JP7769690B2 - Planar lighting device, image display device and optical film - Google Patents

Description

The present invention relates to a surface lighting device, an image display device using this surface lighting device, and an optical film suitable for this surface lighting device.

2. Description of the Related Art Liquid crystal display devices are used in various displays, such as displays for tablet PCs (Personal Computers) and smartphones, image display devices for televisions and monitors, and in-vehicle displays.
A liquid crystal display device has a liquid crystal panel in which a liquid crystal material is sealed between two substrates, including a substrate on which a TFT (Thin Film Transistor) array is formed, and a backlight device, which is a planar lighting device that irradiates the liquid crystal panel with light (backlight) to display an image.

In order to obtain good visibility, it is preferable that the liquid crystal display device has high brightness when observed from the front.
Furthermore, depending on the application of the liquid crystal display device, it is often preferable that the visibility is low when viewed from an oblique direction. Furthermore, if the viewing angle is switchable, it is required that the visibility, particularly from an oblique direction, be low when the viewing angle is narrowed.

Therefore, in a liquid crystal display device, it is preferable that high-intensity light can be incident on the liquid crystal panel from the front, i.e., from the normal direction, and that little light is incident on the liquid crystal panel from an oblique direction, i.e., from a direction at an angle to the normal direction.
Therefore, the backlight device that constitutes the liquid crystal display device is required to have high front brightness, i.e., high brightness of light emitted from the front, and excellent parallel light source properties, meaning that more light enters the liquid crystal panel from the front than from an oblique direction.

To achieve this goal, for example, Patent Document 1 describes a liquid crystal display device that includes an optical film between a backlight device (backlight unit) and a liquid crystal panel, the optical film containing a dichroic dye whose molecules have different light absorption rates in the long axis direction and the short axis direction. In this liquid crystal display device, the dichroic dye in the optical film is oriented such that the long axis direction, which has a relatively high light absorption rate, is perpendicular to the surface (film plane) of the optical film.

JP 2018-36295 A

As described above, the liquid crystal display device described in Patent Document 1 has an optical film containing a dichroic dye whose major axis is oriented perpendicular to the surface of the film.
This optical film transmits light incident from the front direction as is, whereas light incident from an oblique direction is absorbed by the dichroic dye oriented in such a way that the long axis direction, which has high light absorption, coincides with the thickness direction.

Therefore, in this liquid crystal display device, the amount of light incident on the liquid crystal panel from the front direction is relatively greater than the amount of light incident on the liquid crystal panel from an oblique direction.
As a result, according to the liquid crystal display device described in Patent Document 1, in a liquid crystal display device using a horizontal electric field type liquid crystal panel such as an IPS (In-Plane Switching) type or an FFS (Fringe Field Switching) type, the light incident on the liquid crystal panel from an oblique direction (wide angle) can be reduced, thereby improving the contrast ratio.

However, demands for image quality from LCD displays are becoming higher, and there is a demand for backlight devices that have higher front brightness and excellent parallel light source properties.

The object of the present invention is to solve the problems of the prior art by providing a surface lighting device used in backlight devices for liquid crystal display devices, etc., which has high front brightness and excellent parallel light source properties, an image display device using this surface lighting device, and an optical film suitable for this surface lighting device.

In order to achieve this object, the present invention has the following configuration.
[1] A light absorbing anisotropic layer, a light transmitting anisotropic layer, a light diffusing layer, a light source, and a reflective layer, in this order;
The optically absorptive anisotropic layer has a transmittance central axis perpendicular to the surface of the layer,
A planar lighting device, wherein the light-transmitting anisotropic layer satisfies the following requirements 1 and 2:
Requirement 1: When the transmittance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is T0 and the transmittance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal direction of the light-transmitting anisotropic layer is T50, the relationships T0 > T50 and T50 < 70% are satisfied.
Requirement 2: When the absorbance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is A0 and the absorbance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal direction of the light-transmitting anisotropic layer is A50, the relationships A0<0.05 and A50<0.05 are satisfied.
[2] When the reflectance when light with a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is R0, and the reflectance when light with a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal line of the light-transmitting anisotropic layer is R50,
The planar lighting device according to [1], wherein the light transmission anisotropic layer satisfies the relationships R0<R50 and R50>30%.
[3] The planar lighting device according to [1] or [2], wherein the light-transmitting anisotropic layer is a multilayer film in which 50 or more different layers are stacked.
[4] The planar lighting device according to any one of [1] to [3], further comprising a polarization control layer between the light transmission anisotropic layer and the light absorption anisotropic layer, which rotates the polarization direction of incident linearly polarized light within a range of 80 to 100 degrees.
[5] The planar lighting device according to [4], wherein the polarization control layer is a layer containing a liquid crystal compound that is twisted and aligned along a helical axis extending in the thickness direction.
[6] The planar illumination device according to [4], wherein the polarization control layer is a half-wave plate.
[7] An image display device having the planar illumination device according to any one of [1] to [6].
[8] An optically absorptive anisotropic layer having a transmittance central axis perpendicular to the surface of the layer;
An optical film having a light-transmitting anisotropic layer that satisfies the following requirements 1 and 2:
Requirement 1: When the transmittance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is T0 and the transmittance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal direction of the light-transmitting anisotropic layer is T50, the relationships T0 > T50 and T50 < 70% are satisfied.
Requirement 2: When the absorbance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is A0 and the absorbance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal direction of the light-transmitting anisotropic layer is A50, the relationships A0<0.05 and A50<0.05 are satisfied.
[9] The optical film according to [8], which has a polarization control layer between the light transmission anisotropic layer and the light absorption anisotropic layer, which rotates the polarization direction of incident linearly polarized light within a range of 80 to 100 degrees.

The present invention provides a surface lighting device that has high front brightness and excellent parallel light source properties, an image display device that uses this surface lighting device and is capable of displaying high-quality images, and an optical film that is suitable for this surface lighting device.

FIG. 1 is a conceptual diagram showing an example in which the surface illumination device of the present invention is used in a backlight device. FIG. 2 is a conceptual diagram showing another example in which the surface illumination device of the present invention is used in a backlight device. FIG. 3 is a diagram conceptually showing the reflectance of light by a general layer. FIG. 4 is a diagram conceptually showing the reflectance of light by a light-transmitting anisotropic layer. FIG. 5 is a diagram conceptually showing another example of the light transmission anisotropic layer.

The planar lighting device, image display device, and optical film of the present invention will be described in detail below.
The following description is based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
The drawings shown below are conceptual diagrams for explaining the present invention, and therefore the shape, size, thickness, positional relationship, spacing, and other aspects of each component in each drawing do not necessarily match those of the actual device.
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.

