JP7647057B2 - Optical laminate and liquid crystal display device using the same - Google Patents

Description

The present invention relates to an optical laminate and a liquid crystal display device using the same.

Electroluminescent display elements (hereinafter sometimes abbreviated as EL elements) have a wide viewing zone due to their self-luminous nature, and consume less power than plasma light-emitting elements, and so in recent years they have been put to practical use in image display devices. In particular, organic EL elements, which use organic compounds as light-emitting materials, can reduce the applied voltage significantly more than inorganic EL elements, which use inorganic compounds, and so their use as display devices has been widely considered.

Organic EL elements are generally known to have a structure in which a first electrode, a light-emitting layer, and a second electrode are sequentially laminated on a transparent substrate. There are two types of organic EL elements: a bottom-emission type in which a transparent electrode is used as the first electrode and a metal electrode is used as the second electrode, and light emitted from the light-emitting layer is extracted from the transparent substrate side; and a top-emission type in which a metal electrode is used as the first electrode, a transparent electrode is used as the second electrode, and light emitted from the light-emitting layer is extracted from the second electrode side.
In organic EL elements, regardless of the type, metal electrodes with excellent reflectivity are often used to efficiently utilize the light from the light-emitting layer. On the other hand, organic EL elements using such metal electrodes may have a large amount of external light reflection, resulting in a decrease in contrast. In addition, the decrease in contrast due to external light reflection is also a problem in display devices other than those including organic EL elements (for example, display devices including micro LED display elements, and display devices having a resistive touch panel arranged on a display element).

Various methods for suppressing external light reflection in display devices have been investigated. One such method is known to use a so-called circular polarizer, which is made by laminating a retardation plate and a polarizer.

However, general-purpose retardation plates have a wavelength dependency of retardation (positive dispersion of retardation) such that the retardation measured at a long wavelength is smaller than the retardation measured at a short wavelength. For this reason, a circular polarizing plate using a general-purpose retardation plate can sufficiently reduce the reflectance near a wavelength of 550 nm, but does not sufficiently reduce the reflectance in the low and high wavelength ranges, resulting in the problem of leakage of reflected light.

As a method for solving the above problem, for example, a method using a retardation plate formed by laminating a λ/4 retardation layer and a λ/2 retardation layer, and a method using a retardation plate using a liquid crystal compound with reverse dispersion characteristics have been proposed (Patent Document 1, etc.). Reverse dispersion characteristics are the wavelength dependence of the retardation, in which the retardation measured at a long wavelength is larger than the retardation measured at a short wavelength.

Circular polarizers using retardation films such as those in Patent Document 1 can sufficiently reduce the reflectance in the front direction. However, circular polarizers using retardation films such as those in Patent Document 1 do not sufficiently reduce the reflectance in oblique directions relative to the front direction.

Japanese Patent Application Publication No. 5-100114 JP 2007-188033 A

Patent Document 2 discloses an elliptical polarizing plate having a positive C layer in addition to a λ/4 retardation layer and a λ/2 retardation layer.
The elliptically polarizing plate of Patent Document 2 can bring the reflectance in an oblique direction closer to the reflectance in a front direction. However, the elliptically polarizing plate of Patent Document 2 has a strong color when viewed from an oblique direction.
The problem of color tone in oblique directions is also a problem that Japanese Patent Application Laid-Open No. 2003-233663 has.

The present invention aims to provide an optical laminate that suppresses reflection of external light and suppresses color when viewed from an oblique angle, and an image display device using the same.

That is, the present invention provides the following [1] to [10].
[1] An optical laminate comprising a λ/4 retardation layer, a transparent substrate, and a polarizer in this order, wherein the transparent substrate has positive birefringence or negative birefringence, and has a thickness direction retardation of 125 nm or more or −125 nm or less, and the slow axis of the transparent substrate and the absorption axis of the polarizer are disposed approximately parallel or approximately perpendicular to each other.
[2] The optical laminate according to [1], wherein the transparent substrate has an in-plane retardation of 40 nm or more.
[3] The optical laminate according to [1] or [2], wherein the transparent substrate is a polyester film or a polycarbonate film.
[4] The optical laminate according to any one of [1] to [3], further comprising a λ/2 retardation layer between the λ/4 retardation layer and the transparent substrate.
[5] The optical laminate according to any one of [1] to [4], having a total light transmittance of 35% or more and 80% or less.

[6] The optical laminate according to any one of [1] to [5], wherein 3σΔX and 3σΔY calculated from the following measurement 1 are both less than 0.019.
<Measurement 1>
A sample is prepared by laminating the optical laminate on an aluminum plate having an average spectral reflectance of 20% in the wavelength region of 380 nm to 780 nm, and the optical laminate is arranged such that the surface of the optical laminate on the λ/4 retardation layer side relative to the transparent substrate faces the aluminum plate.
Light diffused by an integrating sphere is incident on the surface of the sample from the normal direction, and the reflected light is measured. The X and Y values of the XYZ color system are calculated from the measured reflected light. The measurement and calculation are performed in 0.5 degree increments in the azimuth angle range of 0 degrees to 359.5 degrees with the elevation angle fixed at an angle of 60 degrees from the normal to the surface of the sample, to obtain X and Y values at 720 points.
The average value of the X values at 720 points is defined as "Xave." The deviation of the X value at the nth measurement point from Xave is defined as "ΔXn." The variation 3σ of ΔXn at 720 points is defined as "3σΔX."
The average value of the Y values of the 720 points is defined as "Yave." The deviation of the Y value of the nth measurement point from Yave is defined as "ΔYn." The variation 3σ of ΔYn of the 720 points is defined as "3σΔY."
[7] The optical laminate according to any one of [1] to [6], wherein the average of 3σΔX and 3σΔY calculated from the following measurement 1 is less than 0.018.
<Measurement 1>
A sample is prepared by laminating the optical laminate on an aluminum plate having an average spectral reflectance of 20% in the wavelength region of 380 nm to 780 nm, and the optical laminate is arranged such that the surface of the optical laminate on the λ/4 retardation layer side relative to the transparent substrate faces the aluminum plate.
Light diffused by an integrating sphere is incident on the surface of the sample from the normal direction, and the reflected light is measured. The X and Y values of the XYZ color system are calculated from the measured reflected light. The measurement and calculation are performed in 0.5 degree increments in the azimuth angle range of 0 degrees to 359.5 degrees with the elevation angle fixed at an angle of 60 degrees from the normal to the surface of the sample, to obtain X and Y values at 720 points.
The average value of the X values at 720 points is defined as "Xave." The deviation of the X value at the nth measurement point from Xave is defined as "ΔXn." The variation 3σ of ΔXn at 720 points is defined as "3σΔX."
The average value of the Y values of the 720 points is defined as "Yave." The deviation of the Y value of the nth measurement point from Yave is defined as "ΔYn." The variation 3σ of ΔYn of the 720 points is defined as "3σΔY."
[8] The optical laminate according to any one of [1] to [7], which is used for the front surface of an organic EL display element.

