JP7494445B2 - Display panel and display device - Google Patents

Description

The present invention relates to an optical laminate, a display panel, and a display device.

In recent years, various display devices have become larger and more portable, and as a result, there is a demand for good hues under various viewing environments.
Japanese Patent Application Laid-Open No. 2003-233693 discloses an organic electroluminescence light source device in which changes in hue due to the observation angle are suppressed.

JP 2009-231257 A

It is difficult to obtain high luminance for blue light, and the lifespan of a display device is generally determined by the luminance lifespan of blue light. Therefore, even if the amount of blue light emitted by a display element is the same, it is required to increase the luminance of the blue light that is visually recognized, thereby achieving a longer lifespan.
On the other hand, in a display device including an optical laminate having a retardation plate and a polarizer, a phenomenon called blue shift, in which an image becomes more blue when observed from an oblique direction, may occur.
The present invention aims to provide an optical laminate that can provide a display device that improves the luminance of blue color when observed from the front, thereby extending the life of the display device, and suppresses blue shift in the image when observed from an oblique direction. The present invention also aims to provide a display panel including the optical laminate, a display device including the optical laminate, and a semi-transmissive semi-reflective film, a retardation plate, and a polarizer used in the display panel.

As a result of intensive research into solving the above problems, the inventors have found that the above problems can be solved by an optical laminate having a semi-transmissive semi-reflective film, a retardation plate, and a polarizer, in which the optical laminate contains a compound that has absorption at 480 nm or less, and the semi-transmissive semi-reflective film has a selective reflection wavelength in the range of 380 nm to 480 nm.

The present invention relates to the following items <1> to <18>.
<1> An optical laminate having a semi-transmitting semi-reflective film, a retardation plate, and a polarizer, the optical laminate containing a compound having absorption at 480 nm or less, and the semi-transmitting semi-reflective film having a selective reflection wavelength in the range of 380 nm to 480 nm.
<2> The optical laminate according to <1>, wherein the semi-transmissive semi-reflective film is a liquid crystal layer having a cholesteric structure, and the retardation layer and the polarizer constitute a circular polarizing plate, and the optical laminate has the semi-transmissive semi-reflective film, the retardation plate, and the polarizer in this order.
<3> The optical laminate according to <2>, in which, with respect to light incident from a liquid crystal layer side having a cholesteric structure, the liquid crystal layer having a cholesteric structure reflects right-handed circularly polarized light and the circular polarizer transmits left-handed circularly polarized light, or the liquid crystal layer having a cholesteric structure reflects left-handed circularly polarized light and the circular polarizer transmits right-handed circularly polarized light.
<4> The optical laminate according to <2> or <3>, wherein a reflection wavelength peak of the optical laminate is located on the longer wavelength side with respect to a selective reflection center wavelength of the liquid crystal layer having a cholesteric structure.
<5> The optical laminate according to any one of <2> to <4>, wherein a half width of a reflection peak of the optical laminate is smaller than a half width of a reflection peak of the liquid crystal layer having a cholesteric structure alone.
<6> The optical laminate according to any one of <1> to <5>, further comprising a protective layer.
<7> The optical laminate according to any one of <1> to <6>, further comprising an adhesive layer.
<8> The optical laminate according to any one of <1> to <7>, wherein the retardation plate is a quarter-wave retardation plate.
<9> The optical laminate according to any one of <1> to <7>, wherein the retardation plate is a laminate of a quarter wavelength retardation plate and a half wavelength retardation plate.
<10> The optical laminate according to <8> or <9>, wherein the retardation plate further includes a positive C plate.
<11> A display panel comprising the optical laminate according to any one of <1> to <10> on a light exit surface of a display element.
<12> The display panel according to <11>, wherein the display element has a microcavity structure.
<13> The display panel according to <11> or <12>, wherein a difference between a blue emission peak wavelength of the display element and a reflection peak wavelength of the optical laminate is 20 nm or less.
<14> A display device comprising the display panel according to any one of <11> to <13>.
<15> The display device according to <14>, wherein the display device is an organic electroluminescence display device.
<16> A retardation plate for use in the display panel according to any one of <11> to <13>.
<17> A polarizer for use in the display panel according to any one of <11> to <13>.
<18> A semi-transmissive semi-reflective film for use in the display panel according to any one of <11> to <13>.

According to the present invention, it is possible to provide an optical laminate that can improve the luminance of blue color when observed from the front, thereby enabling the display device to have a longer life, and can provide a display device in which blue shift of the image is suppressed when observed from an oblique direction. Furthermore, according to the present invention, it is possible to provide a display panel including the optical laminate, a display device including the optical laminate, and a semi-transmissive semi-reflective film, a retardation plate, and a polarizer used in the display panel.

FIG. 1 is a cross-sectional view illustrating an example of an optical laminate of the present invention. FIG. 2 is a cross-sectional view illustrating a schematic diagram of another example of the optical laminate of the present invention. FIG. 2 is a cross-sectional view showing a sample prepared in an example. FIG. 4 is a diagram showing the transmittance of a laminate of an adhesive layer containing an absorbing compound and a hard coat layer, the reflectance of a semi-transmissive semi-reflective film alone at an incident angle of 5°, and the reflectance of an optical laminate of an example at an incident angle of 5°. FIG. 5 is a diagram showing the measurement results of the reflectance of the optical laminate of the example for incident light from angles of 5°, 25°, and 45°. FIG. 6 is a diagram showing the measurement results of the luminance at 0° of the organic EL display devices having the optical laminates of the examples and the comparative examples. FIG. 7 is a diagram showing the measurement results of the luminance at 20° of the organic EL display devices having the optical laminates of the examples and the comparative examples. FIG. 8 is a diagram showing the measurement results of the luminance at 40° of the organic EL display devices having the optical laminates of the examples and the comparative examples.

In the following description, the description of "A to B" indicating a numerical range indicates a numerical range including the end points. That is, it indicates "A or more and B or less" (when A<B) or "A or less and B or more" (when A>B). In addition, in the following description, a combination of preferred aspects is a more preferred aspect.
Hereinafter, an embodiment of the present invention will be described.
[Optical laminate]
The optical laminate of the present invention is an optical laminate having a semi-transmitting semi-reflective film, a retardation plate, and a polarizer, and is characterized in that the optical laminate contains a compound having absorption at 480 nm or less, and the semi-transmitting semi-reflective film has a selective reflection wavelength in the range of 380 nm to 480 nm.
In image display devices, particularly organic EL display devices, among red (R), green (G) and blue (B), blue (B) has the shortest lifespan, and a long lifespan of blue is desired.
The present inventors have also found that in image display devices, particularly organic EL display devices, large-screen display devices with a large observation angle and mobile display devices, there is a large tendency for images to blue-shift when viewed from an oblique angle.
In particular, in a display device having a microcavity structure, the tendency of the image to blue shift is significant. The microcavity structure is a structure that utilizes the light resonance effect between the upper and lower electrodes of an organic electroluminescence element (hereinafter referred to as an organic EL element) to emphasize the peak intensity of the emission spectrum. Specifically, the light reflection between the upper and lower electrodes is repeated by matching the light path length between the upper and lower electrodes of the organic EL element to each emission peak wavelength of red (R), green (G), and blue (B) of the organic EL display element, and only the light with the matching light path length is resonated and emphasized. In such a microcavity structure, it is known that the wavelength of the light to be resonated (resonant wavelength) also changes depending on the viewing angle of the organic EL element, and when the viewing angle is large, that is, when the display screen of the organic EL display device or the like is viewed from an oblique direction, the resonant wavelength shifts to the short wavelength side (blue shift), and there is a problem that the original color of the organic EL element cannot be observed.

As a result of extensive investigations, the present inventors have found that in an optical laminate including a semi-transmitting semi-reflective film, the optical laminate contains a compound having absorption at 480 nm or less, and the semi-transmitting semi-reflective film has a selective reflection wavelength in the range of 380 nm or more to 480 nm, thereby making it possible to increase the blue emission luminance when observed from the front, and to suppress the blue shift when observed from an oblique direction.
Although the detailed mechanism by which the above-mentioned effects are obtained is unclear, part of it is thought to be as follows.
When the optical laminate has a semi-transmissive semi-reflective film having a selective reflection wavelength of 380 nm or more and 430 nm or less, the emitted light in the blue region increases when observed from the front, resulting in improved blue luminance.
On the other hand, when observed from an oblique direction, the reflected light is shifted to the shorter wavelength side than the blue region, so the above-mentioned blue brightness improvement effect is low. In addition, since the optical laminate of the present invention contains a compound that absorbs light in the shifted wavelength region, it is considered that the blue shift of the image is suppressed. Furthermore, when observed from an oblique direction, the optical distance of the layer containing a compound having absorption at 480 nm or less is longer than that in the case of front viewing, so that the absorption is increased according to the Lambert-Beer law, which is also considered to contribute to the suppression of the blue shift when observed from an oblique direction.
The present invention will be described in detail below.

<Layer structure of optical laminate>
The optical laminate of the present invention is preferably the following first or second embodiment. Among these, the first embodiment is more preferable from the viewpoint of easiness in designing the selective reflection wavelength.
First embodiment: the semi-transmissive semi-reflective film is a liquid crystal layer having a cholesteric structure (hereinafter also referred to as a "CLC layer"), and the CLC layer, a retardation plate, and a polarizer are laminated in this order.
Second embodiment: A semi-transmissive, semi-reflective film is a reflective polarizing layer (hereinafter also referred to as a "DBEF layer") that transmits only one of light rays having p waves or s waves and reflects the other, and a retardation layer, a DBEF layer, and a polarizer are laminated in this order.

Figure 1 is a schematic cross-sectional view showing a first embodiment of the optical laminate of the present invention. In Figure 1, the optical laminate 10 has a retardation plate 14 that imparts a phase difference of 1/4 wavelength to transmitted light, and a polarizer 16. The polarizer 16 is a linear polarizer, and the retardation plate 14 and the polarizer 16 form a circular polarizing plate 18. In addition, a CLC layer 12 is provided on the side of the retardation plate 14 opposite to the side on which the polarizer 16 is provided. In the following description, the upper side or top means the upper side of the figure, and in Figure 1, it is the side on which the polarizer 16 is provided, and the lower side or bottom means the side on which the CLC layer 12 is provided. Therefore, for example, the bottom of the CLC layer in Figure 1 means the side of the CLC layer 12 opposite to the side on which the retardation plate 14 is provided.

1, a protective layer (not shown) may be provided on the upper or lower side of the polarizer 16. The protective layer may be composed of only one layer or may be composed of two or more layers, and is not particularly limited, but preferably includes at least a protective layer for the polarizer 16 such as TAC, and at least one layer selected from a hard coat layer and an antireflection layer. In addition, a hard coat layer or a protective layer may be provided below the CLC layer 12.
In the case of the optical laminate 10 shown in FIG. 1, the angle between the slow axis of the retardation plate 14 and the absorption axis of the polarizer 16 is preferably 45±5°, and more preferably 45±2°.
In the present invention, in addition to the above-mentioned retardation plate, polarizer, and protective layer, an adhesive layer may be further provided, and the adhesive layer may be provided on the side of the retardation plate 14 opposite to the side on which the polarizer 16 is provided, between the polarizer 16 and a protective layer (not shown), or between protective layers composed of two or more layers. Also, the adhesive layer may be provided below the CLC layer 12.
Furthermore, the optical laminate according to the first embodiment of the present invention may have a protective layer between the retardation plate 14 and the polarizer 16, which is made of, for example, TAC, and is not particularly limited.

