JP4632377B2 - Light guide plate, surface light source device, and liquid crystal display device - Google Patents

Description

  The present invention is capable of forming a surface light source device having excellent light use efficiency and excellent brightness and uniformity, and a reflective and transmissive liquid crystal display device that is bright and easy to see, and can be a light source color conversion type. It relates to a light guide plate.

  Conventionally, as a light guide plate, a side light type is known in which a rough surface or white dots are provided on one of the upper and lower surfaces of a plate-like body, and incident light from the side surface is scattered and emitted to the other of the upper and lower surfaces. It was. Such a side light type light guide plate is used to form a reflection type or a transmission type liquid crystal display device by arranging a light source on the side surface to form a surface light source device and combining it with a liquid crystal cell.

  However, there is a problem that the display quality is poor due to poor brightness and uniformity. There is also a proposal for improving the luminance by arranging light sources on a plurality of side surfaces, but variations in luminance are difficult to improve. In addition, the liquid crystal display device is distinguished from the backlight type and the front light type in the arrangement position of the surface light source device with respect to the liquid crystal cell, but the scattering type described above is difficult to use in the front light type because the display image is disturbed. There was also a problem. In such a front light type, with the spread of liquid crystal display devices to cellular phones and the like, there is also a demand for a device that can convert the emission color as in the case of the backlight type.

The present invention is excellent in light utilization efficiency of luminance and easy rather look bright using a surface light source device excellent in the uniformity of the reflection type liquid crystal display device in possible front lit be a light emitting color conversion formulas Development is an issue.

The present invention comprises a plate-like body having at least two incident side surfaces composed of an upper surface, a lower surface, and a side surface between the upper and lower surfaces. has a light emitting means for emitting incident light from the incident side to the lower surface to the upper surface, a prism to which the light emitting means has a ridge line in a direction along the respective incident side consists opposing faces thereof with the transmission light reflecting surface consists repetitive structure with a constant pitch of 80μm~1mm of Jo irregularities, the projected width the transmission light reflecting surface for facing to the reference plane to the incident side surface at an inclination angle of 30-45 degrees with respect to a reference plane of said lower surface is 3~40μm together with consisting slope on the lower surface of the light guide plate in a surface light source device formed by arranging the light source to the respective incident side of the opposing surface is Ru light guide plate name than the inclination angle of 40 degrees or more slopes with respect to the reference plane, reflector Layering tool There is provided a liquid crystal display device characterized by having a liquid crystal cell.

According to the present invention, the light from the light source is incident from at least two side surfaces of the light guide plate, and the incident light is emitted from the same surface via the light emitting means having a repetitive structure of prismatic irregularities. Can be efficiently converted into a surface light source to obtain a surface light source device having excellent luminance and uniformity, and a bright and easy-to-view reflective liquid crystal display device can be formed by using it as a front light . In addition, a front-light type liquid crystal display device capable of changing the emission color can be formed as a combination of light sources emitting different colors.

The light guide plate used in the liquid crystal display device of the present invention is composed of a plate-like body having at least two incident side surfaces composed of an upper surface, a lower surface, and side surfaces between the upper and lower surfaces, and the incident side surfaces are in the left-right direction and front-back direction And a light emitting means for emitting incident light from each incident side surface to the other of the upper and lower surfaces, the light emitting means in a direction along each incident side surface. It consists of a repeating structure of prismatic irregularities having ridge lines. Examples thereof are shown in FIGS. Reference numeral 1 denotes a plate-like body forming a light guide plate, 11 denotes an upper surface, and 13a and 13b denote incident side surfaces. The lower surface 12 is at a position facing the upper surface 11 as shown in FIG.

  The incident side surface is intended to allow light to enter by placing a light source on the incident side surface. In the present invention, as shown in the examples of FIGS. At least two of the side surfaces between the upper and lower surfaces of the shaped body are used as the incident side surfaces 13a and 13b. As a result, light can be incident from two or more side surfaces through separate light sources, and luminance can be improved and emission colors can be converted.

  On the other hand, the light emitting means formed on one of the upper and lower surfaces of the plate-like body is for emitting incident light from the incident side surface to the other of the upper and lower surfaces. In the present invention, it is exemplified in FIGS. As shown in FIG. 1 and FIG. 2, the prism-shaped unevenness ridgelines A and B are formed in a direction along the incident side surfaces 13 a and b. In addition, in the light-guide plate 1 of FIG. 4, the outline by the (alpha) -beta cross section in FIG. 2 and a (gamma) -delta cross section is shown.

  As described above, the light emitting means corresponding to each of the incident side surfaces can be arranged, and one of the upper and lower surfaces can be used as a common light emitting surface to emit light with good directivity, thereby improving the light utilization efficiency. In the example shown in the figure, a light emitting means is provided on the upper surface 11 and the light is emitted from the lower surface 12, so that the lower surface becomes the light emitting surface. From the point of increasing the optical path length through the thickness of the light guide plate and relaxing and leveling the bright line of the outgoing light through the light emitting means, the uniformity of the light emission is improved as shown in the figure. It is preferable that the light emitting means is formed on the upper surface and the lower surface is the light emitting surface, particularly in the case of a front light type.

