JP7691966B2 - Circularly polarizing plate, optical laminate and image display device - Google Patents

Description

The present invention relates to a circular polarizing plate, an optical laminate, and an image display device.

In display devices such as organic electroluminescence (EL) display devices, flexible displays are known that use flexible materials to enable bending of the display device. In organic EL display devices, it is known that anti-reflection performance is improved by using a circular polarizing plate or the like to suppress a decrease in visibility due to reflection of external light (for example, JP 2020-134934 A (Patent Document 1)). A circular polarizing plate can be obtained by laminating a linear polarizing plate and a retardation layer, and a cured layer of a polymerizable liquid crystal compound may be used as the retardation layer.

JP 2020-134934 A

The object of the present invention is to provide a circular polarizing plate having a new configuration, as well as an optical laminate and an image display device that include the same.

The present invention provides the following circularly polarizing plate, optical laminate, and image display device.
[1] A circular polarizing plate including a linear polarizing plate and a cured liquid crystal layer,
The linear polarizing plate includes a polarizer and a protective film laminated on only one surface of the polarizer,
The circularly polarizing plate comprises the polarizer, the protective film, and the cured liquid crystal layer arranged in this order.
[2] The circularly polarizing plate according to [1], further comprising a hard coat layer between the protective film and the liquid crystal cured layer.
[3] The circularly polarizing plate according to [1] or [2], wherein the polarizer has a boron content of 0.5% by mass or more and 5.5% by mass or less.
[4] The circularly polarizing plate according to any one of [1] to [3], wherein the protective film is a cyclic polyolefin resin film.
[5] The liquid crystal cured layer includes a first liquid crystal cured layer and a second liquid crystal cured layer,
The circularly polarizing plate according to any one of [1] to [4], wherein the polarizer, the protective film, the first liquid crystal cured layer, and the second liquid crystal cured layer are arranged in this order.
[6] The circularly polarizing plate according to any one of [1] to [5], wherein any layer other than the polarizer has light selective absorption properties.
[7] The circularly polarizing plate according to any one of [1] to [6], comprising the polarizer, the protective film, the cured liquid crystal layer, and a pressure-sensitive adhesive layer in this order.
[8] The circularly polarizing plate according to any one of [1] to [7],
A front panel or a touch sensor panel;
An optical laminate for a flexible image display device comprising:
[9] An image display device comprising the circularly polarizing plate according to any one of [1] to [7] or the optical laminate according to [8].

It is possible to provide a circular polarizing plate having a new configuration, as well as an optical laminate and an image display device that include the same.

FIG. 1 is a schematic cross-sectional view showing an example of a layer structure of a circularly polarizing plate according to the present invention. FIG. 4 is a schematic cross-sectional view showing another example of the layer structure of the circularly polarizing plate according to the present invention. FIG. 4 is a schematic cross-sectional view showing still another example of the layer structure of the circularly polarizing plate according to the present invention. FIG. 1 is a schematic cross-sectional view showing an example of a layer structure of an optical laminate according to the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the layer structure of the optical laminate according to the present invention. FIG. 2 is an explanatory diagram for explaining a microscopic Raman spectroscopic analysis of the polarizing plate according to the present invention.

The following describes an embodiment of the present invention with reference to the drawings, but the present invention is not limited to the following embodiment. All of the drawings are presented to aid in understanding the present invention, and the size and shape of each component shown in the drawings do not necessarily correspond to the size and shape of the actual component.

<Circular polarizing plate>
(1) Structure of the circular polarizer FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of the circular polarizer according to the present invention (hereinafter, also simply referred to as "circular polarizer"). The circular polarizer 1 shown in FIG. 1 includes a linear polarizer 10 and a retardation layer structure 20 which is a structure including a retardation layer. In the circular polarizer 1, the linear polarizer 10 and the retardation layer structure 20 are bonded to each other via a first bonding layer 30a. The retardation layer is a liquid crystal cured layer (a cured layer formed by polymerizing and curing a polymerizable liquid crystal compound). The term "circular polarizer" includes an elliptical polarizer.
In addition, it is preferable that the circular polarizer applied to the flexible image display device is bendable. By bendable, it is meant that the layer constituting the circular polarizer can be bent without causing cracks. Such a circular polarizer is required to be thinner in order to have good bending resistance (flexibility). Therefore, it is effective that the linear polarizer included in the circular polarizer is a so-called "one-sided protected polarizer" having a protective film only on one side of the polarizer.

Figure 2 is a schematic cross-sectional view showing another example of the layer structure of a circular polarizer, and shows a specific example of the layer structure of a linear polarizer 10 and a phase difference layer structure 20. In the circular polarizer 2 shown in Figure 2, the linear polarizer 10 and the phase difference layer structure 20 are also bonded to each other via a first bonding layer 30a. As shown in Figure 2, the linear polarizer 10 is a one-sided protected polarizer including a polarizer (linear polarizer) 101 and a protective film 102 laminated only on one side of the polarizer 101. The protective film 102 is laminated on the surface of the polarizer 101 facing the phase difference layer structure 20. Although not shown, the protective film 102 is bonded to the polarizer 101 via an adhesive layer. In the circular polarizer 2, the outermost surface on the linear polarizer 10 side is the surface of the polarizer 101.

In the circular polarizer 2, the polarizer 101, the protective film 102, and the retardation layer structure 20 are arranged in this order, that is, the polarizer 101, the protective film 102, and the liquid crystal hardened layer which is the retardation layer are arranged in this order. In the circular polarizer 2, the retardation layer structure 20 includes, in order from the linear polarizer 10 side, the first liquid crystal hardened layer 201, the second bonding layer 30b, and the second liquid crystal hardened layer 202. In order to bond the circular polarizer 2 to, for example, a display panel, the second liquid crystal hardened layer 202 may include a third bonding layer 30c and a separate film 203 on the opposite side to the second bonding layer 30b.

The layer structure of the circularly polarizing plate is not limited to the structure shown in FIG.
a) The circularly polarizing plate does not need to have either the first liquid crystal cured layer 201 or the second liquid crystal cured layer 202, and the retardation layer structure 20 only needs to have at least one liquid crystal cured layer (retardation layer).
b) It may comprise one or more alignment layers.
c) The second bonding layer 30b may not be provided.
d) A hard coat layer may be disposed between the protective film 102 and the first liquid crystal cured layer 201 (retardation layer structure 20).

Figure 3 is a schematic cross-sectional view showing yet another example of the layer structure of a circular polarizer, and shows a specific example of the layer structure of the linear polarizer 11 and the phase difference layer structure 20. In the circular polarizer 3 shown in Figure 3, the linear polarizer 11 and the phase difference layer structure 20 are also bonded to each other via the first bonding layer 30a. The circular polarizer 3 shown in Figure 3 has a configuration corresponding to d) above, and the linear polarizer 11 includes a polarizer (linear polarizer) 101, a protective film 102 laminated only on one side of the polarizer 101, and a hard coat layer 103 laminated on the surface of the protective film 102 on the phase difference layer structure 20 side. The protective film 102 is laminated on the surface of the polarizer 101 on the phase difference layer structure 20 side. Although not shown, the protective film 102 is bonded to the polarizer 101 via an adhesive layer. In the circular polarizer 3, the outermost surface on the linear polarizer 11 side is the surface of the polarizer 101. Similarly to the circular polarizer 2 shown in FIG. 2, the circular polarizer 3 shown in FIG. 3 may also include a third bonding layer 30c and a separate film 203.

When the circular polarizers 1, 2, and 3 are applied to an image display device such as an organic EL image display device, the circular polarizers 1, 2, and 3 are arranged so that the linear polarizers 10 and 11 side is the viewing side. In this case, as described above, the third bonding layer 30c can be used to bond the circular polarizers 1, 2, and 3 to the image display element (the separate film 203 is peeled off and removed). In other words, when the circular polarizers 1, 2, and 3 are applied to an image display device such as an organic EL image display device, the circular polarizers 1, 2, and 3 are arranged so that the retardation layer structure 20 side is the image display element side.

The circularly polarizing plate according to the present invention has the following advantages.
A) The adhesion between the protective film 102 of the linear polarizer 10 and the first bonding layer 30a or the adhesion between the hard coat layer 103 of the linear polarizer 11 and the first bonding layer 30a is high, and as a result, the durability of the circular polarizer is high. In particular, in a configuration in which the hard coat layer 103 and the first bonding layer 30a are in contact as in the circular polarizer 3 shown in Figure 3, good adhesion between these layers can be obtained even if the bonding surfaces are not subjected to corona treatment or the strength of the corona treatment is low.

When corona treatment is performed over a long period of time, there is a problem in that crystalline foreign matter (such as oxalic acid) adheres to the corona-treated material, resulting in reduced yields. It is also known that corona discharge generates ozone and nitrogen oxides (NOx). By being able to omit corona treatment or reduce the intensity of the corona treatment, the above problems can be eliminated or reduced.

B) When the polarizer 101 is a polyvinyl alcohol-based resin film in which iodine is adsorbed and oriented, the presence of the protective film 102 and further the hard coat layer 103 between the polarizer 101 and the image display element can suppress or prevent iodine from migrating from the polarizer 101 to the image display element, for example, even if the circular polarizer of the present invention is held in a humid and hot environment. This can suppress or prevent deterioration of the retardation layer structure 20, and when an input device such as a touch sensor panel is attached to the circular polarizer of the present invention, deterioration of the touch sensor panel or the like can be suppressed or prevented.

Hereinafter, elements that constitute or can constitute a circularly polarizing plate will be described in detail.
(2) Linear Polarizing Plate The linear polarizing plate includes a polarizer (linear polarizer) 101 and a protective film 102 laminated only on one side of the polarizer 101. The one side of the polarizer 101 is the surface of the polarizer 101 facing the retardation layer structure 20. The linear polarizing plate preferably includes the polarizer 101, the protective film 102 laminated only on one side of the polarizer 101, and a hard coat layer 103 laminated on the surface of the protective film 102 facing the retardation layer structure 20.

(2-1) Polarizer The polarizer 101 is an optical film that has the property of transmitting linearly polarized light having a vibration plane perpendicular to the absorption axis when unpolarized light is incident. The polarizer 101 is preferably a polyvinyl alcohol-based resin film (hereinafter also referred to as a "PVA-based film") in which iodine is adsorbed and oriented. Hereinafter, a PVA-based film in which iodine is adsorbed and oriented, which is a preferred polarizer 101, will be described.

