JP2023173828A - Circularly polarizing plate, optical film using the same, and image display device - Google Patents

Abstract

To provide a circularly polarizing plate which offers high circularly polarizing capability and can reduce reflectance when used for anti-reflection purposes even when a polarizing plate with a low polarization degree is used.SOLUTION: A circularly polarizing plate is provided, consisting of a polarizing plate and a λ/4 retardation plate, the polarization plate having a polarization degree Pe (%) of 99.8% or less. When the angle θ (degrees) is defined for the direction in which the angle between the fast axis of the λ/4 retardation plate and the transmission axis of the polarizing plate is less than 90 degrees, θ satisfies an expression (1) below. expression 1.SELECTED DRAWING: None

Description

The present invention relates to a circularly polarizing plate, an optical film using the same, and an image display device.

Conventionally, flat panel displays such as organic electroluminescent display devices are provided with circularly polarizing plates to reduce reflection of external light on the display surface. As such a circularly polarizing plate, a film that is a combination of a polarizing plate and a λ/4 retardation plate is generally used.
A typical antireflection circularly polarizing plate has a structure in which a polarizing plate and a λ/4 retardation plate are laminated, and the angle between the absorption axis of the polarizing plate and the slow axis of the λ/4 retardation plate is 45 By increasing the temperature, it has the ability to suppress the reflection of external light.

Further, from the viewpoint of suppressing reflection of external light, it is necessary for the λ/4 retardation plate to suppress disturbance of polarization due to scattering, and a plate with low haze is generally used.
For example, Patent Document 1 discloses a circularly polarizing plate for an organic electroluminescent display device in which a polarizer and a λ/4 retardation film are laminated, the slow axis of the λ/4 retardation film and the absorption of the polarizer. linearly polarized light whose angle with the axis is 45 degrees, and whose angle with the electric field vibration plane of the polarized light is 45 degrees with respect to the slow axis of the λ/4 retardation film; A circularly polarizing plate for an organic electroluminescent display device whose internal haze value at the time of incidence is within the range of 0.01 to 0.1% has been proposed (Patent Document 1).

JP2016-218488A

In the circularly polarizing plate disclosed in Patent Document 1, the angle between the electric field vibration plane of polarized light and the slow axis of the λ/4 retardation film is 45 degrees. That is, the bonding angle of the polarizing plate is 45 degrees with respect to the axis of the λ/4 retardation plate, which is theoretically the most suitable angle.
As mentioned above, in a circularly polarizing plate consisting of a polarizing plate and a λ/4 retardation plate, the transmission axis of the polarizing plate and the fast axis of the λ/4 retardation plate usually form an angle of 45 degrees (laminating angle). ) are laminated. A polarizing plate with a high degree of polarization exhibits circularly polarizing plate performance at a lamination angle of 45 degrees, but there is no knowledge of the optimal lamination angle for a polarizing plate with a low degree of polarization.
Therefore, an object of the present invention is to provide a circularly polarizing plate with high circularly polarizing performance that can reduce reflectance when used for antireflection purposes even when a polarizing plate with a low degree of polarization is used. .

As a result of intensive studies, the present inventors calculated the lamination angle according to the degree of polarization of the polarizing plate based on a specific formula, and designed a circularly polarizing plate based on the result. The inventors have discovered that the reflectance when used for antireflection purposes can be reduced even when using the following methods, and have completed the present invention as described below.
That is, the present invention provides the following [1] to [9].

[1] In a circularly polarizing plate consisting of a polarizing plate and a λ/4 retardation plate, the degree of polarization Pe (%) of the polarizing plate is 99.8% or less, and the fast axis of the λ/4 retardation plate and the polarizing plate are A circularly polarizing plate where θ satisfies formula (1) when the angle formed by the transmission axis of is θ (degrees) in the direction of less than 90 degrees.

