JP2003270446A - Light guide plate, surface illuminating device, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate which can suppress light/dark illuminance unevenness of output light, viewed from all directions, on a projection surface, a surface illuminating device, a display device, a portable telephone set, and a portable terminal device. <P>SOLUTION: The light guide plate 101 so constituted that light made incident from a light incidence part is diffused in a plurality of diffusion areas 103 formed on a diffusion surface 106 while propagated inside and then projected from the light projection surface 105 is characterized in that the axes of the plurality of diffusion areas 103 are directed to a certain direction (mean axial direction) on the average when the circumference of a certain position (e.g. Pa, Pb) is viewed, but distributed at random cyclically around the mean axial direction when viewed individually. <P>COPYRIGHT: (C)2003,JPO

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, a surface lighting device, a display device, a mobile phone, and a mobile terminal device.

[0002]

2. Description of the Related Art This thin type backlight is of an edge light type, and generally has a light guide plate on the bottom surface of which a diffusion pattern consisting of a large number of minute diffusion regions (sometimes called microlenses) is formed. , And a light source arranged on the end surface of the light guide plate. In the backlight configured as described above, the light emitted from the light source enters the light guide plate from the end face, and the incident light repeats total reflection between the upper surface and the lower surface of the light guide plate, and travels inside the light guide plate. The light that propagates and is diffused by the diffusion pattern in the meantime is emitted from the upper surface of the light guide plate. Further, the distribution of the diffusion area of the diffusion pattern is optimized, and the light quantity distribution of the light emitted from the upper surface of the light guide plate becomes uniform.

By the way, when a user actually views a display screen of a mobile phone or the like, it is almost always viewed from a direction perpendicular to the display screen (that is, from the front, not obliquely). Therefore, it is desirable that the display screen has high brightness when viewed from the front. That is, the light emitted from the backlight (hereinafter referred to as output light)
, It is desirable to increase the directivity so that the component in the direction perpendicular to the light emitting surface is increased (a ray component having a direction away from the front direction is not observed by the user, and only a loss of power consumption occurs. ).

A conventional example in which the shape and arrangement direction of the diffusion area of the diffusion pattern are optimized for such a purpose is WO98 / 1.
9105 (International application number PCT / JP97 / 0389
2, Japanese Patent No. 3151830).

FIG. 21 is a conceptual diagram showing the arrangement of diffusion regions in this conventional diffusion pattern, FIG. 22 is a diagram showing the shape of the diffusion regions in FIG. 21, (a) is a perspective view, and (b) is a diagram.
FIG. 4A is a cross-sectional view taken along the plane A1A2A3A4 in (a).

As shown in FIGS. 21 and 22, the diffusion pattern 100 is composed of a large number of diffusion regions 103, and each diffusion region 103 is a semi-cylindrical column on the lower surface (hereinafter also referred to as the diffusion surface) 106 of the light guide plate 101. Is formed as a convex portion. The axial directions of all the diffusion regions 103 match the tangential direction of a circle centered on the light source 102 in plan view. In other words, the position of the diffusion region 103 is P, and the light source 1 is
When the position of 02 is S, the direction of the axis 303 of the diffusion region 103 is perpendicular to the direction of the vector SP in plan view. Reference numeral 107 indicates a reflection sheet for returning the light leaked from the diffusion surface 106 of the light guide plate 101 to the inside of the light guide plate 101. Further, the concentric circles drawn in FIG. 21 are for visually representing the arrangement of the diffusion areas 103 in a plan view, and the diffusion areas 103 are actually the diffusion surfaces 10.
6 are arranged so as to be distributed at a predetermined density. 22A and 22B, the diffusion region 103
Is greatly exaggerated.

It will be described with reference to FIG. 23 that the directivity in the front direction can be enhanced by such a configuration. Figure 2
3 is a cross-sectional view schematically showing how the light ray 301 propagates in the plane Π including the normal line of the diffusing surface 106 and the vector SP at the point P in FIG. When the light ray 301 emitted from the light source 102 reaches the diffusion area 103 located at the point P, it is reflected or refracted by the peripheral surface of the diffusion area 103, but the direction of the axis 303 of the diffusion area 103 is perpendicular to the plane Π. Therefore, the normal to the peripheral surface of the diffusion region 103 is included in the plane Π, and thus the reflected ray 301a and the refracted ray are also included in the plane Π. Regarding the refracted light beam, once it goes out of the light guide plate 101, the reflection sheet 107.
Is reflected by and returns to the light guide plate 101 again.
Since the normal line of 07 is also included in the plane Π, all the traveling paths of this refracted ray are included in the plane Π. Therefore, as shown in FIG. 21, if the axial directions of all the diffusion regions 103 on the diffusion surface 106 are perpendicular to the direction of the vector SP,
Of the light rays emitted from the light source 102, those included in the plane Π will propagate only in the plane Π and will be scattered in a direction deviating from the plane Π (it hits the edge of the peripheral surface of the diffusion region 103). There is almost no (except the case such as). That is, most of the output light from the upper surface (hereinafter also referred to as the light emission surface) 105 of the light guide plate 101 is included in the plane Π, and the light has extremely strong directivity. When the directivity of the output light is schematically expressed with respect to the light guide plate 101 in consideration of a polar coordinate system as shown in FIG. 24, the direction distribution 308 of the output light rays indicating the directivity of the output light is shown in FIG. As shown in a), it extends in the direction of the vector SP. In FIG. 25 (a), the components of the respective light rays forming the output light are
This indicates that there are many directions in which the direction distribution 308 of the output light rays extends.

It can be said that the above-mentioned characteristics are obtained because the shape of the diffusion region 103 has a directivity. Here, the diffusion region 103 having directivity means that the diffusion region 10
3 has the same meaning as not having an axis of rotational symmetry perpendicular to the diffusion surface 106. For comparison, as shown in FIG. 26, there is no directionality, that is, the rotational symmetry axis 3 perpendicular to the diffusion surface 106.
Consider the case of a hemispherical diffusion region 103 with 04. In such a case, the normal vector at each point on the spherical surface of the diffusion region 103 is not necessarily parallel to the plane Π including the normal line of the diffusion surface 106 at the point P and the vector SP, so that a ray that hits the diffusion region 103 is obtained. Is reflected or refracted in all directions, and its directivity does not become strong in a specific plane. As a result, the directional distribution 308 of the output light rays, which represents the directivity of the output light, is particularly azimuth (diffusion surface 10).
The rotation angle in 6) has no direction with respect to φ, and
As shown in (b).

The directional distribution 303 of the output rays of FIG.
25B is compared with the directional distribution 304 of the output light rays in FIG. 25B, the directional distribution 303 of the output light rays in FIG. The proportion of components in the front direction (θ = 0 °) increases,
It can be understood that the front brightness increases accordingly.

By the way, in the structure shown in FIG.
However, it is actually necessary to use a plurality of light sources in order to make the display screen of the liquid crystal display device brighter. Therefore, it is also considered to arrange the diffusion region 103 so that the front brightness of the display screen can be increased for a plurality of light sources.
An example is shown in FIG. 27 of the above-mentioned document WO98 / 19105. FIG. 27 shows an arrangement pattern of the diffusion regions 103 in this conventional example. Here, the first
The light sources 102a and 102b are arranged at one end of the light guide plate 101 so as to be bilaterally symmetrical. Then, the position of the first light source 102a is changed to S
1. When the position of the second light source 102b is S2, the axial direction of the diffusion region 103 is perpendicular to the vector P-S1 in the left half region of the light guide plate 101, and in the right half region as well. It is arranged so as to be perpendicular to the vector P-S2. The shape of the diffusion region 103 is a semi-cylindrical shape as shown in FIG. 22, as in the case of one light source. In this way, the first light source 102a is provided in the left half of the light guide plate 101.
Similarly, in the right half, the light from the second light source 102b is output in the front direction with high directivity, and in the end, the high directivity of the output light in the front direction is obtained on the entire surface of the light guide plate 101. Become.

When a plurality of light sources are used, the arrangement pattern of the diffusion region 103 may be as shown in FIG. 21 so that the plurality of light sources are concentrated at the position S. However, such a configuration is not preferable because the temperature rise due to the heat generated by the light source becomes large and the light source and the light guide plate are easily deteriorated. In order to disperse heat effectively, it is desirable to disperse and arrange a plurality of light sources.

[0012]

As described above, FIG.
With the configuration shown in (1), high brightness can be obtained by using a plurality of light sources, and directivity in the front direction can be increased to further increase brightness. Further, since heat can be effectively dispersed, deterioration of the light source and the light guide plate can be prevented.

