JP2010122390A - Light diffusion sheet and liquid crystal display device provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion sheet suppressing chromaticity change in a viewing condition. <P>SOLUTION: The light diffusion sheet 10 includes a high-refractive index area 12 formed of a material having refractive index N1<SB>650</SB>with light having a wavelength of 650 nm, and a low-refractive index area 14 formed of a material having refractive index N2<SB>650</SB>with light having a wavelength of 650 nm, and including a first light reflecting surface R1 having a predetermined inclination and a second light reflecting surface R2 having an inclination different from the first light reflecting surface R1. The low-refractive index area 14 is provided within the high-refractive index area 12. The reflecting direction of the light of 650 nm incident on the first reflecting surface R1 at a critical angle is equal to the reflecting direction of the light of 650 nm incident on the second reflecting surface R2 along the optical axis direction of incident light on a light incident surface of the light diffusion sheet 10. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The light diffusing sheet according to the present invention relates to a light diffusing sheet for widening a viewing angle by being bonded to the surface of an image display device such as a liquid crystal display panel, and a liquid crystal display device including the same.

  Since the liquid crystal display device is not a self-luminous display device, a backlight unit (so-called backlight unit) that supplies light for display to the liquid crystal display panel is required except for some reflection types. The backlight unit provided on the back surface of the liquid crystal display panel (on the side opposite to the observer side) is roughly classified into an edge light type and a direct type. The edge light type is a system in which light emitted from a light source (a cold cathode fluorescent tube (CCFT) or LED) disposed on the side surface of the light guide plate is propagated inside the light guide plate and taken out to the liquid crystal display panel side. is there. The direct type is configured such that a plurality of light sources are arranged on the back surface of the liquid crystal display panel, and light emitted from the light sources is incident on the liquid crystal display panel without using a light guide plate.

  The liquid crystal display panel is designed so that light emitted obliquely from the liquid crystal display panel looks the same as when viewed from the front by optical compensation. However, complete compensation is difficult, and a vertical alignment (VA) liquid crystal display panel has excellent contrast ratio characteristics when viewed from the front, but has a greater sense of change when viewed from the front than when viewed from the front. In other words, the liquid crystal display device has a problem that the appearance of the display varies depending on the viewing direction, that is, the viewing angle characteristic is inferior. In order to solve this problem, it is only necessary to shield the backlight light incident on the liquid crystal display panel at an angle, but in this case, it becomes impossible to visually recognize the image from the oblique direction.

As one method for improving the viewing angle characteristics of a display device, a method has been developed that enables visual recognition from an oblique direction by providing a layer that diffuses light on the viewer side of the display device. As a result, an image viewed from the front and an image viewed from an oblique angle are combined to realize a viewing angle-free display device that does not change the viewing angle. For example, Patent Document 1 discloses a light diffusion sheet provided with a light reflecting portion in which a groove including a slope having an angle that totally reflects image light and a slope having an angle that refracts and transmits image light is filled with resin. A method of using is disclosed. In this light diffusion sheet, the graph of the light diffusion characteristics of the diffused image light is gentle due to the discontinuity of the diffusion angle on the slope that refracts and transmits the image light.
JP 2007-148185 A (released on June 14, 2007)

  However, since the light diffusion sheet described in Patent Document 1 is designed to be used for a rear projection screen, the light diffusion sheet is a light source having a spread like a backlight unit used in a liquid crystal display device. It is not effective for this. That is, no consideration is given to incident light incident at an angle that deviates from the total reflection condition. For this reason, when an image is viewed from an oblique direction, the color appears to be bluish, resulting in a problem that the display quality is remarkably deteriorated.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a light diffusion sheet that suppresses emission light from being bluish within a viewing angle range.

In order to solve the above problems, a light diffusing sheet according to the present invention has a light incident surface and a light emitting surface, and diffuses light incident from the light incident surface, and has a wavelength of 650 nm. A high refractive index region formed by a material having a refractive index N1 ₆₅₀ in the light of the light, and a material having a refractive index N2 _{650 in} light having a wavelength of 650 nm smaller than the refractive index N1 _650. A plurality of low refractive index regions that form a light reflecting surface that reflects light from the incident surface and emits the light from the light emitting surface, and the plurality of low refractive index regions are provided in the high refractive index region. And at least one of the plurality of low refractive index regions forms a first light reflecting surface having a predetermined inclination with respect to an optical axis direction of incident light on the light incident surface. Rate area At least one forms a second light reflecting surface having an inclination different from that of the first light reflecting surface with respect to the optical axis direction, and has a wavelength of 650 nm incident on the first light reflecting surface at a critical angle. And the reflection direction of light having a wavelength of 650 nm incident on the second light reflection surface along the optical axis direction are the same.

  Here, the optical axis direction of the incident light indicates the direction of the angle at which the intensity distribution is maximum in the incident light.

