CN112859421B

CN112859421B - Polarizing plate with retardation layer and image display device

Info

Publication number: CN112859421B
Application number: CN202011236590.XA
Authority: CN
Inventors: 有贺草平; 林大辅
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2019-11-12
Filing date: 2020-11-09
Publication date: 2024-11-01
Anticipated expiration: 2040-11-09
Also published as: KR20210057666A; TW202134698A; TWI853107B; JP2021076759A; JP7382801B2; CN112859421A

Abstract

The invention provides a polarizing plate with a phase difference layer and an image display device. Provided is a polarizing plate with a phase difference layer for an image display device, which can realize a black display with a small luminance in the oblique direction and a small color shift in the oblique direction. The polarizing plate with a retardation layer of the present invention comprises: a polarizing plate including a polarizer; a first retardation layer disposed adjacent to the polarizing plate, and having refractive index characteristics exhibiting a relationship of nz > nx > ny; and a second phase difference layer disposed adjacent to the first phase difference layer, and having refractive index characteristics exhibiting a relationship of nx > ny=nz. Wherein the absorption axis of the polarizer is substantially orthogonal to the slow axis of the first phase difference layer and the absorption axis of the polarizer is substantially parallel to the slow axis of the second phase difference layer.

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 image display devices (for example, liquid crystal display devices), various optical films in which a polarizer and a phase difference film are combined are generally used for optical compensation. A circular polarizing plate as one of the above optical films can be generally manufactured by combining a polarizer with a λ/4 plate. But lambda/4 plates generally exhibit the following so-called "forward dispersion wavelength characteristics": a characteristic that the phase difference value becomes large as the wavelength becomes the short wavelength side; in addition, the dispersion wavelength characteristics thereof are generally large. Therefore, there is a problem that desired optical characteristics (for example, functions as a λ/4 plate) cannot be exhibited in a wide wavelength range. In order to avoid such a problem, a retardation film exhibiting the following so-called "reverse dispersion characteristics" has been proposed in recent years: and a dispersion wavelength characteristic in which the phase difference value becomes larger as the wavelength becomes longer. However, a retardation film exhibiting reverse dispersion characteristics has a problem in terms of cost.

In order to cope with the above-described problems, a technique of correcting the dispersion wavelength characteristics of a λ/4 plate by combining the λ/4 plate having the forward dispersion wavelength characteristics with various phase difference films has been proposed (for example, refer to patent document 1). However, these techniques have problems that the luminance in the oblique direction is not sufficiently small and the color shift in the oblique direction is large at the time of black display.

Patent document 1: japanese patent No. 3174367

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above-mentioned conventional problems, and its main object is to: provided is a polarizing plate with a phase difference layer for an image display device, which can realize a black display with a small luminance in the oblique direction and a small color shift in the oblique direction.

Means for solving the problems

The polarizing plate with a retardation layer according to an embodiment of the present invention includes: a polarizing plate including a polarizer; a first retardation layer disposed adjacent to the polarizing plate, and having refractive index characteristics exhibiting a relationship of nz > nx > ny; and a second phase difference layer disposed adjacent to the first phase difference layer, and having refractive index characteristics exhibiting a relationship of nx > ny=nz. The absorption axis of the polarizer is substantially orthogonal to the slow axis of the first phase difference layer, and the absorption axis of the polarizer is substantially parallel to the slow axis of the second phase difference layer.

In one embodiment, the laminate of the first phase difference layer and the second phase difference layer satisfies the following relationship:

Re(450)/Re(550)＞0.82

Re(650)/Re(550)＜1.18。

According to another aspect of the present invention, an image display device is provided. The image display device includes: an image display unit; and a polarizing plate with a retardation layer disposed on the visual inspection side of the image display unit.

In one embodiment, the image display device is an IPS mode liquid crystal display device.

Effects of the invention

According to the embodiment of the present invention, by disposing the first retardation layer having refractive index characteristics of nz > nx > ny and the second retardation layer having refractive index characteristics of nx > ny=nz in this order from the polarizing plate side in the polarizing plate with the retardation layer, it is possible to obtain the polarizing plate with the retardation layer of the image display device capable of realizing a black display with small luminance in the oblique direction and small color shift in the oblique direction without using the retardation film having the reverse dispersion characteristics.

Drawings

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

Fig. 2 is a color shift chart of the liquid crystal display device of embodiment 1.

Fig. 3 is a color shift chart of the liquid crystal display device of comparative example 1.

Fig. 4 is a color shift chart of the liquid crystal display device of comparative example 2.

Fig. 5 is a color shift chart of the liquid crystal display device of comparative example 3.

Symbol description

10. Polarizing plate

11. Polarizer

12. Protective layer

13. Protective layer

20. First phase difference layer

30. Second phase difference layer

100. Polarizing plate with phase difference layer

Detailed Description

Representative embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

(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 with light having a wavelength of λnm at 23 ℃. For example, "Re (550)" is the in-plane retardation measured with light having a wavelength of 550nm at 23 ℃. Re (lambda) is the concentration of the compound in the layer (film) when the thickness is set to d (nm), the formula is as follows: re (λ) = (nx-ny) ×d.

(3) Retardation in thickness direction (Rth)

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

(4) Nz coefficient

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

(5) Substantially parallel or orthogonal

"Substantially parallel" is intended to include the case of 0 ° ± 5.0 °, preferably 0 ° ± 3.0 °, further preferably 0 ° ± 1.0 °. "substantially orthogonal" is intended to include the case of 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, further preferably 90 ° ± 1.0 °. In the present specification, the term "parallel" or "orthogonal" includes a case where they are substantially parallel or orthogonal.

