JPH103813A - Back light device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a back light device with its superior cost effectiveness and mass-productivity capable of being a surface light source without applying a divergence reflection pattern material. SOLUTION: A light guide body part 8 at which tubular light sources 1, 1 and reflection plates 2, 2 are mounted on both ends thereof is formed of which a light guide layer 3 for transmitting incident light from the tubular light source 1 and a triangular layer 4 with its cross-section formed in the form of saw-teeth for emitting light transmitted from the light guide layer 3. The refractive index of the light guide layer 3 is set to be the largest, and the refractive index of the triangular layer 4 is set to be changed in a direction in which the index increases as it is further removed from the tubular light source 1. The apex angle of the saw-tooth part of the triangular layer 4 is set to increase as it is further removed from the tubular light source 1 so as to strengthen directivity of light emitted from the light guide body part 8 in the front face direction of a liquid crystal panel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device mounted on a liquid crystal display device or the like for irradiating a liquid crystal panel as a display panel from the back side, and in particular, a light source is arranged at an end of a light guide. The present invention relates to an edge light type backlight device.

[0002]

2. Description of the Related Art Conventionally, a backlight device mounted on a liquid crystal display device or the like includes a direct type in which a plurality of light sources are arranged on the back side of a liquid crystal panel and an edge type in which a light source is arranged at an end of a light guide. Although there is a light method, the latter edge light method has been often used in recent years because of the advantages that the thickness can be easily reduced and the structure is simple.

In a conventional edge light type backlight device, as shown in FIG. 17, a tubular light source 31 is disposed at both ends of a transparent light guide 33, and a reflecting mirror 32 is provided so as to cover the tubular light source 31. Are located. The lower surface of the light guide 33 (the side opposite to the side on which the liquid crystal panel is arranged) is provided as shown in FIG.
As shown in FIG. 7, a diffuse reflection pattern 38 that is denser as the distance from the tubular light source 31 increases is provided, so that light from the tubular light source 31 can be emitted from the upper surface of the light guide 33. That is, the light guide 33 and the diffuse reflection pattern object 38 constitute a surface light source means for transmitting, diffusing, and reflecting light.

Further, in order to use light effectively, a diffusion sheet 35 and a prism sheet 39 are disposed on the upper surface side of the light guide 33, and a reflection sheet 37 and the like are disposed on the lower surface side of the light guide 33. Is arranged. As a result, a thin, high-quality, high-efficiency backlight device is realized.

The tubular light source 31 is, for example, a cold cathode fluorescent lamp, the reflecting mirror 32 and the reflecting sheet 37 are white PET (polyethylene terephthalate) films, the light guide 33 is a mirror-finished acrylic plate, Each of the sheet 35 and the prism sheet 39 is formed of a thin sheet made of polycarbonate or the like. Also,
Diffuse reflection pattern object 38 formed on the lower surface of light guide 33
Is made of a white paint such as TiO ₂ or BaSO _{4 in the} form of dots.

[0006] Due to the application, such a backlight device includes a one-lamp type in addition to the two-lamp type shown in FIG. 17, and in the case of the one-lamp type, a tubular member is provided at one end of the light guide. Other configurations and principles are the same as those of the two-lamp type, except that the light source is arranged and a diffuse reflection pattern is applied according to the state of the light source.

[0007]

However, the structure of the above-mentioned conventional backlight device has the following two problems.

One is that a printing process such as silk printing is required to apply the diffuse reflection pattern 38 to the lower surface of the light guide 33 (see FIG. 17). In the diffuse reflection pattern, the luminance distribution as a surface light source is determined by the ratio between the area of application of the dot-shaped white paint and the area of non-application (that is, the mirror surface of the light guide). Therefore, the method using the diffuse reflection pattern object has an advantage that even if the size and thickness of the light guide or the configuration of the light source changes, a surface light source can be easily realized only by changing the pattern, and the uniform brightness is obtained. It is currently the mainstream method of obtaining a distributed surface light source. However, with the recent thinning of backlight devices,
Light guides have been made thinner, and accordingly, the pattern of the diffuse reflection pattern must be made finer.If the pattern becomes finer, printing such as dripping or insufficient coating that causes uneven brightness and bright lines will occur. Defects are more likely to occur at the time of printing, and mass productivity deteriorates.

In addition, it is necessary to prevent dust from entering during printing, and a separate printing process is required even if the light guide itself is molded by a mold to increase mass productivity.
The method of obtaining a diffuse reflection pattern by printing is not necessarily good in mass productivity.

Another point is that an optical sheet such as the above-described prism sheet 39 is required as a separate member in order to enhance the directivity of the emission luminance of the backlight device in the front direction of the liquid crystal panel (see FIG. 1). 17). At present, a so-called prism sheet in which a resin such as acrylic or polycarbonate is arranged in a prism shape having a pitch of about 50 microns and an apex angle of about 90 degrees is often used as an optical sheet. However, due to its nature, this prism sheet has the highest member cost among the members constituting the backlight device, and if scratches or dirt is generated, it directly leads to problems such as uneven brightness, so care should be taken when handling the prism sheet. Work is required, and there are problems in terms of cost and mass productivity.

The present invention has been made in view of the above problems, and has as its object to provide a backlight device which is excellent in cost and mass productivity.

