflection layer formed on the lower surface of the light guide plate 101. Direction, that is, it is emitted to the upper surface side,
It is effectively diffused by the diffusion plate 106 and reaches the liquid crystal display panel arranged above.

By the way, the light propagating inside the light guide plate 101 is emitted by the diffuse reflection layer formed on the lower surface of the light guide plate 101, as described above. If the paint is applied to the entire lower surface of the light guide plate 101, the brightness distribution of the light emitted from the backlight device has a high brightness near the light source 103 as shown in the graph a in FIG. As a result, the brightness decreases gradually, and a uniform brightness distribution cannot be obtained. Therefore, the white paint becomes denser and denser as it is separated from the light source 103.
It is applied to the lower surface of No. 1 so that the emission brightness can be made to have a uniform brightness distribution as shown by the graph b in the figure.

However, in the structure of the backlight device using the conventional light guide plate, since it depends only on the propagation of light by the light guide plate 101, the parallel plate shape as shown in FIGS. 9 and 10 is obtained. Not to mention the light guide plate 101,
Even if the lower surface of the light guide plate is tilted,
The volume of the light guide required to form the light guide plate increases as the area to be illuminated, that is, the screen size of the liquid crystal display panel illuminated by the backlight device increases. As described above, if the required volume of the light guide body is increased, the weight of the backlight device is increased and the material cost of the light guide plate is also increased. For example, when the light guide plate is mounted on the liquid crystal display device, the liquid crystal display device is mounted. There is a problem of preventing the promotion of weight reduction and cost reduction of

Therefore, in order to solve such a problem, although very recently, a structure has been proposed in which the light guide plate, which is heavy in weight, is removed from the backlight device and the light is propagated to the light source separation part only by the air layer. (Published by Nikkei BP, "Flat panel display 1994"; PART3 enhanced portability; see pages 137 to 138).

The backlight device having a structure without the light guide plate is mainly composed of a reflector having a diffuse reflection layer and a cold cathode tube on the side surface. Light emitted from the cold cathode tube is diffusely reflected between air layers in the diffuse reflection layer. The side opposite to the cold-cathode tube is also diffusely reflected by the side surface. The surface treatment of the inner surface of the reflection plate,
Concavo-convex is formed by embossing or special paint is used. Light in the vicinity of the cold cathode tube causes the brightness of the surface of the backlight to become brighter than other parts due to direct light, which reduces the uniformity on the surface and causes the generation of bright lines. A translucent or non-transparent reflector is provided near the tube. Further, one or two special condenser lenses for condensing the light scattered by the irregular reflection layer on the bottom surface are arranged on the upper portion. This condenser lens is particularly important, and at the trial production stage, a condenser lens having less directivity than the conventional lens film, rather having a light dispersion and a condenser property close to those of the current diffusion plate is used.

[0010]

However, in the structure of the backlight device having the structure in which the light guide plate is removed, the light propagating through the air layer repeats total reflection like the light propagating inside the light guide plate. However, since it does not propagate, it is very difficult to propagate light to a light source separation part far away from the light source by propagating only the air layer, and in particular, the distance from the light source to the light source separation part is As a backlight device that illuminates a long and large liquid crystal display panel,
It has a problem that it is difficult to realize.

Therefore, it is an object of the present invention to provide a backlight device which realizes weight reduction and cost reduction and is capable of efficiently irradiating a liquid crystal display panel having a large screen size.

[0012]

In the backlight device according to claim 1 of the present invention, in order to solve the above-mentioned problems, a light source is arranged along an end portion of the light guide plate, and a lower surface of the light guide plate. Is provided with a diffuse reflection layer for diffusing and reflecting the light guided inside the light guide plate. Further, above the light emitting surface facing the lower surface of the light guide plate, the light is emitted from the light emitting surface of the light guide plate. A diffusion layer for diffusing the light is arranged, and an air layer for propagating the light from the light source to the light source separation portion separated from the light source is formed between the diffusion layer and the light guide plate. It has a feature.

In order to solve the above-mentioned problems, the backlight device according to a second aspect of the present invention is the backlight device according to the first aspect, wherein the light guide plate is thick on the end face side where the light source is arranged. The light emitting surface side is formed to be thin, and the air layer is formed in the space above the light guide plate due to the difference in thickness.

