JP2001133631A - Light guide plate, surface light source device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device, capable of efficiently the light from a point light source into a surface light source and and superior in luminance and uniformity, and to provide a light guide plate capable of forming a bright and easily visible transmission or reflection type liquid crystal display device. SOLUTION: This light guide plate is produced by partially connecting a surface light guide plate 11, which converts the incident light from a linear light source into a surface light source and a linear light guide plate 12, which converts the incident light from a point light source 15 into linear light source. The surface light source device 2 is produced, by disposing a point light source for the linear light guide of the light guide plate. The liquid crystal display device includes at least the surface light source device and a liquid crystal cell. By this method, the linear light source can be easily positioned with high accuracy with respect to the entrance side of the surface light guide plate and in a superior state of the incident efficiency of light. Another holding mechanism of the linear light guide plate can be dispensed with, to decrease the number of parts, and therefore, a compact surface light source device or a liquid crystal display device with low consumption of electric power can be obtained with high production efficiency.

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 which efficiently converts light from a point light source into a planar light source and has excellent brightness and uniformity, and a bright and easy-to-see transmission type or reflection type liquid crystal display device. Light guide plate that can be used.

[0002]

2. Description of the Related Art Conventionally, as a surface light source device capable of forming a transmissive or reflective liquid crystal display device in a backlight system or a front light system, a light source is arranged on a side surface of a light guide plate provided with prismatic irregularities. A known sidelight type was known. In such a surface light source device, a cold-cathode tube is usually used as the light source, but the power consumption is large, and there is a drawback that a battery needs to be frequently replaced in a portable use.

[0003] In view of the above, a method has been proposed in which a point light source such as a light emitting diode is arranged on the incident side surface of a light guide plate. Incidentally, according to the light emitting diode, there are advantages such as reduction of power consumption, space saving and weight reduction by eliminating an inverter, and measures against electromagnetic waves. However, in the light guide plate, it is difficult to incorporate a light scattering mechanism from the viewpoint of preventing display image disturbance and improving luminous efficiency. However, there is a problem that brightness uniformity is poor.

There has been proposed a light source in which a light emitting diode is arranged on a side surface of a rod-shaped light guide plate to form a linear light source. However, in order to increase the light incidence efficiency, the light guide plate is arranged on the incident side surface of the light guide plate as compared with a cold cathode tube. High precision positioning is required, and the number of parts is increased due to the addition of a holding mechanism, and the manufacturing efficiency is poor.There is a drawback in that, especially in the case of a thin light guide plate, a rod-shaped light guide plate that becomes a linear light source must be used. It was difficult to dispose it on the incident side surface with high positional accuracy.

[0005]

The present invention relates to a surface light source device capable of efficiently converting light from a point light source to a surface light source, and having excellent brightness and uniformity, and a transmissive or reflective liquid crystal display device which is bright and easy to see. It is an object of the present invention to develop a light guide plate capable of forming a light guide.

[0006]

The present invention provides a planar light guide plate for converting incident light from a linear light source to a planar light source, and a linear light guide plate for converting incident light from a point light source to a linear light source. A light guide plate characterized by being partially connected, a surface light source device in which a point light source is arranged on a linear light guide plate in the light guide plate, and the surface light source device and a liquid crystal cell A liquid crystal display device characterized by having at least

[0007]

According to the light guide plate of the present invention, light from a point light source is converted to a linear light source via a linear light guide plate, and the light is efficiently converted to a planar light source via a planar light guide plate. A surface light source device having excellent luminance and uniformity can be obtained, and a bright and easy-to-see transmissive or reflective liquid crystal display device can be formed by using the surface light source device for a backlight or a front light.

In addition, by integrating the linear light guide plate and the planar light guide plate by partial connection, the linear light source can be positioned with high precision with respect to the incident side surface of the planar light guide plate to easily achieve a state of excellent light incidence efficiency. It is possible to dispose it, and it is not necessary to separately add a holding mechanism for the linear light guide plate, the number of parts can be reduced, and a compact surface light source device or liquid crystal display device with low power consumption can be obtained with high manufacturing efficiency.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A light guide plate according to the present invention comprises a planar light guide plate for converting incident light from a linear light source to a planar light source, and a linear light guide for converting incident light from a point light source to a linear light source. It is formed by partially connecting the light plate. Examples thereof are shown in FIGS. 1 is a light guide plate, 11 is a planar light guide plate, 12 is a linear light guide plate, and 13 and 14 are connection parts. FIG. 1 illustrates the surface light source device 2 as an example, and reference numeral 15 denotes a point light source.

As the planar light guide plate, an appropriate one capable of converting incident light from a linear light source into a planar light source can be used. Generally, an upper surface 11a and a lower surface 11b opposed thereto as shown in the figure.
And a plate-like body having at least an incident side surface 11c composed of a side surface between the upper and lower surfaces, and having a light emitting means for emitting incident light from the incident side surface to one of the upper and lower surfaces to the other of the upper and lower surfaces. Used. In the example shown in the figure, the light emission means is provided on the upper surface, and the light is emitted from the lower surface 11b, so that the lower surface is a light emission surface.

The planar light guide plate which can be preferably used from the viewpoint of light utilization efficiency and the like is provided with irregularities having an inclined surface capable of controlling the optical path through reflection of incident light from the incident side surface, in particular, total reflection.
In particular, a light emitting means having a repeating structure of prismatic irregularities is provided on one of the upper and lower surfaces. Thus, light can be emitted from the light emission surface with high directivity via the light emission means.

The repetitive structure of the inclined surface forming the light emitting means may be formed in a convex portion or a concave portion having an equilateral surface, but the inclined surface or the short side surface and the flat surface may be formed in order to improve the light use efficiency. In addition, it is preferable that the projection is formed of a projection or a depression having at least a long side surface. The above-mentioned convex portion or concave portion depends on whether it protrudes (convex) or depresses (concave) with respect to the reference surface of the surface on which the light emitting means is formed.

The light emitting means preferably emits as much light as possible in the direction perpendicular to the reference plane (normal line) from the light emitting surface of the planar light guide plate. In the case of a light, the direction of the emitted light serving as display light and the direction of light leaking from the planar light guide plate do not overlap as much as possible. When the leakage light overlaps with the display light, the intensity of the display image is reduced, which tends to lower the contrast.

