JPH11281980A - Light transmission plate, surface light source device, and reflection type liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a reflection type liquid crystal display, where the contrast in visual recognition for non-lighting and lighting and the brightness of display are excellent, and a display image passing a light transmission plate is hardly disturbed resulting in an excellent definition, and visual recognizability of the display image is hardly deteriorated by a moire phenomenon, and also to develop a light transmission plate and a surface light source device to form this display. SOLUTION: In a light transmission plate 1, incident light from an incidence side face 13 is emitted from a lower face 12 through a light emission means formed on an upper face 11, and the direction of a maximum intensity of light emitted from the lower face 12 exists within 30 deg. to the normal to a reference plane of the lower face 12, and a maximum intensity of light leaked from the upper face 11 in this direction within 30 deg. is <=1/5 of the maximum intensity on the lower face, and the lower face 12 has fine ruggedness, and incident light from the lower face 12 is transmitted from the upper face 11. The surface light source device has light source in the incidence side face 13 of the light transmission plate 1. The reflection type liquid crystal display has a liquid crystal cell provided with a reflection layer on the lower face side of the surface light source device.

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 capable of forming a reflective liquid crystal display device which is bright and easy to see, and a surface light source device using the light guide plate which is excellent in effective light use efficiency.

[0002]

BACKGROUND OF THE INVENTION While there has been a demand for an illumination device which allows visual recognition in a dark portion of a reflection type liquid crystal display device, the present inventors have changed the backlight used in a transmission type liquid crystal display device to a liquid crystal cell. We tried to apply a front light system placed on the viewer side. Such a backlight uses a light guide plate that emits incident light from a side surface through one of upper and lower surfaces through a light emitting unit, and in a front light system, display contents are visually recognized through the light guide plate. .

[0003] However, the conventional backlight using a light guide plate has a problem that it is difficult to put into practical use due to insufficient contrast at the time of lighting, insufficient brightness at the time of non-lighting, and disorder of display. By the way, in the case of using a light guide plate that uses diffusion dots and fine irregularities as the light emitting means, the contrast is poor when viewed at the time of lighting, and the contrast is poor even when not lit by external light such as indoor lighting. In addition to the poor brightness, the display image via the light guide plate is significantly disturbed, which causes a problem of poor clarity.

On the other hand, even when a light guide plate (JP-A-62-73206) using a stair-like prism structure having a 45-degree inclined surface and a 0-degree flat surface as a light emitting means is used, the light is turned on. A problem arises in that the contrast is poor at the time of visual recognition and the display brightness is also poor.

Further, when viewed from above, the pattern of the light emitting means and the pattern projected on the lower surface of the light emitting means interfere with each other, and the interference shows moire phenomenon as interference fringes depending on the viewing direction. There is also a problem that visibility of the image is significantly reduced.

[0006]

Therefore, the present invention is excellent in contrast in visual recognition at the time of non-lighting and at the time of lighting, excellent in brightness of display, and excellent in clarity because the display image through the light guide plate is hardly disturbed. It is an object of the present invention to develop a reflection-type liquid crystal display device in which the visibility of a display image is not easily reduced due to the moiré phenomenon, and a light guide plate and a surface light source device capable of forming the same.

[0007]

According to the present invention, incident light from an incident side surface is emitted from a lower surface through a light emitting means formed on an upper surface, and the incident light from the lower surface within 30 degrees with respect to a normal to a reference plane of the lower surface. There is a direction of the maximum intensity of the emitted light, and
The maximum intensity of light leaked from the upper surface in a direction within degrees is not more than 1/5 of the maximum intensity on the lower surface, and the lower surface has fine irregularities so that incident light from the lower surface is transmitted from the upper surface. A light guide plate is provided.

Further, the present invention is characterized in that a surface light source device having a light source on an incident side surface of the light guide plate, and a liquid crystal cell having a reflective layer on a lower surface side of the surface light source device. To provide a reflection type liquid crystal display device.

[0009]

According to the present invention, it is possible to obtain a light guide plate in which the light emitted from the lower surface is excellent in the directivity in the vertical direction, and the light leaked from the upper surface is less likely to overlap the display image. Surface light source device with excellent effective utilization efficiency of
Excellent display contrast when not lit and when lit, excellent display brightness, display images through the light guide plate are less likely to be disturbed and excellent in clarity, and moiré phenomenon by the light emitting means is less likely to occur. The reflection type liquid crystal display device excellent in the above can be obtained.

