TW201937211A - Circularly polarizing plate, long broadband [lambda]/4 plate, organic electroluminescence display device, and liquid crystal display device - Google Patents

Abstract

A circular polarizing plate comprising: a polarizing film; a λ/2 plate having a slow axis in a direction of an angle Θh with respect to a transmission axis of the polarizing film, and a transmission axis with respect to the polarizing film The angle Θq has a slow axis λ/4 plate, wherein the aforementioned angle Θh of the λ/2 plate and the aforementioned angle Θq of the λ/4 plate satisfy the following formulas (A1), (A2) and (A3):
Θq±10°=2Θh+45° (A1),
25°<Θh<45° (A2),
95°<Θq<135° (A3),
The degree of wavelength dispersion of the λ/2 plate is different from the degree of wavelength dispersion of the λ/4 plate, and the NZ coefficient NZq of the λ/4 plate satisfies NZq ≦ 0.0.

Description

Circular polarizing plate, strip-shaped broadband λ/4 plate, organic electroluminescence display device and liquid crystal display device

The present invention relates to a circularly polarizing plate, a strip-shaped broadband λ/4 plate, an organic electroluminescence display device, and a liquid crystal display device.

Conventionally, in an organic electroluminescence display device (hereinafter referred to as "organic EL display device") and a liquid crystal display device, a circularly polarizing plate may be provided in order to reduce external light reflection on the display surface. As such a circularly polarizing plate, a film in which a polarizing film and a λ/4 plate are combined is generally used. However, in the conventional λ/4 board, almost all of the light in a specific narrow wavelength range can function as a function of the λ/4 wavelength plate. Therefore, the use of a circular polarizer can reduce external light reflection in a specific narrow wavelength range, but it is difficult to reduce external light reflection.

On the other hand, in recent years, a wide band λ/4 plate of a λ/4 plate and a λ/2 plate has been proposed (Patent Documents 1 to 3). This wide-band λ/4 plate functions as a λ/4 plate over a wide wavelength range, so that a circular polarizing plate that can reduce external light reflection in a wide wavelength range can be realized.

Patent Literature
Patent Document 1: Japanese Patent Publication No. H05-100114, Patent Document 2: Japanese Patent Publication No. 2007-004120, Patent Document 3: Japanese Patent Publication No. 2013-235272

In a circularly polarizing plate in which a polarizing film and a broadband λ/4 plate are combined, a direction of an optical axis called a transmission axis of a polarizing film, a slow axis of a λ/2 plate, and a slow axis of a λ/4 plate is required. The optical axes are adjusted at a specified angle.

However, when the circular polarizing plate is viewed from an oblique direction other than the front direction, the viewing angle of the optical axis may be deviated from the specified angle. Therefore, the conventional circular polarizing plate can reduce external light reflection in the front direction, but it is not possible to effectively reduce external light reflection in an oblique direction other than the front direction. In particular, since a circularly polarizing plate having a wide-band λ/4 plate has not only a λ/4 plate but also a λ/2 plate, the number of optical axes is larger than that of the conventional circular polarizing plate. Therefore, in a circularly polarizing plate having a wide-band λ/4 plate, the deviation of the optical axis in viewing becomes larger than that of the conventional circular polarizing plate having no λ/2 plate, and the external direction is reduced in the oblique direction. The tendency of light reflection to be inferior.

The present invention has been made in view of the above problems, and an object thereof is to provide a circular polarizing plate which can effectively reduce external light reflection in both the front direction and the oblique direction; and can effectively reduce the externality in both the front direction and the oblique direction. A wide-band λ/4 plate of a circularly polarizing plate that reflects light; and an organic EL display device and a liquid crystal display device to which the above-described circular polarizing plate or broadband λ/4 plate is applied.

The present inventors have focused their efforts on solving the above problems, and as a result, it has been found that by appropriately adjusting the optical axis, the degree of wavelength dispersion, and the NZ coefficient by combining a polarizing film, a λ/2 plate, and a λ/4 plate, The present invention is completed by a circularly polarizing plate having excellent reflection suppressing effects in both the front direction and the oblique direction.

That is, the present invention encompasses the following.

[1] A circular polarizing plate, which is sequentially provided:
Polarized film,
a λ/2 plate having a slow axis in a direction θh with respect to a transmission axis of the polarizing film, and a λ/4 plate having a slow axis in a direction θq with respect to a transmission axis of the polarizing film The angle Θh of the λ/2 plate and the aforementioned angle Θq of the λ/4 plate satisfy the following formulas (A1), (A2), and (A3),
Θq±10°=2Θh+45° (A1)
25°<Θh<45° (A2)
95°<Θq<135° (A3)
The degree of wavelength dispersion of the aforementioned λ/2 plate is different from the degree of wavelength dispersion of the aforementioned λ/4 plate,
The NZ coefficient NZq of the aforementioned λ/4 plate satisfies NZq ≦ 0.0.

[2] The circularly polarizing plate according to [1], wherein a phase difference Reh (400) in a plane of the λ/2 plate having a wavelength of 400 nm,
In the in-plane phase difference Reh (550) of the aforementioned λ/2 plate having a wavelength of 550 nm,
In the in-plane phase difference Req (400) of the aforementioned λ/4 plate having a wavelength of 400 nm, and the in-plane retardation Req (550) of the aforementioned λ/4 plate at a wavelength of 550 nm
Satisfy the following formula (B):
Reh (400) / Reh (550) < Req (400) / Req (550) (B).

[3] The circularly polarizing plate according to [1] or [2], wherein a phase difference Reh (400) in a plane of the λ/2 plate having a wavelength of 400 nm,
In the in-plane phase difference Reh (550) of the aforementioned λ/2 plate having a wavelength of 550 nm,
In the in-plane phase difference Req (400) of the aforementioned λ/4 plate having a wavelength of 400 nm, and the in-plane retardation Req (550) of the aforementioned λ/4 plate at a wavelength of 550 nm
Satisfy the following formula (C):
0.04 < Req (400) / Req (550) - Reh (400) / Reh (550) < 1.0 (C).

[4] The circularly polarizing plate according to any one of [1] to [3] wherein the NZ coefficient NZh of the λ/2 plate satisfies 1.0≦NZh≦1.3, and the NZ coefficient NZq of the aforementioned λ/4 plate satisfies -1.5≦NZq≦0.0.

[5] The circularly polarizing plate according to any one of [1] to [4] wherein the λ/4 plate has a layer made of a material having a negative intrinsic birefringence value.

[6] The circularly polarizing plate according to any one of [1] to [5] wherein the λ/2 plate has a layer made of a material having a positive intrinsic birefringence value.

[7] The circularly polarizing plate according to any one of [1] to [6] wherein the circular polarizing plate is elongated.
The transmission axis of the polarizing film is in the width direction of the circular polarizing plate.

[8] A strip-shaped broadband λ/4 plate which is a strip-shaped wide-band λ/4 plate and has:
The λ/2 plate having a slow axis in a direction θh with respect to the width direction of the wide band λ/4 plate, and an angle Θq in the width direction with respect to the aforementioned wide band λ/4 plate a λ/4 plate having a slow axis, wherein the aforementioned angle Θh of the λ/2 plate and the aforementioned angle Θq of the λ/4 plate satisfy the following formulas (A1), (A2), and (A3),
Θq±10°=2Θh+45° (A1)
25°<Θh<45° (A2)
95°<Θq<135° (A3)
The degree of wavelength dispersion of the aforementioned λ/2 plate is different from the degree of wavelength dispersion of the aforementioned λ/4 plate,
The NZ coefficient NZq of the aforementioned λ/4 plate satisfies NZq ≦ 0.0.

[9] The long strip-shaped broadband λ/4 plate according to [8], wherein the λ/2 plate is an obliquely stretched film.

[10] The strip-shaped broadband λ/4 plate according to [8] or [9], wherein the λ/4 plate is an obliquely stretched film.

[11] An organic electroluminescence display device, comprising: the circularly polarizing plate according to any one of [1] to [7], or the length of any one of [8] to [10] A wide-band λ/4 film sheet obtained by cutting out a strip-shaped broadband λ/4 plate.

[12] A liquid crystal display device comprising the circularly polarizing plate according to any one of [1] to [7], or the long-band broadband as described in any one of [8] to [10] A broadband λ/4 film sheet obtained by cutting out a λ/4 plate.

According to the present invention, it is possible to provide a circular polarizing plate which can effectively reduce external light reflection in both the front direction and the oblique direction; and can realize a wide frequency band of a circular polarizing plate which can effectively reduce external light reflection in both the front direction and the oblique direction. /4 plate; and an organic EL display device and a liquid crystal display device to which the above-described circular polarizing plate or broadband λ/4 plate is applied.

The embodiments and examples are disclosed below to explain the present invention in detail. However, the present invention is not limited to the embodiments and examples shown below, and may be arbitrarily changed and carried out without departing from the scope of the invention and the scope of the invention.

In the following description, the "long strip" film means a film having a length of 5 times or more with respect to the width of the film, preferably 10 times or more, and specifically means a roll that can be wound up. A film of a length that is stored or transported. The upper limit of the length of the elongated film is not particularly limited, and is, for example, 100,000 times or less with respect to the width.

