CN118151284A

CN118151284A - Polarizing plate with retardation layer and image display device

Info

Publication number: CN118151284A
Application number: CN202311667990.XA
Authority: CN
Inventors: 有贺草平
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2022-12-07
Filing date: 2023-12-07
Publication date: 2024-06-07
Also published as: TW202425769A; KR20240085206A; JP2024082165A

Abstract

The polarizing plate with a retardation layer of the present invention comprises, in order, a polarizing plate comprising a polarizer, a first retardation layer, a second retardation layer, a third retardation layer, and a fourth retardation layer, wherein refractive index characteristics of the first retardation layer and the third retardation layer show a relationship in which nx > ny > nz, refractive index characteristics of the second retardation layer and the fourth retardation layer show a relationship in which nx > nx=ny, re (550) of the first retardation layer is 200nm to 300nm, re (550) of the third retardation layer is 120nm to 170nm, an angle formed between a slow axis of the first retardation layer and an absorption axis of the polarizer is 5 DEG to 25 DEG, and an angle formed between a slow axis of the third retardation layer and an absorption axis of the polarizer is 65 DEG to 85 deg.

Description

Polarizing plate with retardation layer and image display device

Technical Field

The present invention relates to a polarizing plate with a retardation layer and an image display device.

Background

In recent years, with the popularization of thin displays, image display devices (organic EL display devices) having organic EL panels mounted thereon have been proposed. Since the organic EL panel has a metal layer with high reflectivity, problems such as reflection of external light and reflection of background are likely to occur. Thus, it is known to prevent these problems by providing a circular polarizer on the viewing side. As a general circular polarizer, a circular polarizer in which a retardation layer functioning as a λ/4 plate is laminated so that its slow axis forms an angle of about 45 ° with respect to the absorption axis of a polarizer is known. Further, from the viewpoint of obtaining antireflection characteristics over a wide band and a wide viewing angle, there has been proposed a circular polarizing plate further comprising a retardation layer functioning as a λ/2 plate and/or a retardation layer exhibiting refractive index characteristics of nz > nx=ny (for example, patent documents 1 and 2). On the other hand, there is room for further improvement in the reflection hue when a circularly polarizing plate is applied to an organic EL display device.

Prior art literature

Patent literature

Patent document 1: japanese patent No. 6786640

Patent document 2: japanese patent No. 5822006

Disclosure of Invention

Problems to be solved by the invention

The main object of the present invention is to provide a polarizing plate with a retardation layer, which can realize an excellent reflection hue, more specifically, a neutral reflection hue in which coloring is suppressed, when applied to an organic EL display device.

Means for solving the problems

[1] The polarizing plate with a retardation layer according to an embodiment of the present invention comprises, in order, a polarizing plate including a polarizer, a first retardation layer, a second retardation layer, a third retardation layer, and a fourth retardation layer, wherein refractive index characteristics of the first retardation layer and the third retardation layer show a relationship in which nx > ny > nz, refractive index characteristics of the second retardation layer and the fourth retardation layer show a relationship in which nx=ny, re (550) of the first retardation layer is 200nm to 300nm, re (550) of the third retardation layer is 120nm to 170nm, an angle formed between a slow axis of the first retardation layer and an absorption axis of the polarizer is 5 ° to 25 °, and an angle formed between a slow axis of the third retardation layer and an absorption axis of the polarizer is 65 ° to 85 °.

[2] The polarizing plate with a retardation layer according to the above [1], wherein Rth (550) of the fourth retardation layer is preferably-10 nm to-110 nm.

[3] The polarizing plate with a retardation layer according to the above [1] or [2], wherein Rth (550) of the fourth retardation layer is preferably-10 nm to-70 nm.

[4] The polarizing plate with a retardation layer according to any one of the above [1] to [3], wherein Rth (550) of the second retardation layer is preferably-20 nm to-110 nm.

[5] The polarizing plate with a retardation layer according to any one of the above [1] to [4], wherein Rth (550) of the second retardation layer is preferably-50 nm to-110 nm, and Rth (550) of the fourth retardation layer is preferably-10 nm to-70 nm.

[6] The polarizing plate with a retardation layer according to any one of the above [1] to [5], which can also be used for an organic EL display device.

[7] An image display device according to an embodiment of the present invention includes the polarizing plate with a retardation layer described in any one of [1] to [6] above.

Effects of the invention

According to the embodiment of the present invention, a polarizing plate with a retardation layer that can realize an excellent reflection hue, more specifically, a neutral reflection hue in which coloring is suppressed when applied to an organic EL display device can be provided.

Drawings

Fig. 1 is a schematic cross-sectional view showing a schematic configuration of a polarizing plate with a retardation layer according to 1 embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view showing a schematic configuration of an organic EL display device according to 1 embodiment of the present invention.

Description of symbols

10. Polarizing plate

12. Polarizer

14. Protective layer

20. First phase difference layer

30. Second phase difference layer

40. Third phase difference layer

50. Fourth phase difference layer

60. Adhesive layer

100. Polarizing plate with phase difference layer

200. Organic EL display device

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. In order to make the description more clear, the width, thickness, shape, and the like of each portion are schematically shown in the drawings as compared with the embodiments, but the drawings are merely examples, and do not limit the explanation of the present invention. In the present specification, (meth) acrylic acid means acrylic acid and/or methacrylic acid. In the present specification, "to" representing a numerical range includes numerical values of the upper limit and the lower limit thereof.

(Definition of terms and symbols)

The definitions of terms and symbols in the present specification are as follows.

(1) Refractive index (nx, ny, nz)

"Nx" is a refractive index in a direction in which the in-plane refractive index becomes maximum (i.e., a slow axis direction), "ny" is a refractive index in a direction orthogonal to the slow axis (i.e., a fast axis direction), and "nz" is a refractive index in a thickness direction.

(2) In-plane phase difference (Re)

"Re (λ)" is the in-plane retardation measured by light having a wavelength of λnm at 23 ℃. For example, "Re (550)" is the in-plane retardation measured at 23℃by light having a wavelength of 550 nm. When the thickness of the layer (film) is set to d (nm), re (λ) passes through the formula: re (λ) = (nx-ny) ×d.

(3) Retardation in thickness direction (Rth)

"Rth (λ)" is a phase difference in the thickness direction measured by light having a wavelength of λnm at 23 ℃. For example, "Rth (550)" is a phase difference in the thickness direction measured at 23℃by light having a wavelength of 550 nm. When the thickness of the layer (film) is set to d (nm), rth (λ) is represented by the formula: rth (λ) = (nx-nz) ×d.

(4) Nz coefficient

The Nz coefficient is obtained by nz=rth/Re.

(5) Angle of

In the present specification, when referring to an angle, the angle includes both clockwise and counterclockwise with respect to a reference direction. Thus, for example, "45" refers to 45 clockwise and 45 counterclockwise.

A. Polarizing plate with phase difference layer

The polarizing plate with a retardation layer according to the embodiment of the present invention includes, in order, a polarizing plate including a polarizer, a first retardation layer, a second retardation layer, a third retardation layer, and a fourth retardation layer. The refractive index characteristics of the first retardation layer and the third retardation layer show a relationship in which nx > ny is not less than nz; the refractive index characteristics of the second phase difference layer and the fourth phase difference layer show a relationship of nz > nx=ny; the Re (550) of the first phase difference layer is 200nm to 300nm; re (550) of the third phase difference layer is 120 nm-170 nm; the angle formed by the slow axis of the first phase difference layer and the absorption axis of the polarizer is 5-25 degrees; the angle formed by the slow axis of the third phase difference layer and the absorption axis of the polarizer is 65-85 degrees. By combining the second phase difference layer and the fourth phase difference layer each having refractive index characteristics of nz > nx=ny with the first phase difference layer and the third phase difference layer each functioning as a λ/2 plate and a λ/4 plate, respectively, the above-described configuration can provide a polarizing plate with a phase difference layer capable of realizing a very excellent reflection hue when used in an image display device (for example, an organic EL display device).