FIG. 1 conceptually shows an example in which the surface illumination device of the present invention is used in a backlight device for a liquid crystal display device or the like.
The surface lighting device of the present invention is not limited to backlight devices for liquid crystal display devices and the like, but can be used for various lighting applications. For example, the surface lighting device of the present invention can be used for various applications requiring surface illumination (surface illumination), such as indoor lighting attached to or embedded in ceilings and walls, outdoor environmental lighting, various types of inspection lighting, light boxes, and light tables. Here, as will be described later, the surface lighting device of the present invention has high front brightness and excellent parallel light source properties, and is therefore particularly suitable for use in backlight devices for liquid crystal display devices and the like, as in the illustrated example.
The backlight device 10 shown in FIG. 1 utilizes the planar lighting device of the present invention and includes a reflective layer 12, a light source 14, a light diffusing layer 16, a light-transmitting anisotropic layer 18, and a light-absorbing anisotropic layer 20.
For example, a liquid crystal panel constituting a liquid crystal display device is disposed on the light output side of the backlight device 10, i.e., the upper side in the figure. The light sources 14 are arranged two-dimensionally on the upper surface of the reflective layer 12 in the figure. Therefore, the backlight device 10 has, arranged in this order from the light output side, a light absorption anisotropic layer 20, a light transmission anisotropic layer 18, a light diffusion layer 16, the light source 14, and the reflective layer 12.

Furthermore, the backlight device 10, i.e., the surface lighting device of the present invention, may, if necessary, have layers (components) other than the polarization control layer 26 described below between each layer (component) from the light source 14 to the light-absorbing anisotropic layer 20.
Furthermore, if necessary, the backlight device 10, i.e., the surface lighting device of the present invention, may be provided with a color-adjusting layer containing a dye compound or the like on the light-emitting side of the light-transmitting anisotropic layer 18 in order to neutralize the color of the emitted light.

In the backlight device 10, i.e., the planar lighting device (optical film) of the present invention, the light-transmitting anisotropic layer 18 and the light-absorbing anisotropic layer 20 may be laminated or separated from each other. Similarly, the light-diffusing layer 16 may be laminated on the light-transmitting anisotropic layer 18 or separated from it.
That is, in the planar lighting device of the present invention, there are no limitations on the stacking state of each layer (each component) from the light diffusing layer 16 to the light-absorbing anisotropic layer 20, and various arbitrary configurations can be used. However, in order to make the backlight device 10 thinner, it is preferable to stack components that can be stacked within a range that does not affect the optical characteristics.
The laminated layers may be adhered with OCA (Optical Clear Adhesive) or may be integrated using a frame, a jig, a clip, or the like.
The same applies to the configuration having a polarization control layer 26 described below.

In the backlight device 10, the light source 14 may be any of various known light sources (light-emitting elements) used in so-called direct-type backlight devices.
Examples of the light source 14 include an LED (Light Emitting Diode), an organic EL (Electro Luminescence), and a fluorescent lamp.
In addition, as the light source 14 of the backlight device 10, a combination of a light-emitting element and a layer made of a wavelength conversion material (fluorescent material), such as a combination of a blue LED and a quantum dot layer that emits red and green fluorescent light when blue light is incident on it, can also be used.
The light source 14 may be a white light source, or may be a combination of a red light source, a green light source, and a blue light source that emits white light as a whole.

In the illustrated backlight device 10, the light sources 14 are arranged two-dimensionally on the reflective layer 12 (light reflecting surface).
The arrangement of the light sources 14 may be the same as that of a general direct-type backlight device used in a liquid crystal display device. Therefore, the arrangement of the light sources 14 may be regular or irregular, but is usually regular. Furthermore, the arrangement density of the light sources 14 may be uniform or may vary in the surface direction of the reflective layer 12.

The reflective layer 12 may be made of any of various known materials used in backlight devices for liquid crystal display devices, etc. Examples include a metal plate such as an aluminum plate, and a plate material on which a reflective layer such as an aluminum vapor deposition layer is formed.
The reflective layer 12 may have either specular or diffuse reflectivity.

The backlight device, i.e., the planar lighting device of the present invention is not limited to the direct type. That is, in the planar lighting device of the present invention, the light source may be a so-called edge light type (side light type) light source that uses a light guide plate and linear light emitting elements that emit light from an edge surface of the light guide plate, or point light emitting elements that are arranged in the direction of the edge surface of the light guide plate.
When an edge-light type light source is used in the planar lighting device of the present invention, a reflective layer is provided on the side opposite to the light-emitting surface of the light guide plate. In this case, the reflective layer may be in contact with the light guide plate or may be spaced apart from the light guide plate. As with the light source 14 described above, various known light sources may be used.

The light diffusion layer 16 is disposed downstream of the light source 14. In the present invention, the downstream side refers to the downstream side in the traveling direction of light emitted from the light source 14 and traveling from the light diffusion layer 16 to the light absorption anisotropic layer 20.
The light diffusion layer 16 may be any of various known types used in backlight devices for liquid crystal displays.
Examples include frosted glass, transparent plates that have been roughened by sandblasting or the like, and light diffusion plates (light diffusion films, light diffusion sheets) such as films in which silicone-based, acrylic-based, or other diffusing beads are diffused on a base film made of resin such as polystyrene, polycarbonate, acrylic resin, or methyl methacrylate-styrene copolymer.

A prism sheet can also be used as the light diffusion layer 16. When using a prism sheet as the light diffusion layer 16, one sheet may be used, but it is preferable to use two prism sheets arranged with their ridgelines perpendicular to each other.
Furthermore, the light diffusion layer 16 may be a combination of one or more of the above-mentioned light diffusion plates and a prism sheet.

The light-transmitting anisotropic layer 18 is disposed downstream of the light-diffusing layer 16 .
In the backlight device 10, i.e., the planar lighting device of the present invention, the light-transmitting anisotropic layer 18 has anisotropy in light transmission. Specifically, the light-transmitting anisotropic layer 18 transmits light incident from the front, i.e., light incident in the normal direction of the light-transmitting anisotropic layer 18, as is. In contrast, light incident from an oblique direction, i.e., light incident at an angle to the normal line of the light-transmitting anisotropic layer 18, is not transmitted as is, but is instead reflected or diffused, for example.
The normal direction is a direction perpendicular to the surface of a layer (film, sheet, plate). The normal line is a line perpendicular to the surface of the layer.
Furthermore, the light transmission anisotropic layer 18 has a very low absorptance of incident light.

Specifically, in the backlight device 10, i.e., the surface lighting device of the present invention, the light-transmitting anisotropic layer 18 satisfies Requirement 1, where T0 is the transmittance when light with a wavelength of 550 nm is incident from the normal direction, and T50 is the transmittance when light with a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal, and T0 > T50 and T50 < 70%.
In addition to satisfying requirement 1, the light-transmitting anisotropic layer 18 further satisfies requirement 2, where A0 is the absorbance when light with a wavelength of 550 nm is incident from the normal direction and A50 is the absorbance when light with a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal, and A0<0.05 and A50<0.05.

In the illustrated backlight device 10, the light transmission anisotropic layer 18 preferably reflects light incident from an oblique direction with high reflectance while satisfying the above-mentioned requirements 1 and 2. Specifically, in a preferred embodiment, the light transmission anisotropic layer 18 satisfies the relationships R0<R50 and R50>30%, where R0 is the reflectance when light with a wavelength of 550 nm is incident from the normal direction and R50 is the reflectance when light with a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal.
As will be described in detail later, in the planar lighting device of the present invention, another example of the light-transmitting anisotropic layer diffuses, rather than reflects, light incident from an oblique direction.

