JP2002071965A - Light guide plate, surface light source device, and reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a light guide plate and a surface light source device capable of forming a reflection type liquid crystal display device of a front light system which controls dispersion of luminance in a lighting mode while preventing the reflection of a picture and the generation of a moire owing to reflected light of external light by adding a light diffusing layer, and which is bright and excellent in display grade. SOLUTION: In the light guide plate, the light diffusing layer (12) having fine ruggedness on the surface is stuck via a sticking layer (13) whose refractive index is lower than that of a plate shaped body to the rear surface of the plate shaped body (1) which emits incident light from the incident side surface from the rear surface via a light emitting means (A) formed on the upper surface. In the surface light source device (10), a light source (2) is arranged in one or two or more side surfaces in the light guide plate. In the reflection type liquid crystal display device, a liquid cell having a reflecting layer (21) is arranged in the light emitting 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 excellent in light use efficiency and is bright and has good display quality, and a surface light source device using the same.

[0002]

2. Description of the Related Art Conventionally, an adhesive layer is provided on the lower surface of a light guide plate of a front light type reflection type liquid crystal display device having a surface light source device comprising a side light type light guide plate capable of being visually recognized in a dark part or the like on the viewing side. A light diffusion layer having fine irregularities on the surface is additionally provided through the method (JP-A-11-2819).
No. 80). Such a light diffusing layer prevents diffused reflection and scattering at the time of transmission, such as generation of moire (striped light and dark) due to interference between emitted light (display light) and light reflected by the lower surface of the light guide plate or the liquid crystal cell. And preventing the incident external light from being reflected on the lower surface of the light guide plate and reflected as an image. In the moiré described above, the bright and dark stripes move at the viewing position, and the sight is glaring, and the visibility is significantly reduced. However, in the conventional reflection type liquid crystal display device, the addition of the light diffusion layer has the disadvantage that the brightness in the lighting mode is greatly reduced as the distance from the light source is increased and the variation in brightness is increased. there were.

[0003]

SUMMARY OF THE INVENTION The present invention suppresses variations in luminance in a lighting mode while adding a light diffusion layer to prevent reflection of an image due to external light and the occurrence of moire, thereby achieving bright display quality. It is an object of the present invention to develop a light guide plate and a surface light source device capable of forming a front-light type reflection type liquid crystal display device having excellent characteristics.

[0004]

According to the present invention, there is provided an adhesive layer having a lower refractive index than that of a plate-like body which emits incident light from an incident side surface from a lower surface through a light emitting means formed on the upper surface. A light guide plate characterized in that a light diffusion layer having fine irregularities is adhered to the surface thereof via a substrate, and a surface light source characterized by arranging a light source on one or more side surfaces of the light guide plate An object of the present invention is to provide a reflection type liquid crystal display device comprising a device and a liquid crystal cell having a reflection layer disposed on the light emission side of the surface light source device.

[0005]

According to the present invention, since the light diffusing layer is bonded via the bonding layer having a lower refractive index than the plate-like body, it is possible to greatly suppress the variation in luminance depending on the lighting mode. This is based on the investigation of the problem with the conventional method. That is, conventionally, it is advantageous to suppress the reflection at the interface between the plate and the light diffusion layer to improve the luminance by preventing the reflection loss, and therefore the refractive index of the plate and the light diffusion layer is as large as possible. It has been considered that the smaller the difference in refractive index at each interface by bonding with a close adhesive layer, the more the reflection loss can be suppressed, which is advantageous for improving luminance.

However, in the above case, as illustrated by broken arrows β0, β0 ′, β1 ′, and β1 ″ in FIG. 6, the light β0 incident from the side surface of the plate-like body 1 and the transmission light thereof have a difference in interface refractive index. The lowering makes it easier to pass through the adhesive layer 15 and enter the light diffusion layer 12, and the incident light is scattered β1 ′ at the interface between the fine uneven surface and the air to leak light β0 ′ from the upper and lower surfaces of the light guide plate, Because a large amount of β1 ″ is generated and the incident angle of the lower surface leakage light β0 ′ to the liquid crystal cell 20 is large, the upper and lower surface leakage light does not contribute to the illumination of the liquid crystal cell and is transmitted to the rear of the plate. Reduce the light that is emitted. The upper surface leakage light β1 ″ tends to lower the contrast of the display light. Further, the scattering by the light diffusion layer causes the emission light β1, β2 to become illumination light or display light via a light emission unit or the like. , Β3, and β4 also cause variations, thereby lowering light condensing properties, and enlarging the light distribution to darken the display in the viewing direction.