In order to solve the above-mentioned problems, the backlight device according to claim 3 of the present invention is the backlight device according to claim 2, wherein the light guide plate has a substantially L-shaped cross section or a substantially U-shaped cross section. It is characterized by forming a letter shape.

[0015]

According to the structure of the first aspect of the present invention, an air layer is formed between the diffusion layer and the light guide plate for propagating the light from the light source to the light source separation portion separated from the light source. Therefore, the light emitted from the light source propagates to the light source separating portion via the light guide plate and the air layer. The light propagating through the air layer is diffused by the diffusion layer and then emitted, or reflected by the diffusion layer and guided to the inside of the light guide plate again.
It propagates inside the light guide plate. As described above, the light propagating inside the light guide plate directly or after passing through the air layer once is diffused and reflected by the diffuse reflection layer formed on the lower surface of the light guide plate, and is emitted from the diffusion layer. At this time, by forming the diffuse reflection layer in consideration of the light propagating inside the light guide plate through the air layer, it is possible to make the uniformity of the light emitted from the diffusion layer to the extent that uneven brightness is not felt. Is.

As described above, by combining the air layer and the light guide plate, compared to the structure in which the light is propagated only by the light guide plate,
It is possible to solve the problem that light is difficult to propagate to a light source separation portion far away from the light source, as in the case of a configuration in which the required volume of the light guide body is reduced and only the air layer is propagated.
As a result, it is possible to provide a backlight device that realizes weight reduction and cost reduction and can efficiently irradiate even a liquid crystal display panel having a large screen size.

According to the second aspect of the present invention, the light guide plate is formed such that the end face side on which the light source is arranged is thick and the light emitting face side is thin, and the difference in thickness is provided on the upper part of the light guide plate. Since an air layer is formed in the space generated by, the light emitted from the light source is guided to the inside of the light guide plate through the thick end of the light guide plate, and then the light is formed thinly. The light propagates inside the light plate, or is emitted to an air layer formed above and is emitted from the diffusion layer via the air layer, or is again incident on the inside of the light guide plate via the air layer. As a result, the structure using the air layer tends to occur.
It is possible to effectively prevent the bright line of the light source generated at the end portion on the light source installation side.

According to the third aspect of the present invention, the light guide plate has a substantially L-shaped cross section or a substantially U-shaped cross section. The light guide plate having a substantially L-shaped cross section is suitable for a one-lamp type backlight device in which a light source is arranged at one end side of the light guide plate, and the light guide plate having a substantially U-shaped cross section is provided at both end sides of the light guide plate. It is suitable for a two-light type backlight device in which a light source is arranged in the. With such a shape, for example, a concave lens-shaped depression is formed in the upper portion, and the thickness of the light exit surface of the light guide plate is smaller than that of the end surface on which the light source is disposed. Effectively reduce weight and cost.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. The backlight device according to the present embodiment is applied to, for example, a liquid crystal display device, and illuminates the liquid crystal display panel from the back side.

First, a schematic structure of the backlight device will be described. As shown in FIGS. 1A and 1B, this backlight device includes a light guide plate 1, a light source 3, a reflecting mirror 4, and an air layer 5.
And a diffusing plate 6 and a reflecting plate 7. still,
FIG. 1A is a sectional view taken along line XX shown in FIG.

The light guide plate 1 is made of an acrylic resin such as PMMA (polymethyl methacrylate), which is a light guide having excellent light transmissivity. The light guided inside the light guide plate 1 has a refractive index of the light guide. The light is propagated inside the light guide plate 1 by utilizing the total reflection caused by the difference between the refractive index of the air layer existing on the outer periphery of the light guide plate 1. The air layer here includes the air layer 5. The light guide plate 1 has a substantially L-shaped cross section in which a notch is formed on the upper side of a flat plate main body having a parallel plate shape, leaving one end, and a thick portion 1 on one end side.
a, and a flat thin portion 1 whose lower surface is flush with
b. The thin portion 1b is formed with a size large enough to illuminate the screen of a liquid crystal display panel (not shown) arranged above, and the liquid crystal display panel is formed from the light emitting surface 2d which is the upper end surface of the thin portion 1b. The light that illuminates is emitted.