In the present invention, the transmittance, reflectance, and absorbance of the light-transmitting anisotropic layer 18 may be measured by known methods using a goniophotometer, a polarizing film measuring device, a spectrophotometer, or the like. Examples of methods for measuring the transmittance, reflectance, and absorbance of the light-transmitting anisotropic layer 18 include the methods shown in the examples described below.

That is, in the illustrated backlight device 10, the light-transmitting anisotropic layer 18 transmits light incident in the normal direction, i.e., from the front, with high transmittance without absorbing or reflecting it. On the other hand, the light-transmitting anisotropic layer 18 does not transmit or absorb light incident from an oblique direction, such as a direction at a polar angle of 50° to the normal, and preferably reflects it with high reflectance.
The backlight device 10, i.e., the planar lighting device of the present invention, has such an optically transmissive anisotropic layer 18 and an optically absorbing anisotropic layer 20, which will be described later, and thereby realizes a planar lighting device with high front luminance and excellent parallel light source properties. This will be described in detail later.

In the light transmission anisotropic layer 18, the transmittance T0 of light with a wavelength of 550 nm incident from the normal direction is higher than the transmittance T50 of light with a wavelength of 550 nm incident from a direction at a polar angle of 50° with respect to the normal. If the transmittance T0 is lower than the transmittance T50, inconveniences arise in that sufficient front luminance and parallel light source properties cannot be obtained.
The transmittance T0 is preferably 10% or more, more preferably 25% or more, and even more preferably 40% or more, as long as it is higher than the transmittance T50.
By setting the transmittance T0 to 10% or more, it is possible to improve the front brightness and the parallel light source property, which is preferable.

The light transmission anisotropic layer 18 has a transmittance T50 of less than 70% for light having a wavelength of 550 nm incident from a direction at a polar angle of 50° with respect to the normal.
If the transmittance T50 is 70% or more, there will be inconveniences such as inability to obtain sufficient front luminance and parallel light source properties.
The lower the transmittance T50, the better. The transmittance T50 is preferably less than 50%, and more preferably less than 35%.

In the light-transmitting anisotropic layer 18, the absorbance A0 when light with a wavelength of 550 nm is incident from the normal direction, and the absorbance A50 when light with a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal, are both less than 0.05.
If the absorbance A0 and the absorbance A50 are 0.05 or more, the light utilization efficiency is low, and sufficient front brightness cannot be obtained, which is disadvantageous.
The absorbance A0 and the absorbance A50 are preferably lower, and are preferably less than 0.02, and more preferably less than 0.01.

In a preferred embodiment, the light transmission anisotropic layer 18 shown in the figure has a reflectance R0 for light with a wavelength of 550 nm incident from the normal direction and a reflectance R50 for light with a wavelength of 550 nm incident from a direction at a polar angle of 50° with respect to the normal, satisfying R0<R50 and R50>30%.
By making the reflectance R0 lower than the reflectance R50, it is possible to improve the front brightness and improve the parallel light source property, which is preferable.

A reflectance R50 of more than 30% is preferable in that it can improve the front brightness, improve the parallel light source property, etc. The higher the reflectance R50, the better, and it is more preferably more than 50%, and even more preferably more than 65%.
On the other hand, the lower the reflectance R0, the better. The reflectance R0 is preferably less than 10%, more preferably less than 7%, and even more preferably less than 4%.
By setting the reflectance R0 to less than 10%, it is possible to improve the front brightness and improve the parallel light source property, which is preferable.

As such an optically transparent anisotropic layer, various known materials can be used as long as the transmittance T0 is greater than the transmittance T50 and the transmittance T50 is less than 70%, and further the absorbance A0 and the absorbance A50 are less than 0.05.
One example is a laminated film described in International Publication No. 2009/198635, in which 50 or more layers of different thermoplastic resins are laminated together, the transmittance of light incident from the normal direction being 50% or more, and the reflectance [%] of P waves when incident at angles of 20°, 40°, and 70° to the normal being R20, R40, and R70, respectively, satisfying the relationship R20≦R40<R70, the reflectance R70 being 30% or more, and the saturation of reflected light of P waves when incident at an angle of 70° to the normal being 20 or less. Note that the normal and normal direction both refer to the normal and normal direction of the film surface.

The optically absorbing anisotropic layer 20 is disposed downstream of the optically transmitting anisotropic layer 18 .
The optically absorptive anisotropic layer 20 is a layer whose central transmittance axis is perpendicular to the surface of the layer. In the present invention, the phrase "the central transmittance axis is perpendicular to the surface of the layer" includes not only a completely perpendicular axis to the surface of the layer, but also an angle range of ±5° with respect to the direction perpendicular to the surface of the layer.
The optical film of the present invention comprises the above-described light-transmitting anisotropic layer 18 and the light-absorbing anisotropic layer 20 .

In the present invention, the central axis of transmittance is the direction in which the transmittance is highest when the polar angle and azimuthal angle are changed and the transmittance is measured in various directions from the surface of the layer.
Therefore, the optically absorptive anisotropic layer 20, whose central transmittance axis is perpendicular to the surface of the layer, transmits light incident in the normal direction, i.e., from the front, as is, and absorbs light incident in a direction inclined to the normal, i.e., from an oblique direction.

The optically absorptive anisotropic layer 20 can be made of various layers whose transmittance central axis is perpendicular to the surface of the layer.
As an example, a layer in which the dichroic material is oriented perpendicular to the surface of the layer (within a range of ±5° from the perpendicular) is exemplified.

In the present invention, a dichroic substance refers to a dye whose absorbance varies depending on the direction. A dichroic substance may or may not exhibit liquid crystallinity.

The dichroic substance is not particularly limited, and examples thereof include visible light absorbing substances (dichroic dyes), luminescent substances (fluorescent substances, phosphorescent substances), ultraviolet absorbing substances, infrared absorbing substances, nonlinear optical substances, carbon nanotubes, and inorganic substances (e.g., quantum rods), and any conventionally known dichroic substance (dichroic dye) can be used.
Specifically, for example, paragraphs [0067] to [0071] of JP 2013-228706 A, paragraphs [0008] to [0026] of JP 2013-227532 A, paragraphs [0008] to [0015] of JP 2013-209367 A, paragraphs [0045] to [0058] of JP 2013-14883 A, paragraphs [0012] to [0029] of JP 2013-109090 A, paragraphs [0009] to [0017] of JP 2013-101328 A, paragraphs [0051] to [0065] of JP 2013-37353 A, paragraphs [0012] to [0029] of JP 2012-63387 A [0049] to [0073] paragraphs, [0016] to [0018] paragraphs of JP-A-11-305036, [0009] to [0011] paragraphs of JP-A-2001-133630, [0030] to [0169] paragraphs of JP-A-2011-215337, and [0010-106242] Paragraphs [0021] to [0075], paragraphs [0011] to [0025] of JP-A No. 2010-215846, paragraphs [0017] to [0069] of JP-A No. 2011-048311, paragraphs [0013] to [0133] of JP-A No. 2011-213610, and JP-A No. 2011-237513 Paragraphs [0074] to [0246] of JP 2016-006502 A, paragraphs [0005] to [0051] of JP 2016-006502 A, paragraphs [0014] to [0032] of JP 2018-053167 A, paragraphs [0014] to [0033] of JP 2020-11716 A, paragraphs [0005] to [0041] of WO 2016/060173 A, paragraphs [0008] to [0062] of WO 2016/136561 A, paragraphs [0014] to [0033] of WO 2017/154835 A, paragraphs [0014] to [0033] of WO 2017/154695 A, Examples include those described in paragraphs [0013] to [0037] of International Publication No. 2017/195833, paragraphs [0014] to [0034] of International Publication No. 2018/164252, paragraphs [0021] to [0030] of International Publication No. 2018/186503, paragraphs [0043] to [0063] of International Publication No. 2019/189345, paragraphs [0043] to [0085] of International Publication No. 2019/225468, paragraphs [0050] to [0074] of International Publication No. 2020/004106, and paragraphs [0015] to [0038] of International Publication No. 2021/044843.

