JP7620134B2 - Polarizing plate and display device - Google Patents

Description

The present invention relates to a polarizing plate and a display device.

In recent years, image display devices, such as organic electroluminescence (hereinafter also referred to as organic EL) display devices, have rapidly become popular. Organic EL display devices are equipped with a circular polarizing plate that includes a polarizer and a retardation film (lambda/4 plate). The placement of the circular polarizing plate can prevent reflection of external light and improve the visibility of the screen.

As the demand for thinner image display devices increases with the rise of organic EL display devices, there is also a demand for thinner circular polarizers. It has been considered to change from conventional retardation films made of resin films to retardation films made of liquid crystal compounds that can be made thinner (see, for example, Patent Document 1). Retardation films using polymerizable liquid crystal compounds are manufactured by coating a substrate with a polymerizable liquid crystal compound, orienting the compound, and fixing the orientation state by irradiating the compound with light as necessary. When a circular polarizer having a retardation film made of a polymerizable liquid crystal compound is placed in a high-temperature environment, there is a problem in that the hue of the circular polarizer changes from the initial state to blue or red. Specifically, when the circular polarizer is rectangular, the reflective hue near the four edges of the circular polarizer may change to blue or red, respectively.

JP 2017-54093 A

The object of the present invention is to solve the above problems by providing a circular polarizing plate equipped with a retardation film, which exhibits little change in reflected hue before and after being placed in a high-temperature environment.

[1] A circular polarizing plate having a polarizing plate and a retardation film,
The retardation film includes a retardation layer,
The retardation film has a puncture elastic modulus of 15 gf/mm or more,
The puncture elastic modulus is an elastic modulus measured in a test using a needle having a tip diameter of 1 mmφ and a radius of 0.5 R at a puncture speed of 0.33 cm/sec.
[2] The circularly polarizing plate has a pressure-sensitive adhesive layer on a surface thereof,
The polarizing plate has a polarizer,
The retardation layer includes a layer in which a polymerizable liquid crystal compound is hardened,
The circularly polarizing plate according to [1], wherein the retardation film is disposed between the polarizing plate and the pressure-sensitive adhesive layer.
[3] The circularly polarizing plate according to [2], wherein the polarizer is formed from a layer of a cured liquid crystal compound.
[4] The shape of the circularly polarizing plate is substantially rectangular,
In the polarizing plate, a protective film is laminated on a surface of the polarizer opposite to a retardation film side,
The protective film is a stretched film,
The circularly polarizing plate according to [2] or [3], wherein the stretching direction of the protective film is substantially parallel to the short side direction of the circularly polarizing plate.
[5] The circularly polarizing plate according to any one of [1] to [4], wherein the retardation film includes two retardation layers.
[6] A circularly polarizing plate with a front plate, comprising the circularly polarizing plate according to any one of [1] to [5] and a front plate laminated together via an adhesive layer.
[7] A display device comprising the circularly polarizing plate according to any one of [2] to [4] laminated on a display element via the pressure-sensitive adhesive layer.

The present invention provides a circular polarizing plate equipped with a retardation film, which exhibits little change in reflected hue before and after exposure to a high-temperature environment.

FIG. 2 is a schematic cross-sectional view showing a layer structure of a circular polarizing plate. FIG. 1 is a schematic cross-sectional view illustrating a layer structure of an organic EL display device. FIG. 2 is a top view of a sample for evaluation.

<Circular polarizing plate>
The circular polarizing plate of the present invention includes a polarizing plate and a retardation film. The polarizing plate and the retardation film can be laminated, for example, via an adhesive layer. Examples of the adhesive layer include a pressure-sensitive adhesive layer and an adhesive layer described below. In the present invention, the polarizing plate refers to a laminate consisting of a polarizer and a protective film attached to one or both sides of the polarizer.

An example of the layer structure of the circular polarizing plate of the present invention will be described below with reference to FIG. 1. Note that the adhesive layers for bonding the polarizer 10 and the protective films 11 and 12 are not shown in FIG. 1. The circular polarizing plate 100 shown in FIG. 1(a) has a layer structure in which a polarizing plate 1 in which a first protective film 11 is laminated on one side of the polarizer 10 and a second protective film 12 is laminated on the other side of the polarizing plate 10 and a retardation film 2 including a layer 20 of a cured polymerizable liquid crystal compound are laminated via an adhesive layer 13. Furthermore, the circular polarizing plate 100 has an adhesive layer 14 on the side of the retardation film 2 opposite to the polarizing plate 1. The adhesive layer 14 can be an adhesive layer for bonding to an organic EL display element or the like.

Circular polarizing plate 101 shown in FIG. 1(b) has a layer structure in which polarizing plate 1, in which first protective film 11 is laminated on one side of polarizer 10 and second protective film 12 is laminated on the other side of polarizer 10, and retardation film 2 are laminated via adhesive layer 13. In circular polarizing plate 101, retardation film 2 has a layer structure in which layer 20 of hardened polymerizable liquid crystal compound and layer 21 of hardened polymerizable liquid crystal compound are laminated via adhesive layer 15. Furthermore, circular polarizing plate 101 has adhesive layer 14 on the side of retardation film 2 opposite polarizing plate 1. Adhesive layer 14 can be an adhesive layer for bonding to an organic EL display element or the like.

Circular polarizing plate 103 shown in FIG. 1(c) has a layer structure in which polarizing plate 1, in which first protective film 11 is laminated on one side of polarizer 10, and retardation film 2 are laminated via adhesive layer 13. In circular polarizing plate 103, polarizing plate 1 is a polarizing plate having a protective film only on one side of polarizer 10. In circular polarizing plate 103, retardation film 2 has a layer structure in which layer 20 of hardened polymerizable liquid crystal compound and layer 21 of hardened polymerizable liquid crystal compound are laminated via adhesive layer 15. Furthermore, circular polarizing plate 103 has adhesive layer 14 on the side of retardation film 2 opposite polarizing plate 1. Adhesive layer 14 can be an adhesive layer for bonding to an organic EL display element or the like.

As shown in FIG. 1, the retardation film may have one retardation layer or two retardation layers. The retardation film may also have an alignment film for aligning the polymerizable liquid crystal compound during the manufacturing process. As shown in FIG. 1, the polarizing plate may have a protective film laminated on only one surface of the polarizer, or on both surfaces.

The circular polarizing plate may have layers other than those shown in FIG. 1. Examples of layers that the circular polarizing plate may further have include a front plate and a light-shielding pattern. The front plate may be disposed on the side of the polarizing plate opposite to the side on which the retardation film is laminated.

The light-shielding pattern can be formed on the surface of the front panel facing the polarizing plate. The light-shielding pattern can be formed on the frame (non-display area) of the image display device, preventing the wiring of the image display device from being visible to the user.

The shape of the main surface of the circular polarizing plate can be substantially rectangular. The main surface means the surface having the widest area corresponding to the display surface. Being substantially rectangular means that at least one of the four corners (corners) may be cut or rounded to form an obtuse angle, a part of the end face perpendicular to the main surface may have a recess (notch) recessed in the in-plane direction, or a part of the main surface may have a hole cut out in the shape of a circle, an ellipse, a polygon, or a combination thereof.

The size of the circular polarizing plate is not particularly limited. When the circular polarizing plate is substantially rectangular, the length of the long side is preferably 6 cm or more and 35 cm or less, more preferably 10 cm or more and 30 cm or less, and the length of the short side is preferably 5 cm or more and 30 cm or less, more preferably 6 cm or more and 25 cm or less.

<Polarizing Plate>
In the present invention, the polarizing plate refers to a laminate consisting of a polarizer and a protective film attached to one or both sides of the polarizer. The protective film of the polarizing plate may have a surface treatment layer such as a hard coat layer, an antireflection layer, or an antistatic layer, which will be described later. The polarizer and the protective film can be laminated, for example, via an adhesive layer or a pressure-sensitive adhesive layer. The members of the polarizing plate will be described below.

(1) Polarizer The polarizer of the polarizing plate can be an absorption type polarizer that absorbs linearly polarized light having a vibration plane parallel to its absorption axis and transmits linearly polarized light having a vibration plane perpendicular to the absorption axis (parallel to the transmission axis). As the polarizer of the first layer, a polarizer in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film can be suitably used. The polarizer can be manufactured by a method including, for example, a step of uniaxially stretching a polyvinyl alcohol-based resin film; a step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye to adsorb the dichroic dye; a step of treating the polyvinyl alcohol-based resin film with the adsorbed dichroic dye with a crosslinking liquid such as an aqueous boric acid solution; and a step of washing with water after the treatment with the crosslinking liquid.

As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. Examples of polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate with other monomers that can be copolymerized with vinyl acetate. Examples of other monomers that can be copolymerized 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 at least one selected from acrylic and methacrylic. The same applies to "(meth)acryloyl" and "(meth)acrylate", etc.

The degree of saponification of polyvinyl alcohol resins is usually 85 to 100 mol%, and preferably 98 mol% or more. The polyvinyl alcohol resins may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can be used. The average degree of polymerization of polyvinyl alcohol resins is usually 1000 to 10000, and preferably 1500 to 5000. The average degree of polymerization of polyvinyl alcohol resins can be determined in accordance with JIS K 6726.