[0012]

According to a first aspect of the present invention, there is provided a backlight device disposed on a back side of a display panel for transmitting, reflecting and diffusing light. At least one end of the means, in a backlight device provided with a linear light source and a reflector for reflecting light from the light source to the surface light source means, the surface light source means,
A first layer for propagating incident light from the light source; and a first layer laminated on the first layer and having a surface opposite to the lamination surface formed in a sawtooth cross section. A transparent light guide integrally formed with a second layer for emitting light from the layer; the refractive index of the first layer is larger than the refractive index of the second layer; The ratio is set so as to change in a direction that increases as the distance from the light source increases.

According to this, the refractive index of the first layer in the surface light source means made of a transparent light guide is set to be larger than the refractive index of the second layer. Therefore, a total reflection phenomenon occurs in the first layer. The total reflection angle at this time is determined from the refractive index of the first layer and the second layer by Snell's law, and the closer the refractive index of the first layer and the second layer is, the larger the total reflection angle becomes. Become. This means that, if the refractive index of the second layer is set to be larger as the distance from the light source increases, the chance of light entering the second layer can increase as the distance from the light source increases. Then, in the configuration of claim 1,
The refractive index of the second layer is set to change in a direction that increases as the distance from the light source increases. Thus, the surface light source means having a uniform luminance distribution can be constituted by only one light guide without printing the conventional diffuse reflection pattern.

According to a second aspect of the present invention, there is provided a backlight device which is disposed on a rear side of a display panel and has a linear light source and a light source provided at least at one end of a surface light source means for transmitting, reflecting and diffusing light. In a backlight device provided with a reflector for reflecting the light to the surface light source means, the surface light source means includes a first layer for transmitting incident light from the light source, and a first layer for transmitting the incident light from the light source. A transparent light guide in which a second layer for emitting propagating light from the first layer is integrally formed with the second layer for emitting propagating light from the first layer, the surface being opposite to the stacked surface being formed in a saw-toothed cross section. The refractive index of the first layer is larger than the refractive index of the second layer, and the angle of inclination of the interface between the first layer and the second layer with respect to the surface of the first layer is different from that of the display panel. If the direction inclining to the opposite side is the positive direction, it is the largest on the light source side, and the smaller the further away from the light source, the smaller It is characterized in that it is set to change in AMS1.

Also in this case, the refractive index of the first layer in the surface light source means made of a transparent light guide is set to be larger than the refractive index of the second layer, so that the total reflection phenomenon occurs in the first layer. Occurs. In the configuration of the first aspect, the second
Was changed to change the incidence of light to the second layer. In this case, the incidence of light from the first layer to the second layer was changed to the first Paying attention to the fact that it depends on the inclination angle of the interface between the layer and the second layer, the inclination angle is set to be the largest on the light source side and to decrease in the direction away from the light source. As a result, as the distance from the light source increases, the incidence of light from the first layer to the second layer increases. The surface light source means having a uniform brightness distribution can be constituted by only one light guide without printing the light guide.

According to a third aspect of the present invention, in the backlight device according to the first or second aspect, the light emitted from the surface light source is applied to a surface of the surface light source opposite to the display panel. It is characterized in that reflection means for re-entering the surface light source means is provided.

According to this, the leakage light emitted to the side opposite to the display panel is re-entered into the surface light source means by the reflection means provided on the surface of the surface light source means opposite to the display panel. You. Therefore, light can be effectively used, and a bright backlight device can be realized.

As the above-mentioned reflection means, for example, a reflection member using specular reflection, such as a mirror reflection plate disposed on the surface of the surface light source means, a mirror reflection film laminated on the surface of the surface light source means by vapor deposition or the like, or And a reflection member using diffuse reflection, such as a diffuse reflection plate disposed on the surface of the surface light source means, or a diffusion reflection layer laminated on the surface of the surface light source means by vapor deposition or the like.

According to a fourth aspect of the present invention, in the backlight device according to the first, second or third aspect, the second layer in the surface light source means is so large that the apex angle of the sawtooth portion is further away from the light source. It is characterized by being formed so that it becomes.

According to this, the second layer formed so that the apex angle of the sawtooth portion increases as the distance from the light source increases, without providing a separate expensive and difficult-to-handle prism sheet as in the related art. The directivity of the emitted light can be enhanced in the front direction of the display panel.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] An embodiment of the present invention will be described below with reference to FIGS. FIG. 1A is a cross-sectional view of the backlight device according to the present embodiment, in which the upper side is the liquid crystal panel (not shown) side. FIG. 2B is a bottom view of the backlight device as viewed from the side opposite to the liquid crystal panel side. In the following description, the liquid crystal panel side is referred to as an upper surface side, and the anti-liquid crystal panel side is referred to as a lower surface side.

As shown in FIGS. 1 (a) and 1 (b), this backlight device is of a two-light type, and is provided at both ends of a light guide (surface light source means) 8 composed of an integral transparent light guide. , And one tubular light source (light source) 1 is disposed one by one. On the end side to which these tubular light sources 1.1 are attached, further, reflecting mirrors (reflecting plates) 2.2 for causing light from these tubular light sources 1.1 to efficiently enter the light guide 8. , So as to cover the tubular light sources 1.1. On the upper surface side of the light guide 8, a diffusion sheet 5 for diffusing light emitted from the light guide 8 is provided. The above tubular light source 1
1, the reflecting mirrors 2 are attached to both ends of the light guide layer 3 of the light guide unit 8, which will be described later, and the end side surfaces 3a to which these are attached serve as light incident surfaces.