A-1 integral Structure of polarizing plate with retardation layer

Fig. 1 is a schematic cross-sectional view showing a schematic configuration of a polarizing plate with a retardation layer according to 1 embodiment of the present invention. The polarizing plate with a retardation layer 100 has a polarizing plate 10, a first retardation layer 20, a second retardation layer 30, a third retardation layer 40, and a fourth retardation layer 50 in this order.

The polarizing plate 10 includes a polarizer 12, and further includes a protective layer 14 disposed on the opposite side of the polarizer 12 from the side on which the first retardation layer 20 is disposed. In the illustrated example, no protective layer is disposed between the first retardation layer 20 adjacent to the polarizer 12, and the first retardation layer 20 is disposed adjacent to the polarizer 12. By omitting the protective layer in this manner, the polarizing plate 100 with the retardation layer can be made thinner. The polarizing plate 100 with a retardation layer is preferably used for an organic EL display device in which the polarizer 12 is disposed on the visible side of the first retardation layer 20.

The polarizing plate 100 with a retardation layer further has an adhesive layer 60 on the side of the fourth retardation layer 50 opposite to the side on which the third retardation layer 40 is disposed. The polarizing plate 100 with a retardation layer is made to be attachable to an optical member such as an organic EL panel by an adhesive layer 60, for example. Although not shown, a release liner is practically bonded to the surface of the pressure-sensitive adhesive layer 60. The release liner may be temporarily adhered to the polarizing plate with the retardation layer until it is used. By using a release liner, for example, the adhesive layer 60 can be protected, and a roll of the polarizing plate 100 with a retardation layer can be formed.

The polarizing plate 100 with a retardation layer may further have another functional layer not shown. The kind, characteristics, number, combination, arrangement, and the like of the other functional layers that the polarizing plate with a retardation layer may have can be appropriately set according to the purpose. For example, the polarizing plate with a retardation layer may further have a conductive layer or an isotropic substrate with a conductive layer. The polarizing plate with a retardation layer having a conductive layer or an isotropic substrate with a conductive layer is suitable for a so-called in-cell touch panel type input display device in which a touch sensor is incorporated in an image display panel, for example. As another example, the polarizing plate with a retardation layer may further have another retardation layer. The optical characteristics (for example, refractive index characteristics, in-plane retardation, nz coefficient, photoelastic modulus), thickness, arrangement, and the like of the other retardation layer can be appropriately set according to the purpose. As a specific example, another retardation layer (typically, a layer imparting (elliptical) polarization function, a layer imparting ultra-high retardation) may be provided on the visible side of the polarizer to improve visibility in the case of viewing through polarized sunglasses. By providing such a layer, even when a screen is displayed visually through a polarized lens such as polarized sunglasses, excellent visibility can be achieved, and the layer can be suitably applied to an image display device that can be used outdoors.

Typically, the members constituting the polarizing plate 100 with a retardation layer are laminated via any suitable adhesive layer. Specific examples of the adhesive layer include an adhesive layer and an adhesive layer. Although not shown, the protective layer 14 is bonded to the polarizer 12 via an adhesive layer (preferably, an active energy ray-curable adhesive) for example. For example, the polarizing plate 10 and each retardation layer are laminated via an adhesive layer (preferably, an active energy ray-curable adhesive) or via an adhesive layer (preferably, an acrylic adhesive). The thickness of the adhesive layer is, for example, 0.1 μm or more, preferably 0.3 μm to 5 μm, and more preferably 0.5 μm to 3 μm. The thickness of the pressure-sensitive adhesive layer is, for example, 3 μm or more, preferably 5 μm to 100 μm, and more preferably 10 μm to 50 μm.

The total thickness of the laminated portion from the polarizer 10 to the adhesive layer 60 (including the thickness of the adhesive layer) is, for example, 200 μm or less, preferably 150 μm or less, and further, for example, 30 μm or more, preferably 50 μm or more. The thickness of the laminated portion from the polarizing plate 10 to the fourth phase difference layer 50 (the thickness excluding the adhesive layer 60 from the entire thickness) is, for example, 100 μm or less, preferably 80 μm or less, and further, for example, 20 μm or more, preferably 40 μm or more.

The polarizing plate 100 with the retardation layer may be a single sheet or a long sheet. The term "elongated" as used herein refers to an elongated shape having a length sufficiently long with respect to the width, and includes, for example, an elongated shape having a length of 10 times or more, preferably 20 times or more, with respect to the width. The elongated laminate can be wound into a roll.

A-2 polarizing plate

The polarizing plate 10 includes a polarizer 12, and preferably further includes a protective layer 14 on the side of the polarizer 12 opposite to the side on which the first retardation layer 20 is disposed. The polarizing plate 10 may include a protective layer on the side of the polarizer 12 where the first retardation layer 20 is disposed, if necessary.

A-2-1 polarizer

The polarizer 12 is typically a resin film containing a dichroic substance (e.g., iodine). Examples of the resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially methylalized PVA films, and ethylene-vinyl acetate copolymer partially saponified films.

The thickness of the polarizer is, for example, 18 μm or less, preferably 15 μm or less, more preferably 12 μm or less, and still more preferably 8 μm or less. The thickness of the polarizer is preferably 1 μm or more.

The polarizer preferably exhibits absorption dichroism at any one of wavelengths 380nm to 780 nm. The single body transmittance of the polarizer is, for example, 40.0% to 46.0%, preferably 41.0% to 45.0%, and more preferably 41.5% to 44.5%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and still more preferably 99.9% or more.

The polarizer may be made by any suitable method. Specifically, the polarizer may be made of a single-layer resin film, or may be made of a laminate including a base material.

A typical method of producing a polarizer from the single-layer resin film includes a dyeing treatment and a stretching treatment of the resin film with a dichroic substance such as iodine or a dichroic dye. As the resin film, for example, a hydrophilic polymer film such as a polyvinyl alcohol (PVA) film, a partially methylalized PVA film, or an ethylene-vinyl acetate copolymer partially saponified film can be used. The method may further comprise insolubilization treatment, swelling treatment, crosslinking treatment, and the like. Such a manufacturing method is well known and commonly used in the art, and therefore, a detailed description thereof will be omitted.

