Circular polarizing plate, long broadband wavelength film, method for manufacturing same, and image display device

Abstract

Provided is a circular polarizing plate comprising, in this order: a linear polarizing film; a λ / 2 layer having a slow axis in a direction forming an angle of 22.5°±10° with respect to the absorption axis of the linear polarizing film; and a λ / 4 layer having a slow axis in a direction forming an angle of 90°±20° with respect to the absorption axis of the linear polarizing film, wherein the λ / 2 layer comprises a resin including a cyclic olefin polymer, and the λ / 4 layer comprises a resin including a polymer containing a 4-vinylbiphenyl monomer unit.

Description

Circularly polarizing plate, long broadband wavelength film and its manufacturing method, and image display device

[0001] The present invention relates to a circular polarizer, a long broadband wavelength film and a method for producing the same, and an image display device equipped with the circular polarizer.

[0002] An anti-reflection film is sometimes provided on the display surface of image display devices such as liquid crystal display devices and organic EL display devices to suppress reflection of external light from the display surface. As such an anti-reflection film, a film combining a linear polarizing film and a wave plate is known (Patent Documents 1 to 4). The term "organic EL" refers to "organic electroluminescence" unless otherwise specified. The technology of Patent Document 5 is also publicly known.

[0003] US Patent Application Publication No. 2022 / 0187524 US Patent No. 9,703,013 International Publication No. 2016 / 047465 Japanese Patent No. 7059936 (US Patent Application Publication No. 2019 / 0293852) JP-A-2010-522900 (WO 2008 / 121580)

[0004] For example, a circular polarizer combining a linear polarizing film and a wavelength plate can suppress reflection of external light from the display surface when provided on the display surface of an image display device. When using such a circular polarizer, in order to effectively reduce the reflectance of external light, the circular polarizer is required to block circularly polarized light over a wide wavelength range. In order to achieve blocking of circularly polarized light over such a wide wavelength range, a broadband wavelength film having a combination of a λ / 2 layer and a λ / 4 layer formed of a resin may be used for the wavelength plate. Since the broadband wavelength film can exert its optical function over a wide wavelength range, it is expected that a circular polarizer capable of suppressing reflection of light over a wide wavelength range can be obtained.

[0005] The broadband wavelength film can be produced by co-stretching. Specifically, the broadband wavelength film can be produced by a method including co-stretching a resin layer preceding the λ / 2 layer and a resin layer preceding the λ / 4 layer. The co-stretching method can reduce the number of steps required to produce the broadband wavelength film, thereby improving production efficiency.

[0006] The present inventors have focused on resins containing cyclic olefin polymers, which have excellent mechanical and optical properties, as resins for forming the λ / 2 layer. Hereinafter, "resins containing cyclic olefin polymers" may be referred to as "COP resins." To produce a broadband wavelength film having a λ / 2 layer containing a COP resin by using the above-described co-stretching, the stretching conditions of the co-stretching, such as the stretching temperature and stretch ratio, are limited to a range in which a λ / 2 layer can be obtained by stretching the resin layer containing the COP resin. Therefore, the resin contained in the λ / 4 layer is required to be able to form the desired λ / 4 layer under the restricted stretching conditions.

[0007] The present inventors have investigated resins that can form a λ / 4 layer under the restricted stretching conditions described above. While it was difficult to form a λ / 4 layer with many resins, it was possible to form a λ / 4 layer with some resins. However, it was found that when such resins capable of forming a λ / 4 layer were used, the circularly polarizing plate would exhibit unevenness in the reflectance and color of reflected light.

[0008] The present invention has been devised in view of the above-mentioned problems, and aims to provide a new circular polarizing plate that can suppress unevenness in the reflectance and color of reflected light; a long broadband wavelength film that can be used to manufacture the circular polarizing plate and a method for manufacturing the same; and an image display device that includes the circular polarizing plate.

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, the present inventors have found that the above-mentioned problems can be solved by a circular polarizing plate comprising, in this order, a linear polarizing film, a λ / 2 layer having a slow axis in a specific direction and containing a resin containing a cyclic olefin polymer, and a λ / 4 layer having a slow axis in a specific direction, wherein the λ / 4 layer contains a resin including a polymer containing a 4-vinylbiphenyl monomer unit, and have completed the present invention. That is, the present invention includes the following.

[0010] <1> A circular polarizer comprising, in this order: a linear polarizing film; a λ / 2 layer having a slow axis in a direction forming an angle of 22.5°±10° with respect to the absorption axis of the linear polarizing film; and a λ / 4 layer having a slow axis in a direction forming an angle of 90°±20° with respect to the absorption axis of the linear polarizing film; the λ / 2 layer containing a resin including a cyclic olefin polymer; and the λ / 4 layer containing a resin including a polymer containing 4-vinylbiphenyl monomer units. <2> The circular polarizer according to <1>, in which the proportion of 4-vinylbiphenyl monomer units contained in 100% by weight of the polymer containing 4-vinylbiphenyl monomer units is 70% by weight or more. <3> The circular polarizer according to <1> or <2>, in which the λ / 4 layer has a thickness of 10 μm or less. <4> The circular polarizer according to any one of <1> to <3>, in which the λ / 4 layer has a birefringence Δn of 0.010 or more. <5> A method for producing a broadband wavelength film, comprising, in this order: a first step of preparing a resin layer (A) containing a cyclic olefin polymer as a long obliquely stretched film, a second step of forming a resin layer (B) containing a polymer containing 4-vinylbiphenyl monomer units on the resin layer (A) to obtain a multilayer film, and a third step of stretching the multilayer film in a stretching direction forming an angle of 0°±20° with respect to the longitudinal direction of the multilayer film to obtain a long broadband wavelength film comprising λ / 2 layers and λ / 4 layers. <6> A method for producing a broadband wavelength film according to <5>, wherein the second step comprises applying, onto the resin layer (A), a resin liquid containing a resin containing the polymer containing 4-vinylbiphenyl monomer units and an organic solvent, and drying the applied resin liquid. <7> A long broadband wavelength film comprising: a λ / 2 layer having a slow axis in a direction forming an angle of 22.5°±10° with respect to the longitudinal direction of the broadband wavelength film; and a λ / 4 layer having a slow axis in a direction forming an angle of 90°±20° with respect to the longitudinal direction of the broadband wavelength film; the λ / 2 layer comprises a resin containing a cyclic olefin polymer; and the λ / 4 layer comprises a resin containing a polymer containing a 4-vinylbiphenyl monomer unit. <8> An image display device comprising the circular polarizer according to any one of <1> to <4>.

[0011] According to the present invention, it is possible to provide a new circular polarizing plate that can suppress unevenness in the reflectance and color of reflected light; a long broadband wavelength film that can be used to manufacture the circular polarizing plate and a method for manufacturing the same; and an image display device that includes the circular polarizing plate.

[0012] Fig. 1 is a perspective view schematically showing a circularly polarizing plate according to one embodiment of the present invention. Fig. 2 is a perspective view schematically showing a state in which a circularly polarizing plate according to one embodiment of the present invention is provided on a surface. Fig. 3 is a perspective view schematically showing a resin layer (A) as a long obliquely stretched film prepared in the first step of a preferred example of a method for producing a broad wavelength film. Fig. 4 is a perspective view schematically showing a multilayer film obtained in the second step of a preferred example of a method for producing a broad wavelength film. Fig. 5 is a perspective view schematically showing a broad wavelength film obtained in the third step of a preferred example of a method for producing a broad wavelength film.

[0013] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented with any modifications within the scope of the claims and their equivalents.

[0014] In the following description, the term "long" for a certain member (e.g., a film or layer) means that the length is 5 times or more, preferably 10 times or more, the width, specifically a length that can be wound into a roll for storage or transportation. There is no particular upper limit to the length, and it can be, for example, 100,000 times or less the width.

[0015] In the following description, the in-plane retardation Re of a layer is a value expressed by Re = (nx - ny) x d, unless otherwise specified. Furthermore, the birefringence Δn of a layer is a value expressed by Δn = nx - ny, and therefore expressed as Δn = Re / d, unless otherwise specified. Furthermore, the retardation Rth in the thickness direction of a layer is a value expressed by Rth = [{(nx + ny) / 2} - nz] x d, unless otherwise specified. Here, nx represents the refractive index in the in-plane direction of the layer that gives the maximum refractive index. Unless otherwise specified, "in-plane direction" represents the direction perpendicular to the thickness direction. ny represents the refractive index in the in-plane direction of the layer that is perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer. The measurement wavelength is 590 nm, unless otherwise specified.

[0016] In the following description, unless otherwise specified, a material with positive intrinsic birefringence means a material whose refractive index in the stretching direction is greater than that in the direction perpendicular to the stretching direction. Furthermore, a material with negative intrinsic birefringence means a material whose refractive index in the stretching direction is smaller than that in the direction perpendicular to the stretching direction. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

[0017] In the following description, the term "(meth)acrylic" includes "acrylic", "methacrylic" and combinations thereof unless otherwise specified.

[0018] In the following description, unless otherwise specified, the oblique direction of a long film refers to an in-plane direction of the film, which is neither parallel nor perpendicular to the width direction of the film.

[0019] In the following description, unless otherwise specified, the front direction of a film means the normal direction of the main surface of the film, and specifically refers to the direction of the polar angle of 0° and the azimuthal angle of 0° of the main surface.

[0020] In the following description, unless otherwise specified, the tilt direction of a film means a direction that is neither parallel nor perpendicular to the main surface of the film, and specifically refers to a direction in which the polar angle of the main surface is in the range of greater than 0° and less than 90°.

