Circularly polarizing plate, long strip broadband wavelength film and method for manufacturing the same, and image display device

Abstract

The present invention provides a circular polarizer comprising, in sequence: a linear polarizing film; a λ / 2 layer having a slow axis in a direction at an angle of 22.5°±10° relative to the absorption axis of the linear polarizing film; and a λ / 4 layer having a slow axis in a direction at an angle of 90°±20° relative 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, wherein the polymer contains 4-vinylbiphenyl monomer units.

Description

Technical Field

[0001] This invention relates to circular polarizers, long strip broadband wavelength films and their manufacturing methods, and image display devices having circular polarizers. Background Technology

[0002] In order to suppress the reflection of external light caused by the display surface of image display devices such as liquid crystal display devices and organic EL display devices, an anti-reflective film is sometimes provided. As such an anti-reflective film, a film composed of a linear polarizing film and a waveplate is known (Patent Documents 1-4). Unless otherwise stated, the term "organic EL" refers to "organic electroluminescence".

[0003] Furthermore, the technology in Patent Document 5 is known to the public.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: U.S. Patent Application Publication No. 2022 / 0187524;

[0007] Patent Document 2: U.S. Patent No. 9,703,013;

[0008] Patent Document 3: International Publication No. 2016 / 047465;

[0009] Patent Document 4: Patent No. 7059936 (US Patent Application Publication No. 2019 / 0293852).

[0010] Patent Document 5: Japanese Patent Publication No. 2010-522900 (International Publication No. 2008 / 121580). Summary of the Invention

[0011] The problem the invention aims to solve

[0012] For example, a circular polarizer, which combines a linear polarizing film and a waveplate, can suppress the reflection of external light caused by the display surface when applied to the display surface of an image display device. When using this circular polarizer, from the viewpoint of effectively reducing the reflectivity of external light, it is required that the circular polarizer block circularly polarized light over a wide wavelength range. To achieve this blocking of circularly polarized light over a wide wavelength range, a broadband wavelength film composed of a combination of λ / 2 and λ / 4 layers formed of resin is sometimes used as a waveplate. Since the aforementioned broadband wavelength film can perform its optical function over a wide wavelength range, it is expected that a circular polarizer capable of suppressing light reflection over a wide wavelength range can be obtained.

[0013] The aforementioned broadband wavelength film can be manufactured using co-stretching. Specifically, a broadband wavelength film can be manufactured by a method that includes co-stretching a resin layer in the stage preceding the formation of a λ / 2 layer and a resin layer in the stage preceding the formation of a λ / 4 layer. By using the co-stretching manufacturing method, the number of steps required to manufacture the broadband wavelength film can be reduced, thus improving manufacturing efficiency.

[0014] The inventors have focused on resins containing cyclic olefin polymers with excellent mechanical and optical properties as the resins for forming the λ / 2 layer. Hereinafter, "resin containing cyclic olefin polymers" will sometimes be referred to as "COP resin". In order to manufacture a broadband wavelength film having a λ / 2 layer containing COP resin using the above-described co-stretching, the stretching conditions such as stretching temperature and stretching ratio are limited to a range where the λ / 2 layer can be obtained by stretching a resin layer containing COP resin. Therefore, for the resin contained in the λ / 4 layer, it is required that a desired λ / 4 layer can be formed under these limited stretching conditions.

[0015] The inventors have investigated resins capable of forming a λ / 4 layer under the aforementioned restricted stretching conditions. While forming a λ / 4 layer is inherently difficult with most resins, some resins are capable of doing so. However, it has been established that using resins capable of forming λ / 4 layers results in uneven reflectivity and hue of the reflected light in the circular polarizer.

[0016] The present invention was first developed in view of the above-mentioned problems, and its object is to provide: a new circular polarizer capable of suppressing the inhomogeneity of reflectivity and hue of reflected light; a long strip of broadband wavelength film capable of being used to manufacture the above-mentioned circular polarizer and a method thereof; and an image display device having the above-mentioned circular polarizer.

[0017] Solution for solving the problem

[0018] In order to solve the above-mentioned problems, the inventors conducted in-depth research. As a result, the inventors discovered that the following circular polarizer can solve the above-mentioned problems, thereby completing the present invention. The circular polarizer sequentially comprises a linear polarizing film, a λ / 2 layer, and a λ / 4 layer. The λ / 2 layer has a slow axis in a specific direction and contains a resin containing a cyclic olefin polymer. The λ / 4 layer has a slow axis in a specific direction and contains a resin containing a polymer, which contains 4-vinylbiphenyl monomer units.

[0019] That is, the present invention includes the following contents.

[0020] <1> A circular polarizer, comprising, in sequence:

[0021] Linear polarizing film;

[0022] A λ / 2 layer having a slow axis in a direction at an angle of 22.5° ± 10° relative to the absorption axis of the aforementioned linearly polarized film; and

[0023] The λ / 4 layer has a slow axis in a direction at an angle of 90°±20° relative to the absorption axis of the aforementioned linearly polarized film.

[0024] The aforementioned λ / 2 layer comprises a resin containing a cyclic olefin polymer.

[0025] The aforementioned λ / 4 layer comprises a resin containing a polymer, wherein the polymer contains 4-vinylbiphenyl monomer units.

[0026] <2> according to <1> The circular polarizer, wherein, in 100% by weight of the polymer containing the 4-vinylbiphenyl monomer unit, the content of the 4-vinylbiphenyl monomer unit is 70% by weight or more.

[0027] <3> according to <1> or <2> The circular polarizer, wherein the λ / 4 layer has a thickness of less than 10 μm.

[0028] <4> according to <1> ~ <3> The circular polarizer according to any one of the following methods, wherein the λ / 4 layer has a birefringence Δn of 0.010 or more.

[0029] <5> A method for manufacturing a broadband wavelength film, comprising the following steps:

[0030] The first step is to prepare a resin layer (A) containing a cyclic olefin polymer as a long, inclined stretch film.

[0031] In the second step, a resin layer (B) comprising a polymer containing 4-vinylbiphenyl monomer units is formed on the aforementioned resin layer (A), thereby obtaining a multilayer film; and

[0032] The third step involves stretching the multilayer film at an angle of 0°±20° relative to its length direction to obtain a long strip of broadband wavelength film with λ / 2 and λ / 4 layers.

[0033] <6> according to <5> The method for manufacturing the broadband wavelength film, wherein the second step includes: coating a resin liquid comprising a polymer-containing resin and an organic solvent onto the resin layer (A), wherein the polymer comprises 4-vinylbiphenyl monomer units; and

[0034] The applied resin solution is then dried.

[0035] <7> A long, wideband wavelength film having the following characteristics:

[0036] A λ / 2 layer having a slow axis at an angle of 22.5° ± 10° relative to the length direction of the aforementioned broadband wavelength film; and

[0037] The λ / 4 layer has a slow axis at an angle of 90°±20° relative to the length direction of the aforementioned broadband wavelength film.

[0038] The aforementioned λ / 2 layer comprises a resin containing a cyclic olefin polymer.

[0039] The aforementioned λ / 4 layer comprises a resin containing a polymer, wherein the polymer contains 4-vinylbiphenyl monomer units.

[0040] <8> An image display device having <1> ~ <4> The circular polarizer described in any one of the following.

[0041] Invention Effects

[0042] According to the present invention, it is possible to provide: a novel circular polarizer capable of suppressing the inhomogeneity of reflectivity and hue of reflected light; a long strip of broadband wavelength film for manufacturing the aforementioned circular polarizer and a method thereof; and an image display device having the aforementioned circular polarizer. Attached Figure Description

[0043] Figure 1 A perspective view of a circular polarizer according to one embodiment of the present invention is shown schematically.

[0044] Figure 2 A perspective view illustrating the arrangement of a circular polarizer according to one embodiment of the present invention on a surface.

[0045] Figure 3 A perspective view of a resin layer (A) prepared as a strip of inclined stretching film in the first step of the manufacturing method of the broadband wavelength film involved in the preferred example is shown schematically.

[0046] Figure 4 A perspective view of a multilayer film obtained in the second step of the manufacturing method of a broadband wavelength film according to a preferred example is shown schematically.

[0047] Figure 5 A perspective view of a broadband wavelength film obtained in the third step of the manufacturing method of the broadband wavelength film in a preferred example is shown schematically. Detailed Implementation

[0048] The present invention will now be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented in any way without departing from the scope of the claims and their equivalents.

[0049] In the following description, a component (e.g., a membrane, layer) is referred to as a "strip" as having a length that is 5 times or more, preferably 10 times or more, relative to its width. Specifically, it refers to a length sufficient to be wound into a roll for storage or transport. There is no particular upper limit to the length; for example, it can be set to less than 100,000 times the width.

[0050] In the following description, unless otherwise specified, the in-plane retardation Re of the layer is represented by Re = (nx - ny) × d. Furthermore, unless otherwise specified, the birefringence Δn of the layer is represented by Δn = nx - ny, and is therefore denoted by Δn = Re / d. Moreover, unless otherwise specified, the thickness-direction retardation Rth of the layer is represented by Rth = [{(nx + ny) / 2} - nz] × d. Here, nx represents the refractive index in the direction that imparts the maximum refractive index in the in-plane direction of the layer. Unless otherwise specified, "in-plane direction" refers to the direction perpendicular to the thickness direction. ny represents the refractive index in the direction perpendicular to nx in the aforementioned in-plane direction of the layer. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer. Unless otherwise specified, the measurement wavelength is 590 nm.