The polarizer obtained by using the laminate including the above-mentioned base material can be produced, for example, by using a laminate of a resin base material and a resin film or a resin layer (typically, a PVA-based resin layer). Specifically, it can be manufactured by: coating a PVA-based resin solution on a resin substrate and drying the same to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; the laminate was stretched and dyed to prepare a polarizer from the PVA-based resin layer. In the present embodiment, it is preferable to form a PVA-based resin layer containing a halide and a PVA-based resin on one side of a resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution to stretch the laminate. Further, the stretching may further include, if necessary, subjecting the laminate to air stretching at a high temperature (for example, 95 ℃ or higher) before stretching in an aqueous boric acid solution. In the present embodiment, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being conveyed in the longitudinal direction and is shrunk by 2% or more in the width direction. Typically, the manufacturing method of the present embodiment includes sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an in-water stretching treatment, and a drying shrinkage treatment. By introducing the auxiliary stretching, even when PVA is coated on the thermoplastic resin, crystallinity of PVA can be improved, and high optical characteristics can be achieved. In addition, by increasing the orientation of PVA in advance, problems such as reduction in orientation and dissolution of PVA can be prevented when immersed in water in the subsequent dyeing step and stretching step, and high optical characteristics can be achieved. Further, when the PVA-based resin layer is immersed in a liquid, disturbance of the orientation of PVA molecules and decrease of the orientation can be suppressed, and high optical characteristics can be achieved, as compared with the case where the PVA-based resin layer does not contain a halide. Further, by shrinking the laminate in the width direction by the drying shrinkage treatment, high optical characteristics can be achieved. The polarizer may be obtained on a release surface of the resin substrate after the resin substrate is released from the obtained laminate of the resin substrate and the polarizer, or on a surface of the protective layer opposite to the release surface. Details of such a method for producing a polarizer are described in, for example, japanese patent application laid-open No. 2012-73580 and japanese patent No. 6470455. The entire disclosures of these publications are incorporated by reference into this specification.

A-2-2. Protective layer

The protective layer 14 may be formed of any suitable resin film that can be used as a protective layer of a polarizer, for example. Specific examples of the resin that is the main component of the resin film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based resins, polyvinyl alcohol-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyether sulfone-based resins, polysulfone-based resins, cycloolefin-based resins such as polystyrene-based resins and polynorbornene-based resins, polyolefin-based resins, (meth) acrylic-based resins, and acetate-based resins.

The polarizing plate 100 with a retardation layer is typically disposed on the visible side of the image display device, and the protective layer 14 is disposed on the visible side. Therefore, the protective layer 14 may be subjected to surface treatments such as Hard Coat (HC) treatment, antireflection treatment, anti-blocking treatment, and antiglare treatment, as necessary.

The thickness of the protective layer is, for example, 5 μm to 80. Mu.m, preferably 10 μm to 50. Mu.m, and more preferably 15 μm to 35. Mu.m. In the case of performing the surface treatment, the thickness of the protective layer includes the thickness of the surface treatment layer.

A-3 first phase difference layer

The refractive index characteristics of the first retardation layer 20 show a relationship of nx > ny.gtoreq.nz. In one embodiment, the first phase difference layer may function as a λ/2 plate. The in-plane retardation Re (550) of the first retardation layer is, for example, 200nm to 300nm, preferably 220nm to 290nm, and more preferably 230nm to 280nm. Here, "ny=nz" includes not only the case where ny is completely equal to nz but also the case where ny is substantially equal to nz. Therefore, ny < nz may be sometimes set within a range that does not impair the effects of the present invention.

The Nz coefficient of the first retardation layer is preferably 0.9 to 3, more preferably 0.9 to 2.5, still more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, a very excellent reflection hue can be achieved.

The first retardation layer is disposed such that its slow axis forms an angle of, for example, 5 ° to 25 °, preferably 10 ° to 20 °, and more preferably about 15 °, with the absorption axis of the polarizer 12. By setting the configuration as described above, a polarizing plate with a retardation layer having very excellent circular polarization characteristics (as a result, very excellent antireflection characteristics) can be obtained.

The first phase difference layer may exhibit an inverse dispersion wavelength characteristic in which a phase difference value increases according to an increase in the wavelength of the measurement light, a positive wavelength dispersion characteristic in which a phase difference value decreases according to an increase in the wavelength of the measurement light, and a flat wavelength dispersion characteristic in which a phase difference value does not substantially change according to the wavelength of the measurement light. In one embodiment, the first phase difference layer exhibits an inverse dispersive wavelength characteristic. In this case, re (450)/Re (550) of the first retardation layer is, for example, 0.8 or more and less than 1, and preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent antireflection characteristics can be achieved.

In one embodiment, the first retardation layer comprises a resin having an absolute value of photoelastic modulus of preferably 2×10 ^-11m²/N or less, more preferably 2.0×10 ^-13m²/N～1.5×10^-11m²/N, and still more preferably 1.0×10 ^-12m²/N～1.2×10^- ¹¹m²/N. If the absolute value of the photoelastic modulus is in such a range, a change in phase difference is less likely to occur when shrinkage stress occurs upon heating. As a result, thermal unevenness of the obtained image display device can be prevented well.

The first retardation layer is formed of any suitable material that satisfies the above characteristics. The first retardation layer is constituted of, for example, a resin film or an alignment cured layer of a liquid crystal compound.

Examples of the resin contained in the resin film include polycarbonate-based resins, polyester-carbonate-based resins, polyester-based resins, polyvinyl acetal-based resins, polyarylate-based resins, cycloolefin-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polyamide-based resins, polyimide-based resins, polyether-based resins, polystyrene-based resins, and acrylic-based resins. These resins may be used alone or in combination (e.g., blending, copolymerization). When the first retardation layer exhibits the inverse dispersion wavelength characteristic, a resin film containing a polycarbonate-based resin or a polyester carbonate-based resin (hereinafter, may be simply referred to as a polycarbonate-based resin) may be suitably used. In the case where the first retardation layer exhibits flat wavelength dispersion characteristics, a resin film containing a cycloolefin resin can be suitably used.

Any suitable polycarbonate resin may be used as long as the effects of the present invention can be obtained. For example, the polycarbonate resin contains a structural unit derived from a fluorene dihydroxy compound, a structural unit derived from an isosorbide dihydroxy compound, and a structural unit derived from at least 1 dihydroxy compound selected from the group consisting of alicyclic diol, alicyclic dimethanol, diethylene glycol, triethylene glycol or polyethylene glycol, and alkylene glycol or spiroglycol. Preferably, the polycarbonate resin comprises a structural unit derived from a fluorene dihydroxy compound, a structural unit derived from an isosorbide dihydroxy compound, and a structural unit derived from alicyclic dimethanol and/or a structural unit derived from diethylene glycol, triethylene glycol or polyethylene glycol; it is further preferable that the composition contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from diethylene glycol, triethylene glycol or polyethylene glycol. The polycarbonate resin may contain a structural unit derived from another dihydroxy compound, if necessary. Details of the polycarbonate resin that can be suitably used for the first retardation layer are described in, for example, japanese patent application laid-open publication nos. 2014-10291, 2014-26262, 2015-212816, 2015-212817, and 2015-212818, which are incorporated herein by reference.

The cycloolefin resin is a general term for a resin obtained by polymerizing cycloolefins as polymerization units, and examples thereof include resins described in JP-A-1-240517, JP-A-3-14882, JP-A-3-122137, and the like. Specific examples thereof include a ring-opened (co) polymer of cycloolefin, an addition polymer of cycloolefin, a copolymer (typically, a random copolymer) of cycloolefin and an α -olefin such as ethylene or propylene, a graft modified product obtained by modifying the copolymer with an unsaturated carboxylic acid or a derivative thereof, and a hydride thereof. Specific examples of cycloolefins include norbornene monomers. Examples of the norbornene monomer include norbornene and alkyl and/or alkylidene substituents thereof, and polar group substituents such as halogen of 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene and the like; dicyclopentadiene, 2, 3-dihydro-dicyclopentadiene, and the like; dimethylbridged octahydronaphthalenes, alkyl and/or alkylidene substituents thereof, polar group substituents such as halogen, e.g., 6-methyl-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-ethyl-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-ethylidene-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-chloro-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-cyano-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-pyridinyl-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-methoxycarbonyl-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, etc.; tri-to tetramers of cyclopentadiene, for example 4,9:5, 8-dimethyl-3 a, 4a,5, 8a,9 a-octahydro-1H-benzidine, 4,11:5,10:6, 9-trimethyl-3 a, 4a, 5a,6, 9a,10 a,11 a-dodecahydro-1H-cyclopentaanthracene, and the like.