[0021] In the following description, unless otherwise specified, the directions of elements as "parallel," "vertical," and "orthogonal" may include an error within a range that does not impair the effects of the present invention, for example, within a range of ±5°.

[0022] In the following description, the angle formed by the optical axis (absorption axis, slow axis, etc.) of each layer in a member having multiple layers represents the angle when the layer is viewed from the thickness direction, unless otherwise specified.

[0023] In the following description, unless otherwise specified, the slow axis of a film or layer refers to the slow axis in the plane of the film or layer.

[0024] In the following description, unless otherwise specified, the orientation angle of a film or layer refers to the angle that the slow axis of the film or layer makes with a reference direction perpendicular to the thickness direction. For long films and layers, the longitudinal direction is used as the reference direction unless otherwise specified.

[0025] In the following description, unless otherwise specified, the terms "circular polarizer" and "wave plate" include not only rigid members but also flexible members such as resin films.

[0026] 1 is a perspective view schematically illustrating a circular polarizer according to one embodiment of the present invention. As shown in FIG. 1, a circular polarizer 100 according to one embodiment of the present invention has an absorption axis A １１０ and a linear polarizing film 110 having an absorption axis A of the linear polarizing film 110. １１０ An angle θ of 22.5°±10° １２０ The slow axis A is in the direction １２０ and the absorption axis A of the linear polarizing film 110. １１０ Angle θ of 90°±20° １３０ Direction A １３０ Slow axis A １３０and a λ / 4 layer 130 having the above structure, in this order. The λ / 2 layer 120 also contains a COP resin containing a cyclic olefin polymer. The λ / 4 layer 130 also contains a resin containing a polymer containing a 4-vinylbiphenyl monomer unit. In the following description, a "polymer containing a 4-vinylbiphenyl monomer unit" may be referred to as a "4-vinylbiphenyl-based polymer." A resin containing this 4-vinylbiphenyl-based polymer may be referred to as a "vinylbiphenyl-based resin."

[0027] Fig. 2 is a perspective view showing a schematic view of a circularly polarizing plate 100 according to one embodiment of the present invention provided on a surface 200. As shown in Fig. 2, when the circularly polarizing plate 100 is provided on a surface 200 that can reflect light (such as a display surface or a mirror surface), the circularly polarizing plate 100 according to this embodiment can suppress unevenness in the reflectance and color of the reflected light. Specifically, this is as follows.

[0028] A circularly polarizing plate 100 is provided on a surface 200 such that the λ / 4 layer 130, the λ / 2 layer 120, and the linear polarizing film 110 are arranged in this order from the surface 200 side. The surface 200 is then observed in a tilt direction 10 of polar angle ρ and azimuthal angle φ. Here, the "polar angle" ρ of the tilt direction 10 represents the angle that the tilt direction 10 makes with respect to the normal direction 11 of the surface 200. Furthermore, the "azimuthal angle" φ of the tilt direction 10 represents the angle that the component of the tilt direction 10 parallel to the surface 200 makes with respect to a reference direction 12 parallel to the surface 200. The circularly polarizing plate 100 according to this embodiment can suppress light reflection on the surface 200 and reduce reflectivity. Furthermore, the reflectivity and color of the reflected light can be made uniform, thereby suppressing unevenness in the reflectivity and color of the reflected light. In general, unevenness in reflectance can be visually recognized as unevenness in density, and unevenness in color can be visually recognized as uneven color. Furthermore, preferably, according to the circularly polarizing plate 100 according to this embodiment, when observed in an inclined direction, changes in the reflectance and color of reflected light depending on the azimuth angle φ of the inclined direction can be suppressed.

[0029] The inventors of the present invention speculate that the mechanism by which the above-mentioned effects are obtained is as follows: However, the technical scope of the present invention is not limited to the mechanism below.

[0030] The combination of the λ / 2 layer 120 and the λ / 4 layer 130 included in the circular polarizer 100 forms a broadband wavelength film 140 (see FIG. 1 ). This broadband wavelength film 140 can impart an in-plane retardation of approximately ¼ of the wavelength of light transmitted through the broadband wavelength film 140 over a wide wavelength range. Thus, in the circular polarizer 100, linearly polarized light over a wide wavelength range that has been transmitted through the linear polarizer film 110 is converted into circularly polarized light by the broadband wavelength film 140. Therefore, the circular polarizer 100 can absorb either right-handed or left-handed circularly polarized light over a wide wavelength range and transmit the remaining light, thereby exhibiting a reflection suppressing function.

[0031] As a specific example, as shown in FIG. 2 , when light is irradiated onto a surface 200 on which a circular polarizer 100 is installed, only a portion of the light, linearly polarized light, passes through the linear polarizing film 110. The transmitted linearly polarized light becomes circularly polarized light by passing through the broadband wavelength film 140. This circularly polarized light is reflected by the surface 200 and becomes linearly polarized light by passing through the broadband wavelength film 140 again. This linearly polarized light has a vibration direction (polarization axis) perpendicular to the vibration direction (polarization axis) of the incident linearly polarized light, so it does not pass through the linear polarizing film 110. Thus, the reflection suppression function of the circular polarizer 100 is achieved. Furthermore, because the broadband wavelength film 140 can exhibit its optical function over a wide wavelength range, the reflection suppression function can be obtained over a wide wavelength range, thereby effectively reducing light reflection at the surface 200.

[0032] Furthermore, the 4-vinylbiphenyl polymer exhibits high birefringence. Therefore, a vinylbiphenyl resin containing the 4-vinylbiphenyl polymer can exhibit high birefringence during the process of forming the λ / 2 layer 120 and the λ / 4 layer 130 by co-stretching. Therefore, the λ / 4 layer 130 can have a sufficiently large birefringence, allowing it to be formed thin. A thin λ / 4 layer can improve the surface condition of the layer. For example, the uniformity of the surface height can be increased, resulting in high flatness. Therefore, the magnitude of retardation imparted to transmitted light by the λ / 4 layer 130 and the angle of incidence of light onto the λ / 4 layer 130 can be made uniform. Therefore, the amount and wavelength of light blocked by the circular polarizing plate 100 can be made uniform, thereby suppressing unevenness in the reflectance and color of reflected light, and more preferably, suppressing changes in the reflectance and color of reflected light depending on the azimuth angle φ.

[0033] Furthermore, according to the circular polarizer 100 of this embodiment, it is usually possible to suppress light reflection by the surface 200 not only in the tilt direction but also in the front direction. Furthermore, since the λ / 4 layer 130 can be made thin, it is usually possible to make the entire circular polarizer 100 thin.

[0034] <Linear Polarizing Film> A linear polarizing film is a film having an absorption axis. A linear polarizing film has the function of absorbing linearly polarized light having a vibration direction parallel to the absorption axis and transmitting other polarized light. The vibration direction of linearly polarized light refers to the vibration direction of the electric field of the linearly polarized light.

[0035] A linear polarizing film typically includes a polarizer layer and, if necessary, a protective film layer for protecting the polarizer layer. The polarizer layer may be, for example, a film of a suitable vinyl alcohol-based polymer subjected to appropriate treatments in an appropriate order and manner. Examples of such vinyl alcohol-based polymers include polyvinyl alcohol and partially formalized polyvinyl alcohol. Examples of film treatments include dyeing with iodine and a dichroic substance such as a dichroic dye, stretching, and crosslinking. Typically, in the stretching process for producing a polarizer layer, the unstretched film is stretched in the longitudinal direction. Therefore, the resulting polarizer layer may exhibit an absorption axis parallel to the longitudinal direction of the polarizer layer. The polarizer layer is preferably capable of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, and particularly preferably has an excellent polarization degree. The thickness of the polarizer layer is typically 5 μm to 80 μm, but is not limited thereto.

[0036] Any transparent film can be used as the protective film layer for protecting the polarizer layer. Among them, a film made of a resin excellent in transparency, mechanical strength, thermal stability, moisture blocking property, etc. is preferred. Examples of such resins include acetate resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, cyclic olefin resins, (meth)acrylic resins, etc. Among them, acetate resins, cyclic olefin resins, and (meth)acrylic resins are preferred in terms of small birefringence, and cyclic olefin resins are particularly preferred in terms of transparency, low moisture absorption, dimensional stability, light weight, etc.

[0037] A linearly polarizing film can be produced, for example, by laminating a polarizer layer and a protective film layer. Typically, a long polarizer layer and a long protective film layer are laminated together to produce a long linearly polarizing film. If necessary, the long linearly polarizing film may be cut to obtain a single linearly polarizing film. Furthermore, an adhesive may be used, if necessary, during lamination.

[0038] <λ / 2 Layer> The λ / 2 layer is formed of a COP resin containing a cyclic olefin polymer. Therefore, the λ / 2 layer contains a COP resin, or may contain only a COP resin. The COP resin is usually a thermoplastic resin. Furthermore, the COP resin usually has a positive intrinsic birefringence.

[0039] A cyclic olefin polymer contains a cyclic structure in its molecule. Typically, a cyclic olefin polymer has an alicyclic structure in the repeating unit of the polymer. The cyclic olefin polymer may be a polymer having an alicyclic structure in the main chain, a polymer having an alicyclic structure in the side chain, a polymer having alicyclic structures in the main chain and the side chain, or a mixture of two or more of these in any ratio. From the viewpoint of mechanical strength and heat resistance, the cyclic olefin polymer is preferably a polymer having an alicyclic structure in the main chain.

