JP2019164386A - Liquid crystal display device - Google Patents

Abstract

To provide a liquid crystal display device excellent in changeover performance between a wide viewing angle and a narrow viewing angle, and having excellent image quality.SOLUTION: A liquid crystal display device includes: a liquid crystal panel; viewing angle control means; a prism sheet; and a light guide plate in this order from a visible side. The prism sheet includes a projection part on a side opposite to the visible side. The viewing angle control means changes a transmission state of light from a light source to control broadness and narrowness of a viewing angle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid crystal display device.

  In general, a liquid crystal display device is required to have a wide viewing angle when used in a scene where the viewer's position is not fixed and the viewer is visually recognized from any angle (for example, an electronic advertisement, a commonly used television, a personal computer, etc.). In order to realize a wide viewing angle, various techniques using a diffusion sheet, a prism sheet, a wide viewing angle liquid crystal panel, a wide viewing angle polarizing plate, and the like have been studied. On the other hand, when the position of the viewer is limited to a narrow range, a liquid crystal display device capable of displaying an image with a narrow viewing angle (for example, a mobile phone or a public place) for the purpose of preventing peeping or the like. There is also a need for liquid crystal display devices (used in notebook computers, automatic teller machines, vehicle seat monitors, etc.).

  As a method of narrowing the viewing angle, a technique of arranging a louver film on the viewing side surface of a liquid crystal display device is known (for example, Patent Document 1). The louver film can control the viewing angle by blocking a part of incident light, particularly light having a large incident angle. However, when a louver film is used in a liquid crystal display device, there is a problem that moire, streaks, hue change, and the like occur and the image quality is significantly lowered. Moreover, there is a problem that the louver film is expensive. Further, there is a demand for a liquid crystal display device that can switch between a wide viewing angle and a narrow viewing angle depending on the situation, and further improvement is required for such switching performance.

Special table 2009-528567 gazette

  The present invention has been made in order to solve the above-described conventional problems, and an object of the present invention is to provide a liquid crystal display excellent in switching performance between a wide viewing angle and a narrow viewing angle and capable of realizing excellent image quality. To provide an apparatus.

The liquid crystal display device of the present invention comprises a liquid crystal panel, a viewing angle control means, a prism sheet, and a light guide plate in this order from the viewing side, and the prism sheet has a convex portion on the side opposite to the viewing side. The viewing angle control means controls the width of the viewing angle by changing the transmission state of light from the light source.
In one embodiment, the liquid crystal display device further includes a visible light absorber having a luminous reflectance of 30% or less on the side opposite to the viewing side of the light guide plate.
In one embodiment, the liquid crystal display device further includes a reflective polarizer between the liquid crystal panel and the prism sheet.
In one embodiment, the light guide plate is a light guide plate having prism shapes formed on the back side and the viewing side.

  According to the present invention, by providing the prism sheet that is convex on the side opposite to the viewing side (back side) and the specific viewing angle control means, the switching performance between the wide viewing angle and the narrow viewing angle is excellent, and A liquid crystal display device capable of realizing excellent image quality can be provided. More specifically, since the prism sheet arranged so as to be convex on the back side is excellent in the light condensing effect, the viewing angle can be favorably narrowed when the narrow viewing angle is set. As a result, it is possible to increase the difference in characteristics between setting the wide viewing angle and setting the narrow viewing angle, thereby realizing a liquid crystal display device with excellent switching performance between the wide viewing angle and the narrow viewing angle. Can do. In one embodiment, the liquid crystal display device further includes a visible light absorber between the light guide plate and the backlight unit, so that the viewing angle can be further narrowed when the narrow viewing angle is set. . As a result, it is possible to realize a liquid crystal display device that is further excellent in switching performance between a wide viewing angle and a narrow viewing angle.