A film made from such a polyvinyl alcohol-based resin is used as the raw film for the polarizer. There is no particular limitation on the method for making the polyvinyl alcohol-based resin into a film, and any known method can be used. There is no particular limitation on the thickness of the polyvinyl alcohol-based raw film, but in order to make the thickness of the polarizer 15 μm or less, it is preferable to use one with a thickness of 5 to 35 μm. More preferably, it is 20 μm or less.

The uniaxial stretching of the polyvinyl alcohol resin film can be performed before, simultaneously with, or after dyeing with a dichroic dye. When the uniaxial stretching is performed after dyeing, the uniaxial stretching may be performed before or during the crosslinking treatment. The uniaxial stretching may also be performed in multiple stages.

In uniaxial stretching, the film may be stretched uniaxially between rolls with different peripheral speeds, or may be stretched uniaxially using a heated roll. The uniaxial stretching may be dry stretching in which stretching is performed in the atmosphere, or wet stretching in which the polyvinyl alcohol resin film is stretched in a swollen state using a solvent or water. The stretching ratio is usually 3 to 8 times.

A method for dyeing a polyvinyl alcohol-based resin film with a dichroic dye is, for example, to immerse the film in an aqueous solution containing the dichroic dye. Iodine or a dichroic organic dye is used as the dichroic dye. It is preferable to immerse the polyvinyl alcohol-based resin film in water before the dyeing process.

The crosslinking treatment after dyeing with a dichroic dye usually involves immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid. When iodine is used as the dichroic dye, the aqueous solution containing boric acid preferably contains potassium iodide.

The thickness of the polarizer is usually 30 μm or less, preferably 15 μm or less, more preferably 13 μm or less, even more preferably 10 μm or less, and particularly preferably 8 μm or less. The thickness of the polarizer is usually 2 μm or more, and preferably 3 μm or more. The inventors' studies have revealed that the change in hue of the circular polarizer is caused by the change in the retardation value of the retardation film. Furthermore, it has been revealed that the change in the retardation value of the retardation film is caused by the stress generated when the polarizer shrinks in dimensions in a circular polarizer placed in a high-temperature environment. Therefore, from the viewpoint of reducing the effect of the shrinkage of the polarizer, making the thickness of the polarizer 15 μm or less is effective in preventing the change in hue.

The polarizer may be formed from a layer of a cured liquid crystal compound, as described in, for example, JP 2016-170368 A. Specifically, a dichroic dye may be oriented in a cured film in which the liquid crystal compound is polymerized. As the dichroic dye, one having absorption in the wavelength range of 380 to 800 nm may be used, and it is preferable to use an organic dye. As the dichroic dye, for example, an azo compound may be used. The liquid crystal compound is a liquid crystal compound that can be polymerized while being oriented, and can have a polymerizable group in the molecule. This type of polarizer is obtained by applying a composition containing a liquid crystal compound and a dichroic dye onto an alignment film, and fixing the liquid crystal compound and the dichroic dye by irradiating with ultraviolet light or heating as necessary. In addition, as described in WO 2011/024891 and JP 2018-120229 A, a polarizer may be formed from a dichroic dye having liquid crystal properties. In this way, forming a polarizer from a layer of a cured liquid crystal compound can help reduce dimensional changes in the polarizer in high-temperature environments, and is effective in preventing changes in hue.

When a polarizer containing a layer of a hardened liquid crystal compound is used as the polarizer, the thickness of the polarizer can be 500 nm or more and 3 μm or less.

(2) Protective film The circular polarizing plate of the present invention preferably has a protective film on at least one surface of the polarizer, and preferably has a protective film on the surface of the polarizer opposite to the retardation film side. When the circular polarizing plate is substantially rectangular and the protective film is a stretched film, it is preferable that the stretching direction of the protective film and the short side direction of the circular polarizing plate are substantially parallel. When the circular polarizing plate is substantially rectangular and the protective film is an unstretched film, it is preferable that the direction in which the tensile modulus is the largest in the plane of the protective film and the short side direction of the circular polarizing plate are substantially parallel. When the stretching direction (or the direction in which the tensile modulus is the largest) and the short side direction are in such a relationship, the hue change of the circular polarizing plate tends to be small regardless of the direction of the slow axis of the retardation film. When the stretching direction (or the direction in which the tensile modulus is the largest) of the protective film is parallel to the short side, the contraction force in the stretching direction of the protective film due to the stretch relaxation of the polarizer and the protective film in a high temperature environment is smaller than when it is parallel to the long side, and it is considered that the hue change is small. The tensile modulus of elasticity is measured at 80° C. using, for example, an Autograph (registered trademark) (manufactured by Shimadzu Corporation, model number: AG-IS).

The stretching direction of the protective film and the short side direction of the circular polarizing plate being substantially parallel includes not only the case where they are strictly parallel, but also the case where the angle between them is 0±10°. The angle between the stretching direction of the protective film and the short side direction of the circular polarizing plate is preferably 0±5°. Unstretched films include not only unstretched films, but also films that are substantially unstretched with a stretch ratio of 1.1 times or less.

The protective films laminated on both sides of the polarizer can be films made of a thermoplastic resin having light transmission (preferably optically transparent), for example, a polyolefin resin such as a chain polyolefin resin (polypropylene resin, etc.) or a cyclic polyolefin resin (norbornene resin, etc.); a cellulose resin such as triacetyl cellulose or diacetyl cellulose; a polyester resin such as polyethylene terephthalate or polybutylene terephthalate; a polycarbonate resin; a (meth)acrylic resin such as a methyl methacrylate resin; a polystyrene resin; a polyvinyl chloride resin; an acrylonitrile-butadiene-styrene resin; an acrylonitrile-styrene resin; a polyvinyl acetate resin; a polyvinylidene chloride resin; a polyamide resin; a polyacetal resin; a modified polyphenylene ether resin; a polysulfone resin; a polyethersulfone resin; a polyarylate resin; a polyamideimide resin; a polyimide resin, etc.

Examples of linear polyolefin resins include linear olefin homopolymers such as polyethylene resins (polyethylene resins which are homopolymers of ethylene, and copolymers mainly composed of ethylene) and polypropylene resins (polypropylene resins which are homopolymers of propylene, and copolymers mainly composed of propylene), as well as copolymers made of two or more linear olefins.

Cyclic polyolefin resin is a general term for resins polymerized using cyclic olefins as polymerization units, and examples of such resins include those described in JP-A-1-240517, JP-A-3-14882, and JP-A-3-122137. Specific examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers (typically random copolymers) of cyclic olefins with linear olefins such as ethylene and propylene, and graft polymers modified with unsaturated carboxylic acids or their derivatives, as well as hydrogenated products thereof. Of these, norbornene resins using norbornene monomers such as norbornene or polycyclic norbornene monomers as the cyclic olefin are preferably used.

Polyester resins are resins having ester bonds, excluding the cellulose ester resins described below, and are generally made of a polycondensation product of a polycarboxylic acid or its derivative and a polyhydric alcohol. As the polycarboxylic acid or its derivative, a divalent dicarboxylic acid or its derivative can be used, such as terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. As the polyhydric alcohol, a divalent diol can be used, such as ethylene glycol, propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol. A representative example of a polyester resin is polyethylene terephthalate, which is a polycondensation product of terephthalic acid and ethylene glycol.

The (meth)acrylic resin is a resin whose main constituent monomer is a compound having a (meth)acryloyl group. Specific examples of the (meth)acrylic resin include poly(meth)acrylic acid ester such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymer; methyl methacrylate-(meth)acrylic acid ester copolymer; methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymer; methyl (meth)acrylate-styrene copolymer (MS resin, etc.); and copolymers of methyl methacrylate and a compound having an alicyclic hydrocarbon group (e.g., methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-norbornyl (meth)acrylate copolymer, etc.). Preferably, a polymer whose main component is poly(meth)acrylic acid C _1-6 alkyl ester such as polymethyl (meth)acrylate is used, and more preferably, a methyl methacrylate resin whose main component is methyl methacrylate (50 to 100% by weight, preferably 70 to 100% by weight) is used.

Cellulose ester resins are esters of cellulose and fatty acids. Specific examples of cellulose ester resins include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Other examples include copolymers of these and those in which some of the hydroxyl groups have been modified with other substituents. Of these, cellulose triacetate (triacetyl cellulose) is particularly preferred.

Polycarbonate resins are engineering plastics made of polymers in which monomer units are bonded via carbonate groups.

It is also useful to control the retardation value of the protective film to a value suitable for an image display device such as a liquid crystal display device. For example, in an in-plane switching (IPS) mode liquid crystal display device, it is preferable to use a film with a retardation value of substantially zero as the protective film. A retardation value of substantially zero means that the in-plane retardation value Re(550) at a wavelength of 550 nm is 10 nm or less, and the absolute value of the thickness direction retardation value Rth at a wavelength of 550 nm is 10 nm or less. It is preferable that the absolute value of the thickness direction retardation value Rth at wavelengths of 480 to 750 nm is 15 nm or less. In addition, in order to improve the visibility of the screen when a user wears polarized sunglasses, the in-plane retardation value Re(550) at a wavelength of 550 nm may be set to 70 to 140 nm.