The above-mentioned effects are based on the characteristics imparted to the light guide plate. In other words, the present inventors have conducted intensive studies to overcome the above-mentioned problems, and found that in the light guide plate using the above-described conventional diffusion dots and fine irregularities as light emitting means, FIG.
As shown in FIG. 10, the transmission light incident from the side surface due to the scattering by the light emitting means of the light guide plate 18 diverges in almost all directions, and due to its scattering characteristics, the outgoing light α ₁ from the lower surface also becomes the leakage light β ₃ from the upper surface. Is about 6 with respect to the normal (front direction) H to the lower surface.
The maximum intensities B and b are shown in the 0 ° direction θ ₄ , and the intensities are almost the same. Therefore, the directions effective for visual recognition, particularly, about 15 degrees upward to about 30 degrees downward in the vertical direction with respect to the normal, poor becomes the brightness of the display is small amount of light in the viewing angle range of the left and right about 30 degrees in the lateral direction and the contrast output light alpha ₂ of the lower surface for forming a display image overlaps the leakage light beta ₄ from the upper surface And when not lit, the scattered light γ
_The contrast is poor due to the white spot on the display image by ₂ ,
It has been found that the display light γ ₁ and γ ₃ are mixed with each other due to the scattering by the light guide plate to significantly disturb the display image.

Also in the light guide plate having a prism type light emitting means disclosed in Japanese Patent Application Laid-Open No. 62-73206, light leaking from the upper surface is large similarly to the above, and the light emitted from the lower surface forms a display image. Overlap with and reduce contrast,
In addition, it has been found that the amount of emitted light having a large emission angle is large and the amount of light in a direction effective for visual recognition is small, and the brightness of the display is reduced to cause a problem of deterioration in display quality.

Therefore, to form a bright and clear display image,
The incident light from the side surface is more directional than the lower surface, and is emitted at an angle θ ₃ as close as possible to the direction of the normal H to the lower surface as illustrated in FIG. A light guide plate is required. In a reflection type liquid crystal display device, display is generally made uniform and clear through a rough reflective layer having an average diffusion angle of about 5 to 15 degrees. Therefore, if there is much light incident on the reflective layer at a large angle (FIG. 9:
B, FIG. 10: α ₁ ), the amount of light in a direction effective for viewing is reduced, and bright display becomes difficult. In addition, when viewing at a large angle, the display is easily inverted. Problems such as an increase in size are likely to occur.

In order to improve the contrast, as shown in FIG. 4, leakage light a from the upper surface does not overlap as much as possible light A from the lower surface forming a display image, especially in the above-mentioned viewing angle range. It is required that the duplication is as small as possible. In a reflection type liquid crystal display device, since the contrast ratio is usually 1: 5 to 1:20, the influence of the leakage light and the overlap of the display image on the contrast ratio is large.

Further, in order to prevent a display image from being disturbed, it is required that light transmitted from the upper surface to the lower surface and light transmitted from the lower surface to the upper surface are not scattered as much as possible. The front light provided in the reflection type liquid crystal display device is an auxiliary light source that enables visual recognition in a dark place, and is originally viewed using external light such as room light or natural light for the purpose of reducing power consumption. In the original non-lighting state, the display becomes dark if external light is impeded by the light guide plate, and if light is scattered by the light guide plate, the contrast is reduced due to surface whitening, and the display image is disturbed due to mixing and the like. It will be.

In addition, rather than improving display quality, when viewed from above, moiré formed of interference fringes occurs due to interference between the pattern of the light emitting means and the pattern projected on the lower surface by the light emitting means. There is a need to achieve clear display. The pixel pitch of the liquid crystal display device is 100 to 3 pixels.
Since the thickness is generally 00 μm, it is desired that the influence on the transmitted light of the light guide plate is suppressed as much as possible, and that information having a pitch of about 100 μm can be clearly recognized, and moire due to interference with pixels is suppressed. Display quality is also desired.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A light guide plate according to the present invention emits incident light from an incident side surface from a lower surface through a light emitting means formed on an upper surface, and is 3 ° to a normal line of the lower surface to a reference plane.
There is a direction of the maximum intensity of the light emitted from the lower surface within 0 degrees,
In addition, the maximum intensity of light leaked from the upper surface in the direction within 30 degrees is 1/5 or less of the maximum intensity on the lower surface, and the lower surface has fine irregularities so that incident light from the lower surface is transmitted from the upper surface. What you do.

FIGS. 1 and 2 show examples of a light guide plate according to the present invention.
(A) to (c). 1 is a light guide plate;
Reference numerals 6 and 17 denote upper surfaces on which light emitting means are formed, 12 denotes a lower surface on the light emitting side, 13 denotes an incident side surface, 14 denotes a lateral side surface, and 1 denotes a lateral side surface.
Reference numeral 5 denotes an end facing the incident side surface. In FIG. 2a,
In order to clarify an example of fine irregularities on the lower surface, a perspective state in which the upper and lower surfaces of the light guide plate are reversed and the lower surface 12 is on the upper side is shown.