The irregularities that are preferable from the viewpoint of normalizing the direction of the emitted light and preventing the leakage light from overlapping the display light are the upper and lower surfaces of the planar light guide plate on which the light emitting means is not provided, ie, the light emitting surface. And a flat surface or a long side surface having an inclination angle of 35 to 45 degrees with respect to the reference plane, and a flat surface or a long side surface of 10 degrees or less, especially more than 0 to 10 degrees. .

The inclined surface or the short side surface plays a role of reflecting light incident on the surface out of the incident light from the incident side surface and supplying the light to the light emitting surface. Therefore, the short side surface or the like is formed as an inclined surface facing the incident side surface at a large inclination angle.
In this case, by setting the inclination angle of the short side surface or the like to 35 to 45 degrees, transmission light is reflected with good perpendicularity to the light emission surface, and emission light advantageous for display can be efficiently obtained.

From the viewpoint of the above-mentioned performances such as suppression of total reflection and leakage light based on Snell's law, and suppression of obstruction due to visual reflection, a preferable inclination angle of a short side surface is 38 to 43 degrees, particularly 40 to 43 degrees. 42 degrees. If the angle of inclination of the short side surface or the like is less than 35 degrees, the direction of the light emitted from the light exit surface becomes a large angle with respect to the normal, and the amount of light that can be effectively used for visual recognition decreases, and the brightness tends to decrease. On the other hand, when the angle exceeds 45 degrees, the amount of light leaked from the light emitting means forming surface tends to increase.

On the other hand, the flat surface or the long side surface reflects the transmission light incident thereon and supplies it to the short side surface or the like. The object is to improve the light use efficiency and to transmit a display image from a liquid crystal cell when the front light is used for a reflection type liquid crystal display device. From this point, it is preferable that the inclination angle of the long side surface or the like of the light emitting surface with respect to the reference plane be within the above range.

As described above, the transmission light having an angle larger than the inclination angle is incident on the long side surface or the like and is reflected. In this case, an angle parallel to the light exit surface is determined based on the inclination angle of the long side surface or the like. And is incident on the short side surface or the like, and is reflected and converged well from the light exit surface by the above-mentioned collimation and exits. As a result, in addition to the transmission light directly incident on the short side surface and the like, the transmission light incident on the long side surface and the like via the reflection on the long side surface and the like is reflected by the reflection via the short side surface and the like. Can be supplied to the exit surface,
The light utilization efficiency can be improved by that amount, the incident angle of light reflected on the long side surface and the like incident on the short side surface and the like can be made constant, the dispersion of the reflection angle can be suppressed, and the parallel collection of outgoing light can be suppressed. It can be lightened.

Therefore, by adjusting the inclination angle of the inclined surface or short side surface and the flat surface or long side surface of the unevenness forming the light emitting means, the emitted light can be provided with a high degree of directivity. It is possible to emit light in a direction perpendicular to the light emitting surface or at an angle close thereto.

In the above, the inclination angle of the long side surface or the like is 10
Exceeding the degree, the incidence rate on the long side surface or the like decreases, and the light supply to the side of the opposing end 11d facing the incident side surface 11c is insufficient, so that the light emission tends to be uneven. Also, in the cross-sectional shape of the planar light guide plate, it is difficult to reduce the thickness of the opposite end side, and the amount of light incident on the unevenness is reduced, so that the luminous efficiency is apt to be reduced. Note that the inclination angle of the long side surface or the like may be 0 degree, but it is more than 0 to 8 from the point of the performance such as the condensing of the outgoing light by the parallelization of the transmission light and the suppression of the leak light. Degree, preferably 5 degrees or less.

The long side surface or the like, which is preferable from the viewpoint of the visibility of a display image through the flat surface or the long side surface of the planar light guide plate, has an angle difference of the inclination angle of the entire planar light guide plate. Within 5 degrees, especially within 4 degrees, especially within 3 degrees,
The difference of the inclination angle between the nearest long sides etc. is within 1 degree,
Especially within 0.3 degrees, especially within 0.1 degrees.

When the Freudlight of the reflection type liquid crystal display device is used due to the difference in the inclination angle of the long side surface or the like,
It is possible to suppress the influence on the display image transmitted through the long side surface or the like. If the deflection of the transmission angle due to the long side surface or the like largely differs depending on the location, an unnatural display image is obtained. In particular, if the deflection difference of the transmission image in the vicinity of the adjacent pixel is large, a very unnatural display image is apt to occur.

The angle difference between the above-mentioned inclination angles is based on the premise that the inclination angle of the long side surface or the like is within the above-mentioned range of 10 degrees or less. In other words, it is assumed that such a small tilt angle suppresses the deflection of the display image due to refraction at the time of transmission on the long side surface or the like and keeps it within an allowable value. It is an object of the present invention not to change the optimal viewing direction of the reflective liquid crystal display device optimized by the above.

From the point of obtaining a brighter display image, the projected area of the light emitting surface with respect to the reference plane, such as the long side surface, is 8 times or more, especially 10 times or more, especially 15 times or more of that of the short side surface or the like. Irregularities are preferred. Thus, in the case of a front light of a reflection type liquid crystal display device, most of a display image by a liquid crystal cell can be transmitted through a long side surface or the like. In the case of a backlight of a transmissive liquid crystal display device, a reflective surface having a large area can be secured, which is advantageous for improving light use efficiency.

The size of the inclined surface or short side surface is preferable from the viewpoint of securing the area of the long side surface and the like, preventing the occurrence of moire due to interference with the pixels of the liquid crystal cell, and forming sharp irregularities. Means that the pixel pitch of the liquid crystal cell is 100 to
Considering that 300 μm is generally used, the width is set to 40 μm or less, particularly 3 to 20 μm, particularly 5 to 15 μm based on the projection width of the light emitting surface with respect to the reference plane.

It is preferable that the interval between the short side surfaces and the like is larger than the above-mentioned point. On the other hand, since the short side surface and the like is a substantial emitting function of the side incident light as described above, the interval is wide. If it is too much, the illumination light may be sparse and the display may also be unnatural. In view of them, the repetition pitch P of the unevenness (FIG. 2) is preferably set to 50 μm to 1.5 mm. The pitch may be irregular, such as a random pitch or a random or regular combination of a predetermined number of pitch units. However, the pitch should be constant from the viewpoint of moiré prevention and appearance. Is preferred.