1 is a schematic cross-sectional view of a liquid crystal display device according to an embodiment of the present invention. In the liquid crystal display device by one Embodiment of this invention, it is a schematic diagram explaining the direction of the polar angle of 40 degrees in the at least 1 direction in an output surface. (A) And (b) is a schematic sectional drawing explaining the viewing angle control means used for the liquid crystal display device by one Embodiment of this invention. It is a schematic perspective view explaining the reflective polarizer which can be used for the liquid crystal display device by one Embodiment of this invention. It is a schematic perspective view explaining the prism sheet used for the liquid crystal display device by one Embodiment of this invention. It is a graph which shows the polar angle dependence (standardized) of the brightness | luminance of the up-down direction and the left-right direction in the liquid crystal display device of Example 1 and Reference Example 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

A. 1 is a schematic sectional view of a liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device 100 includes the liquid crystal panel 10, the viewing angle control means 60, the prism sheet 20, and the light guide plate 30 in this order from the viewing side. The liquid crystal display device 100 may further include a reflective polarizer 70 and / or a visible light absorber 40 as shown in the example as needed. Note that the arrangement order of the reflective polarizer 70 and the viewing angle control means 60 may be opposite to that in the illustrated example. The liquid crystal panel 10 is typically disposed on the liquid crystal cell 12, the viewing side polarizing plate 11 disposed on the viewing side of the liquid crystal cell 12, and the opposite side (back side) of the viewing side of the liquid crystal cell. The back side polarizing plate 13 is provided. The prism sheet 20 has a convex portion on the back side. In one embodiment, the light guide plate 30 and, if present, the visible light absorber 40 can be members that constitute a backlight unit. In practice, the backlight unit may further comprise any suitable other member. For example, the backlight unit may further include a light source 50. In the present invention, an edge light type backlight unit having a light source on a side surface is preferably used. The liquid crystal display device may further include any appropriate other member.

  In the present invention, the viewing angle control means 60 controls the width of the viewing angle by changing the transmission state of light from the light source. The configuration of the viewing angle control means will be specifically described in the section C described later. When setting a narrow viewing angle, a prism sheet having a convex portion on the back side has a function of condensing incident light, and a liquid crystal display device with a narrow viewing angle can be realized. Furthermore, in one embodiment, the light collecting function of the prism sheet is obtained by arranging a visible light absorber instead of the reflector provided in the conventional liquid crystal display device (substantially the backlight unit). Can be increased. As a result, it is possible to realize a very good narrow viewing angle, and to realize an image quality far superior to conventional liquid crystal display devices when setting a narrow viewing angle. Such an effect is considered to be obtained by disposing a visible light absorber to suppress reflections that occur remarkably in a reflection plate conventionally provided. In general, a prism sheet having a convex portion on the viewing side is also known as an optical member having a condensing function. However, even if a prism sheet having a convex portion on the viewing side and a visible light absorber are combined, the prism sheet The light collecting function of the sheet cannot be enhanced. This is because the prism sheet having a convex portion on the viewing side easily reflects the light from the light guide plate to the back side, so that the light reflected on the back side is reused in order to secure the amount of emitted light and manifest the light collecting function. This is because a reflector that can reflect the light is indispensable.

  When the narrow viewing angle is set, the liquid crystal display device of the present invention has a luminance at a polar angle of 40 ° (directions b and b ′ in FIG. 2) in at least one direction (for example, direction A in FIG. 2) in the emission surface. However, it is preferably 5% or less, more preferably 3% or less, and 1% to 3% with respect to the luminance in the front direction (polar angle 0 °, direction a in FIG. 2). Is particularly preferred. Note that the direction within the exit surface where the luminance at the polar angle of 40 ° of the emitted light is preferably within the above range is a direction in which a reduction in the viewing angle is desired, for example, a direction in which a peep prevention effect is desired to be expressed. It is. The half-value angle (the sum of both sides) of the maximum luminance is preferably less than 20 °. Further, when the prism sheet is composed of columnar unit prisms as will be described later, the direction may be a direction substantially perpendicular to the longitudinal direction (ridge line direction) of the unit prism. If the brightness at the narrow viewing angle setting is in such a range, for example, a liquid crystal display device having a preferable viewing angle characteristic can be obtained as a liquid crystal display device having a peeping prevention function. On the other hand, when the wide viewing angle is set, the luminance at the polar angle of 40 ° in the above direction is preferably 5% or more with respect to the luminance in the front direction, and more than twice that when the narrow viewing angle is set. It is more preferable that the ratio is not more than twice. Moreover, it is preferable that the half-value angle (the sum of both sides) of the maximum luminance is 20 ° or more. If the luminance at the time of setting a wide viewing angle is in such a range, it is possible to ensure practically acceptable visibility and wide viewing angle characteristics in a situation where it is not necessary to consider peeping or the like. If the brightness at the time of setting the narrow viewing angle and the setting of the wide viewing angle is in the above range, a liquid crystal display device excellent in switching performance between the wide viewing angle and the narrow viewing angle can be realized. In this specification, the polar angle refers to an angle formed between the normal direction (front direction) of the liquid crystal display device and the light emitted from the liquid crystal display device.