[9] An image display device having an optical laminate on a display element, the optical laminate being the optical laminate according to any one of [1] to [7], and the optical laminate being arranged so that a surface on the λ/4 retardation layer side with respect to a transparent substrate of the optical laminate faces the display element.
[10] The image display device according to [9], wherein the display element is an organic EL display element or a micro LED display element.

The optical laminate and liquid crystal display device of the present invention can suppress reflection of external light and suppress color when viewed from an oblique angle.

1 is a schematic cross-sectional view showing one embodiment of an optical laminate of the present invention. FIG. 2 is a schematic cross-sectional view showing another embodiment of the optical laminate of the present invention.

Hereinafter, an embodiment of the present invention will be described.
[Optical laminate]
The optical laminate of the present invention comprises a λ/4 retardation layer, a transparent substrate, and a polarizer in this order, the transparent substrate has positive birefringence or negative birefringence, and has a thickness direction retardation of 125 nm or more or −125 nm or less, and the slow axis of the transparent substrate and the absorption axis of the polarizer are disposed approximately parallel or approximately perpendicular to each other.

Figures 1 and 2 are schematic cross-sectional views showing an embodiment of the optical laminate (100) of the present invention. The optical laminate (100) of Figures 1 and 2 comprises a λ/4 retardation layer (10), a transparent substrate (30), and a polarizer (40) in this order. The optical laminate (100) of Figure 2 also has a λ/2 retardation layer (20) between the λ/4 retardation layer (10) and the transparent substrate (30), and a surface protective material (50) on the side of the polarizer (40) opposite the transparent substrate (30).

The principle of how the optical laminate of the present invention suppresses reflection of external light will be briefly explained with reference to FIG.
When external light is incident on the polarizer (40) side of the optical laminate (100) in FIG. 1, the external light passing through the polarizer (40) becomes linearly polarized light. The linearly polarized light passes through the λ/4 retardation layer (10) and becomes right-handed or left-handed circularly polarized light. The circularly polarized light reflected on the surface of the display element becomes reverse-handed circularly polarized light. When the reverse-handed circularly polarized light, which is the reflected light, passes through the λ/4 retardation layer (10) again, it becomes linearly polarized light in a direction that does not pass through the polarizer (40), and reflection is suppressed.
In the optical laminate (100) of FIG. 2, the λ/4 retardation layer (10) and the λ/2 retardation layer (20) can convert a wide wavelength range into circularly polarized light, thereby further suppressing reflection of external light.
As described above, the optical layered body of the present invention can suppress reflection of external light.
In order to suppress reflection of external light based on the above principle, the slow axis of the transparent substrate (30) and the absorption axis of the polarizer (40) must be arranged substantially parallel or perpendicular to each other. If the slow axis of the transparent substrate (30) and the absorption axis of the polarizer (40) are not arranged substantially parallel or perpendicular to each other, the polarization state of linearly polarized light is disturbed when it passes through the transparent substrate (30).
When the direction of the slow axis is not uniform within the plane of the transparent substrate, the direction of the slow axis of the transparent substrate means the average direction of the slow axis within the plane of the transparent substrate.

In this specification, "approximately parallel" means within 0 degrees ±5 degrees, preferably within 0 degrees ±3 degrees, and more preferably within 0 degrees ±1 degree.
In this specification, "approximately perpendicular" means within 90 degrees ±5 degrees, preferably within 90 degrees ±3 degrees, and more preferably within 90 degrees ±1 degree.

In this specification, the in-plane retardation (Re) and the retardation 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 (nm).
In-plane phase difference (Re) = (nx-ny) x d
Retardation in the thickness direction (Rth) = ((nx + ny) / 2 - nz) x d

In this specification, the in-plane retardation (Re) and the retardation in the thickness direction (Rth) refer to values at a wavelength of 550 nm, unless otherwise specified.
In this specification, the in-plane retardation at a wavelength of X nm may be expressed as "Re(X)" and the retardation in the thickness direction at a wavelength of X nm may be expressed as "Rth(X)". For example, the in-plane retardation at a wavelength of 450 nm may be expressed as "Re(450)" and the in-plane retardation at a wavelength of 650 nm may be expressed as "Re(650)".

The in-plane retardation (Re) and the retardation in the thickness direction (Rth) can be measured using, for example, a product name "RETS-100" manufactured by Otsuka Electronics Co., Ltd., or a product name "KOBRA-WR", "KOBRA-WPR", or "PAM-UHR100" manufactured by Oji Scientific Instruments Co., Ltd.
When measuring the in-plane retardation (Re) and the like using a product name "RETS-100" manufactured by Otsuka Electronics Co., Ltd., it is preferable to prepare for the measurement in accordance with the following procedures (A1) to (A4).

(A1) First, in order to stabilize the light source of the RETS-100, leave it for 60 minutes or more after turning on the light source. After that, select the rotating analyzer method and select the θ mode (a mode for measuring the phase difference in the angular direction and calculating Rth). By selecting this θ mode, the stage becomes a tilting rotating stage.
(A2) Next, the following measurement conditions are input into the RETS-100.
(Measurement conditions)
・Retardation measurement range: Rotating analyzer method ・Measurement spot diameter: φ5mm
Tilt angle range: 0°
Measurement wavelength range: 400 nm to 800 nm Average refractive index of the transparent substrate. For example, in the case of a PET film, N=1.617. The average refractive index N of the transparent substrate can be calculated based on nx, ny, and nz by the formula (N=(nx+ny+nz)/3).
Thickness: Thickness measured separately by SEM or optical microscope (A3). Then, without placing a sample in the device, background data is obtained. The device is a closed system, and this is performed every time the light source is turned on.
(A4) After that, the sample is placed on the stage inside the device and measured.

In this specification, various parameters such as in-plane retardation (Re), thickness direction retardation (Rth), total light transmittance, and spectral reflectance are calculated as the average value of 14 measured values excluding the minimum and maximum values of 16 measured values, unless otherwise specified. The variation 3σ in the angle of the orientation axis of the transparent substrate refers to the average of the variation 3σ measured at 16 points and the variation 3σ of the 14 points excluding the minimum and maximum values.
When the measurement sample is a rectangle, it is preferable to measure 16 points at the intersections of lines obtained by dividing the region inside the rectangle into 5 equal parts vertically and horizontally, with a margin of 0.5 cm from the outer edge of the rectangle, and to calculate the average value. When the measurement sample is a shape other than a rectangle, such as a circle, ellipse, triangle, or pentagon, it is preferable to draw a rectangle with the maximum area inscribed in these shapes, and measure 16 points on the rectangle using the above method.
In this specification, the various parameters are values measured at a temperature of 23° C.±5° C. and a relative humidity of 40% to 65%. Before starting each measurement, the target sample is exposed to the above atmosphere for 30 minutes or more before measurement and evaluation.