[0051] In the following description, unless otherwise stated, a material with positive intrinsic birefringence is one whose refractive index in the stretching direction is greater than that in the direction perpendicular to it. Conversely, unless otherwise stated, a material with negative intrinsic birefringence is one whose refractive index in the stretching direction is less than that in the direction perpendicular to it. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

[0052] In the following description, unless otherwise stated, the term "(meth)acrylic acid" includes "acrylic acid", "methacrylic acid", and combinations thereof.

[0053] In the following description, unless otherwise stated, the tilt direction of the elongated membrane refers to the in-plane direction of the membrane that is neither parallel nor perpendicular to the width direction of the membrane.

[0054] In the following description, unless otherwise stated, the front direction of a membrane refers to the normal direction of the principal surface of the membrane, specifically the direction in which the polar angle and azimuth angle of the principal surface are both 0°.

[0055] In the following description, unless otherwise stated, the tilt direction of a membrane refers to a direction that is neither parallel nor perpendicular to the principal surface of the membrane, specifically, a direction in which the polar angle of the principal surface is greater than 0° and less than 90°.

[0056] In the following description, unless otherwise specified, the orientation of elements as “parallel,” “perpendicular,” and “orthogonal” means that an error within, for example, ±5° may be included without impairing the effect of the invention.

[0057] In the following description, unless otherwise specified, the angle formed by the optical axes (absorption axis, slow axis, etc.) of each layer in a multi-layered component represents the angle when the layer is viewed from the thickness direction.

[0058] In the following description, unless otherwise specified, the slow axis of a membrane or layer refers to the slow axis within the plane of the membrane or layer.

[0059] In the following description, unless otherwise specified, the orientation angle of a film or layer refers to the angle between the slow axis of the film or layer and a reference direction perpendicular to the thickness direction. In long strip films and layers, unless otherwise specified, the length direction is used as the reference direction.

[0060] In the following description, unless otherwise stated, "circular polarizer" and "waveplate" include not only rigid components but also flexible components such as resin films.

[0061] <Overview of Circular Polarizers>

[0062] Figure 1 A perspective view of a circular polarizer according to one embodiment of the present invention is shown schematically. Figure 1 As shown, a circular polarizer 100 according to one embodiment of the present invention sequentially includes: having an absorption axis A 110 The linearly polarized film 110; at the absorption axis A of the linearly polarized film 110 110 An angle θ of 22.5° ± 10° 120 The direction of the slow axis A 120 The λ / 2 layer 120; and the absorption axis A relative to the linear polarization film 110. 110 An angle θ of 90°±20° 130 Direction A 130 Upper has slow axis A 130 The λ / 4 layer 130. Furthermore, the λ / 2 layer 120 comprises a COP resin containing a cyclic olefin polymer. And, the λ / 4 layer 130 comprises a resin containing a polymer having 4-vinylbiphenyl monomer units. In the following description, "polymer containing 4-vinylbiphenyl monomer units" is sometimes referred to as a "4-vinylbiphenyl polymer." Furthermore, the resin containing this 4-vinylbiphenyl polymer is sometimes referred to as a "vinylbiphenyl resin."

[0063] Figure 2This is a perspective view illustrating, schematically, the circular polarizer 100 of one embodiment of the present invention disposed on surface 200. According to this embodiment, the circular polarizer 100, as... Figure 2 As shown, when the circular polarizer 100 is placed on a surface (display surface, mirror surface, etc.) 200 that can reflect light, the inhomogeneity of the reflected light and the uniformity of its color tone can be suppressed. Specifically, as described below.

[0064] A circular polarizer 100 is disposed on a surface 200 such that a λ / 4 layer 130, a λ / 2 layer 120, and a linear polarizing film 110 are arranged sequentially from the surface 200 side. The surface 200 is then observed along the tilt direction 10 of the polar angle ρ and the azimuth angle φ. Here, the "polar angle" ρ of the tilt direction 10 represents the angle formed by the tilt direction 10 relative to the normal direction 11 of the surface 200. Furthermore, the "azimuth angle" φ of the tilt direction 10 represents the angle formed by the component of the tilt direction 10 parallel to the surface 200 relative to a reference direction 12 parallel to the surface 200. According to the circular polarizer 100 of this embodiment, light reflection at the surface 200 can be suppressed, reducing reflectivity. Moreover, the reflectivity and hue of the reflected light can be made uniform, thus suppressing non-uniformity in the reflectivity and hue of the reflected light. Normally, non-uniformity in reflectivity is visually perceived as uneven intensity, and non-uniformity in hue can be visually perceived as uneven hue. Furthermore, preferably, the circular polarizer 100 according to this embodiment can suppress changes in the reflectivity and hue of reflected light when viewed in an inclined direction by adjusting the azimuth angle φ of that inclined direction.

[0065] The inventors speculate the following mechanism by which the above-mentioned effects can be achieved. However, the scope of the present invention is not limited to the following mechanism.

[0066] By combining the λ / 2 layer 120 and the λ / 4 layer 130 contained in the circular polarizer 100, a broadband wavelength film 140 (reference) can be formed. Figure 1 The broadband wavelength film 140 can impart an in-plane delay of approximately one-quarter of the wavelength of light transmitted through it over a wide wavelength range. Thus, in the circular polarizer 100, linearly polarized light over a wide wavelength range transmitted through the linear polarizer 110 is converted into circularly polarized light by the broadband wavelength film 140. Therefore, the circular polarizer 100 can function to absorb either right-handed or left-handed circularly polarized light over a wide wavelength range while allowing the remaining light to pass through, thereby providing an anti-reflection function.

[0067] Give specific examples, such as Figure 2As shown, when light shines on the surface 200 where the circular polarizer 100 is provided, only a portion of the linearly polarized light passes through the linear polarization film 110. The transmitted linearly polarized light passes through the broadband wavelength film 140 and becomes circularly polarized light. This circularly polarized light is reflected by the surface 200 and passes through the broadband wavelength film 140 again, becoming linearly polarized light. Since the linearly polarized light has a vibration direction (polarization axis) perpendicular to the vibration direction (polarization axis) of the incident linearly polarized light, it does not pass through the linear polarization film 110. Thus, the anti-reflection function of the circular polarizer 100 is achieved. Moreover, since the broadband wavelength film 140 can perform its optical function over a wide wavelength range, the above-mentioned anti-reflection function can be obtained over a wide wavelength range, thereby effectively reducing the reflection of light on the surface 200.

[0068] Furthermore, 4-vinylbiphenyl polymers exhibit high birefringence. Therefore, vinylbiphenyl resins containing this 4-vinylbiphenyl polymer can exhibit high birefringence during the process of forming λ / 2 layer 120 and λ / 4 layer 130 through co-stretching. Thus, since the λ / 4 layer 130 can have sufficiently high birefringence, it can be formed thin. A thin λ / 4 layer results in a good surface condition. For example, it can improve the uniformity of surface height, thereby improving flatness. Therefore, the magnitude of the retardation of transmitted light imparted by the λ / 4 layer 130, as well as the incident angle of light onto the λ / 4 layer 130, can be made uniform. Therefore, since the amount and wavelength of light blocked by the circular polarizer 100 can be made uniform, non-uniformity in the reflectivity and hue of reflected light can be suppressed; more preferably, changes in the reflectivity and hue of reflected light can be suppressed by the azimuth angle φ.

[0069] Furthermore, the circular polarizer 100 according to this embodiment is generally able to suppress light reflection caused by the surface 200 not only in the tilt direction but also in the frontal direction. Moreover, since the λ / 4 layer 130 can be thinned, the circular polarizer 100 as a whole can generally be made thinner.

[0070] <Linear polarizing film>

[0071] A linear polarizing film is a film with an absorption axis. It has the function of absorbing linearly polarized light with a vibration direction parallel to the absorption axis while allowing other polarized light to pass through. The vibration direction of linearly polarized light refers to the vibration direction of its electric field.

[0072] Linear polarizing films typically have a polarizer layer, and may also have a protective film layer for protecting the polarizer layer if necessary. As the polarizer layer, a polarizer layer can be used, for example, a film of a suitable vinyl alcohol-based polymer that has undergone appropriate treatment in a suitable order and manner. Examples of such vinyl alcohol-based polymers include polyvinyl alcohol and partially methylallated polyvinyl alcohol. Examples of film treatments include dyeing treatment using dichroic substances such as iodine and dichroic dyes, stretching treatment, and crosslinking treatment. Typically, in the stretching treatment used to manufacture the polarizer layer, the film before stretching is stretched along its length. This results in an absorption axis parallel to the length direction of the polarizer layer. The polarizer layer is capable of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, and is particularly preferably a polarizer layer with excellent polarization degree. The thickness of the polarizer layer is generally 5 μm to 80 μm, but is not limited to this.