For example, depending on the mode of the liquid crystal display device, the protective film may be stretched and/or shrunk to impart a suitable phase difference. For example, a single-layer or multi-layer structure protective film may be used for the purpose of compensating for the viewing angle.

The thickness of the protective film is usually 1 to 100 μm, but from the viewpoints of strength, ease of handling, etc., it is preferably 5 to 60 μm, more preferably 10 to 55 μm, and even more preferably 15 to 40 μm.

The protective films attached to one or both sides of the polarizer may be made of the same type of thermoplastic resin or different types of thermoplastic resin. They may have the same thickness or different thicknesses. Furthermore, they may have the same retardation characteristics or different retardation characteristics.

As described above, at least one of the protective films may have a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, a light diffusion layer, an antireflection layer, a low refractive index layer, an antistatic layer, or an antifouling layer on its outer surface (the surface opposite the polarizer). The thickness of the protective film includes the thickness of the surface treatment layer.

The protective film can be attached to the polarizer, for example, via an adhesive layer or a pressure-sensitive adhesive layer. The adhesive that forms the adhesive layer can be a water-based adhesive, an active energy ray-curable adhesive, or a heat-curable adhesive, and is preferably a water-based adhesive or an active energy ray-curable adhesive. The pressure-sensitive adhesive layer can be one described below.

Examples of water-based adhesives include adhesives made of an aqueous solution of polyvinyl alcohol-based resins, and aqueous two-liquid urethane-based emulsion adhesives. Among these, water-based adhesives made of an aqueous solution of polyvinyl alcohol-based resins are preferably used. Examples of polyvinyl alcohol-based resins that can be used include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl alcohol copolymers obtained by saponifying a copolymer of vinyl acetate and other monomers that can be copolymerized with it, and modified polyvinyl alcohol polymers in which the hydroxyl groups of these copolymers are partially modified. Water-based adhesives can contain crosslinking agents such as aldehyde compounds (such as glyoxal), epoxy compounds, melamine compounds, methylol compounds, isocyanate compounds, amine compounds, and polyvalent metal salts.

When using a water-based adhesive, it is preferable to carry out a drying process to remove water contained in the water-based adhesive after laminating the polarizer and the protective film. After the drying process, a curing process may be carried out, for example, at a temperature of 20 to 45°C.

The above-mentioned active energy ray curable adhesive is an adhesive containing a curable compound that cures when exposed to active energy rays such as ultraviolet light, visible light, electron beams, and X-rays, and is preferably an ultraviolet ray curable adhesive.

The curable compound may be a cationic polymerizable curable compound or a radical polymerizable curable compound. Examples of the cationic polymerizable curable compound include an epoxy compound (a compound having one or more epoxy groups in the molecule), an oxetane compound (a compound having one or more oxetane rings in the molecule), or a combination thereof. Examples of the radical polymerizable curable compound include a (meth)acrylic compound (a compound having one or more (meth)acryloyloxy groups in the molecule), other vinyl compounds having a radical polymerizable double bond, or a combination thereof. A cationic polymerizable curable compound and a radical polymerizable curable compound may be used in combination. The active energy ray curable adhesive usually further contains a cationic polymerization initiator and/or a radical polymerization initiator for initiating the curing reaction of the curable compound.

When laminating the polarizer and the protective film, at least one of the lamination surfaces may be subjected to a surface activation treatment in order to enhance adhesion. Examples of surface activation treatments include dry treatments such as corona treatment, plasma treatment, discharge treatment (glow discharge treatment, etc.), flame treatment, ozone treatment, UV ozone treatment, and ionizing active ray treatment (ultraviolet ray treatment, electron beam treatment, etc.); and wet treatments such as ultrasonic treatment using a solvent such as water or acetone, saponification treatment, and anchor coat treatment. These surface activation treatments may be performed alone or in combination of two or more.

When protective films are attached to both sides of a polarizer, the adhesive used to attach these protective films may be the same type of adhesive or different types of adhesive.

Instead of a protective film, a protective layer may be formed on at least one surface of the polarizer. The protective layer can be formed on the polarizer without an adhesive layer or pressure-sensitive adhesive layer, that is, the protective layer can be formed in contact with the polarizer. The protective layer can be a layer containing a (meth)acrylic resin or a layer containing a water-based resin.

The layer containing a (meth)acrylic resin can be formed by applying a composition containing a (meth)acrylic resin to a polarizer and then heating or irradiating with active energy rays, or by applying a composition containing a (meth)acrylic resin onto a substrate film and then heating or irradiating with active energy rays. In the latter case, a polarizer may be formed on the layer containing a (meth)acrylic resin.

The (meth)acrylic resin refers to a polymer in which a monomer having a (meth)acryloyl group is the main component among the monomers constituting the (meth)acrylic resin. Here, the main component refers to the monomer with the largest content (mass%) among the monomer components constituting the (meth)acrylic resin. By using a (meth)acrylic resin as the material for forming the protective layer, it is also possible to suppress the deterioration of the optical properties of the circular polarizing plate even in a humid and hot environment.

The (meth)acrylic resin is preferably a polymerized photopolymerizable monomer, and may be, for example, a polymerized monofunctional or polyfunctional monomer having a (meth)acryloyl group, either alone or in combination. The (meth)acrylic resin may be a polymerized monomer other than the monomer having a (meth)acryloyl group, for example, a polymerized monomer having a vinyl group.

The monomer having a (meth)acryloyl group is not particularly limited, but examples thereof include compounds having one or more (meth)acryloyl groups in the molecule, which can be used alone or in a mixture of two or more. Specific examples include dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethylene oxide or propylene oxide added compounds of the above (meth)acrylates; oligoester (meth)acrylates, oligoether (meth)acrylates, oligourethane (meth)acrylates, oligoepoxy (meth)acrylates, oligomelamine (meth)acrylates, polyfunctional acrylates having dendrimer structures, etc.

The thickness of the layer containing the (meth)acrylic resin is usually 0.1 μm or more, preferably 0.3 μm or more, and more preferably 0.5 μm or more, and is usually 20.0 μm or less, preferably 15 μm or less, and more preferably 10 μm or less. When the thickness of the layer containing the (meth)acrylic resin is within the above range, it becomes easier to obtain a bendable circularly polarizing plate.

The layer containing the water-based resin can be formed by applying a composition containing the water-based resin to a polarizer and then heating or irradiating with active energy rays, or by applying a composition containing a (meth)acrylic resin onto a substrate film and then heating or irradiating with active energy rays. In the latter case, the polarizer may be formed on the layer containing the water-based resin.

Examples of water-based resins include water-soluble polymers such as polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinylpyrrolidone, starches, methyl cellulose, carboxymethyl cellulose, and sodium alginate, of which polyvinyl alcohol is preferred.

The thickness of the layer containing the water-based resin is preferably 0.1 μm or more, more preferably 0.3 μm or more, and preferably 3 μm or less, more preferably 1.5 μm or less, and even more preferably 1 μm or less. When the thickness of the layer containing the water-based resin is within the above range, it becomes easier to obtain a bendable circularly polarizing plate.

The protective layer may be a single layer or may be formed from multiple layers. An example of a protective layer formed from multiple layers is one in which the protective layer is composed of a layer containing a (meth)acrylic resin and a layer containing a water-based resin.

<Retardation film>
The circular polarizing plate of the present invention has a retardation film. The puncture elastic modulus of the retardation film is 15 gf/mm or more, preferably 20 gf/mm or more, more preferably 25 gf/mm or more, and even more preferably 30 gf/mm or more. The upper limit of the puncture elastic modulus of the retardation film is not particularly limited, and can be, for example, 200 gf/mm or less, and may be 50 gf/mm or less. A retardation film having a puncture elastic modulus in such a range tends to be less likely to change in retardation value under high temperature environment. The larger the puncture elastic modulus, the less likely the retardation value to change due to stress caused by dimensional shrinkage of the polarizing plate.

When the retardation film includes one retardation layer, the puncture modulus of the retardation film is 15 gf/mm or more, preferably 20 gf/mm or more, more preferably 25 gf/mm or more, and even more preferably 30 gf/mm or more. The upper limit of the puncture modulus of the retardation film is not particularly limited, and can be, for example, 200 gf/mm or less, or may be 90 gf/mm or less, or may be 50 gf/mm or less.

When the retardation film includes two retardation layers, the puncture modulus of the retardation film is preferably 30 gf/mm or more, more preferably 40 gf/mm or more, even more preferably 50 gf/mm or more, and particularly preferably 70 gf/mm or more. The upper limit of the puncture modulus of the retardation film is not particularly limited, and can be, for example, 200 gf/mm or less, or may be 150 gf/mm or less, or may be 100 gf/mm or less.

