JP2002109930A - Flat light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a production cost of a flat light source device by simplifying the manufacture of a mold. SOLUTION: A light guide plate 12 makes the light of incidence entered from one side surface 12a go out from an upper surface 12c, and a diffusion sheet 14 arranged upper side of the light guide plane 12 makes the outgoing light from the light guide plate 12 diffuse. A lower surface 12d of the light guide plate 12 has a plurality of flat planes and a plurality of V-shaped grooves. The flat planes are parallel with each other, and the distance between respective flat planes and the upper surface 12c become shorter stepwise in proportion as the location shifts from one surface 12a side to the other surface 12b side. The V-shaped groove extends in the direction parallel with the one side surface 12a. Here, at least two flat planes are put between respective V-shaped grooves, and respective flat planes contacting with V-shaped groove are contiguous to respective inclined planes forming V-shaped groove, and respective flat planes put between V-shaped grooves are combined by the inclined plane which is parallel with the inclined plane at surface 12a side of the inclined planes forming the V-shaped groove.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device,
In particular, for example, the present invention relates to a surface light source device in which a prism sheet is disposed above a light guide plate.

[0002]

2. Description of the Related Art Recently, liquid crystal displays have attracted attention because of their thinness and low power consumption, and are used in portable communication terminals, digital still cameras, car navigation systems, pachinko monitors, television receivers, and the like. Such a liquid crystal display was provided with a surface light source device as shown in FIG.

According to FIG. 16, one side surface 1a of the light guide plate 1 is shown.
A linear light source 2 is provided on the right side, and the periphery of the linear light source 2 is covered with a reflector 3 except for one side surface 1a. A plurality of flat surfaces F are formed on the lower surface 1c of the light guide plate 1 in a stepped manner, and each stepped portion is connected by a groove L and a projection M extending in parallel with the linear light source 2. The reflection sheet 4 is provided so as to cover the lower surface 1c and the other side surface 1b of the light guide plate 1, the light diffusion sheet 5 is provided so as to cover the upper surface 1d of the light guide plate 1, and the prism sheet 6 is provided above the light diffusion sheet 5. Laminated.

[0004]

Generally, the light guide plate is formed by a mold, but the light guide plate 1 needs to be formed with a flat surface F, a groove L and a projection M on the lower surface 1c as in the prior art. Was difficult to mold. In other words, in order to manufacture the mold shown in FIG. 17B, first, a tool corresponding to the flat surface F and the groove L is formed by the cutting tool B1 having a flat tip as shown in FIG. 17A. And
Next, it was necessary to form a mold corresponding to the projection M in the manner shown in FIG. For this reason, it takes time and effort to manufacture a mold, leading to an increase in the manufacturing cost of the surface light source device.

[0005] Therefore, a main object of the present invention is to provide a surface light source device capable of suppressing the manufacturing cost.

[0006]

SUMMARY OF THE INVENTION The present invention provides a light guide plate having one side surface and the other side surface facing each other, and for emitting light incident from one side surface from the upper surface, and a light guide plate disposed above the light guide plate. In the surface light source device including a diffusion sheet that diffuses light emitted from the light plate, the lower surface of the light guide plate is parallel to each other and a plurality of step-shaped flat surfaces in which the distance from the upper surface decreases as going from one side surface to the other side surface, And a plurality of V-shaped grooves extending parallel to one side surface, each V-shaped groove sandwiching at least two flat surfaces,
Each flat surface in contact with the V-shaped groove is continuous with each first slope forming the V-shaped groove, and each flat surface sandwiched between the V-shaped grooves is joined by a second slope parallel to the first slope on one side. The surface light source device is characterized in that:

[0007]

The light guide plate emits incident light from one side surface from the upper surface, and the diffusion sheet disposed above the light guide plate diffuses the light emitted from the light guide plate. The lower surface of the light guide plate has a plurality of flat surfaces and a plurality of V-shaped grooves. The flat surfaces are parallel to each other, and the distance from each flat surface to the top surface decreases stepwise from one side to the other. Also, V
The groove extends parallel to one side surface. Here, each V-shaped groove sandwiches at least two flat surfaces, and each flat surface in contact with the V-shaped groove is continuous with each first slope forming the V-shaped groove, and each of the V-shaped grooves is sandwiched between the V-shaped grooves. The flat surface is the first side
Joined by a second slope parallel to the slope.

As described above, the second slope is formed on the first side on one side.
Since the flat surface is also parallel to the inclined surface, and the respective flat surfaces are also parallel to each other, the mold for forming such a lower surface requires one die.
It can be manufactured by cutting using one cutting tool.

