JPH0894844A - Light guide plate, surface light source using the same, and non-emissive display device - Google Patents

Abstract

(57) [Abstract] [Purpose] To facilitate manufacturing, to attach a light guide plate to a non-emissive display device, and to improve visibility of a reflective and non-emissive display device. [Structure] The light guide plate 10A has a surface 10d opposite to the flat surface 10a.
A prism array in which the top lines T and the valley lines V which are parallel to each other are alternately present, and the valley lines and the top lines are present in virtual planes A1 and A2 which are parallel to the plane 10a, respectively, are formed. An angle α formed between the inclined surface S1 on one side and the virtual plane A1 is substantially equal to a critical angle of the light guide plate with respect to air, and an angle β formed between the inclined surface S2 on the other side of each prism of the prism array and the virtual plane A1. Is about 2 °.
It is more preferable that the angle β is 10 ° or less and that the angle β increases as the distance from the straight tube type illumination lamp 12 increases. This light guide plate is a transmissive type,
The present invention can be applied to any reflective surface light source for liquid crystal display devices.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate suitable for a non-emissive display device such as a liquid crystal display device, a surface light source using the same, and a non-emissive display device.

[0002]

2. Description of the Related Art FIG. 8A shows a conventional edge light type surface light source of this type. On one end face of the light guide plate 10, a straight tube type illuminating lamp 12 is arranged along the end face in a direction perpendicular to the paper surface,
The illumination light is converted into surface illumination light for a transmissive liquid crystal display panel (not shown) arranged on the flat surface 10a side of the light guide plate 10.

Since the transmissive liquid crystal display panel 50 has a viewing angle characteristic, the light guide plate 1 emits light having directivity corresponding to this characteristic.
By emitting light from the 0 plane 10a, the light utilization efficiency can be improved and the power consumption can be reduced. For this purpose, a lenticular lens is superimposed on the flat surface 10a. However, since the lenticular lenses are stacked, the surface light source becomes thick and heavy, and it is expensive. Further, when the lenticular lens is used for the reflection type liquid crystal display panel, the display of the liquid crystal display panel becomes difficult to see due to the blurring of the total reflection layer.

Therefore, in the transmissive liquid crystal display panel, the surface 10b is inclined with respect to the plane 10a, and the surface 10b is inclined.
8B, a step as shown in FIG. 8B is formed, the step portion inclination angle is set to 45 °, and the light incident from the end face 10c is reflected by the step portion inclined surface in a direction substantially perpendicular to the plane 10a. Is proposed. In the figure, 14 is a reflector, 16 and 1
Reference numeral 8 is a reflection plate, and 20 is a diffusion plate.

[0005]

However, since the surface 10b is inclined with respect to the plane 10a, the manufacturing is not easy and the cost is high, and the surface light source is arranged so that the plane 10a is parallel to the display panel. Since it has to be installed, the installation work is not easy. In view of such problems, an object of the present invention is to provide a light guide plate that is easy to manufacture and can be easily attached to a non-emissive display device, a surface light source using the same, and a non-emissive display device.

Another object of the present invention is to provide a light guide plate capable of improving the visibility of a reflective and non-emissive display device, a surface light source using the same, and a non-emissive display device. It is in.

[0007]

According to the first aspect of the present invention, in a light guide plate for allowing light incident from an end face to be emitted from a first plane, the top faces parallel to each other are provided on the second face opposite to the first plane. Lines and valley lines alternate, the valley lines substantially lie in a first imaginary plane parallel to the first plane, and the top line is parallel to the first plane and the first line with respect to the first plane. When a prism array existing substantially in a second virtual plane apart from the virtual plane is formed, and the second surface is divided into a first region and a second region by a line substantially parallel to the top line. Of the prism array in at least one of the regions of the prism array, the angle α between the surface on one side of each prism (total reflection prism inclined surface) of the prism array and the second virtual plane is the critical value of the light guide plate with respect to air. Is substantially equal to the angle, and the other side of each prism of the prism array and the second virtual plane. Angle β is smaller than the angle α with.

