JPH11345513A - Backlight device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlihgt device which concentrates light in the front direction. SOLUTION: A backlight device installed on the back of a liquid crystal plate to illuminate the liquid crystal plate includes a transparent light guide plate 20, a light source 2 placed near the side face of the light guide plate, a planar light reflector 3 provide along the lower surface of the light guide plate, and a transparent direction changing filter 10 provided along the upper surface of the light guide plate and located on the back of the liquid crystal plate. The light guide plate 20 has a lower surface shaped like triangular-cross-section mountains arranged in parallel, the apex angle of each of the triangular-cross-section mountains ranging from 30 deg. to 87 deg. on the light source side γ with respect to the vertical of the upper surface of the light guide plate and ranging from 75 deg. to 87 deg. on the side δ far from the light source. The upper surface of each of the mountains is smooth. The direction changing filter 10 has a lower surface 12 on which light impinges and an upper surface 14 from which light is emitted, the lower surface being shaped like triangular-cross-section prisms arranged in parallel, with the light source side apex angle αof each prism ranging from 0 deg. to 20 deg.. The apex angle βof the side of each prism far from the light source ranges from 32 deg. to 38 deg. and the upper surface is formed of either a flat surface or lenticular lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for liquid crystal, a light guide plate and a direction change filter used in the backlight device.

[0002]

2. Description of the Related Art A backlight device for a liquid crystal is roughly classified into an edge type and a direct type according to the arrangement of a light source on a liquid crystal display surface. In the edge type, a lamp approximated by a line light source is placed on the side of the display surface, light is guided to the back side of the display surface through a transparent light guide, and a reflector and a diffuser are combined, This is a method for making the luminance uniform. The edge type backlight device generally has a merit that it can be made thinner and can reduce the influence of heat generated by a lamp, and is widely used as a backlight for liquid crystal, but has a problem that light use efficiency is low.

A light guide plate used in a conventional backlight device is formed by printing an ink containing a filler in a dot-like manner on a lower surface by screen printing so as to scatter light.
There is a combination with a reflection plate. In general, a diffusion plate is disposed on a light guide plate, and a prism sheet having a prism having a triangular cross section is disposed thereon for use. In such a configuration, the light diffused by the diffusion plate and emitted is changed in direction by the prism sheet and emitted.

[0004] In such a backlight device,
Until now, light was not well controlled. That is, the way light travels in each component of the backlight device has not been sufficiently studied. In particular, studies on controlling the direction of light emission by combining a light guide plate and a prism sheet have been insufficient. Further, such a backlight device has a disadvantage that the number of components is large. There is a case where it is desired to concentrate light in a certain direction depending on the use purpose of the backlight device. For example, a backlight device used for a liquid crystal color television is required to emit light concentrated in a certain direction.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thin backlight device which enhances light use efficiency and concentrates light in the front direction. Another object of the present invention is to reduce the number of components of the backlight device. Also,
An object of the present invention is to provide a direction change filter and a light guide plate used in such a backlight device.

[0006]

It is considered that how light travels in the components of such a backlight device depends on the cross-sectional shape of the light guide plate, the apex angle of the prism of the prism sheet, the refractive index, and the like. The present inventor has proposed a backlight device arranged on the back surface of a liquid crystal plate for illuminating a liquid crystal, wherein a cross section having a triangular cross section is provided on the lower surface of the light guide plate, and the turning filter disposed on the light guide plate has a triangular cross section. It has been found that by providing the prism, light is concentrated and emitted in the front direction of the backlight device. In the backlight device of the present invention, the diffusion plate used conventionally is unnecessary.

According to the present invention, there is provided a backlight device disposed on a back surface of a liquid crystal plate for illuminating the liquid crystal plate, a transparent light guide plate, a light source disposed near a side surface of the light guide plate, and a light source disposed on a lower surface of the light guide plate. A planar light reflector provided along the
A transparent direction change filter provided along an upper surface of the light guide plate and disposed on a back surface of the liquid crystal. The light guide plate is provided with a mountain having a triangular cross section on the lower surface, and the apex angle of the mountain is a light source side γ with respect to a perpendicular to the upper surface of the light guide plate.
Is in the range of 40 ° to 85 °, and the side δ far from the light source is in the range of 75 ° to 87 °. The upper surface of the light guide plate is smooth. The lower surface where the light of the direction change filter is incident is a shape in which prisms having a triangular cross section are arranged in parallel, and the apex angle of the prism is 0 ° with respect to the vertical line from the upper surface of the direction change filter. 20 °, and the side β far from the light source ranges from 32 ° to 38 °.