B. Liquid crystal panel The liquid crystal panel 10 typically includes a liquid crystal cell 12, a viewing side polarizing plate 11 disposed on the viewing side of the liquid crystal cell, and a back side polarizing plate 13 disposed on the back side of the liquid crystal cell. With. The viewing-side polarizing plate 11 and the back-side polarizing plate 13 can be arranged such that their absorption axes are substantially orthogonal or parallel.

B-1. Liquid Crystal Cell The liquid crystal cell 12 has a pair of substrates 1 and 1 ′ and a liquid crystal layer 2 as a display medium sandwiched between the substrates. In a general configuration, a color filter and a black matrix are provided on one substrate, a switching element that controls the electro-optical characteristics of the liquid crystal on the other substrate, and a scanning line that supplies a gate signal to the switching element. In addition, a signal line for supplying a source signal, a pixel electrode, and a counter electrode are provided. The distance between the substrates (cell gap) can be controlled by a spacer or the like. For example, an alignment film made of polyimide can be provided on the side of the substrate in contact with the liquid crystal layer.

  In one embodiment, the liquid crystal layer includes liquid crystal molecules that are aligned in a homogeneous alignment in the absence of an electric field. Such a liquid crystal layer (as a result, a liquid crystal cell) typically exhibits a three-dimensional refractive index of nx> ny = nz. In this specification, ny = nz includes not only the case where ny and nz are completely the same, but also the case where ny and nz are substantially the same. Typical examples of drive modes using such a liquid crystal layer exhibiting a three-dimensional refractive index include an in-plane switching (IPS) mode and a fringe field switching (FFS) mode. The IPS mode includes a super-in-plane switching (S-IPS) mode and an advanced super-in-plane switching (AS-IPS) mode using a V-shaped electrode or a zigzag electrode. The FFS mode includes an advanced fringe field switching (A-FFS) mode and an ultra fringe field switching (U-FFS) mode employing a V-shaped electrode or a zigzag electrode.

  In another embodiment, the liquid crystal layer includes liquid crystal molecules aligned in a homeotropic alignment in the absence of an electric field. Such a liquid crystal layer (as a result, a liquid crystal cell) typically exhibits a three-dimensional refractive index of nz> nx = ny. An example of a drive mode using liquid crystal molecules aligned in a homeotropic alignment in the absence of an electric field is a vertical alignment (VA) mode. The VA mode includes a multi-domain VA (MVA) mode.

B-2. Polarizing plate A polarizing plate typically includes a polarizer and protective layers disposed on both sides of the polarizer. The polarizer is typically an absorptive polarizer.

  The transmittance at a wavelength of 589 nm (also referred to as single transmittance) of the absorptive polarizer is preferably 41% or more, more preferably 42% or more. Note that the theoretical upper limit of the single transmittance is 50%. The degree of polarization is preferably 99.5% to 100%, more preferably 99.9% to 100%. If it is said range, the contrast of a front direction can be made still higher when it uses for a liquid crystal display device.

  Any appropriate polarizer is used as the polarizer. For example, dichroic substances such as iodine and dichroic dyes are adsorbed on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And polyene-based oriented films such as a uniaxially stretched product, a polyvinyl alcohol dehydrated product and a polyvinyl chloride dehydrochlorinated product. Among these, a polarizer obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol film and uniaxially stretching is particularly preferable because of its high polarization dichroic ratio. The thickness of the polarizer is preferably 0.5 μm to 80 μm.

  Polarizers that are uniaxially stretched by adsorbing iodine to a polyvinyl alcohol film are typically produced by immersing polyvinyl alcohol in an aqueous solution of iodine and stretching it to 3 to 7 times its original length. Is done. Stretching may be performed after dyeing, may be performed while dyeing, or may be performed after stretching. In addition to stretching and dyeing, for example, treatments such as swelling, crosslinking, adjustment, washing with water, and drying are performed.