The polarizer 101 may be, for example, a PVA-based film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene-vinyl acetate copolymer partially saponified film, which has been dyed with iodine and uniaxially stretched. Preferably, the PVA-based film in which iodine has been adsorbed and oriented by the dyeing process is treated with an aqueous boric acid solution, and then a washing process is carried out in which the aqueous boric acid solution is washed off. A known method can be used for each process.

Polyvinyl alcohol resins (hereinafter also referred to as "PVA resins") can be produced by saponifying polyvinyl acetate resins. Polyvinyl acetate resins can be copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.
In this specification, "(meth)acrylic" means either acrylic or methacrylic. The "(meth)" in (meth)acrylate has the same meaning.

The degree of saponification of the PVA-based resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The PVA-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can be used. The average degree of polymerization of the PVA-based resin is usually about 1000 to 10000, preferably about 1500 to 5000. The average degree of polymerization of the PVA-based resin can be determined in accordance with JIS K 6726 (1994). If the average degree of polymerization is less than 1000, it is difficult to obtain favorable polarizing performance, and if it exceeds 10000, the film processability may be poor.

The circular polarizing plate of the present invention is particularly suitable for application to flexible image display devices. The thickness of each member constituting a circular polarizing plate for application to such flexible image display devices is preferably thin. The thickness of the polarizer 101 is usually 30 μm or less, preferably 15 μm or less, more preferably 13 μm or less, and even more preferably 10 μm or less. The thickness of the polarizer 101 is usually 2 μm or more, preferably 3 μm or more, and may be, for example, 5 μm or more.

To obtain a polarizer 101 of a preferred thickness, a manufacturing method can be used in which a PVA-based film (thin film PVA-based film) having a thickness of about 15 to 40 μm is used as the starting material, and this thin film PVA film is dyed and uniaxially stretched to obtain polarizer 101. By using a thin PVA-based film in advance, the thickness of the resulting polarizer 101 can be made thin (first manufacturing method).

A thin PVA-based film, which is preferable as a starting material, can also be realized by forming a resin layer made of a PVA-based resin on a suitable base film to obtain a thin PVA-based film with an extremely thin thickness (second manufacturing method). In this case, the manufacturing method of the thin PVA film may include a process of preparing a base film, applying a solution of a resin such as a PVA-based resin (e.g., a PVA-based resin solution) onto the base film, and forming a resin layer on the base film by drying or the like to remove the solvent. A primer layer can be formed in advance on the surface of the base film on which the resin layer is to be formed. As the base film, a film using a thermoplastic resin that can be used for the protective film 102 described later can be used.

The thin PVA-based film, which is the starting material in the first or second manufacturing method, can be transformed into the polarizer 101 by dyeing and uniaxially stretching as described above. In the second manufacturing method, a PVA-based resin solution is applied onto a substrate film, and then the amount of solvent such as water in the resin layer is adjusted as necessary. Thereafter, the substrate film and the resin layer are uniaxially stretched, and the resin layer is then dyed with iodine to adsorb and align the iodine in the resin layer.

The PVA-based film that has been subjected to the dyeing process (iodine adsorption orientation) and uniaxial stretching process is then preferably subjected to a crosslinking process using boric acid. In the first manufacturing method, for example, after the thin PVA-based film is subjected to the dyeing process and uniaxial stretching process, the film may be brought into contact with a solution containing boric acid (boric acid-containing solution). A washing process may also be performed to wash off the boric acid-containing solution adhering to the surface of the film after such a crosslinking process.

The polarizer 101 obtained by the second manufacturing method is similar to the first manufacturing method. That is, the substrate film provided with the resin layer that has been subjected to the dyeing treatment and the uniaxial stretching treatment can be crosslinked by contacting it with a boric acid-containing solution as it is (without peeling off the substrate film). The substrate film provided with the resin layer after the crosslinking treatment can be washed as necessary.

The boric acid-containing solution for crosslinking the PVA-based film or resin layer in which iodine is adsorbed and oriented is preferably a boric acid-containing aqueous solution, and the amount of boric acid in the boric acid-containing aqueous solution is usually about 2 to 15 parts by mass, preferably about 5 to 12 parts by mass, per 100 parts by mass of water. This boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by mass, preferably about 5 to 12 parts by mass, per 100 parts by mass of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50°C or higher, preferably 50 to 85°C, and more preferably 60 to 80°C.

The uniaxial stretching of the PVA-based film, as well as the substrate film and resin layer, may be performed before dyeing, during dyeing, or during the boric acid treatment after dyeing, and uniaxial stretching may be performed at each of these multiple stages. The total stretching ratio is usually 3 times or more, preferably 3.5 times or more, and more preferably 4 times or more. There is no particular upper limit to the stretching ratio, but from the viewpoint of suppressing breakage, etc., it is preferably 8 times or less, and more preferably 6 times or less.

The polarizer 101 preferably has a boron content of 0.5% by mass or more, more preferably 1.5% by mass or more, even more preferably 2.5% by mass or more, and may be 3.5% by mass or more. By having a boron content of 0.5% by mass or more, iodine can be stably retained, and an effect of suppressing a decrease in the polarization degree of the polarizer 101 and, in turn, an effect of improving the durability of the circular polarizing plate can be expected. The boron content of the polarizer 101 is preferably 5.5% by mass or less, more preferably 5.0% by mass or less, and even more preferably 4.5% by mass or less. By having a boron content of 4.5% by mass or less, shrinkage of the polarizer 101 caused by heating can be suppressed.

The boron content in the polarizer 101 can be determined, for example, by dissolving a predetermined mass of the polarizer 101 in, for example, an aqueous mannitol solution and titrating it with an aqueous NaOH solution. The method for measuring the boron content in the polarizer 101 will be described in detail in the examples of this application.

The boron content of the polarizer 101 can be controlled by adjusting the boric acid concentration of the boric acid aqueous solution used in the boric acid treatment, or by the degree to which the boric acid aqueous solution is washed off in the cleaning process.

The "boric acid crosslinking index" of the polarizer 101 is preferably 0.5 or more, more preferably 0.8 or more, and even more preferably 1.0 or more. In this specification, the "boric acid crosslinking index" means an index that indicates the extent to which polyvinyl alcohol molecular chains are crosslinked with boric acid in a polarizer made of a polyvinyl alcohol resin film or the like. The higher the value of the boric acid crosslinking index, the more advanced the boric acid crosslinking between the polyvinyl alcohol molecular chains is in the polarizer, and the boric acid crosslinking index of the polarizer 101 in this range can stably retain iodine. As a result, it becomes easier to prevent the polarization degree of the polarizer 101 from decreasing, and thus the durability of the circular polarizing plate is easier to improve.

The boric acid crosslinking index of the polarizer 101 can be determined by performing microscopic Raman spectroscopy. In the microscopic Raman spectroscopy, a laser Raman spectrophotometer (product name: "NRS-5100", manufactured by JASCO Corporation) is used to determine the Raman scattered light intensity at a wavenumber of 780 cm ^-1 and the Raman scattered light intensity at a wavenumber of 850 cm ^-1 of the polarizer, and then the Raman scattered light intensities at these wavenumbers are divided (Raman scattered light intensity at wavenumber 780 cm ^-1 / Raman scattered light intensity at wavenumber 850 cm ^-1 ) to calculate the boric acid crosslinking index.

Here, FIG. 6 is an explanatory diagram for explaining the microscopic Raman spectroscopy analysis of the polarizing plate according to the present embodiment. As shown in FIG. 6, in the laser Raman spectrophotometer, the laser light is incident on the end face of the polarizer 101 so that the traveling direction of the laser light X and the absorption axis direction of the polarizer 101 are perpendicular to each other. Here, the laser light X is polarized in the thickness direction of the polarizer 101. The measurement position of the laser light is set to the center position in the thickness direction of the polarizer 101. It is preferable to perform cross-sectional processing of the polarizing plate using a microtome before the Raman spectroscopy measurement. The Raman scattered light intensity at a wave number of 780 cm ⁻¹ means the Raman scattered light intensity attributable to the bond between polyvinyl alcohol and boron, and the Raman scattered light intensity at a wave number of 850 cm ⁻¹ means the Raman scattered light intensity attributable to polyvinyl alcohol.

The various conditions used in the above-mentioned microscopic Raman spectroscopic analysis are as follows:
Excitation wavelength: 532 nm
Grating: 600 l/mm
Slit width: 100 x 1000 μm
Aperture: φ40 μm
Objective lens: 100x Objective lens: 100x

The luminosity-corrected polarization degree Py of the polarizer 101 is usually 95% or more, preferably 97% or more, more preferably 98% or more, even more preferably 98.7% or more, even more preferably 99.0% or more, particularly preferably 99.4% or more, and may be 99.9% or more. The luminosity-corrected polarization degree Py of the polarizer 101 may be 99.99% or less. The luminosity-corrected polarization degree Py can be calculated by performing luminosity correction on the obtained polarization degree using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation) with a 2-degree visual field (C light source) according to "JIS Z 8701".

Increasing the luminosity-corrected polarization degree Py of the polarizer 101 is advantageous in terms of improving the function of the circular polarizer as an anti-reflection film and the durability of the circular polarizer. If the luminosity-corrected polarization degree Py of the polarizer 101 is less than 95%, it may not function as an anti-reflection film.

The luminosity-corrected single transmittance Ty of the polarizer 101 is usually 41% or more, preferably 41.1% or more, more preferably 41.2% or more, and may be 42% or more, or may be 42.5% or more. The luminosity-corrected single transmittance Ty of the polarizer 101 is usually 50% or less, may be 48% or less, may be 46% or less, may be 44% or less, or may be 43% or less. If the luminosity-corrected single transmittance Ty is excessively high, the luminosity-corrected polarization degree Py becomes too low, and the circular polarizer may not be able to function as an anti-reflection film. The luminosity-corrected single transmittance Ty can be calculated by performing luminosity correction on the obtained transmittance using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation) using a 2-degree visual field (C light source) according to "JIS Z 8701".

(2-2) Protective Film The protective film 102 laminated on one side of the polarizer 101 is a film for protecting the polarizer, and may be, for example, a light-transmitting (preferably optically transparent) film made of a thermoplastic resin.