[2] The circularly polarizing plate according to [1] above, wherein the θ is in the range of 41 degrees to 44 degrees.
[3] The circularly polarizing plate according to [1] or [2] above, wherein the polarizing plate has a single transmittance of 41% or more.
[4] The average transmittance of the fast axis of the λ/4 retardation plate is in the range of 70 to 95%, and the average transmittance of the slow axis is in the range of 70 to 95%, [1] to The circularly polarizing plate according to any one of [3].
[5] The circularly polarizing plate according to any one of [1] to [4] above, wherein the λ/4 retardation plate has a retardation in a range of 125 to 150 nm at a wavelength of 550 nm.
[6] The circularly polarizing plate according to any one of [1] to [5] above, wherein the polarizing plate is a coated polarizing plate.
[7] An optical film comprising the circularly polarizing plate according to any one of [1] to [6] above.
[8] An image display device comprising the circularly polarizing plate according to any one of [1] to [6] above.
[9] An image display device comprising the optical film according to [7] above.

According to the present invention, even when a polarizing plate with a low degree of polarization is used, it is possible to provide a circularly polarizing plate with high circularly polarizing performance that can reduce reflectance when used for antireflection purposes.

It is a figure showing the transmittance of a polarizer and an analyzer. FIG. 3 is a diagram showing the transmittance of polarizing plate sample Pol-1. FIG. 3 is a diagram showing the transmittance of retardation plate sample Ret-1. It is a figure showing the transmittance of a polarizer and an analyzer. FIG. 2 is a conceptual diagram showing a measurement method using a spectroradiometer. FIG. 3 is a diagram showing the transmittance of polarizing plate sample Pol-2. FIG. 3 is a diagram showing the phase difference of the retardation plate sample Ret-1. FIG. 3 is a diagram showing the retardation of an ideal λ/4 phase difference plate. It is a figure which shows the measurement result of the reflectance of an Al vapor deposition film. It is a figure which shows the relationship between a lamination angle and a lamination deviation angle. FIG. 3 is a diagram showing a transmission axis and an absorption axis of a polarizing plate and a fast axis and a slow axis of a retardation plate that constitute a circularly polarizing plate. It is a figure which shows the relationship between the degree of polarization P _e and the bonding deviation angle Δθ _min .

Next, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.

[Circular polarizing plate]
The circularly polarizing plate of the present invention consists of a polarizing plate and a λ/4 retardation plate, and the degree of polarization Pe (%) of the polarizing plate is 99.8% or less, and the fast axis of the λ/4 retardation plate is A feature is that when the angle formed by the transmission axis of the polarizing plate is θ (degrees) in a direction that is less than 90 degrees, θ satisfies the following formula (1). By satisfying the formula (1), even when a polarizing plate with a low degree of polarization is used, the reflectance can be reduced when used for antireflection purposes.

In the above formula (1), θ is the lamination angle, which is the angle between the transmission axis of the polarizing plate and the fast axis of the λ/4 retardation plate. P _e indicates the degree of polarization of the polarizing plate.
As shown in the above formula (1), it can be seen that the lamination angle θ is a function of the degree of polarization P _e of the polarizing plate, and according to the present invention, the optimal lamination angle θ is determined according to the degree of polarization P _e of the polarizing plate. The combined angle θ can be determined.
Specifically, the bonding angle θ is preferably in the range of 41 degrees to 44 degrees.

Further, it is preferable that the polarizing plate used in the circularly polarizing plate of the present invention has a transmittance of 41% or more as a single unit (hereinafter referred to as “single transmittance”). When the single transmittance is 41% or more, the performance as a circularly polarizing plate is ensured. From the above viewpoint, the single transmittance of the polarizing plate is more preferably 41.5% or more, and even more preferably 42% or more. The higher the single transmittance of the polarizing plate, the better, but the upper limit is usually about 50%.

The single transmittance T _s of the polarizing plate can be calculated as follows.
First, with a combination of a polarizer and a polarizing plate, rotate the polarizer and measure the transmittance at which the transmittance is maximum and minimum, and let them be T _p and T _c respectively, and at the angles at which the transmittance is maximum and minimum. , the transmittances measured only with the polarizer are T ₂ and T ₁ , respectively. From the obtained T _p , T _c , T ₁ and T ₂ , T _t (=T _1t ) and T _a (=T _1a ) are obtained from Equation (4) and Equation (5) described below.
From the obtained T _t (=T _1t ) and T _a (=T _1a ), the single transmittance T _s of the polarizing plate can be calculated using equation (14). As shown in equation (14), the single transmittance T _s of the polarizing plate is the value (Y value) obtained by multiplying the visibility curve function by the integral value of the visibility curve function, and the visibility curve function L is the CIE1931 visibility curve function defined by the International Commission on Illumination (CIE).
The above T _p , T _c , T ₁ and T ₂ can be measured using, for example, an optical material inspection device RETS-100 manufactured by Otsuka Electronics, or a spectral radiance meter CS-2000 manufactured by Konica Minolta, and the measurement wavelength The bands are, for example, 400 to 800 nm and 380 to 780 nm.