On the other hand, according to the present invention, the incident light α0 is easily totally reflected due to the difference in the refractive index from the adhesive layer 13 as illustrated by the polygonal arrows α0 and α1 in FIG. 5, and the total reflection is transmitted backward. The larger the angle of incidence of the light on the adhesive layer, the more likely it is to receive the light. Also, the emitted light α1 via the light emitting means or the like,
The directions of α2, α3, and α4 are hardly varied, so that the light-collecting property is improved, the brightness is improved with a narrow light distribution, and the display in the viewing direction is brightened. As a result, the variation in luminance is reduced, and the uniformity of luminance at the light-exiting surface of the light guide plate is improved. As a result, a surface light source device for a front light system having excellent light use efficiency and excellent brightness and uniformity is obtained. In addition, it is possible to obtain a front-light type reflection type liquid crystal display device which is less likely to cause reflection of an image due to moire or external light reflection and has excellent brightness and display quality in both lighting and external light modes.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A light guide plate according to the present invention has a lower surface of a plate-like body which emits incident light from an incident side surface through a light emitting means formed on an upper surface from a lower surface, and has a refractive index higher than that of the plate-like body. It is obtained by bonding a light diffusion layer having fine irregularities on the surface via a low adhesive layer. Examples thereof are shown in FIGS. 1 is a plate-like body, A is a light emitting means formed on the upper surface thereof, 12 is a light diffusion layer, and 13 is an adhesive layer. 12a
Is a transparent film, 12b is a fine uneven layer, and 14 is an antireflection layer. The arrow indicates the transmission direction (backward) of the incident light from the incident side surface.

[0009] As the plate-like body, an appropriate one that emits the incident light from the incident side surface from the lower surface through the light emitting means formed on the upper surface can be used. In general, a plate-like body having an upper surface, a lower surface opposed thereto and a side surface between upper and lower surfaces as shown in FIGS. 1 and 2 is used. The plate is
It may be of the same thickness type as shown in the figure, or may have a wedge shape or the like in which the thickness of the opposite end facing the incident side surface is thinner than that of the incident side surface. The reduction in the thickness of the opposing end is advantageous from the viewpoint of reducing the weight and improving the efficiency of incidence of light incident on the incident side surface or light transmitted therethrough to the light emitting means formed on the upper surface.

[0010] The light emitting means formed on the upper surface of the plate-like body can be formed of an appropriate one exhibiting the above-mentioned emission characteristics. One that efficiently emits incident light from the incident side from the lower surface through the light emitting means on the upper surface with good directivity, and efficiently transmits incident light from the lower surface from the upper surface without scattering;
Particularly, when the light incident from the incident side surface or the transmitted light is emitted from the lower surface as illustrated in FIG. 1 from the point of good visibility in the front or the vicinity thereof, the maximum intensity K of the emitted light is shown. It is preferable that the direction θ be within 30 degrees with respect to the normal H to the reference plane of the lower surface.

Further, in the above description, since the contrast is prevented from lowering due to the overlap between the leaked light from the upper surface and the display image due to the light emitted from the lower surface, the distance from the normal line H to the normal line H is not more than 30.
It is preferable that the maximum intensity of light leaked from the upper surface in a direction within a degree is 1/5 or less of the maximum intensity K on the lower surface. The light leaked from the upper surface in the above direction easily overlaps with the reflected light of the light emitted from the lower surface through the reflective layer, which shows the maximum intensity K, and it is indicated that the maximum intensity ratio of the upper surface leaked light / lower surface emitted light is large. It is relatively easy to relatively reduce the image intensity and lower the contrast.

A plate-like body which is more preferable from the viewpoint of improvement in display quality such as brightness and contrast in the case of a reflection type liquid crystal display device is in a plane perpendicular to both reference planes on the incident side surface and the lower surface (cross section in the figure). In the above, the above-mentioned θ is within 28 degrees, particularly within 25 degrees, particularly within 20 degrees. Further, when the side of the incident side surface is defined as a negative direction with respect to the normal H, the intensity L of light leaked from the upper surface at the same angle θ as the direction of the maximum intensity K is 1/10 or less of the maximum intensity K, especially 1
/ 15 or less, especially 1/20 or less. Since the leakage light overlaps with the specular reflection direction of the light having the maximum intensity K, when the value of L / K 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 K direction and the maximum intensity K / leakage light intensity L ratio, is as shown in FIGS. Light emitting means A having an optical path changing surface A1,
Light emitting means A having a plurality of irregularities, particularly a repeating structure of the irregularities, having an optical path conversion surface A1 having an inclination angle of 35 to 48 degrees with respect to the reference plane of the lower surface is preferable. A scattering type light emitting means such as a dot which can be used in a backlight method has poor directivity of the above-mentioned emitted light, or scatters light when viewing a display image through the light emitting means to break an image form. It is more unsuitable for a front light system.

The above-mentioned repeating structure of irregularities can be formed even in a convex part or a concave part having an equilateral surface. However, the efficiency of light utilization and the light emitted from the lower surface are inverted by the reflective layer and the front surface (vertical) In particular, the uneven structure is more preferable than that of emitting light with high directivity in the direction. The inclination angle of the lower surface with respect to the reference plane is 35 to 48 degrees (θ1) as shown in the example of FIG. A flat surface having a substantially triangular cross section having an optical path conversion surface A1 inclined downward at an end at a predetermined pitch, and the inclination angle based on the upper surface of the plate-like body 1 being 0 to 10 degrees between the pitches A repeating structure in which 1a is arranged,
The optical path conversion surface A1 as in the example of FIG.
It has a repeating structure of prismatic irregularities composed of long sides A2 (θ2) of 10 degrees.

The above-mentioned unevenness may be a protrusion (convex) or a groove (concave).
It depends. A light emitting means having a groove structure is preferable from the viewpoint of making the optical path conversion surface A1 less likely to be damaged and improving durability.
In the unevenness, the optical path conversion surface A1 plays a role of reflecting light incident on the surface out of the light incident from the side surface and supplying the light to the lower surface.