In the following description, the in-plane phase difference Re of the film is a value represented by Re = (nx - ny) × d unless otherwise noted. Further, the thickness direction phase difference Rth of the film is a value represented by Rth = [(nx + ny) / 2 - nz] × d unless otherwise noted. Further, the NZ coefficient of the film is a value expressed by (nx - nz) / (nx - ny) unless otherwise noted. Here, nx represents a refractive index in a direction perpendicular to the thickness direction of the film (in-plane direction) and giving a direction of maximum refractive index. Ny denotes a refractive index which is in the in-plane direction and orthogonal to the direction of the nx direction. Nz represents the refractive index in the thickness direction. d represents the thickness of the film. The wavelength was measured and was 590 nm unless otherwise noted.

In the following description, the intrinsic birefringence value is positive, and unless otherwise noted, it means that the refractive index in the extending direction is larger than the refractive index in the direction orthogonal thereto. Further, the intrinsic birefringence value is negative, and unless otherwise noted, it means that the refractive index in the extending direction is smaller than the refractive index in the direction orthogonal thereto. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

In the following description, "(meth)acrylic acid" includes "acrylic acid", "methacrylic acid", and combinations thereof.

In the following description, the oblique direction of the long strip film, unless otherwise noted, indicates the direction in which the film is in the in-plane direction and is neither parallel nor perpendicular to the width direction of the film.

In the following description, the front direction of a film, unless otherwise noted, means the normal direction of the principal plane of the film, specifically the direction of the polar angle of the principal plane of 0° and the azimuth angle of 0°.

In the following description, the oblique direction of a film, unless otherwise noted, means that it is neither parallel nor perpendicular to the direction of the principal plane of the film, specifically, the polar angle of the aforementioned principal plane is greater than 0° and less than The direction of the range of 90°.

In the following description, the directions of the elements are "parallel", "vertical" and "orthogonal", and unless otherwise noted, may also include, for example, ±5° within the range not impairing the effects of the present invention. The error within the range.

In the following description, the "polarizing plate", "λ/2 plate" and "λ/4 plate" are not only rigid members but also flexible, for example, made of a resin film, unless otherwise noted. member.

In the following description, the angle of the optical axis (penetrating axis, slow axis, etc.) of each of the films having a plurality of thin films indicates the angle at which the film is viewed from the thickness direction unless otherwise noted.

In the following description, the slow axis of the film, unless otherwise noted, indicates the slow axis in the plane of the film.

[1. Layer structure of circular polarizing plate]

1 is an exploded perspective view of a circularly polarizing plate 100 according to an embodiment of the present invention. In Fig. 1, on the surface of the λ/2 plate 120, a shaft 112 extending in the same direction as the transmission axis 111 of the polarizing film 110 is shown by a dotted line. Further, in Fig. 1, on the surface of the λ/4 plate 130, a shaft 113 extending in the same direction as the transmission axis 111 of the polarizing film 110 is shown by a dotted line.

As shown in FIG. 1, a circularly polarizing plate 100 according to an embodiment of the present invention is provided with a polarizing film 110, a λ/2 plate 120, and a λ/4 plate 130 in this order in the thickness direction of the circular polarizing plate 100.

The polarizing film 110 has a polarizing plate that penetrates the shaft 111 and has a function of penetrating a linearly polarized light having a polarization direction parallel to the transmission axis 111 to absorb the polarized light. The polarization direction of the linearly polarized light means the polarization direction of the electric field of the linearly polarized light. The polarization direction of linear polarization is sometimes referred to as the "polarization axis".

The λ/2 plate 120 is an optical member having a specified phase difference. The λ/2 plate 120 has a slow axis 121 in a direction at a specified angle Θh with respect to the transmission axis 111 of the polarizing film 110.

The λ/4 plate 130 is an optical member having a specified phase difference different from the λ/2 plate 120. This λ/4 plate 130 has a slow axis 131 in a direction at a specified angle Θq with respect to the transmission axis 111 of the polarizing film 110.

The slow axis 131 of the λ/4 plate 130 is at an angle Θq with respect to the transmission axis 111 of the polarizing film 110, and is generally at an angle Θh with respect to the transmission axis 111 of the λ/2 plate 120 with respect to the transmission axis 111 of the polarizing film 110. The same direction. Therefore, for example, when viewed from the thickness direction, the slow axis 121 of the λ/2 plate 120 is at an angle Θh with respect to the transmission axis 111 of the polarizing film 110 in the clockwise direction, the slow axis 131 of the λ/4 plate 130 is relative to The transmission axis 111 of the polarizing film 110 is generally at an angle Θq in a clockwise direction. Further, for example, when viewed from the thickness direction, the slow axis 121 of the λ/2 plate 120 is at an angle Θh with respect to the transmission axis 111 of the polarizing film 110 in the counterclockwise direction, the slow axis 131 of the λ/4 plate 130 is opposed to The transmission axis 111 of the polarizing film 110 is generally at an angle Θq in the counterclockwise direction.

In the circularly polarizing plate 100 having such a structure, the layer portion including the λ/2 plate 120 and the λ/4 plate 130 functions as a broadband λ/4 plate 140 which has a wide band λ/4 plate 140 In the broad wavelength range, the in-plane phase difference of about 1/4 wavelength of the wavelength of the light is imparted to the light that penetrates the portion of the layer. Therefore, the circularly polarizing plate 100 can function as a circularly polarizing plate that absorbs one of the right circularly polarized light and the left circularly polarized light in a wide wavelength range and allows the remaining light to penetrate.

The circular polarizing plate 100 may be a film cut into sheets or an elongated film. In the case where the circular polarizing plate 100 is an elongated film, the direction of the transmission axis 111 of the polarizing film 110 generally coincides with the width direction of the circular polarizing plate 100.

[2. Polarized film]

The polarizing film usually has a polarizer layer, and a protective film layer for protecting the polarizer layer is provided as needed.

As the polarizer layer, for example, a suitable film is applied to a film of a suitable vinyl alcohol polymer in an appropriate order and manner. Examples of the vinyl alcohol polymer include polyvinyl alcohol and partially formalized polyvinyl alcohol. Examples of the treatment of the film include dyeing treatment, elongation treatment, and crosslinking treatment using a dichroic substance such as iodine or a dichroic dye. Generally, in the stretching process for fabricating the polarizer layer, the long strip film before stretching is extended in the longitudinal direction, so that in the obtained polarizer layer, it appears to be parallel to the width direction of the polarizer layer. Through the axis. The polarizer layer is preferably a linearly polarized light transmissive having a polarization direction parallel to the transmission axis, particularly preferably having a high degree of polarization. The thickness of the polarizer layer is generally from 5 μm to 80 μm, but is not limited thereto.

As the protective film layer for protecting the polarizer layer, any transparent film is used. Among them, a film of a resin excellent in transparency, mechanical strength, thermal stability, moisture shielding property, and the like is preferable. Examples of such a resin include an acetic acid resin such as cellulose triacetate, a polyester resin, a polyether oxime resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, and a cycloolefin resin. Methyl) acrylic resin, etc. Among them, in view of the fact that the birefringence is small, an acetate resin, a cycloolefin resin, or a (meth)acrylic resin is preferable, and transparency, low hygroscopicity, dimensional stability, and lightness are preferable. In particular, a cycloolefin resin is preferred.

As the polarizing film, any one of a polarizing film cut into a sheet and a long polarizing film can be used in combination with the shape of a circularly polarizing plate.

The polarizing film is produced by, for example, bonding a polarizer layer and a protective film layer. When bonding, the bonding agent can also be used as needed. Further, in particular, when the polarizing film is formed into a strip-shaped film, the long polarizing film layer and the long protective film layer can be made parallel in the longitudinal direction thereof, and then bonded by roll-to-roll bonding. Therefore, the manufacturing efficiency can be improved. Further, in the case of producing a polarizing film cut into a sheet, it is possible to produce a polarizing film which is cut into sheets by cutting the long polarizing film into a predetermined shape.

[3. λ/2 board]

The λ/2 plate is an optical member having an in-plane retardation of usually 200 nm or more and usually 300 nm or less at a measurement wavelength of 590 nm. By having such an in-plane phase difference with the λ/2 plate, the λ/2 plate and the λ/4 plate can be combined to realize a wide-band λ/4 plate. Therefore, the circular polarizing plate of the present embodiment can exhibit the function of absorbing one of the right circularly polarized light and the left circularly polarized light and penetrating the remaining light in a wide wavelength range. Therefore, by the circular polarizing plate, it is possible to reduce the reflection of light in a wide wavelength range in both the front direction and the oblique direction. In order to particularly effectively reduce external light reflection in the oblique direction, the phase difference in the in-plane of the λ/2 plate having a wavelength of 590 nm is preferably 210 nm or more, preferably 220 nm or more, and preferably 280 nm or less. It is preferably 270 nm or less.