In the circularly polarizing plate of the present invention, it is preferable that the average transmittance of the fast axis of the λ/4 retardation plate is in the range of 70 to 95%, and the average transmittance of the slow axis of the λ/4 retardation plate is in the range of 70 to 95%. It is preferable that there be. When the fast axis transmittance and the slow axis transmittance are within the above ranges, the performance as a circularly polarizing plate tends to be ensured. From the above viewpoint, it is more preferable that the average transmittance of the fast axis is in the range of 80 to 90%, and it is even more preferable that the average transmittance of the slow axis is in the range of 80 to 90%.

The average transmittance of the fast axis and the average transmittance of the slow axis of the λ/4 retardation plate can be calculated as follows.
First, the polarizer is rotated using a combination of a polarizer and a λ/4 retardation plate, and the transmittance at which the transmittance becomes maximum and minimum is measured, and these are defined as T _p and T _c , respectively. Furthermore, the transmittances measured only with the polarizer at the angles at which the transmittance is maximum and minimum are defined as T ₂ and T ₁ , respectively. The angle at which the transmittance is maximized by rotating the polarizer in a combination of a polarizer and a λ/4 retardation plate is the angle at which either the maximum or minimum transmittance is determined in advance for the λ/4 retardation plate. The angle at which the transmittance is minimum when rotating the polarizer with the combination of the polarizer and the λ/4 retardation plate is the angle at which the transmittance is maximum or minimum. The other angle is the predetermined fast axis or slow axis of the λ/4 phase difference plate. From the obtained T _p , T _c , T ₁ and T ₂ , the fast axis transmittance T _fast and the slow axis transmittance of the λ/4 retardation plate can be calculated using equations (6) and (7) described later. The rate T _slow can be calculated. The average transmittance of the fast axis of a λ/4 retardation plate is the average transmittance of the entire measured wavelength range, and is calculated by dividing the value obtained by multiplying T _fast by the visibility curve function by the integral value of the visibility curve function. This is the value (Y value). The average transmittance of the slow axis of a λ/4 retardation plate is the average transmittance of the entire measured wavelength range, and is calculated by dividing the value obtained by multiplying T _slow by the visibility curve function by the integral value of the visibility curve function. This is the value (Y value).
The T _p , T _c , T ₁ and T ₂ can be measured using, for example, an optical material inspection device RETS-100 manufactured by Otsuka Electronics Co., Ltd., and the measurement wavelength band is, for example, 400 to 800 nm.

Further, the retardation of the λ/4 retardation plate at a wavelength of 550 nm is preferably in the range of 125 to 150 nm, more preferably in the range of 130 to 145 nm, and more preferably in the range of 135 to 140 nm. More preferred.

In the circularly polarizing plate of the present invention, even when a polarizing plate with a low degree of polarization is used, an excellent circularly polarizing plate can be provided by determining the lamination angle so as to satisfy the above formula (1). can. Specifically, the polarization degree of the polarizing plate in the present invention must be 99.8% or less, and a polarizing plate with 99.5% or less can be used, and even 99.0% or less. It is also possible to use a polarizing plate. The lower limit of the degree of polarization is preferably 96% or more, more preferably 97% or more.