(6) Angle of

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

A. integral structure of polarizing plate with phase difference layer

Fig. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention. The polarizing plate 100 with a retardation layer of the example of the figure has: a polarizing plate 10, a first retardation layer 20, and a second retardation layer 30. The polarizing plate 10 includes: a polarizer 11, a first protective layer 12 disposed on one side of the polarizer 11, and a second protective layer 13 disposed on the other side of the polarizer 11. One of the first protective layer 12 and the second protective layer 13 may be omitted according to the purpose. For example, in the case where the first retardation layer 20 can also function as a protective layer for the polarizer 11, the second protective layer 13 may be omitted.

The first retardation layer 20 is typically disposed adjacent to the polarizing plate 10 as in the illustrated example. The refractive index characteristics of the first retardation layer 20 show a relationship of nz > nx > ny. The second phase difference layer 30 is typically disposed adjacent to the first phase difference layer 20 as illustrated in the example. The refractive index characteristics of the second phase difference layer 30 show a relationship of nx > ny=nz. In the present specification, "adjacently disposed" means directly laminated or laminated with only an adhesive layer (for example, an adhesive layer or an adhesive layer) interposed therebetween. That is, it means that the optical functional layer (e.g., other retardation layer) is not sandwiched between the polarizing plate 10 and the first retardation layer 20 and between the first retardation layer 20 and the second retardation layer 30. On the other hand, the illustrated configuration is merely an example, and any appropriate optical functional layer according to the purpose may be disposed between the polarizing plate 10 and the first retardation layer 20 and/or between the first retardation layer 20 and the second retardation layer 30.

The first retardation layer 20 is disposed such that its slow axis is orthogonal to the absorption axis of the polarizer 11. The second phase difference layer 30 is disposed such that its slow axis is parallel to the absorption axis of the polarizer 11. By stacking the first phase difference layer 20 and the second phase difference layer 30 each having the above-described specific refractive index characteristics in this order and setting the slow axis direction of the first phase difference layer 20 and the second phase difference layer 30 with respect to the absorption axis direction of the polarizer in this manner, it is possible to obtain a polarizing plate with a phase difference layer of an image display device that can realize a small luminance in the oblique direction and a small color shift in the oblique direction at the time of black display.

The polarizing plate with a retardation layer may further have a conductive layer or an isotropic substrate (not shown) with a conductive layer. The conductive layer or the isotropic substrate with the conductive layer is typically disposed outside the second phase difference layer 30 (opposite to the polarizing plate 10). When a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate with a phase difference layer can be applied to a so-called internal touch panel type input display device in which a touch sensor is incorporated between an image display unit (e.g., a liquid crystal unit, an organic EL unit) and the polarizing plate.

The polarizing plate with a retardation layer may further include other retardation layers. The optical characteristics (for example, refractive index characteristics, in-plane retardation, nz coefficient, photoelastic coefficient), thickness, arrangement position, and the like of the other retardation layer can be appropriately set according to the purpose.

The polarizing plate with the retardation layer may be sheet-shaped or elongated. In the present specification, "elongated" means an elongated shape having a length sufficiently long with respect to a width, and includes, for example, an elongated shape having a length of 10 times or more, preferably 20 times or more, with respect to a width. The long polarizing plate with the retardation layer may be wound in a roll.

In practice, an adhesive layer (not shown) is provided on the opposite side of the second retardation layer from the polarizing plate, and the polarizing plate with the retardation layer is made to be attachable to the image display unit. Further, it is preferable that a release film is temporarily adhered to the surface of the pressure-sensitive adhesive layer until the polarizing plate with the retardation layer is used. By temporarily adhering the release film, the adhesive layer can be protected and formed into a roll.

The total thickness of the polarizing plate with the retardation layer is preferably 20 μm to 200. Mu.m, more preferably 40 μm to 170. Mu.m, particularly preferably 50 μm to 120. Mu.m. Hereinafter, details of each layer constituting the polarizing plate with a retardation layer will be described.

B. Polarizing plate

B-1 polarizer

As the polarizer 11, any suitable polarizer may be used. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of the polarizer composed of a single-layer resin film include: a polarizer obtained by dyeing and stretching a hydrophilic polymer film such as a polyvinyl alcohol (PVA) film, a partially formalized PVA film, an ethylene-vinyl acetate copolymer partially saponified film, or the like with a dichroic substance such as iodine or a dichroic dye, a dehydrated product of PVA, a multi-functional alignment film such as a desalted product of polyvinyl chloride, or the like. In view of excellent optical characteristics, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching the film is preferably used.

The dyeing with iodine can be performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after dyeing treatment or may be performed while dyeing. Alternatively, dyeing may be performed after stretching. The PVA-based film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, and the like as necessary. For example, by immersing the PVA-based film in water before dyeing and washing with water, not only stains and anti-blocking agents on the surface of the PVA-based film can be washed away, but also swelling of the PVA-based film can be prevented to prevent uneven dyeing.

Specific examples of the polarizer obtained by using the laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, and a polarizer obtained by coating a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate. A polarizer obtained by using a laminate of a resin base material and a PVA-based resin layer formed on the resin base material can be produced, for example, by: coating a PVA-based resin solution on a resin substrate, drying the same, and forming 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, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching the laminate. Further, if necessary, the stretching may further include air-stretching the laminate at a high temperature (for example, 95 ℃ or higher) before stretching in the aqueous boric acid solution. The obtained laminate of the resin substrate and the polarizer may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the laminate of the resin substrate and the polarizer and any appropriate protective layer according to the purpose may be laminated on the peeled 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 herein by reference.

The thickness of the polarizer is preferably 15 μm or less, more preferably 1 μm to 12 μm, still more preferably 3 μm to 12 μm, particularly preferably 3 μm to 8 μm. When the thickness of the polarizer is in such a range, curling at the time of heating can be satisfactorily suppressed, and excellent durability of appearance at the time of heating can be obtained.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380nm and 780 nm. The polarizer has a single transmittance of, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. 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.