<Retardation Layer>
The optical layered body of the present invention is required to have a λ/4 retardation layer.
The optical laminate of the present invention preferably has a λ/2 retardation layer in addition to the λ/4 retardation layer. When the optical laminate has a λ/4 retardation layer and a λ/2 retardation layer, it is preferable to arrange the λ/2 retardation layer on the transparent substrate side.
The optical laminate of the present invention preferably has a λ/8 retardation layer in addition to the λ/4 retardation layer.

The λ/4 retardation layer preferably has an in-plane retardation of 100 nm or more and 180 nm or less, more preferably 110 nm or more and 160 nm or less, and further preferably 110 nm or more and 150 nm or less.
The λ/2 retardation layer has an in-plane retardation of 200 nm or more and 300 nm or less, more preferably 220 nm or more and 280 nm or less, and further preferably 220 nm or more and 270 nm or less.

The λ/4 retardation layer and the λ/2 retardation layer preferably have a thickness direction retardation of 30 nm or more and 120 nm or less, and more preferably 50 nm or more and 100 nm or less. The thickness direction retardation described above is particularly suitable as a numerical value when a λ/4 retardation layer and a λ/2 retardation layer are used in combination. When only a λ/4 retardation layer is used, the thickness direction retardation of the λ/4 retardation layer is preferably 120 nm or less, and more preferably 30 nm or more and 100 nm or less.

The λ/4 retardation layer and the λ/2 retardation layer may be ones that exhibit normal dispersion or ones that exhibit reverse dispersion, but from the viewpoint of converting a wide wavelength range into circularly polarized light, those that exhibit reverse dispersion are preferable.
In addition, the reverse dispersion is a characteristic in which the retardation given to the transmitted light increases as the wavelength of the transmitted light becomes longer. Specifically, the relationship between the in-plane retardation (Re450) at a wavelength of 450 nm and the in-plane retardation (Re550) at a wavelength of 550 nm is Re450<Re550. On the other hand, the normal dispersion is a characteristic in which Re450>Re550.

When imparting reverse dispersion characteristics, the ratio of Re450 of the λ/4 retardation layer to Re550 of the λ/4 retardation layer (Re450/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. In addition, Re450/Re550 is preferably 0.78 or more, more preferably 0.80 or more, and even more preferably 0.82 or more.

When imparting reverse dispersion characteristics, the ratio of Re450 of the λ/2 retardation layer to Re550 of the λ/2 retardation layer (Re450/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. In addition, Re450/Re550 is preferably 0.78 or more, more preferably 0.80 or more, and even more preferably 0.82 or more.

The thickness of the λ/4 retardation layer and the λ/2 retardation layer can be adjusted appropriately within the range of 0.1 μm to 40 μm, taking into account the retardation to be imparted.

Retardation layers such as the λ/4 retardation layer and the λ/2 retardation layer can be formed, for example, from a composition containing a liquid crystal compound such as a polymerizable liquid crystal compound, or by stretching a polymer film. Examples of liquid crystal compounds include rod-shaped liquid crystal compounds such as nematic liquid crystal compounds and smectic liquid crystal compounds, cholesteric liquid crystal compounds, and discotic liquid crystal compounds (disk-shaped liquid crystal compounds). Retardation layers such as the λ/4 retardation layer and the λ/2 retardation layer can be general-purpose retardation layers.

The retardation layer formed from a composition containing a liquid crystal compound is preferably formed on a support. The retardation layer formed on the support may be used as it is, or may be transferred to another member (e.g., a transparent substrate). A transparent substrate may be used as the support.

The slow axes of the λ/4 retardation layer and the λ/2 retardation layer and the absorption axis of the polarizer are preferably as follows.
When the optical laminate has a λ/4 retardation layer as in FIG. 1, the angle between the slow axis of the λ/4 retardation layer and the absorption axis of the polarizer is preferably 45±5°, more preferably 45±2°.
When a λ/4 retardation layer and a λ/2 retardation layer are used as in the optical laminate of FIG. 2, the angle between the alignment axis of each retardation layer and the absorption axis of the polarizer varies depending on the wavelength dispersion of the λ/4 retardation layer and the λ/2 retardation layer, but is preferably in 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 layer 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 layer 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 layer 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 layer is preferably 15±8°, more preferably 15±6°.

In addition, as shown in FIG. 2, when a λ/4 retardation layer and a λ/2 retardation layer are used, the in-plane retardation (Re ₄ ) of the λ/4 retardation layer and the in-plane retardation (Re ₂ ) of the λ/2 retardation layer preferably satisfy 1.8≦Re ₂ /Re ₄ ≦2.2, and more preferably satisfy 1.9≦Re ₂ /Re ₄ ≦2.1.

<Polarizer>
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 machine direction, and a polarizer stretched in the cross direction (perpendicular to the transport direction) has an absorption axis perpendicular to the machine direction.

The polarizer preferably has a polarization degree of 99.00% or more and a total light transmittance of 35% or more, more preferably a polarization degree of 99.90% or more and a total light transmittance of 37% or more, and even more preferably a polarization degree of 99.95% or more and a total light transmittance of 40% or more. The total light transmittance of the polarizer is preferably 65% or less, more preferably 55% or less, and even more preferably 45% or less.
In this specification, the total light transmittance refers to the total light transmittance defined in JIS K7361-1:1997.

It is preferable that the polarizer has a protective layer on both sides.
The protective layer may be, for example, a general-purpose plastic film. The protective layer on the λ/4 retardation layer side may be a transparent substrate as described below. The protective layer on the opposite side to the λ/4 retardation layer may be a surface protective material as described below.

<Transparent substrate>
The optical laminate of the present invention has a specific transparent substrate between the λ/4 retardation layer and the polarizer.