Other cycloolefins which can be ring-opened polymerized may be used in combination within a range not to impair the object of the present invention. Specific examples of such cycloolefins include compounds having 1 reactive double bond such as cyclopentene, cyclooctene, and 5, 6-dihydrodicyclopentadiene.

The number average molecular weight (Mn) of the cycloolefin resin measured by Gel Permeation Chromatography (GPC) using a toluene solvent is preferably 25000 to 200000, more preferably 30000 to 100000, and further preferably 40000 to 80000. When the number average molecular weight is within the above range, a resin film excellent in mechanical strength, solubility, formability, and casting workability can be obtained.

In the case where the cycloolefin resin is a resin obtained by hydrogenating a ring-opened polymer of a norbornene monomer, the hydrogenation rate is preferably 90% or more, more preferably 95% or more, and still more preferably 99% or more. If the content is within such a range, the heat deterioration resistance, the light deterioration resistance and the like are excellent.

Various products are commercially available as the cycloolefin resin. Specific examples thereof include "ZEONEX", "ZEONOR", trade name "Arton" by JSR, trade name "TOPAS" by ticna, and trade name "APEL" by mitsunk chemical company.

The first retardation layer can be obtained, for example, by stretching the unstretched resin film. In the stretching, any suitable stretching method, stretching conditions (e.g., stretching temperature, stretching ratio, stretching direction) may be employed. Specifically, various stretching methods such as free end stretching, fixed end stretching, free end shrinkage, and fixed end shrinkage may be used alone or simultaneously or stepwise. The stretching direction may be performed in various directions or dimensions such as a longitudinal direction, a width direction, a thickness direction, and an oblique direction. The stretching temperature is preferably from Tg to 30℃to Tg+60℃, more preferably from Tg to 10℃to Tg+50℃, with respect to the glass transition temperature (Tg) of the resin film.

By appropriately selecting the stretching method and the stretching conditions, a resin film having the desired optical characteristics (for example, refractive index characteristics, in-plane retardation, nz coefficient) can be obtained.

In one embodiment, the first retardation layer is produced by uniaxially stretching or uniaxially stretching the unstretched resin film at the fixed end. As a specific example of the fixed-end uniaxial stretching, a method of stretching a resin film while shifting in the longitudinal direction and while shifting in the width direction (transverse direction) is exemplified. The stretching ratio is preferably 1.1 to 3.5 times.

The thickness of the stretched film of the resin film, that is, the first retardation layer, is, for example, 10 μm to 100. Mu.m, preferably 10 μm to 70. Mu.m, more preferably 10 μm to 60. Mu.m, still more preferably 20 μm to 50. Mu.m.

The alignment cured layer of the liquid crystal compound is a layer in which the liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state thereof is fixed. The term "alignment cured layer" is a concept including an alignment cured layer obtained by curing a liquid crystal monomer as described below. In the first retardation layer composed of the alignment cured layer of the liquid crystal compound, typically, the rod-like liquid crystal compound is aligned (planar alignment) in a state of being aligned in the slow axis direction of the first retardation layer. Examples of the rod-like liquid crystal compound include liquid crystal polymers and liquid crystal monomers. The liquid crystal compound is preferably polymerizable. If the liquid crystal compound is polymerizable, the alignment state of the liquid crystal compound can be fixed by aligning the liquid crystal compound and then polymerizing the liquid crystal compound.

The alignment cured layer (liquid crystal alignment cured layer) of the liquid crystal compound can be formed by applying an alignment treatment to a surface of a predetermined substrate, applying a coating liquid containing the liquid crystal compound to the surface, aligning the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state. As the orientation treatment, any suitable orientation treatment may be used. Specifically, a mechanical alignment treatment, a physical alignment treatment, and a chemical alignment treatment can be cited. Specific examples of the mechanical orientation treatment include a rubbing treatment and a stretching treatment. Specific examples of the physical alignment treatment include a magnetic field alignment treatment and an electric field alignment treatment. Specific examples of the chemical alignment treatment include oblique vapor deposition and photo-alignment treatment. The process conditions of the various orientation processes may be any suitable conditions depending on the purpose.

The alignment of the liquid crystal compound is performed by performing a treatment at a temperature at which a liquid crystal phase is exhibited, depending on the kind of the liquid crystal compound. By performing such a temperature treatment, the liquid crystal compound is in a liquid crystal state, and the liquid crystal compound is aligned in accordance with the alignment treatment direction of the substrate surface.

In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned as described above. In the case where the liquid crystal compound is polymerizable or crosslinkable, the alignment state is fixed by subjecting the liquid crystal compound aligned as described above to polymerization treatment or crosslinking treatment.

As the liquid crystal compound, any suitable liquid crystal polymer and/or liquid crystal monomer may be used. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination. Specific examples of the liquid crystal compound and a method for producing the liquid crystal alignment cured layer are described in, for example, japanese patent application laid-open No. 2006-163343, japanese patent application laid-open No. 2006-178389, and International publication No. 2018/123551. The disclosures of these publications are incorporated by reference into this specification.

The thickness of the first retardation layer, which is the liquid crystal alignment cured layer, is, for example, 1 μm to 10 μm, preferably 1 μm to 8 μm, more preferably 1 μm to 6 μm, and still more preferably 1 μm to 4 μm.

A-4 second phase difference layer

The second phase difference layer 30 is a so-called positive C plate whose refractive index characteristics show a relationship of nz > nx=ny. Here, "nx=ny" includes not only the case where nx and ny are exactly equal but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re (550) of the second phase difference layer may be below 10nm.

The thickness direction retardation Rth (550) of the second phase difference layer is, for example, -10nm to-120 nm, preferably, -20nm to-110 nm, more preferably, -50nm to-110 nm, and even more preferably, -60nm to-100 nm.

The second phase difference layer preferably has a puncture elastic modulus of 50g/mm or more, more preferably 52g/mm or more, and still more preferably 55g/mm or more. The second phase difference layer has a puncture elastic modulus of, for example, 200g/mm or less. When the puncture elastic modulus of the second phase difference layer is within the above range, dimensional changes of adjacent phase difference layers (for example, expansion, shrinkage, and the like of the first phase difference layer and/or the third phase difference layer made of a stretched film of a resin film) can be appropriately suppressed. In the present specification, the puncture elastic modulus refers to a value obtained by dividing a force (g) immediately before breaking (or splitting) of a phase difference film (for example, a second phase difference layer) by a strain (mm) at that time when a needle (puncture jig) punctures perpendicularly to a main surface of the phase difference film. As the needle, a needle having a tip diameter of 1mm phi and 0.5R can be used. The speed of needle penetration can be set to 0.33 cm/sec. The measurement of the puncture elastic modulus can be performed by sandwiching the retardation film between 2 plates provided with circular holes having a diameter of 15mm or less (for example, a diameter of 11 mm) through which the needle passes. The measurement of the modulus of elasticity in puncture can be performed in an environment at a temperature of 23 ℃. For example, the puncture elastic modulus of 5 retardation films may be measured, and the average value thereof may be set as the puncture elastic modulus of the retardation film. For the measurement of the puncture elastic modulus, a commercially available device can be used. As a commercially available device, a portable compression tester "KES-G5 needle penetration force measurement Specification" manufactured by KATO TECH Co., ltd., a small-sized bench tester "EZTest" manufactured by Shimadzu corporation, etc. may be mentioned.