[0008] In the present invention, the interval between the triangular ridges formed on the lower surface of the light guide plate is so small as to be invisible to the naked eye.
Preferably it is in the range of 0.02 mm to 0.5 mm. 0.02mm
The smaller the size, the greater the effect of diffraction, and if it exceeds 0.5 mm, the mountain becomes visible to the naked eye. In the present invention, the thickness of the direction change filter is 0.1 mm.
To 0.5 mm. The distance between adjacent prisms formed on the lower surface of the direction change filter is
It is preferably small enough to be invisible to the naked eye, ie in the range of 0.02 mm to 0.5 mm.

In the present invention, "transparent" means that it is transparent to the extent that it can be used as a light guide. The material of the light guide plate and the direction change filter is preferably a highly transparent material such as an acrylic copolymer.

In the present invention, how the light travels by the triangular cross section formed on the lower surface of the light guide plate and the prisms having different apex angles on the left and right on the lower surface of the direction change filter will be examined. Light that exits the light source and enters the light guide plate from its end surface is considered to travel through the light guide plate by repeating total internal reflection on the upper and lower surfaces of the light guide plate. However, a triangular peak is provided on the lower surface of the light guide plate. In the case where the surface farther from the light source of the mountain is at a small angle with respect to the lower surface of the light guide plate, when the light is totally reflected by the lower surface, the incident angle when the light is next incident on the upper surface becomes smaller than the previous incident angle, It is emitted from the upper surface when the angle of incidence falls below the critical angle. As a result, it is considered that the light is radiated from the upper surface of the light guide plate at a relatively small angle with respect to the upper surface of the light guide plate. This will be described later with reference to FIGS.

Light emitted from the upper surface of the light guide plate at a relatively small angle enters a direction change filter provided on the light guide plate from the lower surface thereof. Here, if the cross section of the prism having a triangular cross section on the lower surface of the direction change filter is not an isosceles triangle, the vertex angle α on the light source side is a relatively small angle, and the vertex angle β on the far side from the light source is an angle larger than α. The light emitted from the upper surface of the light guide plate at a relatively small angle enters the lower surface of the direction change filter from the slope closer to the light source of the prism. Here, the vertex angle of the prism refers to the angle formed by one slope of the prism with respect to the upper surface of the direction change filter. Of the incident light, the percentage of light that enters the upper surface at an angle greater than the critical angle and is totally reflected is small, and the angle that is totally reflected on the surface farther from the light source of the lower prism and is smaller than the critical angle is formed on the upper surface. And the ratio of light incident from the upper surface and emitted from the upper surface is large. The direction change filter has a function of changing the direction of light incident obliquely to the front direction and emitting the light. This will be described later with reference to FIG.

The light totally reflected on the upper surface of the directional change filter is totally reflected again by the prism on the lower surface and finally comes out from the upper surface. Considering the utilization efficiency, it is preferable that the light exits from the upper surface without being totally reflected. In another aspect of the present invention, the inclination of the prism of the direction change filter is different between a portion near the vertex and a portion far from the vertex. In another aspect of the invention, the top surface of the turning filter is a lenticular lens rather than a plane. The size of the lens is from 0.01mm x 0.01mm to 0.
The range is 2 mm x 0.2 mm. In this case, the angle at which light is emitted is wider than in the case of a plane. By changing the curvature of the lenticular lens, the angle at which the light spreads can be adjusted.