The light guide section 8 includes a light guide layer (first layer) 3 having a function of propagating light emitted from the tubular light source 1,
A triangular layer (second layer) 4 whose lower surface is formed in a saw-tooth shape with a function of emitting light propagated in the light guide layer 3.
Are integrally laminated. The refractive index of the light guide layer 3, the refractive index of the triangular layer 4, and the apex angle of the sawtooth portion of the triangular layer 4 are set to values obtained by a computer simulation as described below. A surface light source can be formed without applying a diffuse reflection pattern to the lower surface of the light guide as in the above, and the light emitted from the light guide 8 can be obtained without the need for an optical sheet such as a prism sheet. Directivity can be enhanced in the front direction of the liquid crystal panel.

For the tubular light source 1, for example, a cold cathode fluorescent lamp or a hot cathode fluorescent lamp can be used.
For example, a white PET (polyethylene terephthalate) film or a silver vapor-deposited film having a high reflectivity is used. For the diffusion sheet 5, a film in which the surface of polycarbonate is finely roughened or a film in which acrylic is roughened is used. Can be.

In such a configuration, the tubular light sources 1.1
Is emitted from the light incident surface of the light guide layer 3 directly or via the reflection mirrors 2, propagates through the light guide layer 3, and is diffused and reflected by the triangular layer 4 to be reflected by the light guide layer. The light emitted from the light guide layer 3 and emitted from the upper surface of the light guide layer 3 is diffused by the diffusion sheet 5 and then illuminates a liquid crystal panel (not shown) from the back side.

The refractive index of the light guide layer 3 in the light guide section 8 and the triangular layer 4
And the setting of the apex angle of the sawtooth portion of the triangular layer 4 will be described.

The respective refractive indices of the light guide layer 3 and the triangular layer 4 are derived from the incident angle and intensity of light incident on the light guide layer 3, the refractive index of the light guide layer 3, and the refractive index of the triangular layer 4. , Light guide layer 3
Is determined by the exit angle and the intensity of the exit light of the light guide layer 3 with respect to the incident light, and its theoretical formula will be described first.

In FIG. 2, the refractive index of air n ₁ = 1, the refractive index of the light guide layer 10 is n ₂ , the refractive index of the triangular layer 11 is n ₃ , and the angle of incidence of incident light on the light guide layer 10 is i ₀ and intensity I
_{If 0} , the emission angle r _{4 of the} light emitted from the light guide layer 10,
The intensity I ₄ is obtained as follows.

On the light incident surface 10a of the light guide layer 10, the refraction angle r ₀ and the surface reflection R ₀ are:

[0030]

(Equation 1)

## EQU1 ## Therefore, the intensity I ₁ of the light incident on the light guide layer 10 is

[0032]

(Equation 2)

## EQU1 ## Next, at the interface 12 between the light guide layer 10 and the triangular layer 11, the incident angle i ₁ , the refraction angle r ₁ , and the surface reflection R ₁ are:

[0034]

(Equation 3)

## EQU1 ## Therefore, the intensity I ₂ of the light incident on the triangular layer 11 is

[0036]

(Equation 4)

Is as follows. Here, when the refractive index n ₂ of the light guide layer 10 is larger than the refractive index n ₃ of the triangular layer 11, the total reflection angle Z
₁ is

[0038]

(Equation 5)

The next, the light in the total reflection angle Z ₁ is greater than the incident angle i ₁ is totally reflected at the interface 12 as b shown in FIG. On the other hand, light having an incident angle i ₁ smaller than the total reflection angle Z ₁
The light enters the triangular layer 11 as shown in FIG.

Next, the incident angle i of the light incident on the triangular layer 11
₂ , if the apex angle of the triangular layer 11 is θ ₃ ,

[0041]

(Equation 6)

Is as follows. Here, when the surface of the triangular layer 11 is in the air, the total reflection angle Z ₂ is

[0043]

(Equation 7)

The light having an incident angle i ₂ larger than the total reflection angle Z ₂ is totally reflected at the interface 13. Alternatively, if a specular reflecting means 25 such as a specular reflecting mirror is arranged, the light is reflected as shown in FIG.

Next, again at the interface 12 between the light guide layer 10 and the triangular layer 11, the incident angle i ₃ , the refraction angle r ₃ , and the surface reflection R ₃
Is

[0046]

(Equation 8)

Is as follows. Therefore, the intensity I ₃ of the light incident on the light guide layer 10 is

[0048]

(Equation 9)

Is as follows. The incident angle i ₄ , the refraction angle r ₄ , and the surface reflection angle R _{4 on} the upper surface of the light guide layer 10 are as follows:

[0050]

(Equation 10)

Is as follows. Therefore, the intensity I ₄ of the light incident on the light guide layer 10 is

[0052]

[Equation 11]

Is as follows. Here, when the surface of the light guide layer 10 is in the air, the total reflection angle Z ₃ is

[0054]

(Equation 12)

The light having an incident angle i ₄ larger than the total reflection angle Z ₃ is totally reflected at the interface 14 and does not exit the light guide layer 10.

When the ratio of the light emitted from the light guide layer 10 to the light incident on the light guide layer 10 is determined by simulation based on the above theoretical formula, the result shown in FIG. 3 was obtained. . In the simulation, the light guide layer 1 was used.
0, the refractive index n ₂ = 1.59, and the refractive index n of the triangular layer 11
₃ was changed from 1 to 1.59.

