JP2008257259A - Liquid crystal display device and light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device with superior visibility, which is superior in brightness of both transmission and reflection modes, with which no reversal of display is produced, and with which no lowering of contrast due to light leakage is produced. <P>SOLUTION: The liquid crystal display device is constructed by disposing a liquid crystal shutter (4), having a liquid crystal cell (42) and at least a polarizing plate (41, 43) on the upper side of a light guide plate (1) which emits light incident from a light source (2), arranged on an incident side face(13) from a lower face (12) via a light-emitting means formed on an upper face (11), which has a reflecting layer (3) on the lower face side and in which reflected light of the emitted light is transmitted from the upper face, wherein the retardation in the vertical direction is 40 nm or smaller. Accordingly, any change in the state of a linearly polarized light and display unevenness is less apt to occur inside the light guide plate, lowering of the efficiency of using light produced in the reflective mode, such as absorption loss and reflection loss caused by the light guide plate and so on is only slight, and consequently, the brightness substantially comparable to that of a conventional reflective liquid crystal display device is realized and brightness equal to that of a conventional transmissive liquid crystal display device can be realized in the transmission mode, so as to realize superior uniformity of brightness. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device that is excellent in light utilization efficiency and bright and easy to see, and a light guide plate that can be used for forming the liquid crystal display device.

  Reflective and transmissive liquid crystal display devices that can be visually recognized as transmissive liquid crystal display devices in dark areas by adding an illumination device while taking advantage of a reflective liquid crystal display device with low power consumption are being studied. There have been proposed ones using a reflector, a backlight used in a transmissive liquid crystal display device and a front light arranged on the viewing side of a liquid crystal cell.

  However, in a system using a transflective reflector, the light is separated into reflected light and transmitted light by the half mirror effect, so that there is a difficulty that the brightness does not reach that of a reflective or transmissive-only one in any mode. there were. There is also a proposal to improve by using a reflective polarizer that can selectively reflect polarized light and the sum of reflectance and transmittance can exceed 100%, but in order to prevent reversal of display in reflection and transmission and prevention of floating black display. In the transmission mode, the light use efficiency is 50% or less due to absorption by the light absorber disposed in the area, and there is a problem that the display is difficult to see in any mode in the twilight. Even in the front light system, in the transmissive mode, light reciprocates the liquid crystal cell and the like, so that the display is likely to be darker than a normal transmissive liquid crystal display device, and scratches and contamination of the light guide plate are conspicuous as bright spots, There is a problem in that leakage light from the upper surface of the light guide plate lowers the display contrast.

  It is an object of the present invention to develop a liquid crystal display device with good visibility that is excellent in brightness in both reflection and transmission modes, does not cause display inversion, and does not cause a decrease in contrast due to leakage light.

  In the present invention, incident light from a light source arranged on the incident side is emitted from the lower surface through a light emitting means formed on the upper surface, and a reflection layer is provided on the lower surface side so that the reflected light of the emitted light is transmitted from the upper surface. And a liquid crystal display device comprising a liquid crystal cell and a liquid crystal shutter having at least one polarizing plate disposed on the upper surface side of a light guide plate having a phase difference of 40 nm or less in the vertical direction. It is.

  According to the present invention, the structure in which the light guide plate in which the phase difference is made as difficult as possible is arranged between the liquid crystal cell and the reflective layer makes it difficult for the state of the linearly polarized light to change through the polarizing plate, resulting in variations in brightness. Display unevenness due to light and color unevenness is unlikely to occur, and the decrease in light utilization efficiency that occurs in the reflection mode is mild, such as absorption loss or reflection loss due to the light guide plate, so that the brightness is almost comparable to conventional reflective liquid crystal display devices. In the transmissive mode, the same brightness as that of the conventional transmissive liquid crystal display device can be achieved.

  Further, display inversion is not caused by reflection and transmission, and a liquid crystal display device with good visibility can be obtained without causing a decrease in contrast due to leakage light from the light guide plate. Furthermore, by providing a light emitting means on the top surface, the light path in the light guide plate in the transmission mode can be lengthened, the light spread is increased, and the intensity of the bright line can be reduced, thereby preventing moire and improving display uniformity. Advantageously, the reflective layer can be easily placed in close contact with the lower surface of the light guide plate via an adhesive layer or the like to be integrated.

  In addition, in the case of a light guide plate having light emitting means composed of slopes such as prismatic irregularities, it is possible to efficiently form light that is excellent in directivity of reflected light through the slopes and is advantageous for visual recognition in the transmission mode. A brighter display can be obtained, and a brighter display can be obtained by light emission with excellent light use efficiency and excellent uniformity even in the reflection mode with excellent incident efficiency of external light and transmission efficiency after reflection. Further, the occurrence of moire due to the directivity can be suppressed by the oblique arrangement of the light emitting means, and glare in visual perception can be prevented.