The light guide plate according to the present invention emits incident light from the incident side from the lower surface through the light emitting means formed on the upper surface, and generally emits the light from the upper surface, the lower surface opposed thereto, and the side surface between the upper and lower surfaces. Made of a plate-like object having an incident side surface. The plate-like object may be the same thick plate or the like, but preferably, as shown in the figure, the thickness of the opposite end 15 facing the incident side surface 13 is smaller than that of the incident side surface, particularly, 50% or less. It was done.

By reducing the thickness of the opposing end, as shown by the thick arrows in FIGS. 3 and 4, light incident from the incident side surface efficiently enters the light emitting means formed on the upper surface before reaching the opposing end. There is an advantage that the incident light emitted from the lower surface through reflection or the like can be efficiently supplied to the target surface, and the light guide plate can be reduced in weight. Incidentally, when the upper surface is a straight surface as shown in FIG. 2A, the weight can be about 75% of the light guide plate having a uniform thickness.

The light guide plate may have any of the above-mentioned emission characteristics. Therefore, the light emitting means provided on the upper surface of the above-mentioned plate-like object can be formed of an appropriate means exhibiting such characteristics, but a light emitting means comprising prismatic irregularities is preferable from the viewpoint of attainment of the characteristics.

The above-mentioned prism-shaped unevenness can be formed in a convex portion or a concave portion having an equilateral surface. However, a prism or a concave portion having a short side surface and a long side surface is more preferable in terms of light use efficiency. Preferably, it is formed. An example of the prismatic irregularities is shown in FIG.
(A) and (b). 2a is a convex portion, 2b is a concave portion, 21 and 23 are short side surfaces, and 22 and 24 are long side surfaces.
The convex or concave portion is based on a straight line connecting the intersections of the short side surface and the long side surface and the like with the formation surface, and whether the intersection (vertex) of the short side surface and the long side surface protrudes from the straight line ( It depends on whether it is convex or concave.

That is, based on the example shown in FIG.
The short side surface and the long side surface (21) forming the convex portion 2a or the concave portion 2b
And 22 or 23 and 24), the intersection (vertex) of the short side surface and the long side surface protrudes from the straight line 20 (convex) based on the imaginary line connecting the intersection with the formation surface of It depends on whether it is concave (concave).

In the light guide plate according to the present invention, as shown in FIG. 4, the direction θ ₃ of the maximum intensity A of the incident light (thick arrow) from the incident side surface 13 in the outgoing light from the lower surface 12 is determined by the method with respect to the reference plane of the lower surface. The maximum intensity of light leaked from the upper surface in the direction within 30 degrees with respect to the line H and within the direction of 30 degrees or less is 1/5 or less of the maximum intensity A on the lower surface.

The light leaked from the upper surface easily overlaps with the reflected light of the light having the maximum intensity A via the reflective layer, and if the maximum intensity ratio of the light leaked from the upper surface / light emitted from the lower surface is large, the display image is not displayed. Strength is relatively easily reduced, and contrast is easily reduced.

A light guide plate which is preferable from the viewpoint of improving display quality such as brightness and contrast in the case of a reflection type liquid crystal display device is a plane perpendicular to both reference planes of the incident side surface 13 and the lower surface 12 as shown in FIG. of cross-section) the theta ₃ within 28 degrees at within 25 degrees especially, those that are within particular 20 degrees.

In addition, the incident side 1
When the side of No. 3 is a negative direction, the intensity of the leaked light a from the upper surface 11 at the same angle θ ₃ as the direction of the maximum intensity A is as small as 1/10 or less of the maximum intensity A. , Especially 1/15 or less, especially 1/20 or less. Since the leaked light a overlaps with the specular reflection direction of the light having the maximum intensity A, if the value of a / A is large, the intensity of the display image is relatively reduced, and the contrast is reduced.

A more preferable light emitting means, such as achieving the characteristics such as the maximum intensity direction and the maximum intensity / leakage light intensity ratio, has an inclination angle of the lower surface 12 with respect to the reference plane of 30 to 45 degrees as illustrated in FIG. (2a or 2a) composed of a short side surface (θ ₁ ) and a long side surface (θ ₂ ) of more than 0 to 10 degrees.
It has a repeating structure of b).

In the above, the short side surfaces 21 and 23 formed as slopes inclined downward from the side of the incident side surface (13) to the side of the opposite end (15) enter the surface out of the incident light from the side surface. It serves to reflect light and supply it to the lower surface (light emitting surface). In this case, as illustrated by a broken line arrow in FIG. 3 by the inclination angle theta ₁ to 30-45 degrees narrow side, the normal of the lower surface as shown in FIG. 4 reflects good perpendicularity to the lower surface of the transmission light The bottom emission light showing the direction θ ₃ of the maximum intensity A within 30 degrees with respect to H can be obtained efficiently.