[0040] Examples of the alicyclic structure include saturated alicyclic hydrocarbon (cycloalkane) structures, unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structures, etc. Among these, from the viewpoints of mechanical strength and heat resistance, cycloalkane structures and cycloalkene structures are preferred, and cycloalkane structures are particularly preferred.

[0041] The number of carbon atoms constituting the alicyclic structure is preferably 4 or more, more preferably 5 or more, and preferably 30 or less, more preferably 20 or less, particularly preferably 15 or less, per alicyclic structure. When the number of carbon atoms constituting the alicyclic structure is within the above range, mechanical strength, heat resistance, and moldability are well balanced.

[0042] In the cyclic olefin polymer, the proportion of repeating units having an alicyclic structure to all repeating units is preferably 55% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. When the proportion of repeating units having an alicyclic structure to all repeating units is within this range, the transparency and heat resistance are good.

[0043] Among cyclic olefin polymers, norbornene-based polymers are preferred. Examples of norbornene-based polymers include ring-opening polymers of monomers having a norbornene structure and their hydrogenated products; and addition polymers of monomers having a norbornene structure and their hydrogenated products. Examples of ring-opening polymers of monomers having a norbornene structure include ring-opening homopolymers of one type of monomer having a norbornene structure, ring-opening copolymers of two or more types of monomers having a norbornene structure, and ring-opening copolymers of a monomer having a norbornene structure and any monomer copolymerizable therewith. Examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one type of monomer having a norbornene structure, addition copolymers of two or more types of monomers having a norbornene structure, and addition copolymers of a monomer having a norbornene structure and any monomer copolymerizable therewith. Among these, hydrogenated ring-opening polymers of monomers having a norbornene structure, addition copolymers of monomers having a norbornene structure and α-olefins, and hydrogenated addition copolymers of monomers having a norbornene structure and α-olefins are preferred.

[0044] Examples of monomers having a norbornene structure include bicyclo[2.2.1]hept-2-ene (common name: norbornene), tricyclo[4.3.0.1]hept-2-ene, and the like. ２，５ ]deca-3,7-diene (common name: dicyclopentadiene), 7,8-benzotricyclo[4.3.0.1 ２，５ ]dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo[4.4.0.1 ２，５ .1 ７，１０ ]dodec-3-ene (common name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent on the ring). Examples of the substituent include an alkyl group, an alkylene group, and a polar group. These substituents may be the same or different, and a plurality of them may be bonded to the ring. The monomer having a norbornene structure may be used alone or in combination of two or more.

[0045] Examples of the polar group include a heteroatom or an atomic group having a heteroatom. Examples of the heteroatom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfonic acid group.

[0046] Examples of the monomer capable of ring-opening copolymerization with the monomer having a norbornene structure include monocyclic olefins such as cyclohexene, cycloheptene, cyclooctene, etc., and derivatives thereof; cyclic conjugated dienes such as cyclohexadiene, cycloheptadiene, etc., and derivatives thereof; etc. The monomer capable of ring-opening copolymerization with the monomer having a norbornene structure may be used alone or in combination of two or more.

[0047] A ring-opening polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing the monomer in the presence of a ring-opening polymerization catalyst.

[0048] In the addition copolymer of a monomer having a norbornene structure and an α-olefin, examples of the α-olefin include α-olefins having 2 to 20 carbon atoms, such as ethylene, propylene, and 1-butene, and derivatives thereof. Among these, ethylene is preferred. One type of α-olefin may be used alone, or two or more types may be used in combination.

[0049] An addition polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing the monomer in the presence of an addition polymerization catalyst.

[0050] The hydrogenated products of the ring-opening polymer and the addition polymer described above can be produced, for example, by hydrogenating, preferably to 90% or more, the carbon-carbon unsaturated bonds in a solution of the ring-opening polymer and the addition polymer in the presence of a hydrogenation catalyst containing a transition metal such as nickel or palladium.

[0051] Examples of trade names of norbornene-based polymers include "ZEONOR" and "ZEONEX" manufactured by Zeon Corporation; "ARTON" manufactured by JSR Corporation; and "APEL" manufactured by Mitsui Chemicals, Inc.

[0052] The norbornene polymers may be used singly or in combination of two or more.

[0053] The weight-average molecular weight Mw of the cyclic olefin polymer is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, and is preferably 100,000 or less, more preferably 80,000 or less, particularly preferably 50,000 or less. When the weight-average molecular weight is in this range, the mechanical strength and moldability of the COP resin are well balanced.

[0054] The weight average molecular weight (Mw) can be measured using gel permeation chromatography (GPC). Examples of solvents used in GPC include cyclohexane, toluene, and tetrahydrofuran. When using GPC, the weight average molecular weight is measured as a relative molecular weight, for example, in terms of polyisoprene or polystyrene.

[0055] The amount of the cyclic olefin polymer is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, and even more preferably 90% by weight to 100% by weight, relative to 100% by weight of the COP resin. When the amount of the cyclic olefin polymer is within the above range, high heat resistance and transparency can be obtained.

[0056] The COP resin may contain an optional component other than the cyclic olefin polymer in combination with the cyclic olefin polymer. Examples of the optional component include any polymer other than the cyclic olefin polymer; colorants such as pigments and dyes; plasticizers; fluorescent brighteners; dispersants; heat stabilizers; light stabilizers; ultraviolet absorbers; antistatic agents; antioxidants; fine particles; surfactants, etc. One type of optional component may be used alone, or two or more types may be used in combination.

[0057] The glass transition temperature Tg of the COP resin is preferably 100° C. or higher, more preferably 110° C. or higher, even more preferably 120° C. or higher, and preferably 190° C. or lower, more preferably 180° C. or lower, even more preferably 170° C. or lower. When the glass transition temperature Tg of the COP resin is equal to or higher than the lower limit of the above range, the durability of the λ / 2 layer in a high-temperature environment can be improved. When the glass transition temperature Tg is equal to or lower than the upper limit, the stretching process for obtaining the λ / 2 layer can be carried out smoothly.

[0058] The glass transition temperature of the resin can be measured using a differential scanning calorimeter (for example, "DSC6220SII" manufactured by Nano Technology Co., Ltd.) in accordance with JIS K 6911 at a temperature rise rate of 10°C / min.

[0059] The in-plane retardation range of the λ / 2 layer is usually 240 nm or more, preferably 250 nm or more, and usually 300 nm or less, preferably 280 nm or less, more preferably 265 nm or less, at a measurement wavelength of 590 nm. Since the λ / 2 layer has an in-plane retardation in this range, a broadband wavelength film can be realized by combining a λ / 2 layer and a λ / 4 layer. Therefore, by combining this broadband wavelength film with a linear polarizing film, a broadband circular polarizer can be realized that absorbs either right-handed or left-handed circularly polarized light and transmits the remaining light over a wide wavelength range.

[0060] The in-plane retardation of the λ / 2 layer can be adjusted, for example, by the in-plane retardation and thickness of the resin layer (A) prepared in the first step in the method for producing a circularly polarizing plate described below; and the stretching conditions in the third step, such as the stretching temperature, stretching ratio, and stretching direction.

[0061] The λ / 2 layer has a slow axis in a direction that forms an angle of 22.5°±10° with respect to the absorption axis of the linear polarizing film. More specifically, the angle between the slow axis of the λ / 2 layer and the absorption axis of the linear polarizing film is preferably 12.5° or more, more preferably 17.5° or more, even more preferably 19.5° or more, and preferably 32.5° or less, more preferably 27.5° or less, and even more preferably 25.5° or less. By having the λ / 2 layer have a slow axis in such a direction range, a wideband circular polarizing plate can be obtained in combination with the linear polarizing film and the λ / 4 layer.

[0062] The direction of the slow axis of the λ / 2 layer can be adjusted, for example, by the direction of the slow axis of the resin layer (A) prepared in the first step in the method for producing a circularly polarizing plate described below; and the stretching conditions, such as the stretching direction and stretching ratio, in the third step.

[0063] The thickness of the λ / 2 layer is preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more, and is preferably 80 μm or less, more preferably 70 μm or less, and even more preferably 60 μm or less.

[0064] <λ / 4 Layer> The λ / 4 layer is formed of a vinylbiphenyl-based resin containing a 4-vinylbiphenyl-based polymer. Therefore, the λ / 4 layer contains a vinylbiphenyl-based resin, and may contain only a vinylbiphenyl-based resin. A vinylbiphenyl-based resin is usually a thermoplastic resin. Furthermore, a vinylbiphenyl-based resin usually has negative intrinsic birefringence.

[0065] The 4-vinylbiphenyl polymer refers to a polymer containing a 4-vinylbiphenyl monomer unit. The 4-vinylbiphenyl monomer unit refers to a repeating unit having a structure formed by polymerizing 4-vinylbiphenyl represented by formula (1), and specifically refers to a repeating unit represented by formula (2). Usually, the 4-vinylbiphenyl monomer unit is formed by polymerization of 4-vinylbiphenyl, but the 4-vinylbiphenyl monomer unit also includes repeating units formed by other formation methods.

[0066]

[0067] The proportion of 4-vinylbiphenyl monomer units contained in 100% by weight of a 4-vinylbiphenyl-based polymer is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more. The upper limit is usually 100% by weight or less, and may be 99% by weight or less. When the amount of 4-vinylbiphenyl monomer units is within the above range, the birefringence expression of the vinylbiphenyl-based resin can be effectively enhanced, making it possible to reduce the thickness of the λ / 4 layer to a level that satisfies processability, and effectively suppressing unevenness in the reflectance and color of reflected light. Typically, the proportion of 4-vinylbiphenyl monomer units contained in 100% by weight of a 4-vinylbiphenyl-based polymer corresponds to the ratio (feed ratio) of the 4-vinylbiphenyl to 100% by weight of all monomers used in the polymerization of the 4-vinylbiphenyl-based polymer.