Thermoplastic resins include cellulose resins such as triacetyl cellulose; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyethersulfone resins; polysulfone resins; polycarbonate resins; polyamide resins such as nylon and aromatic polyamide; polyimide resins; polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers; cyclic polyolefin resins having cyclo- and norbornene structures (also called norbornene-based resins); (meth)acrylic resins; polyarylate resins; polystyrene resins; polyvinyl alcohol resins, and mixtures thereof.

The protective film 102 is preferably a cyclic polyolefin resin film, a polyethylene terephthalate film, or a polycarbonate film, and more preferably a cyclic polyolefin resin film.

It is preferable that the protective film 102 does not have a retardation characteristic or is a film with a small retardation value. Specifically, the in-plane retardation value of the protective film 102 at a wavelength of 550 nm is preferably 0 nm to 10 nm, and the retardation value in the thickness direction at a wavelength of 550 nm is preferably -10 nm to +10 nm. In the case where the circular polarizing plate of the present invention has a hard coat layer 103 like the circular polarizing plate 3, it is preferable that the laminate of the protective film 102 and the hard coat layer 103 is a film with a small retardation value as described above.

The thickness of the protective film 102 is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, and may be 10 μm or more. The thickness of the protective film 102 is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less.

The light transmittance of the protective film 102 for visible light is required to be normal in the technical field of polarizing plates. For example, the light transmittance for visible light is preferably 85% or more, and more preferably 90% or more. When the circular polarizing plate of the present invention has a hard coat layer 103 like the circular polarizing plate 3, it is preferable that the laminate of the protective film 102 and the hard coat layer 103 has the light transmittance as described above.

When the protective film 102 or the laminate of the protective film 102 and the hard coat layer 103 has a small phase difference value and a high light transmittance, the luminosity-corrected polarization degree Py and the luminosity-corrected single transmittance Ty of the polarizer 101 can be replaced with the luminosity-corrected polarization degree Py and the luminosity-corrected single transmittance Ty of the polarizer 101 and the polarizer 102 laminated together, or the polarizer 11 in which the polarizer 101, the protective film 102, and the hard coat layer 103 are laminated together.

The distance from the surface of the polarizer 101 facing the retardation layer structure 20 to the surface of the linear polarizing plate 10, 11 facing the retardation layer structure 20 is preferably 3 μm or more, more preferably 4 μm or more, even more preferably 5 μm or more, and even more preferably 10 μm or more, from the viewpoint of suppressing the migration of iodine. From the viewpoint of thinning and bending resistance (flexibility) of the circular polarizing plate, the distance is preferably 40 μm or less, more preferably 30 μm or less.

In the circular polarizing plate of the present invention, preferably, any layer other than the polarizer has photoselective absorption. One or more layers may have photoselective absorption. In the circular polarizing plate of the present invention, more preferably, the layer between the polarizer 101 and the retardation layer structure 20, typically the layer between the polarizer 101 and the liquid crystal cured layer 201 (protective film 102, hard coat layer 103, or first bonding layer 30a) has photoselective absorption. One or more layers may have photoselective absorption. In this specification, "having photoselective absorption" preferably means having absorption for ultraviolet light with a wavelength of 350 nm or the like, more preferably having absorption for ultraviolet light with a wavelength of 350 nm or the like and short-wavelength visible light with a wavelength of around 410 nm.

The protective film 102 having selective light absorption, preferably having absorption for ultraviolet light with a wavelength of 350 nm or the like, and more preferably having absorption for ultraviolet light with a wavelength of 350 nm or the like and short-wavelength visible light with a wavelength of around 410 nm, is advantageous in the following respects.
I) When the circularly polarizing plate is applied to an image display device, the image display element can be protected from ultraviolet rays and short-wavelength visible light.
II) It is possible to suppress a change in the retardation value of the retardation layer structure 20 caused by ultraviolet light or short-wavelength visible light.
III) The reflected hue of the circular polarizing plate can be adjusted by absorbing short-wavelength visible light.
IV) The polarizer 101 can be prevented from being deteriorated by light reflected by an image display element such as an organic EL display element.

The selective light absorption of the protective film 102 may be imparted by using a thermoplastic resin having selective light absorption properties as the thermoplastic resin constituting the protective film 102, or by incorporating an additive (light absorbent) having selective light absorption properties into the protective film 102, or by both. The selective light absorption of the protective film 102 is preferably imparted by at least incorporating a light absorbent into the protective film 102.

Specific examples of preferred light absorbents are given below. Among light absorbents, light absorbents for light with a wavelength of 350 nm (ultraviolet rays) and light absorbents for light with a wavelength of 410 nm are preferably used in the present invention from the viewpoint of the above-mentioned preferred selective light absorption.

As a light absorber for light with a wavelength of 350 nm, various ultraviolet absorbers are readily available on the market. Examples of such ultraviolet absorbers include organic ultraviolet absorbers such as oxybenzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, salicylic acid ester-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and triazine-based ultraviolet absorbers. More specifically, 5-chloro-2-(3,5-di-sec-butyl-2-hydroxylphenyl)-2H-benzotriazole, (2-2H-benzotriazol-2-yl)-6-(straight-chain and side-chain dodecyl)-4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, and 2,4-benzyloxybenzophenone are examples.

As the ultraviolet absorbent, commercially available products may be used as they are. Examples of such commercially available products include triazine-based ultraviolet absorbents such as "Kemisorb 102" manufactured by Chemipro Chemical Co., Ltd., "ADEKA STAB LA46" and "ADEKA STAB LAF70" manufactured by ADEKA Corporation, and "TINUVIN 109", "TINUVIN 171", "TINUVIN 234", "TINUVIN 326", "TINUVIN 327", "TINUVIN 328", "TINUVIN 928", "TINUVIN 400", "TINUVIN 460", "TINUVIN 405", and "TINUVIN 477" (all trade names) manufactured by BASF Japan Ltd. Benzotriazole-based ultraviolet absorbers include "Adeka STAB LA31" and "Adeka STAB LA36" (all trade names) manufactured by ADEKA CORPORATION, "Sumisorb 200", "Sumisorb 250", "Sumisorb 300", "Sumisorb 340" and "Sumisorb 350" (all trade names) manufactured by Sumika Chemtex Co., Ltd., "Kemisorb 74", "Kemisorb 79" and "Kemisorb 279" (all trade names) manufactured by Chemipro Chemical Co., Ltd., and "TINUVIN 99-2", "TINUVIN 900" and "TINUVIN 928" (all trade names) manufactured by BASF Corporation. Two or more types of ultraviolet absorbers may be used in combination in the circular polarizing plate of the present invention, and different light absorbers may be used in multiple layers constituting the circular polarizing plate of the present invention.

The ultraviolet absorber may be an inorganic ultraviolet absorber. Examples of inorganic ultraviolet absorbers include titanium oxide, zinc oxide, indium oxide, tin oxide, talc, kaolin, calcium carbonate, titanium oxide composite oxide, zinc oxide composite oxide, ITO (tin-doped indium oxide), ATO (antimony-doped tin oxide), and the like. Examples of titanium oxide composite oxides include zinc oxide doped with silica and alumina. Two or more of these inorganic ultraviolet absorbers may be used in combination, and may be used in combination with, for example, the commercially available light absorbers (organic ultraviolet absorbers) exemplified above.

As a light absorber for light with a wavelength of 410 nm, a compound having a maximum absorption wavelength in the wavelength band of 360 to 430 nm can be synthesized by a known method and used in the present invention. For example, a compound known as a selective light absorbing compound described in JP-A-2017-120430 can be used as such a light absorber. It is preferable to include a compound having at least one absorption maximum in the wavelength range of 360 nm to 420 nm, and more preferably to include a compound having an absorption maximum in the wavelength range of 380 nm to 410 nm.

The amount of light absorbing agent used is selected so as not to significantly impair the light transmittance of the layer containing the light absorbing agent with respect to visible light. For example, when the mass of the layer is taken as 100 parts by mass, the amount of light absorbing agent contained in the layer is usually 0.01 to 20 parts by mass, preferably 0.05 to 15 parts by mass, and more preferably 0.1 to 10 parts by mass.

In the circular polarizing plate of the present invention, the laminate (protective film 102, hard coat layer 103, and first bonding layer 30a) between the polarizer and the liquid crystal cured layer preferably has an absorbance of 0.5 or more, more preferably 1.0 or more, at a wavelength of 350 nm, and preferably has an absorbance of 0.2 or more, more preferably 0.5 or more, at a wavelength of 410 nm.

In another embodiment, in the circular polarizing plate of the present invention, the laminate of layers other than the polarizer (e.g., the laminate consisting of the protective film 102, the hard coat layer 103, the first bonding layer 30a, the first liquid crystal cured layer 201, the second bonding layer 30b, the second liquid crystal cured layer 202, and the third bonding layer 30c), i.e., the laminate of layers present on the protective film side when the polarizer is used as a reference, has an absorbance at a wavelength of 350 nm of preferably 0.3 or more, more preferably 0.5 or more, more preferably 1.0 or more, even more preferably 2.0 or more, and particularly preferably 3.0 or more. The absorbance at a wavelength of 410 nm is preferably 0.2 or more, more preferably 0.5 or more, even more preferably 0.7 or more, and may usually be 2.0 or less, or 1.5 or less.

The protective film 102 can be laminated to the polarizer 101 via an adhesive layer. The adhesive forming the adhesive layer can be a water-based adhesive or an active energy ray curable adhesive described later. Examples of water-based adhesives include adhesives in which a polyvinyl alcohol resin is dissolved or dispersed in water. The thickness of the adhesive layer between the protective film 102 and the polarizer 101 is usually 0.01 μm or more and usually 10 μm or less in order to ensure adhesion. As described above, when the circular polarizer of the present invention is applied to a flexible image display device, the thinner the thickness of each member constituting the circular polarizer, the more preferable it is. However, if the thickness of the adhesive layer becomes extremely thin, there is a risk that the desired adhesiveness will be impaired. Therefore, the thickness of the adhesive layer is optimized in consideration of the flexibility when the circular polarizer of the present invention is applied to a flexible image display device and the adhesiveness between the polarizer 101 and the protective film 102.