In the present invention, two or more dichroic substances may be used in combination. As an example, from the perspective of making the light absorption anisotropic layer 20 closer to black, it is preferable to use a combination of at least one dichroic substance having a maximum absorption wavelength in the wavelength range of 370 to 550 nm and at least one dichroic substance having a maximum absorption wavelength in the wavelength range of 500 to 700 nm.

The method for forming the light absorption anisotropic layer 20 is not particularly limited, but from the viewpoint of orienting the dichroic material with a high degree of orientation, a preferred method is to form the layer using a liquid crystal composition containing a liquid crystal compound together with the above-mentioned dichroic material.
In the present invention, the liquid crystal compound is a liquid crystal compound that does not exhibit dichroism.
As the liquid crystal compound, either a low-molecular-weight liquid crystal compound or a high-molecular-weight liquid crystal compound can be used, but a high-molecular-weight liquid crystal compound is more preferable in terms of achieving a high degree of orientation. Here, "low-molecular-weight liquid crystal compound" refers to a liquid crystal compound that does not have a repeating unit in its chemical structure. Also, "high-molecular-weight liquid crystal compound" refers to a liquid crystal compound that has a repeating unit in its chemical structure.
Examples of low molecular weight liquid crystal compounds include the liquid crystal compounds described in JP-A-2013-228706.
Examples of the polymer liquid crystal compound include the thermotropic liquid crystalline polymers described in JP 2011-237513 A. The polymer liquid crystal compound may have a crosslinkable group (e.g., an acryloyl group or a methacryloyl group) at its terminal.
The liquid crystal compounds may be used alone or in combination of two or more.
The liquid crystal compound preferably contains a polymer liquid crystal compound, since the degree of orientation of the light absorptive anisotropic layer 20 is superior.
The liquid crystal composition may also contain a solvent, a polymerization initiator, an interfacial improver, an alignment agent, and other components.

For example, when forming the optically absorptive anisotropic layer 20 using such a liquid crystal composition, the liquid crystal composition is first applied to an alignment film that has been imparted with the alignment property of the liquid crystal compound. Next, the liquid crystal composition is heated and/or cooled, or heating and cooling are repeated, thereby aligning the liquid crystal compound in the thickness direction. This alignment of the liquid crystal compound also aligns the dichroic material in the thickness direction.
Thereafter, if necessary, the liquid crystal layer is cured by irradiation with ultraviolet light or the like, thereby forming the light absorption anisotropic layer 20 in which the dichroic material is oriented in the thickness direction.

The operation of the backlight device 10 will be described below with reference to FIG. 1, thereby providing a more detailed explanation of the planar lighting device of the present invention.
In the following description, for convenience, light incident from the normal direction, i.e., from the front, is also referred to as "frontal incidence." Also, light incident from a direction at an angle to the normal, i.e., from an oblique direction, is also referred to as "oblique incidence."

The light emitted by the light source 14 (dashed line) is first diffused by the light diffusion layer 16 and then enters the light-transmitting anisotropic layer 18.

As described above, the light transmission anisotropic layer 18 transmits light that is incident from the front as is and reflects light that is incident obliquely. Therefore, of the light diffused by the light diffusion layer 16, light that is incident from the front on the light transmission anisotropic layer 18 is transmitted as is and enters the light absorption anisotropic layer 20.
As described above, the optically absorptive anisotropic layer 20 transmits light that is incident from the front as is and absorbs light that is incident obliquely. Therefore, light that is incident from the front on the optically absorptive anisotropic layer 18 and that is transmitted through the optically absorptive anisotropic layer 20 is also incident from the front on the optically absorptive anisotropic layer 20, and most of the light is transmitted through the optically absorptive anisotropic layer 20 as is without being absorbed.
When the surface illumination device of the present invention is used as a backlight device for a liquid crystal display device, the light that has passed through the optically absorbing anisotropic layer 20 is also incident from the front onto, for example, a liquid crystal panel that is arranged downstream of the optically absorbing anisotropic layer 20.

On the other hand, of the light diffused by the light diffusion layer 16, the light that is obliquely incident on the light-transmitting anisotropic layer 18 is reflected by the light-transmitting anisotropic layer 18, and then enters the light-diffusing layer 16 and is diffused.
Light that enters the light diffusion layer 16 from the light-transmitting anisotropic layer 18 side and is diffused is reflected by the reflective layer 12, then enters the light diffusion layer 16 and is diffused therein, and then enters the light-transmitting anisotropic layer 18 again.
Here, the light incident on the light diffusion layer 16 travels in various directions due to diffusion by the light diffusion layer 16. Therefore, a portion of the light that re-enters the light transmission anisotropic layer 18 is incident on the light transmission anisotropic layer 18 from the front. As before, the light that is incident on the light transmission anisotropic layer 18 from the front is transmitted as is and enters the light absorption anisotropic layer 20 from the front, and is also transmitted through the light absorption anisotropic layer 20 from the front and enters the liquid crystal panel from the front.
On the other hand, light that is obliquely incident on the light-transmitting anisotropic layer 18 is reflected by the light-transmitting anisotropic layer 18, diffused by the light-diffusing layer 16, reflected by the reflective layer 12, diffused by the light-diffusing layer 16, and re-incident on the light-transmitting anisotropic layer 18 as before.

As described above, in the backlight device 10, i.e., the planar lighting device of the present invention, light that is obliquely incident on the light-transmitting anisotropic layer 18 is repeatedly reflected by the light-absorbing anisotropic layer 20, diffused by the light-diffusing layer 16, reflected by the reflective layer 12, and diffused again by the light-diffusing layer 16. During this repetition, when the light reaches a state in which it is incident head-on on the light-transmitting anisotropic layer 18, it transmits through the light-transmitting anisotropic layer 18, and then is incident head-on on and transmitted through the light-absorbing anisotropic layer 20, before being incident head-on on the liquid crystal panel.
That is, the planar lighting device of the present invention has the light-transmitting anisotropic layer 18 that transmits light incident from the front and reflects light incident from the oblique direction, and the light-absorbing anisotropic layer 20 that transmits light incident from the front and absorbs light incident from the oblique direction, thereby enabling the outgoing light to be concentrated in the front direction. Furthermore, the planar lighting device of the present invention can significantly reduce the amount of light emitted in oblique directions relative to the light emitted in the front direction due to the reflection of obliquely incident light by the light-transmitting anisotropic layer 18 and the absorption of obliquely incident light by the light-absorbing anisotropic layer 20.
As a result, according to the present invention, a surface lighting device can be realized which has high front brightness, i.e., the brightness of light emitted in the front direction, and which has excellent parallel light source properties, with a greater amount of light emitted in the front direction compared to light emitted in oblique directions.