A preferable inclination angle θ ₁ of the short side surface from the viewpoint of the above-mentioned performances such as suppression of leaked light and suppression of visual obstruction caused thereby.
Is 32 to 43 degrees, especially 35 to 42 degrees. Note the inclination angle theta ₁ of the short side surfaces is maximum intensity direction of bottom emission light becomes larger angle to the normal line is less than 30 degrees, tends to lower the brightness amount of light can be effectively utilized for viewing is reduced, 45 degrees When it exceeds, the leakage light from the upper surface tends to increase.

On the other hand, the long side surface is intended to reflect the transmission light incident thereon and supply it to the short side surface, and to transmit a display image from a liquid crystal cell in the case of a reflection type liquid crystal display device. . From this point, the inclination angle theta ₂ of the long side surfaces with respect to the lower surface of the reference plane (12) is preferably 0 super 10 degrees.

[0031] 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 2
In this case, the light is reflected by the lower surface 12 at a parallel angle based on the inclination angle of the long side surface, is incident on the short side surfaces 21 and 23, is reflected, and is reflected by the lower surface 12. The beam is well focused and emitted by the parallelization.

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 via the reflection of the long side surface is also reflected by the short side surface via the short side surface. It can be supplied to the bottom surface, which can improve the light use efficiency, and can stabilize the angle of incidence of light reflected on the long side and incident on the short side, suppressing the variation in the reflection angle Thus, the outgoing light can be collimated. Therefore, by adjusting the inclination angle between the short side surface and the long side surface, the emitted light can be provided with directivity, whereby the light can be emitted in a direction perpendicular to or close to the lower surface. Become.

When the inclination angle θ ₂ of the long side surface is 0 degree, the effect of collimating the transmitted light is poor. When the inclination angle θ ₂ exceeds 10 degrees, the incidence rate on the long side surface decreases, and light is supplied to the opposite end side. And light emission tends to be uneven. In addition, it is difficult to reduce the thickness of the light guide plate on the opposite end side even in the cross-sectional shape, the amount of light incident on the prismatic irregularities is reduced, and the luminous efficiency is likely to be reduced. The preferable inclination angle θ ₂ of the long side surface is 8 degrees or less, especially 5 degrees or less from the viewpoint of the above-mentioned performance such as the condensing of the outgoing light by the parallel light transmission and the suppression of the leak light.

The long side surface, which is preferable from the viewpoint of the visibility of the display image through the long side surface of the light guide plate, has an inclination angle θ _2.
Of the light guide plate as a whole is within 5 degrees, especially within 4 degrees, especially within 3 degrees, and the difference of the inclination angle θ ₂ between the nearest long sides is within 1 degree, especially 0 degrees. 0.3 degrees or less, particularly 0.1 degrees or less.

As described above, the inclination angle θ ₂ of the transmitting long side surface is obtained.
Of the display image due to the difference in 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-described 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 as described above. 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 optimum viewing direction of the liquid crystal display device optimized by the above.

When the display image is deflected, the optimum viewing direction deviates from the vicinity of the vertical direction, and when the display image is largely deflected, it approaches the emission direction of the leaked light from the upper surface of the light guide plate, and is susceptible to the decrease in contrast. In some cases. The condition that the inclination angle θ ₂ of the long side surface is more than 0 to 10 degrees is as follows.
This includes making the influence of dispersion of transmitted light etc. negligible.

From the viewpoint of obtaining a bright display image, it is preferable that the display device has excellent external light incidence efficiency and excellent transmittance or emission efficiency of the display image by the liquid crystal cell. From this point, it is preferable that the projection area of the long side surface with respect to the reference plane of the lower surface be 5 times or more, especially 10 times or more, especially 15 times or more of that of the short side surface. Thereby, most of the display image by the liquid crystal cell can be transmitted through the long side surface.

When the display image is transmitted by the liquid crystal cell, the display image incident on the short side surface is reflected to the incident side surface and does not exit from the upper surface, or the display image transmitted through the long side surface with reference to the normal to the lower surface. Are deflected and emitted in greatly different directions on the opposite end side, and hardly affect the display image via the long side surface. Therefore, it is preferable that the short side surface is not extremely located with respect to the pixels of the liquid crystal cell. By the way, in a polar sense, if the short side surface overlaps with the entire surface of the pixel, it becomes almost impossible to visually recognize a display image near the vertical direction through the long side surface.