In the above configuration, a plurality of low refractive index regions having a refractive index of N2 ₆₅₀ for light having a wavelength of 650 nm are provided in a high refractive index region having a refractive index of N1 ₆₅₀ for light having a wavelength of 650 nm. The refractive index N2 ₆₅₀ is designed to be smaller than the refractive index N1 ₆₅₀ . At least one of the plurality of low-refractive index regions is formed with a first light reflecting surface having a predetermined inclination with respect to the optical axis direction of incident light on the light incident surface. A second light reflecting surface having a different inclination from the first light reflecting surface with respect to the axial direction is formed. Light incident from the light incident surface of the light diffusing sheet is reflected by each light reflecting surface, and the reflected light is emitted from the emitting surface of the light diffusing sheet. The first light reflection surface and the second light reflection surface are a reflection direction of light having a wavelength of 650 nm reflected by being incident on the first light reflection surface at a critical angle, and an optical axis of incident light on the light incident surface of the light diffusion sheet. The reflection direction of the light having a wavelength of 650 nm that is incident on the second light reflection surface along the direction and reflected is the same.

  The reflected light of the light incident on the first light reflecting surface at the critical angle becomes a boundary between total reflection and partial reflection. Therefore, the reflected light changes in chromaticity and becomes bluish light. On the other hand, the reflection by the second light reflecting surface is total reflection. Therefore, the reflected light is not bluish. Furthermore, since the light incident on the second light reflecting surface is light parallel to the optical axis direction of the incident light on the incident surface of the light diffusion sheet, the light intensity is high. Therefore, the reflected light totally reflected on the second light reflecting surface has a high light intensity. As a result, in the outgoing light in the above direction from the light outgoing surface, the light from the second light reflecting surface becomes dominant, and the chromaticity change caused by the partial reflection is canceled out. Accordingly, it is possible to provide a high-quality light diffusion sheet that can prevent the emitted light from being bluish due to light incident on the light diffusion sheet from an oblique direction.

Further, in the light diffusion sheet according to the present invention, a certain cross-sectional shape of the low refractive index region in the optical axis direction is a substantially wedge shape having a base on the light emitting surface side and becoming narrower toward the light incident surface side. The angle between the first oblique side, which is the cross-sectional portion of the first light reflecting surface, and the optical axis direction is an angle α, and the second oblique side, which is the cross-sectional portion of the second light reflecting surface, is the optical axis direction. When the angle formed is an angle β, the refractive index N1 ₆₅₀ and the refractive index N2 _650, and the angle α and the angle β

And,
α <β
It is preferable to satisfy.

  According to the above configuration, the second light is reflected along the reflection direction of the light having a wavelength of 650 nm that is reflected by being incident on the first light reflection surface at the critical angle, and along the optical axis direction of the incident light on the light incident surface of the light diffusion sheet. The first light reflection surface and the second light reflection surface can be easily designed so that the reflection direction of the light having a wavelength of 650 nm reflected by entering the reflection surface is the same. Therefore, it is possible to easily manufacture a light diffusion sheet that can suppress the blueness of the emitted light.

  Further, the light diffusion sheet according to the present invention has the first oblique side and the second oblique side on one side of the side extending from the substantially wedge-shaped bottom side which is a cross section of the low refractive index region to the light incident surface side. It is preferably included.

  According to the above configuration, one low refractive index region includes both the first inclined surface and the second inclined surface, and the first inclined surface and at least one of the oblique sides on both sides of the substantially wedge shape in the cross section in the optical axis direction, The oblique side corresponding to the second slope, that is, the first oblique side having an angle α with respect to the optical axis direction and the second oblique side having the angle β with respect to the optical axis direction are formed. Thereby, since partial reflection can be compensated by a single low refractive index region, the shapes of all the low refractive index regions can be made the same, and the manufacture of the light diffusion sheet is facilitated.

  In the light diffusing sheet according to the present invention, the first reflection region includes at least one first light reflection surface, and the second reflection region adjacent to the first reflection region includes the above-mentioned. At least one second light reflecting surface is included, at least one of the first light reflecting surfaces is on a side close to the second reflecting region, and at least one of the second light reflecting surfaces is the first light reflecting surface. It is preferable that it exists in the side far from 1 reflection area | region.

  According to the above configuration, it is possible to provide a light diffusion sheet that can suppress the bluishness of emitted light even if the first light reflection surface and the second light reflection surface are not formed on the same side surface of the same reflection region. it can. Thus, only a single light reflecting surface can be formed on one side surface of the reflecting region, and the cross section in the optical axis direction can be designed to be a triangle. Therefore, the shape of the low refractive index region becomes simple, and the manufacture becomes easy. That is, it becomes easy to make the diffusion performance uniform even during mass production.