(2-3) Hard Coat Layer The circularly polarizing plate may further have a hard coat layer 103 between the protective film 102 and the liquid crystal cured layer (retardation layer structure 20). The hard coat layer 103 is preferably laminated on the surface of the protective film 102 on the retardation layer structure 20 side, and more preferably directly laminated on the surface.

The hard coat layer 103 can be formed by curing a hard coat composition containing a reactive material that forms a crosslinked structure by irradiation with active energy rays or thermal energy. The hard coat composition is preferably one that is cured by irradiation with active energy rays. In this specification, "active energy rays" include visible light, ultraviolet rays, infrared rays, X-rays, α rays, β rays, γ rays, electron beams, etc., and preferably ultraviolet rays.

The hard coat composition contains at least one polymer of a radically polymerizable compound and a cationic polymerizable compound. A radically polymerizable compound is a compound having a radically polymerizable group. The radically polymerizable group of the radically polymerizable compound may be any functional group capable of causing a radical polymerization reaction, and examples of such groups include groups containing a carbon-carbon unsaturated double bond. Specific examples of such groups include a vinyl group and a (meth)acryloyl group.

As the radical polymerizable compound, from the viewpoint of high reactivity, a compound having a (meth)acryloyl group is preferable, and a compound called a polyfunctional acrylate monomer having 2 to 6 (meth)acryloyl groups in one molecule, or an oligomer having a molecular weight of several hundred to several thousand and having several (meth)acryloyl groups in a molecule, called an epoxy (meth)acrylate, a urethane (meth)acrylate, or a polyester (meth)acrylate, can be preferably used. It is preferable to include one or more types selected from epoxy (meth)acrylate, urethane (meth)acrylate, and polyester (meth)acrylate.

A cationically polymerizable compound is a compound having a cationically polymerizable group such as an epoxy group, an oxetanyl group, or a vinyl ether group. As the cationically polymerizable compound, a compound having at least one of an epoxy group and an oxetanyl group as the cationically polymerizable group is preferable.

Examples of cationic polymerizable compounds having epoxy groups include alicyclic epoxy resins obtained by epoxidizing polyglycidyl ethers of polyhydric alcohols having alicyclic rings or compounds containing cyclohexene rings or cyclopentene rings with a suitable oxidizing agent such as hydrogen peroxide or peracid; aliphatic epoxy resins such as polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts, polyglycidyl esters of aliphatic long-chain polybasic acids, and homopolymers and copolymers of glycidyl (meth)acrylate; glycidyl ethers and novolac epoxy resins produced by reacting bisphenols such as bisphenols A, bisphenol F, and hydrogenated bisphenol A, or derivatives thereof such as alkylene oxide adducts or caprolactone adducts, with epichlorohydrin, and glycidyl ether-type epoxy resins derived from bisphenols.

The hard coat composition may further contain a polymerization initiator. Examples of the polymerization initiator include radical polymerization initiators, cationic polymerization initiators, and combinations thereof. These polymerization initiators are decomposed by at least one of active energy ray irradiation and heating to generate radicals or cations, thereby promoting radical polymerization and cationic polymerization.

Active energy ray radical polymerization initiators include Type 1 radical polymerization initiators that generate radicals by molecular decomposition, and Type 2 radical polymerization initiators that coexist with tertiary amines to generate radicals by hydrogen abstraction reaction, and can be used alone or in combination. Thermal radical polymerization initiators include hydrogen peroxide, organic peroxides such as perbenzoic acid, and azo compounds such as azobisbutyronitrile. Cationic polymerization initiators include aromatic iodonium salts, aromatic sulfonium salts, cyclopentadienyl iron (II) complexes, etc.

The content of the polymerization initiator is, for example, 0.1 to 10% by mass relative to the total amount (100% by mass) of the hard coat composition. If the content of the polymerization initiator is less than 0.1% by mass, curing cannot proceed sufficiently, and the mechanical properties and adhesion of the finally obtained hard coat layer 103 may be insufficient.

The hard coat composition may further contain a solvent, additives, etc. Examples of additives include inorganic particles, leveling agents, stabilizers, surfactants, antistatic agents, lubricants, and antifouling agents.

The thickness of the hard coat layer 103 is preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 3 μm or more, and may be 5 μm or more, from the viewpoint of suppressing scratches that may occur during transportation of the circular polarizing plate of the present invention or during processing of the circular polarizing plate. The thickness of the hard coat layer 103 is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less, from the viewpoint of bending resistance (flexibility) and production efficiency.

The hard coat layer 103 may have light selective absorption. At least one of the protective film 102 and the hard coat layer 103 preferably has light selective absorption, and both may have light selective absorption. The advantages of the hard coat layer 103 having light selective absorption are the same as those of the protective film 102 having light selective absorption. The light selective absorption can be imparted to the hard coat layer 103 by incorporating the above-mentioned light absorbing agent into the hard coat layer 103.

A protective film 102 (protective film with a hard coat layer) having a hard coat layer 103 containing a light absorbing agent can be purchased from the market, and the protective film with a hard coat layer can be used as it is as a component of the circular polarizing plate of the present invention. Similarly, a protective film 102 that does not have a hard coat layer 103 but contains a light absorbing agent can also be obtained. The content of the light absorbing agent contained in such a protective film or protective film with a hard coat layer may be unknown, but in that case, the optimal one can be selected taking into consideration the light transmittance of the protective film or protective film with a hard coat layer to visible light.

(3) Retardation Layer Structure The retardation layer structure 20 is a structure including at least one liquid crystal cured layer (a cured layer obtained by polymerizing and curing a polymerizable liquid crystal compound). As shown in Fig. 2 and Fig. 3, the retardation layer structure 20 preferably includes a first liquid crystal cured layer 201 and a second liquid crystal cured layer 202, and the circular polarizing plate preferably includes a polarizer 101, a protective film 102, a first liquid crystal cured layer 201, and a second liquid crystal cured layer 202 in this order from the viewing side.

The liquid crystal cured layer is a layer (retardation layer) having retardation properties, and is a cured layer in which a polymerizable liquid crystal compound is polymerized and cured in an aligned state to exhibit retardation properties. The retardation layer structure 20 includes at least one liquid crystal cured layer, and may include two or more liquid crystal cured layers. When including two or more liquid crystal cured layers, the retardation layer structure 20 may include a bonding layer (second bonding layer 30b) for bonding these liquid crystal cured layers to each other.

The liquid crystal cured layer can be a 1/2 wavelength retardation layer, a 1/4 wavelength retardation layer, or a positive C plate. The 1/4 wavelength retardation layer may have reverse wavelength dispersion. When the retardation layer structure 20 includes two or more liquid crystal cured layers, the liquid crystal cured layers may have the same retardation characteristics or different retardation characteristics.

As described above, the retardation layer structure 20 preferably includes a first liquid crystal cured layer 201 and a second liquid crystal cured layer 202. The first liquid crystal cured layer 201 and the second liquid crystal cured layer 202 are, for example, a 1/2 wavelength retardation layer and a 1/4 wavelength retardation layer, respectively. Alternatively, one of the first liquid crystal cured layer 201 and the second liquid crystal cured layer 202 is a 1/4 wavelength retardation layer with reverse wavelength dispersion, and the other is a positive C plate. For example, the first liquid crystal cured layer 201 and the second liquid crystal cured layer 202 are a 1/4 wavelength retardation layer with reverse wavelength dispersion, and a positive C plate, respectively.

The polymerizable liquid crystal compound may be a rod-shaped polymerizable liquid crystal compound or a disk-shaped polymerizable liquid crystal compound. Either one of these may be used, or a mixture containing both may be used. When the rod-shaped polymerizable liquid crystal compound is aligned horizontally or vertically to the base layer, the optical axis of the polymerizable liquid crystal compound coincides with the long axis direction of the polymerizable liquid crystal compound. When the disk-shaped polymerizable liquid crystal compound is aligned, the optical axis of the polymerizable liquid crystal compound is in a direction perpendicular to the disk surface of the polymerizable liquid crystal compound. As the rod-shaped polymerizable liquid crystal compound, for example, those described in JP-T-11-513019 (claim 1, etc.) can be suitably used. As the disk-shaped polymerizable liquid crystal compound, those described in JP-A-2007-108732 (paragraphs [0020] to [0067], etc.) and JP-A-2010-244038 (paragraphs [0013] to [0108], etc.) can be suitably used.

In order for the liquid crystal cured layer formed by polymerizing the polymerizable liquid crystal compound to exhibit an in-plane retardation, the polymerizable liquid crystal compound may be aligned in an appropriate direction. When the polymerizable liquid crystal compound is rod-shaped, the in-plane retardation is exhibited by aligning the optical axis of the polymerizable liquid crystal compound horizontally to the plane of the base layer, in which case the optical axis direction and the slow axis direction coincide. When the polymerizable liquid crystal compound is disc-shaped, the in-plane retardation is exhibited by aligning the optical axis of the polymerizable liquid crystal compound horizontally to the plane of the base layer, in which case the optical axis and the slow axis are perpendicular to each other. The alignment state of the polymerizable liquid crystal compound can be adjusted by the combination of the alignment layer and the polymerizable liquid crystal compound.

A polymerizable liquid crystal compound is a compound having at least one polymerizable group and liquid crystal properties. When two or more types of polymerizable liquid crystal compounds are used in combination, it is preferable that at least one type has two or more polymerizable groups in the molecule. The polymerizable group means a group that participates in a polymerization reaction, and is preferably a photopolymerizable group. Here, the photopolymerizable group means a group that can participate in a polymerization reaction by an active radical or acid generated from a photopolymerization initiator described later. Examples of the polymerizable group include a vinyl group, a vinyloxy group, a 1-chlorovinyl group, an isopropenyl group, a 4-vinylphenyl group, an acryloyloxy group, a methacryloyloxy group, an oxiranyl group, an oxetanyl group, a styryl group, and an allyl group. Among them, an acryloyloxy group, a methacryloyloxy group, a vinyloxy group, an oxiranyl group, and an oxetanyl group are preferable, and an acryloyloxy group is more preferable. The liquid crystallinity of the polymerizable liquid crystal compound may be thermotropic or lyotropic liquid crystal, and when thermotropic liquid crystals are classified according to the degree of order, they may be nematic or smectic liquid crystals.