Therefore, in order to prevent an unnatural display due to insufficient transmission of display light, the area where the pixel and the short side face overlap is reduced, and a sufficient light transmittance through the long side face is obtained. It is preferable to secure them. Considering that the pixel pitch of the liquid crystal cell is generally 100 to 300 μm, the side shorter than the above-mentioned point is 40 μm or less based on the projection width of the lower surface with respect to the reference plane, preferably 1 to 20 μm, particularly 5 μm.
Preferably, it is formed to have a thickness of about 15 μm.

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 output function portion of the side incident light as described above, if the interval is too large. In some cases, the illumination at the time of lighting is sparse, resulting in an unnatural display. In view of these, the repetition pitch P of the prismatic irregularities 2a and 2b is as shown in FIG.
Preferably, it 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, a solution for a case where moire occurs in the pitch range becomes a problem.

In the present invention, it is preferable to prevent the moire by forming the prism-shaped irregularities so as to be inclined with respect to the reference plane of the incident side so that the prism-shaped irregularities can be arranged in an intersecting state with respect to the pixels. 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 incident side surface with respect to the reference plane, that is, the inclination angle of the ridge line direction of the prismatic irregularities is within ± 30 degrees, particularly within ± 25 degrees, 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 have an appropriate form as described above. Even in the case of a wedge shape or the like, the shape can be determined as appropriate, such as a straight surface 11 as illustrated in FIG. 2 (a) and curved surfaces 16 and 17 as illustrated in FIGS. 2 (b) and 2 (c). An appropriate surface shape can be used.

Also, the prismatic irregularities forming the light emitting means need not be formed by the linear surfaces 21, 22, 23, and 24 shown in FIG. May be formed. Further, the prismatic irregularities may be composed of a combination of irregularities having different shapes and the like in addition to the pitch. Further, the prismatic irregularities may be formed as a series of convex portions or concave portions in which the ridge line is continuous, or may be formed as intermittent convex portions or concave portions which are arranged discontinuously in the ridge line direction with a predetermined interval. May be.

The lower surface of the light guide plate has a structure having fine irregularities,
Above all, it has a structure in which fine irregularities are provided on a flat surface or the like. This prevents the moiré phenomenon in which the light emitting means and the pattern projected on the lower surface interfere with each other and form interference fringes depending on the viewing direction when viewed from the upper surface, and prevent the display quality from deteriorating due to the moiré. Aim.

The formation of the fine irregularities on the lower surface may be performed, for example, by roughening the surface (lower surface) of the light guide plate by mat treatment such as sand blasting, or by providing fine irregularities via a mold or the like when forming the light guide plate. It can be carried out by an appropriate method according to the conventional diffusion layer, such as a method of attaching a resin layer containing transparent particles to the lower surface of the light guide plate, a method of providing diffusion dots or a sheet provided with the same on the lower surface of the light guide plate. it can. Therefore, the shape of the fine unevenness on the lower surface is not particularly limited, but is preferably a circle or a shape close to a circle rather than the isotropic diffusion. Also, the size of the fine irregularities is not particularly limited, but is not more than 10 μm, particularly 5 μm or less, particularly 3 μm from the viewpoint of the visibility of the display image through the fine irregularities.
Preferably, the diameter is as follows:

In the above, a light guide plate which is more preferable in that the visibility is prevented from deteriorating due to the disturbance of the display image due to scattering and a clear display image is achieved, etc. Has a total light transmittance of 90% or more, particularly 92% or more, and a haze of 45% or less,
Among them, 5 to 40%, especially 10 to 35%.

The shape of the incident side surface of the light guide plate is not particularly limited, and may be appropriately determined. Generally,
Although the surface is perpendicular to the lower surface, the incident light rate can be improved by, for example, a curved concave shape corresponding to the outer periphery of the light source. Further, an incident side structure having an introduction portion interposed between the light source and the light source may be employed. The introduction portion can have an appropriate shape according to the light source and the like.

The light guide plate can be formed of an appropriate material exhibiting transparency according to the wavelength range of the light source. 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 is, for example, a sheet in which light emitting means (upper surface) such as prismatic irregularities or the like and / or fine irregularities (lower surface) are formed on a light guide portion for transmitting light. It may be formed as a laminate of components made of the same or different materials, and need not be formed as an integrated single layer of one material.

The thickness of the light guide plate can be appropriately determined depending on the size of the light guide plate and the size of the light source depending on the purpose of use. A typical thickness when used for forming a 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.

According to the light guide plate of the present invention, the incident light from the upper surface and the lower surface is transmitted more favorably than the lower surface or the upper surface, and the light which has been collimated with high accuracy using the light is excellent in the verticality advantageous for visual recognition. And various devices such as a surface light source device which is excellent in brightness by efficiently using light from a light source and a reflection type liquid crystal display device which is bright and easy to see and has low power consumption.