  In the light diffusing sheet according to the present invention, it is preferable that a substantially wedge-shaped base which is a cross-sectional shape of the low refractive index region exists on the light emitting surface.

  According to the above configuration, the high refractive index material layer having a predetermined-shaped concave portion (having a substantially wedge-shaped cross-sectional shape) on the surface is formed as a high refractive index region, and the concave portion is filled with the low refractive index material. The light diffusion sheet according to the present invention can be formed. Therefore, it is possible to provide a light diffusion sheet that is easy to manufacture.

  In the light diffusion sheet according to the present invention, the low refractive index region preferably contains a substance that absorbs visible light.

  According to the above configuration, the stray light inside is absorbed because the low refractive index region contains the substance that absorbs visible light. Thereby, the contrast reduction resulting from a light-diffusion sheet is not caused, and the visibility in a bright environment can be improved.

  In order to solve the above problems, a liquid crystal display device according to the present invention changes the alignment direction of the liquid crystal by applying a voltage to the liquid crystal, and controls the transmission of light. Is provided, and the light diffusion sheet bonded to the light emitting side surface of the liquid crystal display panel.

  According to the above configuration, incident light that does not adversely affect the viewing angle characteristics is mainly incident on the liquid crystal display panel, and the light that has passed through the liquid crystal display panel can be diffused by the light diffusion sheet according to the present invention. Therefore, the viewing angle improvement effect can be obtained, and the chromaticity change can be suppressed at a predetermined viewing angle.

As described above, the light diffusion sheet according to the present invention includes a high refractive index region having a refractive index of N1 ₆₅₀ in light having a wavelength of 650 nm, and a low refractive index region having a refractive index of N2 ₆₅₀ in light having a wavelength of 650 nm. The refractive index N2 ₆₅₀ is smaller than the refractive index N1 ₆₅₀ , the low refractive index region is provided in the high refractive index region, and at least one of the plurality of low refractive index regions has a predetermined slope. 1 light reflecting surface is formed, and at least one of the plurality of low refractive index regions forms a second light reflecting surface having a different inclination from the first light reflecting surface, and is critical to the first light reflecting surface. The reflection direction of light having a wavelength of 650 nm incident at an angle is the same as the reflection direction of light having a wavelength of 650 nm incident on the second light reflection surface along the optical axis direction of incident light on the light incident surface of the light diffusion sheet. It is the composition which is. Thereby, the light-diffusion sheet which has an effect which suppresses that emitted light becomes bluish when viewing a display from the diagonal direction is realizable.

  In addition, the liquid crystal display device of the present invention includes the light diffusion sheet of the present invention as described above. Therefore, it is possible to realize a liquid crystal display device that has an effect of suppressing the emission light from being bluish when the display is viewed from an oblique direction.

  An embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this.

[Liquid Crystal Display]
FIG. 1 is a perspective sectional view schematically showing a schematic configuration of a liquid crystal display device 100 according to the present embodiment. The liquid crystal display device 100 is a direct-view type liquid crystal display device in which an observer directly observes light emitted from a display surface.

  The liquid crystal display device 100 includes a light diffusion sheet 10, a liquid crystal display panel 20, a backlight unit 30, and an optical sheet 40 according to the embodiment of the present invention.

  The light diffusing sheet 10 has a light incident surface S1 and a light emitting surface S2 that are parallel to each other, and has one light diffusing layer arranged with the light incident surface S1 facing the viewer side surface of the liquid crystal display panel 20. is doing. Here, an example is shown in which the light diffusion sheet 10 is composed of only one light diffusion layer, but a base film (not shown) is provided on the liquid crystal display panel 20 side (light incident side) of the light diffusion layer. May be. Further, an antiglare layer, an antireflection layer, a low reflection layer, or an antireflection layer (all not shown) may be provided on the observer side (light emission side) of the light diffusion layer. Of course, any two or more of these may be combined as necessary.

  The light diffusion sheet 10 and the liquid crystal display panel 20 are bonded together via an adhesive layer (not shown). Since a polarizing plate is generally provided on the outermost surfaces on the light incident side and the viewer side of the liquid crystal display panel 20, the light diffusion sheet 10 is bonded to the polarizing plate on the viewer side of the liquid crystal display panel 20. Become. Here, the liquid crystal display panel 20 with the light diffusion sheet 10 attached (without the backlight unit 30) may be referred to as a liquid crystal display device.

  In addition, as will be described later, the liquid crystal display device 100 may further include a surface scattering sheet that is bonded to the light exit surface S2 of the light diffusion sheet 10.