  A light emitting means that is preferable from the viewpoint of light use efficiency and the like has an inclined surface that can reflect the incident light from the incident side surface, and in particular, can control the optical path to the light emitting surface side through total reflection. The prism-like unevenness having such a slope can be formed with an appropriate uneven structure composed of equilateral surfaces or the like.

  The prism-shaped uneven structure is preferably used when a light is emitted as much as possible in the vertical (normal) direction of the reference plane from the light emitting surface of the light guide plate and is used as a front light of a reflective liquid crystal display device. The direction of the emitted light which becomes display light and the light leakage from the light guide plate do not overlap as much as possible. If the leaked light overlaps with the display light, the strength of the display image is diminished and the contrast tends to be lowered.

  The unevenness that is preferable from the viewpoint of normalizing the emitted light and preventing the overlapping of leakage light and display light is the side having no light emitting means on the upper and lower surfaces of the light guide plate as illustrated in FIG. The transmission light reflecting surface A1 having an inclination angle θ1 of 30 to 45 degrees with respect to the reference plane on the opposite side and the surface A2 having an inclination angle θ2 opposite thereto of 40 degrees or more.

  The transmission light reflecting surface A1 serves to reflect the light incident on the incident light from the incident side surface and supply it to the light emitting surface. In this case, by setting the tilt angle to 30 to 45 degrees, the transmitted light can be reflected with good perpendicularity to the light exit surface, and the emitted light that is advantageous for display can be obtained efficiently. From the viewpoint of the above-mentioned performance such as suppression of total reflection and leakage light based on Snell's law, and suppression of visual interference thereby, the preferable inclination angle of the transmission light reflecting surface is 35 to 44 degrees, especially 38 to 43 degrees. is there.

  If the transmission light reflecting surface has an inclination angle of less than 30 degrees, the direction of the emitted light from the light emitting surface becomes a large angle with respect to the normal, and the amount of light that can be effectively used for visual recognition is reduced, so that the brightness tends to decrease. On the other hand, if it exceeds 45 degrees, the leakage light from the light emitting means forming surface increases and the contrast of the display image tends to decrease.

  On the other hand, the facing surface A2 is a surface that is inevitably generated along with the formation of the transmission light reflecting surface, and the surface portion between the prismatic irregularities is not made as narrow as possible with the projection width of the surface with respect to the reference plane. Is preferred. That is, the upper surface portion 11a between the prism-shaped projections and depressions in the figure is a portion that transmits the display image from the liquid crystal cell when the front light of the reflective liquid crystal display device is used, and the backlight portion of the transmissive liquid crystal display device. Functions as a portion that transmits reflected light through a reflective layer or the like, and when the upper surface portion 11a becomes narrower with the projection width of the facing surface A2, visibility and light utilization efficiency are lowered.

  Therefore, it is preferable that the projection width of the opposing surface does not make the surface portion between the prism-shaped irregularities as narrow as possible. From this point, the inclination angle θ2 of the opposing surface with respect to the reference plane is preferably 40 degrees or more, more preferably 50 degrees or more, particularly 60 degrees or more, and the projection width of the opposing surface is 0 as an inclination angle of 90 degrees or more. It can also be made to overlap with the projection width of the transmission light reflecting surface.

  By adjusting the angle of inclination of the transmission light reflecting surface of the prism-shaped unevenness and the opposing surface forming the light emitting means as described above, it is possible to give the outgoing light a high degree of directivity, and thereby the light emitting surface. It is possible to emit light in a direction perpendicular to or at an angle close thereto. The slopes of the prismatic irregularities forming the light emitting means can be formed in an appropriate surface form including a straight surface, a refracting surface, a curved surface, etc., and can also have a repeating structure of prismatic irregularities having different shapes. Also, the prism-like unevenness may be formed in a series of uneven structures whose ridge lines are continuous, or may be formed in an intermittent concavo-convex structure arranged discontinuously in the ridge line direction with a predetermined interval. Good.

  The size of the transmission light reflecting surface that is preferable in terms of securing the area of the surface portion between the prism-like irregularities described above, preventing the occurrence of moire due to interference with the pixels of the liquid crystal cell, and forming sharp irregularities, etc. Considering that the pixel pitch of the liquid crystal cell is generally 100 to 300 μm, it is 40 μm or less, especially 3 to 20 μm, especially 5 to 15 μm based on the projection width of the light emitting surface with respect to the reference plane.

  In addition, it is preferable that the interval between the transmission light reflecting surfaces is larger than the above point, but on the other hand, the transmission light reflecting surface is a substantial emission function part of the side incident light as described above. In some cases, the light becomes sparse and unnatural display may occur. In view of these, it is preferable that the repetitive pitch P (FIG. 3) of the prism-shaped irregularities is 80 μm to 1 mm. The pitch may be irregular, such as a random pitch or a random or regular combination of a predetermined number of pitch units, but the pitch is constant in terms of moire prevention and appearance. Is preferred.