The retardation layer structure 20 may include an alignment layer. The alignment layer has an alignment regulating force that aligns the polymerizable liquid crystal compound in a desired direction. The alignment layer may be a vertical alignment layer in which the molecular axis of the polymerizable liquid crystal compound is aligned vertically to the substrate layer, a horizontal alignment layer in which the molecular axis of the polymerizable liquid crystal compound is aligned horizontally to the substrate layer, or an inclined alignment layer in which the molecular axis of the polymerizable liquid crystal compound is aligned at an incline to the substrate layer. When the retardation layer structure 20 includes two or more alignment layers, the alignment layers may be the same as each other or different from each other.

As the alignment layer, it is preferable that the layer has a solvent resistance that does not dissolve the liquid crystal layer-forming composition containing the polymerizable liquid crystal compound when applied, and has heat resistance against the heat treatment for removing the solvent and for orienting the polymerizable liquid crystal compound. Examples of the alignment layer include an alignment polymer layer formed from an alignment polymer, a photoalignment polymer layer formed from a photoalignment polymer, and a groove alignment layer having a concave-convex pattern or multiple grooves on the layer surface.

The thickness of the liquid crystal cured layer (first and second liquid crystal cured layers) may be 0.1 μm or more, 0.5 μm or more, 1 μm or more, or 2 μm or more, and is preferably 10 μm or less, and may be 8 μm or less, or 5 μm or less.

The liquid crystal cured layer can be formed by applying a liquid crystal layer forming composition containing a polymerizable liquid crystal compound onto a substrate layer, drying the composition, and polymerizing the polymerizable liquid crystal compound. The liquid crystal layer forming composition may be applied onto an alignment layer formed on the substrate layer.

The substrate layer may be a film made of a resin material, such as a film made of the resin material described above as the thermoplastic resin used to form the protective film 102. The thickness of the substrate layer is not particularly limited, but is generally preferably 1 to 300 μm, more preferably 20 to 200 μm, in terms of workability such as strength and ease of handling. The substrate layer may be incorporated into the circular polarizer together with the cured liquid crystal layer, or the substrate layer may be peeled off and only the cured liquid crystal layer, or the cured liquid crystal layer and the orientation layer, may be incorporated into the circular polarizer.

The second attachment layer 30b is a pressure-sensitive adhesive layer or an adhesive layer. The second attachment layer 30b is preferably an adhesive layer, more preferably an adhesive layer formed by curing an active energy ray-curable adhesive, and even more preferably an adhesive layer formed by curing an ultraviolet ray-curable adhesive. By making the second attachment layer 30b an adhesive layer, it is possible to suppress the occurrence of wrinkles in the liquid crystal cured layer when the circular polarizer is bent or folded, which is preferable. As the pressure-sensitive adhesive layer, the one described below can be used.

Examples of active energy ray-curable adhesives include solvent-free active energy ray-curable adhesives that contain a curable compound that cures when irradiated with active energy rays.

The active energy ray curable adhesive preferably contains either one or both of a cationic polymerizable curable compound and a radically polymerizable curable compound, since these exhibit good adhesive properties. The active energy ray curable adhesive may further contain a cationic polymerization initiator, such as a photocationic polymerization initiator, for initiating the curing reaction of the curable compound, or a radical polymerization initiator.

Examples of cationic polymerizable curable compounds include epoxy-based compounds such as alicyclic epoxy compounds having an epoxy group bonded to an alicyclic ring, polyfunctional aliphatic epoxy compounds having two or more epoxy groups and no aromatic ring, monofunctional epoxy compounds having one epoxy group (excluding those included in alicyclic epoxy compounds), polyfunctional aromatic epoxy compounds having two or more epoxy groups and an aromatic ring; oxetane compounds having one or more oxetane rings in the molecule; and combinations of these.

Examples of radically polymerizable curable compounds include (meth)acrylic compounds (compounds having one or more (meth)acryloyloxy groups in the molecule), other vinyl compounds having radically polymerizable double bonds, or combinations of these.

The thickness of the second bonding layer 30b is not particularly limited. For example, it may be 2 μm or more and 30 μm or less, and preferably 3 μm or more and 20 μm or less. For example, it may be 10 μm or more, but in terms of further thinning, it is preferably 15 μm or less, preferably 10 μm or less, and especially 7 μm or less. When the second bonding layer 30b is an adhesive layer, the thickness is preferably 0.1 μm or more, may be 0.5 μm or more, and is preferably 10 μm or less, and may be 5 μm or less.

(4) First and third bonding layers The first bonding layer 30a is an adhesive layer or a bonding agent layer, and is preferably an adhesive layer. The first bonding layer 30a bonds the linear polarizers 10 and 11 to the retardation layer structure 20. The third bonding layer 30c is usually an adhesive layer. The third bonding layer 30c can be used to bond the circular polarizer to an image display element. The circular polarizer preferably includes a polarizer 101, a protective film 102, a liquid crystal cured layer (first liquid crystal cured layer, and further a second liquid crystal cured layer), and an adhesive layer (third bonding layer 30c) in this order, and more preferably includes a polarizer 101, a protective film 102, a hard coat layer 103, a liquid crystal cured layer (first liquid crystal cured layer, and further a second liquid crystal cured layer), and an adhesive layer (third bonding layer 30c) in this order.

The thickness of the pressure-sensitive adhesive layer that is the first attachment layer 30a may be, for example, 2 μm or more and 30 μm or less, and preferably 3 μm or more and 20 μm or less. For example, it may be 10 μm or more, but in terms of further thinning, it is preferably 15 μm or less, preferably 10 μm or less, and especially 7 μm or less. When the first attachment layer 30a is an adhesive layer, the thickness is preferably 0.1 μm or more, may be 0.5 μm or more, and is preferably 10 μm or less, and may be 5 μm or less.

The first bonding layer 30a may have light selective absorption. It is preferable that at least one of the protective film 102, the hard coat layer 103, and the first bonding layer 30a has light selective absorption, and more than one of these layers may have light selective absorption. The advantages of the first bonding layer 3aa having light selective absorption are the same as those of the protective film 102 having light selective absorption. The first bonding layer 30a can be given light selective absorption by incorporating the above-mentioned light absorbing agent into the first bonding layer 30a.

The thickness of the adhesive layer which is the third bonding layer 30c is not particularly limited and can be set appropriately depending on the application, but may be, for example, 250 μm or less, and from the viewpoint of thinning, is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, particularly preferably 30 μm or less, and even more particularly preferably 20 μm or less. The lower limit of the thickness of the adhesive layer is not particularly limited, but from the viewpoint of durability, it may be, for example, 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 14 μm or more.

As the adhesive, a conventionally known adhesive having excellent optical transparency can be used, for example, an adhesive having a base polymer such as a (meth)acrylic, urethane, silicone, or polyvinyl ether type. In addition, an active energy ray curable adhesive, a heat curable adhesive, etc. may be used. Among these, an adhesive having a base polymer of a (meth)acrylic resin that is excellent in transparency, adhesive strength, removability (hereinafter also referred to as reworkability), weather resistance, heat resistance, etc. is preferable. The adhesive layer is preferably composed of a reaction product of an adhesive containing a (meth)acrylic resin, a crosslinking agent, and a silane compound, and may contain other components.

The adhesive layer may be formed using an active energy ray curable adhesive. The active energy ray curable adhesive is prepared by blending an ultraviolet-curable compound such as a multifunctional (meth)acrylate with the above-mentioned adhesive, forming an adhesive layer, and then curing the adhesive layer by irradiating it with ultraviolet light, thereby forming a harder adhesive layer. The active energy ray curable adhesive has the property of being cured by irradiation with energy rays such as ultraviolet rays and electron beams. The active energy ray curable adhesive has adhesiveness even before irradiation with energy rays, and therefore is an adhesive that has the property of adhering to the adherend and curing by irradiation with energy rays to adjust the adhesion.

Active energy ray-curable adhesives generally contain a (meth)acrylic adhesive and an energy ray-polymerizable compound as the main components. Usually, a crosslinking agent is also blended, and if necessary, a photopolymerization initiator, photosensitizer, etc. can also be blended.

(5) Separate Film The circularly polarizing plate can include a separate film 203 for protecting the outer surface of the third bonding layer 30c. The separate film 203 can be a film in which a release treatment such as silicone treatment has been applied to the surface of the base film on the side of the third bonding layer 30c. The base film is, for example, a film made of a polyethylene-based resin such as polyethylene, a polypropylene-based resin such as polypropylene, or a polyester-based resin such as polyethylene terephthalate.

<Optical laminate>
The optical laminate according to the present invention (hereinafter, also simply referred to as "optical laminate") includes the above-mentioned circular polarizer according to the present invention and other components. Examples of the other components include an image display element 40 (see Figs. 4 and 5) arranged on the liquid crystal cured layer side of the circular polarizer, i.e., on the opposite side of the circular polarizer from the viewing side; a front plate 50 (see Fig. 5) arranged on the polarizer 101 side of the circular polarizer, more specifically, on the surface of the polarizer 101, which is the outermost surface of the circular polarizer; and a protective film (also called a "surface protective film") for temporarily protecting the surface of the polarizer 101.
The optical laminate preferably includes, as the other components, one or more members selected from the group consisting of a front plate 50 and an image display element 40 .

<Image display device>
The circular polarizers 1, 2, and 3 are disposed on the front surface (viewing side) of an image display element and can be used as components of an image display device. The circular polarizer can also be used as an anti-reflection polarizer that imparts an anti-reflection function to an image display device. The image display device is not particularly limited, and examples thereof include image display devices such as organic electroluminescence (organic EL) display devices, inorganic electroluminescence (inorganic EL) display devices, liquid crystal display devices, and electroluminescence display devices. Hereinafter, the main parts of the embodiment in which the circular polarizers (circular polarizers 1, 2, and 3) of the present invention are applied to an image display device, particularly a flexible image display device, will be briefly described.

The image display device may be a flexible image display device. The flexible image display device is composed of an optical laminate for a flexible image display device, which will be described later, and an organic EL display element, and the optical laminate for a flexible image display device is disposed on the viewing side of the organic EL display element and is configured to be foldable.

