JP2000258749A - Surface light source device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface light source device which has excellent uniform brightness and little difference between bright and dark areas, which consumes small electric power and which is excellent in compactness, by providing the entrance face of a light guide plate in which light entering the entering face outgoes from one of the upper and lower faces with two or more light emitting diodes at a specified distance which repeatedly blink. SOLUTION: Two or more light emitting diodes 3 which repeatedly blink are disposed at <=10 mm distance on the light entering face of a light guide plate 1 in which the light entering the entering face outgoes from one of the upper and lower faces. The light guide plate 1 is properly selected from such plates in which the light entering the entering face outgoes from one of the upper and lower faces, and the kind of the plate is not limited. The light guide plate 1 preferably used form the viewpoint of the use efficiency of light has a light emitting means consisting of prismatic irregularities on one of the upper and lower faces. The prismatic irregularities are preferably formed as projections or recesses having surfaces of equal lines.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate type surface light source device which can form a transmissive or reflective liquid crystal display device which is bright and easy to see and has low power consumption and excellent light use efficiency.

[0002]

BACKGROUND OF THE INVENTION For a portable use of a transmissive liquid crystal display device using a side light type surface light source device in which a light source is arranged on a side surface of a light guide plate as a backlight or a reflection type liquid crystal display device using a front light as a backlight. Along with the spread, a surface light source device with lower power consumption has been demanded for the purpose of, for example, extending the continuous use time. It has been pointed out that a device using a cold cathode tube as a light source consumes a large amount of power and requires a high frequency of battery replacement or the like.

Conventionally, as a low power consumption sidelight type surface light source device, there has been known a device in which light emitting diodes capable of emitting light at a low voltage as a light source are arranged linearly on an incident side surface of a light guide plate. However, there is a problem in that the light emitting diode is disposed at a large position and the difference in brightness between the light emitting diodes is large. When the brightness is made uniform by the diffusion of light, the luminous efficiency is greatly reduced, and when the arrangement density of the light emitting diodes is increased, the power consumption is greatly increased.

In view of the above, there is a proposal to arrange a light emitting diode on the side surface of a linear light guide plate to form a linear light source and to arrange it on the incident side surface of a large-sized light guide plate. In short, the variation in the light emission of the linear light source is directly reflected in the variation in the light emission of the large light guide plate, and the light emitting diodes arranged on the side surfaces of the linear light source and the connection portion protrude from the incident side surface of the large light guide plate, When the number of light-emitting diodes is increased for the purpose of improving brightness, the thickness of the linear light source is restricted by matching with the large-format light guide plate, so that a horizontal arrangement is inevitable, and the width is significantly increased. However, there is a disadvantage in that the advantage of compactness is impaired. By the way, when five light emitting diodes are used, the width thereof is about 15 mm in the horizontal arrangement, and it is added to the incident side surface of the large-sized light guide plate as the plane direction of the light guide plate, so that the plane area is remarkably increased.

[0005]

The present invention takes advantage of the advantage of using a light emitting diode capable of emitting light at a low voltage as a light source.
It is an object of the present invention to develop a surface light source device that has a small difference in brightness and is excellent in uniformity of brightness, consumes little power, and is excellent in compactness.

[0006]

The present invention is characterized in that two or more light emitting diodes which repeat blinking are provided at intervals of 10 mm or less on an incident side of a light guide plate which emits incident light from an incident side from one of upper and lower surfaces. And a liquid crystal display device having a liquid crystal cell on the light emitting surface side of the surface light source device.

[0007]

According to the present invention, the power consumption can be reduced by the light emitting diode blinking method, and the arrangement density of the light emitting diodes can be increased when the power consumption is the same as in the continuous lighting method. Further, by controlling the blinking cycle, it is possible to visually form a continuous lighting state in a pseudo manner.

As a result, it is possible to suppress the increase in power consumption while reducing the difference in brightness between the light emitting diodes by arranging the light emitting diodes at a high density, to provide excellent uniformity of brightness by imitating a continuous light emitting state, and to reduce the size of the light emitting diode. Thus, it is possible to obtain a surface light source device having excellent performance, and to take advantage of using a light emitting diode capable of emitting light at a low voltage as a light source.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a surface light source device according to the present invention, two or more light-emitting diodes, which repeat blinking, are arranged at intervals of 10 mm or less on an incident side of a light guide plate which emits incident light from an incident side from one of upper and lower surfaces. Have An example is shown in FIG. Reference numeral 1 denotes a light guide plate, and reference numeral 3 denotes a light emitting diode which repeatedly blinks as a light source. Reference numeral 2 denotes a reflection layer as required.