B-2. Protective layer

The protective layer 12 and the protective layer 13 (when present) are each formed of any appropriate film that can be used as a protective layer of a polarizer. Specific examples of the material that becomes the main component of the film include: cellulose resins such as cellulose Triacetate (TAC), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, polysulfone resins, polystyrene resins, polynorbornene resins, polyolefin resins, (meth) acrylic resins, acetate resins, and the like. In addition, there may be mentioned: and (meth) acrylic, urethane (meth) acrylate, epoxy, silicone-based thermosetting resins, ultraviolet-curable resins, and the like. In addition, for example, a vitreous polymer such as a siloxane polymer can be used. In addition, a polymer film described in Japanese patent application laid-open No. 2001-343529 (WO 01/37007) can also be used. As a material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain, and for example, a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be used. The polymer film may be, for example, an extrusion molded product of the above resin composition.

The polarizing plate with the retardation layer is typically disposed on the visual inspection side of the image display device as described later, and the protective layer 12 is disposed on the visual inspection side thereof. Therefore, the protective layer 12 may be subjected to surface treatments such as hard coat treatment, antireflection treatment, anti-sticking treatment, and antiglare treatment, as necessary. Further, the protective layer 12 may be subjected to a treatment (typically, a (elliptical) polarization function and an ultra-high retardation) as needed to improve the visibility when visual confirmation is performed through a polarized sunglasses. By performing such a treatment, even when the display screen is visually checked through a polarized lens such as polarized sunglasses, excellent visual check can be achieved. Therefore, the polarizing plate with the retardation layer can be applied to an image display device that can be used outdoors.

The thickness of the protective layer 12 is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and still more preferably 10 μm to 30 μm. In the case where the surface treatment is performed, the thickness of the protective layer 12 is a thickness including the thickness of the surface treatment layer.

In one embodiment, the protective layer 13 is preferably optically isotropic. In the present specification, "optically isotropic" means that the in-plane retardation Re (550) is 0nm to 10nm and the retardation Rth (550) in the thickness direction is-10 nm to +10nm. In another embodiment, the protective layer 13 may be a phase difference layer having any suitable phase difference value. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110nm to 150nm. The thickness of the protective layer 13 is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and still more preferably 10 μm to 30 μm. From the viewpoint of thickness reduction, the protective layer 13 may be omitted in one embodiment.

C. First phase difference layer

As described above, the refractive index characteristics of the first retardation layer 20 show a relationship of nz > nx > ny. A layer (film) exhibiting such refractive index characteristics is sometimes referred to as a "positive biaxial plate", "positive B plate", or the like.

The in-plane retardation Re (550) of the first retardation layer is preferably more than 0nm and 70nm or less, more preferably more than 0nm and 60nm or less, still more preferably more than 0nm and 50nm or less, and particularly preferably 10nm to 50nm. The retardation Rth (550) in the thickness direction of the first retardation layer is preferably-200 nm to-50 nm, more preferably-120 nm to-50 nm, and still more preferably-100 nm to-60 nm. The Nz coefficient of the first retardation layer is preferably-1.0 or less, more preferably-10 to-1.0, and still more preferably-8.0 to-1.6. By providing the first phase difference layer having such optical characteristics, the absorption axis of the polarizer can be appropriately compensated, and the luminance in the oblique direction at the time of black display of the image display device can be reduced. In addition, the color shift in the oblique direction can be reduced.

The thickness of the first retardation layer is preferably 1 μm to 170 μm, more preferably 2 μm to 150 μm, still more preferably 3 μm to 120 μm, particularly preferably 4 μm to 50 μm. By setting the thickness of the first retardation layer to such a range, the handleability at the time of manufacture is excellent, and the optical uniformity of the obtained image display device can be improved.

The first retardation layer may have any suitable structure. Specifically, the retardation film may be a single retardation film or a laminate of two or more retardation films which are the same or different. In the case of a laminate, the first retardation layer may include an adhesive layer or an adhesive layer for adhering two or more retardation films. Preferably, the first retardation layer is a separate retardation film. By adopting such a configuration, it is possible to reduce the deviation and unevenness of the phase difference value caused by the shrinkage stress of the polarizer and/or the heat of the light source, and to contribute to the thinning of the obtained image display device.

The optical characteristics of the retardation film may be set to any appropriate value according to the configuration of the first retardation layer. For example, when the first retardation layer is a single retardation film, the optical characteristics of the retardation film are preferably made equal to those of the first retardation layer. Therefore, the phase difference value of the adhesive layer, or the like used when laminating the phase difference film with the polarizer and/or the second phase difference layer, or the like, is preferably as small as possible.

As the retardation film, a film which is excellent in transparency, mechanical strength, thermal stability, moisture shielding property, and the like and is less likely to cause optical unevenness due to strain is preferably used. As the retardation film, a stretched film of a polymer film containing a thermoplastic resin as a main component is preferably used. As the thermoplastic resin, a polymer exhibiting negative birefringence is preferably used. By using a polymer exhibiting negative birefringence, a retardation film having refractive index ellipsoids of nz > nx > ny can be obtained simply. Here, "exhibiting negative birefringence" means that the refractive index in the stretching direction thereof becomes relatively small in the case where the polymer is oriented by stretching or the like. In other words, the refractive index in the direction perpendicular to the stretching direction is increased. Examples of the polymer exhibiting negative birefringence include polymers in which a chemical bond or a functional group having a large polarization anisotropy such as an aromatic ring or a carbonyl group is introduced into a side chain. Specifically, there can be mentioned: acrylic resins, styrene resins, maleimide resins, and the like.

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, polycyclohexyl methacrylate, and the like.