Therefore, we actually made a prototype of the display device by adopting the configuration of FIG. At this time, by optimizing the distribution density of the diffusion region, the brightness when viewed from the front direction of the light guide plate was made uniform. However, even with such optimization, it was observed that when the light guide plate was tilted and viewed from a direction deviated from the front, the brightness was not uniform and the brightness was uneven. That is, it has been clarified that the light guide plate of FIG. 27 has a problem that the brightness when viewed from the front and the brightness when viewed from the diagonal cannot be made uniform at the same time.

The present invention has been made to solve the above problems, and has a light guide plate, a surface illuminating device, a display device, a mobile phone, which has no brightness inclination when viewed from the front or the oblique direction. It is intended to provide a mobile terminal device.

[0015]

In order to solve the above-mentioned problems, a light guide plate according to the present invention is formed on a diffusing surface while at least part of a light-incident part is propagated in the light-incident part. A light guide plate configured to be emitted from a light emitting surface by being diffused by a plurality of cylindrical diffusers, wherein the diffuser surface among the plurality of diffusers formed on the diffuser surface. From the average axial direction obtained by averaging the central axis directions of the semi-cylindrical diffusers existing in the area of the predetermined range, the center of each semi-cylindrical diffuser existing in the area of the predetermined range At least a part of the axis is offset (claim 1). With such a configuration, it becomes possible to control the reflected light azimuth distribution near the position,
It is possible to suppress the brightness inclination when the light guide plate is obliquely generated due to the planar spread of the light emitting region of the light source.

Further, in the light guide plate according to the present invention, the light incident from the light incident portion propagates inside and is diffused by a plurality of diffusers which are formed on the diffusion surface and at least a part of which has a semi-cylindrical shape. The light guide plate is configured to be emitted from the light emission surface by being subjected to the above, and each of the diffusers has a curved central axis (claim 5). Even with such a configuration, it is possible to control the reflected light azimuth distribution in the vicinity of the position, and it is possible to suppress the brightness inclination when the light guide plate is obliquely generated due to the planar spread of the light emitting region of the light source. Becomes

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a vertical sectional view showing a configuration of a liquid crystal display device as a display device according to Embodiment 1 of the present invention, and FIG. 2 shows a diffusion pattern of a light guide plate of the liquid crystal display device of FIG. It is a top view. Further, FIG. 3 is an enlarged view of the array of diffusion regions in the minute regions indicated by A and B in the diffusion pattern of FIG.

1 and 2, a liquid crystal display device 200 according to this embodiment includes a liquid crystal panel 110 and a backlight 109 as a surface lighting device, and a pair of polarizing films 111a and 111b are attached to both surfaces. The liquid crystal panel 110 is configured to be illuminated by the backlight 109 arranged below.

The backlight 109 is of an edge light type, and includes a light guide plate 101 and a light source 102 arranged on an end surface of the light guide plate 101. Since such a backlight 109 has a structure in which the light source 102 is provided not on the lower side of the light guide plate 101 but on the side surface (end surface), it can be thinned and is suitable for use in a mobile phone, a mobile terminal, or the like. It has become a thing.

Further, in the present embodiment, the light guide plate 101
The reflection sheet 107 is arranged on the lower side of the light guide plate 101, and the diffusion sheet 108 is arranged on the upper side of the light guide plate 101. The reflection sheet 107 and the diffusion sheet 108 may be omitted.
Further, if necessary, a lens sheet or a prism sheet for increasing the directivity of output light may be arranged above the diffusion sheet 108.

The light source 102 is an LED as shown in FIG.
The light guide plate 101 includes a point light source such as a light emitting diode. Here, on one end face 104 in the vertical direction of the light guide plate 101, two vertical boundary lines (hereinafter, referred to as vertical center lines) 801a and 801 are provided.
It is composed of first, second, and third light sources 102a, 102b, and 102c arranged symmetrically with respect to b. That is, three light incident portions on the light guide plate 101 are formed.

The light guide plate 101 is made of a resin material such as polycarbonate or a transparent medium having a large refractive index, such as glass, and is formed in a rectangular plate shape having a predetermined constant thickness. Further, in the light guide plate 101, the diffusion pattern 100 is formed on the lower surface 106 to form a diffusion surface, and the upper surface 105 forms a light emission surface. As described in the description of the conventional example, the diffusion pattern 100 is composed of a large number of diffusion regions 103, and each diffusion region 103 is formed in the diffusion surface 106 of the light guide plate 101 as a semi-cylindrical recess.

The diffusion pattern 100 includes a first region R1, a second region R2, and a third region which are respectively formed in the upper part ⅓, the central part ⅓, and the lower part ⅓ of the diffusing surface 106. Region R3. Here, the first region R
Pay attention to the positions indicated by Pa and Pb in 1 and the diffusion regions 103 in the regions A and B near these positions.
3 (a) and 3 (b) respectively show the state of the arrangement. For example, according to FIG. 3B, the neighborhood area B
The direction of the axis 303 of the diffusion region 103 inside (hereinafter referred to as the axial direction of the diffusion region) faces the direction indicated by Dt in the figure (hereinafter referred to as the average axial direction) when viewed as an average in the neighboring region B. However, regarding the individual diffusion regions 103, their axial directions are slightly different. That is, they are randomly deviated by a minute angle from the average axial direction Dt. The same applies to the neighborhood region A, but the variation (standard deviation) of the axis 303 of the individual diffusion regions 103 from the average axial direction Dt is smaller than that of the region B. (Fig. 3
(A)). That is, in the region R1, the standard deviation of the distribution of the diffusion region 103 in the axial direction is small in the portion close to the light source 102a and large in the portion far from the light source 102a. In addition, the diffusion area 1 at the position A and the position B
The average axial direction Dt of 03 is substantially perpendicular to the direction of the light source installation position S1 and the vectors S1Pa and S1Pb connecting these positions in a plan view. That is, the average axial direction is concentric in the region R1.

The first region R1 has been described above, but the second region R2 and the third region R3 have the same arrangement.

The directional field depicted in FIG. 2 is for visually representing the axial direction of the diffusion area in a plan view, and the diffusion area 103 is actually a predetermined area on the diffusion surface 106. It is arranged so as to be distributed in density. That is,
When the light propagates in the light guide plate 101, the light source 102a,
The amount of propagating light is large in the portions near 102b and 102c, and the amount of propagating light decreases as the distance from the light sources 102b, 102a, and 102c increases.
3 is arranged so that the density increases as the distance from the light sources 102b, 102a, and 102c increases. As a result, relatively uniform output light can be obtained over the entire light emitting surface 105.

The size of the diffusion region 103 in the minor axis direction is generally larger than the size of the wavelength of light (several hundreds of nm), and even if they are arranged, they cannot be recognized by the naked eye as the arrangement of the diffusion regions 103. Size (several hundred μm to 1 m
m)) or less. In FIG. 2, the individual diffusion regions 103 are drawn as if they can be recognized for easy understanding, but in general, the individual diffusion regions 103 are illustrated.
Are more closely arranged (ie, diffusion area 1
The total number of 03 is much larger than that shown in Fig. 2).

The term "neighboring region" is used in the above description. This is sufficiently smaller than the area of the diffusing surface 106, but when the statistical average in the axial direction is taken, the number can be sufficiently neglected from the influence of variations in the individual axial directions (at least 10 to several tens). It may be considered as a region including the diffusion region 103). By thinking in this way, the diffusion surface 1
The average axial direction at any position within 06 can be defined as a function of that position.

Further, in the above description, the term "average axis direction" is used as the average value in the axial direction of the diffusion area, and the term "standard deviation" is used as the index indicating the variation in the axial direction. Think of it as purely mathematical definition. That is, assuming that there are N diffusion regions in the neighborhood region, the axial direction in the i-th plan view of them is represented by an angle δi ((to define this angle, the reference direction in the plane is determined in advance). It is necessary, but this can be in any direction), but the average axial direction <δ> is (Equation 1)
Then, the standard deviation σ is expressed by (Equation 2).

[0029]

[Equation 1]

[0030]

[Equation 2]

Further, in the above description, the expression "portion near (far from) the light source" is used, but this can be rephrased as "portion near (far from) the light incident portion", which means exactly the same.