In the case of a light emitting means having a repeating structure of irregularities, moire may occur due to interference with pixels of a liquid crystal cell. Moire can be prevented by adjusting the pitch of the unevenness,
As described above, the pitch of the unevenness has a preferable range.
Therefore, as a solution to the case where moire occurs in the pitch range, it is preferable to form the unevenness so as to be inclined with respect to the reference plane of the incident side surface so that the unevenness can be arranged in the pixel in an intersecting state. In this case, if the inclination angle is too large, the reflection via the short side surface or the like is deflected, causing a large deviation in the direction of the emitted light, and the anisotropy of the emission intensity in the light transmission direction of the planar light guide plate is large. As a result, the light use efficiency is reduced, and the display quality is likely to be reduced.

From the above-mentioned point, the inclination direction of the irregular arrangement direction of the incident side surface with respect to the reference plane, that is, the inclination angle of the ridge direction of the irregularity is ±
It is preferably within 30 degrees, particularly within ± 25 degrees, particularly within ± 20 degrees. The sign of ± means the direction of the inclination with respect to the incident side surface. When moire can be neglected, the arrangement direction of the unevenness is more preferably parallel to the incident side surface.

The planar light guide plate can be formed in an appropriate form. Therefore, as shown in the figure, the same thickness plate or the like may be used, but preferably, the thickness of the opposing end 11d facing the incident side surface 11c is smaller than that of the incident side surface, especially 50% or less. It is. By making the opposite end thinner (such as a wedge shape), the efficiency of incidence on the light emitting means can be increased.

That is, before the light incident from the incident side reaches the opposing end, it efficiently enters the light emitting means formed on one of the upper and lower surfaces, and emits light from the other of the upper and lower surfaces via reflection on the short side surface or the like. The incident light emitted from the surface can be efficiently supplied to the target surface. In addition, there is an advantage that the planar light guide plate can be reduced in weight by making it wedge-shaped. By the way, in the case of a wedge shape consisting of a straight surface, about 7
It can be 5% by weight.

The shape of the planar light guide plate can be appropriately determined also in the case of the above-mentioned wedge shape or the like, and can be an appropriate surface shape such as a refraction surface or a curved surface in addition to a linear surface. In addition, the slope of the unevenness forming the light emitting means may have an appropriate surface form including a linear surface, a refraction surface, a curved surface, and the like. Furthermore, the repetition of the unevenness may be formed by a combination of unevenness having a different shape and the like in addition to the pitch. In addition, the unevenness may be formed as a series of convex portions or concave portions in which the ridge lines are continuous, or may be formed as intermittent convex portions or concave portions arranged at predetermined intervals and discontinuously arranged in the ridge line direction. You may.

The light emitting surface of the planar light guide plate, that is, one of the upper and lower surfaces on which the light emitting means is not formed is usually a flat surface. There is a case where the light emitting means and the pattern projected on the light emitting surface interfere with each other to cause a moiré phenomenon due to interference fringes, and fine irregularities are formed as necessary for the purpose of preventing a decrease in display quality due to the moiré. A light emitting surface structure or the like provided can also be used.

The formation of the fine irregularities on the light emitting surface is performed by, for example, a roughening method using a mat treatment such as sandblasting, a method of providing fine irregularities via a mold or the like when forming a planar light guide plate, or a transparent method. It can be carried out by an appropriate method according to the conventional diffusion layer, such as a method of providing a resin layer containing particles, a method of providing a diffusion dot or a sheet provided with the same on a planar light guide plate.

The shapes of the incident side surface 11c and the left and right side surfaces 11e in the planar light guide plate are not particularly limited, and may be appropriately determined. Generally, the incident side surface is a surface perpendicular to the light emitting surface due to the arrangement of the linear light guide plate.

On the other hand, as the linear light guide plate, an appropriate one that can convert incident light from a point light source into a linear light source and can be partially connected to the above-described planar light guide plate can be used. Generally, as shown in FIG. 1 and FIG. 2, at least six surfaces of upper and lower 12a, 12b, front and rear 12c, 12d, and left and right 12e are provided.
For the front surface 12c, a rod-shaped body having an optical path changing means for emitting incident light from one or both of the left and right surfaces 12e from the rear surface 12d is used.

The linear light guide plate which can be used more preferably, such as partial connectivity with the planar light guide plate and the point where the formed linear light source is efficiently incident on the planar light guide plate, is a rectangular parallelepiped 12 as shown in FIG.
The rear surface 12d facing the left or right surface 12e, on which the light from the point light source 15 is incident, becomes the light emitting surface on the front surface 12c
The optical path changing means has an inclined surface in the vertical direction inclined with respect to the reference plane.

As described above, the light from the point light source made incident from the left and right surfaces 12e of the linear light guide plate efficiently enters the inclined surfaces of the optical path changing means formed in the directions of the upper and lower surfaces 12a and 12b, and is reflected by the inclined surfaces. The light path is changed through the rear surface 12
The light is efficiently emitted with better directivity than d. In this case, the deflection angle of the light due to the change of the optical path through the slope is about 70 from the point that the light is emitted with good directivity in the front direction in the planar light guide plate.
The angle is preferably about 90 degrees, and it is more preferable to use total reflection than to efficiently reflect light at the large deflection angle. Further, from the point of the total reflection, the inclined surface in the optical path changing unit faces the left or right surface which is the incident surface of the linear light guide plate, and is 35 to a rear reference plane which is the light emitting surface.
Preferably, it has a 45 degree tilt angle.

The optical path changing means can be formed by using the above-mentioned inclined surface as the whole front surface of the linear light guide plate. However, the light path changing means is intended to reduce the thickness in the front-rear direction and improve the light emission efficiency. A triangle or trapezoid having a front surface of a linear light guide plate, a slope for directing the optical path of incident light from the left and right side surfaces toward the rear surface, and a flat surface for transmitting the incident light to the other side of the left and right surfaces. It is preferable to form it as an uneven repeating structure having a cross-sectional structure made of other polygons. When arranging point light sources on both the left and right surfaces of the linear light guide plate, it is preferable that the inclined surfaces be provided on both the left and right surfaces by a cross-sectional structure of an isosceles triangle or trapezoid, for example, in order to make the emitted light uniform.