The lower surface 2e of the light guide plate 1 is shown in FIG.
As shown in FIG. 3, a diffuse reflection layer 8 is formed by applying a white paint that diffuses and reflects the light guided in the light guide plate 1. The white paint forming the diffuse reflection layer 8 has a coating area that becomes sparse or dense as the light emitted from the backlight device is separated from the light source 3 so as to prevent uneven brightness as illumination light. Is applied as. Further, in the present embodiment, as will be described later, since the reflecting plate 7 is also provided on the end face side of the light guide plate 1 facing the light incident surface 2a, white reflection is considered in consideration of the reflection of light by the reflecting plate 7. The coating area of the paint is not completely dense or dense,
It is applied so as to be sparse-dense-sparse.

The coating pattern of the diffuse reflection layer 8 is not limited to this, and may be, for example, a diffusion reflection layer 8'having a coating pattern as shown in FIG.

The light incident surface 2a, which is the side end surface of the thick portion 1a, to which the light source 3 is attached, and the inner end surface 2b are in a parallel relationship, and the thick portion with respect to the light incident surface 2a and the inner end surface 2b. The upper end surface 2c of 1a has a right angle relationship, and the upper end surface 2c, the light emitting surface 2d of the thin portion 1b, and the lower surface 2 of the light guide plate 1 are formed.
It is provided so as to have a parallel relationship with e. In this case, it is not always necessary to form such a relationship, but it is preferable that at least the light incident surface 2a and the upper end surface 2c or the lower surface 2e be formed in a right angle relationship so that the light incident inside the light guide plate 1 is formed. It is preferable because total reflection occurs. Also,
Regarding the length C of the thick portion 1a in the light propagation direction, the light source 3
It is desirable that the light guide plate 1 of the present backlight device has a length capable of preventing the bright line due to the direct light from the light diffusion plate 6 from being seen from the diffusion plate 6.

The light source 3 comprises a tubular light source such as a CCFT (cold cathode tube), and is arranged on the light incident surface 2a of the thick portion 1a of the light guide plate 1 along the longitudinal direction of the light incident surface 2a. It is set up. The reflecting mirror 4 is attached to the light incident surface 2a of the light guide plate 1 so as to cover the entire light incident surface 2a together with the light source 3, and reflects the light emitted from the light source 3 in a direction other than the light guide plate 1 direction. The light guide plate 1 is guided to the inside.

The diffusion plate (diffusion layer) 6 is, for example, PET.
It is made of (polyethylene terephthalate), polycarbonate, or the like. Above the thin portion 1b of the light guide plate 1, the thick portion 1a is formed.
Are arranged at the same height on the upper end surface 2c. The diffusing plate 6 is configured to efficiently diffuse the light emitted from the light emitting surface 2d of the light guide plate 1 and irradiate the liquid crystal display panel arranged above. The diffusion plate 6 may have a sheet shape as well as a flat plate shape.

The air layer 5 is formed in the space formed between the thin portion 1b of the light guide plate 1 and the diffusion plate 6,
Like the light guide plate 1, the light from the light source 3 is propagated. The reflection plate 7 is disposed on the lower surface side of the light guide plate 1, and is configured to reflect light leaking from the light guide plate 1 and prevent light leakage. Also, this reflector 7
Covers the end surface of the light guide plate 1 facing the light incident surface 2a and also covers the side end surface of the air layer 5 above the end surface.
As a result, light leakage to the air layer outside the air layer 5 is prevented.

Next, how the light emitted from the light source 3 propagates in the backlight device having such a configuration will be described. The light emitted from the light source 3 enters the light guide plate 1 through the light incident surface 2a directly or after being reflected by the reflecting mirror 4, as shown in FIG. In the figure, the arrow D ₁ indicates the light which is directly incident on the light guide plate 1 from the light source 3, and the arrow D ₁
Reference numeral ₂ shows the light incident through the reflecting mirror 4.

The light incident on the light guide plate 1 is shown in FIG.
As shown in FIG. 2, the inner end surface 2b of the thick portion 1a is reached or the thin portion 1b is propagated. In the figure, an arrow D ₃ indicates light reaching the inner end surface 2b, and an arrow D ₄ indicates light propagating through the thin portion 1b.