  From the standpoint of obtaining a brighter display image, the repetitive pitch of the prism-shaped irregularities is preferably 8 times or more, more preferably 10 times or more, especially 12 times or more, the projection width of the transmission light reflecting surface with respect to the reference plane of the light emitting surface. . As a result, when the front light of the reflective liquid crystal display device is used, most of the display image by the liquid crystal cell can be transmitted through the upper or lower surface portion between the repetitive pitches of the prismatic irregularities. Further, when a backlight of a transmissive liquid crystal display device is used, a large-area reflective surface and transmissive surface can be secured, which is advantageous in improving light utilization efficiency.

  In the case of a light emitting means having a prismatic uneven structure, it may interfere with the pixels of the liquid crystal cell to cause moire. Moire can be prevented by adjusting the uneven pitch, but as described above, there is a preferable range for the uneven pitch. Therefore, as a solution when moire occurs in the pitch range, a method in which the unevenness is formed in an inclined state with respect to the reference plane of the incident side surface so that the unevenness can be arranged in a crossing manner with respect to the pixel is preferable. In that case, if the inclination angle is too large, the reflection through the transmission light reflecting surface or the like is deflected, resulting in a large deviation in the direction of the emitted light, and the anisotropy of the emission intensity in the light transmission direction of the light guide plate increases. As a result, the light utilization efficiency is also lowered, and the display quality is likely to be lowered.

  The inclination direction θa, b of the prism-shaped unevenness with respect to the reference plane of the incident side surface from the above point, that is, the inclination angle θa, b in the ridge line direction of the prism-shaped unevenness is within ± 30 degrees, in particular within ± 25 degrees, in particular within ± 20 degrees. It is preferable to do. The sign of ± means the direction of inclination with respect to the incident side surface. When moiré can be ignored, the arrangement direction of the prismatic irregularities is preferably as parallel to the incident side surface as in the example of FIG.

  In the above description, the light emitting means for one incident side surface has been described. In the present invention, it is preferable that each light emitting means corresponding to each incident side surface satisfies the above. However, the structure and pitch of the prismatic unevenness need not be the same for each light emitting means, and can be determined as appropriate according to the light guide plate, the pixel size in the left-right direction, the front-rear direction, and the like.

  In the present invention, the light emitting means A in the left-right direction and the light emitting means B in the front-rear direction of the plate-like body 1 intersect as in the examples of FIGS. From this point, it is preferable that the ridge lines of the prismatic unevenness as the light emitting means provided for each incident side surface intersect at an angle of 40 degrees or more, especially 60 degrees or more.

  The light guide plate can have any suitable form, but in general, the incident side surfaces 13a and 13b and the opposing ends 14a and 14b facing each other have the same thickness as shown in the figure from the viewpoint of securing the left and right and front and rear incident side surfaces. It is made of a board. The light exit surface of the light guide plate, that is, one of the upper and lower surfaces that do not form the light exit means is usually a flat surface, but the light exit means depends on the viewing direction when viewed from the top as a front light of a reflective liquid crystal display device. And the pattern reflected on the light exit surface may interfere with each other to generate a moire phenomenon due to interference fringes. The light exit surface is provided with fine irregularities for the purpose of preventing deterioration of display quality due to the moire. It can also be a structure or the like.

  The formation of the fine irregularities on the light exit surface described above is, for example, a roughening method by mat processing such as sandblasting, a method of giving fine irregularities through a mold or the like when forming a light guide plate, a resin layer containing transparent particles Can be performed by an appropriate method in accordance with a conventional diffusion layer, such as a method of attaching a diffusion dot or a method of providing a diffusion dot or a sheet provided with it on a light guide plate.

  The shape of the side surface such as the incident side surface of the light guide plate is not particularly limited and may be appropriately determined. In general, the incident side surface is perpendicular to the light exit surface from the viewpoint of the arrangement of the light source, but it may be a concave shape corresponding to the outer shape of the cathode tube. Further, the incident side surface can be formed in a form protruding through the transparent bodies 15a and 15b as illustrated in FIG. Such a protruding form prevents spatial interference of the non-light emitting part due to the electrode part of the light source which is disposed in the left-right direction 13a and the front-rear direction 13b, or increases the optical path length and the light source length is insufficient (short dimension). ) To prevent the occurrence of light emission unevenness at the end or the like.

  In the case of the protruding form described above, the relationship with the light source arranged there contributes to the prevention of uneven emission as described above, but in the relationship with the light source arranged on the other side, it is difficult for light to enter the protruding part and a shadow is formed. It tends to occur. That is, in the example of FIG. 2, the light from the light source in the front-rear direction is less likely to be incident on the protrusion 15a in the left-right direction, and the light from the light source in the left-right direction is less likely to be incident on the protrusion 15b in the front-rear direction. Shadows are likely to occur at the part.