Since the angle α is substantially equal to the critical angle of the light guide plate with respect to the air, the light incident from one end face of the light guide plate is totally reflected by the one side face, and the light from the first plane with respect to its normal line is substantially Since the light is emitted symmetrically, the utilization efficiency of the illumination light for the non-emissive display device is improved. Further, since the angle β is smaller than the angle α, it is possible to prevent the intensity distribution of the light emitted from the first plane from becoming particularly large on the one end face side of the light guide plate.

In the light guide plate of the first aspect of the present invention, since the first virtual surface is parallel to the first plane, it can be manufactured more easily and cheaply than the conventional light guide plate having the inclined surface with respect to the first plane. Moreover, it is easy to attach the light guide plate to the non-emissive display device. Further, since the angle β is smaller than the angle α, the unevenness of the prism array surface is relatively small, and when the light guide plate of the present invention is applied to a reflective and non-emissive display device, the display device is more than a case where a lenticular lens is used. The blur on the display surface is reduced, and the visibility can be improved.

In the first aspect of the first invention, the angle β is 1
It is 0 ° or less, and the interval (prism depth) between the first virtual surface and the second virtual surface is 5 to 50 μm. If the prism depth is too large, the distribution of the intensity of light emitted from the first plane becomes nonuniform, and if it is too small, the area of the total reflection prism inclined surface becomes too small. If this interval is constant,
If the angle β is made too large, the prism pitch becomes too short, and the amount of light reflected by the prism inclined surface on one end face side where the illuminating lamp is arranged increases, and the amount of light that travels to the other end face side that faces is small. Also, the area that can be incident on the prism inclined surface by the front prism becomes narrow. Conversely, the angle β
If is too small, the average optical path length of light in the light guide plate becomes too long, and the loss due to attenuation increases. From these, there is a preferable range of the prism depth and the angle β. The first aspect is an aspect of this preferable range.

In the second aspect of the first invention, the prism array in the first region satisfies the conditions of the angles α and β, and the prism array in the second region has the first region with respect to the dividing line. It is almost symmetrical to the prism array inside.
If the illuminating lamps are arranged along the end surface on the first region side and the end surface on the second region side of the light guide plate of the second aspect, the distribution of the intensity of the emitted light from the first plane is not symmetrical and is set to one end surface. It can be made more uniform than when the illumination lamps are arranged along the line.

In the third aspect of the first aspect of the invention, with respect to the prism array in at least one of the first region and the second region, the angle β becomes larger toward the dividing line side. According to the third aspect, the inclined surface of the prism for total reflection per unit area becomes wider as the distance from the illumination lamp arranged at the end face of the area increases.
It is possible to make the distribution of the intensity of light emitted from the plane more uniform.

In the surface light source of the second invention, any one of the light guide plates described above, an illuminating lamp arranged along the end face of the light guide plate on the side of the first region, and an illuminating lamp opposite to the end face. And a reflector that reflects the light emitted to the side toward the end face side. In the first aspect of the second aspect of the invention, two surface light sources of the second aspect of the invention are doubly arranged in directions opposite to each other.

According to the first aspect, the distribution of the intensity of light emitted from the light source surface can be made more uniform. In the surface light source of the third invention, the light guide plate of the second aspect of the first invention, a first illumination lamp arranged along the first end surface of the light guide plate on the first region side, and the first light source. A first reflector that reflects the light emitted from the illuminating lamp to the side opposite to the first end surface to the first end surface side, and the light guide plate is disposed along the second end surface on the second region side. A second illuminating lamp and a second illuminating lamp that reflects the light emitted from the second illuminating lamp to the side opposite to the second end surface toward the second end surface
And a reflector.

In the first aspect of the third invention, any one of the above
A prism array having a shape of α = β is formed in the prism array of the two light guide plates, and the prism top line faces the first surface side of the light guide plate in a direction substantially perpendicular to the prism top line of the light guide plate. The prism array plate is arranged. According to the first aspect, the directivity in the plane perpendicular to the first surface of the light guide plate and passing through the top line is also improved.

