JP2020194058A - Optical laminate, surface illumination device, and image display device - Google Patents

Abstract

To provide an optical laminate that allows for realizing an easily designable surface illumination device with improved brightness uniformity over an entire plane.SOLUTION: An optical laminate of the present invention comprises first and second optical elements, each having a reflective polarizer, and light transmitting through the first optical element is optically in a cross-Nicol relationship with light transmitting through the second optical element.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical laminate, a surface illumination device and an image display device.

In display boards such as information boards and advertising boards, many internal lighting type display boards equipped with a light source inside are adopted from the viewpoint of improving visibility and legibility. However, when the area of the display board becomes large, there is a difference in illuminance between the vertical direction in which the distance from the light source is the shortest and the diagonal direction in which the angle deviates from the vertical direction. Illuminance unevenness may occur due to this. In particular, in recent years, LEDs (light emitting diodes) that consume less power and generate less heat have been used as light sources, and since LEDs have stronger directivity than conventional light sources such as light bulbs and fluorescent lamps, they have a large area. On the other hand, when the light source is arranged directly underneath, it may be difficult to obtain uniform brightness over the entire in-plane area.

On the other hand, a means for reducing illuminance unevenness can be considered by arranging a light diffusion layer between the surface on the display board on which characters and the like are written and the light source. However, in such means, the length of the optical path through which the light wave passes through the light diffusion layer is the shortest in the vertical direction in which the distance from the light source is the shortest, and is long in the oblique direction. Therefore, the means by installing the light diffusion layer alone cannot substantially improve the illuminance unevenness caused by the highest illuminance in the vertical direction.

Further, in Patent Document 1, a structural plate having a plurality of openings is arranged in front of the exit side of the LED light source, and the opening area is increased from the central portion where the light source is arranged toward the peripheral portion in a plan view. , A surface illumination device capable of uniformly extracting light from the structural plate is disclosed. However, the surface lighting device has a problem that it is difficult to design and it is difficult to follow a complicated shape.

JP 2012-150891

The present invention has been made to solve the above-mentioned conventional problems, and its main purpose is optics that can realize a surface illuminating device that is easy to design and has improved brightness uniformity in the entire surface. The purpose is to provide a laminate.

The optical laminate of the present invention each has a first optical element and a second optical element containing a reflective polarizing element, and transmits light transmitted through the first optical element and the second optical element. The light that is emitted is optically cross Nicol.
In one embodiment, the optical laminate is continuously formed with regions in a uniform cross-nicol state so as to form any surface.
In one embodiment, the first optical element and the reflective polarizer contained in the second optical element are linearly polarized light-separated reflectors or circularly polarized light-separated reflectors, respectively. Is.
In one embodiment, the optical laminate further has a retardation layer between the first optical element and the second optical element.
In one embodiment, the refractive index characteristics of the retardation layer show a relationship of nx>nz> ny.
In one embodiment, the retardation layer has a first retardation layer having a refractive index characteristic of nx>ny> nz and a second position having a refractive index characteristic of nz>ny> ny. Includes a differential layer.
In one embodiment, the refractive index characteristics of the retardation layer show a relationship of nx ≧ ny> nz.
In one embodiment, the first optical element and the reflective polarizer included in the second optical element are linearly polarized light-separated reflective polarizers, respectively, and the linearly polarized light-separated reflective one. The polarizer is a multi-layer laminated body in which layers having double refractive property and layers having substantially no double refractive property are alternately laminated, and the reflection axes of the respective reflective polarizers are substantially orthogonal to each other. ing.
In one embodiment, the first optical element and the reflective polarizer included in the second optical element are circularly polarized light-separated reflective polarizers that transmit circularly polarized light in different rotational directions. ..
In one embodiment, the first optical element and the reflective polarizer included in the second optical element are circularly polarized light-separated reflective polarizers that transmit circularly polarized light in the same rotational direction. Yes, either the first optical element or the second optical element further has a retardation layer.
In one embodiment, the reflective polarizers included in the first optical element and the second optical element are linearly polarized light-separated reflective polarizers, respectively, and the reflection of the respective reflective polarizers. The axes are not substantially orthogonal and either the first optic or the second optic further has a retardation layer.
In one embodiment, the in-plane retardation of the retardation layer is approximately half of the set wavelength.
In one embodiment, the circularly polarized separation type reflective polarizer is a cholesteric oriented solidified layer.
According to another aspect of the present invention, a surface illuminator is provided. This surface illuminating device has the above-mentioned optical laminate and a light source.
In one embodiment, the surface illuminator further has a diffuser on the opposite side of the optical laminate to the light source.
According to yet another aspect of the present invention, an image display device is provided. This image display device includes the above-mentioned optical laminate. Another image display device of the present invention includes the above-mentioned surface illumination device.