The width of the groove having an inverted V-shaped cross section is preferably increased from one side to the other side.

The acute angle formed by the slope with respect to the lower surface is preferably about 47 °. However, when the lens sheet is disposed above the upper surface of the light guide plate, the acute angle formed by the slope with respect to the lower surface should be about 22 °.

[0011]

According to the present invention, the second slope is made parallel to the first slope on one side, and the respective flat faces are also made parallel to each other. The manufacturing cost of the device can be reduced.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
0 includes the light guide plate 12. The light guide plate 12 is formed using an acrylic resin as a material. When viewed from the upper surface 12c side, the shape of the light guide plate 12 is substantially rectangular.
The thickness between the lower surface 12d and the lower surface 12d decreases from one side surface 12a to the other side surface 12b. A plurality of grooves extending parallel to the one side surface 12a are formed in the lower surface 12d, and the one side surface 12a and the other side surface 12a are formed.
The angle between b and the upper surface 12c is substantially 90 °.

The light diffusing sheet 14 is disposed such that the lower surface 14 b faces the upper surface 12 c of the light guide plate 12. The light diffusion sheet 14 is formed by dispersing a transparent spherical material (beads) on a transparent resin. The reflection sheet 16 includes the other side surface 12 b and the lower surface 12 b of the light guide plate 12.
It is arranged so as to cover d. The reflection sheet 16 is formed by, for example, densely dispersing bubbles of several μm to several tens μm inside a transparent resin sheet, or depositing a material having high reflectance such as silver or aluminum on a resin sheet or a metal plate. It is constituted by. Thereby, the reflection sheet 16
Is higher at least on the surface facing the light guide plate 12.

The upper surface 12a of the light guide plate 12 and the upper surface 14a and the lower surface 14c of the light diffusion sheet 14 are parallel to each other.

The linear light source 18 is provided on one side 1 of the light guide plate 12.
2a. As the linear light source 18, for example, a linear arrangement of fluorescent lamps or light emitting diodes such as a hot cathode tube and a cold cathode tube, or an incandescent lamp or an organic light emitting material formed linearly is used. The reflector 20 is arranged so as to cover the linear light source 18 except for the one side surface 12a. The reflector 20 is configured to have a high reflectivity on the inner surface. Such a characteristic is obtained, for example, by depositing a material having a high reflectivity such as silver or aluminum on a resin sheet, and forming the sheet on a thin metal plate or It is obtained by bonding to a resin sheet.

Referring to FIG. 2, lower surface 12d of light guide plate 12
Has a plurality of flat surfaces F substantially parallel to the upper surface 12c of the light guide plate.
Are formed stepwise. Top surface 12c from each flat surface F
Is gradually reduced from one side surface 12a to the other side surface 12b, and there is a step between adjacent flat surfaces F. The step portion includes one side surface 12.
A V-shaped groove L or slope S extending parallel to a is formed. Specifically, each groove L sandwiches at least two flat surfaces F, and each flat surface F in contact with the groove L is continuous with slopes L1 and L2 forming the groove L. Further, each flat surface F sandwiched between the grooves L is joined by a slope S parallel to the slope L1. The slope L1 and the slope S are parallel to each other, and the angle α formed with the flat surface F is 47 °. The width of the groove L gradually increases from one side surface 12a to the other side surface 12b.

Light rays emitted in the normal direction to the upper surface 12c of the light guide plate 12 are as follows. Assuming that the angle formed by the propagation direction of the light beam incident from the linear light source 18 with respect to the flat surface F is β, the light beam near β = 4 ° is totally reflected by the inclined surface L1 or S, and is normal to the upper surface 12c. It is emitted in a linear direction (see rays). When a light beam enters the slope L1 or S beyond a critical angle, the light beam exits the slope L1 or S and is reflected by the reflection sheet 16. The light beam reflected in the normal direction to the upper surface 12c has a flat surface F
From the light guide 12 again, and is emitted in a direction normal to the upper surface 12c (see light rays). On the other hand, the light beam is inclined L1.
Is incident on the slope L2 on the other side surface 12b side, which again forms the groove L, and enters the slope S near β = 4 °. It is emitted in the normal direction (see rays).

The relationship between the luminance of the light beam emitted from the upper surface 12c of the light guide plate 12 and the emission angle (the angle between the normal to the upper surface 12c and the emitted light) is shown by the dotted line A1 in the graph shown in FIG. Changed as shown. The positive direction of the horizontal axis of this graph is on the other side surface 12b side, and the negative direction is on the one side surface 12a side. According to the dotted line A1, the emission angle = 0 °
The vicinity is the central angle of the luminance distribution of the emitted light, and the light emitted from this angle has the highest luminance.