[0068] The 4-vinylbiphenyl polymer may contain an arbitrary monomer unit other than the 4-vinylbiphenyl monomer unit. The arbitrary monomer unit refers to a monomer unit having a structure formed by polymerizing an arbitrary monomer other than 4-vinylbiphenyl. As the arbitrary monomer, a monomer compound capable of radical polymerization with 4-vinylbiphenyl can be used, and examples thereof include (meth)acrylic acid ester monomers such as methyl acrylate and methyl methacrylate; diene compound monomers such as butadiene and isoprene; and maleimide monomers such as N-phenylmaleimide. One type of the arbitrary monomer may be used alone, or two types may be used in combination.

[0069] The 4-vinylbiphenyl polymer may be used alone or in combination of two or more.

[0070] The weight average molecular weight Mw of the 4-vinylbiphenyl polymer is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, and is preferably 200,000 or less, more preferably 150,000 or less, particularly preferably 130,000 or less.

[0071] The amount of the 4-vinylbiphenyl polymer is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, and even more preferably 90% by weight to 100% by weight, relative to 100% by weight of the vinylbiphenyl resin. When the amount of the 4-vinylbiphenyl polymer is within this range, the birefringence of the vinylbiphenyl resin can be effectively increased, and unevenness in the reflectance and color of reflected light can be effectively suppressed.

[0072] The vinylbiphenyl resin may contain an optional component other than the 4-vinylbiphenyl polymer in combination with the 4-vinylbiphenyl polymer. Examples of the optional component include the same components as those that may be contained in the COP resin. One type of optional component may be used alone, or two or more types may be used in combination.

[0073] The glass transition temperature Tg of the vinyl biphenyl resin is preferably 100°C or higher, more preferably 110°C or higher, even more preferably 120°C or higher, and preferably 200°C or lower, more preferably 180°C or lower, and even more preferably 160°C or lower. The glass transition temperature Tg of the vinyl biphenyl resin may be higher than the glass transition temperature of the COP resin. When the glass transition temperature Tg of the vinyl biphenyl resin is within the above range, the birefringence expression of the vinyl biphenyl resin can be effectively increased, and unevenness in the reflectance and color of reflected light can be effectively suppressed. In addition, the orientation relaxation of the λ / 4 layer can usually be reduced.

[0074] From the viewpoint of smoothly adjusting the optical properties of the λ / 2 layer and the λ / 4 layer by co-stretching, it is preferable that the glass transition temperature Tg of the COP resin contained in the λ / 2 layer and the glass transition temperature Tg of the vinyl biphenyl-based resin contained in the λ / 4 layer are not too different from each other. Specifically, the absolute value |ΔTg| of the difference between the glass transition temperature Tg of the COP resin and the glass transition temperature Tg of the vinyl biphenyl-based resin is preferably 50° C. or less, more preferably 40° C. or less, and particularly preferably 30° C. or less.

[0075] The in-plane retardation range of the λ / 4 layer is usually 105 nm or more, preferably 110 nm or more, and usually 154 nm or less, preferably 138 nm or less, more preferably 128 nm or less, at a measurement wavelength of 590 nm. Since the λ / 4 layer has an in-plane retardation in this range, a broadband wavelength film can be realized by combining a λ / 2 layer and a λ / 4 layer. Therefore, by combining this broadband wavelength film with a linear polarizing film, a broadband circular polarizing plate can be realized.

[0076] The range of retardation in the thickness direction of the λ / 4 layer is preferably −300 nm or more, more preferably −250 nm or more, even more preferably −200 nm or more, and preferably −50 nm or less, more preferably −60 nm or less, even more preferably −70 nm or less, at a measurement wavelength of 590 nm.

[0077] The in-plane retardation and thickness direction retardation of the λ / 4 layer can be adjusted, for example, by the thickness of layer (B) formed in the second step in the method for producing a circularly polarizing plate described later; and the stretching conditions in the third step, such as the stretching temperature, stretching ratio, and stretching direction.

[0078] The λ / 4 layer has a slow axis in a direction that forms an angle of 90°±20° with respect to the absorption axis of the linear polarizing film. More specifically, the angle between the slow axis of the λ / 4 layer and the absorption axis of the linear polarizing film is preferably 70° or more, more preferably 80° or more, even more preferably 85° or more, and preferably 110° or less, more preferably 100° or less, and even more preferably 95° or less. When the λ / 4 layer has a slow axis in such a direction range, a wideband circular polarizing plate can be obtained in combination with the linear polarizing film and the λ / 2 layer.

[0079] From the viewpoint of realizing the function of a broadband wavelength film by combining a λ / 2 layer and a λ / 4 layer, it is preferable that the slow axis of the λ / 2 layer and the slow axis of the λ / 4 layer form an angle within a specific range. Generally, when a film combining a λ / 4 layer having a slow axis that forms an angle θ(λ / 4) with a certain reference direction (e.g., the longitudinal direction of the film) with a λ / 2 layer having a slow axis that forms an angle θ(λ / 2) with the reference direction satisfies the formula X: "θ(λ / 4) = 2θ(λ / 2) + 45°," this film becomes a broadband wavelength film that can impart an in-plane retardation of approximately ¼ of the wavelength of light transmitted through the film over a wide wavelength range (see JP 2007-004120 A). Therefore, it is preferable that the slow axis of the λ / 2 layer and the slow axis of the λ / 4 layer satisfy a relationship close to that expressed by the formula X. Specifically, the angle between the slow axis of the λ / 2 layer and the slow axis of the λ / 4 layer is preferably 67.5°±10° (i.e., 57.5° or more and 77.5° or less), more preferably 67.5°±5° (i.e., 62.5° or more and 72.5° or less), and even more preferably 67.5°±3° (i.e., 64.5° or more and 70.5° or less).

[0080] The direction of the slow axis of the λ / 4 layer can be adjusted, for example, by the stretching direction in the third step of the method for producing a circularly polarizing plate, which will be described later.

[0081] The range of the birefringence Δn of the λ / 4 layer is preferably 0.010 or more, more preferably 0.013 or more, and even more preferably 0.016 or more, at a measurement wavelength of 590 nm. The birefringence Δn usually represents the magnitude of the refractive index anisotropy in the in-plane direction. When the birefringence Δn is within the above range, the λ / 4 layer can be made thinner, effectively improving the surface condition of the λ / 4 layer and effectively suppressing unevenness in the reflectance and color of reflected light. From the viewpoint of smooth manufacturing of the λ / 4 layer, the upper limit is preferably 0.025 or less, more preferably 0.020 or less.

[0082] The parameter Rth / d of the λ / 4 layer is preferably −0.07 or more, more preferably −0.05 or more, even more preferably −0.04 or more, and is preferably 0.00 or less, more preferably −0.01 or less, and even more preferably −0.02 or less, at a measurement wavelength of 590 nm. The parameter Rth / d is a value obtained by dividing the thickness direction retardation Rth by the thickness d, and typically represents the magnitude of the refractive index anisotropy in the thickness direction. As represented by the parameter Rth / d, the λ / 4 layer preferably has a negative refractive index anisotropy with a large absolute value in the thickness direction. In this case, even if the λ / 4 layer has a small thickness, it can have a negative thickness direction retardation Rth with a sufficiently large absolute value.

[0083] The thickness of the λ / 4 layer is preferably thin. Specifically, the thickness of the λ / 4 layer is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 7 μm or less. When the λ / 4 layer is so thin, unevenness in the reflectance and color of reflected light can be effectively suppressed. From the viewpoint of smooth production of the λ / 4 layer, the lower limit is preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 4 μm or more.

[0084] <Optional Layer> The circular polarizer may have an optional layer in combination with the linear polarizing film, λ / 2 layer, and λ / 4 layer described above. For example, the circular polarizer may have an optional thin film layer formed between the λ / 2 layer and the λ / 4 layer. The optional thin film layer preferably has optical isotropy. Specifically, the optional thin film layer has an in-plane retardation of preferably 5 nm or less, more preferably 4 nm or less, even more preferably 3 nm or less, and particularly preferably 2 nm or less at a measurement wavelength of 590 nm.

[0085] The optional thin film layer may be formed from a resin. Examples of resins that form the optional thin film layer include acrylic resins, urethane resins, acrylic urethane resins, ester resins, and ethyleneimine resins. From the viewpoint of smoothly obtaining optical isotropy in the optional thin film layer, the glass transition temperature of the resin contained in the thin film layer is preferably lower than the glass transition temperature Tg of the COP resin contained in the λ / 2 layer and the glass transition temperature Tg of the vinyl biphenyl resin contained in the λ / 4 layer. In one example, the difference between the lower of the glass transition temperature Tg of the COP resin contained in the λ / 2 layer and the glass transition temperature Tg of the vinyl biphenyl resin contained in the λ / 4 layer and the glass transition temperature of the resin contained in the optional thin film layer is preferably 5° C. or more, more preferably 10° C. or more, and even more preferably 20° C. or more.

[0086] From the viewpoint of obtaining a thin circularly polarizing plate, the thickness of any thin film layer is preferably less than 2.0 μm, more preferably less than 1.8 μm, and even more preferably less than 1.5 μm. The lower limit of the thickness of the thin film layer is preferably as thin as possible, and can be, for example, 0.1 μm.

