Easily bondable film, polarizing plate, polarizing plate with an adhesive, and image display device

Abstract

The present invention relates to an easily adherable film, a polarizing plate, a polarizing plate with an adhesive, and an image display device. Provided are a polarizing plate in which a decrease in monomer transmittance in a high-temperature environment is suppressed, and an easily adherable film used therein. The easily adherable film (1) has an easily adherable layer (15) on the surface of a transparent film substrate (11). The easily adherable layer contains a binder resin and a water-soluble radical scavenger. The polarizing plate (50) has a configuration in which the above-mentioned easily adherable film (1) is adhered to at least one surface of a polyvinyl alcohol-based polarizing member (5) via an adhesive layer (6).

Description

Technical Field

[0001] The present invention relates to an easily adhesive film having an easily adhesive layer on the surface of a transparent film substrate. Further, the present invention relates to a polarizing plate in which an easily adhesive film is adhered to the surface of a polarizing element, a polarizing plate with an adhesive layer provided on at least one surface of the polarizing plate, and an image display device including the polarizing plate. Background Art

[0002] As various image display devices such as mobile devices, car navigation devices, personal computer displays, and televisions, liquid crystal display devices and organic EL display devices are widely used. From the perspective of their display principles, polarizing plates are arranged on the recognition side surfaces of liquid crystal cells. In a transmissive liquid crystal display device, polarizing plates are arranged on both sides of the liquid crystal cell. In an organic EL display device, in order to suppress external light from being reflected by a metal electrode (cathode) and being recognized like a mirror surface, a circular polarizing plate (typically, a laminate of a polarizing plate and a quarter-wave plate) is sometimes arranged on the recognition side surface.

[0003] A polarizing plate generally has a transparent film (polarizing element protection film) on one or both sides of a polarizing element for the purpose of protecting the polarizing element and the like. As the polarizing element, a polarizing element in which a polyvinyl alcohol (PVA) - based film adsorbs iodine and the molecules are oriented by stretching or the like is widely used.

[0004] As a polarizing element protection film adhered to the surface of a polarizing element, cellulose - based films such as cellulose acetate are widely used because of their excellent adhesiveness to a PVA - based polarizing element. As a polarizing element protection film, films formed of resin materials such as acrylic, polyester, polycarbonate, and cyclic olefin have also started to be used. Compared with cellulose - based films, the films formed of these resin materials have low moisture permeability. A polarizing plate in which a low - moisture - permeability resin film is adhered to the surface of a polarizing element has small changes in optical characteristics even when exposed to a high - humidity environment for a long time and tends to have excellent durability.

[0005] As described above, in a liquid crystal display device and an organic EL display device, a polarizing plate is provided on the recognition side surface of an image display unit. In recent years, on the more recognition - side thereof, for the purpose of preventing breakage caused by impacts from the outer surface, a configuration in which a front - surface transparent plate (also referred to as a "cover window", etc.) such as a transparent resin plate or a glass plate is arranged is widely adopted. For a configuration in which a front - surface transparent plate is adhered to the recognition side of a polarizing plate via an adhesive layer, Patent Document 1, Patent Document 2, etc. point out that in a high - temperature environment, red discoloration occurs in the in - plane central portion of the polarizing plate and the transmittance decreases.

[0006] Regarding the reduction in the transmittance of a polarizing plate, it is considered that one of the reasons is the polyene formation of PVA that constitutes the polarizing element due to a dehydration reaction in a high-temperature environment. In Patent Document 1, it is proposed to reduce the water retained in the polarizing element by controlling the water absorption amount and moisture permeability of the polarizing element protection film attached to the polarizing element, thereby suppressing the polyene formation of PVA. In Patent Document 2, it is proposed to dissipate moisture from the end face of the adhesive layer by controlling the moisture permeability and moisture amount of the adhesive layer that bonds the polarizing plate and the front surface transparent plate, thereby suppressing the polyene formation of PVA.

[0007] Patent Document 3 describes that by including a specific hindered amine compound in a PVA-based polarizing element, an adhesive that bonds the PVA-based polarizing element and the polarizing element protection film, or an adhesive that bonds the polarizing plate, the image display unit, and the front surface transparent member, it is possible to suppress a decrease in the transmittance of the polarizing element caused by the polyene formation of PVA.

[0008] Prior art documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-102353

[0011] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2017-75998

[0012] Patent Document 3: International Publication No. 2020 / 100869 Summary of the invention

[0013] Problems to be solved by the invention

[0014] In the advancement of the enlargement and high brightness of image display devices, there is an increasing demand for the polarizing plate that constitutes the image display device to have small changes in optical characteristics even in more severe environments (such as higher temperature conditions). For the method of controlling the amount of water retained in the polarizing plate as described in Patent Documents 1 and 2, the effect of suppressing the polyene formation of the PVA-based polarizing element is limited.

[0015] For the method of adding a hindered amine compound to a polarizing element, or an adhesive as proposed in Patent Document 3, there is still room for improvement in the interlayer adhesiveness and the like.

[0016] Solutions to solve the problems

[0017] In view of the above situation, the present inventors conducted research and found that by using an easily adhesive film containing a radical scavenger in the easily adhesive layer as the polarizing element protection film attached to the surface of the polarizing element, a polarizing plate with excellent interlayer adhesiveness and suppressed deterioration of the polarizing element can be obtained.

[0018] One embodiment of the present invention is an easy - adhesive film having an easy - adhesive layer on the surface of a transparent film substrate. The easy - adhesive layer contains a binder resin and a water - soluble radical scavenger. The radical scavenger contained in the easy - adhesive layer is, for example, a hindered amine compound, and preferably a compound having a nitroxide group (N - oxyl radical compound). The radical scavenger may also be a compound that can generate a nitroxide group through activation.

[0019] The content of the radical scavenger in the easy - adhesive layer is, for example, about 0.01 to 10% by weight. The easy - adhesive layer may also contain fine particles.

[0020] The easy - adhesive film can be suitably used as a polarizer protection film for a polarizer. Another embodiment of the present invention is a polarizer, in which the above - mentioned easy - adhesive film is adhered to a polyvinyl alcohol - based polarizer via an adhesive layer. The polarizer and the easy - adhesive film can be adhered by a photo - radical - polymerizable adhesive.

[0021] The above - mentioned polarizer can be actually used in the form of a pressure - sensitive adhesive - coated polarizer having a pressure - sensitive adhesive layer on at least one surface. By disposing the polarizer on the surface of an image display unit such as a liquid crystal display unit or an organic EL unit, an image display device can be formed.

[0022] Effects of the Invention

[0023] For a polarizer having an easy - adhesive film with an easy - adhesive layer containing a radical scavenger as a polarizer protection film adhered to at least one surface of a polyvinyl alcohol - based polarizer, even when the image display device is exposed to a high - temperature environment, the change in monomer transmittance is small and the durability is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a cross - sectional view showing a structural example of the easy - adhesive film.

[0025] Figure 2 It is a cross - sectional view showing a structural example of the polarizer.

[0026] Figure 3 It is a cross - sectional view showing a structural example of the pressure - sensitive adhesive - coated polarizer.

[0027] Figure 4 It is a cross - sectional view showing a structural example of the image display device.

[0028] DESCRIPTION OF REFERENCE NUMERALS

[0029] 1 Easy - adhesive film

[0030] 11 Film substrate

[0031] 15 Easy - adhesive layer

[0032] 2 Transparent film

[0033] 5 Polarizing element

[0034] 6, 7 Adhesive layer

[0035] 50 Polarizing plate

[0036] 20, 30 Adhesive layer

[0037] 90 Polarizing plate with adhesive

[0038] 60 Image display unit

[0039] 70 Front surface transparent member

[0040] 100 Image display device Detailed implementation mode

[0041] Figure 1 It is a cross-sectional schematic diagram showing a structural example of an easily bondable film according to an embodiment of the present invention. The easily bondable film 1 has an easily bondable layer 15 on at least one surface of the film substrate 11. The easily bondable layer can also be provided on both sides of the film substrate. The easily bondable film is used by being bonded to other films, glass substrates, etc.

[0042] As a usage mode of the easily bondable film, a polarizing element protection film can be cited. Figure 2 It is a cross-sectional view showing a structural example of a polarizing plate having an easily bondable film 1 as a polarizing element protection film. The polarizing plate 50 has an easily bondable film 1 bonded to one surface (first main surface) of the polarizing element 5 through an adhesive layer 6. Figure 2 In the shown polarizing plate 50, the easily bondable film 1 has an easily bondable layer 15 on the bonding surface with the polarizing element 5 of the film substrate 11. The easily bondable layer can also be provided on the surface where the polarizing element 5 is not bonded. Figure 2 In the shown polarizing plate 50, a transparent protection film 2 is bonded to the other surface (second main surface) of the polarizing element 5 through an adhesive layer 7.

[0043] [Easily bondable film]

[0044] The easily bondable film 1 has an easily bondable layer 15 on at least one surface of the film substrate 11.

[0045] [Film substrate]

[0046] As the thin film substrate 11, a transparent thin film is preferred. The total light transmittance of the transparent thin film substrate is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. As the resin material constituting the thin film substrate 11, acrylic resins, polyester resins, polycarbonate resins, polyolefin resins, cyclic olefin resins, polystyrene resins, polyamide resins, polyimide resins, etc. can be cited. When the easy-bonding thin film is used as a polarizing element protection thin film having optical isotropy, from the aspect of small birefringence, as the resin material of the thin film substrate 11, an acrylic resin or a cyclic olefin resin is preferred, and an acrylic resin is particularly preferred.