The puncture elastic modulus is the value obtained by dividing the force (gf) just before the retardation film breaks (or tears) when a needle (puncture tool) is pierced perpendicularly to the main surface of the retardation film by the strain (mm) at that time. A needle with a tip diameter of 1 mmφ and 0.5R can be used. The needle piercing speed can be 0.33 cm/sec. The puncture elastic modulus is measured by sandwiching the retardation film between two plates with a circular hole of 15 mm or less in diameter through which the needle can pass. The puncture elastic modulus can be measured in an environment at a temperature of 23°C. For example, the puncture elastic modulus can be measured for five retardation films, and the average value can be used as the puncture elastic modulus of the retardation film. A commercially available device can be used to measure the puncture elastic modulus. Commercially available devices include the handy compression tester "KES-G5 Needle Penetration Force Measurement Specification" manufactured by Kato Tech Co., Ltd., and the small tabletop tester "EZ Test" manufactured by Shimadzu Corporation.

The puncture modulus of the retardation film can be controlled, for example, by adjusting the type of polymerizable liquid crystal compound or alignment film used, the degree of hardening of the polymerizable liquid crystal compound, the thickness of the retardation film, etc.

The retardation film has a retardation layer. The retardation layer preferably has a layer composed of a composition containing a polymerizable liquid crystal compound. The layer composed of a composition containing a polymerizable liquid crystal compound specifically means a layer in which the polymerizable liquid crystal compound is hardened. In this specification, the layer that gives a retardation of λ/2, the layer that gives a retardation of λ/4 (positive A layer), the positive C layer, etc. may be collectively referred to as the retardation layer. Furthermore, the retardation film may include an alignment film described later.

The layer that gives a retardation of λ/2 preferably means a layer having an in-plane retardation value of 200 to 280 nm at a wavelength of 550 nm, more preferably a layer having an in-plane retardation value of 215 to 265 nm. The layer that gives a retardation of λ/4 preferably means a layer having an in-plane retardation value of 100 to 160 nm at a wavelength of 550 nm, more preferably a layer having an in-plane retardation value of 110 to 150 nm. The positive C layer can be a layer whose refractive index has a relationship of nx ≒ ny < nz. The retardation value in the thickness direction of the positive C layer can be -50 nm to -150 nm at a wavelength of 550 nm, and can be -70 nm to -120 nm.

The layer of the cured polymerizable liquid crystal compound is formed, for example, on an alignment film provided on a substrate. The substrate may be a substrate formed in a long length, which has a function of supporting the alignment film. This substrate functions as a releasable support, and can support a retardation layer for transfer. Furthermore, it is preferable that the surface of the substrate has an adhesive strength sufficient to enable peeling. Examples of the substrate include the resin films exemplified as materials for the protective film described above.

The thickness of the substrate is not particularly limited, but is preferably in the range of 20 μm to 200 μm. A substrate thickness of 20 μm or more provides strength. On the other hand, a thickness of 200 μm or less can suppress an increase in processing waste and wear of the cutting blade when cutting the substrate into sheet substrates.

The substrate may be subjected to various anti-blocking treatments. Examples of anti-blocking treatments include an easy-adhesion treatment, a treatment for kneading fillers, and an embossing (knurling) treatment. By subjecting the substrate to such anti-blocking treatments, it is possible to effectively prevent the substrates from sticking to each other when the substrates are wound up, i.e., blocking, and it is possible to manufacture optical films with high productivity.

The layer of the cured polymerizable liquid crystal compound is formed on the substrate via an alignment film. That is, the substrate and alignment film are laminated in that order, and the layer of the cured polymerizable liquid crystal compound is laminated on the alignment film.

The alignment film is not limited to a vertical alignment film, and may be an alignment film that aligns the molecular axis of the polymerizable liquid crystal compound horizontally, or may be an alignment film that aligns the molecular axis of the polymerizable liquid crystal compound at an angle. The alignment film is preferably one that has solvent resistance that does not dissolve when a composition containing a polymerizable liquid crystal compound is applied, as described below, and has heat resistance in a heat treatment for removing the solvent and orienting the liquid crystal compound. Examples of the alignment film include an alignment film containing an orienting polymer, a photoalignment film, and a groove alignment film that forms a concave-convex pattern or multiple grooves on the surface to provide alignment. The thickness of the alignment film is usually in the range of 10 nm to 10,000 nm, preferably in the range of 10 nm to 1000 nm, more preferably in the range of 500 nm or less, and even more preferably in the range of 10 nm to 200 nm. When the retardation film has an alignment film, increasing the thickness of the alignment film makes it easier to increase the puncture elastic modulus.

The resin used for the alignment film is not particularly limited as long as it is a resin used as a material for known alignment films, and a cured product obtained by curing a conventionally known monofunctional or polyfunctional (meth)acrylate monomer under a polymerization initiator can be used. Specifically, examples of (meth)acrylate monomers include 2-ethylhexyl acrylate, cyclohexyl acrylate, diethylene glycol mono 2-ethylhexyl ether acrylate, diethylene glycol monophenyl ether acrylate, tetraethylene glycol monophenyl ether acrylate, trimethylolpropane triacrylate, lauryl acrylate, lauryl methacrylate, isobornyl acrylate, isobornyl methacrylate, 2-phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, 2-hydroxypropyl acrylate, benzyl acrylate, tetrahydrofurfuryl methacrylate, 2-hydroxyethyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, methacrylic acid, and urethane acrylate. The resin may be one of these, or a mixture of two or more.

The type of polymerizable liquid crystal compound used in this embodiment is not particularly limited, but can be classified into rod-shaped type (rod-shaped liquid crystal compound) and discotic type (discotic liquid crystal compound, discotic liquid crystal compound) based on their shape. Furthermore, each type can be classified into low molecular type and high molecular type. Note that a high molecular weight generally refers to a material with a degree of polymerization of 100 or more (Polymer Physics, Phase Transition Dynamics, Masao Doi, p. 2, Iwanami Shoten, 1992).

In this embodiment, any polymerizable liquid crystal compound can be used. Furthermore, two or more rod-shaped liquid crystal compounds, two or more discotic liquid crystal compounds, or a mixture of rod-shaped and discotic liquid crystal compounds may be used.

As the rod-shaped liquid crystal compound, for example, those described in claim 1 of JP-T-11-513019 or paragraphs [0026] to [0098] of JP-A-2005-289980 can be preferably used. As the discotic liquid crystal compound, for example, those described in paragraphs [0020] to [0067] of JP-A-2007-108732 or paragraphs [0013] to [0108] of JP-A-2010-244038 can be preferably used.

Two or more types of polymerizable liquid crystal compounds may be used in combination. In this case, at least one type has two or more polymerizable groups in the molecule. In other words, it is preferable that the layer in which the polymerizable liquid crystal compound is hardened is a layer formed by fixing a liquid crystal compound having a polymerizable group by polymerization. In this case, it is no longer necessary for the compound to exhibit liquid crystallinity after it has become a layer.

The polymerizable liquid crystal compound has a polymerizable group capable of undergoing a polymerization reaction. As the polymerizable group, for example, a functional group capable of an addition polymerization reaction, such as a polymerizable ethylenically unsaturated group or a ring-polymerizable group, is preferable. More specifically, as the polymerizable group, for example, a (meth)acryloyl group, a vinyl group, a styryl group, an allyl group, etc. can be mentioned. Among them, a (meth)acryloyl group is preferable. Note that the (meth)acryloyl group is a concept that includes both a methacryloyl group and an acryloyl group.

The layer in which the polymerizable liquid crystal compound is cured can be formed by, for example, applying a composition containing the polymerizable liquid crystal compound onto an alignment film and irradiating it with active energy rays, as described below. The composition may contain components other than the above-mentioned polymerizable liquid crystal compound. For example, the composition preferably contains a polymerization initiator. The polymerization initiator used is selected from, for example, a thermal polymerization initiator or a photopolymerization initiator depending on the type of polymerization reaction. For example, photopolymerization initiators include α-carbonyl compounds, acyloin ethers, α-hydrocarbon-substituted aromatic acyloin compounds, polynuclear quinone compounds, and combinations of triaryl imidazole dimers and p-aminophenyl ketones. The amount of polymerization initiator used is preferably 0.01 to 20% by mass, more preferably 0.5 to 5% by mass, based on the total solid content in the coating liquid.

The composition may also contain a polymerizable monomer from the viewpoint of the uniformity and strength of the coating film. Examples of the polymerizable monomer include radically polymerizable or cationic polymerizable compounds. Among them, polyfunctional radically polymerizable monomers are preferred.

The polymerizable monomer is preferably one that can be copolymerized with the above-mentioned polymerizable liquid crystal compound. The amount of the polymerizable monomer used is preferably 1 to 50% by mass, and more preferably 2 to 30% by mass, based on the total mass of the polymerizable liquid crystal compound.

The composition may also contain a surfactant from the viewpoint of the uniformity and strength of the coating film. Examples of the surfactant include conventionally known compounds. Among them, fluorine-based compounds are particularly preferred.

The composition may contain a solvent, and an organic solvent is preferably used.
Examples of the organic solvent include amides (e.g., N,N-dimethylformamide), sulfoxides (e.g., dimethyl sulfoxide), heterocyclic compounds (e.g., pyridine), hydrocarbons (e.g., benzene, hexane), alkyl halides (e.g., chloroform, dichloromethane), esters (e.g., methyl acetate, ethyl acetate, butyl acetate), ketones (e.g., acetone, methyl ethyl ketone), and ethers (e.g., tetrahydrofuran, 1,2-dimethoxyethane). Among these, alkyl halides and ketones are preferred. Two or more types of organic solvents may be used in combination.