  Any appropriate film is used as the protective layer. Specific examples of the material that is the main component of such a film include cellulose resins such as triacetyl cellulose (TAC), (meth) acrylic, polyester, polyvinyl alcohol, polycarbonate, polyamide, and polyimide. And transparent resins such as polyethersulfone, polysulfone, polystyrene, polynorbornene, polyolefin, and acetate. In addition, thermosetting resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone, or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Moreover, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in the side chain For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film may be an extruded product of the resin composition, for example.

C. Viewing Angle Control Means FIG. 3A is a schematic cross-sectional view illustrating a state when setting a wide viewing angle in an example of the viewing angle control means used in the liquid crystal display device according to one embodiment of the present invention. (B) is a schematic sectional drawing explaining the state at the time of the narrow viewing angle setting in the said viewing angle control means. The viewing angle control means 60 has an upper (viewing side) transparent electrode layer 62a and a lower (back side) transparent electrode layer 62b, and a transmission state variable layer 64 disposed therebetween. The transmission state variable layer 64 includes a polymer matrix 66 and a liquid crystal (typically, a low molecular nematic liquid crystal) 68 dispersed in the polymer matrix 66. In the drawing, the liquid crystal 68 is described as a domain for easy viewing, but such a boundary may or may not be formed.

  When the wide viewing angle is set, the liquid crystal 68 is randomly oriented in the polymer matrix 66 as shown in FIG. 3A by turning off the power supply (not shown) of the viewing angle control means 60. Therefore, the light emitted from the light source is scattered by the liquid crystal when passing through the viewing angle control means 60. As a result, the viewing angle becomes wide, and an image with high brightness can be obtained even when viewed from an oblique direction.

  At the time of setting the narrow viewing angle, the power of the viewing angle control means 60 is turned on and a predetermined voltage is applied between the upper transparent electrode layer 62a and the lower transparent electrode layer 62b, so that the liquid crystal as shown in FIG. 68 is oriented in the polymer matrix 66 in the vertical direction. Therefore, the light emitted from the light source passes through the viewing angle control means 60 as it is (while maintaining the light collection state). As a result, the front luminance is increased and the viewing angle is narrowed.

  By adjusting the voltage applied between the upper transparent electrode layer 62a and the lower transparent electrode layer 62b, the alignment state of the liquid crystal (as a result, the scattering state of light from the light source) can be changed, and the front luminance and The viewing angle characteristic can be adjusted to a desired balance.

  The viewing angle control means is not limited to the illustrated example, and any appropriate configuration can be adopted as long as the effects of the present invention can be obtained. For example, the transmission state variable layer may be composed of only low-molecular liquid crystals or may be composed of only polymer liquid crystals.

D. Reflective Polarizer As described above, the reflective polarizer 70 may be disposed in the liquid crystal display device 100. The reflective polarizer 70 can be disposed, for example, between the liquid crystal panel 10 and the prism sheet 20, typically between the viewing angle control means 60 and the prism sheet 20. The reflective polarizer 70 has a function of transmitting polarized light in a specific polarization state (polarization direction) and reflecting light in other polarization states. The reflective polarizer 70 may be a linearly polarized light separation type or a circularly polarized light separation type. Hereinafter, as an example, a linearly polarized light separation type reflective polarizer will be described. Examples of the circularly polarized light separation type reflective polarizer include a laminate of a film in which cholesteric liquid crystal is fixed and a λ / 4 plate.

  FIG. 4 is a schematic perspective view of an example of a reflective polarizer. The reflective polarizer is a multilayer laminate in which layers A having birefringence and layers B having substantially no birefringence are alternately laminated. For example, the total number of layers in such a multilayer stack can be 50-1000. In the illustrated example, the refractive index nx in the x-axis direction of the A layer is larger than the refractive index ny in the y-axis direction, and the refractive index nx in the x-axis direction and the refractive index ny in the y-axis direction of the B layer are substantially the same. is there. Accordingly, the difference in refractive index between the A layer and the B layer is large in the x-axis direction and is substantially zero in the y-axis direction. As a result, the x-axis direction becomes the reflection axis, and the y-axis direction becomes the transmission axis. The difference in refractive index between the A layer and the B layer in the x-axis direction is preferably 0.2 to 0.3. The x-axis direction corresponds to the extending direction of the reflective polarizer in the manufacturing method described later.