It is preferable that a portion other than the slope such as the top side of the trapezoid be a flat surface having an inclination angle of 10 degrees or less with respect to a reference plane on the rear side from a point where the angle of transmitted light is not largely changed. Therefore, from the viewpoint of its function, the optical path changing means has a repetitive structure of irregularities having a slope having an inclination angle of 35 to 45 degrees and a flat surface of 10 degrees or less according to the light emitting means in the planar light guide plate described above. It can also be formed by a method in which the linear light guide plate is provided in the upper and lower direction. In this case, the surface of the linear light guide plate on which the optical path changing means is provided may be a wedge-shaped surface according to the above-mentioned planar light guide plate.

The repetition pitch of the irregularities forming the optical path changing means is not particularly limited. However, from the viewpoint of the uniformity of the emitted light, it is not more than 1.5 mm, especially not more than 1.0 mm, especially not more than 50 mm.
It is preferably set to 0 μm or less. The pitch may be irregular, such as a random pitch, a combination of a predetermined number of pitch units randomly or regularly, or a pitch that changes gradually, or may be constant.

The shapes of the upper and lower surfaces 12a and 12b, the rear surface 12d, and the left and right surfaces 12e of the linear light guide plate are not particularly limited, and may be appropriately determined. In general, the surface is a flat surface in terms of disposition with respect to the planar light guide plate. The rear surface of the linear light guide plate, which is the light exit surface, may have a diffusion surface structure with fine irregularities according to the above-described planar light guide plate, if necessary. The surface is preferably smooth from the viewpoint of maintenance.

For the formation of the planar light guide plate or the linear light guide plate, an appropriate material exhibiting transparency according to the wavelength range of the light source can be used. Incidentally, in the visible light region, for example, transparent resins and glass represented by acrylic resins, polycarbonate resins, polyester resins, norbornene resins, polyolefin resins, epoxy resins and the like can be mentioned. Those which do not show birefringence or are formed of a material having low birefringence are preferred.

Further, it is preferable to use a planar light guide plate or a linear light guide plate formed of a material having a high refractive index in terms of prevention of leaked light, total reflection efficiency, an emission angle and efficiency thereby, and a transmission angle. When used for a front light, if the refractive index is too high, the surface reflection increases, so that 1.48 to 1.58;
In particular, it is preferably a planar light guide plate formed of a material having a refractive index of 1.50 to 1.54. On the other hand, when used for a backlight, such a problem does not occur. Therefore, a planar light guide plate formed of a material having a refractive index of 1.51 or more is preferable. In addition, about a linear light guide plate, it can correspond to a planar light guide plate.

The planar light guide plate and the linear light guide plate can be formed by a cutting method, and can be formed by an appropriate method. As a preferable manufacturing method from the viewpoint of mass productivity and the like, a method of pressing a thermoplastic resin under heating to a mold capable of forming a predetermined shape and transferring the shape, a thermoplastic resin heated and melted, or via a heat or solvent A method of filling a fluidized resin into a mold that can be molded into a predetermined shape, filling or casting a liquid resin that can be polymerized by heat, ultraviolet rays or radiation into a mold capable of forming a predetermined shape. Examples of the method include a polymerization treatment.

In the present invention, the planar light guide plate or the linear light guide plate is formed, for example, with light emitting means such as unevenness, an optical path changing means, and / or fine unevenness (light emitting surface) in a light guide portion for transmitting light. It may be formed as a laminate of parts made of the same or different materials, such as a bonded sheet, and need not be formed as an integrated single layer of one material.

The thickness of the planar light guide plate or the linear light guide plate can be appropriately determined according to the size of the planar light guide plate or the size of the point light source depending on the purpose of use. When used for forming a transmission type or reflection type liquid crystal display device or the like, the thickness of a general planar light guide plate is 20 mm or less based on the incident side surface, and particularly preferably 0.1 mm or less.
It is 1 to 10 mm, especially 0.5 to 8 mm. Also, the thickness of the linear light guide plate is usually 1 to 1 of the incident side surface of the planar light guide plate based on the rear surface of the linear light guide plate from the point of incidence efficiency to the planar light guide plate.
Doubled.

The light guide plate according to the present invention is a light guide plate in which a planar light guide plate and a linear light guide plate are partially connected. Generally, as shown in the drawing, an incident side surface 11c of the planar light guide plate 11 and a rear surface of the linear light guide plate 12. 12d are partially connected in a state of facing each other via the gap A. With the interposition of the air gap A, the light emitted from the linear light guide plate that enters the incident side surface of the planar light guide plate at a large angle is totally reflected, and the directivity of the incident light to the planar light guide plate can be increased.

The purpose of the partial connection is to enable the planar light guide plate and the linear light guide plate to be integrally handled in addition to the space A. This makes it possible to support the linear light guide plate with the planar light guide plate and eliminate the need for a separate holding mechanism, and to position the linear light guide plate with high accuracy on the incident side surface of the planar light guide plate, thereby enabling the linear light guide plate to be used. The incidence efficiency of the emitted light can be increased.

The partial connection between the planar light guide plate and the linear light guide plate can be performed by an appropriate method. Therefore, the planar light guide plate and the linear light guide plate are integrally formed in a partially connected state, and they are integrally formed. Or can be formed separately and partially connected via an adhesive or the like. Forming the same body has the advantage that the number of assembled parts can be reduced, and forming the separate body has the advantage that the light path can be controlled by the difference in the refractive index as a combination of a planar light guide plate and a linear light guide plate having different refractive indexes.

The connection between the planar light guide plate and the linear light guide plate is as follows:
Although it can be determined appropriately, the connection width is preferably as narrow as possible because leakage light occurs at the connection portion and the incidence efficiency on the incident side surface of the planar light guide plate is easily reduced, and the incidence efficiency and the like are determined. The partial connection method using the peripheral portion of the incident side surface of the planar light guide plate is preferable to the above point.