As the light guide plate, an appropriate one that emits the incident light from the incident side from one of the upper and lower surfaces can be used, and the type thereof is not particularly limited. Therefore, for example, a light emitting means composed of dots or the like is provided on one of the upper and lower surfaces of a plate-like object having an upper surface, a lower surface opposed thereto, and an incident side surface composed of a side surface between the upper surface and the lower surface, and the incident side surface is provided via the light emitting means. An appropriate light according to the related art in which incident light from the light source is emitted from one of the upper and lower surfaces can be used.

FIG. 2 shows an example of the light guide plate. 11 is an upper surface, 12 is a lower surface, 13 is an incident side surface, 14 is a side surface, and 15 is a side end facing the incident side surface 13. In the example of FIG. 2, an example in which the light is emitted from the upper surface 11 through the light emitting means formed on the lower surface 12, and therefore, the upper surface is a light emission surface is illustrated.

A light guide plate that can be preferably used from the viewpoint of light use efficiency and the like is provided with light emitting means formed of prismatic irregularities on one of the upper and lower surfaces. The prismatic irregularities can be formed in a convex portion or a concave portion having an equilateral surface, but are formed in a convex portion or a concave portion including a short side surface and a long side surface from the viewpoint of improving light use efficiency. Is preferred.

FIG. 3 shows an example of the above-mentioned prism-shaped unevenness having the short side surface and the long side surface. 12a is a short side surface, and 12b is a long side surface. In addition, based on the straight line connecting the intersection of the formation side such as the short side surface and the long side surface and the formation surface, whether the intersection (vertex) of the formation side protrudes from the straight line in the prism-shaped unevenness. (Convex) or concave (concave).

That is, in the case of the example shown in FIG. 3, based on a straight line 20 indicated by an imaginary line connecting the intersection of the short side surface 12a and the long side surface 12b, the intersection of the short side surface and the long side surface ( Vertex) protrudes from the straight line 20 (convex),
This depends on whether the prismatic irregularities start from the shorter side surface or the longer side surface from the incident side surface depending on whether they are concave (concave). Therefore, the example of FIG. 3 shows a prism-shaped unevenness composed of a convex portion.

In the above-mentioned light emitting means comprising prismatic irregularities, the light emitting means emits as much light as possible in the direction perpendicular to the reference plane (normal line) from the light emitting surface of the light guide plate, and a reflective liquid crystal display. In the case of a front light of the device, the direction of the emitted light serving as display light and the direction of light leaked from the 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 prismatic irregularities, which are preferable from the viewpoint of normalizing the emitted light and preventing overlap between the leaked light and the display light, are as follows.
As illustrated in FIG. 3, a prism-shaped concave and convex repetitive structure including a short side surface (θ ₁ ) having an inclination angle of 30 to 45 degrees with respect to a reference plane and a long side surface (θ ₂ ) of more than 0 to 10 degrees with respect to a reference plane. It is what it was.

The short side surface serves to reflect light incident on the surface out of the incident light from the incident side surface and to supply the light to the light exit surface. Therefore, the short side surface is formed as an inclined surface facing the incident side surface at a large inclination angle. In this case, by setting the inclination angle theta ₁ to 30-45 degrees narrow side as illustrated by a broken line arrow in FIG. 3, an advantageous outgoing light display by reflecting good perpendicularity to the light emitting surface of the transmission light Can be obtained efficiently.

A preferred inclination angle theta ₁ of the short side surface from the viewpoint of the performance of suppressing such a hindering visibility leakage light suppression and by it, 32 to 43 degrees, especially 35 to 42 degrees. Note the direction of the light emitted from the light emitting surface becomes larger angle to the normal is at an inclination angle theta ₁ of the short side surfaces is less than 30 degrees, the effective available brightness light amount decreases tends to decrease the viewing. On the other hand, if the angle exceeds 45 degrees, the amount of light leaked from the light emitting means forming surface is likely to increase.

On the other hand, the long side surface reflects the transmission light incident thereon and supplies it to the short side surface, and when used as a backlight of a transmissive liquid crystal display device, the light utilization efficiency through a reflective layer or the like is reduced. It is an object of the present invention to transmit a display image from a liquid crystal cell when a front light of a reflection type liquid crystal display device is used. From this point, it is preferable inclination angle theta ₂ of the long side surfaces with respect to the reference plane of the light exit surface in the range of the.

[0020] The above as illustrated by a broken line arrow in FIG. 3, the transmitted light of the inclined angle theta ₂ is greater than the angle Nagahenmen 1
2b, is reflected by the light exit surface 11 at a parallel angle based on the inclination angle of the long side surface, enters the short side surface 12a, is reflected, and is reflected by the light exit surface. The light is well focused and emitted.