The composition may also contain various alignment agents, such as a vertical alignment promoter, such as a polarizer interface side vertical alignment agent and an air interface side vertical alignment agent, and a horizontal alignment promoter, such as a polarizer interface side horizontal alignment agent and an air interface side horizontal alignment agent. Furthermore, the composition may contain, in addition to the above components, an adhesion improver, a plasticizer, a polymer, etc.

The active energy rays include ultraviolet light, visible light, electron beams, and X-rays, and are preferably ultraviolet light. Examples of light sources for the active energy rays include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, xenon lamps, halogen lamps, carbon arc lamps, tungsten lamps, gallium lamps, excimer lasers, LED light sources emitting light in the wavelength range of 380 to 440 nm, chemical lamps, black light lamps, microwave-excited mercury lamps, and metal halide lamps.

The irradiation intensity of the ultraviolet light is usually 100 mW/cm ² to 3,000 mW/cm ^2. The ultraviolet light irradiation intensity is preferably an intensity in a wavelength region effective for activating a cationic polymerization initiator or a radical polymerization initiator. The irradiation time of the ultraviolet light is usually 0.1 seconds to 10 minutes, preferably 0.1 seconds to 5 minutes, more preferably 0.1 seconds to 3 minutes, and even more preferably 0.1 seconds to 1 minute.

The ultraviolet light can be irradiated once or in multiple times. It is preferable that the ultraviolet light is irradiated multiple times. When the polymerization rate of the liquid crystal compound is increased, the puncture modulus is likely to be increased to the range of the present invention. Although it depends on the polymerization initiator used, the integrated light amount at a wavelength of 365 nm is preferably 700 mJ/cm ² or more, more preferably 1,100 mJ/cm ² or more, and even more preferably 1,300 mJ/cm ² or more. The integrated light amount is advantageous for increasing the polymerization rate of the polymerizable liquid crystal compound constituting the retardation film and increasing the puncture modulus of the retardation film. The integrated light amount at a wavelength of 365 nm is preferably 2,000 mJ/cm ² or less, and more preferably 1,800 mJ/cm ² or less. The integrated light amount may cause coloring of the retardation film.

In addition, in order to prevent the alignment of the liquid crystal compound from being disturbed by heat immediately after UV irradiation, it is preferable to provide a cooling step after UV irradiation. By providing a cooling step after UV irradiation, it is possible to suppress the alignment of the liquid crystal compound from being disturbed by heat generated immediately after irradiation. As a result, the alignment degree of the liquid crystal compound increases, and a film having higher rigidity can be obtained. The cooling temperature can be, for example, 20°C or less, and can be 10°C or less. The cooling time can be, for example, 10 seconds or more, and can be 20 seconds or more.

In this embodiment, the thickness of the retardation layer is preferably 0.5 μm or more. The thickness of the retardation layer is preferably 10 μm or less, and more preferably 5 μm or less. The above upper and lower limits can be arbitrarily combined. When the thickness of the retardation layer is equal to or greater than the lower limit, sufficient durability can be obtained. When the thickness of the retardation layer is equal to or less than the upper limit, it can contribute to making the circular polarizing plate thinner. The thickness of the retardation layer can be adjusted so that the desired in-plane retardation value and thickness direction retardation value of the layer that gives a retardation of λ/4, the layer that gives a retardation of λ/2, or the positive C layer can be obtained.

The retardation film may include one layer of a cured polymerizable liquid crystal compound, or may include two or more layers of a cured polymerizable liquid crystal compound. When the retardation film includes two layers of a cured polymerizable liquid crystal compound, the two layers are preferably a layer that provides a phase difference of λ/4 and a positive C layer, or a layer that provides a phase difference of λ/4 and a layer that provides a phase difference of λ/2. When the retardation film includes two layers of a cured polymerizable liquid crystal compound, the retardation film may be manufactured by forming the layers of a cured polymerizable liquid crystal compound on the alignment film and laminating the two layers via an adhesive layer or a pressure-sensitive adhesive layer, or a layer of a cured polymerizable liquid crystal compound may be further formed on the layer of a cured polymerizable liquid crystal compound. After laminating the two layers, the substrate and the alignment film can be peeled off. The thickness of the retardation film is preferably 3 to 30 μm, more preferably 5 to 25 μm.

<Adhesive Layer>
The adhesive layer can be composed of an adhesive composition mainly composed of a resin such as a (meth)acrylic, rubber, urethane, ester, silicone, or polyvinyl ether resin. Among them, an adhesive composition having a (meth)acrylic resin as a base polymer, which is excellent in transparency, weather resistance, heat resistance, etc., is preferable. The adhesive composition may be an active energy ray curable type or a heat curable type. The thickness of the adhesive layer is usually 3 to 30 μm, and preferably 3 to 25 μm.

As the (meth)acrylic resin (base polymer) used in the adhesive composition, for example, a polymer or copolymer containing one or more (meth)acrylic acid esters as monomers, such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, is preferably used. It is preferable to copolymerize a polar monomer into the base polymer. Examples of polar monomers include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, etc., such as (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate.

The adhesive composition may contain only the base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include divalent or higher metal ions that form metal carboxylates with carboxyl groups; polyamine compounds that form amide bonds with carboxyl groups; polyepoxy compounds or polyols that form ester bonds with carboxyl groups; and polyisocyanate compounds that form amide bonds with carboxyl groups. Of these, polyisocyanate compounds are preferred.

<Front panel>
The present invention includes a circular polarizing plate with a front plate, in which a circular polarizing plate and a front plate are laminated via an adhesive layer. The front plate is disposed on the viewing side of the polarizing plate. The front plate can be laminated to the polarizing plate via an adhesive layer. Examples of the adhesive layer include the above-mentioned pressure-sensitive adhesive layer and adhesive layer. As shown in Figures 2(a), (b), and (c), the front plate 4 can be laminated on the protective film 11 of the polarizing plate 1 via a pressure-sensitive adhesive layer 16.

Examples of the front panel include glass and resin films that include a hard coat layer on at least one side. Examples of the glass that can be used include highly transparent glass and reinforced glass. When using a particularly thin transparent surface material, chemically strengthened glass is preferred. The thickness of the glass can be, for example, 100 μm to 5 mm.

A front panel comprising a hard coat layer on at least one side of a resin film can have flexible properties, rather than being rigid like existing glass. The thickness of the hard coat layer is not particularly limited, and may be, for example, 5 to 100 μm.

The resin film may be a film formed of a polymer such as a cycloolefin derivative having a unit of a monomer containing a cycloolefin such as norbornene or a polycyclic norbornene monomer, cellulose (diacetyl cellulose, triacetyl cellulose, acetyl cellulose butyrate, isobutyl ester cellulose, propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose), ethylene-vinyl acetate copolymer, polycycloolefin, polyester, polystyrene, polyamide, polyetherimide, polyacrylic, polyimide, polyamideimide, polyethersulfone, polysulfone, polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetal, polyether ketone, polyether ether ketone, polyethersulfone, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyurethane, or epoxy. The resin film may be an unstretched, uniaxially or biaxially stretched film. Each of these polymers may be used alone or in a mixture of two or more. As the resin film, preferred are polyamideimide film or polyimide film, which has excellent transparency and heat resistance, uniaxially or biaxially stretched polyester film, cycloolefin derivative film, which has excellent transparency and heat resistance and can accommodate large-sized films, polymethyl methacrylate film, and triacetyl cellulose and isobutyl ester cellulose films, which are transparent and optically non-anisotropic. The thickness of the resin film may be 5 to 200 μm, preferably 20 to 100 μm.

The hard coat layer can be formed by curing a hard coat composition containing a reactive material that forms a crosslinked structure by irradiation with light or heat energy. The hard coat layer can be formed by curing a hard coat composition containing a photocurable (meth)acrylate monomer, or an oligomer and a photocurable epoxy monomer, or an oligomer at the same time. The photocurable (meth)acrylate monomer can include one or more selected from the group consisting of epoxy (meth)acrylate, urethane (meth)acrylate, and polyester (meth)acrylate. The epoxy (meth)acrylate can be obtained by reacting an epoxy compound with a carboxylic acid having a (meth)acryloyl group.

The hard coat composition may further include one or more selected from the group consisting of a solvent, a photoinitiator, and an additive. The additive may include one or more selected from the group consisting of inorganic nanoparticles, a leveling agent, and a stabilizer, and may further include components commonly used in the art, such as an antioxidant, a UV absorber, a surfactant, a lubricant, and an antifouling agent.

<Light-shielding pattern>
The light-shielding pattern may be provided as at least a part of a front panel or a bezel or a housing of a display device to which the front panel is applied. The light-shielding pattern may be formed on the display element side of the front panel. The light-shielding pattern may hide each wiring of the display device so that it is not visible to a user. The color and/or material of the light-shielding pattern is not particularly limited, and the light-shielding pattern may be formed of a resin material having various colors such as black, white, gold, etc.
In one embodiment, the thickness of the light-shielding pattern may be in the range of 2 μm to 50 μm, preferably 4 μm to 30 μm, and more preferably 6 μm to 15 μm. In addition, 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 unit, a shape can be imparted to the light-shielding pattern.