In a second aspect of the third aspect of the present invention, there is provided a diffusion plate facing the first surface side of the light guide plate and a reflecting plate facing the second surface side of the surface light source. A non-emissive display device according to a fourth aspect of the present invention includes the surface light source and a transmissive non-emissive display panel that is arranged to face the first surface of the light guide plate. In the non-emissive display device of the fifth invention,
It has the surface light source of the said 2nd invention, and the reflective type and non-emission type | mold display panel opposingly arranged by the said 1st surface side of the said light guide plate.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or similar components are designated by the same or similar reference numerals. [First Embodiment] FIG. 2 shows a surface light source according to the first embodiment.

A straight tube type illuminating lamp 12, for example, a cold cathode tube or a hot cathode tube is arranged on one end face of the light guide plate 10A in a direction perpendicular to the paper surface along the end face, and the illuminating light illuminates the plane 10a of the light guide plate 10. Is converted into surface illumination light emitted from. This surface light source is used for a non-emissive and transmissive display device, for example, a transmissive liquid crystal display panel 50. In order to improve the light utilization efficiency of the transmissive liquid crystal display panel 50 having the viewing angle characteristic, the light guide plate 10A has a surface 10d opposite to the flat surface 10a.
A prism array is formed on the. In this prism array, parallel top lines T and valley lines V extending in the direction perpendicular to the paper surface are alternately present, all the valley lines V are present in the virtual plane A1, and all the top lines T are virtual planes. It exists within A2 and the virtual planes A1 and A2 are parallel to the plane 10a. The inclination angles of the inclined surfaces S1 and S2 on both sides of the valley line V with respect to the virtual surface A2 are angles α and β, respectively.

First, a preferable value of the angle α will be described with reference to FIG. The angle θ from the end face 10c with respect to the normal
The light that has entered the light guide plate 10A travels as indicated by the alternate long and short dash line, and then enters the inclined surface S1 at an angle γ.
To the plane 10a and exit from the plane 10a at an angle η. In this case, the following relational expression holds.

Δ = 90 ° − (θ + 2α) (1) γ = 90 ° − (θ + α) (2) sin η = n · sin δ (3) where n is the conductivity for air. This is the refractive index of the optical plate 10A. Hereinafter, the light guide plate 10A is made of acrylic resin and has a refractive index n.
Is 1.492.

The critical angle in this case is 42 °, and the plane 1
The condition under which light can be propagated in the light guide plate 10A after being totally reflected at 0a is −48 ° ≦ θ ≦ 48 °. The condition that the light incident on the inclined surface S1 is totally reflected by the inclined surface S1 is γ ≧ 42 °. The condition for being totally reflected by the inclined surface S1 and then being able to pass through the flat surface 10a is δ <42. Using these conditions and the expressions (1) to (3), the following numerical relationship is obtained.

Angle α [°] Angle θ [°] Angle γ [°] Angle η [°] 300 0-18 42-60 60 18-48 40 0-8 42-50 3 3-15 43 0-8 42-47 -6 to 6450 to 342 to 45-4.5 to 0480 to -6-9 From the above numerical relationship, the following conclusion can be obtained for the angle α.

(1) When the angle α is 48 ° or more, light cannot be emitted from the plane 10a. (2) When the angle α is small, the range of the angle θ is widened, but the light emitted from the plane 10a has an oblique directivity, which is not preferable. (3) The positive side range and the negative side range of the angle θ are equal when α = 43 °.

Therefore, when the plane 10a is made of acrylic resin, by setting α = 43 °, generally, by setting the angle α to the critical angle of the light guide plate 10A with respect to the air, the normal line to the plane 10a is obtained. Light having a symmetrical intensity distribution is emitted from the plane 10a, which is a preferable condition for the transmissive liquid crystal display panel 50. On the other hand, preferable values of the angle β and the prism depth d (distance between the virtual planes A1 and A2) are as follows.

If the prism depth d is too large, the flat surface 10
If the distribution of the intensity of light emitted from a becomes nonuniform and is too small, the area of the total reflection prism inclined surface S1 becomes too small. If the prism depth d is constant and the angle β is too large, the interval between the adjacent top lines T, that is, the prism pitch becomes too short, and the amount of light reflected by the inclined surface S1 on the end face 10c side increases, The amount of light that travels toward the end face 10e decreases, and the area of the prism in the front that can be incident on the inclined surface S1 decreases. On the contrary, if the angle β is made too small, the average optical path length of light in the light guide plate 10A becomes too long, and the loss due to attenuation becomes large.