The degree of polarization P _e of the polarizing plate can be calculated as follows.
In a combination of a polarizer and a polarizing plate, rotate the polarizer and measure the transmittance at which the transmittance is maximum and minimum, and when T _p and T _c are respectively, formula (4) and formula (5) described below are used. From this, the transmittances T _t (=T _1t ) and T _a (=T _1a ) of the fast axis and slow axis of the polarizing plate are determined.
The degree of polarization P _e of the polarizing plate can be calculated from T _t (=T _1t ) and T _a (=T _1a ) using equation (13). As shown in equation (13), the polarization degree P _e of the polarizing plate is the value (Y value) obtained by dividing the value multiplied by the visibility curve function by the integral value of the visibility curve function, and the visibility curve function L is This is a CIE1931 visibility curve function defined by the International Commission on Illumination (CIE).
The T _p and T _c can be measured using, for example, an optical material inspection device RETS-100 manufactured by Otsuka Electronics, or a spectral radiance meter CS-2000 manufactured by Konica Minolta, and the measurement wavelength band is, for example, 400 nm. ~800nm, 380~780nm.

Specific examples of the polarizing plate include an iodine-based stretched polarizing plate, a dye-based stretched polarizing plate, a coated polarizing plate, a wire grid polarizing plate, and the like. Examples of polarizing plates with a low degree of polarization include iodine-based stretched polarizing plates and dye-based stretched polarizing plates with low stretching ratios, dye-based stretched polarizing plates using dichroic dyes with low dichroic ratios, and coated polarizing plates. It will be done. The coated polarizing plate will be explained below.

(Coating type polarizing plate)
A coated polarizing plate is a polarizing plate produced by applying a material to a base material. Specifically, it is preferable to apply a polarizing film-forming composition described below on a base film.

(Composition for forming polarizing film)
It is preferable that the composition for forming a polarizing film contains a dye. The dye is a substance or compound that absorbs at least a portion of wavelengths in the visible light region, and dichroic dyes are preferably mentioned. Here, the dichroic dye refers to a dye that has a property that the absorbance in the long axis direction of the molecule is different from the absorbance in the short axis direction.
It is preferable that the composition for forming a polarizing film contains a polymerizable liquid crystal compound together with a dye. By polymerizing a polymerizable liquid crystal compound, a coating type polarizing film having film strength can be formed.
The composition for forming a polarizing film may be in a solution, liquid crystal, or dispersed state as long as it does not cause phase separation, but from the viewpoint that it can be easily applied to the base film. Therefore, a solution is preferable. Further, the solid component of the polarizing film-forming composition excluding the solvent is preferably in a liquid crystal phase state at any temperature from the viewpoint of orientation in the base film.
The degree of polarization of the coated polarizing plate produced in this way is usually about 97 to 99.5%.

Examples of the base film include triacetate, acrylic, polyester, polyimide, polyetherimide, polyetheretherketone, polycarbonate, cycloolefin polymer, polyolefin, polyvinyl chloride, triacetylcellulose, or urethane-based films.
In order to control the orientation direction of the dye, the surface of the base film is coated with a known method (rubbing method) described in "Liquid Crystal Handbook" (Maruzen Co., Ltd., published October 30, 2000), pages 226 to 239. , a method of forming grooves (fine groove structure) on the surface of an alignment film, a method of using polarized ultraviolet light/polarized laser (photoalignment method), an alignment method by forming an LB film, an alignment method by oblique vapor deposition of an inorganic material, etc.) , an alignment treatment (alignment film) may be applied. Particularly preferred are alignment treatments using a rubbing method and a photoalignment method.

[Optical film]
Since the circularly polarizing plate of the present invention has excellent polarizing performance, it is most suitable for optical films such as polarizing films.

[Image display device]
The circularly polarizing plate and optical film of the present invention have excellent polarization performance, and can be used in mobile information terminals, personal computers, televisions, projectors, signage, electronic desktop calculators, electronic watches, word processors, wearable displays, foldable displays, electronic paper, etc. It can be suitably used for image display devices such as game consoles, videos, cameras, photo albums, thermometers, audio, and instruments for automobiles and machinery. Specifically, it can be used as a reflection reduction layer for organic EL display type images. It can be suitably used for display devices.
In addition to the above, it is also preferably used for optical communication equipment, medical equipment, building materials, toys, etc.

The process of deriving the above equation (1) will be explained below.