The second phase difference layer is formed of any suitable material. In one embodiment, the second phase difference layer is composed of a resin film. In another embodiment, the second phase difference layer is composed of an alignment cured layer of a liquid crystal compound.

As a material of the resin film constituting the second phase difference layer, a resin material having negative birefringence is typically exemplified. The resin having negative birefringence is a resin that exhibits a property that the refractive index in the direction perpendicular to the stretching direction becomes maximum in the case of uniaxial stretching. Examples of the resin having negative birefringence include resins having a side chain into which a chemical bond or a functional group having a large polarization anisotropy such as an aromatic ring or a carbonyl group is introduced. Specific examples of the resin having negative birefringence include acrylic resins, styrene resins, maleimide resins, modified polyolefin resins, and fumarate resins. The above resin materials may be used singly or in combination of two or more.

The acrylic resin can be obtained, for example, by addition polymerization of an acrylic monomer. Examples of the acrylic resin include polymethyl methacrylate (PMMA), polybutyl methacrylate, and polycyclohexyl methacrylate.

The styrene resin can be obtained, for example, by addition polymerization of a styrene monomer. Examples of the styrene monomer include styrene, α -methylstyrene, o-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2, 5-dichlorostyrene, and p-t-butylstyrene.

The maleimide-based resin can be obtained, for example, by addition polymerization of a maleimide-based monomer. Examples of maleimide monomers include N-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-propylphenyl) maleimide, N- (2-isopropylphenyl) maleimide, N- (2, 6-dimethylphenyl) maleimide, N- (2, 6-dipropylphenyl) maleimide, N- (2, 6-diisopropylphenyl) maleimide, N- (2-methyl-6-ethylphenyl) maleimide, N- (2-chlorophenyl) maleimide, N- (2, 6-dichlorophenyl) maleimide, N- (2-bromophenyl) maleimide, N- (2, 6-dibromophenyl) maleimide, N- (2-biphenyl) maleimide, and N- (2-cyanophenyl) maleimide. The maleimide monomer is available from tokyo chemical industry (co.) and the like.

In the addition polymerization, the birefringent properties of the resulting resin can be controlled by substituting side chains after polymerization, or by carrying out a maleimidation reaction, a grafting reaction, or the like.

The resin having negative birefringence may be copolymerized with other monomers. By copolymerizing other monomers, brittleness, molding processability, and heat resistance can be improved. Examples of the other monomer include olefins such as ethylene, propylene, 1-butene, 1, 3-butadiene, 2-methyl-1-butene, 2-methyl-1-pentene, and 1-hexene; acrylonitrile; methyl acrylate, methyl methacrylate and other (meth) acrylates; maleic anhydride; vinyl esters such as vinyl acetate, and the like.

When the resin having negative birefringence is a copolymer of the styrene monomer and the other monomer, the blending ratio of the styrene monomer is preferably 50 to 80 mol%. When the resin having negative birefringence is a copolymer of the maleimide-based monomer and the other monomer, the blending ratio of the maleimide-based monomer is preferably 2 to 50 mol%. When the amount is within this range, a resin film excellent in toughness and moldability can be obtained.

As the resin having negative birefringence, styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, styrene- (meth) acrylate copolymer, styrene-maleimide copolymer, vinyl ester-maleimide copolymer, olefin-maleimide copolymer, and the like are preferably used. They may be used singly or in combination of two or more. These resins can exhibit high negative birefringence and are excellent in heat resistance. These resins are available from NOVA Chemicals Japan, the chemical industry of waste and Sichuan (Co., ltd.) and the like.

As the resin having negative birefringence, a polymer having a repeating unit represented by the following general formula (I) is also preferably used. Such a polymer can exhibit further higher negative birefringence and is excellent in heat resistance and mechanical strength. Such a polymer can be obtained, for example, by using an N-phenyl-substituted maleimide having an N substituent of a maleimide-based monomer in which a phenyl group having a substituent at least in the ortho-position is introduced as a starting material.

[ Chemical formula 1]

In the general formula (I), R ₁～R₅ independently represents hydrogen, a halogen atom, a carboxylic acid ester, a hydroxyl group, a nitro group, or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms (wherein R ₁ and R ₅ are not simultaneously a hydrogen atom), R ₆ and R ₇ represent hydrogen or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms, and n represents an integer of 2 or more.

The resin having negative birefringence is not limited to the above, and for example, resins having negative birefringence described in japanese patent application laid-open publication No. 2008-544304, japanese patent application laid-open publication No. 2008-544317, and the like can be used.

The resin film forming the second phase difference layer may further contain any suitable additive as needed. Specific examples of the additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, ultraviolet absorbers, flame retardants, colorants, antistatic agents, cosolvents, crosslinking agents, thickeners, and the like. The kind and content of the additive may be appropriately set according to the purpose. The content of the additive in the resin film is, for example, about 3 to 10% by weight.

As a method for producing the second phase difference layer formed of the resin film, any suitable production method can be used. In one embodiment, the resin film containing the above resin material may be used as the second phase difference layer directly (i.e., in a state of no stretching) after the film is formed. For example, when a film is formed by a solution film forming method using a resin solution containing the above resin material, stress is generated by volume shrinkage when the resin solution is dried on a support, and the molecular chains of the polymer tend to be oriented in the in-plane direction. Therefore, when a resin material having high birefringence and negative intrinsic birefringence is used, a coating film having large thickness-direction birefringence can be formed on the support by shrinkage during drying, and the coating film can be used as a positive C plate.

The thickness of the second phase difference layer as the resin film is, for example, 1 μm to 40 μm, preferably 3 μm to 35 μm, and more preferably 5 μm to 30 μm.

As the alignment cured layer of the liquid crystal compound constituting the second phase difference layer, an alignment cured layer of a liquid crystal material whose homeotropic alignment is fixed can be preferably exemplified. The homeotropic alignment-enabling liquid crystal material (liquid crystal compound) may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the retardation layer include those described in [0020] to [0028] of JP-A-2002-333642 and methods for forming the retardation layer.

The thickness of the second phase difference layer, which is the alignment cured layer of the liquid crystal compound, is preferably 0.5 μm to 10. Mu.m, more preferably 0.5 μm to 8. Mu.m, and still more preferably 0.5 μm to 5. Mu.m.

A-5 third phase difference layer

The refractive index characteristics of the third phase difference layer 40 show a relationship of nx > ny.gtoreq.nz. In one embodiment, the third phase difference layer may function as a lambda/4 plate. The in-plane phase difference Re (550) of the third phase difference layer is, for example, 120nm to 170nm, preferably 130nm to 160nm, and more preferably 140nm to 150nm. Here, "ny=nz" includes not only the case where ny is completely equal to nz but also the case where ny is substantially equal to nz. Therefore, ny < nz may be sometimes set within a range that does not impair the effects of the present invention.

The Nz coefficient of the third phase difference layer is preferably 0.9 to 3, more preferably 0.9 to 2.5, still more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, a very excellent reflection hue can be achieved.

The third phase difference layer is disposed such that the slow axis thereof forms an angle of, for example, 65 ° to 85 °, preferably 70 ° to 80 °, and more preferably about 75 °, with the absorption axis of the polarizer 12. The angle between the slow axis of the third phase difference layer and the slow axis of the first phase difference layer is, for example, 50 ° to 70 °, preferably 55 ° to 65 °, and more preferably about 60 °. By setting the configuration as described above, a polarizing plate with a retardation layer having very excellent circular polarization characteristics (as a result, very excellent antireflection characteristics) can be obtained.