  In the above, when the phase difference due to the light guide plate is large, in the reflection mode, the linearly polarized light passing through the polarizing plate of the liquid crystal shutter is elliptically polarized by the phase difference while reciprocating the light guide plate through the reflective layer, and is re-applied to the polarizing plate. When incident, an absorption component is generated, the brightness of the display is lowered, and coloring is caused by wavelength dispersion of the phase difference. Furthermore, if the phase difference varies depending on the light transmission position and transmission direction due to the variation in the phase difference, the brightness varies in that position and direction, causing display unevenness. Coloring in different colors such as brown, dark blue, and blue causes color unevenness, which also causes display unevenness.

  On the other hand, when the light emitting means is provided on the lower surface of the light guide plate, it is necessary to separate and arrange the reflectors from the viewpoint of maintaining the function of the light emitting means, and the structure is complicated by increasing the number of parts and fixing the arrangement. In order to prevent the display from being disturbed due to the generation of wrinkles, a thick support is required and there is a drawback that it becomes heavy.

  Further, in a light guide plate that is a scattering type emitting means such as dots and wrinkled irregularities, the emitted light is emitted at a large angle of about 60 degrees and becomes a transmission mode that is dark and difficult to see in the front (vertical) direction. When the prism sheet is arranged for the purpose of controlling the optical path, light in the reflection mode is scattered, so that most of the light does not contribute and the display becomes very dark. In addition, when a diffusion layer having a strong diffusibility is provided to prevent dots and the like from being clearly seen, incident light in the reflection mode and reflected light from the reflection layer are also scattered, resulting in a dark display.

  The liquid crystal display device according to the present invention emits incident light from a light source disposed on an incident side surface from a lower surface through light emitting means formed on the upper surface, and has a reflective layer on the lower surface side to reflect the emitted light. Is transmitted from the upper surface, and a liquid crystal shutter having a liquid crystal cell and at least one polarizing plate is disposed on the upper surface side of the light guide plate whose top and bottom surface phase difference is 40 nm or less. Can be preferably used. An example thereof is shown in FIG. Reference numeral 1 is a light guide plate, 11 is an upper surface on which the light emitting means is formed, 2 is a light source, 3 is a reflective layer, 4 is a liquid crystal shutter, 41 and 43 are polarizing plates, and 42 is a liquid crystal cell.

  The light guide plate is made of a plate-like material having an upper surface 11, a lower surface 12 opposite to the upper surface 11, and an incident side surface 13 formed between the upper and lower surfaces as shown in FIG. 1, and incident light from the incident side surface is formed on the upper surface 11. The one having a phase difference of 40 nm or less in the vertical direction, which is emitted from the lower surface through the light emitting means, is used.

  As shown in the figure, the light guide plate may be of the same thickness type, or the opposing end 14 facing the incident side surface 13 may be 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 incident efficiency of incident light from the incident side surface on the light emitting means on the upper surface.

  The light emitting means formed on the upper surface of the light guide plate can be formed of any appropriate material that exhibits the above-described emission characteristics. From the point of obtaining illumination light having excellent directivity in the front direction through the reflective layer, a light emitting means having a slope facing the incident side surface, particularly a light emitting means consisting of prismatic irregularities is preferred. The prism-like unevenness can be formed even on a convex portion or a concave portion made of an equilateral surface, but it can be formed by a convex portion or a concave portion made of a short side surface and a long side surface from the viewpoint of light utilization efficiency. preferable. An example of the prismatic unevenness is shown in FIG. 11a is a short side surface and 11b is a long side surface.

More preferable light emitting means, such as the above-mentioned characteristics such as directivity in the front direction, is a repetitive structure of irregularities comprising a slope with an inclination angle of 35 to 45 degrees with respect to a reference plane on the lower surface and a flat surface of 10 degrees or less. In particular, as illustrated in FIG. 2, a short side surface 11 a (θ ₁ ) inclined at a tilt angle of 35 to 45 degrees with respect to the reference plane 12 a of the lower surface 12 from the incident side surface 13 side toward the opposite end 14 side, and It is composed of a prismatic uneven structure having a long side surface 11b (θ ₂ ) having an inclination angle of more than 0 to 10 degrees.

The short side surface 11a formed as a slope inclined downward from the incident side surface to the opposite end side reflects the light incident on the surface out of the incident light from the side surface and supplies it to the lower surface (reflective layer). do. In this case, by setting the inclination angle theta ₁ to 35 to 45 degrees narrow side as illustrated by a broken line arrow in FIG. 3, in the front through the reflective layer 3 reflects good perpendicularity to the lower surface of the transmission light Emission light (illumination light) having excellent directivity can be obtained efficiently. The preferable inclination angle θ ₁ of the short side surface from the viewpoint of directivity to the front is that the total reflection condition based on the refraction according to Snell's law of light transmitted through the light guide plate is generally ± 41.8 degrees. Is 38 to 44 degrees, especially 40 to 43 degrees.