The peak angle of the mountain having a triangular cross section on the lower surface of the light guide plate is set so that the light source side γ is in the range of 40 ° to 85 °. The preferable range of γ is 40 ° to 60 °. When γ is close to 0 °, light is reflected on the light source side surface of the mountain having a triangular cross section, and there is a problem in manufacturing. On the other hand, if γ is too large, the area of the surface far from the light source of the mountain having a triangular cross section cannot be increased, which is not preferable. This is because the surface far from the light source acts to change the angle of the light. Light that travels through the light guide plate and is totally reflected on the upper surface of the light guide plate has an inclination of 48
° or less. Therefore, if γ is smaller than 40 °, the light totally reflected on the upper surface of the light guide plate does not enter the surface near the light source of the mountain having a triangular cross section, but enters the surface far from the light source and is totally reflected. Then, the angle with respect to the upper surface of the light guide plate when the light enters the upper surface next changes. The vertex angle δ on the side remote from the light source was in the range of 75 ° to 87 °. The preferred range of δ is in the range of 80 ° to 86 °. If δ is smaller than 75 °, the range of the emission direction of light emitted from the upper surface is widened, and the effect of concentrating light is weakened. If δ is larger than 87 °, the degree of change in the traveling direction of light is reduced, the rate of light exiting from the upper surface is reduced, the distance that light passes through the light guide plate is increased, and the light is attenuated.

The apex angle α of the prism on the lower surface of the direction change filter near the light source was in the range of 0 ° to 20 °.
The smaller the apex angle α is, the more the light incident from the surface closer to the light source of the prism is made to be more totally reflected on the surface farther from the light source and exits from the upper surface, and the effective ratio of light is increased. , Since a certain angle is required in manufacturing,
° to 20 °. The vertex angle β farther from the light source is
The range was from 32 ° to 38 °. Consider a case in which light emitted from the light guide plate at an angle of 20 ° to 40 ° with respect to its upper surface is incident on the direction change filter. When the vertex angle β is larger than 38 °, the emitted light is not sufficiently directed in the front direction. When the apex angle β is smaller than 32 °, the angle of the light with respect to the upper surface after the light is totally reflected by the surface far from the light source of the prism may exceed 90 °, and there is a problem in manufacturing.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments and examples of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a backlight device according to an embodiment of the present invention, and FIG. 2 is an end side view of the backlight device shown in FIG. 1 along the line II-II. As shown in FIG. 1 and FIG.
A transparent flat light guide plate 20, a light source 2 disposed near one side surface of the light guide plate 20, a flat light reflection plate 3 provided along the lower surface of the light guide plate 20, and a light guide plate 20 Is provided with a transparent diverting filter 10 provided along the upper surface of the filter. The liquid crystal plate 6 is disposed on the direction change filter 10. A bent portion 3a is provided on the side of the light source so that a part of the light reflecting plate 3 is bent so as to surround the light source 2, and the light emitted from the light source 2 is reflected on the light guide plate 20 as much as possible. It has become.

According to the backlight device of the present invention, light incident on the light guide plate 20 from the end face from the light source 2 exits from the upper surface of the light guide plate 20 at a small angle with respect to the upper surface. You can change the direction to the front,
The radiation is concentrated in the front direction.

FIG. 3 is a sectional view of the light guide plate 20 in the YZ plane of FIG. A mountain 22 having a triangular cross section is provided on the lower surface of the light guide plate.
Are formed in parallel, and a mountain having a triangular cross section has a surface 26 closer to the light source and a surface 28 farther from the light source. The upper surface 24 of the light guide plate is flat. With respect to the apex angle of this triangular mountain, the apex angle γ on the light source side with respect to a perpendicular from the upper surface of the light guide plate was 50 °, and the apex angle δ on the far side from the light source was 84 °.

FIG. 4 is a sectional view of the direction change filter 10 in the YZ plane of FIG. As shown in FIG. 4, the direction change filter 10 of the present embodiment has a lower surface in which prisms 12 having a triangular cross section are arranged in parallel. The prism has a surface 16 near the light source and a surface 18 far from the light source.
There is. The upper surface 14 of the direction change filter 10 is flat. The vertex angle α on the light source side of the prism was 10 °, and the vertex angle β on the far side from the light source was 36 °. The interval (pitch p) between the prisms formed on the lower surface 12 is about 50 μ. The thickness t of the direction change filter 10 was about 200 μ.