FIG. 2 shows another example in which the surface illumination device of the present invention is used in a backlight device.
The backlight device 30 shown in FIG. 2 has the same configuration as the backlight device 10 shown in FIG. 1 except for the polarization control layer 26, so the same components are given the same symbols, and the following explanation will mainly focus on the different parts.

2 has a polarization control layer 26 between the light transmission anisotropic layer 18 and the light absorption anisotropic layer 20. That is, the optical film of the present invention described above may have a polarization control layer 26 between the light transmission anisotropic layer 18 and the light absorption anisotropic layer 20.
2, the light-transmitting anisotropic layer 18, the polarization control layer 26, and the light-absorbing anisotropic layer 20 may all be stacked, or two layers may be stacked, or all may be separated. The light-diffusing layer 16 may also be stacked on the light-transmitting anisotropic layer 18, or may be separated.

The polarization control layer 26 rotates the polarization direction of the linearly polarized light that is incident thereon within a range of 80 to 100 degrees.
The backlight device 30, that is, the surface illumination device of the present invention, can further improve the parallel light source properties by having such a polarization control layer 26.

When linearly polarized light is incident on a typical layer, as conceptually shown in FIG. 3, the reflectance is higher for S-polarized light, indicated by the dashed line, than for P-polarized light, indicated by the solid line.
However, according to the investigations of the present inventors, the light transmitting anisotropic layer 18, which transmits light incident from the front and reflects light incident at an angle, is the opposite of a typical layer; as conceptually shown in FIG. 4, the light that is reflected is dominated by the P-polarized component shown by the solid line, and the light that is transmitted is dominated by the S-polarized component shown by the dashed line.
In the present invention, P-polarized light is linearly polarized light whose polarization direction is perpendicular to the surface of the optically absorptive anisotropic layer 20, i.e., the surface of the optically transmissive anisotropic layer 18, and S-polarized light is linearly polarized light whose polarization direction is parallel to the surface of the optically absorptive anisotropic layer 20, i.e., the surface of the optically transmissive anisotropic layer 18.

As described above, the optically absorptive anisotropic layer 20 absorbs obliquely incident light, but like a normal layer, the optically absorptive anisotropic layer 20 has a lower absorption rate for S-polarized light than for P-polarized light.
Therefore, when the light incident on the optically absorptive anisotropic layer 20 contains more S-polarized components than P-polarized components, the absorptivity of the obliquely incident light by the optically absorptive anisotropic layer 20 decreases. As a result, there is a possibility that the proportion of light that is transmitted through the optically absorptive anisotropic layer 20 without being absorbed by the layer 20 increases, even though the light is obliquely incident on the layer 20.

In contrast, in a preferred embodiment, the backlight device 30, i.e., the surface lighting device of the present invention, has a polarization control layer 26 between the light-transmitting anisotropic layer 18 and the light-absorbing anisotropic layer 20, which rotates the polarization direction of incident linearly polarized light within a range of 80 to 100 degrees.
That is, in a preferred embodiment, the backlight device 30 has a polarization control layer 26 between the light-transmitting anisotropic layer 18 and the light-absorbing anisotropic layer 20 that converts S-polarized light into P-polarized light.

As described above, the light transmitted through the light-transmitting anisotropic layer 18 contains more S-polarized components than P-polarized components. Therefore, by providing the polarization control layer 26 between the light-transmitting anisotropic layer 18 and the light-absorbing anisotropic layer 20, the light transmitted through the polarization control layer 26 and incident on the light-absorbing anisotropic layer 20 contains more P-polarized components than S-polarized components.
Therefore, by providing the polarization control layer 26 between the light transmission anisotropic layer 18 and the light absorption anisotropic layer 20, the absorptance of obliquely incident light by the light absorption anisotropic layer 20 can be improved. In other words, the transmittance of obliquely incident light to the light absorption anisotropic layer 20 can be further reduced.
As a result, by having the polarization control layer 26, the proportion of light emitted in a frontal direction relative to light emitted in an oblique direction in the light emitted from the light absorption anisotropic layer 20, i.e., the backlight device 30, can be increased, thereby further improving the parallel light source properties.

There are no limitations on the polarization control layer 26, and various known materials (optical elements) can be used as long as they can rotate the polarization direction of incident linearly polarized light within a range of 80 to 100 degrees.
An example of the polarization control layer 26 is a layer containing a liquid crystal compound that is twisted along a helical axis extending along the thickness direction. That is, an example of the polarization control layer 26 is a layer (optical rotatory layer, optical rotatory film) that contains a liquid crystal compound that is twisted in a helical manner in the thickness direction.

For example, the polarization control layer 26 can be formed using a liquid crystal composition containing a polymerizable liquid crystal compound, such as a rod-shaped nematic liquid crystal compound, and a chiral agent. The chiral agent may be a known chiral agent that has the function of inducing a helical structure in the liquid crystal compound.
Specifically, a liquid crystal composition containing a polymerizable liquid crystal compound and a chiral agent is applied to the surface of an alignment film having an alignment control force. The liquid crystal composition is then dried by heating, and the liquid crystal compound is helically aligned. The liquid crystal composition is then cured by, for example, irradiating it with ultraviolet light, thereby producing a polarization control layer 26 in which the liquid crystal compound is helically aligned in the thickness direction.

In the polarization control layer 26 in which the liquid crystal compound is helically twisted and oriented in the thickness direction, there is no restriction on the twist angle of the liquid crystal compound, and the twist angle can be appropriately set so that the polarization direction of linearly polarized light can be rotated in the range of 80 to 100 degrees depending on the type of liquid crystal compound, etc.
The twist angle of the liquid crystal compound can be adjusted by the type and amount of chiral dopant added.
Furthermore, in the polarization control layer 26 in which the liquid crystal compound is helically twisted and oriented in the thickness direction, there are no restrictions on the Δn of the liquid crystal compound, the film thickness d, and Δnd, and they may be set appropriately so that the polarization direction of linearly polarized light can be rotated in the range of 80 to 100 degrees.

The polarization control layer 26 may also be a half-wave plate.
As the half-wave plate, various known half-wave plates (λ/2 plates, λ/2 retardation plates) that have a phase difference of approximately ½ wavelength at any wavelength of visible light can be used.
A preferred example of the half-wave plate is one having a phase difference of 220 to 330 nm at a wavelength of 550 nm, and a more preferred example is one having a phase difference of 247 to 302 nm.

1 and 2, which uses the planar lighting device of the present invention, the light-transmitting anisotropic layer 18 transmits light incident from the front and reflects light incident from an oblique angle. However, the light-transmitting anisotropic layer in the planar lighting device of the present invention is not limited to this.
In other words, in the surface lighting device of the present invention, various known types can be used as long as they satisfy requirement 1 that the transmittance T0 and transmittance T50 are T0>T50 and T50<70%, and requirement 2 that the absorbance T0 and absorbance T50 are both less than 0.05.

