JP7680963B2 - Polarizing plate with phase difference layer and image display device - Google Patents

Description

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

In image display devices (e.g., liquid crystal display devices, organic EL display devices, quantum dot display devices), a polarizing plate is often arranged on at least one side of the image display cell due to the image formation method. In the polarizing plate arranged on the viewing side of the image display device, a retardation film may be laminated on the image display cell side for the purpose of preventing external light reflection and background reflection, improving color tone, etc. (polarizing plate with retardation layer). As image display devices become thinner, there is a strong demand for thinner polarizing plates with retardation layer. In order to meet such demands, efforts are being made to make polarizers thinner. However, polarizing plates with retardation layer, including thin polarizers, are difficult to handle, and for example, damage marks (typically, numerous fine cracks in a certain area) may occur due to external forces caused by handling errors by workers.

JP 2013-200445 A

The present invention has been made to solve the above problems, and its main objective is to provide a polarizing plate with a retardation layer in which damage marks are suppressed.

The polarizing plate with a retardation layer according to the embodiment of the present invention includes a polarizing plate including a polarizer and a protective layer on at least the viewing side of the polarizer, and a retardation layer bonded to the opposite side of the polarizing plate from the viewing side via an adhesive layer, the polarizer having a thickness of 12 μm or less, and the adhesive layer having a remaining depth of 11 μm or less when a load of 3 N is applied.
In one embodiment, the pressure-sensitive adhesive layer has a thickness of 6 μm to 15 μm.
In one embodiment, the thickness of the protective layer on the viewing side is 30 μm or more.
In one embodiment, the retardation layer exhibits refractive index characteristics of nx>nz>ny. In one embodiment, the retardation layer has an Nz coefficient of 0.3 to 0.7. In one embodiment, the retardation layer has an in-plane retardation Re(550) of 250 nm to 350 nm, a thickness of 150 μm or less, and a photoelastic coefficient of 1.0×10 ⁻¹² m ² /N or more. In one embodiment, the retardation layer contains a cyclic olefin resin.
In one embodiment, the angle between the slow axis of the retardation layer and the absorption axis of the polarizer is substantially perpendicular or substantially parallel.
According to another aspect of the present invention, there is provided an image display device, the image display device including the above-mentioned retardation layer-attached polarizing plate.

According to an embodiment of the present invention, in a polarizing plate with a phase difference layer including a thin polarizer, by using an adhesive layer having a specific residual depth, it is possible to realize a polarizing plate with a phase difference layer in which damage marks are suppressed.

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

The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

(Definition of terms and symbols)
The definitions of terms and symbols used in this specification are as follows.
(1) Refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction.
(2) In-plane phase difference (Re)
"Re(λ)" is the in-plane retardation measured with light having a wavelength of λ nm at 23° C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23° C. Re(λ) is calculated by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Retardation in the thickness direction (Rth)
"Rth(λ)" is the retardation in the thickness direction measured with light having a wavelength of λ nm at 23° C. For example, "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23° C. Rth(λ) is calculated by the formula: Rth(λ)=(nx-nz)×d, where d (nm) is the thickness of the layer (film).
(4) Nz Coefficient The Nz coefficient is calculated by Nz=Rth/Re.
(5) Angle When referring to an angle in this specification, the angle includes both clockwise and counterclockwise angles with respect to a reference direction. Thus, for example, "45°" means ±45°.
(6) Substantially perpendicular or substantially parallel In this specification, the expressions "substantially perpendicular" and "approximately perpendicular" include the case where the angle between two directions is 90°±7°, preferably 90°±5°, and more preferably 90°±3°. The expressions "substantially parallel" and "approximately parallel" include the case where the angle between two directions is 0°±7°, preferably 0°±5°, and more preferably 0°±3°. Furthermore, when simply referring to "orthogonal" or "parallel" in this specification, it is understood that it can include a substantially perpendicular or substantially parallel state.