FIG. 5 illustrates a surface light source device 3 having a light guide plate 1 according to the present invention. The surface light source device can be formed, for example, by disposing a light source 31 on the incident side surface of the light guide plate 1 as shown in the figure, and can be preferably used as a sidelight type front light or the like.

As the light source arranged on the incident side surface of the light guide plate, an appropriate light source can be used. In general, for example (cold, hot)
A linear light source such as a cathode ray tube, a point light source such as a light-emitting diode, an array of such light sources arranged in a linear or planar shape, or a light source using a device that converts a point light source into a linear or luminous state with constant or irregular intervals. And the like can be preferably used. A cold cathode tube is particularly preferable from the viewpoint of low power consumption and durability.

In forming the surface light source device, a light source holder 32 surrounding the light source for guiding the divergent light from the light source 31 to the incident side surface of the light guide plate 1 as shown in FIG.
It is also possible to use a combination body in which appropriate auxiliary means such as the diffusion layer 4 arranged on the lower surface of the light guide plate are arranged in order to obtain uniform surface light emission.

As a light source holder, a resin sheet or a metal foil provided with a high-reflectance metal thin film is generally used.
When the light source holder is bonded to the end of the light guide plate via an adhesive or the like, the formation of the light emitting means can be omitted for the bonded portion.

The diffusion layer is provided, if necessary, in advance for the purpose of equalizing the brightness by preventing uneven brightness and reducing the moire caused by the mixture of adjacent light rays, as necessary, in advance, the light emitting surface of the surface light source device, that is, the lower surface of the light guide plate 1. 12. In the present invention, a diffusion layer having a narrow diffusion range can be preferably used from the viewpoint of maintaining directivity of light emitted from the light guide plate and effective use of light.

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-described fine irregularities on the lower surface, and applying or curing the resin, or applying a transparent resin in which bubbles are dispersed. As appropriate, such as a method of curing, 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 any method, and there is no particular limitation on the formation method. The irregular asperity surface is a mechanical method or / and a chemical method in which a rough surface shape such as a roll or a mold subjected to surface roughening is transferred to the surface of a substrate or a transparent resin coating layer provided thereon. It may be formed by an appropriate method such as a processing method. The transparent particles include, for example, inorganic particles having an average particle size of 0.5 to 100 μm, such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide. Any suitable material such as organic particles such as a crosslinked or uncrosslinked polymer can be used.

As described above, the surface light source device according to the present invention
Providing bright light with excellent light use efficiency and excellent verticality, and being easy to increase in area, it can be preferably applied to various devices as a front light system in a reflection type liquid crystal display device and the like. It is possible to obtain a reflection type liquid crystal display device or the like which is easy to see and has low power consumption.

FIGS. 6 and 7 illustrate a reflection type liquid crystal display device using the surface light source device 3 according to the present invention in a front light system. 5, 51 are polarizing plates, 6 is a liquid crystal cell,
63 is a cell substrate, 62 is a liquid crystal layer, and 7 and 64 are reflection layers. The reflection type liquid crystal display device is formed by arranging a liquid crystal cell 6 having reflection layers 7 and 64 on the light emission side of the surface light source device, that is, on the lower surface side of the light guide plate 1 in the surface light source device as shown in the figure. be able to.

In general, a reflection type liquid crystal display device includes a liquid crystal cell having a transparent electrode functioning as a liquid crystal shutter and an associated driving device, a polarizing plate, a front light, a reflective layer, and a compensating retardation plate if necessary. It is formed by appropriately assembling the components. In the present invention, there is no particular limitation except that the above-described surface light source device is used, and it can be formed according to a conventional example as shown in the figure. FIG. 6
In the example, the entry of the transparent electrode is omitted.

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 O
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.

In the reflection type liquid crystal display device, the reflection layers 7, 64
Is indispensable, but the arrangement position can be provided outside the liquid crystal cell 6 as illustrated in FIG.
It can be provided inside the liquid crystal cell 6 as illustrated in FIG. 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, A reflective sheet supporting an additional layer with a base material,
It can be formed as a suitable reflective layer such as a metal foil according to the related art.

In the case where the reflection layer 64 is provided inside the liquid crystal cell 6 as shown in FIG. 7, the reflection layer may be formed by a method of forming an electrode pattern using a highly conductive material such as the above-mentioned high reflectivity metal or the like. It is preferable to use a reflective layer formed on the electrode pattern by, for example, forming a transparent conductive film using the transparent electrode forming material.

As the polarizing plate, any suitable polarizing plate may be used. However, for example, an iodine-based or dye-based absorption-type linear polarizer may be used instead of obtaining a display with a good contrast ratio by incidence of highly linearly polarized light. Those having a high degree of polarization as described above can be preferably used.