Referring to FIG. 3, light diffusion sheet 12 is made of P
It is obtained by arranging countless beads 14d on the upper surface of a sheet 14c made of ET (polyethylene terephthalate) resin and solidifying the beads 14d with a binder 14e. Therefore, the light beam emitted from the upper surface 12c of the light guide plate 12 is incident from the lower surface of the sheet 14c, and is emitted from the surface of the binder 14e through diffusion by the beads 14d. For this reason, the luminance of the light beam incident on the sheet 14c at the incident angle = 0 ° is reduced when the light beam is emitted from the binder 14e.

The relationship between the luminance of the light beam emitted from the upper surface 14a of the light diffusing sheet 14 and the emission angle (the angle between the normal to the upper surface 14a and the emitted light) is shown by the solid line B1 in the graph shown in FIG. It changed as shown by. That is, the central angle of the luminance distribution is almost 0 ° for both the dotted line A1 and the solid line B1, but the maximum luminance level is 7700c.
d / m ² to 7000 cd / m ² . this is,
As described above, the propagation direction of the light beam incident on the light diffusion sheet 14 at the incident angle = 0 ° is dispersed in different directions by the beads 14d.

Further, as a result of conducting experiments with the incident angles with respect to the lower surface 14b of the light diffusion sheet 14 set to 0 °, 30 °, 45 ° and 60 °, the upper surface 14
The relationship shown in FIG. 4 was established between the emission angle from a and the light intensity. Also in this graph, the positive direction of the horizontal axis is on the other side surface 12b side, and the negative direction is on the one side surface 12a side. According to FIG. 4, as the incident angle increases, the central angle of the luminance distribution moves toward the other side surface 12b, the maximum level of the light intensity gradually decreases, and the spread of the luminance distribution gradually increases. For light beams having incident angles of 30 ° and 45 °, some light intensity can be obtained even at an emission angle of 0 °.

As shown by the dotted line A1 in FIG. 5, not all the light beams emitted from the upper surface 12c of the light guide plate 12 are emitted at an emission angle of ± 45 ° instead of at an emission angle of 0 °. There are many rays. Such a light beam contributes to an increase in the amount of emitted light at an emission angle of 0 ° by diffusion in the light diffusion sheet 14. Therefore, the emission angle = 0 °
Is lower than the luminance at the incident angle = 0 °, but the degree of the decrease is such that all the rays have the incident angle = 0 °.
And becomes smaller than when incident.

FIG. 7 shows, as a comparative example, a luminance characteristic when a light guide plate having a shape as shown in FIG. 6 is used instead of the above-described light guide plate 12. In the light guide plate shown in FIG. 6, a plurality of V-shaped grooves are formed at step portions of each flat surface, and the slope (linear light source side) forming each groove has an angle α with respect to the flat surface.
= 47 °. The light beam incident on such a light guide plate behaves almost the same as when it is incident on the light guide plate 12 of this embodiment, and the luminance characteristic of the light beam emitted from the upper surface is indicated by a dotted line A2 in FIG. To change. Further, the luminance characteristic of the light beam emitted from the light diffusion sheet 14 disposed on the upper surface of the light guide plate changes as shown by a solid line B2 in FIG.

In each of the dotted lines A2 and B2 shown in FIG. 7, the vicinity of the emission angle = 0 ° is the central angle of the brightness distribution of the emitted light, and the light emitted from this angle has the highest brightness. However, while the maximum luminance of the light emitted from the light guide plate is 8200 cd / m ² , the maximum luminance of the light emitted from the light diffusion sheet 14 is reduced to 6400 cd / m ² . In other words, the luminance reduction width before entering the light diffusion sheet 14 and after exiting from the light diffusion sheet 14 is 700 cd / m ² in FIG.
Is 1800 cd / m ² . Moreover, the maximum luminance level of the light emitted from the light diffusion sheet 14 is smaller in the comparative example.

Such a result is obtained because the light emitted in the light guide of the comparative example in the range of an emission angle of ± 45 ° is emitted from the light guide 12 of the present example in the range of ± 45 °.
It is considered that the number of rays is smaller than that emitted in the range of °. In the dotted line A2 shown in FIG.
Because of the sharp rise near 0 °, the emission angle = 0
The maximum brightness in ° is higher than the dotted line A1. However, comparing the outgoing light amount in the range of the outgoing angle = ± 45 °, the outgoing light amount of this embodiment exceeds the outgoing light amount of the comparative example. As a result, even when the light is emitted from the light diffusion sheet 14, Maximum luminance of the embodiment (= 7000 cd / m ² )
Is larger than the maximum luminance (= 6400 cd / m ² ) of the comparative example.