  The A layer is preferably made of a material that exhibits birefringence by stretching. Representative examples of such materials include naphthalene dicarboxylic acid polyesters (for example, polyethylene naphthalate), polycarbonates, and acrylic resins (for example, polymethyl methacrylate). Polyethylene naphthalate is preferred. The B layer is preferably made of a material that does not substantially exhibit birefringence even when stretched. A typical example of such a material is a copolyester of naphthalenedicarboxylic acid and terephthalic acid.

  The reflective polarizer transmits light having a first polarization direction (for example, p-wave) at the interface between the A layer and the B layer, and has a second polarization direction orthogonal to the first polarization direction. Reflects light (eg, s-wave). The reflected light is partially transmitted as light having the first polarization direction and partially reflected as light having the second polarization direction at the interface between the A layer and the B layer. The light utilization efficiency can be increased by repeating such reflection and transmission many times inside the reflective polarizer.

  In one embodiment, as shown in FIG. 4, the reflective polarizer may include a reflective layer R as the outermost layer on the side opposite to the viewing side. By providing the reflective layer R, it is possible to further use the light that has not been finally used and has returned to the outermost part of the reflective polarizer, so that the light use efficiency can be further increased. The reflective layer R typically exhibits a reflective function due to the multilayer structure of the polyester resin layer.

  The total thickness of the reflective polarizer can be appropriately set according to the purpose, the total number of layers included in the reflective polarizer, and the like. The total thickness of the reflective polarizer is preferably 10 μm to 150 μm.

  In one embodiment, in the liquid crystal display device 100, the reflective polarizer 70 is disposed so as to transmit light having a polarization direction parallel to the transmission axis of the back-side polarizing plate 13. That is, the reflective polarizer 70 is arranged so that its transmission axis is substantially parallel to the transmission axis direction of the back-side polarizing plate 13. By setting it as such a structure, the light absorbed by the back side polarizing plate 13 can be reused, utilization efficiency can further be improved, and a brightness | luminance can also be improved.

  Reflective polarizers can typically be made by combining coextrusion and transverse stretching. Coextrusion can be performed in any suitable manner. For example, a feed block method or a multi-manifold method may be used. For example, the material constituting the A layer and the material constituting the B layer are extruded in a feed block, and then multilayered using a multiplier. Such a multi-layer apparatus is known to those skilled in the art. Next, the obtained long multilayer laminate is typically stretched in a direction (TD) orthogonal to the transport direction. The material constituting the A layer (for example, polyethylene naphthalate) increases the refractive index only in the stretching direction due to the transverse stretching, and as a result, develops birefringence. The refractive index of the material constituting the B layer (for example, a copolyester of naphthalenedicarboxylic acid and terephthalic acid) does not increase in any direction even by the transverse stretching. As a result, a reflective polarizer having a reflection axis in the stretching direction (TD) and a transmission axis in the transport direction (MD) can be obtained (TD corresponds to the x-axis direction in FIG. 4 and MD is the y-axis). Corresponding to the direction). In addition, extending | stretching operation can be performed using arbitrary appropriate apparatuses.

  As the reflective polarizer, for example, the one described in JP-T-9-507308 can be used.

E. Prism Sheet FIG. 5 is a schematic perspective view illustrating a prism sheet used in the liquid crystal display device according to one embodiment of the present invention. The prism sheet 20 typically includes a base material portion 21 and a prism portion 22. In addition, you may abbreviate | omit the base material part 21 according to an adjacent member.

  The prism sheet 20 can be bonded to an adjacent member via any appropriate adhesive layer (for example, an adhesive layer or an adhesive layer: not shown).

E-1. Prism Unit In one embodiment, the prism sheet 20 (substantially, the prism unit 22) has a plurality of convex portions on the opposite side (back side) to the viewing side, as shown in FIGS. Unit prisms 23 are arranged in parallel. By disposing the convex portion of the prism sheet 20 toward the back side, the light transmitted through the prism sheet 20 is easily collected. Moreover, if the convex part of the prism sheet 20 is arranged toward the back side, the light reflected without entering the prism sheet is less and the luminance is higher than when the convex part is arranged toward the viewing side. A liquid crystal display device can be obtained.