At this time, the light propagated to the thin portion 1b is
As shown in FIG. 3C, the total light reflection caused by the difference in the refractive index between the light guide plate 1 and the air layer surrounding the light guide plate 1 is repeated. In the figure, it is shown by an arrow D ₈ . At this time, since the thin portion 1b has a parallel plate shape, total reflection is relatively easy to repeat. Then, the light is diffused and reflected by the diffuse reflection layer formed on the lower surface 2 e of the light guide plate 1, advances in the normal direction of the light guide plate 1, and is emitted from the diffuser plate 6.

On the other hand, the light that has reached the inner end surface 2b of the thick portion 1a propagates to the air layer 5, passes through the air layer 5, and is diffused by the diffuser plate 6.
Or reaches the inside of the light guide plate 1 again (in the thin portion 1b) through the air layer 5. Further, the light reaching the diffuser plate 6 is diffusely reflected by the diffuser plate 6 and emitted from the diffuser plate 6, or is reflected by the diffuser plate 6 and again enters the light guide plate 1 (in the thin portion 1b). . Inside the light guide plate 1, that is, the thin portion 1b
The light incident on travels while propagating inside the thin portion 1b,
The light is diffused and reflected by the diffuse reflection layer on the lower surface 2 e of the light guide plate 1, and is emitted from the diffuser plate 6. In the figure, an arrow D ₅ indicates light that reaches the diffuser plate 6 and is diffused and reflected, and an arrow D ₆ indicates light that reaches the diffuser plate 6 and then enters the light guide plate 1 again. The arrow D ₇ indicates the light that enters the light guide plate 1 again without reaching the diffusion plate 6.

As described above, in this backlight device, the light propagating inside the light guide plate 1 is changed from the thick portion 1a to the thin portion 1b.
Light that is incident on and propagates while being totally reflected by the thin portion 1b,
The light that is once emitted from the thick portion 1a to the air layer 5 and then is incident on the thin portion 1b again, and the light layer 5 is temporarily emitted from the thick portion 1a.
To the thin portion 1b.
There are three lights incident on. Therefore, the diffuse reflection layer 8 formed on the lower surface 2e of the light guide plate 1 described above is
It is made in consideration of light. Regarding the method for diffusing and reflecting the light on the lower surface 2e of the light guide plate 1 as described above, the configuration proposed in the related art can be used only because the light propagated through the air layer 5 exists. ,
For example, so-called embossing for roughening the lower surface 2e of the light guide plate 1 may be used. In that case, as the distance from the light source 3 increases, the rough surface treatment area is formed from sparse to dense, or the degree of the rough surface is changed. When the reflection plate 7 is also provided on the end face side of the light guide plate 1 facing the light incident surface 2a as in the present embodiment, the reflection of the light by the reflection plate 7 is also taken into consideration as described above. It is formed densely and sparsely.

Next, FIG. 4 shows a simplified simulation of the light utilization efficiency of the above-described backlight device as compared with the backlight device using the conventional parallel plate-shaped light guide plate 101. . The same figure (a)
The backlight device of the present embodiment and the backlight device of the conventional configuration are shown in FIG. In FIGS. 3A and 3B, the central axis of each light guide plate 1/101 is indicated by OO ′,
It is assumed that the point light source L corresponding to the light source 3 exists on the axis OO ′. A light incident surface 102 indicated by AA ′ in the figure of the light guide plate 101 of the conventional sample used for comparison.
The height dimension of a and the height dimension of the light incident surface 2a of the sample light guide plate 1 of the present embodiment shown by AA ′ in the figure are both equal, and are set to “10”. Further, the inner end surface 2b of the light guide plate 1 of the sample of the present embodiment shown by BB "in the drawing
The height dimension of "7", thin portion 1 shown by B "-B 'in the figure
The height dimension of the light incident portion on b is “3”.

Actually, there is a light guide plate 1/101 on the upper surface side or the lower surface side that changes the reflection / diffusion / directivity. Although the light is emitted to, the light reaching the lower surface of each light guide plate 1/101 and the light emitted to the air layer (including the air layer 5) are all used as illumination light for the sake of simplicity. I think it is available.