Hereinafter, the reason why the presence of a specific transparent substrate between the λ/4 retardation layer and the polarizer can suppress the color tone when viewed obliquely will be described.
First, the reason why a conventional circularly polarizing plate causes a color to be visually recognized in an oblique direction will be explained.
A circular polarizing plate having a retardation layer and a polarizer is designed based on the principle of "suppressing reflection in the front direction" and "suppressing reflection in the vicinity of 550 nm where visibility is high", so its weaknesses are "suppression of reflection in oblique directions" and "suppression of reflection of wavelengths other than 550 nm". Circular polarizing plates that overcome these weaknesses have been proposed in Patent Documents 1 and 2, but it is difficult to completely overcome the weaknesses. For this reason, in conventional circular polarizing plates, the color of wavelengths other than 550 nm is visible in oblique directions.
On the other hand, the optical laminate of the present invention has a specific transparent substrate between the λ/4 retardation layer and the polarizer. Such a specific transparent substrate has a slow axis of the transparent substrate and an absorption axis of the polarizer arranged substantially parallel or perpendicular to each other, and therefore does not substantially act on linearly polarized light. That is, the external light that passes through the polarizer becomes linearly polarized light and passes through the transparent substrate as linearly polarized light. Therefore, the transparent substrate does not impair the suppression of reflection of external light.
In addition, the direction of the orientation main axis of the transparent substrate (when it exhibits positive birefringence, the orientation main axis is the direction of the slow axis, and when it exhibits negative birefringence, the direction perpendicular to the orientation main axis is the direction of the slow axis) is difficult to make completely uniform even by uniaxial stretching, and there is a slight variation. In addition, during the production and processing of the optical laminate, there may be a slight variation in the direction of the orientation main axis of the transparent substrate. When there is a slight variation in the direction of the orientation main axis of the transparent substrate, the polarization state is slightly disturbed. As described later, it is considered that such a slight variation in the orientation main axis is one factor that makes the color in the oblique direction less noticeable. In addition, during the production of the optical laminate, for example, each member is bonded together. In addition, during the processing of the optical laminate, for example, the optical laminate is cut.
The linearly polarized light transmitted through the transparent substrate is transmitted through the λ/4 retardation layer (or the λ/2 retardation layer and the λ/4 retardation layer) to become right-handed or left-handed circularly polarized light, but the wavelength range outside the 550 nm in the oblique direction is likely to deviate from the circularly polarized state. Therefore, in the conventional circularly polarizing plate, the light reflected on the surface of the display element, which has a wavelength range outside the 550 nm in the oblique direction, does not become linearly polarized light when it is transmitted again through the λ/4 retardation layer (or the λ/2 retardation layer and the λ/4 retardation layer), and passes through the polarizer.
The optical laminate of the present invention can neutralize the color in the oblique direction and make it less noticeable by disturbing the light in the wavelength range that is not linearly polarized when retransmitted through the λ/4 retardation layer (or the λ/2 retardation layer and the λ/4 retardation layer) by a specific transparent substrate (a transparent substrate having positive birefringence or negative birefringence and a thickness direction retardation of 125 nm or more or -125 nm or less). It is considered that the cause of the disturbance of the light in the wavelength range that is not linearly polarized by the transparent substrate is the above-mentioned characteristics (having positive birefringence or negative birefringence and a thickness direction retardation of 125 nm or more or -125 nm or less) as well as slight variations in the direction of the orientation main axis of the transparent substrate.

The transparent substrate must have either positive or negative birefringence.
A transparent substrate that does not satisfy these requirements cannot solve the problem of color in oblique directions. For example, even if the retardation in the thickness direction of the transparent substrate is 125 nm or more or −125 nm or less, if the transparent substrate does not have positive birefringence or negative birefringence, the problem of color in oblique directions cannot be solved.
Positive birefringence means that the refractive index (n1) in the direction of the in-plane main axis of orientation and the refractive index (n2) in the direction perpendicular to the main axis of orientation satisfy the relationship n1>n2, while negative birefringence means that the relationship n1<2.
Transparent substrates having positive or negative birefringence include a positive A plate, a negative A plate, a positive B plate, and a negative B plate.
A positive A plate indicates a relationship of nx>ny≈nz, a negative A plate indicates a relationship of nz≈nx>ny, a positive B plate indicates a relationship of nz>nx>ny, and a negative B plate indicates a relationship of nx>ny>nz.

The transparent substrate must have a retardation in the thickness direction of 125 nm or more or −125 nm or less.
A transparent substrate that does not satisfy these requirements cannot solve the problem of color in oblique directions. For example, even if the transparent substrate has positive birefringence or negative birefringence, if the retardation in the thickness direction of the transparent substrate is not 125 nm or more or −125 nm or less, the problem of color in oblique directions cannot be solved.

The phase difference in the thickness direction of the transparent substrate is preferably 500 nm or more or -500 nm or less, more preferably 1000 nm or more or -1000 nm or less, even more preferably 3000 nm or more or -3000 nm or less, and even more preferably 5000 nm or more or -5000 nm or less.

The phase difference in the thickness direction of the transparent substrate is preferably 30,000 nm or less or -30,000 nm or more, more preferably 15,000 nm or less or -15,000 nm or more, even more preferably 10,000 nm or less or -10,000 nm or more, and even more preferably 8,000 nm or less or -8,000 nm or more.

From the viewpoint of easily suppressing color when viewed from an oblique angle, the in-plane retardation of the transparent substrate is preferably 40 nm or more, more preferably 125 nm or more, more preferably 500 nm or more, more preferably 1000 nm or more, more preferably 3000 nm or more, and more preferably 5000 nm or more.
If the in-plane retardation of the transparent substrate is too large, the thickness of the transparent substrate may increase or the tear resistance of the transparent substrate may decrease. Therefore, the in-plane retardation of the transparent substrate is preferably 50,000 nm or less, more preferably 30,000 nm or less, even more preferably 20,000 nm or less, and even more preferably 10,000 nm or less.

The transparent substrate preferably has a variation 3σ of the angle of the alignment axis of 0.01 or more. By having the variation 3σ of the angle of the alignment axis of 0.01 or more, it is possible to easily scatter light in a wavelength range that is not linearly polarized when retransmitted through the λ/4 retardation layer (or the λ/2 retardation layer and the λ/4 retardation layer), and thus to neutralize the color in the oblique direction and make it less noticeable.
If the variation 3σ of the angle of the alignment axis of the transparent substrate is too large, the external light antireflection property of the optical laminate may be reduced. Therefore, the variation 3σ of the angle of the alignment axis of the transparent substrate is preferably 3.00 or less, and more preferably 1.50 or less.

The variation 3σ of the angle of the orientation axis of the transparent substrate is preferably measured at 16 points as described above. At each measurement point, the variation 3σ of the angle of the optical axis can be calculated by dividing each measurement point into micro areas and performing statistical processing of 3σ based on the angle of the optical axis measured for each divided micro area. The area of the micro area is preferably 100 [μm ² ] or more and 500 [μm ² ] or less. In addition, in order to increase the reliability of the variation 3σ, the division number of each measurement point (the number of micro areas at each measurement point) is preferably 1,000 or more, more preferably 10,000 or more.