A. Overall configuration of a retardation layer-attached polarizing plate FIG. 1 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. The retardation layer-attached polarizing plate 100 of the illustrated example has a polarizing plate 10 and a retardation layer 30. The polarizing plate 10 includes a polarizer 11 and a protective layer (viewing-side protective layer) 12 on at least the viewing side of the polarizer 11. In the illustrated example, only the viewing-side protective layer 12 is provided, but another protective layer (inner protective layer) may be provided on the opposite side to the viewing side. The retardation layer 30 is attached to the opposite side to the viewing side of the polarizing plate 10 via a pressure-sensitive adhesive layer 20. The retardation layer 30 has an in-plane retardation and therefore has a slow axis. The angle between the slow axis of the retardation layer 30 and the absorption axis of the polarizer 11 is typically substantially perpendicular or substantially parallel. For practical purposes, another adhesive layer (not shown) is provided on the side of the retardation layer 30 opposite the polarizing plate 10 (i.e., as the outermost layer opposite the viewing side), so that the retardation layer-attached polarizing plate can be attached to an image display cell. Furthermore, it is preferable that a separator (not shown) is temporarily attached to the surface of the other adhesive layer until the retardation layer-attached polarizing plate is used. By temporarily attaching the separator, the other adhesive layer is protected and the retardation layer-attached polarizing plate can be formed into a roll.

In an embodiment of the present invention, the adhesive layer 20 has a residual depth of 11 μm or less, preferably 10.8 μm or less, when a load of 3 N is applied. The smaller the residual depth, the more preferable, and the lower limit thereof may be, for example, 10 μm. The residual depth can be measured, for example, as follows: (1) The adhesive sheet is attached onto a glass plate; (2) The surface of the adhesive sheet is scratched while increasing the load using a microload automatic scratch tester. (3) The indentation depth when scratched with a load of 3 N is measured using a displacement sensor, and this is taken as the residual depth. By optimizing the residual depth of the adhesive layer, damage marks (typically, numerous fine cracks within a certain area) can be significantly suppressed. Damage marks are typically caused by external factors (e.g., impact and/or pressing force) resulting from handling errors by the operator. Furthermore, in a retardation layer-attached polarizing plate having an adhesive layer on one side of the polarizer, damage marks typically occur on the polarizer. Damage marks are prominent in thin polarizers, and are even more prominent in polarizing plates with retardation layers for large image display devices (e.g., televisions) that are more difficult to handle. The present inventors have found that damage marks, which appear to be a collection of fine cracks at first glance, have a completely different cause from cracks, and therefore damage marks cannot be suppressed by crack suppression measures (e.g., adjusting the storage modulus of the adhesive layer). As a result of trial and error, they have found that optimizing the remaining depth (i.e., the degree of return after loading an external force on the adhesive layer) is effective. In other words, the effect of suppressing damage marks by optimizing the remaining depth solves the newly discovered problem of damage marks, and is an unexpectedly excellent effect obtained by trial and error in response to the problem.

In an embodiment of the present invention, the thickness of the polarizer 11 is 12 μm or less. As described above, damage marks are prominent in thin polarizers and are essentially a problem specific to thin polarizers, but according to an embodiment of the present invention, such a problem can be solved.

The retardation layer-attached polarizing plate 100 may further have any appropriate functional layer on the side of the retardation layer 30 opposite the polarizer 10 (image display cell side) according to the purpose (not shown). Representative examples of functional layers include another retardation layer and a conductive layer. The type, number, combination, arrangement position, and characteristics of the functional layer (for example, the optical characteristics of the other retardation layer: specifically, the refractive index characteristics, in-plane retardation, thickness direction retardation, and Nz coefficient) can be appropriately set according to the purpose. By further having a conductive layer, the retardation layer-attached polarizing plate can be suitably used in an inner touch panel type input display device.

The components of a polarizing plate with a retardation layer are described in more detail below.

B. Polarizing Plate B-1. Polarizer The polarizer 11 is typically made of a resin film containing a dichroic material.

As the resin film, any suitable resin film that can be used as a polarizer can be adopted. The resin film is typically a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") film.

Any suitable resin can be used as the PVA-based resin forming the PVA-based resin film. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined in accordance with JIS K 6726-1994. By using a PVA-based resin with such a saponification degree, a polarizer with excellent durability can be obtained. If the saponification degree is too high, there is a risk of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined in accordance with JIS K 6726-1994.

Examples of dichroic substances contained in the resin film include iodine and organic dyes. These can be used alone or in combination of two or more. Iodine is preferably used.

The resin film may be a single-layer resin film or a laminate of two or more layers.