First, assuming that the total light amount of the light source L is L ₁ and the total light amount of the light incident on the light guide plate 101 is L ₂ in the same figure (b), the light guide body (acryl or the like) forming the light guide plate 101 is shown.
The light utilization efficiency P ₁₀₁ is P ₁₀₁ = (L ₂ T / L ₁ ) × 100 [%], where T is the transmittance of

On the other hand, in FIG. 5A, if the total amount of light of the light source L is L ₁ , the light guide plate 1 is the same as in the case of FIG.
Naturally, the total amount of light incident on the inside is also L ₂ . This light amount L ₂ basically reaches the inner end surface 2b without attenuation,
What is different from the case of (b) is what happens after reaching the inner end surface 2b.

(Height dimension of BB "): (Height dimension of B" -B ') = 7: 3, of which light reaching B "-B' is in the case of (b) If no different. also, the light emitted from the inner end face 2b, as shown in FIG. 5, is divided into the light theta ₁ which enters the inside 1 again light guide plate, a light theta ₂ does not enter. the time theta ₁ Since: θ ₂ = 1: 1, half of the light that has reached BB ″ eventually enters the light guide plate 1 again after passing through the air layer 5 once.

From the above, if the transmittance of the light guide (acryl or the like) forming the light guide plate 1 is considered to be T, as in the case of FIG. 4B, the light utilization efficiency P ₁ is P ₁ = (0.3L ₂ T / L ₁ + α) × 100 [%], and the above α is α = (0.7 / 2) TL ₂ / L ₁ + (0.7 / 2) T ² L ₂
Since / L ₁ , the light use efficiency P ₁ is ∴ P ₁ = (0.65TL ₂ + 0.35T ² L ₂ ) / L ₁ .

For clarity, L ₁ = 1 and L ₂
= 0.95 and T = 0.95, P ₁₀₁ = 90.3% P ₁ = 88.7%. This proves that the light utilization efficiency of the backlight device of this embodiment is equivalent to that of the conventional configuration.

As described above, in the backlight device of this embodiment, the light guide plate 1 has a substantially L-shaped cross section, and the air layer 5 is formed between the light guide plate 1 and the diffusion plate 6, and one end of the light guide plate 1 is formed. The light from the light source 3 provided on the side propagates in the thin portion 1b of the light guide plate 1 and also propagates to the other end portion (light source separation portion) of the light guide plate 1 through the air layer 5. Therefore, as compared with the conventional configuration in which the light is propagated only in the light guide plate 1, the volume of the light guide body required for the configuration of the light guide plate 1 is reduced and the weight is reduced because the air layer 5 is used. be able to. Further, by reducing the weight of the light guide plate 1, it is possible to reduce the cost of the light guide plate 1.

Moreover, by making the light guide plate 1 substantially L-shaped in cross section, for example, a concave lens-shaped depression is formed in the upper part so that the thickness of the light exit face of the light guide plate is thinner than the end face of the light source. Than the above, the air layer formed becomes larger, and the weight and cost are effectively reduced.

Table 1 shows the weight and material cost of the light guide plate 1 in the backlight device of this embodiment corresponding to each screen size, and for reference, the above-mentioned FIG. 9 corresponding to each screen size is shown. Table 2 shows the weight and material cost of the light guide plate 101 in the conventional type backlight device shown in FIG.
Table 3 shows the result of comparison between the two.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

The required size of the light guide plate is 3: 4 in the vertical and horizontal directions and the thickness is 10 m so that the diagonal size is the same as the screen size.
m. In the case of the conventional type, the light guide plate size and the screen size are equal, but in this embodiment, the size of the thin portion 1b, that is, the dimension D and the dimension E shown in FIG. 1 are configured to correspond to the screen size. The size of the thick portion 1a is shown in FIG.
Dimension A is 7 mm, Dimension B is 3 mm and Dimension C is 10
mm. Further, both the light guide plate 1 of the present embodiment and the light guide plate 101 of the conventional type backlight device are made of acrylic, and the specific gravity is 1.19 and the material cost is 0.6 yen / cc.

As is clear from Table 3, in the present backlight device, the required weight of the light guide and the material cost can be reduced to about 30% to 40% of those of the prior art. Therefore, it is possible to dramatically reduce the weight and cost of the backlight device.

Further, by combining the air layer 5 and the light guide plate 1 in this way, the light source can be used even in a large-sized backlight device in which the distance from the light source 3 to the light source separating portion is large while achieving weight reduction and cost reduction. The light emitted from the light source 3 can efficiently reach the light source separating portion.