<Method of Manufacturing Circularly Polarizing Plate>
A method for producing a circular polarizing plate will be described using the circular polarizing plate 100 shown in Fig. 1(a) as an example. The circular polarizing plate 100 can be produced by laminating a polarizing plate 1 and a retardation film 2 with a pressure-sensitive adhesive layer 13 interposed therebetween.

The polarizing plate 1 can be manufactured by laminating the polarizer 10 and the protective films 11 and 12 with an adhesive layer between them. The polarizing plate can be manufactured by preparing long members, laminating the respective members by roll-to-roll and then cutting them into a predetermined shape, or by cutting the respective members into a predetermined shape and then laminating them together. After laminating the protective films 11 and 12 to the polarizer 10, a heating process or a humidity adjustment process can be carried out.

The retardation film 2 can be manufactured, for example, as follows. An alignment film is formed on a substrate, and a coating liquid containing a polymerizable liquid crystal compound is applied onto the alignment film. In a state where the polymerizable liquid crystal compound is aligned, active energy rays are irradiated to harden the polymerizable liquid crystal compound. An adhesive layer 14 formed on a release film is laminated onto the layer of hardened polymerizable liquid crystal compound. Next, the substrate and/or the alignment film is peeled off. Next, an adhesive layer 13 formed on a release film is laminated onto a protective film 12. The retardation film 2 may be manufactured by preparing long members, laminating the respective members by roll-to-roll and then cutting them into a predetermined shape, or by laminating the respective members after cutting them into a predetermined shape.

Then, the release film laminated on the adhesive layer 13 is peeled off, and the phase difference film 2 and the polarizing plate 1 are bonded together via the adhesive layer 13, thereby producing the circular polarizing plate 100.

The color difference visible within the plane of the circular polarizer on the reflector after the heat resistance test can be reduced by uniforming the reflected hue within the plane of the circular polarizer after the heat resistance test. Elements necessary for uniforming the reflected hue within the plane of the circular polarizer after the heat resistance test include a uniform reflected hue within the plane of the circular polarizer before the heat resistance test and a small change in reflected hue before and after the heat resistance test.

It is preferable that the reflection hue of the circular polarizer before the heat resistance test is uniform in the plane in order to reduce the reflection hue difference in the plane of the circular polarizer after the heat resistance test. Specifically, the difference between the reflection hue at the center (which may be the center of gravity or the center point 5 shown in FIG. 3) in the main surface before the heat resistance test and the reflection hue at the part other than the center in the main surface (for example, the reflection hue at the point 5 other than the center shown in FIG. 3) is preferably 1.0 or less, more preferably 0.8 or less, and even more preferably 0.6 or less. The reflection hue difference between the center and other parts can be calculated, for example, from the following formula.
Δa*b*=[(Δa*) ² + (Δb*) ² ] ^1/2
In the formula, Δa* is the difference between a* at the center and a* at the other parts than the center, and Δb* is the corresponding difference in b*. If the uniformity of the reflection hue in the plane of the circular polarizer before the heat resistance test is low, the effect of improving visibility may be small even if the change in reflection hue before and after heat resistance is small. The heat resistance test can be performed, for example, by storing the circular polarizer in a dryer set at a temperature of 80° C. for 168 hours.

<Applications>
The circular polarizing plate can be used in various display devices. A display device is a device having a display element, and includes a light-emitting element or a light-emitting device as a light source. Examples of the display device include a liquid crystal display device, an organic EL display device, an inorganic electroluminescence (hereinafter also referred to as inorganic EL) display device, an electron emission display device (for example, a field emission display device (FED) or a surface field emission display device (SED)), an electronic paper (a display device using electronic ink or an electrophoretic element, a plasma display device, a projection type display device (for example, a grating light valve (GLV) display device, a display device having a digital micromirror device (DMD)), and a piezoelectric ceramic display. The liquid crystal display device includes any of a transmissive liquid crystal display device and a semi-transmissive liquid crystal display device. These display devices may be display devices that display two-dimensional images, or may be stereoscopic display devices that display three-dimensional images. The circular polarizing plate can be particularly effectively used in an organic EL display device or an inorganic EL display device.

In Figures 2(a) and (b), the organic EL display devices 104 and 105 have a layered structure in which a circular polarizer is laminated to an organic EL display element 3 via an adhesive layer 14 laminated on a retardation film 20.

(1) Method for Measuring Film Thickness Measurement was performed using a digital micrometer MH-15M manufactured by Nikon Corporation.

(2) Method for Measuring Retardation Value The retardation value was measured using a retardation measurement device KOBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.).

[Preparation of Retardation Film 1]
5 parts of a photoalignment material (weight average molecular weight: 30,000) having the following structure was mixed with 95 parts of cyclopentanone (solvent), and the resulting mixture was stirred at 80° C. for 1 hour to obtain a composition for forming an alignment film.

To 100 parts of a mixture of polymerizable liquid crystal compound A and polymerizable liquid crystal compound B shown below in a mass ratio of 90:10, 1.0 part of a leveling agent (F-556; manufactured by DIC Corporation) and 6 parts of a polymerization initiator, 2-dimethylamino-2-benzyl-1-(4-morpholinophenyl)butan-1-one (Irgacure 369 (Irg369) manufactured by BASF Japan Ltd.) were added.

Furthermore, N-methyl-2-pyrrolidone (NMP) was added so that the solid content concentration became 13%, and the mixture was stirred at 80°C for 1 hour to obtain a composition for forming a liquid crystal cured film.

Polymerizable liquid crystal compound A was produced by the method described in JP-A-2010-31223. Polymerizable liquid crystal compound B was produced according to the method described in JP-A-2009-173893. The molecular structures of each compound are shown below.

(Polymerizable liquid crystal compound A)

(Polymerizable liquid crystal compound B)

[Production of a laminate consisting of a substrate, an alignment film, and a layer of a cured polymerizable liquid crystal compound]
A corona treatment was carried out on a 50 μm thick cycloolefin resin film (trade name "ZF-14-50" manufactured by Zeon Corporation) as a substrate. The composition for forming an alignment film was applied to the corona treated surface with a bar coater. The coating film was dried at 80°C for 1 minute. The dried coating film was irradiated with polarized UV at an axial angle of 45° using a polarized UV irradiation device (trade name "SPOT CURE SP-9" manufactured by Ushio Inc.) to obtain an alignment film. The irradiation with polarized UV was carried out so that the accumulated light amount at a wavelength of 313 nm was 100 mJ/ ^cm2 .

Next, the liquid crystal cured film-forming composition was applied onto the alignment film using a bar coater. The coating film was dried at 120°C for 1 minute. The dried coating film was irradiated with ultraviolet light using a high-pressure mercury lamp (trade name: "Uniquer VB-15201BY-A" by Ushio Electric Co., Ltd.). The ultraviolet light irradiation process was carried out under a nitrogen atmosphere so that the integrated light amount at a wavelength of 365 nm was 250 mJ/ ^cm2 . Immediately after the irradiation, the cured film was placed in an oven set at 5°C for 20 seconds as a cooling process. Immediately after removing from the oven, the ultraviolet light irradiation process and the cooling process were carried out again to obtain a laminate consisting of a substrate, an alignment film, and a layer in which the polymerizable liquid crystal compound was cured.

(Measurement of Phase Difference Value)
An adhesive layer was laminated on the layer of the laminate in which the polymerizable liquid crystal compound was cured. The laminate was attached to glass via the adhesive layer. Thereafter, the substrate provided in the laminate was peeled off to obtain a sample for evaluating the retardation value. As a result, the layer in which the polymerizable liquid crystal compound was cured had the retardation values Re(λ) at each wavelength of Re(450)=121 nm, Re(550)=142 nm, and Re(650)=146 nm. As a result, Re(450)/Re(550)=0.85 and Re(650)/Re(550)=1.03 were calculated. The layer in which the polymerizable liquid crystal compound was cured was a layer that gave a retardation of λ/4.

(Measurement of puncture elasticity)
The puncture modulus was measured as follows. A needle was attached to a handy compression tester "KES-G5 needle penetration force measurement specification" manufactured by Kato Tech Co., Ltd. A needle was pierced perpendicularly into the main surface of a laminate from which the substrate was peeled off, fixed between two plates with a circular hole of 11 mm in diameter, and the force (gf) just before the break was divided by the strain (mm) at that time to calculate the value. This operation was performed on five retardation films (puncture test samples), and the average value was taken as the puncture modulus of the retardation film. A needle with a tip diameter of 1 mmφ and 0.5R was used. The needle was pierced at a speed of 0.33 cm/sec. The puncture modulus of retardation film 1 is shown in Table 1.

[Preparation of Retardation Film 2]
A laminate including a retardation film 2 was produced in the same manner as in [Production of Retardation Film 1], except that the cumulative amount of ultraviolet light irradiated when curing the coating film of the liquid crystal cured film-forming composition was 400 mJ/cm ² at a wavelength of 365 nm (i.e., the cumulative amount of light of two ultraviolet light irradiations in total was 800 mJ/cm ² ). The puncture elastic modulus of the retardation film 2 was measured in the same manner as above. The puncture elastic modulus of the retardation film 2 is shown in Table 1.