[0087] From the viewpoint of thinning the circular polarizer, the λ / 2 layer and the λ / 4 layer may be in direct contact with each other. The two layers being in "direct" contact with each other means that there is no other layer between the two layers. Therefore, the circular polarizer does not need to have any thin film layer between the λ / 2 layer and the λ / 4 layer.

[0088] Examples of the optional layer other than the optional thin film layer include a hard coat layer and a protective film layer for protecting the circular polarizer; an adhesive layer and a pressure-sensitive adhesive layer for attaching the circular polarizer to a display surface; and the like.

[0089] <Shape of Circularly Polarizing Plate> The circularly polarizing plate according to this embodiment usually has a film shape. This circularly polarizing plate may be a long film or a sheet film. For example, the circularly polarizing plate according to this embodiment may be manufactured as a long film and cut into a sheet film having a desired shape for use.

[0090] <Advantages of Circular Polarizer> When the circular polarizer according to this embodiment is provided on a surface capable of reflecting light (such as a display surface or a mirror surface), it can suppress the reflection of light on that surface. In this case, it can suppress the reflection of both light incident in the front direction of the circular polarizer and light incident in an oblique direction of the circular polarizer. Therefore, low reflectance can be obtained in both the front direction and the oblique direction.

[0091] In conventional circular polarizers, the ability to suppress reflection of light in the tilt direction can be uneven within the plane of the circular polarizer, which can cause unevenness in the reflectance and color of the reflected light.In contrast, the circular polarizer of this embodiment can suppress such unevenness in the reflectance and color of the reflected light.

[0092] According to the inventors' investigations, it has been found that this effect can only be achieved in a circular polarizer including a broadband wavelength film of a type in which the slow axis of the λ / 2 layer and the slow axis of the λ / 4 layer satisfy a relationship similar to that expressed by Formula X. That is, a broadband wavelength film of a different type from the broadband wavelength film included in the circular polarizer of this embodiment includes a λ / 2 layer combined with a λ / 4 layer having a slow axis perpendicular to the slow axis of the λ / 2 layer. However, if the λ / 4 layer of this other type of broadband wavelength film is formed from a vinyl biphenyl-based resin, the effect of suppressing unevenness in reflectance and color of reflected light as described above cannot be achieved. Therefore, it can be said that the above effect is not simply achieved by using a vinyl biphenyl-based resin, but is only achieved by a configuration in which a λ / 2 layer and a λ / 4 layer having the above-described slow axis directions are combined.

[0093] Furthermore, since vinyl biphenyl resins have a high birefringence development property, the λ / 4 layer can usually have a small thickness, which allows the circular polarizing plate to be made thin.

[0094] Furthermore, the 4-vinylbiphenyl polymer contained in the vinylbiphenyl resin can exhibit high birefringence even without containing components that may be subject to environmental restrictions, such as fluorine atoms, thereby reducing the burden on the environment.

[0095] <Method for manufacturing circularly polarizing plate> The circularly polarizing plate according to this embodiment can be manufactured by a manufacturing method including the steps of preparing a broadband wavelength film and bonding the broadband wavelength film and a linear polarizing film. In this case, from the viewpoint of efficient manufacturing by a roll-to-roll method, it is preferable to prepare a long broadband wavelength film and a long linear polarizing film and bond them together to manufacture a long circular polarizing plate.

[0096] The long broadband wavelength film is preferably produced by a production method including, in this order: a first step of preparing a resin layer (A) containing a cyclic olefin polymer as a long obliquely stretched film, a second step of forming a resin layer (B) containing a 4-vinylbiphenyl-based polymer on the resin layer (A) to obtain a multilayer film, and a third step of stretching the multilayer film in a stretching direction that forms an angle within a specific range with respect to the longitudinal direction of the multilayer film to obtain a long broadband wavelength film. Furthermore, the production method of this broadband wavelength film may also include a step of forming a thin film layer on the resin layer (A) after preparing the resin layer (A) in the first step.

[0097] Fig. 3 is a perspective view showing a resin layer (A) 320 as a long obliquely stretched film prepared in the first step of the manufacturing method of the broad wavelength film according to the preferred example. Fig. 4 is a perspective view showing a multilayer film 300 obtained in the second step of the manufacturing method of the broad wavelength film according to the preferred example. Fig. 5 is a perspective view showing a broad wavelength film 140 obtained in the third step of the manufacturing method of the broad wavelength film according to the preferred example.

[0098] In the preferred method for producing the broadband wavelength film 140, as shown in FIG. 3, the resin layer (A) 320 prepared in the first step is an obliquely stretched film, and therefore, the slow axis A is usually oriented in the oblique direction. ３２０In the second step, a resin layer (B) 330 is formed on the resin layer (A) 320 to obtain the multilayer film 300 shown in FIG. 4. Thereafter, the multilayer film 300 is stretched to co-stretch the resin layer (A) 320 and the resin layer (B) 330. By the co-stretching, the slow axis A of the resin layer (A) 320 is ３２０ The direction and optical properties of the slow axis A are adjusted to obtain the λ / 2 layer 120. １３０ and optical properties are developed to obtain the λ / 4 layer 130. Thus, as shown in FIG. 5, a broadband wavelength film 140 including the λ / 2 layer 120 and the λ / 4 layer 130 is obtained.

[0099] In the preferred method for producing a broadband wavelength film, the resin layer (A) 320 and the resin layer (B) 330 are stretched together in the third step rather than separately. This reduces the number of stretching processes, thereby reducing the number of steps required to produce the broadband wavelength film 140 and achieving efficient production. Furthermore, in a production method in which the resin layer (A) 320 and the resin layer (B) 330 are co-stretched by stretching the multilayer film 300 to obtain the broadband wavelength film 140, there is no misalignment of the slow axis direction due to lamination, as occurs in a method in which the λ / 2 layer and the λ / 4 layer are laminated together after being manufactured separately. Therefore, it is easy to precisely control the slow axis directions of the λ / 2 layer 120 and the λ / 4 layer 130, thereby enabling the production of a circular polarizer capable of effective reflection suppression. Below, we will explain how to produce this preferred broadband wavelength film, followed by how to produce a circular polarizer using the broadband wavelength film.

[0100] In the first step, a resin layer (A) is prepared as a long obliquely stretched film. The resin layer (A) contains a COP resin, and may contain only a COP resin. This resin layer (A) is typically an obliquely stretched film obtained by stretching a long resin film containing a COP resin in an oblique direction of the resin film. The obliquely stretched film may have a multilayer structure containing two or more layers containing a COP resin, but typically a single-layer structure containing only one layer is used.

[0101] Since the resin layer (A) is an obliquely stretched film, it usually has a slow axis in an oblique direction. The orientation angle that this slow axis makes with respect to the longitudinal direction of the resin layer (A) is set so as to obtain a desired broadband wavelength film. For example, when the multilayer film is stretched in the longitudinal direction of the multilayer film in the third step, the orientation angle of the λ / 2 layer obtained by stretching the resin layer (A) in the third step is smaller than the orientation angle of the resin layer (A). Therefore, in this case, it is preferable that the orientation angle of the resin layer (A) is set to an angle larger than the orientation angle of the λ / 2 layer obtained in the third step.

[0102] The orientation angle of the slow axis of the resin layer (A) relative to the longitudinal direction of the film is preferably greater than 40°, more preferably greater than 41°, even more preferably greater than 42°, and is preferably less than 75°, more preferably less than 73°, and even more preferably less than 60°. When the orientation angle of the resin layer (A) is within the above range, a broadband film having preferable optical properties can be smoothly obtained by stretching the multilayer film in a preferable stretching direction described later in the third step.

[0103] The in-plane retardation of the resin layer (A) can be set depending on the optical properties of a λ / 2 layer obtained by stretching the resin layer (A). In one example, the in-plane retardation of the resin layer (A) is preferably 140 nm or more, more preferably 150 nm or more, even more preferably 160 nm or more, and is preferably 250 nm or less, more preferably 240 nm or less, even more preferably 230 nm or less.

[0104] The thickness of the resin layer (A) can be set within a range that allows a desired broadband wavelength film to be obtained. The specific thickness of the resin layer (A) is preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more, and is preferably 100 μm or less, more preferably 95 μm or less, and even more preferably 90 μm or less.

[0105] The resin layer (A) can be produced by a production method including stretching a pre-stretched film as an appropriate long resin film in an oblique direction of the pre-stretched film.

[0106] The pre-stretched film can be produced by, for example, a melt molding method or a solution casting method. More specific examples of the melt molding method include extrusion molding, press molding, inflation molding, injection molding, blow molding, and stretch molding. Among these methods, in order to obtain a resin layer (A) excellent in mechanical strength and surface precision, extrusion molding, inflation molding, and press molding are preferred, and among these, extrusion molding is particularly preferred from the viewpoint of being able to produce the resin layer (A) efficiently and simply.

[0107] After preparing a long pre-stretch film, the long pre-stretch film can be stretched in an oblique direction to obtain the resin layer (A) as an obliquely stretched film.

[0108] The slow axis of the resin layer (A) is usually expressed by stretching the pre-stretched film in an oblique direction, and therefore the stretching direction of the pre-stretched film is preferably set according to the direction of the slow axis of the resin layer (A). Specifically, the stretching direction of the pre-stretched film is preferably set in a direction parallel to the slow axis of the resin layer (A).