Next, how the light travels inside the light guide plate of the present invention and the direction change filter will be examined. Fig. 5-
FIG. 7 shows how light incident on the light guide plate in three different directions travels through the light guide plate. The angle of the light guide plate with respect to the perpendicular from the upper surface of the light guide plate of the triangular mountain is 50 ° on the light source side γ and 84 ° on the far side δ from the light source. The light guide plate is made of PMMA, and has a refractive index of 1.494. In this case, the critical angle is about 42 °.

In FIG. 5, light L1 entering the light guide plate from the light source on the left side of the light guide plate and traveling in the light guide plate at 40 ° with respect to the upper surface of the light guide plate is incident on the upper surface of the light guide plate at an incident angle of 50 °. Then, the light is totally reflected on the upper surface and travels toward the lower surface. Total reflection at the bottom,
The light is again incident on the upper surface at an incident angle of 38 ° smaller than the first incident angle. Since this angle is below the critical angle, the angle of refraction from the top
Emitted at 66.9 °.

In FIG. 6, light L2 traveling in the light guide plate at 35 ° with respect to the upper surface of the light guide plate is incident on the upper surface of the light guide plate at an incident angle of 55 °, is totally reflected, and travels toward the lower surface. The light enters the lower surface at an incident angle of 49 ° and is totally reflected.
The light is incident at an angle of ° and is totally reflected, then enters the lower surface at an incident angle of 37 °, and is emitted from the lower surface at a refraction angle of 64 °. This light is incident on the underlying reflector at an incident angle of 70 °. It is assumed that the light is reflected by the reflector at the same angle. Then, the surface 2 far from the light source
The light L2a incident on the light 8 enters the surface 28 at an incident angle of 76 °, is refracted at a refraction angle of 40.5 °, and enters the light guide plate. Re-enters the upper surface of the light guide plate at an incident angle of 34.5 ° and refracts 57.8 ° from the upper surface
Radiated at Light L2b reflected at the same angle by the reflector and incident on the surface 26 on the side closer to the light source is incident on the surface 26 at an incident angle of 30.
And enters the light guide plate after being refracted at a refraction angle of 19.6 °. The light enters the upper surface of the light guide plate at an incident angle of 59.6 ° and is totally reflected. However, the area of the surface 26 near the light source is small, and the proportion of the light L2b incident on this surface is small.

In FIG. 7, light L3 traveling in the light guide plate at an angle of 25 ° with respect to the upper surface of the light guide plate is incident on the upper surface of the light guide plate at an incident angle of 65 °, is totally reflected, and travels toward the lower surface. The light enters the lower surface at an incident angle of 47 °, is totally reflected, and is again incident at an incident angle
Incident at °. Totally reflected on the upper surface and again incident angle 47 on the lower surface
Incident at ° and totally reflected. And the incident angle 41 ° on the upper surface
And emitted at a refraction angle of 78.6 °. As shown in FIG. 5-7, light traveling in the light guide plate repeats total reflection and refraction, and the angle of incidence on the upper surface of the light guide plate gradually decreases. When the incident angle becomes smaller than the critical angle, the light guide plate Radiated from the top surface at a relatively small angle to the top surface.

Next, how the light emitted from the upper surface of the light guide plate 20 travels when the light enters the direction change filter 10 from the lower surface will be discussed. In the direction change filter 10 shown in FIG. 8, the apex angle of the prism on the lower surface of the direction change filter 10 is 10 ° on the light source side α and 36 ° on the side β far from the light source with respect to the perpendicular from the upper surface of the direction change filter. . The light emitted from the upper surface of the light guide plate 20 enters the direction change filter 10 from the lower surface. Here, looking at the progress of light incident at 40 ° to the upper surface of the turning filter, the light L4 passing through the peak 17 of one peak of the prism is refracted by the surface 16 close to the light source and is reflected by the turning filter. It faces the upper surface, enters the upper surface at an angle larger than the critical angle, and is totally reflected. Another light L5 is also surface 1
The light is refracted at 6 and travels through the troughs 19 of the prism to the upper surface of the turning filter and is totally reflected at the upper surface. Another light L6
Is refracted at the prism face 16 and totally reflected at the face 18 far from the light source of the prism, is directed toward the upper surface of the diverting filter, is incident on the upper surface 14 at an angle smaller than the critical angle, and is refracted and emitted. .