As a result, in addition to the transmission light directly incident on the short side surface, the transmission light incident on the long side surface and incident on the short side surface via reflection thereof is also reflected on the short side surface by reflection via the short side surface. It can be supplied to the light exit surface, and the light utilization efficiency can be improved accordingly, and the incident angle of the light reflected on the long side surface and incident on the short side surface can be made constant, and variation in the reflection angle can be suppressed. Outgoing light can be collimated.

Therefore, by adjusting the inclination angles θ ₁ and θ ₂ of the short side surface and the long side surface of the prismatic irregularities forming the light emitting means, the emitted light can be provided with directivity. This makes it 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 θ ₂ of the long side surface is 0
When the degree is too low, the effect of collimating the transmitted light is poor. When the degree exceeds 10 degrees, the incidence rate on the long side surface is reduced, and the light supply to the opposite end side is insufficient, and the light emission is likely to be uneven. Also, in the cross-sectional shape of the light guide plate, it is difficult to make the opposite end side thinner,
The amount of light incident on the prismatic irregularities also decreases, and the luminous efficiency tends to decrease. Preferred inclination angle theta ₂ of the long side surface from the point of such a performance of suppressing such a light emitted condensed reduction and leakage light by collimating the transmission light is 8 degrees or less, more than 5 degrees, inter alia.

The longer side surface, which is preferable from the viewpoint of the visibility of the display image through the longer side surface of the light guide plate, has an inclination angle θ _2.
An angular difference within 5 degrees throughout the light guide plate, within 4 degrees above all, which was especially within 3 degrees, within 1 ° difference in inclination angle theta ₂ between the nearest long side surface, especially 0 0.3 degrees or less, particularly 0.1 degrees or less.

[0025] The above, when the Freud light reflection type liquid crystal display device due to differences such as the inclination angle theta ₂ of the long side surface, it is possible to suppress the influence of the display image transmitted through the long side surfaces are subjected. If the deflection of the transmission angle due to the long side surface greatly differs depending on the place, an unnatural display image is produced. In particular, if the deflection difference of the transmission image in the vicinity of the adjacent pixel is large, the display image becomes extremely unnatural.

The above-mentioned angle difference of the inclination angle θ ₂ is based on the premise that the inclination angle θ ₂ of the long side surface is in the range of more than 0 to 10 degrees. That is, based on the assumption that to such small as the inclination angle theta ₂ to suppress the deflection of the display image due to refraction at the long side surface transmittance within the allowable value, which sets the observation point in the vertical direction near 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.

[0027] Also, from the point that a bright display image is obtained, the projected area of the long side surface of the light emitting surface with respect to the reference plane is 5 times or more, especially 10 times or more, especially 15 times or more of that of the short side surface. Irregularities are preferred. Thereby, when the front light of the reflection type liquid crystal display device is used, most of the display image by the liquid crystal cell can be transmitted through the long side surface. 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.

More preferably, the size of the short side surface is such that the area of the long side surface is secured and the occurrence of moire due to interference with the pixels of the liquid crystal cell is prevented, and the pixel pitch of the liquid crystal cell is 100 to 300 μm. Considering the generality, the width is set to 40 μm or less, particularly 1 to 20 μm, particularly 5 to 15 μm based on the projection width of the light emitting surface with respect to the reference plane.

Further, it is preferable that the interval between the short side surfaces is larger than the above-mentioned point. On the other hand, since the short side surface is a substantial emission function portion of the side incident light as described above, if the interval is too large. In some cases, the illumination light may be sparse, resulting in an unnatural display. In view of these, it is preferable that the repetition pitch of the prismatic irregularities is 50 μm to 1.5 mm. The pitch may be constant, or may be irregular, such as a random pitch or a random or regular combination of a predetermined number of pitch units.

In the case of the light emitting means having prismatic irregularities, moire may occur due to interference with the pixels of the liquid crystal cell. Moire can be prevented by adjusting the pitch of the prismatic irregularities, but as described above, the pitch of the prismatic irregularities has a preferable range. Therefore, as a solution to the case where moiré occurs in the pitch range, a method of forming the prismatic irregularities in an inclined state with respect to the reference plane of the incident side surface so that the prismatic irregularities can be arranged in an intersecting state with respect to the pixel. preferable. In this case, if the inclination angle is too large, the reflection via the short side surface is deflected, causing a large deviation in the direction of the emitted light, and the anisotropy of the light emission intensity in the light transmission direction of the light guide plate is increased. The usage efficiency is also reduced, which is likely to cause a reduction in display quality.

From the above points, the inclination direction of the prismatic irregularities in the arrangement direction of the prismatic irregularities with respect to the reference plane of the incident side surface, that is, the inclination angle of the ridgeline direction of the prismatic irregularities is within ± 30 degrees, particularly within ± 25 degrees, and particularly within ± 20 degrees. It is preferable that Note that ±
Means the direction of inclination with respect to the incident side surface.
When moiré can be neglected, the arrangement direction of the prismatic irregularities is more preferably parallel to the incident side surface.