In the case where the peripheral portion of the incident side surface is used, the surface area of the planar light guide plate is increased as shown in FIG. 1 in view of securing the incident area on the incident side surface and supporting the linear light guide plate. 2 mm or less, preferably 1 mm or less, particularly 0.5 mm or less at both ends in the longitudinal direction on the incident side surface of the light plate 1
3, or as shown in FIG. 2, the thickness of one or both of the upper and lower surfaces is 1/4 or less, preferably 1/6 or less, particularly 1/10
It is preferable to connect via the following parts 14.

The surface light source device according to the present invention is intended to be used as a sidelight type backlight or front light in a transmission type or reflection type liquid crystal display device or the like.
As shown in FIG. 1, a point light source 15 is disposed on the linear light guide plate 12 of the light guide plate 1, particularly on one or both of the left and right surfaces 12 e thereof.

As the point light source, for example, a monochromatic light or an appropriate light source exhibiting light emission characteristics in various wavelength ranges can be used according to the purpose of use of the surface light source device, such as a light emitting diode. It is preferable that the surface light source device used for forming the liquid crystal display device has emission characteristics in a wavelength region as wide as possible in a visible light region. The number of point light sources arranged on the left and right surfaces of the planar light guide plate can be appropriately determined according to the area of the left and right surfaces and the like. It is also possible to control so as to repeat blinking by an appropriate method such as a method of applying an alternating current such as a sine wave. In that case, by controlling the blinking cycle, it is possible to simulate a continuous light emission state in which blinking is not perceived, and it is possible to further reduce power consumption.

At the time of forming the surface light source device, as shown in FIG. 2, a light source holder 12f surrounding the linear light guide plate 12 to guide light leaked from the linear light guide plate to the incident side surface of the planar light guide plate.
A suitable auxiliary means such as the above can also be arranged. As the light source holder, a resin sheet, a metal foil, a white sheet, or the like provided with a metal thin film having a high reflectance is generally used. When used as a backlight, a light source holder can be extended on the light emitting surface of the planar light guide plate to serve also as a reflection sheet.

The surface light source device according to the present invention provides a surface light source excellent in brightness by efficiently utilizing light from a point light source, and is easy to increase in area and the like. It can be preferably applied to various devices such as a backlight system and a front light system of a reflection type liquid crystal display device. In particular, the present invention can be preferably used for a portable device such as a mobile phone, an electronic organizer, or a PDA, which uses a battery such as a storage battery as a power source and functions advantageously with low power consumption.

FIG. 3 illustrates a reflection type liquid crystal display device using a surface light source device for a front light system. This is a reflection device having polarizing plates 31 and 33 on the front and back sides of a liquid crystal cell 32 and a reflecting layer 5 on the back surface via a light diffusion layer 4 on the light emitting surface side of the planar light guide plate 11 in the surface light source device. The liquid crystal display unit 3 is formed by arranging a liquid crystal display unit 3 of a type, and can be used as a reflection type liquid crystal display device by external light by turning off the surface light source device.

On the other hand, FIG. 4 illustrates a liquid crystal display device using a surface light source device for a backlight system. This is formed by arranging the liquid crystal display unit 3 via the light diffusion layer 4 above the planar light guide plate 11 in the surface light source device,
The light guide plate 1 has a reflection layer 5 on the light emitting surface of the planar light guide plate 11 and can be used as a liquid crystal display device for both reflection and transmission in addition to a transmission type.

As shown in the above-described example, the liquid crystal display device is formed by using at least a surface light source device and a liquid crystal cell, and arranging the liquid crystal cell on a predetermined surface side of the planar light guide plate 11 in the surface light source device. . In this case, in the reflection type liquid crystal display device using the surface light source device as a front light, the surface light source device 2 has the planar light guide plate on the viewing side of the liquid crystal display unit 3 having the reflection layer 5 on the back surface as shown in FIG. 11 are arranged such that the light emitting means forming surface is on the upper side (viewing side).

Therefore, in the reflection type liquid crystal display device using the front light system, at least the liquid crystal layer of the liquid crystal cell is located between the surface light guide plate of the surface light source device and the reflection layer, and the light emitting means of the surface light guide plate is provided. It is indispensable to arrange such that the forming surface is on the viewing side. The visual recognition is that external light transmitted from the outside through the planar light guide plate of the surface light source device or light emitted by the planar light guide plate at the time of lighting is transmitted through the liquid crystal cell and inverted by the reflective layer,
This is performed by transmitting the inverted light again through the liquid crystal cell and then through the planar light guide plate. The reflection layer can be provided in the liquid crystal cell by being attached to a cell substrate.

On the other hand, as shown in FIG. 4, in a transmissive type liquid crystal display device using a surface light source device as a backlight, a planar light guide plate of the surface light source device is arranged on the back side (viewing back side) of a liquid crystal cell. When used for both transmission and transmission, the planar light guide plate of the surface light source device is disposed between the liquid crystal cell and the reflective layer. In those cases, the surface light source device can be arranged such that the light emitting means forming surface side of the planar light guide plate is on the liquid crystal cell side as shown in the figure, or the light emitting means of the planar light guide plate is opposite to the figure. May be arranged as the liquid crystal cell side.

As shown in the figure, a method of inverting the light from the light emitting means through the reflective layer disposed on the light emitting surface with the light emitting means forming surface side of the planar light guide plate as the liquid crystal cell side is used. By increasing the length, the bright line pattern by the light emitting means can be reduced, and the occurrence of display defects such as moiré can be suppressed as compared with the method in which the light emitting surface side of the planar light guide plate is arranged as the liquid crystal cell side, contrary to the example shown in the figure. There are advantages.

Visual recognition by the above-mentioned transmissive liquid crystal display device is carried out when the light emitted from the surface light source device enters the liquid crystal cell directly or through an inversion through a reflective layer and is transmitted. In the reflection mode, the external light passes through the liquid crystal cell and is inverted by the reflection layer on the back surface of the planar light guide plate. Is transmitted again through the planar light guide plate and the liquid crystal cell.

A liquid crystal display device is generally composed of a liquid crystal cell 32 having a transparent electrode functioning as a liquid crystal shutter as shown in FIGS. 3 and 4 and a liquid crystal display unit comprising a driving device and a polarizing plate attached thereto. It is formed by appropriately assembling components such as a backlight or a front light incorporating a switch for turning off the light and, if necessary, a light diffusion layer 4, a reflection layer 5, an anti-reflection layer, a compensating retardation plate 7, and the like. You.

