JP3351889B2 - Surface light source device with projection preventing function and liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device using an optical element having a function of guiding incident light while scattering the light in a volume region (hereinafter referred to as "light scattering light guide"), and a light source device using the same. The present invention relates to a liquid crystal display device using the device as a backlight light source.

[0002]

2. Description of the Related Art Hitherto, various types of optical elements or devices which emit light in a desired direction by utilizing a scattering phenomenon have been known, and are used as a light source for a backlight of a liquid crystal display device. It is used for As one type of these known techniques, for example, as described in JP-A-2-13925 and JP-A-2-245787, light is incident from the side of an extended plate-shaped transparent material,
A reflective element is arranged on one surface side, and a surface light source is provided as a light emitting surface by giving light diffusivity near the other surface.

In a planar light source using these techniques, light scattering is not generated volumetrically inside the transparent body, and the diffused light and the specular reflection near the surface of the transparent body or at a reflective element are used. Since only the light emission direction has a spread, there has been a fundamental difficulty in sufficiently increasing the ratio of scattered light that can be extracted from the light scattering light guide device.

[0004] Further, when an attempt is made to obtain a planar light source having a uniform illuminance by irradiating light from the side, as will be easily understood from the examples shown in the above-mentioned known documents, the reflection element has It is necessary to have some gradient in the reflectivity etc.
The structure of the light-scattering light-guiding device is complicated and large, and the manufacturing cost must be high.

[0005] Another type of the prior art is to disperse a particulate material having a different refractive index from that of the transparent material in an extended plate-like transparent material. Although this technique is considered to be superior to the first type of technique in that the area having a volume expansion is given a scattering power to change the direction of the incident light toward the light extraction surface, the surface is considered to be superior. A problem remains in that a special device is required to ensure uniformity of brightness as a light source.

For example, JP-A-2-221924, JP-A-2-221925, and JP-A-2-221926 disclose a method of increasing the particle diameter and / or particle concentration as the distance from the light incident surface increases. Has been taken.
Light scattering light guide with such gradient in particle diameter and particle concentration
Manufacture of the body is not technically easy, lacks mass productivity, and is economically disadvantageous. For example, it is difficult to obtain a light-scattering light guide by batch molding using an injection molding technique.

Therefore, the inventor of the present application has first constructed a surface light source device having excellent brightness uniformity by using a light scattering light guide having a tendency to decrease in thickness as the distance from the light incident surface increases. (Japanese Patent Application No. 5-202090).
FIG. 1 is a schematic diagram showing an example of a basic configuration of a surface light source device according to the concept of this proposal.

[0008] Briefly describing this, reference numeral 1 'is a wedge shape.
The light scattering guide has a shape, and a light source (fluorescent lamp) L is arranged near the light incident surface 2. On the light extraction surface 5 side of the light-scattering light guide 1 ' , a light-emitting direction correcting element 4 having an array of prism surfaces 4a, 4b (the function of which will be described later) is arranged, and its flat surface 4e.
Is used as a surface light source to obtain a directional light beam 4f . If a known liquid crystal display device is further disposed above this, a liquid crystal display device is configured.

Reference numeral 3 denotes a pair on the back surface 6 of the light scattering guide 1 '.
Face-to-face reflective means, diffuse reflective
From a white sheet or a specularly reflective silver foil sheet.

In such a surface light source device, light scattering
Since the thickness of the light guide 1 ′ decreases with increasing distance from the light incident surface 2, the level of the brightness as the surface light source becomes uniform due to the repetitive reflection effect of the inclined surface occurring in the light scattering light guide 1 ′ . Once improved. An outline of the reason will be described below with reference to FIG. 2 showing a cross section of the wedge-shaped light scattering light guide 1 ′ and the reflector 3 used in the arrangement of FIG.

Now, from the light incident surface 2 to the inside of the light scattering guide 1 '
When the light taken into the part is represented by the ray B0, B0
Is considered to form a small angle with the horizontal direction as illustrated. Considering the behavior of the light beam B0, the light beam B0 is repeatedly reflected on the light extraction surface 5 and the inclined surface 6 as shown in FIG. It approaches the thinner part of 1 ' . Since the reflections on the surfaces 5 and 6 are specular reflections, the incident angles and the reflection angles in the individual reflections are naturally equal (θ1, θ2, θ3,...). Here, paying attention to the reflection on the light extraction surface 5, θ2>θ4> θ6.
・ ・ It turns out that the relationship is established.

Further, considering the interface transmittance at each reflection, total reflection occurs under the condition of θi> αc (critical angle; 42 ° at the PMMA-air interface), and when θi falls below αc, the transmittance decreases. When the temperature rises sharply and θi is less than a predetermined value (around 35 ° at the PMMA-air interface), the transmittance becomes substantially constant.
In the drawing, the state where the emitted lights B4 and B6 are generated is illustrated according to the relationship of θ2>αc>θ4> θ6.

[0013] This effect is representative rays not limited to B0 (unscattered light), because should occurring Similarly, the primary scattered light and multiple scattering light as a whole light scattering guide 1 ' Is considered to produce an effect of increasing the light emission rate from the light extraction surface 5 as the distance from the light incidence surface 2 increases. When this effect is evaluated by a function f (x) of a distance x from the light incident surface 2, f (x) is an increasing function related to x. on the other hand,
The effect of being close to the light source 5 in the portion near the light incident surface 2 works for both direct light and scattered light. This proximity effect is g
When evaluated by (x), g (x) is a decreasing function.