[0073] As a protective film layer for protecting the polarizer layer, any transparent film can be used. Among them, films made of resins with excellent transparency, mechanical strength, thermal stability, and moisture resistance are 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, and (meth)acrylic resins. Among these, acetate resins, cyclic olefin resins, and (meth)acrylic resins are preferred from the perspective of low birefringence, while cyclic olefin resins are particularly preferred from the viewpoints of transparency, low moisture absorption, dimensional stability, and lightweight.

[0074] Linear polarizing films can be manufactured, for example, by laminating a polarizer layer with a protective film layer. Typically, a strip of linear polarizing film is manufactured by laminating a strip of polarizer layer with a strip of protective film layer. Alternatively, the strip of linear polarizing film can be cut to obtain a single sheet of linear polarizing film as needed. Furthermore, adhesives can be used during lamination as required.

[0075] <λ / 2 layers>

[0076] The λ / 2 layer is formed using a COP resin comprising a cyclic olefin polymer. Thus, the λ / 2 layer may contain COP resin, or it may contain only COP resin. The COP resin is typically a thermoplastic resin. Furthermore, the COP resin generally exhibits positive intrinsic birefringence.

[0077] Cyclic olefin polymers contain cyclic structures within their molecules. Typically, cyclic olefin polymers have alicyclic structures in their repeating units. Cyclic olefin polymers can be polymers with alicyclic main chains, polymers with alicyclic side chains, polymers with alicyclic main chains and side chains, and mixtures of two or more of these polymers in any ratio. From the viewpoint of mechanical strength and heat resistance, cyclic olefin polymers are preferably polymers with alicyclic main chains.

[0078] Examples of alicyclic structures include saturated alicyclic hydrocarbon (cycloalkanes) and unsaturated alicyclic hydrocarbon (cycloalkenes, cycloalkynes). From the viewpoint of mechanical strength and heat resistance, cycloalkanes and cycloalkenes are preferred, with cycloalkanes being particularly preferred.

[0079] The number of carbon atoms constituting the alicyclic structure is preferably 4 or more, more preferably 5 or more, more preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. When the number of carbon atoms constituting the alicyclic structure is within the above range, mechanical strength, heat resistance, and formability are highly balanced.

[0080] In cyclic olefin polymers, the proportion of repeating units with alicyclic structures relative 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 with alicyclic structures relative to all repeating units is within this range, good transparency and heat resistance are achieved.

[0081] 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 hydrides; addition polymers of monomers having a norbornene structure and their hydrides. Examples of ring-opening polymers of monomers having a norbornene structure include: ring-opening homopolymers of a single monomer having a norbornene structure; ring-opening copolymers of two or more monomers having a norbornene structure; and ring-opening copolymers of a monomer having a norbornene structure and any monomer capable of copolymerizing therewith. Examples of addition polymers of monomers having a norbornene structure include: addition homopolymers of a single monomer having a norbornene structure; addition copolymers of two or more monomers having a norbornene structure; and addition copolymers of a monomer having a norbornene structure and any monomer capable of copolymerizing therewith. Among these, preferred are hydrides of ring-opening polymers of monomers having a norbornene structure, addition copolymers of monomers having a norbornene structure with α-olefins, and hydrides of addition copolymers of monomers having a norbornene structure with α-olefins.

[0082] Examples of monomers with a norbornene structure include bicyclic [2.2.1]hept-2-ene (common name: norbornene) and tricyclic [4.3.0.1]hept-2-ene. 2,5 ] Dec-3,7-diene (common name: dicyclopentadiene), 7,8-benzotricyclo[4.3.0.1] 2,5 ] Dec-3-ene (common name: bridged methylenetetrahydrofluorene), tetracyclic [4.4.0.1] 2,5 .1 7,10 Dodecene-3-ene (common name: tetracyclic dodecene) and derivatives of these compounds (e.g., derivatives with substituents on the ring). Examples of substituents include alkyl groups, alkylene groups, and polar groups. These substituents may be the same or different, or multiple substituents may be combined to form a ring. Monomers having a norbornene structure may be used alone or in combination of two or more.

[0083] Examples of polar groups include heteroatoms or atomic groups containing heteroatoms. Examples of heteroatoms include oxygen atoms, nitrogen atoms, sulfur atoms, silicon atoms, and halogen atoms. Specific examples of polar groups include carboxyl groups, carbonyl groups, epoxy groups, hydroxyl groups, oxygen groups, ester groups, silanol groups, silyl groups, amino groups, nitrile groups, and sulfonic acid groups.

[0084] Monomers capable of ring-opening copolymerization with monomers having a norbornene structure include, for example, monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene, and their derivatives; and cyclic conjugated dienes such as cyclohexadiene and cycloheptadiene, and their derivatives. Monomers capable of ring-opening copolymerization with monomers having a norbornene structure can be used alone or in combination of two or more.

[0085] Ring-opening polymers of monomers having a norbornene structure can be manufactured, for example, by polymerization or copolymerization of the monomers in the presence of a ring-opening polymerization catalyst.

[0086] In addition copolymers of monomers having a norbornene structure and α-olefins, examples of α-olefins with 2 to 20 carbon atoms include ethylene, propylene, 1-butene, and their derivatives. Among these, ethylene is preferred. An α-olefin may be used alone or in combination of two or more.

[0087] Addition polymers of monomers having a norbornene structure can be manufactured, for example, by polymerization or copolymerization of the monomers in the presence of an addition polymerization catalyst.

[0088] The aforementioned hydrides of ring-opening polymers and addition polymers can be manufactured, for example, by hydrogenating carbon-carbon unsaturated bonds, preferably more than 90%, in a solution of the ring-opening polymers and addition polymers in the presence of a hydrogenation catalyst containing transition metals such as nickel and palladium.

[0089] Examples of trade names for norbornene polymers include "ZEONOR" and "ZEONEX" manufactured by Zeon Corporation of Japan; "ARTON" manufactured by Japan Synthetic Rubber Co., Ltd. (JSR); and "APEL" manufactured by Mitsui Chemicals Co., Ltd.

[0090] Norbornene polymers can be used alone or in combination of two or more.

[0091] 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, more preferably 100,000 or less, more preferably 80,000 or less, and particularly preferably 50,000 or less. Within this range, the mechanical strength and moldability of the COP resin are highly balanced.

[0092] Weight-average molecular weight (Mw) can be determined 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 determined as a relative molecular weight, for example, converted to polyisoprene or polystyrene.

[0093] The amount of cyclic olefin polymer relative to 100% COP resin is preferably 50% to 100% by weight, more preferably 70% to 100% by weight, and even more preferably 90% to 100% by weight. When the amount of cyclic olefin polymer is within the above range, high heat resistance and transparency can be obtained.

[0094] COP resin can contain any component other than cyclic olefin polymers combined with cyclic olefin polymers. Examples of such arbitrary components include: any polymer other than cyclic olefin polymers; colorants such as pigments and dyes; plasticizers; fluorescent whitening agents; dispersants; heat stabilizers; light stabilizers; ultraviolet absorbers; antistatic agents; antioxidants; microparticles; surfactants, etc. Any component can be used alone or in combination of two or more.

[0095] 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, preferably 190°C or lower, more preferably 180°C or lower, and even more preferably 170°C or lower. When the glass transition temperature (Tg) of the COP resin is above the lower limit of the above range, the durability of the λ / 2 layer in high-temperature environments can be improved. Furthermore, when the glass transition temperature (Tg) of the COP resin is below the upper limit of the above range, the stretching process for obtaining the λ / 2 layer can be performed smoothly.

[0096] The glass transition temperature of the resin can be determined using a differential scanning calorimeter (e.g., Nano Technology's "DSC6220SII") based on the JIS K 6911 standard at a heating rate of 10 °C / min.

[0097] The in-plane retardation of the λ / 2 layer is typically 240 nm or more, preferably 250 nm or more, and typically 300 nm or less, preferably 280 nm or less, and more preferably 265 nm or less, at a measured wavelength of 590 nm. Because the λ / 2 layer has the in-plane retardation within the aforementioned range, it is possible to combine the λ / 2 layer and the λ / 4 layer to realize a broadband wavelength film. 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 over a wide wavelength range while allowing the remaining light to pass through.

[0098] 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 of the circular polarizer manufacturing method described later; and by stretching conditions such as stretching temperature, stretching ratio, and stretching direction in the third step.

[0099] The λ / 2 layer has a slow axis in a direction at an angle of 22.5° ± 10° 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, preferably 32.5° or less, more preferably 27.5° or less, and even more preferably 25.5° or less. By having a slow axis in such a direction as the λ / 2 layer, a broadband circular polarizer can be obtained by combining it with a linear polarizing film and a λ / 4 layer.

[0100] 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 of the method for manufacturing a circular polarizer described later, and by stretching conditions such as the stretching direction and stretching ratio in the third step.

[0101] The thickness of the λ / 2 layer is preferably 20 μm or more, more preferably 25 μm or more, even more preferably 30 μm or more, preferably 80 μm or less, more preferably 70 μm or less, and even more preferably 60 μm or less.

[0102] <λ / 4 layers>

[0103] The λ / 4 layer is formed from a vinyl biphenyl resin comprising a 4-vinylbiphenyl polymer. Thus, the λ / 4 layer may contain vinyl biphenyl resin, or it may contain only vinyl biphenyl resin. Vinyl biphenyl resins are typically thermoplastic resins. Furthermore, vinyl biphenyl resins typically have negative intrinsic birefringence.