In the optical laminate of the present invention, a pair of optical elements, each containing a reflective polarizer, are used to form an optically cross-nicoled state. By using the optical laminate having such a configuration, the transmittance in the peripheral direction is improved as compared with the front direction while suppressing the transmittance in the front direction, and as a result, the uniformity of brightness in the entire in-plane is improved. A surface illuminator can be obtained. Moreover, since the optical laminate of the present invention is configured as a laminated film having a simple structure, complicated structural control is not required. Therefore, it is possible to realize a surface illuminating device that is easy to design according to an arbitrary shape while having the above-mentioned excellent characteristics.

It is a conceptual diagram explaining the optical design by the optical laminate of this invention. It is the schematic sectional drawing of the optical laminated body by one Embodiment of this invention. It is a schematic perspective view of an example of a linearly polarized light separation type reflective polarizing element that can be used for the optical laminate according to the embodiment of the present invention. It is the schematic sectional drawing of the optical laminated body by another embodiment of this invention. It is a schematic sectional drawing of an example of the optical laminated body by still another embodiment of this invention. FIG. 5 is a schematic cross-sectional view of another example of an optical laminate according to yet another embodiment of the present invention. It is a schematic sectional drawing of an example of the optical laminated body by still another embodiment of this invention. FIG. 5 is a schematic cross-sectional view of another example of an optical laminate according to yet another embodiment of the present invention. It is a graph which compares and shows the relative luminance distribution of the surface illumination apparatus of Examples 1 and 2 and Comparative Example 1.

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

A. Optical laminate <Concept of optical design of optical laminate>
The optical laminate according to the embodiment of the present invention has a first optical element and a second optical element each including a reflective polarizer, and the light transmitted through the first optical element and the second optical element are provided. The light transmitted through the element is optically cross Nicol. FIG. 1 is a conceptual diagram for explaining an optical design using such an optical laminate, and shows a state in which a first optical element and a second optical element are separately arranged. As shown in FIG. 1, the optical laminate includes virtual transmitted light incident on the first optical element 10 from the first virtual light source and transmitted through the first optical element 10, and second optics from the second virtual light source. It is designed so that the virtual transmitted light incident on the element 20 and transmitted through the second optical element 20 is optically cross-nicoled. The "optically cross-nicor state" means that, for example, when each transmitted light is linearly polarized light, the respective vibration directions are substantially orthogonal to each other; for example, each transmitted light is a (elliptical) circle. In the case of polarized light, it means that the main axis directions of the ellipses are orthogonal and the rotation directions are opposite. By forming such a cross Nicol state, when the optical laminate is applied to a surface illumination device, the orthogonal transmittance in the normal direction of the illumination surface can be reduced. On the other hand, in the oblique direction, the transmittance can be increased as compared with the normal direction because it deviates from the cross Nicol state. As a result, the difference between the transmittance in the front direction and the transmittance in the peripheral direction becomes small, and it is possible to realize a surface illumination device in which the uniformity of brightness in the entire surface is improved. As is clear from FIG. 1, the optical laminate of the present invention may be formed by separately placing and laminating the first optical element 10 and the second optical element 20, and the first optical layer may be formed. The element 10 and the second optical element 20 may be integrated. Therefore, the optical laminate of the present invention may also include a set of the first optical element 10 and the second optical element 20. Further, regardless of whether the first optical element 10 and the second optical element 20 are integrated or separately placed, the first optical element 10 and the first optical element 10 and the second optical element 20 are as long as they do not adversely affect the cross Nicol state. Any suitable layer or member may be placed between the two optical elements 20. Examples of such a layer or member include an air layer and an optically isotropic film. Further, when a retardation layer is provided between the first optical element 10 and the second optical element 20, as will be described later, the retardation layer, the first optical element 10, and the second optical element 20 At least two of them may be integrated, and the retardation layer, the first optical element 10, and the second optical element 20 may all be placed separately.

In the optical laminate of the present invention, regions in a uniform cross-nicol state are continuously formed so as to form an arbitrary surface. In other words, a uniform cross Nicol state due to the transmitted light of the first optical element 10 (substantially virtual transmitted light) and the transmitted light of the second optical element 20 (substantially virtual transmitted light) is obtained. , Formed in a predetermined area. Further, such a uniform cross Nicol state region may be selectively formed on a part of the optical laminate or may be formed over the entire optical laminate. If a region in a uniform cross Nicol state is formed on a part of the optical laminate, the predetermined region can be formed in any suitable pattern. Specific examples of such a pattern include a striped shape (for example, a striped shape extending in the longitudinal direction, a striped shape extending in the lateral direction, a striped shape extending in the oblique direction), a checkered shape, a dot shape, and a random shape. Can be mentioned.

Hereinafter, typical embodiments that can realize the above optical design will be specifically described. Although the description will be made with reference to the drawing of the laminated body in which each component is integrated for easy understanding, each component may be placed separately as described above.