Accordingly, the proximity effect g (x) is canceled by f (x), and the light is guided farther and the light extraction surface 5
Tend to emit light from the Also,
The chance of the light in the light scattering light guide 1 ′ being incident on the light extraction surface 5 is considered to be increased by the effect of the wedge shape, so that the effect of further improving the luminance level itself as the surface light source can be expected. Will be.

When a regular reflective material (such as a silver foil sheet) is used as the reflector 3, the light transmitted through the back surface of the light scattering light guide 1 ' is not diffused, and the light transmitted through the back surface of the light scattering light guide 1' is not diffused. The effect described above becomes clearer because the probability of re-entering the inside increases.

[0016]

As described above, a surface light source device having excellent brightness uniformity is constructed by using a light scattering guide having a tendency to decrease in thickness as the distance from the light incident surface increases. However, this improved surface light source device still has a problem that the luminance of the surface light source tends to be uneven mainly in a region near the light incident surface. According to the present inventor's consideration, the mechanism by which this phenomenon occurs is roughly described as follows with reference to FIG.

FIG. 3 is a diagram illustrating an extracted area near the light incident surface 2 in FIG. When the light source element L is arranged near the light incident surface 2 as a light supply unit to the light scattering light guide 1 ′ , unless the light source element L emits only a parallel light beam perpendicular to the light incident surface 2, Near the light entrance surface 2
In the light-scattering light guide 1 ' , there are many round-trip reflected light rays having a small incident angle as represented by the light rays C1 and C2. For example, the light enters the light-scattering light guide 1 ' from the light-incident surface 2 at a small angle of incidence on the light-incident surface 2 and enters the position R1 of the back surface 6 of the light-scattering light guide 1' without being scattered.
Considering the ray C1 incident at 1, a part thereof is reflected by R1 and goes to the light extraction surface 5 side. Although not shown, a part of the light not reflected by R1 is also reflected by the reflector 3.
Then, the light is re-entered into the light-scattering light guide 1 ′ , and travels through the same optical path toward the light extraction surface 5.

At the position R2, the light-scattering light-guiding member 1 '
The incident angle φ2 of the light incident from the light source becomes smaller than φ1 and becomes 0 ° because the back surface 6 is inclined with respect to the light extraction surface 5.
, Which is much smaller than the critical angle (for example, about 42 degrees when acrylic resin is used for the light-scattering light guide 1 ′ ). Therefore, most of the light is emitted from the light extraction surface 5.

[0019] As the ray C2, scattered light striking the scattering centers of the light scattering guide 1 'in (heterogeneous structure refractive index), due to the presence of a strong forward scattering properties as described below, also the light
The probability of incidence on the back surface 6 of the scattering light guide 1 'at a small incident angle is high. Therefore, the light beam C2 also undergoes the same repetitive reflection as the light beam C1 on both sides 5, 6 and the reflector 3, and a large amount of outgoing light as shown by C12 in the figure is generated by mixing intensely and weakly. Local unevenness occurs in the luminance of the image. In particular, when a specular reflective material is used for the reflector 3, the possibility that this unevenness appears more clearly is increased.

Since such luminance unevenness can be called a multiple reflection phenomenon of the light source L based on the regular reflection phenomenon, this phenomenon will be simply referred to as “reflection” hereinafter.

It is clear that, when such luminance unevenness due to the reflection occurs, the light extraction surface area having uniform luminance is substantially reduced, which is extremely inconvenient in practical use.
For example, when application to a backlight light source of a liquid crystal display device is considered, it is inevitable to take measures such as shielding a portion where luminance unevenness occurs, and the size of the display surface is limited accordingly. In addition, the light use efficiency is reduced and power saving is impaired.

According to the present invention, in the above-mentioned improved surface light source device utilizing a light-scattering light guide, the projection phenomenon is suppressed, uniform brightness is obtained over a wide range, and substantial light use efficiency is obtained. It is another object of the present invention to provide a surface light source device having a high display quality, and to provide a liquid crystal display device having uniform display quality over the entire display surface by utilizing the features of the surface light source device.

[0023]

According to the present invention, there is firstly provided at least one relatively small light incident surface area, and a relatively large light for extracting outgoing light originating from incident light passing through the light incident surface area. The present invention is applied to a light-scattering light guide having an extraction surface region and a volume region having a uniform scattering ability, and a surface light source device including a light supply unit for causing light to enter the light incident surface region. According to the invention of the present application, the light-scattering light guide has at least a portion excluding a portion near the light incident surface region, in a direction perpendicular to the light extraction surface region when viewed from the light incident surface region side. While the thickness along has a tendency to decrease as it goes away from the light incident surface region, the surface on the side opposite to the light extraction surface region, the inclination with respect to the light extraction surface region is adjusted in the vicinity portion, Thereby, the light supply means It is adapted to be prevented is included in the room rate.
Here, the adjustment of the inclination with respect to the light extraction surface area is performed by
In the vicinity only, the above tendency is reversed,
That is, it is performed so as to be inclined in reverse (claim 1) .

According to the invention of the present application, the above structure further includes "a regular reflection light reflecting means is provided on a side opposite to a light extraction surface area of the light scattering light guide" ( claim 2 ). By imposing the requirement, the brightness of the surface light source when viewed from a predetermined direction is improved, and the significance of the anti-glare means is enhanced.

Further, in the present invention, in order to cope with a case where it is necessary to correct the directivity of the light-scattering light guide, it is necessary to correct the directional light-emitting property of the light-scattering light guide. A scattered light emitting direction correcting means for correcting the directional characteristics is provided integrally with or separately from the light scattering light guide. "
In addition, a surface light source device to which the above constitutional requirement is added is proposed ( claim 3 ).