[0104] 4-Vinylbiphenyl polymers refer to polymers containing 4-vinylbiphenyl monomer units. A 4-vinylbiphenyl monomer unit represents a repeating unit having a structure formed by polymerizing 4-vinylbiphenyl as represented by formula (1), specifically, a repeating unit represented by formula (2). Typically, the 4-vinylbiphenyl monomer unit is formed by the polymerization of 4-vinylbiphenyl, but it may also contain repeating units formed by other methods.

[0105] [Chemical Formula 1]

[0106]

[0107] The proportion of 4-vinylbiphenyl monomer units contained in 100% by weight of the 4-vinylbiphenyl 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 typically 100% by weight or less, and may also be 99% by weight or less. When the amount of 4-vinylbiphenyl monomer units is within the above range, the birefringence of the vinylbiphenyl resin can be effectively improved, thus allowing the thickness of the λ / 4 layer to be reduced to a level that meets processing adaptability, and effectively suppressing the reflectivity and tonal uniformity of reflected light. Typically, the proportion of 4-vinylbiphenyl monomer units contained in 100% by weight of the 4-vinylbiphenyl polymer is consistent with the proportion of 4-vinylbiphenyl in 100% by weight of all monomers used in the polymerization of the 4-vinylbiphenyl polymer (feed ratio).

[0108] 4-Vinylbiphenyl polymers may also contain any monomer units other than the 4-vinylbiphenyl monomer unit. An arbitrary monomer unit refers to a monomer unit having a structure formed by polymerizing any monomer other than 4-vinylbiphenyl. Examples of arbitrary monomers include monomer compounds capable of free radical polymerization with 4-vinylbiphenyl, such as methyl acrylate, methyl methacrylate, and other (meth)acrylate monomers; diene compound monomers such as butadiene and isoprene; maleimide monomers such as N-phenylmaleimide; etc. Any monomer may be used alone or in combination of two or more.

[0109] 4-Vinylbiphenyl polymers can be used alone or in combination of two or more.

[0110] 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, preferably 200,000 or less, more preferably 150,000 or less, and particularly preferably 130,000 or less.

[0111] The amount of 4-vinylbiphenyl polymer relative to 100% vinylbiphenyl resin is preferably 50% to 100% by weight, more preferably 70% to 100% by weight, and even more preferably 90% to 100% by weight. When the amount of 4-vinylbiphenyl polymer is within the above range, the birefringence of the vinylbiphenyl resin can be effectively improved, thereby effectively suppressing the reflectivity and hue inhomogeneity of reflected light.

[0112] Vinyl biphenyl resins may also contain any component other than the 4-vinyl biphenyl polymer in combination with the 4-vinyl biphenyl polymer. Examples of such arbitrary components include those found in COP resins. Any component may be used alone or in combination of two or more.

[0113] 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, 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 can also be higher than that of the COP resin. When the glass transition temperature (Tg) of the vinyl biphenyl resin is within the above range, the birefringence of the vinyl biphenyl resin can be effectively improved, thereby effectively suppressing the reflectivity and tonal inhomogeneity of reflected light. Furthermore, the orientation relaxation of the λ / 4 layer can generally be reduced.

[0114] From the viewpoint of smoothly adjusting the optical properties of the λ / 2 and λ / 4 layers through co-stretching, it is preferable that the glass transition temperature (Tg) of the COP resin contained in the λ / 2 layer is not excessively different from that of the vinyl biphenyl resin contained in the λ / 4 layer. Specifically, the absolute value of the difference |ΔTg| between the glass transition temperature (Tg) of the COP resin and the vinyl biphenyl resin is preferably 50°C or less, more preferably 40°C or less, and particularly preferably 30°C or less.

[0115] The in-plane retardation of the λ / 4 layer is typically 105 nm or more, preferably 110 nm or more, and typically 154 nm or less, preferably 138 nm or less, and more preferably 128 nm or less, at a measurement wavelength of 590 nm. Because the λ / 4 layer has the in-plane retardation within the aforementioned range, it is possible to combine the λ / 2 and λ / 4 layers to realize a broadband wavelength film. Therefore, by combining this broadband wavelength film with a linear polarizing film, a broadband circular polarizer can be realized.

[0116] The retardation range in the thickness direction of the λ / 4 layer is at the measurement wavelength of 590 nm, preferably -300 nm or more, more preferably -250 nm or more, even more preferably -200 nm or more, preferably -50 nm or less, more preferably -60 nm or less, and even more preferably -70 nm or less.

[0117] The in-plane retardation and thickness direction retardation of the λ / 4 layer can be adjusted, for example, by the thickness of the layer (B) formed in the second step of the circular polarizer manufacturing method described later, and by stretching conditions such as stretching temperature, stretching ratio, and stretching direction in the third step.

[0118] The λ / 4 layer has a slow axis in a direction at an angle of 90° ± 20° 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, preferably 110° or less, more preferably 100° or less, and even more preferably 95° or less. By having a slow axis in a direction within such a range, a broadband circular polarizer can be obtained by combining the λ / 4 layer with a linear polarizing film and a λ / 2 layer.

[0119] From the viewpoint of achieving the function of a broadband wavelength film through the combination of λ / 2 and λ / 4 layers, 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 at an angle θ(λ / 4) to a certain reference direction (e.g., the length direction of the film) and a λ / 2 layer having a slow axis at an angle θ(λ / 2) to the aforementioned reference direction satisfies equation X: "θ(λ / 4) = 2θ(λ / 2) + 45°", the film becomes a broadband wavelength film capable of imparting an in-plane delay of approximately 1 / 4 of the wavelength of light transmitted through the film over a wide wavelength range (see Japanese Patent Application Laid-Open No. 2007-004120). Therefore, it is preferable that the slow axes of the λ / 2 layer and the λ / 4 layer satisfy a relationship close to that expressed by the above equation X. Specifically, the angle between the slow axis of layer λ / 2 and the slow axis of layer λ / 4 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).

[0120] 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 manufacturing method of the circular polarizer described later.

[0121] 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 the measurement wavelength of 590 nm. Birefringence Δn generally represents the magnitude of refractive index anisotropy in the in-plane direction. When the birefringence Δn is within the above range, the λ / 4 layer can be thinned, thus effectively improving the surface condition of the λ / 4 layer and effectively suppressing the inhomogeneity of reflectivity and hue of reflected light. From the viewpoint of smoothly manufacturing the λ / 4 layer, the upper limit is preferably 0.025 or less, more preferably 0.020 or less.

[0122] The parameter Rth / d of the λ / 4 layer, at a measurement wavelength of 590 nm, is preferably -0.07 or higher, more preferably -0.05 or higher, and even more preferably -0.04 or higher. Furthermore, it is preferably 0.00 or lower, more preferably -0.01 or lower, and even more preferably -0.02 or lower. The parameter Rth / d is a value obtained by dividing the thickness-direction retardation Rth by the thickness d, and generally represents the magnitude of the refractive index anisotropy in the thickness direction. As indicated by the parameter Rth / d above, the λ / 4 layer preferably has a large absolute value of negative refractive index anisotropy in the thickness direction. In this case, even when the thickness of the λ / 4 layer is small, it is possible to have a sufficiently large absolute value of negative thickness-direction retardation Rth.

[0123] 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, the reflectivity and color uniformity of the reflected light can be effectively suppressed. From the viewpoint of smoothly manufacturing 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.

[0124] <Any layer>

[0125] Circular polarizers can have any combination of layers with the aforementioned linear polarizing film, λ / 2 layer, and λ / 4 layer. For example, a circular polarizer can have any thin film layer formed between the λ / 2 layer and the λ / 4 layer. The arbitrary thin film layer preferably has optical isotropy. Specifically, at a measurement wavelength of 590 nm, the arbitrary thin film layer preferably has an in-plane retardation of 5 nm or less, more preferably an in-plane retardation of 4 nm or less, even more preferably an in-plane retardation of 3 nm or less, and particularly preferably an in-plane retardation of 2 nm or less.

[0126] Any thin film layer can be formed using resin. Examples of resins for forming any thin film layer include acrylic resin, polyurethane resin, acrylic polyurethane resin, ester resin, and ethyleneimine resin. From the viewpoint of readily obtaining the optical isotropy of the arbitrary thin film layer, it is preferable that the glass transition temperature of the resin contained in the thin film layer is 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 vinylbiphenyl resin contained in the λ / 4 layer. In one example, the temperature 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 vinylbiphenyl resin contained in the λ / 4 layer and the glass transition temperature of the resin contained in the arbitrary thin film layer is preferably 5°C or more, more preferably 10°C or more, and even more preferably 20°C or more.

[0127] From the viewpoint of obtaining a thin circular polarizer, 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 thinner the lower limit of the thin film layer thickness, the more preferred; for example, it can be 0.1 μm.

[0128] From the perspective of making the circular polarizer thinner, the λ / 2 layer and the λ / 4 layer can be in direct contact. "Direct" contact between the two layers means that there are no other layers between them. Therefore, the circular polarizer can also be made without any arbitrary thin film layer between the λ / 2 and λ / 4 layers.