From the above, the angle β and the prism depth d have a preferable range for a surface light source. It has been found that, in this practical range, the angle β is generally 10 ° or less and the depth d is approximately 5 μm or more and 50 μm or less. The value of the angle β that is particularly preferable for the surface light source of the transmissive or reflective liquid crystal display device is, as a result of numerical analysis, the light guide plate
0A is an acrylic resin, the depth d is in the above range, and the length (width) between the end faces 10c and 10e is in the range of 30 to 200 mm, which is an extremely small angle of about 2 °. The present inventor has found that.

In FIG. 2, the shape of the inner surface of the reflector 14 that surrounds the illuminating lamp 12 and extends in the direction perpendicular to the paper surface is the end surface 10.
It is preferable that most of the light incident on c is within the range of −8 ° ≦ θ ≦ 8 °, that is, the light does not pass through the inclined surface S1. Further, in order to reduce the loss of the light transmitted through the prism array surface 10d, a reflection plate 16 is arranged facing the prism array surface 10d, and in order to reduce the loss of the light transmitted through the end surface 10e, it is in contact with the end surface 10e. A reflector 18 is arranged. Further, in order to make the intensity distribution of the emitted light uniform, a diffusion plate 20 is arranged in contact with the flat surface 10a. The reflection plates 16 and 18 and the diffusion plate 20 may be thin sheets or films.

The light guide plate 10A is obtained by hot pressing a surface of an injection-molded resin-made transparent parallel plate with a template in which a pattern of a prism array is engraved, and then cooling.
It is easily obtained and can be manufactured more easily and cheaply than the light guide plate 10 of FIG. 8 having an inclined surface. Also, the virtual plane A
Since 2 is parallel to the plane 10a, it is easy to attach the surface light source to the transmissive liquid crystal display panel 50.

[Second Embodiment] FIG. 3 shows a surface light source of a second embodiment. In this surface light source, the end surface 10f of the flat surface 10a is made to be a convex surface like a cylindrical lens, and the light incident on the end surface 10c is −8 ° ≦ θ ≦ 8 more than in the case of FIG.
It is kept within the range of °.

As a result, the amount of light transmitted through the prism array surface 10d is reduced, and the directivity of the light emitted from the plane 10a becomes more symmetrical with respect to the normal line. Also, the diffusion plate 2
Between 0 and the plane 10a, for example, Japanese Patent Laid-Open No. 6-13038.
The prism array plate 22 as disclosed in No. 7 is arranged. The prism array plate 22 is for bending the light obliquely incident thereto toward the normal line side to improve the directivity. As shown in FIG. 3B, the prism array plate 22 has α = β in the prism array of the light guide plate 10A.
And has a vertical angle of, for example, 94 °.

The prism array plate 22 is arranged so that its prism apex is perpendicular to the prism apex T of the prism array surface 10d. By arranging in this way,
The directivity in the plane perpendicular to the paper surface is also improved. [Third Embodiment] FIG. 4 shows a surface light source according to a third embodiment.

In the surface light source of FIG. 2, since the angles β are all the same, the amount of light incident on the inclined surface S1 on the end face 10e side is small even if the angle β is made small. Therefore, the light guide plate 1
For the prism array surface 10g of 0, the prism pitch p is gradually shortened by increasing the angle β as the distance from the end surface 10c to the end surface 10e side increases. As a result, the inclined surface S1 per unit area becomes wider toward the end surface 10e side, so that the distribution of the intensity of light emitted from the flat surface 10a can be made more uniform than in the case of FIG.

The prism array surface 10g may be divided into a plurality of areas, and the prism pitch p may be changed in units of areas. Further, if the angle β is increased, it is obstructed by the front prism and the area that can be incident on the inclined surface S1 is narrowed. Therefore, it is preferable that the range of the angle β is 10 ° or less as described above.

[Fourth Embodiment] FIG. 5 shows a surface light source of a fourth embodiment. This surface light source uses two surface light sources of FIG. However, the reflection plate 16 is omitted from the surface light source on the light emission side, and the diffusion plate 20 is omitted from the other surface light source.