The angle α between the slopes L1 and S is 47 °.
Another experiment confirms that the same result as described above was obtained when the angle was changed in the range of ± 2 °.

As described above, although the maximum luminance of the embodiment is higher than the maximum luminance of the comparative example at the stage of emission from the light diffusion sheet, the production of the mold for forming the light guide plate is performed in this embodiment. The example is simpler. That is, in order to form a mold corresponding to the lower surface of the light guide plate on the surface of the mold, it is necessary to cut the surface with a tool, but the tool used for manufacturing the mold for the light guide plate of this embodiment is You only need one. That is, as shown in FIG. 13, a flat surface is formed at the tip, and the angle between the flat surface and one side surface (the side surface in contact with the mold corresponding to the slope L1 or S) is 133 ° (=
If the surface of the mold is cut using a cutting tool set at 180 ° -47 °), a mold corresponding to the lower surface of the light guide plate of this embodiment can be formed, so that the manufacture of the mold is simple. As a result,
The manufacturing cost of the surface light source device 10 can be reduced.

Referring to FIG. 8, in the surface light source device 10 of another embodiment, the angle α formed by the inclined surfaces L1 and S formed on the lower surface of the light guide plate 12 with the flat surface F is changed to 22 °. ,
1 except that a prism sheet (lens sheet) 22 is disposed on the upper surface 14a of the light diffusion sheet 14. Therefore, a duplicate description of the same points will be omitted as much as possible.

The prism sheet 22 is arranged so that the lower surface faces the upper surface 14 a of the light diffusion sheet 14.
The prism sheet 22 is formed in a two-layer structure using a polyester resin and a high-refractive-index acrylic resin as materials.
On the upper surface, linear projections (prisms) P extending parallel to one side surface 12a of the light guide plate 12 and having an isosceles triangular cross section are provided.
Are formed in large numbers.

The light beam incident from the linear light source 18 propagates through the light guide 12 in the manner shown in FIG. 9 and is emitted from the upper surface 12c. That is, if the incident angle with respect to the slope L1 or S is large, the light ray is totally reflected by the slope L1 or S and is emitted from the upper surface 12c (light ray). If the incident angle with respect to the slope L1 or S is small, the light is once emitted from the slope L1 or S and then reflected by the reflection sheet 16. The reflected light beam enters the light guide 12 again from the flat surface F, and is emitted from the upper surface 12c (light beam). Further, even when the incident angle with respect to the flat surface F is small, the light beam is emitted from the flat surface F, and enters the light guide 12 again after being reflected by the reflection sheet 16. The incident light beam is thereafter emitted from the upper surface 12c (light beam).

The relationship between the luminance of the light emitted from the upper surface 12c and the emission angle (the angle formed by the normal to the upper surface 12c and the emitted light) is represented by a graph shown in FIG. FIG.
The positive direction of the abscissa is the other side surface 12b side, and the negative direction is the one side surface 12a side. This graph was determined by simulation, which shows that
The emission angle around 30 ° is the central angle of the luminance distribution of the emitted light, and the luminance of the light emitted from this angle is the highest.

The light beam emitted from the upper surface 12c is incident on the lower surface 14b of the light diffusion sheet 14 at an incident angle = 30 °,
The light is emitted from the upper surface 14a of the light diffusion sheet 14. As can be seen from FIG. 4, the center of the luminance distribution of the light beam emitted from the upper surface 14a is 25 °. The traveling direction of the light beam emitted from the light diffusion sheet 14 is then corrected by the prism sheet 22. Accordingly, light beams are emitted from the upper surface of the prism sheet 22 in a direction substantially orthogonal to the light diffusion sheet 14.

An experiment similar to that described above was conducted for this embodiment, and it was confirmed that good data was obtained. That is, a light guide plate having substantially the same shape as the light guide plate shown in FIG. 6 (the angle of the slope formed on the lower surface is 22 °) was used as a comparative example, and the luminance characteristics were measured. The level (outgoing angle = 35 °) was higher in the comparative example, but the maximum luminance level (outgoing angle = 30 °) on the upper surface of the light diffusion sheet was almost the same in the comparative example and the example. Further, the angle α of the slopes L1 and S is set to 22 ° ±
Another experiment confirmed that almost the same result was obtained when the angle was changed in the range of 2 °.

As described above, despite the fact that the maximum luminance of the embodiment is almost the same as the maximum luminance of the comparative example at the stage of emission from the light diffusion sheet, the production of the mold for forming the light guide plate is performed as described above. Similarly to this, this embodiment is simpler.
As a result, the manufacturing cost of the surface light source device 10 can be reduced.