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

The maleimide-based resin can be obtained, for example, by addition polymerization of a maleimide-based monomer. Examples of the maleimide monomer 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, N- (2-cyanophenyl) maleimide and the like. The maleimide monomer is available from tokyo chemical industry co.

In the addition polymerization, the birefringence characteristics of the obtained resin can also be controlled by substitution of side chains or by subjecting the side chains to a maleimide reaction, a grafting reaction, or the like after the polymerization.

The above polymer exhibiting negative birefringence may be copolymerized with other monomers. By copolymerizing with 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 polymer exhibiting 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%. In the case where the polymer exhibiting 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 blending is performed in such a range, a polymer film excellent in toughness and molding processability can be obtained.

As the above polymer exhibiting negative birefringence, it is preferable to use: styrene-maleic anhydride copolymers, styrene-acrylonitrile copolymers, styrene- (meth) acrylate copolymers, styrene-maleimide copolymers, vinyl ester-maleimide copolymers, olefin-maleimide copolymers, and the like. These may be used singly or in combination of two or more. These polymers can exhibit high negative birefringence and are excellent in heat resistance. These polymers are available, for example, from NOVA Chemicals Japan, from the chemical industry, inc., of Sichuan, inc.

As the polymer exhibiting negative birefringence, a polymer having a repeating unit represented by the following general formula (I) is preferably also used. Such a polymer can further exhibit high 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 into which an N substituent of a maleimide-based monomer having a phenyl group having a substituent at least in the ortho position as a starting material is introduced.

In the general formula (I), R ₁～R₅ each 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 hydrogen atoms), 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 polymer exhibiting negative birefringence is not limited to the above, and for example, a cyclic olefin copolymer as disclosed in japanese patent application laid-open No. 2005-350544 or the like may be used. Furthermore, a composition containing a polymer and inorganic fine particles as disclosed in JP-A2005-156862, JP-A2005-227427, and the like can also be applied. In addition, as the polymer exhibiting negative birefringence, one kind may be used alone, or two or more kinds may be used in combination. Further, they may be modified by copolymerization, branching, crosslinking, modification of molecular terminals (or capping), stereoregularity modification, or the like.

The polymer film may contain any appropriate additive as required. Specific examples of the additives include: plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, ultraviolet absorbers, flame retardants, colorants, antistatic agents, solubilizers, crosslinking agents, tackifiers, and the like. The kind and content of the additive may be appropriately set according to the purpose. The content of the additive is typically about 3 to 10 parts by mass based on 100 parts by mass of the total solid content of the polymer film. If the content of the additive is too large, the transparency of the polymer film may be impaired or the additive may ooze out of the surface of the polymer film.

As a method for molding the polymer film, any suitable molding method can be used. For example, there may be mentioned: compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP (Fiber Reinforced Plastics, fiber reinforced plastic) molding, solvent casting, and the like. Among these, extrusion molding and solvent casting are preferably used. This is because a retardation film having high smoothness and good optical uniformity can be obtained. Specifically, the extrusion molding method is the following method: a method in which a resin composition containing the thermoplastic resin, a plasticizer, an additive, and the like is heated and melted, extruded in a thin film form on the surface of a casting roll by a T die or the like, and cooled to form a film. The solvent casting method comprises the following steps: a method in which a concentrated solution (dope) obtained by dissolving the resin composition in a solvent is defoamed, and the resin composition is uniformly cast into a film on the surface of a metallic endless belt, a rotary drum, a plastic base material, or the like, and the solvent is evaporated to form a film. The molding conditions may be appropriately set according to the composition, type, molding method, and the like of the resin used.

The retardation film (stretched film) can be obtained by stretching the polymer film under any suitable stretching conditions. Specific examples of the stretching method include: a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse successive biaxial stretching method, a longitudinal and transverse simultaneous biaxial stretching method, and the like. It is preferable to use a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, or a longitudinal and transverse simultaneous biaxial stretching method. This is because a biaxial retardation film can be obtained appropriately. In the polymer exhibiting negative birefringence, since the refractive index in the stretching direction is relatively small as described above, the polymer film has a slow axis in the conveying direction (refractive index in the conveying direction is nx) in the case of the transverse uniaxial stretching method. In the case of the longitudinal and transverse sequential biaxial stretching method and the longitudinal and transverse simultaneous biaxial stretching method, both the conveyance direction and the width direction may be slow axes depending on the ratio of the stretching ratios in the longitudinal and transverse directions. Specifically, if the stretch ratio in the longitudinal (conveying) direction is relatively increased, the transverse (width) direction becomes the slow axis; when the stretch ratio in the horizontal (width) direction is relatively increased, the vertical (conveyance) direction becomes the slow axis.

As the stretching device used for the stretching, any suitable stretching device may be used. As specific examples, there may be mentioned: a roll stretcher, a tenter stretcher, a telescopic or linear motor type biaxial stretcher, and the like. In the case of stretching while heating, the temperature may be changed continuously or gradually. The stretching step may be divided into two or more steps.

The stretching temperature (temperature in the stretching oven when stretching the polymer film) is preferably in the vicinity of the glass transition temperature (Tg) of the polymer film. Specifically, it is preferably from (Tg-10) to (Tg+30) degrees centigrade, more preferably from (Tg+25) degrees centigrade, and particularly preferably from (Tg+5) degrees centigrade to (Tg+20) degrees centigrade. If the stretching temperature is too low, there is a possibility that the retardation value, the slow axis direction becomes uneven, or crystallization (cloudiness) of the polymer film occurs. On the other hand, if the stretching temperature is too high, the polymer film may be melted or the appearance of the retardation may be insufficient. The stretching temperature is typically 110 to 200 ℃. The glass transition temperature can be determined by DSC method according to JIS K7121-1987.

The method of controlling the temperature in the stretching oven may be any suitable method. For example, a method using the following apparatus can be cited: an air circulation type constant temperature oven for circulating hot air or cold air, a heater using microwaves, far infrared rays, etc., a heated roller for temperature adjustment, a heat pipe roller, a metal belt, etc.