In the above case, the inclination angle θ1 is 35 to 48.
The polygonal arrows α0 to α4 shown in FIG.
As described above, the transmission light α1 is reflected with good perpendicularity to the lower surface to obtain the lower surface emission light α2 in which the direction of the maximum intensity K is within 30 degrees with respect to the normal H, and is transmitted to the front through the reflection layer 21 ′. Outgoing light α3, 4 (illumination light, display light) having excellent directivity can be efficiently obtained, and a bright display can be achieved.

The preferable inclination angle θ1 of the optical path conversion surface from the point of directivity to the front and the like is such that the total reflection condition based on the refraction of the light transmitted through the inside of the plate-like body by Snell's law is, for example, 1.5 and the refractive index is 1.5. Considering that it is ± 41.8 degrees, 38
~ 45 degrees, especially 40-44. Some of the light that leaks through the optical path conversion surface without satisfying the total reflection condition is emitted at a large angle of 60 degrees or more with respect to the front direction and hardly affects the visibility near the front direction. , The inclination angle θ1 is 4
If it exceeds 8 degrees, the leakage light from the upper surface tends to increase, which is disadvantageous in light utilization efficiency.

On the other hand, the flat surface 1a and the long side surface A2 between the light path conversion surfaces A1 reflect the transmission light incident thereon and supply the light to the light path conversion surface, and the reflected light from the light path conversion surface as shown in FIG. α2 is inverted (α3) through the reflective layer 21 ′ and transmitted from the upper surface (α4), and external light in the reflection mode is made incident, reflected through the reflective layer 21 ′ and transmitted from the upper surface. With the goal. From this point, the angle of the flat surface 1a with respect to the reference plane of the lower surface or the inclination angle θ2 of the long side surface A2 is preferably 0 to 10 degrees.

The angle of inclination θ2 of the long side surface or the like may be 0 degree (horizontal plane), but if it is more than 0 degree, the transmission light incident on the long side surface or the like is reflected and supplied to the optical path conversion surface. In this case, the transmitted light can be made parallel, and the directivity of the reflected light via the optical path conversion surface can be increased, which is advantageous for display.

On the other hand, if the inclination angle θ2 or the like exceeds 10 degrees, the incidence rate on the long side surface or the like decreases, and the light supply to the opposing end side becomes insufficient, and the light emission tends to be nonuniform. And the amount of light in the front direction decreases, which is disadvantageous for display. In addition, it is difficult to reduce the thickness of the opposite end side even in the cross-sectional shape of the plate-like body, the amount of light incident on the light emitting means is reduced, and the luminous efficiency is likely to be reduced.

From the viewpoint of the above-mentioned performances such as condensing outgoing light, increasing the amount of light in the front direction, and suppressing leak light by making the transmitted light parallel, a preferable inclination angle of a long side surface or the like is 8 degrees or less. Medium 5
Degrees or less. By adjusting the inclination angle between the optical path conversion surface and the flat surface or the long side surface as described above, the emitted light can be given directivity, whereby the light is emitted in a direction perpendicular to or close to the lower surface. It becomes possible to do.

The longer side surface, which is preferable from the viewpoint of the visibility of the display image via the longer side surface of the plate-like body, has an angle difference of the inclination angle θ2 within 5 degrees for the whole plate-like body, particularly 4 degrees. The inclination angle θ2 between the nearest long-side faces is within 1 degree, preferably within 0.3 degrees, particularly within 0.1 degrees. As a result, it is possible to suppress the influence on the display image due to the difference in the inclination angle θ2 of the transmitting long side surface or the like. 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 θ2 is based on the premise that the inclination angle of the long side surface is 10 degrees or less.
That is, it is premised that the small tilt angle θ2 is set to be within an allowable value by suppressing the deflection of the display image due to refraction when transmitted through the long side surface, and the observation point is set near the vertical direction. It is an object of the present invention not to change an optimum viewing direction of an optimized liquid crystal display device.

When the display image is deflected, the optimal viewing direction shifts 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 a decrease in contrast. In some cases. The conditions for setting the inclination angle θ2 of the long side surface or the like to 10 degrees or less include:
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, the projected area of the flat surface or the long side surface with respect to the reference plane of the lower surface is 5 times or more, preferably 10 times or more, especially 1 times or more of that of the optical path conversion surface.
It is preferable that the cross-section be at least five times as large as a triangular or prismatic irregularity. Thereby, most of the display image by the liquid crystal cell can be transmitted through the flat surface or the long side surface.

When a display image is transmitted by the liquid crystal cell, the display image incident on the optical path conversion surface is reflected on the incident side surface and is not emitted from the upper surface, or the display image is transmitted through a long side surface or the like with reference to the normal to the lower surface. The light is deflected and emitted in a direction largely different from the image on the opposite end side, and hardly affects a display image via a long side surface or the like. Therefore, the area where the pixel and the optical path conversion surface overlap with each other is reduced so as to prevent an unnatural display due to insufficient transmission of display light, and to secure a sufficient light transmittance through a long side surface or the like. Is preferred.