  In the present invention, the occurrence of shadows can be prevented by inclining the ridges of the prismatic irregularities of the light emitting means relative to the above. That is, as illustrated in FIG. 2, with respect to the light emitting means A provided on the left and right incident side surface 13a, the ridge line of the prism-shaped irregularities is from the side of the front and rear direction incident side surface 13b with respect to the left and right direction incident side surface. With respect to the light emitting means B provided on the incident side surface 13b in the front-rear direction by making the inclination θa away from the other end 14b, the ridge line of the prism-shaped unevenness is based on the incident side surface in the front-rear direction. By tilting θb in a direction away from the side of the incident side surface 13a in the left-right direction toward the other end 14a, the outgoing light through the transmission light reflecting surface is emitted in the direction of the protruding portion that becomes the shadow, and the shadow This can be prevented by compensating for the lack of light emission.

  For the formation of the light guide plate, an appropriate material showing transparency can be used according to the wavelength range of the light source. Incidentally, in the visible light range, for example, acrylic resins, polycarbonate resins, polyester resins, norbornene resins, transparent resins represented by polyolefin resins, epoxy resins, and the like can be used. Those formed of a material that does not exhibit birefringence or has low birefringence are preferable.

  The light guide plate can be formed by a cutting method and can be formed by an appropriate method. As a preferable production method from the viewpoint of mass productivity, etc., a method of transferring a shape by pressing a thermoplastic resin to a mold capable of forming a predetermined shape under heating, a heat-melted thermoplastic resin, 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 with heat, ultraviolet light, radiation, or the like into a mold that can form a predetermined shape Examples thereof include a polymerization method.

  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. The thickness of a general light guide plate when used to form a reflective or transmissive liquid crystal display device is 20 mm or less, especially 0.1 to 10 mm, especially 0.3 to 5 mm, based on the incident side surface. . The light guide plate may be formed as a laminated body of parts made of the same or different materials, such as a sheet in which a light emitting means is bonded to a light guide portion that carries light transmission. It is not necessary to be formed as an integral single layer of the above materials.

The surface light source device for a liquid crystal display device of the present invention is used as a sidelight type front light or backlight in a reflective or transmissive liquid crystal display device or the like, as illustrated in FIG. 4 or FIG. A light source 21 is disposed on each of the incident side surfaces 13 a and 13 b of the light guide plate 1. The light source is not particularly limited, and a suitable light source that exhibits monochromatic light or light emission characteristics in various wavelength ranges can be used according to the purpose of use of the surface light source device.

  By the way, examples of the light source include point light sources such as (cold and heat) cathode tubes and light emitting diodes, an array of the point light sources, light obtained from the point light source into a linear light source, and an elongated electroluminescence element. Etc. As the surface light source device used for forming the liquid crystal display device, one that exhibits light emission characteristics in a wavelength region as wide as possible in the visible light region is preferable. The combination of the light sources arranged on the light guide plate can be appropriately determined according to the purpose of use, for example, the same type or the different light emission colors. In addition, the light sources can be switched on and off independently or independently by an appropriate method.

  In particular, light-emitting diodes, especially linear light sources using them, are considered in terms of low power consumption, simplification of light source driving devices, simplification of switching on / off, and ease of incorporation of different color light sources. What was obtained is preferable. By the way, as an example, a point light source is arranged on the back and side of a linear light guide plate made of a rectangular parallelepiped formed so as to be arranged on the incident side surface according to the above light guide plate, and from the point light source For example, it is possible to convert incident light into a linear light source. In that case, in the system in which the point light source is arranged on the side surface of the linear light guide plate, an optical path changing means having an appropriate form including a dot structure or a repetitive structure of prismatic unevenness can be provided on the back surface of the linear light guide plate. .

  When forming the surface light source device, as shown in FIGS. 4 and 5, appropriate auxiliary means such as a light source holder 22 that surrounds the light source 21 is disposed to efficiently guide the emitted light from the light source to the incident side surface of the light guide plate. You can also As the light source holder, a resin sheet, a metal foil, a white sheet or the like provided with a highly reflective metal thin film is generally used. Moreover, when using as a backlight, a light source holder can be extended to the light-projection surface of a light-guide plate, and can also serve as a reflective sheet.

The surface light source device for a liquid crystal display device of the present invention provides a surface light source excellent in brightness by efficiently using light from the light source, and is easy to increase in area and the like. The present invention can be preferably applied to various devices as a light system or a backlight system of a transmissive liquid crystal display device.

FIG. 4 illustrates a reflective liquid crystal display device of the present invention in which a surface light source device is used in a front light system. This has polarizing plates 31 and 33 on the front and back of the liquid crystal cell 32 on the light emitting surface (lower surface 12) side of the light guide plate 1 having the light emitting means on the upper surface 11 in the surface light source device 2, and the reflective layer 34 on the rear surface. The reflection type liquid crystal display unit 3 provided is formed and can be used as a reflection type liquid crystal display device using external light by turning off the surface light source device.

On the other hand, FIG. 5 illustrates a liquid crystal display device using a surface light source device in a backlight system as a reference example . This is formed by disposing a transmissive liquid crystal display unit 3 on the upper side of the light guide plate 1 in the surface light source device 2 via a light diffusion layer 4, and the light guide plate 1 has a reflection layer 5 on its light exit surface. It can be used as a liquid crystal display device for both reflection and transmission in addition to the transmission type.