The stretching ratio when stretching the polymer film may be set to any appropriate value depending on the composition of the polymer film, the kind of volatile components and the like, the residual amount of volatile components and the like, the desired phase difference value and the like. Preferably 1.05 to 5.00 times. In addition, the conveying speed during stretching is preferably 0.5 m/min to 20 m/min from the viewpoints of mechanical precision, stability, and the like of the stretching apparatus.

The method of obtaining the retardation film using the polymer exhibiting negative birefringence was described above, but the retardation film may also be obtained using the polymer exhibiting positive birefringence. As a method for obtaining a retardation film using a polymer exhibiting positive birefringence, for example, a stretching method in which the refractive index in the thickness direction is increased as disclosed in japanese patent application laid-open publication No. 2000-231016, japanese patent application laid-open publication No. 2000-206328, japanese patent application laid-open publication No. 2002-207123, and the like can be used. Specifically, a method of bonding a heat-shrinkable film to one or both surfaces of a film containing a polymer exhibiting positive birefringence and performing heat treatment is exemplified. By shrinking the film by the shrinkage force of the heat-shrinkable film by the heat treatment, the film is shrunk in the longitudinal direction and the width direction, and the refractive index in the thickness direction can be increased, whereby a retardation film having refractive index ellipsoids of nz > nx > ny can be obtained.

As described above, the positive B plate used for the first retardation layer can be manufactured using a polymer exhibiting any of positive birefringence and negative birefringence. In general, in the case of using a polymer exhibiting positive birefringence, there are advantages in that the kinds of the selectable polymers are large; in the case of using a polymer exhibiting negative birefringence, there is an advantage in that a retardation film excellent in uniformity in the slow axis direction can be easily obtained due to its stretching method, compared with the case of using a polymer exhibiting positive birefringence.

As the retardation film used for the first retardation layer, a commercially available optical film may be used as it is in addition to the above-mentioned film. Further, a film obtained by subjecting a commercially available optical film to secondary processing such as stretching and/or relaxation may be used.

The transmittance of the retardation film at a wavelength of 590nm is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The theoretical upper limit of the transmittance is 100%, and the achievable upper limit of the transmittance is approximately 94% in terms of surface reflection due to the difference in refractive index between air and the retardation film. The same transmittance is also preferable for the first retardation layer as a whole.

The absolute value of the photoelastic coefficient of the retardation film is preferably 1.0X10 ^-10(m²/N) or less, more preferably 5.0X10 ^-11(m²/N) or less, still more preferably 3.0X10 ^-11(m²/N) or less, particularly preferably 1.5X10 ^-11(m²/N) or less. By setting the photoelastic coefficient to such a range, an image display device having excellent optical uniformity, little change in optical characteristics even under high-temperature and high-humidity environments, and excellent durability can be obtained. The lower limit of the photoelastic coefficient is not particularly limited, but is usually 5.0X10 ^-13(m²/N) or more, preferably 1.0X10 ^-12(m²/N) or more. If the photoelastic coefficient is too small, the performance of the phase difference may be reduced. The photoelastic coefficient is a value inherent to the chemical structure of a polymer or the like, and can be reduced by copolymerizing or mixing a plurality of components having different signs (positive and negative) of the photoelastic coefficient.

The thickness of the retardation film may be set to any appropriate value depending on the material forming the retardation film and the composition of the first retardation layer. When the first retardation layer is a single retardation film, the thickness of the first retardation layer is preferably 1 μm to 170 μm, more preferably 2 μm to 150 μm, still more preferably 3 μm to 120 μm, particularly preferably 4 μm to 50 μm. By having such a thickness, the first retardation layer having excellent mechanical strength and display uniformity can be obtained.

D. Second phase difference layer

As described above, the refractive index characteristics of the second phase difference layer 30 show a relationship of nx > ny=nz. A layer (film) exhibiting such refractive index characteristics is sometimes also referred to as a "positive uniaxial plate", "positive a plate", or the like. Here, "ny=nz" includes not only the case where ny is exactly equal to nz but also the case where ny is substantially equal to nz. Specifically, it means that the Nz coefficient exceeds 0.9 and is less than 1.1. The in-plane phase difference Re (550) of the second phase difference layer is preferably 80nm to 200nm, more preferably 100nm to 160nm, and still more preferably 110nm to 150nm. By providing the second phase difference layer having such optical characteristics, the absorption axis of the polarizer can be appropriately compensated, and the luminance in the oblique direction at the time of black display of the image display device can be reduced. In addition, the color shift in the oblique direction can be reduced.

As a material for forming the second phase difference layer, any appropriate material may be used as long as the above-described characteristics can be obtained. Specifically, the second retardation layer may be an alignment cured layer of a liquid crystal compound (liquid crystal alignment cured layer), or may be a retardation film (stretched film of a polymer film).

In the case where the second retardation layer is a liquid crystal alignment cured layer, by using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be significantly increased compared to a non-liquid crystal material, and thus the thickness of the retardation layer for obtaining a desired in-plane retardation can be significantly reduced. As a result, the polarizing plate with the retardation layer (as a result, the image display device) can be further thinned. In the present specification, the term "alignment cured layer" means a layer in which a liquid crystal compound is aligned in a predetermined direction within a 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 this embodiment, the liquid crystal compound in a typical rod shape is aligned (parallel alignment) in a state of being aligned along the slow axis direction of the second phase difference layer.