The variation 3σ in the angle of the orientation axis can be measured, for example, using an "AxoStep" product manufactured by Axomecrics, following the procedure below.

<Operation Procedure>
1. Execute calibration (1) In the Measurement tab, set the wavelength value to "550" and the number to average value to "20", and then click "Set Axostep".
(2) On the Calibration tab, click "DarkImage" and then click "single calibrate."
(3) The calibration result is displayed in the Calibration Result window. Here, confirm that the Y value (RMS Error value) is 3 or less.
(4) Press Baseline.
(5) On the Measurement tab, press “Measure Once” to measure and save the results.
(6) Click Parameter to Plot and select “Total Retardance (nm)”.
(7) Open the Statistics window, select "Full Graph", and confirm that the Mean value in the Statistics window is 0.0±0.1 nm.
2. Measurement of the standard plate (1) Place the standard plate "CAL-VIS-1" on the stage and perform the measurement.
(2) Select "Total Retardance (nm)" from Parameter to Plot and confirm that the Mean value is 191.6±1.0 nm. At the same time, select "Retardance Orientation (°)" and confirm that the Mean value is 0.0±0.05°.
3. Actual measurement Place the sample on the stage and perform the measurement. When performing the measurement, in the Measurement tab, set the wavelength value to "550" and the number to average value to "20".

In the measurement according to the above procedure, the angle of the optical axis (main alignment axis) of 160 x 128 = 20,480 pixels is measured for each measurement point. Then, the variation 3σ of the optical axis angle for each measurement point is calculated from the 20,480 optical axis angles. The size of one pixel is 432 [μm ² ].

In the optical laminate, the transparent substrate needs to be arranged so that the slow axis of the transparent substrate and the absorption axis of the polarizer are substantially parallel or substantially perpendicular to each other.
If these requirements are not met, the state of polarization is disturbed when linearly polarized light passes through the transparent substrate, making it impossible to suppress reflection of external light.
The range of approximately parallel or approximately perpendicular is as described above.

The transparent substrate is preferably a stretched plastic film obtained by stretching a plastic film such as a polyester film, a polycarbonate film, a cycloolefin polymer film, an acrylic film, polystyrene, etc. Among these, a stretched polyester film or a stretched polycarbonate film is preferred from the viewpoint of easily increasing the in-plane retardation.
The transparent substrate preferably exhibits normal dispersion (the property that the birefringence increases toward the shorter wavelength side). From this viewpoint, the transparent substrate is preferably a stretched polyester film (stretched polyester film).
As the polyester film, a polyethylene terephthalate film (PET film), a polyethylene naphthalate film (PEN film), or the like is preferable.
The transparent substrate may be a substrate in which a liquid crystal layer containing a liquid crystal compound such as a discotic liquid crystal compound is formed on a transparent support such as a plastic film. The transparent substrate may be a substrate obtained by transferring the liquid crystal layer formed on the transparent support as described above to another layer (such as a λ/4 retardation layer or a polarizer).

Examples of the stretching include longitudinal uniaxial stretching, tenter stretching, sequential biaxial stretching, and simultaneous biaxial stretching.
From the viewpoints of ease of handling and thinning, the thickness of the transparent substrate is preferably 5 μm or more and 300 μm or less, more preferably 10 μm or more and 200 μm or less, even more preferably 15 μm or more and 100 μm or less, and even more preferably 20 μm or more and 50 μm or less.

<Surface protection material>
The optical laminate may have a surface protective material on the surface of the polarizer opposite to the transparent substrate.
Examples of surface protective materials include transparent supports such as plastic films and glass.
The surface protective material may have a functional layer on the transparent support. The functional layer may be one or more layers selected from a hard coat layer, an antifouling layer, an antiglare layer, an antireflection layer, and the like.

<Other demographics>
The optical laminate may further include other layers.
Examples of other layers include an adhesive layer for adhering each layer together and an antistatic layer.

<Total light transmittance>
The optical layered body of the present invention preferably has a total light transmittance of 35% or more and 80% or less, more preferably 37% or more and 65% or less, and even more preferably 40% or more and 55% or less.
By setting the total light transmittance of the optical laminate to 35% or more, it is possible to easily improve the visibility of the display element. Furthermore, by setting the total light transmittance of the optical laminate to 80% or less, it is possible to easily suppress the reflection of external light and further to easily suppress the color when viewed from an oblique angle.
It is preferable that the total light transmittance shows the above value regardless of the side from which light is incident on the optical laminate.

<3σΔX, 3σΔY>
In the optical layered body of the present invention, it is preferable that both 3σΔX and 3σΔY calculated from the following measurement 1 are less than 0.019.
<Measurement 1>
A sample is prepared by laminating the optical laminate on an aluminum plate having an average spectral reflectance of 20% in the wavelength region of 380 nm to 780 nm, and the optical laminate is arranged such that the surface of the optical laminate on the λ/4 retardation layer side relative to the transparent substrate faces the aluminum plate.
Light diffused by an integrating sphere is incident on the surface of the sample from the normal direction, and the reflected light is measured. The X and Y values of the XYZ color system are calculated from the measured reflected light. The measurement and calculation are performed in 0.5 degree increments in the azimuth angle range of 0 degrees to 359.5 degrees with the elevation angle fixed at an angle of 60 degrees from the normal to the surface of the sample, to obtain X and Y values at 720 points.
The average value of the X values at 720 points is defined as "Xave." The deviation of the X value at the nth measurement point from Xave is defined as "ΔXn." The variation 3σ of ΔXn at 720 points is defined as "3σΔX."
The average value of the Y values of the 720 points is defined as "Yave." The deviation of the Y value of the nth measurement point from Yave is defined as "ΔYn." The variation 3σ of ΔYn of the 720 points is defined as "3σΔY."

"An angle of 60 degrees from the normal to the surface of the sample" is, in other words, "an angle of 30 degrees from a direction parallel to the surface of the sample."

By making both 3σΔX and 3σΔY less than 0.019, the change in color when viewed from an oblique angle can be further suppressed.
Each of 3σΔX and 3σΔY is more preferably 0.018 or less, further preferably 0.017 or less, and even more preferably 0.016 or less. There is no lower limit for 3σΔX and 3σΔY, but each is preferably 0.005 or more, and more preferably 0.010 or more.

In the optical layered body of the present invention, the average of 3σΔX and 3σΔY calculated from the above measurement 1 is preferably less than 0.018.
By setting the average of 3σΔX and 3σΔY to less than 0.018, the change in color when viewed from an oblique angle can be further suppressed.
The average of 3σΔX and 3σΔY is more preferably 0.017 or less, even more preferably 0.016 or less, and even more preferably 0.015 or less. The lower limit of the average of 3σΔX and 3σΔY is not limited, but is preferably 0.005 or more, and more preferably 0.010 or more.