<Optical laminate for flexible image display device>
The optical laminate for flexible image display devices comprises the circular polarizing plate of the present invention and an organic EL display element, which is an image display element having bending resistance. The optical laminate for flexible image display devices also has a front plate having bending resistance. In addition, a touch sensor panel may be provided as an input means. In this case, the stacking order of the circular polarizing plate, the front plate, and the touch sensor panel may be, for example, from the viewing side, the front plate, the circular polarizing plate, and the touch sensor panel. The stacking order is preferably the front plate, the touch sensor panel, and the circular polarizing plate. If the circular polarizing plate is present on the viewing side of the touch sensor panel, the wiring pattern of the touch sensor panel is less visible, which is preferable because it improves the visibility of the displayed image. Each member can be stacked using an adhesive, a pressure-sensitive adhesive, or the like. The optical laminate for flexible image display devices can also be provided with a light-shielding pattern formed on at least one surface of any one of the layers of the front plate, the polarizing plate, and the touch sensor panel.

<Front plate>
In the image display device, a front plate can be disposed on the viewing side of the circular polarizing plate. The front plate can usually be laminated to the polarizer 101 of the circular polarizing plate of the present invention via a pressure-sensitive adhesive layer or an adhesive layer.

The front panel may be made of glass or a resin film, and may include a hard coat layer on at least one surface of the glass. For example, highly transparent glass or tempered glass may be used as the glass. When using a particularly thin transparent surface material, chemically strengthened glass is preferred. The thickness of the glass may be, for example, 100 μm to 5 mm.

When the circular polarizing plate of the present invention is applied to a flexible image display device, the front plate used is required to be flexible (flexible properties). From this point of view, the front plate is preferably made of a resin film, and as described above, may include a hard coat layer on at least one surface thereof. A front plate made of a resin film and including a hard coat layer is not rigid like existing glass, and can have flexible properties. In this case, the thickness of the hard coat layer is not particularly limited as long as it is within a range that does not impair the flexible properties, and may be, for example, 5 to 100 μm.

The resin film used as the front panel may be made of the same materials as those exemplified as the material of the protective film 102. Of course, even if two or more materials are used, it is sufficient as long as the film has a practical light transmittance. The thickness, etc. of such a resin film can be optimized in consideration of light transmittance, flexibility, durability, etc. As the front panel, a film that does not have a phase difference characteristic (unstretched film) is preferable, but a uniaxially or biaxially stretched film may be used as long as the phase difference value is acceptable. Among them, the resin film used for the front panel is preferably a polyamideimide film or polyimide film with excellent transparency and heat resistance, a uniaxially or biaxially stretched polyester film, a cycloolefin derivative film that is excellent in transparency and heat resistance and can accommodate large-sized films, a polymethyl methacrylate film, and a triacetyl cellulose and isobutyl ester cellulose film that are not transparent and optically anisotropic. In this case, the thickness of the resin film may be 5 to 200 μm, preferably 20 to 100 μm.

<Light-shielding pattern>
The light-shielding pattern is disposed in a part of the periphery of the image display surface of the image display device, called a bezel, for example, for the reason that the wiring is not visible when a viewer views an image from the image display surface side. Such a light-shielding pattern is formed on at least one surface of either the front plate or the circular polarizing plate constituting the optical laminate for an image display device. When a touch sensor panel is attached as an input means to the optical laminate for an image display device, the light-shielding pattern may be provided on the touch sensor panel. As described above, the light-shielding pattern can hide each wiring of the display device so that it is not visible to the user. The color and material of the light-shielding pattern are not particularly limited, and the light-shielding pattern can be formed of a resin material having various colors such as black, white, and gold. In one embodiment, the thickness of the light-shielding pattern may be 2 μm to 50 μm, preferably 4 μm to 30 μm, and more preferably 6 μm to 15 μm. In addition, a shape can be imparted to the light-shielding pattern in order to suppress the inclusion of air bubbles and the visibility of the boundary due to the step between the light-shielding pattern and the display part.

<Touch sensor panel>
The image display device having the circular polarizer of the present invention may further include a touch sensor as an input means, and in this case, it can be realized by incorporating a touch sensor panel. Various types of touch sensor have been proposed, such as a resistive film type, a surface acoustic wave type, an infrared type, an electromagnetic induction type, and a capacitance type, and any type may be used. Among them, the capacitance type is preferable. The capacitance type touch sensor is divided into an active area and a non-active area located on the outer periphery of the active area. The active area is an area corresponding to an area (display area) where a screen is displayed on the display panel, and is an area where a user's touch is sensed, and the non-active area is an area corresponding to an area (non-display area) where a screen is not displayed on the display device. The touch sensor panel may include a substrate having a flexible characteristic; a sensing pattern formed in the active area of the substrate; and each sensing line formed in the non-active area of the substrate for connecting to an external driving circuit via the sensing pattern and a pad part. The substrate having a flexible characteristic may be made of the same material as the transparent substrate of the front plate 50. The substrate of the touch sensor panel preferably has a toughness of 2,000 MPa% or more from the viewpoint of suppressing cracks that may occur in the touch sensor panel. More preferably, the toughness is 2,000 MPa% to 30,000 MPa%. Here, toughness is defined as the area under the curve up to the breaking point in a stress (MPa)-strain (%) curve obtained through a tensile test of a polymer material.

The fourth adhesive layer 30d shown in FIG. 5 is an attachment layer for attaching the front plate 50 to the polarizer 101, which is the top layer of the circular polarizer. For the fourth adhesive layer 30d, the description of the adhesive layer described above is cited.

The optical laminate (including the case of an optical laminate for a flexible image display device) can include a protective film for temporarily protecting the surface of the polarizer 101. The protective film is composed of a base film and an adhesive layer laminated thereon. The above description of the adhesive layer is cited. The resin constituting the base film can be, for example, a thermoplastic resin such as a polyethylene-based resin such as polyethylene, a polypropylene-based resin such as polypropylene, a polyester-based resin such as polyethylene terephthalate or polyethylene naphthalate, or a polycarbonate-based resin. A polyester-based resin such as polyethylene terephthalate is preferable.

The optical laminate (including the case where it is an optical laminate for a flexible image display device) and the circular polarizing plate according to the present invention can be suitably applied to image displays, particularly organic EL image displays.

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

<Measurement and evaluation methods>
(1) Measurement of boron content in polarizer 0.2 g of polarizer was dissolved in 200 g of 1.9 mass% mannitol aqueous solution. The obtained aqueous solution was titrated with 1 mol/L NaOH aqueous solution, and the boron content (mass%) of the polarizer was calculated by comparing the amount of NaOH solution required for neutralization with the calibration curve. The results are shown in Table 1.

(2) Calculation of boric acid cross-linking index The cross-section of the polarizing plate was processed using an ultramicrotome (manufactured by LEICA, product name "LEICA Ultramicrotome EM UC7i"). For the central position in the thickness direction of the polarizer on the cross-section of the obtained polarizing plate, the Raman scattered light intensity at a wave number of 780 cm ^-1 and the Raman scattered light intensity at a wave number of 850 cm ^-1 were measured using a laser Raman spectrophotometer (product name: "NRS-5100", manufactured by JASCO Corporation) under the following conditions, and then the Raman scattered light intensities at these wave numbers were divided (Raman scattered light intensity at wave number 780 cm ^-1 / Raman scattered light intensity at wave number 850 cm ^-1 ) to calculate the boric acid cross-linking index. The results are shown in Table 1.
Excitation wavelength: 532 nm
Grating: 600 l/mm
Slit width: 100 x 1000 μm
Aperture: φ40 μm
Objective lens: 100x Objective lens: 100x

(3) Measurement of Moisture Permeability of Peelable Film The moisture permeability was measured based on JIS Z 0208. The temperature and humidity conditions were a temperature of 40° C. and a relative humidity of 90% RH.

(4) Measurement of single transmittance and luminosity-corrected polarization degree The single transmittance and luminosity-corrected polarization degree of the circular polarizer were measured by making linearly polarized light from a prism incident on the polarizer side of the circular polarizer using a spectrophotometer with an integrating sphere (V7100, manufactured by JASCO Corporation). The MD transmittance and TD transmittance were obtained in the wavelength range of 380 nm to 780 nm, and the single transmittance and polarization degree at each wavelength were calculated based on formulas (A) and (B). Furthermore, luminosity correction was performed using a 2-degree visual field (C light source) according to JIS Z8701 to obtain the luminosity-corrected polarization degree (Py). The "MD transmittance" is the transmittance when the direction of the polarized light coming out of the Glan-Thompson prism is parallel to the transmission axis of the polarizer sample. In formulas (A) and (B), the "MD transmittance" is represented as "MD". In addition, the "TD transmittance" is the transmittance when the direction of the polarized light exiting the Glan-Thompson prism is perpendicular to the transmission axis of the polarizing plate sample, and in formulas (A) and (B), the "TD transmittance" is represented as "TD."
Single-piece transmittance (%) = (MD + TD) / 2 Formula (A)
Degree of polarization (%) = {(MD-TD)/(MD+TD)}×100 Formula (B)

(5) Heat resistance test of circularly polarizing plate The circularly polarizing plate obtained in the example was cut into a rectangle having a size of 140 mm x 70 mm. At this time, the cut was made so that the absorption axis of the polarizer and the short side of the rectangle were parallel to each other. The cut circularly polarizing plate was attached to an alkali-free glass (manufactured by Corning, product number: EAGLE XG (registered trademark)) having a thickness of 0.7 mm via an adhesive layer (2) to prepare an evaluation sample. A heat resistance test was performed in which the evaluation sample was stored for 500 hours under dry conditions at a temperature of 85 ° C., and the evaluation sample after the test was visually observed. The results were classified according to the following criteria and summarized in Table 1.

[Heat resistance test evaluation criteria]
A: No changes in appearance such as lifting, peeling, or foaming were observed.
B: Changes in appearance such as lifting, peeling, and foaming are somewhat noticeable.
C: Significant changes in appearance such as lifting, peeling, and bubbling are observed.

(6) Wet heat durability test of circularly polarizing plate The circularly polarizing plate obtained in the example was cut into a square having a size of 30 mm x 30 mm. At this time, it was cut so that the absorption axis of the polarizer and the side of the square were parallel. The cut circularly polarizing plate was attached to a 40 mm x 40 mm alkali-free glass (manufactured by Corning, product number: EAGLE XG (registered trademark)) via an adhesive layer (2), and further attached to a 40 mm x 40 mm alkali-free glass (manufactured by Corning, product number: EAGLE XG (registered trademark)) on the polarizer surface via an adhesive layer to prepare an evaluation sample. The luminous efficiency corrected polarization degree Py was measured for this evaluation sample.