According to FIG. 3, when the refractive index n ₃ of the triangular layer 11 is smaller than about 1.24, all the incident light is
And totally reflected at the interface 12 of the triangular layer 11 and about 1.24
As the distance becomes larger, the ratio of light incident on the triangular layer 11 at the interface 12 increases, and the light emitted from the light guide layer 10 increases. And, of course, n ₃ = 1.59
Above, there is no total reflection, and all light is in the triangular layer 1
Incident on 1.

Therefore, based on the result of this simulation, if the refractive index n ₃ of the triangular layer 11 is changed as a function of the position from the tubular light source, the position of the triangular layer 11 from the tubular light source disposed at the end of the light guide layer 10 is changed. Accordingly, the light emitted from the light guide layer 10 can be arbitrarily changed. This means
In other words, it means that the adjustment of the luminance distribution based on the occupied area ratio of the diffuse reflection pattern object, which is performed by the conventional backlight device, can be realized by changing the refractive index of the triangular layer 11.

Therefore, the light guide portion 8 of the backlight device is
In the light guide layer 3 and the triangular layer 4, the refractive index of the light guide layer 3 is 1.
59, and the refractive index of the triangular layer 4 is set to 1.2 so that the same outgoing light intensity can be obtained at every position of the light guide 3.
It is set in a range larger than 4 and smaller than 1.59. Basically, the refractive index of the triangular layer 4 is set to increase as the distance from the tubular light source 1 increases. As a result, the light guide section 8 becomes a surface light source having a uniform brightness distribution composed of one light guide without providing a diffuse reflection pattern on the lower surface of the light guide by printing as in the related art. I have.

On the other hand, as can be seen from the above theoretical formula, the angular distribution of the emitted light depends on the apex angle θ ₃ of the triangular layer 11.
Thus, when the angle distribution of the emission angle is obtained by simulation using the apex angle θ ₃ as a parameter, FIG.
(b) and results as shown in FIGS. 5 (a) and 5 (b) were obtained. In the simulation, 1 ° from 0 ° to 90 ° was used.
The angle distribution of the outgoing light was calculated using the aggregate of the light rays having the incident angle i _{0 of the} step (the intensity I ₀ of each light ray is 1) as the incident light.

When θ ₃ = 100 °, the refractive index n ₃ = 1.
The outgoing angle distribution of each of the triangular layers 11 of 3, 1.4, and 1.5 is as shown in FIG. 4A, and the outgoing light intensity in that case is, as shown in FIG. In the negative direction (light source side). On the other hand, when θ ₃ = 110 °, the results are as shown in FIGS. 5A and 5B, and the intensity is shifted in the positive direction (toward the light source side) as a whole.

Basically, it is better to have strength in both positive and negative directions in a well-balanced manner. When such a vertex angle θ ₃ is obtained by simulation, the results shown in FIGS. 6A and 6B are obtained. Was done. That is, the optimum apex angle θ ₃ when n ₃ = 1.3 (hereinafter, the optimum apex angle) is 101.4 ° and the refractive index n
The optimum apex angle θ ₃ of ₃ = 1.4 is 106.1 ° and the refractive index n ₃
= 1.5, the optimum apex angle θ ₃ was 109 °. Note that the above simulation is an example, and the same calculation can be performed for another refractive index of the triangular layer 11 or even when the refractive index of the light guide layer 10 is changed.

Therefore, the apex angle of the sawtooth portion of the triangular layer 4 of the present backlight device also depends on the refractive index of the light guide layer 3 and the refractive index of the triangular layer 4 obtained by the above simulation. Is set to the optimal vertical angle. Basically, the apex angle θ ₃ is set to increase as the distance from the tubular light source 1 increases. Thus, the directivity of light emitted from the light guide 8 can be enhanced in the front direction of the liquid crystal panel without separately providing an optical sheet such as a prism sheet as in the related art.

In the manufacture of the backlight device,
The method of manufacturing the light guide portion 8 is not particularly limited, and for example, the light guide layer 3 and the triangular layer 4 having different refractive indices.
May be formed by die molding, vapor deposition or coating. Also,
The step of forming the shape of the triangular layer 4 into a saw-tooth cross section may be performed by die molding or cutting with a laser beam or the like.

As described above, in the backlight device according to the present embodiment, the light guide section 8 includes the light guide layer 3 having the function of transmitting light and the light propagated through the light guide layer 3. A transparent light guide is formed by integrally laminating a triangular layer 4 having a function of emitting light and having a sawtooth cross section on the lower surface, and the refractive index of the light guide layer 3 is larger than the refractive index of the triangular layer 4, and The refractive index of the triangular layer 4 is basically set so as to increase as the distance from the tubular light source 1 increases. Therefore, a surface light source can be formed by a single light guide without applying a diffuse reflection pattern as in the related art. As a result, problems such as poor printing and dust incorporation, such as when a diffuse reflection pattern is used, and problems such as the inability to mold the light guide and form the diffusion reflection pattern in the same process are solved. Properties can be significantly improved.

Further, by setting the apex angle of the sawtooth portion of the triangular layer 4 to the optimum apex angle, the directivity of light emitted from the light guide 8 can be enhanced in the front direction of the liquid crystal panel. It is not necessary to separately provide an expensive and difficult-to-handle prism sheet as in the related art. As a result, not only the number of parts but also the cost can be greatly reduced, and the mass productivity can be further improved.