The third phase difference layer may exhibit an inverse dispersion wavelength characteristic in which the phase difference value increases according to an increase in the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the phase difference value decreases according to an increase in the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the phase difference value does not substantially change according to the wavelength of the measurement light. In one embodiment, the third phase difference layer exhibits an inverse dispersive wavelength characteristic. In this case, re (450)/Re (550) of the third phase difference layer is, for example, 0.8 or more and less than 1, and preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent antireflection characteristics can be achieved.

In one embodiment, the third phase difference layer comprises a resin having an absolute value of photoelastic modulus of preferably 2×10 ^-11m²/N or less, more preferably 2.0×10 ^-13m²/N～1.5×10^-11m²/N, still more preferably 1.0×10 ^-12m²/N～1.2×10^- ¹¹m²/N. If the absolute value of the photoelastic modulus is in such a range, a change in phase difference is less likely to occur when shrinkage stress occurs upon heating. As a result, thermal unevenness of the obtained image display device can be prevented well.

The third phase difference layer is formed of any suitable material that satisfies the above characteristics. The third phase difference layer is constituted of, for example, a resin film or an alignment cured layer of a liquid crystal compound.

The resin contained in the resin film may be the same as the resin contained in the resin film constituting the first retardation layer. The third phase difference layer can be obtained, for example, by stretching an unstretched resin film. As described for the first retardation layer, any suitable stretching method and stretching conditions (for example, stretching temperature, stretching ratio, stretching direction) may be used in stretching. By appropriately selecting the stretching method and stretching conditions, a resin film having the above-described desired optical characteristics (for example, refractive index characteristics, in-plane retardation, nz coefficient) can be obtained.

The thickness of the stretched film of the resin film, that is, the third phase difference layer, is, for example, 10 μm to 100. Mu.m, preferably 10 μm to 70. Mu.m, more preferably 10 μm to 60. Mu.m, still more preferably 20 μm to 50. Mu.m.

As the liquid crystal compound contained in the alignment cured layer of the liquid crystal compound, any suitable liquid crystal polymer and/or liquid crystal monomer may be used. Specifically, a liquid crystal compound similar to the liquid crystal compound contained in the liquid crystal alignment cured layer constituting the first retardation layer can be exemplified, and the production method thereof is as described above.

The thickness of the third phase difference layer, which is the liquid crystal alignment cured layer, is, for example, 1 μm to 10. Mu.m, preferably 1 μm to 8. Mu.m, more preferably 1 μm to 6. Mu.m, still more preferably 1 μm to 4. Mu.m.

A-6 fourth phase difference layer

The fourth phase difference layer 50 is a so-called positive C plate whose refractive index characteristics show a relationship of nz > nx=ny. Here, "nx=ny" includes not only the case where nx and ny are exactly equal but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re (550) of the fourth phase difference layer may be lower than 10nm.

The thickness direction retardation Rth (550) of the fourth phase difference layer is, for example, -10nm to-120 nm, preferably, -10nm to-110 nm, more preferably, -10nm to-70 nm, and even more preferably, -20nm to-60 nm. In one embodiment, the total Rth (550) of the second phase difference layer and the fourth phase difference layer is, for example, -60nm to-200 nm, preferably, -70nm to-180 nm.

The fourth phase difference layer preferably has a puncture elastic modulus of 50g/mm or more, more preferably 52g/mm or more, and still more preferably 55g/mm or more. The fourth phase difference layer has a puncture elastic modulus of 200g/mm or less, for example. When the puncture elastic modulus of the fourth phase difference layer is in the above range, dimensional changes of the third phase difference layer (for example, expansion, contraction, and the like of the third phase difference layer made of a stretched film of a resin film) can be suitably suppressed.

The fourth phase difference layer is formed of any suitable material. In one embodiment, the fourth phase difference layer is composed of a resin film. In another embodiment, the fourth phase difference layer is composed of an alignment cured layer of a liquid crystal compound.

As a material of the resin film constituting the fourth phase difference layer, the same resin material as the resin film constituting the second phase difference layer can be used. For example, by adjusting the thickness of the resin film, a fourth phase difference layer having a desired thickness direction phase difference can be obtained.

The thickness of the fourth phase difference layer, which is the resin film, is, for example, 1 μm to 40. Mu.m, preferably 3 μm to 35. Mu.m, more preferably 5 μm to 30. Mu.m.

As the alignment cured layer of the liquid crystal compound constituting the fourth phase difference layer and the method of forming the same, the alignment cured layer of the liquid crystal compound constituting the second phase difference layer and the method of forming the same can be similarly applied. The second phase difference layer and the fourth phase difference layer may be made of the same material or different materials. For example, one may be composed of a resin film, and the other may be composed of a liquid crystal alignment cured layer.

The thickness of the fourth phase difference layer, which is the alignment cured layer of the liquid crystal compound, is preferably 0.5 μm to 10. Mu.m, more preferably 0.5 μm to 8. Mu.m, and still more preferably 0.5 μm to 5. Mu.m.

A-7 adhesive layer

The adhesive layer 60 is provided on the side of the fourth phase difference layer 50 opposite to the side on which the third phase difference layer 40 is provided. As described above, the polarizing plate 100 with the retardation layer may be bonded to a member such as an organic EL panel via the pressure-sensitive adhesive layer 60.

The adhesive layer 60 may be composed of any suitable adhesive. Specific examples thereof include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the kind, number, combination and blending ratio of the monomers forming the base resin of the adhesive, and the blending amount of the crosslinking agent, the reaction temperature, the reaction time, and the like, an adhesive having desired characteristics according to the purpose can be produced. The base resin of the adhesive may be used alone or in combination of two or more. As the base resin, an acrylic resin is preferably used. Specifically, the adhesive layer is preferably composed of an acrylic adhesive.

The adhesive layer can be formed by coating an adhesive composition containing an additive such as a base resin and a crosslinking agent and a solvent, and drying the coating. For example, the pressure-sensitive adhesive composition may be directly applied to an adherend to form a pressure-sensitive adhesive layer. For example, the pressure-sensitive adhesive composition may be applied to a substrate such as a base film prepared separately to form a pressure-sensitive adhesive layer, and transferred to an adherend. Drying is typically performed by heating.

The thickness of the pressure-sensitive adhesive layer is, for example, 5 μm or more, preferably 10 μm or more, for example, 100 μm or less, preferably 80 μm or less.

A-8 release liner

Examples of the release liner include a flexible plastic film. Examples of the plastic film include polyethylene terephthalate film, polyethylene film, polypropylene film, and polyester film. The thickness of the release liner is, for example, 3 μm or more and, further, 200 μm or less. The surface of the release liner is coated with a release agent. Specific examples of the release agent include silicone release agents, fluorine release agents, and long-chain alkyl acrylate release agents.

B. Image display device

The polarizing plate with a retardation layer described in item a is typically applicable to an image display device, preferably an image display device having a metal layer, and more preferably an organic electroluminescence (organic EL) display device. Accordingly, the image display device according to the embodiment of the present invention includes the polarizing plate with the retardation layer. The organic EL display device according to the embodiment of the present invention typically includes an organic EL panel and the polarizing plate with a retardation layer disposed on the visible side thereof.

The organic EL display device 200 illustrated in fig. 2 has an organic EL panel 120 and a polarizing plate 100 with a retardation layer disposed on the visible side thereof. The polarizing plate 100 with a retardation layer is disposed so that the first retardation layer 20 is on the organic EL panel 120 side with respect to the polarizer 12, and is bonded to the organic EL panel 120 by the adhesive layer 60. The organic EL panel 120 includes a metal member (e.g., electrode, sensor, wiring, metal layer), but since the polarizing plate 100 with a retardation layer has excellent antireflection property, reflection due to the metal member can be suitably prevented.