  Preferably, the unit prism 23 is columnar. The prism sheet composed of columnar unit prisms collects transmitted light in the unit prism arrangement direction X, that is, in a direction substantially orthogonal to the longitudinal direction (ridge line direction) of the unit prisms. As the cross-sectional shape of the unit prism 23, any appropriate shape can be adopted as long as the effects of the present invention can be obtained. The unit prism 23 may have a triangular shape (that is, the unit prism has a triangular prism shape) in a cross section parallel to the arrangement direction and parallel to the thickness direction, or other shape (for example, one of the triangles). Alternatively, both of the slopes may have a plurality of flat surfaces having different inclination angles. The triangular shape may be a shape that is asymmetric with respect to a straight line that passes through the vertex of the unit prism and is orthogonal to the sheet surface (for example, an unequal triangular shape), or a shape that is symmetric with respect to the straight line (for example, two An equilateral triangle). Furthermore, the apex of the unit prism may be a chamfered curved surface, or may be cut to have a flat tip at a tip, and may have a trapezoidal cross section. The detailed shape of the unit prism can be appropriately set according to the purpose. For example, as the unit prism, the configuration described in JP-A-11-84111 can be adopted. In this specification, the expressions “substantially orthogonal” and “substantially orthogonal” include the case where the angle between the two directions is 90 ° ± 10 °, preferably 90 ° ± 7 °, The angle is preferably 90 ° ± 5 °. The expressions “substantially parallel” and “substantially parallel” include the case where the angle between two directions is 0 ° ± 10 °, preferably 0 ° ± 7 °, more preferably 0 ° ± 5 °. Further, in the present specification, the term “orthogonal” or “parallel” may include a substantially orthogonal state or a substantially parallel state.

  Preferably, the longitudinal direction (ridge line direction) of the unit prism 23 is oriented in a direction substantially orthogonal to the transmission axis of the back-side polarizing plate 13. The prism sheet 20 may be arranged (so-called oblique arrangement) so that the ridge line direction of the unit prism 23 and the transmission axis of the back-side polarizing plate 13 form a predetermined angle. The range of the oblique arrangement is preferably 20 ° or less, and more preferably 15 ° or less.

E-2. When the base material part 21 is provided on the prism sheet 20, the base material part 21 and the prism part 22 may be integrally formed by extruding a single material. The prism portion may be formed on the film for use. The thickness of the base material portion is preferably 25 μm to 150 μm.

  Any appropriate material can be adopted as the material constituting the base member 21 depending on the purpose and the configuration of the prism sheet. When the prism portion is formed on the base film, specific examples of the base film include (meth) acrylic resins such as cellulose triacetate (TAC) and polymethyl methacrylate (PMMA). And a film formed of polycarbonate (PC) resin. The film is preferably an unstretched film.

  When the base material portion 21 and the prism portion 22 are integrally formed of a single material, the same material as the material for forming the prism portion when the prism portion is formed on the base material portion film is used as the material. Can do. Examples of the prism portion forming material include epoxy acrylate-based and urethane acrylate-based reactive resins (for example, ionizing radiation curable resins). In the case of forming an integrally structured prism sheet, a polyester resin such as PC or PET, an acrylic resin such as PMMA or MS, or a light-transmitting thermoplastic resin such as cyclic polyolefin can be used.

  The base material portion 21 preferably has substantially optical isotropy. In this specification, “substantially optically isotropic” means that the retardation value is small enough not to substantially affect the optical characteristics of the liquid crystal display device. For example, the in-plane retardation Re of the base material portion is preferably 20 nm or less, and more preferably 10 nm or less. The in-plane retardation Re is an in-plane retardation value measured with light having a wavelength of 590 nm at 23 ° C. The in-plane phase difference Re is represented by Re = (nx−ny) × d. Here, nx is the refractive index in the direction in which the refractive index is maximum in the plane of the optical member (that is, the slow axis direction), and ny is the direction perpendicular to the slow axis in the plane (that is, the fast phase). (Axial direction), and d is the thickness (nm) of the optical member.

Furthermore, the photoelastic coefficient of the base 21 is preferably ^{-10 × 10 -12 m 2 / N~10} × 10 -12 m 2 / N, more preferably -5 × ¹⁰ -12 ^m 2 / N a ^{~5 × 10 -12 m 2 / N} , more preferably from ^{-3 × 10 -12 m 2 / N~3} × 10 -12 m 2 / N.