On the other hand, the long side surface is reflected in the reflection mode as illustrated by the broken line arrow in FIG. 4 and the reflected light from the short side surface is inverted through the reflective layer 3 as illustrated by the broken line arrow in FIG. The purpose of this is to allow external light to enter and reflect the light through the reflective layer 3 and transmit it. From this point, the inclination angle θ ₂ of the long side surface with respect to the reference plane 12a on the lower surface is preferably 10 degrees or less. Its amount of inclination theta ₂ increases the optical path changed by the refraction exceeds 10 degrees front direction disadvantageous in view decreases.

The inclination angle θ ₂ of the long side surface may be 0 degree (horizontal plane), but when it is greater than 0 degree, the transmission light incident on the long side surface is reflected and supplied to the short side surface. The transmitted light can be converted into parallel light, and the directivity of the reflected light through the short side surface can be enhanced, which is advantageous for display. The preferable inclination angle θ ₂ of the long side surface is 8 degrees or less, and especially 5 degrees or less, from the viewpoint of increasing the amount of light in the front direction and making the transmitted light parallel.

The long side surface which is preferable from the viewpoint of the function of the long side surface of the light guide plate described above has an angle difference of the inclination angle θ ₂ within 5 degrees, particularly within 4 degrees, particularly within 3 degrees. it is those within one degree of difference between the inclination angle theta ₂ between the nearest long side surface, within 0.3 degrees especially, particularly those set to within 0.1 degrees. The angle difference of the inclination angle theta _2, the inclination angle of the long side surface is assumed to be in the 10 degrees or less as described above. In other words, it is assumed that such a small inclination angle θ ₂ suppresses the deflection of the display image due to refraction during transmission on the long side surface and falls within an allowable value. The purpose is to prevent the optimum viewing direction of the optimized liquid crystal display device from being changed.

  From the viewpoint of obtaining a bright display image, it is preferable to have an excellent incident efficiency of external light and an excellent transmittance or emission efficiency of the display image by the liquid crystal cell. From this point, it is preferable that the projected surface area of the long side surface with respect to the reference plane of the lower surface is 8 times or more, especially 10 times or more, especially 15 times or more of that of the short side surface. Thereby, most of the display image by the liquid crystal cell can be transmitted through the long side surface.

  When the display image is transmitted through the liquid crystal cell, the display image incident on the short side surface is reflected on the incident side surface and does not exit from the upper surface, or is opposite to the display image transmitted on the long side surface based on the normal to the lower surface. The light is deflected and emitted in a significantly different direction on the side, and has little influence on the display image via the long side surface.

  Therefore, it is preferable that the shorter side surface than the above point does not exist extremely with respect to the pixel of the liquid crystal cell. Incidentally, in terms of theory, if the short side surface overlaps the entire surface of the pixel, the display image in the vicinity of the vertical direction through the long side surface is hardly visible. Therefore, in order to prevent unnatural display due to insufficient transmission of display light, etc., the area where the pixel and the short side surface overlap is reduced to ensure sufficient light transmittance through the long side surface. Is preferred.

  In general, the pixel pitch of the liquid crystal cell is 100 to 300 μm, and the short side surface is 40 μm or less based on the projection width of the lower surface with respect to the reference plane in view of the above-mentioned points and the formation of prism-like irregularities. It is preferable that the thickness is 1 to 20 μm, particularly 3 to 15 μm.

  By the way, as the projection width becomes smaller, more advanced technology is required to form the short side surface.If the top of the prism-shaped irregularities has a roundness with a certain radius of curvature, a scattering effect will appear and the display image will be disturbed. It may be a cause. Further, as compared with the point where the coherent length of the fluorescent tube is generally about 20 μm or the like, if the projection width of the short side surface is reduced, diffraction or the like is liable to occur, and the display quality is likely to be deteriorated.

  In addition, it is preferable that the interval between the short side surfaces is larger than the above point, but on the other hand, since the short side surface is a substantial emission function portion of side incident light as described above, if the interval is too wide, In some cases, the illumination becomes sparse and unnatural display may occur. In view of these, it is preferable that the repetitive pitch P of the prismatic unevenness is 50 μm to 1.5 mm as illustrated in FIG. The pitch may be irregular, such as a random pitch or a predetermined or random combination of pitch units, but is generally preferably a constant pitch.

  In the case of a light emitting means composed of prism-shaped irregularities, moire may occur due to interference with the pixels of the liquid crystal cell. Moire can be prevented by adjusting the pitch of the prismatic irregularities, but there is a preferred range for the pitch of the prismatic irregularities as described above. Therefore, a solution in the case where moire occurs in the pitch range becomes a problem.