In forming a reflection type liquid crystal display device, for example, a diffusion plate or an antiglare layer, an antireflection film or a protective layer provided on a polarizing plate on the viewing side, or a compensation phase difference provided between a liquid crystal cell and a polarizing plate. An appropriate optical element such as a plate can be appropriately arranged.

The purpose of the above-mentioned compensating phase difference plate is to improve the visibility by compensating the wavelength dependence of birefringence and the like. In the present invention, it is arranged as necessary between the polarizing plate on the viewing side and / or the back side and the liquid crystal cell. As the retardation plate for compensation, an appropriate retardation plate can be used according to a wavelength range or the like, and it may be formed as a single layer or a superposed layer of two or more retardation layers.

The visual recognition of the reflection type liquid crystal display device according to the present invention is carried out through the surface light source device, in particular, the light transmitted through the long side surface of the light guide plate. FIG. 8 illustrates a visual recognition state in the case where the reflection layer 64 is provided in the liquid crystal cell. According to this, when the surface light source device is turned on, the light α emitted from the lower surface of the light guide plate 1
Is reflected through the reflective layer 64 via the polarizing plate 5 and the liquid crystal layer 62 and the like, reaches the light guide plate 1 via the liquid crystal layer and the polarizing plate in reverse, and is transmitted through the long side surface 22 (α). Is visually recognized.

In the above case, in the present invention, the strong leak light β ₁ is emitted in a direction that is greatly deviated from the front direction perpendicular to the liquid crystal cell, and the strong leak light β ₁ is emitted in the front direction.
_Since No. ₂ is weak, a display image with excellent display quality can be visually recognized near the front direction via the long side surface.

On the other hand, even when the surface light source device uses non-lighted external light, the light γ incident from the long side surface 22 of the upper surface of the light guide plate 1 passes through the polarizing plate, the liquid crystal layer, the reflection layer, and the like according to the above. The display image (γ) transmitted to the light guide plate 1 through the transmission and reverse direction and transmitted through the long side surface can be visually recognized in the vicinity of the front direction in a state in which the light guide plate is less disturbed and the display quality is excellent.

In the present invention, optical elements or components such as a light guide plate and a diffusion layer, a liquid crystal cell and a polarizing plate which form the above-mentioned surface light source device and liquid crystal display device are integrally or partially laminated and fixed. Or may be arranged in an easily separable state. It is preferable that the liquid crystal cell is in a fixed state, and that at least the lower surface of the light guide plate and the upper surface of the liquid crystal cell in the surface light source device are in a fixed and adhered state, from the viewpoint of preventing a decrease in contrast by suppressing interface reflection.

An appropriate transparent adhesive such as a pressure-sensitive adhesive can be used in the above-mentioned adhesion and adhesion treatment, and the transparent adhesive layer contains the above-mentioned transparent particles and the like to form an adhesive layer having a diffusion function. Can also.

[0076]

EXAMPLE 1 The upper surface of a transparent plate made of polymethyl methacrylate (PMMA) was cut with a diamond bite to a width of 80 mm.
Depth 130 mm, thickness of incident side 2 mm, thickness of opposing end 0.
8 mm, the lower surface (emission surface) is flat, the upper surface is a curved surface (FIG. 2 b) protruding upward from the incident side surface toward the opposing end and close to a flat surface.
having a pitch of 3 μm, and the inclination angle of the short side surface is 36.5 to 39.
In the range of degrees, the inclination angle of the long side surface changes in the range of 1.1 to 1.5 degrees, the inclination angle change of the nearest long side surface is within 0.1 degrees, and the short side surface is projected on the lower surface. The width is 10 to 21 μm,
A plate-like object having a projected area ratio of the long side surface / short side surface to the lower surface of 17/1 or more was obtained, and a fine uneven sheet was adhered to the lower surface to obtain a light guide plate. The fine irregular sheet has an average particle size of 1.6 μm on a triacetyl cellulose film having a thickness of 80 μm.
A transparent resin layer containing m plastic particles is provided, and the haze is 25%. The above-mentioned prismatic irregularities were formed at a position 2 mm away from the incident side surface.

A cold cathode tube having a diameter of 2.4 mm is arranged on the incident side surface of the light guide plate, and its edge is closely attached to the upper and lower end surfaces of the light guide plate by a light source holder made of a silver-evaporated polyester film. A surface light source device is obtained by connecting an inverter and a DC power source to the cold cathode tube, and a black-and-white reflective TN liquid crystal cell having a reflection sheet corresponding to the light source holder is arranged on the light emission side (the lower surface of the light guide plate) on the back surface. Thus, a reflective liquid crystal display device was obtained.

Comparative Example A surface light source device and a reflection type liquid crystal display device were obtained in the same manner as in Example 1 except that a light guide plate having no fine uneven sheet on the lower surface was used.