[Preparation of Retardation Film 3]
A laminate including a retardation film 3 was produced in the same manner as in [Preparation of Retardation Film 1], except that the cumulative amount of ultraviolet light irradiated when curing the coating film of the liquid crystal cured film-forming composition was 600 mJ/cm ² at a wavelength of 365 nm (i.e., the cumulative amount of ultraviolet light irradiated twice was 1200 mJ/cm ² in total). The puncture elastic modulus of the retardation film 3 was measured in the same manner as above. The puncture elastic modulus of the retardation film 3 is shown in Table 1.

[Preparation of Retardation Film 4]
A laminate including a retardation film 4 was produced in the same manner as in [Production of Retardation Film 1], except that the cumulative amount of ultraviolet light irradiated when curing the coating film of the liquid crystal cured film-forming composition was 800 mJ/cm ² at a wavelength of 365 nm (i.e., the cumulative amount of light of two ultraviolet light irradiations in total was 1600 mJ/cm ² ). The puncture elastic modulus of the retardation film 4 was measured in the same manner as above. The puncture elastic modulus of the retardation film 4 is shown in Table 1.

[Preparation of Retardation Film 5]
As a composition for forming a vertical alignment film, 5 parts by weight of Sunever SE-610 (manufactured by Nissan Chemical Industries, Ltd.), which is a commercially available alignment polymer, and 95 parts by weight of methyl ethyl ketone (solvent) were mixed to obtain a composition for forming a vertical alignment film.

As a composition for forming a vertically aligned retardation layer, 20 parts by weight of a photopolymerizable nematic liquid crystal compound (RMM28B manufactured by Merck) and 1 part by weight of Irgacure 907 (Irg-907 manufactured by BASF) as a photopolymerization initiator were dissolved in 80 parts by weight of propylene glycol monomethyl ether acetate to prepare a coating liquid for forming a vertically aligned retardation layer.

A corona treatment was carried out on a 50 μm thick cycloolefin resin film (trade name "ZF-14-50" manufactured by Zeon Corporation) as a substrate. The composition for forming a vertical alignment film was applied to the corona treated surface with a bar coater. The applied film was heated at 100°C for 120 seconds and cured to form a vertical alignment film.

A coating solution for forming a vertically aligned retardation layer was applied onto the vertically aligned film obtained above, and the coating film was heated at a temperature of 80° C. for 60 seconds. Thereafter, ultraviolet rays (UVB) were irradiated so that the cumulative light amount was 220 mJ/cm ² , and the composition for forming a vertically aligned retardation layer was polymerized and cured to form a vertically aligned retardation layer having a thickness of 0.7 μm on the vertically aligned film. When the retardation value at a wavelength of 550 nm of the obtained vertically aligned retardation layer was measured, it was found to be Re(550)=1 nm and Rth(550)=−75 nm. That is, the vertically aligned retardation layer was a positive C layer that satisfied the relationship of nx≒ny<nz. In addition, since the retardation value at a wavelength of 550 nm of the cycloolefin resin film, which is the base material, is approximately 0, it does not affect the optical properties of the vertically aligned retardation layer.

Next, a layer imparting a λ/4 phase difference was formed on the obtained vertically aligned retardation layer in the same manner as in [Preparation of Retardation Film 2], and a laminate including retardation film 5 was prepared. In this manner, a laminate including retardation film 5 was prepared in which the substrate, vertical alignment film, positive C layer, alignment film, and layer imparting a λ/4 phase difference were laminated in this order. The puncture modulus of retardation film 5 was measured in the same manner as above. The puncture modulus of retardation film 5 is shown in Table 1.

[Preparation of adhesive layer]
Adhesive A: Sheet-shaped adhesive having a thickness of 5 μm ("NCF #L2" manufactured by Lintec Corporation)
Adhesive B: Sheet-shaped adhesive having a thickness of 25 μm ("P-3132" manufactured by Lintec Corporation)

[Preparing the protective film]
Protective film A: A film in which a hard coat layer having a thickness of 3 μm is formed on a stretched film made of a norbornene-based resin having a thickness of 25 μm (trade name "COP25ST-HC" manufactured by Nippon Paper Industries Co., Ltd.)
Protective film B: 20 μm thick triacetyl cellulose film (manufactured by Fujifilm Corporation under the trade name "ZRG20SL").
Protective film C: an unstretched film made of triacetyl cellulose having a thickness of 25 μm

[Preparation of front panel]
A front panel having a hard coat layer on both sides of a substrate film was prepared. The substrate film was a polyimide film having a thickness of 50 μm, and the hard coat layer had a thickness of 10 μm.

[Example 1]
[Preparation of Polarizing Plate]
A 20 μm thick polyvinyl alcohol film (average polymerization degree about 2400, saponification degree 99.9 mol% or more) was uniaxially stretched by about 4 times by dry stretching, and further immersed in pure water at 40 ° C. for 40 seconds while maintaining tension, and then immersed in an aqueous solution of iodine / potassium iodide / water with a weight ratio of 0.052 / 5.7 / 100 at 28 ° C. for 30 seconds to perform a dyeing treatment. Then, immersed in an aqueous solution of potassium iodide / boric acid / water with a weight ratio of 11.0 / 6.2 / 100 at 70 ° C. for 120 seconds. Subsequently, after washing with pure water at 8 ° C. for 15 seconds, it was dried at 60 ° C. for 50 seconds and then at 75 ° C. for 20 seconds while holding it under a tension of 300 N, to obtain a polarizer of 7 μm in thickness in which iodine was adsorbed and aligned in the polyvinyl alcohol film.

A water-based adhesive was applied to one surface of the polarizer, and the protective film A was attached thereto so that the stretching direction of the protective film A was at an angle of 45 degrees to the absorption axis of the polarizer.
A water-based adhesive was applied to the other surface of the polarizer, and a protective film B was attached thereto. The resulting product was then dried to obtain a polarizing plate. The water-based adhesive was prepared by dissolving 3 parts of carboxyl-modified polyvinyl alcohol (trade name "KL-318" available from Kuraray Co., Ltd.) in 100 parts of water, and adding 1.5 parts of a polyamide epoxy-based additive, which is a water-soluble epoxy resin (trade name "Sumirez Resin 650 (30)" available from Taoka Chemical Co., Ltd., an aqueous solution with a solids concentration of 30%).

Adhesive A was laminated on the layer of the cured polymerizable liquid crystal compound in the laminate produced in [Preparation of Retardation Film 2]. Next, the substrate was peeled off from the laminate, and adhesive B was laminated on the surface exposed by the peeling. In this way, retardation film 2 with double-sided adhesive was produced, consisting of adhesive A, the layer of the cured polymerizable liquid crystal compound, the alignment film, and adhesive B.

[Preparation of Circularly Polarizing Plate]
The retardation film 2 with double-sided adhesive was attached to the protective film B of the polarizing plate via the adhesive A of the retardation film 2 with double-sided adhesive. The slow axis of the layer in which the polymerizable liquid crystal compound was cured was at 45 degrees to the absorption axis of the polarizer and at 90 degrees to the stretching direction of the protective film A. In this manner, a circular polarizing plate consisting of the protective film A, the aqueous adhesive layer, the polarizer, the aqueous adhesive layer, the protective film B, the adhesive A, the layer in which the polymerizable liquid crystal compound was cured, the alignment film, and the adhesive B was produced.

The circularly polarizing plate was cut into a rectangle of 140 mm x 70 mm so that the slow axis of the layer in which the polymerizable liquid crystal compound was cured was parallel to the long side. At this time, the stretching direction of the protective film A was parallel to the short side direction. The cut circularly polarizing plate was attached to a glass plate (manufactured by Corning, product number: EAGLE XG (registered trademark)) having a thickness of 0.4 mm via the adhesive B.
In this manner, samples for evaluation were prepared.

[Example 2]
A circularly polarizing plate was prepared in the same manner as in Example 1, except that the laminate prepared in [Preparation of Retardation Film 3] was used instead of the laminate prepared in [Preparation of Retardation Film 2] in Example 1, and a sample for evaluation was prepared.

[Example 3]
A circularly polarizing plate was prepared in the same manner as in Example 1, except that the laminate prepared in [Preparation of Retardation Film 4] was used instead of the laminate prepared in [Preparation of Retardation Film 2] in Example 1, and a sample for evaluation was prepared.

[Example 4] (Comparative)
A circularly polarizing plate was produced in the same manner as in Example 2, and a sample for evaluation was produced, except that protective film A was attached to the polarizer so that the slow axis of the layer in which the polymerizable liquid crystal compound was cured was at an angle of 45 degrees to the absorption axis of the polarizer and at an angle of 0 degrees to the stretching direction of protective film A. In this case, the stretching direction of protective film A was parallel to the long side direction.

[Example 5]
A circularly polarizing plate was prepared in the same manner as in Example 1, except that the laminate prepared in [Preparation of Retardation Film 5] was used instead of the laminate prepared in [Preparation of Retardation Film 2] in Example 1, and a sample for evaluation was prepared.