Generally, the pixel pitch of the liquid crystal cell is 100 to 3
In view of the fact that it is 00 μm, the optical path conversion surface is 40
Preferably, it is formed so as to be not more than μm.
In addition, as the projection width of the optical path conversion surface becomes smaller, advanced technology is required for its formation, and when the top of the unevenness has a roundness having a radius of curvature of a certain value or more, a scattering effect appears and it is likely to cause a disturbance of a display image, and in general, When the projection width of the optical path conversion surface is smaller than the point where the coherent length of the fluorescent tube is set to about 20 μm or the like, the display quality is likely to be reduced due to diffraction or the like. 20 μm, especially 5 to 15 μm.

It is preferable that the distance between the light path conversion surfaces is larger than the above point. On the other hand, since the light path conversion surface is a substantial emission function part of the side incident light as described above, if the distance is too large, the light is turned on. When the illumination at the time is sparse, the display may still be unnatural. In view of them, the repetition pitch of the irregularities having a substantially triangular or prismatic cross section is 50 μm.
m 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 light emitting means having 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 unevenness, but as described above, the pitch of the unevenness 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 use a method in which the unevenness is formed to be inclined with respect to the reference plane of the incident side surface so that the moire is prevented so that the unevenness can be arranged in a crossing state with respect to the pixel. In this case, if the inclination angle is too large, the reflection via the optical path conversion surface or the like will be 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 will increase. The light use efficiency is also reduced, which is likely to cause a reduction in display quality.

From the above-mentioned point, the inclination direction of the irregular arrangement direction of the incident side surface with respect to the reference plane, that is, the inclination angle of the irregular ridge line direction is:
It is preferably within ± 30 degrees, more preferably within ± 28 degrees, particularly within ± 25 degrees. The sign of ± means the direction of inclination with respect to the incident side surface. In the case where the resolution of the liquid crystal cell is low and moiré does not occur, or when moiré can be neglected, the arrangement direction of the unevenness is more preferably parallel to the incident side surface.

The plate-like body can be formed in an appropriate form as described above. In the case of a wedge shape or the like, the shape can be appropriately determined, and an appropriate surface shape such as a linear surface or a curved surface can be used. Further, the optical path conversion surface and the prismatic irregularities forming the light emitting means may be formed in an appropriate surface form such as a linear surface, a refraction surface, and a curved surface.

Further, the unevenness may be composed of a combination of unevennesses having different shapes and the like in addition to the pitch. In addition, the unevenness may be formed as a series of convex portions or concave portions in which the ridge line is continuous, or may be formed as intermittent convex portions or concave portions arranged at predetermined intervals and discontinuously arranged in the ridge line direction. You may.

The shapes of the lower surface and the incident side surface of the plate are not particularly limited, and may be determined appropriately. In general, the lower surface is as smooth and flat as possible and the incident side surface is perpendicular to the lower surface. The incident side surface may have a shape corresponding to the outer periphery of the light source, such as a curved concave shape, for example, to improve the incident light rate. Furthermore, an entrance side structure having an introduction portion interposed between the light source and the light source may be used, and the introduction portion may have an appropriate shape according to the light source or the like.

The plate-like body 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, a norbornene resin, an epoxy resin, or the like can be used. A plate that does not exhibit birefringence or is formed of a material having low birefringence is preferably used.

The plate-like body 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.

The plate-like body is formed by laminating parts made of the same or different materials, for example, a sheet formed by forming a light emitting means (upper surface) such as a prism-shaped uneven part on a light guide part for transmitting light. It may be formed as a body, etc.
It need not be formed as an integral monolayer of different materials.

The thickness of the plate can be appropriately determined according to the size of the light guide plate and the size of the light source according to the purpose of use. When used for forming a liquid crystal display device or the like, a typical thickness is 10 mm or less, especially 0.1
５5 mm, especially 0.3-3 mm. Further, a plate-like body that is more preferable in that it achieves a bright display or a clear display image due to transparency, for example, has a total light transmittance of 90% or more for incident light in the upper and lower surface directions, particularly, vertically incident light from the lower surface to the upper surface. 92% or more, especially 95% or more, haze 30% or less, especially 15
%, Especially 10% or less.

As shown in FIG. 1 and FIG.
The light diffusion layer 12 having fine irregularities on the surface is bonded via the bonding layer 13 having a lower refractive index than the plate-like body, thereby forming a light guide plate. As the light diffusion layer, an appropriate one having fine irregularities on the surface can be used. By the way, as examples, there are a coated hardened layer of fine surface irregularities in which transparent particles of high refractive index are dispersed in a transparent resin of low refractive index, a coated hardened layer of fine surface unevenness of transparent resin in which bubbles are dispersed, and a substrate. A transparent resin layer having a surface with a fine uneven structure by swelling the surface through a solvent to generate craze and a irregular uneven surface,
Alternatively, there may be mentioned those in which those layers are provided on a transparent support substrate, especially a transparent film.

The irregular irregular surface is formed by transferring a roughened surface such as a roll or a mold subjected to a surface roughening treatment onto the surface of a substrate or a transparent resin coating layer provided thereon. And an appropriate method such as a chemical treatment method. For example, the transparent particles have an average particle size of 0.5 to 30.
μm silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, inorganic particles that may be conductive such as antimony oxide, and organic particles such as crosslinked or uncrosslinked polymers. One or two
More than one species can be used. The light diffusion layer may be formed as a single layer as shown in the example of FIG. 1, or may be formed on a transparent supporting substrate 12a such as a transparent film as shown in FIG.
It can also be formed as a multi-layered product such as one provided with 2b. The light diffusing layer preferably has a low diffusivity that does not disturb the displayed image.