Moreover, since the thin portion 1b of the light guide plate 1 is formed in a parallel plate shape, the total reflection is relatively increased, so that the light can be more easily propagated to the light source separating portion.
The configuration is suitable for a liquid crystal display device equipped with a liquid crystal display panel having a larger screen size.

Further, in this backlight device, the light guide plate 1
Has a substantially L-shaped cross section, and the end face side of the light guide plate 1 on which the light source 3 is arranged is formed thicker than the thin portion 1b having the light emitting surface 2a. Since the air layer 5 is formed, the light emitted from the light source 3 is incident on the light incident surface 2 of the thick portion 1 a of the light guide plate 1 which is thick.
From a, the light is once guided inside the light guide plate 1 and then propagates inside the thin portion 1b formed thinly, or is emitted to the air layer 5 formed above and diffused through the air layer 5 and the diffusion plate 6 is formed. Or the light enters again into the light guide plate 1 through the air layer 5. As a result, the light source 3 generated at the end portion on the light source arrangement side, which tends to have a configuration using the air layer 5,
It is possible to effectively prevent the bright line of.

Furthermore, the diffuse reflection layer formed on the lower surface 2e of the light guide 1 in the present backlight device has a thick portion 1a.
To the thin portion 1b and propagates while being totally reflected in the thin portion 1b, light that is once emitted from the thick portion 1a to the air layer 5 and then enters the thin portion 1b, and the thick portion 1a. The light emitted from the backlight device is emitted from the backlight device because the light emitted from the backlight device to the air layer 5 is reflected in the diffuser plate 6 and then incident on the thin portion 1b again. As a result, there is no unevenness in brightness, which is excellent.

When the present invention is applied to a backlight device in which the distance from which the light from the light source 3 is propagated is short or the uniformity of illumination light is not a problem, the thin portion 1b is not necessarily parallel plate-shaped. It is not necessary to form it in, for example, FIG.
The configurations shown in (a) to (d) may be used. The same figure (a)
(c) is formed by raising the lower surface 2e of each of the light guide plates 21 and 41 so as to be inclined or arcuate as the distance from the light source 3 increases, and FIGS.
The light emitting surface 2d of the thin portion 1b in 1 is formed so as to descend in an inclined shape or an arc shape with increasing distance from the light source 3. In this way, by changing the thickness of the thin portion 1b and further reducing the required volume of the light guide body, the volume of the air layer 5 is further increased as compared with that of the above-mentioned embodiment, and as a result,
It is possible to further reduce the weight of the backlight device and reduce the cost.

In the above embodiment, the one-light type backlight device in which the light source 3 is arranged at one end of the light guide plate 1 is illustrated, but as shown in FIGS. 7 (a) and 7 (b), for example. The configuration of the present invention may be adopted in a two-lamp type backlight device in which the light sources 3 are arranged along opposite ends of the light guide plate 1 '. Incidentally, FIG. 7A is a sectional view taken along the line YY shown in FIG.

In this case, the shape of the light guide plate 1'is
It may have a U-shaped cross section in which the thick portions 1a are provided on both sides of the thin portion 1b. In addition, as shown in FIGS. 8A and 8B, the diffuse reflection layers 8 and 8 ′ formed on the lower surface 2e of the light guide plate 1 ′ allow the light emitted from the backlight device to be uneven in brightness as illumination light. In order to prevent the occurrence of the above, the coating area may be formed from sparse to dense as the distance from each light source 3 is increased, that is, the central part of the light guide plate 1 ′ may be densest.

Then, the same effects as those mentioned in the present embodiment can be obtained. Of course, in this case as well, FIG.
As shown in (d), the shape of the thin portion 1b can be changed, and by doing so, the same effect can be obtained.

[0056]

As described above, in the backlight device according to claim 1 of the present invention, the light source is arranged along the end portion of the light guide plate, and the light guide plate is guided to the inside of the light guide plate. A diffuse reflection layer that diffuses and reflects the emitted light is provided, and a diffusion layer that diffuses the light emitted from the light exit surface of the light guide plate is arranged above the light exit surface that faces the lower surface of the light guide plate. An air layer is provided between the diffusion layer and the light guide plate for propagating the light from the light source to the light source separation portion separated from the light source.