[Example 6]
A circular polarizing plate was produced in the same manner as in Example 1, except that the protective film B was not laminated when the polarizing plate was produced. Furthermore, the adhesive layer B was laminated on the protective film A. The front plate and the circular polarizing plate were bonded together via the adhesive layer B. In this manner, a circular polarizing plate was produced, which was composed of the front plate, the adhesive layer B, the protective film A, the aqueous adhesive layer, the polarizer, the adhesive A, the layer in which the polymerizable liquid crystal compound was cured, the alignment film and the adhesive B. Furthermore, a sample for evaluation was produced in the same manner as in Example 1.

[Example 7]
[Surface treatment layer forming composition]
The following components were mixed to prepare a composition for forming a surface treatment layer.
2.0 parts by mass of dendrimer acrylate having 18 functional acrylic groups (Miramer SP1106, Miwon Co., Ltd.),
10.0 parts by mass of urethane acrylate having hexafunctional acrylic groups (Miramer PU-620D, Miwon Co., Ltd.),
8.0 parts by mass of an acrylate monomer having a trifunctional acrylic group (M340, Miwon Co., Ltd.),
Photopolymerization initiator (Irgacure-184, BASF) 2 parts by mass,
Leveling agent (BYK-3530, BYK Corporation) 0.1 parts by mass,
Methyl ethyl ketone (MEK) 77.9 parts by weight

[Polarizer-forming composition]
(Polymerizable liquid crystal compound)
The polymerizable liquid crystal compound is a polymerizable liquid crystal compound represented by formula (1-6) [hereinafter, also referred to as compound (1-6)] and a polymerizable liquid crystal compound represented by formula (1-7) [hereinafter, Compound (1-7) was used.

Compounds (1-6) and (1-7) were synthesized according to the method described in Lub et al. Recl. Trav. Chim. Pays-Bas, 115, 321-328 (1996).

(Dichroic dye)
As the dichroic dye, azo dyes described in the examples of JP-A-2013-101328 and represented by the following formulas (2-1a), (2-1b), and (2-3a) were used.

The composition for forming the polarizing layer was prepared by mixing 75 parts of compound (1-6), 25 parts of compound (1-7), 2.5 parts each of the azo dyes represented by the above formulas (2-1a), (2-1b), and (2-3a) as dichroic dyes, 6 parts by weight of 2-dimethylamino-2-benzyl-1-(4-morpholinophenyl)butan-1-one (Irgacure 369, manufactured by BASF Japan) as a polymerization initiator, and 1.2 parts of a polyacrylate compound (BYK-361N, manufactured by BYK-Chemie) as a leveling agent in 400 parts of toluene as a solvent, and stirring the resulting mixture at 80°C for 1 hour.

The above-mentioned composition for forming a surface treatment layer was applied to the protective film A. The coating film was dried at 80°C for 5 minutes, and then irradiated with ultraviolet light using a UV irradiation device so that the exposure amount was 500 mJ/ ^cm2 (based on 365 nm) to cure the coating film. The UV irradiation device used was SPOT CURE SP-7, manufactured by Ushio Inc. The thickness of the surface treatment layer was 10.0 µm.

The composition for forming an alignment film used in the preparation of the retardation film 1 was applied onto the surface treatment layer of the protective film A by a bar coating method. The coating film was dried at 80°C for 1 minute. Next, the coating film was irradiated with polarized UV using the above-mentioned UV irradiation device and wire grid to impart alignment performance to the coating film. The exposure dose was 100 mJ/cm ² (based on 365 nm). UIS-27132## (manufactured by Ushio Inc.) was used as the wire grid. In this manner, an alignment film was formed. The thickness of the alignment film was 100 nm.

The polarizer-forming composition was applied onto the formed alignment film by a bar coating method. The coating film was heated and dried at 100° C. for 2 minutes, and then cooled to room temperature. The coating film was irradiated with ultraviolet light at an integrated light amount of 1200 mJ/cm ² (based on 365 nm) using the UV irradiation device to form a polarizer. The thickness of the obtained polarizer was 3 μm. A composition containing polyvinyl alcohol and water was applied onto the polarizer so that the thickness after drying was 0.5 μm, and the composition was dried at a temperature of 80° C. for 3 minutes to form a protective layer. In this way, a polarizing plate consisting of a protective film A, a surface treatment layer, an alignment film, a polarizer, and a protective layer was produced.

A circular polarizing plate was produced in the same manner as in Example 6, except that the above polarizing plate was used, and a sample for evaluation was produced. The evaluation sample had a front plate, adhesive layer B, protective film A, a surface treatment layer, an alignment film, a polarizer, a protective layer, adhesive A, a layer of a hardened polymerizable liquid crystal compound, an alignment film, and adhesive B, in that order.

[Example 8]
A circularly polarizing plate was produced and an evaluation sample was produced in the same manner as in Example 7, except that protective film C was used instead of the laminate of protective film A and surface treatment layer. The evaluation sample had a front plate, pressure-sensitive adhesive layer B, protective film C, an alignment film, a polarizer, a protective layer, pressure-sensitive adhesive A, a layer of a cured polymerizable liquid crystal compound, an alignment film, and pressure-sensitive adhesive B in this order.

[Example 9]
Except for not laminating a front panel, a circularly polarizing plate was produced and an evaluation sample was produced in the same manner as in Example 8. The evaluation sample had a protective film C, an alignment film, a polarizer, a protective layer, pressure-sensitive adhesive A, a layer of a cured polymerizable liquid crystal compound, an alignment film, and pressure-sensitive adhesive B in this order.

[Comparative Example 1]
A circularly polarizing plate was prepared in the same manner as in Example 1, except that the laminate prepared in [Preparation of Retardation Film 1] was used instead of the laminate prepared in [Preparation of Retardation Film 2] in Example 1, and a sample for evaluation was prepared.

[Color evaluation before and after heat resistance test]
As the reflector, MIRO (5011GP) manufactured by ALANOD was prepared. This reflector is a specular reflector having a reflecting surface formed by vapor deposition.

The evaluation sample was placed on the reflector. The reflected hue (a*, b*) was measured using a spectrophotometer (Konica Minolta Japan, Inc., product name: CM-2600d). The reflected hue was measured using the SCI method (specular reflected light included) and is the value when the light source is D65.

Specifically, point 5 shown in Figure 3 was used as the measurement point. The nine points 5 shown in Figure 3 are points in an area 5 mm inward from the edge of the circular polarizer, and are positioned at intervals of approximately 30 mm along the short side and approximately 65 mm along the long side.

The evaluation samples prepared in Examples 1 to 9 and Comparative Example 1 above were measured for reflected hue before and after storage for 168 hours in a dryer at 80°C. The absolute value of the hue change Δa*b* at each point was calculated. The hue change value at each point was calculated based on the direction of the hue change, and the difference between the maximum and minimum hue change values of each evaluation sample was taken as Δa*b* (MAX-MIN). The results are shown in Tables 2 and 3.

Δa*=a*(after heat resistance test)−a*(before heat resistance test)
Δb*=b* (after heat resistance test)−b* (before heat resistance test)
Δa*b*=[(Δa*) ² + (Δb*) ² ] ^1/2
When Δa* is 0 or more, the hue change value is represented as Δa*b*, and when Δa* is smaller than 0, the hue change value is represented as Δa*b*×−1.

The present invention is useful because it can provide a circular polarizing plate equipped with a retardation film that exhibits little change in hue before and after placement in a high-temperature environment.

REFERENCE SIGNS LIST 1 Polarizing plate 2 Retardation film 3 Organic EL display element 4 Front plate 5 Point 10 Polarizer 11, 12 Protective film 13, 14, 16 Pressure-sensitive adhesive layer 15 Adhesive layer 20, 21 Layer of hardened polymerizable liquid crystal compound 100, 101, 102, 103 Circularly polarizing plate 104, 105, 106 Organic EL display device

Claims (6)

A circularly polarizing plate in which a polarizing plate and a retardation film are laminated via an adhesive layer,
The circularly polarizing plate has a pressure-sensitive adhesive layer on a surface thereof,
The polarizing plate has a polarizer,
the retardation film is disposed between the polarizing plate and the pressure-sensitive adhesive layer,
The retardation film includes two retardation layers,
The retardation layer includes a layer in which a polymerizable liquid crystal compound is hardened,
The retardation film has a puncture elastic modulus of 30 gf/mm or more and 150 gf/mm or less,
The circular polarizer has a substantially rectangular shape,
The puncture elastic modulus is an elastic modulus measured in a test using a needle with a tip diameter of 1 mmφ and 0.5R at a puncture speed of 0.33 cm/sec, and the test is performed in a state where the retardation film is fixed between two plates with a circular hole with a diameter of 11 mm. The circular polarizing plate according to claim 1, wherein the polarizer has a thickness of 15 μm or less. The circular polarizing plate according to claim 1 or 2, wherein the thickness of the retardation film is 25 μm or less. The circular polarizing plate according to any one of claims 1 to 3, wherein the polarizer is formed from a layer of a cured liquid crystal compound. A circularly polarizing plate with a front plate, in which the circularly polarizing plate according to any one of claims 1 to 4 and a front plate are laminated via an adhesive layer. A display device comprising the circularly polarizing plate according to any one of claims 1 to 4 laminated on a display element via the pressure-sensitive adhesive layer.