[Structure of light diffusion sheet]
Light diffusion sheet 10 includes a first material refractive index in the optical wavelength of 650nm is _{N1 650,} the refractive index in the light of the wavelength of 650nm is a second substance which is _{N2 650} smaller than _{N1 650} . The second substance has a substantially wedge shape in which a shape in a cross section perpendicular to the light emitting surface S2 has a base on the light emitting surface S2 side and becomes narrower toward the light incident surface S1, and two oblique sides having different inclinations from each other. R1 and the hypotenuse R2 are connected. The hypotenuse R1 and the hypotenuse R2 correspond to the first and second light reflecting surfaces formed in the low refractive index region 14. Therefore, in this specification, the hypotenuse R1 and the hypotenuse R2 may be referred to as the first light reflecting surface R1 and the second light reflecting surface R2, respectively. In the light diffusion sheet 10 according to the present embodiment, the second light reflecting surface R2 is formed at a position in contact with the light emitting surface S2, and the first light reflecting surface is connected to the second light reflecting surface, so that the light incident surface S1. The apex is formed by the two first light reflecting surfaces. The cross-sectional shape of the low refractive index region 14 is symmetric with respect to a straight line parallel to the optical axis direction of incident light (hereinafter also simply referred to as the optical axis direction) on the light incident surface S1 passing through this apex.

  As shown in FIG. 1, the low refractive index region 14 has a rectangular shape extending in the horizontal direction when viewed from the normal direction of the light exit surface S <b> 2 of the light diffusion sheet 10. The plurality of low refractive index regions 14 are arranged in parallel to each other. In this case, the light diffusion sheet 10 can improve viewing angle characteristics in a direction perpendicular to the extending direction of the low refractive index region 14 and parallel to the light exit surface S2.

  In a liquid crystal display device, a required viewing angle differs depending on the application. That is, the light diffusion sheet 10 in which a plurality of rectangular low refractive index regions 14 extending in a direction perpendicular to a direction that requires a wide viewing angle (viewing angle required direction) are arranged along the viewing angle required direction. It is effective. In general, importance is attached to the viewing angle in the horizontal direction. In this case, the light diffusion sheet 10 in which a plurality of rectangular low refractive index regions 14 extending in the vertical direction are arranged along the horizontal direction is effective.

  As shown in FIG. 2, the liquid crystal display device 100 may include two light diffusion sheets 10A and 10B. Here, the light diffusion sheet 10 </ b> B has the same configuration as the light diffusion sheet 10 described above. A plurality of low refractive index regions 14 of the light diffusion sheet 10B are arranged in a direction substantially orthogonal to the low refractive index regions 14 of the light diffusion sheet 10A. Thereby, viewing angle characteristics in both the horizontal direction and the vertical direction can be improved.

  The light diffusion sheet 10 may have a configuration in which a plurality of light diffusion layers having different arrangement directions of the low refractive index regions 14 are laminated.

[Chromaticity change]
Here, the chromaticity change that can occur when the liquid crystal display panel is viewed from an oblique direction, particularly when the angle formed with the normal direction of the liquid crystal display panel is increased, particularly the chromaticity change that relatively increases the blue intensity. 9 and FIG.

FIG. 9 is a diagram showing a light path. The transmittance of light incident from the light incident surface of the light diffusion layer is T ₁ , the reflectance of light incident from the light incident surface at the interface with the low refractive index region is R, and the low refractive index region is When the transmittance of a light emitting surface of the light reflected at the interface of the T _2, the transmittance T of the whole is as follows.
T = T ₁ × R × T ₂
Here, T ₁ and T ₂ do not change greatly depending on the refractive index of the resin and the wavelength of light, although there are some differences. However, the value of R varies greatly depending on whether it is partial reflection or total reflection. Further, the refractive index that determines whether it is partial reflection or total reflection has wavelength dependency (also referred to as wavelength dispersion), and the dependency varies depending on the resin that transmits or reflects light.

  As an example, the transmittance is calculated using polycarbonate as the high refractive index resin and PMMA as the low refractive index resin, and the result is shown in FIG.

  FIG. 10 is a graph in which the incident angle of light is changed and the relationship between the emission angle and the transmittance is plotted. 650 nm, 550 nm, and 450 nm are used as typical wavelengths of red, green, and blue light, respectively. As shown in FIG. 10, the wavelength of blue light has a high transmittance up to the highest emission angle. In the figure, the discontinuous point where the transmittance is abruptly changed corresponds to the boundary between total reflection and partial reflection at the interface between the high refractive index resin and the low refractive index resin. That is, in the figure, light having an emission angle smaller than the angle that becomes the discontinuous point causes total reflection at the interface, and light having an emission angle that is larger than the angle that becomes the discontinuous point is partially reflected at the interface. Has caused. This indicates that the critical angle at which partial reflection starts to occur decreases as the wavelength increases.

  In this case, when the emission angle is in the range of about 50 ° to about 55 °, the transmittance of blue light (450 nm wavelength light) is high, and the transmittance of green (550 nm) and red (650 nm) light is low. ing. This is because, as schematically shown in FIG. 11, only blue light causes total reflection at the interface, and green and red light cause partial reflection in this emission angle range. To do. This is the cause of the bluish appearance, that is, the cause of chromaticity change.