By arranging the surface light source device having each of these components as a backlight light source of the liquid crystal display device, a liquid crystal display device reflecting various features corresponding to each of the above configurations is provided. Claim 4-Claim
6 ).

[0027]

First, the scattering irradiation parameter E and the correlation distance a effective in describing and evaluating the scattering characteristics of the light scattering guide used in the present invention will be described with reference to Debye's theory. When the light of intensity I0 passes through the medium in y (cm), and the intensity attenuates to I due to scattering during that time, the effective scattering irradiation parameter E is defined by the following equation (1) or (2).

[0028]

(Equation 1) The above equations (1) and (2) are so-called integral and differential expressions, respectively, and their physical meanings are equivalent. In addition, this E may be called turbidity. On the other hand, the scattered light intensity in the case where light scattering occurs due to a non-uniform structure distributed in the medium is as follows in a normal case (VV scattering) where most of outgoing light is vertically polarized light with respect to vertically polarized incident light. It is represented by equation (3).

[0029]

(Equation 2) It is known that when natural light is incident, the following equation obtained by multiplying the right side of equation (3) by (1 + cos ² Φ) / 2 in consideration of Hh scattering may be considered.

[0030]

(Equation 3) Here, λ0 is the wavelength of the incident light, ν = (2πn) / λ0,
s = 2 sin (Φ / 2), n is the refractive index of the medium, φ is the scattering
The angle , <η ² > is the root mean square of the dielectric constant fluctuation in the medium (hereinafter, referred to as
Τ is appropriately used as <η ² > = τ. ) And γ
(R) is called a correlation function, and is represented by the following equation (6).

According to Debye, when the non-uniform refractive index structure of the medium is dispersed and divided into A phase and B phase with an interface, the correlation function γ is related to the fluctuation of the dielectric constant.
(R), correlation distance a, dielectric constant fluctuation root mean square τ, and the like are represented by the following relational expressions (7) and (8).

[0032]

(Equation 4) Assuming that the non-uniform structure is constituted by a spherical interface having a radius R, the correlation distance a is expressed by the following equation.

[0033]

(Equation 5) Using equation (6) for the correlation function γ (r), equation (5)
When the effective scattering irradiation parameter E when natural light is incident on the medium is calculated based on the above, the result is as follows.

[0034]

(Equation 6) From the relation described above, it is possible to control the scattered light intensity, the angle dependence of the scattered light intensity, and the effective scattered irradiation parameter E by changing the correlation distance a and the dielectric constant fluctuation root mean square τ. I understand. FIG. 4 shows a curve representing a condition for keeping the effective scattering irradiation parameter E constant by taking the correlation distance a on the horizontal axis and the root mean square τ on the vertical axis.
The cases where E = 50 [cm ⁻¹ ] and E = 100 [cm ⁻¹ ] are illustrated.

In general, the larger E is, the larger the scattering power is,
If E is small, the scattering power is small, in other words, it is almost transparent. E = 0 corresponds to no scattering at all. Therefore, when using a light-scattering light guide for a large-area planar light source or a long fiber-like or rod-like uniform illumination light source, it is sufficient to select E to be very small. The criterion is as follows.

For example, if the effective scattering irradiation parameter is E =
When it is about 0.001 [cm ^-1 ], a fiber-like light scattering / guiding member having a size of several tens of meters can be uniformly illuminated. If E = 100 [cm ^-1 ] shown in FIG.
It is suitable for intensively and uniformly illuminating a range of several mm to several cm.

Further, in the case of E = 50 [cm ^-1 ] in FIG. 4, an intermediate size between them (for example, several cm to several tens c.
This is considered to be suitable for uniformly illuminating the light-scattering light guide of m).

The practical range of the effective scattering irradiation parameter E in the case where importance is placed on practicality in the application of a normal-sized backlight light source while taking the above criteria into consideration is E = 0.
It is on the order of 45 to 100 [cm ^-1 ].

On the other hand, the correlation distance a is an amount that is deeply related to the directional characteristics of the scattered light in each scattering phenomenon inside the light scattering light guide. That is, the above equations (3) to (5)
As can be inferred from the form of the equation, light scattering inside the light-scattering light guide generally has a forward scattering property, but the strength of the forward scattering property varies depending on the correlation distance a.

FIG. 5 is a graph illustrating this for two values of a. In the figure, the horizontal axis represents the scattering angle Φ (the traveling direction of the incident light is assumed to be Φ = 0 °), and the vertical axis represents the scattered light intensity assuming natural light, that is, Φ = Value normalized to 0 °, Vvh (Φ)
/ Vvh (0). As shown in the figure, when a = 0.13 μm and 2R = 0.2 μm in terms of the particle size using the above (9), the graph of the normalized scattering intensity shows a gradual decrease in Φ. A = 1.
3 μm, 2R = 2.0 in terms of the particle size converted by the above equation (9)
In the case of μm, the graph of the normalized scattering intensity is a function that sharply decreases in the range where Φ is small.

As described above, the scattering caused by the non-uniform structure of the refractive index in the light-scattering light guide basically shows forward scattering properties. It can be said that the scattering angle range in the scattering tends to be widened. This fact has been confirmed experimentally.

