JP3410766B2 - Prism plate and surface light source device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism plate used for a surface light source device and a surface light source device used for a backlight of a liquid crystal device.

A surface light source device used as a backlight of a liquid crystal device is required to have good viewing angle characteristics and high luminance in a direction normal to a light emitting surface.

[0003]

2. Description of the Related Art As shown in FIG. 14, a conventional surface light source device 10 includes a light guide plate 11 for guiding light, a cold cathode tube 12 having a layer line shape on a side end surface of the light guide plate 11, and a rear surface of the light guide plate 11. The diffuse reflection layer pattern 13 and the reflection plate 14 on the back surface of the light guide plate 11 are provided, and the prism plate 15 and the diffusion plate 16 are provided on the front surface (the surface from which light is emitted) 11a of the light guide plate 12 in an overlapping manner. It is a composition. The upper surface of the diffusion plate 16 is the light emitting surface 17.

As shown in the enlarged view of FIG. 15, the prism plate 15 has two plane slopes 20 and 21 having an apex angle α.
Is one roof-shaped linear prism 22 having an angle of 90 degrees, and a large number of the linear prisms 22 are aligned.

The prism plate 15 is a front surface 11 of the light guide plate 11.
Rays emitted from a, for example, rays 30 to 34 are refracted or refracted and reflected to give rays 30a to 3
The light is emitted as shown by 4a.

The prism plate 15 mainly acts to direct the light rays in a direction (normal direction) perpendicular to the light emitting surface 17 as much as possible.

The prism plate 15 has a viewing angle characteristic shown by a line I in FIG. 16 and a luminous intensity distribution characteristic shown by a line II in FIG.

Therefore, since the prism plate 15 is provided, the luminance of the light emitting surface 17 in the normal direction is reduced.
Compared with the case without (indicated by line III in FIG. 16),
It can be increased about 1.5 times.

Here, observing the viewing angle characteristics of the prism plate 15, when the angle exceeds 30 degrees with respect to the normal line, the brightness sharply decreases, and when the angle exceeds 40 degrees, it recovers. The viewing angle characteristic of the prism plate 15 has a valley portion 40 and a recovery portion 41. Further, the luminous intensity distribution characteristic of the prism plate 15 has a corner 42 on the left and right.

Therefore, when the surface light source device is provided with only the prism plate 15, when the viewing angle is gradually deviated from the normal direction, the light emitting surface 17 becomes sharp when viewed from a direction of about 40 degrees. It gets dark and becomes bright again after this, giving a strange feeling to the user.

Therefore, the diffusion plate 16 is provided on the prism plate 15.

By providing the diffusion plate 16, the light rays emitted from the prism plate 15 are diffused.

As a result, the light emitting surface 17 has a luminous intensity distribution
In FIG. 14, the distribution is as shown by the line III and the angle is eliminated, and the luminance distribution is as shown by the line IV in FIG. 17, which does not have a valley portion.

[0014]

However, in the diffusion plate 16, there is a loss due to multiple optical reflection.

For this reason, it is difficult for the conventional surface light source device 10 to sufficiently increase the luminance in the normal direction.

Although it is conceivable to change the apex of the linear prism 22 in the prism plate 15, even if the apex angle is changed, a valley still appears in the luminance distribution (see FIG. 16).
Inside, line V is the case where the apex angle is 70 degrees), the diffusion plate 16
Cannot be omitted.

Therefore, it is an object of the present invention to provide a prism plate and a surface light source device that can improve the brightness in the normal direction.

[0018]

According to a first aspect of the present invention, in a prism plate in which a large number of linear prisms are aligned, each linear prism is provided with two flat slope portions forming a roof shape, and It consists of a curved top surface that connects two slopes , and the ratio of the curved top surface to the whole
Is 50% or less .

According to a second aspect of the present invention, two linear prisms adjacent to each other are provided in a prism plate in which two planar inclined surfaces forming a roof form a linear prism, and a large number of the linear prisms are aligned. during parts, a configuration having a curved trough surface connecting between the planar inclined surface portions adjacent the songs
The ratio of the planar valley surface portion to the whole is 50% or less
It is configured as follows.

According to a third aspect of the invention, a light source and a light source
Light guide means for guiding light and for emitting the light from a light emitting surface,
A prism arranged in front of the light emitting surface of the light guide means
In a surface light source device including a plate, the prism plate is
The two flat slopes that form the roof and the top and
Linear shape consisting of a curved surface forming at least one of the valleys
A structure in which a large number of prisms are arranged,
The extension direction of the rhythm is 5 degrees with respect to the longitudinal direction of the surface light source device.
The direction is inclined to 85 degrees and the front of the prism plate
The surface is a light emitting surface .