Assuming that the polarizer, which is a Glan-Thompson prism, and the analyzer of the retardation film/optical material inspection device (Otsuka Electronics Co., Ltd. "RETS-100") have the same polarization characteristics, the orthogonal position Tc (polarizer 0 degree /analyzer 90 degrees), parallel position Tp (polarizer 90 degrees/analyzer 90 degrees), polarizer 0 degrees (T ₁ ), and polarizer 90 degrees (T ₂ ), the transmittance was measured (Figure 1 ).
Next, the respective transmittances with wavelength dispersion are T _c (orthogonal position = polarizer 0 degrees), T _p (parallel position = polarizer 90 degrees), T ₁ (polarizer 0 degrees), T ₂ (polarizer 90 degrees), the transmittance in the transmission axis direction (T _t-prism ) and the transmittance in the absorption axis direction (T _a-prism ) of the Glan-Thompson prism are expressed by the following equations (2) and (3), respectively. The transmittance of each wavelength was determined for each wavelength of 1 nm from 400 to 800 nm.

Using a retardation film/optical material inspection device (“RETS-100” manufactured by Otsuka Electronics Co., Ltd.), align the axis using only the polarizer and measure the transmittance of the following polarizing plate samples and retardation plate samples. I did it.
Polarizing plate sample Pol-1; polyvinyl alcohol (PVA) iodine polarizing plate Polarizing plate sample Pol-2; coated polarizing plate, single transmittance T _s 43.4%, polarization degree P _e 97.1%
Retardation plate sample Ret-1; λ/4 retardation plate (“WP140HE” manufactured by Edmund Corporation)

For polarizing plate sample Pol-1, when the 0 degree direction of the polarizing plate sample is the transmission axis, the orthogonal position (polarizer 0 degrees/polarizing plate 90 degrees), parallel position (polarizer 90 degrees/polarizing plate 90 degrees) , the transmittance of the polarizer at 0 degrees and the polarizer at 90 degrees was measured (FIG. 2). When the respective transmittances with wavelength dispersion are T _c (orthogonal position), T _p (parallel position), T ₁ (polarizer 0 degrees), and T ₂ (polarizer 90 degrees), polarizing plate sample Pol-1 The transmittance in the transmission axis direction (T _t ) and the transmittance in the absorption axis direction (T _a ) are calculated using the following equations (4) and (5), respectively, for wavelengths of 400 to 800 nm, and the transmittance of each wavelength is calculated every 1 nm. The transmittance was determined.

Regarding the retardation plate sample Ret-1, when the 0 degree direction of the retardation plate sample Ret-1 is the fast axis, the orthogonal position (polarizer 0 degrees/retardation plate 90 degrees), parallel position (polarizer 90 degrees), The transmittance of the polarizer was measured (FIG. 3). When the respective transmittances with wavelength dispersion are T _c (orthogonal position), T _p (parallel position), T ₁ (polarizer 0 degrees), and T ₂ (polarizer 90 degrees), the retardation plate sample Ret- The transmittance in the fast axis direction (T _fast ) and the transmittance in the slow axis direction (T _slow ) of 1 are calculated every 1 nm for wavelengths of 400 to 800 nm using the following equations (6) and (7), respectively. The transmittance of each wavelength was determined.

Using a spectral radiance meter (“CS-2000” manufactured by Konica Minolta), the polarizer and analyzer were measured at orthogonal positions (polarizer 0 The transmittance of the polarizer was measured at 0 degrees and 90 degrees of the polarizer (FIG. 4). When the respective transmittances with wavelength dispersion are T _c (orthogonal position), T _p (parallel position), T ₁ (polarizer 0 degrees), and T ₂ (polarizer 90 degrees), it is a PVA iodine polarizing plate. The transmittance in the fast axis direction (T _t-PVA ) and the transmittance in the slow axis direction (T _a-PVA ) of polarizing plate sample Pol-1 are calculated using the following equations (8) and (9), respectively. The transmittance of each wavelength was determined for every 1 nm from 400 to 800 nm.
FIG. 5 shows a conceptual diagram showing a measurement method using a spectral radiance meter.