1, a display element is disposed below the CLC layer 12. When the display element is an organic electroluminescence display element (hereinafter also referred to as an "organic EL display element"), the organic EL display element has a reflective film.
Of the light emitted from the display element, only one of the right-handed and left-handed circularly polarized light of a certain wavelength is transmitted by the CLC layer 12, and the other is reflected back downward.
If the CLC layer 12 transmits right-handed circularly polarized light and reflects left-handed circularly polarized light, the right-handed circularly polarized light that has passed through the CLC layer 12 will exit from the polarizer 16 side. The circular polarizer 18, which is composed of the polarizer 16 and the retardation plate 14, is designed to transmit right-handed circularly polarized light in accordance with the CLC layer 12. The left-handed circularly polarized light reflected by the CLC layer 12 is reflected by the reflective film of the organic EL display element, becomes right-handed circularly polarized light, and enters the CLC layer 12 again. Since the CLC layer 12 transmits right-handed circularly polarized light, the right-handed circularly polarized light reflected by the reflective film passes through the CLC layer 12 and exits from the polarizer 16 side.
In other words, it is preferable that the CLC layer 12 reflects right-handed circularly polarized light for light incident from below, and the circular polarizer composed of a retardation plate and a polarizer transmits left-handed circularly polarized light, or that the CLC layer reflects left-handed circularly polarized light for light incident from below, and the circular polarizer transmits right-handed circularly polarized light.
Therefore, when the CLC layer 12 is not provided, the left-handed circularly polarized light is cut by the circular polarizer 18 and only the right-handed circularly polarized light is transmitted, but by providing the CLC layer 12, the left-handed circularly polarized light is reflected by the CLC layer 12, becomes right-handed circularly polarized light by the reflective film provided under the organic EL display element, and is transmitted through the optical stack 10 by being incident again on the optical stack 10. Therefore, the light of some wavelengths reflected by the CLC layer 12 increases the total amount of emitted light. Note that the CLC layer 12 reflects right-handed or left-handed circularly polarized light depending on the wavelength, so the amount of emitted light increases only in the relevant wavelength region.

Fig. 2 is a schematic cross-sectional view showing a second embodiment of the optical laminate of the present invention. In Fig. 2, the optical laminate 20 has a retardation plate 24 that imparts a phase difference of 1/4 wavelength to transmitted light, and a polarizer 26. In addition, a DBEF layer 22 is provided between the retardation plate 24 and the polarizer 26.
Although not shown in Fig. 2, a protective layer (not shown) may be provided on the upper or lower part of the polarizer 26. The protective layer may be composed of only one layer or may be composed of two or more layers, and is not particularly limited, but preferably has at least a polarizer protective layer such as TAC, and at least one layer selected from a hard coat layer and an antireflection layer. In addition, a hard coat layer or a protective layer may be provided below the DBEF layer 22 or the retardation plate 24.
In the case of the optical laminate shown in FIG. 2, the angle between the slow axis of the retardation plate 24 and the absorption axis of the polarizer 26 is preferably 45±5°, and more preferably 45±2°.
In the present invention, in addition to the above-mentioned retardation plate 24, polarizer 26, and protective layer, an adhesive layer may be provided, and the adhesive layer may be provided between the retardation plate 24 and the DBEF layer 22, between the polarizer 26 and the DBEF layer 22, between the polarizer 26 and a protective layer (not shown), or between a protective layer consisting of two or more layers. Also, the adhesive layer may be provided below the retardation plate 24.
Furthermore, the optical laminate according to the second embodiment of the present invention may have, for example, a protective layer made of TAC or a hard coat layer between the retardation plate 24 and the DBEF layer 22, but is not particularly limited thereto.

2, a display element is disposed below the retardation plate 24. When the display element is an organic electroluminescence display element (hereinafter, also referred to as an "organic EL display element"), the organic EL display element has a reflective film.
2, for example, the polarizer 26 and the DBEF layer 22 transmit p-waves. Also, the polarizer 26 absorbs s-waves, and the DBEF layer 22 reflects s-waves of some wavelengths. Unpolarized light emitted from the display element passes through the retardation plate 24, and the p-waves are transmitted by the DBEF layer 22, while the s-waves of some wavelengths are reflected. The p-waves transmitted through the DBEF layer 22 are transmitted through the polarizer 26 and emitted.
On the other hand, the s-wave reflected by the DBEF layer 22 passes through the retardation plate 24 and becomes circularly polarized light. The circularly polarized light is reflected by the reflective film of the organic EL display element, and the direction of the circular polarization is reversed. The circularly polarized light reflected by the reflective film passes through the retardation plate 24, becomes p-wave, and passes through the DBEF layer 22.
Furthermore, when the reflective layer is not a polarization-preserving reflector or when the polarizing plate 26 gives elliptically polarized light, the s-waves of some wavelengths reflected by the DBEF layer 22 become elliptically polarized light when passing through the retardation plate 24, and the s-waves reflected by the DBEF layer 22 are reflected by the reflective film of the organic EL display device, and the direction of the elliptically polarized light is reversed. Since the elliptically polarized light is a mixture of s-waves and p-waves, the p-waves are transmitted by the DBEF layer 22, and the s-waves of some wavelengths are reflected. In this embodiment, the above reflection and transmission are repeated. In this embodiment, the emitted light is the sum of the p-waves emitted for the nth time.
If the DBEF layer is not provided, only p-waves of the light emitted from the display element are transmitted, but by providing the DBEF layer, some of the s-waves of the wavelengths reflected by the DBEF layer are reflected and transmitted as p-waves, thereby increasing the total amount of emitted light.

In the optical laminate of the present invention, the retardation plate and the optical laminate are preferably any one of the following (1) to (5).
(1) The retardation plate is a laminate of a λ/2 retardation plate with positive dispersion and a λ/4 retardation plate with positive dispersion, and has a polarizer on the λ/2 retardation plate side.
(2) The retardation plate further includes a positive dispersion positive C plate in addition to a positive dispersion λ/2 retardation plate and a positive dispersion λ/4 retardation plate. Also, a polarizer is provided on the λ/2 retardation plate side. The position of the positive C plate may be between the λ/2 retardation plate and the polarizer, or may be on the opposite side of the λ/4 retardation plate to the side on which the λ/2 retardation plate is provided, and is not particularly limited.
(3) The retardation plate is a λ/4 retardation plate having reverse dispersion.
(4) The retardation plate is a laminate of a positive C plate having normal dispersion and a λ/4 retardation plate having reverse dispersion. It is preferable that a polarizer is provided on the λ/4 retardation plate side.
(5) The retardation plate is a laminate of a reverse dispersion positive C plate and a reverse dispersion λ/4 retardation plate. It is preferable that a polarizer is provided on the λ/4 retardation plate side.
Among these, (2), (4) or (5) is preferable, and from the viewpoint of the viewing angle compensation effect, (5) is more preferable.
In the second embodiment of the present invention, a DBEF layer is provided between the retardation plate and the polarizer.

When the optical laminate of the present invention has only a λ/4 retarder as a retarder, the λ/4 retarder is preferably a reverse dispersion λ/4 retarder. When the λ/4 retarder has a positive dispersion (positive wavelength dispersion characteristic) or a flat dispersion (flat wavelength dispersion characteristic), the transmitted light of the λ/4 retarder incident from the outside (viewer side) is transmitted to the display element side as elliptical polarized light having a different ellipticity depending on the wavelength. In addition, when the light returning from the display element side passes through the λ/4 retarder and heads toward the viewer side, a phase difference having a different wavelength conversion amount depending on the wavelength is imparted, and the light is emitted from the λ/4 retarder as circularly polarized light or linearly polarized light having a different ellipticity depending on the wavelength. This makes the color shift of the returning light more noticeable. On the other hand, when a reverse dispersion λ/4 retarder is used, the change due to the wavelength is suppressed overall compared to when a positive dispersion λ/4 retarder and a flat dispersion λ/4 retarder are used.
Here, the α of the λ/4 phase difference plate (the ratio (Re450/Re550) of the retardation value at a wavelength of 450 nm (Re450) to the retardation value at a wavelength of 550 nm (Re550)) is preferably 0.95 or less, more preferably 0.93 or less, even more preferably 0.91 or less, and even more preferably 0.89 or less. Moreover, Re450/Re550 is preferably 0.78 or more, more preferably 0.80 or more, and even more preferably 0.82 or more.
It is preferable that α is within the above range, since the state close to λ/4 is maintained widely in the visible region. α is obtained by measuring the retardation value at a wavelength of 450 nm and the retardation value at a wavelength of 550 nm with a phase difference measuring device, and is an index of wavelength dispersion.

When a λ/4 retardation plate and a λ/2 retardation plate are laminated and used as the retardation plate, it is preferable to place the λ/2 retardation plate on the polarizer side.
When a λ/4 retardation layer and a λ/2 retardation layer are used as the retardation layers, the angle between the alignment axis of each retardation layer and the absorption axis of the polarizer is preferably within the range of (i) or (ii) below.
(i) As a first example, the angle between the slow axis of the λ/2 retardation layer and the absorption axis of the polarizer is preferably 15±8°, more preferably 15±6°, and in this case, the angle between the slow axis of the λ/4 retardation layer and the absorption axis of the polarizer is preferably 75±15°, more preferably 75±13°.
(ii) As a second example, the angle between the slow axis of the λ/2 retardation layer and the absorption axis of the polarizer is preferably 75±15°, more preferably 75±13°, and in this case, the angle between the slow axis of the λ/4 retardation layer and the absorption axis of the polarizer is preferably 15±8°, more preferably 15±6°.

Here, the in-plane phase difference (in-plane retardation value, Re) and the phase difference in the thickness direction (retardation value in the thickness direction, Rth) can be expressed by the following formula, where the refractive index in the in-plane slow axis direction is nx, the refractive index in the in-plane direction perpendicular to nx is ny, the refractive index in the direction perpendicular to nx and ny is nz, and the film thickness is d.
In-plane retardation (Re) = (nx - ny) x d
Retardation in the thickness direction (Rth) = ((nx + ny) / 2 - nz) x d

When the optical laminate of the present invention contains a compound having absorption at 480 nm or less in the semi-transmissive semi-reflective film or in any layer on the display element side of the semi-transmissive semi-reflective film, the average reflectance of light incident from the side where the display element is located at 530 to 680 nm is preferably 15% or less, more preferably 12% or less, and even more preferably 10% or less. There is no particular limit to the lower limit, but from the viewpoint of ease of manufacture, it is preferably 3% or more, and more preferably 5% or more. The reflectance is the reflectance at an incident angle of 5°.

The light reflectance of the optical laminate of the present invention is obtained according to the luminous reflectance Y value of the CIE 1931 standard color system. The side opposite to the polarizer in the retardation layer of the optical laminate (the side where the display element is arranged) is set as the incident light side, and light of each wavelength is made incident to measure the reflectance at each wavelength. That is, in the first embodiment, the CLC layer side is set as the incident light side, and in the second embodiment, the retardation plate side is set as the incident light side. In addition, a black plate is placed on the polarizer side.
The light reflectance means the average value of the measured values at 16 points, and can be obtained, for example, by the method described in the Examples. In this specification, the 16 measurement points are preferably the center of measurement when a margin of 1 cm is drawn from the outer edge of the measurement sample, and lines are drawn to divide the inner area of the margin into 5 equal parts vertically and horizontally. When the measurement sample is a rectangle, it is preferable to measure the 16 intersections of the lines dividing the inner area of the margin into 5 equal parts vertically and horizontally with a margin of 1 cm from the outer edge of the rectangle as the center, and calculate the average value. In addition, when the measurement sample is a shape other than a rectangle, such as a circle, an ellipse, a triangle, or a pentagon, it is preferable to draw a rectangle with the maximum area inscribed in these shapes, and measure 16 points on the rectangle by the above method.