[0109] The stretching ratio in the stretching to obtain the resin layer (A) is preferably 1.1 times or more, more preferably 1.2 times or more, and preferably 4.0 times or less, more preferably 3.0 times or less. The stretching temperature in the stretching to obtain the resin layer (A) is preferably TgA ° C. or higher, more preferably "TgA + 2 ° C." or higher, particularly preferably "TgA + 5 ° C." or higher, and preferably "TgA + 40 ° C." or lower, more preferably "TgA + 35 ° C." or lower, particularly preferably "TgA + 30 ° C." or lower. Here, TgA represents the glass transition temperature of the COP resin contained in the resin layer (A). Stretching can usually be performed using a tenter stretching machine while continuously transporting the pre-stretched film in the longitudinal direction. As the tenter stretching machine, for example, one described in International Publication No. 2016 / 047465 may be used.

[0110] The method for producing a broadband wavelength film may optionally include a fourth step of forming a thin film layer on the resin layer (A) after the first step. The thin film layer can be formed, for example, by a method including applying a coating liquid containing a resin as a material for the thin film layer and a solvent onto the resin layer (A). The solvent may be water or an organic solvent. Examples of the organic solvent include the same organic solvents that can be used in forming the resin layer (B) described below. Furthermore, the solvent may be used alone or in combination of two or more types.

[0111] The coating liquid may contain a crosslinking agent. Use of the crosslinking agent can increase the mechanical strength of the thin film layer and improve the binding ability of the thin film layer to the resin layer (A) and the resin layer (B). Examples of crosslinking agents that can be used include epoxy compounds, amino compounds, isocyanate compounds, carbodiimide compounds, and oxazoline compounds. These may be used alone or in combination of two or more.

[0112] The coating method for the coating liquid may be, for example, the same method as the coating method that can be used to form the base layer (B) described below.

[0113] A thin film layer can be formed by applying a coating liquid onto the resin layer (A). This thin film layer may be subjected to a curing treatment such as drying and crosslinking, as necessary. Examples of drying methods include heat drying using an oven. Examples of crosslinking methods include heat treatment and irradiation with active energy rays such as ultraviolet rays.

[0114] The method for producing a broadband wavelength film includes a first step in which a resin layer (A) is prepared, a fourth step in which a thin film layer is formed as needed, and a second step in which a resin layer (B) is formed on the resin layer (A) to obtain a multilayer film. In the second step, the resin layer (B) is formed on the resin layer (A) directly or indirectly via an optional layer such as a thin film layer. Here, "directly" means that there is no optional layer between the layer (A) and the layer (B). The formed resin layer (B) contains a vinyl biphenyl-based resin, and may contain only a vinyl biphenyl-based resin.

[0115] The resin layer (B) is preferably formed by a coating method. Generally, vinyl biphenyl resins tend to have low mechanical strength. However, the coating method makes it possible to easily form the resin layer (B) using a vinyl biphenyl resin with such low mechanical strength. Furthermore, the coating method makes it easy to reduce the thickness of the resin layer (B) itself.

[0116] Furthermore, when a resin layer (B) is formed by a layer formation method such as a coating method, the vinylbiphenyl resin containing the 4-vinylbiphenyl polymer can increase the refractive index nz in the thickness direction of the resin layer (B). Therefore, the parameter Rth / d of the resin layer (B) can have a large absolute negative value, and therefore the retardation in the thickness direction can also have a large absolute negative value.

[0117] When the resin layer (B) is formed by a coating method, the second step usually includes applying a resin liquid containing a vinyl biphenyl resin and an organic solvent onto the resin layer (A) and drying the applied resin liquid. Examples of the organic solvent include cyclopentanone, methyl ethyl ketone, and toluene. The organic solvent may be used alone or in combination of two or more.

[0118] Examples of methods for applying the resin liquid include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, gravure coating, die coating, gap coating, and dipping.

[0119] After the resin liquid is applied onto the resin layer (A), the resin liquid is dried to remove the organic solvent, thereby forming the resin layer (B) on the resin layer (A). Drying can be performed by a drying method such as natural drying, heat drying, reduced pressure drying, or reduced pressure heat drying.

[0120] The resin layer (B) formed in the second step may have an in-plane retardation and a slow axis. When the resin layer (B) has an in-plane retardation and a slow axis, the in-plane retardation and the slow axis of the resin layer (B) are adjusted by the stretching in the third step.

[0121] The thickness of the resin layer (B) can be set within a range that allows a desired broadband wavelength film to be obtained. The specific thickness of the resin layer (B) is preferably 3 μm or more, more preferably 4 μm or more, and even more preferably 5 μm or more, and is preferably 15 μm or less, more preferably 13 μm or less, and even more preferably 11 μm or less.

[0122] In the method for producing a broadband wavelength film, a multilayer film having a resin layer (A) and a resin layer (B) is obtained in the second step, and then the multilayer film is stretched to obtain a long broadband wavelength film in the third step. The stretching in the third step adjusts the direction of the slow axis of the resin layer (A) and adjusts the optical properties of the resin layer (A), resulting in a λ / 2 layer. Furthermore, the stretching in the third step causes a slow axis to appear in the resin layer (B), and optical properties are developed in the resin layer (B), resulting in a λ / 4 layer.

[0123] By the stretching in the third step, the thickness direction retardation Rth of the resin layer (B) is maintained at a negative value, and usually, the absolute value of this negative value can be increased. Therefore, the thickness direction retardation Rth of the λ / 4 layer obtained by stretching the resin layer (B) can be a negative value with a sufficiently large absolute value. In this way, one of the advantages of the production method according to this embodiment is that a λ / 4 layer having a negative thickness direction retardation Rth can be obtained by the simple process of forming and stretching the resin layer (B).

[0124] The stretching in the third step is usually performed in only one direction. The stretching direction in this third step is preferably set so as to obtain a desired broadband wavelength film. Usually, the direction of the slow axis of the resin layer (A) changes to approach the stretching direction by the stretching in the third step. Also, usually, in the resin layer (B), a slow axis appears in a direction perpendicular to the stretching direction by the stretching in the third step. Therefore, it is preferable to set the stretching direction in the third step so as to obtain a λ / 2 layer and a λ / 4 layer having a slow axis in the desired direction by the change in the direction of the slow axis in the resin layer (A) and the appearance of a slow axis in the resin layer (B).

[0125] In particular, the third step preferably includes stretching the multilayer film in a stretching direction that forms an angle of 0°±20° with respect to the longitudinal direction of the multilayer film. More specifically, the angle that the stretching direction in the third step forms with respect to the longitudinal direction of the multilayer film is preferably −20° or more, more preferably −15° or more, even more preferably −10° or more, and preferably 20° or less, more preferably 15° or less, and even more preferably 10° or less. Furthermore, among these, it is preferable that the stretching in the third step is performed in the longitudinal direction of the multilayer film. When stretching is performed in such a stretching direction, it is possible to easily control the direction of the slow axis.

[0126] The stretching ratio in the third step is preferably 1.1 times or more, more preferably 1.15 times or more, particularly preferably 1.2 times or more, and is preferably 2.0 times or less, more preferably 1.8 times or less, particularly preferably 1.6 times or less. When the stretching ratio in the third step is equal to or greater than the lower limit of the above range, the occurrence of wrinkles can be suppressed. When the stretching ratio is equal to or less than the upper limit, the direction of the slow axis can be easily controlled.

[0127] The stretching temperature in the third step is preferably TgA - 20°C or higher, more preferably TgA - 10°C or higher, even more preferably TgA - 5°C or higher, and is preferably TgA + 30°C or lower, more preferably TgA + 25°C or lower, even more preferably TgA + 20°C or lower. Here, TgA represents the glass transition temperature of the COP resin contained in the resin layer (A).

[0128] The stretching temperature in the third step is preferably TgB-50°C or higher, more preferably TgB-40°C or higher, particularly preferably TgB-30°C or higher, and is preferably TgB+30°C or lower, more preferably TgB+25°C or lower, particularly preferably TgB+20°C or lower. Here, TgB represents the glass transition temperature of the vinyl biphenyl resin contained in the resin layer (B).

[0129] The stretching in the third step is preferably performed by free uniaxial stretching. Here, free uniaxial stretching refers to stretching in a certain direction, without applying a restraining force in any direction other than the stretching direction. Therefore, for example, free uniaxial stretching in the longitudinal direction of a multilayer film refers to stretching in the longitudinal direction without restraining the ends of the multilayer film in the width direction. By performing free uniaxial stretching in the third step, the slow axis directions of the λ / 2 layer and the λ / 4 layer can be easily controlled.

[0130] The stretching in the third step described above can be carried out using, for example, a tenter stretching machine or a roll stretching machine. In particular, when the multilayer film is stretched in the longitudinal direction of the multilayer film in the third step, it is preferable to use a roll stretching machine. Free uniaxial stretching can be easily carried out using a roll stretching machine. Free uniaxial stretching using a roll stretching machine is usually carried out while continuously transporting a long multilayer film in the longitudinal direction. As the roll stretching machine, for example, one described in International Publication No. 2016 / 047465 can be used.

[0131] The method for producing the broadband wavelength film described above may further include any optional step in addition to the first, second, third, and fourth steps. For example, the method for producing the broadband wavelength film may include a step of providing a protective layer on the surface of the broadband wavelength film. Furthermore, for example, the method for producing the broadband wavelength film may include a step of performing a surface treatment such as a corona treatment or a plasma treatment on the surfaces of one or more of the resin layer (A), the resin layer (B), and the thin film layer at any time.