The above discussion focuses on the scattering phenomenon itself due to the non-uniform refractive index structure distributed inside the light-scattering light guide. The directional characteristics of light actually emitted from the light extraction surface of the light-scattering light guide are described. In order to evaluate, it is necessary to consider both the phenomenon of total reflection on the light extraction surface and the transmittance at the time of light emission (the escape rate from the light scattering guide).

As described in the related description of FIGS. 2 and 3, when light enters the light extraction surface from the inside of the light scattering light guide, it depends on the refractive index of the medium inside and outside the light scattering light guide. If the critical angle αc exceeds the determined critical angle αc (the normal direction set on the light extraction surface is 0 °), no emission (exit) to the outside (air layer) occurs. In PMMA (refractive index 1.492) which is a typical material used in the present invention, αc = 42 °
Becomes In the case of other materials, the values are not so different (see Tables 1 and 2 described later).

As described above, since the scattering inside the light-scattering light guide generally shows forward scattering properties, in the usual case where the light-incident surface is provided on the side of the light-extracting surface as shown in FIG. It is considered rare that the first-order scattered light generated when the light incident from the incident surface encounters the non-uniform structure immediately satisfies the critical angle condition.

In other words, for light emission from the light extraction surface,
A phenomenon in which light that has passed through the multiple scattering inside the light scattering light guide or the reflection by a reflecting member disposed at or near the back surface side of the light scattering light guide and satisfies the above critical angle condition and is emitted to the outside. Has greatly contributed.

Therefore, when attention is paid only to light that satisfies the critical angle condition, the forward scattering property, which is the attribute of each scattering phenomenon, is considerably reduced, and the light traveling direction distribution has a considerable spread. It should be. As a result, the directional characteristics of light emitted from the light-scattering light guide greatly depend on the angle dependence of the transmittance (escape rate) of the light that satisfies the critical angle condition on the light extraction surface.

In general, when the critical angle condition is barely satisfied, the interface transmittance is extremely low (for example, in the case of an acrylic resin-air interface, a P-polarized component is about 40% and an S-polarized component is about 20%). Falls sharply and rises
It is almost constant under the condition of being lower than 10 ° to 10 °.
S-polarized component 85% or more).

As described above, the angle of incidence on the light extraction surface is 3
It is considered that light of about 5 ° contributes most to light emission from the light extraction surface of the light scattering guide. Taking into account the refraction at the light extraction surface, the light incident on the light extraction surface at an incident angle of about 35 ° is 6 ° with respect to the normal set on the light extraction surface.
0 ° (the refractive index of the light-scattering light guide is usually 1.5
Degree). In other words, the light emitted from the light extraction surface of the light scattering / guiding body becomes light having directivity in a direction rising approximately 30 ° with respect to the surface of the light extraction surface, roughly estimated.

However, it should be noted here that if the value of the correlation distance a is too small, the forward scattering itself will be weakened, and scattered light will be generated in a wide range of directions only by primary scattering. This weakens the directivity. As a tentative measure that such a phenomenon does not become remarkable, the correlation distance a is 0.01 μm or more, in particular, a> 0.
Preferably it is 05 μm. Hereinafter, such a property is referred to as “directivity”.

According to the present invention, a particularly remarkable effect can be obtained when such a light-scattering light guide having directivity is used. Further, in the case where the regular reflection means is disposed on the side opposite to the light extraction surface (claim 2), or in the case where a light emission direction correcting element to be described later is used, the light scattering guide has a directional emission property. It is preferred that

The functions of the particularly advantageous means (specular reflection means and light emission direction correcting means) in combination with these directional light-emitting light-scattering light guides, and the materials and manufacturing methods of the light-scattering light guides are described below. It will be described in an example.

[0052]

FIG. 6 is a schematic diagram showing one embodiment of the surface light source device of the present invention. In FIG. 6, reference numeral 1 denotes light.
A light source (fluorescent lamp) L is disposed on one side surface of the scattering light guide, and light is made to enter from the light incident surface 2 to the left, and light is extracted from the light extraction surface 5. Outside the light extraction surface 5, a light emission direction correcting element 4 having a light columnar prism surface 4a, 4b is arranged, and a directional light beam 4f is obtained by using the flat surface 4e as a surface light source. .
If a known liquid crystal display device is further arranged above this,
A liquid crystal display device is configured.

Along the back surface 6, a specularly reflective silver foil sheet 3 is arranged. As a reflection unit arranged to face the back surface 6, a diffuse reflection unit (for example, a white sheet) is used.
However, in order to make the surface light source have directivity and to increase the brightness as viewed from a required direction, it is preferable to use a specular light source. The reason is as follows. As described in the description of the operation, when a white sheet or the like is arranged on the back surface side of the light-scattering light guide 1, the light traveling direction distribution inside the light-scattering light guide 1 becomes more random (the scrambling effect). ), The effect of transmitting the light on the inclined surface 6b to a distant place is reduced, and the directivity of the light-scattering light guide 1 is reduced. This is not preferable in maintaining the uniformity of the brightness as the surface light source, and also relatively reduces the effectiveness of the light emitting direction correcting means using the refraction effect of the prism surface described below. Therefore, from such a viewpoint, the reflector 3
It is advantageous to use a specular reflection material.

As described above, arranging the regular reflective reflector on the back surface side of the light-scattering light guide has such an advantage. On the other hand, "the problem to be solved by the invention" As described in the section, when a specular reflector is used as the reflector 3, the reflection phenomenon is more likely to occur near the light incident surface 2. Therefore, in the present embodiment, in accordance with the technical idea of the present invention, the light incident surface 2 on the back side of the light scattering guide 1
Projection preventing means 7 for preventing the projection of the light source L in the area near
, A reverse inclined portion 6a is provided.