Specific examples of polarizers made of a single-layer resin film include a PVA-based resin film that has been dyed with iodine and stretched (typically, uniaxially stretched). The above-mentioned dyeing with iodine is performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the above-mentioned uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing process or while dyeing. Alternatively, the film may be stretched and then dyed. If necessary, the PVA-based resin film may be subjected to a swelling process, a crosslinking process, a cleaning process, a drying process, or the like. For example, by immersing the PVA-based resin film in water and washing it before dyeing, not only can dirt and antiblocking agents on the surface of the PVA-based film be washed off, but the PVA-based resin film can also be swelled to prevent uneven dyeing.

Specific examples of polarizers obtained using a laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to a resin substrate and drying the substrate to form a PVA-based resin layer on the resin substrate to obtain a laminate of a resin substrate and a PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer into a polarizer. In this embodiment, stretching typically includes immersing the laminate in an aqueous solution of boric acid and stretching it. Furthermore, stretching may further include air-stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the aqueous solution of boric acid, as necessary. The obtained laminate of resin substrate/polarizer may be used as it is (i.e., 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 resin substrate/polarizer, and any suitable protective layer according to the purpose may be laminated on the peeled surface. Details of the method for producing such a polarizer are described in, for example, JP2012-73580A and Japanese Patent No. 6470455. The entire disclosures of these publications are incorporated herein by reference.

As described above, the thickness of the polarizer is 12 μm or less, preferably 1 μm to 12 μm, more preferably 3 μm to 10 μm, and even more preferably 3 μm to 8 μm. If the thickness of the polarizer is within this range, curling during heating can be effectively suppressed, and good appearance durability during heating can be obtained.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is, 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 even more preferably 99.9% or more.

B-2. Protective layer The viewing side protective layer 12 and the inner protective layer (if present) are each formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that are the main components of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylics, and acetates. In addition, thermosetting resins or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxy resins, and silicones are also included. In addition, glassy polymers such as siloxane polymers are also included. In addition, polymer films described in JP-A-2001-343529 (WO01/37007) can also be used. As the material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, for example, a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrusion molded product of the above resin composition.

The polarizing plate with a retardation layer is typically placed on the viewing side of an image display device, and the viewing-side protective layer 12 is typically placed on the viewing side. Therefore, the viewing-side protective layer 12 may be subjected to surface treatments such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment, as necessary. Furthermore, the protective layer 12 may be subjected to treatments (typically, imparting an (elliptical) polarization function, imparting an ultra-high phase difference) to improve visibility when viewed through polarized sunglasses, as necessary. By performing such treatments, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the polarizing plate with a retardation layer can be suitably applied to image display devices that can be used outdoors.

The thickness of the viewer-side protective layer is preferably 30 μm or more, more preferably 30 μm to 100 μm, and even more preferably 30 μm to 60 μm. If the thickness of the protective layer is in this range, damage marks can be more significantly suppressed due to the synergistic effect with the remaining depth of the adhesive layer. Note that, when the viewer-side protective layer is surface-treated to form a surface treatment layer, the thickness of the viewer-side protective layer includes the thickness of the surface treatment layer.

The inner protective layer (if present) is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re (550) is 0 nm to 10 nm, and the retardation in the thickness direction Rth (550) is -10 nm to +10 nm. The thickness of the inner protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and even more preferably 10 μm to 30 μm. From the viewpoint of thinning, the protective layer may preferably be omitted. In the embodiment of the present invention, the retardation layer 30 preferably doubles as the inner protective layer.