Examples

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The following is a description of various measurement methods. Unless otherwise specified, "parts" and "%" in examples and comparative examples are weight basis.

1. Thickness of (L)

The thickness of 1 μm or less was measured by using a scanning electron microscope (product name "JSM-7100F", manufactured by Japanese electronics Co., ltd.). The thickness exceeding 1 μm was measured using a digital micrometer (manufactured by ANRITSU Co., ltd., product name "KC-351C").

2. In-plane retardation Re (lambda) and thickness direction retardation Rth (lambda)

The in-plane retardation and the thickness-direction retardation at each wavelength at 23℃were measured using a Mueller matrix polarimeter (manufactured by Axometrics Co., ltd., product name "Axoscan").

3. Refractive index

The average refractive index was measured using an Abbe refractometer manufactured by Atago, and the refractive indices nx, ny, nz were calculated from the above-mentioned phase difference values.

4. Monomer transmittance and degree of polarization

The single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc of the polarizing plate were measured using a spectrophotometer (manufactured by Katsukamu electronic Co., ltd., "LPF-200"). These Ts, tp, and Tc are Y values measured and corrected for visibility by a 2-degree field of view (C light source) of JIS Z8701. From the obtained Tp and Tc, the degree of polarization of the polarizing plate (polarizer) was determined using the following formula.

Degree of polarization (%) = { (Tp-Tc)/(tp+tc) } ^1/2 ×100

Production example 1: production of polarizing plate A ]

(Production of polarizer)

As the thermoplastic resin base material, an amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness 100 μm) having a long shape and a Tg of about 75 ℃ was used, and one side of the resin base material was subjected to corona treatment.

In the case of polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%), acetoacetyl-modified PVA (trade name "GOHSENX Z410" manufactured by Mitsubishi Chemical Co., ltd.) was used as a polymer at 9:1 to 100 parts by weight of the PVA-based resin mixed in the above step, 13 parts by weight of potassium iodide was added, and the obtained material was dissolved in water to prepare a PVA aqueous solution (coating liquid).

The PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60 ℃ to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.

The resulting laminate was uniaxially stretched to 2.4 times in the machine direction (lengthwise direction) in an oven at 130 c (air-assisted stretching treatment).

Next, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (insolubilization treatment).

Next, the polarizer was immersed in a dyeing bath (aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ℃ for 60 seconds (dyeing treatment) while adjusting the concentration so that the monomer transmittance (Ts) of the polarizer finally obtained became a desired value.

Then, the resultant mixture was immersed in a crosslinking bath (aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40℃for 30 seconds (crosslinking treatment).

Thereafter, the laminate was subjected to uniaxial stretching (in-water stretching treatment) while immersed in an aqueous boric acid solution (boric acid concentration 4 wt% and potassium iodide concentration 5 wt%) at a liquid temperature of 70 ℃ so that the total stretching ratio became 5.5 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds.

Thereafter, the laminate was immersed in a washing bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20 ℃.

After that, while drying in an oven maintained at about 90 ℃, the material was brought into contact with a SUS heated roller maintained at a surface temperature of about 75 ℃ (drying shrinkage treatment).

In this way, a polarizer having a thickness of 5 μm was formed on the resin substrate.

(Production of polarizing plate A)

An HC-TAC film is bonded as a protective layer to the surface (surface opposite to the resin substrate) of the polarizer obtained via an ultraviolet-curable adhesive. Specifically, the coating was performed so that the thickness of the ultraviolet-curable adhesive became 1.0 μm, and the adhesive was bonded by using a rolling mill. Then, UV light is irradiated from the protective layer side to harden the adhesive. The HC-TAC film was a film in which a Hard Coat (HC) layer (thickness 7 μm) was formed on a triacetyl cellulose (TAC) film (thickness 25 μm), and was bonded so that the TAC film became the polarizer side. Next, the resin substrate was peeled off and removed to obtain a polarizing plate a having a structure of [ polarizer/TAC protective layer with HC ]. The monomer transmittance of the polarizing plate a was 43%, and the degree of polarization was 99.9%.

Production example 2A: production of positive C plate A ]

48 Parts by weight of hydroxypropyl methylcellulose (trade name: metolose60SH-50, manufactured by Xin Yue chemical Co., ltd.), 15601 parts by weight of distilled water, 8161 parts by weight of diisopropyl fumarate, 240 parts by weight of 3-ethyl-3-oxetanyl methyl acrylate and 45 parts by weight of tert-butyl peroxypivalate as a polymerization initiator were charged into an autoclave equipped with a stirrer, a cooling tube, a nitrogen inlet tube and a thermometer, and after 1 hour nitrogen bubbling, the mixture was stirred and kept at 49℃for 24 hours, to thereby carry out radical suspension polymerization. Then, the mixture was cooled to room temperature, and the suspension containing the polymer particles was centrifuged. The polymer obtained was washed with distilled water 2 times and methanol 2 times, and then dried under reduced pressure. The obtained fumarate-based resin was dissolved in a toluene-methyl ethyl ketone mixed solution (toluene/methyl ethyl ketone, 50 wt%/50 wt%) to prepare a 20% solution. Further, 5 parts by weight of tributyl trimellitate was added as a plasticizer to 100 parts by weight of the fumarate resin to prepare a paint. As the support film, a biaxially stretched film (thickness 75 μm) of polyester (polyethylene terephthalate/isophthalate copolymer) was used. The coating material thus prepared was applied to a support film so that the film thickness after drying became 8. Mu.m, and dried at 140 ℃. Thus, a resin film (positive C plate a) exhibiting refractive index characteristics of nz > nx=ny was obtained. The positive C plate A had a thickness of 8 μm and an in-plane retardation Re (550) ≡0nm and a thickness direction retardation Rth (550) of-40 nm.

Production example 2B: production of positive C plate B ]

A resin film (positive C plate B) exhibiting refractive index characteristics of nz > nx=ny was obtained in the same manner as in production example 2A, except that the coating thickness of the resin solution was changed. The positive C plate B has a thickness of 17 μm and an in-plane retardation Re (550) ≡0nm and a thickness direction retardation Rth (550) of-80 nm.

Production example 2C: production of positive C plate C

A resin film (positive C plate C) exhibiting refractive index characteristics of nz > nx=ny was obtained in the same manner as in production example 2A, except that the coating thickness of the resin solution was changed. The positive C plate C has a thickness of 26 μm and an in-plane retardation Re (550) ≡0nm and a thickness direction retardation Rth (550) of-120 nm.

Production example 3: production of lambda/2 plate A (first phase-difference layer)

A liquid crystal composition (coating liquid) was prepared by dissolving 10g of a polymerizable liquid crystal (product name: paliocolor LC242, product name: irgacure 907, product name: BASF) exhibiting a nematic liquid crystal phase and 3g of a photopolymerization initiator (product name: irgacure 907, product name: BASF) for the polymerizable liquid crystal compound in 40g of toluene.

[ Chemical formula 2]

The surface of a polyethylene terephthalate (PET) film (thickness 38 μm) was rubbed with a rubbing cloth, and orientation treatment was performed. The orientation treatment direction was set so that the direction of the absorption axis with respect to the polarizer was 15 ° when viewed from the visual side at the time of bonding to the polarizer. The liquid crystal coating liquid was coated on the alignment treated surface by a bar coater, and the liquid crystal compound was aligned by drying at 90 ℃ for 2 minutes. The liquid crystal layer thus formed was cured by irradiation of light of 1mJ/cm ² with a metal halide lamp, whereby a liquid crystal alignment cured layer (λ/2 plate A) was formed on the PET film. The thickness of the lambda/2 plate A was 2.5 μm and the in-plane retardation Re (550) was 270nm. Further, λ/2 plate a shows refractive index characteristics of nx > ny=nz.