[0132] The above-described manufacturing method can produce a long broadband wavelength film comprising a λ / 2 layer containing a COP resin and a λ / 4 layer containing a vinyl biphenyl resin. The λ / 2 layer of the broadband wavelength film typically has a slow axis in a direction that forms a specific orientation angle with respect to its longitudinal direction. The range of orientation angles of this λ / 2 layer is typically the same as the range of angles that the slow axis of the λ / 2 layer contained in a circular polarizer forms with respect to the absorption axis of a linear polarizer. Therefore, the λ / 2 layer of the long broadband wavelength film can have a slow axis in a direction that forms an angle of 22.5°±10° with respect to the longitudinal direction of the broadband wavelength film. Furthermore, the λ / 4 layer of the broadband wavelength film typically has a slow axis in a direction that forms a specific orientation angle with respect to its longitudinal direction. The range of orientation angles of this λ / 4 layer is typically the same as the range of angles that the slow axis of the λ / 4 layer contained in a circular polarizer forms with respect to the absorption axis of a linear polarizer. Therefore, the λ / 4 layer of a long broadband wavelength film can have a slow axis in a direction that forms an angle of 90°±20° with respect to the longitudinal direction of the broadband wavelength film.

[0133] The total light transmittance of the broadband wavelength film is preferably 80% or more, more preferably 85% or more, and particularly preferably 88% or more. The light transmittance can be measured in the wavelength range of 400 nm to 700 nm using a spectrophotometer in accordance with JIS K0115.

[0134] The haze of the broadband wavelength film is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and ideally 0%. Here, the haze can be measured at five locations using a turbidity meter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K7361-1997, and the average value calculated from the measurements can be used.

[0135] A circularly polarizing plate can be manufactured by a manufacturing method including a step of preparing a long broadband wavelength film and then laminating the long broadband wavelength film and a long linear polarizing film. The lamination is performed so that the linear polarizing film, the λ / 2 layer, and the λ / 4 layer are arranged in this order in the thickness direction. Furthermore, an adhesive layer or a pressure-sensitive adhesive layer may be used for lamination, if necessary.

[0136] The long linear polarizing film preferably has an absorption axis in the longitudinal direction of the linear polarizing film. This preferred linear polarizing film can be bonded to a long broadband wavelength film including a λ / 2 layer having an orientation angle in the above-mentioned range and a λ / 4 layer having an orientation angle in the above-mentioned range to easily produce a circular polarizing plate. In particular, by bonding the above-mentioned combination, a circular polarizing plate can be produced by bonding the long linear polarizing film and the long broadband wavelength film with their longitudinal directions parallel to each other. Therefore, the circular polarizing plate can be produced by a roll-to-roll method, which improves the production efficiency of the circular polarizing plate.

[0137] The method for producing a circular polarizing plate may further include any step in combination with the steps described above. For example, the method for producing a circular polarizing plate may include a step of providing a protective layer on the surface of the circular polarizing plate. Furthermore, for example, the method for producing a circular polarizing plate may include a step of cutting a long circular polarizing plate to obtain individual circular polarizing plates.

[0138] <Image Display Device> As described above, the above-described circular polarizing plate can effectively reduce reflection of external light when provided on a surface capable of reflecting light. The circular polarizing plate is particularly useful in that it can effectively reduce reflection of external light over a wide wavelength range in the visible region. Because it can effectively reduce reflection of external light over such a wide wavelength range, the circular polarizing plate can suppress coloring caused by increased reflection intensity of light at certain wavelengths. Furthermore, the circular polarizing plate can achieve the above-described effects of suppressing reflection and coloring in both the front direction and the oblique direction, and typically in all azimuth angle directions of the film main surface. Taking advantage of this excellent reflection suppression function, the circular polarizing plate can be used as a reflection suppression film in an image display device.

[0139] Typically, an image display device has a display surface on which a circular polarizer is provided. In this case, the circular polarizer is provided so that a linear polarizing film, a λ / 2 layer, and a λ / 4 layer are arranged in this order from the viewing side. Examples of such image display devices include organic EL display devices and liquid crystal display devices. When these image display devices have a circular polarizer on the display surface, it is possible to prevent light incident from outside the device from being reflected within the device and exiting the device, thereby suppressing glare on the display surface of the display device. Furthermore, since the reflection suppression function can be obtained over a wide wavelength range, it is possible to suppress coloring of the display surface.

[0140] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples shown below, and can be practiced with any modifications within the scope of the claims and their equivalents. In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. Furthermore, the operations described below were carried out in air at room temperature and normal pressure (23°C, 1 atm) unless otherwise specified.

[0141] <Evaluation Method> (Method for Measuring Optical Properties of λ / 2 Layer and λ / 4 Layer) A broadband wavelength film was placed on the stage of a retardation meter ("AxoScan" manufactured by Axometrics). The change in the polarization state of polarized light transmitted through the broadband wavelength film before and after transmission through the broadband wavelength film was measured as the transmission polarization characteristics of the broadband wavelength film. This measurement was performed as a multidirectional measurement performed at polar angles ranging from -55° to 55° with respect to the main surface of the broadband wavelength film. The multidirectional measurement was also performed at azimuthal angles of 45°, 90°, 135°, and 180°, with the azimuthal angle direction of the main surface of the broadband wavelength film being defined as 0°. The measurement wavelength for this measurement was 590 nm.

[0142] Next, fitting calculations were performed from the transmission polarization characteristics measured as described above to determine the in-plane retardation Re, thickness direction retardation Rth, and orientation angle of the λ / 2 layer and λ / 4 layer included in the broadband wavelength film. Furthermore, the in-plane retardation Re of the λ / 4 layer was divided by the thickness of the λ / 4 layer to measure the birefringence Δn of the λ / 4 layer. Furthermore, the thickness direction retardation Rth of the λ / 4 layer was divided by the thickness to measure the parameter Rth / d of the λ / 4 layer. The fitting calculations were performed by setting the three-dimensional refractive index and orientation angle of each layer included in the broadband wavelength film as fitting parameters. The fitting calculations were performed using the software ("Multi-Layer Analysis" manufactured by Axometrics) included with the retardation meter (AxoScan).

[0143] (Visual Evaluation Method) A mirror with a flat reflective surface was prepared. This mirror was placed so that the reflective surface was horizontal and facing upward. A circular polarizing plate was attached to the reflective surface of this mirror so that the linear polarizing film side faced upward.

[0144] Then, on a sunny day, the circular polarizer was illuminated by sunlight and visually observed on the mirror in both the following directions: (i) in the front direction with a polar angle of 0° and an azimuth angle of 0°, and (ii) in the tilted direction with a polar angle of 45° and an azimuth angle of 0° to 360°.

[0145] (i) When observed from the front, if the reflection of sunlight was barely noticeable, the circular polarizer appeared black, and neither shading nor color unevenness was visible, the result was judged to be "good." If the reflection of sunlight was visible and the circular polarizer did not appear black, or if shading or color unevenness was visible, the result was judged to be "poor."

[0146] (ii) In the observation in the oblique direction, if the change in reflectance and color was not recognized depending on the azimuth angle and if unevenness in shading and color was not recognized at any azimuth angle, it was judged as "good." If the change in reflectance and color was recognized depending on the azimuth angle and unevenness in shading or color was recognized at a specific azimuth angle, it was judged as "poor."

[0147] (Method of calculating reflectance by simulation) Using "LCD Master" manufactured by Shintech Co., Ltd. as simulation software, the circular polarizers manufactured in each Example and Comparative Example were modeled and the reflectance was calculated. In the simulation model, a structure was set in which a circular polarizer was attached to the reflective surface of a mirror having a flat reflective surface so that the λ / 4 layer side was in contact with the mirror. Therefore, in this model, a structure was set in which a linear polarizing film, a λ / 2 layer, a λ / 4 layer, and a mirror were provided in this order in the thickness direction.

[0148] In the model, the reflectance when the circular polarizer was irradiated with light from a D65 light source was calculated in (i) the front direction and (ii) the tilted direction of the circular polarizer. Here, in (i) the front direction, the reflectance was calculated at a polar angle of 0° and an azimuth angle of 0°. In addition, in (ii) the tilted direction, calculations were performed at a polar angle of 45°, in azimuth angles ranging from 0° to 360°, in 5° increments, and the average of the calculated values ​​was used as the reflectance in the tilted direction of the modeled circular polarizer. In addition, in the simulation, the surface reflection component that actually occurs on the surface of the polarizing film was excluded from the reflectance.

[0149] Example 1 (First step: production of resin layer (A)) Pellet-shaped norbornene-based resin (manufactured by Zeon Corporation; glass transition temperature 126°C) was dried at 100°C for 5 hours. The dried resin was supplied to an extruder, passed through a polymer pipe and a polymer filter, and extruded into a sheet form from a T-die onto a casting drum. The extruded resin was cooled to obtain a long pre-stretched film with a thickness of 60 µm. The obtained pre-stretched film was wound on a roll and recovered.

[0150] The pre-stretched film was pulled out from the roll and continuously fed to a tenter stretching machine. The pre-stretched film was then stretched by this tenter stretching machine in a stretching direction forming an angle of 45° with respect to the longitudinal direction of the pre-stretched film at a stretching temperature of 135°C and a stretching ratio of 1.5 to obtain a long obliquely stretched film as the resin layer (A). The orientation angle of the obtained obliquely stretched film was 45°, and the in-plane retardation Re was 195 nm. The obtained obliquely stretched film was wound up on a roll and recovered.

[0151] (Second step: Formation of resin layer (B)) A resin solution containing poly(4-vinylbiphenyl) (Sigma-Aldrich, weight average molecular weight Mw = 115,000, glass transition temperature 138°C) as a resin having negative intrinsic birefringence and cyclopentanone as a solvent was prepared. The concentration of poly(4-vinylbiphenyl) in this resin solution was 15 wt%.