C. Adhesive Layer Any suitable adhesive may be used as the adhesive forming the adhesive layer 20 as long as it achieves the desired remaining depth. Examples of the base resin of the adhesive include acrylic resin, styrene resin, silicone resin, urethane resin, and rubber resin. Acrylic resin is preferred from the viewpoints of chemical resistance, adhesion to prevent the infiltration of the treatment liquid during immersion, and flexibility to the adherend. That is, the adhesive layer 20 may be preferably composed of an acrylic adhesive (acrylic adhesive composition). The acrylic adhesive composition typically contains a (meth)acrylic polymer as a main component. The (meth)acrylic polymer may be contained in the adhesive composition at a ratio of, for example, 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more of the solid content of the adhesive composition. The (meth)acrylic polymer contains an alkyl (meth)acrylate as a main component as a monomer unit. Note that (meth)acrylate refers to acrylate and/or methacrylate. Examples of the alkyl group of the alkyl (meth)acrylate include linear or branched alkyl groups having 1 to 18 carbon atoms. The average number of carbon atoms in the alkyl group is preferably 3 to 9, more preferably 3 to 6. Examples of monomers constituting the (meth)acrylic polymer include, in addition to the alkyl (meth)acrylate, carboxyl group-containing monomers (e.g., (meth)acrylic acid), hydroxyl group-containing monomers (e.g., hydroxyethyl acrylate), amide group-containing monomers (e.g., acrylamide), aromatic ring-containing (meth)acrylates (e.g., benzyl acrylate), heterocyclic ring-containing (meth)acrylates (e.g., acryloylmorpholine), and (meth)acrylates having a bridged ring structure (e.g., dicyclopentanyl (meth)acrylate). The (meth)acrylic polymer preferably has a carboxyl group-containing monomer unit and a hydroxyl group-containing monomer unit. The content of the carboxyl group-containing monomer unit in the (meth)acrylic polymer is preferably 3% by weight to 7% by weight, and the content of the hydroxyl group-containing monomer unit is preferably 0.05% by weight to 0.1% by weight. With such a configuration, the desired remaining depth of the adhesive layer can be realized. The acrylic adhesive composition may preferably contain a silane coupling agent and/or a crosslinking agent. Examples of the silane coupling agent include an epoxy group-containing silane coupling agent. Examples of the crosslinking agent include an isocyanate-based crosslinking agent and a peroxide-based crosslinking agent. By using a suitable combination of the monomer unit of the (meth)acrylic polymer, the silane coupling agent, and the crosslinking agent, an acrylic adhesive (and, as a result, an adhesive layer) having the desired properties can be obtained. Details of the pressure-sensitive adhesive layer or the acrylic pressure-sensitive adhesive composition are described in, for example, JP 2007-138147 A, JP 2016-190996 A, and JP 2018-028573 A, the disclosures of which are incorporated herein by reference.

The thickness of the adhesive layer 20 is preferably 6 μm to 25 μm, more preferably 6 μm to 15 μm, and even more preferably 10 μm to 15 μm. If the thickness of the adhesive layer is in this range, air bubbles can be suppressed when the polarizer and the retardation layer are bonded together.

The creep value of the adhesive layer 20 is preferably 30 μm/h to 50 μm/h, more preferably 35 μm/h to 45 μm/h. If the creep value of the adhesive layer is in such a range, damage marks can be significantly suppressed. The creep value can be measured, for example, as follows. An adhesive composition is applied to the protective layer of a polarizing plate including a protective layer and a polarizer to form an adhesive layer, and an adhesive layer-attached polarizing plate is produced. The produced polarizing plate is cut to a width of 10 mm x length of 50 mm. Of the cut adhesive layer-attached polarizing plate, a portion of width 10 mm x length 10 mm is attached to a stainless steel plate via the adhesive layer, and then treated in an autoclave (50°C, 5 atm) for 15 minutes, and then left at room temperature for 1 hour. After leaving it, a load (tensile load) of 500 g is applied to the end of the adhesive layer-attached polarizing plate on the side that is not attached to the stainless steel plate at 23°C for 1 hour, and the amount of displacement (deformation) of the adhesive layer after the load is applied is measured using a laser creep tester, thereby allowing the creep value of the adhesive layer to be measured.

D. Retardation Layer The retardation layer 30 has an in-plane retardation and a slow axis as described above. Also, as described above, the retardation layer serves as both a protective layer for the polarizer and a retardation layer (or an optical compensation layer). This configuration eliminates the need to provide a protective layer and an optical compensation layer separately, which can greatly contribute to making the image display device thinner. The in-plane retardation Re (550) of the retardation layer is preferably 250 nm to 350 nm, more preferably 270 nm to 330 nm, and even more preferably 290 nm to 310 nm. If the in-plane retardation Re (550) of the retardation layer is in this range, the movement distance on the Poincaré sphere is short, so that excellent hue and luminance characteristics are realized, and the color shift of the image display panel and the deviation due to the retardation component of the TFT are also reduced.

The retardation layer preferably has a refractive index characteristic that satisfies the relationship nx>nz>ny. When the retardation layer has such a refractive index characteristic, the hue in the diagonal direction of the image display device to which the retardation layer-attached polarizing plate is applied can be improved. Furthermore, such improvement in the hue in the diagonal direction can be achieved without separately providing the retardation layer and a layer that performs optical compensation in the diagonal direction, which can contribute to making the retardation layer-attached polarizing plate (and, as a result, the image display device) thinner.