  In the example of FIG. 5, the surface light source device 2 using the light guide plate 1 having the light emitting means on the upper surface 11 is illustrated as having the transmissive liquid crystal cell 32 arranged on the upper surface side of the light guide plate. The light guide plate formed on the lower surface can be used in the same manner. Therefore, the light guide plate can be arranged on either the liquid crystal cell side of the light emitting means forming surface or non-forming surface. By arranging the means, a liquid crystal display device for both reflection and transmission can be formed.

  As described above, the liquid crystal display device is formed by using at least a surface light source device and a liquid crystal cell and disposing the liquid crystal cell on a predetermined surface side of the light guide plate 1 in the surface light source device. In that case, in the reflection type liquid crystal display device using the surface light source device for the front light, the surface light source device 2 is light of the light guide plate 1 on the viewing side of the liquid crystal display unit 3 having the reflective layer 34 on the back surface as shown in FIG. It arrange | positions so that the output means formation surface may become an upper side (viewing side).

  Therefore, in the reflective liquid crystal display device using the front light system, at least the liquid crystal layer of the liquid crystal cell is located between the light guide plate of the surface light source device and the reflective layer, and the light emitting means forming surface of the light guide plate is on the viewing side. It is indispensable to arrange in this way. The visual recognition is that the external light transmitted through the portion 11a formed between the light emitting means in the light guide plate of the surface light source device or the light emitted from the light guide plate at the time of lighting passes through the liquid crystal cell and is inverted by the reflective layer. The light is transmitted again through the liquid crystal cell and then transmitted through the portion 11a of the light guide plate. The reflective layer can be provided in the liquid crystal cell by attaching it to the cell substrate.

  On the other hand, in a transmissive liquid crystal display device using a surface light source device as a backlight as shown in FIG. 5, a light guide plate of the surface light source device is disposed on the back surface (viewing back surface) side of the liquid crystal cell, and light emitting means is formed on the viewing side. When using a light guide plate having a surface or for both reflection and transmission, the light guide plate of the surface light source device is disposed between the liquid crystal cell and the reflection layer. In those cases, as described above, the surface light source device can be arranged such that the light emitting means forming surface side of the light guide plate is the liquid crystal cell side as shown in the figure, or the light emitting means of the light guide plate is opposite to the figure example. It is also possible to dispose the light emitting surface side without the liquid crystal cell side.

  As shown in the figure, the method of reversing through the reflection layer arranged on the light emitting surface with the light emitting means forming surface side of the light guide plate as the liquid crystal cell side is the optical path length from the light emitting means to the liquid crystal cell as described above. In contrast to the example shown in the figure, the bright line pattern by the light emitting means can be relaxed and the occurrence of display defects such as moire can be suppressed compared to the method in which the light emitting surface side of the light guide plate is arranged on the liquid crystal cell side. is there.

  Visual recognition by the transmissive liquid crystal display device described above is performed when light emitted from the surface light source device enters the liquid crystal cell directly or through inversion by a reflective layer and is transmitted. Further, the visual recognition by the liquid crystal display device for both reflection and transmission is the same as the transmission type in the transmission mode. In the reflection mode, the external light is transmitted through the liquid crystal cell and inverted by the reflection layer on the back surface of the light guide plate. This is performed by transmitting the portion 11a between the light emitting means in the light guide plate and the liquid crystal cell.

  In general, the liquid crystal display device is a liquid crystal cell 32 having a transparent electrode functioning as a liquid crystal shutter as shown in FIGS. 4 and 5, a liquid crystal display unit including a driving device and a polarizing plate attached thereto, and switching on / off as necessary. It is formed by appropriately assembling components such as a backlight or a front light incorporating a switch and, if necessary, a light diffusion layer 4 or a reflection layer 5, an antireflection layer or a compensation retardation plate.

  In the present invention, there is no particular limitation except that the above-described light guide plate or surface light source device is used. Accordingly, the liquid crystal cell to be used is not particularly limited. For example, when the liquid crystal cell is based on the alignment form of the liquid crystal, a twist type or non-twist type such as a TN liquid crystal cell, an STN liquid crystal cell, a vertical alignment cell, a HAN cell, or an OCB cell, a guest host type, An appropriate liquid crystal cell such as a ferroelectric liquid crystal cell can be used. Also, there is no particular limitation on the liquid crystal driving method, and an appropriate driving method such as an active matrix method or a passive matrix method may be used.

4 and 5, the liquid crystal cell 32 is formed by sealing a liquid crystal layer between the cell substrates. In this case, the cell substrate can also serve as a light guide plate . In the example of the figure, the transparent electrode and the accompanying driving device are not shown.

  There is no particular limitation on the polarizing plate provided on one or both of the front and back of the liquid crystal cell. However, as a polarizing plate on the backlight side or the front light side, in particular, from the point of obtaining a good contrast ratio display by incidence of highly linear polarized light. For example, it is preferable to use a material having a high degree of polarization such as an iodine type or dye type absorption linear polarizer.