The vertex angle of the triangular layer 4 may be constant if the directivity is not so high. Also,
The light guide section 8 does not necessarily require the diffusion sheet 5 because there is no conventional pattern pattern. Therefore, the diffusion sheet 5 changes the directivity of the emitted light obtained as described above. Therefore, if the directivity is desired to be considerably increased, it is not necessary to provide the diffusion sheet. Further, even when the diffusion sheet 5 is used, if it is arranged close to the light guide layer 3, a sufficiently strong directivity can be maintained.

Further, in the backlight device of the present embodiment, the light guide layer 3 side of the light guide section 8 is disposed so as to face the liquid crystal panel. However, as shown in FIG. It is also possible to arrange the triangular layer 4 side of the portion 8 so as to face the liquid crystal panel. The principle of light propagation at this time is the same as that described above, but the explanation is omitted. However, since the angle related to the optimal apex angle is different from the above, it is necessary to optimize according to each requirement.

Further, in the backlight device of the present embodiment, no reflecting means is provided on the lower surface side of the light guide 8, but, for example, as shown in FIG.
a and the diffuse reflection layer 7a are laminated, and as shown in FIG. 8 (b), the mirror reflection plate 6b and the diffusion reflection plate 7b are arranged, so that the light emitted to the lower surface side of the light guide unit 8 is leaked. The light is returned into the light guide section 8 again, so that the light can be effectively used, and a bright backlight device can be realized.

The specular reflection film 6a is obtained by directly depositing a substance having a high reflectance such as silver or aluminum on the lower surface of the triangular layer 4, and the specular reflection plate 6b is formed of a material having a high reflectance such as silver or aluminum. It consists of a plate-like material on which a substance is deposited.

The diffuse reflection layer 7 a is obtained by directly applying a white paint having a high reflectance (a diffuse reflection material used for forming a conventional diffuse reflection pattern) directly to the lower surface of the triangular layer 4. The diffuse reflection plate 7b is made of a white PET film or the like having a high reflectance.

At this time, the case of the specular reflection film 6a directly deposited is the same as the above simulation. On the other hand, when the specular reflector 6b is provided, the light emitted from the triangular layer 4 cannot be calculated only by the above-mentioned theoretical formula, but the light re-entering the triangular layer 4 by the specular reflector 6b is considered. Then, each parameter may be optimized.

The diffuse reflection layer 7a and the diffuse reflection plate 7b
In both cases, the diffusion phenomenon occurs, so that the light emitted from the triangular layer 4 cannot be calculated only by the above-mentioned theoretical formula. However, the chief ray can be considered in the same way as above,
After that, each parameter may be optimized in consideration of the diffused light.

The same effect can be obtained by providing such a reflection means on the lower surface side of the light guide layer 3 of the light guide section 8 in the backlight device shown in FIG.

[Second Embodiment] The following will describe another embodiment of the present invention with reference to FIGS. For convenience of explanation, the first embodiment is described.
The members having the same functions as the members indicated by are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 9A is a cross-sectional view of the backlight device according to the present embodiment, in which the upper side is the liquid crystal panel (not shown) side. FIG. 2B is a bottom view of the backlight device as viewed from the side opposite to the liquid crystal panel side. As shown in FIGS. 9A and 9B, the backlight device
The backlight device according to the first embodiment shown in FIGS. 1A and 1B is different from the backlight device according to the first embodiment only in the light guide portion 9, and the other portions have the same configuration.

In the light guide section 8 of the first embodiment, the light guide layer 3
Is higher than the refractive index of the triangular layer 4 and
Is set so as to change in a direction in which the refractive index becomes smaller as the distance from the tubular light source 1 increases within a range where the refractive index of the light guide layer 3 is smaller than the refractive index of the light guide layer 3. The incidence of light on the triangular layer 4 is increased, and the surface light source has a uniform luminance distribution. On the other hand, in the light guide section 9 of the present embodiment, the refractive index of the light guide layer 15 is set to be higher than the refractive index of the triangular layer 16, but the refractive index of the triangular layer 16 is uniform. When the angle of inclination of the interface between the light guide layer 15 and the triangular layer 16 with respect to the surface of the light guide layer 15 is defined as the positive direction, the direction inclining toward the side opposite to the liquid crystal panel is the largest on the tubular light source 1 side. It is set to change in a direction in which the distance decreases from the distance from 1. As a result, similarly to the light guide portion 8, the more light is separated from the tubular light source 1, the more chances of light entering from the light guide layer 3 to the triangular layer 4 are increased, and the surface light source has a uniform luminance distribution. The inclination angle of the interface (hereinafter, referred to as an interface inclination angle) is obtained by computer simulation.

Hereinafter, the settings of the refractive index, the interface tilt angle, and the apex angle of the triangular layer 16 of the light guide layer 15 and the triangular layer 16 in the light guide section 9 by simulation will be described.
As in the case of the first embodiment, the refractive index and the interface tilt angle of the light guide layer 15 and the triangular layer 16 depend on the incident angle and intensity of the incident light on the light guide layer 15 and the refraction of the light guide layer 15. It is determined by the output angle and the intensity of the outgoing light with respect to the incident light which is derived from the refractive index and the refractive index of the triangular layer 16, and its theoretical formula will be described.