The Nz coefficient of the retardation layer is preferably 0.3 to 0.7, more preferably 0.4 to 0.6, and even more preferably 0.45 to 0.55. If the Nz coefficient is in this range, the hue in the oblique direction can be further improved.

The retardation layer may exhibit an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light, may exhibit a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or may exhibit a flat wavelength dispersion characteristic in which the retardation value changes very little depending on the wavelength of the measurement light. The retardation layer typically exhibits a flat wavelength dispersion characteristic.

The absolute value of the photoelastic coefficient of the retardation layer is preferably 15×10 ⁻¹² m ² /N or less, more preferably 10×10 ⁻¹² m ² /N or less. The lower limit of the absolute value of the photoelastic coefficient can be, for example, 1.0×10 ⁻¹² m ² /N. When the absolute value of the photoelastic coefficient of the retardation layer is in such a range, display unevenness of the image display device can be suppressed well.

The retardation layer is typically a retardation film formed of any suitable resin capable of realizing the above characteristics. Examples of resins forming this retardation film include cyclic olefin resins, polyarylates, polyamides, polyimides, polyesters, polyaryletherketones, polyamideimides, polyesterimides, polyvinyl alcohols, polyfumaric acid esters, polyethersulfones, polysulfones, polycarbonate resins, cellulose resins, and polyurethanes. These resins may be used alone or in combination. Cyclic olefin resins are preferred. A typical example of a cyclic olefin resin is a norbornene resin.

The norbornene-based resin is a resin polymerized using norbornene-based monomers as polymerization units. Examples of the norbornene-based monomers include norbornene and its alkyl and/or alkylidene substituted derivatives, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, and polar group substituted derivatives thereof, such as halogen; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, and the like; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, and the like; Octahydronaphthalene, its alkyl and/or alkylidene substituted derivatives, and polar group substituted derivatives such as halogen, for example, 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7 ,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene cyclopentadiene trimers and tetramers such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene and 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene. The norbornene-based resin may be a copolymer of a norbornene-based monomer and another monomer.

The retardation layer (retardation film) is a stretched film formed from the above resin. Any appropriate method can be used to produce the stretched film. A typical example is a method in which a shrinkable film is attached to one or both sides of a resin film and then heated and stretched. The shrinkable film is used to impart a shrinkage force in a direction perpendicular to the stretching direction during heat stretching. By imparting such a shrinkage force, nz can be increased, and as a result, a Z film can be produced. Examples of materials used for the shrinkable film include polyester, polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, etc. Polypropylene film is preferably used because of its excellent shrink uniformity and heat resistance.

As the stretching method, any suitable stretching method can be adopted as long as it can impart tension in the stretching direction of the resin film and a shrinkage force in a direction perpendicular to the stretching direction in the film plane. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the resin film. This is because the retardation value of the resulting stretched film is likely to be uniform, and the film is less likely to crystallize (become cloudy). The stretching temperature is more preferably Tg+1°C to Tg+30°C of the polymer film, even more preferably Tg+2°C to Tg+20°C, particularly preferably Tg+3°C to Tg+15°C, and most preferably Tg+5°C to Tg+10°C. By setting the stretching temperature in such a range, uniform heating and stretching can be performed. Furthermore, it is preferable that the stretching temperature is constant in the film width direction. This is because a stretched film having good optical uniformity with small variation in retardation value can be produced.

The stretching ratio during the above stretching can be set to any appropriate value. It is preferably 1.05 to 2.00 times, more preferably 1.10 to 1.50 times, and particularly preferably 1.20 to 1.40 times. By setting the stretching ratio within such a range, a stretched film with little shrinkage in the film width and excellent mechanical strength can be obtained.

The thickness of the retardation layer is preferably 80 μm to 200 μm, more preferably 90 μm to 150 μm, and even more preferably 110 μm to 150 μm. With such a thickness, the desired in-plane retardation value can be obtained.