In the present invention, there is no particular limitation except that the above-described light guide plate or surface light source device is used, and it can be formed according to a conventional example as shown in the figure. Therefore, the liquid crystal cell to be used is not particularly limited. For example, when the liquid crystal cell is based on a liquid crystal alignment mode, a twisted or non-twisted type such as a TN liquid crystal cell, an STN liquid crystal cell, a vertical alignment cell, a HAN cell, an OCB cell, a guest host system, or the like. An appropriate liquid crystal cell such as a ferroelectric liquid crystal cell can be used. The driving method of the liquid crystal is not particularly limited, and may be an appropriate driving method such as an active matrix method or a passive matrix method.

In FIGS. 3 and 4, the liquid crystal cell 32
A liquid crystal layer is sealed between the cell substrates. In this case, the light guide plate according to the present invention or the planar light guide plate can also be used as the cell substrate. In the illustrated example, the illustration of the transparent electrode and the associated driving device is omitted.

The polarizing plate provided on one or both of the front and back sides of the liquid crystal cell is also not particularly limited. However, from the viewpoint of obtaining a display with a good contrast ratio by incidence of highly linearly polarized light,
In particular, as the polarizing plate on the backlight side or the front light side, it is preferable to use a polarizing plate having a high degree of polarization such as an iodine-based or dye-based absorption linear polarizer.

For the reflective layer, for example, a coating layer containing a powder of a high-reflectance metal such as aluminum, silver, gold, copper, or chromium in a binder resin, an attached layer of a metal thin film by a vapor deposition method, or the like; It can be formed as a suitable reflection layer according to the related art, such as a reflection sheet or a metal foil, in which a layer or an attached layer is supported by a base material. When a reflective layer is provided inside the liquid crystal cell, the reflective layer may be formed by a method of forming an electrode pattern using a highly conductive material such as the above-described high-reflectivity metal, or on a reflective layer formed of a high-reflectivity metal film. It is preferable to use a reflective layer formed by providing a transparent electrode pattern via an insulating layer.

The reflection layer in the reflection type liquid crystal display device can be provided outside the liquid crystal cell, for example, a reflection layer made of a high-reflectance metal film provided on a plastic film. In the case of a transmissive liquid crystal display device, it can be directly attached to a planar light guide plate forming the backlight. The reflecting layer can be provided on either the light emitting means forming surface or the light emitting surface of the planar light guide plate according to the use form of the light guide plate in an appropriate manner exemplified above.

In the formation of the liquid crystal display device, as described above, for example, an antiglare layer or an antireflection film provided on the surface on the viewing side, or a light diffusion plate, a compensating retardation plate, a polarization separation plate, an optical path control, or the like. A suitable optical element such as a prism sheet can be arranged at a suitable position. Note that the antireflection film can also be provided on the light emission surface of the planar light guide plate.

The compensating retardation plate is intended to improve the visibility by compensating for the wavelength dependence of birefringence, etc., and to provide a polarizing plate on the viewing side and / or the backlight side. It is arranged as necessary between the liquid crystal cell and the like. As the retardation plate for compensation, an appropriate retardation plate can be used according to a wavelength range or the like. The retardation plate can be obtained as, for example, a birefringent sheet or a support sheet for a liquid crystal polymer alignment layer obtained by stretching a film made of polycarbonate, polysulfone, polyester, polymethyl methacrylate, polyamide, polyvinyl alcohol, or the like. Alternatively, the retardation sheets may be formed as two or more superposed layers.

The light-diffusing layer is provided at an appropriate position on the liquid crystal display device as required for the purpose of obtaining surface light emission having uniform brightness by preventing uneven brightness and darkness and reducing moire caused by mixing of adjacent light rays. One or two or more layers are arranged.
Incidentally, in the examples of FIGS. 3 and 4, the light diffusion layer 4 is disposed between the light guide plate 1 and the liquid crystal display unit 3. It should be noted that a diffusion layer having a narrow diffusion range can be preferably used from the viewpoint of maintaining directivity of light emitted from the planar light guide plate.

The light-diffusing layer may be formed, for example, by dispersing high-refractive-index transparent particles in a low-refractive-index transparent resin according to the above-mentioned fine irregularities on the light-emitting surface, or by applying and curing the transparent resin. A method of applying and curing a resin, a method of generating a craze by swelling the substrate surface via a solvent, a method of forming a transparent resin layer having an irregular uneven surface, or a method of using a diffusion sheet formed according to the above It can be formed by an appropriate method such as

In the formation of the transmission type liquid crystal display device, a polarization separation plate may be provided between the surface light source device and the polarizing plate for the purpose of improving luminance. The polarization separation plate, for example, a layer having a cholesteric liquid crystal phase, a sheet having a layer composed of a liquid crystal polymer exhibiting a cholesteric phase,
Like a transparent substrate with a dielectric multilayer film,
It has a function of separating natural light into polarized light through transmission and reflection. Incidentally, according to the cholesteric liquid crystal phase, left and right circularly polarized light can be separated through transmission and reflection, and according to the dielectric multilayer film, it can be separated into linearly polarized light of P wave and S wave through transmission and reflection. it can. The circularly polarized light is 1 /
It can be converted to linearly polarized light via a four-wave plate.

Therefore, by making the polarized light transmitted through the polarized light separating plate incident on the polarizing plate with the polarization axes as coincident as possible, absorption loss by the polarizing plate can be suppressed, and the luminance can be improved. Further, in the surface light source device including the light guide plate 1 provided with the reflection layer 5 on the back surface as shown in FIG. 4, the polarization reflected by the polarization separation plate is inverted by the reflection layer 5 and re-entered into the polarization separation plate. Part or all of the inverted light can be transmitted, and the luminance can be improved by improving the light use efficiency.

In the present invention, optical elements or components such as a light guide plate, a liquid crystal cell, and a polarizing plate forming the above-described surface light source device and liquid crystal display device are entirely or partially laminated and integrated and fixed. Alternatively, they may be arranged in an easily separable state. It is preferable to be in a fixed state rather than to prevent a decrease in contrast by suppressing interface reflection. An appropriate transparent adhesive such as a pressure-sensitive adhesive can be used for the fixing and adhesion treatment.