  In the present invention, a method of preventing moire by forming the prism-shaped irregularities in an inclined state with respect to the reference plane of the incident side surface so that the prism-shaped irregularities can be arranged in an intersecting state with respect to the pixels. In that case, if the inclination angle is too large, the reflection through the short side surface is deflected, and a large deviation occurs 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 increases. The use efficiency is also lowered, and the display quality is likely to be lowered.

  From the above points, the inclination angle of the prism-shaped unevenness with respect to the reference plane of the incident side surface, that is, the ridge line direction of the prism-shaped unevenness should be within ± 35 degrees, in particular within ± 30 degrees, especially within ± 25 degrees. Is preferred. Note that the sign of ± means the direction of inclination with respect to the incident side surface. When the resolution of the liquid crystal cell is low and moire is not generated or when moire can be ignored, it is preferable that the arrangement direction of the prismatic irregularities be parallel to the incident side surface.

  As described above, the light guide plate can have an appropriate form. In the case of a wedge shape or the like, the shape can be determined as appropriate, and an appropriate surface shape such as a straight surface or a curved surface can be obtained. Further, the inclined surface and the prism-shaped unevenness forming the light emitting means may be formed in an appropriate surface form such as a straight surface, a refractive surface, or a curved surface.

  The prism-shaped unevenness may be a combination of unevenness having different shapes in addition to the pitch. Further, the prism-shaped unevenness may be formed as a series of convex portions or concave portions having continuous ridge lines, or formed as intermittent convex portions or concave portions arranged discontinuously in the ridge line direction with a predetermined interval. It may be.

  The shape of the lower surface and the incident side surface of the light guide plate is not particularly limited and may be appropriately determined. In general, a flat lower surface and an incident side surface perpendicular to the lower surface are used. With respect to the incident side surface, for example, the incident light rate can be improved by taking a shape corresponding to the outer periphery of the light source such as a curved concave shape. Furthermore, it can also be set as the incident side surface structure which has the introducing | transducing part interposed between light sources. The introduction portion can have an appropriate shape depending on the light source and the like.

  The light guide plate can be formed of an appropriate material showing transparency according to the wavelength range of the light source. Incidentally, in the visible light region, for example, transparent resins and glasses represented by acrylic resins, polycarbonate resins, epoxy resins and the like can be mentioned. In particular, it is preferable to use a material that does not exhibit birefringence or has a small birefringence, from the viewpoint of forming a light guide plate having a phase difference of 40 nm in the vertical direction.

  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. When used for forming a liquid crystal display device or the like, the general thickness is 5 mm or less, especially 0.1 to 3 mm, especially 0.3 to 2 mm, based on the incident side surface. The light guide plate is formed as a laminated body of parts made of the same or different materials, such as a sheet in which light emitting means (upper surface) such as prismatic unevenness is bonded to a light guide portion that carries light transmission. It does not have to be formed as an integral monolayer of one material.

  From the viewpoint of preventing display unevenness, the preferred phase difference in the upper and lower surface direction of the light guide plate is 35 nm or less, especially 30 nm or less, particularly 25 nm or less, and the variation of the phase difference from place to place is as small as possible. preferable. The phase difference can be reduced by a method of removing internal distortion by a method of annealing an existing light guide plate or the like, and may be achieved by an appropriate method. Note that the above phase difference condition only needs to be satisfied in the range used for the display of the light guide plate, and does not need to be satisfied in the entire surface of the light guide plate, but is satisfied in the entire range in the range used for display. Is necessary. The phase difference is preferably based on light in the visible region, particularly light having a wavelength of 550 nm.

  The light guide plate before the reflective layer is more preferable, such as the point of achieving a bright display, has a total light transmittance of 90% or more, particularly 92% or more of incident light in the vertical direction, particularly vertical incident light from the lower surface to the upper surface, In particular, it is 95% or more and haze is 30% or less, especially 15% or less, especially 10% or less.

  According to the light guide plate of the present invention, the incident light from the upper surface and the lower surface is transmitted better than the lower surface or the upper surface, and the light parallelized using the light is emitted in a direction excellent in perpendicularity advantageous for visual recognition. Various devices such as a liquid crystal display device for both reflection and transmission which can efficiently use light from a light source and maintain a good polarization state and are bright and easy to see and have low power consumption can be formed.

  In the liquid crystal display device for both reflection and transmission, the arrangement of the reflection layer is indispensable in order to achieve the display in the reflection mode. In the present invention, the reflection layer is on the side of the lower surface 12 of the light guide plate 1 as illustrated in FIG. Placed in. Although the reflective layer 3 may be separately disposed on the lower surface of the light guide plate, it is preferable that the reflective layer 3 is tightly integrated with the lower surface as illustrated.