According to a fourth aspect of the invention, a light source and a light source
Light guide means for guiding light and for emitting the light from a light emitting surface,
The light guide means is stacked on the front surface of the light emitting surface.
In a surface light source device including a plurality of prism plates,
A prism plate is two flat slopes that form a roof.
And a curved surface forming at least one of the top and the valley
Is composed of a large number of linear prisms
One prism plate and another prism plate
When the extension direction of the prism is relative to the longitudinal direction of the surface light source device,
In the direction inclined by 5 to 85 degrees in the total direction and the counterclockwise direction
The prism plate at the top is the light emitting surface.
It has a certain configuration .

[0022]

[0023]

[0024]

[0025]

[0026]

The curved top surface of the linear prism according to claim 1 is
It acts to direct the light rays toward the horizontal. Curved top
The ratio of the parts to the whole is 50% or less
It acts so as not to reduce the brightness in the normal direction too much.
It

The curved valley surface portion of the linear prism of the second aspect acts so as to direct the light rays toward the horizontal direction. Curved
A structure in which the ratio of the valley portion to the whole is 50% or less
It works so as not to reduce the brightness in the normal direction too much.
To do.

At least one of the top and the valley of claim 3
The curved surface of the prism makes the viewing angle characteristic of the prism plate itself.
Prism plate that acts so as to have no troughs
The light emitting surface is the front surface of the
Acts to eliminate the need for plates. How the linear prism extends
The configuration in which the direction is inclined with respect to the longitudinal direction of the surface light source device is
When used as a backlight for a liquid crystal panel, linear
A fringe is generated due to the interference between the prism and the display electrode of the liquid crystal panel.
It acts to make it difficult to grow .

A structure in which a plurality of prism plates according to claim 4 are stacked.
Acts to widen the viewing angle characteristics. Two prisms
Frame plate and its linear prism in the longitudinal direction of the surface light source device.
In this configuration, the liquid crystal display is tilted in the opposite directions.
When used as a backlight for flannel, the linear prism
Fringes due to interference between the display and the display electrodes of the LCD panel
It acts as a comb.

[0030]

[0031]

[0032]

[0033]

[0034]

【Example】

[First Embodiment] FIGS. 1 and 2 show a surface light source device 50 according to a first embodiment of the present invention.

In each drawing, the same reference numerals are given to the portions corresponding to the constituent portions shown in FIG.

The surface light source device 50 has a structure in which only the prism plate 51, which is an essential part of the present invention, is provided on the light emitting surface 11a of the light guide plate 11 and no diffuser plate is provided, and as a backlight of the liquid crystal panel 60. It is used.

The device 50 has a structure in which the upper surface of the prism plate 51 is the light emitting surface 58.

In the liquid crystal panel 60, the X-direction display electrode 61 extending in the X-direction and the Y-direction display electrode 62 extending in the Y-direction.
Have and. In the X direction, the liquid crystal panel 60, the surface light source device 5
0 and the longitudinal direction of the prism plate 51, which is the Y direction
Is a liquid crystal panel 60, a surface light source device 50, and a prism.
It is the width direction of the plate 51.

Next, the prism plate 51 will be described with reference to FIG.

The prism plate 51 includes a large number of linear prisms 5.
2 is an aligned configuration.

Each of the linear prisms 52 is composed of two flat slope portions 53 and 54 forming a roof shape and a substantially arc-shaped top surface portion 55 connecting the two slope portions 53 and 54. Is.

The inclination angle β of the slopes 53 and 54 is 45 degrees, and the angle γ at which the extended surfaces of the slopes 53 and 54 intersect is 90.
It is degree.

Here, the height of the linear prism 52 is H, and the height occupied by the slope portions 53 and 54 is h.

{(H−h) ÷ H} × 100 is defined as the curved surface ratio, which is the percentage of the curved surface portion to the entire linear prism 52.

The curved surface ratio of the linear prism 52 is 15
%.

Of the linear prism 52, the slope portions 53, 5
The light rays 70 and 71 directed toward 4 are emitted as indicated by reference numerals 70a and 71a.

Light rays 72 and 73 traveling toward the top surface portion 55 are
The light is emitted as indicated by reference numerals 72a and 73a.

The curved top surface portion 55 acts so as to uniformly spread the light rays in a direction away from the normal line direction of the prism plate 51.