As described above, by combining the air layer and the light guide plate, rather than the structure in which the light is propagated only by the light guide plate,
It is possible to solve the problem that light is difficult to propagate to a light source separation portion far away from the light source, as in the case of a configuration in which the required volume of the light guide body is reduced and only the air layer is propagated.

As a result, it is possible to obtain an excellent backlight device which is light in weight, low in cost, and capable of efficiently irradiating even a liquid crystal display panel having a large screen size.

As described above, the backlight device according to a second aspect of the present invention is the backlight device according to the first aspect, wherein the light guide plate is thick on the end face side on which the light source is arranged and has a light emitting surface. The air layer is formed so that the side becomes thinner, and the air layer is formed in the space above the light guide plate due to the difference in thickness.

As a result, in addition to the effect described in claim 1, it is possible to effectively prevent the bright line of the light source generated at the end portion on the side where the light source is disposed, which tends to have a structure using an air layer. Has the effect.

As described above, the backlight device according to claim 3 of the present invention is the backlight device according to claim 2, wherein the light guide plate has a substantially L-shaped cross section or a substantially U-shaped cross section. This is the configuration.

Thus, in addition to the effect described in claim 2, for example, a concave lens-shaped recess is formed in the upper portion to make the thickness of the light exit surface side of the light guide plate thinner than that of the light source installation end surface. In addition, the air layer formed becomes large, and there is an effect that the weight and cost can be reduced more effectively.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, in which (a) is a sectional view of a backlight device and (b) is a plan view thereof.

FIG. 2A is a bottom view of a light guide showing a pattern of a diffuse reflection layer provided on the back surface of the light guide plate in the backlight device, and FIG. 2B is a bottom view of the light guide showing another pattern. Is.

FIG. 3 is an explanatory diagram showing a state of propagation of light emitted from a light source in the backlight device, FIG. 3A shows a state in which the light emitted from the light source enters the inside of the light guide plate; (B) shows a state of propagating in the thick portion of the light guide plate, and (c) shows a state of light propagating in the air layer and the thin portion of the light guide plate.

FIG. 4A is an explanatory diagram in which light propagation in the backlight device is simply simulated,
FIG. 6B is an explanatory view for simplification of light propagation in a device using a conventional type light guide plate for comparison and reference.

FIG. 5 is an explanatory diagram showing a traveling direction of light emitted from the inner end surface of the light guide plate.

6A to 6D are cross-sectional views each showing a configuration of a backlight device according to another embodiment of the present invention.

7A and 7B show another embodiment of the present invention, wherein FIG. 7A is a sectional view of a backlight device and FIG. 7B is a plan view thereof.

8A and 8B are both bottom views of the light guide showing the pattern of the diffuse reflection layer provided on the back surface of the light guide plate in the backlight device of FIG. 7.

9A is a sectional view of a conventional backlight device, FIG.
(B) is the top view.

FIG. 10A is a sectional view of a conventional backlight device,
(B) is the top view.

FIG. 11 is an explanatory diagram showing a state of light propagating in a light guide plate of a conventional backlight device.

FIG. 12 is a graph showing a luminance distribution in a conventional backlight device.

[Description of Reference Signs] 1 light guide plate 2a light incident surface 2d light emission surface 2e lower surface 3 light source 4 reflecting mirror 5 air layer 6 diffuser plate (diffusing layer) 8 diffuse reflecting layer

Claims (3)

[Claims] 1. A light source is arranged along an end portion of a light guide plate, and a diffuse reflection layer for diffusing and reflecting light guided inside the light guide plate is provided on a lower surface of the light guide plate, and further. Above the light emitting surface facing the lower surface of the light guide plate, a diffusion layer for diffusing the light emitted from the light emitting surface of the light guide plate is arranged,
A backlight device characterized in that an air layer is formed between the diffusion layer and the light guide plate for propagating the light from the light source to a light source separation portion separated from the light source. 2. The light guide plate is formed such that the end face side on which the light source is arranged is thick and the light exit face side is thin, and the air layer is formed in the space portion caused by the difference in thickness above the light guide plate. The backlight device according to claim 1, wherein the backlight device is provided. 3. The light guide plate has a substantially L-shaped cross section or a substantially U-shaped cross section.
Backlight device described.