  The reflective layer can be formed of a suitable material according to the conventional art. In particular, for example, a coating layer in which a powder of a highly reflective metal such as aluminum, silver, gold, copper, or chromium or an alloy thereof is contained in a binder resin, and the metal or dielectric multilayer film is vacuum-deposited. A layer formed by an appropriate thin film forming method such as a sputtering method or the like, a reflective sheet in which the coating layer or the attached layer is supported by a substrate made of a film or the like, or a reflective layer made of a metal foil or the like is preferable.

  A reflective layer that is more preferable in terms of prevention of moire due to relaxation of bright line intensity and improvement in display uniformity is one that causes diffuse reflection. Since it is disadvantageous that the diffusion intensity greatly reduces the above-described light directivity, it is preferably about 5 to 15 degrees based on the average diffusion angle, but is not limited thereto. The diffusive reflection layer can be formed by an appropriate method according to the related art, such as a method of roughening the reflection surface.

  The above-described adhesion and integration of the reflective layer to the lower surface of the light guide plate can be performed by a method through an adhesive means such as an adhesive layer or other adhesive layer, or by directly forming the above-described coating layer or attached layer on the lower surface of the light guide plate. An appropriate method such as a method can be used. In that case, it is preferable that the outer surface of the reflective layer is covered and protected from the viewpoint of preventing damage to the reflective surface, oxidation deterioration, and the like. From such a point, the above-described reflection sheet can be preferably used. According to the reflection sheet, the diffusion type reflection layer described above can be easily formed through the roughening of the surface of the film substrate or the like.

  The roughening treatment of the reflective layer and the supporting substrate described above is, for example, a mechanical method such as embossing or buffing, a method of transferring a rough surface shape such as a mold, a chemical treatment method, silica, alumina, A method of containing appropriate particles such as titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and other inorganic particles that may be conductive, and organic particles such as crosslinked or uncrosslinked polymers It can be performed by an appropriate method such as a method of applying a layer.

  When the liquid crystal display device is formed, the light source 2 is disposed on the incident side surface 13 of the light guide plate 1 as illustrated in FIG. As the light source, an appropriate one can be used. For example, a linear light source such as a (cold, hot) cathode tube, a point light source such as a light emitting diode, an array body in which the light source is arranged in a linear or planar shape, or A light source using a device that converts a point light source into a linear light emission state with a constant or irregular interval may be preferably used.

  In the present invention, the light source enables visual recognition in the transmission mode. Therefore, when viewing in the reflection mode, it is not necessary to turn on the light source, so that the light source can be switched on / off. As the switching method, any method can be adopted, and any of the conventional methods can be adopted. The light source can also be arranged in advance as a light guide plate having a light source attached to the light guide plate.

  When forming the liquid crystal display device, a combination body in which appropriate auxiliary means such as a light source holder surrounding the light source is arranged to guide the diverging light from the light source 2 to the incident side surface 13 of the light guide plate 1 as necessary may be used. it can. As the light source holder, a resin sheet or a metal foil provided with a highly reflective metal thin film is generally used. When the light source holder is bonded to the end portion of the light guide plate via an adhesive or the like, the formation of the light emitting means can be omitted for the bonded portion.

  In general, the liquid crystal display device has a transparent electrode (not shown) having a transparent electrode functioning as a liquid crystal shutter as illustrated in FIG. 1 and a driving device associated therewith, polarizing plates 41 and 43, backlights 1 and 2, and reflection. It is formed by appropriately assembling components such as the layer 3 and a compensation phase difference plate as necessary.

  The liquid crystal cell to be used is not particularly limited. For example, when based on the alignment mode of the liquid crystal, a twisted or non-twisted type such as a TN liquid crystal cell, an STN liquid crystal cell, a vertical alignment cell, a HAN cell, or an OCB cell, a guest host type, or a strong An appropriate liquid crystal cell such as a dielectric 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.

  On the other hand, an appropriate polarizing plate can be used, but it can be used for polarization such as an iodine-based or dye-based absorption linear polarizer, for example, in order to obtain a display with a good contrast ratio by incidence of highly linear polarized light. A high degree can be preferably used. The polarizing plate can be provided on both sides of the liquid crystal cell 42 as in the example of FIG. 1, or can be provided only on one side of the liquid crystal cell.

  When forming the liquid crystal display device, for example, an appropriate optical element such as a diffusion plate, an antiglare layer, a protective layer provided on the viewing side, or a retardation plate for compensation provided between the liquid crystal cell and the polarizing plate can be appropriately disposed. . The purpose of the compensation retardation plate is to improve visibility by compensating the wavelength dependence of birefringence.