According to the fourth embodiment, the distribution of the intensity of light emitted from the surface of the light guide plate on the diffuser plate 20 side can be made more uniform than in the case of FIG. [Fifth Embodiment] Since the surface light source of FIG. 5 has a double structure, it becomes thick. Therefore, in the surface light source of the fifth embodiment, as shown in FIG. 6, the prism array surface 10h of the light guide plate 10C is a straight line perpendicular to the middle paper surface of the end face 10c and the end face 10e, and is divided into the region R1 and the region R2. Divide and prism array surface 10
The shape of h is symmetrical with respect to this dividing line. And
Symmetrically with the illumination lamp 12 and the reflector 14 on the end face 10c side,
The illumination lamp 32 and the reflector 34 are arranged on the end face 10e side.

According to the fifth embodiment, it is possible to make it thinner than the surface light source of FIG. 5 and to make the distribution of the intensity of light emitted from the plane 10a more uniform than that of the light guide plate of FIG. [Sixth Embodiment] The surface light source described above is for a transmissive and non-emissive display panel, but as shown in FIG. 7, a reflective and non-emissive display panel, for example, a reflective liquid crystal display panel 50A. Can also be used as a surface light source. In this surface light source, the diffusion plate 20 and the reflection plate 16 are omitted in FIG. 2, the transmissive liquid crystal display panel 50 is replaced with a reflective liquid crystal display panel 50A, and the vertical direction is reversed.

Without this surface light source, it is difficult to see the display of the reflection type liquid crystal display panel 50A in a dark place. However, by disposing such a surface light source with respect to the reflection type liquid crystal display panel 50A, the display is easy to see even in a dark place. In addition, due to the directivity, the illumination light from the illumination lamp 12 can be efficiently used, and power saving can be achieved. Also, α
Since β = 2 ° with respect to = 43 °, most of the prism array surface 10d is almost flat, and blurring on the display surface of the reflective liquid crystal display panel 50A is significantly reduced as compared with the case where a lenticular lens is used. However, the visibility is good.

Since it is sufficient to turn off the illumination lamp 12 in a bright place, the power consumption can be reduced as compared with the transmissive liquid crystal display device.
It is suitable for portable OA equipment. The present invention includes various modifications. For example, it goes without saying that a configuration in which the system of FIGS. 3 to 6 is applied to the configuration of FIG.

Further, the light guide plate 10 is not limited to a transparent material such as acrylic resin, but a material having a light scattering property to the extent that blur is not noticeable in order to make the intensity distribution of light emitted from the flat surface 10a more uniform, For example, it may be formed of a copolymer of methyl methacrylate and vinyl low molecular weight such as vinyl benzoate or trifluorinated methyl methacrylate.

[0040]

As described above, according to the light guide plate of the present invention, and the surface light source and the non-emission type display device using the same,
Since the first virtual surface is parallel to the first plane, it can be manufactured more easily and cheaply than the conventional light guide plate having the inclined surface with respect to the first plane, and the light guide plate can be attached to the non-emissive display device. Has the effect of being easy. Also,
Since the angle β is smaller than the angle α, the unevenness of the prism array surface is relatively small, and when the light guide plate of the present invention is applied to a reflective and non-emissive display device, the display of the display device is more than that when the lenticular lens is used. The effect of reducing blur on the surface and improving visibility can be achieved.

According to the first aspect of the light guide plate of the first invention, the distribution of the intensity of the light emitted from the first plane is made more uniform, and the area which can be incident on the prism inclined surface by the front prism is prevented. Moreover, it is possible to reduce the loss due to the attenuation of light in the light guide plate. According to the second aspect of the first invention, when the illumination lamp is arranged along the end surface on the first region side and the end surface on the second region side of the light guide plate, the distribution of the intensity of light emitted from the first plane is symmetrical. The effect is that it can be made more uniform than when the illumination lamps are arranged along one end face.

According to the third aspect of the first invention, the inclined surface of the prism for total reflection per unit area becomes wider as the distance from the illumination lamp arranged at the end face of the area increases, so that the light emitted from the first plane is emitted. The effect that the distribution of strength can be made more uniform is exhibited. According to the first aspect of the surface light source of the second invention, there is an effect that the distribution of the intensity of light emitted from the light source surface can be made more uniform.