The angle Θh of the slow axis of the λ/2 plate and the angle Θq of the slow axis of the λ/4 plate satisfy the following formula (A1).
Θq±10°=2Θh+45° (A1)

The angles Θh and Θq of the two slow axes are particularly fine-tuned in such a manner that the front characteristics are improved. More specifically, "2Θh+45°" is usually "Θq-10°" or higher, preferably "Θq-7°" or higher, and preferably "Θq-5°" or higher, and usually "Θq+10°" or less. It is better to use "Θq+7°" or less, and it is better to use "Θq+5°" or less.

In general, a λ/4 plate having a slow axis having an angle Θ (λ/4) with respect to a certain reference direction is combined with a λ/ having a slow axis at an angle Θ (λ/2) with respect to the aforementioned reference direction. The multilayer film of 2 sheets satisfies the formula (D): "Θ(λ/4)=2Θ(λ/2)+45°", the multilayer film becomes a broadband λ/4 plate, and the broadband λ/ The four-plate has an in-plane phase difference of about 1/4 wavelength of the wavelength of the light that is transmitted through the multilayer film in a wide wavelength range (refer to Japanese Laid-Open Patent Publication No. 2007-004120). In the circularly polarizing plate according to this embodiment, the λ/2 plate and the λ/4 plate satisfy the relationship represented by the above formula (D), and the λ/2 plate and the λ/4 plate can be used. As a function of the wideband λ/4 board. Accordingly, the circular polarizing plate can reduce the reflection of external light by absorbing circularly polarized light over a wide wavelength range.

The angle Θh of the slow axis of the λ/2 plate satisfies the following formula (A2).
25°<Θh<45° (A2)

In more detail, the angle Θh of the slow axis of the λ/2 plate is usually greater than 25°, preferably greater than 26°, more preferably greater than 27°, and usually less than 45°, preferably less than 44°, It is especially good to be below 43°. By the angle Θh being in the foregoing range, the circular polarizing plate can reduce external light reflection in both the front direction and the oblique direction. In particular, the reflection suppressing effect in the oblique direction can be remarkably improved.

The NZ coefficient NZh of the λ/2 plate is preferably 1.0 ≦ NZh ≦ 1.3. More specifically, the NZ coefficient NZh of the λ/2 plate is preferably 1.0 or more, more preferably 1.3 or less, still more preferably 1.25 or less, and particularly preferably 1.2 or less. By having the NZ coefficient NZh of the aforementioned range, the circular polarizing plate can effectively reduce external light reflection in both the front direction and the oblique direction. In particular, the reflection suppressing effect in the oblique direction can be remarkably improved.

As the λ/2 plate having the above optical properties, a resin film is usually used. As such a resin, a thermoplastic resin is preferred. Further, the λ/2 plate may be a resin film having a single layer structure of only one layer, or may be a resin film having a multilayer structure of two or more layers.

Among them, in terms of ease of manufacture, the λ/2 plate is preferably a layer having a material having a positive intrinsic birefringence value. As a material having a positive intrinsic birefringence value, a resin having a positive intrinsic birefringence value is usually used. Such a resin having a positive intrinsic birefringence value includes a polymer having an intrinsic birefringence value. Examples of the polymer include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; and polyphenylene sulfide and the like. Aryl sulfide; polyvinyl alcohol; polycarbonate; polyarylate; cellulose ester polymer; polyether oxime; polyfluorene; polyaryl fluorene; polyvinyl chloride; cycloolefin polymer such as norbornene polymer; Liquid crystal polymer or the like. These polymers may be used alone or in combination of two or more kinds in any ratio. Also, the polymer may be a homopolymer or a copolymer. Among these, in terms of the phase difference display property and the low temperature elongation property, a polycarbonate polymer is preferable, and mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability, and lightness are preferable. In terms of excellent mass properties, a cycloolefin polymer is preferred.

As the polycarbonate polymer, any polymer having a structural unit containing a carbonate bond (-O-C(=O)-O-) is used. Examples of the polycarbonate polymer include bisphenol A polycarbonate, branched bisphenol A polycarbonate, and o-ortho-tetramethyl bisphenol A polycarbonate.

The cycloolefin polymer is a polymer having an alicyclic structure as a structural unit of the polymer. Examples of the cycloolefin polymer include (1) a norbornene-based polymer, (2) a monocyclic cycloolefin polymer, (3) a cyclic conjugated diene polymer, and (4) a vinyl alicyclic ring. Hydrocarbon polymer, etc. The decene-based polymer is particularly suitable because of its good formability. Examples of the norbornene-based polymer include a ring-opening polymer containing a monomer having a norbornene structure, a ring-opening copolymer containing a monomer having a norbornene structure, and another monomer capable of ring-opening copolymerization. And a hydride of the above; an addition polymer of a monomer having a norbornene structure; an addition copolymer of a monomer having a norbornene structure and another monomer copolymerizable; and the like. Among these, from the viewpoint of transparency, a ring-opening polymer hydride containing a monomer having a norbornene structure is preferred.

The above cycloolefin polymer is selected from the polymers disclosed in, for example, Japanese Patent Laid-Open Publication No. 2002-321302.

As a cycloolefin resin containing a cycloolefin polymer, since a wide variety of products are commercially available, those having desired properties among them can be appropriately selected and used. As an example of the commercial product, the product name "ZEONOR" (made by Nippon Seon Co., Ltd.), "ARTON" (made by JSR Corporation), "APEL" (made by Mitsui Chemicals, Inc.), and "TOPAS" (Polyplastics) Product group of company system).

The weight average molecular weight (Mw) of the polymer contained in the resin having a positive intrinsic birefringence value is preferably 10,000 or more, preferably 15,000 or more, more preferably 20,000 or more, and most preferably 100,000 or less, and 80,000. The following is preferred, and it is preferably 50,000 or less. When the weight average molecular weight is in such a range, the mechanical strength and the formability of the λ/2 plate can be highly balanced and suitable. Here, the weight average molecular weight is a polyisoprene or a gel permeation chromatographic method using cyclohexane as a solvent (but if toluene is used in the case where the sample is not dissolved in cyclohexane) The weight average molecular weight in terms of polystyrene.

The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the polymer contained in the resin having a positive intrinsic birefringence value is preferably 1.2 or more, preferably 1.5 or more, and more preferably 1.8 or more. Preferably, it is preferably 3.5 or less, preferably 3.0 or less, and 2.7 or less. By setting the molecular weight distribution to the lower limit or more of the above range, the productivity of the polymer can be improved, and the production cost can be suppressed. Further, by setting the amount to be lower than the upper limit, the amount of the low molecular component can be reduced, so that the relaxation at the time of high temperature exposure can be suppressed, and the stability of the λ/2 plate can be improved.

The proportion of the polymer in the resin having a positive intrinsic birefringence value is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 90% by weight to 100% by weight. By setting the ratio of the polymer to the above range, the λ/2 plate can obtain sufficient heat resistance and transparency.

The resin having a positive intrinsic birefringence value may contain a blending agent in addition to the above polymer. Examples of the blending agent include coloring agents such as pigments and dyes; plasticizers; fluorescent whitening agents; dispersing agents; heat stabilizers; light stabilizers; ultraviolet absorbers; antistatic agents; ; microparticles; surfactants, etc. These components may be used alone or in combination of two or more kinds in any ratio.

The glass transition temperature Tg _P of the resin having a positive intrinsic birefringence value is preferably 100 ° C or higher, preferably 110 ° C or higher, more preferably 120 ° C or higher, and preferably 190 ° C or lower, and 180 ° C or lower. Preferably, it is preferably 170 ° C or less. By setting the glass transition temperature Tg _P of the resin having a positive intrinsic birefringence value to be equal to or higher than the lower limit of the above range, the durability of the λ/2 plate in a high temperature environment can be improved. Further, by setting it to be equal to or lower than the upper limit value, the stretching process can be easily performed.

The absolute value of the photoelastic coefficient of the resin having a positive intrinsic birefringence value is preferably 10 × 10 ^{− 12} Pa ^{− 1} or less, preferably 7 × 10 ^{− 12} Pa ^{− 1} or less, and 4 × 10 ^{− 12} Pa ^{− 1} or less is especially preferred. Thereby, the variation of the phase difference in the in-plane of the λ/2 plate can be reduced. Here, the photoelastic coefficient C is a value expressed by C=Δn/σ when the birefringence is defined as Δn and the stress is set to σ.

The total light transmittance of the λ/2 plate is preferably 80% or more. The light transmittance was measured in accordance with JIS K0115 using a spectrophotometer (manufactured by JASCO Corporation, ultraviolet visible near-infrared spectrophotometer "V-570").

The haze of the λ/2 plate is preferably 5% or less, more preferably 3% or less, still more preferably 1% or less, and most preferably 0%. Here, the haze was measured by using the "turbidity meter, NDH-300A" manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K7361-1997, and the average value obtained therefrom was measured.

The amount of the volatile component contained in the λ/2 plate is preferably 0.1% by weight or less, more preferably 0.05% by weight or less, still more preferably 0.02% by weight or less, and is preferably zero. By reducing the amount of volatile components, the dimensional stability of the λ/2 plate can be improved, and the optical characteristics such as phase difference can be reduced over time.