The flat slope portions 53 and 54 act to collect the light rays in the normal direction of the prism plate 51.

The prism plate 51 has a viewing angle characteristic shown by a line VI in FIG. 4 and a luminous intensity distribution characteristic shown by a line VII in FIG.

The viewing angle characteristic has such a characteristic that the luminance gradually decreases with distance from the normal direction and does not recover thereafter.

The luminous intensity distribution characteristic has a characteristic having no corner.

The prism plate 51 can be manufactured by an extrusion molding method, a hot pressing method, or an injection molding method.

Next, the arrangement of the prism plate 51 with respect to the liquid crystal panel 60 will be described.

In FIG. 5, reference numeral 56 indicates the extending direction of the linear prism 52.

As shown in FIGS. 2 and 5, the prism plate 5
No. 1 is arranged so that the linear prism 52 is oriented counterclockwise with respect to the X-direction display electrode 61 by an angle δ (= 45 degrees).

Next, the characteristics of the surface light source device 50 having the above structure will be described.

Viewing angle characteristics and luminous intensity distribution characteristics The device 50 has the viewing angle characteristic shown by the line VIII in FIG.

The device 50 also has the luminous intensity distribution characteristic shown by the line IX in FIG.

Although the device 50 does not have a diffuser incorporated, the device 50 has viewing angle characteristics with no troughs.
In addition, it has a luminous intensity distribution characteristic without corners.

Since the normal direction luminance diffuser plate is not provided, there is no loss due to multiple optical reflection in the diffuser plate.

Therefore, the luminance in the direction normal to the light emitting surface 58 of the device 50 is improved as compared with the conventional example.

As can be seen from FIG. 6, the luminance of the device 50 in the normal direction is 4.400 (cd / m ² ). this is,
The brightness of the conventional apparatus shown in FIG. 14 is 4.000 (cd / m
Compared to ^{2), 400 (cd / m} 2), and the percentage is increased by about 10%.

Manufacturing cost Since the diffuser plate is not incorporated, the device 50 is the same as the conventional device 10.
It is cheaper than.

Since the characteristic linear prism 52 when used as a liquid crystal backlight extends in a direction forming 45 degrees clockwise with respect to the X-direction display electrode 61, the linear prism 52 and the liquid crystal panel 60. The generation of the interference fringes with the display electrodes 61 and 62 is most suppressed, and the interference fringes are barely represented. [Second Embodiment] FIGS. 7 and 8 show a surface light source device 80 according to a second embodiment of the present invention.

In each figure, parts corresponding to those shown in FIGS. 1 and 2 are designated by the same reference numerals.

The surface light source device 80 has the same configuration as that of FIGS. 1 and 2 except that the surface light source device 80 is superposed on the prism plate 51, receives another prism plate 51A, and has a two-layer structure.

The device 80 has a structure in which the upper surface of the prism plate 51A is the light emitting surface 81.

The prism plate 51A has substantially the same structure as the prism plate 51, and the linear prism 52A has a curved top surface portion 55A.

The prism plate 51A has a viewing angle characteristic shown by line VI in FIG.

In FIG. 9, reference numeral 82 denotes the extending direction of the linear prism 52A.

As shown in FIGS. 8 and 9, the prism plate 5
No. 1 is arranged so that the linear prism 52 is inclined in the counterclockwise direction by an angle δ (= 45 degrees) with respect to the X-direction display electrode 61. The angle ε is clockwise with respect to the direction indicating electrode 61
(= 45 degrees) It is arranged so as to be inclined.

Next, the characteristics of the surface light source device 80 having the above structure will be described.

Viewing angle characteristic and luminous intensity distribution characteristic The prism plate 51A acts so as to re-spread the light that has spread and emitted from the prism plate 51.

The device 80 has a viewing angle characteristic shown by a line X in FIG.

Further, the device 80 has a luminous intensity distribution indicated by a line XI in FIG.

As can be seen from the line X in FIG. 10, the high-luminance region extends to a range of about ± 20 degrees with respect to the normal line of the light emitting surface.

Further, the viewing angle characteristic has no valley portion, and the luminous intensity distribution characteristic has no angle.

Since the luminance diffuser in the normal direction is not provided, there is no loss due to multiple reflection of light in the diffuser.

Therefore, the luminance in the direction normal to the light emitting surface 58 of the device 80 is improved by slightly less than 10% as compared with the conventional example.

Manufacturing cost Since the diffuser plate is not incorporated, the device 80 is the same as the conventional device 10.
It is cheaper than.