Range of one prism pitch A + B from light passing through one vertex 17 of the prism to light passing through the next peak
Of the prism L from the light L4 passing through the vertex 17
Light incident in the range B up to the light L5 passing through 9 does not enter the surface 18, but enters the upper surface at an angle larger than the critical angle, is totally reflected, and does not exit the upper surface. Light incident in a range A from light L5 to light passing through the next vertex is incident on the surface 18 at an angle greater than the critical angle, is totally reflected, and then impinges on the upper surface of the diverting filter at an angle less than the critical angle. And is emitted from the top surface of the diverting filter at a relatively small angle to the normal of the diverting filter. That is, of the range A + B, the range A is effectively used, but the range B is not effectively used. Here, assuming that the effective ratio F of light is F = A / (A + B) × 100 (%), for light incident at 40 ° on the upper surface of the direction change filter, F = 21.38 / 26.40 × 100 = 81 (%).

FIG. 9 shows the progress of light when light is incident on the upper surface of the prism sheet at 40 ° similarly to the conventional prism sheet 5. The apex angle of the prism is 31.5 ° both on the light source side and on the side far from the light source. As in FIG. 8, the light in the range A from the light L8 to the light passing through the next vertex is totally reflected by the surface 18 and then radiated from the upper surface to be used effectively. Light in the range B from the light L7 to the light L8 is totally reflected on the upper surface and is not used effectively. When the effective ratio F is obtained for the light incident at 40 ° with respect to the upper surface, F = 14.61 / 27.17 × 100 = 53.8 (%). It can be seen that the effective ratio of light of the conventional prism sheet 5 is lower than that of the direction change filter of the present invention.

The upper direction change filter 10 (vertical angle α = 1)
0 °, β = 36 °) and the conventional prism sheet 5 (vertical angle α = 31.5 °, β = 31.5 °), in the range of 30 ° to 50 ° with respect to the upper surface of the diverting filter (or prism sheet). Regarding the case where light enters, similarly to the light incident at 40 °, the light in the range A is totally reflected on the surface 18 and then emitted from the upper surface to be used effectively, while the light in the range B is used effectively. , And are not used effectively because they are totally reflected on the upper surface.

Effective fraction F of light in the range of 30 ° to 50 °
Are shown in Table 1. Table 1 Effective ratio of light F (%) Incident angle of light Redirecting filter Prism sheet α = 10 ° β = 36 ° (conventional) 30 ° 100% 100% 35 ° 100% 86.5% 42.5 ° 71.3% 47.1% 50 ° 48.1% 30.8% According to Table 1, the ratio of the light incident in the range of 30 ° to 50 ° in the redirecting filter of the present invention is smaller than the ratio of the total reflection on the upper surface compared to the conventional prism sheet, and the effective ratio of light It can be seen that F is large. The smaller the apex angle α is, the more light that is incident from the surface closer to the light source of the prism is more fully reflected on the surface farther from the light source and exits from the upper surface. I understand.

Next, according to FIG. 10, the apex angle α of the prism =
A 5 °, β = 36 ° turning filter and a prism apex angle α = 20 °, β = 32 ° turning filter provide light at an angle of 20 ° to 40 ° with respect to the plane of the filter, The angle after the light enters the surface 16 on the side closer to the light source of the prism and is totally reflected by the surface 18 on the side farther from the light source will be described. In FIG. 10, the angle of light is represented by an angle with respect to the upper surface of the direction change filter (the Y direction in FIGS. 1 and 2 is assumed to be 0 °). It can be seen that the light incident in the angle range of 20 ° to 40 ° is incident on the upper surface of the redirecting filter at an angle close to vertical (90 °). Light incident on the upper surface is refracted by the upper surface, changes its angle in the vertical direction, and exits substantially in the front direction. Assuming that the apex angle α is in the range of 0 ° to 20 °, if β is in the range of 32 ° to 38 °, it can be understood that light is radiated almost concentrated in the frontal direction. The range of the vertex angle β was determined with reference to this result.