  As described above, the refractive index has wavelength dependence (also referred to as wavelength dispersion), and the degree of dependence differs depending on the resin that transmits or reflects light. Therefore, the ratio (N2 / N1) of the refractive index (N1) in the high refractive index resin and the refractive index (N2) in the low refractive index resin is included as a parameter as in the above formula (1) according to the present invention. In this case, the wavelength dependency of the refractive index greatly affects the characteristics of the layer containing these resins.

  Ideally, the ratio of N2 / N1 is preferably constant regardless of the wavelength. However, in reality, it is difficult to select a resin that satisfies such conditions. Therefore, the present invention focuses on the angle of the light reflecting surface in the low refractive index region. By using a plurality of reflected lights to compensate for the reduction in light due to partial reflection by total reflection, it is possible to realize display with little change in chromaticity under viewing conditions of a display such as a television.

[Design conditions of light diffusion sheet]
Next, with reference to FIG. 3, the function of a light-diffusion sheet and the structure required in order to exhibit this function are demonstrated.

  FIG. 3 is a diagram illustrating an optical path of light incident on the light diffusion sheet. The light diffusion sheet according to the present invention has two types of light reflecting surfaces with different inclinations. In FIG. 3, the light reflected on each light reflecting surface will be described separately. Therefore, the light path of the light diffusing sheet having the low refractive index region having only the first light reflecting surface is shown in FIG. 3A, and the light diffusing sheet having the low refractive index region having only the second light reflecting surface is shown in FIG. The light path is shown in FIG. 3B, and each will be described below.

The low refractive index region shown in FIG. 3A has a first light reflecting surface whose angle formed with the optical axis direction D is an angle α. When the angle θ formed by the red light (light having a wavelength of 650 nm) L1 incident at a critical angle whether the light is totally reflected on the slope having the angle α or not and the optical axis direction D is the angle θ, the angle θ and the refractive index. Satisfies the relationship of the following formula (2).
sin (90 ° −θ−α) = N2 ₆₅₀ / N1 ₆₅₀ (2)
The above formula (2) can be expressed as the following formula (3).
cos (θ + α) = N2 ₆₅₀ / N1 ₆₅₀ (3)
This angle θ is an angle that separates a region in which chromaticity change occurs (bluish) and a region in which chromaticity change does not occur in the light emitted from the light diffusion sheet.

If the exit angle of the reflected light from the light exit surface is the angle θ ′, the angle θ ′ is
θ ′ = θ + 2α (4)
It can be expressed as.

  Here, if the inclination of the other inclined surface is determined so that the peak of the reflected light from the other inclined surface is emitted at the angle θ ′, the red light reduced by the partial reflection can be compensated. For this purpose, the inclination of the other slope may be designed so that the reflected light of the incident light L2 parallel to the optical axis direction D is emitted at an angle θ ′. Below, the slope which satisfy | fills this condition is demonstrated.

The low refractive index region shown in FIG. 3B has a second light reflecting surface whose angle formed with the optical axis direction D is an angle β. Since incident light parallel to the optical axis direction D is reflected by the second light reflecting surface, and the reflected light is emitted from the light emitting surface at an angle θ ′, the angle θ ′ and the angle β are expressed by the following equation (5). Meet.
θ ′ = 2β (5)
From the above, by incorporating the relationship shown in the above equations (4) and (5) into the conditions defined in the above equation (3), the relationship between the angles α and β and the refractive index is expressed by the following equation (1). Stipulated in

In addition, since incident light L2 parallel to the optical axis direction D, especially incident light of red light, must be totally reflected on the second light reflecting surface, it is necessary to further satisfy the following formula (6).
sin (90 ° −β)> N2 ₆₅₀ / N1 ₆₅₀ (7)
The above formula (7) is
β <cos ⁻¹ (N2 ₆₅₀ / N1 ₆₅₀ ) (8)
It can be expressed as. Here, since the refractive index and the angles α and β satisfy the relationship of the above formula (1), the above formula (8) can be expressed as the following formula (9).
α <β (9)
As described above, by satisfying the two conditions of the above formulas (1) and (9) at the same time and providing the angular light reflecting surface in the direction in which the light of each reflected light is in the same direction, partial reflection on the first light reflecting surface is achieved. The reduction in the generated light can be compensated by the light in the optical axis direction that is totally reflected by the second light reflecting surface. That is, it is possible to prevent the display from becoming bluish when the display is viewed from an oblique direction.

  Next, a change in chromaticity when the following three light diffusion layers A, B, and C are used will be described.