Here, the volatile component is a substance having a molecular weight of 200 or less contained in a trace amount in the film, and examples thereof include a residual monomer and a solvent. The amount of the volatile component can be quantified by dissolving the film in chloroform and analyzing by gas chromatography, and is a total value of a substance having a molecular weight of 200 or less contained in the film.

The saturated water absorption of the λ/2 plate is preferably 0.03% by weight or less, more preferably 0.02% by weight or less, still more preferably 0.01% by weight or less, and is desirably zero. When the saturated water absorption of the λ/2 plate is in the above range, the temporal change in optical characteristics such as the in-plane retardation can be reduced.

Here, the saturated water absorption rate was obtained by immersing the test piece of the film in water at 23 ° C for 24 hours, and the added mass was expressed as a percentage with respect to the mass of the film sample before the immersion.

The thickness of the λ/2 plate is preferably 10 μm or more, more preferably 15 μm or more, still more preferably 30 μm or more, more preferably 100 μm or less, still more preferably 80 μm or less, and still more preferably 60 μm or less. Thereby, the mechanical strength of the λ/2 plate can be improved.

The λ/2 plate as described above can be manufactured, for example, by preparing a first pre-extension film made of a thermoplastic resin and extending the first pre-extension film to develop a desired phase difference. To give a specific example, in the case where the λ/2 plate has a layer made of a resin having a positive intrinsic birefringence value, the λ/2 plate can be prepared by having (a) prepared to have a value of intrinsic birefringence. The first step of the first pre-extension film of the resin layer is produced, and (b) the second step of obtaining the λ/2 plate by extending the prepared first pre-stretch film.

In the first step (a), a first pre-stretch film having a layer of a resin having a positive intrinsic birefringence value is prepared. The film before the first stretching can be produced by a melt molding method or a solution casting method, and a melt molding method is preferred. Further, among the melt molding methods, a extrusion molding method, an inflation molding method or a press molding method is preferred, and a extrusion molding method is particularly preferred.

Usually, the film before the first stretching can be obtained by growing a strip-shaped resin film. By preparing the first pre-stretch film as a strip-shaped resin film, it is possible to carry out a part or all of each step on the production line when the λ/2 plate is manufactured, so that it can be easily and efficiently manufactured.

After the first pre-stretch film is prepared in the first step (a), (b) a second step of extending the first pre-stretch film. In general, since the desired phase difference is exhibited in the layer formed of the resin having a positive intrinsic birefringence value by the stretching in the second step (b), the λ/2 plate can be obtained as a stretched film.

The stretching method in the second step (b) is arbitrarily employed in accordance with the optical characteristics to be expressed by stretching. Accordingly, in the second step (b), uniaxial stretching extending in one direction can be performed, and biaxial stretching extending in both directions can be performed. In general, by performing uniaxial stretching in the second step (b), the uniaxiality of the layer formed by the resin having a positive intrinsic birefringence value can be improved, so that the NZ coefficient NZh of the λ/2 plate can be made close to 1.0. On the other hand, by performing biaxial stretching in the second step (b), the uniaxiality of the layer formed by the resin having a positive intrinsic birefringence value can be reduced, so that the NZ coefficient NZh of the λ/2 plate can be made. Stay away from 1.0.

(b) The extension in the second step preferably comprises an extension in the oblique direction. A λ/2 plate as an obliquely extending film can be obtained by a manufacturing method including extending in an oblique direction. The obliquely stretched film means a film produced by a manufacturing method including extending in an oblique direction. Typically, the obliquely extending film will exhibit a slow axis that is neither parallel nor perpendicular to its width direction. Accordingly, the λ/2 plate as the obliquely stretched film can be easily formed by the slow axis having the aforementioned angle Θh with respect to the width direction. Therefore, the λ/2 plate as the obliquely extending film can be easily bonded to the polarizing film having the transmission axis in the width direction and the λ/4 plate through the roller-to-roller to easily manufacture the circularly polarizing plate.

(b) The stretching ratio in the second step is preferably 1.1 times or more, more preferably 1.3 times or more, more preferably 1.5 times or more, more preferably 4 times or less, and preferably 3 times or less. It is especially preferable to be 2.5 times or less. In the case of extending in two or more directions, it is desirable that the product of the stretching ratio in each direction falls within the above range. By bundling the stretching ratio in the second step (b) to the aforementioned range, it is easy to obtain a λ/2 plate having desired optical characteristics.

(b) The elongation temperature in the second step is preferably Tg _P °C or more, preferably "Tg _P + 2 ° C" or more, more preferably "Tg _P + 5 ° C" or more, and "Tg _P + 40 ° C". The following is preferable, and it is preferable to use "Tg _P + 35 ° C" or less, and preferably "Tg _P + 30 ° C" or less. Here, Tg _P represents a glass transition temperature of a resin having an intrinsic birefringence value. By setting the stretching temperature in the second step (b) to the above range, the molecules contained in the film before the first stretching can be surely oriented, so that the λ/2 plate having desired optical characteristics can be easily obtained.

Further, in the method for producing a λ/2 plate as described above, any step other than the above steps may be further performed.

For example, in the case of manufacturing a long λ/2 plate using the long strip-shaped first pre-stretch film, a trimming process of cutting the λ/2 plate into a desired shape may be performed. By performing the trimming process, a λ/2 plate having a desired shape and cut into sheets can be obtained.

Further, for example, a step of providing a protective layer on the λ/2 plate may be performed.

[4. λ/4 board]

The λ/4 plate is an optical member having an in-plane retardation of usually 75 nm or more and usually 154 nm or less at a measurement wavelength of 590 nm. By having such an in-plane phase difference with the λ/4 plate, the λ/2 plate and the λ/4 plate can be combined to realize a wide-band λ/4 plate. Therefore, the circular polarizing plate of the present embodiment can exhibit the function of absorbing one of the right circularly polarized light and the left circularly polarized light and penetrating the remaining light in a wide wavelength range. Therefore, by the circular polarizing plate, it is possible to reduce the reflection of light in a wide wavelength range in both the front direction and the oblique direction. In order to particularly effectively reduce the external light reflection in the oblique direction, the phase difference in the in-plane of the λ/4 plate having a wavelength of 590 nm is preferably 80 nm or more, more preferably 90 nm or more, and preferably 138 nm or less. It is preferably 128 nm or less.

The angle Θq of the slow axis of the λ/4 plate satisfies the following formula (A3).
95°<Θq<135° (A3)

In more detail, the angle Θq of the slow axis of the λ/4 plate is usually greater than 95°, preferably greater than 96°, more preferably greater than 97°, and usually less than 135°, preferably less than 134°. It is especially good to reach 133°. By the angle Θq being in the foregoing range, the circular polarizing plate can reduce external light reflection in both the front direction and the oblique direction. In particular, the reflection suppressing effect in the oblique direction can be remarkably improved.

The NZ coefficient NZq of the λ/4 plate usually satisfies NZq ≦ 0.0 to satisfy -1.5 ≦ NZq ≦ 0.0. More specifically, the NZ coefficient NZq of the λ/4 plate is preferably -1.5 or more, more preferably -1.2 or more, more preferably -1.0 or more, and usually 0.0 or less, preferably -0.1 or less. It is especially preferable to be below -0.15. By having the NZ coefficient NZq of the aforementioned range for the λ/4 plate, the circular polarizing plate can reduce external light reflection in both the front direction and the oblique direction. In particular, the reflection suppressing effect in the oblique direction can be remarkably improved.

The λ/4 plate has a wavelength dispersion that is different from the wavelength dispersion of the λ/2 plate. Here, the degree of wavelength dispersion of a film is represented by a value obtained by dividing the phase difference in the in-plane wavelength of 400 nm by the phase difference in the in-plane wavelength of 550 nm. Accordingly, the phase difference in the in-plane of the λ/2 plate having a wavelength of 400 nm is set to Reh (400), and the phase difference in the in-plane of the λ/2 plate having a wavelength of 550 nm is set to Reh (550) at a wavelength of 400 nm. The in-plane phase difference of the λ/4 plate is set to Req (400), and the wavelength dispersion of the λ/2 plate is determined when the phase difference in the in-plane of the λ/4 plate having a wavelength of 550 nm is set to Req (550). The degree is expressed by "Reh (400) / Reh (550)", and the degree of wavelength dispersion of the λ/4 plate is expressed by "Req (400) / Req (550)". The external light reflection can be reduced in the front direction of the circularly polarizing plate by combining the λ/2 plate and the λ/4 plate having different degrees of wavelength dispersion with the respective slow axes having the specified angles Θh and Θq.