Using a spectral radiance meter (Konica Minolta "CS-2000"), axis alignment was performed using only a polarizer, and polarizing plate sample Pol-2 (single transmittance T _s 43.4%, polarization degree P The transmittance of the polarizing plate _(e 97.1%) was measured. The optical system configuration of the spectral radiance meter CS-2000 manufactured by Konica Minolta was the same as that of the retardation film/optical material inspection device RETS-100 manufactured by Otsuka Electronics. When the 0 degree direction of polarizing plate sample Pol-2 is taken as the transmission axis, orthogonal position (polarizer 0 degree/polarizing plate 90 degree), parallel position (polarizer 90 degree/polarizing plate 90 degree), polarizer 0 degree, and The transmittance of the polarizer at 90 degrees was measured (Figure 6). When the respective transmittances with wavelength dispersion are T _c (orthogonal position), T _p (parallel position), T ₁ (polarizer 0 degrees), and T ₂ (polarizer 90 degrees), polarizing plate sample Pol-2 The transmittance (T _t ) in the transmission axis direction and the transmittance (T _a ) in the absorption axis direction are calculated using the following equations (10) and (11), respectively, for wavelengths from 380 to 780 nm, and are calculated for each wavelength by 1 nm. The transmittance was determined.

The retardation of the retardation plate sample Ret-1 was measured using a retardation film/optical material inspection device (“RETS-100” manufactured by Otsuka Electronics Co., Ltd.) (FIG. 7).
The retardation of an ideal λ/4 retardation plate is shown in FIG.
In addition, the reflectance of the Al deposited film was measured using a self-recording spectrophotometer (“U-4000” manufactured by Hitachi High-Tech Corporation) (FIG. 9).

Polarizing plate samples Pol-1 and Pol obtained using a retardation film/optical material inspection device (“RETS-100” manufactured by Otsuka Electronics) and a spectral radiance meter (“CS-2000” manufactured by Konica Minolta) -2 transmittance spectrum, transmittance spectrum and retardation spectrum of retardation plate sample Ret-1 obtained using a retardation film/optical material inspection device (“RETS-100” manufactured by Otsuka Electronics Co., Ltd.), and self-recorded From the reflectance of the Al deposited film (reflective film) obtained using a spectrophotometer (Hitachi High-Tech Corporation "U-4000"), light incident on the polarizing plate passes through the retardation plate and is reflected by the reflective film. We investigated the lamination angle between the polarizing plate and the retardation plate that would minimize the transmittance from the retardation plate through the polarizing plate (hereinafter referred to as "reflected transmittance"). The transmission axis transmittance and absorption axis transmittance of the polarizing plate are T _1t and T _1a respectively, the fast axis transmittance and slow axis transmittance of the retardation plate are T _fast and T _slow respectively, and the phase of the retardation plate is The phase angle that deviates from the phase difference λ/4 is Δδ, the reflectance of the reflective film is R, and as shown in Figure 10, the angle formed by the fast axis of the λ/4 retardation plate and the transmission axis of the polarizing plate is less than 90 degrees. When the angle of lamination θ (lamination angle) in the direction deviates from π/4 (lamination deviation angle) is Δθ, and the visibility curve function is L, the reflection transmittance is expressed by the following formula (12). .

At this time, the degree of polarization P _e and the single transmittance T _s are expressed by the following formulas (13) and (14), respectively.

In order to obtain an arbitrary polarization degree P _e-target and a single transmittance T _s-target from the transmittance measurement data (FIG. 6), the coefficients k _t and K _α of the following equations (15) and (16) are , was determined by numerical calculation using an Excel solver so that Δ in the following formula (17) was minimized.

By differentiating the above equation (12), the following equation (18) is obtained. By calculating the case where the differential equation (18) is approximately 0, it is possible to determine Δθ at which the reflection transmittance T _R takes the minimum value.

When Δθ≈0, approximating Δθ _min such that dT _R /dΔθ=0 results in the following equations (19) to (21). Δθ _min is the bonding deviation angle at which T _R is the minimum, and π/4+Δθ _min is the bonding angle θ.

In the circularly polarizing plate shown in FIG. 11, the transmission axis transmittance and absorption axis transmittance of the polarizing plate are T _1t and T _1a , respectively, and the fast axis transmittance and slow axis transmittance of the retardation plate are T _fast , respectively. T _slow is the phase angle at which the phase of the retardation plate deviates from the phase difference λ/4, Δδ, and as shown in Figure 10, the angle formed by the transmission axis of the polarizing plate from the fast axis of the λ/4 retardation plate is less than 90 degrees. When the angle θ (bonding angle) of laminating in the direction of The output vector (T _circularccw ) of the polarizing plate is expressed by the following equation (22).