Next, the luminance characteristics of the backlight device according to the embodiment of the present invention and the backlight device using the conventional prism sheet were measured. As shown in FIG. 2, a luminance meter 70 for the backlight device is used.
The relationship between the tilt angle and the luminance was measured by changing the tilt angle of the backlight device in the YZ plane of the backlight device.
Shown in Here, the horizontal axis in FIGS. 11 and 12 indicates the direction in the ZY plane in FIG. 1, where the Y direction is 0 ° and the angle θ with respect to the Y direction (the counterclockwise direction in FIG. 2 is +). , The same applies hereinafter).

The solid line in FIG. 11 shows the relationship between the direction of light radiated from the upper surface of the light guide plate and the luminance when the direction change filter is removed from the backlight device of the embodiment of the present invention shown in FIG. The solid line C1 indicates the case where the peak angles of the triangular peaks of the light guide plate are γ = 51 ° and δ = 84 °. It can be seen that the light is radiated from the upper surface of the light guide plate in a small angle range of about 10 ° to 40 °. C2 is γ = 51
°, δ = 86.5 °. The light concentration of C2 is lower than that of C1. The dotted line C3 indicates that γ = 0 °,
This is the case when δ = 80 °. It can be seen that when δ is reduced to 80 °, the light is emitted with considerable dispersion.

A dotted line C4 in FIG. 11 shows a luminance characteristic of light emitted from the upper surface of the light guide plate in a backlight device using a conventional light guide plate having dots printed on the back surface for reflection. The emitted light is not concentrated in a narrow direction but is dispersed over a wide angle range. It can be seen from FIG. 11 that the light guide plate of the present invention emits light more concentratedly in a range having a smaller angle with respect to the upper surface of the light guide plate than the conventional light guide plate. Light is dispersed and emitted regardless of whether δ is large or small. In order to emit concentrated light from the directional change filter, it is more convenient for the light to be emitted from the light guide plate in a concentrated manner. The range of the vertex angle δ was determined with reference to this result.

Next, the luminance characteristics of light emitted from the upper surface of the direction change filter were measured. The solid line D1 in FIG.
In the backlight device of the present invention, a luminance characteristic of light emitted from the upper surface of the direction change filter when the direction change filter is mounted on the light guide plate is shown. The light emitted from the top surface of the turning filter is 65 ° to 11 °.
It can be seen that they are concentrated in the range of 5 °. Fig. 13 (a)
FIG. 4 is a cross-sectional view of a direction change filter 50 according to a second embodiment of the present invention. (b) is a plan view of a part of the direction change filter 50. The upper surface 52 of the direction change filter 50 is
It is a lenticular lens of mm x 0.1 mm.

A dashed line D 2 in FIG. 12 represents a lenticular lens on the upper surface in place of the direction changing filter 10.
9 shows luminance characteristics of the second embodiment using the zero direction change filter 50. It can be seen that the light radiated from the upper surface of the direction change filter 50 is spread more than when the upper surface is flat. A dotted line D3 in FIG. 12 indicates a backlight device using a conventional light guide plate instead of the light guide plate 20 of the present invention, and using the conventional prism sheet 5 shown in FIG. 4 shows luminance characteristics of light emitted from the upper surface of the prism sheet 5. The emitted light is less intense than that of the present invention and is spread over a wider range.

FIG. 14 shows a cross section of a prism portion of a directional change filter according to a third embodiment of the present invention. In the third embodiment,
The inclination of the cross section of the prism of the direction change filter 40 on the side close to the light source is defined by a portion 42 near the vertex and a portion 44 farther from the vertex.
And has changed. The apex angle α1 was 20 °, α2 was 3 °, and β was 36 °. The flat portion 4 is located at the valley portion of the prism.
6 were provided. When the prism is formed in such a shape, damage to the ridge portion of the prism can be prevented, and manufacturing can be facilitated. In the third embodiment, each side of the cross section of the prism of the direction change filter 10 is formed by a straight line. However, a ridge line at the vertex of the prism may be rounded with a radius r. In this case, the radius r or the height of the chamfer is preferably not more than ４ of the height of the prism so as not to impair the function of converging light in the front direction of the direction change filter.