Even with the reflective layer, such as aluminum or silver, attached layer of thin metal film of the coating layer, vapor deposition method in which a powder of a highly reflective metal gold or copper or chromium contained in the binder resin, Ya the coating layer It can be formed as an appropriate reflective layer according to the prior art, such as a reflective sheet or a metal foil in which the attachment layer is supported by a base material. When a reflective layer is provided inside the liquid crystal cell, the reflective layer may be a method of forming an electrode pattern with a highly conductive material such as the above-described highly reflective metal or a reflective layer formed of a highly reflective metal film. A reflective layer by a method of providing a transparent electrode pattern through an insulating layer is preferable.

  The reflective layer in the reflective liquid crystal display device can also be provided outside the liquid crystal cell, for example, as a reflective layer made of a highly reflective metal film on a plastic film. In the case of a transmissive liquid crystal display device, it can be directly attached to a light guide plate forming the backlight. The reflection layer can be provided on either the light emitting means forming surface or the light emitting surface of the light guide plate in accordance with the use form of the light guide plate in an appropriate manner exemplified above.

  When forming a liquid crystal display device, as described above, for example, an antiglare layer or an antireflection film provided on the surface on the viewing side, a light diffusion plate, a compensation phase difference plate, a polarization separation plate, a prism sheet for the purpose of optical path control, etc. An appropriate optical element such as can be arranged at an appropriate position. The antireflection film can also be provided on the light exit surface of the light guide plate.

  The compensation phase difference plate is intended to improve the visibility by compensating the wavelength dependence of birefringence, and the polarizing plate and the liquid crystal cell on the viewing side or / and the backlight side It arrange | positions as needed between. As the compensation phase difference plate, an appropriate one can be used according to the wavelength region or the like. The retardation plate can be obtained, for example, as a birefringent sheet obtained by stretching a film made of polycarbonate, polysulfone, polyester, polymethyl methacrylate, polyamide, polyvinyl alcohol, or the like, or a support sheet for a liquid crystal polymer alignment layer. These retardation sheets can be formed as a laminate of two or more layers.

  In addition, the light diffusing layer is formed as a single layer or an appropriate layer on the liquid crystal display device as necessary for the purpose of obtaining surface light emission with uniform brightness by preventing unevenness of light and dark or reducing moire by mixing adjacent light beams. Two or more layers are arranged. Incidentally, in the example of FIG. 5, the light diffusion layer 4 is disposed between the light guide plate 1 and the liquid crystal display unit 3. Note that a diffusion layer having a narrow diffusion range can be preferably used from the viewpoint of maintaining the directivity of the light emitted from the light guide plate.

  The light diffusing layer is coated with, for example, a method of dispersing and curing high refractive index transparent particles in a low refractive index transparent resin or a transparent resin in which bubbles are dispersed in accordance with the fine unevenness of the light exit surface described above. Appropriate methods such as a method of curing, a method of generating a craze by swelling the surface of a substrate through a solvent, a method of forming a transparent resin layer having irregular irregular surfaces, or a method of using a diffusion sheet formed according to the above It can be formed by any method.

  In forming a transmissive liquid crystal display device, a polarization separation plate can be disposed between the surface light source device and the polarizing plate for the purpose of improving luminance. The polarization separation plate transmits natural light, such as a layer having a cholesteric liquid crystal phase, a sheet having a layer made of a liquid crystal polymer exhibiting a cholesteric phase, or a dielectric multilayer film on a transparent substrate. It has a function of separating into polarized light through reflection. Incidentally, the cholesteric liquid crystal phase can be separated into left and right circularly polarized light through transmission and reflection, and the dielectric multilayer film can be separated into P wave and S wave linearly polarized light through transmission and reflection. it can. Circularly polarized light can be converted to linearly polarized light through a quarter-wave plate.

  Therefore, by causing the polarized light that has passed through the polarization separator plate to be incident on the polarizing plate with the polarization axis being matched as much as possible, the absorption loss due to the polarizing plate can be suppressed and the luminance can be improved. Further, in the surface light source device composed of the light guide plate 1 provided with the reflection layer 5 on the back surface as shown in FIG. 5, the polarized light reflected by the polarization separation plate is inverted by the reflection layer 5 and re-entered on the polarization separation plate. A part or all of the inverted light can be transmitted, and the luminance can be improved by improving the light utilization efficiency.

  In the present invention, the optical elements or components such as the light guide plate, the liquid crystal cell, and the polarizing plate forming the surface light source device or the liquid crystal display device may be laminated or integrated in whole or in part. , May be arranged in an easily separated state. It is preferable to be in a fixed state from the viewpoint of preventing a decrease in contrast due to suppression of interface reflection. An appropriate transparent adhesive such as a pressure-sensitive adhesive can be used for the fixing and adhesion treatment.