When used as a liquid crystal backlight, the characteristic linear prism 52 extends 45 degrees clockwise with respect to the X-direction display electrode 61.
Since 2A extends in a direction forming 45 degrees counterclockwise with respect to the X-direction display electrode 61, the occurrence of interference fringes between the linear prism 52 and the display electrodes 61 and 62 of the liquid crystal panel 60 is most suppressed. However, the interference fringes are hardly visible.

In the above first and second embodiments,
Although the angles δ and ε are set to 45 degrees, they are 5 to 85.
It may be an appropriate angle within the range of degrees.

The viewing angle characteristics of the device 50 when the curved surface ratio is appropriately changed in the prism plate 51 (90) will be described with reference to FIG.

In the figure, a line XI shows the viewing angle characteristic of the surface light source device when a prism plate having a curved surface ratio of 20% is incorporated.

Line XII shows the viewing angle characteristics of the surface light source device when a prism plate having a curved surface ratio of 35% is incorporated.

Line XIII shows the viewing angle characteristic of the surface light source device when a prism plate having a curved surface ratio of 50% is incorporated.

From this, the larger the curved surface ratio,
It can be seen that the luminance in the normal direction is stopped and neither valley appears.

Here, if the curved surface ratio is 20% or less,
It can be seen that the luminance in the normal direction can be improved as compared with the device of FIG.

It has been found that when the curved surface ratio is 50% or less, substantially satisfactory luminance in the normal direction can be obtained.

Next, a modified example of the prism plate 51 will be described.
Explain. [First Modification] As shown in FIG. 12, a prism plate 90
Is the linear prism 91_-1(91_-2), The apex angle becomes α
Two flat slopes 92_-1(92_-2) And slope 93
_-1(93 _-2) And adjacent linear prisms 9
1_-1, 91_-2Between adjacent slopes 93_-1, 92_-2of
It has a curved valley surface portion 94 that forms a substantially arcuate surface connecting the spaces.
It is a configuration.

The valley portion 94 can also be formed by partially filling the space between the adjacent linear prisms with a transparent resin.

The prism plate 90, like the prism plate 51, has the viewing angle characteristic shown by the line VI in FIG.

The curved surface ratio is 50% or less. [Second Modification] As shown in FIG.
0 is the prism plate 50 of FIG. 3 and the prism plate 90 of FIG.
This is a combination of and.

The prism plate 100 is a linear prism 101.
Have.

The linear prism 101 is composed of two flat slope portions 102 and 103 forming a roof shape and a curved top surface portion 104 which is a substantially arcuate surface connecting the two slope portions 102 and 103.

Between the adjacent linear prisms 101, there is a curved valley surface 105 which is a substantially arcuate surface connecting the slopes 102 and 103 of the adjacent linear prisms 101.

This prism plate 100, like the prism plate 51, has a viewing angle characteristic close to line VI in FIG.

The curved surface ratio is 50% or less.

The prism plates 90 and 10 are replaced by the prism plate 5
It can be incorporated in place of 1 (51A). The surface light source device has the viewing angle characteristic indicated by the middle line VIII in FIG. 6 and the viewing angle characteristic indicated by the middle line X in FIG.

Further, each of the prisms 51, 51A, 9
In 0 and 100, the top surface portion and the valley surface portion are not limited to circular arc surfaces and may be curved surfaces formed by N-order curves.

[0102]

As has been described above, according to the prism plate of the invention of claim 1, rather it has a valley, and the normal direction
It is possible to obtain a viewing angle characteristic with sufficiently high luminance .

[0103] wherein, according to the prism plate of the invention of claim 2, the valleys rather have, and the normal direction of the brightness is sufficiently high vision
It is possible to obtain angular characteristics .

According to the surface light source device of the third aspect of the invention,
Since there is no diffuser, the loss due to multiple optical reflection inside the diffuser
It is possible to eliminate the loss, and the
The brightness in the line direction can be improved as compared with the conventional one.
In addition, the price of the surface light source device is reduced because the diffuser plate is not installed.
Rukoto can. Also, as the backlight of the liquid crystal panel
Interference fringes with the liquid crystal panel display electrodes
It can be effectively obscured.

According to the surface light source device of the invention of claim 4 ,
Wide viewing angle characteristics compared to the configuration with one rhythm plate
You can Also, as a backlight of the liquid crystal panel
When used, interference fringes with the display electrodes of the liquid crystal panel are effective.
You can make it inconspicuous.