[0047] As the cyclic olefin resin, for example, polynorbornene can be cited. As commercially available products of the cyclic olefin resin, ZEONOR and ZEONEX manufactured by Zeon Corporation of Japan, ARTON manufactured by JSR, APEL manufactured by Mitsui Chemicals, TOPAS manufactured by TOPAS ADVANCED POLYMERS, etc. can be cited. The cyclic olefin-based thin film preferably contains 50% by weight or more of the cyclic olefin resin.

[0048] As the acrylic resin, poly(meth)acrylates such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymer, methyl methacrylate-(meth)acrylate copolymer, methyl methacrylate-acrylate-(meth)acrylic acid copolymer, (meth)acrylate-styrene copolymer (such as MS resin), polymers having an alicyclic hydrocarbon group (such as methyl methacrylate-methyl methacrylate cyclohexyl copolymer, methyl methacrylate-(meth)acrylate norbornene copolymer, etc.) can be cited.

[0049] In this specification, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid. The acrylic resin includes substances having acrylic acid or its derivatives as constituent monomer components, and substances having methacrylic acid or its derivatives as constituent monomer components.

[0050] As the acrylic resin, an acrylic resin having a glutaric anhydride structure described in JP-A-2006-283013, JP-A-2006-335902, JP-A-2006-274118, etc. can be used; and / or an acrylic resin having a lactone ring structure described in JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, JP-A-2005-146084, etc. The acrylic resin having a glutaric anhydride structure and the acrylic resin having a lactone ring structure have high heat resistance, high transparency, and high mechanical strength, and thus are suitable for manufacturing a polarizing plate having a high degree of polarization and excellent durability.

[0051] When the thin film substrate 11 is an acrylic thin film, the content of the acrylic resin in the thin film substrate is preferably 50% by weight or more, more preferably 60 to 98% by weight, and further preferably 70 to 97% by weight. The acrylic thin film may also contain a thermoplastic resin other than the acrylic resin. For example, by blending other thermoplastic resins to eliminate the birefringence of the acrylic resin, an acrylic thin film having excellent optical isotropy can be obtained. In addition, for the purpose of improving the mechanical strength of the thin film, etc., a thermoplastic resin other than the acrylic resin may be blended.

[0052] Examples of the thermoplastic resin other than the acrylic resin include olefin polymers, vinyl halide polymers, polystyrene, copolymers of styrene and acrylic monomers, polyesters, polyamides, polyacetals, polycarbonates, polyphenylene ethers, polyphenylene sulfides, polyether ether ketones, polysulfones, polyether sulfones, polyoxymethyl benzoates, polyamide imides, rubber polymers, etc.

[0053] The thin film substrate 11 may contain additives such as antioxidants, stabilizers, reinforcing materials, ultraviolet absorbers, flame retardants, antistatic agents, colorants, fillers, plasticizers, lubricants, and fillers. The resin material and additives, etc. may also be mixed in advance to form a thermoplastic resin composition such as pellets, and then made into a thin film.

[0054] The thickness of the thin film substrate 11 is about 5 to 200 μm. From the viewpoints of mechanical strength, transparency, and operability, etc., the thickness of the thin film substrate 11 is preferably 10 to 100 μm, more preferably 15 to 60 μm.

[0055] The glass transition temperature Tg of the thin film substrate 11 is preferably 100 °C or higher, more preferably 110 °C or higher. When the thin film substrate 11 is an acrylic thin film, as described above, by using an acrylic resin having a glutaric anhydride structure and an acrylic resin having a lactone ring structure as the acrylic resin, the Tg of the acrylic thin film can be increased and the heat resistance can be improved. The upper limit of Tg of the thin film substrate 11 is not particularly limited, but from the viewpoint of formability and the like, it is preferably 170 °C or lower.

[0056] As a method for manufacturing the thin film substrate 11, a solution casting method, a melt extrusion method, a calendering method, a compression molding method, etc. can be cited. The thin film substrate 11 can be either an unstretched thin film or a stretched thin film. When the thin film substrate 11 is an acrylic thin film, from the viewpoint of improving mechanical strength, the acrylic thin film is preferably a stretched thin film stretched in at least one direction, and particularly preferably a biaxially stretched thin film. By compounding other thermoplastic resins to eliminate the birefringence of the acrylic resin, an acrylic thin film with small retardation and excellent optical isotropy can be obtained even when stretched.

[0057] <Easy adhesion layer>

[0058] The easy adhesion layer 15 provided on the surface of the thin film substrate 11 contains a binder resin and a radical scavenger. By providing the easy adhesion layer 15, the adhesiveness to films such as polarizing members and glass substrates can be improved. By making the easy adhesion layer 15 contain a radical scavenger, the deterioration of the polarizing member 5 can be suppressed in the polarizing plate in which the easy adhesion film 1 and the polarizing member 5 are laminated.

[0059] The easy adhesion layer 15 may further contain fine particles. By making the easy adhesion layer 15 contain fine particles, fine irregularities are formed on the surface of the easy adhesion layer 15, and the slidability of the thin film is improved. Therefore, it helps to reduce the damage of the easy adhesion film 1 during roller conveyance and suppress the adhesion during winding into a roll.

[0060] (Binder resin)

[0061] As the binder resin of the easy adhesion layer 15, from the aspect of excellent adhesion to a thin film substrate such as an acrylic thin film, a resin (polymer) having a reactive group such as a polyurethane resin, an epoxy resin, an isocyanate resin, a polyester resin, a polymer containing an amino group in the molecule, and an acrylic resin having a crosslinkable functional group such as an oxazoline group can be used. As the binder resin of the easy adhesion layer 15, a polyurethane resin is particularly preferred. The easy adhesion layer 15 containing a polyurethane resin binder has high adhesion to the thin film substrate 11. In addition, the easy adhesion film 1 containing a polyurethane resin binder in the easy adhesion layer 15 tends to exhibit high adhesiveness when laminating films such as polarizing members with the aid of an adhesive layer.

[0062] The representative of urethane resin is the reaction product of polyol and polyisocyanate. As the polyol component, preferably use is made of high molecular weight polyols such as polyacrylic polyol, polyester polyol, polyether polyol, etc. As the polyisocyanate, aliphatic diisocyanate, alicyclic diisocyanate and aromatic diisocyanate can be used, and from the viewpoint of transparency, aliphatic diisocyanate or alicyclic diisocyanate is preferred.

[0063] The carbamate resin constituting the easy-adhesive layer 15 preferably has a carboxyl group. By making the carbamate resin have a carboxyl group, a cross-linked structure can be introduced, and there is a tendency to improve the bonding durability of the easy-adhesive film 1 and the polarizer, etc. The carbamate resin having a carboxyl group can be obtained, for example, by reacting a chain extender having a free carboxyl group on the basis of a polyol and a polyisocyanate. As chain extenders having free carboxyl groups, dihydroxycarboxylic acids, dihydroxysuccinic acid, etc. can be listed. As dihydroxycarboxylic acids, dihydroxyalkyl alkanoic acids such as dimethylol alkanoic acid (for example, dimethylol acetic acid, dimethylol butyric acid, dimethylol propionic acid, dimethylol butyric acid, dimethylol valeric acid) can be listed.

[0064] The method for producing the carbamate resin is not particularly limited, and may be any one of a one-step method in which the monomer components are reacted at once and a multi-stage method in which the monomer components are reacted in stages. When a chain extender having a free carboxyl group is used to introduce a carboxyl group into the carbamate resin, a multi-stage method is preferred. When producing the carbamate resin, a carbamate reaction catalyst may be used as needed.

[0065] The number average molecular weight of the urethane resin is preferably 5000 to 600000, more preferably 10000 to 400000. The acid value of the urethane resin is preferably 10 to 50, more preferably 20 to 45.

[0066] As the urethane resin, commercially available products may also be used. Examples of commercially available water-based urethane resins include the "Superflex" series (150, 150HS, 210, 460, 470, 870, etc.) and the "Elastron" series (H-3, etc.) manufactured by Daiichi Kogyo Seiyaku, the "TAKELAC" series (W-6010, W-6020, W-605, W-6061, WS-4000, WS-5100, WSA-5920, etc.) and the "OLESTER" series (UD-350, etc.) manufactured by Mitsui Chemicals, the "HYDRAN" series (AP-20, AP-40F, RCP-A-220, WLS-210, etc.) manufactured by DIC, and the "PERMARIN" series (UA-368, etc.) manufactured by Sanyo Chemical Industries, Ltd.

[0067] The urethane resin may have a crosslinked structure. By introducing a crosslinked structure into the urethane resin, the adhesion durability between the easy-to-bond film 1 and a polarizing member or the like tends to be improved. As the crosslinking agent, a crosslinking agent capable of reacting with the crosslinkable functional group of the urethane resin can be used without particular limitation. When the urethane resin has a carboxyl group, a crosslinking agent containing an amino group, an oxazoline group, an epoxy group, a carbodiimide group, etc. can be used. Among these, a crosslinking agent having an oxazoline group is preferred. Since the reactivity of the oxazoline group with the carboxyl group is small at room temperature, the pot life when mixed with the urethane resin is long, and it can flexibly cope with the lead time of the process.

[0068] The crosslinking agent can be a low-molecular compound or a polymer. From the viewpoint of high solubility in the aqueous composition and excellent compatibility with the urethane resin, an acrylic polymer is preferred as the crosslinking agent. In particular, when an acrylic polymer having an oxazoline group is used as the crosslinking agent, the adhesiveness between the easy-to-bond film 1 and a film such as a polarizing member tends to be improved.