<Embodiment 1>
FIG. 2 is a schematic cross-sectional view of the optical laminate according to the present embodiment. In this embodiment, the above-mentioned cross Nicol state is realized only by the first optical element 10 and the second optical element 20.

In an example of the present embodiment, the first optical element 10 and the second optical element 20 each include a linearly polarized light separation type reflective polarizer. In this case, each of the first optical element 10 and the second optical element 20 may be composed only of a linearly polarized light separation type reflective polarizer. Needless to say, the first optical element 10 and the second optical element 20 may each have an arbitrary appropriate optical functional layer depending on the purpose, in addition to the linearly polarized light separation type reflective polarizer. .. In the optical laminate 100 of the present embodiment, the linearly polarized light separation type reflective polarizers 10 and 20 may be arranged so that their respective reflection axes are substantially orthogonal to each other. In the present specification, the expressions "substantially orthogonal" and "substantially orthogonal" include the case where the angle formed by the two directions is 90 ° ± 7 °, preferably 90 ° ± 5 °, and more preferably 90 ° ± 5 °. Is 90 ° ± 3 °. The expressions "substantially parallel" and "substantially parallel" include the case where the angle between the two directions is 0 ° ± 7 °, preferably 0 ° ± 5 °, and even more preferably 0 ° ±. It is 3 °. Furthermore, the term "orthogonal" or "parallel" in the present specification may include substantially orthogonal or substantially parallel states. Also, when referring to an angle herein, it includes both clockwise and counterclockwise with respect to the reference direction.

FIG. 3 is a schematic perspective view of an example of a linearly polarized light separation type reflective polarizing element. The linearly polarized light separation type reflective polarizing element is a multilayer laminate in which a layer A having birefringence and a layer B having substantially no birefringence are alternately laminated. For example, the total number of layers of such a multi-layer laminate can be 50-1000. In the illustrated example, the refractive index nx in the x-axis direction of the A layer is larger than the refractive index ny in the y-axis direction, and the refractive index nx in the x-axis direction of the B layer and the refractive index ny in the y-axis direction are substantially the same. is there. Therefore, the difference in refractive index between the A layer and the B layer is large in the x-axis direction and substantially zero in the y-axis direction. As a result, the x-axis direction becomes the reflection axis, and the y-axis direction becomes the transmission axis. The difference in refractive index between the A layer and the B layer in the x-axis direction is preferably 0.2 to 0.3. The x-axis direction corresponds to the stretching direction of the reflective polarizer in the method for manufacturing the reflective polarizer.

The layer A is preferably composed of a material that exhibits birefringence by stretching. Representative examples of such materials include polyester naphthalenedicarboxylic acid (eg, polyethylene naphthalate), polycarbonate and acrylic resins (eg, polymethylmethacrylate). Polyethylene naphthalate is preferred. The B layer is preferably composed of a material that does not substantially exhibit birefringence even when stretched. A typical example of such a material is a copolyester of naphthalenedicarboxylic acid and terephthalic acid.

The linearly polarized light separation type reflective polarizer transmits light having a first polarization direction (for example, p wave) at the interface between the A layer and the B layer, and is a second polarization orthogonal to the first polarization direction. Reflects light having a polarization direction of (for example, s wave). At the interface between the A layer and the B layer, the reflected light is partially transmitted as light having a first polarization direction and partially reflected as light having a second polarization direction. By repeating such reflection and transmission in large numbers inside the linearly polarized light separation type reflective polarizer, the efficiency of light utilization can be improved.

As shown in FIG. 3, for example, the linearly polarized light separation type reflective polarizer may include a reflective layer R as the outermost layer. By providing the reflective layer R, it is possible to further utilize the light that has returned to the outermost side of the reflective polarizer without being finally utilized, so that the efficiency of light utilization can be further improved. The reflective layer R typically exhibits a reflective function due to the multilayer structure of the polyester resin layer.

As the linearly polarized light separation type reflective polarizing element, for example, those described in JP-A-9-507308 can be used. As the linearly polarized light separation type reflective polarizer, a commercially available product may be used as it is, or the commercially available product may be used after secondary processing (for example, stretching). Examples of commercially available products include the product name DBEF manufactured by 3M and the product name APF manufactured by 3M.

In another example of this embodiment, the first optical element 10 and the second optical element 20 each include a circularly polarized light-separated reflective polarizer that transmits circularly polarized light in different rotational directions. In this case, each of the first optical element 10 and the second optical element 20 is typically a laminate of a base material and a cholesteric oriented solidified layer formed on the base material. In the optical laminate 100 according to the present embodiment, the cholesteric oriented solidified layer of the first optical element 10 and the cholesteric oriented solidified layer of the second optical element 20 are twisted in different directions when viewed from the traveling direction of light. The opposite direction.