In the light diffusion layer A, the shape of the low refractive index region in the optical axis direction has a base on the light exit surface and a vertex on the light incident surface side, and the bisector of the apex angle is parallel to the optical axis direction. This is a comparative example including only a low refractive index region that is an isosceles triangle. The angle α ′ between the hypotenuse of the isosceles triangle and the optical axis direction is α ′ = 8 °. The light diffusing layer B forms the light diffusing sheet 10 according to the present invention shown in FIG. 1, and the angle α between the first light reflecting surface and the optical axis direction is α = 8 °, and the second light The angle β formed by the reflecting surface and the optical axis direction is β = 15 °. The light diffusion layer C has the same configuration as the light diffusion layer B except for the angle β, and β = 10 °. In this case, the relationship between the angles α and β in the light diffusion layer C does not satisfy the conditions of the present invention. Therefore, the light diffusion layer C is a comparative example. Note that N2 ₆₅₀ / N1 ₆₅₀ = 1.48 / 1.58 in all cases of the light diffusion layers A, B, and C.

  4, 5 and 12 show changes in chromaticity of light emitted from the light diffusion sheet when the light diffusion layers A, B and C are used as the light diffusion sheet, respectively. In these figures, regarding the light emitted from the light diffusion sheet, the horizontal axis represents the emission angle (deg) and the vertical axis represents the chromaticity change (Δu′v ′).

  Referring to FIG. 4, when the light diffusion layer A is used, the emitted light gradually becomes bluish from around 50 ° (viewing angle of 100 °) and before 60 ° (viewing angle of 120 °). The peak of chromaticity change comes. According to “Video viewing conditions at home”, Journal of the Institute of Image Information and Media Studies, 2006, Vol. 60, No. 4, 597-603, the viewing position of a television at a general home is within a horizontal viewing angle of 120 °. It is shown that. Therefore, it is necessary to suppress the occurrence of chromaticity changes at least in the range of the viewing angle of 120 °. When the light diffusing layer A is applied to a liquid crystal display device, the chromaticity greatly changes within the actual use range (relatively the intensity of blue becomes stronger), and the observer watching the television shows the chromaticity. I'm worried about changes.

  Further, referring to FIG. 12, even when the light diffusion layer C whose angle of the light reflecting surface does not satisfy the conditions of the present invention is used, the emitted light gradually becomes bluish from around 50 ° (viewing angle of 100 °). The chromaticity change around 60 ° is increasing. Therefore, even when the light diffusing layer C is applied to a liquid crystal display device, the chromaticity greatly changes within the actual use range (relatively stronger blue intensity), and an observer watching TV I'm worried about chromaticity changes.

  On the other hand, referring to FIG. 5, when the light diffusing layer B is used, the peak at around 60 ° disappears, and a characteristic with no chromaticity change can be obtained over almost the entire region. Thereby, when the light diffusion layer B is applied to the liquid crystal display device, the chromaticity does not change within the actual use range, and the observer watching the television does not feel the chromaticity change.

  Theoretically, such a change in chromaticity can be suppressed by increasing the refractive index difference that is the difference between the refractive index of the resin in the high refractive index region and the refractive index of the resin in the low refractive index region. However, the price of the resin increases as the refractive index of the resin moves away from the vicinity of n = 1.55, which is a general refractive index of the resin. Therefore, in reality, it is difficult to ensure a sufficient difference in the refractive index of the resin from the viewpoint of cost. According to the present invention, by forming a plurality of reflecting surfaces having different inclinations, a change in chromaticity can be sufficiently suppressed even in a light diffusion layer made of a resin having a general refractive index.

  Moreover, the light-diffusion sheet excellent in the brightness | luminance diffusion characteristic can be provided.

  FIG. 6 is a diagram showing a diffusion characteristic when a light is irradiated from a backlight unit in a liquid crystal display device including a light diffusion sheet having a single type of slope, and is a comparative example. FIG. 7 is a diagram showing diffusion characteristics when light is irradiated from the backlight unit 30 in the liquid crystal display device 100 according to the present invention shown in FIG. In these figures, regarding the light emitted from the light diffusion sheet, the horizontal axis represents the emission angle (deg) and the vertical axis represents the luminance (au (Arbitrary Unit)). Referring to FIGS. 6 and 7, in the liquid crystal display device 100 according to the present invention, the unevenness in luminance (for example, a portion surrounded by a broken line in FIG. 6) is eliminated as compared with the case of the liquid crystal display device of the comparative example. I understand that. That is, a smoother change in luminance is realized, and a liquid crystal display device having better display quality is realized.

  The light diffusion sheet 10 can be produced using, for example, the method described in Patent Document 1. The light diffusion sheet 10 can be formed using, for example, a resin such as epoxy acrylate for the high refractive index region 12 and urethane acrylate for the low refractive index region 14. Here, since the light which passed through the high refractive index area | region 12 is used for a display, it is preferable to have high transparency.