[0069] The amount of the crosslinking agent used is preferably 1 to 30 parts by weight, more preferably 3 to 20 parts by weight, relative to 100 parts by weight of the urethane resin.

[0070] (Radical scavenger)

[0071] The radical scavenger contained in the easy-to-bond layer 15 has the effect of suppressing the deterioration of the polarizing member (mainly the decrease in monomer transmittance) in a high-temperature environment. It is considered that in a high-temperature environment, as the water remaining in the polarizing plate moves, the radical scavenger migrates from the easy-to-bond layer to the polarizing member, which helps to suppress the deterioration of the polarizing member.

[0072] From the viewpoint of promoting the migration from the easy-to-bond layer 15 to the polarizing member 5 or the like in the presence of water, the radical scavenger is preferably water-soluble. The solubility of the radical scavenger in water at 25 °C (the mass (g) of the radical scavenger that can be dissolved in 100 g of water) is preferably 1 or more, more preferably 2 or more, and further preferably 5 or more.

[0073] Examples of the water-soluble radical scavenger include compounds having a radical scavenging function such as hindered phenol compounds, hindered amine compounds, phosphorus compounds, sulfur compounds, benzotriazole compounds, benzophenone compounds, hydroxylamine compounds, salicylic acid ester compounds, and triazine compounds. Among these, hindered amine compounds are preferred from the viewpoint of high effect of suppressing the deterioration of the polarizing member.

[0074] The hindered amine compound is a compound in which the carbon atom adjacent to the nitrogen atom in a secondary amine or tertiary amine is substituted with an alkyl group. Examples of the hindered amine compound that functions as a radical scavenger include compounds having the structure represented by the general formula (1).

[0075]

[0076] In the general formula (1), the left side of the dotted line portion is an arbitrary organic group. In the general formula (1), R 1 is an oxygen radical, a hydrogen atom, a hydroxyl group, an acryloyl group, a methacryloyl group, or an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkoxy group, or an acyl group having 1 to 30 carbon atoms.

[0077] In the general formula (1), R 2 ~R 5 are each independently an alkyl group having 1 to 10 carbon atoms, and the number of carbon atoms of the alkyl group is preferably 1 to 6, more preferably 1 to 3. Among them, from the viewpoints of the stability of the compound and the radical scavenging effect, etc., compounds in which R 2 ~R 5 are all methyl are preferred.

[0078] In the general formula (1), n is 0 or 1, and from the viewpoint of the stability of the structure, n is preferably 0. The compound with n = 0 in the general formula (1) is a derivative of 2,2,6,6-tetraalkylpiperidine. The compound with n = 0 and R 2 ~R 5 all being methyl is a derivative of 2,2,6,6-tetramethylpiperidine.

[0079] In the general formula (1), for the compound in which R 1 bonded to the nitrogen atom is an oxygen radical (N-oxyl compound), the nitroxide group has the function of generating a stable nitroxide radical (R 2 N-O·) and scavenging radicals. The nitroxide radical has a reaction cycle of returning to the nitroxide radical by absorbing peroxyacid after scavenging radicals, so even a small amount added continuously has a radical scavenging effect.

[0080] When R 1 is other than an oxygen radical, a nitroxide group (nitroxide radical) is generated by activation such as ultraviolet irradiation. Therefore, the compound represented by the general formula (1) also has a radical scavenging effect even when R 1 is other than an oxygen radical, similar to the N-oxyl compound in which R 1 is an oxygen radical. That is, the radical scavenger is preferably a compound having a nitroxide group or a compound capable of generating a nitroxide group by activation.

[0081] From the aspect that it can exhibit a free radical scavenging effect without being accompanied by activation such as ultraviolet irradiation, as a free radical scavenger, a compound having a nitroxy group is particularly preferred, and R in the above general formula (1) is preferably 1 an oxygen free radical.

[0082] As the compound having the structure represented by the general formula (1), for example, compounds represented by the following general formulas (2) to (5) can be cited.

[0083]

[0084] R in the general formulas (2) to (5) 1 ~R 5 and n are the same as those in the above general formula (1). In the general formulas (2) and (3), R 6 ~R 8 are each independently a hydrogen atom, an alkyl or acyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms. In the general formulas (4) and (5), R 9 ~R 12 are each independently a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 10 carbon atoms, an acyl group, an amino group or an alkoxy group, or an aryl group having 6 to 20 carbon atoms.

[0085] From the viewpoints of water solubility and ease of obtaining the compound, R 6 ~R 8 in the general formulas (2) and (3) is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, particularly preferably a hydrogen atom. From the viewpoints of water solubility and ease of obtaining the compound, R 9 ~R 11 in the general formula (4) is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R 12 in the general formula (5) is preferably a hydroxyl group, an amino group, or an alkoxy group.

[0086] As described above, the N-oxy radical compound has a free radical scavenging effect. For the N-oxy radical compound that functions as a free radical scavenger, for example, compounds described in Japanese Patent Application Laid-Open No. 2003-64022, Japanese Patent Application Laid-Open No. 11-222462, Japanese Patent Application Laid-Open No. 2002-284737, International Publication No. 2016 / 047655, etc. can be cited.

[0087] In addition, even if it is other than the compound represented by the general formula (1), the N-nitroxy compound can also have the function of a free radical scavenger. As examples of the N-nitroxy compound, compounds represented by the following formulas (6) to (8) can be cited.

[0088]

[0089] In the general formula (6), R is a hydrogen atom, an alkyl group or an acyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

[0090] From the viewpoints of water solubility and suppression of deterioration of the polarizing member, the molecular weight of the radical scavenger is preferably 1000 or less, more preferably 500 or less, and still more preferably 300 or less. The radical scavenger contained in the easy-adhesion layer may be only one kind or two or more kinds.

[0091] The content of the radical scavenger in the easy-adhesion layer is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, still more preferably 0.1% by weight or more, particularly preferably 0.15% by weight or more, and may also be 0.2% by weight or more, 0.3% by weight or more, 0.5% by weight or more, or 1.0% by weight or more. The more the content of the radical scavenger contained in the easy-adhesion layer 15 is, the more the amount of the radical scavenger migrating to the polarizing member 5 is, and there is a tendency that the deterioration of the polarizing member is more suppressed. In addition, when the radical scavenger is contained in the easy-adhesion layer, orientation defects, curing inhibition, adhesion inhibition, etc. during stretching are less likely to occur. Therefore, compared with the case where the radical scavenger is contained in the polarizing member, the adhesive layer, the adhesive layer, etc., a larger amount can be added.

[0092] On the other hand, when the radical scavenger is contained in the easy-adhesion layer 15, even if a small amount is added, the radical scavenger easily migrates to the polarizing member 5, and the effect of suppressing the deterioration of the polarizing member is excellent. In particular, when the easy-adhesion layer 15 contains a hindered amine compound having a nitroxyl group as the radical scavenger, an excellent effect of suppressing the deterioration of the polarizing member is exhibited even at a low concentration of 1% by weight or less.

[0093] When the amount of the radical scavenger contained in the easy-adhesion layer 15 is too large, the transparency may sometimes be reduced. In addition, when the amount of the radical scavenger migrating to other layers in the manufacturing process of the polarizing plate and the image display device is large, it may cause adhesion inhibition or the like. Therefore, the content of the radical scavenger in the easy-adhesion layer is preferably 10% by weight or less, more preferably 7% by weight or less, still more preferably 5% by weight or less, and may also be 4% by weight or less, 3% by weight or less, or 2% by weight or less.

[0094] (Fine particles)

[0095] As described above, the easy-adhesion layer 15 may contain fine particles. By making the easy-adhesion layer 15 contain fine particles, a fine concavo-convex shape is formed on the surface of the easy-adhesion layer, the slidability of the easy-adhesion film 1 is improved, and adhesion can be suppressed.

[0096] From the viewpoint of forming unevenness that helps improve slidability, the particle size (average primary particle size) of the fine particles is preferably 10 nm or more, more preferably 15 nm or more, and still more preferably 20 nm or more. The average primary particle size of the fine particles is preferably less than the thickness of the easily adhesive layer. By making the particle size of the fine particles less than the thickness of the easily adhesive layer, it is possible to suppress the fine particles from peeling off from the easily adhesive layer. The particle size of the fine particles is preferably 250 nm or less, more preferably 200 nm or less. In addition, by making the average primary particle size of the fine particles less than the visible light wavelength, it is possible to suppress the scattering of visible light at the interface between the binder resin and the fine particles. From the viewpoint of improving transparency, the particle size of the fine particles is preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less, and particularly preferably 50 nm or less.

[0097] The fine particles of the easily adhesive layer 15 can be either inorganic fine particles or organic fine particles. From the aspect of excellent dispersibility and particle size uniformity, inorganic fine particles are preferably used as the fine particles. Examples of the inorganic fine particles include inorganic oxides such as titanium oxide, aluminum oxide, and zirconium oxide; calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Among these, inorganic oxides are preferred. Examples of the organic fine particles include silicone-based resins, fluorine-based resins, and acrylic-based resins. In order to suppress light scattering caused by the fine particles, it is preferable that the refractive index difference between the binder resin (usually having a refractive index of about 1.5) and the fine particles is small. From the aspect of a small refractive index difference from the binder resin and excellent dispersibility, silica particles are preferably used as the fine particles of the easily adhesive layer 15.