Production example 4: production of lambda/4 plate A (third phase difference layer)

A liquid crystal alignment cured layer (λ/4 plate a) was formed on a PET film in the same manner as in production example 3, except that the coating thickness was changed and the alignment treatment direction was set so that the direction with respect to the absorption axis of the polarizer was 75 ° as viewed from the visual side. The lambda/4 plate A had a thickness of 1.5 μm and an in-plane retardation Re (550) of 140nm. Further, λ/4 plate a shows refractive index characteristics of nx > ny=nz.

Production example 5: production of adhesive layer A ]

Into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, and a cooler, a monomer mixture containing 91.5 parts of butyl acrylate, 3 parts of acrylic acid, 0.5 part of 4-hydroxybutyl acrylate, and 5 parts of acryloylmorpholine was charged. Further, 0.1 part of 2,2' -azobisisobutyronitrile as a polymerization initiator was charged together with 100 parts of ethyl acetate with respect to 100 parts of the monomer mixture, nitrogen was introduced into the flask while stirring slowly to replace nitrogen, and then the liquid temperature in the flask was kept at about 55℃to carry out polymerization reaction for 8 hours. Next, ethyl acetate was added to the obtained reaction solution to adjust the solid content concentration to 12 wt%, thereby preparing a solution of an acrylic polymer having a weight average molecular weight (Mw) of 250 ten thousand.

An acrylic adhesive was prepared by mixing 100 parts of the solid content of the obtained acrylic polymer solution with 0.3 part of benzoyl peroxide (trade name: nyper BMT, manufactured by Japanese fat and oil Co., ltd.), 0.2 part of trimethylolpropane/toluene diisocyanate adduct (trade name: coronate L, manufactured by Tosoh Co., ltd.), and 0.2 part of silane coupling agent (trade name: KBM403, manufactured by Xinyue chemical Co., ltd.).

The obtained acrylic pressure-sensitive adhesive was applied to a release surface of a PET Film (MRF 38, manufactured by Mitsubishi chemical Polyester Film Co., ltd.) having a thickness of 38 μm as a release liner having a release surface subjected to silicone treatment, and dried to form a pressure-sensitive adhesive layer A having a thickness of 20. Mu.m.

Example 1

The λ/2 plate a as a first retardation layer is transferred from a PET film to a polarizer side of the polarizing plate a, and then a positive C plate a as a second retardation layer is attached to the λ/2 plate a, and the λ/4 plate a as a third retardation layer is transferred from the PET film thereto. The positive C plate a as the fourth phase difference layer was bonded to the λ/4 plate a side of the obtained laminate. At this time, transfer (bonding) was performed such that the slow axis of the λ/2 plate a and the slow axis of the λ/4 plate a were at angles of 15 ° and 75 ° clockwise from the visual side with respect to the absorption axis of the polarizer, respectively. The retardation layers were all bonded via an ultraviolet curable adhesive (thickness: about 1 μm).

The adhesive layer a was bonded to the positive C plate a side of the obtained laminate together with a release liner, to obtain a polarizing plate with a retardation layer having a configuration of [ polarizing plate a/λ/2 plate a/positive C plate a/λ/4 plate a/positive C plate a/adhesive layer a/release liner ].

Examples 2 to 9 and comparative examples 1 to 3

Polarizing plates with retardation layers of examples 2 to 9 were obtained in the same manner as in example 1, except that different combinations selected from positive C plates a to C were used as the second retardation layer and the fourth retardation layer. In addition, polarizing plates with retardation layers of comparative examples 1 to 7 were obtained in the same manner as in example 1 except that either one of the second retardation layer and the fourth retardation layer was not used, or only one of the second retardation layer and the fourth retardation layer selected from the positive C plates a to C was used.

Table 1 shows the combinations of positive C plates a to C used for the polarizing plates with retardation layers obtained in examples and comparative examples.

TABLE 1

< Evaluation of reflection hue >

An organic EL display device (product number "Galaxy a41" manufactured by Samsung corporation) was decomposed and an organic EL panel was taken out. The release liners were peeled off from the polarizing plates with retardation layers obtained in examples and comparative examples, and the exposed adhesive layer a was bonded to the organic EL panel to prepare measurement samples. Light was irradiated from the polarizer a side of the measurement sample using a display measurement system (manufactured by KONICAMINOLTA company, "DMS 505") to orient the angle: 0-360 degrees (15 degree scale), polar angle: the value of L x a x b x (SCE mode) was measured at 45 °. Using the obtained value of l×a×b, the reflection hue Δe00 is calculated by the following formulas (1) to (7). The maximum value of Δe00 obtained in each measurement is shown in table 2. The smaller the Δe00 value, the smaller the coloration due to reflection, and the better the reflection hue.

(1)

(2)

(3)a’＝a^*(1+G)

(4)

(5)

(6)SC＝1+0.045×C’/2

(7)

TABLE 2

As shown in table 2, with respect to the polarizing plate with a retardation layer having a polarizer, a λ/2 plate, and a λ/4 plate in this order, by disposing 1 positive C plate between the λ/2 plate and the λ/4 plate or on the side of the λ/4 plate opposite to the side on which the λ/2 plate is disposed, coloring of the reflection hue can be suppressed, and by further disposing 1 positive C plate so as to be configured as [ polarizer/λ/2 plate/positive C plate/λ/4 plate/positive C plate ], more preferable suppression of the reflection hue of coloring can be achieved.

Industrial applicability

The polarizing plate with a retardation layer according to the embodiment of the present invention is useful for an image display device, for example. As the image display device, a liquid crystal display device, an organic EL display device, and an inorganic EL display device are typically exemplified, and an organic EL display device is preferable.

Claims

1. A polarizing plate with a retardation layer, which comprises, in order, a polarizing plate comprising a polarizer, a first retardation layer, a second retardation layer, a third retardation layer and a fourth retardation layer,

The refractive index characteristics of the first phase difference layer and the third phase difference layer show a relationship in which nx > ny > nz,

The refractive index characteristics of the second phase difference layer and the fourth phase difference layer show a relationship of nz > nx=ny,

Re (550) of the first phase difference layer is 200 nm-300 nm,

Re (550) of the third phase difference layer is 120 nm-170 nm,

The angle formed by the slow axis of the first phase difference layer and the absorption axis of the polarizer is 5-25 degrees,

The angle formed by the slow axis of the third phase difference layer and the absorption axis of the polarizer is 65-85 degrees.

2. The polarizing plate with a phase difference layer according to claim 1, wherein Rth (550) of the fourth phase difference layer is-10 nm to-110 nm.

3. The polarizing plate with a phase difference layer according to claim 1, wherein Rth (550) of the fourth phase difference layer is-10 nm to-70 nm.

4. The polarizing plate with a retardation layer as claimed in claim 1, wherein Rth (550) of the second retardation layer is-20 nm to-110 nm.

5. The polarizing plate with a retardation layer as claimed in claim 1, wherein Rth (550) of the second retardation layer is-50 nm to-110 nm,

Rth (550) of the fourth phase difference layer is-10 nm to-70 nm.

6. The polarizing plate with a retardation layer according to claim 1, which is used for an organic EL display device.

7. An image display device comprising the polarizing plate with a retardation layer as claimed in any one of claims 1 to 6.