The bonding of the light diffusion layer 12 to the lower surface of the plate 1 is performed via an adhesive layer 13 having a lower refractive index than that of the plate. Thus, the incident light from the incident side surface or the transmitted light can be efficiently transmitted to the rear of the plate-like body.
From the point of total reflection efficiency to achieve the transmission and the incidence efficiency of external light etc. by suppressing reflection at the interface, the refractive index of the plate-like body is 0.01 or more, especially 0.02 to 0.2, Particularly, an adhesive layer having a low refractive index of 0.05 to 0.15 is preferable. Further, an adhesive layer having a refractive index of 1.47 or less is preferable from the viewpoint of practicality and the like to be balanced with the forming material of the plate-like body.

As the adhesive for forming the above-mentioned adhesive layer, an appropriate one can be used, and the kind thereof is not particularly limited except for the refractive index. An adhesive layer can be preferably used from the viewpoint of the convenience of the bonding operation and the like. The light diffusion layer adhered to the lower surface of the plate-like body 1 via the adhesive layer 13 has a refractive index higher than that of the adhesive layer 13, especially 0.2
Hereinafter, those having a height of 0.01 to 0.15 are particularly preferable in terms of the incidence efficiency due to suppression of reflection of external light and the like at the interface.

As shown in FIG. 2, an antireflection layer 14 can be provided on the fine uneven surface outside the light diffusion layer 12, if necessary. The addition of an anti-reflection layer is effective in suppressing the reflection of incident external light on the lower surface of the light guide plate, but the suppression of the reflection acts disadvantageously in confining the transmitted light in the light guide plate, contributing to the improvement of brightness. do not do. Accordingly, the antireflection layer suppresses the suppression when the reflection by the reflected light from the lower surface of the light guide plate is strong, or when the white spot or the contrast is strongly reduced due to the leakage of light from the upper surface overlapping with the display image by the liquid crystal cell. It is preferable to add it for the purpose. The anti-reflection layer can be appropriately formed as a conventional one such as an interference film.

According to the light guide plate of the present invention, the incident light from the upper surface and the lower surface can be transmitted better than the lower surface or the upper surface, and the light that has been collimated with high accuracy can be used in a direction excellent in 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. 3 illustrates a surface light source device 10 having a light guide plate according to the present invention. The surface light source device can be formed, for example, by arranging the light source 2 on the incident side surface of the plate-like body 1 in the light guide plate as shown in the figure, and can be preferably used as a sidelight type front light. Any appropriate light source can be used as the light source. In general, for example, a linear light source such as a (cold or hot) cathode tube, a point light source such as a light emitting diode, an array in which the light sources are arranged linearly or in a plane, or a linear light emitting state in which the point light sources are arranged at regular or irregular intervals. For example, a light source using a device that converts the light into a light can be preferably used. A cold cathode tube is particularly preferable from the viewpoint of low power consumption and durability. The light source can be arranged on one or more side surfaces of the plate.

In forming the surface light source device, if necessary, appropriate auxiliary means such as a light source holder 3 surrounding the light source to guide the divergent light from the light source 2 to the incident side surface of the plate-like body 1 as shown in FIG. May be combined. As the light source holder, a resin sheet or a metal foil provided with a high-reflectance metal thin film is generally used. In the case where the light source holder is bonded to the end of the plate-like body via an adhesive or the like, the formation of the light emitting means can be omitted for the bonded portion.

As described above, the surface light source device according to the present invention
It provides light that is excellent in light utilization efficiency and is excellent in verticality, and can be easily applied to various devices as a front light in a reflection type liquid crystal display device, etc. because it is easy to enlarge the area, etc. A low power consumption reflective liquid crystal display device and the like can be obtained. The front light type reflection type liquid crystal display device can be formed by disposing a liquid crystal cell having a reflection layer on the light emission side of the surface light source device, that is, via a light diffusion layer on the lower surface side of the plate-like body. In FIG.
5 is shown. Reference numeral 10 denotes a surface light source device, and reference numeral 20 denotes a liquid crystal display panel including a liquid crystal cell having a reflective layer. 22
Are liquid crystal layers, 23, 23 'and 23 "are cell substrates holding liquid crystal, which form a liquid crystal cell. 21 is a reflective layer, and 21' is a reflective layer also serving as an electrode. 24 is a polarizing plate, and 25 is a light diffusion layer.

The reflection type liquid crystal display device generally has a liquid crystal cell having electrodes and functioning as a liquid crystal shutter, a driving device, a polarizing plate, a front light, a reflection layer, and a compensating retardation plate if necessary. It is formed by appropriately assembling components such as a light diffusion layer. 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. Note that illustration of electrodes such as transparent electrodes is omitted in the illustrated example.

Therefore, the liquid crystal cell to be used is not particularly limited. For example, when the liquid crystal cell is based on a liquid crystal alignment mode, a TN liquid crystal cell, STN liquid crystal cell, vertical alignment cell, HAN cell, OC
Appropriate ones such as a twist type or non-twist type such as a B cell, a guest host type or a ferroelectric liquid crystal type liquid crystal cell can be used. The driving method of the liquid crystal is not particularly limited, and may be an appropriate driving method such as an active matrix method or a passive matrix method. Further, the cell substrate and the electrode need not be a transparent substrate or a transparent electrode in a position where it is not necessary to transmit illumination light or display light, and may be formed of an opaque body.