Next, the operation of the liquid crystal display device configured as described above will be described. In this liquid crystal display device, the light emitted from the first and second light sources 102a and 102b is the end surface 1
04 enters the light guide plate 101, and the incident light propagates in the light guide plate 101 while repeating total reflection between the light emitting surface 105 and the diffusion surface 106 of the light guide plate 101, and from the diffusion surface 106 in the meantime. The leaked light is returned into the light guide plate 101 by the reflection sheet 107, and the light diffused by the diffusion pattern 100 is emitted from the light emitting surface 105. The emitted light is diffused by the diffusion sheet 108, and then the liquid crystal panel 11
It is incident on 0. Then, the liquid crystal panel 110 of this incident light
The display is performed by controlling the transmittance in (1) by a driving device (not shown).

Next, a plurality of light sources 1 which is a feature of the present invention
1 to 15 show the effect of suppressing the occurrence of the luminance gradient on the light emitting surface of the light guide plate 101 due to the presence of the light guide plates 02a and 102b.
And FIG. 28.

FIG. 4 is a perspective view showing the coordinate arrangement of a semi-cylindrical diffusion area, and FIG. 5 is a polar coordinate graph showing the azimuth distribution of scattered light by the semi-cylindrical shape of FIG. 4, where (a) is Φ = 0 °. In the case of Φ = 5 °, (b)
Is a diagram showing a case of Φ = 30 °, (d) is a diagram showing a case of Φ = 60 °, and (e) is a diagram showing a case of Φ = 90 °. 6 is a plan view of a conventional light guide plate, and FIG.
(A) and (b) are positions P1 and P in FIG. 6, respectively.
2 is a diagram showing the relationship between the arrangement of diffusion areas and the direction of light rays in FIG. Further, FIGS. 8A and 8B are respectively shown in FIG.
It is a figure which shows the reflected light (scattered light) direction distribution in (a) and (b). 9 (a) and 9 (b) respectively show the reflected light azimuth distributions of FIGS. 8 (a) and 8 (b) superimposed on various incident light azimuths. FIG. 10 is a diagram showing the arrangement of the diffusion areas of the light guide plate of the present invention, and FIGS. 11A and 11B show the relationship between the arrangement of the diffusion areas and the ray direction at the positions P1 and P2 of FIG. FIG. 11C and 11D are examples of the probability density distribution in the axial direction δ of the diffusion region in FIGS. 11A and 11B, respectively. 12
(A), (b), and (c) are respectively FIG. 11 (b).
13A and 13B are views showing the reflected light azimuth distributions with respect to the diffusion regions 103p, 103q, and 103r of FIGS. 13A and 13B, respectively, and FIG. 13A and FIG. 13B are reflection lights from the diffusion regions in various axial directions at positions P1 and P2 of FIG. It is a superposition of azimuth distributions. FIG. 14 shows S1 of the light guide plate of FIG.
It is a graph which shows an example of how to give a standard deviation of distribution of the direction of an axis of a diffusion field on a straight line of -P1-P2. Figure 15
FIG. 6 is another diagram showing the arrangement of diffusion regions of the light guide plate of the present invention. FIG. 28: is a figure which shows another example of how to give distribution of the axial direction of the diffusion area | region in the light guide plate of this invention.

First, let us consider in what direction a light beam is scattered when it enters the semicylindrical diffusion region 103. Since this analysis is described in detail in Japanese Patent Application No. 2000-343614, only a summary thereof will be given below.

It is assumed that there is a semi-cylindrical diffusion area 103 as shown in FIG. 4, into which a ray indicated by a direction ki is incident and reflected by a direction indicated by ko. Here, the coordinates are taken so that the xy plane coincides with the surface 112 of the reflection sheet. And the incident ray vector k
The direction when i is projected on the xy plane is taken as the x axis. Further, at that time, the axis of the diffusion region (the central axis of the cylinder 402) 303 is assumed to face the direction rotated by Φ from the y-axis.

Here, the vectors ki and ko (hereinafter simply referred to as ki and ko, respectively) are expressed by the following equation (3) using the azimuths (θi, 0) and (θo, φo) in polar coordinates, respectively. It is expressed as in equation (4).

[0038] ki = (sin θi, 0, cos θi) (3)   ko = (sinθocosθo, sinθosinφo, cosθo)                                       ... Formula (4) However, ki and ko are assumed to be unit vectors.

At this time, the azimuth of the reflected light (θo, φo)
Is actually calculated, and what is illustrated is the polar coordinate graphs of FIGS. 5A to 5E (this is the same as FIG. 7 of Japanese Patent Application No. 2000-343614).
Here, the inclination angles Φ of the axis 303 of the diffusion region 103 from the y-axis are 0 °, 5 °, 30 °, 60 °, and 90, respectively.
Calculated for the case of °. In these polar coordinate graphs, θo is taken in the radial direction and φo is taken in the circumferential direction.
According to FIG. 5, when Φ = 0 ° (when the axis of the diffusion region and the traveling direction of the incident light beam are perpendicular to each other), the directivity extends in the traveling direction of the incident light beam, but Φ is 0. When the angle becomes larger than ゜, the azimuth of the reflected light becomes the front direction (θo = 0
It shows that it deviates from the (direction of °).

When Φ is negative, | Φ | (= -Φ)
It can be considered that the polar graph for is simply flipped up and down.

The above is a summary of the analysis in Japanese Patent Application No. 2000-343614. Based on this, the conventional light guide plate 101 shown in FIG. 27 is also optimized so that the front luminance becomes uniform. Regardless, consider the cause of the brightness gradient when viewed from an oblique direction. Now, paying attention to the left half region of FIG. 27, consider a position P1 near the light source 102a and a position P2 far from the light source 102a. These positions are as shown in FIG. For simplicity, positions P1 and P
2 is on a straight line extending from the light source installation position S1 in the direction perpendicular to the end surface 104. At this time, the axial directions of the diffusion regions 103 at the positions P1 and P2 are both parallel to the end surface 104, and the axial direction of FIG.
It can be drawn like (a) Ohobi (b).

Generally, the light source is not a perfect point light source, but its light emitting portion has a planar spread. Therefore, even if it is said that the light ray reaches straight from the light source to the positions P1 and P2 (in plan view), the direction of the light ray coming from the left end of the light source light emitting portion is slightly different from that of the light ray coming from the right end. Then, the position P1 is closer to the light source 1 than the position P2.
Since it is close to 02a, the angle ε1 that looks at the light emitting region from the position P1 is larger than that ε2 from the position P2.
Therefore, the position P1 has a larger spread in the direction of the reaching ray than the position P2. For example, in FIG. 7A, a ray reaching the position P1 from the left end of the light source 102a is represented by r1.
(L), the ray reaching the position P1 from the right end is r1 (R)
If expressed by, the range of the direction of the light beam from the light source 102a is included between the direction r1 (L) and the direction r1 (R), and the spread angle is ε1. The same applies to FIG. 7B, and the spread angle in the direction of the light ray is ε2. However, a ray reaching the position P2 from the left end of the light source 102a is r2.
(L), the ray reaching the position P2 from the right end is r2 (R)
It is represented by.

Now, in FIG. 7A, the light ray r1 (L)
Consider the direction of scattering by. Now, assuming that the direction in which the light ray r1 (L) is projected onto the diffusing surface 106 is the x axis and the direction perpendicular to it on the diffusing surface 106 is the y axis, the positional relationship between the light ray r1 (L) and the diffusing area 103 is as shown in FIG. Φ = ε1 / 2 in 4
Is equivalent to For example, if ε1 = 60 °, Φ = 30 °, and the azimuth distribution of scattered light is shown in FIG.
It is represented in the polar coordinate graph of. Figure 7
When redrawn according to the direction of (a), the distribution is as shown in (a) of FIG. Further, the direction of scattering by the ray r1 (R) can be considered in the same manner, and FIG.
The distribution is as shown by. This is substantially bilaterally symmetrical with the scattering distribution by the light ray r1 (L). Further, although not shown in FIG. 7A, the light beam reaching the point P1 from the light source center has a positional relationship with the diffusion region 103 in the case of Φ = 0 ° in FIG.
The distribution extends in the ray direction as shown in the polar coordinate graph of (a). Therefore, the distribution is as shown in FIG. 8 (a). In addition, if various rays having a direction between r1 (L) and r1 (R) are considered in the same manner, it is inferred that the distribution will be sandwiched between the original orientation distributions. Therefore, if all the light rays reaching the position P1 from the light emitting region of the light source 102a are overlapped with the scattering azimuth, it can be drawn as shown in FIG. 9A.

On the other hand, with respect to FIG. 7B, it can be considered in exactly the same manner as in the case of FIG. 7A, and the ray r2 (L),
The scattering orientation distributions for the ray r2 (R) and the ray reaching the point P2 from the center of the light source are shown in FIG.
, And are represented by. Then, the superposition of the scattering directions of all the light rays reaching the position P2 from the light emitting region of the light source 102a has a distribution as shown in FIG. 9B.