E. Image display device The retardation layer-attached polarizing plate according to the embodiment of the present invention can be applied to an image display device. Typically, the retardation layer-attached polarizing plate is disposed on the viewing side of the image display device so that the polarizing plate is on the viewing side. Representative examples of the image display device include a liquid crystal display device, an organic electroluminescence (EL) display device, and a quantum dot display device. A liquid crystal display device is preferred, and an IPS mode liquid crystal display device is more preferred. This is because the hue improvement in the oblique direction is more significant. The image display device is preferably large (for example, for a television of 27 inches or more). This is because the effect of suppressing damage marks by optimizing the remaining depth of the adhesive layer is significant.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The evaluation methods in the examples are as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) Residual Depth An adhesive sheet was formed from the adhesive prepared in the manufacturing example. The adhesive sheet obtained was attached onto a glass plate, and the surface of the adhesive sheet was scratched with increasing load using a microload automatic scratch tester. The indentation depth when scratched with a load of 3N was measured with a displacement sensor, and this was taken as the residual depth.
(2) Damage marks The polarizing plates with retardation layers obtained in the examples and comparative examples were cut into a length of 50 mm and a width of 25 mm to be used as measurement samples. The measurement samples were attached to a glass plate via a normal acrylic adhesive (corresponding to another adhesive layer). A guitar pick with a weight attached was pressed against the adhesive sheet of the measurement sample attached to the glass plate with a load of 3N, and in this state, the guitar pick was moved back and forth in the longitudinal direction using a sliding tester. The number of times of reciprocation was 1, 5, 10, 50, and 70. The measurement samples were then placed in an oven at 95°C for 1 hour. The measurement samples taken out of the oven were checked for the presence or absence of damage marks using a microscope and evaluated according to the following criteria.
Excellent: No damage marks were observed even after 70 round trips. Good: No damage marks were observed after 50 round trips, but were observed after 70 round trips. Poor: No damage marks were observed after 10 round trips, but were observed after 50 round trips. Poor: Damage marks were observed after 1, 5, or 10 round trips. (3) Appearance The polarizing plates with retardation layers obtained in the Examples and Comparative Examples were visually observed for the state of air bubbles between the polarizer and the retardation layer during production (when the polarizer and the retardation layer were bonded together), and evaluated according to the following criteria.
Good: No air bubbles were found. Acceptable: A small amount of air bubbles were found, but not to the extent that they affected the display characteristics. Unacceptable: Air bubbles were found to the extent that they could affect the display characteristics. Appearance evaluation was performed as a secondary evaluation.

[Production Example 1: Preparation of adhesive constituting adhesive layer]
A solution was prepared by adding 100 parts of butyl acrylate, 5 parts of acrylic acid, 0.075 parts of 2-hydroxyethyl acrylate, and 0.3 parts of 2,2'-azobisisobutyronitrile together with ethyl acetate to a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer, and a stirrer. Next, the solution was stirred while blowing in nitrogen gas and reacted at 60°C for 4 hours to obtain a solution containing an acrylic polymer having a weight average molecular weight of 2.2 million. Furthermore, ethyl acetate was added to the solution containing the acrylic polymer to adjust the solid content concentration to 30%, to obtain an acrylic polymer solution (A1).
0.6 parts of a crosslinking agent mainly composed of a compound having an isocyanate group (manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate L") as a crosslinking agent and 0.075 parts of γ-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KMB-403") as a silane coupling agent were mixed in this order relative to 100 parts of the solid content of the obtained acrylic polymer solution (A1) to prepare adhesive A. The remaining depth of the adhesive layer (adhesive sheet) formed from adhesive A was 10.7 mm.

[Production Example 2: Preparation of adhesive constituting adhesive layer]
In a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer and a stirrer, 99 parts of butyl acrylate, 1.0 parts of 4-hydroxybutyl acrylate and 0.3 parts of 2,2'-azobisisobutyronitrile were added together with ethyl acetate and reacted at 60°C for 4 hours under a nitrogen gas stream. Next, ethyl acetate was added to the reaction solution to obtain a solution containing an acrylic polymer having a weight average molecular weight of 1.65 million (solid content concentration 30%). 0.15 parts of dibenzoyl peroxide (manufactured by Nippon Oil & Fats Co., Ltd., product name: Niper BO-Y), 0.08 parts of trimethylolpropane xylene diisocyanate (manufactured by Mitsui Takeda Chemical Co., Ltd., product name: Takenate D110N) and 0.2 parts of a silane coupling agent (manufactured by Soken Chemical Industries, Ltd., product name A-100, an acetoacetyl group-containing silane coupling agent) were added to the acrylic polymer solution per 100 parts of solid content of the obtained acrylic polymer solution to prepare adhesive B. The remaining depth of the adhesive layer (adhesive sheet) formed from Adhesive B was 12.5 mm.