In the reflection type liquid crystal display device, the reflection layers 21, 2
Although the arrangement of 1 'is indispensable, the arrangement position can be determined as appropriate, for example, it can be provided outside the liquid crystal cell as illustrated in FIG. 4 or provided inside the liquid crystal cell as illustrated in FIG. Can also. The reflective layer is, 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, or an attached layer of a metal thin film formed by a vapor deposition method, or the applied layer or the attached layer. Can be formed as a suitable reflection layer according to the prior art, such as a reflection sheet or a metal foil, which is supported by a base material. When a reflective layer 21 'is provided inside the liquid crystal cell as shown in FIG. 5, the reflective layer can be formed of a highly conductive material such as the above-mentioned high reflectivity metal or the like as an electrode, or can be transparent. It can be provided together with an electrode or the like, or can be formed of a transparent electrode.

As the polarizing plate for controlling the display light, an appropriate polarizing plate can be used, and it can be arranged on one side or both sides of the liquid crystal cell as shown in the figure. By the way, examples of the polarizing plate include dichromatic dyes such as iodine and dichroic dyes on hydrophilic polymer films such as polyvinyl alcohol film, partially formalized polyvinyl alcohol film, and ethylene / vinyl acetate copolymer partially saponified film. Polarized films such as a film stretched by adsorbing a hydrophilic substance and a polyene oriented film such as a dehydrated product of polyvinyl alcohol and a dehydrochlorinated product of polyvinyl chloride. Further, a polarizing plate in which a transparent protective layer composed of a resin coating layer, a film laminating layer, or the like is provided on one or both surfaces of the polarizing film for the purpose of protecting water resistance or the like is also included. Further, a polarizing plate having a polarizing layer composed of a liquid crystal polymer or a liquid crystal-containing polymer may be used.

On the other hand, the light diffusion layer provided on the liquid crystal display panel as necessary is provided for the purpose of equalizing the brightness by preventing uneven brightness and reducing the moire caused by the mixture of adjacent light rays. As the light diffusion layer, an appropriate one such as those exemplified above can be used, and the light diffusion layer can also be formed as a light diffusion layer also serving as an adhesive layer in which transparent particles are dispersed in an adhesive layer. One or two or more light diffusion layers can be arranged at appropriate positions on the liquid crystal display panel.

On the other hand, the above-mentioned compensating retardation plate aims at improving the visibility by compensating the wavelength dependence of birefringence and the like, and is provided between the polarizing plate on the viewing side and / or the back side and the liquid crystal cell. It is arranged as needed in a space or the like. 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. As the retardation plate, an appropriate one such as a stretched film made of various resins or a film having an alignment layer of a liquid crystal polymer is used. The stretched film may be stretched by various methods such as uniaxial stretching with a free end or a fixed end, biaxial stretching, and stretching in which molecular orientation is also performed in the thickness direction. In forming the reflection type liquid crystal display device, other appropriate optical elements such as an anti-glare layer may be appropriately arranged.

The visual recognition of the reflection type liquid crystal display device according to the present invention is performed through the surface light source device, in particular, as described above, the light transmitted through the flat surface or the long side surface of the plate. Incidentally, in the case where the reflection layer 21 'is provided in the liquid crystal cell illustrated in FIG. 5, in the lighting mode of the surface light source device, the light α2 emitted from the lower surface of the plate-like body 1 is reflected by the polarizing plate 24 and the liquid crystal layer 22.
And the like, and is reflected via the reflection layer 21 ′ (α3) via the liquid crystal layer, the polarizing plate, etc., to the plate-like body 1, and the long side surface A
The display light α4 transmitted through 2 is visually recognized. In that case, the strong leakage light from the top surface is emitted in a direction that is greatly deviated from the front direction perpendicular to the liquid crystal cell, the leakage light emitted in the front direction is weak, and there is also a contribution from the light diffusion layer. 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 is in the non-lighting external light mode, the light incident from the long side surface A2 of the upper surface of the plate-like body 1 passes through the light diffusion layer, the polarizing plate, the liquid crystal layer, the reflection layer and the like. As described above, the display image reaches the plate-shaped body 1 through transmission and reverse, and the display image transmitted through the long-side surface can be visually recognized in the vicinity of the front direction in a state of excellent display quality with little disturbance by the plate-shaped body. The turning on and off of the surface light source device can be performed by an appropriate method.

In the present invention, optical elements or components such as a liquid crystal cell and a polarizing plate forming the above-mentioned surface light source device or liquid crystal display device may be wholly or partially laminated and integrated and fixed. , May be arranged in an easily separable state. It is preferable to be in a fixed state rather than to prevent reduction in contrast by suppressing interface reflection. An appropriate transparent adhesive such as a pressure-sensitive adhesive can be used for the adhesion and adhesion treatment, and the transparent adhesive layer can also contain the above-mentioned transparent particles and the like to form an adhesive layer having a light diffusion function.