  Further, the light diffusion sheet 10 is formed by forming a high refractive index resin layer having a concave portion (having a substantially wedge-shaped cross section) on the surface and filling the concave portion with a low refractive index resin. Can do.

  Further, the low refractive index region 14 may include a substance that absorbs visible light. Examples of the substance that absorbs visible light include carbon black and a mixture of a blue pigment and a red pigment. In particular, when an ultraviolet curable resin is used for the high refractive index region 12 and the low refractive index region 14, black particles that absorb visible light and transmit ultraviolet light, such as titanium black, are used for the low refractive index region 14. A high OD (optical density) value can be realized. Here, the absorptance of visible light is preferably 95% or more.

[Structure of low refractive index region]
Based on the above conditions, in the low refractive index region 14 of the light diffusion sheet 10, the first light reflecting surface R1 whose angle with the optical axis direction is the angle α and the second light whose angle with the optical axis direction is the angle β. A light reflecting surface R2 is formed. As shown in FIG. 1, the second light reflecting surface R2 is in contact with the light emitting surface S2, and the first light reflecting surface R1 is connected to the second light reflecting surface R2.

  FIG. 8 is a diagram showing an example of a cross-sectional shape for another form of the low refractive index region 14. The form of the low refractive index region 14 is not limited to these.

  A low refractive index region 14 of the light diffusion sheet 10 illustrated in FIG. 8A represents the low refractive index region 14 of the light diffusion sheet 10 illustrated in FIG. 1.

  In the low refractive index region 14 of the light diffusion sheet 10 shown in FIG. 8B, the position where the light reflecting surfaces R1 and R2 are formed is the light reflecting surface R1 in the low refractive index region 14 shown in FIG. And R2 are respectively replaced. That is, the light reflecting surface R1 is formed at a position in contact with the light emitting surface S2, and the light reflecting surface R2 is formed on the light incident surface S1 side.

  As described above, in the low refractive index region 14 shown in FIGS. 8A and 8B, both the first light reflecting surface R1 and the second light reflecting surface R2 are formed in one low refractive index region 14. It is the structure which is done.

  Since the low refractive regions 14 shown in FIGS. 8A and 8B all have the same structure (single structure), it is easy to narrow the pitch of the low refractive regions 14.

  On the other hand, the cross-sectional shape of the low refractive index region 14 shown in FIGS. 8C and 8D is different from the cross sectional shape of the low refractive index region 14 shown in FIGS. ing.

  The low refractive index region 14 of the light diffusing sheet 10 shown in FIG. 8C has a base on the light exit surface S2, a vertex on the light incident surface S1 side, and a hypotenuse on the first reflecting surface in the cross section in the optical axis direction. The isosceles triangles R1 and the isosceles triangles whose base is on the light exit surface S2 and whose apex is on the light incident surface S1 side and whose hypotenuse is the second reflecting surface R2 are alternately arranged. Yes.

  The low refractive index region 14 of the light diffusion sheet 10 shown in FIG. 8D has a bottom in the light exit surface S2 and a vertex on the light incident surface S1 side in the cross section in the optical axis direction. Triangles that are the reflecting surface R1 and the other oblique side is the second reflecting surface R2 are arranged side by side. At this time, the two low refractive index regions 14 adjacent to each other are disposed so that the same type of light reflecting surfaces face each other. That is, the first light reflecting surface R1 of a certain low refractive index region 14 sandwiches the first light reflecting surface R1 of the adjacent low refractive index region 14 and the high refractive index region 12 on the side close to the first light reflecting surface R1. Facing each other. Further, the second light reflecting surface R2 of a certain low refractive index region 14 sandwiches the second light reflecting surface R2 and the high refractive index region 12 of the adjacent low refractive index region 14 on the side close to the second light reflecting surface R2. It is the composition which is facing each other.

  Since the low refractive region 14 shown in FIGS. 8C and 8D has a simple triangular cross section, the light diffusing sheet 10 can be easily manufactured.

[Optical sheet]
The optical sheet 40 is composed of a plurality of stacked sheets, and uniformizes and collects the light emitted from the backlight unit 30 to irradiate the liquid crystal display panel 20. Function as. That is, the optical sheet 40 is a lens sheet that collects light to improve the luminance in the front direction (the direction of the liquid crystal display panel), and reflects one of the polarized components of the light and transmits the other polarized component to display the liquid crystal display. A polarization reflection sheet, a prism sheet, or the like that improves the luminance of the apparatus 100 can be applied. These are preferably used in appropriate combination depending on the price and performance of the liquid crystal display device 100. Further, when the backlight unit 30 itself has a light condensing characteristic, the optical sheet 40 is unnecessary.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The light diffusion sheet according to the present invention can be used as a light diffusion sheet for widening the viewing angle by bonding to the surface of an image display device such as a liquid crystal display panel.