Further, in the in-plane phase difference Reh (400) and Reh (550) of the λ/2 plate having wavelengths of 400 nm and 550 nm, and the in-plane retardation Req (400) and Req (in the in-plane of the λ/4 plate having wavelengths of 400 nm and 550 nm) 550), it is preferable to satisfy the following formula (B). Thereby, external light reflection can be effectively reduced in the front direction of the circular polarizing plate.
Reh(400)/Reh(550)<Req(400)/Req(550) (B)

Furthermore, the phase differences Reh (400) and Reh (550) in the in-plane of the λ/2 plate at wavelengths of 400 nm and 550 nm, and the phase difference Req (400) and Req in the in-plane of the λ/4 plate at wavelengths of 400 nm and 550 nm. It is preferable to satisfy (550) to satisfy the following formula (C).
0.04<Req(400)/Req(550)-Reh(400)/Reh(550)<1.0 (C)

More specifically, the difference between the degree of wavelength dispersion of the λ/2 plate and the degree of wavelength dispersion of the λ/4 plate is "Req(400)/Req(550)-Reh(400)/Reh(550)", which is larger than Preferably, 0.04 is more preferably greater than 0.1, more preferably greater than 0.15, and most preferably less than 1.0, preferably less than 0.95, more preferably less than 0.9. Thereby, external light reflection can be particularly effectively reduced in the front direction of the circular polarizing plate.

As the λ/4 plate having the above optical characteristics, a resin film is usually used. As such a resin, a thermoplastic resin is preferred. Further, the λ/4 plate may be a resin film having a single layer structure of only one layer, or may be a resin film having a multilayer structure of two or more layers.

Among them, in the case where the production can be easily carried out, the λ/4 plate is preferably a layer having a material having a negative intrinsic birefringence value. As a material having a negative intrinsic birefringence value, a resin having a negative intrinsic birefringence value is usually used. Such a resin having a negative intrinsic birefringence value includes a polymer having a negative intrinsic birefringence value. Examples of the polymer include a homopolymer containing a styrene or a styrene derivative, and a polystyrene polymer of a copolymer of styrene or a styrene derivative and any monomer; An acrylonitrile polymer; a polymethyl methacrylate polymer; or a multicomponent copolymer such as these; Further, examples of the above-mentioned arbitrary monomer to be copolymerized with styrene or a styrene derivative include acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene. Further, these polymers may be used singly or in combination of two or more kinds in any ratio.

Among these, in view of the fact that the phase difference of the phase difference is high, it is preferable that the polystyrene polymer is used, and further, the heat resistance is high, and styrene or a styrene derivative is used. Copolymers of maleic anhydride are particularly preferred. In this case, the amount of the maleic anhydride unit is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, and particularly preferably 15 parts by weight or more based on 100 parts by weight of the polystyrene polymer. Preferably, it is preferably 30 parts by weight or less, more preferably 28 parts by weight or less, and particularly preferably 26 parts by weight or less. The above-mentioned term "maleic anhydride unit" means a structural unit having a structure formed by polymerizing maleic anhydride.

The proportion of the polymer in the resin having a negative intrinsic birefringence value is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 90% by weight to 100% by weight. By setting the ratio of the polymer to the aforementioned range, the λ/4 plate exhibits an appropriate optical characteristic.

The resin having a negative intrinsic birefringence value may contain a blending agent in addition to the above polymer. As an example of the blending agent, the same example as the blending agent contained in the resin having a positive intrinsic birefringence value may be mentioned. The admixture may be used singly or in combination of two or more kinds in any ratio.

The glass transition temperature Tg _N of the resin having a negative intrinsic birefringence value is preferably 80° C. or higher, preferably 90° C. or higher, more preferably 100° C. or higher, and more preferably 110° C. or higher, and 120° C. The above is especially good. The glass transition temperature Tg _N of the resin having a negative intrinsic birefringence value is so high that the orientation relaxation of the resin having a negative intrinsic birefringence value can be reduced. Further, the upper limit of the glass transition temperature Tg _N of the resin having a negative intrinsic birefringence value is not particularly limited, but is usually 200 ° C or lower.

Among the resins having a negative intrinsic birefringence value, the mechanical strength is low. For example, a resin containing a polystyrene polymer tends to have low mechanical strength. Therefore, the λ/4 plate including the layer of the resin having a negative intrinsic birefringence value is combined with the protective layer having a layer which can protect the resin having a negative intrinsic birefringence value from the intrinsic birefringence value. A layer made of a negative resin is preferred.

The protective layer may be any layer insofar as it does not significantly impair the effects of the present invention. For example, as the protective layer, a layer made of a resin having a positive intrinsic birefringence value is used. At this time, from the viewpoint of easily adjusting the phase difference in the λ/4 plate, it is preferable that the in-plane phase difference and the thickness direction phase difference of the protective layer are close to zero. As a method of bringing the in-plane retardation and the thickness direction retardation of the protective layer close to zero, for example, the glass transition temperature of the resin in which the resin contained in the protective layer is lower than the intrinsic birefringence value is negative. Tg _N method.

Further, the protective layer may be provided only on one side of the layer formed of the resin having a negative intrinsic birefringence value, or may be provided on both sides.

The total light transmittance of the λ/4 plate is preferably 80% or more.

The haze of the λ/4 plate is preferably 5% or less, more preferably 3% or less, still more preferably 1% or less, and most preferably 0%.

The amount of the volatile component contained in the λ/4 plate is preferably 0.1% by weight or less, more preferably 0.05% by weight or less, still more preferably 0.02% by weight or less, and is preferably zero. By reducing the amount of volatile components, the dimensional stability of the λ/4 plate can be improved, and the optical characteristics such as phase difference can be reduced over time.

The saturated water absorption of the λ/4 plate is preferably 0.03% by weight or less, more preferably 0.02% by weight or less, still more preferably 0.01% by weight or less, and is preferably zero. When the saturated water absorption of the λ/4 plate is in the above range, the temporal change in optical characteristics such as the in-plane retardation can be reduced.

The thickness of the λ/4 plate is preferably 3 μm or more, more preferably 5 μm or more, more preferably 80 μm or less, still more preferably 75 μm or less, and particularly preferably 70 μm or less. By setting the thickness of the λ/4 plate to be equal to or higher than the lower limit of the above range, the desired phase difference can be easily exhibited. Further, by setting it to be equal to or lower than the upper limit, the thickness of the circularly polarizing plate can be reduced.

The λ/4 plate as described above can be manufactured, for example, by preparing a second pre-extension film made of a thermoplastic resin and extending the second pre-extension film to develop a desired phase difference. To cite a specific example, in the case where the λ/4 plate has a layer made of a resin having a negative intrinsic birefringence value, the λ/4 plate can be prepared to have a negative intrinsic birefringence value by including (c) The third step of the second pre-extension film of the resin layer is produced by the third step of (d) extending the prepared second pre-extension film to obtain the fourth step of the λ/4 plate.

In the third step (c), a second pre-stretch film having a layer having a resin having a negative intrinsic birefringence value is prepared. The film before the second stretching can be produced by a melt molding method or a solution casting method, and a melt molding method is preferred. Further, among the melt molding methods, a extrusion molding method, an inflation molding method or a press molding method is preferred, and a extrusion molding method is particularly preferred.

Further, in the case of producing a second pre-extension film as a multilayer film, for example, in the case of a multilayer film having a layer of a resin having a negative intrinsic birefringence value and a protective layer, a co-extruded T-die method is used. a co-extrusion molding method such as a co-extrusion aeration method or a co-extrusion lamination method; a film lamination molding method such as a dry lamination method; and a coating forming method such as a resin solution for coating a layer other than a layer . Among them, the co-extrusion molding method is preferable in that the production efficiency is excellent and the volatile components such as a solvent are not left in the λ/4 plate. Among the co-extrusion forming methods, a co-extruded T-shaped mold method is preferred. Further, the co-extrusion T-die method may be a feed block method or a multi-manifold method, but it is preferable to use a multi-manifold method in order to reduce the variation in the thickness of the layer.

Usually, the film before the second stretching can be obtained by growing a strip-shaped resin film. By preparing the second pre-stretch film as a long strip-shaped resin film, a part or all of each step can be performed on the production line when the λ/4 plate is manufactured, so that it can be easily and efficiently manufactured.

After the second pre-stretch film is prepared in the third step (c), the fourth step of extending the second pre-stretch film is performed. In general, since the desired phase difference is exhibited in the layer formed of the resin having a negative intrinsic birefringence value by the stretching in the fourth step (d), the λ/4 plate can be obtained as a stretched film.

The stretching method in the fourth step (d) is arbitrarily employed in accordance with the optical characteristics to be expressed by stretching. Accordingly, in the fourth step (d), the uniaxial stretching extending in one direction can be performed, and the biaxial stretching extending in the two directions can be performed. In general, by performing uniaxial stretching in the fourth step (d), the uniaxiality of the layer formed by the resin having a negative intrinsic birefringence value can be improved, so that the NZ coefficient NZq of the λ/4 plate can be made close to 0.0. On the other hand, by performing biaxial stretching in the fourth step (d), the uniaxiality of the layer formed by the resin having a negative intrinsic birefringence value can be reduced, so that the NZ coefficient NZq of the λ/4 plate can be made. Stay away from 0.0.

(d) The extension in the fourth step preferably includes an extension in the oblique direction. A λ/4 plate as an obliquely extending film can be obtained by a manufacturing method including extending in an oblique direction. Typically in the obliquely extending film, a slow axis that is neither parallel nor perpendicular to its width direction will appear. Accordingly, the λ/4 plate as the obliquely extending film can be easily formed by the slow axis having the aforementioned angle Θq with respect to the width direction. Therefore, the λ/4 plate which is an obliquely stretched film can be easily bonded to a polarizing film having a transmission axis in the width direction and a λ/2 plate through the roll-to-roller to easily form a circularly polarizing plate.