[0129] Examples of layers other than any thin film layer include: hard coating and protective film layers for protecting the circular polarizer; adhesive layers and bonding layers for attaching the circular polarizer to the display surface; etc.

[0130] <Shape of a circular polarizer>

[0131] The circular polarizer of this embodiment typically has a film shape. The circular polarizer can be a strip film or a single sheet film. For example, the circular polarizer of this embodiment can be manufactured as a strip film and cut into single sheets with the desired shape for use.

[0132] <Advantages of Circular Polarizers>

[0133] When the circular polarizer of this embodiment is placed on a surface capable of reflecting light (such as a display surface or a mirror surface), it can suppress the reflection of light at that surface. In this case, reflection can be suppressed for both light incident in the frontal direction and light incident in the tilted direction of the circular polarizer. Therefore, low reflectivity can be obtained in either the frontal or tilted direction.

[0134] The ability of existing circular polarizers to suppress light reflection in the tilt direction may become non-uniform within the plane of the polarizer, thus resulting in non-uniformity in the reflectivity and hue of the reflected light. In contrast, the circular polarizer according to this embodiment is able to suppress such non-uniformity in the reflectivity and hue of the reflected light.

[0135] According to the inventors' research, this effect can only be obtained in a circular polarizer containing a broadband wavelength film of the type described above, where the slow axes of the λ / 2 layer and the λ / 4 layer of the circular polarizer satisfy a relationship close to that expressed by Formula X. That is, as a broadband wavelength film of a different type from the broadband wavelength film contained in the circular polarizer of this embodiment, there exists a film combining a λ / 2 layer and a λ / 4 layer having a slow axis perpendicular to the slow axis of the λ / 2 layer. However, when the λ / 4 layer of this different type of broadband wavelength film is formed from a vinyl biphenyl resin, the effect of suppressing reflectivity and hue inhomogeneity of reflected light as described above cannot be obtained. Therefore, it can be said that the above effect is not merely an effect obtained by simply using a vinyl biphenyl resin, but rather an effect obtainable only in a structure having a combination of λ / 2 and λ / 4 layers with the aforementioned slow axis direction.

[0136] Furthermore, since vinyl biphenyl resins have high birefringence, the λ / 4 layer can typically have a small thickness, thereby enabling the circular polarizer to be thinner.

[0137] Furthermore, even without fluorine atoms or other components that may be environmentally restricted, the 4-vinylbiphenyl polymers contained in vinylbiphenyl resins can exhibit high birefringence. This reduces the environmental impact.

[0138] <Manufacturing Method of Circular Polarizer>

[0139] The circular polarizer of this embodiment can be manufactured by a manufacturing method including the following steps: a step of preparing a broadband wavelength film; and a step of bonding the broadband wavelength film with a linear polarizing film. At this time, from the viewpoint of efficiently manufacturing by roll-to-roll method, it is preferable to prepare a strip of broadband wavelength film and a strip of linear polarizing film, and then bond them together to manufacture a strip of circular polarizer.

[0140] The elongated broadband wavelength film is preferably manufactured by a manufacturing method comprising the following steps in sequence:

[0141] The first step is to prepare a resin layer (A) containing a cyclic olefin polymer as a long, inclined stretch film.

[0142] In the second step, a resin layer (B) comprising a 4-vinylbiphenyl polymer is formed on the resin layer (A) to obtain a multilayer film; and

[0143] The third step involves stretching the multilayer film in a stretching direction at a specific angle to its length to obtain a long strip of broadband wavelength film.

[0144] Furthermore, the method for manufacturing this broadband wavelength film may also include:

[0145] The process of forming a thin film layer on the resin layer (A) after preparing the resin layer (A) in the first process.

[0146] Figure 3 A perspective view is shown schematically of the resin layer (A) 320, which is a long, obliquely stretched film, prepared in the first step of the manufacturing method of the broadband wavelength film according to the preferred example described above. Furthermore, Figure 4 A perspective view of the multilayer film 300 obtained in the second step of the manufacturing method of the broadband wavelength film according to the preferred example described above is shown schematically. Further, Figure 5 A perspective view of the broadband wavelength film 140 obtained in the third step of the manufacturing method of the broadband wavelength film according to the preferred example described above is shown schematically.

[0147] In the preferred method for manufacturing the broadband wavelength film 140 described above, such as Figure 3 As shown, the resin layer (A) 320 prepared in the first process is an inclined stretch film, and therefore typically has a slow axis A in its inclined direction. 320 In the second process, a resin layer (B) 330 is formed on the resin layer (A) 320 to obtain... Figure 4 The multilayer film 300 is shown. Then, by stretching the multilayer film 300, co-stretching of resin layer (A) 320 and resin layer (B) 330 is performed. Through co-stretching, the slow axis A of resin layer (A) 320 is adjusted. 320The orientation and optical properties were determined to obtain a λ / 2 layer 120. Furthermore, through co-stretching, a slow axis A was observed in resin layer (B) 330. 130 And optical properties, resulting in a λ / 4 layer of 130. Therefore, as Figure 5 As shown, a broadband wavelength film 140 with λ / 2 layer 120 and λ / 4 layer 130 is obtained.

[0148] In the preferred method for manufacturing the broadband wavelength film described above, instead of stretching resin layer (A) 320 and resin layer (B) 330 separately, they are stretched together in the third step. Therefore, the number of stretching processes can be reduced, thus reducing the number of steps required to manufacture the broadband wavelength film 140, thereby achieving efficient manufacturing. Furthermore, in the method of obtaining the broadband wavelength film 140 by stretching the multilayer film 300 to co-stretch resin layer (A) 320 and resin layer (B) 330, the deviation in the slow axis direction caused by bonding, as seen in methods that separately manufacture λ / 2 and λ / 4 layers and then bond them together, is avoided. Therefore, the slow axis directions of the λ / 2 layer 120 and λ / 4 layer 130 can be easily and precisely controlled, resulting in a circular polarizer that effectively suppresses reflection. Hereinafter, the method for manufacturing this preferred broadband wavelength film will be described, followed by the method for manufacturing a circular polarizer using this broadband wavelength film.

[0149] In the first step, a resin layer (A) is prepared as a long strip of tilted stretch film. The resin layer (A) contains COP resin, or it may contain only COP resin. As this resin layer (A), a tilted stretch film obtained by stretching a long strip of resin film containing COP resin along the tilt direction of the resin film is generally used. As the tilted stretch film described above, a multilayer structure film containing two or more layers containing COP resin can be used, but a single-layer structure film containing only one layer is generally used.

[0150] The resin layer (A) is an inclined stretched film, and therefore typically has a slow axis in the inclined direction. The orientation angle between this slow axis and the length direction of the resin layer (A) can be set in a way that yields a desired broadband wavelength film. For example, if the multilayer film is stretched along its length direction in the third process, the orientation angle of the λ / 2 layer obtained by stretching the resin layer (A) in the third process becomes smaller than the orientation angle of the resin layer (A). Therefore, in this case, the orientation angle of the resin layer (A) is preferably set to be larger than the orientation angle of the λ / 2 layer obtained in the third process.

[0151] The orientation angle between the slow axis of the resin layer (A) and the length direction of the film is preferably greater than 40°, more preferably greater than 41°, even more preferably greater than 42°, and 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, by stretching the multilayer film along the preferred stretching direction described later in the third process, a broadband wavelength film with preferred optical properties can be successfully obtained.

[0152] The in-plane retardation of the resin layer (A) can be set according to the optical properties of the 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, preferably 250 nm or less, more preferably 240 nm or less, and even more preferably 230 nm or less.

[0153] The thickness of the resin layer (A) can be set within a range that yields the desired broadband wavelength film. Specifically, the thickness of the resin layer (A) is preferably 20 μm or more, more preferably 25 μm or more, even more preferably 30 μm or more, preferably 100 μm or less, more preferably 95 μm or less, and even more preferably 90 μm or less.

[0154] The resin layer (A) can be manufactured by a manufacturing method that includes stretching a pre-stretching film, which is a suitable strip of resin film, along the inclined direction of the pre-stretching film.

[0155] The pre-stretch film can be manufactured by, for example, melt molding or solution casting. More specific examples of melt molding include extrusion molding, compression molding, blow molding, injection molding, blow molding, and stretch molding. Among these methods, extrusion molding, blow molding, and compression molding are preferred for obtaining a resin layer (A) with excellent mechanical strength and surface finish. Extrusion molding is particularly preferred from the viewpoint of efficiently and simply manufacturing the resin layer (A).

[0156] After preparing a long strip of pre-stretch film, the long strip of pre-stretch film is stretched in an inclined direction to obtain a resin layer (A) as an inclined stretch film.

[0157] Since the slow axis of the resin layer (A) is typically revealed by stretching the pre-stretch film in an inclined direction, it is preferable that the stretching direction of the pre-stretch film is set according to the direction of the slow axis of the resin layer (A). Specifically, it is preferable that the stretching direction of the pre-stretch film is set to be parallel to the slow axis of the resin layer (A).