Scattering orientation distribution of FIG. 9 (a) and FIG. 9 (b)
Comparing the scattering azimuth distributions of Nos. 1 and 2 with attention paid to the portion shown by the cross section X1-X2, the widths of the two are significantly different. This indicates that the brightness gradient occurs in a fairly wide azimuth range. In fact, when the light guide plate is observed from a direction such as the point indicated by the symbol A, which is included in the scattering direction distribution but not included in the scattering direction distribution, bright light is observed near point P1 but near point P2. Will be observed in the dark. Therefore, it is observed as an in-plane luminance gradient.

The above problems are caused by the fact that the light source is not an ideal point light source and the light emitting region has a planar spread. However, conversely, in the case of a backlight configuration in which light is incident from one side (or a plurality of sides) of the light guide plate by a linear light source such as a fluorescent tube, the above problem does not occur. In that sense, this can be said to be a problem peculiar to the case where a light source having a very limited light emitting region (in other words, sufficiently smaller than the side length of the light guide plate) is used.

Therefore, based on the above analysis, a light guide plate capable of preventing the occurrence of a brightness inclination when viewed from an angle was devised. This is the present invention, and the essence is to provide a random distribution centered on the average axial direction in the direction of the diffusion directional axis of each diffusion region (for example, the axial direction of the diffusion region). . Hereinafter, FIG. 2 showing an embodiment of the present invention.
The principle of the present invention will be described for the case of the light guide plate of No. 2 (the difference is that the light guide plate of FIG. 27 of the conventional example has two light incident positions and the light guide plate of FIG. 2 of the present invention has three light incident positions). But this is not an essential difference).

The light guide plate of FIG. 2 showing the embodiment of the present invention is simplified and shown again in FIG. This is the same as FIG. 2, but in order to avoid making the drawing complicated, the arrangement of the diffusion regions is simplified and expressed by concentric circles. For convenience of explanation, the vertical and horizontal directions are interchanged. Now, pay attention to a position P1 near the light source 102a and a position P2 far from the light source 102a in the first region R1 of the light guide plate as shown in FIG. For simplicity, the positions P1 and P2 are on a straight line extending from the light source installation position S1 as a starting point in a direction perpendicular to the end surface 104 (similar to the case of FIG. 6). At this time, the average axial direction Dt of the diffusion regions near the positions P1 and P2 are both parallel to the end surface 104, and the diffusion regions 103 are arranged as shown in FIGS. 11A and 11B, respectively. In any diffusion region 103,
The direction of the axis 303 is given a random distribution from the average axis direction Dt, but the degree of variation (standard deviation) in the direction of the axis 303 is larger in FIG. 11B. For reference, an example of the probability density distribution in the axial direction δ with respect to FIGS. 11A and 11B is shown in FIG.
It becomes like (c) and (d). However, the diffusion region 10
The axial direction of 3 is represented by an angle δ (the counterclockwise direction is positive) δ with respect to the reference direction Dn shown in FIG. The reference direction Dn may be set to any direction, but here, it is set to the direction perpendicular to the end surface 104. Figure 11
In (b), for example, diffusion regions 103p, 103q,
And the axial direction δ of 103r correspond to the portions indicated by p, q, and r in FIG. 11 (d), respectively. Figure 11
Comparing (c) and (d) shows that FIG. 11 (d) has a larger lateral spread and a larger standard deviation.

Note that, in FIGS. 11C and 11D, since it is the distribution in the axial direction of a finite number of diffusion regions in the neighborhood region, strictly speaking, it should be drawn as a discrete probability distribution. However, in order to facilitate understanding, it is drawn as an approximate continuous distribution.

Now, paying attention to FIG. 11B, the diffusion region 1
Consider the azimuth distribution of reflected rays for 03p, 103q, and 103r. Following the example of FIG. 7 in the case of the conventional example, a ray reaching the position P2 from the left end of the light source 102a is r2.
(L), the ray reaching the position P2 from the right end is r2 (R)
In the case of the diffusion region 103q, since the positional relationship between the axial direction and the direction of each light ray is exactly the same as that in FIG. 7B, the azimuth distribution of the reflected light is similar to that in FIG. 9B. Become. This is reproduced as FIG. 12 (b). Also in the case of the diffusion region 103p, the reflected light is reflected based on FIG. 5 with respect to various light rays having directions included between the light rays r2 (L) and r2 (R) by the procedure similar to that performed in FIG. 8 of the conventional example. When the azimuth distributions of A and B are obtained and superposed, a reflected light azimuth distribution as shown in FIG. 12A is obtained. Furthermore, the diffusion region 103
With respect to r, the reflected light azimuth distribution as shown in FIG. 12C is obtained in exactly the same manner.

It is considered that the output light from the light emitting surface 105 at the position P2 corresponds to the superposition of the reflected light at each diffusion region 103 in the region near the position P2. Therefore, the output light azimuth distribution corresponds to the azimuth distribution obtained for each axial direction δ as shown in FIG. 12, weighted with the probability density distribution of FIG. FIG. 13B is obtained as the output light azimuth distribution actually drawn in this way.
In this distribution, the distributions of FIGS. 12A, 12B, and 12C also greatly contribute, and certainly FIG.
Each of these distributions is also included in (b).

Since the light guide plate of FIG. 10 is arranged so that the average axial direction of the diffusion region is perpendicular to the direction of the vector S1P2, the brightness when viewed from the front is the highest. .

As described above, the analysis is performed on FIG. 11B, which is the diffusion area arrangement at the position P2, but the same analysis is performed on FIG. 11A that is at the position P1. The output light azimuth distribution as shown in FIG. 13A is obtained. The diffusion area layout at the position P1 is shown in FIG.
As can be seen from (a), the variation in the axial direction is relatively small, and the configuration is similar to that of FIG. 7 (a) of the conventional example. Therefore, the output light azimuth distribution becomes close to that shown in FIG.

Focusing on the portion indicated by the cross section X1-X2 in the orientation distribution diagrams of FIGS. 13A and 13B, there is almost no difference in the widths of the scattering orientation distributions of the two. This is in contrast to the case where the scattering direction distribution widths in FIGS. 9A and 9B in the case of the conventional example are significantly different.
It is often the case that the display area of a display device such as a mobile phone is actually observed at most within 30 ° from the front, but within this range (the azimuth range within the circle indicated by the broken line in the figure) It can be considered that the distributions of the scattering directions are substantially the same. Therefore, there is almost no azimuth in which a brightness gradient appears like point A in FIG. 9, and even if the light guide plate is viewed from any direction, uniform brightness is observed in the plane.

As described above, a random distribution centered on the average axial direction is given in the axial direction of the diffusion region, and the standard deviation at that time is made small at a position close to the light source and large at a position far from the light source, thereby making it oblique. It was explained that the luminance gradient when viewed can be suppressed and the uniformity can be improved.

In the above description, two positions, that is, a position P1 near the light source and a position P2 far from the light source have been described as representative points. However, at each position other than these, the distance from the light source at that position (or light emission from the light source). It goes without saying that if the standard deviation σ given to the distribution in the axial direction of the diffusion region is defined according to the angle ε) for viewing the region, uniform display can be obtained on the entire surface of the light guide plate when viewed obliquely. Further, in addition to the positions P1 and P2, the average axial direction of the diffusion area is perpendicular to the direction when the position is viewed from the light source installation position, that is, the average axial direction is centered on the light source installation position. It goes without saying that the highest directivity can be obtained in the front direction on the entire surface if the concentric circles are arranged.

By the way, assuming that the light source is an ideal point light source (that is, the angle of the light emitting area of the light source is 0),
Moreover, if the distribution of the diffusion region in the axial direction is completely uniform (that is, the standard deviation of the distribution is 0), the width of the finally obtained scattering orientation distribution in the X1-X2 cross section is close to 0, which is extremely small. It is considered to be sharp. In addition to these two factors, as described above, (1) the spread in the light beam direction based on the planar spread of the light emitting area of the light source, and (2) the standard deviation of the axial distribution of the diffusion area are added. As a result, the width of the scattering direction distribution is widened.
That is, the width of the scattering direction distribution at a certain position is twice the angle ε when the light emitting region of the light source is seen from that position in plan view and the standard deviation σ of the axial distribution of the diffusion directionality of the diffusion region. (The deviation from the average axial direction has positive and negative sides, so the axial angular range should be 2σ instead of σ). Therefore, if σ is given at each position so that the value of 2σ + ε is substantially constant regardless of the position, a uniform display can be obtained on the entire surface of the light guide plate when viewed obliquely. However, in order to specifically define σ in this way, it is necessary that the size of the light emitting region of the light source is given. That is, it is a configuration that can be realized for the first time as a surface lighting device including a light guide plate and a light source.