(d) The stretching ratio in the fourth step is preferably 1.1 times or more, more preferably 1.15 times or more, more preferably 1.2 times or more, more preferably 4 times or less, and preferably 3 times or less. It is especially preferable to be 2 times or less. In the case of extending in two or more directions, it is desirable that the product of the stretching ratio in each direction falls within the above range. By bundling the stretching ratio in the fourth step (d) to the aforementioned range, it is easy to obtain a λ/4 plate having desired optical characteristics.

(d) The elongation temperature in the fourth step is preferably Tg _N °C or more, preferably "Tg _N + 2 ° C" or more, more preferably "Tg _N + 5 ° C" or more, and "Tg _N + 40 ° C". The following is preferable, and it is preferable to use "Tg _N + 35 ° C" or less, and preferably "Tg _N + 30 ° C" or less. Here, Tg _N represents a glass transition temperature of a resin having a negative intrinsic birefringence value. By setting the stretching temperature in the fourth step (d) to the above range, the molecules contained in the film before the second stretching can be surely oriented, so that the λ/4 plate having desired optical characteristics can be easily obtained.

Further, in the method for producing a λ/4 plate as described above, any step other than the above steps may be further performed.

For example, the same process as any of the processes which have been exemplified in the manufacturing method of the λ/2 plate can be performed.

[5. Any layer]

In the circular polarizing plate according to the present embodiment, any layer other than the polarizing film, the λ/2 plate, and the λ/4 plate may be provided in a range that does not significantly impair the effects of the present invention.

For example, a circular polarizer has a protective film layer for preventing scratches. Further, for example, the circularly polarizing plate is provided with a bonding layer or an adhesive layer for bonding the polarizing film and the λ/2 plate, and for bonding the λ/2 plate and the λ/4 plate.

[6. Physical properties of circular polarizers]

In the case of the circular polarizing plate according to this embodiment, when it is disposed on the surface of the reflected light, the external light reflection can be reduced in both the front direction and the oblique direction. In particular, the circular polarizing plate of the present embodiment can effectively reduce external light reflection in the oblique direction.

Since the external light reflection can be suppressed as described above, the unintended coloration of the display surface of the image display device can be suppressed by the circular polarizing plate. Assuming that the external light is reflected as large on the display surface, there is a possibility that the display surface is colored into the color of the reflected light. On the other hand, if the reflection of external light can be suppressed, the reflected light can be reduced, so that the coloring can be suppressed.

Further, the circular polarizing plate according to the present embodiment can function as a wide-band λ/4 plate because of the combination of the λ/2 plate and the λ/4 plate, so that it can be suppressed in a wide wavelength range in the visible light region. External light reflection. Therefore, coloring of the display surface can be effectively suppressed by suppressing reflection in such a wide wavelength range.

The degree of coloring described above is represented by the L*a*b* color space, and the color of the black surface without reflection can be observed by "observing the color measured by the display surface provided with the circular polarizer from the oblique direction" The color difference ΔE*ab of the coloring was evaluated. The coloring described above can be obtained by measuring the spectrum of the light reflected on the display surface, and multiplying the spectrum by the spectral sensitivity (color matching function) corresponding to the human eye to obtain the tristimulus values X, Y. And Z, calculate the coordinates a*, b*, and L* in the L*a*b* color space. Further, the color difference ΔE*ab may be a color space coordinate (a0*, b0*, L0*) in the case where the external light is not irradiated to the display surface, and a color space coordinate (a1* in the case where the external light is irradiated). , b1*, L1*), which is obtained by the following formula (X).

"Number 1"

In general, the color of the display surface caused by reflected light may vary depending on the azimuth of the viewing direction. Therefore, in the case where the display surface is viewed from the oblique direction, the measured color space coordinates may vary depending on the azimuth angle of the observation direction, and thus the color difference ΔE*ab may also be different. Then, in the case of evaluating the degree of coloration when the display surface is observed from the oblique direction, it is preferable to evaluate the coloring by the average value of the color difference ΔE*ab obtained by observation from a plurality of azimuth directions. Specifically, in the range in which the azimuth angle φ (see FIG. 2) is 0° or more and less than 360° in the azimuth direction, the measurement of the color difference ΔE*ab is performed by the measurement. The average value of the color difference ΔE*ab was evaluated for the degree of coloration. The smaller the average value, the smaller the color of the display surface when viewed from the oblique direction.

[7. Method of manufacturing circular polarizing plate]

A circularly polarizing plate according to an embodiment of the present invention can be manufactured by laminating the polarizing film, the λ/2 plate, and the λ/4 plate. At this time, the polarizing film, the λ/2 plate, and the λ/4 plate adjust the optical axis such that the slow axis of the λ/2 plate and the slow axis of the λ/4 plate are at a desired angle with respect to the transmission axis of the polarizing film. The direction is then fitted. Specifically, the circular polarizing plate of the present embodiment can be attached to the polarizing film and the λ/2 plate by including the slow axis of the λ/2 plate at a specified angle Θh with respect to the transmission axis of the polarizing film. The process is a method of manufacturing a step of laminating a λ/2 plate and a λ/4 plate so that the slow axis of the λ/4 plate is at a predetermined angle Θq with respect to the transmission axis of the polarizing film.

In the above production method, the step of laminating the multilayer film and the λ/2 plate and the step of bonding the λ/2 plate and the λ/4 plate may be performed first or both.

Also, adhesives or cements may be used as needed during the bonding process.

The polarizing film, the λ/2 plate, and the λ/4 plate can be bonded together in a state of an elongated film from the viewpoint of achieving roll-to-roll bonding and efficient production. Further, from the viewpoint of facilitating the adjustment of the direction of the optical axis, it is also possible to cut a polarizing film that is cut into a sheet, a λ/2 plate, and a strip-shaped polarizing film, a λ/2 plate, and a λ/4 plate. The λ/4 plate was bonded to the cut polarized film, λ/2 plate, and λ/4 plate, to produce a circular polarizing plate.

[8. Broadband λ/4 board]

The strip-shaped wide-band λ/4 plate according to one embodiment of the present invention has the same shape as the polarizing film in a long circular polarizing plate having a polarizing film having a transmission axis in the width direction. Structure. Therefore, this wide band λ/4 plate is provided with the above λ/2 plate and λ/4 plate. Moreover, the λ/2 plate has a slow axis in a direction at a specified angle Θh with respect to the width direction of the wide band λ/4 plate, and further, the width of the λ/4 plate in relation to the wide band λ/4 plate The direction has a slow axis in the direction of the specified angle Θq.

According to this wide band λ/4 board, at least the following advantages can be obtained.
The wide-band λ/4 plate can impart an in-plane phase difference of about 1/4 wavelength of the wavelength of the light to the light passing through the wide-band λ/4 plate in the front direction in a wide wavelength range.
The wide-band λ/4 plate can impart an in-plane phase difference of about 1/4 wavelength of the wavelength of the light to the light passing through the wide-band λ/4 plate in an oblique direction over a wide wavelength range.
Therefore, the wide-band λ/4 plate can be realized by combining with a polarizing film, and the circular polarizing plate can reduce reflection of light in a wide wavelength range in both the front direction and the oblique direction.

[9. Organic electroluminescent display device]

An organic EL display device according to an embodiment of the present invention includes the above-described circular polarizing plate or a wide-band λ/4 film sheet obtained by cutting out a long strip-shaped wide-band λ/4 plate.

When the organic EL display device includes a circularly polarizing plate, the organic EL display device usually has a circularly polarizing plate on the display surface. Thereby, the circularly polarizing plate can function as an antireflection film of an organic EL display device. In other words, by providing the circular polarizing plate on the display surface of the organic EL display device so that the surface on the side of the polarizing film faces the viewing side, it is possible to suppress light incident from the outside of the device from being reflected inside the device and being emitted to the outside of the device. As a result, glare on the display surface of the display device can be suppressed. Specifically, only a part of the linearly polarized light that has entered from the outside of the device passes through the polarizing film, and then becomes circularly polarized by passing through the λ/2 plate and the λ/4 plate. The circularly polarized light is reflected by the constituting elements (reflecting electrodes or the like in the organic EL element) reflected by the display device, and passes through the λ/4 plate and the λ/2 plate again to become a polarization direction of the linearly polarized light orthogonal to the incident. In the direction of the line, there is a linearly polarized light having a polarization direction, and it does not pass through the polarizing film. Thereby, the anti-reflection function can be achieved.

Further, when the organic EL display device includes a wide-band λ/4 film sheet, the organic EL display device is provided with a wide-band λ/4 film sheet at an arbitrary position.

[10. Liquid crystal display device]

A liquid crystal display device according to an embodiment of the present invention includes the circular polarizing plate or a wide-band λ/4 film sheet obtained by cutting out a long strip-shaped wide band λ/4 plate.