As shown in FIG. 10, the refractive index of air n ₁ =
1, the refractive index n ₂ of the light-guiding layer 20, the refractive index n ₃ of the triangular layer 21, i ₀ the angle of incidence on the light guide layer 20 of the incident light, the intensity I
_{If 0} , the emission angle r _{4 of the} light emitted from the light guide layer 20,
Intensity I ₄ is as follows.

First, on the light incident surface 20a of the light guide layer 20, the refraction angle r ₀ , the surface reflection R ₀ , and the intensity I ₁ are calculated according to [Equation 1] and [Equation 2] shown in the first embodiment. The same is true.

Next, the interface 22 between the light guide layer 20 and the triangular layer 21
Incidence angle i _1, if the surface inclination theta ₁ and in,

[0082]

(Equation 13)

Is obtained. The refraction angle r ₁ , surface reflection R ₁ , intensity I ₂ , and total reflection angle Z ₁ are the same as those of [Equation 3], [Equation 4], and [Equation 5] described in the first embodiment. rays reflection angle Z ₁ is greater than the incident angle i ₁ is totally reflected from the interface 22 as b shown, rays of total reflection angle Z ₁ is smaller than the incidence angle i ₁ is triangular as a layer 21 Incident on.

Next, the incident angle i of the light incident on the triangular layer 21
₂ is an inclination angle of the triangular layer 21 (hereinafter, referred to as a triangular layer inclination angle).
Is θ ₂ ,

[0085]

[Equation 14]

[0086] For even total reflection angle Z ₂ here is the same as that shown in the above-mentioned first embodiment [Equation 7].

Next, the angle of incidence i _{3 at} the interface 22 between the light guide layer 20 and the triangular layer 21 again becomes

[0088]

(Equation 15)

## EQU11 ## The refractive index r ₃ , the surface reflection R ₃ , and the intensity I ₃ are as shown in the above-described first embodiment [Equation 8] and [Equation 9].
Is the same as The incident angle i _{4 on} the upper surface of the light guide layer 20 is

[0090]

(Equation 16)

Is obtained. The refraction angle r ₄ , surface reflection R ₄ , intensity I ₄ , and total reflection angle Z ₃ are the same as those in [Equation 10], [Equation 11], and [Equation 12] described in the first embodiment.

When the ratio of the light emitted from the light guide layer 20 to the light incident on the light guide layer 20 was determined by simulation based on the above theoretical formula, the result shown in FIG. 11 was obtained. . In the simulation, the refractive index n ₂ of the light guide layer 20 = 1.59 and the refractive index n _{3 of the} triangular layer 21
= 1.49, and the interface tilt angle was changed from -24 ° to 25 °.

According to FIG. 11, the ratio of the light incident on the triangular layer 21 at the interface 22 decreases as the interface tilt angle increases in the positive direction, that is, the direction away from the liquid crystal panel, and the interface tilt angle is about 18 °. Above, all the incident light is totally reflected at the interface 22 between the light guide layer 20 and the triangular layer 21, and as the angle of inclination in the negative direction increases, the ratio of light incident on the triangular layer 21 increases at the interface 22, Light emitted from the layer 20 increases.

Therefore, based on the result of this simulation, if the interfacial tilt angle between the light guide layer 20 and the triangular layer 21 is changed as a function of the position from the light source, the position of the tubular light source disposed at the end of the light guide layer 20 can be changed. , The light emitted from the light guide layer 20 can be arbitrarily changed. This means that adjustment of the luminance distribution based on the occupied area ratio of the diffuse reflection pattern object, which is performed by the conventional backlight device, can be realized by changing the interface inclination angle.

Therefore, the light guide portion 9 of the present backlight device is provided.
In the light guide layer 15 and the triangular layer 16, the refractive index of the light guide layer 15 is 1.59, the refractive index of the triangular layer 16 is 1.49,
The interface inclination angle is set so that the same emitted light intensity can be obtained at any position of the light guide 15. As a result, the light guide unit 9 becomes a surface light source having a uniform brightness distribution composed of one light guide without providing a diffuse reflection pattern on the lower surface of the light guide by printing as in the related art. I have.

On the other hand, as can be seen from the above theoretical formula, the angular distribution of the emitted light depends on the triangular layer inclination angle θ ₂ . The triangular layer inclination θ ₂ is a function of the apex angle θ ₃ ′ of the sawtooth portion, and the triangular layer inclination θ ₂ and the apex angle θ ₃ ′ are such that the greater the triangular layer inclination θ _{2, the} smaller the apex angle θ ₃ ′ In a relationship.

Therefore, when the angle distribution of the emission angle is obtained by simulation using the triangular layer inclination angle θ ₂ as a parameter, the results shown in FIGS. 12A and 13B and FIGS. 13A and 13B are obtained. Was. In the simulation, 0 °
The angle distribution of outgoing light was calculated using as an incident light a set of light rays having an incident angle i ₀ in 1 ° steps of 90 ° from each other (assuming that the intensity I ₀ of each light ray is 1).

When θ ₂ = 50 °, θ ₁ = −16 °, 0
The emission angle distribution of each of the triangular layers 21 of 16 ° and 16 ° is shown in FIG.
As shown in (a), the emitted light intensity in that case is shifted as a whole in the positive direction (opposite to the light source) as shown in FIG. On the other hand, when θ ₂ = 20 °, FIG.
(A) and (b), and the intensity is shifted in the negative direction (light source side) as a whole.