Example 1
A light guide plate was obtained by cutting the upper surface of a rectangular plate having the same thickness made of polymethyl methacrylate with a diamond cutting tool so that light emitting means were formed in parallel in the left-right direction and the front-rear direction on each incident side surface. This light guide plate is 38 mm in the left-right direction, 25 mm in the front-rear direction, 1 mm in thickness, has a transparent portion with a projection length of 3 mm on the incident side surface in the left-right and front-rear directions, and the incident side surface in the left-right direction is located on the front side in the front-rear direction. The incident side surface in the front-rear direction is located on the right side in the left-right direction.

  The light emitting means in the left-right direction has a repetitive structure of prism-like irregularities with a constant pitch of 260 μm, the transmission light reflecting surface facing the incident side has an inclination angle of 43 degrees, and the opposite surface has an inclination angle of 62. The projection width on the lower surface of the transmission light reflecting surface is 10 to 16 μm, and the projection width ratio between the upper surface portion / the lower surface of the prismatic unevenness between the pitches of the prismatic unevenness is 10 times or more.

  Further, the light emitting means in the front-rear direction has a repetitive structure of prismatic irregularities with a constant pitch of 310 μm, the transmission light reflecting surface facing the incident side has an inclination angle of 43 degrees, and the opposite surface has an inclination angle of 62 degrees. The projection width of the transmission light reflecting surface on the lower surface is 9 to 16 μm, and the projection width ratio between the upper surface portion and the lower surface of the prismatic unevenness between the pitches of the prismatic unevenness is 12 times or more.

  Next, green and red light emitting diodes are formed on both the left and right sides of a linear light guide plate having an effective light emission width of 41 mm made of a rectangular parallelepiped having a width of 42 mm, a depth of 2.5 mm, and a thickness of 1.5 mm on the incident side surface in the left-right direction of the light guide plate. A linear light guide plate having an effective light emission width of 28 mm, which is a rectangular parallelepiped having a width of 29 mm, a depth of 2.5 mm, and a thickness of 1.5 mm on the incident side surface in the front-rear direction, arranged one by one and connected to a DC power supply for each color. A surface light source device was obtained by disposing one light emitting diode on each of the front and rear surfaces of the light source 2 and connecting the light source 2 connected to a DC power source.

  Then, a reflective twisted nematic liquid crystal display unit was disposed on the lower surface side of the light guide plate in the surface light source device to obtain a front light type reflective liquid crystal display device. The visual recognition is performed via the upper surface side of the light guide plate on which the light emitting means is formed.

Example 2
The light emitting means in the left-right direction is formed so that the ridge line of the prism-shaped unevenness with respect to the incident side surface in the left-right direction has an inclination angle of 14 degrees to the right, and the light emitting means in the front-rear direction is formed on the incident side surface in the front-rear direction. On the other hand, a light guide plate, a surface light source device, and a reflective liquid crystal display device were obtained in the same manner as in Example 1 except that the ridge line of the prism-shaped unevenness was formed so as to rise forward with an inclination angle of 14 degrees.

  As a result of the inclination of the light emitting means, the projection width of the light emitting means in the left-right direction to the lower surface of the transmission light reflecting surface changes to 10 to 18 μm, and the upper surface portion / prism-shaped unevenness between the pitches of the prismatic unevenness. The projected width ratio with respect to the lower surface changed to 8 times or more. Further, in the light emitting means in the front-rear direction, the projection width on the lower surface of the transmission light reflecting surface changes to 9 to 18 μm, and the projection width ratio on the upper surface portion / prism-shaped uneven surface between the prism-shaped uneven pitches is more than 10 times. changed.

Reference example 1
The surface light source device obtained in Example 2 is disposed with the upper and lower surfaces of the light guide plate reversed, a reflector made of a white polyester film is disposed below the light emitting means forming surface (original upper surface), and light A transmissive twisted nematic liquid crystal display unit was disposed on the light exit surface side (original lower surface side) via a diffusion plate to obtain a backlight type transmissive liquid crystal display device.

Reference example 2
A backlight-type transmissive liquid crystal display device is provided by disposing a silver-deposited reflector on the lower surface side of the surface light source device obtained in Example 2 and a transmissive twisted nematic liquid crystal display unit on the upper surface side. Obtained.

Comparative Example 1
Example except that prism-like irregularities made of isosceles triangles with an inclination angle of 43 degrees are formed in a repeating structure with a constant pitch of 260 μm and light emitting means parallel to the incident side surface in the left-right direction is formed, and the light emitting means in the front-rear direction is omitted. 1 was obtained, a light guide plate, a surface light source device, and a reflective liquid crystal display device were obtained. The light emitting means of the light guide plate had a projection width of 12 μm on its lower surface, and the projection width ratio of the upper surface portion / prism-shaped uneven surface to the lower surface of the prism-shaped unevenness was 8 times or more.

Comparative Example 2
A transmissive liquid crystal display device was obtained according to Example 3 except that the surface light source device according to Comparative Example 1 was used.