That is, unlike the structure shown in FIG. 1, the back surface 6 of the light-scattering light guide 1 has a back surface portion 6 a close to the light incident surface 2.
Has a slope in the direction in which the thickness of the light scattering guide 1 increases as the distance from the light incidence surface 2 increases, and the thickness of the light scattering guide 1 decreases as the distance from the light incidence surface 2 increases in the remaining portion 6b. It has an inclination in the direction.

FIG. 7 is a view for explaining the anti-reflection effect of the anti-reflection means, and exemplarily shows the behavior of light in the vicinity of the light incident surface 2 under conditions similar to FIG. is there. The light beam C1 'corresponding to the light beam C1 in FIG. 3 is incident on the light-scattering light guide 1, and then is specularly reflected by the inversely inclined portion 6a (both the incident angle and the reflection angle are φ1').
The reflected light C1 "does not travel in an angle direction perpendicular to the light extraction surface 5, but travels in a direction relatively far away.
Therefore, the possibility that the light source L will cause a reflection phenomenon near the light incident surface 2 by the light beam C1 'represented by such an optical path is extremely small.

After being scattered at the scattering center (non-uniform refractive index structure) in the light-scattering light guide 1 like the light ray C 2 ′, the light beam is inversely inclined at a small incident angle on the back surface 6 of the light-scattering light guide 1. The light ray C2 'incident on 6a is unlikely to cause a projection phenomenon for the same reason.

Considering the light transmitted through the inversely inclined portion 6a and incident on the reflector 3, the same discussion holds. Therefore, the inversely inclined portion 6a eventually reduces the effect of reflection on the reflector 3. Including, it will exhibit the anti-glare function. This anti-glare function, as can be seen from the mechanism described above,
It is needless to say that the reflector 3 is effective regardless of whether it is of a light diffusive type or a regular reflective type, and even if the reflector is not disposed, it is particularly effective to reflect the light source L. The fact that a regular reflecting material can be used as the reflector 3 without having to worry about intrusion causes a more effective use of the operation of the light emitting direction correcting means (light emitting direction correcting element 4 in this embodiment) described below. Is very advantageous.

The operation of the light emitting direction correcting element 4 in the arrangement shown in FIG. 6 will be described below with reference to FIGS. In both figures, the light-scattering light guide 1 is made of polymethyl methacrylate (PMMA; refractive index n1 = 1.4).
92) as a base material, and the light emitting direction correcting element 4
Is made of polycarbonate (PC; refractive index n2 = 1.59).

First, FIG. 8 is a sectional view for explaining the behavior of light in the arrangement shown in FIG. As shown in the figure, the light emitting direction correcting element 4 is arranged facing the light extraction surface 5 of the light scattering guide 1 with its prism surface facing inward. Assuming that the light incident direction is the direction of arrow L ', as described in the description of the operation, the representative light beam B1 satisfying the critical angle condition enters the light extraction surface 5 at an angle of about ψ1 = 35 °, Most of the light is emitted to the air layer AR. The emission angle ψ2 at this time is determined by the refractive index n1 of the light scattering guide 1 = 1.49.
2. Assuming that the refractive index n0 of the air layer AR is 1, it is about 60 °.

After traveling straight through the air layer AR, the representative light beam B 1 is incident on the prism surface 4 a of the light emitting direction correcting element 4 at an angle close to perpendicular. In particular, the vertex angle of the prism surface 面 3 = 60
If the angle is around °, the satisfaction of this condition is high (the ratio of incidence on the opposite prism surface 4b is relatively small). Therefore, the representative light beam B1 travels substantially straight to the opposite prism surface 4b and is specularly reflected.
At an angle close to the vertical direction, and is emitted from the light beam emission direction correcting element 4.

Next, FIG. 9 is a cross-sectional view for explaining the behavior of light when the light emitting direction correcting element 4 in the arrangement shown in FIG. 6 is arranged with its prism surface facing outward. Assuming that the light incident direction is the direction of arrow L ', the representative ray B2 satisfying the critical angle condition is ψ1 = 35 °, as in the case of FIG.
The light enters the light extraction surface 5 at an angle in the front-rear direction, and most of the light is emitted to the air layer AR. The emission angle ψ2 at this time is about 60 °.

After traveling straight through the air layer AR, the representative light beam B 2 is obliquely incident on the flat surface 4 e of the light emitting direction correcting element 4, follows a refraction path as shown, and is perpendicular to the light extracting surface 5. Surface 4 of light emitting direction correcting element 4 at an angle close to the direction
c (the ratio of light emitted from the surface 4d is relatively small).

Since the path of light after incidence on the flat surface 4e of the light emitting direction correcting element 4 varies over a wide range depending on the refractive index n2 of the light emitting direction correcting element 4 and the prism apex angle ψ4, these parameters are selected. Through this, light having directivity in a desired direction can be obtained.

The light emitting direction correcting element 4 is not limited to one having a prism surface formed in a row as shown in the figure, but may be of any type. For example, a film in which a group of triangular pyramidal or dome-shaped protrusions are distributed, a plate-like element having a row-like convex portion having a semi-cylindrical cross section, and the like can be considered.

Further, as a special case, for example, when the light scattering / guiding member 1 is manufactured by using an injection molding technique, the unevenness is formed on the light extraction surface 5 by means such as forming an uneven surface on a mold. It is also possible to adopt a mode in which it is formed and plays the role of a light emitting direction correcting element.