Next, a moist heat durability test was conducted in which the evaluation samples were stored for 500 hours under conditions of a temperature of 60°C and a relative humidity of 95% RH, and the luminosity-corrected polarization degree Py was measured for the evaluation samples after the test. The measured values of the luminosity-corrected polarization degree Py before and after the test, and the absolute value of the difference between them, ΔPy, are shown in Table 1.

(7) Weather resistance test of circularly polarizing plate The circularly polarizing plate obtained in the example was cut into a square of 30 mm x 30 mm. At this time, the cutting was performed so that the absorption axis of the polarizer and the side of the square were parallel to each other. The cut circularly polarizing plate was attached to a 40 mm x 40 mm non-alkali glass (manufactured by Corning, product number: EAGLE XG (registered trademark)) via an adhesive layer (2) to prepare an evaluation sample. The 450 nm single transmittance of this evaluation sample was measured.

Next, the evaluation sample was placed on an aluminum plate (reflector) so that it was irradiated with ultraviolet light from the polarizer 101 side, and placed in a Sunshine Weather Meter (manufactured by Suga Test Instruments Co., Ltd.) for 120 hours under conditions of a black panel temperature of 63°C and a relative humidity of 50%, to conduct a weather resistance test. After the test, the evaluation sample was measured for its 450 nm single transmittance. The absolute value of the difference in the measured values of the 450 nm single transmittance before and after the test is listed in Table 1.

(8) Absorbance Measurement of Laminate A laminate was prepared by laminating the protective film 102, the hard coat layer 103, the first bonding layer 30a, the first liquid crystal cured layer 201, the second bonding layer 30b, the second liquid crystal cured layer 202, and the third bonding layer 30c, excluding the polarizer 101. In addition, in the layer configuration without the hard coat layer, the hard coat layer 103 was not laminated. The laminate was laminated to glass via the third bonding layer 30c. After laminating a pressure-sensitive adhesive layer to a cycloolefin polymer (COP) film (ZF-14 manufactured by Zeon Corporation), the COP film was laminated to the protective film 102 via the pressure-sensitive adhesive layer. In this manner, a laminate for evaluation was prepared.

The evaluation laminate was placed in a UV-2450 spectrophotometer (Shimadzu Corporation), and the absorbance was measured in the wavelength range of 300 to 800 nm in 1 nm steps using the double beam method. The absorbance of the laminate at wavelengths of 350 nm and 410 nm is shown in Table 1. The combined absorbance of the glass and the adhesive-attached COP film at wavelengths of 350 nm and 410 nm was 0.06 or less and can be ignored.

<Preparation of components of circular polarizing plate>
(1) Preparation of Polarizer 1 A polyvinyl alcohol film having a thickness of 20 μm, a degree of polymerization of 2,400, and a degree of saponification of 99% or more was uniaxially stretched to a draw ratio of 4.1 times on a heated roll, and while maintaining the tension, was immersed in a dye bath containing 0.05 part by mass of iodine and 5 parts by mass of potassium iodide per 100 parts by mass of water at 28° C. for 60 seconds.

Then, it was immersed in boric acid aqueous solution 1 containing 5.5 parts by mass of boric acid and 15 parts by mass of potassium iodide per 100 parts by mass of water at 64°C for 110 seconds. Then, it was immersed in boric acid aqueous solution 2 containing 5.5 parts by mass of boric acid and 15 parts by mass of potassium iodide per 100 parts by mass of water at 67°C for 30 seconds. After that, it was washed with pure water at 10°C and dried to obtain polarizer 1. Polarizer 1 had a thickness of 8 μm and a boron content of 4.3% by mass.

(2) Preparation of Polarizer 2 A polyvinyl alcohol film having a thickness of 20 μm, a degree of polymerization of 2,400, and a degree of saponification of 99% or more was uniaxially stretched to a stretching ratio of 4.1 times on a heated roll, and while maintaining the tension, was immersed in a dye bath containing 0.05 part by mass of iodine and 5 parts by mass of potassium iodide per 100 parts by mass of water at 28° C. for 60 seconds.

Then, it was immersed in boric acid aqueous solution 1 containing 5.5 parts by mass of boric acid and 15 parts by mass of potassium iodide per 100 parts by mass of water at 64°C for 110 seconds. Then, it was immersed in boric acid aqueous solution 2 containing 2.3 parts by mass of boric acid and 15 parts by mass of potassium iodide per 100 parts by mass of water at 67°C for 30 seconds. After that, it was washed with pure water at 10°C and dried to obtain polarizer 2. Polarizer 2 had a thickness of 8 μm and a boron content of 3.2 mass%.

(3) Preparation of Protective Films A, B, C, D, E and Peelable Film F The following five types of protective films and one type of peelable film were prepared.
Protective film A: a cycloolefin film (COP-HC) with a hard coat layer having a thickness of 27 μm. The hard coat layer had a thickness of 2 μm and a moisture permeability of 10 g/m ² ·24 hr. It has ultraviolet absorbing properties.
Protective film B: a cycloolefin film (COP) having a thickness of 25 μm. The moisture permeability was 12 g/m ² ·24 hr. It has ultraviolet absorbing properties.
Protective film C: COP having a thickness of 23 μm. Does not absorb ultraviolet light.
Protective film D: COP having a thickness of 13 μm. Has ultraviolet absorbing properties.
Protective film E: COP-HC having a thickness of 27 μm. It has ultraviolet absorption properties and also has absorption properties for short-wavelength visible light around 410 nm.
Peelable film F: TD80UL. A triacetyl cellulose film manufactured by Fujifilm Corporation. The thickness was 80 μm and the moisture permeability was 502 g/m ² ·24 hr.

(4) Preparation of Linear Polarizing Plate 1 Protective film A was attached to one surface of the prepared polarizer 1 via a water-based adhesive, and peelable film F was attached to the opposite surface of protective film A via pure water using a roll laminator, and then dried for 3 minutes at 80° C. Thereafter, peelable film F was peeled off from the polarizer to obtain linear polarizing plate 1 in which a protective film was laminated only on one surface of polarizer 1. Linear polarizing plate 1 was prepared by laminating polarizer 1, adhesive layer, and protective film A in this order.

(5) Preparation of Linear Polarizing Plate 2 Linear polarizing plate 2 was prepared in the same manner as in polarizing linear plate 1, except that the temperature of the drying treatment after lamination using a roll laminator was changed to 100°C.

(6) Preparation of Linear Polarizing Plate 3 Linear polarizing plate 3 was prepared in the same manner as linear polarizing plate 1, except that polarizer 1 was changed to polarizer 2.

(7) Preparation of Linear Polarizing Plate 4 Linear polarizing plate 4 was prepared in the same manner as linear polarizing plate 2, except that polarizer 1 was changed to polarizer 2.

(8) Preparation of Linear Polarizing Plate 5 Linear polarizing plate 5 was prepared in the same manner as in Linear Polarizing Plate 1, except that Protective Film A was changed to Protective Film B.

(9) Preparation of Linear Polarizing Plate 6 Linear polarizing plate 6 was prepared in the same manner as in Linear Polarizing Plate 1, except that Protective Film A was changed to Protective Film C.

(10) Preparation of Linear Polarizing Plate 7 Linear polarizing plate 7 was prepared in the same manner as in Linear Polarizing Plate 1, except that protective film A was changed to protective film D.

(11) Preparation of Linear Polarizing Plate 8 Linear polarizing plate 8 was prepared in the same manner as in Linear Polarizing Plate 1, except that Protective Film A was changed to Protective Film E.

(12) First Liquid Crystal Cured Layer A (Preparation of 1/2 Wavelength Retardation Layer)
A composition for forming an alignment layer was applied onto a substrate layer formed of a transparent resin, and dried to perform λ/2 alignment treatment. Next, a composition for forming a liquid crystal layer containing a discotic polymerizable liquid crystal compound was applied onto the alignment layer, and the alignment of the polymerizable liquid crystal compound was fixed by heating and UV irradiation, thereby forming a 1/2 wavelength retardation layer as a liquid crystal cured layer having a thickness of 2 μm on the alignment layer of the substrate layer.

(13) Second Liquid Crystal Cured Layer A (Preparation of 1/4 Wavelength Retardation Layer)
A liquid crystal layer-forming composition containing a rod-shaped nematic polymerizable liquid crystal compound (liquid crystal monomer) was applied to a rubbed alignment layer on a base layer formed of a transparent resin, and solidified while maintaining the refractive index anisotropy, thereby forming a quarter-wave retardation layer as a liquid crystal cured layer having a thickness of 1 μm on the alignment layer of the base layer.

(14) Preparation of active energy ray-curable adhesive A The components listed below were blended and mixed, and then degassed to prepare active energy ray-curable adhesive A.
[Cationically polymerizable compound]
Neopentyl glycol diglycidyl ether (product name: EX-211L, manufactured by Nagase ChemteX Corporation): 30 parts by mass; 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane (product name: OXT-221, manufactured by Toagosei Co., Ltd.): 13 parts by mass; Bisphenol A type epoxy resin (product name: EP-4100E, manufactured by ADEKA Corporation, viscosity 13 Pa·s (temperature 25°C)): 12 parts by mass; Aromatic-containing oxetane compound (product name: TCM-104, manufactured by TRONLY): 45 parts by mass [Photocationic polymerization initiator]
CPI-100P, manufactured by San-Apro Co., Ltd., 50% propylene carbonate solution: 2.25 parts by mass (solid content)
[Photosensitizer assistant]
1,4-diethoxynaphthalene: 1 part by mass

(15) Preparation of retardation layer structure A with substrate layer The surface of the first liquid crystal cured layer A (1/2 wavelength retardation layer) on the substrate layer and the surface of the second liquid crystal cured layer A (1/4 wavelength retardation layer) on the substrate layer were each subjected to corona treatment. The corona-treated surfaces of the two retardation layers were bonded together using the active energy ray curable adhesive A prepared above so that the angle between the slow axes of these two retardation layers was 60°. Thereafter, the active energy ray curable adhesive A was cured by irradiating ultraviolet light from the 1/4 wavelength retardation layer side with an ultraviolet irradiation device [manufactured by Fusion UV Systems Co., Ltd.] at an integrated light amount of 400 mJ/cm ² (UV-B) to form an adhesive layer. The bonding was performed using a laminator, and the active energy ray curable adhesive A was applied so that the thickness of the adhesive layer after curing was 3 μm. As a result, a retardation layer structure A with a substrate layer was obtained in which the substrate layer, the alignment layer, the 1/2 wavelength retardation layer (first liquid crystal cured layer), the adhesive layer (second bonding layer), the 1/4 wavelength retardation layer (second liquid crystal cured layer), the alignment layer, and the substrate layer were laminated in this order. The total thickness of the 1/2 wavelength retardation layer (first liquid crystal cured layer), the adhesive layer (second bonding layer), and the 1/4 wavelength retardation layer (second liquid crystal cured layer) was 6 μm.