Next, the present invention will be explained in more detail with reference to Examples. The process leading to the above equation (1) will be explained based on the actual measured values described in the examples.

[Reference example 1]
The transmittance of the polarizing plate sample Pol-1 (Figure 2), the transmittance (Figure 3) and phase difference of the retardation plate sample Ret-1 (Figure 7), and the reflectance of the Al deposited film (Figure 9) were measured. , the single transmittance T _s of the polarizing plate was 41.0%, and the polarization degree P _e was 99.9999%. A minimum reflection transmittance T _{R of} 0.456% was obtained by the quadratic approximation of equation (13), and a bonding deviation angle Δθ _min 0.191 degrees that resulted in the minimum reflection transmittance was obtained from equation (20). The average transmittance of the fast axis and slow axis of the retardation plate is 89.7% and 87.9%, respectively, the transmittance (Y value) is 89.8% and 88.6%, respectively, and the wavelength of the retardation plate The phase difference at 550 nm was 138.13 nm.

[Example 1]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. A single transmittance T _{s of} 43.4% and a polarization degree P _{e of} 97.1% were obtained. A minimum reflection transmittance T _{R of} 0.692% was obtained by the quadratic approximation of equation (13), and a bonding deviation angle Δθ _min -3.15 degrees that resulted in the minimum reflection transmittance was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 2]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.990 and the coefficient k _α is set to 0.168 so that the single transmittance T _s is 42.5% and the degree of polarization P _e is 99.5%, Equation (13) A minimum reflection transmittance T _R of 0.520% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −1.20 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 3]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.988 and the coefficient k _α is set to 0.336 so that the single transmittance T _s is 42.5% and the degree of polarization P _e is 99.0%, Equation (13) A minimum reflection transmittance T _R of 0.550% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −1.78 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 4]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.985 and the coefficient k _α is set to 0.505 so that the single transmittance T _s is 42.5% and the degree of polarization P _e is 98.5%, Equation (13) A minimum reflection transmittance T _R of 0.579% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −2.22 degrees, which resulted in the minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 5]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.983 and the coefficient k _α is set to 0.673 so that the single transmittance T _s is 42.5% and the degree of polarization P _e is 98.0%, Equation (13) A minimum reflection transmittance T _R of 0.609% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −2.59 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 6]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.981 and the coefficient K _α is set to 0.841 so that the single transmittance T _s is 42.5% and the degree of polarization P _e is 97.5%, Equation (13) A minimum reflection transmittance T _R of 0.638% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −2.92 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 7]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.979 and the coefficient k _α is set to 0.166 so that the single transmittance T _s is 42.0% and the degree of polarization P _e is 99.5%, Equation (13) A minimum reflection transmittance T _R of 0.508% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −1.20 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 8]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.976 and the coefficient k _α is set to 0.332 so that the single transmittance T _s is 42.0% and the degree of polarization P _e is 99.0%, Equation (13) A minimum reflection transmittance T _R of 0.537% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −1.78 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 9]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.974 and the coefficient k _α is set to 0.499 so that the single transmittance T _s is 42.0% and the degree of polarization P _e is 98.5%, Equation (13) A minimum reflection transmittance T _R of 0.566% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −2.22 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 10]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.971 and the coefficient k _α is set to 0.665 so that the single transmittance T _s is 42.0% and the degree of polarization P _e is 98.0%, Equation (13) A minimum reflection transmittance T _R of 0.594% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −2.59 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 11]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.969 and the coefficient K _α is set to 0.831 so that the single transmittance T _s is 42.0% and the degree of polarization P _e is 97.5%, Equation (13) A minimum reflection transmittance T _R of 0.623% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −2.92 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 12]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 1.002 and the coefficient k _α is set to 0.170 so that the single transmittance T _s is 43.0% and the degree of polarization P _e is 99.5%, Equation (13) A minimum reflection transmittance T _R of 0.533% was obtained by second-order approximation, and a lamination deviation angle Δθ _min −1.20 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 13]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 1.000 and the coefficient k _α is set to 0.340 so that the single transmittance T _s is 43.0% and the degree of polarization P _e is 99.0%, Equation (13) is obtained. A minimum reflection transmittance T _R of 0.563% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −1.78 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 14]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.997 and the coefficient k _α is set to 0.510 so that the single transmittance T _s is 43.0% and the degree of polarization P _e is 98.5%, Equation (13) A minimum reflection transmittance T _R of 0.593% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −2.22 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 15]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.995 and the coefficient k _α is set to 0.681 so that the single transmittance T _s is 43.0% and the degree of polarization P _e is 98.0%, Equation (13) A minimum reflection transmittance T _R of 0.623% was obtained by quadratic approximation, and a bonding deviation angle Δθ _min −2.59 degrees, which resulted in a minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 16]
The transmittance of the polarizing plate sample Pol-2 (Figure 6), the transmittance of the retardation plate sample Ret-1 (Figure 3) and phase difference (Figure 7), and the reflectance of the Al vapor deposited film (Figure 9) were measured. Based on the measurement results of the polarizing plate sample, when the coefficient k _t is set to 0.992 and the coefficient k _α is set to 0.851 so that the single transmittance T _s is 43.0% and the degree of polarization P _e is 97.5%, Equation (13) A minimum reflection transmittance T _R of 0.654% was obtained by second-order approximation, and a lamination deviation angle Δθ _min −2.92 degrees, which resulted in the minimum reflection transmittance, was obtained from equation (20). The average transmittance of the fast axis and the slow axis of the retardation plate, the transmittance (Y value), and the phase difference of the retardation plate at a wavelength of 550 nm are the same as in Reference Example 1.