In the sample, it is preferable that the aluminum plate and the optical laminate are laminated so that there is no air interface between the aluminum plate and the optical laminate. For this reason, it is preferable that the aluminum plate and the optical laminate are bonded together via an adhesive layer or water-bonded together via water.

The reason why "an aluminum plate with an average spectral reflectance of 20% for wavelengths between 380 nm and 780 nm" was used in measurement 1 is because it is a substitute for display elements with high reflectance such as organic EL display elements and micro LED display elements.

In this specification, the average of the spectral reflectance in the wavelength range of 380 nm to 780 nm refers to the reflectance by the SCI method. SCI is a reflectance calculated from the measured values of light applied to the sample surface from all directions using an integrating sphere, closing the light trap and measuring all reflected light including the specular reflection direction. A typical SCI measuring device is configured in accordance with the geometric condition c of JIS Z8722:2009. More specifically, a typical SCI and SCE measuring device has a receiver position at +8 degrees relative to the normal line of the sample, a receiver aperture angle of 10 degrees, a light trap position at -8 degrees relative to the normal line of the sample, and a light trap coverage range of 10 degrees. An example of such a measuring device is the CM-2002 manufactured by Konica Minolta, Inc.

Measurement 1 is performed by fixing the elevation angle at an angle of 60 degrees from the normal to the surface of the sample, and varying the azimuth angle in increments of 0.5 degrees within the range of 0 to 359.5 degrees. An example of a device capable of such measurements is the "Ez-Contrast160" product name by ELDIM.

<Applications>
The optical laminate of the present invention can be used, for example, as an optical laminate for the front surface of a display element.
Examples of the display element include a liquid crystal display element, an organic EL display element, a micro LED display element, etc. Among these, an organic EL display element and a micro LED display element are preferred in that the reflectance of the display element is high and the effects of the present invention can be easily achieved.

[Image display device]
The image display device of the present invention has an optical laminate on a display element, the optical laminate being the optical laminate of the present invention described above, and is arranged so that the surface of the optical laminate on the λ/4 retardation layer side relative to the transparent substrate faces the display element.

Display elements include liquid crystal display elements, organic EL display elements, and micro LED display elements. Among these, organic EL display elements and micro LED display elements are preferred because they have high reflectance and can easily exert the effects of the present invention.

The display element preferably has an average spectral reflectance of 10% or more, more preferably 15% or more, and even more preferably 17% or more, in the wavelength region of 380 nm or more and 780 nm or less. Such a display element is preferable in that it can easily exert the effects of the present invention.
If the average spectral reflectance of the display element is too high, it tends to be difficult to suppress the color when viewed from an oblique angle. For this reason, the average spectral reflectance of the display element is preferably 50% or less, more preferably 40% or less, even more preferably 35% or less, and even more preferably 30% or less.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Note that "parts" and "%" are based on mass unless otherwise specified.

1. Preparation and Fabrication of Materials 1-1. Preparation of Polarizing Plates The following polarizing plates A to C were prepared.
<Polarizing Plate A>
A polarizing plate (polarization degree 99.95%, total light transmittance 40.5%) in which both sides of an iodine-based polarizer formed from polyvinyl alcohol and iodine are protected with optically isotropic triacetyl cellulose films.
<Polarizing Plate B>
A polarizing plate (polarization degree 99.5%, total light transmittance 43%) comprising a dye-based polarizer formed from polyvinyl alcohol and a dichroic dye, both sides of which are protected with optically isotropic triacetyl cellulose films.
<Polarizing Plate C>
A polarizing plate (polarization degree 90%, total light transmittance 45%) comprising a dye-based polarizer formed from a liquid crystal material and a dichroic dye, both sides of which are protected with optically isotropic triacetyl cellulose films.

1-2. Preparation of λ/4 Retardation Layer The following λ/4 retardation layers A to J were prepared.
<λ/4 Retardation Layer A>
A laminate having a λ/4 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=140 nm, Re(450)/Re(550)=0.85.
<λ/4 Retardation Layer B>
A laminate having a λ/4 retardation layer made of a polymerizable liquid crystal compound consisting of a mixture of reverse dispersion liquid crystal and normal dispersion liquid crystal on an optically isotropic triacetyl cellulose film. Re(550)=140 nm, Re(450)/Re(550)=1.00.
<λ/4 Retardation Layer C>
A laminate having a λ/4 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=140 nm, Re(450)/Re(550)=1.09.
<λ/4 Retardation Layer D>
A laminate having a λ/4 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=140 nm, Re(450)/Re(550)=0.90.
<λ/4 Retardation Layer E>
A λ/4 retardation layer made of a cycloolefin polymer. Re(550)=140 nm, Re(450)/Re(550)=1.0.
<λ/4 Retardation Layer F>
A λ/4 retardation layer made of a polycarbonate polymer. Re(550)=140 nm, Re(450)/Re(550)=1.1.
<λ/4 Retardation Layer G>
A laminate having a λ/4 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=120 nm, Re(450)/Re(550)=1.09.
<λ/4 Retardation Layer H>
A laminate having a λ/4 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=120 nm, Re(450)/Re(550)=1.0.
<λ/4 Retardation Layer I>
A laminate having a λ/4 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=80 nm, Re(450)/Re(550)=1.09.
<λ/4 Retardation Layer J>
A λ/4 retardation layer made of a polycarbonate polymer. Re(550)=120 nm, Re(450)/Re(550)=1.1.

1-3. Preparation of λ/2 Retardation Layer The following λ/2 retardation layers A to E were prepared.
<λ/2 Retardation Layer A>
A laminate having a λ/2 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=260 nm, Re(450)/Re(550)=1.09.
<λ/2 Retardation Layer B>
A laminate having a λ/2 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=240 nm, Re(450)/Re(550)=1.0.
<λ/2 Retardation Layer C>
A laminate having a λ/2 retardation layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film. Re(550)=160 nm, Re(450)/Re(550)=1.09.
<λ/2 Retardation Layer D>
A λ/2 retardation layer made of a cycloolefin polymer. Re(550)=275 nm, Re(450)/Re(550)=1.0.
<λ/2 Retardation Layer E>
A λ/2 retardation layer made of a polycarbonate polymer. Re(550)=240 nm, Re(450)/Re(550)=1.1.