[0057]

Reference Example 1 A surface of a brass previously processed into a predetermined shape was cut with a diamond bite to prepare a core for forming an upper surface, which was placed in a mold, and the mold was heated to 100 ° C. After heating, the resultant was filled with molten polymethyl methacrylate (refractive index: 1.50) to form a plate having light emitting means. The plate is
It has a width of 60 mm, a depth of 42 mm, a thickness of the incident side surface of 1.0 mm, and a thickness of the opposite end of 0.6 mm. The upper and lower surfaces are flat and the upper surface has a vertical angle parallel to the incident side surface of 70 ° C. and an inclination angle of 42.5 degrees. A continuous groove having a triangular cross section having an optical path converting surface at a pitch of 240 μm, a flat surface based on the upper surface between the grooves, and a projected width of the lower surface of the optical path converting surface of 10 to 15 μm
And the projection area ratio of the flat surface / the optical path conversion surface to the lower surface was 15/1 or more. The continuous groove with a triangular cross section is 2 mm from the incident side.
It was formed from a remote position.

Reference Example 2 According to the method of Reference Example 1, the width was 60 mm, the depth was 42 mm, the thickness of the incident side was 1.0 mm, and the thickness of the opposite end was 0.6 mm. Adjacent prism-shaped continuous grooves parallel to the side surface at a pitch of 210 μm, the inclination angle of the optical path conversion surface is 42.5 degrees, and the inclination angle of the long side surface is 1.8 to
It changes within a range of 3.3 degrees, the change in the inclination angle of the nearest long side surface is within 0.1 degrees, the projection width to the lower surface of the optical path conversion surface is 10 to 15 μm, and the greater the distance from the incident side surface, the larger the distance. The projected area ratio of the side surface / optical path conversion surface to the lower surface is 1
3/1 or more plate-like bodies were obtained.

Example 1 Silica fine particles were dispersed in an ultraviolet-curable urethane resin (refractive index 1.51), applied to one surface of a transparent modified polyester fill (refractive index 1.51), and cured by ultraviolet irradiation. A light diffusion sheet is formed by attaching a layer having a fine uneven structure on the surface, and the refractive index is 1.
After providing an acrylic adhesive layer of No. 47 and bonding to the lower surface of the plate obtained in Reference Example 1 through the adhesive layer to obtain a light guide plate, a cold cathode tube was arranged on the incident side surface of the plate. It was surrounded by a light source holder made of a silver-evaporated polyester film, and its edges were bonded and fixed to the upper and lower end surfaces of the plate-like body with a double-sided adhesive tape to obtain a surface light source device. Then, a normally white reflective liquid crystal display panel was disposed on the light diffusion layer side of the surface light source device to obtain a reflective liquid crystal display device. The above-mentioned surface light source device can be switched on / off by turning on / off a power supply, and the liquid crystal display device is of a driving type for turning on / off all pixels.

Example 2 A light guide plate, a surface light source device and a reflection type liquid crystal display were used in the same manner as in Example 1 except that the plate obtained in Reference Example 2 was used instead of the plate obtained in Reference Example 1. The device was obtained.

Example 3 A light guide plate was obtained by adhering the light diffusing sheet according to Example 1 to the lower surface of the plate obtained in Reference Example 2 via an acrylic adhesive layer having a refractive index of 1.46. A surface light source device and a reflection type liquid crystal display device were obtained in the same manner as in Example 2 except for using the same.

Example 4 An antireflection layer made of a coherent vacuum-deposited film was added to the outside of the light diffusion layer of the light diffusion sheet according to Example 1, and this was replaced with an acrylic adhesive layer having a refractive index of 1.47. A surface light source device and a reflection type liquid crystal display device were obtained in the same manner as in Example 2 except that a light guide plate was obtained by adhering to the lower surface of the plate-like body obtained in Reference Example 2 and using the same.

Comparative Example 1 The light diffusing sheet according to Example 1 was adhered to the lower surface of the plate obtained in Reference Example 1 via a phenyl group-substituted acrylic adhesive layer having a refractive index of 1.52 to form a light guide plate. 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 it was used.

Comparative Example 2 A light guide plate, a surface light source device and a reflection type liquid crystal display were manufactured in the same manner as in Comparative Example 1 except that the plate obtained in Reference Example 2 was used instead of the plate obtained in Reference Example 1. The device was obtained.

Comparative Example 3 An antireflection layer made of a coherent vacuum-deposited film was added to the outside of the light diffusion layer of the light diffusion sheet according to Example 1, and the refractive index was adjusted to 1.52 according to Comparative Example 1. A surface light source device and a reflection type liquid crystal were obtained in the same manner as in Example 2 except that a light guide plate was obtained by adhering to the lower surface of the plate-like body obtained in Reference Example 2 via a phenyl group-substituted acrylic pressure-sensitive adhesive layer. A display device was obtained.

Evaluation Test In the reflection type liquid crystal display device in the white state obtained in each of the examples and comparative examples, the surface light source device is turned on to set the lighting mode, and each of the light guide plate is 10 mm from the incident side surface at the center in the width direction of the light guide plate and its opposite end.
Brightness (Topcon Corporation, BM-7) at the position (incident part and rear end part) and the visual recognition surface at the center part
And their average values were determined. The results are shown in the table below.