[Example 17]
In Reference Example 1 and Examples 1 to 16, the relationship between the degree of polarization P _e and the bonding deviation angle Δθ _min at which equation (23) is the minimum is as shown in FIG _. It depends only on the degree of polarization _Pe , regardless of the relationship expressed by the following equation (23). The coefficient is a parameter of the characteristics of the retardation plate.

From the above formula (23), assuming actual implementation, π/4 + Δθ _min is the bonding angle θ, taking into account that the angle deviates by about ±0.5 degrees from the optimal value (bonding deviation angle Δθ _min ). Therefore, the unit of polarization degree P _e is set to %, and formula (1) is derived. That is, it was calculated to be larger than 45+3.08-0.5 and smaller than 45+3.08+0.5, and formula (1) was calculated to be larger than 47.58 and smaller than 48.58.

The circularly polarizing plate of the present invention reduces reflectance when used for antireflection applications because the optimal lamination angle can be determined based on the present invention even when a polarizing plate with a low degree of polarization is used. It is possible to do so. Therefore, the circularly polarizing plate of the present invention can be used in portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic clocks, word processors, wearable displays, foldable displays, electronic paper, game consoles, videos, cameras, and photos. It is extremely useful for image display devices such as albums, thermometers, audio equipment, and instruments for automobiles and machinery, and can be said to have high industrial applicability.

Claims (9)

In a circularly polarizing plate consisting of a polarizing plate and a λ/4 retardation plate, the degree of polarization Pe (%) of the polarizing plate is 99.8% or less, and the fast axis of the λ/4 retardation plate and the transmission axis of the polarizing plate are A circularly polarizing plate where θ satisfies formula (1) when θ (degrees) is in a direction in which the angle formed by the angle is less than 90 degrees.
The circularly polarizing plate according to claim 1, wherein the θ is in a range of 41 degrees to 44 degrees. The circularly polarizing plate according to claim 1 or 2, wherein the polarizing plate has a single transmittance of 41% or more. The average transmittance of the fast axis of the λ/4 retardation plate is in the range of 70 to 95%, and the average transmittance of the slow axis is in the range of 70 to 95%. Circularly polarizing plate. The circularly polarizing plate according to claim 1 or 2, wherein the retardation of the λ/4 retardation plate is in the range of 125 to 150 nm at a wavelength of 550 nm. The circularly polarizing plate according to claim 1 or 2, wherein the polarizing plate is a coated polarizing plate. An optical film comprising the circularly polarizing plate according to claim 1 or 2. An image display device comprising the circularly polarizing plate according to claim 1 or 2. An image display device comprising the optical film according to claim 7.