In the present invention, the "average reflectance of light at 530 to 680 nm" is preferably a value obtained by measuring the reflectance at intervals of 1 nm or 2 nm in the wavelength range of 530 nm or more and 680 nm or less and calculating the average value.
It is preferable to measure the spectral reflectance using the SCI method every 1 nm or every 2 nm, but if the measurement wavelength interval of the measurement device exceeds 2 nm, it is preferable to calculate the average reflectance by assuming that the absolute value of the change in reflectance every 1 nm within the measurement interval is uniform.

In the optical laminate of the present invention, when the semi-transmitting semi-reflective film contains a compound having absorption at 480 nm or less, or when any layer on the display element side of the semi-transmitting semi-reflective film contains a compound having absorption at 480 nm or less, it is preferable that X>Y, where X nm is the half-width of the peak reflectance at 400 to 480 nm measured from the front (angle of 5°) and Y nm is the half-width of the peak reflectance at 400 to 480 nm measured obliquely (angle of 25°).
Here, the half-width described above is calculated as a width where the reflectance becomes {b+(a-b)×0.5}%, from the average reflectance of the wavelength of 500 nm or more and 580 nm or less, which is the base reflectance (b%), based on the peak top reflectance (a%) in the range of 400 to 480 nm.
The larger the angle of light incident on the semi-transmissive semi-reflective film, the more the reflected light is shifted to the shorter wavelength side. Since the present invention contains a compound having absorption at 480 nm or less (hereinafter also referred to as an absorbing compound), it is considered that the reflected light shifted to the shorter wavelength side is absorbed by the absorbing compound, and the half width of the reflectance at an incident angle of 25° becomes smaller than the half width of the reflectance at an incident angle of 5°.
XY is preferably 5 nm or more, and more preferably 7 nm or more.

In the optical laminate of the present invention, it is preferable that the reflection wavelength peak of the optical laminate, i.e., the peak wavelength at which the luminance is improved when the optical laminate of the present invention is used in a display panel, is located on the long wavelength side in the region of 480 nm or less with respect to the selective reflection central wavelength of the semi-transmitting semi-reflective film. It is more preferable that the above relationship is satisfied when the semi-transmitting semi-reflective film is a CLC layer. Here, the reflection wavelength peak of the optical laminate is a peak wavelength at which the luminance is improved in the region of 480 nm or less when the optical laminate of the present invention is provided in a display device. The reflection wavelength peak is measured at an incident angle of 5°.
It is preferable that the reflection wavelength peak of the optical laminate is located on the longer wavelength side with respect to the selective reflection central wavelength of the semi-transmissive semi-reflective film, because the reflected light for light incident obliquely is shifted to the shorter wavelength side, and the shifted reflected light is absorbed by the absorbing compound, thereby suppressing the occurrence of a blue shift when observed obliquely.
By designing the selective reflection central wavelength of the semi-transmitting/semi-reflective film to be in a wavelength region where the absorbing compound has absorption, it is possible to obtain an optical laminate that satisfies the above relationship.

In the present invention, when the semi-transmitting semi-reflective film contains a compound having absorption at 480 nm or less, or when any layer on the display element side of the semi-transmitting semi-reflective film contains a compound having absorption at 480 nm or less, it is preferable that the half-width of the reflection peak of the optical laminate is smaller than the half-width of the reflection peak of the semi-transmitting semi-reflective film alone. Note that, when the semi-transmitting semi-reflective film is a CLC layer, it is more preferable that the above relationship is satisfied. The above half-width of the reflection peak is the half-width of the reflection peak in reflectance measurement at an incident angle of 5°.
Here, the half-width described above is calculated as a width where the reflectance becomes {b+(a-b)×0.5}%, from the average reflectance of the wavelength of 500 nm or more and 580 nm or less, which is the base reflectance (b%), based on the peak top reflectance (a%) in the range of 380 to 480 nm.
By absorbing a portion of the short wavelength region of the reflection peak of the semi-transmitting semi-reflective film alone by the absorbing compound, the half-width of the reflection peak of the optical laminate can be made smaller than the half-width of the reflection peak of the semi-transmitting semi-reflective film alone.
By providing an optical laminate that satisfies the above-mentioned relationship, the reflected light is shifted to the shorter wavelength side for light incident obliquely, and the shifted reflected light is absorbed by the absorbing compound, which is preferable because it suppresses the occurrence of a blue shift when observed obliquely.

<Retardation Plate>
The optical layered body of the present invention has a retardation plate.
The retardation plate is preferably a 1/2 wavelength retardation plate (hereinafter also referred to as a "λ/2 retardation plate"), a 1/4 wavelength retardation plate (hereinafter also referred to as a "λ/4 retardation plate"), or a combination thereof. In the present invention, it is preferable to provide at least a λ/4 retardation plate as the retardation plate. In the present invention, the retardation plate is more preferably a λ/4 retardation plate or a laminate of a λ/4 retardation plate and a λ/2 retardation plate, further preferably a λ/4 retardation plate, and even more preferably a λ/4 retardation plate having reverse dispersion.
The λ/2 retardation plate has an in-plane retardation at a wavelength of 550 nm of preferably 200 to 300 nm, more preferably 220 to 280 nm, and further preferably 220 to 270 nm.
The λ/4 retardation plate has an in-plane retardation at a wavelength of 550 nm of preferably 100 to 180 nm, more preferably 110 to 160 nm, and even more preferably 110 to 150 nm.

The retardation plate of the present invention may further include a positive C plate having positive C characteristics. The positive C characteristics are characterized in that, when the refractive index in the X-axis direction along the layer surface is nx, the refractive index in the Y-axis direction perpendicular to the X-axis along the layer surface is ny, and the refractive index in the layer thickness direction is nz, the relationship is nz>nx≒ny, and the optical axis is in the z direction.

The retardation plate may exhibit wavelength dispersion of normal dispersion (hereinafter also referred to as "normal dispersion") or wavelength dispersion of reverse dispersion (hereinafter also referred to as "reverse dispersion").
In addition, the reverse dispersion is a characteristic in which the phase difference given to the transmitted light increases as the wavelength of the transmitted light becomes longer, and specifically, the relationship between the retardation at a wavelength of 450 nm (Re450) and the retardation at a wavelength of 550 nm (Re550) is Re450<Re550. On the other hand, the normal dispersion is a characteristic in which Re450>Re550.
The thickness of the retardation plate can be appropriately adjusted within the range of 0.1 to 10 μm, taking into consideration the retardation to be imparted.

The retardation plate used in the present invention may be made of a retardation support having the desired λ/4 or λ/2 function by itself, may have a retardation layer on a support (transparent support) made of a polymer film, or may be composed of a retardation layer alone. When composed of a retardation layer alone, other layers may be laminated on a support that does not have an optical effect to give the desired λ/4 or λ/2 function. There is no particular restriction on the constituent material of the retardation layer, and it may be a retardation layer formed from a composition containing a liquid crystal compound, a retardation layer obtained by stretching a polymer film, or both layers.
Among these, the retardation plate is preferably a laminate of a transparent support and a retardation layer.

(Transparent Support)
In the present invention, there is no particular limitation on the material of the transparent support. Various polymer films, for example, cellulose acylate; polycarbonate-based polymers; polyester-based polymers such as polyethylene terephthalate and polyethylene naphthalate; acrylic polymers such as polymethyl methacrylate; styrene-based polymers such as polystyrene and acrylonitrile-styrene copolymers (AS resins), etc., can be used. In addition, the support may be prepared using one or more polymers selected from polyolefins such as polyethylene and polypropylene; polyolefin-based polymers such as ethylene-propylene copolymers; vinyl chloride-based polymers; amide-based polymers such as nylon and aromatic polyamide; imide-based polymers; sulfone-based polymers; polyethersulfone-based polymers; polyetheretherketone-based polymers; polyphenylene sulfide-based polymers; vinylidene chloride-based polymers; vinyl alcohol-based polymers; vinyl butyral-based polymers; arylate-based polymers; polyoxymethylene-based polymers; epoxy-based polymers; or a mixture of the above polymers.

When the retardation plate is a laminate of a polymer film (transparent support) and a retardation layer, it is preferably a laminate of a polymer film (transparent support) and a retardation layer formed from a composition containing a liquid crystal compound. A polymer film with small optical anisotropy may be used, or a polymer film that has optical anisotropy expressed by stretching or the like may be used. The support preferably has a light transmittance of 80% or more.
The thickness of the transparent support is preferably from 10 μm to 200 μm, more preferably from 10 to 80 μm, and further preferably from 20 to 60 μm.

(Liquid Crystal Compound)
The type of liquid crystal compound used to form the retardation layer is not particularly limited. For example, a retardation layer obtained by forming a low molecular liquid crystal compound in a nematic orientation in a liquid crystal state and then fixing the orientation by photocrosslinking or thermal crosslinking, or a retardation layer obtained by forming a polymer liquid crystal compound in a nematic orientation in a liquid crystal state and then fixing the orientation by cooling may be used. In the present invention, even if a liquid crystal compound is used in the retardation layer, the retardation layer is a layer formed by fixing the liquid crystal compound by polymerization or the like, and after becoming a layer, it is no longer necessary to show liquid crystallinity. The polymerizable liquid crystal compound may be a multifunctional polymerizable liquid crystal compound or a monofunctional polymerizable liquid crystal compound. In addition, the liquid crystal compound may be a discotic liquid crystal compound or a rod-shaped liquid crystal compound.

In the retardation layer, the liquid crystal compound is preferably fixed in any one of vertical alignment, horizontal alignment, hybrid alignment, and tilt alignment. From the viewpoint of making the viewing angle dependency symmetrical, it is preferable that the disk surface of the discotic liquid crystal compound is substantially perpendicular to the film surface (retardation layer surface), or the long axis of the rod-shaped liquid crystal compound is substantially horizontal to the film surface (retardation layer surface).
The discotic liquid crystal compound being substantially perpendicular means that the average angle between the film plane (retardation layer plane) and the disc plane of the discotic liquid crystal compound is in the range of 70° to 90°, preferably 80° to 90°, more preferably 85° to 90°.
The rod-shaped liquid crystal compound being substantially horizontal means that the angle between the film plane (retardation plane) and the director of the rod-shaped liquid crystal compound is in the range of 0° to 20°, preferably 0° to 10°, more preferably 0° to 5°.

When the retardation plate includes a retardation layer that contains a liquid crystal compound, the retardation layer may consist of only one layer, or may be a laminate of two or more retardation layers.

The retardation layer containing a liquid crystal compound can be formed by applying a coating liquid containing a liquid crystal compound such as a rod-shaped liquid crystal compound or a discotic liquid crystal compound, and optionally a polymerization initiator, an alignment control agent, or other additives, which will be described later, onto a transparent support. It is preferable to form an alignment film on a transparent support and then apply the coating liquid onto the surface of the alignment film to form a retardation layer. The thickness of the retardation layer is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and even more preferably 1 to 5 μm.