[0158] The stretching ratio for obtaining the resin layer (A) is preferably 1.1 times or more, more preferably 1.2 times or more, preferably 4.0 times or less, and more preferably 3.0 times or less. Furthermore, the stretching temperature for obtaining the resin layer (A) is preferably TgA °C or more, more preferably TgA+2 °C or more, particularly preferably TgA+5 °C or more, preferably TgA+40 °C or less, more preferably TgA+35 °C or less, and particularly preferably TgA+30 °C or less. Here, TgA represents the glass transition temperature of the COP resin contained in the resin layer (A). Stretching is typically performed using a widening stretching machine while continuously conveying the pre-stretched film along its length. For example, the widening stretching machine described in International Publication No. 2016 / 047465 can be used as the widening stretching machine.

[0159] The method for manufacturing a broadband wavelength film may also include, as needed, a fourth step after the first step, forming a thin film layer on the resin layer (A). The thin film layer can be formed, for example, by applying a coating liquid containing a resin and a solvent, which are materials for the thin film layer, onto the resin layer (A). Water or an organic solvent can be used as the solvent. Examples of organic solvents include, for instance, the same organic solvent used to form the resin layer (B) described later. Furthermore, a single solvent or a combination of two or more solvents can be used.

[0160] The aforementioned coating liquid may contain a crosslinking agent. By using a crosslinking agent, the mechanical strength of the film layer can be improved, or the adhesion between the film layer and resin layers (A) and (B) can be improved. Examples of crosslinking agents include epoxy compounds, amino compounds, isocyanate compounds, carbodiimide compounds, and α-azoline compounds. Furthermore, these can be used alone or in combination of two or more.

[0161] As a method for applying the coating liquid, examples include the same method as that used to form the resin layer (B) described later.

[0162] A thin film layer can be formed by applying a coating liquid onto the resin layer (A). The thin film layer can then be subjected to curing treatments such as drying and cross-linking as needed. Examples of drying methods include, for example, heating and drying in an oven. Examples of cross-linking methods include, for example, heat treatment or irradiation with active energy rays such as ultraviolet light.

[0163] In the method for manufacturing a broadband wavelength film, after preparing a resin layer (A) in the first step and performing a fourth step to form a thin film layer as needed, a second step is performed to form a resin layer (B) on the resin layer (A) to obtain a multilayer film. In the second step, the resin layer (B) is formed directly on the resin layer (A), or indirectly via any layer such as a thin film layer. Here, "directly" means that there is no arbitrary layer between layer (A) and layer (B). The formed resin layer (B) may contain vinyl biphenyl resin, or it may contain only vinyl biphenyl resin.

[0164] The resin layer (B) is preferably formed by a coating method. Generally, vinyl biphenyl resins tend to have low mechanical strength. However, according to the coating method, vinyl biphenyl resins with such low mechanical strength can be used, and the resin layer (B) can be formed easily. Furthermore, in the coating method, the thickness of the resin layer (B) itself can easily be reduced.

[0165] Furthermore, when a vinylbiphenyl resin containing a 4-vinylbiphenyl polymer forms a resin layer (B) by a layer-forming method such as coating, the refractive index nz in the thickness direction of the resin layer (B) can be increased. Therefore, the parameter Rth / d of the resin layer (B) can be a negative value with a large absolute value, and thus its thickness direction retardation can also be a negative value with a large absolute value.

[0166] When the resin layer (B) is formed by coating, the second step typically 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 organic solvents include cyclopentanone, methyl ethyl ketone, and toluene. Furthermore, one organic solvent may be used alone, or two or more may be used in combination.

[0167] Examples of resin liquid coating methods include curtain coating, extrusion coating, roller coating, spin coating, dip coating, bar coating, spray coating, gliding coating, printing coating, gravure coating, mold coating, gap coating, and impregnation.

[0168] After applying the resin liquid onto the resin layer (A), the organic solvent is removed by drying the resin liquid, thereby forming a resin layer (B) on the resin layer (A). Drying can be carried out by methods such as natural drying, heat drying, vacuum drying, and vacuum heating drying.

[0169] The resin layer (B) formed in the second process can also have in-plane delay and slow axis. When the resin layer (B) has in-plane delay and slow axis, the in-plane delay and slow axis of the resin layer (B) are adjusted by stretching in the third process.

[0170] The thickness of the resin layer (B) can be set within a range that yields the desired broadband wavelength film. Specifically, the thickness of the resin layer (B) is preferably 3 μm or more, more preferably 4 μm or more, even more preferably 5 μm or more, preferably 15 μm or less, more preferably 13 μm or less, and even more preferably 11 μm or less.

[0171] In the method for manufacturing a broadband wavelength film, after obtaining a multilayer film having a resin layer (A) and a resin layer (B) in the second step, a third step is performed to stretch the multilayer film to obtain a strip of broadband wavelength film. Through stretching in the third step, the direction of the slow axis of the resin layer (A) is adjusted, and the optical properties of the resin layer (A) are modified, resulting in a λ / 2 layer. Furthermore, through stretching in the third step, a slow axis appears in the resin layer (B), and optical properties are manifested in the resin layer (B), resulting in a λ / 4 layer.

[0172] According to the stretching in the third process, the thickness retardation Rth of the resin layer (B) remains negative, and the absolute value of this negative value can usually be increased. Therefore, the thickness 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, a λ / 4 layer with a negative thickness retardation Rth can be obtained through such a simple process as forming and stretching the resin layer (B), which is one of the advantages of the manufacturing method of this embodiment.

[0173] The stretching in the third process is typically performed in only one direction. This stretching direction in the third process is preferably set to obtain a desired broadband wavelength film. Generally, the direction of the slow axis of the resin layer (A) is varied in a manner close to this stretching direction through stretching in the third process. Furthermore, in the resin layer (B), a slow axis typically appears in a direction perpendicular to this stretching direction through stretching in the third process. Therefore, the stretching direction in the third process is preferably set in such a way that by varying the direction of the slow axis in the resin layer (A) as described above, and by manifesting the slow axis in the resin layer (B), λ / 2 and λ / 4 layers with slow axes in the desired direction can be obtained.

[0174] The third step preferably includes stretching the multilayer film in a stretching direction at an angle of 0° ± 20° to the length direction of the multilayer film. More specifically, the angle between the stretching direction in the third step and the length direction of the multilayer film is preferably -20° or more, more preferably -15° or more, even more preferably -10° or more, preferably less than 20°, more preferably less than 15°, and even more preferably less than 10°. Furthermore, in these cases, the stretching in the third step is preferably performed along the length direction of the multilayer film. When stretching is performed along such a stretching direction, the direction of the slow axis can be easily controlled.

[0175] The stretching ratio in the third process is preferably 1.1 times or more, more preferably 1.15 times or more, particularly preferably 1.2 times or more, preferably 2.0 times or less, more preferably 1.8 times or less, and particularly preferably 1.6 times or less. When the stretching ratio in the third process is at or above the lower limit of the above range, the occurrence of wrinkles can be suppressed. Furthermore, when the stretching ratio in the third process is at or below the upper limit of the above range, the direction of the slow axis can be easily controlled.

[0176] The stretching temperature in the third process is preferably TgA-20°C or higher, more preferably TgA-10°C or higher, even more preferably TgA-5°C or higher, preferably TgA+30°C or lower, more preferably TgA+25°C or lower, and 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).

[0177] Furthermore, the stretching temperature in the third process is preferably above TgB-50°C, more preferably above TgB-40°C, particularly preferably above TgB-30°C, more preferably below TgB+30°C, more preferably below TgB+25°C, and particularly preferably below TgB+20°C. Here, TgB represents the glass transition temperature of the vinyl biphenyl resin contained in the resin layer (B).

[0178] In the third process, stretching is preferably performed by free uniaxial stretching. Here, free uniaxial stretching refers to stretching along a certain direction without applying any constraint force in directions other than the stretching direction. Therefore, for example, free uniaxial stretching of a multilayer film along its length means stretching along the length direction without constraining the ends of the multilayer film in the width direction. By performing free uniaxial stretching in the third process, the slow axis directions of the λ / 2 layer and the λ / 4 layer can be easily controlled.

[0179] The stretching in the third step described above can be performed using, for example, a spreading stretching machine or a roller stretching machine. Especially when stretching the multilayer film along its length in the third step, a roller stretching machine is preferred. With a roller stretching machine, free uniaxial stretching can be easily performed. Free uniaxial stretching using a roller stretching machine is typically performed while continuously feeding a long strip of multilayer film along its length. As a roller stretching machine, for example, the roller stretching machine described in International Publication No. 2016 / 047465 can be used.

[0180] The aforementioned method for manufacturing a broadband wavelength film may further include any steps in combination with the first, second, third, and fourth steps. For example, the method for manufacturing a broadband wavelength film may include a step of forming a protective layer on the surface of the broadband wavelength film. Furthermore, for example, the method for manufacturing a broadband wavelength film may include a step of performing surface treatments such as corona treatment or plasma treatment on the surface of one or more of the resin layer (A), resin layer (B), and thin film layer at any given time.

[0181] By using the manufacturing method described above, a long, broadband wavelength film comprising a λ / 2 layer containing COP resin and a λ / 4 layer containing vinyl biphenyl resin can be obtained.