Basically, it is better to have a well-balanced strength in both the positive and negative directions. Therefore, when such a tilt angle θ ₂ of the triangular layer 21 is obtained by simulation, FIG.
The results as shown in (a) and (b) were obtained. That is, θ ₁
= -16 ° optimal triangular layer inclination angle (hereinafter, the optimum triangle layer inclination angle) theta ₂ is 21.9 °, the optimum triangle layer inclination angle of θ ₁ = 0 ° θ
₂ was 35.5 °, and the optimum triangular layer inclination θ ₂ at θ ₁ = 16 ° was 50.3 °. Note that the above simulation is an example, and the same calculation can be performed for another interface inclination angle θ ₁ or even when the refractive indexes of the light guide layer 20 and the triangular layer 21 are changed.

Accordingly, the triangular layer 16 of the present backlight device is used.
Also triangular layer inclination angle theta _2, obtained by simulation as described above, the refractive index of the light guiding layer 15, and the triangular layer 16
Refractive index of, and are set to the optimal triangular layer inclination angle in accordance with the interfacial inclination theta _1. Then, as described above, the apex angle theta ₃ 'is a function of the triangular layer inclination angle theta _2, the apex angle theta _3' in other words with respect to, basically, as separated from the tubular light source 1, the apex angle theta ₃ ' Is set to be large. Thus, the directivity of the light emitted from the light guide section 9 is enhanced in the front direction of the liquid crystal panel without separately providing an optical sheet such as a prism sheet as in the related art.

As described in the first embodiment, the vertex angle of the triangular layer 16 may be constant if the strength of the directivity is not so required. Also, in this case, if it is desired to considerably enhance the directivity, the diffusion sheet 5 need not be particularly provided.

Further, in the backlight device of the present embodiment, the light guide layer 15 side of the light guide section 9 is disposed so as to face the liquid crystal panel. Thus, as shown in FIG. 15, the triangular layer 16 side of the light guide section 9 can be arranged to face the liquid crystal panel. The propagation principle of the light beam at this time is the same as that described above, and therefore will not be described. However, since the angle-related factors such as the interface tilt angle θ ₁ and the triangular layer optimum tilt angle θ ₂ are different from those described above, it is necessary to optimize according to the respective requirements.

In the backlight device of the present embodiment, for example, as shown in FIG.
a, by arranging the diffuse reflection layer 7a or arranging the specular reflection plate 6b or the diffusion reflection plate 7b as shown in FIG. The light is returned into the light guide 9 again, and the light can be effectively used.
A bright backlight device can be realized.

Incidentally, such a reflection means is provided in the above-mentioned FIG.
In the backlight device shown in (1), the same effect can be obtained by providing the backlight device on the lower surface of the light guide layer 15 of the light guide unit 9.

[0105]

As described above, in the backlight device according to the first aspect of the present invention, the surface light source means includes the first layer for transmitting the incident light from the light source and the first layer for transmitting the incident light from the light source. Laminated, the surface opposite to the lamination surface was formed in a sawtooth cross section,
A transparent light guide integrally formed with a second layer for emitting light to be propagated from the first layer, wherein the refractive index of the first layer is larger than the refractive index of the second layer; In addition, the refractive index of the second layer is set to change in a direction to increase as the distance from the light source increases.

As a result, the luminance distribution can be controlled by the refractive indexes of the first and second layers constituting the surface light source means, and a surface light source can be formed without applying a diffuse reflection pattern as in the conventional case. Therefore, it is possible to solve the conventional problems such as the above-described printing failure and mixing of dust, molding of the light guide and formation of the diffuse reflection pattern in the same process, and provide a backlight device excellent in mass productivity. This has the effect.

[0107] In the backlight device according to the second aspect of the present invention, the surface light source means is laminated on the first layer for transmitting the incident light from the light source and the first layer. Propagated light having a sawtooth cross-section on the opposite side
A transparent light guide integrally formed with a second layer for emitting light from the first layer, wherein the refractive index of the first layer is greater than the refractive index of the second layer, and The angle of inclination of the interface between the first layer and the surface of the first layer with respect to the surface of the first layer is largest on the light source side, and becomes smaller as the distance from the light source increases, assuming that the direction inclining toward the opposite side to the display panel is the positive direction. The configuration is set to change.

As a result, the luminance distribution can be controlled by the refractive index of the first layer and the second layer constituting the surface light source means and the interface tilt angle, and the surface light source can be formed without applying a diffuse reflection pattern as in the conventional case. This makes it possible to solve the conventional problems such as poor printing and mixing of dust as described above, and the inability to mold the light guide and form the diffuse reflection pattern in the same process. This has the effect that the device can be provided.

According to a third aspect of the present invention, in the backlight device according to the first or second aspect, the light emitted from the surface light source means is applied to the surface of the surface light source means opposite to the display panel. In this configuration, reflection means for re-entering the surface light source means is provided.

Thus, the leaked light emitted to the surface light source means on the side opposite to the display panel can be re-incident on the surface light source means, so that the light can be used effectively. In addition to the effect of the configuration, an effect of realizing a bright backlight device is also achieved.

In the backlight device according to a fourth aspect of the present invention, in the configuration of the first, second or third aspect, the second layer in the surface light source means is so large that the apex angle of the sawtooth portion is farther from the light source. It is a configuration that is formed so that

As a result, the directivity of the emitted light can be enhanced in the front direction of the display panel without separately providing an expensive and difficult-to-handle optical sheet as in the related art. By controlling even the directivity of the emitted light with a smaller number of constituent members than in the configuration of the third embodiment, it is possible to provide a backlight device with more excellent mass productivity.