When the liquid crystal display device includes a circularly polarizing plate, the liquid crystal display device usually has a circularly polarizing plate on the display surface. Thereby, the circularly polarizing plate can function as an antireflection film of a liquid crystal display device. In other words, by providing the circular polarizing plate on the display surface of the liquid crystal display device so that the surface on the side of the polarizing film faces the viewing side, it is possible to prevent light incident from the outside of the device from being reflected inside the device and being emitted to the outside of the device. It can suppress glare on the display surface of the display device.

In the case where the liquid crystal display device includes a wide-band λ/4 film sheet, the liquid crystal display device usually has a wide-band λ/4 film sheet on the viewing side of the liquid crystal panel. Thereby, the wide band λ/4 plate can function as a film for improving the visibility of the display surface by the observer wearing the polarized sunglasses. That is, a circular polarizing plate is provided at a position closer to the display surface than the viewing side polarizing member of the liquid crystal panel of the liquid crystal display device. At this time, the slow axis of the λ/2 plate of the wide-band λ/4 film sheet is set at an angle Θh with respect to the transmission axis of the viewing-side polarizer. Thereby, the linearly polarized light that has passed through the viewing-side polarizer is converted into a circularly polarized light through the wide-band λ/4 film sheet, so that it is possible to stably view the light emitted from the display surface by the polarized sunglasses.

"Embodiment"

The following examples are presented to illustrate the invention. However, the present invention is not limited to the embodiments shown below, and may be arbitrarily changed without departing from the scope of the invention and the scope of the invention.

In the following description, "%" and "parts" indicating the quantity are based on weight unless otherwise noted. Further, the operations described below are carried out under normal temperature and normal pressure unless otherwise noted.

[Evaluation method]

(Measurement method of phase difference and NZ coefficient)

Using a phase difference meter ("AxoScan" manufactured by Axometrics Co., Ltd.), a phase difference between the in-plane phase and the thickness direction was measured at a plurality of points spaced 50 mm apart in the width direction of the film. The average value of the measured values at these points is calculated, and the average value is determined as the in-plane phase difference and the thickness direction phase difference of the film. At this time, the measurement system was performed at a wavelength of 590 nm. Then, the NZ coefficient is calculated from the ratio of the obtained in-plane phase difference and the thickness direction phase difference.

(measurement method of the degree of wavelength dispersion)

The in-plane phase difference of the film at a wavelength of 400 nm and 550 nm was measured by the aforementioned method of measuring the phase difference. Then, the phase difference in the in-plane wavelength of 400 nm was divided by the in-plane retardation at a wavelength of 550 nm to determine the degree of wavelength dispersion of the film.

(by the method of calculating the color difference of the simulation)

The "LCD Master" manufactured by Shintech Co., Ltd. was used as a software for simulation, and the circularly polarizing plates produced in the respective examples and comparative examples were modeled, and the following calculations were performed.

In the simulation model, a configuration is adopted in which a reflecting plate having a planar reflecting surface is provided with a circular polarizing plate having a λ/4 plate, a λ/2 plate, and a polarizing film in this order from the side of the reflecting surface. The users in the respective examples and comparative examples were set as the λ/4 plate and the λ/2 plate. Further, as the polarizing film, a polarizing plate having a degree of polarization of 99.99% generally used was set. Furthermore, an aluminum mirror is set as the mirror.

2 is a schematic perspective view showing the state of an evaluation model set when the calculation of the color space coordinates is performed in the simulation of the embodiment and the comparative example.

As shown in Fig. 2, when illuminated by a D65 light source (not shown), the color space coordinates observed on the reflecting surface 10 of the mirror provided with the circular polarizing plate are calculated. Further, the color space coordinates when not illuminated by the light source are set to a0*=0, b0*=0, L0*=0. Then, from (i) the color space coordinates when illuminated by the light source and (ii) the color space coordinates when not illuminated by the light source, the color difference ΔE*ab is obtained using the above formula (X).

The color difference ΔE*ab is calculated in the observation direction 20 with respect to the polar angle ρ of the reflecting surface 10 of 0°, and the color difference ΔE*ab in the front direction is obtained. The polar angle ρ represents an angle with respect to the normal direction 11 of the reflecting surface 10.

Further, the above-described color difference ΔE*ab is calculated in the observation direction 20 with respect to the polar angle ρ of the reflecting surface 10 of 60°. The calculation of the polar angle ρ=60° causes the observation direction 20 to be moved a plurality of times in the azimuthal direction in the azimuth angle φ of 0° or more and less than 360° in the range of 5°. The azimuth angle φ represents an angle formed by a direction parallel to the reflecting surface 10 with respect to a certain reference direction 12 parallel to the reflecting surface 10. Then, the average of the color differences ΔE*ab calculated in the plurality of observation directions 20 is calculated, and the color difference ΔE*ab in the oblique direction of the polar angle ρ=60° is obtained.

(Evaluation method of circular polarizer by visual observation in the front direction)

Prepare a mirror with a flat reflective surface. The λ/4 plate of the circular polarizer is attached to the reflecting surface of this mirror.

The circular polarizing plate on the mirror was visually observed in a state where the circular polarizing plate was irradiated with sunlight on a clear day. The observation was performed in the front direction of the polar angle of the circular polarizing plate of 0° and the azimuth angle of 0°. As a result of the observation, it was judged as "poor" when the chromatic color was observed, and it was judged as "good" when the chromatic color was not observed.

(Evaluation method of circular polarizer by visual observation in the oblique direction)

Prepare a mirror with a flat reflective surface. The λ/4 plate of the circular polarizer is attached to the reflecting surface of this mirror.

The circular polarizing plate on the mirror was visually observed in a state where the circular polarizing plate was irradiated with sunlight on a clear day. The observation is performed in a direction in which the polar angle of the circular polarizing plate is 60° and the azimuth angle is 0° to 360°. As a result of the observation, the advantages and disadvantages of the reflection brightness and the coloring were comprehensively determined, and the examples and comparative examples were ranked. Then, the ranked examples and comparative examples are given a score corresponding to their ranking (12 points for the first place, 11 points for the second place, and 1 point for the last one).

The above observation was performed by a plurality of people, and the total score of the given score was obtained for each of the examples and the comparative examples. The examples and comparative examples are arranged in the order of the foregoing total scores, and are evaluated in the total score range from the leading rank group in the order of A, B, C, D, and E.

[Examples 1, 3 and 6]

(Manufacture of polarizing film)

A long stretch front film made of iodine dyed or polyvinyl alcohol resin was prepared. The film before stretching was extended in the longitudinal direction at an angle of 90 with respect to the width direction of the film before stretching to obtain a long strip-shaped polarizing film. The polarizing film has an absorption axis along the longitudinal direction of the polarizing film, and has a transmission axis along the width direction of the polarizing film.

(Manufacture of λ/2 board)

A long-chain cycloolefin resin film ("ZEONOR film" manufactured by Nippon Seon Co., Ltd., glass transition temperature: 126 ° C; thickness: 45 μm) obtained by forming a cycloolefin polymer into a film by melt extrusion, as a pre-extension film.

The cyclic olefin resin film was subjected to a stretching treatment in the width direction of the cycloolefin resin film to obtain a long λ/2 plate. The stretching conditions for the stretching treatment in the width direction are set to a λ/2 plate having physical properties as shown in the following Table 1 in the range of the stretching temperature of 120 to 150 ° C and the stretching ratio of 2.0 to 5.0.

The obtained λ/2 plate was evaluated by the aforementioned method.

(Manufacture of λ/4 board)

As a material having a negative intrinsic birefringence value, a styrene-maleic acid copolymer resin (Daylark D332, manufactured by NOVA CHEMICAL Co., Ltd., glass transition temperature: 130 ° C, oligo component content: 3% by weight) was prepared.

"SUMIPEX HT-55X" (glass transition temperature: 105 ° C) manufactured by Sumitomo Chemical Co., Ltd. was prepared as the acrylic resin for the protective layer.

As a bonding agent, a modified ethylene-vinyl acetate copolymer ("MODIC AP A543" manufactured by Mitsubishi Chemical Corporation, Fika softening point of 80 ° C) was prepared.

The prepared styrene-maleic acid copolymer resin, acrylic resin and bonding agent are coextruded to obtain a layer of an acrylic resin, a layer of a bonding agent, and a styrene-maleic acid copolymer resin. The layer of the layer, the layer of the bonding agent, and the strip-shaped pre-stretch film of the layer of the acrylic resin. The thickness of the layer of the styrene-maleic acid copolymer resin of the pre-extension film was 40 μm.

Subsequently, the film before stretching is subjected to a stretching process in the width direction of the film before stretching to obtain a long strip λ/4 plate. The elongation conditions for the stretching treatment in the width direction are set to a λ/4 plate having physical properties as shown in the following Table 1 in the range of the stretching temperature of 110 to 140 ° C and the stretching ratio of 1.5 to 4.0. In the obtained λ/4 plate, no phase difference appeared in the layer of the acrylic resin and the layer of the bonding agent.

The obtained λ/4 plate was evaluated by the aforementioned method.