[0076]

EXAMPLE 1 A high-fluidity polymethyl methacrylate was filled in a mold previously processed into a predetermined shape by heating and melting, and then cooled to reduce the incidence side of the planar light guide plate and the rear surface of the linear light guide plate to 0. A light guide plate partially connected with a thickness of 1 mm was integrally formed at the left and right ends of the incident side face via a gap of 8 mm.

The planar light guide plate has a width of 40 mm, a depth of 25 mm, a thickness of the incident side surface of 1 mm, and a thickness of the opposite end of 0.6 mm. The upper and lower surfaces are flat and the upper surface thereof is parallel to the incident side surface. The convex-concave shape has a pitch of 210 μm, and the inclination angle of the short side surface facing the incident side surface is in the range of 42.5 to 43 degrees, and the inclination angle of the long side surface is in the range of 1.8 to 3.5 degrees. Change, the inclination angle change of the nearest long side is within 0.1 degree, the projection width of the short side to the bottom is 10 to 16 μm, and the projection area ratio of the long side / short side to the bottom is 12 times or more. Having a prism-like unevenness at a position 2 mm away from the incident side surface.

The linear light guide plate is a rectangular parallelepiped having a width (left and right) of 43 mm, a depth (front and rear) of 2.4 mm, and a thickness (up and down) of 1 mm, and has a vertical angle of 94.degree. It has optical path changing means in the vertical direction consisting of prism-shaped grooves of 20 μm in the vertical direction at a pitch of 200 μm over the entire surface in the left and right width directions.

A white light emitting diode was disposed on each of the left and right sides of the linear light guide plate in the above light guide plate, and the periphery thereof was fixed by an adhesive tape, and connected to a DC power supply to obtain a surface light source device.

Example 2 A light guide in which a planar light guide plate and a linear light guide plate were partially bonded in the width direction via a layer having a thickness of 0.2 mm using the side having no light emitting means on the incident side surface of the planar light guide plate. A surface light source device was obtained in the same manner as in Example 1 except that the light plate was used.

Example 3 The thickness of the connecting portion at the left and right ends of the incident side was 0.5 mm.
A light guide plate was obtained in the same manner as in Example 1, and a surface light source device was obtained using the light guide plate.

Example 4 A planar light guide plate and a linear light guide plate were formed separately from each other in the same manner as in Example 1, and an incident side surface and a rear surface thereof were simply arranged to face each other to obtain a surface light source device.

Example 5 A normally white reflective liquid crystal display unit was placed on a stand, and the surface light source device of Example 1 was placed above the unit to obtain a front light type reflective liquid crystal display device. The light guide plate is
The planar light guide plate was arranged such that the light emitting means forming surface of the planar light guide plate was on the viewing side.

Example 6 A reflection type liquid crystal display device of a front light type was obtained according to Example 5, except that the surface light source device of Example 2 was used.

Example 7 A reflection type liquid crystal display device of a front light type was obtained according to Example 5, except that the surface light source device of Example 3 was used.

Example 8 Using the surface light source device of Example 4 to manufacture a reflection type liquid crystal display device of a front light type according to Example 5, the linear light guide plate could not be arranged on the liquid crystal display unit.

Evaluation Test 1 With respect to the reflection type liquid crystal display devices obtained in Examples 5 to 8, the surface light source device was turned on in a state where no voltage was applied to the liquid crystal cell, and the front luminance at the center of the device was measured with a luminance meter (manufactured by Topcon Corporation). BM7). The results are shown in Table 1. Table 1 Example 5 Example 6 Example 7 Example 8 Front luminance (cd / m ² ) 24 21 16 −

Example 9 A light-diffusing and reflecting silver reflector was adhered to the light exit surface of the planar light guide plate of the surface light source device of Example 1 via an adhesive layer, and was placed on a table. A transmissive liquid crystal display unit was arranged on the light emitting means forming surface to obtain a backlight type transmissive liquid crystal display device.

Example 10 A backlight type transmissive liquid crystal display device was obtained in the same manner as in Example 9 except that the surface light source device of Example 2 was used.

Example 11 A backlight type transmissive liquid crystal display device was obtained in the same manner as in Example 9 except that the surface light source device of Example 3 was used.

Example 12 A backlight type transmissive liquid crystal display device was obtained in the same manner as in Example 9 except that the surface light source device of Example 4 was used.

Evaluation Test 2 With respect to the transmission type liquid crystal display devices obtained in Examples 9 to 12, the surface light source device was turned on while the liquid crystal cell was not applied with a voltage, and the front luminance at the center of the device was measured with a luminance meter (manufactured by Topcon Corporation). BM7). The results are shown in Table 2. Table 2 Example 9 Example 10 Example 11 Example 12 Front luminance (cd / m ² ) 28 24 18 25 * 1 * 1: When the surface light source device is arranged on a table, the incident side surface of the planar light guide plate and the linear guide are used. This is a value when the butting arrangement on the rear surface of the light plate is strictly performed and fixed and held so that the arrangement state does not collapse.

Example 13 The surface light source device of Example 1 was placed on a table with the light emitting means forming surface of the planar light guide plate facing down, and the haze 83% light diffusion was performed on the light emission surface of the planar light guide plate. A transmissive liquid crystal display unit was arranged via a film to obtain a backlight type transmissive liquid crystal display device.

Example 14 A backlight type transmissive liquid crystal display device was obtained in the same manner as in Example 13, except that the surface light source device of Example 2 was used.

Example 15 A backlight type transmissive liquid crystal display device was obtained according to Example 13, except that the surface light source device of Example 3 was used.

Example 16 A backlight type transmissive liquid crystal display device was obtained in the same manner as in Example 13 except that the surface light source device of Example 4 was used.

Evaluation Test 3 Regarding the transmission type liquid crystal display devices obtained in Examples 13 to 16, the surface light source device was turned on with no liquid crystal cell applied, and the front luminance at the center of the device was measured using a luminance meter (manufactured by Topcon Corporation). BM7). Table 3 shows the results. Table 3 Example 13 Example 14 Example 15 Example 16 Front luminance (cd / m ² ) 30 27 21 28 * 2 * 2: When the surface light source device is arranged on a table, the incident side surface of the planar light guide plate and the linear guide are used. This is a value when the butting arrangement on the rear surface of the light plate is strictly performed and fixed and held so that the arrangement state does not collapse.