F. Light Guide Plate Any appropriate light guide plate may be used as the light guide plate. For example, a light guide plate in which a lens pattern is formed on the back side and a light guide plate in which a prism shape or the like is formed on the back side and / or the viewing side are used so that light from the lateral direction can be deflected in the thickness direction. . Preferably, a light guide plate having prism shapes formed on the back side and the viewing side is used. In the light guide plate, the prism shape formed on the back side and the prism shape formed on the viewing side are preferably perpendicular to each other in the ridge line direction. If such a light guide plate is used, light that is more easily condensed can be made incident on the prism sheet, and the effect of the present invention becomes remarkable.

G. Visible Light Absorber As described above, the visible light absorber 40 may be disposed in the liquid crystal display device 100. The visible light absorber 40 can be typically disposed on the back side of the light guide plate 30. The visible light absorber 40 absorbs visible light emitted from the light guide plate to the back side. In this specification, visible light refers to light having a wavelength of 380 nm to 750 nm.

  The luminous reflectance of the visible light absorber is 30% or less, preferably 20% or less, more preferably 1% to 10%. If it is such a range, a viewing angle will be narrowed moderately, For example, the liquid crystal display device which has a preferable viewing angle characteristic as a liquid crystal display device which has a peep prevention function can be obtained. The luminous reflectance of the visible light absorber can be adjusted according to the desired viewing angle and luminance. Specifically, if the luminous reflectance is lowered, the viewing angle is narrowed, and if the luminous reflectance is increased, the luminance is increased. In this specification, the luminous reflectance is the reflectance of the Y value in the XYZ color system, and is a reflectance measured according to JIS Z 8722.

  As a material constituting the visible light absorber, any appropriate material can be used as long as it has the luminous reflectance described above. Specific examples of the material constituting the visible light absorber include black-colored paper, black-colored resin film, black-colored metal film, and the like. The resin film colored black includes, for example, a base polymer such as an acrylic resin, an acetal resin, or chloroprene rubber, and a colored body such as a pigment, a dye, or carbon black. Further, as another specific example of the resin film colored black, a resin film formed by applying a black paint on a reflective or transmissive resin film; on a reflective or transmissive resin film Examples thereof include a resin film formed by attaching an inorganic substance. As a metal film colored in black, a metal film formed by applying a black paint on a reflective metal film; a metal film formed by attaching an inorganic substance on a reflective metal film; black anodized Examples thereof include a metal film subjected to any appropriate surface treatment such as an aluminum film.

  The visible light absorber preferably has a thickness of 0.01 mm to 20 mm, more preferably 0.01 mm to 10 mm, particularly preferably 0.02 mm to 5 mm, and most preferably 0.02 mm to 1 mm. is there.

H. Backlight Unit In one embodiment, the light guide plate and the visible light absorber can be members constituting the backlight unit. In practice, the backlight unit may further include a light source. In one embodiment, the backlight unit may include a prism sheet.

  The light source is disposed at a position corresponding to the side surface of the light guide plate. As the light source, for example, an LED light source configured by arranging a plurality of LEDs may be used.

  The backlight unit may further include another member. For example, the backlight unit may further include any appropriate diffusion plate as necessary.

I. Others In the liquid crystal display device 100, the back-side polarizing plate 13, the viewing angle control means 60, the reflective polarizer 70, and the prism sheet 20 if present, may be sequentially laminated on the liquid crystal cell 12, The integrated member may be bonded to the liquid crystal cell 12. That is, an optical member in which a polarizing plate, a viewing angle control means, and a reflective polarizer and a prism sheet are integrated as necessary may be bonded to the liquid crystal cell 12 as a back polarizing plate. Such an optical member may further include any appropriate optical functional layer as necessary. Further, in such an optical member, the arrangement order of the viewing angle control means 60 and the reflective polarizer 70 may be reversed. Such an optical member may include, for example, a low refractive index layer at any appropriate position between the polarizing plate and the prism sheet.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. The tests and evaluation methods in the examples are as follows. Unless otherwise specified, “parts” and “%” in the examples are based on weight.