FIGS. 15A and 15B are an end view (a) and a plan view (b) of the light guide plate according to the fourth embodiment in the YZ plane. Light guide plate 60
As can be seen from the end view, the thickness of the light guide plate decreases from the side closer to the light source (left side in the figure) to the side farther (right side in the figure). As can be seen from the plan view (b) of the light guide plate 60, the peaks having a triangular cross section formed on the back surface of the light guide plate are:
It is formed not on the entire back surface of the light guide plate but on a part thereof.
In this pattern, the area ratio of the portion 64 where no hill is formed on the side closer to the light source is large, and the area ratio of the portion 62 where the hill is formed increases as the distance from the light source increases. The reason why the triangular peaks are formed in such a pattern is to reduce the difference in light intensity between a position far from the light source and a position near the light source. That is, the light becomes weaker as the distance from the light source increases in the light guide plate, but the farther the light is from the light source, the greater the rate of light emission and the more uniform the light intensity. FIG.
Is a fifth example in which a portion where a mountain is not formed in a circular pattern is provided. The area ratio of a portion 68 where a mountain is not formed near the light source is large, and the area ratio of a portion 66 where a mountain is formed as the distance from the light source is increased. Is getting bigger.

FIG. 17 shows a sixth embodiment of the light guide plate. The ridges are formed not in the ridge parallel to the X direction but in two directions inclined from the X direction. FIG. 18 (a) shows an enlarged view of a part of the mountain pattern at 18a in FIG. 17, and bb 'in FIG. 18 (a).
A cross-sectional view is shown in FIG. The function of the present invention can also be achieved with the mountain shape shown in FIG.

Here, a method of manufacturing the light guide plate and the direction change filter will be described. The light guide plate can be formed by a conventional method such as injection molding and compression molding. The direction change filter is formed by injecting an ultraviolet curable resin composition into a metal mold, superimposing a transparent substrate such as a PET film, irradiating ultraviolet light from an ultraviolet light source such as a high-pressure mercury lamp through the transparent substrate, and polymerizing. The direction change filter can be obtained by peeling from the mold. Known resins such as ester (meth) acrylate-based resins, epoxy (meth) acrylate-based resins, and urethane acrylate-based resins can be used as the ultraviolet-curable resin. If necessary, additives such as an antioxidant, an ultraviolet absorber, and a yellowing inhibitor can be added to the ultraviolet-curable resin.

In the manufacture of the direction change filter, instead of using a liquid ultraviolet curing resin as described above,
Using a laminate of a transparent substrate and a semi-polymerized UV-curable resin composition, irradiating ultraviolet rays while pressing the laminate against a mold to cure the semi-polymerized resin composition and change direction. You can also get a filter. The diverting filter can also be molded in one piece. That is,
A prism can be formed by pressing a mold onto a resin such as an acrylic copolymer and transferring the pattern. Further, the prism can be formed by injection molding.

[0039]

As described above, according to the backlight device of the present invention, light is concentrated in the front direction with a small number of parts, light utilization efficiency is greatly improved, and high brightness is obtained in the front direction. Can be obtained. Therefore, an effect is obtained that the liquid crystal panel is bright and easy to see with limited power consumption. Further, when the backlight device of the present invention is used, the direction of the light transmitted through the liquid crystal plate is uniform, and the amount of light transmitted particularly in the oblique direction is small, so that the reflection on the lower surface of the liquid crystal plate is reduced,
The effect is obtained that the influence of the liquid crystal on the adjacent elements is reduced, and the sharpness of the image is improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a backlight device using a light guide plate and a direction change filter 10 according to an embodiment of the present invention.

FIG. 2 is an end side view of the backlight device of FIG. 1 taken along the line II-II.

FIG. 3 is an enlarged sectional view of the light guide plate according to the embodiment of the present invention.

FIG. 4 is an enlarged cross-sectional view of the direction change filter according to the embodiment of the present invention.

FIG. 5 is a diagram showing the progress of light in a light guide plate according to an embodiment of the present invention.

FIG. 6 is a diagram showing the progress of light in a light guide plate according to an embodiment of the present invention.

FIG. 7 is a diagram showing the progress of light in a light guide plate according to an example of the present invention.

FIG. 8 is a diagram showing the progress of light in a turning filter according to an embodiment of the present invention.

FIG. 9 is a diagram showing the progress of light in a conventional prism sheet.