The function of the light emitting direction correcting element is as described above. In accordance with the principle described in the section of the operation, the light beams B1 and B2 shown in FIGS.
Given a situation that more clearly represents the light emitted from the surface light source, the effectiveness of the light emission direction correction function is further enhanced, and a surface light source with significantly improved brightness as viewed from the emission direction of the representative light beam is provided. Will be obtained. It has already been confirmed by experiments that such a situation is realized by arranging the specular light reflecting means 3 on the back side of the light scattering light guide 1.

As described above, the light-scattering light-guiding member 1
The embodiment in which the reverse inclined portion 6a is formed on the back surface (the surface opposite to the light extraction surface) of FIG.
It may be formed as shown. In the example shown in FIG.
A reverse-inclined curved portion 6g is provided in the vicinity of the light incident surface 2 to form a flat surface.
The transition is smoothly made to the inclined portion 6b .

In addition to the reverse inclination of these light scattering guides,
6 or 10 (reverse tilt)
Part) Make the whole or part of 6a, 6g a rough surface (textured surface)
By doing so , the reflection preventing function can be improved. Similarly, with respect to the reflector disposed on the back side of the light scattering light guide 1, the portion facing each anti-reflection prevention portion is reduced in regular reflectance to be diffusely reflective, or has a low reflectance, It is also possible to enhance the anti-glare function by taking measures such as providing a portion without a reflector.

Further, examples of the regular reflective reflector include a sheet in which a reflective film such as an aluminum film is deposited on a substrate in addition to a silver foil. When manufacturing the light-scattering light guide (see the following manufacturing method), the silver foil or the aluminum foil can be fixed to the back surface 6 of the light-scattering light guide by an in-mold molding method.

As for the shape of the light-scattering light guide and the light source (light supply means), those shown in FIGS. 6 and 10 are typical examples, and as long as the requirements described in each claim are complied with. It does not depart from the technical scope. FIG.
It illustrates some of the possible deformation arrangements.

FIG. 11 (1) shows a case 10 in which two substantially wedge-shaped light-scattering light guides 10 each having a reflection preventing portion 6 a formed near the light incident surface 2 are used, and the silver foil 3 is inclined forward. The light sources L, L are provided on both side surfaces only along the portion 6b. 11 (2) is one of the light source L also used to light the supply of the two wedge-shaped light diffusion light guide member 20 and 30, both light scattering guide the reverse slope curved portion 6g as Utsukomi preventing means 20 , 30 are formed.

Then, in FIG. 11 (3), the bent light fluorescent lamp L is used and the light scattering light guide 1 whose thickness changes two-dimensionally.
Light is incident from the two light incident surfaces 2 (only one is shown), and an inversely inclined portion 6a is provided near each light incident surface 2.

It is needless to say that the light emitting direction correcting element can be used in these modifications as well (not shown). Further, it is also possible to adopt a mode in which a concave portion or a hollow portion is provided in the light scattering light guide and the light source element is disposed therein.

Finally, the material of the light-scattering light guide used in the present invention and the method of manufacturing the same will be described. As the light-scattering light guide used in the present invention, various materials based on polymer materials can be used. Representative examples include PMMA as shown in Tables 1 and 2 below.
(Polymethyl methacrylate), PSt (polystyrene), PC (polycarbonate) and the like.

[0076]

[Table 1]

[0077]

[Table 2] The light scattering light guide based on such a polymer material can be manufactured by the following manufacturing method. First, one is a method using a molding process including a step of kneading two or more kinds of polymers. That is, two or more types of polymer materials having different refractive indices mutually different (arbitrary shape may be used. Industrially, for example, a pellet-like material is considered), and are heated and kneaded (kneading step) and kneaded. The liquid material is injected into the mold of the injection molding machine at a high pressure, and then cooled and solidified. The light-scattering light guide formed is removed from the mold, and the light-scattering light guide has a shape corresponding to the shape of the mold. Can be obtained. For example, if a mold having a wedge-shaped one end having a larger thickness and a reversely inclined portion is used, the light-scattering light guide 1 used in the arrangement of FIG. 6 is manufactured. In addition, if the inner surface of the mold of the inversely inclined portion is a rough surface (textured surface), the inversely inclined portion 6a of the light scattering / guiding member 1 can be a rough surface (textured surface).

Since the kneaded two or more kinds of polymers having different refractive indices solidify without being completely mixed, non-uniformity (fluctuation) is generated in their local concentration and fixed.
Uniform scattering power is provided. The kneaded material is poured into a cylinder of an extruder and extruded in a usual manner to obtain a desired molded product.

A wide variety of combinations and mixing ratios of these polymer blends can be selected. The difference in refractive index, the strength and properties of the non-uniform refractive index structure generated in the molding process (scattering irradiation parameter E, correlation distance, etc.) a, dielectric constant fluctuation, root mean square τ, etc.). In addition,
Representative polymer materials that can be used are shown in Tables 1 and 2 above.

Another method of producing the material constituting the light scattering light guide is to use a polymer material having a different refractive index (0.00%).
One or more refractive index differences) are uniformly mixed and dispersed. One of the methods that can be used for uniformly mixing the particulate material is a method called a suspension polymerization method. That is, when the particulate material is mixed in the monomer and the polymerization reaction is carried out in a state of being suspended in hot water, a polymer material in which the particulate material is uniformly mixed can be obtained.
If this is used as a raw material and molding is performed, a light-scattering light guide having a desired shape is manufactured.