  The compensation phase difference plate is arranged between the polarizing plate on the viewing side and / or the back side and the liquid crystal cell as necessary, but in the present invention, the light emission characteristics of the light guide plate described above are maintained as much as possible. Therefore, it is preferable that the number of optical layers disposed between the liquid crystal cell and the light guide plate is as small as possible. As the compensation phase difference plate, an appropriate one can be used according to the wavelength region and the like, and it may be formed as a superposed layer of one layer or two or more phase difference layers.

  The visual recognition of the liquid crystal display device according to the present invention is performed through the transmitted light on the long side surface of the light guide plate as described above. Incidentally, in the transmission mode, the light α emitted from the lower surface of the light guide plate 1 is reflected through the reflection layer 3 and transmitted through the long side surface 11b of the light guide plate 1 in the lighting state of the light source as illustrated by the arrow in FIG. A display image (α) is visually recognized through the polarizing plates 43 and 41 and the liquid crystal cell 42.

  On the other hand, in the reflection mode, with the light source turned off, the external light γ passes through the polarizing plates 41 and 43 and the liquid crystal cell 42 and is linearly polarized by the polarizing plate 43 as shown by the arrows in FIG. After being transmitted through the long side surface 11b, the light is reflected through the reflective layer 3 and transmitted through the long side surface 11b of the light guide plate 1 in the same manner as in the transmission mode. The display image (γ) is visually recognized via the polarizing plates 43 and 41 and the liquid crystal cell 42 again.

  In the present invention, optical elements or components such as a light guide plate, a liquid crystal cell, and a polarizing plate forming the above-described liquid crystal display device may be integrally or partially laminated and fixed, or may be easily separated. It may be arranged in a 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 adhesion and adhesion treatment, and the transparent adhesive layer can contain the above-mentioned fine particles and the like to form an adhesive layer exhibiting a diffusion function.

Example 1
The surface of a polymethylmethacrylate plate processed into a predetermined shape in advance was cut with a diamond tool to obtain a light guide plate having an average phase difference of 4.1 nm, a maximum value of 8 nm, and a minimum value of 0 nm. . This has a width of 40 mm, a depth of 25 mm, a thickness of the incident side of 1 mm, and a thickness of the opposing end of 0.6 mm. The upper and lower surfaces are flat, and the upper surface has prism-like irregularities parallel to the incident side at a pitch of 210 μm. The inclination angle of the short side surface is changed in the range of 42.5 to 43 degrees, the inclination angle of the long side surface is changed in the range of 1.8 to 3.5 degrees, and the inclination angle change of the nearest long side surface is 0.1. The projected width of the short side surface to the lower surface was 10 to 16 μm, and the projected area ratio of the long side surface / short side surface to the lower surface was 12 times or more. The light emitting means was formed at a position 2 mm away from the incident side surface.

  A cold cathode tube (made by Harrison Electric Co., Ltd.) having a diameter of 2.0 mm is arranged on the incident side surface of the light guide plate, and the light source holder made of a white lamp reflection sheet surrounds the light guide plate with its upper and lower end surfaces in close contact with each other. The inverter and DC power supply are connected to the cold cathode tube, a silver reflector bonded to an acrylic plate is installed on the lower surface of the light guide plate, and a normally white black and white TN liquid crystal cell is disposed on the upper surface of the light guide plate. A display device was obtained. The light source can be switched on / off by turning on / off the DC power supply. The silver reflector is a diffusion type in which a silver vapor deposition layer is formed on a mat-treated film substrate, and the surface of the vapor deposition layer is covered and protected with a transparent resin layer.

Example 2
A liquid crystal display device was obtained in the same manner as in Example 1 except that the silver reflecting plate was adhered to the lower surface of the light guide plate through the reflecting surface with an adhesive layer.

Example 3
A liquid crystal display according to Example 1 except that a reflective sheet having a specular silver reflective surface was used in place of the silver reflective plate, and the adhesive surface was mixed with a silicone resin on the lower surface of the light guide plate via the reflective surface. Got the device.

Example 4
Using a mold having a predetermined form, it was heated to 78 ° C., filled with polymethylmethacrylate heated and melted at 260 ° C., molded under cooling, and averaged in the form of phase difference according to Example 1 A light guide plate having a maximum value of 25 nm and a minimum value of 5 nm was obtained at 13.0 nm, and a liquid crystal display device was obtained using the light guide plate. The mold was formed such that the distance from the runner to the gate was 40 mm, and the resin injection gate having a width of 15 mm and a thickness of 0.6 mm was positioned at the center of the opposite end of the light guide plate.