FIG. 10 is a diagram showing the progress of light in a turning filter according to an embodiment of the present invention.

FIG. 11 shows luminance characteristics of light emitted from the upper surface of the light guide plate according to the embodiment of the present invention.

FIG. 12 shows a luminance characteristic of a backlight device using the light guide plate and the direction change filter 10 according to the embodiment of the present invention.

FIG. 13 is an enlarged cross-sectional view of the direction change filter according to the second embodiment of the present invention.

FIG. 14 is an enlarged cross-sectional view of a direction change filter according to a third embodiment of the present invention.

FIG. 15 is a diagram illustrating a light guide plate according to a fourth embodiment of the present invention.

FIG. 16 is a diagram illustrating a light guide plate according to a fifth embodiment of the present invention.

FIG. 17 is a diagram illustrating a light guide plate according to a sixth embodiment of the present invention.

18 is an enlarged view and a cross-sectional view of a part of FIG.

[Explanation of symbols]

 2. Light source 3. Reflecting plate 4. Diffusion plate 5. Prism sheet (conventional) 6. Liquid crystal plate 10. Direction filter 12. Prism 14. Top surface 16. Surface close to light source 18. Surface far from the light source 20 Light guide plate 26 Surface close to the light source 28 Surface far from the light source 40, 50 Direction filter 60 Light guide plate 70 Luminance meter

Claims (8)

[Claims] 1. A backlight device disposed on a back surface of a liquid crystal plate and illuminating the liquid crystal plate, comprising: a transparent light guide plate, a light source disposed near a side surface of the light guide plate, and a lower surface of the light guide plate. The planar light reflection plate provided, comprising a transparent direction change filter provided along the upper surface of the light guide plate and disposed to be located on the back of the liquid crystal plate, the light guide plate, At least a part of the lower surface has a shape in which triangular peaks having a cross section of triangular shape are arranged in parallel, and the apex angle of the triangular peak is 40 on the side closer to the light source with respect to the perpendicular from the upper surface of the light guide plate.
° to 85 ° and the side δ far from the light source is 75 °
From 87 °, the upper surface is smooth, and the turning filter has a shape in which prisms each having a triangular cross section on the lower surface where light enters are arranged in parallel, and the apex angle of the prism is the turning filter. The backlight device is characterized in that the side α closer to the light source is in the range of 0 ° to 20 ° and the side β farther from the light source is in the range of 32 ° to 38 ° with respect to a perpendicular from the upper surface of the backlight device. 2. A vertex angle γ of the light guide plate on a side close to the light source of the triangular mountain is in a range of 40 ° to 60 °, and a vertex angle δ on a side far from the light source is in a range of 80 ° to 86 °. The backlight device according to claim 1, wherein 3. A light guide plate used for a backlight device arranged on a back surface of a liquid crystal plate and illuminating the liquid crystal plate, wherein the light guide plate has at least a part of a lower surface in which triangular cross-sections are arranged in parallel. The apex angle of the triangular peak is 40 ° on the side γ close to the light source with respect to a perpendicular from the upper surface of the light guide plate.
A light guide plate, wherein a side δ far from the light source is in a range of 80 ° to 86 °. 4. The light guide plate according to claim 3, wherein a part of a lower surface of the light guide plate has a shape in which mountains having a triangular cross section are arranged in parallel, and another part of the lower surface is a smooth surface. Light guide plate. 5. A direction change filter disposed on a back surface of a liquid crystal plate and used for a backlight device for illuminating the liquid crystal plate, wherein a cross section of a lower surface on which light is incident has a shape in which triangular prisms are arranged in parallel. The apex angle of the prism is such that the side α close to the light source is in the range of 0 ° to 20 ° and the side β far from the light source is in the range of 32 ° to 38 ° with respect to the vertical line from the top surface of the above-mentioned turning filter. A directional change filter characterized by the features. 6. The direction change filter according to claim 5, wherein an upper surface of the direction change filter is a smooth surface. 7. The direction change filter according to claim 5, wherein an upper surface of the direction change filter is a lenticular lens. 8. The direction changing filter according to claim 5, wherein the inclination of the slope of the prism of the direction changing filter is different between a portion near the vertex and a portion far from the vertex of the prism.