[Brief description of the drawings]

FIGS. 1A and 1B show a configuration of a backlight device according to an embodiment of the present invention, in which FIG. 1A is a cross-sectional view and FIG.

FIG. 2 is a diagram illustrating the principle of ray tracing in a light guide unit of the same type when mounted on the backlight device.

FIG. 3 is an explanatory diagram showing a simulation result of an emission light intensity ratio used for designing a light guide section mounted on the backlight device.

FIG. 4 is an explanatory diagram showing a simulation result of an emitted light angle distribution used for designing a light guide portion mounted on the backlight device.

FIG. 5 is an explanatory diagram showing a simulation result of an emitted light angle distribution used for designing a light guide section mounted on the backlight device.

FIG. 6 is an explanatory diagram showing a simulation result of an emitted light angle distribution used for designing a light guide section mounted on the backlight device.

FIG. 7 is a cross-sectional view illustrating a configuration of a backlight device according to another embodiment of the present invention.

FIGS. 8A and 8B are cross-sectional views each showing a configuration of a backlight device according to another embodiment of the present invention.

9A and 9B show a configuration of a backlight device according to another embodiment of the present invention, wherein FIG. 9A is a sectional view and FIG. 9B is a bottom view thereof.

FIG. 10 is a principle diagram of ray tracing in a light guide unit of the same type when mounted on the backlight device.

FIG. 11 is an explanatory diagram showing a simulation result of an output light intensity ratio used for designing a light guide section mounted on the backlight device.

FIG. 12 is an explanatory diagram showing a simulation result of an emitted light angle distribution used for designing a light guide portion mounted on the backlight device.

FIG. 13 is an explanatory diagram showing a simulation result of an emitted light angle distribution used for designing a light guide section mounted on the backlight device.

FIG. 14 is an explanatory diagram showing a simulation result of an emitted light angle distribution used for designing a light guide portion mounted on the backlight device.

FIG. 15 is a cross-sectional view illustrating a configuration of a backlight device according to another embodiment of the present invention.

16 (a) and (b) are cross-sectional views each showing a configuration of a backlight device according to another embodiment of the present invention.

17A is a bottom view of a conventional two-light type backlight device, and FIG. 17B is a cross-sectional view thereof.

FIG. 18 is an explanatory view showing a diffuse reflection pattern object in a dot shape of a conventional two-light type backlight device.

[Explanation of symbols]

 Reference Signs List 1 tubular light source 2 reflector 3 light guide layer (first layer) 4 triangular layer (second layer) 5 diffusion sheet 6a mirror reflection film (reflection means) 6b mirror reflection plate (reflection means) 7a diffusion reflection layer (reflection) Means 7b Diffuse reflector (reflection means) 8 Light guide (surface light source) 9 Light guide (surface light source) 15 Light guide layer (first layer) 16 Triangular layer (second layer)

[Procedure amendment]

[Submission date] July 25, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0098

[Correction method] Change

[Correction contents]

When θ ₂ = 20 °, θ ₁ = −16 °, 0
The emission angle distribution of each of the triangular layers 21 of 16 ° and 16 ° is shown in FIG.
As shown in (a), the emitted light intensity in that case is shifted as a whole in the positive direction (opposite to the light source) as shown in FIG. On the other hand, when θ ₂ = 50 °, FIG.
(A) and (b), and the intensity is shifted in the negative direction (light source side) as a whole.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] FIG.

[Correction method] Change

[Correction contents]

FIG. 14

Claims (4)

[Claims] 1. A display device, comprising: a display panel;
In a backlight device provided with a linear light source and a reflection plate for reflecting light from the light source to the surface light source unit at least at one end of the surface light source unit for reflecting and diffusing, the surface light source unit is a light source A first layer for transmitting incident light from the first layer, and a first layer for transmitting the light, which is laminated on the first layer and whose surface opposite to the lamination surface is formed in a sawtooth cross section.
A transparent light guide integrally formed with a second layer for emitting light from the second layer, wherein the refractive index of the first layer is larger than the refractive index of the second layer, and A backlight device characterized in that the refractive index is set to change in a direction that increases as the distance from the light source increases. 2. A light source, which is disposed on the back side of the display panel and propagates light.
In a backlight device provided with a linear light source and a reflection plate for reflecting light from the light source to the surface light source unit at least at one end of the surface light source unit for reflecting and diffusing, the surface light source unit is a light source A first layer for transmitting incident light from the first layer, and a first layer for transmitting the light, which is laminated on the first layer and whose surface opposite to the lamination surface is formed in a sawtooth cross section.
A transparent light guide integrally formed with a second layer for emitting light from the first layer, wherein the refractive index of the first layer is greater than the refractive index of the second layer, and The angle of inclination of the interface between the first layer and the surface of the first layer with respect to the surface of the first layer is largest on the light source side, and becomes smaller as the distance from the light source increases, assuming that the direction inclining toward the opposite side to the display panel is the positive direction. A backlight device that is set to change. 3. The surface light source means further comprising a reflection means on the surface of the surface light source means opposite to the display panel, for reflecting light emitted from the surface light source means back into the surface light source means. Item 3. The backlight device according to item 1 or 2. 4. The back according to claim 1, wherein the second layer in the surface light source means is formed such that the vertex angle of the sawtooth portion increases as the distance from the light source increases. Light device.