1-4. Preparation of Transparent Substrates The following transparent substrates A to I were prepared.
The transparent substrates A to F and I had a variation 3σ in the angle of the alignment main axis of 0.01 or more.
<Transparent substrate A>
Polyethylene terephthalate film, a positive A plate satisfying nx>ny, a phase difference in the thickness direction: 2500 nm, and an in-plane phase difference: 5000 nm.
<Transparent substrate B>
Polyethylene terephthalate film, a positive A plate satisfying nx>ny, a phase difference in the thickness direction: 5000 nm, and an in-plane phase difference: 10000 nm.
<Transparent substrate C>
Polyethylene naphthalate film, a positive A plate satisfying nx>ny, a phase difference in the thickness direction: 7,500 nm, and an in-plane phase difference: 15,000 nm.
<Transparent substrate D>
Polyethylene terephthalate film, a positive A plate satisfying nx>ny, a thickness direction retardation of 2000 nm, and an in-plane retardation of 1000 nm.
<Transparent substrate E>
A film having a liquid crystal layer made of a polymerizable liquid crystal compound on an optically isotropic triacetyl cellulose film, a positive A plate satisfying nx>ny, a thickness direction retardation of 25 nm, and an in-plane retardation of 50 nm.
<Transparent substrate F>
Polyethylene naphthalate film, a positive A plate satisfying nx>ny, a phase difference in the thickness direction: 5000 nm, and an in-plane phase difference: 10000 nm.
<Transparent substrate G>
A film having a liquid crystal layer formed by vertically aligning a polymerizable liquid crystal on an optically isotropic triacetyl cellulose film, a positive C plate, and a retardation in the thickness direction: −1000 nm
<Transparent substrate H>
A film having a cholesteric liquid crystal layer on an optically isotropic triacetyl cellulose film, a negative C plate, a retardation in the thickness direction: 1000 nm
<Transparent substrate I>
Triacetyl cellulose film, negative biaxial film satisfying nx>ny>nz (negative B plate), thickness direction retardation: 250 nm, in-plane retardation: 60 nm.

2. Preparation of optical laminate [Example 1]
The λ/4 retardation layer A, the transparent substrate A, and the polarizing plate A were laminated in this order via an adhesive layer to obtain an optical laminate of Example 1. The angle between the absorption axis of the polarizer and the slow axis of the transparent substrate was 90 degrees. The angle between the absorption axis of the polarizer and the slow axis of the λ/4 retardation layer was 45 degrees.

[Examples 2 to 7, 13 to 17], [Comparative Examples 1 to 4]
The materials of the λ/4 retardation layer, the transparent substrate, and the polarizing plate were those shown in Table 1, and the angle between the absorption axis of the polarizer and the slow axis of the transparent substrate was changed to the angle shown in Table 1. The optical laminates of Examples 2 to 7, 13 to 17, and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1.

[Example 8]
The λ/4 retardation layer H, the λ/2 retardation layer B, the transparent substrate B and the polarizing plate A were laminated in this order via an adhesive layer to obtain an optical laminate of Example 8. The angle between the absorption axis of the polarizer and the slow axis of the transparent substrate was 90 degrees. The angle between the absorption axis of the polarizer and the slow axis of the λ/4 retardation layer was 75 degrees. The angle between the absorption axis of the polarizer and the slow axis of the λ/2 retardation layer was 15 degrees.

[Examples 9 to 12], [Comparative Example 5]
The materials of the λ/4 retardation layer, the λ/2 retardation layer, the transparent substrate, and the polarizing plate were those shown in Table 1, and the angles between the absorption axis of the polarizer and the slow axis of the λ/4 retardation layer and between the absorption axis of the polarizer and the slow axis of the λ/2 retardation layer were changed to the angles shown in Table 1. The optical laminates of Examples 9 to 12 and Comparative Example 5 were obtained in the same manner as in Example 8.

[Comparative Examples 6 to 7]
The λ/4 retardation layer E and the polarizing plate A were laminated via an adhesive layer to obtain an optical laminate of Comparative Example 6. In addition, the λ/4 retardation layer F and the polarizing plate A were laminated via an adhesive layer to obtain an optical laminate of Comparative Example 7. The angle between the absorption axis of the polarizer and the slow axis of the λ/4 retardation layer was set to 45 degrees.

3. Preparation of simulated image display device Aluminum deposition films were prepared by depositing aluminum on an optically isotropic acrylic film. The thickness of the deposited film was changed to prepare three types of aluminum deposition films with average spectral reflectance of 20%, 30%, and 40% in the wavelength range of 380 to 780 nm.
The surface of the aluminum vapor deposition film having a spectral reflectance of 40% and the surface of the λ/4 retardation layer of the optical laminate of Example 1 were bonded together via an adhesive layer to obtain a simulated image display device of Example 1.
Except for changing the aluminum vapor deposition film to one having the spectral reflectance shown in Table 1, the same procedure as in Example 1 was carried out to obtain simulated image display devices of Examples 2 to 17 and Comparative Examples 1 to 7.

4. Measurement and Evaluation The simulated image display devices of the examples and comparative examples were irradiated with light from a three-wavelength fluorescent lamp from the polarizing plate side, and the anti-reflection properties and color in oblique directions were evaluated according to the following criteria. The light source was a three-wavelength fluorescent lamp only, and the environment was set so that the brightness on the simulated image display device was 300 to 1000 lux. The results are shown in Tables 1 and 2.
Furthermore, the total light transmittance of each of the optical laminates of the Examples and Comparative Examples was measured. The results are shown in Tables 1 and 2.
In addition, 3σΔX and 3σΔY were calculated for some of the optical laminates of the Examples and Comparative Examples. The results are shown in Table 2.

4-1. Anti-reflection of external light When the simulated image display device was visually observed from the front and at an angle, those for which light leakage due to insufficient anti-reflection was not noticeable were given a score of 3, those for which it was neither noticeable nor noticeable were given a score of 2, and those for which light leakage due to insufficient anti-reflection was noticeable were given a score of 1. The average score of 20 subjects was calculated and ranked according to the following criteria.
<Evaluation criteria>
A: Average score is 2.5 or more. B: Average score is 2.0 or more and less than 2.5. C: Average score is 1.5 or more and less than 2.0. D: Average score is less than 1.5.

When the simulated image display device was viewed obliquely, the surface color was given a score of 3, while the surface color was given a score of 2, and the surface color was given a score of 1. The average score of 20 subjects was calculated and ranked according to the following criteria.
<Evaluation criteria>
A: Average score is 2.7 or more B+: Average score is 2.5 or more and less than 2.7 B: Average score is 2.0 or more and less than 2.5 C: Average score is 1.5 or more and less than 2.0 D: Average score is less than 1.5

4-3. Total light transmittance The total light transmittance of the optical laminates of the examples and comparative examples at wavelengths of 380 nm to 780 nm was measured, and the average value was calculated. The measuring device used was "HM-150" manufactured by Murakami Shikisai Co., Ltd. The light incident surface was the polarizing plate side.