[0098] When the easily adhesive layer 15 is formed from an aqueous composition, fine particles with high water dispersibility are preferably used. The aqueous dispersion of the fine particles can also be blended in the composition. In order to improve the dispersibility of the fine particles, an alkaline component such as amine or ammonia can be added to make the easily adhesive composition weakly alkaline.

[0099] As the water-dispersible silica particles, colloidal silica is preferably used. As the colloidal silica, commercially available products such as Quartron.PL series manufactured by Fuso Chemical Industry Co., Ltd., SnowTex series manufactured by Nissan Chemical Industries, Ltd., AERODISP series and AEROSIL series manufactured by NIPPON AEROSIL Co., Ltd., and SEAHOSTAR KE series manufactured by Nippon Shokubai Co., Ltd. can be used.

[0100] From the viewpoint of improving the slidability of the easy - adhesion film 1 by forming irregularities on the surface of the easy - adhesion layer 15, the content of the fine particles in the easy - adhesion layer 15 is preferably 3% by weight or more, more preferably 5% by weight or more. In particular, when the thickness of the easy - adhesion layer 15 is small, it is preferable to increase the amount (number density) of the fine particles per unit area by increasing the content of the fine particles, thereby forming irregularities uniformly in the plane of the easy - adhesion layer 15. The content of the fine particles in the easy - adhesion layer 15 is preferably 8% by weight or more, more preferably 10% by weight or more, and further preferably 12% by weight or more. When the content of the fine particles in the easy - adhesion layer 15 is too large, sometimes the optical properties may be reduced due to an increase in light scattering at the interface between the binder resin and the fine particles. In addition, as the content of the fine particles increases, the relative content of the binder resin becomes smaller, so sometimes the adhesiveness of the easy - adhesion layer may be reduced. Therefore, the content of the fine particles in the easy - adhesion layer 15 is preferably 50% by weight or less, more preferably 40% by weight or less, and further preferably 30% by weight or less.

[0101] <Formation of the easy - adhesion layer>

[0102] The method for forming the easy - adhesion layer 15 on the surface of the film substrate 11 is not particularly limited. It is preferable to coat an easy - adhesion composition (coating liquid) containing a binder resin, a radical scavenger, and, if necessary, fine particles on the film substrate 11 and heat it to form the easy - adhesion layer 15.

[0103] (Easy - adhesion composition)

[0104] The easy - adhesion composition is preferably an aqueous composition using water as a solvent. The concentration of the solid components (non - volatile components) in the easy - adhesion composition is preferably 1 to 30% by weight, more preferably 2 to 20% by weight, and further preferably 3 to 15% by weight.

[0105] The aqueous easy - adhesion composition contains water as a solvent (and dispersion medium), a binder resin or its precursor substance, and fine particles. In order to improve the dispersibility of the fine particles, etc., the easy - adhesion composition may further contain basic components such as ammonia and amines.

[0106] In addition to containing a binder resin (or its precursor substance), a radical scavenger, and fine particles, the easy - adhesion composition may further contain a cross - linker. The easy - adhesion composition may contain additives such as catalysts such as cross - linking accelerators, antioxidants, ultraviolet absorbers, leveling agents, anti - blocking agents, antistatic agents, dispersion stabilizers, defoaming agents, thickeners, dispersants, surfactants, and lubricants.

[0107] (Formation of the easy - adhesion layer on the film substrate)

[0108] Before applying the easy - adhesion composition on the film substrate 11, surface treatment of the film substrate can also be performed. By performing surface treatment, the wetting tension of the film substrate can be adjusted, and the adhesion with the easy - adhesion layer 15 can be improved. Examples of surface treatment include corona treatment, plasma treatment, ozone blowing, ultraviolet irradiation, flame treatment, chemical treatment, etc. Among these, corona treatment or plasma treatment is preferred.

[0109] Examples of the application method of the easy - adhesion composition include bar coating, roll coating, gravure coating, rod coating, slot - die coating, curtain coating, jet coating, etc. The solvent is removed by heating the applied easy - adhesion composition to form the easy - adhesion layer 15. It is also possible to cure by heating the precursor substance of the binder resin to cause a reaction. For example, when the easy - adhesion composition contains a cross - linker, the cross - linking reaction can be promoted by heating.

[0110] The heating temperature during the formation of the easy - adhesion layer is, for example, about 50 - 200 °C. From the viewpoint of promoting the curing reaction of the resin component in the easy - adhesion composition, the heating temperature is preferably 100 °C or higher, more preferably 120 °C or higher, further preferably 130 °C or higher, and particularly preferably 135 °C or higher. When the easy - adhesion composition contains an alkaline component such as amine or ammonia, from the viewpoint of efficiently volatilizing and removing the alkaline component to reduce the residual alkali amount, the heating temperature is preferably higher than the boiling point of the alkaline component.

[0111] The easy - adhesion layer can also be formed in the manufacturing process of the film substrate. In addition, the easy - adhesion layer can be formed by using the heating during the formation of the film substrate. For example, when the film substrate is a stretched film, the easy - adhesion composition can be applied on the surface of the film before stretching or the longitudinally stretched film, and the drying of the solvent and the curing of the resin can be carried out by using the heating during the transverse stretching by a tenter or the simultaneous biaxial stretching.

[0112] When stretching the film substrate after applying the easy - adhesion composition, from the viewpoint of suppressing defects such as cracks in the easy - adhesion layer, the stretching ratio is preferably 5 times or less, more preferably 4 times or less, further preferably 3 times or less, and particularly preferably 2.5 times or less. The lower limit of the stretching ratio is not particularly limited, but from the viewpoint of improving the film strength, the stretching ratio is preferably 1.3 times or more, more preferably 1.5 times or more. When the film substrate is an acrylic - based film, from the viewpoint of improving the film strength, it is preferred to perform stretching at the above - mentioned stretching ratios along the conveying direction (MD) and the width direction (TD) respectively.

[0113] When performing biaxial stretching of the thin film substrate, the biaxial stretching can be sequential biaxial stretching or simultaneous biaxial stretching. In addition, diagonal stretching can also be performed. When performing sequential biaxial stretching, as described above, the film can be stretched in one direction (MD) by roll stretching, and then an easy-to-bond composition is coated on the film, and the easy-to-bond composition is heated during stretching based on the tenter.

[0114] By adjusting the solid content concentration and coating thickness of the easy-to-bond composition, the thickness of the easy-to-bond layer 15 can be adjusted. In the case where the thin film substrate is stretched after coating the easy-to-bond composition, the thickness of the easy-to-bond layer 15 can also be adjusted by the stretching ratio.

[0115] The thickness of the easy-to-bond layer is not particularly limited, and is usually about 10 nm to 2 μm. From the viewpoints of improving the adhesiveness to a polarizer or the like and increasing the amount of the radical scavenger contained in the easy-to-bond layer to suppress the deterioration of the polarizer, the thickness of the easy-to-bond layer is preferably 50 nm or more, more preferably 80 nm or more, further preferably 100 nm or more, and can also be 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, or 150 nm or more. From the viewpoints of suppressing uneven adhesion when bonding to a polarizer or the like and suppressing stripe-like unevenness when the polarizing plate is exposed to a humid environment, the thickness of the easy-to-bond layer is preferably 500 nm or less, more preferably 300 nm or less, further preferably 280 nm or less, and can also be 250 nm or less or 230 nm or less.

[0116] [Polarizing plate]

[0117] The polarizing plate has a transparent protective film (polarizer protective film) on at least one surface of the polarizer. The polarizing plate can have a polarizer protective film only on one surface of the polarizer, or as Figure 2 shown, it can have polarizer protective films on both surfaces of the polarizer 5.

[0118] By bonding the above-mentioned easy-to-bond film to one surface of the polarizer, a polarizing plate having an easy-to-bond film as a polarizer protective film only on one surface of the polarizer can be formed. It should be noted that, Figure 2 FIG. shows a polarizing plate 50 in which an easy-to-bond film 1 is bonded to one surface of the polarizer as a polarizer protective film and a transparent film 2 is bonded to the other surface. However, as described above, the polarizing plate can have a polarizer protective film bonded only to one surface of the polarizer (so-called "single-protection polarizing plate"). An adhesive layer or the like can be provided on the surface of the single-protection polarizing plate on the side where the polarizer protective film is not provided in contact with the polarizer 5.

[0119] Regarding a polarizing plate having polarizing film protection films on two surfaces of a polarizing element, it is sufficient to bond the above-mentioned easily bondable film to at least one surface of the polarizing element. The polarizing plate may also have the above-mentioned easily bondable film bonded to both surfaces of the polarizing element. The polarizing element 5 and the easily bondable film 1 are bonded via an adhesive layer 6.

[0120] <Polarizing element>

[0121] As the polarizing element 5, a polyvinyl alcohol (PVA)-based polarizing element in which a dichroic substance such as iodine or a dichroic dye is adsorbed on a polyvinyl alcohol-based film such as polyvinyl alcohol or partially methylalated polyvinyl alcohol and oriented in one direction can be used. For example, a PVA-based polarizing element can be obtained by subjecting a polyvinyl alcohol-based film to iodine dyeing and stretching.

[0122] In the manufacturing process of the polarizing element 5, washing, swelling, crosslinking, etc. can be carried out as needed. The stretching can be carried out before or after the iodine dyeing, or can be carried out while dyeing. The stretching can be stretching in the air (dry stretching), or can be stretching in water or in an aqueous solution containing boric acid, potassium iodide, etc. (wet stretching), or they can be used in combination. The film thickness of the polarizing element 5 is not particularly limited, and is usually about 1 to 50 μm.