Examples of the liquid crystal compound include a liquid crystal compound having a liquid crystal phase as a nematic phase (nematic liquid crystal). As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The liquid crystalline property of the liquid crystal compound may be expressed by either a lyotropic type or a thermotropic type. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

In the case where the liquid crystal compound is a liquid crystalline monomer, for example, a polymerizable monomer and/or a crosslinkable monomer is preferable. This is because the alignment state of the liquid crystalline monomer can be fixed by polymerizing or crosslinking the liquid crystalline monomer. After the liquid crystal monomers are aligned, for example, the alignment state can be fixed by polymerizing or crosslinking the liquid crystal monomers. Here, the polymer is formed by polymerization, and a three-dimensional mesh structure is formed by crosslinking, but these are non-liquid crystalline. Therefore, the second phase difference layer formed does not undergo a transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change, which is typical of, for example, a liquid crystalline compound. As a result, the formed second phase difference layer is a phase difference layer extremely excellent in stability, which is not affected by temperature change.

Specific examples of the liquid crystal compound and details of the method for forming the liquid crystal alignment cured layer are described in, for example, japanese patent application laid-open No. 2006-163343 and Japanese patent application laid-open No. 2006-178389. The disclosures of these publications are incorporated by reference into this specification.

The second phase difference layer may be a stretched film of a polymer film as described above. Specifically, by appropriately selecting the kind of polymer, stretching conditions (for example, stretching temperature, stretching ratio, stretching direction), stretching method, and the like, a second phase difference layer having the above-described desired optical characteristics (for example, refractive index characteristics, in-plane retardation, and retardation in the thickness direction) can be obtained. More specifically, the stretching temperature is preferably 110℃to 170℃and more preferably 130℃to 150 ℃. The stretching ratio is preferably 1.37 to 1.67 times, more preferably 1.42 to 1.62 times. As the stretching method, for example, transverse uniaxial stretching can be cited.

Any suitable resin may be used as the resin for forming the polymer film. As specific examples, there may be mentioned: norbornene-based resins, polycarbonate-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polysulfone-based resins, and the like constituting the positive birefringent film. Among them, norbornene-based resins and polycarbonate-based resins are preferable.

The norbornene-based resin is a resin obtained by polymerizing a norbornene-based monomer as a polymerization unit. Examples of the norbornene monomer include: norbornene and polar group substituents such as alkyl and/or alkylidene substituents thereof, for example, 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, and halogen compounds thereof; dicyclopentadiene, 2, 3-dihydro-dicyclopentadiene, and the like; polar group substituents such as dimethylene octahydronaphthalene, alkyl and/or alkylidene substituents thereof, and halogen compounds, for example, 6-methyl-1, 4:5, 8-dimethylene-1, 4a,5,6,7,8 a-octahydronaphthalene 6-ethyl-1, 4:5, 8-dimethylene-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-ethylidene-1, 4:5, 8-dimethylene-1, 4a,5,6,7,8 a-octahydronaphthalene 6-chloro-1, 4:5, 8-dimethylene-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-cyano-1, 4:5, 8-dimethylene-1, 4a,5,6,7,8 a-octahydronaphthalene 6-pyridyl-1, 4:5, 8-dimethylene-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-methoxycarbonyl-1, 4:5, 8-dimethylene-1, 4a,5,6,7,8 a-octahydronaphthalene, and the like; trimers to tetramers of cyclopentadiene, for example 4,9:5, 8-dimethylene-3 a, 4a,5, 8a,9 a-octahydro-1H-benzindene 4,11:5,10:6, 9-trimethylene-3 a, 4a, 5a,6, 9a,10 a,11 a; dodecahydro-1H-cyclopentaanthracene, and the like. The norbornene-based resin may be a copolymer of a norbornene-based monomer and another monomer.

As the polycarbonate resin, an aromatic polycarbonate is preferably used. Aromatic polycarbonates are typically obtained by the reaction of a carbonate precursor with an aromatic dihydric phenol compound. Specific examples of the carbonate precursor include: carbonyl chloride, bischloroformates of dihydric phenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, dinaphthyl carbonate, and the like. Among these, phosgene and diphenyl carbonate are preferable. Specific examples of the aromatic dihydric phenol compound include: 2, 2-bis (4-hydroxyphenyl) propane, 2-bis (4-hydroxy-3, 5-dimethylphenyl) propane, bis (4-hydroxyphenyl) methane, 1-bis (4-hydroxyphenyl) ethane, 2-bis (4-hydroxyphenyl) butane 2, 2-bis (4-hydroxy-3, 5-dimethylphenyl) butane, 2-bis (4-hydroxy-3, 5-dipropylphenyl) propane, 1-bis (4-hydroxyphenyl) cyclohexane, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane and the like. These may be used singly or in combination of two or more. Preference is given to using 2, 2-bis (4-hydroxyphenyl) propane, 1-bis (4-hydroxyphenyl) cyclohexane, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane. Particular preference is given to using 2, 2-bis (4-hydroxyphenyl) propane together with 1, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane.

The thickness of the second phase difference layer may be set so as to obtain desired optical characteristics. When the second phase difference layer is a liquid crystal alignment cured layer, the thickness is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and still more preferably 0.5 μm to 5 μm. In the case where the second phase difference layer is a stretched film of a polymer film, the thickness is preferably 5 μm to 55 μm, more preferably 10 μm to 50 μm, still more preferably 15 μm to 45 μm.

E. laminate of first phase difference layer and second phase difference layer

The laminate of the first phase difference layer and the second phase difference layer preferably satisfies the following relationship:

Re(450)/Re(550)＞0.82

Re(650)/Re(550)＜1.18。

Re (450)/Re (550) of the laminate is more preferably 1.0 to 1.2, and still more preferably 1.0 to 1.1. Re (650)/Re (550) of the laminate is more preferably 0.8 to 1.0, and still more preferably 0.9 to 1.0. According to the embodiment of the present invention, a polarizing plate with a retardation layer of an image display device in which the luminance in the oblique direction at the time of black display is small and the color shift in the oblique direction is small can be obtained, although the first retardation layer and the second retardation layer as a whole do not exhibit ideal reverse dispersion characteristics.