The light guide plate can be formed in any suitable form. Therefore, the same thickness plate or the like may be used, but it is preferable that the thickness of the opposite end 15 facing the incident side surface 13 is thinner than that of the incident side surface, particularly 50% or less as shown in the figure. It is. By reducing the thickness of the facing end (such as a wedge shape), the efficiency of the light emitting means can be increased.

That is, as shown by the thick arrow in FIG. 3, the light incident from the incident side surface 13 is efficiently incident on the light emitting means formed on one of the upper and lower surfaces by the time the light reaches the opposing end 15, and is reflected via reflection or the like. It is possible to efficiently supply incident light to the target surface by emitting light from the light emitting surface formed by the other of the upper and lower surfaces (the surface on which the light emitting means is not formed, the upper surface 11 in FIG. 2). In addition, there is an advantage that the light guide plate can be reduced in weight by making it wedge-shaped. By the way, when the lower surface 12 is a straight surface as shown in FIG. 2, the weight can be about 75% of the light guide plate having a uniform thickness.

The shape of the light guide plate can be determined as appropriate even in the case of the above-mentioned wedge shape or the like.
In addition to the above, an appropriate surface shape such as a refraction surface or a curved surface can be used. Further, the prism-shaped unevenness forming the light emitting means does not need to be formed by the linear surfaces 12a and 12b illustrated in FIG. 3, but may be formed in an appropriate surface form including a refraction surface, a curved surface, and the like. .

Further, the prism-shaped irregularities may be composed of a combination of irregularities having different shapes and the like in addition to the pitch. In addition, the prismatic irregularities may be formed as a series of convex portions or concave portions having continuous ridge lines, or may be formed as discontinuous convex portions or concave portions arranged discontinuously in the ridge line direction with a predetermined interval. It may be.

The light emitting surface of the light guide plate is usually a flat surface, but when viewed from above as a front light of a reflection type liquid crystal display device, the light emitting means and the light emitting means are reflected on the light emitting surface depending on the viewing direction. In some cases, moiré phenomena due to interference fringes occur due to interference between the patterns, and a light-emitting surface structure or the like may be provided with fine irregularities as necessary for the purpose of preventing the deterioration of display quality due to the moiré.

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

The shape of the incident side surface of the light guide plate is not particularly limited, and may be appropriately determined. Generally,
The surface is perpendicular to the light emitting surface from the viewpoint of the arrangement of the light emitting diodes.

In forming the 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, a transparent resin or glass represented by an acrylic resin, a polycarbonate resin, an epoxy resin, or the like can be given. A light guide plate which does not exhibit birefringence or is formed of a material having low birefringence is preferably used.

The 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 light guide plate may be of the same type as a light guide plate, for example, in which a light guide means for transmitting light is bonded with a light emitting means such as a prism-shaped unevenness and / or a sheet on which fine unevenness (light emitting surface) is formed. Alternatively, it may be formed as a laminate of components made of different materials, and need not be formed as an integrated single-layered material of one kind of material.

The thickness of the light guide plate can be appropriately determined according to the size of the light guide plate according to the purpose of use, the size of the light emitting diode as a light source, and the like. A typical thickness when used for forming a transmission type or reflection type liquid crystal display device or the like is 20 mm or less, preferably 0.1 to 10 mm, particularly 0.5 to 8 mm based on the incident side surface.

The surface of the light guide plate where the light emitting means is formed is shown in FIG.
The reflective layer 2 can be provided as needed as shown in FIG. The light guide plate provided with the reflective layer is preferably used for forming a backlight for a transmission type liquid crystal display device. The reflection layer is, for example, a coating layer of a metal powder mixed with a binder resin, an attached layer of a metal thin film by a vapor deposition method, or a sheet mixed with a metal powder, a resin sheet provided with a metal powder mixed layer or a metal thin film, a metal foil, or the like. It can be formed by an appropriate method. Therefore, the reflection layer may be in close contact with the light guide plate as a coating layer or the like, or may be arranged as a reflection plate or the like.

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 illustrated in FIG. 1, two or more light emitting diodes 3 which repeat blinking on the incident side surface of the light guide plate 1 are arranged at intervals of 10 mm or less.

When the distance between the light emitting diodes exceeds 10 mm, the difference between the light emitting diodes and the light-dark difference between the light-emitting diodes is increased, and the object of the present invention cannot be achieved. The light emitting diodes are preferably arranged at intervals of 8 mm or less, particularly 6 mm or less, particularly 4 mm or less, from the viewpoint of the uniformity of the brightness in which the arrangement positions of the light emitting diodes and the brightness difference between them are suppressed, and
Close arrangement without gaps is also possible.