The base material may be composed of a resin film having arbitrary properties (optical properties, mechanical properties, chemical properties) according to the purpose.

As used herein, the term "cholesteric oriented solidified layer" refers to a layer in which the constituent molecules of the layer have a spiral structure, the spiral axis is oriented substantially perpendicular to the plane direction, and the orientation state is fixed. Therefore, the "cholesteric oriented solidified layer" includes not only the case where the liquid crystal compound exhibits a cholesteric liquid crystal phase but also the case where the non-liquid crystal compound has a pseudo structure such as the cholesteric liquid crystal phase. For example, the "cholesteric oriented solidified layer" is formed by applying a twist to a cholesteric structure (spiral structure) by applying a twist with a chiral agent while the liquid crystal material shows a liquid crystal phase, and then subjecting the liquid crystal material to a polymerization treatment or a cross-linking treatment in that state. It can be formed by fixing the orientation (cholesteric structure) of the liquid crystal material. Specific examples of the cholesteric oriented solidified layer include the cholesteric layer described in JP-A-2003-287623.

As described above, the cholesteric oriented solidified layer of the first optical element 10 and the cholesteric oriented solidified layer of the second optical element 20 are twisted in opposite directions when viewed from the traveling direction of light. For example, the twisting direction of the cholesteric oriented solidified layer can be controlled by an appropriate combination of liquid crystal material and chiral agent.

In the present embodiment, a retardation layer (not shown) may be further provided so as not to eliminate the optical cross Nicol state. The retardation layer can be, for example, a retardation layer having an in-plane retardation of 10 nm or less.

<Embodiment 2>
FIG. 4 is a schematic cross-sectional view of the optical laminate according to the present embodiment. In this embodiment, the above-mentioned cross Nicol state is realized by the first optical element 10, the second optical element 20, and the retardation layer 30 arranged between them. That is, even when the cross Nicol state cannot be realized only by the reflective polarizers of the first optical element 10 and the second optical element 20, by arranging the retardation layer 30, the above cross Nicol can be realized. The state can be realized. The retardation layer 30 may be included in either the first optical element 10 or the second optical element 20, and as a separate member, between the first optical element 10 and the second optical element 20. It may be arranged. More specifically, the retardation layer 30 has a function of reversing the polarization direction. That is, in the case of linearly polarized light, the vibration direction is changed by the retardation layer 30 to be orthogonal to each other; in the case of circularly polarized light, the rotation direction is reversed by the retardation layer 30. In the optical laminate 101 according to the present embodiment, the first optical element and the second optical element each include a circularly polarized light separation type reflective polarizer, and are viewed from the traveling direction of light in each cholesteric oriented solidifying layer. The twisting direction is the same. According to the cholesteric oriented solidified layer in which the twisting directions are the same, the above-mentioned cross Nicol state can be realized by the retardation layer 30 where the circularly polarized light in the same rotation direction can be obtained. When forming two cholesteric oriented solidified layers, it is much easier to form a cholesteric oriented solidified layer in which the twisting directions are the same than in forming a cholesteric oriented solidified layer in which the twisting directions are opposite to each other. Is. Therefore, the effect of the present embodiment can be remarkable when the first optical element and the second optical element each include a circularly polarized light-separated reflective polarizer. It should be noted that the first optical element and the second optical element each include a linearly polarized light separation type reflective polarizer, so that the respective reflection axes are not substantially orthogonal (for example, substantially parallel, and for example, for example. The same effect can be obtained by the retardation layer 30 even in the form in which the respective reflection axes form an angle of 0 ° to 80 °). However, in this embodiment, it is easy to change the relationship between the reflection axes to form the configuration of the first embodiment.