In these embodiments, a groove is formed in a part of a step portion of a flat surface formed in a step shape on the lower surface of the light guide plate, and a slope is formed in the remaining step portion.
Instead of such a light guide plate, a light guide plate having grooves formed in all the steps as shown in FIG. 11 or 12 may be used. According to FIG. 11, the width of the groove is gradually increased while the pitch of the groove is constant, and the mold corresponding to this light guide plate uses one tool as shown in FIG. Created. According to FIG. 12, as the width of the groove is gradually widened, the pitch of the groove is gradually narrowed. A mold corresponding to this light guide plate is formed using one cutting tool as shown in FIG. Is done. The angle α formed by the inclined surface on the side of the linear light source with respect to the flat surface is 47 ° when the prism sheet is omitted, and 22 ° when the prism sheet is used.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is an illustrative view showing light beam propagation in a light guide plate applied to the embodiment in FIG. 1;

FIG. 3 is an illustrative view showing light diffusion in a light diffusion sheet;

FIG. 4 is a graph showing a relationship between an emission angle of a light beam emitted from the upper surface of the light diffusion sheet and a light intensity of the emitted light.

FIG. 5 is a graph showing the relationship between the emission angle of the light beam emitted from the upper surface of the light guide plate of this embodiment and the brightness of the emitted light, and B1 is the emission of the light beam emitted from the upper surface of the light diffusion sheet. It is a graph which shows the relationship between the angle and the brightness | luminance of emitted light.

FIG. 6 is an illustrative view showing propagation of light rays in a light guide plate used as a comparative example.

FIG. 7 is a graph showing the relationship between the emission angle of light emitted from the upper surface of the light guide plate of the comparative example and the luminance of the emitted light, and B1 is the emission angle of light emitted from the upper surface of the light diffusion sheet. 6 is a graph showing the relationship between the luminance of the emitted light.

FIG. 8 is a sectional view showing another embodiment of the present invention.

FIG. 9 is an illustrative view showing light beam propagation in a light guide plate applied to the embodiment in FIG. 8;

FIG. 10 is a graph showing a relationship between an emission angle of a light beam emitted from the upper surface of the light guide plate applied to the embodiment in FIG. 8 and luminance of the emitted light.

FIG. 11 is a sectional view showing a light guide plate applied to another embodiment of the present invention.

FIG. 12 is a sectional view showing a light guide plate applied to still another embodiment of the present invention.

FIG. 13 is an illustrative view showing a state of manufacturing a mold corresponding to the light guide plate shown in FIG. 2 or FIG. 9;

FIG. 14 is an illustrative view showing a state of manufacturing a mold corresponding to the light guide plate shown in FIG. 11;

FIG. 15 is an illustrative view showing a state of manufacturing a mold corresponding to the light guide plate shown in FIG. 12;

FIG. 16 is a sectional view showing a conventional technique.

FIG. 17 is an illustrative view showing a state of manufacturing a mold corresponding to the light guide plate of the related art;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Surface light source device 12 ... Light guide plate 14 ... Light diffusion sheet 16 ... Reflection sheet 18 ... Linear light source 20 ... Reflector 22 ... Prism sheet

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Claims (4)

[Claims] 1. A light guide plate having one side surface and the other side surface facing each other and for emitting light incident from the one side surface from an upper surface, and light emitted from the light guide plate disposed above the light guide plate. In a surface light source device including a diffusion sheet for diffusing, a lower surface of the light guide plate is parallel to each other and has a plurality of step-shaped flat surfaces in which a distance from the one side surface to the other side surface decreases as the distance from the one side surface to the other side surface increases, and A plurality of V-shaped grooves extending in parallel to the one side surface, each of the V-shaped grooves sandwiching at least two of the flat surfaces; and each of the flat surfaces contacting the V-shaped grooves forms the V-shaped groove A surface light source, wherein each of the flat surfaces which is continuous with each of the first slopes and which is sandwiched by the V-shaped grooves is connected by a second slope parallel to the first slope on the one side surface side. apparatus. 2. The surface light source device according to claim 1, wherein the width of the groove increases from the one side surface to the other side surface. 3. The first slope on the one side surface and the second slope.
3. The surface light source device according to claim 1, wherein an acute angle between the inclined surface and the lower surface is about 47 degrees. 4. A light guide plate further comprising a lens sheet disposed above the upper surface, wherein an acute angle formed by the first slope and the second slope on the one side surface with respect to the lower surface is about 22 °. The surface light source device according to claim 1, wherein