[0182] The λ / 2 layer of a broadband wavelength film typically has a slow axis in a direction at a specific orientation angle to its length. The range of this orientation angle is generally the same as the range of the angle between the slow axis of the λ / 2 layer contained in a circular polarizer and the absorption axis of the linear polarizing film. Thus, the λ / 2 layer of a long strip of broadband wavelength film can have a slow axis in a direction at an angle of 22.5° ± 10° to the length of the broadband wavelength film.

[0183] Furthermore, the λ / 4 layer of a broadband wavelength film typically has a slow axis in a direction at a specific orientation angle to its length. The range of this orientation angle is generally the same as the range of the angle between the slow axis of the λ / 4 layer contained in a circular polarizer and the absorption axis of the linear polarizing film. Therefore, the λ / 4 layer of a long strip of broadband wavelength film can have a slow axis in a direction at an angle of 90° ± 20° to the length of the broadband wavelength film.

[0184] 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 using a spectrophotometer in the wavelength range of 400 nm to 700 nm according to JIS K0115.

[0185] 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 5 locations using a "turbidity meter NDH-300A" manufactured by Nippon Denshoku Kogyo Co., Ltd., in accordance with JIS K7361-1997, and the average value obtained from these measurements is used.

[0186] A circular polarizer can be manufactured by a manufacturing method that includes a step of bonding the long strip of broadband wavelength film to a long strip of linear polarizing film after preparation. The bonding is performed by sequentially arranging the linear polarizing film, the λ / 2 layer, and the λ / 4 layer in the thickness direction. Furthermore, an adhesive layer or bonding agent can be used for bonding as needed.

[0187] The elongated linearly polarizing film preferably has an absorption axis along its length. This preferred linearly polarizing film can be easily used to manufacture a circular polarizer by bonding it to an elongated broadband wavelength film comprising a λ / 2 layer having an orientation angle within the aforementioned range and a λ / 4 layer having an orientation angle within the aforementioned range. Specifically, based on the bonding combination described above, a circular polarizer can be manufactured by bonding the elongated linearly polarizing film and the elongated broadband wavelength film in a manner parallel to their length directions. Therefore, a roll-to-roll method can be used to manufacture the circular polarizer, thus improving the manufacturing efficiency of the circular polarizer.

[0188] The method for manufacturing a circular polarizer may further include any combination of the steps described above. For example, the method may include a step of forming a protective layer on the surface of the circular polarizer. Furthermore, for example, the method may include a step of cutting a strip of circular polarizer to obtain a single sheet of circular polarizer.

[0189] <Image display device>

[0190] As described above, when the circular polarizer is placed on a surface capable of reflecting light, it can effectively reduce the reflection of external light. In particular, the circular polarizer is useful in that it can effectively reduce the reflection of external light over a wide wavelength range in the visible light region. Furthermore, since it can effectively reduce the reflection of external light over such a wide wavelength range, the circular polarizer can suppress coloration caused by increased reflection intensity of certain wavelengths of light. Moreover, the circular polarizer can achieve the aforementioned effects of suppressing reflection and suppressing coloration in either the frontal or tilted direction, and generally, these effects can be obtained in all azimuth directions of the main surface of the film. Utilizing this excellent anti-reflection function, the circular polarizer can be used as an anti-reflective film for image display devices.

[0191] Typically, image display devices have a display surface on which a circular polarizer is disposed. In this case, the circular polarizer is arranged such that a linear polarizing film, a λ / 2 layer, and a λ / 4 layer are arranged sequentially from the viewing side. Examples of such image display devices include organic EL display devices and liquid crystal display devices. When a circular polarizer is provided on the display surface of these image display devices, it is possible to suppress the reflection of light incident from outside the device within the device and its subsequent emission outside, thereby suppressing glare on the display surface. Furthermore, by achieving the aforementioned anti-reflection function over a wide wavelength range, it is possible to suppress color distortion of the display surface.

[0192] Example

[0193] The present invention will now be specifically described with reference to the embodiments shown below. However, the present invention is not limited to the embodiments shown below, and can be implemented in any way without departing from the scope of the claims and their equivalents.

[0194] In the following descriptions, unless otherwise stated, "%" and "parts" refer to quantities based on weight. Furthermore, unless otherwise stated, the operations described below are performed under atmospheric conditions at normal temperature and pressure (23°C, 1 atm).

[0195] <Evaluation Methods>

[0196] (Methods for determining the optical properties of λ / 2 and λ / 4 layers)

[0197] A broadband wavelength film was placed on the stage of a phase difference meter (AxoScan, manufactured by Axometrics). The change in polarization state of polarized light transmitted through the broadband wavelength film before and after transmission was measured to determine the transmission polarization characteristics of the broadband wavelength film. This measurement was performed as a multi-directional measurement within a range of -55° to 55° relative to the principal plane polar angle of the broadband wavelength film. Furthermore, the multi-directional measurement was performed with a certain azimuth angle of the principal plane of the broadband wavelength film set to 0°, at azimuth angles of 45°, 90°, 135°, and 180°. The measurement wavelength was 590 nm.

[0198] Next, by performing fitting calculations based on the transmission polarization characteristics measured as described above, the in-plane retardation Re, the thickness-direction retardation Rth, and the orientation angle of the λ / 2 and λ / 4 layers contained in the broadband wavelength film are determined. Furthermore, the birefringence Δn of the λ / 4 layer is measured by dividing the in-plane retardation Re of the λ / 4 layer by the thickness of the λ / 4 layer. Additionally, the parameter Rth / d of the λ / 4 layer is measured by dividing the thickness-direction retardation Rth of the λ / 4 layer by the thickness. The above fitting calculations are performed using the three-dimensional refractive index and orientation angle of each layer contained in the broadband wavelength film as fitting parameters. Furthermore, the software (Multi-Layer Analysis) accompanying the aforementioned phase difference meter (AxoScan) is used in the above fitting calculations.

[0199] (Visual evaluation method)

[0200] Prepare a mirror with a flat reflective surface. Place the mirror with the reflective surface horizontal and facing upwards. Attach a circular polarizer to the reflective surface of the mirror with the linear polarizing film side facing upwards.

[0201] Then, on a sunny day, with sunlight shining on the circular polarizer, visually observe the circular polarizer on the mirror. Observe along the following two directions of the circular polarizer:

[0202] (i) The frontal direction with a polar angle of 0° and an azimuth angle of 0°; and

[0203] (ii) Inclination direction with a polar angle of 45° and an azimuth angle of 0° to 360°.

[0204] When viewed from the front, if the reflection of sunlight is almost invisible, the circular polarizer appears black, and unevenness in density and hue is not visually discernible, it is judged as "good". Conversely, if the reflection of sunlight is visually discernible and the circular polarizer does not appear black, or if unevenness in density or hue is visually discernible, it is judged as "bad".

[0205] When observing in the tilt direction, if no change in reflectance and hue with azimuth is visually discernible, and no unevenness in intensity or hue is visually discernible at any azimuth angle, it is judged as "good". Conversely, if a change in reflectance and hue with azimuth is visually discernible, or if unevenness in intensity or hue is visually discernible at a specific azimuth angle, it is judged as "poor".

[0206] (A method for calculating reflectivity based on simulation)

[0207] Using Shintech's "LCD Master" software for simulation, the circular polarizers manufactured in each embodiment and comparative example were modeled, and their reflectivity was calculated. In the simulation model, a structure was established whereby the circular polarizer was bonded to the reflective surface of a mirror having a planar reflective surface, with the λ / 4 layer side in contact with the mirror. Therefore, in this model, a structure was established in which a linear polarizing film, a λ / 2 layer, a λ / 4 layer, and a mirror were sequentially arranged in the thickness direction.

[0208] In the model described above, the reflectivity of light irradiated onto the circular polarizer from light source D65 is calculated in both the (i) frontal direction and (ii) tilt direction. Specifically, in the (i) frontal direction, the reflectivity is calculated at a polar angle of 0° and an azimuth angle of 0°. Furthermore, in the (ii) tilt direction, calculations are performed every 5° along the azimuth direction within a range of 45° polar angle and 0° to 360° azimuth angle, and the average of these calculated values ​​is used as the reflectivity in the tilt direction of the modeled circular polarizer. Additionally, in the simulation, surface reflection components actually generated on the surface of the polarizing film are excluded from the reflectivity calculation.

[0209] <Example 1>

[0210] (First step: Manufacturing of resin layer (A))

[0211] Granular norbornene resin (manufactured by Zeon Corporation, Japan; glass transition temperature 126°C) was dried at 100°C for 5 hours. The dried resin was fed to an extruder, passed through a polymer tube and a polymer filter, and extruded into sheets from a T-die onto a casting drum. The extruded resin was cooled to obtain a long strip of pre-stretched film with a thickness of 60 μm. The obtained pre-stretched film was wound into rolls for recycling.

[0212] The pre-stretched film is drawn from the roll and continuously fed to a stretching machine. Then, using this stretching machine, the pre-stretched film is stretched at a stretching direction at a 45° angle to its length direction, at a stretching temperature of 135°C and a stretch ratio of 1.5 times, to obtain a long strip of inclined stretched film serving as the resin layer (A). The resulting inclined stretched film has an orientation angle of 45° and an in-plane retardation (Re) of 195 nm. The resulting inclined stretched film is then wound into a roll for recycling.