[0123] As the polarizing element 5, a thin PVA-based polarizing element with a thickness of 10 μm or less can also be used. As the thin polarizing element, for example, the thin polarizing elements described in Japanese Patent Application Laid-Open No. 51-069644, Japanese Patent Application Laid-Open No. 2000-338329, WO2010 / 100917 pamphlet, Japanese Patent No. 4691205, Japanese Patent No. 4751481, etc. can be cited. These thin polarizing elements can be obtained by a manufacturing method including a step of stretching a PVA-based resin layer and a stretching resin substrate in a laminated state and an iodine dyeing step. In this manufacturing method, even if the PVA-based resin layer is thin, it is supported by the stretching resin substrate, so stretching can be carried out without problems such as breakage due to stretching.

[0124] The polarizing element may contain a radical scavenger such as a hindered amine compound. By making the polarizing element contain a radical scavenger, the deterioration of the polarizing element in the use environment of the image display device tends to be suppressed. Among them, in order to contain a radical scavenger in the polarizing element, it is necessary to add a radical scavenger to the solution for forming a PVA film (or PVA coating film) and carry out stretching after film formation, or to contain a radical scavenger in the solution for iodine dyeing, or the cleaning liquid after dyeing, etc. Therefore, sometimes the radical scavenger may inhibit the iodine dyeing of PVA and the orientation of iodine during stretching, or there may be desorption of iodine during the adsorption of the radical scavenger to PVA, which may cause a decrease in polarization degree and coloring of transmitted light.

[0125] Therefore, the content of the radical scavenger in the polarizing member is preferably less than 1% by weight, more preferably less than 0.1% by weight, further preferably less than 0.05% by weight, may also be less than 0.01% by weight, less than 0.005% by weight or less than 0.001% by weight. The polarizing member may also contain no radical scavenger. It should be noted that here, the polarizing member before being bonded to the pressure-sensitive adhesive film 1 containing the radical scavenger in the pressure-sensitive adhesive layer 15 is described. As described above, in the polarizing plate in which the pressure-sensitive adhesive film 1 and the polarizing member 5 are bonded, since the radical scavenger migrates from the pressure-sensitive adhesive layer 15 to the polarizing member 5, the polarizing member may also contain a radical scavenger in an amount exceeding the above range.

[0126] <Adhesive>

[0127] As long as the adhesive layer 6 for bonding the polarizing member 5 and the pressure-sensitive adhesive film 1 is optically transparent, there is no particular limitation on its material, and examples thereof include epoxy resins, silicone resins, acrylic resins, polyurethanes, polyamides, polyethers, polyvinyl alcohols, etc. The thickness of the adhesive layer 6 is, for example, about 0.01 to 20 μm, and can be appropriately set according to the type of the adherend, the material of the adhesive, etc. When using a curable adhesive that exhibits adhesiveness through a crosslinking reaction after coating, the thickness of the adhesive layer 6 is preferably 0.01 to 5 μm, more preferably 0.03 to 3 μm.

[0128] As the adhesive, various types of adhesives such as water-based adhesives, solvent-based adhesives, hot-melt adhesive systems, and active energy ray-curable adhesives can be used. Among these, from the aspect of being able to reduce the thickness of the adhesive layer, a water-based adhesive or an active energy ray-curable adhesive is preferred.

[0129] As the polymer component of the water-based adhesive, examples include vinyl polymers, gelatin, vinyl-based latexes, polyurethanes, polyesters, epoxies, etc. Among these, from the aspect of excellent adhesiveness between the pressure-sensitive adhesive film and the polarizing member, a vinyl polymer is preferred, and a polyvinyl alcohol-based resin is particularly preferred. Among the polyvinyl alcohol-based resins, a polyvinyl alcohol containing an acetoacetyl group is preferred.

[0130] From the aspect of adhesiveness, the average degree of polymerization of the polyvinyl alcohol-based resin is preferably about 100 to 5000, more preferably 1000 to 4000. The average saponification degree of the polyvinyl alcohol-based resin is preferably 85 mol% or more, more preferably 90 mol% or more.

[0131] The aqueous adhesive composition (solution) may contain a crosslinking agent in addition to polymers such as polyvinyl alcohol-based resins. As the crosslinking agent, a compound having at least two functional groups reactive with the polymer constituting the adhesive in one molecule can be used. As the crosslinking agent for polyvinyl alcohol-based resins, the following can be cited: alkylene diamines; isocyanates; epoxies; aldehydes; amino-formaldehydes such as hydroxymethyl urea and hydroxymethyl melamine. Among these, amino-formaldehydes are preferred. As the amino-formaldehyde resin, a compound having a hydroxymethyl group is preferred, and hydroxymethyl melamine is particularly preferred. The compounding amount of the crosslinking agent in the adhesive composition is preferably about 10 to 60 parts by weight, more preferably 20 to 50 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol-based resin.

[0132] The active energy ray-curable adhesive is an adhesive capable of radical polymerization, cationic polymerization, or anionic polymerization by irradiation with active energy rays such as electron beams and ultraviolet rays. Among them, from the aspect of being able to cure with low energy, a photo-radical polymerizable adhesive that initiates radical polymerization by ultraviolet irradiation is preferred.

[0133] As the monomers of the radical polymerizable adhesive, compounds having a (meth)acryloyl group and compounds having a vinyl group can be cited. Among them, compounds having a (meth)acryloyl group are suitable. As the compounds having a (meth)acryloyl group, (meth)acrylic acid C 1-20 Chain alkyl esters, (meth)acrylic acid alicyclic alkyl esters, (meth)acrylic acid polycyclic alkyl esters, etc., (meth)acrylic acid alkyl esters; (meth)acrylic acid esters containing a hydroxyl group; (meth)acrylic acid esters containing an epoxy group such as (meth)acrylic acid glycidyl ester, etc. The radical polymerizable adhesive may contain nitrogen-containing monomers such as hydroxyethyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide, and (meth)acryloyl morpholine. The radical polymerizable adhesive may also contain polyfunctional monomers such as tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane diol diacrylate, and EO-modified diglycerol tetraacrylate as crosslinking components.

[0134] Photocurable adhesives such as photo-radical polymerizable adhesives preferably contain a photoinitiator. The photoinitiator can be appropriately selected according to the reaction species. For example, in a radical polymerizable adhesive, as the photoinitiator, a photo-radical generator that generates radicals upon light irradiation is preferably blended. The content of the photo-radical generator is usually about 0.1 to 10 parts by weight, preferably 0.5 to 3 parts by weight, relative to 100 parts by weight of the monomer. It should be noted that when the radical polymerizable adhesive is used in the form of an electron beam curable type, a photoinitiator is not particularly required. In the radical polymerizable adhesive, a photosensitizer represented by a carbonyl compound or the like can also be added as needed. The photosensitizer is used to improve the curing speed and sensitivity based on the electron beam. The amount of the photosensitizer used is usually about 0.001 to 10 parts by weight, preferably 0.01 to 3 parts by weight, relative to 100 parts by weight of the monomer.

[0135] The adhesive may contain appropriate additives as needed. Examples of the additives include coupling agents such as silane coupling agents and titanate coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, anti-degradants, dyes, processing aids, ion scavengers, antioxidants, tackifiers, fillers, plasticizers, leveling agents, foam inhibitors, antistatic agents, heat stabilizers, hydrolysis stabilizers, etc.

[0136] The adhesive may contain a radical scavenger such as a hindered amine compound. By including a radical scavenger in the adhesive, in the usage environment of an image display device or the like, the radical scavenger in the adhesive migrates to the polarizer, so there is a tendency for the deterioration of the polarizer to be suppressed. Among them, when the adhesive contains a radical scavenger, the radical scavenger may inhibit the curing reaction of the adhesive and cause a decrease in the adhesive strength. Especially for a radical polymerization type adhesive, the radicals required for the curing reaction are captured by the radical scavenger, so the influence of polymerization inhibition is large.

[0137] Therefore, the content of the radical scavenger in the adhesive is preferably less than 1 wt%, more preferably less than 0.1 wt%, further preferably less than 0.05 wt%, may also be less than 0.01 wt%, less than 0.005 wt% or less than 0.001 wt%. The adhesive may also not contain a radical scavenger. It should be noted that here, the adhesive before bonding to an adherend such as a polarizer or an easily bondable film (i.e., before curing) is described. In the cured adhesive layer, a radical scavenger migrated from an easily bondable layer or the like may also be contained in an amount exceeding the above range.

[0138] <Manufacture of Polarizing Plate>

[0139] A polarizing plate can be manufactured by bonding an easily bondable film 1 to one surface (the first major surface) of a polarizing element 5 with an adhesive layer 6 interposed therebetween. The easily bondable film 1 may be bonded to the polarizing element 5 with the adhesive layer on the surface where the easily bondable layer is formed, or may be bonded to the polarizing element 5 with the adhesive layer on the surface where the easily bondable layer is not formed.

[0140] As Figure 2 shown, by bonding the polarizing element 5 to the surface of the easily bondable film 1 where the easily bondable layer 15 is formed with the adhesive layer 6 interposed therebetween, the adhesiveness between the polarizing element and the polarizing element protective film (the easily bondable film 1) is excellent. In addition, when the surface where the easily bondable layer 15 of the easily bondable film 1 faces the polarizing element 5, since the distance between the easily bondable layer 15 and the polarizing element 5 is short, in the presence of moisture in the usage environment of the image display device or the like, the radical scavenger contained in the easily bondable layer 15 easily migrates into the polarizing element 5 through the adhesive layer 6, and a more excellent deterioration suppression effect of the polarizing element can be obtained.