An example is a light-transmitting anisotropic layer 34 that transmits light incident from the front as is and diffuses light incident obliquely, as conceptually shown in FIG.
According to this light transmission anisotropic layer 34, in addition to light incident from the front that is transmitted as is, light that is incident obliquely and diffused changes its traveling direction to the front, and is incident from the front on the light absorption anisotropic layer 20 and transmitted therethrough is also generated.
Furthermore, a portion of the obliquely incident light is diffused, and thus its angle with respect to the normal becomes larger. That is, a portion of the diffused light has a deeper oblique incident angle. Such light having a deeper oblique incident angle travels a longer optical path in the optically absorptive anisotropic layer 20, and therefore its absorption rate by the optically absorptive anisotropic layer 20 becomes higher. As a result, the amount of light emitted obliquely from the optically absorptive anisotropic layer 20 can be significantly reduced.

Therefore, by using such an optically transmissive anisotropic layer 34, it is possible to increase the amount of light emitted in the front direction from the optically absorbing anisotropic layer 20, i.e., the surface illumination device, and to decrease the amount of light emitted in an oblique direction.
As a result, by using this light-transmitting anisotropic layer 34, a planar illumination device with high front luminance and excellent parallel light source properties can be realized.

As the light-transmitting anisotropic layer 34 that transmits light incident from the front and diffuses light incident obliquely, various known light-transmitting anisotropic layers can be used.
One example is a light-transmitting anisotropic layer (light control film) using a photocurable resin composition containing at least two types of photopolymerizable monomers or oligomers, each of which has a polymerizable carbon-carbon bond in its molecule and which has a difference in the refractive index of the homopolymer obtained by homopolymerization, as described in JP 2009-157251 A. This light-transmitting anisotropic layer can be formed by forming the photocurable resin composition into a film, using a linear light source and a reflecting member that reflects light from the linear light source and irradiates the composition film with parallel light, and moving the composition film, the linear light source, and the reflecting member relative to each other so that the axial direction of the cleaning light source and the movement direction intersect, thereby irradiating the composition film with light from the linear light source and curing it.
As another example, a light-transmitting anisotropic layer (light control film) that selectively scatters only incident light within a specific angle range can also be used, which is obtained by irradiating a film-like composition with ultraviolet light from a specific direction to cure the composition, the film-like composition containing multiple types of compounds having a polymerizable carbon-carbon double bond as described in JP 2011-186494 A, wherein at least one of the compounds has multiple aromatic rings and one polymerizable carbon-carbon double bond in the molecule, and at least one of the compounds having multiple aromatic rings and one polymerizable carbon-carbon double bond in the molecule is a compound containing an aromatic hydroxyl group, with the content of this compound being 0.1 to 30 parts by weight relative to 100 parts by weight of the film-like composition.
Furthermore, the light-transmitting anisotropic layer 34 that transmits light incident from the front and diffuses light incident obliquely can be a commercially available product such as a vision control film manufactured by Sumitomo Chemical Co., Ltd.

The image display device of the present invention is an image display device that has such a surface illumination device of the present invention.
The image display device of the present invention can be any of various known image display devices, so long as it uses a surface illumination device. A preferred example is a liquid crystal display device (LCD (Liquid Crystal Display)) having a known liquid crystal panel. As described above, the surface illumination device of the present invention has high front brightness and excellent parallel light source properties. Therefore, the image display device of the present invention using such a surface illumination device of the present invention can display high-quality images with high front display brightness and has excellent field of view controllability, which can reduce visibility when viewed from an oblique direction.

The above provides a detailed description of the surface lighting device, image display device, and optical film of the present invention, but the present invention is not limited to the above examples, and various improvements and modifications may of course be made within the scope of the present invention.

The features of the present invention are explained in more detail below with reference to the following examples. The materials, reagents, amounts used, amounts of substances, ratios, treatment details, and treatment procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[Example 1]
<Formation of alignment film>
The surface of a 40 μm thick cellulose acylate film (TAC substrate; Fujifilm Corporation, TG40) was saponified with an alkaline solution, and the following composition for forming an alignment film was applied thereon with a wire bar.
The support on which the coating film was formed was dried with hot air at 60° C. for 60 seconds and then with hot air at 100° C. for 120 seconds to form an alignment film, thereby obtaining a TAC film with an alignment film.
The thickness of the alignment film was 1 μm.

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Composition for forming alignment film------------------------------------------------
・Modified polyvinyl alcohol PVA-1 3.80 parts by mass ・IRGACURE 2959 0.20 parts by mass ・Water 70 parts by mass ・Methanol 30 parts by mass

Modified polyvinyl alcohol PVA-1

<Formation of Optically Absorbing Anisotropic Layer>
On the obtained alignment film, the following composition for forming an optically absorptive anisotropic layer was continuously coated with a wire bar, heated at 120° C. for 60 seconds, and then cooled to room temperature (23° C.).
It was then heated at 80° C. for 60 seconds and cooled again to room temperature.
Thereafter, the alignment film was irradiated with ultraviolet light for 2 seconds using an LED lamp (center wavelength 365 nm) at an illuminance of 200 mW/cm ² to form a light absorption anisotropic layer on the alignment film.
The thickness of the optically absorptive anisotropic layer was 3.5 μm.

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Composition of the composition for forming the optically absorptive anisotropic layer
Dichroic substance D-1 0.63 parts by mass Dichroic substance D-2 0.17 parts by mass Dichroic substance D-3 1.13 parts by mass Polymer liquid crystal compound P-1 8.18 parts by mass IRGACUREOXE-02 (manufactured by BASF) 0.16 parts by mass Compound E-1 0.12 parts by mass Compound E-2 0.12 parts by mass Surfactant F-1 0.005 parts by mass Cyclopentanone 85.00 parts by mass Benzyl alcohol 4.50 parts by mass

Dichroic substance D-1

Dichroic substance D-2

Dichroic substance D-3

Polymer liquid crystal compound P-1

Compound E-1

Compound E-2

Surfactant F-1

The transmittance of the prepared optically absorptive anisotropic layer was measured using AxoScan OPMF-1 (manufactured by OptoScience) while varying the polar angle and azimuthal angle, thereby determining the direction of the transmittance central axis.
As a result, the central axis of transmittance was perpendicular to the surface of the layer.

<Preparation of Light-Transmitting Anisotropic Layer>
Copolymerized PET with a refractive index of 1.57, a melting point of 220°C, and a glass transition temperature of 80°C, and amorphous copolymerized PEN with no melting point, an average refractive index of 1.63, and a glass transition temperature of 80°C were prepared. The copolymerized PET and copolymerized PEN were each fed into two single-screw extruders, melted at a temperature of 290°C, and kneaded.
Subsequently, the kneaded copolymerized PET and the kneaded copolymerized PEN were each weighed and merged in a lamination device with 801 slits to produce a laminate in which 801 layers were alternately laminated in the thickness direction.