The retardation layer 30 can typically be a so-called λ / 2 plate (a retardation film having an in-plane retardation of approximately half the set wavelength). In this case, the in-plane retardation Re (450) of the retardation layer 30 can be, for example, near 225 nm, Re (550) can be, for example, near 275 nm, and Re (650) can be, for example, near 325 nm. From a practical point of view, the in-plane phase difference can be defined as Re (550). The retardation layer 30 may exhibit any suitable refractive index characteristic as long as it can function as a so-called λ / 2 plate. The retardation layer 30 may exhibit, for example, a relationship in which the refractive index characteristics are nx> ny ≧ nz or nx> nz> ny. The retardation layer 30 may exhibit a reverse dispersion wavelength characteristic, may exhibit a positive wavelength dispersion characteristic, or may exhibit a flat wavelength dispersion characteristic. When the retardation layer exhibits the inverse dispersion wavelength characteristic, the Re (450) / Re (550) of the base material is preferably 0.8 or more and less than 1, and more preferably 0.8 to 0.95. When the retardation layer exhibits flat wavelength dispersion characteristics, the base material Re (450) / Re (550) is preferably 0.98 to 1.02. The retardation layer 30 can be typically composed of a stretched film of a resin film. Typical examples of the resin constituting the resin film include cycloolefin-based resins (for example, norbornene-based resins) and polycarbonate-based resins. Details of the retardation layer composed of a stretched film of a resin film are described in, for example, JP-A-2017-54093 and JP-A-2018-60014. The description of these publications is incorporated herein by reference. In the present specification, “Re (λ)” is an in-plane phase difference measured with light having a wavelength of λ nm at 23 ° C. For example, "Re (550)" is an in-plane phase difference measured with light having a wavelength of 550 nm at 23 ° C. Re (λ) is obtained by the formula: Re (λ) = (nx−ny) × d, where d (nm) is the thickness of the layer (film). “Rth (λ)” is a phase difference in the thickness direction measured with light having a wavelength of λ nm at 23 ° C. Rth (λ) is obtained by the formula: Rth (λ) = (nx−nz) × d, where d (nm) is the thickness of the layer (film). "Nx" is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and "ny" is the in-plane direction orthogonal to the slow-phase axis (that is, the phase-advancing axis direction). Is the refractive index of, and "nz" is the refractive index in the thickness direction.

In the present embodiment, a retardation layer (not shown) different from the retardation layer 30 may be further provided so as not to eliminate the optical cross Nicol state. The retardation layer may be, for example, a retardation layer having an in-plane retardation of 10 nm or less.

<Embodiment 3>
FIG. 5 is a schematic cross-sectional view of an example of the optical laminate according to the present embodiment; FIG. 6 is a schematic cross-sectional view of another example of the optical laminate according to the present embodiment. In the present embodiment, the first optical element and the second optical element may each include a linearly polarized light-separated reflective polarizer, or may include a circularly polarized reflective reflector. .. The optical laminate 102 of FIG. 5 further has another retardation layer 40 between the first optical element 10 and the second optical element 20 of the optical laminate of the first embodiment. The optical laminate 103 of FIG. 6 further has another retardation layer 40 between the first optical element 10 and the second optical element 20 of the optical laminate of the second embodiment. In the optical laminate 103, another retardation layer 40 may be provided between the first optical element 10 and the retardation layer 30, and the phase difference from the second optical element 20 as shown in the illustrated example. It may be provided between the layer 30 and the layer 30. Another retardation layer 40 typically shows a relationship in which the refractive index characteristic is nx ≧ ny> nz. By providing such another retardation layer 40, the illuminance can be increased when the optical laminate is applied to the surface illumination device. Further, when the light source of the surface illuminating device has strong directivity and light is emitted in a spot, the area can be expanded. When the refractive index characteristic of another retardation layer 40 shows the relationship of nx = ny> nz, the in-plane retardation Re (550) is usually less than 10 nm. The retardation Rth (550) in the thickness direction of the retardation layer 40 is usually 150 nm to 550 nm. Such a retardation layer 40 may typically be composed of a film of a thermoplastic resin exhibiting positive intrinsic birefringence. Examples of the thermoplastic resin exhibiting positive intrinsic compound refraction include general-purpose plastics such as polyolefin resins, cycloolefin resins, polyvinyl chloride resins, cellulose resins, and vinylidene chloride resins; polyamide resins and polyacetal resins. General-purpose engineering plastics such as resins, polycarbonate-based resins, modified polyphenylene ether-based resins, polybutylene terephthalate-based resins, polyethylene terephthalate-based resins; polyphenylene sulfide-based resins, polysulfone-based resins, polyether sulfone-based resins, polyether ether ketone-based resins, Examples thereof include super engineering plastics such as polyarylate resins, liquid crystal resins, polyamideimide resins, polyimide resins, and polytetrafluoroethylene resins. Preferably, the retardation layer 40 is composed of a resin film containing a cellulosic resin as a main component, and the resin film may be a stretched film or an unstretched film. Details of such a retardation layer are described, for example, in Japanese Patent Application Laid-Open No. 2012-3139 as a second optical compensation layer. The description of this publication is incorporated herein by reference. When the refractive index characteristic of another retardation layer 40 shows the relationship of nx>ny> nz, the in-plane retardation Re (550) is usually 60 nm to 300 nm. The Nz coefficient of the retardation layer 40 is usually 1.1 to 3.0. The Nz coefficient is obtained by Nz = Rth (λ) / Re (λ). Such a retardation layer is also composed of the same thermoplastic resin film as described above. Details of such a retardation layer are described in, for example, JP-A-2015-210459 and JP-A-2016-105166. The description of this publication is incorporated herein by reference.