Comparative Example 3
A surface light source device and a transmissive liquid crystal display device were obtained in the same manner as in Example 3 except that a light guide plate having a rough surface by sandblasting on one side as a light emitting means was used. In addition, it arrange | positioned so that the rough surface of a light-guide plate may become a lower side.

Comparative Example 4
A transmissive liquid crystal display device was obtained according to Example 4 except that the surface light source device according to Comparative Example 1 was used.

Comparative Example 5
A transmissive liquid crystal display device was obtained according to Example 4 except that the surface light source device according to Comparative Example 3 was used.

Evaluation test 1
In the reflective or transmissive liquid crystal display devices obtained in the examples and comparative examples, the light source 1 or the light source 2 is turned on with no voltage applied to the liquid crystal cell, and the central portion of the device, the incident portion on the lighting side, and the opposing portion thereof The front luminance at was measured with a luminance meter (Topcon, BM7). The results are shown in the following table. The light source 1 is green light.

Front brightness (cd / m ² )
Light source 1 light source 2
Incident part Center part Opposing part Incident part Center part Opposing part
Example 1 23 25 26 13 14 14
Example 2 22 24 26 12 12 14
Reference Example 1 39 34 32 19 20 19
Reference Example 2 35 36 34 17 17 15
Comparative Example 1 26 22 18 15 11 8
Comparative Example 2 45 31 27 22 16 13
Comparative Example 3 30 25 22 17 14 10
Comparative Example 4 39 32 29 20 16 13
Comparative Example 5 25 23 18 12 12 11

Evaluation test 2
As a result of appearance observation of the reflective or transmissive liquid crystal display devices obtained in the examples and comparative examples, a uniform and bright light emission state was obtained over the entire surface in the examples. As a result, the luminance greatly decreased toward the opposite portion and the uniformity of light emission was inferior, and in particular, the diffusion type of Comparative Examples 3 and 5 was greatly inferior in brightness compared to the examples.

In the example, green and red emission colors can be converted by the light source 1, and green and red emission colors can be converted by the light sources 1 and 2, and a uniform and bright emission state can be obtained. Further, the red light emission by the light sources 1 and 2 was superior in brightness to a uniform and brighter light emission state than in the case of a single lamp. However, in the comparative example, it was difficult to see due to uneven light emission. Can be switched between emission colors according to the present invention from the above, it can be seen that a reflective-type liquid crystal display device in front light type having excellent display characteristics.

Plane explanatory diagram of light guide plate example Plane explanatory drawing of another example of light guide plate Side explanatory view of an example of light emitting means in the light guide plate Explanatory drawing of an example of a front light type reflective liquid crystal display device Illustration of an example of a backlight type transmissive liquid crystal display device

Explanation of symbols

1: Light guide plate 11: Upper surface (light emitting means forming surface)
A, B: Light emitting means (A1: Transmission light reflecting surface)
12: Lower surface (light emission surface) 13a, b: Incident side surface 15a, b: Projection part by transparent body 2: Surface light source device (21: Light source)
3: Liquid crystal display unit 31, 33: Polarizing plate 32: Liquid crystal cell 34: Reflective layer 4: Light diffusion layer 5: Reflective layer

Claims (5)

Consists upper and lower surfaces and the plate-like body having at least an incident side surface of the two surfaces thereof made of the side surface between the upper and lower surfaces, with the incident side surface is formed of a left-right direction and the longitudinal direction of the side surface of the plate, each incident on the upper surface 80 μm of prismatic irregularities having light emitting means for emitting incident light from the side surface to the lower surface , the light emitting means having a ridge line in the direction along each incident side surface, which consists of a transmission light reflecting surface and its opposing surface The transmission light reflecting surface has an inclined angle of 30 to 45 degrees with respect to the reference plane of the lower surface, and has an inclined surface with a projection width of 3 to 40 μm with respect to the reference plane. together with the the opposing surface lower surface side of the light guide plate in a surface light source device formed by arranging the light source to the respective incident side surface of the Ru light guide plate name than the inclination angle of 40 degrees or more slopes with respect to the reference plane, the liquid crystal of the reflective layer comprises SE The liquid crystal display device characterized by having. 2. The liquid crystal display device according to claim 1 , wherein the light guide plate includes a light guide plate in which the ridges of the prismatic unevenness in the light emitting means provided for each incident side surface intersect at an angle of 40 degrees or more. 3. The incident side surface of the prism-like unevenness in the light emitting means provided on the incident side surface in the left-right direction is formed by projecting the two incident side surfaces with a transparent body according to claim 1 or 2 . With respect to the incident side surface in the front-rear direction, and the ridge line of the prism-shaped unevenness in the light emitting means provided for the incident side surface in the front-rear direction is referred to the incident side surface in the front-rear direction. A liquid crystal display device using a light guide plate that is inclined in a direction away from the incident side surface side in the left-right direction to the other end side. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal display device uses a surface light source device in which a light source of different color light emission that can be switched on and off is disposed. 5. The liquid crystal display device according to claim 1, wherein the light source is a surface light source device that is a linear light source including a point light source and a linear light guide plate that converts incident light therefrom into a linear light source. .

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