-Discotic liquid crystal compound-
In the present invention, it is preferable to use discotic liquid crystal compound for forming retardation layer.Discotic liquid crystal compound is described in various documents (C. Destrade et al., Mol. Crysr. Liq. Cryst., vol. 71, page 111 (1981); Japan Chemical Society, Quarterly Chemistry Review, No. 22, Chemistry of Liquid Crystals, Chapter 5, Chapter 10, Section 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. Comm., page 1794 (1985); J. Zhang et al., J. Am. Chem. Soc., vol. 116, page 2655 (1994) etc.). The polymerization of discotic liquid crystal compounds is described in JP-A-8-27284.

The discotic liquid crystal compound preferably has a polymerizable group so that it can be fixed by polymerization. For example, a structure in which a polymerizable group is bonded as a substituent to the discotic core of the discotic liquid crystal compound is conceivable, but if the polymerizable group is directly bonded to the discotic core, it becomes difficult to maintain the alignment state during the polymerization reaction. Therefore, a structure having a linking group between the discotic core and the polymerizable group is preferred. That is, the discotic liquid crystal compound having a polymerizable group is preferably a compound represented by the following formula:
D(-LP) _n
In the formula, D is a discotic core, L is a divalent linking group, P is a polymerizable group, and n is an integer of 1 to 12. Preferable specific examples of the discotic core (D), the divalent linking group (L), and the polymerizable group (P) in the formula are (D1) to (D15), (L1) to (L25), and (P1) to (P18) described in JP-A-2001-4837, respectively, and the contents described in the same publication can be preferably used. The discotic nematic liquid crystal phase-solid phase transition temperature of the liquid crystal compound is preferably 30 to 300° C., more preferably 30 to 170° C.

- Rod-like liquid crystal compound -
In the present invention, a rod-shaped liquid crystal compound may be used to form the retardation layer of the retardation plate. Preferred examples of rod-shaped liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexane carboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles. Not only the above-mentioned low molecular weight liquid crystal compounds, but also polymeric liquid crystal compounds can be used. It is more preferable to fix the orientation of the rod-shaped liquid crystal compound by polymerization. It is preferable that the liquid crystal compound has a partial structure that can cause polymerization or crosslinking reaction by actinic rays, electron beams, heat, etc., and more preferably has a polymerizable group.
The number of the partial structures is preferably 1 to 6, more preferably 1 to 3. As the polymerizable rod-like liquid crystal compound, those described in Makromol. Chem. , Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Pat. Nos. 4,683,327, 5,622,648, 5,770,107, International Publication WO95/22586, 95/24455, 97/00600, 98/23580, 98/52905, JP-A-1-272551, 6-16616, 7-110469, 11-80081, and compounds described in JP-A-2001-328973 can be used.
Specific examples of the rod-shaped liquid crystal compound include the compounds represented by the following formulas (1) to (17).

Examples of liquid crystal compounds exhibiting reverse dispersion include those described in published patent applications such as JP-T-2010-537954, JP-T-2010-537955, JP-T-2010-522892, JP-T-2010-522893, and JP-T-2013-509458, as well as in patent applications such as Japanese Patent Nos. 5892158, 5979136, 5994777, and 6015655.

The liquid crystal compounds may be used alone or in combination of two or more. When using one type alone, the liquid crystal compound is preferably a polymerizable liquid crystal compound. When using two or more types in combination, it is preferable that at least one of them is a polymerizable liquid crystal compound, and it is more preferable that all of them are polymerizable liquid crystal compounds.

(Polymerization initiator)
The aligned liquid crystal compound is fixed while maintaining the aligned state. The fixation is preferably performed using a polymerization reaction, and the polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. Among these, a photopolymerization reaction is preferable. Examples of the photopolymerization initiator include α-carbonyl compounds (see U.S. Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (see U.S. Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (see U.S. Pat. No. 2,722,512), polynuclear quinone compounds (see U.S. Pat. Nos. 3,046,127 and 2,951,758), a combination of triaryl imidazole dimer and p-aminophenyl ketone (see U.S. Pat. No. 3,549,367), acridine and phenazine compounds (see JP-A-60-105,667 and U.S. Pat. No. 4,239,850), and oxadiazole compounds (see U.S. Pat. No. 4,212,970).

The amount of the polymerization initiator used is preferably 0.01 to 20% by mass, more preferably 0.5 to 5% by mass, based on the total solid content of the retardation layer-forming composition. For light irradiation for polymerization of the liquid crystal compound, ultraviolet light is preferably used. The irradiation energy is preferably 20 mJ/cm ² to 50 J/cm ² , more preferably 100 to 800 mJ/cm ² . In order to promote the photopolymerization reaction, light irradiation may be performed under heating conditions.

(Surfactant)
The retardation layer forming composition preferably contains a surfactant. Among the surfactants, it is preferable to select and use one or more selected from a fluorine-based surfactant having a polymerizable group and a silicon-based surfactant having a polymerizable group.
The content of the surfactant is preferably 0.01 to 2.0% by mass, and more preferably 0.1 to 1.0% by mass, based on the total solid content of the retardation layer forming composition.

(solvent)
The composition for forming the retardation layer usually contains a solvent.
Examples of the solvent include ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, N-methyl-2-pyrrolidone, etc.), ethers (dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, etc.), alicyclic hydrocarbons (cyclohexane, etc.), aromatic hydrocarbons (toluene, xylene, etc.), halogenated carbons (dichloromethane, dichloroethane, etc.), esters (methyl acetate, ethyl acetate, butyl acetate, etc.), alcohols (butanol, cyclohexanol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), cellosolve acetates, sulfoxides (dimethyl sulfoxide, etc.), amides (dimethylformamide, dimethylacetamide, etc.), and mixtures of these may also be used.

The retardation layer can be formed, for example, by applying, drying, and curing a composition for forming a retardation layer. In addition, it is preferable to apply the composition for forming a retardation layer onto an alignment film.

(Vertical Alignment Promoter)
In order to uniformly align the molecules of the liquid crystal compound vertically when forming the retardation layer, it is preferable to use an alignment control agent capable of controlling the alignment of the liquid crystal compound vertically on the alignment film interface side and the air interface side. For this purpose, it is preferable to form the retardation layer using a composition containing a liquid crystal compound and a compound that acts to align the liquid crystal compound vertically on the alignment film by excluded volume effect, electrostatic effect, or surface energy effect. In addition, regarding the alignment control on the air interface side, it is preferable to form the retardation layer using a composition containing a liquid crystal compound and a compound that is unevenly distributed at the air interface when the liquid crystal compound is aligned and acts to align the liquid crystal compound vertically by its excluded volume effect, electrostatic effect, or surface energy effect. As a compound that promotes the vertical alignment of the molecules of the liquid crystal compound on the alignment film interface side (alignment film interface side vertical alignment promoter), a pyridinium derivative is preferably used. As a compound that promotes vertical alignment of the molecules of a liquid crystal compound on the air interface side (air interface side vertical alignment promoter), a compound that promotes uneven distribution of the compound on the air interface side and contains a fluoroaliphatic group and one or more hydrophilic groups selected from the group consisting of a carboxy group (-COOH), a sulfo group ( _-SO3H ), a phosphonoxy group {-OP(=O)(OH) ₂ } and salts thereof is preferably used. Furthermore, by blending these compounds, for example, when the liquid crystal composition is prepared as a coating liquid, the coatability of the coating liquid is improved and the occurrence of unevenness and repelling is suppressed.
For the vertical alignment promoter, see paragraphs 0101 to 0185 of International Publication No. 2013/100115.

(Other additives)
In the present invention, the composition for forming the retardation layer may contain, in addition to the above components, a plasticizer, a polymerizable monomer, etc. It is preferable that these components have compatibility with the liquid crystal compound and do not inhibit the alignment.
The polymerizable monomer may be a radically polymerizable or cationic polymerizable compound, preferably a polyfunctional radically polymerizable monomer, and preferably a compound copolymerizable with the above-mentioned polymerizable group-containing liquid crystal compound. For example, the compounds described in paragraphs 0018 to 0020 of JP-A No. 2002-296423 may be mentioned. The amount of the polymerizable compound to be added is preferably 1 to 50 parts by mass, more preferably 5 to 30 parts by mass, based on 100 parts by mass of the liquid crystal compound.

(Method of Coating Retardation Layer)
The retardation layer forming composition can be applied by a known method (eg, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).

(Alignment film)
The retardation plate may have an alignment film.
The alignment film has a role of facilitating alignment of the liquid crystal compound in the retardation layer when the retardation layer is formed by applying, drying and curing the composition for forming the retardation layer.
Even if the retardation layer has an alignment film at the time of formation, the retardation layer can be transferred to another member and the alignment film can be prevented from being transferred during the transfer process to obtain an optical laminate without an alignment film.

The alignment film can be formed by, for example, applying an alignment layer-forming composition onto a transparent substrate and imparting an alignment control force to the composition. The alignment film-forming composition can be appropriately selected from conventionally known materials such as photodimerization-type materials.
The means for imparting an alignment control force to the alignment film can be a conventionally known method, such as a rubbing method, a photoalignment method, or a shaping method.
The thickness of the alignment film is preferably 1 to 1,000 nm, and more preferably 60 to 300 nm.

<Polarizer>
In the present invention, the optical laminate comprises a semi-transmitting/semi-reflective film, a retardation film, and a polarizer. The polarizer preferably forms a polarizing plate together with a protective film.
As the polarizer, any of an iodine-based polarizer, a dye-based polarizer using a dichroic dye, and a polyene-based polarizer may be used.
Iodine-based polarizers and dye-based polarizers are generally manufactured using polyvinyl alcohol-based films. The absorption axis of the polarizer corresponds to the stretching direction of the film. Therefore, a polarizer stretched in the machine direction (transport direction) has an absorption axis parallel to the longitudinal direction, and a polarizer stretched in the transverse direction (direction perpendicular to the transport direction) has an absorption axis perpendicular to the longitudinal direction.

In the present invention, the above-mentioned retardation plate and polarizer preferably constitute a circular polarizing plate or an elliptical polarizing plate, and it is more preferable to use a linear polarizer as the polarizer and combine it with the above-mentioned retardation plate to constitute a polarizer-integrated optical laminate that functions as a circular polarizing plate.
A circular polarizing plate is disposed on an organic electroluminescence display device or a resistive touch panel, and serves to exhibit anti-reflection properties.
The optical laminate of the present invention has a retardation plate and a polarizer, and the retardation plate and the polarizer may be in the form of a film, or may be formed by coating or the like to form a layer, and are not limited to an embodiment in which they form a plate shape alone.
When the optical laminate of the present invention is applied to a display panel or an image display device, it is preferable that a retardation plate is provided on the light source side.

<Semi-transmissive, semi-reflective film>
The semi-transmitting/semi-reflective film of the optical laminate of the present invention is preferably either a CLC layer or a DBEF layer.
Here, the term "semi-transmissive semi-reflective film" refers to a film that transmits a specific polarized light and reflects other polarized light, and has wavelength dependency on the reflected light. The polarized light means circularly polarized light, linearly polarized light, s-wave, p-wave, etc. The reflectance can be set appropriately and is not limited to 50%.
In particular, the semi-transmitting semi-reflective film preferably has wavelength dependency of the reflected light, and the selectively reflective wavelength is preferably 480 nm or less, more preferably 460 nm or less, and even more preferably 440 nm or less when measured at an incident angle of 5°. The lower limit is not particularly limited, but is preferably 380 nm or more, more preferably 400 nm or more, and even more preferably 415 nm or more. In addition, when the selectively reflective wavelength has a peak, it is preferable that the peak is in the above-mentioned wavelength region, but it is not necessarily required to have a peak, and is not particularly limited as long as selective reflection is possible in the above-mentioned wavelength region. In addition, the semi-transmitting semi-reflective film is preferably a semi-transmitting semi-reflective film having low reflectivity or no reflectivity in the region exceeding 480 nm.
When the maximum reflectance of the semi-transmitting/semi-reflective film from 380 nm to 480 nm is A and the reflectance at 480 nm is B, B/A is preferably 0.5 or less, more preferably 0.3.
When the selective reflection wavelength is within the above range, the light reflected by the semi-transmitting semi-reflective film for incident light from the front is emitted in a blue wavelength region, thereby improving the blue emission luminance. On the other hand, for incident light from an oblique angle, the light reflected by the semi-transmitting semi-reflective film is shifted to the short wavelength side, and the shifted light is absorbed by the absorbing compound, thereby suppressing the occurrence of blue shift.