<Embodiment 4>
FIG. 7 is a schematic cross-sectional view of an example of the optical laminate according to the present embodiment; FIG. 8 is a schematic cross-sectional view of another example of the optical laminate according to the present embodiment. In the present embodiment, the first optical element and the second optical element may each include a linearly polarized light-separated reflective polarizer, or may include a circularly polarized reflective reflector. Good. Typically, the first optical element and the second optical element each include a linearly polarized light separation type reflective polarizer. The optical laminate 104 of FIG. 7 further has another retardation layer 50 between the first optical element 10 and the second optical element 20 of the optical laminate of the first embodiment. The optical laminate 105 of FIG. 8 further has yet another retardation layers 61 and 62 between the first optical element 10 and the second optical element 20 of the optical laminate of Embodiment 1. The retardation layer 50 typically shows a relationship in which the refractive index characteristics are nx>nz> ny. The retardation layer 61 typically shows a relationship of refractive index characteristics of nx>ny>nz; the retardation layer 62 typically shows a relationship of refractive index characteristics of nz>ny> ny. By providing such a retardation layer, the anisotropy of in-plane illuminance caused by linearly polarized light can be suppressed. Hereinafter, the retardation layer 50 and the retardation layers 61 and 62 will be briefly described.

As described above, the retardation layer 50 typically has a refractive index characteristic of nx> nz> ny. The in-plane retardation Re (550) of the retardation layer 50 is usually 270 nm to 330 nm. If the in-plane retardation Re (550) of the retardation layer 50 is in such a range, the illuminance unevenness can be improved. The Nz coefficient of the retardation layer 50 is usually 0.3 to 0.7. When the Nz coefficient is in such a range, the illuminance unevenness can be improved more satisfactorily.

The retardation layer 50 may exhibit a reverse dispersion wavelength characteristic, may exhibit a positive wavelength dispersion characteristic, or may exhibit a flat wavelength dispersion characteristic. The retardation layer 50 preferably exhibits reverse dispersion wavelength characteristics. In this case, the in-plane phase difference of the retardation layer 50 satisfies the relationship of Re (450) <Re (550). Re (450) / Re (550) is preferably 0.8 or more and less than 1, and more preferably 0.8 to 0.95. More preferably, the in-plane retardation of the retardation layer 50 also satisfies the relationship of Re (550) <Re (650). Re (550) <Re (650) is preferably 0.8 or more and less than 1, and more preferably 0.8 to 0.95.

The retardation layer 50 is typically a retardation film made of any suitable resin capable of achieving the above characteristics. Examples of the resin forming this retardation film include polyarylate, polyamide, polyimide, polyester, polyaryletherketone, polyamideimide, polyesterimide, polyvinyl alcohol, polyfumaric acid ester, polyether sulfone, polysulfone, and norbornene resin. Examples include polycarbonate resin, cellulose resin and polyurethane. These resins may be used alone or in combination. Preferably, it is a polyarylate or a polycarbonate resin. The retardation layer 50 is obtained, for example, by stretching a film formed of the above resin.

As described above, the retardation layer 61 typically has a refractive index characteristic of nx> ny> nz. The in-plane retardation Re (550) of the retardation layer 61 is usually 80 nm to 150 nm. The Nz coefficient of the retardation layer 61 is usually 1.1 to 3.0.

The retardation layer 61 may exhibit a reverse dispersion wavelength characteristic, may exhibit a positive wavelength dispersion characteristic, or may exhibit a flat wavelength dispersion characteristic. It is preferable to exhibit flat wavelength dispersion characteristics. Specifically, Re (450) / Re (550) of the retardation layer 61 is preferably 0.99 to 1.03, and Re (650) / Re (550) is preferably 0.98 to 1.03. It is 02.

The retardation layer 61 may be made of any suitable resin film that can satisfy the above characteristics. Typical examples of such resins are cyclic olefin resins, polycarbonate resins, cellulose resins, polyester resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and acrylics. Examples include based resins. Of these, cyclic olefin resins can be preferably used. The retardation layer 61 can be obtained, for example, by stretching a film formed of the above resin.

As described above, the retardation layer 62 typically has a refractive index characteristic of nz> nx ≧ ny. In one embodiment, the retardation layer 62 shows a relationship in which its refractive index is nx = ny. Here, "nx = ny" includes not only the case where nx and ny are exactly equal, but also the case where nx and ny are substantially equal. Specifically, it means that Re (550) is less than 10 nm. In another embodiment, the retardation layer 62 shows a relationship in which its refractive index is nx> ny. In this case, the in-plane retardation Re (550) of the retardation layer 62 is usually 10 nm to 60 nm. The retardation Rth (550) in the thickness direction of the retardation layer 62 is usually 260 nm to −10 nm. The Nz coefficient of the retardation layer 62 is usually −10 to −0.1.