For reference, FIG. 14 shows an example of a concrete method of giving σ. This is a graph of the values of σ, ε, and 2σ + ε on a straight line connecting the light source installation position S1, the position P1, and the position P2 in the light guide plate of FIG. 10, and the horizontal axis indicates the distance from the light source 102a. (This is represented by x). In FIG. 10, the angle ε looking into the light source emission area from each position is given by (Equation 5), where Ws is the width of the light source emission area.

Ε = 2 tan−1 (Ws / 2x) (Equation 5) FIG. 14 shows a curve for Ws = 1.8 mm as an example. The standard deviation σ is 2σ + ε at each position is 60
The value is given in degrees (a value of 60 degrees is an example numerical value and does not necessarily have to be this value). That is, the x dependence of σ is given by (Equation 6).

Σ = (60 ° −2 tan−1 (Ws / 2x)) / 2 (Equation 6) If (Equation 6) is applied as it is, a position very close to the light source (x <(√3 / 2) Ws ( ≈1.56 mm) area)
, Becomes a negative value, and the standard deviation σ is 0 or a positive value. Therefore, we abandon to keep 2σ + ε constant in this region (in this case σ =
0 is given). Even in this case, as long as this area is sufficiently narrow, the uniformity will not be significantly deteriorated. In the present specification, when simply saying “to make 2σ + ε constant”, this region is excluded.

As a matter of course, σ = 0 corresponds to the case where no distribution is given in the axial direction of the diffusion directionality of the diffusion region.

It is not always necessary to give the random distribution in the axial direction of the diffusion direction of the diffusion region to the entire diffusion surface 106. For example, a configuration in which no distribution is given to a portion near the light source (corresponding to FIG. 14 described above) or a side far from the light source (for example, FIG.
Even if the light guide plate of 0 has a structure in which the distribution is provided only in a part of the vicinity of the side facing the end surface 104), the effect of suppressing the brightness gradient can be obtained.

The average axial direction of the diffusion directionality of the diffusion region at a certain position is almost perpendicular to the direction when viewed from the light source installation position (in plan view) from the light source installation position. If there are multiple light incidence parts,
It is sufficient that it is substantially perpendicular to the direction when viewed from at least one of the light source installation positions. Further, it is not always necessary that the average axial direction is substantially perpendicular to the direction when viewed from the light source installation position in the entire diffusion surface 106. For example, when there are a plurality of light incident parts, connection points between regions corresponding to respective light sources (for example, vertical center lines 801a and 801 in the light guide plate of FIG. 2).
In order to prevent the occurrence of luminance discontinuity in b),
A configuration is conceivable in which a transition region is provided between the two regions and the average axial direction of the diffusion region is gradually changed with the position here (for example, Japanese Patent Application No. 2001-343614).
(Corresponding to the essence of the present invention added to the diffusion area pattern arrangement of the light guide plate as shown in FIGS. 15 and 18). In such a case, the average axial direction in such a transition region is not necessarily perpendicular to the direction when viewed from the light source installation position, but it is vertical in most of the regions excluding such transition region. If so, the effect of improving uniformity as in the present invention can be sufficiently obtained.

When the distribution is given in the axial direction of each diffusion region as in the present invention, the width of the scattering direction distribution is widened as shown in FIG. 13B, so that the axial direction of the diffusion region is as described above. The decrease in brightness when deviating from the vertical condition is mitigated.
By utilizing this, it is possible to improve the uniformity without significantly lowering the brightness when viewed from the front. For example, in the light guide plate of FIG. 15, the average axial direction of the diffusion region is not concentric like that of FIG.
It is arranged in a direction close to 04. By doing so, the front luminance is not reduced and the boundary between the first region R1 and the second region R2, or the second region R2 and the third region R3.
At the boundary of (indicated by a one-dot chain line), the sudden change in the average axial direction of the adjacent diffusion regions can be mitigated, and the discontinuous change in brightness when viewed from an oblique direction can be mitigated, resulting in uniformity. The effect of being improved is obtained.

When there are a plurality of light incident portions, each area does not necessarily have to be equally divided into strips as shown in FIG. The area and shape of each region may be different,
The boundary lines may be polygonal lines or curved lines.

A random distribution was assumed as the axial distribution of the diffusion directionality of each diffusion region in the vicinity of a certain position on the diffusion surface, but it does not have to be random, and a certain regularity is required. Of course, it does not matter if the distribution is generated based on For example, when the diffusion regions are arranged in a grid like the light guide plate of FIG. 2, when the row and column numbers are represented by i and j, sin (2πi) is added to the diffusion region designated by (i, j). / A) or sin (2
πj / a) (a represents the period of distribution. As an example, a =
(6, 8 or the like), etc., a method of giving a shift angle proportional to the above can be considered. 28 (a) and 28 (b), sin as the deviation angle from the average axial direction Dt is expressed as sin.
An example when a distribution proportional to (2πj / 8) is given is shown. This method is based on CAD (Computer Aide).
The feature is that it is easy to generate data in d Design).

In the liquid crystal display device 200, the light guide plate 1
Since the display of the liquid crystal panel 110 is controlled by controlling the transmittance of the output light emitted from the light emission surface 105 of the liquid crystal display panel 01, the display of the liquid crystal panel 110 is similar to that of the light guide plate 110. The effect of improving uniformity is obtained.

In the above example, the case where there are three light sources has been mainly described. However, the essence of the present invention is not related to the number of light sources. For example, even if there is only one light source, 2
It does not matter whether the number is four or four. However, in order to obtain sufficient output light brightness, it is desirable that there be two or more light sources (that is, it is desirable that the light guide plate has a plurality of light incident portions). (Embodiment 2) Next, a second embodiment of the present invention will be described. This is based on the use of a diffusion region having a curved central axis rather than a semi-cylindrical shape. The basic structure of the light guide plate, the surface lighting device, or the display device as a whole is the same as that shown in FIG.

FIG. 16 shows the three-dimensional shape of the diffusion region used in the present invention. This is a drawing in which only the concave portion formed on the bottom surface (diffusing surface 106) of the light guide plate is taken out as shown in FIG. Instead of the semi-cylindrical shape as in Figure 4,
It is characterized by a curved shape. The shape of the diffusion region 103 is a semi-circular plane 903 (which is not necessarily a semi-circle, but is regarded as a semi-circle for simplification of description) along a curve 913 included in the diffusion surface 106. It is defined as a solid that is created when moving while satisfying the following conditions. [1] The center of the semicircular plane 903 is included in the curve 913. [2] The chord of the semicircular plane 903 is parallel to the diffusion surface 106. [3] The normal vector of the semicircular plane 903 is The center is parallel to the tangent of the curve 913 at a certain position. Here, the curve 913 (that is, the locus of the semicircular plane 903) is referred to as the central axis 913 of the diffusion region 103, and the semicircle from the start surface to the end surface of the diffusion region 103. The change angle of the normal vector direction in the diffusion surface 106 when the plane 903 is moved will be referred to as a bend angle. It can be said that the bending angle γ is an intersection angle when extending in the radial direction on the starting surface and the ending surface of the diffusion region 103. In addition, a semicircular plane 903 on the starting surface and the ending surface of the diffusing surface 103.
The direction of the straight line connecting the centers of the two is called the average axial direction 803.

The arrangement pattern of the diffusion regions 103 according to the present invention is exactly the same as that shown in FIG. 10 in (Embodiment 1). That is, the average axial direction 8 of the diffusion region 103
03 are concentrically arranged with the light source installation position as the center. The arrangement patterns of the diffusion regions at the positions P1 and P2 in FIG. 10 are shown in FIGS. 17A and 17B, and enlarged top views of the diffusion regions are shown in FIGS. 17C and 17D, respectively. Positions P1 and P2
In any of the above, the diffusion regions 103 are arranged in a grid pattern on the diffusion surface 106, but at a position P2 far from the light incident portion.
In this case, the bending angle γ of the diffusion region 103 is larger than the closer position P1 (γ2> γ1). The average axial direction 803 of the diffusion region 103 is substantially perpendicular to the direction when the respective positions are viewed from the light source installation position S1 in plan view of the light incident portion.