4-4.3σΔX, 3σΔY
A sample was prepared by laminating the optical laminate of Example 14 on an aluminum plate having an average spectral reflectance of 20% in the wavelength region of 380 nm or more and 780 nm or less. Measurement 1 described in the main text of the specification was carried out on the sample, and 3σΔX and 3σΔY of the sample were calculated. The optical laminate of Example 14 was replaced with the optical laminates of Examples 15 to 17 and the optical laminate of Comparative Example 6, and 3σΔX and 3σΔY of the sample were calculated in the same manner. The measuring device used was ELDIM's product name "Ez-Contrast160".

Note 1: In Tables 1 and 2, "Angle 1" means the angle between the absorption axis of the polarizer and the slow axis of the transparent substrate.
Note 2: In Table 1, "angle 2" means the angle between the absorption axis of the polarizer and the slow axis of the λ/2 retardation layer.
Note 3: In Tables 1 and 2, "angle 3" means the angle between the absorption axis of the polarizer and the slow axis of the λ/4 retardation layer.

From the results in Tables 1 and 2, it can be confirmed that the optical laminates of the examples can suppress the reflection of external light and can suppress the color when viewed from an oblique angle.
In addition, from Example 13, it can be confirmed that if the transparent substrate has "positive birefringence or negative birefringence and a thickness direction retardation of 125 nm or more or -125 nm or less", the color in the oblique direction can be suppressed even if the in-plane retardation of the transparent substrate is low. Note that, from the comparison between Example 13 and other examples, it can be confirmed that the larger the thickness direction retardation and the in-plane retardation, the easier it is to suppress the color in the oblique direction.

10: λ/4 retardation layer 20: λ/2 retardation layer 30: Transparent base material 40: Polarizer 50: Surface protection material 100: Optical laminate

Claims (12)

The optical element comprises a λ/4 retardation layer, a transparent substrate, and a polarizer in this order.
the transparent substrate has positive birefringence or negative birefringence and a retardation in a thickness direction of 500 nm or more or −125 nm or less;
the transparent substrate is a positive A plate exhibiting a relationship of nx>ny≈nz or a negative B plate exhibiting a relationship of nx>ny>nz, where nx is a refractive index in an in-plane slow axis direction, ny is a refractive index in an in-plane direction perpendicular to nx, and nz is a refractive index in a direction perpendicular to nx and ny,
An optical laminate, in which a slow axis of the transparent substrate and an absorption axis of the polarizer are arranged approximately parallel or approximately perpendicular to each other. The optical laminate according to claim 1 , wherein the transparent substrate has an in-plane retardation of 1000 nm or more. The optical laminate according to claim 1 or 2, wherein the transparent substrate is a polyester film or a polycarbonate film. The optical laminate according to any one of claims 1 to 3, having a λ/2 retardation layer between the λ/4 retardation layer and the transparent substrate. The optical laminate according to any one of claims 1 to 4, having a total light transmittance of 35% or more and 80% or less. The optical laminate according to any one of claims 1 to 3, wherein 3σΔX and 3σΔY calculated from the following measurement 1 are both less than 0.019.
<Measurement 1>
A sample is prepared by laminating the optical laminate on an aluminum plate having an average spectral reflectance of 20% in the wavelength region of 380 nm to 780 nm, and the optical laminate is arranged such that the surface of the optical laminate on the λ/4 retardation layer side relative to the transparent substrate faces the aluminum plate.
Light diffused by an integrating sphere is incident on the surface of the sample from the normal direction, and the reflected light is measured. The X and Y values of the XYZ color system are calculated from the measured reflected light. The measurement and calculation are performed in 0.5 degree increments in the azimuth angle range of 0 degrees to 359.5 degrees with the elevation angle fixed at an angle of 60 degrees from the normal to the surface of the sample, to obtain X and Y values at 720 points.
The average value of the X values at 720 points is defined as "Xave." The deviation of the X value at the nth measurement point from Xave is defined as "ΔXn." The variation 3σ of ΔXn at 720 points is defined as "3σΔX."
The average value of the Y values of the 720 points is defined as "Yave." The deviation of the Y value of the nth measurement point from Yave is defined as "ΔYn." The variation 3σ of ΔYn of the 720 points is defined as "3σΔY." The optical laminate according to any one of claims 1 to 3, wherein the average of 3σΔX and 3σΔY calculated from the following measurement 1 is less than 0.018.
<Measurement 1>
A sample is prepared by laminating the optical laminate on an aluminum plate having an average spectral reflectance of 20% in the wavelength region of 380 nm to 780 nm, and the optical laminate is arranged such that the surface of the optical laminate on the λ/4 retardation layer side relative to the transparent substrate faces the aluminum plate.
Light diffused by an integrating sphere is incident on the surface of the sample from the normal direction, and the reflected light is measured. The X and Y values of the XYZ color system are calculated from the measured reflected light. The measurement and calculation are performed in 0.5 degree increments in the azimuth angle range of 0 degrees to 359.5 degrees with the elevation angle fixed at an angle of 60 degrees from the normal to the surface of the sample, to obtain X and Y values at 720 points.
The average value of the X values at 720 points is defined as "Xave." The deviation of the X value at the nth measurement point from Xave is defined as "ΔXn." The variation 3σ of ΔXn at 720 points is defined as "3σΔX."
The average value of the Y values of the 720 points is defined as "Yave." The deviation of the Y value of the nth measurement point from Yave is defined as "ΔYn." The variation 3σ of ΔYn of the 720 points is defined as "3σΔY." The optical element comprises a λ/4 retardation layer, a transparent substrate, and a polarizer in this order.
the transparent substrate has positive birefringence or negative birefringence, a thickness direction retardation of 125 nm or more or −125 nm or less, and an in-plane retardation of 500 nm or more;
An optical laminate, in which a slow axis of the transparent substrate and an absorption axis of the polarizer are arranged approximately parallel or approximately perpendicular to each other. The optical element comprises a λ/4 retardation layer, a transparent substrate, and a polarizer in this order.
the transparent substrate has positive birefringence or negative birefringence and a retardation in a thickness direction of 500 nm or more;
An optical laminate, in which a slow axis of the transparent substrate and an absorption axis of the polarizer are arranged approximately parallel or approximately perpendicular to each other. The optical laminate according to any one of claims 1 to 9, which is used for the front surface of an organic EL display element. An image display device having an optical laminate on a display element, the optical laminate being the optical laminate according to any one of claims 1 to 9, and the optical laminate being arranged so that the surface on the λ/4 retardation layer side relative to the transparent substrate faces the display element. The image display device according to claim 11, wherein the display element is an organic EL display element or a micro LED display element.