[0152] The obliquely stretched film was pulled out from the roll, and the resin liquid was applied onto the obliquely stretched film. The applied resin liquid was then dried to form a layer of poly(4-vinylbiphenyl) (thickness 7.0 μm) as resin layer (B) on the obliquely stretched film. This resulted in a multilayer film comprising the obliquely stretched film as resin layer (A) and a layer of poly(4-vinylbiphenyl) as resin layer (B). The resulting multilayer film was wound around a roll and recovered.

[0153] (Third Step: Stretching of Multilayer Film) The multilayer film was pulled out from the roll and continuously fed to a longitudinal stretching machine. Then, using this longitudinal stretching machine, the multilayer film was subjected to free uniaxial stretching in the longitudinal direction of the multilayer film at a stretching temperature of 135°C and a stretching ratio of 1.3. As a result, a broadband wavelength film was obtained as a co-stretched film comprising a λ / 2 layer obtained by stretching the obliquely stretched film and a λ / 4 layer obtained by stretching the poly(4-vinylbiphenyl) layer. The obtained broadband wavelength film was evaluated by the method described above.

[0154] (Production of Circularly Polarized Film) A long linearly polarized film having an absorption axis in the longitudinal direction was prepared. This linearly polarized film and the above-mentioned broadband wavelength film were bonded together with their longitudinal directions parallel to each other. This bonding was performed using a pressure-sensitive adhesive ("CS-9621" manufactured by Nitto Denko Corporation). By bonding, a circularly polarized film having a linearly polarized film, a λ / 2 layer, and a λ / 4 layer in this order was obtained. The obtained circularly polarized film was evaluated using the method described above.

[0155] Comparative Example 1 Polystyrene (manufactured by Sigma-Aldrich, weight average molecular weight Mw=280,000, glass transition point 100°C) was prepared as a resin with negative intrinsic birefringence. An evaluation test was conducted in which this polystyrene was stretched 1.3 times at 135°C, and the birefringence Δn developed by the stretching was confirmed to be 0.00031. Therefore, it was confirmed that in order to obtain a λ / 4 layer having an in-plane retardation Re of approximately 110 nm, similar to that of Example 1, it was necessary to form a λ / 4 layer with a thickness of 355 μm.

[0156] Therefore, we attempted to produce a multilayer film, a broadband wavelength film, and a circularly polarizing film using the same method as in Example 1, except that a resin liquid containing polystyrene was used instead of poly(4-vinylbiphenyl) as the resin liquid, and the coating thickness of the resin liquid was changed so that a λ / 4 layer with a thickness of 355 μm was obtained after stretching.

[0157] However, since the required coating thickness was too thick, it was not possible to form a polystyrene layer with the desired thickness, and therefore it was not possible to produce a multilayer film.

[0158] Comparative Example 2 Poly(4-methylstyrene) (Sigma-Aldrich, weight average molecular weight Mw=72,000, glass transition point 106°C) was prepared as a resin with negative intrinsic birefringence. An evaluation test was conducted in which this polystyrene was stretched 1.3 times at 135°C, and the birefringence Δn developed by the stretching was confirmed to be 0.00037. Therefore, it was confirmed that in order to obtain a λ / 4 layer having an in-plane retardation Re of approximately 110 nm, similar to that of Example 1, it was necessary to form a λ / 4 layer with a thickness of 297 μm.

[0159] Therefore, we attempted to produce a multilayer film, a broadband wavelength film, and a circularly polarizing film using the same method as in Example 1, except that a resin solution containing poly(4-methylstyrene) was used instead of poly(4-vinylbiphenyl) as the resin solution, and the coating thickness of the resin solution was changed so that a λ / 4 layer with a thickness of 297 μm was obtained after stretching.

[0160] However, since the required coating thickness was too thick, it was not possible to form a poly(4-methylstyrene) layer with the desired thickness, and therefore it was not possible to produce a multilayer film.

[0161] Comparative Example 3 Poly(4-chlorostyrene) (Sigma-Aldrich, weight average molecular weight Mw=75,000, glass transition point 106°C) was prepared as a resin with negative intrinsic birefringence. An evaluation test was conducted in which this polystyrene was stretched 1.3 times at 135°C, and the birefringence Δn developed by the stretching was confirmed to be 0.00071. Therefore, it was confirmed that in order to obtain a λ / 4 layer having an in-plane retardation Re of approximately 110 nm, similar to that of Example 1, it was necessary to form a λ / 4 layer with a thickness of 155 μm.

[0162] Therefore, we attempted to produce a multilayer film, a broadband wavelength film, and a circularly polarizing film using the same method as in Example 1, except that a resin solution containing poly(4-chlorostyrene) was used instead of poly(4-vinylbiphenyl) as the resin solution, and the coating thickness of the resin solution was changed so that a λ / 4 layer with a thickness of 155 μm was obtained after stretching.

[0163] However, since the required coating thickness was too thick, it was not possible to form a poly(4-chlorostyrene) layer having the desired thickness, and therefore it was not possible to produce a multilayer film.

[0164] Comparative Example 4 A styrene-maleic anhydride copolymer ("XIRAN3500" manufactured by Polyscope, styrene:maleic anhydride = 3:1, weight average molecular weight Mw = 80,000, glass transition point 130°C) was prepared as a resin with negative intrinsic birefringence. An evaluation test was conducted in which this polystyrene was stretched 1.3 times at 135°C to confirm the birefringence Δn developed by the stretching, which was 0.00016. Therefore, it was confirmed that in order to obtain a λ / 4 layer having an in-plane retardation Re of approximately 110 nm, similar to that of Example 1, it was necessary to form a λ / 4 layer with a thickness of 688 μm.

[0165] Therefore, we attempted to produce a multilayer film, a broadband wavelength film, and a circularly polarizing film by the same method as in Example 1, except that a resin liquid containing a styrene-maleic anhydride copolymer was used instead of poly(4-vinylbiphenyl) as the resin liquid, and the coating thickness of the resin liquid was changed so that a λ / 4 layer with a thickness of 688 μm was obtained after stretching.

[0166] However, since the required coating thickness was too thick, it was not possible to form a layer of styrene-maleic anhydride copolymer having the desired thickness, and therefore it was not possible to produce a multilayer film.

[0167] Comparative Example 5 Poly(2-vinylnaphthalene) (Sigma-Aldrich, weight average molecular weight Mw = 175,000, glass transition point 135°C) was prepared as a resin with negative intrinsic birefringence. A multilayer film, a broadband wavelength film, and a circularly polarizing film were produced and evaluated in the same manner as in Example 1, except that a resin solution containing poly(2-vinylnaphthalene) was used instead of poly(4-vinylbiphenyl) as the resin solution, and the coating thickness of the resin solution was changed so that a 20 μm thick λ / 4 layer was obtained after stretching.

[0168] <Results> The results of the above-mentioned Examples and Comparative Examples are shown in the table below. In the table below, the meanings of the abbreviations are as follows: Re: in-plane retardation Rth: retardation in the thickness direction θ: orientation angle Tg: glass transition temperature Mw: weight average molecular weight

[0169]

[0170] 100 Circularly polarizing plate 110 Linearly polarizing film 120 λ / 2 layer 130 λ / 4 layer 140 Broadband wavelength film 200 Surface 300 Multilayer film 320 Resin layer (A) 330 Resin layer (B)

Claims

1. A circular polarizer comprising, in this order: a linear polarizing film; a λ / 2 layer having a slow axis in a direction that forms an angle of 22.5°±10° with respect to the absorption axis of the linear polarizing film; and a λ / 4 layer having a slow axis in a direction that forms an angle of 90°±20° with respect to the absorption axis of the linear polarizing film; wherein the λ / 2 layer comprises a resin containing a cyclic olefin polymer; and the λ / 4 layer comprises a resin containing a polymer containing a 4-vinylbiphenyl monomer unit.

2. The circularly polarizing plate according to claim 1, wherein the proportion of 4-vinylbiphenyl monomer units contained in 100% by weight of the polymer containing 4-vinylbiphenyl monomer units is 70% by weight or more.

3. The circular polarizer according to claim 1, wherein the λ / 4 layer has a thickness of 10 μm or less.

4. The circular polarizer according to claim 1, wherein the λ / 4 layer has a birefringence Δn of 0.010 or more.

5. A method for producing a broadband wavelength film, comprising, in this order: a first step of preparing a resin layer (A) containing a cyclic olefin polymer as a long obliquely stretched film; a second step of forming a resin layer (B) containing a polymer containing a 4-vinylbiphenyl monomer unit on the resin layer (A) to obtain a multilayer film; and a third step of stretching the multilayer film in a stretching direction forming an angle of 0°±20° with respect to the longitudinal direction of the multilayer film to obtain a long broadband wavelength film comprising a λ / 2 layer and a λ / 4 layer.

6. The method for producing a broadband wavelength film according to claim 5, wherein the second step comprises applying a resin liquid containing a resin including a polymer containing the 4-vinylbiphenyl monomer unit and an organic solvent onto the resin layer (A), and drying the applied resin liquid.

7. A long broadband wavelength film comprising: a λ / 2 layer having a slow axis in a direction forming an angle of 22.5°±10° with respect to the longitudinal direction of the broadband wavelength film; and a λ / 4 layer having a slow axis in a direction forming an angle of 90°±20° with respect to the longitudinal direction of the broadband wavelength film; wherein the λ / 2 layer comprises a resin containing a cyclic olefin polymer; and the λ / 4 layer comprises a resin containing a polymer containing a 4-vinylbiphenyl monomer unit.

8. An image display device comprising the circular polarizer according to any one of claims 1 to 4.

Images