(Liquid crystal layer having a cholesteric structure (CLC layer))
The optical layered body of the present invention preferably has a liquid crystal layer having a cholesteric structure (CLC layer) as a semi-transmissive semi-reflective film.
In this specification, the CLC layer refers to a layer made of liquid crystal molecules that exhibit cholesteric regularity. Cholesteric regularity is a structure in which the molecular axes are aligned in a certain direction on one plane, but the direction of the molecular axes is slightly shifted at an angle on the next plane that overlaps it, and the angle is shifted even further on the next plane, and so on, so that the angle of the molecular axes in the plane shifts (twists) as the light passes through the overlapping planes. A structure in which the direction of the molecular axes is twisted in this way is a chiral structure.

Cholesteric liquid crystal layers generally have the optical rotation selection property of separating optical rotation components in one direction from those in the opposite direction based on the physical molecular arrangement. Light incident on such a liquid crystal layer along the helical axis of the planar arrangement of the liquid crystal is separated into two circularly polarized lights, right-handed and left-handed, one of which is transmitted and the other is reflected. This phenomenon is known as circular dichroism, and by appropriately selecting the direction of rotation in the helical structure of the liquid crystal molecules, circularly polarized light having the same optical rotation direction as the direction of rotation is selectively reflected.

In this case, the maximum reflection of optically rotatory polarized light occurs at a wavelength λ ₀ of the following formula (1): That is, λ ₀ means the central wavelength of the reflected light (selective reflection central wavelength).
λ ₀ = nav · p ... (1)
Here, p is the helical pitch in the helical structure of the liquid crystal molecules, and n a v is the average refractive index in a plane perpendicular to the helical axis.
Moreover, the wavelength bandwidth Δλ of the reflected light at this time is expressed by the following formula (2).
Δλ=Δn·p (2)
Here, Δn is the birefringence value of the liquid crystal material.

The polarization separation effect of the cholesteric liquid crystal layer alone will now be described. When unpolarized light is incident on the cholesteric liquid crystal layer, one of the right-handed or left-handed circularly polarized components of the light within the wavelength bandwidth Δλ centered on the wavelength _λ0 is reflected, and the other circularly polarized component and light in other wavelength ranges (unpolarized) are transmitted. Note that the reflected right-handed or left-handed circularly polarized light is reflected as is without phase inversion, unlike normal reflection.

As described above, the selective reflection central wavelength range of the cholesteric liquid crystal layer is preferably 480 nm or less, more preferably 460 nm or less, and even more preferably 440 nm or less, and is preferably 380 nm or more, more preferably 400 nm or more, and even more preferably 415 nm or more, when measured at an incident angle of 5°. By setting the selective reflection central wavelength within the above range, the luminance of light in the blue region is improved when viewed from the front, and when viewed from an oblique angle, the reflected light is shifted to a shorter wavelength and absorbed by the absorbing compound, suppressing the increase in luminance in the blue region and suppressing the blue shift, which is preferable.
Moreover, a high reflectance of the cholesteric liquid crystal layer is preferable because it increases the amount of light emitted when the optical laminate of the present invention is observed from the front direction.

Examples of the cholesteric liquid crystal layer include a layer made of a cured product of a curable composition containing a liquid crystalline monomer or oligomer having a polymerizable group, and a layer made of a liquid crystalline polymer in a glassy state.
Among the above, the cholesteric liquid crystal layer is preferably a cured product of a curable composition containing a liquid crystalline monomer or oligomer having a polymerizable group, because when the cholesteric liquid crystal layer is a cured product of the above curable composition, the liquid crystal molecules can be optically fixed while remaining in a cholesteric liquid crystal state, and handling properties are improved.
The curable composition may be either ionizing radiation curable or heat curable, but from the viewpoint of the productivity of the filter, it is preferable to use an ionizing radiation curable composition. In this specification, ionizing radiation means electromagnetic waves or charged particle beams having an energy quantum capable of polymerizing or crosslinking molecules, and usually ultraviolet rays (UV) or electron beams (EB) are used, but other types of radiation such as electromagnetic waves such as X-rays and γ-rays, α-rays, and charged particle beams such as ion beams can also be used.

Examples of the polymerizable group include ethylenically unsaturated bond groups such as (meth)acryloyl group, vinyl group, and allyl group, as well as epoxy group, oxetanyl group, etc. From the viewpoint of polymerizability, a (meth)acryloyl group or vinyl group is preferred, and a (meth)acryloyl group is more preferred.
The liquid crystalline monomer or oligomer having a polymerizable group may have at least one of the above-mentioned polymerizable groups, but from the viewpoint of obtaining a cholesteric liquid crystal layer in which the liquid crystalline molecules are optically fixed by three-dimensional crosslinking, it is preferable for it to have two or more polymerizable groups, and a bifunctional liquid crystalline monomer or oligomer having polymerizable groups at both ends is more preferable.

Examples of liquid crystal monomers having a polymerizable group include those disclosed in JP-A-7-258638 and JP-T-10-508882. Examples of liquid crystal oligomers having a polymerizable group include cyclic organopolysiloxane compounds having a cholesteric phase, such as those disclosed in JP-A-57-165480.

A specific example of a liquid crystal monomer having a polymerizable group is a liquid crystal monomer having acryloyl groups at both ends, as represented by the following structural formula (I).

The cholesteric liquid crystal layer is more preferably a cured product of a curable composition containing a liquid crystal monomer or oligomer having a polymerizable group and a chiral agent. When the liquid crystal monomer or oligomer is made into a liquid crystal layer at a predetermined temperature, it becomes a nematic state, and when a chiral agent is added to it, it becomes a chiral nematic liquid crystal (i.e., cholesteric liquid crystal). In addition, the helical pitch in the helical structure of the liquid crystal molecules contained in the cholesteric liquid crystal layer can be adjusted by changing the chiral power by changing the type of chiral agent used or by changing the amount of the chiral agent mixed, thereby adjusting the selective reflection wavelength range of the cholesteric liquid crystal layer.
The cholesteric liquid crystal layer may be made of discotic liquid crystal. The cholesteric liquid crystal layer may be made of a chiral discotic compound as described in, for example, JP-A-2000-086591, or may be made of a copolymer of a non-chiral discotic liquid crystal compound and a chiral discotic compound having a polymerizable group as described in, for example, JP-A-2000-111734, JP-A-2000-171637, JP-A-2000-347039. By making the cholesteric liquid crystal layer from discotic liquid crystal, the cholesteric liquid crystal layer also functions as a positive C plate, which is advantageous in that the positive C plate in the retardation plate can be omitted.

From the viewpoint of obtaining a cholesteric liquid crystal layer in which liquid crystalline molecules are optically fixed by three-dimensional crosslinking, it is further preferable that the cholesteric liquid crystal layer is a cured product of a curable composition containing a liquid crystalline monomer or oligomer having a polymerizable group and a chiral agent having a polymerizable group.
As the chiral agent having a polymerizable group, from the viewpoint of obtaining a cholesteric liquid crystal layer in which liquid crystal molecules are optically fixed by three-dimensional crosslinking, it is preferable to use a chiral agent having two or more polymerizable groups, and more preferable to use a bifunctional chiral agent having polymerizable groups at both ends.As the polymerizable group, there can be mentioned (meth)acryloyl group, vinyl group, allyl group and other ethylenically unsaturated bond groups, as well as epoxy group, oxetanyl group, etc.From the viewpoint of polymerizability, (meth)acryloyl group or vinyl group is preferable, and (meth)acryloyl group is more preferable.

Examples of the chiral agent include the chiral compounds disclosed in JP-A-7-258638 and JP-T-10-508882.
An example of a commercially available chiral agent is "Paliocolor (registered trademark) LC756" (manufactured by BASF Corporation), which has acryloyl groups as polymerizable groups at both ends.

The amount of chiral agent in the cholesteric liquid crystal layer is not particularly limited as long as the desired wavelength selectivity is obtained, but the amount of chiral agent blended is usually 0.5 to 20 parts by mass, preferably 1 to 15 parts by mass, and more preferably 2 to 10 parts by mass when the total amount of the liquid crystal monomer, liquid crystal oligomer, and chiral agent in the curable composition used to form the cholesteric liquid crystal layer is taken as 100 parts by mass.

The curable composition used for forming the cholesteric liquid crystal layer is preferably one that is cured by irradiation with the above-mentioned ionizing radiation. When an electron beam is used as the ionizing radiation, the accelerating voltage can be appropriately selected depending on the material used and the thickness of the layer, but it is usually preferable to cure the composition at an accelerating voltage of about 70 to 300 kV.
When ultraviolet light is used as the ionizing radiation, it is usually emitted containing ultraviolet light having a wavelength of 190 to 380 nm. There are no particular limitations on the source of ultraviolet light, and examples of the source that can be used include high pressure mercury lamps, low pressure mercury lamps, metal halide lamps, carbon arc lamps, etc.

The curable composition used for forming the cholesteric liquid crystal layer preferably further contains a photopolymerization initiator, because this makes it possible to cure the liquid crystalline monomer or oligomer having a polymerizable group and the chiral agent having a polymerizable group in the curable composition by irradiation with ultraviolet light.
The photopolymerization initiator may be one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler's ketone, benzoin, benzyl dimethyl ketal, benzoyl benzoate, α-acyloxime ester, thioxanthones, and the like.
The photopolymerization initiators may be used alone or in combination of two or more.
The amount of the photopolymerization initiator in the curable composition is preferably 1 to 10 parts by mass, and more preferably 2 to 8 parts by mass, in terms of the amount of the photopolymerization initiator blended when the total amount of the liquid crystalline monomer, the liquid crystalline oligomer, and the chiral agent is taken as 100 parts by mass.

The curable composition used to form the cholesteric liquid crystal layer may further contain other components such as a photopolymerization accelerator, a lubricant, a plasticizer, a filler, an antistatic agent, an antiblocking agent, a crosslinking agent, a light stabilizer, an ultraviolet absorber, an antioxidant, a conductive agent, a refractive index adjuster, and a solvent, within the range that does not impair the effects of the present invention.

When the material constituting the cholesteric liquid crystal layer is a liquid crystalline polymer, specific examples thereof include a polymer having a mesogenic group exhibiting liquid crystallinity introduced into the main chain, the side chain, or the main chain and the side chain, and a polymeric cholesteric liquid crystal having a cholesteryl group introduced into the side chain, such as the liquid crystalline polymer disclosed in JP-A-9-133810 and the liquid crystalline polymer disclosed in JP-A-11-293252.
As the liquid crystal polymer, a cholesteric liquid crystal polymer having chiral ability in itself may be used, or a mixture of a nematic liquid crystal polymer and a cholesteric liquid crystal polymer may be used. Such a liquid crystal polymer changes its state depending on the temperature. For example, when the glass transition temperature is 90° C. and the isotropic transition temperature is 200° C., the polymer exhibits a cholesteric liquid crystal state between 90° C. and 200° C., and when the polymer is cooled to room temperature, the polymer can be solidified in a glass state while maintaining the cholesteric structure.