(16) Preparation of the first liquid crystal cured layer B (1/4 wavelength retardation layer) An alignment layer was formed on a base layer formed of a transparent resin, and a liquid crystal layer forming composition containing a rod-shaped nematic polymerizable liquid crystal compound was applied to prepare the first liquid crystal cured layer B. The first liquid crystal cured layer B had a 1/4 wavelength retardation characteristic. The thickness of the first liquid crystal cured layer B was 2 μm.

(17) Preparation of the second liquid crystal cured layer B (positive C layer) 10.0 parts by weight of polyethylene glycol di(meth)acrylate, 10.0 parts by weight of trimethylolpropane triacrylate, 10.0 parts by weight of 1,6-hexanediol di(meth)acrylate, and 1.50 parts by weight of Irgacure 907 as a photopolymerization initiator were dissolved in 70.0 parts by weight of methyl ethyl ketone as a solvent to prepare a composition for forming an alignment layer. Then, 20.0 parts by weight of a photopolymerizable nematic liquid crystal compound and 1.0 part by weight of Irgacure 907 as a photopolymerization initiator were dissolved in 80.0 parts by weight of propylene glycol monomethyl ether acetate as a solvent to prepare a composition for forming a liquid crystal layer.

One side of the base layer was subjected to a corona treatment. The composition for forming the alignment layer prepared above was applied to the corona-treated surface using a bar coater. The applied layer was heat-treated at 80°C for 60 seconds, and then irradiated with ultraviolet light to polymerize and harden the composition for forming the alignment layer. In this way, an alignment layer having a thickness of 2.2 μm was formed on the base layer. The composition for forming the liquid crystal layer prepared above was applied on the alignment layer. The applied layer was heat-treated at 80°C for 60 seconds, and then irradiated with ultraviolet light to polymerize and harden the composition for forming the liquid crystal layer. In this way, a second liquid crystal cured layer B having a thickness of 0.7 μm was formed on the alignment layer. The second liquid crystal cured layer B was a positive C layer.

(18) Preparation of Active Energy Ray-Curable Adhesive B The components shown below were mixed to prepare an active energy ray-curable adhesive B.
3',4'-Epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (product name: CEL2021P, manufactured by Daicel Corporation): 70 parts by mass Neopentyl glycol diglycidyl ether (product name: EX-211, manufactured by Nagase ChemteX Corporation): 20 parts by mass 2-Ethylhexyl glycidyl ether (product name: EX-121, manufactured by Nagase ChemteX Corporation): 10 parts by mass Cationic polymerization initiator (product name: CPI-100, 50% solution, manufactured by San-Apro Co., Ltd.): 4.5 parts by mass (actual solid content 2.25 parts by mass)
1,4-diethoxynaphthalene: 2.0 parts by mass

(19) Preparation of retardation layer structure B with substrate layer The first liquid crystal cured layer B and the second liquid crystal cured layer B were bonded together with an active energy ray curable adhesive B (thickness 1 μm) so that the liquid crystal cured layer surface (the surface opposite to the substrate film) of each layer was bonded. The active energy ray curable adhesive B was cured by irradiating ultraviolet rays to obtain a retardation layer structure B with a substrate layer in which the substrate layer, the alignment layer, the first liquid crystal cured layer B, the adhesive layer (second bonding layer), the second liquid crystal cured layer B, the alignment layer, and the substrate layer were laminated in this order. The thickness of the retardation laminate including the first liquid crystal cured layer B, the adhesive layer (second bonding layer), and the second liquid crystal cured layer B was 6 μm. The retardation layer structure B with a substrate layer has ultraviolet ray absorbing properties.

(20) Preparation of Adhesive Layer The following adhesive layers were prepared.
Adhesive layer (1A): acrylic adhesive layer having a thickness of 5 μm Adhesive layer (1B): acrylic adhesive layer having a thickness of 5 μm Absorbs visible light having a short wavelength of about 410 nm.
Adhesive layer (2): Adhesive layer having a thickness of 15 μm

<Preparation of Circularly Polarizing Plate>
Example 1
The 1/2 wavelength retardation layer exposed by peeling off the substrate layer and the alignment layer on the 1/2 wavelength retardation layer side of the retardation layer structure A with the substrate layer prepared above and the protective film A side (surface of the hard coat layer) of the linear polarizer 1 prepared above were laminated using the adhesive layer (1A) which is the first lamination layer. The lamination of the 1/2 wavelength retardation layer and the linear polarizer 1 was performed so that the angle between the slow axis of the 1/2 wavelength retardation layer and the transmission axis of the polarizer 1 was 15°. Next, the alignment layer and the substrate layer on the 1/4 wavelength retardation layer side were peeled off and the adhesive layer (2) was laminated to the 1/4 wavelength retardation layer exposed to obtain a circular polarizer (1). Each lamination surface was subjected to a corona treatment.

Example 2
A circularly polarizing plate (2) was obtained in the same manner as in Example 1, except that no corona treatment was performed on the bonding surface of the protective film A of the linear polarizing plate 1 (the surface of the hard coat layer) and the bonding surface of the pressure-sensitive adhesive layer (1A).

Example 3
A circularly polarizing plate (3) was obtained in the same manner as in Example 1, except that the linearly polarizing plate 2 was used instead of the linearly polarizing plate 1.

Example 4
A circularly polarizing plate (4) was obtained in the same manner as in Example 1, except that the linearly polarizing plate 3 was used instead of the linearly polarizing plate 1.

Example 5
A circularly polarizing plate (5) was obtained in the same manner as in Example 1, except that the linearly polarizing plate 4 was used instead of the linearly polarizing plate 1.

Example 6
A circularly polarizing plate (6) was obtained in the same manner as in Example 1, except that the linearly polarizing plate 5 was used instead of the linearly polarizing plate 1.

Example 7
A circularly polarizing plate (7) was obtained in the same manner as in Example 1, except that the linearly polarizing plate 6 was used instead of the linearly polarizing plate 1.

Example 8
A circularly polarizing plate (8) was obtained in the same manner as in Example 1, except that the linearly polarizing plate 6 was used instead of the linearly polarizing plate 1, and the pressure-sensitive adhesive layer (1B) was used as the first attachment layer.

Example 9
A circularly polarizing plate (9) was obtained in the same manner as in Example 1, except that the linearly polarizing plate 7 was used instead of the linearly polarizing plate 1.

Example 10
A circularly polarizing plate (10) was obtained in the same manner as in Example 1, except that the linearly polarizing plate 8 was used instead of the linearly polarizing plate 1.

Example 11
The first liquid crystal cured layer B exposed by peeling off the base layer on the first liquid crystal cured layer B side of the retardation layer structure B with the base layer prepared above was bonded to the protective film C side of the linear polarizer 6 prepared above using the adhesive layer (1A) which is the first bonding layer. The first liquid crystal cured layer B was bonded to the linear polarizer 6 so that the angle between the slow axis of the first liquid crystal cured layer B and the transmission axis of the polarizer 1 was 45°. Next, the second liquid crystal cured layer B exposed by peeling off the base layer on the second liquid crystal cured layer B side was bonded to the adhesive layer (2) to obtain a circular polarizer (11). Each bonding surface was subjected to a corona treatment.

The obtained circularly polarizing plate was subjected to the above-mentioned heat resistance test, moist heat durability test, and weather resistance test. The results are shown in Table 1.

1, 2, 3 Circular polarizing plate, 4, 5 Optical laminate, 10, 11 Linear polarizing plate, 20 Retardation layer structure, 30a First bonding layer, 30b Second bonding layer, 30c Third bonding layer, 30d Fourth bonding layer, 40 Image display element, 50 Front plate, 101 Polarizer, 102 Protective film, 103 Hard coat layer, 201 First liquid crystal cured layer, 202 Second liquid crystal cured layer, 203 Separate film.

Claims (8)

A circular polarizing plate including a linear polarizing plate and a liquid crystal cured layer,
The linear polarizing plate includes a polarizer and a protective film laminated on only one surface of the polarizer,
the polarizer, the protective film, and the liquid crystal cured layer are disposed in this order;
The polarizer has a boric acid crosslinking index of 1.0 or more and a boron content of 3.5% by mass or more and 5.5% by mass or less,
A hard coat layer is further provided between the protective film and the liquid crystal cured layer,
A first bonding layer is further provided between the hard coat layer and the liquid crystal cured layer,
The protective film is a circular polarizing plate having selective light absorption properties . The circular polarizing plate according to claim 1, wherein the polarizer has a boric acid crosslinking index of 1.0 or more and 1.3 or less. The circular polarizing plate according to claim 1 or 2, wherein the protective film is a cyclic polyolefin resin film. The liquid crystal cured layer includes a first liquid crystal cured layer and a second liquid crystal cured layer,
The circularly polarizing plate according to any one of claims 1 to 3, wherein the polarizer, the protective film, the first liquid crystal cured layer, and the second liquid crystal cured layer are arranged in this order. The circularly polarizing plate according to any one of claims 1 to 4 , comprising the polarizer, the protective film, the liquid crystal cured layer, and a pressure-sensitive adhesive layer in this order. 6. The circularly polarizing plate according to claim 1, wherein the hard coat layer further has a selective light absorption property. The circularly polarizing plate according to any one of claims 1 to 6 ,
A front panel or a touch sensor panel;
An optical laminate for a flexible image display device comprising: An image display device comprising the circular polarizing plate according to any one of claims 1 to 6 or the optical laminate according to claim 7 .

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