[0141] In the bonding of the polarizing element 5 and the easily bondable film 1, it is preferable that after applying an adhesive composition to either one or both of the polarizing element 5 and the easily bondable film 1, the polarizing element 5 and the easily bondable film 1 are bonded together by a roll laminator or the like, and the adhesive is cured. As a method for applying the adhesive composition to the polarizing element 5 and / or the easily bondable film 1, a roll method, a spray method, an immersion method, etc. can be cited. Before applying the adhesive composition to the surface of the polarizing element 5 and / or the easily bondable film 1, surface treatments such as corona treatment, plasma treatment, and saponification treatment may also be performed.

[0142] After bonding the polarizing element 5 and the easily bondable film 1, the adhesive layer 6 is formed by curing the adhesive according to the type of the adhesive. When a water-based adhesive is used, the adhesive is cured by heating and drying. When a radiation-curable adhesive is used, the adhesive is cured by irradiation with radiation such as electron beams or ultraviolet rays. As described above, by making the adhesive substantially free of radical scavengers, curing inhibition of the adhesive is less likely to occur, and a polarizing plate with a high adhesive force between the polarizing element 5 and the easily bondable film 1 can be obtained.

[0143] <Transparent protective film>

[0144] A transparent protective film 2 may also be bonded to the second major surface of the polarizing element 5 with an adhesive layer 7 interposed therebetween. As the transparent protective film 2, any suitable transparent film can be used. The thickness of the transparent protective film 2 is about 5 to 200 μm. From the viewpoints of mechanical strength, transparency, and workability, etc., the thickness of the transparent protective film 2 is preferably 10 to 100 μm, more preferably 15 to 60 μm. The thicknesses of the easily bondable film 1 and the transparent protective film 2 may be the same or different.

[0145] Examples of the material for forming the transparent protective film 2 include: polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN); cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose; styrene-based polymers such as polystyrene and acrylonitrile-styrene copolymer; cyclic polyolefins such as polynorbornene; polycarbonates, etc.

[0146] The transparent protective film 2 may have an easy-bonding layer (not shown) on the bonding surface with the polarizing member 5. An easy-bonding layer similar to the easy-bonding layer 15 of the easy-bonding film 1 may be provided on the transparent protective film 2. The transparent protective film 2 may be an optical functional film such as a retardation film or a viewing angle compensation film.

[0147] As the adhesive layer 7 for bonding the polarizing member 5 and the transparent protective film 2, adhesives of various types such as aqueous adhesives, solvent-based adhesives, hot melt adhesive systems, and active energy ray-curable adhesives can be used. The adhesive layer 6 and the adhesive layer 7 may use the same adhesive composition.

[0148] The polarizing plate may have optical layers such as a retardation film, a viewing angle compensation film, and a brightness enhancement film on the basis of the transparent protective film 2 as the polarizing member protective film.

[0149] [Polarizing plate with adhesive]

[0150] An adhesive layer 20 for bonding to an image display unit 60 such as a liquid crystal unit or an organic EL unit and an adhesive layer 30 for bonding to the front surface transparent member 70 may be provided on one or both surfaces of the polarizing plate 50.

[0151] Figure 3 Fig. is a cross-sectional view showing a configuration example of a polarizing plate with adhesive 90 having adhesive layers 20 and 30 on both surfaces of the polarizing plate 10. Temporary adhesion release liners (not shown) may be provided on the surfaces of the adhesive layers 20 and 30 for the purpose of preventing contamination of the adhesive layers. As the release liner, a release liner obtained by coating the surface of a plastic film with a release agent such as a silicone-based release agent, a long-chain alkyl-based release agent, or a fluorine-based release agent is preferably used.

[0152] If a polarizing plate with adhesive in which an adhesive layer is pre-attached to the polarizing plate is used, when forming an image display device, there is no need to provide a process of attaching an additional adhesive layer to the polarizing plate 50 for bonding to the image display unit 60 and the front surface transparent member. Therefore, the manufacturing process of the image display device can be simplified.

[0153] As the adhesives for forming the adhesive layers 20 and 30, adhesives based on polymers such as acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based, and rubber-based can be appropriately selected and used. In particular, from the aspects of excellent optical transparency, moderate wettability and cohesion, and excellent weather resistance, heat resistance, etc., acrylic adhesives are preferred.

[0154] If the acid contained in the adhesive layer migrates to the polarizer, it will act as an acid catalyst for polyene formation based on the dehydration of polyvinyl alcohol, which may cause a decrease in the monomer transmittance of the polarizing plate. Therefore, it is preferable that the content of organic acid monomers such as (meth)acrylic acid (free organic acid) in the adhesive layers 20 and 30 provided on the polarizing plate 50 is low. The content of acid monomers in the adhesive layers 20 and 30 is preferably 100 ppm or less, more preferably 70 ppm or less, and further preferably 50 ppm or less. The acid monomer content of the adhesive layer is determined by impregnating the adhesive in pure water, heating it at 100 °C for 45 minutes, and quantifying the acid monomers extracted into the water using ion chromatography.

[0155] In thermosetting and photocuring polymers, the presence of unreacted residual monomers is inevitable. Therefore, in order to reduce the acid monomer content in the adhesive layer, it is preferable to reduce the amount of organic acid monomer components such as (meth)acrylic acid in the monomer components constituting the base polymer. The base polymer of the adhesive preferably contains substantially no organic acid monomers (carboxyl group-containing monomers) as monomer units. The content of the carboxyl group-containing monomer component is preferably 0.5% by weight or less, more preferably 0.1% by weight or less, and further preferably 0.05% by weight or less, relative to the total amount of the monomer components constituting the base polymer.

[0156] The thickness of the adhesive layers 20 and 30 is not particularly limited. From the viewpoints of adhesiveness, workability, etc., it is usually about 5 to 500 μm, and can also be about 10 to 300 μm. The thickness of the adhesive layer 20 disposed on one surface of the polarizing plate 10 and the thickness of the adhesive layer 30 disposed on the other surface of the polarizing plate 10 may be the same or different.

[0157] The adhesive layer may contain a radical scavenger such as a hindered amine compound. By including a radical scavenger in the adhesive, in the usage environment of the image display device or the like, since the radical scavenger in the adhesive migrates to the polarizing member, there is a tendency for the deterioration of the polarizing member to be suppressed. However, in the image display device, the adhesive layers 20 and 30 are arranged at a distance from the polarizing member 5, so the amount of the radical scavenger migrating from the adhesive layers 20 and 30 to the polarizing member 5 is small, and the effect of suppressing the deterioration of the polarizing member is limited. In order to improve the effect of suppressing the deterioration of the polarizing member, it is necessary to increase the amount of the radical scavenger contained in the adhesive. However, when the amount of the radical scavenger is excessive, due to changes in the composition of the adhesive (reduction of components contributing to adhesion), bleeding of the radical scavenger, etc., there is a tendency for the adhesive strength (anchoring force to the adherend) to decrease. In addition, when the adhesive is a photocurable composition, the radical scavenger may cause curing inhibition.

[0158] Therefore, the content of the radical scavenger in the adhesive layer is preferably less than 10% by weight, more preferably less than 5% by weight, further preferably less than 1% by weight, and may also be less than 0.5% by weight, less than 0.1% by weight, less than 0.05% by weight, less than 0.01% by weight, less than 0.005% by weight, or less than 0.001% by weight. The adhesive layer may also contain no radical scavenger. It should be noted that here, the adhesive layer before bonding to an adherend such as a polarizing plate is described. In the adhesive layer after bonding to the polarizing plate, it may contain a radical scavenger migrating from an easy-bonding layer or the like exceeding the above range.

[0159] [Image display device]

[0160] An image display device can be formed by bonding a polarizing plate 10 to the surface of an image display unit 60 such as a liquid crystal cell or an organic EL cell. Regarding the formation of a liquid crystal display device, it is formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate, and a lighting system as needed and incorporating a drive circuit or the like. In an organic EL display device, by bonding a circular polarizing plate formed by combining a polarizing plate and a retardation film (typically a quarter-wave plate) to the surface of the organic EL cell, the re-emission of reflected light of external light caused by a metal electrode or the like can be reduced, and the visibility can be improved.

[0161] Figure 4 A cross-sectional schematic diagram showing one mode of the image display device. In Figure 4 the image display device 100, a polarizing plate 50 is bonded to the recognition side of the image display unit 60 via an adhesive layer 20, and a front surface transparent member 70 is bonded to the more recognition side of the polarizing plate 50 via an adhesive layer 30.

[0162] Note that, although not shown, in a liquid crystal display device having liquid crystal cells, a light source side polarizing plate is attached to the surface of the image display unit 60 opposite to the identification side with an appropriate adhesive layer or bonding agent layer, and then a light source such as a backlight is disposed.

[0163] Examples of the front surface transparent member 70 disposed on the front surface of the image display unit 60 on the identification side include a front surface transparent plate (cover window), a touch panel, etc. As the front surface transparent plate, a transparent plate having appropriate mechanical strength and thickness can be used. As such a transparent plate, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate can be used. As the touch panel, various touch panels such as a resistive film method, a capacitive method, an optical method, an ultrasonic method, a glass plate or a transparent resin plate having a contact type sensor function can be used.