[Example 1]
1. Preparation of a polarizer A long amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of 75° C. was used as a resin substrate. One side of the substrate was subjected to a corona treatment, and an aqueous solution containing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl-modification degree 4.6%, saponification degree 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "GOHSEFYMER Z200") in a ratio of 9:1 was applied to the corona-treated surface and dried at 25° C. to form a PVA-based resin layer having a thickness of 11 μm, and a laminate was prepared.
The obtained laminate was uniaxially stretched at its free end by 2.0 times in the machine direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 120° C. (auxiliary air stretching).
Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (insolubilizing treatment).
Next, the polarizing plate was immersed in a dye bath at a liquid temperature of 30° C. while adjusting the iodine concentration and immersion time so that the polarizing plate had a predetermined transmittance. In this example, the polarizing plate was immersed for 60 seconds in an iodine aqueous solution obtained by mixing 0.2 parts by weight of iodine and 1.5 parts by weight of potassium iodide with respect to 100 parts by weight of water (dyeing treatment).
Next, the plate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (crosslinking treatment).
Thereafter, the laminate was immersed in an aqueous boric acid solution (an aqueous solution obtained by blending 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 70° C., and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds so that the total stretch ratio was 5.5 times (underwater stretching).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 30° C. (cleaning treatment).
Finally, the laminate was dried to obtain a laminate in which a polarizer was formed on the resin substrate. The polarizer had a thickness of 5 μm and a single transmittance of 42.3%.

2. Lamination of protective layer An acrylic resin film (thickness 40 μm) containing a lactone ring structure was laminated as a protective layer on the polarizer surface of the laminate obtained in 1 above via an ultraviolet curing adhesive. Specifically, the curing adhesive was applied so that the total thickness was 1.0 μm, and the layers were laminated using a rolling machine. Thereafter, the adhesive was cured by irradiating it with UV light from the protective layer side. Next, the resin substrate was peeled off to obtain a laminate having a configuration of a protective layer (acrylic resin film)/polarizer.

3. Preparation of Retardation Layer (Retardation Film) A 60 μm thick shrinkable film [manufactured by Toray Industries, Inc., product name "Trefan BO2873"] was attached to both sides of a 130 μm thick norbornene resin film via an acrylic adhesive layer (thickness 15 μm). Then, the film was held in the longitudinal direction by a roll stretching machine and stretched 1.38 times in an air circulating oven at 146 ° C. After stretching, the shrinkable film was peeled off together with the acrylic adhesive layer to prepare a retardation film. The obtained retardation film showed a refractive index characteristic of nx>nz>ny, Re(550)=280 nm, Nz coefficient=0.52, photoelastic coefficient was 4.0 × 10 ^-12 m ² /N, and thickness was 138 μm.

4. Preparation of a polarizing plate with a retardation layer The retardation film (retardation layer) obtained in the above 3. was attached to the polarizer surface of the laminate obtained in the above 2.
The plates were laminated together via the adhesive A (thickness 12 μm) obtained in Production Example 1. In this way, a retardation layer-attached polarizing plate having a configuration of protective layer/polarizer/adhesive layer/retardation layer was obtained. The obtained retardation layer-attached polarizing plate was subjected to the above-mentioned evaluations (2) and (3). The results are shown in Table 1.