1 is an exploded perspective sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention. It is an exploded perspective sectional view showing typically another example of composition of the above-mentioned liquid crystal display. It is a figure which shows the path | route of the light in the light diffusion sheet which has the light reflection surface provided in the light diffusion sheet of this invention, (a) shows the path | route of the light reflected by a 1st light reflection surface, (b) Indicates the path of light reflected by the second light reflecting surface. It is a graph which shows the relationship between the chromaticity change of the light radiate | emitted from a light-diffusion sheet, and an emission angle when light injects into the conventional light-diffusion sheet. It is a graph which shows the relationship between the chromaticity change of the light radiate | emitted from a light-diffusion sheet, and an emission angle when light injects into the light-diffusion sheet which concerns on this invention. It is a graph which shows the diffusion characteristic of the light radiate | emitted from a light diffusion sheet when light injects into the conventional light diffusion sheet. It is a graph which shows the diffusion characteristic of the light radiate | emitted from a light diffusion sheet when light injects into the light diffusion sheet which concerns on this invention. It is a figure which shows another embodiment of the low refractive index area | region of the light-diffusion sheet which concerns on this invention. It is a figure which shows the path | route when light passes a light-diffusion sheet, and the transmittance | permeability and reflectance. It is a graph which shows the relationship between the output angle and the transmittance | permeability when light injects into a light-diffusion sheet for every wavelength of light. It is a figure which shows typically reflection of the light of a different wavelength in a light-diffusion sheet. It is a graph which shows the relationship between the chromaticity change of the light radiate | emitted from a light-diffusion sheet, and an emission angle when light injects into the conventional light-diffusion sheet.

Explanation of symbols

10, 10A, 10B Light diffusion sheet 12 High refractive index region 14 Low refractive index region 20 Liquid crystal display panel 30 Backlight unit 40 Optical sheet 100 Liquid crystal display device S1 Light incident surface S2 Light emitting surface R1 First light reflecting surface R2 Second Light reflecting surface

Claims (7)

A light diffusion sheet having a light incident surface and a light exit surface, and diffusing light incident from the light incident surface,
A high refractive index region formed by a material having a refractive index N1 _{650 in} light having a wavelength of 650 nm;
It is formed of a material having a refractive index N2 _{650 in} light having a wavelength of 650 nm smaller than the refractive index N1 _650, and forms a light reflecting surface that reflects light from the light incident surface and emits it from the light emitting surface. A plurality of low refractive index regions,
The plurality of low refractive index regions are provided in the high refractive index region,
At least one of the plurality of low refractive index regions forms a first light reflecting surface having a predetermined inclination with respect to an optical axis direction of incident light on the light incident surface,
At least one of the plurality of low refractive index regions forms a second light reflecting surface having an inclination different from the first light reflecting surface with respect to the optical axis direction,
The reflection direction of light having a wavelength of 650 nm incident on the first light reflection surface at a critical angle is the same as the reflection direction of light having a wavelength of 650 nm incident on the second light reflection surface along the optical axis direction. A light diffusing sheet characterized in that there is. A certain cross-sectional shape of the low refractive index region in the optical axis direction is a substantially wedge shape having a base on the light exit surface side and narrowing toward the light incident surface side,
The angle formed by the first oblique side, which is the cross-sectional portion of the first light reflecting surface, with the optical axis direction is the angle α, and the angle formed by the second oblique side, which is the cross-sectional portion of the second light reflecting surface, with the optical axis direction. If the angle is β,
The refractive index N1 ₆₅₀ and the refractive index N2 _650, and the angle α and the angle β

And,
α <β
The light diffusion sheet according to claim 1, wherein:   The first oblique side and the second oblique side are included on one side of a side extending from the base of the substantially wedge shape, which is a cross section of the low refractive index region, to the light incident surface side. 2. The light diffusion sheet according to 2. The first reflection region includes at least one first light reflection surface, and the second reflection region adjacent to the first reflection region includes at least one second light reflection surface. And
At least one of the first light reflecting surfaces is on a side close to the second reflecting region, at least one of the second light reflecting surfaces is on a side far from the first reflecting region;
3. The light diffusing sheet according to claim 2, wherein the substantially wedge shape which is a cross-sectional shape of the low refractive index region is a triangle having a base on the light emitting side and a vertex on the light incident side.   5. The light diffusing sheet according to claim 2, wherein a bottom of a substantially wedge shape, which is a cross-sectional shape of the low refractive index region, exists on the light emitting surface.   The light diffusion sheet according to any one of claims 1 to 5, wherein the low refractive index region includes a substance that absorbs visible light. A liquid crystal display panel that controls the transmission of light by changing the alignment direction of the liquid crystal by applying a voltage to the liquid crystal;
A backlight for allowing light to enter the liquid crystal display panel;
A liquid crystal display device comprising: the light diffusion sheet according to claim 1, which is bonded to a light emission side surface of the liquid crystal display panel.

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