(Manufacture of circular polarizer)

Long strip-shaped polarizing film, long λ/2 plate and long λ/4 plate were cut out respectively, and a polarizing film cut into pieces, a λ/2 plate cut into pieces, and a λ/4 plate cut into pieces were obtained. . The polarizing film cut into a sheet, the λ/2 plate cut into pieces, and the λ/4 plate cut into sheets were bonded together using a binder ("CS9621" manufactured by Nitto Denko Corporation) to obtain a polarizing film and adhesion in sequence. Layer, λ/2 plate, adhesive layer and λ/4 plate circular polarizer. The above-mentioned bonding is viewed from the side of the polarizing film, "with respect to the transmission axis of the polarizing film, the angle Θh of the slow axis of the λ/2 plate in the clockwise direction" and "the axis of penetration with respect to the polarizing film, λ" The angle Θq" of the slow axis of the /4 plate in the clockwise direction is the size shown in Table 1.

The obtained circular polarizing plate was evaluated by the aforementioned method.

[Examples 2, 4 to 5, and 7 to 8, and Comparative Examples 1 to 2]

The manufacture and evaluation of the circularly polarizing plate were carried out by the same operation as in the above-described first embodiment except that the first and second points described below were changed.

First: The extension operation of the film before stretching in the process of manufacturing the λ/4 plate is changed as follows. That is, the film before stretching is subjected to an extension process in the longitudinal direction of the film before stretching and an extension process in the width direction. The elongation conditions for the elongation treatment in the longitudinal direction are set to a λ/4 plate having physical properties as shown in the following Table 1 in the range of the elongation temperature of 110 to 140 ° C and the stretching ratio of 1.1 to 2.0. Further, in the extension condition of the stretching treatment in the width direction, a λ/4 plate which can obtain physical properties as shown in the following Table 1 is set in the range of the stretching temperature of 110 to 140 ° C and the stretching ratio of 1.5 to 4.0.

Second: changing the bonding angle of the polarizing film cut into sheets, the λ/2 plate cut into sheets, and the λ/4 sheets cut into sheets to obtain a circular polarizing plate having the structure shown in Table 1 .

[Comparative Examples 3 and 4]

(Manufacture of λ/4 board)

The long-formed cyclic olefin resin film ("ZEONOR film" manufactured by Nippon Seon Co., Ltd., glass transition temperature: 126 ° C; thickness: 45 μm), which is the same as the manufacturer of the λ/2 plate, was used as the pre-extension. film.

The cyclic olefin resin film was subjected to a stretching treatment in the width direction of the cycloolefin resin film to obtain a long λ/4 plate. The elongation conditions for the stretching treatment in the width direction are set to a λ/4 plate having physical properties as shown in the following Table 1 in the range of the stretching temperature of 120 to 150 ° C and the stretching ratio of 1.5 to 2.5 times.

The obtained λ/4 plate was evaluated by the aforementioned method.

(Manufacture of circular polarizer)

The above λ/4 plate formed of a cycloolefin resin was used instead of the λ/4 plate manufactured in Example 1. Further, as shown in Table 1, the polarizing film cut into sheets, the λ/2 plate cut into sheets, and the bonding angle of the λ/4 sheets cut into sheets were changed. Except for the above, the manufacture and evaluation of the circularly polarizing plate were carried out by the same operation as in the first embodiment.

[result]

The results of the examples and comparative examples are disclosed in Table 1 below. In Table 1, the meaning of the abbreviation is as follows.
Reh: The phase difference in the in-plane of the λ/2 plate at a wavelength of 590 nm.
Rthh: The phase difference in the thickness direction of the λ/2 plate at a wavelength of 590 nm.
Θh: viewed from the side of the polarizing film, with respect to the transmission axis of the polarizing film, the slow axis of the λ/2 plate is at an angle of clockwise.
NZh: NZ coefficient of λ/2 board.
Req: The phase difference in the in-plane of the λ/4 plate at a wavelength of 590 nm.
Rthq: The phase difference in the thickness direction of the λ/4 plate at a wavelength of 590 nm.
Θq: viewed from the side of the polarizing film, the angle of the slow axis of the λ/4 plate is clockwise with respect to the transmission axis of the polarizing film.
NZq: NZ coefficient of λ/4 board.
Difference in wavelength dispersion: the difference between the degree of wavelength dispersion of the λ/2 plate and the degree of wavelength dispersion of the λ/4 plate.

"Table 1"
[Table 1. Results of Examples and Comparative Examples]

10‧‧‧reflecting surface

11‧‧‧ normal direction

12‧‧‧ benchmark direction

20‧‧‧ observation direction

100‧‧‧round polarizing plate

110‧‧‧ polarizing film

111‧‧‧ penetration axis

112, 113‧‧‧ axis

120‧‧‧λ/2 board

121‧‧‧ Slow axis

130‧‧‧λ/4 board

131‧‧‧ slow axis

140‧‧‧Broadband λ/4 board

Θh, Θq‧‧‧ angle

Ρ‧‧‧ polar angle

Φ‧‧‧ azimuth

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of a circularly polarizing plate according to an embodiment of the present invention.

2 is a schematic perspective view showing the state of an evaluation model set when the calculation of the color space coordinates is performed in the simulation of the embodiment and the comparative example.

Claims (12)

A circular polarizing plate, which is provided with: a polarizing film; a λ/2 plate having a slow axis in a direction θh with respect to a transmission axis of the polarizing film; and a λ/4 plate opposite to the polarizing film The penetration axis has a slow axis in the direction of the angle Θq; wherein the angle Θh of the λ/2 plate and the angle Θq of the λ/4 plate satisfy the following formulas (A1), (A2) and (A3): Θq±10°=2Θh+45° (A1)25°<Θh<45° (A2) 95°<Θq<135° (A3) The degree of wavelength dispersion of the λ/2 plate and the wavelength dispersion of the λ/4 plate The degree is different; the NZ coefficient NZq of the λ/4 plate satisfies NZq ≦ 0.0. The circularly polarizing plate according to claim 1, wherein the phase difference Reh (400) in the plane of the λ/2 plate having a wavelength of 400 nm, the phase difference Reh (550) in the in-plane of the λ/2 plate at a wavelength of 550 nm, The phase difference Req (400) in the plane of the λ/4 plate having a wavelength of 400 nm, and the in-plane phase difference Req (550) of the λ/4 plate at a wavelength of 550 nm satisfy the following formula (B): Reh (400) /Reh(550)<Req(400)/Req(550) (B). The circularly polarizing plate according to claim 1 or 2, wherein a phase difference Reh (400) in the plane of the λ/2 plate having a wavelength of 400 nm and an in-plane phase difference Reh (550) of the λ/2 plate at a wavelength of 550 nm The phase difference Req (400) in the plane of the λ/4 plate having a wavelength of 400 nm, and the in-plane phase difference Req (550) of the λ/4 plate at a wavelength of 550 nm satisfy the following formula (C): 0.04 < Req (400) / Req (550) - Reh (400) / Reh (550) < 1.0 (C). The circular polarizing plate of claim 1, wherein the NZ coefficient NZh of the λ/2 plate satisfies 1.0≦NZh≦1.3, and the NZ coefficient NZq of the λ/4 plate satisfies -1.5≦NZq≦0.0. The circularly polarizing plate of claim 1, wherein the λ/4 plate has a layer of a material having a negative intrinsic birefringence value. The circularly polarizing plate according to claim 1, wherein the λ/2 plate is provided with a layer of a material having a positive intrinsic birefringence value. The circular polarizing plate of claim 1, wherein the circular polarizing plate has a strip shape, and a transmission axis of the polarizing film is in a width direction of the circular polarizing plate. A strip-shaped wide-band λ/4 plate which is a strip-shaped wide-band λ/4 plate and has a λ/2 plate at an angle Θh with respect to a width direction of the wide-band λ/4 plate Having a slow axis; and a λ/4 plate having a slow axis in a direction Θq relative to a width direction of the wide band λ/4 plate; wherein the angle Θh and the λ/4 of the λ/2 plate The angle Θq of the plate satisfies the following formulas (A1), (A2), and (A3): Θq±10°=2Θh+45° (A1) 25°<Θh<45° (A2) 95°<Θq<135° (A3 The degree of wavelength dispersion of the λ/2 plate is different from the degree of wavelength dispersion of the λ/4 plate; the NZ coefficient NZq of the λ/4 plate satisfies NZq ≦ 0.0. The strip-shaped broadband λ/4 plate of claim 8, wherein the λ/2 plate is an obliquely extending film. A strip-shaped broadband λ/4 plate as claimed in claim 8 or 9, wherein the λ/4 plate is a diagonally extending film. An organic electroluminescence display device comprising: the circularly polarizing plate according to any one of claims 1 to 7, or the strip-shaped broadband λ/4 according to any one of claims 8 to 10; A wide-band λ/4 film sheet obtained by cutting out the sheet. A liquid crystal display device comprising: the circularly polarizing plate according to any one of claims 1 to 7 or the strip-shaped wide-band λ/4 plate according to any one of claims 8 to 10 The obtained wide band λ/4 film sheet.