Next, the light guide plate 101, which is a feature of the present invention.
FIG. 17 shows the effect of suppressing the occurrence of the luminance inclination on the light emitting surface of
An example will be described with reference to FIG. In FIG. 17 (d),
The portions indicated by the symbols p, q, and r are diffusion regions 103.
Represents a minute portion when the is sliced in a plane perpendicular to the central axis 913. Here, for example, if attention is paid only to the minute portion p, it can be considered that this is equivalent to the semi-cylindrical diffusion region 103 without bending as shown in FIG. 4, and the axial direction at that time is at the position P. Given in the tangential direction of the central axis. That is, the minute portion P becomes equivalent to the diffusion region 103p shown in FIG. 11B of (Embodiment 1),
It is considered that the reflected light azimuth distribution is given by the distribution shown in FIG. Similarly, the minute portions q and r are also equivalent to the diffusion regions 103q and 103r in FIG. 11B, respectively, and their reflected light azimuth distributions are given in FIGS. 12B and 12C, respectively. Diffusion region 10 of FIG. 17 (d)
Since the reflected light azimuth distribution from the whole 3 is a superposition of the reflected light azimuth distributions by all the minute portions forming the diffusion area 103, various reflected light azimuths including just FIGS. FIG. 13 obtained by overlapping distributions
It is thought that it will be as in (b).

The above shows that making the central axis of the diffusion region 103 into a curved shape is equivalent to giving axial variation in a certain neighboring region as shown in FIG. At this time, the bending angle γ of the diffusion region 103
Corresponds to (twice) the standard deviation σ in the axial direction in FIG. 11. Furthermore, it can be said that the average axial direction 803 of the diffusion region 103 in FIG. 16 has the same meaning as the average axial direction Dt in FIG. 11.

Considering in this way, in FIG. 17, increasing the bending angle γ1 at a position close to the light incident portion and increasing the bending angle γ2 at a position far from the light incident portion is as shown in FIG.
In No. 1, the standard deviation σ of the axial distribution is made smaller at a position near the light incident portion, and σ is made larger at a position far from the light incident portion. Therefore, similarly to the case of (Embodiment 1), it can be understood that the luminance gradient when viewed obliquely can be suppressed and the uniformity can be improved. Furthermore, if the average axial direction 803 is arranged so as to draw a concentric circle centered on the light source installation position, the highest directivity can be obtained in the front direction on the entire surface, as in the first embodiment.

Although some rewrites have been made in (Embodiment 1), if the word "standard deviation in axial distribution" is read as "bending angle (half of)" in these, then all are satisfied. To do. In particular, if the bending angle γ at each position is given so that the value of the sum of the angle ε and the bending angle γ when looking at the light emitting region of the light source from a certain position is substantially constant regardless of the position in the diffusion surface 106, A uniform display is obtained on the entire surface of the light guide plate when viewed from an angle. For reference, an example of how to give the turning angle γ is shown in FIG.
It shows in 8.

Although the central axis 913 of the diffusion region 103 is drawn in an arc shape in FIGS. 16 and 17 for the sake of clarity, it does not necessarily have to be an arc shape. For example, it may be a sine wave shape, a cycloid shape, a parabolic shape, or the like. Alternatively, the straight line portion and the curved line portion may be connected. It is also possible to obtain a desired scattered light azimuth distribution by optimizing this shape.

The method of giving variation in the axial distribution as described in (Embodiment 1) and the method of making the central axis 913 of the diffusion region 103 into a curve as in (Embodiment 2) are described. It goes without saying that they may be combined.

Here, the first embodiment and the second embodiment
To summarize.

The invention described above is not limited to the above-described embodiment, but can be implemented in the following embodiments.

First, the shape of the diffusion region will be described.
In the above, the diffusion region had a semi-cylindrical shape as shown in FIG. However, the diffusion region does not necessarily have to have a semi-cylindrical shape. For example, Japanese Patent Application No. 2001-3436
14 is an ellipsoidal shape as shown in FIG.
The shape may be an elliptic cylinder as shown in FIG.
It may have a prismatic shape as shown in FIG. 6 (c). Alternatively, as shown in FIG. 26 (d), it may be a shape in which quadrants are added to both ends of a semicylindrical shape (shape in which a sausage is cut in half). Further, in the semi-cylindrical shape of FIG. 22, the cross section does not necessarily have to be a semi-circular shape,
For example, it may be bow-shaped, semi-elliptical, parabolic, hyperbolic, or cycloidal. In any case, any material may be used as long as it does not have the axis of rotational symmetry perpendicular to the diffusion surface of the light guide plate. In each of FIG. 26A to FIG. 26D described above, the direction indicated by the symbol W1 is the axial direction, that is, the direction defined by the diffusion region 103. However, FIG.
In the case of 6 (a) and FIG. 26 (b), it is assumed that W1> W2. In any of these shapes, if the light rays incident on the diffusion region 103 are substantially perpendicular to the axial direction W1, the azimuth distribution of scattered light, that is, the directivity is as shown in FIG.
The directivity of the semi-cylindrical scattered light shown in FIG.

Further, the ratio of the width of the diffusion region 103 in the axial direction to the direction perpendicular thereto (for example, the ratio of W1 and W2 in the case of FIG. 26A) or the diffusion region 103 is projected on the diffusion surface 106. The area (for example, π × W1 × W2 / 4 in the case of FIG. 26A), the height of the diffusion region 103, the arrangement density (pitch) of the diffusion regions 103, and the like are not necessarily set at each position in the diffusion surface 106. It does not have to be constant. Generally, in order to obtain uniform output light brightness over the entire light exit surface of the light guide plate, the density distribution in the diffusion region is often optimally designed. However, even in such a case, in order to effectively obtain the effect of the present invention, it is desirable that the axial direction of the diffusion region gradually changes depending on the position.

Further, in the above configuration example, the diffusion region is shown in FIG.
As shown in FIG. 5, it was formed as a recess in the diffusion surface 106.
However, this may be formed as a convex portion as shown in the cross-sectional view of FIG. 27 of Japanese Patent Application No. 2001-343614.

Further, the diffusion region 103 is formed, for example, in Japanese Patent Application No. 20.
As shown in FIG. 28 of 01-343614, the refractive index η1
The refractive index η2 (η
It is also possible to embed a medium of 1 ≠ η2). The medium in which the medium is air is the diffusion region 103 in the above configuration example.

In the above description, the diffusing region is mainly described as diffusing the light by reflecting the light on the surface thereof, but of course, the diffusing region may also diffract the light by refracting or transmitting the light. It goes without saying that those diffused by both light transmission and transmission are collectively included in the category of "diffusion region".

When the diffusion regions are arranged, they may be arranged along a certain curve, for example, as shown in FIG. 21, or may be arranged in a lattice pattern, as shown in FIGS. Good. That is, assuming a certain pitch in each of the vertical and horizontal directions, the diffusion regions may be arranged on the grid points defined by the pitch. In this case, the latter design and CAD (Compu
ter Aided Design) Data creation is easy. Of course, a staggered arrangement may be used. Moreover, the arrangement of the diffusion regions may be random.

Next, the meaning of "almost vertical" often mentioned above will be explained. Now, for example, in FIG. 4, it is assumed that the projection of the incident light vector ki on the xy plane (corresponding to the diffusion surface) and the axis 303 of the diffusion region are completely perpendicular. That is, Φ = 0 °. At this time, as can be seen from FIG. 5A, the reflected light is scattered directly in front, that is, at the origin (the intersection of the crosses) of the polar coordinate graph of FIG. 5A with high directivity. On the other hand, when the projection and the axis 303 of the diffusion region are deviated from perfect vertical, for example, when Φ = 30 °, as shown in FIG. I can't. Of the directions in which a sufficiently high directivity can be obtained, the direction closest to the front also deviates from the front by about 20 °. However, in general, when the user looks at the screen of the display device, he or she often looks within a range of about 20 ° from the front. Therefore, if we consider the range of 20 ° from the front as “front”,
Even in the case of Φ = 30 ° (same for Φ = −30 °), it can be said that the scattered light is emitted to the front. In that sense, the range of -30 ° ≤Φ≤30 ° is "almost vertical".
You can call it. For example, when it is said that the azimuth φ when a certain position is viewed from the light source installation position and the axial direction δ of the diffusion region are “substantially perpendicular”, the angle formed by φ and δ is considered to be 60 ° or more and 120 ° or less. You may

The light guide plate may be formed so that the diffusion surface and the light emission surface are opposed to each other, and they may not be parallel to each other, and they may be curved surfaces instead of flat surfaces. For example, in the light guide plate used in the monitor section of the digital camera, the light emitting surface is formed obliquely with respect to the diffusing surface, but such a structure may be used.