[0213] (Second step: Formation of resin layer (B))

[0214] A resin solution was prepared comprising poly(4-vinylbiphenyl) (manufactured by Sigma-Aldrich, weight-average molecular weight Mw = 115,000, glass transition temperature 138°C) as a resin with inherently negative birefringence, and cyclopentanone as a solvent. The concentration of poly(4-vinylbiphenyl) in the resin solution was 15% by weight.

[0215] The inclined stretch film is pulled out of the roll, and the aforementioned resin solution is applied to the inclined stretch film. Then, the applied resin solution is dried to form a poly(4-vinylbiphenyl) layer (7.0 μm thick) as resin layer (B) on the inclined stretch film. Thus, a multilayer film having an inclined stretch film as resin layer (A) and a poly(4-vinylbiphenyl) layer as resin layer (B) is obtained. The obtained multilayer film is wound into a roll for recycling.

[0216] (Third process: Stretching of multilayer films)

[0217] The multilayer film is drawn from the roll and continuously fed to a longitudinal stretching machine. Then, the multilayer film is subjected to free uniaxial stretching along its length at a stretching temperature of 135°C and a stretch ratio of 1.3 times. This yields a broadband wavelength film comprising a λ / 2 layer obtained by stretching an inclined stretching film and a λ / 4 layer obtained by stretching a poly(4-vinylbiphenyl) layer. The obtained broadband wavelength film is evaluated using the above method.

[0218] (Manufacturing method of circular polarizing film)

[0219] A linearly polarizing film with an absorption axis along its length is prepared. This linearly polarizing film and the aforementioned broadband wavelength film are then bonded together with their lengths parallel to each other. This bonding is performed using an adhesive (Nitto Denko Corporation's "CS-9621"). Through bonding, a circularly polarizing film is obtained, sequentially comprising a linearly polarizing film, a λ / 2 layer, and a λ / 4 layer. The obtained circularly polarizing film is evaluated according to the above method.

[0220] <Comparative Example 1>

[0221] Polystyrene (Sigma-Aldrich, weight-average molecular weight Mw = 280,000, glass transition temperature 100°C) was prepared as a resin with inherently negative birefringence. The polystyrene was subjected to an evaluation test at 135°C with a stretch of 1.3 times, confirming that the birefringence Δn exhibited by the stretching was 0.00031. Therefore, it was determined that to obtain a λ / 4 layer with an in-plane retardation Re of approximately 110 nm, equivalent to that of Example 1, a λ / 4 layer with a thickness of 355 μm is required.

[0222] Therefore, 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 could be obtained after stretching. In addition, the fabrication of multilayer films, broadband wavelength films and circularly polarized films was attempted by the same method as in Example 1.

[0223] However, because the required coating thickness is too thick, it is impossible to form a polystyrene layer with the desired thickness, and therefore it is impossible to manufacture a multilayer film.

[0224] <Comparative Example 2>

[0225] Poly(4-methylstyrene) (manufactured by Sigma-Aldrich, weight-average molecular weight Mw = 72000, glass transition temperature 106°C) was prepared as a resin with inherently negative birefringence. The polystyrene was subjected to an evaluation test at 135°C with a stretch of 1.3 times, confirming that the birefringence Δn exhibited by the stretching was 0.00037. Therefore, it was determined that to obtain a λ / 4 layer with an in-plane retardation Re of approximately 110 nm, equivalent to that of Example 1, a λ / 4 layer with a thickness of 297 μm is required.

[0226] Therefore, a resin liquid containing poly(4-methylstyrene) 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 297 μm could be obtained after stretching. In addition, the fabrication of multilayer films, broadband wavelength films and circularly polarized films was attempted by the same method as in Example 1.

[0227] However, because the required coating thickness is too thick, it is impossible to form a layer of poly(4-methylstyrene) with the desired thickness, and therefore it is impossible to manufacture a multilayer film.

[0228] <Comparative Example 3>

[0229] Poly(4-chlorostyrene) (manufactured by Sigma-Aldrich, weight-average molecular weight Mw = 75000, glass transition temperature 106°C) was prepared as a resin with inherently negative birefringence. The polystyrene was subjected to an evaluation test at 135°C with a stretch of 1.3 times, confirming that the birefringence Δn exhibited by the stretching was 0.00071. Therefore, it was determined that to obtain a λ / 4 layer with an in-plane retardation Re of approximately 110 nm, equivalent to that of Example 1, a λ / 4 layer with a thickness of 155 μm is required.

[0230] Therefore, a resin liquid containing poly(4-chlorostyrene) 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 155 μm could be obtained after stretching. In addition, the fabrication of multilayer films, broadband wavelength films and circularly polarized films was attempted by the same method as in Example 1.

[0231] However, because the required coating thickness is too thick, it is impossible to form a poly(4-chlorostyrene) layer with the desired thickness, and therefore it is impossible to manufacture multilayer films.

[0232] <Comparative Example 4>

[0233] A styrene-maleic anhydride copolymer (Polyscope "XIRAN3500", styrene:maleic anhydride = 3:1, weight-average molecular weight Mw = 80,000, glass transition temperature 130°C) was prepared as a resin with inherently negative birefringence. The polystyrene was subjected to an evaluation test at 135°C with a stretch of 1.3 times, confirming that the birefringence Δn exhibited by the stretching was 0.00016. Therefore, it was determined that to obtain a λ / 4 layer with an in-plane retardation Re of approximately 110 nm, equivalent to that of Example 1, a λ / 4 layer with a thickness of 688 μm is required.

[0234] Therefore, 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 could be obtained after stretching. In addition, the fabrication of multilayer films, broadband wavelength films and circularly polarized films was attempted by the same method as in Example 1.

[0235] However, because the required coating thickness is too thick, it is impossible to form a layer of styrene-maleic anhydride copolymer with the desired thickness, and therefore it is impossible to manufacture a multilayer film.

[0236] <Comparative Example 5>

[0237] Poly(2-vinylnaphthalene) (manufactured by Sigma-Aldrich, weight-average molecular weight Mw = 175,000, glass transition temperature 135°C) was prepared as a resin with inherently negative birefringence. 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 varied to obtain a λ / 4 layer with a thickness of 20 μm after stretching. Otherwise, the fabrication and evaluation of multilayer films, broadband wavelength films, and circularly polarized films were attempted using the same method as in Example 1.

[0238] <Results>

[0239] The results of the above embodiments and comparative examples are shown in the following table. In the table below, the abbreviations have the following meanings.

[0240] Re: In-plane delay.

[0241] Rth: Delay in the thickness direction.

[0242] θ: Orientation angle.

[0243] Tg: Glass transition temperature.

[0244] Mw: Weight-average molecular weight.

[0245] [Table 1]

[0246]

[0247] Explanation of reference numerals in the attached figures

[0248] 100: Circular polarizer;

[0249] 110: Linear polarizing film;

[0250] 120: λ / 2 layers;

[0251] 130: λ / 4 layers;

[0252] 140: Broadband wavelength film;

[0253] 200: noodles;

[0254] 300: Multilayer film;

[0255] 320: Resin layer (A);

[0256] 330: Resin layer (B).

Claims

1. A circular polarizer, comprising, in sequence: Linear polarizing film; A λ / 2 layer having a slow axis in a direction at an angle of 22.5° ± 10° relative to the absorption axis of the linearly polarized film; and A λ / 4 layer having a slow axis in a direction at an angle of 90° ± 20° relative to the absorption axis of the linearly polarizing film. The λ / 2 layer comprises a resin containing a cyclic olefin polymer. The λ / 4 layer comprises a resin containing a polymer, the polymer containing 4-vinylbiphenyl monomer units.

2. The circular polarizer according to claim 1, wherein, In 100% by weight of the polymer containing the 4-vinylbiphenyl monomer unit, the 4-vinylbiphenyl monomer unit accounts for 70% by weight or more.

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

4. The circular polarizer according to claim 1, wherein, The λ / 4 layer has a birefringence Δn greater than 0.

010.

5. A method for manufacturing a broadband wavelength film, comprising the following steps: The first step is to prepare a resin layer (A) containing a cyclic olefin polymer as a long, inclined stretch film. In the second step, a resin layer (B) containing a polymer with 4-vinylbiphenyl monomer units is formed on the resin layer (A) to obtain a multilayer film; as well as The third step involves stretching the multilayer film at an angle of 0°±20° relative to its length direction to obtain a long strip of broadband wavelength film with λ / 2 and λ / 4 layers.

6. The method for manufacturing a broadband wavelength film according to claim 5, wherein, The second process includes: A resin liquid comprising a polymer-containing resin and an organic solvent is applied to the resin layer (A), wherein the polymer contains the 4-vinylbiphenyl monomer unit; and The applied resin solution is then dried.

7. A long, wide-band wavelength film, having: A λ / 2 layer having a slow axis at an angle of 22.5° ± 10° relative to the longitudinal direction of the broadband wavelength film; and A λ / 4 layer having a slow axis at an angle of 90° ± 20° relative to the length direction of the broadband wavelength film. The λ / 2 layer comprises a resin containing a cyclic olefin polymer. The λ / 4 layer comprises a resin containing a polymer, the polymer containing 4-vinylbiphenyl monomer units.

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

Images