When the refractive index of the retardation layer 62 shows the relationship of nx = ny, the retardation layer 62 is typically a liquid crystal layer fixed in a homeotropic orientation. The liquid crystal material (liquid crystal compound) that can be homeotropically oriented may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the liquid crystal layer include the liquid crystal compounds and the methods for forming the liquid crystal compounds described in [0020] to [0042] of JP-A-2002-333642. When the refractive index of the retardation layer 62 shows a relationship of nx> ny, the retardation layer 62 may be typically composed of a stretched film of a resin film. Such resins can typically be polymers with negative intrinsic birefringence. The polymer having negative intrinsic birefringence refers to a polymer in which the refractive index in the orientation direction becomes relatively small when the polymer is oriented by stretching or the like. Examples of the polymer having a negative intrinsic birefringence include those in which a chemical bond or a functional group having a large polarization anisotropy such as an aromatic group or a carbonyl group is introduced into the side chain of the polymer. Specific examples thereof include modified polyolefin resins (for example, modified polyethylene resins), acrylic resins, styrene resins, maleimide resins, fumaric acid ester resins, and the like. The retardation layer 62 can be obtained, for example, by appropriately stretching a film formed of the above resin.

<Others>
The above embodiments can be combined as appropriate. For example, the embodiment of FIG. 4, 5 or 6 may be combined with the embodiment of FIG. 7; the embodiment of FIG. 4, 5 or 6 may be combined with the embodiment of FIG. Alternatively, industry-renowned configurations may be combined with the above embodiments, depending on the intended purpose.

B. Surface Illumination Device The optical laminate of the present invention according to item A above can be applied to a surface illumination device. Therefore, the present invention also includes such a surface illuminator. The surface illuminator has the optical laminate of the present invention and a light source according to the above item A. By using the optical laminate of the present invention, it is possible to obtain a surface illuminating device that is easy to design and has improved brightness uniformity in the entire surface. More specifically, by using the optical laminate of the present invention, the transmittance in the peripheral direction is improved as compared with the front direction while suppressing the transmittance in the front direction, and as a result, the brightness is uniform in the entire plane. The sex can be improved. Moreover, since the optical laminate of the present invention is configured as a laminated film having a simple structure, complicated structural control is not required. Therefore, it is possible to realize a surface lighting device that is easy to design while having the above-mentioned excellent characteristics. As the light source, any suitable light source can be adopted. Preferably, it is an organic LED or an inorganic LED. Since such a light source has strong directivity, the effect of the optical laminate of the present invention is remarkable when they are used. The surface illuminator may preferably further have a diffuser between the optical laminate and the light source and / or on the opposite side of the optical laminate to the light source. Due to the synergistic effect of the optical laminate of the present invention and the diffuser plate, the uniformity of brightness in the entire in-plane can be further improved.

The wavelength of the light source is not particularly limited. Typically, the set wavelength and the light source wavelength at which the two optical elements form a cross Nicol state are substantially the same. Normally, the set wavelength may be within the range of ± 15 nm with respect to the light source wavelength.

C. Image display device The optical laminate of the present invention described in item A above can also be applied to an image display device. The optical laminate can be used, for example, as a member for a backlight unit or a light diffusing element on the visual side. Further, the surface illumination device of the above item B can also be applied to the image display device. The surface illuminator can be used, for example, as a backlight unit.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows.

<Example 1>
5.67 g of a nematic liquid crystal compound represented by the following chemical formula (1) (BASF: trade name "Pariocolor LC242"), a chiral agent represented by the following chemical formula (2) (BASF: trade name "Pariocolor LC756") 0.33 g, photopolymerization initiator (IGM Resins BV, product name "Omnirad 907" 0.3 g, leveling agent (Big Chemie Japan, product name "BYK-361") 0.003 g, and 14 g of cyclopentanone was mixed so as to be uniform to prepare a liquid crystal coating solution. Next, this liquid crystal coating solution was coated on a long substrate (biaxially stretched PET film) and at 80 ° C. The heat treatment was carried out for 3 minutes, and then the polymerization treatment was carried out by irradiating with ultraviolet rays to form a cholesteric oriented solidified layer. The thickness of the cholesteric oriented solidified layer was 3 μm, the transmission spectrum was 445 nm to 475 nm, and the transmittance was low. The selective reflection region is shown. Two laminates of the substrate / cholesteric oriented solidified layer thus obtained are prepared, and the λ / 2 plate is sandwiched so that the respective cholesteric oriented solidified layers face each other, and the λ / 2 plate is sandwiched and optically laminated. A commercially available cycloolefin-based retardation film (manufactured by Kaneka, product name “KUZ-film”, thickness 33 μm, Re (450) = 225 nm) was used as the λ / 2 plate, while the bottom of the rectangle was used. A diffuser plate was placed on the inner bottom surface of a transparent box body having an open top, and an LED lamp as a light source was placed on the outer lower side of the box body. The LED lamp having an emission peak wavelength of 450 nm was used. A surface illumination device was manufactured by covering the opening of the box with the laminate obtained above and further arranging a diffuser plate on the upper part of the laminate. A brightness unevenness measuring device with the light source turned on. The brightness distribution was measured using (manufactured by Eye System Co., Ltd., model number "EyeScale-4W"). Examples 2 and Comparative Examples are graphs of relative brightness along the long side direction when the center brightness is 1.0. FIG. 9 is shown together with the result of No. 1. As for the graphs of Examples 1 and 2, the graph of Comparative Example 1 as a reference is also described.