Comparative Example 1
The pitch of the prismatic unevenness is 2 mm, the inclination angle of the short side surface is 42.6 to 42.8 degrees, the inclination angle of the long side surface is 1.9 to 3.6 degrees, and the projection width to the lower surface of the short side surface is 100 The average phase difference is 65.6 nm, the maximum value is 70 nm, and the minimum value is 60 nm in the same manner as in Example 1 except that the projected area ratio to the lower surface of the long side surface / short side surface is 11 times or more. A light plate was obtained and used to obtain a liquid crystal display device.

Comparative Example 2
The average value of the phase difference is 37.2 nm and the maximum value according to Example 4 except that a die with a runner-to-gate distance of 7 mm, a resin injection gate width of 5 mm, and a thickness of 0.3 mm is used. A light guide plate having a minimum value of 85 nm and a minimum value of 20 nm was obtained, and a liquid crystal display device was obtained using the light guide plate.

Evaluation Test Phase Difference For the light guide plates obtained in Examples 1 and 4 and Comparative Examples 1 and 2, the phase difference in the vertical direction was examined. The upper side corresponds to the incident side surface. The measurement is based on the Cellnamon method in which a light source, a sample, an optical element, and a detector are arranged on the optical path in consideration of the deflection of the optical path through the light emitting means, and light having a wavelength of 632.8 nm by a helium-neon laser is applied to the light source. It was used for a total of nine points on both ends of the four sides and the central portion thereof, and the entire central portion along the inner 5 mm position around the light guide plate. The above average and maximum / minimum values are based on the measurement results.

The results are shown in Table 1.

  From Table 1, in Examples 1 and 4, the conditions of a phase difference of 40 nm or less were satisfied in the entire range used for display, but in Comparative Examples 1 and 2, particularly Comparative Example 2, it was a part of the conditions. You can see that you are not satisfied.

Colorability The light guide plates obtained in Examples 1 and 4 and Comparative Examples 1 and 2 were placed between a light diffusing reflector and a polarizing plate, and the colorability was examined. According to this test, the phase difference in the direction parallel to the axial direction of the polarizing plate is not affected, but the phase difference in the direction different from that acts to color the reflected light. The coloring due to the phase difference in the different direction changes from an extremely light brown color (having a high reflectance) to a dark color according to the magnitude of the phase difference and changes from amber to blue.

  As a result, in Example 1, almost colorless and transparent, and the coloring was not visually recognized. In Example 4, the generation of a phase difference radially was observed from the gate portion, but the color was almost colorless indicating that the phase difference was small. It was near brown. On the other hand, in Comparative Example 1, the entire surface is colored brown, and in Comparative Example 2, when the polarizing plate is rotated with a clear brown color at the gate, the color changes radially, and a phase difference occurs radially from the gate. In addition, a dark blue color having a phase difference of about 140 nm was observed in the vicinity of the gate.

Luminance The front luminance in the white display state in the transmissive mode and the reflective mode of the liquid crystal display devices obtained in Examples and Comparative Examples was examined using a luminance meter (Topcon, BM7). The transmission mode was evaluated by turning on the light source in the dark room, and the reflection mode by turning off the light source in the dark room, placing a ring illumination device at a position 10 cm above the center of the device, and illuminating it.

The results are shown in Table 2.

  From Table 2, it can be seen that, in the reflection mode, the brightness of Comparative Examples 1 and 2 is lower than that of the Example. In addition, in the examples, uniform display was obtained by observation under room lighting in a non-lighting and non-operating state of the liquid crystal, but in Comparative Example 2, it was dark and colored and uneven in the periphery of the gate portion. It was a display. Moreover, in the comparative example 1, the whole screen was dark and the light brown coloring was recognized compared with the Example.

  On the other hand, in Example 1, when the reflector was intentionally placed with a wrinkle or nick without being reinforced with an acrylic plate, the wrinkle or the like was clearly recognized in both the reflection and transmission modes, and visibility was lowered. When the reflection plate was bonded to the light guide plate as in Examples 2 to 4, no wrinkles or nicks were generated, and a good display was always obtained.

  As described above, in the embodiment, a light source can be switched on / off by turning on / off the power source, and a liquid crystal display device having good display characteristics in both transmission and reflection modes has been realized. It can be seen that the power consumption can be saved and the battery usage time of the portable display device can be greatly extended.