When the liquid crystal material that constitutes the cholesteric liquid crystal layer has a glass transition temperature, such as a liquid crystal polymer, it is possible to control the liquid crystal to be turned on and off by changing the temperature. By utilizing this property, the selective transmission filter of the present invention can be temporarily changed to a total transmission or total blocking filter as necessary. It can also be given a color change function depending on the temperature.

To adjust the selective reflection wavelength range of incident light due to the cholesteric structure of the liquid crystal polymer, the chiral power in the liquid crystal polymer molecule may be adjusted by a known method. In addition, when a mixture of a nematic liquid crystal polymer and a cholesteric liquid crystal polymer is used, the mixture ratio is adjusted.

In the present invention, the cholesteric liquid crystal layer may be a single-layer structure consisting of only one liquid crystal layer, or may be a multi-layer structure in which two or more liquid crystal layers are laminated. By using a structure in which two or more cholesteric liquid crystal layers having different helical pitches of liquid crystal molecules are laminated, it is possible to obtain a filter having multiple or wide selective reflection wavelength ranges.

When the cholesteric liquid crystal layer has a multi-layer structure, the number of layers is not particularly limited. From the viewpoints of productivity, light transmittance, and suppression of alignment disorder of liquid crystal molecules, the number of layers is preferably 2 to 6, and more preferably 2 to 4.
The thickness of the cholesteric liquid crystal layer varies in an optimal range depending on the type of liquid crystal monomer or oligomer, polymer, or chiral agent used, as well as the selective reflection wavelength range of the desired cholesteric liquid crystal layer, but from the viewpoint of increasing the reflectance of incident light, it is preferably 0.2 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. In addition, from the viewpoint of miniaturization and thinning of various members on which the selective transmission filter of the present invention is mounted, the thickness of the cholesteric liquid crystal layer is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 50 μm or less, even more preferably 30 μm or less, even more preferably 20 μm or less, and even more preferably 10 μm or less. The thickness of the cholesteric liquid crystal layer is the thickness of the entire liquid crystal layer, and when there are two or more liquid crystal layers, it is the total thickness.

The thickness of the cholesteric liquid crystal layer can be calculated, for example, by measuring the thickness at 10 points on a cross-sectional image taken with a scanning transmission electron microscope (STEM) and averaging the values at the 10 points. The acceleration voltage of the STEM is preferably 10 kV to 30 kV. The magnification of the STEM is preferably 1,000 to 7,000 times when the measured film thickness is on the order of microns, and is preferably 50,000 to 300,000 times when the measured film thickness is on the order of nanometers.

The method for forming the cholesteric liquid crystal layer is not particularly limited, and any known method can be used. Hereinafter, a case where the cholesteric liquid crystal layer is a cured product of an ionizing radiation curable composition containing the liquid crystalline monomer or oligomer will be described as an example.
First, an alignment film is formed on a glass substrate, and an ionizing radiation curable composition for forming a cholesteric liquid crystal layer, which contains a liquid crystalline monomer or oligomer, a chiral agent, and other components such as a photopolymerization initiator and a solvent, is applied thereon, and the liquid crystalline molecules (liquid crystalline monomer and oligomer) are aligned by the alignment control force of the alignment film. Next, the liquid crystalline monomer or oligomer is three-dimensionally crosslinked by irradiating the liquid crystalline monomer or oligomer in this aligned state, thereby obtaining a cholesteric liquid crystal layer, which is a cured product of the curable composition.
Examples of the method for applying the curable composition include various known methods such as spin coating, dipping, spraying, die coating, bar coating, roll coating, meniscus coating, flexographic printing, screen printing, and bead coating.
When the curable composition contains a solvent, after the curable composition is applied, it is preferable to dry the composition at, for example, 30 to 120° C. for 10 to 120 seconds.

The above-mentioned alignment film can be produced by a conventional method. For example, there are a method of forming a polyimide film on a glass substrate and rubbing it; a method of forming a polymer compound that will become a photoalignment film on a glass substrate and irradiating it with polarized UV (ultraviolet light); a method of using a stretched PET (polyethylene terephthalate) film; a method of patterning using a mask; and the like.

When the cholesteric liquid crystal layer is made of the liquid crystal polymer described above, an alignment film is formed on a glass substrate in the same manner as above, and a composition containing a liquid crystal polymer is applied onto the alignment film by the above method, and the polymer is aligned by the alignment control force of the alignment film. After drying as necessary, the liquid crystal polymer is fixed in a glassy state by cooling, thereby obtaining a cholesteric liquid crystal layer.

When the cholesteric liquid crystal layer has a multi-layer structure, the liquid crystal layers can be laminated in order in the same manner as described above. The liquid crystal layers may be laminated directly or via an optical adhesive layer or any other layer.
When a plurality of liquid crystal layers are laminated, it is preferable that the director directions of the liquid crystal molecules in adjacent cholesteric liquid crystal layers are approximately parallel to each other in order to reduce alignment disturbance.

In the present invention, it is also preferable that the cholesteric liquid crystal layer has reverse dispersion. By making the cholesteric liquid crystal layer reverse dispersion, the half-width of selective reflection can be made small. As a result, when a black image is displayed during front observation, the tendency for red reflected light to become stronger is suppressed, and a higher quality image can be obtained, which is preferable.
A cholesteric liquid crystal layer exhibiting reverse dispersion can be obtained by applying a liquid crystal material exhibiting reverse dispersion wavelength characteristics or a liquid crystal material having a cyclohexane structure.
Examples of liquid crystal materials exhibiting reverse dispersion include liquid crystal compounds described in JP-T-2010-522892, JP-A-2006-243470, JP-A-2007-243470, JP-A-2009-75494, JP-A-2009-62508, JP-A-2009-179563, JP-A-2009-242717, JP-A-2009-242718, Japanese Patent No. 4222360, and Japanese Patent No. 4186981.
In addition, examples of liquid crystal materials having a cyclohexane structure include those prepared by adding a polymerizable group such as an acrylate group to the molecular terminal of a liquid crystal material described in, for example, JP-A-2001-163833, JP-A-2007-91612, JP-A-2007-91796, JP-A-2006-241403, JP-A-2006-70080, JP-A-2006-37005, and JP-A-2006-8928, and materials described in JP-A-2008-274204 can be used.

(DBEF layer)
In the present invention, a DBEF layer may be used as the semi-transmissive semi-reflective film.
Examples of DBEF include multilayer optical film reflective polarizers, such as those described in US Pat. No. 5,882,774, and DBEF-D2-400 and DBEF-D4-400 available from 3M Company.

A DBEF layer transmits light having a single polarization state and reflects the remaining light: DBEF layers generally transmit p-waves (also called p-polarized light, polarized light whose electric field oscillates in the plane of incidence) and reflect s-waves (also called s-polarized light, polarized light whose electric field oscillates perpendicular to the plane of incidence).
Specifically, the DBEF layer is preferably 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 in such a multilayer laminate can be 50 to 1,000. The refractive index nx _A in the x-axis direction of the A layer is larger than the refractive index ny _A in the y-axis direction (nx _A >ny _A ), and the refractive index nx _B in the x-axis direction of the B layer and the refractive index ny _B in the y-axis direction are substantially the same (nx _B ≈ny _B ). Therefore, the refractive index difference 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 is the reflection axis, and the y-axis direction is the transmission axis. The refractive index difference between the A layer and the B layer in the x-axis direction is preferably 0.1 to 0.4, more preferably 0.2 to 0.3. The x-axis direction corresponds to the stretching direction of the DBEF layer in the manufacturing method of the DBEF layer. If the refractive index difference in the x-axis direction between the A layer and the B layer is large, the reflectance increases, and it is therefore possible to reduce the number of layers. On the other hand, in order to increase the refractive index difference, stronger stretching is required, which requires optimization of material selection and process, and furthermore, it is thought that the bowing phenomenon is likely to occur, which tends to reduce productivity.

The A layer is preferably made of a material that exhibits birefringence when stretched. Typical examples of such materials include naphthalene dicarboxylic acid polyesters (e.g., polyethylene naphthalate), polycarbonates, and acrylic resins (e.g., polymethyl methacrylate). Polyethylene naphthalate is preferred. The B layer is preferably made of a material that does not substantially exhibit birefringence even when stretched. Typical examples of such materials include copolyesters of naphthalene dicarboxylic acid and terephthalic acid.

The DBEF layer uses the slight difference in reflectivity between p-waves and s-waves at the interface between layers A and B by repeatedly utilizing the multi-layer structure, completely separating p-waves and s-waves, transmitting one and reflecting the other.

The total thickness of the DBEF layer can be appropriately set depending on the purpose, the total number of layers contained in the DBEF layer, etc. The total thickness of the reflective polarizer is preferably 10 μm to 150 μm.
In one embodiment, in the optical laminate, the DBEF layer is arranged so as to transmit light having a polarization direction parallel to the transmission axis of the polarizer. That is, the DBEF layer is arranged so that its transmission axis is approximately parallel to the transmission axis direction of the polarizer. With this configuration, light that would otherwise be absorbed by the polarizer can be reused.

The DBEF layer can be typically produced by combining coextrusion and transverse stretching. Coextrusion can be performed in any suitable manner. For example, it may be a feed block method or a multi-manifold method. For example, the material constituting the A layer and the material constituting the B layer are extruded in a feed block, and then multi-layered using a multiplier. Such multi-layering devices are known to those skilled in the art. The long multi-layer laminate obtained is then typically stretched in a direction perpendicular to the conveying direction (TD). The refractive index of the material constituting the A layer (e.g., polyethylene naphthalate) increases only in the stretching direction due to the transverse stretching, resulting in birefringence. The refractive index of the material constituting the B layer (e.g., a copolyester of naphthalene dicarboxylic acid and terephthalic acid) does not increase in either direction due to the transverse stretching. As a result, a reflective polarizer having a reflection axis in the stretching direction (TD) and a transmission axis in the conveying direction (MD) can be obtained. The stretching operation can be performed using any suitable device.

As described above, the selective reflection central wavelength range of the DBEF layer is preferably 480 nm or less, more preferably 460 nm or less, and even more preferably 440 nm or less, and is preferably 380 nm or more, more preferably 400 nm or more, and even more preferably 415 nm or more, when measured at an incident angle of 5°. By setting the selective reflection central wavelength within the above range, the luminance of light in the blue region is improved when viewed from the front, and when viewed from an oblique angle, the reflected light is shifted to a shorter wavelength and absorbed by the absorbing compound, thereby suppressing the increase in luminance in the blue region and suppressing the blue shift, which is preferable.
In addition, a high reflectance of the DBEF layer is preferable because it increases the amount of light emitted when the optical laminate of the present invention is observed from the front direction.

<Protective Layer>
The optical laminate of the present invention preferably has a protective layer laminated directly or indirectly on the surface of the polarizer opposite to the surface on which the retardation plate is provided.
In the present invention, the antireflection layer described later may be used as the protective layer, and when a protective layer is laminated separately from the antireflection layer, it is preferable to use a cellulose ester film having high optical isotropy as the protective layer. In addition, the protective layer may have a functional layer such as a hard coat layer or an antiglare layer.
The protective layer is not limited to this, and may be provided on the surface of the polarizer on which the retardation plate is provided, or on the surface of the retardation plate opposite to the surface on which the polarizer is provided, and is not particularly limited.