[Example 2]
A polarizing plate with a retardation layer was obtained in the same manner as in Example 1, except that the thickness of the adhesive A was changed to 23 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 3]
A polarizing plate with a retardation layer was obtained in the same manner as in Example 1, except that the thickness of the adhesive A was changed to 5 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
A polarizing plate with a retardation layer was obtained in the same manner as in Example 1, except that the adhesive B (thickness: 12 μm) was used instead of the adhesive A. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
A polarizing plate with a retardation layer was obtained in the same manner as in Example 1, except that the adhesive B (thickness: 20 μm) was used instead of the adhesive A. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Reference example 1]
1. Preparation of polarizer A polyvinyl alcohol resin film having an average polymerization degree of 2,400, a saponification degree of 99.9 mol%, and a thickness of 50 μm was prepared. The polyvinyl alcohol film was stretched 2.4 times in the conveying direction while swelling by immersing in a swelling bath (water bath) at 20° C. between rolls with different peripheral speed ratios (swelling step), and then stretched 3.7 times in the conveying direction based on the original polyvinyl alcohol film (polyvinyl alcohol film not stretched at all in the conveying direction) while immersing in a dyeing bath (aqueous solution with an iodine concentration of 0.03 wt % and a potassium iodide concentration of 0.3 wt %) at 30° C. so that the single-piece transmittance after the final stretching becomes a desired value (dyeing step). The immersion time at this time was about 60 seconds. Next, the dyed polyvinyl alcohol film was stretched to 4.2 times in the conveying direction based on the original polyvinyl alcohol film while immersed in a crosslinking bath (aqueous solution with a boric acid concentration of 3.0 wt% and a potassium iodide concentration of 3.0 wt%) at 40°C (crosslinking step). Further, the obtained polyvinyl alcohol film was immersed in a stretching bath (aqueous solution with a boric acid concentration of 4.0 wt% and a potassium iodide concentration of 5.0 wt%) at 64°C for 50 seconds to be stretched to 6.0 times in the conveying direction based on the original polyvinyl alcohol film (stretching step), and then immersed in a washing bath (aqueous solution with a potassium iodide concentration of 3.0 wt%) at 20°C for 5 seconds (washing step). The washed polyvinyl alcohol film was dried at 30°C for 2 minutes to prepare a polarizer (thickness 20 μm).

2. Preparation of polarizing plate and polarizing plate with retardation layer An acrylic resin film (thickness 40 μm) containing a lactone ring structure was attached as a protective layer to the surface of the polarizer obtained in 1 above in the same manner as in Example 1 to obtain a laminate having a protective layer (acrylic resin film)/polarizer configuration. The following procedure was performed in the same manner as in Example 1 to obtain a polarizing plate with a retardation layer. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[evaluation]
As is clear from Table 1, it is understood that according to the examples of the present invention, damage marks can be significantly suppressed. Furthermore, as is clear from the reference examples, it is understood that such damage marks are a problem specific to thin polarizers.

The polarizing plate with a retardation layer of the present invention can be suitably used in image display devices such as liquid crystal display devices, organic EL display devices, and quantum dot display devices, and can be particularly suitably used in liquid crystal display devices.

10 Polarizing plate 11 Polarizer 12 Protective layer 20 Adhesive layer 30 Retardation layer 100 Polarizing plate with retardation layer

Claims (9)

A polarizing plate including a polarizer and a protective layer on at least the viewing side of the polarizer, and a retardation layer attached to the opposite side to the viewing side of the polarizing plate via a pressure-sensitive adhesive layer,
The thickness of the polarizer is 3 μm to 8 μm ,
the pressure-sensitive adhesive layer is made of an acrylic pressure-sensitive adhesive composition,
The acrylic pressure-sensitive adhesive composition contains a (meth)acrylic polymer as a main component,
the (meth)acrylic polymer contains 3% by weight to 7% by weight of a carboxyl group-containing monomer unit and 0.05% by weight to 0.1% by weight of a hydroxyl group-containing monomer unit;
The pressure-sensitive adhesive layer has a residual depth of 11 μm or less when a load of 3 N is applied.
Polarizing plate with retardation layer. The polarizing plate with a retardation layer according to claim 1, wherein the thickness of the adhesive layer is 6 μm to 15 μm. The polarizing plate with a retardation layer according to claim 1 or 2, wherein the thickness of the protective layer on the viewing side is 30 μm or more. The polarizing plate with a retardation layer according to any one of claims 1 to 3, wherein the retardation layer exhibits a refractive index characteristic of nx>nz>ny. The polarizing plate with a retardation layer according to claim 4, wherein the Nz coefficient of the retardation layer is 0.3 to 0.7. 6. The polarizing plate with a retardation layer according to claim 4, wherein the retardation layer has an in-plane retardation Re(550) of 250 nm to 350 nm, a thickness of 150 μm or less, and a photoelastic coefficient of 1.0×10 ⁻¹² m ² /N or more. The polarizing plate with a retardation layer according to any one of claims 4 to 6, wherein the retardation layer contains a cyclic olefin resin. 8. The polarizing plate with a retardation layer according to claim 1, wherein an angle between a slow axis of the retardation layer and an absorption axis of the polarizer is 90°±7° or 0°±7° . An image display device comprising a polarizing plate with a retardation layer according to any one of claims 1 to 8.

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