According to the first aspect of the surface light source of the third invention, there is an effect that the directivity in the plane perpendicular to the first surface of the light guide plate and passing through the top line is also improved.

[Brief description of drawings]

FIG. 1 is an optical path diagram showing a principle configuration of the present invention.

FIG. 2 is a sectional view showing a surface light source of a first embodiment of the present invention.

FIG. 3 is a sectional view showing a surface light source of a second embodiment of the present invention.

FIG. 4 is a sectional view showing a surface light source according to a third embodiment of the present invention.

FIG. 5 is a sectional view showing a surface light source of a fourth embodiment of the present invention.

FIG. 6 is a sectional view showing a surface light source of a fifth embodiment of the present invention.

FIG. 7 is a sectional view showing a surface light source of a sixth embodiment of the present invention.

FIG. 8 is a cross-sectional view showing a conventional surface light source.

[Explanation of symbols]

 10, 10A to 10C Light guide plate 10d, 10g, 10h Prism array surface 12, 32 Illumination lamp 14, 34 Reflector 16, 18 Reflector plate 20 Diffuser plate 22 Prism array plate 50 Transmissive liquid crystal display panel 50A Reflective liquid crystal display panel V Valley line T Top line

Claims (11)

[Claims] 1. A light guide plate for causing light incident from an end face to be emitted from a first plane, in which a top line and a valley line parallel to each other are alternately present on a second face opposite to the first plane. A line is substantially in a first imaginary plane parallel to the first plane and the top line is parallel to the first plane and the first
A prism array that is substantially present in a second virtual plane that is farther than the first virtual plane with respect to the plane is formed, and the second surface is divided into a first region and a second region by a line substantially parallel to the top line. With respect to the prism array in at least one region when divided approximately into two equal parts, the angle α formed between the surface on one side of each prism of the prism array and the second virtual plane is the critical angle of the light guide plate with respect to air. A light guide plate, which is substantially equal to each other, and an angle β formed between the other surface of each prism of the prism array and the second virtual plane is smaller than the angle α. 2. The light guide plate according to claim 1, wherein the angle β is 10 ° or less, and the distance between the first virtual surface and the second virtual surface is 5 to 50 μm. 3. The prism array in the first region satisfies the conditions of the angles α and β, and the prism array in the second region is substantially symmetrical to the prism array in the first region with respect to the dividing line. The light guide plate according to claim 1 or 2, wherein 4. The angle β with respect to the prism array in at least one of the first region and the second region.
The light guide plate according to any one of claims 1 to 3, wherein is increased as it approaches the division line side. 5. The light guide plate according to claim 1, an illumination lamp arranged along an end face of the light guide plate on the side of the first region, and the illumination light to the end face. And a reflector for reflecting the light emitted to the opposite side to the end face side. 6. A surface light source, wherein two surface light sources according to claim 5 are doubly arranged in directions opposite to each other. 7. The light guide plate according to claim 3, a first illuminating lamp arranged along the first end surface of the light guide plate on the first region side, and the first illuminating lamp to the first end surface. A first reflector for reflecting light emitted to the opposite side to the first end face side, a second illuminating lamp arranged along the second end face of the light guide plate on the second region side, A second reflector for reflecting the light emitted from the second illumination lamp to the side opposite to the second end face to the side of the second end face, and a surface light source. 8. In the prism array of the light guide plate, α =
A prism array having a shape of β is formed, and a prism array plate is provided on the first surface side of the light guide plate, the prism array plate being opposed to the prism top line of the light guide plate in a direction substantially perpendicular to the prism top line. 8. The method according to claim 5, wherein:
Surface light source described in. 9. The diffusion plate, which is arranged to face the first surface side of the light guide plate, and the reflection plate, which is arranged to face the second surface side of the surface light source. Surface light source. 10. A non-emissive display comprising: the surface light source according to claim 9; and a transmissive and non-emissive display panel that is arranged to face the first surface side of the light guide plate. apparatus. 11. A non-emissive display comprising: the surface light source according to claim 5; and a reflective and non-emissive display panel that is arranged to face the first surface of the light guide plate. apparatus.