The produced laminate was heated with a group of rolls set at a temperature of 60° C., then stretched 3.7 times with rolls set at a temperature of 85° C., and cooled.
After cooling, the film was heated with hot air at a temperature of 90°C, and then stretched at a temperature of 95°C by 3.2 times in the direction perpendicular to the direction of the previous stretching.
After stretching, the film was heat-treated with hot air at 240° C. Following the heat treatment, a 2% relaxation treatment was carried out at 240° C. to form a light-transmitting anisotropic layer of an optical multilayer film.

The light-transmitting anisotropic layer thus formed was measured by the following measurement methods to determine the transmittance T0 when light of a wavelength of 550 nm was incident from the normal direction, and the transmittance T50 when light of a wavelength of 550 nm was incident from a direction at a polar angle of 50° with respect to the normal direction.
The absorbance A0 when light of a wavelength of 550 nm is incident from the normal direction, and the absorbance A50 when light of a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal, and
The reflectance R0 when light with a wavelength of 550 nm was incident from the normal direction, and the reflectance R50 when light with a wavelength of 550 nm was incident from a direction at a polar angle of 50° with respect to the normal were measured.
As a result, it was confirmed that the formed light transmission anisotropic layer satisfied all of the conditions T0>T50 and T50<70%, A0<0.05 and A50<0.05, and R0<R50 and R50>30%.

(1) Measurement of Transmittance The transmittance T0 was measured at a wavelength of 550 nm using an automatic polarizing film measuring device (VAP-7070 manufactured by JASCO Corporation) with an integrating sphere placed on the light receiving side.
Next, using a goniophotometer, light was irradiated at a polar angle of 50° relative to the normal direction of the surface, and the light-receiving side angle was changed in 5° increments from -80° to 80°, and the light intensity of the transmitted light was measured. The light intensity for each light-receiving angle was integrated and normalized by the total amount of light without a measurement sample to determine the transmittance T50. The goniophotometer used was a "Three-Dimensional Goniospectrophotometric Colorimetric System GCMS-3B" manufactured by Murakami Color Research Laboratory. The light-receiving side angle is the polar angle relative to the normal.

(2) Measurement of Reflectance The reflectance R0 was determined by roughening the surface opposite to the incident surface with sandpaper and then treating it with black ink to eliminate back surface reflection, and then measuring the integrated reflectance at a wavelength of 550 nm using a spectrophotometer (manufactured by JASCO Corporation).
Next, using a goniophotometer, light was irradiated at a polar angle of 50° relative to the normal direction of the surface, and the light-receiving side angle was changed in 5° increments from -80° to 35°, and the light intensity of the reflected light was measured. The light intensity for each light-receiving angle was integrated and normalized by the total amount of light when a mirror was placed as the measurement sample, thereby determining the reflectance R50. The goniophotometer used was a "Three-Dimensional Goniospectrophotometric Colorimetric System GCMS-3B" manufactured by Murakami Color Research Laboratory. The light-receiving side angle is the polar angle relative to the normal.

(3) Measurement of Absorbance The absorbance A0 was calculated from the measured transmittance T0 and reflectance R0 using the following formula.
A0=-LOG10(T0+R0)
The absorbance A50 was calculated from the measured transmittance T50 and reflectance R50 using the following formula:
A50=-LOG10(T50+R50)

<Preparation of Optical Film 1>
The light-transmitting anisotropic layer and the light-absorbing anisotropic layer were bonded together using a commercially available adhesive (SK2057, manufactured by Soken Chemical & Engineering Co., Ltd.) to produce optical film 1 in which the light-transmitting anisotropic layer, the light-absorbing anisotropic layer, the alignment film, and the TAC substrate were laminated in this order.

<Fabrication of Backlight Device A1>
The IPS mode liquid crystal display device was disassembled, and the liquid crystal panel (liquid crystal cell) was taken out. The liquid crystal display device used was an "iPad Air (registered trademark) Wi-Fi model 16 GB" manufactured by Apple Inc.
The optical film 1 was placed on the diffusion sheet of the liquid crystal display device from which the liquid crystal panel had been removed, with the light-transmitting anisotropic layer facing the diffusion sheet side, to prepare a backlight device A1.

[Example 2]
<Formation of Color Adjusting Layer>
The following composition for forming a color-adjusting layer was continuously applied onto the light absorption anisotropic layer of the optical film 1 prepared in Example 1 using a wire bar to form a coating film.
Next, the laminate on which the coating film was formed was dried with hot air at 60° C. for 60 seconds and then with hot air at 100° C. for 120 seconds to form a color-adjusting layer, and optical film 2 was produced.
The color-adjusting layer had a thickness of 0.5 μm.
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Color-adjusting layer-forming composition -------------------------------------------------
Modified polyvinyl alcohol PVA-1 3.80 parts by mass IRGACURE 2959 0.20 parts by mass Dye compound G-1 0.08 parts by mass Water 70 parts by mass Methanol 30 parts by mass

Pigment compound G-1

<Fabrication of Backlight Device A2>
A backlight device A2 was produced in the same manner as in Example 1, except that optical film 2 was used instead of optical film 1 in the production of backlight device A1 in Example 1.

[Comparative Example 1]
<Fabrication of Backlight Device B1>
An optical film B1 was prepared in the same manner as in the optical film 1 in Example 1, except that the optical film B1 did not have a light transmission anisotropic layer.
A backlight device B1 was produced in the same manner as in Example 1, except that optical film B1 was used instead of optical film 1 in the production of backlight device A1 of Example 1.

[Example 3]
<Preparation of transfer film>
A peelable support was prepared by rubbing the surface of a 75 μm PET film (manufactured by Fujifilm Corporation).

The following coating solution for an optical rotatory layer was applied to the rubbed surface of the prepared peelable support using a bar coater to form a coating film with a thickness of 3 μm.
The coating surface was then heated to 60°C for 90 seconds for aging. The coating was then irradiated with 300 mJ/ ^cm² of ultraviolet light at 100°C to fix the orientation of the liquid crystal compound and form an optical rotatory layer. This produced a transfer film comprising a peelable support and an optical rotatory layer as a polarization control layer.
In the obtained optical rotatory layer, the liquid crystal compound had a Δn of 0.16, a film thickness d of 3000 nm, and a Δnd of 480. The optical rotatory layer contained a liquid crystal compound that was twisted along a helical axis extending in the thickness direction. Analysis using an AxoScan OPMF-1 (manufactured by Optoscience) confirmed that the twist angle of the helical liquid crystal compound was 90°.
A transfer film containing an optical rotatory layer was placed between two polarizing plates, and the two polarizing plates were rotated in the in-plane direction so that the light passing through the two polarizing plates would be the darkest. By measuring the angle formed by the transmission axes of the two polarizing plates at this time, the rotation angle of the polarization direction of linearly polarized light by the optical rotatory layer, which is a polarization control layer, was measured. As a result, it was found that the optical rotatory layer rotated the polarization direction of linearly polarized light by 90 degrees.