Therefore, the number of light emitting diodes to be arranged is determined by the length of the incident side surface of the light guide plate, that is, the length in the width direction of the light guide plate and the arrangement interval. The arrangement of the light emitting diodes is preferably such that as many as possible can be arranged at predetermined intervals. Generally, as shown in FIG. 4, the light-emitting diodes 3 are arranged in a line in a horizontal line at predetermined intervals in the length direction of the incident side surface 13 of the light guide plate 1.

When the thickness of the incident side surface of the light guide plate allows, the above horizontal arrangement is used as a unit and two
Rows or three or more rows can be arranged. Also, depending on the shape of the light emitting diode, it may be advantageous to use a large number of arrangements, for example, a zigzag arrangement instead of a horizontal arrangement. Therefore, the arrangement of the light emitting diodes can be determined as appropriate.

As the light emitting diode, monochromatic light or an appropriate light emitting diode exhibiting light emission characteristics in various wavelength ranges can be used in accordance with the purpose of use of the surface light source device. As a surface light source device used for forming a liquid crystal display device, a device showing light emission characteristics in a wavelength region as wide as possible in a visible light region can be preferably used.

Each of the light emitting diodes arranged on the incident side surface of the light guide plate is controlled so as to repeat blinking. By controlling the blinking cycle, it is possible to simulate a continuous light emission state in which blinking is not perceived. The blinking of the light-emitting diodes can be performed by an appropriate method such as a method in which each light-emitting diode is connected in parallel and an alternating current such as a rectangular wave or a sine wave is applied to the light-emitting diodes via the AC power supply 32 as shown in the figure.

From the point of simulating the continuous light emission state, it is preferable that each light-emitting diode be lit for an equal time in a blinking cycle with a fundamental frequency of 30 Hz or more, especially 50 Hz or more, especially 100 Hz or more.

In the above, the blinking method of the light emitting diode is arbitrary. That is, the blinking of all the light emitting diodes may be synchronized, or the blinking of each light emitting diode may be provided with a time difference so that the light emitting diodes in the lighting state are sequentially changed. In that case, a time division method can be applied.

That is, light emitting diodes or groups thereof having different blinking operations may be arranged in n units, and the n units of light emitting diodes or groups thereof may be sequentially lit in 1 / n time division. In that case, an AC connection for controlling the blinking of the light emitting diode is usually performed for each unit. However, in the two-split system, the light emitting diodes are alternately arranged by exchanging the positive and negative poles thereof, and they are connected in parallel to connect the AC. Can be achieved by the method of applying.

In the formation of the surface light source device, if necessary, as shown in the drawing, a suitable auxiliary such as a light source holder 31 surrounding the light emitting diode 3 for guiding the divergent light from the light emitting diode to the incident side surface of the light guide plate. Means can also be arranged. As the light source holder, a resin sheet or a metal foil provided with a metal thin film having a high reflectance is generally used. Further, the light source holder may be extended to the light emitting means forming surface of the 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 using light from a light emitting diode, and is easy to increase in area and the like. The present invention can be preferably applied to various devices as a system or 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. 5 illustrates a liquid crystal display device using the surface light source device according to the present invention in a backlight system. This is formed by arranging a liquid crystal cell 5 having polarizing plates 4 and 41 on the front and back sides on the light emitting surface side of the light guide plate 1 of the surface light source device, and the light guide plate 1 is provided on the light emitting means forming surface. It has a reflective layer 2 and can be used as a liquid crystal display device for both reflection and transmission in addition to a transmission type.

FIG. 6 illustrates a reflective liquid crystal display device using the surface light source device according to the present invention in a front light system. This is because a liquid crystal cell 5 provided with a reflective layer 54 via a polarizing plate 4 on the light emitting surface side of the light guide plate 1 of the surface light source device.
Are formed.

The liquid crystal display device is formed by arranging a liquid crystal cell on the light emitting surface side of the surface light source device as shown in the above-mentioned example. In this case, a transmission type or the like using the surface light source device as a backlight is used. In the liquid crystal display device, a surface light source device is disposed on the viewing back side of the liquid crystal cell 5 as shown in FIG. 5, and in a reflection type liquid crystal display device using the surface light source device as a front light, as shown in FIG. The surface light source device is arranged at the bottom.

Further, in the reflection type liquid crystal display device, the arrangement of the reflection layer is indispensable, and the liquid crystal layer of the liquid crystal cell is indispensable between the reflection layer and the surface light source device. The reflective layer must be disposed in the liquid crystal display device for both reflection and transmission, but the reflective layer is disposed on the light guide plate side of the light guide plate.