F. Image display device

The polarizing plate with a retardation layer according to any one of items A to E above can be applied to an image display device. Accordingly, an embodiment of the present invention includes an image display device using such a polarizing plate with a retardation layer. As a representative example of the image display device, there may be mentioned: liquid crystal display devices, electroluminescent (EL) display devices (e.g., organic EL display devices, inorganic EL display devices). The image display device typically has: an image display unit (e.g., a liquid crystal unit, an organic EL unit, or an inorganic EL unit) and the polarizing plate with a retardation layer described in the above items a to E disposed on the visual inspection side of the image display unit. The polarizing plate with the retardation layer is laminated such that the second retardation layer 30 is on the image display unit side (such that the polarizing plate 10 is on the visual inspection side). In one embodiment, the image display device is a liquid crystal display device, preferably an IPS mode liquid crystal display device. In such a liquid crystal display device, the effect of the polarizing plate with a retardation layer according to the embodiment of the present invention is remarkable.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The measurement method of each characteristic is as follows.

(1) Determination of phase difference value

The in-plane retardation of the first retardation layer and the second retardation layer used in examples and comparative examples was automatically measured by using the prince measurement KOBRA-WPR. The measurement wavelength was 550nm and the measurement temperature was 23 ℃.

(2) Brightness at black display

The liquid crystal display devices obtained in examples and comparative examples were displayed with black images, and the black images were measured by the product name "Conoscope" manufactured by AUTRONIC MELCHERS. Specifically, the brightness was measured by changing the direction angle in the range of 0 ° to 360 ° in the direction of the polar angle 60 °. The ratio of the maximum luminance to the luminance in the front direction among the measured luminances was set as the luminance in the present evaluation.

(3) Color shift

The liquid crystal display devices obtained in examples and comparative examples were measured for color tone by changing the direction angle in the direction of the polar angle 60 ° from 0 ° to 360 ° using the product name "EZ Contrast160D" manufactured by ELDIM corporation, and were plotted on an XY chromaticity diagram.

Example 1

1. Manufacture of polarizer

1-1 Manufacture of polarizer

As the thermoplastic resin substrate, an amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long shape, a water absorption of 0.75% and a Tg of about 75℃was used. One side of the resin base material was subjected to corona treatment.

Polyvinyl alcohol (polymerization degree: 4200, saponification degree: 99.2 mol%) and acetoacetyl-modified PVA (product name: GOHSEFIMER Z410,410, manufactured by the chemical industry Co., ltd.) were mixed in a ratio of 9:1 to 100 parts by mass of the PVA-based resin mixed in the above step, 13 parts by mass of potassium iodide was added, and the resultant 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 obtained laminate was subjected to free-end uniaxial stretching to 2.4 times in the longitudinal direction (length direction) between rolls having different peripheral speeds in an oven at 130 ℃.

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

Next, 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 mass of water) at a liquid temperature of 30 ℃, the resulting polarizer was immersed for 60 seconds while adjusting the concentration so that the monomer transmittance (Ts) of the resulting polarizer became a predetermined value (dyeing treatment).

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

Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4.0 wt% and potassium iodide concentration: 5.0 wt%) at a liquid temperature of 70 ℃ and uniaxially stretched (in-water stretching treatment) between rolls having different peripheral speeds so that the total stretching ratio became 5.5 times in the longitudinal direction (longitudinal direction).

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

Thereafter, the resultant was dried in an oven maintained at 90℃and then brought into contact with a SUS-made heating roller maintained at a surface temperature of 75℃for about 2 seconds (drying shrinkage treatment). The shrinkage in the width direction of the laminate due to the drying shrinkage treatment was 5.2%.

Thus, a polarizer having a thickness of 5 μm was formed on the resin substrate.

1-2 Production of polarizing plate

An acrylic film (surface refractive index: 1.50, 40 μm) was bonded to the surface (surface opposite to the resin substrate) of the polarizer obtained as described above as a protective layer via an ultraviolet curable adhesive. Specifically, the cured adhesive was coated so that the total thickness of the cured adhesive became 1.0 μm, and bonded by a roll machine. Thereafter, UV light is irradiated from the protective layer side to cure the adhesive. Then, the both ends were slit, and then the resin base material was peeled off, to obtain a long polarizing plate having a configuration of a protective layer/polarizer. The obtained polarizing plate was punched out to a size corresponding to a liquid crystal cell described later.

2. Fabrication of first phase difference layer

Using a single screw extruder and a T-die, a pellet-shaped resin of a styrene-maleic anhydride copolymer (NOVA Chemicals Japan manufactured by the product name "DYLARKD 232") was extruded at 270 ℃ to cool the sheet-shaped molten resin with a cooling drum, thereby obtaining a film having a thickness of 100 μm. The film was subjected to free-end uniaxial stretching in the conveying direction at a stretching ratio of 1.6 times at a temperature of 130 ℃ using a roll stretcher, whereby a film having a fast axis in the conveying direction was obtained (longitudinal stretching step).

The obtained film was subjected to fixed-end uniaxial stretching in the width direction at 135 ℃ using a tenter stretching machine so that the film width became 1.6 times the film width after the above longitudinal stretching, thereby obtaining a biaxially stretched film having a thickness of 50 μm (transverse stretching step).

The retardation film thus obtained had a fast axis in the transport direction (a slow axis in the width direction), and refractive index characteristics showed a relationship of nz > nx > ny, with an in-plane retardation Re (550) of 37nm, a retardation Rth (550) in the thickness direction of-90 nm, and an nz coefficient of-2.4. The obtained retardation film (positive B plate) was punched out to a size corresponding to a liquid crystal cell described later as a first retardation layer. Here, the punching is performed such that the absorption axis of the polarizer of the polarizing plate is orthogonal to the slow axis of the first retardation layer.