-Anti-reflection layer-
The optical laminate or display panel of the present invention may have an antireflection layer as a protective layer.
In the simplest configuration, the antireflection layer is a configuration in which only a low refractive index layer is coated on the outermost surface of the film. In order to further reduce the surface reflectance, it is preferable to combine a high refractive index layer with a low refractive index layer to form the antireflection layer. Examples of the configuration include a two-layer structure of a high refractive index layer/low refractive index layer, and a structure in which three layers with different refractive indices are laminated in the order of a medium refractive index layer (a layer with a higher refractive index than the lower layer and a lower refractive index than the high refractive index layer)/high refractive index layer/low refractive index layer from the bottom side, and a structure in which more antireflection layers are laminated has also been proposed. Among them, from the viewpoints of durability, optical properties, cost, productivity, etc., it is preferable to have a medium refractive index layer/high refractive index layer/low refractive index layer on the hard coat layer in that order, and examples of the configurations described in JP-A-8-122504, JP-A-8-110401, JP-A-10-300902, JP-A-2002-243906, JP-A-2000-111706, etc. can be mentioned. In addition, a three-layer antireflection film having excellent robustness against film thickness fluctuation is described in JP 2008-262187 A. When the above three-layer antireflection film is installed on the surface of an image display device, the average surface reflectance can be set to 0.5% or less, and reflection can be significantly reduced, resulting in an image with excellent three-dimensional effect. In addition, each layer may be given other functions, such as an antifouling low refractive index layer, an antistatic high refractive index layer, an antistatic hard coat layer, and an antiglare hard coat layer (e.g., JP 10-206603 A, JP 2002-243906 A, JP 2007-264113 A, etc.).
The refractive index of the low refractive index layer is preferably 1.26 to 1.40, more preferably 1.28 to 1.38, and even more preferably 1.30 to 1.32. The thickness of the low refractive index layer is preferably 80 to 120 nm, more preferably 85 to 110 nm, and even more preferably 90 to 105 nm.
The refractive index of the high refractive index layer is preferably 1.55 to 1.85, more preferably 1.56 to 1.70, and the thickness of the high refractive index layer is preferably 200 nm or less, more preferably 50 to 180 nm.

<Adhesive layer>
The optical laminate of the present invention preferably further has an adhesive layer in addition to the above-mentioned retardation plate, polarizer, and protective layer. The adhesive layer may be provided on the surface opposite to the surface on which the polarizer of the retardation plate is provided, may be provided between the retardation plate and the polarizer, may be provided between the polarizer and the protective layer, and may be provided between the protective layers when a plurality of protective layers are provided, and is not particularly limited.
The adhesive layer may be appropriately selected from adhesives that can be applied to this type of optical laminate, and may be formed, for example, from a PSA (pressure sensitive adhesive) adhesive. More specifically, a layer formed from an acrylic adhesive may be exemplified.

<Absorption Compound>
The optical layered body of the present invention contains a compound having absorption at 480 nm or less (also referred to as an "absorbing compound" or "absorber").
The absorbing compound may be contained in any layer of the optical laminate, but it is preferable that the above-mentioned adhesive layer or protective layer (including the hard coat layer) contains the absorbing compound. The retardation plate may also contain the absorbing compound, for example, an embodiment in which the retardation plate further has a positive C plate having positive C characteristics, and the positive C plate contains an absorbing compound is exemplified. Furthermore, the semi-transmitting semi-reflective film may contain an absorbing compound. In this way, when layers such as the adhesive layer, protective layer, positive C plate, and semi-transmitting semi-reflective film contain an absorbing compound, it is preferable because the layer structure is simplified. Note that the present invention is not limited to this, and a layer containing an absorbing compound may be provided separately. In addition, it is preferable that the absorbing compound is contained in a layer other than the outermost surface from the viewpoint of suppressing the color tone during black display. Note that the semi-transmitting semi-reflective film or the retardation layer may contain an absorbing compound, and the alignment film layer to be transferred may contain an absorbing compound. In addition, the absorbing compound may be contained on the display element side of the semi-transmitting semi-reflective film, and is not particularly limited.
From the viewpoint of suppressing reflection of external light, it is preferable that an absorbing compound is present in either the semi-transmitting semi-reflective film or the layer on the opposite side of the semi-transmitting semi-reflective film from the viewing side (the side where the display element is provided). Also, from the viewpoint of improving brightness, it is preferable that an absorbing compound is present in either layer on the viewing side of the semi-transmitting semi-reflective film. In this case, it is preferable that the protective layer or the adhesive layer contains an absorbing compound.
The term "compound having absorption at 480 nm or less" means a compound that, when contained, results in a light transmittance of 10% or less at any wavelength of 480 nm or less.
The maximum absorption wavelength of the absorbing compound is preferably 300 nm or more and 500 nm or less, more preferably 350 nm or more and 450 nm or less, even more preferably 370 nm or more and 440 nm or less, and even more preferably 380 nm or more and 430 nm or less. The maximum absorption wavelength means the wavelength at which the transmittance is the smallest or the wavelength at which the transmittance is 3% or less.

The absorbing compound is not particularly limited as long as it has absorption at a wavelength of 480 nm or less, but it is preferable that the absorbing compound has low absorption in the wavelength region of 500 nm to 780 nm. If the absorption in the wavelength region of 500 nm to 780 nm is large, the color may change when an image is displayed, or a sufficient amount of light may not be obtained.
When the light transmittance in the region of 500 nm or more and 780 nm or less of an optical laminate not containing an absorbing compound is taken as 100%, the light transmittance in the region of 500 nm or more and 780 nm or less of an optical laminate containing the absorbing compound is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and still more preferably 95% or more.
That is, the absorbing compound is preferably a compound that has absorption in the wavelength region of 480 nm or less and has weak absorption of light in the wavelength region of 500 nm or more and 780 nm or less, or has no absorption in the above wavelength region.

The absorbing compound is not particularly limited as long as it has the above-mentioned properties, but specific examples include triazine-based UV absorbers, benzotriazole-based UV absorbers, benzophenone-based UV absorbers, oxybenzophenone-based UV absorbers, salicylic acid ester-based UV absorbers, and cyanoacrylate-based UV absorbers, and these can be used alone or in combination of two or more.

Alternatively, instead of or in addition to the ultraviolet absorbers, a compound having a maximum absorption wavelength in the absorption spectrum of 300 nm to 480 nm may be used. The maximum absorption wavelength of the compound is preferably 350 nm to 450 nm, and more preferably 380 nm to 430 nm.
The structure of the compound is not particularly limited. Examples of the dye compound include organic dye compounds and inorganic dye compounds. Among these, organic dye compounds are preferred from the viewpoints of dispersibility in resin components such as base polymers and maintaining transparency.

Examples of the organic dye compound include azomethine compounds, indole compounds, cinnamic acid compounds, pyrimidine compounds, and porphyrin compounds.
As the organic dye compound, commercially available products can be suitably used. Specific examples of the indole-based compounds include BONASORB UA3911 (trade name, maximum absorption wavelength in absorption spectrum: 398 nm, manufactured by Orient Chemical Industry Co., Ltd.) and BONASORB UA3912 (trade name, maximum absorption wavelength in absorption spectrum: 386 nm, manufactured by Orient Chemical Industry Co., Ltd.), examples of the cinnamic acid-based compounds include SOM-5-0106 (trade name, maximum absorption wavelength in absorption spectrum: 416 nm, manufactured by Orient Chemical Industry Co., Ltd.), and examples of the pyrimidine-based compounds include FDB-009 (trade name, maximum absorption wavelength in absorption spectrum: 394 nm, manufactured by Yamada Chemical Industry Co., Ltd.).

The content of the absorbing compound is not particularly limited and may be appropriately selected.
The absorbing compounds may be used alone or in combination of two or more.

[Display Panel and Display Device]
The display panel of the present invention is not particularly limited as long as it comprises the above-mentioned optical laminate of the present invention and a display element, but is particularly effective for display panels with high electrode reflectance, and is preferably one comprising an organic electroluminescence display element (hereinafter, "organic EL display element") or a micro light-emitting diode display element (hereinafter, "micro LED display element"), and more preferably one comprising an organic electroluminescence display element.
The display panel of the present invention preferably includes the optical laminate of the present invention on the light-emitting surface of the display element. By including the optical laminate of the present invention, it is possible to provide a display device in which the luminance of blue light can be improved and blue shift when observed from an oblique direction is suppressed.

In the present invention, it is preferable that the display element has a microcavity structure. When the display element has a microcavity structure, a display device including the display element has a significant problem of blue-shifting the image, particularly when the viewing angle is large, i.e., when viewed from an oblique direction, because the resonant wavelength shifts to the short wavelength side.

In the present invention, the difference between the blue emission peak wavelength of the display element and the reflection peak wavelength of the optical laminate is preferably 20 nm or less. The reflection peak wavelength of the optical laminate is the peak wavelength of the wavelength that shows the brightness improvement effect by providing the optical laminate for the incident light from the display element side at 5°. The difference between the blue emission peak wavelength of the display element and the reflection peak wavelength of the optical laminate is more preferably 15 nm or less, and further preferably 10 nm or less.
When the difference between the blue emission peak wavelength of the display element and the reflection peak wavelength of the optical laminate is 20 nm or less, the change in color is small when observed from the front, and the desired color can be easily obtained. In addition, when observed obliquely, blue shift is suppressed, which is preferable.

The display device of the present invention is not particularly limited as long as it comprises the display panel of the present invention, but it is preferable that the display device comprises the display panel of the present invention, a drive control unit electrically connected to the display panel, and a housing that accommodates these.
In the present invention, the display device is preferably an organic electroluminescence display device (hereinafter also referred to as an "organic EL display device"). The display of the present invention is not limited thereto, and may be a micro LED display device. Organic EL display devices and micro LED display devices have high electrode reflectance, and therefore are particularly susceptible to the problems of the present invention, and the present invention is particularly suitable for these display devices. Among these, the display device is preferably an organic electroluminescence display device.
The organic EL display device is a display device in which a light-emitting layer or a plurality of organic compound thin films including a light-emitting layer are formed between a pair of electrodes, an anode and a cathode, and the display panel of the present invention is provided on the viewing side of the organic EL display device. The organic compound thin film may have a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, a protective layer, etc. in addition to the light-emitting layer, and each of these layers may have other functions. Each layer, such as the electrodes and the organic compound thin film, of the organic EL display device can be formed using known materials and methods.

The display panel and display device of the present invention are not particularly limited, but are preferably a display panel and display device that are used in a state where the viewing angle is large. Specific examples include portable information terminals, large display devices, signage, etc.
When used in a large display panel or display device, the viewing angle tends to become larger and changes in hue due to reflected light become more problematic, so a display device of 55 inches or more, or a display panel used in a display device of 55 inches or more is preferred. The size of the display device is more preferably 65 inches or more, and even more preferably 70 inches or more. The display panel is more preferably a display panel for a display device of 65 inches or more, and even more preferably a display panel for a display device of 70 inches or more.
The display panel and display device of the present invention are not particularly limited, but are preferably a display panel and display device that are used in a state where the viewing angle is large. Specific examples include portable information terminals, large display devices, signage, etc.