<Example 2>
Two commercially available reflective polarizers (manufactured by 3M, product name "APF V3", thickness 26 μm) were used and laminated so that their reflection axes were orthogonal to each other to prepare an optical laminate. A surface illuminating device was produced in the same manner as in Example 1 except that this optical laminate was used. The obtained surface lighting device was subjected to the same evaluation as in Example 1. The results are shown in FIG.

<Comparative example 1>
A surface illuminating device was produced in the same manner as in Example 1 except that the opening of the box was covered with a diffuser without using an optical laminate. The obtained surface lighting device was subjected to the same evaluation as in Example 1. The results are shown in FIG.

As is clear from FIG. 9, the surface illuminating device using the optical laminate of the embodiment of the present invention suppresses the decrease in brightness of the peripheral portion as compared with the surface illuminating device of the comparative example, and as a result, it is in-plane. The uniformity of brightness in the whole is improved. In the surface illuminating device of the first embodiment, the brightness of the peripheral portion gradually decreases and is smooth, and the display characteristics of the entire surface are excellent. In the surface illumination device of the second embodiment, high brightness is maintained up to the end portion, and a bright display is realized over the entire surface.

The optical laminate of the present invention is suitably used for a surface illumination device and an image display device. The surface lighting device and the image display device are preferably used for an electric display board, digital signage, and the like.

10 First optical element 20 Second optical element 100 Optical laminated body 101 Optical laminated body 102 Optical laminated body 103 Optical laminated body 104 Optical laminated body 105 Optical laminated body

Claims (17)

Each has a first optical element and a second optical element containing a reflective polarizer.
The light transmitted through the first optical element and the light transmitted through the second optical element are optically cross-nicols.
Optical laminate. The optical laminate according to claim 1, wherein a region in a uniform cross Nicol state is continuously formed so as to form an arbitrary surface. The first optical element and the reflective polarizer included in the second optical element are linearly polarized light-separated reflective polarizers and circularly polarized light-separated reflective polarizers, respectively, according to claim 1 or 2. The optical laminate according to 2. The optical laminate according to any one of claims 1 to 3, further comprising a retardation layer between the first optical element and the second optical element. The refractive index characteristic of the retardation layer shows a relationship of nx>nz> ny.
The optical laminate according to claim 4. The retardation layer includes a first retardation layer having a refractive index characteristic of nx>ny> nz and a second retardation layer having a refractive index characteristic of nz>ny> ny.
The optical laminate according to claim 4. The refractive index characteristic of the retardation layer shows a relationship of nx ≧ ny> nz.
The optical laminate according to claim 4. The reflective polarizers included in the first optical element and the second optical element are linearly polarized light-separated reflective polarizers, respectively.
The linearly polarized light separation type reflective polarizing element is a multilayer laminate in which layers having birefringence and layers having substantially no birefringence are alternately laminated.
The reflection axes of each reflective polarizer are substantially orthogonal,
The optical laminate according to any one of claims 3 to 7. Claims 3 to 7, wherein the first optical element and the reflective polarizer contained in the second optical element are circularly polarized light-separated reflective polarizers that transmit circularly polarized light in different rotational directions. The optical laminate according to any one. The first optical element and the reflective polarizer contained in the second optical element are circularly polarized light-separated reflective polarizers that transmit circularly polarized light in the same rotation direction.
Either the first optical element or the second optical element further has a retardation layer.
The optical laminate according to any one of claims 1 to 3. The reflective polarizers included in the first optical element and the second optical element are linearly polarized light-separated reflective polarizers, respectively.
The reflection axes of each reflective polarizer are not substantially orthogonal,
Either the first optical element or the second optical element further has a retardation layer.
The optical laminate according to any one of claims 1 to 3. The optical laminate according to claim 10 or 11, wherein the in-plane retardation of the retardation layer is substantially half of the set wavelength. The optical laminate according to claim 9 or 10, wherein the circularly polarized light separation type reflective polarizer is a cholesteric oriented solidified layer. A surface illuminating device having the optical laminate according to any one of claims 1 to 13 and a light source. The surface illumination device according to claim 14, further comprising a diffuser plate on the opposite side of the optical laminate to the light source. An image display device comprising the optical laminate according to any one of claims 1 to 13. An image display device comprising the surface lighting device according to claim 14 or 15.