3. Fabrication of second phase difference layer

A long norbornene resin film (product name: zeonor, manufactured by Zeon Co., ltd., thickness: 40 μm, photoelastic coefficient: 3.10X10 ^-12m²/N) was uniaxially stretched at 140℃to 1.52 times, whereby a long film having a thickness of 35 μm was produced. The retardation film thus obtained had a slow axis in the transport direction, and refractive index characteristics exhibited a relationship of nz > nx=ny, with an in-plane retardation Re (550) of 135nm and a retardation Rth (550) in the thickness direction of 135nm. The obtained retardation film (positive a plate) was punched out to a size corresponding to a liquid crystal cell described later as a second phase difference layer. Here, the punching is performed such that the absorption axis of the polarizer of the polarizing plate and the slow axis of the second phase difference layer become parallel.

4. Production of polarizing plate with retardation layer

The polarizing plate a with a retardation layer having a structure of polarizing plate/first retardation layer (positive B plate)/second retardation layer (positive a plate) was obtained by sequentially laminating the polarizing plate obtained as described above, the first retardation layer, and the second retardation layer with an acrylic adhesive (thickness: 12 μm) interposed therebetween. In the polarizing plate with the phase difference layer, the absorption axis of the polarizer of the polarizing plate is orthogonal to the slow axis of the first phase difference layer, and the absorption axis of the polarizer is parallel to the slow axis of the second phase difference layer.

5. Fabrication of liquid crystal display device

The liquid crystal cell was removed from "iPad Pro" (an IPS mode liquid crystal cell was mounted thereon) manufactured by Apple corporation, and the polarizing plate a with a retardation layer was attached to the visual inspection side of the liquid crystal cell via an acrylic adhesive (thickness 20 μm). Here, the polarizing plate a with a retardation layer is attached so that the second retardation layer is on the liquid crystal cell side. A commercially available polarizing plate (NPF-SIG 1423DU manufactured by Nito electric company) was attached to the back surface side of the liquid crystal cell via an acrylic pressure-sensitive adhesive (thickness: 20 μm). Here, the polarizer is attached such that the absorption axis of the polarizer is orthogonal to the absorption axis of the polarizer a with the retardation layer. A liquid crystal display device was manufactured by assembling a normal backlight unit or the like to the liquid crystal panel thus obtained. The brightness of the obtained liquid crystal display device was 0.60. The results are shown in table 1 together with the constitution of the polarizing plate with the retardation layer. Further, fig. 2 shows the color shift of the obtained liquid crystal display device.

Comparative example 1

A polarizing plate B with a retardation layer having a constitution of a polarizing plate/a first retardation layer (positive B plate)/a second retardation layer (positive a plate) was obtained in the same manner as in example 1, except that the polarizing plate was laminated so that the absorption axis of the polarizer and the slow axis of the first retardation layer were parallel. A liquid crystal display device was obtained in the same manner as in example 1, except that a polarizing plate B with a retardation layer was used. The brightness of the obtained liquid crystal display device was 0.69. The results are shown in table 1 together with the constitution of the polarizing plate with the retardation layer. Further, fig. 3 shows the color shift of the obtained liquid crystal display device.

Comparative example 2

A polarizing plate C with a retardation layer having a constitution of a polarizing plate/a positive B plate/a positive a plate was obtained in the same manner as in example 1, except that the lamination order of the positive a plate and the positive B plate was reversed. A liquid crystal display device was obtained in the same manner as in example 1, except that a polarizing plate C with a retardation layer was used. The brightness of the obtained liquid crystal display device was 15.36. The results are shown in table 1 together with the constitution of the polarizing plate with the retardation layer. Further, fig. 4 shows the color shift of the obtained liquid crystal display device.

Comparative example 3

A polarizing plate D with a retardation layer having a structure of a polarizing plate/a positive B plate/a positive a plate was obtained in the same manner as in comparative example 2, except that the polarizing plate was laminated so that the absorption axis of the polarizer of the polarizing plate was orthogonal to the slow axis of the positive a plate. A liquid crystal display device was obtained in the same manner as in example 1, except that a polarizing plate D with a retardation layer was used. The brightness of the obtained liquid crystal display device was 0.76. The results are shown in table 1 together with the constitution of the polarizing plate with the retardation layer. Further, fig. 5 shows the color shift of the obtained liquid crystal display device.

TABLE 1

As is apparent from table 1 and fig. 2 to 5, the liquid crystal display device according to the example of the present invention is excellent in both brightness and color shift as compared with the liquid crystal display device according to the comparative example.

Industrial applicability

The polarizing plate with a retardation layer according to the embodiment of the present invention is applicable to an image display device, and particularly to a liquid crystal display device.

Claims

1. A polarizing plate with a retardation layer, comprising:

a polarizing plate including a polarizer;

A first retardation layer disposed adjacent to the polarizing plate, and having refractive index characteristics exhibiting a relationship of nz > nx > ny; and

A second phase difference layer disposed adjacent to the first phase difference layer and having refractive index characteristics exhibiting a relationship of nx > ny=nz,

Wherein the absorption axis of the polarizer is substantially orthogonal to the slow axis of the first phase difference layer,

The absorption axis of the polarizer is substantially parallel to the slow axis of the second phase difference layer.

2. The polarizing plate with a phase difference layer according to claim 1, wherein a laminate of the first phase difference layer and the second phase difference layer satisfies the following relationship:

Re(450)/Re(550)＞0.82

Re(650)/Re(550)＜1.18。

3. An image display device, comprising: an image display unit; the polarizing plate with a retardation layer according to claim 1 or 2 disposed on the visual inspection side of the image display unit.

4. The image display device according to claim 3, which is an IPS mode liquid crystal display device.