In Examples 12 and 16 described above, the luminance greatly changes depending on the distance and position of the arrangement of the planar light guide plate and the linear light guide plate. It was inferior. In Example 8, the front luminance when the planar light guide plate and the linear light guide plate were strictly positioned on the table and fixed and held so that the arrangement state was not collapsed was 22 cd /.
m ² , but when the fixed holding state was displaced by vibration or the like, the luminance was significantly reduced.

In Examples 5 to 7, 9 to 11, and 13 to 15, a good light emitting state can be obtained by simply arranging the surface light source device as in the case of the usual light guide plate, and the fixing and holding means is unnecessary. Was. In Example 5 of the front light type, a thin linear shadow was generated at the end of the planar light guide plate due to the influence of the connection portion. Example 6
In Example 7, almost no shadow was generated, and in Example 7, the display was dark due to light leakage from the connection portion, and stripe-like unevenness was generated in a direction parallel to the linear light guide, making the display difficult to see.

In Examples 9 and 13 of the backlight type, Example 5
No occurrence of a shadow such as was observed. Examples 7 and 1
1. From the comparison of Examples 14 and 15, uniform and bright displays were obtained in Examples 7 and 14, but in Examples 11 and 15, weak stripe-like unevenness occurred and the display was dark. As described above, according to the light guide plate of the present invention, a point light source can be easily converted to a uniform planar light source as a single component that does not require component alignment, and a front-line or backlight-type reflection type excellent in display characteristics is provided. Alternatively, it can be seen that a transmission type liquid crystal display device can be formed.

[Brief description of the drawings]

FIG. 1 is an explanatory perspective view of a surface light source device (light guide plate).

FIG. 2 is an explanatory side view of another light guide plate.

FIG. 3 is an explanatory diagram of a reflection type liquid crystal display device of a front light type.

FIG. 4 is a backlight type transmission type (reflection / transmission type).
Illustration of liquid crystal display

[Explanation of symbols]

 1: Light guide plate 11: Planar light guide plate 11a: Upper surface (surface on which light emitting means is formed) 11b: Lower surface (light emitting surface) 11c: Incident side surface 12: Linear light guide plate 12a, b: Upper and lower surfaces 12c: Front surface (optical path change) Means forming surface) 12d: rear surface (light emitting surface) 12e: left and right surface (light incident surface) 2: surface light source device 15: point light source 3: liquid crystal display units 31, 33: polarizing plate 32: liquid crystal cell 4: light diffusion Layer 5: Reflective layer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // F21Y 101: 00 G02F 1/1335 530 (72) Inventor Takao Suzuki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Hideo Abe 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H038 AA52 AA55 BA01 BA06 2H091 FA23X FA23Z FA45X FA45Z FB02 FC17 FD06 LA12 LA18 5G435 AA02 AA03 BB12 BB15 BB16 DD09 DD14 EE23 EE27 FF03 FF05 FF06 FF08 GG23 GG24 GG26

Claims (11)

[Claims] 1. A planar light guide plate for converting incident light from a linear light source to a planar light source and a linear light guide plate for converting incident light from a point light source to a linear light source are partially connected. A light guide plate, comprising: 2. The light guide plate according to claim 1, wherein the planar light guide plate has at least an incident side surface including an upper surface, a lower surface, and a side surface between the upper and lower surfaces, and receives incident light from the incident side surface on one of the upper and lower surfaces. And a linear light guide plate having at least six surfaces of upper, lower, front, rear, left and right, and incident light from one or both of the left and right surfaces on its front surface. The light guide is formed by partially connecting the incident side surface of the planar light guide plate and the rear surface of the linear light guide plate so as to face each other via an air gap. Light board. 3. The slope according to claim 2, wherein the light emitting means in the planar light guide plate faces the incident side surface at an inclination angle of 35 to 45 degrees with respect to the reference plane on the side of the upper and lower surfaces which is the light emitting surface having no light emitting surface. And at least a flat surface whose inclination angle is 10 degrees or less and whose projected area with respect to the reference plane is at least 8 times that of the inclined surface, and wherein the linear light guide plate is formed of a rectangular parallelepiped, Wherein the optical path changing means formed on the light guide plate has a slope in the vertical direction facing the left or right surface and inclined with respect to the reference plane on the rear surface. 4. The planar light guide plate according to claim 2, wherein the light emitting means in the planar light guide plate has a repetitive structure of prismatic irregularities having short sides and long sides at a pitch of 50 μm to 1.5 mm. Is a slope facing the incident side at an inclination angle of 35 to 45 degrees with respect to the reference plane on the side of the upper and lower surfaces that do not have the light emitting means, and the long side surface is more than 0 to the reference plane. The inclination angle range of 10 degrees, the entire angle difference is within 5 degrees, the inclination angle difference between the nearest long side surfaces is within 1 degree, and the projected area with respect to the reference plane is that of the short side surface. A light guide plate having a slope that is eight times or more. 5. The liquid crystal display device according to claim 3, wherein a projection width of the inclined surface or the short side surface of the light emitting means with respect to the reference plane is 40 μm or less. 6. The light guide plate according to claim 2, wherein the light emitting means in the planar light guide plate has a repeating structure with a constant pitch of 50 μm to 1.5 mm. 7. The method according to claim 1, wherein the thickness ratio of the linear light guide plate / the planar light guide plate is 1 to 2 based on the partial connection surface.
Is a light guide plate. 8. The planar light guide plate according to claim 1, wherein a connecting portion between the planar light guide plate and the linear light guide plate has a length of 2 mm or less at both ends in a longitudinal direction thereof based on an incident side surface of the planar light guide plate. A light guide plate having a thickness of 1/4 or less on one or both sides of the lower surface. 9. The light guide plate according to claim 1, wherein the planar light guide plate and the linear light guide plate are integrally formed by integral molding or are formed separately by an adhesive. . 10. A surface light source device, wherein a point light source is arranged on a linear light guide plate in the light guide plate according to claim 1. Description: 11. A liquid crystal display device comprising at least the surface light source device according to claim 10 and a liquid crystal cell.