The light guide plate may be any one as long as it can guide the incident light from the light incident portion to the diffusion surface and the light emitting surface forming portion, and its planar shape may be any shape.

The surfaces of the light diffusing surface and the light emitting surface of the light guide plate may not be mirror surfaces but may be partially or entirely rough surfaces.

Next, an embodiment of the present invention will be described. In the above-described first and second embodiments, it has been described that, mainly for the light guide plate itself, effects such as suppression of a bright / dark boundary line when viewed obliquely and suppression of uneven brightness when viewed from the front are obtained. . However, this is not limited to the case where it is viewed as the light guide plate itself.
That is, as described in the first embodiment, in FIG. 1, the surface lighting device (backlight 109) mainly including the light guide plate 101 and the light source 102 (and the reflection sheet 107 and the diffusion sheet 108 as the case may be). ) Is considered as one form, the above effect can be obtained. Further, it goes without saying that the above effects can be obtained also in a display device in which a surface lighting device and a display element such as the liquid crystal panel 110 are viewed as a set.

Therefore, by using the backlight and the light guide plate according to the second embodiment in place of the backlight and the light guide plate according to the first embodiment, a liquid crystal display device having these characteristic configurations and the effects thereof can be obtained. be able to.

Although a backlight type liquid crystal display device is shown in FIG. 1, the present invention can be applied to a front light type surface lighting device.
Further, in that case, the above-described effects can be obtained also in a display device that is set with a reflective liquid crystal panel. Specifically, for example, the configuration is as shown in FIG. 29 of Japanese Patent Application No. 2001-343614.

As the display element, in addition to the liquid crystal panel, an optical writing type spatial light modulator (for example, Japanese Patent Laid-Open No. 07-
306418) and the like) can be adopted. Further, the display element does not necessarily have to use liquid crystal. For example, it may be an electro-optical crystal such as BSO (bismuth silicon oxide) or a display element using an electrochromic material. Alternatively, DMD (Deformable Mirror)
A display device using a device) may be used.

Further, the display device of the present invention can obtain the above-mentioned effects by being used in the display portion of a mobile phone or a mobile terminal device. In addition, it is of course possible to use it for a liquid crystal television, a liquid crystal monitor, a liquid crystal monitor for a notebook computer, or a display unit of a car navigation device or the like.

In particular, in the case of a large-screen display device such as a liquid crystal television or a liquid crystal monitor, the size of each diffusion region is relatively smaller than the size of the screen, so that the diffusion regions are random. It is possible to reduce noise due to the arrangement and moire fringes due to the regular arrangement, and the effects of the present invention are effectively exhibited.

Although an LED (light emitting diode) is often used as the light source, a laser light source, an electroluminescence light source, or the like may be used separately. Regarding the emission spectrum of the light source, it may be monochromatic or white. The present invention can of course be applied even when a light source having a plurality of emission spectra such as red, green and blue is installed. In particular, it is of course applicable to a case where a plurality of light sources having different emission spectra are sequentially emitted, as in the field sequential method (for example, described in Japanese Patent Application No. 2001-098657). (Embodiment 3) FIG. 19 is a perspective view showing appearances of a mobile phone and a mobile terminal device according to a sixth embodiment of the present invention, (a) showing a mobile phone, and (b) showing a mobile terminal. 20 is a functional block diagram showing the configurations of the mobile phone and the mobile terminal device of FIG. 19, (a) showing the mobile phone, and (b) showing the mobile terminal device. .

As shown in FIGS. 19 (a) and 20 (a), the mobile telephone 401 of the present embodiment inputs / outputs information including call voice and operation input from operation buttons such as dial buttons. The output unit 403, the antenna 407 for transmitting and receiving radio waves, and the communication unit 406 for mutually converting the transmission signal and the communication information transmitted and received as radio waves by the antenna 407.
A display unit 405 for displaying predetermined information, and a display unit 40
The CPU 402 that exchanges information between the display control unit 404 that controls the display in FIG. 5 and the input / output unit 403, sends out predetermined information to the display control unit 404, and exchanges communication information with the communication unit 406. It has and. And the display unit 4
Reference numeral 05 is a liquid crystal display device using the liquid crystal display device of the first and second embodiments.

With the mobile phone 401 having such a configuration, even when the screen of the display unit 405 is viewed obliquely at the time of display, an unnatural bright-dark boundary line is not produced.

As shown in FIGS. 19 (b) and 20 (b), the mobile terminal device 411 of the present embodiment has a command input unit 413 for inputting an operation input from the operation unit and a transmission signal. A communication data input / output terminal 412 for inputting / outputting,
A communication unit 406 for mutually converting a transmission signal input / output at the communication data input / output terminal 502 and communication information, a display unit 405 for displaying predetermined information, and a display control unit 404 for controlling display on the display unit 405. And the input from the command input unit 503, sends predetermined information to the display control unit 404, and exchanges communication information with the communication unit 406.
U402 and. The display unit 405 is composed of the liquid crystal display device according to the first and second embodiments.

The portable terminal device 501 configured in this way
Then, even when the screen of the display unit 405 is viewed obliquely at the time of display, an unnatural bright and dark boundary line is not generated.

[0100]

The present invention is embodied in the form as described above, and it is possible to suppress the occurrence of brightness unevenness of brightness and darkness on the output surface of the output light viewed from any direction, a surface illuminating device, and a display. There is an effect that a device, a mobile phone, and a mobile terminal device can be obtained.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a liquid crystal display device as a display device according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a diffusion pattern of a light guide plate of the liquid crystal display device of FIG.

3A is a diagram showing an arrangement of diffusion patterns at a position Pa in FIG. 2, and FIG. 3B is a diagram showing an arrangement of diffusion patterns at a position Pb.

FIG. 4 is a perspective view showing a coordinate arrangement of a semi-cylinder formed by the diffusion regions in FIG.

5 is a diagram showing a polar coordinate graph showing the azimuth distribution of scattered light by the semi-cylindrical column of FIG. 4, in which (a) shows a case of Φ = 0 °, and (b) shows a case of Φ = 5 °. The figure (c) shows the case of Φ = 30 °, the figure (d) shows the case of Φ = 60 °, and the figure (e) shows the case of Φ = 90 °.

FIG. 6 is a plan view of a conventional light guide plate.

7 (a) and (b) are positions P1 in FIG. 6, respectively.
And FIG. 6 is a diagram showing the relationship between the arrangement of diffusion areas and the direction of rays in P2.

8 (a) and 8 (b) are views showing a distribution of reflected light (scattered light) directions in FIGS. 7 (a) and 7 (b), respectively.

9A and 9B are diagrams in which the reflected light azimuth distributions of FIGS. 8A and 8B are superimposed and drawn for various incident light azimuths, respectively.

FIG. 10 is a diagram showing an arrangement of diffusion regions of the light guide plate of the present invention.

11A and 11B are diagrams showing the relationship between the arrangement of the diffusion regions and the ray direction at positions P1 and P2 in FIG. 10, and FIGS. 11C and 11D are views in FIGS. 11A and 11B, respectively. Diagram showing an example of the probability density distribution in the axial direction δ of the diffusion region

12 (a), (b), and (c) are diffusion regions 103p, 103q, and 10 of FIG. 11 (b), respectively.
Diagram showing reflected light azimuth distribution for 3r

13A and 13B are views in which reflected light azimuth distributions from the diffusion regions in various axial directions at positions P1 and P2 in FIG. 10 are superimposed on each other.

14 is a diagram showing a graph showing an example of how to give the standard deviation of the axial distribution of the diffusion region on the straight line S1-P1-P2 of the light guide plate of FIG.

FIG. 15 is another diagram showing the arrangement of diffusion regions of the light guide plate of the present invention.

FIG. 16 is a perspective view showing the shape of a diffusion region according to the second embodiment of the present invention.

FIG. 17 is a diagram showing an arrangement pattern of diffusion regions according to the second embodiment of the present invention.

FIG. 18 is a diagram showing a graph showing an example of how to provide a bending angle of a diffusion region on a straight line S1-P1-P2 of the light guide plate of FIG. 10 in the second embodiment of the present invention.

FIG. 19 is a perspective view showing appearances of a mobile phone and a mobile terminal device according to a sixth embodiment of the present invention, where (a) shows the mobile phone and (b) shows the mobile terminal device.

20 is a functional block diagram showing configurations of the mobile phone and the mobile terminal device of FIG. 30, (a) showing the mobile phone, and (b) showing the mobile terminal device.

FIG. 21 is a conceptual diagram showing an arrangement of diffusion areas in a diffusion pattern of a conventional light guide plate.