[0164] Since the image display unit 60 and the front surface transparent member 70 are attached to both sides of the polarizing plate 50 with the adhesive layers 20 and 30 in the image display device 100, it is difficult for moisture to dissipate from the main surface of the polarizing plate 50, and moisture is likely to remain inside the polarizing plate. It is known that when exposed to a high temperature environment for a long time in a state where moisture remains, the polyene formation of the polarizing member is likely to proceed, and the monomer transmittance of the polarizing plate decreases.

[0165] As described above, by making the adhesive layer 15 of the easily adhesive film 1 attached to the polarizing member 5 contain a radical scavenger, even in the image display device 100 having the image display unit 60 and the front surface transparent member 70 on both sides of the polarizing plate 50, the polyene formation of the polarizing member 5 can be suppressed, and thus the decrease in the monomer transmittance of the polarizing plate due to heating is small.

[0166] It is considered that when exposed to a high temperature environment in a state where moisture exists inside the polarizing plate, the radical scavenger contained in the adhesive layer 15 is likely to diffuse (migrate) to other layers by means of moisture, and the radical scavenger also migrates into the polarizing member 5 attached to the easily adhesive film 1, thereby playing a role in suppressing the polyene formation of the polyvinyl alcohol of the polarizing member. That is, it is considered that in an environment where high temperature and moisture exist, which is likely to promote polyene formation, the migration of the radical scavenger from the adhesive layer 15 to the polarizing member 5 is also promoted, so that polyene formation is suppressed and the decrease in the monomer transmittance of the polarizing plate is suppressed.

[0167] As described above, when the polarizing member 5 contains a radical scavenger, it may cause poor iodine staining and poor alignment. When the adhesive layers 6 and 7, and the adhesive layers 20 and 30 contain a radical scavenger, there is a concern about curing inhibition and a decrease in adhesive strength due to exudation, etc. In addition, since the polarizing member protective films 1 and 2 are disposed between the adhesive layers 20 and 30 and the polarizing member 5, the distance between the adhesive layer and the polarizing member is long, and the amount of the radical scavenger migrating from the adhesive layer to the polarizing member is small. Therefore, the polyene inhibition effect is limited.

[0168] In contrast, when the easy-bonding layer 15 of the easy-bonding film 1 adjacent to the polarizing member 5 contains a radical scavenger, curing inhibition and poor adhesion are less likely to occur, and since the distance between the easy-bonding layer 15 and the polarizing member 5 is short, the radical scavenger easily migrates to the polarizing member 5. Therefore, an image display device can be obtained in which a decrease in the monomer transmittance of the polarizing plate in a high-temperature environment is suppressed and the adhesive strength between layers is not decreased.

[0169] It should be noted that Figure 4 FIG. shows a mode in which the easy-bonding film 1 as a polarizing member protective film is provided between the polarizing member 5 and the front surface transparent member 70 in the polarizing plate 50 disposed on the identification side of the image display unit 60. However, the arrangement of the easy-bonding film 1 in which the easy-bonding layer 15 contains a radical scavenger is not limited to this mode. For example, the polarizing member protective film disposed between the polarizing member 5 and the image display unit 60 may be the above-mentioned easy-bonding film. In a liquid crystal display device, the polarizing plate disposed between the image display unit and the light source may include the above-mentioned easy-bonding film as a polarizing member protective film. As described above, the polarizing plate for an image display device may also be a single-protection polarizing plate in which only one side of the polarizing member is bonded with an easy-bonding film as a polarizing member protective film.

[0170] Examples

[0171] Examples are shown below to further specifically illustrate the present invention, but the present invention is not limited by these examples. Hereinafter, the description of "%" for concentration is by weight% unless otherwise specified.

[0172] [Example 1]

[0173] [Production of Easy-Bonding Film]

[0174] [Preparation of Easy-Bonding Composition]

[0175] 16.5 parts by weight of an aqueous polyurethane (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "Superflex 210R") with a solid content of 35%, which contains a polyester urethane as a resin component and isophorone diisocyanate, also contains triethylamine as a curing catalyst and methyl ethyl ketone as a dispersion medium, 4.2 parts by weight of an aqueous solution of an oxazoline-containing polymer with a solid content of 25% (manufactured by Nippon Shokubai Co., Ltd., "Epocros WS-700"), 2.3 parts by weight of 1% ammonia water, 6 parts by weight of a 20% aqueous dispersion of colloidal silica with an average primary particle size of 35 nm (manufactured by Fuso Chemical Industry Co., Ltd., "Quartron PL-3"), and 71 parts by weight of pure water were mixed to prepare an easy-bonding composition A.

[0176] 0.0008 part by weight (equivalent to 0.01 part by weight relative to 100 parts by weight of the solid content of the composition) of a radical scavenger (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl radical) represented by the following formula (9) was added to the easy-bonding composition A to prepare an easy-bonding composition containing a radical scavenger.

[0177]

[0178] (Formation of the easy-bonding layer on the acrylic film)

[0179] An easy-bonding film was produced using a film manufacturing apparatus equipped with a melt extrusion film-forming apparatus, a gravure coater, a simultaneous biaxial stretching apparatus, and a winding apparatus. As the acrylic resin, pellets of an imidized MS resin (glass transition temperature: 120°C) that are the same as those used in the production of the "transparent protective film 1A" described in the examples of JP-A-2017-26939 were used. The acrylic resin was melt-extruded from a T-die and formed into a film with a thickness of 160 μm. Using a gravure coater, the above-mentioned easy-bonding composition was coated on one surface of the film with a wet thickness of about 9 μm, and in a heating furnace at a temperature of 140°C, it was simultaneously biaxially stretched to 2 times along the machine direction (MD) and the transverse direction (TD) using a simultaneous biaxial stretching tenter to obtain an easy-bonding film having an easy-bonding layer with a thickness of 200 nm on one surface of an acrylic film with a thickness of 40 μm.

[0180] <Manufacture of a polarizing plate>

[0181] (Manufacture of a polarizing element)

[0182] While unidirectionally stretching a long strip of a polyvinyl alcohol (PVA)-based resin film (Kuraray Co., Ltd.'s "PE4500") with a thickness of 45 μm 5.9 times in the length direction using a roller stretching machine, the swelling bath, dyeing bath, crosslinking bath 1, crosslinking bath 2, and cleaning bath shown in Table 1 were sequentially conveyed, and dried at 70°C for 5 minutes to produce a polarizing element with a thickness of 18 μm. The iodine concentration and potassium iodide concentration in the dyeing bath were adjusted so that the monomer transmittance of the polarizing element was 43.4%.

[0183] [Table 1]

[0184] Aqueous solution composition Temperature (°C) Drawing ratio Swelling bath Pure water 20 2.2 Dyeing bath Iodine∶Potassium iodide = 1∶7 (weight ratio) 30 1.4 Crosslinking bath 1 5.0% Boric acid, 3.0% Potassium iodide 40 1.2 Crosslinking bath 2 4.3% Boric acid, 5.0% Potassium iodide 65 1.6 Washing bath 2.6% Potassium iodide 20 -

[0185] (Preparation of ultraviolet curable adhesive)

[0186] An ultraviolet curable adhesive was prepared containing 40 parts by weight of N-hydroxyethylacrylamide and 60 parts by weight of acryloylmorpholine as curable components, and further containing 3 parts by weight of 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one (BASF Corporation's "Irgacure819") as a polymerization initiator.

[0187] (Lamination of polarizing element and polarizing element protective film)

[0188] As the polarizing element protective film on one side, the easily adhesive film prepared above was used, and as the polarizing element protective film on the other side, a biaxially stretched cyclic olefin film (Zeonor Film ZF-14 manufactured by Zeon Corporation, Japan) was used. The above ultraviolet curable adhesive was coated on the easily adhesive layer forming surface of the easily adhesive film and the surface of Zeonor Film to a thickness of about 1 μm, laminated on the polarizing element using a roll laminator, and then irradiated with ultraviolet light having an accumulated light amount of 1000 mJ / cm 2 to cure the adhesive, obtaining a polarizing plate having an acrylic film (easily adhesive film) on one surface of the polarizing element and Zeonor Film on the other surface.

[0189] [Examples 2 to 5]

[0190] In the preparation of the easily adhesive composition, the amount of the radical scavenger added to the easily adhesive composition A (relative to the amount of the solid components of the composition) was changed as shown in Table 2. Except for this, an easily adhesive film was produced in the same manner as in Example 1, and the obtained easily adhesive film was laminated on the polarizing element to obtain a polarizing plate.

[0191] [Comparative Example 1]

[0192] In the preparation of the easily adherable composition, the easily adherable composition A is directly used without adding a radical scavenger. Other than this, an easily adherable film is produced in the same manner as in Example 1, and the obtained easily adherable film is adhered to a polarizing element to obtain a polarizing plate.

[0193] [Comparative Example 2]

[0194] In the preparation of the adhesive, a radical scavenger represented by the above formula (9) is added so that the concentration is 10%, and an adhesive containing a radical scavenger is prepared. This adhesive is used in the adhesion of the polarizing element and the easily adherable film. Other than this, a polarizing plate is produced in the same manner as in Comparative Example 1.

[0195] [Comparative Examples 3 and 4]

[0196] The amount of the radical scavenger added to the adhesive (concentration in the adhesive) is changed as shown in Table 2. Other than this, a polarizing plate is produced in the same manner as in Comparative Example 2.