[Retardation Plate, Polarizer, and Semi-Transmissive Semi-Reflective Film]
The retardation plate, polarizer, and semi-transmitting/semi-reflective film are the retardation plate, polarizer, and semi-transmitting/semi-reflective film used in the display panel of the present invention.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

A sample having a layer structure shown in the following Figure 3 was prepared. Figure 3 is a cross-sectional view showing the sample prepared for reflectance measurement.
The layers and compounds used in the examples are as follows.
・λ/4 plate (reverse dispersion (Re450/Re550=0.85), 142 nm)
A liquid crystal material with Re450/Re550=0.85 was diluted with a solvent (toluene/cyclopentanone=7/3) to a solid content of 20%, and the diluted material was applied onto a PET substrate to prepare a retardation plate. The coating thickness was adjusted to obtain the above retardation value. The retardation plate was transferred from the PET substrate. The retardation was measured using a KOBRA-WR manufactured by Oji Measurement Co., Ltd.
TAC: TD60UL, manufactured by Fujifilm Corporation
Polarizer: iodine-doped stretched PVA
Hard coat layer: The following absorbent A was added as an absorbing compound to PET-30 manufactured by Nippon Kayaku Co., Ltd. so that the content in the hard coat layer was 5% by mass, and 3% Irgacure 907 was added. The resultant was adjusted to a thickness of 4 μm and cured with ultraviolet light to form a hard coat layer (refractive index = 1.53).
Adhesive layer: 10 μm thick optical adhesive manufactured by Lintec Corporation Absorbing compound A: BONASORB UA-3911 manufactured by Orient Chemical Co., Ltd.
CLC layer: 93.25 parts by mass of polymerizable liquid crystal monomer, 6.85 parts by mass of chiral agent having acryloyl at both ends (Palicolor (registered trademark) LC756, manufactured by BASF), 4 parts by mass of photopolymerization initiator (IRGACURE (registered trademark) 907; 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one), 0.1 parts by mass of acrylic leveling agent (BYK-361N, manufactured by BYK Japan Co., Ltd.) were diluted with cyclopentanone to a solid content of 20% and applied onto a PET film to prepare a film having a liquid crystal layer (thickness 3.0 μm) having a cholesteric structure. The CLC layer was transferred from the PET substrate and used.

In the experimental and comparative examples, the angle between the absorption axis of the polarizer and the alignment axis of the reverse dispersion λ/4 retardation plate was set to 45°.

[Reflectance and transmittance measurements]
An optical stack was prepared as shown in Figure 3, where the absorbing compound is contained in a hardcoat layer located below the CLC layer.
FIG. 4 shows the transmittance measured only for the hard coat layer containing the absorbing compound (absorbent A in FIG. 4), the reflectance of the semi-transmissive semi-reflective film (CLC layer) alone at an incident angle of 5° (CLC in FIG. 4), and the reflectance of the laminate shown in FIG. 3 at an incident angle of 5° with the CLC layer as the light incident surface (CLC+absorbent A in FIG. 4).
In FIG. 4, absorbent A is the transmittance of the hard coat layer containing an absorbing compound, and the wavelength at which the transmittance is 50% is 424 nm.
4, CLC indicates the reflectance of the semi-transmissive semi-reflective film alone at an incident angle of 5°, the peak wavelength of the reflectance is 431 nm, the reflectance at the peak top is 35.3%, and the half width at this time is 73 nm.
Furthermore, in Fig. 4, CLC + absorbent A indicates the reflectance at an incident angle of 5° of the laminate shown in Fig. 3, and the hard coat layer below the CLC layer contains absorbent A as an absorbing compound. In this case, the peak wavelength of the reflectance was 444 nm, the reflectance at the peak top was 30.3%, and the half-value width at this time was 43 nm.

<Reflectance measurement>
The reflectance was measured by the following method.
The reflectance in the visible region (380 nm to 780 nm) was measured using a V-7100 (automatic absolute reflectance measurement unit: VAR-7010) manufactured by JASCO Corp. The reflectance of light incident from the hard coat layer side of the sample shown in FIG. 3 was measured.

FIG. 5 shows the results of measuring the reflectance of the optical laminate shown in FIG. 3 for incident light at angles of 5°, 25°, and 45°.
In FIG. 5 , the average reflectance (A) for light incident at 5° in the range of 400 nm to 480 nm was 18.4%, the average reflectance (B) for light reflected at 45° in the range of 400 nm to 480 nm was 9.8%, and B/A was 0.53.
The peak top at 5° was 30.3% (444 nm), the peak top at 25° was 26.7 (439 nm), and the peak top at 45° (the peak top on the shortest wavelength side in the range of 400 to 480 nm) was 14.2 (433 nm).
The half width at 5° was 43 nm, and the half width at 25° was 32 nm.

In the optical laminate of the present invention, when the semi-transmitting semi-reflective film or any layer closer to the display element than the semi-transmitting semi-reflective film contains an absorbing compound, it is preferable that B/A is 0.8 or less, where A is the average reflectance of the optical laminate at a wavelength of 400 nm or more and 480 nm or less at an incident angle of 5° for light incident from the display element side, and B is the average reflectance of the optical laminate at a wavelength of 400 nm or more and 480 nm or less at an incident angle of 45°. When the B/A is 0.8 or less, the blue shift of the image is further suppressed when observed from an oblique direction, which is preferable.
The above B/A is preferably 0.75 or less, more preferably 0.70 or less, even more preferably 0.60 or less, and still more preferably 0.50 or less.
The lower limit of the above B/A is not particularly limited, but from the viewpoint of suppressing coloring of the optical laminate itself in the absence of incident light and from the viewpoint of color reproducibility of the display image of a display panel and a display device equipped with the optical laminate, it is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more.

[Evaluation of luminance in image display device (image evaluation)]
An organic EL display device was produced by using the prepared optical laminate in place of a circular polarizing plate and each layer provided on the viewing side of the circular polarizing plate of an organic EL display panel having a display element with a microcavity structure.
As a comparative example, an optical laminate was used that did not have a CLC layer and did not contain an absorbing compound.
The obtained organic EL display device was observed at angles of 0° (front), 20°, and 40° when displaying a white image. The maximum luminance at 0° in the comparative example was taken as 1.0, and the values were expressed as relative values (see FIGS. 6 to 8). The luminance was measured at a measurement angle of 2° and a measurement distance of 50 cm using a spectroradiometer SR-2 manufactured by TOPCON Corporation. Here, as a comparative example, an optical laminate was produced by omitting the CLC layer and hard coat layer in FIG. 3 and using a layer not containing an absorbing compound as the hard coat layer.
As a result, in the comparative example, the ratio of blue luminance to red luminance at an angle (20° and 40°) [oblique blue luminance/oblique red luminance] was greater than the ratio of blue luminance to red luminance from the front [front blue luminance/front red luminance], and the white image appeared bluish when viewed at an angle compared to when viewed from the front.
On the other hand, in the examples, the ratio of blue luminance to red luminance from the front [blue luminance from the front/red luminance from the front] was similar to the relative luminance of blue luminance to red luminance from oblique angles (20° and 40°) [oblique blue luminance/oblique red luminance], so that the white image was less likely to be observed as bluish when viewed obliquely compared to when viewed from the front. Furthermore, in the examples, an improvement in blue luminance was observed when viewed from the front. Also, the improvement in blue luminance from the front was not so extreme as to have a significant effect on visibility.
Therefore, in the embodiment, if the luminance of blue from the front is suppressed by panel design, it is believed that the life of blue will be extended, and as a result, the life of the organic EL display device will be extended. The luminance of blue can be adjusted by lowering the voltage. Furthermore, if the luminance of blue is adjusted in this way, the same color as that of a conventional display device will be achieved when observed from the front, and further, when observed from an oblique angle, the luminance of blue will be further reduced, and the blue shift will be further suppressed.

The optical laminate of the present invention can provide a display panel and a display device that improves the blue emission luminance when observed from the front and suppresses the blue shift of the image even when observed from an oblique direction.

10, 20 Optical laminate 12 CLC layer 14, 24 Retardation plate 16, 26 Polarizer 18 Circular polarizer 22 DBEF layer

Claims (15)

A display panel including an optical laminate having a semi-transmissive semi-reflective film, a retardation film, and a polarizer on a light exit surface of a display element,
the retarder includes a λ/4 retarder,
The optical laminate contains a compound having absorption at 480 nm or less,
the semi-transmitting semi-reflective film has a selective reflection wavelength in the range of 380 nm to 480 nm;
The present invention has the following configuration 1 or 2:
A display panel, wherein X nm is the half-width of the peak reflectance of the optical laminate at 400 to 480 nm measured from the front (angle of 5°) and Y nm is the half-width of the peak reflectance of the optical laminate at 400 to 480 nm measured from an oblique angle of 25°, and X-Y is 5 nm or more (the half-width is calculated as a width at which the reflectance becomes {b+(a-b)×0.5}% from the reflectance of the peak top at 400 to 480 nm (a%), with the average reflectance of the wavelength of 500 nm or more and 580 nm or less being the base reflectance (b%)).
[Configuration 1]
The semi-transmitting semi-reflective film is a liquid crystal layer having a cholesteric structure, the retardation plate and the polarizer constitute a circular polarizing plate, the semi-transmitting semi-reflective film, the retardation plate and the polarizer are arranged in this order, and the semi-transmitting semi-reflective film contains a compound having absorption at 480 nm or less.
[Configuration 2]
The semi-transmitting semi-reflective film is a reflective polarizing layer that transmits only one of light rays having p waves or s waves and reflects the other, the retardation plate and the polarizer constitute a circular polarizing plate, the retardation plate, the semi-transmitting semi-reflective film, and the polarizer are arranged in this order, and the retardation plate or the semi-transmitting semi-reflective film contains a compound having absorption at 480 nm or less. The display panel according to claim 1, having the configuration 1. The display panel according to claim 2, in which, for light incident from the liquid crystal layer side having a cholesteric structure, the liquid crystal layer having the cholesteric structure reflects right-handed circularly polarized light and the circular polarizer transmits left-handed circularly polarized light, or the liquid crystal layer having the cholesteric structure reflects left-handed circularly polarized light and the circular polarizer transmits right-handed circularly polarized light. The display panel according to claim 2 or 3, wherein the reflection wavelength peak of the optical laminate is located on the longer wavelength side with respect to the selective reflection center wavelength of the liquid crystal layer having the cholesteric structure. The display panel according to any one of claims 2 to 4, wherein the half-width of the reflection peak of the optical laminate is smaller than the half-width of the reflection peak of the liquid crystal layer having the cholesteric structure alone. The display panel according to any one of claims 1 to 5, wherein the optical laminate further comprises a protective layer. The display panel according to any one of claims 1 to 6, wherein the optical laminate further comprises an adhesive layer. The display panel according to any one of claims 1 to 7, wherein the retardation plate is a quarter-wave retardation plate with reverse dispersion. The display panel according to any one of claims 1 to 7, wherein the retardation plate is a laminate of a quarter-wave retardation plate and a half-wave retardation plate. The display panel according to claim 8 or 9, wherein the retardation plate further comprises a positive C plate. The display panel according to any one of claims 1 to 10, wherein the compound having absorption at 480 nm or less has a maximum absorption wavelength of 380 nm or more and 500 nm or less. A display panel according to any one of claims 1 to 11, wherein the display element has a microcavity structure. The display panel according to any one of claims 1 to 12, wherein the difference between the blue emission peak wavelength of the display element and the reflection peak wavelength of the optical laminate is 20 nm or less. A display device comprising a display panel according to any one of claims 1 to 13. The display device according to claim 14, wherein the display device is an organic electroluminescence display device.