(1) Luminous reflectance The luminous reflectance of the visible light absorber used in the examples was measured by a method according to JIS Z 8722 using a spectrophotometer “U-4100” manufactured by Hitachi Technologies.
(2) Luminance A white screen was displayed on the liquid crystal display devices obtained in Examples and Comparative Examples, and the luminance in the front direction was measured using a luminance meter (manufactured by AUTRONIC-MELCHERS, trade name “Conoscope”). Furthermore, the luminance of all directions and polar angles from 0 ° to 80 ° was also measured.
(3) Half-value angle With respect to the luminance measured in accordance with (2) above, the polar angle dependence of the luminance in the vertical direction (azimuth angle 90 ° -270 ° direction) and in the left-right direction (azimuth angle 0 ° -180 ° direction) is examined. The sum of both sides of the polar angle at which the luminance is half the maximum luminance was taken as the half-value angle.

[Example 1]
In order from the viewing side, a liquid crystal panel (a liquid crystal panel mounted on Sony's product name VAIO S series, configuration: viewing side polarizing plate / TN mode liquid crystal cell / back side polarizing plate), viewing angle control means, prism A liquid crystal display device including a sheet and a backlight unit was prepared.
As the viewing angle control means, “Umfilm FUM1CRL” manufactured by Nippon Sheet Glass Umm Products Co., Ltd. was used.
As the prism sheet, a prism sheet composed of a base part and a prism part in which a plurality of triangular prism unit prisms are arranged was used. The prism sheet was arranged so that the convex portion was directed to the back side.
The backlight unit includes a light guide plate, an LED light source disposed at a position corresponding to the side surface of the light guide plate, and a visible light absorber disposed on the back side of the light guide plate (produced by Daio Paper Co., Ltd. A backlight unit having the name “C-855” and luminous reflectance: 7%) was used.
About the obtained liquid crystal display device, the brightness | luminance and half value angle when a viewing angle control means was turned on and when it turned off were measured according to the procedure of said (2)-(3). The results are shown in Table 1. Further, FIG. 6 shows a graph showing the viewing angle dependency (standardized) of luminance in the vertical direction and the horizontal direction. Further, when the image quality of the obtained liquid crystal display device was visually confirmed, it was excellent with no roughness, moire and blur.

[Reference Example 1]
A liquid crystal display device was produced in the same manner as in Example 1 except that the viewing angle control means was not provided. The obtained liquid crystal display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1. Further, FIG. 6 shows a graph showing the viewing angle dependency (standardized) of luminance in the vertical direction and the horizontal direction. Further, when the image quality of the obtained liquid crystal display device was visually confirmed, it was excellent with no roughness, moire and blur.

  As is clear from Table 1 and FIG. 6 and the above results, according to the embodiment of the present invention, a liquid crystal display device having excellent switching performance between a wide viewing angle and a narrow viewing angle and having an excellent image quality is actually used. Could get to. More specifically, the liquid crystal display device of the embodiment of the present invention realizes a narrow viewing angle by turning on the viewing angle control means, and the brightness in the front direction is higher than when the viewing angle control means is OFF. The half-value angle (particularly the half-value angle in the left-right direction) is greatly reduced. The characteristics when the viewing angle control means is ON (when the narrow viewing angle is set) are the same as those of the liquid crystal display device of Reference Example 1 having very excellent narrow viewing angle characteristics.

DESCRIPTION OF SYMBOLS 10 Liquid crystal panel 20 Prism sheet 30 Light guide plate 40 Visible light absorber 60 Viewing angle control means 100 Liquid crystal display device

Claims (4)

A liquid crystal panel, a viewing angle control means, a prism sheet, and a light guide plate are provided in this order from the viewing side,
The prism sheet has a convex portion on the side opposite to the viewing side,
The viewing angle control means controls the width of the viewing angle by changing the transmission state of light from the light source.
Liquid crystal display device.   The liquid crystal display device according to claim 1, further comprising a visible light absorber having a luminous reflectance of 30% or less on a side opposite to the viewing side of the light guide plate.   The liquid crystal display device according to claim 1, further comprising a reflective polarizer between the liquid crystal panel and the prism sheet. 4. The liquid crystal display device according to claim 1, wherein the light guide plate is a light guide plate having prism shapes formed on a back side and a viewing side.