[0197] [Evaluation of Polarizing Plate]

[0198] [Adhesion Strength]

[0199] The polarizing plate is cut into a size of 200 mm in the direction parallel to the stretching direction of the polarizing element (absorption axis direction) and 15 mm in the orthogonal direction (transmission axis direction). After making a notch between the easily adherable film and the polarizing element with a cutting knife, the surface on the ZEONOR Film side of the polarizing plate is adhered to a glass plate. Using a tensile-compression testing machine (manufactured by MINEBEA, "TG-1kN"), a peeling test is carried out at a peeling angle of 90° and a peeling speed of 1000 mm / minute to measure the adhesive force between the polarizing element and the easily adherable film.

[0200] [Change in Monomer Transmittance in Heating Test]

[0201] (Preparation of Acrylic Adhesive)

[0202] In a solution of an acrylic polymer having a weight-average molecular weight of 1.8 million obtained by copolymerizing butyl acrylate and 4-hydroxybutyl acrylate at a weight ratio of 99:1, 0.02 parts by weight of an isocyanate-based crosslinking agent ("Takenate D110N" manufactured by Tosoh Corporation) and 0.2 parts by weight of a silane coupling agent ("X-41-1056" manufactured by Shin-Etsu Chemical Co., Ltd.) are compounded with respect to 100 parts by weight of the polymer to prepare an acrylic adhesive composition.

[0203] (Production of Adhesive Layer)

[0204] On the release layer forming surface of a release liner (a polyester film having a silicone release layer on the surface; "MRF38" manufactured by Mitsubishi Chemical), the above acrylic adhesive composition was coated so that the thickness of the dried adhesive layer was 20 μm, dried at 90 °C for 1 minute, and an adhesive layer was formed on the release liner.

[0205] (Fabrication of an evaluation-use simulated image display device)

[0206] The polarizing plate was cut into a square with a side length of 40 mm, and the surface on the ZEONOR Film side was adhered to the glass plate by means of the above adhesive layer. The other side of the polarizing plate (the surface on the easy-to-bond film side) was adhered to another glass plate by means of a non-acidic acrylic adhesive sheet with a thickness of 200 μm ("LUCIACS CS9868" manufactured by Nitto Denko Corporation), and a simulated image display device in which glass plates were adhered to both sides of the polarizing plate by means of adhesive layers was fabricated.

[0207] (Evaluation of the change ΔTs in monomer transmittance based on heating)

[0208] The above simulated image display device was left standing in a hot air oven at a temperature of 105 °C for 48 hours to conduct a heating test. Based on the monomer transmittance Ts 0 before the heating test and the monomer transmittance Ts 1 after the heating test, the reduction amount ΔTs in the monomer transmittance before and after the heating test was calculated by the following formula. It should be noted that the monomer transmittance is the Y value corrected for visual sensitivity through a 2-degree field of view (C light source) of JlS Z 8701-1982, and was measured using a spectrophotometer ("DOT-3" manufactured by Murakami Color Technology Research Institute).

[0209] ΔTs (%) = Ts 0 (%) - Ts 1 (%)

[0210] [Evaluation results]

[0211] The content of the radical scavenger in the easy-to-bond layer of the easy-to-bond film and the adhesive in the polarizing plates of Examples 1 to 5 and Comparative Examples 1 to 4, the adhesive force between the polarizing member and the easy-to-bond film, and the reduction amount ΔTs in the monomer transmittance before and after the heating test are shown together in Table 2.

[0212] [Table 2]

[0213]

[0214] In Comparative Example 1 where the easy-bonding layer does not contain a radical scavenger, the reduction amount ΔTs of the monomer transmittance based on the heating test is 19%. In Example 1 using an easy-bonding film having an easy-bonding layer containing 0.01% of a radical scavenger, ΔTs is 5%, and the reduction of the monomer transmittance of the polarizing plate caused by heating is suppressed. In Examples 2 to 5, ΔTs is further reduced compared to Example 1, and a tendency is observed that the more the amount of the radical scavenger contained in the easy-bonding layer, the more the reduction of the monomer transmittance is suppressed. It is considered that this is because the radical scavenger contained in the easy-bonding layer migrates to the polarizing member in a heating environment and has the effect of suppressing the polyene formation of polyvinyl alcohol.

[0215] In Comparative Examples 2 to 4 where the adhesive layer contains a radical scavenger, a tendency that ΔTs decreases as the addition amount of the radical scavenger increases is similarly observed as in Examples 1 to 5. However, in Comparative Examples 2 to 4, a tendency that the adhesive force between the polarizing member and the easy-bonding film decreases as the addition amount of the radical scavenger increases is observed, and it is known that it is difficult to have both excellent heat durability and adhesive force. In Comparative Examples 2 to 4, it is considered that the radical scavenger contained in the adhesive suppresses the curing reaction of the adhesive, which is the reason for the decrease in the adhesive force.

[0216] [Comparative Examples 5 to 7: Examples of adding a radical scavenger to an adhesive]

[0217] In Comparative Examples 5 to 7, using the polarizing plate produced in Comparative Example 1, in the preparation of an acrylic adhesive, the radical scavenger represented by the above formula (9) is added to a concentration shown in Table 3, and thus a simulated image display device having an adhesive layer containing a radical scavenger with the surface on the ZEONOR Film side of the polarizing plate bonded to a glass plate is produced, and the reduction amount ΔTs of the monomer transmittance before and after the heating test is measured.

[0218] [Measurement of anchoring force]

[0219] An adhesive-containing polarizing plate is produced by bonding the above adhesive layer containing a radical scavenger to the surface on the ZEONOR Film side of the polarizing plate, and it is cut into a width of 50 mm and a length of 200 mm, and the surface on the easy-bonding film side of the polarizing plate is bonded to a glass plate with a double-sided tape. An ITO film cut into a width of 25 mm and a length of 200 mm is bonded to the adhesive layer of the adhesive-containing polarizing plate, and it is allowed to stand at room temperature for 20 minutes to obtain a measurement specimen. Using a tensile-compression testing machine (manufactured by MINEBEA, "TCM-1kNB"), a peeling test is performed at a peeling angle of 180° and a peeling speed of 1000 mm / minute, and the peeling force at the interface between the polarizing plate (ZEONOR Film) and the adhesive layer is obtained and used as the anchoring force of the adhesive.

[0220] In the same manner as described above, the anchoring force between the polarizing plates of Example 1, Example 5, and Comparative Example 1 and the adhesive layer without a radical scavenger was measured.

[0221] [Evaluation Results]

[0222] The content of the radical scavenger in the easy-bonding layer and the adhesive layer of the easy-bonding film in the polarizing plates of Example 1, Example 5, and Comparative Examples 1 and 7 to 8, the anchoring force of the adhesive layer to the polarizing plate, and the reduction amount ΔTs of the monomer transmittance before and after the heating test are shown together in Table 3.

[0223] [Table 3]

[0224]

[0225] In Comparative Example 5 in which the adhesive layer contains 0.01% of the radical scavenger, ΔTs becomes smaller compared to Comparative Example 1. However, when compared with Examples 1 to 5, the effect of suppressing the decrease in the monomer transmittance is limited. One of the reasons for the limited ΔTs reduction effect is considered to be that since a polarizing element protection film is disposed between the adhesive layer and the polarizing element and the two are separated, the amount of the radical scavenger migrating from the adhesive layer to the polarizing element is small.

[0226] In Comparative Example 6 in which the adhesive layer contains 0.2% of the radical scavenger, ΔTs is smaller than that in Comparative Example 5, but the effect of suppressing the decrease in the monomer transmittance is not sufficient. In addition, in Comparative Example 6, a decrease in the anchoring force of the adhesive was observed. In Comparative Example 7 in which the adhesive layer contains 20% of the radical scavenger, ΔTs becomes smaller compared to Comparative Examples 5 and 6. However, since the addition amount of the radical scavenger to the adhesive layer is excessive, the anchoring force of the adhesive is significantly reduced.

[0227] From the results of the above-described examples and comparative examples, it can be seen that by making the easy-bonding layer of the easy-bonding film attached to the polarizing element contain a radical scavenger, it is possible to suppress a decrease in the monomer transmittance of the polarizing plate in a high-temperature environment and have little influence on the polarization characteristics and the adhesiveness between members.

Claims

1. A polarizing plate, comprising: a polyvinyl alcohol-based polarizer having a first major surface and a second major surface; and a polarizer protection film adhered to the first major surface of the polarizer, wherein the polarizer protection film is an easily adherable film having an easily adherable layer on the surface of a transparent film substrate, the easily adherable layer contains a binder resin and a water-soluble radical scavenger, and the content of the radical scavenger in the easily adherable layer is 0.01 wt% or more and less than 1 wt%, the easily adherable layer of the easily adherable film is adhered to the first major surface of the polarizer via an adhesive layer, and the adhesive layer is formed of a cured product of a curable adhesive that exhibits adhesiveness through a crosslinking reaction, the adhesive layer does not contain a radical scavenger or the content of the radical scavenger is less than 1 wt%.

2. The polarizing plate according to claim 1, wherein, the radical scavenger is a hindered amine compound.

3. The polarizing plate according to claim 1 or 2, wherein, the radical scavenger is a compound having a nitroxide group or a compound capable of generating a nitroxide group.

4. The polarizing plate according to claim 1 or 2, wherein, the easily adherable layer further contains fine particles.

5. A polarizing plate with an adhesive, having an adhesive layer on at least one surface of the polarizing plate according to any one of claims 1 to 4.

6. An image display device, having an image display unit and the polarizing plate according to any one of claims 1 to 4.

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