22 is a diagram showing the shape of the diffusion region of FIG. 32, (A) is a perspective view (B) is a cross-sectional view taken along the plane A1A2A3A4 of (a).

FIG. 23 is a cross-sectional view schematically showing how a light ray propagates in a plane Π including a normal to the diffusing surface and a vector SP at a point P in FIG. 32.

FIG. 24 is a diagram schematically showing a polar coordinate system on a light guide plate.

FIG. 25 is an azimuth distribution of the output light rays indicating the directivity of the output light due to the diffusion area, wherein (a) shows the azimuth distribution of the output light rays due to the diffusion area, and (b) shows a semicircular diffusion. Diagram showing the orientation distribution of output rays by region

FIG. 26 is a schematic diagram showing a state of scattering by a semicircular diffusion region.

FIG. 27 is a plan view showing an arrangement pattern of diffusion areas of a conventional light guide plate in the case of having a plurality of light sources.

FIG. 28 is a diagram showing another example of how to give the distribution of the diffusion regions in the axial direction in the light guide plate of the invention.

[Explanation of symbols]

100 Diffusion pattern 101 Light guide plates 102, 102a, 102b, 102c Light sources 103, 103a, 103b, 103c, 103p, 1
03q, 103r Diffusion area 104 End surface 105 Light emission surface 106 Diffusion surface 107 Reflection sheet 108 Diffusion sheet 109 Backlight 110 Liquid crystal panels 111a, 111b Polarization film 112 Reflection sheet surface 113 Display section 115 Phase difference film 200 Liquid crystal display device 301, 301b Incident light ray 301a Reflected light ray 303 Diffuse region axis 304, 308 Output light ray orientation distribution 401 Mobile phone 402 CPU 403 Input / output unit 404 Display control unit 405 Display unit 406 Communication unit 407 Antenna 411 Mobile terminal device 412 Communication data input / output terminal 413 Command Input units 501 to 508 Scattered light orientation distribution 601 Polar coordinate graphs 602, 602a, 602b, 602c Directional distribution of scattered light by light from the first light source 603, 603a, 603b, 603c Second light source? Direction distribution 604, 604a, 604b, 604c of light scattered by the light 701 Direction distribution of light scattered by the third light source 701 Boundary lines 801, 801a, 801b Vertical center line 803 Average axial direction 903 Semicircular plane 913 Center Axis Dn Reference direction Dt Average axial direction R1 First area R2 Second area R3 Third area S1, S2, S3 Light source installation position δ Diffusion area axial direction

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masanori Kimura             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Kazunori Komori             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 2H038 AA55 BA06                 2H091 FA23Z FA31Z FA41Z KA10                       LA18 MA10

Claims (20)

[Claims] 1. The light incident from the light incident part propagates through the inside and is diffused by a plurality of diffusers which are formed on the diffusing surface and at least a part of which has a semi-cylindrical shape so that the light is emitted from the light emitting surface. A light guide plate configured to emit light, the central axis of each of the semi-cylindrical diffusers existing within a region of a predetermined range of the diffuser surface among the plurality of diffusers formed on the diffuser surface. A light guide plate in which at least a part of a central axis of each of the semi-cylindrical diffusers existing in the region of the predetermined range is deviated from an average axial direction obtained by averaging the directions. 2. The standard deviation of the deviation of the central axes of the respective semi-cylindrical diffusers existing in the region closer to the light incident portion from the average axial direction is farther in the region than the light incident portion. The light guide plate according to claim 1, which is larger than a standard deviation of a deviation of a central axis of each of the semi-cylindrical diffusers present in the above from the average axial direction. 3. The average axis direction is perpendicular to the surface that is perpendicular to the diffusion surface and that includes the center of the region and the light incident portion. The light guide plate described. 4. The plurality of light incident parts are provided.
The light guide plate described in. 5. The light incident from the light incident portion propagates through the inside, and is diffused by a plurality of diffusers which are formed on the diffusion surface and at least a part of which is semi-cylindrical so that the light is emitted from the light emission surface. A light guide plate configured to emit light, wherein each of the diffusers has a curved central axis. 6. The diffuser surface is perpendicular to the curved center axis at each end of the curved center axis of each of the semi-cylindrical diffusers existing in the region closer to the light incident portion. The angle formed by the intersection of the straight lines included in the curved line at each end of the curved central axis of each of the semi-cylindrical diffusers present in the region farther from the light incident portion is the curved center. The light guide plate according to claim 5, which is larger than an angle formed by intersecting a straight line that is perpendicular to the axis and that is included in the diffusion surface. 7. A straight line connecting both ends of a curved central axis of each of the semi-cylindrical diffusers is a plane perpendicular to the diffusing surface, and the point and the light incident portion are connected to each other. The light guide plate according to claim 5, which is perpendicular to a plane including the light guide plate. 8. The device according to claim 1, further comprising a plurality of the light incident parts.
The light guide plate described in. 9. A light source and light from the light source is incident from a light incident portion, and the light incident from the light incident portion propagates inside and is formed on a diffusion surface and at least a part of which has a semi-cylindrical shape. A light guide plate configured to be emitted from a light emitting surface by being diffused by a plurality of diffusers, wherein the plurality of diffusers are formed on the diffuser surface. From the average axial direction obtained by averaging the central axis directions of the semi-cylindrical diffusers existing in the area of the predetermined range of the diffusion surface, the semi-cylindrical diffusion existing in the area of the predetermined range A surface lighting device in which at least a part of central axes of the respective bodies is displaced. 10. The standard deviation of the deviation of the central axes of the respective semi-cylindrical diffusers existing in the region closer to the light incident part from the average axial direction is far from the light incident part in the region. 10. The surface illumination device according to claim 9, wherein the standard deviation of the deviation of the central axis of each of the semi-cylindrical diffusers present in the above from the average axial direction is greater than the standard deviation. 11. An angle formed by two straight lines connecting between both ends of the light source and the center of a predetermined range of the diffusion surface is ε, and each semi-cylindrical diffuser existing in the region is defined as ε. Where σ is the standard deviation of the deviation of the central axes of the respective from the average axis direction, (2σ +
10. The surface lighting device according to claim 9, wherein ε) is constant. 12. A light source and light from the light source is incident from a light incident portion, and the light incident from the light incident portion propagates inside and is formed on a diffusing surface and at least a part of which has a semi-cylindrical shape. A surface illuminating device comprising a light guide plate configured to be emitted from a light emitting surface by being diffused by a plurality of diffusers, wherein each of the diffusers has a curved central axis. A surface lighting device having. 13. A diffusion surface that is perpendicular to the curved center axis at each end of the curved center axis of each of the semi-cylindrical diffusers existing in the region closer to the light incident portion. The angle formed by the intersection of the straight lines included in the curved line at each end of the curved central axis of each of the semi-cylindrical diffusers present in the region farther from the light incident portion is the curved center. The surface lighting device according to claim 12, which is larger than an angle formed by intersecting a straight line that is perpendicular to the axis and that is included in the diffusion surface. 14. An angle formed by two straight lines connecting between both ends of the light source and a center of a predetermined range of the diffusion surface is ε, and each of the semi-cylindrical shapes existing in the region is defined as ε. (Γ + ε) is constant when the angle formed by the straight lines included in the diffusing surface is perpendicular to the curved central axis at each end of each of the curved central axes of the diffuser. The surface lighting device according to claim 12. 15. A light source and light from the light source is incident from a light incident portion, and the light incident from the light incident portion propagates inside and is formed on a diffusing surface and at least a part of which has a semi-cylindrical shape. A display device including a light guide plate configured to be emitted from a light emitting surface by being diffused by a plurality of diffusers, and a display element for modulating light emitted from the light emitting surface. From the average axial direction obtained by averaging the central axis directions of the semi-cylindrical diffusers existing in the region of the predetermined range of the diffusion surface among the plurality of diffusers formed on the diffusion surface, A display device in which at least a part of a central axis of each of the semi-cylindrical diffusers existing in the region of the predetermined range is deviated. 16. A light source and light from the light source is incident from a light incident portion, and the light incident from the light incident portion propagates inside and is formed on a diffusion surface and at least a part of which has a semi-cylindrical shape. A display device including a light guide plate configured to be emitted from a light emitting surface by being diffused by a plurality of diffusers, and a display element for modulating light emitted from the light emitting surface. In addition, each of the diffusers has a curved central axis. 17. A mobile phone provided with the display device according to claim 15. 18. A mobile phone provided with the display device according to claim 16. 19. A mobile terminal device comprising the display device according to claim 15. 20. A mobile terminal device comprising the display device according to claim 16.