Also, suspension polymerization is performed for various combinations of particulate materials and monomers (combinations of particle concentration, particle size, refractive index, etc.), and a plurality of types of materials are prepared, and these are selectively blended. Then, light-scattering light guides having various characteristics can be manufactured. Also,
By blending a polymer containing no particulate material, the particle concentration can be easily controlled.

Still another method which can be used for uniformly mixing the particulate material is to knead the polymer material and the particulate material. Also in this case, combinations of various particulate materials and polymers (combinations of particle concentration, particle size, refractive index, etc.)
By performing kneading and molding (pelletization) in advance, and selectively blending these to form and manufacture a light scattering light guide, light scattering light guides having various characteristics can be obtained.

It is also possible to combine the above-mentioned polymer blending method with the method of mixing particulate materials. For example, it is conceivable to mix a particulate material when blending and kneading polymers having different refractive indexes.

Hereinafter, some specific examples of the production method will be described. The shape of the light-scattering light guide to be manufactured is assumed to be used in the arrangement of FIG. 6, and the size is 68 mm long and 85 m wide.
m, the thickness is 3.8 mm, the thickest part (boundary part between 6a and 6b),
The thinnest portion was 0.2 mm, and the light incident surface 2 side end was 1.9 mm.

<Production Example 1> A methacrylic resin pellet (Delvet 80N, manufactured by Asahi Kasei Corporation) was powdered with a silicon-based resin powder having a particle diameter of 0.8 μm (Toshiba Silicon, Tospearl 10).
8) was added in an amount of 0.3 wt%, mixed and dispersed by a mixer, extruded into a strand by an extruder, and pelletized by a pelletizer to prepare a pellet in which a silicon-based resin powder was uniformly dispersed.

The pellets were molded using an injection molding machine under the conditions of a cylinder temperature of 230 ° C. to 260 ° C. and a mold temperature of 50 ° C. to obtain a light scattering light guide having the shape used in the arrangement of FIG. I got it. The correlation distance of the manufactured light-scattering light guide is a = 0.53 μm, and the estimated value of the effective scattering irradiation parameter calculated by the above equation (11) is E = 12.
It was 6 [cm ^-1 ].

<Production Example 2> Silicone resin powder having a particle diameter of 0.8 μm (manufactured by Toshiba Silicon, Tospearl 10
8) was added to obtain a spherical particle in which the powder was uniformly dispersed by a known suspension polymerization method. This was pelletized with a pelletizer in the same manner as in Production Example 1 to prepare a pellet in which the silicone resin powder was uniformly dispersed.

A light-scattering light guide of the same type was obtained under the same conditions as in Production Example 1. This light-scattering light guide was indistinguishable in appearance from the light-scattering light guide produced in Production Example 1. Then, the correlation distance was a = 0.53 μm, and the estimated value of the effective scattering irradiation parameter by the equation (11) was E = 12.6 [cm ⁻¹ ].

<Production Example 3> 0.5 wt% of polymethyl methacrylate (PMMA) with polystyrene (PSt)
The mixture was added and mixed using a V-type tumbler for 10 minutes, and then using a Henschel mixer for 5 minutes. This is diameter 30
Using a 2-mm extruder [manufactured by Nakatani Machinery Co., Ltd.], pellets were prepared by melting and mixing at a cylinder temperature of 220 ° C. to 250 ° C., a screw rotation speed of 75 rpm, and a discharge rate of 6 kg / hr.

Using an injection molding machine, the pellets were subjected to a cylinder temperature of 220 ° C. to 250 ° C., a mold temperature of 65 ° C., a medium injection speed, an injection pressure short shot pressure and 10 k.
By molding under the condition of g / cm ² , a light-scattering light guide having the shape used in the arrangement of FIG. 6 could be obtained.

<Production Example 4> Silicon-based resin powder (Tospearl 120, manufactured by Toshiba Silicon Corp.) having a particle size of 2 μm was added to MMA (methyl methacrylate) at 0.05 wt% and 0.0%, respectively.
Four types of samples uniformly dispersed by adding 8 wt%, 0.10 wt%, and 0.15 wt% and an MMA sample without particles were prepared, and benzoyl peroxide was used as a radical polymerization initiator in each of the five types of samples. (BPO) 0.5wt
%, N-lauryl mercaptan (n-
LM) was added at 0.2 wt% and cast polymerization was performed at 70 ° C. for 24 hours to obtain a light-scattering light guide having the shape used in the arrangement of FIG.

<Production Example 5> 0.025% by weight of silicone oil was added to MMA (methyl methacrylate) and uniformly dispersed, 0.5% by weight of benzoyl peroxide (BPO) was used as a radical polymerization initiator, and n was used as a chain transfer agent. -Butyl mercaptan (n-BM) 0.2 wt
%, Respectively, and after performing solification at 70 ° C. for 30 minutes, casting polymerization is further performed at 65 ° C. for 24 hours to obtain a light-scattering light guide of the same type and dimensions as in Production Examples 1 to 4. Was completed.

[0093]

According to the present invention, in a surface light source device utilizing a light-scattering light guide having a tendency to decrease in thickness as the distance from the light incident surface increases, light supply means generated near the light incident surface Can be easily prevented. That is, in the surface light source device of the present invention, since a light extraction surface having uniform brightness without luminance unevenness on the whole including the end portion can be obtained, the practical light extraction surface region is substantially reduced. Is avoided. Further, when such a surface light source device is applied to a backlight light source of a liquid crystal display device, the display quality is high over a relatively large display surface, and the power use efficiency is high with substantial light utilization efficiency. An excellent liquid crystal display device can be obtained.