Cross-sectional view of an example of a liquid crystal display device Side view of light emitting means in light guide plate Explanatory drawing of visual recognition state by transmission mode Explanatory drawing of visual recognition state by reflection mode

Explanation of symbols

1: Light guide plate 11: Top surface
11a: short side surface 11b: long side surface 12: bottom surface 13: incident side surface 2: light source 3: reflection layer 4: liquid crystal shutter 41, 43: polarizing plate 42: liquid crystal cell

Claims (20)

Incident light from a light source arranged on the incident side surface is emitted from the lower surface through a light emitting means formed on the upper surface, and a reflection layer is provided on the lower surface side so that the reflected light of the emitted light is transmitted from the upper surface. A liquid crystal display device comprising: a liquid crystal shutter having a liquid crystal cell and at least one polarizing plate disposed on an upper surface side of a light guide plate having a retardation in the lower surface direction of 40 nm or less. 2. The liquid crystal display device according to claim 1, wherein the light source arranged on the incident side surface of the light guide plate can be switched on and off. 3. The light guide plate according to claim 1, wherein the light guide plate has an upper surface facing the incident side surface and an inclined angle that is inclined at an angle of 35 to 45 degrees with respect to the reference plane of the lower surface and the reference plane has an angle of 10 degrees or less. And a light emitting means comprising at least a flat surface whose projected area with respect to the reference plane is at least eight times that of the inclined surface. In Claims 1-3, the light emission means on the upper surface of the light guide plate has a repeating structure of 50 μm to 1.5 mm pitch of continuous or discontinuous prismatic irregularities composed of a short side surface and a long side surface, and the short side surface is It is composed of an inclined surface that is inclined downward from the incident side surface to the opposite end side at an inclination angle of 35 to 45 degrees with respect to the reference plane of the lower surface, and the long side surface has an inclination angle range of more than 0 to 10 degrees with respect to the reference plane And the angle difference between the entire long side surfaces is within 1 degree, and the projected area with respect to the reference plane is more than 8 times that of the short side surface. A liquid crystal display device. 5. The liquid crystal display device according to claim 4, wherein the repetitive pitch of the prismatic irregularities forming the light emitting means on the upper surface of the light guide plate is constant. 6. The liquid crystal display device according to claim 4, wherein a projection width of the short side surface of the prism-shaped unevenness forming the light emitting means on the upper surface of the light guide plate with respect to the reference plane is 40 μm or less. 7. The liquid crystal display device according to claim 4, wherein the ridge line direction of the prismatic irregularities forming the light emitting means on the upper surface of the light guide plate is within ± 35 degrees with respect to the reference plane of the incident side surface. 8. The liquid crystal display device according to claim 1, wherein the light guide plate transmits incident light from the lower surface from the upper surface with a total light transmittance of 90% or more. 9. The liquid crystal display device according to claim 1, wherein the reflective layer on the lower surface side of the light guide plate is made of gold, silver, aluminum, or a dielectric multilayer film. The liquid crystal display device according to claim 1, wherein the reflection layer on the lower surface side of the light guide plate is closely integrated with the lower surface of the light guide plate. 11. The liquid crystal display device according to claim 1, wherein the reflection layer on the lower surface side of the light guide plate diffuses and reflects light. Incident light from the incident side surface is emitted from the lower surface through a light emitting means formed on the upper surface, and a reflection layer is integrally formed on the lower surface, and the reflected light of the emitted light is transmitted from the upper surface, and its upper and lower surface directions And a crossing angle between the reference plane and the inclined plane that faces the incident side surface and is inclined at an angle of 35 to 45 degrees with respect to the reference plane on the lower surface. And a flat surface having a projected area with respect to the reference plane and not less than 8 times that of the inclined surface. 13. The light emitting means according to claim 12, wherein the light emitting means has a repeating structure of continuous or discontinuous prism-like irregularities having a short side surface and a long side surface and a pitch of 50 μm to 1.5 mm, and the short side surface is relative to a reference plane on the lower surface. The long side surface has an inclination angle range of more than 0 to 10 degrees with respect to the reference plane, and the entire surface thereof is inclined with an inclination angle of 35 to 45 degrees. A light guide plate comprising an inclined surface having an angle difference of 5 degrees or less, an inclination angle difference between nearest long side surfaces of 1 degree or less, and a projected area with respect to the reference plane being at least 8 times that of a short side surface. 14. The light guide plate according to claim 13, wherein the repetition pitch of the prismatic irregularities forming the light emitting means is constant. The light guide plate according to claim 13 or 14, wherein a projection width of the short side surface of the prism-shaped unevenness forming the light emitting means with respect to the reference plane is 40 µm or less. 16. The light guide plate according to claim 13, wherein the ridge line direction of the prismatic irregularities forming the light emitting means is within ± 35 degrees with respect to the reference plane of the incident side surface. 17. The light guide plate according to claim 12, wherein the light is transmitted with a total light transmittance of 90% or more from the upper surface when light is incident from the lower surface without the reflective layer. 18. The light guide plate according to claim 12, wherein the reflective layer integrated on the lower surface is made of gold, silver, aluminum, or a dielectric multilayer film. The light guide plate according to claim 12, wherein the reflective layer integrated on the lower surface is bonded via the adhesive layer in a state of being supported by the film base material. The light guide plate according to claim 12, wherein the reflective layer diffuses and reflects light.

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