[0067] frontal luminance (cd ^{/ m} 2) entrance portion central rear portion average value Example 1 87 82 76 81.7 Example 2 98 95 85 92.7 Example 3 95 101 93 96.3 Example 4 93 94 82 89.7 Comparative Example 1 91 80 68 79.7 Comparative Example 2 105 94 77 92.0 Comparative Example 3 98 85 68 83.7

Example 1 and Comparative Example 1, Example 2,
As compared with Comparative Example 3 and Comparative Example 2 and Example 4 and Comparative Example 3, there is little variation in the luminance on the display surface due to the lighting mode, and the uniformity is greatly improved. It turns out that it is superior to the comparative example. Also, as compared with 2 and 3 of the embodiment, the larger the refractive index difference between the adhesive layer for adhering the light diffusion layer and the plate-like body, the greater the total reflection effect of the transmitted light and the more effective in improving the luminance and suppressing its variation. It can be seen that it is. Further, also in the external appearance observation, in the example, light emitted at an angle larger than the upper surface was clearly smaller than in the comparative example, and this was particularly remarkable in the example 3 having a large total reflection effect. On the other hand, even in the reflection mode using external light, good display quality was obtained in the examples. From the above, it can be seen that in the embodiment, a front-line reflective liquid crystal display device which is bright and excellent in uniformity in both the lighting and reflection modes and has good display quality is realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a light guide plate.

FIG. 2 is a cross-sectional view of another light guide plate.

FIG. 3 is a cross-sectional view of the surface light source device.

FIG. 4 is a cross-sectional view of a reflective liquid crystal display device.

FIG. 5 is a sectional view of another reflection type liquid crystal display device illustrating an optical transmission state according to the embodiment.

FIG. 6 is an explanatory diagram of an optical transmission state according to a comparative example.

[Explanation of symbols]

 1: Plate-like body 1a: Flat surface A: Light emitting means A1: Optical path conversion surface A2: Long side surface 12: Light diffusion layer 12a: Transparent film 12b: Surface fine unevenness layer 13: Adhesive layer 10: Surface light source device 2: Light source 20: reflective liquid crystal display panel 21: reflective layer 21 ': reflective layer also serving as electrode 22: liquid crystal layer 24: polarizing plate 23, 23', 23 ": cell substrate

Continued on the front page F-term (reference) 2H038 AA55 BA06 2H042 BA02 BA03 BA15 BA20 2H091 FA23X FA31X FA37X FA42X FA45X HA07 HA08 HA09 HA10 HA12 LA17 LA18

Claims (12)

[Claims] 1. A lower surface of a plate-like body which emits incident light from an incident side surface from a lower surface through light emitting means formed on an upper surface,
A light guide plate comprising a light diffusion layer having fine irregularities on the surface thereof bonded through an adhesive layer having a lower refractive index than the plate-like body. 2. The light guide plate according to claim 1, wherein the light diffusion layer comprises a transparent film provided with a fine unevenness layer. 3. The light guide plate according to claim 1, wherein the light diffusion layer has an antireflection layer on the fine uneven surface. 4. The apparatus according to claim 1, wherein the maximum intensity direction of the light emitted from the lower surface is perpendicular to a reference plane of the lower surface in a plane perpendicular to both the lower surface and the incident side surface of the plate-like body. Light guide plate within 30 degrees. 5. A plurality of irregularities having a substantially triangular cross section, wherein the light emitting means formed on the upper surface of the plate-like body has an optical path conversion surface whose inclination angle with respect to a reference plane of the lower surface is 35 to 48 degrees. Light guide plate consisting of. 6. The light emitting device according to claim 1, wherein the light emitting means formed on the upper surface of the plate-like member has a repeating structure of 50 μm to 1.5 mm pitch of prismatic irregularities including an optical path conversion surface and a long side surface, The optical path conversion surface is inclined downward from the incident side surface to the opposite end side at an inclination angle of 35 to 48 degrees with respect to the lower reference plane, and the projection width with respect to the reference plane is 40 μm or less. The plane is at an angle of inclination of 0 to 10 degrees with respect to the reference plane, the entire angle difference is within 5 degrees, the inclination angle difference of the nearest side is within 1 degree, and the projected area with respect to the reference plane is A light guide plate having a slope that is five times or more that of the optical path conversion surface. 7. The light emitting device according to claim 5, wherein the uneven ridge forming the light emitting means is ± 30 ° with respect to the reference plane of the incident side surface.
Light guide plate within the range of degrees. 8. The light-emitting device according to claim 1, wherein the refractive index of the adhesive layer for bonding the light diffusion layer to the lower surface of the plate is 0.01 to 0.2 lower than that of the plate. A light guide plate wherein the refractive index of the diffusion layer is higher than that of the adhesive layer. 9. The light guide plate according to claim 1, wherein a refractive index of an adhesive layer for adhering the light diffusion layer to a lower surface of the plate-like body is 1.47 or less. 10. The light guide plate according to claim 1, wherein the adhesive layer for bonding the light diffusion layer to the lower surface of the plate is an adhesive layer. 11. A surface light source device, wherein a light source is arranged on one or more side surfaces of the light guide plate according to claim 1. Description: 12. A reflection type liquid crystal display device, wherein a liquid crystal cell having a reflection layer is arranged on the light emission side of the surface light source device according to claim 11.