Further, the invention of the present application selects an arrangement in which specular reflection means is arranged on the back side of the light extraction surface of the light scattering light guide, and directs the light emission direction to the front direction of the light extraction surface or the like. Even if a configuration that arranges the light emission direction correction means facing the light extraction surface is selected for correction, the anti-glare function should be performed in a form that makes the most of the advantages of these arrangements and configurations more effectively. Is what makes it possible.

These advantages are extremely significant in improving the display performance and power saving of a liquid crystal display device and a liquid crystal television device for a monitor attached to a portable video camera and a personal computer.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a basic configuration of an improved surface light source device using a light scattering light guide having a tendency to decrease in thickness as the distance from a light incident surface increases.

FIG. 2 shows that the light scattering light guide becomes thinner as it goes away from the light incident surface side. It is a figure explaining the reason once improves.

FIG. 3 is a diagram illustrating a region near a light incident surface in FIG. 2 in an extracted manner in order to explain a projection phenomenon of a light source.

FIG. 4 is a curve showing conditions for keeping the effective scattering irradiation parameter E constant by taking the correlation distance a on the horizontal axis and the root mean square τ of the dielectric constant fluctuation on the vertical axis, where E = 50 [cm −1] and E = 100
It is a graph drawn about the case of [cm-1].

FIG. 5 is a graph illustrating that the forward scattering strength of the light scattering light guide changes depending on the correlation distance a.

FIG. 6 is a sketch showing an outline of the configuration of an embodiment of the present invention.

FIG. 7 is a diagram for explaining an anti-glare effect of the anti-glare means, and exemplarily illustrates the behavior of light in the vicinity of the light incident surface under the conditions according to FIG. 3;

FIG. 8 is a cross-sectional view for explaining the behavior of light when the light-emitting direction correcting element faces the light-extraction surface of the light-scattering light guide and its prism surface faces inward as shown in FIG. FIG.

FIG. 9 is a cross-sectional view illustrating the behavior of light when the light emitting direction correcting element in the arrangement shown in FIG. 6 is arranged with the prism surface facing outward.

FIG. 10 shows another example of the mode of forming the reflection preventing portion by light scattering and light guiding.
It is shown in a sectional view of the body .

FIG. 11 illustrates possible modifications of the shapes and arrangements of the light scattering light guide and the light source (light supply means).

[Explanation of symbols]

1,1 ', 10,20,30 Light scattering light guide 2 Light extraction surface 3 Reflector (silver foil, white sheet) 4 Light emitting direction correcting element 4a-4d Prism surface 4e Light emitting surface of light emitting direction correcting element 4f Outgoing light from light emitting direction correction element 5 Light extraction surface 6 Back surface of light scattering light guide 6a Reverse inclined portion 6b Forward inclined portion 6g Reverse inclined curved portion 7 Reflection prevention means L light source L 'Light incident direction

Continuation of the front page (56) References JP-A-2-139592 (JP, A) JP-A-4-179903 (JP, A) JP-A-5-107542 (JP, A) JP-A-51-88042 (JP) JP-A-59-143202 (JP, A) JP-A-61-140326 (JP, U) JP-A-63-124217 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB Name) G02B 6/00 331 F21V 8/00 601 G02F 1/13357

Claims (6)

(57) [Claims] At least one relatively small light incidence
Surface region, originating from incident light through the light incident surface region
A relatively large light extraction surface area for extracting outgoing light, and
Light-scattering light guide with volume region with uniform scattering power
A body and a light supplying means for allowing light to enter the light incident surface area.
A step; wherein the light-scattering light guide removes a portion near the light incident surface area.
And the light extraction surface area as viewed from the light incident surface area side.
The thickness along the direction perpendicular to the distance from the light incident surface area
The light has a tendency to decrease as
The surface on the side opposite to the extraction surface area is only in the vicinity.
The light extraction surface area so that the tendency is reversed.
A surface light source device characterized by being inclined with respect to. 2. A light extraction surface area of said light scattering light guide and a reciprocal light.
The side to be reflected must be provided with specular light reflecting means.
The surface light source device according to claim 1, wherein: 3. A light extraction surface area of the light-scattering light guide.
Scattered light emission direction correction to correct scattered light emission direction characteristics
Means are provided integrally or separately with the light scattering light guide.
The method according to claim 1 or 2, wherein
Surface light source device. 4. The at least one relatively small light incidence.
Surface region, originating from incident light through the light incident surface region
A relatively large light extraction surface area for extracting outgoing light, and
Light-scattering light guide with volume region with uniform scattering power
A body and a light supplying means for allowing light to enter the light incident surface area.
A step, wherein the light-scattering light guide removes a portion near the light incident surface area.
And the light extraction surface area as viewed from the light incident surface area side.
The thickness along the direction perpendicular to the distance from the light incident surface area
The light has a tendency to decrease as
The surface on the side opposite to the extraction surface area is only in the vicinity.
The light extraction surface area so that the tendency is reversed.
The surface light source device that is inclined with respect to
As a means, it is arranged on the back side of the liquid crystal display element
Liquid crystal display device. 5. The light of the light-scattering light guide of the surface light source device.
Light reflection means is provided on the side opposite to the extraction surface area
The liquid crystal display device according to claim 4, wherein: 6. The light of the light-scattering light guide of the surface light source device.
The scattering surface facing the extraction surface area and correcting the scattered light emission direction characteristics
The scattered light emitting direction correcting means is integrated with the light scattering light guide element.
Or provided separately.
A liquid crystal display device according to claim 5.