Therefore, visual recognition by the transmission type liquid crystal display device is as follows.
The light emitted by the surface light source device is transmitted through the liquid crystal cell, and the visual recognition by the reflection type liquid crystal display device is such that the light emitted by the surface light source device is transmitted through the liquid crystal cell and is inverted at the reflection layer,
This is performed by transmitting the inverted light again through the liquid crystal cell and then through the surface light source device. Further, the visual recognition by the liquid crystal display device for both reflection and transmission conforms to the above-mentioned transmission type in the transmission mode, and in the reflection mode, the external light passes through the liquid crystal cell and is inverted at the reflection layer on the back surface of the light guide plate, and the inverted light is again reflected. This is performed by transmitting light through a light guide plate and a liquid crystal cell.

A liquid crystal display device generally comprises a liquid crystal cell 5 having a transparent electrode functioning as a liquid crystal shutter as shown in FIGS. 5 and 6, a driving device associated therewith, polarizing plates 4, 41, a backlight or a front light, and It is formed by appropriately assembling components such as the reflecting layers 2 and 54, the compensating retardation plate 6, and the diffusion layer 7 as appropriate.

In the present invention, there is no particular limitation except that the above-mentioned surface light source device is used, and it can be formed according to a conventional example as shown in the figure. In FIGS. 5 and 6,
The liquid crystal cell 5 has a liquid crystal layer 52 sealed between cell substrates 51 and 53. In FIG. 6, a reflection layer 54 is disposed inside the liquid crystal cell. In the illustrated example, the illustration of the transparent electrode and the associated driving device is omitted. Further, the cell substrate of the liquid crystal cell can also serve as the light guide plate in the surface light source device according to the present invention.

Accordingly, 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 TN liquid crystal cell, an STN liquid crystal cell, a vertical alignment cell, a HAN cell, an
Appropriate liquid crystal cells such as a twist type or non-twist type such as a CB cell, a guest host type or a ferroelectric liquid crystal type 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.

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, in view 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 additional 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.

As shown in FIG. 6, a reflection layer 54 is provided inside the liquid crystal cell 5.
In the case of providing a reflective layer, a method of forming an electrode pattern with a highly conductive material such as the above-mentioned high reflectivity metal or a reflective layer formed of a high reflectivity metal film via an insulating layer A reflective layer formed by a method of providing a transparent electrode pattern is preferable. The reflective layer in the reflective liquid crystal display device is
For example, it can be provided outside the liquid crystal cell 5 as a material in which a reflective layer made of a high-reflectance metal film is provided on a plastic film.

When the liquid crystal display device is formed, as described above, for example, an antiglare layer or an antireflection film provided on a polarizing plate on the viewing side, a diffusing plate, a compensating retardation plate, a polarization separating plate, an optical path control, or the like is used. An appropriate optical element such as a target prism sheet can be appropriately arranged.

The purpose of the above-mentioned compensating retardation plate is to improve the visibility by compensating the wavelength dependence of birefringence and the like. In the present invention, as shown in FIG. 5, the compensating retardation plate 6 is disposed between the liquid crystal cell 5 and the like between the polarizing plates 4 and 41 on the viewing side and / or the backlight side as necessary.

As the retardation plate for compensation, an appropriate one can be used according to the wavelength range and 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. , Those retardation sheets
It can also be formed as a laminate of layers or more.

The diffusion layer may be provided at an appropriate position on the liquid crystal display device as needed, for the purpose of obtaining uniform surface light emission by preventing uneven brightness and reducing moire caused by mixing of adjacent light rays. One or more layers are arranged. Incidentally, in the example of FIG. 6, the diffusion layer 7 is provided on the light emitting surface of the surface light source device.
Is arranged. Note that a diffusion layer having a narrow diffusion range can be preferably used from the viewpoint of maintaining the directivity of light emitted from the light guide plate.

The diffusion 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, and applying or curing the resin, or a transparent resin in which bubbles are dispersed. Method of applying and curing, a method of generating a craze by swelling the substrate surface through a solvent, a method of forming a transparent resin layer having an irregular uneven surface, a method of using a diffusion sheet formed according to the above, and the like Can be formed by an appropriate method.

In the formation of the transmission type liquid crystal display device, a polarizing beam splitter may be disposed 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 polarization 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 having the reflection layer 2 provided on the back surface as shown in FIG. 5, the polarization reflected by the polarization separation plate is inverted by the reflection layer 2 and re-incident on 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-mentioned surface light source device or 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.