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Coating liquid for optical rotation layer――――――――――――――――――――――――――――――
Methyl ethyl ketone 233 parts by mass Cyclohexanone 12 parts by mass Rod-shaped liquid crystal compound 201 83 parts by mass Rod-shaped liquid crystal compound 202 15 parts by mass Rod-shaped liquid crystal compound 203 2 parts by mass Polyfunctional monomer A-TMMT (manufactured by Shin-Nakamura Chemical Co., Ltd.) 1 part by mass IRGACURE 819 (manufactured by BASF) 4 parts by mass Surfactant 1 0.05 parts by mass Surfactant 2 0.01 parts by mass Chiral agent 0.115 parts by mass

In the preparation of Optical Film 2 in Example 2, prior to bonding the optically absorbing anisotropic layer and the optically transmitting anisotropic layer, a transfer film was bonded to the optically absorbing anisotropic layer using a commercially available pressure-sensitive adhesive (SK2057, manufactured by Soken Chemical & Engineering Co., Ltd.). The transfer film was bonded so that the optical rotatory layer was on the optically absorbing anisotropic layer side. The release support was then peeled off. After peeling off the release support, the optical rotatory layer remained attached to the optically absorbing anisotropic layer side.
Thereafter, a commercially available pressure-sensitive adhesive (SK2057, manufactured by Soken Chemical & Engineering Co., Ltd.) was used to attach a light-transmitting anisotropic layer to the optical rotatory layer in the same manner as in Optical Film 1. Furthermore, a color-adjusting layer was formed on the light-absorbing anisotropic layer in the same manner as in Optical Film 2, to produce Optical Film 3.

<Fabrication of Backlight Device A3>
A backlight device A3 was produced in the same manner as in Example 2, except that optical film 3 was used instead of optical film 2 in the production of backlight device A2 of Example 2.

<Preparation of Optical Film 4>
In the preparation of Optical Film 2 in Example 2, prior to bonding the optically absorptive anisotropic layer and the optically transmissive anisotropic layer, two half-wave plates were laminated to the optically absorptive anisotropic layer using a commercially available adhesive (SK2057, manufactured by Soken Chemical & Engineering Co., Ltd.). The half-wave plates used were "Pure Ace WR W142 (λ/2)" manufactured by Teijin Limited.
Thereafter, a commercially available pressure-sensitive adhesive (SK2057, manufactured by Soken Chemical & Engineering Co., Ltd.) was used to attach the light-transmitting anisotropic layer to a half-wave plate (λ/2) in the same manner as in Optical Film 1. Furthermore, a color-adjusting layer was formed on the light-absorbing anisotropic layer in the same manner as in Optical Film 2, to produce Optical Film 4.

<Fabrication of Backlight Device A4>
A backlight device A4 was produced in the same manner as in Example 2, except that optical film 4 was used instead of optical film 2 in the production of backlight device A2 of Example 2.

[Performance evaluation of backlight device]
The fabricated backlight devices were evaluated for front luminance and parallel light source properties as follows.

<Evaluation of front luminance>
The brightness Y(0) of the fabricated backlight device in the normal direction to the light exit surface (backlight surface) was measured using a measuring instrument, "EZ-Contrast XL88" manufactured by ELDIM.
The front luminance was evaluated as follows.
A: Larger than Y(0) of the backlight device B1, which is a comparative example B: Less than or equal to Y(0) of the backlight device B1, which is a comparative example

<Evaluation of parallel light source properties>
For the fabricated backlight device, a measuring machine was used to measure the luminance Y(0) in the normal direction to the light exit surface and the luminance Y(50) in the direction shifted by 50° in polar angle from the normal direction to the light exit surface, and the parallel light source property was evaluated using the following formula. The measuring machine used was "EZ-Contrast XL88" manufactured by ELDIM.
Parallel light source characteristic evaluation=Y(0)/Y(50)
The parallel light source property was evaluated as follows.
AA: Greater than 1.5 times the Y(0)/Y(50) of the comparative backlight device B1. A: Greater than the Y(0)/Y(50) of the comparative backlight device B1 but not more than 1.5 times. B: Less than or equal to the Y(0)/Y(50) of the comparative backlight device B1. The results are shown in the table below.

As shown in the table, the backlight device of the planar lighting device of the present invention having a light-transmitting anisotropic layer and a light-absorbing anisotropic layer has superior front brightness and parallel light source properties compared to the comparative example, which is a conventional backlight device without a light-transmitting anisotropic layer.
In particular, Example 3 (backlight device A3) and Example 4 (backlight device A4), which have a polarization control layer, an optical rotation layer, and a half-wave plate between the light-transmitting anisotropic layer and the light-absorbing anisotropic layer, have excellent parallel light source properties.
From the above results, the effects of the present invention are clear.

It can be used effectively in liquid crystal display devices, etc.

10, 30 Backlight device 12 Reflective layer 14 Light source 16 Light diffusion layer 18, 34 Light transmission anisotropic layer 20 Light absorption anisotropic layer 26 Polarization control layer

Claims (9)

a light absorption anisotropic layer, a light transmission anisotropic layer, a light diffusion layer, a light source, and a reflective layer, in this order;
the optically absorptive anisotropic layer has a transmittance central axis perpendicular to the surface of the layer;
The light-transmitting anisotropic layer satisfies the following requirements 1 and 2:
Requirement 1: When the transmittance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is T0 and the transmittance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal direction of the light-transmitting anisotropic layer is T50, the relationships T0 > T50 and T50 < 70% are satisfied.
Requirement 2: When the absorbance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is A0 and the absorbance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal direction of the light-transmitting anisotropic layer is A50, the relationships A0<0.05 and A50<0.05 are satisfied. When the reflectance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is R0, and the reflectance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal line of the light-transmitting anisotropic layer is R50,
2. The spread illuminating device according to claim 1, wherein the light transmission anisotropic layer satisfies the relationships R0<R50 and R50>30%. 2. The spread illuminating device according to claim 1 , wherein the light-transmitting anisotropic layer is a multilayer film in which 50 or more different layers are stacked. 2. The planar lighting device according to claim 1 , further comprising a polarization control layer between the light-transmitting anisotropic layer and the light-absorbing anisotropic layer, the polarization control layer rotating the polarization direction of incident linearly polarized light within a range of 80 to 100 degrees. The planar lighting device of claim 4, wherein the polarization control layer is a layer containing a liquid crystal compound that is twisted and aligned along a helical axis extending in the thickness direction. The surface lighting device of claim 4, wherein the polarization control layer is a half-wave plate. An image display device having the surface illumination device described in any one of claims 1 to 6. an optically absorptive anisotropic layer having a transmittance central axis perpendicular to the surface of the layer;
An optical film having a light-transmitting anisotropic layer that satisfies the following requirements 1 and 2:
Requirement 1: When the transmittance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is T0 and the transmittance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal direction of the light-transmitting anisotropic layer is T50, the relationships T0 > T50 and T50 < 70% are satisfied.
Requirement 2: When the absorbance when light having a wavelength of 550 nm is incident from the normal direction of the light-transmitting anisotropic layer is A0 and the absorbance when light having a wavelength of 550 nm is incident from a direction at a polar angle of 50° with respect to the normal direction of the light-transmitting anisotropic layer is A50, the relationships A0<0.05 and A50<0.05 are satisfied. The optical film of claim 8, further comprising a polarization control layer between the light transmission anisotropic layer and the light absorption anisotropic layer, which rotates the polarization direction of incident linearly polarized light within a range of 80 to 100 degrees.