Evaluation Test The following characteristics were examined for the light guide plate, the surface light source device and the reflection type liquid crystal display device obtained in the examples and comparative examples.

Emission intensity The surface light source device was turned on, and the angle characteristics of the emission intensity on the upper and lower surfaces of the central part of the light guide plate were measured with a luminance meter (Brand Thompson;
M7). The measurement was performed while changing the angle in a plane perpendicular to the lower surface and the incident side surface with reference to the normal direction to the lower surface. The obtained measurement value was obtained by multiplying the cosine of the measurement angle θ to obtain the emission intensity at θ in order to keep the measurement area constant, and also the emission direction at the maximum intensity.
The following table shows the maximum intensity and its direction on the lower surface, the maximum intensity direction of the lower surface on the upper surface, and the emission intensity (corresponding emission intensity) in a mirror-symmetric direction with respect to the normal and the lower surface.

A solid jig having a hole having a diameter of 10 mm and a matted black inner surface and having a cylindrical jig facing the illuminometer has a solid angle formed by the hole and the light receiving surface of the illuminometer. A solid angle of 3 on the upper and lower surfaces of the illuminated surface light source device by using the surface light source device that is set at 30 degrees.
The amount of light emitted within 0 ° was examined and is shown in the following table together with the total light transmittance and haze of the light guide plate.

Front Brightness In the driving state of the reflection type liquid crystal display device, the front brightness in the white state and the black state was examined under the lighting state of the surface light source device. The results are also shown in the following table. Note Examination of front brightness of the case is not arranged a surface light source device for reference, 28cd / m ² is white state, in a black state was 1.6 cd / m ^2.

Display Quality, Moiré A display image on the reflection type liquid crystal display device was observed to evaluate the display quality in the front direction, and it was examined whether or not interference fringes (moire) appeared by changing the viewing angle. The results are shown in the following table.

[0084]

In Example 1, interference fringes due to moiré did not occur from any direction, but in the comparative example, interference fringes occurred from a perspective state of about 10 degrees on the opposite side from the light source, deteriorating the display quality.

[Brief description of the drawings]

FIG. 1 is an explanatory perspective view of a light guide plate.

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

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

FIG. 4 is an explanatory diagram of emission characteristics according to an embodiment.

FIG. 5 is a side sectional view of the surface light source device.

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

FIG. 7 is a side sectional view of another reflection type liquid crystal display device.

FIG. 8 is an explanatory diagram of a display image according to the embodiment.

FIG. 9 is an explanatory diagram of emission characteristics according to a conventional example.

FIG. 10 is an explanatory diagram of a display image according to a conventional example.

[Explanation of symbols]

 1: light guide plate 11, 16, 17: upper surface 2a: convex portion 2b: concave portion 21, 23: short side surface 22, 24: long side surface 12: lower surface 13: incident side surface 3: surface light source device 31: light source 4: diffusion Layer 5, 51: Polarizer 6: Liquid crystal cell 7, 64: Reflective layer

Claims (6)

[Claims] 1. An incident light from an incident side is emitted from a lower surface through a light emitting means formed on an upper surface, and a maximum intensity of the light emitted from the lower surface within 30 degrees with respect to a normal to a reference plane of the lower surface. And the maximum intensity of light leaked from the upper surface in the direction within 30 degrees is not more than 1/5 of the maximum intensity on the lower surface, and the lower surface has fine irregularities, and is incident from the lower surface. A light guide plate, wherein light is transmitted from an upper surface. 2. The method according to claim 1, wherein the light emitting means is formed of a continuous or discontinuous prism-shaped unevenness having a short side surface and a long side surface.
It has a repeating structure of 0 μm to 1.5 mm pitch, and the short side surface has an inclination angle of 30 to 45 degrees with respect to the reference plane of the lower surface,
A projection width of 40 μm or less, a slope inclined downward from the incident side surface to the opposite end side, and the long side surface is in an inclination angle range of more than 0 to 10 degrees with respect to the reference plane, and the entire angle difference Is less than 5 degrees, the difference in inclination angle between the nearest long sides is within 1 degree, and the projected area with respect to the reference plane is at least five times that of the short sides. 3. The light guide plate according to claim 2, wherein the ridge direction of the prismatic irregularities is within ± 30 degrees with respect to the reference plane of the incident side surface. 4. The method according to claim 1, wherein the total light transmittance of incident light in the vertical direction is 90% or more and the haze is 45%.
% Or less. 5. A surface light source device having a light source on an incident side surface of the light guide plate according to claim 1. 6. A reflection type liquid crystal display device comprising a liquid crystal cell having a reflection layer on a lower surface side of the surface light source device according to claim 5.