[0074]

Reference Example 1 The upper surface of a transparent plate made of polymethyl methacrylate (PMMA) having a flat upper and lower surface was cut with a diamond bite, and the width was 24 mm, the depth was 50 mm, the thickness of the incident side was 1.2 mm,
The thickness of the opposite end is 0.8 mm, the upper surface has prismatic irregularities parallel to the incident side surface at a pitch of 390 μm, the inclination angle of the short side is in the range of 42 to 44 degrees, and the inclination angle of the long side is Is 1.
It changes within the range of 3 to 3.1 degrees, the inclination angle change of the nearest long side is within 0.1 degrees, the projected width of the short side to the lower surface is 12 to 25 μm, and the long side / short side A light guide plate made of a plate-like material having a projection area ratio of 15/1 or more to the lower surface was obtained.
The above-mentioned prismatic irregularities were formed at a position 2 mm away from the incident side surface. The light incident surface of the light guide plate was roughened.

REFERENCE EXAMPLE 2 The lower surface of a transparent plate made of PMMA and having a flat upper and lower surface was cut with a diamond tool, and the width was 24 mm, the depth was 50 mm, the thickness of the incident side was 1.2 mm, and the thickness of the opposite end was 0.8 mm. And
The lower surface has prismatic irregularities parallel to the incident side surface at a pitch of 390 μm, the inclination angle of the short side surface is in the range of 36 to 38 degrees, and the inclination angle of the long side surface is in the range of 0.8 to 2.7 degrees. And the change in the inclination angle of the nearest long side surface is within 0.1 degrees,
A light guide plate made of a plate-like object having a projection width of 12 to 26 μm on the lower surface of the short side surface and a projection area ratio of 14/1 or more on the lower surface of the long side surface / short side surface was obtained. The above-mentioned prismatic irregularities were formed at a position 2 mm away from the incident side surface.

Example 1 The light guide plate obtained in Reference Example 1 was placed on the incident side face at 1.
A surface light source device is provided in which four sets of a total of eight light-emitting diodes are alternately inverted in polarity at intervals of 3 mm from a position 5 mm apart, and these are connected in parallel to a frequency-variable rectangular wave generating AC power supply. I got This was able to control turning on / off by turning on / off the power supply. The light emitting diode used was of a white type having a size of 2.0 mm × 3.0 mm (the same applies hereinafter).

Example 2 A surface light source device was obtained in the same manner as in Example 1 except that the light guide plate obtained in Reference Example 2 was used. In this case too, the lighting on / off could be controlled by turning on / off the power supply.

Example 3 A commercially available black-and-white reflective TN liquid crystal cell was arranged on the light emitting surface (lower surface) of the surface light source device obtained in Example 1 to obtain a reflective liquid crystal display device. The liquid crystal cell was driven by turning on / off all pixels.

Example 4 A commercially available diffuser plate was placed on the light exit surface (upper surface) of the surface light source device obtained in Example 2, and two prism sheets were placed on the diffuser plate with the array direction intersecting. A TN liquid crystal cell of a black-and-white transmissive type was arranged thereon to obtain a transmissive liquid crystal display device. The liquid crystal cell was driven by turning on / off all pixels.

Comparative Example 1 The incident side surface of the light guide plate obtained in Reference Example 1 was 3 mm away from the end.
A total of four light emitting diodes were arranged at a distance of 6 mm from the distant position with the same polarity, and they were connected in parallel to a DC power supply to obtain a surface light source device. This was able to control turning on / off by turning on / off the power supply.

Comparative Example 2 A surface light source device was obtained in the same manner as in Comparative Example 1 except that the light guide plate obtained in Reference Example 2 was used. In this case too, the lighting on / off could be controlled by turning on / off the power supply.

Comparative Example 3 A reflective liquid crystal display device was obtained in the same manner as in Example 3 except that the surface light source device obtained in Comparative Example 1 was used.

Comparative Example 4 A transmission type liquid crystal display device was obtained in the same manner as in Example 4 except that the surface light source device obtained in Comparative Example 2 was used.

Evaluation Test Continuous Light Emission An AC composed of a rectangular wave of -3 V and +3 V was applied to the light emitting diode of the surface light source device obtained in Examples 1 and 2 via a rectangular wave generating AC power supply, and the frequency was changed to emit light. The condition was observed. As a result, it was difficult to perceive the blinking of the light source at a frequency lower than 30 Hz, but at higher frequencies, the temporal luminance fluctuation was not perceived with an increase in the frequency, and the frequency was not perceived.
Above, blinking of the light source was hardly perceived. At 100 Hz or more, no blinking was perceived and a uniform continuous light emission state was perceived.

Light Emission Characteristics 1 The brightness when the reflective liquid crystal display devices obtained in Example 3 and Comparative Example 3 were displayed in a white state was visually observed, and the emission intensity in the normal direction of the center of the device (front view) (Luminance) was checked with a luminance meter (BM7, manufactured by Thompson). In the third embodiment, a 60 Hz alternating current composed of a rectangular wave of -3 V and +3 V is applied to the light emitting diode via a rectangular wave generating AC power supply.
In Comparative Example 3, a DC voltage of +3 V was applied to the light emitting diode via a DC power supply (the same applies hereinafter).