[0106]

[0107]

[0108]

[0109]

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a surface light source device of the present invention.

FIG. 2 is an exploded perspective view of the surface light source device of FIG.

FIG. 3 is an enlarged view showing a part of a prism plate.

FIG. 4 is a diagram showing viewing angle characteristics of the prism plate of FIG.

FIG. 5 is a diagram showing an arrangement of linear prisms of a prism plate with respect to display electrodes of a liquid crystal panel.

6 is a diagram showing the viewing angle characteristics of the surface light source device of FIG. 1 together with the viewing angle characteristics of a conventional device.

FIG. 7 is a diagram showing a second embodiment of the surface light source device of the present invention.

8 is an exploded perspective view of the surface light source device of FIG.

FIG. 9 is a diagram showing an arrangement of linear prisms of a prism plate with respect to display electrodes of a liquid crystal panel.

10 is a diagram showing the viewing angle characteristics of the surface light source device of FIG. 7 together with the viewing angle characteristics of the devices of the conventional example and the first embodiment.

FIG. 11 is a diagram showing a relationship between a curved surface ratio of a prism plate and a viewing angle characteristic of a surface light source device.

FIG. 12 is a diagram showing a first modification of the prism plate.

FIG. 13 is a diagram showing a second modification of the prism plate.

FIG. 14 is a diagram showing an example of a conventional surface light source device.

FIG. 15 is a diagram showing a prism plate in FIG. 14;

16 is a diagram showing viewing angle characteristics of the prism plate of FIG.

17 is a diagram showing viewing angle characteristics of the surface light source device of FIG.

[Explanation of symbols]

11 Light Guide Plate 11a Light Emitting Surface 12 Cold Cathode Tube 13 Diffuse Reflecting Layer Pattern 14 Reflecting Plate 50 Surface Light Source Device 51, 51A Prism Plates 52, 52A Linear Prism 53, 54 Flat Slope 55 55 Curved Top Surface 56 Line Extending direction of the prism 52 52 light emitting surface 60 liquid crystal panel 61 X direction display electrode 62 Y direction display electrode 80 surface light source device 81 light emitting surface 82 extending direction of the linear prism 52A 90 prism plates 91 _-1 , 91 _-2 line Prisms 92 _-1 , 92 _-2 , 93 _-1 , 93 _-2 Planar slope portion 94 Curved valley surface portion 100 Prism plate 101 Linear prisms 102, 103 Planar slope portion 104 Curved top surface portion 105 Curved valley surface

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shinpei Nagatani 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (56) References JP-A-5-313004 (JP, A) JP-A-6-331831 (JP, A) JP-A-2-277002 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 5/02

Claims (4)

(57) [Claims] 1. A prism plate in which a large number of linear prisms are aligned, each linear prism having two flat inclined surfaces forming a roof shape and a curved surface connecting the two inclined surfaces. And the curved top surface portion occupies 50% or less of the whole.
A prism plate characterized by having the following structure. 2. A prism plate in which two flat slope portions forming a roof shape form a linear prism, and a large number of the linear prisms are aligned, and between the adjacent linear prism portions, The structure has a curved valley portion that connects adjacent flat slope portions, and the ratio of the curved valley portion to the whole is 50% or less.
A prism plate characterized by having the following structure. 3. A light source and a light from the light source are guided to direct the light.
The light guide means for emitting light from the light exit surface and the above light guide means
Surface light composed of a prism plate arranged in front of the light output surface
In the source device, the prism plate has two flat slope portions forming a roof shape, a top portion and
Linear shape consisting of a curved surface forming at least one of the valleys
In the structure in which a large number of prisms are aligned, the extending direction of the linear prism is aligned with the longitudinal direction of the surface light source device.
And the front surface of the prism plate is a light emitting surface.
Surface light source device to be collected. 4. A light source and a light from the light source are guided and the light is emitted from a light emitting surface.
The light guide means and the light emitting surface of the light guide means are stacked and arranged on the front surface.
In a surface light source device composed of a plurality of prism plates, the prism plates are two planar plates that form a roof shape.
A curve that forms a slope and at least one of a top and a valley
With a configuration in which a large number of linear prisms consisting of
Yes, one prism plate and another prism plate are linear prisms
The extending direction of each is clockwise relative to the longitudinal direction of the surface light source device.
Arranged in a direction inclined 5 degrees to 85 degrees in the counterclockwise direction
And the front surface of the uppermost prism plate is the light emitting surface.
A surface light source device characterized by the above.