As a result, in Example 3, the light emitting diode was bright at the position where the light emitting diodes were disposed at about 3 mm from the incident side surface of the light guide plate, and a weak weak brightness was observed between them. Uniform brightness was achieved.
The front luminance in the white state is 15 cd / m ² and 100
The current flowing through the circuit at the application of Hz was 104.5 mA.

On the other hand, in Comparative Example 3, even at a position about 10 mm from the incident side surface of the light guide plate, the LED was bright at the position where the light emitting diodes were arranged, and dark brightness unevenness was observed between them.
In the vicinity, the difference in brightness was remarkable. The front brightness is
At 16 cd / m ² , the current flowing through the circuit was 89.4 mA.

As described above, in Example 3, despite the use of twice as many light emitting diodes as in Comparative Example 3, a flashing method was used to suppress a large increase in power consumption and achieve almost the same front luminance. It can be seen that the brightness uniformity over the entire screen is excellent.

Emission Characteristics 2 Emission characteristics of the transmission type liquid crystal display devices obtained in Example 4 and Comparative Example 4 were examined in accordance with the above. As a result, the above examples by visual observation 3, obtained results corresponding to Comparative Example 3, 24 cd / m 2 front luminance in Example ^4, the current flowing through the 26 cd / m ^2, the circuit in Comparative Example 4 10 in Example 4
7.2 mA and 87.6 mA in Comparative Example 4.

As described above, also in the transmission type of the fourth embodiment,
Despite using twice as many light-emitting diodes as in Comparative Example 4, the blinking method suppresses a significant increase in power consumption and achieves substantially the same front luminance, while achieving uniform brightness over the entire screen. It turns out that it is excellent. From the above, it can be understood that various types of liquid crystal display devices having excellent brightness uniformity, easy to see, and low power consumption can be obtained by using the surface light source device according to the present invention.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a surface light source device.

FIG. 2 is an explanatory perspective view of a light guide plate.

FIG. 3 is an explanatory side view of prismatic irregularities.

FIG. 4 is an explanatory view of an arrangement of light emitting diodes.

FIG. 5 is a side sectional view of a transmissive (reflective / transmissive) liquid crystal display device.

FIG. 6 is a side sectional view of a reflective liquid crystal display device.

[Explanation of symbols]

 1: Light guide plate 11: Upper surface (light emitting surface) 12: Lower surface 12a: Short side surface 12b: Long side surface 13: Incident side surface 2, 54: Reflective layer 3: Light emitting diode 31: Light source holder 32: AC power supply 4, 41 : Polarizing plate 5: Liquid crystal cell

Claims (7)

[Claims] 1. A surface light source device comprising two or more light-emitting diodes that repeat blinking at intervals of 10 mm or less on an incident side of a light guide plate that emits incident light from an incident side from one of upper and lower surfaces. . 2. The surface light source device according to claim 1, wherein each light-emitting diode blinks at a fundamental frequency of 30 Hz or more and lights up for an equal time. 3. A light-emitting diode or a group of light-emitting diodes or groups of light-emitting diodes of different units according to claim 1 or 2, wherein the number of light-emitting diodes or groups of light-emitting diodes or groups of light-emitting diodes is different from each other. Surface light source device that lights up sequentially. 4. The light guide plate according to claim 1, wherein the light guide plate has a prism-shaped unevenness having a short side surface and a long side surface on one of upper and lower surfaces.
a light emitting means having a repeating structure having a pitch of .mu.m to 1.5 mm, wherein the other of the upper and lower surfaces is a light emitting surface, and the short side surface has an inclination angle of 3 with respect to a reference plane of the light emitting surface.
0 to 45 degrees, a projection width of 40 μm or less, and an inclined surface facing the incident side surface, and the long side surface is at an inclination angle range of more than 0 to 10 degrees with respect to the reference plane, and the inclination between the nearest long side surfaces is A surface light source device comprising a slope having an angle difference of 1 degree or less, an angle difference of an inclination angle on a full length side surface of 5 degrees or less, and a projection area with respect to the reference plane of 5 times or more that of the short side surface. 5. The surface light source device according to claim 4, wherein the ridge direction of the prismatic irregularities in the light emitting means of the light guide plate is within ± 30 degrees with respect to the reference plane of the incident side surface. 6. A liquid crystal display device comprising a liquid crystal cell on the light emitting surface side of the surface light source device according to claim 1. 7. A reflection type liquid crystal display device according to claim 6, further comprising a reflection layer, wherein the liquid crystal layer of the liquid crystal cell is disposed between the reflection layer and the surface light source device.